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Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx
PALAEO-04961; No of Pages 23
Contents lists available at ScienceDirect
Palaeogeography, Palaeoclimatology, Palaeoecology
j ourna l homepage: www.e lsev ie r.com/ locate /pa laeo
ARTICLE IN PRESS
F
Geophysical and geological signatures of relative sea level change in the upperWheeler Formation, Drum Mountains, West-Central Utah: A perspective intoexceptional preservation of fossils
S.L. Halgedahl a,⁎, R.D. Jarrard a, C.E. Brett b, P.A. Allison c
a Department^of Geology and Geophysics, University of Utah, 135 South 1460 East, Room 719, Salt Lake City, UT 84112-
^0111, United States
b Department^of Geology, University of Cincinnati, Cincinnati, OH 45221-
^0013, United States
c Department^of Earth Science & Engineering, Imperial College London, Royal School of Mines, South Kensington Campus, London SW7 2AZ, UK
ONCO
⁎ Corresponding author. Tel.: +1 801 585 3964; fax: +E-mail address: [email protected] (S.L. Halgedah
0031-0182/$ – see front matter © 2009 Published by Edoi:10.1016/j.palaeo.2009.02.011
Please cite this article as: Halgedahl, S.L.,Formation, Drum Mountains..., Palaeogeogr
Oa b s t r a c t
a r t i c l e i n f oAvailable online xxxx
Keywords:Wheeler FormationCambrian
^Lagerstätte
^Gamma-
^ray spectrometry
^Magnetic susceptibility
^
The Middle Cambrian Wheegeophysical techniques (gamand fossils are used to charWheeler Formation and thsuccession was deposited oeastward incursion of deepeclearly reveal variations in c
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ler Formation in Utah is renowned for its exceptionally preserved fossils. Herein,ma ray spectrometry and magnetic susceptibility), carbonate analyses, lithofacies,acterize limestones and calcareous mudrocks of the upper portion of the middlee upper Wheeler Formation in the Drum Mountains, West-
^Central Utah. This
n a mixed carbonate-^siliciclastic ramp within the House Range Embayment, an
r water, created and bounded on the southeast by a normal fault. Geophysical dataarbonate versus clay content. Observed patterns among outcrop geophysical data,
lithofacies, and fossils are interpreted within the contexts of relative sea level changes and a sequencestratigraphic model. Above a basal interval of rhythmically-
^bedded limestones interpreted to have been
deposited on the middle part of the ramp during a period of relatively low sea level, lithofacies, rising gammaray and rising magnetic susceptibility track a transgression, which culminates in a maximum flooding surface(MFS). This MFS is near the base of a “hot zone”: an
^~6-
^m^-^thick interval of exceptional preservation (Konservat-
^Lagerstätte), highest magnetic susceptibility, highest gamma ray values, highest clay content, and with a bulkcarbonate content of ~4–
^20%. The basal layer of this zone contains abundant, fully articulated specimens of
agnostids and tiny polymerid trilobites. Exceptionally preserved fossils, such as non-^trilobite arthropods,
priapulid and annelid worms, hyolithids, phyllocarid arthropods with soft parts, algae, and fragile sponges, aremuchmore abundant within this hot zone than in other strata of the succession. These specimens are preservedin very thin-
^bedded to laminated mudrock, only rarely interrupted by macroscopic signs of bioturbation.
Stratigraphically above the hot zone is a thick unit of mudrock in which both gamma ray and magneticsusceptibility decrease, gradually at first and then precipitously to very low levels; in concert, few soft-
^bodied
specimens have been recovered from this upper interval. The gradual decrease in geophysical responses isinterpreted to be the result of gradual shallowing during highstand, caused mainly by progradation of thecarbonate factory; it was followed by an abrupt regression. Mudrocks are capped by burrow-
^mottled grainstone
and stromatolitic boundstone, representing a lowstand or the earliest transgressive phase of the next cycle.These observations lead to the following conclusions: (1) the upper Wheeler Formation represents most of athird or fourth-
^order cycle of relative sea level change on a mixed carbonate-
^siliciclastic ramp, rather than a
period of shallow-^water lagoonal sedimentation as previously proposed; (2) superimposed on this overall cycle
are several (perhaps many) higher-^order fluctuations in relative sea level; (3) when the present results are
coupled with results of earlier workers, who interpreted the lower and middle Wheeler Formation as a majortransgression and regression, the Wheeler Formation of the Drum Mountains involves two major sea levelcycles, rather than one; (4) the Konservat-
^Lagerstätte was preserved in the deepest-
^water, early-
^highstand
portion of the upper Wheeler sequence; and (5) these results support earlier hypotheses that Konservat-
^Lagerstätten in mixed carbonate-
^siliciclastic successions are most likely to occur during late transgression to
early highstand, given that low energy, anoxic conditions prevailed.© 2009 Published by Elsevier B.V.
U1 801 581 7065.l).
lsevier B.V.
et al., Geophysical and geological signatures of relative sea level change in the upper Wheeleraphy, Palaeoclimatology, Palaeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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2 S.L. Halgedahl et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx
ARTICLE IN PRESS
1. Introduction
The Wheeler Formation of^West-
^̂Central Utah contains an im-
portant Middle Cambrian Konservat-^Lagerstätte and shares many taxa
with the celebrated Burgess shale (e.g., Robison and Richards,1981a,b;Briggs and Robison, 1984; Conway Morris and Robison, 1986, 1988;Robison,1991; Bottjer et al., 2002). The causes of localized, exceptionalpreservation and the relationship of such preservation to depositionalenvironment are crucial to understanding the paleoecology of theorganisms so preserved. Here, outcrop geophysical data and litho-facies descriptions are analyzed in a sequence stratigraphic context, toprovide perspectives on taphonomic and depositional environmentswithin the upper Wheeler Formation of the Drum Mountains, Utah.
During the Middle Cambrian, the western edge of the NorthAmerican continent was a passive margin, and Utah was then part of amiogeocline covered by a broad carbonate platform (e.g., Hintze, 1988).Shallow-
^water carbonate production was interrupted by drowning of a
portion of the platform during formation of the House Rangeembayment (Fig. 1A), an eastward incursion (in modern coordinates)of deeper water, bounded on the southeast by a normal fault (Robison,1960; Kepper,1976; Robison,1982; Rees, 1986). Within this embaymentthe Wheeler Formation was deposited on the Swasey Limestone and indeeper water than coeval sedimentation to the north and south. Theembayment depth shallowed subsequently, as the overlying MarjumFormation was deposited (Rees, 1986; Elrick and Snider, 2002).
Two of the most complete outcrops of the Wheeler Formation arefound in the House Range and Drum Mountains of
^West-
^̂Central Utah
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Fig. 1. Maps and photograph of the study area in the Drum Mountains. (^A) Map of Utah sho
study area location. Dotted arrows show the advance of the northern carbonate platform andCambrian (modified from Rees and Robison, 1989). (
^B) Location of the three main geophy
Wheeler Formation along the western profile, bracketed at its top by a thick, burrowed limesright margin of the background mountain is Sawtooth Ridge, which also contains an expos
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
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7(Robison, 1964; Rees, 1986; Hintze and Davis, 2003) (Fig. 1A). The7Wheeler Formation in the House Range is generally calcareous shale,7thought to have been deposited in an open-
^shelf environment
7(Robison, 1964; Rees, 1986). The succession in the Drum Mountains,7in contrast, is thought to have been deposited in shallower water8closer to the “carbonate factory”, resulting largely in limestone to8argillaceous limestone (Robison, 1964). One of the two exceptions to8this strong carbonate dominance in the Drum Mountains is what8Dommer (1980) informally referred to as the upper member of the8Wheeler Formation, which includes a significant interval of clay-
^rich
8mudrock, the focus of this paper.8Though its existence was brief, the House Range embayment is8associated with three of the four Middle Cambrian Konservat-8
^Lagerstätten of Utah: the upper Wheeler Formation of the House
8Range, the upper Wheeler Formation of the DrumMountains, and the9Marjum Formation of the House Range (Robison, 1991). In part,9Robison (1991) distinguished between the two Wheeler Formation9localities because of their ~
^30 km
^geographic separation and subtly
9different assemblages, but mainly because of different inferred9depositional environments. Robison (1991) followed Vorwald9(1984) in considering the upper Wheeler Formation in the Drum9Mountains to be lagoonal, rather than shallow open shelf. In this9paper, we investigate this interpretation.9Sequence stratigraphy can provide a powerful conceptual frame-9work for interpreting paleontological observations (Brett, 1995;1Holland, 1995; Brett, 1998; Holland, 2000). Previous workers studying1the Wheeler Formation in the Drum Mountains have reported ~19 to
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wing the middle Cambrian House Range embayment (after Rees, 1986) and the presentreduction of the zone of basinal, terrigenous deposition during the Drumian stage of thesical profiles (western, central, and eastern). (
^C) Succession of mudrock in the upper
tone (left white arrow) and on its bottom by the T2 limestone (right white arrow). Theure of upper Wheeler Formation (between the two black arrows).
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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20 fifth-^order cycles, superimposed upon a cycle of much longer
duration, possibly of third order (Liddell et al., 1995; Allison et al.,1995; Schneider, 2000; Langenburg, 2003). Although debate sur-rounds the details of these higher order cycles and their boundaries, itis generally agreed that they are attributable to fluctuations of rela-tive sea level (Schneider, 2000; Langenburg, 2003; Brett et al., thisvolume). In this paper, a combination of geophysical measurements(gamma ray spectrometry and magnetic susceptibility), sedimento-logical and carbonate analyses, and fossils are used to delineate alower-
^order cycle of relative sea level in the upperWheeler Formation
in the DrumMountains. In this particular succession, clay and carbonateminerals are the dominant rock constituents (e.g., Langenburg, 2003).Thus, when calibrated with carbonate content measured in the lab-oratory, geophysical logs can provide high resolution records of changesin the ratio of carbonate to clay and thus clues concerning depositionalenvironment. In addition, this study shows that, in this rock succession,exceptional preservation ismost likely to occur during particular phasesof the sea-
^level cycle and that the rocks bearing these fossils have
characteristic geophysical attributes.
2. Locality
Thestudyarea includesa successionofmudrocksand limestones in theDrum Mountains at 39° 30.21′ N, 112° 59.37′ W (
^̂Fig. 1A). At this general
locality, the upper Wheeler Formation crops out discontinuously alongstrike over about
^2^km. Its northwestern-
^most exposure is at Sawtooth
Ridge (^̂Fig. 1C); this locality has been described by Grannis (1982),
Schneider (2000), Langenburg (2003), and Brett et al. (this volume). Thesections studied here in detail are to the southeast of Sawtooth Ridge andare referred to as transects “W”, “C”, and “E”, according to their relativegeographicpositions (
^̂Fig.1B); all three fallwithin thePtychagnostus atavus
Zone of the Drumian Stage (Robison, 1976; Rowell et al., 1982; Babcocket al., 2007). Quarries on transects “C” and “E” have yielded virtually all ofthe exceptionally preserved fossils found by two of the present authors(SLH and RDJ) at this locality (e.g., Briggs et al., 2008).
3. Methods
3.1. Stations
In theDrumMountains, theWheeler Formation is ~270–^300
^m^̂thick
(Schneider, 2000; Langenburg, 2003; this study). The upper member oftheWheeler Formation is ~
^81m
^̂thick and consists of ~
^42m
^̂ofmudrock
bracketed on top and bottom by limestone (Figs. 2 and 3). The contactbetween the middle and upper members of the Wheeler Formationin the Drum Mountains corresponds to a marked change in lithofacies(e.g., Dommer, 1980; Langenburg, 2003). For several tens of metersbelow this contact, rhythmically-
^bedded limestones predominate.
Above this contact, rocks of the upper member are largely calcareousmudrocks and shallow-
^water limestones. Because this contact could
represent a significant change of relative sea level, the upper^20m
^̂of the
middle member were included in this study.TheWheeler Formation is succeeded by the Pierson Cove Formation,
thought to be the stratigraphic equivalent of the Marjum Formation inthe House Range, Utah, about 40
^k^m to the southwest. The boundary
between theWheeler andPiersonCove Formationshas been a subject ofdebate, however. Originally, this formation boundarywas defined as thelithologic contact between calcareous shales of the upper WheelerFormation and overlying, cliff-
^forming limestone capped by thrombo-
lites and stromatolites (Robison, 1962, 1964; White, 1973; Hintze andRobison, 1975; Dommer, 1980). This definition satisfies two funda-mental criteria of a formation boundary: it is lithologically based andregionally distinctive at outcrop. Subsequently, two redefinitions of theboundary have been proposed. Vorwald (1984) suggested that theboundary be placed ~
^45 m
^̂higher, at the top of a 30-
^to-
^40^m^thick
eastward-^thickening interval of mudrock and argillaceous limestone
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
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OOF
that overlies the stromatolites.Hebased this revision on the fact that thisupper unit is faunally similar to the underlying upper WheelerFormation of the present study, as well as to the upper WheelerFormation in the House Range. Schneider (2000) and Langenburg(2003) proposed that the top of theWheeler be placed at the top of thestromatolitic limestone (rather than at its base), where their sequencestratigraphic interpretations place a sequence boundary. Herein, theoriginal definition of this formation boundary is retained, but for thesake of sequence-
^stratigraphic context ~
^9 m
^̂of the cliff-
^forming and
stromatolitic limestones are included in our logs.A total of 287 measurement stations were established along tran-
sects “W”, “C”, and “E” (^̂Fig. 1B), with an average stratigraphic spacing
of ~0.^5 m
^̂. An additional 72 stations were logged along a northern
extension of the “W” transect, in order to sample the^48 m
^̂of
stratigraphic section underlying the three original, detailed profiles.Within this basal part of the survey, some stations were more than 0.
^5 m
^̂apart due to alluvial cover.
Thus a total of ~110 stratigraphic meters was logged to studylithofacies, geophysical responses, and fossils, including ~
^20 m
^̂of the
upper part of the middle member of the Wheeler Formation alongtransect “W”, the ~
^81 m
^̂making up the upper member, and ~
^9 m
^̂of
the Pierson Cove Formation.Three main transects, rather than just one, were surveyed for two
reasons. First, three transects maximized the number of horizonslogged, despite variable amounts of alluvial cover and a dirt roadpassing across two transects. Second, as discussed in a followingsection, lateral variations in both outcrop exposure and thickness ofalluvial cover in the immediate vicinity of each site, as well as he-terogeneities due to weathering, could cause lateral variations ingeophysical readings along a horizon. Therefore, three transects pro-vided a more representative log profile than would be obtained fromjust one survey line.
Two trenches were dug along short stratigraphic intervals ontransects “W” and “C”, in order to remove alluvial cover and to study aseries of grainstones, argillaceous limestones, and shales at highresolution. Within each trench, adjacent stations were spaced ap-proximately 10 stratigraphic centimeters apart.
3.2. Stratigraphic positions
The elevation and geographic location of sites along the threemaintransects were determined using a differential global positioningsystem (DGPS). In addition, this method was used to obtain positionsof several hundred sites extending from the Swasey Limestone to thestratigraphic base of the “W” transect. DGPS measurements weremade with a Trimble 4700 instrument, providing better than 5-
^c^m
accuracy of relative geographic position among stations within ameasurement network.
Strikes and dips at each site were measured with a Bruntoncompass. Using Fisher statistics (Fisher, 1953), a mean dip vector wascalculated for one to three stratigraphic intervals along each transect,in order to account for local variations in bedding attitude due torecent, minor faulting and tilting. The mean dip vector is defined asthe vector perpendicular to the bedding plane. With a standard algo-rithm, bedding attitudes were combined with DGPS locations to ob-tain each site's stratigraphic position within the succession.
Local strike and dip variations were the largest sources of errors indetermining stratigraphic positions. For example, at limestone siteswith very irregular bedding surfaces, replicatemeasurements of strikecould vary by as much as ±5°. As a result, stratigraphic positionscalculated for some stations were accurate only to ±0.
^5 m
^̂.
3.3. Outcrop gamma ray spectrometry
Outcrop geophysical measurements can be used to detect muchsubtler lithologic variations thanmay be evident in outcrop andwith a
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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Fig. 2. Left: generalized stratigraphic column of lithofacies making up the Wheeler Formation in the Drum Mountains (here, datum is top of the Swasey Formation). Right:lithostratigraphy of the interval of this study, which includes the upper member of the Wheeler Formation, the top 20 m of the underlying middle Wheeler Formation, and ~9 m ofthe overlying Pierson Cove Formation (datum is top of middle member of the Wheeler Formation).
4 S.L. Halgedahl et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx
ARTICLE IN PRESS
UNCOmuch closer spacing of stations than is often considered practical with
geochemical analyses of thick rock successions. Spectral gamma ray(γ) and magnetic susceptibility (χ) were used as proxies for clayversus carbonate, producing records that are the outcrop analogues todownhole well logs.
The spectral gamma ray technique has been used for decades indownhole well logging (e.g., Serra et al., 1980; Fertl, 1983a,b,c; Serra,1986). Even earlier than as a well-
^logging tool, gamma ray spectro-
metry was applied to outcrop studies (e.g., Løvborg et al., 1971, 1979;Cassidy, 1981), particularly in support of reservoir modeling of sili-ciclastic successions (e.g., Chidsey, 2001; Love et al., 2004; Ruf andAigner, 2004; Hernandez, 2005). More rarely, this method has beenapplied to mixed carbonate-
^siliciclastic formations (Zelt, 1985; Myers
and Wignall, 1987; Ruffel and Worden, 2000; Ruf and Aigner, 2004),such as those of this study.
γ-^ray measurements were made with an Exploranium GR-
^256
256-^channel portable gamma-
^ray spectrometer containing a sodium
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
2iodide detector crystal (diameter=7.^6^cm, thickness=7.
^6^cm).
2The instrument detects the spectra of γ-^rays emitted by decay of the
2radioactive isotopes of potassium (40K), thorium (232Th), and uranium2(238U) and then converts to total K in %, total U in ppm, and total Th in2ppm. As discussed subsequently, in the Wheeler Formation, these2elements are presentprimarily in clayminerals,mainly illite (e.g., Gaines2et al., 2005). Illite contains K in its crystal structure; Th, which is2insoluble in seawater but present in detrital form, andU,which is readily2dissolved in seawater, are both present in clays through adsorption onto2the surfaces of clay platelets (e.g., Merkel, 1979; Durrance, 1986).2Minerals such as quartz, calcite, and plagioclase are nonradioactive and2make no contribution to the signal. Therefore, in these rocks the γ-
^ray
2log is expected to be a clay-^abundance log.
2On a flat, semi-^infinite surface, about 60% of the total signal comes
2from a hemisphere centered beneath the detector, with a radius of2~
^20
^cm (e.g., see Durrance, 1986 for a more complete discussion). The
2net signal therefore represents an average reading over an effective
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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Fig. 3. Lithostratigraphy of ~56m of the upperWheeler Formation, ~9 m of the overlying Pierson Cove Formation, and photographs of major lithofacies. Lithologic symbols: see Fig. 2.Black scale bars: 1 m; red scale bars: 10 cm. Datum is the contact between the middle and upper members of the Wheeler Formation. (A) Rhythmically bedded limestone of theuppermost part of the middleWheeler Formation, ~25m below the contact between the upper andmiddle members. (B) Plan view of a runnel on the top surface of the T2 limestoneunit. (C) U-shaped cross section of a runnel, showing tan, silty fill. (D) High-relief burrows on the underside of a thin calcareous layer; the top of this layer has abundant inarticulatebrachiopods (not shown). (E) Platy calcareous mudrock, in outcrop (lower portion of photo) and as weathered-out slope cover (top portion). (F) Alternating thin limestones andshalier beds (the latter hidden by soil because they are less resistant to weathering). (G) Cliff-forming, burrow-mottled limestone. (H) Stromatolites in the capping limestone (topview). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
5S.L. Halgedahl et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx
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Please cite this article as: Halgedahl, S.L., et al., Geophysical and geological signatures of relative sea level change in the upper WheelerFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Palaeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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sample size of about 30–^50^̂kg of rock (Løvborg et al., 1971). Portable
γ-^ray instruments are calibrated on a flat half-
^space of material with
uniform composition, such as a concrete pad doped with knownamounts of radioactive substances (e.g., Adams and Gasparini, 1970).However, most outcrops in the Drum Mountains (and in many otherstudies, e.g., Løvborg et al., 1971) do not satisfy the infinite half-
^space
assumption, for two main reasons: (1) many outcrops are limited intheir lateral dimensions and thicknesses (0.5–
^1.^0 m
^) because they are
on hillsides and surrounded by alluvium (^̂Fig. 1C); and (2) because
most sites in this study were on hillsides, the instrument records notjust the signal from the site of interest, but also some signal fromoutcrops and alluvium both stratigraphically above and below themeasurement site. Some investigators have raised the instrumentabove the outcrop, in order to sample γ-
^rays from a wider solid angle
of rock and thereby reduce the problem of irregular surface topo-graphy (Killeen and Carmichael, 1972; Løvborg et al., 1979; Slatt et al.,1992). However, this approach is only effective for small topographicrelief and continuous outcrop exposure; consequently, γ-
^ray was
measured with the detector in contact with the outcrop.Because gamma rays from nearby outcrops and nearby alluvium
enter the sides of the detector and compete with the signal from thesite of interest, they constitute a source of variance. To determine side-
^source effects and to develop a practical field method of minimizingtheir contribution to the total signal, we conducted numerous ex-periments both on a broad concrete slab (representing a semi-
^infinite
half-^space) and on field outcrops, using lead foil and lead bricks
(5.1^^cm×10.
^2^cm×20.
^3^cm) to shield the sides of the detector.
Surrounding the sides with four lead bricks eliminates N99% of theradiation entering the sides (e.g., Schaeffer, 1973). However, four leadbricks weigh more than
^45
^kg; this amount of weight was deemed
impractical in field studies, owing to the many sites on hillsides. Toretain a practical, portable field instrument while reducing the signalfrom side sources, the sides of the detector crystal were wrapped witha^15
^mm-
^thick sleeve of lead foil (e.g., Løvborg,1972). This collimated-
^detector design reduces input from the sides by about 75%, withrespect to results obtained without sleeving. In the field, this methodsubstantially reduces results from nearby alluvium and weights thetotal signal toward γ-
^rays emanating from the rock in contact with the
detector crystal. Measurements with and without the lead sleeving ona concrete half-
^space indicate that the sleeve reduces the total read-
ings of K, U, and Th by 46%; therefore, all measured concentrationsreported here were divided by 0.54.
To average out statistical fluctuations in decay, we used 1-^min
^measurement times at each station. This method yielded standarddeviations of approximately 0.1% for K, 0.3 ppm for U, and 0.6 ppm forTh. One to three measurements were made at each site, depending onsignal strength, and then averaged. Some authors have employedmeasurement times of 2–
^3 min
^̂(Cassidy, 1981; Zelt, 1985; Lüning
et al., 2004). Our experiments in the upper Wheeler Formation haveshown that the main source of signal variability along a given strat-igraphic horizon originates from irregular outcrop geometry andalluvium, rather than the 1-
^min
^measurement time. For this reason,
increasing the number of sites was deemed preferable to increasingthe measurement time at fewer sites.
Raw γ-^ray readings were converted to American Petroleum Ins-
titute (API) units with the formula API=19.7⁎^K(%)+8.1⁎
^U(ppm)+
3.99⁎^Th(ppm) provided by the manufacturer (http://members.
optusnet.com.au/%7Edrpl/Calibration%facilities.html).
3.4. Magnetic susceptibility
Outcropmagnetic susceptibility (χ)measurements weremadewitha hand-
^held SM-
^30 magnetic susceptibility meter manufactured by ZH
Instruments and calibrated with a magnetic susceptibility bridge.Readings were taken by holding the meter in direct contact with theoutcrop. Effects of thermal drift were removed by subtracting from the
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
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3outcrop reading a baseline measured in air about^1 m
^from the outcrop
3both before and after the rock was measured. The meter is capable of3measuring susceptibilities as low as 10−
^7 SI, although all of theWheeler
3sites had susceptibilities stronger than about 10−^5 SI. The standard
3deviation of replicate measurements in relatively strong mudrocks was3generally ~2%, but it was ~15% in relatively pure limestones because of3very low signal strength. Three replicate measurements were made at3each site and then averaged.3According to the manufacturer's specifications for this instrument,3approximately 90% of the signal originates from the top 2.
^4^cm of rock
3just beneath the sensor, and approximately 99% of the susceptibility3signal originates from the top 6.
^5^cm of rock. Consequently, results are
3sensitive to distance between the rock and the detector coil and thus3to an outcrop's surface roughness. At each site, measurements were3made on the smoothest and flattest surface available. Some rocks,3mainly limestones with highly rugose surfaces, were judged as being3too rough to yield reliable results.3In the strictest sense, magnetic susceptibility originates from all3minerals present in a rock, whether permanently magnetic, diamag-3netic, or paramagnetic. From X-
^ray diffraction measurements of
3mudrocks collected from the upper Wheeler Formation in the House3Range, about 30–
^40^̂km southwest of the Drum Mountains, Gaines
3et al. (2005) found that the major mineral components were clays,3carbonates, some quartz, and minor plagioclase. Similar findings were3reportedmuch earlier by Grannis (1982) for theWheeler Formation in3the Drum Mountains. In this study, therefore, magnetic susceptibility3originates primarily from carbonate minerals, minerals making up the3terrigenous component (and their diagenetic products), and second-3ary minerals that grew after deposition.3In terms of their contribution to positive values of susceptibility3here, the most important minerals of terrigenous origin almost cer-3tainly are clays and, possibly, trace amounts of permanently magnetic3minerals, such as magnetite, maghemite, goethite, and hematite (e.g.,3Hunt et al., 1995; Dunlop and Ozdemir, 1997). Clays are paramagnetic,3with susceptibilities of the order 10−
^4 SI (e.g., Hunt et al., 1995;
3Dunlop and Ozdemir, 1997). When present in sufficient quantity, their3net susceptibility can compete with, and even dominate, the signal3from trace amounts of permanently magnetic minerals (e.g., Richter3et al., 1997; Stage, 2001; Handwerger and Jarrard, 2004). Calcium3carbonate, dolomite, and quartz are weakly diamagnetic, with3negative susceptibilities at least one order of magnitude smaller in3absolute intensity than those of clays (e.g., Hunt et al., 1995; Dunlop3and Ozdemir, 1997). Consequently, these latter three minerals make3little contribution to the susceptibilities of clay-
^rich mudrock. As will
3be shown subsequently, however, in some very “clean” limestones the3clay content is sufficiently low that whole-
^rock susceptibility is nearly
3zero, reflecting the competing effects of small amounts of clay and3calcium carbonate minerals on net susceptibility.3Of some concern was the possibility that surface alteration might3bias results from certain mudrock horizons, which were stained red3on their surfaces. Surficial alteration layers (b0.
^2^mm thick) were
3undetected when susceptibility results from red, iron-^oxide-
^stained
3surfaces were compared to those obtained from fresh interior rock.
33.5. Calcium carbonate analysis
3To provide a mineralogical basis for interpreting the γ-^ray and χ
3profiles, weight percent of CaCO3 was determined for rocks from3selected sites by coulometry at Boise State University, using a UIC, Inc.3model CM-
^5012 CO2 coulometer attached to a modified version of a
3CM-^5120 combustion furnace (Lyle et al., 2005). The method is based
3on measuring the amount of CO2 expelled during heating, then cal-3culating weight percent of CaCO3 assuming that all of the CO2 orig-3inates from calcite (calculated CaCO3=total carbon×8.33) (standard3deviation ~0.25% by weight). Calculated weight percentages some-3what overestimate the amount of carbonatewhen (e.g.) either dolomite
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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Fig. 4. Polished slabs of upper Wheeler mudrock showing variations in sedimentaryfeatures up-section. Each scale bar represents 2 cm. Specimens were cut perpendicularto bedding. (A) Sample collected from approximately 66 m above the top of the middleWheeler Formation; note small intraclasts, thin lenses, relatively coarse grain sizes, andirregular bedding contacts. (B) Sample collected from approximately 62 m above thetop of the middle Wheeler. This site exhibits a mixture of finely-laminated andnonlaminated beds. (C) Sample of clay-rich mudrock collected from approximately44 m above the top of the middle Wheeler, within the “hot” zone; note fine grain sizes,thin, parallel beds and laminae.
7S.L. Halgedahl et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx
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or organic carbon is present. Organic carbon measurements were notperformed, because total organic carbon in the Wheeler Formation hasbeen found to be less than 0.12% (Langenburg, 2003).
3.6. Lithofacies and fossils
Throughout the logged section, outcrops were examined forsedimentary structures, macroscopically visible ooids/peloids, macro-scopic signs of bioturbation, and fossils. Polished slabs from majorlithofacies were viewed under the microscope for the aforementionedfeatures which were either too small to be visible under a hand lens ortoo overprinted by surficial weathering to be detectable in the field.
Fossils, many containing soft parts, had been quarried earlier fromfour sites by two of the present authors (SLH and RDJ) (Briggs et al.,2008). The sites encompass about
^6 m
^̂of stratigraphic section along
transects “C” and “E”. At all four quarries, specimen positions wererecorded to within ±
^3^cm. In addition, polymerid and agnostid tri-
lobites, as well as soft-^bodied fossils, were collected from float and
from quarried rocks throughout all logged sections in order to esti-mate their relative abundances.
4. Results
Outcrop geophysical results are described in the first part of thissection. Second, lithofacies are described in detail versus stratigraphicposition for subsequent comparison to the geophysical logs. Lithologicdescriptions are based on the work of Dommer (1980), Grannis(1982), Rees (1986), Schneider (2000), Langenburg (2003), Brett et al.(this volume), and of the present authors. A generalized lithologiccolumn of theWheeler Formation in the DrumMountains is shown inFig. 2, and a more detailed, composite lithologic column based ontransects “W”, “C”, and “E” is shown in Fig. 3. Photographs of threepolished slabs collected from upper Wheeler mudrocks are shown inFig. 4. In the third part of this section, we describe the types of fossilsfound throughout the logged interval.
4.1. Geophysical logs
The crossplots in Fig. 5 demonstrate the following: Th increaseslinearly with K (
^̂Fig. 5A); χ increases linearly with γ-
^ray (
^̂Fig. 5B); and
both γ-^ray and χ decrease linearly as CaCO3 increases (^̂
Fig. 5C and^D).
In these rocks, it is found that U generally makes little contributionto γ-
^ray results (e.g.,
^U^b2–
^4 ppm). All four crossplots yield high
correlation coefficients.Both γ-
^ray and χ are plotted against stratigraphic position in Fig. 6
for the three traverses. Along the eastern traverse, replicate γ-^ray
measurements at each site are plotted to illustrate within-^site
replicability. Fig. 7 shows a high-^resolution, composite γ-
^ray profile
obtained from two trenches dug between three units of shallow-^water
limestone near the base of the upper Wheeler Formation on tran-sects “W” and “C” (T1, T2, T3; see Brett et al., this volume), and a“magnified” view of the γ-
^ray and χ profiles versus stratigraphic
position along the upper part of transect “W”. Both γ-^ray and cal-
culated % CaCO3 are plotted against stratigraphic position in Fig. 8.Also shown in these figures is a generalized stratigraphic column.
Below the stratigraphic datum of^0 m
^̂at the top of the middle
Wheeler Formation, γ-^ray values are quite low and carbonate makes up
nearly 100%of the rocks, indicatingvery “clean” limestone (Fig. 8). In theinterval 0–
^22^m^̂, theγ-
^ray log rises very slowly, whereas from22 to
^38m
^̂γ-^ray values are generally much higher and undergo large, abrupt
fluctuations. The sudden increase of γ-^ray and χ toward the base of a
“hot zone” at 38.^3 m
^̂(Fig. 6) is accompanied by a rapid fall in carbonate
(Fig. 8). The highest γ-^ray andχ values persist for an interval of ~6.
^1 m
^̂.
Above the hot zone, γ-^ray and χ gradually drop, while carbonate rises.
Near the 73-^m^level γ-
^ray drops precipitously, and carbonate
approaches 100% in the capping, cliff-^forming limestones.
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
4.2. Lithofacies versus stratigraphic position
4.2.1. −̂20^m^̂to^0 m
^̂The lowest stratigraphic interval logged here consists of the top
^20 m
^̂of the middle member of the Wheeler Formation, as defined
informally by Dommer (1980). For convenience and brevity, the top ofthe middle member is used as the “
^0 m
^” stratigraphic datum through-
out this paper. According to DGPS measurements, this datum is~^191 m
^̂above the Swasey–
^Wheeler contact.
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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Fig. 5. Crossplots of geophysical and coulometry results. (A) Thorium (ppm) versus potassium (%). The high degree of linear correlation between K and Th suggests that both arepresent in the same clay component throughout the logged section. (B) Magnetic susceptibility (×10−3 SI) versus gamma ray (API). The linear relation between these twomeasurements is strong evidence that both are of terrigenous origin. These two rock properties are measured with instruments that sample different volumes within the rock: thisdifference imparts some dispersion to the relationship. (C) Calcite (wt.%), calculated via coulometry measurements, versus gamma ray (API). (D) Calculated amount of calcite (wt.%)versus magnetic susceptibility (×10−3 SI). Outcrop measurements of gamma ray and magnetic susceptibility decrease linearly with calcite content, indicating that both geophysicallogs serve as a proxy for calcite content.
8 S.L. Halgedahl et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx
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RRERocks in this first interval consist largely of dark gray, rhythmically
bedded, highly peloidal calcisiltite containing lenses of ooliticwackestone, although intervals of thin-
^bedded (b a few centimeters
thick), laminated calcisiltite also occur (Grannis, 1982; Langenburg,2003; this study). Most rhythmite beds are remarkably uniform inthickness (~3–
^5^c^m thick), they exhibit undulatory tops and bottoms
with b1–^2^̂cm of relief, occasionally they contain cross-
^beds, and they
are separated by thin (~1–^2^c^m) layers of tan, silty, dolomitic material
(^̂Fig. 3A). Rare intraclasts mainly occur near bottoms of beds and aregenerally smaller than 0.
^5^cm in size (e.g., Grannis, 1982). Coarse-
^grained, basal bioclastic lags (Grannis, 1982; Schneider, 2000) areoverlain by fine-
^scale laminations (Langenburg, 2003) and generally
fining-^upward material (Grannis, 1982; Schneider, 2000; Langenburg,
2003). Horizontal burrows (~0.5 to a few centimeters in length) arecommon in some horizons (Grannis, 1982; Schneider, 2000; Langen-burg, 2003; this study). Thin sections studied by Grannis (1982) alsorevealed densely packed algal (cyanobacteria) filaments and rarerelicts of algal laminae attached to the tops of some beds.
Rhythmites of the middle Wheeler Formation extend ~^80 m
^̂strat-
igraphically below the rock interval detailed here (Fig. 2), constitutingmuch of the middle member of the Wheeler Formation. Althoughgeophysical logs of this underlying
^80 m
^̂are not presented in this
paper, descriptions of these rocks are important for subsequentinterpretation of lithofacies. Grannis (1982), Schneider (2000), andLangenburg (2003) presented detailed lithologic descriptions of thisinterval, and most of their data have been supported both by field
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
4observations and examination of polished slabs by the present4authors. In general, this lower
^80 m
^̂is very similar to the upper
4~^20 m
^interval of rhythmites reported here.
44.2.2. 0 to^31 m
^̂4The next stratigraphic interval is composed of several lithofacies,4including medium-
^bedded (1–
^3^m^thick) wackestone/packstone,
4very thin-^bedded packstone (2–
^4^̂cm thick), very thin-
^bedded, platy,
4argillaceous limestone (b^2^cm thick), mudrock, and medium-
^bedded
4packstone/grainstone. Medium-^bedded wackestone/packstone dom-
4inates the 0–^16-
^m^interval. These rocks display undulatory bedding,
4three dimensional burrow galleries filled with dolomitic silt, and rare4horizons containing thin stringers of ooids and small-
^scale (a few
4centimeter) cross-^bedding; these beds are interbedded with lami-
4nated gray limestone beds showing few conspicuous signs of4bioturbation (Langenburg, 2003; this study). Very thin-
^bedded
4packstone and very thin-^bedded, platy, argillaceous limestone beds
4often display trilobite fragments on purplish, silty top surfaces, and4some beds contain ooids.4Punctuating the upper half of the interval are three resistant, dark5gray beds of ooidal, highly peloidal, burrow-
^mottled packstone-
5^grainstone containing bioclastic debris (Figs. 2, 3B and
^C) (Grannis,
51980; Langenburg, 2003; Brett et al., this volume; this paper).5These beds range in thickness from about 0.3 to 1.
^0 m
^̂. Although not
5as well exposed here as in the area studied by Brett et al. (this volume)5~1.
^3^km to the northwest, these three resistant limestones correspond
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
DPR
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Fig. 6. Stratigraphic profiles of gamma-ray (solid circles) and magnetic susceptibility (open triangles) in the upper Wheeler Formation for the three individual profiles “W”, “C”, and“E” of Fig. 1B. All three profiles begin at grainstone unit T2. Outcrops and logs along the “C” transect terminated at a rubble-filled stream valley. Replicability of repeat gamma-raymeasurements is illustrated on transect “E”. Datum for all three transects is the contact between the middle and upper members of the Wheeler Formation.
9S.L. Halgedahl et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx
ARTICLE IN PRESS
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to T1, T2, and T3 of Brett et al. (this volume). T2 is a locally prominentmarker that can be traced along strike at least 1–
^2^̂km to the southeast.
Top surfaces of T1, T2, and T3 are furrowed by elongate, quasi-
^linear runnels, several centimeters wide, no more than a few cen-timeters deep, and spaced ~3–
^30^^cm apart (
^̂Fig. 3B and
^C). Many
runnels are filled with tan, silty, material and are commonly asso-ciated with several-
^centimeters-
^wide pockets lined with ferruginous
crust. Some runnels contain “traffic jams” of large (0.^5^cm) oncoids
(e.g, Brett et al., this volume). Thin sections studied by Grannis (1982)show that runnels truncate oncoids and bioclasts anchored within theunderlying rock matrix. Because runnels can be paleoslope indicators(e.g., Allen, 1982), azimuths of the dip vectors for 46 runnels on topsof T1, T2, and T3 were measured with a Brunton compass. Thesemeasurements gave a mean azimuth of 245° (95% confidence intervalof 1.7°) with respect to geographic north.
Natural outcrops of T1, T2, and T3 are largely separated by soilcover. Trenching of soil to depths of 15–
^30^̂cm, however, reveals thin-
^bedded (3–
^5^^cm thick) argillaceous limestones and calcareous
mudrock. Pinkish tops of some limestone beds are covered bydense concentrations of disarticulated polymerid trilobite remains(e.g., Olenoides nevadensis), shells of the mollusk Stenothecoides, andProtospongia spicules.
Overlying and in stratigraphic contact with T2 is a thin (~0.^3 m
^)
bed of bluish-^gray, fissile mudrock containing abundant calcareous
concretions. The majority of concretions are discoid in shape (ratio ofthickness to maximum dimension ~0.1 to 0.5) and with maximumdimensions ranging from ~1
^̂cm to ~
^30
^cm; when found in situ, some
are strongly elongated parallel to the underlying runnels. Immediatelyoverlying the concretion bed is a thin (b0.
^5 m
^) interval of fissile, tan-
^weathering mudrock containing abundant, articulated agnostid tri-lobite fossils.
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
TE4.2.3. 31 to^38 m
^Rocks within this interval are dominantly platy, resistant gray
mudrocks which weather to buff. Many contain very thin (b0.^5^cm),
highly calcareous stringers. At ~35.^5 m
^is a thin (~
^1^cm thick),
resistant limestone bed whose bottom displays prominent horizontalburrows a few centimeters in length (
^̂Fig. 3D); on its top are in-
articulate brachiopods (Acrothele). This bed can be traced laterallyacross the entire study area. Progressing up-
^section, the platy mud-
rocks are occasionally interrupted by thin (b0.^3 m
^) beds of fissile,
bluish-^gray shale containing articulated, diminutive (b
^5^mm) poly-
merid trilobites and well-^preserved agnostids.
4.2.4.^38 m
^to^44 m
^At ~^38 m
^above the base of the upper Wheeler Formation is the
first of three mudrock marker beds whose surfaces weather to red.Beneath the very thin (b0.
^1^mm) red veneer, the relatively un-
weathered mudrock is grey. A few centimeters above the top of thisfirst red marker is a thin (b
^5 c
^m) zone containing abundant agnostid
trilobites (Baltagnostus eurypyx) and tiny (b3 mm) polymerids(Jenkinsonia varga and Brachyaspidion sulcatum) (Fig. 9). On somebedding surfaces these small trilobites can be as abundant as 100/m
^2
to 400/m^2. They exhibit no preferential orientation of their long axes.
The zone of exceptional fossil preservation occurs from ~38.^3 m
^to at least 44.^4 m
^above the base of the upper Wheeler Formation.
Here, rocks consist mainly of dark olive to dark gray, very thin-^bedded
to laminated mudrock. Often, thin beds occur as light gray and darkgray couplets, ~0.5–
^20^̂mm thick (e.g.,
^̂Fig. 4C) (also see Gaines and
Droser, 2005; Gaines et al., 2005). Macroscopic evidence of bioturba-tion is rarely evident, but when present it is in the form of horizontalburrows, ~
^1^cm to a few centimeters in length, sometimes stuffed
with pellets. Most thin beds and laminae are laterally continuous
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
ECTEDPR
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Fig. 7. Expanded plots of two logged intervals, showing spatially high-frequency cycles. Upper plot: γ-ray (solid circles) and χ (open triangles) logged within the upper portion ofcalcareous shale on transect “W”. Lower plot: γ-ray obtained from two trenched sections between limestone units T1 and T3 (see text). Results from these trenches demonstrate thathigher-order cycles are superimposed on the overall trends evident in Fig. 6. Datum is the top of the middle member of the Wheeler Formation.
10 S.L. Halgedahl et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx
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RRand uninterrupted by signs of current or wave activity (^̂Fig. 4C)
(e.g., Gaines et al., 2005).
4.2.5.^44 m
^to^73 m
^Mudrocks in the interval from ~44 to^73 m
^become increasingly
slabby and resistant up-^section (
^̂Fig. 3E and
^F) and form a series of
ledges on the hillsides (e.g.,^̂Fig. 1C). Polished slabs taken from this
interval reveal that while some horizons do consist of thin, parallellaminae, there is an increase up-
^section in the percentage of strata
which exhibit signs of reworking, such as irregular bedding contacts,small intraclasts, thin lenses, and bioclastic fragments (
^̂Fig. 4A and
^B).
At ~^73 m
^a thin, ~
^2^cm-
^thick layer of calcareous mudrock is dis-
rupted on its bottom surface by large, high-^relief, horizontal burrows
which are up to^10
^cm in length and N
^1^cm in diameter. The top of this
same bed is covered by trilobite hash.
4.2.6.^73 m
^to^90 m
^Mudrock at ~^73 m
^is overlain by several meters of strata
consisting of ~3 to^6 c
^-^thick layers of buff-
^colored, nodular limestone
with orange, shaly partings. Overlying these nodular limestones is a^~5–
^7^m^-^thick unit of dark gray, ooidal, intensely burrow-
^mottled
packstone/grainstone which forms a cliff (^̂Fig. 3G). The study section
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
5is capped by ~2–^4^m^of carbonate boundstone containing thrombo-
5lites and stromatolites (^̂Fig. 3H), some as large as 1.
^5 m
^in diameter.
54.3. Fossils
5Both polymerid and agnostid trilobites occur throughout much of5the ~
^48 m
^of mudrock logged here. Fully articulated trilobite fossils
5are relatively rare outside the γ-^ray hot zone, however. Exceptions
5include several very thin, clay-^rich beds of fissile mudrock in the
5~10-^m^interval just beneath and at the base of the hot zone: these beds
5contain dense accumulations of small (b^5^mm), articulated specimens
5of Elrathia kingii,^J. varga,
^B. sulcatum and the agnostid
^B. eurypyx (Fig. 9)
5(also see results in preceding section). Most of these diminutive5trilobites are fully articulated, occur only a few centimeters apart on5single bedding planes, and exhibit no preferential orientation of their6long axes. Throughout much of the remaining hot zone, these small6trilobites are present, though in lesser abundance.6Aboutmidway through the hot zoneoccurs an interval dominatedby6the trilobite
^E. kingii; in this same interval at least one track of an
6unidentifiedmetazoanhasbeen found(T. Abbott, pers. commun., 2004).6The vast majority of soft-
^bodied fossils found by two of the present
6authors (SLH and RDJ) occurs in two intervals: between 38.3 and 39.
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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Fig. 8. Combined gamma ray measurements from the three profiles (small diamonds); carbonate analyses (large solid dots); and lithostratigraphy (Fig. 2). The gamma-raymeasurements are those of Fig. 6, supplemented with a suite of measurements made along the western profile between the T2 limestone unit and the underlying limestone that topsthe middle member of the Wheeler Formation. (Datum: contact between the upper and middle members of the Wheeler Formation.)
11S.L. Halgedahl et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx
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2 m^, and between about 43.6 and 44.
^4 m
^. Several representative
specimens are shown in Fig. 10; these demonstrate the wide diversityof organisms found in the upper Wheeler Formation, including an-nelid worms, priapulid worms, hyolithids, non-
^trilobite arthropods,
lightly skeletonized arthropod appendages (Anomalocaris claws),branchiocarids with telsons, intact algae, and a multitude of poorlypreserved worm-
^like metazoans (e.g., Briggs and Robison, 1984;
Conway Morris and Robison, 1986; Robison, 1991; Briggs et al., 2008).The first specimen of
^E. kingii exhibiting soft parts was found along
transect “C” at ~^44 m
^above the base of the upper Wheeler Formation
(Briggs et al., 2008).A “fossil log” recorded over an ~1-
^m^-^thick interval in the lower
part of the hot zone shows that, to a first approximation, most of thevarious soft-
^bodied organisms occur randomly throughout this
interval, rather than each type being exclusive to a specific horizon(Fig. 11). Exceptions to this observation are Choia sponges, most ofwhich are found in the upper half of this interval.
Many specimens, such as the branchiocarid with telson, a small,undescribed arthropod, somewormswith clear annulations, andmostpoorly preserved vermiform organisms, are preserved as black, re-flective films (Fig. 10). In contrast, other specimens are preserved ascoatings ranging from tan to red in color. Near the base of the hot zone,phyllocarid arthropods often are preserved as black films with bothvalves intact, and sometimes with complete telson (
^̂Fig. 10C) (Briggs
et al., 2008). Within and above the hot zone throughout most ofthe three transects, single phyllocarid valves lacking soft parts are
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
common and they are preserved as buff-^to-
^red colored coatings, even
when split from apparently fresh rock.The two soft-
^bodied intervals quarried most extensively are not
the only stratawhich yield signs of soft-^bodied preservation, however:
float between and up to a few meters above these two intervals hasyielded well-
^preserved specimens of algae (e.g., Marpolia), Selkirkia,
and poorly preserved vermiform metazoans with gut traces (thisstudy). Furthermore, well-
^preserved, articulated Marpolia have been
recovered from finely-^laminated beds about 20–
^25^m^above the soft-
^bodied interval; these latter beds are bracketed by stratawhich exhibitirregular bed-
^to-
^bed contacts (
^̂Fig. 4A and
^B).
5. Interpretation
5.1. Log crossplots
Plots of γ-^ray and χ in Figs. 5 and 6 support the hypothesis that
both γ -^ray and χ serve as terrigenous/carbonate proxies in this
particular geologic setting, as discussed below.The crossplot of Th versus K in Fig. 5A yields a linear relationship
between the two elements throughout the logged section, with a highdegree of correlation. The line that fits these data best has a slope of5.2. Two main conclusions can be drawn from this crossplot.
First, the linear relationship between Th and K and its highcorrelation coefficient strongly suggest that clay mineralogy (e.g., theratios among different clay minerals) is nearly constant through the
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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Fig. 9. Generalized fossil abundances within the upper Wheeler Formation.
12 S.L. Halgedahl et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx
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study interval. If this were not so, then this plot would exhibit either avery large amount of scatter or a nonlinear relation, both indicative ofsignificant changes in dominant clay composition within the loggedsection (e.g., Fertl, 1983a; Schlumberger, 1989; Ryder, 1996).
Second, the Th/K ratio,which is sensitive to claymineralogy (Hassanet al., 1976), is consistent with the dominant clay mineral being illite,which has a Th/K ratio of ~2.0–
^5.5 (Schlumberger, 1989; Ryder, 1996).
Illite displays a fairly wide range of Th/K values, because it commonlycontains interlayers of smectite or chlorite (Moore and Reynolds,1997),both ofwhich raise Th/K (Schlumberger,1989; Ryder,1996). FromX-
^ray
diffraction analyses, Gaines et al. (2005) determined that illite andchlorite are the major clay minerals in mudrocks sampled from theupper Wheeler Formation in the House Range, about 30–
^40^^km
southwest of the Drum Mountains (Fig. 1A). The original depositionalclay mineral assemblage could have been different, however.For example, smectite plus potassium feldspar are transformed intoillite, some chlorite, and quartz by burial to 3–
^5^̂km (e.g., Hower et al.,
1976; Hower,1981;Moore and Reynolds,1997), aswould have occurredduring the Paleozoic when the Wheeler Formation was buried by4.5–
^5.^5^km of overburden (Hintze, 1988). This transformation does
not change overall concentrations of K, Th, and U, but it may explainthe presence of quartz in X-
^ray diffraction spectra of Wheeler
mudrocks from the House Range (Gaines et al., 2005).χ increases linearly with γ-
^ray (
^̂Fig. 5B). With respect to other
plots in Fig. 5, the linear relation in^̂Fig. 5B exhibits higher dispersion.
This dispersion results mainly from the approximately two orders ofmagnitude difference between the volumes measured by the twotechniques: that is, the γ-
^ray tool averages over much more lithologic
heterogeneity than does the χ meter.
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
T 6As discussed earlier, the magnetic susceptibility of these rocks6could be controlled largely by permanently magnetic minerals6(e.g., magnetite, hematite), minerals which are not permanently6magnetic (e.g., paramagnetic clays), or both. Magnetic susceptibil-6ities of illite, smectite, and chlorite are very similar (~3–
^4×10−
^4 SI)
6(Hunt et al., 1995; Dunlop and Ozdemir,1997;Martin-^Hernandez and
6Hirt, 2003) and are close to the maximum values obtained from the6most clay-
^rich mudrocks studied here (
^̂Fig. 5B). Thus, clays can
6account for the observed magnetic susceptibilities of these rocks.6The most likely explanation for the linear increase of χ with γ-
^ray is
6that both geophysical properties primarily reflect clay abundance.6Both γ-
^ray and χ drop linearly as CaCO3 increases (^̂
Fig. 5C and^D).
6These plots indicate that, to first order, the composition of these rocks6is a two-
^component system—
^calcite and terrigenous (clay)—
^with
6the responses of both γ-^ray and χ being proportional to the
7percentage of the terrigenous component. This does not imply that7the terrigenous fraction is exactly uniform in composition; it does7suggest that any variations in terrigenous composition are second-7
^order effects in comparison to the dominant mineralogical variable,
7carbonate dilution.7The linear decrease of γ-
^ray with increasing CaCO3 (
^̂Fig. 5C)
7indicates that, by volume, the ratio of clay minerals to any non-7radioactive minerals of terrigenous origin is approximately constant7throughout the logged section. The same argument holds for the ratios7of magnetic minerals of terrigenous origin, including clays, to other7terrigenous minerals, whose contributions to χ are minimal (
^̂Fig. 5D).
7Thus, minerals of terrigenous origin are “traveling together” in the7same ratios with respect to each other in these rocks. Were this not so,7then either the crossplots in
^̂Fig. 5C and dwould be highly nonlinear or
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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Fig. 10. Examples of soft-body preservation from the gamma-ray “hot zone”. Black scale bars: 2 cm; blue scale bar (Figures e and k): 1 cm. (A) Marpolia, an alga. (B) Yuknessia, aplanktic alga. (C) Branchiocaris with telson and both valves. (D) Choia, a sponge with long, fragile spicules. (E) undescribed segmented metazoan. (F) undescribed arthropod, withgut trace and appendages. (G) and (H) undescribed vermiform metazoans exhibiting signs of decay. (I) Mollisonia (Briggs et al., 2008). (J) part of Fasiculus (?). (K) undescribedannelid worm. (L) Anomalocaris (?) claw. (M) Selkirkia, with spiny grasping tools on proboscis. (For interpretation of the references to colour in this figure legend, the reader isreferred to the web version of this article.)
13S.L. Halgedahl et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx
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they would exhibit a much larger degree of scatter than obtained here,thus reflecting a highly variable partitioning of clay/magneticminerals with respect to other terrigenous minerals that contributelittle to either the γ-
^ray or χ signal. These trends suggest that the type
of source rock that supplied the terrigenous component remained thesame throughout the period when these sediments were deposited.
Thus all four crossplots in Fig. 5 support the hypothesis that bothγ-^ray and χ primarily reflect the same component: minerals of ter-
rigenous origin, primarily clays.
5.2. Lithofacies
5.2.1. Logs and lithofaciesThe plots of γ-
^ray and χ against stratigraphic position (Figs. 6, 7,
and 8) clearly distinguish between carbonate-^rich and clay-
^rich rocks.
Furthermore, the two logs quantitatively reveal trends in clay versuscarbonate which could be difficult to detect in outcrop. Limestones inthe top
^20 m
^of the middle Wheeler Formation are exceptionally
“clean”, with very low values of γ-^ray and χ and with over 90%
carbonate. The stromatolitic limestone at the top of the studiedsection is similarly low in clay. Between 0 and ~
^30m
^, however, there is
a gradual rise in γ-^ray and thus clay content, and near ~24–
^31^m^there
are several γ-^ray spikes indicative of thin, more clay-
^rich intervals.
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
These clay-^rich intervals correspond to the very thinly-
^bedded
argillaceous limestone and mudrock between grainstone beds T1,T2, and T3, as shown in the detailed γ-
^ray profile of Fig. 7.
The^7 m
^just below the γ-
^ray hot zone exhibit a rapid rise in both
γ-^ray and χ, despite the generally monotonous appearance of most
mudrocks in this interval (Fig. 8). The hot zone yields the highestreadings of γ-
^ray and χ, and some of the lowest values CaCO3, ob-
tained throughout the three transects. Note, however, that bothgeophysical properties display spatially rapid oscillations within thiszone, suggesting temporally rapid variations of clay content. Abovethe hot zone the clay content gradually drops; in outcrop, the principalsign of this drop is that mudrock beds become increasingly resistantup-
^section. Above approximately
^73 m
^, mudrocks are visibly inter-
bedded with thin layers of carbonate, until carbonate finally becomesthe dominant component; it is in this short interval that γ-
^ray drops
precipitously to near-^zero levels, above which burrow-
^mottled lime-
stones and stromatolitic limestones consist of over 80% carbonate,based on γ-
^ray, χ, and CaCO3 data.
5.2.2. Lithofacies^model
Several Early Paleozoic mixed carbonate-^siliciclastic rock succes-
sions deposited on ramps bear striking similarities to the lithofaciesof the Wheeler Formation in the Drum Mountains. Particularly
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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Fig.11. Fossil logs from the lowest portion of the “hot zone” at two quarries, showing locations of recovered fossils with a resolution of about±3 cm. The “first red”marker, the datumfor these logs, is ~38 m above the contact between the middle and upper members of the Wheeler Formation.
14 S.L. Halgedahl et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx
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noteworthy is the Nolichucky Formation (Upper Cambrian) and itslateral equivalents in the Appalachian Valley and Ridge Province inVirginia, studied by Markello and Read (1981). They describedlithofacies both along-
^dip and along-
^strike, obtaining three dimen-
sional pictures of these formations. Lithofacies and lithofacies patternssimilar to those observed within the Nolichucky Formation havesubsequently been described for several other Early Paleozoic mixedcarbonate-
^siliciclastic ramps (e.g., Brett et al., 1990; Elrick and Read,
1991; Osleger and Read, 1991; Choi et al., 1999; Smith and Read, 1999;McLaughlin et al., 2004). Of special relevance here are Rees' (1986)study throughout the House Range Embayment and Elrick andSnider's (2002) analyses of lithofacies and high-
^order sea-
^level cycles
in the Marjum Formation (Middle Cambrian) in the House Range,Utah, about
^42
^km southwest of the Drum Mountains (
^̂Fig. 1A).
Markello and Read (1981) interpreted the Nolichucky Formationand its equivalents to have been deposited within an intrashelf basinon a gentle ramp (slope ≪ 1°), largely surrounded by a regional shelfof shallow water carbonates. Owing to the gentle slope of the ramp,gravity slides and/or turbidites were rare in the Nolichucky, butsedimentationwas strongly influenced by storms (Markello and Read,1981). Similarly, the Wheeler and Marjum Formations are thought tohave been deposited on a gently-
^sloping homoclinal ramp (Rees,
1986; Elrick and Snider, 2002).Markello and Read (1981) described and interpreted four general
types of lithofacies in the Nolichucky Formation as one progresses up-
^ramp fromdeep to shallowwater: shales of the basin and/or deep ramp,ribbon limestones of the middle ramp, shallow-
^ramp ooid shoals, and
peritidal–^supratidal carbonates (also see Read,1980; Tucker andWright,
1990). This lithofacies pattern, and a similar one in the MarjumFormation studied by Elrick and Snider (2002), provide the conceptualframework for interpreting the upper part of the middle WheelerFormation and the upper Wheeler Formation in the Drum Mountainsstudied here.
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
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7According to the model of Markello and Read (1981), laminated,7fissile, fine-
^grained, clay-
^rich shales are deposited in a low energy,
7deep water setting below average storm wave base, far from the7carbonate factory. Mainly fine-
^grained, low-
^density clay particles and
7floccules and some fine-^grained, detrital carbonate (later to become
7micrite cement) are deposited in this depositional setting by weak7density currents, because the majority of coarser-
^grained sediments
7are dropped on shallower parts of the ramp or, in the case of very7coarse siliciclastics, are sequestered inland of the coast.7Proceeding up the ramp into somewhat shallower water, basinal8clay-
^rich shales interfinger with and eventually pass into ribbon
8carbonate facies of the middle ramp. Markello and Read (1981) de-8scribed two types of ribbon carbonates. The first type is highly peloidal8calcisiltite, which can be nodular-
^to thin-
^bedded (a few centimeters
8thick), often laminated, and which fines upward into thin mudstone8caps. Such beds may exhibit erosional bases, basal skeletal lags, and8rare cross-
^bedding. These features are interpreted as sediments re-
8worked by storms. Bioturbation is common, mainly in the form of8horizontal burrows on the tops of beds, produced by organisms that8colonized the sea floor between major storms. The laminated and8fining-
^upward layers are interpreted as sediments that settled from
8suspension just after storms, under conditions of waning energy8(Markello and Read, 1981).8Ribbon carbonates of the second sublithofacies on the middle8ramp are thin, ooidal/oncolitic, skeletal wackestones, packstones, and,8rarely, grainstones. These rocks are interpreted to have originated8from deposits carried down-
^ramp from shallow water by large storms
8and deposited on the middle ramp, because they are observed to pass8seaward into basinal facies and lack tidal flat features. Alternatively,8they could represent brief drops in relative sea level and thus short-8
^lived episodes of higher energy and shallow water, with respect to
8conditions usually dominant on this part of the ramp (Markello and8Read, 1981).
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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Ribbon limestones in the Marjum Formation studied by Elrick andSnider (2002) are very similar to the first type of ribbon limestonesdescribed by Markello and Read in the Nolichucky Formation. In theMarjum Formation, rhythmite facies consist of thin (a few centimetersthick), interbedded limestone and argillaceous limestone couplets,which are often laminated and rarely cross-
^laminated. Laminae are
very thin (submillimeter) and consist of graded pellets and microspar(see detailed descriptions of Elrick and Snider, 2002).
Despite very similar descriptions, Markello and Read (1981) andElrick and Snider (2002) interpreted their ribbon limestone faciessomewhat differently. Markello and Read (1981) interpreted eachrhythmite bed to represent a single storm event, on the basis ofgenerally fining-
^upward grain sizes within each bed. By contrast,
Elrick and Snider (2002) interpreted each rhythmite bed in theMarjum Formation to represent sedimentation from a multitude ofstorm events or low-
^density, storm-
^generated currents, on the basis
of many sets of fine laminae within each main bed. In either case,these several authors concluded that the rhythmite limestones weredeposited in deep water just above or slightly below average stormwave base, but in shallower water than were deposited laminated,clay-
^rich shale facies.
According to the model of Markello and Read (1981), the thirdmajor lithofacies consists of ooidal/oncolitic grainstones. These rocksare interpreted to represent ooid shoals in high energy, wave-
^agitated
waters on the shallow part of the ramp. The shallowest-^water
lithofacies are shallow water carbonates, which may contain stroma-tolites, and supratidal carbonates deposited on the back-
^ramp.
5.2.3. Lithofacies Interpretation, middle and upper Wheeler FormationThe rhythmically bedded wackestones–
^packstones in the upper
^20 m
^of the middle Wheeler Formation are interpreted here to be
analogous to the ribbon limestones studied by Markello and Read(1981) in the Nolichucky Formation and to those studied by Elrick andSnider (2002) in the Marjum Formation. By this interpretation, therhythmites are largely storm-
^reworked sediments deposited on the
middle ramp near storm wave base. This interpretation is based onscour features, parallel laminae, abundant peloids, generally fining-
^upward grain sizes, and, occasionally, basal skeletal lags of benthicorganisms, such as trilobites and echinoderms. The fairly regular bedthicknesses and scoured contacts (e.g., Langenburg, 2003) observedover tens of stratigraphic meters could suggest that depositionwas interrupted by rare but periodically occurring major storms(e.g., Markello and Read, 1981). Alternatively, successive laminaewithin individual beds (e.g., Langenburg, 2003) also could beinterpreted as amalgamated suspension deposits, each the productof a storm event (e.g., Elrick and Snider, 2002). Thus, the presentinterpretation of the rhythmically-
^bedded limestones in the middle
Wheeler Formation differs from that of Schneider (2000) andLangenburg (2003), who proposed that these rocks are turbiditescontaining incomplete Bouma sequences. However, the slope of atypical, homoclinal ramp (≪ 1°) probably is too gentle to triggersignificant, periodic turbidite flows (e.g., Read, 1980; Markello andRead, 1981; Tucker and Wright, 1990).
The very low clay content could have resulted from the majority offine-
^grained, low-
^density clay particles and/or clay floccules being
swept past the middle ramp and into the basin, as well as fromdilution of any terrigenous component by abundant carbonate. Thehigh carbonate content could have resulted both from fine-
^to-
^medium-
^grained carbonate washed onto the middle ramp from the
carbonate factory by storms and/or weak currents, and by in-^situ
production of peloids (pellets) by benthic infauna, epifauna and/orbacteria (Grannis, 1982; Chavetz, 1986).
Algal laminae still attached to bedding surfaces in some rhythmitebeds indicate that, at times, the sea floor was colonized (Grannis,1982), so that some carbonate could have been produced in situ.Abundant burrows on the tops of some beds indicate occasionally
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
TEDPR
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well-^oxygenated conditions. Also, thin, dolomitic layers betweenmain
rhythmite beds could have resulted from bioturbation betweenstorms, which opened high permeability pathways for exchange ofions and fluids to create dolomite (e.g., Ekdale et al., 1984). Occasionallenses containing oolites could have been deposited by either thelargest storms, capable of transporting coarse-
^grained material out to
sea, or to short-^lived drops in relative sea level.
Approximately^16 m
^of thin-
^bedded wackestone–
^packstone over-
lie the rhythmites (Fig. 2). Rare cross-^bedding, rip-
^up features,
intraclasts, macroscopically visible ooids, burrowed top surfaces,three-
^dimensional burrow galleries, and large, disarticulated trilobites
have been interpreted (Grannis, 1980; Schneider, 2000; Langenburg,2003) to indicate the near-
^terminal expression of a long-
^term,
shallowing-^upward trend toward a higher energy environment. In a
subsequent section, however, it will be shown that the γ-^ray log
suggests that this interval also could mark the beginning of a trans-gressive event.
The low γ-^ray ooidal/peloidal, skeletal packstone–
^grainstone beds
T1, T2 and T3 (Fig. 7) in the ~23 to^31 m
^interval are interpreted as
being deposited in shallow, wave-^agitated, high-
^energy, ooid shoals
on the shallow ramp (e.g., Markello and Read, 1981). Vigorous bio-turbation indicates well-
^oxygenated conditions capable of supporting
bottom-^dwelling life.
Prominent runnels are evident on the top surfaces of T1, T2 and T3.Truncation of clasts at runnel-
^fill margins indicates that these beds
were lithified before they were scoured by currents (Grannis, 1982).Runnels can form parallel to the paleoslope direction by corrasion of afirm substrate, mostly in the intertidal environment (e.g., McLean,1967; Milliman, 1974; Allen, 1982). The short spacing between mostadjacent runnels (~3–
^30^c^), their corrasional origin, and their cross-
^sectional geometry (
^̂Fig. 3C) distinguish them from deeper-
^water tidal
current ridges, which are usually spaced tens to even hundreds ofmeters apart (e.g., Allen, 1982).
The mean dip azimuth of the runnels (245°, 95% confidence in-terval of 1.7°) obtained here is statistically indistinguishable from thedown-
^slope azimuth (245°, 95% confidence interval of 3.3°) deter-
mined by Grannis (1982) from slumps, folds, and boudins in an ~^5 m
^zone where rhythmically-^bedded limestones in the lowest part of the
middle Wheeler Formation are contorted. This contorted zone hasbeen interpreted as the result of soft-
^sediment deformation during a
localized gravity slide (Grannis, 1982; Schneider, 2000). The agree-ment between these two very different kinds of data sets providesadditional evidence that the runnels point roughly parallel to paleo-slope and normal to the ancient coastline. Because the runnels' azi-muths are highly consistent among beds T1, T2, and T3, we concludethat the downslope direction remained fairly constant throughout theperiod when these beds were deposited.
Grainstone units T1, T2 and T3 are separated stratigraphically bylayers of calcareousmudrock and argillaceous limestone, as exemplifiedby the very detailed γ-
^ray log in Fig. 7 (also see Brett et al., this volume).
Each intervening, more clay-^rich interval with relatively elevated γ-
^ray
readings is interpreted as a short-^lived, deeper-
^water deposit which
shallows upward into the overlying grainstone unit. Dense concentra-tions of fossils, such as shells (Stenothecoides), disarticulated trilobites(e.g., O.
^nevadensis), and sponge spicules (e.g., Protospongia) could
be transgressive lags on starvation surfaces as sedimentation stalledduring deepening. Clay-
^rich beds overlying T2 contain abundant
concretions and articulated agnostids. Articulated agnostids wouldhave been buried rapidly in deep water below storm wave base(e.g., Robison,1972). Although concretions can have complex geochem-ical histories (e.g., Martin, 1999; Vorhies and Gaines, 2005), their initialgrowth stage typically occurs within the sulfate-
^reducing zone, a few
meters below the seafloor. Very low sedimentation rates can promoteprolonged growth of large concretions (Martin, 1999).
The interval of mudrock intercalated with very thin limestonebeds from ~31 to ~
^38 m
^is interpreted to represent a pronounced
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
C
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deepeningevent, generallybelowaverage stormwavebase (e.g.,Markelloand Read, 1981). Although most of these rocks appear monotonousin outcrop, this interpretation is supported by the rapid rise in bothγ-^ray and χ and by the rapid drop in CaCO3 with stratigraphic
position (Figs. 6 and 8). High γ-^ray readings, fine grain size (clay)
and laterally continuous thin beds and laminae are consistent withan energetically quiet depositional setting. Within this interval,somewhat more calcareous, resistant mudrocks are interrupted byseveral thin (b0.
^3 m
^) beds of highly fissile gray shale, some of which
contain abundant, very small (b0.5^̂cm), fully articulated polymerid and
agnostid trilobites. Agnostids may have lived a pelagic, cosmopolitanlife, seaward of high-
^energy coastal waters (Robison, 1972; but also see
Brett et al., this volume), although disarticulated exuviae couldbe washed into shallow water by strong currents or storms. Theabundance and excellent state of preservation of these fossils lendfurther support to the interpretation that these sediments weredeposited rapidly in a low energy, deep-
^water setting.
The first “red marker” bed occurs at ~38.^0 m
^. A few centimeters
above this marker lies a 5-^c^m thick interval of abundant agnostid
trilobites and small polymerids, overlain by a ~6-^m^-^thick zone with
highest γ-^ray, with highest χ, and with exceptional fossil preservation
of a varied biota (Fig. 10) (e.g., Robison, 1991; Briggs et al., 2008; thispaper). Based on the presence of continuous laminae, few macroscopicsigns of bioturbation, very fine grain sizes (i.e., clay) (e.g., Gaines et al.,2005; this study; Brett et al., this volume), abundant and fully-
^articulated agnostids, excellent preservation of fossils, maximumvalues of the γ-
^ray and χ logs, and low values of CaCO3, we interpret
the 38.3–^44.
^4m
^hot zone to represent a deep ramp setting, below storm
wave base, and farthest from the carbonate factory of the rocks studiedhere. The very thin, parallel beds and fine, parallel laminae (
^̂Fig. 4C)
could have resulted from suspension settling of both fine-^grained
siliciclastics, mainly clay, and some fine-^grained carbonate, carried into
deep water by weak density currents generated by tides or storms(distal tempestites) (Rogers,1984; Elrick and Snider, 2002; Gaines et al.,2005). Thus the present interpretation differs from that of Robison(1991), Schneider (2000), and Langenburg (2003), who interpretedthese mudrocks as being deposited in a shallow-
^water lagoon.
Up-^section from the hot zone, mudrocks in the interval ~44.4 to
~^73 m
^are increasingly slabby and resistant, forming a series of ledges
on the hillsides (e.g.,^̂Fig. 1C). Although some beds in this stratigraphic
interval display virtually undisturbed, parallel laminae, most othersshow evidence of bottom current activity, intraclasts, and some signsof horizontal burrowing (
^̂Fig. 4A and
^B). Both γ-
^ray and χ decrease
up-^section, while CaCO3 increases. We interpret this interval to
represent a shallowing-^upward succession, based on all logs, on the
overall scarcity of soft-^bodied fossils and agnostid trilobites, on
nonlaminar bedding, and small intraclasts. The culmination of thisshallowing-
^upward trend is marked by intensely burrow-
^mottled
limestone capped by a stromatolitic limestone, indicative of shallow,oxygenated water (
^̂Fig. 3G and
^H).
On the “W” transect, outcrops afforded sufficiently high spatialresolution to reveal several oscillations on both the γ-
^ray and χ logs
(Fig. 7). These oscillations may indicate high frequency excursionsof shallowing (relatively lower γ and χ) and deepening (relativelyhigher γ and χ) superimposed upon a longer-
^term shallowing-
^upward pattern.
5.3. Changes in relative sea level and sequence stratigraphy
5.3.1. IntroductionNearly all published sequence stratigraphic analyses address either
dominantly siliciclastic margins (e.g., Posamentier and Vail, 1988;Posamentier et al., 1988; Van Wagoner et al., 1990; Schlager, 1993;Posamentier and Allen, 1999; Catuneanu, 2002) or dominantlycarbonate margins (e.g., Aurell, 1991; Loucks and Sarg, 1993; Aurellet al., 1998; Wright and Burchette, 1998; Harris et al., 1999). Although
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
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1rare in the modern oceans, mixed carbonate-^siliciclastic margins are
1common in the rock record, associated with either passive margins1or foreland basins (e.g., Handford and Loucks, 1993). For example,1deposition on the Laurentian margin during Middle Cambrian to1Middle Ordovician involved “grand cycles”, each consisting of a shaly1half-
^cycle which shoals upward into a carbonate half-
^cycle (Aitken,
11966, 1978).1Most of the aforementioned studies address margins with a shelf-1
^break type of geometry. Far fewer studies have focused on mixed
1carbonate-^siliciclastic successions on gentle (≪ 1°) ramps, as the
1Wheeler and Marjum/Pierson Cove Formations of the House Range1Embayment are thought to represent (e.g., Markello and Read, 1981;1Read, 1982; Rees, 1986; Tucker and Wright, 1990; Wright and1Burchette, 1998; Elrick and Snider, 2002). The depositional style on1a gently-
^inclined ramp is particularly sensitive to changes of sea level:
1even a fairly modest change can cause dramatic landward or seaward1shifts of the coastline. Consequently, the depositional system can1migrate landward or seaward by large distances (e.g., Elrick and1Snider, 2002; Coe, 2003).1In the House Range Embayment, Rees (1986) hypothesized that1local accommodation space was provided initially by a combination1of eustatic sea level rise and downward displacement on a normal1fault ~
^50
^km southwest of the Drum Mountains (
^̂Fig. 1A). Faulting
1began during deposition of the uppermost Swasey Formation, which1immediately underlies theWheeler Formation (Fig. 2); its main phase1may have ended during Marjum Formation time (Rees, 1986; Elrick1and Snider, 2002), although some smaller-
^scale rejuvenation may
1have occurred subsequently (Miller et al., 2003). Although faulting is1thought to have caused the initial drowning event (e.g., Rees, 1986),1it has yet to be determined which of the following was the dominant1control on relative sea level during Wheeler time: eustasy, local1tectonics, or the net effects of sediment supply, compaction, and sub-1sidence. Sequence stratigraphic simulations based on two-
^dimensional
1profiles of theWheeler Formation are needed to quantitatively account1for thevariables affecting relative sea level in this rock succession.Also, it1is important to note that the source of siliciclastics within the House1Range Embayment has not been resolved. Proposed source areas and1their inferred transport mechanisms include: the east or northwest1region of the craton near the House Range embayment, via continental1runoff (Hintze and Robison, 1975; Rogers, 1984; Rees, 1986), and a1northwest source as distant as Canada, from which sediment was1transported either bywind or geostrophic currents (Aitken,1997; Elrick1and Snider, 2002).1In view of the unknowns above, the upper part of the middle1Wheeler and the upper Wheeler Formation in the Drum Mountains1are discussed below in terms of a simple sequence stratigraphic model1proposed by Elrick and Snider (2002) in their interpretation of the1Marjum Formation. This model also is consistent with interpretations1of the Nolichucky Formation by Markello and Read (1981). It is1assumed that sedimentation on a carbonate-
^siliciclastic ramp consists
1of shallow-^water carbonate production and supply of detrital
1carbonate from a “carbonate factory”, plus deposition of siliciclastics1derived from an inland source via rivers, currents, or wind (e.g., Read,11980; Markello and Read, 1981; Osleger and Montañez, 1996; Choi1et al., 1999; Elrick and Snider, 2002; Bosence, 2003; McLaughlin et al.,12004). During transgressions and highstands, coarse siliciclastics1(e.g., gravel, sand) are deposited inland of the coast; by contrast, low-1
^density clay floccules can be transported down-
^ramp and even into
1very deep water by gentle currents. Delivery of detrital carbonate to1the distal portion of the ramp would be reduced during transgression1and highstand as the carbonate factory migrated landward, increasing1the transport distance between the carbonate factory and down-
^ramp
1sites. Conversely, a drop in relative sea level, whether caused by1eustasy or sedimentary infilling of accommodation space, would1cause basinward migration of the carbonate factory, shorter transport1distance, and enhanced delivery of detrital carbonate to a given down-
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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ARTICLE IN PRESS
^ramp site. Thus gamma-
^ray and magnetic susceptibility profiles could
be interpreted as indicators of transgressions and regressions on theramp, when used in conjunction with lithofacies observations.
On the basis of this conceptual framework, the broad structure ofthe geophysical and lithofacies profiles presented here is most simplyinterpreted as representing much of a full cycle of relative sea-
^level
change. Proposed sequence stratigraphic systems tracts and changesin relative water depth are plotted beside the CaCO3 log in Fig. 12; thecalcite log was constructed by applying the relation between CaCO3
and γ-^ray shown in
^̂Fig. 5C to the γ-
^ray data of Fig. 8. The last stage of a
basal lowstand systems tract (LST) is overlain by a shaling-^upward
transgressive systems tract (TST). A maximum flooding surfaceseparates the TST from the overlying highstand systems tract (HST).This long, subtly shoaling-
^upward HST abruptly changes to a rapid
drop in clay content, interpreted as the falling-^stage systems tract
(FSST). The boundary between the FSST and the lower part of theoverlying LST, near the transition to massive limestones of the PiersonCove Formation, is the top of the sequence.
5.3.2. Underlying^sequence
The very “clean” rhythmically-^bedded limestones from −̂20 to
^0m
^are interpreted to have been deposited on the deep-^to-
^middle ramp
during a period of somewhat low relative sea level (Markello andRead, 1981). Logs from only the top
^20 m
^of the rhythmites are
reported here, but this lithofacies constitutes a significant part of a^~
^101 m
^interval below the contact between the middle and upper
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Fig.12. Proposed sequence stratigraphic and relative sea level interpretations of the upper meFormation. Calcite percentages have been calculated from the relation between outcroLithostratigraphy is from Fig. 2. Diagram on right represents relative water depths; solidfrequency fluctuations.
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
OOF
Wheeler Formation. The rhythmites are underlain by ~20 meters offissile agnostid-
^rich mudrock, interpreted as part of an earlier high-
stand systems tract that followed retrogradation of the carbonatefactory during latest Swasey and lower Wheeler time (Rees, 1986;Schneider, 2000; Langenburg, 2003).
Subsequent to initial flooding of the Swasey Formation and de-position of deep-
^water mudrock and limestone of the lower Wheeler
Formation, either eustatic sea level dropped, with accompanyingseaward migration of the carbonate factory, or carbonate depositsprograded seaward; this produced the generally shallowing-
^upward
succession making up much of the middle member of the WheelerFormation (Schneider, 2000; Langenburg, 2003). Although depositedin the moderately deep water of the middle ramp, the uppermostportion of this member contains some intervals of oolitic cross-
^beds
and trilobite coquina, which are interpreted here to represent eitherpart of a lowstand systems tract (LST) or the initial phase of asediment-
^starved transgression.
5.3.3. Transgressive systems tractThe γ-
^ray log in the ~
^24 m
^overlying the rhythmites exhibits a
slowly rising trend, indicating a subtly increasing influx of clay withrespect to the very clean, underlying limestone. This gradual increaseis interpreted as the initial stage of a transgression. At 23.
^8 m
^, the
γ-^ray log rises abruptly to relatively high values: this jump is associated
with the thin-^bedded argillaceous limestones and shales between the
low γ-^ray grainstone beds T1 and T2 (Fig. 7). Similarly, γ-
^ray values are
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mber of theWheeler Formation and the top 20m of themiddle member of theWheelerp gamma ray measurements and carbonate determined by coulometry (Fig. 5C).curve indicates smoothed, long-term variations, and dashed curve represents higher-
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
C
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high at ~28.0–^30.
^7m
^, between the lowγ-
^ray grainstonebeds T2 and T3;
this second jump is associated with fissile mudrocks containingconcretions and agnostid trilobites. A third sharp rise in clay contentbetween 33.0 and 38.
^3 m
^is interpreted to represent the culmination of
an overall deepening-^upward, transgressive event.
The interval from approximately 0 to 38.^3 m
^therefore is inter-
preted as a major deepening, or transgressive systems tract (TST).Both the γ-
^ray log and lithofacies suggest that the transgression
occurred through a series of sea level pulses. Grainstone beds T1, T2,and T3 with runnels are interpreted here as being deposited duringrelatively short-
^lived lowstand to early transgressive events in wave-
^agitated, ooid shoals; they are separated by intervals of argillaceouslimestone and mudrock with articulated agnostids, representingdeposition in deeper water. Each of the three grainstones couldrepresent shallow-
^water lithofacies of higher-
^order (5th-
^order?) sea
level cycles superimposed on the TST of a lower-^order cycle (Fig. 12).
The spatially abrupt, deepening-^upward intervals between grain-
stone beds T1, T2 and T3 were not necessarily brief in time, however.For example, nodular-
^like bodies found on the top surface of grain-
stone bed T2 (Brett et al., this volume) and concretions within highlyfissile shale beds between T2 and T3 are interpreted as evidence fora very slow sedimentation rate, permitting growth of concretionswithin a zone of sulfate reduction beneath the sediment–
^water
interface (e.g., Raiswell, 1987; Martin, 1999).Calcareous mudrocks stratigraphically between T3 and ~
^38 m
^are
interbedded with the following: several thin intervals of highly fissileshale containing small, articulated trilobite fossils; occasional, verythinly bedded limestones; and one interval containing high-
^relief,
horizontal burrows, indicating a period of oxygenation. These variablelithologies suggest that the overall transgression above limestone unitT3 also may have been accompanied by several high-
^order sea-
^level
pulses.
5.3.4. Maximum flooding surfaceThe highest γ-
^ray, χ, and clay content occur at 38.3–
^44.
^4 m
^above
datum, where bulk carbonate content ranges from ~4% to ~20%.Although the maximum flooding surface (MFS) cannot be pinpointedprecisely without knowledge of the three-
^dimensional geometry of
the formation (as would be provided by seismic surveys), we place theMFS at, or very near, the initial gamma-
^ray peak at 38.
^5m
^, where local
water depth is interpreted to have been maximum and the carbonatefactory was farthest landward from this locality (e.g., Markello andRead, 1981; Elrick and Snider, 2002).
5.3.5. Highstand systems tractExtending from just above the MFS to nearly the top of the upper
Wheeler Formation at^73 m
^are mudrocks whose carbonate content
increases from near zero to N90% (Figs. 5 and 8). Above ~^53 m
^, soft-
^bodied fossils in the form of algae do occur but only rarely. Articulatedagnostids and phyllocarid/branchiocarid valves are present from theMFS to ~70–
^75^m^(Fig. 9), with relative abundances ranging from
abundant at the base to rare near the top of this interval; both couldindicate an open-
^shelf environment (Robison,1972; Burzin et al., 2001).
The interval from 38 to^72m
^is interpreted as the highstand system
tract (HST). According to this interpretation, the γ-^ray hot zone
represents deposition of clay-^rich sediments onto the deep ramp; the
low percentage of carbonate reflects the long transport distance fromthe carbonate factory, which had migrated farther landward from thispart of the basin in response to rising sea level. Subsequently, cal-careous sedimentation prograded seaward, so by dilution the clay-
^carbonate ratio gradually decreased at down-
^ramp sites.
Within the upper part of the HST, 4-^to 6-
^m^cycles are evident
in the γ-^ray and χ logs, indicating variations in clay-
^carbonate ratio
(Fig. 7). The origin of these cycles is unknown at the present time,although they could indicate 5th-
^order variations in relative sea-
^level.
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
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15.3.6. Falling stage systems tract and next lowstand systems tract1The uppermost few meters of the upper Wheeler Formation1consist of an interval of rapidly increasing carbonate percentage and1associated drop of γ-
^ray (Fig. 12). This transition is more gradual on
1the western traverse than on the eastern one (Fig. 6). In both, it begins1as occasional 1-
^c^m-
^thick, nodular limestone beds within dominantly
1siliciclastic mudrock, followed by increasingly abundant and thicker1nodular limestones with thinner orange shaly partings. Most fossils of1the eocrinoid Gogia spiralis occur here, as well as large, horizontal1burrows (Grannis, 1982; Schneider, 2000; this study).1These uppermost few meters are interpreted to represent the1falling stage systems tract (FSST), on the basis of the spatially abrupt1increase in carbonate up-
^section evident in both outcrop and geo-
1physical profiles (Figs. 3 and 6). This rapid increase may be attri-1butable to a forced regression. We place the boundary between FSST1and HST where the γ-
^ray profile exhibits a break in slope near
^72 m
^1(Fig. 12).1Strongly burrow-
^mottled, ooidal, peloidal, limestone with low
1γ-^ray readings and high CaCO3 occurs near the top of the upper
1Wheeler Formation. This lithofacies is interpreted as the terminal1expression of the shallowing-
^upward FSST, during which the locus
1of deposition was very close to the carbonate factory.1Overlying the burrow-
^mottled limestone are ooidal boundstones,
1including at least^2 m
^of large stromatolites (
^̂Fig. 3G and
^H); both γ-
^ray
1values and carbonate analyses indicate extremely clean carbonate with1little clay. These limestones are interpreted to indicate depositionwithin1a very shallow-
^water back-
^ramp environment (Markello and Read,
11981) during either the LST or earliest part of the next TST (Fig. 12).1It is important to note that ribbon limestones of the middle ramp1discussed at length by Read (1980), Markello and Read (1981), Elrick1and Snider (2002), and the present authors are absent in rocks of the1upper Wheeler Formation assigned here to the FSST or LST. Markello1and Read (1981) described down-
^ramp variations in lithofacies but
1did not place these lithofacies in the context of relative changes of sea1level; more important, they did not consider rates of sea level rise or1fall. Here, we propose that the long succession of ribbon limestones of1the middle Wheeler represents a protracted period of shallowing,1possibly associated with gradual sedimentary filling of the accom-1modation space. By contrast, the stratigraphically abrupt shallowing1within the uppermost Wheeler Formation could represent a tempo-1rally rapid transition into a shallow-
^water, high-
^energy environment,
1during which there was insufficient time for fully-^developed ribbon
1limestones to accumulate.
15.3.7. Erosion, differential subsidence, and the sequence boundary1Along thewestern transect, the shaly limestones of the FSSTappear1to grade smoothly into overlying, more massive, cliff-
^forming lime-
1stone of the upper LST (Fig. 6). Based on bedding attitudes of each1unit, the two units appear to be concordant.1Along the eastern transect, in contrast, several lines of evidence1indicate erosion and/or differential subsidence between FSST and LST.1Carbonate content increases more abruptly than on the western tran-1sect and the overall section is thinner (Fig. 6). The simplest in-1terpretation of these differences between the two gamma-
^ray profiles
1is that ~^5 m
^have been eroded from the top of the FSST at the eastern
1transect. Structural dips change substantially, dropping from an aver-1age of 37° in the upper shaly limestones to 27° in the overlying1massive limestones. Soil cover and bedding attitude prevent con-1firmation of this apparent angular unconformity by visual observation1of bedding surfaces in the field, although limited exposures on the1eastern flank of this hill appear to exhibit an angular unconformity.1We conclude that the FSST here was at least partially eroded away,1owing to rapid emergence of unlithified sediments into a higher-1
^energy shallow-
^water environment. Siliciclastic margins commonly
1exhibit attenuated, or more often missing, FSSTs due to erosion during1late-
^stage regression (e.g., Van Wagoner et al., 1990; Coe, 2003), but
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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similar data for ramp carbonate-^clay successions are rare. Here, the
patterns may be complicated by differential subsidence of the up-permost massive limestone, associated with relatively dense loadingon underlying weak, high-
^porosity muds. For example, simple erosion
cannot account for the 10° angular unconformity on the easternprofile, whereas differential subsidence may explain both this uncon-formity and its location ~1.
^5 m
^above the base of the massive capping
limestones, rather than at their erosional base. The capping limestonesexhibit major lateral variations in thickness, clay content, and stro-matolite size within their 3-
^k^m along-
^strike exposure in the Drum
Mountains (Vorwald, 1984).Whether the sequence boundary occurs at the top or the bottom of
the FSST is still debated (e.g., Coe, 2003). The sequence boundary istentatively placed at the base of the capping, cliff-
^forming limestone,
because this is where erosion clearly has occurred at this locality.In their sequence stratigraphic analysis of other Wheeler sequencesin the Drum Mountains, Brett et al. (this volume) similarly placesequence boundaries at the bases of clean, shallow-
^water carbonates.
5.3.8. Cycle duration and orderThe duration of the Wheeler cycle studied here can be estimated
only roughly, because: (1) the duration of the Wheeler Formationitself is not well constrained, and (2) only the upper fewmeters of theunderlying LST (ribbon limestones) were logged. Field observationsindicate that themiddlemember of theWheeler Formation is largely ashallowing-
^upward package (Schneider, 2000; Langenburg, 2003;
this study), but it is still unclear where the sequence boundary fallswithin the middle member. Assuming that only the top portion of themiddle member is LST, we estimate conservatively that the totalthickness of the middle-
^upper Wheeler relative sea-
^level sequence is
about 100–^120
^m^in thickness, or about one third of the overall
~^272 m
^thickness of the Wheeler Formation in the Drum Mountains
(Fig. 2).The Middle Cambrian stratigraphy of
^West-
^̂Central Utah includes a
series of formations consisting largely of limestones, bracketed at thebottom by the Tatow Member of the Pioche Formation and endingwith the Trippe Limestone (Hintze and Robison, 1975). Usingformation thicknesses for the Drum Mountains and nearby WahWah Mountains, House Range, and Fish Springs (Hintze, 1988), theWheeler Formation represents from 6% (WahWah and House Ranges)to 25% (Drum Mountains) of the overall Middle Cambrian. Assumingthat the middle-
^upper Wheeler sequence represents about one third
of total Wheeler Formation duration, and that the Middle Cambrianspans 12 m.y. (Gradstein et al., 2004), the duration of the WheelerFormation is ~0.7–
^3.0 m.y. and that of this cycle is ~0.2–
^1.0 m.y. Bond
et al. (1989) had estimated ~0.7 m.y. for the duration of the WheelerFormation, based on a similar analysis of the Wah Wah Range(~^100
^km from the Drum Mountains) and a 15 m.y. length for the
Middle Cambrian.The ~0.2–
^1.0 m.y. estimate for the Upper Wheeler cycle indicates
that it is a 3rd-^order cycle, based on Coe's (2003) data summary
indicating an ~0.2–^5 m.y. duration of such cycles. We recognize,
however, that it would be considered 4th-^order according to older
criteria (e.g., ~0.1–^1 m.y., Goldhammer et al. (1990)). In either case, it
would be precipitous to infer a mechanism for these sea-^level changes
from their cycle duration, until additional data encompassing the entireformation are obtained and studied. Whether this cycle was inducedtectonically in associationwith theHouseRange embaymentorwhetherit reflects eustatic sea level change is beyond the scope of this paper.
Earlier work (Grannis, 1980; Rees,1986; Schneider, 2000; Langen-burg, 2003) on the lower and middle Wheeler Formation, DrumMountains, suggests that flooding during lower Wheeler timeculminated in deposition of an ~20-
^m^interval dominated by clay-
^rich mudrocks with abundant agnostid trilobites. This interval occursat ~70–
^90^m^above the Swasey/Wheeler contact (Fig. 2), and it has
been interpreted to represent a deep, basinal setting. The mudrock is
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
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succeeded by rhythmically-^bedded limestone, which makes up a
significant portion of the middle Wheeler Formation; these lime-stones were interpreted as a gradually shallowing-
^upward succession.
When these earlier interpretations are combined with those pre-sented here for the upper part of the middle Wheeler and the upperWheeler Formation, we conclude that, in the Drum Mountains, theWheeler Formation recorded two 3rd-
^order sea level cycles.
5.4. Lagoonal or open-^shelf facies?
The analyses above interpret most of the upperWheeler Formationto represent an open-
^shelf system. However, the upper Wheeler
Formation in the DrumMountains has been considered to be lagoonalby several authors.
In part, the lagoonal interpretation has been extrapolated beyondits original context. Vorwald (1984) redefined the top of the WheelerFormation, raising it by 40–
^50^m^from the previous boundary
(e.g., Robison, 1964; Hintze and Robison, 1975) at the base of themassive, stromatolitic limestone, to include this limestone and anoverlying calcareous shale-
^and-
^limestone unit. Following Rees (1984,
pers. comm. to Vorwald), he interpreted this^50 m
^of “upper Wheeler
Formation” as lagoonal, based mainly on the following observations:rapid lateral facies variations (atypical for open-
^shelf sediments but
typical of lagoonal environments), paucity of agnostids (which areconfined to open-
^shelf pelagic environments away from shallow-
^water coastal turbulence (Robison (1972)), and laminated sediments(attributed to poor circulation). Rees and Robison (1989) and laterRobison (1991) retained this adjustment of theWheeler/Pierson Covecontact and this lagoonal interpretation of the upper
^50 m
^of rocks.
This interval, however, is largely outside the scope of our presentanalysis.
Grannis (1982) interpreted the unit referred to here as the upperWheeler Formation also as lagoonal, based mainly on the lack ofagnostids, on the mottled texture of the nodular limestones, and aninferred shallow-
^water origin of the wackestones. When Schneider
(2000) and Langenburg (2003) applied a sequence stratigraphicanalysis to the Wheeler Formation of the Drum Mountains, bothfollowed the lagoonal interpretation for their final largely-
^shale
parasequence. They, like several previous authors (Robison andRichards, 1981a,b; Grannis, 1982; Rees and Robison,1989), interpretedthis shale as the culmination of an overall shallowing-
^upward pattern
for the middle and upper Wheeler.Robison (1991) combined the fauna of the upper Wheeler For-
mation with those of the thin shale just above the stromatoliticlimestone into a “shallow Wheeler” fauna, which he comparedto three other Cambrian Konservat-
^Lagerstätten from Utah (“Deep
Wheeler” of the House Range, Marjum Formation, and SpenceShale) and to the Burgess Shale. He concluded that all shared re-markably similar proportions of genera within major taxa, but withoverall greater diversity of preserved Burgess genera. He failed tonote, however, that this conclusion is more consistent with all fiveKonservat-
^Lagerstätten representing an open-
^shelf environment,
rather than with four being open-^shelf and the Drum Mountains
section being lagoonal.We conclude that the upper Wheeler Formation of this analysis was
mainly deposited in an open-^shelf ramp environment, rather than
within a lagoon, based on the following observations: (1) a verticalprofile of lithofacies (Fig. 3) and geophysical responses (Fig. 6) that istypical of Early Paleozoic mixed carbonate-
^siliciclastic ramps; (2) the
characteristic open-^shelf facies and faunal sequence pattern described
by Brett et al. (this volume) for theWheeler Formation of both theDrumMountains and House Range; (3) the faunal similarity to other open-
^shelf Middle Cambrian sections, and particularly to the synchronousupper Wheeler Formation of the House Range (Robison, 1991), incontrast to the restricted-
^shelf polymerid fauna characteristic of
deposition within Great Basin inner detrital belts during the Middle
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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Cambrian (Robison, 1976); (4) the lack of any mapped outer reef orbarrier seaward of and correlative to this upper Wheeler Formation;(5) the abundance of fully articulated agnostids—
^thought to be
diagnostic of open-^shelf pelagic fauna—
^particularly at the MFS but
present throughout most of what we interpret as the deeper-^water
portion of the section (Fig. 9); and (6) the abundance of phyllocarids/branchiocarids, which have been reported from open-
^shelf environ-
ments but not lagoonal facies, and whose distributions here are mostsimply interpreted as open-
^shelf nektonic.
6. Exceptional preservation in the Wheeler Formation
Numerous models have been put forth to explain processes ofexceptional preservation in offshore Cambrian sediments. These mod-els include: the absence of burrowers in Cambrian deep-
^water facies
(e.g., Aronson,1992; Allison and Briggs, 1993; Aronson, 1993; Pickerill,1994; Orr et al., 2003); the presence of unique clay mineral as-semblages (Butterfield, 1995) or chemical conditions (Petrovich,2001) that retard decay; carcass sealing by sediment shrouds(Seilacher et al., 1985), which denies nutrients to the decay-
^producing
microbes and thus curtails their activity through build-^up of toxic
metabolites (e.g., Herrero, 1983; Allison, 1990); porosity occlusion,which physically seals organisms frommicrobial attack via collapse ofclay floccules under anoxic conditions, accompanied by earlycarbonate cementation (e.g., Gaines and Droser, 2005; Gaines et al.,2005); and precipitation of mineral films, such as pyrite, ironcarbonate, and apatite (Zhu et al., 2005).
These models agree that isolation of the organism from seawater,sub-
^seafloor fluid flow, and scavenging is needed to establish a
favorable environment for fossilization of soft parts. The modelsdiverge regarding how that isolated environment is attained. It islikely that many pathways could lead to exceptional preservation,depending on the local environment where organisms are entombed.Anoxia is usually considered to be a necessary but not sufficientcondition for soft-
^part preservation, however; for example, most de-
caying organisms quickly generate their own locally anoxic environ-ment, though few are fossilized (Allison, 1988a,b; Allison and Briggs,1991).
Brett (1995) hypothesized that late transgressive to early high-stand deposition might provide the combination of obrution eventsand anoxic conditions that promotes exceptional preservation(Hallam and Bradshaw, 1979; Kauffman, 1981; Wignall and Hallam,1991; Hallam, 1992; Wignall, 1994). On the basis of geophysical logs,lithofacies, and fossils, the hot zone in the upper Wheeler Formation,Drum Mountains, is interpreted here to represent rapid depositionduring early highstand in a low-
^energy, distal ramp setting below
average storm wave base, with most soft-^bodied preservation oc-
curring not far stratigraphically above the maximum flooding surface(e.g., Fig. 12). Rapid burial of both in-
^situ and entrained organisms
may have been accomplished by clouds of clay-^rich sediment that fell
out of suspension from low-^energy currents (Rogers, 1984; Robison,
1991; Gaines and Droser, 2005). Not all of the exceptionally preservedfauna appear to have been transported far, however: articulated Choiasponge specimens (
^̂Fig. 10D) are locally common within the hot zone,
and it is unlikely that their long, delicate spicules could have survivedunbroken if transported and tumbled across significant distances bycurrents.
Above the hot zone, carbonate progradation would have graduallyreduced accommodation space, as suggested by the decrease in γ-
^ray
and χ logs and the increase in CaCO3 up-^section; this would have
caused water depth to decrease accordingly at down-^ramp sites.
Consequently, the seafloor environment stratigraphically above thehot zone could have become either sufficiently oxic or sufficientlyenergetic to shut off exceptional preservation during the mid-
^to-
^later
stages of the sea level cycle (e.g., Figs. 8 and 12). This scenario issupported by
^̂Fig. 4A–
^̂C, which demonstrates that bottom current
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
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1activity was minimal in the hot zone but increased in its intensity up-1
^section. Increased bottom current activity could have introduced
1oxygen to sediments near the sea floor and thus supported scavengers,1as well as mechanically disarticulating and dispersing fragile bio-1logical remains on the sea floor, making them vulnerable to microbial1attack.1Although the vast majority of soft-
^bodied fossils noted in the
1present study are found in the clay-^rich and carbonate-
^poor hot zone
1(~4–^20% CaCO3), soft-^
bodied fossils occasionally do occur well above1the hot zone in rocks which, in bulk, are much less rich in clay1(e.g., ~40–
^50% CaCO3). For example, well-
^preserved, articulated algae
1specimens (e.g., Marpolia) are found in calcareous mudrock with1~30–
^40% CaCO3 along the “W” transect, about
^61 m
^above the base of
1the upper Wheeler Formation; such excellent preservation is the1exception at these stratigraphic levels, however. This particular site1falls near the end of the highstand systems tract, as interpreted here1(Fig. 12) and it contains a mixture of both finely-
^laminated intervals
1and nonlaminated strata (^̂Fig. 4A and
^B). Likewise, Gaines et al. (2005)
1reported nonmineralized fossils in mudrock with comparable bulk1clay-
^carbonate ratios from the Wheeler Formation in the House
1Range. When coupled with the preservation model proposed by1Gaines et al. (2005) and Gaines and Droser (2005), these observations1raise questions about the mineral composition, sedimentary environ-1ment, and geochemical processes necessary for soft-
^part preservation
1in mixed carbonate-^clay sediments deposited on ramps during
1Cambrian times. Even given anoxic and low-^energy burial conditions,
1is there an optimum ratio of clay to fine-^grained carbonate for such
1preservation, but below which ratio local geochemical conditions1surrounding a carcass cannot sufficiently seal the organism against1subsequent incursions of oxic, sediment-
^laden waters capable of
1supporting burrowers and scavengers? Alternatively, is almost any1non-
^zero ratio of clay to fine-
^grained carbonate sufficient to seal a
1carcass, as long as rapid burial occurs under anoxic and low energy1conditions? How much time is required to seal an organism by this1mechanism? In the Wheeler Formation, was exceptional preservation1favored in rocks with a high clay-
^to-
^carbonate ratio, simply because
1clay-^rich sediments dominated deep-
^water, low-
^energy environ-
1ments which sometimes became anoxic near the sea floor?
17. Summary and conclusions
1To first approximation, rocks of the upper member of the Wheeler1Formation in the Drum Mountains lithologically consist of a two-1
^component system: a carbonate and a terrigenous (mostly clay) frac-
1tion. Here, gamma ray and magnetic susceptibility respond primarily1to the clay component, providing proxy measurements of carbonate1versus clay percentage that can bemade non-
^destructively and rapidly
1on outcrops. Although the two techniques yield results which are1generally well correlated, using both measurements is superior to just1one, because of differing sensitivities to outcrop conditions and local1compositional heterogeneity.1Three outcrop geophysical transects of the upper Wheeler1Formation in the Drum Mountains exhibit similar profiles: an overall1pattern of initial shaling upward that culminates in a clay-
^rich “hot
1zone”, followed by a decrease in clay content and increase in car-1bonate up to a capping limestone. Although local sequence strati-1graphic interpretation is non-
^unique without regional context, the
1simplest explanation of this pattern is a single transgressive/re-1gressive cycle, signified by deep-
^water, clay-
^rich mudrocks bracketed
1by shallower-^water carbonates. This interpretation is supported by
1observed patterns of lithofacies, sedimentary structures, and distribu-1tions of fossil taxa. The upperWheeler Formation represents most of a1third or fourth-
^order cycle of relative sea level change on a mixed
1carbonate-^siliciclastic ramp, rather than a period of shallow-
^water
1lagoonal sedimentation as previously proposed. Superimposed on this1overall cycle are several (perhaps many) higher-
^order fluctuations in
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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relative sea level. When coupled with the results of earlier workers,who interpreted the lower and middle members of the WheelerFormation as a major transgression and regression (e.g., Schneider,2000; Langenburg, 2003), results from the present study lead to theconclusion that the Wheeler Formation of the Drum Mountainsinvolves two major sea level cycles, rather than one.
An ~6-^m^-^thick Konservat-
^Lagerstätte has yielded a well-
^preserved
assemblage of soft-^bodied fossils. Its location corresponds with the “hot
zone” in geophysical responses. In accordance with the hypothesis ofBrett (1995), early highstand deposits of clay-
^richmudrock are themost
probable loci for soft-^bodied preservationwithin this locality. While the
sequence stratigraphic context does not lead to a deterministicmodel ofsoft-
^part preservation, in the rocks studied here it does provide a guide
for predicting where some of the conditions needed for exceptionalpreservation aremost likely to occur inmixed clay-
^carbonate sediments
deposited on a ramp. Data presented here indicate that clay-^rich, early
highstand deposition just above themaximum flooding surface and justbelow storm wave base can foster the conditions favoring exceptionalpreservation of soft parts.
Acknowledgements
We sincerely thank Nancy Harris for leading the DGPS surveyingprogram, collecting and preparing samples for carbonate analysis, andobtaining gamma-
^ray data from rocks stratigraphically beneath lime-
stone unit T2. We are grateful to Jeremy Jackson and Sam Fluckiger fortheir valuable assistance in the field. We thank Robert Gaines for hiscomprehensive and constructive review.
References
Adams, J.A.S., Gasparini, P., 1970. Gamma-^ray Spectrometry of Rocks. Elsevier, Amsterdam.
295 pp.Aitken, J.D., 1966. Middle Cambrian to Middle Ordovician cyclic sedimentation,
southern Rocky Mountains of Alberta. Bulletin of Canadian Petroleum Geology14, 405–441.
Aitken, J.D., 1978. Revised models for depositional grand cycles, Cambrian of thesouthern Rocky Mountains, Canada. Bulletin of Canadian Petroleum Geology 26,515–542.
Aitken, J.D., 1997. Stratigraphy of the Middle Cambrian platformal succession, southernRocky Mountains. Geological Survey of Canada Bulletin 398 (322 pp.).
Allen, J.R., 1982. Sedimentary Structures, Their Character and Physical Basis, vol. 2.Elsevier Scientific Publishing Company, Amsterdam. 663 pp.
Allison, P.A., 1988a. The decay and mineralization of proteinaceous macrofossils.Paleobiology 14, 139–154.
Allison, P.A., 1988b. Konservat^-^Lagerstätten: cause and classification. Paleobiology 14,
331–344.Allison, P.A., 1990. Variation in rate of decay and disarticulation of echinodermata:
implications for application of taphonomic data. Palaios 5, 432–440.Allison, P.A., Briggs, D.E.G., 1991. Preservation of soft-
^tissues. In: Allison, P.A., Briggs,
D.E.G. (Eds.), Taphonomy: Releasing the Data Locked in the Fossil Record.Plenum Press, New York, pp. 26–71.
Allison, P.A., Briggs, D.E.G., 1993. Exceptional fossil record: distribution of soft tissuepreservation through the Phanerozoic. Geology 21, 605–608.
Allison, P.A., Brett, C.E., Liddell, W.D., Wright, E., 1995. Repetitive tapho, bio-^and litho
facies, within the Middle Cambrian Swasey Limestone-^Wheeler Shale transition of
Utah. Geological Society of America Abstracts with Programs 27 (6), 374.Aronson, R.B., 1992. Decline of the Burgess Shale fauna:
^ecologic or taphonomic
restriction? Lethaia 25, 225–229.Aronson, R.B., 1993. Burgess Shale-
^type biotas were not just burrowed away:
^reply.
Lethaia 26, 185.Aurell, M., 1991. Identification of systems tracts in low angle carbonate ramps: examples
from the Upper Jurassic of the Iberian Chain (Spain). Sedimentary Geology 73,101–115.
Aurell, M., Badenas, B., Bosence, D.W.J., Waltham, D.A., 1998. Carbonate production andoffshore transport on a late Jurassic carbonate ramp (Kimmeridgian, Iberian Basin,NE Spain); evidence from outcrop and computer modeling. In: Wright, V.P.,Burchette, T.P. (Eds.), Carbonate Ramps. Geol. Soc. London, vol. 149. GeologicalSociety of London Special Publication, pp. 137–161.
Babcock, L.E., Robison, R.A., Rees, M.N., Peng, S., Saltzman, M.R., 2007. The globalboundary stratotype section and point (GSSP) of the Drumian stage (Cambrian) inthe Drum Mountains, Utah, USA. Episodes 30 (2), 84–94.
Bond, G.C., Kominz, M.A., Steckler, M.S., Grotzinger, J.P., 1989. Role of thermalsubsidence, flexure, and eustasy in the evolution of Early Paleozoic passive-
^margin carbonate platforms. Society of Economic Paleontologists andMineralogistsSpecial Publication 44, 39–61.
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
TEDPR
OOF
Bosence, D.W.J., 2003. Application of sequence stratigraphical analysis to ancientcarbonate platforms. In: Coe, A.L. (Ed.), The Sedimentary Record of Sea-
^level
Change. Cambridge Univ. Press, Cambridge, UK, pp. 257–274.Bottjer, D.J., Etter, W., Hagadorn, J.W., Tang, C.M. (Eds.), 2002. Exceptional Fossil
Preservation: A Unique View on the Evolution of Marine Life. Columbia UniversityPress, New York. 403 pp.
Brett, C.E., 1995. Sequence stratigraphy, biostratigraphy, and taphonomy in shallowmarine environments. Palaios 10, 597–616.
Brett, C.E., 1998. Sequence stratigraphy, paleoecology, and evolution:^biotic clues and
responses to sea-^level fluctuations. Palaios 13, 241–262.
Brett, C.E., Goodman, W.M., LoDuca, S.T., 1990. Sequences, cycles, and basin dynamics inthe Silurian of the Appalachian Foreland Basin. Sedimentary Geology 69, 191–244.
Brett, C.E., Allison, P.A., DeSantis, M.K., Liddell, W.D., Kramer, A., this volume, Sequencestratigraphy, cyclic facies, and lagerstätten in the Middle Cambrian, Great Basin,Utah. Palaeogeography, Palaeoclimatology, Palaeoecology.
Briggs, D.E.G., Robison, R.A., 1984. Exceptionally preserved non-^trilobite arthropods and
Anomalocaris from the Middle Cambrian of Utah. University of Kansas Paleonto-logical Contributions 111, 1–23.
Briggs, D.E.G., Lieberman, B.S., Hendricks, J.R., Halgedahl, S.L., Jarrard, R.D., 2008. MiddleCambrian arthropods from Utah. Journal of Paleontology 82 (2), 238–254.
Burzin, M.B., Debrenne, F., Zhuravlev, A.Y., 2001. Evolution of shallow-^water level-
^bottom communities. In: Zhuravlev, A.Y., Riding, R. (Eds.), The Ecology of theCambrian Radiation. Columbia University Press, New York, pp. 217–237.
Butterfield, N.J., 1995. Secular distribution of Burgess Shale-^type preservation. Lethaia
28, 1–13.Cassidy, J., 1981. Techniques of field gamma-
^ray spectrometry. Mineralogical Magazine
44, 391–398.Catuneanu, O., 2002. Sequence stratigraphy of clastic systems: concepts, merits, and
pitfalls. Journal of African Earth Sciences 35, 1–43.Chavetz, H.S., 1986. Marine peloids: a product of bacterially induced precipitation of
calcite. Journal of Sedimentary Petrology 56, 812-187.Chidsey, T.C. (Ed.), 2001. Geological and petrophysical characterization of the Ferron
Sandstone for 3-^D simulation of a fluvial-
^deltaic reservoir—
^final report. U.S. De-
partment of Energy. DOE/BC/14896-^24, 471 pp.
Choi, Y.S., Simo, J.A., Saylor, B.Z., 1999. Sedimentologic and sequence stratigraphicinterpretation of amixed carbonate-
^siliciclastic ramp, midcontinent epeiric sea, Middle
to Upper Ordovician Decorah and Galena Formations,Wisconsin. In: Harris, P.M., Saller,A.H., Simo, J.A.T. (Eds.), Advances in Carbonate Sequence Stratigraphy: Application toReservoirs, Outcrops and Models, 63. SEPM Special Publication, pp. 275–289.
Coe, A.L. (Ed.), 2003. The Sedimentary Record of Sea-^level Change. Cambridge Uni-
versity Press, Cambridge, UK. 288 pp.Conway Morris, S., Robison, R.A., 1986. Middle Cambrian priapulids and other soft-
^bodied. University of Kansas Paleontological Contributions 117, 1–22.
Conway Morris, S., Robison, R.A., 1988. More soft-^bodied animals and algae from the
Middle Cambrian of Utah and British Columbia. University of Kansas Paleontolo-gical Contributions 122, 21–49.
Dommer, M.L., 1980. The geology of the Drum Mountains: Millard and Juab Counties,Utah. Brigham Young University Geology Studies 27 (3), 55–72.
Dunlop, D.J., Ozdemir, O.O., 1997. Rock Magnetism. Cambridge University Press, Cam-bridge UK. 573 pp.
Durrance, E.M., 1986. Radioactivity in Geology: Principles and Applications. EllisHorwood Limited, Chichester. 441 pp.
Ekdale, A.A., Bromley, R.G., Pemberton, S.G., 1984. Ichnology. SEPM, Tulsa OK. 317 pp.Elrick, M., Read, J.F., 1991. Cyclic ramp-
^to-
^basin carbonate deposits, LowerMississippian,
Wyoming andMontana: a combined field and computer modeling study. Journal ofSedimentary Petrology 61, 1194–1224.
Elrick, M., Snider, A.C., 2002. Deep-^water stratigraphic cyclicity and carbonate mud
mound development in the Middle Cambrian Marjum Formation, House Range,Utah, USA. Sedimentology 49, 1021–1047.
Fertl, W.H., 1983a. Gamma ray spectral logging: a new evaluation frontier, Part I—
^Principles. World Oil 196 (4), 79–91.
Fertl, W.H., 1983b. Gamma ray spectral logging: a new evaluation frontier, Part II—
^Application in carbonates. World Oil 196 (5), 87–98.
Fertl, W.H., 1983c. Gamma ray spectral logging: a new evaluation frontier, Part III—
^Measuring source rock potential. World Oil 196 (6), 147–155.
Fisher, R.A., 1953. Dispersion on a sphere. Proceedings, Royal Society of London, Series A217, 295–305.
Gaines, R.R., Droser, M.L., 2005. New approaches to understanding the mechanics ofBurgess Shale-
^type deposits: from the micron scale to the global picture. The
Sedimentary Record 3, 4–8.Gaines, R.R., Kennedy, Droser, M.L., 2005. A new hypothesis for organic preservation of
Burgess Shale taxa in the middle CambrianWheeler Formation, House Range, Utah.Palaeogeography, Palaeoclimatology, Palaeoecology 220, 193–205.
Goldhammer, R.K., Dunn, P.A., Hardie, L.A., 1990. Depositional cycles, composite sea-
^level changes, cycle stacking patterns, and the hierarchy of stratigraphic forcing:
^examples from Alpine Triassic platform carbonates. Geological Society of AmericaBulletin 102, 535–562.
Gradstein, F.M., Ogg, J.G., Smith, A.G., et al., 2004. A geologic time scale 2004. GeologicalSurvey of Canada Report 86. Geological Survey of Canada, Ottawa ON. 1 p.
Grannis, J.L., 1982. Sedimentology of the Wheeler Formation, Drum Mountains, Utah.University of Kansas, Lawrence, unpub. M.S. thesis, 135 pp.
Hallam, A., 1992. Phanerozoic Sea-^Level Changes. Columbia University Press, New York.
266 pp.Hallam, A., Bradshaw, M.J., 1979. Bituminous shales and oolitic ironstones as indicators
of transgression and regression. Journal of the Geological Society of London 136,157–164.
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
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22 S.L. Halgedahl et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx
ARTICLE IN PRESS
UNCO
RRE
Handford, C.R., Loucks, R.G., 1993. Carbonate depositional sequences and systemstracts—
^responses of carbonate platforms to relative sea-
^level changes. In:
Loucks, R.G., Sarg, J.F. (Eds.), Carbonate Sequence Stratigraphy, Recent Develop-ments and Applications, vol. 57. AAPG, pp. 3–41. Memoir.
Handwerger, D.A., Jarrard, R.D., 2004. Neogene changes in Southern Ocean sedimenta-tion based on mass accumulation rates at four continental margins. Paleoceano-graphy 18, 1081. doi:10.1029/2002PA000850.
Harris, P.M., Saller, A.H., Simo, J.A. (Eds.), 1999. Advances in Carbonate SequenceStratigraphy: Application to Reservoirs, Outcrops and Models, vol. 63. SEPM SpecialPublication. 421 pp.
Hassan, M., Hossin, A., Combaz, A., 1976. Fundamentals of the differential gamma-^ray
log. Society of Professional Well Log Analysts, Transactions 17th Annual LoggingSymposium, paper H.
Hernandez, J.C.G., 2005. Outcrop characterization, 3D geological modeling, “reservoir”simulation and upscaling of Jackfork Group turbidites in Hollywood Quarry,Arkansas. University of Oklahoma, Norman OK, unpub. M.S. thesis, 74 pp.
Herrero, A.A., 1983. End-^product inhibition in anaerobic fermentations. Trends in
Biotechnology 1, 49–53.Hintze, L.F., 1988. Geologic History of Utah, vol. 7. Brigham Young University Geology
Studies Special Publication. 202 pp.Hintze, L.F., Robison, R.A., 1975. Middle Cambrian stratigraphy of the House, Wah Wah,
and adjacent ranges in Western Utah. Geological Society of America Bulletin 86,881–891.
Hintze, L.F., Davis, F.D., 2003. Geology of Millard County, Utah. Utah Department ofNatural Resources. Utah Geological Survey Bulletin 133. 305 pp.
Holland, S.M., 1995. Sequence stratigraphy, facies control, and their effects on thestratigraphic distribution of fossils. In: Haq, B.U. (Ed.), Sequence Stratigraphyand Depositional Response to Eustatic, Tectonic, and Climatic Forcing. KluwerAcademic, Dordrecht, Netherlands, pp. 1–23.
Holland, S.M., 2000. The quality of the fossil record: a sequence stratigraphic per-spective. Paleobiology 26 (4, Supplement), 148–168.
Hower, J., 1981. Shale diagenesis. In: Longstaffe, F.J. (Ed.), Clays and the ResourceGeologist. Minerological Association of Canada, Toronto, pp. 60–80.
Hower, J., Eslinger, E.V., Hower, M.E., Peary, E.A., 1976. Mechanism of burialmetamorphism of argillaceous sediments. Geological Society of America Bulletin87, 725–737.
Hunt, C.P., Moskowitz, B.M., Banerjee, S.K., 1995. Magnetic properties of rocks andminerals. In: Ahrens, T.J. (Ed.), Rock Physics and Phase Relations. AGU ReferenceShelf 3, Washington, D.C., pp. 189–204.
Kauffman, E.G., 1981. Ecological reappraisal of the German Posidonienschiefer(Toarcian) and the stagnant basin model. In: Gray, J., Boucot, A.J., Berry, W.B.N.(Eds.), Communities of the Past. Hutchinson Ross, Stroudsburg, pp. 311–381.
Kepper, J.C., 1976. Stratigraphic relationships and depositional facies in a portion of theMiddle Cambrian of the Basin and Range Province. In: Robison, R.A., Rowell, A.J.(Eds.), Paleontology and Depositional Environments: Cambrian of Western NorthAmerica. Geology Studies, vol. 23. Brigham Young Univ., pp. 75–91.
Killeen, P.G., Carmichael, C.M., 1972. Experimental survey with a portable gamma-^ray
spectrometer, Blind River area, Ontario: a case history. In: Brown, S.H., Davis, M.,Ostle, D. (Eds.), Uranium Prospecting Handbook. Institution of Mining and Metal-lurgy, London, pp. 306–312.
Langenburg, E.S., 2003. The Middle Cambrian Wheeler Formation:^sequence strati-
graphy and geochemistry across a ramp-^to-
^basin transition. Utah State University,
Logan, Utah, unpub. M.S. thesis, 120 pp.Liddell, W.D.,Wright, E.J., Wright, S.H., Allison, P.A., Baird, G.C., Brett, C.E., 1995. A sequence
stratigraphicmodel forMiddle Cambrian trilobite assemblages from the eastern GreatBasin. Geological Society of America Abstracts with Programs 27 (6), 374.
Loucks, R.G., Sarg, J.F. (Eds.), 1993. Carbonate Sequence Stratigraphy, Recent Develop-ments and Applications. AAPG Memoir 57. AAPG, Tulsa OK. 545 pp.
Løvborg, L., 1972. Assessment of uranium by gamma-^ray spectrometry. In: Brown, S.H.,
Davis, M., Ostle, D. (Eds.), Uranium Prospecting Handbook. Institution of Miningand Metallurgy, London, pp. 157–173.
Løvborg, L.,Wollenberg, G.H., Sorensen, P., Hansen, J.,1971. Field determination of uraniumand thorium by gamma-
^ray spectrometry, exemplified by measurements on the
Ilimausaq alkaline intrusion, South Greenland. Economic Geology 66, 368–384.Løvborg, L., Botter-
^Jensen, L., Kirkegaard, P., Christiansen, E.M., 1979. Monitoring of
natural soil radioactivity with portable gamma-^ray spectrometers. Nuclear Instru-
ments and Methods 167, 341–348.Love, S.E., Gould, S., Davies, S., 2004. Inter-
^tuff correlation and architecture within the
Moor Cliffs Formation, Lower Old Red Sandstone, southwest Wales; a multi-
^disciplinary approach for reservoir characterization. In: Williams, B.P.J., Marriott,S.B., Hillier, R.D. (Eds.), The Lower Old Red Sandstone of the Anglo-
^Welsh Basin.
Geological Journal, vol. 39, pp. 299–314.Lüning, S., Wendt, J., Belka, Z., Kaufmann, B., 2004. Temporal–
^spatial reconstruction of
the early Frasnian (Late Devonian) anoxia in NW Africa: new field data from theAhnet Basin, (Algeria). Sedimentary Geology 163, 237–264.
Lyle, M., Olivarez Lyle, A., Backman, J., Tripati, A., 2005. Biogenic sedimentation in theEocene equatorial Pacific—
^the stuttering greenhouse and Eocene carbonate compen-
sation depth. In: Wilson, P.A., Lyle, M., Firth, J.V. (Eds.), Proceedings of the OceanDrillingProgram. Scientific Results, vol.199. [Online]. Available fromWorldWideWeb:bhttp://www-odp.tamu.edu/publications/199_SR/219/219.htmN.
Markello, J.R., Read, J.F., 1981. Carbonate ramp-^to-
^deeper shale shelf transitions of an
Upper Cambrian intrashelf basin, Nolichucky Formation, Southwest VirginiaAppalachians. Sedimentology 28, 573–597.
Martin, R.E., 1999. Taphonomy. Cambridge University Press, Cambridge, UK. 508 pp.Martin-
^Hernandez, F., Hirt, A.M., 2003. The anisotropy of magnetic susceptibility in
biotite, muscovite and chlorite single crystals. Tectonophysics 367, 13–28.
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
TEDPR
OOF
1McLaughlin, P.I., Brett, C.E., Taha McLaughlin, S.L., Cornell, S.R., 2004. High-^resolution
1sequence stratigraphy of a mixed carbonate-^siliciclastic, cratonic ramp (Upper
1Ordovician; Kentucky–^Ohio, USA): insights into the relative influence of eustasy
1and tectonics through analysis of facies gradients. Palaeogeography, Palaeoclima-1tology, Palaeoecology 210, 267–294.1McLean, R.F., 1967. Origin and development of ridge–
^furrow systems in beachrock in
1Barbados, West Indies. Marine Geology 5, 181–193.1Merkel, R.H., 1979. Well log formation evaluation. AAPG Continuing Education Course1Note Series #14, AAPG Department of Education, Tulsa. 82 pp.1Miller, J.F., Evans, K.R., Loch, J.D., Ethington, R.L., Stitt, J.H., Holmer, L., Popov, L.E., 2003.1Stratigraphy of the Sauk III interval (Cambrian–
^Ordovician) in the Ibex area, west-
1ern Millard County, Utah and central Texas. Brigham Young University Geology1Studies 47, 23–118.1Milliman, J.D., 1974. Marine Carbonates. Springer Verlag, New York. 375 pp.1Moore, D.W., Reynolds, R.C., 1997. X-
^ray Diffraction and the Identification and Analysis
1of Clay Minerals. Oxford University Press, Oxford UK. 378 pp.1Myers, K.J., Wignall, P.B., 1987. Understanding Jurassic organic-
^rich mudrocks—
^new
1concepts using gamma-^ray spectrometry and palaeoecology: examples from the
1Kimmeridge Clay of Dorset and the Jet Rock of Yorkshire. In: Leggett, J.K., Zuffa, G.G.1(Eds.), Marine Clastic Sedimentology. Graham and Trotman, London, pp. 172–189.1Orr, P.J., Benton, M.J., Briggs, D.E.G., 2003. Post-
^Cambrian closure of the deep-
^water
1slope-^basin taphonomic window. Geology 31, 769–772.
1Osleger, D., Read, J.F.,1991. Relation of eustasy to stackingpatterns ofmeter-^scale carbonate
1cycles, Late Cambrian, U.S.A. Journal of Sedimentary Petrology 61, 1225–1252.1Osleger, D.A., Montañez, I.P., 1996. Cross-
^platform architecture of a sequence boundary
1in mixed siliciclastic-^carbonate lithofacies, Middle Cambrian, southern Great Basin,
1USA. Sedimentology 43, 197–217.1Petrovich, R., 2001. Mechanisms of fossilization of the soft-
^bodied and lightly armored
1faunas of the Burgess shale and of some other classical localities. American Journal1of Science 301, 683–726.1Pickerill, R.K., 1994. Exceptional fossil record: distribution of soft-
^tissue preservation
1through the Phanerozoic: discussion. Geology 22, 183–184.1Posamentier, H.W., Vail, P.R., 1988. Eustatic controls on clastic deposition II: sequence1and systems tract models. In: Wilgus, C.K., Hastings, B.S., Kendall, C.G.St.C.,1Posamentier, H.W., Ross, C.A., Van Wagoner, J.C. (Eds.), Sea Level Changes—
^An
1Integrated Approach, vol. 42. SEPM Special Publication, pp. 125–154.1Posamentier, H.W., Allen, G.P., 1999. Siliciclastic sequence stratigraphy: concepts and1applications. SEPM Concepts in Sedimentology and Paleontology no. 7. 210 pp.1Posamentier, H.W., Jervey, M.T., Vail, P.R., 1988. Eustatic controls on clastic deposition I:1conceptual framework. In: Wilgus, C.K., Hastings, B.S., Kendall, C.G.St.C., Posamen-1tier, H.W., Ross, C.A., Van Wagoner, J.C. (Eds.), Sea Level Changes—
^An Integrated
1Approach, vol. 42. SEPM Special Publication, pp. 110–124.1Raiswell, R., 1987. Non-
^steady state microbiological diagenesis and the origin of
1concretions and nodular limestones. In: Marshall, J.D. (Ed.), Diagenesis of1Sedimentary Sequences, vol. 36. Geological Society of London Special Publication,1pp. 41–54.1Read, J.F., 1980. Carbonate ramp-
^to-
^basin transitions and foreland basin evolution,
1Middle Ordovician, Virginia Appalachians. American Association of Petroleum1Geologists Bulletin 64, 1575–1612.1Read, J.R., 1982. Carbonate platforms of passive (extensional) continental margins:1types, characteristics and evolution. Tectonophysics 81, 195–212.1Rees, M.N., 1986. A fault-
^controlled trough through a carbonate platform:
^the Middle
1Cambrian House Range embayment. Geological Society of America Bulletin 97,11054–1069.1Rees, M.N., Robison, R.A., 1989. Days 5 and 6: Cambrian stratigraphy and paleontology of1the central House Range and Drum Mountains, Utah. In: Hanshaw, P.M. (Ed.), Field1Trips for the 26th International Geological Congress. American Geophysical Union,1Washington, D.C., pp. 59–72.1Richter, C., Valet, J.-
^P., Solheid, P.A., 1997. Rock magnetic properties of sediments from
1Ceara Rise (Site 929): implications for the origin of the magnetic susceptibility1signal. In: Shackleton, N.J., Curry, W.B., Richter, C., Bralower, T.J. (Eds.), Proc. Ocean1Drilling Program, vol. 154, pp. 169–179.1Robison, R.A., 1960. Lower and Middle Cambrian stratigraphy of the Great Basin. In:1Boettcher, J.W., Sloan, W.W. (Eds.), Guidebook to the geology of east-
^central
1Nevada. Intermountain Association of Petroleum Geologists, Annual Field Con-1ference 11th Guidebook, pp. 43–52.1Robison, R.A., 1962. Late Middle Cambrian faunas from the Wheeler and Marjum1Formations of western Utah. Ph.D. thesis, University of Texas, Austin, 294 pp.1Robison, R.A., 1964. Upper Middle Cambrian stratigraphy of western Utah. Geological1Society of America Bulletin 75, 995–1010.1Robison, R.A., 1972. Mode of life of agnostid trilobites. International Geological Congress17, 33–40.1Robison, R.A., 1976. Middle Cambrian trilobite stratigraphy of the Great Basin. Brigham1Young University Geology Studies 23 (2), 93–109.1Robison, R.A., 1982. Some Middle Cambrian agnostoid trilobites from western North1America. J. Paleontol. 56, 143–160.1Robison, R.A., 1991. Middle Cambrian biotic diversity: examples from four Utah Lager-1stätten. In: Simonetta, A., Conway Morris, S. (Eds.), The Early Evolution of Metazoa1and the Significance of Problematic Taxa. Cambridge University Press, Cambridge,1pp. 77–98.1Robison, R.A., Rees, M.N., 1981a. Middle Cambrian stratigraphy and paleontology of the1Drum Mountains, western Utah. In: Taylor, M.E., Palmer, R. (Eds.), Cambrian1Stratigraphy and
^Paleontology of the Great Basin and Vicinity, Western United
1States. U.S. Geological Survey, Denver, CO, pp. 93–101.1Robison, R.A., Richards, B.C., 1981b. Larger bivalve arthropods from the Middle1Cambrian of Utah. University of Kansas Paleontological Contributions 106, 1–28.
gical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
1850185118521853185418551856185718581859186018611862186318641865186618671868186918701871187218731874187518761877187818791880188118821883188418851886
18871888188918901891189218931894189518961897189818991900190119021903190419051906190719081909191019111912191319141915191619171918191919201921
1922
1923
23S.L. Halgedahl et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx
ARTICLE IN PRESS
Rogers, J.C., 1984. Depositional environments and paleoecology of two quarry sites inthe Middle Cambrian Marjum and Wheeler Formations, House Range, Utah.Brigham Young University Geology Series 31, 97–115.
Rowell, A.J., Robison, R.A., Strickland, D.K., 1982. Aspects of Cambrian agnostoidphylogeny and chronocorrelation. Journal of Paleontology 56, 161–182.
Ruf, M., Aigner, T., 2004. Facies and poroperm characteristics of a carbonate shoal(Muschelkalk, south German Basin); a reservoir analogue investigation. Journal ofPetroleum Geology 27, 215–239.
Ruffel, A., Worden, R., 2000. Palaeoclimate analysis using spectral gamma-^ray data from
the Aptian (Cretaceous) of southern England and southern France. Palaeogeo-graphy, Palaeoclimatology, Palaeoecology 155, 265–283.
Ryder, M., 1996. Geological Interpretation of Well Logs, 2nd Ed. Gulf Publishing Co.,Houston. 280 pp.
Schaeffer, N.M., 1973. Reactor shielding for nuclear engineers. National TechnicalInformation Services Report no. TID-
^25951, Springfield VA. 788 pp.
Schlager, W., 1993. Accommodation and supply—^a dual control on stratigraphic
sequences. Sedimentary Geology 86, 111–136.Schlumberger, 1989. Log Interpretation Principles and Applications. Schlumberger
Educational Services, Houston TX.Schneider, L.P., 2000. The sequence stratigraphy of the Middle Cambrian Wheeler
Formation in the Drum Mountains of West Central Utah. Utah State University,Logan, Utah, unpub. M.S. thesis, 82 pp.
Seilacher, A., Reif, W.E., Westphal, F., 1985. Sedimentological, ecological and temporalpatterns of fossil Lagerstatten. Philosophical Transactions of the Royal Society ofLondon B311, 5–23.
Serra, O., 1986. Fundamentals of Well Log Interpretation: The Interpretation of LoggingData. Elsevier, Amsterdam. 684 pp
^.
Serra, O., Baldwin, J., Quirein, J., 1980. Theory, interpretation and practical applicationsof natural gamma ray spectroscopy. Transactions SPWLA Twenty-
^first Annual
Logging Symposium, pp. Q1–Q30.Slatt, R.M., Jordan, D.W., D'Agostino, A., Gillespie, R.H., 1992. Outcrop gamma-
^ray
logging to improve understanding of subsurface well log correlations. In: Hurst, A.,Griffiths, C.M., Worthington, P.F. (Eds.), Geological Applications of Wireline Logs II,vol. 65. Geological Society Special Publication, pp. 3–19.
Smith, L.B., Read, J.F., 1999. Application of high-^resolution sequence stratigraphy to
tidally influenced upper Mississippian carbonates, Illinois basin. In: Harris, P.M.,Saller, A.H., Simo, J.A.T. (Eds.), Advances in Carbonate Sequence Stratigraphy:
UNCO
RREC
Please cite this article as: Halgedahl, S.L., et al., Geophysical and geoloFormation, Drum Mountains..., Palaeogeography, Palaeoclimatology, Pal
ROOF
Application to Reservoirs, Outcrops and Models, 63. SEPM Special Publication, pp.107–126.
Stage, M., 2001. Magnetic susceptibility as carrier of a climate signal in chalk. EarthPlanetary Science Letters 188, 17–27.
Tucker, M.E., Wright, V.P., 1990. Carbonate Sedimentology. Blackwell Science Ltd.,Oxford. 482 pp.
Van Wagoner, J.C., Mitchum, R.M., Campion, K.M., Rahmanian, V.D., 1990. Siliciclasticsequence stratigraphy in well logs, cores, and outcrops. AAPG Methods inExploration Series No. 7. American Association of Petroleum Geologists, Tulsa,OK. 55 pp.
Vorhies, J.S., Gaines, R.R., 2005. Growth mechanisms for carbonate concretions in theWheeler Formation, House Range, Utah; implications for pore water biogeochem-istry. Geological Society of America Abstracts with Programs 37 (4), 47.
Vorwald, G.R., 1984. Paleontology and paleoecology of the upper Wheeler Formation(late Middle Cambrian), Drum Mountains, west central Utah. University of Kansas,Lawrence, unpub. M.S. thesis, 176 pp.
White, W.W., 1973. Paleontology and depositional environments of the CambrianWheeler Formation, Drum Mountains, west-
^central Utah. University of Utah,
unpubl. M.S. thesis, 135 pp.Wignall, P.B., 1994. Black
^shales. Oxford Monographs on Geology and Geophysics 30
(127 pp.).Wignall, P.B., Hallam, A., 1991. Biofacies, stratigraphic distribution and depositional
models of British onshore Jurassic black shales. In: Tyson, R.V., Pearson, T.H. (Eds.),Modern and Ancient Continental Shelf Anoxia, vol. 58. Geological Society of LondonSpecial Publication, pp. 291–310.
Wright, V.P., Burchette, T.P. (Eds.), 1998. Carbonate Ramps, vol.149. Geological Society ofLondon Special Publication. 465 pp.
Zelt, F.B., 1985. Natural gamma-^ray spectrometry, lithofacies, and depositional
environments of selected Upper Cretaceous marine mudrocks, Western UnitedStates, including Tropic Shale and Tanunk Member of Mancos Shale. Ph.D. thesis,Princeton, 372 pp.
Zhu, M., Babcock, L.E., Steiner, M., 2005. Fossilization modes in the ChengjiangLagerståtte (Cambrian of China): testing the roles of organic preservation anddiagenetic alteration in exceptional preservation. Palaeogeography, Paleaoclimato-loy, Palaeoecology 220, 31–46.
P TEDgical signatures of relative sea level change in the upper Wheeleraeoecology (2009), doi:10.1016/j.palaeo.2009.02.011
