PACIFIC OCEAN SEDIMENTS, DEEP SEA DRILLING PROJECT 1deepseadrilling.org/62/volume/dsdp62_15.pdf · sediment has only recently received more attention, be-cause it could be used to

15. REWORKED FOSSILS IN MESOZOIC AND CENOZOIC PELAGIC CENTRALPACIFIC OCEAN SEDIMENTS, DEEP SEA DRILLING PROJECT

SITES 463, 464, 465, AND 466, LEG 621

Jörn Thiede, Department of Geology, University of Oslo, Blindem, Oslo 3, NorwayAnne Boersma, Lamont-Doherty Geological Observatory, Columbia University, Palisades, New York

Ronald R. Schmidt, Institute of Earth Sciences, University of Utrecht, Utrecht 3508 TA, The Netherlandsand

Edith Vincent, Scripps Institution of Oceanography, La Jolla, California

ABSTRACT

Upper Mesozoic and Cenozoic sediments penetrated at deep-sea drill sites in the tropical and subtropical centralPacific Ocean often contain discrete horizons with reworked and displaced biogenic sediment components which can in-clude fossils produced by benthic organisms living in neritic environments and by oceanic plankton. All four drill sitesof Deep Sea Drilling Project Leg 62 in the central North Pacific Ocean received an influx of benthic shallow-waterfossils during the late Mesozoic, and of planktonic as well as shallow-water benthic fossils during the Cenozoic. Ingeneral, reworked and displaced sediment components from these two widely different source areas occur in discretehorizons and separate from each other, although in certain instances they have been observed together. The flux ofshallow-water components to the deep sea is almost entirely restricted to eight intervals of low eustatic sea-level standsduring late Mesozoic and Cenozoic times. Non-contemporaneous pelagic-fossil assemblages which indicate reworkingin intermediate and deep waters are restricted to the Cenozoic sections of the Leg 62 sites, whereas they have not beennoted in the Mesozoic parts of the penetrated sedimentary sequences. A similar difference of pre-Maastrichtian andMaastrichtian-Pleistocene sections has been observed elsewhere in the central Pacific Ocean. This difference seems topoint to a fundamental change from a very quiet and sluggish bottom-water circulation during pre-Maastrichtian timeto a Maastrichtian and Cenozoic paleoenvironment when currents in the intermediate and deep waters eroded wide re-gions of the central Pacific Ocean.

INTRODUCTION

Relatively homogeneous deep-sea sediments oftencontain reworked and displaced contemporaneous andnon-contemporaneous older fossils. These occurrencesdocument times of erosion which remobilized neriticand pelagic sediments. A careful analysis of the occur-rence of such reworked material is expected to offer im-portant information about the vertical and horizontaltransport of sediment components, either within thesame water mass or across oceanic water-mass bound-aries. Since reworking implies mechanical transport ofthe fossil material, the occurrence of reworked sedimentcomponents supplies us with an argument of uniquesimplicity which has not yet been used extensively inpaleoceanography. Although reworked fossil materialoccasionally is enriched in certain intervals, it usuallyrepresents only a minor fraction of the total pelagicsediment. Such fossils therefore are often overlooked,underrated, and not studied in detail during deter-mination of the biostratigraphy and(or) the depositionalenvironment of the Mesozoic and Cenozoic sedimentarysequences penetrated at oceanic drill sites. The distribu-tion of such fossil material which is foreign to its hostsediment has only recently received more attention, be-cause it could be used to document (1) long-distancetransport paths of deep-sea currents across the ocean

Initial Reports of the Deep Sea Drilling Project, Volume 62.

floor (Burckle and Stanton, 1975; van Andel, 1973;Thiede, 1977); (2) erosion of older pelagic sediment se-quences (Riedel, 1971); and (3) the effect of global sea-level changes on the pelagic environment (Premoli Silvaand Boersma, 1977).

Because of their scarcity, displaced fossils in samplesfrom deep-sea drill sites only rarely have received the at-tention they deserve. Only recently, the studies of Beck-mann (1975), Boltovskoy (1977), Cook et al. (1975),Premoli Silva and Boersma (1977), Premoli Silva andBrusa (1981), and Rea and Thiede (1981) have laid someground work for systematically collecting the valuableinformation which can be obtained by studying care-fully and in great detail the stratigraphic distributionand composition of reworked and displaced biogenicdeep-sea sediment components. These studies are im-portant because they provide detailed stratigraphic andpaleontologic data about the host sediment containingthe displaced material, as well as about the displacedfossils themselves. The analysis of processes controllingthe erosion and flux of reworked material to and fromthe ocean floor can therefore now be carried out in amuch more systematic manner than before. Using theexisting data base we want to discuss occurrences of dis-placed pelagic and shallow-water benthic fossils foundat all four drill sites of DSDP Leg 62 in the centralNorth Pacific Ocean (Fig. 1).

In Table 1, we have tried to categorize the type of in-formation which can be gained from the study of dis-placed and reworked fossil material which has been ob-

495

J. THIEDE, A. BOERSMA, R. R. SCHMIDT, E. VINCENT

10° -

170° 180° 170° 160°

Figure 1. DSDP sites on the Mid-Pacific Mountains and on Hess Rise, central North Pacific Ocean.

Table 1. Reworked and displaced fossils in pelagic sediments.

Shallow-WaterBenthic Fossils

Contempo-raneous

Non-contempo-

raneous

Water depth and nature ofadjacent shallow-waterenvironments(paleogeography,paleobathymetry,paleobiogeography)

Mode of transportTiming of global sea-

level low standsSubsidence

Water depth and nature ofshallow-waterenvironments olderthan host sediment

Mode of transportTiming and amount of

global sea-levelchanges

Planktonic Fossils

Calcareous

Current regimes in thedepositionalenvironment

Amount of down-slopetransport (espe-cially displacementinto differentdissolution facies)

Nature and stra-tigraphy of erodedpelagic sedimentsection (mostly inintermediate watersabove the CCD)

Current regimes in thedepositionalenvironments

Siliceous


Long-distance bottom-water transport

Nature and stra-tigraphy of erodedpelagic sedimentsection (mostlydeep water belowthe CCD)


served frequently in Mesozoic and Cenozoic deep-seasediments. Such material often is concentrated in dis-crete intervals or horizons. Shallow-water benthic andplanktonic fossils often are found separate from eachother, although in certain instances they have been ob-served together. In Table 1, we discriminate betweenfossils which are reworked and displaced, but which ap-parently are of the same age as the host sediment (con-temporaneous) and those which are clearly older (non-contemporaneous) and which therefore represent ero-sion and remobilization of stratigraphic sequences laiddown prior to deposition of the host sediment. Bothtypes of occurrences offer insight into the depositionalenvironment of the host sediment, as well as that of thereworked, displaced components. The transport of thebiogenic grains from their original to their final depo-

496

REWORKED FOSSILS

sitional site requires mechanical transport by currents(turbidity currents, slumps, bottom-water currents) alongthe bottom of the ocean. If, for example, shallow-waterbenthic fossils are found in deep waters, or if calcareousmaterial is found below the CCD, both had to crossphysically important water-mass boundaries. Therefore,the hydrodynamic properties of the host sediment, aswell as of the displaced material, offer at least qualita-tive, if not quantitative, information about the shallowand deep-water current regimes of the ocean.

Displaced shallow-water fossils found in pelagicsediments are easily recognized whether the material iscontemporaneous with or older than the host sediment.Displaced shallow-water fossils reveal the presenceand nature of former neritic depositional environments(shoals or coastal regions of oceanic islands and landmasses) which might no longer exist, because of sub-sidence of the oceanic crust. They allow us to date theexistence and subsidence of these environments, and todescribe their mode of transport and in some instancesthe morphology of the transport path. As will be shownlater, their flux to the deep ocean is dominantly con-fined to times of low global sea-level stands.

The presence of reworked and displaced contem-poraneous pelagic sediment components is often diffi-cult to detect, because of the apparently homogeneousnature of many deep-sea sediments and because dis-placed coeval pelagic fossils cannot easily be distin-guished from the autochthonous fossil assemblages.However, we know from observations of modern ocean-floor features (Seibold, 1978) that recent deep-sea sedi-ments often are affected by bottom-water currents. Thetextural properties of deep-sea sediments (van Andel,1973) and sedimentary structures encountered in coresobtained from deep-sea drill sites suggest that this alsohappened in the past, although we often have difficul-ties in evaluating the importance and the proportions ofthe reworked material. Besides sedimentary structurestypical of current transport, the presence of calcareousmaterial at water depths far below the CCD can beassumed to indicate current transport.

Displaced, non-contemporaneous pelagic sedimentcomponents are much easier to evaluate than contem-poraneous material. They offer information about thenature, stratigraphy, depth of deposition, and source ofthe eroded sediment section, and about the current re-gimes of the depositional environments of the host sedi-ment. Calcareous pelagic material has been erodedmostly from intermediate (deeper than neritic, but shal-lower than CCD) waters, pure siliceous displaced fossilassemblages from regions below the CCD. The spreadin age of the reworked material also allows reconstruc-tion of the span of the eroded stratigraphic sequence.

STRATIGRAPHY OF LEG 62 DRILL SITESAND THE OCCURRENCE OF DISPLACED

SEDIMENT COMPONENTSThe four drill sites of DSDP Leg 62 (Fig. 1) are

situated on the Mid-Pacific Mountains (Site 463) and onHess Rise (Sites 464, 465, and 466), in the central NorthPacific Ocean. At all four locations, sedimentary se-

quences of late Mesozoic and Cenozoic age were pene-trated and found to contain displaced and reworkedshallow-water benthic and pelagic fossils (Table 2; Fig.2). Because of the presence of long-lasting hiatuses, thesequences (with the possible exception of Site 464 onnorthern Hess Rise) do not document the continuousevolution of their depositional environment.

Site 463 (western Mid-Pacific Mountains) is situatedin 2525 meters of water, where a dominantly calcareoussequence of oozes, chalks, and limestones ranging in agefrom Barremian to Pleistocene was penetrated (Fig. 2).Lithologic variations of these calcareous deposits allowus to subdivide them into four major units. The oldestunit consists of more than 190 meters of pelagic lime-stone interbedded with shallow-water carbonate debriswhich occurs with increasing abundance down-core(Fig. 3). The overlying unit is 45 meters thick and iscomposed of cyclic, in part carbonaceous limestones ofearly Aptian age, with a number of distinct, dark vol-canic-ash horizons. The organic-carbon content of theindividual carbonaceous horizons reaches values in ex-cess of 4% (Dean et al., this volume). The two youngerunits consist of Aptian to middle Albian multicoloredpelagic-limestone beds, with chert as a common compo-nent, and upper Albian to Pleistocene nannofossil andforaminifer oozes and chalks, as well as some limestone.Hiatuses interrupt the younger two units in severalplaces, and calcareous faunas and floras show signs ofsevere dissolution, despite the shallow location of thesite.

Reworked and displaced sediment components havebeen found both in the Mesozoic and the Cenozoic partsof the sequence penetrated at Site 463. The variation inpreservation of radiolarian skeletons; the low-diversityassemblages; the sorting of abundant, well-preserved,spherical tests; and the fragmentation of all nassellariantests suggest displacement of coeval radiolarian faunasduring the Barremian. Middle Miocene to Cretaceousplanktonic foraminifers were found in Core 4 (upperMiocene). Pliocene calcareous nannofossils occur in theQuaternary sediments of Cores 1 and 2; Miocene to Eo-cene nannofossils occur in Core 4 (upper Miocene); andEocene nannofossils occur in Core 6 (Oligocene). Dis-placed shallow-water components include large benthicforaminifers in Cores 8-12, 16, 20, 22, 23, 37, 38, and49. The interbedded clastic limestones of LithologicUnit IV (Fig. 3) are composed of shallow-water carbon-ates which contain oolites, mollusk and echinodermfragments, stromatolites and algal fragments, and largeforaminifers (Ferry and Schaaf, this volume).

Sites 464, 465, and 466 were drilled on Hess Rise—Site 464 in 4637 meters of water on the western flank ofits northern tip, and Sites 465 and 466 adjacent to eachother at depths of 2161 and 2665 meters, respectively,along the southern boundary of Hess Rise, which fol-lows the Mendocino Fracture Zone. Coring at these sitessampled not only widely distinct parts of Hess Rise, butalso water depths spanning more than 2500 meters. Sur-prisingly, the sediments encountered at all three sitesrange in age to just over 100 m.y., but their lithologiesare distinct because of the difference in location and

497


Table 2. Distribution of hiatuses and reworked fossil material at sites of DSDP Leg 62 in thecentral North Pacific Ocean.

Site

463

464

465

466

Water Depth(m)

2525

4637

2161

2655

Hiatuses(m.y.)

11-27, 50-67

2-54, 73-92

5-39, 48-70, 85-100

Age of Host Sediment(m.y.)

Plio-PleistoceneLate MioceneOligoceneMaestrichtianCenomanianBarremian-AptianLate MaestrichtianSantonian-late

CampanianEarly Albian-CenomanianLate Maastrichtian-

PlioceneConiacian-late

CampanianEarly Cenomanian-late

AlbianPliocene

Late-middle MioceneConiacian-late TuronianLate Albian

Reworked Sediment Components

Age of Shallow-WateiFossils (m.y.)

ContemporaneousContemporaneousContemporaneousContemporaneousContemporaneous

ContemporaneousContemporaneous

Contemporaneous

Contemporaneous


Age of PelagicFossils (m.y.)

PlioceneCretaceous-MioceneEocene

Eocene-Paleocene

Contemporaneous

Late Miocene-lateCretaceous

Eocene-Cretaceous

water depths. Because of the location on crust wellnorth of the equator for most of the past 100 m.y., andbecause of the depth, most of the sediments of Site 464deposited during the past 95 m.y. consist of brown claysor clayey siliceous oozes to siliceous clays. This part ofthe sequence is particularly difficult to date, because ofthe scarcity of fossils, although siliceous fossils in theyoungest part (Sancetta, this volume) and fish bonesand scales in its older part (Doyle and Riedel, this vol-ume) have allowed gross age assignments. These bio-stratigraphies do not allow precise definitions of hia-tuses, and overall accumulation rates therefore remainvery low. However, the oldest intervals of the depositssampled at Site 464 are chert, chalk, and marlstone ofmid-Cretaceous age, which accumulated rapidly whenthe site was crossing beneath the equatorial high-productivity zone (Lancelot and Larson, 1975; Lance-lot, 1978). The reworked material at Site 464 is re-stricted to large benthic foraminifers found in Core 27(Albian).

Holes 465 and 465A, on southern Hess Rise, pene-trated a Pleistocene to upper Albian sequence of cal-careous oozes and chalk above a highly altered, possiblysubaerially extruded (Seifert et al., this volume) trachytebasement. Outstanding sedimentary features of this siteare the olive-gray, laminated upper Albian to Cenoma-nian limestones that in places have high contents oforganic carbon, and the apparently complete sectionacross the Cretaceous/Tertiary boundary (Boersma, thisvolume). The continuity of the overlying sequence ofCenozoic calcareous ooze is interrupted by a long last-ing (>50-m.y.) hiatus. The possibly subaerially ex-truded volcanic basement and the benthic fossils pre-served in the older parts of the section document a loca-tion of this site close to the Albian sea surface andenable a well-controlled reconstruction of the deposi-tional paleoenvironment along southern Hess Rise.

The olive-gray, laminated upper Albian to lower Ce-nomanian limestones penetrated at the base of the Site465 sedimentary sequence display a considerable num-ber of sedimentary structures indicative of bottom-

water currents. Contemporaneous radiolarians are en-riched in thin layers, and the sediments appear to haveundergone considerable sorting. Reworked and dis-placed non-contemporaneous fossils are restricted to theCenozoic interval of Site 465. Below the lower Pliocenesediments, a mixed zone contains lower Eocene and up-per Paleocene sediments mixed with lower and upperPliocene sediments. It is remarkable that the over-100-cm-thick layer of the "G. " eugubina Zone just abovethe Cretaceous/Tertiary boundary did not appear tocontain any reworked material.

Displaced shallow-water carbonate fossils consist offragments of Inoceramus (Fig. 4) and large neritic ben-thic foraminifers. Inoceramus fragments have beenfound in Cores 9, 13, 25, 27, and 28, of late Albian toMaastrichtian age. The large neritic foraminifers havebeen observed in many cores of both the Mesozoic andCenozoic parts of the Site 465 sedimentary column.They were commonly found in cores belonging to theupper Maastrichtian M. mura Zone, the upper Cam-panian T. trifidus Zone, the Santonian G. concavata-G.elevata Zones, and throughout the lower Cenomanianto upper Albian laminated-limestone sequence. Theyalso have been observed in the upper Paleocene cores ofHoles 465 and 465A.

Site 466 also is on southern Hess Rise, but in some-what deeper water than Site 465, which is about 50 kmto the southwest. The stratigraphic sequence at Site 466is very similar to that at Site 465, consisting of a largelycalcareous section with a basal unit of olive-gray, or-ganic-carbon-rich nannofossil chalk and limestone oflate Albian and early Cenomanian age. The overlyingsequence is nannofossil ooze with some chert in itsoldest part, but the continuity of this sequence is inter-rupted by two hiatuses which span 4 to 38 m.y. and 48to 70 m.y.

Shallow-water fossils from Site 466 occur only in theUpper Cretaceous deposits and include fragments of In-oceramus (Cores 9-11, 19, and 21), which have beenobserved in many other deep-sea drill sites (Thiede andDinkelman, 1977), a large orbitoidal shallow-water ben-

498

REWORKED FOSSILS

thic foraminifer (Core 25,CC), and unrecrystallized or-namented benthic foraminifers (Cores 29 and 31), whichare believed to be displaced.

A Pliocene interval from Core 7 (Section 4) to Core 8(Section 1) of Site 466 showed reworking of planktonicforaminifers and calcareous nannofossils from middleand upper Miocene, upper Oligocene, middle to upperEocene, and Upper Cretaceous pelagic sediments. Theplanktonic foraminifers of the upper and middle Eocenenannofossil ooze of Cores 8 to 10 show reworking ofEocene, Paleocene, and Cretaceous species. The ad-mixed Cretaceous components are derived from Maas-trichtian and upper Campanian sediments. The presenceof reworked, excellently preserved specimens of Globo-truncana calcarata is important, because this fossil doesnot occur in the upper Campanian sediments penetrateddeeper in this hole, and because upper Campanian fora-minifers are only moderately well preserved. These ob-servations point to a source farther up-slope and pointto the regional scope of reworking processes. Very littlereworking has been noted in the Pleistocene sediments.

OTHER OCCURRENCES OF REWORKED ANDDISPLACED FOSSILS IN THE TROPICAL

AND SUBTROPICAL PACIFIC OCEAN

All four sites of Leg 62 had been selected to typify thedepositional paleoenvironments along the elevated por-tions of aseismic rises in regions of the North PacificOcean where such information had not been available.Data from these sites therefore have to be seen in con-junction with information collected during the earlierDSDP cruises in the region. The unexpected long-lastinghiatuses in the Cenozoic of the four Leg 62 sites andhorizons containing large amounts of displaced, in partolder, material have made it difficult to interpret thesedimentary history at these locations completely. Asearch therefore has been made in the reports of the pre-Leg 62 drill sites in the tropical and subtropical PacificOcean, in the hope of establishing temporal and spatialpatterns of the distributions of reworked and displacedcontemporaneous and non-contemporaneous shallow-water calcareous and pelagic fossils. The observationsreported in the drill-site records are of widely varyingcharacter, both quantitatively and qualitatively; theyare listed in Table 3. Their spatial distribution is shownon Figure 5, and their age distribution and the dif-ference of the ages of the reworked components andtheir host sediments are plotted on Figures 6 and 7.However, reworked material has not been reportedfrom some drill sites, either because there was none, orbecause it has been overlooked. The ages used in thiscompilation are based on the numerical time scales ofvan Hinte (1976), Hardenbol and Berggren (1978), andBerggren and Van Couvering (1974).

The described sediments of these sites (Table 3) spana long time (from late Jurassic/early Cretaceous toQuaternary) and a wide depth range (> 1.5 to <6 km);and most sites are on the Mesozoic part of the PacificPlate. However, because of the poor coring record ofsites drilled during the early phases of the Deep SeaDrilling Project, and because of the long-lasting hia-

tuses which have been encountered, the deep-sea-basinsites from the central Pacific Ocean are under-repre-sented in comparison to elevated areas. The sites coverthe entire western subtropical and tropical PacificOcean, whose sea floor is dominantly of Jurassic, Cre-taceous, and early Tertiary age (Pitman et al., 1974). Be-cause of the random regional distribution of the drillsite locations (Fig. 5) of such a wide area, a bias towardone deep-sea basin or toward one very specialized depo-sitional environment can be excluded.

Occurrence and Composition of Shallow-Water Fossilsin Deep-Sea Sediments from the Tropical andSubtropical Pacific Ocean

The occurrence and age distribution of displacedshallow-water sediment components (Fig. 6) at manydeep-sea drill sites of the western central Pacific Oceancomes as a surprise, because these sites are at a distancefrom extensive land areas. However, it has been knownfor some time that many of the submarine rises andplatforms in the western central Pacific Ocean formerlyreached close to or above the sea surface. Becauseshallow-water carbonate rocks have been dredged fromtheir flanks (Matthews et al., 1974; Hamilton, 1956) atwater depths of several hundreds to several thousandsof meters (Heezen et al., 1973), these highs indeed mayhave served as sources of such displaced material.

Evidence for displacement of shallow-water carbon-ate fossils from their original depositional environmentinto the adjacent deep sea represents wide intervals inboth space and time (Table 3). Most of the occurrencesdocument the displacement of sediments of approx-imately the same age as the host sediment, whereas evi-dence for erosion of sections considerably antedatingthe time of displacement have been found in very few in-stances. These sites are close to the Tuamotu Islands(Site 76), close to the Line Islands (Site 165), close to theEmperor Seamounts (Site 309), and in the Nauru Basin(Site 462); they are exclusively in Cenozoic sediments,and in areas where extensive reworking of shallow-watersediments has been recorded in deep-sea drill sites (Fig.6). The maximum difference between the age of the re-worked material and the time of displacement is greaterthan 50 m.y. in late Oligocene deposits of Site 462.

Occurrences of contemporaneous shallow-water-de-rived carbonate fossils have been observed in sedimentsranging from Barremian-Aptian to Quaternary age.They are not evenly distributed in age, but seem to pre-fer specific time spans. The earliest event has been ob-served in Barremian-Albian time, the next during theCenomanian. Intensive displacement of shallow-watercarbonates took place during Campanian and Maas-trichtian times, but decreased sharply towards the Cre-taceous/Tertiary boundary. Paleocene deposits have notproduced evidence for reworked shallow-water car-bonates in the central Pacific ocean, but this might bethe result of many and extensive hiatuses over this inter-val, developed during erosion in the deep sea (Fig. 8).During the Cenozoic, the flux of shallow-water compo-nents was particularly important during the early Eo-cene, late Eocene, late Oligocene, late Miocene, and

499


SITE 463OCCURRENCE OF

REWORKED FOSSILS SITE 464OCCURRENCE OF

REWORKED FOSSILS

200-

220-

240-

260-

280-

300-

la Clayeysiliceous ooze

Siliceous clay

Brown clay

Red-brownchert andnannofossillimestone

*>—/\VBasalt

ne tou.EoceneI. Eocene

UpperCretaceous

uppermostAlbian

lowerCenomanian

upper Albian

lower Albianto

upper Aptian

PELAGICBENTHICSHALLOW

Figure 2. Distribution of reworked and displaced planktonic and shallow-water-derived benthic fossils at DSDP Leg 62 sites in the central NorthPacific Ocean (see Fig. 1 and Table 2).

500

REWORKED FOSSILS

SITE 465OCCURRENCE OF

REWORKED FOSSILS SITE 466OCCURRENCE OF

REWORKED FOSSILS

Figure 2. (Continued).

Plio-Pleistocene (Fig. 6). It seems particularly notablethat the influx of shallow-water carbonate fossil debrisduring the entire time span considered here occurred inpulses, and that it represented a sequence of episodicevents rather than a continuous process.

The composition of the shallow-water carbonate fos-sil debris displaced into the deep sea changed consider-ably with time. The Cretaceous events eroded mainlyremains of coralline and green algae, large benthic fo-raminifers (Asterorbis, Pseudorbitoides, Sulperculina,Vaughanina), corals, ostracodes, echinoids, bryozoans,mollusks (especially bivalves such as Inoceramus andrudists). Rich Mesozoic shallow-water fossil assem-blages have been found at Sites 171, 317, 462, and 463.The Tertiary and Quaternary events, insofar as they didnot cut into upper Mesozoic sedimentary strata, resultedin a transfer of much poorer fossil assemblages into thedeep sea—mainly coralline algae, large and small ben-thic foraminifers (Assilina, Amphistegina, Asterocyc-lina, Discocyclina, Elphidium, Heterostegina, Lepido-cyclina, Miogypsinoides, Nummulites, Operculiná), cor-als, bryozoans, ostracodes, bivalves, and echinoderms.Diverse and abundant Cenozoic shallow-water fossil as-

semblages have been found for example at Sites 165,318, and 462. The displaced mollusks, corals, and othermacrofossils usually are fragmented, but they can occuras clasts of several centimeters' diameter in horizons inreworked material, and they therefore are easily ob-served in the relatively fine-grained deep-sea sediments.

Occurrences and Composition of Displaced PelagicSediment Components in Deep-Sea Drill Sites from theTropical and Subtropical Pacific Ocean

The distribution patterns of reworked and displacedfossils produced by oceanic plankton (Fig. 7) are verydifferent from those of fossil debris derived from shal-low-water regions (Fig. 6). The occurrences of displacedpelagic fossils (Fig. 7) include observations made on allmajor four pelagic microfossil groups (diatoms, radio-larians, coccoliths, foraminifers), whose grain-size spec-tra range from silt- to sand-sized material. Most ob-servations (-80%), however, have been obtained fromoccurrences of reworked coccoliths and planktonicforaminifers, and to a minor degree from radiolarians.The information presented is therefore biased towardthe depositional environments of calcareous oozes above

501


85

90

95

100

105

110

20

25

30

35

40

45

50 L

40

45

5 0 -

Figure 3. Clastic shallow-water-derived limestone conglomerates interbedded with Barremian and lower Aptian pelagic limestones,Site 463 (Mid-Pacific Mountains). A. 463-81-1, 85-115 cm. B. 463-85-1, 120-150 cm. C. Detail of B (140-150 cm). D. 463-85-2,30-40 cm. E. 463-85-2, 120-140 cm. F. 463-86-1, 35-50 cm.

the CCD and under the influence of intermediate (Reid,1965), but not the deepest water masses.

Although we know from textural studies that the sur-face sediments of the modern ocean bottom are in-tensively reworked, this cannot be documented as easilyfor older ocean floors. Even though sedimentary struc-tures in deep-sea drill cores often indicate bottom-watercurrents, the amount of reworking and displacement ofcontemporaneous biogenic components is difficult todetect and to assess. However, if reworked fossils areconsiderably older (non-contemporaneous) than thedeep-sea sediments, they can be used as an unequivocalargument for current transport. The properties of the

eroded sediments and sediment particles are evidencefor the strength of the reworking current regimes. InFigure 7, we have plotted therefore only observations ofnon-contemporaneous reworked fossils, which can be asmuch as 70 m.y. older than the host sediment.

The most surprising feature of the distributions of re-worked non-contemporaneous pelagic fossils in the cen-tral Pacific Ocean (Fig. 7) is the almost complete lack ofsuch redeposited pelagic fossil material from most ofthe Mesozoic part of the penetrated sections. The earli-est occurrences were observed in Maastrichtian sedi-ments, but the number of observations remains modestuntil the late middle Eocene, when a major episode of

502

REWORKED FOSSILS

20

2b

30

35

40 -

20

25

30

35-

40 -

35

40

45

50-

Figure 3. (Continued).

erosion in the meso- and bathypelagic water masses ofthe central Pacific Ocean began. The planktonic-fora-minifer faunas of many sites therefore bear ample evi-dence of widespread reworking of Eocene to Cretaceousfaunas (Krasheninnikov, this volume). The past 40 m.y.has been a time of constant reworking of deep-seasediments (Fig. 7), with peaks of erosion at approx-imately 40 m.y., 30 to 32 m.y., 14 to 15 m.y., 7 to 8m.y., and during the past 5 m.y. The number of obser-vations from the intervals 10 to 13 m.y., and in par-ticular from 15 to 25 m.y. and 33 to 38 m.y., are rela-tively small.

The difference between the age of the eroded sectionand the time of final deposition of the reworked mate-

rial can obviously range over a wide time span, and theprecision of this variable is dependent upon the detail ofavailable stratigraphic data. In this context, it has to bekept in mind that the biostratigraphic zonations of Me-sozoic deep-sea sediments are considerably less refined(van Hinte, 1976) than the Cenozoic ones (Harden-bol and Berggren, 1978; Berggren and Van Couvering,1974). It is therefore obvious that the Mesozoic andCenozoic data from the central Pacific Ocean cannot becompared easily.

The age difference of the reworked material and timeof displacement in general can range between zero (re-working of contemporaneous or penecontemporaneousdeposits) and a maximum value determined by the dif-

503


44

45

46

47

3 cm

Figure 4. Large Inoceramus fragment from Maastrichtian sedimentsof Hole 465A.

ference in age of the oldest eroded sediments and thetime of deposition of the reworked components. Itseems to be characteristic of the central Pacific Oceanthat there was no age difference between reworked andhost sediments during most of the Mesozoic part of thepenetrated sedimentary section, and that only coevalsediments—if any—have been reworked. Only sinceMaastrichtian time, when fossils from upper Campa-nian deposits were incorporated into the chalks and cal-careous oozes, has a major age difference begun todevelop. The maximum age difference between oldestreworked fossil components and the host sediment in-creased in a regular fashion from the Maastrichtian toapproximately 38 m.y. ago in late Eocene time, when itreached 30 to 40 m.y. Between the late Eocene and thelate Pliocene to early Pleistocene, the maximum age dif-ference fluctuated between 20 and 70 m.y. High age dif-ferences (Fig. 7) were reached in the late Eocene andearly Oligocene, during the early to middle Miocene,and at the end of the Pliocene, whereas minimal valuesare confined to times when the number of observationsof reworked pelagic material was reduced in general. Adrastic decrease of the maximum difference in age of thereworked sediment components and the host sedimentduring the early and late Pleistocene, which already hadbeen observed at Site 462 in the Nauru Basin (Rea andThiede, 1981), can also be seen in the data collectedhere; this seems to be a general feature of the redepo-sition of older pelagic deposits in the central PacificOcean.

THE OCCURRENCE OF REWORKED ANDDISPLACED FOSSILS IN THE MESOZOIC AND

CENOZOIC OF THE CENTRAL PACIFIC OCEAN:IMPLICATIONS FOR PALEOCEANOGRAPHY

The survey (Tables 2 and 3) of reworked and dis-placed pelagic and shallow-water benthic fossils in thecentral Pacific Ocean in upper Mesozoic and Cenozoic

pelagic sediments is by no means complete, but the col-lected data come from 47 deep-sea sites drilled during 15DSDP legs, and they therefore are considered a repre-sentative sample of observations collected largely by theshipboard sedimentologists and paleontologists. Eventhough the observations from any single leg might bebiased because of the personal interests of the scientistsinvolved, the type of presence-absence data used in thisstudy would tend to remove most of the bias.

Reworked and displaced shallow-water benthic fos-sils which are found in deep-sea sediments from the cen-tral Pacific Ocean bear evidence of the former presenceand nature of the many depositional environments ofshoals which once reached into the photic zone andwhich once were the locales of extensive carbonate de-position (Matthews et al., 1974; Hamilton, 1956). Thepresence of such shallow-water carbonates has beendocumented by deep-sea drill sites and by extensivedredging. Most of the central Pacific guyots have beenfound to be made up of Lower and Upper Cretaceouscarbonates (Heezen et al., 1973) and volcanic rocks ofhighly variable composition (Natland, 1976; Jacksonand Schlanger, 1976). It has been assumed that most ofthe late Mesozoic shallow-water carbonate environ-ments have ceased to exist as a result of submergence(Matthews et al., 1974), owing to rapid eustatic sea-levelrises.

In Figure 6, we have plotted the occurrences ofshallow-water-derived benthic fossils from a consider-able number of drill sites in the western central PacificOcean (Fig. 5; Table 3). The data document repeated in-jection of shallow-water debris into the adjacent deep-sea basins throughout the late Mesozoic and the entireCenozoic in a sequence of short-lived, episodic eventswhich are separated from each other by intervals whenless or no shallow-water-derived benthic-fossil materialreached the floor of the deep-sea basins. The events, ex-cept the Campanian-Maastrichtian one, coincide withlow eustatic sea-level stands (Vail et al., 1977), and theytherefore represent erosion close to the lowered sea levelduring those intervals. The Campanian-Maastrichtianevent is a special case, because it is the most importantone of the late Mesozoic paleoenvironment; it appar-ently did not coincide with very low eustatic sea levels(Vail et al., 1977; McCoy and Zimmermann, 1977), butit preceded an interval of important hiatuses in the cen-tral Pacific Ocean across the Cretaceous/Tertiary bound-ary (Fig. 8). However, this interval was coeval with amajor phase of widespread volcanic activity (Jacksonand Schlanger, 1976) in the central Pacific Ocean, whichled to the deposition of volcanic ash in the MarianaBasin (Site 199), along the Line Islands (Sites 165, 315,and 316), and on Horizon Guyot (Sites 171 and 313).

The occurrence of shallow-water benthic-fossil debrisnot coeval with this time of redeposition in centralPacific Ocean deep-sea sediments is restricted entirely tothe Cenozoic parts of a few drill sites (Fig. 6), for exam-ple Sites 76, 165, 209, 315, and 462. This may documentevents of particularly low eustatic sea-level stands. Be-cause of the locations of these sites in regions of oldoceanic crust, subsidence did not generate important

504

REWORKED FOSSILS

Table 3. Distribution of hiatuses and reworked fossil material at DSDP Sites in the tropical and subtropical Pacific Ocean. Where not specificallyindicated, the data of this table have been extracted from site reports of the respective DSDP legs.

WaterDepth

Leg Site (m) Hiatuses Time of DepositionAge of Reworked

Shallow-Water FossilsAge of Reworked

Pelagic Fossils Source

17

20

30

47 2689 Early Miocene-late Eocene,early Paleocene-lateMaastrichtian

48 2619 Early Miocene-Maastrichtian

65 6130

66 5923

76 4598

164 5944 Quaternary-middle Miocene,

late Oligocene, Paleo-cene-Maastrichtian

165 5053 Quaternary-middle Miocene,Paleocene-Maastrichtian

Late Maastrichtian

Middle Maastrichtian

Quaternary-middleMiocene

Oligocene-lateEocene

QuaternaryLate late MiocenePliocene

Late Oligocene

Early Oligocene

Contemporaneous

Contemporaneous

Eocene

Late-middle Eocene

Middle Eocene

Eocene/Oligocene-lateCretaceous

MioceneEoceneMiocene-Eocene

Eocene andMaastrichtian

Oligocene-Maastrichtian

166

167

171

199

204

205

206

207

208

209

210

285

286

287

288

4962

3176

2290

6090

5354

4320

3196

1389

1545

1428

4643

4658

4465

4632

3000

Turonian-early Oligocene

Early Eocene

Middle Miocene-earlyEocene, early Paleocene-early Maastrichtian

Middle-early Miocene

Early Oligocene-lateEocene

Early Miocene-lateEocene

Early Oligocene-middleEocene, early Eocene-late Paleocene, earlyPaleocene-lateMaastrichtian

Late Oligocene-lateEocene

Early Oligocene-lateEocene

Early Oligocene-middleEocene

Late Eocene-latePaleocene

Early Maastrichtian-late Campanian

Cenomanian-lateAlbian

Quaternary-latePliocene

Middle-earlyCampanian

Middle Eocene

Late CampanianCenomanianLate MioceneMiddle MioceneLate Paleocene

QuaternaryEarly Miocene-

OligoceneEarly(?) CretaceousEarly late-early

MioceneEarly Miocene

Early middle MioceneEarly Paleocene

Late Oligocene

Pleistocene-lateMiocene

Late Miocene

Plio-PleistoceneLate-early OligoceneMiddle EocenePleistocene-late

MioceneLate Pliocene

Middle Miocene

Early Miocene

Late Oligocene

Early Oligocene

Contemporaneous

Contemporaneous



Contemporaneous

Contemporaneous

Contemporaneous

ContemporaneousContemporaneousContemporaneous

Contemporaneous

Miocene and Eocene

Early Eocene-Maastrichtian

Oligocene-EoceneEarly Miocene-

PaleoceneEarly Paleocene-

lateCretaceous

MaastrichtianLate Cretaceous

Early late EoceneMaastrichtian

Eocene

Middle Miocene-lateOligocene

Middle Eocene

Oligocene

Late early Pliocene-Cretaceous

Early Eocene-Maastrichtian

Early Miocene-lateCretaceous

Late Oligocene-earlyEocene

Late early Eocene

See also Site318 report

505


Table 3. (Continued).

Leg

32

33

57

58

59

60

61

Site

305

306307

308309

310

313

314315

316

317318

439441

443

444

445

446

451

458

460462

WaterDepth

(m)

2903

33995696

13311454

3516

3484

52144152

4451

25982641

16565655

4372

4843

3377

4952

2060

3449

64435190

Hiatuses

Early Miocene-late Oligo-cene, middle Eocene

Quaternary-late AlbianQuaternary-early

CenomanianPleistocene-early Eocene

Middle Miocene-Oligocene,Oligocene-middleEocene, early Eocene-Maastrichtian

Middle-early Eocene, earlyEocene-middleMaastrichtian

Quaternary-EoceneLate Paleocene-middle

Maastrichtian

Middle Miocene, late-early Oligocene, earlyOligocene-middleEocene, early Paleocene-late Campanian

Middle-early Miocene, latelate Oligocene-lateEocene, middle Eocene

Quaternary-late Miocene

Quaternary

Late Pliocene-late Miocene,late-middle Miocene,middle-early Miocene,late Paleocene-Maastrichtian

Time of Deposition

Late middle Miocene

Early EoceneQuaternary

Late-middle Eocene

QuaternaryEarly middle

MioceneLate-middle MiocenePlioceneLate OligoceneEarly OligoceneMiddle MaastrichtianLate MioceneEarly PaleoceneEarly Maastrichtian-

late Campanian

Early CretaceousQuaternary-late

PlioceneEarly Pliocene-late

OligoceneMiddle-early

MioceneEarly MioceneLate EoceneMiddle EoceneEarly EoceneEarly MioceneEarly Pliocene-late

MioceneEarly Pliocene-late

MiocenePleistoceneLate MioceneQuaternaryOligocene-middle

EoceneLate MioceneMiddle Oligocene

Early late EoceneLate early EoceneQuaternary-late

MiocenePliocene, late

MioceneEarly MioceneOligoceneEoceneQuaternary-late

Campanian

Age of ReworkedShallow-Water Fossils

ContemporaneousEarly Miocene-late

Oligocene

CampanianLate CretaceousLate Cretaceous

Contemporaneous


ContemporaneousContemporaneousContemporaneousContemporaneous

Contemporaneous

Contemporaneous

Contemporaneous

Contemporaneous

Oligocene

Early Miocene-lateCampanian

Age of ReworkedPelagic Fossils

Oligocene

Miocene(?)

Early Eocene andMaastrichtian

No ages available

Paleocene

Late CretaceousLate CretaceousEarly-middle MioceneCretaceous(?)

Middle Eocene

Early Miocene-lateOligocene

Middle-early Eocene

CretaceousEarly middle-late

early MioceneLate early Miocene

Pliocene-MioceneEarly middle MiocenePliocene

Middle MioceneEarly Oligocene and

Eocene

Late CretaceousPliocene-middle

MioceneNo age available

Early EoceneCretaceousLate Miocene-late

Campanian

Source

Kaneps (1976)Beckmann (1976)Beckmann (1976)Beckmann (1976)Kaneps (1976)

Beckmann (1976)

Kauffmann (1976)Beckmann (1976)

Beckmann (1976)Beckmann (1976)Beckmann (1976)Beckmann (1976)

Premoli Silva andBrusa (1981)

Rea and Thiede(1981)

differences in depth of deposition during the later partof the Mesozoic and during Cenozoic, so that erosionduring low eustatic sea-level stands was able to reach theolder strata.

Erosional events as a consequence of sea-level chan-ges, or their coeval occurrence, also have often beeninvoked to explain major changes of oceanic bottom-

water current regimes. In comparing the timing of theoccurrences of non-contemporaneous pelagic fossils(Fig. 7) with those of benthic shallow-water-derivedfossils (Fig. 6) in the central Pacific Ocean, this co-incidence cannot be confirmed, but the curves seem tobe independent of each other. This incompatibility ofboth data sets, however, might have to do with the fact

506

REWORKED FOSSILS

110° 120° 130° 140° 150° 160° 170° 180° 170° 160° 150° 140° 130° 120° 110° 100c

48 46647 # 309 *465

• 305306

307

Figure 5. Locations of DSDP drill sites in the subtropical and tropical central western Pacific Ocean, discussed in thispaper.

that reworked coeval pelagic biogenic sediment compo-nents only rarely can be distinguished from autoch-thonous components if sedimentary structures and tex-tural characteristics are not used as supportive evidence.Contemporaneous reworking and displacement in pe-lagic sediments has often been underrated, because ofthe lack of suitable data—mostly because of the lack ofstratigraphic resolution. However, the dominance of oc-currences of penecontemporaneous reworked fossils(radiolarians) throughout the Tertiary in a large collec-tion of sediment cores (Table 4) from the tropicalPacific Ocean (Riedel, 1971) can be explained only bythe fact that the youngest sediments available for ero-sion during each time span are also those eroded mostextensively. The same data set (Table 4) indicates also

that the temporal distribution of erosional events in thedeep sea is very irregular through time, because re-worked Cretaceous or Paleocene radiolarians have beenfound in very few instances, and because Pliocenesediments seem to be less affected by reworking thanMiocene and Eocene sediments. The deep-sea drill-sitedata compiled in Tables 2 and 3 and illustrated in Figure7 have added considerable stratigraphic detail to thispreliminary interpretation, but it has to be kept in mindthat most of the radiolarian data displayed in Table 4have been obtained from non-calcareous sediments, incontrast to the deep-sea drill-site data, which are domi-nantly from calcareous deposits. Both sets of data there-fore have been obtained from different depositional pa-leodepth levels in the ocean.

507


PERCENT OFOCCURRENCES

OF NERITIC FOSSILS

(AGE OF DISPLACED < GOMINUS AGE OF HOST w jjjSEDIMENT IN M.Y.) g>

0 1 2 3 4 5 6% 0 10 20 30 40 50

20

40

60

80

100

120

CENTRAL PACIFIC OCEAN

|—QuaternaryPliocene

Miocene

Oligocene

Eocene

Paleocene

Maestrichtian

Campanian

Santoπian

Coniacian

Turanian

Cenomanian

Albian

Aptian

Barremian

Hauterivian

Valanginian

Figure 6. Occurrence and age of displaced shallow-water fossils in drill sites from the subtropicaland tropical central western Pacific Ocean. Occurrence is expressed in percent of total obser-vations. tmax is the maximum time difference between the age of the reworked and displacedmaterial and the time of redeposition. The ages of low eustatic sea-level stands according toVail et al. (1977) have been marked on the right side of the figure.

The most surprising aspect of the distribution of non-coeval reworked pelagic sediment components in thecentral Pacific Ocean is the large difference between theMesozoic and the Cenozoic strata (Fig. 7). Maastrich-tian events which reworked the immediately underlyingCampanian sediments obviously represent the beginningof current regimes in the intermediate water masses ofthe Pacific Ocean, which were able not only to transportand displace coeval sediments, but also to erode theunderlying older sediments. This is different from theSouth Atlantic paleoenvironment, where pelagic sedi-ments as old as Coniacian have been displaced into de-posits of Santonian age (Premoli Silva and Boersma,1977). Even though the available drill-site data (Tables 2and 3) have to be considered preliminary, the largequantitative difference of occurrences of redepositedand reworked planktonic fossils during pre-Maastrich-tian and Maastrichtian-Pleistocene time seems to pointto a fundamental change of the depositional paleoenvi-ronment of the deep central Pacific Ocean, and prob-

ably of the world ocean in general. If the physical prop-erties of deep-sea sediments (Schlanger and Douglas,1974) deposited during the pre-Campanian time in thecentral Pacific Ocean were not drastically differentfrom those laid down during the past 75 m.y., then theirerosional potential should have been approximately thesame. If diagenetic changes have effected the erosionalpotential of the pre-Campanian central Pacific deep-seasediments, then these diagenetic changes must have oc-curred soon after deposition of these sediments. The co-incidence of the lack of non-coeval reworked pelagicfossil material and of the repeated development of oxy-gen-deficient depositional environments between 80 and120 m.y., which must have been accompanied by a veryquiet and sluggish bottom-water circulation, as docu-mented by their laminated sediments (Dean et al., thisvolume), seems to support the interpretation that a widearea of the pre-Campanian central Pacific Ocean hasnot experienced bottom-water currents strong enough toerode older strata and to transport the re-suspended

508

REWORKED FOSSILS

PERCENT OF OBSERVA-TION OF REWORKED

PELAGIC FOSSILS

0 1 2 3 4 5 6%

^ a x AGE OF DISPLACED MINUSAGE OF HOST SEDIMENT (M.Y.)

120

i— Quaternary -

.Pliocene.

Miocene

Oligocene

Eocene

Paleocene

Maastrichtian

Campanian

Santonian

Coniacian

Turonian

Cenomanian

Albian

Aptian

Barremian


Figure 7. Occurrence of non-contemporaneous reworked pelagic fossils (calcareous nannofossils, planktonicforaminifers, and radiolarians) at drill sites of the subtropical and tropical central western Pacific Ocean.Occurrence is expressed in percent of total observations. fmax is the maximum time difference betweenthe age of the reworked material and the time of redeposition.

sediment particles. Relatively rapid currents seem tohave been confined to the upper few hundreds of metersof the water column, especially close to the equatorialdivergence (Dean et al., this volume).

The number of occurrences of reworked non-coevalpelagic fossils (Fig. 7) remained modest from Maas-trichtian to late middle Eocene times, but minor peaksduring the late Paleocene and early middle Eocenerepresent short-lived erosional events of a modest scale.The remainder of the Cenozoic was characterized bydepositional paleoenvironments with erosion at inter-mediate water depths as the rule, not the exception. Thelate middle and early late Eocene, early late Oligocene,early middle Miocene, middle late Miocene, Plioceneand Quaternary were times of particularly strong re-working in the central Pacific Ocean, whereas the lateOligocene to early Miocene seems to have been ratherquiescent. The coincidence of times of important re-working with major changes of the oceanic bottom-water temperature (Fig. 9), as deduced from the δθ 1 8

ratios of the benthonic foraminifers (Savin, 1977; Vin-cent and Berger, in press), suggests that these episodesrepresent major revolutions of the bottom-water currentregimes, because of advection of cold polar bottomwaters (Shackleton and Kennett, 1975). It has to remainopen at the present time if the pre-late middle Eocene

reworking events can be explained by the formation ofmodest quantities of polar bottom waters much earlierthan hitherto presumed.

The age distribution of the reworked and displacednon-coeval pelagic fossils and the difference betweenthe age of reworked components and time of redeposi-tion in the central Pacific Ocean are particularly inte-resting (Fig. 7). The time difference can vary betweenzero and a certain maximum value, as it reflects thelength of the stratigraphic column which was subject toerosion at the time of redeposition. In the central Pa-cific Ocean, this age difference approached zero duringMaastrichtian time, but increased fairly regularlythroughout the Cenozoic to the early Pleistocene. Theregular increase must mean that the entire sediment col-umn which had been laid down since initiation of thiserosional regime in early Maastrichtian time was subjectto continuous erosion and redeposition. Deviationsfrom the regular increase of the maximum time differ-ence between the age of the reworked material and timeof redeposition have been observed for the early andlate Oligocene, as well as the late Miocene and Quater-nary. Minima of this curve (Fig. 7) coincide with epi-sodes of high pelagic accumulation rates (van Andel etal., 1975; Worsley and Davies, 1979), the maxima withthe development of important hiatuses in the western

509


1000

Paleodepth of Hiatuses (m)

2000 3000 4000 5000

140

Figure 8. Paleodepth and age distribution of major hiatuses in the central North Pacific Ocean. The diagramdepicts the time span of major hiatuses and their paleodepth range. Hiatuses are marked with their sitenumbers.

Table 4. Temporal distribution of samples containing pre-Quaternary radiolarians(dominantly cores from the tropical Pacific Ocean). Data from Riedel (1971).Values are percent of observations.

Age ofDisplacement

QuaternaryCalcareous oozeSiliceous oozeClay

Total

PlioceneMioceneOligoceneEocenePaleoceneCretaceous

Pliocene

12167

12

41

Age of Reworked Radiolarians

Miocene

293021

27

2962

Oligocene

242121

22

101369

Eocene

343248

39

192531

100

Paleocene

000

0

00000

Cretaceous

100

1

10000

TotalObservations

119145149

413

121100351401

510

REWORKED FOSSILS

PERCENT OFOBSERVATIONSOF REWORKED

PELAGIC FOSSILS

0 1 2 3 4 5 6

1 8 O, BENTHIC FORAMINIFERS


Figure 9. Oxygen-isotope ratios in benthic foraminifers through thepast 70 m.y. Most measurements have been made on material fromthe North Pacific Ocean (after Vincent and Berger, in press; Savin,1977).

central Pacific Ocean (Moore et al., 1978). The uniquesimplicity of the argument that reworked and displacednon-coeval fossils in deep-sea sediments imply mechani-cal transport suggests that mechanical erosion causedmost of these hiatuses, rather than non-deposition ordissolution.

CONCLUSIONS

1. Reworked and displaced fossils are accessory butcommon components of tropical and subtropical centralwestern Pacific Ocean deep-sea sediments. They consistboth of coeval and non-contemporaneous pelagic andshallow-water-derived benthic calcareous fossils. Theirpresence in fine-grained deep-sea sediments implies me-chanical transport from their original locale to the siteof their final deposition.

2. The composition of the displaced neritic fossil as-semblages changed considerably with time from theCretaceous to the Tertiary. This allows description ofthe evolution of the shallow-water depositional environ-ments of guyots and carbonate platforms in the tropicaland subtropical central western Pacific Ocean.

3. Neritic fossils were transported episodically fromguyots and shoals into the adjacent deep sea duringtimes of low eustatic sea-level stands. Erosional eventswhich reworked non-coeval neritic deposits consider-ably older than the age of redeposition are confined tothe Cenozoic.

4. A major late Campanian-Maastrichtian erosionalevent possibly is not related to low global sea levels, butto an episode of major volcanic activity in the centralwestern Pacific. Sediments of an apparently completesection across the Cretaceous/Tertiary boundary pene-trated at Site 465 on southern Hess Rise do not containreworked material.

5. Reworking and displacement of coeval planktonicfossils is often difficult to detect in dominantly biogenicdeep-sea sediments. A regime of erosion which cut intonon-coeval, older sediments—defined by displaced zonefossils—developed in the central western Pacific Oceanonly during Maastrichtian time. The coincidence of thedevelopment and spread of oxygen-deficient deposi-tional environments, which led to preservation of lami-nated, very fine-grained sediments, with the lack of in-dications of important mechanical erosion during thepre-Maastrichtian Cretaceous suggests very slow inter-mediate water current regimes.

6. The erosional potential of the central westernPacific Ocean depositional environments during thepre-Maastrichtian part of the Cretaceous was drasticallydifferent from that of post-Campanian time, when non-coeval sediments were continuously eroded mechan-ically from outcrops on the ocean floor. Times of highsediment-accumulation rates coincided with a decreaseof the length of the stratigraphic columns available forerosion during the past 70 m.y.

7. The Maastrichtian and lower Tertiary pre-middleEocene erosional regime of the central western PacificOcean suggests formation of modest quantities of coolto cold bottom water from the polar regions muchearlier than hitherto presumed. The coincidence ofabundant reworked pelagic fossils with major changesof the oxygen-isotope ratios of benthic foraminifers,and hence of the bottom-water temperatures during theCenozoic, points to the importance of advection of coolto cold water masses of polar (Antarctic) origin tothe intermediate waters of the central western PacificOcean. This advection resulted in more-rapid currentswhich eroded the ocean floor and generated widespreadhiatuses through reworking and mechanical redeposi-tion of biogenic sediments, rather than through dissolu-tion.

ACKNOWLEDGMENTS

This study is based on data collected during DSDP Leg 62 and de-scriptions of deep-sea drill sites from other DSDP legs in the tropicaland subtropical central Pacific Ocean. The effort to collect these datahas therefore been shared by numerous colleagues, whose skillfulwork is gratefully acknowledged. These ideas have been discussedwith W. H. Berger, Scripps Institution of Oceanography, and P. Vail,Exxon-Houston, whose comments are appreciated.

REFERENCES

Beckmann, J. P., 1976. Shallow-water foraminifers and associatedmicrofossils from Sites 315, 316, and 318, DSDP Leg 33. InSchlanger, S. O., Jackson, E. D., et al., Init. Repts. DSDP, 33:Washington (U.S. Govt. Printing Office), 467-470.

Berggren, W. A., and Van Couvering, J. A., 1974. The late Neogene:biostratigraphy, biochronology and paleoclimatology of the last15 million years in marine and continental sediments. Palaeo-geography, Palaeoecology, Palaβoclimatology, 16:1-216.

Boltovskoy, E., 1977. Neogene deep water benthonic foraminifera ofthe Indian Ocean. In Heirtzler, J. B. (Ed.), Indian Ocean Geologyand Biostratigraphy: Washington (Am. Geophys. Union), pp.599-616.

Burckle, L. H., and Stanton, D., 1975. Distribution of displaced Ant-arctic diatoms in the Argentine basin. Nova Hedwigia Beih., 53:283-292.

Cook, H. E., Jenkyns, H. C , and Kelts, K. R., 1975. Redepositedsediments along the Line Islands, equatorial Pacific. In Schlanger,S. O., Jackson, E. D., et al., Init. Repts. DSDP, 33: Washington(U.S. Govt. Printing Office), 837-847.

511


Hamilton, E. L., 1956. Sunken Islands of the Mid-Pacific Mountains.Geol. Soc. Am. Mem., 64.

Hardenbol, J., and Berggren, W. A., 1978. A new Paleogene numer-ical time scale. Am. Assoc. Petrol. Geol. Stud. Geol., 6:213-234.

Heezen, B. C , Matthews, J. L., Catalano, R., et al., 1973. WesternPacific guyots. In Heezen, B. C , MacGregor, I. D., et al., Init.Repts. DSDP, 20: Washington (U.S. Govt. Printing Office), 653-723.

Jackson, E. D., and Schlanger, S. O., 1976. Regional syntheses, LineIslands chain, Tuamotu Islands chain, and Manihiki Plateau, cen-tral Pacific Ocean. In Schlanger, S. O., Jackson, E. D., et al., Init.Repts. DSDP, 33: Washington (U.S. Govt. Printing Office),915-927.

Kaneps, A. G., 1976. Cenozoic planktonic foraminifers, equatorialPacific Ocean, Leg 33, DSDP. In Schlanger, S. O., Jackson, E.D., et al., Init. Repts. DSDP, 33: Washington (U.S. Govt. PrintingOffice), 361-367.

Kauffman, E. G., 1976. Deep-sea Cretaceous macrofossils: Hole317A, Manihiki Plateau. In Schlanger, S. O., Jackson, E. D., etal., Init. Repts. DSDP, 33: Washington (U.S. Govt. Printing Of-fice), 503-535.

Lancelot, Y., 1978. Relations entre evolution sédimentaire et tec-tonique de la plaque Pacifique depuis la Crétacée inferieur. Soc.Géol. France Mém., N. S., 134.

Lancelot, Y., and Larson, R. L., 1975. Sedimentary and tectonic evo-lution of the northwestern Pacific. In Larson, R. L., Moberly, R.,et al., Init. Repts. DSDP, 32: Washington (U.S. Govt. Printing Of-fice), 925-939.

McCoy, F. W., and Zimmerman, H. B., 1977. A history of sedimentlithofacies in the South Atlantic Ocean. In Supko, P. R., Perch-Nielsen, K., et al., Init. Repts DSDP, 39: Washington (U.S. Govt.Printing Office), 1047-1079.

Matthews, J. O., Heezen, B. C , Catalano, R., et al., 1974. Creta-ceous drowning of reefs on Mid-Pacific and Japanese guyots.Science, 184:462-464.

Moore, T. C , van Andel, Tj. H., Sancetta, C , et al., 1978. Cenozoichiatuses in pelagic sediments. Micropaleontology, 24:113-138.

Natland, J. H., 1976. Petrology of volcanic rocks dredged from sea-mounts in the Line Islands. In Schlanger, S. O., Jackson, E. D., etal., Init. Repts. DSDP, 33: Washington (U.S. Govt. Printing Of-fice), 749-777.

Pitman, W. C , Larson, R. L., and Herron, E. M., 1974. MagneticLineations of the Oceans: Geol. Soc. Am. Map Ser.

Premoli Silva, I., and Boersma, A., 1977. Cretaceous planktonic fora-minifers—DSDP Leg 39 (South Atlantic). In Supko, P. R., Perch-Nielsen, K., et al., Init. Repts. DSDP, 39: Washington (U.S. Govt.Printing Office), 615-641.

Premoli Silva, I., and Brusa, C , 1981. Shallow-water skeletal debrisand larger foraminifers from the Deep-Sea Drilling Project Site462, Nauru Basin, western equatorial Pacific. In Larson, R. L.,Schlanger, S. O., et al., Init. Repts. DSDP, 61: Washington (U.S.Govt. Printing Office), 397-422.

Rea, D. K., and Thiede, J., 1981. Mesozoic and Cenozoic mass-accumulation rates of the major sediment components in theNauru Basin, western equatorial Pacific. In Larson, R. L.,

Schlanger, S. O., et al., Init. Repts. DSDP, 61: Washington (U.S.Govt. Printing Office), 549-556.

Reid, J. L., 1965. Intermediate Waters of the Pacific Ocean. JohnsHopkins Oceanogr. Stud., 2.

Riedel, W. R., 1971. The occurrence of pre-Quaternary radiolaria indeep-sea sediments. In Funnell, B. M., and Riedel, W. R. (Eds.),The Micropaleontology of Oceans: Cambridge (Cambridge Univ.Press), pp. 567-594.

Savin, S. M., 1977. The history of the Earth's surface temperatureduring the past 100 million years. Ann. Rev. Earth Planet. ScL,5:319-355.

Schlanger, S. O., and Douglas, R. G., 1974. The pelagic ooze-chalk-limestone transition and its implications for marine stratigraphy.Internat. Assoc. Sedimentol. Spec. Publ, 1:117-148.

Schlanger, S. O., and Premoli Silva, I., 1981. Tectonic, volcanic, andpaleogeographic implications of redeposited reef faunas of LateCretaceous and Tertiary age from the Nauru Basin and the LineIslands. In Larson, R. L., Schlanger, S. O., et al., Init. Repts.DSDP, 61: Washington (U.S. Govt. Printing Office), 817-828.

Seibold, E., 1978. Mechanical processes influencing the distributionof pelagic sediments. Micropaleontology, 24:407-421.

Shackleton, N. J., and Kennett, J. P., 1975. Paleotemperature historyof the Cenozoic and the initiation of Antarctic glaciation: oxygenand carbon isotope analyses in DSDP Sites 277, 279 and 281. InKennett, J. P., Houtz, R. E., et al., Init. Repts. DSDP., 29:Washington (U.S. Govt. Printing Office), 743-755.

Shipboard Scientific Party, in press. Site 462: Nauru Basin, WesternPacific Ocean, Deep Sea Drilling Project Leg 61. In Larson, R. L.,Schlanger, S. O., et al., Init. Repts. DSDP, 61: Washington (U.S.Printing Office).

Thiede, J., 1977. Textural variations of calcareous coarse fractionsin the Panama Basin (eastern equatorial Pacific Ocean). InAndersen, N. R., and Malahoff, A. (Eds.), The Fate of Fossil FuelCO2 in the Oceans: New York (Plenum), pp. 673-692.

Thiede, J., and Dinkelman, M. E., 1977. Occurrence of Inoceramusremains in late Mesozoic pelagic and hemipelagic sediments. InSupko, P. R., Perch-Nielsen, K., et al., Init. Repts. DSDP, 39:Washington (U.S. Govt. Printing Office), 899-910.

Vail, P. R., Mitchum, R. M., and Thompson, S., 1977. Seismic stra-tigraphy and global changes of sea level. Part 3: relative changes ofsea level from coastal onlap. Part 4: global cycles of relativechanges of sea level. Am. Assoc. Petrol. Geol. Mem., 26:63-97.

van Andel, Tj. H., 1973. Texture and dispersal of sediments in thePanama basin. J. Geol., 81:434-457.

van Andel, Tj. H., Heath, G. R., and Moore, T. C , 1975. Cenozoichistory and paleoceanography of the central equatorial PacificOcean. Geol. Soc. Am. Mem., 143.

van Hinte, J. E., 1976. A Cretaceous time scale. Am. Assoc. Petrol.Geol. Bull., 60:498-516.

Vincent, E., and Berger, W. H., in press. Planktonic foraminifera andtheir use of paleoceanography. In Emiliani, C. (Ed.), The Sea(Vol. 7): New York (Wiley-Interscience).

Worsley, T. R., and Davies, T. A., 1979. Sea level fluctuations anddeep-sea sedimentation rates. Science, 203:455-456.

512

Documents

PACIFIC OCEAN SEDIMENTS, DEEP SEA DRILLING PROJECT 1deepseadrilling.org/62/volume/dsdp62_15.pdf · sediment has only recently received more attention, be-cause it could be used to