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45. SEDIMENT SYNTHESIS: DEEP SEA DRILLING PROJECT LEG 58, PHILIPPINE SEA Stan M. White, 1 Hervé Chamley* 2 Doris Curtis, 3 George deVries Klein, 4 and Atsuyuki Mizuno, 5 with a special contribution on physical properties by David M. Fountain 6 INTRODUCTION Five sites were drilled on DSDP Leg 58 in the north Philippine Sea (Figure 1). The total penetration was 2971.5 meters, with 1591.8 meters recovered (54%). One re-entry operation was completed (Site 442). Primary objectives of Leg 58 (see also introductory chapter in this volume) were to examine the geologic his- tory of the north Philippine Sea and to test two models for the origin of back-arc basins. Those two models are: (1) origin of marginal basins by a rifting process iden- tical to sea-floor spreading, and (2) origin of marginal basins by entrapment of older oceanic crust behind a younger active trench. Three sites were drilled in the Shikoku Basin, where surveys suggested a symmetrical arrangement of magnetic anomalies, to test the spread- ing model, and two sites were drilled in the Daito Ridge and Basin province to test the entrapment model. Leg 58 provided an opportunity to answer several questions relevant to the problems of the sedimentology of back-arc basins in the western Pacific. These prob- lems include (1) an analysis of the variability of sedi- ment styles and processes in each of the basins; (2) the causes of sediment variability; (3) the effect of paleocir- culation on sedimentation in the basins; and (4) the rela- tionship of sediment facies to tectonic evolution in such back-arc basins. The purpose of this chapter is to synthesize the sedi- mentology of the north Philippine Sea. 7 Our synthesis is based on sedimentological studies from Leg 58 sediment cores and focuses on specific problems posed by drilling during Leg 58. 1 Deep Sea Drilling Project, Scripps Institution of Oceanography, La Jolla, California. Present address: Robertson Research (U. S.) Inc., Houston, Texas. 2 Sedimentologie et Géochimie, Université des Sciences et Tech- niques de Lille, U.E.R. des Sciences de la Terre, Villeneuve d'Ascq, France. 3 Shell Development Company, Bellaire Research Center, Houston, Texas. Present address: 16730 Hedgecroft, Suite 306, Houston, Texas. 4 University of Illinois/Urbana-Champaign, Department of Geol- ogy, Urbana, Illinois. 5 Geological Survey of Japan, Kawasaki, Japan 6 University of Montana, Department of Geology, Missoula, Montana. 7 With contributions by Dorothy Echols, Hisatake Okada and Jon Sloan (paleontology); Douglas Waples (organic geochemistry); and Hajimu Kinoshita (Paleomagnetism). SOURCES OF DATA Major sources of data are analyses and interpreta- tions of the visual core descriptions and smear-slide data prepared during the cruise and information derived from post-cruise studies. DSDP laboratories at Scripps Institution of Oceanography provided grain-size, organ- ic-carbon, and calcium-carbonate data (see White, this volume). The introduction to this volume discusses back- ground and objectives of the Leg 58 drilling program and contains explanatory notes relating to core-hand- ling and sediment conventions, as well as specific data on age determinations. The reader is also referred to the site-summary chapters in this volume, as well as to special chapters on selected sediment studies, for de- tailed information on the drilling sites and material con- tained in this synthesis. GEOLOGIC SETTING, SITE OBJECTIVES, AND STRATIGRAPHY Shikoku Basin The Shikoku Basin (Figure 1) is an elongate, trough- shaped marginal basin; its axis is oriented approximate- ly north-northwest to south-southeast. A previous (pre- Leg 58) seismic study of the basin indicated that it has a rough acoustic-basement topography mantled by three clastic wedges (Karig, Ingle, et al., 1975; Marauchi and Asanuma, 1974, 1977). The objectives of drilling in the Shikoku Basin (see also site reports, this volume) included (1) a test of the validity of a symmetrical-spreading model developed from mapping of magnetic anomalies (Tomoda et al., 1975; Kobayashi and Isezaki, 1976; Watts and Weissel, 1975); (2) determination of the petrology of basement rocks from this back-arc basin; (3) the study of paleo- magnetic nature and history of the basin and determina- tion of the source of the magnetic anomaly signal; and (4) a determination of the sediment distribution and sedimentation patterns and, where possible, the nature of paleocirculation in the basin. Site 442 Site 442 is on the west side of an extinct spreading center, on magnetic anomaly 6 (19-21 m.y.), where the anomaly has strong intensity. A total of 286 meters of sediment and 160 meters of basalt were penetrated. A 963

45. SEDIMENT SYNTHESIS: DEEP SEA DRILLING PROJECT …45. SEDIMENT SYNTHESIS: DEEP SEA DRILLING PROJECT LEG 58, PHILIPPINE SEA Stan M. White,1 Hervé Chamley*2 Doris Curtis,3 George

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  • 45. SEDIMENT SYNTHESIS: DEEP SEA DRILLING PROJECT LEG 58,PHILIPPINE SEA

    Stan M. White,1 Hervé Chamley*2 Doris Curtis,3 George deVries Klein,4 and Atsuyuki Mizuno,5 with a specialcontribution on physical properties by David M. Fountain6

    INTRODUCTION

    Five sites were drilled on DSDP Leg 58 in the northPhilippine Sea (Figure 1). The total penetration was2971.5 meters, with 1591.8 meters recovered (54%).One re-entry operation was completed (Site 442).

    Primary objectives of Leg 58 (see also introductorychapter in this volume) were to examine the geologic his-tory of the north Philippine Sea and to test two modelsfor the origin of back-arc basins. Those two models are:(1) origin of marginal basins by a rifting process iden-tical to sea-floor spreading, and (2) origin of marginalbasins by entrapment of older oceanic crust behind ayounger active trench. Three sites were drilled in theShikoku Basin, where surveys suggested a symmetricalarrangement of magnetic anomalies, to test the spread-ing model, and two sites were drilled in the Daito Ridgeand Basin province to test the entrapment model.

    Leg 58 provided an opportunity to answer severalquestions relevant to the problems of the sedimentologyof back-arc basins in the western Pacific. These prob-lems include (1) an analysis of the variability of sedi-ment styles and processes in each of the basins; (2) thecauses of sediment variability; (3) the effect of paleocir-culation on sedimentation in the basins; and (4) the rela-tionship of sediment facies to tectonic evolution in suchback-arc basins.

    The purpose of this chapter is to synthesize the sedi-mentology of the north Philippine Sea.7 Our synthesis isbased on sedimentological studies from Leg 58 sedimentcores and focuses on specific problems posed by drillingduring Leg 58.

    1 Deep Sea Drilling Project, Scripps Institution of Oceanography,La Jolla, California. Present address: Robertson Research (U. S.)Inc., Houston, Texas.

    2 Sedimentologie et Géochimie, Université des Sciences et Tech-niques de Lille, U.E.R. des Sciences de la Terre, Villeneuve d'Ascq,France.

    3 Shell Development Company, Bellaire Research Center, Houston,Texas. Present address: 16730 Hedgecroft, Suite 306, Houston, Texas.

    4 University of Illinois/Urbana-Champaign, Department of Geol-ogy, Urbana, Illinois.

    5 Geological Survey of Japan, Kawasaki, Japan6 University of Montana, Department of Geology, Missoula,

    Montana.7 With contributions by Dorothy Echols, Hisatake Okada and Jon

    Sloan (paleontology); Douglas Waples (organic geochemistry); andHajimu Kinoshita (Paleomagnetism).

    SOURCES OF DATA

    Major sources of data are analyses and interpreta-tions of the visual core descriptions and smear-slide dataprepared during the cruise and information derivedfrom post-cruise studies. DSDP laboratories at ScrippsInstitution of Oceanography provided grain-size, organ-ic-carbon, and calcium-carbonate data (see White, thisvolume).

    The introduction to this volume discusses back-ground and objectives of the Leg 58 drilling programand contains explanatory notes relating to core-hand-ling and sediment conventions, as well as specific dataon age determinations. The reader is also referred to thesite-summary chapters in this volume, as well as tospecial chapters on selected sediment studies, for de-tailed information on the drilling sites and material con-tained in this synthesis.

    GEOLOGIC SETTING, SITE OBJECTIVES, ANDSTRATIGRAPHY

    Shikoku BasinThe Shikoku Basin (Figure 1) is an elongate, trough-

    shaped marginal basin; its axis is oriented approximate-ly north-northwest to south-southeast. A previous (pre-Leg 58) seismic study of the basin indicated that it has arough acoustic-basement topography mantled by threeclastic wedges (Karig, Ingle, et al., 1975; Marauchi andAsanuma, 1974, 1977).

    The objectives of drilling in the Shikoku Basin (seealso site reports, this volume) included (1) a test of thevalidity of a symmetrical-spreading model developedfrom mapping of magnetic anomalies (Tomoda et al.,1975; Kobayashi and Isezaki, 1976; Watts and Weissel,1975); (2) determination of the petrology of basementrocks from this back-arc basin; (3) the study of paleo-magnetic nature and history of the basin and determina-tion of the source of the magnetic anomaly signal; and(4) a determination of the sediment distribution andsedimentation patterns and, where possible, the natureof paleocirculation in the basin.

    Site 442Site 442 is on the west side of an extinct spreading

    center, on magnetic anomaly 6 (19-21 m.y.), where theanomaly has strong intensity. A total of 286 meters ofsediment and 160 meters of basalt were penetrated. A

    963

  • S.M. WHITE ETAL.

    60 N

    4 ‰, %. \%, ' SI /—-si) U ^3000

    135°W 150° 165° 180°W

    Figure 1. Location of sites drilled during Leg 58.

    complete sedimentary section was recovered at Hole442A, whereas at Hole 442B, offset 70 meters to thenorth of Hole 442A, sediments were recovered whichare equivalent to the sediment units in Hole 442A be-tween 267.5 meters sub-bottom and the top of basalticunit 1 (286.1 m sub-bottom).

    The stratigraphic section consists of five lithologicunits of Quaternary to early-Miocene age (Figure 2).The lowermost sedimentary unit, unit V, a 0.4-meter,pink-gray limestone, directly overlies basaltic unit 1 (seeDick et al., this volume).

    The following are some significant characteristics ofthe sediment section drilled:

    1. The sampled section is a continuous representa-tion of the early Miocene (M6-19 m.y.) to the late

    Quaternary and is dominated by muds and(or) clayswith a tendency toward coarser sediments in Cores442A-1 through 442A-4. Sediments of units I to III arehemipelagic, whereas sediments of unit IV are pelagic.The latter are characterized by micronodules and evi-dence of bioturbation.

    Explosive volcanic activity which occurred near thesite is evident throughout the sediment sequence: vol-canic glass and pumice are irregularly disseminated inall sediments.

    2. The entire sediment sequence above unit V is char-acterized by the rarity of calcium carbonate; however,nannofossils are common to abundant in Cores 442A-1to 441A-4. The remainder of the section below Core 4 isvirtually barren of calcareous microfossils, except for

    964

  • SEDIMENT SYNTHESIS

    the limestone of unit V, which contains smaller-fora-minifer tests. Therefore, the depositional surface waseither slightly above or slightly below the carbonate-compensation depth (CCD). Deposition during earlyand early middle Miocene occurred above the CCD, butapparently below the lysocline. From the late middleMiocene through the early Pliocene, deposition oc-curred below the CCD, while during the late Plioceneand Quaternary deposition occurred slightly above theCCD. The exact depth of deposition cannot be deter-mined exactly, because no data exist concerning presentor past elevations of the CCD in the Shikoku Basin (seeSite 442 report, this volume).

    3. Sedimentation rates range from 0.8 to 17.5 m/m.y. for the Miocene through the Pliocene (units Vthrough II), increasing to 30.9 m/m.y. for the Pleisto-cene.8 (See Site 442 report, this volume, and section onsedimentation rates in this paper.)

    4. Hemipelagic clays and claystones of units I, II,and III were deposited in a distal or basinal facies. TheKyushu-Palau Ridge appears to be the most likelysource area, inasmuch as the site is on the eastern edgeof a clastic wedge which thickens westward against theKyushu-Palau Ridge, but this is not proved.

    Site 443Site 443 is on the east side of a supposed extinct

    spreading center, on magnetic anomaly 6A (21-22m.y.), where the anomaly has moderate intensity. Atthis site, 457 meters of sediment and 125 meters of ba-salt were penetrated.

    Five sedimentary units were distinguished, from latePleistocene to early or middle Miocene (Figure 3, backpocket, this volume). Unit V (358.5-457.0 m), a dark-green-gray sequence of interbedded claystone, mudstone,ash, and nannofossil chalk, is the oldest sediment recov-ered (15 m.y.), suggesting a basement age at variancewith the age of magnetic anomaly 6A.

    Below unit V, the basaltic rocks includes pillowbasalts, produced by crust generation at a spreadingcenter, and intrusive basalt sills formed by off-ridge vol-canism.

    Significant characteristics of the sedimentary se-quence are:

    1. The sediment section represents a probably con-tinuous sequence from the early or middle Miocene(about 15 m.y.) to the late Pleistocene and Holoceneand is dominated by mud and mudstone. Clay mineralsare the main components, throughout associated withminor quantities of quartz, feldspars, and volcanicglass. (See Chamley, this volume.)

    The sediments are chiefly hemipelagic, terrigenouscomponents being abundant throughout the section andmixed in variable proportions with planktonic compo-nents. Sediments deposited after the formation of thebasin (unit V) show evidence of strong current activity,possibly indicating moderate and temporary turbidite

    8 Assuming the Pliocene/Pleistocene boundary at 1.6 m.y.

    deposition. Explosive volcanic activity near the drill siteis apparent from the well-defined ash layers throughout.Major volcanic activity occurred during the early middleMiocene (when sedimentation began), the early lateMiocene, and the middle to late Pleistocene.

    2. Calcareous and siliceous fossils occur throughoutthe sedimentary sequence; however, there are wide vari-ations in the amounts of nannofossils and foraminifers,indicating changes in the CCD. This suggests that thedepositional surface was above or near the CCD andprobably below the lysocline.

    3. Sedimentation rates were high during the earlymiddle Miocene and the Pleistocene.

    Site 444Site 444 is on the east side of a supposed extinct

    spreading center, on magnetic anomaly 6A (21-22 m.y.)where the anomaly has moderate intensity. A single-bithole penetrated 272.7 meters of sediment and 37.3 me-ters of basalt.

    The sedimentary succession consists of five lithologicunits, which range in age from early or middle Mioceneto Quaternary. The two basalt units are diabase sills,one of which intrudes middle-Miocene mudstones (Fig-ure 4).

    The lowest sedimentary unit, unit V (272.0-272.7 me-ters), a reddish-brown and greenish-gray, zeolitic, cal-careous claystone (middle Miocene), overlies basalt unit2, a plagioclase phyric basalt and diabase. The age ofthis sediment is 14 to 15 m.y., whereas the age of intru-sion of the basalt sill of unit 1 is 14.7 ±2.1 m.y. (seeMcKee and Klock, this volume). Both basalt units ap-pear to be younger than the initial sedimentation andprobably indicate an episode of off-ridge volcanism inthe Shikoku Basin that post-dates the youngest age ofspreading, reported as 17 m.y. by Kobayashi and Ise-zaki (1976) and Kobayashi and Nakada (1977).

    Significant aspects of the sediments at Site 444 are asfollows:

    1. In general, the sediments are predominantly hemi-pelagic mud, with abundant volcanic glass and largeproportions of terrigenous clay and silt. The pyroclas-tics occur either as discrete layers, or as components ofthe mudstone. Hard, well-lithified mudstone and clay-stone occur in several cores above and between basalts.Pelagic, zeolitic nannofossil claystone or ooze is presentin the lowest meter of sediment above the second basaltlayer.

    2. Volcanic activity was intense in the site vicinityduring deposition of most of the sedimentary sequence;it was less intense during the late Miocene and Pleisto-cene than at other times. Variations in nearby volcanicactivity are reflected also in distribution and thicknessof ash beds, which show graded, upward-fining bed-ding. Where the ash is a relatively pure glass associatedwith nannofossil mud, it represents settling of ash fromsuspension in the absence of currents, rather than tur-bidity-current deposition. In these cases, the ash contentdecreases upward as the nannofossil content increases.

    3. Calcareous nannofossils are present in varyingquantities in most of the section. Siliceous microfossils

    965

  • OON

    Site: 442Water Depth: 4639 m Total Penetration: 313.5 m (Hole 442A); 455.0 m (Hole 442B).

    50-

    150-

    Age

    200 (?)

    early

    LithologicUnit

    Unit 1Dark-green andgray mud, clay.

    -164.0 m-

    Unit IIYellow-brown tobrown and dark-brown mud.

    Unit IIIIlia: Yellow-brownnaud witrxsiliceousfossils.Illbr Gray and dark-green intermixedash and mud.

    *Unit IV_285.7 m.Unit V--286.1 m~289.7 m

    Basalt

    Lithofacies Sand

    0 40

    Silt

    0 100

    Clay

    0 100

    CaCO3

    0 20

    Organic Carbon

    0 20

    Sonic Velocity(km/s)

    2.0 3.0 4.0

    Hemipelagic mudand mudstonewith pyroclastics

    -123.5 m-

    Hemipelagicmud andmudstones

    -256.0 m-Pyroclastics withhemipelagicmudstone

    -276.0 m-Pelagic sediment(non biogenic) with

    | biogenic (calcareous)-286.1m

    -286.1 m-

    *Unit IV (Hole 442A), recovered from 277.1to 285.7 meters,is dark-brown clay and claystone, with zeolites.Unit V (Hole 442A), recovered from 285.7 to 286.1 meters,is hard fine grained,pink limestone; basalt was encounteredat 28 6.1 meters. Unit IV (Hole 442B), recovered from277.0 to 289.7 meters.is dark brown zeolithic clay andaltered ash beds; basalt was encountered at 289.7 meters.

    Figure 2. Stratigraphy, lithofacies, and sediment data, Site 442.

  • Thermal Conductivity

    (mcal/cm2- C•s)Shear Strength

    ( 1 0 5 dynes/cm2)

    8.0

    Wet-Bulk Density

    (g/cm3)

    1.4

    Grain Density

    (g/cm3)

    2.2 3.0

    Water Content

    (wt. %)

    40 50

    Porosity (%)

    70

    mZHCΛ

    ZHacmCO

    Figure 2. (Continued).

  • ON00 Site: 444

    Water depth: 4843 m. Total penetration: 91.5 (Hole 444), 310.0 m(Hole 444A).

    50-

    100-

    150-

    200-

    250-

    Age

    c

    i%K.

    §q

    CD

    cu

    1

    s

    -S!T3

    ε

    S

    LithologicUnit

    Unit 1la: Dark-green-grayand gray mud, vitricmud

    °8 6 mIb: Olive and olive-grayvitric mud, mud, andcalcareous mud

    48 m

    Unit IIOlive-gray-brownmud, vitric mud

    Unit IIIIlia: Brown mud,vitric mud, ash;

    calcareous andsiliceous mud

    120 m

    I l ib: Brown mud,siliceous mud.pumice

    Unit IVIVa: Brown mud,siliceous mud.nannofossil ash,ash

    196 m

    IVb: Greenish-gray andgray mudstone, ash;vitric, siliceous, andcalcareous mudstone

    228.6 m

    IVc: Gray claystone,mudstone, andsandstone; basalt sill(240.6-253 m)

    Lithofacies Sand

    (%)0 2 0 4 0

    Silt

    (%)0 100

    •Hemipelagic mud *and mudstonewith pyroclastics

    ?R R m a n S 6 m fHemipelagic mud andmudstone with «pyroclastics, andpelagic sediment

    ""I (biogenic .calcareous)CO —

    • - — &J m1 53 m *

    Hemipelagic mud andmudstone withpyroclastics

    Hemipelagic mud and 2*mudstone withpyroclastics, andpelagic sediment

    "1 (biogenic, calcareous)

    ••IΛO m

    • *1 02 m 1

    Hemipelagic mud and # Φmudstone with # «pyroclastics

    •Hemipelagic mud *and mudstone withpyroclastics, and

    π pelagic sediment1 (biogenic,calcareous)1 .. -v̂—

    1 / / m

    2 ^ m

    ••Hemipelagic mudand mudstone * *resedimented; # «mudstone withpyroclastics, # #pelagic sediment(biogenic.calcareous,and siliceous)

    •?7? 7 m 979 7 m

    Clay

    (%)0 80

    CaCO3(%)

    0 20 40 60

    ••••• t

    •••••••••••«•

    Organic Carbon

    (%)

    0 20

    ••

    S

    ••

    #Φ•

    *

    I

    *•

    •*Φ

    Φ

    Φ

    Φ

    #

    Sonic Velocity(km/s)

    1 2 3 4

    {

    k _

    UnitVRed-brown and green-gray,zeolitic calcareous, pelagicclaystone and nannofossilooze

    Figure 4. Stratigraphy, lithofacies, and sediment data, Site 444.

  • Thermal Conductivity(mcal/cm2- C-s)

    1 2 3

    Shear Strength(10 5 dynes/cm2)

    4 8 12

    Wet-Bulk Density(g/cm•5)

    1.3 1.4 1.5 1.6

    Grain Density(g/cm3)

    2.2 2.6 3.0 30

    Water Content(wt. %)

    40 50 60 50

    Porosity (%)

    60 70 80

    Figure 4. (Continued).

    oON

  • S. M. WHITE ETAL.

    are discontinuously common in samples from the mid-dle Miocene to late Miocene. Foraminifers are rare orabsent throughout. The depositional surface appears tohave fluctuated both above and below the CCD, but itremained well below the lysocline. Deposition of thehemipelagic clays of unit II and the basal part of unit IBwas below the CCD. The remaining units were depos-ited slightly above the CCD.

    4. The sediment-accumulation rate is generally mod-erate throughout, the greatest rates occurring during thePleistocene and the middle Miocene, when there was anincrease in the volume of ash. The sediment accumula-tion rate for the unit V pelagic red clay is extremely low(

  • SEDIMENT SYNTHESIS

    Pacific (Kennett et al., 1977) and the Indian Ocean(Davies et al., 1975); it may be a result of climatic eventsin Antarctica and paleocirculation changes (van Andelet al., 1975).

    The hiatus at Site 445 suggests similarity of paleocir-culation patterns in the Daito region to those in thesouthern oceans, a finding consistent with the equator-ial paleolatitude of the site during deposition.

    5. Paleomagnetism measurements on sediment sam-ples illustrate a systematic change in magnetic inclina-tion with depth (see also Kinoshita, this volume). Thechange in magnetic inclination indicates that the site hasdrifted in a net northerly direction over the last 47 m.y.At 45 to 47 m.y. ago, the site was close to the presentequator, and it has migrated nearly 2000 km to its pres-ent position at an average rate of 4.4 cm/yr. These dataare in agreement with results obtained by Louden (1976,1977) in the west Philippine Basin.

    Site 446Site 446 is in the Daito Basin, immediately south of

    the Daito Ridge and north of the Oki-Daito Ridge, inthe northwestern Philippine Sea. A single-bit hole pene-trated 628.5 meters of sediment, the lower portion ofwhich was intruded by numerous basalt sills.

    The stratigraphic succession (Figure 6, back pocket,this volume) consists of four lithologic units, one ofwhich comprises sedimentary rocks interlayered withbasalt sills. This lower unit (unit IV, 362.5-628.0 m)consists of interlayered dark-greenish-gray, calcareousclaystone, mudstone, siltstone, and turbidite sandstone,and is the only unit with significant amounts of ash.

    Some sediment interbeds overlying or underlying thebasalt sills appear baked and assume dark brown toblack colors. Recovered sediment types occurring as in-terbeds include (in general order of abundance) mud-stone and claystone; glauconitic sandy mudstone, mud-stone, and claystone; calcareous mudstone and clay-stone; ashy mudstone and siltstone; and ash and alteredash beds or zones. Sediments present in small amountsare zeolitic claystones, chalk or clayey chalk, lithic sand-stones and siltstones, and chert. The sediments for themost part have the following characteristics: laminatedbedding (1 mm to 1-2 cm), silty laminations that fineupward into claystones, evidence of bioturbation, andsoft-sediment deformation features; other sedimentarystructures include cross-beds, graded beds, and rippledor undulating bedding surfaces.

    Although basement was not reached, the age of theoldest recovered sediment is early Eocene (52 m.y.).This date suggests that, if basement is not far below thedepth of penetration, the basement may be as young asearly Eocene. A basalt sill at 459 to 460.5 meters wasdated at 48.2 ±1.0 m.y. (McKee and Klock, this vol-ume).

    Other significant facts concerning the lithology atSite 446 are:

    1. Sedimentation has mostly consisted in early(mostly Eocene) resedimentation by turbidity currents,and later (latest Eocene to present) deposition of pelagicclay.

    2. During the last 44 m.y., rates of sediment ac-cumulation were very slow because of the dominance ofpelagic processes, whereas during the first 8 m.y. ofdeposition the rates were moderate to fast because ofdeposition by turbidity currents (see also Andrews,Packham, et al., 1975).

    3. The relative depth of deposition of the sedimen-tary units suggests that the depositional surface was ator just below the CCD. Deposition was clearly belowthe CCD during deposition of the clays in units I and II.Although calcareous foraminifers and nannofossilswere recovered, they were poorly preserved and appearto have been reworked by currents. During depositionof unit III, when turbidite deposition prevailed, re-worked nannofossils are common, suggesting that thedepositional depth of this unit was also below the CCD.Most of unit IV was also deposited below the CCD.

    4. Paleomagnetism of the sediments and sedimen-tary rocks indicates that the site drifted in a net norther-ly direction over the past 52 million years, and hasmigrated nearly 2000 km to its present position. Thesedata are in agreement with Paleomagnetism measure-ments by Louden (1976, 1977) from the west PhilippineBasin. (See Kinoshita, this volume.)

    SEDIMENTARY FACIESSix major lithofacies and seven subordinate lithofac-

    ies were recognized in Leg 58 cores (Tables 1 and 2).These facies were distinguished by grain-size distribu-tion, mineralogy, lithology, association of sedimentarystructures and fabric, and mode of origin. Subdivisionof lithofacies in this paper follows designations com-monly used in sedimentological studies of outcrops onland, such as those suggested by DeRaaf et al. (1965)and subsequently extended to studies of DSDP cores byBerger and von Rad (1972) and Klein (1975a,b), amongothers. Figures 2 to 6 portray the vertical distribution ofthese facies at each drill site.

    Hemipelagic Clay FaciesHemipelagic sediments (clays) are the most common

    sediments recovered in Leg 58 cores, especially at Sites

    TABLE 1Lithofacies Recognized in Leg 58 Sediment Cores

    Major Facies Subordinate Facies

    Hemipelagic

    Resedimented clastic

    Resedimented carbonate

    Pelagic non-biogenic

    Pelagic biogenic

    Pyro clastic

    Hemipelagic clayHemipelagic mudstone

    Resedimented mudstoneResedimented sandstoneResedimented conglomerate

    Calcareous pelagic biogenicSiliceous pelagic biogenic

    971

  • S. M. WHITE ETAL.

    TABLE 2Litliofacies by Depth at Leg 58 Sites

    Site 442

    Site 443

    Site 444

    Site 445

    Site 446

    Sub-bottomDepth(m)

    0-123.5123.5-256

    256-276276-286.7

    0-44.845-121

    121-181181-199199-216

    217-233233-263.5

    263.5-314314-358358-447

    447-457

    0-3030-53

    53-83.583.5-102

    102-158158-J77

    177-272.7

    0-141.8141.8-208

    208-303

    303-518518-549

    549-609

    609-645645-660660-888

    0-4040-116

    116-173173-362.5

    362.5-514

    514-630

    Lithofacies

    Major

    Hemipelagic mudstoneHemipelagic mudstonePyroclasticPelagic non-biogenic

    Hemipelagic mudstoneHemipelagic mudstone

    Hemipelagic mudstoneHemipelagic mudstoneHemipelagic mudstone

    Hemipelagic mudstoneHemipelagic mudstoneHemipelagic mudstoneHemipelagic mudstoneHemipelagic mudstoneResedimented mudstonePyroclasticHemipelagic mudstonePyroclasticCalcareous pelagic biogenic

    Hemipelagic mudstoneHemipelagic mudstone

    Hemipelagic mudstoneHemipelagic mudstone

    Hemipelagic mudstoneHemipelagic mudstone

    Hemipelagic mudstoneResedimented mudstone

    Calcareous pelagic biogenicResedimented carbonateResedimented carbonate

    Resedimented carbonateResedimented carbonate

    Resedimented carbonate

    Siliceous pelagic biogenicSiliceous pelagic biogenicResedimented mudstoneResedimented sandstoneResedimented conglomerate

    Hemipelagic clayHemipelagic clay

    Hemipelagic clayResedimented mudstone

    (as interbeds)Resedimented mudstone

    (as interbeds)Resedimented mudstone

    Minor

    Pyroclastic

    Hemipelagic mudstoneCalcareous pelagic biogenic

    PyroclasticPyroclasticCalcareous pelagic biogenicPyroclastic

    Calcareous pelagic biogenicPyroclasticCalcareous pelagic biogenic

    PyroclasticCalcareous pelagic biogenic

    PyroclasticPyroclasticCalcareous pelagic biogenicPyroclasticPyroclasticCalcareous pelagic biogenicPyroclasticPyroclasticSiliceous pelagic biogenic

    PyroclasticCalcareous pelagic biogenicSiliceous pelagic biogenicPyroclastic

    PyroclasticCalcareous pelagic biogenicCalcareous pelagic biogenicPyroclasticCalcareous pelagic biogenicCalcareous pelagic biogenicPyroclasticCalcareous pelagic biogenicSiliceous pelagic biogenicHemipelagic clayPyroclastic

    Resedimented conglomerate

    Calcareous pelagic biogenic

    Pelagic non-biogenicPelagic non-biogenicPyroclasticPelagic non-biogenicHemipelagic mudstoneCalcareous pelagic biogenic

    PyroclasticHemipelagic mudstoneCalcareous pelagic biogenicResedimented sandstoneResedimented conglomerate

    Hemipelagic mudstoneCalcareous pelagic biogenic

    442, 443, and 444 (early Miocene to Pleistocene), in theShikoku Basin. Variably colored (brown, yellow, gray,green) according to site location and age, they consistchiefly of terrigenous clay from volcanic arcs, theJapanese Islands, and continental Asia. The dominantsources of clay changed with time, because of variationsin volcanism, tectonic activity, and continental climates(see Chamley, this volume). Clay minerals, dominatedby smectite or illite, are accompanied by detrital feld-spars, quartz, and micas, and sometimes by amphiboles

    and other heavy minerals. Volcanic material occursthroughout the sedimentary column at all drill sites,consisting chiefly of glass. Its proportion is generallylow, but in some intervals, especially the oldest, distinctash or glass levels exist. (See section on pyroclasticfacies.) Calcareous and siliceous tests are often poorlypreserved, likely because of dissolution, except at Site445 (depth less than 3400 m). Calcareous nannofossilsare the most frequent component, followed by radiolar-ians, planktonic foraminifers, and diatoms. Variationsin the proportion of organic debris depend on changesin the CCD with time and on plankton productivity, ordilution by terrigenous material.

    Resedimented Clastic Facies

    Resedimented Mudstone

    The resedimented mudstone facies occurs as inter-beds with hemipelagic clays at Sites 443 and 444 in theShikoku Basin, and as interbeds with the resedimentedconglomerate and resedimented sandstone facies at Site445 (Daito Ridge) and Site 446 (Daito Basin) (Table 2).

    The main attributes of the mudstone that indicateresedimentation are the variety of very small-scale sedi-mentary structures. These include thin (2-cm) gradedbeds of siltstone; parallel laminae of alternating silt andclay (Plate 1, Figure 1); fining-upward gradation of vol-canic-ash laminae into siltstone and claystone laminae;micro-cross-laminae; and sporadic thin breccia zonesconsisting of intraformational clay. At Site 445, inter-vals of the resedimented mudstone facies which are ar-ranged in slump blocks or slump folds commonly con-tain interbedded mudstone layers, which suggests resed-imentation by gravity processes. In addition, the associ-ation of this facies with the resedimented sandstonefacies and the resedimented conglomerate facies furtherindicates resedimentation in the formation of thesemudstones.

    Resedimented Sandstone

    The resedimented sandstone facies occurs at bothSites 445 and 446 (Table 2). It consists of thin tomedium-thick layers of sandstone ranging in grain sizefrom very coarse sand (2 mm) to very fine sand (1/16mm). Conglomeratic sandstones are also present, par-ticularly at Site 445; clasts never exceed fine-pebble size.Most sands are moderately well sorted; individual clastsare sub-rounded to angular.

    The sandstone is compositionally variable, but domi-nantly volcaniclastic, with recognizable fragments ofandesite, phyric basalt, aphyric basalt, and microdoler-ite. Augite, detrital olivine, orthopyroxene, and clino-pyroxene were also observed. Clasts of Nummulitiesboninensis, oolites, pelecypods, and limestone are alsopresent. These sandstones show complex diagenetic andcementation change with depth (discussed more fully byKlein et al , this volume).

    The resedimented sandstone facies shows a varietyof sedimentary structures, including parallel laminae,graded bedding, micro-cross-laminae, dish structures,

    972

  • SEDIMENT SYNTHESIS

    load casts, slump folds, micro-faults, and slump faults.Many of these structures are organized into partial orcomplete Bouma sequences.

    Dish structures. A volcaniclastic-bioclastic sandstoneat 445-57-7, 0-40 cm contained dish structures (Plate 1,Figure 2). These dish structures are concave upward anddemarcated by finer-grained sediment. These dish struc-tures appear to be related to debris flow: grain flow andinternal shear (Stauffer, 1967), fluid escape (Lowe,1976; Lowe and LoPiccolo, 1974), and later shearing ac-tion on unstable surfaces of a debris flow. Later resedi-mentation smooths slope surfaces on such a flow to pro-duce the dish structures (Busch, 1976a,b). Busch'smechanism applies to the dish structures observed atSite 445.

    Load casts. Load casts are common in the resedi-mented sandstone facies, particularly at the base ofsandstone overlying mudstone, or at the basal contactof Bouma sequences, such as at 445-89-2, 73 cm. Theload casts are formed by rapid deposition of the overly-ing sediment on soft, water-saturated clay and ash.

    Microfaults. Microfaults occur within very thinsandstone beds (Plate 1, Figure 3). Vertical displace-ment on these faults is on the order of 5 mm. The micro-faults cut across bedding almost at right angles to thebedding planes, indicating tension related to intrabedslumping.

    Slump blocks and slump folds. Thick intervals ofslump folds and slump faults are very common withinthe resedimented sandstone facies. Cores show inclinedlaminae truncated at the base and the top by horizontallaminae, clearly indicating large-scale mass movementby slumping of certain intervals. Similar slump foldswith near-horizontal or steeply inclined fold axes (70°from horizontal) are common, and the folded intervalsranged from 3 to 5 meters thick. Such intervals alsowere truncated by horizontally laminated sediment.Both the inclined stratified zones and the folded zonesindicate transport of sediment by slumping along un-stable depositional slopes.

    Graded bedding. This structure is very common inthe resedimented sandstone facies and generally ischaracterized by a sharp basal contact with underlyingsediments. The grain-size changes observed in gradedbeds is either from small pebble gravel to medium sand,or from coarse sand to a very fine sand or coarse silt.Graded beds are transitional into overlying units, whichmay consist of parallel-laminated sand or resedimentedmudstone or siltstone.

    The graded beds show a broad range of thickness,ranging from 1 cm to 1.3 meters. The graded beds lessthan 30 cm thick show a particle-size range from a basalcoarse-grained sandstone to a fine-grained sandstone atthe top (Plate 1, Figure 4), whereas graded beds thickerthan 30 cm tend to show a size range from a basal con-glomerate of fine pebble size to coarse sandstone at thetop (Plate 2, Figure 1). These graded beds generally passupward into finer-grained siltstone or mudstone (Plate2, Figure 2).

    Most of the graded beds comprise parts of Bouma se-quences (Plate 1, Figure 1; Plate 2, Figure 1) and clearlyare due to deposition by turbidity currents.

    Parallel laminae. Parallel laminae are common inthe resedimented sandstone (Plate 2, Figure 1), or as theTb interval of partial or complete Bouma sequence(Plate 1, Figure 1; Plate 2, Figure 2). In both instances,the parallel laminae are separated by distinct changes ingrain size from coarse- to medium-grained sand or me-dium- to fine-grained sand. Parallel laminae independ-ent of Bouma sequences also show alternating layers ofthin sand laminae and clay laminae, or clay laminae andnannofossil-rich laminae, such as at 445-68-1, 93-94cm.

    The origin of the parallel laminae appears to be two-fold. Laminae independent of Bouma sequences prob-ably were deposited by ocean currents characterized byregular velocity fluctuations. The parallel laminae as-sociated with Bouma sequences resulted from deposi-tion by decelerating turbidity currents.

    Micro-cross-laminae. This sedimentary structure oc-curs invariably as part of complete or partial Bouma se-quences, representing the Tc interval. The micro-cross-laminae are distinguished by textural, color, and com-positional changes for each lamina (Plate 1, Figure 1;Plate 2, Figure 1). Grain-size changes between suchlaminae normally range from medium sand to fine sand.Some of the micro-cross-laminae are oversteepened intoconvolute laminae (Plate 2, Figure 1).

    The micro-cross-laminae are related to decelerationof turbidity currents.

    Vertical sequences. The sedimentary structures ob-served in the resedimented sandstone facies are orga-nized into preferred sequences showing a systematic ver-tical change in grain size, lithology, and sedimentarystructures. The observed sequences represent completeor partial Bouma sequences. Two examples of such se-quences are shown in Plate 1, Figure 1 and Plate 2, Fig-ure 1.

    The origin of Bouma sequences has been debatedsince they were described in detail by Bouma (1962) andinterpreted hydraulically by Walker (1965). Basically,the sequence records deposition by a decelerating tur-bidity current showing diminishing flow velocity, com-petence, and capacity. Such sequences commonly arerelated to submarine fans (Nelson and Kulm, 1973;Walker and Mutti, 1973; Walker, 1978). Complete se-quences normally are limited to the submarine-channelzone, partial sequences indicating either levee overspilldeposition, or deposition in suprafan lobes or in distalzones. In our opinion, these processes account for thepresence of the Bouma sequences observed in thisfacies.

    The resedimented sandstone facies appears to berelated to deposition by turbidity currents on submarinefans. The source of the sediments was the remnant arcsof the Daito Ridge and Oki-Daito Ridge. Deposition bythese turbidity currents occurred on submarine fanswhich filled the small sediment pond on the Daito Ridge

    973

  • S.M. WHITE ETAL.

    at Site 445, and which prograded basin ward in the DaitoBasin, an inner-arc basin.

    Resedimented Conglomerate Facies

    The resedimented conglomerate facies occurs at bothSites 445 and 446 (Table 2).

    The resedimented conglomerate facies consists ofthin to medium-thick layers of conglomerate. The clastsrange from granules to small cobbles, and are eitherdispersed and enclosed in a matrix of volcaniclasticsandstone and mudstone or are in framework contactPlate 2, Figure 3 and 4). In one instance, resedimentedconglomerates are imbricate in the basal portion ofBouma sequences of turbidite sandstone of the resedi-mented sandstone facies (Plate 2, Figure 1). Frameworkconglomerates comprise also the basal graded portionof several partial and complete Bouma sequences.

    The mineralogy of the conglomerate is varied; thereare two compositional categories. One category is dom-inated by fossil fragments consisting mostly of completeor broken fragments of the larger foraminifer Nummul-ites boninensis. In addition, other foraminifers com-monly occur in the matrix, and pelecypod fragments,algal fragments, and oolites have been reported. Round-ed limestone clasts also occur. The second composi-tional category comprises volcaniclastic grains. Theseare mostly basaltic but include micro-dolerite, andesite,phyric basalt, and aphyric basalt, all of oceanic-crustand island-arc derivation. In addition, some clasts ofschist, gneiss, and granodiorite were present. Our obser-vations are consistent with rocks obtained by dredgehauls from the Daito Ridge and the Oki-Daito Ridge byMizuno et al. (1977) and by Shiki et al. (1977) (Table 3).

    This facies shows almost no sedimentary structures,although a few samples show a crude fabric on the coresurfaces. Most of the conglomerates correspond to Wal-kers (1975) disorganized-bed model: random orienta-tion of clasts either in framework contact or dispersed(Plate 2, Figure 3). Imbrication of clasts was observed insome of these disorganized units (Plate 2, Figure 4)although opposite-dipping imbrication was found atone horizon (Plate 2, Figure 3). Most of this particlealignment is emphasized by the shape of fragments ofNummulites boninensis, but that alignment also paral-lels the orientation of associated disc-shaped clasts ofvolcaniclastic material and limestone fragments (Plate2, Figure 3).

    Imbricated and stratified conglomerates conformingto Walker's (1975) graded stratified model were ob-served in association with the basal portion of Boumasequences, both partial and complete, in interbeddedresedimented sandstones (Plate 3, Figure 1). Normalgrading and a suggestion of reversed grading occurwithin this basal conglomerate zone, which correspondsto both the Bouma Ta and Tb intervals (Plate 3, Figure1).

    The resedimented conglomerate facies very clearlywas emplaced in both a small sediment pond on the rem-nant arc of the Daito Ridge (Site 445) and in an inner-arc basin (Daito Basin) (Site 446). Sedimentation clearlywas by subaqueous gravity processes, including both

    TABLE 3Summary of Resedimented-Conglomerates from Site 445

    and Dredge Hauls from the Daito Ridge

    Site 445 (Unit V)

    Rock Type

    Basalt

    Igneous Alkalibasalt

    Andesite

    Grano-diorite

    Ultrabasic

    Lithic Clasts

    Plagioclasephyric basalt

    Micro-doleriteApyric basaltPlagioclase

    clinopyroxenephyric basalt

    _

    _

    _

    -

    DetritalMinerals

    PlagioclaseAugite

    AegiiineTitaniferous

    augite

    i

    •>

    PicotiteDiopsideEnstatiteMagnetiteSerpentine

    pseudomorphafter olivine

    Dredge Hauls from theDaito Ridge

    Dolerite

    Two-pyroxene andesiteHornblende andesiteAugite andesite

    Hornblende-biotitegranodiorite

    Peridotite(metamorphosed)

    Metamorphic

    Sedimentary

    Biogenic

    Hornblende schist

    ChertNummuli res-bearing

    limestoneSandstone

    Nummulitesboninensis

    Asterocyclina sp.PenuriaOperulinoides sp.

    Greenhornblende

    LpidoteMagnetitellmenite

    1

    -

    Epidote-horn blendeschist

    Hornblende schist

    Nummulites-beaiinglimestone

    SandstoneClaystoneCalcareous rock

    Nummulites boninensisA s tero cy clinα sp.Discocyclinα sp.

    debris flow deposition, represented by the disorganizedconglomerates and conglomerates showing a dispersed-clast fabric, and the transition from debris flow to a tur-bidity current, represented by the imbricated and strati-fied conglomerates associated with Bouma sequences.The source of the sediments was the island arc now rep-resented by the Daito Ridge and the Oki-Daito Ridge.Both volcanic material and coastal carbonate depositswere transported from a shoreline and island setting in-to deeper water by these processes.

    Resedimented Carbonate Facies

    The resedimented carbonate facies was observed onlyat Site 445 on the Daito Ridge; it is interbedded with thepelagic biogenic carbonate facies, the biogenic siliceousfacies, and the hemipelagic clay facies (Table 2).

    The resedimented carbonate facies consists of fora-minifer-nannofossil oozes, chalks, and limestones; nan-nofossil-foraminifer oozes, chalks, and limestones; andinterbedded laminae and beds of volcanic-ash-rich ooze,chalk, and limestone. The carbonate grains range frommedium sand to clay, depending on the proportions offoraminifers and nannofossils in the sample. These car-bonates consist mostly of calcite shells of foraminifersand nannoplankton; they contain accessory hemipelagic

    974

  • SEDIMENT SYNTHESIS

    clay and, in some horizons, interbeds of volcanic ashand sand-sized volcanic-rock fragments.

    This facies is characterized by many types of sedi-mentary structures and fabric, indicating a variety ofresedimentation processes by subaqueous gravity flows.Among the observed structures and fabrics were distor-ted burrows, microfaults, slump folds, slump blocks,load casts, graded bedding, parallel laminae, and micro-cross-laminae. Many of these structures are organizedinto partial or complete Bouma sequences and showdefinite affinities with identical structures in the resedi-mented sandstone facies.

    Distorted burrows. Some of the bioturbated zonesshow evidence of shearing and disruption as a result ofresedimentation. Plate 3, Figure 2 shows part of a coreconsisting of bioturbated, clayey nannofossil ooze, inwhich the upper part of the bioturbated zone is un-disturbed, but the lower part is sheared, and the bur-rows are distorted and smeared. The distorted burrowsare aligned in parallel and demarcate a crude type oflaminar structure. These types of disturbed bioturbatedintervals are fairly common in the resedimented car-bonate facies and suggest a mode of transport of someof this facies by debris flow. The disturbed zone repre-sents the laminar-flow zone associated with debris flows(Hampton, 1972), whereas the overlying undisturbed in-terval may well represent the rigid plug of this debris flow.

    Microfaults. Microfaults were observed in resedi-mented chalks and limestones and occur in beds whichshow sedimentary structures generated by slumping.The microfaulted intervals are generally confined tothin beds of clayey limestone and the enclosing layers(Plate 3, Figure 3). The microfaults cut bedding nearlyat right angles. Some of the faulted blocks show evi-dence of rotation. We interpret these microfaults torepresent a phase of tensional deformation associatedwith down-slope slumping.

    Slump structures. Many varieties of slump structureswere observed in the resedimented carbonate facies.These included slump fractures (or faults), slump blocks,blocks, and slump folds. Each of these structures occursin intervals ranging from 10 cm to 3 meters in thicknessand are demarcated above and below by horizontallybedded carbonate. Slump folding (Plate 3, Figure 4) isaccentuated by changes in bedding controlled by changesin color and composition and invariably shows fold axi-al planes inclined 10 to 20 degrees from the horizontal.Slump blocks (Plate 4, Figure 1) range from 2 cm to 2meters in diameter and are usually set off from enclos-ing sediment by changes in color and composition.

    Vertical slump fractures are also common, either asbounding surfaces of slump blocks, or as planes inter-secting bedding, other sedimentary structures, or partialBouma sequences (Plate 4, Figure 2). These fracturestend to be oriented normal to bedding and show singleor compound vertical displacements ranging from 0.5 to3 cm. They appear as a syndepositional or post deposi-tional resedimentation structure.

    It is our interpretation that these structures are inter-preted to have formed during down-slope mass trans-

    port of sediment by sliding and slumping on unstableslopes.

    Load casts. Load casts were observed in the resedi-mented carbonate facies where carbonate rock litholo-gies were overlying interbedded volcanic ash with sharpcontact. The limestones and chalks overlying the load-cast contact showed well-developed slump folds, slumpblocks, or slump fractures, indicating rapid depositionof carbonate sediments on water-saturated ash beds. Theload casts represent a physical record of this event of rap-id deposition.

    Graded bedding. Graded bedding is one of the mostcommon sedimentary structures in the resedimentedcarbonate facies. Graded bedding always overlies asharp contact and grades upward into the overlying sed-iment. Grading tends to be coarse-tail, and graded inter-vals range from 0.5 to 20 cm in thickness.

    The graded bedding is defined by a transition fromnannofossil-foraminifer ooze, chalk, or limestone intoa foraminifer-nannofossil ooze, chalk, or limestone.These graded beds occasionally contain up to 15 percent siliceous or terrigenous and volcaniclastic grains(Plate 4, Figure 3). Most of these graded beds pass up-ward into a clayey nannofossil ooze, chalk, or limestonewith a gradational contact. Most of the graded bedscomprise parts of complete or partial Bouma sequences(Plate 4, Figure 2) and were deposited by turbidity cur-rents.

    Parallel laminae. This structure is also very commonin the resedimented carbonate facies. The parallel lami-nae are demarcated by changes in grain size from fora-minifer-rich to nannofossil-rich zones and from bio-clastic constituents to clayey limestones, by alternationof carbonate and volcaniclastic components (Plate 4,Figure 3; Plate 5, Figure 1), and (as disclosed by radio-graphy) by alternation of carbonate laminae with hemi-pelagic clay laminae (Plate 5, Figure 1). Some of theselaminae appear as faint, discontinuous laminae on coresurfaces, but are shown to be continuous by a radio-graphy (Plate 5, Figure 1). Most of the parallel laminat-ed beds comprise complete or partial Bouma sequences,and they were produced by deposition from turbiditycurrents.

    Micro-cross-laminae. Micro-cross-laminae also oc-cur in the resedimented carbonate facies. The laminaeare demarcated by changes in grain size from foramini-fer-rich sand to nannofossil-rich clay and silt-sized par-ticles, or by changes in composition from carbonate toclay or from carbonate to volcaniclastic grains. Some ofthese micro-cross-laminae occur in lenses (Plate 1,Figure 1) and appear only in radiographs. A few inter-vals of micro-cross-laminae also grade laterally intoconvolute laminae (Plate 6, Figure 1). The micro-cross-laminae comprise part of complete or partial Bouma se-quences and were deposited by turbidity currents.

    Vertical sequences. The lithologies, grain sizes, andsedimentary structures observed in the resedimentedcarbonate facies are organized into distinct vertical se-quences. One of these sequences is a resedimented-de-bris-flow sequence consisting of a basal clayey nanno-

    975

  • S..M. WHITE ETAL.

    fossil limestone containing disrupted burrows and over-lying identical limestone with undisturbed burrows.This sequence indicates transport by debris flow, andthe transition in the nature of the burrows suggestsa lower laminar-flow phase of debris-flow transport,whereas the undisturbed upper phase indicates a rigid-plug phase of the same debris flow.

    By far the most common sequence is the partialBouma sequence; a few complete Bouma sequenceswere observed. In the resedimented carbonate facies,these members are preserved, although complete se-quences are rare. The most commonly preserved partialsequence consists of the basal graded interval (Ta), theparallel-laminated interval (Tb), and the pelagic interval(Te) (Plate 4, Figure 2). A second common type of par-tial sequence (Plates 5 and 6) shows a basal parallel-laminated interval (Tb) overlain by the micro-cross-laminated interval (Tc), capped by the pelagic-clay inter-val (Te). These sequences indicate resedimentation byturbidity currents.

    The most noteworthy aspect of this facies is its thick-ness. Other resedimented carbonates have been reportedby Klein (1975a, b) and Cook et al. (1976) from otherDSDP sites, but the examples they report involve re-stricted, thin intervals perhaps no more than 100 metersthick. At Site 445, resedimented carbonates reach a totalthickness of 468 meters. Within this interval, thin,pelagic, clayey, biogenic, carbonate beds comprise theTe interval of Bouma sequences. Fully 80 per cent of this468-meter interval consists of resedimented carbonatesediment. Resedimentation was by debris flow, slump-ing, sliding, and turbidity currents.

    Pelagic Non-Biogenic Facies (IV)

    Pelagic clays occur in fairly thin sequences in the Shi-koku Basin at Site 442 (Holes 442A and 442B), and Site444, representing some of the first sediments depositedin the basin. They consist of firm, dark-brown, more orless bioturbated clay to claystone; they contain clayminerals (chiefly smectite), amorphous metal oxides,often manganese-iron micronodules, and sometimeszeolites. At Site 444, a reddish-brown mudstone overly-ing the last basalt sill includes a variable amount ofcalcareous nannofossils.

    The pelagic clay facies also occurs in the Daito Ridgearea at Site 446, in the late Eocene and late Miocene.This facies consists of dark-brown to very dark-grayish-brown clay with 95 per cent or more clay-sized particles.The sediments chiefly include clay minerals, sometimeswith zeolites and micronodules; however, throughoutthey also contain small amounts of quartz, feldspars,volcanic glass, carbonates, and sometimes siliceous fos-sils and chert, suggesting a non-typical pelagic sedimen-tation.

    Pelagic Biogenic Facies

    The pelagic biogenic facies occur as mostly biogenicoozes (calcareous or siliceous) or as transitional sub-facies.

    Distribution of the pelagic biogenic facies in the Leg58 holes is shown in Table 4. The tabulation does not

    reflect the type of occurrence for the facies (lens, bed,etc.) but simply records the presence or absence of thefacies within the cored intervals. A general descriptionof this facies is mose simply presented as follows:

    Biogenic siliceousa•b f

    Biogenic calcareousa'c'e

    Transitional siliceousa b'd>f

    (>50% siliceous: usesiliceous modifer)

    (c>d>e

    (modifer: "marly")

    >30% Siliceous skeletons30% Non-biogenic compon-

    ents (silt and clay)

    aSee Introduction to this volume.bOoze, diatomite, radiolarite, porcellanite, chert.cOoze, chalk, limestone.dSand, silt, clay, mud, or indurated equivalent (shale, if fissile).eSiliceous modifer if 10-20% identifiable siliceous remains.fCalcareous modifer if 10-30% CaCO3.

    Site 442The transitional siliceous facies occurs only in the up-

    permost Pleistocene and Miocene cores at the site. It is asiliceous mud with diatoms, radiolarians, and spongespicules and up to 20 per cent volcanic glass. The colorsare dark gray and dark greenish gray, extremely mottledbecause of drilling disturbance.

    The calcareous facies has a very minor occurrence asa nannofossil-rich mud and limestone (Table 4). The lat-ter overlies lightly weathered aphyric basalt and red-brown pelagic mud. This limestone (early Miocene), isattributed to inorganic precipitation or recrystallizationof a nannofossil ooze by low-temperature diagenesis orthermal metamorphism (Fischer, Heezen, et al., 1971).

    Foraminifers encountered in Holes 442, 442A, and442B are sporadic and poorly preserved. Well- to mod-erately well-preserved nannofossils of the Quaternaryand early to middle Miocene were recovered. The occur-rence of nannofossils at this site is similar to that of Site297 (Leg 31), except for the absence of Pliocene nanno-fossils at Site 442.

    Site 443Except for the transitional siliceous facies in Core 31

    (4.5 meters of gray-brown, upper-Miocene siliceousmudstone; diatoms > radiolarians > spicules) and thebiogenic calcareous facies in Core 35 (olive-gray, mid-dle- or upper-Miocene nannofossil chalk), the transi-tional calcareous facies dominates (Table 4).

    976

  • SEDIMENT SYNTHESIS

    TABLE 4Distribution of Pelagic Biogenic Facies, Leg 58a

    Site 442 Site 443 Site 444 Site 445 Site 446

    (Hole 444)

    ua a « ua, ft- H H

    2 Uo a a «U ft- a, H

    w u

    (Hole 444A)

    αo UO ffi

    (Hole 446)

    a wo. H

    (Hole 446A)

    10

    15

    20

    30

    35

    40

    45

    10

    15

    20

    25

    30

    35

    40

    10

    10

    15

    20

    '

    30

    35

    10

    15

    !

    30

    35

    40

    45

    50

    65

    70

    75

    90

    10

    15

    20

    35

    40

    45

    10

    15

    30

    Symbols (see text): PBS = pelagic biogenic siliceous; PBC = pelagic biogenic calcareous;TS = transitional siliceous; TC = transitional calcareous; = presence ofthe facies within 9-meter core interval.Limestone above basalt.

    The Pleistocene sequence contains the transitionalcalcareous facies as a predominantly dark-green-graynannofossil mud (up to 40% nannofossils) to a dark-green-gray to dark-gray carbonate mud (up to 15%,CaCO3) with minor ash intervals. The Pliocene is repre-sented by 2 to 30-cm units of gray, calcareous mud andnannofossil mud, interbedded with more-massive unitsof ashy mud. Facies in the Miocene consist of nannofos-sil muds and nannofossil mudstones and claystones withclayey nannofossil chalks, generally olive gray, gray, orgreen gray. A restricted Miocene biogenic facies isrepresented by olive-gray nannofossil chalk (up to 90%nannofossils). Core 36 to the first cored basalt containbeds up to 3 meters thick of nannofossil claystone andmudstone, as well as clayey nannofossil chalk. Interbeds

    are mudstone, claystone, and ashy mudstone and clay-stone.

    Site 444

    Upper-Miocene to Quaternary deposits at Site 444primarily contain the transitional calcareous and bio-genic calcareous facies. Below the middle Miocene atHole 444A, only the transitional and biogenic calcare-ous facies are present.

    Calcareous facies at Holes 444 and 444A consist ofcalcareous muds, nannofossil muds, clayey nannofossilooze, nannofossil ooze, and nannofossil mud. All de-posits are brown (olive brown, pale brown, light graybrown, etc.). Calcareous fossils constitute up to 20 percent in the transitional facies.

    977

  • S.M. WHITE ETAL.

    Other facies include siliceous nannofossil oozes, radi-olarian muds, muddy and muddy siliceous (radiolarian)nannofossil oozes, siliceous muds, muddy siliceous(radiolarian) ashes, muddy nannofossil ashes, zeolitic(and radiolarian-bearing) calcareous claystone andmudstone, and chalk. The latter two deposits occur asinterbeds between basalt units.

    Site 445All four subdivisions within the pelagic biogenic fa-

    cies were recovered at Site 445 (Table 4). In order of de-creasing abundance, the subfacies present are the bio-genic calcareous, the transitional calcareous facies, thepelagic siliceous facies, and the transitional siliceousfacies.

    Calcareous facies contain nannofossil and foramini-fer-nannofossil oozes, varying ash or clay content yield-ing the transitional facies. Lower in the section, theoozes become chalks, with similar consolidation of thetransitional facies. Beginning in Core 59, the siliceouscomponent becomes high, yielding siliceous nannofossilchalks, radiolarian nannofossil chalks, and other pelag-ic biogenic or transitional categories.

    In general, foraminifers are abundant in the Pleisto-cene and Pliocene and decrease in numbers, size, anddiversity from the Miocene to the middle Eocene.

    Site 446The pelagic biogenic facies is minimal at Site 446

    (Table 4).Pelagic biogenic calcareous deposits occur as cal-

    careous oozes and/(or) chalk, whereas the siliceousbiogenic facies is absent.

    Pyroclastic Facies

    The pyroclastic facies consists principally of volcanicash, with sporadic and minor quantities of lapillae andbombs. The ash may occur as laminae or thin beds in amajor lithology, or as a lithologic component in anotherlithofacies. Table 5 shows the distribution of pyroclasticmaterials at each site, according to mode of occurrence.Table 6 is a summary of the distribution of ash by sedi-ment age time slices, showing the principal periods ofexplosive volcanism in the Shikoku Basin and the DaitoRidge-and-Basin province.

    Shikoku Basin

    The pyroclastic sediments of Shikoku Basin sites con-sist of ash, pumice, and altered ash. The ash is generallywell-sorted and sand-sized, sand-silt-sized, or silt-sized,but altered ash is clay-like material. Pumice occurs aslapillae or bombs up to 4 cm in diameter. Colors of ashbeds include from light gray to black and pale brown todark brown; altered ash may be yellowish brown, pink,reddish yellow, reddish brown, and reddish black. Theash is composed mostly of clear glass (rhyolitic ?), but ablack, opaque basaltic glass is prominent between 91and 165 meters (late Miocene) in Hole 444A.

    The laminae or beds may be distinctly layered, withsharp contacts above and below, or they may be part ofa normal, fining-upward graded sequence. Sharp basal

    TABLE 5Distribution of Pyroclastic Sediments

    Core

    Site 44212345

    6789

    1(1

    11121314151617181920

    2122232425

    2627282930

    Site 443

    12345

    6789

    10

    1112131415

    1617181920

    21222324252627282930

    As Distinct Bedsor Laminae

    XX

    XX

    X

    X

    XXXX

    XXXXX

    X

    X

    XX

    As a CommonConstituent

    XXXXX

    X

    X

    XX

    X

    XXXXX

    XX

    X

    XX

    XXXX

    XXX

    As a RareConstituent

    X

    XX

    X

    X

    X

    X

    XXX

    XX

    978

  • SEDIMENT SYNTHESIS

    TABLE 5 - Continued TABLE 5 - Continued

    Core

    Site 443

    3132333435

    3637383940

    4142434445

    46474849

    Site 444

    12345

    6789

    10, Al

    A 23456

    789

    1011

    1213141516

    212223

    Site 445

    12345678

    1011

    As Distinct Bedsor Laminae

    XX?X?X?

    XX

    XXXXX

    XXXX

    X

    X

    X

    XX

    XX

    XXX

    XX

    X

    As a CommonConstituent

    XX

    XXX

    X

    XXXX

    XX

    XX

    XX

    XX

    X

    X

    XXX

    X

    XXX

    XX

    XX

    X

    X

    As a RareConstituent

    XX

    X

    XX

    XX

    Core

    Site 445

    1213141516

    1718192021

    2223242526

    2728293031

    3233343536

    3738394041

    4243444546

    4748495051

    5253545556

    5 758596061

    6263646566

    6768697071

    As Distinct Bedsor Laminae

    XX

    X

    X

    XX

    X

    X

    X

    As a CommonConstituent

    X

    X?

    X

    X

    X

    X

    XX

    XXXX?

    X

    As a RareConstituent

    XX

    X

    X

    X

    X

    XX

    X

    X

    X

    XXX

    XX

    X

    X

    979

  • S.M. WHITE ETAL.

    TABLE 5 - Continued TABLE 5 - Continued

    As Distinct Beds As a Common As a RareCore or Laminae Constituent Constituent

    Site 445

    7273 X747576

    7778798081

    8283848586

    87(No reported pyroclastics in cores 88-94)

    Site 446

    1• 2

    345

    678910

    1112131415

    1617181920

    2122232425

    2627282930

    3132333435

    3637383940

    41,Al42, A2

    XX

    XX

    XX

    XX

    XXX

    X

    X

    X

    X

    ;

    As Distinct Beds As a Common As a RareCore or Laminae Constituent Constituent

    Site 446

    43, A3A69

    1012131416

    1718192223

    2425262728

    X

    X

    X

    X

    X

    X

    X

    XX

    XX

    X

    contacts are not common. Mild to intense bioturbationis common and is intense enough in some cases to havedestroyed the laminae. Bioturbation occurs frequentlyat the top of the graded sequences.

    The pyroclastics occur principally within mud-mud-stone and clay-claystone sequences in the Shikoku Ba-sin. In the lower sections at each site, the sequence maybe: mudstone-claystone, pyroclastic, calcareous biogen-ic; or mudstone-claystone, pyroclastic, siliceous biogen-ic. Altered ash overlies a pelagic clay (with manganesenodules, and zeolites) at the base of Hole 442B.

    The wide vertical and lateral distribution of glass as acomponent of a mudstone or claystone lithofacies, andthe discrete ash beds composed almost entirely of vol-canic glass suggest that the pyroclastics in the ShikokuBasin have two origins: laminae and well-defined ashbeds are the direct result of explosive volcanism fromrelatively nearby volcanoes; the ash as a component isprobably resedimented, along with the sediments inwhich it is contained, or in some cases it may be from avery distant source. In the latter case, aerially oraquatically transported ash could have drifted into thebasin and become incorporated into the sediment col-umn, diluted by local hemipelagic sediments.

    The basaltic ash in the upper Miocene at Site 444 issignificant. The tephra layers at Site 442 likely werederived from the Japanese Islands, while those at Sites443 and 444 were derived from a nearby, low-silica vol-canic source.

    The principal explosive volcanic events affecting Site442 were in the Pleistocene (0-1.6 Ma) and in the middleMiocene (13-15 Ma). The principal explosive volcanicevents affecting Sites 443 and 444 were in the Pleisto-cene, Pliocene (1.6-5 Ma), late Miocene (5-10.5 Ma),late middle Miocene (10.5-12 Ma), and early middleMiocene (14-16 Ma). The Pleistocene events appear tobe most frequent and most intensive, judging from the

    980

  • SEDIMENT SYNTHESIS

    TABLE 6Correlation of Volcanic Events

    Age

    PleistocenePliocene

    Late MioceneLate Middle MioceneMid Middle MioceneEarly Middle MioceneEarly MioceneLate Oligocene

    Middle Oligocene

    Middle to early OligoceneLate EoceneMiddle EoceneEarly Eocene

    Site

    Cores withAsh inLayers

    51

    000(1?)4(3?)

    -

    _

    -__-

    442

    Cores withAbundantAdmixed

    Ash

    91

    0000

    -

    _

    ___-

    Site 443

    Cores withAsh inLayers

    72

    1 (0?)3(4?)0

    11

    -

    -

    ___-

    Cores withAbundantAdmixed

    Ash

    86

    39

    010

    _

    _

    ___-

    Site 444

    Cores withAsh inLayers

    12

    250?2

    _

    _

    ___-

    Cores withAbundantAdmixed

    Ash

    42

    56•)

    2 1

    _

    _

    ___-

    Site 445

    Cores withAsh inLayers

    12

    100

    I? (age?)

    0

    0

    320-

    Cores withAbundantAdmixed

    Ash

    23

    300

    0

    2

    0

    23(4?)2-

    Site 446

    Cores withAsh inLayers

    missingmissing

    or 0__

    2 (age?)

    2

    0?

    0?

    0?0?44(3?)

    Cores withAbundantAdmixed

    Ash

    _-

    -_

    1 (age?)

    4

    0? (notidentified?)

    0? (notidentified?)

    0?0?53

    number of cores which contain more than one ash layerand the number of cores which contain ash as a promi-nent lithologic component. Events of the early middleMiocene, apparently associated with intrusion of basal-tic sills and extrusion of sea-floor basaltic flows, arealso conspicuous. The arc supplying pyroclastics to theShikoku Basin from the east appears to have been con-tinuously active during the Neogene, except possibly fora period from 14 to 12 Ma. (The exception may be an ar-tifact of questionable biostratigraphic determinations inthis interval.)

    Daito Ridge and BasinThe pyroclastics at Sites 445 and 446 are much less

    abundant than at Shikoku Basin sites. They consist ofsand- and silt-sized glass, except where ash has been al-tered to clay. Colors are less varied than in the ShikokuBasin: light gray to black, with bluish gray, olive gray,greenish gray, pinkish gray, and grayish brown. Onlythe acidic (rhyolitic?), clear glass is present.

    The ash occurs as laminae or as fining upward, grad-ed beds, some with sharp or even scoured basal con-tacts. The ash in Hole 446A, Cores 12 and 13, is cross-bedded. Bioturbation is not common. Slump structuresare present where pyroclastics are part of a slumped sed-imentary sequence, but such occurrences are rare.

    At Site 445, pyroclastics occur within calcareous bio-genic sequences, such as calcareous biogenic, volcanic,calcareous biogenic—repeatedly alternating. In severalsections calcareous biogenic facies alternate with sili-ceous biogenic and volcanic-ash facies. Clay stone is partof the sequence calcareous biogenic, volcanic, clay-stone, calcareous biogenic in a short interval (549-609m) in the upper Eocene. Volcanics are conspicuously ab-sent in the thick resedimented middle-Eocene sequence,except as resedimented pebbles, fragments, or grains oftransported volcanic debris.

    At Site 446, the pyroclastics occur as part of the hem-ipelagic facies, either in clay-clay stone or mud-mud-stone sequences. We observed only one example of vol-

    canic ash as a prominent lithologic component in a re-sedimented conglomerate, sandstone, mudstone se-quence. Claystone, volcanic, calcareous biogenic se-quences are rare. Pyroclastics as ash beds are most com-mon as interbeds between basalt flows, or as part of abasalt, claystone, mudstone, volcanic, basalt sequence.

    The only prominent expressions of explosive vol-canism at Site 445 are in the upper Miocene to Pleisto-cene, near the middle/lower Oligocene boundary, andin the upper Eocene. (Drilling stopped before reachingthe early middle Eocene.) At Site 446, there is some in-dication of early-Miocene volcanism, and possibly somein the middle Miocene, in sections whose age is indoubt. The late Eocene-early Oligocene episode was notrecorded in the sediments, possibly because of a missingsection. The prominent volcanism associated with basaltflows is of early-and middle-Eocene age.

    SummaryFor a summary of this discussion of lithofacies, the

    reader is referred to a companion paper in this volumeby Curtis and Echols. They have categorized the domi-nant facies sequences in each basin according to timeand region.

    Northern Shikoku Basin

    Late Pleistocene

    Early Pleistocene andPliocene

    Pliocene andLate Miocene

    Late Miocene andMiddle Miocene

    Middle Mioceneand Early Miocene

    Pelagic biogenic (calcareous and sili-ceous), hemipelagic, pyroclastic

    Hemipelagic mudstone

    Hemipelagic mudstone, resedimentedsandstone

    Hemipelagic mudstones

    Pyroclastics

    981

  • S.M. WHITE ETAL.

    Eastern Shikoku Basin

    Pleistoceneand Pliocene

    Late Miocene

    Middle Miocene

    Early Miocene

    Western Shikoku Basin

    Pleistocene,Pliocene,late Miocene

    Middle Miocene

    Early Miocene

    Hemipelagic mudstones, minorpyroclastics

    Hemipelagic mudstones, pyroclastics

    Resedimented sandstones, pelagicbiogenic sediments, pyroclastics

    Pelagic clays

    Hemipelagic mudstones, possibly vol-caniclastic clays in the Pliocene

    Hemipelagic mudstones, pyroclastics

    Pelagic clays, pyroclastics

    SPECIAL TOPICS

    The following summarizes results of detailed studiesof the Leg 58 sediments, or information pertaining tothe lithofacies already described. The reader is alsoreferred to specific chapters in this volume for furtherinformation.

    Physical Properties9

    Sediments recovered by deep-sea drilling in the Shi-koku Basin and Daito Ridge and Basin area vary consid-erably in composition, grain size, and texture. Thisvariability is directly reflected in the physical propertiesof the sediments. The lithofacies established for Leg 58sediments provide a convenient framework in which toexamine the physical properties. Physical properties bydepth for each site are presented in Figures 2-6, and forthe various facies discussed in Figures 7-18.

    Resedimented Clastic Lithofacies

    The compositionally and texturally most varied litho-facies is the resedimented clastic lithofacies, representedby mudstones, sandstones, and conglomerates at Site445 between 600 and 888 meters, and by mudstones be-tween 363 and 504 meters at Site 446. Systematic varia-tions with depth for the mudstones at Site 446 are shownin Figure 6. Sonic velocity increases from 1.5 to 2.0km/s downhole; water content decreases; porosity de-creases; and wet-bulk density increases. Thermal con-ductivity and grain density show no apparent variationwith depth. The porosity-depth and wet-bulk-densi-ty-depth relationships derived for pelagic clay and ter-rigenous clay (Hamilton, 1976) adequately describe thevariations with depth for the resedimented clastic sedi-ments at Site 446.

    Down-hole variations for Site 445, however, are notsimilar to those at Site 446, or to the empirical relation-ships of Hamilton (1976). Variations of physical proper-

    2? 2.0

    Δ

    Δ

    -

    1

    &v A

    I

    • Site 445

    Δ Site 446

    Δ

    I

    Δ

    1

    -

    Δ ^ ^

    i

    60

    Porosity (%)

    Figure 7. Wet-bulk density versus porosity for samplesof the resedimented clastic lithofacies. Hemipelagicmuds are plotted at the high-porosity end. Regressionparameters are given in Table 8.

    • Site 445

    Δ Site 446

    40

    Water Content (wt. %)

    60

    9 By David Fountain, shipboard physical-properties specialist.

    Figure 8. Sonic velocity versus water content for sam-ples of the resedimented clastic lithofacies. Hemipe-lagic muds are plotted at the high-water-content end.Regression parameters are given in Table 8.

    ties for the resedimented clastic lithofacies at Site 445are shown in Figure 5. There is very little systematicchange in any property between depths of 660 meters

    982

  • SEDIMENT SYNTHESIS

    • Site 445

    Δ Site 446

    Hamilton (1978)

    1.2 1.6 2.0

    Wet-Bulk Density (g/cm3)2.4

    Figure 9. Some velocity versus wet-bulk density for sam-ples of the resedimented clastic lithofacies. Hemipe-lagic muds are included at the low-density end. Alsoshown are the empirical relationship for shales (Ha-milton, 1978) and the best fit derived in this study.Regression parameters are given in Table 8.

    • Site 445

    Δ Site 446

    20 40 60

    Porosity (%)

    80

    Figure 10. Sonic velocity versus porosity for samples ofthe resedimented clastic lithofacies. Hemipelagic mudsare included for values of high porosity.

    2.0

    • Site 445

    Δ Site 446

    Ratcliffe(1960)

    20 40

    Water Content (wt. %)

    60

    Figure 11. Thermal conductivity versus water contentfor samples of the resedimented clastic lithofacies.Hemipelagic muds are included for high values of wa-ter content. Also shown are relationships establishedby Ratcliffe (1960) and in this study. Regression pa-rameters are given in Table 8.

    and 800 meters. Below 800 meters, wet-bulk density in-creases, sonic velocity increases, porosity decreases,and water content decreases. Thermal conductivity andgrain density show only minor down-hole variations.

    Down-hole variations for the resedimented clasticlithofacies can be understood best by examining the var-iations in porosity of the studied samples. The averagesand standard deviations of physical properties of thesamples are tabulated in Table 7. The lithofacies is di-vided into mudstones, sandstones, and conglomerates.At Site 445, the sandstones are below the mudstones,and the conglomerates are below the sandstones. Poros-ity is least in the coarse-grained conglomerates, andgreatest in the fine-grained mudstones, as demonstratedby Hamilton (1974). The decrease of porosity down-hole,therefore, reflects the general increase in grain sizedown-hole.

    All other physical properties are dependent onporosity. Wet-bulk density is inversely proportional toporosity, as demonstrated by the excellent linear fit inFigure 7, and the high negative correlation coefficient(Table 8). Hemipelagic mudstones from Site 446 areincluded in Figure 7 to define the large-porosity portionof the relationship. The regression parameters are givenin Table 8. The intercept of the line is 2.722 g/cm3,

    983

  • S.M. WHITE ETAL.

    ? 4.0j

    |

    |

    >-

    ,onα

    uctiv

    | 3 • °

    C

    2.0

    1

    -

    • l .V

    1 1

    • Site 445

    Δ Site 446

    -

    Δ

    \

    \ . Δ

    Δ Δ ^ Δ

    i i20 40 60

    Porosity (%)

    Figure 12. Thermal conductivity versus porosity for sam-ples of the resedimented clastic lithofacies. Hemipe-lagic muds are included at the high-porosity end ofcurve. Regression parameters are given in Table 8.

    2.2 -

    ù 1.

    1.4

    Δ

    Site 445

    Site 446

    i

    oyce (1976b)

    ••

    •••

    »

    c s s % .• * * #20 40 60

    Porosity (%)

    80

    Figure 13. Wet-bulk density versus porosity for samplesof the carbonate lithofacies. The dashed line is a the-oretical relationship from Boyce (1976b).

    which would be the density of a non-porous material ofthe composition of the samples plotted in Figure 7. Thisvalue is within the range of measured grain densities forthe resedimented clastic lithofacies samples (Table 7),suggesting that most of these samples are similar enoughin composition to have nearly the same grain density.Mineralogical differences, therefore, should be a muchless important control on physical properties than po-rosity.

    X 2 -

    Water Content (wt. %)

    Figure 14. Sonic velocity versus water content for sam-ples of the carbonate lithofacies. Regression parame-ters given in Table 10.

    1.4 1.8

    Wet-Bulk Density (g/cm3)

    2.2

    Figure 15. Sonic velocity versus wet-bulk density forsamples of the carbonate lithofacies. Also shown arethe theoretical relationship of Boyce (1976b) and therelationship derived in this study. Regression param-eters are given in Table 10.

    Figures 8, 9, and 10 show the dependence of sonicvelocity on water content, wet-bulk density, and porosi-ty, respectively. Data for hemipelagic mudstone fromSite 446 is also plotted in these diagrams. Because grain

    984

  • SEDIMENT SYNTHESIS

    Porosity (%)

    Figure 16. Sonic velocity versus porosity for samples ofthe carbonate lithofacies. Also shown are the theoret-ical relationship of Boyce (1976b) and the relation-ship derived in this study. Regression parameters aregiven in Table 10.

    Water Content (%)

    Figure 17. Thermal conductivity versus water contentfor samples of the carbonate lithofacies. Also shownare the relationships derived by Ratcliffe (1960) andin this study. Regression parameters are given in Ta-ble 10.

    Porosity

    Figure 18. Thermal conductivity versus porosity forsamples of the carbonate facies. Regression parame-ters are given in Table 10.

    density can be regarded as constant, both water contentand wet-bulk density are dependent on porosity. The re-lationships displayed in Figures 8 and 9, therefore, areconsequences of the porosity dependence established inFigure 10. These relationships can be either linear or ex-ponential. Regression parameters for these fits are givenin Table 7. Also shown in Figure 9 is the velocity-densi-ty relationship of Hamilton (1978) for shales. The curvepredicts velocities too large for given densities of sam-ples of the resedimented clastic lithofacies.

    Figures 11 and 12 show the dependence of thermalconductivity on water content and porosity, respective-ly. Thermal conductivity is inversely proportional towater content, as demonstrated by Ratcliffe (1960), butthe curve does not follow Ratcliffe's empirical relation-ship for high-water-content values. Linear or powerlaws can be fit to the thermal-conductivity data. Theregression parameters for these fits are given in Table 8.

    Water content, wet-bulk density, sonic velocity, andthermal conductivity are all related to sediment porosityfor the resedimented clastic lithofacies. The down-hole

    985

  • S.M. WHITE ETAL.

    TABLE 7Summary of Physical Properties of Resedimented Clastic Lithofacies, Sites 445 and 446 a

    Site

    445445445

    446

    Lithology

    MudstonesSandstonesConglomerates

    Mudstones

    Porosity

    Avg.

    43.5833.80826.170

    56.980

    >)

    σ

    4.8216.0800.226

    9.907

    Water Content(wt.

    Avg.

    21.71016.04011.355

    32.995

    a

    2.6434.0280.106

    8.166

    Wet-BulkDensity

    (g/cm3)

    Avg. a

    2.008 0.0502.135 0.1542.305 0.003

    1.764 0.158

    GrainDensity

    (g/cm3)

    Avg. σ

    2.801 0.1822.710 0.1022.770 0.00

    2.785 0.092

    SonicVelocity(km/s)

    Avg. σ

    2.149 0.1292.691 0.4943.153 0.132

    2.074 0.390

    ThermalConductivity

    (mcal/cm2-°C-s)

    Avg. σ

    3.195 0.1604.208 1.7062.799 0.402

    2.799 0.402

    See also Table 8.σ = standard deviation.

    TABLE 8Regression Parameters for Physical-Property Relationships,

    Resedimented Clastica and Hemipelagic Mudstone^ Lithofacies

    X

    PorosityWater contentWet-bulk densityPorosityPorosityWater content

    y

    Wet-bulk densitySonic velocitySonic velocitySonic velocityThermal conductivityThermal conductivity

    y

    m

    -0.0167-0.0268

    1.3943-0.0253-0.0246-0.0270

    = mx + b

    b

    2.7222.918

    -0.4543.4374.2713.814

    r*

    -0.978-0.8140.820

    -0.854-0.840-0.848

    k

    _

    8.5571.030

    24.70815.789

    7.766

    y = kx™

    m

    _

    -0.4271.163

    -0.632-0.430-0.293

    _

    -0.8990.848

    -0.904-0.825-0.850

    ^See also Table 7.See also Table 11.

    *r = correlation coefficient.

    variations in physical properties for the lithofacies aretherefore best understood by the down-hole decrease inporosity, which is at least partly controlled by grain size(Hamilton, 1974).

    Resedimented and Pelagic Biogenic Carbonate Lithofacies

    Table 9 summarizes the averages and standard devia-tions of physical properties for both the resedimentedcarbonate lithofacies and the pelagic biogenic carbonatelithofacies. Because the average grain densities and cal-cium-carbonate contents are so similar for samples fromeach lithofacies, the two will be considered together.

    Table 9 shows that the physical properties of theresedimented lithofacies consistently differ from theproperties of the pelagic biogenic lithofacies. Bothlithofacies occur at Site 445, where the pelagic car-bonates occur above the resedimented carbonate litho-facies. Inspection of Figure 6 shows that there are syste-matic down-hole changes in physical properties which

    cause the discrepancy in average physical properties forthe two lithofacies. Systematic down-hole variations inthe carbonate sediments include an increase in wet-bulkdensity, sonic velocity, and thermal conductivity, and adecrease in porosity and water content. Most changesare large and occur between the sea floor and the500-meter level. Sonic velocity increases from 1.7 toabout 2.0 km/s; thermal conductivity increases from 2.7to 4.5 mcal/cm2-°C-s; and water content decreases by30 per cent. Down-hole variations are similar to thosereported by van der Lingen and Packham (1975) for Leg30 carbonates, and to those summarized by Hamilton(1976) and Scholle (1977). The porosity-depth and wet-bulk-density-depth relationships derived by Hamilton(1976) adequately describe the down-hole variations ofcarbonates displayed in Figure 6.

    Figure 13 shows the dependence of wet-bulk densityon porosity. Also shown in Figure 13 is the theoreticalrelationship between wet-bulk density and porosity for a

    TABLE 9Summary of Physical Properties of the Pelagic Biogenic Carbonate and Resedimented Carbonate Lithofacies, Site 4 4 5 a

    Site

    445445

    Lithology

    Pelagic biogenicResedimented

    aSee also Table 10.

    Porosity

    (%)

    Avg. σ

    65.608 3.48053.032 7.267

    WaterContent(wt. %)

    Avg. σ

    40.654 3.33629.5 82 6.500

    Wet-BulkDensity(g/cm3)

    Avg. σ

    1.618 0.0681.831 0.176

    GrainDensity(g/cm3)

    Avg. σ

    2.805 0.1862.763 0.214

    SonicVelocity

    (km/s)

    Avg. σ

    1.544 0.0401.883 0.256

    Thermal

    Conductivity

    (mcal/cm2-°C-s)

    Avg. σ

    2.864 0.1603.524 0.696

    986

  • SEDIMENT SYNTHESIS

    porous solid with the grain density of calcite (e.g.,Boyce, 1976b). The least-squares linear fit is indisting-uishable from the theoretical curve and is not plotted.The regression parameters are given in Table 10. Wet-bulk density is primarily controlled by porosity, but thescatter displayed in Figure 13 may indicate a secondarycontrol, such as minor mineralogical differences amongsamples.

    Properties such as sonic velocity and thermal conduc-tivity are also related to porosity. Figures 14, 15, and 16show the relationships between sonic velocity and watercontent, wet bulk density, and porosity, respectively.The dependence of velocity on wet-bulk density andwater content is a reflection of the dependence of thosetwo parameters on porosity. Also shown in Figures 15and 16 are theoretical curves for porous sediments com-posed entirely of calcite (e.g., Boyce, 1976b). In bothcases, a greater sonic velocity is predicted by theory.The samples from Site 445, however, have a significantamount of clay minerals, which would cause the dis-crepancy. There is also considerable scatter of data inFigures 14, 15, and 16, which may be related to mineral-ogical variations or grain-size variations in the samples.

    Thermal conductivity is inversely related to watercontent (Figure 17) as demonstrated by Ratcliffe (1960),and therefore is inversely related to porosity (Figure 18).Thermal conductivity values, however, are greater thanRatcliffe's curve predicts. The discrepancy is caused bythe high thermal conductivity of calcareous sediments(e.g., Clark, 1966; Hyndman et al., 1974).

    Porosity is the primary control of physical-propertyvariations for the carbonate lithofacies samples. Grainsize variations and mineralogical differences, however,are apparently responsible for the scatter in the data.The down-hole decrease in porosity is similar to thatobserved in thick sections of chalk (Scholle, 1977) andmay be related to cementation involving pressure solu-tion and local re-precipitation (e.g., Scholle, 1977).

    Hemipelagic Clay and Mudstone LithofaciesHemipelagic clays are the dominant lithofacies at the

    Shikoku Basin sites, whereas the hemipelagic mudstonelithofacies appears in the upper part of the section atSite 446 in the Daito Basin. All hemipelagic lithofaciessections occur between the sea floor and 360 meters be-low the sea floor. Smectite and illite are the dominant

    TABLE 10Regression Parameters for Physical-Property Relationships,Resedimented Carbonate and Biogenic Pelagic Lithofacies3

    .V

    PorosityWater contentWet-bulk

    densityPorosityPorosity

    Water content

    y

    Wet-bulk densitySonic velocity

    Sonic velocitySonic velocityThermal

    conductivityThermal

    conductivity

    aSee also Table 9.*r = correlation coefficient.

    y

    m

    -0.0182-0.0280

    0.9822-0.0245

    -0.0626

    -0.0763

    = mx + b

    b

    2.7972.678

    0.0353.153

    6.839

    5.784

    r*

    0.846-0.819

    0.743-0.826

    -0.826

    -0.855

    k

    _

    8.173

    1.01128.824

    139.242

    30.335

    y = kx

  • S.M. WHITE ETAL.

    TABLE 11Summary of Physical Properties of Hemipelagic Clay and Mudstone Lithofacies, Sites 442, 443, 444, 446 a

    Porosity

    Site Lithology Avg. <

    WaterContent(wt. %)

    Avg.

    Wet-BulkDensity(g/cm3)

    Avg. σ

    GrainDensity(g/cm3)

    Avg. c

    SonicVelocity(km/s)

    Avg.

    Thermal

    Conductivity

    (mcal/cm-°C-s)

    Avg. σ

    442443444446

    ClaysClaysClaysMuds

    71.14171.77772.56575.156

    6.3.4.8.

    342333106528

    48.09148.07249.49652.585

    4348

    .505

    .038

    .797

    .389

    1.4811.4941.4721.445

    0.0630.0530.0640.106

    2.6932.7642.7272.835

    0.3350.2320.1120.198

    1.5571.5521.5191.539

    0.2020.0780.0420.059

    2.1642.3152.3272.277

    0.5390.2880.1530.132

    See also Table 8.

    TABLE 12Summary of Physical Properties of Pelagic Non-biogenic and Pyroclastic Lithofacies, Site 442

    Porosity

    Site Lithology Avg.

    WaterContent(wt. %)

    Avg.

    Wet-BulkDensity(g/cm3)

    Avg. σ

    GrainDensity(g/cm3)

    Avg. c

    SonicVelocity(km/s)

    Avg. σ

    Thermal

    Conductivity

    (mcal/cm-°C-s)

    Avg. σ

    442 Pelagic non-biogenic 72.905 4.685 51.048 5.378 1.433 0.063 2.610 0.178 1.581 0.023 1.941 0.588443 Pyroclastic 68.513 5.313 51.350 10.377 1.367 0.117 2.705 0.332 1.754 0.491 1.843 0.463

    Pyroclastic Lithofacies

    A few samples from the pyroclastic lithofacies comefrom a thin interval (20 meters thick) at Site 442. Prop-erties within this lithofacies are variable, as indicatedby large standard deviations tabulated in the summary(Table 12). Average sonic velocity is greater than theaverages for hemipelagic sediments (Table 11). Ther-mal conductivity, wet-bulk density, grain density, andwater content, however, are smaller than averages forthe hemipelagic sediments (Table 11). The variabilityof properties for this lithofacies reflects the varyingamount of volcanic ash in the sediment.

    Conclusions

    Physical properties of Leg 58 sediments and sedimen-tary rocks are directly related to sample porosity andcomposition. Properties within each lithofacies are di-rectly related to down-hole variations in porosity. Min-eralogical and grain-size variations within each lithofa-cies are minor influences on physical properties. Thelithofacies, however, differ considerably in composi-tion, texture, and grain size. Thus, the carbonate litho-facies is easily distinguished from the other lithofacieson the basis of various physical properties. The down-hole variability in properties (Figures 2-6) is the resultof overall changes in sediment composition and closureof pore space.

    Site 445 is particularly interesting because drillingpenetration was deep enough to allow study of down-hole variations in thick sections of the pelagic biogeniccarbonate and resedimented carbonate lithofacies andresedimented clastic lithofacies. In both the carbonateand clastic lithofacies, physical properties change syste-matically as pore space closes. Pore closure in the car-bonates is probably related to diagenetic processes (e.g.,van der Lingen and Packham, 1975; Scholle, 1977),

    whereas porosity loss in the resedimented clastic faciescan be related to a general down-hole increase in grainsize (e.g., Hamilton, 1974).

    Sections of hemipelagic sediments within a few hun-dred meters of the sea floor (Sites 442, 443, 444, and446) show neither the range of properties nor themagnitude of changes with depth that the composition-ally and texturally varied sediments of Site 445 do.Although the clay mineralogy may vary at each site,there are no significant associated changes in the physi-cal properties. Thick sections of hemipelagic sediments,however, will show substantial property changes down-hole as pore space is reduced.

    Paleomagnetism of Sediments

    Approximately 925 minicores were sampled from thecores of Sites 442 through 446 for Paleomagnetism stud-ies. The results of the present work (see Kinoshita, thisvolume) are in agreement with other Paleomagnetismresults from the area.

    Three significant results have been obtained. First,the paleolatitude obtained from Pleistocene sediments issmaller by about 10 degrees than the present value. Thisappears to result from distortion of the NRM inclina-tion of the sediments by drilling and handling. Second,the present latitude of the Daito region is significantlygreater than the paleolatitude during the Eocene. There-fore, the Daito region must have drifted northwardsince the Eocene by about 2000 km. Assuming a con-stant rate of motion and due-north drift of the region,the rate of spreading is at least 5 cm per year. Third,although it is not clear whether the Daito region was inthe northern or the southern hemisphere during the Eo-cene, the region seems to have crossed the equator about45 Ma, although this is not definite. A similar argumentis presented by Louden (1977) in a Paleomagnetism

    988

  • SEDIMENT SYNTHESIS

    study of sediment cores from the western PhilippineBasin.

    Measurement of NRM over a 15-meter interval ofnannofossil-chalk cores from Site 445 revealed fourmagnetic-polarity transitions about 25 Ma.

    Two of the four polarity transitions were rapid, andthe polarity changed within 6000 years. The remainingtransitions were slow, and the polarity switched over25,000 to