12. SITE Shipboard Scientific Party 2

Transcription

1 . SITE64 Shipbard Scientific Party HOLE 64 Date ccupied: Octber 98, LCT Date departed: Octber 98, 7 LCT Time n hle: hr. Psitin: 5 4.8'N, 86 8.'W Water depth (sea level; crrected m, echsunding): m Water depth (rig flr; crrected m, echsunding): m Bttm felt (m, drill pipe): 4. Penetratin (m): 7 Number f cres: 5 Ttal length f cred sectin (m): 7 Ttal cre recvered (m): 7.7 Cre recvery (%): Oldest sediment cred: Depth subbttm (m): 7 Nature: Sand Age: Pleistcene (Ericsn Zne Y) Measured velcity (km/s):.58 Basement: N/A HOLE 64A Date ccupied: Octber 98, 7 LCT Buma, A. H., Cleman, J. M., Meyer, A. W., et al., Init. Repts. DSDP, 96: Washingtn (U.S. Gvt. Printing Office). Addresses: Arnld H. Buma (CChief Scientist), Gulf Research and Develpment Cmpany, P.O. Bx 748, Hustn, TX 776, (present address: Chevrn Oil Field Research Cmpany, P.O. Bx 656, Hustn, TX 776); James M. Cleman (CChief Scientist), Castal Studies Institute, Luisiana State University, Batn Ruge, LA 78; Audrey W. Meyer (Shipbard Science Representative), Deep Sea Drilling Prject, Scripps Institutin f Oceangraphy, La Jlla, CA 99, (present address: Ocean Drilling Prgram, 5 University Drive West, Texas A&M University, Cllege Statin, TX 7784); James Brks, Department f Oceangraphy, Texas A&M University, Cllege Statin, TX 7784; William R. Bryant, Department f Oceangraphy, Texas A&M University, Cllege Statin, TX 7784; Richard Cnstans, Palentlgy Sectin, Chevrn U.S.A. Inc., 95 Gravier Street, New Orleans, LA 7; Michel Cremer, Département de Gélgie et Oceangraphic Université de Brdeaux I, Avenue des Facultés, 45 Talence Cedex, France; Laurence I. Dr, Labratire de Gédynamique SusMarine, 6 VillefranchesurMer, France; Tbshi Ishiuka, Ocean Research Institute, University f Tky, Tky 64, Japan; Mahln C. Kennicutt II, Department f Oceangraphy, Texas A&M University, Cllege Statin, TX 7784; Barry Khl, Chevrn U.S.A. Inc., 95 Gravier Street, New Orleans, LA 7; William R. Nrmark, Pacific Branch f Marine Gelgy, US. Gelgical Survey (MS999), 45 Middlefield Rad, Menl Park, CA 945; Suanne 'Cnnell, LamntDherty Gelgical Observatry f Clumbia University, Palisades, NY 964, (present address: Ocean Drilling Prgram, 5 University Drive West, Texas A&M University, Cllege Statin, TX 7784); Mary Parker, Department f Gelgy, Flrida State University, Tallahassee, FL 6, (present address: AMOCO Prductin Cmpany, P.O. Bx 5879, New Orleans, LA 75); Kevin T. Pickering, Department f Earth Sciences, University f Lndn, GldsmitlTs Cllege, Lndn SE 4 6NW, United Kingdm; (present address: Department f Gelgy, University f Leicester, Leicester LEI 7RH, United Kingdm); Claudia Schreder, Department f Gelgy, Dalhusie University, Halifax, Nva Sctia BH J5, Canada; Charles E. Stelting, Gulf Research and Develpment Cmpany, P.O. Bx 748, Hustn, TX 776, (present address: Chevrn Oil Field Research Cmpany, P.O. Bx 656, Hustn, TX 776); Drrik A. V. Stw, University f Edinburgh, Edinburgh EH9 JW, Sctland, United Kingdm, (present address: Gelgy Department, University f Nttingham, Nttingham NG7 RD, United Kingdm); William E. Sweet, Mineral Management Service, P.O. Bx 7944, Metairie, LA 77; Andreas Wetel, Gelgisches Palaentlgisches Institut der Universitàt, Sigwartstrasse, D74 Tubingen, Federal Republic f Germany; and Jean K. Whelan, Chemistry Department, Wds Hle Oceangraphic Institutin, Wds Hle, MA 54. Date departed: 4 Octber 98, 4 LCT Time n hle: day, 4 hr. Psitin: 5 4.8'N, 86 8.'W Water depth (sea level; crrected m, echsunding): Water depth rig flr; crrected m, echsunding): Bttm felt (m, drill pipe): 4. Penetratin (m): 5. Number f cres: Ttal length f cred sectin (m):. Ttal cre recvered (m): Cre recvery (%): 49 Oldest sediment cred: Depth subbttm (m): 5. Nature: Clay Age: Pleistcene (Ericsn Zne Y) Measured velcity (km/s):.7 Basement: N/A BACKGROUND AND OBJECTIVES Hles 64 and 64A were drilled in the lwer Mississippi Fan. The site is lcated in the seaward thinning sectin f the yungest fan lbe f the Pleistcene Mississippi fan cmplex. The site lcatin was selected s as t encunter ne f these thinning units in the uppermst t 4 m f the sectin and t penetrate the entire yungest fan lbe. At the site, sidescan snar images shw an extremely cmplex seaflr mrphlgy cnsisting f strngly reflecting linear features that ften display multiple rientatins. Highly reflective small targets are fund in the immediate vicinity f the site. Bathymetric relief is variable with maximum relief being n the rder f m. The subbttm prfiler recrds display welldevelped reflectin hrins that range in thickness frm t 5 m. Individual reflectrs can ften be crrelated fr distances f up t 5 km. Nearsurface reflectrs are generally cnfrmable with the surface tpgraphy, indicating the absence f any significant seaflr ersin during emplacement. Site 64 was drilled t satisfy the fllwing bjectives:. T determine the sedimentlgical, palentlgical, gechemical, and getechnical prperties f a lwer fan lbe.. T assess the amunt f sand depsited at the distal ends f a fan lbe and t evaluate the mechanisms respnsible fr its depsitin.. T evaluate whether Mutti's "cmpensatin cycles" exist in the distal ends f the Mississippi Fan. 87

2 SITE 64 OPERATIONS Ft. Lauderdale Prt Call Leg 96 had its fficial beginning at 654 hr., 6 September 98 with the first mring line at Berth Tw f Prt Everglades in Frt Lauderdale, Flrida. Shrtly after arrival, it was necessary t shift t Berth One. This was accmplished by hr., and prt call activities then fficially began. Principal wrk items included the tp verhaul f number nine engine, repair f number ne gyrcmpass, U.S. Cast Guard inspectin f Glmar Challenger, crew change, fflading f cres, nlading f sacks f barite and miscellaneus freight, and an pen huse fr lcal visitrs. With all scheduled wrk cmpleted, the vessel departed her berth at 88 hr., 9 September. Ft. Lauderdale t Site 64 Excellent speed was achieved n the transit t the initial perating area. A nearshre cuntercurrent f the Gulf Stream, cmbined with a fllwing wind and calm seas, prduced a speed f ver knts as Challenger runded the Flrida Peninsula and turned west past the Flrida Keys. A few hurs after leaving the cuntercurrent, the vessel encuntered anther current (Lp Current) which carried her tward the perating area at speeds increasing t abut knts. This unexpectedly strng current hampered maneuvering fr the relatively cmplex preliminary prfiling survey. After a 4 /hr. survey, a psitining beacn was launched at hr., Octber, marking arrival at Site 64. The drill site was lcated abut mi. westnrthwest f the Dry Trtugas Islands and abut 5 mi. nrthnrthwest f Cuba. Hle 64 The apprach prfile was extended abut 5 min. beynd the beacn drp pint befre the vessel was turned and the twed seismic gear retrieved. While the vessel apprached the beacn t take statin, the beacn's acustic signal weakened abruptly and develped pulse characteristics that were rejected by the psitining system. Using LORANC navigatin, the ship struggled back t the drp crdinates against the strng current and an alternatefrequency beacn was drpped at 5 hr. Satisfactry psitining was finally achieved at 645 hr., and the pipe trip began. The current pushed the bttmhle assembly (BHA) s strngly against the mnpl bracing that it was necessary t let the vessel drift mmentarily t facilitate setting the upper guide hrn int psitin. The drill string cntinued t be frced strngly against the pipe restraint and t vibrate vilently fr the duratin f the pipe trip. The precisin depth recrder (PDR) reading estimated the seaflr t be between and m belw the rig flr. The cre bit was psitined at 4 m fr the first attempt with the advanced hydraulic pistn crer (APC). The crer strked t.5 m and was recvered nearly filled with cre (9. m) (Table ). One jint f pipe was set back and anther cre was "sht" frm 9.5 m higher t ascertain that n sediment had been missed. It was necessary t interrupt this peratin fr Table. Site 64 cring summary. Cre a Hle 64 H H H 4H 5H Hle 64A H H H 4H 5H 6H 7H 8H 9H H UH X X Date (Oct. 98) Time Depth frm drill flr (m) Depth belw seaflr (m) Length cred (m) Length recvered (in) Amunt recvered (%) 99 >IOO 9 96 >IOO >IOO >IOO >IOO >8 9 8 H fllwing cre number indicates hydraulic pistn cre, X indicates extended cre barrel cre. hr. when the current and wind pushed the vessel abut 6 m ff statin. The crer was recvered with n trace f sediment, and the water depth was established at 4. m. Tw additinal mud cres f gd quality were taken t 8 m belw the seaflr, where sft, lse sand was encuntered. Penetratin and recvery were reduced t er, and the same interval was cred three times befre a m sand cre was recvered (Cre 644; Table ). As the crer was being lwered fr the next attempt, a sudden drp in sand line weight indicated that the cring assembly had been lst. On recvery f the sand line, it was fund that the wireline swivel had cme apart, leaving the APC, the sinker bar assembly, and the lwer prtin f the swivel in the pipe. The dimensins f the swivel prhibited recvery frm the pipe by wireline fishing. A rund trip was therefre necessary t cntinue peratins. In the meantime, hwever, the dressed crer had settled int psitin in the uter cre barrel. The bit was lwered t the bttm f the hle and the pipe was pressured t actuate the crer befre the drill string was recvered. The crer was recvered frm the BHA at the drill flr at 7 hr., Octber, cntaining abut 8 m f lse sand (Cre 645; Table ). Hle 64A With the rund trip cmplete, Hle 64A was spudded at 4 hr., Octber. The bit was "washed" dwn t 7 m belw seaflr, the ttal penetratin f Hle 64 (Table ). Anther m f lse sand was cred befre mud and clay strata were again encuntered. APC cring cntinued in sediments cnsisting f alternating sand and mud beds, with sand predminating. Cre recvery was unexpectedly high, althugh penetratin f the crer, as expected, was limited. This was held t as little as m in the cleaner and carser sands. At abut 5 m subbttm, the clay became much suffer and became a factr in bth reduced penetratin and increased 49 88

3 SITE 64 verpull n retrieval. At m subbttm, the APC was retired in favr f the extended cre barrel (XCB). Tw XCB cres were attempted with nly a few centimeters recvered each time. At this pint, the scientific bjectives were cnsidered t be sufficiently accmplished and cring peratins were terminated at a ttal drill string depth f m. The drill string was recvered and the vessel was under way at 4 hπ, 4 Octber. SEISMIC STRATIGRAPHY AND ACOUSTIC FACIES At Site 64, the mdern Mississippi fan lbe is apprximately m thick. Tw reginal seismic reflectin hrins f late Pleistcene age ("" and ""; see intrductry chapter, this vlume) have been crrelated with the detailed seismic stratigraphy in the Mississippi Canyn area. Hrin "" is the base f the mdern fan lbe and was a primary target fr hydraulic pistn cring at this site. The seismic cverage fr this site is shwn in Figure. Seismic Stratigraphy Site 64 was lcated near the western end f Cnrad Line 7 in an area f numerus relatively cntinuus, clsely spaced, subparallel reflectin hrins as seen n the watergun recrd (Fig. ). The detailed survey shws that the site is near the western margin f an area f slightly cnvexupward relief that might indicate either a depsitinal lbe r a brad levee feature. Several prminent reflectin hrins in the upper 5 m f prfile can be traced acrss this part f the fan. These hrins may crrelate with lithlgic cntacts at Sites 64 and 65. Acustic Fades The.5kH shipbard prfiles and the 4.5kH deeptw data can be used t define at least fur separate surficial acustic facies units within the general survey area (O'Cnnell et al., this vlume). Site 64 is lcated within the acustic facies that is characteried by shrt, multiple, subparallel reflectrs f variable width (Figs. A, B). Depth f acustic penetratin varies between 5 and 5 ms. This type f acustic unit als underlies the western levee f the main fan channel just abve its terminatin (Site 65). Bth the.5 and 4.5kH prfiles (Figs. A, B) shw that lcally cnvexupward relief n subbttm reflectrs in this acustic facies extend ver distances f a kilmeter. In additin, sme f these irregular deeper reflectrs are strng and diffuse in character, similar t 5 'N Seismic reflectin Sea MARC OOOZ/7 Dec ' \ / 9 Dec ^.67 : Fig. A 69 '7 '7\ 7 5 C 59 5 km 86 'W 86 ' 86 r 85 5' Figure. Map shwing Cnrad site survey tracklines and lwer fan Sites 64 and 65. Lcatins f prfiles shwn in Figures and are indicated with heavy lines. 89

4 SITE J km Figure. Watergun seismic prfile frm Cnrad, Line 7 site survey that passes near Site 64 (see Fig. fr lcatin) W B Figure. Subbttm reflectin prfiles frm site survey cruise that passes near Site 64 (see Fig. fr lcatin). A..5kH prfile. B. Deep twed 4.5kH prfile (Sea MARC I). 9

5 SITE 64 seaflr reflectins in areas f sand depsitin n ther fans (Damuth, 978; Nrmark et al., 979; see O'Cnnell et al., this vlume). Seismic Stratigraphy Results Drilling at Site 64 penetrated tw prminent reflectrs abve seismic Hrin "" (Fig. ). These reflectrs can be traced acrss this part f the fan and shuld have been encuntered near 85 and 47 m subbttm depth. The upper reflectr shuld have been lcated in Cre 64A6, hwever, nly cm f sand were recvered in this interval. The deepest cre frm Hle 64A may have penetrated the deeper f the tw reflectrs at 47 m, but again the nly sample recvered was 8 cm f sand in the cre catcher (Cre 64A). Thus n lithlgic bundaries were cred at Site 64 that crrelate with the relatively cntinuus reflectin hrins in the area. Where these same hrins were cred at Site 65, the upper reflectr has been tentatively crrelated with the tp f a thick sand bed (r sectin) and the lwer reflectr ccurs near the tp f a muddy sectin underlying interbedded sand and mud. The general character f the singlechannel seismic prfiles shws numerus, discntinuus reflecting surfaces with variableamplitude and irregular relief, especially abve 5 m (Fig. ). This character is cnsistent with the predminantly sandy sequences encuntered at Site 64. The sectins between each areawide reflectin hrin shw slight (tens f meters) changes in thickness ver the width f the detailed survey area, suggesting changes in lcal surce and sme cmpensatin fr lcal relief created during each interval. The shallwest reflectrs bserved at this site crrespnd t the reflectrs seen n the.5kh prfiles that mark sme f the shallwest sand beds in the area. Cring at this site cnfirmed the sandy nature f the upper 5 m f sectin, but the interpretatin f the acustic stratigraphy requires crrelatin with the sectin at Site 65. The results frm this site suggest that.5kh recrds are valuable fr deriving acustic facies maps indicating areas f sand depsitin fr bth the seaflr and shallw subbttm reflectrs. BIOSTRATIGRAPHY AND SEDIMENTATION RATES Bistratigraphy The sectin penetrated in Hles 64 and 64A is Quaternary and crrelates with the planktnic framinifer Zne N and the calcareus nannfssil Zne NN. This interval includes the Hlcene Zne Z and upper Wiscnsin glacial Zne Y f Ericsn and Wllin (968) (see Explanatry Ntes, this vlume). The warm interstadial f the Wiscnsin (Zne X r the Glbrtalia ßexusa Zne) was nt encuntered t the ttal cred depth f 5. m (Fig. 4). The Y Zne cntained mstly rewrked Cretaceus framinifers and calcareus nannfssils within the displaced sands and muds. 5 5 Age ihlcenef cnsin glacial) α> leistcene (la Zne Y ±Cre A 4A 5A 6A 7A 8A 9A A Cre recvery r~ ~r^r Oe/muddy e Lithlgy I J A A A Siltlaminated mud C..X..T_. ;^7.;.';. ^:;. ;.v: ;. : r B&lll:;:;:;:;:;:;: ~ ^,T^_ ;:: 7 /~.TvJr. ; Unit LU II Vertical successin V. Fining >^ upward N^interval 7 Sand and silt Figure 4. Lithstratigraphic summary f Site 64 shwing age, cre recvery, lithlgy, and lithlgic units and intervals. Framinifers Framinifers frm Hles 64 and 64A are Quaternary, Zne N (Blw, 969). A warmwater highdiversity planktnic e ccurs at the tp f Cre 64. This fauna cntains abundant G. menardii and G. tumida, alng with bathyal benthic framinifers such as Cibicides wuellerstrfi and Melnis pmpiliides. The remainder f Hle 64 and all f Hle 64A cntain interbedded sands and muds f Pleistcene age with a very prly develped framiniferal fauna. Rewrked Cretaceus framinifers and radilarians ccur thrughut this interval. The ccurrence f shallwwater (neritic) framinifers such as Amphistegina gibbsa, Hanawaia spp., and Elphidium spp. suggests that sme f the Pleistcene sand and mud has been displaced frm a neritic envirnment. Rapid sedimentatin is indicated by the absence f bathyal benthic framinifers. N hemipelagic muds were encuntered belw the Hlcene but there is a slight increase in Pleistcene planktnic framinifers in Sample 64A,CC. 9

6 SITE 64 Calcareus Nannfssils All samples bserved at this site are interpreted t be in the Emiliania huxleyi Zne (NN) f Martini (97). The framinifer e in Sectin 64 cntains abundant, wellpreserved calcareus nannfssils. These samples are dminated by very small cccliths, which can nly tentatively be identified as E. huxleyi. Few rewrked Cretaceus nannfssils are cntained in this e. Rewrked Cretaceus nannfssils are the majr cnstituent f the remainder f Hle 64 and all f Hle 64A. Because f the rapid sedimentatin rate at this site, nly trace t rare Pleistcene nannfssils are present in the samples examined. A slight increase in Pleistcene species is encuntered in the bttm f Hle 64A in Sample 64A,CC. Prbable E. huxleyi is identified in this sample. N distinctin between the sand and mud lithlgies in this interbedded sandmud sequence can be made n either the abundance r diversity f calcareus nannfssils. Bth the sands and muds appear t have been depsited by the same depsitinal prcess. Sedimentatin Rates The sedimentatin rates are calculated n the basis f tw datums. An age f. Ma is used fr the Hlcene/Pleistcene bundary (Z/Y nal bundary) and an age f.85 Ma fr the Y/X nal bundary (see Explanatry Ntes, this vlume). A sedimentatin rate f 4. cm/ yr. is cmputed fr the Hlcene. This is a minimum rate assuming cmplete Hlcene recvery (Fig. 5). The Y/X nal bundary was nt encuntered. By using a seismic prjectin t the tp f the X Zne (468 m fr seismic Hrin ""; see intrductry chapter, this vlume), a prjected minimum sedimentatin rate f 64 cm/ yr. is cmputed fr the Y ne. These calculatins were based n nndecmpacted sediment thicknesses. LITHOSTRATIGRAPHY At Site 64 we recgnie tw lithlgic units n the basis f cmpsitin (Table, Fig. 4). Lithlgic Unit I: Oe and Muddy Oe This unit ccurs in a thin layer (abut 4 cm thick) at the very tp f the sectin. It is a lightclred bigenic e cmpsed mainly f planktnic framinifers with less than lθ / calcareus nannfssils and siliceus rganisms, and with minr terrigenus material. It appears hmgeneus and is prbably thrughly biturbated. Lithlgic Unit II: Muds, Silts, and Sands Sand and Silt Facies The dminant facies at Site 64 is silty sand, cmprising 54% f the recvered sectin and an estimated 7% f the cmplete sectin (Fig. 6A). It ccurs in me Table. Lithlgic units f Site 64. Lithlgic unit I II Sediment Oe and muddy e Muds, silts, and sands Cred interval 64, 4 cm 64, 4 cm thrugh 645; 64A thrugh 64A Subbttm depth (m).4 m.45. m 4. cm/ yr. Time ( yr.) m 5. cm/ yr. (minimum based n Zne X encuntered immediately belw T.D.) 5. m E 64 cm/ yr. ^ (minimum rate based n seismic prjectin t Hrin ) m 6 Figure 5. Site 64 sedimentatin rates. 9

7 SITE B L 89 L 67 "NMöt<β Figure 6. Examples f lithlgic fades frm Hles 64 and 64A. A. Graded sand and silt beds with sme silt laminae (Sample 64A7, 6898 cm). B. Silt laminae in mud verlying sand (Sample 64A8, 5989 cm). C. Silt laminae in mud (Sample 64A, 767 cm). 9

8 SITE 64 dium t very thick beds, frm cm t at least m in thickness. Many f the thicker sandy intervals recvered cmmnly shw lss f sand by washut r an increase f sand due t flwin during the cring prcess. Mst f the sand beds appear structureless. Prly develped nrmal grading ccurs in sme f the mediumbedded sands. A carsetail grading is bserved ver several meters in the thicker layers. Rare reverse grading was fund at the base f sme beds. Bth tp and bttm cntacts are sharp, mre rarely gradatinal, and lcally scured at the base. Large mud clasts (5 cm diameter) ccur in the middle f a few beds. All the sands are very prly srted, with a maximum grain sie f 7 t µm (carse t very carse sand), a mean grain sie f t 5 µm (fine sand), and a relatively high prprtin f silt. Many f the larger grains are well runded and sme appear well plished, whereas smaller grains are cmmnly subangular t angular. The sand cmpsitin is mainly terrigenus (9598%) cmprising dminant quart (clear, white, range, and rse), secndary feldspars, micas, calcite and heavy minerals (especially amphibles and paques), and accessry glaucnite and lithic fragments. The small bigenic cmpnent (5%) includes rewrked framinifers, brken shell debris, and variable amunts f lignite and wdy material. SiltLaminated Mud Fades Muds, silty muds, clayey muds, and silts are the secnd mst imprtant sediments at Site 64, making up ver 4% f the recvered sectin (Fig. 6B, C). They ccur in sectins frm a few centimeters t ver m thick between sand beds. Individual silt beds frm layers frm less than mm t abut 5 cm thick within the mud sectins. The muds appear structureless, slightly banded r laminated. In sme sectins they have dispersed silt and sand grains and lenses. The silts mst cmmnly display a range f sedimentary structures typical f finegrained turbidites. These include sharp scured bases, parallel and crsslaminatin, and lwamplitude ripples. Additinal structures include cnvlute layers, discntinuus laminatin, and prbable micrburrwing. They are typically nrmally graded, have bth sharp and gradatinal cntacts with the verlying mud, and shw cmpsitinal srting. Bth silts and muds are lcally highly disturbed, either because f cring r as a result f sediment mvement. Texturally, the muds are mainly silty r very silty. The silts range frm finegrained and clayey t medium r carsegrained and may be mderately well srted. The grains are granular t subrunded in shape. Mst f the muds are terrigenus, cmmnly cntaining up t 5% calcareus nannfssils. The silts have a terrigenus character similar t the sands described abve, with dminant quart but a higher prprtin f carbnate grains f indeterminate rigin. Lignite and ther wdy debris is lcally present and a few silt layers are rich in vlcanic ash. Vertical Successin The lwer half f the 5m sectin was incmpletely cred, and much f the washedut material was prbably sand. The facies recvered are arranged in three distinct intervals, which we describe frm bttm t tp:. An incmplete carseningupward interval frm 5 t abut 5m depth f turbidite muds and silts passing upward int sands.. A "blcky successin" f thick sands interbedded with thin t thick muds frm 5 t abut 5 m. The sands are massive r prly graded and have very abrupt tp and bttm cntacts with the interbedded muds, giving a blcklike appearance t the sectin.. A finingupward interval ver the tp 5 m f sectin with sands decreasing in thickness and silt laminae decreasing in frequency upward. The uppermst mud then grade int e and muddy e facies f lithlgic Unit I. GEOCHEMISTRY Organic Gechemistry Very lw levels f gaseus hydrcarbns were bserved in Hles 64 and 64A. At this site, interstitial water sulfate levels remain near seawater values thrughut, s that a sulfatefree ne where methangenic bacterial activity might have ccurred was nt bserved. Inrganic Gechemistry Six whlerund samples f cm length were cllected fr interstitial water analyses. Belw Cre 64A6 (89 m subbttm) the cres are very shrt and sandy, making interstitial water analyses impssible. The shipbard results shw a relatively cnstant salinity, a minr increase in ph with depth, and a significant initial increase in alkalinity with depth (see Ishiuka, Kawahata, et al., this vlume). PHYSICAL PROPERTIES Wetbulk density increases frm a lw f.4 g/cm measured in muds at the seaflr t a high f. g/cm at 4m depth. The highest values reflect the presence f sandy sediments. Deeper in the sediment clumn, values between.8 and. g/cm are fund (Fig. 7A). Wet water cntent reflects a rapid change in the physical prperties frm the seaflr t a depth f 7 m, the start f the sands. Over this interval, the wet water cntent ranges frm 55 t % (Fig. 7B). Belw 7 m subbttm, water cntent ranges frm 7 t 4% and averages abut %. Prsity and vid rati (Fig. 7D) reflect trends similar t bulk density and water cntent. This is nt unusual since they are all interrelated. Grain density varies widely in the upper 5 m but averages abut.75 g/cm, which is the density f the particular type clays fund in this area. Sand density averages.8 g/cm. Undrained shear strength measurements are pltted in Figure 7E. Shear strength increases at an average rate 94

9 SITE 64 Wetbulk density Wet water cntent (g/cm ) (%).. 4 c~ ~i I i r A. B Dry water cntent 5 ~i i i r Prsity (%) E Shear strength (kpa) Sund velcity (km/s) Parallel t bedding + Perpendicular t bedding i I L Figure 7. Mass physical prperties f Site 64 sediments. A. Wetbulk density. B. Water cntent related t weight f wet sediment. C. Water cntent related t weight f dry sediment. D. Prsity. E. Undrained shear strength. F. Sund velcity. 95

10 SITE 64 f.8 kpa/m t a subbttm depth f 9 m. Belw the 9m level the sediments have anmalusly high undrained shear strengths. At the m level, the shear strength ranges frm 6 t 8 kpa. Snic velcity in the upper 7 m f sediments is less than that f seawater at the same temperature,.5 km/s (Fig. 7F). The lwest velcity measured was.48 km/s in Sectin 64. The highest value (.57 km/s) was fund in Sectin 64 at 6.5m depth. N attempt was made t measure the snic velcity f the sands fund in the cres f Hle 64A. It was felt that any such measurements wuld be highly misleading because f the disturbed nature f the material. In Hle 64A, anmalusly high velcity clays are encuntered between 48 and 54 m subbttm (Fig. 7F). The clays in this regin als pssess a high acustic anistrpy. The velcity parallel t the bedding is up t % higher than that measured perpendicular t it. This is als true fr the sediments f Sectin 64A at 7 m. The velcity at the 7m level averages arund.58 km/s. These are the velcities expected f clay at that depth. The velcity f the sediments at the 8 and 7m levels is anmalusly high fr clayey sediments at thse depths. The anmalusly high velcities f certain sediments in Hles 64 and 64A are attributed t the presence f sand and silt (fr details see Bryant et al., this vlume). SUMMARY AND CONCLUSIONS At Site 64, we drilled tw hles, Hles 64 and 64A, and cred t a ttal penetratin f 5. m belw the mud line. The site was lcated in the lwer fan. Strng currents, an abundance f sand, and stiff Pleistcene clay resulted in incmplete cre recvery, but the data acquired satisfied the majr bjectives utlined fr this site. The lwer fan regin f the Mississippi Fan is characteried by numerus verlapping fan lbes, with the yungest lbe cnsisting f apprximately 5 t m f late Wiscnsin sediments derived frm the shelf and delivered t the lwer fan via a single, large sinuus channel. In the lwer fan, numerus small channels, switching thrugh time, have laid dwn a thick sequence f carse sandy sediment capped by alternating fine sands, silts, and clays. With the exceptin f the upper.5 m (Hlcene framinifer e), the entire cred sectin seems t be within Ericsn's Zne Y, the late Wiscnsin glacial stage. The Glbrtaliaßexusa Zne, dated at.85 Ma, was nt reached, thus the ttal cred sequence was extremely yung in age. The sediments cmprising the sectin were very pr in pelagic framinifers and included benthic micrfauna, indicating transprt frm a shelf edge r shallwer water envirnment. The vertical sequence is dminated by sandy sediment, with fine sand cmprising sme 4.4% f the upper m f cred sectin and 7.8% f the lwer.m cred sectin. In the lwermst sectin f the hle, stiff, pssibly vercnslidated, clays were encuntered. These clays display sme fine intercalated silt layers. The sands and sandy muds cntain large quantities f rganic material, much f it highly lignitic, which suggest that it is f an lder rigin. In sme instances, nes cnsisting f high percentages f transprted rganics were present. Sedimentary structures in the interbedded sand, silt, and clay sequences indicate transprt by unidirectinal currents, and nly a few nes f distrted (slump) sediments were encuntered. The clays display sme scattered biturbatin, but in general burrwing was minimal thrughut the sequence. The carsergrained sequence cntains a large number f graded beds, and mst f the thinner sands shw finingupward (turbidite) sequences. The thicker sands were cmmnly disturbed by cring peratins, and sedimentary structures were prly defined. Visual inspectin f the cres did nt reveal the presence f gas within the cred sectins. Nne f the cres displayed expansin ut f the liners. The preliminary cnclusins are as fllws:. The sediment sectin penetrated in Hles 64 and 64A is Quaternary, crrelating with the planktnic framinifer Zne N and the calcareus nannfssil Zne NN. This interval includes the Hlcene (< m thick) and upper Wiscnsin glacial (Zne Y). The warm interstadial f the Wiscnsin (Zne X r G. ßexusa Zne) was nt encuntered t a ttal depth at 5. m. The Y Zne cntains mstly rewrked Cretaceus framinifers and calcareus nannfssils within the displaced sands and muds.. Relatively carse displaced sediments have been transprted sme 6 km frm the shelf edge near the head f the Mississippi Canyn t the site during the late Wiscnsin glacial stage. A minimum thickness f 49 m f displaced sediments has accumulated at Site 64 in a relatively shrt perid f gelgic time.. The lithlgic breaks in the upper m f sectin are recgniable n.5kh prfiler recrds. The tp and base f the dminant sandy sectin (8 m) can be recgnied in the seismic recrds and can be used t map this facies. 4. Medium t thick bedded, very fine mediumgrained sand turbidites frm 54% f the sectin recvered and an estimated 7% f the ttal sectin penetrated. Cring distrtin bliterated many lithlgic cntacts, and it can nly be stated that individual units up t m thick are present. The sands cntain significant prprtins f terrigenus plant debris. 5. Muds and silts frm 46% f sectin, interbedded with thick sands. They were depsited frm turbidity currents r ther lw cncentratin flws. Pelagic and hemipelagic sediments are almst entirely absent except in the upper half meter. 6. The lwer 5 m f the sectin appears t be a carseningupward sequence related t lwer fan lbe develpment. The middle 9 m is a "blcky sequence" f thick sands and thinner muddy interbeds. The uppermst 5 m is a finingupward sequence thught t be related t climatic ameliratin and sea level rise thrugh the latest Wiscnsin and Hlcene. It can be cncluded that the area f this site has been relatively inactive fr the past, t 5, yr. 7. N bservable gas expansin cracks r bubbles sufficient fr cllectin and analysis were bserved. The lack f substantial accumulatin f gaseus hydrcarbns may be a result f: () the rapid rates f sediment 96

11 SITE 64 accumulatin, () the carseness f the sediment, () lw micrbial activity because f lw temperatures, high pressure, and lw rganic cntent, (4) the lw gethermal gradient, and (5) lss f gas during cring peratins. 8. The cncept f the develpment f a fan lbe and f sand transprt t the lwer fan area has maintained its validity and n evidence has been fund at this site that disagrees with the basic premise. REFERENCES Blw, W. H., 969. Late middle Ecene t Recent planktnic framiniferal bistratigraphy. In Brönnimann, P., and Ren, H. H. (Eds.), Prc. First Int. Cnf. Plankt. Micrfssils: Leiden (E. J. Brill), : 994. Damuth, J. E., 978. Ech character f the NrwegianGreenland Sea; relatinship t Quaternary sedimentatin. Mar. Gel., 8:6. Ericsn, D. B., and Wllin, G., 968. Pleistcene climates and chrnlgy in deepsea sediments. Science, 6:74. Martini, E., 97. Standard Tertiary and Quaternary calcareus nannplanktn natin. In Farinacci, A. (Ed.), Prc. II Plankt. Cnf. Rma: Rme (Ediini Tecnsciena), : Nrmark, W. R., Piper, D. J. W., and Hess, G. R., 979. Distributary channels, sand lbes, and mestpgraphy f Navy submarine fan, Califrnia Brderland, with applicatins t ancient fan sediments. Sedimentlgy, 6:

12 SITE 64 HOLE CORE CORED INTERVAL 4..5 mbsl;,9.4 mbsf SITE 64 HOLE CORED INTERVAL.5.8 mbsl; mbsf ::trr ~r_ Sectin, 4 cm: MUDDY NANNO FORAM OOZE, live brwn t dark brwn (.5Y 4/4YR 4/I in clr. Sectin, 4 cmcre Catcher: SILTY MUD and CLAYEY MUD, dark gray brwn t dark gray (YR/ 5Y 4/) with thin SILT and SANDY SILT layers. SILTY MUD and CLAYEY MUD, dark gray t dark live gray (YR 4/E>Y /} with thin SILT and SANDY SI LT layers and laminae, and thin SAND beds. MUDS appear structureless, rarely with pssible biturbatin, and are dminantly detrital (quart and carbnate silts and clays), SILTS and SANDY SILTS are cmmnly less than 5 c in thickiihj s, but range up t cm thick as shwn. They SILTS and SANDY SILTS are less than 5 cm thick (quart with minr feldspar and carbnate). Sme f the siltfilled burrws. SMEAR SLIDE SUMMARY (%):. 5,87 D M (qu Nte that the number f silt layers recvered in this { greater than that which appears in the Graphic Lith clumn. These silts are t numerus and thin t illu n this Barrel Sheet, SMEAR SLIDE SUMMARY (%):, 4, 9, Clay Cmpsi unspecified and altered),68 cm = 9%, 77 cm =.5%, 485 cm =.5% Clay 65 Vlcanic glass T Carbnate uπspec. Plant debris Other I,68 cm» 7.%, 68 cm =.5%

13 SITE 64 HOLE CORE CORED INTERVAL.84. mbsl; mbsf SITE 64 HOLE CORE 4 CORED INTERVAL mbsl; 8.. mbsf SILTY MUD and CLAYEY MUD, dark gray t dark live gr; (YR 4/ 5Y /) with thin SILT layers and laminae am SAND, dark gra gray (5Y 4/5Y.5/) SAND beds. MUDS are mainly laminated with either fine silt r darker mud laminae. SILTS range frm less than mm t a few cm in thickness. They are SANDS are dminantly terrigenus (quartrich) and very prly s Catcher include all f the ecvered duri srted (maximum grain sie is abut 7 µm). The thickest send bed SMEAR SLIDE SUMMARY (% SMEAR SLIDE i Sand Silt Clay cm=6.%. 55 cm =.% ered, 5456 cm =.5%, 8 cm =.% 4, 88 cm =.%

14 SITE 64 HOLE CORED INTERVAL mbsl;.7. mbsf SITE 64 HOLE A CORED INTERVAL mbsl; mbsf!5 Sectin, cm: SAND. SILTY SAND WITH INTERBEDDED MUD and SILT. Sectin, 4 cm: defrmed MUD layer. Sectin, 495 cm: SAND and MUD drilling breccia. leneus, SILTY SAND that changes in clr fri live gray (5Y /) t very dark gray (5Y /) dv. Sectin, 95cm5, Cre Catcher: thick SANDY SILT t S LTY SAND bed. Apart frm nrmal grading frm SILTY SAND at the base (maximum grain sie 8 µm) t SANDY SILT at the tp (maximum grain sie = dminantly terrigenus (quartrich). Olive gray (5Y 4/). SMEAR SLIDE SUMMARY (%): 9 cm. Interbedded MUD and SILT (SANDY SILT) layers c at Sectin, cm and Sectin, 567 cm. The SILTS are live gray (6Y 4/); the MUDS range frm dark gray (5Y /) t dark live gray (5Y /). Quart Feldsps, 55 cm =.%, cm =.5%.cm=.% 5, 8 cm ".5% fijt)

15 SITE 64 HOLE A CORE CORED INTERVAL mbsl; mbsf MUD and SILTY SAND. s f highly disturbed. (5Y / MUD. rganic fragments, suggest SMEAR SLIDE SUMMARY (% *, 8688 cm = 8.% 6, 6769 cm = 9.% SITE > 8 I 64 O rx r JBIO! > ^ c 5 S HOLE A FOSS CHARAC j < L TER I"QMS CORE n: l 4 CA s.5. _ Ẕ ; i/5 S;: i\;i:' : ii; : ;jv. : :: :!;: W)^S v>?ss I KS : SSS/Wj : : :ft : ; V:'/ V.\\ v. : : :' i Z ; I CORED GRAPHIC LITHOLOGY y : λ : r :: Y: :.'ir:' : 'i : '. : : '': V:VJ'.' '^'i ':' ' '*" ' '>'/ X;);y..*:!;;:..: ;:.';:.;'.':;'. ;. ';.. ;:; V V.':';!. :'\:::" ; '.. : ;; ;;V Λ>V;: '.'::. : Λ ;. ;.:'..::.::;; i^s^v: i;;.';! ;:?ii : ó :/"/ '. : i ;.lv:'f.'i: :. :.; : ' : ; ; _ I %&* * INTERVAL mbsl; mbsf I S <l = SU SS * SILTY SAND. Entire cre cnsists f slightly supy, dark live gray (5Y /), quartrich, hmgeneus SILTY SAND. SMEAR SLIDE SUMMARY (%):, D Texture: Sand 4 Silt 58 Clay Cmpsitin: Quart 65 Feldspar Mica Carbnate unspec. Calc. nannfssils T Altered minerals, cm =.% FP) CC 5 ; O

16 O NJ SITE 64 HOLE A CORED INTERVAL mbsl; mbsf SITE 64 HOLE A CORED INTERVAL mbsl; mbsf SILTY SAND with interbedded SILTY MUD, SILT, and MUD laminae. Sectin, cm Sectin, cm: this interval cnsists f slightly t mderately defrmed interbedded MUD, SILTY MUD, and SILTY SAND. MUD and SILTY MUD Sectin, 757 cm cntains laminated and bedded MUDS with silty bases and ne SILT bed (869 cm). The dark laminae and beds are dark live gray (5Y /); the light nes are dark gray (5Y 4/). The amunt f the rganicrich laminae is black (.5Y /). The SILTY SAND bed is nrmallygraded with sharp bttm and gradatinal tp cntacts. Sectin, 565 cm cntains interbedded SILTY SAND and SILTY MUD with gradatinal cntacts. blebs and layers are dminantly dark live gray (5Y /); SILTY SANDS are live gray (5Y 5/). Varying prprtins f MUD/SILTY MUD and SILTY SAND dwn Sectin, cmsectin 4,5 cm: this interval cnsist (5Y /), hmgeneus SAND layer. SMEAR SLIDE SUMMARY (%):, 8, 6 4, Quart Feldspar, 485 cm =.%, 5759 cm =.5%, 9 cm = 7.%, 4 cm =.%

17 SITE 6 HOLE A CORE 5 CORED INTERVAL mbsl; mbsf SITE 64 HOLE A CORE 7 CORED INTERVAL mbsl; mbsf E Hi cf y a. H BIO! N> * ^ " ui i FOR FOSS L CHARACTER Θ I CC ;TION V) 4 5 TERS ~ I I GRAPHIC LITHOLOGY :Y: HjlH :}V;^ "" : ":V I *: ". : : VVΛ IllIll ' ; 'y '''/' J.'; '.''?.' KO Vi \:Ay>;."J _: /;^ ;:_.>"V: ';;:.\V; v. : :'. Y : v^::!v *.;:y^ 'iyjj:;:"!;*..:;;;::':/.' v Vt^^^'!\^''.'.'^. ;v. ;... :. :'^' ;.fv ;:' :.. :;yyv/v;:v.v; J DB O i" S * * KB SILTYSAND. Entire cre cnsists f slightly supy, dark live gray (5Y /), very prly srted, quartrich, hmgeneus SILTYSAND. Small MUD blebs (rip up clasts?) ccur at Sectin, 44 cm and Sectin cm. Smewhat denser (less supy) SILTY SAND intervals ccur at Sectin, 544 cm; Sectin, 87 cm, 4555 cm. and 99 cm; and Sectin 5, 56 cm. SMEAR SLIDE SUMMARY (%):,8, 5 D D Texture: Sand 55 Silt 4 5 Cmpsitin: Quart 65 Feldspar Mica Heavy minerals Clay 5 85 Pyrited/paques Carbnate unspec. Framinifers T Calc. nannfssils T Plant debris T Other *, 77 cm =.% O E itigr/ ONE ST 5 i Ni FOSSIL CHARACTER IIL < 5 s 5 LU CC TERS GRAPHIC LITHOLOGY I 8 i ^ D si 55 SS i ill = Sectin, cm: SILTY SAND. Slightly defrmed. live gray (5Y 4/), very prly srted, quartrich. nrmallygraded, and hmgeneus. MUD) and MUD. Light clred laminatins are dark live gray (5Y /); dark clred laminatins are black (5Y /). These laminatins range frm.. cm thick. and are smewhat indistinct at Sectin, cm. and blebs f SILT. MUD is dark live gray (5Y /); SILT is dark gray (5Y 4/). Number f discntinuus Sectin, 995 cm: SILTY MUD. Welllaminated, and rganicrich. Sectin,954 cm: SILTY SAND. Slightly defrmed. rich, and hmgeneus. Tw thin rganicrich layers ccur at 4 and 5 cm. Cre Catcher: well laminated MUD (Cre Catcher, cm) and SILTY SAND (Cre Catcher, cmbase). Laminatins are mm thick. SMEAR SLIDE SUMMARY (%): Texture:,, 6 D D Sand 6 Silt 5 7 Clay 5 9 Cmpsitin: Quart 8 5 Feldspar Mica Heavy minerals Clay 5 9 Pyrite/paques Carbnate unspec. 5 Framinifers Calc. nannfssils Plant debris Altered minerals 5 Sectin, 994 cm =.%

18 Z SITE 64 HOLE A CORED INTERVAL mbsl; mbsf.ithologic DESCRIPTION Sectin. cmsectin, 9 cm: MUD interbedded with numerus SILTY MUD, MUDDY SILT, and SANDY SILT layers. The MUD is dark live gray (BY.5/). Interbedded SILTS are thin (less than t cm thick); sme are graded and crsslaminated. Sectin, 9 cmsectio", 6 cm; hmgeneus dark gray/live gray (5Y 4/.5), quartrich SILTY SAND. Nte: lcatins f interbedded SILTS are schematically shwn by slid lines in the Sedimentary Structures clumn. SITE 64 LU O itigr/ ONE cc BIOST ) : > g. N =» ^LLj I=FORAR, S HOLE FOSS L CHARACTER u LL θ I < I CORE 9 UJ TERS.5. CORED NTERVAL mbsl; mbsf GRAPHIC LITHOLOGY fffjggj 7.;; :..; ; :..;' : :;;^;. ; ;::.; : WËËÈ~ \ m ^ ID 5 O! Is LU SAMPL * SILTY SAND. This cre cnsists dminantly f dark live gray (5Y.5/). SILTY SAND. The SILTY SAND in Sectin, 557 cm and Sectin cntains dark live gray (5Y /) MUD clasts and blebs. The MUD clast at Sectin, 566 cm is laminated. SMEAR SLIDE SUMMARY (%): Texture: Sand 74 Silt 5 Clay Cmpsitin: Quart 7 Feldspar 5 Mica Heavy minerals Clay Pyrite/paques Carbnate unspec. 6 Framinifers T Calc. nannfssils Plant debris, D T T Altered minerals 5 Sectin, 664 cm =.%,99 cm = 8.%, 68 cm = 6.% SITE 64 HOLE A CORE CORED INTERVAL mbsl; mbsf dark gray I5Y /) MUD. This MUD cntains blebs and thin, discntinuus layers f SILTY MUD frm cm, 4 cm, and 64 cm. The Cre Catcher was badly disturbed during cring and deck handling and cnsists f intermixed dark live gray MUD (5Y /) and SILTY SAND (5Y.5/). Sectin,S688cm 4.5%

19 \ _ " ". " " _ " ^ β iw V SITE 64 HOLE A CORE CORED INTERVAL mbsl; 7 mbsf SITE 64 HOLE A CORE CORED INTERVAL mbsl;.4.7 mbsf MME ROC UNIT STRATIGR/ ZONE BIO FOF FOSS L CHARACTER j I SECTION METERS.5.? \ GRAPHIC LITHOLOGY y ':: 'i : &r~~'~.'. ü s I => H ^i T" Vid Wh f t d f j. bdt f variable thickness (ranging frm less than t mre than cm). These turbidites are typically graded frm FINE SILT r SANDY SILT at the base t MUD at the tp, with the standard vertical sequences f clrs and structures detailed in the diagram belw. Variatins: sme f the turbidites grade frm muddy silt TIME ROCK UNIT BIOSTRATIGRAPHIC ZONE F: Zne Y N: E. huxleyi INN) FOSS CHARAC O L TER SECTION METERS GRAPHIC LITHOLOGY :.:r.it:_:_. i Z D Sectin, 9 cm: MUD with tiny SILTY MUD blebs and ne discntinuus SILTY MUD layer at 5 cm. MUD is dark live gray (5Y /). Sectin, 9 cm: a cmpsite f the MUD chunks fund in the Cre Catcher. This mud is identical t that recvered in Sectin, 9 cm. Pleistci > fi CC : : ifllil; I rtt > OGP at the base t mud upsectin and are f a darker grayish clr. Sme f the turbiditic silts are whiter in clr mu in erva s may be s ig y urrwe. COLORS Medium grey I5Y/I 5Y.5/ and fnterlaminated STRUCTURES AND GRAIN SIZE \ Structureless gray mud.:'. \ silt blebs (biturbatin?) A Paralellammatln _ ^_\ Lwamplitude crsslaminatin SITE 64 HOLE A CORE CORED INTERVAL mbsl; mbsf ; >V_''\ Crsslaminatin Black (.5Y /) Light gray (5Y.5/).";.' i". "\ Cnvlute laminatin i. _rl. :\ "Carser" layer f lignitic sand ": '"..' '. :' '"!y \ ' ''.' :':;*'' : :. ' J l^!,"^,, para e i Cre Catcher nly. Scured base. SMEAR SLIDE SUMMARY (%):, 6, D D Texture: Sand Silt 8 6 Clay Cmps tin: Quart 5 7 Feldspar 4 T Mica T Heavy minerals Clay Palagn te T Pyrite/paques Micrndules T Carbnate unspec. 8 Framinifers Calc. nannfssils T Plant debris Altered minerals, etc. 5, 665 cm = 7.%, 485 cm.%

20 SITE 64 (HOLE 64) Ocm, ,CC L 5 6

21 SITE 64 (HOLE 64) ~~ ,CC ,CC L 5 7

22 SITE 64 (HOLE 64) n ,CC

23 SITE 64 (HOLE 64A) p Ocmi h5 H5 h75 M I 5,CC l 5 9

24 ,CC SITE 64 (HOLE 64A) r n. m im \j cm M M a a a a a B B M B M I M ^ I ^ p ^M^^^ ββ i» r~ h5 I 5,CC h75 I 4.CC I 5 5

25 p cm i SITE 64 (HOLE 64A) ,CC , : '.mi 6,CC 5 5

26 SITE 64 (HOLE 64A) cm i 8 9 9,CC h5. CC h5 h75 M h5,cc 5