Rea, D.K., Basov, I.A., Scholl, D.W., and Allan, J.F. (Eds.), 1995Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 145

13. COMPOSITE DEPTH SCALE AND STRATIGRAPHY FOR SITES 885/8861

Gerald R. Dickens,2 Hilde Snoeckx,2 Eve Arnold,3 Joseph J. Morley,4 Robert M. Owen,2 David K. Rea,2 and Lynn Ingram5

ABSTRACT

Shipboard whole-core volume magnetic susceptibility records at Holes 885A, 886A, 886B, and 886C were aligned accordingto sedimentary depth to construct a composite depth scale for Sites 885/886. The composite depth scale then was checked forstratigraphic equivalence at each of the four holes with available polarity chron boundaries and isochronous radiolarian events.Samples from Holes 885A, 886B, and 886C subsequently were analyzed for Ba, Fe, La, and Se by instrumental neutron activationanalysis. Downcore profiles of these elements (as well as results presented in other papers of this volume) indicate the compositedepth scale typically allows for intercorrelation to within 0.4 m between holes at Sites 885/886. This composite depth scale hasimportant ramifications toward understanding the stratigraphy of Sites 885/886.

INTRODUCTION

Ocean Drilling Program (ODP) Sites 885/886 are located in thecentral subarctic Pacific Ocean approximately 60 km south of theChinook Trough. The two sites are proximal (within 2.3 km), and con-sist of four holes cored with the advanced hydraulic piston corer (APC):Hole 885A (44°41.296'N, \6%°\63WW), Hole 886A (44°41.384'N,168°14.416'W), Hole 886B (44°41.384'N, 168°14.416'W), and Hole886C (44°41.384'N, 168° 14.400^). Drilling disturbance initially wasreported as minimal at all four holes (Rea, Basov, Janecek, Palmer-Julson, et al., 1993). Sediment recovered at the holes predominantlyconsists of variable proportions of clay, diatoms, and Fe-Mn oxy-hydroxides (Rea, Basov, Janecek, Palmer-Julson, et al., 1993).

Primary drilling objectives at Sites 885/886 included trackingchanges in the accumulation rates of Cenozoic eolian inputs anddetermining the timing and onset of Neogene siliceous sedimentationin the central North Pacific (Rea, Basov, Janecek, Palmer-Julson, etal., 1993). Realization of these objectives requires accurate placementof age datums and reasonable estimates for the amount of sedimentdeposited between age datums. It is of interest, therefore, to intercor-relate Holes 885A, 886A, 886B, and 886C according to a compositedepth scale such that (1) age datums from one hole may be transferredto an adjacent hole where ages have not yet been determined, and (2)depth offsets, intervals of distortion, and hiatuses can be accountedfor (see review in Hagelberg et al., 1995).

PROCEDURE

Individual cores from each hole were adjusted along a compositedepth scale such that variations in magnetic susceptibility recordsoccurred at similar depth horizons (magnetic susceptibility recordsdetermined by the automated multisensor track were used because theydisplay the largest variability of any high-resolution shipboard mea-surement at Sites 885/886). Where distances between common pointsof variation in a single core differed between proximal holes, it wasassumed that either (1) the lesser interval represented sedimentarycompression and/or contained a hiatus; or (2) the greater interval repre-sented sedimentary expansion. In this paper (in contrast to Murray and

Rea, D.K., Basov, LA., Scholl, D.W., and Allan, J.F. (Eds.), 1995. Proc. ODP, Sci.Results, 145: College Station, TX (Ocean Drilling Program).

2 Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1063, U.S.A.

3 Graduate School of Oceanography, University of Rhode Island, Narragansett, Rl02882-1197, U.S.A.

4 32 West End Avenue, Westwood, NJ 07675, U.S.A.5 Department of Geology and Geophysics, University of California, Berkeley, CA

94720, U.S.A.

Prell, 1991; Hagelberg et al., 1992), we chose to linearly stretch (orbreak) lesser intervals such that distances between common points ofvariation are equivalent at each hole. This choice is favored becausethe composite sedimentary record at Sites 885/886 is relatively short(a maximum of eight cores at Hole 886C) and because several lengthy(>l.O m) intervals of nondeposition occur within individual cores.After completing this step, distances between the base and top ofsuccessive cores were assumed to be either recovery gaps (positivevalues) or coring overlaps (negative values). The intercorrelationprocess, therefore, involved splicing together pieces of different holesto provide a continuous sedimentary record. Such intercorrelationrenders a composite record that typically is a different length (oftenlonger) than the length of any hole used to construct the compositerecord (e.g., Murray and Prell, 1991; Hagelberg et al., 1992, 1995).Hence, depths on the composite record are reported in meters com-posite depth (med) to distinguish them from "true" depths.

Although sedimentary inputs likely were similar through time atthese four proximal holes, postdepositional processes may have dif-fered significantly between Hole 885A and the three holes at Site 886.Therefore, we attempted to use magnetic susceptibility datums fromcores at Site 886 to construct the composite depth scale; that is,datums at Hole 885A only would be tied to those of Holes 886A,886B, and 886C subsequent to alignment of holes at Site 886. How-ever, because sediment appears to be missing in Core 145-886C-4H,and because of incomplete recovery of Core 145-886C-5H, intervalsfrom Hole 8 85A are needed to piece together the entire compositedepth scale.

The final steps in our hole intercorrelation involved verificationthat selected magnetic susceptibility datums were indeed stratigraphi-cally equivalent. This first was accomplished by checking that polar-ity chron boundaries and isochronous radiolarian events occurred atsimilar composite depth in each of the four holes. However, becausethese markers are limited in number and nonexistent in lowermostsediment at Sites 885/886 (Rea, Basov, Janecek, Palmer-Julson, et al.,1993; Morley and Nigrini, this volume), we plotted bulk elementalconcentrations downcore in the anticipation that chemical variationsat each hole also could be aligned according to composite depth(Heath et al., 1985). It is assumed that downcore variations in geo-chemistry at each of the four holes record changes in lithology and/orpaleoceanography but that these changes are not "time transgressive"over the 2.3 km distance between the four holes.

Bulk sediment Ba, Fe, La, and Se concentrations were determinedon discrete 5-cm samples from all cores at Holes 885A and 886B, andon Cores 145-886C-7H and -8H by instrumental neutron activationanalysis (INAA) using the nuclear reactor and counting facilities at thePhoenix Memorial Laboratory, University of Michigan. Individualsamples were freeze-dried, homogenized (within a ceramic mortar and

G.R. DICKENS ET AL.

300

Depth (mbsf)

B 300

£ 200 -

Q.α>o

100 -j

Φ

1 1 1 1 1

886C

: \

" , 886A .'• ;. , ;"'. ,

» 885 A "^V j

i i i i

i i i i 1

\

i i i i 1

• • i i

i/fjl 886B K

, .*

1 f ' \

Depth (mcd) 10 15

Figure 1. Example demonstrating how cores can be adjusted along a depth scale such that prominent variations in whole-core volume magnetic susceptibility willoccur at a similar composite depth. A. The magnetic susceptibility records in the upper 15 m at Holes 885A, 886A, 886B, and 886C clearly are not aligned accordingto meters below seafloor (mbsf). B. These records, however, can be aligned according to composite depth (mcd). The magnetic susceptibility records of Holes886A, 886B, and 886C have been offset by successive 50-mA/m increments for clarity.

pestle), and analyzed as follows. Approximately 250 mg of each sam-ple was enclosed within a prewashed, high-purity quartz tube, irradi-ated for 20 hr on a rotating holder, counted for 67 min after a decay of1 week, and analyzed for Ba and La. These same samples were re-counted for 67 min after a decay of 5 weeks, and analyzed for Fe andSe. Samples received a thermal neutron flux of approximately 5 × I012

neutrons/cm2/s and were counted using a pair of multiplexed Ge-Ligamma detectors. Gamma lines used for analysis were 496.26,1099.25,1596.54, and 889.25 KeV for Ba, Fe, La, and Se, respectively. Concen-trations for all four elements were obtained through standard compari-son with NBS-SRM-1633a (coal fly ash), and with half-lives listed inBrowne and Firestone (1986). Analytical precision (lσ) typically wasless than 4% for analyses of Fe, La, and Se, and less than 8% for Ba.

RESULTS AND DISCUSSION

Hole Intercorrelation

Downcore variations in magnetic susceptibility at Holes 885A,886A, 886B, and 886C do not correlate with respect to depth whenplotted according to meters below seafloor (mbsf). This depth offsetbetween holes is arrant over the length the sedimentary column (Rea,Basov, Janecek, Palmer-Julson, et al., 1993, p. 313) and pronouncedin the upper 15 m (Fig. 1 A). However, prominent variations in mag-netic susceptibility can be aligned such that they occur at a similarcomposite depth. Such alignment is demonstrated in detail for theupper 15 m (Fig. IB) and can be extended to the entire sedimentary

column at Sites 885/886 (Fig. 2). The depths of the magnetic suscep-tibility datums (to the nearest 0.05 m) that have been used for thisprocedure are listed in Table 1. The intercorrelation presented here(Fig. 2, Table 1) differs somewhat from that in Rea, Basov, Janecek,Palmer-Julson, et al. (1993, pp. 313,318). In particular, (1) lowermostsediment at Hole 885 A (>50.6 mbsf) is correlated to lowermost sedi-ment at Hole 886C (>71.1 mbsf), (2) the uppermost intense peak atHole 885A (5.00 mbsf) is correlated to the uppermost intense peaksat Holes 886A (4.25 mbsf) and 886B (11.05 mbsf), and (3) the broadpeaks at 13.10 and 16.70 mbsf at Hole 886C are the same peak.

Shipboard determinations of polarity chron boundaries at each ofthe four holes provide a first check on the suggested magnetic suscep-tibility alignment. Depths of 13 (of the identified 15) polarity chronboundaries are consistent with hole intercorrelation, inasmuch astheir composite depth positions at each hole lie within 0.3 m of oneanother (Table 2). The Matuyama/Gauss boundary only is aligned towithin 0.8 m (Table 2). The likely cause for the misalignment of thispolarity chron boundary between Hole 885A and Holes 886B and886C is discussed below. The polarity chron boundary observed at51.3 mbsf at Hole 885A is not listed in Table 2 because it clearly isnot the onset of C5n.2n as suggested by Rea, Basov, Janecek, Palmer-Julson, et al. (1993, p. 318). Strontium isotopic analyses offish teeth(Ingram, this volume; Snoeckx et al., this volume) and geochemical/tectonic arguments (Dickens and Owen, this volume) indicate thatsediment at this depth at Hole 885A was deposited during the LateCretaceous rather than during the late Miocene.

206

COMPOSITE DEPTH SCALE

~. 300

200 -

-

_-

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CO

1 °Q-

< CD

CL CL

CMQ. «

c

C<5^ CL

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CL

A

o

0 .

rt

ft‰-^.

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Depth (mcd) 15

« 150

Depth (mcd)

Figure 2. Aligned whole-core volume magnetic susceptibility records for the entire sedimentary column at Sites 885/886. The records at Holes 885A, 886A, 886B,and 886C have been aligned according to datums listed in Table 1 with linear stretching/compression between datums. The "splices" used as references to stretch/compress intervals at other holes are listed in Table 5.

A second evaluation concerning the stratigraphic alignment ofmagnetic susceptibility datums are downcore changes in radiolarianfauna. Isochronous radiolarian events (first or last occurrences ofcertain radiolarian species) at Holes 8 85A and 886C (Morley andNigrini, this volume) indeed occur at similar composite depth hori-zons (Table 2). Hence, available time datums (polarity chron bounda-ries and isochronous radiolarian events) indicate that the compositedepth scale is stratigraphically equivalent at all four holes at lowresolution within the upper 52 mcd. This is illustrated best by a plotof isochronous datums at two holes according to mcd (Fig. 3).

Downcore bulk concentrations of Ba, Fe, La, and Se (Table 3) gen-erally support the suggested intercorrelation of Holes 885A, 886B,

and 886C at a much higher resolution. Variations in these elementsare aligned to within 0.4 m (Fig. 4), with the exception of three inter-vals. Between 12 and 15 mcd, depths at Holes 885A and 886B areoffset (observed best in the downcore Ba profile). The chemicalrecords at Holes 885 A and 886B also are dissimilar at or near 30 mcd.These two discordant depth intervals are discussed below. Sedimentbetween 20 and 22 mcd is intercorrelated poorly as evident in bothdowncore chemistry and magnetic susceptibility records (Figs. 2 and4), but a better alignment on the basis of prominent magnetic suscep-tibility datums is not obvious.

Importantly, bulk chemistry analyses support the proposed corre-lation of magnetic susceptibility variations in lowermost sediment at

207

G.R. DICKENS ET AL.

Table 1. Magnetic susceptibility datums used to intercorrelate holes atSites 885/886.

Hole 886C depth (mcd)10 20 30 40 50 60

Datum

PeakOPeak OBPeak IAAPeak 1APeak IBTroughPeak 2TroughPeak 3APeak 3Peak 4Peak 5Peak 6APeak 6Peak 7Step 7BPeak 8Peak 9Peak 10Step 10BPeak 11Peak 12Peak 13TroughPeak 14Step 15Peak 16Peak 17Peak 18Peak 18BPeak 19APeak 19Peak 20Step 21Step 22Peak 23Peak 24APeak 24TroughPeak 25APeak 25TroughStep 26AAStep 26ATroughPeak 26TroughTroughStep 27Peak 28TroughPeak 29Peak 30Step 31TroughBasalt contact

Hole885A

0.350.801.551.902.102.402.853.403.854.055.006.757.407.708.058.15?8.609.259.75

10.5011.4513.3013.7514.8015.8518.8021.8526.5530.0030.9532.4533.0033.6034.7535.5536.6039.8540.5042.0543.6544.6546.1546.9047.5047.7548.1048.60

748.7048.9549.35

NR49.5550.6551.4552.30

Depth (mbsf)

Hole886A

TH0.751.101.351.752.603.053.203.504.256.156.807.007.307.457.858.509.00EH

Hole886B

0.351.05

?RGRGRGRG2.002.10

2.25?, 10.2511.05RGRGRGRG

11.4012.1012.9513.5514.7016.1018.6519.15

7

22.8025.05

9

32.4035.4036.4038.1038.5539.7040.4041.4042.8546.7047.50

RG50.0050.9552.30

753.5053.6054.4555.2556.4556.7057.8058.30

NRNRNRNR

68.80

Hole886C

0.401.102.002.552.803.154.104.50

74.80

76.206.65RG7.207.508.008.909.5011.20

13.10,16.7018.9519.4022.3024.45

30.1533.7035.8537.1039.1539.70NRNRNRNR

48.3549.0551.1552.8054.1055.5556.8057.8057.9558.2058.8060.3060.8061.8562.1062.7064.1571.2071.90EH

Depth(mcd)

0.401.102.002.552.803.154.104.554.705.005.757.658.308.508.808.959.35

10.2510.8512.5514.4517.0017.5020.4022.5525.5028.5532.1035.1036.1037.8038.2539.4040.5541.5543.0046.9047.6549.7551.4052.7054.0554.7055.2555.3555.6056.2057.7058.2059.2559.5060.1062.3069.3570.0570.90

Notes: Identification of magnetic susceptibility datums shown in Figure 2. Depths ofmagnetic susceptibility datums reported to the nearest 0.05 m. TH = top of hole, EH= end of hole, RG = recovery gap, and NR = not recovered.

Holes 885A and 886C (in contrast to Rea, Basov, Janecek, Palmer-Julson, et al., 1993, p. 313). Shipboard work suggested that the peak(our Peak 30) at 49.55 mbsf and trough at 51.45 mbsf at Hole 885 Awere aligned to the peak (our Peak 29) at 62.70 mbsf and trough at63.60 mbsf at Hole 886C. Although these shipboard interpretationsare acceptable on the basis of magnetic susceptibility values, theyclearly are inconsistent with bulk chemistry (particularly Fe and Laconcentrations; Table 3, Fig. 4).

Changes in rock magnetic parameters (fig. 1 in Arnold et al., thisvolume) and weight percentage of extracted component (fig. 4 inSnoeckx et al., this volume) are aligned to within 0.4 m, excluding theaforementioned intervals between 12 and 30 mcd.

Stratigraphic Implications of the Composite Depth Scale

Assuming similar sedimentation rates at Holes 885A, 886A, 886B,and 886C, the suggested intercorrelation of these holes implies that

Figure 3. Plot of polarity chron boundaries and isochronous radiolarian eventsat Holes 885A and 886C according to composite depth (mcd). As evident byall data positioned on a line with an origin (0, 0 mcd) and slope = 1, the twoholes are aligned such that they are stratigraphically equivalent. Error bars fordepths of polarity chron boundaries are assumed to be 0.10 m, whereas thosefor radiolarian events are assumed to be the sampling distance in which theevent occurs.

recovery gaps range from 0.10 to 2.85 m at Sites 885/886 (Table 4,Fig. 5). Several coring overlaps also occur, and these range from 0.10to 3.60 m (Table 4, Fig. 5). The range of depth offsets (including bothgaps and overlaps) is similar to that observed at sites drilled duringODP Leg 138 (Hagelberg et al., 1992) and other sites drilled duringLeg 145 (Rea, Basov, Janecek, Palmer-Julson, et al., 1993) with thenotable exception of the 3.60 m overlap between Cores 145-886C-2Hand -3H. Three of the core breaks are associated with minor drillingdisturbance (<25 cm in length), but only the overlap between Cores145-886C-6H and -7H occurs in highly disturbed sediment (Table 4).Thus, the proposed 3.60 m coring overlap at Hole 886C might seemspurious. However, although we cannot explain its origin, this lengthyoverlap is supported by a 3.0 to 4.5 m repetition of radiolarian faunaassemblages in the lowermost three sections of Core 145-886C-2Hand the uppermost three sections of Core 145-886C-3H (Morley andNigrini, this volume). The above depth offsets at core breaks only canbe offered as rough estimates because postdepositional processes atthese holes were dissimilar (i.e., there are intervals within cores inwhich the length of sediment at one or more holes is significantly lessthan at other holes, see below).

The break between Cores 145-886C-7H and -8H has no adjacenthole in which to determine depth offset; however, the significantchange in chemistry (Table 3) across this core break suggests eithera recovery gap and/or the presence of a hiatus. On the basis of mod-eling the flux of hydrothermal materials to this lowermost sediment,Dickens and Owen (1993) initially estimated that a recovery gap ofapproximately 0.75 m spanned this core break. This model did notinclude the possibility that a prominent hiatus might exist at or nearthe core break (as suggested by strontium isotopic analyses of fishteeth, see below). Thus, although this 0.75 m recovery gap has beenretained for construction of the composite depth scale, it must beregarded as an arbitrary value.

The interval surrounding 30 mcd (within the core of the "diatomdump"; >95 % biogenic silica, Snoeckx et al., this volume) poses anintercorrelation problem: there is a paucity of magnetic susceptibilityinformation at Holes 885A, 886B, and 886C; the bottom of Core145-886B-4H was not recovered (including possibly, Peak 16); and

208

COMPOSITE DEPTH SCALE

Table 2. Composite depths for polarity chron boundaries and isochronous radiolarian events at Sites 885/886.

Boundaryor event

RRPPPRPPPRPRRPPPPRPRRPPR

Datum

LO S. acquiloniumLO S. universusBrunhes/MatuyamaTermination JaramilloOnset JaramilloLO L. heteroporosTermination OlduvaiOnset OlduvaiMatuyama/GaussF0 C. davisiana davisianaGauss/GilbertLO D. bullatusLO S. peregrina (see below)Termination C3An.lnOnset C3An.InTermination C3An.2nOnset C3An.2nFO L. heteroporosTermination C4n.InT S. delmontensis-S. peregrinaF0 S. acquiloniumOnset C4n.2nTermination C4AnLO L. nipponica magnacornuta

Age(Ma)

0.40.550.780.981.051.71.761.982.602.93.554.2

-5.05.715.956.086.386.57.257.557.77.898.538.8

Hole885A

1.52-3.671.52-3.67

4.855.706.14

6.56-8.109.5910.6015.14

14.86-16.9323.75

27.95-29.4531.80-33.14

35.4837.0538.4940.61

41.83^13.7845.98

47.35^19.3449.34-51.57

51.3052.01

51.57-53.24

Depth (mcd)

Hole886A

4.885.716.20

9.5510.5214.58

23.61

35.4637.31

46.11

Hole886B

14.6015.29-16.99

23.7526.40-28.29

45.89

Hole886C

1.14-2.642.64^.14

5.84-9.309.3810.53

31.34-33.75

37.90-44.63

47.51^9.0449.04-50.54

51.2551.72

50.54-52.90

Notes: Ages and unconverted depths (mbsf) for polarity chron boundaries (P) and radiolarian events (R) are found in Rea, Basov, Janecek, Palmer-Julson, et al. (1993) and Morley andNigrini (this volume). For radiolarian events, LO = last occurrence, FO = first occurrence, and T = species transition. The LO of 5. peregrina is diachronous throughout the NorthPacific (Morley and Nigrini, this volume), but is assumed to be isochronous at Sites 885/886.

core breaks occur at Holes 885A and 886B. We have chosen to useHole 886C to construct the composite record across this intervalbecause it does not contain a core break. This interpretation impliescoring overlaps between Cores 145-885A-3H and -4H (1.15 m), andbetween Cores 145-886B-4H and -5H (0.75 m). However, Core 145-886C-4H appears to be compressed by up to 1.5 m on the basis oflengths between available magnetic susceptibility peaks. Intercorre-lation between holes at or near 30 mcd, therefore, may be off by up to1.5 m. Indeed, studies concerning sedimentation rates should con-sider the possibility that some degree of compression may haveoccurred at all holes at or near 30 mcd as a result of drilling throughsoft diatom ooze.

In addition to expected depth offsets between successive cores, theintercorrelation of Holes 885A, 886A, 886B, and 886C presentedhere has several important implications concerning the stratigraphyof Sites 885/886 (Table 4, Fig. 5).

First, the middle portion of Core 145-886B-2H is a conundrum.Between 2.60 and 10.25 mbsf, no obvious correlation is presentbetween the magnetic susceptibility record at Hole 886B and therecords observed at the other three holes. This correlation problemalso is apparent in comparison of downcore magnetic inclinationrecords (Rea, Basov, Janecek, Palmer-Julson, et al., 1993, p. 312).Because inclusion of this 7.50 m depth interval renders unreasonablelinear sedimentation rates at Hole 886B, we conclude that it is "extra"sediment (i.e., sediment is not "missing" at the other three holes).However, because this interval does not appear to be "flow in," aslump deposit, or a repeated section, the origin of this interval remainsinexplicable. We suggest that future investigations avoid the middleportion of Core 145-886B-2H until a good hypothesis concerning itsorigin is forwarded.

Second, a hiatus exists at Hole 886C between 4.80 and 6.10 mbsf,and represents 1.25 m of depth offset relative to the composite sedi-mentary record. The hiatus is observed in the sedimentary column bygradational and sharp contacts between 5.86 and 6.10 mbsf (Rea,Basov, Janecek, Palmer-Julson, et al., 1993), and also is inferred fromradiolarian fauna assemblages by the limited depth range of Eucyr-tidium matuyamai (Morley and Nigrini, this volume). This particularhiatus at Hole 886C appears to be hole specific.

Third, the interval between 9.75 and 15.85 mbsf at Hole 885A isgreatly compressed relative to stratigraphically equivalent sediment

at Holes 886B and 886C, and represents 5.60 m of depth offsetbetween Hole 885 A and the composite sedimentary record. Althoughup to 1.85 m can be accounted for by a recovery gap between Cores145-885B-2H and -3H, portions of this interval (1) were depositedmore slowly than at Site 886, (2) have been compressed during drill-ing, and/or (3) contain multiple hiatuses. The latter two possibilitiesseem more reasonable given the proximity of Sites 885 and 886 toeach other. However, because drilling disturbance and/or sedimentarycontacts are not evident in this interval at Hole 885A, available dataprevent discrimination between any of these possibilities. Moreover,the aforementioned misalignment of the Matuyama/Gauss boundaryand bulk chemistry values suggests that simple linear stretching of thesediment in the "compressed" interval at Hole 885A is not valid.

Fourth, Sections 145-885A-6H-5 and -6H-6 contain three con-spicuous hiatuses. Based upon a combination of the results frommagnetic susceptibility and bulk chemistry analyses, these hiatusesoccur between 48.65 and 48.70 mbsf, 49.41 and 49.55 mbsf, and50.40 and 50.65 mbsf, and represent approximately 2.00, 1.90, and5.95 m, respectively, of "missing" sediment relative to Holes 886Band/or 886C. A color change (apparent in color photographs but notdescribed in core barrel sheets) is observed at approximately 50.30mbsf at Hole 885 A; this color variation likely marks the lower of thethree hiatuses. Although a color change and/or a sedimentary contactis not observed for either of the upper two hiatuses, ages determinedfrom strontium isotopic analyses of fish teeth (Ingram, this volume;Snoeckx et al., this volume) are consistent with such an interpretation,inasmuch as they indicate that >IO m.y. of sedimentation is missingbetween 44.60 and 47.6 0 mbsf, and that >25 m.y. of sedimentation ismissing between 49.10 and 52.10 mbsf. Evidence provided by stron-tium isotopic analyses further suggests that the upper two hiatuses arepresent at Site 886. Lengthy (> 10 m.y.) gaps in the sedimentary recordoccur between 54.27 and 55.05 mbsf at Hole 886B, and between57.15 and 58.65 mbsf, and 61.90 and 68.15 mbsf at Hole 886C(Ingram, this volume; Snoeckx et al., this volume). The depth intervalof the composite record between approximately 55 and 62 mcd there-fore represents a time where hiatuses occur at both Sites 885 and 886,but where more sediment effectively was removed at Hole 885Athan at Holes 886B and 886C. The roughly exponential decrease inhydrothermal deposition through time at Hole 886C (Dickens andOwen, this volume), however, does suggest that Core 145-886C-8H

G.R. DICKENS ET AL.

Table 3. Elemental concentrations for samples from Holes 885A, 886B, and 886C.

Core, section,interval (cm)

145-885A-1H-1,5-101H-1,80-851H-2, 5-101H-2, 80-851H-3, 5-101H-3, 80-851H-CC, 5-102H-1.5-102H-1, 80-852H-2, 5-102H-2, 80-852H-3, 5-102H-3, 80-852H-4, 5-102H-4, 80-852H-5, 5-102H-5, 80-852H-6, 5-102H-6, 30-352H-6, 80-852H-7,5-103H-1,5-1O3H-1 ,80-853H-2, 5-103H-2, 80-853H-2, 105-1103H-3, 5-103H-3, 80-853H-3, 105-1103H-4, 5-103H-4 , 80-853H-5, 5-103H-5, 80-853H-6, 5-103H-6, 80-853H-7, 5-104H-1, 5-104H-1, 85-904H-2, 5-104H-2, 85-904H-3, 5-104H-3, 85-904H-4, 5-104H-4, 85-904H-5.5-104H-5, 85-904H-5, 105-1104H-6.5-104H-6, 85-904H-7, 5-105H-1,5-1O5H-1, 80-855H-2, 5-105H-2, 30-355H-2, 80-855H-2, 105-1105H-3 ,5-105H-3, 30-355H-3 , 80-855H-3, 105-1105H-4, 5-105H-4, 80-855H-5, 5-105H-5, 80-855H-6, 5-105H-6, 80-855H-7, 5-106H-1.5-106H-1,81-866H-2, 5-106H-2 , 80-856H-3, 5-106H-3, 80-856H-4,5-106H-4, 80-856H-5, 5-106H-5, 30-356H-5, 81-866H-5, 105-1106H-6, 5-106H-6, 30-356H-6, 80-856H-6, 105-1106H-7, 5-106H-7, 30-35

145-886B-

lH-l' 80-851H-2, 5-10

Depth(mbsf)

0.050.801.552.303.053.804.454.655.406.156.907.658.409.159.90

10.6511.4012.1512.4012.9013.6514.1514.9015.6516.4016.6517.1517.9018.1518.6519.4020.1520.9021.6522.4023.1523.6524.4525.1525.9526.6527.4528.1528.9529.6530.4530.7531.1531.9532.6533.1533.9034.6534.9035.4035.6536.1536.4036.9037.1537.6538.4039.1539.9040.6541.4042.1542.6543.4144.1544.9045.6546.4047.1547.9048.6548.9049.4149.6550.1550.4050.9051.1551.5351.78

0.050.801.25

Depth(mcd)

0.061.102.003.034.224.675.405.406.187.007.788.469.15

10.1111.1912.8514.3515.4115.7616.4517.3919.7520.6022.1423.1023.3523.8524.6024.8525.3526.1026.8527.6028.3529.1029.8529.2030.0030.7031.5032.1932.8833.4934.1934.8035.6035.9336.3737.2537.9638.9539.7040.4540.7441.3641.6942.3842.7243.3643.6644.2545.1546.0446.9347.8548.8749.8550.4551.2152.0852.9253.5954.2754.9455.4656.2559.0459.5562.4062.9063.1569.5769.7970.1370.38

0.060.851.30

Ba(ppm)

2,1771,269

9732,0841,7842,8701,8891,8021,9532,2343,0412,7962,2543,1965,0236,1575,4084,5103,2576,5326,1333,2982,1123,5385,9183,5343,9242,5122,9463,0452,9902,1972,3652,3982,8322,4132,8232,2371,9583,5664,3795,1935,9853,8224,4775,8416,0365,2883,2684,0775,6855,8577,2044,8812,3782,9942,9703,1833,4142,3972,6482,1152,5373,9479,3766,8046,6336,3465,496

15,27012,54015,55014,17010,4404,2031,319

695723***941

1,3554,1434,0423,6213,582

1,7032,7611,264

La(ppm)

30.428.528.628.928.822.232.833.531.732.028.620.130.522.730.230.527.732.711.916.323.817.115.725.316.212.49.87.96.85.97.09.14.55.76.13.97.03.23.25.77.1

13.512.510.710.112.215.58.26.8

10.218.919.819.213.99.9

15.417.712.611.29.1

10.25.29.3

18.835.930.427.130.324.244.641.948.453.953.284.8

168.2114.8233.9260.3320.6240.7244.6260.3239.6271.7

30.028.3

Fe(%)

4.664.714.644.614.763.784.874.985.044.594.494.794.534.654.113.954.113.231.192.013.702.311.592.191.501.051.340.790.870.700.880.670.540.400.480.280.240.390.220.630.771.401.771.121.231.101.140.910.740.982.281.731.860.690.941.251.770.860.980.570.690.651.151.823.463.212.652.902.153.894.424.544.464.794.576.095.567.718.43

11.4216.9227.4125.6026.0226.93

4.574.244.67

Se(ppm)

23.8623.1422.2723.3224.5220.6225.2023.6124.8624.1326.2826.1924.4626.6826.1024.4225.1123.7512.1616.1925.3817.9014.2717.3612.209.34

10.696.716.856.567.446.855.134.284.433.674.243.923.586.247.06

13.2513.2011.959.07

10.8111.178.797.678.43

19.9717.4715.9610.029.05

12.2313.829.757.737.425.635.738.73

15.6527.6228.3721.3023.4718.3431.8338.3242.7942.1846.6036.3536.8430.7841.8242.1242.6829.8017.6314.3014.1812.34

22.9222.4422.31

Core, section,interval (cm)

1H-CC, 5-102H-1.5-102H-1,80-852H-6, 105-1102H-7, 5-102H-7, 30-353H-1,30-353H-1,80-853H-2, 5-103H-2, 80-853H-3, 5-103H-3, 80-853H-4, 5-103H-4, 80-853H-4, 105-1103H-5, 5-103H-5, 30-353H-5, 55-603H-5, 80-853H-5, 105-1103H-6, 5-103H-6, 80-853H-6, 105-1104H-1.5-104H-1,80-854H-2, 5-104H-2, 30-354H-2, 80-854H-2, 105-1104H-2, 130-1354H-3, 5-104H-3, 30-354H-3, 80-854H-3, 105-1104H-4, 5-104H-4, 80-854H-5, 5-104H-5, 80-854H-6, 5-104H-6, 80-855H-l,5-105H-1, 80-855H-2, 5-105H-2, 80-855H-3,5-105H-3, 30-355H-3, 80-855H-4, 5-105H-4, 80-855H-4, 105-1105H-5, 5-105H-5, 80-855H-6, 5-105H-6, 80-855H-7, 5-106H-l,5-106H-1, 30-356H-1, 80-856H-2, 5-106H-2, 80-856H-3, 5-106H-3, 80-856H-4, 5-106H-4, 80-856H-5, 5-106H-5, 30-356H-5, 80-856H-5, 105-1106H-6, 5-106H-6, 30-356H-6, 80-856H-7, 5-107H-l,5-107H-1,80-857H-2, 5-107H-2, 80-857H-3, 5-107H-3, 80-857H-3, 105-1107H-3, 130-1357H-4, 5-107H-4, 80-857H-5, 5-107H-5, 80-857H-6, 5-107H-6, 80-857H-7, 5-107H-CC, 5-10

145-886C-7H-L5-10

Depth(mbsf)

1.631.852.60

10.3510.8511.1011.6012.1012.8513.6014.3515.1015.8516.6016.8517.3517.6017.8518.1018.3518.8519.6019.8520.8521.6022.3522.6023.1023.3523.6023.8524.1024.6024.8525.3526.1026.8527.6028.3529.1030.3531.1031.8532.6033.3533.6034.1034.8535.6035.8536.3537.1037.8538.6039.3539.8540.1040.6041.3542.1042.8543.6044.3545.1045.8546.1046.6046.8547.3547.6048.1048.8549.3550.1050.8551.6052.3553.1053.3553.6053.8554.6055.3556.1056.8557.6058.3559.04

54.35

Depth(mcd)

1.684.455.205.095.565.809.079.37

10.1410.9211.9813.0414.1014.9515.2015.7015.9516.2016.4516.7017.2017.9518.2020.1521.0321.9822.3022.9423.2723.6023.9324.2524.9125.2425.8026.5527.3028.0528.8029.5530.0530.8031.5532.3033.0533.3033.8034.5535.3035.5536.0536.8037.5538.3039.0540.0040.2540.7541.5042.2543.0043.7544.5045.2546.0046.2546.7547.0047.5047.7548.2549.0050.5151.5452.5653.3554.1054.8555.1055.3555.4255.7156.3357.2658.4259.0859.5359.87

53.41

Ba(ppm)

1,1843,8111,6581,6632,1471,9052,1411,8523,4083,0944,9254,6855,4836,6125,7122,3294,7343,7765,3126,2753,1963,1893,7974,3054,3904,7133,6554,8254,4202,7014,4931,2873,2622,3892,8031,7782,6962,4711,9332,4772,9552,0353,4483,8265,9795,6314,2653,7963,9035,0605,7352,6303,4972,7493,1215,8676,9073,6782,9763,9282,1861,8532,3343,3232,9903,2935,2404,2237,8518,1167,8646,3625,745

10,64014,43012,34012,0908,9639,473'5,3723,403

977700781473***372260

12,230

La(ppm)

27.622.735.936.534.228.134.028.121.821.030.731.727.726.030.34.8

12.115.513.917.520.519.223.021.218.423.120.921.015.116.410.66.38.14.27.87.85.94.43.56.25.83.35.49.2

15.814.411.47.9

11.913.412.68.78.09.2

13.518.117.59.8

17.416.021.0

8.57.76.7

13.210.618.918.836.035.832.532.026.244.840.642.252.249.752.164.091.8

184.592.983.491.273.0

129.3144.0

37.9

Fe(%)

4.353.174.754.784.904.914.554.794.234.794.054.103.993.513.340.501.151.161.792.802.972.532.702.202.152.012.342.181.240.801.040.670.970.550.910.790.650.800.240.680.380.390.450.521.740.751.040.981.290.731.651.100.231.791.452.051.370.931.611.702.370.720.960.641.190.791.961.613.703.283.313.112.583.404.494.504.014.824.164.114.506.204.534.734.915.035.636.42

3.82

Se(ppm)

20.3518.2422.2021.2924.5424.4423.5724.5325.2826.7624.7625.2024.6423.8624.51

3.8511.7812.7414.6619.3520.5122.0421.3118.1719.2518.0619.7517.8710.7410.529.266.317.555.746.965.974.814.313.305.906.123.426.185.51

15.0210.789.758.42

11.519.89

12.809.835.53

11.9511.8617.6114.7610.5812.9013.7615.686.747.327.008.918.16

17.5014.8524.7226.9029.0727.5521.1225.4631.9640.6437.2746.2942.1434.9935.6137.0731.0336.0232.6830.5933.1038.08

31.66

210

COMPOSITE DEPTH SCALE

Table 3 (continued).

Core, section,interval (cm)

7H-2, 5-107H-2, 80-857H-3.5-107H-3, 80-857H-4, 5-107H-4, 80-857H-5, 5-107H-5, 80-857H-6, 5-107H-6, 30-357H-6, 80-857H-6, 105-1107H-7, 5-107H-7, 30-358H-1,5-1O8H-1,30-358H-1,80-858H-1. 105-1108H-2.5-108H-2, 30-358H-2, 80-858H-2, 105-1108H-3, 5-108H-3, 30-358H-3, 80-858H-4, 5-108H-4, 80-858H-4, 105-1108H-5, 5-108H-5, 30-358H-5, 80-858H-5, 105-1108H-6, 5-108H-6, 30-358H-6, 80-85

Depth(mbsf)

55.8556.6057.3558.1058.8559.6060.3561.1061.8562.1062.6062.8563.3563.6063.8564.1064.6064.8565.3565.6066.1066.3566.8567.1067.6068.3569.1069.3569.8570.1070.6070.8571.3571.6072.10

Depth(mcd)

54.2054.5955.0055.5056.2557.0057.7558.5059.2559.5060.0060.2560.7561.0062.0062.2562.7563.0063.5063.7564.2564.5065.0065.2565.7566.5067.2567.5068.0068.2568.7569.0069.5069.7570.25

Ba(ppm)

15,5609,501

11,2404,282

979873823408505569

******934

***467

***718553730734656

:

:::

,277,103***,455,126,923,819,964,941,887,677

4,0512,6302,611

La(ppm)

54.650.049.287.3

101.582.178.685.289.8

137.2130.7158.1112.9117.7248.3283.7212.4234.2193.0199.9197.1225.9251.8276.8272.9584.8497.3482.4358.8341.0360.4363.8184.6173.8293.4

Fe(%)

4.334.614.644.624.714.574.654.875.525.386.405.964.925.128.98

11.4811.5612.4913.8614.4416.5018.4620.1321.7828.3929.4227.2427.7027.4527.4825.7625.9832.2530.3323.75

Se(ppm)

39.5445.0042.0336.8529.8936.8233.4033.5730.3634.1737.3836.7829.1432.4040.2643.2338.8238.1432.0231.1531.1131.6430.1130.7728.5931.7924.2324.4420.5619.3620.9821.309.49

11.5618.32

Notes: Values have not been rounded to reflect significant digits. Triple asterisks (***)= below detection limit.

(between 62 and 69.5 mcd) is a relatively continuous sedimentaryrecord, and that the lowermost hiatus at Hole 885A is not present atHole 886C. Stepwise drops in the rate of hydrothermal accumulation(as at Hole 885A) would be expected if the record at Hole 886Ccontained a time interval(s) of significant nondeposition.

The composite depth scale also can be used to revise depths oflithologic boundaries at Sites 885/886. Sediment at these sites hasbeen divided into three basic lithologic units (Rea, Basov, Janecek,Palmer-Julson, et al., 1993): Unit I is composed predominantly ofclay, Unit II is composed primarily of diatom ooze, and Unit IIIconsists of clay with variable amounts of Fe-Mn oxyhydroxides. Onthe basis of shipboard smear-slide analyses, the Unit I/II boundarywas placed at approximately 14.1 mbsf at Hole 885A, 25.3 mbsf atHole 886B, and 17.1 mbsf at Hole 886C, and the Unit II/III boundarywas placed at approximately 45.8 mbsf at Hole 885A, 52.3 mbsfat Hole 886B, and 54.3 mbsf at Hole 886C. Although the latter bound-ary is stratigraphically equivalent (Table 1), the suggested Unit I/IIboundary occurs at significantly different composite depths withineach of Holes 885 A, 886B, and 886C. This discrepancy likely reflectsthe low sampling resolution taken for smear-slide analyses at Sites885/886 (1 to 3 samples per core), rather than differential sedimenta-tion at the three holes. The Unit I/II boundary therefore has beenrealigned in Figure 5, such that it occurs at the same composite depthwithin holes at Sites 885/886. The depth of this boundary has beenplaced at approximately 23.8 mcd because this depth is where down-core variations in bulk chemistry (Table 3, Fig. 4) display the greatestchange (it is assumed that variations in bulk Fe, La, and Se withinUnits I and II primarily reflect changes in the proportion of clay to

biogenic silica). Finally, Unit III should be divided into Subunits IIIAand IIIB (Fig. 5) to stress that the lowermost sediment of this unit (>62mcd) predominantly is composed of hydrothermally derived Fe-Mnoxyhydroxide precipitates (as evident in the downcore Fe profile, Fig.4, and discussed in Dickens and Owen, this volume).

CONCLUSIONS

A composite sedimentary record for Sites 885 and 886 can be con-structed from splices of Holes 885 A, 886A, 886B, and 886C such thatisochronous datums and changes in various physiochemical parame-ters at each hole occur at common depth horizons. This compositerecord (Fig. 6) implies recovery gaps ranging from 0.05 to 2.70 m,and coring overlaps ranging from 0.15 to 3.60 m. It suggests theexistence of intervals that are significantly compressed and/or containprominent hiatuses that occur in one hole but not in other holes. Toavoid recovery gaps and/or certain hiatuses, we suggest that futuresampling should be conducted according to Table 5.

ACKNOWLEDGMENTS

Shannon Miller and Ed Birdsall provided significant help withsample preparation for INAA analyses. We are very grateful to T.K.Hagelberg, N.G. Pisias, and T.C. Moore, Jr., for valuable commentsbased on an early version of this manuscript. Funding for G. Dickenswas furnished by the U.S. Department of Energy under appointmentto Graduate Fellowships for Global Change administered by OakRidge Institute for Science and Education (ORISE).

REFERENCES*

Browne, E., and Firestone, R.B., 1986. Table of Radioactive Isotopes: NewYork (Wiley).

Dickens, G.R., and Owen, R.M., 1993. Chinook Trough rifting and late Cre-taceous hydrothermal deposition at ODP Site 886. Eos, 74:355. (Abstract)

Hagelberg, T., Shackleton, N., Pisias, N., and Shipboard Scientific Party, 1992.Development of composite depth sections for Sites 844 through 854. InMayer, L., Pisias, N., Janecek, T., et al., Proc. ODP, Init. Repts., 138 (Pt.1): College Station, TX (Ocean Drilling Program), 79-85.

Hagelberg, T.K., Pisias, N.G., Shackleton, NJ., Mix, A.C., and Harris, S.,1995. Refinement of a high-resolution, continuous sedimentary section forstudying equatorial Pacific Ocean paleoceanography, Leg 138. In Pisias,N.G., Mayer, L.A., Janecek, T.R., Palmer-Julson, A., and Van Andel, T.H.(Eds.), Proc. ODP, Sci. Results, 138: College Station, TX (Ocean DrillingProgram), 31^6.

Heath, G.R., Kovar, R.B., Lopez, C, and Campi, G.L., 1985. Elementalcomposition of Cenozoic pelagic clays from Deep Sea Drilling ProjectSites 576 and 578, western North Pacific. In Heath, G.R., Burckle, L.H.,et al., Init. Repts. DSDP, 86: Washington (U.S. Govt. Printing Office),605-646.

Murray, D.W., and Prell, W.L., 1991. Pliocene to Pleistocene variations incalcium carbonate, organic carbon, and opal on the Owen Ridge, northernArabian Sea. In Prell, W.L., Niitsuma, N., et al., Proc. ODP, Sci. Results,117: College Station, TX (Ocean Drilling Program), 343-363.

Rea, D.K., Basov, LA., Janecek, T.R., Palmer-Julson, A., et al, 1993. Proc.ODP, Init. Repts., 145: College Station, TX (Ocean Drilling Program).

Abbreviations for names of organizations and publications in ODP reference lists followthe style given in Chemical Abstracts Service Source Index (published by AmericanChemical Society).

Date of initial receipt: 4 April 1994Date of acceptance: 10 August 1994Ms 145SR-144

211

G.R. DICKENS ET AL.

4000

Ba (ppm)

8000 12000 16000

70

g Q I I I I I I • 1 I • I I I 1 I I I I I I I I I I I I I • I • I I

10 15 20 25 30 35

100 200 300 400 500 600

Figure 4. Downcore variations in bulk Ba, Fe, La, and Se at Holes 885A (solid diamonds), 886B (open diamonds), and 886C (plus signs) plotted according to thecomposite depth scale (mcd). Breaks in records indicate coring gaps or hiatuses. Note depth offsets between 12 and 15 mcd, 20 and 22 mcd, and at approximately30 mcd (discussed in text). Concentrations of Ba that are below the detection limit (between 59.08 and 65.25 mcd; see Table 2) are shown as zero.

212

COMPOSITE DEPTH SCALE

Table 4. Stratigraphic implications of hole intercorrelation at Sites 885/886.

Upperdepth(mbsf)

4.609.75

14.1023.6033.1042.6048.6549.4150.4052.10

Hole 885A

Lowerdepth(mbsf)

4.6015.8514.1023.6033.1042.6048.7049.5550.65

OverlapCompressedRecovery gapOverlapRecovery gapOverlapHiatusHiatusHiatusEnd of hole*

Length(m)

-0.203.75b

1.85"-1.15

0.55-0.10

1.902.605.95

Upperdepth(mbsf)

0.009.70

Hole 886A

Lowerdepth Length(mbsf) (m)

0.75 Core topa 1.25End of hole

Upperdepth(mbsf)

1.802.60

11.3020.8028.8030.3039.8049.3058.80

Hole 886B

Lowerdepth(mbsf)

1.8010.2511.3020.8030.3030.3039.8049.30

Recovery gapUnknown0

Recovery gapRecovery gapNot recoveredOverlapd

Recovery gapRecovery gapEnd of hole'

Length(m)

2.55-7.50

2.850.95

(1.50)-0.75

0.451.25

Upperdepth(mbsf)

4.806.80

16.3025.8035.3039.8044.8054.3063.8072.40

Hole 886C

Lowerdepth(mbsf)

6.106.80

16.3025.8035.3044.8044.8054.3063.80

HiatusRecovery gapOverlapOverlapRecovery gapNot recoveredRecovery gapOverlap"5

Recovery gapEnd of hole'

Length(m)

1.250.10

-3.60-0.70

0.85(5.00)0.20

-0.500.75s

Notes: "Length" column is the amount of sediment "missing" from (positive values) or "added" to (negative values) composite sedimentary record. Values in parentheses do notaccount for "missing" sediment.

"Amount of sediment either not recovered (missing core top) and/or compressed relative to the composite depth scale.bCompressed interval and recovery gap together represent 5.60 m of depth offset (see text).The middle of Core 145-886B-2H contains approximately 7.50 m of sediment of unknown origin (see text).''Coring overlaps at approximately 30 mcd may alternatively reflect compression at Hole 886C (see text).eSediment in Section 145-886C-6H-1 is highly disturbed and may account for some of the coring overlap.'Depth of lowermost recovered sediment.gThe 0.75-m "gap" between Cores 145-886C-7H and -8H is an arbitrary value (see text).

Table 5. Suggested composite record for Sites 885/886.

Depth(mcd)

0.00-4.104.10-9.359.35-14.45

14.45-17.5017.50-22.5522.55-28.5528.55-32.1032.10-39.4039.40-40.5540.55-47.6547.65-52.7052.70-55.3555.35-basalt

Splice

Hole,core

886C-1H886A-1H886C-2H886B-3H886C-3H885A-3H886C-4Ha

886B-5H885A-5H886B-6H886C-6H886B-7H

886C-7H, -8H

Interval(mbsf)

0.00-4.102.60-7.858.00-13.10

16.10-19.1519.40-24.4515.85-21.8530.15-33.7032.40-39.7033.60-34.7540.40-47.5049.05-54.1050.95-53.6057.95-72.40

"Because of intercorrelation problems across this interval, samples also might be takenfrom lowermost Core 145-885A-3H and uppermost Core 145-885A-4H.

213

G.R. DICKENS ET AL.

0 • -

10

20

30

40

50

60

70

80 "̂~

1H

3Hm

5H

2H

4H

6H

Hole 885A

IIIA

IIIB

Lith. unit

Coring overlap (0.20 m)

Compressed (see text)

Recovery gap (1.85 m)

Compressed (see text)

Coring overlap (1.15 m; see text)

Recovery gap (0.55 m)

Coring overlap (0.10 m)

Hiatus (1.90 m)

Hiatus (2.60 m)

Hiatus (5.95 m)

Lowermost sediment

|T j | Clay/claystone

CF\ Diatom ooze

[St] Distal hydrothermal precipitates

Figure 5. Core descriptions for Holes 885A, 886A, 886B, and 886C according to composite depth. The stratigraphic implications of the composite depth scale arelisted to the right of each figure, and the revised lithologic description (see text) is displayed in the middle of each figure.

COMPOSITE DEPTH SCALE

10

10

20

30

40

50

60

1H

1H

3H

5H

7H

2H

4H

6H

Hole 886A

Hole 886B

Missing top (1.25 m)

Lowermost sediment

Recovery gap (2.55 m)

Unknown (7.50 m; see text)

Recovery gap (2.85 m)

Recovery gap (0.95 m)

Not recovered (1.50 m)Coring overlap (0.75 m; see text)

Recovery gap (0.45 m)

Recovery gap (1.25 m)

IIIA

Lith. unit

Clay/claystone

Diatom ooze

Figure 5 (continued).

Hiatus (see text)

Lowermost sediment

215

G.R. DICKENS ET AL.

Hole 886C

0 r-

10

20

30

S 40

50

60

70

80

1H

i • ! • ! • ; •i

3H

5H

7H

2H

4H

6H

8H

1IMA

IIIB

Lith. unit

Clay/claystone

Diatom ooze

Distal hydrothermal precipitates

Figure 5 (continued).

Hiatus (1.25 m)

Recovery gap (0.10 m)

Coring overlap (3.60 m)

Coring overlap (0.70 m)

Compressed? (see text)

Recovery gap (0.85 m)

Not recovered (5.00 m)Recovery gap (0.20 m)

Disturbed zone andCoring overlap (0.50 m)

Hiatus (see text)

Recovery gap/hiatus

(assumed 0.75 m; see text)

Lowermost sediment

COMPOSITE DEPTH SCALE

Radiolarian Events

£. 40

i:;

IMA

Basalt

~~i S. acquiloniumT S. universus

L heteroporos

Polarity Chrons

C1n (Brunhes)

C1r.1n (Jaramillo)

C2n (Olduvai)

_ J C. davisiana davisianamà c2An.1n (Upper(Upper Gauss)

C2An.3n (Lower Gauss)

T

1

J

—

D. bullatus

S. peregrine

L. heteroporos

S. delmontensis-r• S. peregrinay S. acquilonium

L. nipponicamagnacornuta

=

i••

i

C3An.1n

C3Aπ.2n

C4n.1n

C4n.2n

C4An

Age (Ma)

0.4

— 2.9

-5.0

5.7135

6.08

8 5 3 8.8*-10-12

Oligocene

Late Cretaceous

I Normal

(TJ Clay/claystone ] Reversed

Q Diatom ooze Q Indeterminate

g j Distal hydrothermal precipitates

Λ Λ Hiatus

Figure 6. The composite stratigraphic record at Sites 885/886 with ages andapproximate depth positions of isochronous radiolarian events and polaritychron boundaries (Table 2).

217