5. SITE 186
The Shipboard Scientific Party1

SITE DATA

Date Occupied: 9-12 Aug 71.
Position:
51°07.8l'N
174°00.34'W.
Water Depth: 4522 meters.
Penetration: 926 meters.
Number of Holes: One.
Number of Cores: 28.
Total Core Recovered: 140.7 meters.
Acoustic Basement:
Depth: Approximately 850 meters
Nature: Deformed sediments
Velocity: 2.0 km/sec.
Age of Oldest Sediment: late Miocene, with a short (<60m) enclosed section of middle Miocene fault block or
slump block.
Basement: upper Miocene deformed sediments.
SUMMARY

Site 186 is located near the outer or southern edge ofAtka Basin, Aleutian Terrace, in water 4522 meters deep
(Figure 1). The sediment sequence penetrated is 926 meters
thick and consists predominantly of diatomaceous silty clay
ranging in age from late Pleistocene through early Pliocene.
A section (at 622 m) less than 60 meters thick of middle
Miocene diatomaceous silty clay is enclosed within a larger
section of lower Pliocene silty clay. The micro fossils, which
include calcareous forms, suggest that the middle Miocene
unit is an allochthonous block. Reworked middle Miocene
forms also occur in the associated Pliocene beds.
Volcanic ash is interbedded throughout the section andash beds are particularly common above 20 meters. A
middle Pleistocene pumice-bearing ash layer 4.5 meters
thick occurs at 165 meters. Beds of sand and silt up to 4.5
meters thick are commonly intercalated in the diatomaceous silty clay. Benthic foraminifera in the thick sandy

1David W. Scholl, U.S. Geological Survey, Menlo Park, California; Joe S. Creager, University of Washington, Seattle, Washington; Robert E. Boyce, Scripps Institution of Oceanography, La
Jolla, California; Ronald J. Echols, University of Washington,
Seattle, Washington; Timothy J. Fullam, Standard Oil Company ofCalifornia, La Habra, California; John A. Grow, Massachusetts
Institute of Technology, Cambridge, Massachusetts; Itaru Koizumi,
Osaka University, Osaka, Japan; Homa J. Lee, Naval Civil Engineering Laboratory, Port Hueneme, California; Hsin Yi Ling, Universityof Washington, Seattle, Washington; Richard J. Stewart, Universityof Washington, Seattle, Washington; Peter R. Supko, Scripps
Institution of Oceanography, La Jolla, California; Thomas R.
Worsley, University of Washington, Seattle, Washington.

-"50°

Figure 1. Base map showing location of Site 186.

layer of Cores 10 to 11 (middle to lower Pleistocene) areapparently displaced from shallower depths and imply thatthe sands are turbidites. Thin layers of calcite-cemented
siltstones and diatomaceous, calcitic silt are present in the
middle Pliocene between 386 and 509 meters.
The lens-shaped mass of generally undeformed sedimentary deposits underlying Atka Basin, Aleutian Terrace,
is approximately 2000 meters thick and consists chiefly of
diatomaceous clay younger than late Miocene. Siliceous
microorganisms constitute about 35 percent of these
Neogene beds. The bulk, about one-half, of the accumulated debris was contributed by the nearby Aleutian Ridgeas either hemipelagic silt- and clay-size particles (40%) or
sandy turbidite layers (10%) bearing shallow-water foraminifera. Vitric volcanic debris, although rather abundantin the Pleistocene section, is a minor constituent (5%)
throughout most of the drilled section.
Atka Basin is guarded by an outer ridge that is underlain
by an acoustically unresolvable structure. The deepest
prominent acoustic reflector (about 815 m) at Site 186 was
not identified stratigraphically but occurs within the lower
Pliocene. Drilling at Sites 186 and 187 established that thisridge is in part constructed of uplifted and deformed
Pliocene and upper Miocene basin deposits.

217

SITE 186
BACKGROUND AND OBJECTIVES
Description

Atka Basin forms the Aleutian Terrace south of Atka
Island, Aleutian Islands. Site 186, 4522 meters, is locatednear the basin's southern edge, which is commonly marked
by a "basement" ridge underlain by acoustically unresolvable structures. Reflection profiles show that Atka Basincontains at least 2000 meters of largely undeformed
stratified deposits. Along the inner or northern side of thebasin these deposits overlie an acoustic basement thatapparently can be traced to outcrops of early Tertiary(pre-Neogene) rocks exposed on nearby Atka and Adakislands. Near the southern side of the basin the lower
deposits sweep upward and appear to lap onto the"basement" rock of the outer ridge (Figure 2). These beds
also become folded in the vicinity of the outer ridge. Site
186 was positioned over the upturned lower beds a few
kilometers north of the outer ridge. Hemipelagic, pelagic,
and turbidite beds were anticipated.
Objectives

Formation of Atka Basin can be linked to several
mechanisms: (1) graben-like collapse of a segment of the
Aleutian Ridge, possibly in conjunction with formation of
the adjacent Aleutian Trench; (2) sedimentary infillingbehind a deeply submerged volcanic ridge; (3) depositional

infilling behind a ridge largely formed by offscraped
sedimentary and igneous masses derived from a subducted
Pacific plate; and (4) infilling behind a ridge composed ofolder terrace or archipelagic apron deposits that have been
deformed and uplifted by some mechanism (e.g., folding,faulting, or diapirism) to form the present outer ridge ofAtka Basin and possibly also the inner wall of the Aleutian
Trench.
The principal objective in drilling Site 186 was todetermine the age and lithology of the strata underlying thebasin as well as that of the acoustic basement beneaththem. Presumably, this sort of information would allow
some conclusions regarding the dominant mode of sedimentation over the terrace, especially the importance of the
nearby Aleutian Ridge as a volcanic and detrital sedimentsource, and the time of formation of the basin. The
pre-basin history could be deduced if basement rocks wereobtained. Considered together, the finds at Site 186 would
aid in understanding the origin of the basin as well as its
relation to the tectonic and igneous history of the Aleutian
Ridge and north Pacific region.
OPERATIONS
Pre- and Post-drilling Survey

Site 186 was approached with a ship's heading of 130°T.
Although it was recognized at the time that our location

10 km

2-way
time,
sec.

NeaflM86
Near'187—6

Figure 2. Reference seismic reflection profile, collected by E. L. Hamilton, 2 August 1970.

218

SITE 186

was some mile or more west of the site selected, it waspresumed that a similar section would be present along theapproach track. This proved to be incorrect. The course waschanged to a heading of 325°T which was maintained until
we intersected the line of the reference profile collected by
E. L. Hamilton of 2 Aug 70 (Figure 2). The ship thensteered a course of 116°T, which is reciprocal to thereference track. This heading was maintained until astructure similar to that of the reference profile was seen.
The beacon was dropped on the fly at 1225 hrs on 9 Aug
71. The finally accepted satellite position is: 51°07.8l'N;
174°00.34'W. The reference seismic profile is shown in
Figure 2 and the air-gun profile taken crossing the site on
approach is shown in Figure 3. A post-drilling survey
air-gun track through Sites 186 and 187 can be seen in
Figure 3 of Site 187. A map showing the pre-drilling survey
is given as Figure 4 (this site).
Drilling Program

Site 186 was occupied from 1225 hrs (beacon away) 9
Aug 71 until 1000 hrs 12 Aug 71 with alternate coring andwashing from the sea floor to a subbottom depth of 926

meters. At this depth the sediment is a firm clayey siltstone(almost shale) with interbedded gaseous sands containing
measurable ethane. Because of the drilling difficulty, an age
that was still late Pliocene, and the desire to obtainbasement if possible, it was decided to abandon the holeand move 3 miles southeast to a point where bedrock
appeared nearer the surface.
Using Matthews Tables and information from the U.S.
Navy Undersea Research and Development Center, thesonic depth of 2398 fms was corrected to 4476 meters
giving a water depth of 4482 meters and a drill-floor depthof 4492 meters. This compares with 4532 meters below
drill floor established on the basis of the first core. The
difference in depths is attributed to inadequate correction
factors and a settling of the beacon into water slightly
deeper than taken from the echo sounder. The 4532 meters
below drill floor, or 4522 meters below sea level, is theaccepted depth for this site.
The entire section drilled and cored to a total depth of
926 meters consisted of diatomaceous clayey silts and silty
clays with layers of ash and volcanic sand and traces ofmethane. Ethane was detected in a few cores. DrillingmCOt o GO
C£
IC

ε

<

LO
•

o IX)
o CO
^ 1 - C\J
<NJ t—QLU
L U J—Q - Q_ 1—1

Lu

on QL J J h—

0
1—

CO
+J

in

ε

O
CD
• CO
CO

o

Q

re

CO GO
CC
4 - rπ

Q

Lu

LU
Q_
CO

h-

Q_
LU
Q

LU

s:
i—i

Figure 3. Glomar Challenger air-gun profile across Site 186.

219

SITE 186->*

Figure 4. Glomar Challenger track showing approach and departure, Sites 186 and 187.

became progressively harder with depth and mud wasspotted at subbottom depths of 216 to 245 meters, 618 to
627 meters, and 814 to 861 meters to clean out the hole,necessitated because of slumping associated with sandstringers. One hundred barrels of 10.6# mud was placed at
the bottom of the hole before abandonment as a precautionary measure since the ethane content of the sediment
here was measurable. A coring summary in given in Table 1.
LITHOSTRATIGRAPHY

The entire 926-meter sedimentary section at Site 186 is
dominantly diatomaceous silty clay. Volcanic ash is interbedded throughout the section, and ash beds are particularly common above 20 meters. A pumice-bearing ash layer
at least 4.5 meters thick occurs at 165 meters.
Beds of sand and silt are frequently intercalated in the
diatomaceous silty clay in layers up to 4.5 meters thick.
Diatomaceous calcite silts are present between 386 and 509
meters. One calcite-cemented siltstone is present.
Degree of induration increases sharply in the interval
214 to 245 meters and continues to increase downward to
the bottom of the hole. Inclined bedding is present at 440
meters and may occur stratigraphically higher.

220

At about 622 meters an anomalous section of middle
Miocene diatomaceous silty clay is sandwiched in between
lower Pliocene diatomaceous silty clays.
Dominant Lithology
Most of the sediments at Site 186 are olive graydiatomaceous silty clay and diatom ooze. Diatoms typicallyconstitute 30 to 40 percent of the sediment, some of whichis spicule-bearing. The terrigenous silt/clay ratio is usually
about 1:2. Near the top of the section much of thesediment is diatom ooze (50 to 75 percent diatoms). Lightolive gray diatomaceous calcite silt layers appear at 448 and509 meters, and much of the diatomaceous silty clay in theunit is carbon ate-bearing. The calcitic layer apparently
represents concentrations of nannofossil plates that havebeen altered by crystal solution and regrowth. Original
nannofossil structures are not detectable.
Volcanic Ash

Beds of volcanic ash occur sporadically throughout mostof the section but are particularly abundant in the upper 20
meters. The ashes are light gray and brownish gray. The
vitric debris in the ashes is colorless to light brown andSITE 186

TABLE 1
Coring Summary - Site 186
Recovered

Cored Interval
Core

(m)

(m)

(m)

(%)

1
2
3
Wash
4

0-2
2-11
11-20

2
9
9

2.0
6.0
9.1

100.0
66.7
101.1

49-58

9

9.3

103.3

96-105105-114114-123

9
9
9

1.6
6.0
9.5

17.8
66.7
105.6

8
Wash
9
10
Wash

133-142

9

7.0

77.8

161-170
170-179

9
9

9.5
8.3

105.6
92.2

11
Wash
12
Wash
13

207-216

9

8.5

94.4

245-254

9

LO

11.1

291-300

9

2.0

22.2

338-347

9

0.8

8.9

385-394394-403

9
9

1.2
2.5

13.3
27.8

422-431

9

3.5

38.9

440-449449-458

9
9

3.8
6.0

42.2
66.7

458-467

9

6.5

72.2

506-515

9

3.4

37.8

562-571

9

3.9

43.3

618-627

9

3.7

41.1

683-692

9

4.3

47.8

731-740

9

3.0

33.3

805-814

9

3.0

33.3

861-870

9

9.3

103.3

917-926

9

8.0

88.9

245

142.7

58.0

Wash
5
6
7
Wash

Wash
14
Wash
15
16
Wash
17
Wash
18
19
20
Wash
21
Wash
22
Wash
23
Wash
24
Wash
25
Wash
26
Wash
27
Wash
28

meters, 100 to 220 meters, 380 to 600 meters, and 850 to
926 meters. The sand layers are up to 4.5 meters thick are
medium to coarse grained, and represent crystal concentrates of disaggregated volcanic rocks. Typical compositions
are 40% feldspar, 30% pyroxene, and 10% glass grains, withsmaller quantities of quartz, amphibole (both common
hornblende and basaltic hornblende), chlorite, diatoms, andsponge spicules. Lithic fragments are present in variable
concentrations (10 to 40%) and are either microlitic
volcanic grains or "alterite," opaque, iron-oxide coatedgrains of unknown origin. Many of the sand layers haveparallel laminations, and the thicker beds display good size
grading and convolute laminations (see Figure 5). At 920
meters an exceptionally coarse-grained bed rich in shale
grains and pebbles is present.
A thin calcite-cemented siltstone bed appears in thesection at 386 meters. In the upper 200 meters gas bubbles
were noted in several of the sand layers (see Figure 6).

unaltered. Grayish green iron-stained (?) bands occur in thelower portions of several beds.
At 161 to 165 meters a distinctive, pumice-bearing ash
layer occurs. The bed is dark grayish brown, and as is true
with all ashes recovered at Site 186, the fragments arecomposed of light colored glass.
Silt and Sand Beds
Beds of brownish gray to very dark gray silt and sand areinterbedded at some levels within the section: 0 to 20

Figure 5. Convolute laminations in sand layer (186-27-2,
61-69 cm). Full core width.

221

SITE 186

Figure 6. Deformation by gas bubbles in a volcanic sand layer (196-9-1, 80-83 cm). Full core width.
Induration

Middle Miocene Sediments

Degree of induration increases sharply in the uncoredinterval 214 to 245 meters and continues to increase
downward to the bottom of the hole.

The lowermost meter of Core 23 contains middle
Miocene diatom flora anomalously older than the lower
Pliocene sediments found above and below. The middle
Miocene sediment is not particularly distinctive, being
diatomaceous silty clay. There is, however, a prominentcolor break at 621 meters, which apparently marks the topof the middle Miocene unit. The contact is sharp, with olive
gray silty clay above in contrast to the grayish olive silty
clay of the middle Miocene section.
Below the anomalous middle Miocene unit, the sediments are again olive gray to dark gray diatomaceous silty
clay, volcanic sand, and ash of early Pliocene age.

Inclined Bedding

Beginning with Core 18, 440 meters below bottom,
bedding becomes inclined at an angle of 15 degrees and isinclined throughout the remainder of the core. The steepest
dip, 35 to 40 degrees, occurs in the vicinity of theanomalous middle Miocene section encountered in Core 23.
Below about 700 meters, bedding inclinations decrease to
15 degrees and continue at this angle to the bottom of thehole.
Above Core 18, bedding may also be inclined; however,drilling operations fragmented Cores 13 through 17 andbedding attitudes were not observable. Bedding is horizontal in Core 12 (245 m below bottom).

222

PHYSICAL PROPERTIES

Physical properties measured at Site 186 include bulk
density, water content, natural gamma radiation, acoustic
velocity, vane shear strength, and residual pore pressure.

SITE 186

Bulk density was measured with the GRAPE system,
calculated from shore laboratory water content determinations, and, for the harder materials, measured by thewater displacement method.
The bulk densities obtained with the GRAPE system arepresented on the site summary sheet. In a majority of thecores, the expansion of gases produced a number of voids
distributed along the length of the samples. The GRAPE
records obtained, therefore, consist of a series of density
peaks separated by zones of zero apparent density. The
dashed line plots shown on the core summary sheets
represent the envelopes of the density peaks in corescontaining many voids. Solid lines are drawn for corescontaining fewer voids and are a direct representation of
the GRAPE records.
Characteristic GRAPE densities are given for eachsection on the site summary sheet. The characteristic
density is defined as the apparent mean of the envelope of
the peak densities for the sections containing numerous
voids, and as the mean density for the intact sections. Also
shown on the site summary are the water displacement
densities, shore laboratory densities, and acoustic velocities.
Bulk Density

GRAPE densities were measured to a sediment depth of
735 meters. Below this point, the material did not fill thecore liner and could not be tested accurately. A number ofwater displacement densities are shown for the deeper
material. These agree relatively well with the GRAPE
densities.
The general trend of the bulk densities at Site 186 is a
rapid increase from 1.5 to 1.8 g/cm3 over the sediment
depth range 0 to 200 meters. This is followed by a gradualincrease from 1.8 to almost 1.9 g/cm3 at 900 meters. No
sharp breaks in the density-depth distribution are apparent.
Acoustic Velocity
Acoustic velocity measurements were difficult to obtainat Site 186 because of the high gas content of the sediment.
To a sediment depth of 450 meters, the material wasincapable of transmitting the acoustic signal used in the
Hamilton Frame well enough for velocity measurements.
From 450 to 740 meters, only a very weak signal could bereceived. The material from 860 to 930 meters, however,
responded as well as the sediment at other sites.
The velocities measured do not indicate any sharp
lithologic changes. The general trend is an approximately
linear increase from 1.8 km/sec at 450 meters to around 2.0
km/sec at 900 meters. These values may differ significantly
from the in situ velocities because of the disturbanceintroduced by gas expansion.
Summary

The physical property data at Site 186 do not disclose
any sharp changes in lithology over the 900 metersinvestigated. The density and acoustic velocity increasesystematically with depth, but this would be expected withany relatively homogeneous sediment.
The problem of gas expansion complicated the physicalproperty measurements at Site 186. Many of the reported

values, therefore, may differ significantly from the in situ
situation.
PALEONTOLOGY

Abundant diatoms and common to rare radiolarians andsilicoflagellates provide good stratigraphic control throughout the cored section. Except for fragments of arenaceous
tests, foraminifera were found only in the sands of Cores 10
and 11, middle to lower Pleistocene, and in the bottom ofCore 23. The bottom of Core 23, middle Miocene,
contained the only nannofossils found at this site.
Foraminiferal faunas in the sand of Cores 10 and 11 areouter sublittoral hlandiella assemblages, probably transported to Site 186 by turbidity currents. No other sand at
this site yielded displaced faunas.
The lower 1.5 meters of Core 23 contains a fossil
microbiota very different from that in sediments above andbelow. The diatom assemblages compare to middle Miocene
assemblages of North Sakhalin while diatom assemblages
below Core 23 are clearly lower Pliocene, although withreworked middle Miocene index species. Among the silicoflagellates of Core 23, there is also a middle Miocene index
species, but it is one previously unknown in the North
Pacific; sediments above and below Core 23 have only
characteristic lower Pliocene silicoflagellates. The foraminiferal fauna of Core 23 could be upper middle Miocene,
although a younger age cannot be ruled out. Pliocene
sediments above and below Core 23 have no foraminiferal
fauna at all, which is typically the case for Pliocene deposits
at other North Pacific and Bering Sea sites. Nannofossils inCore 23 are not age-diagnostic. Their occurrence is significant because they are absent above and below. Because allthese various elements of the fossil microbiota are somarkedly different from those found in sediments aboveand below, it is believed that resemblances of the diatom
flora to a known middle Miocene flora is not fortuitous andthe middle Miocene index fauna are not reworked in Core23, although they are reworked above and below.
Taken together, then, the evidence indicates that thelower 1.5 meters of Core 23 is older than sediments below
it. Furthermore, because the microbiota appears to be acoherent assemblage rather than a mixture of older andyounger elements and because it occurs in a sedimentdistinguished by color, although not by texture, from lower
Pliocene sediment above and below, the lower 1.5 meters ofCore 23 is interpreted as an exotic block of middle Miocene
sediment within the lower Pliocene section.
Because the inferred exotic block in Core 23 contains
relatively common calcareous fossils it is concluded thateither the carbonate compensation depth was much lower
in middle Miocene than in Pliocene time or that the exotic
block is derived from a water depth considerably less thanthat in which the Pliocene sediment on either side of it was
deposited. Because an indigenous middle Miocene calcareous microbiota was not found at Site 183, which isfrom a water depth similar to Site 186, the latterinterpretation is preferred.. However, the benthic foraminiferal fauna contains abyssal indicators, including
Melonis pompilioides, therefore an upper limit of about
2000 meters can be placed on the deposition depth of thesediment from which the block was derived.

223

SITE 186
Foraminifera

Examination of core catcher samples yielded only threesignificant foraminiferal faunas; these three are from Cores
10, 11, and 23. The core catchers of Cores 10 and 11 have amoderately abundant, generally well-preserved benthic
fauna dominated by Islandiella limbata, I. californica, andElphidiella arctica. This assemblage, typical of outer sublittoral or possibly upper bathyal depth zones, is obviously
displaced and indicates that the thick sand beds of Cores 10
and 11 are derived from these depth zones. The faunas,
therefore, are supporting evidence that the sand beds are
turbidites. A sparse assemblage of sinistrally coiling
Globorotalis (T ) pachyderma is present.
The core catcher of Core 23 also contained a moderately
abundant, well-preserved benthic fauna. All extant species
in this fauna are known from lower bathyal depths of themodern ocean; Melonis pompilioides indicates a paleodepthof deposition in excess of 2000 meters. The dominant
species, Spirosigmoilinella compressa, is restricted in northeastern Japan to Miocene sediments inferred to have been
deposited at lower bathyal depths (Asano, et al., 1969).
There, as in Core 23, it is associated with Martinottiellacommunis. A sparse, dominantly dextral population of G.
(T.) pachyderma is also present in Core 23. Previously, thelowest reported occurrence of this species is upper middle
Miocene. Earliest populations are dextral in the lower
Funakawa Formation of northeastern Japan (Asano, et al.,1969) as they are in Core 23, becoming sinistral in theupper Miocene.
Calcareous Nannoflora
The site is essentially barren of calcareous nannofossils
with the exception of Core 23, Section 3. This apparently
displaced sediment block contains rare but well-preserved
specimens resembling Reticulofenestra dictyoda and R.
umbilica and other small (2-3µ) placoliths. This flora issimilar to that encountered at Sites 184 and 185.
Radiolaria and Silicoflagellates
All the sediments examined from Site 186, except Core28, yielded radiolarians and/or silicoflagellates. Sparsity ofradiolarian specimens (Table 5, Chapter 28) continues atthis site. Furthermore, most of the forms encountered are
members of the modern North Pacific and the Bering Sea(surface sediments) fauna and apparently they are rather
long-ranging species in these regions.
Occurrence of silicoflagellates from Site 186 is shown in
Table 5, Chapter 27. The Pleistocene and early Pliocene
microfloral succession of Cores 1 to 21 is similar to thatobserved at Site 185. In Core 23, the occurrence of
Naviculopsis lata is noted. This species has been reported
only from Europe and from exposures in Italy; it is foundin Calocycletta costata and C. virginis (radiolarian) zones ofSanfilippo (1971). Fragments of possibly Mesocena apiculata were also noted in the same core sediments.

224

Diatoms
The stratigraphic sequence at Site 186 can be divided
into five zones as shown in Table 4, Chapter 30. As
indicated in the table and as will be discussed in detail later,
the microflora of the lower 1.5 meters of Core 23 (from theanomalous section described earlier) is largely dominatedby Coscinodiscus symbolophorus and Coscinodiscus marginatus forma, but it also contains some specimens of such
good middle Miocene marker species as Actinocyclus
ingens, Annelus californicus, Denticula lauta, Kieselavia
carina, and Raphibodiscus marylandicus.
CORRELATION BETWEEN REFLECTION PROFILEAND STRATIGRAPHIC COLUMN
Sites 186 and 187

The reflection profile that was used for selecting Sites
186 and 187 (taken by E. L. Hamilton in 1971) is shown in
Figure 7 along with the stratigraphic column and physicalproperties for Site 186. The measurements of physicalproperties at Site 186 was often very difficult due to gassy
cores or brittle, fractured sediments, and only very grosstrends are apparent in the density and velocity data.
Although the lithology at Site 186 was somewhat
uniform, diatomaceous silty clay with various admixturesof volcanic sand, ash, calcareous siltstone, and semilithified
mudstone, the reflectors in the upper 400 meters on the
profile correlate quite well with lithologic changes. The
reflectors are generally sandy or semi-indurated units.
Below 400 meters other diffuse reflecting horizons can beseen, but they do not clearly correlate with obvious
lithologic variations. Part of the poor correlation below 400
meters may be due to the fact that the ship was positioned
0.5-1.0 km closer to the basement ridge than planned. At
Site 187 four cores of upper Miocene diatomaceous silty
clay were drilled between 164 and 370 meters. All fourcores were within the "acoustical basement." Therefore, it
is possible that somewhere between 400 and 926 meters(T.D.) at Site 186 we entered rocks of the acoustic
basement drilled at Site 187. The anomalous occurrence ofthe middle Miocene core at 620 meters at Site 186(between two lower Pliocene cores) and the presence of 30
to 35 degree bedding inclination further suggest that a zoneof deformed terrace sediments may have been reached in
the deeper part of the hole. A detailed discussion of intervalvelocities is not possible with this hole; however, thereflectors in the upper 400 meters seem to correlate fairly
well with a 1.65 km/sec velocity.
REFERENCES
Asano, K., Ingle, J. C. and Takayanagi, Y., 1969. Neogene
planktonic foraminiferal sequence in NortheasternJapan. In Proc. 1st Intern. Conf. Plank. Microfossils.
Geneva, 1967. 14.
Sanfilippo, A., 1971. Neogene radiolarians of the Mediterranean and western Pacific. In Farinacci, A. (Ed.). Proc.
2nd Intern. Plank. Conf. Rome. II, 1121.

SITE 186

DENSITY VELOCITY
o o

•~

LU
I/)

o o —iSILTY
WITH_ASJi

3 1
4 1

<

r-^ (NJ
1'

DIATOM
OOZE

o
5
'
a
-o -

LU

8

LEIS TOCE

Z.

WITH
VOLC.
SANDS

9
o

o.

• o 1 1 1
CM

•t

•

*n
•V.
V

12
SEMIINDURATED

o
13
- σ -

-

14
15

o
16
- σ -

17

20
LO

21

22

c£ —

——

"" VOLC.
H SANDS« WITH
l! CALCITEo CEMENT

•

11 1

LU

O
O

WITH
VOLC.
SAND

•10o -

o

24

• o •

M. MIO. M.MK
EXOTIC
BLOCK
RARE
ASH

•

25

LU

z.

o
o
o.

o
σ - 26
co27
NORTH (TERRACE)

SOUTH (TRENCH)o• o σ> 28

β
#

I

°-

Q

O

23

#

•~

•
•••
•••

•

VÒLC!
SAND

1(BURROWED)•///////////
HOLE TERMINATED

Figure 7. Correlation of the seismic reflection profile with physical properties and the lithologic column, Sites 196 and 187.

225

SITE 186

to
to
OS

SITE 186

DENSITY(gm/cc)Mean GRAPE Density, +Shore Laboratory Density, x
Water Displacement Density, A(m)

LITHOLOGICDESCRIPTION

.0

2.0

3.01.5DENSITY(gm/cc)Mean GRAPE Density, +Shore Laboratory Density, >Water Displacement Density,

COMPRESSIONALWAVE
VELOCITY(km/sec)
2.0

LITHOLOGIC DESCRIPTIONUNIT A(see sheet 1)

scattered carbonate-richhorizons
UNIT A
DIATOMACEOUS SILTY CLAY
some DIATOM OOZEin upper part
Numerous layers of
VOLCANIC ASH
andSAND
olive graycalcite cemented silt
sandZ r--•------

I

bedding inclined up to 15°

sand layers

increase in induration

.0

2.0

3.01.5COMPRESSIONALWAVE
VELOCITY(km/sec)
2.0

2.5

SITE 186

DENSITY(gm/cc)Mean GRAPE Density, +Shore Laboratory Density, x
Water Displacement Density, A(m)

LITHOLOGIC DESCRIPTION

2.0

3.01.5DENSITY(gm/cc)Mean GRAPE Density, +Shore Laboratory Density, x
Water Displacement Density, A

COMPRESSIONALWAVE
VELOCITY(km/sec)
2.0

2.

(m)

LITHOLOGIC DESCRIPTION

volcanic sandcarbonate-rich horizon

2

ashsize-graded sand

UNIT Atsee sheet 1)

UNIT A(see sheet 1)

sand
ash
bedding inclined 15°

bedding inclined 30°

MIDDLE
MI0CENE(?)
EXOTIC

pumice pebble

to

1 .0

2.0

COMPRESSIONALWAVE
VELOCITY(km/sec)

3.0 1 .5

2.0

2.5

SITE 186

2

r

n
—*

1111 1 1 1 1 1 1 11 1 1(D) Denticuia seminae

UPPER PLEISTOCENE

O

3

Explanatory notes in Chapter 1

228

Basic lithology
DIATOM RICH SILT
olive gray (5Y 3/2)

•ys

-<^r

-130
-5

1

SILT BEARING SAND, 60% feldspar, 40% pyroxene

-50

-v^
>/

ys

-87 1

DIATOM OOZE, yellowish brown (10YR 4/4)
Core Catcher:
D A G

-xy

ys
Core
Catcher

LITHOLOGIC DESCRIPTION

VOID

•ys

j

LITHO.SAMPLE

METERSPRES.

ABUND.

FOSSIL

ZONE

AGE

LO

R M

LITHOLOGY

1 1 1 1 |1 1 1 1 |l 1 1 1

1

i

i

R
S

Cored Interval; D-2

Core 1

FOSSILCHARACTER

DEFORMATIONHoleSECTION

Site 186

-s^•

ΛJ•

N
R
S
PF
BF

F
F
R
-

M
M

SITE 186

WET-BULK DENSITY, gm/cc
1
2
3
11 i i i I i i i i i ' ' ' • i ' 'POROSITY,%
100
0

SECTION
CM
-0

«i

Grain
Density
32 «

J3§»

ù-

1-

-25

2-

-50
3-

4-75

5-

-100

7-

-125

8-

-150

186-1-1 186-1-2

229

SITE 186
Site 186

Hole

Core 2

Cored I n t e r v a l : 2 - 1 1

FOSSILCHARACTER

LITHOLOGY

LITHOLOGIC DESCRIPTION

-27
0.5 —

VITRIC ASH
PUMICE PEBBLE

-75
1.0-

Basic lithology, Sections 1 and 2
DIATOMACEOUS SILTY CLAY
very dark gray (5Y 3/1) todark greenish gray (5GY 4/1)

Slide 1-75
40$ clay, 35% diatoms, 25% silt (feldspar, qtz, pyroxene.
glass)
pod of CALCAREOUS DIATOM OOZE
pods of SANDY SILT, black (5YR 2.5/1) in Section 2

VOID

-92

SPICULE BEARING CLAY RICH DIATOM OOZE
iron oxide staining

VOID
SILT BEARING CLAY RICH DIATOM OOZE
olive gray (5Y 4/1)
80% diatoms, 15% clay, 5% silt (qtz, feldspar)
VOID

DIATOMACEOUS SILTY CLAY to
SILT BEARING CLAYEY DIATOM OOZE
olive gray (5Y 4/1)
sections 3, 4, 5 contain bands of iron staining

occasional voids due to drilling disturbance
-74

Core
Catcher
Explanatory notes in Chapter 1

230Core Catcher:
D A G
PF BF _N R R M
S R M

SITE 186
WET-BULK DENSITY, gm/cc
1

2

SECTION
CM

3

ro

M
O-i

1-

-25

2-

-50

3-

4-75

5-

-100

6-

-125

8-

1-150

186-2-1 186-2-2 186-2-3 186-2-4 186-2-5

231

SITE 186
Site 186

Hole

Core 3

Cored Interval .-11-20

LITHOLOGIC DESCRIPTION

ASH, light gray (N7)SANDY SILT, black (5YR 2.5/1)
PUMICE pebble, 4 x 3 x 2 cm

Slide 2-75
50% clay
25% terrigenous silt
25% diatoms

SILTY SAND
ASH

Basic lithology
SANDY SILT Sharply and gradationally interbedded
DIATOMACEOUS SILTY CLAY
CLAYEY DIATOM OOZE and
SILT RICH
SILT
and CLAY RICH DIATOM OOZEDIATOM OOZE
olive gray and dark olive gray (5Y 3/2) toASH
dark greenish gray (5GY 4/1)

SILTY
DIATOM OOZE

ASH

interbeds of:1) light colored VITRIC ASH
2) SILTY SAND and SANDY SILT (probably fromvolcanic source terrane)
black (5YR 2.5/1)
composition:
30 - 40% feldspar
20 - 25% glass
5 - 1 0 % pyroxene
3 - 10% clay
20 - 35% lithic fragments, opaque

ASH
PUMICE LAPILLISILTY SANDSILTY SAND

Explanatory notes in Chapter 1

232

Core Catcher
D F M
PF BF N R F M
R M

SHE 186

WET-BULK DENSITY, gm/cc
1
2
3
POROSITY,*
100
0

SECTIONCM

Grain
Density
M
ü-η

1-

-25

-50
3-

-75

5-

6-

-100

•-

7-

-125

O _

-fi
9- 1
L—150

-.a* >
186-3-1 186-3-2 186-3-3 186-3-4 186-3-5 186-3-6

233

SITE 186
Site186

Hole

Core 4

Cored Interval:49-58

LITHOLOGIC DESCRIPTIONSPICULE BEARING, SILT RICH CLAYEY DIATOM OOZE
dark gray (2.5Y 4/0)
Slide 1-75
50% diatoms, 30% clay, 15% qtz, feld., 5% spicules
grades downward to:

SILT BEARING CLAY RICH DIATOM OOZE
gray (5Y 4/1)
Slide 3-75
75% diatoms, 15% clay, 10% qtz, feld, opaque
5-10 mm long white pods of sponge spicules
at 91, 99, and 103 cm (section 3)

SPONGE
Slide 103
100% spicules

DIATOM RICH SILTY CLAY
medium dark gray (N4)SPICULE and DIATOM BEARING SANDY SILTSILT and CLAY BEARING DIATOM OOZE

grades downward to:Core Catcher:D
PF BF N - Entire core is gassy, numerous voids R R M
S - -CLAYEY DIATOM OOZE

234

SITE 186

WET-BULK DENSITY, gm/cc
1
2
3
POROSITY,*
100
0

SECTION
CM

ro

Grain
Density

i
•

l-

-25

-50
3-

4-75

5-

-100

7-

-125

8-

9- 1
«-150

186-4-1 186-4-2 186-4-3 186-4-4 186-4-5 186-4-6

235

SITE 186
Core 5

Cored Interval:96-105

CQ

o;
Q-

1ETERS

o
"*"

CO
LU

o
ECTIOI

CO

ND.

SIL

AGE

ZONE

FOSSILCHARACTERCOdB.

LITHOLOGY

Qu

O.SAM

Hole

ORMAT

Site 186

Lu
LU

T :

LITH0L0GIC DESCRIPTION

"*

VOID

-

0.5-

1

-\×
_
1.0-

VOID
, _. ._. ._. .—^*s

1 1 1 11IΛ

ctonari

o

o

2

s1

O

CΛ

a

2
_^
Q

J

VOID

Jg
w

.J-

3

CO

_.._.._..—-

'
Qi CO

R

M

—v^

..
1 1 i i i i 1 1

-

_
-

Core
Catcher
Explanatory notes in Chapter 1

236

-130

DIATOMACEOUS SILTY CLAY
gray (N4)

_
—
_
-

LU

LU

P

-

1 ll 1

jrvirosi

CO

Q.

._

^

rOCEN

Z

LU

_. ._.

ii

S l i d e 1-130
30% diatoms
30% t e r r i g e n o u s
40% c l a y

Gassy core

VOID

1— —O

•yr
-

•

-

-

Core C a t c h e r :D A GPF BF N
R
R M
S R M

/^/
%

silt

SITE 186
WET-BULK DENSITY, gm/cc
1

2

SECTION

3

CM
-0

1-

-25

'

2-

-50
CO

3-

4-

CJ3
O

-75
O

5-

-100

6-

7-

-125

8-

-150

1

186-5-1 186-5-2 186-5-3 186-5-4

237

SITE 186
Site 186

Hole

Core 6

Cored Interval:105-114

FOSSILCHARACTER
LITHOLOGIC DESCRIPTION

LITHOLOGY

1.0—

VOID

DIATOMACEOUS SILTY CLAY
olive gray (5Y 4/1)

Slide 3-70
40% clay
20% feldspar
5% qtz
5% heavy, opaque
30% diatoms

VOID

.~ c

-70
-82
119

VOID

SAND, black, volcanic source terrane (?)
CLAY RICH DIATOM OOZE
SAND

Gassy core - numerous voids fromgas expansion
SAND Core Catcher:Core
Catcher
Explanatory notes in Chapter 1

238

D
PF
BF
N
R
S

C
_
_
_
R
R

G
_
M
M

SITE 186

WET-BULK DENSITY, gm/cc
1
2
3

SECTIONCM

POROSITY,*
100
0

Grain
Density
-32 o
3

-25

X
3
^

50

j
^

3-

l

4-

5-

6-

-100

7-

-125

8-

9- 1
150

186-6-1 186-6-2 186-6-3 186-6-4

239

SITE 186
Site 186

Hole
FOSSILCHARACTER

Core 7

Cored Interval:114-123

LITHOLOGIC DESCRIPTION

LITHOLOGY

VOID
0.5-

1.0-120143

spicule bearing
DIATOMACEOUS SILTY CLAY
olive gray (5Y 3/2)

-70

with interbeds of-40

SILT RICH SAND
black (5YR 2.5/1) to dark brownish
gray (5YR 2/1)

composition suggests volcanic source-120
Slide 1-120
30% glass
30% lithic fragments (andesite)
25% feldspar
5% quartz
5% pyroxene
5% chlorite, biotite

Slide 1-143
40% clay
20% quartz, feldspar
40% diatoms-75

Slide 2-70
40% clay
15% qtz, feldspar (silt)
2% spicules
40% diatoms

Gassy core - numerous voids fromgas expansion - enough sediment
for a 7th section was extruded fromthe core liner.
Core Catcher

D
PF
BF

Core
Catcher
Explanatory notes in Chapter 1

240

M
IN

R
S

A
_
-

G

F
R

M
M

SITE 186
WET-BULK DENSITY, gm/cc
1
2
3|i 1 i i I • i " > I
POROSITY,*
100

0

" ' M

SECTIONCM-0> « 'I

Grain
Density
M
O-l

-25

-50

4-75

5-

-100
6-

7-125
8-

-150

186-7-1 186-7-2 186-7-3 186-7-4 186-7-5 186-7-6

241

SITE 186
Site 186

Hole
FOSSILCHARACTER

Core 8

Cored I n t e r v a l ; 133-142

LITHOLOGIC DESCRIPTION

LITHOLOGY

0.5-.J/üll

hi 00

1.0—

SPICULE BEARING, SILT and DIATOM RICH CLAY
dark greenish gray (5GY 3/1)

VOID

Slide 1-100
50% clay
20% quartz and feldspar
7% spicules
25% diatoms

grades downward to:

SPICULE BEARING, DIATOM BEARING SILTY CLAY
dark greenish gray (5GY 3/1)

Slide 5-100
60% clay
35% quartz, feldspar (silt)
5% diatoms

Gassy core - voids from gas expansion

-100

Core
Catcher
Explanatory notes in Chapter 1

242

XR 3-90
Core Catcher:
76% aπtorph. D A G
5% quartz
PF _6% plag.
BF _6% micaN
2% chlor.
R R M
4% mont.
S

SITE 186

WET-BULK DENSITY, gm/cc
I
2
3
I1 i i 1 1 1 i 11 I •» •POROSITY,%
100
0

11

SECTION
CM
- 0

i 11

Grain
Density

3&

0-

-25

2-

-50
3-

1
)

4-75

5-

-100
6-

7-

-125

8-

-150

186-8-1 186-8-2 186-8-3 186-8-4 186-8-5

243

SITE 186
Site786

Hole

Core 9

Cored Interval:161-170

LITHOLOGIC DESCRIPTIONPUMICE LENSVITRIC ASH
olive gray (5Y 4/2) todark grayish brown (10YR 4/2)
spicule and diatom bearing near top of core
PUMICE PEBBLES, 1 mm to 1 cm
SILTY SAND, dusky brown (5YR 2/2)

DIATOMACEOUS SILTY CLAY
very dark gray (5Y 3/1)

Gassy core
Numerous gaps, 5-10 cm, due to gas
expansion; enough material extruded toform sections 7 and 8.

244

SITE 186
WET-BULK DENSITY, gm/cc
1

2

ro

Grain
Density

POROSITY,*
100
0

I

SECTION
CM

3

I

I

*

1

\

l,è

M

33O1

Q_

l-

MB

H

|

.,

-25

2-

-50
3-

4-75

5-

-100

6-

7-

-125

8-

9-1
«—150

186-9-1 186-9-2 186-9-3 186-9-4 186-9-5 186-9-6

245

SITE 186

WET-BULK DENSITY, gm/cc]

2
POROSITY,*

100

0

3

SECTION
CM
rθ

Grain
Density-3 2 o
Jj

O

Jai

o-

-25

2-

-50
3-

-75

5-

6-

-100

7-

-125
8-

g

L-150

186-9-7 186-9-8

246

SITE 186
Site 186

Hole

Core 10

Cored Interval: 170-179

LITHOLOGIC DESCRIPTION

DIATOMACEOUS SILTY CLAY
very dark gray (5YR 3/0)

Gassy core
Numerous 1-10 cm voids caused
by gas expansion

Slide 4-75
40% clay
35% terrigenous silt
25% diatoms

248

SITE 186

WET-BULK DENSITY, gm/cc
1
2
3
11 i i i I i i i i i

SECTIONCM-0> > ' i i > i >i

POROSITY,*
1000
I i T i ^πGrain
Density

M °
I3I

M
O-i

1-

-25

2-

-50
3-

-75

1
3
5k

6-

-100

7-

-125

8-

-150

186-10-1 186-10-2 186-10-3 186-10-4 186-10-5 186-10-6

249

SITE 186
S i t e 186

HoleCore 11

Cored I n t e r v a l : 207-216

FOSSILCHARACTER

LITHOLOGY

LITHOLOGIC DESCRIPTION

0.5-

1.0-

-95
SILTY SAND
very dark gray (5Y 2/1)
probable volcanic source
Slide 1-95
40% opaques, lithic fragments
20% feldspar
12% glass
10% pyroxene
3% amphibole
5% quartz
5% diatoms

-95

-50

SILTY CLAY
olive gray (5Y 4/1)
contains disturbed pods of silty sand-115?

SILTY SAND
very dark gray (2.5Y 3/0)
composition suggests probable
volcanic source
disturbed zone oflarge CLAY pods

PUMICE PEBBLE

Gassy coreCore
Catcher
Explanatory notes in Chapter 1

250Core Catcher:
D A G
PF R N
BF C
N
R
R M
S
-

XR 6-40
72% amorph.
4% q u a r t z
15% p l a g .
2% mica
1% c h l o r .
2% mont.
3% a u g i t eSITE 186

WET-BULK DENSITY, gm/cc
1
2
3
I' ' ' I ' ' ' ' i ' • • ' i ' ' i
Grain
POROSITY
Density

SECTION

CM
-0

M
ü-

1-

-25

2-

-50

-75

-100

-125

-150

186-11-1 186-11-2 186-11-3 186-11-4 186-11-5 186-11-6

251

SITE 186

LITHO.SAMPLE |LITHOLOGY

LITHOLOGIC DESCRIPTION

VOID

π

1 11 1PRES.

ABUND.

FOSSILZONE

AGE
LOWER PLEISTOCENE

Cored I n t e r v a l ; 245-254

DEFORMATIONCore 12FOSSILCHARACTER

METERSHoleSECTION

Site 186

1

*
R
S

R M
A G

DIATOM RICH SILTY CLAY
dark olive gray (5Y 3/2)

•v^

V

1.0-

-+S
•‰S

PUMTfF PFRRIF
PUMILL PLBBLt'..-..JT-T.:
-N-r

Core
CatcherCore Catcher:
D A G
_
p(_
BF N
R
R M

-118

Gassy core
nassy core

-^/

-o!

s

R

M

Slide 1-118
20% diatoms
5Q%c ] a y30% silt: qtz, feldspar
pyroxenehornblende
chlorite.glass*(D) Actinocyclus oculatus(S) Dictyocha subarctios
Site 186

Hole

Core 13

Cored I n t e r v a l ; 291-300

LITHOLOGIC DESCRIPTION

Semi-indurated
DIATOMACEOUS SILTY CLAY
olive gray (5Y 3/2)
-23

ERRATIC PEBBLE
4 x 3 x 3 cm

Core Catcher: Slide 2-23
45% diatoms
D
C G
15% silt
PF 40% clay
BF N
- R
R M
S R M
Gassy core?

Explanatory notes in Chapter 1

252

SITE 186

WET-BULK DENSITY, gm/cc
1
2
3
11 i • > I ' •' i • > «POROSITY,*
100
0

SECTIONCM-0i • « » • I

Grain
Density
M

O-i

\

-25

i

I

-50
3-

4-75

5-

-100

6-

7-

-125

8-

-150

186-12-1 186-13-1 186-13-2

253

SITE 186
Core 14LITHOLOGY

LITHO.SAMPLE |METERSPRES.

ABUND.

FOSSIL

ZONE

Cored I n t e r v a l : 338-347

Semi-indurated, fractured

1*

SPICULE BEARING DIATOMACEOUS SILTY CLAY
olive gray (5Y 3/2)

y— —\
s~

-

~

•

-

~

•

-120

—v

-

Core
Catcher

UPPER PLIOCENE

LITHO.SAMPLE |LITHOLOGY

zabelinae

LITHOLOGIC DESCRIPTION

VOID

-

\s

0.5*

Slide 1-120
40% diatoms
35% clay
25% terrigenous s i l t

Cored Interval:385-394

METERSPRES.

ABUND.

FOSSILZONE

AGE

SECTION

Core 15

FOSSILCHARACTER

DEFORMATION |HoleCore Catcher:
D A G
PF BF N
- R
R M
S
- -

*(D) Thalassiosira

Explanatory notes in Chapter 1
Site 186

LITHOLOGIC DESCRIPTION

VOID

0.5o
I I11 1 1 1

UPPER PLIOCENE

AGE

FOSSILCHARACTER

DEFORMATION |HoleSECTION

Site 186

N

•\J-

1

V
•\-r

1.0-

44
46

DIATOM RICH CLAYEY SILT and SILTY CLAYo l i v e gray (5Y 3/2)
XR 1-10
. . .
. . ,
,
7 U amorph.
semi-indurated, fractured
5% q u a r ^ zCore Catcher:
D A G
pp

• \ _ ^C A L C I T E CEMENTED S I L T

Ly-

1

C Dre
Cat cher'•i•"'•' r• Λ

Explanatory

254

notes i n Chapter 1

-

'

'• •

:

* ( D ) T h a l a s s i o s i r a zabelinae\ Jj]^"
4% c h l o r .
2% mont.
1% amph.

λλ

^F
R
S

"
R M
- -

SITE 186

WET-BULK DENSITY, gm/cc
1
2
3
POROSITY,*
100
0

SECTION

CM

ro

Grain
Density-a 2 o
M

-25

2-

-50
3-

4-75

5-

-100
6-

7-

-125

8-

9-1
1-150

186-14-1186-15-1

255

SITE 186
Site 186

Hole

Core 16

Cored Interval.- 394-403

FOSSILCHARACTER

LITHOLOGY

LITHOLOGIC DESCRIPTION

0.5-

SILTY SAND layers
black

1.0-

CARBONATE BEARING DIATOMACEOUS SILTY CLAY
olive gray - light olive gray (5Y 3/2 - 4/2)

VOID
-70
100
-120

SILTY SAND, graded

pods of SILTY SAND
volcanic source (?)

Core
CatcherSite 186

Hole
FOSSILCHARACTER

Core 17Slightly gassy core
Cored Interval:422-431

LITHOLOGIC DESCRIPTION

LITHOLOGY

0.5-

Slide 1-92
40% clay
40% diatoms
10% terrigenous s i l t
10% carbonate
Core Catcher

VOID

1.0-

Semi-indurated, fractured
DIATOMACEOUS SILTY CLAY
greenish black (5G 2/1)
o .;zSlightly gassy core.

burrowedCore
Catcher
Explanatory notes in Chapter 1
256

XR 3-100
Core Catcher
75% amorph.
D
C G
5% quartz
PF _7% plag.
BF 7% micaN_
2% chlor.
R
R M
4% mont.
S
R M

D A G
PF _
BF _
N _
R _
S
R M

SITE 186
WET-BULK DENSITY, gm/cc
1
2
3
POROSITY,*
100
0

SECTIONCM
Grain
Density

ro
M
ù-

1-

2-

I-50

3-J

WET-BULK DENSITY, gm/cc
1
2
3
POROSITY,*
100
0

Grain
Density
2 o

h75

hioo

r-125

'150 H••B • H 9 I • • •U

186-16-1 186-16-2 186-17-1 186-17-2 186-17-3

257

SITE 186
Site 186

Hole

Core 18

Cored Interval:440-449

FOSSILCHARACTER

LITHOLOGY

0.51.0-

LITHOLOGIC DESCRIPTION

VOID

-100

carbonate and spicule bearing
DIATOMACEOUS SILTY CLAY
dark olive gray (5Y 2/2)
Slide 1-100
40% clay
40% diatoms
10% silt

5% carbonate (nanno elements ?)5% spicules

lens of volcanic sandpod of SAND, very dark gray (5Y 2/1)
DIATOMACEOUS SILT RICH LIMESTONE
light olive gray (5Y 5/2)
50% calcite
30% diatoms
18% silt
2% spiculesCore
Catcher

Explanatory notes in Chapter 1

258

SITE 186

WET-BULK DENSITY, gm/cc
1
2
3| i l i i| ' ' • ' I ' ' ' ' M

POROSITY,*
100
0

SECTION

CM

' « I

r°

Grain
Densityio§M•3 3 "=F>

ù-i

1-

-25

2-

-50

3-

,

J

4-75

5-

-100

7-

-125

8-

-150

186-18-1 186-18-2 186-18-3

259

SITE 186
S i t e 186

HoleCore 19

Cored I n t e r v a l : 449-458

FOSSILCHARACTER
LITHOLOGY

LITHOLOGIC DESCRIPTIONVOID

SPICULE and CARBONATE BEARING,
DIATOMACEOUS SILTY CLAY

0.5-H

-100

1.0—

SILTY
SAND

olive gray (5Y 3/2)
30 - 40% diatoms
35 - 45% clay
15 - 20% silt
3% spicules
1 - 5% carbonate

VOID

-3

VITRIC ASH
light gray

VOID

XR 3-3077% amorph,
3% quartz
12% plag.
1% mica
1% chlor.
1% mont.
3% augite

SANDY SILT

α> oo

-25

SPICULE RICH VOLCANIC SAND
dusky brown (5YR 2/2)

SPICULE BEARING
DIATOMACEOUS SILTY CLAY
medium dark gray (N3)-95Core Catcher:
pod of SANDCoreCatcher
Explanatory notes in Chapter 1

260

D
PF

BF
N
R
S

C
_
_
_
R
R

G

_

M
M

XR 4-2077% amorph
3% quartz
12% plag.
2% mica
i°/ chlor.
1hΛ °/ mont.
1 I0
9"/
Lh
augiteSITE 186
WET-BULK DENSITY, gm/cc
1

2

11 i i i I i i i i i i > i > i « ' i

SECTION
CM

3
i

ro

Grain
Density

POROSITY,%
100
0

rη

13I

M
O-i

1-

-25

2-

.

T

-50
3-

4-

1

-75

J

5-

6-

-100

j
7-125

:

I

w"•

. m

—

8-

•
q_

L-150

\ j
LU

186-19-1 186-19-2 186-19-3 186-19-4

261

SITE 186
Sitel86

Hole

Core 20

Cored Interval:458-467

FOSSILCHARACTER

LITHOLOGIC DESCRIPTION

LITHOLOGY

0.5-

VOID

1.0-

SPICULE BEARING
DIATOMACEOUS SILTY CLAY
olive gray (5Y 3/1 - 3/2)
numerous thin beds of laminated
SAND and SANDY SILT
olive black (5Y 2/1)

VOID
-60

main lithology composition
40 - 50% clay
35 - 40% diatoms
5 - 25% silt
2% spicules

.127?
-136?

-50
PUMICE PEBBLE

-131
150

-95

Core
Catcher
Explanatory notes in Chapter 1

262

Core Catcher
D A G
PF _
BF _
N _ _
R R M
S _ _

SITE 186

WET-BULK DENSITY, gm/cc
SECTION

CM
ro

r.

M
O-i

1-

-25

2-

-50

3-

4-75

5-

-100

6-

7-

-125

8-

9-1

L-150

186-20-1 186-20-2 186-20-3 186-20-4 186-20-5

263

SITE 186
S i t e 186

HoleCore 21

Cored I n t e r v a l ; 5 0 6 - 5 1 5

FOSSILCHARACTER

LITHOLOGY

0.5—

1.0-

LITHOLOGIC DESCRIPTION

VOID

-100
SPICULE BEARING
DIATOMACEOUS SILTY CLAY
olive gray (5Y 3/2)
few, thin, black SAND laminae
-74

-32

-110

Core
Catcher
Explanatory notes in Chapter 1

264

Slide 1-100 (silt rich diatomaceous clay)
60% clay
30% diatoms
10 - 15% silt
3% spiculesburrows
DIATOM BEARING SILTY LIMESTONE
5% diatoms, 10% terrig. silt, 85% calciteburrows
Core Catcher:
XR 3-3077% amorph.
D A G
Slide 3-110
2% quartz
PF 40% diatoms
9% plag.
BF \O% clay
1% micaN- 18% s i l t
2% mont.
R M
2% spicules
1% clinop,
1% anal.
1% amph.
5% augite

SITE 186

WET-BULK DENSITY, gm/cc
1
2
3

SECTIONCM

I ' I ' ' I >l ' ' I '

ro

Grain
Density

POROSITY,%
100
0

2 ü
o
T

I

1-

-25

2-

-50
3-

-75

5-

-100
6-

7-

-125

8-

9-1
L-150

186-21-1 186-21-2 186-21-3

265

SITE 186
S i t e 186

HoleCore 22

Cored I n t e r v a l : 5 6 2 - 5 7 1

FOSSILCHARACTER

LITHOLOGY

LITHOLOGIC DESCRIPTION

VOID
0.5-

1.0-

-100
DIATOMACEOUS SILTY CLAY
olive gray - dark greenish gray(5Y 3/2 - 5G 4/1) interlayered-40-66

VITRIC ASH
light gray (N7)

grades downward to

SPICULE and DIATOM BEARING SILTY CLAY
dark gray (2.5Y 4/0)
laminae of dark volcanic sand-60
SAND, dusky brown (10YR 2/2)
SILT and SAND, size graded
145
Core
Catcher
Explanatory notes in Chapter 1

266Core Catcher
D A G
PF _
BF _
N R R M
S R M

sand/silt/clay % for graded interval, sect. 3
sect. 3, 104 cm 34, 60, 6
124 cm 61, 30, 9 142 cm 89. 8. 3

SITE 186
WET-BULK DENSITY, gm/cc
12

3| 1 l i • | ' ' ' • M' ' ' I • ' i ' I

SECTIONCM
i-o

POROSITY,*

M
On

1-

-25

2-

-50
3-

4-75

5-

-100

6-

-125

8-

L-150

186-22-1 186-22-2 186-22-3

267

SITE 186
Sitel86Hole
FOSSILCHARACTER

Core 23

Cored Interval:618-627

LITHOLOGY

LITHOLOGIC DESCRIPTION

XR 2-60, 3-20, 3-110

0.5—

VOID

6%
7%
5%
2%

1.0-

68%
1%
22%

73%

amorph.

9%
7%
6%
2%

quartz

TR
TR

plag.
mica
chlor.
mont.

DIATOMACEOUS SILTY CLAYo l i v e gray (5Y 3/2)

few thin SAND and SILT laminae

-75

-10

-110
118

268

diatoms more abundant (~45%)
silt coarser and more abundant ('trace of nannos
Core Catcher:Dgrayish olive (10Y 4/2)
N R M
R R
S R
PF F
BF C

Core
Catcher

Explanatory notes in Chapter 1

SAND

MIDDLE MIOCENE

M
M

clinop.
anal.
pyriteamph.
augiteSITE 186

WET-BULK OENSITY, gm/cc
1
2
3| i i i « I

i

M '

' I

' i

ro

Grain
Density-a 2 uPOROSITY,*
100
0

!

SECTIONCMI

I I I I I

Jai

li'

M
On

1-

-25

2-

-50
3-

4-75

5-

-100
6-

7-

-125

8-

L-150

186-23-1 186-23-2 186-23-3

269

SITE 186
Site186

Hole

Core 24

Cored Interval:683-692

LITHOLOGIC DESCRIPTIONSPICULE BEARING
DIATOMACEOUS SILTY CLAYo l i v e gray (5Y 3/2)

Slide

ERRATICStKKAI1Li'80

40% clay
20% s i l t

35% diatoms
3% spicules

PUMICE PEBBLE
scattered sponge remains
few t h i n s i l t y laminae

Bedding i n c l i n e d up to 30°

some gas i n core

270

Core Catcher:
D A G
BF PF N R R M
S -SITE 186

WET-BULK DENSITY, gm/cc
1
2
3
POROSITY,*
100
0

SECTION

CM
-0

Grain
Density

§;

M
o-i

l-

-25

2-

-50

S

3-

4-75

5-

-100
6-

7-

-125

8-

9-150

186-24-1 186-24-2 186-24-3

271

SITE 186

LITHO.SAMPLEPRES.

ABUND.

FOSSILLITHOLOGIC DESCRIPTION

DIATOM RICH SILTY CLAY
olive gray (5Y 3/2)
50% clay, 30% silt, 20% diatoms

1

-80
i n .

I .U

"IrZ~Z~Z
1111 111 11 1 1I 1 1

ZONE

LITHOLOGY

0.5-(S) Cannopilus hemisphaericus(D) Denticula seminae - D. kamtschatica

LOWER PLIOCENE

AGE

FOSSILCHARACTER

Cored Interval:731-740
DEFORMATIONCore 25

METERSHoleSECTION

Site 186

2

DIATOM RICH SANDY SILTY CLAY
olive gray (5Y 3/2)

136

SPICULE BEARING SILTY CLAY
med. to dark gray (N4 - N3)_: -67-145

SAND LAMINAECore
CatcherSite 186

Hole

Core 26

gassy coreCore Catcher:DC G
PF BF N- R
S R M

Cored Interval.805-814

FOSSILCHARACTER
LITHOLOGY

LITHOLOGIC DESCRIPTION

0.5 —

1.0-

-100

-51

SPICULE BEARING, DIATOM RICH SILTY CLAY
olive gray (5Y 3/2)
Slide 1-100
60% clay
20% diatoms
15% terrig. silt
5% spicules
grades downward to:

DIATOMACEOUS SILTY CLAY

lü
PF
BF
N
R
S

-146
Core
Catcher

Explanatory notes in Chapter 1

272

XR 2-30, 2-120
80%78% amorph
quartz
5%
5%
plag.
7%
7%
mica
3%
6%
2% chlor.
2%
λl mont.
clinop1%
anal.
TRamphibTR
augite1%\ I0

SPICULE BEARING, DIATOM RICH CLAYEY SILT
dark olive gray (5Y 3/2)
40% silt, 25% clay, 20% diatoms, 5-10% spiculesSITE 186

WET-BULK DENSITY, gm/cc
1
2
3| i l i i I i i i ' I i ' i ' M

SECTIONCM' ' > I

Grain
Density

POROSITY,*

ro

2

J S
1 I

l

M
O-i

1-

-25

2-50

3-

WET-BULK DENSITY, gm/cc
1
2
3
POROSITY,*
100
0

-75

Grain
Density

Λ

3 2 «
3
u

-100

1-

2-

-125

1—150

186-25-1 186-25-2 186-26-1 186-26-2

273

SITE 186
Site 186

Hole
FOSSILCHARACTER

Core 27

Cored Interval.861-870

LITHOLOGY

LITHOLOGIC DESCRIPTION

0.5-1
DIATOM and SILT BEARING CLAY
olive gray (5Y 3/2)
75% clay, 10% silt, 5% glass, 5% diatoms
2% carbonate

1.0-

zone of parallel sand and silt laminae-90

convolute graded laminae-85

SPICULE and DIATOM BEARINGSILTY CLAY
olive gray (5Y 3/2)
-85
laminated sand and silty sand layers (up to 10 cm
thick) and thin sand laminae throughout coreburrowed
bedding inclined about 15C

Core
Catcher
Explanatory notes in Chapter 1

274

VITRIC ASH, light grayCore Catcher:
D F G
PF _
BF _
N _
R _
_ _
GO

-77

XR 3-30, 6-80
76%73% amorph
6%6% quartz
1%
7% plag.
6%8% mica
2%
3% chlor.
1%
3% mont.
V/cclinopTRanal.
TR
1% amphib

SITE 186
WET-BULK DENSITY, gm/cc
1

2

3

11

i i i I i i i i i i i i i i i i •11

POROSITY,* 0100

SECTIONCMro

SlS!jtDensityu
M
U

1-

\
\
\
\
\
/
/
/
/
/
/

-

-25

2-

-50

3-

4-

\

-75

-

5-

•

\
\

-100

6-

\

\
\

-

1

1
I

7-

I

—

1
1
1
\
\
\
\
\
\

-

-125

8-

91-150186-27-1 186-27-2 186-27-3 186-27-4 186-27-5 186-27-6

275

SITE 186
S i t e 186

HoleCore 28

Cored I n t e r v a l ; 9 1 7 - 9 2 6

FOSSILCHARACTER

LITHOLOGY

0.5—

LITHOLOGIC DESCRIPTION

VOID

1.0—
120

-112

-51
_75
"78

SAND black
40% feldspar, 25% pyroxene, 15% opaque, 10% qtz,
5% amphibole
SHALE PEBBLE CONGLOMERATE
rounded clasts, 3 x 6 cm, of same composition as remainderof coreBasic lithology
SPICULE and DIATOM BEARING SILTY CLAY
and SILT RICH CLAY
olive gray (5Y 3/2)

1 cm thick interbeds aredark greenish gray to greenish black(5G -4/1 - 2/1) and contain more chlorite
than lighter layers

entire core extensively burrowed
bedding inclined 15 - 20°
XR 2-110, 3-60
59%72% amorph.
7% quartzn32%
8% plag.
O/a
1%
mica
chlor.
2% mont.
V/o amph.
4%
3%
augite
1%
magn.

-111

Core Catcher:
D R M
u_

Core
Catcher
Explanatory notes in Chapter 1

276

N
R
S

-

SITE 186

WET-BULK DENSITY, gm/cc
1
2
3

SECTIONCM| I I i U ' ' • ' M ' • ' I ' • ' i I

POROSITY,*
100
0

ro

Grain
Density
2 «

'•.

M
On

1-

-25

2-

-50

3-

4-75

5-

-100

6-

7-

-125

8-

L-150

186-28-1 186-28-2 186-28-3 186-28-4 186-28-5 186-28-6

277