-
36. GEOCHEMICAL HISTORY OF POST-JURASSIC SEDIMENTATION IN THE
CENTRALNORTHWESTERN PACIFIC, NORTHERN HESS RISE, DEEP SEA DRILLING
PROJECT SITE 4641
I. M. Varentsov, B. A. Sakharov, M. A. Rateev, and D. Ya.
Choporov, Geological Instituteof the U.S.S.R. Academy of Sciences,
Moscow, U.S.S.R.
ABSTRACT
Results describe the chemical composition of post-Jurassic
sediments penetrated by Deep Sea Drilling Project Hole464 (northern
Hess Rise), peculiar features in the distribution of chemical
components through the section, and modesof their occurrence
determined by factor analysis and from the data on mineralogy,
lithology, and accumulation ratesof sediments and chemical
components.
Three main stages in the geochemical history of sedimentation in
the region are outlined: I. Late Mesozoic stage(Early
Albian-Cenomanian). la. Early phase (Late Aptian-Early Albian).
This early phase is characterized by ac-cumulation of dark-red and
brown, calcareous silica-clay oozes, considerably enriched by
volcanogenic (mostlyhyalopelite basalt volcaniclastic) material.
High accumulation rates of sediments (22.5 mm 10~3yr-1) and
chemicalcomponents are noted. Ib. Late phase (late
Albian-Cenomanian). Accumulation of relatively light-colored,
calcareous,essentially silicic sediments took place at that time.
The amount of volcaniclastic material, iron, and other heavy
metalsin these sediments is much less than in the early Albian
deposits. Relatively high accumulation rates of sediments (17.9mm
10~3yr~') and of some of the components (SiO2, A12O3, etc.) were
recorded. The obtained data are in good cor-relation with the model
which implies that in the Albian the northern part of Hess Rise was
in the equatorial zone, withhigh biological productivity, while the
Pacific Plate moved northward. II. Late Cretaceous (Early
Turonian?-MiddleMiocene). During that time, relatively local
accumulation of fine volcaniclastic material (ash) took place; this
materialwas transformed into clay (montmorillonite-hydromica)
enriched by ferric hydroxide, and to a lesser degree by
Mn-hydroxide and associated heavy metals. III. Late Cenozoic stage
(upper Miocene-Pleistocene) was the time of ac-cumulation of
clay-silica, mostly radiolarian oozes, in chemical composition and
accumulation rates similar to thetypical clay-silica sediments of
the modern open ocean at depths below the level of carbonate
compensation. Theoutlined stages, phases of geochemical history of
sedimentation in the region, represent the evolution of sediment
ac-cumulation in the basin.
INTRODUCTION
Hess Rise is one of the largest submarine aseismicstructures of
the northwestern Pacific. The Shatsky andMagellan Rises, the
Ontong-Java and Manihiki sub-marine plateaus, and the Mid-Pacific
Mountains alsobelong to this kind of structure. The data now
availableallow us to surmise that during the greater part of
post-Jurassic time these structures were normally above
thecarbonate-compensation depth (CCD). Therefore, theymay contain a
relatively complete section of sediments.
The objective of this work is to outline the majorfeatures of
the geochemical history of sedimentation inthat region, as recorded
in the chemical and mineralcomposition of sediments, on the basis
of study of thechemistry of major components, heavy metals,
traceelements, and data on mineralogy and lithology.
This article is one of the series of works on the geo-chemical
history of sedimentation in the northwesternPacific bored on DSDP
Leg 62 by D/V Glomar Chal-lenger (see Varentsov et al., this
volume).
MATERIALS AND METHODS
The work is based on observational data on chemical and
mineralcomposition, and lithologic features of deposits penetrated
by Hole464, as analyzed at the Geological Institute, U.S.S.R.
Academy ofSciences. Data on lithologic-mineralogical studies are
presented in
Initial Reports of the Deep Sea Drilling Project, Volume 62.
other parts of this volume. The technique of research is given
ingreater detail in the paper on geochemical history of
sedimentation forHole 463 (Varentsov et al., this volume).
Determination of chemical components of sediments was made atthe
Geological Institute: the main components by the method of
bulkchemical analysis, and heavy metals by optical emission
spectroscopy,with application of international reference standards
(Zolotarev andChoporov, 1978).
The chemical analyses were recalculated on a
terrigenous-free,silica-free, carbonate-free basis to exclude the
diluting effect of bio-genic and clastic components, and to adjust
the sediment to a certaingeochemically comparable basis (Varentsov
and Blazhchishin, 1976).
Analytical data were processed by a computer (EC-1022) at
theLaboratory of Mathematical Methods of Research, Geological
Insti-tute (D. A. Kazimirov, P. K. Riabushkin), using the program
of fac-tor analysis (R-, Q-mode; Davis, 1973; Harman, 1967).
It should be noted that the section of Hole 464 is represented
by acomparatively limited number of core samples, especially the
Meso-zoic deposits (early Cenomanian-Albian), mostly composed of
car-bonate silicic rocks.
The shortage of core samples and their inadequate
paleontologicaland biostratigraphical characteristics, and the few
chemical analysesmake the obtained conclusions only tentative and
speculative for thenorthern part of Hess Rise. Interpretation of
this material can bemade only within the context of geological,
lithologic, and geo-chemical, information on that region.
The stratigraphic subdivision of the "brown clay" unit was
made,therefore, according to the results of study of ichthyolith
remains(Doyle and Riedel, this volume). Moreover, the stratigraphic
capacityof the lower part of the unit (Cores 9 and 10) dated by
these authorson the whole as Late Cretaceous, is conditionally
interpreted in thepaper as Turonian-Maastrichtian, from correlation
with adjacentregions (Holes 171 and 310). It was inferred that the
"brown clay"unit is composed of genetically similar deposits which
accumulatedwithout notable hiatuses.
805
-
I. M. VARENTSOV, B. A. SAKHAROV, M. A. RATEEV, D. YA.
CHOPOROV
PARAGENETIC ASSEMBLAGESOF COMPONENTS
The study of paragenetic assemblages of componentswas carried
out using the analytical data processed byfactor analysis. Two
types of determinations were in-vestigated: (1) actual data of
chemical analyses, repre-sented in weight percent to air-dry
weight, (2) recalcula-tion to a terrigenous-free, silica-free,
carbonate-freebasis. In the first case, the determined groups of
chemi-cal components, clusters, are definitely related to exist-ing
mineral phases. In the second case, provided in par-ticular that
the carbonate- and silica-dilution effect iseliminated, clearly
outlined features of a number ofauthigenic mineral phases become
more evident: hy-droxides, hydrothermal exhalates, products of
post-sed-imentary transformations, etc.
Data of Chemical Analysis (Tables 1-3; Fig. 1)
Assemblage IA ( + ): SiO2(0.98)-Corg(0.21)-Ca(0.12).This
assemblage is represented by biogenic silica of theopal-CT type,
with which Co r g associates rather weakly.The assemblage is most
conspicuous in the Cenomanianopal-clay sediment (Sample 11-1, 28-29
cm) with essen-tially altered hyalopelite material, relics of
diatoms, pat-ches of chalcedony, quartz. Early Pliocene
tuffogenicsediments (Sample 3-1, 60-64 cm; Fig. 1) are similar
incomposition; the content of relics of diatoms in them isup to
40%, of spicules of siliceous sponges up to 20%,of radiolarians up
to 10%.
Assemblage IB (-): A12O3( - 0.29)-Mg( - 0.97)-N2O(-0.52)-K
2O(-0.36)-Fe(0.86)-Mn(-0.70)-P(- 0.17)-Cr( - 0.34)-Ni( - 0.49)-V( -
0.74)-Cu( - 0.34)-Co(-0.25)-Pb(-0.56)-Mo(-0.48). This assemblage
isrepresented by essentially altered hyalopelite
basalticvolcaniclastic material, composed of tephra remains, Fe-and
Mn-hydroxides, montmorillonite-illite compo-nents. This group can
be considered as an example ofmultistage formation of an
assemblage: (1) oxidation ofbasaltic hyalopelite volcaniclastics,
development ofcrusts and patches of Fe- and Mn-hydroxides
(Samples9-1, 30-32 cm; 5-5, 70-72 cm, etc.) after
volcanogenicparticles promoting concentration of heavy metals;
(2)transformation of volcaniclastic material into mixed-layer,
fine-grained phases, i.e., montmorillonite-mica(Fig. 2) was
followed by scavenging of Mg and K fromsolutions and from the
bottom water.
Distinct localization of this group of components inthe section
should be noted (Fig. 1). Its most obviousmanifestation is observed
in sediments marking the be-ginning of a burst of explosive basalt
volcanism, mainlyat the base of volcanogenic "brown clay" unit of
theLate Cretaceous-middle Miocene (Doyle and Riedel,this volume);
these clays are deposited on red-brownsilicates, to a lesser extent
limestones of the Ceno-manian. To a relatively lesser extent, this
assemblage isdeveloped in the lower layers of essentially
volcanogenicsiliceous clays of the middle Miocene, and at the base
ofargillaceous radiolarian oozes and argillaceous siliceousoozes of
the late Pliocene-Pleistocene.
Assemblage IIA:
SiO2(0.13)-Al2O3(0.38)-Na2O(0.78)-P(0.73)-Cr(0.32)-V(0.33)-Cu(0.72)-Mo(0.37).Comparison
of the combination of components in thisgroup with observational
data on mineral compositiongives grounds to assume that this
assemblage is repre-sented by aluminosilicate phases of the zeolite
type, withclosely associated phosphorus, copper, and a number
ofheavy metals. The group is confined to volcanogenicsiliceous
hyalopelite sediments in the top layers of theearly Cenomanian, and
to the volcanogenic "brownclay" unit of the Late Cretaceous-middle
Miocene.
Assemblage IIB ( - ) : CaO( -
0.86)-CO2(0.87)-Corg(-0.62)-Ge(-0.62). This assemblage is
represented bybiogenic calcium carbonate, with which Co r g is
closelybound. Being one of the group, Ge is obviously associ-ated
with Co r g and forms metallo-organic compounds.The assemblage
occurs in deposits of the early Plio-cene-Pleistocene, with
carbonate nannofossil micrite re-mains (up to 20%).
Assemblage IIIA ( + ):
Al2O3(0.80)-MgO(0.16)-K2O(0.65)-Fe(0.35)-Mn(0.67)-P(0.53)-Cr(0.80)-Ni(0.82)-V(0.49)-Cu(0.30)-Co(0.93)-Pb(0.57)-Ga(0.90)-Ge(0.47)-Mo(0.72).
Results of mineralogical studies andthe composition of this
assemblage provide evidence tobelieve that it is represented by
fine hyalopelite basalticmaterial, essentially altered to illite
components. Thistransformation may have been accompanied by the
ap-pearance of Fe- and Mn-hydroxide patches, encrusta-tions, and
aluminophosphate and iron phosphate com-pounds in close association
with heavy metals such asCr, Ni, Co, Ga, and Mo.
Assemblage IIIB (-): CO2(-0.46)-SiO2(-0.09)-C( - 0.01)-CaO(?).
The nature of phases in this assem-blage is not quite clear from
the study of its compo-
Table 1. Chemical composition of Mesozoic-Cenozoic deposits,
central northwestern Pacific, northern Hess Rise, Site 464.
Sample(interval in cm)
464-2-1, 115-1193-1,60-644-1, 130-1345-5, 70-726-2, 95-976-3,
94-967-3, 120-1228-2, 13-159-1, 30-3211-1, 28-29
SiO 2
40.5351.5143.7344.8546.5346.7546.3646.9926.5982.68
A12O3
4.673.964.48
12.5312.7714.6512.9812.937.%3.68
Fe 2 O 3
6.745.255.88
10.1513.687.98
11.3312.2828.77
2.14
CaO
16.308.30
11.813.743.013.971.401.632.630.82
MgO
3.222.623.123.813.122.943.622.875.481.76
MnO
0.170.210.072.270.841.770.280.402.690.01
Na2O
4.004.534.213.462.513.183.462.892.991.05
Components
(wt.%)
K2O
2.052.012.403.293.723.294.586.102.440.96
co211.305.107.75
—-―
__
—
C
0.150.01___
__
—
P2O5
0.110.070.131.480.721.400.240.380.990,55
Fe
4.713.674.117.109.575.587.928.59
20.121.50
Mn
0.130.160.051.760.651.370.220.312.080.01
P
0.050.030.060.650.310.610.100.170.430.24
Cr
18202258586260704014
Ni
4811265
500178500
9875
21515
V
434972
140170130135142400
28
(wt.% ×
Cu
11510862
202190160135130245152
Co
13201887448424322710
10 ~ 4 )
Pb
16161967365911146410
Ga
5779
1198855
Ge
< l1.31.211.11.41
< l< l< l
Mo
1.62.81.5
8030
1003.9
8980
1.5
806
-
POST-JURASSIC SEDIMENTATION, SITE 464
Table 2. Results of factor analysis (R-mode) forchemical
components (wt.%), Cenozoic andMesozoic sediments of central
northwesternPacific, northern Hess Rise, Site 464.
No.
123456789
1011121314151617181920
Factor Loading (after
Component
Siθ2A12O3CaOMgONa2θK 2OCO2CFeMnPCrNiVCuCoPbGaGeMo
Input in dispersion
(%)1
Total dispersion (%)
I
0.98-0.29
-0.97-0.52-0.36
0.010.21
-0.86-0.70-0.17-0.34-0.49-0.74-0.34-0.25-0.56
0.12
-0.48
51.13
-51.13
rotation)
II
0.130.38
-0.860.030.78
-0.87-0.62
0.730.32
-0.060.330.72
-0.620.37
19.96
71.09
III
-0.090.80
0.16
0.65-0.46-0.01
0.350.670.530.800.820.490.300.930.570.900.470.72
11.77
82.87
Table 3. Stratigraphic distribution of factor scores (R-mode)for
chemical components (wt.%) in Cenozoic and Mesozoicsediments of
central northwestern Pacific, northern HessRise, Site 464.
No.
12345
6
789
10
Sample(interval in cm)
2-1, 115-1193-1, 60-644-1, 130-1345-5, 70-726-2, 95-96
6-3, 94-96
7-3, 120-1228-2, 13-159-1, 30-3211-1, 28-29
Age
U. Plio.L. Plio.L. Plio.Mio.U. Eoc.L. Mio.U. Eoc.L.
Mio.Paleoc.Paleoc.U. Cret.Cenom.
Factor Score(after rotation)
I
-0.600.630.06
-0.420.09
0.39
-0.080.14
-2.212.00
II
-0.82-1.86-1.38
0.430.43
-0.16
0.380.510.941.52
III
-1.46-0.02-0.56
1.030.95
1.75
0.050.36
-0.71-1.39
nents, but correlation of the intervals of its most defin-itely
manifested development with the actual mineralcomposition of
sediments, as observed in thin sectionsunder microscrope and
revealed by X-ray diffracto-grams, implies that it is represented
by calcium carbon-ate, which occurs as nannofossil micritic
remains. Inthis aspect, the group is similar to assemblage IIB
(-)discussed above. As indicated, the latter is representedmostly
by calcium carbonate in the form of foraminiferand nannofossil
micritic components.
Data on Chemical Analysis Recalculated(Tables 4-6; Fig. 3)
Assemblage IA ( + ):
Fe(0.84)-Mn(0.72)-P(0.31)-Cr(0.64)-Ni(0.39)-V(0.79)-Co(0.15)-Ga(0.29)-Mo(0.79).This
assemblage is represented mostly by oxyhydroxidecompounds of iron
and manganese, and associatedheavy metals. The ferrous phosphate
phases are appar-ently of special importance. The group is
distinctly con-fined to the volcanogenic "brown clay" unit (Unit
II) ofthe Late Cretaceous-middle Miocene. Elimination ofthe
diluting effect of silicate components allows therevelation of the
geochemical significance of Fe- andMn-hydroxides in basaltic
volcaniclastics, and as sepa-rate patches (see assemblages IIA (+),
IIIA (+); Fig. 1;Tables 1-3). The combination of components of
thisassemblage testifies, therefore, that the geochemicalrole of
collectors, concentrating heavy metals, belongsmostly to Fe- and
Mn-hydroxides.
Assemblage IB ( - ) :
CaO(-0.12)-MgO(-0.85)-Na2O(-0.83)-Cu(-0.36). The combination of
compo-nents in this group, peculiar features of its occurrence
inthe section (Fig. 3), and the data on mineral composi-tion allow
us to state that the group is represented by asmectite phase. This
phase is not connected with vol-caniclastics, which are a rather
essential component ofthe intervals in the section of the lower
Pliocene/Pleis-tocene and lower Cenomanian (Fig. 3).
Assemblage IIA (+):
CaO(0.35)-Mg(0.17)-K2O(0.59)-P(0.65)-Cr(0.72)-V(0.39)-Cu(0.67)-Co(0.43)-Ga(0.90)-Ge(0.58)-Mo(0.15).
This assemblage is repre-sented by illite phases, which occur
separately and asmixed-layer components of the
montmorillonite-micatype, developed in fine volcaniclastic, mostly
hyalopel-ite material of basaltic composition. Phosphorus
(alum-ophosphate compounds) and heavy metals, predomi-nantly Cr,
Ga, Cu, Ge, etc., are closely associated withthe illite minerals
proper. The group is confined to sedi-ments in the top part of the
lower Cenomanian and tothe volcaniclastic "brown clay" (Unit II),
probablyLate Cretaceous-middle Miocene (Fig. 2).
Assemblage IIB ( - ) : Na2O(-0.39)-Fe(-0.12)-Mn( - 0.27). This
assemblage is represented by hydrox-ides of manganese and to a
lesser extent iron, and by as-sociated sodium. The assemblage
contains no heavymetals, and it is located at the base of the
volcaniclastic"brown clay" and siliceous, essentially
volcanogenicsediments (Units IA, IB; early
Pliocene-Pleistocene);these facts allow to state that this group is
representedby late-diagenetic, epigenetic patches of
Mn-hydrox-ides, with a slight iron admixture, which formed as
theresult of volcaniclastic alteration. Similar patches
aredistinctly observed, in fairly limited amounts, in thinsection
under the microscope (not more than 5%).
Assemblage IIIA ( + ): Na2O(0.12)-K2O(0.24)-Fe(0.31). This
assemblage is represented by hydroxides ofiron and K- and Na-bound
alkalis. The genetic nature ofthis group and its occurrence in the
section are similar tothose of assemblage IIB (-) , described
above. In this
807
-
00o00
LITH0L0GY FACTOR ASSEMBLAGES (SCORES)
FACTOR ASSEMBLAGESCLAY COMPONENTS
Polymineral assemblage, mainly illite,mixed-layer
montmorillonite—illite, andchlorite, with an admixture of
quartz,tridymite, and cristobalite
Dominantly mixed-layer montmorillon-ite—illite, with a slight
admixture ofillite .chlorite, and zeolite
1.0
0.8
0.6
0.4
0.2
0
0.2
0.4
0.6
0.8
1.0
1
o u
Figure 1. Stratigraphic distribution of factor scores for the
main paragenetic assemblages of chemical components in the
post-Jurassic sedimentary section of the central
northwesternPacific, northern Hess Rise, DSDP Site 464 (chemical
analyses recalculated to air-dry weight). Lithologic symbols are
those used in the DSDP Initial Reports.
-
POST-JURASSIC SEDIMENTATION, SITE 464
SAMPLE 7-5, 45-48 cm
3.23
BSAMPLE 10-3, 72-75 cm
12,0
1) NATURALORIENTED
2.572.52
2) GLYCERINATED
3.34
3.21 10.0
3) HEATEDAT 550 °C
Figure 2. X-ray diffractograms of natural samples of
volcanogenic "brown clays" (radiation: CuKα), Site 464. 1.Natural,
oriented sample. 2. Oriented after saturation with glycerine. 3.
After heating to 550°C. Sample 7-5,45-48 cmis represented by
disordered, rather finely dispersed mixed-layer
montmorillonite-mica, with variable contents of ex-panding and
non-expanding layers; trace quantities of hydromica are present;
admixture: basic plagioclase oflabradorite-bytownite type, zeolite
of phillipsite type, quartz. Sample 10-3, 72-75 cm is composed of
rather finely dis-persed, mixed-layer, disordered
montmorillonite-mica; admixture: hydromica, zeolite of
clinoptilolite type, quartz.
Table 4. Chemical composition of Mesozoic-Cenozoic sediments,
central northwestern Pacific, northern Hess Rise, Site 464.
Sample(interval in cm)
464-2-1, 115-1193-1,60-644-1, 130-1345-5, 70-726-2, 95-976-3,
94-967-3, 120-1228-2, 13-159-1, 30-3211-1, 28-29
CaO
8.1498.8948.705
15.63313.10818.8596.5587.2077.250
12.886
MgO
20.69417.74020.16915.92513.58713.96616.95712.69015.10627.657
Na2θ
29.08035.47930.87714.46210.93115.10716.20812.7798.242
16.500
K2O
10.75011.90313.69013.75216.20015.62921.45426.972
6.72615.086
Fe
30.08524.46525.83129.67741.67626.50837.10037.98255.46123.571
Mn
0.8751.1980.2707.3572.8316.5081.0311.3715.7340.157
Component(wt.
-
I. M. VARENTSOV, B. A. SAKHAROV, M. A. RATEEV, D. YA.
CHOPOROV
Table 5. Results of factor analysis (R-mode) forchemical
components (recalculated wt.%) ofCenozoic-Mesozoic sediments,
central north-western Pacific, northern Hess Rise, Site 464.
No.
123456789
10111213141516
Input(%)
Factor Loading (after rotation)
Component
CaOMgONa2θK2OFeMnPCrNiVCuCoPbGaGeMo
in dispersion
Total dispersion (%)
I
-0.12-0.85-0.83
0.840.720.310.640.390.79
-0.360.150.080.29
0.79
43.77
43.77
II
0.350.17
-0.390.59
-0.12-0.27
0.650.72
0.390.670.430.060.900.580.15
21.57
65.34
III
-0.91
0.120.240.31
-0.56-0.54-0.19-0.84
-0.79-0.92-0.24
-0.50
14.61
79.95
Table 6. Stratigraphic distribution of factor scores (R-mode)
forchemical components (recalculated wt.%) in
Cenozoic-Mesozoicsediments, central northwestern Pacific, northern
Hess Rise, Site464.
No.
123456789
10
Sample(interval in cm)
2-1, 115-1193-1, 60-644-1, 130-1345-5, 70-726-2, 95-976-3,
94-967-3, 120-1228-2, 13-159-1, 30-3211-1, 28-29
Age
U. Plio.L. Plio.L. Plio.Mio.U. Eoc.-L. Mio.U. Eoc.-L.
Mio.Paleoc.Paleoc.L. Cret.Cenom.
Factor Scores(after rotation)
I
-1.11-1.08-0.93
0.400.630.330.511.191.51
-1.45
II
-1.10-0.98-0.98-0.08
0.800.130.550.55
-1.032.13
III
0.67-0.20
0.41-1.58-0.31-1.83-1.39
1.200.200.05
Among the altered volcaniclastic components of thevolcanogenic
unit (II) of brown clay, two groups can bedistinguished: (1) the
main, dominating group, IA ( + ),represented by hydroxides of iron
and to a lesser extentmanganese, by ferrous phosphates and
associated heavymetals; it occurs mainly in the lower half of the
unit(Late Cretaceous-Paleocene; Fig. 3); (2) a
relativelysubordinate group, IIIB (-) , which contains
Mn-hy-droxides, phosphates, and associated heavy metals, andappears
in the upper half of the unit (late Eocene/late-middle Miocene;
Fig. 3). The separation obviousthroughout the section between
groups of componentsassociated with Fe- and Mn-hydroxides suggests
varyingcontributions from volcanic exhalates and hydrother-mal
solutions, along with the dominating volcaniclasticmaterial at the
initial and final phases of sedimentaryaccumulation in this unit.
Iron compounds were preva-lent in initial phases; manganese
compounds dominatedat final stages.
AVERAGE CONTENTS AND ACCUMULATIONRATES OF COMPONENTS (Table 7;
Figs. 4-6)
Distribution of Average Contents
The basic elements of calculation of average contentswere
discussed in our paper on site 463 (Varentsov et al.,this volume).
It should be noted that in order to revealgeneral geochemical
tendencies in the history of sedi-mentation the average contents
were calculated fordefinite lithologic types of the main
geochronologicalsubdivisions.
Analysis of distribution of average contents of com-ponents
(Table 7; Figs. 4, 5) in the studied section allowsto distinguish
three major geochemical stages of sedi-mentation: (1) late Mesozoic
(late Aptian-Cenomanian);(2) Late Cretaceous (Turonian?)/middle
Miocene (timeof accumulation of the volcanogenic "brown clay"unit);
(3) late Cenozoic (late Miocene-Pleistocene).
Late Mesozoic (late Aptian-Early Cenomanian)
Lithologic and geochemical data on the sedimentsconstituting
this interval of the section are rather frag-mentary and tentative.
According to the shipboard files(see Site 464 report, this volume),
the sediments form aunit of red-brown cherts (III). However,
considering theextreme core shortage, waste of debris of chalk,
marl,lithified clays, and speed of drilling, the authors of thesite
report (Thiede, Valuer, et al., this volume) believethat chalk and
marl dominate in the composition of theunit, whereas chert makes
not more than 10%. There-fore, the data on average contents and
accumulationrates given below can be analyzed only provided an
al-lowance is made for the noted restrictions.
On the whole, the late Mesozoic is characterized byaccumulation
of maximally high contents of silica andphosphorus in this section
of Mesozoic and Cenozoicdeposits (Table 7; Fig. 4).
Recalculation of data (Fig. 5) distinctly reveals ex-cessive
amounts of K2O and MgO, which might in-directly indicate the
presence of illite-smectite com-ponents formed after volcaniclastic
material.
Late Cretaceous (Turonian?)/Middle Miocene(?)(accumulation
period of the "brown clay"
volcanogenic unit)
In this volume, the age interval of this stage is deter-mined by
ichthyoliths (Doyle and Riedel, this volume).
Volcanogenic nature of these deposits and their im-pregnation by
Fe- and Mn-hydroxides are distinctlyrecorded in concentrations of
iron, manganese, phos-phorus, and associated heavy metals, which
are unusu-ally high for normal sediments (Tables 1, 7; Fig. 4).
Theoccurrences of these components are described above.The data on
recalculation (Table 4; Fig. 5) also give evi-dence of high
contents of Fe, Mn, and heavy metals, ascompared to sediments in
the other intervals of the sec-tion.
The following features should be emphasized: (1) thelower, basal
horizons of the unit (Turonian-Maastrich-tian?) are distinguished
by maximal contents of Fe(20.12%) and Mn (2.08%), at relatively low
valuesof aluminosilicate components (SiO2, 26.59%; A12O3,
810
-
LITHOLOGY FACTOR ASSEMBLAGES (SCORES)
Middle-lateioceng
Early MioceneLate Eocene
CLAY COMPONENTSPolymineral assemblage, mainly illite,mixed-layer
montmorillonite—illite, andchlorite, with an admixture of
quartz,tridymite, and cristobalite
Dominantly mixed-layer montmorillon-ite—illite, with a slight
admixture ofillite, chlorite, and zeolite
FACTOR ASSEMBLAGES
II
o o
III
" O
1.0
0.8
0.6
0.4
0.2
0
0.2
0.4
0.6
0.8
1.0
Figure 3. Stratigraphic distribution of factor scores for the
main paragenetic assemblages of chemical components in the post
Jurassic section of sediments in the central northwesternPacific,
northern Hess Rise, DSDP Site 464 (chemical analyses recalculated).
Symbols as in Figure 1.
O
tin
c>in
nmö
m
I
-
I. M. VARENTSOV, B. A. SAKHAROV, M. A. RATEEV, D. YA.
CHOPOROV
Table 7. Average contents and mean linear accumulation rates of
chemical components for major geochronological subdivisions of the
sectionof post-Jurassic sediments, central northwestern Pacific,
northern Hess Rise, Site 464.
Unit
IA
IB
II
III
Lithology
Clayey radiolarian oozes,clayey silicic oozes
Siliceous clays
Brown volcanogenic clays
Red-brown silica, chalk,limestone
Cores
2-3
3-5
5-11
11-34
Sub-bottomDepth
(m)
3.5-18.8
18.8-36.1
36.1-89.0
89.0-307.6
Thickness(m)
15.3
17.3
52.9
218.6
Stratigraphy
L. Pleist.U. Plio.L. Plio.
U.-M. Mioc.
M. Mioc.L. Mioc.-U. Eoc.L. Eoc.-Paleoc.U. Cret.U.
Maastr.(?)-Turonian
-
POST-JURASSIC SEDIMENTATION, SITE 464
Table
Age(m.y.)
1.0
{2.0
10.0
4.525.04.5
11.5
27.0
8.53.0
7. (Continued).
SedimentationRates
(mean linear)
(mm10~3yr )
7.5
10.5
0.45
1.110.181.111.65
0.70
17.8822.50
(mg.çm 2
lO~V~1)
367.5
499.8
21.42
84.8013.7584.80
126.06
53.48
3540.244455.0
40.53
47.62
44.8546.14
46.68
26.59
82.68
SiO2Ace. Rate
148.9
238.0
38.036.34
58.84
14.22
2927.07
4.67
4.22
12.5313.71
12.96
7.96
3.68
Average content (wt.%) and Accumulation Rates of Components(mg c
m - 2 1 0 - 3 yr~ !)
A12O3Ace. Rate
17.16
21.1
10.621.89
16.34
4.26
130.28
CaCθ3
(
-
I. M. VARENTSOV, B. A. SAKHAROV, M. A. RATEEV, D. YA.
CHOPOROV
Figure 4. Distribution of average contents (wt. %, air-dry) of
SiO2, A12O3, Fe, Mn, P, and the normative molecule CaCO3 in
post-Jurassic sediments of the central northwestern Pacific,
northern Hess Rise, DSDP Site 464.
cial handling of actual values of accumulation rates
ofcomponents (Table 7, Fig. 6). Nevertheless, assumingon the basis
of mineralogy and lithology of these sedi-ments a reasonable
variation range of the chemical com-position of late Aptian-early
Albian and middle Al-bian-Cenomanian deposits, it is possible to
note rela-tively high accumulation rates of SiO2, A12O3, and
othercomponents. These data can be interpreted as evidencethat the
northern part of Hess Rise during the Albianwas in the equatorial
zone of high biological productiv-ity, with the general northward
movement of the PacificPlate. Somewhat reduced values of these
rates, as com-pared to the known values of that zone, and
largeamounts of siliceous material, imply that sediment
ac-cumulation took place considerably below the lysocline,and
sometimes below the CCD.
Early phases of this stage are extremely interesting.Limited
amounts of material allow to assume only that
during the late Aptian-Early Albian a significant role inthe
total sedimentation balance belonged to accumula-tion of
volcaniclastic material, i.e., products of explo-sive volcanism
from the surrounding islands, whereas atthe very base of the
section the same role belonged tometal-bearing sediments (Site 464
report, this volume).
Late Cretaceous (Turonian-Maastrichtian?)/Middle Miocene
(accumulation time ofvolcaniclastic "brown clay" unit)
As emphasized earlier, the data on ichythyoliths(Doyle and
Riedel, this volume) allows us to believe thatthe volcanogenic
"brown clay" unit (53-m thick) coversthe period from Late
Cretaceous (Turonian?) to middle(Late?) Miocene. The bottom part
(Cores 8-10; LateCretaceous-Paleocene) contains particles of brown
ba-salt glass of sand-silt size (up to 20-40%), hyalopelitematerial
essentially altered to clayey matter, patches of
814
-
POST-JURASSIC SEDIMENTATION, SITE 464
+ + + ++ + 27.66+ ++ + + +
Figure 5. Distribution of average content (wt. °/o, recalc.) of
Fe, Mn, P, K2O, and MgO in the section of post-Jurassic sediments
of the central northwestern Pacific, northern Hess Rise, DSDP Site
464.
hematite (up to 20%), zeolite (up to 10-20%), basic
pla-gioclases (labradorite-bytownite; up to 5-10%). Thebasal part
(Turonian-Maastrichtian?) of the unit sam-ple 9-4, 106-109 cm)
contains gravel debris of recrystal-lized silicified limestones. It
is important to note that thegroundmass (up to 70-90%) of these
sediments is com-posed of hyalopelite and silty basaltic material
essen-tially transformed into clayey matter. Analysis of
X-raydiffractograms of these sediments (Fig. 2) shows thatthe main
components are represented by a combinationof disordered, finely
dispersed mixed-layer phases, i.e.,montmorillonite-mica, with a
variable content of ex-panding (montmorillonite) and non-expanding
(mica)layers; quartz, heulandite, and plagioclases of
labrador-ite-bytownite type are present as admixtures. In the
up-per half (middle Miocene-Paleocene) of the unit (Sam-ple
5-7,CC), the general mineral composition of sedi-
ments, on the whole, remains the same. It should benoted,
however, that in separate intervals occur appreci-able amounts of
colorless glass of acid to intermediatecomposition (up to 10-20%;
for example in the Paleo-cene, Sample 7-6, 43-46 cm), patches of
nannofossilmicrite, opal-quartz material, and relative reduction
inthe amount of Fe-hydroxides (by as much as 10%). Ac-cording to
X-ray diffractograms, the type of zeolite ischanged; phillipsite
dominates.
Mineral compositions have good correlation withgeochemical
results, in particular with the distributionof paragenetic groups
of chemical components, ana-lyzed above (Figs. 1,2).
These data allow us to believe that the "brown clay"unit is a
deep-water (below CCD) accumulation of rela-tively fine-grained
hyalopelite volcaniclastic materialsof basaltic composition, which
are products of explosive
815
-
I. M. VARENTSOV, B. A. SAKHAROV, M. A. RATEEV, D. YA.
CHOPOROV
COMPONENTS (mg • cm"2- 10"3• yr"1)
L./M. Mio.
-
POST-JURASSIC SEDIMENTATION, SITE 464
Late Cenozoic Gate Miocene-Pleistocene)
During this period, pelagic clayey-siliceous
sedimentsaccumulated, forming Sub-units LA (clayey
radiolarianoozes, clayey siliceous oozes) and IB (siliceous
clays).These sediments (Unit IB) are deposited on volcano-genie
"brown clay" (Site 464 report, this volume).
The major biogenic components of both sub-unitscontain in
variable proportions remains of radiolarians,diatoms, sponge
spicules, and to a lesser extent nanno-fossil micrite. The
groundmass is represented by finehyalopelite material altered to
clay matter. A charac-teristic admixture is represented by
sand-silt particles ofbrown basalt (up to 5-15%), to a lesser
extent by color-less acid glass. A slight admixture of micronodules
ofFe- and Mn-hydroxides is also noted.
The following tendency is observed in this interval:on the one
hand, a relative reduction of volcaniclasticcomponents upward in
the section, and, on the otherhand, an increase in the content of
siliceous (and to alesser extent carbonate) biogenic remains.
According to X-ray structural analysis, the greaterpart of the
clay (Cores 2-5) is represented by two majorcomponents present in
approximately equal propor-tions: (1) illite and a mixed-layer
phase of mica-mont-morillonite with a few (
-
I. M. VARENTSOV, B. A. SAKHAROV, M. A. RATEEV, D. YA.
CHOPOROV
Thus, in the geochemical history of post-Jurassicsedimentation
of the northern part of Hess Ress, themost essential phases of
development can be outlined,with different degrees of clarity,
which reflect thegeneral evolution of the basin.
ACKNOWLEDGMENTS
The authors express their gratitude to the colleagues at
theGeological Institute, U.S.S.R. Academy of Sciences, P. K.
Ryabush-kin, D. A. Kazimirov, N. I. Kartoshkina, and N. Yu.
Vlasova, for ef-ficient assistance in processing analytical data by
computer, recalcula-tion of analyses, and technical help; to V. A.
Drits and T. G. Eleseevafor X-ray structural analysis of samples;
to P. P. Timofeeva and V. I.Koporulin for the provided materials
and helpful discussions of work;to V. S. Zelinsky, N. K. Mirskaya,
and K. A. Scheponnikova forassistance in graphic presentation of
materials; and to L. L. Morozov-skaya for translation of the papers
into English.
The authors greatly appreciate the reviewing of the papers
andhelpful comments by N. G. Brodskaya and A. G. Kossowskaya.
REFERENCES
Arrehenius, G., 1963. Pelagic sediments. In Hill, M. N., (Ed.),
TheSea (Vol. 3); New York (Interscience), 655-727.
, 1967. Deep sea sedimentation: a critical review of U.S.works.
Trans. Am. Geophys. Union, 48:604-631.
Bender, M. L., Brocker, W., Gornitz, V., et al., 1971.
Geochemistryof three cores from the East Pacific Rise. Earth
Planet. Sci. Lett.,12:425-433.
Bezrukov, P. L., and Romankevich, E. A., 1970. Rate of
sedimenta-tion in Pacific ocean. In Bezrukov, P. L. (Ed.), Pacific
Ocean:Sedimentation in Pacific Ocean (Vol. 2): Moscow (Nauka),
288-300.
Bogdanov, Yu. A., and Chekhovskikh, E. M., 1979. Rates of
sedi-mentation and absolute masses. In Smirnov, V. I. (Ed.),
Metal-liferous Sediments of South-Eastern Pacific Ocean:
Moscow(Nauka), pp. 280.
Boström, K., 1973. The origin and fate of ferromanganoan
activeridge sediments. Stockholm Contri. Geol, 27:149-243.
Davis, J. C , 1973. Statistics and Data Analysis in Geology: New
York(Wiley).
Harman, H. H., 1967. Modern factor analysis: Chicago (Univ.
ofChicago Press).
Lisitzin, A. P., 1974. Sedimentation in Oceans: Moscow
(Nauka).
, 1978. Processes of Oceanic Sedimentation. Lithology
andGeochemistry: Moscow (Nauka).
MacArthur, J. M., and Elderfield, H., 1977. Metal
accumulationrates in sediments from Mid-Indian Oceanic Ridge and
MarieCeleste Fracture Zone. Nature, 266:437-439.
Varentsov, I. M., and Blazhchishin, A. I., 1976.
Ferromanganesenodules. Geology of Baltic Sea: Vilnus (Mokslas), pp.
307-348.
Zolotarev, B. P., and Choporov, D. Ya., 1978. Petrochemistry of
ba-salts D/V. Glomar Challenger, Leg 45, Holes 395, 395A, 396.
InMelson, W. G., Rabinowitz, P. D., et al., Init. Repts. DSDP,
45:Washington (U.S. Govt. Printing Office), 479-492.
818