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The structure and sediments of Surveyor Deep-Sea ChannelNess, Gordon Everett 09 February 1972 (has links)
Surveyor Deep-Sea Channel extends for approximately 700 km
over the northern Alaskan Abyssal Plain. It originates near the base
of the continental slope opposite Dry Bay and Alsek Strath and terminates
in the Aleutian Trench south of Kodiak Island. East of Giacomini
Seamount, the axial gradient of the channel is in the order of 10 m/km
and its morphology is in agreement with prediction, assuming a depositional
equilibrium with channelized turbidity currents. West of
Giacomini Seamount, the axial gradient increases to values as high as
7.5 m/km, as the channel course turns toward the northwest and
plunges into the trench. Over this part of its length the measured
center channel relief and cross-sectional area of the channel increase,
contradicting prediction. The lower channel is found to be erosional
in nature, this effect being a response to downwarping of the northern
rim of the Pacific Plate into the Aleutian Trench.
The channel originated in early to middle Pliocene time coeval
with the initiation of pronounced tectonism and intense glaciation in
southeastern Alaska. At this time, the channel was located perhaps
200 km south of its present position with relation to the North
American Plate, and may have been linked with one of the fossil sea-channels
on the eastern Aleutian Abyssal Plain. Throughout its
history, the channel has not been linked with any consistent river
drainage system, its sediment source instead being the large system
of piedmont glaciers in southeastern Alaska.
The distribution of coarse sedimentary material over the
northern Gulf of Alaska strongly suggests that turbidity current activity
has not been confined to only those regions close to Surveyor
Deep-Sea Channel. / Graduation date: 1972
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Holocene sedimentation and potential placer deposits on the continental shelf off the Rogue River, OregonChambers, David Marshall 25 September 1968 (has links)
Changes in sea level during the past 20,000 years are recorded
in sediments taken from the continental shelf off the Rogue River,
Oregon. Sea level has risen approximately 125 m. during the
Holocene (Curray, 1965) and the general transgression has been
interrupted by several stillstands and minor regressions.
Box core samples taken in the area of investigation depict the
nature of sedimentation during the last rise of sea level as well as
present-day equilibrium sediment relationships. Three sediment
facies, a recent fine-grained mud, a basal transgressive sand, and
an intermediate sediment, believed to be a mixture of the other two,
are defined on the shelf on the basis of textural parameters. The
mud facies dominates surface sediment on the central shelf while
the sand facies is the most commonly exposed on both the inner and
outer shelf.
The percentage of sand generally increases with depth in the
box cores, often producing a change in sediment facies with depth and
demonstrating the transgressive nature of the sediments. Grain-size
analysis of the sand fraction of the offshore sediments reveals that
offshore sands are finer-grained and better sorted than those occurring
on the present beaches. The offshore sands most likely
represent relict nearshore deposits and not ancient beach sands
which would occur lower in the sediment sequence.
High concentrations of heavy minerals are found in the sand
fraction of the offshore sediments as well as in beach sands in the
area. Brief stillstands of sea level may be reflected in depths where
the offshore sands contain anomalously high percentages of heavy
minerals.
Opaque minerals, chiefly magnetite, occur in placer accumulations
on the present beaches and high percentages of these minerals
in the offshore sands may be indicative of submerged beach environments
associated with stillstands of sea level. The magnetite may be
concentrated in sufficient quantity in the placers to produce detectable
magnetic anomalies, several of which have been recorded in the area.
Other lines of evidence used to determine the depths of
probable stillstands of sea level are bathymetric relief, the distribution
of shallow water fauna in sediments from deep water, and the
distribution of rounded gravels on the shelf. A compilation of the
several lines of evidence suggests several stillstands of sea level
associated with the Holocene transgression occurring at depths of
18, 29, 47, 71, 84, 102, and 150 meters. / Graduation date: 1969
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Holocene accumulation rates of pelagic sediment components in the Panama Basin, Eastern Equatorial PacificSwift, Stephen Atherton 18 March 1976 (has links)
Holocene bulk sediment and component accumulation rates were
measured in twenty-eight piston and gravity cores taken from the
floor of the western Panama Basin and on the surrounding ridges.
Radiocarbon ages and oxygen isotope curves provided Holocene age
control in nine cores. Time datums in nineteen other cores were
inferred by correlation of calcium carbonate curves to the dated
cores. Dry bulk densities were measured in ten cores and were
estimated in the others by an empirical relationship between dry
bulk density and the percentages of sand, clay, and calcium carbonate.
Other studies of the textural, mineralogical and sand fraction composition
of near surface sediments in these cores provided analyses
which could be used to obtain accumulation rates for these components.
A general similarity between the map pattern of surface productivity
and the patterns of carbonate and opal accumulation rates
suggests a first order control of biogenic sedimentation by fertility
of surface waters. Accumulation rates of terrigenous components
are highest near the continents; the map and depth patterns suggest
dispersal by currents shallower than 2000 m or by winds. It is inferred
from textural component accumulation rate patterns that no
significant regional redistribution of sediment by winnowing occurred
during the Holocene. Deposition from deep thermohaline circulation
probably increased the accumulation rates of silt, clay, and opaline
components in the gaps between the western and eastern troughs.
Calcium carbonate accumulation rates at equal depths are generally
lower within 250 km of the edge of the continental shelf. Below
2000 m in high productivity regions > 250 km from the shelf calcium
carbonate accumulation rates decrease linearly with depth according
to a gradient of -3.3 gm CaCO₃/cm²/1000 yrs/ km. From this
gradient, two independent estimates of the lysocline in this region,
and a model of calcium carbonate accumulation, the average Holocene
rate of supply of calcite from the surface is calculated to be
5-10 gm/cm²/1000 yrs. / Graduation date: 1976
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Sediments and tectonics of the Gorda-Juan de Fuca platePhipps, James B. 05 September 1973 (has links)
Cores taken from the ridge areas of the Gorda-Juan de Fuca
plate have a sedimentation rate that is appropriate for the study of
late Quaternary stratigraphy. An analysis of the clay and silt
mineralogy of the cores using X-ray diffraction methods and by
noting changes in the foraminiferan-radiolarian abundances in the
cores were utilized in developing a stratigraphic sequence.
The clay fractions of these sediments consists of chlorite,
illite and smectite. Cores taken from bathymetric highs contain,
on the average, less smectite than do the turbidites from the adjacent
lowlands. The low smectite content suggests eolian enrichment of
these sediments since dusts collected from the nearby continent also
have low smectite concentrations.
Changes in the relative abundances of radiolaria and foraminifera
are used to put biostratigraphic constraints on the correlation of
mineralogical datums. Two changes in the foraminiferan-radiolarian
ratios, marked by sharp increases in the abundance of radiolaria,
occurred at 12,500 years B.P. and 83,000 years B.P. as dated by
carbon-14 and sedimentation rate extrapolations, respectively. Such
faunal changes serve as an independent check of correlations of the
mineralogical datums.
In the 2 to 20 micron, silt fraction, quartz, chlorite, mica and
feldspar are the predominant minerals. Intervals in which the relative
abundance of quartz changes can be dated by carbon-l4 and
sedimentation rates, and related to late Quaternary climatic events.
The quartz-rich zones are synchronous with periods of high insolation, high stands of sea-level, and to a lesser degree with the
catastrophic floods of the Columbia River. The correlation with high
solar radiation reflects quartz enrichment of the sediment due to an
increased eolian contribution. The coincident high sea level stands
effectively decreased the sedimentation rate of quartz-poor continental
detritus that otherwise dilutes the eolian component. The
periodic floods of the Columbia River, caused by the failure of ice
dams, swept quartz-rich loess from eastern Washington down the
river and injected into the marine environment. Such sediment also
increased the quartz abundance in the quartz-rich zones on the
ridges. Thus, the late Quaternary stratigraphy of the cores can be
related to global late Quaternary climatic variations as well as to
events recorded on the adjacent continents.
The structural development of the Gorda-Juan de Fuca plate
over the last 10 million years can be explained by north-south
shortening coupled with the normal tectonism associated with a
spreading sea floor.
This hypothesis for the development of the plate is based on the
presently known magnetic anomaly pattern. A series of reconstructions
of this pattern back through the past 10 million years shows
that both the Gorda and Juan de Fuca portions of the plate have grown
steadily smaller. The incorporation of sequentially shorter Gorda
ridge anomalies into the Pacific plate appears to have led to the
northwest-southeast orientation of the Blanco Fracture Zone, with
consequent changes in the direction of spreading of the Juan de Fuca
Ridge. On the Juan de Fuca portion of the plate, the shortening was
accomplished by shear faulting in Cascadia Basin. Furthermore,
this faulting resulted in the rapid subduction of this portion of the
plate, which, in turn, produced a disconformity in the sediments of
Cascadia Basin. The reconstruction strengthens the notion that right
lateral strike slip motion between the Pacific and Gorda-Juan de Fuca
plate does, indeed, exist. / Graduation date: 1974
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Peruvian deep-sea sediments : evidence for continental accretionRosato, Victor Joseph 28 December 1973 (has links)
In order to determine whether the sediments found on the landward
wall of the Peru Trench are accreted Nazca Plate sediments,
the clay mineralogy and organic carbon contents of 52 surface
samples were submitted to factor analysis. Q-mode factor analysis
resolved the data from the Nazca Plate and Peru continental margin
into three factors. The most important factor (oceanic assemblage)
is strongly associated with Nazca Plate sediments and is comprised
of smectite and aeolian illite. In contrast, upper continental margin
sediments are dominated by either of the two continental factors (A or
B). The principal difference between the continental factors is that
mixed-layer smectite-chlorite clays are characteristic only of continental
assemblage A. Lower continental margin sediments are
characterized by either an oceanic or continental factor dominance.
The boundary between sediments dominated by the oceanic
factor and those dominated by the continental factor was as much as
100 km to the west of its present position earlier in the Quaternary.
The seaward shift in the boundary is attributed to westward shoreline
displacement in response to glacially-induced sea level changes,
increased erosion rates on land during more humid times, and
deposition of continental factor dominated sediments seaward of the
present Peru Trench axis.
Quaternary sediments from 27 cores reveal minor fluctuations
with time in factor loadings in Nazca Plate and upper continental
margin cores and significant variations in some areas near the trench
axis and on the middle to lower continental slope. Displacement of
oceanic sediments into areas with continental sediments is determined
with respect to the factor dominance boundary. Using this
method, continental accretion is indicated for five cores, located up
to 3000 m above the trench floor. One core on the middle continental
slope off Lima, Peru, contains diatom-rich Quaternary dolomite
that probably originated as calcareous sediment on the Nazca Ridge.
If this is true, left-lateral strike-slip motion of the Nazca Ridge along
the Peru Trench axis is indicated.
The bulk of the 28 cores recovered from the acoustically complex
landward wall of the Peru Trench contain sand-silt turbidites of
continental origin. Even though there is a distinct overprint of
terrigenous sedimentation, accreted oceanic sediments can be
recovered in a tectonically active convergent plate boundary. / Graduation date: 1974
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Trace element studies of metalliferous sediments in cores from the East Pacific Rise and Bauer Deep, 10⁰ SKendrick, John William 02 October 1973 (has links)
Major (Fe, Mn, Al) and minor (Cr, Mo, Pb, Zn, Cd) element
analyses of metalliferous sediments in cores from the East Pacific
Rise and Bauer Deep indicate that the Bauer Deep sediments are
similar in chemistry and origin to metalliferous sediments of the
East Pacific Rises.
Fe, Pb, and Zn are strongly associated in both cores and are
probably related to the hydrothermal processes which are postulated
to occur on the East Pacific Rise. Incomplete Cd data suggest that
Cd may also be released during hydrothermal leaching of basalt
Mn may originate by precipitation from hydrothermal solutions or by
normal authigenic precipitation from sea water. The similar
accumulation rates of Mo in both cores, and poor correlation of Mo
with Fe imply that Mo is being extracted from sea water. The low
abundances of Cr and Al in metalliferous sediments suggest that
detritus is a minor component of the sediments.
Poorly crystalline smectites constitute a major mineralogical
phase of metalliferous sediments. Chemical and mineralogical
studies indicate that the smectite is an iron-rich montmorillonite,
similar in composition to the bulk sediment.
Information on sedimentation rates in the two cores indicate
that most elements are accumulating faster on the East Pacific Rise
than in the Bauer Deep. Accumulation rates of metals in the Bauer
Deep have decreased up to the present and are currently similar to
those for normal pelagic sediments. It is inferred that the sedimentation
rates in the Bauer Deep are influenced by the proximity of the
East Pacific Rise, It appears that sediments in the Bauer Deep are
largely the product of hydrothermal processes on the East Pacific
Rise, and that the precipitates are transported in suspension to the
Bauer Deep. Authigenic precipitation of elements from sea water
also occurs, having a stronger influence on the sediments as the
precipitation of rise-crest material decreases away from the ridge. / Graduation date: 1974
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Sedimentary texture--a key to interpret deep-marine dynamicsAllen, David William 19 September 1969 (has links)
The processes responsible for transporting and depositing thick
sections of coarse-grained terrigenous clastics on the abyssal floor
and for forming associated sedimentary structures are still conjectural.
Many workers attribute coarse deep-sea sediments and their
probable lithified equivalent, the graywackes of flysch deposits to
some type of density movement.
Deductions concerning the processes operating in a density flow
generally are made from flume studies--in which an artificial situation
may develop, or from lithified units--where the magnitude of
post-depositional change is unknown. Both approaches contribute to
our knowledge, but the unconsolidated elastics themselves should
contain a unique key to understanding the dynamics of abyssal sedimentation.
To test this theory, divisions of parallel lamination, found in
deep-sea sand and silt, were selected for analysis. Since individual
laminae closely approach discrete populations of particles assembled
under contrasting conditions, their use carries environmental sampling
to its practical limits.
Northeast Pacific sediments of late Pleistocene and Holocene
age, from deep-sea channel and abyssal plain environments, and
representing two or three provenances were studied. A total of 115
light-colored and 84 dark-colored laminae were sampled from eight
sequences at five locations. Samples averaged about 0.8 gram and
were quantitatively processed using quarter-phi calibrated sieves and
decantation techniques. Statistical evaluation of the procedure shows
better than 95 percent sample recovery, and indicates that textural
variance between laminae is significantly greater than within-sample
variance.
The classic concept of density transport--that coarsest material
is carried by the nose of the current, and that clastic size grades tail-ward
and upward in a uniformly decreasing manner--is not substantiated
by moment measures, sand-silt-clay percentages or factor analysis
of grain-size distributions, at least during deposition of the
coarse division of parallel lamination.
Coarse abyssal lamination develops within a narrow range of
current velocity, the limits of which are defined texturally. Absolute
velocity values for these limits can only be related, at the present
time, to the few flume or in situ bottom current measurements
available. Texture indicates that while the total amount of sand
carried in suspension varies, lamination does not begin to form
until a current is essentially depleted of all material coarser than
fine sand--establishing an upper competency limit. At that time,
coarse suspended material is distributed throughout the flow mostly
in large eddies or vortices whose velocities are estimated on the
order of about one meter/sec. Mean current velocity must be sufficient
to maintain a dispersed traction carpet without deformation of
bedform into ripples. This is postulated at about 50 cm/sec.
A current model, based on textural evidence, is proposed to
account for lamination. It is suggested that the critical stage in the
formation of coarse abyssal lamination occurs while sediment is
being dragged along the bottom as bedload. The flowing clastic traction
carpet acquires kinetic energy as the current bypasses material
lost from suspension. In turn, this energy results in grain shear.
When the concentration of granular material in traction is large, it
dissipates the energy of bottom shear mostly in collision contacts
between gliding grains. The dispersive stresses developed tend to
maintain grain separation and prevent settling. Eventually, turbulence
in seawater entrapped between grains is suppressed and the net
path of grans impelled by repeated collisions becomes quasi-laminar.
Within this quasi-laminar traction system, dispersive pressure
causes some migration of finer sizes toward the base of the carpet
and a concentration of coarser grains in the upper bedload. As new
material is introduced in large quantities from suspension, the zone
of internal shear--the base of the moving carpet--is displaced progressively
upward. As it passes, sediment compacts to a fraction
of its dispersed thickness and a population of grains with a slightly
finer size distribution than the carpet load comes to rest. This is
buried by new deposition and a densely-packed, dark layer continues
to accrete upward as long as a moving traction carpet is sustained
and a dense rain of clastics is contributed from suspension.
When a sand-laden eddy impinges on the bottom, it releases its
coarsest load into traction and the dark layer then accreting increases
significantly in grains larger than 44 microns. Any eddy, whether
laden or not, on striking bottom adds to, or deducts its velocity from
the velocity of the traction carpet and either increases or decreases
bottom shear. Additional impulse given to tractive shear by eddies
merely results in more effective size sorting.
However, an eddy whose velocity of rotation is opposed to current
movement may reduce shear below the critical necessary to
maintain a thick carpet by dispersive pressure, The dispersed carpet
collapses and instantaneously ceases moving. This less-densely
packed layer has a slightly higher sand content than the accreted
material below. When partially dried or weathered, alternate layers
exhibit different moisture retention properties--the less-porous,
accreted layers appearing dark and the more loosely packed layers
appearing light. / Graduation date: 1970
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A seismic refraction study of the Monterey Deep Sea Fan and a comparison of velocity structures among fan subunitsDwan, Shufa F. 10 January 1986 (has links)
A deep source-receiver seismic refraction experiment was conducted
on the upper part of the Monterey Deep Sea Fan. The aim of this thesis is
to construct the velocity structure of the upper Monterey Fan and to examine
the lateral seismic velocity variations among the upper, middle and lower
fan subunits. Using primary waves and whispering gallery phases (the
multiply-reflected refraction waves), the sediment velocity structure was
modeled by the tau-zeta travel time inversion process. The changes in
velocity gradients with depth of the upper Monterey Fan are
morphologically similar to that found on both the Central Bengal Fan and
the Nicobar Fan, an abandoned lower fan of the Bengal Fan Complex. The
velocity gradient of the upper Monterey Fan at depth, 0.59 s⁻¹ is
significantly lower than both the middle Bengal Fan (0.68 s⁻¹) and the
Nicobar Fan (0.81 s⁻¹). The upper fan subunit, which is closer to its
sediment source, is characterized by higher porosities caused primarily by
a higher sedimentation rate than the lower fan subunits. Since seismic
velocity is inversely related to porosity, the upper fan subunit should have
lower velocity gradients and seismic velocities than the other fan subunits.
If porosity and velocity variations exist, then these variations can be used to
constrain various models of deep sea fan formation. No definite conclusion
can be drawn at this time due to a fault within 1 km of the Nicobar Fan site;
however, a systematic velocity variation pattern of deep sea fans is
revealed.
Some portions of the Monterey Fan data contain refracted waves
which have bottomed within the underlying acoustic basement structure.
The entire velocity structure was solved by both the general and the
"stripping" solving schemes. The results of basement structure show a
velocity ranging from 3.4 to 5.8 km/s indicating that the uppermost part may
be pre-existing continental rise sediments. / Graduation date: 1986
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A microprobe study of metalliferous sediment componentsEklund, William Alan 09 August 1973 (has links)
Examination of polished sections of manganese micronodules
from metalliferous sediments from the Bauer Deep reveals sequences
of ferromanganese deposition which are consistent for micronodules
from a single sediment sample and imply a common depositional
history for members of such assemblages. The relatively simple
'stratigraphy' of manganese micronodules, as compared to macronodules,
makes stratigraphic correlation of depositional histories
easier and more conclusive for micronodules than macronodules.
Quantitative microprobe analysis and X-ray mircodiffraction
patterns indicate that the major authigenic silicate component of
metalliferous sediment is an iron- and magnesium-rich, low-aluminum
nontronite.
Microprobe and X-ray microdiffraction analyses of manganese
micronodules establish todorokite as the predominant crystalline
component. Comparison of the distributions of lanthanum, cerium,
and samarium in micronodules and phosphatic fish debris indicates
that bulk sediment REE distribution is determined by the relative
abundances of cerium-enriched micronodules and cerium-depleted
biogenic phosphate. / Graduation date: 1974
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The respiration characteristics of ocean bay sediments and selected marine isolatesGawel, Len Joseph 12 July 1965 (has links)
Graduation date: 1966
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