Marine Sedimentology Frontiers, Prof.
Zhifei Liu
2015-10-21
Chapter 5
Hemipelagic advection and periplatform sedimentation
 About 90% of the sediment
load generated by
weathering and erosion on
land is deposited at the
ocean margins. Major
filters in the source-to-sink
sediment transfer are the
continental shelves, which
are regarded as conduits
for sediments to the
continental margins.
 Compositional variations of
periplatform oozes mainly
reflect changes in
depositional conditions on
the shallow-water
platforms.
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Marine Sedimentology Frontiers, Prof.
Zhifei Liu
2015-10-21
1. Contribution of fluvial supply
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In many regions of the ocean, river supply is by far the most
important contributor of terrigenous material. The amount of
sediment supplied by rivers has been shown to the proportional to
the surface area of the drainage basin. It also depends on uplift
rates and the climate.
Diffusive transport (by waves and tides) and advective (by currents)
transport are assumed to control the mud distribution on the
margins, and gravity-driven flows are thought to be important for
moving sediment down the continental slope.
Fine-grained fluvial sediment dispersal systems: estuarine
accumulation-dominated (EAD), canyon-captured (CC), proximal
accumulation-dominated (PAD), marine dispersal-dominated (MDD)
and subaqueous delta clinoform (SDC) systems.
Frequency, size and distribution of various dispersal systems
strongly depend on shelf geometry and oceanography.
Fluvial freshwater discharge (Milliman and Farnsworth, 2011)
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Marine Sedimentology Frontiers, Prof.
Zhifei Liu
2015-10-21
Fluvial sediment discharge (Milliman and Farnsworth, 2011)
Sediment discharge
from Taiwan
(Dadson et al., 2003)
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2015-10-21
Marine dispersal-dominated (MDD) in the Taiwan Strait
(from Liu JP et al., 2008)
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2015-10-21
2. Contribution of terrigenous dust
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In arid and semi-arid tropical and subtropical ocean provinces, dust
supply is by far the most important terrigenous contribution to
pelagic and hemipelagic sedimentation.
Saharan dust is regularly transported from its source areas along
three main transport paths: westward over the North Atlantic Ocean,
northward across the Mediterranean to Europe, and along easterly
trajectories across the eastern Mediterranean.
Long-distance transport of central Asian dust by the westerly jet
results in it crossing the Pacific in 12-18 days.
With respect to supply rates, the Sahara is the most important
source region, export estimates being 0.6-0.7 Pg/a, whereas Asian
dust transport rates into the North Pacific are two orders of
magnitude lower.
The hyper-arid core region of the Sahara expanded during glacials,
while dust export to the ocean significantly increased, and
deposition of aeolian sand turbidites occurred on the slope.
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Zhifei Liu
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University
2015-10-21
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Marine Sedimentology Frontiers, Prof.
Zhifei Liu
2015-10-21
3. Contribution of glaciomarine material
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Sea ice, continental ice sheets and their outlet glaciers influence the
pelagic realm and atmospheric circulation fundamentally.
Mechanisms incorporating sediment into sea ice include: Aeolian
transport; in shallow shelf regions: stirring up, re-suspension and
freeze-in of fine-grained terrigenous sediments; in near coastal
areas: river discharge onto sea ice and rock fall from cliffs.
Icebergs release sediments of all grain sizes, sorting classes and
composition. In most cases, the iceberg sediments contain large
amounts of terrigenous coarse material, called “ice-rafted debris
(IRD)”.
Quantitative studies from the Nordic seas have shown that IRD
contents can be correlated to the onshore glacial history.
However, in the Antarctic region, extensive ice-shelf environments
developed under extreme polar aridity, resulting in generally low
sedimentation rates on the shelf and slope because of very
restricted meltwater production and supply of IRD.
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Zhifei Liu
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Marine Sedimentology Frontiers, Prof.
Zhifei Liu
2015-10-21
4. Quantification and provenience
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Grain-size spectra of the suite of remaining terrigenous particles
after removing organic, carbonate and opal fractions, were
frequently used to decipher the variable input sources and transport
modes.
Three basic types of current-influenced sediments can be
distinguished: (1) sediments deposited by low-energy processes; (2)
sediments representing remnants of erosional processes; (3) wellsorted sediments.
“Sortable silt”: terrigenous 63-10 m fractions, its mean grain size
as an indicator for the deep-ocean current strength. “Koopmann
index”: relationship between the modal grain size of terrigenous
fraction (>6 m) and the proportion of this fraction relative to the
bulk sediment, to distinguish between aeolian and fluvial sediment
supply and current sorting.
Clay minerals are considered as another important terrigenous
proxy in deep-sea sediments.
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2015-10-21
McCave and Hall (2006, G3)
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Zhifei Liu
2015-10-21
5. Periplatform carbonates
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Pelagic sediments gradually merge into carbonate oozes that
include a growing proportion of shallow-water carbonate debris and
mud. Off-bank transport of coarse-grained material from carbonate
platform occurs mainly during the passage of storms along open
leeward bank margins.
Compositional variations in periplatform oozes mainly reflect
changes in depositional conditions on the shallow-water platforms.
Impact of both sea-level fluctuations and climatic changes on the
accumulation patterns of periplatform sediments is high.
Compositional variations also depends on the orientation of
carbonate platform with respect to the prevailing wind direction and
its type of margin setting.
Response to glacial/interglacial changes, reverse correlations in
grain-size distribution patterns have been recognized.
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