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Sedimentary Environments and Facies
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
The deposits of the continental slope and talus include debris sheets, rudite sheets and sedimentary breccias of very large dimensions. The latter are called olistostromes (Greek: Olistomai—to slide, Stroma—layer). Derived from shallow water siliciclastic and carbonate deposits, the slope breccias may be of diverse composition, varying from well-bedded calcareous sands and calcarenites to rounded blocks of reefal limestones resembling bioherms. Downslope they may grade into deep-water pelagic or hemipelagic sediments. The pelagic sediments are open sea deposits containing calcareous ooze, skeletal remains of foraminifera, pteropods and coccolithophorids. The terrigenous component is small (< 20%) in these sediments but very fine-grained pyroclastics (tephra) are common. Siliceous (radiolaria, diatoms) ooze and skeletal remains are common below the Carbonate Compensation Depth. Hemipelagic sediments are admixtures of fine-grained pelagic and coarser grained terrigenous components.
Characterization of Marine Sediments
Published in Ronald C. Chaney, Marine Geology and Geotechnology of the South China Sea and Taiwan Strait, 2020
Berger and von Rad (1972) followed this effort with a classification system for the predominate deep-sea sediments: pelagic and hemipelagic materials (Table 5.5). Hemipelagic sediments are not deposited as slowly as pelagic sediments. They are deposited on continental shelves and rises, and ordinarily accumulate too rapidly to react chemically with seawater. Berger’s classification system does not extend to a variety of other sediments. The DSDP (deep-sea drilling project) has also developed a couple of classification systems. During the first three phases of the DSDP from 1968 to 1976 the description and classification evolved from a poorly defined qualitative system to a more rigorous system.
Ocean Disposal
Published in Stephen M. Testa, Geological Aspects of Hazardous Waste Management, 2020
Abyssal hills are characterized as broad sedimentary deposits of relatively low relief. Slopes range from about 1 to 15% and commonly undergo slumping on the deeper slopes and localized erosional processes. These regions cover vast areas of some ocean basins (i.e., 80 to 85% of the Pacific Ocean floor) and are considered seismically passive. Sediments are primarily comprised of pelagic and hemipelagic clays of relatively low permeability with varying amounts of carbonate and siliceous material.
Origin and diagenetic priming of a potential slow-slip trigger zone in volcaniclastic deposits flanking a seamount on the subducting plate, Hikurangi margin, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2022
Sydney M. Allen, Kathleen M. Marsaglia, Julia Morgan, Alison Franco
At Site U1520, located 16 km seaward of the deformation front (Figure 1), a representative stratigraphic section was drilled along the western flank of Tūranganui Knoll. Two holes were cored (Holes U1520C and U1520D), sampling much of the stratigraphy to a depth of ∼1050 m below seafloor (mbsf). The composite stratigraphy was subdivided into six lithostratigraphic units (Barnes et al. 2019), ranging from Pleistocene to Cretaceous in age based on shipboard biostratigraphy (Figure 2A). Units I and III consist of Quaternary age clay-rich hemipelagic sediments with silt and sand interlayers. Unit II is compositionally similar but is interpreted to be a mass transport deposit. Unit IV consists of Paleocene to Pleistocene pelagic facies dominated by marl and chalk, with several debris-flow deposits containing dispersed volcaniclastic debris. Unit V is a 168m-thick (848.45–1016.24 mbsf) succession of Late Cretaceous volcaniclastic conglomerate and sandstone with an intervening marl interval. The underlying Unit VI is also Late Cretaceous in age and contains a mixture of lithologies including volcaniclastic conglomerate, sandstone, and siliceous mudstone, along with minor siltstone, organic-rich mudstone, basalt, and limestone (Barnes et al. 2019). The base of the hole sampled amygdular basalt of uncertain origin, possibly an in situ flow or a clast.
Geochemistry of seafloor surface sediment and submarine hydrothermal signature of Tomini Bay, Indonesia
Published in Australian Journal of Earth Sciences, 2022
A. Yuliyanti, H. Permana, I. Setiawan, H. Nurohman, S. Purwo Saputro
Field examination shows that the recovered seafloor sediments were composed of mudline and sandy layer (SC-02), gritty ooze (SC-03;04) and olive-green hemipelagic ooze with several thin sandy layers (SC-11). The top of the core, i.e. the exposed seafloor surface, shows a red-brown oxidation sign and a darker diagenetic band at the interface with the underlying sediment (Table A1). The bulk sediment geochemistry classification using log SiO2/Al2O3vs log Fe2O3/K2O (after Herron, 1988) shows that most core samples can be classified as shale, wacke and Fe-sand (Figure 3). The geochemical compositions of the seafloor sediments are presented in the supplemental data (Table A2).
Distribution of surficial sediments in the ocean around New Zealand/Aotearoa. Part A: continental slope and deep ocean
Published in New Zealand Journal of Geology and Geophysics, 2019
Helen Bostock, Chris Jenkins, Kevin Mackay, Lionel Carter, Scott Nodder, Alan Orpin, Arne Pallentin, Richard Wysoczanski
The seabed of the continental slope and deep basins of this region are blanketed by mud (Figure 3(A); S1A), most of which is terrigenous (from the land) sediment from the rivers along the west coast of the South Island (Stoffers et al., 1984) and to a lesser extent from the North Island, while further west the deep-sea muds and clays in the Tasman Basin contain a component of Australian dust (Hesse, 1994). Manganese crusts and nodules have been found on the in the deep Tasman Basin (Glasby et al., 1986). The presence of these crusts and nodules suggest that these regions have either very low sedimentation rates, or sufficient flow speeds to winnow fine-grained sediment (Davies, 2018). The latter is unlikely in this region as the deep-water flows are weak in the eastern Tasman Basin (Chiswell et al., 2015). On the continental slope the terrigenous muds are mixed with carbonate to produce hemipelagic (see glossary) sediments, the carbonate content increases with depth on the slope as the sediment become increasingly pelagic (Figure 3(D); S1D). The carbonate content is high on the Challenger Plateau and various rises (40–100%; Figure 3(D); S1D), which are dominated by sand-sized sediment (40–80%; Figure 3(B); S1B) and described as pelagic ooze (Nelson et al., 1986; McDougall, 1975). There are some regions of with very high sand and minor gravel on the Challenger Plateau and New Caledonia Trough (Figure 3(C); S1C), which may also be influenced by carbonate from benthic organisms such as deep-sea corals (Tracey et al., 2011; Bostock et al., 2015) or the occasional manganese crust (Nodder unpublished Ocean Survey 2020 observations, research voyage TAN0707). Sediment carbonate contents rapidly decline below 3,700 m water depth in the Tasman Basin due to dissolution and diagenesis (Eade and van der Linden, 1970; Martinez 1994), although insufficient samples have been taken to define the depth of the carbonate compensation depth (CCD) in this basin, where the CCD is defined as the depth where CaCO3% <20% (Bostock et al., 2011).