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Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition. Sediments and sedimentary rocks are characterized by bedding , which occurs when layers of sediment, with different particle sizes are deposited on top of each other. [ 1 ]
Bouma A is the first layer deposited by a flow, provided the flow has sufficient energy. Otherwise Bouma B, C or D will be the first layer deposited. Bouma A is deposited when the flow energy is high enough that fluid turbulence is able to keep the coarsest grains in suspension. When energy drops below a critical level, the grains tend to ...
As the sand concentration of a flow increases, grain-to-grain collisions within the turbid suspension create dispersive pressures that become important in hindering further settling of grains. As a consequence, a slightly different set of sedimentary structures develops in turbidites deposited by high-density turbidity currents.
This turbidite from the Devonian Becke-Oese Sandstone of Germany is an example of a deposit from a sediment gravity flow. Note the complete Bouma sequence.. A sediment gravity flow is one of several types of sediment transport mechanisms, of which most geologists recognize four principal processes.
Marine sediment, or ocean sediment, or seafloor sediment, are deposits of insoluble particles that have accumulated on the seafloor.These particles either have their origins in soil and rocks and have been transported from the land to the sea, mainly by rivers but also by dust carried by wind and by the flow of glaciers into the sea, or they are biogenic deposits from marine organisms or from ...
The lugworm Arenicola marina Gobies keeping watch outside a shrimp burrow. The evaluation of the ecological role of bioturbators has largely been species-specific. [8] However, their ability to transport solutes, such as dissolved oxygen, enhance organic matter decomposition and diagenesis, and alter sediment structure has made them important for the survival and colonization by other ...
Animals like worms, mollusks and echinoderms can enhance resuspension and mixing through movement and construction of burrows. [8] Microorganisms such as benthic algae can stabilize sediments and keep the sediment-water interface in a more stable condition by building mats .
[24] [4] Sediment in the initially buoyant hypopycnal flow accumulates at the base of the surface flow, [25] so that the dense lower boundary become unstable. The resulting convective sedimentation leads to a rapid vertical transfer of material to the sloping lake or ocean bed, potentially forming a secondary turbidity current.