What types of sediments and sedimentary structures usually reflect deposition in a deep-sea setting?

To begin, it is essential to understand that deep-sea sediments are primarily deposited in the abyssal plains, the flat, featureless expanses that cover a large portion of the ocean floor. These areas are characterized by high water pressure, low temperatures, and extreme darkness. As a result, the sediments found in these settings are distinct from those found in shallower water environments, such as beaches or river deltas.

The deep-sea sediments can be classified into three main categories: 1. Terrigenous sediments: These sediments are derived from land and transported to the ocean floor by various means, like rivers, wind, and ice. They are primarily composed of clay minerals, quartz, and other silicate minerals. 2. Pelagic sediments: These sediments are primarily composed of organic matter that sinks to the ocean floor. This includes the remains of tiny marine organisms known as phytoplankton and zooplankton, as well as the shells of larger organisms like foraminifera and diatoms. In addition, pelagic sediments can contain trace amounts of volcanic ash and cosmic dust. 3. Hydrogenous sediments: These sediments are formed directly from the dissolved materials in seawater. Examples include manganese nodules, phosphorite, and other authigenic minerals like dolomite and glauconite. These are relatively rare compared to the other sediment types.

The sedimentary structures commonly found in deep-sea settings reflect the deposition processes at work in these environments. Some well-known structures include: 1. Turbidites: Turbidites are graded layers of sediment deposited by turbidity currents, which are underwater flows of sediment-rich water. They typically display a fining-upward sequence, with coarser sediments at the base and progressively finer sediments toward the top of each layer. 2. Contourites: Contourites are created by the action of deep-sea currents, which sort and redistribute the sediments along the ocean floor. They are characterized by parallel or subparallel layering and are commonly found in areas influenced by strong bottom currents. 3. Pelagic ooze: This is a homogenous, fine-grained sedimentary structure formed by the slow accumulation of the remains of marine organisms, such as the shells of foraminifera or diatoms. In conclusion, deep-sea sediments comprise of terrigenous, pelagic, and hydrogenous sediments, each with their unique composition. Deep-sea sedimentary structures typically include turbidites, contourites, and pelagic ooze, reflecting the different processes at work in these environments.