Ocean Sediments

Summary

This educational video delves into the intriguing world of oceanic sediments, categorizing them into muds, sands, and gravels based on size. It explores their distribution across neritic and oceanic zones, influenced by water energy and currents. The video highlights the sediment's sources, including lithogenous from rock weathering, biogenous from marine organism shells, hydrogenous from precipitated minerals, and cosmogenous from extraterrestrial materials. It further discusses the dominance of abyssal clays, siliceous, and calcareous oozes in oceanic muds, shaped by factors like upwelling and the calcium carbonate compensation depth, providing a comprehensive understanding of the complex dynamics of ocean sedimentation.

Takeaways

• 🌊 Ocean sediments are categorized into three main sizes: muds (<1/16 mm), sands (between muds and gravels), and gravels (>2 mm).
• 📍 The distribution of sediment sizes in the ocean is influenced by water energy levels, with larger grains settling in still water and smaller grains in high-energy environments.
• 🌍 Ocean environments are divided into neritic (over the continental shelf) and oceanic zones (over the slope, rise, abyssal plains, mid-ocean ridges, and trenches).
• 🏞 Neritic zones have faster currents that can move larger sediment grains, while oceanic zones have deep, still waters where only fine sediments like muds can settle.
• 🌿 The majority of the world's ocean sediment comes from lithogenous (rock-derived) sources, including weathering on land, glaciers, and airborne dust and ash.
• 🐚 Biogenous sediments, originating from the remains of organisms like plankton, are particularly significant in oceanic zones, forming siliceous and calcareous oozes.
• 💧 Hydrogenous sediments are formed through the precipitation of minerals from seawater, often in areas of high evaporation or where ions become supersaturated.
• 🌌 Cosmogenous sediments, such as meteorites and tektites, are rare but more abundant in the oceans due to the slow sedimentation rates.
• 🌐 Abyssal clays, primarily lithogenous, dominate near high-volume rivers and deltas, or where there is significant airborne dust and ash.
• 🌡 The distribution of siliceous and calcareous oozes is influenced by water temperature and nutrient availability, with siliceous oozes prevalent in cold, nutrient-rich upwelling areas.

Q & A

What are the three categories of sediment size used to describe ocean sediments?

The three categories of sediment size are muds, sands, and gravels. Gravels are sediment grains larger than 2 mm in diameter, muds are less than 1/16 mm, and sands are everything in between.

How do ocean environments affect the settling of different sediment sizes?

The largest and heaviest sediment grains, like gravels, settle quickly in still water and require high-energy water to be picked up and carried. The smallest grains, like muds, require perfectly still water to settle out. Neritic waters, over the continental shelf, have faster-moving currents that can shift larger sediment grains, while oceanic waters are deep with no currents touching the bottom, allowing only suspended muds to settle.

What are the two major geographic zones of ocean environments?

The two major geographic zones of ocean environments are neritic, which is over the continental shelf, and oceanic, which includes the slope, rise, abyssal plains, mid-ocean ridges, and trenches.

Why do gravels tend to stay close to shore?

Gravels tend to stay close to shore because they are the largest and heaviest sediment grains, which require high-energy water to be picked up and carried. Neritic waters near the shore have faster-moving currents that can carry these larger grains, but they do not get transported far from the shore into oceanic waters.

What are the sources of muds in the oceanic zone?

Muds in the oceanic zone come from nearby rivers with a lot of suspended sediment, airborne dust and ash that settles on the surface, and the shells and debris of organisms that live in the surface waters and settle to the seafloor when they die.

Why does the margin environment have the thickest sediment layer in the world?

The margin environment has the thickest sediment layer because it collects sediment much faster, at rates from 0.5 to 800 meters per 1000 years, compared to the oceanic zones where sediment collects at its fastest at 1 cm per 1000 years.

What are the four major sources of sediment to the ocean?

The four major sources of sediment to the ocean are lithogenous or terrigenous sediment from rock weathering on land, biogenous sediment from shells of dead organisms, hydrogenous sediment from minerals produced by precipitation, and cosmogenous sediment from meteorites and tektites.

How does the process of precipitation contribute to the formation of hydrogenous sediment?

Hydrogenous sediment is formed when ions dissolved in seawater reach a concentration that is higher than can be dissolved by the water anymore, often due to evaporation or an influx of dissolved ions. This state of supersaturation leads to the precipitation of minerals, forming hydrogenous sediment.

What are the differences between abyssal clays, siliceous oozes, and calcareous oozes?

Abyssal clays are lithogenous sediments, often composed of clay minerals, and are found in oceanic zones. Siliceous oozes are composed of the silica shells of organisms like diatoms and radiolaria, and dominate in areas of upwelling. Calcareous oozes are composed of the calcium carbonate shells of organisms like coccolithophores and foraminifera, but their shells can dissolve in deeper, more acidic waters.

Why do calcareous shells dissolve in deeper waters?

Calcareous shells dissolve in deeper waters because cold temperatures and high pressure at depth lead to more carbon dioxide being dissolved in the water, making it more acidic. This increased acidity can dissolve the calcium carbonate shells, especially below the calcium carbonate compensation depth (CCD), where the acidity is high enough to prevent the accumulation of calcareous shells.