Marine Sediments & Oceanography 8

Marine Sediments Definition

Unconsolidated organic or inorganic particles that accumulate on the seafloor.

K-T Impact Layer Element

Iridium, which is rare on Earth but common in meteorites.

K-T Impact Stratigraphy Layers

From bottom to top: Ejecta Layer, Fireball Layer, and Post-Extinction Layer.

Primary Sources Percentages

Terrigenous (~45%), Biogenous (~55%), and Hydrogenous (

Deep Ocean Accumulation Rate

Less than 1 cm per 1,000 years.

Grain Size & Hydrodynamic Energy

Particle diameter directly correlates with the energy required for transport and deposition.

Abyssal Plain Sediment Burial

Fine falling particles act like snow, completely burying mountains >1,000 m tall after ~100 million years.

Terrigenous Primary Mineral

Quartz (SiO2), due to its high physical and chemical resistance.

Iceland Basalt Beaches

Weathered volcanic basalt lacks quartz, producing distinctive black sand beaches instead of white quartz sand.

Terrigenous Transport Mechanisms

Rivers, wind (aeolian dust), glaciers, and gravity.

Biogenous Ooze Definition

Any pelagic sediment composed of 30% or more biogenous plankton debris.

Calcareous Ooze Components

Foraminifera (forams) and coccolithophorids (coccoliths).

Siliceous Ooze Components

Radiolarians and diatoms.

Diatomaceous Earth Uses

Insecticides (bedbugs), cat litter, filtration, insulation, toothpaste, and dynamite.

Microbial Loop Function

Recycles ~50% of phytoplankton, returning nutrients and CO2 to solution via respiration.

Particle Accelerators (Fecal Pellets)

Zooplankton ingest phytoplankton and package debris into compact pellets sinking >100 m/day.

Marine Snow Definition

Aggregation of plankton cells, detritus, and fecal pellets sinking rapidly (>100 m/day) to the seafloor.

Hydrogenous Sediments Definition

Minerals that precipitate directly out of seawater (

Manganese Nodules Economic Value

They contain iron, manganese, cobalt, copper, and nickel critical for green energy technologies.

Evaporites Formation

Formed when seawater evaporates rapidly in restricted basins under dry climates (e.g., halite and gypsum).

Limestone Composition

Silt glued together by calcium carbonate.

Chert Origin

Amorphous silicate rock derived from siliceous phytoplankton (diatoms).

Black Shale Environment

Formed from organic-rich mud under oxygen-poor conditions, frequently containing fossils.

Honeycomb Weathering

A cavernous rock texture occurring on coastal and desert sandstone through salt-crystal weathering.

Marine sediment

Unconsolidated organic or inorganic particles that accumulate loosely on the ocean floor.

Element indicating the K-T boundary impact layer

Iridium, a chemical element that is extremely rare in Earth's crust but abundant in extraterrestrial meteorites.

Relative abundance of marine sediment sources

Terrigenous ($\sim 45\%$), biogenous ($\sim 55\%$), and hydrogenous ($<1\%$).

Deep-ocean sediment accumulation rate

Extremely slow pelagic settling, typically accumulating at less than $1\,\text{cm}$ per $1{,}000\,\text{years}$.

Relationship between sediment grain size and transport energy

Particle diameter directly correlates with hydrodynamic energy; coarse grains require high-energy currents to move, while fine grains settle only in low-energy environments.

Ocean floor sedimentary ripples vs. smooth muds

Rippled seafloor textures indicate active, high-velocity bottom currents, whereas smooth, featureless muds indicate calm, low-energy depositional settings.

Sedimentary burial of abyssal plain topography

A persistent rain of fine settling particles gradually blankets the ocean floor like falling snow, completely submerging seamounts taller than $1{,}000\,\text{m}$ over roughly $100\,\text{million years}$.

Terrigenous sediment

Mineral particles derived from the mechanical and chemical weathering of continental rocks, transported to the sea via rivers, wind, glaciers, and gravity.

Dominant mineral in terrigenous marine sediments

Quartz ($SiO_2$), owing to its exceptional physical hardness and resistance to chemical weathering.

Geological cause of Icelandic black sand beaches

Weathering and mechanical erosion of quartz-free volcanic basalt, producing dark grains rich in iron and magnesium.

Aeolian dust transport

Wind-blown plumes from arid, unvegetated regions that travel thousands of kilometers offshore, delivering essential micronutrients like iron to open-ocean ecosystems.

River delta sediment deposition

The rapid settling of suspended terrigenous particles near continental margins where river velocity abruptly decreases upon meeting the ocean.

Biogenous ooze

Pelagic ocean sediment composed of at least $30\%$ microscopic skeletal remains of planktonic organisms.

Calcareous ooze

Biogenous sediment formed primarily from the calcium carbonate ($CaCO_3$) tests of coccolithophores and foraminifera.

White Cliffs of Dover geological origin

Massive chalk formations created by the compaction and lithification of ancient coccolithophore blooms and calcareous ooze over millions of years.

Siliceous ooze

Biogenous sediment composed primarily of the hydrated silica ($SiO_2$) skeletal structures of diatoms and radiolarians.

Diatomaceous earth (diatomite)

A lightweight, porous, and absorbent sedimentary material derived from fossilized diatom frustules, utilized in filtration, pest control, absorbents, and dynamite.

Marine primary production equation

$$CO_2 + H_2O \rightarrow \text{organic carbon} + O_2$$

Marine organic decomposition equation

$$\text{organic carbon} + O_2 \rightarrow CO_2 + H_2O$$

Microbial loop

An ecological pathway in which marine bacteria consume and remineralize approximately $50\%$ of phytoplankton biomass, releasing dissolved nutrients and $CO_2$ back into the water column.

Zooplankton fecal pellets

Compacted organic waste packages that sink rapidly at speeds exceeding $100\,\text{m/day}$, allowing biological material to bypass microbial decomposition and reach the seafloor.

Marine snow

Macroscopic aggregates of plankton cells, detritus, and fecal particles that descend rapidly ($>100\,\text{m/day}$), efficiently exporting organic carbon to deep waters.

Hydrogenous sediment

Mineral precipitates formed directly out of dissolved seawater ions under specific geochemical conditions, representing less than $1\%$ of total marine sediments.

Manganese nodules

Hydrogenous seafloor concretions enriched in manganese, iron, copper, cobalt, and nickel that precipitate at rates of roughly $10\,\text{mm}$ per million years.

Evaporites

Water-soluble mineral deposits, such as halite and gypsum, produced by rapid evaporation of seawater in isolated or restricted basins with arid climates.

Limestone

A sedimentary rock composed predominantly of silt-sized fragments and calcite cement derived from calcium carbonate ($CaCO_3$).

Chert

A dense, microcrystalline or amorphous silicate sedimentary rock derived from the accumulated remains of siliceous phytoplankton.

Banded Iron Formation

A Precambrian sedimentary rock characterized by repeating, thin layers of hydrogenous iron oxides and chert.

Black shale

A fine-grained, laminated sedimentary rock formed from mud rich in organic carbon deposited in anoxic deep-water basins.

Honeycomb weathering

A cavernous, pitted surface texture developed on porous coastal and desert sandstones due to the growth and expansion of salt crystals.