Marine Sedimentation - Chapter 4

Flashcards covering the classification of marine sediments, biogenous and lithogenous types, transport mechanisms, and key geological terminology for Marine Sedimentation.

Biogenous deposits

Particles derived from biological processes, such as shell matter, tests, and other remnants of life, which form oozes on the deep-sea floor.

Ooze

A deep-sea sediment consisting of at least $30\%$ skeletal remains of microscopic floating organisms, with the remainder being mostly fine-grained clay minerals.

Lithogenous deposits

Inorganic sediments composed of rock and mineral fragments of terrestrial origin, generally used to refer to pelagic sedimentation far from shore.

Terrigenous deposits

Land-derived (rock and mineral) deposits found on the continental shelves and slopes, categorized by particle size regardless of origin.

Hydrogenous deposits

Sediments that form by chemical precipitation directly from seawater.

Volcanogenic deposits

Particles erupted from volcanoes, classified by size into volcanic ash (fine), lapilli, and blocks and bombs (very large).

Cosmogenous deposits

Primarily micrometeorites that fall through the earth's atmosphere without burning completely, occurring mainly in the deepest ocean basins where other sediment accumulates slowly.

Micrometer

A metric unit equal to one one-thousandth ($0.001$) of a millimeter ($mm$), used to measure fine-grained sediments and microscopic organisms.

Wentworth Scale

A grain size scale developed in 1922 used to classify sediments from boulders ($> 256\,mm$) to clay ($< 0.004\,mm$).

Siliceous ooze

Biogenous sediment composed of opal ($SiO_2 \cdot nH_2O$), further divided into radiolarian and diatom oozes.

Radiolarian ooze

Silt-sized ($50-100\,\mu m$) marine protozoa remains found in abundance in equatorial waters.

Diatom ooze

Remains of single-celled plants ($10-500\,\mu m$) most abundant in nutrient-rich polar regions.

Calcareous ooze

Biogenous sediment composed of calcium carbonate ($CaCO_3$), including foraminiferal, coccolith, and pteropod oozes.

Foraminiferal ooze

Skeletons of sand-sized ($1-300\,\mu m$) marine protozoan animals.

Coccolith ooze

Very tiny, clay-sized ($1-20\,\mu m$) plates and fragments of one-celled plants (algae).

Pteropod ooze

Small ($1-2\,mm$) shells of a pelagic gastropod.

Carbonate Compensation Depth (CCD)

The depth in the ocean, currently about $4500\,meters$, where the rate of carbonate solution equals the supply; below this 'snow line,' all carbonate is dissolved.

Antarctic Bottom Water (AABW)

A cold, saline, high-pressure water mass that forms as pack ice develops; it is undersaturated with carbon dioxide at depth, causing carbonate particles to dissolve.

Red clay (Brown mud)

Very slowly accumulating fine-grained sediment (average $1\,mm$ per $1000\,years$) that covers about $38\%$ of the deep-ocean floor and gains its color through iron oxidation.

Manganese nodules

Hydrogenous deposits composed of iron and manganese oxides that grow slowly on the sea floor; they contain economically valuable copper, nickel, and cobalt.

Fecal pellets

Aggregates of fine mineral particles excreted by organisms that 'vacuum clean' coastal waters, causing nearly $90\%$ of terrigenous sediments to settle near their source.

Turbidity currents

Dense, sediment-laden currents reaching velocities over $20\,km/h$ that slide from continental slopes to the deepest ocean floor.

Turbidites

Distinctive deposits formed by turbidity currents where individual grains grade upward from coarse to fine.

Source rocks

Fine sediments with high organic content, often accumulated in anoxic areas, that can produce hydrocarbons (oil and gas) after burial.

Reservoir rocks

Coarse deposits of sand or gravel with high porosity that can hold oil and gas much like a sponge sops up water.

Anoxic

Condition without oxygen; denotes water or sediment from which free oxygen has been removed by oxidation of organic matter or chemicals.

Minerals

Naturally occurring, inorganic, crystalline substances with a definite range of chemical composition and physical properties.

Igneous rock

Crystalline rocks formed from molten material, such as granite and basalt.

Sedimentary rock

A rock resulting from the consolidation or cementation of loose sediment accumulated in layers, such as sandstone, shale, and limestone.

Metamorphic rock

Rock formed from preexisting rock as a result of heat, pressure, or chemically active fluids, such as marble and slate.

Slide (mass movement)

A mass of sediment accumulated on a slope that eventually moves downslope as a mass, often triggered by earthquakes or overloading.