Marine Sediments: Classification, Distribution, and Composition

Flashcards covering marine sediment classification, collection methods, lithogenous, biogenous, hydrogenous, and cosmogenous sediment characteristics, and ocean floor distribution patterns.

How are marine sediments classified based on their origin?

Marine sediments are classified into four categories: Lithogenous (derived from land), Biogenous (derived from organisms), Hydrogenous or Authigenic (derived from water), and Cosmogenous (derived from outer space).

What is the primary mineral constituent of lithogenous sediments?

Quartz ($\text{SiO}_2$).

What physical factor is sediment grain size proportional to?

The energy of transportation and deposition.

Which scale is used to classify marine sediment grain size?

The Wentworth scale of grain size.

What are the distinguishing characteristics of neritic sediment deposits?

They are shallow-water deposits located close to land, are dominantly lithogenous, and are typically deposited quickly.

What are the distinguishing characteristics of pelagic sediment deposits?

They are deeper-water deposits consisting of finer-grained sediments that accumulate slowly on the ocean floor.

What are the four main types of neritic lithogenous deposits?

Beach deposits (mainly wave-deposited quartz-rich sands), continental shelf deposits (relict sediments), turbidite deposits (graded bedding), and glacial deposits (formed by ice rafting on high-latitude continental shelves).

What are the primary sources of pelagic lithogenous sediment?

Volcanic ash from volcanic eruptions, wind-blown dust, and fine-grained material transported by deep ocean currents.

What distinguishes macroscopic biogenous sediments from microscopic biogenous sediments?

Macroscopic sediments are visible to the naked eye (such as shells, bones, and teeth), whereas microscopic sediments consist of tiny shells or tests of algae and protozoans that form biogenic ooze.

What are the two most common chemical compounds found in biogenous sediments?

Calcium carbonate ($\text{CaCO}_3$) and silica ($\text{SiO}_2$ or $\text{SiO}_2 \cdot n\text{H}_2\text{O}$).

Which two groups of microscopic organisms produce silica ($\text{SiO}_2$) biogenous sediments?

Diatoms (photosynthetic algae) and radiolarians (protozoans that use external food).

What sedimentary rock forms from the lithification of siliceous diatom ooze?

Diatomaceous earth.

What are coccolithophores, and what sedimentary rock is produced from their lithified ooze?

Coccolithophores are photosynthetic algae (nannoplankton) that produce individual calcium carbonate plates called coccoliths; their lithified ooze forms rock chalk.

What are foraminifera, and what type of sediment do they form?

Foraminifera are protozoans that consume external food; their microscopic calcium carbonate tests accumulate to form calcareous ooze.

What three processes determine the distribution of biogenous sediments?

Productivity (number of organisms in surface waters), destruction (dissolution of tests at depth), and dilution (deposition of other sediments decreasing biogenous percentage).

What proportion of all sedimentary rocks on Earth is formed by ancient marine carbonates?

$$25\%$$

What are stromatolites, and where do modern examples occur?

Stromatolites are fine carbonate layers produced by cyanobacteria in warm, shallow, high-salinity oceans; modern stromatolites live near Shark Bay, Australia.

What is the calcite compensation depth (CCD)?

The ocean depth where the rate of calcium carbonate ($\text{CaCO}_3$) supply equals the rate of dissolution, causing $\text{CaCO}_3$ to readily dissolve below it.

What is the lysocline?

The depth in the ocean at which a significant amount of calcium carbonate ($\text{CaCO}_3$) begins to dissolve rapidly.

How do hydrogenous marine sediments form, and what are key examples?

They form by direct precipitation of dissolved minerals from seawater via chemical reactions; examples include manganese nodules, phosphorites, oolites, and metal sulfides.

What are the components of cosmogenous marine sediments?

Macroscopic meteor debris, microscopic iron-nickel and silicate spherules (such as tektites), and space dust.

How do microscopic biogenous tests sink quickly ($10\text{--}15\text{ days}$) to the seafloor instead of taking $10\text{--}50\text{ years}$?

Most biogenous tests are packaged into larger fecal pellets by organisms, allowing them to sink rapidly.

What consortium was formed by the National Science Foundation (NSF) in 1963 to collect deep ocean sediment cores?

Joint Oceanographic Institutions for Deep Earth Sampling (JOIDES).

What is the maximum operating water depth of the drilling vessel JOIDES Resolution?

$8200\text{ meters}$ ($27{,}000\text{ feet}$).