CHAPTER 4 Marine Sediment Classification A Shape Size

CHAPTER 4 Marine Sediment Classification: A. Shape, Size, Variation B. Formation Processes: • • • Lithogenic (rock) Biogenic (organic based) Authogenic/Hydrogenous (precipitated from water) Volcanic Cosmogenic (outer space)

Sediment Transport Fluid velocity determines the size of the particles that can be moved

Sediment Texture • Grain size sorting – Indication of selectivity of transportation and deposition processes • Textural maturity – Increasing maturity if • Clay content decreases • Sorting increases • Non-quartz minerals decrease • Grains are more rounded (abraded)

Sediments • • Reflect composition of rock from which derived Coarser sediments closer to shore Finer sediments farther from shore Mainly mineral quartz (Si. O 2)

Terrigenous & Lithogenic sediments (from land) • • • Rivers Winds (aeolian) Glaciers (ice-rafted debris, IRD) Turbidites Sea level changes

Terrigenous Sediments: • derived from weathering of rocks at or above sea level (e. g. , continents, islands) • two distinct chemical compositions – ferromagnesian, or ironmagnesium bearing minerals – non-ferromagnesian minerals – e. g. , quartz, feldspar, micas • largest deposits on continental margins (less than 40% reach abyssal plains) • transported by water, wind, gravity, and ice • transported as dissolved and suspended loads in rivers, waves, longshore currents

River sediment loads (~109 tons/yr)

Sediment Distribution • Neritic – Shallow-water deposits – Close to land – Dominantly lithogenous – Typically deposited quickly • Pelagic – Deeper-water deposits – Finer-grained sediments – Deposited slowly

Neritic Lithogenous Sediments • Beach deposits – wave-deposited sand • Continental shelf deposits • Turbidite deposits • Glacial deposits – High latitude continental shelf – Currently forming by ice rafting

Pelagic Deposits • Fine-grained material • Accumulates slowly on deep ocean floor • Pelagic lithogenous sediment from – Volcanic ash (volcanic eruptions) – Wind-blown (aeolian) dust – Fine-grained material transported by deep sea currents

• Dust (LANDSAT image). • Dust comprise much of the fine-grained deposits in remote open-ocean areas (red clays) • primary dust source is deserts in Asia and North Africa

Distribution of Sediment on Continental Shelf by Grain Size

Submarine canyons (cut into the c. slope) Abyssal plain Seafloor Features: Continental Margins Continental shelf Continental rise Abyssal plain Continental slope

Glacial (Ice-rafted debris)

• boulder to clay size particles also eroded and transported to oceans via glacial ice • glacier termination in circum-polar oceans results in calving and iceberg formation • as ice (or icebergs) melt, entrained material is deposited on the ocean floor • termed 'ice-rafted' debris

Biogenic sediments (from living things) Forams Calcareous (Ca. CO 3) Foraminifera -- animals Coccolithophores -- plants Siliceous (Si. O 2) Radiolaria -- animals Diatoms -- plants Diatoms Radiolarian

Biogenic Sediment • Two major types: – Macroscopic • Visible to naked eye • Shells, bones, teeth – Microscopic • Tiny shells or tests • Biogenic ooze • Mainly algae and protozoans

mm = micron = millionth of a meter!

mm = micron = millionth of a meter!

mm = micron = millionth of a meter!

mm = micron = millionth of a meter!

Biogenic Sediments: • composed primarily of marine microfossil remains • median grain size typically less than 0. 005 mm (i. e. , silt or clay size particles) • characterized as Ca. CO 3 (calcium carbonate) or Si. O 2 (silica) dominated systems • sediment with biogenic component less than 30% termed calcareous, siliceous clay • calcareous or siliceous 'oozes' if biogenic component greater than 30%

• siliceous oozes (primarily diatom oozes) cover ~15% of the ocean floor – distribution mirrors regions of high productivity – common at high latitudes, and zones of upwelling – radiolarian oozes more common in equatorial regions

• calcareous oozes (foraminifera, coccolithophores) cover ~50% of the ocean floor • level below which no Ca. CO 3 is preserved is the 'carbonate compensation depth‘ (CCD) • This change in dissolution rate is called the lysocline. Below the lysocline, more and more calcium carbonate dissolves, until eventually, there is none left. The lysocline typically occurs at a depth of 3000 to 4000 m

Sediment Accumulation

Calcium Carbonate Content in Pelagic Oceanic Sediment

Rates of Deposition of Marine Sediment

Temporal Succession of Pelagic Sediment at Spreading Centers

Sediment Succession in Absence of Siliceous Ooze

Cosmogenous Marine Sediments • Macroscopic meteor debris • Microscopic ironnickel and silicate spherules (small globular masses) – Tektites – Space dust • Overall, insignificant proportion of marine sediments

Marine Sediment Mixtures • Usually mixture of different sediment types • Typically one sediment type dominates in different areas of the sea floor.

Distribution of Marine Sediments: • • sediments thickest along continental margins, thin at midocean ridges coastlines – dominated by river-borne and wave reworked terrigenous sediments – shelf and slope characterized by turbidites and authigenic carbonate deposits – glacial deposits and ice-rafted debris common at high latitudes – high input of terrigenous sediments 'dilutes' biogenous components deep-sea (pelagic) basins – abyssal clays (wind blown deposits) common – lower quantities of biogenic material distribution of biogenous sediments dependent upon three primary factors – production in surface waters – dissolution in deep waters – dilution by other sediments types