Seafloor Sediment Identification Guide

Biogenic Sediments

PLANTS ANIMALS

CalciumCarbonate(CaCO3)

biogenicsilica(bSiO2)

appx 1 µm appx 50 µm

appx 50 µmappx 50 µm

coccoliths forams

diatoms radiolaria

Credit: Steve Hovan, IUP

The majority of biogenic sediments are composted the hard parts of unicellular organisms, mainly coccoliths, forams, diatoms, and radiolaria.

Biogenic Sediments

Radiolarians are delicate single-celled zooplankton that absorb silica from ocean water to form their shells.

Look for: microfossils shaped like cones, discs, spheres, or rings with “arms” or spokes.

Foraminiferan, “forams” for short, have calcium carbonate shells like clams and corals. Forams add chambers as they grow. Forams are found at many depths. Some are pelagic (free floaters) and others benthic (live on the ocean floor).

Look for: microfossils with sections or chambers; some can look like fish eggs or snail shells.

Credit: Steve Hovan, IUP

Biogenic Sediments

Diatoms are delicate and unicellular (made of one cell). There are two kinds: pinnate and radial. They are found in areas with high primary productivity (photosynthesis)

Look for: circular-shaped or long skinny

microfossils.

Coccolithophores are ultra small, often spherical tests made up of disk-like plates. This is what real chalk is made of. You can find these in areas with moderate primary productivity (photosynthesis) but their shells will dissolve and leave no trace in waters deeper then <4500m.

Look for: tiny spheres or the individual disks.

Credit: Steve Hovan, IUP

Non-biogenic Sediments

Volcanic ash

coccoliths

diatoms

Photo Credit: Ivano Aiello – Mossing Landing, CA

Sand

Red Clays are found in deep waters away from continents, where the primary productivity is low.

Silt

Sand and silt arefound along the edges of continents and inareas where rivers and glaciers drain

Credit: Phil Rumford, TAMU