l Biogenous
– Remains of once living organisms make up >30% of the deposits
Biogenous sediment is derived from the remains of hard parts of once-living Organisms
l Two major types:
– Macroscopic : relatively rare
– Microscopic: more abundant
l Macroscopic biogenous sediments
Visible to naked eyes; Shells, bones, teeth Microscopic organisms produce tiny shells called tests
l What are the main organisms that contribute to biogenous sediments?
Algae: are aquatic, eukaryotic Photosynthetic organisms, ranging from microscopic single cells to
large organisms.
Protozoans: are single-celled, eukaryotic, non-photosynthetic organisms
l Composition of Biogenous Sediment ?
Two most common chemical compounds:
– Calcium carbonate (CaCO3 , which forms the mineral calcite)
– Silica (SiO2 or SiO2·nH2O): SiO2·nH2O is the hydrated form of silica, which is called opal
l Most of the silica in biogenous ooze comes from microscopic algae called Diatoms and protozoans called Radiolarians. ?
Diatoms ?
•Diatoms are photosythetic, planktonic (free floating) algae, so they need sunlight and are found near ocean surface.
•Diatoms have a shell built from silica. Their tests (shells) have two parts that fit together. Small holes in tests allow nutrients to pass in and waste pass out
Radiolarians ?
Radiolarians are microscopic, single celled protozoans. Most of them are planktonic.
They have siliceous shell and spikes or rays. They are not photosynthetic, so the rely on external
food sources such as bacteria or other plankton
Calcium Carbonate in Biogenic Sediments ?
Coccolithophores
– Single-celled Photosynthetic algae
– Most are planktonic;
– Also called nannoplankton
Foraminifers
– Single-celled protozoans, most are planktonic, in size from microscopic
to macroscopic.
– Non-photosynthetic, use external food
– Their tests have an openning in one end.
