Overview
This lecture explains biochemical sedimentary rocks, their formation from marine organisms, key types, and distinguishing properties.
Formation of Biochemical Sedimentary Rocks
- Biochemical sedimentary rocks form from the remains of marine organisms, mainly phytoplankton.
- Marine phytoplankton use minerals like calcium carbonate and silica to create shells and structures.
- After these organisms die, their remains accumulate on the ocean floor as siliceous or calcareous ooze.
- Over time, these deposits undergo lithification (turning into rock) to form biochemical sedimentary rocks.
Main Types of Biochemical Sedimentary Rocks
- Limestone forms mainly from calcium carbonate shells, especially from marine phytoplankton.
- Dolomite forms when limestone's calcite is chemically altered during lithification.
- Fossiliferous limestone contains visible fossils (shells) embedded in limestone.
- Coquina is made of loosely cemented shell fragments that are not fully fossilized.
- Chalk forms from the accumulation of coccolithophore remains, a type of marine phytoplankton.
- Micrite is a very fine-grained limestone made of calcareous mud, often containing microfossils visible only under a microscope.
Identification and Classification
- Biochemical sedimentary rocks are identified by their mineral composition and physical description.
- Limestone reacts (fizzes) with diluted hydrochloric acid, confirming the presence of calcite.
- Classification involves examining both the composition and the textural/chemical properties.
Key Terms & Definitions
- Biochemical Sedimentary Rock — rock formed from the remains of living organisms through chemical processes.
- Phytoplankton — microscopic marine organisms that produce shells from minerals.
- Lithification — the process that turns loose sediment into solid rock.
- Limestone — sedimentary rock mainly composed of calcite from marine organisms.
- Dolomite — rock formed from chemically altered limestone.
- Fossiliferous Limestone — limestone containing visible fossils.
- Coquina — rock made of loosely cemented shell fragments.
- Chalk — soft, white rock from compacted remains of coccolithophores.
- Micrite — fine-grained limestone composed of lime mud and microfossils.
Action Items / Next Steps
- Review how to identify biochemical sedimentary rocks based on composition and reaction to acid.
- Familiarize yourself with examples and key differences between rock types mentioned.