Geol 135 Sedimentation
J Bret Bennington
Reading assignment for next class:
Nichols, Ch. 1 and 2, p. 1-24
First half of course - sedimentology - the study of how sedimentary rocks form and the processes that
create their unique characteristics
Second half of course - stratigraphy - the study of sedimentary layers and their development in tectonic
Third "half" of the course - depositional environments - the detailed analysis of facies
Discuss reasons for studying sedimentary rocks
- Earths surface is dominated by sedimentary layers. All geologists
routinely encounter sedimentary rocks.
- Geochronology - geologic time scale developed by stratigraphers
- Earth history is based primarily on the sedimentary record.
- Environmental change
- Geographic change
- Climate change
- Sea level change
- Record of tectonic processes - rates of subsidence, uplift, structural
record of tectonic movements, basin evolution
- Record of astronomical processes - orbital parameters, impacts
- Record of atmospheric and ocean chemistry
- Fossils are found in sedimentary rocks. To study fossils is to
study sedimentary processes as well.
- History of life and evolution and extinction of species and ecosystems.
- Most jobs in geology involve working with sedimentary rocks -
oil, coal, natural gas, groundwater, building materials, and many
ore deposits are found in sedimentary rocks. Sedimentary rocks
are by far the most economically important type of rock.
Review - Different types of sedimentary rocks
- Clastics - quartz and clay, some feldspar, dark igneous minerals
- derived from erosion of pre-existing rock, also called extrabasinal. Conglomerate, Breccia, Arkose, Sandstone, Graywacke, Siltstone,
Biogenic and chemical rocks:
- Carbonates - calcite, dolomite - derived from precipitation of
minerals in water (organically or inorganically), also called
intrabasinal. Limestones, Dolostones
- Evaporites - halite, gypsum, anhydrite - derived from precipitation
of minerals in water due to evaporation, also intrabasinal. Rock halite, etc.
- Authigenic - pyrite, chert, limonite, others - derived from precipitation
of minerals, usually localized in other types of sedimentary rock.
- Carbonaceous - coal - derived from the accumulation of undecayed
- Pyroclastic - tuff - derived from the deposition of airborn volcanoclastics.