Geol 135 Sedimentation

J Bret Bennington

Introductory Class

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 basins.

Third "half" of the course - depositional environments - the detailed analysis of facies

Discuss reasons for studying sedimentary rocks

• Earth’s 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

Terrigenous:

• 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, Mudstone, Shale

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.

Others:

• Carbonaceous - coal - derived from the accumulation of undecayed plant matter.
• Pyroclastic - tuff - derived from the deposition of airborn volcanoclastics.