GLG 101
Chapter 6
Sediment and Sedimentary Rocks
Also see: http://geology.wr.usgs.gov/docs/usgsnps/rxmin/rock2.html
sedimentary rocks: derived from preexisting rocks
sediment: detrital or chemical
classification by: grain size and composition
Sediment transport and deposition
transported by: wind, glaciers, water (running water)
abrasion: reduction of grain size
rounding
sorting
depositional environment
Lithification: sediment to sedimentary
rock
lithification: process of transforming sediment
into sedimentary rock
compaction: reduction of pore spaces
cementation: binding of grains with cement (e.g. calcite, quartz)
Sedimentary rocks
detrital (clastic)
sedimentary rocks:
consist of clasts (transported grains) with clastic texture
- conglomerate
- sedimentary breccia
- sandstone: e.g. quartz sandstone, arkose, lithic sandstone
- mudrocks: e.g. siltstone, mudstone, claystone, shale
chemical and biochemical sedimentary rocks:
originate from substances taken into solution during chemical weathering
they have a crystalline texture
- limestone, dolostones: carbonates (e.g. chalk,
coquina, oolithic limestone)
- evaporites (rock salt, gypstone
- chert (e.g. flint, jasper)
- coal
Sedimentary facies
facies: all the characteristics of a rock (lithology and organic components)
Transgression and regression
transgression: shoreline moves inland
regression: shoreline moves seaward
Sedimentary structures:
- strata or beds (bedding plane)
- graded bedding
- cross bedding (indicate paleocurrents)
- ripple marks (current ripples, wave-formed ripples)
- mud cracks
Fossils
remains or traces of ancient organisms (body fossils, trace fossils)
mold: cavity in rock previously containing a shell or hard part
cast: filled in mold
Environment of deposition
e.g.
Natural resources in sedimentary rocks
- petroleum and natural gas
- uranium
- banded iron formations