Sedimentary Rocks . Deposited on or Near Surface of Earth by Mechanical or Chemical Processes. What Rocks Tell Us . Types of Sedimentary Rock. Clastic (terrigenous or detrital) Conglomerate or Breccia Sandstone Siltstone Shale Chemical/biochemical Evaporites
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Deposited on or Near Surface of Earth by Mechanical or Chemical Processes
Depositional environments in ancient sediments are recognized using a combination of sedimentary facies, sedimentary structures and fossils
Grain size greater than 2 mm
1. If rounded clasts = conglomerate
2. If angular clasts = breccia
distance of transportation (method of erosion)
Sedimentary rocks made of silt- and clay-sized particles are collectively called mudrocks, and are the most abundant sedimentary rocks.
Fine gravelly lithounit
lithounit (cross stratified)
Cross-stratified sst. Paleo-flow from right to left
Limestone - Dolomite
Plagioclase – Albite
Diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification.
CementationClastic particles ranging from silt-size to boulder-size may be deposited on the sea floor. As they are buried, ion-laden sea water may deposit minerals in the porespaces between the grains, thus effectivelycementing them together. By this process the sediments become rocks such as siltstone, sandstone and conglomerate.
CompactionClastic particles smaller than silt, such as mud are deposited on the sea floor. As they are buried, the weight of overlying sediments presses downward on the mud particles and compacts them, resulting in the formation of rocks such as claystone,mudstone or shale.
Chemical & Organic rocks
Form due to decomposition of organic remains under temperature and pressure eg. Coal/Lignite etc.
Form basically from CaCO3 – both by chemical leaching and by organic source (biochemical) eg. Limestone; dolomite
These rocks are formed
due to evaporation of saline water (sea water)
eg. Gypsum, Halit
These rocks are formed within the a depositional basin from chemical substances dissolved in the seawater or lake water.
Non-Clastic Sedimentary Particles IBroken fragments of calcite, mostly from algae.Shallow sub tidal sediments from the Yucatan, Holocene.
Largest fragments are about 1 mm in length.
Non-Clastic Sedimentary Particles Broken shell fragments of calcite frombivalve molluscs. These shell fragments accumulated on a beach and are cemented together.
This rock is almost100 percent shell fragments,and is therefore called a coquina.Largest fragments about 2 cm in length.
Characteristics and names of some common clastic sedimentary rocks.
smooth feel, layered appearance
mud (mud sized particles: < 0.063 mm)
smooth feel, massive to layer
silt(silt sized particles:0.063 - 0.004 mm)
slightly gritty feel, may have layered appearance
sand(sand-sized particles:0.0625-2.0 mm)
rough gritty feel, constituent grains clearly visible, including quartz, feldspar, other minerals, and rock fragments.
granules, pebbles, cobbles, boulders (granule to bouldersized particles:2 mm - > 256 mm)
large rounded fragments composed of older rock materials
granules, pebbles, cobbles, boulders (granule to boulder sized particles:2 mm - > 256 mm)
large angularfragments composed of older rock materials
Characteristics of common non-clastic sedimentary rocks that will not react with dilute HCl.
very fine grained:can't see constituent particles with naked eye
hard, scratches glass, typically white, green, or red; tends to haveconchoidal fracture
variable grain size
soft, can be scratched with fingernail; may be translucent or opaque
Characteristics of common non-clastic sedimentary rocks that will react with dilute HCl.
very fine grained, can't make out particles with naked eye
Pure white, powdery, light-weight, will write on sidewalks or walls
variable in grain size
dense and soft, with a crystalline or dull (earthy) luster
medium grained, particles commonly visible with naked eye
fragments of fossils, usually shells of invertebrates
variable in grain size
dense and soft, may be crystalline or dull, with visible fossils, such as snail or clam shells or other taxa
Review Of Sedimentary ProcessesThis chart is a review of the various steps involved in the formation of sedimentary rocks that have been discussed above.