Sedimentary Rocks

Sedimentary Rocks - Sedimentary Rocks A sedimentary rock is...

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Unformatted text preview: Sedimentary Rocks A sedimentary rock is formed by the accumulation sedimentary and compaction of sediments (rock pieces, minerals, animal parts, or chemical precipitates) minerals, Sediments are derived from weathering of Sediments rocks rocks Chemical weathering – Dissolution or Chemical decomposition of minerals grains due to chemical reactions chemical Bowen’s Reaction Series: The last minerals to crystallize are the most resistant to weathering. Susceptible to weathering Resistant to weathering Mechanical weathering – Breakage of rock due Mechanical to cracking, scratching, crushing, freezing, thawing, and abrasion thawing, There are 3 different types of sediments 1) Detrital (clastic) sediments – Pieces of eroded rock fragments and minerals grains. Sediments of this type form Detrital Sedimentary Rocks Detrital There are 3 different types of sediments Detrital (clastic) sediments – Pieces of eroded rock fragments and minerals grains. Sediments of this type form Detrital Sedimentary Rocks Detrital Chemical sediments – Minerals precipitated from water due to chemical reactions (ex. calcite, gypsum, halite). These sediments form Chemical Sedimentary Rocks Chemical There are 3 different types of sediments Detrital (clastic) sediments – Pieces of eroded rock fragments and minerals grains. Sediments of this type form Detrital Sedimentary Rocks Detrital Chemical sediments – Minerals precipitated from water due to chemical reactions (ex. calcite, gypsum, halite). These sediments form Chemical Sedimentary Rocks Chemical Biochemical sediments – Mineral remains of organisms or minerals precipitated due to biological processes (ex. shells, plant fragments, carbon). Sediments of this type form Biochemical Sedimentary Rocks Biochemical Detrital sedimentary rocks are classified Detrital according to their grain characteristics: according Size of the grains: refers to the range of sizes of Size the individual sediment pieces found within the rock. Can be divided into three categories: coarse-grained coarse-grained • Boulder, cobble, pebble, granule medium-grained • Sand fine-grained fine-grained • Silt, clay Classification of Clastic Sedimentary Rocks based on grain sizes Category: Sediment: Coarse Medium Boulder | Cobble | Pebble | Sand Size (mm): 256 Rock Name: Conglomerate Conglomerate 64 2 Fine | 0.062 Sandstone Sandstone Silt | Clay 0.0039 Siltstone Shale Shale Grain shape refers to the roundness of the Grain minerals. Grains that are well-rounded indicate they have traveled a long distance they Angular Rounded Well-Rounded Grain sorting refers to the amount of similar Grain size pieces within a sample size Well-Sorted Poorly-Sorted Chemical and Biochemical sedimentary Chemical rocks are classified by their chemical composition Common chemical sedimentary rocks include: 1) Crystalline Limestone (calcite = CaCO3) 2) 2) Chert Chert (quartz = SiO2) (quartz 3) Rock Salt Rock (halite = NaCl) (halite 4) 4) Rock Gypsum Rock (gypsum = CaSO4 · 2H3O) (gypsum Common biochemical sedimentary rocks Common include: include: 1) Fossiliferous Limestone Fossiliferous (well cemented calcite body parts) 2) 2) Coquina (poorly cemented calcite shells) 3) Bituminous Coal Bituminous (Carbon compounds from partially decayed plant matter) matter) A depositional environment is any place depositional where sedimentary rocks form where Environments can be characterized as high, Environments medium or low energy medium The larger the pieces being moved, the The higher the energy of the environment higher Mountain river, alluvial fan = high energy Swamp, deep ocean = low energy The more the pieces are being moved about, The the higher the energy of the environment the Swash zone of beach = high energy Floodplain, playa lake = low energy Sedimentary structures are features Sedimentary preserved in rocks that give information about the depositional environment. about Common examples include: Common (a) cross-beds, (a) (b) ripples, and (b) (c) bioturbation ...
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