Sedimentary Rocks A sedimentary rock is formed by the accumulation and compaction of sediments (rock pieces, minerals, animal parts, or chemical precipitates)

Sediments are derived from weathering of rocks Chemical weathering – Dissolution or decomposition of minerals grains due to chemical reactions

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 to cracking, scratching, crushing, freezing, thawing, and abrasion

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

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 Chemical sediments – Minerals precipitated from water due to chemical reactions (ex. calcite, gypsum, halite). These sediments form Chemical Sedimentary Rocks

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 Chemical sediments – Minerals precipitated from water due to chemical reactions (ex. calcite, gypsum, halite). These sediments form Chemical Sedimentary Rocks 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

Detrital sedimentary rocks are classified according to their grain characteristics: Size of the grains: refers to the range of sizes of the individual sediment pieces found within the rock. Can be divided into three categories: coarse-grained Boulder, cobble, pebble, granule medium-grained Sand fine-grained Silt, clay

Classification of Clastic Sedimentary Rocks based on grain sizes Category: Coarse Medium Fine Sediment: Boulder | Cobble | Pebble | Sand | Silt | Clay Size (mm): 256 64 2 0.062 0.0039 Rock Name: Conglomerate Sandstone Siltstone Shale Conglomerate Sandstone Shale

Grain shape refers to the roundness of the minerals Grain shape refers to the roundness of the minerals. Grains that are well-rounded indicate they have traveled a long distance Angular Rounded Well-Rounded

Grain sorting refers to the amount of similar size pieces within a sample Well-Sorted Poorly-Sorted

Chemical and Biochemical sedimentary rocks are classified by their chemical composition Common chemical sedimentary rocks include: Crystalline Limestone (calcite = CaCO3)

Chert (quartz = SiO2) Rock Salt (halite = NaCl)

Common biochemical sedimentary rocks include: Rock Gypsum (gypsum = CaSO4 · 2H3O) Common biochemical sedimentary rocks include: Fossiliferous Limestone (well cemented calcite body parts)

Coquina (poorly cemented calcite shells) Bituminous Coal (Carbon compounds from partially decayed plant matter)

A depositional environment is any place where sedimentary rocks form Environments can be characterized as high, medium or low energy

The larger the pieces being moved, the higher the energy of the environment Mountain river, alluvial fan = high energy Swamp, deep ocean = low energy The more the pieces are being moved about, the higher the energy of the environment Swash zone of beach = high energy Floodplain, playa lake = low energy

Sedimentary structures are features preserved in rocks that give information about the depositional environment. Common examples include: (a) cross-beds,

(b) ripples, and (c) bioturbation