What is a sedimentary rock? Sedimentary rocks result from mechanical and chemical weathering Comprise ~ 5% of Earth’s upper crust Contain evidence of past environments Record how sediment is transported Often contain fossils

Fossil Fish - 50 Million Year Old Lakes in southern Wyoming Sediment is fine-grained mudstone

Turning sediment into rock Changes occur in sediment after it is deposited Diagenesis – chemical and physical changes that take place after sediments are deposited

Turning sediment into rock Diagenesis Recrystallization – growth of stable minerals from less stable ones Lithification – loose sediments is transformed into solid rock by compaction and cementation Natural cements include calcite, silica, and iron oxide

Types of sedimentary rocks Detrital rocks – transported sediment as solid particles Chemical rocks – sediment that was once in solution

Detrital sedimentary rocks Constituents of detrital rocks can include Clay minerals Quartz Feldspars Micas Particle size is used to distinguish among the various types of detrital rocks

Detrital sedimentary rocks Common detrital sedimentary rocks Shale Mud-sized particles deposited in thin layers called laminae

Detrital sedimentary rocks Sandstone

Detrital sedimentary rocks Conglomerate and breccia Both composed of particles > 2mm in diameter Conglomerate consists largely of rounded clasts Breccia is composed of large angular particles

Chemical sedimentary rocks Precipitated material once in solution Precipitation of material occurs two ways: Inorganic processes Organic processes (biochemical origin)

Chemical sedimentary rocks Common chemical sedimentary rocks Limestone Most abundant chemical rock Made of the mineral calcite Marine biochemical limestones form as coral reefs, coquina (broken shells), and chalk (microscopic organisms) Inorganic limestones include travertine and oolitic limestone

Coquina

Fossiliferous limestone Note shells and lime matrix

Chalk Outcrops in SE USA Hand Specimen

Travertine forming in Hot Spring Hand Specimen

Chemical sedimentary rocks Common chemical sedimentary rocks Dolostone Typically formed secondarily from limestone Common in ancient rocks, rare today Chert Made of microcrystalline quartz Usually deposited as siliceous ooze in deep oceans (can be diatomaceous) chert Diatomaceous chert

Chemical sedimentary rocks Common chemical sedimentary rocks Evaporites Evaporation triggers deposition of chemical precipitates Examples include rock salt and rock gypsum

Chemical sedimentary rocks Common chemical sedimentary rocks Coal Different from other rocks because it is composed of organic material

Metamorphic Rocks The transformation of rock by temperature and pressure Metamorphic rocks are produced by transformation of: Igneous, sedimentary and igneous rxs

Metamorphism Metamorphism progresses from low to high grades Rocks remain solid during metamorphism

Metamorphism Three types of metamorphic settings: Contact metamorphism – from a rise in temperature within host rock Hydrothermal metamorphism – chemical alterations from hot, ion-rich water Regional metamorphism -- Occurs in the cores of mountain belts and makes great volumes of metamorphic rock

Metamorphic Environments Metamorphic grade A group of minerals that form in a particular P-T environment Zeolite (really low T,P; <200C) Greenschist (low T, P; 200-450C, 10-15 km) Blueschist (low T, high P - subduction zones) Amphibolite (high T, P; 450-650C, 15-20 km) Granulite (super high T, P; >700C, >25km)

What are metamorphic textures? Texture refers to the size, shape, and arrangement of mineral grains within a rock Foliation – planar arrangement of mineral grains within a rock

Common metamorphic rocks Nonfoliated rocks Quartzite Formed from a parent rock of quartz-rich sandstone Forms in intermediate T, P conditions

Common metamorphic rocks Nonfoliated rocks Marble Coarse, crystalline Parent rock usually limestone Composed of calcite crystals Fabric can be random or oriented

Common metamorphic rocks Foliated rocks Slate Very fine-grained Made by low-grade metamorphism of shale

Common metamorphic rocks Foliated rocks Phyllite Grade of metamorphism between slate and schist Composed mainly of muscovite and/or chlorite

Common metamorphic rocks Foliated rocks Schist Medium- to coarse-grained Comprised of platy minerals (micas) The term schist describes the texture

Common metamorphic rocks Foliated rocks Gneiss Banded appearance High-grade metamorphism Composed of light-colored feldspar layers with bands of dark mafic minerals

Outcrop of foliated gneiss

The rock cycle

The rock cycle - Series of processes by which rocks changes into other types of rocks Illustrates various processes and paths as earth materials change both on the surface and inside the Earth - What are the three main rocks ? 1- Igneous 2- Metamorphic 3- Sedimentary

The rock cycle

Fundamental Rock Types Igneous Rocks: solidify from melt, e.g. lava (extrusive) or magma (intrusive) Sedimentary Rocks: are made at the Earth’s surface from particle and chemical remnants of other rocks Metamorphic rocks: form when other rocks are heated, squeezed, and deformed.