Types of sedimentary Rocks All sedimentary rocks are classified by their MODE of formation— (that is, how they formed).

Angular vs. Rounded Some grains are jagged while others are rounded. What do you think leads to each of these differences? Jagged = closer to the source (carbonate sand) Rounded = travelled far before being deposited

Evidence of Past Life Fossils are some of the best known features of sedimentary rock. Fossils: preserved remains, impressions or other evidence of once-living organisms. Fossils provide evidence of the types of organisms that lived in the distant past.

Clastic Sedimentary Rocks Clastic sedimentary rocks are formed from the abundant deposit of loose sediments that accumulate on Earth’s surface. Can be further classified based on particle (grain) sizes.

Coarse-Grained Rocks

Coarse-Grained Rocks Coarse-grained rocks are sedimentary rocks consisting of gravel-sized rock and mineral fragments. Conglomerates: rounded, gravel-sized particles Large mass = travelled via high-energy flows of water. Breccia: composed of angular, gravel-sized particles Angularity indicates that sediments from which they formed did not have time to become rounded. Deposited close to source.

Medium-Grained Rocks Sedimentary rocks that contain sand-sized rock and mineral fragments are classified as medium-grained clastic rocks. Stream and river channels, beaches and deserts often contain sand-sized sediments.

Sandstone Contains many features of interest to scientists. Ripple marks/cross bedding indicate the direction of current flow High Porosity (30-40%) Porosity: % of open spaces between grains in a rock. Reservoirs of oil, natural gas and groundwater

Fine-Grained Rocks Sedimentary rocks consisting of silt- and clay-sized particles (siltstone + shale) are fine-grained rocks. Form in environments like swamps, ponds and deep ocean Low porosity Layer horizontally

Chemical and Biochemical Sed. Rocks Processes involve evaporation and precipitation of minerals. Weathering  Minerals are dissolved and carried into bodies of water Water evaporates  dissolved minerals are left behind, higher concentration

Chemical Sedimentary Rocks Concentration of dissolved minerals in water reaches saturation, crystals can precipitate out and settle at the bottom. Evaporties: layers of chemical sedimentary rocks that form after precipitating Form in arid regions and continent coasts with low levels of freshwater input.

Biochemical Sedimentary Rocks Formed from the remains of once-living organisms. Limestone is key player; made of calcite that has been lithified Living creatures use calcium carbonate in ocean to make shells When they die, shells settle to the bottom to make carbonate layers.

Biochemical Sedimentary Rocks Limestone is common in shallow-water environments. Coral reefs thrive in 15 to 20 m of water; not much deeper These coral will eventually form limestone as well! Origins of creatures range from large-shelled organisms to micro unicellular organisms.