Chapter 7 SEDIMENTARY ROCKS THE THREE ROCK GROUPS Igneous rocks formed by cooling and consolidation of magma Sedimentary rocks formed by chemical precipitation of material from water at the Earth s surface or by deposition and cementation of particles and debris transported by water wind or ice Metamorphic rocks igneous or sedimentary rocks that have been changed under high temperatures and or high pressures SEDIMENTARY ROCKS Sedimentary rocks form layers like the pages of a book The layers record a history of ancient environments The layers occur only in the upper part of the crust Sedimentary rocks cover underlying basement rock TYPES OF SEDIMENTARY ROCKS Clastic solid fragments and grains cemented together Biochemical consist of shells of organisms Organic consist of carbon rich remnants of plants Chemical made from minerals precipitated directly from water CLASTIC SEDIMENTARY ROCKS Clastic sediments are formed by weathering and erosion Solid material is transported by wind and water Deposition occurs WEATHERING Processes that break up rock to create sediment Physical Mechanical breakage and disintegration Chemical Decomposition by reaction with water Weathering processes occur at Earth s surface Rocks react with hydrosphere atmosphere and biosphere Low temperature and pressure LITHIFICATION Transforms loose sediment into solid rock Compaction burial adds pressure to sediment Squeezes out air and water Cementation minerals grow in pore spaces Often quartz or calcite Glue sediments together GRAIN SIZE Clast size the diameter of fragments or grains Range from very coarse to very ne Boulder cobble pebble sand silt and clay Gravel coarse grained sed boulder cobble pebble Mud ne grained silt and clay As transport distance increases grain size decreases SANDSTONE Sandstone clastic rock made of sand sized particles Often deposited in beach and dune settings Common in Ohio Quartz is by far the most common mineral in sandstones SHALE Shale clastic rock made of clay sized particles Clay sized particles often deposited in quiet water environments Organic rich shales are source of natural gas Common in Ohio E g Fracking is going on in the Marcellus Utica shales in Ohio Park is great Google glen echo park Columbus Shales are common in exposed GLEN ECHO RAVINE PARK rock formations CROSS BEDS When blowing sand builds into sand dunes in a desert the sand tumbles up the windward side of the dune and settles in quieter air on the leeward side BIOCHEMICAL SEDIMENTARY ROCKS Biochemical Limestone Made from shells corals or carbonate mud Shells typically no longer visible Note Limestone can also be produced by chemical processes Chert Formed from quartz silica shells of plankton FOSSILIFEROUS LIMESTONE KAIBAB LIMESTONE Permian 250 500 Ma limestone forms Marble Canyon AZ WOTAN S THRONE Canyon rim is Kaibab Limestone BIOCHEMICAL DEPOSITION ENVIRONMENT ORGANIC SEDIMENTARY ROCKS Plants under pressure and heat become coal CHEMICAL SEDIMENTARY ROCKS Comprised of minerals precipitated from water solution Evaporites Created from evaporated seawater Evaporation triggers deposition of chemical precipitates Examples include halite rock salt and gypsum TRANSGRESSION REGRESSION Sea level changes Deposition strongly linked to sea level Changes in sea level are commonplace geologically Transgression ooding due to sea level rise Regression exposure due to sea level fall SEDIMENTARY STRUCTURES A series of beds are referred to as strata A sequence of strata that is suf ciently unique to be recognized on a regional scale is termed a formation The formation is the fundamental geologic mapping unit