Sedimentary Rocks Sedimentary rock is formed by erosion Sediments are moved from one place to another Sediments are deposited in layers, with the older ones on the bottom The layers become compacted and cemented together http://www.fi.edu/fellows/payton/rocks/create/sediment.htm

Sedimentary Rock Sedimentary Rocks are formed at or near the Earth’s surface No heat and pressure involved Strata – layers of rock Stratification – the process in which sedimentary rocks are arranged in layers

Sediments -pieces of material left by: *wind *ice *chemical precipitation *water *gravity Step 1: WEATHERING Chemical- minerals are chemically broken down

* Physical – minerals remain chemically unchanged

Step 2: EROSION * transporting weathered materials to another location * Wind, water, gravity and glaciers transport

Step 3: DEPOSITION * sediments are deposited and sorted

* deposited into depressions called “sedimentary basins” Step 4: BURIAL * deposited into depressions called “sedimentary basins” * the deeper it gets, the more pressure on it til…… 2 ROCK BURIAL

Step 5 : LITHIFICATION (FYI – lithos: Greek for stone) * physical and chemical process that changes it to sedimentary rock 1st Compaction 2nd Cementation & Solidification new minerals precipitate more of the same type around existing ones crystallize around existing ones

FEATURES OF SEDIMENTARY ROCKS BEDDING – *horizontal layers *if sorted, graded bedding CROSS-BEDDING - *inclined layers move forward like sand dunes ))

RIPPLE MARKS * when sediment is moved into small ridges by wind or wave action * back & forth waves yield symmetrical waves * currents, (like in rivers) asymmetrical waves Sand dune – ripple marks from wind

Asymmetrical ripple marks

FOSSILS *animals die, buried, lithified * some plants replaced by other minerals * shells, bones, etc. could leave impressions

CONCRETIONS * lumps of fine grained silica * called chert *also called nodules CHERT

MUD CRACKS *wet clay dries and contracts * cracks later fill with sediment

TYPES OF SEDIMENTARY ROCKS CLASTIC formed by lithifications Coarse Medium Fine gravel sand silt & mud some rocks sandstone siltstone conlglomerates mudstone POROSITY * percent of open space between grains of sand *good reservoirs for oil, natural gas, and H2O * permeable if water can pass through

Porous Rock

a. rocks formed by evaporation 2. CHEMICAL a. rocks formed by evaporation - called evaporites ex: calcite, halite & gypsum S DEAD SEA SALT CALCITE

b. organic sedimentary rock -formed from the remains of living things - most abundant is limestone (mostly calcite) CaCO3 from shells if shells are high in silica, they form siliceous ooze - Coal – from remains of plant material…almost entirely carbon Siliceous ooze CALCAREOUS OOZE