Sedimentary Rocks

http://www.fi.edu/fellows/payton/rocks/create/sediment.htm

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

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 *gravityStep 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

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 rock1st Compaction

2nd Cementation & Solidificationnew minerals precipitate more of the same type

around existing ones crystallize around

existing ones

FEATURES OF SEDIMENTARY ROCKSBEDDING – *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 ROCKS1. CLASTIC formed by lithifications

Coarse MediumFine

gravel sandsilt & mud

some rocks sandstonesiltstone

conlglomeratesmudstone

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

2. CHEMICALa. rocks formed by evaporation

- called evaporites ex: calcite, halite & gypsum

S

CALCITE

DEAD SEA SALT

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

CALCAREOUS OOZE Siliceous ooze