Chapter 10Sedimentary Rocks

Sedimentary Rocks

Accumulations of various types of sediments

Compaction: pressure from overlying sediments squeezes out air and water

Cementation: dissolved minerals in water form a “glue” that holds sediments together

Sedimentary Rocks

Classified by…Kind of sediments

Size of sediments

that form them

Clastic Sedimentary Rocks

Rock fragments carried by wind, water, ice and deposited

Classified by size

Clastic

Conglomerate: Rounded gravel fragments or pebbles

Clastic

Conglomerate wall

Clastic

Breccia:Angular gravel fragments with sharp corners

Clastic

Breccia wall

Clastic

Sandstone:Sand-sized grains

Mostly quartz

Pore spaces- allow groundwater and oil to flow

Clastic

ShaleClay-sized particles

Cemented and compacted under pressure

Flat, flaky layers

Chemical Sedimentary RocksMinerals dissolved in water, settle out with change in temperature

Ex. Limestone when calcite settles out of ocean water

Evaporites: dissolved minerals left over when water evaporates; turns to rock

Chemical

Ex: Gypsum, halite

Ex: Great Salt Lake, UT

Organic Sedimentary Rocks

Organic: formed from the remains of living things

Ex: coal

Organic

LimestoneShell build up on ocean floor, from

• Clams

• Oysters

• Plankton

Ex: chalk

Organic

White Cliffs of Dover, England

Sedimentary Rock Features

Easily identifiable

Include:Stratification (layering)

Ripple marks

Mud cracks

Fossils

Concretions

Stratification

Change in type of sediment deposited

Layers!!

Vary in thickness

Stratification

Cross bedding

Stratification

Graded bedding: where in the layer do you think the largest and heaviest grains of sediment settle?

Ripple Marks

Formed by action of wind or water on sand

Preserved when sand sandstone

Mud Cracks

Formed when muddy deposits dry and shrink

River plains, dry lake bed

New deposits fill in

Fossils

Remains or traces of ancient plants and animals

Buried as sediments build up

Hardest parts sometimes remain, but often dissolve into rock

Concretions

Lumps, or nodules, of rock with composition different from main rock body

Minerals precipitated from solutions build up around rock particles

Concretions

Groundwater deposits quartz, calcite

Geodes