Chapter 6: Sedimentary Rock

Sediment

Loose fragments of rocks or minerals broken off bedrock, mineral crystals precipitated from water, or shells; result from weathering of pre-existing rock.

Regolith

Loose debris covering bedrock, including sediment and soil.

Weathering

Processes breaking up and corroding solid rock into loose debris; includes physical and chemical breakdown.

Clast

Fragment or grain from physical or chemical weathering of pre-existing rock; forms grains.

Jointing

Naturally formed cracks in rock, breaking bedrock into separate blocks.

Talus

Rock rubble at the base of a slope, carried away by rivers.

Erosion

Breaking off and removal of rock or sediment.

Frost Wedging

Freezing in joints forces them to open, breaking blocks free from bedrock.

Chemical Weathering

Chemical reactions altering minerals when rock contacts water or air.

Soil

Rock or sediment modified by physical, chemical interaction with organic material, rainwater, and organisms at or below the earth's surface.

Intracontinental basins

Basins that develop within the interiors of continents due to subsidence over a rift.

Foreland basins

Basins that form on the continental side of a mountain belt due to forces from convergence or collision pushing rock up faults onto the continent's surface.

Transgression

The inward migration of a shoreline as a result of rising sea levels.

Regression

The seaward migration of a shoreline caused by a decrease in sea level.

Diagenesis

The combination of physical, chemical, and biological processes that transform sediment into sedimentary rock and alter its characteristics after formation.

Physical weathering

The process of breaking solid rocks into unconnected grains or chunks.

Salt wedging

Dissolved salt in groundwater precipitates in open pore spaces in rocks, crystallizing and pushing apart surrounding grains.

Root wedging

Roots of tree push through joints.

Thermal expansion

Heat of intense forest fires bakes a rock, the outer layer of the rock expands.

Animal attack

Burrows created by creatures can move rock fragments.

Dissolution

Water solvent flows over or through rock and dissolves minerals (affects salts and carbonate minerals).

Hydrolysis

Water reacts chemically with minerals and breaks them down to form minerals.

Oxidation

Rocks transform iron-bearing minerals into a rusty brown mixture of iron-oxide and iron-hydroxide minerals.

Hydration

Absorption of water into the crystal structure of minerals causing certain minerals to swell, weakening the rock.

Zone of leaching

The area close to the surface where the water extracts ions, picks up clay, and carries this material downward.

Zone of accumulation

An area deeper below the surface where new mineral crystals precipitate out of the percolating water, and because the rate of water movement slows, the water leaves behind its load of fine clay.

Soil horizons

Distinct zones within soils defined by certain characteristics.

Soil profiles

Vertical sequences of distinct zones.

Sedimentary rock

Rock that forms either by cementing together of fragments, broken off, pre-existing rock, or by the precipitation of mineral crystals out of water solutions at or near the earth surface.

Clastic sedimentary rock

Rocks formed from cemented together clasts, solid fragments and grains broken off of pre-existing rocks.

Biochemical sedimentary rock

Rocks that consist of shells.

Organic sedimentary rock

Rocks that consist of carbon-rich relicts of plants or other organisms.

Chemical sedimentary rock

Rocks are made up of minerals that precipitated directly from water solutions.

Deposition

Sediment that settles out of the transporting medium.

Lithification

The transformation of loose sediment into solid rock through compaction and cementation.

Compaction

When the weight of overburdened squeezes air or water out from between grains, so the grains can fit together more tightly.

Cementation

When minerals, commonly quarts or calcite, precipitate from ground water, and fill the remaining spaces between clasts, to form a cement that binds grains together.

Clast composition

The makeup of clasts in the rock.

Recrystallization

A process where new crystals grow at the expense of old ones.

Evaporites

Salt deposits that form as a consequence of precipitation from saline water.

Bed

A single layer of sediment or sedimentary rock with a recognizable top and bottom.

Bedding plane

The boundary between two beds is a bedding plane.

Stratification

Several beds together constitute strata and the overall arrangement of sediment into a sequence of beds.

Ripple marks

Relatively small (generally no more than a few centimeters high), elongate ridges that form on a bed surface at right angles to the direction of current flow.

Dune

A pile of sand generally formed by deposition from the wind.

Rift basins

Form in continental rifts, regions where the lithosphere is stretching horizontally. Low areas, narrow basins bordered by elongated mountain ridges. Fill with terrestrial sediment.

Passive-margin basins

Form along edges of continents that are not plate boundaries. Underlain by stretched lithosphere. form because subsidence of stretched lithosphere continues long after rifting ceases.