Page 177 - Laboratory Manual in Physical Geology

SEDIMENTARY PROCESSES

TRANSPORTATION:
BEDROCK SOURCE: Detrital (siliciclastic) sediments like gravel,
Physical and chemical sand, and mud are transported downslope by
weathering of bedrock streams. Large grains are sorted from smaller
produces detrital grains by different velocities of flowing water.
(siliciclastic) sediment Physical and chemical weathering continues. Evaporation
and chemicals in of water
solution in the surface
and groundwater.

Chemical sediments:
Detrital sediment: salt crystals and chemical
Biochemical sediments: gravel, sand, and residues. Crystals precipitate
shells accumulate in situ (in a mud deposition. and form crystalline rock in
place close to where they lived situ (in the place where they
in, on, or above the sea floor). formed from evaporating
water; they are not
BASIN transported).
OF DEPOSITION
(ocean basin)

CONTINENTAL
BEDROCK:
Mostly
metamorphic and Layers of sediment (beds, strata)
igneous rocks. LITHIFICATION:
compaction and
cementing of
sediments

SEDIMENTARY
ROCK

FIGURE 6.1 Sedimentary processes. Sedimentary processes include everything from the formation of detrital (siliciclastic), biochemical

(bioclstic), and chemical sediments to the lithification (hardening) of sediments that results in sedimentary rock.
broken and transported away from bedrock surfaces (cliffs, detrital sediment is eroded (loosened, removed) from
valley walls, other outcrops) are detrital grains comprising its source and transported (moved, carried) over
detrital sediment. Detrital sediment is not in situ ; it is great distances. Agents of erosion and transportation
transported away from its source. Plants and animals are include wind, water, ice, organisms, and gravity. For
fragmented into bioclastic biochemical sediment made of example, gravity forces water to flow downhill, and
things like shells, fragmented shells, twigs, and leaves. This water is a physical agent that picks up and carries
kind of sediment is easily broken, worn, and chemically sediment. Eventually, the water flows into a basin
decayed, so it is generally in situ . If you find a fossil (any (depression where water and sediment accumulate),
evidence of ancient life), then the organism probably lived becomes part of a lake or ocean, and sediment
where it was fossilized. deposition occurs. Deposition is what happens when
transportation stops and sediment accumulates by
Erosion, Transportation, and Deposition settling out of the water (or air or melting ice) that
of Sediment carried it. (In contrast, chemical and biochemical
sediment is usually not transported, so it is deposited
The place where sediment originates or forms is called in situ —where it forms.)
its source . Although most biochemical and chemical
sediment remains close to where it formed (is in situ ),

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