Sedimentary Depositional Environments Review Exercise

Earth Science Extras

by Russ Colson

Glacial hanging valley (background) and tidal flats (foreground) in Alaska,2002.

Different types of sediment are deposited in different types of depositioinal environments, reflecting the energy of the environment (how fast the water is flowing, how vigrorous the waves are, or how strong the wind is) and other environmental factors (e.g. evaporation rate vs rainfall, glacial conditions, presence of turbidity currents, conditions appropriate for reef development, etc). The exercise below is intended as a review of some of the sediment characteristics that are typical of these environments.

The illustrations below show in simplified and conceptual form the locations of some important depositional (and erosional) environments that will be used in the following challenge.

Value: 26

Match the letters seen in the two illustrations above with the correct sediment description below. Each letter is used only once.

LETTER

Fine grained, lime-rich sediment (carbonate rich)

evaporite layers, or salt grains interspersed with sediment

algal mats, mudcracks common

often crosscut by channels

LETTER

Bouma sequences (with graded bedding)

black shales, courser clastics include lots of volcanic rock fragments (immature)

chert

LETTER

Bouma sequences (with graded bedding)

black shales

pelagic and nektonic fossils (floaters and swimmers, few bottom dwellers)

LETTER

Well sorted, mature, sand, mostly quartz, some conglomerates

some broken shells,

cross bedding, symmetric and asymmetric ripples

LETTER

Dark shale, plant material common

bioturbated

thin storm-deposited sandy layers

LETTER

Well sorted, mature sand, mostly quartz

large-scale (10s of meters thick sometimes) steep (30 degrees) crossbeds,

ripples rare or absent, red, brown, and white colors

rare trace fossils (tracks), other fossils even more rare

heavy minerals concentrated in laminae

LETTER

Interbedded conglomerates, sandstones, siltstones and mudstones,

mudcracks, burrows, tracks and trails

plant and animal fossils common

soil horizons common in mudrocks

cross-bedding, assymmetric ripples

graded bedding and reverse graded bedding

common reddish color

LETTER

Unsorted mix of gravel, sand, mud

sediment immature

Rare plant fossils, other fossils absent

No lamination or crossbedding

Large clasts sometimes striated

LETTER

Evaporites and mudrocks

mudcracks, raindrop prints, tracks

Body fossils rare or absent

LETTER

Poorly sorted sandstones and conglomerates

Red, Brown, white colors

commonly feldspar rich (arkosic)

graded bedding and reverse graded bedding

laminated and crossbedded, fossils rare

LETTER

Poorly sorted sandstone and conglomerate

Red, Brown, dark colors

commonly contains rock fragments (volcanic) indicating immaturity

graded bedding and reverse graded bedding

laminated and crossbedded, fossils rare

LETTER

Gray and green shale

fossils common, mollusc, brachiopod

bioturbated, glauconitic

LETTER

Highly fossiliferous limestone, may be oolitic or peloidal

usually light gray

fossils include coral, byrozoa, brachiopods, molluscs,

high diversity

Value: 3

Note: Deltaic environments are complex and varied environments, but often produce silty sediment. Glacial lake deposits depend on the depth of the lake and may vary from the shore into the lake interior. They sometimes produce varves, sediment laminae that alternate in color from summer to winter deposition. Caves and hot springs often have both erosion and deposition of calcium carbonate or silica sediments.

last updated 8/7/2020. Thanks to Jennifer Lepper for the artwork for the secon of the depositional environments illustrations. Other text and pictures are the property of Russ Colson.