Geology by Frank H. T. Rhodes

Author:Frank H. T. Rhodes [Rhodes, Frank H. T.]
Language: eng
Format: epub
ISBN: 978-1-4668-6473-3
Publisher: St. Martin's Press
Published: 1991-04-21T23:00:00+00:00

A typical coal mine operation

THE SIZE, SHAPE, AND SORTING of sedimentary structures within rocks may provide clues to the depositional environment that existed during their formation. Rounded, frosted, well-sorted grains, for example, indicate wind-deposited sand.

CROSS-BEDDING is a term applied to sweeping, arclike beds that lie at an acute angle to the general horizontal stratification. It is common in stream and deltaic deposits, in deeper marine waters, and in sand dunes. Cross-bedding reflects the direction of current flow.

GRADED BEDDING is due to differential settling of mineral grains, and is useful for determining the correct “way up” in folded strata. The layers of coarse rock have a sharp base and gradually grade upward into finer-grained materials.

VARVED BEDDING is a type of thin, graded bedding that has alternate laminations of coarse and fine-grained material. Especially common in glacial lake deposits, it is characteristic of seasonal deposition, each pair of varves representing a year. (See here.)

MUD CRACKS form where lake and mud deposits are dried by the sun and are preserved by burial under mud.

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