Definitions and images to illustrate geological terms, links to images and website articles


Strata (sing. stratum) are distinctive layers or beds, of sediments or sedimentary rocks deposited consecutively, or with interruption by unconformities, atop other rocks. Each sedimentary stratum has approximately the same composition throughout, reflecting conditions at the time of deposition.

Biostratigraphy is employed to correlate the age of rocks within strata according to their fossil assemblages.

[images : Cerro de Cristo Rey, New Mexico, rock layers in the Anapra formation, 2, 3, close-up of cross-bedding; cross-bedding and flowing water; cross-lamination Pease Bay; cross-bedding Navajo Sandstone; cross-bedding Hawkesbury Sandstone; cross-bedding Kaibab; Scout Lookout; sandstone layering; cross-bedding Glenshaw Formation; slumped and deformed lacustrine sediments of Morale Claim Maar]

For a comprehensive glossary of terminology related to rock strata, see GGIPAC BeddingPattern (pdf) or html version.

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