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Abstract

Intraclast - A fragment of penecontemporaneous, commonly weakly consolidated, carbonate sediment that has been eroded and redeposited, generally nearby, within the same depositional sequence in which it formed (Folk, 1959 and 1962).

Lumps - In modern sediments, irregular composite aggregates of silt- or sand-sized carbonate particles that are cemented together at points of contact: in ancient carbonates, similar-appearing lobate grains that are composed of carbonate mud (micrite). After Illing (1954); no longer widely used.

Grapestone - Sometimes used to describe aggregates of silt-sized carbonate crystals (or grains), but more properly applied to grape-like clusters of such aggregates bound together by cements or organic encrustations.

Extraclast - A detrital grain of lithified carbonate sediment (lithoclast) derived from outside the depositional area of current sedimentation (Folk, 1959).

Calclithite - A rock formed chiefly of carbonate clasts (extraclasts) derived from older, lithified limestone, generally external to the contemporaneous depositional system. Commonly located in arid settings, along downthrown sides of fault scarps. Term coined by Folk (1959).

Intraclasts and extraclasts are found in deposits of any age from Archean to Recent. Intraclasts are especially common in Precambrian to Mid. Ordovician strata, where they form widespread flat-pebble conglomerates. Such deposits probably reflect the abundance of microbial deposits and the scarcity or absence of macrofaunal grazers and burrowers during that time period (e.g., Garrett, 1970).

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