GRADATIONAL SEDIMENTARY PRODUCTS OF CALCAREOUS ALGAE

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Abstract
SUMMARY: Penecontemporaneous calcareous algal products are very complex in both texture and mode of origin. For example, all gradations exist between stromatolites and pseudo‐stromata, different types of oncolites are transitional and are often difficult to distinguish from other allochthonous algal material, algal pellets form the final product of abrasion and they too are very similar despite variations independent of their original source; and some Algae may break down into “algal dust” or carbonate needles.Algal limestones of different ages and environments may supply detritus that is indistinguishable from one another. Therefore, in petrographic investigations of carbonate sediments the descriptive term “limeclast” is less ambiguous than the genetic terms “intraclast” and “calclithite”. If a combination of field‐work and thin‐section studies permits precise genetic and environmental interpretations, the limeclasts can be genetically described as “intraclasts” and “extraclasts”. If the extraclasts form the predominant components, the sediment is a “calclithite” and is a type of terrigenous rock (FOLK, 1959).In general, four possible relations exist between limestone frameworks and micrite matrices. Both allochthonous fragment accumulations and autochthonous growths may have either detrital matrices or matrices that formed in situ. The autochthonous algal micrite matrices give no indication of a degree of turbulence and winnowing in contrast to allochthonous matrices.Apparently minute differences, which are, however, significant in the genesis of limestone components may become more important with an increase in isotope, trace element and diagenetic investigations where the identity of the carbonate material is of special importance.

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