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Thrombolites and stromatolites; two distinct types of microbial structures

John M. Kennard and Noel P. James
Thrombolites and stromatolites; two distinct types of microbial structures
Palaios (October 1986) 1 (5): 492-503


Thrombolites and stromatolites are distinct types of microbial (cryptalgal) structures characterized, respectively, by mesoscopic clotted and laminated internal fabrics. Although thrombolites commonly contain skeletal metazoans and may be burrowed and bored, their clotted fabric is a primary microbial feature and not a disrupted or modified laminated fabric. The individual mesoscopic clots (mesoclots) within thrombolites are interpreted as discrete colonies or growth forms of calcified, internally poorly differentiated, and coccoid-dominated microbial communities. In contrast, the individual laminae (stromatoids) within stromatolites are generated by the episodic sediment-trapping and/or carbonate-precipitating activities of mat-like microbial communities that are dominated by filamentous microbes. A simple tripartite field classification of microbial structures, modified after Aitken (1967), is proposed on the basis of the dominant type of constructive, mesoscopic, constituent. The three end members are stromatolites, thrombolites, and undifferentiated microbial boundstones. Thrombolites are not uniformly distributed in the rock record, but are essentially a Cambrian and Lower Ordovician phenomenon. Their distribution appears to have been controlled by, first, the appearance of calcareous microbes (including such forms as Girvanella, Renalcis, Epiphyton, and Nuia) and the approximately synchronous radiation and skeletonization of grazing and bioturbating Metazoa at the beginning of the Phanerozoic eon; and second, niche competition from newly evolved, reef-building, skeletal metazoans and algae, and possibly increased predation by molluscs, in Early and Middle Ordovician time.

ISSN: 0883-1351
Serial Title: Palaios
Serial Volume: 1
Serial Issue: 5
Title: Thrombolites and stromatolites; two distinct types of microbial structures
Affiliation: Mem. Univ. Newfoundland, Saint John's, NL, Canada
Pages: 492-503
Published: 198610
Text Language: English
Publisher: Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States
References: 90
Accession Number: 1987-032080
Categories: Sedimentary petrologyStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
N46°30'00" - N51°40'00", W59°19'60" - W52°30'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 1987
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