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GEOREF RECORD

Covariance of microfossil assemblages and microbialite textures across an upper Mesoproterozoic carbonate platform

Andrew H. Knoll, Sarah Woerndle and Linda C. Kah
Covariance of microfossil assemblages and microbialite textures across an upper Mesoproterozoic carbonate platform
Palaios (July 2013) 28 (7): 453-470

Abstract

Early diagenetic chert nodules and beds in the upper Mesoproterozoic Angmaat (formerly Society Cliffs) Formation, Baffin and Bylot islands, preserve microfossils and primary petrofabrics that record microbial mat deposition and lithification across a range of peritidal carbonate environments. Five distinct microfossil assemblages document the distribution of mat-building and mat-dwelling populations across a gradient from restricted, frequently exposed flats to more persistently subaqueous environments. Mats built primarily by thin filamentous or coccoidal cyanobacteria give way to a series of more robust forms that show increasing assemblage diversity with decreasing evidence of subaerial exposure. Distinct fabric elements are associated with each microbial assemblage, and aspects of these petrofabrics are recognizably preserved within unsilicified carbonate in the same beds. These include some features that are distinctly geologic in nature (e.g., seafloor cements) and others that reflect microbial growth and decomposition (e.g., tufted microbialites). A particularly distinctive, micronodular fabric is here interpreted as carbonate infilling of primary voids within microbial mat structures. Such structures mark the co-occurrence of cyanobacterial photosynthesis that produced oxygen gas, filamentous mat builders that imparted the coherence necessary to trap gas bubbles, elevated carbonate saturation required to preserve void fabrics via penecontemporaneous cementation, and a relative paucity of detrital sediment that would have inhibited mat growth. Petrofabrics preserved in Angmaat samples are widespread in upper Paleoproterozoic and Mesoproterozoic carbonate successions but are rare thereafter, perhaps recording, at least in part, the declining carbonate saturation state of seawater. Covariation of microfossil assemblages with petrofabrics in both silicified and unsilicified portions of carbonate beds supports hypotheses that link stromatolite microstructure to the composition and diversity of mat communities.


ISSN: 0883-1351
Serial Title: Palaios
Serial Volume: 28
Serial Issue: 7
Title: Covariance of microfossil assemblages and microbialite textures across an upper Mesoproterozoic carbonate platform
Affiliation: Harvard University, Department of Organismic and Evolutionary Biology, Cambridge, MA, United States
Pages: 453-470
Published: 201307
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
References: 75
Accession Number: 2013-073945
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. geol. sketch map
N72°00'00" - N73°00'00", W81°00'00" - W79°00'00"
Secondary Affiliation: Universite Lyon I Claude Bernard, FRA, FranceUniversity of Tennessee, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 201344
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