Biolaminated Siliciclastic Deposits
“Biolaminated deposits” (Gerdes and Krumbein 1987) originate from microbial growth and activity interacting with environmental, physical and chemical processes like sedimentary deposition and mineral precipitation. The resulting “primary” sedimentary stru
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1 Introduction “Biolaminated deposits” (Gerdes and Krumbein 1987) originate from microbial growth and activity interacting with environmental, physical and chemical processes like sedimentary deposition and mineral precipitation. The resulting “primary” sedimentary structure was named “growth bedding” by Pettijohn and Potter (1964), with clear reference to in situ formed limestones and with “stromatolitic bedding” as the most prominent example (see also Pettijohn 1975). Subsequently, it was recognized that “growth bedding” mediated by microbial mats is not restricted to carbonate environments but may occur also in peritidal siliciclastic depositional systems. Respective sedimentary deposits have been termed “siliciclastic biolaminites” (Gerdes and Krumbein 1987) which basically consist of quartz sand and interlayered dark laminae originating from monolayered microbial mats or successive generations of mats. The process leading to siliciclastic biolaminites includes periods of non-deposition in which organisms produce and establish mat layers on a sediment surface, and periods of sedimentation in which the mat is covered by a thin layer of fine-grained sediment through which motile bacteria (or other motile organisms) can move upwards to establish a new mat atop (for details see Gerdes et al. 1991, 2000). Laboratory and field experiments (Gerdes and Klenke 2003, 2007) have shown that a new, though still thin and soft mat layer may form on the new sediment surface within few days only, whereas to establish a mature and resistant mat with fair
E.H. Bouougri (*) Department of Geology, Faculty of Sciences Semlalia, Cadi-Ayyad University, 40020 Marrakech, Morocco e-mail: [email protected] H. Porada Geosciences Centre, Georg-August University of G€ ottingen, Goldschmidt-Straße 3, 37077 G€ ottingen, Germany
J. Reitner et al., Advances in Stromatolite Geobiology, Lecture Notes in Earth Sciences 131, DOI 10.1007/978-3-642-10415-2_30, # Springer-Verlag Berlin Heidelberg 2011
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preservation potential, a period of non-deposition of several months may be required. The main effect of microbial mats in the process of “biosedimentary accretion” of siliciclastic biolaminites is biostabilization of the sediment surface and resistance against erosion, thus allowing deposition of a new sediment layer even from stronger currents. The accretion process may encompass (1) layers of thin to thick stacks of microbial mats which, by trapping and binding (Black 1933; see review in Schieber 2004), include sediment particles as isolated grains in their fabrics; (2) thin layers or lenses of sediment laid down during inundation or by wind action; (3) thicker layers of sediment deposited during events such as storms and sheet floods. Siliciclastic biolaminites are basically sedimentary deposits whose accretion, however, was mediated by microbial communities (mats) on the momentary sediment surface. They are thus microbialites (Burne and Moore 1987) in the broadest sense, but deviate from “stromatolites” in
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