HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Full Text (PDF) Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (24) Citing Articles via Google Scholar Google Scholar Articles by NOFFKE, N. Articles by GROTZINGER, J. P. Search for Related Content GeoRef GeoRef Citation

Sedimentary Controls on the Formation and Preservation of Microbial Mats in Siliciclastic Deposits: A Case Study from the Upper Neoproterozoic Nama Group, Namibia

¹ Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138
² Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139

Shallow-marine, siliciclastic depositional systems are dominated by physical sedimentary processes, with penecontemporaneous cementation playing only a minor role in sediment dynamics. For this reason, microbial mats rarely form stromatolites in siliciclastic environments; instead, mats are preserved as wrinkle structures on bedding surfaces.

Microbial mat signatures should be widespread in siliciclastic rocks deposited before the Cambrian Period; however, siliciclastic shelf successions of the upper Neoproterozoic Nudaus Formation, Nama Group, Namibia, contain only sparsely distributed wrinkle structures. The facies distribution of observed structures reflects the superposition of a taphonomic window of mat preservation on the ecological window of mat development. Mat colonization is favored by clean, fine-grained, translucent quartz sands deposited at sites where hydrodynamic flow is sufficient to sweep mud from mat surfaces but insufficient to erode biostabilized laminae. During periods of reduced water agitation, microbial baffling, trapping, and binding entrain quartz grains into mat fabrics, increasing the thickness of the living mat layer. Mat preservation is facilitated by subsequent sedimentary events that bury the microbial structures without causing erosional destruction. Pressure originating from sediment loading forms molds and casts at bedding planes, inducing the formation of wrinkle structures.

In storm-influenced shelf successions of the Nudaus Formation, wrinkle structures are restricted to quartz-rich fine sandstone beds, 2–20 cm thick, that alternate with thin interlayers of sandy mud- or siltstones. Such a lithological facies developed only sporadically on the Nudaus shelf, but is common in shallow-marine siliciclastic rocks of older Neoproterozoic age exposed in the Naukluft Nappe Complex. The observed relationship between sedimentary environment and microbial mat preservation can be observed in other Proterozoic and Phanerozoic siliciclastic rocks, as well as in modern environments. This facies dependence provides a paleoenvironmental and taphonomic framework within which investigations of secular change in mat abundance must be rooted. Understanding the physical sedimentary parameters that control the formation and preservation of microbial structures in siliciclastic regimes can facilitate exploration for biological signatures in early sedimentary rocks on Earth or other planets.

This article has been cited by other articles:

				H. Porada, J. Ghergut, and E. H. Bouougri Kinneyia-Type Wrinkle Structures--Critical Review And Model Of Formation Palaios, February 1, 2008; 23(2): 65 - 77. [Abstract] [Full Text] [PDF]

				G. Acenolaza and F. Acenolaza Insights in the Neoproterozoic Early Cambrian transition of NW Argentina: facies, environments and fossils in the proto-margin of western Gondwana Geological Society, London, Special Publications, January 1, 2007; 286(1): 1 - 13. [Abstract] [Full Text] [PDF]

				J. V. BAILEY, F. A. CORSETTI, D. J. BOTTJER, and K. N. MARENCO Microbially-Mediated Environmental Influences on Metazoan Colonization of Matground Ecosystems: Evidence from the Lower Cambrian Harkless Formation Palaios, June 1, 2006; 21(3): 215 - 226. [Abstract] [Full Text] [PDF]

				S. JENSEN and G. E. BUDD Introduction to thematic set of papers on the Ediacaran-Cambrian palaeoecology, sedimentology and stratigraphy of Namibia Geological Magazine, September 1, 2005; 142(5): 463 - 464. [Full Text] [PDF]

				S. Douglas Mineralogical footprints of microbial life Am J Sci, June 1, 2005; 305(6-8): 503 - 525. [Abstract] [Full Text] [PDF]

				M. Calner A Late Silurian extinction event and anachronistic period Geology, April 1, 2005; 33(4): 305 - 308. [Abstract] [Full Text] [PDF]

				Patterns of distribution in the Ediacaran biotas: facies versus biogeography and evolution Paleobiology, June 1, 2004; 30(2): 203 - 221.

				Proliferation of Early Triassic wrinkle structures: Implications for environmental stress following the end-Permian mass extinction Geology, May 1, 2004; 32(5): 461 - 464.

				Early Colonization of the Deep Sea: Ichnologic Evidence of Deep-marine Benthic Ecology from the Early Cambrian of Northwest Argentina Palaios, December 1, 2003; 18(6): 572 - 581.

				A. H. Knoll and A. H. Knoll Biomineralization and Evolutionary History Reviews in Mineralogy and Geochemistry, January 1, 2003; 54(1): 329 - 356. [Full Text] [PDF]