Botoman (Lower Cambrian) turbid- and clear-water reefs and associated environments from the High Atlas, Morocco
Published:January 01, 2007
J. Javier Álvaro, Sébastien Clausen, 2007. "Botoman (Lower Cambrian) turbid- and clear-water reefs and associated environments from the High Atlas, Morocco", Palaeozoic Reefs and Bioaccumulations: Climatic and Evolutionary Controls, J. Javier Álvaro, Markus Aretz, Frédéric Boulvain, Axel Munnecke, Daniel Vachard, Emmanuelle Vennin
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Exposures of the Botoman (Lower Cambrian), Lemdad and Issafen formations on the Lemdad syncline, southern High Atlas, provide an excellent example of the interactions between tectonic events, magmatic activity and carbonate productivity. The major factors that controlled the nucleation of carbonate factories on the Botoman High Atlas platform were: (i) synsedimentary tectonism, as normal faulting resulted in tilting of fault blocks causing irregular topographies and subsequent sharp erosion; (ii) volcanism, because pyroclastic influx smothered carbonate factories except in distal areas of the platform or during quiescent episodes of volcanic activity; and (iii) the influence of successive shoaling parasequences. The Botoman reefs exhibit a wide range of external morphologies, including tabular (biostromes) and domal (bioherms and patches) boundstones, which do not exceed 3.5 m of thickness. Although archaeocyathan–microbial reefs only developed under clear-water conditions, microbial reefs grew also under turbid-water conditions. Domal and digitate stromatoids, Girvanella crusts, Epiphyton bushes and thromboid–stromatoid intergrowths document the ability of some microbial communities to develop heterotrophic strategies when submitted to a moderate terrigenous input. Turbidity was a major ecological factor that constrained development of filter/suspension-feeder and phototrophic organisms, but not necessarily of benthic non-phototrophic microbial communities.
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Palaeozoic Reefs and Bioaccumulations: Climatic and Evolutionary Controls
The geological record contains a fascinating diversity of reefs and shell accumulations. As my other biosedimentary structures, their facies characterization requires careful observation at outcrop and sample scale, and in thin-section to provide information about the global geometries, fabrics and textures respectively.
This collection of papers encompasses the breadth of sedimentary geometries and facies displayed by Palaeozoic reefs, shell accumulations, and transitional composite deposits. The definition of reefs and shell concentrations has given rise to variations in nomenclature. The papers in this volume cover specific problems regarding the nomenclature and facies characterization of reefs, shell accumulations and transitional composite deposits. However, rather than attempt a complete revision of terms, the authors have touched on some of the important issues at this stage of development in the field: the main climatic, environmental and evolutionary factors that controlled the Palaeozoic development of shell accumulation and reefs.