Matground structures and redox facies

摘要: A characteristic succession of sedimentary structures was observed in clastic Silurian tempestites the Murzuk Basin southwest Libya. The ("Manchuriophycus," syneresis cracks, "Astropolithon," load palimpsest ripples, "Kinneyia," microfault sets, and millimeter ripples) occur sandstones siltstones that show evidence unusual cohesive behavior (cracks resulting from shrinking or degassing; resistance to erosion). In a sequence ranging fully aerobic anoxic graptolite shales, these characterize several zones increasing redox stress, which correspond ichnofacies zonation. It is postulated microbial mats develop on sediment surface whenever grazing burrowing are suppressed. Depending local conditions, biomats were leathery, felt-like, gel-like. matground resulted interaction storm waves with stabilization progressively finer-grained sediments. Whereas such ubiquitous Precambrian clastics, they became restricted hostile environments Phanerozoic, where can be used indicate environmental (mostly redox) possibly hydrocarbon potential, lacking other indicators.