Middle and Upper Ordovician biogenic structures and paleoenvironments, southern Nevada

The Ordovician Eureka Quartzite-lowermost Ely Springs Dolomite sequence in the Arrow Canyon Range, southern Nevada, can be divided into five lithofacies, each with a characteristic set of physical and biogenic structures, fossils and lithologies. This succession of lithofacies reflects changes in depositional processes from those prevalent in modern shoreface zones (Eureka Quartzite) to those dominant in offshore environments (Ely Springs Dolomite). The lithofacies resulting from high energy depositional processes, such as those active in modern shoreface and shoal environments, are characterized by dwelling burrows (including Skolithos) and escape structures. Sediments deposited under more quiet water conditions have few physical sedimentary structures, are thoroughly bioturbated and contain the trace fossils Chondrites and ?Planolites . Alternation of these lithofacies gives further indication that substrate and related factors control the distribution of organisms producing various biogenic structures.