Abstract
Organically enriched terrigenous marine sediments are commonly associated with near-bottom waters containing low concentrations of dissolved oxygen, as well as with sediment pore waters high in dissolved sulfides. Today such habitats are typically dominated by dense aggregations of opportunistic polychaetes which intensively pelletize surface sediments while deposit-feeding. Laboratory study of one such species, Capitella sp. I, indicates that these polychaete aggregations and their associated agglutinated tubes have a low probability of direct preservation in the sedimentary column. Synthetic lutites prepared from these sediments, however, contain pelletal sedimentary fabrics indicative of the former presence of polychaetes. To evaluate the effectiveness of these criteria for paleoecological reconstructions of OMZs, we undertook a study of the Sonyea Group (Upper Devonian Catskill Shelf and Basin). Wedge-shaped thin sections of rocks from a range of environments in the Upper Devonian Catskill Shelf and Basin Complex were examined. Only sections from the slope facies fulfilled the necessary criteria for postulating the presence of an OMZ. Methods are given for the preparation of synthetic lutites in order to identify these cryptic, yet paleocologically important, sedimentary fabrics. Recognition of such fabrics in otherwise "barren" shales may allow for more detailed reconstructions of ancient hypoxic and anoxic basins.
