| In the Appalachian foreland basin of the eastern United States, major sedimentologic and geochemical changes occurred during the Upper Ordovician (Sandbian-Katian). The modification of ocean circulation patterns, introduction of turbid, cool waters across eastern Laurentia, and the transport of fine-grained siliciclastics from the Taconic highlands have been attributed to biofacies replacments and faunal turnover in the basin. This study is a suite of systematic, paleoecological, and sedimentological studies on the trilobite faunas and their associated sedimentary environments during this time interval. High-resolution sequence statigraphic studies provide sea-level context, and facilitate geographic and temporal comparison of trilobite biofacies within similar depositional environments. Cumulatively, these studies demonstrate broad paleoecological and systematic similarities in trilobite faunas during the deposition of late Whiterockian and Mohawkian strata in two different Laurentian basins in Oklahoma and Virginia. These similarities diverge due to the effects of foreland basin development (relative sea level deepening, increase in siliciclastic input, and enhanced upwelling of colder, dysoxic water), which resulted in diachronous trilobite extinction events, and the spread of low diversity deep-water trilobite biofacies in Virginia. Moreover, many classic trilobite associations (e.g., illaenid-chierurid buildup association) were extirpated from the Taconic foreland basin during the same time interval. In regions outside the foreland basin during the same stratigraphic time interval (Bromide-Viola transition) in Oklahoma, diversity actually increases in similar environments, suggesting there is a unique environmental signal in the foreland basin. |
