Burchard D. Carter

Substrate preferences and biofacies distributions of Egyptian Eocene echinoids

Functional morphology of echinoids, particularly spatangoids, from the Eocene rocks of Egypt suggests a fauna strongly dominated by individuals of species tolerant of fine, impermeable bottom sediments. This might be predicted from the extreme dominance of muddy sediments in the Egyptian Eocene apparent in published sedimentologic studies. Species diversity, in contrast, is about equally distributed between mud-dwellers and sanddwellers. Thin sections of the strata enclosing the echinoids confirm inferences of sediment type based on functional morphology. In the Lower Libyan (Ypresian) rocks, nearshore sediments contain low diversity faunas with abundant sanddwellers. More seaward sediments contain high diversity communities of predominantly mud-dwellers

Late Eocene echinoid biofacies of Florida

Combining the substrate preferences of Jacksonian (late Eocene) echinoid species of Florida (Carter et al., 1989) with their geographic distributions (Carter, 1987a) allows construction of biofacies maps reflecting the spatial distribution of carbonate mud-rich and carbonate sand-rich sediments in the Ocala Group of Florida. Both cluster analysis and interpretation of individual localities suggest a consistently sandy bottom over most of the shelf in the early Jacksonian, with a north-south gradient developing during the middle and late Jacksonian. In the middle Ocala, some mud-tolerant species are present in the northern part of the Florida peninsula, toward the Suwannee Strait, and the middle Ocala of the western panhandle is dominated by mud-tolerant species. In the upper Ocala, most localities contain a significant proportion of mud-dwelling species, and the northward prevalence of mud-tolerant assemblages is even more pronounced, with those assemblages closer to the Suwannee Strait entirely dominated by mud-dwellers. These data suggest that the Ocala Bank of Cheetham (1963) was more of a northward sloping carbonate ramp than a carbonate shelf.

Brissus bridgeboroensis, a New Spatangoid Echinoid from the Lower Oligocene of Southwestern Georgia

A new species of Brissus is described from the lower Oligocene (Rupelian-Vicks- burgian) Bridgeboro limestone of southwestern Georgia. Brissus bridgeboroensis n. sp. most closely resembles the Recent Brissus unicolor (Leske) of the West Indies and the Gulf of Mexico, but it differs primarily in features of the posterior paired petals. Brissus bridgeboroensis is the oldest known member of the genus from continental North America.

Environmental aspects of Middle Ordovician limestones in the central Appalachians

Abstract Black River and Trenton limestones of the outcrop belts in West Virginia and Maryland were deposited on a gentle carbonate ramp that sloped eastward into a deep-water shale basin. The overwhelming sediment type on the ramp was lime mud, laid down below wave base. Water turbidity and circulation fluctuated, which precluded many epifauna. Burrowing infauna, however, were common. The consistency of the mud was generally soft, but hardgrounds developed locally. Another common sediment type, fossiliferous lime mud, represents muddy substrate patches more abundantly inhabited by organisms. These communities, dominated by echinoderms, trilobites, and brachiopods, had both low densities and diversities. Such patches were initially established by large, flat brachiopod pioneers but did not greatly expand because of the high physiological stress and the soft consistency of adjacent substrate. Occasionally, bioclastic sands were produced by storms reworking skeletal grains of the patches. These storm deposits cut into underlying sediments, and the bioclastic debris was clearly locally derived. Other skeletal sands, containing abundant calcareous algae and Tetradium corals as well as peloids and intraclasts, were deposited above wave base on shallower portions of the ramp. Rare cross-laminated peloid sands were confined to small lenses and channels at various depths, and intermittent storm currents were probably responsible for their deposition. Into progressively deeper water on the ramp, skeletal sediments decreased in abundance, storm- and current-laid sediments also decreased, and shale increased. Carbonate sedimentation eventually ended when the ramp facies were overstepped by basinal shales.

Environmental Aspects of Middle Ordovician Limestones in Central Appalachians: ABSTRACT

Black River and Trenton limestones of the outcrop belts in West Virginia and Maryland were deposited on a gentle carbonate ramp that sloped eastward into a deep-water shale basin. The overwhelming sediment type on the ramp was lime mud, deposited below wave base. Water turbidity and circulation fluctuated, which precluded many epifauna. Burrowing infauna, however, were common. The consistency of the mud varied from soft to firm, and hardgrounds developed locally. The more coherent muds were probably stabilized by early dewatering and cementation. Another common sediment type, fossiliferous lime mud, represents patches of organisms that inhabited the muddy substrate. These communities, dominated by echinoderms, trilobites, and brachiopods, had both low densities and divers ties. Patches were initially established by large, flat brachiopod pioneers but did not greatly expand because of the high physiologic stress and the soft consistency of adjacent substrate. Occasionally, bioclastic sands were produced by storms reworking skeletal grains of the patches. These storm deposits cut into underlying sediments, and the bioclastic debris was clearly locally derived. Other skeletal sands, containing abundant calcareous algae and Tetradium corals as well as peloids and intraclasts, were deposited above wave base on shallower portions of the ramp. Rare cross-laminated peloid sands were confined to small lenses and channels at various depths, and intermittent bottom currents were probably responsible for their deposition. Into progressively deeper water on the ramp, keletal sediments decreased in abundance; storm- and current-laid sediments also decreased; and shales increased. Carbonate sedimentation eventually ended when the ramp facies were overstepped by basinal shales. End_of_Article - Last_Page 1917------------