Oriented Fossils as Paleocurrent Indicators in Paleozoic Lutites of Southern Appalachians

Abstract

ABSTRACT Orientation measurements of 13,000 fossils in Paleozoic shales and fine siltstones at nine sites in the southern Appalachians demonstrate tire feasibility of using fossils as paleocurrent indicators in fine lutites. Preferred orientation was detected by vector mean and Rayleigh test procedures described by Curray (1956) and Pincus (1956), supplemented by chi-square calculations. Prior stratigraphic knowledge was used in this trial study to infer paleoslope directions so that a particular extinct fossil could be oriented relative to paleocurrents. Measurement of hundreds of individuals per sample yielded highly significant orientations which could be related to inferred paleoslope directions. Fossil groups studied include graptolites, brachiopods, criccoconarids, ostracods, gastropods, and the spore-like Tasmanites. A single section of Ordovician Athens Shale was studied in detail at Calera, Alabama, to evaluate vertical consistency of paleocurrent information from graptolites (transport direction averaged due west). On a regional pattern, this agreed with a westerly transport direction for Athens muds at Centerville and Kingsport, Tennessee. Regional consistency of a single stratigraphic horizon was demonstrated for the basal portion of the Chattanooga Shale at Clinch Mountain eastern Tennessee. Biota measured include Ambocoelia, Leiorhynchus, Styliolina, Tentaculites, and Tasmanites. These gave remarkably uniform results at four localities with an average current movement toward N75°W.