Trace fossils, paleosalinity, and depositional environment of the Northview Formation, southwest Missouri, USA

Abstract

ABSTRACT The Early Mississippian Northview Formation is a siliciclastic deposit reaching 25 m in thickness along an east-west trend in southwest Missouri, USA. Along this trend, the formation coarsens upward from shale to coarse siltstone with shaley interbeds and channel fills. The siltstones have high concentrations of two trace fossils: Nereites missouriensis and Zoophycos. Thus, the ichnofauna is dominated by namesake genera of the two deepest marine ichnofacies. Nevertheless, the Northview was deposited on a shallow carbonate platform. The vertical succession of trace fossils is consistent with deltaic deposition. The lowest shale is dominated by common elements of the Phycosiphon prodelta ichnofacies, and the lowest overlying siltstone is dominated by elements of the Rosselia delta-front ichnofacies. N. missouriensis occurs abundantly and dominates the overlying siltstones, with Zoophycos covering bedding planes near the top, a pattern found within the lower plain of other Paleozoic deltas. Geochemical proxy measurements indicate paleosalinity decreasing upward through the formation and an approaching freshwater (fluvial) source, raising questions about Early Mississippian source areas and tectonics.