CHARACTERIZING BIOTURBATION INTENSITY AND SEDIMENTARY MIXED LAYER DEVELOPMENT IN THE DEVONIAN OF THE APPALACHIAN BASIN

The advent of modern-style sediment mixing in ancient oceans would have resulted in significant biological and chemical disruption, including increased infaunal tiering, changes in nutrient cycling, and destruction of hardgrounds. However, sediment mixing significantly lags the appearance of other forms of bioturbation, remaining well below modern depths through the Silurian. By further constraining the time at which the sedimentary mixed layer deepened, we will gain a more complete understanding of the environmental changes brought about by intensifying bioturbation.

Here we present a field-based stratigraphic exploration of bioturbation intensity in Devonian-aged rocks of the northern Appalachian Basin. Our focus on the Devonian provides a window into the relationship between the sedimentary mixed layer, bioturbation intensity, and the diversification of “biological bulldozers,” deposit-feeding animals that are among the most efficient and extensive bioturbators in modern oceans. Lower Devonian strata in the northern Appalachian Basin are primarily carbonate-dominated, but alternating shale and limestone beds in the Kalkberg Formation provide measurements of bed thickness, important for quantitative analysis of bioturbation intensity. Middle (Panther Mountain, Moscow, and Geneseo Formations) and Upper (Hatch, Grimes, Lock Haven, and Catskill Formations) Devonian sandstones are generally well-bioturbated on bedding planes, with abundant and diverse horizontal trace fossil assemblages reaching centimeter-scale diameters. Despite the presence of some centimeter-deep individual vertical burrows, however, ichnofabric index is generally low and vertical burrowing is relatively sparse. The Appalachian Basin contains a homogenous record of bioturbation across the Devonian, one that we plan to place in a global context via forthcoming sampling of other mid-Paleozoic basins.