THE BEAUTY OF BURROWS: TRACE FOSSILS REVEAL RAPID FLUCTUATIONS IN DEVONIAN BLACK SHALES

Black shale is a common lithology that is well exposed in Devonian aged strata of the Appalachian basin. There are many methods to explore the redox dynamics of this enigmatic lithology and ultimately better understand the oceanographic conditions associated with epeiric seaways. Trace fossils provide unambiguous evidence of metazoan life, and ultimately, the presence of oxygen in the bottom water. The trace fossil signal preserved in Middle and Late Devonian strata of New York and Ohio provide clear evidence of short-lived oxygenation events within rocks that preserve a geochemical record of anoxia or euxinia. One intriguing example in the Upper Cleveland black shale, revealed through CT scanning, preserves two distinct populations of pyritized burrows in otherwise barren black shales, including larger (mm scale) vertical burrows, and abundant, smaller (< 0.5 mm in burrow width), horizontal to sub-horizontal burrows, likely produced by nematodes. These burrows are interpreted to preserve an interval of rapidly fluctuating bottom water conditions that is likely common in epeiric seaway settings, and further emphasize the utility of trace fossils in high-resolution paleoenvironmental reconstruction necessary to capture transient changes in basin conditions through long stretches of deep time.