HUNTING FOR THE HANGENBERG CRISIS: GEOCHEMICAL EVIDENCE OF THE HANGENBERG EVENT FOUND IN NON-BLACK SHALE LITHOLOGY FROM WESTERN UTAH

One of the largest extinction events during the Phanerozoic occurred at the Devonian - Carboniferous (D-C) boundary, correlated with a worldwide ocean anoxia event known as the Hangenberg Crisis. The climate during this time was characterized by instability and fluctuating sea levels, due to glaciation in southern Laurussia and western Gondwana. This sudden climate shift is a possible explanation for the Hangenberg Crisis, which is typically preserved in the rock record as an extensive organic-rich black shale overlain by a regressive sandstone unit. However, not all localities that contain a continuous D-C boundary succession exhibit the Hangenberg Crisis in this characteristic lithologic sequence. During the Devonian, western Utah was a massive carbonate shelf off the western coast of Laurussia. The Great Basin Region of western Utah contains sediments that span the D-C boundary, with limestones of the Guilmette Formation and silty carbonates of the Pilot Shale. Samples from the Shade Tree section were analyzed using scanning electron microscopy with energy-dispersive X-ray microanalysis (SEM-EDS) in addition to whole-rock geochemistry (major, trace, and REEs). SEM-EDS analysis showed an abundance of large pyrite framboids with samples that are consistent with the biostratigraphic location of the D-C boundary. Further SEM-EDS analysis of pyrite framboids indicates samples near the proposed D-C boundary are consistent with anoxic environments, even though they are not visible in the field as black shales. Whole rock geochemical data of units with framboids showed significant spikes in Al-normalized trace elements V, As, Co, Sb, Mo, U, Zn, and Ni, also consistent with marine anoxia. It is likely that the Hangenberg Crisis can be identified in the Great Basin region of western Utah in a different lithology than an organic-rich black shale, indicating that anoxia was widespread throughout the Laurussian paleocontinent at this time.