USING ICHNOFABRICS TO STUDY BENTHIC OXYGEN THROUGHOUT THE WESTERN INTERIOR SEAWAY FOR THE DURATION OF OCEANIC ANOXIC EVENT II

Western Interior Seaway (WIS) strata, ~93.5 Ma, show a strong positive δ13Corganic excursion for the ≤ 1Ma duration of Oceanic Anoxic Event II (OAE II). Recent studies in the WIS show benthic oxygen concentrations were dysoxic (2.0 - 0.2 ml of O2/l of H2O) rather than anoxic during OAE II. Dysoxia could be represented as persistent moderate levels of oxygen or could result from intermittent anoxia-dysoxia/dysoxia-oxia/anoxia-oxia. The purpose of this report is to describe the type of dysoxia that occurred throughout the WIS by examining trace fossils in outcrop from beds spanning OAE II. Ichnological observations as well as a combination of geophysical, geochemical, and taphonomical studies have been used to interpret benthic oxygen levels in samples collected. Change in benthic oxygen was determined by categorizing ichnofossils into oxygen-related ichnofabrics that are based on the different traces present, along with burrow depth, burrow diameter, and degree of bioturbation. Taphonomy of calcite bioclasts and concentrations of redox-sensitive trace metals corroborate ichnological observations and interpretations. Study sites are organized along West-East and North-South transects in order to track any spatial variations in benthic oxygen content so an oxygen curve could be produced for the duration of OAE II. This study was designed to better define the role that the OAE II had on benthic oxygen content within the WIS, and to better describe the impact of the positive δ13Corganic excursion in the WIS on the paleoenvironment and hydrocarbon potential of WIS sediments versus the impact of OAEII on the global ocean.