Abstract: Improved Regional Ties to Global Geochronology using Pb-Isotope Signatures of Volcanic Glass Shards from Deep Water Gulf of Mexico Ash Beds

Abstract

ABSTRACT Sedimentary beds rich in volcanic ash (ash beds) have been confirmed in several recent offshore Gulf of Mexico (GOM) exploratory wells. A petrographic/scanning electron microscope survey for volcanic glass shards on well cuttings and sidewall cores donated by the petroleum industry is currently ongoing at University of New Orleans (UNO). Fifteen separate ashes have been documented in our preliminary survey. We have also determined the paleontological ages of these GOM ashes with industry micro-paleo reports. The paleo-ages of these ash beds appear to be correlative with the ages of maximum flooding surfaces on industry sea-level curves. Due to their distinctive log and seismic response, thick ash beds are ideal candidates for use as precise time markers in the GOM subsurface if they can be tied to known eruptive events. Based on proximity in time, we believe that the most likely sources for these ashes are the Huckleberry, Lava Creek, Mesa Falls, Bishop, and other eruptive events that occurred in the Yellowstone Plateau from 0.6 to 12 mya. These eruptions had enormous ash volumes that covered much of the ancestral Mississippi drainage area. Isotopic analyses of glass shards from GOM ash beds indicate a lead isotope signature that matches volcanic tuffs in the Yellowstone Plateau and precludes other ash sources for the GOM ash beds.