MECHANISMS FOR THE WIDESPREAD DISTRIBUTION OF VOLCANIC ASH BEDS IN THE GULF OF MEXICO

Volcanic eruptions centered at Yellowstone were some of the largest eruptions ever recorded. Volcanic ash was spread over a tremendous area of the United States, and has been recovered from a wide variety of locations in the western US, the Great Plains, the Gulf of Mexico, and even the Pacific Ocean. Ongoing research at the University of New Orleans has collected Plio-Pleistocene ash from over 25 wells offshore Louisiana, and from several outcrop locations in Kansas. A fluvial mechanism is proposed for the deposition of Yellowstone ash in the Gulf of Mexico.

The ash outcrops in Kansas show evidence of a system overwhelmed with ash. Exotic boulders and large tree limbs are totally enclosed in ash, similar to recent deposits formed by the eruption of Mt. Pinatubo. These outcrops record a time when the Mississippi River drainage system was literally choked with ash, that in a short time span reached the depocenters in the Gulf of Mexico. Once the ash slug reached the Gulf of Mexico, ash piled up on the shelf, before deposition into deepwater as turbidity flows. The volcanic glass shards were concentrated in submarine channels active during this time, and result in the thick ash deposits reported from several wells. We have also observed a consistent background level (<1%) of ash from shales coeval with the Huckleberry Ridge eruption, which records the deposition of non-channel deposits.

The model proposed for the deposition of these ashes, while not as swift as an air-fall event, is still rapid enough for the ash beds to represent a brief time interval. This makes the Plio-Pleistocene ash beds excellent lithostratigraphic markers when found.