IMPLICATIONS OF K/T BOUNDARY DEPOSITS FROM DE SOTO CANYON, GULF OF MEXICO

Impact ejecta have previously been found in high-energy Cretaceous-Tertiary Boundary (KTB) deposits at numerous sites in the Gulf of Mexico. To further constrain the effects of the KTB bolide impact on the geology of the Gulf of Mexico, we analyzed three Eureka Boreholes (E67-128, E68-139, E68-151A) taken from deep water regions of the De Soto Canyon off the western coast of Florida. Core E68-139 contained a nearly complete calcareous nannofossil biostratigraphic record across the KTB, despite poor core preservation. At the paleontological boundary, we found clay-rich spherules that are interpreted as altered tektites. In samples just above the boundary we found numerous "disaster" species of nannofossils. These opportunistic species (e.g. Braarudosphaera bigelowii, Thoracosphaera spp.) typically occur in great abundance immediately above the KTB. Also, light microscope analysis revealed an immediate increase in micrite above the boundary. This may suggest downslope transport from shallower areas where non-diagenetic automicrite typically forms. The micrite found in these cores may represent the distal portions of turbidites derived from shallower areas near the coast.

Cores E67-128 and E68-151A contained unconformities from Upper Campanian to Middle Paleocene age. This is possibly due to truncation of Upper Cretaceous beds, as seen in seismic studies from sections across the De Soto Canyon area, and sediment bypass associated with seismic shaking and tsunamis that resulted from the KTB impact. Destabilization of the margin and a eustatic sea level low during the early Paleocene may account for the hiatus as seen in core and seismic studies from the De Soto Canyon area. The results of this investigation agree with the hypothesis that the initial formation of the De Soto Canyon was linked to the KTB impact.