SPHERULITE ALTERATION IN TERMINAL CRETACEOUS CALCARENITES IN ALABAMA

Spherules and tektites have been reported in several terminal Cretaceous sandstones in the southeastern United States. They are interpreted as having been derived as ejecta from the Chicxulub impactor. We confirm through thin section petrography that calcarenites collected from Shell Creek Alabama contain spherules and we are examining sandstones from other outcrops in the region where ejecta may be located. Shell Creek spherules are severely altered. Their outer layers are composed of iron-oxide stained phyllosilicates. Their interiors are filled with coarse equant calcite spar that is petrographically indistinct from the cement that fills intergranular pore spaces in the rest of the sandstone. This suggests that the spherules were either originally hollow or that their glassy interiors were diagenetically replaced by calcite during lithification. These options will be evaluated using detailed petrographic observations and electron microprobe analysis.