EXPERIMENTAL MODELING OF GAS-ESCAPE VS. RAINDROP ORIGIN OF CIRCULAR PITS IN SHALES OF THE POTTSVILLE FORMATION, STEVEN C. MINKIN PALEOZOIC FOOTPRINT SITE (PENNSYLVANIAN, ALABAMA)
The aim of this study was to compare morphology and distribution of experimentally-produced gas escape structures and raindrop impression in a mud-silt mixture designed to simulate the sediment preserved in the Pottsville shales. Gas escape structures were generated by adding a sugar-yeast-water mixture to a water-saturated silty mud and allowing gas bubbles to be produced by the yeast. The production and abundance of gas escape structures was strongly dependent on the ratio of mud to silt. Raindrop impressions were difficult to produce in water-saturated sediment, and are better preserved in sediment that is dry at the surface, supporting the idea that raindrop impressions should co-occur with mud cracks. Preliminary results suggest that the morphology, distribution, and depositional setting of circular pits in the Pottsville shales are consistent gas-escape structures and unlikely to be raindrop impressions.
Reference: Rindsberg, A.K., 2005, Alabama Paleontology Society Monograph 1 (Buta et al., eds.), pp. 177-183.