IT (PROBABLY) CAME FROM OUTER SPACE! A FIRST REPORT OF MICROTEKTITES FROM PLIO-PLEISTOCENE SHELL BEDS OF SOUTHWESTERN FLORIDA

The Plio-Pleistocene Upper Tamiami Formation (Pinecrest beds) of Florida is well known for its fossiliferous shell beds, but not for its extraterrestrial material. Here we report the first occurrence of tiny (~200 µm in diameter) silica-rich micro-spherules from this unit and from the state. This material was analyzed using petrographic and elemental methods (EDS). The majority of the micro-spherules are glassy and translucent in reflected light with some displaying ‘contact pairs’ (equal-sized micro-spherules attached to each other) or with smaller ‘budding’ spherules attached to them. Broken micro-spherules cleave conchoidally, often with small internal spherical vesicles, but most lack any other evidence of internal features, such as layering. Using the EDS data, the micro-spherules were compared to volcanic rocks, microtektites, and cosmic spherules. Based on their physical characteristics and elemental compositions (including high abundances of Na present), these are likely microtektites. This material may be derived from an undocumented impact event or possibly reworked from the North American Strewn Field. Because of the focus on molluscan fossils in southwestern Florida shell beds, microtektite material have likely been overlooked in the past, and it is probable that these micro-spherules are in abundance elsewhere in these units and possibly throughout the region.