A first report of microtektites from the shell beds of southwestern Florida

1,2Mike Meyer,3Peter J. Harries,4Roger W. Portell
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13299]
1Earth and Environmental Science Department, Harrisburg University, Harrisburg, Pennsylvania, 17101 USA
2Geophysical Laboratory, Carnegie Institution for Science, Washington, DC, 20005 USA
3Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina, 27695 USA
4Florida Museum of Natural History, University of Florida, Gainesville, Florida, 32611 USA
Published by arrangement with John Wiley & Sons

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 microspherules from this unit and from the state. This material was analyzed using petrographic and elemental methods using energy dispersive X‐ray spectroscopy (EDS). The majority of microspherules are glassy and translucent in reflected light with some displaying “contact pairs” (equal‐sized micro‐spherules attached to each other). Broken microspherules 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 microspherules were compared to volcanic rocks, microtektites, and cosmic spherules (micrometeorites). Based on their physical characteristics and elemental compositions these are likely microtektites or a closely related type of material. The high Na content in the examined material deviates significantly from the abundances usually found in micrometeorites and tektite material; this is enigmatic and requires further study. This material may be derived from a nearby previously unknown impact event; however, more material and sites are required to confirm the source of this material. Because of the focus on molluscan fossils in southwestern Florida shell beds, microtektite material has likely been overlooked in the past, and it is probable that these microspherules are in abundance elsewhere in these units and possibly throughout the region.

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