Paper No. 337-4
Presentation Time: 9:00 AM-6:30 PM
MICROTEKTITE-LIKE GLASSY SPHERULES NEAR THE FRASNIAN-FAMENNIAN BOUNDARY, LATE DEVONIAN, NEW ALBANY SHALE, FLOYD COUNTY, INDIANA
Five great mass extinction events are recognized in the past 500 million years. Although the extinction events are agreed upon, only the Cretaceous (K-T) event has produced enough positive evidence that suggests a bolide impact. Although impacts have been suggested for other extinction events, volcanism, climate change, changes in CO2 levels, and evolutionary diversity have also remained viable triggers for consideration. The lack of evidence remains the primary reason for the dismissal of an impact causation triggering other mass extinction events, including the Kellwasser Event that occurred in the Late Devonian. Iron-bearing microtektite-like glassy spherules were identified in the Late Devonian Clegg Creek Member of the New Albany Shale in a zone which corresponds to the Frasnian-Famennian boundary. These microtektite-like glassy spherules are: (1) too large and dense to have been transported at the time of shale deposition; (2) of a composition and morphology that does not represent material that would have formed in situ by groundwater; and (3) are in areas free of overburden that might have contaminated the shale. It must be considered that the source of these microspheroids originated from above the shale then fell into the sediments before lithification. An extraterrestrial source seems the most viable. Scanning Electron Microscopy/Energy Dispersive X-ray (SEM/EDX) analyses of the microspheroids indicates a roughly spherical shape with a glassy composition, magnetic and iron-rich, in a vitrified to semivitrified matrix. This suggests that these microtektite-like glassy spherules are in fact ballistic impact ejecta and originated from an event during this time.