METALLIC/MAGNETIC MICROSPHERULES: EVIDENCE SUPPORTING AN IMPACT EVENT HORIZON IN THE BLACK DRAGON MEMBER OF THE MOENKOPI FORMATION, SAN RAFAEL SWELL, UTAH

Microspherules ranging in size from 18µm to 44µm have been discovered in breccia at the base of the Black Dragon member of the Moenkopi formation, San Rafael Swell, Utah. These particles and the breccia in which they are found suggest the presence of a bolide impact event horizon in the Black Dragon. This unit is currently considered to be lower Triassic age; however, the apparent lack of fossils in this unit makes dating difficult.

The morphology and chemistry of these microspherules has been studied employing a scanning electron microscope (SEM) with energy dispersive spectrometry (EDS). The results of the SEM/EDS research appears consistent with bolide impact as a generator of these particles.