HOW MANY IMPACT-GENERATED MICROSPHERULE LAYERS IN THE UPPER EOCENE

Upper Eocene microspherules (microtektites and microkrystites) have be en found in deep-sea sediments from the western North Atlantic, Caribb ean, Gulf of Mexico, equatorial Pacific, and eastern equatorial Indian Ocean. Recent studies proposed that there are three or four microsphe rule layers: the North American microtektite and microkrystite couplet in chron C15, and one (or two) significantly older layer(s) in chron C16 in DSDP Sites 216, 292 and 612. Based on calcareous nannofossil bi ochronologic and morphometric data, I Suggest that the microspherules in the latter sites correlate with the North American microtektite-mic rokrystite couplet. My results as well as previously published data ar e all compatible with the model of one couplet of microtektites-microk rystites. The inference of three or four microspherule layers in the u pper Eocene is shown to be an artifact of interpretation.