Upper Eocene microspherules (microtektites and microkrystites) have been found in deep-sea sediments from the western North Atlantic, Caribbean, Gulf of Mexico, equatorial Pacific, and eastern equatorial Indian Ocean. Recent studies proposed that there are three or four microspherule 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 biochronologic and morphometric data, I suggest that the microspherules in the latter sites correlate with the North American microtektite-microkrystite couplet. My results as well as previously published data are all compatible with the model of one couplet of microtektites-microkrystites. The inference of three or four microspherule layers in the upper Eocene is shown to be an artifact of interpretation.

Microspherule depths in Sites 17-167, 22-216, 31-292, and 61-462 are modified from Glass et al. (1985) to comform with DSDP depth format; microspherule depth in Site 95-612 is from Glass (1989). The last occurrence of Discoaster saipanensis is 34.0 +/- 0.2 Ma and that of Chiasmolithus grandis is 37.0 +/- 0.2 Ma in the geomagnetic polarity time scale of Cande and Kent (1992). The last occurrence of Reticulofensestra reticulata (34.8 +/- 0.2 Ma) is at 157 m in Site 95-612.

Supplement to: Wei, Wuchang (1995): How many impact-generated microspherule layers in the Upper Eocene? Palaeogeography, Palaeoclimatology, Palaeoecology, 114(1), 101-110