Nannofossil datums and occurrence of microspherules in Upper Eocene sediments of the lower latitudes (Table 1)

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.

在西北大西洋、加勒比海、墨西哥湾、赤道太平洋以及东赤道印度洋的深海沉积物中，已发现始新世晚期微球粒（microspherules，包括微玻璃陨石（microtektites）与微晶陨石（microkrystites））。近期研究提出存在三层或四层微球粒层：即地磁极性时C15中的北美微玻璃陨石-微晶陨石配对层，以及深海钻探计划（Deep Sea Drilling Project, DSDP）216、292与612站位中，位于地磁极性时C16内的一层（或两层）年代显著更老的层位。基于钙质超微化石生物年代学与形态计量学数据，笔者认为上述站位中的微球粒与北美微玻璃陨石-微晶陨石配对层具有相关性。笔者的研究结果与已发表的相关数据均与“仅存在一组微玻璃陨石-微晶陨石配对层”的模型相符。研究表明，关于始新世晚期存在三层或四层微球粒层的推论实为解释性假象。