THE PALEOCENE/EOCENE BOUNDARY AND THE TETHYAN SHALLOW BENTHIC ZONATION

In the beginning of the 21 century, the International Commission on Stratigraphy officially defined the Paleocene/Eocene (P/E) boundary as “the onset of carbon isotope excursion” during the Paleocene-Eocene thermal maximum (PETM). However, the topic where the P/E boundary is in the shallow benthic zonation (SBZ) is still in dispute. This paper reviews the last 20 years’ progresses on this topic, and concludes that the P/E boundary should be placed within SBZ5, not at the transition between SBZ4 and SBZ5 as traditionally thought. At the P/E boundary, no evident change in larger foraminiferal composition happens. Within the PETM-CIE recovery (about 50?120 kyr after the CIE onset), however, larger foraminifera experienced a drastic extinction. This extinction event was defined as larger foraminiferal extinction and origination. The larger foraminiferal extinction and origination event, in essence, differs from the larger foraminiferal turnover event. The former is likely caused by short-term seawater eutrophication that might have resulted from intensified continental weathering during the CIE recovery, while the latter represents an evolutionary success during the long-term stay in a stable environment. After reviewing previous studies on the P/E boundary, I think that discontinuity/incompleteness of many sedimentary sections close to the P/E boundary is the main cause for the dispute.

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