古近纪 Danian 期早期热事件 Dan-C2 研究进展

The early Paleogene was a typical greenhouse climate period in the Cenozoic, during which a series of rapid and short-lived warming events (termed “hyperthermals”) occurred. Hyperthermals were characterized by negative carbon isotope excursion. Among them, the Dan-C2 thermal event of the early Danian is considered to be the first to occur after the biological mass extinction at the end of the Cretaceous; thus, its environmental significance and ecological effects have received widespread attention. However, as research continues, controversies regarding the Dan-C2 event continue to grow: ① The global significance is controversial; in the marine records, the δ¹³C negative excursions during the Dan-C2 event were restricted to planktonic foraminifera and bulk records in parts of the Atlantic and Tethys Oceans, while benthic foraminifera rarely recorded this event, suggesting that it may only be a regional carbon perturbation event. Furthermore, the warming indicated by the oxygen isotopes (δ¹⁸O) of bulk and planktonic foraminifera during this event was limited to surface waters in parts of the North Atlantic, with evidence of warming in bottom waters generally lacking. At the same time, although evidence of the terrestrial Dan-C2 event has been discovered, the terrestrial records still have significant deficiencies in terms of quantification, chronology, and continuity compared with the marine records, which makes it difficult to conduct in-depth and effective comparisons between the terrestrial and marine records; therefore, the global significance of the Dan-C2 event is questioned. ② The trigger mechanism is controversial; the high-precision chronological frame shows that the Dan-C2 event occurred at the eccentricity maximum, indicating that the orbital cycle had a certain influence on the event. Simultaneously, the temporal coincidence of the Dan-C2 event with the last phase of the eruption of the Deccan Traps volcanism implies that greenhouse gas emissions from volcanic activity may have contributed to warming during the Dan-C2; however, the relative magnitudes of both contributions to the event is difficult to assess. Future research should focus on the following: ① Exploring the variability of the Dan-C2 event records in different areas and revealing the reasons for the absence of deep-ocean water records. ② Establishing more reliable terrestrial records and further exploring the global significance of the Dan-C2 event and its triggering mechanism.