Glomospira acme during the paleocene-eocene thermal maximum: Response to caco_3 dissolution or to ecological forces?

摘要

The Paleocene-Eocene Thermal Maximum (PETM) event at -55.5 Ma, is characterized by globally elevated temperatures, a negative 5~(13)C excursion and major biotic changes on land and in the oceans, including the major extinction of deepsea benthic foraminifera. Increased acidity of the oceans and associated shallowing of the calcite compensation depth led to dissolution of deep-sea carbonates in various ocean basins during the PETM. As a result, the post-extinction benthic foraminiferal assemblages, which were locally dominated by agglutinated taxa such as Glomospira spp.l Repmanina charoides, have been traditionally interpreted as a result of dissolution of calcareous-shelled species. We carried out a thorough bibliographic revision of the post-extinction assemblages in widely distributed land-based sections and marine cores to: 1) document the paleogeographical extent on the so-called "Glomospira acme," 2) compare the characteristics among sites where the acme is present, and 3) assess the paleoenvironmental conditions that could have potentially controlled the occurrence of the Glomospira acme. We recognized the early Eocene (calcareous plankton biozones NP9 and P5) Glomospira acme in the Tethys and along the eastern margin of the North Atlantic Ocean. The comparison of the sedimentological and paleoenvironmental evolution across the PETM in these areas led us to conclude that the proliferation of Glomospira spp.lR. charoides may have been related not only to CaCO_3 dissolution, but also to the pulsed input of siliciclastic material resulting from continental erosion or gravitational fluxes. Increased terrestrial runoff in nearshore-marine sediments is consistent with an enhanced hydrological regime or higher seasonality or episodicity, as previously proposed for the PETM, and with the paleogeographical distribution of the continental margins and slopes in the Tethys and northeast Atlantic region, where the Glomospira acme has been recorded. As a result of the increased siliciclastic input, low-quality refractory organic matter would be transported to the seafloor, allowing the rapid proliferation of Glomospira splR. charoides.