Paleoenvironmental response of midlatitudinal wetlands to Paleocene-early Eocene climate change (Schoningen lignite deposits, Germany)

摘要

The early Paleogene is marked by multiple negative carbon isotope excursions (CIEs) that reflect massive short-term carbon cycle perturbations that coincide with significant warming during a high-p CO2 world, affecting both marine and terrestrial ecosystems. Records of such hyperthermals from the marine-terrestrial interface (e.g., estuarine swamps and mire deposits) are therefore of great interest as their present-day counterparts are highly vulnerable to future climate and sea level change. Here, we assess paleoenvironmental changes of midlatitudinal late Paleocene-early Eocene peat mire records along the paleo-North Sea coast. We provide carbon isotope data of bulk organic matter (delta(TOC)-T-13C), organic carbon content (% TOC), and palynological data from an extensive peat mire deposited at a midlatitudinal (ca. 41 degrees N) coastal site (Schoningen, Germany). The delta(TOC)-T-13C data show a carbon isotope excursion of -1.3% (mean decrease in delta(TOC)-T-13C; -1.7% at the onset of CIE) coeval with a conspicuous Apectodinium acme. Due to the exceptionally large stratigraphic thickness of the CIE at Schoningen (10m of section) we established a detailed palynological record that indicates only minor changes in paleovegetation leading into and during this event. Instead, paleovegetation changes mostly follow natural successions in response to changes along the marine-terrestrial interface. The available age constraints for the Schoningen Formation hamper a solid assignment of the detected CIE to a particular hyperthermal such as the Paleocene-Eocene Thermal Maximum (PETM) or any succeeding hyperthermal event such as the Eocene Thermal Maximum 2 (ETM2).Compared to other nearby peat mire records (Cobham, UK; Vasterival, F) it appears that wetland deposits around the Paleogene North Sea have a consistent CIE magnitude of ca. 1 : 3% in delta(TOC)-T-13C. Moreover, the Schoningen record shares major characteristics with the Cobham Lignite PETM record, including evidence for increased fire activity prior to the CIE, minor plant species change during the hyperthermal, a reduced CIE in delta(TOC)-T-13C, and drowning of the mire (marine ingressions) during much of the Schoningen CIE event. This suggests that either the Schoningen CIE reflects the PETM or that early Paleogene hyperthermals similarly affected paleoenvironmental conditions of a major segment of the paleo-North Sea coast.