Greenhouse conditions in lower Eocene coastal wetlands?—Lessons from Schöningen, Northern Germany

Abstract

The Paleogene succession of the Helmstedt Lignite Mining District in Northern Germany includes coastal peat mire records from the latest Paleocene to the middle Eocene at the southern edge of the Proto-North Sea. Therefore, it covers the different long- and short-term climate perturbations of the Paleogene greenhouse. 56 samples from three individual sections of a lower Eocene seam in the record capture the typical succession of the vegetation in a coastal wetland during a period that was not affected by climate perturbation. This allows facies-dependent vegetational changes to be distinguished from those that were climate induced. Cluster analyses and NMDS of well-preserved palynomorph assemblages reveal four successional stages in the vegetation during peat accumulation: (1) a coastal vegetation, (2) an initial mire, (3) a transitional mire, and (4) a terminal mire. Biodiversity measures show that plant diversity decreased significantly in the successive stages. The highly diverse vegetation at the coast and in the adjacent initial mire was replaced by low diversity communities adapted to wet acidic environments and nutrient deficiency. The palynomorph assemblages are dominated by elements such as Alnus (Betulaceae) or Sphagnum (Sphagnaceae). Typical tropical elements which are characteristic for the middle Eocene part of the succession are missing. This indicates that a more warm-temperate climate prevailed in northwestern Germany during the early lower Eocene.

Early Eocene carbon isotope excursions in a lignite-bearing succession at the southern edge of the proto-North Sea (Schöningen, Germany)

“…56 Ma for the Main Seam (see above), CIE 1 most probably represents the PETM. As a consequence, we now locate the Paleocene-Eocene boundary within the Main Seam, thus confirming the earlier supposition of Lenz et al (2021).…”

“…Mixing and reworking of organic matter cannot be excluded for the interbeds of the Schöningen succession, since multiple flooding and thus reworking events may have happened (Methner et al, 2019). However, within individual lignite seams no mixing of organic material should have occurred, since it formed in situ from an ombrotrophic (rain-fed) peat mire consisting mostly of mosses, ferns, and an associated hardwood mire forest (Riegel et al, 2012;Inglis et al, 2015;Lenz et al, 2021). Therefore, the isotope record of the Main Seam may indeed reflect a stepwise injection of carbon into the atmosphere.…”

“…(b) Cross-section through the study area, showing the Helmstedt-Staßfurt salt wall and related synclines (modified after Brandes et al, 2012). (c) Generalized scheme of the Paleogene succession in the western syncline of the Helmstedt Mining District (adapted from Brandes et al, 2012;Lenz et al, 2021). The blue and red lines indicate the stratigraphic position of the studied sections.…”

Early Eocene carbon isotope excursions in a lignite bearing succession at the southern edge of the proto-North Sea (Schöningen, Germany)

“…Especially pronounced is the change in pollen assemblages at the beginning of the CIE. In the lower part of the Main Seam they are characterized by abundant Inaperturopollenites averaging 18.4% of the total assemblage and frequent Nyssapollenites probably representing a Nyssa-Taxodium swamp forest which has already been invoked for the near-coastal vegetation of Seam 1 (Lenz et al, 2021). In this part of the Main Seam δ 13 C TOC values fluctuate constantly between -26.8 ‰ and -25.4 ‰ (Fig.…”