Sequence stratigraphy of a Paleogene coal bearing rim syncline: interplay of salt dynamics and sea‐level changes, Schöningen, Germany

Abstract

Salt rim synclines contain important hydrocarbon and coal resources in central Europe. The Sch€ oningen salt rim syncline is filled with >300 m of Early to Middle Eocene unconsolidated clastics with interbedded lignitic coal seams that are mined at the surface. In this study, 357 lithologic logs are integrated with measured outcrop sections and paleo-botanical data to interpret the depositional environments and sequence stratigraphic framework of the rim syncline fill. As salt withdrew, it generated an elongate mini-basin that mimicked an incised valley. The sustained accommodation and slow broadening of the syncline affected the stratigraphic architecture and contributed to the preservation of coal units. The clastic units in the syncline filled in seven depositional stages: (1) tidally influenced fluvial estuarine channels; (2) mixed tide-and wave-dominated estuaries; (3) prograding wave dominate deltas; (4) transgressive shoreline deposits; (5) braided fluvial channels; (6) estuaries; and (7) prograding tide-dominated channels. The succession defines four 3rd order sequences and several higher order sequences that are possibly related to Milankovitch cycles. The higher order sequences are dominantly characterized by stacked transgressive cycles of thick, lowstand coals overlain by estuarine sands. The nearly continuous warm and wet Eocene climate was conducive to continuous peat production with a climatic overprint recorded in the mire type: ombrotrophic mires developed in wetter times and rheotrophic mires developed in relatively drier conditions pointing to the presence of orbitally controlled seasonality. Both mire types were impacted by the interplay of subsidence and base-level. The continuous dropping of the mires below base-level via subsidence protected the mires against erosion and may account for the absence of coals outside of the rim synclines in the region.

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

“…It comprises ∼ 150 m of alternating lignite seams and clastic interbeds ( Fig. 1b) (Brandes et al, 2012;Osman et al, 2013;Riegel et al, 2012). Detailed age constraints of the Schöningen Formation are weak and restricted to dinocyst assemblages and scattered radiometric ages from a core at Emmerstedt ca.…”

“…Silts to mediumgrained sands dominate the clastic interbeds. There is still debate about the prevailing deposition conditions of the clastic interbeds (Osman et al, 2013;Riegel et al, 2012). Interbed 1 includes Apectodinium spp., mostly in low numbers, and shows little evidence for fully marine conditions but rather indicates local emergence (occurrence of driftwood and occasional rooting).…”

The Middle Pleistocene tunnel valley at Schöningen as a Paleolithic archive

“…), which comprises mostly Triassic limestone. The main infill of the rim syncline consists of an up to 366 m thick marginal marine lignite-bearing Paleogene succession Osman et al, 2013), which is unconformably overlain by up to 45 m thick Middle to Upper Pleistocene deposits (Elsner, 2003;Lang et al, 2012). The Pleistocene succession (Fig.…”

Response of salt structures to ice-sheet loading: implications for ice-marginal and subglacial processes

“…Although the salt layer has become very thin (>200 m) below the southwestern rim syncline, a salt weld is not developed. The infill of the rim synclines consists of up to 360 m thick unconsolidated Palaeogene coal-bearing marginal marine deposits Osman et al, 2013).…”