Sequence stratigraphy of Middle Triassic carbonates and terrigenous deposits (Muschelkalk and Lower Keuper) in the SW Germanic Basin: maximum flooding versus maximum depth in intracratonic basins

We analyze the sequence stratigraphy of the Middle Muschelkalk to the Lower Keuper strata (Middle Triassic) in the SW Germanic Basin. The sequences are interpreted on the basis of a synthesis of facies in the neritic carbonates, terrigenous sediments and evaporites along a basin margin to center transect. Continental sediments (CS, lower Middle Muschelkalk) occur at the base of the Middle-Upper Muschelkalk sequence. Thick retrogradational marginal-marine sediments overlain by open-marine deposits (middle Middle Muschelkalk to lower Upper Muschelkalk) form the transgressive systems tract. In the basin center, only bathymetric criteria are available for recognition of this systems tract. The maximum flooding surface (mfs) at the basin margin differs in age from the maximum depth interval in the basin center. Maximum depth surfaces or intervals (mdi, new term) should be recognized in many deep basins where flooding is not recorded. The highstand systems tract (upper Upper Muschelkalk) is strongly progradational. The upper sequence boundary (Muschelkalk/Keuper boundary) is characterized by subaerial exposure at the basin margin and submarine erosion in most other sections. Along this boundary, the low paleo-relief resulted in a lack of coarse-grained elastic deposits. In the basin center, a strongly regressive succession (lower Lower Keuper) allows, possibly for the first time in an intracratonic basin, the distinction of an early or late lowstand systems tract (ELST or LLST). High-frequency, low-amplitude sea-level fluctuations resulted in parasequences in the open-marine Upper Muschelkalk, but in high-frequency sequences in the coastal plain sediments of the overlying parts of the Lower Keuper. (C) 2002 Elsevier Science B.V. All rights reserved.