Sedimentary structures and facies analysis of shallow marine carbonates

Interpretation of the sediments and structures of the Lower Muschelkalk in terms of sedimentation, erosion, deformation, and diagenesis yielded a model for the mode of formation of shallow marine carbonates. Some uncommon sedimentary structures typical to the sequence under consideration, such as wavy tidal lamination, ? Kinneyia-ripples? (= real micro-ripples), shear slab joints (= small-scale intrastratal faulting), and channel-slumping, may indicate an intertidal calcareous environment. Early dolomitization is frequent. In the sandy marginal facies, abundant load structures suggest sudden changes in sedimentation rate. The frequency of deformational structures gave rise to discuss the occurrence of earthquakes. The evolution of the basin is shown by maps and profiles. Above the terrestrial and near-shore red beds of the Buntsandstein (A) a change from shallow and hypersaline to deeper and normal sea water conditions is shown by the following sequence: red clay and siltstone with evaporites (B)-stromatolitic lagoonal dolomites (C) - barrier-like shell banks (D) - marly shallow-shelf sediments (E) - dark stillwater marls (F). This was followed by a facies development not unidirected and represented by the sequence: bioturbate marls (G) - well bedded marls with cross-bedded carbonates (H) - black stillwater shales (I). The Lower Muschelkalk ends with the reverse of the first-mentioned sequence: marly shelf deposits (K) - tidal flat sediments (L/M) - barrier-like oolitic shell banks (N) - laminated, bituminous marls (O) - stromatolitic, hypersaline dolomites (P) - evaporites with marginal red beds (Q), pointing to a return of evaporitic conditions fully developed later in. the Middle Muschelkalk. Within this sequence one unit (L) runs unconformable through at least two facies units as a marker layer which is considered as the most reliable isochronous horizon of the Lower Muschelkalk.