Abstract

A sequence-stratigraphic and subsidence analysis in the SE German Molasse basin was carried out based on well and seismic data. The sequence-stratigraphic study revealed that the basin fill is composed of five second-order sequences. Sequences 3 and 4 can be subdivided into several third-order sequences. Seismic facies maps illustrate the temporal and spatial evolution of the study area. Comparison of an accommodation curve of the Molasse basin with the eustatic sea-level curve of Haq et al. (Science, 1987, 235, 1156–1167) showed, that the sequence stratigraphic subdivision was mainly controlled by eustatic sea-level fluctuations.

Subsidence analysis revealed a major flexural event in the SE German Molasse basin from late Eocene to early Miocene (late Egerian), followed by a possible visco-elastic relaxation of the lithosphere responsible for the formation of an angular unconformity between the two classical transgressive-regressive megacycles of the Molasse stratigraphy (early Miocene, late Egerian-Eggenburgian boundary). A phase of relatively uniform, decreasing subsidence followed until the end of Molasse sedimentation, when an isostatic rebound resulted in the uplift of the basin. The subsidence analysis also revealed, that even though eustacy controlled sequence boundary formations, the interplay between subsidence and sedimentation rates, both governed by tectonics, controlled the transgressive-regressive megacycles. However, the coupling of the two factors depends on the tectonic process.