Middle Miocene depositional evolution of the central Roer Valley Rift System

Abstract

Correlations between bio‐ and/or lithostratigraphically analysed boreholes provide new insights on the late‐early to early‐late Miocene depositional evolution of the central Roer Valley Rift System (RVRS) as part of the southern North Sea Basin. This evolution started with a major regression that occurred in two steps, one during the late Burdigalian and another during the earliest Langhian. Each step coincides with a coarsening of the grain size, reduction in the content of glauconite and increase in the lignite content. The amount of open marine dinocysts also showed a strong decrease. Regression continued up to the middle Langhian as a large delta system builded out in the central RVRS. The main phase of regression ended in the late Langhian. Around the Langhian/Serravallian boundary, a major marine ingression drowned the former delta system. Transgression was evidenced by an increase in the content of glauconite and open marine dinocysts and a decrease in the lignite content. Maximum flooding occurred in the middle/late Serravallian and was followed by another regression. This regression ended in a regional latest Serravallian‐earliest Tortonian hiatus with locally deep erosion. During the early Tortonian, the whole region was transgressed again which was expressed by an increase in the content of glauconite and open marine dinocysts and decrease in the lignite content in the central RVRS. The late‐early to early‐late Miocene depositional evolution of the southern North Sea Basin corresponds very well with that previously described for the eastern and central (Danish) part of the North Sea Basin, but not with the global sea‐level curves, which show mainly the opposite trends. These mismatches could be explained by tectonics and/or changes in sedimentation rates.