Miocene sequences and depocentres in the Roer Valley Rift System

The Miocene sequence in the Roer Valley Rift System consists of alternating open-to-shallow marine, coastal and fluvio-deltaic deposits. In this study, well logs, bio-chronostratigraphy and seismostratigraphy are used to characterize major units and their bounding unconformities and to infer sediment dispersal patterns. Three major unconformities occur in the sequence: the early, middle and late Miocene unconformities (EMU, MMU and LMU). The EMU formed due to tectonic motions related to the Savian phase. After formation of the EMU, a broad depocentre developed in the south-eastern part of the Roer Valley Graben (RVG). Sediment accumulation increased during this period and peaked in the middle Langhian, after which it diminished again to a low level during the late Serravallian. The decrease in sediment accumulation coincided with a period of tectonic subsidence along the major bounding fault zones (i.e. the Peel Boundary Fault System, the Feldbiss Fault System and the Veldhoven Fault System). The resulting transgression caused sediment starvation in the central RVG. Subsequently, global sea-level fall during the early Tortonian caused large-scale erosion, and formation of incised valleys on the highs adjacent to the RVG (Peel Block and Campine Block), as well as the south-eastern RVG, forming the MMU. However, sedimentation continued during this period in the central part of the RVG where no erosional hiatus developed. From the Tortonian onwards, accumulation rates increased again. The depocentre shifted towards the north-west and clinoforms developed in the RVG. During the latest Miocene, the depocentre was concentrated along the south-western margin of the RVG. Meanwhile, the depositional environment of the entire RVRS gradually shallowed as the LMU was formed.