An updated and revised stratigraphic framework for the Miocene and earliest Pliocene strata of the Roer Valley Graben and adjacent blocks

Abstract

In the Netherlands, the bulk of the Miocene to lowest Pliocene sedimentary succession is currently assigned to a single lithostratigraphical unit, the Breda Formation. Although the formation was introduced over 40 years ago, the definition of its lower and upper boundaries is still problematic. Well-log correlations show that the improved lecto-stratotype for the Breda Formation in well Groote Heide partly overlaps with the additional reference section of the older Veldhoven Formation in the nearby well Broekhuizenvorst. The distinction between the Breda and the overlying Oosterhout Formation, which was mainly based on quantitative differences in glauconite and molluscs, gives rise to ongoing discussion, in particular due to the varying concentrations of glauconitic content that occur within both formations. In addition, the Breda Formation lacks a regional-scale stratigraphic framework which relates its various regionally to locally defined shallow marine to continental members. In order to resolve these issues, we performed renewed analyses of material from several archived cores. The results of archived and new dinocyst analyses were combined with lithological descriptions and wire-line log correlations of multiple wells, including the wells Groote Heide and Broekhuizenvorst. In this process, the updated dinocyst zonation of Munsterman & Brinkhuis (2004), recalibrated to the Geological Time Scale of Ogg et al. (2016), was used. To establish regionally consistent lithostratigraphic boundaries, additional data was used along a transect across the Roer Valley Graben running from its central part (well St-Michielsgestel-1) towards the southern rift shoulders (well Goirle-1). Along this transect, chronostratigraphic and lithostratigraphic analyses were integrated with well-log correlation and the analyses of seismic reflection data to constrain geometrical/structural relationships as well. The results led to the differentiation of two distinct seismic sequences distinguished by three recognisable unconformities: the Early Miocene Unconformity (EMU), the Mid-Miocene Unconformity (MMU) and the Late Miocene Unconformity (LMU). The major regional hiatus, referred to as the Mid-Miocene Unconformity, occurs intercalated within the present Breda Formation and compels subdivision of this unit into two formations, viz. the here newly established Groote Heide and the younger Diessen formations. Pending further studies, the former Breda Formation will be temporally raised in rank to the newly established Hilvarenbeek subgroup, which comprises both the Groote Heide and Diessen formations. Whereas these two sequences were already locally defined, a third sequence overlying the LMU represents two newly defined lithostratigraphical units, named the Goirle and the Tilburg members, positioned in this study at the base of the Oosterhout Formation. Besides their unique lithological characteristics, in seismic reflection profiles the Goirle and the Tilburg members stand out because of their distinct seismic facies. Use of an integrated, multidisciplinary and regional approach, an improved southern North Sea framework and more comprehensive lithostratigraphic subdivision of Neogene successions is proposed for the Netherlands, to make (cross-border) correlations more straightforward in the future.

Middle Miocene depositional evolution of the central Roer Valley Rift System

“…We selected four boreholes for our study for the following reasons: The Molenbeersel borehole (DOV‐code: kb18d49w‐B225; BGD‐code: 049W0225) is located in the strongly subsiding Roer Valley Graben (i.e., relatively complete Miocene sequences; Figure B) and has log data that allow correlations with the other boreholes (Figure ). Deckers () furthermore correlated part of the Miocene stratigraphy in the Molenbeersel borehole with crossing seismic lines to study mass transport deposits in the delta‐system that filled the central RVRS with the Heksenberg Sands (i.e., Genk Sands in this study; Figure ). The Groote Heide borehole has detailed biostratigraphic analyses of the Neogene interval by Munsterman et al () and the presence of log data (Figure ). The Gruitrode borehole (DOV‐code: kb18d48w‐B186; BGD‐code: 048w0185) has log data and is located nearby (±1 km) the Wijshagen borehole (Figure ). The Wijshagen borehole (DOV‐code: kb18d48w‐B181; BGD‐code: 048w0180) has detailed lithological descriptions, and it was analysed biostratigraphically by Louwye and Laga () and stratigraphically reinterpreted and correlated with the Gruitrode borehole by Deckers and Louwye (); Figure ). …”

“…From the Chattian to late Burdigalian, the shallow (restricted‐ to open) marine glauconitic sands and clays of the Veldhoven Formation were deposited throughout the northern and central RVRS (Munsterman et al, and references therein; Figure ). The latter authors show that from the late Burdigalian up to the latest Messinian, the open to marginal marine sands of the Hilvarenbeek Subgroup, comprising the Groote Heide and Diessen formations, were deposited in more or less the same area (Figure ).…”

“…Sequences B to F of Rasmussen (), phases 1 to 6 of this study and the Miocene temperature and δ 18 O curves from Miller et al () and Zachos, Pagani, Sloan, Thomas, and Billups (), respectively, are shown on the righthand side. This figure was modified after Munsterman et al () [Color figure can be viewed at wileyonlinelibrary.com]…”

“…Since the latter lignite seam is not always recognized in the study area, this separation has not been possible here and the Genk Sands have been adopted here. Diest Formation: green to orange, glauconiferous, non‐calcareous, at most coarse sands of late Miocene age. The Belgian Diest Sands are considered equivalent to the Dutch Diessen Sands (Munsterman et al, ; Figure ).…”

“…Recently, however, the Miocene succession in the northern and central RVRS was bio‐ and lithostratigraphically (re‐)analysed in a series of deep boreholes by Deckers and Louwye () and Munsterman et al () which allow correlations with the Molenbeersel borehole. In this study, we present these well‐(log) correlations in order to study the main sedimentary units that filled the central RVRS during the late‐early to early‐late Miocene.…”