Provenance of the Lower Triassic Bunter Sandstone Formation: implications for distribution and architecture of aeolian vs. fluvial reservoirs in the North German Basin

Abstract

Zircon U–Pb geochronometry, heavy mineral analyses and conventional seismic reflection data were used to interpret the provenance of the Lower Triassic Bunter Sandstone Formation. The succession was sampled in five Danish wells in the northern part of the North German Basin. The results show that sediment supply was mainly derived from the Ringkøbing‐Fyn High situated north of the basin and from the Variscan belt located south of the basin. Seismic reflection data document that the Ringkøbing‐Fyn High was a local barrier for sediment transport during the Early Triassic. Hence, the Fennoscandian Shield did not supply much sediment to the basin as opposed to what was previously believed. Sediment from the Variscan belt was transported by wind activity across the North German Basin when it was dried out during deposition of the aeolian part of the Volpriehausen Member (lower Bunter Sandstone). Fluvial sand was supplied from the Ringkøbing‐Fyn High to the basin during precipitation events which occurred most frequently when the Solling Member was deposited (upper Bunter Sandstone). Late Neoproterozoic to Carboniferous zircon ages predominate in the Volpriehausen Member where the dominant age population with a peak age of 337 Ma corresponds to the culmination of Variscan high‐grade metamorphism, whereas a secondary age population with a peak at 300 Ma matches the timing of volcanism and magmatism at the Carboniferous/Permian boundary in the northern Variscan belt. Parts of the basement in the Ringkøbing‐Fyn High were outcropping during the Early Triassic and zircon ages similar to this Mesoproterozoic basement are present in the Bunter Sandstone. The heavy mineral assemblage of the Solling Member is uniform and has a high garnet content compared to the contemporaneous sediments in the Norwegian‐Danish Basin and in the southern part of the North German Basin. This finding confirms that a local source in the Ringkøbing‐Fyn High supplied most of the fluvial sediment in the northern part of the North German Basin. The northernmost part of the Bunter Sandstone is situated on a platform area that is separated from the basin area by a broad WNW–ESE‐oriented fault zone. The most promising reservoir in the basin area is the aeolian Volpriehausen Member since the sandstone has a wide lateral distribution and a constant thickness. The alluvial to ephemeral fluvial Solling Member may be a good reservoir in the platform area and marginal basin area, but the complex sand‐body architecture makes it difficult to predict the reservoir quality.

Quartz and zircon decoupling in sandstone: Petrography and quartz cathodoluminescence of the Early Triassic continental Buntsandstein Group in Germany

“…The central lake was shallow and mostly endorheic with temporal desiccation when its position partly shifted (e.g. Becker, ; Röhling & Lepper, ; Olivarius et al ., ). During lake‐level lowstands, aeolian sandflat and dune sedimentation dominated (Maaß et al ., ; Tietze & Röhling, ).…”

Pre-drilling assessments of average porosity and permeability in the geothermal reservoirs of the Danish area

“…1). In general the formation thins towards the Ringkøbing-Fyn High, and it is locally absent on the High (Nielsen and Japsen 1991;Olivarius et al 2015b). The reservoir quality of the formation varies considerably, as the lithology varies from sandstones with a subordinate amount of mudstones, to siltstones and mudstones with few sandstone layers (Berthelsen 1980;Clemmensen 1985).…”

“…The Bunter Sandstone formation was deposited in an arid to semi-arid climate, and the sandstones represent deposition by fluvial channel systems and eolian dunes, whereas the mudstones mainly were deposited in lakes and on flood plains (Clemmensen 1985). Eroded material was supplied from the Ringkøbing-Fyn High by alluvial-fluvial systems and by wind transport across the North German Basin (Olivarius et al 2015b;Clausen and Pedersen 1999).The sandstone layers are generally continuous, especially the eolian sandstones, and consist mostly of very fine to medium-grained sand (Olivarius et al 2015b). Similarly, eroded material from the Fennoscandian Shield was transported into the Danish Basin (Bertelsen 1980;Olivarius and Nielsen 2016).…”

New insights on subsurface energy resources in the Southern North Sea Basin area

“…However, Kortekaas et al (2018) described the presence of reservoir sands in the northern Dutch offshore, north of the main southern sourced fairway. In the North German Basin, locally sourced fluvial sediments from the Ringkøbing-Fyn High were observed alternating with southerly sourced aeolian sands (Olivarius et al 2017). Based on well and seismic analysis, Kortekaas et al (2018) suggest the local presence of Early Triassic depocentres in the Step Graben area, west of the Dutch Central Graben.…”