Seismic stratigraphic subdivision of the Triassic succession in the Central North Sea; integrating seismic reflection and well data

Abstract

The Triassic sedimentary succession in the Central North Sea has been investigated to establish a broader understanding of the Triassic Period, from the combined interpretation of seismic reflection data and well data. The Triassic succession has been subdivided into four seismic units, where unit boundaries are characterized by regional seismic amplitude anomalies, reflecting changes in gross sedimentary facies or rock properties. A successful correlation between sedimentary facies, interpreted within the well sections and distinct seismic reflection patterns, allowed a thorough mapping of the gross palaeoenvironment throughout the Triassic. The method presented of subdividing a continental sedimentary succession into seismic units should be applicable elsewhere in other basins. The main source area during the Triassic was Scandinavia to the north, and sediment transportation was mainly along north–south- and NE–SW-trending lineaments, which are at present located onshore southern Norway, and in the Åsta Graben and the Varnes Graben offshore. An uplifted Skagerrak Graben area acted as source area in the Early and early Middle Triassic, with sediment dispersal to the south and SW. High relief existed for a longer period in western Scandinavia than in eastern Scandinavia, which supports an asymmetric shape of the Scandinavian mountains during the Triassic. Accommodation space in the Early Triassic was mainly controlled by the relief inherited from a Late Carboniferous–Permian rift phase. Although thermally induced regional subsidence continued in the Middle and Late Triassic, creation of local accommodation space was mainly limited to halokinesis, including redistribution and withdrawal of salt from the subsurface. The Upper Triassic succession is eroded across the western and central parts of the study area, although the Upper Triassic unit is preserved in synforms adjacent to salt structures. In the western part of the study area, dry, playa conditions prevailed during the Early Triassic, although fluvial systems supplied long-transported sandy detritus southeastwards in the late Early Triassic. More sandy detritus was transported into the sedimentary basin in the Middle and Late Triassic, concurrently with a gradually wetter climate. Supplementary material: Uninterpreted seismic sections are available at www.geolsoc.org.uk/SUP18726 .

Regional correlation and seismic stratigraphy of Triassic Strata in the Greater Barents Sea: Implications for sediment transport in Arctic basins

“…The climate also became more humid in the GBSB, and in northern Pangea in general, in part due to northward continental drift out of the arid subtropics and into more humid latitudes (e.g. Francis, 1994; Jarsve et al., 2014). This lead to an increase in both weathering and transport capacity of rivers.…”

Syn- to post-rift alluvial basin fill: seismic stratigraphic analysis of Permian-Triassic deposition in the Horda Platform, Norway

“…A review by Lervik (2006) collated available information to systemize and unify the stratigraphic nomenclature schemes, which are applied here. Jarsve et al, (2014) used seismic facies and regionally continuous seismic reflections to subdivide and map the central North Sea Triassic deposits. The same procedure is applied here to the Triassic Hegre Group in the Horda Platform.…”

“…The Hegre Group was deposited in a continental basin covering most of the current North Sea area (Steel and Ryseth, 1990;Frostick et al, 1992;Steel, 1993;Nystuen and Fält, 1995;McKie et al, 2010;McKie, 2014;Jarsve et al, 2014;Nystuen et al, 2014). The succession features several coarsening-and fining-upwards alluvial sandstone and mudstone sequences of higher-and lowerorder (Nystuen et al, 1989;Steel and Ryseth, 1990).…”

Strain migration during multiphase extension, Stord Basin, northern North Sea rift

“…The main depocentre is located in the centre of the basin, where Syn‐RP2 is up to 820 ms TWT [c. 1,500 m] thick (Figure 7a). This depocentre is not located in the immediate hanging wall of any fault and is associated with a set of westward‐prograding clinoforms known as the Hardangerfjord Delta (Gabrielsen et al., 2001; Jarsve et al., 2014; Jarsve, et al., 2014; Sømme et al., 2013). Faults that were active during syn‐RP2 are located at the eastern (ØFS3‐5 and F3) and western (UEF2‐5) basin margins (Figure 7a).…”