Triassic stratigraphy of the northern North Sea: new paleogeographic reconstructions of the Triassic basin

ABSTRACT This study aims to reconstruct the Triassic paleogeographic setting and refine the chronostratigraphic framework of the Permo-Triassic of the Northern North Sea (NNS) basin though time, using new palynological data, wireline-logs, and core data. Four age-constrained mudstone units and five sandstone units are defined in the Triassic succession. Sedimentological analysis indicates that these units are composed of three facies associations: channel-fill (CFA), splay (SFA), and floodplain (FFA). Using petrophysical signatures from cores calibrated to wireline logs, proportions of facies association are estimated for each age-constrained unit. During sandstone-unit development, the Horda Platform and parts of the Tampen Spur area, have high (> 75%) CFA percentages with single-story channel bodies > 12 m in thickness with an average grain size of medium sand. During deposition of the mudstone units, the entire basin is dominated by high floodplain (> 75%) and splay facies proportions (15–20%), while channel deposits are very limited (< 10%). Variabilities in CFA content, channel thickness, and grain size suggest that the Triassic paleogeographic setting represents a 160-km-wide, distributive fluvial system (DFS) that is soured from the Norwegian mainland. Comparisons between our refined Triassic NNS framework with the UK Central North Sea chronostratigraphic framework may set the foundation for a unified Triassic North Sea stratigraphic scheme, facilitating regional cross-border correlations. A comprehensive Triassic paleographic reconstruction of the NNS provides information on the spatial and temporal distribution of sedimentary facies and enhances predictions of future reservoir distribution.