Clinoform development and topset evolution in a mud-rich delta - the Middle Triassic Kobbe Formation, Norwegian Barents Sea

Tore Grane Klausen, Jonas Aas Torland, Christian Haug Eide, Behzad Alaei, Snorre Olaussen, Domenico Chiarella

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Clinoform surfaces are routinely used to mark transitions from shallow waters to deep basins. This concept represents a valuable tool for screening potential reservoir intervals in frontier basins where limited data are available. Variations in the character of clinoform geometries and shoreline and shelf-edge trajectories are indicators of a range of different factors, such as palaeobathymetry, changes in relative sea-level and sediment supply. Applications of conceptual and generalized models might however lead to erroneous assumptions about the supply of coarse-grained material to the delta front and basin when superficial similarities between clinoform geometries are not treated holistically. The present study examines the mudstone-dominated Middle Triassic Kobbe Formation – a potential hydrocarbon reservoir interval in the Barents Sea, where prodeltaic to deltaic deposits can be examined in cores, well logs and two-dimensional and three-dimensional seismic data. Despite pronounced acoustic impedance contrast to the surrounding shale, channel belt networks are not observed close to the platform-edge in seismic datasets, even at maximum regressive stages. However, sub-seismic prodeltaic deposits observed on the shallow platform indicate that prodeltaic deposits were sourced directly from the delta plain. Clinoform surfaces with different geometries and scale are observed basinward of the palaeo platform-edge of underlying progradational sequences, correlative to mudstone-dominated prodeltaic core sections. Results indicate that platform-edge deltas developed at discrete sites in the basin due to normal regression, but the positions of these deltas are not directly relatable to variations in clinoform geometries. Transitions from third-order to fourth-order clinoform geometries record discrete transgressive–regressive cycles but are not necessarily good indicators of sandstone deposition. Because of prolonged periods with high accommodation, channel avulsions were frequent and only very fine-grained sandstone was deposited in heterolithic units at the delta front. Sandstones with good reservoir properties are predominantly found along basin margins.
Original languageEnglish
Pages (from-to)1132-1169
Number of pages38
Issue number4
Early online date27 Sept 2017
Publication statusPublished - Jun 2018

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