The article “The Lower Cretaceous succession of the northwestern Barents Shelf: Onshore and offshore correlations” by Sten-Andreas Grundvåg, D. Marin, B. Kairanov, K.K. Śliwińska, H. Nøhr-Hansen, A. Escalona, and S. Olaussen has been accepted by the Journal Marine and Petroleum Geology.
- By combining new biostratigraphic data with conventional outcrop data from Svalbard and sequence stratigraphic framework defined from well and seismic data offshore, this study shed new light on the palaegeographic development of the Lower Cretaceous in the northwestern part of the Barents Shelf.
- It is suggested that three offshore sequences (S1–S3) of latest Valanginian–earliest middle Albian age correspond and correlate to the Lower Cretaceous succession onshore Svalbard, which includes the Rurikfjellet (Valanginian–Hauterivian/early Barremian), Helvetiafjellet (early Barremian–early Aptian) and Carolinefjellet formations (early Aptian in its lower part, middle Albian in its upper part).
- Clinoforms within the offshore sequences generally show a south to southeastward progradation-direction, a trend which coincides with palaeocurrent directions in both the Rurikfjellet and Helvetiafjellet formations onshore. This strongly indicates that the onshore and the offshore depositional systems were parts of the same large-scale palaeo-drainage system.
- The presence of a regionally extensive subaerial unconformity onshore Spitsbergen indicates that the entire northwestern part of the shelf were uplifted during the early Barremian. The presence of Barremian dinocyts in the strata above and immediately below the unconformity further suggests a minor hiatus and that the shelf was exposed for only a relatively short period of time (<2 million years).
- The apparent lack of sand in the majority of the largest-scale clinoforms (relief >150 m) may relate to the physiographic conditions in the receiving basin (storm waves, along shore currents plus strong tidal currents), which eventually resulted in sand being trapped in coastal plain and in inner shelf areas and a net basinward transport of mud.
- Due to outcrop limitations, clinoform geometries at the scale of shelf-margins are yet to be recognized onshore. However, based on the large scale (minimum slope lengths of 30–40 km) and low-angle geometries (foreset dips < 1deg;) of some of the offshore clinoforms, as well as the occurrence of thick successions of gravity flow deposits containing rafted blocks of coastal plain origin in some of the onshore wells, it is speculated that clinoforms may be present in the up to 400 m thick Rurikfjellet Formation (Valanginan–Hauterivian/early Barremian).
The Lower Cretaceous succession in the Barents Sea is listed as a potential play model by the Norwegian Petroleum Directorate. Reservoirs may occur in deep to shallow marine clastic wedges located in proximity to palaeo-highs and along basin margins. In addition, shelf-prism-scale clinoforms with high amplitude anomalies in their top- and bottomsets have been reported from reflection seismic but they have never been drilled. In Svalbard, the exposed northwestern corner of the Barents Shelf, Lower Cretaceous strata of shelfal to paralic origin occur, and includes the Rurikfjellet (Valanginian–Hauterivian/lowermost Barremian), Helvetiafjellet (lower Barremian–lower Aptian) and Carolinefjellet formations (lower Aptian–middle Albian). By combining sedimentological outcrop studies and dinocyst analyses with offshore seismic and well ties, this study investigate the link between the onshore strata and the offshore clinoforms. Age-vise, only three (S1–S3) of the seismic sequences defined in the offshore areas correlate to the onshore strata; S1 correspond to the Rurikfjellet Formation, S2 to the Helvetiafjellet Formation and the lower Carolinefjellet Formation, and S3 to the upper Carolinefjellet Formation. Offshore, all three sequences contain generally southward prograding shelf-prism-scale clinoforms. A lower Barremian subaerial unconformity defines the base of the Helvetiafjellet Formation, and its extent indicates that most of the Svalbard platform was exposed and acted as a bypass zone in the early Barremian. Onshore palaeo-current directions is generally towards the SE, roughly consistent with the clinoform accretion-direction towards the S. The local occurrence of a 150 m thick succession of gravity flow deposits transitionally overlain by prodelta slope to delta front deposits in the Rurikfjellet Formation, may indicate that shelf-edges also developed in Svalbard. The late Hauterivian age of theses deposits potentially highlights the inferred offlapping nature of the Lower Cretaceous strata as they predate the lower Barremian unconformity, and thus record a hitherto unknown regression in Svalbard. The presence of the lower Barremian subaerial unconformity in Svalbard, the general southeastward palaeo-current directions, and the age-equivalent clinoform-packages south of Svalbard, suggests that the onshore and offshore strata is genetically linked and was part of the same palaeo-drainage system.
Grundvåg, S.-A., Marin, D., Kairanov, B., Śliwińska, K.K., Nøhr-Hansen, H., Escalona, A., Olaussen, S. (2017): The Lower Cretaceous succession of the northwestern Barents Shelf: Onshore and offshore correlations. Marine and Petroleum Geology. Available online 24 June 2017. DOI: 10.1016/j.marpetgeo.2017.06.036 [intranet]