Controls of basin margin tectonics on the Lower Cretaceous sedimentation in the Norwegian Barents Sea

Structural styles and stratigraphic patterns along North Atlantic margins display a large spectrum of complexity and variability. An extensive amount of subsurface data from the north-central and south-western Barents Sea are used to: (1) at a larger scale understand how various plate tectonics regimes controlled structuring, faulting and sedimentation along the northern and southern margins of the Barents Sea; (2) at a smaller scale understand how the structural evolution of basin bounding faults impacted sedimentation in basins which were affected by one or more phases and multiple directions of extension; and (3) improve the knowledge about the paleogeography of the Barents Sea. In order to fulfil these objectives, this research consists of a systematic analysis which is summarized in five journal articles. Paper 1 improves the existing knowledge of the Early Cretaceous tectonostratigraphic development of the north-central Barents Sea based on observations from subsurface data, structural and plate tectonic restorations in an area distal from the northern margin of the Barents Sea. As result of this work, compressional tectonics in the Early Cretaceous is suggested to be induced by the opening of the Canada Basin which triggered reactivation of Late Palaeozoic normal faults in reverse mode. Reverse movement along these faults caused the formation of NE oriented structural highs and anticlines, which controlled and routed the progradation of Lower Cretaceous clastic material from the northern to the southern margins of the Barents Sea. The second paper focuses on understanding the Early Cretaceous structural evolution of the Tromsø Basin (proximal southern margin of the Barents Sea) in the context of the geodynamic processes acting in the southwestern Barents Sea. We propose an Early Cretaceous structural evolution of the Tromsø Basin which explains the formation of compressional features during rifting in the south-western Barents Sea. 2D gravity modelling and 2D structural restoration along a key regional composite seismic section, facilitated the interpretation and assessment of geodynamic constrains for the deeper structures below the Lower Cretaceous. These reveal thinner crust below the Tromsø Basin as compared to the Sørvestnaget and Hammerfest basins, which is suggested as the result of oblique extension in the southwestern margin of the Barents Sea. In the third paper and at a smaller scale, we integrate stratigraphic and structural observations with throw backstripping and time thickness maps to define the growth processes of a basin-bounding normal fault in the northern Polhem subplatform. During the initial Early Cretaceous rifting, the fault system consisted of at least five en-echelon segments, which were ca. 5–10 km long. Throw backstripping indicates that fault segments were hard-linked after this initial stage to form a single 40 km long fault zone. Cross fault incised valleys provide additional information on the topographic response to fault growth. Major valley incisions at the fault linkage zones outline the extent of the individual fault segments and support early isolated fault growth. The fourth paper focuses on a genetic correlation of the Lower Cretaceous succession between the north-central and south-western Barents Sea and Svalbard. The structural framework defined in paper 1 is used to locate the main sediment routes and progradation directions. The latest Valanginian to earliest middle Albian sequences in the offshore Barents Sea are correlated with the onshore Rurikfjellet, Helvetiafjellet and Carolinefjellet formations in Svalbard. This results in the reconstruction of four paleogeographic maps that show the progressive evolution and sediment distribution over the Norwegian Barents Sea for: (1) the earliest Valanginian, (2) the latest Hauterivian, (3) the middle to late Barremian and (4) the latest Aptian. In the fifth paper, three tectonic events are suggested to control the deposition of the diachronous Lower Cretaceous clastic wedges around the Loppa High: 1) the latest Jurassic – earliest Cretaceous uplift of the Loppa High which triggered the deposition of the older wedges progressively eastwards in the northern Hammerfest Basin; 2) the late Barremian–Aptian faulting episode in the western flank of the Loppa High, which resulted in the deposition of shallow and probably deep marine wedges; and 3) the latest Aptian to earliest Albian tilting of the Hammerfest Basin and the Loppa High, which modified the sedimentation patterns in the region. The results of this research can be applied beyond the Barents Sea, as they provide insights into margins and basins evolution, specifically on how: (1) oblique deformation along margins can control the inversion of pre-existing structures and routing of sediments, as well as modify paleogeography; (2) the growth of basin-bounding normal faults can affect sedimentation, with incised channels reflecting the early stage of fault growth; (3) paleogeographic reconstructions that reflect both the tectonic and stratigraphic setting can be used to understand sand distribution and sediment partitioning

Reservoir characterization of Sognefjord and Fensfjord formations across Gjøa field, North Sea, Norway

Master's thesis in Petroleum Geoscience engineeringThe Gjøa field was discovered in 1989 and first production started in 2010 located about 40 kilometers north of the Fram field. The reservoir contains gas above a relatively thin oil zone in Jurassic sandstones in the Viking, Brent and Dunlin Groups. The main reservoir units of Gjøa field are Fensfjord and Sognefjord formations, Viking group. The stratigraphic evolution from Callovian to Kimmeridgian Fensfjord and Sognefjord formations in the greater Gjøa field hasn’t been subject of previous work, but they form perspective reservoir intervals on neighborhood areas like Troll and Brage fields. The Fensfjord and Sognefjord formations interpreted as tide, wave and fluvial dominated delta environment. The facies association indicates shelfal, pro-delta, delta-front, delta-plain, shoreface and estuarine depositional environments. The seismic interpretation of the study area revealed changes in structural regimes during deposition of Fensfjord and Sognefjord formations. The N-S extension changed to NW-SE in E. Oxfordian – M. Oxfordian periods, which highly affected the depositional processes of Fensfjord and Sognefjord formations. The main goal of this study is an integration of data analysis and provided conceptual geological model for tectono-stratigraphic evolution of Gjøa field from Callovian to Kimmeridgian period

The Lower Cretaceous of Svalbard and its relevance for exploration in the northern Barents Sea

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 shelfedges 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

The Lower Cretaceous succession of the northwestern Barents Shelf: Onshore and offshore correlations

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