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[Abstract Syn‐rift successions contain both prolific organic‐rich and coarse‐grained rocks, but these rocks are usually studied independently. Thus, the interplay among organic matter deposition, tectonics and sediment supply is not commonly assessed. In this study, we use well logs, Total Organic Carbon (TOC) content, biostratigraphy and seismic data from the SW Barents Sea to unravel the variability of organic‐rich successions and its interaction with potential reservoir rocks in areas affected by active normal faulting versus tectonically stable areas. Four Transgressive‐Regressive (T‐R) sequences were defined for the Middle to Upper Jurassic Fuglen Formation and for the organic‐rich Upper Jurassic to lowermost Cretaceous Hekkingen Formation. Three TOC trends, controlled by palaeobathymetric variations, and organic matter dilution, were identified within the two main organic‐rich sequences (sequences 2 and 3): (a) wells with the highest TOC values (>10 wt %) at the base of the succession; (b) wells with the highest TOC values at the top of the succession and (c) wells with high TOC values at the base and top of the succession. Our interpretation indicates that fault activity controlled the TOC trends in two different ways: Firstly, by creating a sharp topographic contrast‐triggering hyperpycnal flows, and shallowing the footwalls, where higher oxygen content and less developed stratified waters lowered organic matter preservation. Secondly, by significantly increasing the input of clastic material, which inherently led to dilution of organic matter and resulted in lower TOC values (

Prominent high-value gamma-ray spikes in the maximum flooding surfaces of the Middle Oxfordian-Kimmeridgian succession (Alge Member) display stratigraphic and regional variations in the southwestern Barents Sea. These variations suggest heterogeneities in the composition of the Alge Member, thus, challenging the common perception that this interval is a homogenous succession of organic-rich black shale. This study explores the overall variation in; clay mineral composition, source rock quality, minerals and macerals, core logs and seismic facies of the Alge Member. Gamma-log fluctuations were found to be independent of these variations. Uranium precipitates on sea bottom sediments when conditions change from oxic to anoxic. Fluctuations in sea level may result in such changes and, hence, guide gamma-ray responses. Sea level fluctuations also lead to a changing distance to the shoreline, which again influences sediment types, grain sizes, and source rock quality. Thus, indirectly sea level appears to be the common denominator, which sometimes matches source rock richness with spikes on gamma logs. Presence and absence of gamma-ray spikes are, hence, an additional tool to reveal the redox conditions in the SW Barents Sea, which has implications for the understanding of the paleogeography (or paleobathymetry) during deposition.

Summary The Upper Jurassic Hekkingen Formation is an important element of the petroleum system in the Barents Sea as the formation is the most prolific source rock in the area and in addition functions as a hydrocarbon seal. Current knowledge suggests that deposition of the Hekkingen Formation occurred during an early stage of rift initiation and a regional transgressional event, causing the detritus to be deposited in a restricted to open shelf environment. Paleogeographic interpretations commonly display the Hekkingen Formation to have a homogenous depositional environment over large areas, but the unit shows great variation in thickness and composition both laterally and vertically, indicating that the current understanding is to general. Two maximum flooding surfaces in the Alge Member of Hekkingen Formation display prominent high value spikes. The prominent spike could be caused by the total organic content (TOC) in the formation, or alternatively the spike could be caused by the mineralogical composition. The preliminary interpretations show that there is a difference in how the gamma-ray signal responds to the TOC content of the wells. This may indicate that other factors than TOC influence the gamma-ray readings in the source rock.