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The Middle Jurassic Garn Formation of the Haltenbanken area has been studied using mineralogical and geochemical data from 21 wells, ranging in burial depths from 2.0 to 4.1 km relative to seafloor (RSF). K-feldspar and plagioclase contents show variations on a regional scale both laterally and as a function of burial depth. The content of pore-filling authigenic illite increases sharply, and the content of K-feldspar and kaolinite decreases in Garn sandstones presently at depths greater than 3.6-3.7 km RSF (120-130؇C). The depletion in Kfeldspar below 3.7 km RSF is not accompanied by lower potassium values in the bulk chemical composition (wt % K 2 O). This suggests that the potassium released during K-feldspar dissolution is retained in the sandstones and is precipitated as illite. The variations in bulk contents of potassium and sodium are therefore considered to be related principally to primary variations in sandstone mineralogy.The shallower sandstones (Ͻ 3.7 km RSF) with average wt % K 2 O greater than 0.95 (K/Al molar ratio Ͼ 1/3) have a K-feldspar:kaolinite ratio greater than one. The deeply buried (Ͼ 3.7 km RSF) sandstones with similar potassium contents contain excess K-feldspar and most of the kaolinite is illitized. However, deeply buried sandstones containing an average of 0.38 wt % K 2 O (K/Al molar ratio Ͻ 1/4) contain a significant amount of kaolinite but negligible K-feldspar. This suggests that the K-feldspar:kaolinite ratio before the onset of illitization was less than one, and hence that the kaolinite-illite reaction has been restricted by an insufficient supply of potassium (absence of K-feldspar). This illustrates how illitization of kaolinite depends upon K-feldspar as a local source of potassium. Prediction of illitization in sandstones, therefore, must be based on integration of models for provenance, facies, and early diagenesis in addition to burial and thermal history. The formation of pore-filling authigenic illite in these sandstones is an important influence on the total reservoir quality.

Sandy clinothems are of interest as hydrocarbon reservoirs but there is no proven, economic, clinothem reservoir in the Norwegian Barents Sea. We used high‐resolution, 2D and 3D seismic, including proprietary data, to identify a previously untested, Barremian, clinoform wedge in the Fingerdjupet Subbasin (FSB). Data from recent well 7322/7‐1 plus seismic have been used to characterize this wedge and older Lower Cretaceous clinoforms in the FSB. In the latest Hauterivian – early Barremian, during post‐rift tectonic quiescence, shelf‐edge clinoforms (foreset height > 150 m) prograded into an under‐filled basin. Increased sediment input was related to regional uplift of the hinterland (northern Barents Shelf). Early Barremian erosion in the north‐western FSB and mass wasting towards the SE were followed by deposition of delta‐scale (<80 m high), high‐angle (c. 8°) clinoform sets seaward of older shelf‐edge clinoforms. This may be the local expression of a regional, early Barremian, regressive event. By the close of the Barremian, clinoforms had prograded, within a narrow, elongate basin, across the FSB and towards the uplifted Loppa High. A seismic wedge of high‐angle (10–12°), low‐relief, delta‐scale (25–80 m) clinoform sets occurs between shelf‐edge clinoforms to the NW and the uplifted area to the SE. Well 7322/7‐1, positioned on a direct hydrocarbon indicator, <1 km NNW of the high‐angle, low‐relief, delta‐scale clinoforms, found upward coarsening siltstone‐cycles linked to relative sea‐level fluctuations on a marine shelf. Sand may have accumulated, offshore from the well, in high‐angle, low‐relief foresets of the delta‐scale clinothems (which are typical geometries elsewhere interpreted as ‘delta‐scale, sand‐prone subaqueous clinoforms’). Deposition was controlled by the paleosurface, storms and longshore currents on an otherwise mud‐dominated shelf. The study highlights challenges associated with exploration for sandstone reservoirs in seismic wedges on an outer shelf.

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Dual-sensor cable seismic data has been acquired over the Eastern Mediterranean area. The data has improved the seismic quality, and this has enhanced the understanding of the subsurface of the region. In this paper, we take this dual-sensor data, merged with conventional seismic data to review the offshore areas of Cyprus and Lebanon in the Eastern Mediterranean. The regional geology of the area has been summarized, and the horizons and intervals most significant for hydrocarbon exploration have been described. A brief introduction to the dual-sensor technology and its benefits are described, but the main focus of the paper is to show how the regional geological understanding has been increased based on the new seismic data. Selected regional profiles over the Levantine and Herodotus Basins with their associated areas including the Eratosthenes Continental Block, the Cyprus Arc and deformation front and the Levant Margin illustrate the principal tectonic features and regional key horizons. In addition, specific seismic lines are presented to illustrate particular depositional features, as a possibly large clastic system in the north-eastern part of the Levantine Basin. Isopach maps are used to describe the thickness variations across the area. Parts of the region may contain all the ingredients for a working petroleum system with the key ingredients of potential source, seal, reservoir and trap in place. In addition it is possible that the size, geological complexity and lack of well-data, mean that the existence of ‘yet to be discovered’ play-types in the area cannot be entirely discounted?