Comparison of Permo-Triassic and deep structure of the Forties-Montrose and Jaeren highs, Central Graben, UK arid Norwegian North Sea

Abstract

Recent acquisition of high resolution, deep penetration seismic in the Central North Sea has permitted imaging of the basement structure. The results indicate strong similarities between the deep structures of the Jaeren and Forties–Montrose highs. The Triassic and Zechstein strata show a distinctive relationship on these graben margin and median highs. Interpretation of the pre-Zechstein structure may indicate the distribution of Devonian and Carboniferous intervals in an area where previous imaging of the deep section has not been successful. Southern parts of both the Jaeren and Forties–Montrose highs show the presence of a sub-Permian reflective package; this (?possible Carboniferous) sequence is absent in the north, where reflectors may be recognized within the deep section. A prominent horizontal reflector may represent a Middle Devonian limestone marker or the Devonian basal unconformity. This reflector may alternatively mark the top of Upper Paleozoic volcanic rocks. A deeper, westward- or northwestward-dipping reflector may represent the top of the crystalline basement or a deeper fault or shear zone of Caledonide origin. The potential occurrence of Carboniferous strata at depth over extensive areas of the Central Graben and surrounding highs would have important implications for exploration in the area. Carboniferous coal measures might provide a sub-Zechstein gas-prone hydrocarbon source.