CRETACEOUS DEPOSITIONAL SYSTEMS IN THE NORWEGIAN SEA - HEAVY MINERAL CONSTRAINTS

Deep-water Cretaceous sandstones in the Norwegian Sea were deposited b y a number of distinct sediment transport systems tapping different se diment source terrains. Three distinct sandstone types (K1, K2, and K3 ) have been identified, distinguished, and mapped on the basis of a co mbination of heavy mineral parameters, Sandstone type K1 occurs on the Trondelag Platform, Halt-en Terrace, and Nordland Ridge, but does not appear to be present in the deeper water Voring Basin. Sandstone type K1 was ultimately derived from the Scandinavian landmass with detritu s sourced from metasediments of the Caledonian fold belt, intrusives o f the Trans-Scandinavian Igneous belt, and, to a smaller extent, Sveco fennian basement, K1 sandstones were deposited on an unstable slope by debris flows and slumps, with minor reworking by bottom currents. San dstone type K3 was derived from the Western Gneiss region farther sout h on the Scandinavian landmass. Sandstone type K2 occurs in more basin al locations in the Norwegian Sea and was not supplied by the systems operating along the Scandinavian margin because its mineralogy contras ts with that of K1 and K3. K2 mineralogy is not consistent with a sour ce in the Lofoten area or East Greenland; therefore, K2 is believed to represent the deposits of a separate axial transport system fed by a source that lay in northeast Greenland. K2 zircon ages indicate involv ement of Early Proterozoic (approximately 2000 Ma) and Ardlean basemen t, together with metasediments of the Caledonian fold belt. Previous s edimentological models for the Cretaceous of the Norwegian Sea suggest that sand deposition occurred as slumps and debris flows along the co ntinental slope, resulting in discontinuous and unpredictable sandston e units, unless they become amalgamated into thick reservoir sequences , The mineralogical evidence indicates that this model can be applied only to sandstone types K1 and K3. By contrast, sandstone type K2 repr esents sediment introduced from the conjugate margin of the basin and occurs up to 200 km from its detrital source region; therefore, K2 is likely to occur as more predictable, sheetlike bodies on the basin flo or.