UPPER ORDOVICIAN-LOWER SILURIAN STRATA AND BIOTA FROM OFFSHORE SOUTH NORWAY

The shallow stratigraphic core 13/2-U-2 drilled northeast of the Farsu nd Basin penetrated 76.5 m of clastics and limestones of Late Ordovici an and Early Silurian age. The well represents the first record of Low er Palaeozoic rocks offshore south Norway and is the westernmost known extension of the Lower Palaeozoic Scandian foreland deposition area. Lithologically: the core can be subdivided into four units. The lower Unit A (Late Ashgill, Rawtheyan) comprises nodular limestones and shal es. The overlying Upper Ordovician Units B (Rawtheyan) and C (Hirnanti an) are predominantly of siltstones but also contain shale and limesto nes. The boundary between Unit B and Unit C seems to correlate with a locally defined reflector P marked on the digital seismic. Chronostrat igraphically, the Ordovician-Silurian boundary coincides with the boun dary between Unit C and the overlying Unit D, although basal Llandover y strata have nor been identified. Unit D, of early Silurian (Llandove ry, Rhuddanian) age, comprises shales with some siltstone and limeston e beds. All the units were deposited in shelf environments. The core d isplays a regression for the lower three late Ashgill units (A, B and C). This is transgressively overlain by Llandovery sediments deposited in slightly deeper water (Unit D). This development is comparable to what is observed in the contemporaneous successions of the western and northern areas of the Oslo Region.