A NEW PERSPECTIVE ON THE ZONATION AND CORRELATION OF BARREN STRATA: AN INTEGRATED HEAVY MINERAL AND PALAEOMAGNETIC STUDY OF THE SHERWOOD SANDSTONE GROUP, EAST IRISH SEA BASIN AND SURROUNDING AREAS

The integration of data from high-resolution heavy mineral and palaeomagnetic analyses of samples from nine East Irish Sea wells, and from onshore sections at St Bees Head and the North Cheshire Basin, has generated a temporally-constrained heavy mineral stratigraphy and regional correlation within the Triassic Sherwood Sandstone Group. These results have shown that the combined application of these two techniques offers an effective tool for extending the donation and correlation of barren strata into uncored wells. The lateral persistence of the heavy mineral zones, and the significant differences in the distributions of the heavy mineral varieties between individual zones, ay reflect tectonic events and, to a lesser extent, climatic variations. Plaeomagnetic results indicate that the original magnetisation of the analysed samples as acquired as a detrital remanent magnetisation and that the characteristic remanent agnetisation in the red beds was acquired during and shortly after deposition. agnetopolarities have been interpolated using the available data from which a composite eference section has been constructed. ll well sequences exhibit a regionally persistent three-fold zonation (Zones A, Band C, locally with subzones), defined by systematic changes in characteristic heavy mineral suites. Using a common sample set, the independently erected heavy mineral stratigraphy was tied to specific magnetostratigraphic Chrons. Heavy mineral Zone A coincides with a period of dominantly normal polarity, fixed hy a 244 Ma Chron of Middle Scythian age. A change in polarity from normal to reversed at >243 Ma coincides with the boundary of zones A/B. Zone B is Middle to Upper Scythian and shows a dominantly reversed polarityʹ. A well-defined Chron of 242.7 Ma has been detected close to the boundary of Zones B/C. Zone C is Anisian in age and is characterised hy a dominantly normal polarity.