Abstract
A composite magnetic polarity pattern of the Portland and Purbeck Beds (Portlandian to Berriasian age) is constructed from nine sections in the Dorset and Wiltshire regions of southern England. This pattern is tentatively correlated to the Tithonian-Berriasian magnetic polarity time scale of the Tethyan faunal realm. The shallow-marine Portland Beds began deposition during polarity chron M21r (mid-Tithonian), contain a transgressive hiatus encompassing chron M20r, and were terminated by emergence during chron M19r (Late Tithonian), corresponding to the base of the Durangites ammonite Zone in the Tethyan realm. The terrestrial to marginal-marine Purbeck Beds encompass polarity chrons M19r through M14r, implying deposition from latest Tithonian (Late Portlandian) to the beginning of the Valanginian stage. The Cinder Bed transgression of the middle Purbeck Beds occurred at the beginning of chron M17n, corresponding to the Berriasella privasensis ammonite Subzone in the Tethyan realm. The mean paleomagnetic pole of the Purbeck Beds is at 71.2°N, 207.8°E (dp/dm=3.6°/5.1°), implying a paleolatitude of 34°N.
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