Abstract. The ostracod fauna of a thin unit of shelly mudstones encountered directly beneath the Great Oolite Group in a recently drilled borehole in north Lincolnshire confirms the presence of the Scarborough Formation, formerly thought of as being confined to the Cleveland Basin. Sandstones and coals separating the Scarborough Formation from typical upper Lincolnshire Limestone calcarenites were probably deposited by delta progradation and are correlated with the regressive Yons Nab Beds and lower Gristhorpe Member of the Cleveland Basin.

Discovery of the Gristhorpe Member and the Scarborough Formation beneath the basal Great Oolite unconformity on the East Midlands Shelf suggests that the youngest limestone facies of the Lincolnshire Limestone can be no younger than earliest sauzei Zone, and that the erosional event which preceded deposition of the Great Oolite is of late humphriesianum Zone or younger age.

A revised palaeogeography for Scarborough Formation times envisages that following initial westward marine transgression along the axis of the Cleveland Basin, the sea broadened and at its maximum extent covered much of the Market Weighton Block.