The Bajocian ‘Cornbrash’ of Raasay, Inner Hebrides: palynology, facies analysis and a revised geological map

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Abstract
Synopsis: The ‘Cornbrash’ of Raasay, so long an enigma of Upper Bathonian facies reconstructions for the Inner Hedrides, is shown to be of late Bajocian ( subfurcatum Zone) age. Informally renamed the Glam Sandstone, it forms the uppermost part of the Raasay Sandstone Member of the Bearreraig Sandstone Formation and correlates with similar facies on the neighbouring Isle of Skye. The palynofloras of the Glam Sandstone and strata of known late Bathonian–early Callovian age on Skye are compared. The Glam Sandstone was deposited in a marine sand belt on an exposed shelf, and the coarse-grained terrigenous component reflects severe erosion of basin margins and surrounding hinterland during eustatic sea-level fall. Upward facies change to ammonitiferous shale reflects the late Bajocian global sea-level rise. A revised geological map of eastern central Raasay is presented. NW-SE trending step-faults explain the repetition of the Middle Jurassic sequence across the island.

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