Abstract

Jurassic Corallian Formation outcrops along the Dorset coast, composed of carbonate and siliciclastic shallow-marine facies, are classic sites for British geologists. They have been regarded as typical of cyclically deposited strata, characterized by repeated sandstone, mudstone, and carbonate lithologies. The stratigraphy has been interpreted as evidence for rapid eustatic sea-level change throughout the Oxfordian. This study's basinwide database, however, shows that study of the outcrops alone has led to oversimplified conclusions. The stratigraphy records the migration of siliciclastic source areas through time. Pulses of terrigenous sand reflect local uplift and increased weathering, rather than rapid eustatic sea-level falls. The recognition of mixed siliciclastic-carbonate beds makes an argument for rapid changes in water depth less convincing, and reveals that lateral migration of shallow-water facies is a more plausible explanation for the observed stratigraphy. Coeval carbonate and siliciclastic deposition around the basin shows that neither eustasy nor climatic change can be solely responsible for the stratigraphy. The strata reflect, instead, a complex interplay of episodic local tectonism, siliciclastic source area migration, and marine circulation patterns.

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