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Geological Society, London, Special Publications; 1987; v. 29; p. 315-324;
DOI: 10.1144/GSL.SP.1987.029.01.24
© 1987 Geological Society of London

Part III Descriptive

Syn-sedimentary and burial related deformation in the Middle Jurassic non-marine formations of the Yorkshire Basin

J. Alexander

Department of Earth Sciences, The University of Leeds, Leeds LS2 9JT

The non-marine formations of the middle Jurassic Ravenscar Group consist of channel sandstone bodies set in interbedded mudstones, silts and thin sheet sandstones. These rocks contain syn-sedimentary and burial related deformation structures.

Frequent discharge fluctuations are deduced to have enhanced inherent river bank instability and with occasional tectonic movements produced a wide range of bank collapse structures. These had a low preservation potential and are observed at various stages of erosion.

Several faults associated with channel sandstones can be related neither to tectonic activity nor to bank collapse. They may be explained as compensation structures formed during differential compaction of the sandstones and adjacent mudstones. Differential compaction structures form on a smaller scale around plant material, early diagenetic nodules and sandstone dykes.

Continued sedimentation on the alluvial plain, together with differential compaction, produces a positive topography over channel sandstones. This effect was reduced by variations in deposition rate and facies. Laterally continuous beds deposited on this topography form gentle folds that are exaggerated by differential compaction during burial.

Although most of the deformation seen in the Ravenscar Group is related to alluvial processes or sediment burial, some is connected to syn-sedimentary tectonic activity.





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