Abstract

Stratigraphic evidence suggests that Rochester shale facies belts are elongate east-west parallel both to a northern paleoshoreline and also to the present outcrop trend. The Rochester Shale consists of sparsely to richly fossiliferous, gray, shaley mudstone with abundant interbedded carbonates, including intrasparrudites, lenticular biosparites and biomicrites (= calcarenites) and laminated pelmicrites (= calcisiltites). Such interbeds provide evidence for episodic concentration and transport of carbonate sediments by storm-wave action on a gently southwards-sloping shelf. Calcarenite lenses were formed as erosion-lag deposits in regions within storm-wave base. Vertical facies changes in the Rochester Shale are attributed to north-south shifting of environmental belts, due to migration of the northern paleoshoreline. As a whole, the formation comprises two (eustatic?) transgressive-regressive cycles. The Lewiston Member represents a nearly symmetrical cycle of deepening (units A-C) and shallowing (units C-E), while the upper units (Burleigh Hill, Stoney Creek) reflect aspects of an asymmetrical, shallowing-upward hemicycle. During the last event, allodapic carbonate sedimentation was considerably increased, as a result of migrating crinoidal bars, inhibiting the growth of bryozoans and other organisms.--Modified journal abstract.

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