Abstract

The Upper Devonian (lower Famennian) Cove Fort Quartzite and associated strata of western Utah comprise three stratigraphic sequences, each containing a thick (as much as 65 m) lowstand systems tract. Coarse-grained shoreface quartz arenite and lagoonal dolomicrite of the lowstand systems tracts display the following features characteristic of forced regression: (1) they contain coarse-grained proximal shoreline deposits that overlie an erosional surface (sequence-bounding unconformity) cut into fine-grained distal-marine carbonate facies; (2) they lie seaward of a zone of sediment bypass, and are spatially detached and separated from the previous highstand shoreface; (3) they are confined geographically to a relatively narrow zone less than 30 km wide; (4) they are onlapped and overlain by transgressive systems tract deposits consisting of deep subtidal carbonates (West Range Limestone); and (5) landward of the lowstand shoreline pinch-out, the sequence-bounding unconformity beneath them merges with a transgressive surface of erosion above them. A thick wedge of siliciclastic forced-regression deposits is present at the base of each depositional sequence. The stratigraphic position of each wedge above the basal sequence boundary was controlled by eustatic sea-level fall. The forced-regression deposits are geographically restricted to a narrow strike belt along the eastern margin of the Pilot basin, which coincides with the trace of the Cordilleran Hingeline, a zone of crustal discontinuity. The geographic confinement and unusual stratal thickness of barrier-bar complexes in the lowstand systems tract, as well as the stratigraphic stacking of the forced-regression deposits, were controlled by flexurally induced high subsidence rates focused at the Cordilleran Hingeline.

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