In an early stage of building of the Devonian Catskill delta complex of New York state, a submarine topographic high developed 100 km offshore. On the landward side of the high, in an intermittently subsiding trough, sediment from an eastern source terrane accumulated as a landward-thickening and coarsening lithosome (Gilboa Formation) of interlensing gray siltstone and shale and very fine-grained sandstone with subordinate coquinite lenses. Locally abundant in the lithosome are ball-and-pillow structures, thin conglomerates, trace fossils, fossil seed ferns, sole markings, shallow cross-bedding, laminations, and ripple marks. The high was a barrier to clastic influx. On its seaward side, a carbonate lithosome (Tully Formation) formed. This formation has been subdivided into facies including: abraded calcarenite, chamoside oolite, skeletal calcilutite, barren shaly calcilutite, mound calcilutite, back-mound calcilutite, and encrinite. The effect of combined intermittent subsidence in the basin-margin trough and variation in rate of terrigenous influx is well expressed in the seaward part of the siliciclastic lithosome. Rapid subsidence and low terrigenous influx finally resulted in a short-lived carbonate transgression across the barrier prior to overwhelming of the shelf by terrigenous influx.

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