Abstract

The Catskill facies of continental sediments consists principally of graywackes interbedded with conglomerates and of red sandstones and shales with a small percentage of green and dark shales and massive conglomerates. The Catskill sedimentation was introduced in early Hamilton times and represents a great series of alluvial-plain deposits laid down upon the land surface at the base of the re-elevated Taconic Mountains and grading into the sediments of an inland sea. The red shales are interpreted as flood-plain and deltaic subaerial topset beds into which the graywackes of the alluvial plain graded. Continental conditions of deposition were exaggerated as the Upper Devonian progressed, for the Katsberg beds in the east are increasingly conglomeratic.

The Catskill deposits are characterized by the extreme angularity of the grains of the sandstones. The pebbles of the conglomerates, on the other hand, are well rounded.

Barrell contended that the Catskill sediments were derived in the main from the western limits of the old Appalachian landmass, thus placing the source rocks to the southeast and east in an area now covered by Connecticut coastal plain deposits. The present author disagrees with this viewpoint and claims that the sediments had their origin in a near-by source to the north and east. The Taconic Mountain area is the most likely source, for it is situated in a suitable location and contains metamorphic rocks and quartz veins of similar character to the grains making up the graywackes and conglomerates. Moreover, sufficient evidence from structural considerations can be adduced to support strongly the hypothesis that orogenic forces were active in the Taconic area during Middle to Late Devonian.

In early Hamilton times the first orogenic movements began. These raised western New England above the shallow early Devonian seas and started the cycle of continental deposits. Short, rapid streams carried large amounts of detritus from the highlands and dumped their loads quickly on emerging upon a flat shore at the base of the mountains. Gradually an alluvial plain was built out and as the sea moved back, due both to further uplift and to the deposition of alluvial materials, an intermediate zone of flood-plain and delta materials developed between the alluvial plain and the sea. In this intermediate zone were deposited the red sediments that gave rise to the red beds. As time progressed, the shore line varied as did the depositional zones. Periods of quiescence or aridity moved the red-bed zone closer to the foot of the mountains, while renewed uplift increased the area covered by the coarse, angular deposits. Orogenic movements continued throughout the Upper Devonian with increasing vigor. There is no evidence to indicate an arid climate during the Middle and Upper Devonian, and the abundance of plant remains in the graywackes suggests a temperate climate with moderate but seasonal rainfall. . . .

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