Anyway, on Wednesday, May 23, we examined early Devonian rocks from the Helderburg Group up through the Hamilton Group (for those who know what I'm talking about) exposed in the mid-Hudson Valley from Kingston up through Catskill. These rocks consist of a whole series of limestones above the Taconic angular unconformity and extending upward into more shaly rocks. They're all marine witnessed by the abundant fossils of marine invertebrates including numerous species of bryozoa, brachiopods, gastropods (snails), trilobites, and corals (all of which we found in these rocks).
The Taconic angular unconformity. One day I'll write an entire post on
what this represents but for now I'll just say it shows the tilted Late Silurian
Rondout Formation on the left atop the almost-vertical Mid-Ordovician
Austin Glen Group on the right. Route 23, Catskill.
Even more significantly, these rocks are heavily folded into upward arching anticlines, downward sagging synclines, and cut through with fractures (joints), thrust faults, and mineral-filled veins. This package of early Devonian rocks in the Hudson Valley have been significantly shortened in a roughly east-west direction.
Hiking on vertically-bedded fossiliferous Becraft Limestone on the Catskill Creek.
These rocks form a small-scale fold-thrust belt (it has folds and thrust faults) that is very well-exposed and easy to study. Still, generations of geologists haven't really settled one important fact about these rocks - which orogenic event(s) deformed them - Acadian (Devonian) and Alleghanian (Pennsylvanian/Permian) or two different phases of the Alleghanian.