Last week, I visited the Taconian Unconformity in the Catskills region of New York. I found out about the outcrop via the informative website the USGS put together in 2003 to explain southeastern New York's varied and interesting geology (Click here for a map).

Here's me at the angular unconformity, demonstrating the layering with my forearms:


Here's the same outcrop, sans goofball, avec annotations:


This is a classic angular unconformity. It even graced the cover of the (excellent) GSA publication Excursions in Geology and History: Field Trips in the Middle Atlantic States (Frank Pazzaglia, editor; cover photo by Marli Miller). Why should we care? Because like the "original" angular unconformity at Siccar Point in Scotland (described by James Hutton), this outcrop represents a lot of geologic time. First, during the Ordovician period, the Austin Glen formation had to be deposited as layers of clastic sediment in an ocean basin. Then, during the late Ordovician Taconian Orogeny, those layers had to be deformed: folded and buckled so they stood up on end, and then eroded down to their nubs. Then, on that newly-formed erosional surface, a fresh layer of sediment had to be laid down, in this case, the Rondout Formation was deposited as a layer of carbonate mud during the late Silurian period. Then, that too was deformed, during the Devonian period's Acadian Orogeny. Finally, the whole package had to be uplifted to the surface and exposed (in this case, when a highway roadcut was completed). That's a lot of time!

I'm delighted to have had the opportunity to visit it first-hand!

Labels: devonian, maps, mountains, new york, ordovician, silurian, structure, travel, unconformities