Key:

      RED circle — Panther Mountain Impact Structure
      YELLOW circles — Other possible impact structures
      H — Hudson River
      A — Ashokan Reservoir
      P — Pepacton Reservoir
      GREEN line — Great Wall of Manitou (Catskills eastern escarpment)
      K — City of Kingston, NY
      S — Village of Saugerties, NY
      W — Town of Woodstock, NY

In the eastern Catskill Mountains stands a strangely circular mountain, Panther Mountain, 3730 feet (1136 m) tall. The Esopus and Woodland Creeks wrap around three-quarters of the mountain's base before flowing into the Ashokan Reservoir. It's not Karst topography, as this is all shale and sandstone rock. In the 1940s, geologist George Chadwick thought that a natural gas deposit might be pushing up rock and forming a dome. The Dome Gas Company drilled a 6000 foot (1828 m) deep well and found gas, but not in commercial quantities. In the 1970s, New York State Geological Survey geologist Yngvar Isachsen studied it as a possible impact crater. The heavy jointing around it suggested a sharp discontinuity in the bedrock, such as a buried crater, and seismic and magnetic studies confirmed that there was something very odd here. Examination of the gas well's tailings (rock chips) found breccia and shocked quartz, very strongly suggesting the strike of an asteroid or comet some 375 million years ago.

Anyone looking at a relief map of the Catskills will notice a cluster of somewhat circular structures (stream beds cut down around higher ground), with Panther Mountain in the middle of the gently arcing cluster. Wouldn't it be interesting if these structures were also buried impact craters? What if a larger celestial body had broken up (perhaps by tidal stresses) as it neared Earth, creating a whole series of impacts (within seconds) in the late Devonian? It would not have been a good day for anything living in the area, but there was as of yet very little life on dry land. The cumulative impact (pardon the pun!) on Earth wouldn't quite approach something like the Chicxulub event, but it would still be nothing to sneeze at. These circular structures are indicated in yellow on the map (Panther Mountain is in red).

The astute reader will notice a number of other vaguely circular stream structures, particularly north of the main stream, possible multiple overlapping structures along the south shore of the Pepacton Reservoir, and possibly a huge double- (or even triple-) ringed one 18.6 miles (30 km) in diameter just south of Panther Mountain. These are a bit vague, so they are marked in a thin yellow line, but should be considered as possibilities. Any given circular arc stream bed could be a coincidental random occurrence, but there are so many here in a small area (in a region that otherwise exhibits dendritic stream drainage patterns) that other explanations should be explored.

How big an impactor?

An article^[1] suggests that to dig out a 6 mile (9.7 km) diameter crater would take about 16 Gigatons' worth of explosive energy, a roughly 2300 foot (700 m) diameter rock (at typical speeds and composition). Larger rocks appear to be less slowed by the atmosphere, so I'll assume that impact energy scales up with the cube of the rock diameter, and the excavated crater diameter with the cube root of the energy. For two impacts, add the energies together and calculate the original rock size and the resulting crater from these relationships. Taking the six most prominent circular structures (including Panther Mountain), if I did the math right, this would be about 96 Gigatons, producing (single impactor) an 11.3 mile (18.2 km) diameter crater from a 4200 foot (1280 m) diameter rock. Adding in the other 8 plus or so more speculative structures (including the 18.6 mile (30 km) diameter biggie), we get 512 Gigatons, producing a single 50 mile (80 km) diameter crater from a 18400 foot (5.6 km) rock. Not quite a Chicxulub, but it would still be bad for your health to be anywhere near such an event! If it was that bad, it might even take the blame for one of the late Devonian mass extinctions, such as the Kellwasser events. On the other hand, it's possible that even if some of these other structures are craters, that they might still be secondary impacts from debris tossed into the air.

Anyway, it would be interesting for geologists to consider the possibility of a multiple asteroid or comet fragment strike in the late Devonian, of considerable cumulative size. Seismic and magnetic studies wouldn't be terribly expensive, but drilling for tektites, breccia, iridium, and shocked quartz evidence might be a bit on the steep side, particularly if there is no prospect for mineral or fossil fuel wealth on the investment.

Practical effects

Unless we got lucky, and these were iron- and nickel-rich asteroid fragments, it is unlikely that more than tiny traces of valuable elements would be found. That would be fine by most people around here, as they would not be happy to have huge mines like Sudbury (Ontario) opening up.

A somewhat more likely scenario would involve the hydrocarbon-rich (natural gas) Marcellus Shale formation that the craters formed in. The more deeply buried Utica Shale layer might also be involved. The region's bedrock would be shattered to a considerable depth, which could have positive or negative effects on natural gas availability. It's not impossible that the broken rock would be "pre-fracked", allowing easy extraction of gas without the mess and dangers of hydraulic fracturing. That the test well drilled decades ago produced relatively little gas would suggest that this is not going to be the case. Another possibility is that over hundreds of millions of years, most of the trapped gas has already leaked out of the shattered shale, and there's not much left. A final possibility is that the gas is still there, but the bedrock has "healed" and would still require fracking to extract it. As most people in this region oppose fracking for obvious reasons, they would not be happy to have the area opened up to gas production. Even if non-fracked wells could be used, the disruption from burying pipelines and running noisy compressor stations would not be appreciated by most. This area is New York City's primary water supply, and the City would also be unhappy to see disruptions to the purity of its water from any sort of drilling activity.

https://www.parwestlandexploration.com/docs/(Revised)%20PantherMountainarticle%20for%20web%20site.pdf
https://craterexplorer.ca/panther-mountain-structure/
https://www.discovermagazine.com/the-sciences/the-panther-mountain-crater
https://en.wikipedia.org/wiki/Panther_Mountain_(New_York)
https://en.wikipedia.org/wiki/Late_Devonian_extinction

• ^[1]  https://en.wikipedia.org/wiki/Impact_event