*The term “structure” is used to define an impact crater that is severely altered by erosion.
Type: Central peak (inverted relief)
Age (ma): ~375 (geological analysis)**
Diameter: 10 km
Location: New York, USA. N 42° 04′ W 74° 24′
Shock Metamorphism: Magnetic spherules, microtektites with gas bubbles and PDF in quartz.
**The relationship of the structure with the bedrock and the covering sedimentary layers suggest this impact passed through the Middle and Lower Devonian section (Y.W. Isachsen, 1999, 2000).
The Panther Mountain circular feature is located in the Catskill Mountains in the town of Shandaken in Ulster County, NY. It is a circular mountain mass, 10 km in diameter and surrounded by an annular drainage pattern formed by Esopus Creek and its tributary Woodland Creek. The circular pattern made by the two creeks suggested to the late Yugvar Isachsen that the circular feature may be an impact crater buried beneath the surface. To prove his hypothesis, Isachsen had several geologic and geophysical studies of the feature. Ground exploration studies indicated unusually closely spaced fractures in the valleys of Esopus and Woodland Creeks thought to be due to overlap of sediments over the rim of the crater. Gravity studies indicated a small gravity low over the mountain believed to be caused by low density fractured rock in the crater. Finally, a study of over 660 cuttings from the Herdman gas well in the crater revealed the presence of black magnetic spherules, and pressure deformation features (PDFs) in quartz.
More recent seismic reflection surveys were conducted along Little Peck Hollow at the west side of the crater. No reflections occur above the 0.7 seconds two-way-travel time (1.7 km depth) suggesting no stratification or layering above 1.7 km. A reflection at 1.7 km depth may be interpreted as evidence of impact. A reflection at 1.02 secs (2.2 km depth) could be due to limestone beneath the crater. A reflection at 1.3 secs (3,000m) is due to the Precambrian metamorphic rocks (Occhi et al 2011).
The Catskill Mountains have evolved with the erosion of kilometres thick sedimentary rock over a period of 375 million years. The landsat image (Courtesy NASA/LPI) of the Catskills reveals the randomness of this mountain forming erosion. The circular anomaly indicated in the center of the superimposed square is postulated to be the result of an impact event. For reference, the Hudson River is on the right. A magnified view of the round anomaly illustrates the circular valley formed by the Esopus Creek and suggests a “crater like” structure. It was from these images that Y.W. Isachsen began his study of this structure to seek evidence of an impact event.
Scientists speculate that the fractured rock in the crater itself could act as a reservoir for natural gas. The Panther Mountain crater may intersect rock layers that produce natural gas in other parts of the state, and similar craters have been tapped for fuel. At one time Dome Oil Company had drilled a well into Panther Mountain and for a time was producing 50,000 cubic feet of gas a day.
In the Devonian Quaternary, the probable time of impact, this landscape was a gentle sloping plain with the Acadian Mountains to the east and the saltwater Kaskaskia Sea to the west. The life forms on earth at that time included early land plants, amphibians and ammonites. Over the next 375 million years;
Erosion reduced the Acadian Mountains creating an alluvial plain to the west;
The impact site was first filled then covered by kilometres of this sediment;
The sediment hardened into a kilometres thick sedimentary rock cover;
The layer of fractured rock under the crater compressed and caused the sedimentary rock layer above it to sag. The sagging caused the sedimentary rock to stretch over the crater rim. This formed small easy to erode joints at these stress points;
Throughout the Catskills the natural cracks in the sedimentary rock are formed approximately every three meters. The cracks in the joints around the crater rim are ten times that density.
These cracks allowed the accelerated erosion of the rim sedimentary rock from glaciers, rivulets, springs and creeks. The alluvial plain evolved into the present day Catskill Mountains, and;
The Esopus creek eroded a circular valley through the small joints over the rim of the crater.
Aerial Exploration of the Panther Mountain Structure
We approached the structure from the north along its eastern rim. This plot shows the random pattern we flew over the structure to get our images. We were limited to 3000’ above ground because of cloud cover and at this low altitude the crater feature was not easy to identify. I understood how large the feature was before I started on this trip, but when I first saw the structure, its immensity astonished me! I used the GPS to confirm that I was actually looking at the crater structure.
These images are documented as we circled the crater structure in a counter-clockwise direction. Looking northwest from the eastern rim (images upper left & right), the circular shape of the feature is obvious. In these images note the road and valley veering off to the left background. This is the eroded valley directly over the crater structure rim. The distance from the valley floor to the peak of Panther Mountain is approximately 800 meters. Seismographic studies inferred that there are concentrated joints in all parts over the crater structure rim. The joints make it relatively easier for streams to erode the rocks over the crater rim and form the circular shape.
A negative gravity anomaly centered at this peak gives evidence that there is a zone of shattered rock deep beneath the mountain. Specifically, the Earth’s gravity is slightly weaker above the mountain than was expected (confirmed by gravitometer). This suggests that the rock beneath the mountain has been disturbed, making it less dense. The zone of disturbed rock, in turn, could account for the larger number of joints found along the edge of the circle. As the fractured rock material settled, the overlying sedimentary rocks sagged, and the joints formed around the edge of the circle to relieve the stress.
The amount of sedimentary rock deposition and the erosion that has occurred over the past 375 million years is displayed. The crater structure itself is over 800 meters below the peak of Panther Mountain. This is the area of the upper part of the Esopus Creek where closely-spaced joints in the bedrock near the stream were documented. In the lower reaches of the stream (to the north), the bedrock is buried beneath glacial deposits.
Ground Exploration of the Panther Mountain Structure
Following my crater exploration tradition, I just had to physically stand on the structure that was formed under Panther Mountain. I wanted to do this even though the “crater” of Panther Mountain is under approximately a kilometre (~3300 feet) of sedimentary rock and is not physically accessible.
It is a relatively easy but long climb and hike from the south parameter parking lot to the summit. Panther Mountain at approximately 1,135 metres (3,720 feet) in elevation is the 18th highest in this uplifted Catskills region.Hundreds of millions of years ago the eroded remnants of the Acadian Mountains to the east were deposited here to form Panther Mountain and the Catskills. The sediments traveled westward and formed a delta into the sea that covered the area at that time. This delta was then uplifted and eroded.
I took this image at the top of the structure looking to the north-east. Starting from the left of the image and panning to the right you will notice the “blue” colour of the distant hills compared to the true colour of the foreground hills. Hidden behind the foreground hills is a valley made from the creeks eroding through the rocks that cover the circular crater rim. The actual crater structure rim is buried under several hundreds of metres of rock. Looking toward the crater rim from here gave me an appreciation of the magnitude of this impact as the distance to that hidden valley is only the radius of the structure.
In summary, approximately 375 million years ago an impactor made contact here in a shallow sea creating a 10 km (6.21 mile) diameter crater. This crater eventually filled with sediments and through the process of uplift and erosion became Panther Mountain. The mountain took the shape of a longitudinal ridge in the center of the rough circle eroded by Esopus and Woodland creeks. The resulting “inverted relief” structure (described below) is BIG, and I am looking forward to researching any future geological investigations here.
Panther Mountain Crater “Analog” on Mars
An “analog” of the Panther Mountain meteorite crater was recently documented on the surface of MARS by the MARS EXPRESS of the European Space Agency.This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, shows part of a heavily eroded impact crater at Solis Planum, in the Thaumasia region of Mars.
This circular plateau may be an old impact crater which was filled by sediments. Over time these sediments in the crater developed a harder consistency than the surrounding material. Later, the more easily eroded surrounding material was removed by erosion and the harder inner filling remained forming the circular plateau. This phenomenon is called ‘Inverted Relief’.
Inverted relief, inverted topography, or topographic inversion refers to landscape features that have reversed their elevation relative to other features. In the case of Panther Mountain, the geological fractures around the crater rim had greater susceptibility to differential erosion. The less resistant surrounding “rim” material eroded at a faster rate creating the circular valley around the mountain.
Panther Mountain, located in the Catskill Mountains, New York, is a circular mass, 10 km in diameter, defined by an anomalous circular drainage pattern. Earlier surface and gravity studies led to the conclusion that the circular valley reflects the rim of a deeply buried impact crater 10 km in diameter. The nearest subsurface information is provided by well cuttings from the 2000 m-deep Herdman gas test well located near the northern edge of Panther Mountain. Some 660 bags of washed cuttings were examined microscopically for evidence of impact. Seven black magnetic spherules, measuring 200-950 micrometers in diameter were found in the Herdman well at the Middle-Upper Devonian boundary and three much smaller ones at the same stratigraphic position in the Armstrong well, one crater diameter distant. Most spherules retain a core of iron + nickel beneath an ablation rind of magnetite, and are clearly of cosmic origin. Their presence, combined with their decrease in size and number going outward from the structure, support the proposed model of a buried complex impact crater, but do not prove it. Current studies, however, confirm the existence of an “intact impact” beneath Panther Mountain. Seventy-five thin sections of quartz-rich layers in the Herdman and Armstrong wells were prepared to search for pressure deformation features (PDFs), which would prove impact. Examination of several thousand grains to date reveals numerous examples of PDFs. Initial thin-section study focused on the stratigraphic intervals where spherules had been found earlier in both wells. In the Herdman well, a 10 meter interval near the Middle-Upper Devonian boundary contains both PDFs and metallic cosmic spherules. PDFs and spherules are also found at this stratigraphic position in the Armstrong well. Thus PDFs exist in both the fallback zone and the fallout apron. Inasmuch as the central fracture zone of the crater transects Lower and Middle Devonian strata, which contain numerous gas producing formations in central and western New York State, the structure possesses economic potential for gas production and storage.
New York State Geological Survey/State Museum, Albany, NY 12230, firstname.lastname@example.org; HANLEY, Kristy, Dept. of Earth and Atmospheric Sciences, University at Albany, Albany, NY 12222
Principal investigator: Yngvar W. Isachsen Project years:1994 – Present
Keywords: impact craters, spherules, pressure deformation features (PDF’s)
Geographic extent: Catskill Mountains, West of Kingston
Project description: Searching for terrestrial impact craters was greatly stimulated by the manned lunar landing experiment, and has resulted in the discovery of more than 160 craters to date, a third of them buried from view by post-impact sediments. The Panther Mountain circular feature in the Catskills has such an explanation. The mountain, located west of Kingston, is defined by an anomalous circular valley that is easily recognized in the highway pattern on a road map. Earlier evidence from satellite images, surface geologic and geophysical studies (reference below), and the recent discovery of minute cosmic spherules of iron + nickel, cobalt and chromium in deep well cuttings, led to the interpretation that the circular valley reflects the rim of a deeply buried impact crater 10 km in diameter. An ongoing study of 75 thin sections of deep well cuttings has revealed the presence of impact-generated deformation lamellae in quartz grains, which confirms this interpretation. The buried crater provides a large potential reservoir of impact-fractured rock for natural gas accumulation and storage.
Present research, some of it described in an illustrated Albany Times Union article in early March, 1999, builds on that continued in an earlier publication: Isachsen, Y.W., Wright, S.F., and Revetta, F.A., 1994, The Panther Mountain circular feature possibly hides a buried impact crater. Northeastern Geology, v. 16, no. 2, p. 123-136.
Kaatskill Life Magazine
A non-technical article on the impact crater hypothesis, based on an earlier paper by Isachsen and others, appears in a 1992 issue of Kaatskill Life Magazine. It was written by Professor Robert Titus, and is titled “The Panther Mountain asteroid impact”.
The Panther Mountain circular structure is located in the Catskill Mountains near the eastern edge of the Allegheny Plateau where depth through the sedimentary section to basement is about 3200 m. The structure is distinguished from the rest of the Plateau only by its physiography. It is a circular mountain mass, 10 km in diameter, defined by an anomalous annular drainage pattern formed by Esopus Creek and its tributary Woodland Creek. Because of pervasive fluvial cross bedding in the sedimentary pile, the authors were unable to determine whether the structure is slightly domical, sightly basinal, or unwarped. North-south and east-west gravity profiles were next made and modeled to look for a subsurface explanation for the structure. The only computed profiles that matched the measured values were those for a shallowly-buried meteorite crater with its underlying breccia lens, lying beneath the Panther Mountain. Renewed interest in the structure led them to make 125 new gravity measurements, in a study that is continuing. Gravity values are corrected using the International Gravity Formula of 1967 and densities of 2.67 and 2.50 gms/cm[sup 3]. Terrain corrections were computed using an inner radius of .895 km and an outer radius of 166.70 km. The complete Bouguer gravity anomaly was separated into its regional and residual components to obtain a third order residual gravity map for computer modeling. The residual gravity map confirms the earlier detected gravity low and leaves the buried meteorite crater model as a viable model.
Journal Volume: 25:2; Conference: 28. annual Geological Society of America (GSA) Northeastern Section meeting, Burlington, VT (United States), 22-24 Mar 1993
Isachsen, Y.W. and Hanley, K., 2000, Panther Mountain buried impact crater is confirmed. Geological Society of America Abstracts with Programs, vol. 32, no. 1, p. A26.
Isachsen, Y. W., Cosmic spherules support the interpretation of a buried impact crater beneath Panther Mountain in the central Catskill Mountains, New York. In Detre, C. H. [ed.] Terrestrial and Cosmic Spherules, Proceedings of the 1998 Annual Meeting TECOS. Akademiai Kiado, Budapest, p.73-79, 2000.
OCCHI, Michela and REVETTA, Frank, IS PANTHER MOUNTAIN CIRCULAR FEATURE A CRATER?. Geological Society of America Abstracts with Programs, Vol. 43, No. 1, p. 84, 2011