PANTHER MOUNTAIN STRUCTURE

Detailed gravity mapping of the Panther Mountain circular structure, Catskill Mountains, New York

Isachsen, Y W ; Revetta, F A

Abstract
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. 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; Journal ID: ISSN 0016-7592

METALLIC SPHERULES AND A MICROTEKTITE SUPPORT THE INTERPRETATION OF A BURIED IMPACT CRATER BENEATH PANTHER MOUNTAIN IN THE CENTRAL CATSKILL MOUNTAINS, NEW YORK.
Y. W. Isachsen, New York State Geological Survey/State Museum, Albany NY 12230, USA (e-mail: yisachse@mail.nysed.gov)

Introduction: Panther Mountain is located in the Catskill Mountains, a region of flat-lying Paleozoic sedimentary rocks that forms the eastern edge of the Allegheny Plateau. It is a circular mass, 10 km in diameter, located immediately west of Phoenicia, New York, and rises 800 m above the valley floor. The mountain is defined by an anomalous circular drainage pattern, vividly shown on Landsat images, that invites a geological explanation. Initial work included photogeology (Landsat and stereo airphotos), surface geologic study, shallow seismic refraction profiling, gravity and magnetic measurements, and gravity modeling [1].

Pervasive fluvial cross-bedding in the terrigenous strata of the region made it impossible to determine whether the feature is slightly domical, slightly basinal, or unwarped. However, it was clear that high joint density accounts for the greater erosion that produced the circular valley.

Gravity mapping defined a crudely-circular negative anomaly with a relief of 6 mGals, most anomalous for an area of flat-lying stratigraphy 3000 m thick. A measured gravity profile was satisfied by a computed profile of a shallowly buried (~1 km) complex impact crater with a diameter of 10 km and a central uplift of brecciated and shattered rock ~1 km in thickness. The modeled crater, a syndepositional structure, would pass through the Middle and Lower Devonian section. The relatively high joint density that is responsible for erosion of the ring valley is attributed to the influence of the buried crater rim on the geometry of sedimentation, especially factors of differential compaction and cementation. The failure of fracture-controlled linear valleys north and south of Panther Mountain to extend across the mountain mass is explained by absorption of the regional stress energy by impact-produced brecciation below.

Investigation: The only direct access to subsurface information is provided by the 2000-m-deep Herdman gas test well located near the northern edge of Panther Mountain. The hole, produced by a percussion drill, yielded mainly 1–2- mm size rock cuttings. Such cuttings are customarily bagged for every 3–4-m depth interval, and used to construct the stratigraphic section. Before study, however, each bag of cuttings is placed in a liter beaker of water, stirred vigorously, and decanted, to remove the fine-grained “dust” fraction. Some 600 bags of such washed cuttings were painstakingly searched for spherules and microtektites, using a binocular microscope with zoom lens. Thin sections were made of selected grain mounts to search for planar deformation lamellae in quartz and other features of shock metamorphism. Observations: Seven magnetic spherules, measuring 0.2–0.8 mm were found at the depth interval 573–578 m in the Herdman well, and three at 902–904-m depth in the Armstrong well, 12 km to the west. A pale brown microtektite with gas bubble hollows was identified at 627–630 m in the Herdman well. No impact features were recognized in the thin secitons.

Interpretations: The washing of the samples probably removed most microtektites that might have been present, as well many of the very small spherules. The magnetic spherules found in the Herdman and Armstrong wells fall in the same stratigraphic interval and thus appear to represent the stratigraphic position of impact, which happens to be at or near the Middle-Upper Devonian boundary. The microtektite could also have originated at this position and become dislodged from the wall when the drill bit had reached the lower levels.

Future Work: Microprobe analyses will be made of representative spherules. Cuttings from several more distant deep gas test wells will be examined for further evidence of impact.

References: [1] Isachsen Y. W et al. (1994) Northeastern Geology, 16, 123–136

INTERPRETATION OF GEOPHYSICAL DATA OVER PANTHER MOUNTAIN CIRCULAR STRUCTURE
Michael and REVETTA, Frank, Geology, SUNY Potsdam, 44 Pierrepont Avenue, Potsdam, NY 13676, revettfa@potsdam.edu
The Panther Mountain circular structure is located in the Catskill Mountains near the eastern edge of the Allegheny Plateau. It is a circular mountain mass, 10km in diameter and surrounded by a annular drainage pattern formed by Esopus Creek and its Tributary Woodland Creek. It is believed by the late Y.W. Isachsen that the feature is a meteorite crater. North-south and east west gravity profiles conducted across the mountain indicate a small gravity low over the mountain which would be consistent with low density breccia in the crater. Also support of the crater hypothesis is in the study of seventy five thin sections of quartz rich layers showing pressure deformation features (PDF) and black magnetic spherules, which suggest an impact origin.

In 2000, several universities loaned their exploration seismographs to conduct seismic reflection surveys. The seismic traverses were conducted along Little Peck Hollow Road in the southwestern area of the structure. The purpose of the survey was to image the area around the rim to determine if strata outside the rim was undisturbed while the structure inside the rim was disturbed.

The seismic survey indicated that a reflection inside the crater area shown on the Little Peck section also occurs on the Maben-Hill section outside the Panther Mt. region. This does not support the crater hypothesis however, more seismic surveys, to see if the reflector at .7s is disrupted in the crater, are needed. – March 2007

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.