GEOMORPHOLOGY
The scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or near the Earth’s surface. The following examples illustrate the shortcoming of using geomorphology in crater identification:
Alsever Lake (image LEFT) is located at the southern boundary of Algonquin Park. It is similar in appearance to the Brent impact crater (image RIGHT) at the northern boundary of Algonquin Park. Both structures have two distinct bodies of water forming a circular patterns.
Presqu’Ile Impact structure – IMPACTLake Skootamatta – NON IMPACT
Scootamatta Lake (image LEFT) is located in Southern Ontario. It is similar in appearance to the Presqu’ile impact crater (image RIGHT) located in north central Quebec. Both structures have distinct bodies of water forming circular patterns.
Merewether structure (image LEFT) is located in Labrador. It is similar in appearance to the Whitecourt Impact Crater in Alberta. Both structures are bowl shaped.
In August 2020, the RAS Institute of Oil and Gas Problems, supported by the local Yamal authorities, conducted a major expedition to the new crater. Skoltech researchers were part of the final stages of that expedition Credit: Evgeny Chuvilin
The Holsinger meteorite is the largest discovered fragment (639 kilograms) of the meteorite that created Meteor Crater and it is exhibited in the crater visitor center. (From Wikipedia)TOP: The shocked Coconino Sandstone (Kieffer 1971) is weakly shocked sandstone (<10 GPa) that lacks remnant porosity and contains abundant grain comminution and fracturing. Note the “rock flour” on the shocked sample. BOTTOM: The unshocked Coconino Sandstone consists of a fine to medium-grained, moderately well-sorted, rounded quartz arenite with ~ 20 vol% porosity. Coconino sandstone layers are typically buff to white in color. It consists primarily of sand deposited by eolian processes (wind-deposited) approximately 260 million years ago.Shocked Coconino sandstone (3 X magnification)Possible coesite sample within the Barringer crater shocked Coconino sandstone. COESITE – high-pressure polymorph (crystal form) of silica, silicon dioxide (SiO2).
Carswell structure – geomorphology (courtesy of the University of New Brunswick).Carswell structure – Interior (pink) = GRANITE; Inner ring (yellow) = DISTURBED ATHABASCA FORMATION; Outer ring (green) = CARSWELL FORMATION (dolomite) – (Sawatzky).
Thin-section from a quartz crystal , [localized shear planes seen intersecting on sectioned or naturally exposed surfaces are frequently referred to as adiabatic shear bands (ASB’s)]. found in Precambrian basement gneiss collected from the central uplift of the Carswell Lake impact structure (Canada) viewed under polarized light. Original image from French, 1998, Traces of Catastrophe, 1998.
Fault zone and differing geology under the Charlevoix impact structure. I superimposed a schematic of the geologic faulting under the Charlevoix crater onto this aeronautical chart of the crater area. A line drawn west to east on the chart corresponds to the physical position of the schematic illustrating the fault zone and differing geology under the crater.Charlevoix impact structure Digital Elevation Model with Earthquake EpicentresImpact melt (mylolisthenite*) _.found in the Charlevoix impact structure. Note the country rock fragment in the inclusion.
The differential subsidence in the geology at the rim of the Chesapeake impact structure diverting the James and York Rivers – circled. (Poag, 1999). The abrupt diversions of the lower courses of the James and York Rivers (indicated by the small circles in the map above) coincide with the Chesapeake crater rim. (see side-note #4 [St Martin] below).Cross section showing main features of Chesapeake Bay impact crater and three coreholes that provided data on these features.
The 21 shocked and unshocked zircon crystals dated in this study were separated from this ~30 cubic centimeters of unconsolidated late Eocene sediment obtained from Ocean Drilling Project site 1073, hole A. Credit: Biren/ASU
The age of the 85-kilometer-diameter Chesapeake Bay impact structure (35 million years old) and the composition of some of its breccia clasts are consistent with the structure being the source of the North American tektites.Reidite is a rare mineral that has been found only in four crater impacts: the Chesapeake Bay Crater in Virginia, Ries Crater in Germany, Xiuyan Crater in China, and Rock Elm Crater in Wisconsin (Wiki).
Reflection seismic cross-section of Chicxulub along Chicx-A and -A1 (Bell et al. Forthcoming). The post-impact Tertiary sediments are clearly identifiable as high-frequency reflections from 0 to ~1 sec two-way travel time (TWTT). A topographic peak ring, with draped sediments, is identifiable on the floor of Chicxulub and separates the central basin from a surrounding annular trough. (GRIEVE et al 2003)This Stevens Klint Denmark example of the Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary, is a geological signature, usually a thin band of rock containing much more iridium than other bands. The K–Pg boundary marks the end of the Cretaceous Period, the last period of the Mesozoic Era, and marks the beginning of the Paleogene Period, the first period of the Cenozoic Era. Its age is usually estimated at around 66 million years, with radiometric dating yielding a more precise age of 66.043 ± 0.011 Ma.Low Magnification of the Stevens Klint Denmark example of the Cretaceous–Paleogene (K–Pg) boundary.Carbonaceous chondrites are the most primitive objects in the solar system, and examination of them provides valuable insights as to the conditions that existed during the very earliest days of the solar system (Tagish Lake sample – authors private collection).
The wall (light) and melt vein (dark) of West Clearwater Impact Structure-14-AR-016 in plane polarized light, showing pieces of the wall (plagioclase) being incorporated into the melt vein. All the identified mineralogical compositions of the basement are evident in the melt vein through EDS analysis. Not only were the plagioclase clasts included in the vein the same composition of the host rock but they also exhibit the undulatory extinction and shock deformation twinning seen in the plagioclase that comprise the host rock. (Osinski et al 2015)The recognition of unique shock-produced “deformation lamellae” or planar deformation features (PDFs) in quartz in the 1960s was a critical development in the identification of ancient meteorite impact structures: a) first published description of “deformation lamellae” identified in breccias from the Clearwater West impact structure, as an abstract in the Journal of Geophysical Research (McIntyre 1962) (reproduced by permission of the American Geophysical Union); b) photomicrograph of quartz grain in breccia from Clearwater West, showing multiple sets of PDFs (McIntyre 1968). Plane-polarized light. The quartz grain is about 1.4 mm long (French 2004).
Structural contour map on the pennsylvanian Tensleep Formation (modified from Stone 1999). Contour interval is 200 ft (60 m). Base level datum is mean sea level. The trace of the outer rim fault zone just below the Tr-J unconformity is marked by the largest dashed circle. The smallest dashed circle near the center of the map is the annular fault zone that encircles the central peak. Within this annular peak-ring fault zone (the area marked by a gray stippled pattern), the coutoured tensleep horizon is missing (by ejection and/or erosion) and Amsden Formation rocks are uplifted and truncated at the Tr-J unconformity.Structural cross-section B-B’ restored by flattening on the Sundance datum to remove the effects of Laramide deformation. Formation symbols are identified in the figure to the left. (Stone et al 2003). Comparison of the “standard” stratigraphic column on the Casper Arch and the section found in the central peak of the Cloud creek impact structure. Stratigraphic uplift (SU) of the Madison Formation in the central peak area above its normal elevation outside the crater is ~520 m. At the Tr-J unconformity, there is progressive onlap of Sundance members over and around the central peak (Stone et al 2003).
Topography and bathymetry of Deep Bay. Also indicated are location of drill holes and a geologic cross-section based on these drill holes (bottom). Innes et al (1964). PDF in quartz grains and feldspar were recovered from the drill site DOM 66-1 (Dence et al 1968..At Deep Bay the circular fracture zone marks approximately the outer limit of the fractured zone and may be interpreted as a hinge line about which the granitic rocks forming the rim have been uplifted. Indeed the rocks within this circle, have the general appearance of having been uplifted and shattered into huge blocks without having undergone much horizontal movement. (Innes et al 1964).
The 8-km diameter Des Plaines Structure exhibits complex faulting and shock features such as percussion fractures and strain lamellae, as well as a few shatter cones. The center of the crater lies under Big Bend Lake on the Des Plaines River. Seismic reflection data suggest that there are numerous other faults within the bedrock of Cook County. Courtesy of United States Meteorite Impact Craters.
[Images courtesy of Carl Alwmark, associate professor Department of Geology Lund University]
Quartz grain displaying two sets of decorated PDFs, one set oriented parallel to ω {10″1″ ̅3} equivalent orientations and one set oriented along the basal plane c (0001). A third set of PDFs, not visible on this image but observable under the U-stage microscope, are oriented parallel to ω {10″1″ ̅3}.Quartz grain with two sets of decorated PDFs, both sets oriented parallel to ω {10″1″ ̅3} equivalent orientations. Another three sets of PDFs, not visible on this image, but observable under the U-stage microscope, are oriented parallel to ω {10″1″ ̅3}, ω {10″1″ ̅3}, and {10″1″ ̅4}, respectively.Large quartz grain displaying four sets of PFs, penetrating the entire grain.A large quartz grain with three sets of PFs, all oriented parallel to ξ {11″2″ ̅2} equivalent orientations.
The (WISCAH), evaluation presents evidence that the black mat stratum at Glover Bluff is the depositional result of an ET event due to its clear association with ejecta strata. Additional geological analysis is recommended at Glover Bluff to establish the exact timing, and to determine the relationship, if any, to known phenomena. The impact origin was confirmed in 1983, by the discovery of shatter cones (Read, 1983).Polymictic impact breccia; Glover Bluff impact structure (Wisconsin, USA). Structure diameter 8 km, Cambrian age, or younger (ERNSTSON CLAUDIN IMPACT STRUCTURES – METEORITE CRATERS).
A new geological map of Calder Island based on our field expedition. The darker tone for each lithology represents outcrops visited and mapped during fieldwork. The lighter tone signifies the inferred presence each lithology. Impact melt-bearing breccia outcrops are too small to appear on the map and so are indicated with a star symbol.Optical photomicrographs in cross-polarized light of target rocks and lithic impact breccias. (a) Target rock from the crater rim region. Sample 4.12. (b) Parautochthonous target rock from Calder island displaying evidence for in situ brecciation. Sample 1.28. (c) Lithic impact breccia from Calder island. Sample 7.08. (d) Lithic impact breccia from Calder island. Sample 5.06. All these images display a mix of quartz, K-feldspar, and plagioclase, plus minor biotite visible in some images due to its brown pleochroism.Optical photomicrographs and BSE images of clast-rich impact melt rocks (a–c) and red impact melt rocks (d–f). (a) Optical photomicrograph in plane-polarized light of the clast-rich impact melt rocks. All clasts in this view are either quartz or feldspar mineral clasts. Sample 1.17. (b) BSE image showing the fine-grained nature of the K-feldspar (Kfs)-dominated groundmass of the clast-rich impact melt rock. Several quartz mineral clasts are also present (Qz-cl). Sample 5.13. (c) Optical photomicrograph of PDFs in quartz in the clast-rich impact melt rock. Sample 2.01. (d) Optical photomicrograph in plane-polarized light of the red impact melt rocks. Note the clast-poor nature compared to (a). The brownish groundmass is dominated by K-feldspar (see (e)). The clasts visible in this image are quartz and biotite. Sample 2.10. (e) BSE image showing K-feldspar-dominated groundmass of the red impact melt rocks. Sample 2.19. (f) Clast of ballen silica in the red impact melt rock.Optical photomicrographs and BSE images of impact melt-bearing breccia (a–c) and green impact melt rocks (d–f). (a) Optical photomicrograph of impact melt-bearing breccia with a large flow-textured vitric particle taking up the left half of the image. Sample 1.21. (b) BSE of impact melt-bearing breccia with prominent altered flow-textured vitric particles (Gl) in the upper half of the image. The clastic matrix is visible in the bottom half of the image (cf., (d) and (f)). Sample 7.03. (c) BSE image of a vitric particle within impact melt-bearing breccia. A quartz clast (Qtz-Cl) appears ductilely deformed and the groundmass is comprised of altered glass (Gl) plus microscopic plagioclase (Pl) crystallites. Sample 7.03. (d) BSE image of a typical green impact melt rock with a glassy groundmass. Sample 7.06. (e) BSE image of the same sample as (d) with a more crystalline groundmass of plagioclase (Pl) and minor interstitial glass. Sample 7.06. (f) Optical photomicrograph of a clast of ballen silica in the green impact melt rock.
The Space Wanderer (world’s largest pallasite meteorite) In 1949, H.O.Stockwell, with the aid of a modern metal detector and equipment rigged at the Peck farm, uncovered the largest pallasite found to date, the Space Wanderer, weighing 1,000 pounds (454 kg). The pallasite was placed in the Greensburg Big Well Museum in 1949. There is a similar specimen weighing 740 pounds (336 kg) from the same meteor shower at the Smithsonian in Washington D.C.
Profile of the Holleford Crater as reconstructed from drill-hole and surface observations. It will be seen that the original crater surface dips nearly 800 feet below plain level, while the zone of fractured rock extends to an estimated depth of about 2,400 feet. The estimate of breccia depth at the centre depends on theoretical considerations advanced by J.A. Rothenberg.Looking North from the South East rim, note the “steep scarps”.
Limestone from the sedimentary rock with which the crater was filled since impact.(left) polymictic breccia – angular clasts from different origin intermixed in a consolidated matrix cemented together, which formed in the crater’s original floor and (right) the undisturbed bedrock out of which the crater was blasted.
Several fragments within the breccia from the Ile Rouleau Impact Structure contain silty quartz grains. Many of these show planar deformation features. A few grains show multiple sets of features. These features were caused by the passage of a shock wave from impactor contact through the country rock that changes the structure of some of the minerals.This photograph is of a 0.03 mm thick and 1 mm across grain of quartz from the structure. The shock wave has produced several different sets of planar features, called shock lamellae. The occurrence of multiple sets of planar lamellae is a diagnostic feature of shock metamorphism (Data Courtesy Denis W. Roy).Impact breccia from the Ile Rouleau structure.
This false-color image shows a green ring depression that surrounds a central peak. The ring depression contains the Manicouagan Reservoir.Autochthonous impact breccia in the Manicouagan impact crater on the inner plateau of the central peak island at location #2. Note the different types of rock fragments forming the breccia within the fine grained matrix mylolisthenite*. Also note the white margin around the large breccia fragment. This white margin is a heat affected zone. The matrix material was hot enough during the formation of this breccia to produce a recrystallized band around the clast , a Heat Affected Zone, but there was not sufficient heat that flowed into the clast to melt it (Dr. Lynn B. Lundberg, PhD).The Manicouagan impact crater – breccia on the inner plateau of the central peak island at location #3 . At the point of impact, the rocks were instantaneously evaporated/melted/shattered by the energy released. The shattered white “country” rocks shown on the image were imbedded in what is interpreted to be a fine grained matrix mylolisthenite*. It’s possible that the extremely small size of the grains within the matrix were formed by the very high pressure of the gas generated upon impact.Planar deformation features in quartz. This sample is from the Manicouagan impact crater.The documented late Triassic spherule layer of SW England deposit (illustrated here) contains an abundance of spherules, common shocked quartz and a suite of accessory minerals believed to have been derived direct from the impact site. These include garnets, ilmenites, zircons and biotites. Garnets and ilmenites are highly fractured, and biotites show prominent kink bands indicative of shock.The Late Triassic ejecta deposit of SW Britain where impact melt spherules have been completely altered to clay. Radiogenic dating of this deposit shocked biotites (observed exclusively in this Late Triassic ejecta deposit) yielded ages consistent with the Grenvillian target rocks at Manicouagan (Thackrey 2009).
Shock-characteristic planar deformation features (PDFs) in a quartz grain (in distal ejecta from the Manson impact crater, found in South Dakota). Width of the grain ca. 100 mm. Multiple intersecting sets of PDFs are clearly visible (Christian Koeberl).
3-D perspective of the Maple Creek (White Valley) structure. Both the Belly River (RED) and Mississippian (BLUE) horizons are depicted. The general morphology of the complex crater can be seen in the Belly River horizon. (Westbroek et al 1995).The trough and central uplift are imaged by seismic data (Westbroek, 1997).The Maple Creek (White Valley) structure in southwestern Saskatchewan has been interpreted as a <75 Ma old impact feature. This structure has many of the morphological characteristics of a complex impact crater. The structure is interpreted to have a diameter of about 7 km with an annular trough and a raised central uplift.
The I-94 drill project results confirmed the seismic interpretation of an impact crater. Rocks penetrated by the 1,646-m well can be subdivided into three sequences (Friedenreich 1988)
Wonderfully preserved outcrop of the contact between impact melt rock (top) and polymict impact breccia (bottom) at Coté Creek, Mistastin Lake impact structure. Credit: Cassandra Marion, 2021
Structure maps generated from the interpreted basement horizon in Newporte Crater. The evident concave shape and uplifted rim are visible. A vertical exaggeration of 2.5 was utilized. Image from Forsman et al (1996).Macroscopic view of Newporte core sample – granitic frag-mental breccia D9462.0 (from Duerre 43-5 core) showing one quartz-nich angular granitic fragment (bright area top centre) with other darker granitic fragments in a ark, fine-grained, clast-rich matrix.(After Koeberl and Reimold, 1995)
Topographic documentation of the area around the Pingualuit Crater.The impact melt rocks correspond to a chemical mixture of some of the local target rocks. They contained mineral and lithic clasts, some of which showed diagnostic shock-produced Planar Deformation Features in quartz. They also contain enrichments in Ir, Ni, Co and Cr suggesting that the impacting body was chondritic in composition with siderophile element enrichment (Grieve 1991).
Seismic intersect image, Red Wing Creek Field. Image courtesy of Roger Barton and True Oil.
Shocked quartz grain from a drill core into the Red Wing Creek impact structure, North Dakota, depth 2301 m, within brecciated Kibbey sandstone, with PDFs of 2 different orientations; width of image 375 micrometers, crossed polars (see Koeberl and Reimold, 1995a, Koeberl et al., 1996b);
Rock Elm structure, Wisconsin (French et al. 2004)Researchers discovered the mineral, called reidite, at the Rock Elm impact structure in western Wisconsin.Reidite is a rare mineral that has been found only in four crater impacts: the Chesapeake Bay Crater in Virginia, Ries Crater in Germany, Xiuyan Crater in China, and Rock Elm Crater in Wisconsin (Wiki).
Topographical Map of the Slate Islands Impact Structure.Section across the Slate Islands complex impact structure showing distribution of breccias investigated. Minor polymictic clastic matrix breccias are also present further away from the centre of the structure than shown here. Profile is based on bathymetric information from around the archipelago and on topographic maps of the islands. From Dressler and Sharpton (1997).In situ polymict breccia on Patterson Island east within the Slate Islands impact structure. Polymict Breccias. The dominant type of breccia on the Slate Islands is polymict breccia and this typically occurs as veins and dikes varying in width from ~5 cm to 5 m. The matrix is typically fine grained and grey in colour. It contains a wide variety of angular to sub-rounded clasts of different lithologies, ranging in size from <1 mm to 10s of centimeters. Some of the clasts can also be seen to contain shatter cones. (Kerrigan et al, 2014)
Simplified core ST003 log and geologic map showing sampling location, Steen River impact structure (SRIS; Alberta, Canada) (modified from Molak et al., 2001). Details on post-impact sedimentary strata can be found in Data Repository (see footnote 1). Inner circle approximates ~9 km wide base of central uplift. Outermost solid circle delineates the structural rim of the crater. (Walton et al 2017)
Core ST003 showing the various breccia units, as logged by Walton et al. (2017), as well as the sampled locations for this study. Photographs on the right-hand side show the cm-sized clasts of granitic basement rocks entrained within breccia (sampled at depths of 285.6 and 324.5 m) and shock veins from the bottom 11 m of the core, which penetrated the side of the central uplift (378.5 m). Biotite in the cm-sized granitic clasts and along shock vein margins is the subject of this study.
St. Martin impact structure – preserved with 100 m of Jurassic sediment cover.Landsat-5 satellite image of Lake Saint Martin in Manitoba, Canada (scene path 032, row 024, acquired on 04 April 2010) and outline of the estimated outer limits of the largely sediment-and water-covered ∼40 km-diameter impact structure according to Bannatyne and McCabe(1984).
Geologic schematic of the Sudbury impact structure (courtesy of F. Brunton).The Sudbury impact structure – black pseudotachylite.The Sudbury impact structure – black pseudotachylite.Sudbury pseudotachylite dikes range from veins less than 1 mm thick to massive zones measuring up to 1 km thick and extending for approximately 45 km. Formations of SB are found up to 100 km north of the SIC . The pseudotachylite here is injected into the pink gneiss country rock (the toe of my boot is for scale).The Sudbury impact structure – Matachewan Breccia Dykes.The Sudbury impact structure – felsic norite breccia rocks. “Norite” – composed of intergrown crystals of light-coloured minerals (feldspar) and dark-coloured magnesium-iron-silicate minerals (pyroxene), giving the rock a salt-and-pepper texture, formed by crystal growth from melted rock (igneous rock – gabbro),Immediately interfacing the upper SIC is the grey Whitewater breccia that contains many large angular rock fragments floating in a glass like amorphous rock. These fragments are the fallback particles from the surrounding Huronion supergroup country rock that were deposited immediately after the impact.The Sudbury impact structure – darker Whitewater breccia. Further into the structure is the darker Whitewater breccia containing smaller rock fall-back fragments originating from the igneous quarts granite north range footwall. Here the breccia indicates the introduction of carbon.Sudbury Impact Distal Ejecta at Hillcrest Park, Thunder Bay Ontario – 2013.
The 2.44 km diameter 110 m deep West Hawk Impact Crater (the deepest lake in Manitoba) is enclosed and completely submerged within West Hawk Lake (Ogilvie 1984). The depth of crater is indicated in feet, courtesy of Freshwater Institute, Department of Fisheries and Oceans, 2001 (in Boyd et al., 2002).Subbottom acoustic profile across the center of West Hawk Lake basin, showing bedding in upper *20 m of the sedimentary sequence (H. Thorleifson 1993, personal communication, unpublished); lake is 3.8 km across and water depth is 111 m.
Whitecourt Crater – perspective view from SE. This image is derived by Light Detection And Ranging (LiDAR) technology. (Department of Earth and Atmospheric Sciences, University of Alberta)The largest Whitecourt meteorite presently discovered, a regmaglypted individual found in October 2010. Copyright the Department of Earth and Atmospheric Sciences, University of Alberta. CENTEMETRE SCALEThe largest Whitecourt meteorite presently discovered (a second view), a regmaglypted individual found in October 2010. Copyright the Department of Earth and Atmospheric Sciences, University of Alberta. CENTEMETRE SCALE“Shrapnel” Whitecourt Meteorite. Image courtesy of Chris George Zuger, producer and host of the Den of Lore Show.TOP: A recently created meteorite impact crater is hidden underneath thick growth in western Canada. BOTTOM: Scientists used the optical remote sensing technology LiDAR to “strip” away the vegetation and reveal the 36-metre wide circular impression (University of Alberta). (Department of Earth and Atmospheric Sciences, University of Alberta)A summary diagram, which illustrates the meteorite distribution, local sample sites and auger holes, ejecta blanket, and the proposed flight path of the impactor. Grid spacing is 50 m (Kofman et al – Meteoritics & Planetary Science 2010).
A magnetic survey did not reveal the presence of a large buried meteorite in the immediate vicinity of the crater. Clear evidence of an overturned flap has not been observed (Kofman et al, 2010). The red box around the crater designates the 200-metre by 200-metre protected zone within which meteorite collecting is prohibited – subject to a $50,000 fine or one year in jail.
A) Bare-Earth LiDAR image of the crater and nearby surroundings. B) Surface contours at 1 m intervals. (Kofman et al – Meteoritics & Planetary Science 2010)
Cross sections of the ejecta blanket along 038° and 110° with a reference figure showing the location of the sections. Approximate distribution of the ejecta blanket and the main soil pit and auger hole site locations are also provided. (Kofman et al – Meteoritics & Planetary Science 2010)An image of the contact between the ejecta and the top of the paleosol, organics (charcoal), and underlying Ah horizon, used to delineate the ejecta blanket as revealed in the sample chamber of the auger. In this image, the overlying ejecta represents ejected Ae horizon material. Way up is to the left.Proximal ejecta located at the first sample site southwest of the crater rim along the A–A′ . The horizons indicated are disturbed, and represent sediment from which the ejecta was derived.
Ground penetrating radar survey and interpretation of the Bloody Creek structure. Ground-penetrating radar traverses were obtained when the site was frozen in winter. They confirm the crater morphology of the structure, and the distinction of the shallow levels from the undisturbed bedrock. (Spooner et al 2009)
Image showing the remnants of a crater that UAlberta researchers theorize was left by a massive meteorite strike sometime in the last 70 million years. Colour variation shows metres above sea level.
Seismic data in the James River 3-D volume. Several interpreted horizons are shown. The upper horizon corresponds to the top of the Cambrian, the middle horizon corresponds to the Cambrian ‘event’, and the lower horizon corresponds to the Precambrian. Faulting in the James River dataset is divided between shallow rim faults and deep central and rim faults.
Generalized geologic and topographic map of the Merewether (possible) impact crater and vicinity. Traced from vertical photograph USAF T.P.12, run #22-209.
The layers of sedimentary rock that covered the crater sagged, stretching the rock at the rim causing differencial cracking. The fractures (joints) developed above the rims of the crater were eroded during the last ice age. The glacial erosion of the joints which formed about the crater rim formed the course of the Esopus and Woodland Creeks.
The Victoria Island structure is characterized by a concentric, annular, terraced rim and trough surrounding a structurally uplifted central peak. Contour lines of equal thickness over an area (Isopach map) of interval between upper Nortonville Shale marker and lower Domengine Formation marker, showing series of concentric circular ridges and troughs, together with positions of several major, curvilinear normal faults that surround the structure and cut the lower part of the isopached interval.Contour lines of equal thickness over an area (Isopach map) of potential crater infill, between upper Nortonville Shale marker and base Nortonville Shale/top Domengine Formation marker.
A) Bare-Earth LiDAR image of the crater and nearby surroundings. B) Surface contours at 1 m intervals. (Kofman et al – Meteoritics & Planetary Science 2010)
