[meteorite-list] Preliminary Evaluation of a Proposed “Younger Dryas Impact” Crater
From: Paul H. <oxytropidoceras_at_meteoritecentral.com>
Date: Sat, 5 Nov 2011 10:40:24 -0500 Message-ID: <20111105114025.RDYB3.56425.imail_at_eastrmwml29> Using Google Earth terrain maps, Mr. Thomas Lee Elifritz found what he speculates might be impact crater of the ?12,900 BP Younger Dryas Clovis cometary ice sheet impact? (Anonymous 2011, Elifritz 2009a, 2009b). His interpretation is based solely upon a vague circular feature, which is centered around 49? 10? 41? N., 88? 43? 9? W. and is about 25 to 26 km in diameter. The edge of this feature lies at the southern end of Black Sturgeon Lake, along cliffs just north and east of Nonwaith Lake, along a well-defined ridge, Fox Mountain, just east and north of Disraeli Lake, and through middle of Black Mountain Lake. As noted by Hart and Magyars (2004), this area was mapped by Coates (1972) at a scale of 1:63 360. This geologic map included an interpreted geological section. Later, Sutcliffe (1982) mapped the geology of the northeast part of this area from immediately south of Lake Nipigon to the southern edge of Black Sturgeon Lake at a scale of 1:50 000. Also, various studies, i.e. Sutcliffe (1987), Hart and McDonald (2007), Heaman et al. (2007), and Hollings et al. (2007) have investigated in detail the areal intrusive rocks, Nipigon diabase sills and ultramafic intrusions of the Disraeli and Seagull?Lecky lakes areas. The sedimentary rocks of the Sibley Group, which underlie this area have also been studied by various investigators, i.e. Franklin et al. (1980), Chile (1986), Regale (2003), and Frolic and Zanies (2011). Recent geologic mapping, reports, and talks, Hart and Magyars (2004), Magyars et al. (2004), Hart 2005a, 2005b), and Hart and Olson (2005) provide very detailed discussion, geologic maps, and subsurface cross-sections of the northern Black Sturgeon River?Disraeli Lake region based upon detailed field work conducted during the summer of 2003 and existing subsurface data. Finally, frequent mineral exploration and prospecting has occurred within this area. This exploration has created a collection of lithologic logs of and actual cores from numerous drill holes from which cross-sections of the subsurface geology of this area have been created by Coates (1972), Hart and Magyars (2004), Magyars et al. (2005), Hart and Thompson (2007) and others. The above research provide a wealth of information about the surface and subsurface geology of this hypothesized extraterrestrial impact structure. This feature, including its northern, southern, and western edges, are underlain by undeformed, relatively flat-lying sedimentary rocks of the Sibley Group (Coates 1972;Cheadle, 1986; Regale, 2003; Hart and Magyars, 2004; Hart, 2005a; Magyars et al., 2005). These sedimentary rocks are interlayered with thick, concordant Nipigon Diabase Sills (Hart, 2005a, 2005b; Hart and Magyars, 2004; Magyars et al., 2005; Hart, 2007; Easton et al., 2007; Hollings et al., 2007). The northeastern edge of this feature consists of a thick, relatively flat-lying, and undeformed diabase sill, which have intruded metasedimentary rocks and granitic and tonalite intrusives of the Quetico Subprovince (Coates, 1972; Hart, 2005a; Hart and Magyars, 2004; Magyars et al., 2005). Both sedimentary rocks of the Sibley Group and the Nipigon Diabase Sills exhibit a lack of any deformation that can be associated with the entire circular feature hypothesized to be an impact crater. These strata are flat-lying to slightly dipping. They are disturbed only by regional north and northwest-trending faults that are interpreted to have locally created a block-faulted asymmetric basin or graben. These faults are considered the result of the reactivation of earlier Archean structures during the Late Proterozoic (Coates, 1972; Franklin et al., 1980; Hart and Magyars, 2004; Magyars et al., 2005). Only along the northeast rim is faulting even roughly associated with the rim of this feature. The rim is not the direct result of fault movement. Rather, its is the result of differential erosion of less resistant sedimentary rocks of the Sibley Group and more resistant metasedimentary and tonalite intrusives of the Quetico Subprovince on either side of faults. In addition, the faults are high angle faults with orientations and dips typical of regional faulting (Coates, 1972; Franklin et al., 1980; Hart and Magyars, 2004; Magyars et al., 2005). These faults lack the characteristics of those exhibited by extraterrestrial impact structures (Melosh 1989). Furthermore, There is a complete lack of any evidence for any recognizable structural control of the western and southern edge of this feature, which is composed of roughly arcuate ridges, Fox, Wolf, and Eagle mountains. The geologic mapping and cross-sections of Coates (1972), Hart 2005a, Hart and Magyars (2004), Magyars et al. (2005), and Hart and Thompson (2007) show that they consist of relatively flat-lying and undeformed sedimentary rocks of sedimentary rocks of the Sibley Group and interlayered sills of the Nipigon Diabase. There is a complete absence of any deformation that could be associated with an extraterrestrial impact (Melosh 1989). If there is structural control to these ridges, it is the result something considerably more subtle and cryptic than an extraterrestrial impact. Concerning the circular feature, which Elifritz (2009a, 2009b) proposed to be a possible Younger Dryas Impact, there exists sufficient information to make a preliminary evaluation of this hypothesis. The undeformed and relatively flat-lying nature of the sedimentary strata and interlayered diabase sills readily refutes any idea that this feature is an impact structure any sort or age given the 25-km diameter of this feature. An extraterrestrial origin of this feature is further refuted by the lack of any significant consistent relationship between regional faults and the feature and the age of the faulting. Despite its roughly circular shape, it appears that this circular feature is combined result of past differential weathering and glacial and glacial and meltwater erosion of the Proterozoic sills and Sibley Group metasedimentary strata that has been influenced by Proterozoic faulting and possible cryptic structural controls. If anything, this feature is most likely a example of the problems with relying entirely on terrain maps (digital elevation models) as a basis for identifying extraterrestrial impact crates. It shows that existing geological research also needs to be consulted before proposing any circular feature as an impact crater. This feature is likely a classic example of Riemold (2007)?s ?Impact Crater Bandwagon.? References Cited, Anonymous (2011) Clovis Comet Crater? The Cosmic Tusk (Oct. 10, 2011) http://cosmictusk.com/clovis-comet-crater . Chile, B. A., 1986, Alluvial-playa sedimentation in the lower Keweenawan Sibley Group, Thunder Bay District, Ontario. Canadian Journal of Earth Science. vol. 23, pp. 527-542. http://www.nrcresearchpress.com/doi/abs/10.1139/e86-053 Coates, M. E., 1972, Geology of the Black Sturgeon River area, District of Thunder Bay. Geoscience Report no. 98, Ontario Department of Mines and Northern Affairs, Toronto, Ontario. 41p. Easton, R. M., T. R. Hart, P. Hollings, L. A. Heaman, C. A. MacDonald, and M. Smyk, 2007, Further refinement to the timing of Mesoproterozoic magmatism, Lake Nipigon region, Ontario. Canadian Journal of Earth Sciences. vol. 44, pp. 1055-1086. http://www.nrcresearchpress.com/doi/abs/10.1139/e06-117 http://www.nrcresearchpress.com/toc/cjes/44/8 Elifritz, T. L., 2009a, Younger Dryas Cometary Impact Crater Near Lake Nipigon. Unpublished manuscript dated March 20, 2009. http://www.scribd.com/doc/68237039/Clovis-Comet-Crater http://webpages.charter.net/tsiolkovsky/Clovis_Comet_Crater.pdf http://webpages.charter.net/tsiolkovsky/Clovis_Comet_Crater.jpg Elifritz, T. L., 2009b, Darwin?s Valentine - A Cometary Impact Remnant Transposed Upon Glacial Terrain Near Lake Nipigon? Unpublished manuscript dated February 28, 2009. http://webpages.charter.net/tsiolkovsky/Darwin's_Valentine.pdf http://webpages.charter.net/tsiolkovsky/Darwin's_Valentine.jpg Frolic, P., and K. Zanies, 2011, Sedimentology of a wet, pre-vegetation floodplain assemblage. Sedimentology. Article first published online, Oct. 20, 2011 DOI: 10.1111/j.1365-3091.2011.01291.x http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3091.2011.01291.x/abstract Franklin, J. M., W. H. McIlwaine, K. H. Poulsen, and R. K. Wanless, 1980, Stratigraphy and depositional setting of the Sibley Group, Thunder Bay District, Ontario, Canada. Canadian Journal of Earth Sciences. vol. 17, pp. 633-651. http://www.nrcresearchpress.com/doi/abs/10.1139/e80-060 http://www.nrcresearchpress.com/toc/cjes/17/5 Hart, T.R., 2005a, Precambrian geology of the southern Black Sturgeon River and Seagull Lake area, Nipigon Embayment, northwestern Ontario. Open File Report no. 6165, Ontario Geological Survey, Toronto, Ontario. 63 pp. http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/OFR6165/OFR6165.pdf Hart, T. R., 2005b, Lake Nipigon Regional Geoscience Initiative: Proterozoic and Archean Geology of the Southern area of the Western Nipigon Embayment. Ontario Geological Survey, poster, Northwest Mines and Minerals Symposium, Thunder Bay, Ontario, April 5-6. http://www.mndm.gov.on.ca/mines/ogs/Posters/OEGS_2004/Hart_OEGS_2004.pdf Hart, T. R., and Z., Magyars, 2004, Precambrian geology of the northern Black SturgeonRiver and Disraeli Lake area, Nipigon Embayment, northwestern Ontario. Open File Report no. 6138, Ontario Geological Survey, Toronto, Ontario. 56p. http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/OFR6138/OFR6138.pdf Hart, T. R., and C. A. McDonald, 2007, Proterozoic and Archean geology of the Nipigon Embayment: implications for emplacement of the Mesoproterozoic Nipigon diabase sills and mafic to ultramafic intrusions. Canadian Journal of Earth Sciences. vol. 44, pp. 1021-1040. http://www.nrcresearchpress.com/doi/abs/10.1139/e07-026 http://www.nrcresearchpress.com/toc/cjes/44/8 Hart, T.R., and Olson, A. 2005. The Precambrian geology of the south Black Sturgeon River ? Seagull Lake area, Geological Cross Sections, Nipigon Embayment, Northwestern Ontario. Preliminary Map no. P.3563, scale 1:50,000, Ontario Geological Survey, Toronto, Ontario. http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/P3563/P3563.pdf Magyars, Z., T. R. Hart, P. Frolic, R. Metsaranta, G. J. Heggie, P. Hollings, and A. Richardson, 2004, Northern Black Sturgeon River area geological cross-sections, Nipigon Embayment, northwestern Ontario. Preliminary Map no. P.3540, scale 1:50 000. Ontario Geological Survey, Toronto, Ontario. http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/P3540/P3540.pdf Melosh, H. J., 1989, Impact cratering : a geologic process. Oxford University Press, Oxford, United Kingdom. 245 pp. Reimold, W. U., 2007, The Impact Crater Bandwagon (Some problems with the terrestrial impact cratering record) Meteoritics & Planetary Science. vol. 42, no. 9, pp. 1467-1472. http://digitalcommons.arizona.edu/objectviewer?o=uadc://azu_maps/Volume42/Number9/p1467-1472 Regale, B., 2003, The Sibley Group: a lithostratigraphic, geochemical and paleomagnetic study; unpublished MS. thesis, Lakehead University, Thunder Bay, Ontario, 254 p. Sutcliffe, R. H., 1982, Precambrian geology of the Wabigoon? Quetico Subprovince boundary, Orient Bay sheet, Thunder Bay District. Preliminary Map no. P.2531, scale 1:50 000, Ontario Geological Survey, , Toronto, Ontario. Sutcliffe, R.H. 1986. Proterozoic rift related igneous rocks at Lake Nipigon, Ontario. unpublished PhD thesis, University of Western Ontario, London, Ontario, 325p. Yours, Paul H. Received on Sat 05 Nov 2011 11:40:24 AM PDT |
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