[meteorite-list] A Western Crater Field? - Flathead_Lake
From: Paul H. <oxytropidoceras_at_meteoritecentral.com>
Date: Sat, 2 Jun 2012 23:06:33 -0500 Message-ID: <20120603000633.T7MWX.1124479.imail_at_eastrmwml114> In ?A Western Crater Field?? at http://six.pairlist.net/pipermail/meteorite-list/2012-May/085463.html E.P. Grondine wrote: ?Hi all - A while back, I related to you the Assiniboine memories of the Holocene Start Impact Event (HSIE): ? URLs to unrelated previous posts omitted? ?I think that there is data to suspect that the lake the Assinboine remembered waz Flathead Lake: http://en.wikipedia.org/wiki/Flathead_Lake If you look at the current west-north-west exit of the lake in this image: http://en.wikipedia.org/wiki/File:Flathead_lake.jpg you will see what appear to be several astroblemes. The exit of this lake prior to their formation appears to have been south down a river which would have formed a rather perfect animal migration path. Whether they are or not will require proper geological field examination.? The structural and Quaternary geology of Flathead Lake has been studied in great detailed and the results of these studies have been published in a series of peer-reviewed journal papers and other scientific publications. This research included detailed field study, including geologic mapping, of the Flathead Lake area; high-resolution gravity surveys of the Flathead Lake area; 270 km of single channel, 3.5 kHz reflection seismic reflection data of sediment underlying Flathead Lake; a set of eight, 5 to 11.5 m long, piston cores taken from the bottom of Flathead Lake; and additional low-frequency seismic data gathered by the United States Geological Survey. All of this data and research clearly demonstrates a lack of any evidence for extraterrestrial impact having been associated with the formation of Flathead Lake and soundly refutes any such hypothesis. This research demonstrates that Flathead Lake occupies the actively subsiding southern end of a rift valley known as the Rocky Mountain Trench. The seismic data shows five different periods of increased tectonic activity and associated subsidence have occurred during the last 15,000 years. The core and seismic data show that acoustically-stratified, undisturbed Pleistocene glacial lake and Holocene sediment underlies the bottom of Lake Flathead. The cores and seismic data demonstrates that the oldest of these sediments date to about 14,475?150 cal yr BP, the maximum age of the oldest varves. This is when the main Flathead Lake basin was at least partially deglaciated and lake sediments could start accumulating within the basin now occupied by Flathead Lake. Field studies of the area around Flathead Lake show that the southern shore of this lake is formed by a recessional moraine of glacial origin, which acts as dam. The north shore of Flathead Lake consists of younger recessional glacial moraines. Although volcanic ash beds are preserved in lake and glacial sediments, there is a complete absence of any disturbance or event beds, which can be interpreted as being related to any sort of extraterrestrial impact since the deglaciation of the area between 13,000 to 15,000 years. References about Flathead Lake include: Edwards, J., 2006, Evidence for Glacial Outburst Floods along the Lower Flathead River: Results from Geologic Mapping, Geomorphologic Analysis, and a Gravity Survey near Polson, Montana. unpublished MSc thesis, University of Montana, Missoula, Montana. http://etd.lib.umt.edu/theses/available/etd-02282007-160250/ Hoffmann, M. H., 2005, Sedimentary record of glacial dynamics, lake level fluctuations, and tectonics: Late Pleistocene-Holocene structural and stratigraphic analysis of the Flathead Lake basin and the Mission Valley, Montana, USA. Unpublished PhD. dissertation, University of Montana, Missoula, Montana. http://gradworks.umi.com/32/05/3205772.html Hofmann, M. H., and M. S. Hendrix, 2010, Depositional processes and the inferred history of ice-margin retreat associated with the deglaciation of the Cordilleran Ice Sheet: The sedimentary record from Flathead Lake, northwest Montana, USA Sedimentary Geology. vol. 223, no. 1-2, pp. 61?74 http://www.sciencedirect.com/science/article/pii/S0037073809002322 Hofmann, M. H., M. S. Hendrix, J. N. Moore, and M. Sperazza, 2006a, Late Pleistocene and Holocene depositional history of sediments in Flathead Lake, Montana: evidence from high-resolution seismic reflection interpretation. Sedimentary Geology. vol. 184, no. 1, pp. 111?131. http://www.sciencedirect.com/science/article/pii/S0037073805003325 Hofmann, M. H., M. S. Hendrix, J. N. Moore, and M. Sperazza, 2006b, Neotectonic evolution and fault geometry change along a major extensional fault system in the Mission and Flathead Valleys, NW-Montana. Journal of Strucutral Geology. vol. 28, no. 7, pp. 1244?1260. http://www.sciencedirect.com/science/article/pii/S0191814106000885 LaFave, J. I., L. N. Smith, and T. W. Patton, 2004, Ground-water resources of the Flathead Lake Area: Flathead, Lake, and parts of Missoula and Sanders counties. Montana Ground-Water assessment Atlas no. 2, The Montana Bureau of Mines and Geology, Butte, Montana. http://www.mbmg.mtech.edu/mbmgcat/public/ListCitation.asp?pub_id=10310& Smith, L. N., 2001. Hydrogeologic framework of the southern part of the Flathead Lake Area, Flathead, Lake, Missoula, and Sanders Counties, Montana. Montana Bureau of Mines and Geology, Montana Ground-Water Assessment Atlas No.2, Part B, Map 10. Smith, L. N., 2004. Late Pleistocene stratigraphy and implications for deglaciation and subglacial processes of the Flathead Lobe of the Cordilleran Ice Sheet, Flathead Valley, Montana, USA. Sedimentary Geology, vol. 165, No. 3-4, pp. 295?332. http://www.sciencedirect.com/science/article/pii/S0037073803003427 http://gsa.confex.com/gsa/2004RM/finalprogram/abstract_72168.htm Wold, R. J., 1982. Seismic reflection study of Flathead Lake, Montana. Miscellaneous field studies map no. MF-1433, scale 1:117,647. U.S. Geological Survey, Reston, Virginia Best wishes, Paul H. Received on Sun 03 Jun 2012 12:06:33 AM PDT |
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