in southern Quebec, detailed 12.9 Ka YDB evidence by Mukul Sharma et al, spherules and magnetic grains: Rich Murray 2013.09.13
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in southern Quebec, detailed 12.9 Ka YDB evidence by Mukul Sharma et al, spherules and magnetic grains: Rich Murray 2013.09.13
 
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in southern Quebec, detailed 12.9 Ka YDB evidence by Mukul Sharma et al, spherules and magnetic grains: Rich Murray 2013.09.13 http://rmforall.blogspot.com/2013/09/in-southern-quebec-detailed-129-ka-ydb.html It's fascinating how much data can be extracted from tiny samples -- revealing proof of air bursts -- to my eye, as a complete geology layman, Google Earth indicates that all of Quebec province and far more have been scoured by a dense cluster storm of air bursts, instantly removing the km thick ice cover and leaving a ragged shotgun blast badlands landscape -- such ubiquitous evidence is hard to see, as in the case for central northern Mexico and for California hilltops from San Diego to Fresno, as described in detail by Dennis Cox and a bit by me. Look for cracked, overturned, and rounded rocks of all sizes, much the same from top to bottom on the sides of 100-1000 m hills and mountains, with surface glazes and coatings, say, the NE corner of Santee... hill .687 km elevaion by .564 km elevation lake to E, so .123 km high by Lac Pipmuacan, Quebec 49.553404 -70.306005 32.878538 -116.968926 .329 km elevation, 12 m long white boulders, NE corner of Santee, CA http://www.nature.com/news/evidence-found-for-planet-cooling-asteroid-1.13661 http://cosmictusk.com/ gives free full text via Scribd on September 2, 2013 http://www.pnas.org/cgi/doi/10.1073/pnas.1304059110
Origin and provenance of spherules and magnetic grains at the Younger Dryas boundary Yingzhe Wu a,1, Mukul Sharma a,2, Malcolm A. LeCompte b, Mark N. Demitroff c, and Joshua D. Landis a, a Radiogenic Isotope Geochemistry Laboratory, Department of Earth Sciences, Dartmouth College, Hanover, NH 03755; b Center of Excellence in RemoteSensing Education and Research, Elizabeth City State University, Elizabeth City, NC 27909; and c Department of Geography, University of Delaware, Newark,DE 971 6 Edited* by Steven M. Stanley, University of Hawaii, Honolulu, HI, and approved July 23, 2013 (received for review March 5, 2013) One or more bolide impacts are hypothesized to have triggered the Younger Dryas cooling at ∼12.9 ka. In support of this hypothesis, varying peak abundances of magnetic grains with iridium and magnetic microspherules have been reported at the Younger Dryas boundary (YDB). We show that bulk sediment and/or magnetic grains/microspherules collected from the YDB sites in Arizona, Michigan, New Mexico, New Jersey, and Ohio have 187 Os/188 Os ratios ≥ 1.0, similar to average upper continental crust (= 1.3), indicating a terrestrial origin of osmium (Os) in these samples. In contrast, bulk sediments from YDB sites in Belgium and Pennsylvania exhibit 187 Os/188 Os ratios <<1.0 and at face value suggest mixing with extraterrestrial Os with 187 Os/188 Os of ∼0.13. However, the Os concentration in bulk sample and magnetic grains from Belgium is 2.8 pg/g and 15 pg/g, respectively, much lower than that in average upper continental crust (=31 pg/g), indicating no meteoritic contribution. The YDB site in Pennsylvania is remarkable in yielding 2- to 5-mm diameter spherules containing minerals such as suessite (Fe-isilicide) that form at temperatures in excess of 2000°C. Gross texture, mineralogy, and age of the spherules appear consistent with their formation as ejecta from an impact 12.9 ka ago. The 187 Os/188 Os ratios of the spherules and their leachates are often low, but Os in these objects is likely terrestrially derived. The rare earth element patterns and Sr and Nd isotopes of the spherules indicate that their source lies in 1.5-Ga Quebecia terrain in the Grenville Province of northeastern North America. Author contributions: Y.W. and M.S. designed research; Y.W., M.S., and J.D.L. performed research; M.A.L. and M.N.D. contributed samples; Y.W., M.S., and J.D.L. analyzed data; and Y.W., M.S., M.A.L., and M.N.D. wrote the paper. The authors declare no conflict of interest. *This Direct Submission article had a prearranged editor. 1 Present address: Lamont – Doherty Earth Observatory, Columbia University, Palisades,NY 10964-8000. 2 To whom correspondence should be addressed. E-mail: mukul.sharma@...
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1304059110/-/DCSupplemental. † Higgins MD, et al., Bathymetric and petrological evidence for a young (Pleistocene?) 4-km diameter impact crater in the Gulf of Saint Lawrence, Canada. Lunar and Planetary Science Conference XXXXII, March 7 – 11, 2011, abstr 1608.... The proponents of the YDB impact hypothesis have pointed out, however, the lack of traditional impact markers in a number of widely accepted impact events (e.g., Australasian tektites, Libyan Desert glass, the Tunguska event), all suggested to have resulted from non-crater – producing airbursts (19, 20). Thus, a lack of traditional markers at the YDB may possibly be the result of one or more impactors exploding in the atmosphere or striking the Laurentide Ice Sheet (10). Recently, a submerged 4-km-wide candidate impact crater (Corossol Crater) has been discovered in the Sept Iles, Gulf of St. Lawrence, Canada and has been provisionally dated to 12.9 ka. † Two other features, one (Charity Shoal) submerged in Lake Ontario (21) and the other (Bloody Creek) in Nova Scotia (22), may represent additional or alternate impact craters associated with the YDB event. They have not been accurately dated, but their proposed range of dates spans the YD onset.... 21. Holcombe TL, Warren JS, Reid DF, Virden WT, Divins DL (2001) Small rimmed depression in Lake Ontario: An impact crater? J Great Lakes Res 27(4): 510 – 517. 22. Spooner I, et al. (2009) Identification of the Bloody Creek structure, a possible impact crater in southwestern Nova Scotia, Canada. Meteorit Planet Sci 44(8): 1193 – 1202.
Microspherule Clusters from Melrose, PA and Newtonville, NJ. Microspherules from Melrose and Newtonville are ∼5 – 50 μm in diameter (Fig. S2). Their major element compositions were estimated using SEM-energy dispersive X-ray spectroscopy and were found to be dominated by Al, Si, and Fe. The microspherule clusters were analyzed for Os, Sr, Nd, and Sm, using a procedure that permits sequential separation of these elements from a given sample (Fig. S3). We measured the microspherules as clusters because individual microspherules are small and adhere to eachother (Fig. S2). The Os, Sr, and Nd isotope data for the microspherules are shown in Tables 1 and 2. The [Os] of these objects is extremely high compared with the average crustal value but with high uncertainty. 187 Os/188 Os ratios are ∼1. The Sr isotope composition (Table 2) of the cluster of microspherules from Pennsylvania is radiogenic (= 0.7124). The Nd isotope composition of this cluster is nonradiogenic («Nd = −11.5). The Sr and Nd isotope data indicate that the provenance of these spherules is most likely not meteoritic, but rather ancient upper crust (see below). Individual Objects from Melrose, PA. Individual spherules from the YDB layer at Melrose range from 2 mm to 5 mm in diameter(Fig. 1). SEM images of these polished sections revealed the presence of a variety of high-temperature minerals and textures (Figs. 2 – 4), indicating melting followed by rapid cooling.... Provence of Melrose spherules A 4-km diameter impact crater with an estimated age 12.9 ka † was found off Corossol Island near the city of Sept Iles, Gulf of St. Lawrence, Canada. The Corossol Crater is the largest known crater within the last 900,000 y, is the largest in North America in the last 35 My, and is ∼1,200 km away from the Melrose site. The impact occurred in Ordovician limestones that overlie the 564-Ma Sept Iles intrusive suite †. The impact may have also excavated the rocks from the intrusive suite. We explored the Corossol Crater as the source of the Melrose spherules. From the Sr isotope evolution of sea- water it is evident that the 87 Sr/86 Sr ratio of Ordovician carbonates should range from 0.708 to 0.709 (56). These values are much lower than those observed in Melrose spherules. Similarly,the whole-rock Sr isotope ratios from the Sept Iles Intrusion (= 0.7038 on average) are much lower than those of the Melrose spherules. The lithologies underlying the Corossol Crater are therefore not the source of Melrose spherules. The depleted mantle Nd model ages for the Melrose spherules (TDM) range from 1.4 Ga to 1.8 Ga (Table 2). These ages suggest that the target is Grenvillean in age. Intriguingly, the measured «Nd values of the spherules (and also of the microspherule cluster from Newtonville) are identical to those measured for the Grenville age gray gneisses exposed just north and west of the Corossol Crater (57, 58). Using the Nd isotope model age map of Grenville fromDickin (57), we find that the spherule model ages are consistent with the target being in the “Quebecia” (Fig. S6), which is a Mesoproterozoic arc terrain consisting mainly of massif anorthosites, gabbros, and granitic gneisses. Because the Corossol Crater also lies within the Quebecia terrain, we suggest that there were more than one impact in this region that were closely associated in time. The spherules are not enriched in Ca and lack a pronounced positive Eu anomaly that is found associated with Grenvillean anorthosites and so we can preclude this lithology being the target. As the spherules display chondrite-normalized light REE-enriched patterns with negative Eu anomalies and unradiogenic 187 Os/188 Os ratios the target rocks could be a mixture of weathered gabbros and granitic gneisses with Re/Os ∼0. An alternative scenario to the above could also be suggested. The Laurentide Ice Sheet flowed from the north in Quebec through the Laurentide channel past Anticosti Island and into the Atlantic Ocean (59, 60). Just before the Younger Dryas, the ice sheet had retreated rapidly close to the north shore of the present St. Lawrence estuary (Fig. S6). However, the extent to which the ice sheet occupied the future Corossol impact crater site is not clear at this time due to a lack of detailed paleogeographic reconstruction. Regardless, it is likely that till from the Quebecia terrain occupied the area during the impact. The extent to which pre-YDB sediment was present in the St. Lawrence estuary around Sept Iles is not known. A recent study combines seismic reflection data, multibeam bathymetry, and core and chronostratigraphic data to infer that ~26 – 93 m of pre-Holocene till was deposited in the Lower St. Lawrence estuary farther to the west of Sept Iles (61). If Quebecia-derived till blanketed the Ordovician limestone around Sept Iles at the time of the Corossol impact, it could be the source of Melrose(and Newtonville) spherules. However, this scenario is less likely as the expected 187 Os/188 Os ratio of the Quebecia till is ∼1.3. The Quebecia terrain is therefore the likely source of Melrose (and Newtonville) spherules. A search should be conducted to locate other craters in this region.... [ Supporting Information, pages 11-19, including maps and photos ] Melrose, PA This sampling site, initially investigated by ref. 2 and also examined by Bunch et al. (3), is located in northeastern Pennsylvania, near the village of Melrose (41° 92′ 38.4″ N; 75° 50′ 31.4″ W) (Fig. S1 A ). Bulk sediment samples were collected from 0 to ∼40 cm, and the bottommost sample included channery loam fragipan. Channery silt loam colluvium from 28 to 40 cm included low levels of ~70 magnetic spherules per kilogram. Atop the till, a carbon-rich 5-cm stratum from 23 to 28 cm was sampled, which is interpreted as including postglacial sediment that could include sediments from the Younger Dryas (YD) cooling interval, dated by Bunch et al. (3), but not well constrained. This layer contained ∼400 microspherules per kilogram. In comparison with the spherules from other YDB sites, these spherules are much larger (2 – 5 mm in diameter). Newtonville, NJ This site is a sand pit located in southern New Jersey (39° 34′ 4.6″ N; 74° 54' 36.5″ W). The A-horizon is single-grain loamy sand that was recently bladed off and stockpiled. Two distinct loamy-sand horizons are present, separated by a clear wavy boundary (Fig. S1 B ). The first is an ashen-gray layer at 25 – 40 (50) cm below the present surface composed of organic matter, charcoal,and sand grains that are mostly coated with glass-like carbon. The second is a yellowish-brown layer at 40 (50) cm to 60 (120) cm that is low in organic matter, displaying no glasslike carbon coatings on grains. Its contact with underlying fragipan is abrupt and undulating due to cryoturbation during thermokarst ∼40 – 30 ka and marks the past permafrost table. Optically stimulated luminescence (OSL) dating of frost-crack in fill (16.8 ± 1.7 ka) derived from the second horizon material indicates this cover-sand is late Wisconsian (4). A 10-cm-thick sample was taken from the bottom of the ashen-gray layer, and it contained 1,840 magnetic microspherules per kilogram, and a 10-cm-thick sample from the top of the yellow-brown layer contained 2,000 microspherules per kilogram. A third offset sample taken ~100 cm deeper contained no detectable spherules.... 12.8 Ka impact confirmed by details from MUM7B site in Northern Andes, William C. Mahaney et al: Rich Murray 2013.08.14 http://rmforall.blogspot.com/2013/08/128-ka-impact-confirmed-by-details-from.html Evidence for deposition of 10 million tonnes of impact spherules across four continents 12,800 y ago, James H. Wittke et al, PNAS: Rich Murray 2013.05.22 http://rmforall.blogspot.com/2013/05/evidence-for-deposition-of-10-million.html Dennis Cox blog, plain text, with images of samples of magnetic black glaze on melt rocks from 13 Ka ice comet fragment extreme plasma storm geoablation in Fresno, California: Rich Murray 2010.07.02 http://rmforall.blogspot.com/2010/07/dennis-cox-blog-plain-text-with-images.html pertinent features near Campbell Mountain, studied by Dennis Cox, by his house in Fresno, CA: Rich Murray 2011.06.27 http://rmforall.blogspot.com/2011/06/pertinent-features-near-campbell.html http://craterhunter.wordpress.com/the-planetary-scaring-of-the-younger-dryas-impact-event/california-melt/ 19 images of Fresno mountains and rock samples ?cid=5d6b9f6c30c6fe9f&sc=photos&id=5D6B9F6C30C6FE9F%21\1348 photo of typical air burst geoablation glaze on hard bedrock at top of Mount Helix park, E San Diego: Rich Murray 2012.03.15 http://rmforall.blogspot.com/2012/03/redbrown-glaze-on-hard-crystalline.html http://rmforall.blogspot.com/2012/03/photo-of-typical-air-burst-geoablation.html 10 m broken rock hill with black glazes, W of Rancho Alegre Road, S of Coyote Trail, W of Hwy 14, S of Santa Fe, New Mexico, tour of 50 photos 1 MB size each via DropBox: Rich Murray 2011.07.28 2011.08.03 http://rmforall.blogspot.com/2011/08/10-m-broken-rock-hill-with-black-glazes.html http://rmforall.blogspot.com/2011/08/35479730-106085926-1865-km-el-top-10-m.html photos 3-5 of 50 within the fellowship of service, Rich Murray, MA Boston University Graduate School 1967 psychology, BS MIT 1964 history and physics, 254-A Donax Avenue, Imperial Beach, CA 91932-1918 rmforall@... <a href="tel:505-819-7388" value="+15058197388" target="_blank">505-819-7388 cell <a href="tel:619-623-3468" value="+16196233468" target="_blank">619-623-3468 home http://rmforall.blogspot.com ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com |
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