[meteorite-list] Discovery of distal ejecta from Sudbury impact event

From: David Freeman <dfreeman_at_meteoritecentral.com>
Date: Mon Mar 21 13:24:55 2005
Message-ID: <422F33AD.6010806_at_fascination.com>

"...unicellular organisms" "...photosynthetic microbial mats" AKA
"stromatolites".
A site named fossilmall.com has pictures of the gunflint chert...and
specimens for sale.

Dave F.
eBay user ID mjwy
and seller of stromatolites and classic meteorwrongs



Paul H wrote:

>Discovery of distal ejecta from the 1850 Ma Sudbury
>impact event
>from "March Geology and GSA TODAY" media highlights
>at:
>
>http://www.eurekalert.org/pub_releases/2005-02/gsoa-mga022805.php
>http://www.gsajournals.org/gsaonline/?request=get-current-toc&issn=0091-7613
>
>Addison, W. D., and others, 2005, Discovery of
>distal ejecta from the 1850 Ma Sudbury impact
>event. Geology: Vol. 33, No. 3, pp. 193-196.
>
> Addison et al. announce the discovery of impact
>ejecta from the Sudbury, Ontario, Canada,
>structure, the second largest and third or fourth
>oldest extraterrestrial Earth impact site. At 1.85
>billion years old, these Paleoproterozoic ejecta
>are three times older than the previous oldest
>dated ejecta linked to a specific impact (Acraman,
>Australia, 0.59 billion years old). It is also larger
>than the well-known Chicxulub, Mexico (0.065
>billion years old) impact linked to the extinction
>of the dinosaurs and many other species. The
>young Chicxulub impact, particularly its well-
>preserved worldwide ejecta debris layers, have
>produced criteria to judge other large ejecta
>deposits. Foremost is the occurrence of sets of
>microscopic parallel lamellae in quartz and
>feldspar grains produced by the intense shock
>generated at the point of impact. Secondarily,
>the impact generated a megaplume of vaporized,
>melted, and crushed crustal rocks, creating molten
>droplets containing bubbles of gas, and larger
>accreted balls of dust and rock shards called
>impact accretionary lapilli. These features, and
>more, are seen in the Sudbury debris. The debris
>(ejecta) studied here, landed 650 km west northwest
>of Sudbury near Thunder Bay, Ontario, Canada, and
>875 km west of Sudbury near Hibbing, Minnesota,
>United States. This huge impact likely deposited
>debris all around Earth, but it is very difficult to
>find because so much of the evidence has been
>destroyed in the recycling of Earth's crust by plate
>tectonics. Life at the time of the Sudbury impact
>was confined to the oceans and consisted of
>unicellular and colonial unicellular organisms. So
>far, Addison et al. have found no evidence of
>extinction of this life. However, future studies may
>link this impact and its ejecta with changes in the c
>lassic Gunflint Iron Formation unicellular organisms
>and their photosynthetic microbial mats, which
>helped produce Earth's atmospheric oxygen.
>
>
>
>
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Received on Wed 09 Mar 2005 12:34:37 PM PST