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

From: Gerald Flaherty <grf2_at_meteoritecentral.com>
Date: Mon Mar 21 13:24:55 2005
Message-ID: <006801c52508$eb90d230$6401a8c0_at_Dell>

Excellent abstract Paul, thank you, Jerry
----- Original Message -----
From: "Paul H" <bristolia_at_yahoo.com>
To: <meteorite-list_at_meteoritecentral.com>
Sent: Tuesday, March 08, 2005 11:26 PM
Subject: [meteorite-list] Discovery of distal ejecta from Sudbury impact
event


> 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 07:34:28 PM PST