[meteorite-list] Possible Crater Detected Under Central California

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sun, 18 Mar 2007 20:56:43 -0700 (PDT)
Message-ID: <200703190356.l2J3uh923466_at_zagami.jpl.nasa.gov>

http://news.bbc.co.uk/2/hi/science/nature/6458841.stm

'Crater' spied under California
By Paul Rincon
BBC News
March 16, 2007

Oil exploration work in California's Central Valley region has uncovered
a possible space impact crater.

The 5.5km-wide bowl is buried under shale sediments west of Stockton, in
San Joaquin County, and is thought to be between 37 and 49 million years
old.

Researchers are continuing to analyse cuttings from oil exploration
wells drilled in the structure.

Details of the discovery were presented at the Lunar and Planetary
Science Conference in Houston.

Data from a 3D seismic survey of an ancient sea bed clearly shows a
circular structure buried 1,490-1,600m (4,890-4,250ft) below sea level.

The Victoria Island structure, as it has been named, has a concentric
rim surrounding a "central uplift" - a peak at the centre - which are
both characteristic of impact craters.

Co-investigator Professor Jared Morrow, from San Diego State University,
said the context of the crater in relation to surrounding rock layers
suggested it dated from the middle Eocene Epoch.

Crater pair

Preliminary estimates for the age of the crater suggest it is just too
early for an episode of multiple impacts on Earth known as the late
Eocene bombardment, which occurred about 35 million years ago.

One of the largest impact craters in the world - the 45km-wide (28
miles) Chesapeake Bay structure on the eastern shore of North America -
is from this period.

"It would be interesting if our crater dated to that time, but we can't
make that association at the moment," said co-author Jared Morrow, from
San Diego State University.

The team plans to look for characteristic geological signatures of
impact sites in cuttings drilled from wells in and around the structure.

These include a type of quartz deformed under intense pressure - known
as shocked quartz - as well as glass and melt particles, and an
enhancement of the element iridium.

Victoria Island is not the first crater proposed for the Central Valley.
A 1.3km-wide (0.8 miles) feature to the north known as the Cowell
structure, dating to the Miocene (5 to 24 million years ago), has also
been put forward as the location of a space impact.
Received on Sun 18 Mar 2007 11:56:43 PM PDT