"Impacts on Earth in the Late Triassic"

[MKIRKALDY@aol.com]

The September 10, 1998 issue of Nature (395, 126) has two articles on 
"Impacts on Earth in the Late Triassic" which concern the five impact
structures which are thought by Spray et al. to be a "multiple impact
event."   Dennis V. Kent says no, because of opposite geomagnetic
polarities in the rocks.   John G. Spray replies, with the explanation
that:   "Palaeomagnetic fields are acquired when magnetic mineral 
phases pass through their Curie points (the temperatures at which
iron minerals assume magnetic order and remain with their magnetic 
moments parallel to the Earth's magnetic field at that time). Critically, 
this does not necessarily coincide with the time of formation of the host 
rocks."

These multiple impacts were discussed on this list a month or two ago.

Mary
mkirkaldy@aol.com