May 7th, 2005--New Revelations about Impact Crater

Dallas Abbott has shared her investigations about underwater impact craters during the past few E2C series. It is always a pleasure to hear her discuss her latest discoveries.

Click here for her PowerPoint (in pdf format).

This year, she will describe work she and colleagues have done in the central Indian Ocean. Below is an abstract about this research from a recent scientific conference.

Burckle Abyssal Impact Crater: Did this Impact Produce a Global Deluge?
Dallas H. Abbott1, W. Bruce Masse3, Dee Breger2, and Lloyd Burckle1
1
Lamont Doherty Earth Observatory of Columbia University, Palisades, NY 10964
2
Los Alamos National Laboratory, Los Alamos, NM 87545n
3
Drexel University, Philadelphia, PA

             We have found an impact crater that is likely < 6000 years old.   Burckle Crater is in the central Indian Ocean at 30.87 S 61.36E. The crater is 311 km wide.  The crater is deepest SE of its center.  There is a deep gouge in the surface topography to the SE and a topographically smooth area NW of the crater rim.  These topographic features suggest that the impactor came from the SE and that the tektite field lies NW of the crater rim.  We are looking for tektites in young abyssal sediments from NW of the crater.  Because the impactor hit a fracture zone wall, the rim of Burckle crater is unusually well defined.  The crater rim shows evenly spaced notches that we interpret as resurge gullies.  Near Burckle crater, we found a 26 cm thick layer with high magnetic susceptibility that extends to the top of core DODO132P.   DODO132P has a basal age of Pleistocene.  The high susceptibility layer contains numerous Mn oxide coated rock fragments, as expected for an ejecta layer from an impact that fragmented a fracture zone wall.  These fragments do not resemble typical Mn nodules.   We also found clear fragments of mid-ocean ridge type plagioclase and a grain of NiC with a metallic luster.  The NiC is clearly a fragment of the impactor as it has an ablation rind of oxidized NiC that forms drops on the surface of the grain.  The NiC contains no significant Fe and we interpret it as a piece of a comet.  Burckle crater impact event is in the right location to be the source of devastating rains, tsunamis, winds, and associated social upheaval around 2807 B.C.

(Masse W.B. (in press) The archaeology and anthropology of Quaternary period cosmic impact.  In:  P Bobrowsky and H Rickman (eds.) Comet/Asteroid Impacts and Human Society.  Springer.)

Dallas frequently uses an impact effect model created by Robert Marcus, H. Jay Melosh, and Gareth Collins:
http://www.lpl.arizona.edu/impacteffects/