GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 205-12
Presentation Time: 9:00 AM-6:30 PM


BURCHARD, Hermann G.W., Mathematics, Oklahoma State University, 6310 W CANTERBURY ST, STILLWATER, OK 74074-1008

As a major scientific discovery, the long-sought crater of the Eltanin impact is in plain view on Google Earth @ 57º52'50''S, 90º56'59''W, the apex of the central uplift, a giant multi-ring structure > 250 km possibly as large as 300 km, clearly recognizable although we do not have a high resolution image. The impact had been discovered in 1981 by UCLA geologist Frank Kyte using two piston cores collected on a 1964 cruise of the research vessel USNS Eltanin. The impact date is 2.588 Ma, accepted by the International Geophysical Union as official date for the beginning of the Pleistocene. Early searches had been unsuccessful mainly because researchers expected a crater of moderate size. A geographical impact structure substantially never had been identified, although known to exist in the Bellingshausen Sea–SW of Chile. This was so, despite 1995 & 2001 cruises of RV Polarstern, Alfred Wegener Institut, Bremerhaven, by Rainer Gersonde & Frank Kyte, who had recovered piston cores containing impact debris in a search box near the crater, its midpoint offset from the crater center by 47 km. The impact structure is substantially identical with the Freeden Seamounts, formerly San Martin Seamounts, known site where the impact occurred but in fact the result of the impact explosion. The impact energy can be estimated from large cracks or faults toward the NW & then W of the impact, the Eltanin Fault System or Fracture Zone, splitting the seafloor for 4,000 nautical miles. Hence the asteroid must have come in at a shallow angle trajectory from the E or SE. The impact did not break through the crust, although it must have caused a maximal magnitude >9 quake. Submarine craters can get to be extremely large due to giant mud waves & high velocity mudflows. This one is 300 km, from a 1 km asteroid, a size relation that would be impossible on land. Kyte & Gersonde were looking for the impact crater but misidentified the Freeden sea mounts which they mention as the locality where impact debris is found as "large, irregular seamounts," unaware this is the crater/ impact structure that they are looking for, close to piston cores E13-4 and PS2708-1, its center about 11 km & 14 km to the S of the cores. An antipodal quake may have produced chaotic terrane near the city of Krasnoyarsk, tall granitic plutons, the Stolby Nature Preserve, popular with rock climbers. The antipodes have been displaced by 334 km from tectonic plate motion, for a combined annual 129 mm/a.