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Title: 	The Late Pliocene *Eltanin* *Impact*: Documentation From
Sediment Core Analyses
Author(s): 	Gersonde, R.; Kyte, F.; Flores, J. A.; Becquey, S.

Abstract: 	The expeditions ANT-XII/4 (1995) and ANT-XVIII/5a (2001) of
the RV POLARSTERN collected extensive bathymetric and seismic data sets
as well as sediment cores from an area in the Bellingshausen Sea
(eastern Pacific Southern Ocean) that allow the first comprehensive
geoscientific documentation of an asteroid *impact* into a deep ocean
(approx. 5 km) basin, named the *Eltanin* *impact*. *Impact* deposits
have now been recovered from a total of more than 20 sediment cores
collected in an area covering about 80,000 km2. Combined
biomagnetostratigraphic dating places the *impact* event into the
earliest Matuyama Chron, a period of enhanced climate variability.
Sediment texture analyses and studies of sediment composition including
grain size and microfossil distribution reveal the pattern of *impact*-
related sediment disturbance and the sedimentary processes immediately
following the *impact* event. The pattern is complicated by the San
Martin Seamounts (approx. 57.5 S, 91 W), a large topographic elevation
that rises up to 3000 m above the surrounding abyssal plain in the area
affected by the *Eltanin* *impact*. The *impact* ripped up sediments as
old as Eocene and probably Paleocene that have been redeposited in a
chaotic assemblage. This is followed by a sequence sedimented from a
turbulent flow at the sea floor, overprinted by fall-out of airborne
meteoritic ejecta that settled trough the water column. Grain size
distribution reveals the timing and interaction of the different
sedimentary processes. The gathered estimate of ejecta mass deposited
over the studied area, composed of shock-melted asteroidal material and
unmelted meteorites including fragments up to 2.5 cm in diameter, point
to an *Eltanin* asteroid larger than the 1 km in diameter size
originally suggested as a minimum based on the ANT-XII/4 results. This
places the energy released by the *impact* at the threshold of those
considered to cause environmental disturbance at a global scale and it
makes the *impact* a likely transport mechanism explaining the presence
of extinct Cenozoic microfossils in the transantarctic Sirius Unit.
Although a crater structure representing *Eltanin* ground zero has not
been discovered, the distribution pattern of sediment disturbance and
ejecta deposits now allows to better determine the central target area
north of the San Martin Seamounts.