Computer Science – Sound
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p51a1181w&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P51A-1181
Computer Science
Sound
5420 Impact Phenomena, Cratering (6022, 8136), 6022 Impact Phenomena (5420, 8136), 8136 Impact Phenomena (5420, 6022)
Scientific paper
In the late 1950's, geophysical field parties undertaking gravity surveys across Antarctica observed over a large area of Wilkes Land (> 240km across) an exceptionally pronounced negative free air anomaly ((to -158.3 mgal). This area was later interpreted as a possible meteor impact site because the gravity profiles were similar to those of known impact sites (apparent rim structures, circular basins, central peaks or rings), they possessed appropriate aspect ratios (e.g., crater diameter vs crater depth), anomalously steep negative free air gravity anomaly gradients (to 4.71 mgal/km) were characteristic of impact craters and uncharacteristic of solely mantle-related or geologic crustal variations, etc. The condition of the ice covering the anomaly (heavily crevassed), the apparent lack of isostatic compensation with surrounding environs, etc suggested the impact was geologically recent and that perhaps a tektite strewn field was associated with it. The distance from the postulated impact to the Australian strewn field was appropriate as are the ages of the tektites there. This early work has been augmented with the detection of a dominant cluster of negative free air gravity anomalies crossing the continental-oceanic boundary, and the East and West Antarctic structural boundary (i.e., Transantarctic Mountains). These anomalies are coincident with complex subglacial craterform topographic features inferred from radiosounding (to -500m below MSL). The major interior positive free air gravity anomalies are associated with subglacial topographic highs. The elliptical distribution of the negative gravity anomalies resemble known multiple impact distributions (scatter ellipses with the larger anomalies forward and the lesser ones aft). This more recent information favors expanding the original proposal to that of a multiple meteoroid impact. The multiple impact hypotheses would explain aeromagnetic surveys revealing ring-shaped structures in the subglacial rock surface much like those of known impact structures (the magnetic anomalies are unusual in magnitude themselves: amplitudes to 3600nT for sensors at 3.5 km elevation). Deviations from this topography can be attributed to glacial scour. Certainly glacial surging should accompany such an impact. The distribution of the apparent impact structures extends beyond the original discovery and on the basis of negative free air anomalies, into the Wilkes Subglacial Basin to the south, athwart the Transantarctic Mountains and into the Ross Embayment to the east. No multiple impact sites of comparable size on Earth have been reported. The above suggestions have been augmented by recent work on cores taken from the Ross Sea which has revealed the presence of material of high magnetic susceptibility often taken as an indicator of meteor impact and tektites. The age of this material is placed in the Late Pliocene. The oldest ages reported for meteorites collected from the Antarctic Blue Ice is ca. 700,000y.
Rice Alex
van der Hoeven F.
Weihoupt J. W.
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