Mathematics – Logic
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....13189h&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #13189
Mathematics
Logic
Scientific paper
Glass fragments have long been an enigmatic stratigraphic component in loessoid sequences of the Pampean basin, Argentina. Although many mechanisms have been proposed to explain the origin of these 'escorias', it is now clear that certain escorias represent meteorite impact-derived melt materials that have been preserved as a result of characteristics endemic to the Pampean basin. Our work since the early 1990's focused on the origin, age, and stratigraphic context for escorias in type sections. An important example includes the age of 3.3±0.1 Ma for meteorite impact glasses collected in the sea cliffs near Chapadmalal. The challenges presented in dating such material are formidable, as the glasses are commonly highly vesicular (with trapped, extraneous argon), exhibit various stages of alteration, contain varying amounts of xenocrystic material, and they typically occur in sections that lack other stratigraphic markers (e.g., volcanic ash). Through the past several years we have refined our 40Ar/39Ar technique in dating these materials, and combined our geochronologic research with other isotopic and geochemical, paleomagnetic, stratigraphic and paleontologic tools in order to explore other prominent sections of the Pampean loess sequences. Our recent work enables us to define more than five distinct impact-glass horizons, the youngest of which has yielded an age of 6 Ka. The motivation for undertaking such painstaking and integrated study is strong, as the resulting data can provide much needed insights for the Miocene-Recent impact history of the southern hemisphere, the flux rate for meteorite impacts, and chronostratigraphic markers to the rich faunal record of the Pampean loessoid sequences. Such an integrated approach is also absolutely required, because of reworking and similarities in appearance of some escorias, and thus the true radiometric age, geochemical composition, and stratigraphic setting must be established for each escoria occurrence prior to correlation with other escorias or geologic events.
Hames W.
King Ji
Renne Paul
Schultz Peter
Zarate Marcelo
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