Carbon isotopes and the K-T boundary in Argentina and Chile

CARBON ISOTOPES AND THE K-T BOUNDARY IN ARGENTINA AND CHILE

V

¹¹

MIGUEL A. PARADA ², ALEJANDRO J. TOSELLI ³ and FLORENCIO G. ACEÑOLAZA ³

¹NEG-LABISE, Dept. de Geologia, UFPE, 50732-970 Recife, PE.

²Dept. de Geologia, Universidad de Chile, Santiago, Chile.

³INSUGEO, Universidad de Tucuman, S.M. Tucuman, Argentina, 4000.

In South America, only in few localities the K-T boundary is recorded in limestones: (a) Pernambuco-Paraiba coastal basin, NE Brazil, (b) Yacoraite and Neuquen basins, Argentina and (c) Darwin's Navidad and Magellan basins, Chile.

At the Yacoraite basin, Jujuy and Salta provinces, NW Argentina, the K-T boundary has been recorded in a 2m-thick reddish marl layer at the bottom of the Tunal Fm. which overlies limestones of the Yacoraite Fm. (e.g. at Cabra Corral, 70 km NW from Salta town) and also at Maimara, north of Jujuy, where Tertiary sandstones with calcitic cement overlie 50 m-thick Maastrichtian limestones.

At Punta Topocalma, Darwin's Navidad basin, the K-T boundary is represented by a thin conglomerate layer, on top of Maastrichtian calcitic sandstones and coquina beds, which is covered by unfossiliferous sandstones with calcitic cement. At Punta Algarrobo, very fossiliferous Maastrichtian gray marls are separated by a thin conglomerate layer from a Tertiary marls with trace fossils.

In the Magellan basin, Upper Maastrichtian glauconitic arenite, sandstones with calcareous cement and limestone concretions of the Punta Rocallosa Fm. are covered by sandstones, claystones, limestones with limestones concretions of the Upper Maastrichtian-Lower Paleocene Chorillo Chico Fm. The K-T boundary is at the lower portion of the Chorillo Chico Fm.

The Yacoraite Fm. (Maimara and Cabra Corral localities) exhibits C values between +1 and +2 ^o/_^ooPDB, and a remarkable drop in the K-T boundary to values of -4 ^o/_^ooPDB. In the Tunal Fm., values range from -3 to -1 ^o/_^ooPDB. At Punta Rocallosa, C varies from -4 to -33 ^o/_^ooPDB, and the lowest value within the Chorillo Chico Fm. marks the K-T transition. At Topocalma, C shows negative values whose minimum value (-30 ^o/_^ooPDB) probably corresponds to the K-T boundary. Oxygen isotopes suggest that temperature drop drastically at the K-T boundary in NE Brazil, while in Chile and Argentina, temperature raised abruptly. (May 19, 2000)

Publication Dates

• Publication in this collection
  05 Jan 2001
• Date of issue
  Dec 2000