THE TRANSITION FROM MARINE TO CONTINENTAL DEPOSITS IN THE DEVONIAN OF THE PRECORDILLERA, WESTERN ARGENTINA.

Authors

  • Alfredo J. Cuerda
  • Oscar G Arrondo
  • Eduardo Morel
  • Luis A. Spalletti

Keywords:

sedimentology, Devonian,

Abstract

The Devonian Punta Negra Formation is made up of a 1.700 m thick turbidite succession. Recent investigations carried out in the Precordillera of San Juan (Bachongo area) have shown that the upper levels of this Formation grade upwards to red shales and sandstones. Correlatively, it was observed an increase in the grain size and the appearence of trough cross-bedded strata. This red unit, 65-70 m thick, has be en interpreted as a progradational de1taic sequence formed during a period of low-stand sea-leve!. Analysis of the detrital modes in this de1taic unit shows the predominance of quartz-feldespathic sandstones, probably derived from intracratonic blocks. It is considered that this sequence represents the first gondwanic continentalization event in the Precordillera region. The sedimentary column is bounded at the top by an unconformity upon wlúch lies the basal conglomerate of the continental Carboniferous sequence (Andapaico Formation).

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