Stratigraphy of the La Yesera Formation (Cretaceous): basal synrift fill of the Salta Group, Northwest Argentina

Abstract

The red beds of La Yesera Formation, which are the basal strata of the Salta Rift, accumulated from the Late Neocomian to the Cenomanian. The La Yesera Formation is thicker than 700 meters in the Alemanía sub-basin. The unit is made up of three sections: the lower and upper ones are dominated by conglomerates, and the middle section consists of sandstone and siltstone. It is proposed here to consider these sections as formal members. The lower section, or Yacutuy Member, is composed of alluvial-fan conglomerates and scarce mud-flat sandstone and siltstone. The middle section, previously identified as Las Chacras Member, consists of mud flat siltstone and sandstone. The upper section, or Don Bartolo Member, is composed of alluvial-fan conglomerates and lava flows of the Isonza Basalt. La Yesera Formation is thicker than 2,000 meters in the Brealito sub-basin. In the upper portion of the middle section was recognized the section called Brealito Member. It is composed almost entirely of siltstone with scarce calcareous mudstone and green shale. The basement of the basin is composed of rocks of the Pampean Massif, and Ordovician to Devonian sedimentary units. These two types of basement, of different rheology, probably determined different scenarios in response to tensional stress during basin formation. Four volcanic events controlled by NE-trending lineaments were recognized in the basin.