Late Carboniferous intra-arc sediments in the north Chilean Andes: Stratigraphy, paleogeography and paleoclimate

Abstract

Thick terrestrial Late Carboniferous to Triassic volcanosedimentary successions, a prominent feature of the Chilean and Argentinian High Andes, were formed on the active continental margin of Gondwanaland. Their stratigraphic position and the paleogeographic and paleoclimatic relations to neighbouring successions are poorly defined. A more precise age has been obtained for alluviolimnic intra-arc sediments (Miembro Medio), which are intercalated in the Late Carboniferous-Triassic volcano-sedimentary successions in the Salar de Atacama area of northern Chile. The ostracodes Carbonita cf. pungens and Paraparchites sp., which occur in the lower part of the Miembro Medio, are of Late Carboniferous, probably Westphalian age. The diverse taphoflora, which occurs in a higher stratigraphic level than the ostracodes, includes sphenophytes, ferns, gymnosperms and pteridophylls, for which we assume a late Westphalian-Early Permian age. Considering radiometric data of under-and overlying volcanic rocks, a Westphalian-Stephanian (to? Early Permian) age is inferred for the Miembro Medio. Fauna and flora indicate that warm-humid and seasonal climatic conditions existed during the deposition of the lower fossiliferous part of the Miembro Medio. This coincides with the sedimentary paleoclimatic indicators of the Miembro Medio and the climate which was assumed to have predominated in wide parts of the Central and Southern Andes during the Latest Carboniferous. © 1992 Institut für Palaentologie, Universitat Erlangen.