Integrated U-Pb zircon and palynological/palaeofloristic age determinations of a Bashkirian palaeofjord fill, Quebrada Grande (Western Argentina)

Victoria Valdez Buso*, Mercedes di Pasquo, Juan Pablo Milana, Benjamin Kneller, Claus Fallgatter, Farid Chemale Junior, Paulo Sérgio Gomes Paim

*Corresponding author for this work

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

This work presents a new age framework for the main Bashkirian glacio-eustatic transgression in Argentina, including the first absolute age for the Jejenes Formation, San Juan Province, based on radiometric dating of a crystal-rich tuff, supported by palynological and palaeofloristic studies, and presented within a revised palaeogeographic setting. The Jejenes Formation represents the glacial to postglacial fill of the Quebrada Grande palaeofjord carved in the Eastern Precordillera. The succession has been subdivided into five stages, the youngest of which suggests a previously unrecognised glacial event for this locality. Six productive levels for palynology were found within proglacial strata, and in the base and top of the succeeding interglacial stage. Palynoassemblages are characterized by poorly preserved trilete spores and monosaccate pollen grains along with a large amount of terrestrial phytoclasts. Main species indicating the Raistrickia densa-Convolutispora muriornata SubZone (DMa SZ) are Vallatisporites ciliaris, Cristatisporites rollerii, C. stellatus, C. chacoparanensis, C. inconstans and monosaccates such as Circumplicatipollis plicatus. This DMa SZ is estimated as Serpukhovian/Bashkirian and characterizes the glacial-related Guandacol Formation and equivalents units of the western Paganzo Basin. A tuffaceous level in the proglacial unit, bearing platyspermic seeds, plant remains and palynomorphs, yielded first-cycle volcanic zircons that were analysed by SHRIMP. An absolute age of 321.3 ± 5.3 Ma confirms a Bashkirian age for the main postglacial transgression in the Paganzo Basin, and offers a novel calibration for the palynoassemblages of DMa SZ that occurs elsewhere in Western Argentina.

Original languageEnglish
Pages (from-to)202-222
Number of pages21
JournalJournal of South American Earth Sciences
Volume73
Early online date18 Dec 2016
DOIs
Publication statusPublished - Jan 2017

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Keywords

  • Isotopic age
  • Jejenes formation
  • Late palaeozoic ice age
  • Paganzo basin
  • Palynology
  • Platyspermic seeds

ASJC Scopus subject areas

  • Geology
  • Earth-Surface Processes

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