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

TY - JOUR

T1 - Integrated U-Pb zircon and palynological/palaeofloristic age determinations of a Bashkirian palaeofjord fill, Quebrada Grande (Western Argentina)

AU - Valdez Buso, Victoria

AU - di Pasquo, Mercedes

AU - Milana, Juan Pablo

AU - Kneller, Benjamin

AU - Fallgatter, Claus

AU - Junior, Farid Chemale

AU - Gomes Paim, Paulo Sérgio

N1 - This work is part of a research project supported by BG Brazil E&P Ltda. entitled “Carboniferous deglacial record in the Paran a Basin and its analogue in the Paganzo Basin of Argentina: Impacts on reservoir predictions” undertaken at the Universidade do Vale do Rio dos Sinos (UNISINOS), Brazil, in partnership with Universidad Nacional de San Juan, and University of Aberdeen, United Kingdom; and with funds from Consejo Nacional de Investigaciones Científicas y Tecnicas CONICET PIP 0305 (2011-2013). This contribution is part of the PhD of the senior author funded by BG Brazil E&P Ltda. A special acknowledgment is made to Carla Puigdomenech, Carol Aquino, Deise Silveira, Fabiano Rodrigues and Willian Matsumura, who have collaborated during field work. To Professors Andrea Sander and Wilson Wilder, who helped with the petrographic analysis of the tuffite. Thanks are also given to Lic. Leonardo Silvestri for his help in sample processing at the CICYTTP-CONICET. At last, the authors would like to acknowledge the ANP (Agencia Nacional do Petroleo, Gas Natural e Biocombustível) for their economic assistance.

PY - 2017/1

Y1 - 2017/1

N2 - 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.

AB - 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.

KW - Isotopic age

KW - Jejenes formation

KW - Late palaeozoic ice age

KW - Paganzo basin

KW - Palynology

KW - Platyspermic seeds

UR - http://www.scopus.com/inward/record.url?scp=85007565868&partnerID=8YFLogxK

U2 - 10.1016/j.jsames.2016.12.009

DO - 10.1016/j.jsames.2016.12.009

M3 - Article

VL - 73

SP - 202

EP - 222

JO - Journal of South American Earth Sciences

JF - Journal of South American Earth Sciences

SN - 0895-9811

ER -