Middle Ordovician graptolite biostratigraphy from volcaniclastic turbidites and a new U-PB zircon age from the Huaytiquina section, western Puna, Argentina

Abstract

Graptolites studies constitute the main scientific contribution to the understanding, dating, and correlation of early Paleozoic sedimentary sequences in the Argentine Puna. They also recently provided pioneering insights for a high-resolution stratigraphy in the region, based on the comparison with the conodont results. This study analyzes, for the first time, the ages independently obtained from the graptolite biostratigraphic framework of the western Puna, at the Huaytiquina section, and the U-Pb zircon age of a tuff layer found at the top of this section, corresponding to the Puna Turbidite Complex. Graptolite records from the Huaytiquina section allowed the assignment of the lower part of the Puna Turbidite Complex to the Azygograptus lapworthi Biozone (early Dapingian, Dp1). In the middle part of the sequence, specimens of Isograptus sp. and Tetragraptus bigsbyi, associated with the conodont Baltoniodus cf. B. navis, suggest a middle Dapingian age (Dp2) for the carbonate-bearing levels. Furthermore, the presence of Isograptus divergens in the Catua section, located a few kilometers southeast of Huaytiquina, supports the hypothesis that deposits corresponding to the late Dapingian (Dp3) to early Darriwilian(Dw1) may also be present in the upper part of the Huaytiquina section. The U-Pb ages maximumlikelihood age of deposition (MLA) or maximum depositional age (MDA) obtained from a tuff layer identified at the top of the Huaytiquina section is 479 ± 8 Ma, with youngest zircons of darriwilian ages (461 ± 22 Ma). In addition, the recycling zircons populations are Cambro-Ordovician ages, with a smaller proportion of Neoproterozoic and Paleoproterozoic zircons. As a result, the biostratigraphic information based on recent graptolite records helps to bridge the gap between the ages of the bearer levels and the age suggested by the analyzed zircons at the Huaytiquina section.