First record of the Valanginian positive carbon isotope anomaly in the Mendoza shelf, Neuquén Basin, Argentina: palaeoclimatic implications

Alejandro R Gómez Dacal,Daniel G Poiré,Alcides N Sial,Aron Siccardi,Lucía E Gómez Peral,Luis A Spalletti

doi:10.5027/andgeov45n2-3059

Alejandro R Gómez Dacal, Daniel G Poiré + Show 4 more

Open Access

https://doi.org/10.5027/andgeov45n2-3059

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Abstract

The Tithonian-Valanginian time interval in the Mendoza Shelf (Neuquén Basin, Argentina) is well exposed in the Río Salado, Puesto Loncoche and Cuesta del Chihuido sedimentary sections. From those localities, more than fifty preserved oyster shells of the genus Aetostreon sp. were selected and sampled in order to perform the first δ13C curves for this particular time interval. Mineralogical and cathodoluminiscence properties, inner micromorphology of the valves, added to major and trace element geochemistry were analyzed in order to highlight the best C-O isotopic preservation. The δ13C isotope curves show values varying between 0 and -3‰ VPDB for the Tithonian-Berriasian basal section, and a positive excursion of ~2.4-2.7‰ VPDB in the Valanginian upper section. This δ13C up section trend is here considered in order to reveal eminent correlations with other sections from the Neuquén Basin, as well as the Weissert Event from the Tethys area, also on the basis of their ammonite faunal zones. The palaeotemperatures obtained from δ18O preserved values, added to a detailed sedimentological study suggest that observed δ13C anomaly may responds to a global climatic change from warm and dry to warm and humid conditions.

Highlights

The Valanginian positive δ13C excursion was first recorded by Cotillon and Río (1984) in the Gulf of Mexico (DSDP Site 535)
The Mn/Sr ratio is below 1.5 (Table 1), except for three samples (PL88, CDC35 and CDC38, excluded from further interpretation), which are as high as Mn/Sr=6 and are considered as probably being diagenetically altered
The occurrence of the well-established midValanginian positive δ13C excursion is documented, and it is recognized in the upper section of the Chachao Formation and characterized by the O. atherstoni Ammonite Zone in the Río Salado, Puesto Loncoche and Cuesta del Chihuido areas

Summary

Introduction

The Valanginian positive δ13C excursion was first recorded by Cotillon and Río (1984) in the Gulf of Mexico (DSDP Site 535) It was described by many authors in different basins throughout the northern hemisphere (Lini et al, 1992; Weissert et al, 1998; Hennig et al, 1999; Melinte and Mutterlose, 2001; Bartolini, 2003; Erba et al, 2004; Duchamp-Alphonse et al, 2007; Price and Nunn, 2010; Charbonnier et al, 2013; Meissner et al, 2015; Silva-Tamayo et al, 2016), and subsequently in the Neuquén Basin (Aguirre-Urreta et al, 2008; Gómez Peral et al, 2012) (Fig. 1), in the southern hemisphere. Such hypothesis is supported by glendonites (Kemper, 1987; Tarduno et al, 2002), dropstones, as well as by the nature of calcareous nannofossils (Melinte and Mutterlose, 2001)

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