Facies and microfacies of the Tithonian-Berriasian ramp from the Neuquén basin (Vaca Muerta Formation) in the Loncoche creek section - Malargüe, Mendoza

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Diego A. Kietzmann
Ricardo M. Palma
graciela S. Bressan

Abstract

Facies association of the Tithonian-Berriasian Vaca Muerta Formation from the Loncoche creek section, Neuquén Basin, west central Argentina, allow the distinction and definition of 12 lithofacies and 8 microfacies, which are dominated by molluscs, echinoderms, foraminifera, brachiopods, serpulids and radiolarians. The Vaca Muerta Formation consists of a rhythmical alternation of black shales, grey shales, marls and siltstones, with bioclastic mudstones, wackestones, packstones, floatstones and rudstones. Facies associations corresponding to four types of depositional settings were distinguished: basin, outer ramp (distal and proximal), and middle ramp. The Nassellaria/Spumellaria ratio was used for bathymetrical interpretation and allows an estimation minor than 200 m depth. The strata pattern and vertical facies distribution show three depositional sequences between a tithonian homoclinal ramp and a berriasian steep homoclinal ramp system. The depositional sequence 1 consists of basin and distal outer ramp facies and it is characterized by a retrogradational pattern. It reaches 124 m in thickness, and may be assigned to the Virgatosphinctes mendozanus Zone up to the base of Corongoceras alternans Zone. Depositional sequences 2 and 3 consist of outer ramp and middle ramp facies. They are characterized by agradational and progradational patterns. The thickness of the sequences 2 is 66 m and is assigned to Corongoceras alternans Zone, meanwhile sequence 3 reachs 78 m and corresponds to Substeueroceras koeneni and Spiticeras damesi Zones.

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Kietzmann, D. A., Palma, R. M., & Bressan, graciela S. (2008). Facies and microfacies of the Tithonian-Berriasian ramp from the Neuquén basin (Vaca Muerta Formation) in the Loncoche creek section - Malargüe, Mendoza. Revista De La Asociación Geológica Argentina, 63(4), 696-713. Retrieved from https://revista.geologica.org.ar/raga/article/view/1324
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