Basin circulation affecting sediment partitioning in a fine-grained carbonate–siliciclastic, subaqueous clinoform: the Upper Jurassic–Lower Cretaceous Vaca Muerta Formation, Neuquén Basin, Argentina

Abstract

Fine-grained sediments deposited under oxygen-deficient conditions are enriched in organic matter and hold considerable economic interest as unconventional reservoirs. The present analysis integrates sedimentological, ichnological, and geochemical datasets to understand depositional processes in the Upper Jurassic–Lower Cretaceous Vaca Muerta Formation (Argentina), the most important economical unconventional play outside North America. For this purpose, cores from eight wells and one outcrop were examined. The succession comprises thirteen facies associations corresponding to marginal-marine, basin, drift, and slope environments, deposited in a mixed carbonate-siliciclastic, shelf-margin, subaqueous clinoform system. Estuarine circulation during warm and humid climates produced a stable stratification. Sediment delivery was dominated by pelagic processes in the bottomset, and hemipelagic processes and fluid mud flows in the foreset. However, the typical estuarine circulation changed to weakened estuarine or anti-estuarine during cool and arid climates, triggering wind- and thermohaline-driven contour (bottom) currents that reworked and oxygenated the complete clinoform system. The analysis suggests that distal-proximal trends are of lesser importance for the delineation of sedimentary environments in settings with contrasting basin circulation regimes and provides several insights to understand sediment partitioning in fine-grained clinoform systems. Supplementary material: Stratigraphic context of the Vaca Muerta Formation, example of facies distribution in a well, trace-fossil descriptions, and XRD and TOC geochemical data is available at https://doi.org/10.6084/m9.figshare.c.6294914

Microbial mats and their palaeoenvironmental analysis in offshore – shelf facies of the Los Molles Formation (Toarcian – Lower Callovian) in the Chacay Melehue area, Neuquén Basin, Argentina

“…Fossil records of microbial activity in shallow coastal environments is well known (Carmona et al., 2012; Homann et al., 2015; Noffke, 2010; Noffke et al., 2008, 2013; Paz et al., 2021, 2022; Schieber et al., 2007; Seckbach & Oren, 2010; Tang et al., 2012). However, they are less common in deeper settings such as offshore or shelf environments (Banerjee & Jeevankumar, 2005; Logan et al., 1999; Noffke et al., 2002, 2003; Noffke, Beukes, et al., 2006; Noffke, Eriksson, et al., 2006; Pflüger, 1999).…”

“…Fossil records of microbial activity in shallow coastal environments is well known (Carmona et al, 2012;Homann et al, 2015;Noffke, 2010;Noffke et al, , 2013Paz et al, 2021Paz et al, , 2022Schieber et al, 2007;Seckbach & Oren, 2010;Tang et al, 2012).…”