New contributions to the palaeoenvironmental framework of the Los Molles Formation (Early-to-Middle Jurassic), Neuquén Basin, based on palynological data

Abstract

Being the main oil-bearing basin of Argentina, the Neuquén Basin contains a well-documented stratigraphic record of continental and marine sedimentation during the Jurassic and Cretaceous in the western margin of Gondwana. Marine sedimentation started in the Early Jurassic with the deposition of the offshore to prodelta shales of the Los Molles Formation, the basal unit of the Cuyo Group. A palynological study of outcrop samples of the Los Molles Formation at two localities, Puente Picún Leufú, southern Neuquén Basin, and Cordillera del Viento, central basin area, is presented. The palynological evidence allows inferring two different palaeoceanographic contexts during the deposition of the Los Molles Fm. At Puente Picún Leufú and the lower part of the Cordillera del Viento localities, the record of acritarchs and prasinophytes suggests a stratified water column, suboxic-to-anoxic bottom conditions, and a reduced salinity within the photic zone, associated with a marginal marine environment under restricted oceanic circulation. These conditions would have last at least until the Early Bajocian. Conversely, at the middle and mainly the upper part of Cordillera del Viento locality, the predominance of dinocysts in the assemblages indicates a hydrographically unstable shelf (non-stratified water mass column) with welloxygenated bottom waters developed under open-marine settings with non-restricted oceanic circulation. The abundance and diversity of dinocyst assemblages are comparable with those observed in the Late Callovian Lotena Formation. These evidences suggest an open oceanic circulation due to the establishment of different seaways in the Neuquén Basin, during the final accumulation of the Los Molles Formation (Early Callovian).

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

“…The Beggiatoaceae family includes recognized genera such as Beggiatoa and Thioploca , among others, capable of building microbial mats (Noffke et al., 2003; Teske & Salman, 2014). They are currently considered indicator organisms of aquatic habitats with partial or advanced (anoxia) oxygen depletion and sulfidic bottom conditions (Teske & Salman, 2014), similar to those described by other authors for the Los Molles Formation (Al‐Suwaidi et al., 2022; Campetella et al., 2020; Olivera et al., 2020; Rodriguez et al., 2018). Flood et al.…”

“…Considering this evidence, it is possible to infer, for this section of the Los Molles Formation, that the presence of these ichnogenera reflects dysoxic conditions that existed at the watersediment interface, with a seafloor rich in benthic food and sediments with low-oxygen concentration (Campetella et al, 2020;Damborenea & Manceñido, 2005;Savrda & Bottjer, 1991;Uchman, 1995). In this regard, Olivera et al (2020) proposes two contrasting scenarios of paleoenvironmental conditions in the study area, based on the palynological content. From the Pleinsbachian to the early Bajocian, these settings would have been characterized by a stratified water column with suboxic to anoxic bottoms and reduced salinities in the photic zone, due to a restricted circulation.…”

Palaeoenvironments and palaeoclimate of the uppermost Cuyo Group and lowermost Lotena Group at Quebrada Álvarez, Picún Leufú Sub-basin, Patagonia, Argentina: a preliminary study based on palynology

“…A noteworthy feature of the palynological matter in the samples studied at the Quebrada Álvarez section is the high proportion of phytoclasts, except in one sample of the Bosque Petrificado Formation (UNSP-QA5882) in which amorphous organic matter is predominant (Figures 6 and 8(b)). Several authors (Tyson 1995; Oboh-Ikuenobe and Villiers 2003; Martínez et al 2008; Olivera et al 2020; among others) have mentioned that a high percentage of phytoclasts would indicate proximal conditions to the source area and/or a high terrestrial input into the basin. The relationships between the op:tp and eo:bo ratios provide significant information for palaeoenvironmental interpretations.…”

“…The relationships between the op:tp and eo:bo ratios provide significant information for palaeoenvironmental interpretations. Thus, the op:tp ratio is related to distance and/or duration of transport, whereas the eo:bo ratio is associated with variations in flow velocity (Olivera et al 2020; Chalabe et al 2022).…”

Integrated source rock evaluation along the maturation gradient. Application to the Vaca Muerta Formation, Neuquén Basin of Argentina

“…The thickness increases from approximately 500–900 m following the main NW–SE axis of the basin. However, important differences in thickness are related to inherited topography of the underlying rift depocenters (Legarreta & Villar, 2011; Olivera et al., 2020). Based on TOC contents, the lowermost part (ca.…”