BASIN CIRCULATION CONTROLLING THE SEDIMENTOLOGIC AND ICHNOLOGIC RECORD OF THE FINE-GRAINED VACA MUERTA FORMATION (UPPER JURASSIC-LOWER CRETACEOUS, ARGENTINA)

PAZ, MAXIMILIANO; BUATOIS, LUIS ALBERTO; MÁNGANO, MARÍA GABRIELA; DESJARDINS, PATRICIO RAFAEL; RODRIGUEZ, MAXIMILIANO NICOLÁS; MINISINI, DANIEL; TOMASSINI, FEDERICO GONZALEZ; PEREIRA, EGBERTO; CARMONA, NOELIA BEATRIZ; FANTÍN, MANUEL; VALLEJOS, MARÍA DOLORES

Dubrovnik

Congreso; 36th International Meeting of Sedimentology; 2023

International Asociation of Sedimentology

Black shale studies have traditionally highlighted the impact of basin circulation in the stratigraphic and sedimentologic record of ancient basins, due to its effect in the distribution of sediments and the renewal of deep water masses. A sedimentologic and ichnologic analysis was carried out in the Vaca Muerta Formation fine-grained clinoform system (Upper Jurassic-Lower Cretaceous, Argentina) to create a robust depositional model and evaluate the control of basin circulation during deposition. Sedimentary facies were defined in cores from eight wells and one outcrop (total of 988.5 m). Forty-one facies were clustered into thirteen facies associations, constituting marginal marine, basin, drift, and slope environments. The marginal marine deposits comprise fine- to coarse-grained sandstone, bindstone and mudstone accumulated in beach and bay environments. The basin deposits are composed of fine mudstone interbedded with tuff, produced by pelagic, hemipelagic and rare flow, current and storm deposition. The drift deposits consist of crinoidal mudstone and fine to coarse mudstone and originated under contour current reworking. The slope deposits comprise calcareous fine to coarse mudstone, generated by pelagic, hemipelagic, and fluid mud deposition. Basin-wide circulation is interpreted as the underlying control for these deposits. During estuarine circulation, bottomset and foreset record basin and slope environments showing pelagic, hemipelagic, and fluid mud sedimentation. Anoxic or euxinia to lower dysoxic conditions were dominant. In contrast, weakened estuarine or anti-estuarine circulation developed bottomset and foreset with basin and drift environments affected by pelagic, hemipelagic, and contour current transport. Dysoxic to oxic conditions were common. A relative cooling and arid event during the late Tithonian indicates that climate could have been the triggering factor for anti-estuarine circulation, associated with higher winter convection and decreased freshwater input. Hence, this study demonstrates the critical effect of basin circulation on sediment distribution and bioturbation along a clinoform system, suggesting that its evaluation should be adequately considered in depositional models.