Ichnology of muddy shallow-water contourites from the Upper Jurassic-Lower Cretaceous Vaca Muerta Formation, Argentina: Implications for trace-fossil models.

• Autores: Paz, Maximiliano; Mángano, Gabriela; Buatois, Luis; Desjardins, Patricio; Notta, Raul; Gonzalez Tomassini, Federico; Carmona, Noelia Beatriz
• Año de publicación: 2022
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Ciencias Exactas y Naturales; Vaca Muerta; Organic Rich; Paleontología; Ciencias Exactas y Naturales
• Institución: Universidad Nacional de Río Negro

Fil: Paz, Maximiliano.University of Saskatchewan, Department of Geological Sciences, 114 Science Place, S7N 5E2 Saskatoon, Canada
Fil: Mángano, Gabriela. Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2, Canada,
Fil: Buatois, Luis. Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2, Canada,
Fil: Desjardins, Patricio. Shell Exploration and Production Company, 200N Dairy Ashford St, Houston, Texas 77019, USA
Fil: Notta, Raul. Shell Exploration and Production Company, 200N Dairy Ashford St, Houston, Texas 77019, USA
Fil: Gonzalez Tomassini, Federico. Phoenix Global Resources, Alem 855, C1001AAQ, Buenos Aires, Argentina
Fil: Carmona, Noelia Beatriz. Universidad Nacional de Río Negro, Instituto de Investigacion en Paleobiología y Geología. Río Negro, Argentina.
Contourites are increasingly being recognized in ancient fine-grained depositional environments. However, detailed ichnologic analyses focusing on shallow-water examples of these deposits are scarce. The Upper Jurassic?Lower Cretaceous Vaca Muerta Formation from Argentina constitutes an important unconventional reservoir that displays dm- to m-thick, laminated, rippled and bioturbated, crinoidal mudstone and fine to coarse mudstone deposited by wind- and thermohaline-driven contour currents. Four ichnofabrics were recognized in three faciesassociations. The Palaeophycus heberti ichnofabric is dominant in facies association 1, forming highly bioturbated intervals. The Palaeophycus heberti, Nereites isp., and Phycosiphon incertumichnofabrics are present in facies association 2, displaying highly, moderately and sparsely bioturbated intervals, respectively. This association is locally characterized by m-thick successions comprising an upward decrease and then increase in bioturbation index, which may have a similar origin to bigradational sequences. The Equilibrichnia-Fugichnia ichnofabric mostly occurs infacies association 3 and less commonly in 2, forming distinctive bioturbated intervals within sparsely bioturbated successions. Benthic activity was controlled by food distribution, oxygenation, hydrodynamic energy, and water turbidity. Food was delivered to the surface or in suspension by currents, promoting deposit- or suspension-feeding strategies in the infauna, respectively. Oxygen levels increased during contour current activity yet remained relatively low (upper dysoxic). Hydrodynamic energy controlled bioturbation intensity, resulting in lower degrees of bioturbation during higher energy events. Suspension-feeding strategies suggest that water turbidity was relatively low during current transport. The herein example increases our understanding of environmental controls of shallow-water contour currents, supporting the fact that high bioturbation levels are typical of contourite deposits and providing an example of muddy contourites showing high preservation of sedimentary structures due to oxygen deficiency in bottom waters.
Contourites are increasingly being recognized in ancient fine-grained depositional environments. However, detailed ichnologic analyses focusing on shallow-water examples of these deposits are scarce. The Upper Jurassic?Lower Cretaceous Vaca Muerta Formation from Argentina constitutes an important unconventional reservoir that displays dm- to m-thick, laminated, rippled and bioturbated, crinoidal mudstone and fine to coarse mudstone deposited by wind- and thermohaline-driven contour currents. Four ichnofabrics were recognized in three faciesassociations. The Palaeophycus heberti ichnofabric is dominant in facies association 1, forming highly bioturbated intervals. The Palaeophycus heberti, Nereites isp., and Phycosiphon incertumichnofabrics are present in facies association 2, displaying highly, moderately and sparsely bioturbated intervals, respectively. This association is locally characterized by m-thick successions comprising an upward decrease and then increase in bioturbation index, which may have a similar origin to bigradational sequences. The Equilibrichnia-Fugichnia ichnofabric mostly occurs infacies association 3 and less commonly in 2, forming distinctive bioturbated intervals within sparsely bioturbated successions. Benthic activity was controlled by food distribution, oxygenation, hydrodynamic energy, and water turbidity. Food was delivered to the surface or in suspension by currents, promoting deposit- or suspension-feeding strategies in the infauna, respectively. Oxygen levels increased during contour current activity yet remained relatively low (upper dysoxic). Hydrodynamic energy controlled bioturbation intensity, resulting in lower degrees of bioturbation during higher energy events. Suspension-feeding strategies suggest that water turbidity was relatively low during current transport. The herein example increases our understanding of environmental controls of shallow-water contour currents, supporting the fact that high bioturbation levels are typical of contourite deposits and providing an example of muddy contourites showing high preservation of sedimentary structures due to oxygen deficiency in bottom waters.