ICHNOLOGY OF MUDDY SHALLOW-WATER CONTOURITES FROM THE UPPER JURASSIC–LOWER CRETACEOUS VACA MUERTA FORMATION, ARGENTINA: IMPLICATIONS FOR TRACE-FOSSIL MODELS

ABSTRACT Contourites are increasingly being recognized in ancient fine-grained depositional environments. However, detailed ichnologic analyses focusing on shallow-water examples of these deposits 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 fine coarse deposited by wind- thermohaline-driven contour currents. Four ichnofabrics were three facies associations. Palaeophycus heberti ichnofabric is dominant association 1, forming highly bioturbated intervals. heberti, Nereites isp., Phycosiphon incertum present 2, displaying highly, moderately sparsely intervals, respectively. This locally characterized m-thick successions comprising upward decrease then increase bioturbation index, which may have a similar origin bigradational sequences. Equilibrichnia-Fugichnia mostly occurs 3 less commonly distinctive intervals within successions. Benthic activity was controlled food distribution, oxygenation, hydrodynamic energy, water turbidity. Food delivered the surface or suspension currents, promoting deposit- suspension-feeding strategies infauna, Oxygen levels increased during current yet remained relatively low (upper dysoxic). Hydrodynamic energy intensity, resulting lower degrees higher events. Suspension-feeding suggest turbidity transport. herein example increases our understanding environmental controls supporting fact high typical contourite providing muddy contourites showing preservation sedimentary structures due oxygen deficiency bottom waters.