THE INFLUENCE OF TOPOGRAPHY ON SUBAQUEOUS GRAVITY FLOWS: A CASE STUDY FROMTHE JURASSIC LOS MOLLES FORMATION, NEUQUÉN BASIN, ARGENTINA

Subaqueous sediment gravity flows experience modifications when they interact with slope and basin-floor topography, impacting facies, geometries, and architectural patterns of the deposits. Understanding these processesis critical for reservoir-quality and trap predictions in deep-water stratigraphic plays. A comprehensive literaturesummary of the topographic influence on subaqueous gravity flows and an interpretation applied to the basin-floorturbidite system of the late synrift Los Molles Formation in the Neuqu & eacute;n Basin of Argentina are provided. In thestudy area, a high-resolution satellite image, drone imagery, and 30 logs (about 5000 m total thickness) weremeasured, focusing on facies analysis, paleocurrents, bed thicknesses, and large-scale thickness variations. Studiesdescribing topographic confinement of sediment gravity flows have used five approaches: 1) Paleocurrent analysis:paleocurrents following structural trends and variations within the same bed (flow deflection and reflection).2) Facies analysis: complex facies variations on short distances and increased number of hybrid beds and debritesnear barriers (flow transformation), loading, convoluted structures, and bidirectional ripples (flow reflection), andsand-mud couplets or thick mudcaps (flow ponding). 3) Small-scale (decimeter to meter) thickness variations: bedsthickening towards topography, beds thinning on top of topography (onlaps), and low thinning rates (loss of flowcompetence, flow containment). 4) Architectural analysis: aggradational stacking, lateral stacking away fromtopographic barriers, and fill-spill successions. 5) Large-scale thickness (tens of meters) variations: increased fansystem thickness across topographic lows. An extended version of an existing classification scheme on degree ofconfinement is proposed: C0 (unconfined): no flow modification evidence present, and compensational stacking is aclassic architectural pattern. C1 (weakly confined): variations in regional paleocurrent directions, minor thicknessvariations against small-relief barriers, large (basin scale) thickness variations. C2a (confined) to C2b (highlyconfined): onlaps against high-relief barriers, paleocurrent direction variations on the same bed, bed thickeningagainst topography, facies evidencing flow reflection, increased number of hybrid beds, aggradational stacking, andhigh percentage of beds continuous over 500 m distances (tabular beds). C2a and C2b are considered end membersof a spectrum where the amount of evidence listed can vary. C3 (ponded): sand mud couplets or thick mudcaps.Higher confinement categories might have indicators from the weaker confinement categories. The lower fan in theLos Molles Fm. turbidite system is classified as weakly confined. A complex sediment routing followed structuraltrends inherited from the rift phase of the basin. The basin-floor had irregular water depths that led to preferredsites of deposition. Hybrid beds are mostly found at the fringes of the lower part of the succession and might beassociated with an above-grade slope profile on a footwall scarp. Lastly, the Los Molles Fm. basin-floor beds presenthigh thinning rates (average 1.5 m/km) and the system stacks compensationally, pointing to null interaction againstbasin margins.