Stratigraphy and depositional architecture of the Viamonte Formation, Miocene, Tierra del Fuego, Argentina: the interplay between deep-marine transverse and longitudinal depositional systems

ABSTRACT.- In the Atlantic coast of Tierra del Fuego, Miocene, foreland Austral basin strata of the Viamonte Formation are currently interpreted as deep marine channel-levee complexes. New data on sedimentary facies, paleocurrents, and stratigraphic relationships documents, however, more complex settings. We recognize in the Viamonte Formation three higher-rank architectural elements: 1) a transverse system of gullies and other slope deposits, including gully axis, gully off-axis/gully margin, and slope-gully abandonment sub-elements; 2) an axial system, the channel belt, including channel fill, lateral accretion, internal-levee/terrace, and basal slumps sub-elements; and 3) another axial system, the external levee. Gullies in the transverse system are carved into external-levee deposits of the Viamonte Formation or older lobe deposits. Dominant sedimentary facies are mass transport deposits in the gully fill; thin-bedded turbidites in the external levee, internal levee, and terraces; and thick, high-density turbidite sandstones in the channel fill. In the transverse system, paleocurrents are directed to the NW-NE, down dip high-relief progradational clinoforms, and in the axial systems to the SE, parallel to the basin foredeep. Axial systems are located either at the base, or at subtle slope-breaks of transverse clinoforms. The envisaged depositional architectures of these axial and transverse systems offer excellent analogues for similar, poorly exposed Upper Cretaceous-Paleogene Austral basin turbidites and may help to interpret the source and routing of sand-rich deposits in the adjacent Malvinas foreland basin.