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Shelf-margin clinoforms of the Vaca Muerta- Picún Leufú system in the Neuquén Basin, Argentina

Abstract

The Tithonian outcrops in the Sierra de la Vaca Muerta expose the prograding shelf-margin clinoforms of the Vaca Muerta-Picún Leufú system in the Neuquén basin, which are the combined result of gravitational and current deposition. Overall, the clinoforms of this mixed carbonate- siliciclastic system display sigmoidal geometries with low shelf-to-slope gradients that increase from ~0.5° to ~4°. The topsets are typically an alternation of sandstones, deposited in the intertidal to shallow shoreface environment, that are capped by in situ produced peritidal carbonates. The carbonates start occupying the shallow shelf when siliciclastic supply from longshore currents decreases during sea-level highstands. Several shelf edges are shoreface sandstones overlain by oyster beds; towards the shelf interior the carbonates transition from grainstone to packstone and wackestone facies. The dominant lithofacies in the foresets and bottomsets are calcareous and siliciclastic mudstones of the Vaca Muerta Formation. Most fine-grained slope carbonates are transported from the shelf during sea level highstands. The thickest (~100m) carbonate wedge is recognized as the Los Catutos Member within the Vaca Muerta Formation. In the lower foresets and bottomsets, the Vaca Muerta Formation contains several levels enriched in organic matter. Slope instability leads to large scars in the foresets and resultant mass transport complexes and fine-grained turbidites in the bottomset. Small-scale foresets and current ripples, however, also document lateral transport of the mud by bottom currents.