Compositional Changes Related to Fluvial-Fan Sedimentation, the Miocene Sedimentary Infill of the Central Argentinian Foreland (Mariño and La Pilona Formations, Mendoza Province)

Abstract

Sedimentary infills related to foreland basins are accurate recorder of processes acting at the time of an orogenic uplift. The effects of allogenic forcing on foreland sedimentation are well known at basin-scale but uncertainties remain in recognizing them at higher resolution, and in distinguishing them from the superimposed effect of autogenic processes. This project aims to provide a detailed reconstruction of paleoenvironmental dynamics and to unravel the relative roles of climate and tectonics, using a high-resolution, integrated compositional (QEMSCAN®, XRF, heavy minerals, isotopes) and sedimentologic analysis of the Miocene sedimentary infill of the Central Argentinian Foreland. In order to offer insights into the understanding of comparable sedimentary successions in the subsurface, we also want to test the effectiveness of chemostratigraphy for correlation within fluvial-fan successions along thick stratigraphic intervals. We studied two sections of 1500 m and 800 m in thickness of a siliciclastic sequence that records depositional environments ranging from floodplains, fluvial channels to an aeolian erg system that can be correlated throughout the foothills of the Andes. The large scale stratigraphy is interpreted as the progradation of a fluvial fan over the proximal margin of the foreland basin recording the continuous sediment supply from the rising Principal Cordillera and the first stages of the uplift of the Frontal Cordillera. We recognize compositional variations related to the evolution of the basin infill and due to 4 phases of non-steady state weathering conditions. The A-CN-K diagram displays low to moderate weathering values and shows the evolution of the composition towards the illite pole. Intermediate source rock composition is inferred using geochemistry. Comparison between compositional changes in the sandstones and the associated mudstones indicate poor mineral and geochemical fractionation except in the upper part of the section. More proximal sedimentary facies are characterized by scarce composition due to the advance of the thrust front coupled with inputs from the uplifting Frontal Cordillera. The integration of heavy minerals and isotopic data is being performed to constrain source area changes. Besides providing an extensive outcrop analogue for the characterization and prediction of subsurface reservoirs, the project represents a ground-based assessment of quantitative methods for reservoir correlation and evaluation.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017