Carbonate rich paleolakes of the Triassic Cuyana rift basin

BENAVENTE, CECILIA ANDREA; MANCUSO, ADRIANA CECILIA; GIERLOWSKI-KORDESCH, ELIZABETH

Reno

Congreso; 6th International Limnogeology Congress; 2015

The Santa Clara Arriba Formation consist of Triassic continental deposits found in the Santa Clara sub-basin, located in the middle area of the Cuyana rift basin of west-central Argentina. This Triassic rift is composed of several asymmetric half-grabens with sedimentary fill representing diverse lacustrine systems from the post-rift phase of the basin (Fig. 1). Paleolakes in other sub-basins of the Cuyana rift (e.g. Cerro Puntudo and Potrerillos sub-basins, respectively located north and south from the Santa Clara Arriba Formation) developed on the passive margins of the rift during the synrift stage, provide limnogeologic data for comparison. Interestingly, most of the paleolakes show carbonate sedimentation. This allows for a detailed comparative study of carbonate accumulation within different settings of the rift during synrift and post-rift. The Santa Clara Arriba Formation contains finely laminated shales with sandstone and limestone interbeds that are finely stratified as well. An aggradational stacking pattern of parasequences points to a constant sediment + water supply with continuous subsidence during sedimentation in this lacustrine system. The shales contain bioturbation features and they have been secondarily cemented by carbonates (spar). Thin section analysis shows limestones with well-laminated micrite also showing features linked to biogenic activity, including fenestrae. Laminae are planar or crenulated and average 40 µm in thickness. Diagenesis consists of voids and cracks replacements by sparitic calcite. Abundant siliciclastic mud aggregates composed of brown reddish clays are dispersed within the limestones. This aggregates measure 5-10 µm in diameter and can be interpreted as pedogenic in origin. Biogenic limestones are present in the paleolakes of the post-rift stage of the Cuyana Basin in the high accommodation zone of this rift (Santa Clara sub-basin) as well as in the synrift stage in the low accommodation zones (Cerro Puntudo and Potrerillos sub-basins). This strengthens the hypothesis that provenance and hydrology are the main controls in carbonate accumulation within rift systems.