The modern muds of Laguna Mar Chiquita (Argentina): Particle size and geochemical trends from a large saline lake in the "thick-skinned" Andean foreland

Laguna Mar Chiquita (central Argentina; ~latitude 31°S, longitude 63°W) provides an outstanding opportunity to examine organic facies development and petroleum source-rock potential in a modern thick-skinned foreland basin lake. In this case study, we define profundal, paleodelta, and lake-margin depositional environments based on trends in bathymetry and lake-floor sediment particle size. Sedimentary geochemical analyses indicate that organic carbon–rich muds accumulate in profundal environments during the extant lake-level highstand. The lateral variability of organic facies is minimal. The quality of organic facies is controlled by lake level and depositional environment, both of which dictate patterns of algal productivity, siliciclastic dilution, and early diagenesis. We present conceptual models of lacustrine source rocks in both thick-skinned and thin-skinned foreland basins based on modern analog data from both Laguna Mar Chiquita and other lakes in the central Andean foreland. Over relatively short time intervals (10²–10⁴ yr), climatically driven water-level fluctuations influence the source-rock potential of these basins. Over time intervals >10⁵ yr, contraction and lateral migration of the basin flexural profile control stratal stacking patterns and the potential for hydrocarbon play development.