THE EVOLUTION OF TOPOGRAPHIC CLOSURE AND FORELAND BASIN LAKES: A MODERN TIME-SLICE PERSPECTIVE FROM THE ANDES

A source of water and the development of topographic closure are fundamental requirements for the formation of lacustrine environments of deposition. Lakes that form in tectonic basins are especially important because of their potential to yield high-fidelity sedimentary records of Earth history over expanded periods of time. Whereas our understanding of the evolution of rift lakes is fairly mature, few studies have considered the evolution of topographic closure and lake systems adjacent to major fold-thrust belts in foreland basins. It is likely that foreland basin lakes evolve in very different ways from rift lakes as a result of the high potential sediment supply/accommodation space ratio of the former versus the latter. Using digital elevation and precipitation datasets, we explore: (1) patterns of topographic closure and (2) modern lacustrine morphometrics and hydrology across the wedgetop, foredeep, forebulge and backbulge depozones of the modern Andean foreland of South America. Where basinal subsidence outpaces sediment supply, hydrologically-closed lakes are present. In contrast, hydrologically-open lacustrine systems are common in regions where erosion and sediment supply apparently outpace subsidence. Andean lake-basin evolution is likewise influenced by climate, with humid regions favoring enhanced runoff, deposition and overfilled lakes and wetlands, while arid zones curtail sediment production and thus favor expansive, underfilled lakes and salinas. Our analysis suggests that foreland basin lakes will display hierarchical stratigraphic development that can record the evolution of lacustrine environments into swamps or rivers as topographic closure is overcome due to prolonged tectonic quiescence and/or increased regional rainfall. Consequently, the stratigraphic sequences of foreland basin lakes may provide an untapped resource for highly-resolved records of mountain building and surficial processes in compressional orogens.