Terminal Moraines, Outwash Plains, and Lake Terraces in the Vicinity of Lago Cardiel (49°S; Patagonia, Argentina)—Evidence for Miocene Andean Foreland Glaciations
Nine late Miocene glacier advances are identified in the Lago Cardiel region (49°S, 72°15′W in southern South America), a region that until now has been assumed to be unglaciated. Several dating results indicate a minimum age of 6.4 Ma for four advances of the Monte San Lorenzo lobe terminating east of Lago Cardiel and 6.6 Ma for the three oldest glaciations of the San Martín lobe terminating south of this lake. Two further advances have a minimum age of 5.4 Ma. Eleven to 14 m.y. old basaltic lava, which partly covers Patagonian Gravel, indicates the maximum age of these advances. The two oldest terminal moraines of the San Martín glacier are only modestly incised into the Patagonian Gravel suggesting an age of 9 to 10.5 Ma. These age estimates are especially accurate for both meseta glaciations of the San Lorenzo lobe. These glaciers were about 240 km long during their Miocene maximum, which is four times their length during the Last Glacial Maximum. Hence, the late Miocene glacier advances require colder and/or more humid conditions that were considerably longer lasting than the Pleistocene glaciations. Due to glacial meltwater, Lago Cardiel was significantly larger and served as a regional catchment area during these early glaciations in southern South America. The erratic boulders of the southeastern lake terraces at more than 350 m above modern lake level may be attributed to the oldest late Miocene moraine or outwash plain.