| Popis: |
North of the Gallegos River valley, glacigenic deposits outcrop in two altimetric levels. The Meseta Latorre is the highest level (1,064 m a.s.l.), a relic of the ancient Andean piedmont. A degraded basal moraine and a frontal/lateral ridge occupy the summit of the tableland. Their deposits are here recognized as the Meseta Latorre Drift, and considered as Late Miocene in age. The second piedmont level is located eastwards at an altitude of ~100 m lower than the highest one. At its surface, two nested systems of marginal moraines, with glaciofluvial deposits, are recognized. The outer system is herein defined as the Los Vascos Drift, whereas the inner one is the Bella Vista Drift, dated at ~1 Ma. This drift is equivalent to the Great Patagonian Glaciation within the Gallegos River valley. Volcanic cones, lava flows, phreatomagmatic deposits and fluvial sediments were partially/totally buried by both drift deposits. Volcanic activity is basaltic, transitional and alkaline in composition and it took place between 8.0 and 9.0 Ma, according to Ar40/Ar39 dating. This paper presents new evidence about the extent of ancient glaciations that occupied the extra-Andean tablelands and its relationship with tectonism and volcanism, as well as the landscape evolution. |
