Barendregt, Rene

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Browsing Barendregt, Rene by Author "Ercolano, Bettina"

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    Early and Middle Pleistocene glaciation of the southern Patagonian plain
    (Elsevier, 2022) Griffing, Corinne Y.; Clague, John J.; Barendregt, René W.; Ercolano, Bettina; Corbella, Hugo; Rabassa, Jorge; Roberts, Nicholas J.
    Evidence of at least three Early to Middle Pleistocene glaciations is recorded in the stratigraphic exposures near the outer limit of glaciation in southern Patagonia. At Cabo Vírgenes, at the mouth of the Strait of Magellan, up to 70 m of till, gravel, sand, and stony silt were deposited in a grounding-line environment at the front of the Magellan lobe along a front several tens of kilometres wide. Accommodation space for the sediments was produced by glacio-isostatic depression resulting from the advance of the Magellan lobe to the Atlantic coast. At that time, the ‘moat’ in which the sediments accumulated may have been seaward of the modern Atlantic shoreline because the continental shelf is shallow and sea level was much lower than it is today. The sediments at Cabo Vírgenes are normally magnetized, carry no reversed overprints, and thus probably date to the Brunhes Chron (<0.774 Ma). Seacliff exposures south of the Strait of Magellan along the Atlantic coast of northern Tierra de Fuego expose two tills separated by glaciofluvial sediments. Although not dated, the tills record two advances of the Magellan lobe onto the Atlantic continental shelf. The location of the exposures relative to Cabo Vírgenes indicates that the upper of the two tills may correlate with the Cabo Vírgenes drift. The Tres de Enero highway cut, 90 km northwest of Cabo Vírgenes, exposes lodgement tills deposited during the Great Patagonian glaciation (GPG) – two stacked, normally magnetized tills overlie a reversely magnetized till. Truncated sand wedges separate each of the three tills, indicating that the tills record three separate Early to Middle Pleistocene glaciations. The younger of the two normally magnetized tills, and perhaps both, were deposited in the Brunhes Chron; the lowest, reversely magnetized till records extensive glaciation late during the Matuyama Chron (2.608–0.780 Ma). At Bella Vista in the Río Gallegos valley, a 0.89-Ma-old basalt flow caps a thick unit of normally magnetized glaciofluvial gravel, which was probably deposited during the Jaramillo Subchron (1.075–0.991 Ma), but certainly not later. Sediments at Tres de Enero and Bella Vista show that the GPG is not a single event as originally thought, but rather at least three glaciations, perhaps spanning several hundred thousand years.
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    Pliocene and Early Pleistocene glaciation and landscape evolution on the Patagonian Steppe, Santa Cruz province, Argentina
    (Elsevier, 2020) Clague, John J.; Barendregt, René W.; Menounos, Brian; Roberts, Nicholas J.; Rabassa, Jorge; Martinez, Oscar; Ercolano, Bettina; Corbella, Hugo; Hemming, Sidney R.
    At least seven late Pliocene tills cap plateaus (mesetas) south of Lago Viedma, just east of the Andes in Argentine Patagonia. Chronologic constraints on the tills are provided by 40Ar/39Ar ages and magnetic polarities on associated basalt flows and sediments. The tills were deposited by piedmont glaciers that reached at least 80 km east of the crest of the Andes and flowed on a low-relief surface sloping gently downward in that direction. The oldest of the tills is about 3.6 Ma old. Glacial deposits dating to the Pliocene-Pleistocene transition are present at least 40 km beyond the east limit of the Pliocene tills at Lago Viedma, and tills of similar age occur at Condor Cliff in the Río Santa Cruz valley to the southeast. A sequence of at least seven Early Pleistocene (2.1–1.1 Ma) tills is present between basalt flows in the Cerro del Fraile meseta south of Lago Argentino. The glaciers that deposited these Early Pleistocene tills reached far beyond the Marine Isotope Stage 2 limit in the Río Santa Cruz valley. Based on positions, extents, and ages of the un-deformed, basalt-capped mesetas flanking Lago Viedma, we conclude that the topography in this area was profoundly changed during the Pleistocene – the low to moderate relief Pliocene surface was deeply incised by glaciers that became increasingly confined to, and flowed within, troughs. The valley floors today are up to 1350 m below the late Pliocene surface.