The ‘Rodados Patagónicos’ (Patagonian shingle formation) of eastern Patagonia: environmental conditions of gravel sedimentation

Abstract

The gravel mantels known as 'Rodados Patagónicos' of Eastern Patagonia are one of the most distinctive features of the regional landscape. Their significant roundness, along with additional sedimentary and geomorphological evidence, indicates their origin is linked to fluvial action. Currently, no natural processes exist on Earth potentially generating equivalent deposits, either in Patagonia or elsewhere around the world. The hydrological conditions responsible for the gravel formation were thus likely very different from those currently prevailing in Argentine Patagonia, suggesting the gravel mantels formed during the Late Cenozoic, when surface drainage networks of relatively high energy existed in the region. Such high energy was induced by powerful flow rates and/or strong water gradients, attributable to tectonism, epirogenesis and/or lowering of sea level. Periods with water flow regimes significantly higher than at present characterized the full glacial phases lasting several thousands of years, corresponding to each of the many glaciations of the Pliocene and Pleistocene. The capacity for erosion and water transport would have been increased by the sea level drop characteristic of each full glacial phase. There were also much shorter periods, known as 'terminations', representing the abrupt ending of the main glacial events during which large amounts of water were released as a result of the intensive melting of the Cordilleran ice sheet. During interglacial periods, in the absence of large masses of ice in the mountains and with average temperatures similar to or higher than at present, layers of gravel were deposited as a result of tectonic or epirogenic movement or by reactivation of drainage networks produced by sea level lowering (glacio-eustatism). These endogenous landscape reactivations were also independent of and longer than the climatic fluctuations and therefore overlapped with both interglacial and glacial periods. Finally, some units of the 'Rodados Patagónicos' may also have been deposited during major pluvial events, characterized by higher mean annual precipitation over sufficiently long periods. The current evidence suggests that, at various times since the Late Miocene, varied climatic conditions have allowed the production and accumulation of large gravel beds covering much of extra-Andean Patagonia.Los mantos de gravas de Patagonia oriental, conocidos como 'Rodados Patagónicos', constituyen por su extensión y homogeneidad uno de los elementos del paisaje más distintivos de la Patagonia oriental. El marcado redondeamiento de estos sedimentos, junto con otras evidencias sedimentológicas y geomorfológicas, indica que su origen se vincula inexorablemente con el escurrimiento superficial (acción fluvial). Puesto que en la actualidad no existen procesos que estén generando depósitos o geoformas equivalentes (en Patagonia o en otro sitio de la superficie terrestre), debe asumirse que las condiciones hídricas que permitieron su formación fueron muy distintas a las que imperan actualmente en ...

Evolutionary Drivers of Diversification and Distribution of a Southern Temperate Stream Fish Assemblage: Testing the Role of Historical Isolation and Spatial Range Expansion

“…The palaeorivers of the LGM have been proposed as a plausible explanation for the common occurrence of Pseudobarbus lineages across currently-isolated river systems in the CFR [13], [14], [63]. Interconnections of rivers following exposure of the continental shelf during glacial periods [69], [70] have also been inferred to have facilitated dispersal of Percicthys trucha , a Patagonian freshwater fish with an extensive geographical range, but lacking phylogeographic structuring [71].…”

Phylogeographic history of Patagonian lizards of theLiolaemus elongatuscomplex (Iguania: Liolaemini) based on mitochondrial and nuclear DNA sequences

“…This complex inhabits north‐western Patagonia, a geographically complex region characterized by mountains up to 4500 m, large volcanic fields, deep canyons and high plateaus. These features are the products of an Andean orogenic history that includes sporadic volcanic eruptions and cyclic glacial advances and retreats that produced pronounced climatic changes throughout the last myr (Rabassa and Clapperton ; Ramos and Kay ; Ramos and Ghiglione ; Martínez and Kutschker ; Ramos and Folguera ). As a result, this climate history superimposed on a complex topography likely fostered multiple population‐divergence processes across different geographical and temporal scales (Morando et al.…”

La identificación del uso de fuentes secundarias de materiales líticos asistida por SIG: el Arroyo Chasicó (Argentina) como caso de estudio

“…Por último, al sur de la Región Pampeana se extiende el NE patagónico, donde la fuente predominante de rocas útiles para la talla es el denominado Manto de Rodados Tehuelches o Patagónicos. Este es un depósito de clastos gravosos depositados, principalmente, como producto del escurrimiento superficial generado bajo condiciones hídricas de gran energía vinculadas con procesos glacifluviales que se dieron en distintos momentos del Mioceno tardío, Plioceno y Pleistoceno (Martínez & Kutschker, 2011). Las dimensiones predominantes de estos cantos rodados oscilan entre 25-30 cm hasta unos pocos cm, disminuyendo su tamaño en sentido sudoeste-noreste (Martínez et al, 2009;Martínez & Kutschker, 2011).…”

“…Este es un depósito de clastos gravosos depositados, principalmente, como producto del escurrimiento superficial generado bajo condiciones hídricas de gran energía vinculadas con procesos glacifluviales que se dieron en distintos momentos del Mioceno tardío, Plioceno y Pleistoceno (Martínez & Kutschker, 2011). Las dimensiones predominantes de estos cantos rodados oscilan entre 25-30 cm hasta unos pocos cm, disminuyendo su tamaño en sentido sudoeste-noreste (Martínez et al, 2009;Martínez & Kutschker, 2011). Dicho manto posee una alta variación litológica, pero con cierto predominio de rocas alóctonas volcánicas básicas y mesosilíceas y rocas plutónicas ácidas, con una menor proporción de calcedonias, cuarcitas, xilópalos, esquistos, cuarzos y otras rocas (Cortelezzi et al, 1968;Fidalgo & Riggi, 1965, 1970Martínez et al, 2009;Martínez & Kutschker, 2011).…”

“…Las dimensiones predominantes de estos cantos rodados oscilan entre 25-30 cm hasta unos pocos cm, disminuyendo su tamaño en sentido sudoeste-noreste (Martínez et al, 2009;Martínez & Kutschker, 2011). Dicho manto posee una alta variación litológica, pero con cierto predominio de rocas alóctonas volcánicas básicas y mesosilíceas y rocas plutónicas ácidas, con una menor proporción de calcedonias, cuarcitas, xilópalos, esquistos, cuarzos y otras rocas (Cortelezzi et al, 1968;Fidalgo & Riggi, 1965, 1970Martínez et al, 2009;Martínez & Kutschker, 2011).…”