Paleomagnetic record from glacial varves in Alto Río Mayo, Patagonia, Argentina

Sylwan, Claudio A.; Beraza, Luis A.

doi:10.1016/0031-9201(90)90107-9

Cited by 5 publications

(3 citation statements)

References 17 publications

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“…Rhythmically laminated shales, dated at around 13 000 ka BP , are interpreted as varves or annual cycles of sedimentation in the proglacial lake. Widely distributed but isolated outcrops of these shales at altitudes of between 450 m and 600 m above sea level on hillsides and in valleys in the region show that they represent the eroded remnants of much more extensive deposits (Sylwan 1990;Sylwan and Beraza 1990;Kaplan et al . 2004).…”

Section: Timing Of Eventsmentioning

confidence: 99%

Punctuated drainage of an ice‐dammed quaternary lake in southern south america

Bell

2008

Geografiska Annaler: Series A, Physical Geography

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. A chain of east‐west elongated lakes fringes the eastern flank of the Andes Mountains between 39 and 52°S in southern Chile and Argentina. These deep lakes fill valleys left by the retreat of outlet glaciers of the Patagonian Icefield about 16000 years ago. Two of the lakes, Lago General Carrera/Buenos Aires and Lago Cochrane, represent the shrunken remnants of a much larger lake (called here the predecessor lake) that developed in a moat alongside the icefield. A series of seven stepped lacustrine braid deltas on the southeastern shore of Lago General Carrera/Buenos Aires mark the progressive, punctuated drainage of the predecessor lake. The deltas were formed by the build‐out of fans of sand and gravel into the lake. They have the form of Gilbert deltas, with virtually flat subaerial topset beds and steeply inclined subaqueous foreset beds. The exposed delta fronts are marked by a series of small terraces produced by wave erosion during falling lake levels. On either side of the fans are embayments with beaches formed by deposition in the lee of the pro‐grading fans. These embayments are filled with ridges of well‐sorted gravel deposited by wave‐driven long‐shore drift. About 13 000 years ago the regional drainage underwent a remarkable change. Rivers flowing eastwards into the Atlantic reversed their direction to flow westwards through the Andes Mountains and into the Pacific Ocean. The watershed moved some 200 km to the east. The cause of this change, and the falling lake levels, was melting of the Patagonian Icefield. As the ice retreated the icefield split into north and south components. This broke the ice dam that impounded the western end of the predecessor lake. The stepped, progressive fall of the lake level suggests that as the ice melted a series of lower overflow sills of hard rock were exposed. Each of the major episodes of sudden drop in lake level was followed by a long period of up to thousands of years when lake level remained constant. Terraces on the delta fronts indicate that each major episode of fall in the lake level was punctuated by up to ten minor episodes possibly representing major storm events or annual cycles of freezing and melting, blocking the overflow sills.

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Section: Timing Of Eventsmentioning

confidence: 99%

Punctuated drainage of an ice‐dammed quaternary lake in southern south america

Bell

2008

Geografiska Annaler: Series A, Physical Geography

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“…Isolated occurrences of rhythmically laminated shales, interpreted as varves or annual cycles of sedimentation deposited in the proglacial lakes, are common at other locations in the region. They represent the eroded remnants of more extensive deposits (Sylwan, 1990;Sylwan and Beraza, 1990;Kaplan et al, 2004) deposited when the lakes were much larger than at present and, presumably, during a time when more abundant fi ne sediment was provided by the outwash of silty or muddy glacial rivers.…”

Section: Depositional Environments and Processesmentioning

confidence: 99%

Quaternary lacustrine braid deltas on Lake General Carrera in southern Chile

Bell

2009

AndGeo

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ABSTRACT.A series of Quaternary lacustrine braid deltas on the shores of Lake General Carrera in southern Chile formed as a result of falls in lake level. Each delta comprises two components, the delta fan and the beach embayment, each in turn comprising an onshore subaerial and an offshore subaqueous element. The delta fans have a classic Gilbert form with a braided delta top and a steeply inclined delta front. Adjacent to the fans are concave beach embayments that formed parallel with the deltas as they prograded into the lake. The delta sediments consist predominantly of matrix-and clast-supported gravels to a total composite thickness exceeding 400 m. The depositional environments are dominated by ephemeral river fl ooding and by storm-driven waves. Beach sediment is sorted, rounded, winnowed and transported alongshore by waves to fi ll the beach embayment with ridges of very well sorted and well-rounded gravel. A gentlydipping shoreface platform occurs up to 100 m offshore between the beach and the brink point. From the brink point, in water depth of about 8 m, sediment cascades down the steep delta front slope to form long foresets extending to the lake fl oor. The sedimentary successions therefore wedge in the opposite direction from those of tectonically controlled basin margins where fan growth keeps pace with basin subsidence. RESUMEN. Deltas entrelazados lacustres del Cuaternario en el lago General Carrera, sur de Chile. Una serie de deltas entrelazados lacustres, pertenecientes al Cuaternario, ubicados en las costas del lago General Carrera, en el sur de Chile, se formaron como resultado de caídas en el nivel del lago. Cada delta consta de dos componentes: el abanico deltaico y la zona de embahiamiento. Cada uno de ellos tiene, a su vez, un elemento subaéreo costero y un elemento subacuático. Los abanicos deltaicos tienen una forma Gilbert clásica con una parte superior de ríos entrelazados y un frente deltaico empinado. Adyacente a los abanicos aluviales existen bahías cóncavas de playa que se formaron de manera paralela a los deltas a medida que estos progradaron hacia el lago. Los sedimentos deltaicos consisten predominantemente de gravas matriz y clastosoportadas con un grosor total compuesto que excede los 400 m. Los ambientes depositacionales están dominados por inundaciones efímeras del río y por olas de tormenta. Los sedimentos de playa están seleccionados, redondeados y fueron transportados a lo largo de la costa por las olas para rellenar el embahiamiento de la playa con dorsales de gravas muy bien clasifi cadas y redondeadas. Una plataforma del 'shoreface' de baja pendiente ocurre hasta 100 m agua adentro, entre la orilla y el borde. Desde el borde del lago, en el agua hasta los 8 m de profundidad, el sedimento cae en cascadas por la empinada pendiente del frente deltaico para formar grandes 'foresets' que se extienden hacia el fondo del lago. La sucesión sedimentaria se acuña, en consecuencia, en una dirección opuesta a la de aquella, de márgenes de cuenca controlados tectónicamente ('bri...

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“…Early palaeomagnetic studies at LGC-BA (Mörner & Sylwan, 1987, 1989 and LC-P (Sylwan, Beraza, & Casteli, 1991) established that some of the outer terminal moraines formed at the time of the Matuyama Reversed Chron over ∼780 ka ago (Singer & Pringle, 1996 Tables 2 and 3. Morphostratigraphic = study focused on relative depositional order of ice-marginal and/or glaciolacustrine landforms.…”

Section: Ice Lobe Chronologymentioning

confidence: 99%

The glacial geomorphology of the Lago Buenos Aires and Lago Pueyrredón ice lobes of central Patagonia

2017

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This paper presents a glacial geomorphological map of landforms produced by the Lago General Carrera-Buenos Aires and Lago Cochrane-Pueyrredón ice lobes of the former Patagonian Ice Sheet. Over 35,000 landforms were digitized into a Geographical Information System from high-resolution (<15 m) satellite imagery, supported by field mapping. The map illustrates a rich suite of ice-marginal glacigenic, subglacial, glaciofluvial and glaciolacustrine landforms, many of which have not been mapped previously (e.g. hummocky terrain, till eskers, eskers). The map reveals two principal landform assemblages in the central Patagonian landscape: (i) an assemblage of nested latero-frontal moraine arcs, outwash plains or corridors, and inset hummocky terrain, till eskers and eskers, which formed when major ice lobes occupied positions on the Argentine steppe; and (ii) a lake-terminating system, dominated by the formation of glaciolacustrine landforms (deltas, shorelines) and localized ice-contact glaciofluvial features (e.g. outwash fans), which prevailed during deglaciation. ARTICLE HISTORY

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Paleomagnetic record from glacial varves in Alto Río Mayo, Patagonia, Argentina

Cited by 5 publications

References 17 publications

Punctuated drainage of an ice‐dammed quaternary lake in southern south america

Punctuated drainage of an ice‐dammed quaternary lake in southern south america

Quaternary lacustrine braid deltas on Lake General Carrera in southern Chile

The glacial geomorphology of the Lago Buenos Aires and Lago Pueyrredón ice lobes of central Patagonia

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