Seismic Stratigraphy of Neoglacial Ice Fluctuations in Lago Argentino (Patagonia, Argentina)
Abstract
We present results of a marine seismic survey that imaged lacustrine sedimentary and geomorphic features in the submerged glacial valleys of Lago Argentino that drain 8 outlet glaciers of the Southern Patagonian Icefield. Throughout the Neoglacial, the ice experienced a series of glacial fluctuations that have been mapped on land across the present-day valleys. Here we present the marine record of the glacial variations, as preserved in ice-proximal and -distal sediments of the proglacial lake and imaged by high-resolution multi-channel and CHIRP seismic reflection data. The data were used to map the basement, measure the total sediment thickness in the glacial sub-basins, and to characterize the basins fill, which in places reaches the thickness of 600 m and consists of glacial and glaciolacustrine sediments. Seismic facies analysis defines 5 predominant depositional units across the areas sub-basins: internally-chaotic facies with a ridge morphology (I); discontinuous to chaotic reflectors in an unstratified facies (II); nearly transparent facies with weak reflections (III); sub-horizontal to horizontal strongly layered facies that onlap and fill underlying units (IV); and chaotic to moderately layered facies observed along basin edges that often pinch out toward the basin center (V). We interpret facies I as the submerged continuations of moraines mapped and dated on land. We interpret facies II as ice-proximal till marking the remnant of the glacial deposits associated with the Neoglacial 1,100-6,000 and 700-<300 yr BP Pearson 1 and 2 readvances, respectively. Above II, we interpret glaciolacustrine drift and outwash deposits (III) while the thick, stratified units above (IV) mark the establishment of the ice-distal glaciolacustrine environment. Finally, we interpret facies V as periglacial mass wasting deposits from the valley slopes. Within the ice-distal unit IV, we observe variations in acoustic characteristics and erosion surfaces, which we interpret as sub-units corresponding to readvances of the glacier front, including pulses of each of the Pearson 1 and 2 readvances. Using the thicknesses of these sub-units, we present first-order estimates of glacial sedimentation and erosion rates related to each of the Neoglacial readvances published for this area.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMEP15A..08F