Post‐Last Glacial Maximum evolution of a “fjord‐type” lake based on high‐resolution seismic data: the Lago Roca/Acigami (southern Tierra del Fuego, Argentina/Chile)

Abstract

Lago Roca/Acigami is a “fjord‐type” lake located in the southernmost part of South America, in the proximity of the Beagle Channel. A high‐resolution seismic survey was carried out to analyse the seismic stratigraphy of the lake and to shed some light on the post‐Last Glacial Maximum history of the area. Six seismic units were recognised, and their nature and depositional context were interpreted using seismic stratigraphy and acoustic facies analysis. A buried large ridge was identified within the glacial unit (SU1), interpreted as a frontal moraine that indicates a stabilisation phase. After retreat of the glacier from the basin, the trough was flooded by meltwater and a lake developed (SU2). The seismic facies, from bottom to top, depict a transition from ice‐contact (SU2; SU3) to ice‐distal proglacial conditions (SU4). A thick draping unit (SU5) marks a marine transgressive event and the instauration of a fjord environment in the basin. The marine transgression was a rapid event preceded by a fall in the lake level that caused an erosional unconformity. During the fjord phase the sedimentation remained controlled by meltwater discharge. Sea level fall, and subsequent disconnection from the Beagle Channel was accompanied by a progradation of the glaciofluvial deltaic sediments and the occurrence of several mass‐wasting deposits (SU6). © 2019 John Wiley & Sons, Ltd.

Depositional setting of the southern arms of Lago Argentino (southern Patagonia)

“…The result of this procedure was the compilation of two-way traveltime (TWT) grids with 0.001°spacing for: (i) the top of the acoustic basement, (ii) the top of the glacier unit: and (iii) the thickness of the glacio-lacustrine sequence. An analogous methodology was applied in the lakes of Tierra del Fuego, like Lago Fagnano (Esteban et al, 2014), Lago Yehuin (Lozano et al, 2018a), Lago Chepelmut (Lozano et al, 2018b) and Lago Roca (Bran et al, 2019).…”

Active faulting in the Beagle Channel (Tierra del Fuego)

“…Finally, the identification of widespread subaerial and subaqueous MTDs nearby active faults in the BC region (this work, Bran et al (2020), Bran et al (n.d.)) suggest a potential link of slope failure with seismic activity. In this sense, the stacked deposits in Figure 9 imply a recurrence of slope failures events, as was observed by Waldmann et al (2011) in Lago Fagnano to the north.…”

Structure, seismostratigraphy, and tectonic evolution of Lago Roca (southern Patagonia, Argentina)

“…SF‐4 shows similar characteristics in some sections, and could be interpreted in the same way. These processes are common in periglacial lakes, as was recognized in Lago Fagnano (Waldmann, Ariztegui, et al, 2010), Lago Yehuin (Lozano, Tassone, Lodolo, et al, 2018), and Lago Acigami (Bran et al, 2019), all located in Tierra del Fuego. In addition, gravitational processes of this type also occurred recently in the northern arms of Lago Argentino, particularly in Brazo Upsala in 2013 (Winocur, Goyanes, & Vieira, 2015).…”

“…Based on the seismic facies observed for the LU and its areal distribution (Figure 6b), the unit is interpreted as a till deposit. Deposits of this type were interpreted by seismic signatures similar to submerged glacial deposits described in several Patagonian lakes (i.e., Bran et al, 2019;Waldmann et al, 2008), and are typical in periglacial lakes. Particularly, these deposits were also recognized in the neighbouring Brazo Rico and Brazo Sur branches Lozano et al, 2020;Lozano, Bran, Lodolo, Tassone, & Vilas, 2021).…”