Lake sedimentation and landscape evolution since ∼31 ka in Isla Grande de Chiloé, northwestern Patagonia (42°S)

Abstract

We combine sedimentological analysis, high-resolution imaging, and X-ray fluorescence data to investigate sedimentary processes and landscape evolution from lake records in central Isla Grande de Chiloé (42°23′S, 72°49′W), northwestern Patagonia between ∼31-1.6 ka. The oldest section consists of laminated inorganic silts with a local geochemical signature deposited in a low-energy environment (Stage 1: ∼31-26 ka), interrupted by hiatuses and coarse-grained allochthonous deposits associated with high-energy events (Stage 2: ∼26-18 ka). The end of laminated facies and increasing organic matter led to a rising productivity trend and slope stability (Stages 3 and 4: ∼18-14.1 ka, ∼14.1-10.8 ka), along with volcaniclastic influx advected from the Andean Southern Volcanic Zone (Stage 5: ∼10.8 -1.6 ka). We interpret sedimentation in proglacial lakes fed by varying intensities of glacier meltwater from the western margin of the Golfo Corcovado piedmont lobe during the LGM in Patagonia, followed by a sudden change to closed-basin lakes driven by glacier withdrawal at the onset of the Last Glacial Termination (∼18 ka). This detachment shifted the facies composition and arrangements toward predominance of climate and distal volcanic processes until ∼1.6 ka. Our records capture salient millennial-scale features of the environmental evolution from western Patagonia since ∼31 ka, and match paleoclimate records at zonal and hemispheric scales. Our facies analysis underscores the presence of centennial fluctuations and instantaneous processes through glacial and non-glacial lake regimes.