Glacial and tectonic control on fjord morphology and sediment deposition in the Magellan region (53°S), Chile

In the Patagonian Andes erosion by temperate Pleistocene glaciers has produced a deeply incised fjord system in which glacial and non-glacial sediments were deposited since the Late Glacial glacier retreat. So far, fjord bathymetry and structures in the sediment infill were widely unexplored. Here we report the results of an investigation of morphology and sediment characteristics of a 250 km long fjord transect across the southernmost Andes (53°S), using multibeam and parametric echosounder data, and sediment cores. Subaquatic morphology reveals continuity of on-land tectonic lineaments mapped using field and remote sensing data. Our results indicate that glacial erosion and fjord orientation are strongly controlled by three major strike-slip fault zones. Furthermore, erosion is partly controlled by older and/or reactivated fracture zones as well as by differential resistance of the basement units to denudation. Basement morphology is regionally superimposed by Late Glacial and Holocene subaquatic moraines, which are associated to known glacier advances. The moraines preferentially occur on basement highs, which constrained the glacier flows. This suggests that the extent of glacier advances was also controlled by basement morphology. Subaquatic mass flows, fluid vent sites as well as distinct Late Glacial and Holocene sediment infills have furthermore modified fjord bathymetry. In the western fjord system close to the Strait of Magellan subaquatic terraces occur in 20 to 30 m water depth, providing an important tag for proglacial lake level during the Late Glacial.