THE SEISMIC RECORD OF POST-LGM GLACIAL RETREAT FROM PATAGONIAN AND ANTARCTIC PENINSULA FJORDS

We present seismic data analysis from glacially influenced fjords ranging from western Patagonia (46°S) to the Antarctic Peninsula (AP; 65°S), including records from Patagonian fjords draining San Rafael, Gualas, Europa and Marinelli glaciers, and from the AP fjords Maxwell Bay, Herbert Sound, Lapeyrère Bay, and Andvord Bay. Acquisition systems include air-gun single channel streamers and sub-bottom hull mounted profilers.

The most notable difference between the sedimentary sections of Patagonian and AP fjords is the seismic facies character and stratigraphic architecture of older deposits in these basins. In the Patagonian fjords, the earliest post-glacial deposits are characterized by dipping reflections that prograde from basement highs or drape the basement surface. This is interpreted to be generated by sediment gravity flows off morainal banks when glaciers were pinned on basement highs and the banks were active. Similar seismic facies were either not imaged, are rare, or are smaller scale in the AP. The oldest fill corresponds to glacimarine sediments that onlap or drape either the basement or a transparent basal unit interpreted as subglacial fill. In Maxwell Bay (AP), the total volume of sediment fill and bedrock relief is similar to Marinelli Glacier (Patagonia) proglacial basins, yet there is no seismic evidence of progradational features associated with bedrock highs that could be indicators of high sediment flux. In the AP, lower sediment fluxes and/or more rapid retreat of the grounding line prevented the development of substantial morainal banks as seen in Patagonia, where glacier retreat was characterized by periods of standstill and high sediment flux at decadal timescales.

We discuss potential influence of mechanisms acting on the early sediment infill facies during initial grounding line retreat. For instance, deglaciation ages indicate that glacier retreat from AP fjords does not appear to have been triggered by significant atmospheric warming. Conversely, glacier retreat in Patagonian fjords coincided with the end of the ACR cold phase and the subsequent warming trend shown in Antarctic ice core records, as well as with sea surface temperature increase recorded in ODP Site 1233. The influences of sea level rise, warm water incursion, local lithology and morphology are also discussed.