Glacimarine Sedimentation

The metasedimentary sequence of the Cushamen Formation in the western North Patagonian Massif is 540 m thick and comprises six sedimentary lithofacies associations related to a glacimarine environment. Four of these lithofacies represent distal glacimarine environments, whereas another one was deposited in proximal glacimarine environments, and the last includes subglacial environments. The organization and configuration of these lithofacies associations represent the advance and retreat of the glacier masses. The maximum glacial advance is correlatable with the G2 glacial interval of the Pennsylvanian Pampa de Tepuel, Las Salinas and Valley Chico, formations of the Extraandean Chubut, and the southern part of Neuquén Cordillera. Contemporaneously, in southern Chile there are marine and glacimarine sediments. The chronostratigraphic relationships between the Silurian to Permian units allow five paleogeographic stages to be distinguished. The middle Silurianelate Devonian igneous rocks represent the first magmatic stage. The second stage, which is transitional to the first, is represented by a marine basin that includes the late Devonianeearly Carboniferous Esquel and Río Pescado formations and the Llanquihue Complex. The third stage (earlyelate Carboniferous) includes granitoids of the second magmatic event that partially overlapped the first magmatic igneous belt. The fourth stage belongs to the late Carboniferous sedimentation of the Cushamen and equivalent formations. The extended early Permian magmatism was the last Paleozoic event in the studied area.

This work provides a regional perspective on the links between glacial, glacimarine and marine sedimentary processes occurring since the Last Glacial Maximum along the Central Bransfield Basin (Antarctic Peninsula), from shallow to deep areas, by combining information provided by gravity cores from shelf to deep basin settings, swath bathymetry and high-resolution reflection seismic and sub-bottom (TOPAS) profiles. Seven lithofacies have been identified. Their textural, compositional and X-radiographic characteristics, as well as their spatial distribution allow the differentiation of two stages of deposition, involving distinct sedimentary processes. The Last Glacial Maximum was characterised by subglacial deformation by the Antarctic Peninsula Ice Sheet as it reached its most extended position on the distal mid-slope platforms of the Central Bransfield Basin. Proglacial debris flows occurred on the external edges of the mid-slope platforms and lower slope. Since the last deglaciation, glacimarine (proglacial debris flows, glacimarine proglacial processes and turbid glacial meltwater) and open-marine sedimentary processes (turbidity currents, sliding and contour current activity) have predominated in the Central Bransfield Basin. Glacial cyclicity is the main factor controlling the sedimentary processes in the basin, but several secondary factors, including physiography, sediment entry points and oceanography, have been identified as local controls on the sediment distribution. The unusual physiography of the Central Bransfield Basin, where slope platforms form wide flat surfaces seaward from glacial troughs, is a key factor in the widespread occurrence of glacial and glacimarine processes on the entire continental margin.

This work provides a regional perspective on the links between glacial, glacimarine and marine sedimentary processes occurring since the Last Glacial Maximum along the Central Bransfield Basin (Antarctic Peninsula), from shallow to deep areas, by combining information provided by gravity cores from shelf to deep basin settings, swath bathymetry and high-resolution reflection seismic and sub-bottom (TOPAS) profiles. Seven lithofacies have been identified. Their textural, compositional and X-radiographic characteristics, as well as their spatial distribution allow the differentiation of two stages of deposition, involving distinct sedimentary processes. The Last Glacial Maximum was characterised by subglacial deformation by the Antarctic Peninsula Ice Sheet as it reached its most extended position on the distal mid-slope platforms of the Central Bransfield Basin. Proglacial debris flows occurred on the external edges of the mid-slope platforms and lower slope. Since the last deglaciation, glacimarine (proglacial debris flows, glacimarine proglacial processes and turbid glacial meltwater) and open-marine sedimentary processes (turbidity currents, sliding and contour current activity) have predominated in the Central Bransfield Basin. Glacial cyclicity is the main factor controlling the sedimentary processes in the basin, but several secondary factors, including physiography, sediment entry points and oceanography, have been identified as local controls on the sediment distribution. The unusual physiography of the Central Bransfield Basin, where slope platforms form wide flat surfaces seaward from glacial troughs, is a key factor in the widespread occurrence of glacial and glacimarine processes on the entire continental margin.

This work provides a regional perspective on the links between glacial, glacimarine and marine sedimentary processes occurring since the Last Glacial Maximum along the Central Bransfield Basin (Antarctic Peninsula), from shallow to deep areas, by combining information provided by gravity cores from shelf to deep basin settings, swath bathymetry and high-resolution reflection seismic and sub-bottom (TOPAS) profiles. Seven lithofacies have been identified. Their textural, compositional and X-radiographic characteristics, as well as their spatial distribution allow the differentiation of two stages of deposition, involving distinct sedimentary processes. The Last Glacial Maximum was characterised by subglacial deformation by the Antarctic Peninsula Ice Sheet as it reached its most extended position on the distal mid-slope platforms of the Central Bransfield Basin. Proglacial debris flows occurred on the external edges of the mid-slope platforms and lower slope. Since the last deglaciation, glacimarine (proglacial debris flows, glacimarine proglacial processes and turbid glacial meltwater) and open-marine sedimentary processes (turbidity currents, sliding and contour current activity) have predominated in the Central Bransfield Basin. Glacial cyclicity is the main factor controlling the sedimentary processes in the basin, but several secondary factors, including physiography, sediment entry points and oceanography, have been identified as local controls on the sediment distribution. The unusual physiography of the Central Bransfield Basin, where slope platforms form wide flat surfaces seaward from glacial troughs, is a key factor in the widespread occurrence of glacial and glacimarine processes on the entire continental margin.

The metasedimentary sequence of the Cushamen Formation in the western North Patagonian Massif is 540 m thick and comprises six sedimentary lithofacies associations related to a glacimarine environment. Four of these lithofacies represent distal glacimarine environments, whereas another one was deposited in proximal glacimarine environments, and the last includes subglacial environments. The organization and configuration of these lithofacies associations represent the advance and retreat of the glacier masses. The maximum glacial advance is correlatable with the G2 glacial interval of the Pennsylvanian Pampa de Tepuel, Las Salinas and Valley Chico, formations of the Extraandean Chubut, and the southern part of Neuquén Cordillera. Contemporaneously, in southern Chile there are marine and glacimarine sediments. The chronostratigraphic relationships between the Silurian to Permian units allow five paleogeographic stages to be distinguished. The middle Silurianelate Devonian igneous rocks represent the first magmatic stage. The second stage, which is transitional to the first, is represented by a marine basin that includes the late Devonianeearly Carboniferous Esquel and Río Pescado formations and the Llanquihue Complex. The third stage (earlyelate Carboniferous) includes granitoids of the second magmatic event that partially overlapped the first magmatic igneous belt. The fourth stage belongs to the late Carboniferous sedimentation of the Cushamen and equivalent formations. The extended early Permian magmatism was the last Paleozoic event in the studied area.