The Late-Quaternary deposits of the Piedra Buena Terrace (Patagonian continental slope, SW Atlantic): An example of interaction between bottom currents and seafloor morphology

ISOLA, J.I.; BRAVO, M.E.; BOZZANO, G.; PALMA, F.I.; ORMAZABAL, J.P.; PRINCIPI, S.; SPOLTORE, D.; MARTIN, R.; ESTEBAN, F.D.; TASSONE, A.A.

MARINE GEOLOGY

ELSEVIER SCIENCE BV

Año: 2021 vol. 435

0025-3227

The Piedra Buena Terrace (PBT),situated in the Patagonian continental slope, is swept by the vigorous flow ofAntarctic-sourced bottom water masses, and intersectedby a considerable submarine canyon system. It thusrepresents a world-class natural laboratory toinvestigate the sedimentary dynamics of deep-ocean settingsinfluenced by both, along-slope, and down-slopesedimentary processes. In the framework of the Pampa Azulproject, the PBT was surveyed with swath bathymetry anda high-resolution parametric sub-bottom seismicprofiler and sampled at several locations with a 7 mlong gravity corer. Through the integration of the acousticdata, grain size results from a sediment core and twoAMS 14C ages this work attempts to: (1) describe for thefirsttime the detailed geomorphology of a poorly knownregion of the Patagonian continental slope; (2) depict theprincipal sub-surface seismic units, illustrating theirinternal structure, geometry, and distribution; (3) establish acorrelation between sub-surface seismic facies andsediment deposits using the first age constraints for this region; (4) proposea model with the depositional history of the PBT, focusing on the interactionbetween alongslope and down-slope processes and seafloor morphology. Theacquired bathymetric data imaged with unprecedent detail the geomorphology ofthe southern part of the PBT revealing the presence of a field ofkilometricsized, sub-circular, crater-like depressions, and a submarine canyon.The analyzed seismic sub-bottom profilesshowed that the shallow sedimentary structure of thestudy area is represented by patchy-mounded depositscharacterized by three distinctive features: cyclicstacks of two seismic facies (FA and FB), mounded shape, andpreferential location northwards the morphologicaldepressions and the submarine canyon. Integration of aseismic sub-bottom profile with one sediment coreindicates that the alternation of seismic facies reflects variations in thehydrodynamic conditions. FA is related to a high to moderate energy medium withinput ofterrigenous material and FB is related to a low energyenvironment with a limited contribution of sediments fromthe continent. The patchy distribution, mounded shapeand preferential location are associated with hydrodynamic processes occurringbetween the geomorphological features and the north-flowing Antarctic bottomcurrents, which result in the deposition of moundedcontourites in the northern flank of depressions and hybridalong-slope down-slope deposits northwards a submarinecanyon. The 14C ages constrain the chronologicalframework of these sediments to the Late-Pleistocene.This is in contrast with previous investigations that havesuggested much older ages (Late Miocene) for thesub-surface sediments of PBT. Finally, a conceptual model ishere proposed to illustrate the Late Quaternarysediment depositional history of the PBT where the interactionbetween north-flowing bottom contouritic currents andseafloor relief played an important role in the depositionand preservation of sediments in this area.