ELLIPTICITY OF MEGA-POCKMARKS IN THE PATAGONIAN CONTINENTAL MARGIN: AN INTERPLAY BETWEEN TECTONIC STRUCTURE AND OCEAN CURRENTS

JOSÉ IGNACIO ISOLA; JUAN PABLO ORMAZABAL; GONZALO FLORES; SEBASTIÁN ARISMENDI; MARÌA DRUET; ARACELI MUÑOZ; MARÍA GOMEZ BALLESTEROS; JOSÉ DEL RÍO; SILVIA ETIENOT; NÉSTOR BOLATTI; ALEJANDRO ALBERTO TASSONE

Atenas

Conferencia; Regional Conference on Geomorphology; 2019

International Association of Geomorphologists

Analysis of high-resolution multi-beam bathymetry and seismic data revealed the presence ofwidespread fluid escape features in the middle slope of the Patagonian Continental Margin(Western South-Atlantic). On the sea-bottom these features correspond to elliptical megapockmarks, while in the sub-surface are represented in the seismic records by several gasrelated acoustic anomalies. The objective of this work is to discuss the controls on thedistribution and ellipticity of the mega-pockmarks in relation to the geological structures andbottom currents circulation. Most of the mega-pockmarks are located above a re-activatedand inversed Mesozoic graben controlled by NW-SE and NE-SW striking faults. The morphometrical analysis of pockmarks revealed two preferential directions of elongation which are coincident with the strike of the graben’s faults, suggesting that faults and fractures might have acted as pathways for upwards migration of fluids. We also infer that these faults and fractures control the asymmetry of pockmarks. A swarm of fractures would provide a weaker rheological behavior in preferential directions on which the erosive agents, such as ocean currents, will elongate the pockmarks. Regarding pockmarks distribution, we observed that even though acoustic evidence of fluid flow occurs in all the study area, the incidence of pockmarks is constrained just to depths shallower than 1200 m. We hypothesize that the rheological behavior of the superficial deposits in deeper areas where Eocene rocks outcrops or subcrops did not allow the genesis of pockmarks. We conclude that the distribution of pockmarks in the study area was likely controlled by the presence of a source for fluid/gas and soft sediments on the seafloor, while their asymmetry is consequence of the enhanced erosion of bottom currents on weak directions associated with faults and fractures.