Seismostratigraphy and Cenozoic Evolution of Nágera and Perito Moreno Terraces

ISOLA J. I.; TASSONE A. A,

Rimousky

Workshop; Workshop on the Promess Project: Results and Opportunities; 2017

Universidad de Quebec en Rimousky

The continental passive margins, as the ArgentineContinental Passive Volcanic Margin (MCAPV)(Franke et al., 2007; Schnabel et al., 2008; Beckeret al., 2012), preserve in their sedimentary recordeustatic changes and variations in the dynamics ofthe ocean currents, from global changes, as openingand closure of ocean gateways, to local variations, aschanges in depth in the boundary of different watermasses.The Patagonian Continental Margin (MCP) is theportion of the MCAPV located south to the ColoradoFracture Zone (Fig. 1 a, b). The major features shapingthe surface of the continental slope in the MCP arefour contouritic terraces (Fig. 1b), from west to east:Nágera Terrace (TN), Perito Moreno Terrace (TPM),Piedra Buena Terrace and Valentín Feilberg Terrace.The genesis and evolution of the four terracesis linked to the activity of antartic sourced bottomcurrents. Previous works have described the seismostratigraphyand the oceanographic controls in thestructural building of the two easternmost terraces,(e.i., Piedra Buena and Valentín Feilberg terraces).On the contrast, very little is known on the evolutionof the Nágera and Perito Moreno terraces.This work aims to describe the Cenozoic stratigraphyof the TN (~600 a 1000 m) and TPM(~1000 a 1500 m), in relation to the major climaticand oceanographic changes occurred in the SouthAtlantic Ocean during this time. The study is basedon the interpretation of two monochannel seismiclines acquired in 2014 on board of the Canadianvessel Coriolis II, and one multichannel seismic lineprovided from Secretaría de Energía de la NaciónArgentina.Through the interpretation of the seismic lines(Figs. 2-4), following the seismostratigraphic method(Mitchum et al., 1977), four mayor unconformitieswere recognized (Table 1). These unconformities areinterpreted as sequence boundaries. After correlatethis unconformities with: previous works in theMCA (data published of Tayra well by Continanzia etal., 2011; and cores published by Ewing & Lonardi,1971) and main oceanographic-climatic changes,five seismic units (U0, U1, U2, U3 and U4; see table1) were defined for this part of the margin.Finally, by the interpretation of these units, fourstages of evolution for the TN and TPM could bedefined (Fig. 5):1) Paleocene - Eoceno, is characterized by thermalsubsidence, as well as hemipelagic and gravitationalsedimentation with negligible activity of deep oceancurrents.2) Eocene - Oligocene to mid Miocene, is characterizedby the presence of a shallow marine environmentwith clinoforms in the outer shelf to middle slope,and it is interpreted as a deltaic progradation in ashallow sea environment.3) Middle Miocene to Pliocene, is characterized bythe first evidence of current activity in the area. Itfinishes with a strong erosive surface, and formationof the Nágera and Perito Moreno terraces.4) Pliocene to Holocene is characterized by highocean currents activity in the upper and middleslope, strong interaction between ocean currents andthe seafloor, and development of contouritic deposits.