The Neogene Forearc Basins of the Ecuadorian Shelf (1°N-2°20’S): Preliminary Interpretation of a Dense Grid of Mcs Data
Résumé
Forearc basins serve as a sedimentary archive of sea-level variations and subduction-related tectonic processes. Along the Ecuadorian convergent margin (0°40’N-2°20’S) we interpreted a dense network (one profile every 4 km) of MCS reflection profiles acquired by the Ecuadorian State during the 2009 SCAN cruise with a 8-km-long, 640-channel streamer, and an array of 4000 in3total volume air guns to improve our understanding of the dynamic processes that shape forearc basin stratigraphy and tectonic structures.
Isopach and structural maps of the acoustic basement show two structural segments on the margin. The northern segment (0°45’S-0°40’N) is characterized by - three sedimentary basins called Pedernales, Bahía-Jama and Caráquez basins, - N30°-50° trending transcurrent faults and -N80°-90° trending normal faults dipping to the south. The southern segment (2°S-0°45’S) is characterized by acoustic basement high, NS-trending until 1°10’S, with small localized sedimentary basins and by N320°-340° trending normal faults dipping to the north. At least five seismic units separated by unconformities are evidenced in the northern basins. Tentative correlations with geological data from the offshore Caraquez-1 well and the on-shore geology, suggest the following Neogene deformation steps: 1) sedimentary basins were initiated along N80°-90° trending normal faults in a regional N30°-50° trending strike slip system during lower Miocene; 2) deformation ended by a regional erosion (underlined by a flat regional unconformity) after the lower Miocene; 3) subsidence began by an undersea regional erosion after the Middle-Upper Miocene (underlined by an irregular regional unconformity), and 4) uplift and locally subsidence of the shelf edge with reactivation of a strike slip fault system from Pliocene (?) to Present. The arrival of the Carnegie ridge and associated seamounts to the trench axis is proposed at the origin of this last stage.