IMPACT OF THE SUBDUCTION OF THE CARNEGIE RIDGE ON THEECUADORIAN SHELF AND SLOPE BASINS DURING THE LAST 1MA

Description

The subduction of the Nazca Plate below the South American Plate shows the subduction ofaseismic ridges of different origins and morphologies. One of them is the Carnegie Ridge (400kmwide, 2km high) produced by the relationship between the Galapagos Hotspot and the GalapagosSpreading Center. The ages and the effects of the Carnegie Ridge subduction on the Ecuadorianmargin are still a matter of debate. Newly acquired offshore data complementing the onshorerecord help to highlight part of this history.The goal of this study is to describe the last 1Ma sedimentary record of Ecuadorian continentalshelf to improve our understanding of the impact of the Carnegie ridge subduction on sea floor andshoreline morphologies. For this aim, we acquired high-resolution (50-450Hz frequency) multichannel(72 channels) and single channel (Sparker) seismic data, piston cores, sediment profiles(3.5khz) and high-resolution multibeam bathymetry, during the ATACAMES cruise of the RVL'Atalante, in 2012.In the offshore, we identified two types of Quaternary basins: the platform basins locatedat northern limit of the Carnegie Ridge, and the slope basins located along the margin in front ofCarnegie Ridge subduction. All of them exhibit three major angular unconformities, whichencompass some minor unconformities that limit transgressive-regressive sequences (T-R se- quences),which correlate to 100 to 40kyrs Milankovitch cycles. The E-W (dip) seismic profiles, perpendicularto the coastline, show that these angular unconformities mark the progressive mi- gration of successivedepocenters in a landward direction. This landward stepping started by 1.4 Ma in agreement with theage postulated by some author for the beginning of the Carnegie ridge subduction. The highlysubsiding platform basins bordering the northern side of the Carnegie Ridge are bounded by a set ofregional faults, which includes the Jama fault zone. The subsidence of these basins might haveaccompanied the relative movement between the EW convergence of the Nazca Plate and the NEdextral escape tectonic along the Jama Faults of the North Andean Block

Abstract

National audience

Additional details