Quaternary sedimentation and active faulting along the Ecuadorian shelf: preliminary results of the ATACAMES Cruise (2012)

Abstract

International audienceSelected high-resolution seismic-reflection profiles and multibeam bathymetry acquired along the convergent Ecuador margin during the ATACAMES cruise on onboard the R/V L’Atalante (Jan.15–Feb.18, 2012) allow a preliminary evaluation of the neotectonic development and stratigraphic evolution of the margin based on the sismo-stratigraphic analysis of Quaternary sediment preserved on the margin shelf and upper slope. We present three major preliminary results. (1) The evolution of the Esmeraldas, Guayaquil and Santa Elena canyons. The head of the Esmeraldas canyon is the location of a continuous significant sediment transport. The Guayaquil canyon shows several episodes of deposition and incision. Aggrading sedimentation pattern in the canyon records several changes in relative sea-level. The subsidence of the Gulf of Guayaquil probably contributes to the good preservation of the canyon filling stages. The Santa Elena canyon is controlled by a SW–NE trending normal fault. (2) Variations of sediment accumulation and relative vertical motions are shown along-strike the shelf edge. Offshore the uplifted Manta peninsula, a pronounced subsidence of the shelf edge is documented by sedimentary clinoforms that have deposited in a morphological reentrant, and have migrated upslope testifying of a local subsidence meanwhile the adjacent La Plata Island area underwent uplift. In the Esmeraldas canyon area, a local uplift of the shelf is documented. (3) Two neotectonic fault systems with a possible transcurrent component are imaged across the shelf edge and upper margin slope offshore Jama, and Cape Galera. This possible transcurrent motion could be related to the reactivation of ancient faults of the upper plate by the subduction. These preliminary results indicate that the ATACAMES data set has a strong potential to evaluate the spatial and temporal contribution of tectonic and climate changes on the structural development and stratigraphic evolution of the Ecuador continental margin

3D Local Earthquake Tomography of the Ecuadorian Margin in the Source Area of the 2016 Mw 7.8 Pedernales Earthquake

“…(2004) and Michaud et al. (2015) have suggested that the JFS extends offshore forming an active flower‐like fault structure in the marine forearc; however, our model does not show clear evidence to support that hypothesis. Southernmost profiles P9 and P10 image reduced ratios covering a large area in the overriding plate.…”

“…In the upper crust, several small‐ to large‐scale faults might have been activated after the 2016 Pedernales earthquake. The shallow clustered seismicity observed close to the Esmeraldas segment (∼1°N, P1) is related to crustal extension (Agurto‐Detzel et al., 2019; Hoskins et al., 2020) and can be associated with the activation of the Tanigüe fault (Michaud et al., 2015—see F11 in Figure 1b) which may extend down to ∼15 km reaching a low Vp/Vs rounded‐like body (∼1.80) capable to produce this type of confined earthquakes. To the south (∼1°S), we observe clustered vertically aligned seismicity, at ∼10–15 km depth, in the southernmost profile P9.…”

The Esmeraldas Canyon: A Helpful Marker of the Pliocene‐Pleistocene Tectonic Deformation of the North Ecuador‐Southwest Colombia Convergent Margin

“…The strong tectonic activity of the EC region is supported by (1) the background seismicity (Manchuel et al, 2011), (2) the 1906, 1942, 1958, 1979 to 8.8 megathrust earthquakes (Kanamori & McNally, 1982;Mendoza & Dewey, 1984;Nocquet et al, 2016), (3) the strong seafloor deformation along the Ancon fault system (Collot et al, 2008;Ratzov et al, 2011), (4) the shelf uplift during the Pleistocene (Michaud et al, 2015), and (5) the uplifted Pleistocene marine terraces along the Ecuador northern coast (Pedoja et al, 2006).…”

“…Four tributary canyons join the main canyon. Upslope, the NS trending Atacames, Sua, and Same Canyons incise the edge of the Esmeraldas Platform and the upper margin slope (Michaud et al, 2015). Further down slope, the ENE trending Ancon Canyon (AC) originating from the Manglares Basin incises the lower margin wedge.…”

Interannual Variability of Mixed Layer Dynamics in the Ecuadorian Ocean

“…The Ecuadorian Sea is located in the far eastern boundary of the equatorial Pacific, between the Galápagos triple junction and the South American plate, where the oceanic crust and lithosphere of the Nazca plate (Carnegie Ridge) begin their decent into the mantle beneath South America (Michaud et al, ; Figure ). The country of Ecuador is almost evenly divided by the equator and thus occupies a somewhat unique position oceanographically where the Coriolis force goes to zero.…”