Segmentation along the Ecuadorian shelf (1°20’N-2°20’S) from interpretation of Satellite Altimetry and dense grid of MCS data
Résumé
The Ecuadorian convergent margin is characterized by the subduction of the Nazca oceanic plate beneath South America at an average of 6-7 cm/year (Nocquet et al., 2014). The geodynamic evolution of the margin is influenced by the subduction of the Carnegie Ridge and by the NE migration of the North-Andean Block.
Along the continental shelf, the satellite altimetry (NGDC-NOOA, Smith & Sandwell, 2004; Sandwell et al., 2014) shows positive and negative values despite a relatively constant water depth (80-100 m), which suggests a 1st order geological and structural margin segmentation. From the analysis of Free Air Anomaly (FAA) we propose dividing the margin in 4 segments: North, Central North-South and South (Fig. 1). The interpretation of the MCS reflection profiles (Propriety of the Secretaría Hidrocarburos del Ecuador, 4000in3 air gun seismic source, 640-channel, SP 25m, 160-fold coverage) allows us to determine the geological structures that characterize each segment. The North Segment (1°20’N-0°45’N) is characterized by a positive gravimetric anomaly (20 mGal, anomaly 1 in Fig.1) related to a 0.7 stwt-shallow acoustic basement. The Central-North segment (0°45’N-0°45’S) is defined by the presence of three negative anomalies (-30 mGals, anomalies 2, 3 and 4 in Fig.1) corresponding to 3stwt-thick sedimentary basins. The Central-South Segment (0°45’S – 2°20’S) is characterized by a positive gravimetric anomaly (up to 50 mGals, anomalies 5 and 7 in Fig.1) related to a 1.5 stwt-shallow acoustic basement. Finally, the South Segment (2°20’S – 3°30’S) is well defined by a regional negative anomaly (-80 to -150 mGals, anomaly 8 in Fig.1) that corresponds to the sedimentary fill of 6 to 7 km of thickness (Witt et al., 2006).
We identify and propose a new spatial arrangement and geometry of the principal sedimentary basins. The spatial distribution of interpreted seismic units, the deformation along regional structures and the correlation with well data allow us to discuss the timing of the segmentation along the Ecuadorian shelf.