Development of the Gulf of Guayaquil (Ecuador) during the Quaternary as an effect of the North Andean block tectonic escape

Abstract

Interpretation of industrial multichannel seismic profiles and well data are used to identify the main tectonic features of the Gulf of Guayaquil (GG) area. These include two E‐W trending major detachments: the Posorja and the Jambelí detachment systems, which represent half grabens with oppositely dipping detachments, to the south and to the north, respectively. The NE‐SW trending Puná‐Santa Clara fault system developed as a transfer fault system between the Posorja and the Jambelí detachments. The Esperanza and the Jambelí basins exhibit 3–4 km of sediment that accumulated during the past 1.6–1.8 Myr. The Puná‐Santa Clara fault system bounds the Esperanza and the Jambelí basins, evidencing that the evolution of these basins is tightly controlled by the two detachments at depth. To the west, the N‐S trending Domito fault system bounding the Posorja detachment system and the Esperanza basin to the west acted as a transfer zone between the shelf area and the continental slope. The Pliocene series show no significant variations in thickness throughout the Gulf of Guayaquil area suggesting that no important tectonic deformation occurred from 5.2 to 1.8–1.6 Ma. The major period of tectonic deformation in the Gulf of Guayaquil area occurred during the Pleistocene times. Three main tectonic steps are identified. From early Pleistocene to ∼180 ka, major subsidence occurred along the Esperanza and Jambelí basins. From ∼180 to ∼140 ka, most of the Gulf of Guayaquil area was above sea level during the isotope substage 6 low stand. From ∼140 ka to Present, tectonic activity is restricted along the normal faults bounding the Esperanza basin, the Tenguel fault, and the Puná‐Santa Clara and Domito fault systems. A N‐S trending tensional stress regime characterizes the Pleistocene times throughout. The northward drifting of the North Andean block is proposed to control the tectonic evolution and associated subsidence of the Gulf of Guayaquil area. It is also accepted that the collision of the Carnegie ridge with the trench axis has to play a major role in controlling the North Andean block northward drift. Because the Carnegie ridge subduction is possibly an ongoing process, which began prior to the Pliocene, we postulate the along‐strike morphology of the ridge at the origin of interplate coupling variations. The subduction of an along‐strike positive relief of the ridge is proposed at the origin of the major tectonic reorganization of the GG area occurring at ∼1.8–1.6 Ma.