Tectonic and Sedimentary Insights Into Transtensional Basins Along the Pacific-North American Plate Boundary in the Northern Gulf of California

Abstract

In its northern sector, the Gulf of California presents intricate tectonic and sedimentary characteristics, offering insights into the region's geologic evolution. Based on two-dimensional seismic reflection profiles, we explore its structural style and sedimentary properties. Sedimentary thicknesses range from 7 km to over 10 km, heavily influenced by Colorado River sediments filling fault-bounded axial basins, including the Wagner, Consag, Upper Delfín, and Lower Delfín basins. The Wagner Basin comprises two asymmetric sub-basins trending NNE. A low-angle fault controls the northern sub-basin, which lacks bathymetric expression. In contrast, oblique faults influence the southern sub-basin, 12–15 km wide, as they merge into the Wagner Fault and transfer strain to the Cerro Prieto Transform Fault. Late Pliocene deformation is evident, with significant subsidence reflected in the top Pliocene horizon. Axial basins in the northern Gulf exhibit composite separation geometry with four north–south trending sub-basins linked by transform faults, including the Canal de Ballenas in the south and Cerro Prieto in the north. Strain transfer from the Canal de Ballenas fault produces a complex horsetail network, resulting in distributed transpressional deformation within the Upper and Lower Delfín basins. Active faults predominantly cut the seafloor west of the Tepoca Fault Zone, defining the modern rift's eastern boundary. Fault-bounded marginal basins, such as those on Tiburón Island and the adjacent Gulf coast of Sonora, expose late Miocene faulted non-marine deposits, indicating NE–SW extension and rift basin formation. Lower Pliocene marine deposits reveal marine incursions due to Pacific–North American plate movements. NE-trending normal and oblique faults govern the active depocentres in the Wagner, Consag, Upper Delfín, and Lower Delfín basins. In the Upper Delfín Basin, four to five asymmetric depocentres are evident, shaped by tectonic activity. The Lower Delfín Basin features a NE-trending symmetric rift parallel to the Ángel de la Guarda structural high, highlighting its tectonic alignment. The Tiburón Basin, characterised by a poorly defined acoustic basement, reveals substantial basin fill overlying the lower continental crust, indicating significant sedimentary accumulation. The Tiburón and De Mar faults control the NE-oriented asymmetric depocentres in the Tiburón Basin. Abandoned basins along the eastern margin, including Tiburón, Tepoca, Peñasco, and Altar, are separated from active basins by structural highs. Basement irregularities in the Delfín and Consag basins reflect remnants of hyper-extended continental crust, with intra-basin structural highs resembling boudins of lower continental crust. This study underscores the importance of tectonic and sedimentary processes in shaping the northern Gulf of California, highlighting the role of major faults in its geological and topographical evolution.