The Gulf of California is an excellent example of how new ocean basins form. Tectonically, the northern Gulf of California is an incipient ocean basin and studies on it have defined acoustic basement and reveal the presence of new oceanic crust and intrusive bodies. Some recent studies report fundamental differences between the basins of the northern and southern Gulf of California: that the latter have well-developed oceanic crust beneath a thin cover of sediments, whereas the northern basins show proto-ocean basins, which may reflect thermal insulation of the thick sedimentary cover, the presence of lowangle faults, and more diffuse and distributed deformation. During the 1970s, Petróleos Mexicanos (PEMEX) undertook a 2D seismic reflection survey in the northern Gulf of California, over many active rift basins, including the Consag Basin. Through the processing and interpretation of these data, we describe the structural characteristics of the Consag Basin beyond 2 km depths. Using seismic reflection data, we identified an intrusion in the central part of this basin that may represent new oceanic crust buried by more than 4 km of sediments.
The Laguna Salada Basin in northeastern Baja California, México, is an active half-graben with subsidence principally controlled by two major faults along the eastern basin margin-the Cañada David detachment fault and the dextral oblique Laguna Salada fault. Active-source, seismic-reflection data constrain the geometry of the active detachment fault and indicate two structural domains. The south domain is a supradetachment basin controlled by the Cañada David detachment fault. Two seismic profiles indicate the detachment fault dips 17°-20° west, has a minimum of 10.1 km of slip, and accumulates a sedimentary wedge more than 2.5 km thick in the west-central part of this basin domain. This estimation indicates that the subsurface portion of the Cañada David detachment accommodates 24% of extension in the western main plate boundary zone. The north domain is a dilatational stepover (or pull apart) controlled by the northwest-trending, west-dipping, dextral-oblique Laguna Salada fault and the north-trending, dip-slip Cañón Rojo fault, which defines the south boundary of the pull-apart basin domain. The Cañón Rojo fault accumulates more than 2 km of subsidence, but geometric considerations indicate that the basement in the hanging wall of the Laguna Salada fault projects to a depth of ~3.8 km and intersects the 70° west-dipping Laguna Salada fault. Several faults cut the west margin of the floodplain lagoon and the hanging wall of both the Cañada David detachment and the Laguna Salada fault. The largest fault is west dipping and produces ~500 m of vertical offset. Its location projects south of the Cañón Rojo fault, and we speculate these two faults may correlate. Seismic facies reflect its sedimentary environment and processes. Seismic facies 1 is high-amplitude, laterally continuous reflectors that represent flooding and prolonged lacustrine conditions. Seismic facies 2 is high-to low-amplitude, laterally discontinuous reflectors also representing flooding conditions. Seismic facies 3 is low-amplitude, poorly contrasted continuous to discontinuous reflectors interpreted as subaerial distal fan sandstone deposits. Seismic facies 4 is high-amplitude, discontinuous, imbricated to a chaotic pattern of reflectors. We interpret facies 4 as coarse-grained, high-energy alluvial fan deposits prograding over the basin floor from the west in the range front of Sierra Juarez. Seismic facies 1 and 2 predominate in the east and central portions of seismic profiles where the depocenter accumulates thicker sedimentary sequences.
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