Tectonics of the Pliocene Loreto Basin, Baja California Sur, Mexico, and evolution of the Gulf of California

The Pliocene Loreto basin is a transtensional basin that consists of nonmarine to marine sedimentary rocks and interbedded tuffs. On the basis of stratigraphic study and ⁴⁰ Ar/ ³⁹ Ar dating of tuffs, the southern Loreto basin began to form at ~3.4 Ma as an alluvial basin with moderate rates of subsidence. Between 2.46 and 2.36 Ma, extremely rapid subsidence of the basin was accompanied by deposition of vertically stacked Gilbert-type fan deltas. During this period, the southernmost basin began to be cut by an array of dextral-normal faults. The basin returned to a moderate rate of subsidence from ~2.36 to ~2.0 Ma. The major change in the Loreto basin at 2.46 Ma may be coeval with the beginning of faulting in southern California on the Elsinore and San Jacinto faults. -from Authors