Marine incursion synchronous with plate-boundary localization in the Gulf of California

Volcanic strata on southwest Isla Tiburon define the age of interstratified marine rocks and, through revision of existing correlations, the age of the proto–Gulf of California marine incursion. A 5.7 ± 0.2 Ma ash flow was emplaced at the base of the marine section. A rhyodacite dike and its related lava flow, dated as 11.2 ± 1.3 Ma, 3.7 ± 0.9 Ma, and 4.2 ± 1.8 Ma, intrudes and overlies, respectively, the marine rocks. The 11.2 Ma age, which was the core datum for a middle Miocene proto–Gulf of California origin for the underlying rocks, is discordant with all other isotopic and microfossil ages. An alternative interpretation, utilizing all available geologic and geochronologic data except this discordant age, is that marine strata on Isla Tiburon are latest Miocene to early Pliocene age. Reinterpretation of these strata supports a simplified history of marine incursion into the Gulf of California. Marine rocks as old as 8.2 Ma in the southern Gulf of California indicate an early marine incursion, perhaps flooding a region of more intense proto–Gulf of California continental extension. Flooding of the entire basin by 6.5–6.3 Ma correlates to the sudden onset of significant Pacific–North American plate-boundary motion within the Gulf of California.

[1]  A. Carreño.  Biostratigraphy of the late Miocene to Pliocene on the Pacific island Maria Madre, Mexico , 1985 .

[2]  R. G. Gastil,et al.  Reconnaissance geology of coastal Sonora between Puerto Lobos and Bahia Kino , 1977 .

[3]  E. Nagy,et al.  Age and stratigraphic relationships of pre- and syn-rift volcanic deposits in the northern Puertecitos Volcanic Province, Baja California, Mexico , 1999 .

[4]  E. Nagy,et al.  Structural controls on the continent‐ocean transition in the northern Gulf of California , 2000 .

[5]  J. Barron,et al.  Neogene stratigraphy, foraminifera, diatoms, and depositional history of Maria Madre Island, Mexico: Evidence of early Neogene marine conditions in the southern Gulf of California , 1988 .

[6]  A. Carreño.  Neogene microfossils from the Santiago diatomite, Baja California Sur, México , 1992 .

[7]  J. Stock,et al.  An age constraint on Gulf of California rifting from the Santa Rosalía basin, Baja California Sur, Mexico , 2000 .

[8]  P. J. Patchett,et al.  Sr isotope evidence for a lacustrine origin for the upper Miocene to Pliocene Bouse Formation, lower Colorado River trough, and implications for timing of Colorado Plateau uplift , 1997 .

[9]  R. Crippen,et al.  Middle Miocene extension in the Gulf Extensional Province, Baja California: Evidence from the southern Sierra Juarez , 1996 .

[10]  K. Hodges,et al.  Pre‐Pliocene Extension around the Gulf of California and the transfer of Baja California to the Pacific Plate , 1989 .

[11]  J. Stock,et al.  Rapid localization of Pacific–North America plate motion in the Gulf of California , 2001 .

[12]  Jay Robert Neuhaus.  Volcanic and nonmarine stratigraphy of southwest Isla Tiburon, Gulf of California, Mexico , 1989 .

[13]  A. Carreño,et al.  Neogene sedimentary evolution of Baja California in relation to regional tectonics , 1999 .

[14]  D. Karig,et al.  The proto-Gulf of California , 1972 .

[15]  A. Cruz.  Bioestratigrafía y significado paleoceanografico de los radiolarios de la protoboca del golfo de California , 1994 .