Stratigraphic record of basin development within the San Andreas fault system: Late Cenozoic Fish Creek-Vallecito basin, southern California

Abstract

The Fish Creek-Vallecito basin contains a 5.5-km-thick section of late Miocene to early Pleistocene sedimentary rocks exposed in the hanging wall of the West Salton detachment fault. These deposits preserve a high-fi delity record of late Cenozoic subsidence and basin fi lling that resulted from deformation in the San Andreas fault system of southern California. Existing and new paleomagnetic data, combined with new U-Pb zircon ages of two tuffs high in the section, show that the section ranges in age from ca. 8.0 ± 0.4 Ma at the base to ca. 0.95 Ma at the top. Geohistory analysis reveals: (1) moderate subsidence (0.46 mm/yr) from ca. 8.0 to 4.5 Ma; (2) rapid subsidence (2.1 mm/yr) from 4.5 to 3.1 Ma; (3) moderate subsidence (0.40 mm/yr) from 3.1 to 0.95 Ma; and (4) rapid uplift and erosion that has exhumed the section since ca. 1 Ma. Onset of sedimentation at ca. 8.0 ± 0.4 Ma records earliest extension or transtension in the area, possibly related to localization of the Pacifi c-North America plate boundary in the Salton Trough and Gulf of California. Alternatively, marine incursion at 6.3 Ma may be the earliest record of plate-boundary deformation in the Gulf of California-Salton Trough region. A thick interval higher in the section records progradation of the Colorado River delta into and across the basin starting ca. 4.9 Ma. Progradation continued during an abrupt increase in subsidence rate at 4.5 Ma, and fl uvial-deltaic conditions persisted for 1.4 m.y. during the rapid-subsidence phase, indicating that delta progradation was driven by a large increase in rate of sediment input from the Colorado River. Uplift and inversion of the basin starting ca.

Punctuated Sediment Discharge During Early Pliocene Birth of the Colorado River: Evidence from Regional Stratigraphy, Sedimentology, and Paleontology

“…The lower megabreccia is overlain by the Fish Creek Gypsum and locally-sourced turbidites of the Latrania Formation (Lycium Member), which record marine incursion into the Salton Trough region ~6.3Ma ( Fig. 15A; Dorsey et al, 2007Dorsey et al, , 2011. Lycium Member turbidites are overlain by a second megabreccia that was emplaced catastrophically into a marine basin (Kerr and Abbott, 1996;Abbott et al, 2002) immediately prior to the end of the Miocene epoch (Fig.…”

“…15, 16). Thick-bedded sandstones of the Wind Caves member record deposition by sand-rich turbidity currents in a submarine canyon that was fed by early Pliocene input from the Colorado River Dorsey et al, 2007Dorsey et al, , 2011Kimbrough et al, 2015;Cloos, 2014). Colorado River-derived turbidites of the Wind Caves member are restricted to an ~10-km wide paleocanyon, and pinch out over b10-15 km in the down-transport direction to the Coyote Mountains where the Wind Caves member is absent and the Coyote Clay rests directly on older deposits Bykerk-Kauffman, 2017) Shirvell, 2006).…”

“…This age assignment is consistent with independently determined correlation of magnetic reversals to the geomagnetic polarity timescale (Dorsey et al, 2007. Amphistegina gibbosa became extinct in the northern Gulf and Salton Trough region at approximately 5.3 Ma (Ingle, 1974;McDougall et al, 1999;Dorsey et al, 2007Dorsey et al, , 2011. The first occurrence of T. anfracta is 5.8 Ma, the range of S. globigerus in the equatorial Pacific is 5.45 to 3.6 Ma, and the range of G. multiloba is Miocene to Pliocene (Blow, 1979;Resig, 1989Resig, , 1993Miranda-Martínez et al, 2017;A.Y.Miranda-Martínez, personal communication, 2017).…”

Evolution of oceanic margins : rifting in the Gulf of California and sediment diapirism and mantle hydration during subduction

“…7 Ma, ~0.5-1.0 m.y. before the earliest marine incursions in the northern Gulf of California (e.g., McDougall, 2008;Dorsey et al, 2011;Bennett et al, 2012b).…”

“…7 Ma, ~0.5-1.0 m.y. before the earliest marine incursions in the northern Gulf of California (e.g., McDougall, 2008;Dorsey et al, 2011;Bennett et al, 2012b).The Late Miocene rocks of the Santa Rosalía Basin inform us of conditions during deposition of the associated EGE. This basin is fl oored by scattered marine limestone and gypsum units that unconformably overlie heavily faulted prerift Comondu arc volcanic rocks (Wilson and Rocha, 1955), indicating that these units represent the fi rst deposition in proto-gulf extensional basins.…”