Viejo Formation: A New Formation for the Imperial Group Sediments in the Southern Coyote Mountains, Salton Trough , Southern California

Abstract

Kidwell and Winker (1996) describe the Andrade Member of the Latrania Formation, Imperial Group as a marine progradation (transgression) over the non-marine fanglomerate of their Garnet Formation, Split Mountain Group in the Coyote Mountains (CM). Our detailed mapping in the CM indicates that their Garnet Formation is composed of several (4+) distinct fresh-water fanglomerates. We also have divided their Andrade Member into several (8+) transgression-regressional (T-R) marine (Imperial Group) sequences that bracket some of our fresh-water fanglomerates. The transgressions have a recognizable, predictable and repeated marine sedimentary sequence consisting of a basal conglomerate followed by sandstone and then a mudstone. These marine sedimentary sequences are capped by unconformities representing regressions. Imperial marine sediments interfingers with one of our freshwater fanglomerates. Fresh water limestones are associated with at least two of our fanglomerates. Our fresh-water fanglomerates and T-R marine sequences make up our Viejo Formation (VF).The lower part of the VF has a siltstone (Woodring's Outcrops [ Morgan and Morgan, 2015]) that is interbedded with basalts of the Alverson Formation (17 Ma, Morgan et al., 2012). The youngest member of the VF has a distinctive basal conglomerate ( Dark Cuesta Member [DCM]), described as having resistant, well-rounded, quartz rich pebbles in a course, granitic, arkosic matrix with granitic lithic fragments. The matrix and lithic fragments are responsible for the desert varnish that is often found on this member. We believe this youngest basal conglomerate may be, in part, reworked from a run out debris flow that came from an unidentified granitic terrane. When this basal conglomerate was being deposited, younger VF already covered the CM. Winker and Kidwell (1996) describe the Latrania Formation as a marine turbidite section in a subsiding basin in the Fish Creek-Vallecito-Split Mountain area. The VF is made up of marine transgressions and regressions intermingling with fresh-water sediments deposited at sea level on the subsiding CM. An early part of the VF was deposited in the Basin and Range extensional environment when the CM were in the State of Sonora,

Extensional Tectonics, a Slab Window and the Arrival of the Gulf of California About 17ma, While the Coyote Mountains of Southern California, Usa Undergo 90° Clockwise Rotation in Sonora, Mexico

“…The base of the Alverson is dated by Morgan et al (2012) at 17.1 Ma using zircons. White represents the marine and fresh water units of the Imperial Group (Winker and Kidman, 1996), which interfingers with the volcanics of the Alverson Canyon Formation (Woodring, 1932;Morgan and Morgan, 2016). AC-Alverson Canyon (Fossil Canyon).…”

“…The Red Fanglomerate and the volcanics of the Alverson Canyon Formation of the SMG are syn-extensionally related to the second episode of extensional found in the CMs. The Red Fanglomerate interfingers with the Alverson Canyon Formation (Ruisaard, 1979) with the Viejo Formation also interfingering with the Alverson (Woodring, 1931;Morgan and Morgan 2016). This second episode appears to be related to continuing Basin and Range extension and the arrival of the Gulf of California (Viejo Formation).…”