Santa Cruz Island Reserve

17 Feb, 03 AM - 21 Feb, 07 AM

The reconstruction of the Southern California Continental Borderland is constrained by interpretation of widespread Tertiary fluvial-deltaic systems, which contain a primary record of tectonics and sedimentation. Well known extraregional Poway rhyolite porphyry clasts of the Eocene Ballenas Channel of San Diego have been recognized in the Channel Islands far to the North East and constitute a key piercing point in the palinspastic reconstruction of the borderland. The Tertiary section on Santa Cruz Island records distinct changes in provenance starting with Eocene Poway-clast bearing conglomerates overlain by late Oligocene-early Miocene Vaqueros Formation containing much larger fractions of plutonic detritus, which in turn is overlain by blueschist-bearing Miocene strata of the San Onofre Breccia. Much work has been done on these Eocene conglomerates, mostly during the late 60's and early 80's and directed at determining the ages of microfossils and locating the source of these exotic Poway clasts, which identified a Sonoran and/or southern Arizona source (Minch, 1972; Abbot & Smith 1978; Kies, 1982; Abeid, 2010). New laser ablation ICPM zircon U-Pb ages from rhyolite porphyry in Sonora and Eocene San Diego and Santa Cruz Island conglomerate clasts all yield middle Jurassic ages that tie these areas to a common source-transport-depositional system. The younger Vaqueros Formation conglomerates contain clasts suggesting extra-regional but distinctly different sources compared to the Eocene; these include middle Jurassic diorite and dacite porphyry as well as a middle Cretaceous metavolcanic clasts. The Vaqueros assemblage displays more similarity to the widespread Sespe Formation red beds of the Los Angeles basin which have been linked by previous workers to sources in the Mojave Desert (Howard, 2006). Paleocurrent data for Eocene strata on Santa Cruz Island together with Vaqueros Formation Sespe conglomerates present potential problems for the Bohannon and Geist (1998) proposed borderland reconstruction.

Visit #27395 @Santa Cruz Island Reserve

Approved

Under Project # 24873 | Research

Provenance of mid-Tertiary sandstone and conglomerates from the California Continental Borderland; implications for paleogeographic reconstructions

graduate_student - San Diego State University (CSU)

Reservation Members(s)

Group of 2 Graduate Student Feb 17 - 21, 2012 (5 days)

Reserve Resources(s) | Create Invoice