Detrital Zircon Investigation of the Age and Provenance of the Goldstein Peak Formation, Western Sierra Nevada Mtns., California: Reconstruction of an Early Cretaceous Fluvial System
The Goldstein Peak formation is a newly recognized non-marine deposit dominated by fluvial metaconglomerates surrounding a lens of metavolcanic rocks. A granite dike discordant with the Goldstein Peak metaconglomerates and displaying wet-sediment intrusion structures provides a minimum depositional age estimate of 139 ± 1 Ma. LA-MC-ICPMS analysis of seven detrital zircon populations from a suite of conglomerate samples collected through a 1-km thick section suggest a maximum depositional age of 135.7 ± 5.2 Ma. Together these two data sets appear to bracket the depositional age of the Goldstein Peak formation to between 144 and 138 Ma. This age is unusual, as Lower Cretaceous non-marine rocks in California are extremely rare. What is not known is where the rivers that deposited the Goldstein Peak sediments originated and to where these rivers flowed. Paleogeographic considerations support a roughly westward flow direction, with a drainage basin in the highstanding Sierra Nevada arc and/or North American craton and a mouth in the Great Valley forearc basin. Detrital zircon data suggest that the clastic protoliths were derived from the volcanic carapace of the Mesozoic arc, from the exhumed Sierra Nevada batholith, and from metasedimentary wall rocks surrounding the Jurassic and Cretaceous plutons. Detrital zircon U-Pb age comparisons to the Triassic-Jurassic Kings Sequence suggest that at least some of the pre-Mesozoic zircons could have been derived from the metamorphic framework of the batholith but do not exclude the possibility that Goldstein Peak rivers may have sourced the Mesozoic foreland basin. Statistical comparisons to coeval samples of the Great Valley Group, a suite of siliciclastic rocks deposited in the Sierra Nevada fore-arc basin, are consistent with the hypothesis that the Early Cretaceous Goldstein Peak rivers delivered arc-derived sediment to the forearc basin.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California