The Modern Detrital Record of Northern and Central California: Assessing the Propagation of Geochronological and Geochemical Provenance Signals
Abstract
We couple U-Pb detrital zircon geochronology (n=30) and bulk sediment geochemistry (n=41) from modern Sacramento and San Joaquin Rivers, the Sacramento-San Joaquin Delta, San Francisco Bay, and offshore sediments to assess the propagation of provenance signals across the sediment dispersal system. Detrital zircon U-Pb ages show pronounced down-system variations that progressively become homogenized within the Delta. La/Yb ratios show a systematic north to south increase along the Central Valley reflecting the variability of more primitive arc and ophiolitic rocks within the Klamath Mountains and northern Sierra Nevada to more fractionated arc rocks and plutons in the central and southern Sierra Nevada batholith. Proximal to the Klamath Mountains, the Sacramento River contains abundant Early Paleozoic zircon that is rapidly diluted downstream. Similarly, sands from west-flowing Battle Creek carry almost 100% 500 ka zircon from the Mount Lassen area while none is recovered in the downstream Sacramento River. Samples are initially enriched in Jurassic and then 100-85 Ma zircon down the Sacramento River, particularly south of the American River. Similarly, in the north-flowing San Joaquin River, upstream samples are dominated by Early Cretaceous and Jurassic zircon, while downstream samples become progressively enriched in 100-85 Ma grains from major tributaries. The Delta samples most resemble the Sierra Nevada batholith. Sediment deposited downstream in San Francisco Bay and offshore is further modified by sediment eroded from Cretaceous-Cenozoic Franciscan Coast Range strata. Overall, our results highlight the ability of large detrital zircon data sets to discriminate smaller-scale point sources, demonstrate how geochronological and geochemical provenance proxies are propagated down-stream, and reveal how bulk geochemical tracers can effectively highlight larger-scale trends in the composition of source regions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMEP11C..07M
- Keywords:
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- 1115 Radioisotope geochronology;
- GEOCHRONOLOGYDE: 1140 Thermochronology;
- GEOCHRONOLOGYDE: 8169 Sedimentary basin processes;
- TECTONOPHYSICSDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS