First Name:
Jessica
Last Name:
Norman
Major Department:
Geology
Thesis Director:
Cynthia Liutkus
Date of Thesis:
May 2010
Frazier Mountain is an important paleoseismic site on the Big Bend of the San Andreas Fault ~80 km north of Los Angeles, CA. This site preserves the fault traces of paleoearthquake events and has the added benefit of charcoal (for radiocarbon dating) and carbonate nodules throughout the stratigraphy. It is a widely accepted technique to describe climate variations using the δ18O and δ13C variations recorded in carbonate nodules with a known origin. Since the Frazier Mountain site has both radiocarbon potential as well as climate data (recorded in nodules), it can serve as a location to test whether paleoearthquake events along the San Andreas Fault can be correlated using climate data and thereby be a correlation tool when sites do not contain charcoal for 14C analysis. The nodules at the Frazier Mountain site are phreatic (formed in equilibrium with local roundwater). These nodules have indurated, well-cemented centers with more fenestral rims and zoned dogtooth calcite crystals growing inwards into voids suggesting multiple precipitation events by calcite-rich groundwater. Individual nodules show variations in δ18O and δ13C values that indicate climate shifts on the order of 10's of years (e.g., the formation time of one nodule). Nodules in the upper half of the trench show coherent isotopic patterns and potentially record ENSO events or seasonality. When the δ18O and δ13C values of the individual nodules are plotted with depth (as a proxy for time) there is a shift to a cooler, drier climate until shortly after 1359 cal YBP (noted by an increase in the average δ18O value). The isotope values then indicate a shift towards a wetter, warmer climate (lower δ18O values). Limited radiocarbon ages from the Frazier stratigraphy prevent an accurate date on this climate shift. However, compiled southern California climate data shows a trend towards wetter and warmer conditions around 800 cal YBP, the occurrence of the Medieval Warm Period (MWP) between 900 cal YBP to 600 cal YBP (~1100 AD to ~1375 AD), and a 200 year drought 2 prior to the onset of the MWP. With more analysis and firmer radiocarbon age dating of the sediments, it may be determined that this is consistent with the trends recorded by the carbonate nodules at the Frazier Mountain site. Therefore, climate variations within individual nodules represent short-term climate change (on the order of years to 10s of years) and the overall change in the average isotopic values with depth (as a proxy for time) indicates long-term climate shifts (on the order of 100s of years). The conclusions of this thesis indicate that climate shifts indicated in the Frazier Mountain nodules can be used to correlate paleoearthquake events but more data (from nodules and radiocarbon) are needed.