FACIES ANALYSES AND HYDROCLIMATE SIGNALS FROM SPRING-ASSOCIATED CARBONATES IN THE SANTA CRUZ, CA REGION

Spring-associated carbonates that form under ambient temperatures in freshwater systems—often referred to as tufa—are valuable Quaternary paleoenvironmental archives as the formation of tufa has been shown to record periods of greater groundwater recharge. In this study, we analyzed two previously undescribed ancient tufa deposits in Santa Cruz, CA to understand regional hydroclimate conditions during tufa formation. One spring-associated carbonate deposit, located in Pogonip Park, is exposed along the Spring Trail and is approximately 15 meters across with a laterally varying thickness of 3-4 meters. The second deposit in Henry Cowell State Park, approximately 7 km away from Pogonip, is a perched spring-line carbonate deposit that is approximately 4 meters thick and spans the length of ~7.5 meters. The presence of the calcite microstructure of Oocardium stratum, a freshwater algae that is endemic to tufa environments at both sites, implies the mounds formed under high stream velocities and are of meteoric origin. These spring-associated carbonate features are currently dry and away from modern spring flow, indicating their formation was a result of accelerated groundwater recharge. Preliminary infrared-stimulated luminescence (IRSL) dating results of the carbonates at the Pogonip site indicate the spring was active at least 10 ka, corroborating other regional proxies that imply a pluvial event may have occurred from 12 ka to 4.5 ka. Analyses are underway to identify other carbonate growth episodes to compare to existing local and regional records.