A HOLOCENE RECORD OF TERRIGENOUS SEDIMENT PROVENANCE AND ANOXIA FOR THE GUAYMAS BASIN IN THE GULF OF CALIFORNIA

Paleoceanographic study of the Gulf of California has been a centerpiece of John Barron’s research for the last three decades. Ranging from developing diatom biostratigraphies of the Oligocene to synthesizing Holocene paleoclimate records of the North American Monsoon, John Barron’s interest in the climactic evolution of the Gulf of California has greatly increased our understanding of this key region. Building upon this extensive body of research, our team is developing a new multi-proxy Holocene marine sediment record from the western Guaymas Basin (MD02-2517; 27°29.10’N, 112°04.46’W, 887 m water depth) using a combination of diatom and silicoflagellate micropaleontology, diatom-bound trace metal geochemistry, organic biomarkers, and stable isotope geochemistry. In this presentation, we focus on new bulk sedimentary ICP-MS rare earth element (REE) and trace metal concentrations placed on a preliminary foraminiferal ¹⁴C-based chronology to (1) examine detrital sediment provenance and (2) develop a record of marine anoxia intensity. Distributions of key lithophile element concentrations and REE spidergram patterns in MD02-2517 are very similar to adjacent terrestrial volcanic sources, particularly the Quaternary Volcan Las Tres Virgenes andesite suite and the Miocene calcalkaline andesites of the Sierra San Francisco (Sawlan, 1991), suggesting downcore variability in these elements can be used as a proxy of local terrestrial erosion intensity in MD02-2517. Additionally, enrichments in the trace elements uranium (U), molybdenum (Mo), and other redox-sensitive elements far above global mean upper continental crust values argue for substantial authigenic precipitation under anoxic conditions, either in the shallow sediment column or bottom waters of the Guaymas Basin. An increase in the lithophile and REE concentrations occurs between ~4400 to 3700 cal yrs BP, while an abrupt increase in authigenesis is observed around ~4000 cal yrs BP. The timing of these two events suggests a land-ocean connection preserved in MD02-2517, possibly related to changes in terrestrial erosion patterns (wind/precipitation/fluvial run-off) which could lead to enhanced stratification and reduced ventilation of the local Gulf of California.