Friday Night Lecture April 10

  • Cramer Hall 1721 SW Broadway Portland, OR, 97201 United States

High Altitude Dentistry: Using Fossil Teeth to Understand How and When the Andes Formed

Dr. John Bershaw PSU Geology Dept.

The Altiplano and Andes Cordillera of South America are one of the most significant topographic features on Earth. Though basic models exist to explain how they formed, the details are not well understood.

Recent paleoelevation constraints from fossil leaves and stable isotopes of sedimentary carbonates suggest that significant surface uplift may have occurred over a relatively short period of time, shedding light on the geodynamic mechanisms responsible for the topography seen today.

Dr. Bershaw has examined teeth from modern and extinct mammals spanning the late Oligocene (~29 Ma) to present which preserve a record of surface water isotopes that animals ingested while their teeth were mineralizing. A predictable relationship between tooth isotopes and elevation exists across the Andes. Tooth data show substantially more positive isotopic compositions (δ18O) for the late Oligocene compared to mid-late Miocene teeth.

This suggests that the Andean plateau was at a very low elevation during the late Oligocene and had risen to present-day elevation by the late Miocene. In addition, these data suggest modern climate variations across the Andean plateau have persisted since the late Miocene. Ongoing research indicates that modern climate has complex effects on environmental isotopes across the Altiplano.

Dr. John Bershaw is a Professor in the Department of Geology at Portland State University. Prior to coming to PSU, he was an Exploration Geologist for Chevron and received his PhD in Geology from the University of Rochester.

Dr. Bershaw’s research interests include Stable and Radiogenic Isotope Geochemistry, Sed/Strat, Atmospheric Science, Tectonics, and Basin Analysis. He has been involved in projects focused on the uplift history of the Altiplano, Pamir, and Tibetan Plateau through a combination of sed/strat and geochemistry. John is researching stable isotope geochemistry of water throughout Tibet and Central Asia to better understand modern atmospheric circulation and how climate was affected by the rise of Tibet. He is also exploring the basin history of the Willamette Valley and topographic history of the greater Pacific Northwest through stable isotopes of volcanic glass and modern water.