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Geology Club Seminar

Thursday, January 17, 2019
4:00pm to 5:00pm
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Arms 151 (Buwalda Room)
Lithium isotopes: Controls on modern riverine and brachiopod compositions and insights into Cenozoic seawater composition
Kirstin Washington, University of Southern California,

During this talk we will explore two aspects of stable lithium isotope systematics (δ7Li (‰)): (1) controls on riverine δ7Li fluxes through two modern weathering case studies and (2) the utility of brachiopods as archives of modern and paleo- seawater δ7Li compositions, with a comparison between a new, brachiopod-derived Cenozoic seawater δ7Li record with the foram-derived record (Misra and Frolich, 2012, Science).

Seawater δ7Li composition is a promising proxy for changes in past continental silicate weathering. Modern weathering studies suggest that the wide range of riverine δ7Li compositions (2–40‰) is likely controlled by weathering regime (Penniston-Dorland et al., 2017, Rev. Mineral Geochem).  While there have been numerous studies of modern rivers, few have investigated the impacts of continental hydrothermal activity on riverine δ7Li compositions. The first case study investigates this problem in the active volcanic field (AVF) of Mount Aso, Japan and addresses potential sources of scatter in the global relationship between temperature and basalt weathering rates for AVFs (Hartmann et al., 2016, EPSL).  The second case study examines whether hydrothermal activity overprints low-temperature weathering signals imparted on small rivers of southeastern Taiwan. The last portion of the talk is on potential biological controls on recent brachiopod δ7Li compositions and the effect of diagenesis on fossil Cenozoic brachiopod δ7Li compositions. Finally we will examine whether changes in Cenozoic seawater δ7Li compositions inferred from forams are robust.