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X-WR-CALNAME:Geological Sciences Seminar:  Dr. François Tissot\, Caltech
X-WR-TIMEZONE:Pacific Time (US & Canada)
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DTSTAMP:20261007T062052Z
UID:tag:localist.com\,2008:EventInstance_39462999498835
DTSTART:20220517T191500Z
DTEND:20220517T201500Z
DESCRIPTION:The U paleoredox proxy: it’s not just for deep time anymore\n
 \nIn less than 15 years\, the 238U/25U ratio has seen its status completel
 y transformed: from a long-cherished constant value onto which U-Pb ages c
 ould reliably be anchored\, to a powerful tracer of seafloor anoxia in Ear
 th’s past. Indeed\, improvements in mass spectrometry have revealed vari
 ability in 238U/235U at the permil to sub-permil level\, which has opened 
 new avenues of research in cosmochemistry\, high-T geochemistry\, and pale
 oredox reconstruction. This latter has received unparalleled attention in 
 recent years (see figure)\, and the 238U/235U is now arguably the most wid
 ely used proxy for global ocean anoxia reconstructions in Earth’s past. 
 In this talk\, I will begin by discussing how the U system became such a p
 revalent tool\, and highlighting key milestones that established the stren
 gths and limitations of the system. I will then present some recent and on
 going work in my group that aims to tackle the question "how robust and qu
 antitative is the U paleoredox proxy?”. In particular\, we will look at 
 (i) how U isotope signatures are modified during carbonate diagenesis\, (i
 i) the potential for inverse modeling approaches to overcome the pitfalls 
 of illustrative forward modeling when estimating the extent of oceanic ano
 xia from the U data\, and (iii) the promise of biogenic carbonates as reco
 rders of subtle redox variations in the recent past (i.e.\, Quarternary). 
 \n\nDr. François Tissot is an isotope chemist and broad-based Earth scien
 tist. He trained as an engineer in Geology at the ENSG (France) and receiv
 ed his Ph.D. in Geochemistry and Cosmochemistry from the University of Chi
 cago in 2015. François was also the W.O. Crosby Postdoctoral Fellow at th
 e Massachusetts Institute of Technology from 2016 to 2017. He joined Calte
 ch in 2018 where he created the Isotoparium: a state-of-the-art facility f
 or high-precision isotope studies. His research focuses on both cosmochemi
 cal and geochemical problematics such as (i) the evolution of the Solar Sy
 stem through the isotopic characterization of meteorites and their inclusi
 ons\, (ii) the reconstruction of paleo-redox conditions in the ocean/atmos
 phere system\, and (iii) the potential of non-traditional stable isotopes 
 for studying magmatic processes. When science allows\, he enjoys climbing\
 , answering the many questions of his two young daughters\, photography\, 
 and Mel Brooks’ musicals. \n\n \n\nFor the Zoom information\, please con
 tact Rey Garduño (rgarduno@stanford.edu)
LOCATION:Braun Corner Building 320 room 220 and Zoom
SUMMARY:Geological Sciences Seminar:  Dr. François Tissot\, Caltech
URL;VALUE=URI:https://events.stanford.edu/event/geological_sciences_seminar
 _francois_tissot_caltech
CATEGORIES:Class/Seminar
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