Periodic Reporting for period 1 - CARBCHRON (Carbonate boundstone as a geochronometer)
Reporting period: 2021-09-01 to 2023-08-31
Investigations of global biological and geochemical changes through time use Earth’s sedimentary rock archive as our best record of Earth’s past surface environments. The ages of the rocks that record these shifts clarify the causes and consequences of changes in Earth’s biosphere and habitats. These archives of Earth's ancient environments and climate provide crucial ground-truth data we can use to better predict environmental and climatic change in the future. Recent analytical developments are reinvigorating the study of carbonate as a geochronometer and a growing scientific community is working to directly date carbonate rocks—repositories of some of our richest geochemical and paleobiological archives. The ability to directly date carbonate rocks will unlock previously inaccessible archives of Earth history. The goal of this project is to test, validate, and examine the utility of a particular type of carbonate--boundstones--as a dating technique.
During the reporting period, Cantine characterized 300+ individual samples over 30+ analytical sessions using U-Pb as well as trace and rare elemental analysis, Sr isotope analysis, and B isotope analysis. In addition to boundstone samples, Cantine characterized sedimentary carbonate samples. The work performed in this project contributed to 16 presentations delivered at 16 institutions and conferences in the last 2 years.
Scientific results: We found that carbonate boundstones were datable, but that other sedimentary phases (marine and diagenetic cements) were far more reliable. We moved forward testing these phases in multiple stratigraphic successions worldwide, and constructed a database of published results comparing the depositional and measured U-Pb ages of carbonates globally. In multiple locations, we found that U-Pb ages of carbonates were consistent with depositional or early post-depositional processes, and identified previously under-discussed modes of failure for this geochronometer (scatter leading to erroneously too-old ages). We found that, on average, the measured U-Pb ages of sedimentary and diagenetic carbonate phases falls within <20 million years of its depositional age.Social impacts: In June 2022, Cantine taught an intensive seminar-style class to high school students in Mississippi, United States through the program Freedom Summer Collegiate. Mississippi has among the lowest-performing schools in the nation and students consistently face obstacles on the road to higher education. Freedom Summer Collegiate intervenes to provide talented high school students the opportunity to practice the critical thinking and learning skills they will need to succeed in a university setting. Cantine planned, programmed, and taught a 4-week long class that met daily for 70 minutes, and supported another teacher as a teaching assistant in a second class. The topic of Cantine’s class was physics and gravity, which allowed students to participate in classic active laboratory experiments including measuring the speeds of falling objects and designing a vehicle capable of protecting an egg from a 3-meter fall. Cantine drew on her prior three years of experience teaching with Freedom Summer Collegiate to deliver hands-on lessons that challenged students while providing them ample support. Seven students attended regularly and participated in class.