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This grant allowed us to make some important steps forward in understanding the behavior of the K-Ca geochronometer in sedimentary systems and its potential for sedimentary chronology. We documented that the 40Ca/42Ca ratios (and other stable Ca isotopic ratios) can be accurately and precisely measured with a multicollector ICP-MS instrument and that the technique can potentially lead to faster and cheaper measurements of samples for Ca isotopes. 

K-Ca ages of Cambrian glauconites from the Llano uplift, central Texas, were determined in order to re-evaluate the ability of the K-Ca system to constrain the timing of deposition of sedimentary packages. All of the K-Ca ages were found to be younger than their stratigraphic ages.  In addition to being too young, the K-Ca ages are also highly variable, ranging in age from Silurian to Permian.  The oldest subset of glauconite ages are in agreement with previously published Rb-Sr ages from the same outcrop and provide further evidence for there having been a postdepositional thermal or recrystallization event that reset both the Rb-Sr and K-Ca systems.  The range of younger glauconite K-Ca ages are not seen in the Rb-Sr data, but are similar to the distribution of available apatite fission track ages for the Llano basement. K-Ca ages are interpreted as thermochronologic data reflecting partial retention of Ca in thermally fluctuating basin conditions.  Estimates of the closure temperature of Ca in glauconite are found to be 75 - 90 °C for cooling rates of 0.3 - 1 °C/My. These results indicate that the K-Ca system could be used as a low temperature thermochronometer with closure temperatures <100 ⁰C, and has potentially significant applications in unraveling the thermal evolution of petroleum-bearing basins.

The project represented the bulk of the PhD thesis of Ms. Mary Robinson Cecil (PhD 2010), presently a postdoc at Caltech. In addition, two undergraduate students, Ms. Emily Mortazavi (BS, 2009 and currently a PhD student at USC) and Joshua Golden (BS, 2009, currently employed by Phelps Dodge), were trained in the lab and involved in the research process.

Results of this research were presented to the oil industry community in talks given to geoscientists from Chevron ETC (San Ramon, 2008) and ExxonMobil (Houston, 2009), as well as to the academic community via a presentation at AGU (San Francisco, 2009) and two manuscripts submitted to scholarly journals, currently in press (as of August 2010).