K/Ar age dates and U, Th, K geochemistry of the (Catahoula) Gueydan formation of south Texas
Four K/Ar age dates on biotite separated from the Gueydan produced results ranging from Middle or Late Eocene to Early Oligocene. These ages are somewhat older than was previously hypothesized (Oligocene-Miocene). However, the author believes that there has been no significant reworking of biotitle and/or leaching of K from the biotite, either of which would increase the apparent age. These ages are thought to be correct, but, because of the complex stratigraphy, younger ages could also be possible. The Th, U, and K averages yielded results which are somewhat lower than they should be if the Gueydan is inferred to be an acidic volcanic rock originally. The lower averages are thought to be due to leaching and therefore the Gueydan was not originally deficient in these radioelements. The Th, U, and K distribution within the Gueydan approximates a log normal distribution, with minor fluctuations.
Duex, Timothy W. "K/Ar age dates and U, Th, K geochemistry of the (Catahoula) Gueydan formation of south Texas." (1970) Master’s Thesis, Rice University. https://hdl.handle.net/1911/89934.