K♯°/AR♯° age dating on glauconites and paleontologic interpretation near the Cretaceous-Tertiary transition in Texas.
Gammill, Laura M.
Adams, John A. S.
Master of Arts
Several exposures of the Cretaceous-Tertiary contact in Texas were searched for material suitable for radiometric age dating. Glauconites from Littig Pit, Travis County, Texas were sufficient in quality and quantity. K4/Ar4 dating on glauconites from Littig Pit indicates that 4 to 6 Ma of lowermost Tertiary section are missing. At least one nannofossil zone and at least two foraminiferal zones missing from the lowermost Tertiary limit the unconformity to 2.5 to 5 Ma. The concordant radiometric and paleontologic dates refute the view of Odin that all low potassium glauconites are suspect. The uppermost Cretaceous represents an undetermined amount of time. It is possible that the Midway Group was deposited rapidly during the last major Paleocene transgression of Vail et al (1977). The data supports the conclusion of Berggren and Aubert (1975) that the Midway fauna are correlatable worldwide. The iridium layer of Alvarez et al (1982) is missing at the Littig Pit, confirming missing section and illustrating how this iridium layer may be used as a worldwide time marker.