Potassium-40/Argon-40 Age Determinations on Low-Potassium Glauconites Near Missing Cretaceous-Tertiary Transition at Littig Pit, Travis County, Texas: ABSTRACT

Abstract

Potassium-40/Argon-40 dating on glauconites from Littig Pit, Travis Co., Texas, indicates that 4 to 6 Ma of lowermost Tertiary section are missing. The glauconite-containing samples were examined biostratigraphically. At least 1 calcareous nannofossil zone and at least 2 planktonic foraminiferal zones missing from the lowermost Tertiary limit the missing section to 2.5 to 5 Ma. These paleontologic data are fully consistent with the radiometric dates obtained on low potassium glauconites and refute the view of Odin that all low potassium glauconites are suspect. A missing nannofossil zone in the uppermost Cretaceous represents an undetermined amount of time. A strong probability exists that the Midway Group at Littig Pit and elsewhere was deposited rapidly during one of the earliest Paleocene transgressions described by Vail and others, and our data support the conclusion of Berggren and Aubert that the Midway fauna are correlatable worldwide. The iridium layer of Alvarez and others is missing at the Littig End_Page 478------------------------------ Pit, confirming missing section and illustrating how this iridium layer is proving useful as a worldwide time marker. End_of_Article - Last_Page 479------------