GULF SERIES

major division of Upper Cretaceous rocks (66.4 to 97.5 million years old) in the Gulf coastal region of the United States. The Gulf Series has been divided into several groups of rocks. The lowermost groups of limestone and clay are overlain by the Eagleford Shale, about 145 m (475 feet) of clayey shales, which in turn is overlain by the Austin Chalk, about 130 m (420 feet) of chalks and marls. The Taylor Marl overlies the Austin Chalk and consists of about 370 m (1,200 feet) of marls, limestones, sandstone, and chalk. The Navarro Group, the uppermost division of the Gulf Series, consists of about 200 m (650 feet) of limestones, marls, shales, and clays. Extensive reefs constructed by corals and other animals existed during the time that rocks of the Gulf Series accumulated.