Upper Cretaceous (upper Santonian)Boehmocerasfauna from the Gulf Coast region of the United States

Abstract

AbstractAn upper Santonian fauna dominated by the curved baculitidBoehmocerasRiedel, 1931, occurs as phosphatic moulds in the Tombigbee Sand Member of the Eutaw Formation in Mississippi and Alabama, and also is reworked into the base of the Mooreville Chalk; a similar assemblage is present in the middle part of the Pen Formation of the Big Bend area, Texas. The assemblage is:Pseudoschloenbachia(Pseudoschloenbachia)mexicana(Renz, 1936),Placenticeras syrtale(Morton, 1834),Reginaites leei(Reeside, 1927a),Reginaites exilissp. nov.,Texanites(Texanites) sp. juv. cf.gallicusCollignon, 1948,Texanites(Plesiotexanites)shiloensisYoung, 1963, Texanitinaeincertae sedis, Hyphantoceras(?)amapondense(van Hoepen, 1921).Glyptoxocerasspp.,Boehmoceras arculus(Morton, 1834) andScaphites(Scaphites)leeiReeside, 1927a, form I. The assemblage is referred to the uppermost SantonianTexanites(Plesiotexanites)shiloensiszone of the Gulf Coast sequence. Common occurrence ofScaphites(S.)leeiI andReginaites leeisuggest correlation with the Upper SantonianDesmoscaphites erdmannizone of the U.S. Western Interior; common occurrence ofBoehmoceras arculus(= B.loescheriof European authors) suggests correlation with theMarsupites–granulatazone at the top of the North German Santonian. These data strengthen intercontinental correlation of the Santonian–Campanian boundary sequence. They also provide a biostratigraphic link to a numerical age of 84.2±0.9 Ma from a bentonite at a slightly lower level in the Tombigbee Sand Member of the Eutaw Formation in Mississippi.