Ammonites at the Cenomanian–Turonian boundary in the Sergipe Basin, Brazil

Abstract

Two distinctive ammonite faunas are described from the Cenomanian–Turonian boundary interval in the Sergipe Basin, Brazil. The Jardim 1 section assemblage comprises Euomphaloceras costatum Cobban, Hook & Kennedy, 1989, Burroceras transitorium Cobban, Hook & Kennedy, 1989, Pseudaspidoceras pseudonodosoides Choffat, 1898, and Vascoceras cf. gamai Choffat, 1898. This same association is found in New Mexico, where it occurs with the upper Cenomanian index fossil Neocardioceras juddii (Barrois & Guerne, 1898). On this basis the Sergipe assemblage is referred to the N. juddii Zone, and correlated with beds 79–84 of the Pueblo, Colorado section. These lie 1.14–0.63 m below the Global boundary Stratotype Section and Point (GSSP) for the base of the Turonian Stage, the base of bed 86, which corresponds to the first occurrence of the ammonite Watinoceras devonense Wright & Kennedy, 1981. The Japaratuba 16 locality in Sergipe yielded an assemblage of Pachydesmoceras kossmati Matsumoto, 1987, Watinoceras coloradoense (Henderson, 1908), Pseudaspidoceras flexuosum Powell, 1963, Pseudovascoceras nigeriense (Woods, 1911), Vascoceras globosum globosum (Reyment, 1954), V. simplex (Barber, 1957), and Pseudotissotia nigeriensis (Woods, 1911). The co-occurrence of W. coloradoense and P. flexuosum is also found in the Pueblo section, in bed 97, 1.65 m above the base of the Turonian. These ammonite records thus allow the placement of the Cenomanian–Turonian boundary in the Sergipe-Alagoas Basin, and correlation with the Global Boundary Stratotype Section and Point at Pueblo.