University of Iowa, United States

The Bass River borehole (ODP Leg 174AX) recovered approximately 200 ft of upper Cenomanian to lower Turonian strata (nannofossil Zones CC10/CC11; Complexiopollis-Atlantopollis pollen Zone) from the New Jersey Coastal Plain. The Cenomanian/Turonian (C/T) boundary recognized at approximately 1937 ft is based on the contact of nannofossil zones CC10/CC11. Carbon isotopic records of both Gavelinella and Epistomina show a large (>1 per mil) increase across the C/T boundary, with maximum values at 1937.5 ft of 6 per mil in Epistomina and 4. 3 per mil in Gavelinella. The carbon isotopic offset between these taxa is constant and we conclude that they both faithfully track global carbon isotopic changes across the C/T boundary. The basal Turonian interval of very high carbon isotopic values at Bass River is associated with high organic carbon and correlates with peak global carbon isotopic values, peak global carbon isotopic extraction, and the Bonarelli bed. We recognize two major unconformity-bounded sequences in this interval: 1) a lower sequence that spans the C/T boundary that shallows upsection from middle neritic to inner neritic to delta front environments; and 2) an upper sequence that coarsens and shallows upsection from prodelta to delta front to fluvial environments. Within the lower sequence, there are at least 3 shallowing-upward parasequences that are reflected by changes in abundance and type of Epistomina species. Changes in speciation of Epistominas may also be related to changes in the oceanic chemistry because they correlate with changes in the global carbon isotopic record. The last occurrence of E. cretosa is at the base of the positive carbon excursion, and the last occurrences of E. stelligara, E. carpenteri, and E. partschiana appear to be associated with the termination of the carbon isotopic excursion.