Abstract:
The Bass River and Ancora boreholes (ODP Leg 174AX, New Jersey Coastal Plain) recovered thick, continuous Cenomanian to Santonian strata. The Cheesequake Formation comprises a marine Santonian sequence that overlies two poorly-dated nonmarine-marginal marine Magothy Formation sequences. At Ancora, both Magothy sequences are assigned to pollen Zone V (Santonian-upper Turonian); in contrast, the lower sequence at Bass River is assigned to Zone IV (early Turonian). The Bass River Formation at both boreholes records continuous deposition across the Cenomanian/Turonian (C/T) boundary and a record of a dramatic global carbon burial (Bonarelli/Ocean Anoxic Event 2) event. Carbon isotopic values increase by >2 per mille immediately below C/T boundary. Elevated carbon isotopic values and sedimentary organic carbon values continue into the lower Turonian, culminating in a sharp carbon isotopic decrease. This global carbon extraction event lasted approximately 400-500 k.y. and occurs within a 1-2 m.y. long uppermost Cenomanian-lowermost Turonian sequence in New Jersey that indicates little relationship with sea-level change on the m.y. scale. Within the sequence spanning the carbon event, there are at least 4 shallowing-upward parasequences (durations approximately 350-460 k.y.) indicated by changes in abundance and type of Epistomina species, oxygen isotopic variations, and minor lithologic variations. The Bass River borehole only penetrated uppermost Cenomanian strata, while the Ancora borehole recovered at least 3 Cenomanian sequences: 1) the uppermost sequence described above (Zone CC10b-CC11 equivalent); 2) a middle-upper Cenomanian sequence spanning Zone CC10a-10b; and 3) a lower to middle Cenomanian sequence spanning Zones CC9-CC10. Several possible sequences within the uppermost Potomac Group can only be dated as ?lower Cenomanian.