Abstract:
The Bass River borehole (ODP Leg 174AX) recovered approximately 200 ft (61 m) of upper Cenomanian to lower Turonian strata from the New Jersey Coastal Plain, USA, including the expression of a global carbon burial event. The Cenomanian/Turonian (C/T) boundary is recognized at Bass River at approximately 1935.5 ft (589.9 m) based on the contact of nannofossil Microstaurus chiastius and Eiffellithus eximius Subzones of the Parhabdolithus asper Zone. Carbon isotopic records of both Gavelinella and Epistomina show a large (>2 per mil) increase immediately below the C/T boundary, with maximum values of 6 per mil in Epistomina and 4.3 per mil in Gavelinella. The delta (super 13) C offset between these taxa is constant and we conclude that Epistomina, like Gavelinella, faithfully records seawater delta (super 13) C changes. Above the sharp delta (super 13) C increase, elevated delta (super 13) C and sedimentary organic carbon (>0.9 per mil) values continue into the lower Turonian, culminating in a sharp delta (super 13) C decrease. High delta (super 13) C values in the uppermost Cenomanian-lower Turonian at Bass River correlate with a global carbon burial event recorded in Europe and the U.S. Western Interior; we estimate the duration of this event at Bass River as 400-500 k.y. Although the carbon burial event occurred during a long-term eustatic rise (10 m.y. scale), it occurs within a 1-2 m.y. long sequence at Bass River that indicates no relationship with sea-level lowering on the m.y. scale. The carbon burial event does not appear to be associated with maximum flooding either, indicating little correlation with sea-level rise on a 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, delta (super 18) O variations, and minor lithologic variations. The highest occurrences of 6 Epistomina species and the origination of Epistomina sliteri Olsson n.sp. are associated with the parasequences and possibly with higher delta (super 18) O values. There is no clear association of parasequence boundaries inferred at Bass River with the carbon burial event; thus, there does not appear to be a relationship of the event with sea-level change on the 100 k.y. scale. We conclude that while the organic carbon burial event was associated with a general long-term (10 m.y. scale) eustatic rise, the initiation and termination of the peak organic burial event itself were unrelated to sea-level change.