Abstract

We use Sr-isotope stratigraphy to correlate the Miocene Kirkwood Formation of the New Jersey Coastal Plain to the Geomagnetic Polarity Time Scale (GPTS) and to ascertain the age of Miocene depositional sequences. Sr-isotope stratigraphy confirms diatom biostratigraphy, which delineates three Kirkwood sequences corresponding to East Coast Diatom Zone (ECDZ) 1, ECDZ 2, and ECDZ 6 of Andrews (1988). Sr-isotope age estimates of the lowermost sequence (= ECDZ 1) range from 19.2 to 22.6 Ma ± 0.5 m.y. The middle sequence (= ECDZ 2) ranges from 15.5 to 17.4 Ma ± 0.5 m.y.; a disconformity within ECDZ 2 at the Belleplain State Forest borehole and the Wildwood 198A well separates it into two sequences, with a possible hiatus from 17 to 16 Ma. Sr-isotope age estimates of the upper Kirkwood sequence (= ECDZ 6) are not as certain and range from 11.5 to 13.6 Ma ± 0.8 Ma. A shorter age range of 12.2-13.6 Ma for this sequence is supported by its assignment to the D. stauracanthus silicoflagellate Subzone. Sedimentation rates were as high as 40 m per million years during deposition of the Kirkwood Formation, suggesting possible tectonic influences on depositional history. The timing of lower to middle Miocene sequence boundaries from the New Jersey Coastal Plain compares well with other indicators of sea-level change, including oxygen isotopes (Miller and others, 1991b), the global sea-level record of Haq and others (1987), and the offshore New Jersey sequence boundaries of Greenlee and others (1992). Thus, both tectonic and eustatic changes influenced Miocene depositional history of the New Jersey Coastal Plain.

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