11. PALYNOLOGICAL DELINEATION AND REGIONAL CORRELATION OF LOWER THROUGH UPPER MIOCENE SEQUENCES IN THE CAPE MAY AND ATLANTIC CITY BOREHOLES, NEW JERSEY COASTAL PLAIN1

Laurent de Verteuil2

ABSTRACT

Dinocyst and strontium isotopic stratigraphies from two boreholes are integrated to develop a fine chronology for the lower through upper Miocene succession in New Jersey. These results represent the best constrained and most detailed subdivision of New Jersey Miocene strata to date, including the first confirmed record of upper Miocene deposits in the New Jersey Coastal Plain. The latter is based on dinocyst stratigraphy calibrated to the 1995 Neogene time scale of Berggren and co-authors (Zone DN8; ~11.0 to 8.5 m.y.), and appears to date the early development of a proto-Delaware River system.

More specifically, 16 third-order stratigraphic sequences are delineated in the New Jersey Miocene succession. There is excellent agreement between Sr-isotopic ages and independently derived dinocyst datums for the nine lower to lower middle Miocene sequences (Kw0 to Kw3a). The Kw0 sequence contains the oldest known Miocene sediments in the middle Atlantic coastal plain (~23.6 m.y.) and represents the basal Miocene transgression following the well-established and widespread latest Oligocene regression. Within the upper middle Miocene, Sr-isotopic ages are consistently younger than those inferred from dinocysts (by ~1.5 m.y.; Kw3b and Ch1 sequences); this calibration problem is due to unresolved complexities in global geochronology. The upper Miocene New Jersey chronology is based solely on dinocyst stratigraphy and comprises four sequences delineated at the Cape May Site only (Ch3 to Ch6).

Direct dinocyst correlations permit the first detailed comparison of this record with classic neritic sequences in Maryland and Virginia. There are clear one-to-one equivalents for most sequences but the upper Miocene correlations need refinement. The integration of the Salisbury Embayment and New Jersey records yields 19 third-order Miocene sequences of 0.2-1.0 m.y. duration. Most intrasequence hiatuses are 0.1-0.5 m.y. duration; the only notable exception is the ~1.5 m.y. Kw0/Kw1a hiatus (22.2-20.8 m.y.).

Second-order glacioeustatic trends inferred from delta18O records agree in timing and magnitude with lithostratigraphic relationships in the coastal plain: lower Miocene paleoenvironments deepen upsection to a maximum in the Kw2c/SE5 sequence (~14.5 m.y.); the major 13.0-14.5 delta18O increase is marked by successive regressive facies relationships, culminating with the onset of deposition of the Choptank and Cohansey formations (~13 m.y.). Comparison of the delta18O proxy of third-order glacioeustasy (e.g., Mi1-Mi7 events) with the Miocene sequences suffers from calibration and resolution problems that still confront both systems. The uneven correlation is nevertheless sufficiently good to suggest the primacy of glacioeustasy for determining the timing and architecture of Miocene sequences on the U.S. Atlantic Margin.

Two dinocyst datums, the lowest occurrence of Exochosphaeridium insigne and highest occurrence of Cordosphaeridium cantharellus, are used to divide the Sumatradinium soucouyantiae Interval Zone into three subzones (DN2a, DN2b, and DN2c).

1Miller, K.G., and Snyder, S.W. (Eds.), 1997. Proc. ODP, Sci. Results, 150X: College Station, TX (Ocean Drilling Program).
2Department of Geology, Earth Sciences Centre, University of Toronto, 22 Russell Street, Toronto, Ontario, M5S 3B1, Canada. (Present address: Geological Services Laboratory, Petroleum Company of Trinidad and Tobago Limited, Pointe--Pierre, Trinidad, West Indies.) devert@petrotrin.com