Magnetostratigraphy of lower Eocene to lower Miocene sediments in cores from the New Jersey Coastal Plain

Abstract

This paper describes the magnetostratigraphy of lower and middle Eocene, lower and upper Oligocene, and lower Miocene terrigenous sediments recovered in three on shore borecores on the New Jersey coastal plain (Island Beach, Atlantic City, Cape May Sites; Ocean Drilling Program Leg 150X). Near-shore, terrigenous sediments are quite often very weakly magnetized. Thus, to improve the practical measuring sensitivity of the magnetometer, I have taken high-volume (120 cm 3 ), whole-round samples from these cores. Most samples were alternating-field (AF) demagnetized to 50 mT in a large-diameter solenoid, and pilot samples from Island Beach were thermally demagnetized. At two of the three Leg 150X sites (Island Beach and Atlantic City), magnetic field polarity reversals are found in Oligocene and Eocene passive margin sequences bounded by disconformities (sequence boundaries). There are also two short, lower Miocene sections at the Cape May Site that have a series of polarity reversals. In limited stratigraphic sections, where biostratigraphic (planktonic foraminifers, calcareous nannofossils) and Sr-isotope data are available, correlations are made to the geomagnetic polarity time scale. These data help to date sediments at discrete stratigraphic levels in the cores and to estimate the duration of hiatuses at sequence boundaries.