4. CLAY MINERALOGY OF CENOZOIC SEDIMENTS OF THE ATLANTIC CITY BOREHOLE, NEW JERSEY1P. Vanderaveroet2 and J.F. Deconinck2, 3 |
ABSTRACTA great diversity of clay mineral assemblages are identified in sediments from the Atlantic City borehole. Detrital as well as authigenic clays are identified. The first group characterizes clayey intervals and includes chlorite, illite, randomly interstratified minerals, and kaolinite, whereas authigenic minerals, which are comprised of smectite, kaolinite, halloysite, and glauconite, occur mainly in Oligocene and middle Miocene sands and sandy sediments. Detrital clay minerals are similar to those deposited off New Jersey, and a similar trend in the composition of clay assemblages is observed from Eocene to Pleistocene. A major change in clay mineralogy occurs within the middle Eocene from sediments rich in illite/smectite mixed layers at the base to kaolinite-dominated sediments in the upper part. Dominant detrital clay minerals characterize the middle part of the Kirkwood Formation. The three sequences, Kw1b, Kw2, and Kw3, which are separated by unconformities, show distinct clay assemblages. From Kw2 to Kw3, increasing proportions of illite, also recorded in coeval sediments from offshore sites, reflect the intensification of erosion following a tectonic uplift in the Appalachians. Chlorite and illite/vermiculite mixed layers are typical of Pleistocene sediments. |
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