The Basal Contact Of The Hornerstown Formation In New Jersey

Abstract

In New Jersey the Hornerstown greensand overlies the Tinton, Red lank, Navesink, and Mount Laurel formations, and the contact is an unconformity which represents a greater amount of missing time in southwestern New Jersey than it does in the northeastern section of the Coastal Plain. Although the Hornerstown is lithologically persistent along strike, the underlying sediments change considerably. Paradoxically the underlying sediments in the southwest are lith­ologically similar to the Hornerstown while those in the northeast differ. Abundance of glauconite, fine grain size, and the dominance of illitic and montmorillonitic type clays indicate that the Navesink and lower Red Bank, which underlie the Hornerstown in the southwest, were deposited in a middle to outer shelf environment, as was the Hornerstown. Coarser grain size, the abundance of detrital quartz, and the dominance of kaolinitic clays indicate that the Tinton and upper Red Bank, which underlie the Hornerstown north of 40° 5' latitude, are part of a elastic wedge which thickens northward. The authigenic minerals within the Tinton and Red Bank, in addition to reported spheroidal weathering of the top of the Tinton, indicate that these formations were subaerially exposed prior to the deposition of the Hornerstown. It is concluded that after the deposition of the Navesink, and prior to the deposition of the Hornerstown, southwestern New Jersey experienced neither sedimentation nor erosion. During this time the Red Bank and Tinton were being deposited in the northeastern section of the New Jersey Coastal Plain, but prior to the deposition of the Hornerstown they were subaerially exposed. The Hornerstown environment then inundated the previously exposed Red Bank and Tinton formations.