Abstract

Factors controlling the concentration of titanium-iron oxides in the sands of the Cohansey Formation of New Jersey include source rock, climate, and depositional environment. The microtextures of the titanium-iron oxides in the Cohansey sands match those in Precambrian gneisses that crop out in the New Jersey highlands and eastern Pennsylvania. Palynological evidence indicates a warm subtropical climate during titanium-rich sand deposition. Such a subtropical environment favors deep saprolitic weathering of the source rock.The highest heavy mineral values (5-25 wt %) found in the Cohansey Formation correlate with the highest degrees of sorting (standard deviation 0.5-0.8), with positive to slightly negative skewness (0.8--0.4), and with a laminated and burrowed sand facies found in the lower portion of the formation. Peat interbedded with titanium-rich sand contains subtropical palynomorph suites and dinoflagellates. The peat is interpreted as a lagoonal deposit that was flooded with marine water. The titanium-iron oxide-rich sands are interpreted as a backshore beach and dune facies that was preceded by sublittoral Kirkwood Formation sand deposition.Present climatic and physiographic conditions of Georgia and South Carolina, where thick titanium-rich saprolites, fluvial placers, and beach placers occur, are analogous to the conditions that prevailed in the New Jersey area during the deposition of the Cohansey titanium-iron oxide-rich sands. This warm Cohansey event represents the last major Neogene warming trend and on the basis of climatic periodicity modeling coincides with the Miocene-Pliocene boundary.

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