Some Aspects of the Mineralogy of the Northern Atlantic Coastal Plain

Johan J. Groot and Herbert D. Glass
Delaware Geological Survey, Newark, Delaware, and Illinois State Geological Survey, Urbana, Illinois

Abstract: Studies of the mineralogy of the northern part of the Atlantic Coastal Plain indicate that the heavy mineral content of the Cretaceous and Cenozoic sediments consists basically of two suites, a restricted mineral suite characterized by very stable minerals, and a full suite consisting of a great variety of igneous and metamorphic minerals. The restricted suite occurs in the nonmarine sediments and the full suite in the marine deposits.

The nonmarine Cretaceous deposits consist of kaolinite, with variable amounts of illite and its alteration products. Transition sediments like those of the Magothy formation contain kaolinite, illite, chloritic material and, occasionally, some montmorillonite. The marine sediments are characterized primarily by illite and montmorillonite. Thus, a limited heavy mineral suite and kaolinite are associated in nonmarine deposits, and a full suite and montmorillonite are found in marine sediments.

On the basis of available data the conclusion is reached that the different heavy mineral and clay mineral suites are a result of different source areas for the marine and non-marine sediments.

The suggestion is made that the formational concept cannot be employed with regard to the nonmarine sediments of the northern Coastal Plain but that, instead, a new concept be adopted based on depositional conditions within the framework of the control of the heavy and clay mineral assemblages.

Clays and Clay Minerals; 1958 v. 7; no. 1; p. 271-284; DOI: 10.1346/CCMN.1958.0070117
© 1958, The Clay Minerals Society
Clay Minerals Society (www.clays.org)