Petrography of the Upper Cambrian dolomites of Warren County, New Jersey

Abstract

Petrographic investigation of the Upper Cambrian dolomites along the Delaware River in Warren County, New Jersey, has led to the distinction of six different microfacies each representing a specific sedimentary environment. In order of decreasing relative depth these microfacies are: dololutite, dolarenite, oolitic dolarenite, dolorudite, cryptozoan dolomite and desiccation dolorudite. Over 1,200 samples spaced at an average interval of 1.8 feet were collected from two measured sections, one at Riegelsville, N. J., and another at Carpentersville, N. J. Thin sections, cut perpendicular to the bedding were made and analyzed according to the method used by Albert V. Carozzi which consists of the statistical measurement of the sizes and frequencies of detrital, authigenic and organic components of a sedimentary rock. In this investigation, three general types of parameters were investigated: detrital components, degree of crystallinity and chemical composition. The detrital components present in sufficient abundance for study are quartz, pyrite, oolites and reworked lithic fragments. The maximum size of the largest optically continuous dolomite crystals for each thin section was measured to obtain the degree of crystallinity. Chemical composition was investigated by means of an X-ray diffractometer. The results of the statistical measurements are interpreted by means of a bathymetrical curve showing the variations of relative depth as a function of thickness. The oscillations in the bathymetrical curve exhibit superposed asymmetrical cycles of sedimentation. The ideal cycle begins with structureless dololutite (deepest water facies) and grades upward through progressively shallower facies and terminates with desiccation dolorudite. Immediately overlying this dolorudite is a dololutite which begins the superjacent cycle. The bathymetrical curve also displays a rhythmic occurrence of series of cycles or megacycles. Within each megacycle, each superposed cycle terminates in a progressively shallower microfacies. The two investigated sections do not overlap stratigraphically and therefore correlation could not be attempted. Although correlation on the basis of individual cycles is probably limited to short distances, the megacycles and the major groups of cycles could provide a valuable means of correlation in this general area.