Kope and Fairview Ripple Marks: Brown and Adams Counties, Ohio

The directional data of cross-laminae and ripple marks in the Kope and Fairview Formations in Brown and Adams Counties, Ohio, show no statistically significant difference in mean orientation. The prevailing paleocurrent direction was towards the northnorthwest. A significant difference, however, exists between the wave lengths of the ripples in the Kope and Fairview. Ripple marks are larger in the Kope Formation and gradually decrease in size upward into the overlying Fairview Formation. This may well have resulted from gradual local shallowing of the Cincinnatian sea as carbonate detritus accumulated. The ripple marks are interpreted to have been formed by currents and modified by waves. INTRODUCTION The sequence of siltstones, shales, and highly fossiliferous limestones that crops out in southwestern Ohio, southeastern Indiana, and northern Kentucky, and that includes the type section of the Upper Ordovician Cincinnatian Series, has been the subject of numerous investigations. Early reports dealt primarily with general geology and systematic paleontology. More recently a number of papers have been published on lithostratigraphy (Ford, 1967; Peck, 1966; Osborne, 1968). Rather few studies have been conducted on the primary sedimentary structures, especially those on the east side of the Cincinnati arch. Careful study and analysis of primary sedimentary structures, combined with stratigraphic data, should reveal paleoslope and direction of transport of sediments. Therefore systematic observations were made on ripple marks and cross-laminae, and the data were analyzed quantitatively. The directional sigfinance of these prima,ry sedimentary structures is displayed for each of several subdivisions of the Kope and Fairview Formations. The study was designed similarly to those of Hofmann (1966b) and of Osborne (1968); the results of this study are compared with theirs from areas just west of and on top of the Cincinnati arch. METHODS Field work was done in 1966 in the Ohio parts of the Higginsport, Russellville, Maysville West, and Maysville East 7.5-minute quadrangles (fig. 1). All exposures were carefully examined for primary sedimentary structures, among which Manuscript received February 18, 1970. THE OHIO JOURNAL OF SCIENCE 71(3): 129, May, 1971. 130 SYED A. ALI AND MALCOLM P. WEISS Vol. 71 cross-laminae and ripple marks dominate. Because outcrops are almost wholly confined to road cuts and creek beds, a geographically uniform sampling pattern could not be obtained. Ripple marks were distinguished as symmetrical or asymmetrical in the field, and ripple heights, wavelengths, and azimuths of the crests were measured. Ripple height is the vertical distance from a ripple crest to the bottom of an adjacent trough; wavelength is the horizontal distance between adjacent crests. The ratio of wavelength to ripple height, the "vertical-form index" of Bucher (1919), was calculated for each ripple measured. A total of 695 measurements O S J I B M j O SCALE IN MILES FIGURE 1. Index map. of ripple trend were obtained from 101 different exposures. Usually several measurements were made on a single rippled bed at each locality. Some of the rippled limestone beds are cross-laminated, and thereby yield additional directional information. For stratigraphic control of directional data, each formation was divided arbitrarily into lower, middle, and upper thirds (see Tables 1 through 5). Such division permitted testing of variability of structures within, as well as between formations. Oriented samples of ripple-marked limestone were collected at nearly every locality for detailed fabric analysis by transmitted infrared photography (Ali and Weiss, 1968b). No. 3 KOPE AND FAIRVIEW RIPPLE MARKS, OHIO 131 STRATIGRAPHY The lowest fully exposed unit in the area studied is a sequence of pelitic rocks with a subordinate amount of limestone: the Kope Formation (Weiss and Sweet, 1964; Weiss and others, 1965), formerly called Eden shales. Shales comprise 75 to 80 percent of the formation, are bluishto brownish-gray and thin-bedded, and alternate with thin slabby limestones. The shales generally appear massive when dry, and fissile when wet. Lateral changes in thickness of individual beds TABLE 1 Statistical Summary of Observations on Ripple Marks Wavelengths (in CM) Number of Observations Mean Wave Length Maximum X Minimum X Standard Deviation Coefficient of Variation Number of Observations Mean Ripple Index Maximum Ripple Index Minimum Ripple Index Standard Deviation Coefficient of Variation Total Fairview