The Gatesburg Formation of Late Cambrian age in central Pennsylvania consists of cyclic deposits ranging from nearly pure dolomite to nearly pure quartzite containing less than 5 percent clay and 2 percent other minerals. Principal-components and multiple-regression analyses of the petrographic variables of size, shape, sorting, and packing indicate that the degree of packing (quartz-grain to quartz-grain contacts) is the primary property influencing intergranular porosity. The degree of packing accounts for 36 percent of the total variation in porosity explained by linear multiple-regression analysis. Principal-components analysis shows these two variables to be significantly related to each other or associated with common causes. This carbonate-quartz system is interpre ed as a beach-lagoon-dune sedimentary system. Development of intergranular porosity, ranging from 2 to 20 percent, is related causally to a quartz-grain supported framework that isolates and preserves pores where the quartz-carbonate ratio is equal to or greater than 1:1. Of the variables tested, statistically significant correlations were found between (1) packing and amount of quartz, (2) packing and porosity, and (3) amount of quartz and porosity. Almost 50 percent of the total variation in porosity is explained by packing and the amount of quartz; however, the partial correlation coefficient (r_13.2) between porosity and amount of quartz, with the influence of packing removed, is not significant (r_13.2 = 0.173 at the 5 percent significance level). An unexpected c nclusion is that intergranular porosity is not related to grain size in this system.

Permeability values determined for the dolomitic sandstone, dolomitic quartzite, and orthoquartzite are several orders of magnitude higher than those for the sandy dolomite, and range from less than 0.01 to 1,361 md in the carbonate-quartz system.

Results and conclusions of this investigation should be applicable to other carbonate-quartz systems of similar cyclic character.