Grain-size analyses of Ordovician sandstones from the Midwestern states

Certain Ordovician sandstones of the Midwestern States were investigated for the purpose of determining the range in size of constituent sand grains. Although many size analyses of the same formations have been reported in the literature, the methods of sample collection, preparation, and sieving were not uniform, and the results of the different studies therefore are not comparable. This investigation is intended to supply a uniform data base that will be useful for a variety of practical and scientific purposes. A total of 276 samples was collected from the St. Peter Sandstone and Everton, Oil Creek, McLish, and Tulip Creek Formations at the 29 locations shown on figure 1. At each location 4-14 samples were taken at about equal intervals from the base to the top of the sandstone exposure. Each sample of about 500 gm was obtained from a strati-graphic interval of no more than 10 cm. Each sample was air dried, and lumps were broken with a rubber pestle (some samples were case-hardened but none was firmly cemented). A representative fraction of 50 to 120 gm was separated by use of a sample splitter. This fraction was then weighed to the nearest .1 gm and agitated for 30 seconds in water in a kitchen blender. The process efficiently broke apart the remaining small lumps and freed the sand surfaces of clay and almost all of the iron oxide. The sample was then washed on a sieve having openings of .06 mm in order to remove clay and silt-size particles. The remaining sample, composed of clean loose sand, was then oven-dried. Each sample of dry sand was sieved for 10 minutes in a stack of 12 or more sieves on a mechanical shaker, and the size fractions were weighed to the nearest .1 gm. The weight of the discarded silt and clay fraction was determined by subtracting the weight of the sand from the weight of the unwashed sample.

In the following tables, the figures at the left are diameters of sieve openings; samples, numbered on the top line, run from base of section (or exposure) to the top of the formation; figures in the body of the tables are grams of samples retained on the indicated sieves; bars in place of figures indicate unused sieves.