SISSON MEMBER NAME EXTENSION TO THE NE RIM OF THE ILLINOIS BASIN

The northeastern rim of the Illinois Basin in Indiana contains, among other lithologies, shallow water high-purity carbonates that include stone suitable for aggregates, cement manufacturing, building stone and chemical uses such as scrubber stone. Until now much of the Putnam County high quality aggregates were produced from the Ste. Genevieve or the upper St. Louis. As the quarries were being deepened in the first half of the 2000’s, a stone that has the properties needed for high quality aggregate was confirmed at the apparent stratigraphic position of the Sisson Member (Keller and Becker-1980 IGS) in the lower St. Louis. Putnam County is outside of the area of the 1980 report.

In these new exposures, like the deep basin Sisson Member described by Keller and Becker, the stones above this unit, in the St. Louis, are finer grained and contain dark materials. Also like the Sisson in the 1980 publication, the stone below this unit are coarsely grained Salem-type calcarenites. For aggregate production, there are some physical properties associated with the dark colored lower St. Louis units and different physical properties associated with the Salem that impact aggregate production.

Physical property testing; with core, ledge and production sampling, has shown that this northeastern rim unit in the apparent stratigraphic position of the deep basin Sisson Member has properties suitable for high quality aggregate purposes such as used in bituminous mixtures and Portland cement concrete.

In order to distinguish this lithologic unit from the units above (St. Louis) and below it (Salem), and in order to avoid creating more cumbersome nomenclature, we have extended the deep basin name to the unit that has been tested and is suitable for use, and have been referring to these exposed rocks on the northeastern rim of the Illinois Basin as the Sisson Member.