PETROGRAPHY OF THE UPPERMOST ORDOVICIAN THROUGH LOWER SILURIAN IN A CORE FROM THE POE AGGREGATES QUARRY NEAR FORT WAYNE, INDIANA

We present a petrographic study of a core from Poe Quarry near Fort Wayne, Indiana. The studied stratographic interval exends from the upmost Upper Ordovician “Elkhorn Formation” through the base of the Silurian Waldron Shale. Rocks of this age, particularly those of the Ordovician, have been relatively neglected in northern Indiana. This study will contribute to the understanding of these rocks, including their depositional environments and diagenetic processes. These rocks are commonly mined in aggregate quarries for construction use, with a large portion utilized for paving asphalt. Our aim is to establish a relationship between petrographic characteristics and suitability of a rock in making high quality asphalt. This is to both improve evaluation techniques for the aggregate industry and to serve as a foundation for a better understanding of the behaviors different lithologies exhibit in asphalt mixes.

The 2.5 inch core used for this study was measured in decimal feed and described in approximately 1 foot units and each lithology was described at a half inch resolution. After description, we collected three samples 2 to 6 inches each (as broken out by the driller) from every ten feet of core, taking care to obtain at least one sample of every unique lithology previously described. We are making continuous thin sections for each sample. Previously described, the Upper Ordovician rock is blue-gray, fossiliferous interbedded shale and limestone. The Brassfield Formation ranges from near white to dark gray and is a fine-grained, sucrotic, and calcerous dolomite. Above, the Salamonie is a lightly colored, fine-grained dolomite; oolitic in the upper portion. The Waldron Shale is dark brown in color and silty with interbedded limestone.

Coring is a common practice for mining operations to canvass potential areas for future excavation. Speculation on the suitability of stone is usually done through bulk sampling and testing of the cores. Mining is an expensive and cumbersome venture, so detailed and accurate speculation is important to the success of any aggregate mining enterprise. If successful, this study will result in more guided decisions in respect to future mining initiatives, which will result in the conservation of resources and more efficient use of land.