SEDIMENTOLOGY, PETROGRAPHY, AND MINERALOGY OF THE TALLAHATTA FORMATION NEAR THE TOWN OF MERIDIAN, MISSISSIPPI

The Tallahatta Formation is rock unit that was deposited in Mississippi during the Eocene time. It is currently exposed along an arcuate outcrop belt extending from east-central to north-central part of the state. We investigated sedimentology, petrography, and mineralogy of an exposure of this rock unit in a road cut along Interstate 20 highway west of the town of Meridian, Mississippi. Here, the Tallahatta Formation displays a rhythmic sedimentation pattern consisting of alternation of two lithofacies. The first is the bioturbated and nodular mudstone consisting of centimeter-thick beds of irregular siltstone that alternate with thin layers of highly argillaceous soft mudstone. The second lithofacies is the white, massive mudstone.

Petrographic studies of thin sections prepared from thirteen samples from this outcrop indicate that bioturbated and nodular mudstone consists of a mixture of quartz silt and other very fine-grained particles. In contrast, the white massive mudstone lithofacies consists of very fine-grained amorphous grains, most likely volcanic glass. These properties suggest that beds of white, massive mudstone lithofaices are volcanic ash layers.

The absence of shallow water indicators such as cross beds, the dominance of fine grain lithology, and the abundance of bioturbation indicate that Tallahata Formation was deposited in low energy waters below wave base in the study area. The abundance of amorphous grains points to presence of volcanic ash as a major sediment source.