Environmental Study of a Portion of the Middle Ordovician in Sequatchie Valley, Eastern Tennessee

A detailed depositional environmental analysis of a portion of Middle Ordovician Carters Limestone and Hermitage Formation in Sequatchie Valley in East Tennessee was made using six stratigraphic sections as closely spaced as permitted by reasonably complete outcrops. The approximately 60 feet of rocks of this stratigraphic interval include 18 distinct lithologies as determined from a field study and examination of samples collected at one foot intervals and closer with changes in lithology. Two bentonite beds generally accepted as being isochronous units offer a time framework. In all 565 samples were collected and of these 447 were cut, polished, and an acetate peel made from the acid-etched surfaced. Two hundred and forty-four 2X3 inch thin-sections were also prepared. The peels and thin-sections were the basis for a petrographic study with point counts of selected thin-sections.

The investigation disclosed a sequence of environmental changes for the area of study beginning with subtidal conditions and an abundant carbonate generating fauna. This was followed by a tidal flat environment with mudbanks and supratidal islands. The next environment of deposition was another subtidal episode. These environments, an apparent regressive-transgressive sequence, fit into the carbonate bank portion of the model for Middle Ordovician strata proposed by Walker and Alberstadt (1973).