Upper Ordivician Sequatchie Formation Essay, Research Paper

Rocks belonging to the Ordovician System are exposed along Interstate 75 between Cleveland and Chattanooga in a road cut in White Oak Mtn or sometimes called Green Gap. These rocks show the upper portion of the Middle Ordovician Catheys Formation and all of the Upper Ordovician Sequatchie Formation including the Fernvale Member.

The road cut exposes a section of rock that was measured at two hundred and seventy-five feet. This stratigraphic section was examined in detail to determine the paleodepositional environment in which these sections of rock were deposited. There are a total of five units that have been identified and the lithography studied in detail. These five units will be split up and described separately to clarify the content of each unit more easily.

Unit 1

Unit one represents the Catheys Formation. This unit grades upward and has a scoured bottom. This unit consists of mostly calcirudite and shale layers with occasional siltstone overlying the calcirudite. There are nine cycles present in this unit. There are skeletal debris as well as burrows present in these layers. These rocks are carbonate-rich as well. The siltstone suggests a low energy environment of deposition, but the burrows tell of slightly more energetic conditions.

Unit 2

Unit two represents the Sequatchie Formation. There are thin beds of calcareous siltstone that range in thickness from 1 to 1 . There are fossil remnants here as well. The siltstone is rippled and cross-beds are present. Some red shales are present, which may hint to us a beach was present at that particular time of deposition. This will account for the green as well as the red rocks and also the thin-bedded ripples present.

Unit 3

Unit three represents the Sequatchie Formation as well. The rocks present in this unit are mostly of green color, which leads us to believe they were oxidized. This unit shows evidence of a tidal flat or tidal complex. This idea stems from the oxidization and reduction of the rocks present. The sedimentary sequences are cyclic in this unit as well. The first layer is intraformational conglomerate red mud chips in calcareous siltstone. This grades upward into gray, pink or red laminated calcareous siltstone. Next are rippled and cross-bedded gray, pink or red calcareous siltstone. The siltstones are made up largely of micrite peloids. Birdseye s are present here as well.

Unit 4

This unit is yet again the Sequatchie Formation. This unit shows rocks largely red or red and green with lesser gray zones. Calcareous siltstone, having been laminated and burrowed, make up the majority of Unit four. Due to extensive bioturbation it is virtually impossible to determine original bed thicknesses. Dolomite is present in the rock, which possibly formed in early digenesis of the rock. Extensive biotubation leads us to believe that these rocks were deposited in the bottom of a lagoon.

Unit 5

Unit five is representative of the Fernvale Member of the Sequatchie Formation. Tan and pink calcirudite and cacarenite plus silty gray shale make up the major portion of unit five. This unit is approximately twenty feet thick and consists of eight layers of tan calcirudite. These rocks are shoal deposits or were deposited on a shell bank. Low energy environment is typical of the deposition shown in this unit.