Anatomy of the middle ordovician sevier shale basin,eastern Tennessee |
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| Authors: | Ganapathy Shanmugam Kenneth R Walker |
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| Institution: | 1. Mobil Field Research Laboratory, P.O. Box 900, Dallas, TX 75221 U.S.A.;2. Department of Geological Sciences, University of Tennessee, Knoxville, TN 37916 U.S.A. |
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| Abstract: | The Sevier Shale basin in eastern Tennessee comprises one of the thickest clastic sequences (nearly 2500 m) of Middle Ordovician age in North America. The lower one-half of the sequence is composed of Lenoir, Whitesburg, Blockhouse and Sevier Formations, in ascending order. The sequence ranges in age from Whiterockian to lower Wilderness in North American stages.The Middle Ordovician sequence exhibits tidal flat (Mosheim Member of Lenoir Fm.), subtidal (main body of Lenoir Fm.), slope (Whitesburg Fm.), anoxic basin (Blockhouse Fm), turbidite and contourite (Sevier Fm.) facies. The Sevier basin evolved in five stages: First, a widespread marine transgression initiated carbonate-shelf deposition in the study area. Second, a major tectonic downwarping event caused the stable shelf to break and subside rapidly at a rate of 60–65 cm 1000 yrs?1, and areas of shelf facies became areas of slope and basin facies. Third, global transgressions maintained the deep anoxic conditions for nearly 10 Ma. Fourth, turbidites began to fill the basin from a westward-prograding submarine fan system. Fifth, contour currents reworked the turbidites and progressively ventilated the Sevier basin. The basin-filling process terminated with shallow-water/subaerial clastics at the end of Middle Ordovician. |
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