Lower Middle Ordovician of Southwest Virginia and Northeast Tennessee

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The lower middle Ordovician of southwest Virginia and northeast Tennessee may be divided into 29 lithologic and faunal units, many of which are remarkably persistent throughout the area. Important lithologic changes were largely attributed to the presence or absence of individual units in the section, while changes by lateral gradation were considered of importance only in restricted parts of the section and in somewhat localized areas. Barrier control of facies is well illustrated by the comparison of the limestones directly northwest and southeast of Clinch Mountain in Virginia. The two median belts directly autochthonous to the Saltville thrust show the most complete sections, containing in some areas all of the lithologic and faunal units of the standard section of Tazewell County, Virginia. Evidence of a large hiatus was observed in the northwest belts of the Saltville autochthone, indicating northwestward convergence of some of the units. The sections southeast of Clinch Mountain (Saltville allochthone) are considerably thicker and more clastic than those northwest of Clinch Mountain. Limestones of the latter area thicken and become more clastic along the strike of the median belts from Virginia into Tennessee. Detailed sections measured along seven belts were compared with the revised classification of Tazewell County, Virginia. The Blackford, Five Oaks, Lincolnshire, Thompson Valley (new), upper Peery, Benbolt, Wardell, Bowen, Witten, and Moccasin formations extend into northeast Tennessee. The Ward Cove (restricted), lower Peery, and Gratton formations largely disappear in southwest Virginia. The Mosheim, Holston, Ottosee, and Bays should be discontinued as definite formational names. The further use in this area of such terms as Stones River group, Blount group, Murfreesboro limestone, and Lowville limestone is not recommended. The Lenoir limestone and Sevier shale were redefined to preserve their validity. The Holston marble of the Knoxville, Tennessee, area was assigned a new name. The current classification of major boundaries in Virginia and Tennessee needs revision but should await further detailed comparisons with the standard sections.