Paleontology and stratigraphy of the Nolichucky Formation in southwest Virginia and northeast Tennessee

Abstract

The paleontology and stratigraphy of the Nolichucky and adjacent formations in the region from Giles and Montgomery counties, Virginia, to the latitude of Knoxville, Tennessee, is described from 27 measured sections and 22 isolated localities. Over 3,600 fossil specimens were collected and identified. The faunas range from late Middle Cambrian (Bolaspidella Zone) to late Upper Cambrian (Trempealeau), but the majority are of Dresbachian age. Trilobites are the most common faunal element with M8 genera and 85 species represented. Two new genera and eight new species are described.

The late Middle Cambrian fauna occurs in the Nolichucky and Maryville formations and includes species of Acrocephalops, Kochaspis, and Modocia. The Dresbachian fauna contains representatives of the Cedaria, Crepicephalus, and Aphelaspis zones and is restricted to the Nolichucky except for two localities where the Cedaria Zone occurs in the Honaker and Maryville formations. The Dresbachian trilobite fauna includes the following genera: Amiaspis, Aphelaspis, Ataktaspis,Arcuolimbus, Blountia, Blountiella, Bonneterrina, Bynumia, Cedaria, Cedarina, Cheilocephalus, Coosella, Coosia, Coosina, Crepicephalus, Densonella, Dresbachia, Dunderbergia, Dytremacephalus, Genevievella, Glaphyraspis, Hardyoides, Ithycephalus, Kingstonia, Komaspidella, Kormagnostus, Llanoaspis, Loxoparia, Madarocephalus, Maryvillia, Meteoraspis, Modocia, Norwoodella, Norwoodia, Pemphigaspis, Pseudggnostina, Shickshockia, Talbotina, Terranovella, Tricrepicephalus, "Uncaspis", and Welleraspis. In addition the Dresbachian fauna includes the molluscans, Palaeacmaea and Proplina, the sponge Chancelloria, inarticulate brachiopods, and one articulate brachiopod.

No Franconian faunas were identified.

Trempealeauian trilobites were collected from two formations. The top of the Copper Ridge Dolomite near Blacksburg, Virginia, contains Tellerina, Prosaukia, and Triarthropsis. The Conococheague Formation near Damascus, Virginia, contains Plethometopus convexus 580 feet above the Crepicephalus Zone.

The Nolichucky Formation is predominantly limestone and shale with abrupt lateral gradation into silty dolomite or pure limestone in some areas.

Northwest of the Pulaski Fault near the southwest margin of the region in Tennessee, the Nolichucky is nearly 900 feet thick and consists of limestone and shale representing the Bolaspidella through Aphelaspis zones. The formation thins and the base becomes younger northeastward to Bland County, Virginia, where the Nolichucky is 150 feet thick and includes only the Crepicephalus and Aphelaspis zones. In Bland County the Cedaria Zone is contained in the underlying Honaker Dolomite. Northeastward from Tazewell and Bland counties, Virginia, the Nolichucky thins to about 50 feet of silty dolomite, containing at its northeasternmost outcrop only the upper part of the Crepicephalus Zone.

Southeast of the Pulaski Thrust, in Washington County, Virginia, the Nolichucky is represented by 150 feet of oolitic limestone which is underlain and overlain by dolomite and which contains the upper part of the Crepicephalus Zone. This same oolitic limestone is recognizable to the southeast as part of the typical Nolichucky.

The Nolichucky Formation was deposited during a single transgressive-regressive cycle, beginning in Bolaspidella time and reaching maximum transgression in late Crepicephalus time. The Maynardville Limestone, here considered the uppermost member of the Nolichucky, was deposited during the regressive phase in Aphelaspis time.