Browsing by Author "Derby, James Richard"

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    Geology of the Damascus area
    Derby, James Richard (Virginia Polytechnic Institute, 1961)
    Marine sedimentary rocks ranging in age from Early Cambrian(?) to Middle Ordovician, inclusive, crop out in the Damascus area. Approximately 13,000 feet of beds are exposed, comprising 14 formations. The stratigraphic succession is rather complete and is broken by a single recognizable hiatus which represents most of late Early Ordovician time. Clastic rocks of questionable Early Cambrian age are about 3,600 feet thick. Rocks of known Cambrian age are about 6,800 feet thick and consist of, in ascending order, elastic rocks, dolomite, shale and carbonate rocks, and mixed carbonate rocks. Carbonate rocks of Early Orodovician age range from 1,000 to 6,000 feet in thickness. Middle Ordovician rocks aggregate approximately 800 feet in thickness, the basal 100 feet of which is limestone and the remainder is shale and sandstone. The Elbrook formation of middle and Late Cambrian age is herein divided into four members of which one, the Widener limestone member, is formally named and mapped. A crepicephalus fauna from the Widener limestone, and a single trilobite, Plethometopus sp. From the Conococheague formation are illustrated. The strata have been folded into five synclines and four anticlines and are broken by two major thrust faults, and Lodi thrust and the Holston Mountain thrust. The faults were initially low-angle thrusts which have been folded with the overridden rocks so that locally the fault planes have steep dips.
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    Paleontology and stratigraphy of the Nolichucky Formation in southwest Virginia and northeast Tennessee
    Derby, James Richard (Virginia Polytechnic Institute, 1965)
    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.