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Research about Alabama, Georgia, North Carolina, South Carolina

Source-linked reports with geographic coverage including Alabama, Georgia, North Carolina, South Carolina.

5 recordsLinked to original sources
USGS2015

A Laurentian margin back-arc: the Ordovician Wedowee-Emuckfaw-Dahlonega basin

Independent researchers working in the Talladega belt, Ashland-Wedowee-Emuckfaw belt, and Opelika Complex of Alabama, as well as the Dahlonega gold belt and western Inner Piedmont of Alabama, Georgia, and the Carolinas, have mapped stratigraphic sequences unique to each region. Although historically considered distinct terranes of disparate origin, a synthesis of data suggests that each includes lithologic units that formed in an Ordovician back-arc basin (Wedowee-Emuckfaw-Dahlonega basin—WEDB). Rocks in these terranes include varying proportions of metamorphosed mafic and bimodal volcanic rock suites interlayered with deep-water metasedimentary rock sequences. Metavolcanic rocks yield ages that are Early–Middle Ordovician (480–460 Ma) and interlayered metasedimentary units are populated with both Grenville and Early–Middle Ordovician detrital zircons. Metamafic rocks display geochemical trends ranging from mid-oceanic-ridge basalt to arc affinity, similar to modern back-arc basalts. The collective data set limits formation of the WEDB to a suprasubduction system built on and adjacent to upper Neoproterozoic–lower Paleozoic rocks of the passive Laurentian margin at the trailing edge of Iapetus, specifically in a continental margin back-arc setting. Overwhelmingly, the geologic history of the southern Appalachians, including rocks of the WEDB described here, indicates that the Ordovician Taconic orogeny in the southern Appalachians developed in an accretionary orogenic setting instead of the traditional collisional orogenic setting attributed to subduction of the Laurentian margin beneath an exotic or peri-Laurentian arc. Well-studied Cenozoic accretionary orogens provide excellent analogs for Taconic orogenesis, and an accretionary orogenic model for the southern Appalachian Taconic orogeny can account for aspects of Ordovician tectonics not easily explained through collisional orogenesis.

Alabama, Georgia, North Carolina, South Carolina↗
USGS2014

Early to Middle Ordovician back-arc basin in the southern Appalachian Blue Ridge: characteristics, extent, and tectonic significance

Fault-dismembered segments of a distinctive, extensive, highly allochthonous, and tectonically significant Ordovician (ca. 480–460 Ma) basin, which contains suites of bimodal metavolcanic rocks, associated base metal deposits, and thick immature deep-water (turbiditic) metasediments, occur in parts of the southern Appalachian Talladega belt, eastern Blue Ridge, and Inner Piedmont of Alabama, Georgia, and North and South Carolina. The basin's predominantly metasedimentary strata display geochemical and isotopic evidence of a mixed provenance, including an adjacent active volcanic arc and a provenance of mica (clay)-rich sedimentary and felsic plutonic rocks consistent with Laurentian (Grenvillian) upper-crustal continental rocks and their passive-margin cover sequences. Geochemical characteristics of the subordinate intercalated bimodal metavolcanic rocks indicate formation in a suprasubduction environment, most likely a back-arc basin, whereas characteristics of metasedimentary units suggest deposition above Neoproterozoic rift and outer-margin lower Paleozoic slope and rise sediments within a marginal basin along Ordovician Laurentia's Iapetus margin. This tectonic setting indicates that southernmost Appalachian Ordovician orogenesis (Taconic orogeny) began as an extensional accretionary orogen along the outer margin of Laurentia, rather than in an exotic (non-Laurentian) arc collisional setting. B-type subduction polarity requires that the associated arc-trench system formed southeast of the palinspastic position of the back-arc basin. This scenario can explain several unique features of the southern Appalachian Taconic orogen, including: the palinspastic geographic ordering of key tectonic elements (i.e., back-arc, arc, etc.), and a lack of (1) an obducted arc sensu stricto on the Laurentian margin, (2) widespread Ordovician regional metamorphism, and (3) Taconic klippen to supply detritus to the Taconic foreland basin.

Alabama, Georgia, North Carolina, South Carolina↗
USGS1997

Hybridization between introduced spotted bass and smallmouth bass in reservoirs

Introductions of black basses Micropterus spp. beyond their native ranges have led to hybridization within the genus. In the southeastern USA, the potential for hybridization appears high because species introductions have been common in reservoirs. We determined the extent of hybridization between smallmouth bass M. dolomieu and spotted bass M. punctulatus in reservoirs in which introductions of either species into the native range of the other species had occurred. Three allozyme loci were used to distinguish the two species and their hybrids. Significant hybridization occurred in two of three reservoirs where introductions had been reported. In Lake Chatuge, Georgia–North Carolina, where the Alabama subspecies of spotted bass M. p. henshalli was introduced, 77 of 276 fish had hybrid genotypes, and only 2 fish had genotypes of the native smallmouth bass. In Thurlow Reservoir, Alabama, where smallmouth bass were introduced and Alabama spotted bass were native, 3 of 17 fish had hybrid genotypes. Only I fish with a possible hybrid genotype was identified in two reservoirs containing native smallmouth bass and northern spotted bass M. p. punctulatus .

Alabama, Georgia, North Carolina, South Carolina↗
USGS1989

The Macon Complex; An ancient accretionary complex in the southern Appalachians

The Macon Complex, which extends from eastern Alabama to northern North Carolina, is a late Precambrian–Middle Cambrian accretionary complex comparable in size to the Franciscan Complex of California and Oregon. Much of the complex is tectonic, sedimentary, and metamorphic chaos, properly termed mélange, where well-rounded to angular fragments, blocks, and slabs of contrasting metamorphic grades, different igneous parentages, drastically different sedimentary facies, and different degrees of deformation “float” in highly imbricated and tectonized matrices, the whole having been intruded by Devonian mafic plutons and associated syenites, and by Carboniferous granitic plutons. We have divided the complex into three mélanges that probably reflect different structural regimes within the accretionary wedge: (1) the Juliette mélange, with two tectonostratigraphic lithofacies, the clastic-rich, partly olistostromal Potato Creek facies and the Gladesville facies, rich in mafic and ultramaflc fragments, blocks, and slabs; (2) the Po Biddy mélange, characterized by metamorphosed manganiferous sediments, metavolcaniclastic rocks, graphitic schists, and locally by metamorphosed thinly bedded pyritiferous limestones, and a wide variety of mineral deposits; and (3) the Falls Lake mélange, which is quite similar to the Juliette mélange and probably represents the same tectonostratigraphic horizon in the accretionary prism. The matrices of the mélanges contain a wide variety of metaigneous and metasedimentary exotic clasts, including mafic and ultramaflc rocks. The Macon Complex is structurally overlain by the late Precambrian–Middle Cambrian Little River Complex, made up of thick piles of mostly felsic calc-alkaline metavolcanic rocks, and lesser amounts of metaplutonic rocks, that originated in a continental-margin volcanic arc (Little River arc). Trilobites from near the top of one of the youngest sections are restricted to the upper two-thirds of the Middle Cambrian and are characteristic of the Atlantic faunal province. The Little River Complex is overlain, beneath the Atlantic Coastal Plain, by the African cratonic Northern Florida platform sequence; the Macon and Little River complexes and the Northern Florida platform sequence make up the Little River thrust stack. The magmas of the Devonian plutons that have intruded the Macon Complex probably formed when the Little River stack was thrust upon the underlying Georgiabama thrust stack, which was itself still being thrust toward the North American craton. The Macon Complex is interpreted to have formed between a trench and the Little River island arc at the oceanward edge of what was either a microcontinent off the African continent or the core of the present African continent. Many mafic and all ultramaflc bodies in the mélange are probably pieces of Iapetus Ocean crust and mantle offscraped from the downgoing slab and imbricated into the accretionary wedge. Rocks of the Macon Complex have previously been assigned to the “Charlotte,” “Kiokee,” “Kings Mountain,” and “Lowndesville” belts and to parts of the “Uchee,” “Raleigh,” “Pine Mountain,” and “Inner Piedmont” “belts.”

Alabama, Georgia, North Carolina, South Carolina↗