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A number of Grenvillian basement massifs occur in the southern Appalachian Blue Ridge. The largest are contained in the Blue Ridge anticlinorium, which extends northward from its widest point in western North Carolina to Maryland. The Tallulah Falls dome, Toxaway dome, and Trimont Ridge area contain small internal basement massifs in the eastern and central Blue Ridge of the Carolinas and northeastern Georgia. All are associated with Paleozoic antiformal culminations, but each contains different basement units and contrasting Paleozoic structure. The Tallulah Falls dome is a broad foliation antiform wherein basement rocks (coarse augen 1158 ± 19 Ma Wiley Gneiss [ion microprobe, 207 Pb/ 206 Pb], medium-grained 1156 ± 23 Ma [ 207 Pb/ 206 Pb] and 1126 ± 23 Ma [ 207 Pb/ 206 Pb] Sutton Creek Gneiss, and medium-grained to megacrystic 1129 ± 23 Ma Wolf Creek Gneiss [sensitive high resolution ion microprobe, SHRIMP, 207 Pb/ 206 Pb]) form a ring and spiral pattern on the west, south, and southeast sides of the dome. Basement rocks are preserved in the hinges of isoclinal anticlines whose axial surfaces dip off the flanks of the dome. The Wiley Gneiss was intruded by Sutton Creek Gneiss. The Toxaway dome consists predominantly of coarse, banded 1151 ± 17 Ma and coarse augen 1149 ± 32 Ma (SHRIMP 206 Pb/ 238 U) Toxaway Gneiss folded into a northwest-vergent, gently southwest- and northeast-plunging antiform that contains a boomerang structure of Tallulah Falls Formation metasedimentary rocks in the core near the southwest end. The coarse augen gneiss phase constitutes a larger proportion of the Toxaway Gneiss toward the northeast. Field evidence indicates that the augen phase intruded the banded Toxaway lithology; U/Pb isotopic ages of these lithologies, however, are statistically indistinguishable. The Trimont Ridge massif occurs in an east-west–trending antiform west of Franklin, North Carolina, and consists of felsic gneiss that yielded a 1103 ± 69 Ma SHRIMP 207 Pb/ 206 Pb age. An ε Nd -depleted mantle model age of 1.5–1.6 Ga permits derivation of all of these basement rocks (including most from the western Blue Ridge) from eastern granite-rhyolite province crust, except the Mars Hill terrane rocks, which yield 1.8–2.2-Ga model ages. The small Grenvillian internal massifs were probably rifted from Laurentia during the Neoproterozoic, and became islands in the Iapetus ocean that were later swept onto the eastern margin of Laurentia during Ordovician subduction and arc accretion. These massifs were additionally penetratively deformed and metamorphosed during the Taconian and Neoacadian orogenies.

The deformed wedge of Paleozoic sedimentary rocks in the southern Appalachian foreland fold-thrust belt is defined by the configurations of the undeformed basement surface below and the base of the Blue Ridge–Piedmont megathrust sheet above, together with the topographic free surface above the thrust belt. The base of the Blue Ridge–Piedmont sheet and undeformed basement surface have been contoured using industry, academic, and U.S. and state geological survey seismic-reflection and surface geologic data. These data reveal that the basement surface dips gently SE in the Tennessee embayment from Virginia to Georgia, and it contains several previously unrecognized normal faults and an increase in dip on the basement surface, which produces a topographic gradient. The basement surface is broken by many normal faults beneath the exposed southern Appalachian foreland fold-thrust belt in western Georgia and Alabama closer to the margin and beneath the Blue Ridge–Piedmont sheet in Georgia and the Carolinas. Our reconstructions indicate that small-displacement normal faults form beheaded basins over which thrust sheets were not deflected, whereas large-displacement normal faults (e.g., Tusquittee fault) localized regional facies changes in the early Paleozoic section and major Alleghanian (Permian) structures. These basement structures correlate with major changes in southern Appalachian foreland fold-thrust belt structural style from Virginia to Alabama. Several previously unrecognized structures along the base of the Blue Ridge–Piedmont sheet have been interpreted from our reconstructions. Large frontal duplexes composed of rifted-margin clastic and platform rocks obliquely overridden along the leading edge of the Blue Ridge–Piedmont sheet are traceable for many kilometers beneath the sheet. Several domes within the Blue Ridge–Piedmont sheet also likely formed by footwall duplexing of platform sedimentary rocks beneath, which then arched the overlying thrust sheet. The thickness and westward limit of the Blue Ridge–Piedmont sheet were estimated from the distribution of low-grade foot-wall metamorphic rocks, which were observed in reentrants in Georgia and southwestern Virginia, but are not present in simple windows in Tennessee. These indicate that the original extent of the sheet is near its present-day trace, whereas in Georgia, it may have extended some 30 km farther west. The southern Appalachian foreland fold-thrust belt consists mostly of a stack of westward-vergent, mostly thin-skinned thrusts that propagated westward into progressively younger units as the Blue Ridge–Piedmont sheet advanced westward as a rigid indenter, while a few in northeastern Tennessee and southwestern Virginia involved basement. Additional boundary conditions include temperatures <300 °C and pressures <300 MPa over most of the belt. The southern Appalachian foreland fold-thrust belt thrusts, including the Blue Ridge–Piedmont megathrust sheet, reach >350 km displacement in Tennessee and decrease both in displacement and numbers to the SW and NE. Much of the Neoproterozoic to Early Cambrian rifted-margin succession was deformed and metamorphosed during the Taconic orogeny, and it is considered part of the rigid indenter. Only the westernmost rocks of the rifted-margin succession exhibit ideal thin-skinned behavior and thus are part of the southern Appa-lachian foreland fold-thrust belt. Palinspastic reconstructions, unequal thrust displacements, and curved particle trajectories suggest that deformation of the belt did not occur by plane strain in an orogen that curves through a 30° arc from northern Georgia to SW Virginia. Despite the balance of many two-dimensional cross sections, the absence of plane strain diminishes their usefulness in quantifying particle trajectories. Coulomb behavior characterizes most individual faults, but Chapple's perfectly plastic rheology for the entire thrust belt better addresses the particle trajectory problem. Neither, however, addresses problems such as the mechanics of fault localization, out-of-sequence thrusts, duplex formation, three-dimensional transport, and other southern Appalachian foreland fold-thrust belt attributes.

Abstract Nearly two thirds of the state of Georgia lies within the Coastal Plain province. A small area in the northwest corner of the state is occupied by highly folded and faulted Paleozoic rocks of the Valley-and-Ridge and the Blue Ridge provinces, and the remainder of the northern part of the state is covered by crystalline rocks of the Piedmont (Fig. no). In the Coastal Plain, the Cenozoic and Mesozoic strata range in thickness from a wedge edge at the northwest margin to more than 7,500 feet in the southwestern part of the state; in southeastern Georgia they range from 3,500 to 4,500 feet. Underlying the Cenozoic and Mesozoic deposits in southern Georgia, early Paleozoic clastic rocks were encountered in several wells, but their full thickness has not been penetrated. The volume of the sedimentary section in the Coastal Plain of Georgia is estimated to be 20,000 to 25,000 cubic miles. The rocks underlying the Coastal Plain of Georgia range in age from pre-Cambrian to Recent, but the greater part of the sedimentary rocks are Cretaceous and Tertiary (Fig. 113). Schistose rocks and granite in the buried extension of the rocks of the Piedmont were encountered in shallow wells in the northeastern part of the Coastal Plain, and granite was encountered in two wells in Pierce County in the southeastern part of the state. Two wells in southeastern Georgia terminated in volcanic rocks that are considered to be of pre-Cambrian or early Paleozoic age. Seven wells in south-central Georgia and a

Abstract Trail Ridge is located in southeastern Georgia and northeastern Florida (Fig. 1). The ridge is a Pleistocene coastal terrace that forms the eastern margin of Okefenokee Swamp, a large freshwater swamp. Trail Ridge is accessible by automobile where U.S. 1 and 23 crosses the Ridge about 20 mi (32 km) southeast of Waycross, Georgia. The road from Georgia 23 and 121 to the Suwannee Canal Recreation Area (Camp Cornelia) and Georgia 94 west of St. George, Georgia also cross Trail Ridge.

Abstract The Martinsburg-Reedsville, Juniata-Sequatchie, and Tuscarora-Clinch-Rockwood-Red Mountain Formations, (Upper Ordovician to Lower Silurian) comprise the major part of the Taconic clastic wedge in southwestern Virginia, eastern Tennessee, northeastern Alabama, and northwestern Georgia. This clastic wedge constitutes the fill of a peripheral foreland basin which formed in response to thrust loading. The well-known disconformity at the base of the Tuscarora Fm. in the eastern Valley and Ridge of Virginia was recently traced as a paraconformity to the northwest (i.e., basinward). A white, thick-bedded "upper" Tuscarora abruptly overlies the Martinsburg or Juniata Formations. with a distinctive basal conglomerate in the southeastern Valley and Ridge; a yellowish, thin-bedded, more mudstone-rich "lower" Tuscarora interpreted as facies-equivalent for parts of the Juniata Formation, occurs beneath the "upper" Tuscarora in the northwestern Valley and Ridge. This regional unconformity, with maximum lacuna towards the southeast, divides the clastic wedge into two parts. The nature of the unconformity along and across structural strike, its regional extent and disappearance towards Tennessee, and the overall tectonic setting all favor a tectonic origin for this unconformity. Basin rebound following the cessation of thrusting, concomitant with erosional/tectonic unloading of the Taconic orogen farther to the southeast, is suggested as the causal mechanism for the erosional unconformity. This interpretation contrasts markedly with stratigraphic relationships observed in eastern Tennessee, northeastern Alabama and northwestern Georgia, where the equivalent stratigraphic interval exhibits a small lacuna between the Juniata-Sequatchie and Clinch-Rockwood-Red Mountain Fms. Basin development was not related to collisional tectonism, but represents a "left-over moat" of the Blount-phase. Paleosols occur within the upper Juniata Fm. in the eastern Valley and Ridge, sharply overlain by a 0.6- to 3-m thick, very fine- to medium-grained and phosphatic, highly bioturbated, transgressive sandstone of marine shoreface origin that occurs in the basal Clinch, Rockwood and Red Mountain Fms. This regionally correlative sandstone, informally known as the "basal transgressive sandstone" (bts), was deposited along ravinement surfaces during erosional shoreface retreat; it therefore documents a lowstand followed by a eustatic rise. To the west, the bts overlies open-marine shale and limestone deposits containing a typical Ashgillian brachiopod fauna; shelf strata above the bts contain a Lower Llandovery (A1-2) brachiopod fauna. Hence, the magnitude of the lacuna appears decrease in a northwesterly direction, where the Ordovician to Silurian boundary is nearly conformable.

Abstract The eastern Gulf Coast, comprising the states of Mississippi and Florida and those portions of Alabama and Georgia not included in the Appalachian Mountains and the Piedmont Plateau, covers about 166,000 square miles. About 95,000 cubic miles of Paleozoic sediments are included in this area, occupying two widely separated basins. The better known of these is the Black Warrior basin, of northeastern Mississippi and northwestern Alabama, in which the first hydrocarbon production of both these states was found. The other, herein named the "Suwannee River basin," lies in southern Georgia, southeastern Alabama, and northern Florida. It is nonproductive. The most important basin within the eastern Gulf Coast from the standpoint of oil production is the Mississippi salt basin, which is continuous with a similar basin in Louisiana on the west, and extends into Alabama on the east. Minor production has been obtained from four of the 49 shallow salt domes proven by drilling in this basin. The major production from Mesozoic reservoirs in the province is derived from salt-uplifted structures which flank the salt basin on the north and south. Important Tertiary (Eocene Wilcox) production is largely confined to four counties in southwestern Mississippi. It is obtained principally from structurally modified stratigraphic traps. Southern Florida, since early Cretaceous time at least, has been a shallow platform area characterized by carbonate and evaporite deposition with no important noncarbonate clastics. Two fields have been discovered to date, producing from a highly organic limestone of Lower Cretaceous, Glen Rose age. The present northeastern boundary of rich Miocene production in South Louisiana and the Louisiana tidelands is approximately coincident with the 10,000-foot isopach of Miocene sediments. Present information, which indicates rapid thinning of the Miocene and its gradation to a carbonate facies east and northeast of this line, suggests objectives for exploration in the Mississippi-Alabama-Florida coastal and offshore areas will be in sediments other than Miocene, on structures other than salt domes.