The Appalachians are a Paleozoic orogen that formed in a complete Wilson cycle along the eastern Laurentian margin following the breakup of supercontinent Rodinia and the coalescence of all of the continents to form supercontinent Pangea. The Appalachian Wilson cycle began by formation of a Neoproterozoic to early Paleozoic rifted margin and platform succession on the southeastern margin of Laurentia. Three orogenies ultimately produced the mountain chain: the Ordovician Taconic orogeny, which involved arc accretion; the Acadian–Neoacadian orogeny, which involved north-to-south, transpressional, zippered, Late Devonian–early Mississippian collision of the Carolina superterrane in the southern-central Appalachians and the Avalon-Gander superterrane in the New England Appalachians, and Silurian collision in the Maritime Appalachians and Newfoundland; and the Alleghanian orogeny, which involved late Mississippian to Permian collision of all previously formed Appalachian components with Gondwana to form supercontinent Pangea. The Alleghanian also involved zippered, north-to-south, transpressional, then head-on collision. All orogenies were diachronous. Similar time-correlative orogenies affected western and central Europe (Variscan events), eastern Europe and western Siberia (Uralian events), and southern Britain and Ireland; only the Caledonide (Grampian–Finnmarkian; Caledonian–Scandian) events affected the rest of Britain and the Scandinavian Caledonides. These different events, coupled with the irregular rifted margin of Laurentia, produced an orogen that contains numerous contrasts and nonthroughgoing elements, but it also contains elements, such as the platform margin and peri-Gondwanan elements, that are recognizable throughout the orogen.

Abstract DNAG Transect E-3. Part of GSA’s DNAG Continent-Ocean Transect Series, this transect contains all or most of the following: free-air gravity and magnetic anomaly profiles, heat flow measurements, geologic cross section with no vertical exaggeration, multi-channel seismic reflection profiles, tectonic kindred cross section with vertical exaggeration, geologic map, stratigraphic diagram, and an index map. All transects are on a scale of 1:500,000.

Seismic reflection profiles and SeaMARC II imagery from the southwest Panama margin demonstrate that oblique convergence is presently occurring along what had previously been thought of as a transform margin. Our seismic profiles image landward-dipping thrust faults and seaward-verging folds at the toe of the slope. The frontal deformation zone as imaged on the SeaMARC II mosaic is 12 to 15 km wide with individual east-west-trending folds and thrusts that are laterally continuous for 5 to 10 km. Much of the terrigenous trench sediment is offscraped and accreted, forming an accretionary prism (South Panama deformed belt). Three linear ridges (part of the Panama Fracture Zone complex) are being obliquely subducted along the southwest Panama margin. The oblique convergence causes the ridges to sweep eastward along the trench. The SeaMARC II mosaic shows that the regional structure of the South Panama deformed belt is dominated by east-west-trending trench segments that are separated by the north-south fracture zone ridges. The trench shallows where the ridges intersect the trench, and the deformation front is warped around the ridges. On the east side of each ridge the accretionary complex bends to a northwest-southeast trend, suggesting that the ridges are deforming the accretionary complex. As the accretionary prism rides up over each ridge, it thickens markedly. By the time the prism reaches the top of the ridge, its surface slope has been greatly oversteepened and large portions of accreted material slump into the trench. After passage of the ridge, the system returns to its “normal” state, and accretion resumes, adding the slumped material back into the accretionary prism. The accretionary prism is thus only temporarily disrupted by the subduction of the Panama Fracture Zone system ridges.

Abstract The Gulf of California is an excellent laboratory for studying sedimentary processes on time scales that are not resolvable in the open ocean. The high biological productivity and the unique physical character of the gulf combine to produce sedimentological processes that preserve annual phenomena. This volume is organized into six sections. Part 1 covers historical exploration of the area. Part 2 includes 5 chapters detailing information contained on the 5 fold-out maps that accompany the volume. Part 3 consists of chapters on regional geophysics and geology. Part 4 covers satellite geodesy. Part 5's seven chapters discuss physical oceanograpy, primary productivity, and sedimentology. Part 6 covers hydrothermal processes.

Abstract DNAG Transect A-3. Part of GSA’s DNAG Continent-Ocean Transect Series, this transect contains all or most of the following: free-air gravity and magnetic anomaly profiles, heat flow measurements, geologic cross section with no vertical exaggeration, multi-channel seismic reflection profiles, tectonic kindred cross section with vertical exaggeration, geologic map, stratigraphic diagram, and an index map. All transects are on a scale of 1:500,000.

Abstract The Stress Map of North America , constructed on four 42 inch by 55 inch sheets, plots modern maximum horizontal stress (SHmax) orientations for North America inferred from a variety of geophysical and geologic data. These data are described and discussed in the companion DNAG volume Neotectonics of North America. A brief description of the various stress indicators is given in the legend.

Abstract The 10 papers contained in this publication are oriented toward the hydrocarbon potential of Antarctica. Contents include regional seismic surveys involving tectonic and stratigraphic interpretations extending from the Adelie Coast margin, over the Ross Sea and Bellingshausen Sea, throughthe Bransfield Straight and along the northern Antarctic Peninsula. Mesozoic sedimentary basins are compared in detail, and a tectonic synthesis of Antarctica and the surrounding southern seas is presented.

Parts of the central and southern Appalachian orogen appear to have evolved away from Proterozoic North America (Laurentia) and to have been accreted to it during the Paleozoic orogenies that collectively formed the orogen. Identifying each tectonostratigraphic terrane is a necessary step in understanding the evolution of the orogen. The terranes in the central and southern Appalachians are delineated, interpreted, and classified with varying degrees of confidence as: (1) Laurentian native terranes, (2) internal continental terranes of the Appalachian orogen, (3) disrupted terranes, (4) possible oceanic crustal remnants, (5) volcanic-arc terranes, (6) a continental terrane of Gondwanaland affinity, and (7) metamorphic complexes of undetermined affinity. The Laurentian native terranes consist of external massifs of Laurentian basement (Grenvillian and older), their rift- and shelf-facies cover rocks, and slope-rise prism deposits. External massifs are present in the Blue Ridge tectonic province, Reading Prong, and Honey Brook Upland. Rocks of the Talladega block are stratigraphically tied to Laurentia and, with the possible exception of the Hillabee greenstone, are also considered native. Offshore, deep-water, post-rift deposits of the Hamburg and Westminster terranes have no direct stratigraphic ties to Laurentia and are considered discrete native (not suspect) terranes. The internal continental terranes of the Appalachian orogen are isolated massifs of Middle Proterozoic (Grenvillian) continental basement and their cover sequences that occur within the metamorphic core of the orogen. These terranes, the Baltimore, Sauratown, and Pine Mountain terranes, could be either structurally isolated outliers of Laurentia or microcontinental fragments of Laurentian crust displaced by rifting or transcurrent faulting and later reassembled. Disrupted terranes in the central and southern Appalachians contain mélange complexes as well as more coherent terrane fragments (volcanic, ophiolitic, or continental) intermingled with the mélange complexes. Those identified include the Jefferson, Potomac, Smith River, Inner Piedmont, Falls Lake, Juliette, and Sussex terranes. The Bel Air–Rising Sun terrane (Baltimore Complex) in Maryland and Pennsylvania is the only terrane named separately as a possible oceanic crustal remnant. Similar mafic and ultramafic complexes are present in all of the disrupted terranes, but are too small to consider as separate terranes. Volcanic-arc terranes include the Chopawamsic, Carolina, Spring Hope, Roanoke Rapids, and Charleston terranes. The only terrane recognized as a continental terrane of Gondwanaland affinity is the Suwannee terrane, which contains rocks believed to correlate with those now exposed in west Africa. Metamorphic complexes of undetermined affinity are terranes that could not be clearly classified on the basis of available data. These include the Milton, Gaffney, Uchee, Crabtree, Goochland, Wilmington, and Hatteras terranes. The Penobscottian, Taconian, Acadian, and Alleghanian Paleozoic compressional events collectively assembled the various terranes into what is now the Appalachian orogen. Only the central and southern parts of the U.S. Appalachians are considered here. The Penobscottian orogeny, about 550 to 490 Ma, amalgamated the Potomac, the Chopawamsic, probably the Bel Air–Rising Sun, and possibly other exotic terranes at some unknown distance from Laurentia. This was followed by the Taconian orogeny, about 470 to 440 Ma, which accreted the previously amalgamated terranes and probably other terranes such as the Carolina terrane to Laurentia. The younger age limit for the Taconian event is partly constrained by Middle and Late Ordovician faunal assemblages in successor basin deposits of the Arvonia Slate and Quantico Formation. The significance of the Acadian orogeny, dated about 400 to 380 Ma in New England, is unclear in the central and southern Appalachians. In the Talladega block of Alabama and Georgia, an Early to Middle Devonian dynamothermal event is firmly bracketed between Early Devonian fossils and K-Ar ages that indicate a thermal peak no later than Middle Devonian time. A regional tectonothermal event and faulting of approximately this age are also suggested by isotopic studies in terranes to the east. The late Paleozoic (Alleghanian) continental collision between Laurentia and Gondwanaland, which formed the supercontinent Pangea, marks the final stage of accretionary history in the Appalachian-Caledonide orogen. Effects evident in the central and southern Appalachian region include: (1) the accretion of the Suwannee terrane and perhaps the Charleston terrane to what is now North America, (2) slicing and shifting of terranes along dextral strike-slip faults, particularly in the eastern Piedmont, (3) westward transport of native and previously accreted terranes in the western Piedmont and Blue Ridge as part of a composite crystalline thrust sheet, (4) deposition of clastic wedges in the Appalachian foreland, and (5) imbricate thrusting and folding of the resultant strata in the Valley and Ridge Province.