The northwestern New England and adjacent Quebec region is an area of 30,000 square miles on the northwest side of the northeastern Appalachian Mountains belt, and extends into the adjacent Hudson, Champlain, and St. Lawrence Valleys to the northwest. It is athwart a major change in trend of this belt from northerly to northeasterly. The synthesis is a rationale of the tectonic relations of this region, discussed in chronological order. The Precambrian basement, exposed at the core of a Paleozoic anticlinorium in the mountain belt, is made up of complexly deformed diaphthoritic miogeosynclinal rocks intruded by granitic plutons and pegmatite dikes. The exposed rocks are part of a northeast-trending Precambrian mobile shelf at least 300 miles wide that includes a wide belt to the northwest in the North American craton. The lower (Cambrian and Ordovician) and middle (Silurian and Devonian) Paleozoic orthogeosyncline, which coincides mainly with the Appalachian belt, includes a broad eugeosynclinal zone, a miogeosynclinal zone to the northwest and probably also to the southeast of the eugeosynclinal zone, several geanticlines, and a quasi-cratonic belt; it thus contrasts with the broadly miogeosynclinal Precambrian rocks of the basement. The eugeosynclinal deposits, whose maximum thickness is more than 50,000 feet, average at least three times the thickness of those in the miogeosynclinal zone. Pelitic and semipelitic rocks dominate the upper deposits and lap over geanticlines, a quasi-cratonic belt, and the margin of the craton. The sources of sediments include cratonal areas, geanticlines that formed tectonic islands, and volcanic islands. The transition between the miogeosynclinal and eugeosynclinal zones is one of sedimentary facies and thickness change, and of stratigraphic convergence and unconformity. In the lowest Paleozoic rocks the transition is west and north-west, respectively, of the Green and Sutton Mountains. The miogeosynclinal zone is missing in Quebec northwest of the northern Sutton Mountains and the eugeosynclinal zone extends to the northwestern margin of the orthogeosyncline. The belt of transition, however, moved southeast in younger rocks, so that in the middle Paleozoic rocks it lies between the Green, Sutton, and Notre Dame Mountains and the Connecticut and St. Johns Rivers. Unconformities indicate stillstand in the miogeosynclinal zone, and general uplift of the northwestern part of the orthogeosyncline, followed by subaerial denudation of the geanticlines in both the eugeosynclinal and the miogeosynclinal zones and by repeated geosynclinal folding. The unconformities are within the lower Paleozoic (especially beneath the Middle Ordovician), are the most extensive between the lower and middle Paleozoic, and are within the middle Paleozoic (especially beneath the Lower Devonian). Geanticlines, two of which coincide with gravity highs, are recognized by unconformable overlap and convergence of bedded rock units toward their axes. The lower Paleozoic Vermont-Quebec geanticline is northwest of the Green and Sutton Mountains in northwestern Vermont and neighboring parts of Quebec, but to the south and northeast it swings more into line with the mountains. It coincides with the lower Paleozoic belt of northwest-southeast transition from the miogeosynclinal to the eugeosynclinal zone, except near the north end of the Sutton Mountains where it trends into the eugeosynclinal zone. The lower Paleozoic Stoke Mountain geanticline coincides with the Stoke Mountains in Quebec, contains eugeosynclinal lower Paleozoic rocks, and is a little north-west of the belt of transition southeastward between the middle Paleozoic miogeosynclinal and eugeosynclinal zones. The lower and middle Paleozoic Somerset geanticline, which nearly coincides with the upper Connecticut River valley and the Boundary Mountains between Quebec and Maine, is cored by rocks of the lower Paleozoic eugeosynclinal zone and is truncated by the unconformity beneath middle Paleozoic rocks. The distribution of the preorogenic igneous rocks of the eugeosynclinal zone reflects the southeastward retreat of this zone during the lower and middle Paleozoic. These rocks include mafic to intermediate metavolcanic and hypabyssal bodies, prevailingly of oceanic theoleiitic composition, and mafic and ultramafic plutons. The plutons reach Lower Cambrian to possibly Middle Ordovician stratigraphic levels. The eugeosynclinal zone, and to a lesser extent the miogeosynclinal zone, are sites of regional metamorphism, shown most universally by the foliation that began to form with compaction of the shales. Isograds climb from low stratigraphic levels in the geanticlines to higher stratigraphic levels in the intervening geosynclinal troughs, showing a direct correlation between the thickness of bedded rocks and metamorphic intensity. Zones of highest grade metamorphism coincide with uplifts, but were probably originally deepest in the geosynclines. Undeformed garnet and staurolite-kyanite coincide with domes and arches, and deformed garnet and chloritoid-kyanite zones with anticlines. Some staurolite and sillimanite zones adjoin granitic plutons, but others are not so associated. Retrograde metamorphic effects in the Precambrian basement include replacement of garnet and hornblende by biotite and chlorite, and sillimanite by muscovite; these effects are caused by folding of the dry basement with the wet Paleozoic. In wet Paleozoic rocks, midway between the dry terranes of the basement and the domes and arches, garnet was replaced by chlorite and kyanite was replaced by muscovite as a result of uplift, denudation and cooling. In Quebec, an exogeosyncline containing about 5000 feet of rocks overlies the northwestern part of the orthogeosyncline and the adjoining craton north-west of the Sutton Mountains. This is a secondary geosyncline northwest of the Vermont-Quebec geanticline. It contains Upper Ordovician sandstone, shale, and limestone which overlie shale at the top of the lower Paleozoic miogeo-synclinal zone but which are eroded from the eugeosynclinal zone. The orthogeosyncline swings through the wide bend of the northwesterly bulge of the New England salient in northern New England and adjacent Quebec—all facies zones and tectonic features show a similar salient. It is deepened near the axis of the salient in a transverse trough that contains as much as 80,000 feet of strata. This section thins by stratigraphic convergence to less than 50,000 feet toward the flanks of the salient. The rocks are most varied in the salient, but thick sections of mafic volcanic rocks and carbonaceous pelites are characteristic. Similar (passive and flexural flow) folds confined to the lower and middle Paleozoic bedded rocks and commonly overturned to the northwest toward the craton, are of an early regime of variously oriented folds. Cross folds, chiefly minor folds, trend northwest at right angles to the northeast structural trends. Longitudinal folds, slides, intrastratal intrusions, and syntectonic bodies of ultramafic rock that intruded in the solid state parallel the latter trends. Oblique folds parallel the flanks of the New England salient and swing into continuity with the longitudinal folds northeast and south of the salient and at its axis. The largest major longitudinal folds are thousands of feet above the Precambrian basement. The recumbent middle Paleozoic Skitchewaug nappe, the best known of the major longitudinal folds, is rooted to the southeast in the eugeosynclinal zone. Other recumbent folds exist, but their relations are more controversial. A middle Paleozoic intrastratal diapiric fold has been described west of the Skitchewaug nappe. Major longitudinal folds northwest of the Stoke Mountain geanticline underlie a Middle Ordovician unconformity; others in the same area are truncated by a pre-Silurian unconformity. Longitudinal folds on the Vermont-Quebec geanticline in the vicinity of the international boundary are nearly upright rather than overturned to the northwest. The lower Paleozoic Taconic slide is beneath Cambrian and Lower and Middle Ordovician eugeosynclinal rocks in the Taconic klippe and above autochthonous miogeosynclinal rocks of the same age west of the Vermont-Quebec geanticline and south of the New England salient. The oblique folds face southwest on the south flank of the New England salient in general harmony with the west-facing longitudinal folds, but on the northeast flank of the salient they face southeast. The largest of the oblique folds, like the large longitudinal folds, are thousands of feet above the basement. The early folds and slides were produced by laminar flow and slip and by minimal flexing and thrusting, principally to the northwest. Several episodes of uplift in the eugeosynclinal deposits are probably accountable. The New England salient provided a basement framework that deflected, blocked, or reversed the northwestward movements to form especially the oblique folds and possibly the cross folds. The westward movement of the Taconic slide was probably assisted by maintenance of fluid pore pressure in the root zone near the top of the Vermont-Quebec geanticline by means of westward migration of water expelled from the thick eugeosynclinal deposits to the east during metamorphism. The semiconcordant ultramafic, mafic, and intermediate intrusive rocks in the eugeosynclinal zone are subparallel to the foliation of the bedded rocks and syntectonic with the early longitudinal folds. The ultramafic rocks were emplaced in a solid and cool state, after transport that is interpreted as northwestward movement as the enclosing strata were folded. The less widely distributed gabbro and diorite, which lost their mobility with crystallization from magma, participated less actively in the folding. Concordant calc-alkalic plutons, also emplaced in eugeosynclinal rocks, are synkinematic magmatic features that are less commonly parallel to foliation than are the semiconcordant intrusive rocks and are truncated upward by unconformities at successively higher levels in the direction of southeastward offlap of the eugeosynclinal zone. Regional foliation, subparallel to both the axial surfaces and limbs and the axial-plane cleavage of the early folds, approaches parallelism with the bedding in most places inasmuch as early minor folds are sparse. Thus restored, the foliation conforms to the geosynclines and geanticlines, masking the Taconic slide. Sericitic mica and fine-grained chlorite, the principal foliate minerals, are features of low-grade regional metamorphism that progressed upward as the eugeosynclinal deposits accumulated, as shown by successive unconformities that mark sharp upward decreases in the foliate condition of the bedded rocks. A longitudinal tract of middle Paleozoic domes and arches, characterized by drag folds that face downdip and some of which are cored by Precambrian basement rocks, trends northeastward across the Vermont-Quebec geanticline in southern Vermont. Largest in this tract is the Strafford-Willoughby arch which extends about equal distances northeast and southwest of the axis of the New England salient. The reverse drag folds are in the regional foliation, which near the crest of the domes and arches is obliterated by a new foliation that parallels the axial surfaces of the drag folds. The reverse drags indicate that the domes and arches were raised by vertical upward pressure, probably of buoyant rock beneath. Grossly parallel (concentric) or flexural folds that trend northeast with the Appalachian structural trends, and the largest of which include the Precambrian basement, are of a late, middle Paleozoic regime. Smaller and variously oriented steeply plunging folds of this regime are above the basement. The principal form surfaces of these folds are the regional foliation in the eugeosynclinal zone and the bedding in the miogeosynclinal zone. Thrust faults, also of this regime, parallel the trend of the major folds. Axial-plane cleavage varies from fracture cleavage through crenulation cleavage to slip cleavage and slip-cleavage schistosity. The parallel fold style gives way to similar (passive-slip and flow) folds in parts of the eugeosynclinal zone. In these parts the form surfaces are offset on the axial-plane cleavage in directions both the same and the opposite of that of flexural drag folds, and the offsets opposite in sense predominate, accentuating the amplitude of the folds. Mineral lineations, less commonly slickensides, and some minor folds plunge downdip on the bedding and bedding foliation near thrust faults and on steep homoclinal limbs of major folds. The late folds form anticlinoria that rudely coincide with the previously formed geanticlines, and synclinoria that coincide with the intervening and adjoining geosynclinal troughs. The axial surfaces of most folds in and south of the New England salient dip steeply southeast and the folds face northwest, but to the north of the axis of the salient the folds are nearly upright. The folds are also nearly upright in eastern Vermont, New Hampshire, and neighboring areas The orientation of the axial surfaces of the folds changes gradually to subparallel with the flanks and tops of the domes and arches as the latter are approached. The folds in the northwestern part of the orthogeosyncline are tipped over to the northwest toward the craton, and the thrust faults in this same belt dip east in the same direction as the axial surfaces of the folds. The late folds of first magnitude are, from northwest to southeast, the Middlebury-Hinesburg-St. Albans synclinorium, the Green Mountain-Sutton Mountain anticlinorium, the Connecticut Valley-Gaspé synclinorium, the Bronson Hill-Boundary Mountain anticlinorium, and the Merrimack synclinorium. The Middlebury-Hinesburg-St. Albans synclinorium is a major foreland fold in lower Paleozoic miogeosynclinal rocks and correlative allochthonous eugeosynclinal rocks of the Taconic klippe. This synclinorium is bordered to the west and east by thrust faults, which are most extensive on the south flank of the New England salient. The Green Mountain-Sutton Mountain anticlinorium, containing chiefly lower Paleozoic eugeosynclinal rocks, coincides with the Vermont-Quebec geanticline in the Green Mountains in central Vermont and the Notre Dame Mountains in Quebec, but near the axis of the New England salient it is southeast of the geanticline. The Connecticut Valley-Gaspé synclinorium, which contains middle Paleozoic rocks transitional from the miogeosynclinal to the eugeosynclinal zone, coincides with a geosynclinal trough between the Stoke Mountain and Somerset geanticlines and southeast of the southern part of the Vermont-Quebec geanticline. The configuration of the folds in the synclinorium is determined principally by the domes and arches near the synclinorial axis The Bronson Hill-Boundary Mountain anticlinorium, which contains both lower and middle Paleozoic rocks, coincides in its northern parts with the Somerset geanticline. The Merrimack synclinorium to the southeast, which also contains lower and middle Paleozoic rocks, is a relic of a geosynclinal trough southeast of the Somerset geanticline. The late folds and thrust faults were probably produced by subhorizontal movements as part of outward spread from the rising domes and arches. Rocks moved from the southeast into the New England salient. Steeply plunging minor folds, free from basement control, evolved in response to horizontal adjustments between major folds, and domes and arches in the thick eugeosynclinal section in the salient. Thrust faults evolved in the miogeosynclinal rocks south of the axis of the salient. The resulting counterclockwise movement of the thrust slices and their included folds and the folded rocks to the east of them in the eugeosynclinal zone continued until the present northward trend was achieved. Monoclinal flexures and related kink layers, which dip northwest and parallel to which rock to the northwest was displaced upward and to the southeast, have been recognized in north-central and northwestern Vermont. Joints include systematically oriented undeformed planar sets that dip almost vertically and cross the trend of the longitudinal folds and thrust faults at large angles. They also include less extensive nonsystematic joints that are curved or irregular and that end against the systematic joints. Some conjugate joint sets, the bisectrices of whose acute angles trend at right angles to the axes of the longitudinal folds, are possibly shear joints. Tension produced by bending of folds into the New England salient seems a doubtful cause of the joints, especially in the thick and deeply confined rocks of the eugeosynclinal zone. Discordant and commonly nonfoliate middle Paleozoic calc-alkalic plutons are postkinematic magmatic features randomly emplaced in rocks deformed in both the early and late folds. They are most abundant near the axis of the New England salient where it crosses the eugeosynclinal zone. Superimposed unconformably on the southeastern part of the orthogeosynclinal belt is an epieugeosyncline, containing upper Paleozoic clastic coal-bearing rocks. Before being eroded it probably covered wider areas of the eugeosynclinal zone, especially in the Merrimack synclinorium. Systems of early Mesozoic high-angle faults, made up of nearly parallel longitudinal sets, strike north-northeast south of the axis of the New England salient and northeast north of the salient axis, parallel to the trends of the late longitudinal folds. Faults in the foreland belt of the Champlain-St. Lawrence Valley are downthrown to the southeast of domal structural features, and others in the Connecticut Valley are downthrown mainly to the northwest of similar features. Lower Mesozoic terrestrial clastic and mafic volcanic (and hypabyssal) rocks unconformably overlie the eugeosynclinal zone and the epieugeosynclines (in taphrogeosynclines bounded by the high-angle faults) in southern New England and the Maritime Provinces. Discordant and nonfoliate Mesozoic alkalic plutons are in curvilinear tracts that transect both the orthogeosynclinal belt and the craton. Dike rocks, also alkalic, are associated with the plutons and occur widely in areas between the plutons. The chronology of the region is supported by biostratigraphic, radiometric, and structural data punctuated by unconformities. The Precambrian chronologic record is inherently scanty. Metasedimentary basement rocks exposed in the Green Mountain-Sutton Mountain anticlinorium in Vermont provide late Precambrian radiometric ages and a regional metamorphic overprint dating from about a billion years ago. Comparable metasedimentary rocks in the basement of the Adirondack Mountains were deposited in the late Precambrian. Pegmatites provide radiometric ages about the same as those of the metamorphic overprint, which records erosional unloading and cooling that restarted the potassium-argon systems about 0.4 b.y. before the end of the Precambrian. The earliest Paleozoic rocks, which are assigned to the Cambrian(?), overlie the Precambrian basement unconformably and are overlain conformably by miogeosynclinal strata containing fossils of Early, Middle, and Late Cambrian and Early and Middle Ordovician age. All epochs of the Cambrian and Ordovician are represented in the eugeosynclinal zone, and Late Ordovician fossils are found in the exogeosyncline. Potassium-argon radiometric values corresponding to Middle and Late Ordovician are mostly hybrids, between Cambrian to Early Ordovician metamorphic dates and the dates of widespread middle Paleozoic metamorphic overprints that with yet later overprints, have been revealed by Rb-Sr whole-rock isochron dating. Granitic plutons emplaced in Middle Ordovician rocks have yielded Middle or Late Ordovician Rb-Sr whole-rock isochron ages. Quasi-cratonic middle Paleozoic strata, eroded from the Champlain-St. Lawrence Valley belt, were probably Upper Silurian or higher. Chiefly in the miogeosynclinal zone, or in comparable thin lithofacies, southeast of the Green Mountain-Sutton Mountain anticlinorium, are Early, Middle, and Late Silurian and Early and Middle Devonian fossils. The middle Paleozoic K-Ar values suggest mainly the time of metamorphism and several are probably hybrids of early dates and true Devonian dates. Southeast of the belt of rocks of hybrid ages is a belt that shows true K-Ar dates of Middle (?) Devonian Acadian metamorphism and deformation about 360 m.y. ago; this belt is without later (Appalachian?) metamorphic overprint, contains Early Devonian fossils, and its tightly folded strata are overlain unconformably by gently flexed strata of Middle Devonian age. Discordant calc-alkalic granitic plutons of comparable radiometric age transect some of the late folds. Rb-Sr whole-rock and Pb/alpha determinations to the southeast in the area of the post-Devonian overprint approximate the Acadian metamorphic date. The late Paleozoic chronology in the northwestern New England and Quebec region is limited to a middle Permian metamorphic overprint with a K-Ar age of 250 ± 10 m.y. in the Merrimack synclinorium and environs. Unmetamorphosed felsic volcanic rocks that lie unconformably on the metamorphic rocks are possibly of Permian age. If this age is correct, the unconformity marks the Appalachian orogeny. The Mesozoic chronology is furnished by high-angle faults that bound the Late Triassic taphrogeosynclinal deposits in southern New England, and by alkalic intrusives of various radiometric ages (96 m.y.-to-180 m.y.), that intersect or are transected by the faults. The Cenozoic chronology is recorded by valleys and uplands produced by a continued selective downwasting, by Tertiary residual deposits containing lignite that were let down into valleys formed partly by solution of carbonate rocks, and by various Quaternary features related principally to glaciation. The orthogeosyncline was formed in the earliest Paleozoic or possibly the latest Precambrian. The Vermont-Quebec geanticline started to form during the Cambrian by tectonic stillstand relative to subsiding adjacent geosynclinal troughs; other geanticlines probably first appeared in the Early to Middle Ordovician. As the geosynclinal troughs subsided, especially in the New England salient, volcanics were extruded and sediments that were derived from the craton, from geanticlines, from volcanic accumulations, and from intrageosynclinal uplifts, were deposited mainly in the troughs. Ultramafic, mafic, and intermediate plutonic rocks were first emplaced at the end of the Cambrian or beginning of the Ordovician in the eugeosynclinal zone, and the ultramafics were transported northwestward tectonically as serpentinization continued. Albitic granitic plutons were emplaced in the Early or Middle Ordovician. Regional foliation that had first appeared in the Cambrian as the geosynclinal troughs subsided continued to form. In the Middle Ordovician, stillstand of the Vermont-Quebec and Stoke Mountain geanticlines gave way to general uplift and denudation which included a westward sliding of the Taconic allochthon. During the late Middle and Late Ordovician, the Somerset geanticline appeared, granitic rocks were emplaced, and the other geanticlines continued as sources of sediments deposited in adjacent geosynclinal troughs, including the exogeosyncline. New generations of early folds formed as geosynclinal subsidence and uplift was renewed. The early Paleozoic closed with general uplift and erosion at and northwest of the Somerset geanticline, culminating in the climax of the Taconic disturbance. The northwestern part of the orthogeosyncline stabilized to a quasi-cratonic belt early in the middle Paleozoic. The miogeosynclinal zone overlapped south-eastward on the eugeosynclinal zone and eventually across the Stoke Mountain geanticline in the Late Silurian and Early Devonian. In the Late Silurian, rapid subsidence resumed in a geosynclinal trough southeast of both the Stoke Mountain geanticline and the southern part of the Vermont-Quebec geanticline that contained the belt of lateral transition from the miogeosynclinal to the eugeosynclinal zone. Meanwhile, the Somerset geanticline continued as a source of part of the eugeosynclinal clastics. An intrageosynclinal uplift from which sediments, recumbent folds, and intrastratal diapiric folds moved northwest and possibly southeast, probably formed in the geosynclinal trough southeast of the Somerset geanticline. Mafic to felsic intrusive rocks, especially concordant calc-alkalic plutons, continued to be emplaced and the regional foliation continued to form in the eugeosynclinal zone. Growth of the domes and arches and concomitant evolution of the late longitudinal folds and thrust faults during the Acadian orogeny climaxed the middle Paleozoic. The discordant calc-alkalic plutons were emplaced soon after, and then, 360 m.y. ago, northwest of the Merrimack synclinorium uplift and erosion followed, as did cooling, opening of joints, and restarting of K-Ar systems. In the late Paleozoic the Merrimack synclinorium stood still, or possibly resumed subsidence to form the northwestern extremity of the epieugeosyncline that is preserved in southeastern New England. The epieugeosyncline was folded, faulted, and uplifted in the Appalachian orogeny, and then, with the adjacent Acadian uplift, was deeply eroded in the early Mesozoic. The taphrogeosyncline in southern New England was formed in the early Mesozoic and was followed in the middle Mesozoic by the alkalic intrusives. Thereafter until the present time, the Paleozoic and Mesozoic terranes were selectively weathered and eroded, and streams that possibly survived from the Appalachian orogeny flowed north-westward in northwestern New England and adjacent Quebec.

Miocene-Pliocene history is recorded in south-central Colorado by sediments deposited in subsiding basins bounded by fault-block mountains and by faulted sedimentary and volcanic deposits lying on a channeled late Eocene erosion surface of regional extent. The San Luis Valley and upper Arkansas Valley are en echelon segments of the Rio Grande trough that are constricted and faulted south of Salida at the northern end of the Sangre de Cristo Range. Great movements on the bounding faults during Neogene time are indicated by clastic and volcanic trough fill, which may be 10,000 m thick near Alamosa and 1,500 m thick near Salida, and by adjoining mountains which stand as much as 1,500 m above the valley floors. The Sangre de Cristo Range owes most of its present elevation to Neogene faulting that cut the Miocene-Pliocene Dry Union Formation and some volcanic deposits in Oligocene-Miocene paleovalleys. Valley fill in the Wet Mountain Valley graben is as much as 1,500 m thick, and at least the upper 300 m of it consists of pinkish beds correlated with the Santa Fe(?) Formation. The crest of the Wet Mountains was uplifted about 400 m above the valley to the west of the mountains and nearly 1,200 m above the high plains which lie to the east. To the north, Neogene faulting elevated the Rampart Range at the front of the Rocky Mountains, dropped the Fourmile Creek graben nearly 400 m, formed complex fault-bounded basins at the southern margin of South Park, and segmented volcanic deposits in paleovalleys that once crossed the upper Arkansas Valley.

Abstract Bristol Dry Lake is situated in the Mojave Desertregion of southeastern San Bernardino County near Amboy, California (Figure 1). It is the largest (155 km-)in a system of three northwest-southeast trending dry lakes (playas) located in a structural trough between the Bristol and Sheep hole Mountains to the north and the Bullion Mountains to the south. This location is one of the most arid places in the U.S.; consequently, Bristol Dry Lake is filled with over 500 m of sediment in the basin center, of which 260 m is almost pure halite. Due to the position of the basins and the amount of sediment that these basins contain, the Bristol-CadizDanby Dry Lake system is important in determining the structural, hydrological, and paleoclimatic development of the Mojave region since the Pliocene.

Abstract Part 3 of this volume contains five papers that illustrate some of the various effects of climate on sedimentation, including studies of climatic controls on sediment supply in marine environments and in desert environments, numerical modeling of ancient climates, and climate influences on the occurrence of petroleum. The paper by Edgar and Cecil relates spatial changes in sedimentation in the Peru–Chile trench (off the west coast of South America) to spatial changes in climate along the Andes Mountain chain. They show that the deepest part of the trench is sediment starved adjacent to the zone where the Andes Mountains are highest and the climate is hyperarid. Fluvial sediment supply is climate dependent, regardless of the heights of mountains in provenance regions. As the climate becomes progressively wetter north and south of the sediment-starved region, the trench is progressively filled, even though the height of the Andes decreases. As an example of climate effects on basin fill, the spatial distribution of sediment in the Peru–Chile trench and the climate of western South America are used as an analogue for the late Paleozoic sediment fill of the Ouachita trough of North America. Edgar and Cecil suggest that the onset of filling of the Ouachita trough is related to the northward drift of the North American craton (from the dry tropics into the wet tropics) rather than the onset of tectonism. The article by Edgar et al. presents shallow seismic interpretations derived from the modern Gulf of Carpentaria, in northern Australia. The seismic data suggest that numerous Pliocene to Recent transgressive–

Abstract The Arkoma basin is in east-southeastern Oklahoma and in west-central Arkansas. The basin was once a part of the large Ouachita geosyncline, and now is one of several structural basins that lie along the northern margin of the Ouachita mountain system, which traverses the southern and southeastern United States. The basin exends for approximately 250 mi in an east-west direction, and is 20-50 mi wide from north to south. The deepest part of this arcuate trough is adjacent to the Ouachita mountain system where the sedimentary column is estimated to be 30,000 ft thick. Rocks in the basin have been highly deformed by a combination of forces. The stability of the Ozark plateau on the north during basin subsidence caused tensional forces to develop which resulted in the evolution of major block faulting in the basin. Evidence indicates that some of these faults were growing contemporaneously with deposition of Lower Pennsylvanian beds. Early Permian (Ouachita) mountain building on the south compressed Arkoma basin beds into a series of long, narrow, east-west anticlinal and synclinal folds. Overthrusting along anticlinal axes near the mountain front is common. Some of the folds have surface expressions extending 75 mi or more. Sedimentary strata in the basin are predominantly dark-gray shale of the Lower Pennsylvanian Atokan Series (Pottsville). Most of the gas production in the Arkoma basin is from lenticular, finegrained sandstone within the Atoka sequence. Sandstone content in the Atoka increases from west to east in the basin, and the entire Atoka sequence is estimated to be 20,000 ft thick along the mountain front in Arkansas. Individual sandstone units in the Atoka are difficult to correlate because of their lenticularity. The basal Atoka sandstone, the Spiro, is an exception. It is the major gas-productive unit in the basin to date, and can be traced over a large area. The Arkoma basin is essentially a dry-gas province with the gas being approximately 95 per cent methane. To date there are about 25 gas-producing zones in the basin, ranging in age from early Des- moinesian (Pennsylvanian) to Simpson (Ordovician). Natural gas first was discovered in the basin in 1902, and sporadic development continued until 1959 when gas was found in the deep Red Oak and Spiro Sands (Atokan) in Latimer County, Oklahoma. This discovery sparked an intensive leasing and deep-drilling campaign. The largest single gas reserve found to date in the basin is the Red Oak field in Latimer County, Oklahoma. The field is 20 mi long and six mi wide at the widest point. The principal productive units are the Red Oak sandstone found near 7,500 ft and the Spiro at about 12,000 ft. Although trapping in some instances is structural, mounting evidence indicates that trapping is primarily stratigraphic in the Arkoma basin. Lack of market and excessive drilling costs have beeen detrimental to development in the past. Major gas outlets now are available, and drilling problems and high expenses have been reduced greatly by use of air and gas as a drilling medium. Topographic problems warrant careful consideration in the planning of drilling operations, because the surface of most of the basin is rugged valley-and- ridge country. It is speculated that the Ouachita mountain area just south of the Arkoma basin will become a new oil- or gas-productive province.

Abstract Traditionally, an abrupt and massive influx of siliciclastic sediments into an area of deposition has been attributed to tectonic uplift without consideration of the influence of climate or climatic change on rates of weathering, erosion, transportation, and deposition. With few exceptions, fluvial sediment transport is minimal in both extremely arid climates and in perhumid (everwet) climates. Maximum sediment transport occurs in climates characterized by strongly seasonal rainfall, where the effect of vegetation on erosion is minimal. The Peru–Chile trench and Andes Mountain system (P–CT/AMS) of the eastern Pacific Ocean clearly illustrates the effects of climate on rates of weathering, erosion, transport, and deep-sea sedimentation. Terrigenous sediment is virtually absent in the arid belt north of lat. 30° S in the P–CT, but in the belt of seasonal rainfall south of lat. 30° S terrigenous sediment is abundant. Spatial variations in the amount and seasonality of annual precipitation are now generally accepted as the cause for this difference. The spatial variation in sediment supply to the P–CT appears to be an excellent modern analogue for the temporal variation in sediment supply to certain ancient systems, such as the Ouachita Trough in the southern United States. By comparison, during the Ordovician through the early Mississippian, sediment was deposited at very slow rates as the Ouachita Trough moved northward through the southern hemisphere dry belt (lat. 10° S to lat. 30° S). The deposystem approached the tropical humid zone during the Mississippian, coincident with increased coarse clastic sedimentation. By the Middle Pennsylvanian (Atokan), the provenance area and the deposystem moved well into the tropical humid zone, and as much as 8,500 m of mineralogically mature (but texturally immature) quartz sand was introduced and deposited. This increase in clastic sediment deposition traditionally has been attributed solely to tectonic activity. However, we contend that the principal control on the introduction of abundant terrigenous sediment was the movement of the deposystem from an arid or semiarid climate into a seasonally wetter climatic regime. The physical and mineralogical maturity of the quartz sand is the result of tropical weathering in provenance areas.

Fossils and rock samples were collected from the Snowy Range Formation at 24 sections measured in the Horseshoe Hills and Bridger Mountains of Montana and eight sections in the vicinity of Yellowstone National Park in Montana and Wyoming. Where the Snowy Range Formation is overlain by the Maywood unit (Devonian), both were measured and sampled, although the Maywood proved to be unfossiliferous. Lowermost of the three members of the Snowy Range is the Dry Creek Shale which lies conformably on the Pilgrim Limestone. It consists of about 50 feet of purplish, thin-bedded, fissile to slightly plastic shale with a few irregular beds of brownish-gray, platy, dolomitic siltstone in the lower three fourths, and some thin beds of silty limestone or limestone-pebble conglomerate in the upper quarter. No evidence is present in this area for subaerial erosion between the Pilgrim and Snowy Range Formations, although beds of siltstone in the Dry Creek may reflect uplift and erosion at the source of terrigenous sediments. The middle member is the Sage, which averages about 200 feet thick where complete. Its base is marked at most localities by a 1-20-foot bioherm of columnar algal limestone; the remainder is a fairly regular alternation of 1–2-foot beds of limestone or limestone-pebble conglomerate with 2–4-foot beds of green shale or very argillaceous greenish-gray limestone. The upper part contains beds of noncolumnar algal limestone. This member was deposited far from shore in shallow turbid water that contained abundant calcium in solution. Microcrystalline calcite ooze, along with fine fragments of fossils and pellets, collected in ripple troughs and other depressions in the mud of the sea floor. These small accumulations became sufficiently consolidated to maintain coherence when excavated by currents that swept away clay particles and concentrated the limestone “pods” into beds that later were cemented to form limestone-pebble conglomerate. The uppermost member, the Grove Creek, is nowhere complete in this area; the upper part was removed by erosion at some localities and by faulting at others. The member consists of about 25 feet of dolomitized limestone-pebble or cobble conglomerate with intercalated beds of dolomitized, gray, splintery shale. This member owes much of its distinctive character to weathering that took place before deposition of the Upper Ordovician Bighorn Formation. The Maywood unit is a Devonian soil or weathered zone that overlies some part of the Snowy Range Formation in the northwestern part of the area of study but overlies formations as low as those in the Precambrian Belt Series or as high as the Upper Ordovician Bighorn Formation in other parts of Montana. It consists of a greatly varying thickness (averaging about 55 feet) of reddish-orange or brown, thin-bedded, silty dolomite or dolomitic limestone. At a few localities it is coarse-grained, thick-bedded, light-brown dolomite. No fossils were found in the Maywood of the area studied, but Devonian fossils have been collected from it in other parts of Montana. Fossils described are 80 species assigned to 48 genera of trilobites, 20 species assigned to 14 genera of brachiopods, four species in four genera of gastropods, two species in one genus of conodonts, one species of sponge, one of graptolite, two form species of algal limestone, and problematica . New taxa are the trilobites Comanchia lippa n.sp., Geragnostus ? insolitus n.sp., Monocheilus demissus n.sp., Pinctus ? artus n.sp., P. ? pullus n.sp., Pseudagnostus sentosus n.sp., Rasettia snowyensis n.sp., Saratogia carita n.sp., S. fracida n.sp., and Taenicephalus gallupensis n.sp.; the brachiopods Angulotreta catheta n.sp., A. glabra n.sp., A. vescula n.sp., Eoorthis remnicha var. A. n. var. and Huenella texana var. fortis n.var. Fossil species in the Snowy Range Formation are assigned to local zones that are based on ranges of genera and species of trilobites and which can be correlated with standard zones of the Cambrian Correlation Chart or with local zones of other areas. A few species from scattered localities near the base of the formation belong to the Aphelaspis or Dunderbergia zones of the Dresbachian Stage. Most species belong to zones in the Franconian. Lower-most of these is the Elvinia Zone (with Camaraspis Subzone and Irvingella major Zonule in the upper part) which corresponds to the Elvinia Zone of the Cambrian Correlation Chart. Next higher is the Taenicephalus Zone (with Parabolinoides Subzone at base) which correlates with the Conaspis Zone of the Chart. Above this is the Idahoia Zone (with basal I. wyomingensis Subzone, middle I. wisconsensis Subzone, and upper I. serapio Subzone) which correlates with the Ptychaspis Subzone of the Ptychaspis-Prosaukia Zone of the Chart. The uppermost zone of the Franconian is the Prosaukia Zone, which is equivalent to the Prosaukia Subzone of the Chart. Species of the Trempealeauan Stage are assigned to the Illaenurus Zone which corresponds to the Lower Trempealeauan of Texas or the lower part of the Saukia Zone of the upper Mississippi Valley. An alternative zonation is offered, based on the ranges of genera and species of brachiopods. Boundaries of most brachiopod zones fall near the levels of the boundaries of trilobite zones, but some do not. The Apsotreta expansa Zone belongs to the Dresbachian Stage. The Linnarssonella Zone and the Angulotreta tetonensis Zone (with Ceratreta-Eoorthis Subzone at base) correspond respectively to the Elvinia and Taenicephalus Zones of the lower part of the Franconian Stage. The Angulotreta vescula Zone corresponds to all but the uppermost part of the Idahoia Zone, and the A. catheta Zone (with Finkelnburgia osceola Subzone at top) is equivalent to this uppermost part of the Idahoia Zone and the entire Prosaukia Zone of the Franconian Stage as well as the entire Illaenurus Zone of the Trempealeauan Stage. No Franconian-Trempealeauan boundary is apparent in the brachiopod zonation.

Abstract The Aquitanian Basin in southwestern France is surrounded by Variscan massifs to the north, northeast, and east, and by a Tertiary chain, the Pyrenees, with a Variscan core, to the south. Toward the west, the extension of the basin beneath the Atlantic remains unknown. The basin is asymmetric, inasmuch as there is a very gentle regional dip of Tertiary and Mesozoic rocks into the basin along the massifs, whereas complicated structural conditions exist along the mobile belt in the south. The denudation products of the Variscan mountains were laid down in the lowlands of the continent during upper Carboniferous and Permian time in the form of sandstones and shales, locally with some coal, covered by red conglomerates and sandstones. The Triassic sediments consist of detritic rocks and evaporites with a short marine invasion in the south; this is the facies of the Germanic or epicontinental Triassic. At the beginning of the Jurassic a marine invasion came from the east, but the facies remains neritic-epicontinental and no trace of a geosynclinal development along the Pyrenees can be seen. During Triassic and Jurassic time the region had already developed a basin-like appearance with the north and east margins rather similar to today's, while the Pyrenees probably formed an island chain. In Lower Cretaceous time a zone of subsidence developed along the general area of the Pyrenees, widening toward the west, and marine sediments several thousand meters in thickness were laid down, while the northern and northeastern part of the basin became dry land. This is the first indication of geosynclinal development in the region of the Pyrenees. During the Upper Cretaceous, two marine invasions took place at about the same time, both coming definitely from the west. The first formed a narrow, long graben-like channel continuing in a restricted way the Lower Cretaceous zone of subsidence; this is the Pyrenean Flysch zone with sediments several thousand meters thick. The second invasion formed a wide and shallow gulf with the base along the Atlantic coast, covering the northern half of the basin. Although contemporaneous with the Flysch zone, limestones of shallow water epicontinental facies, less than 1,000 meters thick, were deposited in this gulf. This sea extended farther northward than that of Lower Cretaceous time and transgressed over the Jurassic. During the Tertiary the gulfs from the Atlantic became gradually smaller, and almost disappeared from the present basin in Pliocene time. Quaternary fluviatile deposits, derived from the Pyrenees and the old massifs, cover much of the older beds, and are in turn covered in the coastal region by aeolic sands. The main orogenic phase in the Pyrenees took place in Eocene time. The structure of the Flysch is very complicated and the Flysch seems to be upthrust onto the foreland. The Jurassic of the basin forms folds with east-west as the predominant trend. The intensity of folding decreases in the Cretaceous and more so in the Lower Tertiary. The Upper Tertiary is almost horizontal. Faulting seems to have been particularly active during Tertiary time; on the margins of the basin a northwestern trend parallel to the grain of the old massifs is very conspicuous, but many other faults of different directions are indicated by seismics. Doubtlessly the movements of the basement have influenced the structure of the sedimentary cover. Almost all surface seepages of oil or gas are located along the Pyrenees, within or close to the Flysch trough. Many are connected with Triassic diapirs and range in age from Miocene to Aptian. Numerous shows have been encountered in wells in the same area, from Eocene to Triassic. Triassic oil shows have been found by recent drilling northwest and southeast of Bordeaux. Many structures in and close to the foothill belt have been drilled, but most of them are dry. At present one gas field is producing from Cenomanian at St. Marcet in the Flysch zone. One oil field at Lacq, close to the Flysch zone, is producing heavy sulfurous oil from the Senonian; a gas deposit in the Lower Cretaceous is not yet producing. In 1954 what appears to be a major oil field with rather light sweet oil in Lower Cretaceous dolomite, was discovered at Parentis, 80 kilometers southwest of Bordeaux.