tectonostratigraphy of the north alpine foreland basin correlation of tertiary depositional cycles and orogenic phases abstract tectonostratigraphic analysis of the depositional history of the north alpine foreland basin indicates that temporal relationships exist between short term events in the foredeep and the adjacent alpine orogen the foredeep can be divided stratigraphically into an alpine foredeep thanetian bartonian pre molasse basin latest bartonian earliest rupelian and molasse basin rupelian tortonian their general and tectonostratigraphic development includes time significant cycle sets and so called cenozoic rift and foredeep crf sequences which are apparently correlative to both foreland and orogen deformation events as well as to changes in global sea level individual basin fill sequences and consequently general stratigraphic and palaeogeographical aspects of the evolving basin system are thus found to be frequently defined by contemporaneous widely distributed tectonics and eustasy successive dominant depositional states underfilled steady state and overfilled episodes and facies flysch molasse are correlated with different concurrently progressing phases of the convergence and subduction history of the european and apulian plates

comparative tertiary stratigraphy of the rhine graben bresse graben and molasse basin correlation of alpine foreland events abstract comparative tectonostratigraphic analysis of the tertiary middle eocene pliocene of the rhine bresse graben system and the western molasse basin demonstrates the occurrence of eleven correlative sequences crf i xi these show a close relationship between intra basinal tectonics and depositional history their punctuated sediment accumulation can be related to phases of extra alpine taphrogenesis and alpine orogenesis and to coeval eustatic changes in sea level apparent simultaneity in rift and foredeep sequence development structural deformation and global change in sea level suggests a common causal control in which the development of the alps played an important role

tectonics climate and the rise and demise of continental aquatic species richness hotspots continental aquatic species richness hotspots are unevenly distributed across the planet in present day europe only two centers of biodiversity exist lake ohrid on the balkans and the caspian sea during the neogene a wide variety of hotspots developed in a series of long lived lakes the mechanisms underlying the presence of richness hotspots in different geological periods have not been properly examined thus far based on miocene to recent gastropod distributions we show that the existence and evolution of such hotspots in inland water systems are tightly linked to the geodynamic history of the european continent both past and present hotspots are related to the formation and persistence of long lived lake systems in geological basins or to isolation of existing inland basins and embayments from the marine realm the faunal evolution within hotspots highly depends on warm climates and surface area during the quaternary icehouse climate and extensive glaciations limnic biodiversity sustained a severe decline across the continent and most former hotspots disappeared the recent gastropod distribution is mainly a geologically young pattern formed after the last glacial maximum 19 ky and subsequent formation of postglacial lakes the major hotspots today are related to long lived lakes in preglacially formed permanently subsiding geological basins

groundwater and microbial processes of alabama coastal plain aquifers 1 we integrate groundwater geochemistry microbiology and numerical modeling techniques to study the origin of elevated salinity and chemical evolution of groundwaters in the coastal plain aquifers of alabama our field data indicate that chemical composition of groundwater evolves by various geochemical and microbial processes as it moves deeper into the subsurface sequential peaks of ca2 mg2 k and na along flow paths indicate that separation of ions may be driven by cation exchange microbial mediated reactions are important for the formation of several discrete hydrochemical zones containing fe2 mn2 sr2 and so42 rich groundwaters elevated fe2 mn2 and sr2 concentrations may be derived from bacterial iron and manganese reduction high sulfate concentrations observed a short distance from the recharge may be partly explained by microbial sulfur oxidation and nitrate reduction denitrification the presence of denitrifying and sulfur oxidizing bacteria in water further supports these reactions major ion compositions and d and 18o values are used to determine the source of salinity and the nature of mixing of different groundwaters three water types were identified these include carbonate groundwater brines associated with evaporites and groundwater of meteoric origin groundwater age differences and flow velocities were calculated using the 36cl cl ratios calculated groundwater flow velocities within the eutaw and tuscaloosa aquifers are about 0 20 m yr and 0 15 m yr respectively we modeled basin scale hydrologic and solute transport processes in a cross section extending from the aquifer outcrops to the gulf coast the modeling result shows that the buried jurassic louann salt can significantly increase groundwater salinity in the overlying coastal plain aquifers by density driven advection and hydrodynamic dispersion the modeling results are consistent with cl br ratios and o h isotope signatures which indicate that salinity of the groundwater could be derived from seawater that has been evaporated beyond halite saturation the predicted groundwater flow pattern reveals the mixing of meteoric water carbonate groundwater from the ordovician knox group and saline brines associated with the louann salt the hydrologic model is consistent with the hydrochemical facies distribution in the alabama coastal plain

sedimentary sequences seismic facies subsidence analysis and evolution of the burdigalian upper marine molasse group central switzerland the sedimentological interpretation of seismic and borehole data derived from the burdigalian upper marine molasse group of the central north alpine foreland basin enables a detailed reconstruction of the shallow marine architecture the different seismic facies are assigned to the shoreface foreshore nearshore and offshore depositional systems mapping of the seismic facies on the seismic line reveals the presence of two prograding sequences luzern and st gallen formations that are separated by an unconformity the subsidence analysis suggests that the evolution of the upper marine molasse was primarily controlled by the interaction between tectonic subsidence and sediment supply the distal transgressions of the luzern and st gallen formations and the establishment of shallow marine environments were caused by enhanced subsidence rates in the distal reaches associated with increased sediment supply rates the development of the sequence boundaries separating the luzern and st gallen formations and the regression at the end of the st gallen formation however were controlled by uplift in the distal part of the basin the subsidence and sediment flux analyses of the upper marine molasse allow an improved understanding of the tectonic and denudation history of the northern alps out of sequence thickening in the rear of the northern alps by underplating of the aar massif and forward thrusting of the helvetic nappes is interpreted to have controlled uplift in the distal part of the basin and the formation of the sequence boundaries in sequence crustal thickening at the tip of the orogenic wedge by forward underthrusting of lower freshwater molasse thrust sheets beneath molasse deposits associated with enhanced erosion of the northern alps caused a northward shift of the location of the major orogenic load and an increase of the sediment supply to the molasse basin these processes are interpreted to have controlled the distal shifts of the basin depocenter and the distal transgressions of the luzern and st gallen formations

intraplate stresses a new tectonic mechanism for fluctuations of relative sea level stress variations in the lithosphere of a few hundred bars can explain the major part of the seismostratigraphic record at passive margins and intracratonic basins however to induce apparent sea level fluctuations with magnitudes greater than 50 m changes in stress level of more than 1 kbar are required these must be related to major reorganizations at convergent plate boundaries fragmentation of plates or collision processes specific rapid falls in the vail et al curves can be associated quantitatively with particular plate tectonic reorganizations of lithospheric stress fields the seismostratigraphic record may provide a new source of information on paleo stress fields to be correlated with results of independent numerical modeling of intraplate stresses

emplacement age of post tectonic granites in southern guinea west africa and the peninsular florida subsurface implications for origins of southern appalachian exotic terranes the coyah granite of guinea intruded western portions of the rokelide orogen following a tectonothermal event at ca 550 ma it records a biotite muscovite plus whole rock rb sr isochron age of 533 7 m y mswd 1 6 which is interpreted to closely date crystallization the osceola granite represents a major lithotectonic element in the pre cretaceous crystalline basement of peninsular florida five biotite concentrates from cuttings recovered from four wells penetrating the pluton record 40ar 39ar plateau ages ranging between 527 4 1 9 m y and 534 6 2 0 m y petrographic characteristics of the four samples suggest relatively rapid post magmatic cooling and the plateau ages are interpreted to closely date emplacement of the pluton similarities in age and petrographic characteristics combine to suggest that the coyah and osceola granites were initially part of a sequence of plutons emplaced along the northwestern margin of the gondwana continent portions of this terrane amalgamated with laurentia during late paleozoic assembly of pangea various exotic lithotectonic terranes which had previously accreted or were at least proximal to the north american craton were transported to their present structural position in the southern central appalachian orogen during this collision

tectonostratigraphy of the west alpine foreland correlation of tertiary sedimentary sequences changes in eustatic sea level and stress regimes abstract analysis of the tertiary depositional history of the west alpine foreland shows that its different basins were governed by essentially synchronous tectonostratigraphic scenarios the tectono sedimentary records of the west alpine foredeep and molasse basin and the rhone and massif central grabens demonstrate successions of tectonic deformation events and so called cenozoic rift and foredeep crf sequences which correlate to both changes in eustatic sea level and coeval modification in foreland stress regime since correlative successions developed in the north alpine foreland it seems likely that the western and northern alpine foreland stress fields were repeatedly modified at the same time compressional stresses associated with the intermittent tectonic and sedimentary changes in the foreland originated firstly from the alpine and pyrenean orogens in conjunction with the episodic history of the foreland stress regime the syn orogenic accumulation of widespread tectono sedimentary sequences reflects sequential kinematic events in the adjacent mountain chains the apparent synchroneity of the tectonostratigraphic events in the principal basins of the west alpine foreland testifies for a common geodynamic cause for the occurrence of correlative series of widespread tectonic phases and crf subdivisions

refraction seismic investigations of the northern massif central france abstract new refraction seismic data have been obtained in the northern french massif central seven shots were recorded simultaneously on two parallel nnw sse i e perpendicular to the surface structures oriented profiles allowing for inline and fan interpretations the results of a 2d interpretation reveal a large scale updoming of the moho of about 2 km compared to average western europe corresponding to the cenozoic uplift of the massif central local crustal thinning of up to 20 is restricted to the cenozoic grabens as seen at the surface beneath the volcanic area of cantal one of the largest cenozoic european shield volcanoes which was active in miocene to recent times significant crustal thickening of 2 3 km is observed velocities in the upper mantle are generally in the range of 7 9 8 1 km s beneath the limagne graben and surrounding undisturbed areas underneath the volcanic area of cezallier however velocity is reduced to about 7 7 km s corresponding to the area of crustal thickening therefore the low velocity in this zone is explained by the remainders of cooling magma chambers and heating by ascending hot plume material the cenozoic tectonic evolution of the massif central has affected crust and upper mantle in different ways oligocene rifting corresponds well to local crustal thinning but no correlation is detected to velocities of the upper mantle in contrast the volanic event occurring since miocene times is related to upper mantle velocity reduction and crustal thickening due to underplating

tectonics of the southern and central appalachian internides the appalachian orogen was constructed along the ancient precambrian continental margin of eastern north america by a series of compressional events that began in the ordovician and episodically spanned much of the paleozoic era the processes of accretion of suspect and exotic terranes together with terrane collision and ultimately completion of the wilson cycle by continent continent collision resulted in construction of the appalachian orogen figure 1 these paleogeographic elements are rep resented by the various lithotectonic units visible today in the southern and central appalachians figure 2 these subdivisions represent the late precambrian rifted margin and early paleozoic platform that were formed directly upon north american grenvillian basement cumberland allegheny plateau valley and ridge and western blue ridge the offshore north american slope rise assemblage hamburg klippe southern appalachian eastern blue ridge and inner piedmont and higher thrust sheets of the maryland northern virginia piedmont and the exotic carolina or avalon and wilmington terranes the carolina ter rane contains the alleghanian high grade metamorphic core these elements form the basis for this analysis and review of the present state of knowledge of the tectonic history of the southern and central appalachian internides the appalachian orogen has been the subject of study by geologists at least since the early nineteenth century early fundamental concepts such as the geosynclinal theory of mountain building dana 1873 hall 1883

some comparisons of the structure and evolution of the southern appalachian ouachita orogen and portions of the trans european suture zone region abstract many aspects of the tectonic history of the appalachian ouachita orogen and the trans european suture region are similar in a tectonic sense they are geographically linked because at the end of the paleozoic one could travel from texas to poland following a continuous orogenic belt much of each of these orogenic belts is however buried by younger strata and thus geophysical studies are a key element of efforts to better understand them many more geophysical data are needed to provide a comprehensive picture of the deep structure but in several areas new models of the lithospheric structure are emerging in this paper we review some of these models and introduce two new ones for the southern appalachians in addition we explore the implications of these models for the evolution of these orogenic belts drawing attention to similarities and differences in their structure and evolution the appalachian and caledonian orogens represent temporally parallel development along irregular late proterozoic continental margins but the crustal structure is different because of different accretionary elements and complications in the geometry of the original margins lateral transport via thrusting can confuse efforts to tie geologic structures identified on the surface with deep structures for example in the appalachian ouachita orogen the thrust related transport distance for major features such as the blue ridge piedmont sheet and the benton uplift is at least 200 km on a crustal scale deformation in the appalachian ouachita orogen varies greatly in style and intensity in the ouachita orogen the late proterozoic continental margin seems to be preserved while in the northern appalachians crustal scale deformation is intense along the us appalachians the major crustal structure variation is the thin dense crust of avalonia abutting the relatively thick crust of laurentia along the ouachita orogen several large crustal blocks can be identified that are unlike anything seen along the appalachians

miogeoclines and suspect terranes of the caledonian appalachian orogen tectonic patterns in the north atlantic region the caledonian appalachian orogen was formed by the closing of a paleozoic iapetus ocean the continental margins of iapetus are identified in the deformed early paleozoic miogeoclines of the caledonian appalachian orogen ophiolitic vestiges of iapetus its oceanic plateaus microcontinents and volcanic arcs are caledonian appalachian suspect terranes these were assembled in interior parts of the orogen and locally they were emplaced structurally upon the adjacent miogeoclines the modern north atlantic ocean opened along an axis that traversed the paleozoic orogen longitudinally its opening dispersed the elements of the paleozoic orogen and led to the present arrangement of disjunct paleozoic miogeoclines and suspect terranes throughout the north atlantic borderlands the western or north american margin of iapetus is represented by the miogeoclines along the west flank of the north american appalachians and caledonides of east greenland a small north american miogeoclinal segment occurs in the britis

mississippian fossils from southern appalachian metamorphic rocks and their implications for late paleozoic tectonic evolution fossils of periastron reticulatum unger emended beck recovered from the erin slate of the talladega slate belt of alabama establish that these rocks have a mississippian kinderhookian tournaisian age the talladega slate belt the southwestern extension of the western blue ridge belt was interpreted to have been affected by regional dynamothermal metamorphism and coeval deformation as a result of the acadian orogeny this fossil find indicates that metamorphism and deformation of the talladega belt occurred after the early carboniferous alleghanian requiring a reevaluation of tectonic interpretations of the southernmost appalachians

stress field changes in the rhone valley from the miocene to the present abstract study of the deformation of neogene and quaternary deposits in the rhone valley shows that the end miocene e w greatest principal compression 1 that deformed the western alps did not continue into the quaternary at least between vienne and montelimar the middle to upper miocene molasse on the east side of the rhone valley was affected by e w compression at the end of the miocene causing reverse faulting and n s folding st lattier and varacieux anticlines in contrast the pliocene sands and clays of the rhone valley are unaffected by folding and show only small normal faults with a maximum throw of l m trending between n s and nw se these were caused by e w to ne sw extension which is incompatible with the e w compression that characterises the latest miocene alpine phase these structures are the surface expression of extension that was probably induced locally by the overall compressive regime that exists to the present day in this part of western europe the transcurrent extensional regime of philip 1983 ustl thesis montpellier this stress field results from the collision of the african and european plates that began in the tertiary west of the frontal pennine thrust the present day direction of compression which is deduced from calculated focal mechanisms and from in situ stress measurements varies between n s and nw se in the grenoble region and the northern massif central the focal mechanisms indicate transcurrent movement with 1 horizontal and oriented between n s and nw se and with 2 vertical in the southwestern massif central and the vendee however they indicate an extensional tectonic regime with 1 vertical and 2 horizontal and oriented nw se 3 trends ne sw this orientation is similar to that which would have caused the small pliocene normal faulting observed in the rhone valley between vienne and montelimar in this part of the rhone valley west of the frontal pennine thrust the e w stress resulting from the collision of apulia italy with the west european plate has not been in evidence since the pliocene the e w compression has been replaced by n s to nw se compression resulting directly from the collision between the african and european plates transmitted through the straits of gibraltar and the iberian microplate in the west and the corsica sardina block in the east the piercing effect of the apulian block is no longer dominant in the rhone valley

is the brunswick magnetic anomaly really the alleghanian suture the southeastern margin of the united states presents a complex picture of accreted paleozoic terranes and a rift related mesozoic overlap assemblage buried by a thick veneer of coastal plain sediments basement terranes have been defined on the basis of drilling and geophysical data their relationship to each other and to plate tectonics is in debate the brunswick magnetic anomaly in georgia has been cited as the location of the late paleozoic suture between north america and a continental fragment with african affinities known from the northern florida subcrop this paper poses a new plate model for this region based upon the following assumptions 1 that deep well tests furnish a reasonable data set for the discrimination of various basement rock types across the region and 2 that the brunswick anomaly is the outboard limit of the north american piedmont avalon terrane we propose that the area between the northwest limit of african rocks and the trace of the brunswick anomaly is a region of crustal overlap as african related rocks were overthrust to the northwest the original irregular outline of the north american continental margin and the landward extensions of oceanic fracture zones are intimately related to the kinematics of suspect terranes in the appalachian orogen the implications of the model suggest that differential shortening during collision and differential extension during subsequent rifting accommodate movements on repeatedly activated transforms

horizontal shortening control of middle miocene marine siliciclastic accumulation upper marine molasse in the southern termination of the savoy molasse basin northwestern alps southern jura

successive post variscan stress fields in the french massif central and its borders western european plate comparison with geodynamic data abstract structural analysis and particularly microtectonic methods have made it possible to define the different stages of brittle deformation of the massif central basement and the surrounding sedimentary cover from the end of the hercynian orogeny to the end of the tertiary during the stephanian a compressional tectonic regime prevailed regional faults appeared or were react vated reactivation as a result of initial n s compression becoming nw then e w these regional strike slip faults caused local extension which led to the formation of small coal bearing basins this compressional regime which marked the end of the formation of pangea was followed by a series of extension episodes permian triassic extension oscillating around n s e w to nw se extension in the early and middle jurassic and finally n s to ne sw extension in the late jurassic to cretaceous the normal faults formed during these episodes strongly influenced the distribution of emerging continents and sedimentary basins from the campanian 75 ma to the present the convergence of africa and eurasia involved the distribut on of stresses in the west european plate several tectonic episodes are distinguished in the massif central during the eocene approximately n s compression predominated general e w extension in the late eocene oligocene resulted in grabens with general northerly strike mainly in the centre of the massif central and on its east and southeast borders lastly compression varying from nw se to e w in the north and south of the massif central prevailed during the alpine orogenic phase at the end of the miocene these successive stages of brittle deformation are interpreted in the context of the evolution of the west european plate and its displacement in relation to the african plate the correspondences between the major geodynamic periods and the distribution of stresses over the west european continent are noted as well as the problems which remair to be resolved

the provenance of sediments in the barreme thrust top basin haute provence france abstract this paper records the results of an integrated analysis of heavy minerals sedimentary facies palaeocurrents and structural data the objective of the study was to evaluate the provenance of the sediments of the barreme thrust top basin this basin contains a late eocene to late oligocene succession of shallow marine alluvial and lacustrine sediments late eocene marine transgression resulted in starvation of clastic supply to the basin hence the calcaires nummulitiques received only a limited influx of heavy minerals derived from local sedimentary sources augmented by the first appearance of assemblages with andesitic affinities at c 42 41 ma clastic members associated with the overlying marnes bleues record a significant diversification of provenance and sediment transport paths clastic detritus supplied to the shallow marine gres de ville were derived from permo triassic sediments to the south conglomeratic submarine channels of the la poste member mark the introduction of alpine ophiolite blueschist derived minerals at c 37 35 ma eroded from the embrun ubaya thrust complex to the ne the deltaic st lions member is dominated by volcaniclastic assemblages completing the marine fill the shoreface gres de senez received detritus from the southerly maures esterel crystalline massif the succeeding oligocene continental sediments record an increasing supply of minerals from alpine lithologies the alluvial molasse rouge contains reworked sedimentary detritus including material cannibalized from the underlying marine tertiary and first cycle alpine minerals the succeeding lacustrine serie saumon serie grise show the increasing diversity of alpine suites the youngest sediments the fluvial gres verts signal a major influx of alpine derived assemblages related to reactivation of the embrun ubaye thrusts between c 28 27 and 25 24 ma

from passive margin to continental collision a tectonic scenario for the western alps general transverse section just south of the pelvoux massif european margin of tethys an ancient atlantic type margin it was subject to extension from triassic to the beginning of late cretaceous times and to collision thereafter as the result of convergence of the eurasian and african continents paleogeographic evolution is outlined a new alpine tectogenetic reconstruction is proposed an attempt is made to establish how the previous extensional structures influenced the later tectonic evolution modified journal abstract

velocity structure and seismicity of southeastern tennessee the seismic zone in southeastern tennessee is at the confluence of major crustal features which have been interpreted largely from potential data and their relation to seismicity could help us understand why major earthquakes sometimes occur in the eastern united states in this paper we solve for the previously unknown velocity structure of the upper crust by an inversion of travel time residuals from relocated earthquakes the gravity anomalies are included by using a linear relation between average anomalous density and average anomalous velocity the velocity model demonstrates that the seismicity is concentrated in areas of average to below average velocity and does not appear to be associated with one of the previously identified major crustal features the high velocity zones mark areas that are generally lacking in seismicity the association of earthquake hypocenters with regions of low velocity crustal rocks is consistent with other intraplate seismic zones and this association supports the conjecture that intraplate earthquakes occur in crust that may have been weakened the velocity anomalies at midcrustal depths do not support the new york alabama ny al lineament as a linear feature extending through southeastern tennessee and parallel to contours in gravity anomalies as originally proposed a continuation of the ny al lineament to the southwest requires either a 15 degree southwestward change in direction or a displacement to be consistent with the velocity anomalies the seismically active areas in southeastern tennessee do not appear to be constrained by the major crustal features but instead the seismicity is characterized by the distribution of hypocenters and their association with low velocity regions at midcrustal depths

reactive transport of trace elements and isotopes in the eutaw coastal plain aquifer alabama 1 we integrate groundwater geochemistry mineralogy and numerical modeling techniques to study the reactive transport of heavy metals and isotopes in the eutaw coastal plain aquifer alabama geochemical data show that the elevated concentrations of fe mn and sr can be correlated with high ph and alkalinity these geochemical correlations suggest that that elevated metal concentrations may be derived from bacterial iron and manganese reduction geochemical modeling of bacterial fe iii and mn iv reduction shows that the biotransformation of iron and manganese minerals could control mobility and concentrations of fe and mn in coastal plain aquifers petrographic sem and edax studies of sediments show the formation of biogenic siderite rhodochrosite and pyrite in sediments associated with fe and mn rich groundwater rhodochrosite and siderite occur together as spheroids 1 0 mm in which rhodochrosite forms the center and siderite forms an outer rind which is consistent with the redox sequence of mineral precipitation predicted by the geochemical modeling the low 13c ratios of siderite and rhodochrosite 14 4 to 15 4 pdb and groundwater dic 20 6 to 14 1 pdb imply carbon of biogenic origin higher dic 13c levels are found to be correlated with elevated fe and mn concentrations and high ph values of groundwater this unexpected result implies novel carbon isotopic fractionation processes associated with bacterial fe iii reduction we used 36cl cl ratios of groundwater and isotope transport modeling to calculate the residence time of regional groundwater in the eutaw aquifer the calculation considering the natural decay only would yield 36cl levels that are significantly higher than field data suggesting that a significant mixing with cl rich older groundwater at depth is an important reason for substantial 36cl depletion along flow path

late paleozoic orogenies in western africa and eastern north america the diachronous closure of theic ocean the carboniferous evolution in western morocco southeastern canada and new england was dominated by intracontinental processes the subsidence of pull apart sedimentary basins and their subsequent deformation during middle carboniferous to early permian times with the development of autochthonous structures and mainly low to medium grade metamorphism on the other hand the structural style of the late carboniferous deformation in the southern appalachians and to a substantial degree also in new england that is related to a continental collision is characterized by deep seated northwest vergent thrusts and medium to high grade metamorphism the mauritanides structures are symmetrically east vergent thrusts this pattern is explained by the diachronous closure of the theic ocean that separated the avalon and carolina microcontinental blocks from paleo gondwana the closure of the theic ocean occurred during devonian times between the northern appalachians and the northwestern edge of paleo gondwana morocco whereas it was achieved only at the end of carboniferous times between the southern appalachians and western africa mauritania senegal the late devonian to early carboniferous counterclockwise rotation of gondwana induced the opening of the pull apart basins of canada new england and morocco as well as later the oblique collision in the southern appalachians and the generalized late paleozoic dextral transcurrent faulting along the northern edge of paleo gondwana

magsat equivalent source anomalies over the southeastern united states implications for crustal magnetization the magsat crustal anomaly field depicts a previously unidentified long wavelength negative anomaly centered over southeastern georgia examination of magsat ascending and descending passes clearly identifies the anomalous region despite the high frequency noise present in the data using ancillary seismic electrical conductivity bouguer gravity and aeromagnetic data a preliminary model of crustal magnetization for the southern appalachian region is presented a lower crust characterized by a pervasive negative magnetization contrast extends from the new york alabama lineament southeast to the fall line in southern georgia and eastern alabama coincident with the brunswick terrane the model calls for lower crustal magnetization contrast of 2 4 a m northern georgia and the carolinas are modeled with contrasts of 1 5 a m large scale blocks in the upper crust which correspond to the blue ridge charlotte belt and carolina slate belt are modeled with magnetization contrasts of 1 2 a m 1 2 a m and 1 2 a m respectively the model accurately reproduces the amplitude of the observed low in the equivalent source magsat anomaly field calculated at 325 km altitude and is spatially consistent with the 400 km lowpass filtered aeromagnetic map of the region

a new isostatic residual gravity map of the conterminous united states with a discussion on the significance of isostatic residual anomalies to display more clearly the gravity anomalies caused by geologic bodies in the upper parts of the crust a new colored isostatic residual gravity map of the conterminous united states has been prepared using the gravity data set compiled for the gravity anomaly map of the united states society of exploration geophysicists 1982 the new isostatic residual gravity map is based on an airy heiskanen model of local compensation in which the surface load requiring compensation is defined by 5 min topographic and bathymetric data sets a colored first vertical derivative map of isostatic residual gravity further enhances the short wavelength anomalies produced by bodies at or near the surface and emphasizes the regional fabrics and trends in the gravity field for the purpose of displaying gravity anomalies caused by shallow bodies of geologic significance the nature of the isostatic model and the values of its parameters are of lesser importance than the application of an isostatic correction of some sort most isostatic models result in residual gravity maps that appear nearly identical in their main patterns and features anomalies on isostatic residual gravity maps should not be casually interpreted in terms of undercompensation or overcompensation because large amplitude anomalies can be produced by crustal bodies in complete local isostatic equilibrium many isostatic residual gravity anomalies less than several hundred kilometers wide can be related to known geologic bodies we present here a classification scheme that attempts to categorize such anomalies on the basis of tectonic environment in general highs correlate with intruded or accreted mafic material or with upthrusted crustal sections whereas lows occur over low density sedimentary or volcanic sections felsic intrusive bodies or down warped crustal sections although some longer wavelength anomalies such as the broad gravity high centered over montana could be manifestations of density contrasts deep in the mantle many such anomalies can also be modeled by geologically reasonable density contrasts that are isostatically compensated and confined to depths of less than several hundred kilometers so that their source bodies need not be deep the fact that certain of these broader anomalies have well defined boundaries which correlate with near surface geologic features increases the likelihood that their sources lie entirely within the lithosphere if so then the density contrasts required to explain the gravity data imply fundamental anomalies in chemical composition or thermal state for the crustal and upper mantle columns under these regions we have investigated spectral analysis as a method to quantitatively characterize regional anomaly patterns contoured plots of normalized amplitude spectra were prepared for various areas of the isostatic residual gravity field of the united states these fourier domain representations show characteristic patterns that can be interpreted in terms of the trends and wavelengths of anomalies and may help to more objectively distinguish geologic basements with different origins or tectonic histories

truncation of the appalachian piedmont beneath the coastal plain of alabama evidence from new magnetic data a new aeromagnetic survey of a part of southern alabama reveals that magnetic signatures of the appalachian piedmont are truncated by a major magnetic lineament beneath the gulf coastal plain mylonitic rocks have been recovered from a drillhole along this lineament which is probably a fault zone of late paleozoic and or triassic jurassic age we suggest that this fault zone may initially have been the alleghanian convergent suture between the north american craton and accreted terranes to the southeast the zone may have been locally reactivated as part of an extensive buried triassic jurassic graben system

surface deformation in houston texas using gps abstract surface deformation in the houston area has been quantified by using a variety of methods including lidar insar extensometers drilling to approximately 100 m and ground penetrating radar in this paper we report on gps data acquired during the period between 1995 and 2005 that found evidence of ongoing subsidence up to 56 mm year in northwestern houston and of possible horizontal surface movement towards the gulf of mexico up to 6 mm year we describe the methods of data processing used in the study and speculate on the possibility that the active elevation of salt domes mainly at the south and east of the city may indirectly influence other surface movements including fault movements and subsidence over areas 1 km 2 making use of our observations and analysis could help in natural hazard mitigation in the houston area and possibly also indicate approaches to surface subsidence study that might be used in other urban areas

pangea in permian to jurassic time the apparent polar wander paths apwps for the northern and southern continents have been redetermined using revised time scales and data when plotted on the conventional pangea pangea a the paths are distinct but essentially linear and parallel from late carboniferous to late permian time both paths then undergo a sharp change in direction and converge so as to overlap in early to middle jurassic time if the permo triassic magnetic field was an axial dipole then paleomagnetic data show that pangea was mobile during most and possibly all of the mid triassic to mid jurassic interval because of the uncertainties in pole ages and positions and errors in measurements the new apwps are consistent with a range of pangeas in particular the data are compatible with two paleomagnetic pangeas a2 and a new class of pangea here named the d pangeas these resemble morel and irving s 1981 pangea b and the c pangeas of smith et al 1981 unlike the a2 pangeas the b c and d pangeas all require large 2000 km relative motion between the northern and southern continents geological data require the transition from an earlier pangea to pangea a to take place along a transform zone here named the pangea transform zone or ptz the ptz is considered to be technically analogous to the great glen fault of scotland four types of possible ptz are examined passing through either the western or eastern end of the brunswick magnetic anomaly of eastern north america or north and south of iberia the geological data suggest that those pangeas that require large displacements on ptzs that pass east of the brunswick magnetic anomaly are improbable b and c pangeas are snapshots giving precise paleomagnetic reconstructions d pangeas fit long stretches of the apwps as well as possible a2 pangeas fit the apwps moderately well but also require the geological displacement to be smaller the differences in displacement between the d and a2 pangeas reflect geometrical relationships between euler poles ptz curvature and the apwps the general geological evidence suggests that d pangeas are less probable than a2 pangeas but that they cannot be rejected transition from a2 to a is most likely to have occurred via a sequence of rotations about different poles rather than a single rotation in detail the conventional pangea requires modification africa must be broken into at least two fragments along the benue trough and its northern continuation northwest africa then fits more tightly into northern south america which modifies the apwps and reduces the gap between them by including the effects of continental extension and using detailed geological data the gap can be reduced to one in which the a63 circles touch or overlap non dipole fields or an expanding earth need not be invoked to explain the mismatch of the apwps on the conventional pangea the finite rotation required for the older pangea to pangea a is very close to van der voo and french s 1974 single rotation for a2 to a but is actually the sum of three smaller rotations that reflect the modification to pangea a continental extension and the postulated ptz displacement of the possible ptzs a ptz parallel to the west african continental magnetic anomaly with a displacement of about 170 km gives a better fit of this anomaly to the east coast magnetic anomaly of north america further refinements to pangea a2 will depend on a better knowledge of stretching factors on the passive continental margins of the modified pangea a and incorporation of rotations due to major faults such as the south atlas fault in morocco

gravity evidence for an alpine buckling of the crust beneath the paris basin abstract the processing of the gravity data of the paris basin has enlightened the existence of crustal ridges these ridges correspond to the zones of different crustal thicknesses in plan view the ridges are concentric with the alpine orogen and were probably controlled by this tertiary alpine mountain building the thinned zones related with the mesozoic and pre mesozoic basins were already existing before the alpine deformations these are of limited size and clearly associated with the basins on a large scale two different domains have been recognized the first one corresponds with a zone where the crust is 37 km thick it is also the place where the tertiary depocentres developed the second one relates with a zone where the crust is 29 30 km thick it has been uplifted during the alpine orogeny these two observations suggest the existence of a tertiary lithospheric buckling beneath the paris basin