an alternative interpretation of the cayman trough evolution from a reidentification of magnetic anomalies magnetic data were collected during the wilkes 1973 and seacarib ii 1987 cruises to the cayman trough a new interpretation of magnetic data is carried out an isochron pattern is drawn up from our anomaly identifications an early eocene age 49 ma ypresian for cayman trough opening is proposed instead of the late oligocene or middle eocene ages suggested by previous studies our plate tectonic reconstruction is simpler and fits the on land geology jamaica and cuba and the tectonics our reconstruction shows a southward propagation of the spreading centre between magnetic anomalies 8 and 6 26 and 20 ma the trough width increases by 30 km in this period the southward propagation of the cayman spreading centre from the middle oligocene to the early miocene induced the development of the restraining bend of the swan islands the formation of a 1 km high scarp on the eastern trace of the cayman trough transform fault walton fault and the formation of a pull apart basin hendrix pull apart magnetic anomalies and magnetization maps give information about the deformation and the rocks the proposed evolutionary model of the cayman trough from the inception of seafloor spreading to the present configuration is presented in relation to the tectonic escape of the northern boundary of the caribbean plate from the maastrichtian to the present

structural evolution of the la trocha fault zone oblique collision and strike slip basins in the cuban orogen 1 the la trocha fault zone acted as a major left lateral transfer zone and is bounded by the la trocha ltf zaza tuinicu ztf cristales ctf and taguasco tgf faults these faults were consistent with the clockwise rotation of convergence and shortening in central cuba from the paleocene to the early eocene 65 48 ma a ssw nne shortening produced transtension in the ltf and transpression in the ztf subsequently during the middle eocene 48 37 ma shortening shifted to a sw ne direction resulting in the normal component of the ltf and transpression in the ztf and ctf since the late eocene 37 ma central cuba has been welded to the north american plate the post welding deformation gave rise to transtension of the ltf and tgf this deformation is consistent with a wsw ene shortening and reflects activity in the transform boundary of the cayman trough both the normal and thrust displacements of these previous faults are corroborated by structural data whereas left lateral displacement is deduced from the concordance between oblique collision and structural features plate kinematics and the structural evolution of the la trocha fault zone indicate that the related central basin is a strike slip polygenetic basin and that the formation of this system i e fault zone strike slip basin was a consequence of the paleogene oblique collision between the caribbean volcanic arc and the bahamas borderland north american plate

magnetostratigraphy of the miocene chiang muan formation northern thailand implication for revised chronology of the earliest miocene hominoid in southeast asia abstract a paleomagnetic study has been conducted on the miocene chiang muan formation in northern thailand in order to provide a chronology for the earliest large bodied miocene hominoid in southeast asia the chiang muan formation is mainly composed of clay silt and sand beds indicating lacustrine and fluvial environments paleomagnetic samples were collected from 124 horizons along an approximately 150 m thick section from the chiang muan formation at the opencast chiang muan mine rock magnetic experiments and stepwise thermal demagnetizations revealed that the main carrier of the magnetization of the sediments is magnetite and the samples have stable magnetization exceptionally stable magnetization is also carried by hematite which is represented by red colored sediments characteristic remanent magnetization chrm directions calculated by the principal component analysis revealed normal or reversed polarities of magnetization which allow the application of the reversal test of mcfadden and mcelhinny mcfadden p l mcelhinny m w 1990 classification of the reverse test in paleomagnetism geophys int 103 725 729 the mean paleomagnetic directions of the normal and reversed polarities passed the reversal test with a classification c indicating that the chiang muan formation preserved the primary magnetization in total five normal and four reversed polarity zones are recognized from the studied section based on paleontological age constraints this magnetostratigraphic column of the chiang muan formation correlates best with chron c5aan c5n of the geomagnetic polarity time scale gpts from the geological time scale gts2004 developed by gradstein et al gradstein f ogg j smith a eds 2004 a geological time scale 2004 cambridge univ press cambridge uk p 589 this correlation revealed that sedimentation of the chiang muan formation began approximately at 13 ma and continued until 9 8 ma with a mean sedimentation rate of approximately 4 2 cm ky the age of the earliest southeast asian hominoid is between 12 4 and 13 0 ma

geochemistry of the mabujina complex central cuba implications on the cuban cretaceous arc rocks the margins of the caribbean plate are marked by cretaceous island arc basalts associated with accreted fragments of the cretaceous colombian caribbean oceanic plateau in cuba the cretaceous volcanic island arc rocks are in fault contact with the mabujina complex interpreted as an oceanic jurassic to early cretaceous arc basement with local island arc rocks the cuban cretaceous island arc consists of early to late cretaceous volcanic series associated with limestones while the pre albian arc rocks consist of tholeiitic basalts and rhyolites the post albian volcanic series is characterized by calc alkaline andesites the cretaceous lavas have sr and nd isotopic compositions similar to the intraoceanic arcs and the pb isotopic initial ratios are close to the east pacific rise mid ocean ridge basalt field according to our data the mabujina arc rocks are tholeiites and calc alkaline basalts developed in a jurassic and or early cretaceous intraoceanic island arc their nd sr and pb isotopic compositions indicate that they derive from a depleted mantle source contaminated by sediments this subduction magmatism is not related to the classic early cretaceous caribbean tholeiitic series but is similar to the late jurassic to early cretaceous guerrero arc terrane from mexico and may represent its southernmost extension thus the different tectonic units of central cuba cannot be easily correlated with those of hispaniola our data also indicate that two different island arcs were tectonically juxtaposed in central cuba the classical lower and upper cretaceous suites of the greater antilles arc and a jurassic to early cretaceous island arc suite with a pacific provenance

actively evolving microplate formation by oblique collision and sideways motion along strike slip faults an example from the northeastern caribbean plate margin abstract the pattern of folding faulting and late quaternary coral reef uplift rates in western and central hispaniola haiti and dominican republic suggest that the elongate gonave microplate a 190 000 km2 area of the northeastern caribbean plate is in the process of shearing off the caribbean plate and accreting to the north american plate late cenozoic transpression between the southeastern bahama platform and the caribbean plate in hispaniola has inhibited the eastward motion of the northeastern corner of the plate transpression is manifested in western and central hispaniola by the formation of regional scale folds that correspond to present day anticlinal topographic mountain chains continuous with offshore anticlinal ridges areas of most rapid quaternary uplift determined from onland coral reefs 125 ka and younger coincide with the axial traces of these folds offshore data suggest recent folding and faulting of the seafloor onshore reef data do not conclusively require late quaternary folding but demonstrate that tectonic uplift rates of the axial areas of the anticlines decrease from the northwest peninsula of haiti 0 37 mm yr to to the central part of the coast of western haiti 0 19 mm yr to the south central part of western haiti 0 mm yr formation of the 1200 km long enriquillo plantain garden walton fault zone as a bypass strike slip fault has isolated the southern edge of the gonave microplate and is allowing continued unimpeded eastward motion of a smaller caribbean plate past the zone of late neogene convergence and quaternary uplift of coral reefs in hispaniola offshore seismic reflection data from the jamaica passage the marine strait separating jamaica and haiti show that the enriquillo plantain garden fault zone forms a narrow but deep active fault bounded trough beneath the passage the active fault is continuous with active faults mapped onshore in western haiti and eastern jamaica the bathymetric deep is present because the jamaica passage fault segment represents a 50 km wide transtensional left step of the fault trace between haiti and jamaica onshore satellite imagery and field observations suggest that the enriquillo plantain garden fault forms a continuous trace extending from central hispaniola east of lake enriquillo dominican republic to the westernmost end of the southern peninsula of haiti the regional lineament corresponds to a recent fault scarp in quaternary alluvium of the clonard pull apart basin in the central part of the southern peninsula of haiti and suggests that at least this part of the lineament has undergone recent slip calmus 1983 has suggested a total offset of 30 50 km of the enriquillo plantain garden fault zone in the southern peninsula of haiti using the apparent offset of lithologic units seismic reflection data from lake enriquillo document recent deformation of quaternary lake sediments where the lineament crosses the lake leveling of the crest of a late holocene coral reef and associated algal tufa around lake enriquillo demonstrate late holocene vertical movement and tilting in a 1500 m wide zone parallel to the fault trend lateral offset is difficult to show in the enriquillo valley area because of rapid recent sedimentation into the valley the pattern of inactive strike slip faults and fold belts of cenozoic age in cuba and the yucatan basin suggest that two elongate microplates were sheared off the proto caribbean plate and accreted to the north american plate by a similar process in paleocene and eocene times age of terminal deformation in western central and eastern cuba is consistent with southeastward younging and migration of arc collision the similarity of the size and sequence of events in cuba suggests that the process of oblique collision and sideways motion of the plate along a new strike slip fault towards a free face may be an important process of microplate formation and interplate transfer in other areas

magnetic polarity stratigraphy stochastic properties of data sampling problems and the evaluation of interpretations a statistical model has been derived which can be used either to test the interpretation of a given magnetic stratigraphy or to make time estimates from the paleomagnetic data the model is based on the presently accepted statistical properties of the earth s magnetic field and the stochastic nature of the paleomagnetic sampling process given knowledge of the number of paleomagnetic sites the distribution of the sites an estimate of the geologic time span sampled and the mean length of the magnetic polarity zones the expected success of the sampling program can be calculated and compared with its actual performance in a number of test cases the theoretical results have agreed with realized results the mean time span for polarity intervals in the late neogene has been established from existing data at 120 000 years once the mean time span for polarity intervals has been established estimates for stratigraphic time span can be made by means of the statistical model of three models studied a time uniform sampling program is the most efficient for establishing a local magnetic polarity stratigraphy the least efficient strategy is an exponential distribution of samples

palaeogene neogene present day growth folding in the bahamian foreland of the cuban fold and thrust belt the santaren anticline constitutes the frontal termination of the cuban fold and thrust belt within the bahamian foreland new well and seismic data allow us to constrain in detail the evolution of this anticline pre growth and syntectonic partly post tectonic units separated by a major unconformity are associated with the santaren anticline their geometrical features are consistent with a detachment fold the precise age of the beginning of fold growth remains unknown however the complete record of well dated syntectonic sediments documents its kinematic evolution from mid eocene to pliocene present day and reveals an approximately constant and very slow growth rate from early miocene to pliocene present day the timing of evolution of the santaren anticline is not consistent with previous models that postulate that deformation associated with the cuban fold and thrust belt ended in the eocene our data suggest that the most external part of the cuban fold and thrust belt was still being deformed under a compressional regime during the late palaeogene neogene and probably during the quaternary we propose that this folding may result from compressive stresses transmitted approximately 400 km northwards from the actual plate boundary as a result of slow convergence between the n and s american plates

mantle circulation models with variational data assimilation inferring past mantle flow and structure from plate motion histories and seismic tomography summary mantle convection models require an initial condition some time in the past because this initial condition is unknown for earth we cannot infer the geological evolution of mantle flow from forward mantle convection calculations even for the most recent mesozoic and cenozoic geological history of our planet here we introduce a fluid dynamic inverse problem to constrain unknown mantle flow back in time from seismic tomographic observations of the mantle and reconstructions of past plate motions using variational data assimilation we derive the generalized inverse of mantle convection and explore the initial condition problem in high resolution 3 d spherical mantle circulation models for a time period of 100 myr roughly comparable to half a mantle overturn we present a synthetic modelling experiment to demonstrate that mid cretaceous mantle structure can be inferred accurately from fluid dynamic inverse modelling assuming present day mantle structure is well known even if an initial first guess assumption about the mid cretaceous mantle involved only a simple 1 d radial temperature profile we also demonstrate that convecting present day mantle structure back in time by reversing the time stepping of the energy equation is insufficient to model the mantle structure of the past the difficulty arises because such backward convection calculations ignore thermal diffusion effects and therefore cannot account for the generation of thermal buoyancy in boundary layers as we go back in time inverse mantle convection modelling should make it possible to infer a number of flow parameters from observational constraints of the mantle

the tectonics and active faulting of haiti from seismicity and tomography oblique convergence of the caribbean and north american plates has partitioned strain across a major transpressional fault system that bisects the island of hispaniola the devastating mw 7 0 2010 earthquake that struck southern haiti rupturing an unknown fault highlighted our limited understanding of regional fault segmentation and its link to plate boundary deformation here we assess seismic activity and fault structures across haiti using data from 33 broadband seismic stations deployed for 16 months we use travel time tomography to obtain relocated hypocenters and models of vp and vp vs crustal structure earthquake locations reveal two clusters of seismic activity the first corresponds to aftershocks of the 2010 earthquake and delineates faults associated with that rupture the second cluster shows shallow activity north of lake enriquillo dominican republic interpreted to have occurred on a north dipping thrust fault crustal seismic velocities show a narrow low velocity region with an increased vp vs ratio 1 80 1 85 dipping underneath the massif de la selle which coincides with a southward dipping zone of hypocenters to a depth of 20 km beneath southern haiti our observations of seismicity and crustal structure in southern haiti suggests a transition in the enriquillo fault system from a near vertical strike slip fault along the southern peninsula to a southward dipping oblique slip fault along the southern border of the cul de sac enriquillo basin this result consistent with recent geodetic results but at odds with the classical seismotectonic interpretation of the enriquillo fault system is an important constraint in our understanding of regional seismic hazard

twenty five million years of subduction accretion exhumation during the late cretaceous tertiary in the northwestern caribbean the trinidad dome escambray complex central cuba the trinidad dome escambray complex central cuba forms part of an accretionary wedge built up during intra oceanic subduction in the caribbean from the late cretaceous 75 ma to tertiary fieldwork microscopic studies p t estimates and new 40ar 39ar isotopic data indicate a tectono metamorphic evolution involving five deformation phases three main stages d1 d2 and d3 were responsible for the subduction exhumation of the units during metamorphic development 40ar 39ar isotopic data allow for the first time an evaluation of the complete time interval from subduction collision to final exhumation d1 deformation took place at 60 5 0 6 ma during subduction and was characterized by a prograde path with hp peak metamorphic conditions in eclogite facies in the monforte nappe the highest structural nappe and greenschist metamorphism in the la sierrita yaguanabo and rio chiquito nappes at lower structural levels d2 deformation 56 32 0 40 ma included a short lived heating event in the lower nappes that caused incipient recrystallization at lower amphibolite facies but was generally linked to decompression and retrograde metamorphism to greenschist conditions during folding and nne thrusting of all nappes parallelism of the main s2 foliation and serpentinite lenses indicates d2 was the main phase of exhumation during d3 exhumation and nne thrusting continued as the units were progressively incorporated into the growing accretionary wedge until about 50 ma structures related to d4 are post metamorphic and reflect the domal structure d5 strike slip and normal faults cut the tectonic pile and low angle normal faults are more abundant towards the dome rim indicating exhumation of the escambray field observations structures and the inverted distribution of the p t conditions in the wedge suggest exhumation mechanisms by underthrusting underplating and erosion combined with extension at the surface subduction accretion exhumation in the trinidad dome thus occurred from 75 to 50 ma indicating a period of 25 million years of deformation history in the northern caribbean realm

the northern caribbean plate boundary in the jamaica passage structure and seismic stratigraphy multibeam bathymetry data and multichannel seismic reflection profiles have been collected at the end of 2012 along the enriquillo plantain garden fault zone epgfz in the jamaica passage between jamaica and hispaniola analysis of the data set reveals the tectonic evolution and the stratigraphic complexity of the northern caribbean boundary stratigraphic correlations with previous marine and on land studies are proposed to place the identified seismic sequences in their regional tectonic history two distinct crustal domains are interpreted typical stratigraphic sequences for the rifted blocks of the eastern cayman trough margin are identified in five basins of the jamaica passage highlighting the eastward limit of the cayman trough margin these inherited basins are deformed and folded during a first phase of compression that could correspond to the regional tectonic rearrangement recorded in the early miocene about 20 ma a distinct crustal domain that we propose to relate to the carib beds caribbean typical reflectors a b and v is identified in the southern part of the jamaica passage indicating that the caribbean large igneous province could extend up to the extreme northeast part of the lower nicaragua rise the left lateral epgfz currently cuts across two pre existing basins the morant and matley basins during the activity of the epgfz these basins are deformed and folded indicating a second phase of compression in contrast the navassa basin located in the middle of the jamaica passage results from the strike slip motion of the epgfz and is interpreted as an asymmetrical basin bordered by the epgfz only on its northern side

paleobiogeography of africa how distinct from gondwana and laurasia abstract although africa was south of the tethys sea and originally belonged to the gondwana its paleobiogeographical history appears to have been distinct from those of both gondwana and laurasia as early as the earliest cretaceous perhaps the late jurassic this history has been more complex than the classical one reconstructed in the context of a dual world gondwana vs laurasia geological and paleobiogeographical data show that africa was isolated from the mid cretaceous albian aptian to early miocene i e for ca 75 million years the isolation of africa was broken intermittently by discontinuous filter routes that linked it to some other gondwanan continents madagascar south america and perhaps india but mainly to laurasia interchanges with gondwana were rare and mainly out of africa dispersals whereas interchanges with laurasia were numerous and bidirectional although mainly from laurasia to africa despite these intermittent connections isolation resulted in remarkable absences poor diversity and emergence of endemic taxa in africa mammals suggest that an african faunal province might have appeared by late jurassic or earliest cretaceous times i e before the opening of the south atlantic during isolation africa was inhabited by vicariant west gondwanan taxa i e taxa inherited from the former south american african block that represent the african autochthonous forms and by immigrants that entered africa owing to filter routes nearly all or all immigrants were of laurasian origin trans tethyan dispersals between africa and laurasia were relatively frequent during the cretaceous and paleogene and are documented as early as the earliest cretaceous or perhaps late jurassic i e perhaps by the time of completion of the tethys between gondwana and laurasia they were permitted by the mediterranean tethyan sill a discontinuous route that connected africa to laurasia and was controlled by sea level changes interchanges first took place between southwestern europe and africa but by the middle eocene a second eastern route the iranian route involved southeastern europe and southwestern asia the iranian route was apparently the filtering precursor of the definitive connection between africa and eurasia the relationships and successive immigrations of mammal mostly placental clades in africa allow the recognition of five to seven phases of trans tethyan dispersals between africa and laurasia that range from the late cretaceous to the eocene oligocene transition these dispersal phases involve dispersals toward laurasia and or toward africa immigrations the immigrations in africa gave rise to faunal assemblages the african faunal strata afss all successful and typical african radiations have arisen from these afss we recognize four to six afss each characterized by a faunal association even major old african clades such as paenungulata or the still controversial afrotheria which belong to the oldest known afs involving placentals ultimately originated from a laurasian stem group africa was an important center of origin of various placental clades their success in africa is probably related to peculiar african conditions endemicity weak competition although strongly marked by endemicity the african placental fauna did not suffer extinctions of major clades when africa contacted eurasia the present geographic configuration began to take shape as early as the mid cretaceous at that time the last connections between africa and other gondwanan continents began to disappear whereas africa was already connected to eurasia by a comparatively effective route of interchange

evidence for late paleozoic and mesozoic non dipole fields provides an explanation for the pangea reconstruction problems abstract paleomagnetic pole positions have long been calculated with the assumption that the ancient geomagnetic field was purely that of a geocentric dipole but in recent years it has become a concern that this assumption is not always valid because of long term contributions from non dipole fields in particular octupole fields we tested for the presence of a zonal octupole field in the late carboniferous permian mesozoic and early tertiary by comparing the observed paleomagnetic paleolatitude distributions for the laurentian north america and greenland and european landmasses with those predicted from the mean paleopoles such a test is possible for a good sized continent not subsequently deformed when numerous and reliable paleomagnetic results exist from sites that cover a wide range of paleolatitudes if the field were purely dipolar coeval results should form a coherent dataset such that a regression line through the individual points in an observed versus predicted paleolatitude plot has a slope of 1 if the slopes of regression lines are systematically different from 1 0 for successive time intervals and granted that the earth s radius stayed the same then it is likely that non dipole fields can be held responsible regression line slopes standard errors for three intervals analyzed are 0 78 0 04 200 300 ma 0 93 0 11 120 200 ma and 0 82 0 06 40 120 ma as might be expected with a non dipole contribution to the total geomagnetic field paleomagnetic results from the most northerly areas of laurentia and europe i e ellesmere greenland and svalbard show clearly anomalous paleolatitudes because of the agreement between the equatorial locations determined independently by paleomagnetism and equatorial rain forest occurrences d v kent p e olsen earth planet sci lett 179 2000 311 324 we argue that long term quadrupole fields are less likely than octupole fields to be the cause of the paleolatitude discrepancies estimates of the magnitude of the octupole dipole field ratio are not very precise but center around 0 1 which could cause errors in conventional paleopole determinations using the dipole formula of 7 5 because of the antisymmetry of octupole fields a comparison of paleomagnetic poles from mid northern and mid southern hemisphere locations could thus be off by as much as 15 the well known misfit between the paleomagnetic results from the laurentia european and gondwana continents in a classical pangea a configuration could be explained by such errors due to octupole fields this explanation would negate the need to seek tectonic pangea b type solutions for the misfit these solutions have generally remained unacceptable in terms of the geology of the gondwana laurussia borderzone

40ar 39ar and u pb evidence for late proterozoic grenville age continental crust in north central cuba and regional tectonic implications renne p r mattinson j m hatten c w somin m onstott t c millfin g and linares e 1989 4 ar 39ar and u pb evidence for late proterozoic grenville age continental crust in north central cuba and regional tectonic implications precambrian res 42 325 341 central cuba is composed of fault bounded tectonostratigraphic terranes juxtaposed and deformed during plate collision and subsequent transform motion between the caribbean and north american plates in the late mesozoiccenozoic one of these the las villas terrane contains crystalline basement rocks thought to be pre upper jurassic on stratigraphic grounds the socorro complex occurs in the northwestern las villas terrane and consists of marbles and siliciclastic metasedimentary rocks and the rio carla granite an 4 ar 39ar plateau date of 903 5 7 1 ma for phlogopite from a marble corroborates previous k ar dates from this unit and establishes unambiguously a late proterozoic age for high grade metamorphism discordance of the 4 ar agar age spectrum can be reliably attributed to diffusive ar loss which if modeled as an episodic thermal event implies a reheating age that closely coincides with the late cretaceous paleogene collision between the caribbean and north american plates u pb zircon data indicate an intrusive age of 172 4 ma for the rio carla granite and reveal an inherited zircon component with an age of 900 ma radio isotopic data from the socorro complex display no evidence of pan african age thermal overprinting these observations combined with constraints provided by published results from nearly pangean landmasses suggest that the complex lay substantially to the southwest present day co ordinates during the early paleozoic following its genesis in the mid mesozoic the caribbean plate evidently transported fragments of an extensive grenville age belt that spanned the americas during the late proterozoic

cenozoic tectonic history of the north america caribbean plate boundary zone in western cuba structural studies of well dated jurassic to lower miocene rocks in western cuba constrain the sequence of structural events affecting this oblique collisional zone between the late cretaceous island arc and the jurassic cretaceous north america passive margin in the southeastern gulf of mexico and straits of florida results of detailed mapping and collection of fault slip data at 34 sites define a regionally consistent five phase tectonic model for the period from the late paleocene to the post early miocene during the late paleocene to the early eocene the cuban island arc collided with the north american passive margin bahamas platform northwest ward overthrusting during the collision defines tectonic phase i a nne ssw compression concurrent with early eocene left lateral strike slip faulting along the pinar fault zone defines phase ii this result is consistent with structural mapping showing sinistral shear within the 065 striking pinar fault zone an ene wsw to e w compression defining phase iii overprinted phase ii faults in the lower eocene and older rocks post early miocene normal faulting characterizes phase iv inversion of fault slip data indicates two contemporaneous directions of tension of 120 and 170 strike slip faults that overprint phase iv normal faults yield a 120 compression phase v the direction of compression associated with the arc continent collision rotates clockwise from nw se in the late paleocene early eocene phase i to nne ssw phase ii and to ene wsw by the middle eocene phase iii the rotation in the compression direction occurred because the arc turned toward an oceanic area in the present day area of central and eastern cuba progressive collision led to complete subduction of the remnant oceanic crust by middle to late eocene time

evaluation of one dimensional site response techniques using borehole arrays abstractnumerical techniques commonly used to compute the dynamic response of soil deposits under earthquake shaking are investigated by analyzing data from instrumented borehole arrays eleven instrumented vertical arrays are investigated using over 650 recorded ground motions that span a range of shaking intensities based on data from the selected borehole arrays site response predictions using one dimensional equivalent linear eql analysis equivalent linear analysis with frequency dependent soil properties eql fd and fully nonlinear nl analysis are compared with the borehole observations the results across all sites indicate that at peak shear strains less than about 0 1 all three site response techniques predict on average site amplification within 20 of observed at peak shear strains larger than 0 1 and at periods less than about 0 4 s eql and nl analyses underpredict site amplification and eql fd analyses overpredict site amplification the underprediction for the eql and nl tech

chronology of the eocene continental deposits of africa magnetostratigraphy and biostratigraphy of the el kohol and glib zegdou formations algeria despite numerous discoveries that have considerably enriched the african arabian tertiary fossil record over the last decades our knowledge of the evolutionary history of many continental african vertebrate groups during the paleogene period remains inadequate particularly when it is compared with the fossil records of europe or north america the eocene epoch in africa is especially poorly documented being restricted to few fossiliferous localities our understanding of the early tertiary emergence diversification and paleobiogeographic history of african arabian mammals has been further hindered by the lack of a precise temporal framework for these sites we conducted magnetostratigraphic analyses associated with biostratigraphic studies in the fossiliferous sequences exposed in the northwestern hammadas of the saharan platform in the glib zegdou area and in the saharan atlas at the el kohol locality algeria to further define the age of these eocene continental deposits based on biostratigraphic constraints the six polarity zones identified in the el kohol section can be correlated with chrons c24n to c22r providing the first direct age estimates for the el kohol fossiliferous strata between 52 and 51 ma correlation to the geomagnetic polarity time scale using previously published biostratigraphic data for the glib zegdou fauna suggests an age ranging between 49 and 45 ma for this section the high resolution magnetostratigraphic study of the poorly known continental eocene epoch of algeria provides new insights into the early tertiary stratigraphy of northwest africa the placement of the algerian localities into a consistent chronological framework constitutes considerable advancement to achieve biostratigraphic correlation of the paleogene african arabian mammal localities

structural and tectonic evolution of western cuba fold and thrust belt 1 we present balanced and restored cross sections across the western cuba fold and thrust belt to illustrate its structure and tectonic evolution based on the interpretation of multichannel seismic profiles field data and balancing techniques the nnw sse trending soroa cross section intersects from south to north 1 the los palacios basin 2 the sierra del rosario antiformal stack 3 the bahia honda thrust unit 4 the frontal 3 km thick imbricated thrust sheets and 5 the foredeep basin at depth a duplex that links the sierra del rosario unit and the frontal imbricates is defined using the thickness of the cover thrust sheets of the imbricated north american margin the minimum calculated shortening is of 130 km in a sse or south direction to fit large scale plate tectonic reconstructions however a more allochthonous alternative using thinner cover sequences is also discussed which restores the bahia honda unit 220 km to the south of its present position syntectonic deposits in combination with a forward kinematic model provide a good constraint for the tectonic evolution of the orogen the internally deformed bahia honda unit overthrusted the north america margin cover successions during danian and selandian times 65 5 60 ma before the stacking of these cover rocks during selandian and thanetian times 60 56 ma the growth of a large antiformal stack beneath the sierra del rosario occurred at early middle eocene 56 45 ma generating about 4 km of structural relief between the paleoisland of cuba and the synorogenic seafloor before the final infill of the foredeep

episodic folding inferred from syntectonic carbonate sedimentation the santaren anticline bahamas foreland abstract sedimentation coeval with growth of the santaren anticline provides an excellent opportunity to study the relationships between sedimentation and anticline uplift through time the santaren anticline is a kilometre scale nw se trending fold offshore of cuba in the bahamas foreland of the cuban fold and thrust belt the growth strata associated with this anticline consist of a thick package of carbonate sediments that were deposited without major interruptions from neogene and perhaps before to present day the excellent seismic resolution and age control of a number of seismic horizons within the growth strata allowed us to define 25 growth beds each of them representing between 0 1 and 3 2 ma an analysis of the thickness of these beds allowed us to determine accurate quantitative values of cumulative decompacted thickness and crestal structural relief at the time of their deposition in addition for the same periods sedimentation and fold uplift rates were calculated moreover some information on relationships between sedimentation and fold uplift rates was inferred from the growth stratal geometry growth beds that overlap the fold crest and thin over it indicate that sedimentation rates outpaced fold growth rates during their deposition some overlapping beds have constant thickness indicating that no fold uplift occurred during their sedimentation the rest of the growth beds exhibit onlap offlap geometries that do not indicate a unique sedimentation fold uplift rate relationship only in those cases in which the geometry of the underlying bed at the end of its deposition is known is it possible to infer a specific sedimentation fold uplift rate relationship as a result of this analysis we have been able to 1 illustrate that the geometry of the growth strata associated with the santaren anticline results from competition between sedimentation and tectonic fold uplift 2 document the episodic and non steady nature of fold growth and 3 show that short term rates at the scale of hundreds of thousands years provide much insight into the interplay between sedimentation and tectonic fold uplift that control the growth stratal patterns

structure and tectonic evolution of the southwestern trinidad dome escambray complex central cuba insights into deformation in an accretionary wedge abstract the trinidad dome escambray complex cuba forms part of an accretionary wedge built during intra oceanic subduction in the caribbean from the late cretaceous to cenozoic the structure reflects syn subduction exhumation during thickening of the wedge followed by extension field mapping metamorphic and structural analysis constrain the tectonic evolution into five stages three ductile deformation events d1 d2 and d3 are related to metamorphism in a compressional setting and formation of several nappes d1 subduction fabrics are only preserved as relict s1 foliation and rootless isoclinal folds strongly overprinted by the main s2 foliation the s2 foliation is parallel to sheared serpentinised lenses that define tectonic contacts suggesting thrust stacks and underthrusting at mantle depths thrusting caused an inverted metamorphic structure with higher grade on top of lower grade nappes exhumation started during d2 when the units were incorporated into the growing accretionary wedge along nne directed thrust faults and was accompanied by substantial decompression and cooling folding and thrusting continued during d3 and marks the transition from ductile to brittle ductile conditions at shallower crustal levels the d4 5 events are related to extension and contributed to the final exhumation likely as a core complex d4 is associated with a regional spaced s4 cleavage late open folds and numerous extension veins whereas d5 is recorded by normal and strike slip faults affecting all nappes the p t path shows rapid exhumation during d2 and slower rates during d3 when the units were progressively incorporated into the accretionary prism the domal shape formed in response to tectonic denudation assisted by normal faulting and erosion at the surface during the final stages of structural development these results support tectonic models of sw subduction of the proto caribbean crust under the caribbean plate during the latest cretaceous and provide insights into the tectonic evolution of accretionary wedges in an intra arc setting

relative motion between the caribbean and north american plates and related boundary zone deformation from a decade of gps observations global positioning system gps measurements in 1986 1994 and 1995 at sites in dominican republic puerto rico cuba and grand turk define the velocity of the caribbean plate relative to north america the data show eastward motion of the caribbean plate at a rate of 21 1 mm yr 1 standard error in the vicinity of southern dominican republic a factor of 2 higher than the nuvel 1a plate motion model prediction of 11 3 mm yr independent measurements on san andres island and an euler vector derived from these data also suggest a rate that is much higher than the nuvel 1a model available data combined with simple elastic strain models give the following slip rate estimates for major left lateral faults in hispaniola 1 the north hispaniola fault offshore the north coast of hispaniola 4 3 mm yr 2 the septentrional fault in northern dominican republic 8 3 mm yr and 3 the enriquillo fault in southern dominican republic and haiti 8 4 mm yr the relatively high plate motion rate and fault slip rates suggested by our study combined with evidence for strain accumulation and historical seismicity imply that seismic risk in the region may be higher than previous estimates based on low plate rate low fault slip rate models and the relatively low rate of seismicity over the last century

crustal structure of western hispaniola haiti from a teleseismic receiver function study haiti located at the northern caribbean plate boundary records a geological history of terrane accretion from cretaceous island arc formations to the eocene to recent oblique collision with the bahamas platform little is presently known about the underlying crustal structure of the island we analyze p waveforms arriving at 27 temporary broadband seismic stations deployed over a distance of 200 km across the major terrane boundaries in haiti to determine the crustal structure of western hispaniola we compute teleseismic receiver functions using the extended time multi taper method and determine crustal thickness and bulk composition vp vs using the h stacking method three distinctive and fault bounded crustal domains defined by their characteristic moho depth distributions and bulk crustal vp vs are imaged across haiti we relate these domains to three crustal terranes that have been accreted along the plate boundary during the northeastwards displacement of the caribbean plate and are presently being deformed in a localized fold and thrust belt in the northern domain made up of volcanic arc facies the crust has a thickness of 23 km and vp vs of 1 75 0 1 typical of average continental crust the crust in the southern domain is part of the caribbean large igneous province caribbean lip and is 22 km thick with vp vs of 1 80 0 03 consistent with plume related rocks of late cretaceous age significantly thicker the crust in central haiti has values of moho depths averaging 41 km and with vp vs of 1 80 0 05 we propose that the central domain is likely constructed of an island arc upper crust with fragments of dense material originating from mafic lavas or lip material we produce a crustal profile along a n s transect across haiti accounting for the surface geology shallow structural history and new seismological constraints provided by variations of crustal thickness and bulk composition

model for the formation of large transtensional basins in zones of tectonic escape tectonic escape is strike slip dominated motion of colliding continental or arc crust in the direction of subductable oceanic crust i describe four examples of large transtensional basins in cenozoic zones of tectonic escape and propose that these basins formed along newly formed transtensional faults formed between the collided and escaping parts of the plate the reoriented direction of the escaping plate split along the new transtensional fault zone is determined by the presence of a free face or subductable oceanic crust continued subduction toward the free face is driven by the force of gravity acting on dense oceanic crust slab pull the four examples presented here show that a variety of transtensional deformational styles can be generated within this specific type of divergent tectonic setting these transtensional styles include pull apart basins at fault stepovers more asymmetrical rift like basins thought to be formed under conditions of fault normal extensional stresses and single or multiple short spreading ridges transtensional styles may be controlled more by the type and age of crust present than the angle of reorientation of the escaping plate

age and spreading history of the cayman trough as determined from depth heat flow and magnetic anomalies the opening of the cayman trough records aspects of relative motion between the north american and caribbean plates essential to accurate reconstruction of caribbean evolution assessment of opening rates based upon basement subsidence analysis as well as magnetic anomaly interpretation shows that the trough may have opened at one third to one half previously proposed rates depths to basement show that the crust has subsided away from the present axis in two stages a younger stage characterized by substantial and asymmetric greater to the east subsidence preceded by an older stage of slight increases of depth with distance depth to age relations calculated from subsidence curves which accommodate lateral as well as vertical cooling of the accreting slab indicate that the trough has opened at an overall rate of less than 15 mm yr since 25 30 ma and at 20 30 mm yr prior to 30 ma marine magnetic anomalies show lineations perpendicular to the trough including a distinct central anomaly but the pattern is neither well defined nor symmetrical about the present axis however partial anomaly sequences can be identified on both sides of the axis and the distribution of these sequences indicates that spreading may have involved frequent short ridge jumps mostly eastward the overall rate of opening as indicated by this interpretation of the magnetics is about 15 and 30 mm yr since and prior to 26 ma both subsidence and magnetics indicate that the trough opened by at least 45 50 ma

palaeomagnetism of the central cuban cretaceous arc sequences and geodynamic implications abstract a detailed palaeomagnetic study of cretaceous age volcanic and sedimentary arc rocks from central cuba has been carried out samples from 32 sites 12 localities were subjected to detailed demagnetisation experiments nineteen sites from the los paso matagua provincial and cabaiguan formations yielded high unblocking temperature dual polarity directions of magnetisation which pass the fold tests with confidence levels of 95 or more and are considered to be primary in origin the palaeomagnetic inclinations are equivalent to palaeolatitudes of 9 n for the aptian 18 n for the albian a synfolding remanence identified in 5 sites from the younger hilario formation indicates a late cretaceous remagnetisation at a palaeolatitude of 16 n our results are in good agreement with previous palaeogeographic models and provide the first high quality palaeomagnetic data demonstrating the gradual northward movement of the cretaceous volcanic arc throughout the cretaceous the declination values obtained all indicate significant and similar amounts of anticlockwise rotation from the oldest sequences studied through to the late cretaceous remagnetisation this rotation is most likely related to collision of the arc with the north american plate and transpressional strike slip movement along the northern margin of the caribbean plate as it progressed eastwards into the large proto caribbean basin

implications of a nonlinear 40ar 39ar age progression along the louisville seamount trail for models of fixed and moving hot spots 1 the louisville seamount trail has been recognized as one of the key examples of hot spot volcanism comparable to the classic volcanic hawaiian emperor lineaments the published total fusion 40ar 39ar data of watts et al 1988 showed an astonishing linear age progression firmly establishing louisville as a fixed hot spot in the south pacific mantle we report new 40ar 39ar ages based on high resolution incremental heating 40ar 39ar dating for the same group of samples showing a marked increase in both precision and accuracy one of the key findings in our reexamination is that the age progression is not linear after all the new data show a significantly decreased apparent plate velocity for the louisville seamount trail older than 62 ma but confirm the linear trend between 47 ma and the present day although based on only three samples over 2150 km the most recent volcanic activity in the louisville seamount trail has now been dated at 1 11 0 04 ma for the most southeastern seamount located at 50 26 s and 139 09 w these results indicate that the louisville age progression should be interpreted on the basis of both plate and hot spot motion in this paper we examine our new results in conjunction with the numerical mantle flow models of steinberger et al 2004 that also predict marked deviations from simple linear age progressions with these models we can achieve a good fit to the geometry of both the hawaiian and louisville seamount trails and their age progressions as well as the 15 paleolatitudinal shift observed by tarduno et al 2003 for the hawaiian hot spot between 80 and 47 ma if the model is restricted to pacific hot spots only we can improve the fit to the nonlinear age trend for the louisville seamount trail by allowing an additional rotation change of the pacific plate around 62 ma and by decreasing the initiation age of the louisville plume from 120 to 90 ma this improved model features a significant eastward hot spot motion of 5 between 80 and 30 ma for the louisville hot spot which is quite dissimilar to the southward motion of the hawaiian hot spot during the same time interval followed by a minor 2 latitudinal shift over the last 30 myr if hot spot tracks are considered globally the age trend observed for the oldest part of the louisville seamount trail does not entirely follow the numerical model predictions this may indicate some remaining inaccuracies in the global plate circuit but it may also indicate that the louisville hot spot experienced a motion somewhat different than in the numerical model faster in the interval between 62 and 47 ma but slower before that

critical parameters affecting bias and variability in site response analyses using kik net downhole array data because of the limited number of strong motion records that have measured ground response at large strains any statistical analyses of seismic site response models subject to strong ground motions are severely limited by a small number of observations recent earthquakes in japan including the m w 9 0 tohoku earthquake of march 2011 have substantially increased the observations of strong motion records that can be used to compare alternative site response models at large strains and can subsequently provide insight into the accuracy and precision of site response models using the kiban kyoshin network kik net downhole array data in japan we analyze the accuracy bias and variability precision resulting from common site response modeling assumptions and we identify critical parameters that significantly contribute to the uncertainty in site response analyses we perform linear and equivalent linear site response analyses at 100 kik net sites using 3720 ground motions ranging in amplitude from weak to strong 204 of these records have peak ground accelerations greater than graphic 1 at the ground surface we find that the maximum shear strain in the soil profile the observed peak ground acceleration at the ground surface and the predominant spectral period of the surface ground motion are the best predictors of where the evaluated models become inaccurate and or imprecise the peak shear strains beyond which linear analyses become inaccurate in predicting surface pseudospectral accelerations psa presumably as a result of nonlinear soil behavior are a function of vibration period and are between 0 01 and 0 1 for periods 0 5 s do not display noticeable effects of nonlinear soil behavior online material site specific information and model residuals at 100 kik net stations 1 embed inline graphic 1 gif

discordant mid cretaceous paleomagnetic pole from the zaza terrane of central cuba thermal demagnetization of samples from five sites in mid cretaceous volcaniclastic and carbonate rocks of south central cuba reveals two or more components of magnetization a pre folding magnetite borne component is recognized in all but was difficult to isolate from secondary components in many specimens remagnetization circle analysis using data for 42 specimens from all five sites yields a pole at 30 7 degree n lat 193 3 degree e long this pole is discordant with respect to the north american apwp indicating 43 degree plus minus 16 degree of anticlockwise rotation and 8 degree plus minus 6 degree of northward displacement since the mid cretaceous this result suggests that part or all of cuba was transported on the caribbean plate before accretion to north america in the eocene

geoframework coupling multiple models of mantle convection within a computational framework solver coupling can extend the capability of existing modeling software and provide a new venue to address previously intractable problems a software package has been developed to couple geophysical solvers demonstrating a method to accurately and efficiently solve multiscale geophysical problems with reengineered software using a computational framework pyre pyre is a modeling framework capable of handling all aspects of the specification and launching of numerical investigations we restructured and ported citcoms a finite element code for mantle convection into the pyre framework two citcoms solvers are coupled to investigate the interaction of a plume at high resolution with global mantle flow at low resolution a comparison of the coupled models with parameterized models demonstrates the accuracy and efficiency of the coupled models and illustrates the limitations and utility of parameterized models

variation of palaeostress patterns along the oriente transform wrench corridor cuba significance for neogene quaternary tectonics of the caribbean realm abstract in this study we address the late miocene to recent tectonic evolution of the north caribbean oriente transform wrench corridor in the southern sierra maestra mountain range se cuba the region has been affected by historical earthquakes and shows many features of brittle deformation in late miocene to pleistocene reef and other shallow water deposits as well as in pre neogene late cretaceous to eocene basement rocks these late miocene to quaternary rocks are faulted fractured and contain calcite and karst filled extension gashes type and orientation of the principal normal palaeostress vary along strike in accordance with observations of large scale submarine structures at the south eastern cuban margin initial n s extension is correlated with a transtensional regime associated with the fault later reactivated by sinistral and or dextral shear mainly along e w oriented strike slip faults sinistral shear predominated and recorded similar kinematics as historical earthquakes in the santiago region we correlate palaeostress changes with the kinematic evolution along the boundary between the north american and caribbean plates three different tectonic regimes were distinguished for the oriente transform wrench corridor otwc compression from late eocene oligocene transtension from late oligocene to miocene d1 and transpression from pliocene to present d2 d4 when this fault became a transform system furthermore present day structures vary along strike of the oriente transform wrench corridor otwc on the south eastern cuban coast with dominantly transpressional compressional and strike slip structures in the east and transtension in the west the focal mechanisms of historical earthquakes are in agreement with the dominant ene wsw transpressional structures found on land

testing the depths to 1 0 and 2 5 km s velocity isosurfaces in a velocity model for japan and implications for ground motion modeling

a plate tectonic model for the mesozoic and early cenozoic history of the caribbean plate abstract we present a model in which the caribbean plate is an intra american feature formed along the caribbean spreading center as opposed to the current model that considers the caribbean plate as a far travelled crustal segment that formed in the pacific region paleomagnetic data which cover an age range from jurassic through paleocene indicate the ophiolite complexes in costa rica and panama formed in an equatorial position the ophiolites did not fundamentally change their position relative to south america since their origin basaltic rocks of the lower part of the ophiolites are of mid ocean ridge type suggesting formation at a spreading center they are interpreted to have formed as part of the proto caribbean crust at a spreading axis in an intra american position during jurassic and early cretaceous times the upper part of the ophiolites is mainly built up by island arc and intraplate basalts the island arc basalts evolved at the central american landbridge which started in the middle cretaceous the intraplate basalts are related to the caribbean plateau basalt which thickened and stiffened the caribbean crust in middle cretaceous to probably campanian times changes in relative plate motions along the middle american convergent plate margin are reflected by orientations and time sequences of paleostress tensors calculated from fault slip data in southern mexico and costa rica kinematic indicators from mylonite zones display sinistral movement along secondary shear zones within the southern mexican crustal complexes and along the northern boundary of the chortis block in the motagua polochic fault system this reflects the eastward drift of the chortis block since the beginning of the cenozoic at this time the chortis block became part of the caribbean plate which moved more than 1000 km towards the east relative to the north and south american plates during the cenozoic

oblique collision in the northeastern caribbean from gps measurements and geological observations 1 previous caribbean gps studies have shown that the rigid interior of the caribbean plate is moving east northeastward 070 at a rate of 18 20 3 mm yr relative to north america this direction implies maximum oblique convergence between the island of hispaniola on the caribbean plate and the 22 27 km thick crust of the bahama carbonate platform on the adjacent north america plate we present a tectonic interpretation of a 15 site gps network which spans the hispaniola bahama oblique collision zone and includes stable plate interior sites on both the north america and caribbean plates measurements span the time period of 1994 1999 in a north america reference frame gps velocities in puerto rico st croix and the lesser antilles indicate that these areas move as a single block in an east northeast direction 070 at a rate of 19 20 mm yr consistent with the movement of the rigid interior of the caribbean plate gps velocities at six sites in central and eastern hispaniola dominican republic show drastically different behavior with more eastwardly strikes 080 and much slower rates 4 17 mm yr than areas of the stable caribbean plate the boundary between the relatively slower moving hispaniola collisional zone and the relatively faster moving uncollided puerto rico virgin islands area is the mona passage where late neogene rifting occurs in a broad zone elastic modeling favors strain partitioning with oblique slip on the outer low angle submarine thrust faults north hispaniola muertos and strike slip on the inner subvertical subaerial strike slip faults septentrional enriquillo

attenuation and velocity structure for site response analyses via downhole seismogram inversion a seismic waveform inversion algorithm is proposed for the estimation of elastic soil properties using low amplitude downhole array recordings based on a global optimization scheme in the wavelet domain complemented by a local least square s fit operator in the frequency domain the hybrid scheme can efficiently identify the optimal solution vicinity in the stochastic search space whereas the best fit model detection is substantially accelerated through the local deterministic inversion results presented for selected aftershocks of the mw 7 0 sanriku minami earthquake in japan recorded by the kik net strong motion network illustrate robustness of the impedance structure estimation by contrast the attenuation structure is shown to be sensitive to the frequency content of seismic input data attributed to the deterministic description of the continuum in the forward model that cannot simulate late arrivals of multiple scattered energy sensitivity analyses illustrate that for the same forward model results can be substantially different based on the definition of the objective function it is concluded that even for engineering purposes inversion should aim to decouple intrinsic and scattering attenuation mechanisms

the origin of intraplate deformation in the atlas system of western and central algeria from jurassic rifting to cenozoic quaternary inversion abstract analysis of petroleum exploration data supplemented by paleostress data enabled discussion of the origin of the deformation in the western and central saharan atlas algeria this intraplate area has recorded the breakup of pangea late triassic the opening of the maghrebian tethys since the dogger and subsequently its closure oligocene to present however the two periods of strong coupling between europe and africa late lutetian and pleistocene which correspond to rapid uplifts of the atlas system and important deformations are not collision related they can be correlated to the beginning and the end of the development of the western mediterranean sea

a reconnaissance paleomagnetic study of cretaceous rocks from central cuba we applied thermal demagnetization to 12 sites of mid and upper cretaceous volcanics and sediments of the zaza terrane central cuba consistent directions of low and or high temperature components were obtained from eight sites the fold test performed on a short wave fold in the upper cretaceous arimao formation is negative as well as the conglomerate test on lava boulders from the same formation whereas site means for the entire data set are better grouped after tilt correction we conclude that the entire cretaceous succession of the zaza terrane was remagnetized in the campanian the measured latitude is lower by 15 6 with respect to the north american apwp indicating ca 1600 600 km northward displacement of the zaza terrane since the campanian also discordant is the measured declination implying 37 11 counterclockwise rotation of the zaza terrane

impediments to predicting site response seismic property estimation and modeling simplifications abstract we compare estimates of the empirical transfer function etf to the plane sh wave theoretical transfer function ttf within a laterally constant medium for invasive and noninvasive estimates of the seismic shear wave slownesses at 13 kiban kyoshin network stations throughout japan the difference between the etf and either of the ttfs is substantially larger than the difference between the two ttfs computed from different estimates of the seismic properties we show that the plane sh wave ttf through a laterally homogeneous medium at vertical incidence inadequately models observed amplifications at most sites for both slowness estimates obtained via downhole measurements and the spectral analysis of surface waves strategies to improve the predictions can be separated into two broad categories improving the measurement of soil properties and improving the theory that maps the 1d soil profile onto spectral amplification using an example site where the 1d plane sh wave formulation poorly predicts the etf we find a more satisfactory fit to the etf by modeling the full wavefield and incorporating spatially correlated variability of the seismic properties we conclude that our ability to model the observed site response transfer function is limited largely by the assumptions of the theoretical formulation rather than the uncertainty of the soil property estimates

magnetostratigraphy and biostratigraphy of the neogene deposits of kastellios hill central crete greece abstract the kastellios hill section is situated in central crete and composed mainly of mudstones and silts deposited in lacustrine brackish or estuarine environments several levels of this section have yielded the remains of mammals foraminifera ostracoda pollen and spores the palynological analysis shows that the region was forested in the upper miocene with a vegetation confined to climates warmer than the present the age indicated by foraminifera is early tortonian while the mammals were attributed to late vallesian in continental biochronology of this section 88 m have been sampled for a magnetostratigraphic study several experiments have been made on the magnetic properties of these sediments showing that they are suitable for a paleomagnetic study moreover x ray diffraction and microprobe analysis of 19 samples regularly distributed over the section show that no major changes occurred in the chemical composition from 77 separate sites 241 samples have been demagnetized thermally 215 or by alternating field 26 the main result of this study is the definition of a long reversed polarity period interrupted by two short normal intervals this magnetostratigraphic sequence can be correlated using biostratigraphic data with a part of chron 5 r of the geomagnetic time scale in other words this section is probably younger than 11 47 my and older than 10 30 my

magnetic polarity stratigraphy and ages of siwalik group rocks of the potwar plateau pakistan abstract six magnetic polarity sections have been established over the potwar plateau region of pakistan including the major stratotypes of the siwalik group in all six sections the dominant feature of the magnetic polarity stratigraphy is a long normal polarity zone which is contained within the nagri formation this conspicuous normal polarity zone has been radiometrically dated at 9 5 0 6 m y which identifies it as magnetic chron 9 radiometric dates from the upper siwalik formation have also been used to identify the chron 2 3 boundary in two of the sections the magnetic polarity stratigraphy of three of the sections has been correlated securely with the accepted magnetic polarity time scale so that the ages of the local stratigraphy are indexed accordingly based exclusively on data from stratotype sections the chinji nagri and dhok pathan formations have nominal age ranges of 10 1 13 1 7 9 10 1 and 5 1 7 9 m y age fluctuations on the order of 105 years may be anticipated for these formational boundaries within radius of some 20 km of the designated stratotype mean sediment accumulation rates during the chinji nagri and dhok pathan interval range from 13 to 52 cm 103 yr essentially linear sediment accumulations are locally maintained over time intervals of several million years the chinji nagri lithofacies boundary marks a transition from slow to faster sediment accumulation over much of the potwar plateau indicating a fundamental sedimentary tectonic change at this time

structure of the accretionary prism and the evolution of the paleogene northern caribbean subduction zone in the region of camaguey cuba the deformation history of sedimentary units incorporated in the north cuban fold and thrust belt in the paleocene to middle late eocene was associated with major shortening between the caribbean and north american plates this led to the formation of an intensely deformed tectonic pile comprising from top to bottom of a volcanic arc nappe a deformed mafic ultramafic complex with mesozoic ophiolite components and a serpentinitic melange with blocks of sedimentary the placetas belt and meta morphic rocks and the structurally lower unit composed of folded and thrusted sediments of the southern promontory of the bahamas platform in this paper we study the deformation history of sedimentary units incorporated in the north cuban fold and thrust belt associated with this shortening history we find that the occurrences of the placetas sedimentary rocks within the foliated serpentinite melange show varying styles and intensity of deformation and varying number of deformation phases they form isolated blocks within the serpentinite melange and do not represent a coherent nappe underlying the allochtonous mafic ultramafic complex the deformation of the remedios belt part of the bahamas platform underwent a single phase of folding and thrusting with shortening perpendicular to the plate contact this folding occurred in the middle to late eocene and marks the arrest of subduction and arc continent collision we find no evidence for a component of strike slip during collision the volcanic arc is thrusted upon the mafic ultramafic complex and the original forearc ophiolite appears to be shortened this shortening may attest to a period of subduction erosion thrusting of the volcanic arc led to deposition of the paleocene lower eocene taguasco olistostrome which may date this event we show that careful analysis of the complexly deformed cuban fold and thrust belt may allow identification of subduction erosion and subduction accretion episodes expanding the analysis carried out in this paper to the scale of the northern caribbean fold and thrust belt may provide a new and independent geological tool to constrain the geodynamic processes associated with subduction and arc continent collision along the northern caribbean margin

first carbon isotope chemostratigraphy of the ouled abdoun phosphate basin morocco implications for dating and evolution of earliest african placental mammals abstract the well known maastrichtian ypresian vertebrate bearing phosphate series in the ouled abdoun basin morocco is classically dated using regional selachian biostratigraphic zonation these marine sediments yielded paleocene and eocene mammals comprising the earliest known placentals from africa this study provides the first insight into the organic carbon isotope chemostratigraphy 13 c org of the moroccan phosphate series and a refined dating of its vertebrate bearing levels four paleocene eocene sections in the ne ouled abdoun quarries show consistent 13 c org long term evolutions from the base to the top 1 positive trend in phosphorite bed iia beginning with the lower bone bed yielding mammals such as eritherium ocepeia abdounodus lahimia of early thanetian and selandian age 2 transitional negative trend in the intercalary phosphorite beds ii i that includes the otodus obliquus and phosphatherium escuilliei bone bed of earliest ypresian age 3 negative trend to the lowermost 13 c org values that are correlative to the early middle ypresian interval including etm 2 and etm 3 hyperthermal events in the global record 4 positive trend in chert enriched facies containing the middle ypresian eeco global climatic event our chemostratigraphic study of the ouled abdoun phosphate series provides a new chronostratigraphic framework for calibrating the beginning of the evolution of placental mammals in africa the lower bone bed level from the paleocene phosphorite bed iia yielding eritherium is not younger than early thanetian and is most likely selandian the phosphatherium bone bed in the intercalary beds ii i is earliest ypresian the phosphorite bed 0 from which daouitherium probably came is early middle ypresian just below the eeco this suggests that the first large proboscideans evolved after the petm during mid ypresian warming events the 13 c org study does not support the presence of lutetian in the ne ouled abdoun phosphate series and suggests that a noticeable part of the upper thanetian is absent

influence of parameterization on inversion of surface wave dispersion curves and definition of an inversion strategy for sites with a strong vs contrast inversion of the fundamental mode of the rayleigh wave dispersion curve does not provide a unique solution and the choice of the parameterization number of layers range of velocity and thickness values for the layers is of prime importance for obtaining reliable results we analyzed shear wave velocity profiles derived from borehole tests at 10 sites where soil layers overlay bedrock in various geologic contexts one to three seismic layers with linear velocity laws could model all of them three synthetic models defined from this preliminary study were used to understand the influence of parameterization on the dispersion curve inversion this analysis resulted in the definition of a two step inversion procedure for sites exhibiting a strong impedance con trast in the first step the dispersion curve is inverted with an increasing number of layers over half space the evolution of the minimum misfit and bedrock depth with number of layers allows the estimation of the true bedrock depth range in the

late cretaceous magmatism in madagascar palaeomagnetic evidence for a stationary marion hotspot late cretaceous basaltic volcanics in the morondava basin sw madagascar possess high quality and pre fold palaeomagnetic data declination 353 5 inclination 54 8 95 2 4 the palaeomagnetic data are all of normal magnetic polarity and remanence acquisition is linked to the terminal stages of the cretaceous normal superchron 83 ma this is sustained by an 40ar 39ar age of 83 6 1 6 ma from one of the tested basaltic flows a precise u pb zircon baddeleyite age from northeast madagascar demonstrates magmatism at least back to 91 6 0 3 ma thus reliable isotope ages for the madagascar cretaceous igneous province span a range of 8 million years late cretaceous palaeomagnetic data obtained from volcanics and dolerites all over madagascar are directionally concordant and the combined palaeomagnetic pole latitude 68 5 n longitude 230 3 e a95 5 5 n 8 studies sampling age range ca 84 90 ma represents one of the best late cretaceous poles for the former gondwanan elements the collective palaeomagnetic data yield a palaeolatitude of 45 3 s 5 3 4 7 for the proposed focal point of the marion plume volcan de l androy southeast madagascar during the late cretaceous this is in perfect agreement with hotspot controlled reconstructions that place the marion hotspot 46 0 s beneath southeast madagascar during the late cretaceous setting true polar wander aside hotspot movements in the indian ocean do not appear to exceed ca 0 75 cm yr and the marion hotspot appears stationary within the resolution power of palaeomagnetic data

elastic and large strain nonlinear seismic site response from analysis of vertical array recordings abstractstrong ground motions from the mw 6 6 2007 niigata ken chuetsu oki earthquake were recorded by a free field downhole array at a nuclear power plant site conditions consist of about 70 m of medium dense sands overlying clayey bedrock with groundwater located at 45 m ground shaking at the bedrock level had a geometric mean peak acceleration of 0 55g which reduced to 0 4g at the ground surface indicating nonlinear site response one dimensional ground response analysis of relatively weak motion aftershock data provides good matches of the observed resonant site frequencies and amplification levels provided small strain damping levels somewhat larger than those from laboratory tests are applied nonlinear ground response analyses of strong motion data using laboratory based modulus reduction and damping relations valid up to moderate strain levels 0 5 produce unrealistic strain localization at a velocity contrast a procedure is presented to more realistically represent the large strain por

global plate motion frames toward a unified model 1 plate tectonics constitutes our primary framework for understanding how the earth works over geological timescales high resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals mid ocean ridges transform faults and seafloor spreading cementing the plate tectonic paradigm however so called absolute plate motions describing how the fragments of the outer shell of the earth have moved relative to a reference system such as the earth s mantle are still poorly understood accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent ocean distributions change with time a fundamental problem with deciphering absolute plate motions is that the earth s rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 ma and ideally would require knowledge about the motions within the convecting mantle in contrast models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of earth s history but cannot provide paleolongitudes because of the axial symmetry of the earth s magnetic dipole field we analyze four different reference frames paleomagnetic african fixed hot spot african moving hot spot and global moving hot spot discuss their uncertainties and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a hybrid model for the time period from the assembly of pangea 320 ma to the present for the last 100 ma we use a moving hot spot reference frame that takes mantle convection into account and we connect this to a pre 100 ma global paleomagnetic frame adjusted 5 in longitude to smooth the reference frame transition using plate driving force arguments and the mapping of reconstructed large igneous provinces to core mantle boundary topography we argue that continental paleolongitudes can be constrained with reasonable confidence

kinematic reconstruction of the caribbean region since the early jurassic abstract the caribbean oceanic crust was formed west of the north and south american continents probably from late jurassic through early cretaceous time its subsequent evolution has resulted from a complex tectonic history governed by the interplay of the north american south american and paleo pacific plates during its entire tectonic evolution the caribbean plate was largely surrounded by subduction and transform boundaries and the oceanic crust has been overlain by the caribbean large igneous province clip since 90 ma the consequent absence of passive margins and measurable marine magnetic anomalies hampers a quantitative integration into the global circuit of plate motions here we present an updated quantitatively described kinematic reconstruction of the caribbean region back to 200 ma integrated into the global plate circuit and implemented with gplates free software our reconstruction includes description of the tectonic units in terms of euler poles and finite rotation angles our analysis of caribbean tectonic evolution incorporates an extensive literature review to constrain the caribbean plate motion between the american continents we use a novel approach that takes structural geological observations rather than marine magnetic anomalies as prime input and uses regionally extensive metamorphic and magmatic phenomena such as the great arc of the caribbean the clip and the caribbean high pressure belt as correlation markers the resulting model restores the caribbean plate back along the cayman trough and major strike slip faults in guatemala offshore nicaragua offshore belize and along the northern andes towards its position of origin west of the north and south american continents in early cretaceous time we provide the paleomagnetic reference frame for the caribbean region by rotating the global apparent polar wander path into coordinates of the caribbean plate interior cuba and the chortis block we conclude that formation of the caribbean plate west of the north and south americas as a result of panthalassa pacific spreading leads to a much simpler plate kinematic scenario than proto caribbean atlantic spreading placing our reconstruction in the most recent mantle reference frames shows that the clip originated 2000 3000 km east of the modern galapagos hotspot and may not have been derived from the corresponding mantle plume finally our reconstruction suggests that most if not all modern subduction zones surrounding the caribbean plate initiated at transform faults two of these along the southern mexican and nw south american margins evolved diachronously as a result of migrating trench trench transform triple junctions

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements

structure and tectonics of the yucatan basin caribbean sea as determined from seismic reflection studies the yucatan basin preserves a record of the late cretaceous to paleogene caribbean north american convergent history that is largely unaffected by neogene strike slip tectonics of the current plate boundary an examination of seismic basement within the yucatan basin based upon available seismic reflection data including extensive multichannel data shows that the basement comprises nine domains distinguished on the basis of internal reflection character and surface topography these domains encompass three distinct crustal types or blocks the first underlies the western flank of the basin and represents the offshore continuation of the adjacent yucatan platform the second includes the topographically heterogeneous domains of the eastern two thirds of the basin and is dominated by a subsided volcanic rise or arc cayman rise resting upon probable oceanic crust of pre tertiary age the eastern edge of the rise and adjacent basins dips northeast beneath the cuban margin along a sediment filled trench the third type of crust occupies a rectangular deep within the western third of the basin available evidence indicates that this crust is oceanic in character and represents a large mature pull apart basin set within a wide paleo transform zone between the western platform and eastern oceanic basin this zone defines the northwestern portion of the caribbean north american convergent plate boundary paleocene to middle eocene transform motion was left lateral along north south to nne ssw trends with a displacement of about 350 km a long middle eocene transcurrent fault of about 50 km left lateral displacement cuts the basin diagonally from sw to ne and continues onland in cuba as la trocha fault this reconstruction is consistent with known eocene regional tectonics but the timing of regional events raises questions about present interpretations of plate geometry in the northwestern caribbean

soil amplification with a strong impedance contrast boston massachusetts abstract in this study we evaluate the effect of strong sediment bedrock impedance contrasts on soil amplification in boston massachusetts for typical sites along the charles and mystic rivers these sites can be characterized by artificial fill overlying marine sediments overlying glacial till and bedrock where the depth to bedrock ranges from 20 to 80 m the marine sediments generally consist of organic silts sand and boston blue clay we chose these sites because they represent typical foundation conditions in the city of boston and the soil conditions are similar to other high impedance contrast environments the sediment bedrock interface in this region results in an impedance ratio on the order of ten which in turn results in a significant amplification of the ground motion using stratigraphic information derived from numerous boreholes across the region paired with geologic and geomorphologic constraints we develop a depth to bedrock model for the greater boston region using shear wave velocity profiles from 30 locations we develop average velocity profiles for sites mapped as artificial fill glaciofluvial deposits and bedrock by pairing the depth to bedrock model with the surficial geology and the average shear wave velocity profiles we can predict soil amplification in boston we compare linear and equivalent linear site response predictions for a soil layer of varying thickness over bedrock and assess the effects of varying the bedrock shear wave velocity vsb and quality factor q in a moderate seismicity region like boston many earthquakes will result in ground motions that can be modeled with linear site response methods we also assess the effect of bedrock depth on soil amplification for a generic soil profile in artificial fill using both linear and equivalent linear site response models finally we assess the accuracy of the model results by comparing the predicted linear site response and observed site response at the northeastern university neu vertical seismometer array during the 2011 m 5 8 mineral virginia earthquake site response at the neu vertical array results in amplification on the order of 10 times at a period between 0 7 0 8 s the results from this study provide evidence that the mean short period and mean intermediate period amplification used in design codes i e from the fa and fv site coefficients may underpredict soil amplification in strong impedance contrast environments such as boston

paleozoic paleogeography of north america gondwana and intervening displaced terranes comparisons of paleomagnetism with paleoclimatology and biogeographical patterns new paleomagnetic data have become available in the past 5 yr that require modifications in previously published paleogeographic reconstructions for the silurian and devonian in this paper the new paleopoles are compared to published paleogeographic models based on paleoclimatologic and biogeographic data the data from the three fields of paleomagnetism paleoclimatology and biogeography are generally in excellent agreement and an internally consistent paleogeographic evolutionary picture of the interactions between north america gondwana and intervening displaced terranes is emerging during the interval of the ordovician silurian and devonian north america stayed in equatorial paleoposition while rotating counter clockwise the northwest african part of gondwana was in high southerly latitudes during the late ordovician and was fringed by peri gondwanide terranes such as southern europe armorica and avalonian basement blocks now found in eastern newfoundland nova scotia the boston basin the appalachian piedmont and northern florida subsequently gondwana and the peri gondwanide terranes displayed rapid drift with respect to the pole this drift translates into the following pattern of movement for northwest africa during the latest ordovician early silurian this area moved rapidly northward from polar to subtropical latitudes followed by equally rapid southward motion from subtropical to intermediate about 50 s paleolatitudes during the late silurian middle devonian it is likely that significant east to west motion accompanied the latter shift in paleolatitudes with the caledonian acadian orogeny the result of silurian to early devonian convergence and collision between gondwana and north america this collision sandwiched several of the intervening displaced terranes between gondwana and north america subsequent to this collision gondwana was separated in the late devonian by a medium width ocean from north america and the avalonian and southern european blocks which were left behind adjacent to north america this new ocean closed during the carboniferous and the resulting convergence and collision were the cause of the hercynian alleghanian orogenic belt problems remaining for future research besides the further gathering of reliable paleopoles involve the uncertain pre devonian position of the southern british isles in this scenario and the very rapid velocity with respect to the pole that results from the rapid late ordovician silurian apparent polar wander for gondwana

estimation of site specific kappa κ0 consistent damping values at kik net sites to assess the discrepancy between laboratory based damping models and observed attenuation of seismic waves in the field in this article we compare field estimates of near surface attenuation as captured by site specific o values i e o0 with laboratory based estimates of minimum shear strain damping min we propose models for min based on o0 measured at selected stations of the kik net database which are found to be generally larger than lowstrain damping values obtained from laboratory testing the latter can only quantify intrinsic material damping whereas other attenuation mechanisms such as scattering of the wavefield contribute to field based estimates in addition we evaluate the difference in damping at the surface and at borehole stations to determine the contribution of shallow layers to attenuation as captured by o0 values at the surface thus values of o0 are computed at the surface and at the downhole instrument depth the difference between both values correlates well with the averaged shear wave velocity over the top 30 m of the profile vs30 and with the depth to bedrock estimates of o0 for hard rock and stiff sites in japan are also examined and compared with other regional o0 values proposed for high vs30 materials in new zealand greece and switzerland two values of o0 which are lower than the corresponding estimates for the aforementioned regions are deemed potential descriptors of hard rock conditions in japan the ability of the proposed o0 consistent damping models to predict ground motions using the vertical array data from the kik net sites has yet to be tested