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

origin of the penalver formation in northwestern cuba and its relation to k t boundary impact event abstract the uppermost maastrichtian penalver formation and its equivalents in northwestern cuba are characterized by thick normal graded calcarenite with distinct basal conglomerate and have been suspected as deposits related to the cretaceous tertiary boundary k t impact however its depositional mechanism is not well understood and clear evidence for its association with the impact has never been presented in this study detailed field survey and petrographic observations were carried out on the penalver formation in order to clarify its sedimentary processes and to test its relation to the k t impact the penalver formation at the type locality near havana is approximately 180 m thick and is subdivided into the basal lower middle upper and uppermost members based on its lithology the basal member consists of massive poorly sorted calcirudite with grain supported fabric which contains abundant macrofossils of shallow marine origin and occasional large intraclasts of the underlying strata suggesting that it was formed by a grain flow from a carbonate platform on the cretaceous cuban arc the lower to uppermost members consist of massive calcarenite and calcilutite that show upward fining composition of the calcarenite is distinctly different from that of the basal member the homogeneous appearance coarse tail normal grading abundant water escape structures and abundant reworked fossils in these members are consistent with those of the mediterranean homogenite a deep sea tsunami induced deposit that was formed by settling from a high density suspension repetition of thin conglomerate beds in the lower member that contain well sorted well rounded mud clasts and shallow marine fossils is considered to reflect intermittent lateral flow possibly induced by a series of tsunami waves during an early stage of settling of grains from a high density suspension altered vesicular glass of probable impact origin and shocked quartz are discovered in the basal and the lower to upper members respectively together with the biostratigraphically constrained age of the penalver formation this evidence suggests that the penalver formation has a genetic relation to the k t impact distribution of altered vesicular glass and shocked quartz grains can explain the sequence of the initial grain flow and the following tsunami waves

reef development at the frasnian famennian mass extinction boundary a newly compiled global reef database indicates that the 5 6 myr long frasnian late devonian metazoan reef episode had relatively lowdiversity compared to middle devonian highs w ith over 200 genera of calcitic rugose and tabulate corals following an initial early rise after late givetian coral and stromatoporoid extinctions reefs expanded for the last time during mid frasnian sealevel highstands but declined markedly in the late frasnian rhenana linguiformis conodont zones belowthe frasnian famennian f f boundary globally metazoan reefs were wiped out by the end frasnian some famennian reefs while partly retaining the structure of the underlying carbonate platform were built by cyanobacterial consortia such as renalcis rothpletzella girvanella and epiphyton during the famennian foraminiferans with calcite walls became abundant for the first time in the phanerozoic adding a newdimension to carbonate platforms colonial rugose corals phaceloid cerioid and thamnasterioid modules were absent in the early post extinction phases up into the mid famennian and very rare and non reefbuilding later but solitary deep water lazarus corals survived locally coral sponge reefs are unknown from the 21 myr long famennian also a time of very lowplatform carbonate production rare small isolated stromatoporoid sponge and lithistid sponge patch reefs returned episodically during the famennian in north america western europe australia and china the aragonitic stromatoporoids became extinct at the end of the famennian during a late devonian tectonically very active collisional caledonian mountain building phase oceanic and atmospheric cooling accompanied by sealevel lowstand systems exposed most carbonate platforms accelerating coastal erosion and karsting this increased the amount of clastics in the shelf slope setting in the last 1 3 myr prior to the f f boundary often burying reefs immediately following there were protracted losses in nearly all major tropical shelf benthic marine invertebrates exceeded only by the end permian extinctions in severity there is no apparent link between black organic rich horizons and reef demise at or close to the f f boundary the f f boundary not also marks the largest change from widespread flooded early and mid paleozoic continental cratons to narrow distal shelves but also spikes the largest known global phanerozoic shift in atmospheric o2 enrichment and co2 drawdown this threshold matched the rise of the first tropical rainforests and expansion of terrestrial biomes on the tropical coastal lowlands formerly occupied by carbonate platforms 6 2002 elsevier science b v all rights reserved

geodynamic models of crustal scale episodic tectonic accretion and underplating in subduction zones we investigate the dynamics of crustal scale episodic accretion at convergent margins using a finite element model of subduction the numerical model incorporates effects from flexure subduction loading and large scale variations in material properties the model is used to assess the influence of these parameters on the discrete transfer of units from the lower to the upper plate during subduction the primary controls investigated are spatial variations in density material strength and thickness of material layers these controls correspond to natural examples where episodic accretion results from the thermal structure of subducting lithosphere giving rise to areas of thermally activated ductile creep attempted subduction of small crustal blocks density frictional and or ductile strength variations interaction between well attached basement blocks and overlying detachable sediments and spatial changes in thickness of sediment and crust in the experiments accretion of small continental terranes within a model subduction zone can cause crustal scale fold nappes and shear zones to develop with accompanying tectonic underplating and or frontal accretion the model results may provide insight into real cases of episodic accretion for example the emplacement of the upper penninic nappe stack of the central alps

paleogeographic differences in temperature water depth and conodont biofacies during the late devonian the famennian late devonian started after and ended with two of the seven largest crises of the phanerozoic the kellwasser and hangenberg events respectively in between global environmental trends have been identified involving cooling and eustatic regression tropical and subtropical marine faunas were largely cosmopolitan overall this suggests that the famennian was marked by long term environmental changes occurring in a relatively homogeneous manner despite being punctuated by several short term events of limited faunal impact how these trends were modulated according to geographic location is investigated in this study by comparing two continuous outcrops in the montagne noire col des tribes section france and in saxo thuringia buschteich section germany both were located in the subtropical area during this period and belonged to two former microcontinents bracketed between the closing rheic ocean and gondwana sedimentary facies oxygen isotopes and the generic conodont composition biofacies were studied in a high resolution and in the same rock samples sedimentary facies provided an estimate of water depth and oxygen isotopes were used as pa leotemperature proxy conodont biofacies were analyzed using a principal component analysis allowing the expression of the variations in the two outcrops on the same axes and a quantitative comparison with the other proxies sea level and temperature variations were different between the two areas saxo thuringia displayed stable deep and warm conditions throughout in contrast the environment of the montagne noire was shallower and cooler during the late and latest famennian compared to the early and middle famennian congruent with the global change evidenced elsewhere the location of saxo thuringia close to the first point of closure of the rheic ocean might have favored active tectonics causing a local departure from the eustatic trend the stable temperatures at bu during the late and latest famennian may be due to the position of saxo thuringia in the remnant rheic ocean limiting water mass exchange with open seas and favoring the persistence of warm conditions offshore taxa persisted later at high abundance in the saxo thuringian record the two conodont biofacies records were otherwise very comparable this suggests that other factors mitigated the water depth forcing on these conodont assemblages

detrital zircon geochronology of jurassic sandstones of western cuba san cayetano formation implications for the jurassic paleogeography of the nw proto caribbean clastic sediments of the early to late jurassic oxfordian san cayetano formation of western cuba are interpreted to reflect syn rift sedimentation coeval with the breakup of pangaea this sedimentary unit is the oldest known in the guaniguanico mountains and cuba u pb shrimp dating of 19 detrital zircon grains from two samples of san cayetano micaceous sandstone provided concordant ages ranging from 398 to 2479 ma the oldest zircon population is of paleoproterozoic age 2479 1735 ma but most zircons have early mesoproterozoic and grenvillian ages 1556 985 ma whereas still younger ages are pan african 561 ma ordovician 451 ma and early devonian 398 ma we discuss the possible origin of these zircons and conclude that the most likely source terrain s are precambrian and early paleozoic massifs in northern south america colombia and or venezuela and the yucatan peninsula in mexico this is compatible with paleogeographic reconstructions of the caribbean that imply that sediments of the san cayetano formation were still part of the disintegrating supercontinent pangea in pre mid oxfordian time

petrogenetic interpretation of granitoid rock series using multicationic parameters abstract granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la roche and his coworkers this shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors these suggest that most granitoid series result from a two stage process first fractional crystallisation of clinopyroxene olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition this magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series

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

diachronous exhumation of hp lt metamorphic rocks from south western alps evidence from fission track analysis new fission track ages on zircon and apatite zft and aft from the southwestern alpine paleo accretionary wedge document a contrasting cooling history from east to west in the eclogitic monviso ophiolites the zft ages are 19 6 0 8 ma and the aft ages are 8 6 1 7 ma in the ht blueschist eastern queyras zft ages range from 27 0 1 5 ma to 21 7 1 6 ma and aft ages from 14 2 2 0 to 9 4 1 1 ma in the lt blueschist western queyras zft ages are between 94 7 3 1 ma and 63 1 2 9 ma and aft ages are between 22 2 1 6 and 22 6 1 5 ma the chenaillet ophiolite yields ages of 118 1 3 7 ma on zft and of 67 9 8 5 ma on aft these new ft data combined with petrological and geochronological constraints record a diachronous exhumation in the paleo accretionary wedge during subduction and collision

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

biostratigraphic significance of brachiopods near the devonian carboniferous boundary the biostratigraphic significance of selected uppermost famennian upper devonian and lower tournaisian mississippian brachiopod genera belonging to the orders rhynchonellida e g araratella spiriferida e g sphenospira prospira spiriferinida syringothyris and productida except chonetidina is discussed owing to the difficulties of identifying productidine and strophalosiidine genera in contrast to rhynchonellides and spiriferides the biostratigraphic potential of the former has generally been overlooked brachiopods flourished in neritic environments that were unfavourable for conodonts and ammonoids in the absence of the latter traditional marker fossils they are potentially important for locating the devonian carboniferous boundary in shallow water depositional settings in conjunction with rugose corals and foraminifers on a worldwide scale further work is required to reach a better assessment of the aftermath of the hangenberg biological crisis on brachiopods notably in revising the faunas from the classical areas of the famennian and tournaisian stages in western europe

reconnaissance paleomagnetic results from western cuba abstract a paleomagnetic study of mesozoic rocks from the sierra de los organos and sierra del rosario fold belts of western cuba revealed postfolding magnetisation in diabases of the late jurassic el sabalo formation and carbonates of the middle cretaceous pons and the late cretaceous carmita and moreno formations steep components with inclinations of about 70 were isolated from all three formations at the same time postfolding shallow components were also found in a few samples of the pons limestones we rule out a possibility to account for these results by either horizontal movements or non dipole field anomaly neither very appealing is a hypothesis of a post remagnetization tilt of the entire region all the components appear to be confined to a plane perpendicular to the main structural trends we hypothesize that the remanences might have been distorted or re aligned during deformation this assumption however is far from being proven in contrast well defined characteristic components were isolated from basalts of the aptian albian encrucijada d i 247 23 k 14 a95 9 0 and the late cretaceous orozco d i 228 22 k 110 a95 4 7 formations from the bahia honda zone in the north of western cuba the remanence in the encrucijada formation is shown to predate deformation mean inclinations in both formations match those in cretaceous volcanics from central cuba and all the results show lower latitudes than expected from the reference data for the north american plate thus implying that volcanic domains of cuba were displaced northward by about 1000 km prior to the middle eocene cretaceous declinations in western and central cuba differ by about the same amount as the major structural trends of these two areas suggesting oroclinal bending of cuba at the same time both areas are rotated counterclockwise with respect to north america thus implying movements on a broader scale

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

age and tectonic setting of the camaguey volcanic intrusive arc cuba late cretaceous extension and uplift in the western greater antilles abstract ar ar ages determined on rocks and minerals from the camaguey area in central cuba provide age constraints on events that accompanied the northward migration of cuba into the caribbean region and its subsequent collision with the bahamas bank whole rock samples from the camujiro and piragua formations part of the camaguey volcanic sequence yielded ar ar ages of 74 72 ma distinctly younger than the 100 80 ma ages indicated by fossils in interlayered sedimentary rocks syenite and granodiorite in the camaguey batholith which cut these volcanic rocks yield generally similar ar ar ages of 75 72 ma for hornblende biotite and feldspar these ages are interpreted to reflect relatively rapid uplift and cooling of most of the volcanic intrusive arc additional constraints on the timing of this uplift are provided by ar ar ages of 71 75 ma for rhyolite rhyodacite domes of the la sierra formation and 52 ma for andesitic basalt of la mulata formation which appear to have been emplaced onto erosion s

famennian rhynchonellides brachiopoda from deep water facies of the ougarta basin saoura valley algeria in the saoura valley ougarta basin saharan algeria the lower upper famennian part of the essentially shally marhouma formation is characterized by deep water facies and includes horizons rich in ammonoids goniatites and clymeniids and blind to eye reduced phacopide trilobites they are also rich in small sized and smooth rhynchonellide brachiopods investigated here for the first time in order to detail their post kellwasser recovery rhynchonellides clearly predominate in the brachiopod assemblages representing 90 of the whole assemblage with 10 species composed otherwise of athyridides orthides and spiriferides rhynchonellides are mostly represented by relatively flat leiorhynchids and rozmanariids consistent with poor oxygenation on the sea floor one new species is described evanidisinurostrum saouraense sp nov four genera previously known only from the south eastern margin of laurussia are reported for the first time from the northern margin of gondwana the leiorhynchid sphaeridiorhynchus and the rozmanariids leptoterorhynchus pugnaria and novaplatirostrum

age of the los ranchos formation dominican republic timing and tectonic setting of primitive island arc volcanism in the caribbean region this study reports u pb ages for zircons from the los ranchos formation which is part of the primitive island arc sequence the oldest volcanic rocks in the greater antilles zircons were analyzed from three samples quartz porphyry quartz keratophyre from the lower part of the formation quita sueno member fragmental quartz porphyry from the upper part of the formation pueblo viejo member and the cotui quartz diorite stock that intrudes the lower part of the formation the lower part of the los ranchos formation represented by the quita sueno sample formed at either 113 9 0 8 or 118 6 0 5 ma depending on interpretation of the data whereas the upper part represented by the pueblo viejo sample formed ca 110 9 0 8 ma the cotui stock rd 73 601 was emplaced ca 111 8 0 6 ma or 112 9 0 9 ma depending on whether eight grains reflect subtle inheritance these results show that the los ranchos formation was emplaced during the aptian albian transition that the cotui stock could have supplied magma to the volcanic sequence and fluids to the pueblo viejo gold silver deposit in the upper part of the formation and that carbonaceous sediments in the upper part of the formation formed at the same time as ocean anoxic event 1b paquier caribbean plate tectonic models involving invasion of anomalous pacific crust into the caribbean region appear to agree best with this age because they provide a mechanism for the change from primitive island arc pia to calcalkaline magmatism and account for the restricted ocean circulation necessary to generate regional anoxic conditions

climate controlled mass extinctions facies and sea level changes around the devonian carboniferous boundary in the eastern anti atlas se morocco abstract detailed sedimentological and biostratigraphical studies of successions in the eastern anti atlas se morocco focused on changing depositional environments and reconstructions of sea level changes during the late famennian to middle tournaisian the investigations cover a transect from the central maider to the easternmost and southern tafilalt regions near the moroccan algerian border the moroccan data are compared with the standard succession of the german rhenish massif and with the regional and global stratigraphic record the results testify to high frequency sea level changes including two global transgressive and anoxic events the main hangenberg event hangenberg black shale level at the top of the wocklumeria zone upper devonian vi e and the lower alum shale event at the lower middle tournaisian lower carboniferous i ii boundary regionally both anoxic intervals coincided with mass extinctions followed by rapid radiation especially of pelagic biota a significant shallowing and regression occurred just below the devonian carboniferous boundary at the northern margin of gondwana and caused the sudden n nw progradation of a large deltaic complex over 300 500 km thick siliciclastic successions filled fast subsiding synsedimentary troughs of the maider and amessoui syncline southern tafilalt correlation with the glacial phases of southern gondwana south america south africa indicates a glacial eustatic origin of sea level changes and a major sea level fall in the scale of 100 m or more coinciding with the main regressive phase of the extended hangenberg crisis interval the new results are in accord with the hypothesis of an episode of cool humid climate at the end of the devonian that allowed contemporaneous glacial buildup in high latitudes and extensive clastic discharge in the middle latitudes of nw africa

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

tectonic history of subduction zones inferred from retrograde blueschist p t paths many phanerozoic convergent plate junctions are marked by discontinuous blueschist belts reflecting relatively high pressure p prograde trajectories common blueschist paragneisses such as those of the western alps exhibit widespread overprinting by greenschist and or epidote amphibolite facies assemblages for this type of high p belt retrograde metamorphism involved fairly rapid nearly isothermal decompression some terranes underwent continued heating during early stages of pressure release uplift probably occurred as a consequence of the entrance of an island arc oceanic plateau or segment of continental crust into the subduction zone collision resulting in marked deceleration or cessation of underflow and buoyant approximately adiabatic rise of the stranded recrystallized subduction complex other high p belts such as the franciscan of western california preserve metamorphic aragonite and lack a low p overprint retrogression approximately retraced the prograde p t temperature path or for early formed high grade blocks occurred at even higher p t ratios parts of this type of metamorphic belt evidently migrated slowly back up the subduction zone in response to isostatic forces during continued plate descent and refrigeration upward motion took place as tectonically imbricated slices as laminar return flow in melange zones and perhaps partly a lateral spreading extension of the underplated accretionary prism retrograde p t trajectories of high pmore belts therefore provide important constraints on the tectonic evolution of convergent plate junctions less

famennian and tournaisian recoveries of shallow water rugosa following late frasnian and late strunian major crises southern belgium and surrounding areas hunan south china and the omolon region ne siberia abstract the rugosa remained almost totally absent from the platform environments of southern belgium and surrounding areas hunan and omolon during the long time interval between the end frasnian crisis and the early part of the late famennian marginifera zone probably owing to cool climatic conditions they first reappear in the upper marginifera zone but are uncommon and poorly diversified few of them belong to pre famennian genera it is only near the beginning of strunian time that rugose corals radiated and became common their morphological and allometric variabilities were very large indicating their high potential for adaptation to free niches this first radiation was abruptly terminated by an extinction event and a second radiation quickly began mainly from new taxa and only from a few previously known ones in western europe and in hunan this second radiation was also stopped abruptly while species were evolving by the hangenberg event at the end of the strunian in omolon where the position of the devonian carboniferous boundary is doubtfull the second radiation may have been completed before the end of the strunian and probably the corals affected by the end famennian event were new ones resulting from a third radiation in the three regions and at each recovery the rugose corals are endemic indicating that marine connections were poor after the hangenberg event surviving rugosa reappeared almost immediately except in south china and were widespread indicating good marine connections however they remained poorly diversified sometimes until the late tournaisian the two major extinctions end frasnian and end famennian and the strunian ones were responsible for the major taxonomic differences between pre famennian and post famennian rugosa

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

exhumation rates of high pressure metamorphic rocks in subduction channels the effect of rheology 1 exhumation of high pressure metamorphic rocks can take place with typical plate velocities of cm year this is consistent with a model of forced flow in a subduction channel the micro structural record of exhumed metamorphic rocks indicates that stresses are generally too low to drive deformation of the bulk material by dislocation creep according to a power law rheology instead deformation appears to be localized in low strength shear zones and is dominated by dissolution precipitation creep or fluid assisted granular flow implying a newtonian rheology 1d modeling shows that the effective rheology of the material in the subduction channel has a significant influence on the rate of exhumation when the subduction flux either equals or exceeds the return flux the maximum exhumation rate for newtonian behavior of the material is at least twice as high 1 3 of the subduction burial rate compared to that for power law creep 1 6 of the subduction burial rate

global time scale and regional stratigraphic reference scales of central and west europe east europe tethys south china and north america as used in the devonian carboniferous permian correlation chart 2003 dcp 2003 the boundaries of the devonian carboniferous and permian stages of the global stratigraphic reference scale abbreviated to global stratigraphic scale gss are described in relation to the biostratigraphic and or lithostratigraphic units of the regional stratigraphic reference scales abbreviated to regional stratigraphic scales rss of central and west europe east europe tethys south china eastern tethys and north america in their type regions the boundaries of gss units rarely coincide with those of homonymous rss units moreover the definitions of some rss units have changed several times over the last decades and subsequent misunderstanding of the stratigraphical significance of these changes has often introduced errors into proposed global correlation charts the stratigraphic framework proposed in our global devonian carboniferous permian correlation chart 2003 dcp 2003 devonian carboniferous permian correlation chart 2003 menning m schneider j w alekseev a s amon e o becker g von bitter p h boardman d r bogoslovskaya m braun a brocke r chernykh v chuvashov b i clayton g dusar m davydov v i dybova jachowicz s forke h c gibling m gilmour e h goretzki j grunt t a hance l heckel p h izokh n g jansen u jin y g jones p kading k ch kerp h kiersnowski h klets a klug ch korn d kossovaya o kotlyar g v kozur h w laveine j p martens th nemyrovska t l nigmadganov a l paech h j peryt t m rohn r roscher m rubidge b schiappa t a schindler e skompski s ueno k utting j vdovenko m v villa e voigt s wahlman g p wardlaw b r warrington g weddige k werneburg r weyer d wilde v winkler prins c f work d m 2004 abschlusskolloquium dfg schwerpunktprogramm 1054 evolution des systems erde wahrend des jungeren palaozoikums im spiegel der sedimentgeochemie abstracts univ erlangen germany 2004 p 43 herein abbreviated to dcp 2003 and cited as dcp 2003 in references is an attempt to reduce these errors the dcp 2003 is the stratigraphic base for project 1054 of the deutsche forschungsgemeinschaft dfg the evolution of the late palaeozoic in the light of sedimentary geochemistry this composite time scale has been carefully balanced as far as data allows to remove unnecessary artificial compression and expansion of time intervals biozonations and depositional events the ages selected in dcp 2003 are markedly different to those in the geologic time scale 1989 gts 1989 harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge pp 1 263 and in gradstein and ogg gradstein f m ogg j 1996 a phanerozoic time scale episodes 19 1 2 3 4 insert whereas they are closer to those of the geologic time scale 2004 gts 2004 gradstein f m ogg j g smith a g 2004 a geologic time scale 2004 cambridge univ press cambridge pp 1 589 mostly the ages are rounded to the nearest 0 5 ma in order to avoid estimates of questionable accuracy whereas ages of 0 1 ma in the gts 2004 and their error bars of 0 4 ma to 2 8 ma for the devonian to permian stage boundaries suggest an improved accuracy in contrast in the dcp 2003 questionable ages and positions of stratigraphic boundaries are marked by arrows c 2006 elsevier b v all rights reserved

40ar 39ar dating of single muscovite grains in jurassic siliciclastic rocks san cayetano formation constraints on the paleoposition of western cuba the san cayetano formation of western cuba is the thickest and most extensive subaerial exposure of jurassic siliciclastic rocks between the southeastern united states and northern south america previous workers have speculated that siliciclastic rocks of the san cayetano formation were derived from one of the following sources 1 yucatan peninsula 2 florida and 3 northern south america to address the problem of the provenance of the san cayetano formation and the mesozoic position of western cuba we present the results of 40ar 39ar isotopic dates from 67 single detrital mica grains from four samples of the san cayetano formation these mica grains have ages that fall within the age ranges of well known precambrian crustal age provinces and paleozoic orogenic belts in eastern north america and the yucatan peninsula the lack of grains with ages in the 700 550 ma range suggests that pan african brasiliano orogenic belts that exist in northern south america northwestern africa and beneath florida did not contribute significant amounts of detritus to the san cayetano basin we propose that the late jurassic san cayetano basin formed as a post rift deltaic complex along the southeastern margin of the yucatan peninsula and was detached and transported to its present position in western cuba in paleogene time by the northeastward migration of the caribbean arc

comparative study of late devonian famennian brachiopod assemblages sea level changes and geo events in northwestern and southern china abstract abundant brachiopods have been recovered from the upper devonian of western junggar xinjiang northwestern china however their diversity and succession as well as a detailed comparison with other regions remain to be explored these issues are of importance since conodonts and ammonoids are generally sparse for dating the sequence based on collections in the past years from the famennian sequence of the bulongguoer section and adjacent sections we recognize five brachiopod assemblages in ascending order the caenanoplia aff logani assemblage the palaeospirifer megalopterorhynchus assemblage which can be divided into the cyrtospirifer sulcifer subassemblage and the rugaltarostrum subassemblage the ambocoelia cf unionensis assemblage the austrospirifer sp assemblage and the syringothyris spirifer assemblage comparison of these assemblages with those of the xikuangshan and other sections central hunan southern china indicates a strong biogeographic differentiation there are opposite trends of raw diversity changes during the middle famennian in these two regions whereas similar trends with a decline followed by an increase in diversity occurred during the late and latest famennian two transgression regression cycles are recognized in the bulongguoer section of western junggar comparisons of sea level changes among the bulongguoer section western junggar central hunan platform facies of south china and euramerica indicate that regional tectonic activities may have played important roles in both western junggar and central hunan in the palmatolepis rugosa trachytera conodont zone sea level rose gradually to the maximum at approximately the annulata level in the bulongguoer section whereas a contemporaneous prolonged lowstand oujiachong regression was recognized in central hunan the replacement of the rugaltarostrum subassemblage by the ambocoelia cf unionensis assemblage in western junggar is correlative to the oujiachong event the regression and brachiopod diversity decline in south china at the top of palmatolepis marginifera zone during the latest famennian the syringothyris spirifer assemblage replaced the austrospirifer sp assemblage in western junggar as a response to the hangenberg event

oscillatory zoning in eclogitic garnet and amphibole northern serpentinite melange cuba a record of tectonic instability during subduction exotic blocks of eclogite from distant localities along the northern serpentinite melange of cuba have comparable p t histories that include high pressure prograde sections 450 600 c 15 kbar associ ated with subduction of oceanic lithosphere and retrograde sections within the albite epidote amphibolite facies 500 c 10 kbar related to melange uplift 40 ar 39 ar and rb sr cooling ages 118 103 ma of one of the blocks indicate pre aptian subduction and aptian albian uplift detailed x ray imaging and profiling further reveals that minerals in these eclogite blocks notably garnet and amphibole display subtle but well defined oscillatory zoning that developed along the prograde trajectory of the rocks previous to attainment of peak eclogitic conditions the chemistry e g coupled changes of mg and mn in garnet and of si ti al and na in amphibole and geometry euhedral to anhedral shapes of the oscillations can be interpreted in terms of subtle fluctuations in p t during the general prograde subduction related metamorphic path a near equilibrium model is presented for the formation of oscillations at near peak conditions by means of recurrent dissolution growth reaction processes this model for near peak conditions and the chemical signatures of earlier oscillations notably in amphibole suggest that episodes of retrogression upward movement affected parts of the subducting slab it is proposed that these retrograde episodes record the tectonic rupture of the subducting slab and probably of the upper plate mantle either due to the intrinsic dynamic behaviour of subduction systems or to the effects of the plate tectonic rearrangement of the caribbean region during the early cretaceous

multidisciplinary studies of global carboniferous stage boundaries towards a better definition and global correlations an introduction earth was very dynamic during the carboniferous with major components of the pangea supercontinent being assembled from late famennian to latest pennsylvanian times although maximum consolidation occurred during late permian early triassic time during the carboniferous period our planet also underwent at least three major icehouse periods the first two in late famennian early tournaisian and late visean bashkirian times indicate the onset of the late palaeozoic ice age lpia with ice sheets being confined to the alpine regions of southern gondwana the third icehouse regime during gzhelian early permian time represents the main episode of the lpia when a continental ice sheet developed on the australian antarctic and southern african components of southern gondwana during the tournaisian equatorial areas in euramerica were occupied by extensive arid belts in which massive carbonate deposits formed on vast platforms in that time from the late tournaisian into the visean and serpukhovian much of the equatorial belt developed into a humid tropical realm and the former arid belt split and shifted to higher latitudes shelf carbonate deposition continued over extensive areas of the continental shelves and western palaeo tethys but coal swamps were developing in the forelands of the rising appalachian and variscan orogens the late serpukhovian early bashkirian interval saw the closure of the rheic ocean and a continent continent collision between euramerica laurussia and gondwana to form pangea as a consequence a marked transition from visean carbonate deposition to the development of coal swamps and deposition of siliciclastics during the serpukhovian stage occurred in many regions

volcanism around k t boundary time its role in an impact scenario for k t extinction events abstract a widespread debate on the cretaceous tertiary k t boundary 65 1 ma extinctions has largely revolved around an impact or a volcanic cause evidence for both events is strengthened by recent work impact triggered deccan volcanism or independent impact and mantle plume events have been suggested this review examines evidence for both events and suggests that they overlapped in time but with globally uneven effects the combined effects produced generally inhospitable k t environments leading to mass extinctions although some life forms flourished afterwards volcanic contributions to the k t boundary environment probably include increased platinum group element pge and acid rain fall out particularly from large scale mantle upwellings e g deccan cameroon and coral sea events a previously proposed post k t greenland starting plume apparently already existed in the cretaceous k t features such as the iridium ir anomaly most likely include longer term volcanic as well as sudden meteoritic impact contributions volcanic contributions were greatest from southern hemisphere sources whereas meteorite impacts featured in the northern hemisphere

thrust emplacement of the hispaniola peridotite belt orogenic expression of the mid cretaceous caribbean arc polarity reversal articulo sobre el emplazamiento fallero en la zona de peridotitas de la hispaniola republica dominicana estudiando si es la expresion orogenica de la polaridad reversa en la zona del caribe en el cretacico medio

a plate kinematic framework for models of caribbean evolution abstract we define the former relative positions and motions of the plates whose motions have controlled the geological evolution of the caribbean region newly determined poles of rotation defining the approximate spreading histories of the central north and the south atlantic oceans are given for the late jurassic early cretaceous anomaly sequence of the central north atlantic we have used previously published definitions of fracture zone traces and magnetic anomaly picks redetermining the pole positions and angular rotations for various isochrons on an evans and sutherland interactive graphics system for magnetic anomalies younger than the cretaceous quiet period in both oceans we 1 used seasat altimeter data to help define fracture zone traces and 2 identified and used marine magnetic anomalies to determine the positions of spreading isochrons along the flowlines indicated by the fracture zones by the finite difference method the relative paleopositions and the relative motion history between north and south america were computed this analysis defines the size and shape and the rate at which the size and shape changed of the interplate region between north and south america since the middle jurassic thus a plate kinematic framework is provided for the larger plates pertaining to the caribbean region in which can be derived more detailed scenarios for gulf of mexico and caribbean evolution north and south america diverged to approximately their present relative positions from late triassic to early campanian about 84 m y ago time this is the period during which the gulf of mexico and a proto caribbean seaway were formed since the campanian only minor relative motion has occurred from early campanian through to middle eocene times south america diverged only another 200 km and since the middle eocene minor n s convergence has occurred these very minor post early campanian motions have probably been accommodated by imperfect shear and compression along the atlantic fracture zones to the east of the lesser antilles and along the northern and southern borders of the caribbean plate accordingly it is suggested that from campanian time to the present the relative motions between the north and south american plates have had only minor effects on the structural development of the caribbean region primarily using the data of engebretson et al the convergence history of pacific plates with north america was calculated for two points near the western caribbean by completing finite difference solutions the convergence history of the pacific plates with the caribbean and south american plates can be approximated the direction and rate of convergence of the pacific plates with the americas may have controlled the style of subduction and possible microplate migration along the north american south american and western caribbean boundaries that define the eastern pacific plate margin