carbon isotope excursions and sea level change implications for the frasnian famennian biotic crisis new carbon and oxygen isotope data from carbonates spanning the frasnian famennian f f boundary in the guilin area south china show a broad positive 13 c rise and fall with sharp short lived negative 13 c events this pattern is comparable to that in europe and north america the integration of the isotope stratigraphy with high resolution sequence stratigraphy corroborates the onset of the positive 13 c excursion during a third order sea level fall in the latest frasnian this can best be explained through increased burial of c org during the sea level fall brought about by increased organic productivity caused by increased continent derived nutrient flux to the ocean due to enhanced weathering through the proliferation of land plants in the devonian this scenario would have resulted in anoxic and eutrophic conditions over epicontinental seas and blooms of cyanobacteria creating a highly stressful and fragile ecosystem for oligotrophic normal marine benthic organisms and leading to their massive decline the global third order sea level fall near the end of the frasnian may have led to gas hydrate dissociation giving the negative 13 c events and caused wild climatic fluctuations the subsequent short term events of sea level rise anoxia and eutrophication in the latest part of the f f transition would have placed additional environmental stresses on the already weakened biota leading to their further demise

the effect of environmental changes on the evolution and extinction of late devonian trilobites from the northern canning basin western australia the frasnian famennian virgin hills formation represents fore reef facies deposited as part of the extensive late devonian reef system that fringed the sw kimberley block in western australia it contains a rich trilobite fauna dominated primarily by proetids and to a lesser extent harpetids phacopids scutelluids and odontopleurids to date 49 taxa have been described 40 of these being restricted to the frasnian herein five frasnian taxa are described three in open nomenclature and two the new species telopeltis intermedia and otarion fugitivum evolutionary trends in the virgin hills trilobites are dominated by a reduction in body size and eye size and to a lesser extent a reduction in exoskeletal vaulting although recording no sedimentological signature the fauna was strongly affected by the two globally recognized kellwasser extinction events the first at the end of conodont zone 12 affected taxa at the species and genus level the second within zone 13b had a much greater impact on the fauna causing extinctions at the familial and ordinal levels evidence is presented to suggest that evolutionary trends in the trilobites during the late frasnian reflect selection for forms adapted to low nutrient conditions the two intensive kellwasser extinction episodes may reflect periodic massive inputs of nutrients from the terrestrial into the shallow marine environment

the depositional record of the frasnian famennian boundary interval in a fore reef succession canning basin western australia abstract the effects of the global frasnian famennian f f biotic crisis on the shallow marine reef builders and associated biota in a laterally extensive late frasnian reef complex on the lennard shelf northern canning basin are recorded in the well exposed fore reef succession napier formation of the napier range the conodont defined f f boundary lies within a distinctive and mappable stratigraphic interval up to 15 m thick which separates highly fossiliferous frasnian from markedly less fossiliferous famennian carbonate and siliciclastic lithofacies marked lateral facies variation within the interval means that the actual boundary is not represented by a discrete bed or surface the interval is characterised by a range of lithofacies that record very low sedimentation rates on the slope and reworking and bioturbation of slope strata indicating a condensed interval with negligible sediment input from contemporaneous carbonate platform production siliciclastic lithofacies and abundant sponge debris are locally developed macrofossil content is generally very low but there is no evidence for anoxic or hypoxic conditions during deposition at a range of palaeowater depths allochthonous blocks of stromatoporoid bearing limestone are absent from the uppermost frasnian fore reef strata and stromatoporoid debris is significantly reduced prior to the end of the frasnian this suggests that extinction of the stromatoporoid reef margins occurred before the f f boundary with microbial communities dominating the platform margins prior to the famennian sedimentological and biostratigraphic evidence suggests that a series of sea level fluctuations in response to basin tectonism generated recurring or ongoing environmental stress in the stromatoporoid dominated reefal communities because of recurring reductions in living space influxes of siliciclastic sediment supply from the proximal highlands and quite possibly generation of toxic too saline or too nutrient rich lagoonal water these conditions were potentially superimposed on a global regime of incipient cooling climate leading to widespread glaciation in the late carboniferous

early palaeozoic palaeobiogeography of the variscan regions abstract the palaeobiogeographic method appears to be an attractive alternative for reconstruction of the palaeogeography of the variscan regions during the palaeozoic the evolution of faunal assemblages and climatic characteristics from the cambrian up to the end of the devonian demonstrates that baltica and north gondwana represent two major and independent palaeogeographic entities separated by a mid european rheic ocean which opened as early as the cambrian and closed progressively from the devonian the south armorican ocean whose closure generated the so called ligerian orogen is regarded as a branch of the rheic ocean both a tornquist s sea separating baltica from its western extension avalonia during the ordovician and a proto tethys ocean extending between southwestern europe and north africa during the devonian are excluded from our reconstructions

biodiversity distribution and patterns of extinction of the last odontopleuroid trilobites during the devonian givetian frasnian biostratigraphical ranges and palaeogeographical distribution of mid givetian to end frasnian odontopleurids are investigated the discovery of leonaspis rhenohercynica sp nov in mid givetian strata extends this genus unexpectedly up to the late middle devonian new material of radiaspis radiata goldfuss 1843 and the first koneprusiine in britain koneprusia sp are described from the famous lummaton shell bed torquay devon new taxa of koneprusia k serrensis k aboussalamae k brevispina and k sp a and k sp b are defined ceratocephala leonaspis harborti richter richter 1926 is revised and reassigned to gondwanaspis feist 2002 two new species of gondwanaspis g dracula and g spinosa plus three others left in open nomenclature are described from the late frasnian of western australia a further species of gondwanaspis g prisca is described from the early frasnian of montagne noire species of gondwanaspis are shown to possess a number of paedomorphic features a functional analysis suggests that unlike other odontopleurids gondwanaspis actively fed and rested with the same cephalic orientation the sole odontopleurid survivors of the severe terminal mid givetian biocrisis taghanic event belong to the koneprusiine koneprusia in the late givetian and frasnian and of cryptogenic origin the acidaspidine gondwanaspis in the frasnian whereas the former became extinct in the late frasnian at the lower kellwasser event the latter disappeared and with it the entire odontopleuroidea at the terminal frasnian upper kellwasser global biocrisis

sea beam survey of an active strike slip fault the san clemente fault in the california continental borderland the san clemente fault located in the california continental borderland is an active northwest trending right lateral wrench fault sea beam data are used to map the major tectonic landforms associated with active submarine faulting in detail unavailable using conventional echo sounding or seismic reflection data in the area between north san clemente basin and fortymile bank the major late cenozoic faults are delineated by alignments of numerous tectonic landforms including scarps linear trenches benches and sags character and spatial patterns of these landforms are consistent with dextral wrench faulting although vertical offsets may be substantial locally the main trace of the san clemente fault cuts a straight path directly across the rugged topography of the region evidence of a steeply dipping fault surface basins or sags located at each right step in the en echelon pattern of faults are manifestations of pull apart basin development in a right slip fault zone seismic reflection profiles show offset reflectors and a graben in late quaternary turbidites of the navy fan where the fault zone follows a more northerly trend modern tectonic activity along the san clemente fault zone is demonstrated by numerous earthquakes with epicenters located along the fault s trend the average strike of the san clemente fault is parallel to the predicted pacific north american relative plate motion vector at this location therefore we conclude that the san clemente fault zone is a part of the broad pacific north american transform plate boundary and that the southern california region may be considered as a broad shear zone

correlations between the evolution of benthic faunal communities and convergent movements of lithospheric blocks from the silurian to the late devonian in the mid palaeozoic uralian basin abstract the palaeogeographical interrelationships between benthic communities of middle palaeozoic carbonate platforms from both sides of the urals are compared the evolution of endemism in time as well as of taxonomic diversity and affinity trends in silurian and devonian brachiopods tabulate corals and trilobites are investigated for the first time using the internationally adopted standard of biozonation preliminary results indicate that in all considered biotas diversity and affinity rates were extremely low at the beginning of the silurian they increase thereafter until the late middle devonian and the late devonian where a high degree of identity was reached the observed overall increase in biogeographic affinity is interpreted as being the result of convergent plate movements between the eastern uralian oceanic domain where platform carbonates were deposited either on island arcs or on microplates and the passive east european margin a certain delay in the progress of faunal relationships is observed in the early middle devonian which may be related to the emplacement of the magnitogorsk volcanic megazone at that time

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

fluid inclusion and stable isotope studies of pb zn fluorite barite mineralization in the lower and middle benue trough nigeria lead zinc fluorite barite veins in the lower and middle benue trough nigeria are located within the lower cretaceous albian carbonaceous shales limestones and arkosic sandstones of this intracontinental rift structure the veins in the lower benue through consist of sphalerite galena marcasite chalcopyrite barite in a gangue of siderite and quartz hosted by carbonaceous shales whereas in the middle benue trough fluorite barite quartz and similar sulfide minerals are hosted by limestone and sandstone fluid inclusion temperatures in vein minerals range from 95 c to 200 c without pressure corrections and salinities range from 14 to 24 equiv wt nacl oxygen isotope compositions of limestone wall rocks middle benue have been lowered from premineralization 18o values of about 25 per mil to approximately 16 per mil fluid in equilibrium with vein calcite has a calculated 18o of 2 6 per mil at 130 c the 87sr 86sr ratio of this calcite 0 71497 suggests that strontium and calcium had a considerably more radiogenic source than the cretaceous limestone or evaporite did 87sr 86sr 0 7073 0 7078 observed strontium data lead isotope compositions of galena and ree patterns in fluorite suggest that the lower paleozoic basement rocks in the trough or their weathered equivalents are likely sources for the benue trough ore components sulfur isotope data suggest that the sulfur was probably contributed from the cretaceous evaporites in the trough

new constraints on relative motion between the pacific plate and baja california microplate mexico from gps measurements summary we present a new surface velocity field for baja california using gps data to test the rigidity of this microplate calculate its motion in a global reference frame determine its relative motion with respect to the north american and the pacific plates and compare those results to our estimate for pacific north america motion determination of pacific plate motion is improved by the inclusion of four sites from the south pacific sea level and climate monitoring project these analyses reveal that baja california moves as a quasi rigid block but at a slower rate in the same direction as the pacific plate relative to north america this is consistent with seismic activity along the western edge of baja california the baja california shear zone and may reflect resistance to motion of the eastern edge of the pacific plate caused by the big bend of the san andreas fault and the transverse ranges in southern california

anoxic events in the late frasnian causes of the frasnian famennian faunal crisis carbon isotope data collected from five frasnian famennian boundary sections in central europe show two positive 13 c excursions in the late frasnian 367 ma both anomalies coincided with the deposition of the bituminous lower and upper kellwasser horizons the carbon isotope patterns indicate two phases of enhanced burial and subsequent recycling of organic carbon a maximum formation of warm saline waters on the subtropical to tropical epicontinental shelves during late frasnian transgressive episodes may have induced oceanic oxygen deficits variations in the c org burial rates may have resulted in changes in the co 2 concentrations in the oceans and in the atmosphere culminating in global climatic changes we propose that the repeated co occurrences of sea level fluctuations anoxic conditions and global climatic changes during the late frasnian would affect especially the subtropical to tropical shallow water communities and reef ecosystems which were severely affected during the frasnian famennian faunal crisis

sensitivity of the southern san andreas fault system to tectonic boundary conditions and fault configurations the southern big bend of the san andreas fault saf accommodates transpression along numerous non vertical non planar and intersecting active surfaces using three dimensional boundary element method bem models we test the sensitivity of fault slip rates to a range of tectonic boundary conditions constrained by global positioning system gps studies of the region 45 50 mm yr and 320 325 using this approach our models provide a range of distributed fault slip rates associated with both spatial variations in geometry and present day uncertainties in plate motion model slip rates match most of the available geologic slip rates and discrepancies may owe to inaccurate fault geometries more northerly plate velocity 325 produces greater transpression along the saf system associated with greater uplift of the san bernardino mountains greater reverse slip rates along range bounding reverse thrust faults lower strike slip rates along the san andreas and san jacinto faults and greater strike slip rates along the eastern california shear zone ecsz and garlock fault these results suggest that the degree of regional transpression controls the partitioning of deformation between uplift and slip along both the saf system and the ecsz the insensitivity of modeled slip rates to applied velocity along the southern san andreas and san jacinto faults suggests that fault geometry greatly influences slip rates within the san bernardino mountains region a northerly shift in plate velocity orientation could account for the abandonment of the mill creek strand of the saf 95 ka and development of the present day active geometry which accommodates greater uplift

coastal tectonics on the eastern margin of the pacific rim late quaternary sea level history and uplift rates channel islands national park california usa abstract the pacific rim is a region where tectonic processes play a significant role in coastal landscape evolution coastal california on the eastern margin of the pacific rim is very active tectonically and geomorphic expressions of this include uplifted marine terraces there have been however conflicting estimates of the rate of late quaternary uplift of marine terraces in coastal california particularly for the northern channel islands in the present study the terraces on san miguel island and santa rosa island were mapped and new age estimates were generated using uranium series dating of fossil corals and amino acid geochronology of fossil mollusks results indicate that the 2nd terrace on both islands is 120 ka and the 1st terrace on santa rosa island is 80 ka these ages correspond to two global high sea stands of the last interglacial complex marine isotope stages mis 5 5 and 5 1 respectively the age estimates indicate that san miguel island and santa rosa island have been tectonically uplifted at rates of 0 12 0 20 m ka in the late quaternary similar to uplift rates inferred from previous studies on neighboring santa cruz island the newly estimated uplift rates for the northern channel islands are however an order of magnitude lower than a recent study that generated uplift rates from an offshore terrace dating to the last glacial period the differences between the estimated uplift rates in the present study and the offshore study are explained by the magnitude of glacial isostatic adjustment gia effects that were not known at the time of the earlier study set in the larger context of northeastern pacific rim tectonics channel islands uplift rates are higher than those coastal localities on the margin of the east pacific rise spreading center but slightly lower than those of most localities adjacent to the cascadia subduction zone the uplift rates reported here for the northern channel islands are similar to those reported for most other localities where strike slip tectonics are dominant but lower than localities where restraining bends such as the big bend of the san andreas fault result in crustal shortening

assessing long term postseismic deformation following the m7 2 4 april 2010 el mayor cucapah earthquake with implications for lithospheric rheology in the salton trough the 4 april 2010 mw 7 2 el mayor cucapah emc earthquake provides the best opportunity to date to study the lithospheric response to a large m6 magnitude earthquake in the salton trough region through analysis of global positioning system gps data in conjunction with the earthscope plate boundary observatory pbo we installed six new continuous gps stations in the months following the emc earthquake to increase station coverage in the epicentral region of northern baja california mexico we modeled the pre emc deformation field using available campaign and continuous gps data for southern california and northern baja california and inferred a pre emc secular rate at each new station location through direct comparison of the pre and post emc secular rates we calculate long term changes associated with viscoelastic relaxation in the salton trough region we fit these velocity changes using numerical models employing an elastic upper crustal layer underlain by a viscoelastic lower crustal layer and a mantle half space forward models that produce the smallest weighted sum of squared residuals have an upper mantle viscosity in the range 4 6 1018 pa s and a less well resolved lower crustal viscosity in the range 2 1019 to 1 1022 pa s a high viscosity lower crust despite high heat flow in the salton trough region is inconsistent with felsic composition and might suggest accretion of mafic lower crust associated with crustal spreading obscured by thick sedimentary cover

sea level history during the last interglacial complex on san nicolas island california implications for glacial isostatic adjustment processes paleozoogeography and tectonics abstract san nicolas island california has one of the best records of fossiliferous quaternary marine terraces in north america with at least fourteen terraces rising to an elevation of 270 m above present day sea level in our studies of the lowest terraces we identified platforms at 38 36 m terrace 2a 33 28 m terrace 2b and 13 8 m terrace 1 uranium series dating of solitary corals from these terraces yields three clusters of ages 120 ka on terrace 2a marine isotope stage mis 5 5 120 and 100 ka on terrace 2b mis 5 5 and 5 3 and 80 ka mis 5 1 on terrace 1 we conclude that corals on terrace 2b that date to 120 ka were reworked from a formerly broader terrace 2a during the 100 ka sea stand fossil faunas differ on the three terraces isolated fragments of terrace 2a have a fauna similar to that of modern waters surrounding san nicolas island a mix of extralimital southern and extralimital northern species is found on terrace 2b and extralimital northern species are on terrace 1 on terrace 2b with its mixed faunas extralimital southern species indicating warmer than present waters are interpreted to be from the 120 ka high sea stand reworked from terrace 2a the extralimital northern species on terrace 2b indicating cooler than present waters are interpreted to be from the 100 ka sea stand the abundant extralimital northern species on terrace 1 indicate cooler than present waters at 80 ka using the highest elevations of the 120 ka platform of terrace 2a and assuming a paleo sea level of 6 m based on previous studies san nicolas island has experienced late quaternary uplift rates of 0 25 0 27 m ka these uplift rates along with shoreline angle elevations and ages of terrace 2b 100 ka and terrace 1 80 ka yield relative local paleo sea level elevations of 2 to 6 m for the 100 ka sea stand and 11 to 12 m for the 80 ka sea stand these estimates are significantly higher than those reported for the 100 ka and 80 ka sea stands on new guinea and barbados numerical models of the glacial isostatic adjustment gia process presented here demonstrate that these differences in the high stands are expected given the variable geographic distances between the sites and the former laurentide and cordilleran ice sheets moreover the numerical results show that the absolute and differential elevations of the observed high stands provide a potentially important constraint on ice volumes during this time interval and on earth structure

earthquake locations in the inner continental borderland offshore southern california the inner continental borderland region offshore southern california is tectonically active and contains several faults that are potential seismic hazards to nearby cities however fault geometries in this complex region are often poorly constrained due to a lack of surface observations and uncertainties in earthquake locations and focal mechanisms to improve the accuracy of event locations in this area we apply new location methods to 4312 offshore seismic events that occurred between 1981 and 1997 in seven different regions within the borderland the regions are defined by either temporal or spatial clustering of seismic activity in the southern california seismic network scsn catalog obtaining accurate locations for these events is difficult due to the lack of nearby stations the limited azimuthal coverage and uncertainties in the velocity structure for this area our location procedure is based on the l 1 norm grid search waveform cross correlation method of shearer 1997 except that we use a nearest neighbor approach astiz et al 2000 to identify suitable event pairs for waveform cross correlation and we explore the effect of different velocity models on the locations and associated station terms in general our relocated events have small estimated relative location errors and the events are more clustered than the scsn catalog locations a quarry on the south tip of catalina island provides a test of our location accuracy and suggests that under ideal conditions offshore events can be located to within 1 to 2 km of their true locations our final locations for most clusters are well correlated with known local tectonic features we relate the 1981 santa barbara island m l 5 3 earthquake with the santa cruz fault the 13 july 1986 oceanside m l 5 3 sequence with the san diego trough fault zone and events near san clemente island with the known trace of the san clemente fault zone over 3000 of the offshore events during this time period are associated with the 1986 oceanside earthquake and its extended aftershock sequence our locations define a northeast dipping fault plane for the oceanside sequence but in cross section the events are scattered over a broad zone about 4 km thick this could either be an expression of fault complexity or location errors due to unaccounted for variations in the velocity structure events that occur near coronado bank in the scsn catalog are relocated closer to the san diego coast and suggest a shallow angle northeast dipping fault plane at 10 to 15 km depth manuscript received 12 february 1999

crustal architecture of the southern uralides from true amplitude processing of the urals seismic experiment and integrated studies urseis vibroseis profile true amplitude processing of the urals seismic experiment and integrated studies urseis vibroseis deep reflection seismic data acquired by the urseis consortium shows the southern uralide crust to be composed of four major blocks with distinctive reflection characteristics these blocks are juxtaposed along crustal scale boundaries the foreland thrust and fold belt developed from the east european craton crust is imaged as subhorizontal to east dipping reflectivity that can be related to its paleozoic and older tectonic history the moho beneath the foreland thrust and fold belt is not imaged in the vibroseis data set the main uralian fault the major arc continent suture is unreflective but its subsurface location can be inferred by the truncation of the reflection pattern of the east european craton and its contrast with that of the magnitogorsk arc the magnitogorsk arc reflectivity is characterized by patchy noncoherent to coherent reflections in the upper 10 15 km that are interpreted to be related to the arc volcanic rocks below this reflectivity is diffuse or the arc crust is transparent and the moho is not imaged the east magnitogorsk fault zone which juxtaposes the arc against the east uralian zone is not imaged by the data the upper 5 to 6 km of the east uralian zone corresponding to the dzhabyk granite is transparent below the granite the crust is characterised by east dipping patches of moderately coherent high amplitude reflections that in the east become shallowly west dipping a 10 km thick west dipping band of coherent high amplitude reflections between 12 and 35 km depth corresponding to the kartaly reflection sequence extends beneath almost the entire east uralian zone the crust beneath the easternmost east uralian zone reaches 53 km in thickness the upper and middle crust of the trans uralian zone is characterized by a series of east and west dipping concave upward moderately coherent high amplitude reflections the lowermost middle and lower crust displays thin bands of west dipping coherent low amplitude reflectivity the moho is imaged as a sharp transition from reflective lower crust to transparent upper mantle at 49 km depth and the lower crustal reflections appear to merge with it the urseis vibroseis data are integrated with results from the explosion source reflection data the wide angle reflection data and the surface geology to place constraints on the crustal architecture of the orogen and on the timing of its assemblage

influence of fault connectivity on slip rates in southern california potential impact on discrepancies between geodetic derived and geologic slip rates along the san bernardino strand of the san andreas fault saf and across the eastern california shear zone ecsz geologic slip rates differ from those inverted from geodetic measurements which may partly be due to inaccurate fault connectivity within geodetic models we employ three dimensional models that are mechanically compatible with long term plate motion to simulate both fault slip rates and interseismic surface deformation we compare results from fault networks that follow mapped geologic traces and resemble those used in block model inversions which connect the san jacinto fault to the saf near cajon pass and connect distinct faults within the ecsz the connection of the saf with the san jacinto fault decreases strike slip rates along the saf by up to 10 and increases strike slip rates along the san jacinto fault by up to 16 however slip rate changes are still within the large geologic ranges along the saf the insensitivity of interseismic surface velocities near cajon pass to fault connection suggests that inverse models may utilize both an incorrect fault geometry and slip rate and still provide an excellent fit to interseismic geodetic data similarly connection of faults within the ecsz produces 36 greater cumulative strike slip rates but less than 17 increase in interseismic velocity when using overconnected models to invert gps for slip rates the reduced off fault deformation within the models can lead to overprediction of slip rates while the nature of fault intersections at depth remains enigmatic fault geometries should be chosen with caution in crustal deformation models

a new gps velocity field for the pacific plate part 1 constraints on plate motion intraplate deformation and the viscosity of pacific basin asthenosphere

a unified analysis of crustal motion in southern california 1970 2004 the scec crustal motion map 1 to determine crustal motions in and around southern california we have processed and combined trilateration data collected from 1970 to 1992 vlbi data from 1979 to 1992 and gps data from 1986 to 2004 a long temporal coverage required in part by the occurrence of several large earthquakes in this region from a series of solutions for station positions we have estimated interseismic velocities coseismic displacements and postseismic motions within the region from 31 n to 38 n and east to 114 w the final product includes estimated horizontal velocities for 1009 gps 190 trilateration and 16 vlbi points with ties between some of these used to stabilize the solution all motions are relative to the stable north american reference frame snarf as realized through the velocities of 20 gps stations this provides a relatively dense set of horizontal velocity estimates with well tested errors for the past quarter century over the plate boundary from 31 n to 36 5 n these velocities agree well with those from the plate boundary observatory which apply to a later time period we also estimated vertical velocities 533 of which have errors below 2 mm yr most of these velocities are less than 1 mm yr but they show 2 4 mm yr subsidence in the ventura and los angeles basins and in the salton trough our analysis also included estimates of coseismic and postseismic motions related to the 1992 landers 1994 northridge 1999 hector mine and 2003 san simeon earthquakes postseismic motions increase logarithmically over time with a time constant of about 10 days and generally mimic the direction and relative amplitude of the coseismic offsets

are some fossils better than others for inferring palaeogeography the early ordovician of the north atlantic region as an example different kinds of fossils have different patterns of palaeogeographical distribution this has led to differing palaeocontinental reconstructions in the early palaeozoic we take the early ordovician of the north atlantic region as a test case to investigate the influence of taxonomic group upon palaeogeographical interpretation using both single linkage duster analysis and parsimony methods of biogeographical analysis on fossil faunas and floras of various groups within this region it is shown that the patterns of similarity obtained and their relationship to supposed oceanic separations vary widely from one group to another some planktic fossils graptolites acritarchs do not see a separation between gondwana and baltica which is strongly supported by evidence from other groups trilobites and ostracodes in particular reveal patterns which conform well with other geological and geomagnetic evidence at least in the arenig uanvirn time period geographical separation is seen as a more important control on faunal composition than was biofacies considering the better fossil groups for biogeographical discrimination different analytical methods produce similar biogeographical results

40ar 39ar u pb and sm nd constraints on the timing of metamorphic events in the maksyutov complex southern ural mountains new 40 ar 39 ar u pb and sm nd data from 13 metamorphic samples constrain the formation and exhumation of the high pressure maksyutov complex in the southern uralide orogen the maksyutov complex records the highest pressure metamorphism in the southern uralides and is part of the thrust stack that composes the footwall beneath the main ural fault the new isotopic data from eclogite in the lower unit of the maksyutov complex include 40 ar 39 ar data from phengite u pb data from rutile and apatite and sm nd data from garnet clinopyroxene rutile and apatite these data indicate that eclogite facies metamorphism occurred in the mid devonian epoch c 380 ma corresponding with eastward subduction of the east european craton beneath the magnitogorsk island arc after partial exhumation the lower unit was juxtaposed c 360 ma based on 40 ar 39 ar white mica data with the middle and upper units at mid crustal levels during the development of a d 3 shear zone within the subduction zone by the late carboniferous epoch the maksyutov complex was exhumed to upper crustal levels compatible with sedimentologic evidence that at this time the foreland thrust and fold belt began to form and material was shed off it into the foreland basin

guadalupe island mexico as a new constraint for pacific plate motion 1 we use gps data collected on isla de guadalupe and in northern baja california mexico to estimate site velocities relative to pacific plate motion the velocities of all three geodetic monuments on guadalupe fit a rigid pacific plate model with residuals of 1 mm yr using the guadalupe data and data from five igs stations on the pacific plate chat kokb kwj1 mkea and thti we estimate an angular velocity for this plate that is consistent with other recently published estimates our results indicate that isla de guadalupe lies on the pacific plate and that gps data collection on the island usefully constrains pacific plate motion and rigidity

new kinematic models for pacific north america motion from 3 ma to present ii evidence for a baja california shear zone we use new models for present day pacific north america motion to evaluate the tectonics of offshore regions west of the californias vandenburg in coastal alta california moves at the pacific plate velocity within uncertainties 1 mm yr after correcting for strain accumulation on the san andreas and san gregorio hosgri faults with a model that includes a viscoelastic lower crust modeled and measured velocities at coastal sites in baja california south of the agua blanca fault a region that most previous models consider pacific plate differ by 3 8 mm yr with coastal sites moving slower that the pacific plate we interpret these discrepancies in terms of strain accumulation on known on shore faults combined with right lateral slip at a rate of 3 4 mm yr on additional faults offshore peninsular baja california in the pacific offshore seismicity offset quaternary features along the west coast of baja california and a discrepancy between the magnetically determined spreading rate in the gulf rise and the total plate rate from a geological model provide independent evidence for a baja california shear zone

patterns of extinction and recovery of phacopid trilobites during the frasnian famennian late devonian mass extinction event canning basin western australia a diverse fauna of phacopid trilobites is described from the late devonian middle frasnian to early famennian of the northern canning basin western australia one new genus and four species in two genera are described from zones 11 13a and 13b of the middle and late frasnian trimerocephaloides sinevisus gen nov and sp nov t linguiformis sp nov acuticryphops acuticeps kayser 1889 and a klapperi sp nov late frasnian phacopines are either blind as shown for the first time in trimerocephaloides sinevisus or show trends to decreasing eye size up to the frasnian famennian kellwasser mass extinction event this evolutionary trend in acuticryphops is demonstrated to have been global at this time one new genus and six species of early famennian phacopids are described from the upper triangularis crepida and rhomboidea zones houseops gen nov with the new taxa h canningensis sp nov h beckeri sp nov and h sp a babinops planiventer feist becker 1997 b minor sp nov trimerocephalus tardispinosus feist becker 1997 and t mimbi sp nov in contrast to european sections where exclusively blind phacopids are known in earliest famennian sites initial recovery following the mass extinction event in canning peri reefal environments is characterized by oculated forms these trilobites must have evolved from conservative ancestors with normal eyes that had succeeded in surviving the kellwasser biocrises in reef related shallow water niches thus the origin of post event phacopids from shallow water environments is demonstrated for the first time descendant lineages show increasing eye size increased cephalic vaulting and effacement during the early famennian of the five orders of trilobites that are present during the frasnian stage at the beginning of the late devonian only two the proetida and the phacopida survived into the famennian the presence of a conformable sequence of trilobite bearing fore reef limestones the virgin hills formation that form part of the late devonian reef system in the northern part of the canning basin in western australia allows the patterns of evolution and extinction of the late frasnian and early famennian trilobites to be assessed in these deposits the three orders that became extinct during the frasnian famennian biocrises were the corynexochida mcnamara feist 2006 the lichida feist mcnamara 2007 and the harpetida mcnamara feist ebach in press here we focus on one of the groups that survived this event the phacopida although with a single exception they are rare elements of the trilobite fauna in the canning basin the phacopids are generically the most diverse of the

motion and rigidity of the pacific plate and implications for plate boundary deformation 1 using up to 11 years of data from a global network of global positioning system gps stations including 12 stations well distributed across the pacific plate we derive present day euler vectors for the pacific plate more precisely than has previously been possible from space geodetic data after rejecting on statistical grounds the velocity of one station on each of the pacific and north american plates we find that the quality of fit of the horizontal velocities of 11 pacific plate pa stations to the best fitting pa euler vector is similar to the fit of 11 australian plate au velocities to the au euler vector and 20 better than the fit of nine north american plate na velocities to the na euler vector the velocities of stations on the pacific and australian plates each fit a rigid plate model with an rms residual of 0 4 mm yr while the north american velocities fit a rigid plate model with an rms velocity of 0 6 mm yr our best fitting pa au relative euler vector is located 170 km southeast of the nuvel 1a pole but is not significantly different at the 95 confidence level it is also close 70 km in position and 3 in rate to a pole derived from transform faults identified from satellite altimetry suggesting that the vector has not changed significantly over the past 3 myr our relative euler vector is also consistent with all known geological and geodetic evidence concerning the au pa plate boundary through new zealand the gps sites offshore of southern california are presently moving 4 5 1 mm yr relative to predicted pacific velocity with their residual velocities in approximately the opposite direction to pa na relative motion likewise the easternmost sites in south island new zealand are moving 3 1 mm yr relative to predicted pacific velocity with the residuals in approximately the opposite direction to pa au relative motion these velocity residuals are in the same sense as predicted by elastic strain accumulation on known plate boundary faults but are of a significantly higher magnitude in both southern california and new zealand implying that the plate boundary zones in both regions are wider than previously believed index terms 1206 geodesy and gravity crustal movements interplate 8155 1208 geodesy and gravity crustal movements intraplate 8110 1243 geodesy and gravity space geodetic surveys 8158 tectonophysics evolution of the earth plate motions present and recent 3040 8159 tectonophysics evolution of the earth rheology crust and lithosphere keywords pacific plate motion plate rigidity plate boundary deformation

long term fault slip rates distributed deformation rates and forecast of seismicity in the western united states from joint fitting of community geologic geodetic and stress direction data sets 1 the long term average velocity field of the western united states is computed with a kinematic finite element code community data sets include fault traces geologic offset rates geodetic velocities principal stress directions and euler poles there is an irreducible minimum amount of distributed permanent deformation which accommodates one third of pacific north america relative motion in california much of this may be due to slip on faults not included in the model all data sets are fit at a common rms level of 1 8 datum standard deviations experiments with alternate weights fault sets and euler poles define a suite of acceptable community models in pseudoprospective tests fault offset rates are compared to 126 additional published rates not used in the computation 44 are consistent another 48 have discrepancies under 1 mm a 1 and 8 have larger discrepancies updated models are then computed novel predictions include dextral slip at 2 3 mm a 1 in the brothers fault zone two alternative solutions for the mendocino triple junction slower slip on some trains of the san andreas fault than in recent hazard models and clockwise rotation of some domains in the eastern california shear zone long term seismicity is computed by assigning each fault and finite element the seismicity parameters coupled thickness corner magnitude and spectral slope of the most comparable type of plate boundary this long term seismicity forecast is retrospectively compared to instrumental seismicity the western united states has been 37 below its long term average seismicity during 1977 2008 primarily because of temporary reduced activity in the cascadia subduction zone and san andreas fault system

paleomagnetism of the gays river zinc lead deposit nova scotia pennsylvanian ore genesis the gays river zinc lead deposit is the largest known mississippi valley type deposit in the mississippian windsor group of atlantic canada thermal and af demagnetization show that both ore and host rock have very similar magnetic characteristics stability tests constrain the magnetization to be mid mississippian to late pennsylvanian the pole position from the ore and host rock sites falls next to the pennsylvanian apw path suggesting an 8 clockwise rotation of the meguma platform relative to the craton regional thermal history and geochemical evidence suggest that the zinc lead ore magnetization and host rock remagnetization are coeval

the mechanisms of earthquakes and faulting in the southern gulf of california abstract accurate earthquake locations and their focal mechanisms can illuminate the distribution and mode of deformation at rifted continental margins the pacific north america pa na plate boundary within the gulf of california goc provides an excellent opportunity to explore the evolution and kinematics of rifting as continental extension in the north transitions to seafloor spreading in the south from october 2005 to october 2006 an array of eight four component ocean bottom seismographs deployed in the goc recorded seismicity as part of the sea of cortez ocean bottom array scooba experiment by combining the data with those from the onshore network of autonomously recording seismographs nars baja array we detect and locate 700 earthquakes m w 2 2 6 6 mainly along the northwest southeast striking transform faults that delineate the plate boundary for 36 events m w 3 5 6 6 with high signal to noise ratio in a long period 10 20 s band we determine deviatoric moment tensors and associated double couple focal mechanisms by regional waveform inversion many focal mechanisms are consistent with right lateral strike slip faulting along the pa na transform fault system which suggests that the transform faults primarily accommodate seismic deformation within the gulf in addition we capture a swarm of events on baja california along the right lateral northwest southeast striking las viboras el azufre fault which may be related to ongoing geothermal activity and volcanic deformation within the peninsula the combination of high resolution earthquake locations and focal mechanisms improves our understanding of the distribution of seismic deformation within the greater extensional zone in the southern goc online material earthquake catalog of the 695 events detected and located during our combined on offshore deployment of seismometers

structural geometry of a sector of the colorado river delta baja california mexico based on seismic reflections a structural study in the sw section of the colorado river delta using seismic reflection data is presented the study area is located along the cerro prieto transform fault which extends from the northern gulf of california through the mexicali valley and is an active fault within the pacific north american plate boundary zone the research was supported by a database of five seismic profiles with a total length of 215 km collected in the early 80 s by petroleos mexicanos the results show a high density of faults most of which are buried by sediments within the cerro prieto fault zone several faults were identified such as palmas mesa and pangas viejas until now unknown in addition even though the indiviso fault was investigated and superficially identify prior to this work herein mapped at depth west of the cerro prieto fault zone lies the las tinajas basin bound by the dunas and saldana faults and by the montague basin to the southeast the deformation zone along the plate boundary is 18 km wide stretching from the cerro prieto fault in the east to the pangas viejas fault in the west the orientations of the faults are nw se and if projected from the southern side of the sierra cucapah southward the faults tend to join the cerro prieto fault in the las tinajas basin the acoustic basement is deeper than 5 000 m some of the largest vertical displacements generated by the 2010 7 2 mw el mayor cucapah earthquake occurred southeast of the epicenter and coincided with the location of the pangas viejas fault which is buried by sediments before this event seismic activity was very low and no structures were known in the area in this paper we demonstrate that there are at least seven major faults that may now pose a high seismic hazard

post subduction volcanism in the baja california peninsula mexico the effects of tectonic reconfiguration in volcanic systems abstract late cenozoic volcanism in the baja california peninsula records the effects of cessation of subduction at a previously convergent plate margin prior to 12 5 ma the predominant volcanic activity had a calc alkaline signature however after 12 5 ma during the period of tectonic transition from a convergent to a strike slip boundary the style and composition of the magmatic products changed dramatically it has been proposed that the origin of the post subduction anomalous slab melt related magmas i e adakites niobium enriched basalts magnesian andesites is linked to regional tectonic events such as the subduction of an active ridge the breakoff of the subducted slab or the tearing of the stalled slab here we compile already published data on this volcanism and critically examine the tectonic models proposed to explain its origin an alternative approach based on a physical model of volcanic systems suggests that post subduction volcanism is strongly influenced by more local aspects including the stress field and the tensile strength of the rock overlying the zones where partial melting occurred this interpretation allows us to reconcile the apparent contradictory observations of the temporal and spatial distributions of post subduction activity providing a more adequate explanation of many characteristics of the baja california post subduction volcanism

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

global positioning system constraints on fault slip rates in southern california and northern baja mexico we use global positioning system gps estimates of horizontal site velocity to constrain slip rates on faults comprising the pacific north america plate boundary in southern california and northern mexico we enlist a simple elastic block model to parameterize the distribution and sum of deformation within and across the plate boundary we estimate a pacific north america relative plate motion rate of 49 3 mm yr one standard deviation consistent with nuvel 1a estimates we are able to resolve robust slip rate estimates for the southernmost san andreas san jacinto and elsinore faults 26 2 9 2 and 6 2 mm yr respectively and for the imperial and cerro prieto faults 35 2 and 42 1 mm yr respectively accounting for about 86 of the total plate motion the remaining 14 appears to be accommodated to the west of these fault systems probably via slip along the san clemente fault and or the san miguel vallecitos rose canyon and newport inglewood fault systems these results are highly consistent with paleoseismic estimates for slip rates implying that off fault strain accumulation within the deforming zone of the plate boundary is largely elastic we estimate that the seismically quiescent southernmost san andreas fault has incurred about 8 2 m of slip deficit over the last few hundred years presumably to be recovered during a future large earthquake

isotopic constraints on the genesis of zn pb mineralization at gays river nova scotia canada the gays river zn pb deposit is hosted in a carboniferous carbonate bank on the southern marginal platform of the major 8 km deep fundy magdalen basin fluid inclusion homogenization temperatures 130 degrees 215 degrees c and structural control of the mineralization determined in our previous study of the immediate mine area suggest affinities with both mississippi valley type and irish type deposits new isotopic work extending to within a 2 km radius of the mine area significantly constrains genetic hypotheses for the deposit preliminary hydrogen isotope measurements of inclusion fluids together with calculated oxygen isotope compositions suggest that the mineralizing fluids were basinal brines delta d 39ppm delta 18 o 3 3ppm strontium isotope composition of ore stage calcite 87 sr 86 sr 0 7117 indicates that components of the strontium and calcium had a source considerably more radiogenic than mississippian carbonate or evaporite 87 sr 86 sr 0 7085 0 7090 these and limited lead isotope data suggest that the fluids had a strontium and metal source in cambro ordovician basement rocks or their immediate clastic derivatives sulfur probably derived from the voluminous mississippian evaporites delta 34 s 14 or 1ppm was probably carried as sulfate in a fluid with neutral ph to the depositional site where complete nonbiogenic reduction at asymp 200 degrees c occurred this is supported by the lack of extensive dissolution and brecciation and the close similarity of the delta 34 s sub sigma s value for the mineralizing fluids and the delta 34 s value of the evaporites the carbon budget of the ore forming fluids was dominated by oxidized carbon from a carbonate source with delta 13 c value near 2 per mil locally influenced by organic carbon with low delta 13 c values which is abundant in the gays river carbonate bank a basinal brine expulsion model is favored the hot mineralizing fluid must have originated at a 4 km depth and interacted with elastic carbonate and evaporite sedimentary rocks on its way to the depositional site the likely age for this mineralizing event is approximately 300 m y

oxic facies and the late devonian mass extinction canning basin australia the close association of anoxic or dysoxic sedimentary rocks and the major late devonian frasnian famennian mass extinction has focused considerable attention on anoxia as the major cause or as a major factor in a multicausal scenario the record of the late devonian biotic crisis in the well known reef complexes of northwestern australia canning basin in contrast to many localities elsewhere does not display sedimentological evidence of anoxia through the frasnian famennian boundary interval analysis of continuous drill core through this interval has yielded three positive 13 c isotopic excursions only one of which coincides with total organic carbon toc maxima in our data multi element geochemical proxies suggest that toc maxima preceding positive shifts in 13 c most likely resulted from higher productivity caused by nutrient influx from continental weathering given the close association between toc maxima and regional relative sea level falls our interpretation supports the view that anoxia was not a fundamental driver of mass extinction and stresses the importance of integrated data sets and understanding regional controls on environmental changes and or stresses

instantaneous global plate motion model from 12 years of continuous gps observations 1 we estimate a global plate motion model for 17 major and minor tectonic plates solely on the basis of analysis of data from 106 globally distributed continuous gps stations spanning the period from january 1991 to july 2003 site positions estimated from 24 hour segments of data are aligned day by day to the international gps service igs realization of the itrf2000 reference frame using a similarity transformation thereby ensuring that the itrf2000 no net rotation condition is preserved linear velocities of a carefully selected set of stations are estimated from the position time series along with annual and semiannual fluctuations and position offsets due to gps instrument changes a white noise plus flicker noise model is applied to estimate realistic uncertainties for the site velocities which are then propagated into the derived plate motion model parameters we also examine the vertical velocities in the site selection process at the scripps orbit and permanent array center we have implemented a procedure whereby the plate motion model is updated on a regular monthly basis to improve its precision and reliability as new data become available and as a baseline against which anomalous motions can be detected

slicing up the san francisco bay area block kinematics and fault slip rates from gps derived surface velocities received 26 october 2004 revised 11 february 2005 accepted 10 march 2005 published 16 june 2005 i observations of surface deformation allow us to determine the kinematics of faults in the san francisco bay area we present the bay area velocity unification bavu bay view a compilation of over 200 horizontal surface velocities computed from campaign style and continuous global positioning system gps observations from 1993 to 2003 we interpret this interseismic velocity field using a three dimensional block model to determine the relative contributions of block motion elastic strain accumulation and shallow aseismic creep the total relative motion between the pacific plate and the rigid sierra nevada great valley sngv microplate is 37 9 0 6 mm yr 1 directed toward n30 4 w 0 8 at san francisco 2 fault slip rates from our preferred model are typically within the error bounds of geologic estimates but provide a better fit to geodetic data notable right lateral slip rates in mm yr 1 san gregorio fault 2 4 1 0 west napa fault 4 0 3 0 zone of faulting along the eastern margin of the coast range 5 4 1 0 and mount diablo thrust 3 9 1 0 of reverse slip and 4 0 0 2 of right lateral strike slip slip on the northern calaveras is partitioned between both the west napa and concord green valley fault systems the total convergence across the bay area is negligible poles of rotation for bay area blocks progress systematically from the north america pacific to north america sngv poles the resulting present day relative motion cannot explain the strike of most bay area faults but fault strike does loosely correlate with inferred plate motions at the time each fault initiated