the evidence for middle wisconsin peopling of beringia an evaluation abstract broken large mammal fossil bones in eastern beringia have been used to argue for a middle wisconsin or earlier time of human entry into north america it has been inferred that these controversial pleistocene bones are artifacts because 1 they are similar to those found in archaeological sites and 2 they can be reproduced in the laboratory by replication however fractured flaked polished faceted cut and scratched bones similar to the purportedly human artifacts described from beringia are known to be produced by natural processes new experimental data demonstrate that identifications of pleistocene bone artifacts on the basis of differential staining and fresh breakage are suspect physical processes such as the violent forces of river ice breakups in the north and bone crushing by mammalian scavengers produce similar pseudo artifacts additionally the middle wisconsin dates associated with some of the finished tools and human and dog bones from beringia are open to question the lack of credible dates on these artifacts raises doubt about the model of human colonization of beringia developed in the 1960s which proposed an interstadial colonization of the new world

a revised chronology of the lowest occupation layer of pedra furada rock shelter piaui brazil the pleistocene peopling of the americas abstract the present work revisits the chronology of the archaeologically controversial pedra furada rock shelter of southeast piaui brazil using an improved radiocarbon laboratory pre treatment and measurements on charcoal samples the procedure known as abox sc acid base wet oxidation followed by stepped combustion has previously been used to secure radiocarbon dates of 40 ka for the antiquity of human occupation of australia and south africa and now has been applied to charcoal from the previously dated oldest occupation layer of the pedra furada site previous radiocarbon dating had obtained only lower limits of 40 45 ka bp for the pedra furada basal layer nine charcoal samples from well structured hearths were subjected to the abox sc procedure and their radiocarbon content determined by accelerator mass spectrometry measurements on five of the samples returned ages of greater than 56 ka bp from graphites produced from abox pre treated charcoal combusted at 910 c two other samples were greater than 50 ka bp the remaining two samples were essentially completely combusted at 650 c with no material surviving to make a 910 c co 2 fraction their ages were 41 3 and 47 2 ka bp ages obtained from graphites generated from the 650 c combusted fraction are considered minimum ages

an ammonite zonation for the lower jurassic of canada and the united states the pliensbachian this is the first in a series of papers intended to establish a lower jurassic ammonite zonation that takes into account the biostratigraphic and biogeographic peculiarities of the north american succession its development has been spurred by the need for high resolution correlation between allochthonous terranes and the need for a standard to which microfossil sequences may be coupled in north america the lower boundary of the pliensbachian is drawn above the last echioceratids the lower pliensbachian is divided into in ascending order the imlayi whiteavesi and freboldi zones the upper pliensbachian into the kunae and carlottense zones the fannin bay section in the queen charlotte islands is designated the stratotype for the whiteavesi freboldi and kunae zones ideal stratotypes for the imlayi and carlottense zones are not presently known reference sections former illustrating the faunal associations that characterize all the zones are designated in western nevada the sunrise formation nor

an ammonite zonation for the toarcian lower jurassic of the north american cordillera this is the second in a series of papers intended to establish a lower jurassic ammonite zonation that takes into account the biostratigraphic and biogeographic peculiarities of the north american succession in north america the lower boundary of the toarcian is drawn at the first appearance of dactylioceras above the last occurrence of amaltheus and fanninoceras the lower toarcian is represented by the kanense zone the middle toarcian by the planulata and crassicosta zones and the upper toarcian by the hillebrandti and yakounensis zones section 5 on the yakoun river in the queen charlotte islands is designated the stratotype for the planulata crassicosta and hillebrandti zones section 3 on the yakoun river is designated the stratotype for the yakounensis zone an ideal stratotype for the kanense zone is not presently known reference sections further illustrating the faunal associations that characterize the zones are designated in eastern oregon snowshoe formation and northern british columbia

microbial deposits in the aftermath of the end permian mass extinction a diverging case from the mineral mountains utah usa the lower triassic mineral mountains area utah usa preserves diversified smithian and spathian reefs and bioaccumulations that contain fenestral microbialites and various benthic and pelagic organisms ecological and environmental changes during the early triassic are commonly assumed to be associated with numerous perturbations productivity changes acidifica tion redox changes hypercapnia eustatism and temperature changes post dating the permian triassic mass extinction new data acquired in the mineral mountains sediments provide evidence to decipher the relationships between depositional environments and the growth and distribution of microbial structures these data also help to understand better the controlling factors acting upon sedimentation and community turnovers through the smithian early spathian the studied section records a large scale depositional sequence during the dienerian spathian interval during the transgression depositional environments evolved from a coastal bay with continental deposits to intertidal fenestral microbial limestones shallow subtidal marine sponge microbial reefs to deep subtidal mud dominated limestones storm induced deposits microbialite sponge reefs and shallow subtidal deposits indicate the regression three microbialite associations occur in ascending order i a red beds microbialite association deposited in low energy hypersaline supratidal conditions where microbialites consist of microbial mats and poorly preserved microbially induced sedimentary structure ii a smithian microbialite association formed in moderate to high energy tidal conditions where microbialites include stromatolites and associated carbonate grains oncoids ooids and peloids and iii a spathian microbialite association developed in low energy offshore conditions that is preserved as multiple decimetre thick isolated domes and coalescent domes data indicate that the morphologies of the three microbialite associations are controlled primarily by accommodation hydrodynamics bathymetry and grain supply this study suggests that microbial constructions are controlled by changes between trapping and binding versus precipitation processes in variable hydrodynamic conditions due to the presence of numerous metazoans associated with microbialites throughout the smithian increase in accommodation and spathian decrease in accommodation the commonly assumed anachronistic character of the early triassic microbialites and the traditional view of prolonged deleterious conditions during the early triassic time interval is questioned

total sulfur content of late quaternary sediments in shibakawa lowland saitama prefecture central japan and its relation to the sedimentary environment abstract the total sulfur content of the pleistocene to holocene sediments in the shibakawa lowland northwest of tokyo central japan was measured and compared with the analytical results of fossils such as diatoms pollen and spores the marine sediments in the shibakawa lowland are found at two horizons one is between 10 0 and 6 0 m and the other between 0 1 and 2 6 m vs sea level the former horizon has been assigned to the interstadial musashino age of the wurm glacial stage and the latter to the early jomon transgression correlative with the neolithic transgression on the basis of the 14 c dating of wood fragments collected from the beds which are correlated with these horizons of the shibakawa lowland it has been revealed that the total sulfur content increases with an increase of marine diatoms and a decrease of freshwater ones this tendency suggests that the period when the total sulfur content was increasing was the time of seawater invasion into the lowland

the nature extent and subsequent dispersal of the permian tethys on the basis of the sedimentary and biotic facies characteristics of permian strata deposited in different climatic zones scepticism is expressed about some recent palaeogeographical reconstructions that demand a vast wedge shaped tethys in asia or movement over considerable latitudes of allochthonous terranes

late palaeozoic palaeomagnetic data for wrangellia resolution of the polarity ambiguity wrangellia and the alaska peninsula terrane are two of the many allocthonous terranes making up southern alaska today palaeomagnetic data from these areas clearly indicate low palaeolatitudes in the early mesozoic because of local and regional rotations the mean declination of the palaeomagnetic vectors is uncertain this in addition to incomplete temporal coverage has led to an ambiguity in the polarity of the vector and hence an ambiguity in whether the palaeolatitudes determined are in the northern or southern hemisphere the data considered here have resolved the ambiguity for wrangellia and by implication for the alaska pennisula terrane and also allow the construction of a highly speculative apparent polar wander curve

geographic differentiation of triassic brachiopods abstract the main palaeobiogeographic patterns and trends of triassic brachiopods are analysed during the triassic taxonomic diversity of brachiopods increased and this was accompanied by intensification of their geographic differentiation thus the maximum differention was attained during the late triassic for which at least five biochores of first rank boreal northern tethyan peri gondwanian notal or maorian and eastern pacific may be distinguished

early history of scleractinian corals and its geological consequences conventional views have implied that scleractinian corals were hermatypic and thus were potentially reef building from the onset of their appearance in early mesozoic time in shallow shelf carbonate environments however for almost 25 m y they held rather subordinate positions and generally did not participate in extensive ecologic reef framework evidence from both north america and europe demonstrates that triassic corals had ecologic preferences quite different from those in the cenozoic a key step in the evolutionary success of these corals may have been the advent of a symbiotic association with algae this association believed to have developed at the end of the triassic could have been responsible for thrusting scleractinians into prominent positions as reef builders and may account for their dramatic radiation in mesozoic time

oldest scleractinian coral reefs on the north american craton upper triassic carnian northeastern british columbia canada abstract bioclastic accumulations composed of crinoids brachiopods molluscs spongiomorphs and scleractinian corals occur within upper triassic strata of the lower baldonnel formation at pardonet hill in northeastern british columbia canada these small buildups 100 to 500 m3 have planar bases and broadly convex tops these mounds are interpreted as small patch reefs composed of packstone bioclastic floatstone rudstone and carbonate breccia intercalated with mixed siliciclastic carbonate sediments deposited in a shallow subtidal setting i e above fairweather wave base amalgamated hummocky cross stratified to current ripple laminated quartz dominated sandstone beds and numerous sharp based normally graded bioclastic commonly encrinitic packstone grainstone quartz sandstone couplets characterize inter reef lithologies conodont biostratigraphy indicates that the pardonet hill patch reefs occur within strata dated as earliest upper carnian lower nodosus zone the pardonet hill patch reefs originated and developed during an interval of regional sea level lowstand strata within which these patch reefs occur represent the westernmost migration of the triassic shoreline in western canada disappearance of coral reefs in the study area may have been affected by rapid marine transgression and failure of reef faunas to recolonize the new shore zone further to the east the pardonet hill locality occurred on the western margin of the north american craton during the triassic prior to their discovery reef like structures dominated by corals in the western panthalassa were limited to allochthonous terranes now part of the cordillera the pardonet hill patch reefs occur at approximately 30 triassic paleolatitude in modern settings this is at the extreme latitudinal margin of subtropical zooxanthellate reef development the presence of benthic faunas characteristic of low paleolatitude settings on the northwestern coast of pangea has significant implications in paleotectonic and paleoenvironmental reconstructions

reflection of the internal tide in upper loch linnhe a scottish fjord abstract results from an observational study of the internal tide of upper loch linnhe a fjord on the west coast of scotland are presented between november 1992 and june 1993 moorings containing current meters measuring velocity temperature and salinity were deployed at two sites in the loch observations of the horizontal velocities show the presence of an energetic first mode linear internal tide at the m 2 frequency with surface amplitudes of up to 0 57 m s 1 cf 0 03 m s 1 for the barotropic component independent evidence of the m 2 internal tide is provided by vertical velocities inferred from salinity and temperature variations in june 1993 an undulating ctd was used to study the horizontal propagation of the semi diurnal internal tide the results show that over the inner reaches of the loch the internal tide behaves as a standing wave with a large proportion of the internal tide energy being reflected at the landward end of the loch using the phase relationship between the velocity components from the mooring data it is demonstrated that there is a significant standing wave component present throughout the 7 month observational period closer to the sill the undulating ctd observations show the formation of an intense hydraulic jump on the flood tide suggesting the area immediately landward of the sill to be a region of complicated dynamics and high dissipation

early mesozoic southward migration of cordilleran transpressional terranes oblique plate convergence can cause forearc arc and back arc regions of active margin orogenic belts to behave as semi independent terranes relative to bordering continental and oceanic lithospheric plates these terranes called here transpressional terranes are bound by the subduction zone on one side by arc parallel strike slip faults in the forearc in the volcanic arc or in the back arc region on the other and are underlain by throughgoing basal decollements these terranes undergo shortening in a direction perpendicular to the subduction zone and migrate as coherent structural bodies parallel to the subduction zone along bounding strike slip faults many terranes of the north american cordillera may have behaved in this manner and perhaps did not travel across the pacific basin but rather were always peripheral to north america we propose that during the triassic to mid cretaceous portions of the cordillera borderland generally were displaced southward with respect to the north american craton due to left oblique convergence since the mid cretaceous they moved northward due to right oblique subduction the proposed displacements are consistent with structural paleomagnetic and paleontologic data and with the relative and absolute motions of north america and the pacific basin plates based on hotspot reference frame models

timing of the early triassic carbon cycle perturbations inferred from new u pb ages and ammonoid biochronozones based on analyses of single thermally annealed and chemically abraded zircons a new high precision u pb age of 251 22 0 20 ma is established for a volcanic ash layer within the kashmirites densistriatus beds of early smithian age early triassic from the luolou formation northwestern guangxi south china this new date together with recalculated uncertainties of previous u pb ages from the same section m ovtcharova h bucher u schaltegger t galfetti a brayard j guex new early to middle triassic u pb ages from south china calibration with ammonoid biochronozones and implications for the timing of the triassic biotic recovery earth planet sci lett 243 2006 463 475 allows constraining the time framework of the early triassic and leads to an estimated duration of i ca 0 7 0 6 my for the smithian and ii a maximal duration of ca 1 4 0 4 my for the griesbachian dienerian time interval the new u pb age considerably reduces the absolute age gap comprised between the permian triassic boundary and the spathian late early triassic the new age framework provides the basis for the calibration of a new carbonate carbon isotope and ammonoid records of the early triassic luolou fm which in turn are of high significance for global correlations and for carbon cycle modeling this calibration indicates that the most significant and fastest early triassic carbon isotope perturbations occur between the earliest smithian and the early spathian thus spanning a time interval of about 1 my whatever caused these carbon cycle shifts of high intensity and short duration there is evidence for connections between these fluctuations the pulsate recovery of ammonoids and conodonts as well as climate changes

global radiolarian zonation for the pliensbachian toarcian and aalenian jurassic radiolarians from 220 samples in queen charlotte islands b c williston lake b c east central oregon baja california sur southern spain austria slovenia turkey oman japan and argentina were studied in order to construct global zonation for the pliensbachian toarcian and aalenian stages well preserved faunas from continuous stratigraphic sections in queen charlotte islands provide the most detailed record for this time interval and all collections are tied to north american ammonite zones or assemblages collections from nearly all other areas lack independent dating except for early toarcian carbon isotope dating in slovenia and late aalenian ammonites in spain a database of 197 widely distributed updated taxonomic species was used to construct a unitary association ua zonation for the interval a global sequence of 41 uas was obtained for the top of the sinemurian to the base of the bajocian the first and the last uas represent the late sinemurian and the early bajocian respectively the remaining 39 uas were merged into nine zones four early pliensbachian one late pliensbachian one early toarcian one middle late toarcian and two aalenian according to prominent radiolarian faunal breaks and ammonite data the new zones are the canutus tipperi katroma clara zone latest sinemurian earliest pliensbachian zartus mostleri pseudoristola megaglobosa hsuum mulleri trillus elkhornensis and gigi fustis lantus sixi zones early pliensbachian eucyrtidiellum nagaiae praeparvicingula tlellensis zone late pliensbachian napora relica eucyrtidiellum disparile zone early toarcian elodium pessagnoi hexasaturnalis hexagonus zone middle and late toarcian higumastra transversa napora nipponica zone early aalenian and mirifusus proavus transhsuum hisuikyoense zone late aalenian these zones can be correlated worldwide and link previously established ua zonations for the hettangian sinemurian and the middle to upper jurassic the new zonation allows high resolution dating in the studied interval and provides a solid basis for analyzing faunal turnovers and the paleobiogeography of jurassic radiolarians

high resolution carbon isotope records of the toarcian oceanic anoxic event early jurassic from north america and implications for the global drivers of the toarcian carbon cycle the mesozoic era experienced several instances of abrupt environmental change that are associated with instabilities in the climate reorganizations of the global carbon cycle and elevated extinction rates often during these perturbations oxygen deficient conditions developed in the oceans resulting in the widespread deposition of organic rich sediments these events are referred to as oceanic anoxic events or oaes such events have been linked to massive injections of greenhouse gases into the ocean atmosphere system by transient episodes of voluminous volcanism and the destabilization of methane clathrates within marine environments nevertheless uncertainty surrounds the specific environmental drivers and feedbacks that occurred during the oaes that caused perturbations in the carbon cycle this is particularly true of the early jurassic toarcian oae 183 1 ma here we present biostratigraphically constrained carbon isotope data from western north america alberta and british columbia canada to better assess the global extent of the carbon cycle perturbations we identify the large negative carbon isotope excursion associated with the oae along with high frequency oscillations and steps within the onset of this excursion we propose that these high frequency carbon isotope excursions reflect changes to the global carbon cycle and also that they are related to the production and release of greenhouse gases from terrestrial environments on astronomical timescales furthermore increased terrestrial methanogenesis should be considered an important climatic feedback during ocean anoxic events and other similar events in earth history after the proliferation of land plants

middle triassic biostromes from the liard formation british columbia canada oldest examples from the mesozoic of nw pangea abstract mesozoic carbonate accumulations are rare in northwestern pangea this is due initially to the demise of many carbonate secreting organisms during the terminal permian biotic crisis and subsequently to increased siliciclastic sedimentation resulting from the tectonic development of western north america ecological voids resulting from the extinction however resulted in new opportunities for surviving taxa terebratulid brachiopod echinoderm dominated biostromes within the primarily siliciclastic liard formation middle triassic ladinian of northeastern british columbia provide a unique example the liard biostromes are composed primarily of whole and unabraded terebratulid brachiopods aulacothyroides liardensis articulate crinoid elements isocrinus sp and cidaroid echinoid spines and interambulacral plates miocidaris sp many of the terebratulid brachiopods are characterized by the pedicle attachment trace fossil podichnus other organisms which occupied the biostromes include discinid cf orbiculoidea sp and spiriferid spiriferina abichi brachiopods bivalves including oysters and gastropods as well as rare bryozoans and possibly scleractinian corals sedimentary units deposited on the margins of the biostromes are characterized by an abundance of body fossils decapod crustaceans bivalves and ophiuroids and trace fossils asterosoma cylindrichnus palaeophycus rosselia teichichnus and thalassinoides this trace fossil assemblage contains a mix of dwelling traces horizontal deposit feeding traces and vertical suspension feeding traces consistent with deposition in a lower shoreface setting hiatal surfaces and laterally restricted bioclastic sandstone layers and lenses within these features suggest that frequent turnover of infaunal and epifaunal communities occurred at the edges of the liard brachiopod echinoderm biostromes development of the liard brachiopod echinoderm biostromes depended on initial storm induced concentration of shell material to create patches or zones of stable substrate promoting colonization by terebratulid brachiopods discinid brachiopods crinoids and cidaroid echinoids

a low oxygen tolerant east pacific flat clam posidonotis semiplicata from the lower jurassic of the canadian cordillera flat clams represent a loosely defined group of thin shelled flat valved bivalves their distribution and high concentration in some especially mesozoic rocks have attracted interest and several contrasting paleoecologic interpretations have been proposed to explain their occurrence we present a comprehensive study of posidonotis semiplicata hyatt an early jurassic flat clam common in western north and south america posidonotis symmetrica hyatt posidonotis balteata crickmay and posidonotis cancellata leanza are interpreted as subjective junior synonyms in north america p semiplicata occurs in the upper sinemurian to lower toarcian of several cordilleran allochthonous terranes the south american record is restricted to upper pliensbachian to lower toarcian occurrences suggesting that the species originated in the northeast pacific in late sinemurian time and spread to the southeast pacific by the late pliensbachian the closely related posidonotis dainellii losacco sporadically kno

metallogenetic evolution of the east alpine paleozoic basement paleo metallogenetic sketch maps of the east alpine area are presented for the ordovician silurian the devonian lower carboniferous and the upper carboniferous permian mineralization and tectonic evolution are then discussed in the frame of a plate tectonic model compatible with recent results in western europe

a new genus and species of polychelid lobster crustacea decapoda eryonidae from the early jurassic hettangian of british columbia a single specimen of decapod crustacean preserved in ventral view and compressed represents a new genus and species of eryonid lobster wrangelleryon perates the discovery in lower jurassic hettangian sediments of the sandilands formation in british columbia represents the first occurrence of eryonidae in north america and reinforces a global distribution of the family in the jurassic the occurrence in british columbia on the wrangellia terrane supports the lower latitude setting in which the species lived resume un specimen unique de crustace decapode preserve en vue ventrale et comprime represente un nouveau genre et une nouvelle espece de homard eryonide wrangelleryon perates la decouverte dans des sediments du jurassique inferieur hettangien de la formation de sandilands en colombie britannique represente la premiere occurrence d un eryonide en amerique du nord et consolide la these d une repartition planetaire de cette famille au jurassique la presence du specimen en colombie britannique dans le terrane de wrangellie appuie la these voulant que l espece ait vecu abasse latitude traduit par la redaction

mesozoic evolution of exotic terranes and marginal seas western north america abstract regional terrane analysis has been combined with a global evaluation of plate kinematics to produce a new tectonic model for the mesozoic evolution of western north america and its associated marginal seas the model employs a two tiered data reliability ranking system to resolve conflicts within data sets the lower tier of the ranking system involves the assignment of a numerical rank to paleomagnetic and or paleobiogeographic data based on each data set s reliability the upper tier of the ranking system places the paleomagnetic and paleobiogeographic data in perspective by assigning a relative order of importance to different types of data the most reliable data are considered to be departure rift and arrival collision times that are tightly constrained by independent data sets evidence of subduction and or strike slip motion also ranks high in the master ranking system paleomagnetic and vertebrate paleobiogeographic data come next in the hierarchy followed by invertebrate and floral paleobiogeographic data application of this approach to a case study the baja british columbia controversy has resulted in a coherent model for the entire region results derived from the application of this modelling approach to the problem of the mesozoic assembly of western north america suggest that its evolution may be modeled using a minimum of 57 large terranes oblique convergence may have been the dominant tectonic process along the western north american margin during the mesozoic causing large scale latitudinal transport of many exotic terranes the motions of the terranes produced a number of marginal seas yukonia etc that were short lived but important components of western margin tectonics a combination of collision events side swiping episodes and changes in plate kinematics led to the initiation of several regional tectonic upheavals including the nevadan and sevier orogenies

river ice as a taphonomic agent an alternative hypothesis for bone artifacts abstract the annual freezeup and violent breakup of temperate and high latitude rivers produces unique geomorphic features that can be recognized in ancient sediments the forces and materials involved in the breakup process could modify entrained bones in ways similar to those attributed to human activity an intuitive taphonomic model is developed to explain how river ice may affect bones and to predict the modifications expected partial testing of the model by experiments designed to simulate river breakup produced bone modifications such as fractures flakes facets striations isolated cuts and polish the taphonomic effects of river ice must be discounted prior to the interpretation of such features as human in origin

atypical diagenetic effects on strontium isotope composition of early jurassic belemnites queen charlotte islands british columbia canada in this study strontium carbon and oxygen isotope data are reported from early jurassic belemnites from yakoun river queen charlotte islands qci british columbia assuming that the established ammonite correlations between canada and europe are accurate the seawater 87sr 86sr curve between europe and qci should be similar however the rarenodia planulata and phymatoceras crassicosta ammonite biozones from yakoun river record 87sr 86sr values that are lower than expected this shift is interpreted to be a result of diagenetic alteration by later hydrothermal fluid 87sr depleted in general the diagenetic samples have more negative 13cbel and 18obel values and higher mn concentrations but show no difference in fe concentration a 13cbel curve from diagenetically screened samples exhibits only slightly depleted values with respect to a similar curve generated from europe a similar curve for 18obel shows a striking similarity with that generated from europe this study illustrates that dia

tectonic rotations and translations in western canada new evidence from jurassic rocks of vancouver island the lower jurassic bonanza group sinemurian and pliensbachian lavas and tuffs about 205 to 195 ma on northwestern vancouver island possesses a stable remanent magnetization with a mean direction d i of 276 42 13 sites distributed through 1800 m of section 128 specimens kb 50 95 6 palaeopole 22 n 154 e dm dp 9 6 reversals are present but one polarity is dominant and most directions are westerly the palaeolatitude is 24 6 with the usual ambiguity as to whether it is north or south of the palaeoequator to determine the relative motions between ancestral north america and vancouver island these data are compared with determinations from peri atlantic igneous rocks dated radiometrically in the same time interval the use of model apparent polar wander paths for this purpose is criticized a net post jurassic northerly motion of 9 7 or 57 7 is indicated depending on the chosen hemisphere of origin the net post jurassic rotations relative to cratonic north america are 66 7 anticlockwise or 114 7 clockwise for the northern and southern hemispheres respectively such large rotations are apparently a common feature of early mesozoic rocks of the canadian cordillera it is suggested that these large and variable rotations characterize the deformation occurring during the pre mid cretaceous amalgamation of the various terranes of british columbia

multiple sulfur isotope signals associated with the late smithian event and the smithian spathian boundary abstract the early triassic is generally portrayed as a time of various high ecological stresses leading to a delayed biotic recovery after the devastating end permian mass extinction this interval is notably characterized by repeated biotic crises e g during the late smithian large scale fluctuations of the global carbon nitrogen and sulfur cycles as well as harsh marine conditions including a combination of ocean acidification anoxia extreme seawater temperatures and shifting productivity observations from different paleolatitudes suggest that sulfidic h2s rich conditions may have developed widely during the early triassic possibly reaching up to ultra shallow environments in some places however the existence and the spatio temporal extent of such redox swings remain poorly constrained in order to explore early triassic paleoceanographic redox changes and their potential influences on the biotic recovery we analyzed multiple sulfur isotopes 32s 33s 34s and 36s of sedimentary pyrite and carbonate associated sulfate 34scas from the mineral mountains section utah sediments from this section were mainly deposited in shallow waters and span the smithian and lower spathian we report a 68 range of variations in 34spy associated with 33spy varying from 0 01 to 0 12 whereas the 34scas varies between 19 5 and 34 8 we interpret the observed signal of multiple sulfur isotopes as reflecting the operation of pore water synsedimentary microbial sulfate reduction in open system with respect to sulfates before the late smithian evolving to a closed system sulfate limited rayleigh type distillation across the smithian spathian boundary ssb and immediately after the ssb we argue that this marked change is driven by the effectiveness of the connection between the sedimentary pore waters and the overlying water column which is in this case controlled by the local sedimentological conditions such as the bioturbation intensity and the sedimentation rate therefore our results suggest that changes in the sulfur cycle before and across the ssb at mineral mountains is probably a local consequence of the loss of the mixed sedimentary layer during the late smithian extinction event as opposed to reflecting the development of a lethal anoxic ocean at the global scale

evidence from neodymium isotopes for mantle contributions to phanerozoic crustal genesis in the canadian cordillera sm nd and rb sr isotopic studies of several phanerozoic orogenic belts have shown that much of the crust in these belts is composed of reworked pre existing continental crust in contrast isotopic data collected from two of the largest terranes in the canadian cordilleran orogenic belt the alexander and stikine terranes show that these tectonic fragments are composed of mantle derived continental crust in many respects the style and rate of crustal accretion of these and related terranes appear similar to those of some proterozoic crustal regions

allochthonous terranes in alaska implications for the structure and evolution of the bering sea shelf abundant evidence has been gathered in support of the concept that much of the pacific margin of north america consists of allochthonous terranes that were accreted during mesozoic and early tertiary time in particular southern alaska is almost completely composed of separate terranes whose stratigraphy and paleomagnetism indicate distant origins the bering sea continental shelf is among the largest shelves in the world almost half as large as alaska itself some of the allochthonous terranes in alaska probably continue beneath the continental shelf but their distribution beyond the shoreline has not been determined we believe that much of the continental shelf is probably composed of allochthonous terranes in much the same way as southern alaska geophysical data from the bering continental shelf have been used to test this hypothesis although inconclusive without extensive drilling multichannel seismic profiles and magnetic data indicate the composite character of the shelf basement the magnetic anomalies can be separated into specific domains of limited extent these magnetic variations suggest a corresponding variation of rock terranes beneath the shelf in addition multichannel seismic profiles show possible thrust faults within the shelf basement that could be sutures between separate terranes

cache creek terrane entrapment oroclinal paradox within the canadian cordillera exotic and far traveled oceanic crustal rocks of the cache creek terrane cc are bordered by less exotic quesnel qn and stikine st arc terranes to the east north and west all of these terranes are enveloped by an arcuate belt of displaced continental margin rocks the kootenay ko nisling ns and parts of the yukon tanana ytt terranes that have indirect ties to ancestral north america na initial 87sr 86sr isopleths conform to this arcuate pattern such a pattern of concentric belts presents a geological conundrum how did the qn st and cc come to be virtually enveloped by terranes with ties to na past and current models that explain assembly of the canadian cordillera are deficient in their treatment of this problem we propose that early mesozoic qn and st were joined through their northern ends as two adjacent arc festoons that faced south toward the cache creek ocean panthalassa oceanic plateau remnants within the cc today were transported from the tethyan realm and collided with these arcs during subduction of the cache creek ocean counterclockwise oroclinal rotation of st and ns terranes in the late triassic to early jurassic caused enclosure of the cc rotation continued until these terranes collided with qn in the middle jurassic paleomagnetic declination data provide support for this model in the form of large average anticlockwise rotations for permian to early jurassic sites in st but moderate clockwise rotations for sites in qn specific modern analogues for the cordilleran orocline include the yap trench where the caroline rise is colliding end on with the mariana arc and the banda arc located on the southeastern tail of the asian plate which is being deformed into a tight loop by interactions with the australian and pacific plates

evaluation of the baja controversy using paleomagnetic and faunal data plume magmatism and piercing points abstract the controversy over late cretaceous locations of baja alaska baja bc stikinia and western quesnellia centres around whether a they were within 1000 km of their present positions or b located 1000 5000 km south along the western coast of laurentia to be transported northwards by the kula plate during the late cretaceous and cenozoic the latter is supported by paleomagnetic data including data that pass a fold contact or reversal test whereas the former is based upon correlation of strata across faults although various critical tests have been proposed and tried interpretations are equivocal e g alternative interpretations for the source of detrital zircons in baja bc we propose that the presence of plume magmatism provides unique vertical piercing points thus correlation of the 70 ma plume magmatism in northern stikinia with the yellowstone hotspot locates stikinia 2000 km to the south and 1000 km off the western coast of laurentia on the other hand the absence of 90 70 ma yellowstone plume magmatism in the presently adjacent baja bc but the presence of 60 47 ma yellowstone plume spreading ridge magmatism in southern baja bc southern vancouver island and coast ranges of washington and oregon implies that it moved at least 1200 km northwards between 70 and 60 ma i e a rate of 12 cm year the spreading ridge may be correlated with the kula farallon ridge furthermore the presence of middle late triassic plume magmatism in wrangellia and the peninsula and alexander terranes suggests 2000 km of relative dextral movement between baja alaska and baja bc applying these conclusions to pre 90 ma paths of baja alaska bc across the pacific ocean suggests that it had three components 1 northeasterly between 230 and 180 ma 2 eastsoutheasterly between 180 and 140 ma and 3 northeasterly between 140 and 90 ma whereas the latter component is consistent with published terrane tracks the 180 140 ma component is at odds suggesting that this latter segment be reassessed the weight of evidence in favour of correlating geological piercing points across the gulf of california appears to outweigh paleomagnetic evidence for 1000 2500 km of apparent northward displacement of baja california in the cretaceous and early tertiary which may be explained by 15 20 tilting of fault blocks recorded by 40 ar 39 ar cooling ages thus we conclude that whereas baja alaska baja bc stikina and western quesnellia were transported between 1000 and 5000 km northwards along the western margin of laurentia during the late cretaceous and cenozoic baja california has not moved more than that required to open the gulf of california

the early triassic ammonoid recovery paleoclimatic significance of diversity gradients ammonoids recovered much faster than other marine shelly invertebrates after the end permian mass extinction based on a refined global data set at the basin level we investigate the paleobiogeographical global latitudinal and longitudinal diversity patterns in terms of climatic changes during the early triassic such analysis differs from already published qualitative or quantitative studies in that it estimates faunal patterns and endemicity at an ecologically meaningful level of spatial resolution i e at the basin level during the early triassic the global first order trend in increasing ammonoid diversity was accompanied by a progressive change from cosmopolitan to latitudinally restricted distributions this led to the emergence of a clear latitudinal diversity gradient during most of the smithian and spathian stages which entails increased steepness of the sea surface temperature gradient during the late early triassic however two brief episodes of ammonoid cosmopolitanism combined with low global diversity interrupted the first order increasing trend at the very beginning of the smithian and at its very end the longitudinal analysis of smithian distributions indicates a westward decrease of diversity within the tethys which faded away during the spathian analysis of endemicity indicates a rapid biogeographical maturing and structuring of faunas concomitant with the edification of the latitudinal diversity gradient

paleoecology biogeography and evolution of reef ecosystems in the panthalassa ocean during the late triassic insights from reef limestone of the sambosan accretionary complex shikoku japan upper triassic reefs from the panthalassa ocean have been understudied in comparison to their tethyan counterparts and are therefore pivotal to understanding the global reef evolution during the late triassic to fill this gap upper triassic reef limestone from ten localities of the sambosan accretionary complex at shikoku island japan has been investigated biotic assemblages quantitative microfacies analysis and integrated biostratigraphy allow us to characterize two types of reefs those attributed to the ladinian early carnian and those attributed to the late carnian rhaetian at the regional scale our data refine the biostratigraphic framework of the upper triassic sambosan limestone at the global scale multivariate analyses support a strong paleobiogeographic affinity of the western panthalassa reef biota with those of the south tethys ocean during the ladinian carnian and norian rhaetian additionally they indicate connections with east panthalassa reefs during the norian rhaetian

carbon isotopic excursions and detailed ammonoid and conodont biostratigraphies around smithian spathian boundary in the bac thuy formation vietnam abstract the smithian spathian boundary is indicated by the first occurrence of the ammonoid tirolites cf cassianus in the olenekian bac thuy formation northeastern vietnam the boundary is intercalated within organic rich dark gray mudstone that accumulated under anoxic to dysoxic conditions in the an chau and nanpanjiang basins on the south china block in lang son area three conodont zones novispathodus ex gr waageni novispathodus ex gr pingdingshanensis and icriospathodus collinsoni are recognized in the formation the smithian spathian boundary is intercalated within n ex gr pingdingshanensis conodont zone the positive excursion in 13c with values increasing from around 2 3 to 5 7 was recorded in the uppermost smithian xenoceltites variocostatus ammonoid beds and n ex gr pingdingshanensis conodont zone the 13c values decrease across the smithian spathian boundary these 13c isotopic patterns are correlated with well known positive excursions around the smithian spathian boundary globally

lower to middle jurassic pliensbachian to bajocian stratigraphy of the northern spatsizi area north central british columbia the lower to middle jurassic pliensbachian to lower bajocian spatsizi group in the northern spatsizi area of north central british columbia is formally defined and subdivided into the joan wolf den melisson abou and quock formations each formation reflects deposition in a different dominantly fine clastic environment with a varying input of volcanic epiclastic or pyroclastic detritus the spatsizi group represents the basinward sedimentary equivalent of the coeval cold fish volcanics a group of calc alkaline flows and breccias that accumulated in a volcanic arc along the southern flank of the stikine arch arc to basin facies trends are best developed in the joan and wolf den formations and are characterized by a decrease in the volcaniclastic component of the sediments an overall reduction in grain size and a progressively deeper water environment of deposition as inferred from both sedimentological and faunal evidence in the study area the spatsizi group underlies with a slight angular di

new u pb zircon ages integrated with ammonite biochronology from the jurassic of the canadian cordillera the accuracy of published jurassic time scales is compromised by a paucity of sufficiently accurate and stratigraphically well constrained isotopic dates u pb dating of volcaniclastic rocks within fossiliferous marine successions is a method suitable of providing additional useful calibration points stikinia and wrangellia two of the major accreted terranes of the canadian cordillera comprise volcanosedimentary assemblages of magmatic arc origin within them we selected sections from which we report 14 new u pb zircon ages that are integrated with ammonite biochronology at the zonal level poor zircon recovery and complex u pb systematics made it difficult to obtain precise ages for many of the samples the following ages were determined with 2 errors 194 0 9 1 1 8 ma from the plesechioceras harbledownense assemblage upper sinemurian 191 5 0 8 ma from the plesechioceras harbledownense assemblage upper sinemurian to the whiteavesi zone lower pliensbachian 185 6 6 1 0 6 ma from the frebo

the smithian spathian boundary late early triassic a review of ammonoid conodont and carbon isotopic criteria abstract the transition from the smithian substage to the spathian substage of the olenekian stage of the late early triassic was a critical time marked by a series of biological and environmental changes during the multimillion year recovery interval following the end permian mass extinction however the smithian spathian boundary ssb does not yet have an agreed definition a shortcoming that complicates high resolution analysis of events during the smithian spathian transition here we review key biostratigraphic i e ammonoid and conodont studies of the smithian and spathian substages in historically important regions e g the canadian arctic for the boreal realm western north america for the eastern panthalassic ocean and more recently re studied locations e g pakistan and india in the southern tethys south china in the eastern tethys as well as the carbon isotope chemostratigraphy of 29 major smithian spathian sections globally key ammonoid genera e g wasatchites anasibirites glyptophiceras and xenoceltites of the late smithian and bajarunia tirolites and columbites of the early spathian conodont species e g scythogondolella milleri novispathodus waageni and borinella buurensis of the late smithian and triassospathodus hungaricus neogondolella aff sweeti and icriospathodus spp of the early spathian and carbonate carbon isotope excursions provide appropriate markers for constraining the ssb use of the first occurrence of the conodont novispathodus pingdingshanensis as a potential marker of the ssb is also discussed based on correlations of biostratigraphic and carbon isotope data globally we propose to revise previous placements of the ssb transition in some sections finally we show that the smithian thermal maximum stm herein named was middle smithian in age and not correlative with the ssb as inferred in some earlier studies and that the ssb coincided with a subsequent major global cooling event

nd and sr isotopic characterization of the wrangellia terrane and implications for crustal growth of the canadian cordillera nd and sr isotopic data are reported from samples of most of the major lithologic units of the wrangellia terrane exposed on vancouver island and the queen charlotte islands initial epsilon nd values range from 1 0 to 7 3 and initial 87 sr 86 sr ratios range from 0 70323 to 0 70481 these ratios are similar to those of modern island arcs and demonstrate the unevolved juvenile nature of this terrane these data indicate that wrangellia probably resided in an intra oceanic environment until its accretion to north america nd crustal residence ages for clastic sedimentary rocks of wrangellia mean t cr 0 77 pm 0 33 ga t dm 0 57 pm 0 35 ga are much closer to their stratigraphic ages than is the case for the ages of many other phanerozoic sedimentary rocks thus providing strong evidence for phanerozoic crustal addition to north america early proterozoic crustal components cannot comprise more than about 6 of wrangellia therefore the terrane consists of 94 new mantle d

smithian and spathian early triassic ammonoid assemblages from terranes paleoceanographic and paleogeographic implications early triassic paleobiogeography is characterised by the stable supercontinental assembly of pangea however at that time several terranes such as the south kitakami massif sk south primorye sp and chulitna respectively and presently located in japan eastern russia and alaska straddled the vast oceans surrounding pangea by means of quantitative biogeographical methods including cluster analysis non metric multidimensional scaling and bootstrapped spanning network applied to smithian and spathian early triassic ammonoid assemblages we analyze similarity relationships between faunas and suggest paleopositions for the above cited terranes taxonomic similarities between faunas indicate that primary drivers of the ammonoid distribution were sea surface temperature and currents possible connections due to current controlled faunal exchanges between both sides of the panthalassa are shown and terranes such as sk sp and chulitna played an important role as stepping stones in the dispersal of ammonoids sk and sp terranes show strong sub equatorial affinities during the smithian thus suggesting a location close to south china at the same time the chulitna terrane shows strong affinities with equatorial faunas of the eastern panthalassa this paleoceanographic pattern was markedly altered during the spathian possibly indicating significant modifications of oceanic circulation at that time as illustrated by the development of a marked intertropical faunal belt across tethys and panthalassa

northern and southern hemispheres ostracod palaeobiogeography during the early jurassic possible migration routes abstract the purpose of this paper is to review the palaeobiogeographical distribution of early jurassic ostracod species worldwide to establishing possible migration pathways between the north and south hemispheres in direction and timing and in particular to examine the existence of a seaway through central america the hispanic corridor from at least the pliensbachian toarcian a detailed taxonomic revision of over 270 early jurassic ostracod species from europe north africa south america asia and australia a revision of every figured specimen and or taxon included in each list of synonymous taxa has been undertaken each assemblage was subjected to a quantitative analysis this metric was calculated using the dice similarity index in order to ascertain the degree of similarity between ostracod assemblages from both hemispheres the obtained results indicate that there is a clear differentiation between australian and argentinean ostracod assemblages in relation to european ostracod assemblages the australian faunas are similar to western tethyan and central european assemblages probably indicating a communication route along the western tethys aided by the action of western currents moreover the argentinian ostracod assemblages exhibit a high degree of similarity with north western european portugal grand banks the fasnet basin and wales and north african assemblages through the detailed analysis of ostracod spatial and temporal distribution the coeval occurrence of taxa in argentina and western europe and the differences between australian and argentinian faunas and the pattern of ocean currents derived from climate models simulations it would infer the existence of the hispanic corridor

jurassic foraminifera from the queen charlotte islands british columbia canada biostratigraphy paleoenvironments and paleogeographic implications abstract lower and middle jurassic sinemurian to callovian foraminifera were examined from 66 localities of the queen charlotte islands british columbia canada over 200 species of well preserved benthic calcareous and agglutinated taxa belonging to 50 genera were identified foraminifera from the lower jurassic are represented by an abundant and diverse tethyan derived calcareous assemblage with boreally derived agglutinated taxa becoming gradually more dominant in the upper lower jurassic to lower middle jurassic sedimentary strata and their faunal components and position of hiatuses correlate approximately with the jurassic eustatic sea level curve sea level changes have resulted in a variety of depositional environments ranging from deep water euxinic shales with abundant tuff beds characterized by small pyritized foraminifera to a well oxygenated outer shelf setting characterized by a major faunal increase to shoreface sandstones and conglomerates with absent to rare benthic foraminifera a gradual shallowing from a slope to a shelf dominated deposition with a magmatic arc provenance is suggested for the lower jurassic changing in the middle jurassic to an inner shelf to upper shoreface setting dominated by sedimentary strata of volcaniclastic origin a marked faunal turnover is observed in the lower jurassic whiteaves formation middle toarcian with the extinction of several earlier species and the appearance of a new diverse assemblage of 225 taxa this turnover is also observed in the ammonite and radiolarian assemblages of the queen charlotte islands in comparison to the dominantly tethyan derived taxa of pre middle toarcian age many of the species from the middle toarcian are found in northern latitudes such as on the northern slope of alaska arctic islands and the northwest territories hence foraminifera in conjunction with existing radiolarian and ammonite data suggest a northward displacement of the queen charlotte islands from low to mid paleolatitudes by late early jurassic toarcian to early middle jurassic bajocian time

synchrony between early jurassic extinction oceanic anoxic event and the karoo ferrar flood basalt volcanism a well known second order mass extinction took place during the pliensbachian and toarcian stages of the early jurassic first recognized as a minor pliensbachian peak in the global extinction rate it has alternatively been interpreted as a regional response to the early toarcian oceanic anoxic event detailed studies established it as a global long term event spanning five successive ammonoid zones here we present a revised time scale based on highprecision u pb ages resolved to the zone level which suggests that elevated extinction rates were sustained for about 4 m y and peak extinction occurred at 183 ma recent isotopic dating of flood basalts from the southern gondwanan karoo and ferrar provinces documents a culmination in volcanic activity ca 183 ma the onset of volcanism is recorded as an inflection and start of a rapid rise of the seawater 87 sr 86 sr curve the synchrony of voluminous flood basalt eruptions and biotic crises as already noted for three of the major mass extinctions permits a causal relationship which in this case may be mediated by widespread oceanic anoxia

significance of tethyan fossils in the american cordillera equatorial faunas of the ancient tethyan seaway which extended from western europe to southeastern asia comprise some of the most diverse marine taxa in the fossil record comparable or identical tethyan species that occur far from the tethyan seaway in paleozoic and mesozoic rocks of the north and south american cordillera have long been considered as a major biogeographic anomaly two leading theories to account for the occurrence of these anomalous tethyan faunas in the cordillera are that they were transported long distances to the east on tectonic blocks suspect terranes that originated near the tethys or that they migrated westward via undiscovered marine corridors through continental areas of pangea an alternative model is that these tethyan fauna were pantropic species that extended with attenuated diversities into the eastern proto pacific ocean this pantropic model can better account for the distribution patterns of many paleozoic and early mesozoic tethyan species in the american cordillera and provides a steady state hypothesis against which the other models can be tested the distribution of pre cretaceous tethyan faunas is similar to the known pantropic distribution of many cretaceous and cenozoic tropical biotas during the cenozoic taxa were most diverse in the tethys and indo west pacific regions but extended with attenuated diversity to many parts of the equatorial pacific ocean including the west coasts of north and south america the eastern pacific occurrence of many indo west pacific species provides a modern analog for the occurrence of many anomalous tethyan fossils in the american cordillera

new saurorhynchus actinopterygii saurichthyidae material from the early jurassic of alberta canada saurichthyidae are a family of elongate piscivorous actinopterygian fishes with a stratigraphic range extending from the late permian to the middle jurassic there are four recognized early jurassic species all from europe and all referred to the genus saurorhynchus only a single non european jurassic occurrence has been reported a partial saurorhynchus skull from the fernie formation of western alberta canada here we evaluate the saurorhynchus material from canada including a new skull from ya ha tinda alberta and a fragmentary mandible from canyon creek alberta all diagnostic canadian saurorhynchus specimens are consistent with the european species saurorhynchus acutus on the basis of external narial morphology and reduced dermal ornamentation saurorhynchus acutus was present in the toarcian of western north america from the tenuicostatum zone to the late serpentinum early bifrons zone similar to the stratigraphic range documented in europe the absence of divergence between eastern pan

a groundwater hypothesis for the origin of fire areas on the northern channel islands california abstract pleistocene areas of red sediments and carbonized vegetation on the northern channel islands california have in the past been interpreted as caused by fires of either natural or human origin some are associated with darkened mammoth and bird fossils and these fossils have been considered as having been burned by early man reevaluation of these so called fire areas indicates that the above phenomena are the result of low temperature 100 c nonheating processes occurring in groundwater evidence for this conclusion is derived from field observations on fossil carbonized vegetation and the geology of the areas additional evidence derives from experiments on the red sediments and fossil wood x ray diffraction analyses magnetic analyses studies on the clay minerals smectite and illite and the demonstration that fossil mammoth bone contains sufficient fe and mn to account for their discoloration much of the carbonization of vegetation probably occurred in water rather than in fire radiocarbon dates from the islands will probably need to be reevaluated these data provide evidence contrary to the concept of the occurrence of significant fires either natural or set by early man on the northern channel islands

a u pb and 40ar 39ar time scale for the jurassic published time scales provide discrepant age estimates for jurassic stage boundaries and carry large uncer tainties the u pb or 40 ar 39 ar dating of volcaniclastic rocks with precisely known stratigraphic age is the preferred method to improve the calibration a radiometric age database consisting of fifty u pb and 40 ar 39 ar ages was com piled to construct a revised jurassic time scale accepted ages have a precision of 5 ma 2 or better and are con fined to no more than two adjacent stages the majority of these calibration points result from integrated bio and geochronologic dating in the western north american cordillera and have not been previously used in time scales di rect dates are available only for the triassic jurassic boundary and the initial boundary of the crassicosta chron and the callovian stage the chronogram method was used to estimate all early and early middle jurassic zone boundaries attempted here for the first time late middle jurassic substage boundaries and late jurassic stage boundaries signif icant improvement is achieved for the pliensbachian and toarcian where six consecutive zone boundaries are deter mined the derived zonal durations are disparate varying between 0 4 and 1 6 ma the latest jurassic isotopic database remains too sparse therefore chronogram estimates are improved using interpolation based on magnetochronology the initial boundaries of jurassic stages are proposed as follows berriasian jurassic cretaceous 1418 18

smithian spathian boundary event evidence for global climatic change in the wake of the end permian biotic crisis one of the most important carbon cycle perturbations following the end permian mass extinction event straddles the smithian spathian boundary ssb olenekian early triassic this anomaly is characterized by a prominent positive carbon isotope excursion known from tethyan marine rocks its global signifi cance is established here by a new high paleolatitude record spitsbergen paleontological evidence such as boreal palynological data barents sea norway and global patterns of ammonoid distribution indicates a synchronous major change in terrestrial and marine ecosystems near the ssb the reestablishment of highly diverse plant ecosystems including the rise of woody gymnosperms and decline of the formerly dominating lycopods is interpreted as an effect of a major climate change this hypothesis is supported by modeling of ammonoid paleobiogeography the distribution patterns of which are interpreted as a proxy for sea surface temperatures sst the latest smithian thus appears to have been a time of a warm and equable climate as expressed by an almost fl at pole to equator sst gradient in contrast the steep spathian sst gradient suggests latitudinally differentiated climatic conditions we propose that this drastic climate change and the global carbon cycle perturbation were triggered by a massive end smithian co2 injection the ssb event could therefore represent one of the causes for stepwise and delayed recovery of marine and terrestrial biotas in the wake of the end permian biotic crisis

integrated ammonite biochronology and u pb geochronometry from a basal jurassic section in alaska new results from integrated biochronologic and geochronometric studies on the basal jurassic section at puale bay alaska peninsula improve the calibration of the early jurassic time scale previously the interval around the triassic jurassic system boundary was poorly dated which hampered our understanding of geologic and biotic events e g the end triassic mass extinction and subsequent recovery published suggestions for the presence of the earliest hettangian planorbis zone and a continuous boundary section at puale bay are not substantiated although the kamishak formation is likely to contain an uninterrupted sedimentary record pre middle hettangian strata are locally faulted resulting in an apparent rhaetian to early hettangian gap in the fossil record the hettangian ammonite zonal schemes developed locally for nevada and the queen charlotte islands permit reliable correlation with alaska but have limited applicability the faunal succession recorded at puale bay is useful in the development of a regional zonation for north america we obtained three u pb zircon dates that are tied into an ammonite biochronology at the zonal level a middle hettangian tuff layer from near the top of the kamishak formation is dated at 200 8 2 7 2 8 ma tuffs from the overlying talkeetna formation are bracketed by middle and late hettangian ammonites and yield crystallization ages of 197 8 1 2 0 4 and 197 8 1 0 ma these new calibration points require that the hettangian sinemurian boundary be younger than 199 ma the triassic jurassic boundary is likely to fall between 200 and 205 ma similar studies are needed for the uppermost triassic to obtain tighter constraints zircon u pb systematics of two samples revealed strong proterozoic and late archean inheritance patterns that require revised tectonic models to account for the proximity of the talkeetna arc to evolved crustal blocks

resistance to barotropic tidal flow in straits by baroclinic wave drag energy transfer from barotropic tides to baroclinic motions may take place at the ends of straits connecting stratified basins implying generation of internal waves propagating into the basins different aspects of this have been described in the literature including quantification of the energy transfer studies of the resulting internal tides and the relationship to diapycnal mixing in the basins however the accompanying resistance to oscillatory barotropic strait flows by so called baroclinic wave drag has not been implemented earlier in models for strait flow in the present paper a formulation for the instantaneous baroclinic wave drag force is suggested this leads to a linear relationship between the strait flow and the synoptic sea level difference between the adjacent basins the model is used to study tidal response in land locked basins the response is computed for three fjords where the resistance to the barotropic flow comes essentially from baroclinic wave drag it is concluded that the strait flow model handles baroclinic wave drag in a satisfactory way since the observed responses are well predicted by the model baroclinic wave drag should provide the major resistance to surface tides in the deep ocean which indicates its importance in a wider context several mechanisms may cause resistance to barotropic flow in straits and channels friction against the sea bed is certainly the most commonly considered type of flow resistance it is often modeled with a quadratic relationship between the bottom stress and the barotropic velocity using a drag coefficient to characterize the frictional properties of the sea bed another type of flow resistance is due to large scale longitudinal variations of the vertical cross sectional area of the strait causing contraction followed by expansion of the flow this class of flow resistance appropriately termed barotropic form drag includes the resistance caused by contraction expansion induced by the ends of straits having smaller vertical cross sectional areas than the adjacent basins in the cases of frictional drag and largescale form drag barotropic energy is transferred to turbulence in the bottom boundary layer in the strait and to large scale eddies in the expanding current downstream of the strait respectively the present paper however draws attention to a third class of resistance operating on oscillating barotropic strait flow it is due to generation of baroclinic internal waves in the adjacent stratified basins by the ends of the strait and is

spatial variability of diapycnal mixing and turbulent dissipation rates in a stagnant fjord basin two microstructure profilers two ships and four moorings with acoustic doppler current profilers and conductivity temperature loggers were used in an intensive effort to map the spatial and temporal variations of vertical mixing in the stagnant deep basin of gullmar fjord sweden during three days in the beginning of august 2001 a continuous time series of turbulent kinetic energy dissipation profiles was obtained with one microstructure profiler at a fixed position near the deepest part of the fjord during the same period the other microstructure profiler was used to obtain six sections of dissipation through the length of the basin two moorings were deployed in the fjord basin for one month from the end of july to the end of august the mapping of dissipation rates reveals that the dissipation in the deep basin is confined to areas just inside the sill more than 77 of the dissipation in the fjord basin happens above the sloping bottoms closest to the sill

early jurassic south american pectinaceans and circum pacific palaeobiogeography abstract in the light of new data from south america high latitude southern bivalve faunas are now recognized for the early jurassic it is proposed that an austral realm was in continuous existence throughout jurassic times some bivalve genera palmoxytoma kolymonectes radulonectites agerchlamys n gen and groups of species of plicatula harpax show a bipolar distribution suggesting climatic control in the early jurassic a distinctive group of high latitude bivalves included monotidae kalenteridae oxytomidae and some pectinidae and plicatulidae based on the pectinacean s l bivalves the east west faunal differentiation was weaker than the latitudinal one in the early jurassic pacific the southern andes were situated in a transitional area between the tethyan and austral realms as shown by the mixed influence of the local bivalve faunas

cordilleria a newly defined canadian microcontinent palaeomagnetic data and geological field evidence indicate that most of the western canadian cordillera lay 1 500 km south of its present position in the early cretaceous we suggest that this region comprised a microcontinent termed cordilleria which moved on the kula plate and collided with the craton 100 myr ago to form first the mackenzie mountains and then the rockies

offset of an upper pliensbachian geographic zonation in the north american cordillera by transcurrent movement the north to south climatic zonation of upper pliensbachian ammonites known in europe has been recognized in the north american cordillera this simple geographic arrangement has been disrupted by northwest trending dextral transcurrent faults with further documentation the amount of offset of these zones should provide a measure of the amount of movement on these faults since pliensbachian time and further document the allochthoneity of the western part of the cordillera

triassic ammonoid biostratigraphy an overview abstract the triassic chronostratigraphic scale was built on two centuries of research on ammonoid biostratigraphy and biochronology two triassic stage bases and all of the triassic substages are currently defined by ammonoid bioevents the study of triassic ammonoids began during the late 1700s and in 1895 edmund von mojsisovics wilhelm waagen and carl diener published an essentially complete triassic chronostratigraphic scale based on ammonoid biostratigraphy this scale introduced many of the triassic stage and substage names still used today and all terminology of stages and substages subsequently introduced has been based on ammonoid biostratigraphy early triassic ammonoids show a trend from cosmopolitanism induan to latitudinal differentiation olenekian and the four lower triassic substage griesbachian dinerian smithian and spathian boundaries are globally correlated by widespread ammonoid biotic events middle triassic ammonoids have provinciality similar to that of the olenekian and provide a basis for recognizing six middle triassic substages late triassic ammonoids provide a basis for recognizing three stages divided into five substages the main uncertainty for the future of triassic ammonoid biostratigraphy is not the decline of the ammonoids as a tool for dating and correlation of triassic strata but rather the dramatic decrease in the number of specialists due to the lack of replacement of experienced palaeontologists who started their activity in the 1950s and 1960s

dependence of currents and density on the spring neap cycle and the diurnal inequality in burrard inlet british columbia simulations and observations abstract observations of the circulation in a hole near a constriction in burrard inlet are simulated using a two dimensional i e laterally integrated numerical model the model uses a level 2 version of the mellor yamada turbulence closure scheme during spring tides when mixing is at its most intense the density in the hole decreases increases during the large small floods and there is an up inlet current pulse into the hole during each flood regardless of the flood s strength during the large floods in particular the simulation is significantly improved if the explicit influence of horizontal spatial variations on the production of turbulent kinetic energy is taken into account during neap tides the simulated density is much less variable and the currents in the hole are much weaker in agreement with the observations the model differs from the observations in that the simulated current pulses are significantly weaker than the observed pulses possibly because the cross channel averages

the energetics and tidally induced reverse renewal in a two silled fjord a laterally integrated two dimensional numerical model is used to examine the influence of the m2 tide on the circulation in the saguenay fjord a two silled fjord with a large inner and a small outer basin located on the north shore of the st lawrence estuary it is found that the m2 tide is more vigorous in the outer than in the inner basin and that more vertical mixing occurs in the outer basin therefore the density at depth in the outer basin decreases faster than it does in the inner basin and the resulting horizontal pressure gradient causes a bottom flow of water from the inner to the outer basin across the inner sill this reverse renewal is evident in both the available observations and the simulation according to the model much of the m2 energy withdrawn from the surface tide is fed into the internal tide significant tidal energy is also advected by the mean flow velocity approximately 25 of the net energy flux into the fjord is dissipated within 2 km of the outer sill because of the baroclinic pressure i e the total pressure but with the influence of the surface displacement removed the subtidal circulation is associated with very large energy fluxes within the fjord these fluxes are much larger than the net rate at which tidal energy enters the fjord and they are greater than the subtidal advective energy flux they represent a large redistribution of energy within the fjord and their horizontal divergence along the fjord is almost in balance with the time rate of change of potential energy when a flux richardson number is calculated for the inner basin below sill depth a value of 0 075 is obtained which is close to values found for other fjords

the pliensbachian toarcian early jurassic extinction a global multi phased event abstract during the pliensbachian toarcian interval of the early jurassic there is a well known second order marine extinction that is observable at the species and genus levels ammonite diversity data from successions throughout europe and parts of the arctic suggest that this extinction may have been multi phased with diversity declining over six separate intervals the main phase of decline begins at the pliensbachian toarcian boundary and extends into the lower toarcian to a level that is correlative with the tenuicostatum serpentinum zone boundary to date only the main phase of extinction has been demonstrated as being global in extent and affecting multiple taxonomic groups this multi phased extinction has been attributed to regional and global controlling mechanisms that are associated with the volcanic greenhouse scenario which links the eruption of the karoo ferrar large igneous province lip to global warming and mass extinction we compare stratigraphic ranges of ammonite and foraminiferal species in pliensbachian toarcian successions of western north america to the record in europe and parts of the arctic in order to test the geographic extent of the multiple phases of extinction our results show six intervals of species level decline that correlate with those recognized in europe 1 middle of the lower pliensbachian middle whiteavesi middle freboldi zones 2 middle of the upper pliensbachian upper kunae lower carlottense zone 3 pliensbachian toarcian boundary into the lower toarcian upper carlottense middle kanense zones 4 middle toarcian upper planulata lower crassicosta zones 5 upper middle lower upper toarcian middle crassicosta hillebrandti zones and 6 upper toarcian lower yakounensis zone recognition of this multi phased event in three separate ocean basins paleo pacific paleo arctic and tethys oceans in at least two taxonomic groups greatly expands the known geographic extent of this multi phased event and argues for a controlling mechanism that is global in its reach in relation to the volcanic greenhouse scenario our study shows that four of the six pulses of extinction occur within the main phase of karoo magmatism the decline in the early pliensbachian previously thought to be separate from this event occurs within error range of the onset of karoo magmatism and the decline in the late toarcian coincides with the later stages of magmatism these observations extend the known duration of this multi phased extinction event to the early pliensbachian and support the volcanic greenhouse scenario specifically the eruption of the karoo ferrar lip as a preeminent factor driving the multi phased extinction of the pliensbachian toarcian

the permo triassic paleotethys in mainland southeast asia and adjacent parts of china aspects of the geodynamic evolution of mainland southeast asia and china are discussed in consideration of the permo triassic paleotethys problem it is shown that all sutures in thailand vietnam and yunnan already closed during the paleozoic era and that the entire region must be regarded as part of the northern continents the permo triassic paleotethys must be expected south of tibet and in burma

lithiotis bivalvia bioherms in the lower jurassic of east central oregon u s a abstract the epifaunal rudist like bivalve lithiotis formed extensive bioherms during the pliensbachian and toarcian ages of the early jurassic the best developed bioherms in north america occur in the pliensbachian robertson formation of east central oregon a unit deposited in a shallow sea transgressing across the suplee shelf a typical bioherm consists of three biofacies that coexisted laterally and replaced each other vertically the reef flank assemblage is the most diverse consisting of nerinea gastropods terebratulid brachiopods and lithiotis debris in a calcarenite or calcilutite matrix the death assemblage consists of tightly packed current aligned lithiotis valves with gastropods and brachiopods much reduced in numbers the core of the reef is built almost exclusively of in situ lithiotis forming a bafflestone with a calcilutite matrix lithiotis inhabited a stressful environment inimical to most invertebrates since diversity is very low and there is no evidence of bioerosion during the pliensbachian lithiotis formed an endemic centre encompassing western north america and the tethyan ocean linked through central america and the central atlantic by the hispanic corridor by the close of the pliensbachian it had disappeared from north america but in the toarcian made its first appearance in south america by the end of the toarcian lithiotis was extinct

partition of energy loss from the barotropic tide in fjords abstract as the barotropic tide propagates into and out of a fjord it loses energy to friction internal tides and high frequency internal waves estimates of these losses for three british columbia fjords using current meter data indicate that friction is negligible in two but important in one inlet the length and depth of the sill determines the importance of friction when friction is not important most of the energy lost goes into the internal tide but less than half of this energy propagates away from the sill simple models of the internal tide predict the correct energy transfer to satisfy an energy budget but do not agree with observations of the internal tidal energy flux away from the sill energy loss from the internal tide in or near the generation zone would account for the discrepancy the energy flux of the high frequency internal wave field is relatively small about 2 of the energy lost

the tides in the arctic ocean from a finite element model the two main diurnal i e k1 and o1 and semidiurnal i e m2 and s2 tidal waves have been computed from a hydrodynamic finite element spectral model the spatial resolution of the model varies from a few kilometers at the coastline to 100 km in the deepest regions an optimization of the open boundary conditions has been performed to improve the solution accuracy the bottom topography used in this model has been originally extracted from the earth topography 5 minutes grid etopo5 and corrected from various sources of data the impact of the input parameters like the friction coefficient the loading effects and the parameterisation of the additional friction due to the arctic ice cover is investigated the tidal elevations are compared to a set of in situ observations and validated they also are compared to the kowalik and proshutinsky 1993 model these comparisons mainly show good agreement between the two models nevertheless significant differences are observed where small wavelength structures are produced by the topographic trapping of the tidal energy the velocities associated with the elevations are also presented the potential rate of work the dissipation and the energy fluxes are computed from these elevations and velocities because of the uncertainties of the velocities at the open boundaries we are restricted to a qualitative analysis of the energy equation terms which appears to be consistent with the previous studies on arctic tides

the significance of an early jurassic toarcian carbon isotope excursion in haida gwaii queen charlotte islands british columbia canada abstract during the early toarcian there was a significant disruption in the short term active carbon reservoir as revealed by carbon isotope records which show a broad positive shift that is interrupted by a large 5 7 negative excursion 13 c org carbon isotope excursion co occurs with the deposition of organic rich shales in many areas this perturbation in carbon isotopes is thought to be indicative of severe climate change and marine anoxia the two leading hypotheses as to the cause of this event invoke either global or regional controls here we present carbon isotope data from haida gwaii british columbia canada showing a significant perturbation within a temporally constrained early toarcian succession that was deposited in the northeastern paleo pacific ocean these data reinforce the concept that the short term active carbon reservoir was affected globally and assist with the correlation of ammonite zonal schemes between western north america and europe the 13 c org data show a broad positive shift that is interrupted by a sharp and pronounced negative excursion of 7 8 5 in 13 c wood in the early toarcian kanense zone this negative excursion also coincides with increasing total organic carbon toc from 0 4 to 1 2 these data suggest that the early toarcian carbon isotope perturbation was indeed global and imprinted itself on all active global reservoirs of the exchangeable carbon cycle deep marine shallow marine atmospheric

taphonomy of two last glacial maximum mammoth sites in the central great plains of north america a preliminary report on la sena and lovewell abstract two mammoth sites from the central great plains of north america each containing one adult columbian mammoth mammuthus columbi were excavated from last glacial maximum lgm loess and fine grained alluvial deposits respectively taphonomic data from both sites indicate that the mammoth skeletons exhibit numerous spirally fractured limb elements dynamic loading points are present on midshafts of large limb bones bone flakes produced from the partial thickness of thick cortical bone are also present hypotheses of carnivore activity mammoth trampling and human induced fracturing are evaluated as possible causes of the fractured limb bone testing the hypotheses using modern data from actualistic taphonomic studies of elephant skeletons paleontological data from two proboscidean natural death sites experimental data from elephant bone fracturing and archaeologically derived data concerning late pleistocene human modification of mammoth limb bone indicates that the first two hypotheses can be rejected while the third hypothesis is supported

tidal conversion and dissipation at steep topography in a channel poleward of the critical latitude abstractin high latitude fjords and channels in the canadian arctic archipelago walls support radiating internal tides as kelvin waves such waves allow for significant barotropic to baroclinic ti

reconstruction of eastern gondwanaland substantial additions of large continental blocks to the smith et al 1 model of eastern gondwanaland are proposed here largely on the basis of the distribution of key land floras tropical and subtropical marine faunas lithofacies patterns and the identification of a triassic magmatic arc that characterized all the eastern margin of gondwanaland the continental fragments that must have been rifted from northern australia new guinea in the jurassic are identified as south tibet burma thailand malaya and sumatra the original site of deposition of the subtropical permian limestones and tropical late triassic limestones overthrust onto the northern margin of australia by the late cenozoic collision2 is located in this greater gondwanaland palaeomagnetic data except those from malaya3 support this reconstruction

early and mid jurassic molluscan biogeography and the establishment of the central atlantic seaway abstract a new analysis of lower and middle jurassic bivalve faunas of western north america and the southern andes in comparison to europe supported by evidence from other molluscs throws further light on the establishment of a central atlantic epicontinental seaway prior to the formation of a true oceanic strait between eastern north america and africa south america some restriction to free communication persisted until the early callovian but there was an episode of relatively free intermigration in the toarcian to early bajocian time interval which is associated with major rise of sea level one of the most significant consequences of this event was a spread into northwest europe of taxa which were previously confined to the pacific margins to occupy niches vacated as a result of an early toarcian extinction event

a upb age from the toarcian lower jurassic and its use for time scale calibration through error analysis of biochronologic dating abstract the early jurassic is the most poorly constrained part of the geochronologic scale within the mesozoic owing to the scarcity of calibration points we report a new u pb zircon age of 181 4 1 2 ma 2 from an ash layer within the type section of crassicosta zone a north american regional standard ammonite zone in the middle toarcian for time scale calibration the isotopically dated level needs to be tied to the jurassic chronostratigraphic framework established in northwest european successions three major contributing factors difference between local observed and true ranges uncertainties of correlation and taxonomic noise are assessed to determine the maximum biochronologic dating error the local ammonite distribution data are robust in that 95 confidence level extensions of observed ranges of common ammonite taxa would not significantly modify the zonal assignment the computer assisted unitary association ua method is used for world wide biochronologic correlation representative north and south american western tethyan and northwest european sections were selected to establish the global maximum ranges for 103 middle toarcian ammonite taxa and a sequence of 40 ua maximum permissible correlatives of the crassicosta zone lie between the northwest european standard semipolitum subzone late bifrons zone and bingmanni subzone early thouarsense zone in particular the dated tuff layer cannot be older than the semipolitum subzone or younger than the illustris subzone variabilis zone taxonomic inconsistencies are present in the source data but their effect in corrupting ua based correlation is shown to be negligible the precise u pb age 2 error

evidence of displaced terranes from permian to jurassic faunas around the pacific margins for the permian to jurassic time interval tethyan marine invertebrate faunas which are generally accepted as having lived at low latitude can be distinguished from less diverse higher latitude faunas displacement of these low latitude faunas to positions of high latitude around the pacific margins therefore provides key evidence for the movement of so called suspect or displaced terranes the fullest story so far has been worked out for the western margin of n america as far north as southern alaska but there is also convincing evidence for the substantial northward movement of continental segments along the ne asian margin as regards the southern hemisphere the torlesse terrane of new zealand appears to have moved a considerable distance southwards but there is no fauna1 evidence of comparable far travelled suspect terranes along the andean margin of south america not only tethyan and boreal but e and w pacific elements are detectable in the faunas and the distribution of these argues for a panthalassia studded with islands of various sizes fringing the adjacent continents rather than for the disintegration of a single continent pacifica

marine triassic faunas of north america their significance for assessing plate and terrane movements the distribution of marine triassic invertebrate faunas in north america is reviewed to recognize forms that may have paleolatitudinal significance

evolution of early triassic outer platform paleoenvironments in the nanpanjiang basin south china and their significance for the biotic recovery detailed microfacies and paleoenvironmental analyses were conducted through the early triassic interval of the outer platform ammonoid rich series of the nanpanjiang basin luolou formation guangxi province south china extensive investigations on outcrops and on thin sections reveal that the widely reported well diversified latest permian fauna dominated by abundant corals calcareous algae calcareous sponges crinoids brachiopods gastropods ostracods and foraminifera is abruptly replaced by decimated early triassic communities essentially composed of low diversity bivalves microgastropods ostracods and rare foraminifera along with this drastic change in faunal assemblages the recolonization of devastated habitats by calcimicrobial frameworks is observed in the aftermath of the end permian mass extinction calcimicrobialites of griesbachian age are followed by mixed ammonoid and conodont rich carbonate siliciclastic series consisting of dark suboxic laminated mudstones intercalated with organic rich shales of dienerian to late smithian age the carbonate siliciclastic series are interrupted by a brief carbonate episode during the early middle smithian massive carbonate production resumes only from the early spathian onward and persists throughout the spathian the initial deposition of both carbonate episodes is coeval with i re establishment of well oxygenated conditions ii a marked early smithian to extreme early spathian ammonoid conodont diversification iii a significant increase in the skeletal grain diversity and abundance and iv peak carbon isotope values a short interval of black organic rich shales precedes the onset of these two distinct carbonate events which are both marked by a positive carbonate carbon isotope excursion known from other tethyan marine localities the comparison between the early triassic stratigraphic evolution of tethyan outer platform paleoenvironments and platform basin margin settings of the nanpanjiang basin suggests a causal connection between large fluctuations of the global carbon cycle climate shifts sea level changes oxygen availability in the oceans and the biological rediversification in the wake of the end permian biotic crisis

population response during an oceanic anoxic event the case of posidonotis bivalvia from the lower jurassic of the neuquen basin argentina abstract benthonic marine species show a wide range of biological reactions to seawater chemical changes through time from subtle adjustments to extinction the early toarcian oceanic anoxic event t oae was recently recognized in the neuquen basin argentina confirming its global scope the event was identified chemostratigraphically on the basis of a relative increase in marine organic carbon and a characteristic negative carbon isotope excursion 13corg in bulk rock and fossil wood in the upper pliensbachian lower toarcian interval in the arroyo lapa section neuquen simultaneously with collection of lithological samples a high resolution biostratigraphical survey was carried out and the scarce benthonic fauna was collected in order to check the biotic response to changing marine geochemical conditions we present here an analysis of size and abundance data from the t oae interval in the neuquen basin for the dominant bivalve species the paper clam posidonotis cancellata leanza and relate these data to geochemical proxies toc and 13corg obtained at the same locality the abundance of p cancellata increased when the rest of the benthos diminished reaching a maximum at the onset level of the t oae and then decreasing size frequency distributions show a noteworthy lack of juvenile shells shell size shows a positive correlation with toc in the whole section though over the t oae interval proper it decreases below the level where the maximum toc value is attained and increases above it posidonotis cancellata shows features of opportunistic species such as high tolerance to hypoxia strong dominance in impoverished environments and a strong dependence on primary productivity but at the same time had a reproductive strategy more similar to equilibrium species with relatively low juvenile mortality rates several anatomical features suggest adaptation to permanently dysaerobic environments the species disappeared just before the minimum negative carbon isotope value was reached and by the same time the genus became extinct worldwide

biochronology of triassic bivalves substantial advances by numerous researchers over the past 20 years have made it possible to develop a composite biochronological scheme for the triassic based on the bivalves claraia peribositria enteropleura daonella halobia eomonotis and monotis these bivalves exhibit temporal durations nearly equal to ammonoids and conodonts widely distributed across the tethys panthalassa and boreal regions these bivalves occur in a wide variety of marine facies and water depths but are most notable for their thick shell accumulation in deeper water oxygen deficient environments they were most likely resting or reclining benthos may have housed chemosymbionts and were part of episodic opportunistic palaeocommunities in or near oxygen deficient settings a new biochronological zonation for bivalves is presented that encompasses the entire triassic and is integrated with standard ammonoid schemes the lower triassic is characterized by 2 3 zones of claraia most notably from the eastern tethys representing the entire induan and lower portion of the olenekian later in the olenekian and most notably from the boreal realm species of peribositria included by some workers within bositra provide useful zonal indexes the middle triassic is well represented by enteropleura middle anisian and daonella upper anisian through ladinian in the tethys and north america with significant occurrences through out the circum pacific and boreal realms the upper triassic can be subdivided into 8 13 bivalve zones based on the succession of halobia eomonotis and monotis sensu lato species with best representation in the tethys boreal and eastern panthalassa regions

bivalve palaeobiogeography and the hispanic corridor time of opening and effectiveness of a proto atlantic seaway abstract the hispanic corridor is an embryonic seaway between the eastern pacific and western tethyan oceans that has been postulated to have preceded middle jurassic drifting and the birth of the atlantic ocean by many millions of years in this study the distribution of pectinoid bivalve morphotypes is analysed to examine the origin of the hispanic corridor and its effectiveness during early jurassic times a comparison of pectinoid faunal similarities based on similarity coefficients between various regions at opposite ends of the corridor suggests that it opened progressively during early jurassic times however with this approach it is difficult to exclude alternative dispersal routes and to determine when faunal interchange began analysis of the percentage of pectinoid morphotypes that were 1 present at opposite sides of the corridor 2 simultaneously absent in the western pacific eastern tethys and 3 confined to relatively low palaeolatitudes provides evidence that the hispanic corridor developed from an effective barrier in earlier early jurassic hettangian to sinemurian times into a filter allowing the passage of a few morphotypes during later early jurassic pliensbachian and toarcian times the apparently two way faunal exchange through the hispanic corridor is consistent with the establishment of a megamonsoonal circulation for pangaea which may have caused seasonally changing directions of oceanic surface currents through the corridor

early triassic gulliver gastropods spatio temporal distribution and significance for biotic recovery after the end permian mass extinction a reduction in body size lilliput effect has been repeatedly proposed for many marine organisms in the aftermath of the permian triassic pt mass extinction specifically reduced maximum sizes of benthic marine invertebrates have been proposed for the entire early triassic this concept was originally based on observations on early triassic gastropods from the western usa basin and the dolomites n italy and it stimulated subsequent studies on other taxonomic groups however only a few studies have tested the validity of the lilliput effect in gastropods to determine whether the paucity of large sized gastropods is a genuine signal or the result of a poor fossil record and insufficient sampling in combination with a review of the literature we document numerous new abundant large sized gastropods from the griesbachian outcrops of greenland and from the smithian early spathian interval in the southwestern usa we show that large sized gulliver gastropods i were present soon after the pt mass extinction ii occurred in various basins sedimentary facies and environmental contexts from shallow to deeper settings and iii belong to diverse higher rank taxa focusing on the western usa basin we investigate areas from which microgastropod shell beds were previously presented as being typical however we show that gulliver gastropods do occur in the very same areas insufficient sampling effort is probably the main reason for the rarity of reports of large early triassic gastropods which is supported by preliminary rarefaction based simulations finally it appears that the recently documented middle to late smithian climate shifts and the severe end smithian extinction of nekto pelagic faunas did not reduce maximum shell sizes of gastropods

observed damping of barotropic seiches through baroclinic wave drag in the gullmar fjord baroclinic wave drag due to internal wave generation at steep topography is shown to be a mechanism that effectively subdues barotropic seiches in fjords a two layer model for a fjord with a sill at the mouth is applied to the gullmar fjord sweden the damping of the fundamental seiche mode observed from sea level records is well predicted by the model this includes the observed seasonal variation in damping due to the corresponding variation in vertical stratification it is shown that ordinary bottom friction should contribute less than 1 to the damping in this fjord simultaneous current records from different depths obtained on the slope of the sill in the fjord are analyzed spectra of all records show a significant energy peak at the seiche frequency the vertical variation of the phase of the current at this frequency shows that the motion is essentially baroclinic

late early triassic climate change insights from carbonate carbon isotopes sedimentary evolution and ammonoid paleobiogeography the late early triassic sedimentary facies evolution and carbonate carbon isotopemarine record 13ccarb of ammonoid rich outer platform settings show striking similarities between the south china block scb and the widely distantnorthern indianmargin nim the studied sections are located within the triassic tethyshimalayan belt losar section himachal pradesh india and the nanpanjiang basin in the south china block jinya section guangxi province respectively carbon isotopes from the studied sections confirm the previously observed carbon cycle perturbations at a time of major paleoceanographic changes in the wake of the end permian biotic crisis this study documents the coincidence between a sharp increase in the carbon isotope composition and the worldwide ammonoid evolutionary turnover extinction followed by a radiation occurring around the smithian spathian boundary based on recent modeling studies on ammonoid paleobiogeography and taxonomic diversity we demonstrate that the late early triassic smithian and spathian was a time of a major climate change more precisely the end smithian climate can be characterized by a warm and equable climate underlined by a flat pole to equator sea surface temperature sst gradient while the steep spathian sst gradient suggests latitudinally differentiated climatic conditions moreover sedimentary evidence suggests a transition froma humid and hot climate during the smithian to a dryer climate fromthe spathian onwards by analogywith comparable carbon isotope perturbations in the latedevonian jurassic andcretaceouswe propose that high atmosphericco2 levels could have been responsible for the observed carbon cycle disturbance at the smithian spathian boundary we suggest that the end smithian ammonoid extinction has been essentially caused by a warm and equable climate related to an increased co2 flux possibly originating froma short eruptive event of the siberian igneous province this increase in atmospheric co2 concentrations could have additionally reduced the marine calcium carbonate oversaturation and weakened the calcification potential of marine organisms including ammonoids in late smithian oceans

jurassic and cretaceous plutonic and structural styles of the eagle plutonic complex southwestern british columbia and their regional significance the eagle plutonic complex is an elongate north northwest trending body of deformed middle to late jurassic and middle cretaceous rocks which underlies the southwestern margin of the intermontane terrane new mapping of the complex and its country rocks in concert with geochronometry has defined episodes of contractional ductile deformation in the middle to late jurassic and middle cretaceous as well as brittle deformation in tertiary time synkinematic middle to late jurassic eagle tonalite at the eastern margin of the eagle complex intrudes mylonitic nicola group rocks and structurally overlies them along a southwest dipping belt of high strain eagle shear zone with a structural thickness of 1 km and a strike length of 100 km in the central and western eagle complex eagle tonalite grades into tonalite orthogneiss eagle gneiss and both are crosscut by mid cretaceous muscovite bearing plutons of the fallslake plutonic suite fallslake suite rocks are themselves ductilely deformed along the

context and environment in taphonomic analysis examples from alaska s porcupine river caves abstract field investigations of caves along alaska s porcupine river document three major mechanisms which modify bone in patterns similar to alterations produced by man 1 carnivore fracture 2 rodent gnawing and 3 rock fall and rubble scarring a late wisconsin faunal assemblage composed of equus sp rangifer tarandus ovis dalli bison sp proboscidean numerous small mammal species birds and fish is well documented this faunal assemblage suggests a mosaic environment of grassland tundra forest in the immediate vicinity of these caves and implies that the late wisconsin environment in north central alaska may have been characterized by a number of microenvironments and colder dryer steppe conditions taphonomic data which have historically been interpreted to support human occupation of eastern beringia during the pleistocene are critically examined and the context of these discoveries not the specimens themselves provides the test essential to document the antiquity of man in north america prior to 12 000 yr ago