first greenland record of the shark genus ptychodus and the biogeographic significance of its fossil assemblage abstract a tooth of ptychodus decurrens chondrichthyes selachii and part of a calcified chondrichthyan vertebra from mudstone exposed in the kangerdlugssuaq area southern east greenland are referred to the late turonian early coniacian on the basis of belemnites and dinoflagellates the belemnite assemblage including actinocamax cf manitobensis connects european faunas with belemnites known from the north american continent one or both shark specimens represent the first greenland record of ptychodus and the first occurrence of p decurrens outside europe they are the only known vertebrate remains from the sediments subjacent to the kangerdlugssuaq plateau basalts palaeocontinental reconstruction suggests a late cretaceous position near europe at ca 52 n palaeolatitude known occurrences point to a late cretaceous marine distribution of the genus ptychodus south of ca 55 n palaeolatitude

a late cretaceous turonian ichthyofauna from lac des bois northwest territories canada with paleobiogeographic comparisons with turonian ichthyofaunas of the western interior seaway a fish fauna from a turonian sequence of the great bear basin at lac des bois is described the fauna includes examples of ichthyodectes cf osmeroides a euteleost and several aulopiforrn fishes such as enchodus cimolichthys and a juvenile that cannot be further identified the fauna of lac des bois most closely resembles other arctic fish assemblages of the western interior seaway based on a upgma unweighted pair group method with arithmetic averages cluster analysis of various north american turonian localities there are also slight differences between eastern and western localities along the seaway the north south differences of the ichthyofauna can be explained by current patterns distributing the fishes in the seaway or transgressive events during the turonian the east west differences may be due to changes in water depth from east to west

continental rift jumps abstract continental rift jumps analogous to jumps of oceanic spreading ridges are here proposed to be common good examples exist in iceland and afar both transitional from ridge to rift jumps west africa benue trough and cameroon volcanic line and kenya indeed the kenya rift appears to have jumped c 100 km eastward c 10 m y ago and is currently jumping further to the east possible jumps exist in the baikal rift the limagne bresse rift pair and parallel to ancient continental margins e g the triassic basins of the eastern u s to baltimore canyon and georges bank continental rifts jump distances that are approximately equal to local lithosphere thickness suggesting that jumped rifts are controlled by lithosphere fracturing but there appears to be no reason for the fracturing except migration of hot spots

origin of the oslo graben in relation to the hercynian alleghenian orogeny and lithospheric rifting in the north atlantic abstract the contemporaneous extrusion of basalts in the oslo graben and intrusion of dolentes in northern britain and southern sweden at 295 ma calls for a common explanation two hypotheses are investigated 1 1 the graben and dykes resulted from extensional stresses associated with progressive lithosphere separation to the northwest of europe in the late carboniferous 2 2 the dykes and therefore the graben were related in some way to oblique collision of plates in the hercynian orogeny which was developing to the south the first hypothesis is mechanically more satisfying and makes a number of testable predictions it states that in late carboniferous times the lithosphere separated in two places along the orogenic grain to the west of britain and norway the two embryonic oceanic rifts were divided by thick cold lithosphere with an archaean crust to the north of scotland extensional stresses were focussed in this region fanning out in an arcuate zone to the south and east causing failure where the lithosphere was relatively thin in norway the strain was restricted to a zone previously thinned and weakened in the early palaeozoic i e the oslo graben in britain the caledonoid grain is oblique to the expected direction of extensional strain and a dyke swarm trending e w and about 300 km wide was formed the first hypothesis predicts that the dykes should die out to the west but continue along an arc and widen to the east northeast under the western north sea interpretation of aeromagnetic maps shows that the dykes behave as predicted by hypothesis one but that their trends and extent are at variance with the expectations of hypothesis two the apparent contradiction of rifting to the northwest of europe occurring at the same time as compression and oblique collision in the heart of europe is resolved in principle by two plate tectonic reconstructions of pangaea drawn for late carboniferous and early permian times the oslo graben was conceived in mid carboniferous times and born towards the end of the carboniferous as the thin lithosphere failed and allowed the extrusion of basalt magma it was then abandoned as the two collinear oceanic rifts to the west and northwest joined up but the graben carried on a life of its own as the mafic magma cushion caught in the density trap beneath the crust continued to differentiate and alkali magma pods rose buoyantly to freeze in the upper crust or extrude on the graben floor

age relations among oslo rift magmatic rocks implications for tectonic and magmatic modelling abstract this paper presents a compilation of 67 published and unpublished radiometric age determinations by the rb sr method on magmatic rocks in the continental oslo rift in southeast norway the data include most major rock types and structural units in the subaerial part of the rift the implications of these data with respect to the tectonomagmatic evolution of the rift and processes in the mantle and crust are discussed the oslo rift was active for about 60 million years the earliest recorded magmatic activity was the intrusion of basaltic and syenitic sills in the pre rift lower paleozoic sediments at about 300 ma extrusion of plateau lavas of basaltic and intermediate composition rhomb porphyries started about 295 ma and lasted to about 275 ma with largest magma volumes and highest extrusion rate from 295 to 285 ma in the vestfold graben segment gs one flow per 250 000 years and 0 30 km3 per 103 years the main faulting activity and graben formation occurred during this period the plateau volcanism was succeeded by a stage of bimodal central volcanoes most of which later underwent caldera collapses ring dykes and central intrusions in these calderas give ages in the range 268 266 ma in the vestfold and 266 243 ma in the akershus gs large composite intrusive complexes were emplaced in the periods 27 268 and 273 241 ma in the vestfold and akershus gs respectively a rate of propagation of the rift from ssw towards the nne has been estimated to 1 2 cm y 1 on the basis of 87 sr 86 sr initial ratios and type of magmatic products we estimate magmas to have been emplaced into the crust only during the first 20 25 ma of the magmatic period some of the magmatism appears to be initiated by movement along precambrian fault zones which were reactivated during the oslo rifting event

faunal assemblages from the upper horseshoe canyon formation an early maastrichtian cool climate assemblage from alberta with special reference to the albertosaurus sarcophagus bonebed the faunal assemblage from the early maastrichtian portion of the horseshoe canyon formation is described on the basis of four new vertebrate microfossil localities and remains from the albertosaurus bonebed all of the localities sampled were deposited during a cool dry climate at a palaeolatitude of 58 n thus these assemblages provide insight into a northern cool climate assemblage in the early maastrichtian of western north america this fauna is characterized by the presence of taxa with more northern affinities such as holostean a champsosaurs troodon and toothed birds warm climate taxa such as crocodylians large and diverse turtles and albanerpetontids are notable in their absence the albertosaurus bonebed locality at the top of unit 4 of the horseshoe canyon formation was deposited during the initial stages of a trend to a warmer and wetter climate that is represented in unit 5 the bonebed shares many taxa with the underlying vertebrate microfossil localities however a notable diffe

late cretaceous restructuring of terrestrial communities facilitated the end cretaceous mass extinction in north america the sudden environmental catastrophe in the wake of the end cretaceous asteroid impact had drastic effects that rippled through animal communities to explore how these effects may have been exacerbated by prior ecological changes we used a food web model to simulate the effects of primary productivity disruptions such as those predicted to result from an asteroid impact on ten campanian and seven maastrichtian terrestrial localities in north america our analysis documents that a shift in trophic structure between campanian and maastrichtian communities in north america led maastrichtian communities to experience more secondary extinction at lower levels of primary production shutdown and possess a lower collapse threshold than campanian communities of particular note is the fact that changes in dinosaur richness had a negative impact on the robustness of maastrichtian ecosystems against environmental perturbations therefore earlier ecological restructuring may have exacerbated the impact and severity of the end cretaceous extinction at least in north america

the oslo rift its evolution on the basis of geological and geophysical observations abstract the formation and evolution of the oslo rift have puzzled geoscientists for more than a century we have reexamined this problem in view of recent detailed geophysical information bearing on crust and lithosphere structures in the general rift area for example the rift contours closely correlate with a moho elevation of 3 5 km the crustal thinning partly predates the rifting and apparently the same is the case for lithospheric deformations cambro silurian sediments are found mainly within the present day rift and this implies rifting contemporaneous with uplift the southern rift segment the skagerrak graben appears to be somewhat different from the northern segment the oslo graben with relatively less magmatism and larger subsidence crustal laminae are found inside and especially outside the rift area including sub moho dipping reflectors whose origin is attributed to magmatic intrusions and or stretching the strength of the lithosphere increases northwards with increasing thicknesses of both the brittle crust and the lithosphere a variety of continental rifting mechanisms has been examined in view of the observational data at hand basically a passive rifting mechanism is presumed with dominant east west tensional stresses albeit we are unable to be specific on driving forces the model presented in this paper reflects concepts introduced by dunbar and sawyer 1988 and neugebauer 1983 on preweakening of the crust and lithosphere and diapirism as a transport mechanism the essential elements of the model are 1 1 the area in question was preferential for rifting in view of previous crust and lithosphere deformations from late precambrian to silurian times 2 2 lithosphere stretching is needed for creating favorable conditions for diapirism 3 3 the shield strength increases rapidly towards the northern part of the rift preventing further migration

continental rifting and porphyry molybdenum occurrences in the oslo region norway abstract the overall structure of the oslo rift system can be viewed as the result of interference between a n s trending permian fault system and a regional ne sw trending precambrian shear zone the rift system comprises four mutually opposed horst and graben structures in a centrosymmetrical arrangement igneous activity occurred only in two en echelon segments both of which possess a notable symmetric distribution of rocks and structures around the central axis of the rift system the axial zone is occupied by cambro silurian sediments which have been intruded by major granite bodies extensive lava plateaus occur on each side of this axial zone the adjacent zones contain the most prominent cauldrons of province further away from the axis follows a zone of batholitic intrusions emplaced as composite diapirs and plutonic ring complexes hornfelsed sediments and volcanics in narrow bands occur at the lateral borders of the province possibly preserved as the result of marginal tectonics associated with batholith emplacement the formation of the oslo rift system apparently reflects a passive continental rifting which was gradually succeeded by considerable igneous activity important porphyry molybdenum mineralization in the oslo region is associated with shallow level magmatism in the glitrevann and hurdal areas the porphyry mo mineralization in these prospects have several evolutionary features in common 1 1 an initial period of effusive eruptions of pyroclastic flows followed by 2 2 the formation of large scale ring structures partly accompanied by peripheral syenite granite intrusions 3 3 the emplacement of a multiple intrusive central stock of sub alkaline granite composition which is terminated by 4 4 the injection of a highly differentiated aplogranite granophyre closely associated with the development of the mineralizing hydrothermal porphyry system molybdenum mineralization of the oslo province is closely associated with highly differentiated alkali granites which possess striking similarities to mo related granites of the colorado mo province and evolved rapakivi or a type granites usually considered to be typically associated with bimodal magmatism of crustal extension and continental rifts the discovery of significant porphyry mo mineralization in the oslo rift associated with permian igneous rocks draws attention to the possible economic potential of rift structures elsewhere

crustal structure and composition of the oslo graben norway abstract although more than 250 my old the oslo graben has retained a distinctive distribution of p wave velocities associated with rifting intrusion and underplating of the thinned crustal section we calculate poisson s ratio values from crustal p and s wave velocities along an 400 km long profile across the southern scandinavian peninsula with a focus on the oslo graben plutonic rocks are now exposed at the surface in the graben due to post rifting erosion and the corresponding low 5 5 km s p wave velocities extend to depths of 3 km the p wave velocity and poisson s ratio between depths of 6 and 34 km are 5 higher inside than outside the rift boundaries which together with thickening of the 7 km s lower crust beneath the rift indicate magmatic intrusions poisson s ratio of 0 27 and high 7 1 7 4 km s velocities indicate a heterogeneous composition lower crust the thickened high velocity lower crust is 1 5 times wider than the surface expression of the rift and extends to both the east and west of the main rift axis depth dependant extension may have occurred within the rift and may account for the significant volumes of volcanic output despite the small surface extension observed the added volume of intrusive material may explain why the moho up warp is small as little as 2 km at the rift based on the new p wave velocities poisson s ratio measurements and the thickness of the magmatic underplate apparent values for the rift are estimated to be 1 5 but when intrusion within the crust is included could be as high at 2 3

mapping geoelectric fields during magnetic storms synthetic analysis of empirical united states impedances empirical impedance tensors obtained from earthscope magnetotelluric data at sites distributed across the midwestern united states are used to examine the feasibility of mapping magnetic storm induction of geoelectric fields with these tensors in order to isolate the effects of earth conductivity structure we perform a synthetic analysis calculating geoelectric field variations induced by a geomagnetic field that is geographically uniform but varying sinusoidally with a chosen set of oscillation frequencies that are characteristic of magnetic storm variations for north south oriented geomagnetic oscillations at a period of t0 100 s induced geoelectric field vectors show substantial geographically distributed differences in amplitude approximately a factor of 100 direction up to 130 and phase over a quarter wavelength these differences are the result of three dimensional earth conductivity structure and they highlight a shortcoming of one dimensional conductivity models and other synthetic models not derived from direct geophysical measurement that are used in the evaluation of storm time geoelectric hazards for the electric power grid industry a hypothetical extremely intense magnetic storm having 500 nt amplitude at t0 100 s would induce geoelectric fields with an average amplitude across the midwestern united states of about 2 71 v km but with a representative site to site range of 0 15 v km to 16 77 v km significant improvement in the evaluation of such hazards will require detailed knowledge of the earth s interior three dimensional conductivity structure

sr nd and pb isotope geochemistry of the oslo rift igneous province southeast norway abstract sr nd and pb isotopic compositions are presented for a series of 290 to 250 ma old basaltic to granitic rocks from the oslo rift southeast norway a large group of basalts larvikites and rhomb porphyry lavas cluster within a restricted range of initial isotope ratios tsr 3 to 16 tnd 3 3 to 4 2 206 pb 204 pb i 18 9 to 19 3 207 pb 204 pb i 15 59 to 15 66 208 pb 204 pb i 38 6 to 39 1 the remainder of the rocks trend towards higher initial sr and lower initial nd and pb isotopic ratios data are tested against mantle crust mixing models the oslo rift magmatic rocks originated from a somewhat heterogeneous mildly depleted source located in the subcrustal lithosphere the isotopic character of this source has been inherited by the rocks showing uniform isotopic ratios which have thus not suffered significant crustal contamination the rest of the mafic to intermediate rocks and the syenites were contaminated in the intermediate to lower crust which increased slightly their sr but decreased their nd and pb isotopic ratios as much as 40 50 contamination is suggested for some of the samples strong increases in radiogenic sr seen primarily in the granites are attributed to contamination in the upper crust the mildly depleted mantle proposed as the source for the oslo rift mafic rocks has an isotopic character which can only be explained in terms of a multistage history which included periods of relatively high u pb and th pb ratios resulting from a relatively short depletion history in the subcontinental lithosphere and metasomatic enrichment of the mantle in selected elements

paleozoic paleo cover of the southern part of the fennoscandian shield fission track constraints abstract granitic intrusions older than 1200 ma from an area west of lake vanern south sweden show fission track ages of 680 50 ma 2 late precambrian for sphene and 220 10 ma late triassic for apatite the samples were taken at the present post glacial erosion surface which is close to the sub cambrian peneplain the c 680 ma sphene fission track ages are thought to be related to the uplift of the area which led to the establishment of this erosion surface at c 600 ma ago the much younger apatite fission track ages and the confined spontaneous track length distributions along with regional stratigraphic constraints suggest that the basement was subsequently buried under 3 4 km of paleozoic supracrustals this induced in the basement a rise in temperature which obliterated the older apatite fission tracks but not those in sphene which has a higher closure temperature at the beginning of the mesozoic the area was uplifted again the cover rocks were removed and the basement rocks cooled slowly below the temperature range of fission track annealing in apatite

internal structure of the dead sea leaky transform rift in relation to plate kinematics abstract the structures along the dead sea transform rift are related to the motions of the sinai and arabia plates which border it and to the irregularities of their boundaries the total slip was 105 km left lateral but the present structures were formed mainly during the last 40 km of slip which probably occurred in the plio pleistocene along the southern half of the transform the strike slip motion takes place on en echelon faults this produces rhomb shaped grabens or pull aparts which are sometimes composite and in which there is local crustal separation thus much of the transform is leaky these structures occur in a morpho tectonic rift valley delimited by normal faults which express a small component of transverse extension along a few segments the shape of the transform is such that lateral motion produces local transverse compression the geometric relations of the structures along the transform define an eulerian pole of relative plate motions at 32 8 n 22 6 e 0 5 the older motion was somewhat different and is described by a pole located about 5 west of the above then the component of transverse extension and crustal separation was much smaller than now while local transverse compression was more important the northern half of the dead sea transform has an irregular shape and the bordering plates did not remain rigid as lateral motion continued here transverse compression is often important

models of lithospheric thinning lithospheric thinning denotes a gcodynamieal process that is associated with extensional tectonic phenomena in plate tectonics the lithosphere is a layer of strength compared with the underlying asthenosphere its thick ness is commonly defined by the depth to a particular isothermal or by a fraction of the melting temperature of rocks a typical thickness is of the order 100 km and includes the earth s crust and parts of the upper mantle this definition is equivalent to that used in seismology but it does not necessarily correspond to the elastic thickness derived from flexural defor mations in response to loading according to its thermal regime state of stress and lithology we expect the lithosphere to contain layers of predominantly brittle and ductile deformation the oceanic and continental lithospheres have distinctive origins structures and compositions while the age of the oceanic litho sphere is only of order 108 myr the continental lithosphere contains the oldest rocks known on earth the latter has therefore the most com prehensive record of past geodynamical processes lithospheric thinning is expressed by a variety of tectonic and epeiro genic manifestations such as domal uplifts and hotspot swells crough 1983 continental rifts morgan baker 1983 platform basins sleep et ai 1980 and plateau uplifts on the other hand our understanding of the thinning mechanisms is based on physical concepts in association with observations reheating of the lithosphere b uoyantly driven diapiric pene tration or stretching under isostatic conditions are the most frequently discussed models they implicitly define the nature of the source of thin ning

geodynamics of rifting and implications for hydrocarbon habitat abstract rifting activity is probably mainly governed by frictional forces exerted on the base of the lithosphere by the convecting sub lithospheric upper mantle combined with deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system and by far filed stresses controlling the interaction of lithospheric plates moving relative to each other mantle plumes rising from the deep mantle do not appear to be a major driving force of rifting therefore it is questioned whether a distinction between active and passive rifts is still justified lithospheric extension triggers by decompression partial melting of the lower lithosphere and upper asthenosphere magmatic processes contribute materially to thinning of the subcrustal lithosphere and probably also of the lower crust this could explain the frequently observed discrepancy between upper crustal extension by faulting and lower crustal attenuation as defined by refraction and deep reflection seismic data the duration of the rifting stage of palaeorifts and passive margins is highly variable depending on plate interaction crustal separation can be achieved after as little as 7 ma and as much as 280 ma of rifting activity the availability of crustal discontinuities does not appear to play a significant role in the time required for crustal separation to be achieved the structural style of rifts is controlled by the physical state of the lithosphere the mode and amount of its extension and the lithological composition of pre and syn rift sediments subsidence of rift basins is controlled by the balance between isostatic adjustment of the crust to lithospheric stretching and uplift induced by mechanical and thermal attenuation of the subcrustal lithosphere post rift basin subsidence is mainly governed by the decay of rift induced thermal anomalies densification of the lower crust and intra plate stresses provide overprinting effects in view of this it is unlikely that quantitative analyses of post rift basin subsidence give a direct measure of lithospheric extension tectonically active rifts palaeorifts and passive margin basins contain major hydrocarbon provinces their hydrocarbon charge can rely exclusively on pre rift syn rift or post rift sedimentary sequences or a combination thereof maturation of source rocks can be achieved during the syn and or post rift stage of basin evolution during rifting conductive and convective heat transfer accounts for elevated geothermal gradients these play an important role in the maturation of pre and syn rift source rocks thermal gradients decrease asymptotically during the post rift stage

organic petrography and geochemical characterization of the upper cretaceous second white specks and upper belle fourche alloformations west central alberta analysis of local maturity anomalies abstract the second white specks is an enigmatic unconventional shale play in the western canada foreland basin wcfb this play has an inconsistent production performance that has impacted exploration and production risk preventing extensive development in this contribution geochemical properties are studied with the purpose to identify possible geochemical factors that could contribute to the production variability of this unconventional petroleum system the studied succession consists of the second white specks sws and upper belle fourche ubf alloformations which are part of the sws shale play organic petrology and rock eval pyrolysis were combined to characterize the organic matter om and assess om richness thermal maturity and hydrocarbon generation potential in the foredeep section of the basin the results show that the om richness and hydrocarbon generation potential in this area is good and comparison with other studies show that they do not exhibit major lateral variations the kerogen is marine type ii and is dominated by liptinite vitrinite inertinite macerals and solid bitumen alginite and bituminite are the most abundant macerals altered bituminite provides evidence of anaerobic bacteria degradation there is a modest contribution of inertinite that may be responsible for a dilution effect of the pyrolyzable carbon the thermal maturity indicators in this study such as vitrinite reflectance tmax and alginite uv fluorescence color indicate that the controls on thermal maturity and hydrocarbon generation are not well understood there are lateral short scale variations or maturity anomalies that require further investigation to reduce the exploration risk

compositional variations among gabbroic intrusions in the oslo rift magmatic activity associated with the formation of the oslo rift south norway in permo carboniferous time includes formation of a series of gabbroic intrusions of minor volume the rock types in these intrusions range from pyroxenite and gabbro to monzonite and anorthosite the mafic units bear evidence of the crystallization order ol cpx opx plag whereas the more evolved rock types have crystallized olivine and plagioclase before clinopyroxene amphibole occasionlly represents an early phase major and trace element data imply that removal of clinopyroxene has dominated the early crystallization history of all these rocks this is also true for rocks which give petrographic evidence of crystallization of cpx after plag rb sr isotope data define a whole rock age of 265 11 for the snaukollen and a mineral age of 266 5 ma for the dignes intrusion whole rock samples from the other intrusions however do not define isochrons but cover a range of 87sr86sr ratios from 0 70395 to 0 71187 it is concluded that the gabbroic oslo rift rocks are produced through a two stage crystallization history combined with crustal contamination 1 1 mafic magmas ascending from some melt region in the mantle were retained in the lower crust where they crystallized olivine and clinopyroxene 2 2 at different stages of evolution residual magmas rose to their present position in the upper crust depending on composition the crystallization sequence there was ol cpx plag or ol plag cpx 3 3 during the final stage of evolution the magmas were to different degrees contaminated by precambrian amphibolite facies and cambro silurian carbonaceous country rock early crystallization of amphibole combined with interstitial calcite in some rocks and highly variable fe3 contents in clinopyroxene imply significant variations in the volatile phase of the magmas which gave rise to the gabbroic rocks these differences may have been introduced through the contamination however the possibility of primary compositional contrasts cannot be excluded

a new species of mosasaur squamata mosasauridae from the pierre shale lower campanian of manitoba plioplatecarpus nichollsae sp nov from the lower campanian pembina member pierre shale formation is diagnosed by the following a thickened ventral rim of the external naris a short supratemporal fenestra a frontal shield with well developed posterolateral lappets that overlap the parietal dorsally proximal rib shafts with an approximately circular but not inflated cross section a scapula shaped as in other plioplatecarpus species but approximately the same size not larger than the coracoid and a moderately large parietal foramen that reaches the frontoparietal suture but does not invade the frontal the last two characters require that the diagnosis of the genus plioplatecarpus be emended with other plioplatecarpus species p nichollsae shares a robust humerus with a distal expansion at least as great as the total length of the bone a rectangular preorbital frontal shield a peg and socket postorbitofrontal jugal articulation a transversely directed ectopterygoid process of the pter

marine reptiles from the nanaimo group upper cretaceous of vancouver island a new fauna of fossil marine reptiles is described from the late cretaceous nanaimo group of vancouver island the fossils are from the haslam and pender formations upper santonian near courtenay british columbia and include elasmosaurid plesiosaurs turtles and mosasaurs this is only the second fauna of late cretaceous marine reptiles known from the pacific coast the other being from the moreno formation of california maastrichtian the new nanaimo group fossils are some 15 million years older than those from the moreno formation however like the california fauna there are no polycotylid plesiosaurs and one of the mosasaurs is a new genus this reinforces the provinciality of the pacific faunas and their isolation from contemporaneous faunas in the western interior seaway

biogeography of terrestrial and freshwater vertebrates from the late cretaceous campanian western interior of north america abstract previous biogeographic studies of late cretaceous late campanian vertebrate faunas in the western interior basin wib of north america have suggested the presence of faunal and floral provincialism characterized by distinct northern and southern biomes however the provincialism hypothesis has been questioned based largely on the contention that the investigated faunas were recovered from a series of diachronous time transgressive deposits and are therefore non correlative extensive work in several fossiliferous units of late campanian age including the dinosaur park judith river two medicine kaiparowits fruitland kirtland and aguja formations has greatly increased understanding of wib vertebrate faunas and their chronostratigraphic relationships here updated and greatly expanded faunal and chronostratigraphic datasets are utilized to undertake an extensive biogeographic analysis of these six terrestrial fossiliferous formations within the wib of north america quantitative biogeographic comparisons of the formations and their constituent faunas are conducted using four statistical methods analysis of similarity q mode cluster analysis parsimony analysis of endemicity and correspondence analysis the results of this study provide strong support for highly divergent faunas in northern and southern regions of the wib with a latitudinal faunal gradient as an interface yet the nature of the interface between these faunas remains unclear with possibilities including 1 two or more discrete provinces separated by a zone or zones of faunal mixing and 2 a continuous latitudinal gradient or cline with no discrete zones of endemism lacking evidence of any physiographic barrier to north south dispersal climatic variation within the wib is regarded as the most likely explanation for the overarching biogeographic patterns observed for late campanian vertebrate taxa

taphonomy and sedimentology of storm generated continental shell beds a case example from the cretaceous western interior basin abstract an extraordinary continental shell bed is reported from the upper cretaceous kaiparowits formation in southern utah this shell bed referred to as the kaiparowits blues ceratopsian shell bed is highly unusual among fluvial estuarine shell beds for its great thickness surface area and shell density and its geometry it covers 850 m2 ranges from 85 to 280 cm thick and consists of a series of 10 50 cm thick low angle dipping beds the shells are generally undamaged and articulated 75 commonly with valves still closed and strongly oriented normal to the dip orientation of the shell layers the shell bed is interpreted as a lateral accretion bar set that developed in a point bar or midchannel bar setting nearly 45 of shells are encrusted by the brackish water bryozoan conopeum sp indicating that deposition transpired within the upper fluvial to mixed fluvial marine part of an estuarine channel system at least five unionoid unionoidea shell morphotypes are present representative of

new constraints on the timing of late carboniferous early permian volcanism in the central north sea the permo carboniferous evolution of the central north sea is characterized by three main geological events 1 the development of the west european carboniferous basin 2 a period of basaltic volcanism during the lower rotliegend latest carboniferous early permian and 3 the development of the northern and southern permian basins in late permian times the timing of the late carboniferous permian basaltic volcanism in the north sea is poorly constrained as is the timing of extensional tectonic activity following main inversion during the westphalian due to the propagation of the variscan deformation front results of high precision ar ar dating on basalt samples taken from a core from exploration well 39 2 4 amerada hess in the uk sector of the central north sea suggests that basaltic volcanism was active in the late carboniferous at c 299 ma the presence of volcanics below the dated horizon suggests that the onset of permo carboniferous volcanism in the central north sea commenced earlier probably at c 310 ma westphalian c this is contemporaneous with other observations of tholeiitic volcanism in other parts of nw europe including the oslo graben the north east german basin southern sweden and scotland interpretations of available seismic data show that main extensional faulting occurred after the volcanic activity but the exact age of the fault activity is difficult to constrain with the data available

mass estimates of cumulates and residues after anatexis in the oslo graben the magmatic province of the permian oslo rift southeast norway is dominated by rocks of monzonitic to granitic composition most of the monzonitic rocks are believed to have formed by fractional crystallization from mantle derived magmas whereas melts produced by anatexis in the lower crust are important to the formation of the syenitic and granitic rocks these processes have left dense cumulates and dense residues after melting in the crust the surplus masses of cumulates and residues at depth in the crust can be estimated by using petrological and geological information on the rocks exposed today quantitative estimates for the oslo graben are comparable to corresponding data derived from geophysical crustal models the petrological geological estimates suggest excess masses of 7 10 1010 kg per linear meter assuming prismatic bodies along the rift axis in the southern and 5 7 1010 kg m in the northern part of the oslo region these estimates are dependent upon the volume proportion of trapped liquid in the cumulates and the ratio of cumulates to residues after anatectic melting in the crust the amount of trapped liquid appears to be low less than 25 the results agree well with estimates by wessel and husebye 1986 of excess mass in the crust based on gravimetric data which gave 5 7 1010 kg m this agreement testifies to the validity of making mass estimates on the basis of petrological and geological data the data bear on the composition and evolution of the upper lithosphere in the graben area some cumulates may reside in the subgraben mantle

offshore electrical exploration of sedimentary basins the effects of anisotropy in horizontally isotropic layered media our electrical method for exploring beneath the sea consists of a long vertical bipolar ac source extending downward from the sea surface to the bottom of the sea and a remote encapsulated microprocessor controlled magnetometer located on the sea floor the amplitude and phase of the magnetic field are measured over a range of suitable frequencies and transmitter magnetometer separations at the low frequency static limit apparent resistivity curves similar to standard schlumberger resistivity sounding curves are constructed as an aid in the direct interpretation of isotropic crustal resistivity an intermediate relatively resistive or relatively conductive zone is detectable when the transmitter receiver separation exceeds the order of twice the depth to the zone the physical property resolved by the method in an anisotropic crust which has different horizontal and vertical resistivities is the geometric mean of the two independent resistivities the thickness of a layer is indeterminate a la

on induction effects at eiscat and image magnetometer stations summary when ground based magnetometer data are used for ionospheric magnetospheric studies it is important to know the external ionospheric magnetospheric and internal telluric contributions to the observed total variation to study them we calculate geomagnetic induction vectors and apply the siebert kertz separation method using data from the eiscat and image magnetometer stations in fennoscandia induction vectors in the period range 20 2560s show the expected and dominating ocean effect near the arctic ocean at masi a small scale inland anomaly is detected in addition to the ocean effect at hankasalmi a man made anomaly due to the nearby stare radar is present the source effect on induction vectors at high latitudes is briefly investigated by separating the magnetic variations of several bay events at image stations into external and internal parts we study the importance of the large scale induction in the recordings depending very much on the particular event the internal horizontal part is 10 30 per cent of the total field in the auroral electrojet region and its relative contribution increases in more distant regions the internal contribution of the vertical field at inland stations is 10 40 per cent having an opposite sign to the total field or 10 30 per cent having the same sign as the total field depending on the location with respect to the ionospheric currents and to the ocean results are also discussed using a thin sheet model

magnetotelluric constraints on the tectonic setting of grenville aged orogenesis in central australia abstract magnetotelluric mt data were collected over a 480 km long profile in central australia extending from the mesoarchaean palaeoproterozoic gawler craton into the mesoproterozoic neoproterozoic musgrave province the two regions have contrasting geological histories and many reconstruction models of proterozoic australia propose that they were juxtaposed during the mesoproterozoic despite the significant differences in geological background between the gawler craton and the musgrave province the mt data did not image an electrical structure or any change in electrical character between them mt models suggest that southern central australia is electrically separated into two parts the first comprising the northernmost gawler craton and the musgrave province has a 5 km thick layer of moderate resistivity overlying highly resistive crust the second comprising the central northern gawler craton displays moderate resistivity to the base of the crust the lithospheric mantle underlying both electrical regions is uniformly highly resistive our results suggest that the musgrave province and gawler craton are more closely related than is currently recognized we propose that the gawler craton forms basement to the musgrave province and that the grenvillian musgrave orogeny was an intracratonic reworking event that overprinted the older basement

initiation of melting beneath the oslo rift a melt inclusion perspective abstract this study of the most primitive magmas in the permo carboniferous oslo magmatic system aims at understanding the initial phases of magmatism in a rift related environment primary melt inclusions are investigated from two compositional types of pyroxene cr diopside and ti augite found within the alkaline skien basalts southern norway data from the analyses of melt inclusions in this tectonic setting indicate that the melting process is complex in both types of pyroxene two groups of melt inclusions can be identified together with rare co 2 fluid inclusions in the cr diopsides these are termed the cd high fe feo 9 wt and cd low fe feo the two groups of melt inclusions found in the ti augites are called ta high na na 2 o 2 wt and ta low na na 2 o 2 o 5 contents

high grade contact metamorphism of calcareous rocks from the oslo rift southern norway shallow level plutons caused extensive contact metamorphism of lower paleozoic shale and carbonate sequences in the permian oslo rift a 500 m long and 100 m wide shale limestone xenolith embedded within monzonites belonging to the skrim plutonic complex experienced high grade contact metamorphism and generation of minerals and mineral assemblages rarely reported from metamorphic rocks the peak metamorphic stage i assemblages in calcite saturated rocks include wollastonite melilites fassaitic pyroxenes phlogopite titanian grossular kalsilite nepheline perovskite cuspidine baghdadite pyrrhotite and occasional graphite mineral reactions involving detrital apatite produced a series of silicate apatites including the new mineral species ca sub 3 5 th u sub 1 5 si 3 o 12 oh this assemblage equilibrated at t 820 870 degrees c with a c rich internally buffered pore fluid 20 40 mol co 2 ch 4 during cooling the shale limestone xenolith experienced infiltration of c poor 2 fluids triggering the formation of retrograde stage ii mineral assemblages comprising monticellite tilleyite vesuvianite grandite garnets diopside and occasional hillebrandite rare potassium iron sulfides rasvumite and djerfisherite formed at the expense of primary pyrrhotite these assemblages probably formed near 700 degrees c formation of diffuse sodalite bearing veinlets was associated with breakdown of nepheline and the replacement of kalsilite and wollastonite by potassium feldspar the sodalite bearing stage iii assemblage formed by the infiltration of saline brines at a maximum temperature of 550 degrees c low temperature stage iv retrogression of the stage i iii assemblage produced scawtite giuseppettite hydrogrossulars phillipsite thomsonite and three hitherto undescribed mineral species

hesperornis aves from ellesmere island and palynological correlation of known canadian localities a tarsometatarsus of hesperornis from the kanguk formation on ellesmere island is described and illustrated and constitutes the northernmost occurrence of the genus palynological evidence and stra

cataclastic rocks along the nesodden fault oslo region norway a reactivated precambrian shear zone abstract the nesodden fault segment nfs is the northern segment of the oslofjorden fault of which separates the precambrian rocks in the east from palaeozoic rocks in the west the nfs is characterized by two groups of fault rocks group 1 comprises a series of crush breccias to ultracataclasites containing material derived from the precambrian basement these fault rocks were formed at a depth greater than 5 km by attrition brecciation and distributed crush brecciation at some time between the sveconorwegian orogeny 950 ma and the deposition of the cambrian alum shale 540 505 ma group 2 comprises five crush breccias with a similar quartz matrix containing fragments of older rocks and permian intrusive rocks they were formed at a depth of less than 3 5 km by the interaction of cataclasis and hydrothermal percolation attrition and implosion brecciation during the formation of the permo carbonifereous oslo rift 300 230 ma evidence of repeated hydrothermal fluid flow and fluidization has been recognized in the youngest breccias the seven different fault rocks emphasize the importance of fault reactivation and show that old fault zones commonly act as planes of weakness along which repeated deformation takes place and act as pathways for hydrothermal fluids

linking changes in tectonic style with magmatism in northern europe during the late carboniferous to latest permian abstract early carboniferous to permian magmatism associated with rifting within the northern foreland of the variscan orogen was widespread across europe during the long period of magmatic activity the regional tectonic setting changed across the region from early carboniferous extension and basin formation to a rifting wrenching style of deformation in the late carboniferous stephanian to early permian wrenching and faulting were accompanied by widespread voluminous and episodic magmatic extrusion intrusion and underplating this was followed by thermal relaxation and the development of the northern and southern permian basins in later permian times thermal relaxation was punctuated by a permo triassic phase of extension and graben formation 40ar 39ar ar step heating dating for mineral separates and whole rock samples of magmatic rocks from southern scandinavia oslo graben and south sweden and rugen north germany provides further radiometric evidence for three of the proposed periods of magmatic activity in the region latest carboniferous to earliest permian ages c 300 310 ma were obtained for volcanic rocks in the oslo graben and dolerite sills and dykes in south sweden and north germany this phase can be time correlated with magmatic activity that occurred throughout europe during large scale dextral wrenching that followed the variscan orogeny a second phase of alkaline intrusions is confined to the oslo graben and related to caldera collapse around c 275 ma the third permo triassic phase c 250 ma is considered to be related to a new tectonic cycle involving extension that triggered minor melting of enriched fertile mantle

an ichthyornithiform bird from the campanian of canada the geographic range of the ichthyornithiform birds is extended to the canadian province of manitoba the associated fauna from the pembina member of the vermilion river formation of southern manitoba closely resembles that from the sharon springs member of the pierre shale formation in kansas south dakota and wyoming

mesozoic marine reptile palaeobiogeography in response to drifting plates abstract during the mesozoic various groups of reptiles underwent a spectacular return to an aquatic life colonizing most marine environments they were highly diversified both systematically and ecologically and most were the largest top predators of the marine ecosystems of their time the main groups were ichthyosauria sauropterygia thalattosauria and several lineages of testudinata crocodyliformes rhynchocephalia and squamata here we show that the palaeobiogeographical distribution of these marine reptiles closely followed the break up of the supercontinent pangaea and that they globally used the main marine corridors created by this break up to disperse most mesozoic marine reptile clades exhibit a cosmopolitan or at least pandemic distribution very early in their evolutionary history the acquisition of morphological adaptations to a fully aquatic life combined to special thermophysiological characteristics are probably responsible for these animals to become efficient long distance open marine cruisers generally early triassic taxa were near shore animals mainly linked to the tethys or panthalassa coastlines by the end of the triassic and during the jurassic the break up of pangaea resulted in the formation of large marine corridors connecting the tethys to the north atlantic and pacific realms a trend increasing on during the cretaceous with the expansion of the atlantic ocean and the break up of the southern gondwana allowing open sea marine reptiles to spread out over large distances however if large faunal interchanges were possible at a global scale following a dispersal model some provinces such as the mediterranean tethys were characterised by a peculiar faunal identity illustrating an absence of migration with time despite the apparent lack of barriers so if continental drift enabled global circulations and faunal interchanges via dispersals among mesozoic marine reptiles other parameters such as ecological and biological constraints probably also played a role in the local endemic distribution of some of these marine groups as they do today

crystallization history of a permian composite monzonite alkali syenite pluton in the sande cauldron oslo rift southern norway monzonitic rocks larvikite occur as megarafts embedded in younger alkali syenite in the sande central pluton mineral equilibrium data are presented in order to establish a crystallization history for the members of the complex the larvikites in part orthopyroxene bearing have followed cooling paths close to the qfm buffer during intrusion of the alkali syenite nordmarkite the older intrusives were reheated to the solidus with sencondary buffered cooling taking place at higher oxygen fugacity levels roughly equivalent to the nno buffer which are within the o2 range estimated for the nordmarkite magma gradual transitions between larvikite and nordmarkite are results of the secondary reheating

characterization of apatite resources in norway and their ree potential a review abstract apatite is a necessity for the production of phosphorus fertilizers and presents a potential raw material for the extraction of ree and y a wide spectrum of apatite deposits is found in norway including sedimentary igneous and vein type deposits the igneous deposits which appear to have the greatest potential for exploitation occur associated with alkaline complexes massif type anorthosite complexes and monzonitic complexes one of the most promising is found in the monzonoritic bjerkreim sokndal layered intrusion of the early neoproterozoic rogaland anorthosite province in southwest norway the intrusion hosts three cumulate units with high grade ore zones the most promising resource is confined to mcu iv which is 50 170 m thick and nearly 10 km long with average normative contents of 10 2 apatite 12 4 ilmenite and 7 3 vanadium rich magnetite the late neoproterozoic cambrian carbonatite bearing alkaline complexes are generally of low grade to represent potential resources of apatite as the sole commodity however apatite may represent a byproduct of potential nb and ree y mineralisation in the fen complex in southern norway the late ordovician silurian misvaerdal complex comprising multiple alkali clinopyroxenite intrusions in the uppermost allochthon of the caledonides in northern norway contains 1 1 5 km long and 100 200 m wide ultrapotassic clinopyroxenite dykes with average contents of 7 10 wt apatite and with intermediate levels of trey 0 5 wt however high levels of th in the apatite make it less suitable as a raw material for fertilizer production apatite fe ti oxide ores being characteristic for the monzonitic complexes are especially well developed in the permian oslo igneous province where apatite rich magnetite clinopyroxenite cumulates are found in the larvik plutonic complex the kodal body has an inferred open pit ore reserve calculated to 70 mt with approximately 11 6 wt apatite 3 0 wt ilmenite and 26 5 wt ilmenomagnetite the apatite contains about 1 wt ree comparable types of deposits of palaeoproterozoic age have recently been recognized in the alkali calcic mangeritic to syenitic intrusions in the lofoten vesteralen mangerite complex in northern norway whereas complexes with variable proportions of anorthosites s s jotunites and mangerites occurring in the middle allochthon of the caledonides in south norway also are known to host apatite bearing fe ti oxide deposits some high in apatite these complexes represent potential areas for green field exploration the trey tree y contents of the apatite in the igneous deposits are discussed and comprise very low levels in the bjerkreim sokndal layered intrusion intermediate levels in the carbonatites and pyroxenites of the alkaline complexes as well as nelsonite dykes and mangerite associated deposits to high levels in the monzonite associated deposits

a crustal conductor on eyre peninsula south australia short period variations in the geomagnetic field components were recorded in a closely spaced network of sites on southern eyre peninsula south australia they reveal the existence of a linear zone of very good electrical conductivity within the late archaean early proterozoic gawler craton there is strong enhancement of the horizontal component variations transverse to the zone and an abrupt phase change in the vertical component particularly for periods near 2 103s these features are consistent with a line or narrow thin sheet of current flowing in a conductor at a depth 10 km this almost certainly requires a major fracture or shear zone within the crystalline basement for which there is supporting geophysical evidence superficial cenozoic deposits blanket much of the area and consequently the basement geology is not known in detail although there are structures parallel to the conductor 20 km to the east identification of a major linear crustal feature in such an area demonstrates the usefulness of geomagnetic variation studies for understanding deep geology

the electrical resistivity of canada s lithosphere and correlation with other parameters contributions from lithoprobe and other programmes over the last 30 years through lithoprobe and other programmes modern high quality magnetotelluric mt measurements probing deep into the lithosphere and underlying asthenosphere have been made at over 6000 sites across canada in all provinces and territories except nova scotia some regions are well covered particularly alberta southern british columbia and western ontario whereas others remain poorly covered such as quebec and large swaths of nunavut prior publications from individual studies have added significantly to the wealth of canada s geoscience knowledge and have demonstrated that mt can contribute significantly to understanding of the tectonic processes that have shaped canada however to date no continent scale maps of lithospheric electrical parameters have been constructed from the extensive mt database herein we review the contributions made by the mt components of lithoprobe and present new continental scale maps of various electrical parameters at crustal and upper mantle

skagerrak graben the offshore continuation of the oslo graben abstract new seismic mapping of skagerrak reveals eight structural provinces in particular the skagerrak graben appears to be the continuation of the oslo graben the skagerrak graben is defined by two major late paleozoic faults trending northeast southwest connecting with the faults bounding the oslo graben extensive rotated block faulting is observed within the graben and a thickness of more than 2 s twt of lower paleozoic sediments has been preserved along the boundary faults sediments of probable late paleozoic age have been deposited as erosional products from the fault scarps and a central uplifted area a substantial part of these sediments may have a volcaniclastic origin the skagerrak graben continues to the north as a province of igneous rocks exposed at the sea floor with precambrian basement on either side the skagerrak graben is flanked by small half grabens containing probable early paleozoic sediments indicating that a wider area was involved in the rift process the formation of the skagerrak graben is related to the dextral strike slip movements along the sorgenfrei tornquist zone in late paleozoic time the kimmerian extensional movements along this zone indicate however a decoupling of the skagerrak graben at this time only minor inversion in the southwestern part of the skagerrak graben reflects the major inversion tectonism along the sorgenfrei tornquist zone in late cretaceous early tertiary times

relationship between deeper lithospheric processes and near surface tectonics of sedimentary basins interactions between upper lithosphere deformation as manifested in the structure and evolution of sedimentary basins and lower lithospheric deformation presumably reflect large scale regional or global tectonic events we review the current state of knowledge regarding these interactions and suggest areas of research which may lead to an improvement in this knowledge understanding the development of sedimentary basins requires insight into the processes responsible both for basin subsidence and also for distribution and preservation of sediments within the basins while some classes of basins are better understood than others there remain significant gaps both in our ability to account for available data and also in the data available to test current models and develop new ones subsidence in some classes of basins can be related to lithospheric scale processes occurring as part of the overall plate tectonic paradigm for example it is widely accepted that passive margin basins subside as a result of lithospheric extension mckenzie 1978 and that foreland basins are flexural consequences of collision between a continent and outboard terranes beaumont 1981 on the other hand models for the origin of intracratonic forearc and trans tensional basins are essentially still at cartoon level involving processes that are difficult to quantify and evaluate in the following we review a number of fundamental questions of vital interest for understanding of the relationship between deeper lithospheric processes and near surface tectonics

paleostress reconstruction from kinematic indicators in the oslo graben southern norway new constraints on the mode of rifting abstract the oslo graben southern norway is a n s trending carboniferous permian rift system characterized by major mafic to silicic magmatism n s trending faults reactivation of preexisting precambrian faults and formation of half grabens magmatism is expressed by the presence of lavas dyke injections cauldron formation and the intrusion of batholiths paleostress analyses mainly based on slickensides have been performed in the area both within and outside the rift structure combined with the current tectono magmatic model of the oslo graben area the analyses show the following stress evolution from the caledonian orogeny with its compressional tectonics in the silurian to the late stages of the carboniferous permian rifting nw se compression occurred in silurian times due to the continental collision of the caledonian orogeny after a long period of a missing geological record the area was affected by n s compression during the late carboniferous a shallow sedimentary basin developed indicative for the pre and proto rift phases the transition from the proto rift phase to the initial rift phase is marked by a transition from a transpressional regime into a transtensional regime during the early permian the stress regime changed from pure extension to radial extension we suggest that the oslo graben can not simply be explained in terms of or passive or active rifting but that a combination of both evolving through time is more suitable to explain the observations we propose a model in which the oslo graben is initially triggered by far field stresses in the latest carboniferous and earliest permian which infers opening due to passive rifting these far field stresses are suggested to be linked to the hercynian orogeny active to the south in central europe in carboniferous times and the reorganisation of the pangea supercontinent in early permian times the stress regime caused radial extension indicative for uplift and a change to an active mode of rifting simultaneously with the radial extension large volumes of magma are emplaced at near surface levels despite all alternative models an anomalous thermal gradient is necessary to create these large volumes of magmatic material we propose therefore that shortly after the onset of rifting the dominant rifting mode becomes active plume related although far field stresses might still be present

marine turtles from the late cretaceous of alberta canada previously reported and new specimens of marine turtles from the late campanian of alberta canada provide additional information on the diversity and distribution of chelonioid turtles at this time an articulated carapace from the bearpaw formation previously interpreted as lophochelys niobrarae is considered to be a juvenile of a specifically indeterminate chelonioid and is referred to lophochelys sp isolated neurals and a hyoplastron from nonmarine estuarine deposits in the uppermost beds of the dinosaur park formation are tentatively referred to lophochelys sp these specimens suggest that this chelonioid could enter freshwater environments a new chelonioid kimurachelys slobodae gen et sp nov is recognized on the basis of two mandibles and a maxilla from the uppermost beds of the dinosaur park formation of southeastern alberta a partial postcranial skeleton of an indeterminate chelonioid from the bearpaw formation provides additional evidence that chelonioids of this formation included taxa that were phylogenetically intermediate between chelonioids of the late santonian and members of the crown group

paleobiogeography of the cretaceous western interior seaway of north america the vertebrate evidence abstract distribution patterns of marine vertebrates of the cretaceous western interior seaway of north america are analysed in a biogeographical context the analysis is based on fossil vertebrate assemblages from the following lower campanian localities 1 anderson river fauna n w t 2 pembina fauna southern manitoba 3 sharon springs fauna south dakota wyoming 4 niobrara fauna kansas 5 mooreville fauna alabama due to the cosmopolitan nature of many marine vertebrates relative abundance is used in preference to presence absence data in identifying faunal distribution patterns the analysis demonstrates the presence of two faunal subprovinces in the seaway the northern interior subprovince is characterized by a low diversity in all groups and is dominated by plesiosaurs hesperornithiforms and the mosasaur platecarpus the southern interior subprovince is characterized by a high diversity in all groups and is dominated by sharks turtles and the mosasaur clidastes these biogeographical subdivisions support the hypothesis of warm temperature and cool temperate zones in the seaway that have been proposed on the basis of invertebrate faunas

crustal extension in the oslo graben se norway a method incorporating magmatism and erosion abstract three methods for determining crustal extension were examined for use in the late paleozoic oslo graben of southeast norway 1 1 analysis of faults and dikes 2 2 volume budget isostasy 3 3 analysis of crustal thickness distribution assuming constant crustal volume during extension these methods were found not to be suitable mainly due to rift age and magmatism instead a new integrated model which combines the effect of moho contours volumes of mantle injecta and erosion was used volumes of intracrustal mantle injecta are found from a model combining data on upper crustal felsic magmatic rocks with petrological and gravity inversion models for the vestfold graben segment in the south this implies twice the stretching estimate as compared to stretching derived from moho contours alone and two to three times the estimate from an inadequate set of fault and dike information the batholiths mark zones of high crustal thinning and magmatism was most likely caused by a combination of a thermal anomaly and lithospheric stretching

tectonic evolution of proterozoic australia proterozoic australia has long been interpreted as a single intact continent in which all tectonic and magmatic activity was intracratonic this paper proposes an alternative hypothesis in which numerous fragments of continental crust were assembled by plate tectonic processes the assembly was completed between 1300 and 1100 ma when the crustal fragments were combined as an early component of the rodinian supercontinent rifting and fragmentation of archaean continents began in the late archaean and continued into the proterozoic passive margin deposits such as those of the hamersley basin accumulated on isolated fragments of archaean crust these numerous fragments were subsequently assembled into three cratons by 1830 ma a west australian craton was established by collision of the archaean pilbara and yilgarn cratons which were joined along the capricorn orogen similarly a south australian craton developed by amalgamation of the proto gawler and proto curnamona cratons along the kimban orogen a north australian craton appears to have formed by accretion of numerous crustal fragments including the kimberley pine creek lucas and altjawarra cratons with sutures marked by the king leopold halls creek tennant creek and proto isan orogens the southern margin of the north australian craton was the site of repeated terrane accretion and orogenic activity between 1880 ma and 1400 ma this included an orogenic event at 1880 1850 ma the strangways 1780 1730 ma argilke 1680 1650 ma and chewings 1620 1580 ma orogenies and the intracratonic anmatjira uplift 1500 1400 ma intracratonic rifting at 1750 to 1710 ma and 1640 to 1600 ma produced the mcarthur basin and related minor basins parts of which were deformed by the isan orogeny at 1600 and 1530 ma rifting along the line of the capricorn orogen led to deposition in the overlying intracratonic bangemall basin between 1630 and 1300 ma along the eastern margin of the south australian craton the 1670 to 1600 ma olarian orogeny marks interaction with now obscured continental crust to the east tectonic activity between 1300 and 1100 ma led to the assembly of proterozoic australia as an early component of the supercontinent of rodinia this first involved the amalgamation of the west australian and north australian cratons followed by collision with the south australian craton the centralian superbasin developed over the junction of the north south and west australian cratons between 830 and 750 ma rifting to the east formed the adelaide geosyncline at 830 ma this was followed by the breakup of rodinia with the rifting apart of laurentia and gondwanaland along the eastern margin of proterozoic australia at 750 ma and the subsequent formation of the palaeo pacific ocean after the breakup of rodinia a series of northeast southwest compressional events followed by periods of relaxation reflect the assembly of a new supercontinent old lines of weakness were reactivated culminating in the intracratonic king leopold paterson petermann ranges and pinjarra orogenies between 620 and 540 ma subsequent reactivation continued into the phanerozoic with the widespread eruption of continental flood basalts and the formation of intracratonic basins 540 530 ma

electrical conductors in archean mantle result of plume interaction 1 from long period magnetotelluric data across the gawler craton we obtain a three dimensional resistivity image of the lithosphere and provide constraints on tectonothermal events dating back to the proterozoic contrary to common observations of archean cratons displaying high electrical resistivity in the mantle lithosphere the magnetotelluric data show low resistivity of around 10 m at 80km depth underneath the 1595ma gawler range volcanics a silicic large igneous province the resistivity distribution appears to be a signature of plume modified orogenesis with low degree partial melting at the base of the lithosphere in a back arc setting the enhanced conductivity is explained through higher hydrogen and iron content in the crystal lattice and also along the grain boundaries of the mantle constituting minerals older arc related magmatism to the southwest across 1620 1610ma st peter suite does not display enhanced conductivity and suggests a depleted mantle lithosphere the data show that yellowstone type mantle plume analogues are preserved through time and still display an elevated electrical signature in the lithosphere today

physical characteristics and evolutionary trends of continental rifts rifts may be defined as zones beneath which the entire lithosphere has ruptured in extension they are widespread and occur in a variety of tectonic settings and range up to 2 600 m y in age the object of this review is to highlight characteristic features of modern and ancient rifts to emphasize differences and similarities in order to help characterize evolutionary trends to identify physical conditions favorable for initiation as well as termination of rifting and to provide constraints for future modeling studies of rifting rifts are characterized on the basis of their structural geomorphic magmatic and geophysical features and the diverse character of these features and their evolutionary trends through time are discussed mechanisms of rifting are critically examined in terms of the physical characteristics and evolutionary trends of rifts and it is concluded that while simple models can give valuable insight into specific processes of rifting individual rifts can rarely if ever be characterized by well defined trends predicted by these models more data are required to clearly define evolutionary trends and the models require development to incorporate the effects of lithospheric heterogeneities and complex geologic histories

late cretaceous campanian actinopterygian fishes from the kristianstad basin of southern sweden although a diverse range of aquatic vertebrates are documented from the upper cretaceous mid campanian marine strata of the kristianstad basin in southern sweden only chondrichthyans and marine amniotes have been described in detail to date in contrast coeval actinopterygians are virtually unreported yet their remains are extremely abundant at most sampled localities a comprehensive assessment of these fossils has identified the first late cretaceous actinopterygian fauna from the fennoscandian shield incorporating indeterminate lepisosteids the durophagous pycnodontid anomoeodus subclavatus the predatory pachycormid protosphyraena sp a large ichthyodectid pachyrhizodontids resembling pachyrhizodus the enchodontid enchodus cf gladiolus and indeterminate small teleosts these taxa are diagnosed mainly from isolated teeth and scales implying substantial taphonomic loss prior to burial moreover the prolific recovery of actinopterygian skeletal remnants in recent excavations suggests that historical collecting biases rather than ecological paucity have contributed to their under representation in the swedish cretaceous record palaeobiogeographically the kristianstad basin actinopterygians show compositional resemblance to assemblages from the northern european platform and the western interior seaway of north america advocating distributional communication across the boreal proto atlantic ocean

the oslo graben gravity high and taphrogenesis abstract the paleo oslo rift oslo graben system is geophysically characterized by a pronounced gravity high a reinterpretation of gravity data in the region using a flexible inversion scheme indicates that the causative body has a density contrast of 0 06 g cm 3 the inversion results also suggest that this body is most likely located in the upper part of the lower crust and extends eastward well outside the graben area proper estimates of crustal thicknesses before and after the rifting aborted suggest that rifting commenced in the south and then progressed northwards the corresponding pole of rotation was located approximately 240 km nne of the city of oslo the hypocentres of 7 small local earthquakes were found to be located on the periphery of the anomalous body as derived from gravity modeling seismic investigations including 3 d imaging using norsar data have failed to provide conclusive evidence on intrusion of asthenospheric material in the lithosphere as part of the oslo graben taphrogenesis the explanation proposed here is that the geophysical imprints of oslo rift oslo graben evolutionary processes within the upper mantle have been considerably weakened over the associated time span of some 150 200 ma finally it is hypothesized that the asthenospheric injection into the lithosphere took place over a relatively small cross sectional area of the moho the further ascent of the gabbroic magma was partly hindered by the relatively rigid upper crust thus causing extensive lateral flow eastwards outside the oslo graben proper in the 10 20 km depth range

mapping the carpentaria conductivity anomaly in northern australia abstract a band across northern queensland australia was studied in 1995 by a magnetometer array experiment in two parts a western part q1 and an eastern part q2 forty three sites were occupied in all by flinders university magnetometers which recorded in three components at intervals of 1 min a major purpose of the study was to further clarify the position and indeed the existence of a major electrical conductivity anomaly suspected to exist in the area from earlier reconnaissance observations the arrays were successful in clearly delineating the path of the conductivity anomaly here termed the carpentaria conductor it is seen to continue up the eastern side of the mt isa inlier from where it was mapped in detail previously in southern queensland the results show the anomaly to be offset from the tasman line which is thought to indicate a major structural boundary in the australian continent and which possibly has a conductivity anomaly associated with it further south elsewhere the array results give a clear measure of the coast effect of northeast australia and they set the magnetic variations recorded at charters towers observatory in the context of the coast effect

crustal imaging of a mobile belt using magnetotellurics an example of the fowler domain in south australia 1 a long period magnetotelluric data set was obtained in 2005 along a two dimensional profile across the western part of the late archaean early proterozoic gawler craton south australia the study is aimed at delineating the electrical conductivity structure of the crust and upper mantle underneath an east west trending profile extending from the gawler range volcanics in the east crossing the nuyts domain and the highly prospective meso proterozoic fowler domain and terminating in the eucla basin to the west the resistivity model shows a very electrically resistive crust and upper mantle underneath the nuyts and fowler domain possibly representing the cratonic root of the gawler craton extending to depths of 160 km the resistive cratonic root is closer to the surface underneath the fowler domain compared to the nuyts domain which supports findings from outcrops of metasediments of higher metamorphic grade in the fowler domain a subvertical conductor marks the western terminus of the fowler domain and is imaged to upper mantle depths on the eastern side of the fowler domain another subvertical conductor extends to similar depths these features spatially coincide with the tallacootra and coorabie shear zone at the surface respectively and their higher conductivity is likely due to a reduction in grain size of olivine associated with an increase in influence of grain boundary diffusion and thus enhanced conductivity a comparison of the results with other surveys across mobile belts worldwide shows a more resistive response of the interpreted mobile belt of the fowler domain raising questions as to the nature of the domain

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

ankylosaurian dinosaur palaeoenvironmental associations were influenced by extirpation sea level fluctuation and geodispersal abstract more species of nodosaurid ankylosaurians than ankylosaurid ankylosaurians have been found in marine sediments and some previous quantitative studies of global dinosaur occurrences provide support for an association between nodosaurids and marine depositional environments we compiled a dataset of global ankylosaurian occurrences and found that the geographic distribution of marine ankylosaurian occurrences is regionally biased with 54 of records stemming from western north america in the cretaceous a time of regional highstands in sea level and epicontinental flooding coupled with differential extirpation of ankylosaurian subclades inhabiting the western interior basin wib within the western interior basin we found little statistical support for an association between ankylosaurian subclades and palaeoenvironment in a chronological context only the albian cenomanian transgressive regressive cycle had statistical support for an overabundance of nodosaurids in marine environments compared to ankylosaurids the apparent overabundance of nodosaurids relative to ankylosaurids in marine sediments in the western interior basin overall cannot be decoupled from the extirpation of north american ankylosaurids during the cenomanian and the subsequent absence of ankylosaurids in north america during the turonian to early campanian prior to the immigration of asian ankylosaurine ankylosaurids the north american ankylosaurian record highlights the difficulty in interpreting habitat preferences in the context of a shifting seaway regional extinctions and intercontinental dispersals

further constraints on the temporal evolution of the oslo rift from precise u pb zircon dating in the siljan skrim area abstract precise u pb ages have been obtained from zircon and baddeleyite in plutonic rocks from the siljan skrim area in the vestfold graben segment in the south western part of the permian oslo rift in addition common lead data from feldspars in the same rocks are presented the measured common pb compositions of the feldspars are used to correct for initial common pb in the zircons the common pb data indicate that u has been present in the feldspars since the time of crystallisation probably in a late magmatic volatile phase in fluid inclusions the siljan skrim area comprises two intrusive complexes the northern skrim mykle complex consists of two large composite intrusive bodies the skrim larvikite and the mykle ekerite the southern siljan hvarnes complex consists of a series of monzonitic to syenitic intrusions which are nested in a systematic way indicating decreasing emplacement age from east to west u pb zircon ages range from 281 2 0 6 ma 2 to 279 8 0 7 ma for three samples from the northern part of the siljan skrim area and from 278 5 0 8 ma to 277 3 0 8 ma for four samples from the southern part of the area the geochronological data suggest that large amounts of magma were emplaced within very short time spans i e less than 2 ma for each of the two complexes the high precision of the u pb age results allows discrimination between intrusive activity in the northern and southern parts of the siljan skrim area and suggests that emplacement of magmas was episodic

recent benthic foraminiferal provinces between newfoundland and yucatan in 219 papers published over 130 years 1 241 species of recent benthic foraminifera were recorded from 968 localities on the atlantic continental margin of north america and in the gulf of mexico on the atlantic continental margin 876 species were recorded and in the gulf of mexico 848 483 species 39 of 1 241 occur in both areas on the atlantic continental margin 149 species occur at 4 or more of 542 localities and in the gulf of mexico 295 species occur at 4 or more of 426 localities 71 of these species 19 of 373 commonly occur in both areas these comparisons show that the two areas differ fundamentally in faunal composition cluster analysis of presence or absence distributional data live and dead foraminifera delimited seven large provinces on the atlantic continental margin and four provinces in the gulf of mexico atlantic continental margin a northern coastal province b northern shelf province c northern outer shelf and slope province d northern slope and rise province e southern shelf province f southern slope province g bahaman province gulf of mexico a coastal province b inner shelf province c outer shelf province d slope and abyssal plain province bottom water mass and provincial patterns show good spatial correlation on the atlantic continental margin and in the gulf of mexico

mid cenomanian vertebrate faunas of the western interior seaway of north america and their evolutionary paleobiogeographical and paleoecological implications abstract the western interior seaway wis was an epicontinental sea that extended north south through the middle of north america during the last half of the cretaceous linking the tethys sea to the south with the boreal paleo arctic ocean to the north aptian maastrichtian sedimentary deposits from the seaway crop out in the western interior basin of canada and the united states vertebrate remains are commonly well preserved and in certain stratigraphic units abundant the classic vertebrate fauna of the wis from the upper cretaceous niobrara chalk has been studied for 150 years but relatively little has been known of the seaway s earlier faunas until recent years studies of mid cenomanian vertebrate faunas particularly from lag deposits bonebeds and calcarenites in canada and the united states have significantly altered the previous picture of the overall biodiversity and biogeography of the wis during the mid cretaceous these mid cenomanian faunas include diverse fish assemblages of chondrichthyans cartilaginous fishes and osteichthyans bony fishes as well as various forms of tetrapods including marine turtles plesiosaurs and hesperornithiform and ichthyornithiform birds our compilation of faunas indicates that at least 70 vertebrate taxa are recorded from five mid cenomanian wis localities situated in alberta saskatchewan the black hills region of south dakota and wyoming kansas and colorado the faunas include 41 chondrichthyans 21 osteichthyans 10 non avian tetrapods and five avian taxa our study combined with previous faunal studies suggests that the combination of the following eight chondrichthyan species characterizes mid cenomanian time which has been referred to as the woodbinian age in the marine realm of north america ptychodus decurrens p occidentalis squalicorax curvatus cretodus semiplicatus carcharias amonensis c saskatchewanensis eostriatolamia tenuiplicatus and cretomanta canadensis this is the geologic time when non ptychodontid hybodonts became rare faunal components in most areas and when a number of other fish lineages particularly teleosts emerged and diversified many of these persisted into the early campanian or the niobrara age that followed the woodbinian therefore mid cenomanian time in the wis can also be characterized by the genesis of the niobraran fauna a significant radiation and diversification of fish taxa the five mid cenomanian wis localities highlighted in this study are separated by as much as 18 latitude a north south distance of more than 2300 km these faunas demonstrate some clinal trends such as more diverse faunas of benthic chondrichthyans mixed with dolichosaurid lizards to the south and a more diverse fauna of birds to the north however the faunas overall show strong taxonomic homogeneity particularly among many chondrichthyans that were cosmopolitan indicating that passage throughout the seaway as well as to both the boreal and tethys oceans was utilized these faunas also demonstrate high osteichthyan diversity in the northern waters of the wis which were once thought to have supported only a depauperate cold adapted fauna because of the surprisingly great diversity in vertebrate taxa ecosystem structure and dynamics of the wis during the mid cenomanian were unquestionably complex

geomagnetic deep sounding experiment in the central flinders ranges of south australia abstract a closely spaced geomagnetic deep sounding array study was conducted in the central flinders ranges of south australia the results indicate an anomaly which follows the main fold trend to the east rather than the north south trend suggested by earlier studies although the coast effect obscures some of the detailed characteristics of the anomaly the data particularly at high frequencies favour an interpretation in terms of a crustal anomaly probably associated with the lower members of the adelaide geosyncline the torrens hinge zone which is a major tectonic boundary at the western margin of the adelaide geosyncline has no associated induction anomaly

a stretching model for the oslo rift abstract data on the tectonic and magmatic activity crustal thickness seismic velocity and gravity have been integrated to constrain a stretching model for the late carboniferous early permian oslo rift the crustal structure and numerical modelling of temperature and melt generation during rifting suggest that the oslo rift in skagerrak developed in response to crustal stretching with a factor between 1 4 and 1 6 however upper crustal extension by faulting accounts for a stretching factor of only 1 1 1 2 thermal expansion of the lithosphere due to an increased asthenospheric potential temperature the intrusion of melted mantle material into the lower crust and probably a lowering of the erosional base by a fall in sea level all contributed to the erosion of 2 4 km of lower palaeozoic pre rift sediments over large areas the lateral extent of the thermal anomaly reached far beyond the oslo and skagerrak grabens

lithospheric reworking at the proterozoic phanerozoic transition of australia imaged using auslamp magnetotelluric data abstract seventy four stations from the long period australia wide auslamp australian lithospheric architecture magnetotelluric project dataset were used to image the electrical resistivity beneath the neoproterozoic ikara flinders ranges and adjacent palaeo mesoproterozoic curnamona province results from 3d inversions using modem software show a relatively resistive ikara flinders ranges with two parallel arcuate conductors at 20 to 80 km depth in the nackara arc there is a good correlation of diamondiferous kimberlites occurring over conductors which we interpret as evidence for these conductors to be residing on large lithospheric structures that have been conduits for partial melt and volatile movement in the jurassic the curnamona province is remarkably conductive for a region that is thought to have a cratonic core with delamerian reworking only at its edges the conductor covers most of the province at depths of 10 40 km and its presence at lower crustal depths suggests that conductive sediments can not entirely explain it fluids associated with subduction may have pervasively modified the crust in the past resulting in an enrichment of carbon enhancing the conductivity additionally we conclude that the notion of a single continuous arcuate flinders conductivity anomaly is unlikely and that the anomalous response observed is instead a result of the combined response of three separate anomalies the curnamona province conductor and the two nackara arc conductors

rifting in heterogeneous lithosphere inferences from numerical modeling of the northern north sea and the oslo graben oslograbenevolvedinthecoldandstableprecambrian lithosphere of fennoscandia whereas the northern northsearifttookbirthinfreshlyreworkedcaledonian lithosphere huge volumes of magmatic rocks characterize the relatively narrow oslo graben in contrast little magmatism is documented for the wide northern north sea rift differences in timing between both rifts are inferred but still debated we present numerical thermomechanical models along a lithospheric e w section that involves both the oslo graben and the northern north sea area because the modeled section crosses the boundary between caledonian and proterozoic provinces thermal and compositional heterogeneities are considered as is suggested by various geophysical data sets we also consider lithospheric thickness heterogeneities in the precambrian lithosphere modeling results suggest that the northern north sea was on top of weak lithosphere very sensitive to far field stresses consequently we suggest that rifting in the northern north sea began as early as regional extension was effective i e late carboniferous early permian and does not postdate the oslo graben as it is commonly assumed rifting in the strong precambrian lithosphere is unexpected modeling results suggest thatapre existinglithosphericthicknesscontrastwithin the fennoscandian lithosphere favored rifting in the oslo graben index terms 8109 tectonophysics continental tectonics extensional 0905 8159 tectonophysics evolution of the earth rheology crust and lithosphere 8020 structural geology mechanics 9335 information related to geographic region europe 9614 information related to geologic time paleozoic keywords numerical modeling rifting rheology lithosphere oslo graben north sea citation pascal c and s a p l cloetingh rifting in heterogeneous lithosphere inferences from numerical modeling

enhanced bioturbation on the down drift flank of a turonian asymmetrical delta implications for seaway circulation river nutrients and facies models extant models predict delta front environments down drift of river mouths as unfavourable for organisms because of the physico chemical stresses caused by sediment and fresh water influx this study however finds evidence for near optimal living conditions down drift of contemporaneous mouth bars and distributary channels as well as at the tops of abandoned lobes in part of the asymmetrical notom delta complex of the ferron sandstone turonian south eastern utah usa presented herein is a sedimentological and ichnological model using thirty two detailed measured sections along a 16 km transect through two continuously exposed ca 10 m thick allomembers containing delta front mouth bar and distributary channel facies azimuths from sedimentary structures show south eastward deflection of near shore palaeocurrents relative to the inferred north south shoreline as well as minor reversal of flow two end member trace fossil suites are recognized in delta front sandstones i a stressed suite of low abundance low diversity diminutive traces reflecting mobile deposit feeding resting and locomotion behaviours and ii a comparatively unstressed high abundance moderate diversity suite with a regular heterogeneous distribution of deep vertical or u shaped suspension feeding burrows which in places thoroughly homogenize the sandstones the down drift side of the delta was colonized by suspension feeders during seasonal reversal of the seaway gyre when mud plumes were swept northward or when river derived nutrients were sufficiently concentrated relative to fresh water and sediment input during normal seaway circulation very high sedimentation rates and mud laden wave dampened waters down drift of the river mouths heightened the preservation potential of the pervasively bioturbated facies up drift of the river mouths these bioturbated facies were either not preserved or not developed until the lobe was abandoned this alternative model for delta planform asymmetry contributes to the refinement of facies models for deltaic systems and provides a framework for predicting the distribution of bioturbation enhanced porosity and permeability in lobe deflected deltas

isotopic evaluation of ocean circulation in the late cretaceous north american seaway the role of the north american seaway in creating and maintaining late cretaceous global greenhouse conditions has been unclear an isotopic analysis of marine turtle and fish fossils from western kansas and the mississippi embayment reveals that the inflow of tethyan surface waters to the seaway was limited during the mid and late cretaceous period north america was split by the north south oriented western interior seaway its role in creating and maintaining late cretaceous global greenhouse conditions remains unclear different palaeoceanographic reconstructions portray diverse circulation patterns1 2 3 the southward extent of relatively cool low salinity low 18o surface waters critically distinguishes among these models but past studies of invertebrates could not independently assess water temperature and isotopic compositions here we present oxygen isotopes in biophosphate from coeval marine turtle and fish fossils from western kansas representing the east central seaway and from the mississippi embayment representing the marginal tethys ocean our analyses yield precise seawater isotopic values and geographic temperature differences during the main transition from the coniacian to the early campanian age 87 82 myr and indicate that the seaway oxygen isotope value and salinity were 2 and 3 lower respectively than in the marginal tethys ocean we infer that the influence of northern freshwater probably reached as far south as kansas our revised values imply relatively large temperature differences between the mississippi embayment and central seaway explain the documented regional latitudinal palaeobiogeographic zonation4 5 and support models with relatively little inflow of surface waters from the tethys ocean to the western interior seaway2 3

a new hesperornithiform aves specimen from the late cretaceous canadian high arctic with comments on high latitude hesperornithiform diet here we describe a new hesperornithiform specimen from the upper cretaceous kanguk formation of devon island nunavut canada this specimen nuvf 286 is referred to cf hesperornis sp based on size and shape of femora and teeth preserved with other skeletal elements previous osteohistologic analyses indicate a subadult ontogenetic stage at the time of death this new cf hesperornis specimen includes the first teeth associated with a high latitude hesperornithiform allowing for comments on the trophic behavior of these birds paleoecological reconstructions based on current knowledge of polar assemblages and comparisons to modern birds suggest that high latitude hesperornithiform birds may have had more varied diets than previously assumed

cretaceous marine turtles from the western interior seaway of canada late cretaceous marine turtles are rare in canada but specimens are known from three formations toxochelys latiremis cope and protostega sp from the pierre shale pembina member lower campanian

the first record of the mosasaur hainosaurus reptilia lacertilia from north america hainosaurus pembinensis a new species of tylosaurine mosasaur is described from the pembina member of the pierre shale campanian late cretaceous of manitoba hainosaurus differs from tylosaurus in having a larger number of vertebrae anterior to the chevron bearing caudals a greater length of the femur relative to the humerus and a greater length of the external nares hainosaurus pembinensis is distinguished from other species of this genus by its long supratemporal fenestra and homodont dentition this is the first record of hainosaurus from north america and represents both a geographic and stratigraphic range extension for the genus

receiver function analysis of the crust and upper mantle in fennoscandia isostatic implications abstract the mountains across southern norway and other margins of the north atlantic ocean appear conspicuously high in the absence of recent convergent tectonics we investigate this phenomenon with receiver functions calculated for seismometers deployed across southern fennoscandia these are used to constrain the structure and seismic properties of the lithosphere and primarily to measure the thickness and infer the bulk composition of the crust such parameters are key to understanding crustal isostasy and assessing its role or lack thereof in supporting the observed elevations our study focuses on the southern scandes mountain range that has an average elevation 1 0 km above mean sea level the crust mantle boundary moho is ubiquitously imaged and we occasionally observe structures that may represent the base of the continental lithosphere or other thermal chemical or viscous boundaries in the upper mantle the moho resides at 25 30 km depth below mean sea level in southeastern coastal norway and parts of denmark 35 45 km across the southern scandes and 50 60 km near the norwegian swedish border that section of thickest crust coincides with much of the transscandinavian igneous belt and often exhibits a diffuse conversion at the moho which probably results from the presence of a high wave speed mafic lower crust across inner fennoscandia a zone of thinned crust

progress in deep lithospheric exploration of the continental china a review of the sinoprobe abstract the sinoprobe deep exploration in china is a multidisciplinary earth science research program that aims at revealing the composition structure and evolution of the continental lithosphere in china the sinoprobe 2008 2012 has successfully conducted research and field experiments on determining the crustal and mantle structures using new deep seismic and magnetotelluric mt exploration this has allowed the accumulation of new exciting data that have significantly accelerated china s development on deep lithospheric exploration the new data also led to new understandings on the mesozoic and cenozoic geological evolution of the continental china the main results of the sinoprobe so far include 1 a collection of ca 6000 km long seismic reflection profile data 2 a nation wide geochemical baseline 3 a nation wide 4 4 mt array and regional 1 1 mt arrays in the north china and the qinghai tibet plateau 4 three dimensional 3 d exploration of ore districts in the eastern china 5 several continental scientific drilling holes 6 regional in situ stress monitoring networks 7 geodynamic modeling of the lithosphere underneath the continental china and 8 instrumentation development for deep exploration in china etc for the first time the sinoprobe has obtained deep seismic reflection evidence for the moho surface below the thick crust of the central qinghai tibet plateau it also reveals dipping fabrics in the lithospheric mantle beneath the northeastern china the preliminary results from mt array observation of the sinoprobe show an abnormal electric conductivity structure of the lithosphere beneath the ordos basin providing important evidence for the evolution mechanism of the north china craton ncc generally the sinoprobe has conducted successfully during its initial phase 2008 2012 which has settled a foundation for the next phase of the sinoprobe in the future

lithospheric necking a dynamic model for rift morphology abstract rifting is examined in terms of the growth of a necking instability in a lithosphere consisting of a strong plastic or viscous surface layer of uniform strength overlying a weaker viscous substrate in which strength is either uniform or decreases exponentially with depth as the lithosphere extends deformation localizes about a small imposed initial perturbation in the strong layer thickness for a narrow perturbation the resulting surface topography consists of a central depression and uplifted flanks the layer thins beneath the central depression the width of the rift zone is related to the dominant wavelength of the necking instability which in turn is controlled by the layer thickness and the mechanical properties of the lithosphere for an initial thickness perturbation with a width less than the dominant wavelength deformation concentrates into a zone comparable to the dominant wavelength if the initial perturbation is wider than the dominant wavelength then the width of the zone of deformation is controlled by the width of the initial perturbation deformation concentrates in the region of enhanced thinning and develops periodically at the dominant wavelength a surface layer with limiting plastic stress exponent n behavior produces a rift like structure with a width typical of continental rifts for a strong layer thickness consistent with various estimates of the maximum depth of brittle deformation in the continental lithosphere the width of the rift is essentially independent of the layer substrate strength ratio for a power law viscous surface layer n 3 the dominant wavelength varies with layer substrate strength ratio to the one third power and is always larger than for a plastic surface layer of the same thickness the great widths of rift zones on venus may be explained by unstable extension of a strong viscous surface layer

magnetotelluric evidence for a deep crustal mineralizing system beneath the olympic dam iron oxide copper gold deposit southern australia the iron oxide copper gold olympic dam deposit situated along the margin of the proterozoic gawler craton south australia is the world s largest uranium deposit and sixth largest copper deposit it also contains significant reserves of gold silver and rare earth elements gaining a better understanding of the mechanisms for genesis of the economic liberalization is fundamental for defining exploration models in similar crustal settings to delineate crustal structures that may constrain mineral system fluid pathways coincident deep crustal seismic and magnetotelluric mt transects were obtained along a 220 km section that crosses olympic dam and the major crustal boundaries in this paper we present results from 58 long period 10 104 s mt sites with site spacing of 5 10 km a two dimensional inversion of mt data from 33 sites to a depth of 100 km shows four notable features 1 sedimentary cover sequences with low resistivity 1000 m archean crustal core from a more conductive crust and mantle to the north typically 500 m 3 to the north of olympic dam the upper middle crust to 20 km is quite resistive 1000 m but the lower crust is much more conductive 100 m and 4 beneath olympic dam we image a low resistivity region 100 m throughout the crust coincident with a seismically transparent region we argue that the cause of the low resistivity and low reflectivity region beneath olympic dam may be due to the upward movement of co2 bearing volatiles near the time of deposit formation that precipitated conductive graphite liberalization along grain boundaries simultaneously annihilating acoustic impedance boundaries the source of the volatiles may be from the mantle degassing or retrograde metamorphism of the lower crust associated with proterozoic crustal deformation