finite deformation in and around a fluid sphere moving through a viscous medium implications for diapiric ascent abstract different types of geodynamically active regions like mountain belts hot spots or areas of salt tectonics are characterized by diapirism one key for the reconstruction of the dynamic history of such structures is the progressive strain which can sometimes be determined from field observations successful interpretation of such observations requires a quantitative model of the finite strain in and around a rising diapir a constant viscosity fluid sphere of radius r rising through another isoviscous fluid is assumed to approximate the buoyant motion of a diapir known analytical solutions for the velocity fields are used to numerically evaluate the finite deformation in and around the sphere regions of very high strains are found in a tube with a radius 1 2 r behind the sphere and in a shell of thickness of 0 1r around the sphere the following three dimensional strain regimes can be identified in the half space above the sphere down to its equator finite strains are oblate behind the sphere they progressively change to plane strain in the diapiric source region they are prolate viscous drag at the sphere s surface leads to an internal circulation with one overturn after 10r of rise if the sphere has a relatively low viscosity finite strains within the fluid sphere show a continuous increase with superimposed cyclic straining and unstraining after several body radii of rise the strains become highly inhomogeneous inside the sphere except along the vertical axis and just inside the sphere s surface where strong prolate and oblate strains are observed respectively finite strain determinations in a falling ball experiment cruden 1988 are compared with the theoretical results at horizontal distances of a few body radii from the fall axis the effect of confining container walls is clearly seen in the experimental strain data the results are compared briefly with available strain data from the field which seem to be significantly lower than predicted proposed explanations include a short memory of the rock fabric and a lack of recognition of the strain concentration which would be expected for a temperature dependent rheology it might also be possible that few natural diapirs rise more than a few radii in the solid state

latest cretaceous earliest paleogene vegetation and climate change at the high southern latitudes palynological evidence from seymour island antarctic peninsula abstract fluctuations in late cretaceous climate were already influencing biotic change prior to the environmental upheaval at the cretaceous paleogene k pg boundary but their general nature magnitude and timing remain controversial a high resolution dataset on terrestrially derived palynomorphs is presented from the high southern palaeolatitudes that unlocks details of small scale climate variability throughout this period of significant global change specifically this is a quantitative spore and pollen analysis of an expanded uppermost cretaceous to lowermost paleogene maastrichtian earliest danian shallow marine sedimentary succession from seymour island off the northeastern tip of the antarctic peninsula then as now located at 65 s using nearest living relatives the first detailed vegetation habitat and climate reconstruction is presented for the emergent volcanic arc at this time on the coastal lowlands a cool to warm temperate rainforest is envisaged growing in a riverine landscape with both wet river margin pond and relatively dry interfluve canopy gap habitats diverse podocarps and southern beech trees grew alongside angiosperm herbs and shrubs in mean annual temperatures of 10 15 c higher altitude araucarian forests gave way to open ericaceous heathland beyond the tree line in subalpine to alpine conditions with mean annual temperatures of a cold 5 8 c there is no exact modern botanical equivalent but the closest modern flora is that of the andes of southern chile and argentina maastrichtian climate is shown to have fluctuated from cool humid conditions through a rapid warming 2 million years prior to the k pg transition followed by cooling during the earliest danian a trend supported by previous work on this interval

late cretaceous sea level changes in tunisia a multi disciplinary approach a multi disciplinary study of sea level and climate proxies including bulk rock and clay mineral compositions carbon isotopes total organic carbon toc sr ca ratios and macro and microfaunal associations reveals seven major sea level regressions in the southwestern tethys during the last 10 million years of the cretaceous late campanian c 74 2 ma 73 4 72 5 ma and 72 2 71 7 ma early maastrichtian 70 7 70 3 ma 69 6 69 3 ma and 68 9 68 3 ma and late maastrichtian 65 45 65 3 ma low sea levels are generally associated with increased terrigenous influx low kaolinite chlorite mica ratios high toc and high sr ca ratios whereas high sea levels are generally associated with the reverse conditions these sea level changes may be interpreted as eustatic as suggested by the global recognition of at least four of the seven major regressions identified 74 2 ma 70 7 70 3 ma 68 9 68 3 ma and 65 45 65 3 ma climatic changes inferred from clay mineral contents correlate with sea level changes warm or humid climates accompany high sea levels and cooler or arid climates generally accompany low sea levels

strontium isotope correlation of the basal maastrichtian stage in antarctica to the european and us biostratigraphic schemes new 87 sr 86 sr dating allows the correlation of a marker horizon within the prolific late cretaceous gunnarites antarcticus faunal assemblage of the cape lamb member snow hill island formation vega island antarctica with reference sections in europe and the usa this horizon is between 81 5 and 96 5 m above the base of the g antarcticus assemblage replicate analysis of six macrofossils from within it yielded a mean value for 87 sr 86 sr of 0 707 735 9 0 000 004 3 2 s e n 17 this ratio in turn yields a numerical age of 71 0 0 2 ma when compared to the standard 87 sr s6 sr reference curve for the latest cretaceous for which the campanian maastrichtian boundary is placed at 71 3 0 5 ma the value of 0 707 735 9 0 000 004 3 correlates to a level in the belemnella lanceolata belemnite zone of the chalk of northwestern germany that is 2 5 5 m beneath the base of the overlying b pseudobtusa zone and 7 5 m above the campanian maastrichtian belemnite boundary and to an interval within the ammonite zonation of the us western interior that spans the early maastrichtian baculites baculus and b eliasi zones but with a most likely level within the b eliasi zone an earliest maastrichtian age is thereby determined for the antarctic horizon and indeed for the entire g antarcticus assemblage gunnarites sensu lato is an important ammonite marker for the base of the maastrichtian throughout the southern high latitude regions and the associated large heteromorph ammonite diplomoceras may comprise a macrofossil link back to the maastrichtian type sections

ascent of a granitoid diapir in a temperature varying medium a relationship for the ascent velocity of a granitoid diapir is derived and used in conjunction with a crustal heat flow model which incorporates a depth dependent temperature to predict emplacement histories ascent rate is strongly dependent on the width of a deformation layer of variable viscosity that is formed by the transfer of heat to the country rock and on the buoyancy force which propels the diapir through it ascent velocity is described by the expression u 2 gd3z 0r where is the density contrast between diapir and country rock g is gravitational acceleration d is the deformation zone width z is a parameter which describes the increase in viscosity across the zone 0 is the country rock viscosity at the contact and r is the diapir radius the width of the deformation zone as dictated by the temperature distribution and rheological function is the point at which the viscosity increases by a factor f from the contact value although ascent rates vary with choice of this parameter ascent distances are not strongly dependent on f results of simulations which incorporate a spectrum of input parameters reveal that ascent distance is strongly dependent on both the rheology and ambient temperature of the encompassing rock but only weakly dependent on the initial diapir temperature ascent velocity varies with the diapir size with larger bodies moving more slowly and ascending for longer periods relative to smaller plutons as a result of the proportionately larger amount of thermal energy available for ascent larger bodies will rise greater distances than smaller diapirs however the additional ascent appears nominal relative to the contrast in available energy modeling diapirs using a no slip boundary condition decreases ascent velocity by a factor of about 3 relative to results incorporating a stress free boundary condition the time scale of granitoid diapirism over crustal distances cannot be less than 104 years due to the rate limiting effect of thermal conduction above the body and not greater than 105 years reflecting solidification times of kilometer sized plutons a consequence of ascent by a deformation zone mechanism is the generation following emplacement of a mechanically weakened crust which extends from beneath the diapir to near the source perhaps explaining the relatively common occurrence of synmagmatic to postmagmatic mafic dikes within granites believed to be derived from interaction of basalt with the lower crust

field relationships and stable isotope geochemistry of concretions from james ross island antarctica abstract early diagenetic precompactional concretions are abundant throughout the cretaceous tertiary marambio group larsen basin antarctica four distinct concretion types are recognised 1 spherical subspherical concretions 2 sheet concretions 3 fossil nucleated concretions and 4 concretionary burrow networks all concretion types have a micritic to microsparry variably non ferroan to ferroan calcite cement stable isotope analyses show a wide spread in both 18o and 13c 13c values are typically negative ranging between 3 38 and 39 15 o pdb usually 16 to 230 18o ranges between 1 28 and 13 81 pdb with most of the values between 5 and 10 the 13c signature is interpreted to represent carbon sourced from sulphate reduction and or methane oxidation with minor input from shell dissolution and is consistent with a shallow burial early diagenetic origin a single mudstone hosted concretion has a 18o composition indicative of precipitation of carbonate from seawater the low 18o signatures in the sandstone and siltstone hosted concretions are possibly due to early diagenetic modification of the pore water composition through volcaniclastic mineral dissolution reprecipitation reactions and perhaps through input of meteoric water concretion distribution is related to a changes in sedimentation rate and b the dominance of diffusion on concretion cementation

local displacement of diapir contacts and its importance to pluton emplacement study abstract the extent to which mid crustal plutons have grown by diapirism cannot be deduced from the horizontal shortening of ductilely deformed host rocks and associated displacement of lateral intrusive contacts by contrast the vertical shortening above plutons and upward displacement of their roof contacts may provide a good measure of the diapiric component of pluton emplacement this is related to the vertical bulk translation of buoyant material in immature diapirs and associated escape flow of overlying rocks the length change of a vertical material line situated above the crest of an immature upright diapir corresponds to the upward displacement of the local contact the length change of horizonal material lines situated at lateral contacts of model diapirs however differs markedly from the contact displacement this is related to the absence of horizontal symmetry planes in the finite strain field about upright diapirs of any shape and the importance of vertical shear at the lateral contacts the host rock strain held of a hypothetical pluton grown in situ by spherical expansion ballooning has an infinite number of symmetry planes the strain held is characterized by large volume losses but the length change of all radial lines corresponds to the local magnitude of contact displacement this precludes the possibility of differentiating in ductile host rocks above plutons between vertical diapirism and spherical expansion unless gauges of volume change are available

palaeoclimate reconstructions of the middle jurassic of kachchh western india an integrated approach based on palaeoecological oxygen isotopic and clay mineralogical data abstract the middle jurassic sedimentary succession of the kachchh basin shows significant changes in lithology faunal content and diversity across the bathonian callovian boundary the change in lithology from predominantly carbonates in the middle and late bathonian to siliciclastics in the callovian is accompanied by a drop in species diversity from high to moderate characteristic faunal elements of the bathonian corals sponges the bivalves eligmus and members of the opinae are absent or rare in the callovian in contrast callovian sediments contain comparatively high proportions of nuculid bivalves the clay mineral assemblage reveals prominent variations in the smectite vs kaolinite abundance especially during the bathonian to callovian transition from the bajocian to the middle bathonian smectite becomes the dominant clay mineral and is nearly exclusively present in the late bathonian towards the middle callovian its content gradually decreases and kaolinite becomes the dominant clay mineral illite generally is only a minor component throughout the middle jurassic based on these results the bajocian to middle bathonian time interval is interpreted to represent subtropical climatic conditions with seasonal droughts and a moderate supply of terrigenous clastics to the basin the late bathonian was a period with a semi arid climate hot seasonal droughts and a minor input of terrigenous clastics the increase in kaolinite contents in the callovian suggests a subtropical humid climate with less prominent seasonal droughts and a higher input of siliclastics into the basin accompanied by a higher nutrient influx oxygen isotope ratios measured on bathonian to early callovian brachiopod shells give palaeotemperatures of 19 24 c callovian to oxfordian paleotemperatures calculated from oxygen isotopes measured on belemnite rostra range from 11 to 21 c the lower palaeotemperatures estimated from the oxygen isotopic composition of belemnite calcite are explained by assuming that the belemnites spent most of their life span in colder regions of the malagassy gulf and migrated into the warmer subtropical waters of the kachchh basin combining these various lines of evidence the changes in lithology and faunal composition taking place in the kachchh basin during the middle jurassic appear to reflect largely a change towards increasing humidity rather than a distinct decrease in water temperature

late cretaceous cenozoic climatic variations of the northern antarctic peninsula new geochemical evidence and review aptian to pliocene time series of x ray fluorescence data from the antarctic peninsula are used to assess the degree of chemical weathering and maturity of sediments deposited prior and subsequent to the establishment of glaciation in west antarctica a continuous palaeoclimatic signal is inferred from comparing the results with previously published palaeotemperature and palaeobotanical data aptian cenomanian warm cool and santonian early paleocene warm cold cycles were followed by the global late paleocene early eocene climatic optimum subsequent steady decline in temperatures resulted in glacial conditions in the northern antarctic peninsula by early oligocene time under alternating cenozoic frigid cold climates and in sedimentary regimes dominated by physical weathering geochemical signatures were primarily indicative of provenance the development of cretaceous arboreal vegetation in the northern antarctic peninsula can be correlated with the major climatic cycles

community associations and structure in the late cretaceous vegetation of southeast australasia and antarctica abstract the structure and species richness of the late cretaceous santonian maastrichtian vegetation in the otway basin southeast australia is reconstructed based on knowledge of palaeolatitudes palaeotemperatures plant taxa identified from fossil spores and pollen and ecophysiological relationships established for present day ecosystems the vegetation which grew at palaeolatitudes of 60 65 s and at mean annual palaeotemperatures of 16 5 19 c comprised tall open forests foliage projective cover 60 70 height about 30 m containing austral conifer and proteaceous taxa having coriaceous notophyll sized leaves today the taxa podocarpus dacrydium dacrycarpus knightia gevuina macadamia from a minor component of upland closed forests usually termed rainforests of tropical northeast australia and new caledonia a conical shaped crown to the trees of the tall open forests situated in high latitudes during the cretaceous would enable some light to penetrate the canopy to a shrubby understorey of proteaceae winteraceae trimeniaceae nothofagus and ilex and a ground stratum of diverse cryptogams on nutrient poor waterlogged sites fringing the forest sclerophyllous leaved taxa adenanthos stirlingia epacridaceae and possibly beauprea developed with wetland swamps of callitriche ferns and some epacrids in cooler localities in new zealand and antarctica the productivity of the forests would have been greater and the canopy taxa mainly with coriaceous microphyll sized leaves austral podocarps and proteaceae occurred in the canopy of new zealand forests whereas the canopy of antarctic forests contained podocarps and nothofagus

fracturing and fluid migration during palaeogene compression and neogene extension in the catalan coastal ranges spain the catalan coastal ranges ne part of the eastern iberian margin correspond to a system of grabens formed at the north western margin of the valencia trough extensional activity in the catalan coastal ranges occurred at least from early to late miocene and reactivated earlier transpressive faults related to the palaeogene compression in the central part of the catalan coastal ranges tectonic micro and macrostructures faults joints stylolites are well developed in the mesozoic mainly cretaceous limestones as well as in the miocene graben fill deposits in these rocks seven generations of fractures which formed during different tectonic phases have been distinguished type 1 4 fractures affect only the cretaceous limestones type 5 and 6 fractures the cretaceous and miocene deposits and type 7 fractures only the miocene sediments the fractures are filled with calcites and locally with an internal sediment or a dolomite cement the cretaceous host rock has an average 18o value of 4 3 pdb peedee belemnite an average 13c value of 0 6 pdb a 87sr 86sr ratio of 0 70741 up to 5630 p p m of mg2 up to 2615 p p m of sr2 and up to 1560 p p m of fe2 type 2 fractures are related to palaeogene compression the calcite cement filling this type of fracture has an average 18o value of 8 2 pdb an average 13c value of 0 6 pdb a 87sr 86sr ratio of 0 70714 up to 4560 p p m of mg2 up to 3275 p p m of sr2 and up to 3540 p p m of fe2 these results indicate a fluid characterized by a high rock fluid interaction approaching a closed system equilibrium type 5 fractures are related to the syn rift stage the calcite cement filling this type of fracture has an average 18o value of 6 9 pdb an average 13c value of 4 3 pdb a 87sr 86sr ratio of 0 70787 up to 5375 p p m of mg2 up to 1750 p p m of sr2 and up to 2855 p p m of fe2 these results indicate a fluid characterized by a low rock fluid interaction and an open hydrogeological system the cements filling the compressional fractures are characterized by undulose extinction subgrain formation and deformed mechanical twin planes indicating formation under stressed conditions in contrast cements filling extensional fractures are characterized by translucent crystals with uniform extinction indicating free growth not subjected to stress

cretaceous tertiary boundary extinction pattern and faunal turnover at agost and caravaca s e spain abstract planktonic foraminiferal extinctions at caravaca and agost occurred over an extended time period similar to el kef and brazos river some species disappeared well below the boundary about 39 45 of the species but less than 15 of the individuals in the population became extinct at or near the k t boundary a second phase of extinction occurred at the top of the boundary clay po pla and the remaining cretaceous species except g cretacea disappeared in subzone pla species extinctions were selective eliminating geographically restricted large complex and deeper dwelling forms first and favoring survival of cosmopolitan small simple surface dwellers only surface dwellers survived the k t boundary event whereas all deeper dwelling species as well as some surface dwellers disappeared at the boundary we interprete the selective abundance decline during the latest cretaceous as a result of the seal level regression that reached a maximum just prior to the k t boundary the highly selective nature of the two phased species extinctions at and above the boundary we believe to be related to the major reduction in surface productivity and the breakdown in the water mass stratification that was associated with the rapid sea level transgression across the k t boundary a bolide impact however may have hastened the demise of an already declining cretaceous fauna

palaeoenvironmental implications and diagenesis of inoceramid shells bivalvia in the mid maastrichtian beds of the sopelana zumaya and bidart sections coast of the bay of biscay basque country inoceramid bivalve shells from the mid maastrichtian beds of the sopelana zumaya and bidart sections in the basque country were tested for their post depositional diagenetic alteration petrography cathodoluminescence cl and scanning electron microscope sem observations together with geochemical analyses indicate that the coarsely prismatic calcite of the shells from the sopelana and zumaya sections have undergone diagenetic alteration without there being substantial textural changes in the original prismatic microstructure a generalized bright yellowish to red colour is seen in all the samples observed by cl the 18o values obtained from the shell prisms range from 2 94 to 5 18 with a mean value of 3 6 0 5 in the sopelana section whereas in the zumaya section they range from 1 88 to 4 71 with a mean value of 3 2 0 3 these values are clearly lower than those from the bidart section from 0 32 to 1 48 mean value 0 7 0 3 other evidence of diagenetic alteration is inferred from both whole shell geochemistry and microprobe analysis a complementary zonation in the distribution of diagenetic tracers can be detected from the inner shell layer isl to the outer shell layer osl of inoceramid shells together with a rare earth element ree enrichment in the shells which have lighter 18o values in contrast the inoceramid bivalve shells and their host rock from the bidart section were less altered the calculated mean palaeotemperature 15 c and the value of 13 c estimated from the non luminescent middle shell layer seem to be consistent with palaeolatitudes about 30 n for deep marine waters of mid maastrichtian time as the last step of the long term climatic cooling of the late cretaceous greenhouse

palaeoceanography of organic rich rocks of the loma chumico formation of costa rica late cretaceous eastern pacific the late cretaceous late cenomanian campanian loma chumico formation consists of laminated to massive bedded siliceous shales cherts ash fall tuffs volcanic glass beds and volcaniclastic sandstones the loma chumico formation is at least 630 m thick core data in the tempisque basin and can be subdivided in the subsurface into organic rich and organic lean total organic carbon 1 facies rock eval total organic carbon toc data show that toc in the organic rich facies averages 15 5 with values as high as 33 inorganic geochemical petrological and sedimentological analyses indicate that all the lithologies of the loma chumico formation were deposited in middle shelf to outer slope environments adjacent to an active subaerial island arc the organic geochemistry and palaeontology of the loma chumico formation help constrain the factors that controlled biological productivity in the region during the late cretaceous biomarkers identified in organic rich facies by gas chromatography mass spectrometry gc ms show a high abundance of total steranes relative to hopanes in the morote 1 core indicating algal dominated organic input the hopane to sterane ratio of the extract from the manzanillo 1 core indicates a relatively high bacterial component to the organic matter upwelling and extrusive volcanism were the most important factors that controlled nutrient supply including silica flux and biological productivity within the loma chumico formation depositional system episodic radiolarian dinoflagellate or diatom blooms instigated by rapid infusions of volcanogenic silica may have resulted in expansion of the oxygen minimum zone omz enhancing the preservation of organic matter productivity appears to have been uniform even during deposition of the organic lean facies the findings of this study suggest that ocean wide anoxia in the eastern pacific was unlikely during the late cretaceous high toc contents of organic rich radiolarites from central caribbean deep sea drilling project dsdp sites may be related to upwelling produced in the eastern pacific by convergence of the easterly trade winds eastern pacific equatorial upwelling zone or may be part of a more complex pacific atlantic ocean interaction the end of deposition of organic rich rocks began near the end of the latest santonian earliest campanian in the central caribbean and costa rica palaeoceanographic models suggest that improved circulation and ventilation of bottom waters due to early opening of the north atlantic south atlantic seaway may explain this observation this may represent the influx of a previously unrecognized source of colder oxygenated intermediate bottom water proto antarctic intermediate water into the late cretaceous central atlantic and eastern pacific oceans

δ 18 o of carbonate quartz and phosphate from belemnite guards implications for the isotopic record of old fossils and the isotopic composition of ancient seawater belemnite guards of cretaceous and jurassic age were found to contain varying amounts of quartz deposited both on the external surface and inside the rostrum the oxygen isotopic composition of coexisting carbonate quartz and phosphate from the same rostrum was measured according to well established techniques none of these compounds showed isotopic values in equilibrium with one another assuming 18o values of the diagenetic water within the range of meteoric waters the 18o sio2 yield temperatures in agreement with the apparent secondary origin of this phase the 18o co32 range with a certain continuity between 10 8 and 0 97 pdb 1 with most of the intermediate values being within the range of the carbonate isotopic values of mesozoic fossils the most positive isotopic results obtained from phosphate are close to 23 24 v smow they can hardly be related to a secondary origin of the phosphate or to the presence of diagenetic effects since these results are among the most positive ever measured on phosphate as far as we know there is no widespread diagenetic process determining an 18o enrichment of phosphate the very low concentration of phosphate did not allow the determination of its mineralogical composition all the available 18o po43 values from belemnite and non belemnite fossils of marine origin of tertiary and mesozoic age are reported along with the newly measured belemnites the following conclusions may be drawn from the data reported 1 the pristine oxygen isotope composition of fossil marine organisms either carbonate or phosphate may easily undergo fairly large changes because of oxygen isotope exchange processes with diagenetic water this process is apparent even in the case of geologically recent fossils 2 the 18o po43 of belemnite rostra seems to be at least in the case of the most positive results in isotopic equilibrium with environmental water because of the similarity between the results from cretaceous belemnites and the results from cretaceous and lower tertiary pelecypods and fish teeth 3 if so the only feasible interpretation that can be suggested for the 18o enriched data is the possibility of a relatively large variation of the oxygen isotopic composition of ocean paleowater from jurassic to recent time

deformation around a rising diapir modeled by creeping flow past a sphere a new experimental method for determining the pattern of flow and three dimensional progressive finite deformation of fluid elements in low reynolds number re viscous flow has been applied to creeping flow past a rigid sphere falling in a cylinder this is intended as a model analogue of natural rock deformation associated with magmatic and solid state diapirs rising through ductile crust the kinematics of finite strain in such analogue experiments may give useful information on the development of natural structures the experiment and a new method for quantifying the progressive finite deformation of fluid volumes in the transparent newtonian test fluid used sgm36 are discussed in detail the progressive finite deformation of fluid flowing along specific streamlines passing the sphere appears to be complex and largely a function of the initial distance of fluid volumes and the particular streamlines which they follow from the flow axis the progressive deformation history in the material surrounding a rising spherical diapir is characterized by progressive flattening and rotation of material above and progressive stretching below the sphere the results compare favorably with the external strain pattern associated with post tectonic mesozonal diapiric intrusions

co2 forced climate thresholds during the phanerozoic abstract the correspondence between atmospheric co2 concentrations and globally averaged surface temperatures in the recent past suggests that this coupling may be of great antiquity here i compare 490 published proxy records of co2 spanning the ordovician to neogene with records of global cool events to evaluate the strength of co2 temperature coupling over the phanerozoic last 542 my for periods with sufficient co2 coverage all cool events are associated with co2 levels below 1000 ppm a co2 threshold of below 500 ppm is suggested for the initiation of widespread continental glaciations although this threshold was likely higher during the paleozoic due to a lower solar luminosity at that time also based on data from the jurassic and cretaceous a co2 threshold of below 1000 ppm is proposed for the initiation of cool non glacial conditions a pervasive tight correlation between co2 and temperature is found both at coarse 10 my timescales and fine resolutions up to the temporal limits of the data set million year timescales indicating that co2 operating in combination with many other factors such as solar luminosity and paleogeography has imparted strong control over global temperatures for much of the phanerozoic

aureole deformation by flattening around a diapir during in situ ballooning the cannibal creek granite the cannibal creek granite a foliated pluton within a strongly deformed aureole shows several diagnostic features of a diapir the intensity of the aureole deformation diminished away from the contact the aureole foliation is continuous with that of the granite and forms closed elliptical trend lines and the contact metamorphic minerals are synkinematic with regard to the aureole foliation the pluton deformed its aureole in three stages involving initially brittle then ductile and finally brittle deformation styles initial intrusion of a low strength magma stoped kinked and flexed aside its overburden crystallization of the magma prevented further rise and it ballooned and deformed its aureole evidently entirely by ductile bulk shortening perpendicular to the contact this the major stage of aureole deformation records no evidence of vertical movement of the pluton or of progressive simple shear along its margin during this stage the magma may have been theologically a high strength bing

diapiric ascent of magmas through power law crust and mantle there has never been a convincing explanation of the way in which diapirs of molten granite can effectively rise through mantle and crust we argue here that this is mainly because the country rocks have previously been assumed to be newtonian and we show that granitoid diapirs rising through thermally graded power law crust may indeed rise to shallow crustal levels while still molten the ascent velocity of diapirs is calculated through an equation with the form of the hadamard rybczynski equation for the rise of spheres through newtonian ambient fluids this well known equation is corrected by factors dependent on the power law exponent n of the ambient fluid and the viscosity contrast between the drop and the ambient fluid these correction factors were derived from results reported in the fluid mechanical and chemical engineering literature for the ascent of newtonian drops through power law fluids the equation allows calculation of the ascent rates of diapirs by direct application of rheological parameters of rocks the velocity equation is numerically integrated for the ascent of diapirs through a lithosphere in which the temperature increases with depth the depth of solidification of the diapir is systematically studied as a function of the geothermal gradient buoyancy of the body solidus temperature of the magma and rheological parameters of the wall rock the results show that when the wall rock behaves as a power law fluid the diapir s ascent rate increases without a similar increase in the rate of heat loss in this way diapirs rising at 10 to 102 m yr can ascend into the middle or upper crust before solidification strain rate softening rather than thermal softening is the mechanism that allows diapirism to occur at such rates the thermal energy of the diapir is used to soften the country rock only at late stages of ascent the transport of magmas through the lower crust and mantle as diapirs is shown to be as effective as magmatic ascent through fractures

the pan african toro complex northern nigeria magmatic interactions and structures in a bimodal intrusion the toro complex is one of the pan african older granites of nigeria first described as a reversely zoned pluton made of a central dioritic mass surrounded by a broad granitic rim it has been thoroughly reinvestigated both from the petrographic and structural points of view with the help of systematic anisotropy of magnetic susceptibility ams measurements the granite main body is a hornblende biotite porphyritic monzogranite characterized by an early submagmatic fabric displaying a concentric pattern of foliations and west plunging lineations stage 1 this fabric is overprinted by a later one due to solid state strain along north south subvertical dextral shear zones stage 2 in the vicinity of the diorite an evengrained granite displays magmatic structures that are contemporaneous with this strike slip event the diorite granite contact is a complex zone where field petrographic and geochemical data enable recognition of the effects of mixing and mingling between a mafic and a felsic magma tonalites cropping out within this contact zone are interpreted as hybrid rocks the reverse zonation of the diorite itself is also the result of some hybridization process magmatic interactions mainly resulted from in situ infiltration of granitic liquid into the dioritic mass the detailed history of this bimodal intrusion began with the emplacement of the granitic magma acquiring a first stage fabric before full crystallization of the granitic core intrusion of the dioritic magma permitted reheating of the granitic magma that then crystallized with specific structural characters the second stage structures whether characterized by magmatic fabric near the diorite or by solid state strain features in north south shear zones elsewhere in the granite are related to late pan african dextral strike slip tectonics in the basement of northern nigeria the bimodal toro complex is therefore considered as a late pan african syntectonic pluton

isotopic evidence for late jurassic early cretaceous climate change abstract strontium oxygen and carbon isotope ratios have been determined from late jurassic early cretaceous belemnites from the volga basin russia and kawhia harbour new zealand 87sr 86sr ratios derived from well preserved belemnites from the volga basin support a middle tithonian age derived from the analysis of the endemic ammonite fauna the kawhia harbour section records a gradual rise in 87sr 86sr values and in comparison with the published 87sr 86sr curve suggests that the lower part of the section is latest oxfordian in age whilst the upper part of the section correlates well with the biostratigraphic correlation suggestion of an early middle tithonian age although the published strontium calibration curve shows a degree of scatter our new data confirm the uniform rise in 87sr 86sr values from the late jurassic into the early cretaceous such an increase may result from either a decrease in mid oceanic ridge spreading and or an increase in weathering rates and flux of radiogenic strontium although a eustatic drop in sea level and concurrent western cordillera uplift suggests that weathering may have been the controlling factor of late jurassic seawater strontium isotope composition palaeotemperatures derived from the well preserved belemnite 18ocarb values from the volga basin indicate that the middle volgian late kimmeridgian was warm 14 20 c followed by a slight cooling and a subsequent gradual increase to the jurassic cretaceous boundary the 18ocarb values from new zealand located at a palaeolatitude of 80 s if interpreted in terms of palaeotemperature indicate a high degree of variability such variability may not be related to palaeotemperature but to changes in oceanic chemistry resulting from the formation and dissolution of an ice sheet and or snow during the oxfordian kimmeridgian carbon isotope trends for the late jurassic show a fall in values from the oxfordian with lowest values occurring in the early middle tithonian before rising but without reaching values obtained in the oxfordian the overall low 13ccarb may be related to a global increase in continental weathering and or upwelling of cooler oceanic water enriched in oxidised organic carbon 12c enriched

rheology of some continental lower crustal rocks abstract to gain insight into the rheology of selected feldspar bearing rocks from the continental lower crust clc three granulites from exposed lower crustal terrains and a microgabbro have been deformed to ca 10 strain at confining pressures of 0 8 1 0 gpa temperatures of 600 900 c and constant strain rates of 10 4 10 7 s 1 the most extensive work was done on the mafic pikwitonei and felsic adirondack granulites the pikwitonei mg hornblende plag an70 2 px has only a limited t range of apparent steady state behavior and strain softens at t 800 c at 10 5 10 6s 1 apparently associated with developing shear zones this strain softening is pressure insensitive from pc 0 8 1 0 gpa at t 850 c 10 6s 1 even though the dominant strain accommodation mechanisms change from semibrittle cataclastic to crystal plastic including dynamic recrystallization with increasing pressure plagioclase appears to bear more of the creep strain than amphibole at most experimental conditions except in those runs where both plagioclase and amphibole recrystallization occurs kapuskasing plag cpx gt granulite deformed at 800 c and at 850 c 10 6 s 1 has deformed in the steady state at stress levels only slightly greater than the pikwitonei the stillwater microgabbro and adirondack granulite are appreciably weaker and the latter exhibits homogeneous semibrittle steady state behavior over the entire range of conditions investigated for the adirondack 2 felds 2 px gt qtz granulite quartz 21 appears to control the creep rate at these low strains and steady state mechanical data fit well a creep power law with a 8 10 3 mpa ns 1 qc 243 kj mol and n 3 1 extrapolation of this flow law and of preliminary power law creep relations for the pikwitonei and microgabbro to a range of physical conditions assumed to encompass those at the continental moho supports geological and geophysical inferences that a mechanical discontinuity occurs at this transition zone with the lower crust generally being the weaker material in addition the stain softening exhibited by the pikwitonei may bear directly on the development of detachment zones at mid to lower crustal depths during prograde metamorphism

characterization of groundwater and surface water mixing in a semiconfined karst aquifer using time lapse electrical resistivity tomography groundwater flow in karst includes exchange of water between large fractures conduits and the surrounding porous matrix which impacts both water quality and quantity electrical resistivity tomography combined with end member mixing analysis emma and numerical flow and transport modeling was used to study mixing of karst conduit and matrix waters to understand spatial and temporal patterns of mixing during high flow and base flow conditions to our knowledge this is the first time emma and synthetic geophysical simulations have been combined here we interpret an 8 week time lapse electrical resistivity data set to assess groundwater surface mixing we simulate flow between the karst conduits and the porous matrix to determine fractions of water recharged to conduits that has mixed with groundwater stored in the pore space of the matrix using a flow and transport model in a synthetic time lapse resistivity inversion comparing the field and synthetic inversions our results enable us to estimate exchange dynamics spatial mixing and flow conditions results showed that mixing occurred at a volumetric flux of 56 m3 d with a dispersivity around 1 69 m during the geophysical experiment for these conditions it was determined that conduit water composition ranged from 75 groundwater during base flow conditions to less than 50 groundwater in high flow conditions though subject to some uncertainties the time lapse inversion process provides a means to predict changing hydrologic conditions leading to mixing of surface water and ground water and thus changes to water quantity and quality as well as potential for water rock reactions in a semiconfined sink rise system

late cretaceous maastrichtian shallow water hydrocarbon seeps from snow hill and seymour islands james ross basin antarctica fossil hydrocarbon seeps are present in latest cretaceous maastrichtian volcaniclastic shallow shelf sediments exposed on snow hill and seymour islands james ross basin antarctica the seeps occur in the snow hill island formation on snow hill island and are manifest as large sized cement rich carbonate bodies containing abundant thyasirid bivalves and rarer ammonites and solemyid bivalves these bodies have typical seep cement phases with 13c values between 20 4 and 10 7 and contain molecular fossils indicative of terrigenous organic material and the micro organisms involved in the anaerobic oxidation of methane including methanotrophic archaea and sulphate reducing bacteria on seymour island the seeps occur as micrite cemented burrow systems in the lopez de bertodano formation and are associated with thyasirid solemyid and lucinid bivalves and background molluscan taxa the cemented burrows also have typical seep cement phases with 13c values between 58 0 and 24 6 there is evidence from other data that hydrocarbon seepage was a common feature in the james ross basin throughout the maastrichtian and into the eocene the snow hill and seymour island examples comprise the third known area of maastrichtian hydrocarbon seepage but compared to most other ancient and modern seep communities the james ross basin seep fauna is of very low diversity being dominated by infaunal bivalves all of which probably had thiotrophic chemosymbionts but which were unlikely to have been seep obligates absent from the james ross basin seep fauna are typical obligate seep taxa from the cretaceous and the cenozoic reasons for this may have been temporal palaeolatitudinal palaeobathymetric or palaeoecological

the evidence and implications of polar ice during the mesozoic abstract the mesozoic perhaps representing the longest period of warmth during phanerozoic earth history contains in general sparse and frequently equivocal evidence for polar ice although this time is undoubtedly punctuated by oscillations in climate whether sufficient to lead to polar cooling and the formation of polar ice an inviting mechanism to account for faunal and floral distribution patterns and large scale sea level change has been widely debated mesozoic evidence for glacial conditions includes abraded rock surfaces generally unsorted stone rich beds and the presence of dropstones rafted by ice within a finer grained host sediment faunal and floral evidence has also been utilised to determine the presence or absence of cold or sub freezing polar conditions together with more indirect evidence for glacial conditions derived from general circulation model gcm simulations of climate the analysis of clay mineral distributions glendonite abundance and palaeontological and sedimentological evidence for globally synchronous sea level change the extent of possible glacial environments during the mesozoic has been established by plotting published reports of glacial sediments on palaeogeographic reconstructions the general clustering of evidence at high palaeolatitudes suggests that the extent of polar ice during the mesozoic is likely to have been approximately one third the size of the present day based on such evidence a number of episodes of cold or sub freezing polar climates during the bajocian bathonian tithonian volgian valanginian and aptian are recognised evidence exists possibly also for a cold episode during the early jurassic pliensbachian although poorly constrained owing to limited biostratigraphical control the longevity of these events may be represented by a cold snap within a stage although undoubtedly the possible smearing of ages may have had the effect of lengthening and hence promoting the importance of these proposed events the climate regime of the earth during these times may be hypothesised to be characterised by a relatively steep pole to equator temperature gradient where low latitude regions are as warm or warmer than today the evidence to support such reasoning includes sharp increases in the areal distribution of both glendonites and deposits with affinities to glacial tillites and dropstones for these times coincidental falls of sea level arid events and an increased bipolarity of faunas at these times imparts further confidence that these events were of a magnitude to effect the earth as a whole

late cretaceous oceans and the cool tropic paradox oxygen isotopic proxies of paleo sea surface temperatures ssts suggest that maastrichtian about 66 million years ago tropical ssts were lower than those of today they also demonstrate that maastrichtian latitudinal sst gradients were much lower than those of the present the low maastrichtian sst gradients indicate that meridional heat transport was much greater or latitudinal differences in the balance of radiation to and from the sea surface were much less extreme during the latest cretaceous than they are today or that both conditions were true these findings challenge traditional interpretations of greenhouse late cretaceous climates

the genesis ascent and emplacement of the northern arran granite scotland implications for granitic diapirism integrated structural and petrological data are used to trace the evolution of the northern arran coarse granite during the latter stages of its ascent and its emplacement structural analysis of the aureole of the granite suggests that it rose as a single body of magma which is confirmed by petrological data during its ascent the pluton intersected the downward dipping limb of an existing synform refolding and displacing it upward to form a concentric or rim synform this direct evidence of vertical displacement of the country rocks confirms that the pluton is a diapir diapiric ascent was permitted by a reduction in wall rock viscosity and hence viscous drag forces on the pluton aided by heat loss due to crystallization during ascent most of the deformation within the aureole can be attributed to ascent of the pluton the early rim synform is overprinted by flattening strains and faulting caused by in situ radial expansion which represents the ultimate evolution of a diapiric body the final shape of the pluton is determined by inhomogeneous deformation of the aureole which is partly controlled by pre existing faults

isotopic signals from late jurassic early cretaceous volgian valanginian sub arctic belemnites yatria river western siberia this contribution presents the first detailed oxygen and carbon isotope record from the latest jurassic early cretaceous interval of the yatria river subpolar urals siberia isotopic compositions have been determined on well preserved belemnite samples from the genera lagonibelus cylindroteuthis and acroteuthis these new data indicate a shift to lower temperatures from the late volgian into the late valanginian with some warmer phases recognized within the ryazanian and earliest valanginian the lowest temperatures of the late valanginian consistent with subfreezing polar temperatures are coincident with an inferred eustatic sea level fall a late valanginian positive shift in carbon isotopes correlates with the carbon isotope excursion recorded from tethyan successions the most positive carbon isotope values correspond to the most positive oxygen isotope values and hence lowest palaeotemperatures in the absence of widespread valanginian organic rich black shale deposition the carbon isotope excursion may point to increased storage of organic carbon in coastal areas and or enhanced preservation within stratified waters in high latitude basins at these higher latitudes where rates of weathering were presumably much lower because of the prevalent cold climate the isotopic data may point to pulses of productivity being brought about by increased riverine nutrient transfer and also by nutrients being released by the melting of ice the correlation between positive carbon isotopes and cool climates may indicate the effectiveness of these high latitude carbon sinks and their ability to draw down atmospheric co 2 resulting in an inverse greenhouse effect

evolution and extinction of maastrichtian late cretaceous cephalopods from the lopez de bertodano formation seymour island antarctica one of the most expanded records to contain the final fortunes of ammonoid cephalopods is within the lopez de bertodano formation of seymour island james ross basin antarctica located at 65 south now and during the cretaceous this sequence is the highest southern latitude onshore outcrop containing the cretaceous paleogene k pg transition we present comprehensive new biostratigraphic range data for 14 ammonite and one nautiloid species based on the collection of 700 macrofossils from high resolution sampling of parallel sedimentary sections dated maastrichtian to earliest danian in age across southern seymour island we find evidence for only a single abrupt pulse of cephalopod extinction at the end of the cretaceous when the final seven ammonite species disappeared consistent with most evidence globally in the lead up to the k pg extinction in the james ross basin starting during the campanian ammonite diversity decreased overall but the number of endemic taxa belonging to the family kossmaticeratidae actually increased this pattern continued into the maastrichtian and may be facies controlled linked to changes in sea level and seawater temperature during the early maastrichtian ammonite diversity dropped significantly with only two species recorded from the basal lopez de bertodano formation on seymour island the subsequent diversification of endemic taxa and reappearance of long ranging widespread species into the basin resulted in an increase in ammonite diversity and abundance during the mid maastrichtian this was coincident with an apparent period of warming temperatures and sea level rise interpreted from palynology and sedimentology perhaps reflecting a high latitude expression of the mid maastrichtian event late maastrichtian diversity levels remained stable despite reported climatic and environmental variation ammonite diversity patterns during the maastrichtian parallel those of microfossil species such as nannofossil and planktonic foraminifera suggesting that dynamic climatic and environmental changes affected many planktonic and nektonic organisms during the latest cretaceous however we suggest that these perturbations had a minimal effect on overall diversity prior to the catastrophic extinction event at the k pg boundary

concentration of carbon dioxide in the late cretaceous atmosphere stable carbon isotope data from late cretaceous maastrichtian palaeosols in india are used to estimate the concentration of carbon dioxide in the late cretaceous atmosphere we show that the maastrichtian atmosphere is unlikely to have contained more than about 1300 ppm by volume of co 2 this value agrees with an independently modeled value of co 2 in the late cretaceous atmosphere a low concentration of the greenhouse gas carbon dioxide in the maastrichtian atmosphere relative to concentrations in the earlier cretaceous is consistent with palaeotemperature information from terrestrial plant and marine fossils which suggest that the global climate cooled toward the end of the cretaceous period

introduction to special section mechanisms and consequences of melt segregation from crustal protoliths much of petrological effort has been concentrated on attempts to discern define and interpret regularly recurring patterns of igneous and metamorphic petrogenesis i do not wish to deny the existence of discernable order in petrological phenomena but every geological event is unique if we concentrate too heavily on discernment of order and pattern may we perhaps overlook or underrate the unique quality of each igneous or metamorphic episode possibly uniqueness may have as great significance as conformity to pattern when we attempt to fit the phenomena of petrology into the broad framework of geology francis j turner presidential address to the mineralogical society of america november 11 1969

ammonoid habitats and habits in the western interior seaway a case study from the upper cretaceous bearpaw formation of southern alberta canada abstract multidisciplinary research on the habitats and life habits of ammonoids of the upper cretaceous bearpaw formation is based on hydrostatics and hydrodynamic aspects of shell shapes occurrence in lithofacies evidence of predation and stable isotopic data the large and well streamlined oxyconic placenticeras with large chitinous anaptychus had the weakest shells known and suffered mosasaur tooth perforations at minimal ambient pressure anomalously light 18 o signatures preserved in their aragonitic shells suggest that they grew in brachyhaline water juveniles and some adults of orthoconic baculites had a vertical life orientation and primarily resided in the lower to middle levels of the water column flourishing during oxygenation events some adults however may have changed to a mainly horizontal swimming habit in mid water attitudinal change is indicated by relative shortening of the body chamber during late ontogeny neutral buoyancy at maturity could have been achieved only with a partially liquid filled phragmocone implying the exceptional use of cameral liquid as an apical counterweight juvenile scaphitids were planktic or sluggishly nektic as implied by sphaeroconic and discoconic immature whorls respectively the adults had different habits as indicated by their strongly modified body chambers which gave high stability suited to vertical swimming adult hoploscaphites and most jeletzkytes with open hooked scaphitoconic body chambers were demersal and lived close to the sea floor during oxygenation events whereas adult rhaeboceras with an elliptical contracted body chamber elliptosphaerocone lived in mid water

high northern palaeolatitude jurassic cretaceous palaeotemperature variation new data from kong karls land svalbard abstract the traditional view of warm equable global climates in the mesozoic with weakly developed latitudinal temperature gradients has been challenged by several recent studies however reliable high palaeolatitude palaeotemperature data is still rare in this study palaeotemperature data based on oxygen stable isotope palaeothermometry of well preserved mid jurassic to lower cretaceous belemnites from kong karls land svalbard are presented these data show cool high latitude marine isotopic palaeotemperatures for endemic species during the lower to mid valanginian 7 7 c which may be compatible with the formation of high latitude ice middle bathonian to kimmeridgian samples give warmer isotopic palaeotemperatures 9 4 c whilst samples from the aalenian to bajocian give isotopic palaeotemperatures which are warmer still 12 7 c comparison of the callovian temperatures with those from a mid latitude location shows them to be warmer than would be expected if previous latitudinal temperature gradients are correct this may be due to the ameliorating effect of oceanic heat transport pole wards from the panthalassa ocean via the south anyui ocean

a multi proxy approach to determine antarctic terrestrial palaeoclimate during the late cretaceous and early tertiary fossil wood is abundant throughout the cretaceous and tertiary sequences of the northern antarctic peninsula region the fossil wood represents the remains of the vegetation that once grew at the southern high palaeolatitudes at 59 62 s through the general decline in climate from the late cretaceous global warmth through to the mid eocene cool period prior to the onset of glaciation this study draws on the largest dataset ever compiled of antarctic conifer and angiosperm woods in order to derive clearer insights into the palaeoclimate parameters including mean annual temperature mean annual range in temperature cold month mean warm month mean mean annual precipitation are recorded the fossil wood assemblages have been analysed using anatomical physiognomic characteristics to determine the palaeoclimate variables from the coniacian campanian to the middle eocene these results are compared with data derived from coexistence analysis of the fossil floras composed of leaves wood and palynomorphs and published data based on leaf physiognomic characters these studies indicate a relatively warm and wet late cretaceous that becomes drier and cooler in the early paleocene and subsequently returns to warmer wetter conditions by the latest early paleocene during the eocene the climate becomes relatively cool and dry once again the discrepancies obtained from these two methods coupled with other published data are discussed in the context of the fluctuations in the temperatures of the surrounding oceans and global patterns of climate change

palaeotemperatures indicated by upper jurassic kimmeridgian tithonian fossils from mallorca determined by oxygen isotope composition abstract the oxygen and carbon composition of calcite has been determined for belemnites ammonite aptychi and the matrix surrounding these fossils from the kimmeridgian tithonian of mallorca petrography cathodoluminescence and trace element analyses indicate that both ammonite aptychi and matrix has been diagenetically altered whereas the belemnites have been undergone minimal or no modification the belemnites give the heaviest oxygen isotope values of 0 04 to 0 99 pdb and lighter values of 0 71 to 3 98 pdb come from the ammonite aptychi and matrix the carbon isotopic compositions obtained from all the fossils are positive and are similar to those derived from modern marine shallow water skeletons palaeotemperatures calculated on the basis of the oxygen isotopic composition of the belemnites give a range of values from 13 6 to 16 c these results agree with late jurassic palaeotemperatures from similar palaeolatitudes

cool cretaceous climates new data from the albian of western australia although previous geological palaeobotanical and geochemical data from the albian of australia have suggested the possibility of cool palaeoclimates there are few well constrained stable isotope palaeotemperatures studies from this region in this paper we present the results of stable isotope analyses of dimitobelid belemnites from the albian gearle siltstone carnarvon basin western australia oxygen isotope values for diagenetically least altered samples give values ranging between 18 o 0 02 and 0 85 pdb which equate to a mean palaeotemperature of 10 08 c assuming w of 1 2 smow this value is broadly consistent with recently published isotope data from the albian antarctic and with estimates for mid cretaceous latitudinal temperature gradients implying that cool palaeoclimates occurred during a period of 9greenhouse9 earth

fault and fluid interaction in a rifted margin integrated study of calcite sealed fault related structures southern corinth margin this work integrates microstructural petrologic microthermometric and geochemical analysis of calcite sealed fault related structures of the major faults of the southern margin of the corinth rift greece it draws attention to the main deformational processes and fault fluid inter action in fault zones along the whole margin data analysed come from the compact breccia located immediately adjacent to major fault planes samples were collected at different positions alongside different faults juxtaposing synrift continental deposits hanging wall against the prerift pindus limestones footwall this implies hectometric fault displacements and that the fault zones have recorded a relatively long evolution of deformation our study identifies four main defor mation features common to all studied faults calcite cemented breccia extensional veins shear veins and fault slip surfaces the integrated data analysis shows that deformation structures and fault rocks that coexist in the same outcrop formed at different depths and times during inferred upward fault propagation the style of deformation evolved from distributed brecciation to loca lized slip surfaces and from a closed system with fluid rock equilibrium during brecciation to a more open one with limited influx of meteoric water during extensional and shear fracturing this implies relative uplift of the footwall during fault propagation and fault interaction with different water aquifers as the fault propagates upwards the results demonstrate similar fault evolution and fault fluid interaction through the entire rifted margin and during the whole rifting period

the rise of solid state diapirs when magma inside a diapir solidifies it increases in density and becomes a stiff power law fluid if the diapir is still positively or negatively buoyant after solidification it will continue to rise or start to sink the results presented here suggest that solidified diapirs may rise sink a distance of up to a few kilometres in geologically reasonable times rocks and bubble and or crystal rich magmas behave as power law fluids this paper compares numerical results of viscosity and strain rate profiles across power law and newtonian diapirs and wall rocks the comparison shows that the core of power law diapirs deforms more slowly and the margins much faster than in newtonian diapirs this pattern of strain rate distribution leads to the often observed isotropic or weakly deformed core surrounded by a strongly sheared margin furthermore the results suggest that the strain rate of the ambient fluid wall rock is imposed across the contact into a power law diapir resulting in similar strains on either side of the contact and that power law wall rocks in contrast to newtonian wall rocks deform into a rim synform as the diapir rises

geophysical signatures of fracture traces in a karst aquifer florida u s a abstract numerous studies have shown that photolinears are associated with zones of increased fracture density porosity and permeability in carbonate terranes increased solution along the fractures leads to pronounced surface expressions of subsurface fracture zones such as sags sinks and linear depressions such features often have several meters of relief and may be as much as 200 300 m wide r r parizek and others have shown that well yields up to 100 times that of adjacent strata are associated with narrow zones within the surface expressions of the photolinears these zones are seldom more than a few tens of meters wide and often only a few meters wide a study conducted at cross bar ranch wellfield pasco county florida demonstrates that several surface geophysical techniques can be used to delineate zones of higher yield within the wider surface expression of photolinears seismic refraction and d c electrical resistivity proved to be the most useful techniques the geophysical signatures result from the effect of increased karstic solution on overburden thickness and stratigraphy over the inferred fracture zone microgravimetry also appears to be an effective technique showing a distinctive and linearly consistent gravity low of 0 1 0 3 mgal over the inferred fracture zone the geophysical signatures of these methods appear to delineate zones of increased fracture density even where overburden thicknesses exceed 20 m however due to the density of data needed to delineate these zones these methods may be practical only in areas where the locations of such zones are critical and not as a reconnaissance tool

climatic and oceanographic isotopic signals from the carbonate rock record and their preservation stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases terrestrial carbonates meteoric cements calcretes and speleothems similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover primary environmental isotopic signals may be obscured by the effects of post depositional diagenetic alteration cementation and replacement reactions can take place in a wide range of diagenetic environments the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting together with subsequent changes in relative sea level and burial history carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration water rock interaction and fluid mixing may produce non linear distributions attempts to determine long term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow water limestones must include an assessment of the diagenetic history of the materials analysed petrographic examination using conventional microscopy backed up where appropriate by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary environmental isotopic signals recent research has shown that these techniques can be successfully employed in both phanerozoic and precambrian sediments

oxygen carbon isotope composition of middle jurassic cretaceous molluscs from the saratov samara volga region and main climate trends in the russian platform caucasus

effect of changes in d18o content of the surface ocean on estimated sea surface in past warm climate 1 using a coupled climate model of intermediate complexity including oxygen 18 climber 2 we investigate the evolution of the distribution of surface water 18o composition under warm climate conditions we then determine the impact of changes of the surface water 18o distribution on ocean surface temperatures inferred from calcite oxygen 18 our results show that published temperature reconstructions based on oxygen 18 from calcite are systematically biased by 2 to 4 c in the absence of major oceanic circulation changes and up to 7 c in the presence of major oceanic circulation changes as the bias introduced is shown to vary with latitude our work has major implications on past latitudinal temperature gradient reconstructions based on oxygen 18 measurements

tectonic processes and geomorphological design abstract deep seated geodynamic processes are the cause of the existence of the geotectonic stress field the influence of the latter and therefore of deep seated processes in surface geomorphology is investigated it is noted that the features caused by deep seated geotectonic processes can be distinguished from those caused by exogenic agents weather erosion etc by their statistical characteristics all statistically systematic features are of geotectonic origin random features are of exogenic origin in this paper various types of morphological features are analyzed with regard to their origin it is shown that lineaments seen on air photographs may not be of recent geotectonic origin specific examples of such lineaments being erosion scarps are given next it is shown that the orientation patterns inherent in fluvial and glacial valleys are indeed affected to a large extent by neotectonic processes the same is naturally the case for rift valleys and chains of volcanoes a further interesting subject is presented by the so called tectonic landforms inselbergs cirques the shapes of mountain summits etc are all shown to be directly or indirectly caused by deep seated processes the mass movements on slopes are also of great importance although it is often thought that these are triggered by meteorological conditions it is shown that their basic design is influenced to a large extent by deep seated processes amongst other things this is borne out by a correlation between landslide and earthquake activity finally it is mentioned that the common joints on rock outcrops are also designed by the neotectonic stress field and that the latter can in fact be determined by an analysis of joint orientations in summary it may be stated that although exogenic agents may be responsible for many morphological features deep seated processes have nevertheless a great influence on the fundamental design of such features

re examining pluton emplacement processes discussion in a recent review paterson fowler 1993 showed decreasing away from the pluton as discussed by gughow estimated volumes of displaced wall rock are lielmo 1993b smaller than pluton volumes and how the widths of laboratory experiments indicate that rocks behave as strain aureoles around natural plutons are considerably power law fluids with exponents n between 2 5 and 5 narrower than in models of diapirs where spheres rise hansen carter 1982 kirby 1983 wilks carter through newtonian fluids cruden 1988 schmeling et 1990 the power law exponent n of a viscous fluid is a al 1988 they then argued that mechanisms other than measure of the sensitivity of its viscosity stress or ductile flow of the wall rocks were necessary to account strain role for n 1 newtonian fluid the viscosity is for these observations although i accept that several constant for any strain rate for n 1 the fluid softens mechanisms may act simultaneously and change in imwith increased strain rate the strain rate dependency of portance as plutons are emplaced i argue here that i the viscosity of power law fluids has important effects on the displaced volumes of wall rocks may be underestithe velocity and flow patterns of the ambient fluid mated because of difficulties in assessing the shape and around rising spheres or diapirs and therefore the size of the three dimensional flow cell in the wall rocks width of their strain aureoles crochet et al 1984 caused by pluton emplacement and more importantly kawase moo young 1986 weinberg podladchikov ii the narrow strain aureoles may result from diapiric in press in the following discussion the difficulties in rise of plutons through power law rocks and or result determining the volumes of rock displaced by diapir from the effects of thermal softening of the wall rocks emplacement are first considered the effect which several field studies have measured the width of the power law rocks might have on the width of the strain strain aureole caused by pluton emplacement see gugaureole is then discussed and finally the possible effects lielmo 1993a paterson fowler 1993 and references of thermal softening of the wall rocks by the diapir are therein the measured width depends on three main examined factors i the finite strain of the wall rocks which depends on the velocity field imposed by the diapir this in turn depends on the diapir s mechanism and depth of rock volumes displaced by diapirs emplacement and on the rheology and physical boundaries of its wall rocks the longer a rock volume is paterson fowler 1993 studied horizontal shortensubmitted to a particular strain rate velocity field the ing in strain aureoles around plutons and then integrated larger is its strain the velocity of flow decreases with shortening to three dimensions around plutons of differdistance from the contact of rising spheres so that ent shapes the amount of shortening they obtained for strains have to accumulate a long time to be distinguishseveral natural examples only accounted for about 30 able from any background strain ii late deformation of the volume of the plutons they argued that this will mask the strain aureoles of pre tectonic plutons volume difference implies that other mechanisms such while interference with regional tectonic strains will as doming of the roof stoping assimilation and rigid affect the width of the aureoles of syn tectonic plutons translation of wall rock must have operated at the same guglielmo 1993b iii the measurable width of the time as viscous flow of the wall rock aureole depends on distinguishing the strain due to the however this discrepancy may largely be due to pluton from regional strains of any age paterson difficulties in measuring small pluton related strains fowler 1993 this distinction becomes increasingly beyond the obvious strain aureole and difficulties in more difficult as strains are spread over larger volumes determining the shape of the flow cell around the pluton the width of the strain aureole around a rising sphere depends on the power law exponent n of the country current address research school of earth sciences anu act rocks it is widest in newtonian fluids and narrows as n 6200 canberra australia increases however even in the case of rocks with high n

high paleolatitude late cretaceous paleotemperatures new data from james ross island antarctica oxygen isotope analysis of well preserved macrofossils from the santonian campanian of james ross island and the maastrichtian of vega island antarctica indicates that cool high paleolatitude temperatures prevailed during the late cretaceous and suggests that cooling occurred between the santonian campanian and the maastrichtian although more than 50 of the material showed diagenetic alteration 52 unaltered aragonite and calcite samples were analyzed mean delta sup 18 o and calculated paleotemperature values were minus 0 23 per thousand and 13 6 c respectively for the santonian campanian and 0 66 per thousand and 11 7 c respectively for the masstrichtian in conjunction with recent late cretaceous paleoclimatic data from high northern paleolatitudes these data indicate the presence of cool polar regions with broad climatic zonation during the late cretaceous this may have partly controlled faunal distributions

cretaceous and early tertiary climates of antarctica evidence from fossil wood abstract fossil wood is abundant in cretaceous and early tertiary sediments of the northern antarctic peninsula region the wood represents the remains of vegetation that once grew in high palaeolatitudes when the polar regions were warmer during former greenhouse climates fossil wood is a unique data store of palaeoclimate information analyses of growth rings and anatomical characters in fossil wood provide important information about temperature rainfall seasonality and climate trends for this time period in antarctica climate signals from fossil wood supported by sedimentary and geochemical evidence indicate a trend of cool climates during the early cretaceous followed by peak warmth during the coniacian to early campanian narrower growth rings suggest that the climate cooled during the maastrichtian and palaeocene cool wet and possibly seasonal climates prevailed at this time with tentatively estimated mean annual temperatures mats falling from 7 c to 4 8 c respectively determined from dicotyledonous dicot wood anatomy the late palaeocene early eocene was once again warm with estimated mats of 7 15 c from dicot wood analysis but conditions subsequently deteriorated through the latter part of the eocene when cold seasonal climates developed ultimately leading to the onset of cenozoic ice sheets and the elimination of vegetation from most of antarctica

magmatic strains and foliation triple points of the merrimac plutons northern sierra nevada california implications for pluton emplacement and timing of subduction abstract cross cutting relationships between regional structures and post tectonic plutons of known age are commonly used to date regional deformation in orogenic belts in order to show that a pluton is post tectonic one must demonstrate that the strains within the pluton are not due to regional tectonic processes this paper reports strain measurements associated with pluton emplacement in northern sierra nevada these strain data and a microstructural analysis indicate that strains within the merrimac plutons are due to igneous not tectonic processes which strengthens the hypothesis that the plutons were emplaced after the formation of regional structures and melanges radiometric ages of the merrimac pluton in concert with structural data place a more reliable upper jurassic limit on the age of the subduction in the western belt of northern sierra nevada this paper also reports constrictional strains around plutons and suggests that the merrimac plutons contributed significantly to the ductile strains observed in the wall rocks

stratigraphical architecture at the muddy margin of the cretaceous western interior seaway southern utah the tropic shale and correlative tununk shale member of the mancos shale accumulated during cenomanian turonian time within prodeltaic environments near the western margin of the western interior seaway of north america stratigraphical and sedimentological analysis has revealed a detailed history of relative sea level change in the thick fine grained succession the tropic and tununk shales were deposited during the greenhorn second order sea level cycle over a time span of about 2 5 million years in southern utah six depositional sequences are superposed upon the record of this long term sea level change the sequences developed during third order relative sea level cycles of hundreds of thousands of years duration and are composed of at least 37 parasequences arranged in retrogradational aggradational and progradational parasequence sets the tropic shale and tununk shale member accumulated just basinward of the axis of maximum subsidence of a foreland basin stratal geometries and facies distribution patterns in the succession indicate that in southern utah the greenhorn cycle was tectonically controlled during the greenhorn transgression and highstand rapid rates of tectonic subsidence trapped terrigenous sediment to the west of the study area in the more proximal foreland at this time hemipelagic facies accumulated at relatively slow rates in southern utah and type 2 sequences developed during third order sea level cycles in contrast during the greenhorn regression rates of thrust induced subsidence in the proximal foreland basin evidently slowed and deltaic clinoforms prograded across the study area at least one forced regression occurred in southern utah at this time and type 1 sequences developed the formation of type 1 sequence boundaries in the upper part of the tropic shale and tununk shale member points to episodes of base level fall and indicates that the six third order sea level cycles recorded in the succession were not the result of changes in sediment supply alone the third order cycles may have been a consequence of episodic tectonism the timing of these cycles however suggests that development of sequences and parasequences in the tropic shale and tununk shale member may have been related to orbital forcing in the milankovitch band glacioeustasy or climatically related fluctuations in the amount of groundwater stored on continents may explain these high frequency sea level changes

campanian maastrichtian cretaceous stratigraphy of the james ross island area antarctica one of the most important outcrops of uppermost cretaceous campanian maastrichtian sedimentary rocks in the southern high latitudes occurs within the james ross island group northeastern antarctic peninsula these rocks comprise a 1500 2000 m thick sequence of predominantly shallow marine clastic sediments that were deposited within a retro arc basin they are virtually undeformed and have yielded prolific invertebrate and vertebrate faunas and a wide range of plant taxa campanian maastrichtian strata are contained within two component formations of the upper cretaceous lower tertiary marambio group the lower santa marta formation is approximately 1100m thick and has three constituent members ammonites within the santa marta formation indicate an early to late campanian age assignment dinoflagellates suggest that the lower levels of the formation may range into the santonian stage in the northern james ross island to vega island region there is a conformable transition into the overlying lopez de bertodano formation here the basal cape lamb member is unconformably overlain by the sandwich bluff member although there are some lithological and fauna1 discrepancies which are attributed to marked lateral facies changes across the basin it is believed that the cape lamb member can be correlated with the lower to middle regions of the 1200 m thick sequence of undifferentiated lopez de bertodano formation lithologies exposed on seymour island molluscan data indicate a late campanian palaeocene age range for this upper formation dinoflagellates again suggest that the lowest beds may be slightly older the correlation presented provides the basis for a formal subdivision of the campanian and maastrichtian stages in the southern high latitudes it has also revealed two major basin shallowing events in the late campanian early maastrichtian and latest maastrichtian respectively and the existence of a major fault fault zone across southeastern james ross island the improved temporal framework will aid late cretaceous palaeoclimatic and palaeobiological studies in antarctica

palaeoclimate analysis of late cretaceous angiosperm leaf floras james ross island antarctica the fossilized remains of cretaceous angiosperm leaves are preserved within sandstones and siltstones of the coniacian hidden lake formation gustav group and the santonian early campanian santa marta formation marambio group in the james ross basin antarctic peninsula region the leaves represent the remains of vegetation that grew at approximately 65 s on an emergent volcanic arc now represented by the antarctic peninsula and were subsequently transported and buried in marine sediments in the adjacent back arc basin some of the angiosperm leaf morphotypes show similarities to leaves of living families such as sterculiaceae lauraceae winteraceae cunoniaceae and myrtaceae palaeoclimate analysis based on physiognomic aspects of the leaves such as leaf margin analysis indicates that the mean annual temperatures for the hidden lake and santa marta formations were 13 21 c mean 17 c and 15 23 c mean 19 c respectively the fossil plants are indicative of warm climates without extended periods of winter temperatures below freezing and with adequate moisture for growth this period of cretaceous warmth in antarctica corresponds with the cretaceous thermal maximum an interval of peak global warmth from the turonian to the early campanian

late cretaceous climatic trends and a positive carbon isotope excursion at the santonian campanian boundary in british columbia northeastern pacific abstract this study presents oxygen and carbon isotope data obtained from well preserved ammonite and bivalve fossils of the upper cretaceous nanaimo group of southwestern british columbia canada palaeotemperatures for the late santonian campanian of british columbia determined on the basis of oxygen isotopic analysis suggest a odirect relationship with basic late cretaceous climatic trends e g temperature fall toward the cool climates of the maastrichtian the coolest campanian palaeotemperatures were calculated from the ammonite pachydiscus cf ootacodensis stoliczka 11 3 26 4 c and the bivalve inoceramus vancouverensis shumard about 19 7 c from the late campanian occidentalis zone northumberland formation in contrast the highest palaeotemperatures were obtained from the shells of presumed earliest campanian bivalves and varied between 25 1 and 33 7 c which we assume to represent the regional expression of the early campanian warming event the santonian campanian boundary in british columbia is associated with a positive 13c excursion to 4 2 which appears to be contemporaneous with the santonian campanian boundary event reported recently from other regions i e europe tunisia japan and tibet the lack of organic rich laminated black shales indicating strong oxygen depletion in the marine realm through the santonian campanian of the nanaimo group including the santonian campanian boundary interval seems to be in agreement with the suggestion that most of the world s oceans were characterised by oxygen rich deep waters during coniacian campanian time

re examining pluton emplacement processes abstract previous pluton emplacement studies have attempted to explain how space is made during pluton emplacement in fact the only means of making space during emplacement of mantle derived magmas in the crust are 1 lowering the moho or 2 outward displacement of the earth s surface other pluton emplacement mechanisms are material transfer processes mtps that do not increase the volume of the crust one frequently cited mtp for emplacement of concentrically zoned and ballooning plutons is ductile flow of wall rocks around the plutons the expected structures and total strains near such plutons are dependent on the three dimensional pluton shape the width of the deforming aureole whether the pluton is a piercing or non piercing diapir and in the latter case the number of body radii the pluton travels we have re examined a few such plutons and calculated the amount of material transfer caused by ductile flow in no case is more than 40 and in most cases only 15 35 of the required material transfer accommodated by wall rock flow the contact aureoles around these plutons are too narrow and or strains too low indicating that the plutons are predominantly discordant bodies with narrow 0 1 0 4 pluton radii concordant aureoles a comparison of strains in natural contact aureoles and those made in mechanical models of diapirs indicates that natural strains are at least an order of magnitude less than model strains we suggest that the similarities between models of diapiric ascent of spherical bodies and concentrically zoned plutons are superficial because the models are too simplistic instead we argue that the ascent and emplacement of magmas require multiple near field and far field mtps these mtps will show gradients with depth distance from the magma and with time rates of near field mtps must be rapid whereas far field rates are probably nearer to long term average rates of orogenic processes

evidence for significant granite space creation by the ballooning mechanism the example of the ardara pluton ireland the emplacement mechanism of the ardara granite a caledonian pluton located on the northwestern seaboard of ireland has been a widely cited and a key point of reference in the debate about the granite space problem for nearly half a century early models related its subcircular tailed shape concentric foliation pattern and concentrically deformed envelope to diapirism it was subsequently reinterpreted using strain data as a ballooning pluton that was created by 70 in situ expansion at the emplacement site and was later cut by a regional shear zone recently it was the leading example in a wide ranging review of forcefully emplaced plutons of this type and was reinterpreted as a series of nested diapirs associated with only modest amounts 30 of forceful space creation but a large component of inferred early block stoping we report the results of the complete remapping and extensive collection of new structural data from this 8 km diameter normally zoned three phase calc alkaline pluton we confirm the existence of the steeply inclined internal foliation pattern and that it was formed in the magmatic state although this and the outline of the pluton are modified by late stage high temperature solid state regional transcurrent shear zones along two of the pluton contacts structural mapping has failed to identify a macroscopic lineation in the magmatic foliation planes and this is confirmed by strain determinations using mafic enclave populations and magmatic crystal separations for the magmatic state deformation that show nearly pure flattening type strains k 0 strains measured by these techniques show an apparently smooth gradient increasing outward toward the pluton contacts from an inner low strain zone we argue that these features together with the simple normal petrographic zonation a lack of small scale structures that would indicate the pluton had moved up relative to the wall rocks and an exposure level that is not in the roof zone are inconsistent with diapirism either singly or multiply but are most easily explained by a ballooning emplacement mechanism synmagmatic shear sense data from both the pluton and the adjacent country rocks indicate however that within the overall context of radial ballooning there was a limited amount of late stage nonradial northward injection of magma an inversion of the deformed enclave and crystal spacing strain determinations and strain determinations within the country rocks suggest that more than 80 of the volume of the pluton was accommodated by the ballooning mechanism

some limitations in using leaf physiognomic data as a precise method for determining paleoclimates with an example from the late cretaceous pautut flora of west greenland abstract plant parts of the late cretaceous west greenland pautut flora are derived from vegetation growing in lower delta plain delta upland and levee habitats a large river system drained the uplands and deposited leaves from species there and levee areas into a shallow bay setting the large drainage area of the rivers caused a great diversity of species to be preserved in the bay when these upland and levee species are combined with those that grew and were deposited in the lower delta plain areas 12 fern six cycad cycadeoid 1 ginkgoalean 35 conifer and over 85 angiosperm species represent the pautut flora when the paleotemperature derived from the angiosperm leaf margin ratio of the complete pautut flora 8 c is compared to other paleobotanical data and oxygen isotope values warm temperate to subtropical there is a serious discrepancy that puts the leaf physiognomic approach for precisely determining paleoclimate in the cretaceous in serious doubt also paleoclimatic interpretations based on the angiosperm leaf margin data of leaves from the lower delta plain species would indicate slightly cooler conditions than that suggested by the upper delta plain species leaf size would indicate wetter conditions in the lower delta plain even though other leaf features e g drip tips suggest moist conditions did occur in the upper delta plain these preservation enough that regional paleoclimate scenarios drawn from only one depositional setting or loclity can be erroneous a sampling size of less than 30 angiosperm species for a fossil flora also is suspect for reliably indicating climatic conditions unless the flora was originally impoverished of angiosperm species taphonomic factors play a significant role in fossil leaf preservation so collected fossil assemblages must closely represent the original vegetation before paleoclimatic interpretations based on leaf physiognomy can have a degree of credibility a limit to plausibility is especially significant in cretaceous floras because they have a limited diversity due to evolutionary constraints and appear to have consisted of more successional species than younger floras thus displaying intermediate climatic conditions moisture and arctic light levels further restrict determination of paleoclimatic conditions derived from leaf margin ratios and leaf size

global cooling inferred from dropstones in the cretaceous fact or wishful thinking traditionally the cretaceous has been considered as a long period of global warmth a greenhouse world this view has been challenged in recent years by several lines of evidence palaeobotany stable isotopes and palaeoclimatic modelling in particular however although these data demonstrate that cooling is likely the only first hand evidence which demonstrates the presence of substantial ice build up in cretaceous high palaeolatititudes are dropstones these outsized or exotic clasts set in a fine grained sediment are often interpreted as a direct result of ice rafting the reliability of this dropstone evidence and particularly its validity is questioned in demonstrating ice age interludes within the cretaceous greenhouse

application of the fujita ziegler paleoclimate model early permian and late cretaceous examples abstract the fujita ziegler model is a new semi quantitative technique for reconstructing atmospheric circulation and resulting rainfall patterns of the geological past using uniformitarian assumptions in this paper we evaluate the performance of the model when applied to geographic and climatic conditions that were significantly different from the recent a late cretaceous maastrichtian reconstruction permits a test of the performance of the technique during a time that apparently lacked polar ice caps and steep latitudinal temperature gradients an early permian sakmarian reconstruction is used to evaluate the performance of the technique when the equator to pole temperature gradient was steep more like today but all major land masses had merged to form one large supercontinent pangea for both the maastrichtian and sakmarian the model produced more detailed retrodictions of surface air pressure and precipitation continuity than previously published paleoclimate reconstructions the results compare favorably with the known distribution of climatically sensitive sediments such as coals evaporites and phosphorites although the model considers complex relationships among land and sea distribution air pressure surface winds ocean currents and specific precipitation mechanisms it is still relatively simple and easy to apply therefore it is an excellent learning tool for the student of paleoclimate and should be an important technique to complement other methods of paleoclimate reconstruction

fault deformation mechanisms and fault rocks in micritic limestones examples from corinth rift normal faults abstract a multidisciplinary study investigates the influence of different parameters on fault rock architecture development along normal faults affecting non porous carbonates of the corinth rift southern margin here some fault systems cut the same carbonate unit pindus and the gradual and fast uplift since the initiation of the rift led to the exhumation of deep parts of the older faults this exceptional context allows superficial active fault zones and old exhumed fault zones to be compared our approach includes field studies micro structural optical microscope and cathodoluminescence geochemical analyses 13 c 18 o trace elements and fluid inclusions microthermometry of calcite sin kinematic cements our main results in a depth window ranging from 0 m to about 2500 m are i all cements precipitated from meteoric fluids in a close or open circulation system depending on depth ii depth in terms of p t condition determines the development of some structures and their sealing iii lithology marly levels influences the type of structures and its cohesive non cohesive nature iv early distributed rather than final total displacement along the main fault plane is the responsible for the fault zone architecture v petrophysical properties of each fault zone depend on the variable combination of these factors

demersal habitat of late cretaceous ammonoids evidence from oxygen isotopes for the campanian late cretaceous northwestern pacific thermal structure comparison of oxygen isotope data for exceptionally well preserved cooccurring plankton and benthos from the campanian of hokkaido japan with nine species of ammonoids clearly indicates the demersal nektobenthic habitat of ammonoids unlike nautilus the ammonoids studied did not engage in significant short term vertical migrations in the water column the new foraminiferal isotopic data suggest that sea surface and sea bottom temperatures were 26 and 18 c respectively at 40 n in the campanian northwestern pacific the temperatures were significantly warmer than those in the modern northwest pacific this finding provides the first reliable evidence for the warm late cretaceous mid latitude north pacific isotopic analyses of ammonoids show that the average calcification temperature of all ammonoid shells analyzed was 19 c comparable to those of cooccurring benthos none of these ammonoids display calcification temperatures equivalent to those of planktonic foraminifers

thermal evolution of cretaceous tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels 1 the evolution of subtropical 30 35 n upper ocean temperatures through the cretaceous is inferred from the oxygen isotope compositions of 64 fish teeth enamel coming from the western tethyan platform mean 18o values of 22 at the berriasian valanginian boundary decrease with oscillations to 18 5 around the cenomanian turonian boundary and progressively increase to 21 5 by the end of the cretaceous the similarity of this oxygen isotope curve for bioapatites from platform environments with those for foraminifera and bulk carbonates that were deposited in deeper waters and at other paleolatitudes indicates that they record global climatic signals major cooling events at the million year scale can be distinguished 1 at the berriasian valanginian boundary and 2 during the earliest late valanginian a third cooling event is detected during the earliest aptian these events already proposed as icehouse interludes during the lower cretaceous are also recorded at subtropical latitudes a progressive warming is identified from the aptian to the cenomanian turonian interval that corresponds to a thermal optimum and then upper ocean temperatures decreased to the maastrichtian minimum isotopic temperatures range from 15 c to 28 c assuming a 18oseawater of 1 for an ice free world taking more realistic 18oseawater values of 0 for tropical waters during glacial periods within the berriasian valanginian interval and earliest aptian or with above average salinities possibly the maastrichtian temperatures are increased by 4 5 c temperature differences between climatic extremes of the valanginian and cenomanian turonian are estimated to have been 10 c latitudinal thermal gradients for the albian cenomanian turonian and maastrichtian were 0 2 0 3 c latitude and thus weaker than modern oceanic values at about 0 4 c latitude

interference between pluton expansion and non coaxial tectonic deformation three dimensional computer model and field implications abstract structures in orogenic belts are greatly controlled by interactions between pluton related and tectonic related strain fields however many aspects of the geometry and evolution of these structures are poorly known for example 1 what is the geometry of these structures if regional deformation is coaxial 2 how does this geometry change with progressive deformation this paper describes a three dimensional simulation of strain shape and magnitude as well as foliation and lineation patterns formed by interactions between pluton expansion and homogeneous coaxial deformation this simulation suggests that interactions between pluton expansion and regional uniaxial shortening generate patterns that are distinct from the patterns produced by regional uniaxial extension or regional non coaxial deformation for example shortening produces doughnut shaped constrictional rings about the pluton whereas extension produces apple shaped flattening regions around the pluton in addition shortening produces one continuous doughnut shaped low strain region around the pluton on the other hand extension creates two separate ellipsoidal low strain regions at the ends of the pluton furthermore shortening forms foliation rings that have triangular two dimensional sections and lineation is concentric around the axis of maximum shortening in contrast extension produces two separate foliation and lineation cones at the ends of the pluton all these structural and strain elements migrate away from the pluton with increasing expansion rates and towards the pluton with increasing tectonic deformation rates although structural studies around plutons should always integrate microstructural radiometric and field measurements simulation generated patterns can be used to evaluate 1 origin geometry and evolution of structures around plutons 2 mechanisms that explain inclusion trails within porphyroblasts 3 contribution of pluton related strains to strains measured in the country rock and 4 type and three dimensional orientation of regional kinematic schemes

cenomanian palaeotemperatures derived from the oxygen isotopic composition of brachiopods and belemnites evaluation of cretaceous palaeotemperature proxies sixty low magnesium calcite samples from cenomanian articulate brachiopods belemnites and oysters from the epicontinental shelf sea of europe were geochemically and microscopically studied in order to evaluate their preservation and potential as carriers of palaeoenvironmental information the sampled localities in northern spain germany and southern england cover the transition between subtropical 25 30 n and temperate 33 38 n climates mean cenomanian salinity adjusted palaeotemperatures of diagenetically unaltered terebratulid and rhynchonellid brachiopods are 25 5 1 3 c in spain and 19 4 1 9 c in southern england the resulting low to mid latitude meridional temperature gradient of 0 7 c per degree latitude is similar to the gradient today and suggests modern heat transport values for cenomanian low latitudes oxygen isotopic composition of unaltered specimens of the upper cenomanian belemnite praeactinocamax plenus mean 0 2 is enriched in 18o by 1 in comparison to brachiopod shells correspondingly upper cenomanian palaeotemperatures derived from belemnite calcite 13 0 1 3 c underestimate modelled mid latitude sea surface temperatures by 6 c since p plenus occurs as boreal pulse fauna during a short interval in the late cenomanian its heavy oxygen isotopic composition can be attributed either to migration from a cooler and or deeper water mass or to unknown vital effects

diapir driven crustal convection decompression melting renewal of the magma source and the origin of nested plutons abstract this paper studies numerically the rise of diapirs and the consequences of diapir driven crustal flow the ascent of diapirs imposes a convective flow pattern concentrated mostly in the low viscosity lower crust in which the rocks immediately surrounding the diapir are dragged upwards and rocks a few radii to the sides of the diapir are pushed downwards to fill the gap left by the rising mass there are two main consequences of this flow one warm and water undersaturated rocks may undergo decompression melting when dragged upwards this is shown to enhance the ability of a diapir to intrude the crust because the partially molten wall rocks gain buoyancy and add to the total buoyancy of the diapir which regains part of the energy it spent on heating and dragging the surroundings two the downward flow of rocks renews the magma source with potentially fertile rocks which may undergo melting and give rise to a new diapir which will follow the same path as the first one and repeat the process giving rise to a sequence of diapirs whereas source renewal is a direct result of diapirism magma transport through dykes leads to the accumulation of refractory restite in the source which will eventually prevent further melting diapirism and decompression melting may lead to strong recycling of the lower crust and give rise to large volumes of melt sequential diapirism may explain nested plutons and multipulse mid to upper crustal batholiths

cretaceous climatic oscillations in the bering area alaska and koryak upland isotopic and palaeontological evidence abstract new isotopic palaeotemperatures estimated from 18 o values of early albian latest campanian and early maastrichtian ammonoid shells of southern alaska as well as our previously published data on the cretaceous of the koryak upland have been used to reconstruct palaeonvironmental changes in the bering area significant seasonal contrast marked in alaska and the adjacent area during the early albian as well as the coniacian was partly connected apparently with the possible penetration of cooler waters from the polar area via the strait of alaska data suggest that the bering land bridge existed during the post aptian cretaceous with the exception of the early albian and coniacian both the stable isotope and the floral data on the post aptian cretaceous of the bering area suggest the existence of warm climatic conditions in the late albian latest cenomanian coniacian santonian to early campanian latest campanian and also late early maastrichtian recurrent terrestrial cooling in northern alaska reflected in the composition of corresponding floras took place possibly because of a barrier to poleward oceanic heat transport via the western interior seaway wis of north america during the turonian and santonian through early campanian then during the late maastrichtian through danian