field measurements of wet deposition in an extended region of complex topography a model designed to predict the enhancement of rainfall and the wet deposition of aerosol in complex terrain has been extended and compared with field data the results of five separate field studies performed over an extensive region of complex terrain in northern england are presented and compared with the model predictions it is found that the main features of the data are predicted by the model in widely varying conditions but the full details of a particular case study cannot be reproduced quantitatively owing to the complexities of the meteorology over the extended distances and collection periods the main physical processes controlling the deposition pattern have been established and it is concluded that a simple model of the seeder feeder process is able to give reasonable descriptions of deposition patterns in complex terrain both for individual episodes and for longer period averages

igneous and metamorphic petrology of the eclogitic seljeneset meta anorthosite and related jotunites western gneiss region norway abstract the seljeneset meta anorthosite consists of deformed and metamorphosed anorthosite and mafic rocks is situated in the high grade western gneiss region wgr of norway and is adjacent to the 1 52 ga flatraket quartz monzonite mangerite the wgr was metamorphosed to eclogite fades during caledonian tectonism 414 16 ma ago the meta anorthosite contains 46 57 wt sio 2 and displays chondrite normalized ree patterns typical of anorthosite indicating that metamorphism did not significantly affect ree abundances norms indicate that igneous anorthosite consisted of 90 modal plagioclase minor mafic silicates and 1 fe ti oxide mafic rocks 43 48 wt sio 2 are rich in total fe 2 o 3 13 20 tio 2 3 4 and p 2 o 5 1 3 poor in cr jotunites which are characteristic of proterozoic anorthosite mangerite complexes jotunite originally consisted of 50 modal andesine 25 mafic silicates 10 fe ti oxide and up to 7 apatite ree patterns of jotunite are highly variable which reflects variable igneous abundances and modification by metasomatism filter pressing of residual liquid trapped between cumulus plagioclase may have been important in the evolution of anorthosite and jotunite anorthosite contains ultramafic xenoliths high mgo cr and ni and depleted in lree which suggests that some mantle derived peridotite was present in the baltic crust by mid proterozoic time this may extend the crustal history of norwegian garnet peridotites by over one billion years seljeneset rocks display evidence of retrogression from eclogite through amphibolite facies meta anorthosite consists of ovoidal clots of margarite quartz plagioclase and relict kyanite set in a matrix of zoisite clinozoisite plagioclase quartz hornblende and biotite phase equilibria analysis of sequential assemblages shows that meta anorthosite records a retrograde p t path from 15 17 kbar to 4 3 8 2 kbar at 450 600 c mafic rocks vary from moderately well preserved eclogite through varieties containing symplectite to dynamically recrystallized amphibolite in one sample the rare na ca amphibole magnesio alumino taramite appears to be part of the eclogite assemblage calculations indicate eclogite formation at p 16 18 kbar at 750 c some mafic rocks contain veins and segregations of biotite muscovite pyrite allanite and zircon that considered together with geochemical data indicate metasomatic introduction of k rb ba ga s and rare earth and other high field strength elements by channelized fluids during retrogression the seljeneset meta anorthosite associated jotunites and adjacent flatraket quartz monzonite likely constitute a single complex here named the nordpollen plutonic complex this complex was emplaced 1 52 ga ago metamorphosed to eclogite facies during silurian continent continent collision largely retrograded to amphibolite facies during uplift of the orogen and locally metasomatised during retrogression

magmatic and metamorphic controls on chemical variations within the eiksunddal eclogite complex sunnmore western norway the eiksunddal eclogite complex is one of the larger group b country rock eclogites within the western gneiss region wgr of norway whole rock chemical data suggest a magmatic origin for the rocks within the eclogite complex the chemical variations among the eclogitic rocks were controlled by accumulation of olivine fo80 and plagioclase an70 and probably magnetite the composition of the interstitial trapped liquid is derived by linear regression methods and is a high al orthopyroxene normative basalt the most likely conditions of crystallization are t 1150 c p 10 kbar the al rich nature of the interstitial liquid may have implications for the formation of anorthosites and leucogabbros associated with similar mafic rocks elsewhere in the wgr trace element characteristics are compatible with a continental origin of these rocks during the subsequent metamorphic history the marginal parts of the complex have suffered variable degrees of contamination abundant amphibole inclusions in large garnets in garnet websterites suggest local hydration at pre eclogitic stages this may be associated with introduction of radiogenic sr as previously reported by w l griffin and h k brueckner during prograde metamorphism alkali exchange occurred during growth of garnet clinopyroxene and biotite at the expense of pargasitic amphibole and orthopyroxene the most extensive metasomatism however was probably associated with the introduction of fluid during amphibolitization retrogression of the eclogitic rocks three model reactions eqs 5 7 qualitatively explain the relation between degree of retrogression and the observed metasomatic effects whether si and ca are gained or lost during retrogression seems to be controlled by the extent of amphibole growth in diopside plagioclase symplectites initially formed by breakdown of omphacite alumina has behaved in a more or less immobile way during metasomatism low mobility of al is also reflected by the formation of subsilic al rich amphiboles and al rich plagioclase during garnet breakdown this demonstrates the importance of kinetic factors in controlling mineral chemistry

sequence stratigraphic significance of sedimentary cycles and shell concentrations in the upper jurassic lower cretaceous of kachchh western india abstract upper jurassic and lower cretaceous siliciclastic shallow water sediments of the kachchh basin western india form strongly asymmetric coarsening upward cycles which are interpreted as recording changes in relative sea level deepening shallowing cycles these cycles correspond to depositional sequences in which deposits of the lowstand systems tract are not present the sequence boundary coinciding with the transgressive surface shell concentrations are found in the transgressive lags at the base of the transgressive systems tract tst in the maximum flooding zone mfz and at or close to the top of the highstand systems tract they belong to six assemblages five of them dominated by large bivalves such as seebachia herzogina gryphaea gervillella megacucullaea pisotrigonia and indotrigonia the sixth by the coral amphiastraea three types of shell concentrations can be distinguished that differ from each other in a number of ecological and taphonomic features such as species diversity preservation quality orientation in cross section percentage of disarticulation and degree of biogenic alteration characteristic features of concentrations at the base of the tsts are moderate time averaging sorting a preferred convex up orientation and nearly total disarticulation of shells they are suggestive of an environment in which reworking and local transport were frequent events similar features are shown by concentrations near the tops of the hsts except that there shells were largely concentrated in lenses and in pavements rather than in beds as in the transgressive lags associated sedimentary structures indicate deposition above fair weather wave base in a high energy environment concentrations occurring in the mfz in contrast are autochthonous and highly time averaged having accumulated during times of low rates of sedimentation below storm wave base this is supported by their high preservation quality comparatively high percentage of articulated shells shells of infaunal organisms commonly preserved in life position biogenic alteration being the most important taphonomic agent the dominant elements of these shell concentrations i e seebachia megacuccullaea and indotrigonia in the upper jurassic and pisotrigonia in the lower cretaceous are endemic to the ethiopean faunal province and belong to lineages that rapidly evolved during this time period

eclogite facies relics and inferred ultrahigh pressure metamorphism in the north dabie complex central eastern china mineral assemblages and microstructures of a newly identified retrogressed eclogite sensu lato in the north dabie complex ndc central eastern china indicate early very high pressure metamorphic relics preserved in a dominant amphibolite facies host where no eclogite sensu stricto has been positively identified before the investigated eclogitic rock shows distinct multistage recrystallization with granulite and amphibolite facies assemblages overprinting eclogite facies relics the minimum temperature for the eclogite facies metamorphism is estimated to be 800 820 c a spectacular microstructure of oriented quartz needles 2 20 m wide 5 200 m long in matrix ca na clinopyroxene implies the prior existence of a non stoichiometric supersilicic omphacite stabilized at ultrahigh pressure uhp 25 kbar conditions although no coesite or coesite pseudomorphs have been found in the samples the absence of coesite may be due to the lack of free silica at uhp conditions or the consumption of silica during retrograde reactions the inferred uhp conditions metamorphism is further supported by sm nd ages that are equivalent to triassic metamorphic ages from uhp eclogites in the southeastern dabie mountains this finding expands the uhp terrane northward about 50 km spatial distribution of subduction collision related uhp rocks includes parts of the ndc

a gabbro to eclogite transition on flemsoy sunnmore western norway the migmatitic gneisses on the nordoyane islands western norway enclose abundant inclusions of coronitic gabbros and different types of country rock eclogites gabbros on flemsoy show a prograde step wise transition to eclogite via a transitional stage in which garnet and orthopyroxene form coronas between igneous olivine and sodic plagioclase relics after igneous plagioclase cumulates eclogitization proceeds by a complex set of continuous and discontinuous reactions opx and spinel form as transient phases but are consumed in various omphacite forming reactions during eclogite recrystallization relict igneous clinopyroxene shows a continuous increase in jd content while garnet becomes less calcic and more homogeneous from the corona stage to recrystallized eclogite the reactions are strongly diffusion controlled and have been enhanced locally by oxidation and the presence of a fluid phase and deformation while low strain areas of the gabbros remained coronitic whole rock chemistry mineral parageneses and calculated p t conditions are similar for the gabbroeclogites and two types of country rock eclogites some of the layered country rock eclogites appear to have been derived from the coronite bodies p estimates are in the order 15 20 kbar while kgarcpxd values suggest maximum t values of 750 60 c for the eclogite metamorphism in the area

importance of fracturing during retro metamorphism of eclogites presented textural and petrological data show that the deep to intermediate continental crust may fracture and that microfractures are the locus of fluid and mass transfer necessary for retrograde metamorphism kyanite eclogites from ulsteinvik norway underwent partial retrogression to granulite and amphibolite facies assemblages during near isothermal exhumation from depths equivalent to more than 2 0 gpa at temperatures of 700 800 c plagioclase bearing assemblages rich in hydrous phases formed along margins of eclogite lenses and along mesoscopic fracture systems hydrated zones are from 1 50 cm thick with adjacent wall rock eclogite replaced by symplectites at a low degree of reaction the secondary minerals in the wall rock are found along intra and intergranular microfractures typically 50 100 m wide minerals filling the microfractures include orthopyroxene plagioclase spinel in garnet plagioclase sapphirine plagioclase corundum and plagioclase spinel in kyanite and diopside plagioclase in omphacite the microfractures are often arranged en echelon and are connected through microfaults releasing bends filled with amphibole and spinel form along microfaults in garnet the faulting and fracturing caused localized chemical change in garnet the damage zones close to faults are enriched in feo and mno with steep compositional gradients 8 wt feo over 20 m these feo and mno enriched zones form wedge like structures around the tip of the faults horsetail structures and rose or flame like structures at sticking points along faults they may represent examples of stress induced chemical transport during fracture propagation the change from dry to amphibole bearing assemblages at the tip of the fracture and fractures ending in splays of fluid inclusions trails reflect the involvement of a fluid phase during fracture propagation this suggests that the dry granulite facies retrogression was also driven by fluid infiltration and that metamorphism at depth in collision zones may not be controlled by pressure and temperature alone

intermittent euxinia reconciliation of a jurassic black shale with its biofacies isorenieratane is ubiquitous in the organic carbon rich peterborough member callovian uk of the oxford clay formation indicating a temporal overlap of the euphotic and sulphidic zone in the water column

siluro devonian alpine reefs and pavements palaeozoic sediments of austria are separated by the periadriatic fault into eastern alpine upper middle and lower austroalpine and southern alpine units we herein present six case studies showing up the different development of shallow marine communities with special regard to carbonate factories and shell pavements occurring in both regions during the siluro devonian time span upper silurian upper devonian deposits of the eastern alps comprise accumulations of serpulid tubes southern burgenland and septatrypa pavements amphipora mounds coral stromatoporoid biostromes and stachyodes auloporoid beds regarded as pioneer reef communities graz palaeozoic respectively lower silurian strata of the southern alps consist of pelagic sediments persisting to the upper silurian and therefore differ from contemporaneous successions in the eastern alps intercalated in ludlow orthocerid limestone beds cardiola pavements appear carnic alps within the lower devonian sequence mounds were built by baffling calcareous algae and tabulozoan communities coral stromatoporoid patch reefs occur during the pragian givetian and frasnian stages investigation of silurian upper devonian reefs and reef related successions within austria s borders has a long tradition a survey of these developments is compiled in a stratigraphic scheme representing all non metamorphic units of austria generally all palaeozoic strata suffered differing post depositional destruction i e tectonic splitting dolomitization metamorphic overprint etc during variscan and alpidic orogenesis thus complicating or limiting to some respect their investigation from southern burgenland the graz palaeozoic the carnic alps and the karawanken mountains reefs which cover a time segment of some 55 ma are presented in overview stratigraphical framework of dismembered

smnd isotopic systematics of a gabbro eclogite transition abstract sm nd isotopic systems have been studied in 1 a sequence of coronitic olivine gabbros showing different degrees of transition to eclogite 2 coronitic leuco gabbro norite and 3 country rock eclogite all from the nordoyane brattvag area western norway isochrons defined by combinations of whole rock samples and relict igneous phases give ages of 1198 56 and 1289 48 ma olivine gabbro and 926 70 ma leuco gabbro norite and have been interpreted in terms of two different episodes of igneous intrusion in gabbro with advanced corona formation relict augite tends to retain its original nd isotopic composition while plagioclase may show selective disturbance related to recrystallization and partial replacement by garnet in completely eclogitized samples there is a correlation between the degree of isotopic equilibrium and microstructural equilibrium whole rock eclogites occurring within gabbro are characterized by pseudomorphs after igneous phases and preserve original igneous nd isotopic composition results for eclogite minerals suggest caledonian ages but these phases have not achieved complete isotopic equilibrium in contrast nd isotopic systems in texturally equilibrated and strongly deformed eclogite within adjacent gneisses have been disturbed on a whole rock scale minerals from an external eclogite define a sm nd isochron with an age of 400 16 ma which is interpreted to date synkinematic eclogite equilibration at high p and t conditions

diffusion between olivine and spinel application to geothermometry abstract heating experiments were carried out at 1100 c and 1200 c under controlled oxygen fugacity on olivine spinel assemblages from new caledonia this mineral pair constitutes a perfect experimental material for such studies the result was a marked change in chemical composition of the minor phase olivine it becomes enriched in iron and chromium and the magnesium and nickel contents decrease careful studies of the influence of oxygen fugacity show that though it has a strong effect on the rate of re equilibration it does not affect the equilibrium composition of the phases the stability limits of the mineralogical assemblage used are also examined our results show the possibility of an important subsolidus re equilibration in natural assemblages containing olivine and spinel a new equation for the geothermometer based upon fe 2 mg 2 partitioning between olivine and spinel is proposed and some applications discussed

palaeoenvironmental significance of storm coquinas in a lower cretaceous coastal lagoonal succession vectis formation isle of wight southern england thin bioclastic limestone beds coquinas in the vectis formation wealden group lower cretaceous of the isle of wight southern england exhibit a range of biofabrics and internal stratigraphies these features are attributed to both simple and complex storm deposition of allochthonous biogenic and siliciclastic materials in coastal lagoons and on adjacent mudflats these modes of deposition facilitated preservation of dinosaur trackways desiccation cracks shallow tier trace fossils and in situ bivalve colonies through rapid burial the coquinas thus preserve a record of surficial muds commonly lost through reworking the principal components of the coquinas comprise dispersed elements from within the argillaceous background facies some of these beds are laterally traceable for up to 27 km providing the foundations for a high resolution event stratigraphic framework

a three dimensional model of airflow and orographic rainfall enhancement a three dimensional model of airflow over hills has been used in conjunction with a two dimensional model of orographic rainfall enhancement this development has allowed the accurate production of rainfall contour maps in areas of complex terrain a comparison has been made using a variety of atmospheric stability profiles between the wind fields and rainfall distributions over a bell shaped hill and those over a two dimensional ridge of similar height the results show that in conditions of either stably stratified air or with an inversion layer aloft three dimensional airflow effects can lead to much reduced rainfall over a bell shaped hill it is shown that in such situations the use of a two dimensional approximation can introduce significant errors an example is presented of the rainfall distribution in complex hill terrain over south kintyre on the western coast of scotland

palaeoenvironments and palynofacies of a pulsed transgression the late devonian and early dinantian lower carboniferous rocks of southeast wales two boreholes in the vale of glamorgan have provided new data on the nature of the early dinantian courceyan transgression in south wales this transgression is manifested by the transition from the largely fluviatile late devonian upper old red sandstone quartz conglomerate group to the predominantly marine early dinantian lower limestone shale group the marine sequence comprises five shoaling upwards cycles constructed from a suite of sedimentary lithofacies which record deposition in environments ranging from coastal plain peritidal lagoon barrier and embayment to subtidal open marine shelf each cycle represents a pulse of the transgression and each successive pulse appears to have been larger than the preceding one introducing progressively less restricted and more distal marine environments thirty seven samples were processed for palynological analysis miospore biozonation supports the cycle correlations between the two boreholes suggested by the sedimentary event stratigraphy detrital kerogens from the samples comprise both terrestrially derived and marine types in varying proportions each kerogen type is described as well as the size sorting and preservation of each assemblage a palynofacies profile is presented for eachof the depositional environments recognized

carbonate dissolution in nearshore terrigenous muds the role of physical and biological reworking because shallow marine sediments generally underlie waters which are saturated with respect to arago nite and calcite physical chemical dissolution of carbonate in these environments is sometimes discounted the present investigation as well as others before it show such an assumption to be unwarranted in this case study of terrigenous mud deposits from long island sound u s a demonstrates extensive dissolution of molluscan shell debris near the sediment water interface net buildup of carbonate varies significantly between different regions of the sound despite fairly uniform production of shell debris and similar total sedimentation rates aside from this apparent discrepancy between rate of supply and net carbonate sedimentation evidence for carbonate dissolution comes from the pitting of shells elevated ca levels in pore water and calculated undersaturation of pore waters with respect to carbonate minerals models of pore water distributions and carbonate supply imply dissolution ra

tectonics of the scandian orogeny and the western gneiss region in southern norway two crust forming events dominate the precambrian history of the western gneiss region wgr at about 1800 1600 ma and 1550 1400 ma the influence of the sveconorwegian orogeny 1200 900 ma is restricted to the region south of moldefjord romsdalen a series of anorthosites and related intrusives are present possibly derived from the now lost western margin of the baltic craton that may have been emplaced in the wgr as an allochthonous unit before the ordovician

microdiamond in high grade metamorphic rocks of the western gneiss region norway three grains of microdiamond were recovered from high grade gneiss exposed in the western gneiss region norway identification and characterization of the diamond grains by raman and infrared spectroscopy indicate the presence of substitutional impurities of h and n primary fluid inclusions in garnet and quartz in the diamond bearing rock demonstrate the evolution of metamorphic volatile fluids from reduced n 2 co 2 compositions during the peak phase of metamorphism to n 2 ch 4 h 2 o bearing compositions during retrograde metamorphism compatible geologic petrologic and fluid composition data imply a metamorphic origin for the microdiamonds if so the metamorphic and fluid conditions recorded by the microdiamonds and gneissic host may be applicable to microdiamond investigations in other high pressure regionally metamorphosed orogens

provenance of microcrystalline carbonate cement in limestone marl alternations lma aragonite mud or molluscs aragonite derived from marine molluscs is evaluated as the source for microcrystalline carbonate cements of limestone marl alternations lma calculations demonstrate that extremely low levels of mollusc derived aragonite well below the production rates of molluscs in modern marine settings could have provided sufficient carbonate to cement examples of ordovician silurian and jurassic lma in non tropical or tropical settings it is likely that even in the palaeozoic molluscs provided sufficient carbonate entirely to source microcrystalline cements of lma autochthonous molluscan aragonite is the only viable aragonite precursor for lma microcrystalline cements of cool water settings where temperatures precluded calcified algae and abiotic carbonate precipitation in calcite seas where mg ca ratios inhibited both abiogenic aragonite precipitation and aragonite generation by calcified algae molluscan aragonite was again the most likely main contributor in some epeiric seas where brackish wedges switched off the shallow water carbonate mud factories molluscan aragonite is the parsimonious source of carbonate for lma microcrystalline cements

a reassessment of facies and faunas in the type llandeilo ordovician wales abstract detailed analysis of the lithological and faunal successions of the type llandeilo forms the basis of an evaluation of the sequence of depositional environments and a quantitative description of the entombed faunas comprising mainly brachiopods trilobites and ostracods recorded distribution patterns confirm the validity of the existing trilobite trinucleid biostratigraphic zones but emphasize the importance of benthic bivalved taxa which are particularly abundant in the lower llandeilo groups of assemblages comprising localized faunules or associations despite exhibiting evidence of transportation are readily identified as representative of more widespread contemporary palaeocommunities recently described from wales and the welsh borderland the relationship between these palaeocommunities and the transgressive llandeilo sequence indicates a shoreface to open shelf zonation of ecosystems controlled primarily by substrate conditions rather than depth

rainfall redistribution over low hills due to flow perturbation abstract a simple potential flow model is developed for airflow over low hills the model readily allows incorporation of simple rain microphysics so that drop trajectories can be traced in the region of a hill complex rainfall intensity variations are found in the horizontal and in the vertical and a straightforward modification to the model allows for time dependence to be studied the model is shown to serve as a useful diagnostic tool to describe rain drop redistribution due to perturbed airflow in particular increased rainfall is predicted in the lee of hill peaks and depleted rainfall is predicted on ridges the redistribution effects dominate at low levels in contrast to predictions based on seeder feeder enhancement comparison with field measurements shows good qualitative agreement over low hills and in some cases close quantitative agreement redistribution of rain appears to be a significant process that should be considered in rainfall interpolation and prediction schemes involving hilly terrain

patterns in bioclastic accumulation through the phanerozoic changes in input or in destruction evolutionary changes in the ecology and diversity of organisms that produce and destroy calcareous skeletons suggest that bioclastic concentrations themselves might have changed in nature through the phanerozoic empirical data from marine siliciclastic records of ordovician silurian jurassic and neogene ages indicate a significant increase in the thickness of densely packed bioclastic concentrations over geologic time from a primarily thin bedded brachiopod dominated record in the ordovician silurian to a mollusk dominated record with many more and thicker shell beds in the neogene jurassic shell beds vary in thickness with the paleozoic or modern affinities of the chief constituents suggesting along with other evidence that the phanerozoic increase was determined neither by diagenesis nor by a shift in taphonomic conditions on the sea floor but rather by the evolution of bioclast producers namely groups with 1 more durable low organic skeletons 2 greater ecological success in high energy habitats and 3 on the basis of indirect evidence higher rates of carbonate production these results suggest that 1 reproductive and metabolic output has increased in benthic communities over time and 2 the scale of time averaging in benthic assemblages has increased owing to greater hard part durability of modern groups

environmental oxygen fluctuations and the adaptive response of marine benthic organisms oxygen depletion is widespread in modern and ancient benthic environments most modern examples exhibit a significant cyclic fluctuation in o 2 availability ranging from tidal to seasonal cycles and longer term periods e g el nino in contrast only long term changes have been generally recognized in ancient environments benthic organisms adapt along two pathways 1 to low o 2 values and free h 2 s including chemosymbiosis 2 synchronization of individual life cycles to the o 2 fluctuation cycle by living as planktonic larvae in oxygenated surface waters using oxygenated periods in bottom waters during the adult stage examples of both adaptive pathways can be recognized in the benthic faunas of fossil oxygen controlled environments thus recording short and longer term fluctuations

taphonomic windows and molluscan preservation recent studies on silicified fossil biotas have suggested that substantial skewing of the molluscan record resulted from early aragonite dissolution in mid outer carbonate ramp settings if those rare skeletal lagerstatten are representative then the quality and completeness of the molluscan record are thrown into doubt yet database studies suggest that the bivalve fossil record is actually relatively complete if so then biodiversity must be captured by other processes that preserved shells vulnerable to early dissolution and which operated on a relatively high frequency i e less than the species duration for bivalves storm beds shell plasters and submarine hardgrounds are identified as fossil deposits that can preserve the labile aragonitic component of the fauna and thus represent potential taphonomic windows many storm event beds include rich accumulations of shelly benthos differences between storm bed faunas and those of the background facies could reflect transportation effects however some storm bed assemblages are rich in originally aragonitic infaunal bivalves that are not represented in background facies or more proximal shelf equivalents and here rapid burial and removal of organic matter by winnowing may be the keys to aragonite shell preservation despite palaeozoic to cenozoic changes in the thickness and frequency of shell beds that reflect the predominant bioclast producers shallow infaunas are commonly concentrated together with epifauna in such deposits some low energy organic rich mud dominated settings are associated with preservation of aragonitic molluscs infaunal bivalves are a prominent component of shell plasters or pavements in such settings linked to episodic bottom water anoxia decaying algal blooms drew the redox boundary up above the sediment water interface and brought populations of infaunal bivalves to the surface where they died isolated from the oxic taphonomically active zone the shells were not dissolved and were buried as thin shell layers in similar settings aragonitic shells were preserved as moulds through early pyritisation or even through preservation of original shell aragonite in oxic environments bioturbational reworking of surface sediment destroyed moulds of aragonitic shells after early dissolution in some hardgrounds these delicate moulds were preserved due to synsedimentary cementation probably using carbonate released by aragonite dissolution the examples included here come from both intervals of calcite and aragonite seas and it is not possible to assess whether the saturation state with respect to aragonite of the ambient sea water played a role in the selective removal of aragonitic shells while taphonomic windows may have captured the diversity of individual groups it is clear from quantitative data involving skeletal lagerstatten that the scale of loss from early aragonite dissolution has drastically altered the trophic composition of some fossil assemblages commonly used as the basis for reconstructions of past communities

airflow over hills of moderate slope a three layer model is presented this describes the flow on an inversion capped boundary layer over hills of moderate size and slope the linearized vorticity equation is solved using non linear boundary conditions the pressure field developed in the boundary layer is used to calculate a modified inner region velocity field jackson and hunt 1975 a low level inversion with height i 2h is found to decrease the speed up near the ground when i 2h the flow of the inversion layer shows an increasing tendency to be subcritical this leads to a much increased speed up increasing the stability of air above the inversion increases the asymmetry of the flow this causes an upwind lull and a subsequent rapid increase in the flow speed with very high wind speeds at the summit and downwind comparison of the theory with simple observations made on great dun fell cumbria shows encouraging agreement

incomplete high p t metamorphic transitions within the kvamsoy pyroxenite complex west norway a case study of disequilibrium the kvamsoy pyroxenite complex consists of olivine websterite olivine gabbro and leucogabbro norite which have been subjected to regional high p t hpt metamorphism the metamorphism has resulted in a range of disequilibrium textures with the development of coronas and pseudomorphism of the igneous phases reactions between felsic and mafic mineral domains have been controlled by variable and selective diffusion of elements resulting in a variety of local plagioclase breakdown reactions and in significant compositional variations for the product garnet restricted diffusion favours transient reaction stages with garnet spinel corundum zoisite after calcic plagioclase in olivine gabbro and olivine websterite and garnet spinel kyanite quartz sodic plagioclase in leucogabbro norite complete hpt reaction has produced garnet pyroxenite which consists of garnet diopside hornblende zoisite in gabbroic rocks while amphibolitization continued during the cooling and uplift history grt ky pl qtz geobarometry suggests pressures in the range 13 16 kbar for t 750 c comparable with the regional eclogite forming metamorphism

metamorphic evolution of the eiksunddal eclogite complex western norway and some tectonic implications the metamorphic evolution of the western gneiss region of norway wgr can be evaluated from examination of eclogites formed as an integral part of the gneiss terrain ie in situ petrologic data from one of the larger country rock eclogites within the northwestern part of wgr have been used to construct a p t t path for this crustal volume textural relations as well as mineral composition and zonation suggest an early period of amphibolite facies conditions followed by movement along a very steep positive p t gradient towards very high pressure p 25 kb and moderate temperature t 600 c orthopyroxene coexisting with garnet at such conditions was poor in al 0 5 wt al2o3 and is preserved in the cores of orthopyroxene grains in garnet websterites the increasing al content of orthopyroxene towards garnet and increasing edenite substitution rimwards in zoned amphiboles suggest a period of decompression accompanied by heating towards the metamorphic maximum at t 750 c p 20kb garnet zoning reflects a general prograde history but the reactions that control the zoning are insensitive to pressure changes jadeitic pyroxenes may have formed in the gneisses at p max but would revert to plagioclase subsequent to the metamorphic maximum giving rise to the observed mineralogy further decompression and cooling continued towards high rank amphibolite facies conditions this p t t path reflects crustal thickening to 80 90 km during caledonian time the uplift path is qualitatively similar to theoretically derived paths in which uplift is assumed to be controlled by erosion however uplift following the metamorphic maximum may have been accelerated by a period of suture progradation

kyanite eclogite to amphibolite fades evolution of hydrous mafic and pelitic rocks adula nappe central alps in the southern adula nappe central alps two stages of regional metamorphism have affected mafic and pelitic rocks earlier eclogite facies with a regional zonation from glaucophane eclogites to kyanite hornblende eclogites was followed by a tertiary overprint which varied from greenschist to high grade amphibolite facies despite a common metamorphic history contrasting equilibration conditions are often recorded by high pressure mafic eclogite and adjacent predominantly lower pressure pelite assemblages this pressure contrast may be explained by different overprinting rates of the two bulk compositions during unloading the rates are controlled by a mechanism in which dehydrating metapelites provide the h2o required for simultaneous overprinting of enclosed mafic eclogites by hydration

palaeoecological evidence for early aragonite dissolution in ancient calcite seas it has been proposed that shallow carbonate seas of upper ordovician and jurassic ages precipitated calcite as the primary calcium carbonate phase1 3 unlike such settings today it is expected that such seas were undersaturated with respect to the more soluble aragonite so that aragonitic invertebrate skeletons would have tended to dissolve here we describe examples in which this seems to have been the case our evidence consists of submarine cemented horizons in which aragonite fossils have been dissolved out to leave open moulds the walls of the moulds are encrusted by contemporaneous organisms confirming the early timing of the aragonite dissolution

middle triassic anisian diversified bivalves depositional environments and bivalve assemblages in the leidapo member of the qingyan formation southern china abstract the middle triassic anisian leidapo member of the qingyan formation which crops out in southwestern china consists of basin floor and slope deposits with abundant benthic fossils and records two transgressions and one regression the well preserved bivalves are grouped into four assemblages the allochthonous cassianella elegantinia and protostrea cassianella assemblages as well as the autochthonous palaeonucula assemblage are found in slope deposits the allochthonous assemblages exhibit several modes of occurrence in sediment gravity flow deposits the parautochthonous posidonia assemblage is preserved in slope and basin deposits the genus level compositions of these bivalve assemblages are similar to those from the early carnian of tethyan europe it is probable that a significant diversification of bivalves took place in the anisian

metamorphic evolution of norwegian country rock eclogites as deduced from mineral inclusions and compositional zoning in garnets abstract detailed studies of pre early syn and post eclogite mineral associations in some west norwegian country rock eclogites have made it possible to reconstruct their metamorphic evolution pre eclogite stages are represented by various amphibolite facies associations found in the central parts of prograde zoned garnets early and syn eclogite stages are represented by various eclogitic assemblages containing low and high jd omphacites respectively the former located in the intermediate zones and the latter in the outermost rims of prograde zoned garnets and in the matrix post eclogite stages include granulite amphibolite and greenschist facies associations representing replacement phases after higher grade assemblages p t estimates indicate a prograde evolution along an extremely steep p t gradient 7 9 kbar over 100 200 c while the initial post eclogite evolution involved a nearly adiabatic decompression on the order of 10 kbar

a unique permian triassic boundary section from the neotethyan hawasina basin central oman mountains in the wadi wasit area central oman mountains dienerian breccias are widespread these breccias consist mostly of guadalupian reefal blocks often dolomitised and some rare small sized blocks of lowermost triassic bivalve bearing limestones a unique block with a size of about 200 m3 including permian and earliest triassic faunas has been studied in detail the so called wadi wasit block consists of three major lithological units a basal unstratified grey limestone is rich in various reef building organisms rugose corals calcareous sponges stromatoporoids and has been dated as middle permian it is disconformably overlain by well and thin bedded light grey to yellowish coloured limestones rich in molluscs two major lithologies coquina limestone respectively bioclastic limestone unit characterise the shelly limestones their contact seems gradual these two units are well dated they are of griesbachian age and contain three conodont zones the parvus zone the staeschei zone and the sosioensis zone and two ammonoid zones the ophiceras tibeticum zone and an unnamed interval the third unit consists of a grey marly limestone containing neospathodus kummeli basal dienerian it is the first record of well dated basal triassic sediments in the arabian peninsula the coquina limestone is dominated by the bivalve promyalina with some claraia and eumorphotis this bivalve association is interpreted as a pioneering opportunistic assemblage towards the top of the bioclastic limestone unit the faunal diversity increases and contains probably more than 20 taxa of bivalves microgastropods crinoids brachiopods ammonoids echinoid spines ostracods and conodonts the generic diversity of this biofacies exceeds by far any other griesbachian assemblage known our data give new evidence for the geodynamical history for the distal carbonate shelf bordering the hawasina basin a break in the sedimentation characterises the late permian the basal triassic shows a steady transgression and the breccias may record a distinct gravitational collapse of platform margins linked with sea level low stand at the end of induan time late dienerian basal smithian 13ccarb isotopic analyses were performed and yield typical permian values of around 4 for the reefal limestone with a strong negative shift across the permian triassic boundary during the griesbachian values shift positively from 0 5 to 3 1 parallel to an increase in faunal diversity and probably primary productivity the detailed faunal analysis and the discovery of an unexpected diversity give us a new understanding of the recovery of the early triassic marine ecosystem

evolution of metamorphic volatiles during exhumation of microdiamond bearing granulites in the western gneiss region norway fluid inclusions in garnet kyanite and quartz from microdiamond bearing granulites in the western gneiss region norway document a conspicuous fluid evolution as the rocks were exhumed following caledonian high and ultrahigh pressure hp uhp metamorphism the most important of the various fluid mixtures and daughter minerals in these rocks are n2 co2 magnesian calcite n2 co2 ch4 graphite magnesian calcite n2 ch4 n2 ch4 h2o co2 and h2o nacl cacl2 nahcolite rutile also occurs in the n2 co2 inclusions as a product of titanium diffusion from the garnet host into the fluid inclusions volatiles composed of n2 co2 magnesian calcite characterise the ambient metamorphic environment between hp uhp peak and early retrograde metamorphism during progressive decompression the mole fraction of n2 increased in the fluid mixtures as amphibolite facies conditions were reached ch4 and later h2o appeared in the fluids concomitant with the disappearance of co2 and magnesian calcite graphite is ubiquitous in the host lithologies and fluid inclusions thermodynamic modelling of the metamorphic volatiles in a graphite buffered c o h system demonstrates that the observed metamorphic volatile evolution was attainable only if the fo2 increased from c 3 5 0 3 to 0 8 0 3 log units relative to the fmq oxygen buffer external introduction of oxidising aqueous solutions along a system of interconnected ductile shear zones adequately explains the dramatic increase in the fo2 the oxidising fluids introduced during exhumation were likely derived from dehydration of oceanic crust and continental sediments previously subducted during an extended period of continental collision in conjunction with the caledonian orogeny