the flank margin model for dissolution cave development in carbonate platforms the bahama islands contain many abandoned dissolution caves at elevations between two and seven metres above current sea level the development of dissolution caves in tropical carbonate islands is dependent on the position and nature of the freshwater lens lens position is controlled by sea level which in stable carbonate platforms like the bahamas is a function of glacioeustatic sea level still stands caves in the bahamas that are currently subaerial must have developed during past higher sea levels during the late quaternary sea levels higher than present have been relatively short lived and that limits the amount of time that a freshwater lens could be situated at the elevation required for the cave formation the bahama islands are low lying landforms where only aeolian ridges extend to elevations higher than six metres above current sea level past high sea level events greatly reduced the exposed land area of the bahama islands thus also limiting both the catchment for and size of freshwater lenses caves must be younger than the rock in which they are developed most subaerial bahamian caves are found in limestones that are less than 150000 years old development of large dissolution caves under these limitations of time and lens size requires a powerful dissolutional mechanism the mixing of discharging freshwater with tide pulsed incoming marine water under the flanks of emergent dune ridges may have produced the conditions necessary bahamian caves formed by this process are phreatic chambers with complex interconnections and blind tubes their presence demonstrates that significant dissolution can occur rapidly as a result of the mixing of fresh and marine waters beneath small carbonate islands

precise and accurate isotope fractionation factors α17o α18o and αd for water and caso4 2h2o gypsum gypsum caso4 2h2o is a hydrated mineral containing crystallization water also known as gypsum hydration water ghw we determined isotope fractionation factors 17o 18o and d between ghw and free water of the mother solution in the temperature range from 3 c to 55 c at different salinities and precipitation rates the hydrogen isotope fractionation factor dgypsum water increases by 0 0001 units per c between 3 c and 55 c and salinities 150 g l of nacl the dgypsum water is 0 9812 0 0007 at 20 c which is in good agreement with previous estimates of 0 981 0 001 at the same temperature the 18ogypsum water slightly decreases with temperature by 0 00001 per c which is not significant over much of the temperature range considered for paleoclimate applications between 3 c and 55 c 18ogypsum water averages 1 0035 0 0002 this value is more precise than that reported previously e g 1 0041 0 0004 at 25 c and lower than the commonly accepted value of 1 004 we found that nacl concentrations below 150 g l do not significantly affect 18ogypsum water but dgypsum water increases linearly with nacl concentrations even at relatively low salinities suggesting a salt correction is necessary for gypsum formed from brines unlike oxygen isotopes the dgypsum water is affected by kinetic effects that increase with gypsum precipitation rate as expected the relationship of the fractionation factors for 17o and 18o follows the theoretical mass dependent fractionation on earth 0 529 0 001 we provide specific examples of the importance of using the revised fractionation factors when calculating the isotopic composition of the fluids

gypsum precipitation dissolution as an explanation of the decrease of sulphate concentration during seawater intrusion the precipitation of gypsum during the intrusion of seawater in a coastal aquifer is shown to be a possible cause of the decrease of the sulphate concentration with respect to the conservative freshwater seawater mixing observed in many field studies results of previously published laboratory column experiments and the application of a multicomponent reactive transport model show that gypsum precipitates during the first stages of seawater intrusion causing a decrease in sulphate concentration as the resultant front advances the water becomes undersaturated with respect to gypsum when the content of seawater 50 at that point water samples exhibit a deficit of sulphate of several mmol l in the range of the field values reported in papers on intrusion in coastal aquifers thus in addition to bacterial sulphate reduction by organic matter gypsum precipitation is a possible explanation for the non conservative behaviour of sulphate during seawater intrusion

relative displacement between eurasia and north america prior to the formation of oceanic crust in the north atlantic abstract the relative positions of north america and eurasia prior to the opening of the north atlantic can be reconstructed using three independent data sets ocean floor magnetic anomalies and fracture zones the shape of the shelf line at the continental margins of north america and eurasia and the apparent polar wander paths apwps of these two continents together with geological constraints we here examine the internal consistency of these reconstructions discuss the tectonic implications of the inconsistencies and show how all three data sets can be combined to obtain a best fit reconstruction pole in our analysis we find that the combined errors of the new north american and european apwps are smaller for 290 240 ma than at earlier or later times therefore this interval was used rotation poles derived from magnetic anomalies from the north atlantic do not bring the apwps into coincidence a rotation pole located at 88 n 215 e with rotation angle 42 superimposes the two apwps and is reasonably consistent with the geology of the continental margins in the north atlantic the difference between the rotation pole based on apwps and that based on magnetic anomalies probably reflects relative motion of the two cratons between the early triassic and the late cretaceous cratonal germany moving about 800 km to the east relative to north america and norway moving about 500 km northeast relative to greenland this motion is expressed in extension in the north sea and the continental shelves on the other side of the globe in the vicinity of siberia and alaska our reconstruction places cratonal north america farther away from cratonal eurasia than do reconstructions based on north atlantic magnetic anomalies this greater separation is consistent with the presence in the late paleozoic and early mesozoic of a sea way in siberia located in the gap between eurasia and north america the magnitude of this gap is uncertain because of mesozoic deformation in alaska and siberia

the cenozoic denali fault system and the cretaceous accretionary development of southern alaska the juxtaposition of disparate geologic terranes in southern alaska has been previously interpreted to be mainly the result of several hundred kilometers of right lateral offset along the denali fault system in cenozoic time recent geologic investigations in the healy quadrangle strongly suggest that cenozoic horizontal displacements of such magnitude along the denali fault system do not exist in the healy quadrangle isograds and metamorphic facies boundaries of an early late cretaceous metamorphic belt trend across the cenozoic mckinley strand of the denali system without significant horizontal offsets the present geologic makeup of most of southern alaska is primarily the result of the talkeetna superterrane consisting of the previously assembled peninsular terrane and wrangellia colliding with and subsequently being thrust upon the yukon tanana and nixon fork terranes of the ancient north american continent in about middle cretaceous time the leading edge of the talkeetna superterrane faces a wide complexly deformed zone that contains numerous northwestward thrust miniterranes tectonically intermixed with jurassic and cretaceous flysch the flysch is interpreted to have been deposited mostly in the narrowing and subsequently collapsed oceanic basin between the converging continental blocks the postcollisional denali fault system developed in cenozoic time across the already accreted continental margin in eastern alaska along an older cretaceous suture

the role of condensation in the evolution of dissolutional forms in gypsum caves study case in the karst of sorbas se spain abstract the karst of sorbas se spain is one of the most important gypsum areas worldwide its underground karst network comprises over 100 km of cave passages rounded smooth forms condensation cupola and pendant like features appear on the ceiling of the shallower passages as a result of gypsum dissolution by condensation water meanwhile gypsum speleothems formed by capillarity evaporation and aerosol deposition such as coralloids gypsum crusts and rims are frequently observed closer to the passage floors the role of condensation dissolution mechanisms in the evolution of geomorphological features observed in the upper cave levels has been studied by means of long term micro erosion meter mem measurements direct collection and analysis of condensation waters and micrometeorological monitoring monitoring of erosion at different heights on gypsum walls of the cueva del agua reveals that the gypsum surface retreated up to 0 033 mm yr 1 in mem stations located in the higher parts of the cave walls the surface retreat was negligible at the lowest sites suggesting higher dissolution rates close to the cave ceiling where warmer and moister air flows monitoring of microclimatic parameters and direct measurements of condensation water were performed in the covadura cave system in order to estimate seasonal patterns of condensation direct measurements of condensation water dripping from a metal plate placed in the central part of the el bosque gallery of covadura cave indicate that condensation takes place mainly between july and november in coincidence with rainless periods the estimated gypsum surface lowering due to this condensation water is 0 0026 mm yr 1 microclimatic monitoring in the same area shows differences in air temperature and humidity of the lower parts of the galleries colder and drier with respect to the cave ceiling warmer and wetter this thermal sedimentation controls the intensity of the condensation evaporation mechanisms at different heights in the cave

tectonic evolution of northeastern siberia and adjacent regions abstract previous models for the tectonic evolution of northeastern siberia have proposed the existence of a kolyma plate composed of the kolyma and omolon massifs of presumed precambrian age lithologic similarities between the siberian platform and the cherskiy mountains and the presence of oceanic and island arc type deposits in the kolyma indigirka interfluve suggest that no such plate exists the eastern margin of the siberian plate is suggested to lie along a line between the ulakhan sis range the alazeya uplift and the arga tas range the cherskiy mountains and the verkhoyansk fold belt are parts of the siberian plate the paleozoic deposits of the omolon massif are unlike those found in the cherskiys or siberia paleomagnetic data from the omolon massif are discordant from data from siberia it is suggested that the omolon massif represents a microplate which accreted onto siberia in the jurassic ophiolites in central chukotka are of the same emplacement age as in the western brooks range and may have been emplaced at the initiation of the rotation of arctic alaska geometric and limited stratigraphic data suggest that the east siberian sea may be floored by oceanic crust left by an incomplete closure between arctic alaska siberia and omolon the tectonic position of the prikolymsk massif remains ambiguous

continental rifting and the implications for plate tectonic reconstructions previous plate tectonic reconstructions have tried to recreate the pre rifting pangea configuration of the continents by matching contours or lineaments that are thought to represent the continental boundaries such reconstructions have the inherent assumptions that no extension occurs within the continent during rifting that the continental boundaries are isochrons and that the continents rift without distortion this paper proposes a model for continental breakup with distortion where ocean basins are formed by propagating rifts this model challenges the assumptions made by previous reconstructions and presents a new method for representing the prerift geometry of the continents as rifts propagate through a continent the region in front of the rift extends by continental faulting and crustal thinning while the region behind the rift expands by seafloor spreading the propagating rift model implies that large amounts of continental extension up to 150 km occur and that the continental boundaries are not isochrons this extension due to rifting results in apparent overlap when the continents are returned to their original configuration because of the gradational nature of this extension the best representation of the pre rift configuration is obtained by matching the initial rifting point and having overlap increase in the direction of rift propagation the overlap is equivalent to the amount of extension that has taken place on both continental edges reconstructions based on this model are presented for the gulf of california the gulf of aden the norwegian greenland sea and the south atlantic ocean they are able to resolve the discrepancies that occur when rigid plate tectonics are applied this model has implications that can be used to predict the age and structure of the continental shelves and the location and orientation of the oldest magnetic isochrons

salt weathering influence of evaporation rate supersaturation and crystallization pattern micro and macroscale experiments which document the dynamics of salt damage to porous stone have yielded data which expose weaknesses in earlier interpretations previously unexplained differences are found in crystal morphology crystallization patterns kinetics and substrate damage when comparing the growth of mirabilite na2so4 10h2o and thenardite na2so4 versus halite nacl the crystallization pattern of sodium sulphate was strongly affected by relative humidity rh while a lesser rh effect was observed for sodium chloride macroscale experiments confirmed that mirabilite crystallizing at rh 50 per cent and thenardite crystallizing at rh 50 per cent tend to form subflorescence in highly localized areas under conditions of constant rh and temperature this crystallization pattern was more damaging than that of halite since halite tended to grow as efflorescence or by filling the smallest pores of the stone in a homogeneous fashion a result which contradicts wellman and wilson s theoretical model of salt damage low rh promoted rapid evaporation of saline solutions and higher supersaturation levels resulting in the greatest damage to the stone in the case of both sodium sulphate and sodium chloride crystallization at any particular crystallization condition sodium chloride tended to reach lower supersaturation levels resulting in the crystallization of isometric crystals and created negligible damage while sodium sulphate reached higher supersaturation ratios resulting in non equilibrium crystal shapes resulting in significant damage esem showed no damage from sodium sulphate due to hydration instead after water condensation on thenardite crystals rapid dissolution followed by precipitation of mirabilite took place resulting in stone damage by means of crystallization pressure generation it is concluded that salt damage due to crystallization pressure appears to be largely a function of solution supersaturation ratio and location of crystallization these key factors are related to solution properties and evaporation rates which are constrained by solution composition environmental conditions substrate properties and salt crystallization growth patterns when combined with a critical review of salt damage literature these experiments allow the development of a model which explains variations in damage related to combinations of different salts substrates and environmental conditions

paleomagnetism and late diagenesis of jurassic carbonates from the jura mountains switzerland and france a crucial fold test for magnetizations measured in bajocian through kimmeridgian limestones from the jura mountain region shows that rare blue gray limestones found in this sequence preserve a prefolding magnetization in contrast tan limestones which predominate in this sequence contain secondary magnetizations acquired after folding in the late miocene the postfolding magnetizations in tan limestones appear to be carried in goethite and because reversed as well as normal polarity directions are present the magnetization in these limestones is probably a post miocene pre brunhes 700 000 yr chemical remanent magnetization crm field relations between tan and blue gray limestones which are present in some cases in the same rock unit for example the hauptrogenstein suggest that the tan limestones may have formed from alteration of blue limestones whereas goethite pseudomorphs after pyrite are found in tan limestones the occurrence of pyrite in the blue limestones supports this model indicating that goethite could have formed from oxidation of pyrite abundant meteoric water probably was available for such an oxidation process during uplift of these strata subsequent to deformation natural remanent magnetization in blue limestones appears to be carried in magnetite the positive fold test for the characteristic magnetization in these rocks is significant at the 99 confidence level k values for 24 site mean directions before and after tilt correction are 9 3 and 43 2 respectively the simplest interpretation for the origin of observed remanence in magnetite in the blue limestones is a primary magnetization of depositional or biogenic origin characteristic directions in these rocks yield a mean paleopole position of 77 7n 148 4e k 26 0 a95 5 9 this pole is in reasonable agreement with one other upper jurassic pole from western europe and with other middle to upper jurassic poles from the atlantic bordering continents after rotation of these continents to a reconstructed configuration for middle to late jurassic time

paleomagnetic investigations in the thuringer forest g d r abstract in the thuringer forest the whole rotliegende is well exposed and was chosen as beginning of a permian traverse via czechoslovakia austria into italy rockmagnetic experiments established haematite as main carrier of the nrm except a few localities where magnetite was found to be present sediments and volcanites show consistent chrm directions the comparison with krs s 1978 compilation proves a good permian pole position

paleomagnetism and mesozoic cenozoic paleocontinental maps a method of making paleocontinental reconstructions based on ocean floor magnetic anomaly data and land based paleomagnetic data is briefly described and its limitations are assessed synthetic polar wander paths for the period 20 200 ma are presented for australia antarctica india africa eurasia north america and south america comparison is made with observed paths except for antarctica for which the data are too sparse there are no significant differences between observed and synthetic paths a plot of inclination anomaly against paleolatitude shows a large scatter that limits the precision of the paleogeographic grid on continental reassemblies the absence of any systematic trend to this scatter with time suggests that the field has had the same average behavior over the past 180 ma and that large scale expansion of the earth cannot have occurred in this period south america has undergone the least change in position relative to the poles in the past 160 ma

the origin of honeycomb weathering honeycomb weathering occurs throughout the world but the origin remains a matter of controversy wind erosion exfoliation frost shattering and salt weathering have been proposed as explanations although few attempts have been made to substantiate these hypotheses with chemical or mineralogical studies chemical analyses and field observations indicate that honeycomb weathering in coastal exposures of arkosic sandstone near bellingham washington results from evaporation of salt water deposited by wave splash microscopic examination of weathered surfaces show that erosion results from disaggregation of mineral grains rather than from chemical decomposition thin walls separating adjacent cavities seem to be due to protective effects of organic coatings produced by microscopic algae inhabiting the rock surface cavity walls are not reinforced by precipitation of elements released by weathering as has often been suggested at other locations honeycomb weathering develops rapidly and can be observed on surfaces that were planar less than a century ago

unconventional non magmatic sulfur source for the mazarron zn pb cu ag fe epithermal deposit se spain the present study shows the existence of textural mineralogical microthermometric and isotopic data that evidences processes such as thermochemical sulfate reduction tsr that are not typical features of volcanic hosted epithermal deposits formed at shallow submarine and or subaerial environments geological evidence and mineralogical fluid inclusion temperature and geochemistry data suggest that the mazarron zn pb cu ag fe deposit is a volcanic hosted epithermal deposit it is hosted by dacites with different alteration halos k ar dating of illite from the argillic alteration gives an age of 9 7 1 2 ma which suggests that mineralization took place very close to the volcanism the fluid inclusion study in the ore veins shows epithermal temperatures between 190 and 260 c but moderate salinities between 12 and 18 wt nacl eq compatible with mixing between surface waters and polygenic deep hydrothermal fluids evolution of the hydrothermal activity shows the existence of three stage of mineralization in the first and last stages with fe sulfides as main phases mineralization was mainly formed by interaction between basinal fluids that leached triassic sulfates surface waters and c bearing reduced deep waters during interaction of both fluids the sulfur was subjected to extreme and geologically unusual fractionation under tsr conditions with ranging from 2 9 to 28 4 34s reaching exceptional values up to 53 34s the intermediate stage is mainly formed by sphalerite galena chalcopyrite fahlore bearing sulfides this event is compatible with the influx of a magmatic fluid discharge finally this study suggests that mazarron could be classified as an intermediate sulfidation deposit

marginal faunal belts and their structural implications with examples from the lower palaeozoic fossils provide an independent criterion for testing structural hypotheses generated from field evidence or geochemistry as well as functioning in their traditional role in the dating of rocks or determining biogeographic realms on a global scale the identification of exterior oceanic biofacies may be of use in discriminating the course of former continental margins the isograptid graptolite biofacies early to middle ordovician can be distinguished from contemporary epicratonic graptolite biofacies its worldwide occurrence corresponds with continent margins reconstructed from other criteria hence a new isograptid record from irian jaya e new guinea although based on a small sample suggests that there may have been an ordovician oceanic site there on a continental scale the tectonic juxtaposition of different biofacies or of different stratigraphical packages contributes to an understanding of tectonics and can serve to quantify displacement the accretionary prism hypothesis for the southern uplands of scotland is supported and contrasted with the rearrangement of biofacies in the cambro ordovician cow head group of western newfoundland which reveals not only the original shelf margin slope topography now vanished but also provides an estimate of the movement involved in the emplacement of one taconic allochthon on a more local scale faunal evidence is used in assessing the original position of 9suspect9 marginal areas using the simplest possible model this shows for example that anglesey was not greatly separated from gondwana in the early ordovician but strike slip movement cannot be disproved local changes in relative sea level are determinable from sediments and faunas in marginal belts these may differ from the global eustatic curve and when this happens it is a measure of local tectonic activity particular sea level curves may serve to define structurally coherent units within mobile belts new sea level curves are contrasted for a segment of n wales north of the bala fault with that for central sw wales arenig llandovery the s welsh area mostly responded passively to the eustatic curve which can adequately account for shifts in facies and faunas while n wales had a curve often at odds with eustasy and reflecting its structural history

paleomagnetism and the evolution of pangea we present new apparent polar wandering apw paths for the latest carboniferous to middle jurassic of europe northern asia north america and gondwana the paths have been constructed by ordering the paleopoles into a time sequence and calculating running averages globally this statistical analysis cannot be carried back before the latest carboniferous because the paleomagnetic record becomes inadequate the polar paths have all been rotated along with the land masses from which they have been observed into the classical configuration of wegener pangea a as quantified by later workers the mean paleopoles agree in the early jurassic but disagree in the latest carboniferous permian and early triassic this result is insensitive to reasonable choices made regarding the arrangement of the continents within gondwana it is true either for results from gondwana as a whole or from africa and south america alone this disagreement in apw paths suggests but does not prove that pangea a lasted for only a short interval of time in the early to middle jurassic 190 170 m y and perhaps the latest triassic 200 m y alternatively we may say either that the paleomagnetic record is biassed by sampling inadequacies or by systematically incorrect age assignments or that the earth s field has been non dipolar we regard these explanations as less likely although they cannot be discounted the polar paths can be reconciled by rotating gondwana anticlockwise by about 35 relative to laurasia placing africa beneath europe and south america beneath eastern north america this configuration is called pangea b pangea b could be a valid reconstruction for the latest carboniferous and early permian approximately 290 260 m y pangea b provides a statistically satisfactory resolution of the paleomagnetic problem it also provides a symmetrical arrangement of the continents bordering the appalachian hercynian fold belt for the late paleozoic which pangea a does not it provides a satisfactory framework for the early evolution of the gulf of mexico and it provides an explanation of the absence of geological evidence for a tethys ocean in the paleozoic the transition between b and a cannot be accurately reconstructed from the paleomagnetic data because the resolution of the record is as yet inadequate but it presumably occurred by a 3500 km minimum dextral megashear between laurasia and gondwana during the late permian and triassic approximately 250 200 m y without the formation of ocean between them and was accompanied by lesser motions between north america and europe the sense of megashear is the same as that invoked by arthaud and matte 1977 on geological grounds but the magnitude and timing are different our interpretation favors the idea that continental drift is a continuous process not confined to jurassic and later times but extending backwards into the triassic and permian we suggest that pangea was not an immobile configuration as envisaged by wegener and most subsequent workers but that it evolved more or less continuously

northward displacement and accretion of wrangellia new paleomagnetic evidence from alaska wrangellia is a vast terrane that accreted along the pacific margin of north america from oregon to central alaska previous paleomagnetic studies of the triassic volcanic rocks of wrangellia in south central alaska and british columbia have given paleolatitudes of 10 17 which are anomalously low in comparison to results from similar aged rocks of nuclear north america the discrepancy in paleolatitude implies substantial northward drift of the terrane relative to the craton we have extended paleomagnetic sampling to the northern boundary of the terrane in the mount hayes and healy quadrangles of the central alaska range this collection of 46 triassic lava flows yields a mean paleolatitude of 13 9 95 3 8 the polarity of the data and hence the hemisphere of origin are not resolved with certainty in contrast triassic paleomagnetic poles from the stable part of north america predict a paleolatitude of 42 1 n 95 4 6 for the region the northernmost fragment of wrangellia probably reached mainland alaska in the middle cretaceous when upper jurassic and lower cretaceous flysch within the intervening basin underwent severe deformation tertiary transcurrent faulting has modified the positions of wrangellian fragments in alaska but such displacements are probably minor as indicated by paleomagnetic data from early tertiary volcanic rocks that overlap the terrane

hypogene sulfuric acid speleogenesis and rare sulfate minerals in baume galiniere cave alpes de haute provence france record of uplift correlative cover retreat and valley dissection the oxidation of hydrocarbons and sulfide sources h2s pyrite produces sulfuric acid that strongly reacts with bedrock causing limestone dissolution and complex interactions with other minerals from the bedrock or from cave fillings mainly clays this type of cave development known as sulfuric acid speleogenesis sas is a subcategory of hypogene speleogenesis where aggressive water rises from depth it also produces uncommon minerals mainly sulfates the typical byproducts of sas baume galiniere is located in southern france in the vaucluse spring watershed this small maze cave displays characteristic sas features such as corrosion notches calcite geodes iron crusts and various sulfate minerals sulfur isotopes of sas byproducts jarosite and gypsum clearly show they derive from pyrite oxidation using xrd and micro raman spectroscopy thirteen minerals were identified including elemental sulfur calcite quartz pyrite goethite gypsum and fibroferrite plus all of the six members of the jarosite subgroup jarosite argentojarosite ammoniojarosite hydroniumjarosite natrojarosite plumbojarosite the baume galiniere deposits are the first documented cave occurrence of argentojarosite and the second known occurrence of plumbojarosite hydronium jarosite ammoniojarosite and fibroferrite in the vaucluse watershed there were numerous upwellings of deep water along major faults located at the contact of the karstic aquifer and the overlying impervious covers the mixing of deep and meteoric waters at shallow depths caused pyrite depositions in numerous caves including baume galiniere sulfuric acid speleogenesis occurred later after base level drop when the cave was under shallow phreatic conditions then in the vadose zone with oxidation of pyrites generating sulfuric acid attenuated oxidation is still occurring through condensation of moisture from incoming air baume galiniere cave records the position of the semi impervious paleo cover and documents its retreat in relationship to valley incision caused by uplift and tilting of the vaucluse block during the neogene

tectonic evolution of the north sea basin crustal stretching and subsidence summary the lithospheric stretching model for the formation of sedimentary basins was tested in the central north sea by a combined study of crustal thinning and basement subsidence patterns a profile of crustal structure was obtained by shooting a long range seismic experiment across the central graben the main axis of subsidence a seabed array of 12 seismometers in the graben was used to record shots fired in a line 530 km long across the basin the data collected during the experiment were interpreted by modelling synthetic seismograms from a laterally varying structure and the final model showed substantial crustal thinning beneath the graben subsidence data from 19 exploration wells were analysed to obtain subsidence patterns in the central north sea since jurassic times changes in water depth were quantified using foraminiferal assemblages where possible and observed basement subsidence paths were corrected for sediment loading compaction and changes in water depth through time the seismic model is shown to be compatible with the observed gravity field and the small size of observed gravity anomalies is used to argue that the basin is in local isostatic equilibrium both crustal thinning and basement subsidence studies indicate about 70 km of stretching across the central graben during the mid jurassic to early cretaceous extensional event this extension appears to have occurred over crust already slightly thinned beneath the graben and the seismic data suggest that total extension since the early permian may have been more than 100km the data presented here may all be explained using a simple model of uniform extension of the lithosphere

triple oxygen and hydrogen isotopes of gypsum hydration water for quantitative paleo humidity reconstruction abstract atmospheric relative humidity is an important parameter affecting vegetation yet paleo humidity proxies are scarce and difficult to calibrate here we use triple oxygen 17 o and 18 o and hydrogen d isotopes of structurally bound gypsum hydration water ghw extracted from lacustrine gypsum to quantify past changes in atmospheric relative humidity an evaporation isotope mass balance model is used together with monte carlo simulations to determine the range of climatological conditions that simultaneously satisfy the stable isotope results of ghw and with statistically robust estimates of uncertainty we apply this method to reconstruct the isotopic composition of paleo waters of lake estanya ne spain and changes in normalized atmospheric relative humidity rh n over the last glacial termination and holocene from 15 to 0 6 cal kyrs bp the isotopic record indicates the driest conditions occurred during the younger dryas yd 12 13 cal kyrs bp we estimate a rh n of 40 45 during the yd which is 30 35 lower than today because of the southward displacement of the polar front to 42 n it was both windier and drier during the yd than the bolling allerod period and holocene mean atmospheric moisture gradually increased from the preboreal to early holocene 11 to 8 cal kyrs bp 50 60 reaching 70 75 rhn from 7 5 cal kyrs bp until present day we demonstrate that combining hydrogen and triple oxygen isotopes in ghw provides a powerful tool for quantitative estimates of past changes in relative humidity

transcurrent faulting and the anomalous position of pre carboniferous anglesey the marked differences of pre carboniferous geology between anglesey and of mainland north wales are accouonted for by devonian transcurrent faulting probably caused by stresses resulting from the closure of the lapetus ocean displacement along this fault is thought to have exceeded 100 km so that the lake district and not anglesey would formerly have been in juxtaposition with north wales

relative motions between eurasia and north america in the bering sea region knowledge of the relative motion of the north american and eurasian plates during the late mesozoic and cenozoic provides insight into the observed timing and style of deformational events in the bering sea region periods of strong convergence from 70 to 50 ma maastrichtian to paleocene are correlated with compressional deformation between the chukotsk peninsula and northern alaska and movement along the denali fault the convergence may also be the cause of a previously proposed counterclockwise rotation of western alaska transform motion between these plates from 50 to 38 ma middle to late eocene correlates with subsidence of the bering shelf creation of a series of pull apart basins along the bering margin and cessation of calc alkaline volcanism in western alaska slight compressive convergence from 37 ma to the present may be responsible for the anticlinal deformation of basin filling sediments in the anadyr and khatyrka basins

isotopic analysis of sulfur cycling and gypsum vein formation in a natural co2 reservoir abstract in order to assess the long term security of geologic carbon storage it is crucial to study the geochemical behavior of sulfur in reservoirs that store co2 fossil fuel combustion may produce mixtures of carbon dioxide and sulfur gases and the geochemical effects of sulfur co2 cosequestration are poorly understood this study examines sulfur mineralization from a core drilled in a stacked sequence of natural co2 reservoirs near the town of green river utah these reservoirs include the entrada and navajo sandstone which are separated by the carmel formation caprock and transected by a system of co2 degassing normal faults through which saline co2 charged brines discharge our objective in this study is to evaluate the mechanisms and timing of secondary mineral formation particularly gypsum formation in the co2 reservoirs and intervening caprock the carmel formation contains beds of gypsum within a fault zone secondary veins of gypsum exist throughout the entrada sandstone and carmel formation we report sulfur and oxygen isotope data 34sso4 and 18oso4 respectively measured in gypsum and 34s measured in pyrite and the oxygen and hydrogen isotope composition 18o and d respectively of gypsum hydration water the multiple isotope approach allows us to trace the sources of sulfur in the reservoirs and when combined with structural and petrological evidence the progress of fluid rock reactions and relative timing of vein mineralization the secondary gypsum veins in the carmel formation derive from mixing of fluids with two isotopically distinct sulfate sources sulfate from the gypsum beds within the carmel formation and sulfate rich brines that originate from evaporites in the underlying carboniferous paradox formation the gypsum veins in the entrada sandstone have a relatively wide range of 18oso4 both isotopically more enriched in 18o and more depleted in 18o than the primary gypsum sources we suggest that some aqueous sulfate in the entrada sandstone may cycle through multiple valence states as it undergoes reduction and reoxidation resulting in the replacement of its oxygen atoms and allowing the occasional formation of gypsum with anomalous low 18oso4 our data from gypsum hydration water indicates that groups of gypsum veins formed at two different times gypsum veins in the entrada sandstone and some veins in the carmel formation likely formed during quaternary co2 charged brine discharge events while other veins located close to the gypsum beds in the carmel formation formed earlier likely during cycles of dehydration and rehydration associated with the laramide age 40 mya faulting we conclude that calcium sulfate mineral formation in brine filled fractures may play an important role in inhibiting fluid migration in geologic reservoirs that contain co2

middle miocene gypsum gulf of suez marine or nonmarine abstract middle miocene gypsum on the eastern coast of the gulf of suez west central sinai includes massive and bedded selenite these selenites are interpreted as primary deposits because of their textures and fabrics such as vertically oriented crystals primary fluid inclusions in gypsum are used to interpret depositional settings and parent water chemistries the final melting temperatures of ice in fluid inclusions nearly all fall between 0 0 c and 8 0 c fluid inclusions with ice melting temperatures above 1 9 c melting temperature of ice in seawater show that some of the gypsum must have formed from a relatively dilute non seawater parent water the nearly total absence of fluid inclusions with final ice melting temperatures below 7 0 c melting temperature of ic in evaporated seawater at gypsum saturation indicates that the gypsum did not form from simple evaporative concentration of seawater rather the fluid inclusion data suggest that gypsum grew from 1 recycled seawater enriched in caso4 whereby seawater dissolved surrounding gypsum or anhydrite deposit or 2 mixed seawater nonmarine waters sulfur and oxygen isotope analyses 34s values of 21 9 to 23 6 cdt and 18o values of 10 1 to 12 7 smow suggest a marine sulfate source but do not rule out any of the above parent waters given the rift tectonic setting the most likely interpretation is that the parent waters were seawater with input of marginal nonmarine groundwaters and surface waters all of which may have recycled caso4 via dissolution of gypsum or anhydrite miocene gypsum deposits formed in a subsidiary closed ba in that may have been separated from the main gulf of suez trough during periods of low sea level or active faulting the marginal closed basin may have been cut off from the gulf of suez and thus completely nonmarine the same basin would have become a marine fed lagoon if it had been connected to the gulf of suez and flooded by seawater during high sea level stands or breaching of tectonic barriers

paleomagnetism of the paleocene ghost rocks formation prince william terrane alaska the mean paleomagnetic inclination of paleocene volcanics from two regions on kodiak island in the ghost rocks formation suggests that the prince william terrane originated at mid latitudes about 25 south of its expected alaskan latitude in paleocene time the remanent magnetization of these rocks passes both the fold and reversal tests and is well constrained in age the mean declinations of the two regions however differ by approximately 120 suggesting they have rotated with respect to each other perhaps during emplacement we suggest that despite the lack of evidence for a major tertiary suture zone between the prince william terrane and central alaska the prince william and perhaps adjacent terranes may have lain substantially south of their present position in the early tertiary

using stable isotopes δ 17 o δ 18 o and δd of gypsum hydration water to ascertain the role of water condensation in the formation of subaerial gypsum speleothems abstract we analyzed the stable isotopes 17 o 18 o and d of gypsum hydration water ghw in a variety of speleothems as well as condensation and infiltration waters in five caves of the semiarid gypsum karst of sorbas basin almeria se spain microclimate parameters air temperature relative humidity and effective condensation rate were also monitored over an annual cycle we found that the mother solution from which the majority of gypsum speleothems grow is composed of a mixture of condensation 60 and infiltration water 40 that undergoes evaporation although evaporation of infiltration water alone was thought to be responsible for secondary gypsum precipitation in vadose caves our results suggest that condensation can be a major source of water for the formation of gypsum speleothems the modelled d excess and 17 o trajectories of water during the evaporative process confirm that the majority of speleothems precipitate from a mixture of condensation and infiltration water under relative humidity of 75 85 similar to that measured in the cave atmosphere during winter these findings have important implications for future studies of gypsum speleothems as paleoenvironmental archives

palaomagnetische untersuchungen im schilfsandstein trias km2 westeuropas von insgesamt 46 beprobten profilen aus dem schilfsandstein trias km2 westeuropas wurden bislang 41 profile mit 343 einheiten und 870 handstucken mit 1897 einzelkernen auf ihren palaomagnetischen inhalt untersucht

lower jurassic palaeomagnetic results from yorkshire england and their implications palaeomagnetic study of middle liassic siltstones shows a stable magnetization with a mean direction of d 12 3 i 64 6 n 60 k 26 95 3 9 corresponding to a palaeomagnetic pole at 79 8 n 125 6 e similar to that for southern germany and confirming predictions based on palaeogeographic reconstructions using north american data sideritic concretions of lower liassic age show a higher magnetic stability with a mean direction of d 12 6 i 61 4 n 125 k 50 95 1 8 which is not significantly different from the siltstones this confirms the sedimentological evidence that suggests that such concretions grew very shortly after deposition i e within the liassic and suggests that similar concretions of other ages could thus be used for palaeomagnetic studies although the liassic palaeomagnetic pole 76 9 n 134 7 e based on this work appears valid it is still not possible to evaluate a sensible mesozoic polar wandering curve for the north atlantic bordering continents

rates and patterns of bedrock denudation by coastal salt spray weathering a seven year record rapid surface lowering of bedrock is taking place in the supratidal zone by salt spray weathering a seven year run of data demonstrates a mean rate of lowering of 0 625 mm a 1 considerable variation exists in annual point lowering values within measurement sites although between site variation is not significant aggregate year to year variations in surface lowering are not significant spatial variation in individual point values may be compensated by temporal variation over an 11 year period there is a marked summer maximum in surface lowering rate and this is strongly correlated with monthly air temperature spatially and temporally episodic swelling of the rock surface is demonstrated this does not correlate statistically with any available climatic variable and is deemed to be a real and largely stochastic phenomenon it is interpreted as rock bursting at the granular scale due to haloclasty the processes most likely to be responsible for the observed rapid denudation are crystallization and thermal expansion of halite both of which are enhanced by high summer temperatures

propagating rifts crustal extension during continental rifting propagating rifts may not be incompatible with plate tectonic tenets which are considered at the appropriate scale propagation of a rift is a natural consequence of relative motion about a pole of rotation it is not necessarily valid that 1 rifts propagate in one direction or 2 crustal stretching increases with progressive propagation of a rift

physical weathering of carbonate host rock by precipitation of soluble salts in caves a case study in el oron arco cave region of murcia se spain abstract the dissolution of carbonate host rock by freshwater in phreatic or vadose conditions is the most common mechanism for the formation of caves however circulation of saline solutions through carbonate materials and precipitation of soluble salts may also play an important role we studied the stable isotope composition 18o and 34s of sulfate 18o and d of structurally bound gypsum hydration water and 87sr 86sr and salinity of fluid inclusions in gypsum speleothems found in el oron arco cave cartagena se spain we suggest that physical weathering of carbonate host rock was driven by precipitation of soluble sea salts mostly gypsum and halite and this process controlled the recent geomorphological evolution of the cave the triassic carbonate host rock shows clear evidence for salt weathering including gypsum halite infillings in cracks of the bedrock mechanical spalling of the carbonate and detachment of rock fragments that lead to the formation cave voids and in situ accumulations of piles of unsorted rubble sulfur and oxygen isotopes of gypsum sulfate 3 0

paleomagnetism and potassium argon age of the messejana dike portugal and spain angular limitation to the rotation of the iberian peninsula since the middle jurassic abstract a paleomagnetic and potassium argon dating investigation has been carried out on a 530 km long dike system which transects the western iberian peninsula in a northeasterly direction the k ar age determinations were made on mineral separates exclusively they range between 160 and 200 ma and the authors suppose that this reflects the actual time interval of the intrusion in accord with previous results the paleomagnetic pole derived from 12 sites regularly distributed along the dike 71 n 236 e coincides well with other mesozoic paleomagnetic poles from the western africa a contemporaneous pole from stable europe is tentatively deduced from african and north american late triassic early jurassic poles using different reconstruction models around the north atlantic ocean the divergence between this pole and the iberian pole corresponds to the result obtained for permian poles

the cretaceous opening of the northeast atlantic abstract a continuous rift system from the rockall trough through the faeroe shetland channel and the more and voring basins up to the tromso and bear island basins is inferred to have developed during the cretaceous oceanic crust was generated in its southern part but its width presumably decreases toward the northeast and probably ends in the more basin this rift spreading system requires a clockwise rotation of greenland and the rockall plateau during the cretaceous around a rotation pole at its northern end at about 74 n 21 e north of the pole of rotation crustal shortening must have occurred this compression is interpreted to have taken place on west spitsbergen the orogeny there is reinterpreted as 1 1 a cretaceous folding phase 2 2 a phase of overthrusting at the paleocene eocene boundary and 3 3 an extensional faulting phase during the oligocene this plate tectonic model can resolve a series of problems in the northeast atlantic region the connection of the caledonian fronts of scotland and greenland can be easily established the northern ends of the west shetland basin and the north sea graben the unusual depth of the more and voring basins the marked obliqueness of structural trends between the northeast greenland shelf and the norwegian shelf the fact that the western hammerfest basin was intersected by a younger north south trending graben which formed the deep tromso basin all these enigmatic observations can be explained by the cretaceous rift system

paleomagnetic implications on the evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we first re examined the apparent polar wander curves for stable eurasia and africa since the triassic these curves were then combined together with curves of north and south america according to the kinematics of the atlantic ocean and a synthetic polar wander curve was given then most of the paleomagnetic results from the tethys mobile belt from the atlantic to the pamirs were analysed several groups of plates microplates and blocks can be seen first relatively stable regions like maghreb and sicily which have not moved much then we have a group formed by iberia sardinia italy and to a lesser extent corsica and the western and central alps for these blocks movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of africa but they are sometimes stronger to the east a major change takes place the north of the aegean sea and the ionian zone are clockwise rotated and these rotations are recent oligocene miocene for the first part pliocene to the present for the second part a major problem arises in turkey caucasus and iran paleomagnetic results indicate a position far to the south of eurasia and at the same time geological evidence is in favour of a position close to eurasia we discuss these discrepancies

coupled measurements of δ18o and δd of hydration water and salinity of fluid inclusions in gypsum from the messinian yesares member sorbas basin se spain we studied one cycle cycle 6 of gypsum marl deposition from the messinian yesares member in sorbas basin spain the objective was to reconstruct the changing environment of deposition and its relation to astronomically forced climate change the 18o and d of gypsum hydration water caso4 2h2o and salinity of fluid inclusions were measured in the same samples to test if they record the composition of the mother fluid from which gypsum was precipitated water isotopes are highly correlated with fluid inclusion salinity suggesting the hydration water has not exchanged after formation the relatively low water isotope values and fluid inclusion salinities indicate a significant influence of meteoric water whereas 34s 18oso4 and 87sr 86sr support a dominant marine origin for the gypsum deposits the discrepancy between water and elemental isotope signatures can be reconciled if meteoric water dissolved previously deposited marine sulfates supplying calcium and sulfate ions to the basin which maintained gypsum saturation this recycling process accounts for the marine 34s 18oso4 and 87sr 86sr signatures whereas the low 18o and d values of gypsum hydration water and fluid inclusion salinities reflect the influence of freshwater the cyclic deposition of gypsum and marl in the yesares member has previously been interpreted to reflect changing climate related to earth s precession cycle we demonstrate that the 18o d and salinity of the parent brine increased from low values at the base of the cycle to a maximum in the massive gypsum palisade and decreased again to lower values in the supercones at the top of the cycle this pattern together with changes in mineralogy calcite dolomite gypsum is consistent with a precession driven change in climate with wettest conditions summer insolation maxima associated with the base of the calcium carbonate marls and driest conditions summer insolation minima during formation of the gypsum palisade

the isotopic record of gypsum diagenesis in diluted solutions observations in natural salinas and experiments abstract gypsum deposits are often considered as reliable components of evaporitic series for reconstructing their conditions of precipitation from saturated marine or non marine calcium sulfate solutions the isotopic compositions of the hydration water and of the sulfate are thought to provide the composition and thus the origin of the parent solution assuming that the primary signals are preserved the present study demonstrates that dissolution recrystallization of gypsum from natural salinas and in experiments where gypsum reacted with diluted solutions was responsible for the rapid modification of the primary isotopic signal by the incorporation of the reacting water in the crystal lattice of the new gypsum generation it is also shown that gypsum diagenesis may cause significant changes of the isotopic composition of the sulfate due to fractionation between the resulting dissolved and new gypsum phases

a kinematic model for the collision and complete suturing between gondwanaland and laurussia in the carboniferous maps of middle to late carboniferous strike slip faults in western europe northern africa and eastern north america have been compiled from geological gravity and magnetic onshore and offshore data a large majority of these faults can be interpreted in terms of a logical syn to post collisional pattern superimposed on the initial suture between the african i e gondwana and north american european laurussian continental margins the pre collision positions of the major continents are derived from paleomagnetic data and when combined with the general distribution of the strike slip faults lead to a kinematic model of the complex middle late carboniferous collision in this model the west african precambrian craton acted as a rigid promontory or die with respect to the partially rigid plastic zones between it and the large north american craton these partially rigid plastic zones comprise the external appalachian and canadian maritime margins the mauritanide and hercynian margins of north

geology and paleobiology of islands in the ordovician iapetus ocean review and implications a history of islands in the iapetus ocean and their destruction is recorded by widespread occurrences of lower to upper ordovician volcanic and epiclastic rocks and some limestone through the axial parts of the appalachian caledonide orogen in north america and northwestern europe assemblages of arenigian and llanvirnian benthic shelly fossils chiefly brachiopods from these rocks constitute the celtic biogeographic province that is distinguished by its endemic genera and by some that are older than in other biogeographic provinces some that are younger than elsewhere and others that have not hitherto been found together evidence from these fossils and from the geology of the rocks pertaining to them suggests that north american terranes that included islands of arenigian llanvirnian age lay at middle to high latitudes both in mid ocean and within the armorican continental margin whereas coeval rocks in west central ireland and norway that have toquima table head shelly fossils were originally part of the laurentian continental margin eradication of the celtic assemblage and the reduction of ordovician faunal provinciality in the appalachian caledonide region coincide with llanvirnian obduction subduction of hundreds of kilometres of iapetus ocean crust late llanvirnian and younger ordovician rocks in the remnant basin including some of peri insular origin have brachiopods of scoto appalachian affinities no discrete islands of ashgillian age have been recognized although fossiliferous volcaniclastic and polymictic conglomerates indicate intermontane basins in some places shelly fossils in these rocks and those in the siltstones and limestones from the gaspe peninsula are like those of ashgillian age elsewhere

did late miocene messinian gypsum precipitate from evaporated marine brines insights from the piedmont basin italy during the first stage of the late miocene messinian salinity crisis 5 97 5 60 ma deposition of sulfates the primary lower gypsum occurred in shallow silled peripheral subbasins of the mediterranean undergoing restricted water exchange with the atlantic ocean fluid inclusions in messinian selenite crystals from the piedmont basin northwest italy have surprisingly low salinities average of 1 6 wt nacl equivalent suggesting that parent waters were depleted in na and cl compared to modern seawater modern gypsum from a mediterranean salt work in contrast contains fluid inclusions with elevated salinities that match the normal evaporation trend expected for seawater the salinity data indicate that the messinian sulfate deposits from the piedmont basin formed from hybrid parent waters seawater mixed with ca 2 and so 4 2 enriched freshwaters that dissolved coeval marginal marine gypsum such mixed parent waters and complex recycling processes should be taken into account when explaining the genesis of other messinian gypsum deposits across the mediterranean basin

late glacial temperature and precipitation changes in the lowland neotropics by tandem measurement of δ18o in biogenic carbonate and gypsum hydration water we applied a new method to reconstruct paleotemperature in the tropics during the last deglaciation by measuring oxygen isotopes of co occurring gypsum hydration water and biogenic carbonate in sediment cores from two lakes on the yucatan peninsula oxygen and hydrogen isotope values of interstitial and gypsum hydration water indicate that the crystallization water preserves the isotopic signal of the lake water and has not undergone post depositional isotopic exchange with sediment pore water the estimated lake water 18o is combined with carbonate 18o to calculate paleotemperature three paired measurements of 1200 yr old gypsum and gastropod aragonite from lake chichancanab mexico yielded a mean temperature of 26 c range 23 29 5 c which is consistent with the mean and range of mean annual temperatures mat in the region today paired measurements of ostracods gastropods and gypsum hydration water samples were measured in cores from lake peten itza guatemala spanning the late glacial and early holocene period 18 5 10 4 ka the lowest recorded temperatures occurred at the start of heinrich stadial hs 1 at 18 5 ka inferred temperatures from benthic ostracods ranged from 16 to 20 c during hs 1 which is 6 10 c cooler than mat in the region today whereas temperatures derived from shallow water gastropods were generally warmer 20 25 c reflecting epilimnetic temperatures the derived temperatures support previous findings of greater tropical cooling on land in central america during the late glacial than indicated by nearby marine records temperature increased in two steps during the last deglaciation the first occurred during the bolling allerod b a from 14 7 to 13 ka when temperature rose to 20 24 c towards the end of this period the second step occurred at 10 4 ka near the beginning of the holocene when ostracod inferred temperature rose to 26 c reflecting modern hypolimnetic temperature set during winter whereas gastropod derived temperature attained 30 c reflecting modern summer epilimnetic temperature

the source of gypsum in mammoth cave kentucky mammoth cave kentucky usa is the world9s longest human navigable cave system gypsum caso 4 2h 2 o crystals line many dry passages of the limestone cave and the source of sulfur for the gypsum remains uncertain previous workers have suggested sulfate from pyrite oxidation mississippian aged sulfate evaporites and pleistocene soil sulfate as possible sulfur sources we use sulfur isotopes 34 s to constrain the gypsum sulfur source by comparing the 34 s values of different possible sources to that of gypsum throughout the cave 34 s gypsum values n 106 from 12 different locations within the mammoth cave system are along a continuum of 34 s values from 12 0 to 12 8 with little variability along the crystal growth axis or between samples within the same cave chamber neither sulfur from coeval sedimentary evaporites i e gypsum anhydrite nor from formations overlying the cave is required to explain the 34 s gypsum data rather the range of pyrite 34 s in strata immediately surrounding the cave is sufficient to generate the spectrum of observed 34 s gypsum modern water 34 s so 4 values are similar to the host formation 34 s pyrite suggesting that oxidized pyrite from the host formation continues to be a major sulfur source to this day together these observations strongly suggest a significant local source of sulfur for mammoth cave gypsum the majority 66 100 of which is derived from the oxidation of pyrite in strata adjacent to the cave