the tectonothermal evolution of the cadomian belt of northern brittany france a neoproterozoic volcanic arc abstract the neoproterozoic cadomian belt northern brittany france results from the accretion of crustal blocks that record distinctive p t deformation paths in addition abundant gabbro dioritic to granitic intrusions during and after deformation influence the thermal pattern and are used as time markers as a whole the deformation history of the cadomian belt is characterised by a migration in time of the active zones which become younger towards the southeast relics of eocadomian rocks reveal that arc development took place at about 660 640 ma abundant calc alkaline magmatism intruding strongly deformed palaeoproterozoic orthogneisses characterise the northernmost unit of the cadomian belt i e the tregor unit which cooled before 600 ma the lanvollon basin a short lived intra arc rift containing abundant mafic and felsic volcanics followed by greywackes opened at about 600 580 ma the subsequent tectonothermal history of the cadomian belt is divided into two major episodes the first episode is related to the shortening of the intra arc rift and its southwestward thrusting over the guingamp unit this led to crustal thickening inducing partial melting in the guingamp unit exhumation of the latter rocks is accommodated by late extensional shearing along the boundary between the saint brieuc and guingamp units cooling of the saint brieuc unit is dated at about 570 560 ma the second episode is dominated by sinistral wrenching mainly localised in the eastern part of the cadomian belt at the boundary between the domnonean i e the arc domain and mancellian possibly a fore arc basin domains several shear zones developed during this episode some of them being associated with minor granitic intrusions dated around 550 ma the sinistral shear located southeast of the arc domain is reworking or crosscutting earlier high temperature fabrics within the saint brieuc unit in addition the vertical component of this shearing episode contributes significantly to the exhumation of the saint malo migmatites near the proterozoic cambrian boundary cordierite biotite granitoids intruded at shallow depths the fougeres unit their emplacement outlasting deformation of the sedimentary sequences minor stocks of muscovite leucogranites of cambrian age are possible equivalents of the abundant volcanism in an adjacent nw se trending rift this marks a major change in the kinematic framework with predominance of extension finally minor reactivation of the cadomian structures occurred during the carboniferous associated with the variscan orogeny

basalt sills of the u reflector newfoundland basin a serendipitous dating technique high core recovery at ocean drilling program odp leg 210 site 1276 provided a high resolution porosity depth relationship and an equally impressive age depth model based on first and last occurrences of microfossils site 1276 was drilled over transitional crust in the newfoundland nonvolcanic margin offshore canada between known continental crust on the west and apparent oceanic crust on the east as identified by seafloor spreading magnetic anomalies m3 to m0 barremian aptian 129 8 124 8 ma at site 1276 two diabase sills were drilled at depths equivalent to the u reflection a bright reflection that overlies transitional crust interpreted from seismic reflection profiles throughout the newfoundland basin the sills were emplaced within uppermost aptian fine to coarse grained sediments 100 200 m above basement as estimated from seismic reflection data magma emplacement occurred at shallow levels within the sediment column as evidenced by 1 the occurrence of vesicles in the sill and 2 compaction induced folding of calcite veins that were emplaced near vertically in the sediments and are assumed to be coeval with the intrusion by calculating the degree of shortening of the calcite veins and determining the reconstructed porosity of the sediments during vein emplacement the age of magma emplacement can be deduced from the porosity age curve the age of sill emplacement is estimated to be 82 5 109 1 ma consistent with recent 40ar 39ar radiometric dating of the upper sill that gave ages of 105 95 1 78 ma and 104 7 1 7 ma the source of magmatism responsible for the diabase sills is necessarily postrift and the sills are temporally equivalent to alkali basalts dredged from the newfoundland seamounts the simplest explanation for the site 1276 diabases and the widespread distribution of the u reflection relates to the migration of the azores madeira and canary plumes across the newfoundland basin between 80 and 120 ma

formation temperatures of clays from the volcaniclastic series of site 841 odp an oxygen isotopic record of a paleothermal flux into the tonga forearc oxygen isotopic compositions of clay minerals were determined on representative samples of the volcano sedimentary series from site 841 odp tonga forearc this isotopic study has demonstrated an abnormally high crystallisation temperature of the clay minerals with respect to temperature expected in burial diagenesis formation temperatures obtained using 18o reach up to 200 c in a fe chlorite corrensite paragenesis found in the vicinity of basaltic andesite sills intruded into the miocene tuffs the paleothermal flux resulting from the cooling of the sills has produced very low grade contact metamorphism in the miocene tonga forearc deposits the consequence of this was the formation of a large amount of hydrous silicates characterised near the sills by a fe clays analcime mineralogical association

accommodation and sediment supply controls on clastic parasequences a meta analysis this study combines data from many published case studies to undertake a quantitative characterization of clastic parasequences with the aim to determine how accommodation sediment supply and autogenic sediment storage dynamics are recorded in their sedimentary architecture and stacking patterns results of this study are used to critically evaluate the validity of paradigms and models that are routinely used to explain and predict trends in the anatomy and arrangement of parasequences data on 957 parasequences from 62 case studies of clastic shallow water successions were coded in a relational database which includes outcrop and subsurface datasets of ancient and quaternary examples these units cover the preserved records of both river dominated deltas and wave dominated coasts representing shoreline transits over a breadth of timescales likely of both local and regional extent the role of extant accommodation rates of creation of accommodation and rates of sediment supply in determining parasequence architecture is assessed through analysis of relationships between i proxies of these variables at different scales rates of aggradation and progradation facies belt shoreline trajectories systems tract type parasequence set stacking patterns parasequence progradation angle and stratigraphic rise size of feeder rivers and ii parameters that describe the geometry and stacking style of parasequences and associated shallow water sand bodies statistical analyses of database outputs indicate which proxies of accommodation sediment supply and accommodation sediment supply ratio are significant as predictors of parasequence architecture and allow for interpretations of the importance of allogenic and autogenic factors the principal results of this study reveal the following i parasequence thickness varies as a function of water depth accommodation generation and erosional truncation and these variations are also reflected across types of systems tracts and parasequence sets ii the dip length of parasequence sand bodies demonstrates scaling with measures of accommodation sediment supply ratio at multiple scales partly in relation to the possible effect of sediment supply on progradation rates iii in systems tracts stratigraphic trends in parasequence stacking due to autogenic mechanisms or to acceleration or deceleration in relative sea level fluctuations are not revealed quantitatively iv some association is seen between the abundance of deltaic or river dominated parasequences and progradational stacking v positive but modest correlation is observed between measures of river system size and the dip length of shallow marine parasequence sand bodies the resulting insights can be applied to guide sequence stratigraphic interpretations of the rock record and the characterization of sub seismic stratigraphic architectures of subsurface successions

variations in natural levee morphology in anastomosed channel flood plain complexes abstract natural levees are common features of alluvial river systems yet their origin and evolution are poorly understood in this paper we present morphologic and sedimentologic data from two anastomosed rivers and offer a hypothesis of natural levee growth in these systems based on mechanisms of sediment transport in settings where floodbasins fill at the same rate as the channel levees form by turbulent diffusion of suspended sediment away from a high velocity thread into a floodbasin of relatively stagnant water the theory of diffusive transport suggests that these levees should be narrow steep and display abrupt decreases in grain size due to rapid decreases in carrying capacity with distance into the floodbasin in environments where an appreciable water surface slope is maintained between the main channel and the floodbasin levees form by advection of sediment out of the channel and into the floodbasin advective transport theory indicates that these levees should be broad and gently sloped with grain sizes gradually decreasing away from the main channel natural levees occurring in the anastomosed reach of the upper columbia river in se british columbia display significantly different morphology from levees in the cumberland marshes region of the lower saskatchewan river in east central saskatchewan at the upper columbia site the rise in stage of the floodbasin water nearly keeps up with that of the channel water because of good communication between channel and floodbasins through crevasses this inhibits the establishment of a water surface slope and the bulk of the escaping sediment is deposited close to the channel in contrast the cumberland marshes region is characterized by wide and volumetrically large floodbasins these conditions keep floodbasin water surface elevations relatively low and maintain an appreciable elevation head between the channel and its floodbasin fostering levee growth by advective transport

ice water pits upon the yellow river delta plain abstract the erosion circular pit is a common sedimentary structure but its genesis is complex many erosion pits occur on the yellow river delta plain with some formed by ice water erosion the ice water pits are generally circular or semi circular in cross section and are typically 2 40 cm across and 2 20 cm in depth we identify four types of pits on the basis of their origin i pits that formed by liquefaction and tight arrangement ii pits that formed by spattering iii pits that formed by lateral leakage and iv pits that formed by bottom leakage the formation of the ice water pits is likely a function of many complex variables including frequent runoff channel structure ice run and fine sediment size the example of ice water pits from the yellow river delta plain offers a useful frame of reference for the interpretation of formation conditions and environment significances of some circular pits pot or pothole in ancient rocks

alterations of cretaceous siltstones and sandstones near basalt contacts nugssuaq greenland abstract the influence of the intrusion of basaltic dykes and sills was investigated on sandstones and siltstones of the atane formation turonian coniacian from the sarqaq area nugssuaq peninsula central west greenland in the unaltered rock sequence the siltstones are dominated by kaolinite quartz and feldspar no cementation was observed the sandstones which are prevalent in this formation are arkoses and lithic arkoses with quartz feldspar ratios of about 1 with variable contents of rock fragments and with minor amounts of matrix the matrix consists mainly of kaolinite less frequently of illite muscovite and smectite or interstratified illite smectite cement minerals include calcite fe calcite both mainly in concretions and subordinate fe oxide hydrates the porosity of the sandstones and siltstones indicates a former maximum depth of burial of 1000 m in the sarqaq region adjacent to thin dykes and sills 1 2 m the above described rocks are altered as follows in sandstones albite fibrous quartzine smectite goethite were all formed at the expense of kaolinitic matrix and aragonite cement in siltstones interstratified illite smectite illite smectite and low cristobalite replaced kaolinite these minerals especially smectite exclude temperatures above 200 c they were probably formed during a cooling period adjacent to thicker basalt intrusions only sills over 5 m thick and no dykes are known from this area the following alterations are observed in sandstones two textural types of albite were formed in addition to 1 fibrous albite mentioned above 2 undulose lath shaped albite 3 coarse twinned non undulose replacement albite moreover brownish luminescing undulose quartz muscovite chlorite epidote nontronite and anatase occur in siltstones the mineral association muscovite chlorite pyrophyllite albite occurs suggesting temperatures in the range of 250 500 c additionally a 22 26 a mixed layer mineral chlorite muscovite formed at the contacts of thick as well as thin basalt intrusions the detrital grains directly adjoining the basalt are partly fractured potassium feldspar grains show also a chemical disintegration the temperatures calculated by application of a cooling model are higher than those indicated by the mineral alterations observed convective heat transfer by pore water is suggested as an explanation

sediment budget of the yellow river delta china the importance of dry bulk density and implications to understanding of sediment dispersal abstract this study constructs sediment budgets for the delta of the yellow river one of the world s largest muddy rivers and based on these budgets discusses the characteristics and related mechanisms of sediment dispersal at the river mouth the sediment budgets are derived from quantifying deposits in the deltaic lobe formed at the diaokouhe mouth of the river a detailed investigation of the dry bulk density of deposits in the delta which yields models of dry bulk density of deposits in the main depositional settings of the delta guarantees the reliability of the sediment budgets results show that deposits behind the delta front of the diaokouhe lobe over the period of 1965 to 1974 account for 73 5 of the incoming sediment the constructed sediment budgets reveal that the proportions of the deposits accumulated behind the delta front vary considerably over time the main factor responsible for the variations is the change in sediment discharge of the river there is no evidence for the anticipated positive relationships between the proportion of sediment escaping from the delta and water discharge clay content of incoming sediment or mouth channel efficiency the characteristics of sediment dispersal on the delta are related to the rapid extinction of sediment charged hyperpycnal underflows which are dominant in the plumes off the yellow river mouth and sediment deposition in the overbank flow on the delta plain because both of these processes trap a higher proportion of sediment at a higher sediment discharge

differential behaviour of the rb sr and k ar systems of spilitic flows and interbedded metasediments the spilite group of erquy brittany france paleomagnetic implications the erquy series cotes du nord france consists in its upper part of spilitic pillow lavas with some interbedded volcano sedimentary horizons

facies provenance and paleoclimate interpretation using spectral gamma logs application to the lower cretaceous of the scotian basin abstract spectral gamma logging has been useful in some settings for correlation of wells for identification of sediment facies and for interpretation of hinterland paleoclimate we have taken advantage of the hundreds of geochemical analyses of sandstones and shales from conventional core that are available from the scotian basin to test the relationship of the elements k u and th measured by spectral gamma to sedimentary facies these elements are also known to be useful in characterising provenance of sediment to different parts of the basin the geochemical and spectral gamma data both show that there are subtle differences in k u and th in different lithofacies such as higher th u in low sedimentation rate facies but they are not sufficiently distinctive to identify the lithofacies of any unknown interval the main control on abundance of these elements is the effect of grain size that is the proportion of sand to mud in sediment volcanic sources have a high k th ratio and early albian sediments with relatively high volcanic component have unusually high k th in distal shale prone successions the grain size effect is sufficiently small that climate controlled variations in th k ratio are recognised in the early cretaceous with the ratio being higher at times of humid weathering on land the variations in th k ratio through time are broadly similar to those known from western european sections notably with topmost hauterivian and topmost aptian humid events overall this study provides an assessment of the use and pitfalls of spectral gamma logs in a deltaic succession

geochemistry of the lower cretaceous chaswood formation nova scotia canada provenance and diagenesisgeological survey of canada contribution 20080004 the fluvial chaswood formation records a complex history of tectonic reactivation of basement horsts and shedding of clastic sediment previous mineralogical studies indicate sources from both local and more distant basement rocks of the appalachians because such mineralogical studies identify only particular source rocks the geochemistry of 60 samples from a complete section through the chaswood formation in borehole rr 97 23 was investigated to determine the character of bulk sediment supply the detrital signature is partially obscured by diagenetic processes that caused concentration of k p sr and u at three regional unconformities the elements ti in ilmenite and its alteration products zr in zircon th and y are largely controlled by the abundance of heavy minerals in the rocks ilmenite is the dominant first cycle heavy mineral whereas much of the zircon is of polycyclic origin therefore the ti zr ratio is a guide to the proportion of first cycle sediment supply from crystalline basem

sedimentary facies of the tide dominated paleo changjiang yangtze estuary during the last transgression abstract a large estuary was formed by marine inundation of the paleo changjiang yangtze incised valley during the transgression after the last glacial maximum this paper presents the sedimentary facies and architecture of the estuary fill based on the analysis of three sediment cores cm97 js98 and hq98 obtained from the present changjiang delta plain estuary fill deposits showing an upward fining succession were grouped into five depositional facies tidal river distributary channel muddy intertidal to subtidal flats transgressive lag and estuary front based on sedimentary textures lithology and physical sedimentary structures sand mud couplets are common in these deposits indicating that tides played a significant role in producing these sedimentary structures and that the estuary type was tide dominated some of the successive sand mud couplets probably recorded neap spring cycles as well as semidiurnal tidal cycles the nature of the estuary was very different from other representative tide dominated estuaries in sediment facies its distribution and sediment source for estuarine fill unlike the other estuaries that receive sediments mainly from the sea the paleo changjiang estuarine fill deposits were supplied largely from the river this difference would also have a great influence on the sedimentological and morphological component in the estuary the sediment distribution of the estuary showed fining seaward and estuary mouth sand bodies fed by marine source sand were absent the architecture model of tide dominated estuaries should be divided into two types by the degree of fluvial sediment supply the paleo changjiang estuary shows a good example for an estuary of large rivers

man s influence on the erosion and transport of sediment by asian rivers the yellow river huanghe example during the holocene sediment input from the yellow river to the yellow sea and adjacent areas has amounted to about 3000 km 3 detailed records from river gauging stations over the past 70 yrs together with estimates based on earlier historic records suggest that the river has contributed 2300 km 3 of sediment during the last 2300 yrs an average discharge of 1 km 3 yr 1 x 10 9 t yr prior to extensive agricultural use of the loess plateau in northern china beginning about 200 bc therefore the river s load must have been about 0 1 km 3 yr an order of magnitude lower than that at present a broad delta 20 m below sea level suggests that early holocene rates were higher than the pre agricultural average and therefore that middle holocene loads were low

geochemistry and regional significance of the early cretaceous bimodal basalt felsic associations on grand banks eastern canada cretaceous mafic rocks are present in several wells on the grand banks of newfoundland near the southwest grand banks jurassic transform margin and along the trend of the collector magnetic anomaly in the brant and mallard wells felsic volcanic subvolcanic and pyroclastic rocks are several hundreds of meters thick seismic reflection profiles show that the volcanic rocks are locally bounded by rejuvenated faulted margins of early rift basins beneath the mid cretaceous postrift unconformity the early cretaceous age of the volcanic rocks is confirmed by k ar geochronology trace element and isotopic composition of both mafic and felsic rocks are quite different from those of plume related cretaceous rocks elsewhere on the eastern north american margin mafic rocks have a pb isotopic composition unusually enriched in 207 pb 204 pb which is similar to late triassic early jurassic mafic rocks along the eastern appalachians nd isotopic compositions are closer to typical ocean island basalt oib sources observed isotopic compositions suggest mafic magma was partially melted from continental margin lithospheric mantle enriched with small amounts of hydrous or silica rich phases of oib affinity whole rock geochemistry isotopic composition and mineral chemistry show that the felsic rocks resemble alkaline a type granite those from mallard have some crustal contamination those from brant which is located closer to the continental margin edge have almost pristine mantle isotopic characteristics indicating an oib source magma the spatial distribution of cretaceous volcanic products suggests that magma was generated along the reactivated transform margin and that major faults in continental crust acted as magma conduits partial melting of continental margin lithospheric mantle resulted from extensional decompression probably aided by a weak plume related thermal anomaly as on other transform margins magmatic products reflect a complex mantle history

an integrated chemical and stable isotope model of the origin of midocean ridge hot spring systems chemical and isotopic changes accompanying seawater basalt interaction in axial midocean ridge hydrothermal systems are modeled with the aid of chemical equilibria and mass transfer computer programs incorporating provision for addition and subtraction of a wide range of reactant and product minerals as well as cation and oxygen and hydrogen isotopic exchange equilibria the models involve stepwise introduction of fresh basalt into progressively modified seawater at discrete temperature intervals from 100 to 350 c with an overall water rock ratio of about 0 5 being constrained by an assumed 18 o h 2o at 350 c of 2 0 per mil h craig personal communication 1984 this is a realistic model because 1 the grade of hydrothermal metamorphism increases sharply downward in the oceanic crust 2 the water rock ratio is high 50 at low temperatures and low 0 5 at high temperatures and 3 it allows for back reaction of earlier formed minerals during the course of reaction progress the results closely match the major element chemistry von damm et al 1985 and isotopic compositions craig et al 1980 of the hydrothermal solutions presently emanating from vents at 21 n on the east pacific rise the calculated solution chemistry for example correctly predicts complete loss of mg and so 4 and substantial increases in si and fe however discrepancies exist in the predicted ph 5 5 versus 3 5 measured and state of saturation of the solution with respect to greenschist facies minerals the calculated d h 2o is 2 6 per mil in excellent agreement with analytical determinations the calculated chemical mineralogic and isotopic changes in the rocks are also in good accord with observations on altered basalts dredged from midocean ridges humphris and thompson 1978 stakes and o neil 1982 as well as with data from ophiolites gregory and taylor 1981 predicted alteration products include anhydrite and clay minerals at low temperatures and a typical albite epidote chlorite tremolite greenschist assemblage at 350 c the models demand that the major portion of the water rock interaction occur at temperatures of 300 350 c interaction at temperatures below approximately 250 c results in negative 18 o h 2o shifts contrary to the observed positive 18 o values of the fluids exiting at midocean ridge vents hydrogen isotope fractionation curves by suzuoki and epstein 1976 lambert and epstein 1980 and liu and epstein 1984 among others are compatible with the model and require d h 2o to increase at all temperatures as a result of seawater basalt interaction

testing morphodynamic controls on the location and frequency of river avulsions on fans versus deltas huanghe yellow river china a mechanistic understanding of river avulsion location and frequency is needed to predict the growth of alluvial fans and deltas the huanghe china provides a rare opportunity to test emerging theories because its high sediment load produces regular avulsions at two distinct nodes where the river debouches from the loess plateau avulsions occur at an abrupt decrease in bed slope and reoccur at a time interval 607 yrs consistent with a channel filling timescale set by the superelevation height of the levees downstream natural deltaic avulsions reoccur at a timescale that is fast 7 yrs compared to channel filling timescale due to large stage height variability during floods unlike the upstream node deltaic avulsions cluster at a location influenced by backwater hydrodynamics and show evidence for episodic downstream migration in concert with progradation of the shoreline providing new expectations for the interplay between avulsion location frequency shoreline rugosity and delta morphology

emplacement of lobate sheet flows with hyaloclastites onto soft sediment the erquy neoproterozoic lava pile armorican massif france abstract the neoproterozoic volcano sedimentary succession of the heussaye headland erquy belongs to the cadomian block located in the north east of the armorican massif france the volcanism dated at approximately 608 7 ma zircon u pb data occurred in a back arc basin this site exhibits a noteworthy verticalized pile of moderately metamorphosed greenschist facies basaltic andesite flows of arc back arc tholeiite affinity alternating with metasedimentary layers sandstones and siltstones a large range of volcanic facies characteristic of an underwater soft substrate environment can be continuously studied for over than 200 m parallel to the flow edges they include pillow lavas lava lobes fluidal peperites and sediment matrix hyaloclastites the presence of parallel lava lobes in a sector where one lava flow is capped by a variably thick hyaloclastite carapace together with the occurrence of asymmetric turbiditic folds in interbedded metasedimentary layers suggests the existence of an easterly facing gentle paleoslope the sudden thinning of this hyaloclastite carapace in two spots located approximately 60 m from each other is attributed to the synvolcanic activity of two conjugate normal paleofaults this hypothesis is supported by the observation of a hyaloclastite accumulation in one of the two spots close to a strike slip fault which may have been extensional at the time of the volcanism water entered the lava flow along the faults resulting in an interstitial network of hyaloclastites by quench fragmentation in the upper part of the hanging wall block all these observations are consistent with a model of lava emplacement along a subaqueous slope resulting from synmagmatic extensional faulting in a marginal basin context

elemental fluxes during hydrothermal alteration of the trinity ophiolite california u s a by seawater abstract the trinity ophiolite has undergone hydrothermal alteration in greenschist to transitional amphibolite facies conditions the mineralogical assemblages and sr isotopic results reveal a widespread seawater circulation which has principally affected the upper part of the oceanic crust the interface between sheeted dikes and isotropic gabbros has reacted with the largest amount of heated seawater with water rock ratios w r up to 16 w r ratios and temperature are the most important parameters in determining the direction and amplitude of chemical changes during seawater rock interaction in addition calculation of elemental fluxes by mass balance on a crustal section reveals the important role of magma chemistry and related variations of primary model compositions the large chemical fluxes calculated in trinity rocks agree with their strong degree of alteration the w r of 8 in the trinity basalts are larger than those from hole 504b and east pacific rise 1 5 this is a possible consequence of a longer life time convective hydrothermal system in relation with a slow spreading center generating a thin crust contrasting with hole 504b this hydrothermal pattern is likely able to equilibrate the chemical budget for mg na and partly for k between seawater and oceanic crust the strong degree of alteration recorded by ophiolites corresponds to the time integrated effects of both initial and off axis hydrothermal activity ophiolites certainly represent valuable probes in tracking the chemical budget of the oceanic reservoir

fundamental processes controlling the first stage of alteration of a basalt glass by seawater an experimental study between 200 and 320 c the first stage of alteration of a basalt glass by seawater has been studied experimentally between 200 and 320 c under vapor pressure following both the chemical evolution of the reacting solutions during the experiments and the chemical and mineralogical transformations of the altered glass surface via microprobe scanning transmission electron microscope and resonant nuclear reactions the alteration is controlled by diffusion of dissolved species through an altered layer and not by surface chemical reaction selective removal of cations with respect to sio2 leads to the formation of a thick porous protonated surface layer enriched in sio2 aqueous diffusion of dissolved species from the reacting glass and from solution through the pores of this layer results in the formation of an amorphous silicate gel which is the precursor of normal crystalline clays saponites appearing in a later stage computer simulations of the alteration generated with the eq3 6 computer software package account for the chemical composition of the rim and the sequence of secondary minerals found in the experiments

odp leg 137 borehole fluid chemistry in hole 504b borehole fluid samples collected from site 504b during odp leg 137 provide the best opportunity to date to study water rock interaction within the ocean crust chemical composition of the borehole fluids reveal the results of seawater basalt interaction at elevated temperatures the borehole fluids can be described as a two component mixture consisting of a reacted fluid component and seawater which has convectively mixed into the borehole from the seafloor progressive trends in fluid chemistry with time suggest that the fluid rock reactions have changed as the borehole has been drilled deeper into the hotter formation based on data from this study and comparisons to fluid studies from past visits to site 504b indications are that these reactions are occurring within the borehole environment

rift related magmatism on magma poor margins structural and potential field analyses of the mesozoic notre dame bay intrusions newfoundland canada and their link to north atlantic opening abstract the magma poor newfoundland margin formed following lithospheric stretching rifting and breakup resulting in the separation of the grand banks from iberia and northern newfoundland from ireland mesozoic igneous rocks contemporaneous with rifting have been documented on and offshore newfoundland with later offshore magmatism occurring post breakup the notre dame bay magmatic province ndbmp is a jurassic cretaceous potentially rift related occurrence of igneous rocks onshore newfoundland that includes the gabbroic budgell harbour stock bhs and marginal lamprophyre dykes in addition to the nearby potentially related dildo pond intrusion dpi and leading tickles stock lts although the bhs is penetrated by wells it is poorly exposed at surface and the deeper structure remained unknown here results of field based mapping combined with inversion of full tensor gradiometry ftg and aeromagnetic data covering the bhs are presented although the ftg data are of a higher resolution than the magnetic data comparable results were obtained from these independent datasets we found that the dykes form clusters at the ends of density and susceptibility anomalies interpreted to be lobe like magmatic conduits furthermore potential field analysis has revealed the irregular geometry and southward dipping nature of the bhs in addition to the presence of multiple near surface anomalies that may correspond to dyke clusters or other igneous bodies structural analysis indicates that emplacement of the dykes was controlled by pre existing geological structures and that they have probably been deformed post intrusion potentially via the reactivation of pre rift faults the potential field investigations and observations of dyke margin lineations from field based structural analysis indicate that multiple dyke sources and bodies similar to the bhs may also exist finally this study demonstrates that magma poor margins such as the newfoundland margin may host significant volumes of extension related magmatic rocks challenging the concept of a distinction between magma rich and magma poor rifting

seawater sediment basalt interactions stable isotope h o and elemental fluxes within the ordovician volcano sedimentary sequence of erquy brittany france the ordovician volcano sedimentary succession of erquy northern brittany is made of immature sediments thermally metamorphosed at the contact of intruding basic sills pillow lavas constitute the upper part of the sequence the trace element geochemistry of sills and pillow lavas suggests that they were derived from a tholeiitic source located beneath a passive margin this volcanic sequence was metamorphosed under low to moderate greenschist facies conditions in this study the direction and amplitude of chemical and isotopic fluxes in the basalt sediment water system were established and the oxygen and hydrogen isotope compositions of the aqueous fluid that reacted with the volcanic rocks were characterized cationic thermometry on chlorites and isotopic thermometry on plagioclase chlorite pairs indicate closure metamorphic temperatures in the range 200 250 c for the basaltic sills stable isotope compositions of iron rich chlorites 18o 5 5 d from 60 to 50 and plagioclases 18o from 9 to 10 reveal that the source of the fluid was certainly seawater the 18o variations within the sills are strongly correlated with the rate of progress of the main metamorphic reaction clinopyroxene plagioclase ilmenite chlorite albite epidote quartz sphene that produced major element mobility at the scale of the volcanosedimentary sequence calculation of elemental fluxes by mass balance combined with oxygen isotopic compositions of basalts shows that the highest water rock ratios 1 were at sill sediment boundaries and within pillow lavas at the top of the pile the volcanosedimentary sequence of erquy was a net sink for na and a source for ca no mg uptake could be detected whereas the hydrothermal alteration of the sediments released fe si and k trapped by the volcanic rocks the 18o value of the fluid reacting with sills appears to have shifted no more than 4 after percolation at low temperature through immature sediments 18o 12 the erquy volcano sedimentary sequence represents a marine hydrothermal system dominated by low temperature exchange which allowed a general 18o enrichment of the volcanic rocks and a 18o depletion of sediments

stratigraphy and sedimentary environments during the late quaternary in the eastern bohai sea north china platform abstract the bohai sea is a shallow sea at the east coast of china it communicates with the yellow sea through a narrow strait during and since the late pleistocene the bohai sea has been a filled subsiding basin submitted to successive regressive transgressive cycles in the east bohai sea a number of finger shaped ridges are present near the strait where tidal currents are dominant very high resolution seismic reflection data have been interpreted relative to sedimentological data provided by a formerly drilled borehole seven seismic units are identified and correlated with the following events units u7 u6 with the bohai relative sea level rise 65 000 53 000 yr b p and a relative sea level fall 53 000 39 000 yr b p unit u5 with the xianxian relative sea level rise 39 000 22 000 yr b p unit u4 with the period of the late wurm glaciation 22 000 15 000 yr b p units u3 u2 with the transitional period from the end of the pleistocene to the beginning of the holocene 15 000 9000 yr b p and unit u1 with the holocene huanghua marine intrusion in the bohai sea since 9000 yr b p in the bohai sea formation of the tidal ridges is probably due to a substantial increase in tidal current velocities during the late holocene rise of sea level constriction due to the strait amplifies the tidal process so that the sediments of the late holocene transgressive sequence have been remodeled as tidal ridge

early cretaceous opening of the north atlantic ocean implications of the petrology and tectonic setting of the fogo seamounts off the sw grand banks newfoundland the lower cretaceous fogo seamounts and the j anomaly ridge formed along the transform margin of the southwestern grand banks synchronous with volcanism on the adjacent continental shelf off southeastern canada this volcanism took place during the nonvolcanic rifting of iberia from the grand banks chemical composition and radiogenic isotopes show that basalts from the seamounts range from mildly alkalic to mildly tholeiitic the voluminous tholeiitic magmas resulted principally from decompression melting and the ocean island basalt signature of the alkalic rocks also suggests upwelling of deeper asthenosphere the distribution of the seamounts has been determined from magnetic bathymetric and seismic data some seamounts are flat topped and resemble guyots in that they are capped by carbonate platform rocks the distribution of the seamounts suggests that they developed from edge controlled convection in the upper mantle due to thermal and density gradients at the transform transition between the spreading ocean and the continental block of the grand banks the thermal effects of the volcanism promoted mid crustal partial melting and detachment faulting on the grand banks and the development of the asymmetric grand banks iberia rift system the location of the volcanic centers was strongly influenced by crustal scale strike slip faulting although the fogo seamount chain thus has a different tectonic origin compared with many oceanic seamount chains the young seamounts from another area off the transform californian margin also show many geochemical similarities and may have a similar origin

the effects of strike slip motion along the cobequid chedabucto southwest grand banks fault system on the cretaceous tertiary evolution of atlantic canada the newfoundland fracture zone the southwest grand banks transform and the cobequid chedabucto fault zone form a linked strike slip fault system from the atlantic ocean to southeastern canada this paper suggests that several large scale geological features in southeastern canada are the result of a small amount of strike slip motion on the system during the mid cretaceous and oligocene regional extension features developed in the releasing bend in the laurentian sub basin during the mid cretaceous but the same area experienced oligocene compression this tectonic model accounts for the distribution of mid cretaceous volcanism fault bounded basins and regional unconformities as well as mid to late cretaceous subsidence of the scotian basin and oligocene uplift of the eastern scotian shelf

spatial and temporal evolution of an avulsion on the taquari river distributive fluvial system from satellite image analysis avulsion processes have been observed and analyzed using field based studies however they have rarely been analyzed through use of satellite imagery even though such an approach allows documentation of spatial and temporal variations of the resulting deposits in order to document changes that are occurring at the caronal avulsion on the taquari river brazil a time series of landsat imagery from 1985 to present 2010 was compiled as of july 2010 the imagery shows that the avulsion is not yet complete with discharge being routed to both the parent channel and the avulsion channel in the floodbasin the avulsion was initiated as flow was diverted from the parent channel to the floodbasin through two small crevasses allowing the development and evolution of splays with a single splay stabilizing only since 1999 the avulsion area is marked by the growth of new splays the formation of an avulsion belt and progradation of avulsion deposits into the floodbasin the parent channel downstream of the avulsion site has experienced decreasing width through time associated with the higher volumes of water and sediment being captured by the avulsion channel because this avulsion is not yet complete we expect more morphological changes to occur as the avulsion belt evolves into the primary channel rapid sedimentation caused by this avulsion and the 24 year time series of imagery that captured this change allowed us to construct a 3d block representing the evolution of depositional environments associated with avulsion using time in the vertical dimension thus we could represent the evolution of geomorphological patterns including floodbasin proximal levee distal levee and channel deposits and project their distributions through time this block of evolving sedimentary settings can be used as a guide for future sedimentologic studies by offering visual clues regarding the way which depositional systems track avulsion initiated changes

the shallow marine architecture knowledge store a database for the characterization of shallow marine and paralic depositional systems abstract the shallow marine architecture knowledge store smaks is a relational database devised for the storage of hard and soft data on the sedimentary architecture of ancient shallow marine and paralic siliciclastic successions and on the geomorphological organization of corresponding modern environments the database allows incorporation of data from the published literature which are uploaded to a common standard to ensure consistency in data definition the database incorporates data on geological entities of varied nature and scale i e surfaces depositional tracts architectural elements sequence stratigraphic units facies units geomorphic elements including attributes that characterize their type geometry spatial relations hierarchical relations and temporal significance furthermore geological entities are assigned to depositional systems or to parts thereof that can be classified on multiple parameters e g shelf width delta catchment area tied to metadata e g data types data sources the smaks permits the quantitative characterization of modern and ancient shallow marine and paralic clastic depositional systems it aims to serve as a repository of analogue information for hydrocarbon bearing successions and as a research tool that can be applied to aid the development of facies models or to assess the sensitivity of depositional systems to particular controlling factors for example to demonstrate the wide applicability of the database in fields of both fundamental and applied research example database output is presented that i includes data from wave tide and fluvial dominated shallow seas and sedimentary successions and ii covers a wide depositional spectrum from backshore to shelf edge settings the examples include information on the facies organization of different types of paralic sub environments on the hierarchical arrangement of architectural elements that form deltaic constructional units in quaternary deltas on the morphometry of modern and quaternary tidal sand ridges and on the geometry of parasequence scale nearshore sandstone belts from the upper cretaceous of the western interior seaway in utah usa

seismic and core investigation on the modern yellow river delta reveals the development of the uppermost fluvial deposits and the subsequent transgression system since the postglacial period abstract postglacial stratigraphy and environmental evolution onshore and offshore the modern yellow river delta were investigated and analyzed through 1200 km high resolution seismic profiles and four boreholes together with previous publications four seismic units su 1 4 top to bottom that are bounded by seismic surfaces t1 t4 were identified in seismic profiles while four depositional units du 1 4 top to bottom were recognized in representative boreholes these seismic units and depositional units exhibit good correlation we interpreted su 1 du 1 as the modern yellow river deltaic deposits su 2 du 2 as the holocene neritic sediments su 3 du 3 as a pleistocene holocene transitional layer and su 4 du 4 as the lowstand fluvial sediments apart from t1 seafloor t2 deltaic base t3 shoreface ravinement and t4 transgressive surface all dip seaward but their dipping gradients reduced from t4 to t2 therefore the thicknesses of su 2 3 were observed seaward thicker trends presumably in relationship with different spatial sedimentation rates additionally down core distributions of environmental proxies e g grain size microfossils and geochemical characteristics reveal the transgression system du 2 and 3 can be further subdivided into 5 intervals associated with sharp environmental changes based on above evidences we raised an evolutionary model of the postglacial depositional environment at the modern yellow river delta and adjacent marine areas suggesting the study area evolved from riverine estuarine coastal shoreface neritic to final prodeltaic deltaic environment since the post last glacial maximum lgm in relationship with eustatic and climatic events as well as sediment input in the model we redefined the two phase channel systems that exhibited in our previous study liu et al 2014 as the tributaries of the lgm paleo yellow river and the tidal estuarine tidal channels that formed at the early holocene besides we speculated that two hiatuses erosions occurred at younger dryas and 4 3 cal kyr bp and further divided the study area into three depositional zones based on their different sedimentation rates of the transgression system

the cretaceous peri atlantic alkaline pulse paap deep mantle plume origin or shallow lithospheric break up abstract although the early jurassic initial phases of atlantic rifting were marked by the tholeiitic basalt flows and dikes of the central atlantic magmatic province camp the cretaceous era was characterised by widespread alkaline igneous activity on widely separated peri atlantic continental margins nearly half the peri atlantic alkaline rocks dated between 250 to 50 ma fall within the 125 80 ma range this period of intense alkaline activity during the mid cretaceous formed the peri atlantic alkaline pulse paap the mechanisms for the opening of the atlantic ocean as well as for the camp and later paap magmatic events have been attributed either to deep mantle plumes or to a combination of tensional forces lithospheric rifting and structural controls we describe the paap event for the first time and test the plume and structural models the paap displays evidence of strong structural control and appears to be related to reactivation of pre existing lithospheric structures throughout the peri atlantic zone early stages of continental separation and abrupt changes in plate motion were the most likely mechanisms for the reactivation of favourably oriented pre existing structures mid cretaceous pulses in alkaline magmatic activity were closely associated with major atlantic tectonic events the opening of the south atlantic the change in intensity and direction of both seafloor spreading and plate motion and the consequent fluctuation in intra plate stresses were responsible for two spikes in peri atlantic alkaline magmatism at 125 ma and 85 80 ma the general lack of evidence for a deep hotspot associated with the peri atlantic zone seems incompatible with a mantle plume origin on the other hand the spatial distribution of the paap along passive continental margins suggests an ideal setting for the development of edge driven convection we propose that the periodic reactivation of deep seated pre existing zones of weakness during the major stages of atlantic tectonic evolution combined with coeval asthenospheric upwelling due to edge driven convection and continental insulation flow enhanced the ascent of alkaline magmas this mechanism of shallow small scale upwelling during periodic structural reactivation provides a more likely explanation for the paap than the commonly proposed deep mantle plume scenario

the rift to drift transition in the southern north atlantic a stuttering start of the morb machine comment and reply comment jagoutz et al 2007 1 argue for a long history of alkaline to mid oceanic ridge basalt morb type magmatism occurring during the transition from amagmatic to magmatic rifting at the iberia newfoundland conjugate margin u pb zircon ages suggest that magmatism spanned the range of 110 127

on the origin of crevasse splay amalgamation in the huesca fluvial fan ebro basin spain implications for connectivity in low net to gross fluvial deposits abstract floodplain deposits are abundant in low gradient dryland river systems but their contribution to connected reservoir volumes has not yet been fully acknowledged due to their poor detectability with typical wireline log suites and relatively lower reservoir quality this study presents an analysis of stacked crevasse splays in the distal part of the miocene huesca fluvial fan ebro basin spain vertical stacking of crevasse splays implies local aggradation of the active channel belt lateral amalgamation of crevasse splays created an elevated rim around their feeder channel raising its bankfull height subsequent crevasse splays were deposited on top of their predecessors creating sand on sand contact through incision and further raising the active channel belt this process of channel belt super elevation repeated until an upstream avulsion occurred amalgamated crevasse splays constitute connected reservoir volumes up to 107 m3 despite their lower reservoir quality they effectively connect channel deposits in low net to gross fluvial stratigraphy and hence their contribution to producible volumes should be considered unswept intervals of amalgamated crevasse splays may constitute a secondary source of natural gas their interval thickness can serve as a proxy for feeder channel dimensions which can in turn be used to estimate the degree of stratigraphic connectivity

hydrothermal alteration in oceanic ridge volcanics a detailed study at the galapagos fossil hydrothermal field abstract the galapagos fossil hydrothermal field is composed of altered oceanic crust and extinct hydrothermal vents within the eastern galapagos rift between 85 49 w and 85 55 w the discharge zone of the hydrothermal system is revealed along scarps thus providing an opportunity to examine the uppermost mineralized and highly altered interior parts of the crust altered rocks collected in situ by the submersible alvin show complex concentric alteration zones microsamples of individual zones have been analysed for major minor trace elements and strontium isotopes in order to describe the complex compositional details of the hydrothermal alteration interlayered chlorite smectite and chlorite with disequilibrium compositions dominate the secondary mineralogy as replacement phases of primary glass and acicular pyroxene phenocrysts and matrix grains of plagioclase are unaffected during alteration using a modification of the gresens equation we demonstrate that the trivalent rare earth elements rees are relatively immobile and calculate degrees of enrichment and depletion in other elements strontium isotopic ratios increase as sr concentrations decrease from least altered cores to most altered rims and cross cutting veins in individual samples and can be modeled by open system behaviour under low fluid rock ratio

sediment transport of fine sands at high velocities the predictive capability of the sediment transport formulas of ackers white engelund hansen and van rijn at high flow velocities is investigated total load transport at high velocities over a fine sand bed 100 400 m is studied by analyzing data from the literature and data from new flume and field measurements flume experiments were performed to measure flow velocity and sand concentration profiles in a self eroding flow initially free of sediment the flow velocities were up to 2 7 m s a two dimensional vertical mathematical model for suspended sediment was applied to compute the equilibrium transport rates finally predicted transport rates are compared with measured transport rates under flume and field conditions the formulas of engelund hansen and van rijn predict transport rates that are in reasonable agreement with the measurements

low temperature alteration of basalt by interstitial seawater mururoa french polynesia chemical and isotopic analysis of interstitial fluids and secondary phases in two drill cores from the volcanic pile of the mururoa atoll french polynesia permits documentation of the lowtemperature alteration by seawater of basalt and secondary minerals as a function of rock water ratio r w up to 110 g l as r w increases in this system up to 70 g l the interstitial waters exhibit an almost total removal of mg and k a net decrease of ph and eh a marked enrichment in ca sr and si and depletion of 18o and d with further increases in r w above 70 g l a reversal of mg ca exchange is observed mg accumulates in the fluid while ca is removed in addition the enrichment of 18o and d is also observed in the fluids at these high r w these chemical and isotopic reversals are shown to result from the transformation of early precipitated mg rich saponite into ca na saponite chemical and isotopic reactions take place at two separate solid solution interfaces 1 1 an interface at the surface of the fresh basalt that leads to the formation of a hydrated amorphous layer which progressively crystallizes into clay and 2 2 a second interface between the interstitial bulk fluid and the resultant clay layer consequently geochemical codes which fail to account for both aqueous diffusion in altered layers and the existence of multiple reaction interfaces cannot accurately describe alteration at high rock water ratios

low temperature alteration of the upper oceanic crust and the alkalinity budget of seawater abstract while the input of river alkalinity into seawater is relatively well known the complementary acidity production is poorly understood using the major element budget of seafloor alteration of the upper 500 m of 120 ma old oceanic crust at dsdp odp sites 417a 417d and 418a in the central western atlantic we estimate the acidity flux associated with the low temperature weathering of the upper oceanic crust the acidity flux is calculated based on major element fluxes and charge balance considerations the relevant chemical fluxes from seawater to the upper crust are 4 1 0 1 1 4 1 4 2 2 0 6 and 12 2 1011 mol yr 1 for k mg na and silicate ca respectively the associated acidity flux is 3 5 3 1011 eq yr 1 relative to continental weathering these fluxes are significant for k and silicate ca but are minor for na mg and acidity thus riverine fluxes of alkalinity are not significantly balanced by acidity fluxes from low temperature upper ocean crust alteration

volcanic ash in the lower cretaceous chaswood formation of nova scotia source and implicationsgeological survey of canada contribution 20100082 lignites and coals because of their low sedimentation rates of terrigenous detritus may preserve a record of volcanic ash fall lignite from the lower cretaceous chaswood formation in central nova scotia was studied to identify whether any volcanic ash is present and can be correlated to known early cretaceous volcanism in southeastern canada and adjacent new england the bulk mineralogy and geochemistry of lignite and lignitic mudstones was determined by x ray diffraction and whole rock geochemical analysis of ashed samples selected samples were examined by electron microprobe and scanning electron microscope much of the terrigenous component of some lignites consists of detrital sediments in some lignites distinctive rare earth element patterns are due to leaching from monazite and concentration in organic matter some lignites however lack illite and or quartz indicative of detrital sources but show unusual abundance of stable high field strength elements such as nb ta and hf suggesting a

mass transfer during sub seafloor alteration of the upper troodos crust cyprus five major alteration zones in the extrusive series and the sheeted dike complex of the troodos ophiolite are each characterized by a distinct elemental changes compared to the original composition and b secondary mineralogy the upper ca 300 m of the extrusive crust the highly oxidatedcold seawater alteration zone csa is strongly enriched in k2o and depleted in na2o it is followed downwards by alow temperature alteration zone 170 c which is most widespread in the troodos extrusives and where na2o and k2o are enriched the latter less strongly than in the csa zone three types ofhigh temperature alteration zones 440 c hta i iii are found in the sheeted dike complex all are marked by thorough leaching of k2o while the behavior of na2o e g unchanged in type iii and cao depleted in type i enriched in types ii iii is variable mass budgets of elemental changes are quantified by calibration of whole rock analyses via systematic stable element variations of fresh glasses found throughout the extrusive section the troodos extrusive crust and upper sheeted dike complex are a major sink for mgo k2o and na2o and a source for cao the overall scale of fluxes drastically exceeds estimates based on fresh basalt compositions from present ocean crust

overbank and channelfill deposits of the modern yellow river delta abstract the huanghe is noted for its high transport rate of silt and clay which may reach depth averaged values of 200 kg m 3 during peak discharge the sediment load transported through the river on entering the delta plain amounts to 1012 kg per year in contrast to most other large deltas only one distributary channel is active at any one time the high sediment load causes the rivermouth to prograde at a yearly rate of 1 4 km into the shallow less than 20 m deep bohai gulf the vertical aggradation of the channel belt and mouth bar complex is also rapid decimetres per year on average so that after a normal average of twelve years increasing channel instability and avulsion create the start of a new delta lobe a series of satellite images covering the last fifteen years has provided insight in the evolution of the river pattern as well as the progradation of the delta front a newly developed distributary passes from a multichannel to a single straight channel system and ends with the formation of meanders the protruding mature delta lobe shows a radiating pattern of crevasse channels overbank crevasse deposits are made of vertically stacked dm scale waning flow sequences structurally characterized by from bottom to top small scour and fills even parallel lamination and climbing ripple crosslamination accumulation rates on crevasse splays can be predicted on the basis of estimated river sediment discharge it can be concluded that each sequence has been deposited within a few hours and that tidal waterlevel fluctuations may have played a role in the generation of a single sequence

introduction to the river dominated shelf sediments of the east asian seas peter d clift1 jan harff2 3 jiaxue wu4 yan qiu5 department of geology and geophysics louisiana state university baton rouge la 70803 usa university of szczecin institute of marine and coastal sciences mickiewicza 18 pl 70 383 szczecin poland leibniz institute for baltic sea research seestrasse 15 d 18119 rostock warnemunde germany centre of coastal ocean science and technology sun yat sen university guangzhou 510275 china guangzhou marine geological survey china geological survey guangzhou 510760 china

hydrothermal alteration of a 1 km section through the upper oceanic crust deep sea drilling project hole 504b mineralogy chemistry and evolution of seawater basalt interactions deep sea drilling project hole 504b penetrates 1076 m into oceanic layer 2 and is the first hole to pass through the transition from pillow basalts altered at low temperatures into hydrothermally metamorphosed sheeted dikes alteration of the crust at site 504 occurred in four stages related to the movement of the crust away from the spreading axis 1 dikes reacted with seawater 200 300 c in the upwelling zone of an axial convection cell at the spreading axis resulting in the formation of greenschist facies parageneses in veins and host rocks mixing of the upwelling hydrothermal fluids with seawater circulating in the overlying more permeable pillow section occurred in the upper part of the lithologic transition zone causing a steep temperature gradient at the base of the pillow section secondary minerals formed in the lower pillow section from the resultant reducing mixed fluids at temperatures of around 100 c at the same time the initial effects of seafloor weathering began in the upper 320 m of the pillow section at low temperatures 50 c and under conditions of open circulation of oxidizing seawater 2 following refracturing of the dikes a second stage of axial upwelling occurred hydrothermal fluids 200 380 c were probably similar to those presently sampled from spreading ridges on the seafloor mixing of these fluids with seawater in the lithologic transition zone caused deposition of quartz epidote and sulfides in veins and formation of a sulfide rich stockworklike zone within this transition zone alteration of the pillow section proceeded under the prior conditions with the effects of seafloor weathering extending progressively downward into the crust 3 seawater recharge penetrated to depths of at least 1075 5 m subbasement and deposited anhydrite locally in veins 4 off axis alteration of the dikes was characterized by formation of zeolites calcite and prehnite in veins and host rocks from more highly evolved and lower temperature 100 250 c fluids alteration in the upper pillow section evolved from seafloor weathering conditions to more reducing and rock dominated as cracks in the basalt were sealed with secondary minerals and the basement was covered with a layer of sediment zeolites and calcite were the last phases to form throughout the pillow section sealing of the crust to convective cooling also allowed conductive reheating of the crust from below calculations of seawater crustal chemical fluxes from whole rock data are complicated by the low recovery and heterogeneity of alteration effects but indicate that basalt seawater interactions are a sink for seawater mg and k and a source for si and ca

on the geological significance of clastic parasequences abstract parasequences recognized in clastic sedimentary successions of shallow marine origin are considered by some geologists to be the fundamental building blocks of depositional sequences even though problems in their definition and application have been identified by others who instead advocate their abandonment as formal sequence stratigraphic units to elucidate the geological significance of clastic parasequences and inform the debate on their use in stratigraphy a quantitative characterization of the geometry facies characteristics and timescale of deposition of 1163 parasequences has been undertaken based on a synthesis of data from outcrop and subsurface studies that are available in the scientific literature through a database compilation the attributes of the studied parasequences are analysed with respect to the interpreted geological origin of the units and with consideration of sources of bias and uncertainty particular emphasis is placed on assessing the following i the importance of heuristics and of data types and coverage in the recognition of parasequences ii differences in parasequence characteristics observed across deltaic and shoreface depositional systems and between the quaternary and the ancient rock record iii possible explanations for the range in timescales of deposition of parasequences and iv the role of autogenic dynamics on the development of deltaic parasequences partly based on a comparison with the recent evolution of modern deltas the results demonstrate that parasequence definition and physical correlation suffer from subjectivity and that significant variability exists in the spatio temporal and architectural attributes of clastic parasequences this gives rise to uncertainty that affects the use of parasequences as a framework for comparison of the architecture of packages of strata originating via shoreline regression this uncertainty must be considered when using analogue data for subsurface predictions or when attempting comparative studies of clastic successions

early cretaceous volcanism in the scotian basin1 1this article is one of a series of papers published in this cjes special issue on the theme of mesozoic cenozoic geology of the scotian basin early cretaceous volcanism is widespread in the eastern scotian basin the stratigraphic position of volcanic rocks within wells was re evaluated and the volcanological character of the rocks was refined by study of cuttings and well logs hauterivian barremian volcanic rocks on the sw grand banks and aptian albian volcanic rocks in the orpheus graben and se scotian shelf resulted from strombolian type eruptions more extensive hawaiian type flows were mapped from seismic profiles near the mallard and brant wells on the sw grand banks and they appear to have been derived from local basement highs with a positive magnetic anomaly interpreted as volcanic centres igneous rocks in the hesper well on the se scotian shelf are the erosional remnant of basaltic flows that terminated at the paleoshoreline they correlate with basalt flows both in extensive outcrop on scatarie ridge and in several orpheus graben wells the interpretation of the hesper basalts as an erosional remnant of more extensive basalt flows

a chlorite solid solution geothermometer the los azufres mexico geothermal system chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites in the active geothermal system of los azufres mexico electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition correlation coefficients among chemical constituents were calculated it is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content and there is almost no correlation with the octahedral aluminium and magnesium content a procedure is proposed to select end members and substitution vectors and to give a general formula for these chlorites

linking river flood dynamics to hyperpycnal plume deposits experiments theory and geological implications turbid river plumes entering ocean or lake water of lesser density i e hyperpycnal plumes can plunge to form turbidity currents providing an important link between terrestrial sediment sources and marine depositional sinks a leading hypothesis suggests that hyperpycnal plume deposits accurately record the rising and falling discharge of a flooding river in terms of sediment size grading bedform sequence and deposit thickness which if correct has significant implications for unraveling river dynamics reservoir potential and earth history from marine event beds herein we present one of the first experimental flume studies aimed at testing this hypothesis results indicate that depth averaged hyperpycnal plume velocities can be uncorrelated or even anti correlated with river discharge at certain seabed locations because of translation of the plunge point resulting from temporal variations in discharge and sediment concentration through the duration of a river flood an advection length scale of settling sediment is found to be an important control on hyperpycnal plume deposits where coarse sediment sand is most likely to record multiple flow accelerations and decelerations related to plunge point translation even for a river flood with a single peaked hydrograph in contrast fine sediment mud is relatively insensitive to local plunge point dynamics and is most likely to preserve directly rising and falling river discharge finally it was found that the necessary fluvial sediment concentration to form a plunging plume can be much larger than the concentration typically used assuming density equivalence because of deposition upstream of the plunge point

the progradation and retrogradation of two newborn huanghe yellow river delta lobes and its influencing factors abstract in this paper 342 landsat satellite images were used to study the evolution of the qingshuigou and qing8 lobes during 1976 2016 sea level correction and statistical analysis were used to eliminate the effect of sea level fluctuations on the shoreline positions the results revealed that the evolution of the two newborn huanghe delta lobes was mainly influenced by the river sediment discharges river channel changes course shifts floods droughts and marine hydrodynamic forces during 1976 2016 the total land gain of the two lobes was 377 km2 according to mean tide line and the average epeirogenetic efficiency of river sediment discharge was 0 020 m2 ton which was greatly less than that when the channels were natural the artificial stabilization of the deltaic channels had negative impact on the land gain assuming no artificial adjustment to the deltaic channels the total land gain would increase 435 km2 the land gain of the two lobes was a function of the cumulative sediment discharges shoreline lengths and course shift bonuses under the circumstance of historical river channel changes the critical sediment discharge maintaining the area balance of the two lobes was a function of historical shoreline lengths which increased linearly from 61 m ton in 1976 to an average of 163 m ton during 1996 2016 in the future there are two ways to increase the land gain under the less huanghe sediment discharge reducing artificial disturbance of deltaic channels and letting the river enter the sea through the southwest coast of qingshuigou lobe

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

characterization of sills associated with the u reflection on the newfoundland margin evidence for widespread early post rift magmatism on a magma poor rifted margin author posting the authors 2010 this article is posted here by permission of john wiley sons for personal use not for redistribution the definitive version was published in geophysical journal international 182 2010 113 136 doi 10 1111 j 1365 246x 2010 04635 x

extreme 18o enriched volcanics and 18o evolved marine water aljustrel iberian pyrite belt transition from high to low rayleigh number convective regimes abstract quartz eye keratophyric tuffs at aljustrel s portugal iberian pyrite belt possess unusually high uniform whole rock values up to 18 1 with a mean of 16 7 0 7 because the quartz eye cores have 18o 12 0 to 13 5 the felsic tuffs may have had an original whole rock oxygen isotope composition of 10 to 11 the deduced enrichments of up to 8 in keratophyric derivatives is attributed to isotope exchange with abundant marine water under temperatures which diminished to 100 c during thermally driven convective cooling the isotopic uniformity requires elevated permeability of 10 8 cm2 such that the second critical rayleigh number was exceeded and drifting non steady state convection cells dominated with relatively smooth thermal structures in mineralised counterparts of the tuffs beneath the feitais estacao zn pb cu massive sulphide orebodies whole rock values are 12 and quartz 13 3 15 4 chlorite 3 2 6 3 fractionations correspond to temperatures of 220 270 c and a calculated fluid 18o of 1 4 to 5 7 this local isotopic overprinting in vent domains of the regionally high 18o was induced by a stable second stage convective regime imposed by drastic reduction of permeability accompanying capping of the geothermal discharge by hydrothermal cherts and or progressive spilitisation of the tuffs at lower water rock coupled with higher temperatures the recirculating marine water underwent variable 18o enrichment up to 5 7 by exchange with the high 18o tuffs an upwards increase in 18o quartz and quartz reflects progressive cooling of the geothermal discharge from 15 4 270 c in the stockwork through 18 3 220 240 c in the orebody to 20 1 110 130 c in overlying hydrothermal cherts probably induced by entrainment of ambient marine bottom water in sub seafloor aquifers

modeling deltaic lobe building cycles and channel avulsions for the yellow river delta china river deltas grow by repeating cycles of lobe development punctuated by channel avulsions so that over time lobes amalgamate to produce a composite landform existing models have shown that backwater hydrodynamics are important in avulsion dynamics but the effect of lobe progradation on avulsion frequency and location has yet to be explored herein a quasi 2 d numerical model incorporating channel avulsion and lobe development cycles is developed the model is validated by the well constrained case of a prograding lobe on the yellow river delta china it is determined that with lobe progradation avulsion frequency decreases and avulsion length increases relative to conditions where a delta lobe does not prograde lobe progradation lowers the channel bed gradient which results in channel aggradation over the delta topset that is focused farther upstream shifting the avulsion location upstream furthermore the frequency and location of channel avulsions are sensitive to the threshold in channel bed superelevation that triggers an avulsion for example avulsions occur less frequently with a larger superelevation threshold resulting in greater lobe progradation and avulsions that occur farther upstream when the delta lobe length prior to avulsion is a moderate fraction of the backwater length 0 3 0 5l b the interplay between variable water discharge and lobe progradation together set the avulsion location and a model capturing both processes is necessary to predict avulsion timing and location while this study is validated by data from the yellow river delta the numerical framework is rooted in physical relationships and can therefore be extended to other deltaic systems

hidden cretaceous basins in nova scotia early cretaceous unconsolidated quartz sand and kaolinitic clay deposits in the lowlands of nova scotia are preserved in narrow half grabens obscured by glacial drift the chaswood formation sediments can be subdivided into three members upper and lower members dominated by cyclical sand mud facies of fluvial origin and the middle member with lignitic clay of lacustrine origin ferruginous oxisols are common in the fine grained facies of the upper and lower members seismic data indicate that chaswood formation strata in the elmsvale basin are deformed into steeply dipping faults and fault related folds rutherford road fault zone an aptian albian age for this tectonic event is inferred from synsedimentary deformation and from the angular unconformity spanning the late cretaceous and tertiary that truncates the chaswood formation exhumation of a thick cover of mesozoic sediment 1 2 km is needed to account for the preservation of chaswood formation outliers after 80 ma of erosion the half grabens that host the chaswood formation were formed in the mesozoic and were antecedent to the present day structurally controlled lowlands

historical changes in the yellow river delta china abstract the lower yellow river delta has experienced numerous avulsions during the last 2000 years and the floodplain can be divided into four provinces alluvial fan western plain middle plain and eastern plain coastal deltas the yellow river delta complex is composed of several delta superlobes resulting from shifts in the lower river channel and each delta superlobe consists of several smaller lobes formed by shifts in the distributary channels these two kinds of channel shifts have resulted in a complicated imbrication pattern in the delta complex two imbricated delta superlobes are divided by a reworked bed and buried shelf deposits shelly ridges form the surface boundaries between the various delta superlobes the delta superlobes passed through an active stage a reworking stage and were then finally overlain by later superlobes

ophiolites as faithful records of the oxygen isotope ratio of ancient seawater the solund stavfjord ophiolite complex as a late ordovician example

paleohydrogeological and thermal events recorded by fluid inclusions and stable isotopes of diagenetic minerals in lower cretaceous sandstones offshore nova scotia canada upper jurassic lower cretaceous sandstones of the scotian basin offshore eastern canada are important gas reservoirs previous studies of fluid inclusions in jurassic limestones and apatite thermochronology of cretaceous sandstones have suggested a late mesozoic thermal event fluid inclusions in different authigenic cements were analyzed to determine the temperature and composition of basinal fluid at the time of precipitation and the timing of hydrocarbon migration and entrapment fifty one sandstone samples were analyzed for stable isotope composition 18o and 13c of carbonate cements trapping temperatures for primary aqueous inclusions hosted in quartz overgrowths 89 175c and in late carbonate cements 138 173c are higher than predicted by two dimensional modeling from burial alone based on postrift geothermal gradients these inclusions contain high salinity fluids mostly 19 22 wt nacl equivalent second predominantly aqueous inclusions have much lower salinities 5 2 6 7 wt nacl equivalent and some contain liquid hydrocarbons late fe calcite cement in hauterivian sandstone shows negative values of 13 17 to 9 2 whereas cements in deeper and shallower sandstones have higher 13c values these data indicate that high temperature high salinity fluids preceded hydrocarbon migration the oldest and youngest rocks studied show less effect of high temperatures than do rocks that were buried to depths of at least 2 km 1 2 mi after 135 ma and before 100 ma both fluid inclusions and 13c of carbonate cement suggest that highest temperatures were achieved during burial at 115 to 105 ma this early cretaceous thermal event had a geothermal gradient of at least 55c km it is earlier than the previously reported event based on apatite fission tracks but is consistent with the fission track data the event is synchronous with regional evidence of volcanism and its peak coincides with rapid salt tectonic deformation in the deep basin hydrocarbon charge to the outer shelf wells occurred after this thermal event and thus not before the late cretaceous

the huanghe yellow river and changjiang yangtze river deltas a review on their characteristics evolution and sediment discharge during the holocene abstract today asian rivers play an important role in delivering sediment from the land to the oceans however past sediment discharge before human activities modified the landscape is not well known and is estimated to have been roughly one third to one half of the present level chinese rivers have been strongly influenced by human activities and their sediment discharge has changed over the last 6000 years for the study of the long term human impact on rivers and catchment basins chinese rivers provide excellent examples because continuous historical records are available here the characteristics evolution and sediment discharge during the holocene of the deltas of two large chinese rivers huanghe yellow river and changjiang yangtze river are summarized the huanghe and changjiang deltas are different with respect to coastal environments water and sediment discharge the pattern of development of the delta lobe thickness of holocene sediments and basal topography of the incised valleys formed during the last glacial period the huanghe delta is characterized by a high concentration of sediment huge sediment discharge thin holocene deltaic sediments a lateral delta lobe shift and a steep longitudinal profile in its lower reaches the changjiang delta is characterized by a large water discharge a large interseasonal water level change a tide dominated coastal environment continuous seaward progradation with isolated river mouth sand bodies thick holocene sediments and a deep incised valley formed during the last glacial period based on the sediment volume of prograding deltaic sediments over the last 6000 years the sediment discharge of huanghe 1000 years ago is estimated to have been 1 10 8 tons year 1 10 of the present level an abrupt increase occurred at ca 1000 years ago as a consequence of human activities on the loess plateau especially involving cultivation and deforestation moreover the estimated sediment load of huanghe at sanmenxia station prior to 1000 years was 2 7 4 0 10 8 tons year or about 20 15 25 of the present level our recent study estimated that the sediment discharge of changjiang before 2000 years bp was ca 2 4 10 8 tons year total sediment discharge of both rivers before 2000 years bp is estimated to have been 3 4 10 8 tons year or only about 20 of the present level moreover the total sediment load to the lower reaches is estimated to have been 5 6 10 8 tons year or one fourth the present level

transgressive depositional systems of the mississippi delta plain a model for barrier shoreline and shelf sand development abstract depositional sequences generated in the mississippi river delta plain consist of a regressive and a transgressive component the transgressive component has been considerably less studied but accounts for the majority of the surface area on the lower mississippi river delta plain and up to 50 percent of the total sequence thickness in shallow water deltas the development and preservation of transgressive depositional systems in abandoned delta complexes follows the process of transgressive submergence in which the horizontal component of reworking occurs during shoreface retreat combined with a vertical component of submergence acting to preserve the sequence the evolution of transgressive depositional systems in each of the abandoned holocene mississippi river delta complex s can be summarized in a three stage model beginning with stage 1 an erosional headland and flanking barriers in this stage regressive sand deposits contained within abandoned deltaic headlands are reworked by the eroding shoreface and dispersed longshore into contiguous flanking barriers enclosing restricted interdistributary bays submergence of the delta plain during relative sea level rise generates an intradeltaic lagoon separating the former stage 1 sand body from the shoreline forming stage 2 a transgressive barrier island arc the landward migrating barrier island arc is unable to keep pace with relative sea level rise and the retreating mainland shoreline resulting in submergence and the formation of stage 3 an inner shelf shoal following submergence the former barrier island arc sand body continues to be reworked into a marine sand body on the inner continental shelf during stage 3 this sequence of coastal evolution provides direct evidence of barrier island formation with each stage producing a distinctive stratigraphic signature the current sea level rise models of shoreface retreat and in place drowning developed for the u s atlantic continental shelf do not adequately explain either the morphology or the stratigraphy of transgressive mississippi river delta sand bodies current models of mississippi deltaic stratigraphy emphasize the deep water artificially maintained balize delta which differs considerably from the shallow water shelf phase delta complexes that are the primary depositional constituents of he holocene mississippi river delta plain

oxygen and hydrogen isotopes in the volcano sedimentary complex of huelva iberian pyrite belt example of water circulation through a volcano sedimentary sequence abstract the minerals of basic and acidic rocks from the volcano sedimentary sequence in the huelva area spain iberian pyrite belt display an extended 18o enrichment quartz 18o values from quartz keratophyres vary from 10 5 to 17 0 and feldspar 18o values from 14 4 to 16 0 for the spilite or spilitized dolerites 18o values vary from 9 9 to 13 4 for feldspar from 6 4 to 9 8 for chlorite from 3 7 to 4 3 for ilmenite and from 13 6 to 14 0 for quartz but pyroxene exhibits magmatic values from 5 3 to 6 1 with an exception at 7 5 the chlorite d values vary from 34 to 43 this is attributed to hydrothermal alteration with seawater enriched in 18o by circulation through sediments the temperatures of interaction determined from isotopic fractionations between minerals range from 400 to 520 c calculated d and 18o values for water in equilibrium with the minerals at isotopic temperatures range from 16 to 5 and from 8 3 to 12 8 respectively a model of circulation of seawater through a pile of sedimentary rocks and then through basaltic rocks is proposed to explain the high18o compositions of the rocks from the huelva district water rock mass ratios calculated from this model range between 0 3 and 0 7 for the determined range of temperatures

electrical resistivity imaging of anastomosing river subsurface stratigraphy and possible controls of fluvial style change in a graben like basin czech republic abstract subject to frequent channel avulsions due to the increased frequency of floods rise of base level and or sediment overloading anastomosing rivers are sensitive to external climatic or tectonic forcing in sedimentary basins the morava river czech republic shows a well developed holocene anastomosis confined to the pull apart type upper morava basin umb we studied the stratigraphy and aggradation rates of the umb using electrical resistivity tomography ert dipole electromagnetic profiling demp core data and radiocarbon ages with the aim of identifying factors triggering the anastomosis at the pleistocene holocene transition the ert and demp proved to be excellent tools to visualize the shape and thickness of floodplain depositional units abandoned meanders scroll bars etc the major geophysical surfaces identified are the base of the late weichselian braided stream deposits osl age 34 53 3 42 ka interpreted as a palaeo stream gradient of the morava river and their transition to holocene floodplain deposits in the late weichselian the river aggraded at an average rate of 0 2 mm yr the holocene oldest 14c age 7 066 0 072 ka short term aggradation rates reached up to 13 7 mm yr but the average long term rates 0 07 to 0 4 mm yr are comparable to the late weichselian the stratigraphy and sediment ages indicate that the onset of anastomosis was not likely associated with accelerated basin subsidence possible controls of the anastomosis include upstream control by numerous tributaries large wood debris in the floodplain forests and changes in land use the tectonic and geomorphic context of the umb pull apart basin probably favoured the development of the anastomosis