calculated volumes of individual shield volcanoes at the young end of the hawaiian ridge abstract high resolution multibeam bathymetry and a digital elevation model of the hawaiian islands are used to calculate the volumes of individual shield volcanoes and island complexes niihau kauai oahu the maui nui complex and hawaii taking into account subsidence of the pacific plate under the load of the hawaiian ridge our calculated volume for the island of hawaii and its submarine extent 213 103 km3 is nearly twice the previous estimate 113 103 km3 due primarily to crustal subsidence that had not been accounted for in the earlier work the volcanoes that make up the island of hawaii mahukona kohala mauna kea hualalai mauna loa kilauea and loihi are generally considered to have been formed within the past million years and our revised volume for the island indicates that magma supply rates are greater than previously estimated 0 21 km3 yr as opposed to 0 1 km3 yr this result also shows that compared with rates calculated for the hawaiian islands 0 6 ma 0 095 km3 yr the hawaiian ridge 0 45 ma 0 017 km3 yr and the emperor seamounts 45 80 ma 0 010 km3 yr magma supply rates have increased dramatically to build the island of hawaii

new evidence for the origin of hypersaline pore fluids in the mediterranean basin abstract the br cl li cl and b cl ratios and boron isotope compositions of hypersaline pore fluids from dsdp sites 372 and 374 were measured in an attempt to evaluate the origin of the brines in site 374 the relationships between the cl concentrations up to 5000 mm and br cl 12 10 3 na cl as low as 0 1 b cl 2 5 10 3 and 11b values 43 55 o ofthedeepporewererbetween 300 and 055 mfsf loceted withinthe mesniniansediments feflecrremnantoof 65 fold evaporated sea water the original evaporated sea water was modified by 1 dilution with overlying or less saline water by about 30 and 2 slight dissolution of nacl evaporites the variations in 11b show a continuous increase in 11b values with depth in site 374 up to 66 7 oat adepthof 000 mfsf upperpliocene marlsecliments hhe conspicuous 11b enrichment trend is consistent with elemental boron depletion which was calculated from the expected boron concentrations of evaporated sea water with corresponding br cl and na cl ratios li cl variations also show a depletion of li relative to evaporated sea water the apparent depletions of b and li as well as the 11b enrichment reflect uptake of these elements by clay minerals at low water sediment ratios

exhumation of messinian evaporites in the deep sea and creation of deep anoxic brine filled collapsed basins abstract the first part of the paper summarizes some basic concepts concerning a the distribution of messinian evaporites in the deepest parts of the mediterranean sea and b the mediterranean ridge accretionary wedge and its peculiar characteristics deriving from the presence of a substantial evaporitic body in the deforming sedimentary prism then five brine filled anoxic collapsed basins tyro bannock urania atalante and discovery discovered from 1983 to 1994 are presented and discussed in their physiographic geologic hydrologic and geochemical characters high density brines deriving from submarine dissolution of outcropping or subcropping evaporites accumulate at the bottom of collapsed basins if they are not swept away by submarine currents the interface separating normal sea water from high density brines is sharp with a density contrast of about 20 and lies at 3200 3500 m below sea level strong bacterial activity is developing at the interface and living bacteria have been recovered from the anoxic salty brines thickness of the brines may be up to 500 m thermal stratification has been observed in three brine lakes exhumation and dissolution of messinian evaporites in the mediterranean ridge occur in different tectonic settings pull apart basin tyro subducting seamount close to the outer deformation front bannock basin top of a backstop urania atalante and discovery basins chemistry of the brines is strongly variable and suggests dissolution of different layers or levels of the messinian suite discovery brines are the saltiest ever recorded in natural environment their saturation in mg chloride bischofite the end product of sea water evaporation suggests that the deepest parts of the eastern mediterranean were close to dryness at the end of the salinity crisis strongly supporting the deep basin desiccation model

tectono stratigraphy of the orhaniye basin turkey implications for collision chronology and paleogene biogeography of central anatolia abstract located along the izmir ankara erzincan suture iaes the maastrichtian paleogene orhaniye basin has yielded a highly enigmatic yet poorly dated paleogene mammal fauna the endemic character of which has suggested high faunal provincialism associated with paleogeographic isolation of the anatolian landmass during the early cenozoic despite its biogeographic significance the tectono stratigraphic history of the orhaniye basin has been poorly documented here we combine sedimentary magnetostratigraphic and geochronological data to infer the chronology and depositional history of the orhaniye basin we then assess how our new data and interpretations for the orhaniye basin impact 1 the timing and mechanisms of seaway closure along the iaes and 2 the biogeographic evolution of anatolia our results show that the orhaniye basin initially developed as a forearc basin during the maastrichtian before shifting to a retroarc foreland basin setting sometime between the early paleocene and 44 ma this chronology supports a two step scenario for the assemblage of the central anatolian landmass with incipient collision during the paleocene early eocene and final seaway retreat along the iaes during the earliest late eocene after the last marine incursion into the foreland basin our dating for the orhaniye mammal fauna 44 43 ma indicates the persistence of faunal endemism in northern anatolia until at least the late lutetian despite the advanced stage of iaes closure the tectonic evolution of dispersal corridors linking northern anatolia with adjacent parts of eurasia was not directly associated with iaes closure and consecutive uplifts but rather with the build up of continental bridges on the margins of anatolia in the alpine and tibetan himalayan orogens

youngest volcanism about 1 million years ago at kahoolawe island hawaii abstract young volcanic deposits in kahoolawe island cutting up through the caldera filling lava colluvium and talus in the west wall of kanapou bay had long been stratigraphically considered the rejuvenated stage products new k ar ages combined with magnetic polarity data show that young volcanism was at about 0 98 1 04 ma and indicate no substantial quiescence between the filling of the caldera and the young volcanism this result and the tholeiitic characteristics of the young deposits suggest they are a component of late shield stage volcanism

age and petrology of alkalic postshield and rejuvenated stage lava from kauai hawaii at the top of the waimea canyon basalt on the island of kauai rare flows of alkalic postshield stage hawaiite and mugearite overlie tholeiitic flows of the shield stage these postshield stage flows are 3 92 ma and provide a younger limit for the age of the tholeiitic shield stage the younger koloa volcanics consist of widespread alkalic rejuvenated stage flows and vents of alkalic basalt basanite nephelinite and nepheline melilitite that erupted between 3 65 and 0 52 ma all the flows older than 1 7 ma occur in the west northwestern half of the island and all the flows younger than 1 5 ma occur in the east southeastern half the lithologies have no spatial or chronological pattern the flows of the koloa volcanics are near primary magmas generated by variable small degrees of partial melting of a compositionally heterogeneous garnet bearing source that has about two thirds the concentration of p2o5 rare earth elements and sr of the source of the honolulu volcanics on the island of oahu the same lithology in the koloa and honolulu volcanics is generated by similar degrees of partial melting of distinct source compositions the lavas of the koloa volcanics can be generated by as little as 3 percent to as much as 17 percent partial melting for nepheline melilitite through alkalic basalt respectively phases that remain in the residue of the honolulu volcanics such as rutile and phlogopite are exhausted during formation of the koloa volcanics at all but the smallest degrees of partial melting the mantle source for kauai lava becomes systematically more depleted in 87sr 86sr as the volcano evolves from the tholeiitic shield stage to the alkalic postshield stage to the alkalic rejuvenated stage at the same time the lavas become systematically more enriched in incompatible trace elements on a shorter timescale the lavas of the koloa volcanics display the same compositional trends but at a lower rate of change the source characteristics of the koloa volcanics considered along with those of the honolulu volcanics support a mixing model in which the source of rejuvenated stage lava represents large percent melts of a plume source mixed with small amounts of small percent melts of a heterogeneous mid ocean ridge source

discovery of an anoxic basin within the strabo trench eastern mediterranean we report here the discovery of a basin which we call the tyro basin in the eastern mediterranean in which anoxic conditions exist and organic rich sediments are accumulating bottom water samples show extremely high salt concentrations a horizontal midwater sound reflector about 70 m above the basin floor was observed in a seismic reflection profile across the basin from shipboard observations we conclude that dissolution of messinian evaporites exposed by faulting in the sides of the basin causes stagnant bottom conditions this basin provides an opportunity to test some of the hypotheses concerning the formation of sapropels present in cores collected from the same area cores taken in an adjacent similar basin for which we propose the name kretheus basin indicate a recent change from anoxic to oxygenated conditions which was probably caused by tectonic activity associated with the strabo trench

quaternary history of the lake magadi basin southern kenya rift tectonic and climatic controls abstract sediments from the magadi basin south kenya rift preserve a one million year palaeoenvironmental record that reflects interactions between climatic volcanic and tectonic controls climate changes that impacted sedimentation include wet dry cycles on variable timescales and an overall progressive trend towards greater aridity volcanic influences involved inputs of tephra to the basin significant inflow of geothermal fluids and the effects of weathering erosion and transportation of clastics from trachyte and basalt terrains tectonic controls which were often step like reflect the influence of faults that provided pathways for fluids and which controlled accommodation space and drainage directions intensified aridity and evaporative concentration resulted in salinity and ph increasing with time which led to a change from calcite deposition in mildly saline lakes before 380 ka to the later formation of zeolites from reactions of volcaniclastic debris with highly alkaline lake and pore water after 105 ka hyperalkaline conditions led to trona accumulation and increasingly variable rare earth elements rees the presence of mixed saline and freshwater diatom taxa between 545 and 16 ka indicates climate variability and episodic inputs of fresh water to saline lakes calcrete formed in lake marginal settings during semi arid periods tectonic controls operated independently of climate but they interacted together to determine environmental conditions aquatic deposition was maintained during periods of increasing aridity because fault controlled ambient and geothermal springs continued to flow lakewards this recharge in turn limited pedogenesis palaeosols are common in other rift floor sequences trona formed when aridity and evapoconcentration increased but its precipitation also reflects increased magmatic co2 that ascended along faults basin fragmentation and north south fractures caused loss of cross rift east west drainage from rift marginal basalts resulting in reduced transition metals after 545 ka the magadi basin demonstrates how a careful reconstruction of these complex tectono climatic interactions is essential for accurate palaeoenvironmental reconstruction in continental rifts and in other tectonic settings

solute sources and chemical weathering in the owens lake watershed eastern california 1 chemical and strontium isotope analyses of solutes in a series of streams representing the bulk of the water reaching the 8500 km2 owens lake watershed provide a unique opportunity to evaluate factors that control stream chemistry on a regional scale the streams drain terrain that is dominated by mesozoic granitoids of the sierra nevada batholith but that also contains irregularly distributed roof pendants of paleozoic metasedimentary sequences mass balance modeling indicates that plagioclase feldspar weathering is the dominant contributor to stream chemistry and that carbonate dissolution is also a significant source of solutes for most streams the calculated ratio of plagioclase to carbonate is highly sensitive to the assumed weathering product of plagioclase kaolinite versus smectite and we suggest that the importance of carbonate could be exaggerated in cases where only the plagioclase to kaolinite reaction is considered strontium isotope 87sr 86sr ratios range from 0 70685 to 0 71958 with a flow weighted mean of 0 70911 to the extent that this value represents the water that would be flowing into owens lake were it not diverted by the los angeles aqueduct system the flow weighted mean 87sr 86sr ratio is consistent with ratios measured in owens lake core carbonates ranging in age up to 25 kyr the overall sr budget of the watershed is determined by the relative contributions of carbonate dissolution and plagioclase feldspar weathering and is dominated by reactions related to pyrite oxidation and hydrothermal fluid input from just two subbasins the impact of these processes needs to be considered when modeling regional and global riverine sr budgets climate related shifts in the relative importance of silicate mineral weathering reactions appear to be only second order effects on a regional scale

rainy periods and bottom water stagnation initiating brine accumulation and metal concentrations 1 the late quaternary a working hypothesis is proposed to account for the present accumulation of brines in isolated pockets of the ocean floor and for the formation of the underlying organic and metal rich sediments these are the tyro and bannock basins in the east mediterranean the red sea deeps and the orca basin in the northern gulf of mexico initiation of brine derived deposition in the red sea deeps and orca basin occurred between 12 000 and 8000 years b p this time bracket also encompasses the formation of the latest east mediterranean sapropel and the wettest global climate since the last glacial maximum this wet period first appeared in the tropics around 12 000 years b p then in the subtropical and middle latitudes during the same period the 23 000 year precession cycle brought the summer insolation of the northern hemisphere to its peak at 11 000 years b p with retreating northern hemisphere ice sheets the red sea deeps and the orca basin became anoxic during this humid period and metal rich sapropel deposition then began in contrast the tyro and bannock basins began accumulating a brine long before and persisted beyond this climatic stage the hypothesis involves two propositions 1 as in the eastern mediterranean sea marine anoxia was mainly the consequence of the large influx of continental runoff and local precipitation longer residence time of bottom waters so called stagnation in silled rimmed basins would have resulted from lower salinity at the sea surface in areas of deep water formation in the eastern mediterranean the red sea and the gulf of mexico and 2 miocene or older evaporites underlie these basins or outcrop on their flanks leaching from these evaporites was an ongoing process before the quasi stagnation phase but the initial leachate much less saline than the present brines was continuously flushed by bottom circulation the climate induced quiescence of bottom waters in these basins enabled the leachate to accumulate the feedback of stagnation by increased density progressively raised the salinity of entrapped bottom waters to the present brine concentration the high density has resisted brine removal by bottom circulation until present time long after cessation of the initiating wet period the brines therefore are stagnant fossil waters

the green river salt mystery what was the source of the hyperalkaline lake waters abstract bicarbonate rich source waters were needed to form the largest sodium carbonate evaporite deposits in the geologic record the early and middle eocene green river trona nahco 3 na 2 co 3 2h 2 o in the bridger basin wyoming and nahcolite nahco 3 in the piceance creek basin colorado large modern and pleistocene trona deposits are associated with magmatic activity and na hco 3 rich hydrothermal inflow waters either within the depositional basin lake magadi kenya or at great distances searles lake california no evidence exists for magmatic sources of co 2 near the green river formation several regional volcanic centers were active 300 km or more to the north but drainage reconstructions show that waters from these areas did not discharge into the green river formation lakes during evaporite deposition alternatively na hco 3 rich waters could have drained northwestward from the colorado mineral belt to the bridger basin via the proposed aspen river a river originating in the colorado mineral belt sawatch uplift could also have provided source waters to the piceance creek basin field evidence however has not yet documented these flow paths and specific eocene volcanic centers and hydrothermal source areas have yet to be identified other explanations for the elevated alkalinities needed to form thick sodium carbonate evaporites include accelerated silicate mineral weathering rates during a period of high atmospheric p co 2 and eocene warmth amplified chemical weathering may explain the cluster of sodium carbonate evaporites in the usa and china that are eocene in age another possible source of alkalinity to the green river lakes is fault controlled upward migration of a deep sedimentary source of co 2 the large amount of organic matter preserved in the evaporitic wilkins peak and parachute creek members raises the possibility that decay of organic matter in green river lakes could have added sufficient co 2 and alkalinity to produce waters capable of precipitating trona and nahcolite although such degradation of organic matter has not created hyperalkalinity in modern lakes

volcanic and morphological evolution of la gomera canary islands based on new k ar ages and magnetic stratigraphy implications for oceanic island evolution the spatial and chronological evolution of canary islands volcanism is due to eastward progression of the slow moving african plate over a mantle plume la gomera is located between the western shield stage islands 12 ma with 23 k ar ages and palaeomagnetic data we can constrain the timing of the main subaerial volcanic phases of la gomera the shield volcano c 9 4 8 0 ma the postshield peripheral lava flows c 7 4 5 0 ma the postshield horizontal lava flows c 5 4 4 3 ma and late intra canyon lava flows c 1 9 ma the horizontal lava flows fill a 10 km wide depression formed by a giant landslide garajonay the entire structure of la gomera is in relief inversion declining volcanic construction rates from the shield to the postshield stages are correlated with increasing erosion rates whereas the period of volcanic quiescence hiatus has low erosion rates the succession and duration of the hotspot volcanic stages in the canary islands are compared with those in the hawaiian islands thus underlining differences between slow moving and fast moving plate settings

carbon and oxygen isotope composition of foraminifera in two cores from the bannock basin area eastern mediterranean abstract two cores from the bannock basin in the eastern mediterranean have been analysed for 18 0 and the 13 c in planktonic foraminifera one core 02 pc was extracted from the anoxic brine the other 08 gc from a plateau east of the brine the absence of sapropelic muds in core 08 gc from the two holsteinian euxinic cycles together with the presence of isotopic spikes suggests that the plateau has risen during the last ca 200 000 years by ca 2 5 mm yr the 18 0 amplitude of globigerinoides ruber in eastern mediterranean cores is only ca 0 5 larger than for this species in north atlantic cores this suggests that the surface oxygen isotopic composition of both bodies of water followed each other fairly closely during the late pleistocene except during the stagnant phases

a thermal model for the origin of post erosional alkalic lava hawaii abstract the model of lithospheric thinning and reheating for the origin of the hawaiian swell assumes that the lower lithosphere 60 km is rapidly reset to an asthenospheric temperature as it passes over the hot spot it is shown that this heat input induces melting in a few kilometer thick layer of lithosphere just above the thermal anomaly by solving the appropriate energy equation the mean degree of melting in the molten layer was estimated to be 1 5 with a total melt thickness of 25 150 m the minimum width of the thermal anomaly required to account for the observed rate of post erosional eruptions is of the order of 10 40 km which is probably satisfied the melt generated by this process matches the petrological and geochemical characteristics of hawaiian post erosional lava and their typical morb related isotopic signature because small degrees of melting are involved the extraction time scale is long a few million years and is consistent with the time span of post erosional eruptions also the characteristic sequence of hawaiian volcanism can be explained if the source for hawaiian lava is considered as a molten layer with melt fraction decreasing upward

middle and late quaternary depositional sequences and cycles in the eastern mediterranean although most of the quaternary sediments of the eastern mediterranean appear reworked extensive areas of hemipelagic sediments occur mainly in the central part of the basin mediterranean ridge the most obvious character of these muddy sediments is the numerous changes in colour they result from the organic carbon content as well as from concentration and chemical form of metallic elements mn fe cu zn the succession of coloured layers is arranged into sequences developed between two sharp contacts a complete sequence involves five lithofacies from an oxidized layer at the base to a reduced sapropel at the top and displays progressive internal changes of colour from ochre beige greyish beige grey and black layers several sequence variants top truncated base truncated recurrent are identified these sequences are a consequence of changes in oceanographic conditions i e from oxidizing to reduced environments resulting in different organic and mineral contents based on detailed studies of quaternary sediments collected by coring a synthesized standard succession representative of the ordered sequences in the eastern mediterranean is proposed from about 650 000 yr as deduced from the calculated rate of sedimentation of 1 7 mm 1000yr 1 this succession appears modulated by cyclic events large scale periods 200 000 yr of reduced and oxidized sequences correlate with major alternate phases of flooding and reduced flow of the nile river during the quaternary subsequent sequences of shorter time scale 20 000 50 000 yr results from two factors heaviest monsoons leading to an increase of the influx of the nile river and global climatic changes eurasian ice sheet meltwater these two factors act synchronously or independently along the studied time span these interplaying factors result in periodic stages of increasingly restricted conditions in the basin and explain the complexity of the eastern mediterranean succession at least since 650 000 yr ago

redox zonation of elements at an oxic post oxic boundary in deep sea sediments abstract deep sea sediments generally provide limited evidence of redox control on the post depositional redistributions of elements this is because only a fraction of any element is reactive and observed elemental distributions are the result of a number of competing processes which are simultaneously active so that redox effects are not dominant a detailed investigation is reported of a core which is unusual in showing unequivocal evidence of direct redox control operating in a homogeneous environment that is relatively free from competing processes a progressive oxidation front has migrated slowly downwards into a uniform turbidite over a long period ca 250 ky the reactive fractions of several redox sensitive elements now show a remarkable degree of organisation around the redox boundary of this front with the different elements exhibiting individual responses solid phase enrichments are not coincident but are arranged in a clear succession of concentration peaks along the redox gradient from oxic to postoxic conditions the succession is mn i fe se and pt cu and pb v zn and sb and u the movement directions of most elements can be inferred from the peak shapes against the homogeneous turbidite background composition the system seems to have been essentially isolated within the sediment for most elements so that no loss or gain can be ascribed to redox processes exceptions are u and v which have been augmented by uptake from ocean bottom waters into the sediments by an efficient redox trap mechanism

degassing of mantle derived co2 and he from springs in the southern colorado plateau region neotectonic connections and implications for groundwater systems groundwaters of the southern colorado plateau arizona transition zone region are a heterogeneous mixture of chemically diverse waters including meteoric epigenic fluids karst aquifer waters and deeply sourced endogenic fluids we investigate the composition of travertine depositing co 2 rich springs to determine the origin transport and mixing of these various components the san francisco mountain recharge area has little surface flow instead waters discharge through major springs hundreds of kilometers away about 70 9340 l s of the total recharge 13 500 l s discharges 100 km to the north in the incised aquifer system at grand canyon most of this water 85 8070 l s emerges through two travertine depositing karst spring systems blue springs 6230 l s and havasu springs 1840 l s about 30 of recharge 4150 l s flows to the south and discharges along nw striking faults in the arizona transition zone forming the base flow for the verde river geochemical data define regional mixing trends between meteoric recharge and different endogenic end members that range from bicarbonate waters to sulfate waters water quality in the region is dictated by the percentage and character of the endogenic inputs that cause a measurable degradation of groundwater quality for water supply sources for the high co 2 include dissolution of limestone and dolostone c carb and external carbon c external c external is computed as the bicarbonate alkalinity dissolved inorganic carbon dic minus the c carb c external dic c carb c external is deconvolved using carbon isotopes into biogenically derived sedimentary carbon c organic and deep co 2 inputs c endogenic measured 13 c values are 17 to 3 versus pee dee belemnite pdb assuming 13 c carb 2 13 c organic 28 and 13 c endogenic 5 water chemistry mixing models indicate that an average of 42 of the total dic comes from dissolution of carbonate rocks 25 from organic carbon including soil respired co 2 and 33 from deep endogenic sources helium isotope values 3 he 4 he in gases dissolved in spring waters in the southern colorado plateau region range from 0 10 to 1 16 r a relative to air indicating that a significant component of the deeply derived fluid is from the mantle mean of 5 asthenospheric or 10 subcontinental lithospheric mantle source measured co 2 3 he ratios of 2 10 9 to 1 4 10 13 are adjusted by removing the proportion of co 2 from c carb and c organic to give values 10 for all but four samples various mixing models using co 2 3 he suggest that the mantle derived components of the co 2 load are highly variable from spring to spring and may make up an average of 10 of the total co 2 load of the regional springs fluid rock interactions involving endogenic fluids are suggested by 87 sr 86 sr 18 o and other tracers the endogenic co 2 component multiplied by discharge for each spring yields an integrated annual flux of deeply derived co 2 to the groundwater system of 1 4 10 9 mol yr this co 2 emission from the colorado plateau region reflects a complex tectonic evolution involving laramide hydration of the lithosphere above the farallon slab addition of fluids from mid tertiary mantle tectonism during slab removal and ongoing fluid movement induced by neotectonic small scale asthenospheric convection

evaporitic carbonates in the pre salt of santos basin genesis and tectonic implications abstract since the first discoveries of oil accumulations in the carbonate reservoirs of the lower cretaceous barra velha formation of the santos basin their genesis has been the subject of intense discussion different depositional models have been proposed with some authors advocating a microbial origin while others an abiotic origin as travertines or travertine like rocks this search for a modern carbonate analogue for these unusual rocks may have disregarded an intriguing alternative an evaporative model supported by our petrographical and geochemical data evaporitic sediment patterns in endorheic basins in a depositional framework of brine drawdown are dominated by ephemeral salt pan hydrology bedded salt crusts form a stack of subaqueous aligned crystal beds at the sediment water interface salt grows diagenetically within saline and mud layers beneath the dry pan surface finally laminated sediments are deposited we observe a similar cyclic pattern in the pre salt core we described beds of shrub like crystals and diagenetic spherulites growing in magnesium clay matrix are followed by laminites the model we propose attempts to contribute solving the puzzle of pre salt carbonate deposition by integrating sedimentology and geochemistry with basin tectonics our observations and basin tectonics point to the exciting possibility that the sag phase carbonates of the santos campos basin were deposited as the initial transitional stage of a closed sub sea level evaporite basin whose rising salinities culminated in the deposition of halite and bittern salts carnallite sylvite tachyhydrite basinwide evaporites are singular events in the geological record they form when a giant sub sea level basin becomes a sump of continental marine and hydrothermal fluids producing unexpected brine compositions in unusual depositional settings present in ancient evaporitic basins but absent from most modern ones the novelty in this paper is that we apply to pre salt carbonate deposition the sedimentology hydrology and geochemistry of ancient evaporitic basins with this concept in mind we propose a geochemical model for the unusual pre salt carbonate precipitation of the santos basin regarding the walvis rio grande volcanic high as a topographic barrier during the aptian we suggest that the main sources of calcium to the barra velha paleolake were hydrothermal brines mostly from infiltrating seawater that reacted at depth with the basalts of the volcanic barrier hyperextension of the lithosphere with a shallow moho increased geothermal gradients to levels favorable for the generation of hydrothermal cacl2 brines a process facilitated by the already elevated ca ion and low sulfate concentration of the cretaceous ocean these cacl2 rich fluids would pass through the volcanic barrier into a sub sea level paleolake in the rift basin the high salinity paleolake would become saturated in calcium bicarbonate carbonate as internally drained nahco3 bearing alkaline waters formed by physical chemical weathering of penecontemporaneous basaltic rocks mix with the cacl2 bearing hot brines percolating through the barrier producing a hybrid brine 2nahco3 cacl2 ca hco3 2 2nacl such a depositional system integrating the geochemical depositional controls of sag phase carbonates with those of the south atlantic evaporites has important implications for unravelling the genesis of these exotic deposits

anatomy of a suspended seafloor in the dense brine waters of the deep hypersaline urania basin abstract when micron sized particles are suspended into the dense brine waters of a deep hypersaline basin in the absence of biological packaging their settling velocities should be greatly attenuated we observed this phenomenon in the anoxic brine water of the urania basin in the eastern mediterranean we found that the deepest part of this basin is filled with a high density about 110 m thick homogenous fluid mud layer mainly containing microfossils of coccoliths and nannoplankton of pleistocene and pliocene age that float in a hot methane laden brine overlaid by a clear brine the top of the fluid mud forms a secondary suspended seafloor that has been stable for at least the last two decades since the discovery of the basin the geochemical characteristics of the fluid mud e g lower salinity than the clear brine methane rich point to a deep source for the fluids while the age of the microfossils suggests that the floating biogenic particles came from shallower post messinian pelagic deposits such as those exposed along the walls and the rim of the urania basin we hypothesize that catastrophic gravity failures and mass mobilization of the post messinian sedimentary layers triggered by earthquake activity are one of the main sources of the sediment in the fluid mud because of both the dense brine fluids the continuous mixing by thermal convection and the very fine grained nature of the particles the re mobilized sediments have never settled and stay suspended as if they were frozen in time the prolonged residence time of the supersaturated fluids and the associated microbial activity have also fostered the precipitation of the authigenic gypsum crystals and micron sized authigenic carbonates that occur mixed with the fluid mud sediments

a 36cl chronology of lacustrine sedimentation in the pleistocene owens river system we have used 36 cl to date climatically sensitive saline lake sediments from hydrologically closed basins in southeastern california primarily sediments from searles and panamint basins during wet periods of the past 2 0 m y lakes that formed in the closed basins fluctuated in size in direct response to the balance between runoff and evaporation we have compiled a chronology for the km 3 core from searles lake based on ages determined by 36 cl for the evaporites together with those determined by 14 c and u th series for younger sediments and by magnetostratigraphy for older sediments this chronology along with other criteria such as correlations between searles and panamint basins the chloride budget and sedimentology is used to reconstruct the history of lake fluctuations in the paleo owens river system we infer that searles lake desiccated at most twice since 600 ka during the interval around 290 ka and from 10 ka to the present the lake history curve shows that the holocene epoch is anomalously arid major overflows from searles to panamint occurred during the intervals between 1 3 ma and 1 0 ma 750 ka and 600 ka 500 ka and 400 ka and 150 ka and 120 ka comparing the lake fluctuation chronology to the 18 o record of marine foraminifera we infer that the strongest similarity is in the periodicities of the cycles 40 to 50 kyr before the matuyama brunhes magnetic reversal 730 ka and 100 kyr thereafter we find however that at searles lake this fluctuation in the lake chronology is modulated by longer term cycles of aridity and humidity thus although the mid latitude quaternary climate record reflects the mid to high latitude ice volume fluctuations that dominate the marine 18 o record it also contains evidence for climatic forcing of a different type

mineralogic controls on the composition of natural waters dominated by silicate hydrolysis a detailed mineral solute mass balance spreadsheet model has been developed to improve understanding of mineralogic controls on water composition in surface waters and groundwater systems dominated by silicate lithologies the spreadsheet based approach is used to investigate mass balance solutions over a range of mineral compositions for predominant multi element phases such as plagioclase biotite chlorite amphibole and dioctahedral smectite the mass balance technique has been applied to a variety of hydrogeologic environments including calibrated watersheds springs and groundwater systems lithologic settings include plutonic metamorphic minor volcanic and sedimentary alluvial and glacial deposits materials sites investigated most of which allowed comparison with earlier work include ephemeral and perennial springs of the central sierra nevada mountains california the loch vale colorado high altitude watershed four catchments in the inyo mountains california and nevada watersheds in the catoctin mountain maryland area and ground water flow systems in vekol valley arizona and in the trout lake area wisconsin analytical mass balances were derived with a novel approach that permits graphic analysis of the functional dependency of mineral mass transfer coefficients on variations in major silicate composition a 10 x 10 matrix of mineral solute reaction equations was used to solve for the best mass balances alternative methods were developed to investigate cases where the number of mineral phases exceeds the number of solute constraints 10 that are commonly found in clastic silicate dominated systems with diverse sources and or phase mixtures of variable chemistry such as an assortment of plagioclase compositions techniques were also developed to allow for important structurally controlled compositional variation in clay minerals final mass balance choices were tempered by thermodynamic stability calculations for various minerals under near surface weathering conditions mineral mass transfer ratios were also found to be useful in restricting mass balances additional constraints were provided by establishing consistent sets of similar mineral assemblages and mineral compositions for a series of wells along a ground water flow path or through comparison of multiple nearby watersheds subject to similar climatic and vegetative conditions whereas unique analytical solutions from spreadsheet mass balances were not always possible a surprisingly limited range was obtained for mineral assemblages and compositions satisfying observed mineral occurrences and thermodynamic stability conditions our results demonstrate the importance of having well characterized mineral compositions for both reactant and product phases the mass balance results are particularly sensitive to the compositions of plagioclase dioctahedral smectite and a few primary mafic mineral groups trioctahedral mica amphibole and pyroxene in addition to mineral controls the specific examples studied demonstrate effects of dolomite and calcite overprints on silicate weathering biomass fluctuations road salt contamination and on buried evaporite salts a comparison of the mass balance results from surface and groundwater systems indicates strong similarities suggesting that similar processes dominate the mineral controls in both settings and that under soil weathering conditions ion exchange might have been overemphasized except under conditions where pre existing waters are displaced by solutions of significantly different composition

dissolution and collapse features on the eastern mediterranean ridge abstract morphologic features similar to subaerial karstic dolines and zanjones have been observed on the eastern mediterranean ridge using a near bottom towed geophysical instrument package these features are found only on the floors of certain large depressions which lie above the crests of subcropping evaporite diapirs the coincidence of dissolution controlled morphology with the subcropping soluble evaporite confirms earlier suggestions that the large depressions result from dissolution of the evaporites and collapse of the overlying strata

the timing of crustal extension and the eruption of continental flood basalts the association between mantle plumes continental flood basalt eruption and the extension and rifting of the crust is well recognized1 3 but there has always been controversy as to whether the plume or the rifting was the initiating factor4 5 was rifting triggered by doming above the thermal plume2 3 6 or was rifting the driving force preceding the associated volcanicity7 8 here i show that recent flow by flow mapping of two continental flood basalt provinces the columbia river basalt group and the deccan basalt group allows one to infer the relative timing of volcanicity and crustal extension in both provinces eruption of the main tholeiitic phase preceded significant extension and crustal thinning this suggests that the primary event in the formation of these provinces was the upwelling of a mantle plume and that the subsequent crustal extension rifting and decompression was in part a consequence of the initiation of that plume

geochemistry of an exotic sediment layer above sapropel s 1 mud expulsion from the urania basin eastern mediterranean in a gravity core from the eastern mediterranean sea a chemically and mineralogically distinct 5 5 cm thick layer is present above sapropel s 1 and overlain by hemipelagic marls calcite is completely absent in this exotic layer dolomite is present only in small amounts and the cr concentrations are significantly enhanced the layer was deposited primarily under reducing conditions but the distributions of redox sensitive elements show that a large part of the exotic layer is now oxidised by a downward progressing oxidation front sediments from within the nearby anoxic hypersaline urania basin are similar to those from the exotic layer in particular in s c and o isotope distributions of pyrite and dolomite as well as increased cr concentrations mud expulsion due to expansion of gas rich mud is proposed to explain the presence of the exotic layer outside the urania basin the deposition of an anoxic layer above s 1 shielded the sapropel from oxidation which resulted in the rare occurrence of a complete preservation of s 1 and provides the first minimum age for the start of anoxic mud accumulation in the urania basin

alkali elements na k rb and alkaline earth elements mg ca sr ba in the anoxic brine of orca basin northern gulf of mexico abstract a profile of filtered seawater and brine samples was collected in the summer of 2003 from a depth of 1500 m down to the bottom of the anoxic hypersaline orca basin northern gulf of mexico using ion chromatography and inductively coupled plasma mass spectrometry icp ms these samples were analyzed for alkali cations na k rb alkaline earth cations mg 2 ca 2 sr 2 ba 2 and the major anions chloride cl and sulfate so 4 2 major ion concentrations in the brine are consistent with previous studies confirming that na plus cl make up more than 95 of its composition hence governing its density and hydrodynamic stability binary mixing plots across the interface between deep gulf of mexico seawater and the anoxic brine are generally linear but display substantial deviations from conservative behavior at the steepest part of the pycnocline for all analytes except na cl and ca negative deviations signify localized cation removal by an adsorption or ion exchange process probably associated with the dense layers of particles that are trapped there especially strong mg removal may be indicative of dolomitization whereby the concomitant release of ca counters its adsorption resulting in zero net ca removal a positive deviation for sulfate is attributed to bacterial sulfide oxidation concentrations of rb sr and ba in the homogeneous brine reported here for the first time are enriched by factors of 1 5 1 4 and 9 respectively with respect to the overlying seawater unlike ca and sr ba concentrations in the brine are clearly controlled by the solubility of its sulfate salt barite causing a maximum of 670 nmol kg at the interface several independent lines of evidence suggest that the brine is formed outside the basin most likely by the interaction of seawater with regionally extensive evaporite deposits a simple mass balance shows that the dissolution of about 280 g of halite per kg of seawater can account for the extreme concentrations of na and cl in the orca basin brine the same mass balance was applied to a number of minor constituents k rb mg ca sr so 4 br total iodine in order to calculate what abundances in the halite are required to reproduce their concentrations in the brine as measured in the present work and by others the results are entirely compatible with the composition of the jurassic louann salt specifically with the median of compositions published for a transect spanning early to late stage halites elevated abundances of k and rb point to contributions from bittern facies modified by prior diagenetic contact with seawater

rejuvenated stage volcanism after 0 6 m y quiescence at west maui volcano hawaii new evidence from k ar ages and chemistry of lahaina volcanics abstract west maui s rejuvenated stage lahaina volcanics were erupted from four discrete sites new k ar ages indicate two pulses of volcanism the older about 0 6 ma and the younger about 0 4 ma compositionally the lava flows are entirely basanitic but each pulse is diverse the underlying postshield stage honolua volcanics were emplaced by about 1 2 ma on the basis of previously published ages therefore the duration of volcanic quiescence prior to rejuvenation is about 0 6 m y at west maui much longer than estimated previously

active post depositional oxidation of the most recent sapropel s1 in sediments of the eastern mediterranean sea abstract over a wide area of the eastern mediterranean basin two mn rich layers have been observed above the most recent sapropel s1 one immediately above the sapropel top and one a few centimetres closer to the sediment surface different mechanisms have been proposed to explain the occurrence of these two mn peaks either both peaks have a diagenetic origin in which case the upper mn peak is actively forming or the lower peak is actively forming and the upper peak has a different formation mechanism high resolution porewater including a gel sampler used for the first time in marine sediments and solid phase data are now used to demonstrate that the oxidation front is located at the level of the lower mn peak which therefore is presently being formed a barium organic carbon relationship is used to calculate the initial organic carbon profile of the s1 sapropel the palaeoproductivity profiles generated by this method demonstrate that the original sapropel unit was bounded by the upper mn peak this implies that the interval between the two mn peaks where a low organic carbon content is now observed was originally part of the sapropel the initially deposited organic carbon has been oxidised by a progressive downwards moving oxidation front the penetration depth of this oxidation front i e the distance between the two mn peaks is mainly determined by the organic carbon content the sediment accumulation rate and the bioturbation depth the upper mn peak appears to have formed as a result of either mn precipitation upon oxygenation of previously anoxic eastern mediterranean deep water or preservation of a surficial mn peak at the end of the high productivity episode in either case the upper mn peak marks the end of sapropel formation as indicated by the ba profiles this means that formation of the s1 sapropel ceased more recently than is indicated by radiocarbon dating of the visible top of s1

short time scale variability in ventilation and export productivity during the formation of mediterranean sapropel s1 1 high resolution laser ablation inductively coupled plasma mass spectrometry la icp ms scanning of laminated sediments from the urania basin is used to investigate short time scale variability in export productivity and redox conditions during the formation of eastern mediterranean sapropel s1 sedimentary enrichments of molybdenum mo vanadium v and uranium u reflect deep water redox conditions most likely those near to the seawater brine interface while enrichment of ba is related to biogenic barite and hence to export productivity the enrichments of all four elements show strong variability on multidecadal to multicentennial time scales throughout s1 a partial decoupling of export productivity from redox conditions at the height of sapropel formation suggests that hydrographic changes i e a variable ventilation rate of the eastern mediterranean played an important role in determining deep water redox conditions a pronounced switch is observed in the enrichments of redox sensitive trace metals from dominantly 300 600 year variability during early s1 to dominantly 100 300 year variability during late s1 indicating a change in the mean frequency of variability in the ventilation rate the presence of a similar shift in the frequency of tropical and extratropical climate records at this time suggests that ventilation of the eastern mediterranean was coupled to global climate variability

the messinian salinity crisis past and future of a great challenge for marine sciences forty years after the image of the mediterranean transformed into a giant salty lake was first conceived the fascinating history of the messinian salinity crisis msc still arouses great interest across a large and diverse scientific community early outcrop studies which identified severe palaeoenvironmental changes affecting the circum mediterranean at the end of the miocene were followed by investigations of the marine geology during the 1950s to 1970s these were fundamental to understanding the true scale and importance of the messinian event now after a long period of debate over several entrenched but largely untested hypotheses a unifying stratigraphic framework of msc events has been constructed this scenario is derived mainly from onshore data and observations but incorporates different perspectives for the offshore and provides hypotheses that can be tested by drilling the deep mediterranean basins the msc was an ecological crisis induced by a powerful combination of geodynamic and climatic drivers which had a great impact on the subsequent geological history of the mediterranean area and on the salinity of the global oceans these changed the mediterranean s connections with both the atlantic ocean and the freshwater paratethyan basins causing high amplitude fluctuations in the hydrology of the mediterranean the msc developed in three main stages each of them characterized by different palaeoenvironmental conditions during the first stage evaporites precipitated in shallow sub basins the msc peaked in the second stage when evaporite precipitation shifted to the deepest depocentres and the third stage was characterized by large scale environmental fluctuations in a mediterranean transformed into a brackish water lake the very high resolution timescale available for some late miocene intervals in the mediterranean makes it possible to consider environmental variability on extremely short time scales including in some places annual changes despite this fundamental questions remain some of which could be answered through new cores from the deepest mediterranean basins improvements in seismic imaging and drilling techniques over the last few decades make it possible to plan to core the entire basinal messinian succession for the first time the resulting data would allow us to decipher the causes of this extreme environmental change and its global scale consequences

a stable isotope study of pyrite formation in the late pleistocene and holocene sediments of the black sea the abundance and isotopic composition of total and pyrite sulphur have been determined in a core in the central black sea pyrite varies in concentration from roughly 2 wt in the sapropel unit 2 to 0 8 wt in the modern horizon unit 1 and ca 0 1 wt in the lowermost horizons of unit 3 lake beds an intermediate mud flow horizon and the upper part of the lake beds have similar values to those in the modern sediments the degree of pyritization dop is lowest 0 05 in the lower lake beds and highest 0 55 in unit 1 the sapropel has values of ca 0 48 34spyrite varies from a minimum of 37 in the sapropel to 33 in unit 1 up to 15 in the upper lake beds and 0 in the lower lake beds the unit 1 and sapropel values are similar to the 34s values reported by fry et al 1991 of dissolved sulphide immediately below the water column oxic anoxic interface 36 to 38 but significantly heavier than those in the deep waters of the basin ca 41 these results are interpreted as a reflection of the presence of four different types of pyrite in the sediments of the black sea 1 pyrite in units 1 and 2 that is formed within the upper part of the water column immediately below the oxic anoxic interface where 34s of dissolved sulphide is 36 2 pyrite in the mud flow layer lying between unit 1 and the sapropel unit 2 with a significantly heavier isotopic composition that was formed around the margins of the basin under conditions that were probably more closed with respect to dissolved sulphate than those in which the pyrite in units 1 and 2 were formed 3 pyrite in the upper part of the lake beds unit 3 that was formed under closed system conditions by reaction between excess reducible fe remaining in these freshwater sediments and downward diffusing sulphate and or sulphide from the overlying organic rich sapropel and 4 pyrite in the lower part of the unit 3 representing a phase formed from the ambient sulphate in the freshwaters of the late pleistocene lake the isotopic information supports earlier suggestions that pyrite in the modern sediments of the black sea forms mainly in the water column with only minor amounts forming in the sediment because of the severe fe limitation of the bottom sediments that accumulate 2 000 m below the main fe and hs reaction zone at the oxic anoxic interface at shallow depths in the water column

relics of evaporated sea water in deep basins of the eastern mediterranean abstract reexamination of data on hypersaline bottom brines from the deep anoxic tyro and bannock basins in the eastern mediterranean reveals that despite their similar chlorinity 6 0 mole kg h 2 o their chemical composition is significantly different the brine in the tyro basin has a na chloride composition na cl 1 with conspicuously low ratios of conservative elements to chloride br cl 2 4 10 4 li cl 1 4 10 5 b cl 1 6 10 4 indicating dissolution of halite in contrast brines from the bannock basin are characterized by an mg chloride signature na cl 0 78 with relatively high ratios of conservative elements to chloride br cl 1 7 10 3 li cl 5 2 10 5 b cl 8 4 10 4 the contents of na mg k li cl br and b in the deep bannock brines brine ii are identical to those in evaporated sea water of a degree of evaporation of 12 13 whereas ca is enriched and so 4 is depleted in contrast to previous studies it is suggested that brine ii from the bannock basin is a relic of ancient evaporated sea water that was slightly modified by sulphate reduction and gypsum dissolution the interstitial ancient evaporated sea water was liberated and accumulated on the sea floor probably during the formation of the deep basins in the bannock area

setting and tectonic evolution of some eastern mediterranean deep sea basins abstract nine discrete deep sea basins seven from the calabrian and mediterranean ridges and two from the strabo trench were explored geologically during several cruises carried out from 1978 to 1984 in the eastern mediterranean the seven basins displaying similar geological features calabrian and mediterranean ridges may be divided into three groups on the basis of their size 1 very small basins botticelli and raffaello basins whose area ranges from 1 1 to 4 3 km 2 2 small basins ares aphrodite and katia basins from 7 to 13 km 2 and 3 large basins bannock and cleft basins from 22 to 74 km 2 the two basins from the strabo trench tyro and kretheus basins whose areas range from 16 to 20 km 2 are considered separately tectonics is the most important element affecting basin formation processes progressive folding and faulting of messinian pliocene and quaternary sediments in the calabrian and mediterranean ridges allows the infiltration of water into the subbottom and dissolution of messinian evaporites so that collapse of the overlying unconsolidated plio quaternary cover creates local distensive tectonics superimposed on the regional compressive tectonic setting the size of the basins reflects different steps in this process very small basins are related to the fracturing occurring at the top of anticlines small basins originate when anticlines are faulted and large amounts of water are able to reach the evaporites and increase the intensity of leaching finally large basins are related to regional tectonic lineaments both compressive large reverse faults overthrusts and strike slip salt diapirism may be associated with some of these situations the process responsible for the tyro and kretheus basins formation is the pull apart mechanism connected with the strike slip motion occurring in that area the geometric position of subaqueously dissolved evaporites seems to influence the environment on the basin floor brines originating from the dissolution of buried evaporites are thought to disperse in the subbottom whereas brines originating from dissolution of evaporites cropping out on the basin walls can flow to the floor and cause stagnation only if the shape of the basin prevents the action of bottom currents

unspiked k ar dating of the honolulu rejuvenated and ko olau shield volcanism on o ahu hawai i many mantle plume volcanoes undergo rejuvenated volcanism after a period of construction and erosion of their shield the cause of this renewed volcanism has been enigmatic and various models have been proposed however the lack of geochronological data has hindered evaluation of these models unspiked k ar ages on groundmass in 41 samples from 32 vents of honolulu volcanics and eight samples of underlying kodolau volcanics were determined in order to reveal the temporal distribution of rejuvenated vents and the length of the hiatus between the end of shield and start of rejuvenated volcanism the new geochronological results show that kodolau shield volcanism ended at 2 1 ma and that rejuvenated volcanism started at 0 8 ma resulting in a 1 3 million year hiatus in volcanic activity two distinct pulses were found for honolulu volcanism at 0 80 0 35 and 0 1 ma during the first pulse the eruption frequency increased with time and there was no spatial pattern in vent distribution although three vents along a nne ssw trend produced similar compositions and may have been coeval volcanism apparently waned from 0 35 0 12 ma with only one eruption the second pulse occurred along two rifts that trend n s and ne sw although the ages for the 10 dated flows are indistinguishable at around 0 1 ma lavas from the two rifts have distinct compositions weakly alkalic vs melilite nephelinite the first more widely distributed pulse of volcanism is probably related to secondary melting downstream from the hawaiian plume stem which may be related to lithospheric thinning the second pulse focused along two rifts may be related to decompressional melting as the shield passed over the flexural arch d 2005 elsevier b v all rights reserved

gypsum precipitation from cold brines in an anoxic basin in the eastern mediterranean in 1968 hot brines from which gypsum had precipitated were discovered in the red sea in a divergent plate boundary setting with hydrothermal activity1 we now report the discovery of cold brines in an entirely different geodynamic situation a convergent plate boundary in the eastern mediterranean where the heatflow is very low2 and no hydrothermal activity occurs decimetric pure gypsum crystals precipitate from the cold brines which occupy the bottom of a rimmed anoxic basin near the southern edge of the mediterranean ridge close to the sirte abyssal plain nucleation of the crystals does not occur at the surface but from the deep brines because the salinity of the water is normal down to the depth of 3 000 m we propose the name bacino bannock for this basin after the consiglio nazionale delle ricerche r v bannock from which the bottom water brines were surveyed and sampled

organic carbon accumulation in bannock basin evaluating the role of productivity in the formation of eastern mediterranean sapropels abstract three sediment cores from bannock basin a hypersaline anoxic basin in the eastern mediterranean have been studied to evaluate the importance of productivity on organic carbon accumulation and sapropel formation in this region organic carbon accumulation rates were determined for two cores from within the anoxic hypersaline zone and for one core from the oxygenated portion of this basin organic carbon accumulation rates are higher by an order of magnitude in the surficial sediments of the anoxic zone due to better preservation an empirically derived preservation factor which allows calculation of paleoproductivity during the deposition of the most recent sapropel si indicates that productivity increased by an order of magnitude during the formation of si we conclude that increased productivity was coupled with a density stratification and a circulation reversal in the eastern mediterranean which together led to sapropel formation

influence of magmatic hydrothermal activity on brine evolution in closed basins searles lake california evaporites in a 700 m long core km 3 from searles lake california preserve a record of the chemical evolution of inflow waters chemical analyses of fluid inclusions in halite and evaporite minerals show that the major ion composition of inflow waters to searles lake was changed by distant hydrothermal activity associated with magmatism at long valley caldera between 1 27 and 1 0 m y ago below core depths of 291 m the evaporites consist of ca bearing sulfates anhydrite glauberite and halite fluid inclusions in the halite show that parent waters were na cl so42 rich waters above 291 m the evaporites include sodium carbonates pirssonite trona and halite and fluid inclusion brines are na k hco3 co32 cl so42 rich these fluctuations in mineralogy and brine chemistry document an alkalinity spike beginning between 1 27 and 1 0 ma when inflow waters to searles lake crossed the caco3 chemical divide and began to produce alkaline brines that precipitated trona upon evaporation the owens river is a modern chemical analog for inflow water into searles lake beginning between 1 27 ma and 1 0 ma a major contributor of solutes to the owens river is hot creek in long valley caldera which is fed by hydrothermal springs with high alkalinity from magmatically derived co2 the timing of magmatism in owens valley and the appearance of sodium carbonate minerals in core km 3 suggest a causal relationship volcanism and hydrothermal activity provided co2 and elevated alkalinity to searles lake inflow waters 0 5 0 2 m y before the eruptions that formed the bishop tuff and long valley caldera

paleoenvironmental setting mechanism and consequence of massive organic carbon burial in the permian junggar basin nw china abstract the junggar basin in northwestern china is a typical walled sedimentary basin that has a prolonged basin evolution history from the paleozoic to cenozoic and is rich in petroleum resources permian strata reach thousands of meters in thickness and have been intensively studied for their record of regional tectonics and paleoenvironments they have also been exploited for oil and gas for the past several decades in this paper we summarize perspectives on tectonic evolution stratigraphic framework sedimentary environments and the paleoclimate of the permian junggar basin and the adjacent turpan basin further we discuss the mechanism and consequences of massive organic carbon burial based on a compilation of published radiometric dating datasets an updated chronostratigraphic framework was proposed for the junggar basin this framework constrains the ages of two main petroleum source intervals the fengcheng formation and the lucaogou and equivalent formations as early permian and middle permian respectively although a global warming and drying trend was present throughout the permian period the regional climate over the junggar basin was drier in early permian and more humid in the middle late permian with short term climatic fluctuations during the deposition of the two petroleum source intervals dry and temperate climate prevailed and evaporative lacustrine environment dominated organic matter enrichment was promoted by stable salinity stratification and limited dilution by inorganic sediments leading to one of the richest lacustrine source rock deposits in the world the average organic carbon burial rates were 11 2 gc m2 yr for the lucaogou formation and 3 5 gc m2 yr for the fengcheng formation lower than the average organic carbon burial rate in modern lakes however considering the large areas of global tectonic lakes in the permian period organic carbon burial in lacustrine environments could act as a significant carbon sink and impact the global carbon cycle and climate evolution

anoxic basins of the eastern mediterranean an overview it is well known that the mediterranean sea underwent several episodes of basin wide stagnation in the plio pleistocene but extant anoxic basins were first discovered between 1983 and 1984 in the strabo trench and in the southwestern slopes of the mediterranean ridge facing the sirte abyssal plain since then several expeditions were carried out to investigate the geology and physiography of the basins as well as the physical and chemical characters of the water column although the geodynamic settings of the tyro and bannock basins are quite different they are very deep closed and filled by dense salty cold brines whose presence is attributed to submarine dissolution of messinian evaporites bannock basin is interpreted as a collapse basin with a complex configuration central domes and several satellite basins most of which are anoxic unlike the tyro basin it is characterized by precipitation of gypsum occurring as euhedral crystals within the sediments and dredged along the steep wall bordering the main basin to the east the interface separating normal seawater from the brines corresponds to a well defined pycnocline with a density contrast of approximately 20 where strong bacterial activity seems to occur and a sudden decrease in transmittance is recorded studies on the water column document drastic changes of all the various parameters measured o2 h2s ca po4 ba across the interface sediments deposited beneath the brines are anoxic this kind of geologically induced anoxia is persistent and diachronous in contrast with the isochronous episodic repetitive and climatically induced anoxia recorded in the same area of the eastern mediterranean

the role of attenuation in the formation of the railroad valley structural basin east central nevada detachment control of petroleum reservoirs the eastern boundary of railroad valley has long been considered a large displacement steep normal fault by mapping a low angle fault called the white pine detachment wpd from the ranges into the valley we show that steep normal faulting was not a significant process in the formation of railroad valley the wpd or its equivalent extends throughout the white pine and grant ranges as shown by mapping of previous authors well data show that it is also present in railroad valley our structure contour map of the wpd based on surface and subsurface data shows that the wpd dips uniformly from the ranges into railroad valley and is not displaced significantly by high angle faulting even if high angle faulting were assumed the maximum displacement consistent with the data would be 2000 ft 610 m much smaller than the total structural relief of at least 16 000 ft 4880 m between the grant range and the adjacent valley structural elevations in the valley are low because the paleozoic section has been greatly attenuated a related contribution to structural relief is uplifting of the ranges caused by diapiric emplacement of plutons in response to tectonic unloading the wpd is only one of many detachments in railroad valley we propose that most or all of the oil reservoirs are in attenuated brittle blocks between detachments seals are provided by detachments or by the discontinuous nature of associated fracturing attenuation by juxtaposing hot infrastructure rocks with rocks that normally occur thousands of feet above the granitic and metamorphic basement may have contributed to maturation of source rocks begin page 1154

excess helium and argon of radiogenic origin in mediterranean brine basins extraordinary helium and argon signatures were observed in a recently discovered brine lake district in the eastern mediterranean sea at water depths of 3500 m in the urania basin 4he concentrations are enriched by a factor of up to 32000 compared to normal seawater low 3he 4he ratios of 1 10 7 and high 40ar 36ar ratios of up to 470 indicate a radiogenic source these data represent by far the highest radiogenic supersaturations ever observed in an oceanic environment we propose a new conceptional model assuming that the urania basin is fed by advective transport from a deep fluid reservoir below the messinian evaporite sequence the evaporite seal provides the unique condition for accumulating the extraordinary high amounts of radiogenic helium from deep sedimentary strata injection of radiogenic helium from brine pools like the urania basin may contribute significantly to the inventory of terrigenic helium in the deep waters of the eastern mediterranean

petroleum geology of cretaceous tertiary rift basins in niger chad and central african republic this overview of the petroleum geology of rift basins in niger chad and central african republic car is based on exploration work by exxon and partners in the years 1969 1991 the work included 50 000 km of modern reflection seismic 53 exploration wells 1 000 000 km2 of aeromagnetic coverage and about 10 500 km of gravity profiles the results outline ten cretaceous and tertiary rift basins which constitute a major part of the west and central african rift system wcars the rift basins derive from a multiphased geologic history dating from the pan african approximately 750 550 ma to the holocene main rifting was probably caused by the stretching and subsidence of african crustal blocks during the breakup of gondwana in the early cretaceous and by r activated plate movements in the early tertiary wcars in the study area is divided into the west african rift subsystem was and the central african rift subsystem cas was basins in niger and chad are chiefly extensional and are filled by up to 13 000 m of lower cretaceous to holocene continental and marine clastics the basins contain five oil 19 43 api and two oil and gas accumulations in upper cretaceous and eocene sandstone reservoirs the hydrocarbons are sourced and sealed by upper cretaceous and eocene marine and lacustrine shales the most common structural styles and hydrocarbon traps usually are associated with normal fault blocks cas rift basins in chad and car are extensional and transtensional and are filled by up to 7500 m of chiefly lower cretaceous continental clastics the basins contain eight oil 15 39 api and one oil and gas discovery in lower and upper cretaceous sandstone reservoirs the hydrocarbons are sourced by lower cretaceous shales and sealed by interbedded lacustrine and flood plain shales structural styles range from simple fault blocks through complex flower structures the main hydrocarbon traps are in contractional anticlines geological conditions favor the discovery of potentially commercial volumes of oil in wcars basins of niger chad and car

organic carbon distribution and isotopic composition in three records from the eastern mediterranean sea during the holocene we investigated the distribution of organic carbon toc and bulk organic 13 c org values in two cores from the aegean sea and one from the libyan sea eastern mediterranean sea ems with a focus on the timing and regional expression of sapropel s 1 deposition in the early holocene our data indicate that the onset of s 1 occurred earlier in the libyan sea 9 8 kyr bp than in the aegean sea 8 9 kyr bp implying that dysoxia anoxia started earlier in the deeper sites of the ems than in the shallower sites in the aegean sea accumulation rates of organic matter om during the s 1 period have a clear decreasing gradient from north to south with higher values in the aegean sea and toc contents higher in the deep basin the three sedimentary sequences exhibit 13 c org values that fall within the range of algal om 25 to 20 shifts to lighter 13 c org values within sapropel intervals in the aegean sites can be interpreted as the result of elevated marine production enhanced inflow of light terrestrial dissolved inorganic carbon and or of the shoaling of the pycnocline along with the presence of a deep chlorophyll maximum dcm during the s 1 period

new k ar ages for calculating end of shield extrusion rates at west maui volcano hawaiian island chain thirty seven new k ar ages from west maui volcano hawai i are used to define the waning stages of shield growth and a brief episode of postshield volcanism all but two samples from shield stage strata have reversed polarity magnetization so conceivably the exposed shield is not much older than the olduvai normal polarity subchron or about 1 8 ma the oldest ages obtained are in the range 1 9 2 1 ma but have large analytical error shield volcanism ended about 1 35 ma and postshield volcanism followed soon thereafter persisting until about 1 2 ma exposed shield stage strata were emplaced at a rate of about 0 001 km3 per year a rate smaller than historic hawaiian magmatic rates by a factor of 100 stratigraphic accumulation rates are similar to those measured previously at wai anae volcano o ahu or the upper part of the mauna kea shield sequence hilo drill core hawai i these rates diminish sharply during the final 0 3 0 5 m y of the shield stage hawaiian shield volcanoes begin waning well before their last 0 5 m y of life then end quickly geologically speaking if west maui is representative

a genetic model for na carbonate mineral precipitation in the miocene beypazari trona deposit ankara province turkey abstract the miocene beypazari trona deposit in central anatolia turkey with estimated reserves of 250 million of tons of soda ash sodium carbonate is the second largest na carbonate deposit in the world petrographic observations of sodium carbonate evaporites from basin center cores show that the evaporites and associated minerals underwent significant early diagenetic mineral transformations in the beypazari basin trona pirssonite and nahcolite are the major evaporite minerals with subordinate bradleyite shortite and thenardite pirssonite occurs in organic rich muds oil shales pirssonite is not a primary mineral but rather appears to have formed diagenetically from displacive gaylussite trona precipitated subaqueously in lake waters and as interstitial phase in playa muds nahcolite is a later diagenetic mineral replacing both trona and pirssonite beds evaporite minerals are closely related to pyrite in oil shales and are also associated with diagenetic silicates mg rich smectites zeolites k feldspar searlesite and idiomorphic quartz formed by reaction of alkaline brines with pyroclastic deposits the proposed sedimentary model involves an alkaline lake in which water depth fluctuated from deep perennial meromictic stratified stages to shallow ephemeral playa lake stages lake margin clastic deposits are absent in the center of the basin wherein na carbonate minerals were formed suggesting the prevalence of a groundwater regime during drawdown events

geochemistry of eastern mediterranean sediments primary sediment composition and diagenetic alterations abstract two cores recovered in the eastern mediterranean were analysed for major minor and trace elements the primary chemical composition of the sediment is different at each location probably because the lithological sources and the relative biogenic contributions differ carbonates are important for the concentration of ca mg and sr whereas aluminosilicates determine the concentration of si al k li y and be and to a lesser extent that of fe cr ti mg zn and zr in sapropels organic carbon and sulphur seem to be closely related bromine mo p fe v cu zn co ni and cr are closely associated with organic and sulphidic compounds the concentration versus depth profile for organic carbon in two sapropels points to a rapid establishment of conditions that gave rise to sapropel formation followed by a gradual transition back to normal conditions the primary composition is overprinted by diagenetic processes sulphate reducing conditions occurred during and just after sapropel deposition a progressive oxidation front mechanism which became active after sapropel deposition is responsible for additional major geochemical changes this diagenetic phenomenon has strong implications for the chemistry of fe mn ni co zn cu cr v u as and sb

spatial transition from compression to extension in the western mediterranean ridge accretionary complex the mediterranean ridge has been described since 1982 as an accretionary prism related to the hellenic subduction zone however little attention has been paid to the actual mechanical boundary between the sedimentary wedge and the crustal backstop of the outer hellenic arc using seismic velocity structures from recent esp s pasiphae cruise we propose a new interpretation of existing geological and geophysical data around the western hellenic trenches the velocity structure of the inner unit of the mediterranean ridge suggests that the late neogene to quaternary sequences were deposited above a high velocity rigid body we propose to correlate the boundary of this rigid body backstop of the accretionary wedge with a series of oblique reflectors dipping to the southwest near dsdp sites 126 and 377 the backstop extends further south than previously thought and decreases by one third the total width of the compressional wedge it has thus major implications on the volume of accreted material the short wavelength folding of plio quaternary sediments observed on the outer wall of the south matapan trench is probably a consequence of gravity gliding layers above the high velocity body gently dipping 2 to the northeast using the messinian evaporite as a decollement on the other hand the hellenic trenches appear to be narrow half grabens affected by the widespread extensional deformation active on the outer hellenic arc they are situated on the landward boundary of a wider and poorly sedimented fore arc basin we conclude that extensional deformation extends at least over the width of the hellenic trenches on the continental side of the backstop whereas compressional deformation stops near the edge of the backstop itself 100 km to the southwest

coastal erosion rates of lava deltas around oceanic islands abstract rates of coastal erosion are needed for planning purposes and to improve understanding of how the shelves of islands develop ultimately becoming submerged banks near shore submarine platforms created by erosion of lava deltas of known age provide an opportunity to quantify erosion rates and to investigate how those rates vary between different types and ages of lava flows as well as how they vary with wave climate we have compiled data on deltas formed during historical and holocene eruptions age 6 ka from both a and p hoehoe lava flows and from diverse localities azores and hawaiian islands and ascension island near shore platforms were interpreted from multibeam sonar bathymetric light detection and ranging lidar and historical sounding data from them we estimated time averaged shoreline retreat rates from the seaward distances between the modern coastlines and the submarine platform edges the 35 interpreted platforms have rugged dipping surfaces left behind by erosion with an average gradient of 5 range 2 10 eroded distance of 436 m 78 1119 m and depth of platform edge of 25 m 5 56 m to evaluate the latter depths we computed seabed orbital speeds due to surface waves at the platform edges depths of platform edges correlate only modestly with those speeds suggesting that platform surfaces have adjusted to wave conditions with a wide range of particle sizes and hence thresholds of motion the largest retreat distances 800 m are associated with platforms of the central azores islands which are exposed to higher waves however retreat rates are highly varied 0 08 12 5 m yr and weakly correlated with measures of wave power suggesting that waves are only a secondary influence given that lack of correlation we suspect that the main factor contributing to variability arises from varied cliff resistance to erosion blocks between joints in lava flows and hence resistance to erosion vary greatly in size from the thicker and less densely jointed a flows to the thinner and shell like layered lavas in p hoehoe flows

boron isotope and geochemical evidence for the origin of urania and bannock brines at the eastern mediterranean effect of water rock interactions the origin of hypersaline brines from urania and bannock deep anoxic basins in the eastern mediterranean sea has been investigated by integrating geochemical data and boron isotopic ratios bottom brines from urania basin have chloride contents up to 4200 mmole kg h2o and a marine na cl ratio 0 87 all the other ionic ratios are different from the marine ratios and show a relative enrichment in ca k br and b and depletion in mg and so4 as normalized to the chloride ion the 11b values of the urania brines 11b 29 8 2 9 n 7 are lower than that of mediterranean seawater 39 the concentrations of cl and na which make up 95 of the total dissolved ions in molal units suggest that the urania brines were derived from eightfold evaporated seawater the relative enrichment of ca and depletion of mg and so4 reflect dolomitization gypsum precipitation and sulfate reduction processes which modified the original evaporated seawater while the brines were entrapped as interstitial waters in the sedimentary section of the mediterranean the relative enrichments of br b and k and the low 11b value of the urania brines suggest high temperatures interactions of the evaporated sea water with sediments mass balance calculations suggest that desorption of exchangeable b from the sediments 11b 20 modified the marine b isotopic composition of the original eightfold evaporated seawater potassium was also leached from clay minerals whereas br was contributed from degradation of organic matter in the sediments this is consistent with a thermal anomaly up to 45 c recorded at depth in the region of urania basin in contrast bottom brines and shallow interstitial fluids from bannock basin with low temperatures 15 c show marine 11b 11b 39 6 2 8 n 5 38 5 2 2 n 5 respectively and b cl ratios 7 10 4 the b isotope data confirm that the bannock brines were derived from twelvefold evaporated seawater we argue that the brines from both basins are relics of fossil evaporated seawater that was entrapped in late miocene sediments and accumulated in the deep basins of the mediterranean seafloor

redistribution and geochemical behaviour of redox sensitive elements around s1 the most recent eastern mediterranean sapropel the youngest eastern mediterranean sapropel s1 is generally believed to have formed 7 9 14c ky b p the distribution of redox sensitive elements above in and below the sharply defined organic rich unit reveal that s 1 has already suffered heavy diagenetic alteration its present thickness based on its dark colour is only a fraction of its original thickness in one core visual evidence of s1 with an inferred initial thickness of 6 cm has been destroyed and a similar thickness appears to have been lost from the tops of another two examples this is caused by oxidation of the upper reaches of s 1 by a progressive oxidation front which commenced 5 2 5 4 14c ky ago and still appears to be active in the three cores studied diagenetic relocation of many redox sensitive elements has occurred most elements expected to be enriched in sapropels or sulphide rich sediments already have maximum concentrations above or below rather than in the present s 1 layers similarities are observed in the geochemical behaviour of as fe and p of co cu mn ni and zn and of cd mo sb ti u and v the behaviour of ba is distinctive and its immobility as barite makes it an indicator for palaeoproductivity and the original high s1 corg content the elements se and i exhibit particularly large sharp concentration peaks and together are proposed as useful indicators of the present boundary between oxic and post oxic conditions

geochemical constraints on the role of oceanic lithosphere in intra volcano heterogeneity at west maui hawaii 87 sr 86 sr 206 pb 204 pb variation in the stratigraphically lowest lavas is orthogonal to the all hawaii variation indicating that it is not the result of mixing between components normally sampled by hawaiian shield stage magmas we compare our west maui data with observed compositions of pacific oceanic basaltic and gabbroic crust and predicted compositions for 2ga basaltic and gabbroic oceanic crust the observed fine scale compositional variability in the stratigraphically lowest west maui lavas is consistent with 10 15 mixing of small degree 2 partial melts of the pacific gabbroic oceanic crust with plume derived kea type magmas mass balance considerations indicate that this geochemical signal can be present in no more than 5 of the total volume of lavas erupted at west maui

early organic diagenesis the significance of progressive subsurface oxidation fronts in pelagic sediments abstract porewater and solid phase geochemical data at two contrasting ne atlantic stations are reported station 10552 on the cape verde abyssal plain is a site of slow pelagic accumulation ca 0 4 cm kyr 1 molecular oxygen is present in the sediment column to at least 2 m and probably much deeper labile organic carbon is almost totally consumed in the upper few centimetres of the sediment by contrast at station 10554 on the madeira abyssal plain the pelagic sequence has been interrupted by the occasional deposition of organic rich turbidites porewater oxygen and nitrate profiles show that subsurface organic metabolism of the organic carbon associated with the uppermost turbidite layer is a significant fraction of the overall metabolism in the sediment column this metabolism occurs at a relatively thin reaction front which progresses deeper into the turbidite with time this phenomenon exerts a controlling influence on the present nutrient profile and redox succession in a less extreme form substrate distributions of this latter type are not uncommon in atlantic sediments a model has been developed which is controlled by both oxygen and nitrate data this model permits a vertical profile of metabolic activity to be derived and also gives estimates of the reaction rate constants and solid phase mixing rates at these two contrasting stations about 30 of the total activity at station 10554 is located within the turbidite at the deepening reaction front this is a non steady state condition in fact it is found that the integrated metabolic activity at the two stations is not dissimilar ca 1 2 10 13 moles cm 2 sec 1 the striking differences in redox profile are therefore primarily attributable to differences in the distribution of metabolic activity within the column

stratigraphy and sedimentation in the western strabo trench eastern mediterranean abstract three piston cores ranging in length from 501 to 921 cm raised from the adjacent mediterranean tyro and kretheus basins and their intervening sill confirmed previous findings of persistent anoxia and extended our knowledge of the stratigraphic record the two cores from the basinal settings contain a bronze age homogenite this tsunami induced turbidite is only 28 cm thick in the shallower kretheus basin whereas it has a thickness of 235 cm in the deeper tyro basin the recovery of the homogenite in these subbasins of the western strabo trench demonstrates that the tsunami wave turned west of crete and arrived here with a velocity sufficient to remobilize unconsolidated sediments draping the basin slopes the holocene and uppermost pleistocene sedimentary record is characterized by numerous millimetric to centimetric sand layers containing reworked pliocene and miocene foraminifers the repetitive siliciclastic turbidites interfered with the normal eastern mediterranean succession of sapropels and tephras and document a strong neotectonic activity related to the presence of an active trench on the floor of ponded rimmed basins like the tyro and kretheus basins the sand layers are associated with anoxic sediments whereas they are associated with normal well oxygenated marls on the sill which lies above the anoxic oxic interface basin anoxia is interpreted as the result of submarine dissolution of messinian evaporites giving rise to deep seated brines extraformational reworking documents the occurrence of pre messinian fossiliferous sediments exposed on the trench wall and subject to submarine erosion the stratigraphic time framework is given by nannofossil biostratigraphy corroborated by lithostratigraphic correlation of isochronous lithologies sapropel and tephra chronology a drastic change in sedimentary regime is recorded at approximately 70 ka b p emiliania huxleyi acme e huxleyi zonal boundary older sediments which were only recovered in core 37 from the sill separating the tyro and kretheus basins are pelagic with an almost typical eastern mediterranean succession of sapropels and tephras no siliciclastic turbidites and no extraformational reworking are noticed in sediments older than 70 000 years we conclude that the trench system became active just at that time a thick layer of plurimillimetric pumice bubbles was discovered within sapropel s 6 indicating a strong explosion of a nearby volcano at 180 ka b p but we have no analytical data yet to substantiate the provenance of the volcanogenic deposits

sediment geochemistry of the thetis hypersaline anoxic basin eastern mediterranean sea abstract the thetis basin is a deep hypersaline anoxic basin in the western part of the mediterranean ridge eastern mediterranean sea it is characterised by highly sulphidic nacl saturated brine with one of the highest values of salinity reported from similar basins s 348 the strong pycnocline at the seawater brine interface induces permanent anoxic bottom conditions driving depositional processes and distribution patterns of redox sensitive metals in the sediments this work presents a high resolution dataset of sedimentological mineralogical and geochemical features and planktonic foraminifera distribution derived from the exploration of a 52 cm long box core sampled in the thetis sediments basing on direct comparisons with available data from other hypersaline records and ancient anoxic organic rich deep sea records sapropels and black shales we aim to explore the potential of these anoxic basins as natural laboratories to better understand the mechanisms driving geochemical patterns in recent ancient anoxic sediments

the role of excess co2 in the formation of trona deposits abstract the prevailing theory for the formation of trona na3 co3 hco3 2 h2o relies on evaporative concentration of na hco 3 water produced by silicate hydrolysis of volcanic rock or volcaniclastic sediments given the abundance of closed drainage basins dominated by volcanics it is puzzling that there are so few trona deposits and present day lakes that would yield dominantly na co3 minerals upon evaporation groundwater in the san bernardino basin southeastern arizona usa and northeastern sonora mexico would yield mainly na co3 minerals upon evaporation but waters in the surrounding basins would not analysis of the chemical evolution of this groundwater shows that the critical difference from the surrounding basins is not lithology but the injection of magmatic co2 many major deposits of trona and na co3 type lakes appear to have had excess co2 input either from magmatic sources or from the decay of organic matter it is proposed that along with the presence of volcanics addition of excess co2 is an important pre condition for the formation of trona deposits

spatial and temporal variability of the chemistry of the shallow groundwater in the alluvial fan area of the luanhe river north china groundwater in the alluvial fan area of the luanhe river north china was monitored every 2 months for a year subsequently the temporal and spatial variability in the hydrochemical characteristics of the water was investigated using hierarchical cluster analysis hca and a trilinear piper diagram it is found that the spatial variability in the groundwater composition from different monitoring wells has obvious differences even if the distance between many of the wells is small also the difference in the ion concentration was found to be up to fivefold for the same monitored well research has indicated that the groundwater s chemical characteristics are mainly controlled by soil type the amount of precipitation the luanhe river the groundwater and human factors the thickness and continuous distribution of clay influences the velocity and ion exchange rate of the groundwater flow this results in the amount of total dissolved solids in the groundwater increasing from upstream to downstream in the flood season june july and august ion concentration gradually decreases as a result of the increased recharging of the groundwater due to precipitation classification using hca indicates that the samples can be clustered into different groups according to correlation coefficients also the chemical composition of the water from monitoring wells near the luanhe river is approximately consistent with that from the luanhe river this implies that the samples have some compositions resulted from the mixing of groundwater and river water the piper diagram indicates that ca2 mg2 and hco3 ions are the predominant ones present i e the type of groundwater is of the ca mg hco3 type

deep mid water bacterial mats from anoxic basins of the eastern mediterranean peculiar pellicles have been recorded in the extant anoxic hypersaline basins of the bannock area and the western strabo trench eastern mediterranean discrete layers of pellicles were found in 29 cores they are oriented parallel to bedding planes or are folded within the sandy base of turbidites and within slumped sediments in addition similar pellicles occur at the surface of or interlocked within gypsum crystals recovered from the bannock area the pellicles are 0 5 3 mm thick and dark greenish grey in colour they foliate into very small 1 mm undulating and anastomosing microlaminae entrapping abundant biogenic and inorganic particles the amorphous organic matter of the pellicles is most probably produced by bacterial masses linked to mineralization processes of the organic debris anaerobic sulphate reducing bacteria desulphovibrio are abundant and the presence of methane bacteria is likely detailed analyses with the light microscope and scanning electron microscope yielded differences and similarities concerning ultrastructure content abundance and morphotypes of the bacterial pellicles from the bannock area and the western strabo trench a consistently well developed ultrastructure comprising thin microlaminae characterizes the bannock pellicles whereas the ultrastructure of the tyro and poseidon pellicles is usually not organized siliceous microfossils are abundant in samples from both sites but centrate diatoms prevail in the bannock pellicles whereas pennate diatoms are overwhelmingly dominant in the tyro and poseidon pellicles calcareous micro and nannofossils together with pyrite framboids are more abundant in samples from the bannock area bacteria are extremely abundant in samples from the bannock area and three different morphological types have been distinguished only one type of bacteria was commonly observed in pellicles from the western strabo trench basins pellicles form at the normal seawater brine interface as substantiated by transmittance profiles and bacteriological investigations therefore the term deep mid water bacterial mats is proposed herein for these peculiar layers after bacterial mats grow at the interface they are included within the sediments by following one of two different paths a when pelagic sedimentation prevails pellicles sink to the basin floor due to the increasing load of biogenic and inorganic detritus and b under a tectonically active regime turbidity currents and slumps can disrupt the interface and destroy the floating mats in the latter case fragments of pellicles are transported to the bottom within the gravity flows

hydrogeochemistry of the middle rio grande aquifer system fluid mixing and salinization of the rio grande due to fault inputs abstract deeply derived fluids influence river and groundwater hydrochemistry at the socorro constriction in the central new mexico rio grande rift new hydrochemical transects in the rio grande rift provide three dimensional perspectives on sources contributing to surface and groundwaters in addition to abrupt salinity increases in the rio grande major and trace ion chemistry 18o d 13c 87sr 86sr 3h and 3he 4he variations in springs and wells across the rift are best explained by mixing of deeply derived endogenic fluids containing both mantle and crustal inputs with shallow groundwater endogenic fluids ascend along rift bounding and intra rift faults and can cause increased salinity accompanied by an increase in metals and overall degradation of water quality our data reinforce models that attribute a downstream increase in salinity to geological not agricultural influences hydrochemical mixing of endogenic waters along faults in shallow aquifers has a major influence on groundwater and surface water quality and variability in arid tectonically active regions with important ramifications for water management

present day coccolith fluxes recorded in central eastern mediterranean sediment traps and surface sediments two sediment traps were deployed in time series collection from november 1991 to august 1994 at 3000 and 3500 m respectively above and below the oxygenated sea water anoxic brine interface in the bannock basin central eastern mediterranean here the coccolithophore flux and its contribution to the carbonate particulate flux are presented for the 3000 m trap and compared with the record in eastern mediterranean surface sediments a marked seasonal variation is observed in the fluxes of total mass total coccoliths and whole coccospheres with flux maxima in late winter and spring the annual coccolith flux of 1 1010 coccoliths m 2 year 1 measured in the deep waters of bannock basin is much lower than published data from most other oceanographic settings even when corrected for the trap efficiency of 23 calculated from the 230th flux the biogenic and lithogenic fluxes are primarily controlled by coccolithophore production and saharan dust input respectively the calculated coccolith and coccosphere settling rates estimated from the comparison of maximum pigment concentration in the surface ocean and arrival of maximum flux at 3000 m water depth ranged from 17 to 25 m day 1 for coccoliths and 100 m day 1 for coccospheres at the study site carbonate dissolution is a minor process at both the trap depth and at the sea floor in both oxic and anoxic conditions and there is a high preservation of coccolith caco3 coccolithophores are the main contributor to the biogenic carbonate flux followed by thoracosphaerids emiliania huxleyi and florisphaera profunda followed by syracosphaera helicosphaera carteri and calcidiscus leptoporus are the dominant species in the sediment trap and surface sediments

geological evidence for mud diapirism on the mediterranean ridge accretionary complex abstract a mud breccia has been repeatedly cored from four mud diapir fields located on the crest of the mediterranean ridge this breccia is composed of subrounded clasts supported by a clay rich matrix and ranges in age from cretaceous to early miocene sedimentological analysis allows identification of a primitive intrusive and a reworked mud breccia the latter being formed by mud extrusion and gravitational reworking of the former homogeneous mud sorted by grain size which occurs at the top of the diapirs has been interpreted as a lake deposit based on composition and carbon isotopic ratios gases present within the diapiric material suggest a partial thermogenic origin and gas escape structures have been identified in the mud breccia and host sediments carbonate crusts occurring in the host sediments are not related to bacterial oxidation of methane and consequent authigenic calcite precipitation their carbon and oxygen isotopic ratios reveal that they are characteristic of early deep sea lithification in the mediterranean sea the presence of a marker bed composed of mn nodules and bacterial colonies the mud lake deposits showing lower carbonate content than primitive mud breccia and the gas escape structures suggest the presence of active fluid vents in the vicinity of the diapiric structures evidence of active mud diapirism can be found from about 300 000 yrs b p to the present

new k ar ages and the geologic evidence against rejuvenated stage volcanism at haleakalā east maui a postshield stage volcano of the hawaiian island chain the postshield and previously inferred rejuvenated stage history of haleakal volcano is reevaluated on the basis of 52 new k ar ages 42 from the postshield kula volcanics and 10 from the overlying h na volcanics postshield extrusion was robust from 0 93 to 0 76 ma a period of low extrusion rate or volcanic quiescence occurred between 0 76 and 0 65 ma well within kula time a chemical change to increasingly alkalic lava occurred at this time as the volcano changed from broadly hawaiitic to basanitic in its eruptive products and robust extrusion resumed a slightly longer period of low extrusion rate or quiescence occurred after ca 0 4 ma but only trifling change in geochemical character is observed geochemically the h na volcanics unit chiefly basanitic overlaps greatly with the upper part of the kula volcanics there is a weak tendency to slightly more alkaline character among the h na volcanics the age of the kula h na boundary is ca 0 15 0 12 ma thus volcanic quiescence of only 0 03 m y separates the two formations much shorter than the previously known limit of 0 25 0 30 m y the brevity of this hiatus coupled with coincident vent loci and broadly similar geochemical characteristics for the h na and the upper part of the kula volcanics indicates that the h na volcanics unit comprises deposits of postshield stage volcanism that has waned substantially since ca 0 4 0 3 ma haleakal has not yet begun a classically defined rejuvenated stage our findings support recent numerical modeling of plume lithosphere interactions that predict that haleakal is near the end of its postshield growth

facies analysis of pleistocene sediments from the bannock basin area a key to the reconstruction of its tectonic evolution abstract facies analysis was carried out on 21 selected cores from the bannock area in order to investigate the relationships between sedimentation and tectonism bannock basin is a large 3500 m uncorrected deep subcircular depression near the deformation front of the mediterranean ridge facing the sirte abyssal plain the basin is divided into several sub basins aligned along a rim syncline surrounding a central elevated area salt dome high density brines and anoxic sediments occupy the deepest part of the depressions the facies distribution is controlled by the bottom configuration in that pelagic facies typically occur on plateaus and domes debris flow deposits in base of slope settings and turbidites in basinal settings the facies distribution may therefore be used to reconstruct the evolution of the various parts of the rim syncline erosional gaps may be related to tectonism or may be features created by the passage of major turbiditic events the results of our study of the facies associations and of the rates of sediment accumulation indicate that the collapse of the eastern part of the rim syncline pre dates the collapse of the western part the western basins are deeper and larger than the eastern ones and unlike the latter are aligned at the foot of a strike slip fault with a vertical offset of at least 700 m

the geometry and rates of microplate motions in the eastern mediterranean sea quantitative constraints by using anoxic basins as piercing points abstract anoxic conditions encountered in small basins on the flanks of the mediterranean ridge are due to the formation of brine pools caused by exposure of messinian evaporites seismic reflection profiles and structural data indicate young active strike slip faulting and thrusting due to collision between microplates to be responsible for the continued isolation of the basins an estimate of 100 000 years for the age of initiation of the tyro and kretheus basins using a finite microplate rotation model for the central and eastern mediterranean sea is in close agreement with coring results in the kretheus basin rates of relative motion with respect to africa of more than 8 cm a 1 along the western strabo trench are supported by these results this study indicates that regional deformation resulting from active plate convergence appears to bear a simple relation to a few finite rotation poles for relative movement between plates and microplates

ka ena volcano a precursor volcano of the island of o ahu hawai i ka ena and wai alu ridges form prominent submarine ridges nw of the island of o ahu hawai i we evaluate whether or not either one of these ridges represents a submarine extension of wai anae volcano on o ahu using new bottom observations geophysical surveys and geochemical data acquired on new samples from the region wai alu ridge has the morphology of a submarine rift zone but is too shallow for its distance from the o ahu shoreline ka ena ridge also is unusually shallow and is surmounted by two topographic shields ka ena and wai alu ridges have similar magmatic and volcanic evolutionary histories beginning ca 5 ma with a submarine shield phase of volcanism that produced high sio 2 low feo tholeiites with higher 208 pb 204 pb than in the adjacent wai anae volcano late shield volcanism included transitional and alkalic rock types with lower sio 2 and enrichment in incompatible elements especially p 2 o 5 nb zr ti and light rare earth elements the transition from shield to late shield stage occurred as the edifice was beginning to emerge from the sea geological observations and k ar ages indicate that ka ena emerged above sea level ca 3 5 ma reaching a maximum height of 4000 m above the abyssal ocean floor and 1000 m above sea level relatively weak gravity anomalies topographic lineaments and the orientation of dike complexes indicate a volcanic structure that is independent of wai anae volcano thus volcanic structure geochemistry and age all indicate a precursor volcano to the island of o ahu which we call ka ena volcano after emergence ka ena volcano tilted 2 to the south we estimate a total volume of 20 27 10 3 km 3 for ka ena volcano taking into account overlapping geometry of concurrently active volcanoes sample compositions from the ka ena landslide deposit are entirely consistent with derivation from ka ena whereas most samples from the wai anae slump are likely derived from wai anae volcano uniformly oriented dikes in the wai anae nw rift zone likely reflect buttressing by a preexisting ka ena volcano unusual isotopic compositions of some wai anae samples including unique hydrous silicic lavas probably reflect interaction with underlying ka ena crust a newly recognized lava flow field on the southern flank of ka ena ridge extends the previously known distribution of secondary volcanism in the kaua i channel putative submarine volcanic activity in the region in 1956 cannot have built a large edifice and is unlikely to have produced pumice that was found on o ahu shores this eruptive activity therefore remains unconfirmed

recent sapropel formation in the eastern mediterranean during the 1983 expedition of the rv tyro in the eastern mediterranean a combined programme of seismological micropalaeontological and geochemical research was performed the geochemical research focused mainly on the interstitial water and the chemical composition and origin of sapropels for this purpose box cores piston cores and bottom water samples were collected we report here that some of these cores showed clear evidence of long term stagnant bottom water conditions in a small basin south of crete for which we propose the name tyro basin 1 the bottom water is strongly anoxic whereas the sediment down to at least 400 cm is sapropel to sapropelic as salt concentrations in the bottom water are eight times higher than in normal seawater the anoxic conditions in this basin are probably due indirectly to dissolution of salt from a nearby diapir

temporal stability and origin of chemoclines in the deep hypersaline anoxic urania basin submarine brine lakes feature sharp and persistent concentration gradients between seawater and brine though these should be smoothed out by free diffusion in open ocean settings the anoxic urania basin of the eastern mediterranean contains an ultrasulfidic hypersaline brine of messinian origin above a thick layer of suspended sediments with a dual modeling approach we reconstruct its contemporary stratification by geochemical solute transport fundamentals and show that thermal convection is required to maintain mixing in the brine and mud layer the origin of the urania basin stratification was dated to 1650 years b p which may be linked to a major earthquake in the region the persistence of the chemoclines may be key to the development of diverse and specialized microbial communities ongoing thermal convection in the fluid mud layer may have important yet unresolved consequences for sedimentological and geochemical processes also in similar environments

integrated geophysical geochemical and hydrogeological investigation of shallow groundwater resources in parts of the ikom mamfe embayment and the adjoining areas in cross river state nigeria information generated from geophysical geochemical and hydrogeological data has been used in assessing the groundwater resource potential quality and usability and in mapping flow directions within the shallow subsurface of the mamfe embayment cross river state nigeria the electrical resistivity technique in which the schlumberger s vertical electrical sounding field procedure has been adopted was the geophysical method employed lithology logs from drilling records discharge rates static water level information were the hydrogeological information utilized while the geochemical techniques involve analyses of water samples apparent resistances were measured using different resistivity meters including oyo mcohm model 2115 abem terrameter sas300b and sas1000 models and igis ssp ats mrp model with maximum current electrode separation reaching 1 km in some communities geological information was used as control in the modelling and interpretation of all geophysical data the physico chemical parameters of the water samples from the different water sources in the area were determined using different analytical techniques and in some cases by in situ direct measurement of some parameters measured values of electrical conductivity static water level available aquifer discharge information and calculated sar and na were integrated into the geophysical and hydrogeological results the shallow subsurface of the area is segmented into four hydrogeological provinces crystalline basement province cbp cross river plain province crpp nkporo afikpo shales province nasp and alluvial buried river province abrp with localized groundwater flow patterns results indicated that the alluvial discharge rate of 3 83 l s fractured sandstone discharge rate of 2 43 l s and basement discharge rate of 1 80 l s aquifers are more yielding than the aquifers in areas covered with deformed shales discharge rate of 0 62 l s and siltstone aquifers discharge rate of 0 97 l s the aquifer horizons are inhomogeneous and anisotropic with topography and lithology exerting significant influence on groundwater flow direction however there appears to be some high yielding aquifers at depths greater than 100 m in the crpp areas although researches on their distribution are still ongoing precipitation is the major source of recharge and the water is enriched with na k ca2 mg2 text hco 3 cl text so 4 2 and text no 3 throughout the year graphical analyses of hydrochemical data using piper and stiff diagrams show that ca mg co3 hco3 is the dominant water facies results from ec sar and na show that the water is fresh and belongs to the good to excellent class and is therefore suitable for domestic agricultural and industrial use