the sedimentary expression of oceanic anoxic event 1b in the north atlantic abstract the aptian albian oceanic anoxic event 1b contains the record of severalperturbations in the global carbon cycle and multiple black shale levels particularly in the western tethys the local lithological expression of anoceanic anoxic event depends on palaeogeographical and depositional settingas well as on regional palaeoclimate marine sediments at a particular locationmay therefore be more or less organic rich or not at all and they may consistof different lithologies in most studies however much of the lithologicalvariability associated with oceanic anoxic events is left unaccounted for and thus the exact processes leading to the enrichment of organic matter in thesemarine sediments and their subsequent preservation in the geological recordare unknown this study focuses on the local sedimentary processes behindthe deposition of organic rich sediments at deep sea drilling project site 545and ocean drilling program sites 1049 and 1276 in the north atlantic duringoceanic anoxic event 1b although speci cally dealing with the sedimentsdeposited during this particular event at these localities it is expected that thesame processes were responsible for determining the exact sedimentaryproducts at localities in similar settings as well as during other similar eventsin the mesozoic here it is shown that the deposition of organic richsediments during oceanic anoxic event 1b was a consequence of theenhanced productivity favoured by upwelling and by riverine nutrientinput or aeolian fertilization of the euphotic zone depending ongeographical location slope instability processes resulted in the transfer ofpart of these organic rich sediments from the shelf to deep sea depocentres asmud laden organic rich turbidites especially in the northern north atlantic the so called black shales are much more varied than their name implies the end product of sedimentation during an oceanic anoxic event at aparticular location is commonly the result of several equi nal processes actingon a local scale rather than the direct result of basinal or even globalmechanisms keywords aptian albian kilian event north atlantic oae 1b oceandrilling program oceanic anoxic event paquier event

origin of fibrous gypsum in the newark rift basin eastern north america abstract cores from the red beds constituting the upper triassic passaic formation a syn rift sequence in the newark basin display subhorizontal fractures veins filled with satin spar gypsum such veins are apparent in the shallow subsurface 100 300 m below present ground level but are not observed in outcrops or in quarries because of groundwater dissolution these fractures are roughly parallel to the present ground surface in the basin suggesting topographic influence on their formation fractures observed in cores are seen to crosscut stratigraphic boundaries indicating that the veins formed after stratal tilting and faulting and thereby post date the early late jurassic the gypsum crystals making up the vein fill grew perpendicular to the fracture walls suggesting that opening and filling of the fractures was contemporaneous and that the fractures are extensional that gypsum crystallizes from meteoric and connate waters and is derived by dissolution of associated evaporites is reflected in the d 18o 34s and 87sr 86sr isotopic compositions of the sulfate fractures are interpreted to be a result of unloading and exhumation fractures were initiated after major depositional and tectonic events took place and post date the late jurassic satin spar precipitated in those fractures carried in by gypsum saturated brines derived either by dissolution of the near surface sulfate evaporites or rehydration of more deeply buried anhydrite such satin spar veins are not evaporites but are composed of chemically remobilized sulfate

testing 87sr 86sr as a paleosalinity indicator on mixed marine brackish water and terrestrial vertebrate skeletal apatite in late paleocene early eocene near coastal sediments mississippi abstract mixed marine brackish water and terrestrial vertebrate skeletal apatite is found in the late paleocene early eocene tuscahoma and bashi formations of mississippi the co occurrence in these near coastal marine deposits of skeletal apatite with different provenances offers a unique opportunity for unraveling the effects of diagenesis on apatite 87sr 86sr composition with bearings on the use of this isotope pair as paleosalinity indicator the results show that the sr isotopes of all originally poorly ordered phases of skeletal apatite have extensively re equilibrated with pore water with significantly lower 87sr 86sr ratios than late paleocene early eocene seawater for example marine shark and ray teeth from the bashi formation all have clearly nonmarine 87sr 86sr ratios 0 7073 0 7075 compared with a coeval seawater ratio in the range 0 7077 0 7078 however separated shark tooth enamel with a high original crystallinity appears to have retained all or most of its in vivo sr isotopic signature until the present here we also show that 87sr 86sr results on recent vertebrate skeletal material from different environments are in good agreement with expected values for respective habitat earlier analyses of calcite material from the bashi formation indicated the existence of a shift in seawater 87sr 86sr to a lower value at the paleocene eocene boundary the strong influence of pore water with low nonmarine 87sr 86sr on the apatite in the bashi formation suggests that the proposed isotopic shift may be an artifact related to diagenetic processes

satellite radar interferometry for monitoring ice sheet motion application to an antarctic ice stream satellite radar interferometry sri provides a sensitive means of monitoring the flow velocities and grounding line positions of ice streams which are indicators of response of the ice sheets to climatic change or internal instability the detection limit is about 1 5 millimeters for vertical motions and about 4 millimeters for horizontal motions in the radar beam direction the grounding line detected by tidal motions where the ice goes afloat can be mapped at a resolution of 0 5 kilometer the sri velocities and grounding line of the rutford ice stream antarctica agree fairly well with earlier ground based data the combined use of sri and other satellite methods is expected to provide data that will enhance the understanding of ice stream mechanics and help make possible the prediction of ice sheet behavior

application of strontium isotopes to understanding the hydrology and paleohydrology of the altiplano bolivia peru abstract strontium concentrations and strontium isotopic ratios were measured in natural waters and carbonate sediments from throughout the bolivian and peruvian altiplano in order to improve hydrologic and paleohydrologic mass balances with the ultimate goal of better understanding the paleoclimatic history of the central andes rivers flowing into lake titicaca have a wide range of strontium isotopic ratios that exhibit spatial patterns consistent with the lithologies of the different drainage basins because of the limited exchange of water between the two main sub basins of lake titicaca lago grande and lago huinaimarca and between the sub basins of lago huinaimarca there are significant differences in strontium isotopic ratios between the sub basins calculated elemental balances of strontium in lake titicaca are in reasonable agreement with previously published budgets of water and major elements however the strontium isotopic budget indicates that the lake is not in isotopic steady state this also implies that the major element budgets are unlikely to be in steady state lake titicaca had a higher than modern strontium isotopic ratio during the early and middle holocene elevated values persisted in lago grande until at least 2000 cal yr bp consistent with other evidence that modern hydrologic conditions namely overflow were not established until that time an isotopic budget calculated for late pleistocene paleolake tauca in the central altiplano suggests that between 70 and 83 of its riverine inputs were derived from lake titicaca overflow this calculated flow represents about a 30 fold increase over the average discharge of the modern rio desaguadero at desaguadero or a seven fold increase over its average discharge into lago poopo the strontium isotopic budget if complete precludes the possibility that decreased evaporation alone could have accounted for the existence of paleolake tauca

linking lacustrine cycles with syn sedimentary tectonic episodes an example from the codo formation late aptian northeastern brazil the codo formation exposed in the eastern grajau basin northeastern brazil consists mostly of black shales limestones and evaporites arranged into several shallowing upward cycles formed by progradation of lake deposits three ranks of cycles are distinguished the lower rank cycles correspond to millimetric interbeddings of bituminous black shales with evaporites calcimud stones or peloidal wackestone packstone grey green shale with calcimudstone peloidal wackestone packstone or ostracodal wackestone grainstone and ostracodal wackestone grainstone and or calcimudstones with cryptomicrobial mats and ooidal pisoidal packstones the intermediate rank cycles average 1 7 m in thickness and are formed by complete and incomplete cycles complete cycles show a transition from central to intermediate and then to marginal facies associations and include two types c1 cycle with central lake deposits consisting of evaporites and black shales and c2 cycle with central lake deposits formed by grey green shale complete cycles were produced by the upward gradation from central to marginal environments of the lake or saline pan sabkha system incomplete cycles are those where at least one facies association is lacking having been formed by successions either with central and intermediate facies associations i1 or intermediate and marginal facies associations i2 the higher rank cycles are on average 5 2 m thick and consist of four depositional units that display shallowing upward successions formed by complete and incomplete intermediate rank cycles that vary their distribution upward in the section and are bounded by sharp surfaces while the lower rank cycles display characteristics that reveal their seasonal signature detailed sedimentological characterization and understanding of stratal stacking patterns related to the intermediate and higher rank cycles support a genesis linked to syn sedimentary tectonic activity this is particularly suggested by the high facies variability limited lateral extension and frequent and random thickness changes of the intermediate rank cycles additionally the four higher rank cycles recognized in the codo formation match with stratigraphic zones having different styles of soft sediment deformation structures attributed to seismic activities therefore the several episodes of lake shallowing recorded in the codo formation are linked to seismic pulses that alternated with sediment deposition this process would have created significant changes in the lake water level and resulted in sharply bounded successions with upward gradation from deeper to relatively shallower facies associations

seawater 87sr86sr for the late permian delaware basin evaporites new mexico u s a abstract the delaware basin southeastern new mexico u s a contains a thick section of marine evaporites the three uppermost units all of ochoan age of evaporites are in ascending order castile formation salado formation and rustler formation the castile consists predominantly of bedded and massive anhydrites the salado of massive halite with numerous interbeds of anhydrite sylvite and minor other units and the rustler of impure anhydrites gypsums halites silty and clayey units dolomites and others the previously established seawater 87 sr 86 sr curve for the late latest permian is marked by a dramatic increase from 0 7068 at 250 ma ago to 0 7072 by the permian triassic boundary data are not shown for rocks of approximate ochoan age however the results of our study show the following average 87 sr 86 sr values for the rocks samples castile 0 706880 0 000005 salado 0 70688 0 000004 and rustler 0 706976 0 000008 thus a systematic increase in 87 sr 86 sr is observed from castile to salado and especially to rustler consistent with a previous prediction these data are submitted for the seawater curve for the ochoan group upper evaporites of late permian age

land atmosphere ocean interactions in the southeastern atlantic interannual variability land atmosphere ocean interactions in the southeastern south atlantic and their connections to interannual variability are examined using a regional climate model coupled with an intermediate level ocean model in austral summer zonal displacements of the south atlantic subtropical high sash can induce variations of mixed layer currents in the benguela upwelling region through surface wind stress curl anomalies near the namibian coast and an eastward shifted sash is related to the first pacific south american mode when the sash is meridionally displaced mixed layer vertically integrated ekman transport anomalies are mainly a response to the change of alongshore surface wind stress the latitudinal shift of the sash tends to dampen the anomalous alongshore wind by modulating the land sea thermal contrast while opposed by oceanic diffusion although the position of the sash is closely linked to the phase of el nino southern oscillation enso and the southern annular mode sam in austral summer an overall relationship between benguela upwelling strength and enso or sam is absent during austral winter variations of the mixed layer ekman transport in the benguela upwelling region are connected to the strength of the sash through its impact on both coastal wind stress curl and alongshore surface wind stress compared with austral summer low level cloud cover change plays a more important role although wintertime sea surface temperature fluctuations in the equatorial atlantic are strong and may act to influence variability over the northern benguela area the surface heat budget analysis suggests that local air sea interactions dominate

strontium isotope record of paleohydrology and continental weathering eocene green river formation wyoming sr isotope ratios in carbonate rich lacustrine strata provide highly resolved and geo graphically specific records of past changes in weathering and regional drainage patterns the eocene green river formation is perhaps the best documented pre quaternary la custrine unit in the world therefore these strata are ideally suited for studying the be havior of sr the 87 sr 86 sr ratios measured for primary carbonate in lake expansion contraction cycles of the laney member are directly linked to changing lake facies four distinct cycles are preserved in a 6 4 m interval of the arco washakie basin no 1 core each represented by a vertical succession of transgressive stromatolite facies containing dolomicritic intraclasts laminated micrite facies deposited during lake highstands and lake marginal dolomicrite facies which represent subsequent lowstands initial 87 sr 86 sr ratios range from 0 711 99 to 0 713 31 the least radiogenic isotope compositions are as sociated with laminated micrite that records increased regional runoff from phanerozoic marine carbonate and tertiary volcanic rocks during lacustrine highstands the most radiogenic isotope compositions are associated with dolomicrite recording a higher pro portion of runoff from basin bounding precambrian uplifts and the exposed lake plain during lacustrine lowstand the observed 87 sr 86 sr variations may also be due in part to changes in differential weathering of the surrounding landscape where drier climates are associated with decreased differential weathering and therefore higher 87 sr 86 sr in runoff

origin of satin spar veins in evaporite basins abstract satin spar fibrous gypsum veins occur in rocks overlying evaporites in the amadeus basin australia appalachian basin usa cheshire basin england elk point basin canada palo duro basin usa paradox basin usa and zechstein basin england these antitaxial veins which are characterized by central partings and near vertical fibers fill horizontal and inclined fractures most satin spar veins occur in highly fractured or brecciated clastic strata that overlie or are associated with bedded halite anhydrite and gypsum saline springs are commonly present indicating that halite dissolution is active the similarities in morphology and occurrences of these veins suggest a common genesis satin spar veins result from several simultaneously active processes recharge of low salinity surface water results in dissolution of shallow 200 m to 750 m deep halite development of cavernous porosity and formation of extensional fractures in the rock column overlying salt dissolution zones greater solubility of anhydrite than gypsum at low temperatures and at salinities below halite saturation causes hydration of anhydrite to gypsum which takes place without significant volume change once groundwater is saturated with respect to gypsum any further anhydrite hydration and solution must result in supersaturation and the excess caso4 carried by ground water flowin from dissolution zones precipitates as gypsum in open high permeability fractures

deciphering the sedimentological imprint of paleoseismic events an example from the aptian codo formation northern brazil abstract a stratigraphic horizon bearing several styles of soft sediment structures occurs sandwiched within entirely undisturbed deposits in the lacustrine codo formation aptian located in the eastern part of the grajau basin northern brazil these deposits show a variety of sedimentary features distinguished according to their deformation style as follows from bottom to top a zone 1 consisting of widespread molar tooth structures i e fine grained spar filled cracks that are interconnected with small scale faults fissures and stylolites inclined at a high angle to bedding b zone 2 represented by complex convolute folds with lateral gradation of smooth synclines and anticlines into isoclinic folds and internal layers that retain the normal bedding features recumbent folds nappe folds with associated thrust faults pseudonodules and mound and sag structures c zone 3 consisting of normal faults and fissures that are vertical to near vertical show ragged morphology with small delicate peaks taper both downward and upward after a few centimeters and are associated with large up to 2 5 m long collapsed boulders and d zone 4 characterized by shales with irregular convolute folds these deformation zones are interpreted to reflect sediment rheology and alternating periods of sediment accumulation and deformation under the influence of synsedimentary seismic events as suggested mostly by 1 occurrence between undeformed deposits 2 lateral correlation for several kilometers of distance 3 similarity with other features formed in areas affected by seismic activity 4 presence of structures attesting to sediment deformation in an unconsolidated to semi consolidated state and 5 complex association of brittle and ductile deformation structures hence zone 1 records small scale cracking and faulting of early cemented cohesive deposits zone 2 is dominated by ductile deformation structures formed on water saturated unconsolidated sediments probably as a reflex of compressional stress zone 3 records a change in tectonic style to dominantly distension as evidenced by the horizon with normal faults finally zone 4 shows structures attributed to ductile deformation of water saturated muds which was probably formed during the same episode of deformation responsible for the faults and fissures in zone 3 this succession of deformation events appears to be consistent with transtensional and compressional shear stresses during the sedimentary evolution of the grajau basin

sedimentary facies depositional environments and palaeogeographic evolution of the neogene denizli basin sw anatolia turkey abstract the denizli basin southwestern anatolia turkey contains a record of environmental changes dating since the early miocene detailed facies analysis of the neogene formations in this half graben enables us to document successive depositional regimes and palaeogeographic settings sedimentation commenced in the early miocene with the deposition of alluvial fan and fluvial facies kizilburun formation at this stage alluvial fans sourced from elevated areas to the south prograded towards the basin centre the middle miocene time saw the establishment of marginal lacustrine and wetland environments followed by the development of a shallow lake sazak formation the uppermost part of this unit consists of evaporitic saline lake and saline mudflat facies that grade upward into brackish lacustrine deposits of late miocene pliocene age kolankaya formation the lake became shallower at the end of the pliocene time as is indicated by expansion shoreface foreshore facies in the early quaternary the denizli basin was transformed into a graben by the activation of ese trending normal faults alluvial fans were active at the basin margins whereas a meandering river system occupied the basin central part oxygen isotope data from carbonates in the successive formations show an alternation of wetter climatic periods when fresh water settings predominated and very arid periods when the basin hosted brackish to hypersaline lakes the neogene sedimentation was controlled by an active ese trending major normal fault along the basin s southern margin and by climatically induced lake level changes the deposition was more or less continuous from the early miocene to late pliocene time with local unconformities developed only in the uppermost part of the basin fill succession the unconformable base of the overlying quaternary deposits reflects the basin s transformation from a half graben into a graben system

paleohydrology of an upper aptian lacustrine system from northeastern brazil integration of facies and isotopic geochemistry abstract the codo formation records the initial evolutionary stages of an intracontinental rift system formed along the brazilian equatorial margin in the late aptian deposits of this unit exposed on the eastern margin of the grajau basin include gypsum bituminous black shales and limestones these lithologies were formed in a low energy well stratified anoxic and hypersaline lake system developed in a dominantly arid semi arid climate this lacustrine succession is internally organized into three categories of shallowing upward cycles with the first and second order cycles being related to seismic activity associated with fault reactivations and the third order cycles recording climatic fluctuations studies emphasizing petrography and analysis of the geochemical tracers fe mg sr mn na and ca helped to identify the sedimentary facies that kept a primary signal which were thus appropriate for isotopic investigations aiming paleoenvironmental and paleohydrologic reconstructions the results of this study revealed a wide distribution of dominantly low carbon and oxygen isotope values in carbonates ranging from 5 69 to 13 02 and from 2 71 to 10 80 respectively this paper demonstrates that at least in the particular case of oxygen the isotope ratios vary according to seismically induced shallowing upward cycles with values in general lower at their bases where central lake deposits dominate and progressively higher upward where marginal lake deposits are more widespread in addition to confirming a depositional signature for the analysed samples this behavior allowed the development of a seismic induced isotope model the lighter isotope ratios appear to be related to flooding events promoted by subsidence which resulted in the development of a perennial lake system while heavier isotope values are related to ephemeral lake phases favored by uplift and or increased stability furthermore the results show that a closed lake system dominated as indicated by the overall good positive covariance i e 0 42 to 0 43 between the carbon and oxygen isotopes though open phases are also recorded by negative covariance values of 0 36 during closed phases the 18 o displayed the highest range of variation i e 3 63 to 4 89 due to increased residence time while this variation was low i e 0 09 to 1 87 during open lake phases when there was a balance in the water isotope composition maintained by continuous basin inflow

reconstruction of the miocene western amazonian aquatic system using molluscan isotopic signatures abstract strontium isotopic ratios and sr contents of molluscs from the miocene pebas formation in colombian amazonia indicate that the bulk of the pebas formation was deposited in a freshwater environment predominantly draining the andes with minor contribution from the shield regions the molluscan oxygen and carbon isotopic composition does not provide a palaeosalinity proxy but points to a lacustrine palaeoenvironment the faunal character confirms such an interpretation sr isotopic ratios further suggest that a marine incursion that reached the area was composed of a mixture of shield derived freshwater and seawater with a maximum salinity of about 5 psu faunistic components of this incursion level support a shield seawater mixing the incursion most likely reached western amazonia from the north probably along the western guyana shield

abu dhabi sabkha persian gulf revisited application of strontium isotopes to test an early dolomitization model a study of brines and diagenetically altered minerals from coastal sabkha of abu dhabi persian gulf was undertaken to test the flood recharge evaporative pumping model for early dolomitization using strontium isotopes as a tracer the sup 87 sr sup 86 sr ratio of the sabkha brines defines a pattern of both horizontal and vertical mixing of coastal seawater and continental ground water consistent with a previously proposed model the sup 87 sr sup 86 sr ratio of the diagenetic dolomites indicates early dolomitization by marine recharge waters the sup 87 sr sup 86 sr ratio of gypsum from the dolomitization area 1 4 to 4 4 km from high tide mark and seaward reflects precipitation from marine brines but more landward 6 to 9 km gypsum and anhydrite record a continental signal in the minerals suggests a paragenetic evaporative sequence dolomite yields gypsum yields anhydrite the dolomitizing fluid is evaporated seawater that recharges the sabkha aquifer during supratidal flooding and is afterward pumped upward through the saturated zone by evaporative processes

effects of subglacial geothermal activity observed by satellite radar interferometry we use one day synthetic aperture radar sar interferograms from data of the earth remote sensing satellites ers 1 and ers 2 to study ice flow and uplift of two surface depressions within the vatnajokull ice cap iceland the ice cauldrons are created by melting at sub glacial geothermal areas meltwater accumulates in a reservoir under the cauldrons over 2 to 3 years until it drains in a jokulhlaup under the ice dam surrounding the reservoir the ice surface in the depressions drops down by several tens of meters during these draining events but rises again as ice flows into the depressions until a jokulhlaup occurs again using sar interferograms we quantify an uplift rate of about 2 to 18 cm day within the jokulhlaup cycle varying with the surface slope of the depressions the uplift rate is high during the first months after a jokulhlaup when the cauldron is relatively deep with steep slopes but the uplift rate decreases as the cauldron is gradually filled a simple axisymmetric model simulating the ice flow into one of the depressions describes quantitatively the filling rate of the cauldron and qualitatively the shape of the ice flow field the best fit model has an ice flow law parameter a0 that is about one order of magnitude lower than typically estimated for temperate glaciers

development of microbial carbonates in the lower cretaceous codo formation north east brazil implications for interpretation of microbialite facies associations and palaeoenvironmental conditions the study of microbial carbonates has acquired new significance with the recognition that they retain valuable information related to biomineralization processes associated with microbial activity throughout geological time additionally microbialites have a demonstrated economic potential to serve as excellent hydrocarbon reservoirs the lower cretaceous codo formation located in the parnaiba basin of north east brazil comprises a unique stratigraphic sequence of up to 20 m thick well preserved carbonate microbialites deposited in a continental basin during the initial break up and separation of south america from africa in the early cretaceous this lacustrine carbonate sequence provides an excellent example to investigate the palaeoenvironmental conditions controlling microbialite facies development based on macroscopic and microscopic observations of outcrop and drill core samples four microbialite facies stromatolite lamina massive and spherulite were defined and distinguished by textures and microbial fossil content changes in facies type are related to alternating palaeo water depths as reflected by 87sr 86sr cycles resulting from fluctuations in the sources of meteoric water clumped isotope measurements of stromatolitic fabrics yield precipitation palaeo temperatures with an average value of 35 c the 18 o values of bulk carbonate 6 8 to 1 5 vienna pee dee belemnite imply precipitation from water with calculated 18 o values between 1 6 and 1 8 vienna standard mean ocean water reflecting precipitation from variably modified meteoric waters the 13 c values of bulk carbonate 15 5 to 7 2 vienna pee dee belemnite indicate a significant input of carbon derived from aerobic or anaerobic respiration of organic matter combined the data indicate that the evolution of the codo formation occurred in a closed lacustrine palaeoenvironment with alternating episodes of contracting and expanding lake levels which led to the development of specific microbialite facies associations the results provide new insights into palaeoenvironmental settings biogenicity and early diagenetic processes involved in the formation of ancient carbonate microbialites and by extension improve the knowledge of the reservoir geology of correlative units in deep waters offshore brazil

using strontium isotopes to determine the age and origin of gypsum and anhydrite beds the variation of 87sr 86sr in seawater with time can be used to determine the age of calcium sulfate beds precipitated from brine derived from seawater the determination of a marine origin can be established by the consistency of strontium isotope results from samples at different stratigraphic levels in a single gypsum anhydrite bed collected at separated sites the scatter of strontium isotope results in the gypsum anhydrite samples examined here is interpreted to result from the contribution of meteoric strontium to the salina strontium isotope results from three evaporite settings the jurassic todilto formation from new mexico the permian blaine formation from blaine county oklahoma and the permian salado formation from new mexico are used to determine the age and origin of the parent brine for these gypsum anhydrite beds the calcium sulfate beds from each of these formations precipitated from salinas that originated with a marine flooding but show at different times and localities volume do

marine to non marine sedimentation in the upper miocene evaporites of the eastern betics se spain sedimentological and geochemical evidence abstract several neogene basins in the eastern betics contain a record of thick upper miocene evaporites the inner basins those located distal to the mediterranean coast include evaporite units ranging from the late tortonian to the early messinian whereas the marginal basins those located in the vicinity of the mediterranean coast include evaporite units corresponding to the late messinian that are linked to the salinity crisis the sedimentological and geochemical comparison of the evaporites in the inner and marginal basins enable us to show their differences in the modes of deposition under local structural controls and differentiated palaeogeography in the inner basins of the murcia alicante region a number of evaporite units have been differentiated whose gypsum lithofacies have 1 variable strontium contents with mean values primary gypsum between 1121 and 2380 ppm 2 isotopic compositions of sulphur 34 s ranging from those characteristic of the tertiary marine water 20 3 to 25 5 to those characteristic of the triassic sulphates 8 0 to 16 0 the latter suggesting recycling of the sulphate anion in meteoric waters intermediate values 17 4 to 19 6 are attributed to mixed mother brines and 3 strontium ratios 87 sr 86 sr comprised between 0 70804 and 0 70888 these values range from those of the tertiary marine water to those exceeding the triassic sulphates suggesting additional continental contributions from country rocks and hydrothermal solutions the comparison between the sulphur and strontium isotopic compositions of the sulphates together with the study of the biota present in the marls associated with the gypsum allows us to distinguish between marine continental and mixed units in the marginal basins of the eastern betics where single evaporite units characterized by selenitic gypsum prevail 1 the strontium contents are more homogeneous with mean values primary gypsum between 493 and 625 ppm 2 the isotopic compositions of oxygen 18 o and sulphur 34 s are comprised between 12 2 and 14 8 and between 22 0 and 23 5 respectively and 3 the strontium ratios 87 sr 86 sr vary from 0 70890 to 0 70895 all these isotopic values reveal a marine origin and the lack of contribution of significant continental water during the late messinian evaporite deposition in the betic strait these characteristics are similar to those of the lower evaporite

spring peas from new york state nucleation and growth of fresh water hollow ooliths and pisoliths abstract delicate hollow spheroids 1 to 2 mm composed of radially fibrous calcite occur in and on the surface of calcareous travertine being deposited from water of the orenda spring saratoga springs new york state field observations suggest that spheroids form by the precipitation of calcite on the surface of water droplets that contain newly formed bubbles of co2 although many of the spheroids subsequently disintegrate some grow by the addition of laminae consisting of radial bundles of fibrous calcite commonly separated by thin seasonal laminae of fine grained calcite and detritus these spheroids are either incorporated into laminar travertine sheets or grow by successive increments into fresh water ooliths and pisoliths with both a concentric and a radial structur

cambrian skeletal halite crystals and experimental analogues a suite of unusual highly skeletal halite pseudomorphs is described from the lower middle cambrian rocks that crop out at ardmore in the georgina basin northern australia the pseudomorphs are preserved as both moulds and casts within a dark and light colour banded chert they are orientated parallel to bedding and represent halite crystal growth within a brine pool laterally equivalent rocks are characterized by sedimentary textures and structures indicative of periodic emergence and desiccation laboratory grown halite crystals are also described and compared with the pseudomorphs from ardmore experimentally produced halite crystals formed from either 1 brine solutions obtained as residues after organic matter extraction from phosphate rocks or 2 solutions of naci and distilled water both pyramidal rafted hoppers and floor nucleated cuboids formed in solutions containing only naci and distilled water whereas in the residue solutions that contained humic acids rafted pyramidal forms were absent and crystal nucleation was restricted to the floor of the evaporative dish as brine depth decreased the halite precipitation rate increased and resulted in a suite of excrescent highly skeletal crystals that formed as a result of brine evaporation to dryness the variable crystal morphology depended upon both the brine depth and slope of the evaporative dish floor horizontally orientated chevron halite crystals formed where the evaporative dish was inclined and precipitation preferentially occurred on cube faces pagoda reticulate ridge and dendritic forms represent an increasingly skeletal crystal suite characterized by the preferential precipitation of naci on cube edges and corners rather than faces using the experimentally grown crystals as analogues the pseudomorphs at ardmore are interpreted as forming in very shallow brine pools that evaporated to dryness

mid cretaceous strontium isotope stratigraphy of deep sea sections large variations exist between published mid cretaceous late barremian to early turonian stages seawater sr isotope stratigraphies this has resulted in disparate interpretations of crustal production rates we report on a detailed investigation of seawater sr isotope stratigraphy based on foraminifers and where available on inoceramid bivalves from 12 mid cretaceous deep sea drilling project and ocean drilling program sections the effects of diagenesis are assessed using scanning electron microscope observations and traceelemental analyses but are best distinguished by comparing the 87 sr 86 sr values of similarage samples from different sites strontiumisotope analyses compiled from 9 of 12 sites that have detailed age control define one band of common values this band is used as a composite curve which presumably represents seawater 87 sr 86 sr values the composite curve shows a trough of markedly lower 87 sr 86 sr values in the aptian and early albian stages higher but constant values for the middle albian cenomanian stages followed by a decrease in 87 sr 86 sr values in the early turonian

evaporites marine or non marine division of evaporites into those types that retain information about primary mineralogy textures and structures primary evaporites and those types so extensively altered that few or no primary features remain secondary evaporites only primary evaporites can give unequivocal data bout their marine or non marine origin to help evaluate such primary deposits they have been further divided using the following attributes 1 whether the depositional setting was marine or non marine 2 whether the source water was a seawater b meteoric c hydrothermal d diagenetic e volcanogenic or f mixed specific criteria for making distinctions are 1 kinds of fossils 2 sedimentology of the associated non saline facies 3 kinds of primary saline minerals 4 association of such saline minerals both in qualitative and quantitative terms 5 trace element isotope and fluid inclusion geochemistry of such saline minerals modified journal abstract

marine to nonmarine facies transition in permian evaporites of the palo duro basin texas geochemical response the late paleozoic palo duro basin evolved from a marine to nonmarine environment as it was infilled the evaporitic part of the sequence leonardian through ochoan is composed of regressive carbonate anhydrite halite cycles that displaced open marine environments toward the south during basin filling systematic vertical changes in evaporite geochemistry through the evaporite section include increasing 87sr 86sr ratios and decreasing altered from marine 34s in anhydrite decreasing recycled bromide content of the halite and increasing meteoric influence on the stable isotopic composition of fluid inclusions in halite geochemical changes correspond to changes in evaporite sedimentology and document the evolution from marine dominated to partly nonmarine evaporites geochemical tracers when used with sedimentological and facies analysis provide reliable indicators of the sources of water and solutes in an anhydrite halite facies tract perennial intermittently stratified and ephemeral brine pool conditions affect the amount of synsedimentary recycling variable rates of reflux and marine recharge control residence times of brines in the depositional environment these are two key processes in relating evaporite geochemistry to depositional environment

an upper aptian saline pan lake system from the brazilian equatorial margin integration of facies and isotopes facies and isotope sr and s data were combined in order to discuss the genesis and palaeohydrology of an upper aptian evaporite succession formed during the initial development of an intra continental rift from northern brazil comparison of facies distribution between two investigated areas shows i stable well stratified and hypersaline lakes with periods of anoxia and closure in the eastern margin of the basin where there was evaporite precipitation only in central lake environments and ii more ephemeral conditions in the eastern margin of the basin where a saline pan complex developed and evaporite precipitation took place mainly in marginal salinas and surrounding mudflats in both areas expansion contraction cycles developed as sedimentation took place accompanied by a decrease and then an increase in 87 sr 86 sr and d 34 s isotope values this combined with the wide distribution of sr and s isotope data within individual depositional cycles as well as petrographic and scanning electronic microscopic sem images led to the conclusion that diagenesis was not enough to obscure the primary geochemical signature a non marine brine source is suggested by 87 sr 86 sr ratios between 0ae707824 and 0ae709280 which are higher than those from upper aptian sea water i e between 0ae70720 and 0ae70735 the d 34 s value varies from 16ae12 to 17ae89 in the eastern margin of the basin which is in disagreement with upper aptian marine values 13 to 16 both geochemical tracers were influenced by facies characteristics and thus a model is provided where 87 sr 86 sr values respond to changes in expansion and contraction

stable δ13c δ18o and strontium isotopes through the paleocene at gebel aweina eastern tethyan region abstract stable 13 c 18 o and strontium 87 sr 86 sr isotopic records have been established through the paleocene section at gebel aweina in the eastern desert egypt the section has been formed in a shelf upper bathyal environment and spans the interval from planktonic foraminiferal zones p1d to p6a or p6b integrated evaluation of isotopic results and scanning electron microscope observations suggest that strontium and whole rock 13 c records reflect primarily original isotopic trends whereas 18 o and foraminiferal 13 c values have been severely affected by diagenesis the whole rock 13 c record exhibits a continuous increase of 4 from the early paleocene to middle late paleocene the increase is followed by a stepwise 13 c decrease of the same magnitude through the late late paleocene and onwards the gross trends of this 13 c record have earlier been registered in many coeval deep sea sections but there are also some significant disparities at aweina for example the paleocene carbon isotopic changes have a higher amplitude in the deep sea the mid to late paleocene 13 c increase has been interpreted to reflect high biological productivity and or changes in the global carbon mass balance the 13 c decrease in the upper part of the aweina section can be identified as the paleocene eocene transitional long term 10 3 kyr negative 13 c shift which may reflect a major reorganisation in global oceanic circulation patterns the well known latest paleocene deep sea benthic foraminiferal extinction event has been found in the upper part of the aweina section and coincides with a distinct and rapid 13 c decrease of 1 5 the benthic extinction event and the associated 13 c anomaly thus represent important stratigraphic markers also in more shallow environments the gebel aweina 13 c record shows considerably lower values compared to the global 13 c record during early and early late paleocene and in the latest paleocene in the early late paleocene foraminiferal zones p3a to the base of p4 the aweina 13 c values increase rapidly by 1 5 and converge with the global record thereafter the two records covary up to the benthic extinction event after which they diverge the convergence between the records may reflect sea level rise and more open water mass exchange between the eastern tethys and the world ocean the similarity of pilot 13 c records from greece and tunisia with the aweina record support this interpretation diagenetic processes however cannot be ruled out and further studies are required to determine the significance of the 13 c depletions in the eastern tethyan sediments the 87 sr 86 sr ratios through the paleocene at gebel aweina are remarkably invariable close to a value of 0 7077 this is the same trend that has been reported in some earlier detailed studies conducted on well preserved calcitic material from the paleocene indicating original sr isotopic signatures at gebel aweina the homogeneity of sr isotopic ratios throughout the paleocene contrasts with the prominent changes observed in the carbon isotope record indicating a decoupling of the mechanisms regulating the mass fluxes of these elements the invariable sr isotopic ratios suggest stable conditions as regards to relative changes in mass fluxes of riverine and or hydrothermal sr during the paleocene

deposition and early alteration of evaporites summary the depositional settings for primary and early diagenetic evaporite deposits generally fall into three categories marginal mixed shallow subaqueous and subaerial shallow and deep subaqueous these three environmental groupings hold for both marine and nonmarine settings although the details of continental evaporites may be far more complex than in most marine fed water bodies the primary evaporite morphologies from many continental playa hypersaline marine and marine marginal depositional settings are reasonably well understood because of the numerous detailed studies of recent holocene and cenozoic deposits that serve as models for sedimentary interpretation the sedimentological features that develop in deeper water settings are inferred based on examination of unaltered cenozoic deposits each environmental setting develops characteristic depositional features and patterns and one facies grades into the next because there may be significant physiochemical changes in water composition during deposition as well as sudden change s in both water depth and basinal circulation description and interpretation of evaporative rocks should not be based on mineralogy alone but on the distinct sedimentary characteristics of each part of a deposit in cases where sediments still reflect their primary mineralogy and morphology most of the environments can now be recognized however geochemical studies are commonly required to determine the source s of the original water the determinative geochemical techniques that presently serve as a support to sedimentologic study include studies of fluid inclusions bromine content of chloride salts and the stable isotopes of strontium sulphur carbon and oxygen only after these and perhaps other chemical analyses are considered can the full depositional history of a region be reasonably unravelled