genesis of the late eocene bedded halite in the qaidam basin and its implication for paleoclimate in east asia abstract it has long been suggested that the eocene climate in east asia was characterized by three latitudinally distributed zones one middle arid zone and two humid zones to its north and south the middle arid zone was firstly proposed based on the widespread red beds and evaporites in a nww trending zone of china however this long standing model has recently been challenged by increasing doubts about the effectiveness of these arid climate indicators the qaidam basin as one of the eocene evaporites bearing basins in china can be studied to test whether the bedded evaporites can validly indicate arid climate over 300 m halite beds have been found in the late eocene upper xiaganchaigou uxg formation in a local saline center shizigou area of the qaidam basin its coexistence with source rocks and limited distribution together with the absence of red beds make it difficult to explain the halite genesis with the conventional climatic controlled playa model based on stratigraphic correlation lithological and mineralogical observation and oxygen carbon and chlorine isotopic analysis we identify several characteristics about the shizigou saline center 1 undulated lake floor 2 shallow water 3 limited hydrothermal impact 4 evaporation induced precipitation 5 high eolian influence and 6 fluctuated climate background according to these investigations we suggest a new model for the genesis of the bedded halite in the qaidam basin the tectonic climatic model the key point for this model is that the undulated topography caused by tectonic activity and the fluctuated climate together leaded to the hydrological isolation of the shizigou area the shizigou area was isolated from the larger brackish qaidam paleolake for independent evaporation during arid climate stage while connected with it during humid climate stage causing alternatively water influx and evaporation and inducing the occurrence of interbedded halite and source rocks thus the widespread bedded halite in the eocene strata over china may indicate fluctuated rather than arid climate in east asia

a unique lacustrine mixed dolomitic clastic sequence for tight oil reservoir within the middle permian lucaogou formation of the junggar basin nw china reservoir characteristics and origin abstract the middle permian lucaogou formation in the jimusaer sag of the southeastern junggar basin nw china was the site of a recent discovery of a giant tight oil reservoir this reservoir is unusual as it is hosted by lacustrine mixed dolomitic clastic rocks significantly differing from other tight reservoirs that are generally hosted by marine lacustrine siliciclastic calcitic sequences here we improve our understanding of this relatively new type of tight oil reservoir by presenting the results of a preliminarily investigation into the basic characteristics and origin of this reservoir using field petrological geophysical including seismic and logging and geochemical data field and well core observations indicate that the lucaogou formation is a sequence of mixed carbonate mainly dolomites and terrigenous clastic mainly feldspars sediments that were deposited in a highly saline environment the formation is divided into upper and lower cycles based on lithological variations between coarse and fine grained rocks in particular dolomites and siltstones are interbedded with organic rich mudstones in the lower part of each cycle whereas the upper part of each cycle contains few dolomites and siltstones tight oil accumulations are generally present in the lower part of each cycle and dolomites and dolomite bearing rocks are the main reservoir rocks in these cycles including sandy dolomite dolarenite dolomicrite and a few dolomitic siltstones optical microscope back scattered electron and scanning electron microscope imaging indicate that the main oil reservoir spaces are secondary pores that were generated by the dissolution of clastics and dolomite by highly acidic and corrosive hydrocarbon related fluids

a petrogenetic grid for pelites in the ballachulish and other scottish thermal aureoles the ballachulish granite is a composite devonian intrusive complex surrounded by a distinctive thermal aureole developed in regionally deformed and metamorphosed dalradian sediments on the w coast of scotland the most abundant rocks in the aureole are pelites which show a progression of assemblages from quartz muscovite chlorite up to a variety of high grade assemblages involving combinations of cordierite corundum spinel and rarely hypersthene and garnet metamorphic zones have been mapped around the granite which are defined by the following reactions going upgrade mu chl q cd bi v mu bi q cd kf v or mu cd q bi as v mu q as kf v q bi as cd kf v or mu cd bi as kf v mu cor kf v bi as cor kf cd v the restricted occurrences of assemblages involving spinel hypersthene and garnet do not allow higher grade zones to be mapped variations in the reaction sequence as a consequence of bulk compositional factors in particular the development of quartz bearing versus quartz absent assemblages are described details of the mineral assemblages from ballachulish are combined with high grade assemblage data from the belhelvie lochnagar and comrie aureoles to construct a comprehensive schematic petrogenetic grid the grid involves the minerals quartz chlorite muscovite biotite cordierite alumino silicate k feldspar corundum spinel hypersthene and garnet whose assemblage relationships are modelled in the system k 2 o feo mgo al 2 o 3 sio 2 h 2 o kfmash

chemistry and environments of dolomitization a reappraisal abstract dolomitization of calcium carbonate can best be expressed by mass transfer reactions that allow for volume gain preservation or loss during the replacement process experimental data as well as textures and porosities of natural dolomites indicate that these reactions must include co 3 2 and or hco 3 supplied by the solution to the reaction site since dolomite formation is thermodynamically favoured in solutions of a low ca 2 mg 2 ratios b low ca 2 co 3 2 or ca 2 hco 3 ratios and c high temperatures the thermodynamic stability for the system calcite dolomite water is best represented in a diagram with these three parameters as axes kinetic considerations favour dolomitization under the same conditions and additionally at low as well as at high salinities if thermodynamic and kinetic considerations are combined the following conditions and environments are considered chemically conducive to dolomitization 1 environments of any salinity above thermodynamic and kinetic saturation with respect to dolomite i e freshwater seawater mixing zones normal saline to hypersaline subtidal environments hypersaline supratidal environments schizohaline environments 2 alkaline environments i e those under the influence of bacterial reduction and or fermentation processes or with high input of alkaline continental groundwaters and 3 many environments with temperatures greater than about 50 c subsurface and hydrothermal environments whether or not massive replacive dolostones are formed in these environments depends on a sufficient supply of magnesium and thus on hydrologic parameters most massive dolostones particularly those consisting of shallowing upward cycles and capped by regional unconformities have been interpreted to be formed according to either the freshwater seawater mixing model or the sabkha with reflux model however close examination of natural mixing zones and exposed evaporitic environments reveals that the amounts of dolomite formed are small and texturally different from the massive replacive dolostones commonly inferred to have been formed in these environments many shallowing upward sequences are devoid of dolomite it is therefore suggested that massive replacive dolomitization during exposure is rare if not impossible rather only small quantities of dolomite cement or replacement are formed which may act as nuclei for later subsurface dolomitization alternatively large scale dolomitization may take place in shallow subtidal environments of moderate to strong hypersalinity the integration of stratigraphic petrographic geochemical and hydrological parameters suggests that the only environments capable of forming massive replacive dolostones on a large scale are shallow hypersaline subtidal environments and certain subsurface environments

sources of non glacial loess size quartz silt and the origins of desert loess abstract descriptions of peridesertic loess deposits and possible non glacial origins for silt size quartz are reviewed including direct release from weathered bedrock results from salt and frost weathering experiments are presented and methods by which sufficient energy can be imparted to sand size grains to release silt size fragments are identified these fragments may then be entrained by aeolian or fluvial action results from fluvial comminution experiments indicate that high energy mixed sediment fluvial systems may be very effective in generating quartz silt purely aeolian attrition is also seen as a major source of silt size and finer material results from aeolian abrasion experiments performed using crushed quartz sand are complemented by trials using sands from deeply weathered granite and pannonian sands from hungary field and laboratory observations are therefore seen to argue for the existence of deposits that can be classified as desert loess

heterogeneous brittle ductile deformation at shallow crustal levels under high thermal conditions the case of a synkinematic contact aureole in the inner northern apennines southeastern elba island italy abstract we present an example of interaction between magmatism and tectonics at shallow crustal levels in the late miocene the metamorphic units of the eastern elba island northern apennines were intruded at very shallow crustal levels by a large pluton 60 km 2 with the development of an hectometre sized contact aureole defined by growth of low pressure high temperature mineral assemblages p max max 650 c structural data show that the contact aureole is associated with a km sized antiform of the foliation and by several metre to decametre thick high strain domains consisting of strongly foliated rocks containing synkinematic ht lp mineral assemblages and ductile shear zones of variable thickness these shear zones are characterized by a mylonitic foliation variably overprinted by cataclasis quartz microfabrics indicate that the dynamic crystallization processes progressively changed from grain boundary migration associated with the thermal peak of contact metamorphism to subgrain rotation and bulging recrystallization the latter mostly associated with the cataclastic overprint these transitions of recrystallization mechanisms in quartz are related to a progressive decrease of temperature during deformation deformation accompanied the development and cooling of the contact aureole which recorded the switch from high temperature ductile to low temperature brittle conditions the geometry of the studied deformation structures is consistent with the constraints of the regional tectonic evolution and its local interaction with the localized and transient thermal anomaly related to the coeval emplacement of igneous rocks

evidence for li rich brines and early magmatic fluid rock interactionin the larderello geothermal system abstract the geochemical features of fluids accompanying the first stages of geothermal activity linked to magmatic intrusions have been documented for the larderello geothermal system italy deep drilling has provided samples which preserve evidence of this early geothermal activity four wells san pompeo 2 monteverdi 7 sasso 22 and serrazzano vc 11 penetrated the deeper parts of the larderello system located in a metamorphic basement underlying the tertiary nappe complex which constitutes the main aquifer at larderello the drill holes terminated close to the inferred roof of a granitic complex thought to be responsible for geothermal activity fluid inclusion data were obtained from recrystallized quartz lenses and quartz veins in samples displaying high temperature assemblages plagioclase actinolite biotite tourmaline clinopyroxene andradite wollastonite and also from magmatic quartz in a leucogranite dike the inclusions are mainly secondary in origin oriented in fluid inclusion planes fip related to hydrothermal circulation in the larderello system several generations of high temperature fluids were trapped and include 1 1 h2o co2 dominated vapors displaying variable but significant contents of ch4 and n2 2 2 aqueous vapors containing licl with variable salinity 3 3 aqueous licl brine often oversaturated with respect to halite at room temperature 4 4 complex brine always oversaturated at room temperature with respect to two halite and sylvite or more n 4 salts the presence of licl was confirmed by identification of the salt hydrate licl 5h2o at very low temperature using raman spectroscopy bulk salinities could be roughly estimated at around 30 wt eq licl for the licl brine geometric and chronologic relationships between fip reveal close relationships and mutual contamination between the h2o co2 vapors and licl brine indicating synchronism in their trapping these fluids were generated and trapped at pressures of 100 130 mpa nearly 23 mpa above the estimated present day lithostatic pressure this implies a denudation rate between 0 2 and 0 5 mrn a 1 since the onset of hydrothermal activity compatible with the setting of larderello in a young tortonian collision belt fluid inclusion trapping temperatures 425 650 c show a monotonous increase towards the inferred granite and are around 100 200 c higher than the highest present day temperatures the results are interpreted as recording the interaction between magmatic and contact metamorphic fluids in the early larderello system the h2o co2 vapors resulted from the reheating of the basement metamorphic series often c rich under relatively high temperatures during contact metamorphism lirich fluids expelled from an underlying li rich leucogranite migrated through the metamorphic series and the already cooled granite dikes and experienced local boiling the fluid inclusion data demonstrate the involvement of magmatic fluids during the initial development of this high energy geothermal field

geological structure of a long living geothermal system larderello italy we have examined the data of 600 geothermal wells and re interpreted approximately 500 km seismic profiles through the field of larderello italy we conclude that the two main seismic reflectors present below the geothermal area host two different fluids 1 superheated steam in the upper h horizon reached by drillholes and 2 supercritical fluid in the deeper k horizon reached by few unproductive or damaged wells the superheated steam has the physical and chemical connotation of the geothermal fluid exploited so far at larderello whereas the supercritical fluid represents a potential unconventional deep seated resource still to be assessed the high temperatures existing in correspondence of the k horizon suggest that the silica rich rocks are close to a plastic state and the fluids should remain confined in a medium sealed to the confining rocks unless occasional fluid overpressure and abrupt high strain rates occur

alpine tectonothermal evolution of the tuscan metamorphic complex in the larderello geothermal field northern apennines italy on the internal tyrrhenian side of the northern apennines high heat flow and geothermal gradient in the larderello geothermal field are evidence of a large scale thermal anomaly related to the emplacement of a large batholith of pliocene age extending from the upper to middle crust these intrusions relate to the miocene to recent northern apennines magmatism which developed as a result of crustal extension and upwelling of the asthenosphere at the base of the thinned crust in the subsurface of the larderello geothermal field medium and high grade metamorphic rocks tuscan metamorphic complex cored in several geothermal wells have previously been considered to be variscan basement new structural and petrographic data on these metamorphic rocks indicate an alpine tectonometamorphic history and provide evidence that medium to high grade mineral assemblages are related to pliocene thermal metamorphism centred on intrusions at shallow depth these data allow a new interpretation of the tuscan metamorphic complex as a tectonic wedge of the late palaeozoic triassic units and in particular highlight the considerable extent of pliocene thermal metamorphism and hydrothermal circulation as a result of convective cooling of intrusions

vein development during folding in the upper brittle crust the case of tourmaline rich veins of eastern elba island northern tyrrhenian sea italy abstract detailed structural analysis of tourmaline rich veins hosted in the contact aureole of the 6 ma porto azzurro granite in southeastern elba island northern tyrrhenian sea is presented using geometric features of the veins the physical conditions at the time of vein formation are estimated namely the stress ratio 2 3 1 3 driving stress ratio r p f 3 1 3 and fluid overpressure p o p f 3 two vein sets a veins and b veins have been recognized based on orientation and thickness distributions and infilling material analysis of vein pole distributions indicates 0 57 and r 0 24 for the a veins and 0 58 and r 0 47 for the b veins and fluid pressures less than the intermediate stress magnitude analysis of geometric features of the veins gives estimated fluid overpressures of between 16 mpa a veins and 32 mpa b veins we propose a model for the tectonic environment of vein development in which formation of secondary permeability in the deforming thermal aureole of the porto azzurro pluton was controlled by ongoing development of fracture systems in the hinge zone of a regional nnw sse trending fold that favored transport and localization of hydrothermal fluids

how to find high quality petroleum source rocks in saline lacustrine basins a case study from the cenozoic qaidam basin nw china abstract despite having made significant contributions to global hydrocarbon occurrences source rocks in saline lacustrine basins show great mineralogical and organic geochemical heterogeneity and the controlling mechanism is weakly studied here we use the cenozoic qaidam basin as an example to compare the organic and inorganic parameters of fine grained sediments in different lacustrine facies and to figure out the characterization and distribution of effective petroleum source rocks in saline lacustrine systems organic inorganic database of six selected boreholes show that in the bench margin high gradient lacustrine system fine grained sediments in sublittoral brackish mesosaline zones containing low chlorides

pliocene crustal shortening on the tyrrhenian side of the northern apennines evidence from the gavorrano antiform southern tuscany italy the northern tyrrhenian sea and the inner northern apennines are classically regarded as a late miocene pleistocene back arc system developed as a consequence of slab rollback along active subduction zones we present new geological and structural data on the gavorrano antiform a key sector of the inner northern apennines lying close to the northern tyrrhenian sea it provides clear evidence of pliocene shortening deformation and magma emplacement the orientation of 1 n50 e n80 e derived by fault slip data inversion is consistent with a general ene wsw shortening direction furthermore this ene wsw trending orientation of 1 is compatible with the compressive deformation recorded in coeval sedimentary basins on this basis we suggest that the inner northern apennines were affected by crustal shortening during the pliocene this scenario matches well geophysical data suggesting that since the late messinian 6 5 ma subduction rollback and back arc extension strongly decreased in the northern tyrrhenian sea whereas they continued as active processes in the southern tyrrhenian sea

origin of oil in the sureste basin mexico geochemical and biological marker analyses of oils and rock samples from the sureste basin of mexico were effective in identifying and geographically limiting four major oil families related by age and source rock depositional environment oxfordian tithonian early cretaceous and tertiary the source rocks giving rise to the jurassic and cretaceous oils are associated with marine carbonate environments in contrast the source rocks giving rise to the tertiary oils are associated with a marine deltaic siliciclastic depositional setting biomarker and isotope differences observed in the oils derived from marine carbonate environments can be interpreted in terms of salinity clay content and oxygen depletion variations these differences provide diagnostic criteria for recognizing and differentiating five distinct organic rich depositional regimes as the sources for these oil types an anoxic hypersaline marine carbonate environment associated with a narrow and shallow semirestricted sea oxfordian age family 1 oil an anoxic marine carbonate environment associated with a silled basin geometry tithonian age family 2 oils subtype 2a an anoxic marine carbonate environment associated with a shallow gentle broad marine carbonate ramp in a distal position tithonian age family 2 oils subtype 2b a clay rich suboxic anoxic marine carbonate environment associated with a carbonate platform in a proximal position tithonian age family 2 oils subtype 2c and an anoxic marine evaporitic environment early cretaceous age family 3 oils the tertiary oils family 4 are derived from bacterially reworked terrigenous and marine organic source materials deposited in a marine deltaic environment the tithonian related oils in the mexican southern side of the gulf of mexico accumulated both offshore and onshore and throughout the stratigraphic column from kimmeridgian to pleistocene reservoirs suggesting vertical pathways as the principal secondary migration mechanism the lateral variations of these oils can be interpreted to reflect the tithonian paleogeography in the area and could be useful in predicting differences in the oil compositions

crustal structures in the geothermal areas of southern tuscany italy insights from the crop 18 deep seismic reflection lines abstract two deep seismic reflection lines named crop 18a and 18b and roughly nnw sse oriented were acquired to investigate the crust between the larderello and the mt amiata geothermal areas both located in southern tuscany since the early middle miocene southern tuscany has been affected by extensional tectonics and since the pliocene by widespread magmatism presently extension is demonstrated by ne dipping normal faults and brittle shear zones which affect the crust down to the brittle ductile transition in the larderello area these shear zones are seismically evidenced by ne dipping weak reflections and by the loss of the k horizon reflectivity a regional mid crustal high amplitude reflector located at the top of the brittle ductile transition the crop 18a and 18b lines were reprocessed down to 10 s twt down to the crust mantle boundary their reflectivity results are closely related to the direction of the survey a clear decrease in reflectivity occurs when the survey plane intersects the crustal shear zones along strike nevertheless both lines display segments with low reflectivity and homogeneous acoustic impedance which indicate intrusive magmatic bodies at different crustal levels a wide partially crystallised granitoid may be sited at about 7 8 km depth underneath the larderello geothermal field in the lower part of the crust the crop 18a and 18b transects show group of bright reflections mainly related to the occurrence of pressurised fluids and or lithological differences the base of the crust is located at about 20 km depth

magma emplacement in a thrust ramp anticline the gavorrano granite northern apennines italy 1 magma emplacement in the upper crust is often associated with crustal extension whereby space for intrusions is made by dilation along transtensive and strike slip faults the lenticular shape of several intrusions indicates that a further mechanism for magma intrusion is laccolith emplacement with roof uplift of the overburden additionally melts exploit rheological discontinuities e g sedimentary layering during their ascent we present an emplacement model for intrusion of the shallow level gavorrano granite northern apennine italy which is located at the core of an open anticline the shape of the intrusion and structural features of the host rocks are indicative of a synkinematic emplacement in a growing thrust anticline space was provided by the opening of dilatation zones at the core of anticline as a consequence of different amounts of translation between hanging wall and footwall units which were separated by evaporitic rocks these evaporitic units acted as major decollement layers analog models provide results in good agreement with the structural setting of the anticline and emphasize the possibility that melts filled the dilatation zone with the decollement layers further facilitating intrusion

estimation of fracture zone geometry from steady state hydraulic head data using iterative sequential cokriging the hydrogeology of fractured crystalline rock is often controlled by a few highly conductive features such as faults and or fractures zones accurate modeling of fluid flow and transport in these systems requires that the geometry of these conductive features be characterized explicitly a new method for estimating the geometry of these features is presented the method is an extension of the recently developed geostatistical technique of sequential cokriging in this extension the geometry of the fracture zone is iteratively updated until an update increases the discrepancy between the estimated and observed hydraulic heads results from two hypothetical examples demonstrate that the method can accurately estimate the geometry of highly conductive fracture zones

use of hydrogen and carbon stable isotopes characterizing oils from the potiguar basin onshore northeastern brazil hydrogen and carbon isotopic abundances were measured in representative samples of marine evaporitic lacustrine and mixed oils from the onshore potiguar basin the isotopic data together with chemical compositions and geological information were used to investigate relationships among ddoil and d13coil and source thermal maturity biodegradation mixing and the distance of secondary migration of these oils the marine evaporitic oils are depleted in deuterium 135 to 114 and the lacustrine oils are enriched 101 to 88 values of dd for mixed oils are intermediate 113 to 104 between those of marine evaporitic and lacustrine oils showing that ddoil is a reliable tool to identify oils that differ genetically values of ddoil were not directly related to thermal maturation biodegradation or distance of the secondary migration hydrogen isotopic compositions of the oils can be related mainly to the ddwater in the paleoenvironments in which the primary producers lived therefore ddoil values can provide rough estimates of ddwater in the depositional environments of the source rocks and consequently may provide evidence about paleoclimatic conditions at the site marine evaporitic oils are enriched in 13c 26 5 to 25 7 and lacustrine oils are depleted 33 6 to 30 2 in 13c relative contributions of marine evaporitic and lacustrine sources to mixed oils thus can be calculated independently from carbon or hydrogen isotopic mixing models when these calculations are done independently the mixed oils separate into two families and a previously unrecognized component possibly associated with environments that formed during the lacustrine to marine transition is revealed the investigation thus demonstrates the superior resolving power of two element mixing systematics

anhydrite diagenesis in a vegetated sabkha al khiran kuwait arabian gulf abstract in the al khiran sabkha supratidal anhydrite occurs in three distinct morphological forms a hair cream anhydrite which occurs exclusively in association with the halophyte halocnemum strobilaceum and b nodular laminated cottage cheese anhydrite which is associated with a bacterial cyanobacterial mat the former occurs as a massive layer up to 4 cm thick with the ahydrite initially pseudomorphing gypsum crystals while in the latter the layers are up to 7 cm thick and the anhydrite occurs as microcrystalline laths giving an aphanitic texture c sub aqueous anhydrite formed by the alteration of prismatic gypsum crystals growing in drainage channels on the death of the halophyte the gypsum g rlhar2 anhydrite a metastable equilibrium is upset and the hair cream anhydrite undergoes a reverse transformation to microcrystalline alabastrine secondary gypsum followed by gypcrust formation the above changes result in a series of characteristic diagenetic textures that were studied in detail by scanning electron microscopy sem the major diagenetic mechanism during the g rlhar2 a transformation is a dissolution reprecipitation process that is only partially controlled by physico chemical factors a climatic and biological influence also plays a significant role in this sometimes annual change depending on the rainfall intensity in contrast type b shows better preservation potential the intimate relationship between the plant and its soil water requirements results in a particular hydrodynamic behaviour of the capillary groundwater brines in the vadose zone hence it is inferred that the individual diagenetic stages are also correlatable with the changing hydrological conditions of the sabkha type c represents a rare occurrence in sabkhas and is more akin to some deeper water occurrences albeit on a very small scale anhydrite is always formed after a gypsum precursor and under predictable physico chemical conditions an average annual temperature of 30 c and brine chlorinity of 4 mol cl kg 1 although it is confined to the vegetated zone of the marine sabkha stable isotope analysis indicates a dominantly continental origin for the groundwaters and coexisting sulphate minerals on a regional scale the vegetated kuwait sabkhas appear to occupy a climatic position intermediate between the classic uae sabkhas and those of the mediterranean region al khiran is the northernmost limit of the evaporite belt containing anhydrite in the arabian gulf the palaeoclimatic and sedimentological implications of this distribution may be of potential value in the rock record

geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy abstract serri g innocenti f and manetti p 1993 geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 117 147 the neogene quaternary magmatism of the northern apenninic arc took place in four phases separated in space and time which become progressively younger from west to east phase i 14 ma phase ii 7 3 6 0 ma phase iii 5 1 2 2 ma phase iv 1 3 0 1 ma this magmatism is the result of the activation of three physically separate sources 1 the adriatic continental crust extracted from the mantle in the late proterozoic 2 a strongly refractory recently k enriched harzburgitic mantle located in the mechanical boundary layer mbl of the lithosphere and 3 a recently metasomatized cpx rich mantle compositionally variable from iherzolite to wehrlite clinopyroxenite interpreted as an ephemerally k enriched asthenosphere the adriatic continental crust is the dominant source of the acid plutonic and volcanic rocks of the tuscan region the acid magmatism is mostly found inside an ellipsoidal area about 150 300 km centred on giglio island here defined as the tuscan crustal dome within this area mantle derived magmas unaffected by important crustal contamination processes and mixing with crustal anatectic melts have so far not been found pure crustal magmas are rare but are represented for example by some of the san vincenzo and roccastrada rhyolites virtually all the tuscan acid centres show evidence of mixing with potassic mantle derived magmas major and trace elements as well as 87 sr 86 sr and 143 nd 144 nd data on primitive rocks mg 65 reveal two groups of mantle derived magmas these define two distinct mantle enrichment trends both essentially due to the additions of k rich components which metasomatized separate compositionally diverse upper mantle sectors in both cases the most remarkable mineralogical effect of these enrichment processes is the production of variable amount of phlogopite through reaction between fluids and or melts with the mantle the rocks of group i ol hy and q normative lamproites ultrapotassic high mg latites ultrapotassic shoshonites and shoshonites saturated trend are considered to be derived by partial melting at low pressure 87 sr 86 sr 0 717 ce sr 0 3 and k 2 o na 2 o 6 7 and low ratios of 143 nd 144 nd 0 5121 0 5120 and ba la 87 sr 86 sr 0 712 and k 2 o na 2 o 8 9 values and low 143 nd 144 nd ba la 0 10 ratios these constraints do not allow to exclude a complete identity between the k rich components which metasomatized the mantle sources of the saturated and undersaturated trend magmas the geochemical and isotopic features of the components that metasomatized the mantle sources of the northern apenninic arc magmatism can be explained by a geodynamic process which causes a large amount of crustal materials to be incorporated within the upper mantle we propose that the delamination and subduction of the adriatic continental lithosphere related to the still ongoing northern apennine continental collision provide a viable mechanism to explain the genesis and eastward discontinuous migration of the magmatism in central italy the subduction of delaminated lithospheric mantle with lower crustal slivers would have exposed uppermost mantle adriatic mbl and crustal units previously imbricated in the apennine chain to the heating advected by the upwelling of a recently and ephemerally k enriched asthenospheric mantle wedge and by the underplating of magmas derived from it we consider that the diapiric uprising of a hot crustally contaminated asthenosphere occurs in the wake left above the sinking of the adriatic delaminated subducting continental lithosphere the delamination subduction process of the adriatic lithosphere has probably started in the early middle miocene but earlier than 15 14 ma ago as indicated by the age and petrologic characteristics of the first magmatic episode sisco lamproite of the northern apennine orogenesis

geochronology of the larderello geothermal field new data and the closure temperature issue the larderello geothermal field is generally accepted to have been produced by a granite intrusion at 4 9 km depth hydrothermal parageneses and fluid inclusions always formed at temperatures greater than or equal to the current ones which implies that the field has always undergone a roughly monotonic cooling history fluctuations 40 k since intrusion of the granite at 4 ma the heat required to maintain the thermal anomaly over such a long period is supplied by a seismically anomalous body of 32000 km3 rooted in the mantle borehole minerals from larderello are thus a unique well calibrated natural example of thermally induced ar and sr loss under geological conditions and time spans the observations biotites retain ar above 450 c agree well with other albeit less precise geological determinations but contrast with laboratory determinations of diffusivity from the literature we therefore performed a hydrothermal experiment on two larderello biotites and derived a diffusivity dlab 370 c 5 3 10 18 cm2s 1 in agreement with published estimates of diffusivity in annite from dlab and the rejuvenation of the k ar ages we calculate maximum survival times at the present in hole temperatures they trend smoothly over almost two orders of magnitude from 352 ka to 5 3 ka anticorrelating with depth laboratory diffusivities are inconsistent not only with geological facts but also among themselves from the geologically constrained lifetime of the thermal anomaly we derive a diffusivity dg 370 c 3 81 1021 cm2s 1 3 1 orders of magnitude lower than dlab the cause of these discrepancies must be sought among various laboratory artefacts overstepping of a critical temperature t enhanced diffusivities in wet experiments presence of fast pathway dislocation and pipe diffusion and of dissolution reprecipitation reactions which we imaged by scanning electron microscopy these phenomena are minor in geological settings in the absence of mineral transformation reactions complete or near complete resetting is achieved only by volume diffusion therefore laboratory determinations will necessarily result in apparent diffusivities that are too high compared to those actually effecting the resetting of natural geochronometers

anatomy of late orogenic extension the northern apennines case abstract late orogenic extensional structures overprint the compressional structures of the northern apennines fold and thrust belt the tyrrhenian sea is the result of major continental extension and rifting which started in the thickened zone of the apulian corso sardinian collision it is believed to have commenced as early as in the late oligocene or early miocene in the corsica basin extension post dates the collision by approximately 20 ma the extensional stress field observed in the internal part of the northern apennines co exists with compression in the foreland part of the belt field borehole and refraction and reflection data were used to investigate the geometry of extension and how it affected the compressional abric in the northern apennines analysis of the collected data has revealed a complex geometry for the extension across the belt a geological cross section from the island of elba to the west of the italian peninsula to ancona in the east as well as a geodynamic model for the evolution of the northern apennines is presented and discussed from the early miocene stretching of the collision thickened crust created a n s rift which evolved into the present northern tyrrhenian sea typically two sets of extensional faults a low angle e dipping and a w dipping one are observed across the chain usually the w dipping faults have similar attitudes to those of the older reverse faults reactivating some of the thrusts as normal faults the e dipping normal faults however cut down section through the pre existing thrusts and in the internal part of the belt accommodate most of the displacement associated with extension a change in fault polarity occurs in the tuscan region and major faults dip towards the west a type subduction of the apulian crust under the corso sardinian block occurred after collision leading to the delamination of the apulian lithospheric mantle away from the crust collision induced delamination of the mantle lithosphere away from the zone of collision resulted in mechanical thinning of the lithosphere beneath the orogenic belt this process induced late orogenic crustal stretching in the internal zone of the northern apennines as the convergence between the apulian and corso sardinian blocks continued the extensional and compressional fronts accompanied by the delamination migrated from the hinterland towards the foreland of the orogen

stable isotope studies and the hydrological regime of sabkhas in southern kuwait arabian gulf the marine sabkhas in al khiran kuwait were formed by sedimentary offlap and relative fall in sea level since the last holocene transgressive maximum 4500 4700 years bp in the absence of significant marine flooding of the coastal sabkhas today due to the presence of chenier ridges their hydrological regime is almost entirely controlled by sub surface continental groundwater influx this topographic hydrologic framework is also reflected in the isotopic data and to some extent in the chemistry of the groundwaters where the major ions show a steady evaporative concentration from inland to coast and from coast to sabkha with a high chloride plateau in the central parts of the marine sabkha monitoring of the groundwater table gwt over a three year period indicates that a when the gwt depths are 1 2 m the sabkha is in a state of depositional equilibrium b gwt fluctuations due to drawdown or recharge exceed 0 5 m yr 1 and c calculations based on measured fall in gwt levels porosities of the sediments and the volume of anhydrite formed in the sabkha suggest that in the last 4700 years since progradation commenced only about 2 4 cm yr 1 net of groundwater is lost from the sabkha surfaces a surprisingly low rate for this arid region this is interpreted as due to recharge of the marine sabkha hosted by marine sediments by significant lateral flow of continental groundwater from the regional system a process that maintains long term stability of the sabkhas and without which deflationary processes would dominate the oxygen and deuterium isotopic compositions of the marine and continental sabkha waters form a group 18o 0 2 d 10 7 isotopically distinct from local meteoric water and pleistocene formation waters they represent evaporation of the old formation waters with a characteristic increase in the heavier isotopes only sabkha waters in areas of tidal flooding the narrow creek areas can be shown to be evaporated seawater the 18 o and d values of the residual brine increase to about 6 and 23 respectively when they reverse and are arrested at the halite precipitation point only a minor amount of mixing between these two evaporated waters could take place isotopic analyses of sulphur and oxygen in dissolved sulphate of sabkha waters and precipitated mineral sulphate confirm a minor contribution of seawater sulphate 34s 19 2 18o 11 in the tidal areas but show that the bulk of the marine sabkha water sulphate 34s 14 2 18o 14 1 and coexisting sulphate minerals is dominantly of continental origin at al khiran gulf of sirte libya and in abu dhabi united arab emirates 34s values of sabkha sulphate decrease to 14 on the landward side close to the values between 13 and 16 for continental sabkhas and continental getch gypsum this pervasive homogeneous sulphate source may be recycled particulate sulphate distributed by major dust storms these results have important implications in evaporite sedimentology

relationships of modern gypsum nodules in sabkhas of loess to compositions of brines and sediments in northern egypt the host sediment is a desert loess forming a gypsiferous sonochak soil with a thin salt crust the nodules occur only in areas where the capillary fringe intersects the ground surface usually where the surface is within 1 5 m of the water table nodules a few centimeters beneath the surface are white very fine grained gypsum nodules at lower levels are of more coarsely crystalline gypsum phreatic groundwater brines although saturated for calcium sulfate are only moderately hypersaline about 60 per mil new evidence suggests that they are mainly of marine origin surface evaporation causes capillary brines above the water table to move upwards through the loess and to increase in salinity a marked increase in the m mg super 2 m ca super 2 ratio of the interstitial brines at the zone of fine grained nodules demonstrates active precipitation there of calcium sulfate it is because of the existence of a very high salinity zone 300 per mil with halite at the top of the profile that gypsum precipitation takes place beneath the surface so as to form nodules rather than a surface crust na super and cl super ions in addition to ca super 2 and so 2 super 2 ions seem to be necessary for the development of gypsum nodules by the per ascensum mechanism modified journal abstract

crustal models of the geothermal areas of southern tuscany italy abstract geological and geophysical data gathered in the geothermal areas of southern tuscany located in the inner part of the northern apennines indicate the presence of granite intrusions the most relevant data are 1 regional asthenospheric ascent to a depth of 40 50 km 2 granitic dykes as old as 3 8 2 9 ma and a widespread contact aureole found in several deep geothermal wells 3 very high heat flow values interpreted as the result of convective circulation of hot fluids above shallow magmatic bodies 4 the presence of low density bodies inferred from low gravity values often correlated with positive heat flow anomalies 5 the occurrence of a highly reflective horizon named k in a depth range of 3 12 km in the geothermal areas as shown by seismic reflection data 6 a 30 40 km wide low velocity body below the k horizon whose existence is supported by local earthquake tomography and teleseismic studies 7 the presence of a conductive body which correlates well with the anomalous tomographic and teleseismic body as revealed by magnetotelluric surveys the goal of the paper is to test different alternative crustal models by using these data the models are 1 granite intrusion 2 geopressurized fluids below impervious layers 3 contact metamorphic aureole 4 mylonite layers at the upper lower crust transition and 5 some combination of the four the occurrence of shallow intrusive bodies still partially molten and associated with saline brines is considered the most tenable model

schorl dravite ferridravite tourmalines deposited by hydrothermal magmatic fluids during early evolution of the larderello geothermal field italy electron microprobe and petrographic data on tourmaline rich assemblages in addition to available data from fluid inclusions and geochronological studies are used to model the early stage of hydrothermal metamorphism in the larderello geothermal field italy during this early stage different hydrothermal events are characterized by deposition of tourmaline biotite calcic plagioclase k feldspar quartz and pyrrhotite at lithostatic pressures of 0 75 to 1 kbarsand temperatures in the range 400 degrees to 600 degrees c pressures exceeding hydrostatic values and inferred temperatures of 450 degrees to 460 degrees c at the bottom of well san pompeo 2 suggest a possible present day deposition of tourmaline in the deepest levels of the central and hottest part of the field hydrothermal tourmalines appear to have crystallized at temperatures in excess of 370 degrees c they show significant replacement of al by fe super 3 in the z site substitutions of al for si in the tetrahedral site and slight vacancies in the x and y sites produced by limited cation and proton deficient substitutions in the hydrothermal tourmaline nearest to the inferred granitic contact and in the tourmaline of a leucogranitic dike crossed by well vcll a negative correlation existing between mg and fe super 2 reveals significant reciprocal substitutions of these elements in the y site tschermak9s and aluminobuergerite substitutions and an increase in the molecular fractions of schorl and elbaite in the schorl dravite and schorl elbaite solid solutions were observed from rim to core of the vcll magmatic tourmalines rims and intermediate growth zones of magmatic tourmalines and most of the hydrothermal tourmalines have compositions falling in the field of metamorphic tourmalines this behavior reveals the dominant control of the host rock on fluid chemistry some growth zones and most cores have compositions that plot in the field of tourmalines from granitoids a gradual schorl or ferridravite enrichment from magmatic to hydrothermal tourmalines with increasing distance from the granite contact is also present in a microprobe traverse from the base to the tip of an acicular tourmaline four peaks of fe super 3 replacing al can be ascribed to four distinct hydrothermal events generated by episodic ascent from below of magmatic fluids that became more and more oxidized with increasing distance from the granite contact owing to an easier hydrogen leakage in the shallower and more fractured levels the studied mineral assemblages and available fluid inclusion data reveal close analogies between the deepest and hottest part of the larderello geothermal system and quartz tour maline and k silicate alteration zones of porphyry tin and copper deposits the mineralizing fluids are inferred to have been of magmatic origin and were characterized by t 400 degrees to 600 degrees c pressure varying between hydrostatic 0 2 0 35 kbars and lithostatic 0 75 1 kbars commonly near lithostatic values high f sub o 2 as inferred by the presence of hematite and anhydrite among fluid inclusion daughter minerals and very high salinities up to 50 60 equiv wt nacl

cover thrust reactivations related to internal basement involvement during neogene quaternary evolution of the northern apennines up to recently the neogene quaternary evolution of the northern apennines italy has been described by the classic model of a migrating eastward compressive external front with an extensional regime in the back areas connected with the tyrrhenian basin formation however in the last few years new structural data have been collected in the internal marine and continental episutural basins and in the external exposed thrust belt a complex structural evolution has now been reconstructed with coeval main tectonic phases that affect both areas with stress field change four main tectonic phases have been identified since late tortonian times these are dated as messinian late pliocene middle and late pleistocene the thrust belt has a complex evolution detected in a wide external area of the chain after the first emplacement of the main thrust sheets with reactivations and out of sequence thrusting these reactivation phases fit very well with the compressive phases affecting the sediments of the internal basins suggesting a direct relationship within a single evolutive model the increased knowledge of the deep structure of the northern apennines through geophysical and subsurface data acquired in the last few years indicates the basement involvement at least for the internal side of the northern apennines this basement involvement also played an important role in the tectonic evolution of the external sector of the apennines in this paper a new model is proposed that integrates field data geophysical evidence and geodynamic constraints the thrust reactivations and the out of sequence structures of the external area are related to internal crustal thrust activity the deformed sediments of the neogene quaternary basins are dating the thrust activity all the evidences point to a late neogene rejuvenation of the tectonic evolution but some inferences can be drawn on the development of the foredeep

organic geochemical characterisation of depositional palaeoenvironments of source rocks and oils in brazilian marginal basins abstract an investigation of bulk isotopic and molecular features of a wide selection of source rocks and oils from brazilian marginal basins ranging from lower cretaceous to tertiary in age provides a number of organic geochemical criteria that characterise and distinguish their depositional palaeo environments the methods employed include evaluation of organic carbon contents rock eval pyrolysis vitrinite reflectance measurements determination of carbon isotope ratios elemental and visual kerogen analysis assessment of oils and solvent extracts by liquid and gas chromatography and quantitative biological marker investigations using gc ms for aliphatic hydrocarbons and uv vis spectrophotometry for metalloporphyrins selected data were evaluated using principal component analysis the results enable the recognition and differentiation of seven depositional regimes lacustrine freshwater lacustrine saline water marine evaporitic marine carbonate marine deltaic marine highly anoxic with a predominance of calcareous mudstone lithology and marine anoxic with predominance of siliciclastic lithology diagnostic features in the biological markers from these depositional environments include the carbon number distributions of n alkanes pristane phytane ratios absolute concentrations of carotane higher acyclic isoprenoids c 30 hopane and steranes and the abundance of the latter relative to 4 methylsteranes the occurrence and abundance of particular biological markers such as gammacerane tricyclic and tetracyclic terpanes 18 h oleanane 28 30 bisnorhopane and 25 28 30 trisnorhopane and the relative abundances of nickel and vanadyl porphyrins

age and temperature constraints on metamorphism and exhumation of the syn orogenic metamorphic complexes of northern apennines italy abstract the apennine range is a young convergent orogen that formed over a retreating subduction zone syn orogenic metamorphic rocks are exposed in the mid tuscan ridge tuscan coast and tuscan archipelago and provide information about processes of continental subduction and exhumation associated with accretion and retreat apatite and zircon fission track analyses were applied to some of these syn orogenic metamorphic rocks the new low temperature thermochronological data helped to constrain the timing of the metamorphic peak and the age and modality of exhumation of these rocks that were structurally buried at 20 to 40 km depth during the main tectonogenic phase of the northern appenine belt in the giglio and elba islands and in the monti dell uccellina along the coast minimum ages of partially reset zircon samples yielded a first time constraint on the late oligocene age of the metamorphic peak the ca 27 ma obtained at the monti dell uccellina is coeval to that found in the alpi apuane located at the northern termination of the mid tuscan ridge the data from the tuscan archipelago point to a slightly older age in the monti pisani south of the alpi apuane and in the argentario promontary along the coast south of the monti dell uccellina completely reset zircon samples but composed by different populations were behaving as multiple thermochronometers and confirm the already proposed isothermal nature of the exhumation occurred after the metamorphic peak zircon p1 peak indicated that at 13 10 ma rocks were already at shallow crustal levels

facies architecture and controlling factors induced depositional model of the quaternary carbonate eolianites in the northwestern mediterranean coast of egypt

sulfate mineralogy of fumaroles in the salton sea geothermal field imperial county california abstract the salton trough lies in the transition between the san andreas fault and oblique spreading centers and transform faults in the gulf of california the salton sea geothermal field is the northernmost expression of those spreading centers in 2007 two ammonia emitting fumarole fields that had been submerged beneath the salton sea were exposed for the first time in nearly 50 years as the sea level continued to drop these fields have developed a number of boiling pools mud pots gryphons and a unique suite of ammonium sulfate minerals these have been studied over time with long wave infrared remote sensing coupled with ground truth surveys backed by laboratory analyses of the minerals many vents lie at the center of concentric rings of mineralization with systematic occurrence of different minerals from center to edge three semi concentric zones fumarole transition and evaporite have been defined with respect to ammonia emitting vents and bubbling pools the scale of these zones range from several meters localized around individual vents to that of the fumarole fields as a whole the fumarole zone is closest to the vents and locally contains cavernous sulfur crystals and significant deposits of gypsum mascagnite boussingaultite and other ammonium sulfates the transition zone comprises a dark brown surficial band of inconspicuous sodium nitrate underlain by anhydrite bassanite that is thought to have formed by ammonia oxidizing microbes interacting with the ammonium sulfates of the outer fumarole zone the evaporite zone is the outermost and contains blodite thenardite and glauberite which are typical of the sulfates associated with the shoreline of the salton sea remote sensing has shown that the mineral zones have remained relatively stable from 2013 to 2017 with minor variations depending on rainfall temperature and levels of agricultural runoff

the baganuur coal deposit mongolia depositional environments and paleoecology of a lower cretaceous coal bearing intermontane basin in eastern asia abstract the investigations involved geophysical sedimentological palynological chemical and mineralogical studies supported by field based infrared spectrometry the baganuur basin central mongolia is among the rift or pull apart basins which subsided at the boundary between the jurassic and the lower cretaceous in east asia during the berriasian peat accumulation began in the area under study in central mongolia the palynoflora is akin to the siberian palynological province based on the phytoclast assemblages and the ratios of total sulfur content to total organic content marine transgressions into this intermontane basin may be ruled out the coal interseam sediments were laid down prevalently under neutral to slightly alkaline conditions only in some carbonaceous sediments the ph of intrastratal solutions was lowered suboxic to anoxic conditions persisted during almost the entire lower cretaceous period in the baganuur basin based on the distribution of fining and coarsening upward sequences and the organic matter the basin fill has been subdivided into seven depositional units a fluvial swamp b fluvial lacustrine c deltaic fluvial d fluvial e fluvial deltaic lacustrine floodplain f lacustrine deltaic swamp g swamp fluvial a conspicuous change in the fluvial lacustrine regime and an increase in the sediment supply may be observed at the boundary between depositional units b and c a strong uplift triggered the onset of an intensive delta sedimentation lithoclasts heavy minerals e g apatite zircon garnet anatase brookite epidote sphene tourmaline and phyllosilicates e g kaolinite smectite mica chlorite attest to a mixing of detrital material one provenance area was abundant in acidic plutonic rocks as shown by the granitic lithoclasts the other in volcanic rocks which produced the vitroclastic debris deposited as tephra fallout post depositional alteration of the siliciclastic interseam sediments was favored by a distinctive facies association of transmissive and sealing horizons it led to a re deposition of ca u and sr in the siliciclastics post depositional alteration of the organic material converted it into lignite to subbituminous c coal

sb hg ore deposit distribution controlled by brittle structures the case of the selvena mining district monte amiata tuscany italy abstract this paper deals with the tectonic control on the hydrothermal system that gave rise to sb hg ore deposits in the monte amiata area that was one of the most relevant mining district for the exploitation of mercury in italy the study area selvena mining district is located in southern tuscany inner northern apennines one of the most important mineralized area in the western mediterranean region southern tuscany was severely affected by middle late miocene low angle normal faults later dissected by pliocene pleistocene faults coeval magmatism late miocene pleistocene and hydrothermal activity pliocene present the selvena mining district is located south of middle pleistocene monte amiata volcanic complex our structural and kinematic study is based on the integration among fieldwork borehole and mine data the results highlight two pleistocene holocene left lateral transtensional shear zones linked by normal faults defining a coeval pull apart structure here the sb hg mineralization transported by meteoric hydrothermal fluids mainly is particularly diffuse and concentrated in the cataclasites and in damage zones of the normal faults furthermore a widespread mineralization also occurs in the cataclasites of miocene low angle normal faults mine evidence suggests that ore bearing fluids percolated through structural conduits located along the fault planes and resulting parallel to the intermediate stress axis geological structures and ore deposit distribution are related to a single hydrothermal circuit with meteoric water channelled to depth through conduits parallel to the intermediate stress axis of the transcurrent shear zones then hydrothermal fluids mainly ascended through the almost vertical deformation zones located at the intersection between normal and strike slip faults thus hydrothermal fluids permeated also the middle late miocene cataclasites this study shed light on the relationships between geological structures and mineralization in southern tuscany and underlines the importance to investigate mine areas to understand hydrothermal fluids path

tertiary extensional tectonics in tuscany northern apennines italy abstract two extensional events have been recognized in the tertiary evolution of tuscany the first event occurred in the period between the late oligocene and late tortonian and caused a stretching of 120 or greater the second event occurred between the late tortonian and quaternary periods and caused a stretching not greater than 10 the first event is characterized by the exhumation of middle crust rocks and therefore by the development of core complexes the most significant structures of the first event are low angle normal faults which characterize the upper plate of the core complexes and ductile shear zones which characterize the lower plate the low angle normal faults tend to die out in the late triassic evaporite level which constitutes the main detachment of the core complexes the main structures of the second extensional event are high angle normal faults which dissect all the previous tectonic features these faults border tectonic depressions which were the site of clastic sedimentation from late tortonian to quaternary time these normal faults may tend to flatten in a seismic lozenge shaped band explained as an active extensional shear zone which is located at the brittle ductile boundary a similar explanation is given for the detachment located in the late triassic evaporite level during the first extensional event while the first extensional event is in the framework of the northern apennine post collisional evolution the second extensional event because it affects an already stretched crust could be attributed to the southern tyrrhenian opening which began during late tortonian

characterization of organic matter from a restricted evaporative sedimentary environment late miocene of lorca basin southeastern spain the lorca basin located within the tectonically evolving betic cordillera of southeastern spain developed as a rapidly subsiding basin in an open marine setting during much of the late miocene the basin underwent sporadic phases of circulatory restriction with marked production and preservation of organic matter culminating in evaporative sedimentation latest miocene an organic geochemical study using biomarker analyses clarifies the degree of mixing between inflowing water sources both marine and nonmarine gives clues to the complex and variable circulation within the water and helps determine the extent of basinal hypersalinity as the water in this basin evolved toward evaporative conditions a number of organic rich depositional phases 25 wt toc he e termed pre evaporative took place during the early parts of these phases the upper water is interpreted as nutrient rich and comparatively normal and the bottom water as anoxic this was followed by rising salinities and short phases of evaporite formation such a sedimentary history may serve as a model for understanding of evaporite related source rocks and related hydrocarbons in other areas of the world

gypsum anhydrite transformations in messinian evaporites of central tuscany italy abstract the messinian succession of tuscany central italy contains three evaporitic units among the several exposed evaporitic lithofacies only selenitic gypsum precipitated directly from evaporating brines all the other facies nodular microcrystalline gypsum gypsarenites and gypsum laminites despite their macroscopic differences display the same petrographic textures indicating that they are the product of dehydration of gypsum to give anhydrite which has been successively rehydrated to secondary gypsum these secondary facies show an entire array of textures ranging from cloudy ameboid xenotopic with anhydrite relics to idiotopic without anhydrite relics that are here interpreted as a sequence of progressive stages of rehydration the presence of completely hydrated petrofacies at the core of nodules which display a less hydrated rim suggests that these rocks have undergone at least two cycles of a dehydration rehydration process this interpretation is supported by the presence of satin spar veins that are replaced by microcrystalline gypsum satin spar itself is considered to be a by product of anhydrite hydration the first dehydration rehydration event affected the entire gypsum deposit producing a completely hydrated idiotopic facies together with satin spar veins the second affected only veins fractures and the rims of nodules turning the first generation of satin spar and idiotopic gypsum into cloudy ameboid gypsum sedimentary structures typical of sabkha environments indicate for the youngest formation that the first dehydration and rehydration process occurred syndepositionally the preservation of primary gypsum facies only at sites with condensed sections indicate for the oldest two formations that the first dehydration event occurred upon burial this event has been estimated to have occurred in the earliest pliocene after the early pliocene dehydration was favored even at shallow depths due to an increased heat flow related with the emplacement of local crustal magmatic bodies rehydration possibly occurred when these formations were uplifted and exposed to ground and or meteoric water the volterra basin has undergone alternating subsidence and uplift events that can account for two dehydration rehydration processes at least also driven by alternating circulation in the tectonic fractures of fresh and salty water the latter derived from dissolution of messinian halite

last interglacial stratigraphy in the burg el arab region of the northwestern coast of egypt abstract the northwestern coast of egypt a stable carbonate platform is characterized by the presence of successive coastal ridges that extend parallel to the present shoreline study of marine deposits at the bottom of gebel maryut ridge from the drain cut of bahig together with analyses of core samples raised from four boreholes drilled in the el dekheilla depression to the depths of 10 15 m reveal the presence of two phases of beach boulders the lower older phase b b 1 wedge eolianites e 1 at an elevation of 3 4 m and show an average 18o of 0 82 the upper younger phase b b ii wedge eolianites e 2 at 6 7 m a s l with an average 18o of 1 5 these beach boulders are overlained by thick fossiliferous limestones and geosoils they record the last interglacial high sea level isotope substage 5e and aminozone e with an interpolated age of 125 ka which was globally 6 8 m higher than present sea level with characteristic warm wet tropical climatic conditions a bed composed of marine molluscs and foraminifera shells with ooids and pellets below the loamy calcareous and evaporites of the el dekheilla depression was also examined this bed is located 1 4 m b s l with an average 18o of 0 25 it is related to aminozone c isotope substage 5c 5a with an interpolated age of 110 ka and related to a transgressive sea with a mean sea level possibly equal to or slightly lower than the present one with evidence for less warm climatic conditions

the possible roles of precambrian biota in the origin of magmatogene and hydrothermal silver bearing vein deposits the origins of silver bearing polyelement vein associations in the great bear lake region and elsewhere in the world might be traced back to possible organic rich precambrian sedimentary protoliths these protoliths could have yielded a characteristic spectrum of elements to hydrothermal systems during regional metamorphism or during anatexis to form s type granitoids wholesale capture of metals and metalloids by microbiota and their remains may have been a characteristic of some early proterozoic marginal marine mesosaline environments two possible atmosphere hydrosphere lithosphere models are considered in light of recent theories the metallogenic effects of early proterozoic organic rich sedimentary environments could be of great significance they might account for the polyelemental signatures of many younger remobilized metal liferous systems

organic geochemical characteristics and organic matter enrichment of mudstones in an eocene saline lake qianjiang depression hubei province china abstract the qianjiang depression is a typical eocene hypersaline lake basin developing good source rocks in the qianjiang formation which have recently been identified as a potential target for saline lacustrine shale oil exploration previous studies have only focused on estimates of source rock potential and reservoir quality however studies on organic matter enrichment mechanisms in evaporative environments are limited based on organic geochemical and mineralogical data as well as sedimentological analyses we researched the factors controlling differences in organic matter enrichment in the basin the results show that total organic carbon toc contents are closely associated with lithofacies with distinct variations three main lithofacies associations las were identified 1 glauberite rich la1 with medium toc 2 carbonate rich la2 with high toc and 3 anhydrite rich la3 with low toc the distribution of biomarkers from 14 samples indicate both higher land plants and aquatic organisms were involved in the organic matter accumulations combining experimental results on gammacerane c30 hopane extended tricyclic terpane ratio etr sr ba v ni and sedimentary characteristics we analyzed the sedimentary environments of the three las la1 was deposited in a salinity stratified waterbody with strong evaporation la2 was deposited in a still stratified deep waterbody whereas la3 was deposited in a disturbed saline waterbody sedimentary environments not only controlled the formation of the lithofacies but also influenced the organic matter sources and preservation relatively low salinity strong anoxic condition without physical disturbance appropriate nutritional terrigenous material inputs and algal blooms produced the best organic matter enrichment in the saline lake system

fluid circulation in the upper brittle crust thickness distribution hydraulic transmissivity fluid inclusion and isotopic data of veins hosted in the oligocene sandstones of the macigno formation in southern tuscany italy abstract we present structural analysis fluid inclusion data on calcite and quartz and isotopic composition of calcite forming veins occurring in the upper crustal level and hosted in oligocene sandstone in southern tuscany italy the veins have been analysed in two sites few kilometres apart along well exposed coastal cliffs and in an abandoned quarry these two sites were at a different depths at the time of the vein formation with a h 100 m structural analysis of veins provided estimations of stress ratio 2 3 1 3 driving stress ratio r pf 3 1 3 and fluid overpressure po pf 3 at the time of vein formation the estimated po is in the range of 42 103 mpa 0 24 and r 0 45 indicating that fluid pressure was higher than the intermediate principal stress at the time of veins formation the veins thickness t shows a clear power law distribution d 1 8835 and r2 0 9762 in the lowermost site coast and a negative exponential distribution a 0 6943 and r2 0 9921 in the uppermost site abandoned quarry the vein thickness distributions have been used to compute the average transmissivity of the veins in the two sites the computed transmissivity for the vein formation is 10 4 m2 s 1 with higher values attained by the veins having negative exponential thickness distribution fluid inclusions studies highlighted that in both calcite and quartz water rich inclusions with salinities of 2 2 4 3 wt nacl equiv and methane rich inclusions were coevally trapped during fluid un mixing processes thermogenic origin from thermal maturation of organic matter present in the macigno formation is proposed for methane whereas the similarity between the 18o from 14 9 to 17 4 and 13c from 0 4 to 2 4 data of representative calcite veins and the isotopic composition 18o 16 1 13c 1 0 of host rock carbonate component indicates that the fluid which formed calcite was in isotopic equilibrium with the carbonates present in the oligocene sandstones the calculated pressure temperature conditions during the formation of these inclusions are prevalently within the 40 145 mpa and 160 260 c ranges the highest pressure values approximate the lithostatic pressure 120 mpa computed from geological data and are coherent with a geothermal gradient ranges of 35 45 c km whereas the lower pressure values are comparable with hydrostatic pressure conditions the pressure range indicated by fluid inclusion data is also comparable with the fluid pressure estimated from structural analysis the considerable pressure range can be related to pressure cycling between lithostatic and hydrostatic conditions as a consequence of fault valve actions and rock fracturing with subsequent pressure recover due to self sealing process

analytical solutions for analysing pumping tests in a sub vertical and anisotropic fault zone draining shallow aquifers summary we present new analytical solutions for examining the influence during a pumping test in a well of an infinite linear and anisotropic strip aquifer that drains shallow aquifers of different diffusivity and thickness the whole system is confined and the aquifer geometry can be represented by a t an aquifer geometry resembling a sub vertical fault or a sub vertical vein cross cutting shallower aquifers the proposed solutions are based upon an unconventional application of well image theory without limitation of the diffusivity contrast between the three domains solutions for drawdown were developed for the three domains i e the strip aquifer and the two shallow compartments and flow signatures are discussed in detail and compared to numerical modelling the proposed solutions are not shown to be exact solutions to the appropriate partial differential equation but very good and useful approximations the solutions were applied to a 63 day pumping test in a steep fault zone in crystalline aquifer rock of brittany france after that the flow contributions of the fault zone and of the shallow aquifers deduced from groundwater dating were compared to analytical solutions the solutions and theoretical type curve examples can help in understanding flow processes from tests conducted in settings that are similar to such a conceptual model

phase relations in andalusite sillimanite type fe rich metapelites tono contact metamorphic aureole northeast japan mineral assemblages in metapelites of the contact aureole of the tono granodiorite mass northeast japan change systematically during progressive metamorphism along an isobaric path at 2 3 kbar the bulk rock compositions of metapelites are aluminous with a values on an afm projection larger than that of the chlorite join the metapelites commonly contain paragonite in the low grade zone with increasing temperatures andalusite is formed by the breakdown of paragonite the importance of pyrophyllite as a source of al2sio5 polymorphs is limited in typical pelitic rocks the most common type of metapelite in the study area has feo feo mgo 0 5 0 6 and develops assemblages involving chlorite andalusite biotite cordierite k feldspar sillimanite and almandine with paragenetic changes similar to other andalusite sillimanite type aureoles rocks with feo feo mgo 0 8 progressively develop chloritoid bearing assemblages from bt chl cld and bt cld to and bt at temperatures between the breakdown of paragonite and the appearance of cordierite in the more common pelitic rocks in the aureole the paragenetic relations are explained by a kfmash univariant reaction of chl cld and bt located to the low temperature side of the formation of cordierite by the terminal equilibrium of chlorite a p t model depicting the relative stability of chloritoid and staurolite at low and medium pressure conditions respectively is proposed based on the derived location of the chl cld and bt reaction combined with the theoretical phase relations among biotite chlorite chloritoid garnet and staurolite

depositional environments and paleogeography of the cretaceous gypsum horizon in west central jordan abstract in the upper cretaceous upper cenomanian gypsum horizon of west central jordan the lithofacies of gypsum limestone and dolomite as well as their sedimentary structures and petrography indicate a coastal intertidal supratidal sabkha environment very much like the persian gulf model 1500 km 2 in area and elongated n s parallel to the dead sea rift fact that this is the second time in the cenomanian of the mujib area that total emergence has happened is taken as an example of synsedimentary tectonics in an unstable area along the not yet existing dead sea rift

photochemical sulfurization of sedimentary organic matter a widespread process occurring at early diagenesis in natural environments abstract the possibility of light induced formation of sedimentary organo sulfur compounds has been investigated with simulation experiments these experiments using mono and diunsaturated hydrocarbons and reduced sulfur species in particular h 2 s and elemental sulfur were conducted under mild conditions sunlight low temperature likely to occur in the photic zone of anoxic environments these experiments showed an efficient sulphurization of the organic matter under sunlight conditions leading to the formation of organo sulfur compounds such as thiophenes and sulfur cross linked macromolecules very similar to those occurring in sediments deposited in anoxic environments these results show the potential for photochemically induced sulfurization of organic matter in environments with photic zone anoxia such a process would be especially favored in evaporitic environments with a shallow anoxic boundary extending well into the photic zone

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

lower miocene gypsum palaeokarst in the madrid basin central spain dissolution diagenesis morphological relics and karst end products the miocene sedimentary record of the madrid basin displays several examples of palaeokarstic surfaces sculpted within evaporite formations one of these palaeokarstic surfaces represents the boundary between two main lithostratigraphic units the miocene lower and intermediate units of the madrid basin the palaeokarst formed in lacustrine gypsum deposits of aragonian age and corresponds to a surface palaeokarst epikarst further buried by terrigenous deposits of the overlying unit karst features are recognized up to 5ae5 m beneath the gypsum surface exokarst and endokarst zones are distinguished by the spatial distribution of solution features i e karren dolines pits conduits and caves and collapse breccias sedimentary fills and alteration of the original gypsum across the karst profiles the development of the gypsum palaeokarst began after drying out of a saline lake basin as supported by recognition of root tubes later converted to cylindrical and funnel shaped pits at the top of the karstic profiles the existence of a shallow water table along with low hydraulic gradients was the main factor controlling the karst evolution and explains the limited depth reached by both exokarst and endokarst features synsedimentary fill of the karst system by roughly laminated to massive clay mudstone with subordinate carbonate and clastic gypsum reflects a punctuated sedimentation regime probably related to episodic heavy rainfalls typical of arid to semi arid climates duration of karstification is of the order of several thousands of years which is consistent with previous statements that gypsum karstification can develop rapidly over geologically short time

characterization of a high transmissivity zone by well test analysis steady state case a method is developed to analyze steady horizontal flow to a well pumped from a confined aquifer composed of two homogeneous zones with contrasting transmissivities zone 1 is laterally unbounded and encloses zone 2 which is elliptical in shape and is several orders of magnitude more transmissive than zone 1 the solution for head is obtained by the boundary integral equation method nonlinear least squares regression is used to estimate the model parameters which include the transmissivity of zone 1 and the location size and orientation of zone 2 the method is applied to a hypothetical aquifer where zone 2 is a long and narrow zone of vertical fractures synthetic data are generated from three different well patterns representing different areal coverage and proximity to the fracture zone when zone 1 of the hypothetical aquifer is homogeneous the method correctly estimates all model parameters when zone 1 is a randomly heterogeneous transmissivity field some parameter estimates especially the length of zone 2 become highly uncertain to reduce uncertainty the pumped well should be close to the fracture zone and surrounding observation wells should cover an area similar in dimension to the length of the fracture zone some prior knowledge of the fracture zone such as that gained from a surface geophysical survey would greatly aid in designing the well test

highly extended terrains lateral segmentation of the substratum and basin development the middle late miocene radicondoli basin inner northern apennines italy 1 this paper deals with the evolution of sedimentary basins not delimited by normal faults with a substratum characterized by an upward concave shape and with infilling sediments synclinally deformed we describe the middle late miocene radicondoli basin representing an example of such bowl shaped basins its tectonic origin is controversial being related both to compression and extension these opposite interpretations bear significant consequences on the geodynamic context in which the inner northern apennines developed during the middle late miocene the results of our structural studies carried out in the substratum and infilling sediments indicate that the radicondoli basin is an example of a hanging wall basin developed in an extensional setting extensional tectonics determined the lateral segmentation of the substratum competent levels i e tuscan nappe and verrucano group and the consequent collapse of overlying less competent levels i e the ligurian units with the formation of a bowl shaped tectonic depression here the syntectonic sediments serravallian late messinian are deformed in a large syncline characterized by minor gravity driven folds with vergences toward the depocenter and traces of their axial planes parallel to the basin margins this paper highlights the role of the competence contrast during the postcollisional tectonic evolution and the influence of substratum lateral segmentation for the accommodation of syntectonic sediments

characteristics and origin of lacustrine source rocks in the lower cretaceous erlian basin northern china abstract four lacustrine rift sub basins in the erlian basin one of the most petroliferous basins in northern china have been analyzed to characterize source rock potential to reveal environmental and ecological changes and to construct depositional models for lacustrine source rocks in different tectonic settings the first member of the tengger formation in these sub basins is characterized by a wide range of total organic carbon contents hydrogen indices and kerogen types these sub basins have dissimilar boundary fault activities and sedimentation rates the differences in border fault activity and sedimentation rate are consistent with changes in productivity redox conditions and clastic influx input the carbon isotopic composition of carbonates in mudstone samples suggests that the productivity of aer and wuli sub basins is higher than that of naoer and saihan sub basins differences in tectonic conditions also result in different redox conditions of depositional environments total reduced sulfur and pr ph ratios show an oxidizing environment in aer and wuli sub basins while a reducing environment was present in naoer and saihan sub basins with more active boundary faults and higher sedimentation rates the terrigenous organic matter inputs to aer and wuli sub basins are higher than naoer and saihan sub basins this can be confirmed by relative steranes abundances different tectonic conditions existed in different sub basins which lead to variations in ecological communities in the lake systems these environmental and ecological changes enable us to construct models for the deposition of lacustrine source rocks under different tectonic backgrounds during source rock deposition in aer and wuli sub basins the high influx of clastic sediments carrying high terrigenous organic matter and dissolved inorganic carbon and nitrate into the lake might have sustained high productivity and oxidizing conditions due to high influx of clastic sediments and unstable water column stratification the depositional environment of aer and wuli sub basins are oxidizing in a high productivity lake there is still significant organic matter accumulation in oxidized environment after oxidative degradation the high productivity is the dominant factor controlling the formation of organic rich sediments and the deposition of source rocks in aer and wuli sub basins in naoer and saihan sub basins the depositional environment during source rock formation is reducing due to low influx of clastic sediments with low productivity in low productivity lakes such as naoer and saihan sub basins which are low productivity lakes redox condition substitutes for productivity and becomes the predominant factor controlling the formation of lacustrine source rocks it is evident that the synergetic evolution of depositional environments and organisms in a lake system accounts for the formation of source rocks with different characteristics the proposed models may have important implications for source rock prediction in other lacustrine rift basins

the depositional and diagenetic evolution of the coastal ridges of northwestern egypt since the lower pliocene successive generations of coastal ridges made up of mixed oolitic and biogenic grainstones formed along the mediterranean coastline of egypt west of alexandria and have undergone progressive stages of diagenesis the ridges are complex structures resulting from several phases of deposition in which shallow marine components are partially and progressively reworked as subaerial and aeolian deposits diagenetic alteration resulted from increasing freshening of the pore waters in the ridges diagenesis began with marine phreatic cementation followed by freshwater phreatic cements aggrading recrystallization of microcrystalline calcite to microspar and minor dolomitization non marine hypersaline diagenesis soil profiles developed on the upper surfaces of the oldest dunes

episodic hydrothermal alteration recorded by microscale oxygen isotope analysis of white mica in the larderello travale geothermal field italy abstract microscale oxygen isotope analysis 18o 16o of minerals can identify distinct events of fluid rock interaction this method is however still limited to a few major and accessory minerals of which most are anhydrous minerals we present the systematic study of oxygen isotope distribution in white mica by secondary ion mass spectrometry sims texturally and chemically distinct white mica populations in granitic and contact metamorphic rocks from the larderello travale geothermal field ltgf italy record stages of magmatic crystallization metamorphic hydrothermal replacement and fluid rock interaction the large range in intra and inter grain white mica 18o values between 1 and 14 reflects varying protoliths and degrees of fluid mineral interaction at variable temperatures 180 450 c present day temperatures p d t this variability reflects the large scale circulation of both 1 magmatic syn intrusive to early contact metamorphic hydrothermal fluids with high 18o values and 2 meteoric fluids with 18o values of 7 during a post intrusive late hydrothermal stage metasedimentary rocks from the upper reservoir contain distinct white mica populations occurring in close proximity m scale including detrital grains 18o 12 14 high na low mg partially altered white mica 18o 8 9 and late hydrothermal white mica 1 6 low na mid mg the late hydrothermal white mica has similar 18o values to other secondary minerals and is in equilibrium with meteoric dominated fluids with a 18o of 6 to 0 5 which circulated in the late hydrothermal stage downhole towards the lower reservoir white mica from two contact metamorphic micaschist samples shows either 1 homogeneous 18o values of ca 9 likely due to recrystallization in the contact metamorphic hydrothermal stage t ca 600 c or 2 a large spread in 18o from 2 to 12 within and across grains of variable texture and chemistry in the host rock and a cross cutting quartz white mica vein ca 300 c present day temperature hereafter p d t this contrasting 18o signature of white mica is also recorded in granite cored at up to 4 6 km depth the carboli granite contains white mica with a homogeneous magmatic 18o of 10 0 6 whereas older granite samples from radicondoli have magmatic to hydrothermal white micas that vary in 18o from 4 to 10 a pronounced intra grain 18o variability of up to 6 occurs in white mica domains with higher fe mg ti halos around inclusions of chloritized biotite as a result of interaction with dominantly meteoric fluids that infiltrated to depths of at least 4 6 km in the porto azzurro granite on elba italy altered white mica has 18o values of 2 6 down from 10 in unaltered grains the distribution of oxygen isotope ratios in white mica is thus firstly a result of pervasive versus selective fluid alteration at depth sample and grain scale secondly the actual preservation of these m scale variabilities indicates that volume diffusion is not detectable at microscale at p d t at or below 350 c where most of the heterogeneous white mica is found selective sample and grain scale fluid penetration occurs episodically and anisotropically on micro and megascale along faults fractures and cleavages producing lower 18o white mica at various times in zones of higher secondary permeability and active hydrothermal fluid circulation

isotopically heavy carbon in the c21 to c25 regular isoprenoids in halite rich deposits from the sdom formation dead sea basin israel abstract a series of miocene pliocene halite deposits with extremely low organic carbon contents from the sdom formation dead sea basin israel have been studied distributions and 13c contents of biomarkers have been determined using gc ms and irm gcms analyses respectively the hydrocarbon fractions consist mainly of pristane phytane and c21 to c25 regular isoprenoids the predominance of c21 regular isoprenoids in the dead sea halites and other hypersaline deposits indicate that these components could be derived from ether bound membrane lipids of halophilic archaea the lack of intact ether bound lipids in the polar fractions indirectly infers that such components have already been released at early stages of diagenesis their 13c contents are enriched in 13c by up to 7 compared to the biomarkers of presumed phytoplanktonic origin i e steranes and hopanes within the same sediment sample in agreement with a source other than algae and cyanobacteria thus tentatively assigned as halophilic archaea based on biomarker distributions 13c contents and mineral compositions these sediments appear to have been deposited in a salinity stratified water body with a bottom water brine continual evaporation and deposition of the higher salts i e carnallites are favourable conditions for the growth of halophilic archaeal communities

depositional cycles and source rock development in an epeiric intra platform basin the hanifa formation of the arabian peninsula abstract the upper oxfordian to lower kimmeridgian hanifa formation was deposited in an intra platform basin on the broad epeiric shallow water carbonate platform that extended over much of the middle east during the mesozoic the formation consists of organic rich carbonate mudstones bioturbated mudstones and sulphates the organic rich mudstones are considered to be one of the major hydrocarbon source rocks in the middle east oil province the correlation of sedimentary facies shows a hierarchical stacking pattern of transgressive regressive depositional cycles within the hanifa formation since these cycles occur at a basin wide scale it is assumed that they are related to relative changes of sea level the superimposed scales of cyclicity determine the occurrence of source rock and sulphates major source rock development occurs in transgressive dominated cycles sulphates on the other hand are more common during periods of overall regression

migration of geothermal fluids in extensional terrains the ore deposits of the boccheggiano montieri area southern tuscany italy an integrated study based on fluid inclusion 18o composition and structural analyses was carried out on a pliocene fossil hydrothermal system located to the south of the present active larderello geothermal field in the boccheggiano montieri area the study area is typified by mineralized cataclastic levels related to late oligocene early miocene thrust surfaces and to the following two generations of normal faults of miocene and pliocene ages respectively within the damage zone of the pliocene boccheggiano fault the mineralization is mainly made up of quartz and pyrite quartz pb zn sulfides or quartz pb zn sulfides fluorite carbonates assemblages occur instead in the older cataclastic levels two generations of liquid rich fluid inclusions were recognized in quartz and fluorite the first one with homogenization temperatures ranging between 172 and 331 c and salinity between 0 0 and 8 8 wt naclequiv records the early stage of hydrothermal activity the second generation of fluid inclusions documents a later stage with homogenization temperature from 124 to 288 c and salinity from 0 2 to 1 9 wt naclequiv fluid inclusions analyses also indicate that mixing of fluid with distinct salinities and or temperatures was a widespread process during the early stage and that fluid temperatures decreased moving from the boccheggiano fault toward the more distal and older cataclastic levels the 18o values of water in equilibrium with hydrothermal quartz which range from 5 7 to 0 1 are related to the circulation of meteoric water mixed with saline water that leached the evaporite level and enriched in 18o through water rock interaction and or with magmatically derived fluids results indicate that the damage zone of the pliocene boccheggiano fault represented the main channel for the flow of meteoric water which was heated at depth then mixed with high salinity fluids and finally ascend to infiltrate along the older cataclastic levels our results based on fluid inclusions oxygen isotopic compositions and structural analyses indicate that a single fluid flow path run through the damage zone of the boccheggiano fault and the older cataclasites which were thus hydraulically connected

early neoproterozoic sequence stratigraphy and acritarch biostratigraphy eastern officer basin south australia abstract the early neoproterozoic torrensian latest tonian 800 750 ma succession in the central and eastern officer basin was deposited in an intra cratonic rift basin the outcropping pindyin sandstone consists of basal lowstand conglomerate and upward fining transgressive sandstone and is conformably overlain by marine highstand shale of the alinya formation in the giles 1 well the pindyin sandstone contains aeolian to fluvial deposits and is overlain by peritidal and sabkha sediments of the alinya formation seismic interpretation suggests that the succession is thin on the murnaroo platform and thickens toward the munyarai trough the two sedimentary provinces are separated by the ungoolya hinge which probably marks the southeastern margin of the fraser musgrave fold belt highstand organic rich shale in the alinya formation is probably an important petroleum source rock acritarchs occur in both chert and shale in the alinya formation and their distribution was probably controlled by sedimentary environments similar assemblages from outcrop and subsurface provide a reliable evidence for regional correlation the assemblages in giles 1 are dominated by benthic coccoids and contain many distinct spinose acritarchs which are particularly abundant in the subtidal grey shale whereas mainly phytoplankton is present in the chert the assemblage represented by trachyhystrichosphaera vidalii t aimica cymatiosphaeroides kullingii can be used for global correlation in the early neoproterozoic the abundant microfossils from the alinya formation and equivalent beds around the world probably indicate a microorganism explosion at 750 800 ma prior to the neoproterozoic glaciations thirty seven acritarchs spheroids and seven cyanobacterial filaments are briefly described in this study including 5 new species comasphaeridium tonium eoentophysalis gilesis goniosphaeridium alinyum gorgonisphaeridium pindyium and gorgonisphaeridium torrensium and a newly combined species archaeoellipsoides karatavicus comb nov

hydrogeologic processes in saline systems playas sabkhas and saline lakes abstract pans playas sabkhas salinas saline lakes and salt flats are hydrologically similar varying only in their boundary conditions thus in evaluating geochemical processes in these systems a generic water and solute mass balance approach can be utilized a conceptual model of a coastal sabkha near the arabian gulf is used as an example to illustrate the various water and solute fluxes analysis of this model suggests that upward flux of ground water from underlying formations could be a major source of solutes in the sabkha but contribute only a small volume of the water local rainfall is the main source of water in the modeled sabkha system with a surprisingly large recharge to rainfall ratio of more than 50 the contribution of seawater to the solute budget depends on the ratio of the width of the supratidal zone to the total width and is generally confined to a narrow zone near the shoreline of a typical coastal sabkha because of a short residence time of water steady state flow is expected within a short time 50 000 years the solute composition of the brine in a closed saline system depends largely on the original composition of the input water the high total ion content in the brine limits the efficiency of water rock interaction and absorption because most natural systems are hydrologically open the chemistry of the brines and the associated evaporite deposits may be significantly different than that predicted for hydrologically closed systems seasonal changes in temperature of the unsaturated zone cause precipitation of minerals in saline systems undergoing evaporation thus during the hot dry season months minerals exhibit retrograde solubility so that gypsum anhydrite and calcite precipitate evaporation near the surface is also a major process that causes mineral precipitation in the upper portion of the unsaturated zone e g halite and carnallite provided that the relative humidity of the atmosphere is less than the activity of water the slope of the fresh brine water interface in saline lake systems is shallower than in fresh seawater interface because of the greater density difference between the fresh brine water bodies the interface between sabkha brines and seawater slopes seaward unlike normal marine fresh water systems that slope landward moreover the brine seawater interface does not achieve steady state because it is pushed toward the sea by the sabkha s brine

rb sr and k ar ages on minerals at temperatures of 300 400 c from deep wells in the larderello geothermal field italy rb sr and k ar ages have been obtained on six biotites two muscovites and one hornblende from samples of micaschist gneiss and amphibolite of lower paleozoic to precambrian age at a depth exceeding 2 000 m in basement rocks of the larderello travale geothermal region most of the data cluster in the range 2 5 3 7 ma revealing the existence of a pliocene thermal event to which the origin of the field may be attributed the resulting duration of the larderello geothermal field is unexpectedly long in the basement levels of the two wells examined unstabilized minimum temperatures of 290 and 380 c were measured all the biotites show almost complete 40ar and 87sr retention at the measured well temperatures petrologic evidence stilpnomelane stability and experimental data activation energies and diffusion coefficients also favour a closure temperature above 400 c for rb sr and k ar in biotites in agreement with recent direct experimental determinations

sedimentology and paleoenvironmental evolution of messinian evaporites in the iskenderun hatay basin complex southern turkey abstract messinian evaporites which resulted from the salinity crisis during the final closure of the mediterranean sea are exposed in se turkey these evaporites formed in two isolated sub basins iskenderun arsuz ia and hatay samandag hs which belong to different depositional configurations and tectonic structures the neogene fill of these sub basins consists of a thick sedimentary succession that started with early miocene terrestrial clastics followed by reefs middle miocene and shallow water siliciclastics tortonian early to late miocene and finally messinian evaporates these sub basins accumulated in a diverse range of depositional environments from very shallow to deeper water evaporite facies in the ia sub basin consist of sabkhas saline lagoons and ponds they are mainly represented by chemical deposits such as scattered gypsum nodules and balls nodular bedded gypsum laminated gypsum type a and selenites type s1 evaporites in the hs sub basin mainly consist of detrital gypsum composed of gypsum laminae type b c gypsum arenite rudites and deeper water selenites 20 m and resedimented selenites type s2 which were deposited on a sulfate platform with a slope basin transitional zone secondary gypsum with alabastrine and porphyroblastic textures as well as satin spar veins is commonly associated with the sabkha type evaporites of the ia sub basin deeper water clastic evaporites of the hs sub basin have generally remained as primary gypsum or have only been slightly affected by diagenetic alterations the isotope values 87 86 sr 18 o smow and 34 s cdt from the different kinds of gypsum lithofacies of the sub basin are similar to those of the messinian evaporites in other peri mediterranean basins indicating an origin from marine water without external or basinal contributions the messinian evaporites examined in this paper are overlain by early pliocene zanclean deposits composed of shallow and deep water siliciclastics and carbonates with local intercalations of lago mare type strata throughout the messinian evaporitic stage the ia sub basin was mainly comprised of shallow water evaporites while the hs sub basin underwent deepening related to regional tectonics induced by the dead sea fault during the construction of the hatay graben

trace fossils and rhizoliths as a tool for sedimentological and palaeoenvironmental analysis of ancient continental evaporite successions abstract recognition of evaporite formations from continental tertiary basins of spain provides evidence that trace fossils including rhizoliths can be abundant in some saline lake systems and their study helps in palaeoenvironmental interpretation of ancient continental evaporite sequences six main types of trace fossils have been distinguished and include 1 networks of small rhizoliths 2 large rhizoliths 3 tangle patterned small burrows 4 isolated large burrows 5 l shaped traces and 6 vertebrate tracks rhizoliths were related to both marginal areas of hypersaline lakes and lakes of moderately high saline waters in these settings pedoturbation resulted from colonization by grasses and bushes of distinct lake subenvironments the activity of burrowing invertebrate faunas was especially intense in lakes of moderately concentrated brines from which gypsum was the main evaporite mineral deposited a specific gypsum lithofacies bioturbated gypsum deposits forming thick massive beds has a widespread occurrence in many of the basins tangle patterned small burrows and minor isolated large burrows constitute the typical trace fossil types within the gypsum the traces are interpreted as having been caused by burrowing insect larvae probably chironomids coleopterans and annelids the behaviour of these organisms in recent lake environments yields information about the salinity range of lake waters from which gypsum precipitated concentration values averaging 100 150 g l may be thus deduced though some organisms involved in the formation of the traces can tolerate higher salinities the combined analysis of lithofacies and trace fossils from the lacustrine evaporite sequences contributes to the study of distinct saline lake subenvironments as well as changes in the sedimentary evolution of the lake systems consequently trace fossils can provide valuable insight for palaeoenvironmental analysis of at least some evaporite formations that accumulated in continental settings

cross correlation analysis and information content of observed heads during pumping in unconfined aquifers 1 using a first order cross correlation analysis this paper investigates the relationship between observed heads and hydraulic properties in the saturated and vadose zones at different times and locations of three dimensional unconfined aquifers during pumping tests cross correlation analysis is a weighted sensitivity analysis casted into a stochastic framework it determines the relative impact of each parameter with respect to others in time and space on the observed heads according to uncertainty or spatial variability of each parameter it reveals the information content in measured drawdowns about heterogeneity during a pumping test in an unconfined aquifer which is critical for aquifer parameter estimation based on a synthetic numerical example our cross correlation analysis reveals that heads in the saturated zone at late times carry the greatest nonsymmetrically weighted information content about the hydraulic conductivity ks distribution within the cone of depression on the other hand heads in the saturated zone at early times contain the most information about the specific storage ss heterogeneity in a narrow region between the observation and pumping locations during intermediate and late times heads in the saturated zone largely reflect the effects of saturated water content s and pore size parameter in the thin unsaturated region near the water table above the pumping and observation locations at last heads in the vadose zone at late times carry the greatest information about s and around the observation point

source rock potential of evaporitic environment examination of modern saline lakes solar evaporation ponds and lagoons shows that the evaporitic environment can be very productive of organic matter few species survive in the brines but those that do commonly exist in great profusion in a marine evaporitic embayment the flow of surface currents is persistently toward regions of highest salinity so that there is a continual supply and concentration of nutrients prolific growth of phytoplankton may be similar to that in areas of upwelling in modern oceans only carbonates precipitate in the mesosaline part 4 to 12 salinity of such an evaporitic environment and no great dilution of organic matter by clastic or biogenic sediments occurs because stratification of brine may occur and reducing conditions may be a sociated with the bottom waters much of the organic matter produced can be preserved upon maturation the result may be a rich carbonate source rock frequently unrecognized in the geologic column in the middle east mesosaline conditions are known to have occurred many times from the triassic to cretaceous and may be responsible for the vast reserves of petroleum in the area evaporitic conditions may also have played a part in the petroleum productivity of many other areas including the michigan and paradox basins

boiling and fluid mixing in the chlorite zone of the larderello geothermal system abstract the geochemical features of the geothermal fluids produced within the boiling zone in the relatively shallow parts of the larderello geothermal system italy have been documented as a result of deep drilling which provided samples from 1480 to 2500 m depth four wells monteverdi 1 monteverdi 2a sasso 22 and capannoli 2b have been sampled in the intermediate parts of the larderello aquifer located in a metamorphic basement underlying the tertiary nappe complex which constitutes the shallow aquifer at larderello fluid inclusions from recrystallized quartz lenses and quartz veins in samples displaying a predominant quartz chlorite epidote adularia paragenesis have been studied by microthermometry and raman spectroscopy the inclusions are primary and pseudo secondary in origin when formed in authigenic quartz or of secondary origin when located in fluid inclusion planes related to microfracturing of metamorphic quartz lenses several generations of fluids are present and include h 2 o co 2 dominated vapours and liquids and a series of aqueous liquids for the most part of relatively low salinity the t m ice of both early and late inclusions are mostly between 0 0 and 4 5 c indicating that the salinities of the hydrothermal fluid were very low to moderate however rare fluid inclusions with lower t m ice from 4 9 to 25 0 c were also observed these inclusions may record the occasional input of saline fluids which may be derived from the interaction of the hydrothermal waters with the evaporites present in the shallow part of the larderello field at capannoli 2b earliest h 2 o co 2 liquids were trapped under minimal pressures of 610 645 bars which bracket the estimated present day lithostatic pressure 640 bars in all other samples the main stage of quartz chlorite crystallization occurs under boiling conditions attested by the presence of liquid and vapour rich inclusions that in some instances can be texturally interpreted to be coeval their trapping conditions 350 375 c 160 215 bars are higher than the present day temperatures at the same depth later fluid inclusions attest to a significant cooling of the fluids down to temperatures similar to the present day temperatures during this time pressures were close to hydrostatic conditions most fluid inclusions were trapped within the liquid field this indicating that a significant pressure drop has since affected the main aquifers or fractured zones which are at present under vaporstatic conditions

evolving fluvial architecture during a marine transgression upper buntsandstein triassic central spain abstract the sedimentation in central spain during the late anisian middle triassic limos y areniscas de rillo formation recorded the evolution from an alluvial environment into a coastal one with a diversity of environments this evolution was the result of one of the episodes of the tethys sea transgression over iberia during the first and second stages of this evolution mixed load low sinuosity channels evolved upwards into a distal braidplain with ephemeral run off and poorly defined channels during a third stage the characteristics of the sediments indicate the existence of both continental and marine waters in a transitional zone with seasonal hydrological fluctuations the fourth stage records the sedimentation in an upper intertidal to supratidal environment in a semiarid coastline with the presence of thin cryptalgal sheets and chicken wire textures the final evolution consists of an environment with a high percentage of fluvial channel deposits probably related to a meandering pattern this evolution has been correlated with the depositional sequences established for the ne of spain where the anisian transgressive event resulted in the formation of an inter to supratidal carbonate ramp so lowstand transgressive and highstand system tracts from depositional sequence 1 have been recognized in the centre of spain

thermal aureoles of igneous intrusions some possible indications of hydrothermal convective cooling the size and shape of metamorphic aureoles is investigated as a possible indicator of hydrothermal convective cooling of epizonal igneous intrusions a simple family of numerical models illustrates the effect of convective cooling on maximum temperatures attained in the country rock surrounding an intrusion boundary layer approximations have also been applied to describe convection of vaporizing groundwater near the contact of an intrusion early in its cooling history maximum temperature isotherms are taken to reflect the width and shape of thermal aureoles defined by preserved mineral assemblages as appears to be reasonable based on several well studied conductively cooled intrusions the thermal aureoles of intrusions for which oxygen and hydrogen isotope data indicate convective groundwater circulation have been examined on the basis of the simple numerical and boundary layer models the shape of the low temperature alteration aureole of the well mapped el salvador porphyry copper deposit suggests co

a much warmer earth surface for most of geologic time implications to biotic weathering the authors present two scenarios for the temperature history of earth one scenario is conventional the other relies on a warmer history both scenarios include surface cooling determined by the evolution of the biosphere and are similar until the proterozoic period the warmer scenario requires a higher plant lichen terrestrial biota to increase weathering intensity justification for a warmer surface includes period temperatures from the oxygen isotope record of coexisting phosphates and cherts an upper limit of 58 degrees c from primary gypsum precipitation and the lack of fractionation of sulfur isotopes between sulfide and sulfates in archean sediments

determination of the effective hydraulic conductivity for heterogeneous porous media using a numerical spectral approach 1 method using the numerical spectral method described in the companion paper dykaar and kitanidis this issue the effective conductivity of a three dimensional isotropic stationary lognormally distributed hydraulic conductivity is computed six cases were investigated for variances in log conductivity ranging between 1 and 6 the results show that averaging volumes of at least 30 integral scales are required before the effective conductivity reaches its asymptotic value the results support matheron s 1967 hypothesis that ke kg exp y2 6 where ke is the effective hydraulic conductivity and kg and y2 are the geometric mean and variance respectively of the hydraulic conductivity field we also find that for a gaussian covariance function heterogeneities smaller than about 1 3 integral scales do not significantly contribute to the effective conductivity in two dimensions averaging volumes of more than 80 integral scales are required before the effective conductivity reaches the analytic infinite domain result of the geometric mean while the effective conductivity is insensitive to heterogeneities less than 2 integral scales in size the method is also applied to data from a shale and sandstone formation and the results are compared with those from other methods

classification and depositional environments of quaternary pedogenic gypsum crusts gypcrete from east of the fayum depression egypt abstract the eastern boundary of the fayum depression 45 m below sea level is bounded by a 99 m high hill inselberg of girza that slopes gently eastward towards the nile valley the inselberg and the surrounding plain are encrusted with 50 130 cm thick gypsum crusts that exhibit well defined pedogenic horizons also east of the nile valley the qattamia plateau is encrusted with gypsum crusts that form 50 m wide pavements that are scattered at different levels the gypsum crusts range in thickness from 20 to 50 cm and do not form characteristic vertical horizons the individual gypcrete pavements exhibit massive mottled or powdery structure using structural fabric and textural criteria three main types of crusts are distinguished 1 eluvial horizon massive to spongy like powdery gypsum crusts found at the land surface and consisting of gravels and sands cemented with gypsum 2 illuvial horizon a massive indurated gypsum crusts that consist dominantly of white gypsum with horizontal and sub vertical black gypsum veinlets 3 illuvial horizon b massive mottled gypsum crusts that consist of carbonate or shale fragments floating in gypsum cement petrographically the gypsum crusts in the girza and qattamia areas comprise a varying abundance of microcrystalline fine lenticular coarse lenticular porphyroblastic prismatic or poikilotopic gypsum lenticular and microcrystalline gypsum crystals are usually observed filling rhizotubules in all crusts the origin of the gypsum crusts is related to pedogenic processes which involved the leaching of gypsum from the underlying or adjoining gypsiferous shale or marl layers and the subsequent displacive crystallization of gypsum in the upper soil horizon cycles of wetting rain fall and drying are believed to account for the dissolution and translocation of gypsum from the upper eluvial horizon and its recrystallization as microcrystalline and fine lenticular gypsum in the illuvial horizon a the poikilotopic gypsum crystals in the illuvial horizon b reflect the abundance of gypsum enriched groundwater in the phreatic zone the dominant processes of gypsum growth are by displacive and or inclusive crystallization reflecting formation in pedogenic setting the existence of gypsum crusts capping the inselberg and the surrounding plain of girza area resist eastward deepening of the fayum depression on the other hand the gypsum crusts on the surface of the qattamia plateau favor the development of relief inversion due to the removal of the surrounding soft materials therefore the gypsum crusts provide useful paleoclimatic and geomorphic indicators to the study areas