distinguishing climatic and tectonic signals in the sedimentary successions of marginal basins using sr isotopes an example from the messinian salinity crisis eastern mediterranean the evolution of oceanic 87 sr 86 sr through the tertiary has been sufficiently well documented to provide a useful stratigraphic tool for carbonate rich marine sediments which were deposited in basins connected to the global oceans in isolated basins sea water 87 sr 86 sr will diverge from coeval oceanic values thus if independent age information exists the geochemical signature can constrain the timing of isolation in marginal basins formed in tectonically active settings the timing of isolation is critical to the assessment of the relative importance of climate or tectonic controls on that event previously isolation has been assumed to coincide with the last occurrence of open marine fauna however in an example from the eastern mediterranean 87 sr 86 sr data challenge that assumption and can be interpreted as indicating a protracted period of isolation c 3 ma during which time marine conditions prevailed prior to the messinian salinity crisis at the end of the miocene this allows tectonic and climatic signals to be distinguished since although convergence of africa with eurasia was responsible for isolation of this part of the mediterranean it is more likely that later climatic change triggered desiccation

changing perspectives in the concept of lago mare in mediterranean late miocene evolution abstract the cenozoic alpine orogeny caused the partition of tethys into several basins during the late neogene the mediterranean attained its final configuration whereas eastwards the paratethys isolated from the world ocean disintegrated progressively into a series of smaller basins as a result an endemic fauna developed in these basins mainly composed of brackish to freshwater faunas indicating an environment affected by changes in water salinity these small basins of the paratethys were named sea lakes by andrusov andrusov d 1890 les dreissenidae fossiles et actuelles d eurasie geol min 25 1 683 in russian subsequently this name was translated into lac mer gignoux m 1936 geologie stratigraphique 2 edition masson paris in the mediterranean isolated from the atlantic at the end of the miocene messinian thick evaporites deposited consisting of a marine lower evaporite unit and an upper evaporite unit mainly of continental origin ruggieri ruggieri g 1962 la serie marine pliocenica e quaternaria della val marecchia atti acad sci lett arti palermo 19 1 169 used the term lago mare to characterize the brackish to fresh water environment which occurred within the mediterranean at the end of the messinian during recent decades numerous scientific investigations concerning the history of the messinian within the mediterranean were devoted to the understanding of conditions prevailing after the deposition of the marine evaporites brackish to freshwater faunas are found in several outcrops and boreholes in the mediterranean both in the uppermost beds of gypsum and inter bedded within the clastic sediments of the upper evaporite unit immediately preceeding the flooding by the marine pliocene waters these faunas because of their similarities with the fauna described in the paratethys were named paratethyan or caspi brackish fauna this leading some authors to imply a migration of these fauna from paratethys to the mediterranean however others refute this hypothesis new data induced some researchers to consider that exchanges existed between the mediterranean and the eastern paratethys and also between the mediterranean and the atlantic ocean at the miocene pliocene transition these investigations now take advantage of the accurate time scales established by authors biostratigraphy cyclostratigraphy magnetostratigraphy allowing good stratigraphic correlations between the mediterranean and the paratethys and precisions on the geodynamic evolution of this area furthermore sediments at the base of the zanclean mpl1 locally containing brackish to fresh water faunas conducted authors to attribute this formation to an infra or pre pliocene and also to a lago mare event thus the lago mare concept drifted from its original meaning and is evolving because of progresses in the understanding of the mediterranean geodynamics and the adjacent areas during the miocene pliocene transition

modelling the effect of evaporation on the salinity 87 sr 86 sr relationship in modern and ancient marginal marine systems the mediterranean messinian salinity crisis abstract palaeosalinity reconstructions in marginal marine environments based on sr isotope data assume simple two end member mixing of river and ocean water an improved model that incorporates the effect of evaporation is used to demonstrate that this approach is not valid in evaporation dominated systems however sr isotope records combined with faunal and lithological constraints on salinity can be used to assess the palaeohydrological conditions of ancient marginal marine systems this new method is used to interpret deviations from the global seawater sr isotope curve observed in mediterranean successions during and up to 3 myr prior to messinian evaporite deposition results suggest that no absolute change in the net evaporation flux is required to explain the three to four fold rise in salinity of mediterranean water at the carbonate evaporite transition modelled sr isotope records indicate that this increase in salinity was synchronous with an increase in the dominance of atlantic water inflow in the hydrological budget of the mediterranean the messinian salinity crisis may therefore have been the response to a marine transgression

evaporites and siliciclastics of the permian nippewalla group of kansas usa a case for non marine deposition in saline lakes and saline pans the mid permian nippewalla group of kansas consists of bedded evaporites red bed siliciclastics and grey siliciclastics deposited in a non marine environment lithologies and sedimentary features indicate lacustrine and aeolian deposition subaerial exposure and palaeosol formation grey siliciclastic mudstones characterized by planar and convolute laminations ostracods peloids and plant material represent a freshwater brackish perennial lake facies bedded anhydrites containing gypsum crystal pseudomorphs clastic anhydrite grains and grey mud drapes and partings suggest deposition in saline lakes bedded halites consist of chevron and cumulate crystals dissolution surfaces and pipes and mudcracked microcrystalline salt crusts which were deposited in saline pans dominated by flooding evaporative concentration and desiccation chaotic halite composed of red bed mudstone and siltstone with displacive halite crystals formed in saline mudflats red bed mudstone and siltstone with little or no displacive halite but with abundant cracking root and plant features suggest deposition in a dry mudflat red bed sandstone composed of well sorted well rounded quartz grains cemented with halite indicate aeolian and rare shallow water deposition most deposition took place in halite dominated ephemeral saline lakes surrounded by saline and dry mudflats sandflats and sand dunes evaporation desiccation flooding and wind played significant roles in this environment the nippewalla group siliciclastics and evaporites represent an evolution from a perennial lacustrine system to a non marine acidic saline pan system in the mid continent of north america the problem of distinguishing between ancient marine and non marine evaporites as well as recognizing those evaporites deposited in acid settings with detailed field core and petrographical study of both evaporite deposits and associated sedimentary rocks has successfully been addressed in addition interpretations of mid permian palaeoclimate data in the form of short term air temperature proxies within longer term wet dry trends have been made these data provide a new palaeogeographic and palaeoclimatic model for the mid permian of western pangaea

no tectonic rotation of the tuscan tyrrhenian margin italy since late messinian extensive paleomagnetic sampling of 38 late miocene and pliocene sites has been carried out in the western tuscan basins in italy these basins are located along the tyrrhenian margin and the studied formations were deposited at the same time as the opening of the tyrrhenian sea the laboratory analyses show that in most of the sites pseudo single domain magnetites are the main magnetic carrier the paleomagnetic data obtained from 27 suitable sites indicate that the tuscan tyrrhenian margin has not been affected by significant regional rotation since at least the late messinian early pliocene about 5 5 m y these data demonstrate that the rotations previously measured in the meso cenozoic units of the apennines and of the apulia foreland cannot be directly related to the late messinian pliocene phases of rifting in the tyrrhenian sea moreover the data presented here conflict with published results from coeval formations in the apennines and sicily in areas subjected to strong thrusting and shortening in these areas the rotations control the orientation of the main compressional structures and give rise to the typical arcuate shape of the apenninic chain we suggest that the tectonic evolution of the northern tyrrhenian sea apenninic chain system involved thrusting and shortening of the external eastern domains with rotations of the allochthonous units followed by gravitational collapse of the western sector this second phase involved no tectonic rotation of the newly formed extensional basins

the mediterranean mare nostrum of earth sciences the mediterranean area is one of the most appealing natural laboratories in the world to study geodynamic and paleoclimatic processes on different scales consequently the mediterranean sea can be considered as the mare nostrum our sea of earth sciences its semi enclosed land locked configuration in a convergent setting between africa in europe in combination with its latitudinal position makes the mediterranean extremely suitable to study both fundamental plate tectonic processes and astronomically induced oscillations in climate for many years to come the mediterranean will certainly remain a fascinating area where an integrated and multi disciplinary approach will increasingly contribute to our understanding of geological geophysical geodetical and geochemical processes in an accurate and high resolution time frame

the messinian post evaporitic deposits of the gafares area almeria nijar basin se spain a new view of the lago mare facies abstract the exceptional exposures of the evaporitic and post evaporitic messinian deposits in the gafares area ne almeria nijar basin se spain make it possible to elucidate those processes affecting this region during the critical period of the messinian salinity crisis the contact between the pre evaporitic and the evaporitic units is an erosional unconformity the transition from the evaporitic to the post evaporitic units is gradual since the gypsum beds of the evaporitic unit thin upward and the siliciclastic interbeds concomitantly thicken thus passing gradually to the overlaying post evaporitic unit the presence of globorotalia miotumida group in the last pelitic intercalation of the evaporitic unit as well as throughout the post evaporitic one indicates a messinian age the post evaporitic unit consists of a variety of sediments formed in continental and marine settings continental facies are characterised by fluvial channel filled conglomerates and alluvial plain sands and silts marine sediments are represented by silty marls with foraminifers a river dominated delta developed in the transitional zone at the nw edge of the gafares area localised fan delta deposits coming from the ese also occur in the southeastern part of the study area microbial carbonates locally colonised the fan delta conglomerates during the deposition of the lower half of the post evaporitic unit sedimentation took place in a sheltered embayment with restricted water circulation and relatively isolated from the mediterranean sea by an e w trending sill located at the south of the study area in this palaeogeographic context freshwater influx from the delta exerted a certain influence on the distribution of microorganisms thus brackish settings developed close to the river outflows that were occupied by caspibrackish ostracod assemblages the presence of gastropods of the family cerithiidae as well as fishes attributable to the genus aphanius organisms that preferentially inhabit sheltered lagoons is consistent with these settings beyond the freshwater influx foraminifers dominated the microfossil assemblages in the upper half of the post evaporitic unit microfossil assemblages dominated by planktonic forms are consistently found thus revealing a better connection of the semi enclosed gafares area with the marine domain this is related to the deepening of the sill due to a progressive rise of the sea level the continental and brackish deposits zorreras like facies have been equated with the lago mare facies which were supposed to spread throughout the whole mediterranean at the end of the messinian nevertheless in the gafares area these deposits change laterally to and interbed with marine deposits this stratigraphic architecture and facies relationship has two important implications on the one hand marine waters at the latest messinian occupied at least the western mediterranean predating the long claimed early pliocene deluge on the other hand the continental brackish lago mare facies were spatially restricted as a consequence neither the presence of the caspibrackish ostracods nor the continental brackish facies can be plausibly taken to support the hypothesis that widespread lago mare facies occupied the whole mediterranean synchronously at the end of the messinian therefore this type of facies is expected to be found albeit with varying degrees of development in marginal basins at different times but not throughout the mediterranean

successive pore fluid generations in a lower permian brine aquifer palo duro basin texas panhandle u s a abstract the successive presence of four compositionally distinct pore fluids in lower permian carbonate strata of the palo duro basin texas panhandle is interpreted from 1 lithological minerlogical and petrographic evidence for depositional conditions 2 isotopic compositions of c o and sr in limestone and dolomite 3 limited data on fluid inclusions in sphalerite and 4 chemical and isotopic analyses of formation water wolfcamp carbonate mudstone containing normal marine fauna was initially deposited on an open shallow shelf the c and o isotopic compositions indicate precipitation from permian seawater with minor terrestrial and meteoric influence sr isotopic compositions document a leonardian seawatersource of material conditions gradually became more restricted and seawater was concentrated by evaporation resulting in deposition of penecontemporaneous dolomite and anhydrite in overlying wichita strata reflux of wichita brine dolomitized underlying wolfcamp carbonate mudstone and generated the upper wolfcamp aquifer isotopic compositions of sr in wolfcamp dolomite suggest that the reflux brine was evaporatively concentrated leonardian seawater expulsion of warm saline formation water from deeper in the basin through the upper wolfcamp aquifer is recorded in fluid inclusions in sphalerite this change in pore fluid composition occured before and during regional tertiary uplift and tilting of the texas panhandle more recently meteoric water has recharged at least the western one third of the upper wolfcamp aquifer this modern flow regime was established within the past 10 15 ma

assessing effects of sulfate minerals on petroleum generation in sedimentary basins using hydrous pyrolysis i light alkanes abstract a series of hydrous pyrolysis experiments were conducted to assess the role of sulfate minerals on the chemical and isotopic compositions of light hydrocarbons generated during thermal degradation of kerogen the shale source rock with low maturity tmax 425 c from eagle ford formation in southeast texas was used in the experiments at 330 c for the duration of 72 h while the abundance of gypsum in each experiment varies from 0 0 5 to 1 wt under experimental conditions the positive effect of gypsum on the yields of gaseous alkanes c1 c4 and co2 has been explicitly observed with an exponential relationship between the yield of each gas and the amount of gypsum while the relative abundance of c2 c4 alkanes has shown an increasing trend with gypsum the gas dryness c1 c1 4 however decreased from 73 1 with no gypsum to 49 6 with gypsum of 1 wt it was attributed to lower overall yields and corresponding higher increased generation rates of c2 c4 alkanes than methane through thermal cracking of kerogen and other organic compounds the carbon isotope value of each alkane reached the highest in the experiment with 1 wt gypsum compared to the experiment without gypsum there was an increase of 11 5 for the 13c value of methane with 1 wt gypsum the extent of this 13c enrichment between experiments with different amount of gypsum became less for c2 to c4 the 13c value of co2 was the highest among generated gases ranging from 4 7 to 2 1 combined with chemical compositions of gases it suggested that enhanced thermal cracking reactions were predominant in generation of light alkanes with the presence of gypsum whereas dissolution of carbonates was the main source of co2 the reactions involving thermochemical sulfate reduction tsr were minor if present under experimental conditions most likely due to the small quantity of gypsum up to 1 wt and neutralization of acidity by carbonates nonetheless the changes in chemical and isotopic compositions of light alkanes which were ultimately caused by the presence of gypsum need to be incorporated into geochemical proxies for assessing source rocks maturation in particular and their generation potential

correlation of late miocene to early pliocene sequences between the mediterranean and north atlantic ocean drilling program odp site 982 in the north atlantic contains a complete latest miocene to early pliocene section that was tuned to the astronomical timescale by correlating the record of gamma ray attenuation gra bulk density to summer insolation at 65 n and the benthic 18o signal to orbital obliquity for the interval from 4 6 to 7 5 ma the astronomical tuning of the site 982 record permits a direct bed to bed correlation to the cyclostratigraphy of messinian sections in the mediterranean krijgsman et al 1999a 2001 the benthic 18o signal at site 982 records a latest miocene glacial period that lasted from 6 26 to 5 50 ma and consisted of 18 glacial to interglacial oscillations that were controlled by the 41 kyr cycle of obliquity although the intensification of glaciation at 6 26 ma may have contributed to the restriction of the mediterranean it preceded the depositional onset of the lower evaporite unit at 5 96 ma by some 300 kyr the transition from stage tg12 to tg11 at 5 5 ma marks the end of the latest miocene glacial period and precedes the miocene pliocene boundary by 170 kyr although benthic 18o values are relatively low and 18o of bulk carbonate reaches a minimum at the miocene pliocene boundary at 5 33 ma there is no single event that would indicate deglaciation and sea level rise as the cause of the reflooding of the mediterranean we conclude that glacioeustatic changes alone were not responsible for either the start or end of evaporite deposition during the messinian suggesting that tectonic or local climate changes in the mediterranean region were the dominant cause s

diagenetic origin of basal anhydrite in the cretaceous maha sarakham salt khorat plateau ne thailand development of a diagenetic anhydrite bed at the base of the cretaceous maha sarakham saline formation the basal anhydrite member of the khorat plateau in north eastern thailand took place due to leaching and or pressure dissolution of salt at the contact between an underlying active sandstone aquifer system and an overlying massive halite dominated evaporite sequence basal evaporites composed of halite with intercalated anhydrite of the latter sequence are undergoing dissolution as a result of subsurface flushing with anhydrite produced as the insoluble residue the result is a 1ae1 m thick interval of nodular anhydrite displaying unique basin wide continuity observed textures petrographic features and chemical data from the anhydrite and associated authigenic minerals support the origin of the basal anhydrite member as an accumulation residue from the dissolution of the maha sarakham salts petrographically the anhydrite in this unit is made up of crystals that are blocky and recrystallized sheared generally elongated and broken and is bounded at the bottom by organic rich stylolite surfaces authigenic and euhedral dolomite and calcite crystals are associated with the anhydrite traces of pyrite galena and chalcopyrite are present along the stylolite surfaces suggesting supply of fresh water from the underlying sandstone at highly reducing conditions of burial the d 34 s of sulphate in the basal anhydrite averages 15 cdt and falls within the isotopic composition of the anhydrite in the cretaceous maha sarakham formation proper and the cretaceous values of marine evaporites measured d 18 o in dolomite range from 4ae37 to 14ae26 pdb suggesting a re equilibration of dolomite with basinal water depleted in 18 o and possible recrystallization of dolomite under relatively elevated temperatures the d 13 c however varies from 1ae57 to 2ae53 pdb suggesting a contribution of carbon from oxidation of organic matter this basal anhydrite bed similar to basinwide beds found at the bottom of many giant evaporite sequences has always been considered to be depositional here at the base of the maha sarakham formation we demonstrate that the anhydrite is diagenetic in origin and was formed by accumulation of original anhydrite by dissolution of interbedded halite from waters circulating though the underlying aquifer it represents an upsidedown caprock

late miocene stable isotope stratigraphy of se atlantic odp site 1085 relation to messinian events abstract high resolution benthic oxygen isotope and xrf fe and ca records from site 1085 drilled in the mid cape basin odp leg 175 are used to investigate global climate changes during the late miocene in relation to messinian geological events the cyclic fluctuations of the time series at site 1085 enable us to establish a reliable chronology for the time interval 7 3 4 7 ma spectral analysis of the 18o record indicates that the 41 kyr period of orbital obliquity dominates the late miocene record a global climate record was extracted from the oxygen isotopic composition of benthic foraminifera both long and short term variabilities in the climate record are discussed in terms of sea level and deep water temperature changes the time interval 7 3 6 25 ma characterized by low amplitude 18o variations is followed by a period marked by maximum in the 18o values 6 25 5 57 ma at about 5 56 ma a rapid decrease in 18o values is documented that may reflect a warming of deep water temperature associated with a global warming period comparison between the timing of the oceanic isotope events and the chronology of the mediterranean salinity crisis suggest that global eustatic processes were not essential in the mediterranean salinity crisis history from our data we infer that the global warmth documented in the early mid pliocene probably started during the late miocene at 5 55 ma at the same time the onset of evaporite deposition in the central basin of the mediterranean sea took place sharp changes in the sedimentation rates mainly driven by terrigenous input at this site are observed during the messinian stage

coastal sabkha and salt pan deposition of the lower clear fork formation permian texas abstract middle permian leonard series evaporites carbonates and red beds of the lower clear fork formation in the texas panhandle display many features common to modern coastal and continental sabkha facies similarities among lithofacies patterns and sequences sedimentary structures and anhydrite halite textures and fabrics of both the lower clear fork formation and modern sabkha facies permit construction of a model of halite deposition in coastal sabkha salt pan environments which may be generally applicable to other ancient sabkha facies in intracratonic basins and around stable or rifted continental margins inferred coastal sabkha and marine inner shelf environments and lithofacies recognized in the lower clear fork formation are largely based upon analogous modern depositional se tings and include the following 1 red siltstone to mudstone deposited in a wadi or desert alluvial eolian plain and inner sabkha mud flats both passing basinward into 2 chaotic mudstone halite of an inner sabkha saline mud flat which flanked 3 inner sabkha salt pans bearing banded to massive halite and laminated anhydrite and 4 nodular nodular mosaic and massive anhydrite and dolomite deposited in marginal sabkha and inner shelf environments salt pans may have formed in the inner sabkha as a result of displacive gypsum anhydrite growth and jacking up of the marginal sabkha surface which impeded seaward drainage of floodwater off the sabkha modern process sediment analogs include alluvial fans saline mud flats and salt pans of the coastal sabkhas in baja mexico the trucial coast and kutch india evaporites and terrigenous clastics in bristol dry lake california exhibit many features analogous with the permian suggesting that this setting though strictly continental serves as a process analog bromide values in lower clear fork halite average 40 ppm which is less than an unaltered marine halite but still within the range of marine halite that has undergone diagenesis upward decreasing values in the lower clear fork upper cycle may indicate a decrease in salinity during deposition or that the younger halite beds suffered more diagenesis than the underlying halite

displacive halite hoppers from the dead sea some implications for ancient evaporite deposits abstract large hopper shaped halite cubes up to 10 cm on a side grow displacively within holocene sediments near the southern end of the dead sea under conditions of high temperatures ionic concentrations and rapid rates of crystallization two theories of formation are presented downward diffusion of ions versus upward diffusion and evaporative pumping both alternatives are considered possible and the correct choice probably depends upon the location of the sediments at the time of precipitation whether subaqueous or subaerial a choice indeterminate at present because of human disturbance to the sediments prior to collection displacively formed halite crystals similar in morphology to the dead sea cubes are common in evaporite bearing carbonate rocks of many regions such as the salina fm u silurian michigan basin the kirkham mudstone u triassic cumbria england and the u miocene gessoso solfifera fm of sicily these are believed to have formed under conditions analogous to those in the present dead sea these observations taken together with those of other authors may now be used for the facies interpretation of ancient halite deposits

structural collapse in kaolinite montmorillonite and illite clay and its role in the ceramic rehydroxylation dating of low fired earthenware the rehydroxylation dating of ancient pottery estimates the age of ceramic manufacture based upon the total hydroxyl oh accumulation since initial firing the diffusion of oh is impacted by the structural porosity of the ceramic that becomes progressively or suddenly closed with increasing temperature as the clay structure collapses changes in ceramic mineral structure along the temperature continuum occur at certain thermal set points infrared spectroscopic analysis of heat treated kaolin illite and montmorillonite reveals that shifts in the si o band correlate with the extent of structural collapse occurring between 600 and 1000 c accelerated rehydroxylation experiments reveal that the activation energy of rehydroxylation decreases with greater structural collapse and indicates that the rate of rehydroxylation will be faster for ceramics fired at more elevated temperatures

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

lithofacies and faunal succession faunal phase analysis as a tool in unravelling climatic and tectonic signals in marginal basins messinian miocene sicily many basins are filled under the influence of tectonics and variable climatically driven processes unravelling the relative contributions of these is generally easier in fossiliferous sequences if faunal diversity patterns are considered in conjunction with lithofacies analysis this approach has been successfully applied to late miocene strata of sicily where progressive restriction and desiccation within the sicilian caltanissetta region occurred under a semi arid climate during the messinian stage this restriction was partly due to antarctic cooling which produced palaeo mediterranean sea level oscillations during the early messinian as a prelude to closure of the atlantic connections in addition regions within this afro european plate collision zone were also subjected to syndepositional tectonic deformation associated with progressive perched basin development above foreland south verging thrust sheets the relative impacts of climatic eustatic versus tectonic control on sedimentation patterns within these perched basins has been debated at length however progress towards resolving this problem by a combined approach involving lithofacies analysis and faunal phase analysis provides clues for separating the effects of the controlling factors faunal phase analysis identifies general faunal associations with minimal emphasis on species diversity the resulting phase plots for early messinian strata appear to be transgression skewed when controlled by eustatic cyclicity and regression skewed when driven by regional tectonics associated with perched basin tectonics

a sulfur and strontium isotopic investigation of lower permian anhydrite palo duro basin texas u s a abstract lower permian wolfcamp and wichita carbonates and anhydrites palo duro basin texas panhandle record a change from a normal marine to marine evaporite depositional environment isotopic compositions of s and sr in anhydrite were determined to investigate the age of wolfcamp and wichita strata and the paragenesis of eight anhydrite forms bedded nodular mosaic wichita and replacive nodular wolfcamp anhydrites have s and sr isotopic compositions that record precipitation from early permian wolfcampian to leonardian seawater silicified nodular coarsely crystalline nodular fossil filling and vein filling anhydrites have enriched s isotopic compositions relative to permian seawater whereas euhedral and anhedral replacive anhydrites have depleted s the sr isotopic composition of most anhydrite forms indicates an early permian marine origin however sr in anhydrite veins is slightly radiogenic compared to permian seawater the sr isotopic compoition of bedded nodular mosaic anhydrite indicates as leonardian seawater source of material the 34 s values are slightly enriched relative to values predicted from the s age curve suggesting an excursion of the s isotopic evolution trend of early permian seawater replacive nodular anhydrite 87 sr 86 sr ratios are slightly higher than those of bedded nodular mosaic anhydrite reflecting incorporation of sr from older marine pore waters or replaced sediments or from dissolution of detrital siliciclastic minerals anhydrite paragenesis is interpreted from stratigraphic mineralogic petrographic and isotopic data bedded nodular mosaic and replacive nodular anhydrite precipitated as marine evaporite strata prograded across underlying normal marine carbonate sediments siliified and coarsely crystalline nodules and anhydrite fossil filling precipitated at essentially the same time as bedded and replacive nodular anhydrite but in environments where sulfate reduction was more extensive euhedral anhedral replacive anhydrite formed in shallower environments where s redox cycling occurred prior to caso 4 precipitation anhydrite vein fills formed last and incorporated radiogenic sr released during alteration of detrital siliciclastic grains

no major deglaciation across the miocene pliocene boundary integrated stratigraphy and astronomical tuning of the loulja sections bou regreg area nw morocco 1 an integrated high resolution stratigraphy and orbital tuning is presented for the loulja sections located in the bou regreg area on the atlantic side of morocco the sections constitute the upward continuation of the upper messinian ain el beida section and contain a well exposed continuous record of the interval straddling the miocene pliocene m p boundary the older loulja a section which covers the interval from 5 59 to 5 12 ma reveals a dominantly precession controlled color cyclicity that allows for a straightforward orbital tuning of the boundary interval and for detailed cyclostratigraphic correlations to the mediterranean the high resolution and high quality benthic isotope record allows us to trace the dominantly obliquity controlled glacial history our results reveal that the m p boundary coincides with a minor partly precession related shift to lighter interglacial values in d18o this shift and hence the m p boundary may not correlate with isotope stage tg5 as previously thought but with an extra weak obliquity controlled cycle between tg7 and tg5 consequently the m p boundary and basal pliocene flooding of the mediterranean following the messinian salinity crisis are not associated with a major deglaciation and glacio eustatic sea level rise indicating that other factors such as tectonics must have played a fundamental role on the other hand the onset of the upper evaporites in the mediterranean marked by hyposaline conditions coincides with the major deglaciation step between marine isotope stage tg12 and tg11 suggesting that the associated sea level rise is at least partly responsible for the apparent onset of intermittently restricted marine conditions following the main desiccation phase finally the loulja a section would represent an excellent auxiliary boundary stratotype for the m p boundary as formally defined at the base of the trubi marls in the eraclea minoa section on sicily

reconstruction of the paleoenvironmental changes around the miocene pliocene boundary along a west east transect across the mediterranean abstract in order to reconstruct the environmental changes at the end of the messinian salinity crisis a multidisciplinary study has been carried out with a high sampling resolution of the late messinian early zanclean zone mpl 1 sediments along a west east mediterranean transect the studied examples comprise sections from southern spain vera almanzora balearic basin odp site 975 tyrrhenian basin odp site 974 sicily eraclea minoa zakynthos kalamaki corfu aghios stefanos crete aghios vlasis previously analyzed sections from the levantine basin cyprus and odp sites 968 and 969 are used for comparison the sections have been correlated using planktonic foraminiferal assemblages sedimentological and stable isotope variations and compared to the astronomical cyclicity defined in the miocene pliocene boundary stratotype of eraclea minoa sicily variations of caco3 content stable isotopes of carbonates 18o 13c and foraminiferal assemblages indicate similar environmental transition at the miocene pliocene boundary in all of the investigated sections the latest messinian deposits are barren of fossils or characterized by only reworked planktonic foraminifers except for the sporadic presence of ammonia tepida brackish or lacustrine ostracods and brackish mollusks typical of the lago mare facies the oxygen and carbon isotopic compositions of carbonates usually exhibit large variations with dominantly low values indicating freshwater dilution the earliest pliocene mpl 1 cycle 1 shows a rapid and progressive increase of the 18o values which indicates the restoration of marine conditions after the lago mare event normal marine environments were definitely established and stabilized at the top of cycle 1 these data confirm that the inflow of marine waters occurred contemporaneously within the whole mediterranean at the base of pliocene although stable marine conditions occurred only about 20 kyrs later

and ratios in skeletal calcite of mytilus trossulus covariation with metabolic rate salinity and carbon isotopic composition of seawater minor element and isotopic compositions of marine bivalve calcite are frequently used as proxy records of seawater temperature and salinity although molluscan calcite is secreted at or near oxygen isotope equilibrium the influence of metabolic activity i e vital effects on skeletal srca ratios and 13c values is not well known we present measurements of skeletal chemistry from a consecutive samples milled in chronological order from the organism s final year of growth and b adjacent samples within three separate growth bands of the marine mussel mytilus trossulus to investigate chemical disequilibrium effects among different parts of the shell seawater temperature and salinity were monitored for one year at squirrel cove british columbia at the end of the year a young rapidly growing mussel mussel a and an old slowly growing mussel mussel b were harvested from this site growth bands within the shells were sampled to provide a chronological record of shell carbonate chemistry results from consecutive samples show 1 a significantly higher average srca ratio in mussel a than that in mussel b and 2 13c values that correlate well with salinity in mussel a but not in mussel b results from time equivalent adjacent samples show 1 higher srca and 13c values near the ventral margin than at time equivalent regions on lateral margins of the shell and 2 little or no variation in 18o values these observations suggest that skeletal chemistry srca and 13c is primarily controlled by rate of mantle metabolic activity and secondarily modified by variation in seawater salinity because metabolic activity in the mantle at the site of carbonate precipitation varies with shell curvature the composition of calcite secreted along lateral margins is influenced to a greater extent by metabolic activity than calcite secreted coevally at the central margin of the shell hence the chemistry of calcite secreted at the ventral margin is precipitated in near equilibrium with seawater and allows accurate estimation of seawater srca ratios and carbon isotopic composition in contrast shell precipitation along lateral margins is dominantly controlled by metabolic activity and calcite chemistry is not in equilibrium with ambient seawater in this context we present a biomineralization model where variations in skeletal srca and 13c values are explained in the context of mantle metabolic activity and seawater salinity

biological behaviour and accretion rates of patella coerulea l as indicated by oxygen isotope measurements abstract oxygen isotope measurements have been carried out on shells of p coerulea l from the coast of tuscany italy the results obtained indicate that the caco3 of the shells is precipitated under isotopic equilibrium conditions with the environmental water the deposition of caco3 takes place all year round even though the accretion rate of the shells apparently decreases during summer the accretion rate is quite fast shells of about one year showing a major axis of about 30 mm or more different ecotypes with different thermal optima seem to exist in nearby areas under similar climatic conditions

mg ca sr ca and stable isotope δ18o and δ13c ratio profiles from the fan mussel pinna nobilis seasonal records and temperature relationships 1 we present new annually resolved 18o 13c mg ca and sr ca ratio records for two shells of the fast growing mediterranean fan mussel pinna nobilis collected from proximal spanish coast sea grass meadows the relationship between the potential geochemical proxies and ontogenetic and environmental controlling factors is investigated specifically the use of shell mg ca and sr ca ratios as potential calcification temperature proxies the latter calculated from measured shell 18o values has been assessed the 18o cycles along the growth axis indicate that our p nobilis specimens are 10 5 and 4 5 years old shell sr ca ratios do not exhibit any consistent interannual cyclicity and are not correlated to temperature a subtle ontogenetic effect on shell mg ca ratios was observed during the first 4 5 years of recorded growth but was highly evident during the organism s later growth years in p nobilis shells different mechanisms influence ontogenetic variation in shell mg ca and 18o records shell mg ca ratios from the first 4 5 years of growth correlate significantly to temperature in a best fit relationship described by the equation mg ca 17 16 1 95 exp 0 022 0 004 t p nobilis shell mg ca records therefore are a valid temperature proxy only during an early growth phase for the same range of temperatures shell mg ca ratios in p nobilis are approximately 1 3 lower than those reported for inorganic calcite but 3 to 4 times higher than in another bivalve species mytilus trossulus and 4 to 16 times higher than in foraminifera we suggest these offsets are due to a higher degree of similarity between seawater and calcification fluid composition in p nobilis than in other bivalves and foraminifera the observed shell mg ca ratio change per c of 2 2 also is lower than that observed for inorganic and other biogenic calcites our findings strongly support taxon and species specific mg ca temperature relationships for bivalves and other calcifying organisms an appreciation of the physiology and calcification mechanisms of any biogenic carbonate archive therefore is paramount prior to the application of stable isotope and element ca ratio proxies for paleotemperature reconstructions

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

stratigraphy and depositional mosaics of lower clear fork and wichita groups permian northern midland basin texas the stratigraphy depositional environments and reservoir potential of the wichita group and overlying lower clear fork permian in the northern midland basin are described on the basis of seismic interpretations log correlations and lithologic analyses the wichita in this area is divided into a lower member of slope to basinal limestones and shales and an upper member of shelf dolomites varicolored shales and evaporites only a starved lower wichita section is present in areas to the south fusulinid evidence and physical correlations suggest that the wolfcampian leonardian boundary occurs within the wichita and ascends stratigraphically toward the north these data in conjunction with the upward shoaling aspect of the wichita establish a progradational relatio between shelf facies of the upper member and slope to basinal facies of the lower member the lower clear fork beneath the tubb member records continued southward progradation of similar shelf facies these lithologies are represented in the basin by limestones and shales beneath and possibly including lowermost dean sandstones depositional systems of the wichita and pre tubb clear fork sections are carbonate dominated rimmed shelves adjoining deeper basins periods of rapid progradation and offlapping shelf edge accretion were cyclic being coincident with periods of low sea level the tubb section records a change to a mixed siliciclastic and carbonate rimmed shelf system deposition of shelf tubb and basinal dean facies was related to a mosaic of cyclic reciprocal siliciclastic carbonate sedimentation rapid shelf outbuilding occurred at low sea level stands during the siliciclastic phases of sedimentation the formation of the shallow north platform was more a consequence of constructional sedimentary processes during the late wolfcampian and early leonardian than of structural influences over much of the northern midland basin study area potential stratigraphic hydrocarbon reservoirs are in wichita and lower clear fork strata such reservoirs occur as separate offlapping shelf marginal dolomitized oolite grainstone shoals rather than organic buildups as was described in earlier studies

seawater temperature records from stable isotopic profiles in the shell of modiolus modiolus abstract the hypothesis that the sea urchin disease which devastated populations along the atlantic coast of nova scotia in 1980 83 is temperature related requires a record of bottom seawater temperatures over this period a time series of 18o values from two modiolus shells collected in a cove in nova scotia were used to reconstruct bottom water temperatures and as an independent method to age the mussels a fine scale of resolution was achieved with up to 15 discrete samples per year of shell deposition records from two shells showed similar trends the 18o values of the shells clearly tracked seasonal temperatures they suggested that bottom seawater temperatures were not unusually warm at this site in 1980 the year in which the sea urchin disease was first noticed ages of mussels determined from the oxygen isotope record were consistent with those estimated from annual growth lines on the shells

sedimentology and evaporite genesis in a holocene continental sabkha playa basin bristol dry lake california bristol dry lake a 155 km2 continental sabkha playa basin in the mojave desert of south eastern california is filled with at least 300 m of interbedded terrigenous clastics gypsum anhydrite and halite evaporite facies conform approximately to a bull s eye pattern with gypsum and anhydrite surrounding a basin centre accumulation of halite transects through bristol dry lake from the alluvial fan to the centre of the playa reveal 1 crudely bedded alluvial fan clastics interfingering with 2 playa margin sand flat and wadi sand and silt followed by 3 gypsum anhydrite chaotic mud halite and clay of the saline mud flat and 4 salt pan halite beds terrigenous clastics were deposited in bristol dry lake by sheetflow and by suspension settling from ponded floodwater some sediment has been reworked by aeolian processes to form barchan dunes around the playa margin thin nodular like beds of anhydrite and several types of gypsum occur across most of the playa giant hopper shaped halite cubes are suspended in saline mud flat facies suggesting that they grew displacively in brine soaked sediment just below the surface thick beds 4 m of halite in the playa centre may have formed through a complex alternating history of subaqueous and intrasedimentary precipitation under the influence of periodic floods intense evaporation and brine level lowering and capillary discharge of brines the stratigraphy in the playa centre is cyclic an ideal cycle consists of 1 chaotic mud halite at the base overlain by 2 green to red clay with abundant giant hoppers and at the top 3 red clay gypsum and anhydrite with flaser to wavy bedded sand and silt this type of cycle probably records a gradual progradation of mud flat facies over salt pans bristol dry lake sediments are nearly identical to some of the permian evaporites of the permian basin region u s a and they can serve as modern analogues for ancient sabkha facies analysis

origin and age of the mediterranean messinian evaporites implications from sr isotopes strontium isotope ratios from the messinian late miocene 6 4 to 4 85 ma evaporites of the mediterranean basin 1 2 support a subdivision into stratigraphically lower predominantly marine deposits lower evaporites lev lower gypsum and main salt characterized by sr isotopic ratios generally equivalent to those of messinian seawater and stratigraphically higher deposits upper evaporites uev with 87sr 86sr ratios lower than messinian seawater the range of 87sr 86sr ratios of the lev unit from the eastern mediterranean overlap with values obtained from essentially coeval red sea evaporites 3 strontium isotopic ratios measured from the upper evaporites however are lower and a high proportion of this sr was probably derived from low 87sr 86sr continental runoff that characterizes much of this basin 4 these results therefore strongly support depositional models utilizing a deep desiccated basin 1 with a constant marine inflow during the early stages including salt formation followed by a series of long lasting and sometimes isolated desiccation events that produced a strong but variable continental influence on the sr isotopic compositions of the uev strontium isotopic measurements can also be used to asses the actual timing of the deposition of the lev ratios obtained from oyster fragments and foraminifers from pre evaporitic units at odp site 654 tyrrhenian sea suggest that the major rifting phase in this region occurred between 8 and 6 5 ma ratios obtained from the early lev from the mediterranean sea suggest that initiation of evaporite deposition began about 5 65 ma ago results from units immediately overlying the uev in sicily suggest termination of evaporite deposition about 4 9 ma ago errors associated with these age estimates are about 0 5 ma 2

high frequency cyclicity in the latest messinian adriatic foreland basin insight into palaeoclimate and palaeoenvironments of the mediterranean lago mare episode abstract late messinian lago mare deposits show high frequency cyclicity in the whole mediterranean basin both millimeter and centimeter scale cyclicities have been observed in several odp sites as well as in stratigraphic sections from the mediterranean borderland we have analyzed a well exposed late messinian lago mare section from the adriatic side of the central apennines italy at the fonte dei pulcini section se majella mts millimeter and centimeter scale white and dark couplets have been observed in the field a 50 cm regular spaced sampling has been performed in the uppermost 53 m of the late messinian lago mare clays on the 107 collected samples geochemical caco 3 content mineralogical xrd analyses and micropalaeontological investigations have been performed in addition sem and microprobe investigations as well as mineralogical and micropalaeontological analyses have been carried out on single lamina from a 34 cm thick interval of millimeter scale laminites besides the 10 3 cycles m and 10 2 cycles m frequencies observed in the field spectral analyses performed on the caco 3 data set indicated other high frequency cyclicities 0 47 cycles m 0 35 cycles m and 0 17 cycles m taking into account the estimated sedimentation rate these frequencies correspond respectively to periodicities of 1 year 10 years 2 1 kyr 2 8 kyr and 5 6 kyr these sub milankovitch cyclicities have been related to annual and sunspot solar activity the millimeter scale couplets are interpreted as varves sedimented in an ephemeral water environment marginal to a perennial brackish water lagoonal basin these varved sediments reflect a marked seasonality characterized by the alternation of arid and more humid climatic phases the presence of high values of smectite 60 80 in the clay minerals of the analyzed samples could be a consequence of these climatic oscillations from drier to moister conditions the climatic scenario suggested in this paper for the late messinian lago mare episode is in agreement with the monsoon system that according to some authors starting from 5 8 ma developed in the mediterranean area

integrated stratigraphy and astrochronology of the messinian gssp at oued akrech atlantic morocco a much improved high resolution integrated stratigraphy calcareous plankton biostratigraphy magnetostratigraphy cyclostratigraphy is presented for the classic section of oued akrech atlantic morocco straddling the tortonian messinian boundary magnetobiostratigraphic correlations with time equivalent and astronomically dated sections in the mediterranean indicate that cyclic alternations of indurated light beige coloured marls and softer more clayey and reddish coloured marls are dominantly precession controlled characteristic sedimentary cycle patterns in particular those reflecting precession obliquity interference allow for one possible tuning thus providing accurate astronomical ages for cycles calcareous plankton events and magnetic reversals the tuning further indicates that the reddish layers are the equivalent of sapropels in the mediterranean the messinian global boundary stratotype section and point gssp has recently been formally defined at the base of the reddish layer of cycle no 15 in section oued akrech this level coincides closely with the first regular occurrence of the globorotalia miotumida group and is astronomically dated at 7 251 ma the global correlation potential is guaranteed by the straightforward calibration of the oued akrech magnetostratigraphy to the geomagnetic polarity time scale locating the gssp within c3br 1r in the marine realm the calcareous nannofossil genus amaurolithus provides a series of extremely useful events to delimit the boundary on a global scale the astronomical tuning guarantees a direct first order calibration of the messinian gssp to the standard geological time scale once as anticipated the late miocene part of the astronomical time scale has been incorporated fl 2000 elsevier science b v all rights reserved

extremely acid permian lakes and ground waters in north america evaporites hosted by red beds red shales and sandstones some 275 265 million years old extend over a large area of the north american mid continent1 they were deposited in non marine saline lakes pans and mud flats2 settings that are typically assumed to have been alkaline here we use laser raman microprobe analyses of fluid inclusions trapped in halites from these permian deposits to argue for the existence of highly acidic ph 1 lakes and ground waters these extremely acidic systems may have extended over an area of 200 000 km2 modern analogues of such systems may be natural acid lake and groundwater systems ph 2 4 in southern australia3 4 5 6 7 8 9 both the ancient and modern acid systems are characterized by closed drainage arid climate low acid neutralizing capacity and the oxidation of minerals such as pyrite to generate acidity the discovery of widespread ancient acid lake and groundwater systems demands a re evaluation of reconstructions of surface conditions of the past and further investigations of the geochemistry and ecology of acid systems in general

origin of helium and nitrogen in the panhandle hugoton field of texas oklahoma and kansas united states helium and nitrogen variations in panhandle hugoton field phf gases are products of interaction between hydrocarbon gas from the anadarko basin and at least two water masses with dissolved nitrogen and helium the two most distinct water masses are from the palo duro basin highest he n2 and the hugoton embayment lowest he n2 geochemical data indicate several hundred million years of helium generation in porous rock helium migrated to the gas by diffusion through water saturated rock and by west to east water flow sediment and basement helium generation and helium migration were modeled to validate timing and source of phf helium models indicate a predominantly sedimentary helium source with some basement helium charge on the amarillo uplift helium in the central and eastern phf diffused from underlying rocks whereas gases on the west and southwest sides were enriched in nitrogen and helium delivered by hydrodynamic water flow nitrogen in high nitrogen gases was probably sourced as ammonium released from clays by cation exchange with brines derived from overlying salt units the amount of mudrock nitrogen and helium source relative to other potential helium sources arkose radioactive dolomite correlates to decreasing gas he n2 the high helium concentrations in phf gases result from multiple favorable circumstances old pore water accumulated dissolved helium during hundreds of millions of years of helium generation in sediment high water gas and low pressure favored higher helium concentrations in gas hydrodynamic flow delivered helium rich pore water from basins west of the phf

paleoenvironmental changes at the messinian pliocene boundary in the eastern mediterranean southern cyprus basins significance of the messinian lago mare abstract the study of the late messinian early pliocene sediments in south cyprus pissouri and polemi basins and the comparison with the offshore coeval deposits drilled in the odp leg 160 boreholes provide new data illustrating the environmental changes which occurred in the eastern mediterranean at the end of the salinity crisis the messinian pliocene transition is marked by a very rapid environmental change indicated by sharp variations in lithology sedimentology microfaunal assemblages and stable isotope composition the latest messinian interval is dominated by the lago mare oligo mesohaline environments the most striking feature in the pissouri basin is the intercalation between the uppermost gypsum bed and the base of the zanclean deposits of four main horizons of paleosols interbedded with carbonates and conglomerates paleosols indicate periods of subaerial exposure long enough to permit pedogenesis to develop conglomerates indicate intense erosion of the troodos massif and its sedimentary cover as a result of the water level drop tectonic activity and more humid climatic conditions thus several subaerial exposure phases occurred in the marginal areas like the pissouri basin whereas shallow oligohaline conditions persisted in the deeper parts of the basin as indicated at odp site 968 both in the pissouri basin and on the flank of the erathostenes seamount the late messinian paleosols are directly overlain by the lowermost pliocene sediments deposited in well oxygenated deep marine conditions this drastic change of water depth shows that the water level of the late messinian saline to brackish lakes dropped far below that of the world ocean at least more than several hundred meters both these base level fluctuations and the oligohaline conditions caused intensive erosion karstification of the upper gypsum beds as also reported from many other mediterranean regions moreover the study of the polemi sections shows that oligohaline conditions had already started during the deposition of the upper gypsum sub unit typical brackish and fresh water assemblages are present in the last two gypsum layers and intergypsum beds this indicates that freshwater dilution i e the lago mare conditions resulted from a progressive change of the hydrological budget which started during deposition of the upper evaporites and climaxed after the deposition of the uppermost gypsum layer classical lago mare facies during this time periods of increased evaporation over precipitation led to deposition of the uppermost gypsum layers this evolution is interpreted as being due both to the severance from the open ocean and to the increasing contribution of the runoff precipitation versus marine inputs in the hydrological budget of the mediterranean

evolution of permian evaporite basin in texas panhandle permian leonardian to ochoan evaporites in the texas panhandle were deposited in a range of marine shelf to supratidal environments along an arid coastline carbonates in these strata generally were deposited in inner shelf systems and include subtidal to supratidal facies landward of shelf environments evaporites were deposited in brine pans and salt flats brine pan facies are laminated anhydrite and banded salt that formed in shallow hypersaline waters such as restricted lagoons or supratidal salines salt flat facies are mainly chaotic mixtures of mudstone and halite possibly formed by salt deposition on and within mud flats that bordered brine pans or in brine soaked mud flat depressions periodically mud flats built across the evaporite systems and were suppl ed with red terrestrial clastics mainly mud and silt these facies occur together in at least three different types of lithogenetic units strata in the clear fork group leonardian are considered deposits of a coastal evaporite basin that was progressively filled by terrestrial clastics these rocks exhibit regressive cycles of brine pan salt flat and mud flat facies in contrast san andres strata guadalupian were deposited in a broad marine embayment with persistent brine pan conditions and contain cycles of inner shelf and brine pan facies post san andres strata late guadalupian and ochoan were deposited in the inner reaches of a broad interior salt basin and are composed mainly of mud flat salt flat and halite rich brine pan facies

evolution of depositional environments after the end of messinian salinity crisis in nijar basin se betic cordillera abstract the messinian succession is exceptionally well preserved in the intramontane sedimentary basin of nijar in the internal betic cordillera se spain gypsum olistostromes and large slabs of the azagador member are unconformably overlain by the latest messinian sediments of the feos formation these deposits which are studied in detail in the rambla los feos outcrop basinal area are characterized by a sedimentary cyclicity and two lithostratigraphic units can be distinguished 1 a lower one that mainly consists of calcarenitic intervals with laminated pelites and limestone beds 2 an upper unit showing a cyclic alternation of fluvial fan deposits and lacustrine marls that corresponds to the lago mare episode the sedimentary succession records very precisely the strongly fluctuating environmental conditions during the upper messinian as well as the paleomorphological and paleogeographical changes that are likely related to late miocene and pliocene tectonic uplift of the sierra cabrera betic basement the dominant fossil content present throughout the upper unit in the lacustrine white marls of the feos formation is represented by ostracods of the loxocorniculina djafarovi fa an assemblage of non marine aquatic communities which lived in brackish water bodies lago mare fauna extant ostracod faunas similar to those documented in the messinian fossil record and characterised by cyprideis tyrrhenocythere loxoconchids and leptocytherids occur in hypohaline water bodies in a salinity range of approximately 5 15 mesohaline water however the number of species of parathetian affinity is low as observed in other perimediterranean areas i e apennines the marine fauna association foraminifera present at levels is thought to be partly reworked even though a marine influence at the end of the lago mare stage is not excluded

paleoenvironmental significance of messinian post evaporitic lacustrine carbonates in the northern apennines italy the post evaporitic messinian in the northern sector of the adriatic foredeep is characterized by the occurrence of abundant terrigenous deposits which have been subdivided into two allostratigraphic units p ev1 p ev2 separated by an erosional unconformity of regional importance the p ev1 consists of basal complex of resedimented evaporites overlain by monotonous succession of mudstone siltstone alternations thin bedded turbidites with an overall coarsening and shallowing upwards trend it is possibly related to the rapid basin infill after the end of the salinity crisis the upper unit p ev2 shows in the most marginal areas a clear cyclical stacking pattern made up of three fining up sequences with fan delta conglomerates at the base of each cycle here a peculiar feature of the p ev2 deposits is the occurrence of three distinct laminated limestone horizons termed colombacci interbedded with fine grained varved mudstones these limestones are abiotic despite the occurrence of abundant ostracod assemblages lago mare fauna in the interbedding pelites and are interpreted as inorganically precipitated deposited in a relatively deep water environment possibly anoxic and related to permanent stratification of water mass events during periods of lake level maxima the combination of petrographical and geochemical observations on carbonate layers reveals that they correspond to events characterized by significant variations of environmental conditions however 18o 5 30 0 2 and 13c 9 28 1 68 signatures suggest that the precipitation of low mg calcite often occurred in a non marine environment and that meteoric water input had a considerable influence on late messinian sedimentation moreover the limestones have a uniform 87sr 86sr composition 0 70864 0 70875 in the range of other lago mare sediments from elsewhere in the mediterranean suggesting that some of the major mediterranean basins were likely interconnected during the lago mare phase a strongly reduced rate of hydrological exchange with the ocean is also possible but the possibility of marine influence during this stage is not completely excluded

did the mediterranean marine reflooding precede the mio pliocene boundary paleontological and geochemical evidence from upper messinian sequences of tuscany italy abstract the events related to the messinian salinity crisis are among the most deeply investigated of earth s history according to the current hypothesis of neogene paleogeographic evolution approximately 5 5 ma ago after evaporitic sedimentation and before the mio pliocene boundary the mediterranean was characterized by the widespread development of non marine environments inhabited by molluscs and ostracods of brackish affinity the messinian post evaporitic deposits that testify such a dramatic environmental change are commonly referred to as lago mare and have been reported from several outcrops and boreholes throughout the entire mediterranean basin the origin of lago mare conditions is commonly interpreted as the result of the synergistic effect of both the humid climatic conditions and change of the drainage patterns at the mediterranean scale with the capture of paratethyan brackish waters a few recent studies however suggest that such a scenario probably represents an oversimplification of the original context from both a paleogeographical and paleoenvironmental point of view unfortunately the results of these studies have never been commonly accepted and the proposed evidences have been considered questionable in this paper we describe the fish assemblages from the lago mare deposits of two localities cava serredi and podere torricella located in the neogene hinterland basins of tuscany central italy these assemblages consists of a mixture of marine euryhaline and stenohaline taxa suggesting that the depositional environments were characterized by permanently open connections with a marine basin filled with normal marine waters in order to better define the paleontological significance of these upper messinian fish assemblages the oxygen carbon and strontium isotopic composition of fish otoliths and other fossils has been measured these isotopic compositions are strongly indicative of the presence of normal marine conditions close to the depositional environments testified by the sedimentary sequences thereby implying that the interpretation of the geochemical results are consistent with those derived from the paleoecological analyses of the fish assemblages based on the integrated paleoichthyological geochemical approach discussed in this paper it is possible to unambiguously demonstrate that normal marine rather than fresh or brackish waters were present in the mediterranean at least during the upper part of the lago mare event providing an unquestionable evidence that the marine refilling of the basin preceded the mio pliocene boundary

sedimentology of ancient saline pans an example from the permian opeche shale williston basin north dakota u s a abstract the mid permian opeche shale of north dakota consists of bedded evaporites and red bed siliciclastics detailed core and petrographic study has documented sedimentary and early diagenetic features in order to develop a depositional model and to refine paleoclimatic data and paleogeographic setting for the late paleozoic of the u s midcontinent lithologies and sedimentary features indicate lacustrine distal alluvial and minor eolian deposition subaerial exposure and soil formation bedded halites consisting of chevron and cumulate crystals dissolution surfaces and pipes and mudcracked microcrystalline salt crusts were deposited in a saline pan dominated by flooding evaporative concentration and desiccation bedded halites containing chevron and cumulate crystals but lacking any dissolution or desiccation features formed in perennial saline lakes chaotic halite composed of red mudstone and siltstone with displacive halite crystals represents saline mudflat deposits red mudstone and siltstone with little or no displacive halite but with abundant cracks and root features suggest deposition in a dry mudflat red bed sandstones and conglomerates composed of poorly sorted subrounded quartz grains cemented with halite indicate distal alluvial deposition with possible transport by ephemeral streams sheet floods and debris flows most deposition took place in halite dominated shallow perennial and ephemeral saline lakes surrounded by saline and dry mudflats evaporation desiccation flooding and wind played significant roles in this environment therefore the opeche evaporites and red beds are representative of an ancient saline pan system an inland playa setting is favored as a depositional model for the opeche shale the abundance of soil features and halite dominance as well as lack of nearshore carbonates and lack of restricted marine fossils suggest a closed basin nonmarine setting for the mid permian of the u s midcontinent

comparison of sequences formed in marine sabkha subaerial and salina subaqueous settings modern and ancient marine evaporites occurring in modern subaqueous salina settings and subaerial sabkha settings are different subaqueous holocene evaporites occur as shoaling upward lacustrine sequences up to 10 m thick they are evaporite dominated and are composed primarily of bottom nucleated crystals that may be deposited as massive laminated or rippled units each coastal lake is dominated by laminated evaporites with subordinate carbonate sediments in plan view they show a well developed bull s eye pattern with a sulfate center and a carbonate rim in contrast subaerial sabkha evaporites occur as part of a laterally prograding shoaling upward peritidal sequence in which the supratidal unit is usually no more than 1 m thick sabkha sequences are matrix dominated not ev porite dominated with the bulk of the sulfate phase occurring as diagenetic nodules enteroliths or diapirlike structures these sulfates were formed during syndepositional diagenesis by replacement and displacement processes the various facies of the sequence tend to accumulate in belts parallel with the shoreline relative to the sea level or the brine level sabkhas tend to form over paleotopographic highs whereas salinas tend to occur in paleotopographic lows some of the characteristics that distinguish holocene subaerial and subaqueous evaporite sequences can be used to do the same for similar ancient facies even when gypsum has been converted to nodular anhydrite the distinction is important for it can be used by explorationists in the oil industry to define the paleotopography of the associated underlying porous and nonporous carbonates

the north tyrrhenian northern apennines post collisional system constraints for a geodynamic model the north tyrrhenian northern apennines post collisional system ntas has been analysed on the basis of marine reflection profiles and bibliographic sources with the aim of providing an up to date geotectonic and evolutive framework consistent with structural data the continental rifting began to affect the most internal western side of the system in the middle upper miocene while the most external eastern zones were touched by rifting only in pleistocene times the birth and development of extensive asymmetric basins took place with a progressive speeding up of rifting towards the external sectors a diachronous regionally extended and eastward rejuvenating unconformity recognizable within the neogene quaternary basins marks the passage from the syn rift to the post rift tectonic regime while the first is everywhere dominated by extension the second one produces vertical movements reflection terminations related to this unconformity are interpreted in terms of vertical tectonic component three zones that experienced different post rift vertical movements are thus recognized in the ntas subsidence in the north tyrrhenian deep water region tectonic stability or alternation of moderate subsidence and uplift in the continental shelf and western tuscany strong uplift in eastern tuscany the updated structural data demonstrate that the ntas upper crust is crosscut by both tyrrhenian dipping and apennine dipping low angle detachment planes above which the upper crustal blocks rotated and experienced extensional transport along two opposite directions to the west and to the east respectively the coexistence of opposite dipping crustal surfaces bears two fundamental implications for the ntas geodynamics first it stresses the importance of the anti apennine transfer faults since they separate crustal blocks of opposite extension polarity secondly it testifies that the extension tectonics not only re utilized former crustal thrust planes but also gave origin to new significant e and ne dipping detachment planes plan and crossview geometries of faults together with considerations on the role of the metamorphic core complexes point to an interpretation of the ntas structure that is more consistent with the anastomosing shear model rather than the simple shear or the delamination ones

are the intensities and durations of small scale pottery firings sufficient to completely dehydroxylate clays testing a key assumption underlying ceramic rehydroxylation dating rehydroxylation rhx dating was recently suggested as a simple cheap and accurate method for dating ceramics it depends on the constant rate of rehydroxylation the slow reintroduction of oh of clays after they are fired and dehydroxylated purged of oh during the production of pots bricks or other ceramics the original firing of the ceramic artifact should set the dating clock to zero by driving all hydroxyls out of the clay chemical structure to examine whether this assumption holds especially for pot firings of short duration and low intensity as those in small scale traditional settings we performed thermogravimetric analysis of clay samples of known mineralogy at temperatures and for durations reported from traditional sub saharan american and south asian pottery firings results demonstrate that in the majority of samples complete dehydroxylation dhx did not occur within or even beyond the conditions common in traditional firings consequently between 0 01 and 1 5 of a sample s mass in residual oh may remain after firings analogous to those observed in the ethnographic record lack of complete dhx at the scales we have observed can result in the over estimation of ceramic ages by decades to tens of thousands of years depending largely on the age of the sample and the amount of residual oh present thus in many cases a key assumption underlying current rhx dating methods is unlikely to have been met introducing considerable error in dates

a dynamic model for the permian panhandle and hugoton fields western anadarko basin panhandle hugoton the largest north american gas field has long been controversial because of extreme subnormal pressures variable gas composition and tilted fluid contacts commonly attributed to hydrodynamic flow despite the absence of an effective updip aquifer these anomalies are addressed in terms of a basin scale petroleum system history largely independent of the geographically underlying pre permian system hydrocarbons were already being generated in the deep anadarko basin during the early permian with efficient southward migration from all potential source rocks via bounding faults and pennsylvanian permian alluvial fans giant amarillo uplift drape structures trapped hydrocarbons immediately following permian evaporite deposition the pre laramide panhandle field at maximum burial depth and pressure contained most of the oil and gas now found in mid continent permian reservoirs the early tertiary laramide orogeny redistributed panhandle field fluid columns possibly spilling gas into the hugoton embayment subsequent erosion of permian reservoir facies in eastern kansas allowed water discharge to outcrops at elevations below the regional hydraulic head as regional pressure dropped in response the panhandle field gas cap expanded rapidly forcing a late tertiary quaternary mass movement of gas northward to fill hugoton and associated fields panhandle hugoton pressures upon discovery were subnormal relative to drilling depth but normal relative to reservoir outcrop elevations in eastern kansas indicating that pressures are controlled by aquifer communication with the surface instead of burial depth variations in fluid contacts pressure and gas composition suggest that reservoir fluids are still moving driven by decompression and the rapid volumetric expansion of a supergiant gas accumulation

mediterranean messinian salinity crisis constraints from a coeval marginal basin sorbas southeastern spain abstract the extent timing and effects of late miocene desiccation and evaporite deposition in the mediterranean sea remain controversial marginal basins containing messinian 5 3 7 1 ma sequences now exposed onland supplement information from the deep mediterranean but have evaporites of a variety of ages some of these messinian evaporites pre date and others post date deep desiccation none appears to be exactly coeval with those of the deep mediterranean in the betic cordillera of southern spain basins e g granada basin far from the present day mediterranean lost connection with the mediterranean due to uplift 1 ma before the salinity crisis and have marine evaporites of early not late messinian age in contrast basins such as the sorbas basin in southeastern spain adjacent to the present day mediterranean record events directly reflecting the course of the salinity crisis the sorbas basin retained marine connection with the western mediterranean up until evaporative drawdown in the mid messinian and was rapidly reflooded immediately afterwards the sorbas messinian sequence is up to 320 m thick it is complete and normal marine except for an incised basinwide erosion surface overlain by a 130 m thick gypsum deposit we propose that this surface marks the interval of deep desiccation of the adjacent mediterranean basin erosion occurred shortly after 5 9 ma and the irregular unconformity has relief of at least 240 m confirming mediterranean drawdown significantly below the atlantic level sorbas gypsum deposits overlie the unconformity and are intercalated with marls estimated at 5 5 ma containing normal marine messinian biotas these gypsum deposits therefore post date deep desiccation and formed in a silled basin immediately following marine reflooding they mark the end of the salinity crisis and are overlain by 70 m of normal marine sediments containing unreworked foraminifers of latest messinian age this succession demonstrates that the salinity crisis occurred faster and was completed sooner than previously believed it took place within 0 4 ma time scale of berggren et al 1995b is 0 2 ma on the time scale of baksi 1993 and was completed before the end of the messinian this corrects previous views that the salinity crisis continued until the early pliocene there is no evidence in the sorbas basin for brackish lago mare conditions and the normal marine biotas that directly precede and follow drawdown rebut earlier suggestions of prolonged salinity effects

sr isotope constraints on the mediterranean environment at the end of the messinian salinity crisis probably the most profound event that has affected the mediter ranean is the desiccation which occurred at the end of the miocene1 8 during this period there was a very rapid change from deep open marine conditions to environments of shallow water carbonate and massive evaporite deposition1 10 here we show that ostracod valves found in messinian lago mare lake sea sediments have a uniform but generally lower sr isotopic composition than contemporary sea water thus providing evidence that some of the major mediterranean basins for example balearic and levantine basins formed large lacustrine systems that were probably interconnected towards the end of the messinian salinity crisis1 3 after the major evaporites were deposited the most likely source of fresh water is from continental rivers flowing from the eastern european inland paratethys sea or perhaps the nile river in the lower part of the lago mare some ostracods have sr isotopic compositions identical to contemporary sea water indicating a transient influence of marine derived water sr compo sitions greater than that in contemporary sea water are only found in ostracods from onshore sediments in the sorbas basin4 5 of southeastern spain suggesting that this small basin adjacent to the straits of gibraltar became isolated after the deposition of the major evaporite sequences

the oxygen and carbon isotope distribution in the mediterranean water masses abstract the oxygen and carbon stable isotope compositions of the present day mediterranean waters have been measured in order to evaluate their variability which is related to the specific climatic and hydrological conditions within the basin the experimental equation between the 18 o value and the salinity of water based on 300 measurements on surface intermediate and deep waters sampled during the vicomed 2 and 3 cruises in the western central and eastern mediterranean has a slope of 0 27 a value which is significantly lower than the slope of 0 45 as defined in the northeast atlantic ocean this difference in the 18 o salinity relationship which occurs immediately in the alboran basin is basically a characteristic of the climatic regime of the mediterranean i e of an excess evaporation over fresh water input the largest variations of these two parameters 18 o of water and 13 c of co 2 are observed in the surface waters mostly in the western mediterranean this evolution mirrors the progressive eastward restriction which separates the less evaporated and more productive western basins from the more evaporated and less productive eastern basins the intermediate waters constitute a homogeneous layer however their 18 o values decrease eastward by 0 35 at maximum due to progressive dilution by mixing with overlying and underlying water masses their 13 c values decrease also eastward by 0 35 at maximum due to an increasing input of nutrients issued from the regeneration of sinking organic particles the deep waters have similar 18 o values but slightly higher 13 c values often by less than 0 1 than the overlying intermediate waters indicating generally well ventilated conditions due to active winter convection

on the effect of organic carbon on rehydroxylation rhx dating scientific dating is an invaluable tool to understand the development of human civilizations from prehistoric to historic times ceramics is the most abundant material recovered from archaeological excavations but a satisfactory scientific dating method is still lacking so called rehydroxylation rhx dating promises precise age information but the validity of the method still has to be proven we have investigated one possible obstacle imposed by the presence of organic carbon in the samples such a contamination can lead to significant deviations of the dating result the amount of co2 released from the following samples was determined a medieval clay brick from alkoven austria two authentic archaeological samples from the iron age from megiddo israel a 1600 ad earthenware sherd from enkhuizen netherlands which had been successfully dated with rhx at another laboratory we investigated several possibilities to remove such contamination