subduction and volcanism in the iberia north africa collision zone from tomographic images of the upper mantle abstract new tomographic images of the upper mantle beneath the westernmost mediterranean suggest that the evolution of the region experienced two subduction related episodes first subduction of oceanic and or extended continental lithosphere now located mainly beneath the betics at depths greater than 400 km took place on a nw se oriented subduction zone this was followed by a slab tear process that initiated in the east and propagated to the west leading to westward slab rollback and possibly lower crustal delamination the current position of the slab tear is located approximately at 4 w and to the west of this location the subducted lithosphere is still attached to the surface along the gibraltar arc our new p wave velocity model is able to image the attached subducted lithosphere as a narrow high velocity body extending to shallow depths coinciding with the region of maximum curvature of the gibraltar arc the occurrence of intermediate depth earthquakes and anomalously thick crust this thick crust has a large influence in the measured teleseismic travel time residuals and therefore in the obtained p wave tomographic model we show that removing the effects of the thick crust significantly improves the shallow images of the slab and therefore the interpretations based on the seismic structure

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

an evaluation of elemental mobility during metamorphism of a turbidite sequence greenland group new zealand the extent of elemental mobility during lower greenschist to amphibolite facies metamorphism of a uniform turbidite suite greenland group new zealand has been evaluated using data for major elements and 19 trace elements simple comparison of average compositions at 2 wt al 2 o 3 intervals in the data suites shows little contrast between lower greenschist protolith and upper greenschist and amphibolite facies equivalents except for enrichment of cao and sr and loss of ba and rb particularly in the sandier end members division into psammitic and pelitic suites using tio 2 al 2 o 3 and zr al 2 o 3 ratios allows delineation of individual residual enrichment models on ti reference element plots and both lithotypes can be used to assess potential elemental mobility these plots show that a large number of elements ti al fe mg ce cr ga la nb ni sc th v zn and zr constitute immobile reference species with abundances equal to their equivalent lithotype in the protolith and little mass loss or residual enrichment k and rb also largely conform to the residual model but in the amphibolite facies some exchange between pelite and psammite may occur a number of elements show enrichment mn cu pb u na p or depletion y in a small number of samples but the significance of these contrasts is questionable due to relatively large variation in the protolith in contrast ca and sr show progressive and marked enrichment with increasing grade and ba and as are clearly depleted in amphibolite facies psammites in the amphibolite facies some si may have been lost by psammites and gained by the pelites although there has been no mass change from the suite as a whole a large part of the ca and sr enrichment in the amphibolite facies can be accounted for by metasomatic homogenization of calcareous concretions which occur in the lower grade protolith the metamorphism of the greenland group is thus considered to be essentially isochemical

electron microprobe and la icp ms study of monazite hydrothermal alteration implications for u th pb geochronology and nuclear ceramics this paper presents new data that quantify the response of magmatic monazite to three main types of hydrothermal alteration namely sericitization chloritization and greisenization the samples were taken from three paleozoic granites the st nectaire granite massif central france the carnmenellis granite cornwall england and the skiddaw granite lake district england fluid inclusion thermometry and hydrothermal parageneses indicate that alteration took place at temperatures ranging from 260 to 340 c and salinities from 3 to 18 wt nacl equivalent possible monazite alteration mechanisms found in the course of this study using backscattered scanning electron microscopy bse sem electron microprobe laser raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry la icp ms include cationic substitutions monoclinic to hexagonal structure transition accompanied by chemical exchanges selective th removal dissolution reprecipitation and dissolution with replacement by a different mineral these results show that despite the compositional and crystallographic simplicity of monazite it exhibits varied chemical responses to different mineral fluid interactions elemental and isotopic measurements by la icp ms for the unaltered monazites yield statistically significant 232th 208pb and 238u 206pb magmatic crystallization ages in some cases it was possible to give a reasonable estimate of the age of mineral fluid interaction using the altered parts of the monazites or newly precipitated crystals for other minerals 232th 208pb and 238u 206pb systematics were strongly disturbed by variable inputs and or depletions of u th and pb the data suggest that monazite like nuclear waste forms would be good hosts for tetravalent actinides but may release the lanthanides and actinides with lower and higher valencies especially if the fluids are oxidizing or tend to dissolve monazite

origin and mixing history of brines palo duro basin texas u s a formation waters in the palo duro basin texas u s a fall into four major groups based on integrated chemical and isotopic characteristics 1 interbed brines within the major permian evaporite aquitard these are the most chemically concentrated and18o rich fluids in the basin and are interpreted as evaporatively concentrated sea water which has been hydrologically isolated since the permian 2 brines below the salt on the eastern side of the basin have clbr divalent cation and isotopic systematics indicating a mixture of evaporatively concentrated sea water and meteoric water of d 20 3 brines below the salt on the western side of the basin have chemical and isotopic systematics suggesting a mixture of two pulses of meteoric water one with d 20 and the other with d 55 and 4 waters above the salt have the isotopic composition of meteoric waters diagenetic alteration of the cation chemistry has occurred for brines within and below the salt aquifers below the salt on the eastern side are interpreted as having been charged with dense permian evaporite brines which subsequently mixed in various amounts with a basin wide pulse of triassic meteoric water on the western side the descending triassic meteoric waters became saline by dissolution of halite and are currently mixing with a tertiary pulse of meteoric water initiated by the laramide uplift to the west the hydrochemistry suggests flow on the western side of the basin and static conditions on the eastern side an unrecognized approximately n s permeability restriction or discontinuity in the potentiometric flow surface is inferred for major aquifers in the central area of the basin

mantle dynamics in the mediterranean the mediterranean offers a unique opportunity to study the driving forces of tectonic deformation within a complex mobile belt lithospheric dynamics are affected by slab rollback and collision of two large slowly moving plates forcing fragments of continental and oceanic lithosphere to interact this paper reviews the rich and growing set of constraints from geological reconstructions geodetic data and crustal and upper mantle heterogeneity imaged by structural seismology we proceed to discuss a conceptual and quantitative framework for the causes of surface deformation exploring existing and newly developed tectonic and numerical geodynamic models we illustrate the role of mantle convection on surface geology a coherent picture emerges which can be outlined by two almost symmetric upper mantle convection cells the downwellings are found in the center of the mediterranean and are associated with the descent of the tyrrhenian and the hellenic slabs during plate convergence these slabs migrated backward with respect to the eurasian upper plate inducing a return flow of the asthenosphere from the backarc regions towards the subduction zones this flow can be found at large distance from the subduction zones and is at present expressed in two upwellings beneath anatolia and eastern iberia this convection system provides an explanation for the general pattern of seismic anisotropy in the mediterranean first order anatolia and adria microplate kinematics and may contribute to the high elevation of scarcely deformed areas such as anatolia and eastern iberia more generally the mediterranean is an illustration of how upper mantle small scale convection leads to intraplate deformation and complex plate boundary reconfiguration at the westernmost terminus of the tethyan collision

evidence for slab rollback in westernmost mediterranean from improved upper mantle imaging this work is funded by the picasso project nsf grant ear 0808939 the deployment and data processing for spanish stations was funded by consolider ingenio 2010 project topo iberia csd2006 00041 as well as alert es cgl2010 19803 c03 02

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

multiple applications of dipmeter curves for analyzing evaporite formations examples from paleogene of bresse trough france the microresistivity curves recorded by dipmeters give much diverse information about evaporitic formations because these curves have a fine vertical resolution approximately 1 cm and show the very high contrast in resistivity between evaporites with high resistivity and clay and carbonate rocks which are porous and conductive examples are taken from the paleogene salt sequence and its overlying formations of the bresse trough in southeastern france the consistency of the 4 to 8 dipmeter curves allows clear recognition of different salt facies primary salt secondary salt and mixed patches of clay and carbonate within displacive halite layers and sulfate facies massive anhydrite nodular anhydrite etc the correlation of thin continuous carbonate and clastic beds using resistivity curves discloses with a high degree of precision the geometry of the various formations between wells examples show the detection of small magnitude halite dissolution a few meters vertically and the lateral effect of anhydrite hydration in this paper a method is proposed for determining structural dip of salt beds by computing dip angle and azimuth of thin conductive beds within the salt using the dualdip computer program a frequency distribution plot of these dip angles and azimuths gives a good indication of the dip of the salt beds

depleted arc volcanism in the alboran sea and shoshonitic volcanism in morocco geochemical and isotopic constraints on neogene tectonic processes abstract samples of volcanic rocks from alboran island the alboran sea floor and from the gourougou volcanic centre in northern morocco have been analyzed for major and trace elements and sr nd isotopes to test current theories on the tectonic geodynamic evolution of the alboran sea the alboran island samples are low k tholeiitic basaltic andesites whose depleted contents of hfs elements 0 5 n morb especially nb 0 2 n morb show marked geochemical parallels with volcanics from immature intra oceanic arcs and back arc basins several of the submarine samples have similar compositions one showing low ca boninite affinity 143nd 144nd ratios fall in the same range as many island arc and back arc basin samples whereas 87sr 86sr ratios on leached samples are somewhat more radiogenic our data point to active subduction taking place beneath the alboran region in miocene times and imply the presence of an associated back arc spreading centre our sea floor suite includes a few more evolved dacite and rhyolite samples with 87sr 86sr 0 up to 0 717 that probably represent varying degrees of crustal melting the shoshonite and high k basaltic andesite lavas from gourougou have comparable normalized incompatible element enrichment diagrams and ce y ratios to shoshonitic volcanics from oceanic island arcs though they have less pronounced nb deficits they are much less lil and lree enriched than continental arc analogues and post collisional shoshonites from tibet the magmas probably originated by melting in subcontinental lithospheric mantle that had experienced negligible subduction input sr nd isotope compositions point to significant crustal contamination which appears to account for the small nb anomalies the unmistakable supra subduction zone ssz signature shown by our alboran basalts and basaltic andesite samples refutes geodynamic models that attribute all neogene volcanism in the alboran domain to decompression melting of upwelling asthenosphere arising from convective thinning of over thickened lithosphere our data support recent models in which subsidence is caused by westward rollback of an eastward dipping subduction zone beneath the westernmost mediterranean moreover severance of the lithosphere at the edges of the rolling back slab provides opportunities for locally melting lithospheric mantle providing a possible explanation for the shoshonitic volcanism seen in northern morocco and more sporadically in se spain

nodular and enterolithic gypsum the sabkha tization of salt flat playa west texas abstract the sediment in the continental sabkha of salt flat west texas is typically millimeter laminated and composed of evaporitic and diagenetic minerals including gypsum dolomite halite calcite and aragonite these laminated evaporites were originally deposited on the floor of a late pleistocene perennial brine lake and now constitute the matrix of the modern sabkha sediments in the playa as climate changed from the more humid phase of the pleistocene to the more arid conditions of the holocene the lake dried up and these laminated evaporites were deflated into gypsum dunes or overprinted by a sabkha related hydrology near surface gypsum rich layers were transformed by capillary evaporation into coalescing nodular horizons at the same time in shallow vadose sediments less than 1 2 m subsurface the gypsum was dissolved and replaced either by halite or dolomite diagenetic gypsum was co precipitated as gypsum overgrowths and a patchwork of cement from a highly saline interstitial brine avg 156 000 mg l tds these processes of early diagenetic enlargement and coalescence of gypsum crystals created holocene gypsum nodules within the laminated host sediment diffuse growth of nodules in the lower vadose zone created chicken wire textures gypsum growth in the upper vadose zone was often concentrated along particular layers and formed enterolithic bands pleistocene lacustrine evaporites were in effect sabkhatized by a fall in the lake water level

arc related high k magmatism in the ceuta peninsula internal rif spain discovery and consequences we document the occurrence of micro diorite magmatic sills with magmatic enclaves in the ceuta peninsula within metapelites from the lower sebtides units internal rif all magmatic rocks show a primary magmatic mineralogy and geochemical signature diagnostic for high k calc alkaline to shoshonitic island arc magmatism moreover these rocks are significantly affected by secondary metamorphic transformations under greenschist to amphibolite facies conditions regionally dated at c 21 ma geometric relationships between the sills and the main regional foliation developed under intermediate pressure granulite facies conditions at c 28 ma demonstrate that the sills emplaced during the late stage of this main tectonic event new u pb in situ analyses of monazite performed on the micro diorite sills provide an age of 20 64 0 19 ma coherent with this chronological framework and interpreted as the age of greenschist facies re equilibration the discovery of pre miocene high k calc alkaline to shoshonitic arc related magmatism is clearly consistent with the subduction context proposed for the alboran basin evolution according to geophysical investigations in this framework the lower sebtides units could be considered as part of the upper plate of the subduction system while the upper sebtides must be regarded as the lower subducted plate

sedimentology and geochemistry of a mid proterozoic lacustrine unit from northern australia abstract the wollogorang formation is an unmetamorphosed middle proterozoic sedimentary unit ca 100 m thick in the highly mineralized mcarthur basin of northern australia based on sedimentology three of the six lithofacies in this unit can be confidently interpreted to be of continental origin facies 1 evaporitic red beds deposited in highly saline mudflats on an irregular volcanic landsurface at the base of the formation facies 3 varved organic rich black shales deposited in a quiet water distal lacustrine setting in the middle of the formation and facies 5 conglomeratic cross bedded poorly sorted dolomitic sandstones deposited in braided fluvial environments near the top of the formation a detailed geochemical study mainly of facies 3 was carried out to see if the two studies would complement each other and to show what geochemical criteria may be useful in defining proterozoic depositional environments dolomite concretions which are present in the carbonate poor black shales of facies 3 are shown to be early diagenetic the 87 sr 86 sr ratio from one of these concretions is 0 7139 significantly above the accepted range for marine carbonates of this age 0 705 0 708 these concretions and surrounding black shales often contain relatively high pyrite contents the concretions have 13 c values similar to the average host dolomite value of 0 6 and pyrite 34 values range from 3 5 to 5 8 c av 2 4 0 these data agree with the sedimentology and indicate a low sulfate lacustrine environment with little activity from the sulfate reducing bacteria disseminated pyrite 34 s values from facies 2 and 4 up to 11 8 0 suggest similar low sulfate environments this combined with carbonate 18 o values of around 23 facies 1 4 suggests there was only one water source present during deposition diagenesis and lithification when these data are viewed in the light of the regional stratigraphic setting and the gradational facies relationships they suggest a non marine setting for the bulk of the wollogorang formation and support previous observations of an abundance of rift related continental environments in this highly mineralized region the relatively high pyrite s organic c ratios found during this study are interpreted as indicating some addition of hydrothermally formed pyrite this result is similar to that found in the black shales from the younger more highly mineralized rocks of the mcarthur basin and may support the originally perceived mineral ootential of units such as the wollogorang formation jackson 1981a

sulfate minerals in evaporite deposits evaporite deposits preserve a wealth of information on earth s past surface conditions the deposits are sensitive indicators of depositional environment and climate recorded in a wide variety of mechanically and chemically produced sedimentary structures and fabrics unique to evaporite deposits is the record they carry of the hydrochemistry of surface waters including seawater sulfate minerals are important components in understanding the hydrochemistry of ancient surface waters sedimentological aspects of evaporite deposits were compiled by melvin 1991 in the compilation sedimentology specific to ca bearing sulfates was described by warren 1991 lowenstein and hardie 1985 handford 1991 and smoot and lowenstein 1991 discussed the sedimentology of evaporites in general these general principles can be applied specifically to the sulfate minerals in evaporite deposits sedimentological aspects of sulfate minerals in evaporite deposits are not discussed here for this information the reader is referred to the above references hardie et al 1985 and spencer and lowenstein 1988 discussed the petrography of evaporites and the interpretation of fabrics of evaporite minerals examples of petrographic aspects of sulfate minerals in evaporites are presented here along with references specific to the sulfate minerals for a more complete understanding of these aspects the reader is referred to the above references the major focus of this chapter is on the chemical aspects of the common sulfate minerals that occur in evaporite deposits the discussion begins with an explanation of the concept of chemical divides and the determination of evaporation paths and the evolution of brines in accordance with mineral solubility and the composition of dilute inflow waters determination of the precipitation pathways of the more soluble salts is more complex examples of sulfate mineral assemblages in evaporation systems calculated via thermochemical modelling are given for both marine and non marine systems the mineralogy of evaporite deposits is

sequence stratigraphic context of extensive basin margin evaporites middle jurassic gypsum spring formation wyoming u s a abstract ancient marine evaporites are commonly far more extensive than any known modern evaporite system this is true not only for basin central saline giants but also for evaporites that occur in basin margin settings and the origin of these basin margin systems is unclear extensive basin margin evaporites of the middle jurassic gypsum spring formation are well exposed along the eastern flank of the bighorn basin in wyoming usa and a facies and sequence stratigraphic analysis was undertaken to understand the origin of these evaporites and associated deposits the gypsum spring formation was deposited on a northwestward dipping mixed evaporate carbonate siliciclastic ramp with facies and depositional environments that include distal ooid shoal grainstone open marine shallow subtidal peloidal skeletal wackestone to packstone restricted shallow subtidal laminated lime mudstone peritidal dolostone and microbialite as well as red mudstone and gypsum deposited on mud flats sabkhas and salinas three depositional sequences are present with the j 1 j 1a and j 1b sequence boundaries characterized locally by chert pebble lags silicified horizons and iron rich paleosols evaporites accumulated in a basin margin position with 1 6 m beds of gypsum forming in salinas and sabkhas and nodular anhydrite and gypsum forming in red mudstones deposited on sabkhas and mud flats the limited lateral extent of salina type gypsum beds and the variable number of these beds among the exposures indicates substantial autocyclic control on the formation of salinas salinas are well developed in the tst of the j 1 sequence and sabkhas and mud flats are well developed in the j 1 hst the j 1a hst and the j 1b tst the great lateral extent of the gypsum spring evaporites reflects the original expanse of the depositional environment in which they formed and is not the result of diachroneity of a narrow evaporite precipitating belt such as the modern day coastal sabkhas of the trucial coast the great lateral extent of gypsum spring evaporites suggests that they were precipitated mainly from continental brines on an expansive desert mudflat

ams 14c dates for extinct lemurs from caves in the ankarana massif northern madagascar abstract an extensive late quaternary fauna including many extinct giant lemurs has been collected recently in a 110 km system of caves in the ankarana massif of northern madagascar ams 14c dates for the acid insoluble collagen gelatin fraction of bones of the giant lemur megaladapis 26 150 400 and 12 760 70 yr b p confirm its presence in the area during the late pleistocene and provide the first pleistocene 14 c ages from bones of the extinct megafauna of the island the first date from bones of the recently described extinct babakotia radofilai 4400 60 yr b p shows that it was present in northern madagascar in mid holocene times a comparatively recent age of 1020 50 yr b p for the extinct archaeolemur indicates survival of this genus for at least a millennium after the first direct evidence for humans in madagascar this suggests that the island s extinction window may have represented a longer time span than would have been expected under the blitzkrieg model of late quaternary extinctions a mid holocene age 4560 70 yr b p for a bone sample of the small extant lemur hapalemur simus indicates that the disappearance of this now restricted species from the ankarana occurred after this date new data from the ankarana and other sites on the island add to the consensus that major biotic changes occurred on madagascar in the late holocene

low temperature alteration of monazite fluid mediated coupled dissolution precipitation irradiation damage and disturbance of the u pb and th pb chronometers abstract low temperature alteration of monazite is documented in three centimeter sized monazite crystals from norway arendal madagascar ambato and sri lanka the three crystals have different chemical compositions especially in their u th y and pb contents and have 208 pb 232 th ages ranging from 491 to 900 ma optical microscope om scanning electron microscope sem and transmission electron microscope tem images and electron microprobe analyses epma show that all three preserve a similar patchy texture this texture is interpreted as resulting from an alteration reaction in which unaltered monazite mnz1 reacts to form a secondary th u y depleted high th u monazite mnz2 accompanied by thorite huttonite thsio 4 thorianite tho 2 and xenotime ypo 4 the proportions of which are dependent upon the initial composition of the monazite mnz1 images reveal variably intense internal fracturing with cracks filled with th rich fe rich phases monazite xenotime thermometry demonstrates that the pristine monazites mnz1 interacted with a low temperature fluid the alteration process is interpreted to follow a mechanism of fluid mediated coupled dissolution precipitation chemical dating with the electron microprobe shows no th u pb age differences between primary and secondary monazites except in the case of the ambato monazite in which altered domains yield older 750 ma apparent ages than the pristine mnz1 domains u pb and th pb isotope dating using la icp ms yields ages consistent with electron probe dates for pristine mnz1 zones however disturbance of these systems in the altered monazite domains leads to variable age results for these depending on sample in the case of sri lanka and arendal only 208 pb 232 th dates provide a reasonable estimate of the age of alteration which are constrained to be 450 and 864 ma respectively u pb systems are disturbed due to common pb contamination up to 40 and u fractionation relative to th during alteration responsible for depletion of u in altered monazites and increase of th u in contrast for the ambato monazite both the u pb and th pb systems were affected and yield inconsistent older dates for altered zones this is attributed to significant common pb contamination up to 80 which affects all pb isotopes and explains why electron probe ages are erroneous th u silicate contamination during measurement resulting from the presence of a numerous nano phases and nano fractures filled with th u silicates that are visible only under tem also contributes to the anomalously old ages for these disturbed mnz2 domains these results demonstrate the important role of radiation damage effects in particular swelling induced fracturing and the essential role of porosity and cracks which allow fluid charged with elements migration through monazite during low temperature alteration

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

contrasting siliciclastic evaporite strata in subsurface and outcrop an example from the permian nippewalla group of kansas u s a abstract geologists tend to expect that rocks as they appear in outcrop are a very good approximation of the same strata in the subsurface but this is not the case in mixed siliciclastic evaporite units strata that contain both a siliciclastic and an evaporite mineral component distinct differences in lithologic and stratigraphic descriptions of ancient siliciclastic evaporite strata exist between outcrop and core these differences present challenges in stratigraphic nomenclature lithologic correlation age determinations and interpretations about past depositional environments diagenetic history and paleoclimate an example of siliciclastic evaporite strata is the middle permian to early triassic gypsum and or anhydrite hereby referred to as gypsum anhydrite and halite bearing red beds throughout the midcontinent of north america and equivalent strata from other pangean deposits here we use core and field observations of the middle permian nippewalla group in kansas to show the range of similarities and differences in lithologies and thicknesses of specific lithofacies in outcrop and at various depths for example the displacive halite lithology consisting of red mudstones dominated by randomly oriented halite crystals is abundant in cores and interpreted as saline mudflat deposits the outcrop counterpart is less common friable massive red mudstones with some gypsum anhydrite pseudomorphs after displacive halite crystals we interpret these lithologic differences of this saline mudflat lithofacies as the result of excellent preservation of buried displacive halite and late stage dissolution of near surface halite additionally bedded halite and intergranular halite cements in siltstones and sandstones are also vulnerable to late stage dissolution near the surface further modifying lithologies and thicknesses thickness of the nippewalla group in the amoco rebecca k bounds core of western kansas is 931 feet 284 meters thick but it is estimated to be only half as thick in the outcrop belt of south central kansas to estimate amount of rock lost to late stage dissolution we conducted dissolution experiments on displacive halite units from cores which resulted in 60 95 loss of rock thickness and mass due to dissolution of halite the unconsolidated red sediment resulting from these dissolution experiments compares favorably with much of the fine massive red siliciclastics that make up the greater part of the nippewalla group outcrops we propose that major lithologic differences resulting from near surface diagenetic processes must be expected in any evaporite bearing siliciclastic unit besides guiding correlation attempts between surface and subsurface this knowledge is vital for making accurate interpretations of depositional and diagenetic history of siliciclastic evaporite units

alluvial playa sedimentation in the lower keweenawan sibley group thunder bay district ontario the middle proterozoic sibley group is a mixed clastic carbonate red bed sequence located in the thunder bay nipigon area on the north shore of lake superior the lowest unit the pass lake forma

holocene coastal carbonates and evaporites of the southern arabian gulf and their ancient analogues abstract the holocene sediments of the coast of the united arab emirates in the southeastern arabian gulf are frequently cited in the literature as type examples for analogous assemblages of carbonates evaporites and siliciclastics throughout the geologic record this paper is intended as a convenient single source for the description of sediments of this region providing information on how to reach the classic localities and some of the analogs the holocene sediments of the region accumulate over an area that is 500 km long and up to 60 km wide the sediments collecting offshore are predominantly pelecypod sands mixed with lime and argillaceous mud with these latter fine sediments increasing as the water deepens the pelecypod rich sediments also collect east of abu dhabi island both in the deeper tidal channels between the barrier island lagoons and in deeper portions of the protected lagoons west of abu dhabi island the shallow water margin is the site of coral reefs and coralgal sands whereas to the east oolites accumulate on the tidal deltas of channels located between barrier islands grapestones accumulate to the lee of the reefs and the oolite shoals where cementation becomes more common they are particularly common on the less protected shallow water margins of the lagoons west of abu dhabi island pelleted lime muds accumulate in the lagoons in the lee of the barrier islands of the eastern abu dhabi lining the inner shores of the protected lagoons of abu dhabi and on other islands to the west are cyano bacterial mats and mangrove swamps landward of these a prograding north facing shoreline is formed by supratidal salt flats sabkhas in which evaporite minerals are accumulating this paper describes the localities associated with 1 the mangrove swamps of the west side of the al dhabaiya peninsula 2 the indurated cemented carbonate crusts cyanobacterial flats and sabkha evaporites on the shore of the khor al bazam south of qanatir island 3 the reef and oolitic sand flats on the coast just east of jebel dhana and 4 the marine travertine and aragonite coats associated with the beach sediments in a small bay south of jebel dhana and 5 the sabkha mutti between jebel barakah and al sila similar sedimentological associations of carbonate and evaporites to those of the holocene of the united arab emirates are to be found in the tertiary and mesozoic sedimentary rocks of the immediate subsurface in the arabian gulf other analogs to this setting include the paleozoic carbonates of the western usa europe and asia mesozoic carbonates of the gulf of mexico europe and middle east and tertiary sedimentary rocks in the middle east

genesis of the lower triassic bonebeds from gogolin s poland the impact of microbial mats on trapping of vertebrate remains abstract three bone bearing horizons consisting of seven bone bearing beds with fish and reptile remains were recently discovered in the uppermost rot buntsandstein lower triassic peritidal and shallow marine carbonates in the vicinity of gogolin s poland the aim of this study is to recognize the genesis and depositional environments of the bonebeds detailed fieldwork microfacies analysis and sem eds analysis reveal that the vertebrate remains occur to a great extent alongside evidence for former microbial activity the reptile remains represent at least dactylosaurus and nothosaurus sauropterygia genera while the fish remains belong to the chondrichthyes and actinopterygii the vertebrate remains were deposited in a transitional zone between the costal sabkha and the epicontinental sea the first bone bearing horizon originated in the most landward setting in the uppermost intertidal zone likely at the margins of a pond or coastal lagoon the second bone bearing horizon was formed in the upper intertidal zone the vertebrate remains of the third bone bearing horizon were accumulated in two different settings in the lower intertidal zone in a small palaeopond and in the subtidal zone in a protected back shoal lagoon three bone accumulations occur within planar stromatolites while the other bone bearing beds reveal more indirect evidence for former microbial activity in our opinion the presence of the sticky microbial mats in the intertidal settings was the crucial factor that allowed the establishment of and controlled these accumulations of vertebrate remains the soft gluey substrates trapped vertebrate remains that were transported across them once trapped the vertebrate bioclasts were efficiently immobilized and thus protected against damage due to sedimentological agents the lack of any orderly arrangement of the vertebrate bioclasts suggests that they may have been delivered to the individual mat surfaces by diverse media from various directions and also at different times

halite depositional facies in a solar salt pond a key to interpreting physical energy and water depth in ancient deposits subaqueous deposits of aragonite gypsum and halite are accumulating in shallow solar salt ponds constructed in the pekelmeer a sea level salina on bonaire netherlands antilles several halite facies are deposited in the crystallizer ponds in response to difference in water depth and wave energy cumulate halite which originates as floating rafts is present only along the protected upwind margins of ponds where low energy conditions foster their formation and preservation cornet crystals with peculiar mushroom and mortarboard shaped caps precipitate in centimetre deep brine sheets within a couple of metres of the upwind or low energy margins downwind from these margins cornet and chevron halite precipitate on the pond floors in water depths ranging from a few centimetres to approximately 60 cm halite pisoids with radial concentric structure are precipitated in the swash zone along downwind high energy shorelines where they form pebbly beaches this study suggests that primary halite facies are energy and or depth dependent and that some primary features if preserved in ancient halite deposits can be used to infer physical energy conditions subenvironments such as low to high energy shorelines and extremely shallow water depths in ancient evaporite basins

paired metamorphic belts revisited abstract the modern plate tectonics regime is characterized by a duality of thermal environments one representing the subduction zone and the other representing the arc backarc or orogenic hinterland this duality is the hallmark of one sided asymmetric subduction and the characteristic imprint of one sided subduction in the geological record is predicted to be the broadly contemporaneous occurrence of two contrasting types of metamorphic belt one of high dt dp type and the other low dt dp type the broadly contemporaneous occurrence of granulite and ultrahigh temperature metamorphism with eclogite high pressure granulite metamorphism in the geological record since the neoarchean era is evidence of dual thermal environments and indicates that subduction has operated on earth since that time classic paired metamorphic belts in which an inboard high dt dp metamorphic belt is juxtaposed against an outboard low dt dp metamorphic belt along a tectonic contact such as the ryoke and sanbagawa belts in japan are found in phanerozoic accretionary orogens of the circum pacific generally they appear to result from juxtaposition of terranes with different metamorphic facies series that may or may not be exactly contemporaneous and that may or may not be far traveled this is a consequence of the difference between globally continuous subduction generating a low to intermediate dt dp environment in the subduction zone and a high dt dp environment in the arc backarc system and metamorphic imprints in the geological record that represent discrete events due to changes in plate kinematics or subduction boundary dynamics or as a result of collision of ridges arcs or continents with the upper plate at the trench the concept of paired metamorphic belts may be generalized and extended more widely than in the original proposition to subduction to collision orogenic systems in addition to accretionary orogenic systems in this wider application the term paired metamorphic belts may be used for penecontemporaneous belts of contrasting type of metamorphism that record different apparent thermal gradients one warmer and the other colder juxtaposed by plate tectonics processes brown 2009 this extends the original concept of miyashiro 1961 beyond the simple pairing of high dt dp and low dt dp metamorphic belts in circum pacific accretionary orogens and makes it more useful in the context of our better understanding of the relationship between thermal regimes and tectonic settings this is particularly useful in subduction to collision orogenic systems where the suture and lower plate materials will register the imprint of low to intermediate dt dp and the upper plate will register penecontemporaneous high dt dp metamorphism commonly manifested at shallow crustal levels by the occurrence of granites in the rock record

permian clear fork group north robertson unit integrated reservoir management and characterization for infill drilling part i geologic analysis north robertson unit nru produces from highly heterogeneous shallow marine platform carbonate reservoirs of the permian leonardian clear fork and lowermost glorieta formations discovered in 1955 the productive area encompasses 5366 ac 2173 ha along the northern border of the central basin platform cbp in the permian basin of west texas clear fork glorieta production is widespread in this portion of the basin with most fields including nru now under waterflood primary production was on 40 ac 16 ha spacing with enhanced recovery dependent upon a combination of 20 ac 8 ha infill drilling and waterflooding total recoveries in these fields have been typically below 25 with many waterfloods performing below prediction due to a high level of lateral and vertical reservoir heterogeneity detailed geological and petrophysical analysis of new and existing cores from nru performed as part of a combined industry u s department of energy doe sponsored project has resulted in greatly improved reservoir characterization of the clear fork productive interval ultimately allowing for the quantification and mapping of specific productive intervals within the 1000 ft 300 m gross reservoir interval relevant data have been used to identify optimal sites for strategic 10 ac 4 ha infill development aimed at maximizing the efficiency and profitability of future oil reserve growth within the unit a total of 14 producing wells and 4 injector wells were drilled on the basis of the new geologic engineering model results of these wells were impressive and confirmed the value of targeted infill development in such a complex reservoir part i of this article summarizes field data and geologic information essential to the reservoir characterization effort in nru part ii of this article to appear in the november issue of the bulletin will discuss petrophysical and engineering data as well as the targeted infill drilling effort and its results

textural features of holocene perennial saline lake deposits of the taoudenni agorgott basin northern mali abstract the holocene salt lake deposits of the taoudenni agorgott basin northern mali mainly consist of sediments with a high glauberite na2ca so4 2 content the remainder of the deposits largely consists of salt beds with a bloedite na2mg so4 2 4h2o thenardite na2so4 or halite nacl composition a petrographical study of the deposits demonstrates that they formed in a perennial lake that experienced a gradual decrease in water depth textural features of the glauberite dominated deposits are found to be related to water depth through the control that this factor exerts on the sensitivity of the lake to changes in water supply and to short term variations in evaporation rates in this way layering due to variations in glauberite content and crystal size is inferred to be typical of deposits that formed in shallow water whereas unstratified deposits are the product of high lake level stages halite textures are found to be indicative of the place within the water column where crystal growth occurred along the lake bottom or higher which is mainly determined by water depth and partly by evaporation rates the oldest halite beds are largely unaltered cumulate deposits whereas the youngest layers developed exclusively through bottom growth the basal part of one thick halite bed at a level between these two groups of halite layers developed by an alternation of both types of growth in response to variations in evaporation rates variations in mineralogical composition between and within the salt beds that formed during the earliest periods with a higher salinity up to the first stage with halite formation record a change in lake water chemistry with time but they are in one instance also determined by an early diagenetic mineral transformation