contrasting nature of petroliferous mesozoic cenozoic basins in eastern and western china onshore petroliferous basins of mesozoic cenozoic age in china include two distinct geographic geotectonic groups eastern extensional rifted basins and western compressional orogenic basins eastern basins are faulted depressions and crustal sags that formed where incipient intracontinental rifting thinned the crust and developed tilted fault blocks and half grabens bounded by normal faults western basins are flexural downbows that were depressed under the tectonic load of adjacent thrust sheets associated with the folded mountain ranges of central asia source beds in both groups of basins are dominantly dark lacustrine mudstones of terrestrial facies associations and reservoirs are mainly fluviodeltaic sandstones hydrocarbon traps in the eastern basins include e tensional rollover anticlines compactional drape anticlines diapiric salt domes buried hill highs in the substratum and stratal pinch outs on the flanks of buried highs simple or faulted anticlinal traps are dominant in the western basins multiple reservoir horizons are characteristic of oil fields in both groups of basins orogenic compression which developed the western basins is attributed to the successive collision of microcontinents with the southern edge of the composite eurasian continental mass crustal extension which developed the eastern basins is attributed to incipient rifting within and behind magmatic arcs along the margin of the pacific ocean basin

preliminary results from tree increment and playa sediment cores from the paroo north western new south wales australia abstract the paroo ecosystem of far north west new south wales is sensitive to enso the paroo is also currently subject to contention for water extraction aquat conserva mar freshwater ecosystems 8 1998 361 in which information about long term ecosystem dynamics may be useful the environmental history of the paroo has not been described despite the existence of potential records in saline lakes dunes and callitris trees geomorphic and pollen analyses are used to determine the duration and nature of the pollen record in both lake and dune deposits a 2 m core recovered from one unnamed lake informally named palaeolake and the slow accumulation of sediment ca 175 years cm 1 shows the record may cover 38 k years discontinuities in the lake sediments are expected to be less than the larger southern salinas and the gaps will be partly recorded in the dune materials in tandem the tree rings from two stands of callitris glaucophylla have been tested to determine the high resolution dendroclimatological record available ring width patterns were matched between trees using skeleton plots the temporal variability of these patterns and the uniform response of the trees indicates that ring width geometry is dependant upon climate preliminary results for organic material mineral magnetic susceptibility and stratigraphy of the playa and dune facies promise a good record of pleistocene climatic change the results show that the lake records give long but temporally discontinuous information whereas tree rings provide short and relatively continuous information together they record climate changes over the last few thousand years and the impact of european management on the vegetation and rates of sediment deposition

paleoenvironmental and paleohydrochemical conditions of dolomite formation within a saline wetland in arid northwest australia abstract groundwater dolocrete occurring within the fortescue marsh a large inland wetland in the pilbara region of northwest australia has been investigated to provide paleoenvironmental and paleohydrological records and further the understanding of low temperature dolomite formation in terrestrial settings over the quaternary period two major phases of groundwater dolocrete formation are apparent from the presence of two distinct units of dolocrete based on differences in depth 18o values and mineral composition group 1 g1 occurs at depth 20 65 m b g l below ground level and contains stoichiometric dolomite with 18o values of 4 02 0 71 group 2 g2 is shallower 0 23 m b g l occurring close to the current groundwater level and contains ca rich dolomite secondary calcite with a comparatively lower range of 18o values 7 74 and 6 03 modelled 18o values of paleogroundwater from which older g1 dolomite precipitated indicated highly saline source water which had similar stable oxygen isotope compositions to relatively old brine groundwater within the marsh developed under a different hydroclimatic regime the higher 18o values suggest highly evaporitic conditions occurred at the marsh which may have been a playa lake to saline mud flat environment in contrast g2 dolomite precipitated from comparatively fresher water and modelled 18o values suggested formation from mixing between inflowing fresher groundwater with saline brine groundwater within the marsh the 18o values of the calcite indicates formation from brackish to saline groundwater which suggests this process may be associated with coeval gypsum dissolution in contrast to the modern hydrology of the marsh which is surface water dependent and driven by a flood and drought regime past conditions conducive to dolomite precipitation suggest a groundwater dependent system where shallow groundwaters were influenced by intensive evaporation

marine isotope stage 4 in australasia a full glacial culminating 65 000 years ago global connections and implications for human dispersal patrickde deckker lee j arnold sandervan der kaars germain bayone jan berend w stuut kerstin perner raquel lopes dos santos ryu uemura martina demuro

little ice age aridity in the north american great plains a high resolution reconstruction of salinity fluctuations from devils lake north dakota usa the little ice age was an interval between about ad 1500 and 1850 characterized by advancing glaciers in mountainous regions of europe and western north america however it is unclear whether this cool moist period was truly global in extent or how it was manifested in other regions with different climatic controls a high resolution reconstruction of salinity fluctuations in devils lake north dakota based on fossil diatoms ostracode shell geochemistry and bulk carbonate geochemistry indicates that saline conditions prevailed throughout much of the recent past these results suggest an arid climate in the northern great plains throughout the little ice age and that during this interval climatic gradients between the great plains and regions to both the east and west may have been quite steep

petrographic and geochemical evidence for the formation of primary bacterially induced lacustrine dolomite la roda white earth pliocene central spain upper pliocene dolomites white earth from la roda spain offer a good opportunity to evaluate the process of dolomite formation in lakes the relatively young nature of the deposits could allow a link between dolomites precipitated in modern lake systems and those present in older lacustrine formations the la roda mg carbonates dolomite unit occur as a 3 5 to 4 m thick package of poorly indurated white massive dolomite beds with interbedded thin deposits of porous carbonate displaying root and desiccation traces as well as local lenticular gypsum moulds the massive dolomite beds consist mainly of loosely packed 1 to 2 m sized aggregates of dolomite crystals exhibiting poorly developed faces which usually results in a subrounded morphology of the crystals minute rhombs of dolomite are sparse within the aggregates both knobbly textures and clumps of spherical bodies covering the crystal surfaces indicate that bacteria were involved in the formation of the dolomites in addition aggregates of euhedral dolomite crystals are usually present in some more clayey sepiolite interbeds the thin porous carbonate mostly dolomite beds exhibit both euhedral and subrounded bacterially induced dolomite crystals the carbonate is mainly ca dolomite 51 54 mol caco3 showing a low degree of ordering degree of ordering ranges from 0 27 to 0 48 calcite is present as a subordinate mineral in some samples sr mn and fe contents show very low correlation coefficients with mg ca ratios whereas sio2 and k contents are highly correlated 18o and 13c values in dolomites range from 3 07 to 5 40 pdb mean 0 06 1 75 and from 6 34 to 0 39 pdb mean 3 55 1 33 respectively samples containing significant amounts of both dolomite and calcite do not in general show significant enrichment or depletion in 18o and 13c between the two minerals the correlation coefficient between 18o and 13c for dolomite is extremely low and negative r 0 05 whereas it is higher and positive r 0 47 for calcite the lacustrine dolomite deposit from la roda is interpreted mainly as a result of primary precipitation of dolomite in a shallow hydrologically closed perennial lake the lake was supplied by highly saturated hco3 co32 groundwater that leached dolomitic mesozoic formations precipitation of dolomite from alkaline lake waters took place under a semi arid to arid climate however according to our isotopic data strong evaporative conditions were not required for the formation of the la roda dolomite a significant contribution by bacteria to the formation of the dolomites is assumed in view of both petrographic and geochemical evidence

lithification of peritidal carbonates by continental brines at fisherman bay south australia to form a megapolygon spelean limestone association abstract groundwater springs in the supratidal zone at fisherman bay south australia are the sites of aragonite precipitation and cementation of holocene marine carbonates lithification which commenced less than 3000 years bp and is still active has formed a cavernous limestone containing megapolygons tepees and speleothems including pisoliths floe aragonite and aragonitic pool deposits the emerging waters are from a continental source and have evolved from low alkalinity waters of pleistocene sand and clay coastal plain aquifers which have passed through an underlying tertiary marine carbonate aquifer the resulting waters have high pco2 total carbonate ca and sulphate concentrations they are close to saturation with respect to aragonite and their mmg2 mca2 ratios approach or exceed the critical aragonite precipitation value aragonite is precipitated from these waters when they approach the surface and evolve co2 features which taken together may diagnose ancient examples of this process include 1 primary aragonitic cements with high msr2 mca2 values 2 nonmarine 34s values in associated gypsum 3 two superimposed networks of surface polygons one delineated by extensional boundaries the other by tepees 4 high water vadose zone isopachous grain cements 5 interconnected speleothem lined cavities and 6 the presence of evaporites only in surface sediments possible ancient examples of peritidal carbonate lithification by saline spring waters rising from confined aquifers are recognized in descriptions of carbonates from west texas lombardy and the atlas mountains the areal extent of each of these deposits suggests that the process may be a geologically important feature and its products may be diagnostic of semi arid or arid zone paralic sedimentation

sedimentary processes related to the groundwater flows from the mesozoic carbonate aquifer of the iberian chain in the tertiary ebro basin northeast spain abstract in this work the importance of groundwater in the formation and evolution of evaporitic lacustrine facies in the iberian chain and ebro basin contact spain is studied there are outcrops of geological materials from palaeozoic to quaternary times these materials have been classified into eight hydrostratigraphic units the jurassic carniolas and limestones in the iberian chain hu 4 and 5 are the materials which have the best hydraulic properties for underground water catchment and for forming the regional aquifer the triassic gypsum and marl of hu 3 form the impermeable substratum of the overlying jurassic and cretaceous carbonated aquifers and they are therefore the impermeable base of the aquifers being studied the equipotential line map of the regional aquifer shows the pattern of the groundwater flowing to specific points which mark the springs producing the underground drainage of the iberian chain the volume of water throughout the aquifer is currently evaluated at approximately 250 hm3 year which discharge through springs with high flowrates or through diffuse discharges in the riverbeds and in wetlands saline lakes the water discharged in these springs has a high mineralisation with a dry residue of over 1000 mg l calcium sulphate compositions dominate originating in the presence of soluble anhydrous materials within the lias and keuper formations the current sedimentation in relation to the groundwater flows from the iberian chain can only be found in the areas of diffuse discharge where the evaporitic sedimentation can be observed because of the frequently endorheic character on the right bank of the ebro river more than 60 depressions are known where very mineralised lakes form these are locally referred to as saladas during the miocene the hydrogeological functioning would be similar to the present one leaving the groundwater and the dissolved salts in a non marine basin they would therefore accumulate in large areas of diffuse discharge creating lakes where the evaporites would precipitate the deep regional groundwater flows would ascend to the surface from the overthrust lamina fronts going through thick tertiary alluvial deposits in the ebro basin and therefore the discharges were mainly diffuse

relationship of two lacustrine ostracode species to solute composition and salinity implications for paleohydrochemistry nonmarine ostracode species are indicative of the physical and chemical nature of lacustrine environments although salinity has traditionally been regarded as one of the more important parameters that affect the occurrence patterns of lacustrine ostracodes examination of the solute composition and salinities of the lakes where limnocythere sappaensis and l staplini live reveals that solute composition and not salinity is the most critical factor that controls their occurrence the occurrence of these taxa in the modern world is mutually exclusive l sappaensis lives in water that is enriched in na hco 3 and depleted in ca 2 l staplini lives in water that is enriched in various combinations of na mg 2 ca 2 cl and is depleted in hco 3 these solute compositions are the product of the mineral fractionation processes described by eugster and hardie the positive correlation between these two species occurrences and the mineralogic fractionation processes suggests that these taxa may be used as reliable paleohydrochemical indicators studies in progress dealing with other ostracode taxa suggest that saline lacustrine ostracodes can provide a precise method for reconstructing paleohydrochemistry

palaeontological and sedimentological observations on nonmarine lameta formation upper cretaceous of maharashtra india their palaeoecological and palaeoenvironmental significance abstract the lameta formation upper cretaceous is exposed in parts of central and western india as detached outcrops and covers an area of nearly 5000 km 2 it generally rests on precambrian and gondwana rocks and is invariably capped by deccan trap volcanic flows in the nand and dongargaon areas of the chandrapur and nagpur districts of maharashtra the lameta formation covers more than 400 km 2 attains a thickness of 20 m and is richly fossiliferous the palaeontological and sedimentological observations strongly indicate alluvial limnic environment for the deposition of the lameta sediments under semi arid conditions different lithofacies representing channel overbank paludal and lacustrine subenvironments have been identified the biota represents terrestrial semiaquatic and aquatic communities and is represented by dinosaurs fishes crocodiles chelonia gastropods ostracodes charophytes coniferales and angiosperms the biota appears to be mainly controlled by the different lithofacies thereby suggesting strong palaeoecological and taphonomical control over their occurrence records of mass death of clupeids have been observed in many layers within the lacustrine clays a nesting site of sauropods has been found near pavna along with evidence of site fidelity a clutch with small oblong shaped eggs of avian like affinity has been also unearthed from this nesting site the lameta sediments were deposited in a freshwater environment that provided the preferred ecological niche for large scale breeding and nesting of sauropods

limnic food web and salinity of the upper miocene bicorb palaeolake eastern spain abstract in an attempt to arrive at a preliminary reconstruction of the limnic food web of the upper miocene bicorb basin eastern spain and to obtain new palaeontological information regarding the salinity of its palaeolake studies were made of the fossil assemblages of aquatic organisms in the outcrops of facies associations 2 and 3 subunit b of the upper unit established in 1998 by anadon et al these outcrops known as venus cantera and bicorb insectos 1 and 3 are typical konservat lagerstatten we here describe four specimens of a new species of the cyprinodontid genus aphanius a bicorbensis sp nov plus several chironomid insects and coprolites mainly from the venus outcrop two morphotypes of chironomid pupal exuviae were found both of which were attributed to the subfamily chironominae the larger morphotype was attributed to chironomus sp tribe chironomini and the smaller to tanytarsini gen et sp indet coprolites were separated into two types c1 and c2 based on their contents i e the remains of chironomids or miliolid foraminifers respectively the miliolid foraminifers belonged to the family hauerinidae possibly to the genus quinqueloculina it is concluded that aphanius fish were second level consumers feeding on chironomids and miliolid foraminifers primary producers were mainly represented by the aquatic plant potamogeton botryococcus green algae and microbial mats almost certainly photosynthetic this notably simple limnic food web and this aquatic fossil assemblage suggest that the bicorb palaeolake was saline or brackish the living taxa related to this assemblage are notably tolerant of high salinity this salinity is related to the presence of a triassic diapir on the southern side of the bicorb basin in addition non bioturbated finely laminated calcareous mudstones and exceptionally well preserved delicate insects indicate the lake water to have shown a halocline leading to meromictic episodes with the development of microbial mats at the lake bottom

hydrology of lake eyre australia el nino link abstract all major ephemeral rivers of australia lie in the lake eyre basin dry for years on occasions they carry enormous floods with annual volumes of 40 km 3 and instantaneous discharges of the order of 30 000 m 3 s 1 mean annual runoff of the basin is 4 km 3 or 3 5 mm significantly less than the 57 mm for the whole of australia this paper examines lake eyre and its drainage basin describing the historical hydrology of the catchment both in terms of instrument records and inflows hindcast using a model based on the technique of coral fluorescence palaeohydrological reconstruction coral fluorescence is a function of nearby river discharge and can be used to reconstruct annual river outputs reconstruction coral fluorescence is a function of nearby river discharge and can be used to reconstruct annual river outputs beyond the instrument period the burdekin river catchment runoff history is strongly paralleled by the volumes of lake eyre inflows during the period of common reliable instrument gaugings the burdekin runoff data have been extended back to 1735 a d using the correlation between river discharge and annual growth band fluorescence in an old coral from pandora reef off the north queensland coast for the instrument period 1952 to 1980 73 of the variance between coral fluorescence and burdekin discharge is common during the period 1949 1980 41 of the variance between coral fluorescence and lake eyre inflow data is common modelled inflows to lake eyre for the period 1885 1948 are based on the latter data set

evidence of a quaternary dammed lake in the mawat chwarta area western zagros kurdistan region ne iraq abstract the mawat chwarta valley is located north of the sulaimania city at northern iraq and is surrounded by high mountains on all sides white laminated sediments with annual varves on a millimetre scale have been recorded at eight localities on the valley gentle slopes sedimentological palaeontological and geomorphological data of these sediments suggest that a lake occupied the valley during the quaternary the sediments are of two types purely fine grained and fine grained with coarse interbeds the two types occur at an elevation difference of about 62 m the two types are interpreted as representing deep abyssal and shoreline deposits respectively and indicate the approximate depth of the lake the sediments contain the fresh water green algae of the genus botryococcus in addition to a few leaves scattered plant debris and some pollen grains mainly of herbaceous plants contrary to the general south western drainage pattern in northern iraq the mawat chwarta valley is drained to the north where the mawat river passes now through deep and narrow gorges along which rock slides and debris plugs are known to have occurred in the past these mass wasting events are considered here to have blogged the runoff of the valley in the past and eventually led to the formation of a large dammed lake numerical chronology work failed which requires further investigation in the future

a unified nomenclature for tectonic structures on the surface of enceladus abstract enceladus has experienced widespread and diverse tectonic deformation the diversity and nonuniform distribution of structures visible on the surface attests to a complicated and perhaps long lived tectonic history currently no fundamental classification scheme based on morphology exists for the tectonic structures on enceladus which limits analysis and discussion of tectonic structures and regional and global tectonic histories characterization and classification of structures on enceladus is an important first step in understanding its tectonic history here we propose a global morphologic i e nongenetic classification scheme for tectonic structures on enceladus five classes of tectonic structures on enceladus have been identified based on images and limited topographic data troughs scarps chasmata ridges and bands morphological variation of structures exists within these classes reinforcing the complicated tectonic history of this small body

paleolimnology and taphonomy of some fish deposits in fossil and uinta lakes of the eocene green river formation utah and wyoming abstract in four sections in the lacustrine eocene green river formation in utah lake uinta fish are preserved on carbonate mudflats along high energy carbonate shorelines in the littoral zone and in deeper profundal areas scattered bones and scales are found throughout dropped from disintegrating floating carcasses gar scales typify shallow water deposits partly due to habitat preference beach concentrations of greatly abraded bones and scales grade offshore into storm lag layers and lenses which grade to loosely packed horizons or patches of unworn remains littoral fish fossils range from dropped bones to good skeletons with much floating lifting and scavenging preservation improves away from the waterline not only into deep and cold profundal waters where the carcasses are protected from scavenging by anoxia and prevented from floating by temperature and pressure but also onto mudflats where stranding and burial of carcasses can also protect them a section through an isolated part of the green river formation in wyoming fossil lake also ranged from profundal to littoral with minor emergence dropped body parts were found throughout but preservation quality of the best specimens improved with presumed depth the beds with the best specimens seem to have accumulated at the bottom of a deep stratified warm monomictic lake our lake uinta sections were generally shallower and suggest more fluctuations in water level but this is not relevant to broad paleolimnological interpretations because they represent marginal zones which are necessarily more sensitive to changes in depth overall fish fossils are especially informative in deeper waters where sedimentary distinctions fail

the pleistocene palaeoenvironmental record of lake buchanan an atypical australian playa lake buchanan is an intermontane playa located in subdued topography astride the great dividing range in central queensland undated multiple beach ridges on the western shore and cliffed lacustrine sediments on the eastern shore both up to 5 m above the present lake floor attest to previous permanent lake phases due to its position astride the continental divide for much of the tertiary lake buchanan probably escaped the acid weathering regime and attendant gypsum formation of the continental interior present surface and groundwaters 140 210 salinity are atypical of other australian salt lakes which are commonly mg2 rich and similar to evaporated ocean water for lake buchanan ionic ca2 mg2 and the sr2 95 ppm and f 12 ppm contents are very high and br exceedingly low 0 02 ppm the unusual water compositions are considered to reflect the chemical composition of the attachment rocks which are mesozoic and tertiary clay rich sandstones this relationship argues against the universal applicability of marine aerosol transport and marine salt recycling as sources of salts for australian playas sediments cored from the lake floor are uniform non laminated sandy clays composed of quartz 35 weight kaolinite 30 and illite 25 there is no primary chemically precipitated carbonate or gypsum low magnesium calcite occurs as a biogenic detritus of shelly fauna charophyte gyrogonites and pedogenic nodules apart from the upper 20 50 cm the sediment is devoid of organic carbon a sequence of palaeosols indicates exposure of the lake floor during at least 13 episodes in the pleistocene for a 15 m core bu 1 palaeomagnetic analysis has identified the brunhes matuyama boundary 0 73 ma at 5 0 m and probably the top of jaramillo subchron 0 92 ma at 6 3 m an extremely slow sedimentation rate of 7 m ma is indicated for the last 1 ma from 6 5 to 10 5 m in this core intense iron staining pedogenesis has confounded designation of palaeomagnetic polarity extrapolation might suggest an age of between 1 5 and 2 ma for the base of this core fossil biota from bu 1 and bu 9 include abundant ostracods and charophyte remains and less commonly gastropods fish fragments and foraminifers water depth is interpreted from ostracod and charophyte assemblages for the last 0 73 ma we recognize four major wet phases the early history of bu 1 below 12 m 16 ma alternated between dry playa and shallow lake

mediation of endoevaporitic microbial communities in early replacement of gypsum by dolomite a case study from miocene lake deposits of the madrid basin spain abstract based on petrographic mineralogical isotope and facies assemblage analysis a microbial origin is established for the formation of dolomite associated with gypsum in miocene evaporite lake deposits of the madrid basin central spain in these deposits dolomite is present as both intercalated carbonate beds locally showing domal stromatolite structures between packages of selenite christmas tree like gypsum and patches replacing macrocrystalline gypsum texture of the dolomite is characterized by crystal aggregates showing a variety of crystal sizes and morphologies e g platelets rhombs micro rods and rings whilst larger crystals are commonly spherical and or wheat grain shaped organic remains in the form of filaments shrubs micro fibrils and strands are also common and contain significant amounts of carbon these textural features are also recognized in dolomite replacing gypsum where fe oxide and sulfide as well as celestite are ubiquitous mixed with the dolomite groundmass the dolomite whether primary or replacing gypsum is poorly ordered and slightly ca rich thus non stoichiometric stable isotope compositions are characterized by negative values for both oxygen and carbon dolomite beds featuring domal stromatolites have 18o values ranging from 2 99 and 3 79 and 13c values ranging from 4 67 and 7 35 whilst 13c values determined in the dolomite replacive of gypsum shows a small range of variation between 5 70 and 6 96 by contrast 18o values of replacive dolomite oscillate in a wider range from 3 04 to 7 99 formation of the dolomite was associated mainly with microbial mats having taken place in relatively diluted lake water further evaporative concentration resulted in precipitation of gypsum crystals sealing the mats and creating endoevaporitic microenvironments in which endolithic cyanobaterial activity produced extensive boring and corrosion of the gypsum crystals hiatuses in gypsum growth caused an intensification of the corrosion process and favored the precipitation of dolomite mediated by microbes resulting in pervasive replacement of the sulfate

classification and genesis of calcrete and gypsite lithofacies in paleodrainage systems of inland australia and their relationship to carnotite mineralization calcrete and gypsite lithofacies are chemical sedimentary rocks irre spective of age and or stratigraphic position the depositional environments of these deposits indicate that since early tertiary silting up of inland drainage developed internal salt lake systems with gypsite as the dominant evaporitic lithotype elongate bodies of phreatic calcrete formed in paleochannels almost all primary calcretes and gypsites have been modified by phreatic and vadose diagenetic processes because the diagenetic processes are complex stratigraphic analysis is difficult carnotite mineralization is probably not contemporaneous with calcretization assuming that waters from fertile uraniferous sources are flowing through the sediments several controls will govern carnotite mineralization ponding by physical or chemical barriers solution chemistry p co2 co 3 hco 3 v u and k concentrations eh ph and postdepositional physical or chemical changes for significant carnotite bodies to remain primary deposition must have been followed by a freezing mechanism to preserve the deposit diagenetic conditions which may cause remobilization vary between deposits therefore it may be unwise to use a single deposit as the basis for a widely applicable exploration model modified journal abstract

holocene ooids of aitutaki atoll cook islands south pacific although oolitic sands are widespread throughout the phanerozoic carbonate rock record and they are abundant in some modern shallow marine carbonate systems recent ooids have not been recognized from any locality in the pacific basin on aitutaki atoll cook islands south pacific oolitic sands occur in water depths of 2 1 6 3 m within the lagoon and less abundantly on shallower reef aprons most ooids are between 150 and 300 m in diameter have between 1 and 25 concentric to irregular laminae and occur with peloids and skeletal grains cortical laminae include mg calcite crystals with radial tangential and random orientations the occurrence and distribution of oolitic sands on aitutaki are facilitated by a convergence of hydrodynamic and chemical factors wave driven currents combined either with flow separation over a sharp increase in depth at the reef apron lagoon interface or with oceanward flow in the lee of islands serve to transport ooids without flushing them from the system here ph alkalinity and carbonate supersaturation are at some of the highest levels in the tropical pacific the restricted occurrence of holocene oolitic sands in areas of the pacific and atlantic basins with elevated ph and total alkalinity reflects the importance of carbonate saturation thresholds in limiting the spatial distribution of these sands in modern shallow marine settings these recent examples are consistent with interpretations of the importance of these variables in determining the distribution abundance and cortical mineralogy of oolitic sands throughout the phanerozoic stratigraphic record of carbonate accumulation

curtain eruptions from enceladus south polar terrain observations of the south pole of the saturnian moon enceladus revealed large rifts in the terrain that were found to be the sources of the observed jets of water vapour now it is shown that much of the eruptive activity can be explained by broad curtain like eruptions many of which were probably misinterpreted previously as discrete jets images taken by the cassini probe have revealed large fractures bounded by rifts towards the south pole of saturn s moon enceladus these features popularly known as tiger stripes reach higher temperatures than their surroundings and are thought to be the sources of observed jets of water vapour and icy particles joseph spitale et al compare cassini images with simulated curtains of material erupting from enceladus south polar terrain to produce detailed maps of the emissions at various times much of the eruptive activity can be explained by broad curtain like eruptions many of which were probably misinterpreted previously as discrete jets phantom jets in the synthesized curtains correspond closely to regions of enhanced brightness in the cassini images observations of the south pole of the saturnian moon enceladus revealed large rifts in the south polar terrain informally called tiger stripes named alexandria baghdad cairo and damascus sulci these fractures have been shown to be the sources of the observed jets of water vapour and icy particles1 2 3 4 and to exhibit higher temperatures than the surrounding terrain5 6 subsequent observations have focused on obtaining close up imaging of this region to better characterize these emissions recent work7 examined those newer data sets and used triangulation of discrete jets3 to produce maps of jetting activity at various times here we show that much of the eruptive activity can be explained by broad curtain like eruptions optical illusions in the curtain eruptions resulting from a combination of viewing direction and local fracture geometry produce image features that were probably misinterpreted previously as discrete jets we present maps of the total emission along the fractures rather than just the jet like component for five times during an approximately one year period in 2009 and 2010 an accurate picture of the style timing and spatial distribution of the south polar eruptions is crucial to evaluating theories for the mechanism controlling the eruptions

biological and sedimentary facies of australian salt lakes abstract four main types of salt lakes are recognized in australian 1 large playa lakes 2 small closed lakes or pans 3 crater lakes and 4 coastal lakes not connected to the sea basically all have an nacl chemistry biological and sedimentary facies characteristic of these salt lakes can be arranged into three basic groups which relate to particular phases in lake regimes these phases are 1 wet phases of ephemeral shallow lakes 2 dry lakes and 3 deep water lakes all elements of the salt lake biota with fossilizable remains are discussed with a detailed account of the palaeo ecological information they offer elements of the nonaquatic biota associated with salt lake sediments are also analysed sedimentary features of australian salt lakes pertinent to palaeoecology are discussed in the context of their association with the biota using numerous illustrations the distribution of the biota on lake floors for example its concentration in particular areas of the lake or its destruction during particular episodes such as lake filling and drying is mentioned in the context of recognizing different facies three major lake regime phases are presented with emphasis on the biological and sedimentary facies which characterize them the paper concludes with a brief discussion of the relevance of recognizing particular salt lake facies and changes in lake histories for the study of palaeoclimates and for mineral and oil exploration

surface evolution of salt encrusted playas under extreme and continued dryness miocene continental saltpans are scattered in the central valley of the atacama desert one of the driest regions on earth these evaporitic deposits are hydrologically inactive and are detached from groundwater brines or aquifers the surface of the saltpans also known as salars comprises desiccation polygons commonly with nodular salt structures along their sides the morphology and bulk mineralogy of salt polygons differs between and within salars and the shape and internal structure of salt nodules varies between different polygon types based on field observation and mineralogy and crystallography data we generated a conceptual model for the genesis and evolution of these surface features whereby rare rainfall events are responsible for the transformation of desiccation salt polygons and the initial formation of salt nodules along polygon borders in addition frequent but less intense deliquescence events further drive the evolution of salt nodules resulting in a characteristic internal structure that includes laminations and changes in porosity and crystal morphologies as a result and despite the extreme dryness the surfaces of fossil salars are dynamic on timescales of several years to decades in response to daily cycles in atmospheric moisture and also to rare and meager rainfall events we propose that fossil salars in the atacama desert represent an end stage in the evolution of evaporitic deposits under extreme and prolonged dryness

geochemical and microbiological fingerprinting of airborne dust that fell in canberra australia in october 2002 during the night of 22 23 october 2002 a large amount of airborne dust fell with rain over canberra located some 200 km from australia s east coast and at an average altitude of 650 m it is estimated that during that night about 6 g m 2 of aeolian dust fell we have conducted a vast number of analyses to fingerprint some of the dust and used the following techniques grain size analysis scanning electron microscope imagery major trace and rare earth elemental plus sr and nd isotopic analyses organic compound analyses with respective compound specific isotope analyses pollen extraction to identify the vegetation sources and molecular cloning of 16s rrna genes in order to identify dust bacterial composition dna analyses show that most obtained 16s rrna sequences belong mainly to three groups proteobacteria 25 bacteriodetes 23 and gram positive bacteria 23 in addition we investigated the meteorological conditions that led to the dust mobilization and transport using model and satellite data grain sizes of the mineral dust show a bimodal distribution typical of proximal dust rather than what is found over oceans and the bimodal aspect of size distribution confirms wet deposition by rain droplets the inorganic geochemistry points to a source along near the darling river in nw new south wales a region that is characteristically semiarid and both the organic chemistry and palynoflora of the dust confirm the location of this source area meteorological reconstructions of the event again clearly identify the area near bourke cobar as being the source of the dust this study paves the way for determining the export of australian airborne dust both in the oceans and other continents

collapse sinkholes and radar interferometry reveal neotectonics concealed within the dead sea basin 1 the dead sea ds pull apart basin is one of the more seismically active segments of the ds transform plate boundary in the last decade hundreds of collapse sinkholes have been formed along the ds coastlines in israel and jordan causing severe damage to the regional infrastructure the formation of these sinkholes is attributed to the dissolution of a buried salt layer by fresh groundwater due to the drop of the ds and the associated groundwater levels here we show that the sinkhole distribution combined with gradual land subsidence measured by radar interferometry insar track young fault systems suspected as active concealed within the fill of the ds rift this notion is supported by 1 sinkholes clustering along discrete lineaments with a striking trend similarity to that of the exposed rift margin faults 2 prominent discontinuities in seismic reflection profiles offsetting young sediments several kyrs old below sinkhole lines and 3 straight boundaries of gradual subsidence features that coincide with or parallel sinkhole lines combined the sinkhole lineaments and the insar measurements reveal a zigzag pattern of buried faults within the ds rift fill

the middle late jurassic forced regression and disconformity in central portugal eustatic tectonic and climatic effects on a carbonate ramp system successions across the middle upper jurassic disconformity in the lusitanian basin west central portugal are highly varied and were probably developed on a large westward inclined hangingwall of a half graben the disconformity is preceded by a complex forced regression showing marked variations down the ramp and provides an example of the effects of rapid relative sea level falls on carbonate ramp systems in the east middle jurassic inner ramp carbonates candeeiros facies are capped by a palaeokarstic surface veneered by ferruginous clays or thick calcretes in the west mid outer ramp marls and limestones brenha facies are terminated by two contrasting successions 1 a sharp based carbonate sandbody capped by a minor erosion surface overlain by interbedded marine lagoonal deltaic deposits with further minor erosion exposure surfaces 2 a brachiopod rich limestone with a minor irregular surface overlain by marls lignitic marls with marine and reworked non marine fossils and charophytic limestones with further minor irregular surfaces and capped by a higher relief ferruginous erosional surface the age ranges from late bathonian in the east to late callovian in the west this disconformity assemblage is succeeded by widespread lacustrine lagoonal limestones with microbial laminites and evaporites cabacos facies attributed to the middle oxfordian over the whole basin increasingly marine facies were deposited afterwards in middle jurassic inner ramp zones in the east the overall regression is marked by a major exposure surface overlain by continental sediments in middle jurassic outer ramp zones to the west the regression is represented initially by open marine successions followed by either a sharp marine erosion surface overlain by a complex sandbody or minor discontinuities and marginal marine deposits in both cases capped by the major lowstand surface reflooding led to a complex pattern of depositional conditions throughout the basin from freshwater and brackish lagoonal to marginal and shallow marine settings additional complications were produced by possible tilting of the hangingwall of the half graben the input of siliciclastics from westerly sources and climate change from humid to more seasonally semi arid conditions the middle late jurassic sea level fall in the lusitanian basin is also recorded elsewhere within the iberian and other peri atlantic regions and matches a transgressive to regressive change in eustatic sea level curves indicating that it is related in part to a global event

high resolution saline lake sediments as enhanced tools for relating proxy paleolake records to recent climatic data series abstract lake level in an endorheic saline lake in southern europe has been inferred for the last 105 years 1889 1994 at an annual level of resolution using two independent methods first ordination analyses factor analysis fa correspondence analysis ca and detrended correspondence analysis dca have been used to point out the mineral successions of the sedimentary record these successions are evidenced by the arch disposition of both samples and mineral phases in the plane defined by the first two eigenvectors calculated by these analyses these temporal evolutions are the same as those obtained during the drying and refilling phases of saline lakes relay indices ri were obtained from distances to the first two eigenvectors which accurately reconstructed the lake level evolution during this period second an inferred lake level series was obtained using a multivariate time series model from the average maximum temperatures and total rainfall six main drought periods were found which coincided with known droughts in the area a high level of agreement was found between the two reconstructions which offered the possibility of directly extending the instrumental record back into the past therefore climatic changes could be reconstructed from saline lakes provided that an accurate chronological control of sedimentary processes is available

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

lake qinghai china closed basin like levels and the oxygen isotope record for ostracoda since the latest pleistocene abstract in 1985 a sino swiss limnogeological expedition to china s largest inland lake recovered seismic profiles and piston cores to help calibrate palaeoclimatic models of monsoon and insolation fluctuations over the northern tibet qinghai plateau since the last glacial maximum lake qinghai a perennial lake with an area of 4278 km2 1985 at 3194 m above sea level receives drainage from 30 000 km2 of catchment near the northwest corner of the plateau the 26 5 m deep terminal lake 1985 with brackish alkaline magnesium sulphate rich waters 14 g 1 1 tds has not overflowed since the last glacial but its levels have responded to climatic and hydrologic changes seismic reflection profiles for the sub bottom sediment structures revealed a complex topography with channels relict terraces tectonic tilting and deformation in deposits buried under a 4 6 m packet of mainly flat bedded sediments from which core samples were recovered the lowermost cored material 14 500 yr b p comprises mainly water lain loess deposited in a smaller flood plain lake of up a few metres depth under cold arid climatic conditions ams radiocarbon dating indicates average sedimentation rates for latest pleistocene and holocene deposits in central basin regions of 0 3 0 5 mm yr 1 the 18o values of fossil ostracod valves provide a record of changes in the isotopic chemistry of the lake waters that can be related to the precipitation evaporation budgets which have controlled the palaeo levels for lake qinghai the precipitation evaporation budget for the lake qinghai region is largely determined by the asian monsoon system the lake qinghai sediment record shows that there was no large influx of glacoer melt waters into the lake basin during the post glacial the regional climate remained arid until at least 12 500 yr b p when an incipient monsoon was possibly initiated river transported silts first reached the basin centre at 11 800 yr b p when the lake depth may have increased to 5 m possibly a monsoonal weakening for several centuries after 10 800 yr b p europe younger dryas caused a further period of aridity at 10 200 yr b p the basin began filling towards modern lake dimensions in response to a permanent strengthening of the asian monsoon substantial lake level rises probably characterised the periods 10 200 9800 9500 8500 8300 7200 yr b p and through perhaps a century at about 6800 yr b p decreasing levels probably characterised the intervening intervals short term lake level fluctuations through the mid holocene climatic optimum were minimal indicating a very stable climatic hydrologic regime an isotopic steady state for the lake waters since 3000 500 yr b p obscures the climatic hydrologic regime dependent 18o gradient but there is little stratigraphic evidence to suggest that the lake level has been significantly below its present level since that time three negative 18o excursions for the lake waters may correspond to known glacier advances on the plateau at 3000 2000 and 1500 yr b p during china s neoglacial

a fracture history on enceladus provides evidence for a global ocean 1 the region surrounding the south pole of saturn s moon enceladus shows a young pervasively fractured surface that emanates enough heat to be detected by the cassini spacecraft to explain the elevated heat and eruptive icy plumes originating from large cracks informally called tiger stripes in the surface many models implicitly assume a global liquid ocean beneath the surface here we show that the fracture patterns in the south polar terrain spt of enceladus are inconsistent with contemporary stress fields but instead formed in a temporally varying global stress field related to nonsynchronous rotation of a floating ice shell above a global liquid ocean this finding increase to at least three the number of outer planet satellites likely to possess a subsurface liquid water layer

an account of the techniques using ostracodes in palaeolimnology in australia abstract ostracodes are common in australian waters especially in saline lakes where they are particularly diverse this makes them indispensable tools for australian palaeolimnological studies especially since many australian lakes are saline the following types of subjective information can be obtained from the study of australian fossil ostracode faunas without knowledge of the ecology or taxonomy of their living representatives the search for a life assemblage can lead to detection of the presence of water currents and the effects of reworking in addition to the identification of particular facies such as a lake shoreline or a desiccation phase rate of sedimentation can be estimated as well as the amount of sediment compaction of drying information on water oxygenation and acidification can be obtained and finally presence of seasonality affecting lakes can be identified with additional reference to the ecology of particular species permanency of lake water can be assessed and so can the variability of rainfall and even at times the detection of whether a lake was close to a summer winter rainfall boundary shell ornamentation can inform on water depth in addition salinity data can be obtained as well as some information on water chemistry and temperature the latter from trace elements mg sr and stable isotope 18 o studies of ostracode shells

fossil diatoms and neogene paleolimnology abstract diatoms have played an important role in the development of neogene continental biostratigraphy and paleolimnology since the mid 19th century the history of progress in quaternary diatom biostratigraphy has developed as a result of improved coring techniques that enable sampling sediments beneath existing lakes coupled with improved chronological control including radiometric dating and varve enumeration improved statistical treatment of fossil diatom assemblages from qualitative description to influx calculations of diatom numbers or volumes and improved ecological information about analogous living diatom associations the last factor diatom ecology is the most critical in many ways but progresses slowly fortunately statistical comparison of modern diatom assemblages and insightful studies of the nutrient requirements of some common freshwater species are enabling diatom paleolimnologists to make more detailed interpretations of the quaternary record than had been possible earlier and progress in the field of diatom biology and ecology will continue to refine paleolimnological studies the greater age and geologic setting of tertiary diatomaceous deposits has prompted their study in the contexts of geologic history biochronology and evolution the distribution of diatoms of marine affinities in continental deposits has given geologists insights about tectonism and sea level change and the distribution of distinctive extinct diatoms has found utilization both in making stratigraphic correlations between outcrops of diatomaceous deposits and in various types of biochronological studies that involve dating deposits in different areas a continental diatom biochronologic scheme will rely upon evolution such as the appearance of new genera within a family in combination with regional environmental changes that are responsible for the wide distribution of distinctive diatom species the increased use of the scanning electron microscope for the detailed descriptions of fossil diatoms will provide the basis for making more accurate correlations and identifications and the micromorphological detail for speculations about evolutionary relationships

dinosaurs nesting on tidal flats abstract the discovery of a dinosaur clutch in upper cretaceous tidal flat deposits in the tremp formation in biscarri isona lleida spain provides insight into the mode of life of some dinosaurs the clutch occurs in grey marls that were originally waterlogged muddy sediments the seven elongated eggs are parallel to each other and with their long axis almost vertically oriented a mound nest is inferred in contrast to hole nest described so far for similar eggshell types the permeability of the eggshell oospecies megaloolithus siruguei was highly enhanced by a braided network of multicanaliculate pore canals the nest style eggshell porosity and tidal flat environment point to a periaquatic habitat for these dinosaurs a modern analogue occurs in crocodiles alligators and some birds living in periaquatic environments with nesting on plant mounds above waterlogged soils or even on floating vegetation

modern and holocene carbonate sedimentology of two saline volcanic maar lakes southern australia the basin lakes are two adjacent maar lakes located in the centre of the western volcanic plains district of victoria australia both lakes are saline and alkaline west basin lake is meromictic whereas east basin is a warm monomictic lake the carbonate mineral suite of the modern offshore bottom sediments of these basins consists mainly of dolomite and calcite with smaller amounts of hydromagnesite and magnesite in west basin and monohydrocalcite in east basin the dolomite hydromagnesite magnesite and monohydrocalcite are endogenic in origin being derived by primary inorganic precipitation within the water columns of the lakes or at the sediment water interface the calcite is biologically precipitated as ostracod valves in addition to the carbonates in the modern offshore deep water sediments the lakes also contain a girdle of nearshore carbonate hardgrounds both beachrock and microbialites algal boundstones are present these modern lithified carbonate units exhibit a wide range of depositional and diagenetic fabrics morphologies and compositions in west basin the hardgrounds are composed mainly of dolomite hydromagnesite and magnesite whereas dolomite and monohydrocalcite dominate the east basin sediments aragonite high mg calcite kutnahorite siderite and protohydromagnesite also occur in these lithified carbonate units stratigraphic variations in the carbonate mineralogy of the holocene sediment record in the lakes were used to help decipher the palaeochemistry and palaeohydrology of the basins these changes in conjunction with fluctuations in organic remains and fossil content indicate a pattern of lake level histories similar to that deciphered from other maar lakes in western victoria

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

geochemical and hydrological processes controlling groundwater salinity of a large inland wetland of northwest australia abstract understanding mechanisms of hydrochemical evolution of groundwater under saline and brine wetlands in arid and semiarid regions is necessary to assess how groundwater extraction or injection in large scale basins may affect the natural interface between saline fresh aquifers in those systems we investigated the evolution of groundwater of the fortescue marsh a large inland wetland of northwest australia that is mainly supplied by floodwater from the upper fortescue river catchment the marsh is located in the pilbara region one of the world s major iron ore provinces where mining activities often occur below water tables here we quantified the stable isotope and chemical composition of groundwater surface water and rainfall in and around the marsh to better understand how saline marshes and playa lakes function geochemically hydrologically and ecologically the deep groundwater 50 m depth of the fortescue marsh is highly saline 100 g l 1 whilst shallow groundwater 0 20 m depth and surface water are mainly fresh or brackish currently the marsh is mainly recharged by occasional floodwater consequently salt in the marsh is concentrated by evaporation of rainfall we expected that the hydrochemical composition of surface and groundwater would therefore reflect the chemical composition of rainwater we analysed 206 water samples for stable isotope composition 2 h 18 o and water chemistry including ph dissolved oxygen electrical conductivity ec and total dissolved solids tds as well as na ca mg k si fe hco 3 so 4 cl sr and br we then developed geochemical models and a salt inventory to estimate the geological time of salt accumulation and to decouple geochemical characteristics of salt from modern groundwater we found that groundwater associated with the marsh can be divided into two distinct groups that are characterised by their stable isotope compositions i fresh and brackish groundwater tds 1 18 o 8 0 0 9 and ii saline and brine groundwater tds 10 g l 1 18 o varies from 2 5 to 7 2 fresh groundwater was evaporated by

unusual twinning features in large primary gypsum crystals formed in salt lake conditions middle miocene madrid basin spain palaeoenvironmental implications reply abstract a gypsum formation in the middle miocene saline lake deposits of the madrid basin is composed of large twinned crystals displaying an unusual habit characterised by the twin re entrant angles systematically opening downward such a habit is an exception to the commonly accepted mottura s rule for the growth of large twinned crystals which have been observed in marine derived evaporitic settings the crystals twinned along 100 are composed of elongated sub crystals formed by the intersection of the pinacoid 010 and the hemipyramid 111 field and petrographic evidence indicate a primary origin by subaqueous growth on the bottom ruling out a secondary origin brine composition dominated by ca na so 4 cl can be one of the several factors potentially controlling the selective growth of this habit further observations could indicate that such inverted twinned crystals may be considered diagnostic of gypsum growth in continental settings as such a pattern has not been recognised in marine evaporite formations

paleohydrological indicators in playas and salt lakes with examples from canada australia and africa abstract the sedimentary records of playas and salt lakes provide some of the best evidence for hydrological change in a region these records are comprised of siliciclastic sediments and chemically precipitated minerals that typically vary temporally and spatially in some cases the interpretation is straightforward with mineralogical sequences related to changing brine concentrations and hydrology as well as to climate in other cases it is difficult to identify the controlling factors which include climate groundwater geological setting and basin morphology in addition diagenesis commonly affects the sedimentary record models of lake level fluctuations are given for basins in the canadian prairies and southeastern australia the lake manitoba model is based mainly on secondary changes associated with pedogenesis that alters the deeper water sediment during low water stages smaller canadian lakes in more arid regions display a larger variety of diagnostic paleohydrological indicators such as specific carbonate and salt mineralogy nature of bedding grain size and secondary alterations decreasing water levels in shallow lakes tend to show a progression from clastics to carbonates to salts and then back to clastics as groundwater levels fall below the lake floor similar parameters are used in australian lakes the hydrological model for the lake tyrrell playa in victoria whose present ionic composition is similar to seawater shows clastics being deposited when average lake levels are high followed by deposition of primary carbonates gypsum and halite once seasonal drying on the lake floor begins secondary gypsum grows within already deposited sediment and clay pelletization in the capillary fringe of surface sediment leads to basin deflation and the accumulation of adjacent eolian lunettes continued water level decline leads to pedogenesis subsequent lake level rises in all of these models may initiate sedimentation in any part of the hydrological cycle and a complete cycle in the sedimentary record appears to be uncommon

hydrochemistry on the yilgarn block western australia ferrolysis and mineralisation in acidic brines abstract in the southeastern part of western australia internal drainage and a semi arid climate have resulted in extensive development of playas the brines beneath the playas wedge outwards and force local infiltration to crop out at playa margins as discharge zones the discharging water contains dissolved fe2 oxidation and hydrolysis ferrolysis of which generates very acidic water ph 2 8 at least some of the alkalinity generated by the original reduction of fe3 has been sequestered as subsurface calcrete within local soils the acidity causes the dissolution of kaolinite which is abundant in playa sediments and as a thick capping on weathered bedrock giving water with a low ph and high concentrations of dissolved al and si evaporation and mixing with playa brines containing high concentrations of k and so4 causes alunite to precipitate as ph rises from a minimum of 2 8 at chlorinities of 1 to 2 m to 6 at chlorinities of 4 8 m the alunite deposits formed by this process are many orders of magnitude larger than occurrences elsewhere in the world the large scale mobilisation of si during this process may be one mechanism for the formation of silica cemented rocks silcrete that are widespread in the australian regolith

the maastrichtian danian maimara tracksite yacoraite formation salta group quebrada de humahuaca argentina environments and ichnofacies implications fil console gonella carlos alfredo consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet tucuman instituto superior de correlacion geologica universidad nacional de tucuman facultad de ciencias naturales e instituto miguel lillo departamento de geologia catedra geologia estructural instituto superior de correlacion geologica argentina

enceladus extreme heat flux as revealed by its relaxed craters 1 enceladus cratered terrains contain large numbers of unusually shallow craters consistent with deformation by viscous relaxation of water ice under conditions of elevated heat flow here we use high resolution topography to measure the relaxation fraction of craters on enceladus far from the active south pole we find that many craters are shallower than expected with craters as small as 2 km in diameter having relaxation fractions in excess of 90 these measurements are compared with numerical simulations of crater relaxation to constrain the minimum heat flux required to reproduce these observations we find that enceladus nominal cold surface temperature 70 k and low surface gravity strongly inhibit viscous relaxation under such conditions less than 3 relaxation occurs over 2 ga even for relatively large craters diameter 24 km and high constant heat fluxes 150 mw m 2 greater viscous relaxation occurs if the effective temperature at the top of the lithosphere is greater than the surface temperature due to insulating regolith and or plume material even for an effective temperature of 120 k however heat fluxes in excess of 150 mw m 2are required to produce the degree of relaxation observed simulations of viscous relaxation of enceladus largest craters suggest that relaxation is best explained by a relatively short lived period of intense heating that decayed quickly we show that infilling of craters by plume material cannot explain the extremely shallow craters at equatorial and higher northern latitudes thus like enceladus tectonic terrains the cratered regions of enceladus have experienced periods of extreme heat flux