hydrochemical evolution of regional groundwaters to playa brines in central australia abstract a large scale groundwater system in central australia discharges to a chain of playas recharge in calcrete and fractured rock aquifers gives rise to relatively low salinity hco 3 cl so 4 groundwaters which evolve through regional saline groundwaters to highly saline playa brines the hydrochemical evolution of the groundwaters follows the anionic sequence hco 3 cl so 4 cl bhco 3 so 4 cl so 4 hco 3 cl so 4 cl with increasing salinity there is a relative increase in na k mg cl and so 4 however there is a relative decrease in hco 3 ca and sio 2 owing to the precipitation of carbonate sulphate and silicate minerals and the resultant brines are depleted in these ions significant chemical variation in the composition of playa brines is a result of complex processes of solution evaporative concentration precipitation and mineralogical change including dolomitisation thermodynamic calculations based on the pitzer equations have enabled a general model to be developed for these evolutionary processes in saline groundwaters up to the stage of halite saturation at an early stage the regional groundwaters are saturated with respect to the carbonate minerals dolomite first then calcite with increasing salinity sulphate minerals begin to precipitate saturation with respect to gypsum is attained at a chlorinity of 19 and saturation with respect to anhydrite is attained at 122 the playa brines attain saturation with respect to halite at a chlorinity of 144 solute budgets based on a chloride concentration factor show that final playa brines are 178 times more concentrated than recharge groundwaters and confirm the virtually complete loss of hco 3 ca and sio 2 through precipitation there are subtle differences in the hydrochemistry of different central australian playa brines and also vis a vis playa brines described from other parts of the world most australian playas have brines of the cl na type with so 4 and mg also important the generally accepted hardie eugster model for brine evolution and mineral precipitation sequences has therefore been modified and extended three pathways are defined following calcite precipitation on the basis of the ratio of molar ca to alkalinity these pathways lead to saline waters with different compositions subsequent evolution of the brines depends on the ratios between molar so 4 mg ca and alkalinity

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

tertiary diachronic extrusion and deformation of western indochina structural and 40ar 39ar evidence from nw thailand the wang chao and three pagodas fault zones cut the western part of the indochina block and run parallel to the red river fault evidence of intense ductile left lateral shear is found in the lansang gneisses which form a 5 km wide elongated core along the wang chao fault zone dating by 40 ar 39 ar shows that such deformation probably terminated around 30 5 ma the wang chao and three pagodas faults offset the north striking lower mesozoic metamorphic and magmatic belt of northern thailand 40 ar 39 ar results suggest that this belt suffered rapid cooling in the tertiary probably around 23 ma these results imply that the extrusion of the southwestern part of indochina occurred in the upper eocene lower oligocene it probably induced rifting in some basins of the gulf of thailand and in the malay and mekong basins in the oligo miocene the continuing penetration of india into asia culminated with the extrusion of all of indochina along the ailao shan red river fault this occurred concurrently with the onset of e w extension more to the south plotting in a geographical reference frame the diachronic time spans of movement on left lateral faults east and southeast of tibet implies that the northward movement of the indian indenter successively initiated new strike slip faults located farther and farther north along its path

geochemistry of brines of the chott el jerid in southern tunesia application of pitzer s equations abstract in the chott el jerid in southern tunisia waters are strongly concentrated by evaporation under an arid climate the diluted waters are of the ca 1bmg 1bso4 type whereas the brines are of the na 1bcl type relatively concentrated in k and mg in concentrated waters ca and silica concentrations remain at a very low level the use of pitzer s equations for calculating the ion activities has permitted accurate saturation tests and a fairly good evaluation of the mineral sequences controlling the geochemistry of the basin

spatial variability and hydrologic evolution of australian lake basins analogue for pleistocene hydrologic change and evaporite formation abstract processes evident in basins across hydrologic gradients from humid to arid regions today provide analogues for systems that may have operated in some individual basins during periods of past hydrologic change thus lakes in humid regions today with low salinity sedimentary facies and with morphology controlled largely by wave action may closely resemble past lacustral pluvial phases experienced in zones which today are relatively arid and saline conversely playas controlled today by groundwater and in some cases subject to defletion may resemble those arid and dune building stages experienced by basins in sub humid regions today as they underwent glacial age desiccation in any such sequence of spatial or temporal gradients from humid to more arid conditions the frequency of basin filling and drying modulates the rate of evaporitive loss of interstitial waters from the exposed basin surface this in turn controls the salinity evolution of the interstitial and local groundwaters the notion of closed systems for terminal lakes while satisfactory for analysis of surface water budgets is quite inapplicable to the evolution of brines where surfacewater groundwater exchange during the high salinity drying stages becomes a controlling factor affecting all salt budgets in these systems evaporites may only be preserved when the sub surface waters have evolved to salinites near saturation for the salts concerned if sub surface waters are frequently diluted by surfacewater groundwater exchange evaporites will not be preserved in the record even though the surface system appears hydrologically closed the process of interstitial water evolution which controls efflorescence deflation and salt weathering exerts a dominating influence on basin geomorphic expression as well as on hydrochemical fractionation

water salinization in arid regions observations from the negev desert israel abstract the processes affecting salinization of precipitation surface water vadose water and groundwater were studied in the negev desert israel observations spanning 18 years included the collection of rainfall at three rain sampling stations flood water at six flood stations vadose water from four coreholes penetrating chalk formations and groundwater from 16 monitoring wells tapping the chalk aquitard dissolved carbonate dust and evaporation of the falling raindrops result in ca hco 3 2 facies and increased ion concentration of the rainwater with respect to inland more humid regions the exposure of flood water to evaporation during flood events is minimal the observed ca hco 3 2 facies and salt enrichment by a factor of three to five in the flood water with respect to precipitation results primarily from interactions of the flood water with the chalk and limestone bedrock including ion exchange on na and k bearing minerals and the dissolution of calcite gypsum and halite the presence of these salts at and near land surface results from the complete evaporation of rainwater in land surface depression storage areas following most rain events except for a small portion moving through the low permeability chalk matrix most of the vadose water moves through preferential pathways and is typically not exposed to evaporation this dual movement of water accounts for the nacl facies of vadose water and the variable rates of isotopic depletion and salt dilution observed in the underlying heterogeneous groundwater in the saturated zone although the variable mixing with low salinity isotopically depleted water percolating from the fractures accounts for the depleted isotopic composition of the groundwater its relatively low solute content cannot modify the groundwater nacl facies consequently only groundwater salinity in the chalk is reduced by the preferentially flowing water but the ca hco 3 2 facies prevailing in the rainwater and flood water disappears and the nacl imprint from the vadose zone prevails

the hydrogeology of the amadeus basin central australia abstract two hydrogeological environments are defined in the major sedimentary semi arid amadeus basin 155 000 km 2 of central australia the environments are structurally controlled and occur in palaeozoic strata in the north central part of the basin an area of broad wavelength folds contains extensive identifiable sandstone aquifers elsewhere strong folding and faulting has resulted in the development of a regional fractured rock aquifer because of the combination of lithological and structural control the two hydrogeological environments are only locally connected within the north central area three aquifers have been defined with groundwater flows eastwards into the fractured aquifer erosion and facies changes result in hydraulic continuity occurring between the three aquifers close to their junction with the fractured aquifer over pressured groundwater is present in the lowest of the three aquifers beneath hydrocarbons in two major structures adjacent to normally pressured groundwater

structural development of the mid tertiary doi suthep metamorphic complex and western chiang mai basin northern thailand abstract the northern western ranges of thailand contain mylonitic gneisses of the doi suthep metamorphic complex dsmc near chiang mai mylonitic foliations outline a southeast trending dome and stretching lineations trend n80 w low grade metasedimentary rocks and tertiary fanglomerates flank the dome on the east and widespread chloritic breccia marks the intervening doi suthep detachment fault we interpret that the metamorphic complex developed between triassic and early miocene with detachment faulting mylonitization and uplift during oligocene to miocene within the dsmc dikes of mutually cross cutting hence coeval granitic pegmatite and aplite cut mylonitic orthogneiss although the contacts of the dikes are sharp the dikes contain a mylonitic fabric that parallels the fabric in the surrounding mylonitic orthogneiss thus we infer that intrusion occurred during mylonitization east of doi suthep tertiary fanglomerates of the mae rim formation overlie the doi suthep detachment fault variable strikes with dips of 10 50 and several outcrop scale fold hinges suggest that the mae rim formation is deformed into a set of non cylindrical folds numerous variably striking high angle normal faults suggest either multiple deformations or deformation in a three dimensional strain field the discovery of an intraformational angular unconformity confirms that the mae rim formation accumulated during folding

hydrochemical processes in ground water discharge playas central australia a large groundwater system in the amadeus basin central australia discharges to a chain of playa lakes 500 km long the playas contain highly concentrated brines these are sodium chloride rich waters with appreciable magnesium and sulphate and very low concentrations of calcium and bicarbonate gypsum glauberite and other evaporite minerals are precipitating in the playas the groundwaters evolve to brine by concurrent processes of dissolution evaporative concentration mineral precipitation and mineralogical change chemical evolution is considered with reference to a concentration factor based on chloride ion transfer calculations demonstrate losses of magnesium and bicarbonate throughout as a result of precipitation sodium potassium calcium and sulphate are gained initially as a result of dissolution but lost subsequently as a result of precipitation larger playas in the chain exemplified by lake amadeus have dual shallow and deep groundwater flow paths whereas the smaller playas exemplified by spring lake have only shallow flow paths brines in the larger playas are diluted by deep groundwaters and this is reflected in the degree of saturation attained with respect to particular minerals thus saturation with respect to gypsum and glauberite is attained earlier in spring lake than in lake amadeus saturation with respect to halite is attained in spring lake but not in lake amadeus both playas are undersaturated with respect to hexahydrite and sylvite although these minerals occur in efflorescent crusts in spring lake

groundwater discharge processes at a central australian playa abstract water balance studies have been undertaken at a groundwater discharge playa spring lake near curtin springs in arid central australia hydraulic calculations indicate that the groundwater inflow to the playa is about 2000 m 3 d 1 this is equivalent to evaporative discharge integrated over the playa surface area 15 km 2 of about 49 mm yr 1 as the mean annual rainfall is 226 mm the total evaporative discharge is about 275 mm yr 1 measured water losses from the playa surface during a 3 month dry period july september 1985 ranged from 0 28 to 0 45 mm d 1 this is of the expected order of magnitude for the cooler half of the year the rate of water loss is variable over the playa surface the playa is surrounded by sand dunes monitoring of water level fluctuations indicates that annual rainfall events induce groundwater recharge in the playa marginal zone where the water table is within 4 m of the ground surface evaporation from the playa has resulted in the development of highly saline brines with density 1 20 or more and containing more than 250 g 1 2 total dissolved solids the brines are sodium chloride waters with appreciable magnesium and sulphate at the playa margin a transition zone has developed between saline regional groundwaters which underlie sand dunes and the playa hypersaline brines salt may be diffusing downwards beneath the regional grounwaters gypsum is precipitating in the playa the effects of seasonal and longer term drought are shown by the development of gypsum fields on the playa bed and playa marginal gypsum terraces which are later colonised by halophytic plants long term reduction in groundwater head results in the vegetation of playas which no longer actively discharging groundwater become susceptible to alluviation or aeolian sand drift thus playas migrate by a process playa capture analogous to river capture but induced by groundwater head decay

timing of metamorphism of the lansang gneiss and implications for left lateral motion along the mae ping wang chao strike slip fault thailand the mae ping fault mpf western thailand exhibits dominantly left lateral strike slip motion and stretches for 600 km reportedly branching off the right lateral sagaing fault in myanmar and extending southeast towards cambodia previous studies have suggested that the fault assisted the large scale extrusion of sundaland that occurred during the late eocene early oligocene with a geological offset of 120 150 km estimated from displaced high grade gneisses and granites of the chiang mai lincang belt exposures of high grade orthogneiss in the lansang national park part of this belt locally contain strong mylonitic textures and are bounded by strike slip ductile shear zones and brittle faults geochronological analysis of monazite from a sample of sheared biotite k feldspar orthogneiss suggests two episodes of crystallization with core regions documenting th pb ages between c 123 and c 114 ma and rim regions documenting a significantly younger age range between c 45 37 ma these data are interpreted to represent possible magmatic protolith emplacement for the lansang orthogneiss during the early cretaceous with a later episode of metamorphism occurring during the eocene textural relationships provided by in situ analysis suggest that ductile shearing along the mpf occurred during the latter stages of or after this metamorphic event in addition monazite analyzed from an undeformed garnet two mica granite dyke intruding metamorphic units at bhumipol lake outside of the mae ping shear zone produced a th pb age of 66 2 1 6 ma this age is interpreted to date the timing of dyke emplacement implying that the mpf cuts through earlier formed magmatic and high grade metamorphic rocks these new data when combined with regional mapping and earlier geochronological work show that neither metamorphism nor regional cooling was directly related to strike slip motion

zircon and monazite upb dating of the doi inthanon core complex northern thailand implications for extension within the indosinian orogen abstract the doi inthanon metamorphic core complex occupies a prominent central position within the northwestern thai gneiss belt which has been inferred to be as old as precambrian and as young as permo triassic u pb dating of zircon from core orthogneisses of the complex suggests that the orthogneisses were derived from granitic protoliths with essentially the same late triassic early jurassic age as the mae cham pluton 205 3 4 ma to the west of the doi inthanon complex monazite ages from the orthogneisses indicate that low pressure and high temperature metamorphism and migmatitization occurred in the late cretaceous 84 72 ma limited published radiometric age data from elsewhere in the migmatitic gneiss belt suggest that widespread minor plutonism accompanied this thermal event a younger u pb data of 26 8 0 5 ma for zircon and monazite from the mae klang granite which intruded mylonitic gneisses on the eastern side of the doi inthanon complex indicates that there was also significant plutonism in the late oligocene these u pb ages constrain the development of the complex and hence of the migmatitic gneiss belt as a whole to an interval between late cretaceous and early miocene ductile shearing uplift and tectonic denudation via detachment faulting chronologically overlap the initiation of extensional basin development to the east and southeast of the gneiss belt and imply a genetic connection thus oligocene early miocene thermal rifting from the gulf of thailand northward into mainland thailand may have been the direct product of crustal extension rather than the transtensional product of regional strike slip faulting

groundwater chemistry and palaeorecharge in the amadeus basin central australia abstract carbon isotope chemistry indicates episodic palaeorecharge of groundwater in the arid amadeus basin central australia in this hydrogeologically complex region groundwater has been recharged by three important mechanisms direct infiltration of rainwater through sand dune cover or fissures in calcrete through river bed sands following floods and through joints in bedrock outcrops modern and holocene groundwaters 0 5000 years b p are found in the unconfined calcrete and sand dune aquifers which have evolved hydrochemically to cl so4 na waters with ca and mg as a result of evaporative concentration holocene groundwaters 3 10 000 years b p have been dated in river bed recharge situations these groundwaters are mainly of the hco3 cl na type with ca and mg and preserve the hydrochemical signature of the flood recharge waters most groundwater sampled in the folded and jointed rocks of the basin has a low modern 14c content and was recharged in the holocene and late pleistocene 12 32 000 years b p these waters are intermediate in their ionic composition covering a spectrum between the hco3 cl na and cl so4 na types solution is the dominant process int heir hydrochemical evolution stable isotope signatures and derived parameters indicate that the intensity of rainfall is an important factor in the evolution of arid zone groundwaters modern reharged is limited implying that projected large scale groundwater development in this region will use an effectively nonrenewable resource and should be managed accordingly

the widespread occurrence of low angle normal faults in a rift setting review of examples from thailand and implications for their origin and evolution abstract at least 31 low angle 1 km cenozoic normal faults are identified on seismic reflection data onshore and offshore thailand although some faults have been moderately rotated to lower angles pre rotation dips still indicate formation at low angles about 25 and 35 the dominant east dip of low initial fault dips suggest that pre existing fabrics controlled the fault dip direction in the mergui basin patches of gently dipping basement reflections on seismic reflection data support this observation well data points to a pre rift basement with a widespread component of slaty phyllitic and chlorite schist lithologies that are associated with significant strength anisotropy the subduction zone setting of se asia with a high fluid flux into the crust associated with high levels of co2 has parallels with the setting for lanfs in italy where it is suggested high pore fluid pressures played an important role in lanf reactivation in cross section most lanfs curve from a high angle in sedimentary section to planar or stepped in basement until they reach the brittle ductile transition zone in a few cases lanfs have a convex up geometry some long segmented faults are composed of mixed regions of high and low angle segments the local mix of high and low angle faults indicates that the principal stresses probably were vertical and horizontal during fault formation any rotation of stresses would have to be local not regional lanfs in the mergui basin have very high displacement gradients as low as 2 1 indicating the same fault segments some 20 30 km long have repeatedly slipped while displacements can decline dramatically at key discontinuities the lanf segments are inferred to be very weak and probably slipped mostly aseismically while adjacent lower displacement high angle segments were probably seismically active hence in areas of mixed high and low angle fault segments seismicity may erroneously suggest that high angle normal faults are the dominant fault type the presence of such a high concentration of low and high displacement lanfs in a non metamorphic core complex setting demonstrates that lanfs can form initially at a low angle that isostatic rotation of initially high angle faults to a low angle is not necessary or appropriate to explain the faults and that low angle normal faults are not just features associated with orogenic collapse

evidence for ultra cold traps and surface water ice in the lunar south polar crater amundsen abstract the northern floor and wall of amundsen crater near the lunar south pole is a permanently shaded region psr previous study of this area using data from the lunar orbiter laser altimeter lola diviner and lamp instruments aboard lunar reconnaissance orbiter lro shows a spatial correlation between brighter 1064 nm albedo annual maximum surface temperatures low enough to enable persistence of surface water ice we find features in far ir emissivity 50 400 m could be attributed to either or a combination of two effects i differential regolith emissive behavior between permanently shadowed temperature regimes and those of normally illuminated polar terrain perhaps related to presence of water frost as indicated in other studies or ii high degrees of anisothermality within observation fields of view caused by doubly shaded areas within the psr target that are colder than observed brightness temperatures the implications in both cases are compelling the far ir emissivity curve of lunar cold traps may provide a metric for the abundance of micro cold traps that are ultra cool i e shadowed also from secondary and higher order radiation absorption and re radiation or scattering by surrounding terrain or for emissive properties consistent with the presence of surface water ice

kinematics and tectonic implications of the mae kuang fault northern thailand abstract in order to test the hypothesis that northeast trending strike slip faults partially accommodated mid tertiary east west extension in northern thailand we investigated a prominent lineament that marks the trace of the mae kuang fault the trace of the this fault follows the linear mae kuang valley for approximately 30 km through the mae tho range northeast of chiang mai where it cuts granitic rocks of the fang mae suai batholith and roof pendants of paleozoic terranes along the trace of the fault we identified offset contacts and slickenlines on fault surfaces that suggest a total sinistral slip of 3 5 km and a dip slip of 600 m the fault also offsets three north flowing tributaries to the mae kuang river by 400 700 m at its southwestern end the mae kuang fault is apparently truncated by the right lateral mae tha fault and does not extend to the west side of the chiang mai basin therefore it cannot be accommodating the transfer of extension from basin to basin however it may accommodate small amounts of differential rotation between adjacent crustal blocks the fault probably initiated between 20 and 5 ma simultaneous with the slip inversion on the mae ping and red river faults

reconstruction of the neanderthal and modern human landscape and climate from the fumane cave sequence verona italy using small mammal assemblages abstract fumane cave located at an altitude of 350 m a s l in the monti lessini in the veneto pre alps northeastern italy is a reference site for southern europe for the study of the behaviour of neanderthals and anatomically modern humans amh from marine isotope stages 5 to 2 mis5 mis2 it is one of the few well dated and closely studied sites in the italian peninsula with a finely layered sedimentary sequence from the mousterian to gravettian in this paper we present for the first time a palaeoenvironmental and palaeoclimatic reconstruction of the mis3 and mis2 sequence based on the small mammal insectivore bat and rodent assemblages the environmental and climatic results coupled with the radiocarbon dating together with previous studies on large mammals birds and charcoal and other studies on small mammals and pollen for the same time span in italy enable us clearly to identify distinct climatic periods within our data heinrich event 5 in units a7 to a6 greenland interstadial 12 in units a5 a6 to a4 heinrich event 4 in units a3 to a1 and heinrich event 3 in unit d1e finally the study shows that neanderthals and anatomically modern humans were well adapted to the different climatic and environmental conditions of mis3 at the foot of the alps

exhumation of west sundaland a record of the path of india abstract the indian plate commenced its northward migration towards eurasia in the early cretaceous the lateral effect of this migration on the western edge of the sunda plate in southeast asia still remains equivocal in order to assess this effect we evaluate several key sectors characterized by deep crustal exhumation along a n s transect from the southern malay peninsula to the east himalayan syntaxis the evaluation is aided by a structural analysis of vertical movements and basin development five major metamorphic domes with similar geodynamic evolution maximum p t burial conditions and exhumation are studied exhumation of these domes migrated with time between late cretaceous in the stong complex north malaysia in the south and late miocene in the gaoligong shear zone south china in the north as documented by published work and our new fission track data presented herein deformation is characterized by a n s oriented extension that followed the more regional e w oriented plate tectonic shortening creating local core complexes and syn kinematic magmatism in the footwall of crustal scale detachments which displays a consistent temporal northward migration the n s extension was associated with the onset of hanging wall deposition in the sedimentary basins of western sundaland e g malay sumatra and thai basins during continuous exhumation of the footwall to upper brittle levels our multifaceted analysis of structural and thermochronological data shows a similar succession of tectonic thermal and sedimentary events in west sundaland that was driven by the gradual northward migration of india starting from cretaceous times we infer that the principal mechanism was driven by the subduction of an excess topography of greater india rifted continental margin during its underplating resulting in uplift thermal anomalies extensional exhumation and associated subsidence