glacial lake invermere upper columbia river valley british columbia a paleogeographic reconstruction terraces of thick lacustrine silt and deltaic gravel flank parts of the valley floor of the rocky mountain trench between skookumchuck and donald british columbia these indicate the presence of f

decoupling δ13c response to palaeoflora cycles and climatic variation in coal a case study from the late permian bowen basin queensland australia abstract the late permian coal measures of the bowen basin australia express both environmental and climatic changes that occurred prior to the permian triassic p t boundary in order to decouple the influence of environmental factors salinity ph base level and temperature from depositional and climatic factors atmospheric co2 in organic 13c a high resolution study was performed on 24 coal seams total 24 6 m in the late permian stratigraphy in the northern bowen basin the late permian stratigraphy of the bowen basin records a transition from deltaic and lacustrine conditions within the tinowan formation and black alley shale formation to fluvial deposition in the kaloola and bandanna formations intermittent volcanism is recorded by tuff layers during periods of peat accumulation variations of coal lithotypes were recorded and formed the basis of sampling for petrography and isotope analysis coal samples were etched to expose cellular anatomy and systematically identified to recognise palaeoflora assemblages when observed within seam 13c of the coal varied cyclically 13c enriched depleted enriched as a response to environmental changes expressed in palaeoflora communities the total range of 13c was 26 6 to 21 9 the overall trend of 13c progresses to increasing 13c enrichment corresponding with dull lithotypes rich in inertinite which indicate fluctuations in base level the 13c enrichment peaks at 22 5 within the kaloola member and shifting rapidly toward a depletion maximum 26 6 of 13c in the upper bandanna formation prior to the p t boundary these changes are expressed in palaeoflora communities where ecosystems shifted from dominant glossopteris flora to climax community flora including palaeosmunda cycadales and ginkgo suited to temperate early mesozoic climates the results of this study represent an insight into the effects of environmental variables on 13c uptake of plants the identification of flora within coal gives an insight into palaeowetland evolution and can be partnered with classic petrographical techniques for integrated analysis in coals both the geochemistry and the anatomical aspects of coal represent an important tool for future palaeowetland research

the thermal history of the bowen basin queensland australia vitrinite reflectance and clay mineralogy of late permian coal measures abstract the thermal history of the bowen basin queensland australia has been investigated using vitrinite reflectance data and clay mineralogy vitrinite reflectance data combined with a study of clay mineral reactions indicates that the maximum temperatures which induced organic maturation of the bowen basin coals and extensive clay mineralisation are not related to deep burial metamorphism during the latest middle triassic earliest late triassic as previously believed the results of the present study indicate that the development of a zone of high heat flow in the latest late triassic had a major control on the thermal history of the bowen basin high palaeogeothermal gradients estimated in the northern bowen basin are interpreted to result from convective heat transfer during a hydrothermal event variable heat distributions due to localised fracture enhanced permeable zones acting as hot reservoirs in the deeper part of the basin may have been responsible for some significant local thermal anomalies in the lower coal measures the estimated palaeogeothermal gradients in the southern bowen basin also indicate high heat flow in the lower sections of the stratigraphy sections in the southern bowen basin however are believed to reflect a rock dominated semi closed system with low water rock ratio where rocks are impervious to circulating fluids and thus heat transfer may have occurred by conduction the correlation between vitrinite reflectance and clay mineralogy shows a delay in illitisation reaction relative to organic maturity for many illite smectite i s mixed layer clays in the northern bowen basin this phenomenon can be explained as a result of insufficient time for the completion of mineral reactions and a variable potassium supply in relatively impermeable rocks the relationship between i s expandability and vitrinite reflectance for the bowen basin data compared to basins with known tectonic regimes suggests a thermal history in a rift setting for the bowen basin the effect of thin igneous intrusions on clay mineral reactions is very limited intensive illitisation due to heating of intrusions can only be observed in narrow zones immediately adjacent to intrusive bodies this further demonstrates that mineral reactions are too slow to record the effect of extremely short heating duration in contrast to organic maturity indicators these differences between mineral and organic parameters aid in the identification of local contact metamorphic effects

an oceanographic nowcast forecast system for the red sea we describe the application of a nowcast forecast system for three dimensional currents temperature and salinity to the red sea the modeling system is constructed around a high resolution 6 7 km primitive equation numerical circulation model with complete thermodynamics and an imbedded turbulence closure submodel it is coupled to near real time databases containing meteorological forecasts and remotely sensed and in situ temperature and salinity data the temperature and salinity data are ingested into the model daily using a nudged objective analysis technique because the red sea is a relatively narrow basin bounded by typically high and complex orography a single layer atmospheric boundary layer submodel has been used to increase the effective resolution of the original 40 km resolution meteorological fields by taking into account orographic steering of the low level winds in order to validate the modeling system two very complete hydrographic surveys of the red sea were undertaken and their results are described both the surveys and the modeling system nowcasts demonstrate that the circulation pattern of the red sea is variable and often composed of a series of eddies or subgyres mainly anticyclones immediately before one survey the winds tended to be along axis while just before the second they tended to be cross axis the red sea circulation was much more eddy like when the winds were cross axis by forcing the modeling system with and without orographically steered winds we were able to establish that the complex eddy structure is a response to a wind field which can be highly structured and vorticity rich because of interaction with the high and variable adjacent orography when the winds are more along axis there is less interaction with the adjacent orography and consequently there are fewer eddies in the red sea

exchange through the bab el mandab during the last 10 years there have been a number of important developments in the understanding of the exchange flow in the bab el mandab new and improved estimates of the fluxes of mass heat and salt through the strait have been made directly from oceanographic measurements and indirectly from air sea flux data hydraulic theory has been applied to explain the seasonal variations in the exchange flow and in particular the three layer summer circulation the effects of wind stress friction and seasonal sea level variability on hydraulic control are addressed in this paper analyses of oceanographic data have failed to provide direct evidence of hydraulic control but they have highlighted the importance of tidal scale variability and differences between real continuously stratified fluids and idealised layer flows often used in hydraulic theory other studies have investigated the coupling between the flow in the strait and the circulation within the red sea

a study of hardness and fracture propagation in coal the surface hardness of coal was estimated using a shore scleroscope rebound hardness ssrh tester ssrh can be related to fracture toughness and strength and was trialled as a quick field test to illustrate variability in these properties for coal seam gas reservoirs therefore samples were selected to include different coal ranks and lithotypes from a suite of boreholes that intersect permian coal seams within the bowen basin in queensland australia the tests were conducted unconfined on slabbed coal core and confined on epoxy encased coal blocks used for coal petrographic examination the test results of the unconfined samples show that the hardness varies with lithotype it increases with decreasing amount of bright bands moreso than coal rank or thermal maturity the test results of the confined samples show little variation with lithotype but show a parabolic correlation of hardness with rank similar to the behaviour found with hardgrove grindability tests the resulting fractures of the ssrh test were analysed under the microscope to understand the fracture pattern which can be scaled up to understand fracture propagation in natural systems and when induced in gas reservoirs

an oceanic general circulation model ogcm investigation of the red sea circulation 2 three dimensional circulation in the red sea 1 the three dimensional circulation of the red sea is studied using a set of miami isopycnic coordinate ocean model micom simulations the model performance is tested against the few available observations in the basin and shows generally good agreement with the main observed features of the circulation the main findings of this analysis include an intensification of the along axis flow toward the coasts with a transition from western intensified boundary flow in the south to eastern intensified flow in the north and a series of strong seasonal or permanent eddy like features model experiments conducted with different forcing fields wind stress forcing only surface buoyancy forcing only or both forcings combined showed that the circulation produced by the buoyancy forcing is stronger overall and dominates the wind driven part of the circulation the main circulation pattern is related to the seasonal buoyancy flux mostly due to the evaporation which causes the density to increase northward in the basin and produces a northward surface pressure gradient associated with the downward sloping of the sea surface the response of the eastern boundary to the associated mean crossbasin geostrophic current depends on the stratification and b effect in the northern part of the basin this results in an eastward intensification of the northward surface flow associated with the presence of kelvin waves while in the south the traditional westward intensification due to rossby waves takes place the most prominent gyre circulation pattern occurs in the north where a permanent cyclonic gyre is present that is involved in the formation of red sea outflow water rsow beneath the surface boundary currents are similarly intensified southward undercurrents that carry the rsow to the sill to flow out of the basin into the indian ocean index terms 4243 oceanography general marginal and semienclosed seas 4255 oceanography general numerical modeling 4532 oceanography physical general circulation keywords red sea marginal sea oceanic general circulation model water mass formation

coal rank variation in the bowen basin queensland abstract isoreflectance maps for selected stratigraphic horizons in the bowen basin show regular rank trends and there is general parallelism between reflectance contours and structural contours in the basin these features imply that coalification is due to a rise of temperature with increasing depth of burial depth reflectance profiles calculated from coal bearing horizons across the basin show that reflectance increases with depth and reflectance gradients increase with increasing reflectance coal rank in the bowen basin is interpreted to be due to increased temperatures due to burial under conditions of high geothermal gradient during the permo triassic

distribution and origin of minerals in high rank coals of the south walker creek area bowen basin australia the coals of the south walker creek area in the northern bowen basin with a vitrinite reflectance rvmax of 1 7 to 1 95 are among the highest rank coals currently mined in australia x ray diffraction studies have identified an unusual mineral variation through the vertical sequence with kaolinite rich assemblages typical of other australian coals at the top and bottom of the seam section and an illite chlorite assemblage resembling a metamorphic association in the middle calcite and ankerite are also abundant in parts of the vertical sequence diaspore is abundant in the middle section of the seam in some areas and paragonite dickite or nacrite occurs in some locations as well the distribution of the non carbonate mineral assemblages cross cuts the seam stratigraphy and appears to be primarily controlled by faults and other structural features integration of the mineral distribution with optical and electron microscope data on the coal and non coal bands chemical data from coal ash analysis and information from x ray micro tomography suggests that the illite chlorite and diaspore bearing assemblages resulted from hydrothermal effects associated with fluid migration through the middle part of the coal seam this is further confirmed by the development of metamorphic textures in a tonstein band also altered to illite and chlorite in the illite rich part of the seam section in contrast to a tonstein with more normal sedimentary textures and a kaolinite composition in the kaolinite rich upper part of the seam detailed studies of cleat mineralisation suggest that fluids rich in ca mg and al were introduced relatively early in the seam s post depositional history associated with heat flow sufficient to alter the minerals in the coal and tonstein in the affected part of the seam section the relatively uniform vitrinite reflectance profile observed through the seam section may indicate that the coal was already of high rank before the fluids were introduced or that any localised heat effects on the organic matter associated with the changes in clay mineralogy were overprinted by subsequent wider ranging rank advance processes

on the circulation of atlantic water in the arctic ocean an idealized eddy resolving numerical model and an analytic three layer model are used to develop ideas aboutwhatcontrolsthecirculationofatlanticwaterinthearctic ocean thenumericalmodelisforcedwith a surface heat flux uniform winds and a source of low salinity water near the surface around the perimeter of an arctic basin despite this idealized configuration the model is able to reproduce many general aspects of the arctic ocean circulation and hydrography including exchange through fram strait circulation of atlantic water a halocline ice cover and transport surface heat flux and a beaufort gyre the analytic model depends on a nondimensional number and provides theoretical estimates of the halocline depth stratification freshwater content and baroclinic shear in the boundary current an empirical relationship between freshwater content and sea surface height allows for a prediction of the transport of atlantic water in the cyclonic boundary current parameters typical of the arctic ocean produce a cyclonic boundary current of atlantic water of o 1 2 2sv where 1sv 10 6 m 3 s 21 and a halocline depth of o 200m in reasonable agreement with observations the theory compares well with a series of numerical model calculations in which mixing and environmental parameters are varied thus lending credibility to the dynamics of the analytic model in these models lateral eddy fluxes from the boundary and vertical diffusion in the interior are important drivers of the halocline and the circulation of atlantic water in the arctic ocean

stable isotope geochemistry of authigenic clay minerals from late permian coal measures queensland australia implications for the evolution of the bowen basin oxygen and hydrogen isotope analyses were carried out on authigenic clay minerals from late permian coal measures of the bowen basin australia in the northern bowen basin the oxygen isotope compositions of the mixed layer illite smectite show significant irregular variations with respect to depth which parallel the changes in the extent of the illitisation reaction and are interpreted as reflecting changes in water rock ratio in turn related to permeability the o and d values of illite smectite and kaolinite in the northern bowen basin and the calculated fluid isotopic composition o 3 to 1 d 70 to 90 in equilibrium with these clays are considerably lower than those typically reported for deeply buried sedimentary basins these stable isotope data together with relatively high inferred palaeotemperatures up to 235 c and abnormally high geothermal gradients are consistent with a hydrothermal origin for clay mineral formation in the northern bowen basin the hydrothermal system is interpreted to be a result of the late triassic extensional tectonic regime which developed in large parts of eastern australia and affected the northern part of the bowen basin in the southern bowen basin by contrast clays are more enriched in o and deuterium which is explained by lower temperatures in the shallow coal measures and a significant enrichment in the fluid isotopic composition o 3 6 to 5 6 d 66 to 35 under low water rock ratio conditions especially in deeper pelitic rocks c 2000 elsevier science b v all rights reserved

seasonal overturning circulation in the red sea 1 model validation and summer circulation the overturning circulation in the red sea exhibits a distinct seasonally reversing pattern and is studied using high resolution mit general circulation model simulations in the first part of this study the vertical and horizontal structure of the summer overturning circulation and its dynamical mechanisms are presented from the model results the seasonal water exchange in the strait of bab el mandeb is successfully simulated and the structures of the intruding subsurface gulf of aden intermediate water are in good agreement with summer observations in 2011 the model results suggest that the summer overturning circulation is driven by the combined effect of the shoaling of the thermocline in the gulf of aden resulting from remote winds in the arabian sea and an upward surface slope from the red sea to the gulf of aden set up by local surface winds in the red sea in addition during late summer two processes associated respectively with latitudinally differential heating and increased salinity in the southern red sea act together to cause the reversal of the contrast of the vertical density structure and the cessation of the summer overturning circulation dynamically the subsurface northward pressure gradient force is mainly balanced by vertical viscosity resulting from the vertical shear and boundary friction in the strait of bab el mandeb unlike some previous studies the three layer summer exchange flows in the strait of bab el mandeb do not appear to be hydraulically controlled

modeling of thermal maturation and hydrocarbon generation in two petroleum systems of the taroom trough australia thermal maturity modeling using first order reaction kinetics of a permian and a triassic source rock in the taroom trough was employed to determine the time over which petroleum generation migration and accumulation occurred and to explain the observed distribution of oil and gas modeling shows that the maximum paleotemperatures were attained in these two source rock units by burial at the south end of the taroom trough during the late cretaceous in the north maximum paleotemperatures were caused by increased heat flow as well as burial to maximum depth in the southern part of the study area the permian triassic source rocks started expelling hydrocarbons during the jurassic early cretaceous these hydrocarbons migrated updip to the east and west where structural stratigraphic traps had formed in response to triassic compressional deformation kinetic modeling supports biomarker and other geochemical evidence that the oil and gas currently produced from sandstone reservoirs were sourced mainly from the carbonaceous shales of the upper permian blackwater group hydrocarbon output from the middle triassic snake creek mudstone was minor but sufficient to produce a second petroleum system north of the study area early triassic generation of hydrocarbons and subsequent jurassic cretaceous burial resulted in an overmature permian section at present able to generate only dry gas the bulk of its hydrocarbons most likely have seeped to the surface only late mature expulsion products which subsequently migrated southward could have contributed to the petroleum reserves of the region

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

on the crossover of boundary currents in an idealized model of the red sea the west to east crossover ofboundarycurrents has been seen in mean circulationschemes fromseveral past models of the red sea this study investigates the mechanisms that produce and control the crossover in an idealized eddy resolving numerical model of the red sea the authors also review the observational evidence and derive an analytical estimate for the crossover latitude the surface buoyancy loss increases northward in the idealized model and the resultant mean circulation consists of an anticyclonic gyre in the south and a cyclonicgyreinthenorth in themidbasin thenorthwardsurfaceflow crossesfromthewestern boundarytothe eastern boundary numerical experiments with different parameters indicate that the crossover latitude of the boundary currents changes with f0 b and the meridional gradient of surface buoyancy forcing in the analytical estimate which is based on quasigeostrophic b plane dynamics the crossover is predicted to lie at the latitude where the net potential vorticity advection including an eddy component is zero various terms in the potential vorticity budget can be estimated using a buoyancy budget a thermal wind balance and a parameterization of baroclinic instability

mechanisms of coal metamorphism case studies from paleozoic coalfields controls on coal metamorphism can be complex in this paper we examine four paleozoic coalfields the western kentucky portion of the illinois basin the pennsylvania anthracite fields the south wales coalfield and the bowen basin an increase in temperature with depth of burial is certainly a factor in coal metamorphism in many coalfields however including the coalfields reviewed here it has become apparent that such a simple mechanism does not explain the coal rank patterns observed the flow of hydrothermal fluids through the coals has been proposed as a cause of coal metamorphism evidence includes inverted rank gradients elevated cfl as an indicator of brine fluids isotopic evidence for hydrothermal fluids and vein and cleat mineral assemblages in any case multiple hypotheses must often be evaluated in the examination of any coalfield since the simple paradigm of coal rank increases with a simple increase in temperature with increasing depth does not fit the evidence observed in many cases

postdepositional history of the permian sequence in the denison trough eastern australia the diagenesis of permian siliciclastic sedimentary rocks of the denison trough is interpreted in terms of evolving pore water composition related to the burial history of the basin in the sandstones early precipitation of pyrite siderite and grain rimming illite smectite was followed by development of quartz overgrowths that incorporated silica released by pressure solution recrystallization of lithics and smectite illite reaction later as the sequence reached maximum burial during the late triassic strongly 18 o depleted siderite and ankerite which incorporated iron and magnesium liberated by leaching of detrital mafic minerals and continuing smectite illite reaction precipitated from connate meteoric pore water expelled upward from the underlying overpre sured continental reids dome beds this implies the existence of significant cross formational pore water flow prior to and during attainment of maximum burial regional late triassic to earliest jurassic compression resulted in major uplift and exposure of the permian sequence attendant strata concordant invasion of meteoric water led to labile grain and ferroan carbonate dissolution and to the formation of strongly 18 o depleted kaolinite and a second generation of quartz overgrowths later postdepositional events which occurred during a second cycle of burial and uplift include the precipitation of 18 o depleted calcite and dawsonite and hydrocarbon entrapment

interpretation of vitrinite reflectance depth profiles in the northern denison trough bowen basin australia abstract the denison trough bowen basin australia is a mature hydrocarbon province that contains permian to triassic coal and gas bearing sediments deposited in deltaic to shallow marine shelf conditions the sandstone reservoirs of the permian aldebaran sandstone freitag formation and catherine sandstone of the northern denison trough ndt were evaluated for their co2 storage potential as part of the queensland government s zerogen co2 capture and storage project which found that diagenetic processes acting on the sandstones have resulted in poor permeability and reduced porosity making them unsuitable for large scale injection and storage in this area to better understand the factors acting to degrade these reservoirs the purpose of the current study was to establish a thermal maturity framework for the permian sandstone reservoirs of the northern denison trough based on vitrinite reflectance measurements of coals and rock eval analysis of coals and shales from the aldebaran sandstone through to the catherine sandstone mean maximum vitrinite reflectance of coals rmax ranges from 0 55 to 0 93 and estimated maximum burial temperatures calculated from vitrinite reflectance fall between 83 oc 125 oc calculation of palaeotemperatures from vitrinite reflectance data has been hampered by inversions of depth reflectance profiles at the top of the aldebaran sandstone and scatter in vitrinite reflectance data this has been attributed to depositional effects including the major marine flooding surfaces at the top of the aldebaran sandstone that have affected vitrinite reflectance evolution in the ndt producing low reflecting fluorescing perhydrous vitrinite near marine flooding surfaces and subhydrous vitrinite when oxidising conditions prevailed a vitrinite reflectance difference of up to 0 2 rmax is detected in an isometamorphic coal an equivalent palaeotemperature difference of approximately 19 oc the abundance of perhydrous vitrinite has resulted in largely suppressed vitrinite reflectance throughout the examined permian interval in the northern denison trough and the presence of both perhydrous and subhydrous vitrinite introduces an error in palaeotemperature calculation in high volatile bituminous coals rock eval analysis provides supporting and calibrating maturity data tmax over the studied interval ranges from 421 oc to 447 oc generating a positive broadly linear correlation between rmax and tmax that is applicable specifically to the ndt tmax suppression was also detected in perhydrous coals hydrogen index serves to evaluate the level of vitrinite reflectance suppression through an inverse relationship between the two parameters the rock eval data confirms the oil generation potential of coals in the ndt while shales associated with the same stratigraphic intervals have lower hydrocarbon generation potential this study brings new insights into the thermal maturity framework in the ndt and highlights the importance of reliable vitrinite reflectance data for calculation of maximum burial temperatures particularly in underexplored or frontier areas

low temperature thermochronology of the northern thomson orogen implications for exhumation of basement rocks in ne australia abstract the tasmanides of eastern australia record much of the phanerozoic tectonic development of the retreating pacific australia plate boundary and are an oft cited example of an orogen that has undergone tectonic mode switching to begin to constrain the timing of exhumation of basement rocks that are now exposed in portions of the ne tasmanides we measured apatite and zircon u th he ages from the thomson orogen and overlying paleozoic strata in the back arc of the new england orogen in ne australia zircon u th he ages from basement samples including those recovered from boreholes at depths of up to 1 1 km are characterized by large inter and intra sample variability and range from approximately 180 ma early jurassic to 375 ma late devonian u th he zircon ages from several individual samples are negatively correlated with effective uranium eu a pattern that is also true of the dataset as a whole suggesting that variations in u and th zoning and radiation damage are partially responsible for the age variability the oldest zircon u th he cooling ages coincide with the formation of regionally extensive late devonian early carboniferous back arc basins suggesting that late devonian extension played a significant role in exhumation of parts of the northern thomson orogen apatite u th he ages from a basement sample and a late permian sandstone in the overlying bowen basin which are also marked by intra sample variability and age eu correlations span from the early cretaceous through oligocene in general agreement with previous apatite fission track data in conjunction with observations of key geologic relationships and prior k ar and 40ar 39ar data our results suggest four overall phases in the thermal history of the northern thomson orogen 1 cambrian early silurian metamorphism during the delamerian and benambran orogenies 2 protracted cooling during the late devonian through mid permian that likely resulted from extensional exhumation 3 permian triassic reheating during burial beneath thick sedimentary basins and 4 cretaceous and paleogene cooling during uplift and erosion

influence of tectonics on permian coal rank patterns in australia abstract coal in the australian permian basins is dominantly subbituminous coal to medium volatile bituminous coal the subbituminous coal and higher rank bituminous coals are generally the result of burial diagenesis localized low volatile bituminous coal to anthracite is commonly associated with igneous activity extensive zones of high rank coal in the eastern part of the bowen basin are due to uplift of deeply buried coal measure sequences during late permian and triassic tectonism high rank coals in the sydney basin are due to uplift of deeply buried permian rocks preceding sea floor spreading in the tasman sea during the late cretaceous and early tertiary although this conclusion is controversial localized semianthracite and anthracite at depths greater than 2 500 m in the cooper basin were formed either by enhanced heat flow from radiogenic basement granites or by vertical movement of hot fluids through the fractured granitic bodies during the tertiary permian coals in the pedirka and arckaringa basins in the center of the continent and the perth carnarvon canning bonaparte and officer basins in the west are generally low in rank due to either shallow depths of burial or slight heat flow or both the fitzroy trough of the canning basin is an exception there significant tectonic activity has occurred since the permian

red sea during the last glacial maximum implications for sea level reconstruction the red sea is connected to the indian ocean via a narrow and shallow strait and exhibits a high sensitivity to atmospheric changes and a reduced sea level we used an ocean general circulation model to investigate the hydrography and circulation in the red sea in response to reduced sea level and modified atmospheric conditions occurring during the last glacial maximum lgm the model salinity shows high sensitivity to sea level reduction together with a mild atmospheric impact sea level reduction affects the stratification and alters the circulation pattern at the strait of bab el mandab which experiences a transition from a submaximal flow to a maximal flow the best correlation to reconstructed conditions during lgm exists when the water depth of the hanish sill the shallowest part in the strait of bab el mandab is 33 10 75 m which would be affected by a sea level lowering of approximately 105 m our results support the reconstructed maximum salinity of around 57 practical salinity units because of a simple model that takes into account mixing processes along the strait and comparison of the surface salinity gradient to reconstructions based on isotopic records from sedimentary cores the salinity and 18o are sensitive to the mixing process at the strait and the sensitivity increases as the sea level is further reduced a local relative sea level reduction of approximately 105 m is also in close agreement with the inference of the lgm low stand of the sea at the location of the sill based on the ice 5g vm2 model

petrographic and isotope constraints on the origin of authigenic carbonate minerals and the associated fluid evolution in late permian coal measures bowen basin queensland australia authigenic carbonate minerals are ubiquitous throughout the late permian coal measures of the bowen basin queensland australia in the northern bowen basin carbonates include the following assemblages siderite i delta o 18 smow 11 4 to 17 delta c 13 pdb 5 3 to 120 fe mg calcite ankerite siderite ii mineral association delta o 18 smow 7 2 to 10 20 delta c 13 pdb 10 9 to 1 80 for ankerite and a later calcite delta o 18 smow 5 9 to 14 60 delta c 13 pdb 11 4 to 4 40 in the southern bowen basin the carbonate phase consists only of calcite delta o 18 smow 12 5 to 14 80 delta c 13 pdb 19 4 to 0 80 where it occurs extensively throughout all stratigraphic levels siderite i occurs in mudrocks and sandstones and predates all other carbonate minerals this carbonate phase is interpreted to have formed as an early diagenetic mineral from meteoric waters under cold climate and reducing conditions fe mg calcite ankerite siderite il occur in sandstones as replacement of volcanic rock fragments clay minerals illite smectite chlorite and kaolinite postdate ca fe mg carbonates and precipitation of the later calcite is associated with clay mineral formation the ca fe mg carbonates and later calcite of the northern bowen basin are regarded as having formed as a result of hydrothermal activity during the latest triassic extensional tectonic event which affected this part of the basin rather than deep burial diagenesis during the middle to late triassic as previously reported this hypothesis is based on the timing relationships of the authigenic mineral phases and the low delta o 18 values of ankerite and calcite together with radiometric dating of illitic clays and recently published regional geological evidence following the precipitation of the ca fe mg carbonates from strongly o 18 depleted meteoric hydrothermal fluids continuing fluid circulation and water rock interaction resulted in dissolution of these carbonate phases as well as labile fragments of volcaniclastic rocks subsequently the later calcite and day minerals precipitated from relatively evolved o 18 enriched fluids the nearly uniform delta o 18 values of the southern bowen basin calcite have been attributed to very low water rock ratio in the system where the fluid isotropic composition was buffered by the delta o 18 values of rocks c 2000 elsevier science b v all rights reserved

coal rank variation in the intrasudetic basin sw poland abstract the upper carboniferous coal bearing sequence of the intrasudetic basin sw poland includes coals ranging from high volatile bituminous to anthracitic rank the lowest values of reflectance are recorded around the basin margins 0 6 r0 max the highest ones appear in the center of the basin exceeding 4 r0 max reflectance gradients are very high reaching 0 6 100 m in the centre of the basin a comparison of the isoreflectance maps for three lithostratigraphical units the walbrzych bialy kamien and zacler formations with the present day burial depth and the depth of burial during the westphalian b c indicates that there is a strong relationship between reflectance and the sediment cover during the westphalian b c particularly in the vicinity of walbrzych and lubawka this suggests that the increase in coal rank is related to the increase in cover which permitted the temperature to build up to high values in the eastern and central parts of the basin and the nowa ruda area higher reflectance than that derived from burial depth is observed which is believed to result from higher heat flow from the basement the volcanic rocks of the intrasudetic basin appear to have little effect on coal rank and are not considered to be a significant contributor to the heat flow of the region during coalification the oldest westphalian coal seams were buried to about 700 m and the youngest seams of the walbrzych formation to 900 m around the basin margins the coals had reached their present day rank by the westphalian b c and in the central part probably by the end of the stephanian most effective coalification took place during the westphalian a b occupying a period of less than 20 million years the coalification temperature is calculated to be 160 170 c with a geothermal gradient of 8 10 c 100 m these geothermal conditions support the suggestion of a volcanic origin for the intrasudetic basin

cleat mineralization of upper permian baralaba rangal coal measures bowen basin australia coals from the permo triassic bowen basin have been investigated using a variety of complementary analytical techniques face cleat minerals in the studied samples are dominated by authigenic clays notably pure illite or illite chlorite mixtures butt cleats and joints are dominated by carbonates mostly calcite with less abundant ferroan calcite ankerite and siderite k ar ages of cleat fill illites and one fracture illite smectite fill indicate three phases of illite formation during the triassic 1 an early phase with ages clustered around 244 ma ago 2 a second phase about 232 ma ago and 3 the latest phase about 219 ma ago thermal modelling of selected boreholes from the study area and other geological data indicate that the first phase of illitization occurred when the coal seams were about 1000m below the surface and at a temperature of between 70 and 80 c at a time when the basin was rapidly subsiding these early illites were stable and retained their 1m polytype even after being exposed to temperatures of 150 190 c during maximum burial in the southeastern bowen basin the second phase of illitization at 232 3 occurred at about the time of maximum burial the latest phase took place between 223 3 and 212 3 ma ago and occurred in a wider temperature range between 170 and 100 c during a rapid uplift in the late triassic the bowen basin area experienced a second cycle of subsidence that commenced in the early jurassic with the formation of the surat basin which overlies the bowen basin and forms part of the great artesian basin system regional uplift and erosion in middle cretaceous times terminated sediment accumulation in the surat basin during the second cycle of burial widespread carbonate mineralization in butt cleats and joints took place calcite fluid inclusions indicate that calcite was precipitated from meteoric water at about 80 c the widespread carbonate mineralization in butt cleats and the near absence of carbonates in the face cleats is here attributed to permeability anisotropy caused by a change in the direction of lateral compressive stress during jurassic cretaceous times relative to that during the triassic hunter bowen orogeny