chemistry of sands from the modern indus river and the archean witwatersrand basin implications for the composition of the archean atmosphere both the indus river and the witwatersrand basin contain sand with grains of detrital uraninite because this mineral is easily oxidized its presence in archean strata as a detrital particle has been used as evidence for a low oxygen atmosphere before 2 5 ga however its presence in modern sand from the indus river system has been used to argue that detrital uraninite does not provide information about the oxygen concentration of earth s early atmosphere petrographic and chemical study of sand from these two sources reveals differences that suggest the modern indus sand cannot be used as an analog for the archean witwatersrand occurrences the witwatersrand quartzites are depleted in ca mg and na indicating that the original sand from which they formed had been subjected to intense weathering the chemical index of alteration cia a commonly used indicator of degree of weathering yields an average value of about 0 80 for witwatersrand quartzites comparable to modern tropical streams such as the orinoco that drain deeply weathered terrains under tropical conditions cia 0 75 in contrast the cia for indus sand is 0 45 indicating virtually no chemical weathering the significance of archean quartz pebble conglomerates is not just that they contain unstable detrital phases like uraninitemore and pyrite but that these particles are associated with rocks whose compositions suggest intense weathering these conglomerates must have been subjected to intense weathering under tropical conditions either in their source area or at the site of deposition and the preservation of minerals like uraninite such conditions is indeed strong evidence for a low oxygen atmosphere less

provenance and weathering control on river bed sediments of the eastern tibetan plateau and the russian far east abstract we investigated the petrography and major trace and rare earth element compositions of the bed sediments from the large rivers draining the eastern tibetan plateau etp the huang he yellow chang jiang yangtze hong he red mekong and salween the combined drainage spans tropical temperate and arid climate zones in addition samples from the lena river draining the verkhoyansk and sette daban ranges in an arctic to sub arctic climate zone in siberia were also studied for their major and trace element composition the sub angular texture the quartz feldspar rock fragment classification in the lithic arenite field and the relatively low chemical index of alteration cia 42 79 indicate that these sediments are texturally petrographically and chemically immature and immobile trace elements can be used to obtain some information about the lithologic provenance the etp river sediments are felsic and similar to the upper continental crust with the salween most felsic and the lena most mafic the sediments show a gradation in maturity that is not clearly related to present climatic or physiographic regime this suggests that maturity itself is a relict feature inherited from previous sedimentary cycles the high physical erosion in such high energy and relief systems seems to inhibit intense weathering and manifests a provenance control from local rocks on the sediment compositions

chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks abstract chemical weathering indices are commonly used for characterizing weathering profiles by incorporating bulk major element oxide chemistry into a single metric for each sample generally on homogeneous parent rocks weathering indices change systematically with depth however the weathering of heterogeneous metamorphic rocks confounds the relationship between weathering index and depth in this paper we evaluate previously defined chemical weathering indices for their suitability in characterizing weathering profiles developed on felsic heterogeneous metasedimentary bedrock from coweeta hydrologic laboratory north carolina usa among the weathering indices evaluated here the weathering index of parker wip is the most appropriate for application to weathering profiles on heterogeneous and homogeneous parent rock because the wip includes only the highly mobile alkali and alkaline earth elements in its formulation it yields values that differ greatly from those of the parent rock in addition the wip allows for aluminum mobility unlike other weathering indices these characteristics combine to make the weathering index of parker the most applicable index for studying the weathering of heterogeneous metasedimentary rocks however the wip should be applied judiciously as alkali and alkaline earth metals may be readily depleted during weathering in addition to reflecting weathering the chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and vogt s residual index v may be sensitive to subtle geochemical changes such as hydrothermal alteration along a fault and or alteration at the water table weathering indices that include iron in their calculations were not included in this study because they do not distinguish between ferric and ferrous iron the oxidation state and distribution of iron in a weathering profile is influenced by the proportion of oxidation states in the pre weathered metamorphic rock and interaction with groundwater during weathering

petrography and chemistry of the bed sediments of the red river in china and vietnam provenance and chemical weathering abstract the red hong river straddles southwestern china and northern vietnam and drains the eastern indo asian collision zone we collected bed sediments from its tributaries and main channel and report the petrographic point counts of framework grains and major oxide compositions as well as organic and inorganic carbon contents the q f rf ratios and q f l l c ratios of the bed load indicate quartz poor mineralogically immature sediments of recycled orogen provenance the weathering indices based on major oxides the chemical index of alteration cia and the weathering index of parker are also consistent with the recycled sedimentary nature of the bed sediments using geographic information system gis we calculated for each sample basin such parameters as temperature precipitation potential evapotranspiration runoff basin length area relief and areal exposure of igneous metamorphic and sedimentary rocks statistically meaningful correlations are obtained between the two weathering indices between cia and sedimentary to metamorphic rock fragments ratio s s m and between cia and sedimentary rock cover but otherwise correlations are poor the bed sediments preserve signatures of their provenance but the effect of weathering is not clearly seen subtle differences in the bed sediments are observed between the red and the himalayan rivers indus ganges and brahmaputra as well as between sub basins within the red river system and are attributed mainly to differences in lithology

advection of fluids at the front of the sicilian neogene subduction complex abstract the sicilian accretionary prism shows a large southward imbricated system of thrust sheets the frontal part of the belt has been tectonically emplaced in plio pleistocene times major decollement surfaces and sole thrusts at the base of and inside the prism consist of melanges with a blocks in matrix fabric in the frontal part two superposed decollement levels are recognized the upper one located at the base of the paleogene neogene sedimentary series and the basal one at the base of duplexes triassic miocene sedimentary series syntectonic dewatering of the sedimentary sections occurred along decollements and thrust faults involving hydrofracture and mineralized vein development inside the deep sole thrusts rooted in the basal decollement hydrofractured blocks show different generations of syntectonic quartz and calcite extensional veins while in the upper decollement only calcite veins have been observed both quartz and calcite veins show aqueous primary fluid inclusions of low salinity with low trapping temperature for fluids in the upper decollement if we assume that at the time of deformation the main heat source was the regional conductive geothermal gradient the trapping temperatures of the fluids inside veins of the deep sole thrusts are higher than those predicted by the pilo pleistocene gradient for this subduction zone and correspond to a thermal anomaly we suggest that the frontal sicilian prism supported localized transient fluid flow of deep freshwater sourced from two different origins a shallow one for fluids now trapped in the upper decollement and a deep internal origin 6 10 km minimum depth for the hot fluids channelized along the basal decollement and now trapped inside the sole thrust of the mt scalpello duplex area

geomorphic constraints on surface uplift exhumation and plateau growth in the red river region yunnan province china field observations digital elevation model dem data and longitudinal profi le analysis reveal a perched low relief upland landscape in the red river region yunnan province china which correlates to an uplifted regional low relief landscape preserved over the eastern margin of the tibetan plateau as with other major rivers of the plateau margin the red river has deeply incised the lowrelief upland landscape which we interpret to be the remnants of a pre uplift or relict landscape we examine longitudinal river profi les for 97 tributaries of the red river most profi les consist of three segments separated by sharp knickpoints an upper lowgradient channel segment a steeper middle channel segment and a very steep lower channel segment upper channel segments correspond to the relict landscape and have not yet experienced river incision steeper middle and lower segments indicate onset of rapid two phase river incision on the basis of which changes in external forcings such as climate or uplift can be inferred in terms of two end member scenarios two phase incision could be the result of pulsed plateau growth in which relatively slow uplift during the fi rst phase is followed by rapid uplift during the second phase or it could refl ect adjustments of the main channel to changing climate conditions against the backdrop of steady plateau growth reconstruction of the paleo red river indicates 1400 m river incision 1400 1500 m surface uplift and a maximum of 750 m vertical displacement across the northern red river fault elevating the northern ailao shan range above the surrounding relict landscape on the basis of stratigraphic constraints incision along the red river likely began in pliocene time

revision of archive recovery tests using analytical and numerical methods on thermal water wells in sandstone and fractured carbonate aquifers in the vicinity of budapest hungary this study offers a reinterpretation of archive aquifer tests predominantly on the basis of recovery data from an original datasheet of thermal water wells located in carbonate and sandstone aquifer units in the vicinity of budapest hungary the study compares the hydraulic conductivity k and specific storage ss values derived in the first instance from an aquifer test evaluation this included an initial application of the classical analytical cooper and jacob method subsequently the visual two zone vtz numerical method was applied then third a more complex model namely wt software it was found that the simple analytical solution is not able to represent the field conditions accurately while in the course of the application of the vtz model it proved possible to alter the various hydraulic parameters within reasonable limits to fit the field data in the case of the vtz model the researcher is required to calculate the accuracy of the fitted model separately while with the wt model this is automatic the software seeks out the best fit in addition to vtz parameters the wt model can efficiently incorporate data on up to 500 model layers water level and pressure the optimization of the parameters may be achieved by automatic calibration improving the accuracy of the numerical results recovery tests for 12 wells were numerically simulated to obtain values for vertical and horizontal hydraulic conductivity and specific storage for triassic and eocene fractured carbonate and the upper miocene pliocene granular sandstone aquifer units when an analytical solution is applied only average values could be obtained the conclusion reached was that the results of the analytical solution can be improved by the use of numerical methods these methods are able to incorporate basic information on well design aquifer material and the hydrogeological environment in the course of the evaluation the revision of the archive recovery data using numerical methods may assist in the quest for better data for numerical flow and transport simulations without the need to perform new tests in addition the methods employed here can explain cases in which the original analytical interpretations proved unable to yield reliable data and predictions

comparative analyses of pumping tests conducted in layered rhyolitic volcanic formations the rhyolitic volcanic formations are modeled as multilayer flow systems composed of high permeability fractured zones separated by less permeable depth intervals referred to as matrix zones the multilayer or linear cross flow model is applied which considers lateral flow in all units the vertical cross flow between the model layers is calculated as the product of the head difference and the vertical inter layer conductance the axi symmetrical well flow simulation software wt i applies either analytical or numerical drawdown simulators in the formation ii assumes uniform well bore drawdown conditions in the pumping wells and iii considers drawdown driven induced flow in the observation well the interpretation of the pumping recovery test in the well megyaszo k 9 hungary includes 7 low permeability and 6 screened water yielding zones and applies analytical method to compute the formation response the benchmark drill hole wash pumping test nevada with pumped and monitoring open boreholes involves 5 fracture and 8 matrix zones the radial formation heterogeneity is approximated by the bi zonal flow domain and numerical method is used for drawdown simulation in the formation appropriate agreement with the measured drawdown data both tests and flow logging data drill hole wash is achieved computer aided calibration is used for the parameter estimation the results of the presented evaluations are compared with outputs of independent analyses

deep water massive sands facies processes and channel geometry in the numidian flysch sicily abstract the sedimentology of the numidian flysch in northern sicily has been little studied in the last twenty years with most works concentrating on the structural complexities of the area rather than the facies characteristics the numidian basin was intensively deformed during its complex tectonic history and the basin deposits have become segmented into different structural units the oligo miocene aged flysch comprises predominantly quartzarenitic sandstones and interbedded mudstones both of turbiditic affinities and most likely derived from a nw african source the sediments are well exposed along the coast and in dry river valleys in northern sicily and provide excellent examples of deep water massive sands i e very thick 4 25 m units of structureless sandstone associated with turbidites and related facies the overall characteristics of the examined sections indicate that the sandstones were deposited within both isolated channels and larger channel complexes that fed across a mud dominated slope the more proximal sections e g ponte finale and pollina have a high proportion of pebble conglomerates shale clast conglomerates and very thick bedded structureless pebbly sandstones deposited by high density turbidity currents debris flows and slumping other sections either more distal or with a more uniform sand rich source e g contrada di romano are dominated by very thick bedded and amalgamated structureless sandstones with extensive zones of water escape structures the massive sands are thought to originate from the gradual aggradation of sediment beneath steady or near steady flows with rapid deposition from final stage modified grain flows forming the water escape features

correlation of diagenetic data from organic and inorganic studies in the apenninic maghrebian fold and thrust belt a case study from eastern sicily abstract temperature dependent clay mineral assemblages and vitrinite reflectance data have been used to investigate levels of diagenesis from the apenninic maghrebian fold and thrust belt in eastern sicily at the footwall of the peloritani calabride arc data are from units sampled along a regional transect between the nebrodi mountains to the north and mount judica to the south these units developed in very different tectonic settings from those of oceanic to passive continental margin domains deformed during the cenozoic mountain building and related active margin deposits the integration of organic and inorganic thermal indicators allowed us to distinguish among different tectonic settings with thermal maturity generally decreasing from hinterland to foreland as a result of progressively less severe thermal evolution and or tectonic loading during the mountain building specifically the highest vitrinite reflectance vro values ca 0 60 0 75 and percentages of illite layers in illite smectit

syn rift geofluids in fractures related to the early middle miocene evolution of the valles penedes half graben ne spain abstract the valles penedes half graben located in the central part of the catalan coastal ranges is ne sw oriented 10 14 km wide and up to 100 km long and is filled mainly with continental to marine siliciclastic deposits ranging from late oligocene early miocene to late miocene the syn rift burdigalian continental deposits are well stratified s 0 approx 090 15n red beds affected by nnw sse trending nearly vertical extensive fractures middle burdigalian early langhian in age these extensive fractures which cut quasi perpendicularly the stratification are filled with calcite veins presenting two filling stages the first stage is formed by millimetric to centrimetric thick bands of crystalline calcite consisting of palisade calcite cement anhedral spar texture and rhombic calcite cement non to dull orange luminescent with 18 o values ranging from 9 0 to 5 2 pdb 13 c values varying from 9 3 to 6 7 pdb 87 sr 86 sr ratios ranging from 0 71088 to 0 71361 relatively high values of mg and variable values of mn sr and fe this stage is interpreted as subaerial speleothems rimstones which developed in meteoric vadose conditions the second stage is formed by euhedral spar megaspar cement and coconut meat cement with zoned bright yellow to orange luminescence with 18 o values ranging from 16 2 to 9 9 pdb 13 c values varying from 7 4 to 1 9 pdb 87 sr 86 sr ratios ranging from 0 71608 to 0 71800 and relatively low values of mg mn sr and fe this stage is interpreted as subaquatic cements developed in meteoric phreatic conditions the two stages of calcite fillings reflect successive circulation of two meteoric fluids with very different geochemical compositions and represent the change from vadose to phreatic environment during the evolution of the syn rift stage middle late burdigalian to late langhian the meteoric fluid producing the first filling stage was a superficial fluid proceeding directly from the surface influenced by soil co 2 the meteoric fluid generating the second stage was a more evolved fluid which had previously undergone interaction with sediments and reservoir effect the beginning of the thermal subsidence coupled with a change from a more arid to a hotter and perhaps wetter climate could had been the ultimate reasons for the observed evolution

quantitative analysis of detrital modes statistically rigorous confidence regions in ternary diagrams and their use in sedimentary petrology abstract detrital modes are the basic type of quantitative data used in sedimentary petrology they represent estimates of the petrographic framework composition of sand or sandstone obtained by point counting of thin sections at present geological inferences from analysis of these numerical data are semi quantitative only because many of the data processing methods employed in sedimentary petrology lack a firm theoretical basis a review of existing methods reveals a number of fundamental statistical problems associated with the use of univariate statistics and the construction of so called hexagonal fields of compositional variation it is shown that these problems can be overcome by using multivariate methods that honour the non negativity and unit sum constraints on compositional data and incorporate the covariance structure spread in compositional data can be modelled on two levels 1 by regarding the grain as unit of observation and the total point count as a sample from a multinomial distribution 2 by regarding the total count as unit of observation and a set of counts as a sample from an additive logistic normal distribution numerical methods are presented for constructing statistically rigorous confidence regions in ternary diagrams by inversion of significance tests for these two distributions statistical analyses of the framework composition and heavy mineral assemblages of modern beach and river sands illustrate their use the case histories are followed by a brief overview of popular multivariate methods for reconstructing sediment provenance

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

fracturing and fluid migration during palaeogene compression and neogene extension in the catalan coastal ranges spain the catalan coastal ranges ne part of the eastern iberian margin correspond to a system of grabens formed at the north western margin of the valencia trough extensional activity in the catalan coastal ranges occurred at least from early to late miocene and reactivated earlier transpressive faults related to the palaeogene compression in the central part of the catalan coastal ranges tectonic micro and macrostructures faults joints stylolites are well developed in the mesozoic mainly cretaceous limestones as well as in the miocene graben fill deposits in these rocks seven generations of fractures which formed during different tectonic phases have been distinguished type 1 4 fractures affect only the cretaceous limestones type 5 and 6 fractures the cretaceous and miocene deposits and type 7 fractures only the miocene sediments the fractures are filled with calcites and locally with an internal sediment or a dolomite cement the cretaceous host rock has an average 18o value of 4 3 pdb peedee belemnite an average 13c value of 0 6 pdb a 87sr 86sr ratio of 0 70741 up to 5630 p p m of mg2 up to 2615 p p m of sr2 and up to 1560 p p m of fe2 type 2 fractures are related to palaeogene compression the calcite cement filling this type of fracture has an average 18o value of 8 2 pdb an average 13c value of 0 6 pdb a 87sr 86sr ratio of 0 70714 up to 4560 p p m of mg2 up to 3275 p p m of sr2 and up to 3540 p p m of fe2 these results indicate a fluid characterized by a high rock fluid interaction approaching a closed system equilibrium type 5 fractures are related to the syn rift stage the calcite cement filling this type of fracture has an average 18o value of 6 9 pdb an average 13c value of 4 3 pdb a 87sr 86sr ratio of 0 70787 up to 5375 p p m of mg2 up to 1750 p p m of sr2 and up to 2855 p p m of fe2 these results indicate a fluid characterized by a low rock fluid interaction and an open hydrogeological system the cements filling the compressional fractures are characterized by undulose extinction subgrain formation and deformed mechanical twin planes indicating formation under stressed conditions in contrast cements filling extensional fractures are characterized by translucent crystals with uniform extinction indicating free growth not subjected to stress

grain size and geochemistry of surface sediments in northwestern continental shelf of the south china sea eighty six surface sediments collected from the northwestern continental shelf of the south china sea scs were analyzed for grain size distribution calcium carbonate organic carbon and major and trace element compositions to investigate sediment provenance and factors controlling their geochemical composition sediments from the eastern continental shelf of hainan island have higher sand and lower clay content while the samples from the nearshore hainan island have higher contents of gravel and clay calcium carbonate contents in samples show a positive correlation with water depth in northwestern shelf of scs suggesting that it is related to biological factors however the nearshore sediments have higher contents of organic carbon compared to those of the outer shelf possibly suggesting that the terrigenous organic matter usually deposited in nearshore environments such as bays and estuaries compared with the upper continental crust the samples have relatively lower contents of sio2 and al2o3 higher than those of the pearl and red river sediments the low contents of k2o and na2o in sediments from the northwestern continental shelf are consistent with intense chemical weathering in the river basin due to the seasonally hot and humid climate regime the sediments mainly consist of three components including the gravel fraction composed of calcareous debris the sand fraction composed of quartz and the silt and clay fractions mainly composed of clay minerals the content of each component depends on grain size sediment source biogenesis and hydrodynamic conditions which finally controls the chemical composition of the sediments the distributions of co al2o3 cr al2o3 and zr sc ratios for sediments in the northwestern continental shelf suggest that source rocks are mainly composed of felsic rocks rather than mafic rocks there is a distinct difference in sediment source between eastern and western shelf sediments the eastern shelf sediments are characterized by high zr sc ratios mainly derived from the pearl river while the western shelf sediments have relatively low values of zr sc indicating a main contribution possibly sourced from the red river basin terrigenous materials from hainan island usually influence the geochemistry of sediments deposited in the nearshore area

new constraints on the structure thermochronology and timing of the ailao shan red river shear zone se asia new structural petrographic and 40ar 39ar data constrain the kinematics of the asrr ailao shan red river shear zone in the xuelong shan xls geochronological data reveal triassic early tertiary and oligo miocene thermal events the latter event 33 26 ma corresponds to cooling during left lateral shear in the fansipan fsp range thrusting of the sapa nappe linked to left lateral deformation and cooling of the fsp granite occurred at 35 ma rapid cooling resumed at 25 29 ma as a result of uplift within the transtensive asrr in the daynuiconvoi dncv foliation trends nw se but is deflected near large scale shear planes stretching lineation is nearly horizontal on steep foliations shear criteria indicate left lateral shear sense zones with flatter foliations show compatible shear senses petrographic data indicate decompression from 6 5 kbar during left lateral shear temperatures 700 c 40ar 39ar data imply rapid cooling from above 350 c to below 150 c between 25 and 22 ma without diachronism along strike along the whole asrr cooling histories show two main episodes 1 rapid cooling from peak metamorphism during left lateral shear 2 rapid cooling from greenschist conditions during right lateral reactivation of the asrr in the nw part of the asrr xls diancang shan we link rapid cooling 1 to local denudations in a transpressive environment in the sw part ailao shan and dncv cooling 1 resulted from regional denudation by zipper like tectonics in a transtensive regime the induced cooling diachronism observed in the ailao shan suggests left lateral rates of 4 to 5 cm yr from 27 ma until 17 ma dncv rocks always stayed in a transtensive regime and do not show cooling diachronism the similarities of deformation kinematics along the asrr and in the south china sea confirms the causal link between continental strike slip faulting and marginal basin opening

fluid sediment interactions at eastern mediterranean mud volcanoes a stable isotope study from odp leg 160 abstract pore fluids from two odp sites at eastern mediterranean mud volcanoes have been analyzed for their cl concentration and their 18o and d isotopic composition the cl data span a wide range of concentrations from extremely depleted with respect to seawater as low as 60 mm at the crest of milano dome site 970 to strongly enriched up to 5 4 m at napoli dome site 971 chloride enrichment is known to be due to dissolving messinian evaporites whereas the source of the low cl fluid is deduced from stable isotope data presented here the isotopic composition of the endmember fluid is found to be 10 for 18o and 32 for d for low as well as for high cl waters from this signature it can be concluded that neither gas hydrates nor meteoric water play a significant role in the freshening of the pore water several other processes altering the 18o d composition of pore waters are discussed and considered to be of only negligible influence the process characterizing the isotopic composition of the fluid is found to be clay mineral dehydration mainly smectite illite transformation corresponding to a depth range of 3 5 7 km and an elevated temperature of about 120 165 c a quantitative estimate shows that this reaction is capable of producing the observed extreme cl depletion

pumping test data analysis in wells with multiple or long screens abstract a computer method is presented to estimate the drawdown and the flow rate development in wells with multiple or long screens the mathematical model involves the following processes unsteady quasi three dimensional laminar flow in a multiple leaky aquifer system laminar and or turbulent radial flow in the skin zone including the screens turbulent axial flow and change of the kinetic energy in the screen pipe and the effect of well storage the numerical accuracy was checked against analytical theis wikramaratna and semianalytical numerical laplace inversion solutions the low error of numerical drawdown and flow rate simulation achieved during testing is acceptable in most of the practical cases two case studies demonstrate the calibration of aquifer and screen parameters the method may also be used as an approximate tool to analyse the three dimensional flow around wells with long partially penetrating screens in thick vertically heterogeneous aquifers analysis of the approximation error and some results of practical application are given

zebra dolomitization as a result of focused fluid flow in the rocky mountains fold and thrust belt canada discordant zebra dolomite bodies occur locally in the middle cambrian cathedral and eldon formations of the main ranges of the canadian rocky mountains fold and thrust belt they are characterized by alternating dark grey a and white b bands forming an abba diagenetic cyclicity these bands developed parallel to both bedding and cleavage dark grey a bands consist of fine 300 m non planar crystalline impure dolomite the white b bands are composed of coarse up to several millimetres milky white pure saddle dolomites b1 which are often covered by pore lining zoned dolomite b2 the b phases often possess a saddle shaped morphology in contrast to the replacement origin of the a dolomite the zoned b2 dolomite rims are interpreted as a cement formed in open cavities the b1 dolomite is interpreted as the result of recrystallization with diagenetic leaching of non carbonate components all the zebra dolomites studied are nearly stoichiometric and are characterized by enriched na and depleted sr concentrations fe and mn concentrations in these dolomites differ depending on the sample locality fluid inclusion data indicate that the dolomites formed from relatively hot th 130 200 c saline 20 23 wt cacl2 eq fluids a diagenetic high temperature origin is also supported by depleted 18o values 20 to 14 vpdb a contribution of 87sr enriched fluids is reflected in the 87sr 86sr values 0 7091 0 7123 zebra dolomite development is explained by focused fluid flow which exploited areas of structural weaknesses e g basin platform rim areas faults etc expulsion of hot basinal brines in a tectonically active regime generated overpressures which explains the development of secondary porosity during zebra dolomitization as well as the intra zebra fracturing at decimetre to micrometre scale

deep freeze petrology of lena river sand siberia modern sand from the vast 2 430 000 km 2 high latitude lena river watershed occupies a low lying mostly unglaciated craton covered by thick widespread permafrost totally different from the watersheds of large temperate and tropical rivers whose sands have been previously studied to establish modern baselines for the interpretation of ancient sandstones fifty nine lena sands are rich in rock fragments and feldspar and reflect well the three major tectonic provinces that underlie it platform shield and collisional suture although the platform and shield sands are still very immature long exposure to cool middle tertiary climates at first and dry sub arctic to arctic climates later is the underlying cause of the mineralogically immature river sands of the lena river

sand petrology and focused erosion in collision orogens the brahmaputra case abstract the high relief and tectonically active himalayan range characterized by markedly varying climate but relatively homogeneous geology along strike is a unique natural laboratory in which to investigate several of the factors controlling the composition of orogenic sediments coupling of surface and tectonic processes is most evident in the eastern namche barwa syntaxis where the tsangpo siang brahmaputra river draining a large elevated area in south tibet plunges down the deepest gorge on earth here composition of river sands changes drastically from lithic to quartzofeldspathic after confluence with the lohit river draining the transhimalayan equivalent mishmi arc batholiths sediment composition remains remarkably constant across assam indicating subordinate contributions from himalayan tributaries independent calculations based on petrographical mineralogical and geochemical data indicate that the syntaxis representing only 4 of total basin area contributes 35 6 to the total brahmaputra sediment flux and 20 of total detritus reaching the bay of bengal such huge anomalies in erosion patterns have major effects on composition of orogenic sediments which are recorded as far as the bengal fan in the brahmaputra basin in spite of very fast erosion and detrital evacuation chemical weathering is not negligible sand sized carbonate grains are dissolved partially in mountain reaches and completely in monsoon drenched assam plains where clinopyroxenes are selectively altered plagioclase instead is preferentially weathered only in detritus from the shillong plateau which is markedly enriched in microcline most difficult to assess is the effect of hydraulic sorting in bangladesh where quartz garnet and epidote tend to be sequestered in the bedload and trapped on the coastal plain whereas cleavable feldspars and amphiboles are concentrated in the suspended load and eventually deposited in the deep sea high resolution petrographic and dense mineral studies of fluvial sands provide a basis for calculating sediment budgets for tracing patterns of erosion in mountain belts and for better understanding the complex dynamic feedback between surface processes and crustal scale tectonics

northwest trending middle cenozoic left lateral faults in southern yunnan china and their tectonic significance abstract the northwest striking jianshui qujiang and chuxiong faults and probably the zhongdian fault south china show evidence for different amounts of middle cenozoic pre pliocene and post early paleogene left lateral displacement that range from 6 to 25 km the age and orientation of the left lateral faults suggest that the faults are related to a regional deformational event associated with important left lateral shear on the ailao shan shear zone which lies 50 70 km to the south identification of these faults extends left lateral shear during this deformational event farther to the northeast than previously recognized unlike the ailao shan shear zone these faults do not appear to be part of a through going nw trending shear zone these faults are interpreted to be the northernmost part of a nw trending boundary whose main structure the left lateral ailao shan shear zone forms a broad zone of mylonitic rocks bounding a crustal fragment that rotated clockwise around the eastern himalayan syntaxis following middle cenozoic left lateral displacement only the jianshui and qujiang faults exhibited a reversal of displacement in post miocene time this reversal is interpreted to be the result of counterclockwise rotation within the broad n s striking left lateral xiaojiang fault zone none of the post miocene displacement on these two faults appears to be related to post miocene right lateral displacement on the red river fault system the chuxiong fault may have reversed its early left lateral displacement but evidence from surface geology for young and active right lateral displacement is not clear the zhongdian fault appears to have undergone only left lateral displacement some of which may be middle cenozoic in age and some post miocene in age active displacement on the zhongdian fault is interpreted to mark the eastern boundary for a small crustal fragment that rotates clockwise around the eastern himalayan syntaxis

environmental controls on the petrology of a late holocene speleothem from botswana with annual layers of aragonite and calcite abstract a carbonate stalagmite from drotsky s cave in northwestern botswana consists of alternating layers of calcite and aragonite layer counts and radiocarbon ages indicate that the calcite aragonite pairs are annual layers representing about 1500 years of deposition the annual layering probably resulted from highly seasonal rainfall comparison of the uppermost layers of the speleothem with meteorological records shows that precipitation of caco3 in drotsky s cave was controlled by climate thickness of calcite layers correlates with rainfall suggesting that calcite precipitation was largely dependent on the quantity of water supplied to the speleothem by contrast thickness of aragonite layers correlates with temperature although variation in temperature cannot explain greater aragonite abundance on the sides of the speleothem compared to its center mg ca ratios in calcite layers increase upward to the bases of overlying aragonite layers and analyses of cave waters suggest that fluid mg ca ratios reach levels sufficient to cause aragonite precipitation increasing evaporation which caused greater ionic strength and supersaturation resultant increasing mg ca ratios in the fluid and perhaps increasing temperature probably combined to cause aragonite precipitation detailed petrographic analysis suggests that each annual cycle of caco3 precipitation began with relatively intense fluid flow sometimes sufficient to dissolve some of the underlying aragonite before precipitation of calcite calcite precipitation under a thick fluid layer allowed euhedral crystals to form at first but thinning of the fluid to a film allowed only flatly terminated calcite crystals by season s end as fluid flow diminished increasing evaporation increasing mg ca ratios in the fluid and perhaps increasing temperature combined to cause aragonite precipitation to begin particularly on the sides of the speleothem in some years fluid flow diminished to the point that dust accumulated on aragonite surfaces before the onset of the next year s precipitation p

transient well flow in layered aquifer systems the uniform well face drawdown solution abstract previously a hybrid analytical numerical solution for the general problem of computing transient well flow in vertically heterogeneous aquifers was proposed by the author the radial component of flow was treated analytically while the finite difference technique was used for the vertical flow component only in the present work the hybrid solution has been modified by replacing the previously assumed uniform well face gradient uwg boundary condition in such a way that the drawdown remains uniform along the well screen the resulting uniform well face drawdown uwd solution also includes the effects of a finite diameter well wellbore storage and a thin skin while partial penetration and vertical heterogeneity are accommodated by the one dimensional discretization solutions are proposed for well flow caused by constant variable and slug discharges the model was verified by comparing wellbore drawdowns and well face flux distributions with published numerical solutions differences between uwg and uwd well flow will occur in all situations with vertical flow components near the well which is demonstrated by considering 1 partially penetrating wells in confined aquifers 2 fully penetrating wells in unconfined aquifers with delayed response and 3 layered aquifers and leaky multiaquifer systems the presented solution can be a powerful tool for solving many well hydraulic problems including well tests flowmeter tests slug tests and pumping tests a computer program for the analysis of pumping tests based on the hybrid analytical numerical technique and uwg or uwd conditions is available from the author

the influence of calcite dissolution on reservoir porosity in miocene sandstones picaroon field offshore texas gulf coast abstract middle miocene sandstones occur in picaroon field corsair trend offshore texas gulf coast at depths of approximately 4 9 to 5 2 km 16 17 000 ft these deltaic sandstones contain evidence of the following sequence of diagenetic events 1 formation of chlorite coatings on detrital grains 2 partial dissolution of detrital feldspar 3 quartz cementation 4 calcite cementation 5 dissolution of calcite cement and grains 6 ankerite cementation the reservoir quality of the sandstones is largely a function of porosity enhancement by calcite dissolution calcite cement was emplaced at depths of approximately 1 8 to 2 6 kin the calcite has 87 86sr values of 0 7083 0 7086 eliminating coeval 15 myr seawater and marine carbonate 0 70873 0 70885 as the primary source of strontium the 87 86sr composition of calcite cement implies that mass transfer of calcite from older marine sources to younger sediments has occurred fluid inclusion measurements indicate that ankerite cement formed at minimum temperatures of 120 188 c 3 0 5 1 km oxygen isotope modeling predicts that at these depths shales would expel waters with 18osmow of 5 to 9 during smectite illite conversion ankerite 18opdb 7 8 would be in isotopic equilibrium with these waters at temperatures similar to those derived from fluid inclusions ankerite cements have relatively radiogenic 87 86sr ratios 0 7097 which are consistent with their formation from shale derived fluids calcite dissolution occurs between the precipitation of calcite and ankerite it is therefore concluded that calcite cement dissolution occurred at burial depths of 2 6 to 3 0 km 107 120 c

two unique weathering regimes in the changjiang and huanghe drainage basins geochemical evidence from river sediments the present research reconstructs the histories of chemical weathering in the drainage basins of the changjiang and huanghe based on the chemical compositions of the river sediments the silicate weathering of the changjiang basin is strong and naand ca silicate minerals are considerably dissolved while other silicate minerals are less attacked in comparison the huanghe basin is characterized by very weak silicate weathering and the weathering degree corresponds well with that of the loess which is the predominant source of the huanghe sediment overall the changjiang and huanghe basins constitute a consistent weathering spectrum from the early to intermediate stage the similarity of chemical compositions between upper continental crust and the huanghe sediments as well as the low degree of chemical weathering in the huanghe basin imply that the river sediments can be considered to be the representative of ucc and are suitable for studying the evolution of continental crust our observations indicate that climate is the predominant factor controlling silicate weathering in both river basins while controls by source rocks and relief are subordinate highly erosive river basins such as the huanghe produce poorly weathered materials which casts doubt on the idea that strong physical weathering naturally contributes much to chemical weathering differences in silicate weathering processes between the changjiang and huanghe basins may provide more constraints in estimating atmospheric co2 budget in china d 2003 elsevier b v all rights reserved

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

paleogene retroarc flexural basin beneath the neogene pannonian basin a geodynamic model abstract the neogene middle miocene recent pannonian basin is superimposed on an earlier paleogene middle eocene early miocene basin complex as a result of back arc extension although the stratigraphy of the latter is very well known due to raw material exploration its formation and structural evolution is much less understood a transtensional origin was generally proposed for the paleogene basin of hungary assuming an origin analogous to that of the overlying neogene pannonian basin we suggest an alternative geodynamic scenario for the development of the paleogene basin complex as we think that the observations are better understood in terms of a retroarc foredeep basin model according to this a flexural basin developed south of the backthrust inner west carpathian units the thrust load resulted in a generally deep underfilled flysch basin during middle eocene early oligocene times in the late oligocene early miocene predominantly shallow marine and continental deposition occurred indicating the gradual cessation of thrusting in the adjacent thrust fold belt and the beginning of molasse sedimentation throughout the whole paleogene a shift can be observed of the bathyal dominantly siliciclastic in the axis of the foredeep and neritic partly carbonate in the foreland flank of the foredeep facies belts this migration of the middle eocene early miocene depocenters of the hpb hungarian paleogene basin to the east northeast in present day coordinates is the result of two processes 1 1 the advancement of backthrusting to the southeast 2 2 along strike shift of thrusting to the northeast while a thin skinned thrust front can be reconstructed for the late eocene buda anticline the diosjeno hurbanovo line is interpreted as the result of a major thick skinned thrusting event at the base of the np24 zone 31 ma the subsidence pattern the distinct depositional environments and the structural observations can be more easily integrated into a flexural basin model than into a wrench basin model based on the flexural basin model of this work the early tertiary western carpathians formed a compressional arc while this arc probably developed above a b subduction zone during the late eocene with a corresponding trench magura a forearc basin central carpathian or podhale and a retroarc flexural basin hungarian paleogene from the early oligocene to the early miocene it was characterized by a subduction with a corresponding peripheral foredeep dukla and silesian and a retroarc flexural basin hungarian paleogene

mesozoic plate tectonic reconstruction of the carpathian region abstract palaeomagnetic palaeobiogeographic and structural comparisons of different parts of the alpine carpathian region suggest that four terranes comprise this area the alcapa tisza dacia and adria terranes these terranes are composed of different mesozoic continental and oceanic fragments that were each assembled during a complex late jurassic cretaceous palaeogene history palaeomagnetic and tectonic data suggest that the carpathians are built up by two major oroclinal bends the alcapa bend has the meliata oceanic unit correlated with the dinaric vardar ophiolite in its core it is composed of the western carpathians eastern alps and southern alcapa units transdanubian range bukk this terrane finds its continuation in the high karst margin of the dinarides further elements of the alcapa terrane are thought to be derived from collided microcontinents czorsztyn in the n and a carbonate unit tisza in the se the tisza dacia bend has the vardar oceanic unit in its core it is composed of the bihor and getic microcontinents this terrane finds its continuation in the serbo macedonian massif of the balkans the bihor getic microcontinent originally laid east of the western carpathians and filled the present carpathian embayment in the late palaeozoic early mesozoic the vardar ocean occupied an intermediate position between the western carpathian austroalpine transdanubian high karst margin and the bihor getic serbo macedonian microcontinent the vardar and pindos oceans were opened in the heart of the mediterranean adriatic microcontinent in the late permian middle triassic vardar subducted by the end of jurassic causing the bihor getic serbo macedonian microcontinent to collide with the internal dinaric western carpathian margin an external penninic vahic ocean tract began opening in the early jurassic separating the austroalpine western carpathian microcontinent and its fauna from the european shelf further east the severin ceahlau magura also began opening in the early jurassic but final separation of the bihor getic ribbon and its fauna from the european shelf did not take place until the late middle jurassic the alcapa and the tisza dacia were bending during the albian maastrichtian the two oroclinal bends were finally opposed and pushed into the gates of the carpathian embayment during the palaeogene and neogene at that time the main n s shortening in distant alpine and hellenic sectors was linked by a broader right lateral shear zone along the former vardar suture

importance of the vertical component of groundwater flow a hydrogeochemical approach in the valley of san luis potosi mexico fractured volcanics exert a control on groundwater flow in the san luis potosi slp valley the chemical composition and temperature of water pumped from boreholes partially penetrating the fractured volcanics indicate that the produced water originates from an upward vertical flow most of the thermal groundwater has been detected in areas related to regional faults and lineaments intensive and uncontrolled pumping from the upper 14 of the aquifer total depth 1500 m causes the rise of water from a deep regional flow system that mixes with the shallower waters the deep waters contain high fluoride concentrations that contaminate the mixture and cause substantial health related effects the recharge controls on the regional flow system require further research however hydrogeochemical evidence supports the view that the origin of this recharge is limited to the western bounding sierra madre occidental higher levels of dissolved na li f and so4 2 derived from tertiary volcanics have been introduced into the exploited region the concentrations indicate lengthy and deep circulation flow li concentration was used as an indicator of groundwater residence time and therefore of the length of the groundwater flow path hydrogeochemical interpretation indicates the presence of three flow systems a shallow local one controlled by a clay layer that subcrops most of the valley floor an intermediate system in which water infiltrates just beyond the boundary of the clay layer and a deep regional system which originates outside the surface catchment the local and intermediate systems circulate through materials with comparatively low hydraulic conductivity low cl concentrations suggest rapid flow in the regional system concentrations of li and f can be used to calculate percentages of waters in mixtures of regional and intermediate flows concentrations of na ca2 and so4 2 appear to be controlled by water rock reactions uncontrolled pumping increases will tend to enhance fluoride concentration and its undesirable effects lack of management of aquifers in basins similar to the slp valley can result in groundwater contamination not only from surface anthropogenic sources but also from natural water rock interactions

sedimentary carbonates through phanerozoic time plate tectonic processes play a critical role in the origin and distribution of sedimentary carbonates through phanerozoic time the phanerozoic age distribution of sedimentary properties like calcite dolomite ratio inferred ooid and cement mineralogy and survival rate of continental carbonates is cyclic the cycles appear to be coupled to plate tectonic processes that give rise to global sea level change and changes in the properties of the ocean atmosphere system first order changes in sea level are driven by the accretion of mid ocean ridges high accretion rate high sea level low accretion rate low sea level although correlations between sea level and sedimentary carbonate properties are not strong high sea level over an extended period of time appears to be correlated with low calcite dolomite ratios lack of inferred aragonite ooids and cements and maxima in the survival rate of continental carbonates the opposite is true for extended periods of low mid ocean ridge accretion rates and global sea levels the lack of strong correlations may reflect an insufficient data base and the possibility of lags between sea level change and change in carbonate properties furthermore the survival rate of continental carbonates appears to be affected by differential cycling and therefore may not be directly related to accumulation rate it appears that the environmental conditions for early dolomitization and calcite ooid and cement formation are best met during extended times of high sea level when atmospheric co2 levels are high and the saturation state of seawater with respect to carbonate minerals relatively low during low sea levels early dolomitization is less favored and aragonite precipitates are more abundant because of low atmospheric co2 levels and enhanced seawater carbonate saturation states differential cycling has modified the phanerozoic sedimentary carbonate mass age distribution because of erosion of younger units within continental carbonate cycles it may be difficult to derive an unequivocal record of the partitioning of carbonate between the deep sea and shallow water realms of deposition during the phanerozoic this difficulty must be considered in further quantification of geochemical models describing the geologic history of atmospheric co2 and climate change

geochemical characteristics of water and sediment of the indus river trans himalaya india constraints on weathering and erosion abstract the indus river carries a huge amount of chemical and sediment load while traversing the himalayas the present study deals with the chemistry of major ions ca mg hco3 na k cl so4 sio2 and trace metal contents ba sr zn ni cu co mn of the river indus one of its major tributaries the river beas many adjoining hot and cold water springs and the high altitude lake 5700 m kyung tso although anthropogenic activities like farming grazing and tourism have started in large parts of this terrain our study indicates that chemistry of indus water is influenced mostly by the lithology of the basin and most of its ionic concentration appears to have been derived from weathering of carbonates and silicates in the catchment area for the first time bed and suspended sediments of the river indus have also been studied and compared with average post archean shale pas and greywacke the sediments of the indus river in its headwater region closely reflect the exposed portion of the crust in its catchment area the headwater part of the indus basin in ladakh and karakorum is characterised by rapid uplift and therefore subject more to intense physical weathering than chemical weathering as is evidenced by the suspended and dissolved load carried by the river physical weathering and erosion is expected to have major controls on the grain size and therefore the chemical nature of the sediments

the influence of climate and topography on rock fragment abundance in modern fluival sands of the southern blue ridge mountains north carolina chemical weathering influences the detrital composition of sand size sediment derived from source areas subject to different amounts of precipitation in the coweeta basin north carolina of the grain types studied rock fragments are most sensitive to chemical degradation therefore their abundance is the best indicator of cumulative weathering effects destruction of sand size rock fragments by chemical weathering is a function of both the intensity and duration of chemical weathering experienced by grains in regoliths of the source area in the coweeta basin the intensity of chemical weathering is directly related to the climate via effective precipitation in individual subbasins whereas the duration of chemical weathering is inversely related to the relief ratio of the watershed therefore soils in watersheds with low relief ratios and high discharge per unit area experience the most extensive chemical weathering and sediments derived from these watersheds contain the lowest percentage of rock fragments the effects of climate alone cannot explain the systematic variation of rock fragment abundance in sediments from the coweeta basin the compositional imprint left on these sediments by chemical weathering is a function of both climate and topographic slope in the sediment source area

major and trace element and sr isotope constraints on fluid circulations in the barbados accretionary complex part 1 fluid origin abstract we measured the chemical and sr isotope compositions of vent and pore fluids and associated sediments from a diapiric field located near 13 5 n east of the deformation front of the barbados accretionary complex the two diapiric structures with the largest thermal anomalies and characterized by active fluid conduits exhibit the strongest chemical and 87 sr 86 sr variations these two diatremes atalante and cyclope also have low chloride contents and non radiogenic 87 sr 86 sr which may be explained by interaction between seawater and volcanic ash or with underlying oceanic crust in the central zone of the two structures 87 sr 86 sr varies little with depth which implies that fluid expulsion is at such a high rate that it is not affected by seawater 87 sr 86 sr the expelled fluids probably circulate along the decollement zone and ascend along faults which act as channels a deep component is probably located in the decollement zone whereas another component may be recirculated seawater the ascending fluid interacted with numerous materials causing dehydration of clay minerals and alteration of volcanic ash and or underlying oceanic crust to explain the low chloride contents of the atalante fluids gas hydrate decomposition yielding dilution of the fluid without modifying its sr isotope ratio needs to be superimposed on the mixing between seawater and the deep component the occurrence of gypsum in these two diatremes implies higher fluid temperatures and more intense activity at least temporarily to allow the deposition of such a mineral

stress induced late stage subsidence anomalies in the pannonian basin abstract subsidence sedimentation and tectonic quiescence of the pannonian basin was interrupted a few million years ago by tectonic reactivation this recent activity has manifested itself in uplift of the western and eastern flanks and continuing subsidence of the central part of the pannonian basin low to medium magnitude earthquakes of the carpathian pannonian region are generated mostly in the upper crust by reverse and wrench fault mechanisms there is no evidence for earthquakes of extensional origin 2 d model calculation of the subsidence history shows that a recent increase in magnitude of horizontal compressional intraplate stress can explain fairly well the observed quaternary uplift and subsidence pattern we propose that this stress increase is caused by the overall europe africa convergence in late pliocene consumption of subductible lithosphere at the eastern margin of the pannonian basin was completed and the lithosphere underlying the pannonian basin became locked in a stable continental frame consequently extensional basin formation has come to an end and compressional inversion of the pannonian basin is in progress

fluid mixing and recycling during pyrenean thrusting evidence from fluid inclusion halogen ratios abstract syntectonic fluids have been sampled through fluid inclusion microthermometry and crush leach analyses cations and halogens from a 50 km n s transect through the central southern pyrenees the fluid inclusions are contained in syntectonic quartz veins in triassic redbeds cretaceous carbonates and hercynian basement rocks with some calcite and dolomite data from limestones and evaporites in more external parts of the belt the main datasets come from 1 alpine shear zones cutting the neouvielle granodiorite in the hercynian axial zone at the north end of the transect 2 an imbricate zone beneath the alpine gavarnie thrust at the pic de port vieux 3 several localities in the footwall and hangingwall of the gavarnie thrust on the southern margin of the axial zone the inclusion fluids generally decrease in salinity from 27 35 at the northern end of the transect to 7 22 on the southern margin of the axial zone the majority of the inclusions have cl br ratios lower than seawater and are interpreted as relict fluids after seawater evaporation and halite precipitation in the upper trias this interpretation is supported by cl br na systematics which are consistent with a change from halite to halite sylvite precipitation with progressive evaporation fluids in the basement shear zones are interpreted to have essentially the same evaporitic origin as those still contained in sedimentary formations although it is possible that final concentration of brines in the neouvielle massif involved retrograde hydration reactions with removal of water by precipitation of hydrous minerals the fluids are also very similar in salinity and halogen chemistry to those found in veins associated with mesozoic pb zn f deposits which predate the thrusting the lower salinities seen at the southern margin of the axial zone are interpreted to reflect mixing of the brines with a higher level fluid connate or meteoric water circulating within the mesozoic carbonates of the higher thrust sheets at one locality where triassic evaporites are still present high cl br ratios at relatively low salinities are present in inclusions within the underlying triassic redbeds but low cl br ratios at higher salinities are seen lower in the sequence this is consistent with dissolution of halite by a dilute fluid but with limited penetration downwards we suggest that the fluid history of the pyrenees evolved through a series of stages 1 upper triassic evaporite formation with sinking of brines into underlying redbeds and fractured basement rocks 2 circulation of brines with formation of pb zn deposits along faults at some time between the triassic and the upper cretaceous 3 renewed extension with erosion of triassic rocks in many areas and further drawing down of triassic brines into the basement 4 deposition of u cretaceous and palaeocene carbonates containing connate waters of marine origin 5 formation of the pyrenean thrust belt with overpressuring and expulsion of the brines along shear zones and faults 6 creation of topography with a high level circulation system in the mesozoic thrust sheets driven largely by topography at the southern margin of the axial zone there was limited mixing of the deeper overpressured brines with these more dilute hydrostatically pressured fluids an important point is that because of their density hypersaline brines are difficult to expel from the upper crust and may be involved in a succession of alteration and mineralisation events in the same general area over hundreds of millions of years

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

karst controlled reservoir heterogeneity in ellenburger group carbonates of west texas petroleum production from restricted shelf carbonates of the lower ordovician ellenburger group is commonly considered to have been a result of a pervasive relatively homogeneous tectonic fracture system within the reservoir rock however regional facies and diagenetic paleokarst studies of ellenburger strata based on cores and wireline logs have demonstrated that significant reservoir compartmentalization was caused by karst modification in the upper part of the unit ellenburger group carbonates which attain a thickness of over 1 700 ft 520 m record sedimentation on a shallow water restricted shelf occupying most of west texas logging of over 10 000 ft 3 050 m of core from 63 wells has allowed recognition of six facies assemblages 1 lithic arenite 2 mixed siliciclastic carbonate packstone grainstone 3 ooid peloid grainstone 4 mottled mudstone 5 laminated mudstone and 6 gastropod intraclast packstone grainstone these facies assemblages record initial transgression and subsequent progradation and aggradation paleoslope was generally south and east from the texas arch toward the ouachita and marathon orogenic belts all facies assemblages with the local exception of the ooid peloid grainstone assemblage are characterized y very low intergranular and intercrystalline porosity porosity development in ellenburger group carbonates is directly related to a prolonged period of subaerial exposure that coincided with a middle ordovician eustatic lowstand prior to transgression of simpson group siliciclastics during this episode a widespread system of caves sinkholes joint controlled solution features and collapse breccias developed of particular importance to reservoir development was the formation of a regionally extensive cave system between 100 and 300 ft 30 and 90 m beneath the exposed ellenburger surface infill of this cave system by simpson group sand and clay segmented the upper ellenburger into three karst facies which are in descending order 1 cave roof dolomites fracture and mosaic breccias 2 laterally persistent cave fill facies siliciclastic matrix supported and carbonate matrix supported breccias and 3 lower collapse facies chaotic clast supported breccias of the cave floor pronounced vertical segregation of permeable zones defined by the three karst facies is evident in the emma andector martin block 13 and several other major ellenburger reservoirs lateral reservoir heterogeneities formed by localized laterally extensive collapse structures such as in the shafter lake reservoir also contribute to compartmentalization of producing zones within the upper ellenburger group secondary and tertiary recovery programs in these ellenburger reservoirs can be optimized by integrating concepts of lateral and vertical heterogeneity predicted by the karst model

magnetic properties of sediments of the red river effect of sorting on the source to sink pathway and its implications for environmental reconstruction we conducted a mineral magnetic study of river bank and subaqueous delta sediments from the red river in order to examine the role of sedimentary sorting on the variation of sedimentary magnetic properties from source to sink the magnetic mineralogy mainly consists of magnetite and hematite bulk sediment particle size variations have a strong influence on magnetic properties with the frequently used magnetic parameters fd arm arm and arm sirm exhibiting positive correlations with the 5 m water depth part of the subaqueous delta have lower and sirm values a finer ferrimagnetic grain size and higher proportions of hematite consistent with selective loss of coarse ferrimagnetic grains on the source to sink pathway we suggest that variations in magnetic properties in response to particle size compositions and therefore depositional environment changes should be carefully addressed when magnetic proxies such as arm sirm are used in the study of coastal and marine environmental changes e g sea level change in such cases the combined use of magnetic properties and geochemical indicators such as al ti ratio may provide better results for paleoenvironmental reconstruction

petrology of indus river sands a key to interpret erosion history of the western himalayan syntaxis the indus river has been progressively transformed in the last decades into a tightly regulated system of dams and channels to produce food and energy for the rapidly growing population of pakistan nevertheless indus river sands as far as the delta largely retain their distinct feldspar and amphibole rich composition which is unique with respect to all other major rivers draining the alpine himalayan belt except for the brahmaputra both the indus and brahmaputra rivers flow for half of their course along the india asia suture zone and receive major contributions from both asian active margin batholiths and upper amphibolite facies domes rapidly exhumed at the western and eastern himalayan syntaxes compositionofindussandschangesrepeatedlyandmarkedlyinladakhandbaltistan indicatingoverwhelmingsedimentflux from each successive tributary as the syntaxis is approached provenance estimates based on our integrated petrographic mineralogical data set indicate that active margin units karakorum and transhimalayan arcs provide 81 of the 250f50 10 6 t ofsedimentsreachingthetarbelareservoireachyear partitioningofsuchfluxamongtributariesandamongsourceunitsallowsus to tentatively assess sediment yields from major subcatchments extreme yields and erosion rates are calculated for both the karakorum belt up to 12 500f4700 t km 2 year and 4 5f1 7 mm year for the braldu catchment and nanga parbat massif 8100f3500t km 2 yearand3 0f1 3mm year thesevaluesapproachdenudationratescurrentlyestimatedforsouthkarakorum and nanga parbat crustal scale antiforms and highlight the major influence that rapid tectonic uplift and focused glacial and fluvial erosion of young metamorphic massifs around the western himalayan syntaxis have on sediment budgets of the indus system detailed information on bulk petrography and heavy minerals of modern indus sands not only represents an effective independent method to constrain denudation rates obtained from temperature time histories of exposed bedrock but also

double porosity models for a fissured groundwater reservoir with fracture skin theories of flow to a well in a double porosity groundwater reservoir are modified to incorporate effects of a thin layer of low permeability material or fracture skin that may be present at fracture block interfaces as a result of mineral deposition or alteration the commonly used theory for flow in double porosity formations that is based upon the assumption of pseudo steady state block to fissure flow is shown to be a special case of the theory presented in this paper the latter is based on the assumption of transient block to fissure flow with fracture skin under conditions where fracture skin has a hydraulic conductivity that is less than that of the matrix rock it may be assumed to impede the interchange of fluid between the fissures and blocks resistance to flow at fracture block interfaces tends to reduce spatial variation of hydraulic head gradients within the blocks this provides theoretical justification for neglecting the divergence of flow in the blocks as required by the pseudo steady state flow model coupled boundary value problems for flow to a well discharging at a constant rate were solved in the laplace domain both slab shaped and sphere shaped blocks were considered as were effects of well bore storage and well bore skin resultsmore obtained by numerical inversion were used to construct dimensionless type curves that were applied to well test data for a pumped well and for an observation well from the fractured volcanic rock terrane of the nevada test site less

natural controls of fluvial denudation rates in major world drainage basins we present a new compilation of estimates of modern rates of mechanical and chemical denudation for externally drained basins exceeding 5 105 km2 in area these estimates are based on sediment and solute load data selected in order to represent natural rates as far as possible chemical denudation rates have been calculated by deducting the nondenudational component of solute load mechanical denudation rates range from 1 mm kyr 1 for the st lawrence and dnepr basins to 670 mm kyr 1 for the brahmaputra basin chemical denudation rates vary from 1 mm kyr 1 kolyma niger nile and rio grande basins to 27 mm kyr 1 chiang jiang basin the kolyma basin has the lowest 4 mm kyr 1 and the brahmaputra basin the highest overall rate of denudation 688 mm kyr 1 relationships between denudation rates and a range of morphometric hydrologic and climatic variables are investigated through correlation and regression analysis morphometric variables such as mean local relief are accurately calculated for large basins for the first time by using the national geophysical data center 10 minute topographic database variables expressing basin relief characteristics and runoff are found to be most strongly associated with both mechanical and chemical denudation rates with more than 60 of the variance in total denudation being accounted for by basin relief ratio and runoff basin area runoff variability and mean temperature however are only weakly associated with rates of denudation although direct comparisons cannot be made it appears that rates of basin denudation derived from present day mass flux estimates are not overall significantly different from estimates of long term rates based on sediment volume and thermochronologic data it therefore appears that the key factors identified as controlling denudation rates here are also applicable to the geological time spans relevant to the interaction between tectonic and denudational processes

tectonic versus climatic control on the evolution of fluvio deltaic systems in a lake basin eastern pannonian basin abstract the pannonian basin is a back arc lake basin situated inside the central european carpathian loop surrounded by the orogenic belts of the eastern alps carpathians and dinarides integrated stratigraphical and sedimentological research reported here focuses on palaeogeographical evolution and particularly the response of the fluvio deltaic systems to climatic and tectonic controls in the late neogene sedimentary succession in the eastern part of the pannonian basin this work has been carried out using subsurface data including regional composite seismic profiles and well logs dip sections were studied to define the stratigraphical architecture depositional environments and sequence stratigraphy and to interpret the sedimentary evolution of the area the eastern pannonian basin is characterized by sediment input from the north east which was one of the main routes of the fluvial deltaic systems entering and progressively filling lake pannon from 11 6 2 6 ma the formations studied were deposited in environments that ranged from the deep water basin plain slope delta front and coastal plain to alluvial plain causing the deposition of characteristic lithofacies associations and characteristic biofacies these form laterally continuous lithofacies units that can be correlated through the basin all depositional facies units have considerable thicknesses 300 1000 m in the deepest parts of the sub basins sequence stratigraphical interpretation was carried out correlating 3rd and 4th order sequences ma to ky in range through a regional composite seismic profile network in the dip direction stratigraphical architecture and sedimentary facies indicate that the 3rd order cycles were controlled by tectonic driving forces while 4th order cycles were probably driven by large scale climatic changes within the milankovitch band in the 3rd order time interval pa 3 between 9 1 and 6 8 ma a major tectonostratigraphic event occurred highlighting the role of strike slip faulting related transtensional subsidence in the derecske sub basin superimposed on the regional post rift thermal subsidence of the eastern pannonian region the substantial base level fall at sb pa 4 at 6 8 ma over 200 m perhaps amplified by subsequent tectonic movements can be related to the onset of a new compressional phase of structural evolution in the basin

environmental geochemistry and quality assessment of surface and subsurface water of mahi river basin western india the hydrogeochemical study of surface and subsurface water of mahi river basin was undertaken to assess the major ion chemistry solute acquisition processes and water quality in relation to domestic and irrigation uses the analytical results show the mildly acidic to alkaline nature of water and dominance of na and ca2 in cationic and hco3 and cl in anionic composition in general alkaline earth elements ca2 mg2 exceed alkalis na k and weak acids hco3 dominate over strong acids so42 cl in majority of the surface and groundwater samples ca2 mg2 hco3 is the dominant hydrochemical facies both in surface and groundwater of the area the weathering of rock forming minerals mainly controlled the solute acquisition process with secondary contribution from marine and anthropogenic sources the higher concentration of sodium and dissolved silica high equivalent ratios of na k tz na k cl and low ratio of ca2 mg2 na k suggest that the chemical composition of the water is largely controlled by silicate weathering with limited contribution from carbonate weathering and marine and anthropogenic sources kaolinite is the possible mineral that is in equilibrium with the water implying that the chemistry of river water favors kaolinite formation assessment of water samples for drinking purposes suggests that the majority of the water samples are suitable for drinking at some sites concentrations of tds th f no3 and fe are exceeding the desirable limit of drinking however these parameters are well within the maximum permissible limit except for some cases to assess the suitability for irrigation parameters like sar rsc and na were calculated in general both surface and groundwater is of good to suitable category for irrigation uses except at some sites where high values of salinity na and rsc restrict its uses

a simplified analysis of parameters controlling dewatering in accretionary prisms abstract one of the many dynamic geologic processes taking place at subduction zones is the compaction driven dewatering of seafloor sediments as they are accreted to the overriding plate the rate of dewatering is equal to the divergence of the sediment matrix velocity field this rate can be estimated analytically if simplifying assumptions are made about the geometry of the prism and motion of the sediments the analytical expression depends only on the sediment accretion velocity thickness of the accreted section prism taper angle and sediment porosity distribution a sensitivity analysis of the solution shows that the fluid production distribution is relatively insensitive to the sediment porosity distribution however the solution is very sensitive to the taper angle of the wedge high angle wedges expel almost all of the incoming water within 20 km while low angle wedges may retain a significant fraction of the incoming water for 50 or more kilometers thickness of the incoming section is also important dewatering of thin accreted sections is more concentrated near the toe of the wedge analyses of transects through the northern barbados makran vancouver and nankai accretionary prisms illustrate a range of dewatering rates and spatial distributions of dewatering

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

fluid flow reconstruction in karstified panormide platform limestones north central sicily implications for hydrocarbon prospectivity in the sicilian fold and thrust belt diagenetic analysis based on field and petrographic observations isotope and microthermometric data was used to reconstruct the fluid flow history of the cretaceous shallow water limestones from the panormide platform exposed in north central sicily analysis focused on diagenetic products in cavities and dissolution enlarged fractures of the karstified limestones that occur just below a regional unconformity the fluid flow history could be broken down into five stages that were linked to the kinematic and burial history of the region 1 petrography zoned cathodoluminescence and speleothem textures and stable isotopes 6 5 18ov pdb 3 5 and 0 13cv pdb 14 indicate that the earliest calcite phase was associated with karstification during emergence of the platform limestone dissolution at this stage is important with regard to possible reservoir creation in the panormide palaeogeographic domain 2 fine grained micrite sedimentation dated as latest cretaceous by nannopalaeontology and its 87sr 86sr isotope ratio 0 7078 marks replacement by marine fluids during subsequent submergence of the karstified platform 3 the following calcite cement was still precipitated by marine derived fluids 7 0 18ov pdb 5 0 and 3 0 13cv pdb 0 5 tm 2 to 5 c but at increasingly higher temperatures th 60 120 c this has been interpreted as precipitation during oligocene foredeep burial 4 hot th 130 180 c low saline tm 2 5 c fluids with increasingly higher calculated 18osmow signatures 6 to 14 subsequently invaded the karst system these fluids most likely migrated during fold and thrust belt development the low salinity and relatively high 18osmow signatures of the fluids are interpreted to be the result of clay dewatering reactions the presence of bitumen and associated fluorite with hydrocarbon inclusions at this stage in the paragenesis constrains the timing of oil migration in the region 5 finally high saline fluids with elevated 87sr 86sr 0 7095 0 7105 signatures invaded the karst system this last fluid flow event was possibly coeval with localized dolomitization and calcite cementation along high angle faults of pliocene age as suggested by identical radiogenic signatures of these diagenetic products

interpretation of transient borehole flow metering data in a fissured granite formation summary heat pulse flowmeter hpf data obtained in a fractured granite formation under transient pumping conditions are interpreted using a borehole flow model the phraeatic formation is modeled using cylindrically symmetric layers composed of thick low permeability intervals between thin layers of much higher permeability corresponding to fracture zones the inflow to the borehole at fracture zones generates sharp increases in the flow profiles obtained during pumping heat pulse flowmeter measurements are given as a function of depth and time drawdown and pumping rate are also recorded during the measurement period the numerical flow model is used to calculate the drawdown and evolving profile of borehole flow as a function of time during the pumping period the model allows for vertical flow across the horizontal interfaces between layers and accounts for borehole storage effects the model is also designed to allow for changes in fracture zone permeability with distance from the borehole bi zonal flow by allowing for changes in permeability with radial distance the model uses a finite difference technique to compute borehole flow and drawdown during pumping the accuracy of the finite difference code was checked against available analytical and semi analytical solutions derived by integral transform techniques the model was calibrated using estimates of formation properties and distance to lateral boundaries derived from short medium and long term packer tests results of two borehole flow experiments are evaluated for experiments in boreholes with 7 and 4 discrete fracture zones distributed over 59 50 and 121 16 m of open borehole interval

neogene and quaternary rollback evolution of the tyrrhenian sea the apennines and the sicilian maghrebides reconstruction of the evolution of the tyrrhenian sea shows that the major stage of rifting associated with the opening of this basin began at similar to10 ma it involved two episodes of back arc extension which were induced by the rollback of a west dipping subducting slab the first period of extension 10 6 ma was prominent in the northern tyrrhenian sea and in the western part of the southern tyrrhenian sea the second period of extension mainly affected the southern tyrrhenian sea began in the latest messinian 6 5 ma and has been accompanied by subduction rollback at rates of 60 100 km myr 1 slab reconstruction combined with paleomagnetic and paleogeographic constraints indicates that in the central apennines the latest messinian 6 5 ma arrival of a carbonate platform at the subduction zone impeded subduction and initiated a slab tear and major strike slip faults these processes resulted in the formation of a narrow subducting slab beneath the ionian sea that has undergone faster subduction rollback and induced extreme rates of back arc extension

paragenesis of cretaceous to eocene carbonate reservoirs in the ionian fold and thrust belt albania relation between tectonism and fluid flow this paper examines the diagenetic history of dual i e matrix and fracture porosity reservoir lithologies in cretaceous to eocene carbonate turbidites of the ionian fold and thrust belt close to the oil producing centre of fier ballsh central albania the first major diagenetic event controlling reservoir quality was early cementation by isopachous and syntaxial low mg calcite these cements formed primarily around crinoid and rudist fragments which acted as nucleation sites in sediments in which these bioclasts are the major rock constituent this cement can make up 30 of the rock volume resulting in low effective porosity in strata in which these bioclasts are mixed with reworkedmicrite isopachous syntaxial cements stabilized the framework and matrixporosity is around 15 the volumetric importance of these cements their optical and luminescence character distribution and dull orange luminescence and stable isotopic signal 18o and 13c averaging respectively 0 5 vpdb and 2 vpdb all support a marine phreatic origin within these turbidites and debris flows several generations of fractures alternated with episodes of cementation a detailed reconstruction of this history was based on cross cutting relationships of fractures and compactional and layer parallel shortening lps stylolites the prefolding calcite veins possess orange cathodoluminescence similar to that of the host rock their stable isotope signatures 18o of 3 86 to 0 85 vpdb and 13c of 0 14 to 2 98 vpdb support a closed diagenetic rock buffered system a similar closed system accounts for the selectively reopened and subsequently calcite cemented lps stylolites 18o of 1 81 to 1 14 vpdb and 13c of 1 52 to 2 56 vpdb within the prefolding veins brecciated host rock fragments and complex textures such as crack and seal features resulted from hydraulic fracturing they reflect expulsion of overpressured fluids within the footwall of the frontal thrusts after folding and thrust sheet emplacement some calcite veins are still rock buffered 18o of 0 96 to 0 2 vpdb and 13c of 0 79 to 1 37 vpdb whereas others reflect external i e extraformational and thus large scale fluid fluxes some of these veins are linked to basement derived fluid circulation or originated from fluid flow along evaporitic decollement horizons 18o around 3 0 vpdb and 13c around 1 5 vpdb others are related to the maturation of hydrocarbons in the system 18o around 7 1 vpdb and 13c around 9 3 vpdb an open joint system reflecting an extensional stress regime developed during or after the final folding stage this joint system enhanced vertical connectivity this open joint network can be explained by the high palaeotopographical position and the folding of the reservoir analogue within the deformational front the joint system is pre burdigalian in age based upon a dated karstified discordance contact sediment filled karst cavity development is linked to meteoric water infiltration during emergence of some of the structures despite its sediment fill the karst network is locally an important contributor to reservoir matrix porosity in otherwise tight lithologies development of secondary porosity along bed parallel and bed perpendicular i e layer parallel shortening stylolites is interpreted as a late stage diagenetic event associated with migration of acidic fluids during hydrocarbon maturation development of porosity along the lps system enhanced the vertical reservoir connectivity

deposition and diagenesis of carbonate conglomerates in the kremenara anticline albania a paragenetic time marker in the albanian foreland fold and thrust belt this paper addresses the diagenesis of carbonate conglomerates in that it assesses the potential of conglomerates in refining the paragenetic history in complex structural areas such as the albanian foreland fold and thrust belt of major interest are stylolites burial and tectonic which are restricted to conglomerate fragments or which crosscut the conglomerate matrix based on the inferred age of stylolite development in relation to burial uplift and tectonic history and the lower to middle miocene age of the conglomerates the succession of diagenetic events was subdivided into several stages the pocem polymict transgressive carbonate conglomerate kremenara anticline central albania was deposited in a shallow marine environment these conglomerates are covered by intertidal rhodolithic packstones grainstones the stable isotope signature of these packstones grainstones 18ov pdb 1 0 to 0 7 13c 1 0 to 1 4 plots is within the range of marine early and middle miocene values shortly after deposition of the conglomerates micritization geopetal infill and acicular calcite cementation took place a first calcite vein generation is interpreted as having formed from a messinian brine during shallow burial burial stylolites developed during further burial in the pliocene these stylolites serve as an important diagenetic time marker the post burial stylolite meteoric calcite vein cement probably precipitated during the following telogenetic stage karstification and calcite concretion precipitiation pre date overturning of the western limb of the anticline reopening of subvertical fractures and tectonic stylolites in the western limb of the kremenara anticline followed by oil migration represents one of the latest diagenetic events these fractures and stylolites provide major pathways for hydrocarbon production

alluvial deposits from the strike slip fault lo river basin oligocene miocene red river fault zone north western vietnam abstract the lo river basin lrb is one of several narrow sedimentary basins associated with the main faults of the red river fault zone separating the south china and indochina microplates the basin is located on the ne boundary of the high grade metamorphic con voi massif and the sedimentary and metasedimentary viet bac fold zone in north eastern vietnam the lrb is filled with over 6000 m of oligocene miocene alluvial deposits the source area was probably located on the ne margin of the basin and was composed mostly of low grade metamorphic rocks with a minor component of sedimentary rocks three alluvial systems are recognised the oldest system was a proximal braided river system with the minor occurrence of alluvial fans the younger systems record changes in clast composition and lithofacies which suggests a transition from a distal braided river to a distal braidplain system the lrb fill shows a range of features characteristic of strike slip fault basins the origin of the lrb is correlated with the left lateral transtensional regime the present shape of the basin is a result of post sedimentation tectonic activity

massive hydrothermal dolomites in the southwestern cantabrian zone spain and their relation to the late variscan evolution abstract large scale massive burial dolomitization affected upper carboniferous carbonates of the southwestern variscan cantabrian zone spain replacive and void filling dolomites formed and were post dated by calcite cementation the process of dolomitization was due to the circulation of hypersaline and hydrothermal marine derived brines controlled by rock anisotropies the dolomites probably formed in early permian time during post thrusting orocline formation in an extensional setting lithospheric delamination induced increased heat flow and allowed thermal convection of the fluids the dolomites from the cantabrian zone are excellently exposed and represent an interesting outcrop analogue for hydrocarbon reservoirs elsewhere in comparable geotectonic settings of the european variscan orogen large masses of similar dolomites could have formed if mg rich brines were available

late cenozoic subduction complex of sicily abstract besides remnants of hercynian deformations in the peloritani nappe and of pre oligocene alpine structures in the troiani nappe most compressive structures observed in the sicilian accretionary wedge result from the late cenozoic tortonian to present continental subduction of the apulia iblei block and are thus synchronous with distensive structures related to the opening of the tyrrhenian sea syntectonic deposits fill southward migrating foredeeps in a sequential fashion and the dating of these deposits helps to constrain the timing of deformation similarly plio quaternary sediments eroded from the accreted units rest on top of the allochthon in either compressive piggy back depressions or extensional basins the age and configuration of these overlap deposits constrain our reconstructions of the subsurface geometry of the underlying peri tyrrhenian detachment faults or s verging thrust faults post depositional erosion normal faulting and syntectonic filling of basins contribute to maintaining the critical taper of the prism whose geometry is continuously altered owing to frontal accretion underplating and isostatic uplift

geochemical and hydrogeological characterization of thermal springs in western sicily italy abstract thermal and cold waters from castellammare alcamo western sicily italy were collected between may 1994 and may 1995 and studied for their chemical and isotopic composition during the same period mean monthly samples of meteoric water were also collected and measured for their isotopic composition the main purpose of this study was the characterization of the acquifers and if possible of their recharge areas according to the results obtained the acquifers were divided into three main groups a selenitic waters b cold carbonatic waters and c deep thermal waters resulting from the mixing of the other two types besides a mixing process between carbonatic and selenitic waters contamination processes of thermal waters by seawater take place during their ascent the water temperature of the acquifer feeding the thermal springs was estimated by means of various geothermometers to range between 60 c and 97 c isotope data on rainwater samples show a wide seasonal variation of both 18 o and d values the fairly constant values of thermal waters through time and the lack of an apparent correlation with the isotopic values of rainwater suggest the existence of a deep circuit determining an almost complete homogenisation of the seasonal variations of the isotopic values

detrital zircon ages and heavy mineral composition along the gulf of tonkin implication for sand provenance in the yinggehai song hong and qiongdongnan basins abstract neogene reservoir sand in the yinggehai song hong ygh shb and qiongdongnan basins qdnb was derived from the red river hainan island and the vietnamese truong son belt we investigate the sand dispersal pathways through comparisons of detrital zircon geochronology and heavy mineral analyses of modern vietnamese river sand holocene to recent near coastal sand from hainan island and vietnam and offshore neogene sand and we evaluate the methodologies eleven distinct zircon age clusters characterize the gulf of tonkin provenances red river sand contains the most complex age pattern with 35ma 88ma 155ma 250ma 440ma peaks and broader pre cambrian clusters the 88ma peak uniquely occurs in red river sand northern truong son belt sand contains 35ma 250ma 440ma peaks and pre cambrian clusters comparable to the red river the lack of cretaceous zircons and a high proportion of 250ma relative to 440ma zircons distinguishes the northern truong son belt from the red river the southern truong son belt is characterized by low proportions of 250ma relative to 440ma zircons and the absence of cretaceous and cenozoic zircons hainan island sand is identified by the presence of 100 ma zircons and the absence of cenozoic and 88 ma zircons the zircon age patterns suggest simple although dynamic sand dispersal pathways with mixed sand sources over much of the basins likely resulting from sediment reworking and down stream river merging induced by neogene sea level fluctuations sand in the western ygh shb was mainly sourced from the truong son belt the red river sourced the northern and central ygh shb and qdnb and hainan sand was primarily deposited along the island margin heavy mineral compositions in the gulf of tonkin primarily reflect sediment compositional maturity epidote amphibole pyroxene and garnet indicate immaturity whereas a high zircon content tends to indicate high maturity the use of heavy minerals as provenance indicator should proceed with the utmost caution

cenomanian palaeotemperatures derived from the oxygen isotopic composition of brachiopods and belemnites evaluation of cretaceous palaeotemperature proxies sixty low magnesium calcite samples from cenomanian articulate brachiopods belemnites and oysters from the epicontinental shelf sea of europe were geochemically and microscopically studied in order to evaluate their preservation and potential as carriers of palaeoenvironmental information the sampled localities in northern spain germany and southern england cover the transition between subtropical 25 30 n and temperate 33 38 n climates mean cenomanian salinity adjusted palaeotemperatures of diagenetically unaltered terebratulid and rhynchonellid brachiopods are 25 5 1 3 c in spain and 19 4 1 9 c in southern england the resulting low to mid latitude meridional temperature gradient of 0 7 c per degree latitude is similar to the gradient today and suggests modern heat transport values for cenomanian low latitudes oxygen isotopic composition of unaltered specimens of the upper cenomanian belemnite praeactinocamax plenus mean 0 2 is enriched in 18o by 1 in comparison to brachiopod shells correspondingly upper cenomanian palaeotemperatures derived from belemnite calcite 13 0 1 3 c underestimate modelled mid latitude sea surface temperatures by 6 c since p plenus occurs as boreal pulse fauna during a short interval in the late cenomanian its heavy oxygen isotopic composition can be attributed either to migration from a cooler and or deeper water mass or to unknown vital effects