fluid inclusions and hydrothermal alteration on the dixie valley fault nevada footwall rocks of the 1954 rupture segment of the dixie valley fault show extensive hydrothermal alteration related to fluids that were present on the fault during tectonic events hydrothermal alteration of granitic host rocks consists of temporally and spatially overlapping mineral assemblages an early biotite feldspar assemblage is followed by later fe chlorite and epidote both chlorite and epidote are replaced by hydrothermal sericite and cross cut by calcite hematite and quartz calcite veins biotite is partially replaced by prehnite the latest hydrothermal minerals are stilbite laumontite kaolinite alunite smectite illite and pervasive replacement of rock units with fine grained quartz chalcedony and opal secondary fluid inclusions trapped in healed microfractures in igneous quartz include type i inclusions that contain a moderate salinity aqueous liquid and vapor type ii inclusions that contain a moderate salinity aqueous liquid and co2 type iii inclusions that show eutectic melting temperatures below the nacl h2o eutectic and contain substantial cacl2 and type iv inclusions containing halite and other daughter minerals microthermometric measurements on these inclusions yield variable compositions and homogenization temperatures salinities of type i inclusions vary from 0 1 to 12 9 wt nacl with the mode in the interval 0 to 1 salinities of type ii co2 bearing inclusions range from 0 62 to 6 81 wt nacl relative to h2o and salinities of type iii inclusions with low eutectic melting temperatures are 12 9 to 25 3 nacl equivalent wt salinities of halite bearing inclusions are 30 1 to 39 2 wt nacl homogenization temperatures span the range 120 to 400 c the processes of isochemical cooling with upward displacement of the footwall mixing of cool low salinity water with hotter components and mixing of cool evaporite brine with hotter components could be responsible for variable fluid inclusion compositions homogenization temperatures and densities the p t path of the fault fluids is established by mineral equilibria and fluid inclusion characteristics the path includes a lithostatic fluid pressure at 305 c and 1570 bars along with cooling and escape of co2 from fluids the fluid p t path probably approaches hydrostatic pressure conditions at lower temperatures hydrothermal alteration product minerals fluid temperatures pressures and compositions in the footwall of the dixie valley fault constrain minimum fault age to 20 to 25 ma displacement to 6 km with about 3 km of pre 10 to 13 ma and 3 km of post 10 ma uplift fluid compositions and p t data suggest the following mechanism for rupture initiation and arrest ruptures may be initiated as a result of high fluid pressures then opening of dilatant fractures causes drastic decrease in fluid pressure separation of steam and co2 the drastic reduction in fluid bulk modulus that accompanies volatile phase separation permits propagation of the ruptures even though fluid pressure is reduced in areas where fluid pressure reduction is not accompanied by phase separation fractures are arrested by dilatant hardening

burial history of palaeozoic strata in belgium as revealed by conodont colour alteration data and thickness distributions thickness distributions of devono carboniferous formations and their relationship to conodont colour alteration indices cais from over 500 sample locations in belgium and northern france have been studied to reconstruct the thermal alteration and burial history of palaeozoic rocks the depositional centre during eifelian through visean times was located in the subsiding southern part of the dinant basin forming a thick sedimentary pile of probably more than 3 5 km in order to explain conodont cais chiefly resulting from upper carboniferous sedimentation two different depositional centres are considered giving rise to approximately 4 5 km of sediment in the central part of the dinant and namur basins as a consequence of the northward shifting variscan fold belt the upper carboniferous succession in the southern part of the dinant basin and in the rocroi area was reduced or absent conodont cais together with other thermal alteration data from the condroz massif indicate that this area was a structural high for most of the devonian the brabant massif was probably covered with approximately 1 5 2 0 km of upper carboniferous sediments in the south and less than 1 0 km in the central and northern parts in the central campine basin visean strata could have been buried by 3 5 4 5 km of upper carboniferous rocks

post rift tectonic history of the songliao basin ne china cooling events and post rift unconformities driven by orogenic pulses from plate boundaries

multiple impacts across the cretaceous tertiary boundary abstract the stratigraphy and age of altered impact glass microtektites microkrystites ejecta layers from the chicxulub crater are documented in late maastrichtian and early danian sediments in mexico guatemala belize and haiti in northeastern mexico two to four ejecta layers are present in zone cf1 which spans the last 300 ky of the maastrichtian the oldest ejecta layer is dated at 65 27 0 03 ma based on sediment accumulation rates and extrapolated magnetostratigraphy all younger ejecta layers from the maastrichtian and early danian parvularugoglobigerina eugubina zone pla l may represent repeated episodes of reworking of the oldest layer at times of sea level changes and tectonic activity the k t boundary impact event 65 0 ma is not well represented in this area due to widespread erosion an early danian pla l ir anomaly is present in five localities bochil actela coxquihui trinitaria and haiti and is tentatively identified as a third impact event at about 64 9 ma a multiimpact scenario is most consistent with the impact ejecta evidence the first impact is associated with major deccan volcanism and likely contributed to the rapid global warming of 3 4 c in intermediate waters between 65 4 and 65 2 ma decrease in primary productivity and onset of terminal decline in planktic foraminiferal populations the k t boundary impact marks a major drop in primary productivity and the extinction of all tropical and subtropical species the early danian impact may have contributed to the delayed recovery in productivity and evolutionary diversity

cyclostratigraphy and orbital tuning of the terrestrial upper santonian lower danian in songliao basin northeastern china abstract the songke 1 north sk 1n borehole recovered a continuous 1541 66 m late santonian early danian terrestrial succession in songliao basin sb northeastern china it provides a unique record for improving our understanding of continental paleoclimate and ecological system in cretaceous greenhouse world here we use thorium th logging data as a paleoenvironmental and paleoclimatic proxy to conduct a detailed cyclostratigraphic study on the sk 1n core power spectra evolutionary fast fourier transformation and wavelet analysis all reveal significant decameter to meter scale sedimentary cycles in the nenjiang k 2 n sifangtai k 2 s and mingshui k 2 m formations the ratios of cycle wavelengths in these stratigraphic units are 20 5 2 1 and are interpreted as milankovitch cycles of 405 kyr and 100 kyr eccentricity 38 4 kyr obliquity and 20 kyr precession cycles respectively an astronomical time scale ats is established by tuning filtered 405 kyr eccentricity cycles to a target curve of the astronomical solution la2010d based on the magnetostratigraphic time framework of the sk 1n borehole this ats provides precise numerical ages for stratigraphic boundaries biozones geological and geophysical events and serves as a basis for correlation of strata and events between marine and terrestrial systems the cretaceous paleogene k pg campanian maastrichtian santonian campanian boundaries are estimated at core depths of 318 m 752 8 m and 1751 1 m respectively a 3 8 myr long hiatus between the nenjiang k 2 n and sifangtai k 2 s formations occurs from 76 1 to 79 9 million years ago the ages and durations of magnetochrons c33r to c30n are precisely estimated and provide new constraints on the late cretaceous geomagnetic polarity time scale gpts and south atlantic sea floor spreading rates

coupled uranium mineralisation and bacterial sulphate reduction for the genesis of the baxingtu sandstone hosted u deposit sw songliao basin ne china the baxingtu deposit is a typical redox front tabular shaped uranium deposit hosted in sandstones of the late cretaceous yaojia formation deposited within a braided river environment during the post rift stage of the songliao basin in northeast china this study proposes the first metallogenic model for the baxingtu deposit and provides new data on genetic processes involved in the uranium mineralisation of sandstone type deposits that were characterised through petrographic observations whole rock geochemistry and geochemical and or mineralogical study of iron disulphide uranium minerals fe ti oxides epma la icp ms and organic matter rep the 34s value has been measured in situ by sims on the different generations of iron disulphide within regional primary reduced sandstones pre ore uranium enrichment umean 7 6 ppm in whole rock was identified on altered fe ti oxides along with minor concentrations on organic matter respectively 26 3 and 1 3 of the whole rock u content which together represent a significant source of uranium for the mineralisation additional pre ore uranium concentrations may also be associated with clay minerals petrographic observations and rep data indicate that organic matter occurring in the host sandstone is mainly inherited from land plants and corresponds to type iii or type iv kerogens ore stage iron disulphides largely occur as framboids and in replacement of organic matter or also as sub idiomorphic to idiomorphic cement and crystal trace element signatures detected within framboids are likely indicative of formation mainly from a single event framboids and iron disulphide in replacement of organic matter have a light sulphur isotope signature characterised by 34s values from 72 0 to 6 2 suggesting that sulphur originated from bacterial sulphate reduction which was mainly responsible for 1 the liberation of u from fe ti oxides and organic matter 2 the generation of ore stage iron disulphides 3 the bioreduction of uranium and 4 the production of a secondary h2s rich reducing barrier also involved in uranium reduction uranyl and sulphate ions were transported through the host sandstone by low temperature oxygenated groundwater and u iv was precipitated at the redox interface as nano to microcrystals of pitchblende and coffinite dominantly associated with bacterial substrate and as intergrowth with biogenic iron disulphide or directly associated with organic matter and residual ti fe oxides the uranium mineralisation does not replace ore stage iron disulphides therefore the combined mineralogical geochemical and isotopic characteristics of the baxingtu tabular uranium deposit characterise dominantly biogenic processes for the genesis of the uranium mineralisation

paleoatmospheric pco2 fluctuations across the cretaceous tertiary boundary recorded from paleosol carbonates in ne china abstract a dramatic change in atmospheric composition has been postulated because of global carbon cycle disruption during the cretaceous k tertiary t transition following the chicxulub impact and deccan trap eruptions here pedogenic carbonates were collected from drill core of a borehole sk 1 n straddling the late cretaceous and early paleocene strata in the songliao basin northeast china to reconstruct atmospheric co 2 concentrations using a paleosol paleobarometer our estimates for atmospheric pco 2 from paleosol carbonates range between 277 115 ppmv and 837 164 ppmv between 67 8 ma and 63 1 ma one large 66 65 5 ma and several small co 2 spikes 64 7 64 2 ma during the latest maastrichtian to earliest danian are reported here and incorporated with previously published pco 2 estimates also estimated from paleosol carbonates these co 2 spikes are attributed to one million year long emplacement of the large deccan flood basalts along with the extraterrestrial impact at the k t boundary

on the interaction between bathymetry and climate in the system dynamics and preferred levels of the great salt lake 1 the great salt lake is a terminal lake whose level is determined by the balance between inflows and outflows we examine the causes for multimodality in the distributions of lake level and hence volume and area that have previously been examined from a system dynamics perspective we focus on the role of bathymetry in the dynamics of this system and show that some of the modes that are observed and that represent preferred system states are attributable to features of the bathymetry described using the topographic area volume relationship being a terminal lake the only outflow is evaporation which depends directly on lake area which adjusts with stochastic fluctuations to balance inflows where the topographic side slopes are relatively flat and the lake goes through a large change in area for a given increase in level the outflux evaporation will go through a corresponding large change tending to stabilize the lake at that point conversely where topographic side slopes are relatively steep the stabilizing effect is diminished this effect was quantified using the derivative of the lake area lake volume function determined from u s geological survey topographic and bathymetric surveys we show how some of the observed modes that represent preferred lake volume states are attributable to peaks in this area volume derivative while a complete description of the observed distribution of lake volume requires combining the bathymetry represented by the area volume derivative with a multimodal lake area distribution that may be connected to multimodality in the aggregate hydrological forcing

paleoenvironmental reconstruction of the late santonian songliao paleo lake the late cretaceous is often characterized as having a variable greenhouse climate however the relatively few continental sites preserving geologic records from this time exist limiting information on terrestrial climate and environments worldwide the songliao basin slb of northeastern china is one of the largest cretaceous age continental rift basins thus this well preserved lacustrine deposit provides a unique record of terrestrial paleoenvironmental conditions during the cretaceous here we report organic geochemical data from late cretaceous age lacustrine deposits lower nenjiang formation from the eastern side of the slb outcrop samples were collected from the houjingou section and the following analyses were performed 1 total organic carbon toc content and isotopic composition 2 biomarker distribution including the identification and determination of relative amounts of both aliphatic and aromatic hydrocarbons and steranes and 3 compound specific stable carbon and hydrogen isotopic compositions of n alkanes the biomarker distribution and stable carbon isotopic values 13c of the toc indicate organic matter om from the uppermost section of the first member of the nenjiang formation upper k2n1 was mainly sourced from aquatic macrophytes and land plants in the lower part of the second member of the nenjiang formation lower k2n2 the biomarker distribution and 13c of both the toc and n alkanes indicate that om was sourced from a mixture of algae bacteria and higher plants as a result of marine transgression seawater incursions indicated by the presence of 24 n propyl cholestanes and 24 iso propyl cholestanes occurred episodically in lower k2n2 the negative hydrogen isotopic composition 2h of short chain n alkanes in lower k2n2 indicates an extremely humid environment and it is likely that an influx of freshwater caused large scale flooding of the songliao paleo lake high resolution biomarker and stable isotope records from the houjingou section demonstrate abrupt environmental changes in the songliao paleo lake following seawater incursions during the late cretaceous

the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary the cretaceous paleogene boundary similar to 65 5 million years ago marks one of the three largest mass extinctions in the past 500 million years the extinction event coincided with a large asteroid impact at chicxulub mexico and occurred within the time of deccan flood basalt volcanism in india here we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction notably a single ejecta rich deposit compositionally linked to the chicxulub impact is globally distributed at the cretaceous paleogene boundary the temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations for example darkness and cooling lead us to conclude that the chicxulub impact triggered the mass extinction

multistage dolomitization in rainbow buildups middle devonian keg river formation alberta canada abstract more than 80 partially to completely dolomitized buildups of middle devonian keg river formation occur in the rainbow sub basin of northwestern alberta in six buildups a b e f g and tehze four petrographic types of dolomites are identified gray fine crystalline dolomite floating dolomite rhombs patches matrix dolomite and saddle dolomite the petrographic and geochemical data indicate that these dolomites probably formed in three principle stages of dolomitization during progressive burial gray fine crystalline dolomite less than 1 of total dolomite by volume is interpreted as penecontemporaneously dolomitized lime muds by either normal marine waters or evaporitic brines during early exposure the following evidence suggests that this dolomite probably formed early 1 it usually occurs in fractures and breccias presumably related to the early exposure of the buildups 2 it is absent in rugs and molds that formed in the subsurface environment and 3 locally clasts of gray fine crystalline dolomite are embedded in marine limestones rhomb patch dolomite is the major type of dolomite in dolomitic limestones and is widespread throughout the limestone buildups matrix dolomite is fabric destructive and is most abundant in the dolostone buildups both these dolomites probably formed during shallow to intermediate burial because they 1 postdate stylolites 2 are widespread throughout the buildups and crosscut various facies and 3 have light oxygen isotope compositions and low sr but high fe and mn concentrations dolomitizing fluids for dolomite rhombs patches and matrix dolomites were possibly derived from 1 mechanical compaction 2 dehydration of the adjacent muskeg gypsum at relatively shallow burial depths and 3 intermediate depth basinal fluids conducted updip along porous and permeable conduits during d vonian and carly carboniferous times compaction fluids were probably responsible for the early dolomite rhombs and patches however the main phase of matrix dolomitization took place later probably during late mississippian to jurassic time when the east side of the basin was intermittently tilted and uplifted causing updip flow of intermediate depth basinal brines saddle dolomite occurs as late stage vug and fracture fillings it is most depleted in 18o but most enriched in mn and fe suggesting precipitation during deeper burial from warm basinal fluids these fluids were expelled during upper cretaceous sedimentary and tectonic loading of the western side of the basin and then moved up the east side of the basin along existing platform fault and fracture conduits the source of the mg is uncertain some or most of the mg may have resulted from chemical compaction of the earlier matrix dolomite

gold quartz veins in metamorphic terranes and their bearing on the role of fluids in faulting gold quartz vein fields in metamorphic terranes such as greenstone belts provide evidence for the involvement of large volumes of fluids during faulting and may be products of seismic processes near the base of the seismogenic regime in the val d or district of the abitibi greenstone belt canada quartz tourmaline carbonate veins form a vein field 30 15 km in the hanging wall of a crustal scale fault zone which was the main channelway for upward migration of the deeply generated fluids the veins occur in small high angle reverse faults and in adjacent horizontal extensional fractures extending up to 75 m in intact rocks they have formed incrementally during active reverse faulting in response to crustal shortening at depths corresponding to those at the base of the seismogenic zone in actively deforming crust detailed structural and fluid inclusion studies provide evidence for generally lithostatic but fluctuating fluid pressures p of the order of 200 mpa and for cyclic stress reversals during vein formation and provide good support for the fault valve model a comparison of vein characteristics with standard earthquake rupture parameters suggests that each slip increment along veins in reverse faults was accompanied by a small earthquake 4 m 3 or less the large vein field thus represents both the extent of fluid dispersion in the hanging wall of a crustal scale channelway and the distribution of small earthquakes integrated over the lifetime of the hydrothermal system it is proposed that such small earthquakes along veins in reverse faults are related to large earthquakes m 6 nucleating near the base of the seismogenic regime along the nearby crustal scale fault either as aftershocks or as a precursory smarm

mesozoic cenozoic tectonic evolution and dynamics of the songliao basin ne asia implications for the closure of the paleo asian ocean and mongol okhotsk ocean and subduction of the paleo pacific ocean abstract the songliao basin in northeast china in the eastern part of the central asia orogenic belt is the largest accretionary orogen belt in the world however to date previous studies have not extensively examined the dynamic mechanism of its formation and evolution especially the pre cretaceous in this study the mesozoic cenozoic tectonic style stratigraphic records sedimentary time magmatic activity and tectonic evolution in the songliao basin were systematically analysed and summarised we propose that songliao basin experienced multi stage basin superposition processes the foreland compression stage syn rift and post rift stage and structural inversion stage after palaeozoic deposition the basin experienced a strong orogeny with the formation of the triassic middle jurassic foreland basin during the syn rift period three tectonic movements occurred at the end of the shahezi formation late valangnian 135 ma the end of first member of the yingcheng formation late hauterivian 129 ma and the end of the yingcheng formation late barrenian 125 ma in the songliao basin which ended the evolutional history of the rift in the post rift period three tectonic events occurred at the end of the nenjiang formation middle campanian 79 ma the mingshui formation late maastrichtian 66 ma and the yi an formation late chattian 23 ma which determined the deformation characteristics of the middle and shallow strata of the basin such as folding and reverse faults the rudimentary shape formed at the end of the nenjiang formation was finalised at the end of the mingshui formation and formed at the end of the yi an formation the largest depth and width influence of the two events was at the end of the mingshui and yi an formations which played a decisive role in the generation migration and accumulation of oil and gas in the middle and shallow strata of songliao basin after a series of asthenospheric mantle upwelling crustal uplift and extension and volcanic activity songliao basin was eventually formed the formation and structural evolution of the songliao basin were mainly influenced by the paleo asian ocean the mongol okhotsk ocean and the pacific ocean the closure of the paleo asian ocean in the late permian early triassic was influenced by the siberian plate which began to contact and collide with the xingan mongolian block from west to east causing the mongol okhotsk ocean to close in a scissor like structure from west to east in the early middle jurassic the subduction and movement of pacific rim tectonic systems such as the farallon izanagi pacific and philippine plates led to the formation of songliao basin which has experienced a foreland period via compressive pressure since the triassic syn rift period and post rift period via extensional stress and then a structural inversion period

late metamorphic veins record deep ingression of meteoric water a la icpms fluid inclusion study from the fold and thrust belt of the rhenish massif germany abstract the fluid evolution of late metamorphic quartz vein systems in the fold and thrust belt of the rhenish massif has been studied by microthermometry and la icpms microanalysis the quartz veins are hosted by very low grade organic matter rich metasiltstones and metapelites of the hunsruck nappe complex the veins record two major stages of textural evolution a massive vein filling assemblage with elongate blocky quartz chlorite albite and apatite and a later open space filling assemblage with euhedral crystals of quartz ankerite dolomite and minor calcite and sulfides the euhedral quartz crystals host well preserved fluid inclusion assemblages which made it possible to reconstruct the chemical evolution of the fluid system with time the fluid inclusions are all aqueous two phase with low salinity and three successive fluid generations record a systematic decrease in salinity from 4 7 5 3 to 3 1 3 9 and then to 1 4 1 7 wt eqv nacl the salinity decrease is paralleled by a decrease in homogenization temperatures from 210 225 c to 148 164 c and 124 139 c using la icpms microanalysis of individual fluid inclusions reproducible elemental concentrations of li na k rb cs mg ca ba sr b al as sb s cl and br could be determined the concentrations of the alkali metals and of boron arsenic and antimony are correlated with the fluid salinity element concentrations are highest in the early fluid generation and decrease systematically in the latter two generations the systematic changes in fluid composition salinity homogenization temperature and elemental concentrations are best explained by fluid mixing between a hot metamorphic fluid of moderate salinity that carried elevated concentrations of b as and sb and a cooler dilute fluid that was of meteoric origin the fluid evolution therefore signals deep ingression of meteoric water during late metamorphic exhumation and uplift the molar cl br ratios of the fluid inclusions lie on a linear array that extends from close to seawater to values that are substantially below seawater because evaporitic sources are conspicuously absent in the shallow water marine sequence of the rhenish massif the elevated br concentrations and cl br ratios below seawater are best explained by fluid rock interaction and liberation of br from the organic matter in the metasediments

litho stratigraphic effect on variscan fluid flow within the prague synform barrandian evidence based on c o sr isotopes and fluid inclusions the palaeozoic sedimentary sequence of the prague synform ordovician devonian in the centre of the bohemian massif underwent variscan deformation and thermal overprint events variscan veins widespread throughout the sedimentary strata have precipitated from syntectonic aqueous and hydrocarbon rich fluids homogenization temperatures of aqueous inclusions increased from 70 up to 226 degc in the cambrian rocks underlying the prague synform seawater modified due to intensive water rock interaction was the main fluid component fluid flow was limited and restricted to the lithostratigraphic compartments forming a rock buffered system stable isotopic modelling c o and final interpretations of the confined hydrostratigraphic fluid migration was supported by the 87sr 86sr ratio in veins and wall rocks siliciclastic cambrian and ordovician rocks and the associated intersecting veins yielded similar isotopic signatures and consequently the fluid migration is restricted to layer and formation scales gradually downwards increasing fluid temperature and compositional changes reflect burial at oil window conditions an open fluid system could be expected in proximity of major faults of the prague syncline and at the top of the sedimentary sequence

evolution of metamorphic fluids at the variscan fold and thrust belt in eastern belgium abstract quartz veins in the southern greenschist facies metamorphic border of the stavelot venn massif belgium have been examined a detailed petrographical study of these quartz veins indicates the presence of eleven quartz stages a microthermometric analysis shows the expulsion of three main fluid types during the palaeozoic in the first quartz stage i of caledonian age mixed aqueous gaseous h 2 o co 2 nacl fluid inclusions are present the post caledonian and pre variscan second stage ii is characterised by gaseous co 2 n 2 inclusions occurring along inter crystal grain boundaries and by aqueous h 2 o nacl intra crystal inclusions the quartz stages iii vi which formed during the variscan period contain primary mixed aqueous gaseous h 2 o co 2 nacl inclusions all with an equal bulk chemical composition post variscan quartz stages vii xi could not be investigated microthermometrically the combination of microthermometry chlorite geothermometry and geothermal gradients reveals minimum trapping conditions of 200 mpa and 200 c for stage i quartz and 175 275 mpa and 385 435 c for quartz stages iii vi the trapping conditions of stage ii quartz could not be determined due to the strong recrystallisation of the quartz veins at the lower metamorphic variscan thrust front distinct temperature anomalies are associated with thrust faults as indicated by conodont colour alteration index cai vitrinite reflectance data chlorite geothermometry and fluid inclusion microthermometry the expulsion of metamorphic fluids generated at the southern part of the stavelot venn massif could have caused the distinct temperature anomalies along variscan thrust faults alternatively some of these anomalies could have been induced by deeply circulating meteoric fluids

fluid evolution at the variscan front in the vicinity of the aachen thrust quartz carbonate chlorite veins were studied in borehole samples of the rwth 1 well in aachen veins formed in devonian rocks in the footwall of the aachen thrust during variscan deformation and associated fluid flow primary fluid inclusions indicate subsolvus unmixing of a homogenous h2o co2 ch4 n2 na k cl fluid into a h2o na k cl solution and a vapour rich co2 h2o ch4 n2 fluid the aqueous end member composition resembles that of metamorphic fluids of the variscan front zone with salinities ranging from 4 to 7 nacl equiv and maximum homogenisation temperatures of close to 400 c pressure estimates indicate a burial depth between 4 500 and 8 000 m at geothermal gradients between 50 and 75 c 26 mpa but pressure decrease to sublithostatic conditions is also indicated probably as a consequence of fracture opening during episodic seismic activity a second fluid system mainly preserved in pseudo secondary and secondary fluid inclusions is characterised by fluid temperatures between 200 and 250 c and salinities of 5 nacl equiv bulk stable isotope analyses of fluids released from vein quartz calcite and dolomite by decrepitation yielded dh2o values from 89 to 113 13cch4 from 26 9 to 28 9 vpdb and 13cco2 from 12 8 to 23 3 vpdb the low d and 13c range of the fluids is considered to be due to interaction with cracked hydrocarbons the second fluid influx caused partial isotope exchange and disequilibrium it is envisaged that an initial short lived flux of hot metamorphic fluids expelled from the epizonal metamorphic domains of the stavelot venn massif the metamorphic fluid was focused along major thrust faults of the variscan front zone such as the aachen thrust a second fluid influx was introduced from formation waters in the footwall of the aachen thrust as a consequence of progressive deformation mixing of the cooler and lower salinity formation water with the hot metamorphic fluid during episodic fluid trapping resulted in an evolving range of physicochemical fluid inclusion characteristics

biostratigraphy magnetostratigraphy and geochronology of lower miocene aoerban strata in central inner mongolia abstract the aoerban region of central inner mongolia china is an important early miocene fossil site that contains a diverse mammalian record unrivaled by other asian sites of similar age in this paper we present lithostratigraphic biostratigraphic and magnetostratigraphic data from aoerban formation to better understand faunal changes between the xiejian and shanwangian chinese land mammal ages with new biochronological constraints magnetochrons in the aoerban formation can be correlated to c6an 2n to c5cr with an age range of 20 71 16 72 ma of the astronomically tuned neogene timescale atnts2012 the strata of the aoerban region contain a number of important mammalian first appearance data including several morphotypes of deer cervidae horses anchitherium pika alloptox cricetid rodents megacricetodon and possibly the local earliest record of gomphotheres i e the proboscidea event although the ranges for most of these taxa are still poorly known some of them alone or in combination are useful in defining the base the shanwangian land mammal age within this finely calibrated chronologic framework the faunas of the aoerban region are important for better understanding mammalian evolution biogeography and paleoenvironment

detrital zircon u pb geochronology and stratigraphy of the cretaceous sanjiang basin in ne china provenance record of an abrupt tectonic switch in the mode and nature of the ne asian continental margin evolution abstract the age spectra obtained from 505 spots of detrital zircon u pb ages of five representative sandstone samples from the sanjiang basin in ne china point to a significant change in its provenance during the coniacian santonian the predominant detrital source for the sanjiang basin during the early cretaceous was the zhangguangcai range magmatic belt and jiamusi block along its western and southern periphery whereas it changed in the late cretaceous to its eastern periphery the timing of these inferred changes in the detrital source regions and drainage patterns nearly coincide with the age of a regional unconformity in and across the basin the time interval of non deposition and unconformity development was coeval with a transitional period between an extensional tectonic regime in the early cretaceous and a contractional deformation episode in the late cretaceous the sanjiang basin evolved during this time window from a backarc to a foreland basin the migration of the coastal orogenic belt and the fold and thrust belt development farther inland during the late cretaceous marked the onset of regional scale shortening and surface uplift in the upper plate of a flat or very shallow dipping subduction zone the stratigraphic record the detrital source and geochronology of the basinal strata and the internal structure of the sanjiang basin present therefore an important record of a tectonic switch in the nature of continental margin evolution of northeast asia during the late mesozoic

the application of a multichannel laser raman microprobe microdil 28 to the analysis of fluid inclusions abstract the application to the analysis of fluid inclusions of laser excited raman microspectrometry with a multichannel detection system has two important features connected with the very short time needed to acquire one single spectrum 1 5 s the accumulation of a great number of the same spectral range results in an averaged spectrum with a very high signal to noise ratio with corresponding low detection limits and good counting statistics on the other hand the rapid acquisition of spectra enables the analysis of many individual inclusions in a relatively short time

the boudinage question in the high ardenne slate belt belgium a combined structural and fluid inclusion approach abstract the terms boudin and boudinage 1 were first introduced as descriptive terms for particular geometric features associated with quartz veins in competent metaquartzitic layers in the high ardenne slate belt belgium the occurrence of the boudins has subsequently been used to draw kinematic conclusions on a pre variscan extensional event in the rhenohercynian belt in this paper a combined structural and fluid inclusion approach allows proposing a new and more representative kinematic model for the development of the veins and associated structures moreover the kinematic significance of interboudin veins is emphasized in this regard microthermometry of primary co 2 n 2 fluid inclusions in the quartz of the interboudin veins suggests that the origin of vein development is hydraulic fracturing in an already compressional setting this suggestion implies the presence of fluid and near lithostatic fluid pressures to permit fracturing at great depths where the rocks otherwise would be either stable or in the realm of ductile behaviour the vein filling fluid had a local origin and was most likely related to the formation of bedding parallel dissolution seams within the host rock veining is followed by layer parallel shortening resulting in the development of double sided mullions at both interfaces of metaquartzitic layers pinned by pre existing veins subsequently these polyphase structures behave passively in the variscan deformation

conditions for hydrofracture and the fluid permeability of accretionary wedges abstract the dewatering of fine grained sediment piles in accretionary wedges is controlled by zones of active deformation episodic hydrofracture in these zones enhances permeability enabling fluid flow to be faster than the speed of underthrusting here i investigate the mechanics of simultaneous shear failure and hydrofracture in muddy rocks as a function of the faulting mode the physical properties of model rock types are chosen to represent uncemented mud or cherty marly mudstones that have undergone significant diagenesis during thrust faulting hydrofracture always requires pore fluid pressures in excess of the lithostatic load whereas shallow level wrenching or normal faulting permits hydrofracture at hydrostatic pressures significantly lower than lithostatic load all three faulting modes are expected to occur in an accretionary wedge attempting to dynamically maintain its critical taper the model computations indicate that in the upper 80 120 m of a section of soft mudstone hydrofracture inevitably accompanies wrench or normal faulting hard mudstones inevitably hydrofracture to depths of up to 1400 m during normal faulting these differences in mechanical behaviour have profound consequences for fluid venting capabilities of accretionary wedges they influence hydrocarbon trapping and play a role in the localisation of mud diapirs and mud volcanism

chronology of the terrestrial upper cretaceous in the songliao basin northeast asia the cretaceous was a period of great environmental biological and geodynamical change but a paucity of an accurate time frame for continental strata has prevented our understanding of the terrestrial processes and the integration of marine and terrestrial records here we present an integrated chronology for the terrestrial upper cretaceous in east asia based on new high resolution magnetostratigraphic results and previously published sims u pb zircon analyses of the cretaceous continental scientific drilling borehole sequence from the songliao basin in northeast china hereafter termed ccsd sk i which consists of a sedimentary sequence from the upper quantou formation k2q to the mingshui formation k2m correlation to the geomagnetic polarity timescale was achieved by combining magnetostratigraphic and sims u pb zircon geochronologic data and lithostratigraphy our correlation suggests that the ccsd sk i sedimentary sequence spans from the upper chron c34n to chron c29r the age of the sedimentary sequence from the upper quantou formation k2q to the mingshui formation k2m in the songliao basin can thus be constrained to an interval from the turonian to the maastrichtian ages in addition our correlation puts the cretaceous paleogene boundary in the upper part of member 2 of the mingshui formation k2m2 the constructed comprehensive chronology allows the precise correlation of the terrestrial upper cretaceous of the songliao basin to marine strata as well as other continental sequences

empirical calibration of the oxygen isotope fractionation between quartz and fe mg chlorite abstract an empirical calibration has been made of the oxygen isotope fractionation between chlorite and quartz using samples from localities in metamorphic terrains where the formation temperature has been constrained by independent methods e g fluid inclusion homogenization temperatures mineral assemblages and petrology of the host rocks to the veins thermodynamic modeling and raman spectrometry textural equilibrium of chlorite and quartz was a pre requisite and the chemical composition of chlorite was determined the chlorite analyzed had a range in fe mg varying between 0 35 and 0 7 except for pure mg chlorite fe mg substitution within the range measured does not change the oxygen isotope fractionation between quartz and chlorite measurably the results support a linear correlation for chlorite quartz fractionation over the temperature range given by this study 240 550 c 1000 ln 0 01323 0 002 t c 10 97 0 92 the presently established geothermometer can be applied to quartz chlorite fractionations in low grade metamorphic rocks and may be extrapolated to diagenetic systems

evolution of palaeofluids at the variscan thrust front in eastern belgium the geochemical evolution of the fluids migra ting at the variscan thrust front in eastern belgium has been investigated by a petrographic mineralogical and geoche mical study of ankerite quartz and ferroan calcite veins hosted by lower devonian rocks three vein generations have been recognized the first generation consists of quartz chlorite and ankerite filling pre to early variscan extensional fractures the second generation is present as shear veins of variscan age and contains quartz chlorite and ferroan calcite the third generation consists of ankerite filling post variscan fractures the oxygen and carbon isotopic composition of the two ankerite phases and of the ferroan calcites are respectively between 16 4 and 11 4 pdb between 17 8 and 1 7 pdb this range is greater than that of calcite nodules in the lower devonian siliciclastic sediments 18o 15 6 to 11 1 pdb and 13c 13 4 to 10 2 pdb this suggests precipitation of the carbonate veins from a fluid which was at most only partly isotopically buffered by the calcite nodules in the host rock the calculated oxygen isotopic composition of the ambient fluid from which the calcite veins formed is between 7 8 and 10 0 smow two main fluid types have been recognized in fluid inclusions in the quartz and carbonates the first fluid type is present as secondary fluid inclusions in the first and second vein generations the fluid has a salinity of 0 5 7 2 eq wt nacl and a high but variable homogenization temperature th 124 188 c two origins can be proposed for this fluid it could have been expelled from the lower devonian or could have been derived from the metamorphic zone to the south of the area studied taking into account the microthermometric and stable isotope data and the regional geological setting the fluid most likely originated from metamorphic rocks and interacted with the lower devonian along its migration path this is in agreement with numerical simulations of the palaeofluid and especially the palaeotempera ture field which is based on chlorite geothermometry and vitrinite reflectance data the second fluid type occurs as secondary inclusions in the shear veins and as fluid inclusions of unknown origin in post variscan ankerite veins therefore it has a post variscan age the inclusions are characterized by a high salinity 18 6 22 9 eq wt cacl2 the composition of the fluid is similar to that which caused the development of mississippi valley type pb zn deposits in belgium

fluid evolution in a slate belt gold deposit a fluid inclusion study of the hill end goldfield nsw australia auriferous quartz veins in the hill end goldfield nsw australia comprise bedding parallel vein sets and minor extension and fault controlled veins which are hosted by a multiply deformed late silurian slate metagreywacke turbidite sequence fluid inclusions in quartz either from bedding parallel veins or from narrow steeply n dipping veins leader veins indicate a similar range in homogenisation temperatures th from 350 c to 110 c within this range th data demonstrate five groupings in the temperature intervals 350 280 c 280 250 c 250 190 c 190 150 c and 150 110 c corresponding to a variety of primary and secondary inclusions developed during five periods of vein growth under a generally declining temperature regime inclusion fluids are characterised by a low salinity of around 0 1 to 3 6 wt nacl equivalent laser raman microprobe inclusion analysis indicates that gas phase compositions relate to the paragenetic stage of the host quartz h2o g and n2 dominate in the primary inclusions from barren stage i quartz ch4 and ch4 h2o g are important in inclusions related to the early gold forming events equivalent to stages ii and iii quartz but inclusions developed during the last episode of gold deposition are characterised by h2o g co2 rich and liquid co2 bearing fluids precipitation of gold was aided by sulphidation reactions or phase separation in response to periods of vein opening late in the paragenesis gold deposition may have been promoted by oxidation of the ore fluid

sedimentary history of the coastal plain of the south yellow sea since 5 1 ma constrained by high resolution magnetostratigraphy of onshore borehole core gzk01 abstract the thick sedimentary sequences of the east asian continental shelves are archives of information on tectonics sea level fluctuations flood plain evolution and changes in the east asian monsoon climate however long sedimentary sequences with a reliable chronological framework from this setting are scarce here we present an integration of lithostratigraphic rock magnetic and magnetostratigraphic results for the sedimentary sequence of a 285 0 m core gzk01 recovered from the northern jiangsu coastal plain of the onshore south yellow sea eastern china alluvial fluvial lacustrine and marine deposits were identified according to lithofacies analysis and detrital magnetite and hematite are the main magnetic carriers the magnetostratigraphic results show that core gzk01 records the brunhes matuyama gauss and gilbert chrons and has an extrapolated basal age of 5 1 ma this record is the oldest sedimentary sequence yet reported from the continental shelf of the south yellow sea integrating the geochronological framework with changes in lithofacies a conceptual model of the environmental evolution of the northern jiangsu coastal plain is proposed for a long interval during the pliocene the drilling area was a lacustrine environment from the late pliocene to the early pleistocene the disappearance of the paleolake and a transition to a fluvial and marine environment suggests the peneplanation of the northern jiangsu coastal plain cumulative land sea interactions since 0 8 ma subsequently shaped the modern geomorphology the observed process of sedimentary evolution was possibly controlled by regional tectonics and long term climate changes

mineral magnetism to probe into the nature of palaeomagnetic signals of subtropical red soil sequences in southern china summary magnetic polarity stratigraphy has proved to be useful in dating of both marine and terrestrial sedimentary sequences over the world however the reliability of magnetostratigraphic results of red soil sequences in subtropical southern china has been found to be variable in different regions to probe into the capabilities of recording magnetic polarity stratigraphy in the red soils three red soil sequences have been selected for detailed mineral magnetic petrographic and or palaeomagnetic analyses these include the xuancheng and qiliting sequences which are located in the lower reaches of the yangtze river and the damei sequence in the bose basin near the tropic of cancer palaeomagnetic results indicate that the xuancheng sequence has recorded the brunhes chron and the late matuyama chron including a short interval probably representing the santa rosa geomagnetic event the xuancheng and qiliting sequences have faithfully recorded the palaeogeomagnetic field behaviour while the damei sequence has failed detailed mineral magnetic and petrographic measurements suggest that four magnetic minerals magnetite maghemite haematite and goethite are contained in the three studied sequences but the characteristic remanent magnetization chrm carriers are different for the xuancheng and qiliting samples the chrm carriers are magnetite and haematite which are all of detrital origin however the chrms of damei samples are carried by pedogenic haematite with an unblocking temperature tb of about 630 640 c which has overprinted the primary remanence of the damei red soil deposits this pedogenic haematite is mainly produced by chemical weathering which is commonly intensified by the climate of high temperature and rainfall it further suggests that climatic conditions have a great effect on the nature of palaeomagnetic signals of the red soil sequences in addition the red pigment components in the red soils may be used to indicate the degree of remagnetization

quantifying closed basin lake temperature and hydrology by inversion of oxygen isotope and trace element paleoclimate records lake systems are important paleoclimate archives that preserve ecosystem and hydrologic responses to critical periods in earth history such as carbon cycle perturbations and glacial interglacial cycles geochemical measurements of biogenic carbonate for example 18o 13c 87sr 86sr li u sr and mg are indicators of hydrologic variability in lake systems throughout the geologic record in this study we present a new closed basin lake modeling approach hybim the hydrologic balance inverse model that employs a system of total differential equations and uses the measured 18o sr ca and mg ca of biogenic carbonate to determine changes in temperature runoff and lake evaporation using equally spaced time steps these equations are simultaneously solved to constrain the hydrologic parameters of the lake as recorded in biogenic carbonate we use a monte carlo approach to account for uncertainty in the input parameters such as 18o temperature relationships partition coefficient uncertainty and watershed solute chemistry for illustrative purposes we apply the model to two ostracod valve datasets covering different timescales 1 the cretaceous songliao basin northeast china and 2 holocene lake miragoane haiti modern water measurements of water isotopes and cation concentrations from each location are required as model inputs we compare our modeling results with author interpretations and geologic observations the modeling approach presented in this study can be applied to other closed basin lake records can be modified for other calcifying species for example gastropods or mollusks or with calibration to inorganic lacustrine carbonate in addition this approach holds promise for extension with additional proxy measurements that is d u ca or li ca and changing source area on tectonic timescales using proxies that reflect changing source lithology that is sr and pb isotopes future incorporation of age model uncertainty in the monte carlo approach will also provide utility by quantifying temporal uncertainty on the hydrologic response recorded by lake sediments

nonlinear dynamics of the great salt lake dimension estimation we study the possibility that variations in the volume of the great salt lake gsl a large closed basin lake may be described as a low dimensional nonlinear dynamical system there is growing evidence for structure in the recurrence patterns of climatic fluctuations that drive western united states hydrology moreover the time behavior of such lakes is generally more regular than that of the climatic forcing this suggests the possibility that an analysis of the 144 year biweekly time series of the gsl volume may shed some light on the underlying dynamics of lake variations three methods correlation dimension nearest neighbor dimension and false neighbor dimension of estimating attractor dimension are applied and compared the analysis suggests that the gsl dynamics may be described by a dimension of about four implications of such analyses relative to low frequency variations and colored noise and limitations of such analyses are discussed

fluid evolution during burial and variscan deformation in the lower devonian rocks of the high ardenne slate belt belgium sources and causes of high salinity and c o h n fluids fluid inclusions in quartz veins of the high ardenne slate belt have preserved remnants of prograde and retrograde metamorphic fluids these fluids were examined by petrography microthermometry and raman analysis to define the chemical and spatial evolution of the fluids that circulated through the metamorphic area of the high ardenne slate belt the earliest fluid type was a mixed aqueous gaseous fluid h2o nacl co2 ch4 n2 occurring in growth zones and as isolated fluid inclusions in both the epizonal and anchizonal part of the metamorphic area in the central part of the metamorphic area epizone in addition to this mixed aqueous gaseous fluid primary and isolated fluid inclusions are also filled with a purely gaseous fluid co2 n2 ch4 during the variscan orogeny the chemical composition of gaseous fluids circulating through the lower devonian rocks in the epizonal part of the slate belt evolved from an earlier co2 ch4 n2 composition to a later composition enriched in n2 finally a late variscan aqueous fluid system with a h2o nacl composition migrated through the lower devonian rocks this latest type of fluid can be observed in and outside the epizonal metamorphic part of the high ardenne slate belt the chemical composition of the fluids throughout the metamorphic area shows a direct correlation with the metamorphic grade of the host rock in general the proportion of non polar species i e co2 ch4 n2 with respect to water and the proportion of non polar species other than co2 increase with increasing metamorphic grade within the slate belt in addition to this spatial evolution of the fluids the temporal evolution of the gaseous fluids is indicative for a gradual maturation due to metamorphism in the central part of the basin in addition to the maturity of the metamorphic fluids the salinity of the aqueous fluids also shows a link with the metamorphic grade of the host rock for the earliest and latest fluid inclusions in the anchizonal part of the high ardenne slate belt the salinity varies respectively between 0 and 3 5 eq wt nacl and between 0 and 2 7 eq wt nacl while in the epizonal part the salinity varies between 0 6 and 17 eq wt nacl and between 3 and 10 6 eq wt for the earliest and latest aqueous fluid inclusions respectively although high salinity fluids are often attributed to the original sedimentary setting the increasing salinity of the fluids that circulated through the lower devonian rocks in the high ardenne slate belt can be directly attributed to regional metamorphism more specifically the salinity of the primary fluid inclusions is related to hydrolysis reactions of cl bearing minerals during prograde metamorphism while the salinity of the secondary fluid inclusions is rather related to hydration reactions during retrograde metamorphism the temporal and spatial distribution of the fluids in the high ardenne slate belt are indicative for a closed fluid flow system present in the lower devonian rocks during burial and variscan deformation where fluids were in thermal and chemical equilibrium with the host rock such a closed fluid flow system is confirmed by stable isotope study of the veins and their adjacent host rock for which uniform 180 values of both the veins and their host rock demonstrate a rock buffered fluid flow system

a rapid hydroclimate change and its influence on the songliao basin during the santonian campanian transition as recorded by compound specific isotopes abstract reconstruction of the paleoclimate and paleoenvironment of the songliao basin has important theoretical and practical significance to reveal the regional continental climate characteristics and continental organic matter accumulation under the cretaceous greenhouse climate conditions here we report the composition of biomarkers and the stable carbon and hydrogen isotope compositions of n alkanes from nenjiang formation sediments in the songliao basin which provide information on the source of organisms paleoenvironmental conditions and paleoclimate changes during the late cretaceous our hydrogen isotope records of n alkanes displayed a significantly negative shift indicating that a dramatically wet climate occurred during the santonian campanian transition a wet climate such as that during a prolonged rainfall event had a significant impact on the lake and resulted in the lake level increasing and the salinity decreasing in the surface water during this period however the freshwater input increased the salinity difference between the upper and lower water layers which caused stable water stratification to occur in the lake in addition the high total organic carbon toc content indicates high primary productivity because of increased precipitation carrying more terrigenous nutrients into the lake which resulted in eutrophication during this period notably the increased aryl isoprenoid ratios and the occurrence of isorenieratane indicates that photic zone euxinia pze was enhanced during the santonian campanian transition which was possibly due to the dramatic change in the hydroclimate we speculate that the large freshwater input promoted the formation of pze in the lake then pze restricted the habitat available for aerobic organisms which had fatal effects on the lake ecosystem

stress state evolution of the brittle upper crust during compressional tectonic inversion as defined by successive quartz vein types high ardenne slate belt germany abstract in the frontal part of the rhenohercynian fold and thrust belt high ardenne slate belt germany two successive types of quartz veins oriented normal and parallel to bedding respectively are interpreted to reflect the early variscan compressional tectonic inversion of the ardenne eifel sedimentary basin fracturing and sealing occurred in lower devonian siliciclastic multilayers under very low grade metamorphic conditions in a brittle upper crust a geometrical and microthermometric analysis of these veins has helped to constrain the kinematic and pressure temperature conditions of both vein types allowing the reconstruction of the stress state evolution in a basin during tectonic inversion it is demonstrated that bedding normal extension veins which developed under low differential stresses and repeatedly opened and sealed crack seal under near lithostatic fluid pressures reflect the latest stage of an extensional stress regime bedding parallel veins which developed at differential stresses that were still low enough to allow the formation of extension veins cross cut the bedding normal veins and preceded the regional fold and cleavage development these veins show a pronounced bedding parallel fabric reflecting bedding normal uplift and bedding parallel shearing under lithostatic to supra lithostatic fluid pressures during the early stages of a compressional stress regime this kinematic history corroborates that fluid overpressures are easy to maintain during compressional tectonic inversion at the onset of orogeny

magnetostratigraphy of the dali basin in yunnan and implications for late neogene rotation of the southeast margin of the tibetan plateau 1 the rotation pattern and fault activity in the southeast margin of the tibetan plateau semtp provide meaningful constraints on the geodynamic evolution of the plateau however the lack of cenozoic paleomagnetic studies and accurate age constraints on neogene sediments prevents a better understanding of the late cenozoic tectonic activity in this area to clarify the tectonic rotation pattern and deformation history of the semtp we report new magnetostratigraphic data from a late neogene sedimentary sequence in the dali basin northwestern yunnan province china rock magnetic analyses indicate that both magnetite and hematite are the main carriers of the characteristic remanent magnetizations chrms magnetostratigraphic results show that the sedimentary profile spans from chron c4n 1r to chron c2n the age of the sedimentary sequence in the dali basin can thus be paleomagnetically constrained to an interval from late miocene to early pleistocene the basal age of the sediments is 7 6 ma which indicates that the unroofing of diancang shan and activation of the dali fault system were initiated at this time the appearance of conglomerates and syntectonic sediments suggests the reactivation of the dali fault system at 2 5 ma moreover the overall mean chrm direction suggests that the dali basin experienced significant 4 4 2 5 but minor post late miocene rotation this indicates that most of the clockwise rotation demonstrated by previous paleomagnetic studies in the semtp occurred prior to late miocene and may be concentrated between eocene and miocene which is contemporaneous with the sinistral slip of the ailao shan red river fault

cretaceous paleogeography and paleoclimate and the setting of ski borehole sites in songliao basin northeast china article i nfo as a paradigm of greenhouse climate in earth s history the cretaceous provides significant rock records of global climate changes under conditions of greenhouse climate the songliao basin among the longest dura tion 85 90 m y of continental sedimentary basins provides an excellent opportunity to recover a nearly complete cretaceous terrestrial sedimentary record extensive lake deposits ten kilometers deep and cover ing an area of 260 000 km 2 of the songliao basin provide unique detailed records that can be tied to the glob al stratigraphic time scale thereby improving our understanding of the continental paleoclimate and ecological system the two coreholes at skis and skin sites were drilled into this basin and completed with a total length of 2485 89 m of recovered core that spanned the complete middle to upper cretaceous strata in the basin the unique geological setting of long term continuous subsidence within the largest cretaceous landmass in the world makes the cretaceous songliao basin of northeastern china an ideal place to study cretaceous climate change on the continent this paper reviews the literature on the paleogeography and paleoclimate of the northern east asia and the songliao basin during the cretaceous based on the climatolog ically sensitive deposits oxygen isotope studies and paleontology the climate during the cretaceous in the songliao basin was temperate and humid with relatively abundant rainfall during the period significant changes four cooling three warming and three semiarid events are generally consistent with the oxygen isotope data from east asia and the four cooling events in berriasian valanginian aptian albian early santonian and campanian maastrichtian may be related to potential glaciations in cretaceous

syn to late orogenic quartz veins marking a retrograde deformation path in a slate belt examples from the high ardenne slate belt belgium abstract an integrated structural petrographic and microthermometric methodology has been applied on syn to late orogenic quartz veins from the high ardenne slate belt belgium to define their relative timing the quartz precipitates which do not show any mutual cross cutting relationships represent the meso scale brittle accommodation during fold initiation amplification and locking crystal plastic deformation structures and p t trapping conditions indicate that the different processes accommodating folding occurred in a progressive manner along a retrograde deformation path associated with the gradual exhumation of the slate belt from ca 7 5 to 6 km depth successive veining occurred from peak metamorphic conditions ca 300 c and 190 mpa measured in extrados veins to subsequent lower p t conditions in the periphery of a lenticular vein ca 275 c and 180 mpa late orogenic saddle reef filling ca 245 c and 160 mpa and the core of a lenticular vein ca 220 c and 150 mpa open cavity growth and fluid assisted brecciation indicate that veining occurred under overpressured fluid conditions it is therefore fair to assume that the high ardenne slate belt acted at least episodically as a mid crustal overpressured fluid reservoir not only in the earliest and latest stages but also during the main stage of orogeny

a fluid inclusion study of fluid pressure and salinity variations in the footwall of the rector branch thrust north carolina u s a abstract last melting and homogenization temperatures of fluid inclusions from plastically deformed bedding parallel quartz veins in the footwall of the rector branch thrust north carolina were studied as a function of distance from the thrust fluid inclusions and microstructures in mylonitic rocks within the thrust zone were also examined fluid inclusions in quartz veins which display evidence for intracrystalline plasticity e g subgrain polygonization occur along subgrain boundaries and have higher homogenization temperatures tn and a wider range 120 320 c compared to less deformed samples maximum th values which approach the temperature of deformation 300 20 c apparently reflect leakage of inclusions along subgrain boundaries minimum th values 120 160 c on the other hand record near lithostatic conditions 2 6 kb at 300 c maximum last melting temperatures tm increase from 20 to 4 c with decreasing distance to the thrust corresponding to a decrease in salinity of the fluid from 23 to 3 wt nacl equivalent the decrease in salinity towards the fault is interpreted as due to infiltration of the fault at depth to approximately 10 km by surface derived waters during periods of fault zone dilatancy inclusions along healed microcracks in quartz from the fault zone display higher salinity 17 26 wt nacl equiv and are interpreted to reflect enhanced fluid rock interaction in the fault zone due to hydration reactions the fluid pressure and salinity variations are consistent with a combined dilatancy hydraulic fracturing model for the rector branch thrust previously documented bulk rock volume losses for this fault zone are inferred to have been produced by the fluxing of the fault zone with undersaturated surface derived fluids

cyclostratigraphy and astrochronology case studies from china abstract a high precision geologic time scale is the essential key for understanding the earth s evolutionary history and geologic processes astronomical tuning of orbitally forced stratigraphic records to construct high resolution astronomical time scales ats has led to a progressive refinement of the geologic time scale over the past two decades in turn these studies provide new insights regarding the durations and rates of major earth events evolutionary processes and climate changes all of which provide a scientific basis for contextualizing and predicting future global change trends south china hosts some of the best exposed and well dated neoproterozoic through mesozoic stratigraphic sections in the world many of which are suitable for cyclostratigraphy and calibrating the geologic time scale in north china several cenozoic oil bearing basins have deep boreholes with continuous sampling and or well logging that enable derivation of astronomically tuned time scales for an improved understanding of basin evolution and hydrocarbon generation this special issue focuses on case studies of astrochronology and applied cyclostratigraphy research using reference sections within china in this introductory overview we 1 summarize all existing astrochronology studies of the neoproterozoic through cenozoic sections within china that have been used to enhance the international geologic time scale 2 examine briefly the astronomically forced paleoclimate information recorded in various depositional systems and the modern techniques employed to analyze the periodicity of these signals encoded within the sedimentary record and 3 summarize the 20 contributions to this special issue of palaeogeography palaeoclimatology palaeoecology on cyclostratigraphy and astrochronology case studies from china

stress state differences between sedimentary cover and basement of the songliao basin ne china in situ stress measurements at 6 7 km depth of an icdp scientific drilling borehole sk ii abstract the stress state down to the basement within sedimentary basins yet remains poorly understood the anelastic strain recovery asr method was employed to measure the stress state in the sk ii borehole in the songliao basin northeast china the results show that the stress state differs significantly between the sedimentary cover and basement in the sedimentary cover 6296 6335 m the maximum principal stress 1 is nearly vertical which is in the normal faulting stress regime dominated by gravitation in accordance with the normal faults observed on seismic reflection profiles within the sedimentary cover in contrast the basement 6646 6846 m shows that 1 is nearly horizontal suggesting a strike slip or reverse faulting regime the stress state of the basement is close to the reasonable stress condition for the eurasian plate far from a western pacific plate subduction zone and consistent with the focal mechanisms of earthquakes 7 15 km in the vicinity of icdp sk ii borehole the difference of stress state may imply that the far field stress generated by the western pacific plate has limited effects on the sedimentary cover an increase in thickness correlates with an increasing influence of tectonic stress with depth

the floating astronomical time scale for the terrestrial late cretaceous qingshankou formation from the songliao basin of northeast china and its stratigraphic and paleoclimate implications abstract the upper cretaceous qingshankou formation k 2 qn in the songliao basin slb of northeast china consists of up to 550 m thick lacustrine mudstone and shale that constitute one of the most important source rocks of the daqing oil field a high resolution cyclostratigraphic analysis of the natural gamma ray logging from 10 wells of the qingshankou formation k 2 qn reveals orbital cycles of precession 20 ka obliquity 40 ka and eccentricity 100 ka and 405 ka providing strong evidence for astronomically driven climate changes in the late cretaceous terrestrial environments floating astronomical time scales ats are established for all sections which demonstrate variable durations of k 2 qn across the basin 1 09 ma 5 20 ma and strong diachroneity of the lacustrine strata four periods of high depositional rates can be identified in the central parts of the basin possibly recording deposition during times of sustained wet climate and high chemical weathering an ats established from well m206 in the central depression zone of the basin where the most complete and stable milankovitch cycles are present suggests that the maximum duration of the k 2 qn is 5 20 ma from 94 27 ma to 89 07 ma late cenomanian to early coniacian the lacustrine anoxic event 1 lae1 at the cenomanian turonian boundary lasted 210 310 ka during which the most prolific petroleum source rocks in slb were deposited the onset 94 21 94 18 ma and duration 210 310 ka of lae1 in slb are comparable to those of the oceanic anoxic event 2 oae2 onset at 94 21 ma and duration of 320 900 ka suggesting that the same trigger mechanism such as increased atmospheric co 2 from large scale igneous activity may have initiated high primary productivity and organic carbon burial in both marine and terrestrial systems

burial diagenesis and porosity evolution upper jurassic smackover arkansas and louisiana the jurassic upper smackover ooid lime grainstone of the central gulf coast has been a major hydrocarbon exploration target for nearly half a century study of the geologic and sedimentologic framework petrography two phase fluid inclusions and trace element and stable isotope chemistry indicates the following diagenetic history the upper smackover is a blanket ooid grainstone ranging in thickness from 300 to 400 ft 91 to 122 m and covering at least 4 000 sq mi 10 400 sq km in the northern part of the arkansas shelf a regional meteoric water system was established in the grainstone shortly after deposition and prior to significant burial this meteoric water system gave way to conditions which were increasingly more marine toward the south near the louisiana arkansas state line the fresh to marine hydrologic gradient is responsible for the strong precompaction regional diagenetic overprint that eventually controlled available diagenetic pathways for the unit during burial three diagenetic zones are present 1 a northern zone dominated by oomoldic porosity and preburial spar cementation 2 a sou hern zone characterized by compaction effects late subsurface cement primary porosity preservation and late secondary subsurface porosity generation and 3 a transitional zone having characteristics common to both the northern and southern zones during the shallow burial phase compaction became increasingly more important to the south in zones dominated by marine connate fluid whereas rock integrity and a secondary oomoldic porosity system had already been established in the northern zone as burial increased brine originating in the underlying louann salt reached the shelf grainstone and began to displace the original connate fluid the brine triggered the inversion to calcite of remaining grains and cement composed of unstable mineralogy when the louann brine had displaced the original connate fluid caso4 replacement as gypsum and anhydrite was common across all three diagenetic zones also precompaction fine cement associated with oomoldic porosity was recrystallized and reequilibrated with the concentrate brine localized replacement dolomitization may well have developed throughout the burial history of the sequence but was most commonly postcompactional postcompaction poikilitic calcite cement and baroque dolomite were precipitated from the louann brine under conditions of elevated temperature and pressure as subsidence continued organic material from the basinward equivalents of the upper smackover lime grainstone arrived on the shelf and catalyzed so4 reduction resulting in pyrite and galena replacement in the southern and transitional zones as hydrocarbon maturation continued in the fine grained equivalents of the upper smackover h2s and co2 by products of these processes began to increase in the brine of the southern and transitional zones ultimately causing regional dissolution of existing carbonate and significantly enhancing preserved porosity porosity in the northern zone was established early and preserved through moderate burial although porosity is well developed permeability has been largely destroyed by recrystallization dolomitization is a prerequisite for economic reservoir development in the northern zone porosity in the southern zone is solution enhanced preserved primary intergranular porosity compaction is the most important porosity destruction process compaction in the absence of an early diagenetic overprint is affected primarily by grain type and secondarily by size and sorting pellets and oncolites compact easily yet destroy porosity during burial ooids and rhodolites resist compaction during burial therefore are related to porosity preservation grain type distribution as well as size and sorting are controlled by depositional environment processes with the most favorable areas for porosity development concentrations of ooids and rhodolites associated with early salt related structural movement porosity distribution in the southern zone therefore can be outli ed with the aid of geophysical end page 597 techniques porosity in the transitional zone is early secondary or preserved primary intergranular or a combination porosity in this zone therefore is highly unpredictable and a strong potential exists for diagenetic traps unrelated to structure or original depositional environment documentation of significant deep subsurface secondary porosity possibly associated with hydrocarbon maturation opens the potential for hydrocarbon exploration in deeply buried carbonate dominated basins this would include carbonate rocks heretofore thought to be well below the depth of carbonate porosity maintenance because of lithostatic load

sulfur isotope constraints on marine transgression in the lacustrine upper cretaceous songliao basin northeastern china abstract organic rich cretaceous source rocks of the petroliferous songliao basin in northeast china are considered to be lacustrine in origin but paleontological and organic geochemical evidence suggest episodic marine incursions as a test of this hypothesis we applied time series measurements of elemental and isotopic abundances on core and cutting samples to evaluate fluctuations in the sulfur and carbon cycles across the santonian campanian transition preserved in the upper yaojia and lower nenjiang formations the data reveal a spike in pyrite sulfur abundance and a marked negative excursion in 34s at the base of the nenjiang formation when the basin expanded to its maximal extent the elemental and isotopic data suggest that flooding was associated with rapid marine transgression that enhanced sulfate concentrations which promoted microbial sulfate reduction in anoxic bottom waters that were episodically euxinic subsequent restriction of the basin and a decline in marine influence is supported by progressive upsection 34s enrichment up to 30 in nenjiang member i which are interpreted to reflect the distillation of sulfate through enhanced pyrite burial followed by a gradual return to lacustrine conditions that prevailed in overlying strata

structural and sedimentary evolution of the southern songliao basin northeast china and implications for hydrocarbon prospectivity the southern songliao basin manifests itself as a wide rift system that developed in northeast china from the late jurassic to early cretaceous individual basins in the system experienced marked rift subsidence but the postrift subsidence was insignificant in most of the basins contrasting strikingly with the tectonic subsidence history of the northern songliao basin two types of rift basins are defined according to whether the basins underwent prominent postrift subsidence type 1 basins are characterized by thick postrift accumulations type 2 basins although experiencing minor postrift subsidence represent most of the southern songliao basin and can be subdivided in accordance with bounding fault geometry and areal extent basins bounded by high angle faults type 2a basins bounded by low angle faults type 2b and basins with limited spatial area type 2c many rift basins are expressed as narrow belts in map view and are composed internally of several segments linked through different types of transfer zones depositional processes and facies architecture of the basins are controlled primarily by dips and migration of active bounding faults synrift depocenters occur close to high angle bounding faults and deep lake deposition commonly persists through much of the synrift subsidence lacustrine deposition can be enhanced by the backward or toward the footwall stepping of active bounding faults depocenters controlled by low angle bounding faults in contrast tend to shift basinward through time and deep lake facies commonly develop in the middle stage of rifting at the end of the cretaceous basin inversion was evident in type 1 basins such as the shiwu basin on the north but other basins appear to have mostly escaped the contractional deformation gravitational collapse of the previously thickened crust is considered the cause for the generation of the rift basins and lateral flow of the ductile lower crust may explain the significantly induced postrift subsidence of type 2 basins effective plays occur in basins bounded by high angle faults and therefore type 1 and type 2a basins are suggested to be the main targets of future oil exploration synrift source rock maturation might be partially attributed to the heating of early cretaceous magmatism because shallower burial alone could not elevate temperatures high enough for petroleum generation

orogeny and relative plate motions example of the japanese islands abstract the paleogeography of the eastern margin of asia near japan for the past 250 ma has been reconstructed on the basis of the relative motions between the oceanic plates and the eurasian plate engebretson et al 1982 and on land geology the relationships between the plate kinematics and orogeny are as follows calc alkaline magmatism is related to the presence of subduction when a plate boundary is a transform fault there is no volcanism very slow convergence rates do not give rise to magmatism migration of rft type triple junctions or ridge subduction produces forearc volcanism near the trench and also a wider volcanic zone uplift of low p t type regional metamorphic belts is related to collision episodes the uplift of the high p t blueschist belts on the contrary is not contemporaneous with them they appear to be related to the start of the subduction of a young plate after the migration of an rft type triple junction because the formation of a voluminous accretionary complex is contemporaneous with this and thrusting of this young accretionary complex beneath the uplifted metamorphic belt is often observed the underplating of the young accretionary complex beneath the older accretionary complex would be the cause of the uplift of the high p t type metamorphic belt the subduction of a young plate would thus be an important factor causing these orogenic events highly oblique convergence also results in formation of a serpentinite melange zone with fragments of blueschists presumably along a mechanical plate boundary in the forearc

hot dry rock geothermal potential of the xujiaweizi area in songliao basin northeastern china a series of studies was conducted to determine a suitable site for enhanced geothermal systems egss in mainland china first the xujiaweizi xjwz area in the songliao basin in northeastern china was identified to possess several features indicating a huge potential for hot dry rock hdr resource development from the aspects of tectonics geology geophysics and geothermics then a hydraulic fracturing model based on the real geological and logging data of well ys 2 and field fracturing experience in this region was established and the geometric dimension and flow conductivity of the induced fracture were imported into a 3d hydrothermal coupled model established using tough2 eos1 the electricity generation potential of the fractured reservoir using three horizontal well production patterns is evaluated finally three enhanced methods are proposed and discussed based on the simulation results results indicate that hdr resources in the xjwz area demonstrate a significant potential for development from the aspect of geology the yingcheng formation is selected as the potential target formation the gel proppant fracturing method is adopted in consideration of the undeveloped natural fractures in the target formation the generalized egs reservoir region possessed a considerable length of 600 m the maximum production flow rate is determined to be 1 kg s the water flow impedance is relatively high during the heat production process for economic exploitation such an egs reservoir has poor electricity generation capacity a naturally fractured reservoir with a higher temperature should be targeted for electricity generation

mechanisms of fine extinction band development in vein quartz new insights from correlative light and electron microscopy fine extinction bands febs also known as deformation lamellae visible with polarized light microscopy in quartz consist of a range of nanostructures inferring different formation processes previous transmission electron microscopy studies have shown that most feb nanostructures in naturally deformed quartz are elongated subgrains formed by recovery of dislocation slip bands here we show that three types of feb nanostructure occur in naturally deformed vein quartz from the low grade metamorphic high ardenne slate belt belgium prismatic oriented febs are defined by bands of dislocation walls dauphine twin boundaries present along the feb boundaries probably formed after feb formation in an example of two sub rhombohedral oriented febs developed as two sets in one grain the finer feb set consists of elongated subgrains similar to febs described in previous transmission electron microscopy studies the second wider feb set consists of bands with different dislocation density and fluid inclusion content the wider feb set is interpreted as bands with different plastic strain associated with the primary growth banding of the vein quartz grain the nanometre scale fluid inclusions are interpreted to have formed from structurally bounded hydroxyl groups that moreover facilitated formation of the elongate subgrains larger fluid inclusions aligned along febs are explained by fluid inclusion redistribution along dislocation cores the prismatic feb nanostructure and the relation between febs and growth bands have not been recognized before although related structures have been reported in experimentally deformed quartz

a chlorite solid solution geothermometer the los azufres mexico geothermal system chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites in the active geothermal system of los azufres mexico electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition correlation coefficients among chemical constituents were calculated it is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content and there is almost no correlation with the octahedral aluminium and magnesium content a procedure is proposed to select end members and substitution vectors and to give a general formula for these chlorites

quartz veins with associated sb pb ag au mineralization in the schwarzwald sw germany a record of metamorphic cooling tectonic rifting and element remobilization processes in the variscan belt a combination of textural observations from 38 permian sb pb ag au bearing quartz veins in the schwarzwald sw germany with isotopic fluid inclusion and geochemical data allows to refine genetic models for this common type of mineralization to understand the origin of mineralogical diversity and the correlation with large scale tectonic events textures record four main mineralization stages i fe as sb au ii pb zn cu iii pb sb and iv ag sb stage i sulfides dominated by pyrite and arsenopyrite formed due to cooling of low salinity metamorphic fluids during the permian with maximum homogenization temperatures of 400 c invisible gold in arsenopyrite pyrite marcasite and stibnite was remobilized and locally precipitated as electrum at the end of stage i minerals of stages ii and iii comprise a rich diversity of sb bearing sulfosalts including e g bournonite zinkenite and jamesonite this assemblage formed during jurassic times due to mixing of high salinity mid and upper crustal fluids up to 27 wt nacl cacl2 with homogenization temperatures between 50 and 250 c stage iii is marked by a rich variety of pb sb sulfosalts its local abundance is directly related to the presence of stage i mineralization and its extent of remobilization during a significant influx of pb in the jurassic cretaceous the formation of the upper rhine graben during the tertiary reactivated especially ne sw oriented veins percolating ag rich fluids reacted with earlier stage iii pb sb sulfosalts forming ag rich minerals stage iv such as miargyrite pyrargyrite and stephanite the transition from metamorphic fluids to basinal saline e g pb bearing brines over hundreds of millions of years as is shown in this study and present in other variscan occurrences indicates a possibly typical poly stage characteristic of sb deposits worldwide which has however not been investigated in detail so far

coherence between the great salt lake level and the pacific quasi decadal oscillation the lake level elevation of the great salt lake gsl a large closed basin lake in the arid western united states is characterized by a pronounced quasi decadal oscillation qdo the variation of the gsl elevation is very coherent with the qdo of sea surface temperature anomalies in the tropical central pacific also known as the pacific qdo however such coherence denies any direct association between the precipitation in the gsl watershed and the pacific qdo because in a given frequency the precipitation variation always leads the gsl elevation variation therefore the precipitation variation is phase shifted from the pacific qdo this study investigates the physical mechanism forming the coherence between the gsl elevation and the pacific qdo pronounced and coherent quasi decadal signals in precipitation streamflow water vapor flux and drought conditions are found throughout the great basin recurrent atmospheric circulation patterns develop over the gulf of alaska during the warm to cool and cool to warm transition phases of the pacific qdo these circulation patterns modulate the water vapor flux associated with synoptic transient activities over the western united states and in turn lead to the qdo in the hydrological cycle of the great basin as the gsl integrates the hydrological responses in the great basin the hydrological qdo is then transferred to the gsl elevation because the gsl elevation consistently lags the precipitation by a quarter phase about 3 yr in the quasidecadal time scale these processes take an average of 6 yr for the gsl elevation to eventually respond to the pacific qdo this creates a half phase delay of the gsl elevation from the pacific qdo thereby forming the inverse yet coherent relationship between them tree ring reconstructed precipitation records confirm that the quasi decadal signal in precipitation is a prominent feature in this region

post rift geodynamics of the songliao basin ne china origin and significance of t11 coniacian unconformity abstract the t11 unconformity lies between the qingshankou and yaojia formations in the post rifting sequence of the cretaceous songliao basin ne china it is intimately associated with petroleum reservoirs and considered to be a disconformity forming in the tectonic quiet stage we present the interpretations from new seismic surveys and cored sections of the cretaceous continental scientific drilling borehole ccsd sk 1 in order to resolve the nature and origin of t11 unconformity the t11 is often a low angle unconformity with underlying qingshankou formation having been deformed and eroded prior to deposition of the yaojia formation in the post rift evolution of the basin it marks an abrupt change from a deep lake to shallow lake or subaerial environment documented by reddening of the lacustrine mudstone extinction of the ostracod assemblages and a great increase of coarse detrital inputs the sharp change of depositional environment the truncation of gentle folds and the cluster of volcanic and paleoearthquake activities all happened simultaneously immediately before the development of t11 unconformity indicating a significant regional compressional uplift event in the basin the timing of the t11 unconformity formation is within the interval 88 86 2 ma correlations with coeval unconformities in other cretaceous sedimentary basins in eastern asia indicate that this compressional uplift coincided with an episode of global plate reorganization between the eurasian and paleo pacific plates that culminated at 88 87 ma during this short interval the northeast asian margin in eastern china south korea japan and russian far east experienced widespread violent volcanic and granite emplacement activity triggered by compression resulting from rapid and orthogonal slab subduction the post rift basin tectonic inversion occurred during t11 coniacian time thereafter the basin again evolved in an extension regime two subsidence phases in post rift history took place as the direct consequence of coniacian compression peak which defined the distribution of oil sources and reservoirs

sulphur isotope geochemistry of black shale hosted antimony mineralization arnsberg northern rhenish massif germany implications for late stage fluid flow during the variscan orogeny vein type and bedding concordant mesothermal 180 410 c stibnite sulphosalt mineralization at arnsberg ne rhenish massif germany is hosted by carboniferous pyrite rich black shales and siliceous limestones a detailed sulphur isotope study of the stibnite sulphosalt mineralization and pyrite from a variety of regional host rock lithologies has been carried out using an in situ laser combustion technique the 34 s values of stibnite of various textural types are distinctly negative and lie in a narrow range between 23 9 and 17 1 mean 20 1 in contrast regional sedimentary diagenetic pyrites display a large variation of their 34 s values between 45 4 and 9 3 there is little evidence for significant modification of the hydrothermal fluid during deposition and the s isotope signatures suggest that the sulphur of the stibnite mineralization was not locally derived the 34 s values of pyrite in givetian shales display a significantly narrower range of 28 2 to 7 5 and their mean composition 17 1 is close to the 34 s values of the arnsberg stibnite deposits considering the temperature dependent isotopic fractionation between stibnite and reduced sulfur species the 34 s values of the mineralizing fluid 16 8 200 c and the givetian rock source are essentially identical therefore we propose a model of leaching and isotopic homogenization of sulphur from the middle devonian shales and a subsequent northward migration of these fluids the fluids were trapped in permeability controlled positions within anticlinal zones where fluid cooling induced deposition of stibnite and sulphosalts

epigenetic to low grade tourmaline in the gdoumont metaconglomerates belgium a sensitive probe of its chemical environment of formation abstract this study reports the first observation and compositional data of tourmaline overgrowths in the post caledonian basal gdoumont conglomerates of the belgian part of the rhenohercynian basin authigenic tourmaline occurs as monopolar hemimorphic and bipolar asymmetrical foitite overgrowths within fractures and along the margins of detrital tourmaline grains and tourmalinite pebbles formulae calculated from electron microprobe analyses reveal high amounts of vacancies in the x site 61 to 84 placing this tourmaline amongst the most alkali deficient tourmaline recorded to date besides the alkali deficiency gdoumont overgrowths are characterized by high al low na and ca and low to moderate mg fe mg ratios these characteristics reflect the composition of the host conglomerates and suggest local derivation of the chemical components slightly differing zoning patterns sample scale and differences between localities regional scale indicate heterogeneity of the low grade host rock host tourmaline grains as well as tourmaline occurring in quartz veins crosscutting the gdoumont metasediments have distinctly different compositions the absence of discontinuous zoning suggests growth of the authigenic tourmaline in just one stage it is most likely that tourmaline formed from boron released by metamorphic breakdown of detrital minerals e g illite and or k feldspar based on their crystal chemistry and the observed optical properties the overgrowths must have developed during diagenetic to lower greenschist facies conditions scarce concurrency of bipolar overgrowths isolated neoblasts and cryptocrystalline nests of tourmaline indicates limited growth until middle greenschists facies conditions

evidence of deterministic chaos in the pulse of storm rainfall abstract rainfall data obtained by a highly sensitive raingage have been analyzed for the presence of strange attractors analysis of three storms that occurred in cambridge massachusetts revealed for each storm the presence of a low dimensional strange attractor with correlation dimension that was less than 4 the datasets consist of the discrete time series of the interarrival times of one hundredth of a millimeter rainfall amounts in all cases the number of data points in the datasets was at least 3300 which makes the evidence of determinism in storm rainfall strong

an 11 million year long record of astronomically forced fluvial alluvial deposition and paleoclimate change in the early cretaceous songliao synrift basin china abstract in the cretaceous songliao basin northeastern china boreholes have recovered detailed geologic data from sub basins that developed during the early rifting of the basin among these the lower cretaceous shahezi formation k1s in the songshen 4 ss4 well is represented by an 836 m thick succession of fluvial alluvial deposits with coals distributed throughout the upper part of the formation gamma ray gr logging data are quantitatively related to grain size defined litho facies that recur throughout the succession with high gr values in mudstones and low gr values in sandstones cyclostratigraphic analysis of the gr log reveals depositional cycling at frequencies that are consistent with those of the earth s astronomical parameters the results also indicate that occurrence of coal beds occur every 100 kyr when development of vegetation at the depositional site was promoted by humid climate we propose a model of astronomically forced hydroclimate change to explain the cycling of depositional environments between fluvial and alluvial conditions the model describes a principally fluvial environment that episodically experienced at one extreme advancing alluvial conditions involving a drop in base level lake recession and increased aridity conglomerates and coarse sands and at the other extreme an advancing lakeshore with a rise in base level and increased humidity fine sands silts muds and coal a floating astronomical time scale was established by calibrating long orbital eccentricity 405 kyr cycles interpreted along the gr series the results indicate that the duration of the k1s is 11 14 myr 27 5405 kyr long orbital eccentricity cycles corresponding to an average sedimentation rate of 6 55 cm kyr the recognition of astronomical forcing in this early cretaceous fluvial alluvial dominated depositional setting offers a new framework for interpreting the sedimentary cyclicity and dynamics of early rift basins and for developing time scales

mixing of h2o co2 in fluid inclusions geobarometry and archean gold deposits abstract a modified redlich kwong mrk equation of state for h 2 o and co 2 was used to calculate bulk molar volumes mole fractions and co 2 densities for mixed volatile fluid inclusions the results allow very useful p t diagrams to be constructed for fixed co 2 density and contoured with volume percent co 2 observed in the laboratory these diagrams permit rapid qualitative or quantitative determination of the p t path for a bulk inclusion isochore above the solvus in the system h 2 o co 2 nacl the calculations suggest peak metamorphic pressures of 3 5 kb for some archean greenstone gold deposits insights gained from this work may require reinterpretation of pressure estimates in published fluid inclusion studies

the use of a combined structural stable isotope and fluid inclusion study to constrain the kinematic history at the northern variscan front zone bettrechies northern france abstract a detailed structural stable isotope and fluid inclusion study of distinct vein generations has been performed in a kilometre scale syncline to correlate the temperature pressure conditions of vein formation with specific deformation episodes the structural relationship of the veins with cleavage folds faults and with one another allows the identification of pre syn and post variscan carbonate vein generations the stable isotope composition of the vein calcites and dolomites is very similar to that of the surrounding limestones and dolostones respectively this indicates that the cements were precipitated from fluids buffered by the host rock and implies that the temperature pressure characteristics of the fluids reflect the thermal history of the deformation history within the syncline microthermometric data of primary fluid inclusions were used to estimate the temperature pressure conditions at precipitation time and thus of the deformation pressure corrected trapping temperatures for the veins show a temperature evolution from pre variscan 310 c to variscan 260 200 c and post variscan 75 c this evolution indicates that the syncline developed not at a specific depth but rather as an active progressive deformation process during transport along the northern variscan thrust front

continental scientific drilling project of cretaceous songliao basin scientific objectives and drilling technology abstract the continental scientific drilling project at the cretaceous age songliao basin is a drilling initiative under the framework of the international continental scientific drilling program to recover a nearly complete cretaceous terrestrial sedimentary record in the songliao basin northeastern china the recovered cores will provide unique opportunities for the geosciences community to advance the understanding of climate change in the cretaceous greenhouse world and provide a documentation of geological events relevant to the carbon cycle during this time period this drilling project will address significant geological questions such as the identification of important stratigraphic boundaries and the marine terrestrial correlations of stratigraphy the reasons for the biotic response to the terrestrial environmental changes the terrestrial response to the cretaceous oceanic anoxic events the formation of terrestrial petroleum source rocks and the mechanisms for the cretaceous magnetic normal superchron cns in the first stage of this drilling project the ski drilling rock cores of 2485 89 m in total length were recovered and the recovery ratio reached 96 46 a series of drilling and coring technologies including regular confined directional and sealed coring were utilized to ensure a higher recovery ratio for the core and will be described at the end of this paper well loggings were conducted right after coring core handling and storage were arranged in such a way that the scientific research was conducted on half of each core whereas the other half of each core was preserved for long term storage the upcoming second stage the skii drilling will combine with data from the existing ski to provide complete high resolution climate records of the terrestrial environment for the whole cretaceous time period

mid latitude terrestrial climate of east asia linked to global climate in the late cretaceous reply the late cretaceous late campanian to maastrichtian was characterized by a variable greenhouse climate with evidence for cooling and or glaciation and warming events most of these climatic signals are derived from marine records and knowledge of the terrestrial climate especially in the mid latitudes is limited due to fragmentary geological records on continents here we report mid latitude terrestrial stable oxygen and carbon isotope data from pedogenic carbonates in the nearly continuous late cretaceous age sk 1 core drilled in the songliao basin northeastern china our data indicate a punctuated mid latitude terrestrial climate in the late cretaceous we interpret the negative excursion of pedogenic carbonate 18o in the early maastrichtian to be the result of decreasing temperature and or strengthened westerlies during global cooling and possible glaciation providing valuable mid latitude terrestrial evidence for this event the negative 13c isotopic excursion ca 66 ma is modeled as higher primary productivity caused by increasing temperature and precipitation in response to a warming climate in the latest cretaceous our continuous stable isotopic records in the songliao basin are in accordance with previously published global late cretaceous records of climate variability from marine and terrestrial regions and demonstrate the sensitivity of mid latitude terrestrial climate in a greenhouse world

late cretaceous stratigraphy songliao basin ne china sk1 cores abstract the songliao basin is the largest cretaceous oil and gas producing lacustrine basin in china with its greatest aerial extent in the middle cretaceous a coring program sk1 has to date yielded 2485 89 m of continuous core 96 46 recovery and provides significant material for cretaceous research the sequence of the core consists mainly of lacustrine sandstone dark grey mudstone shale and oil shale the upper cretaceous stratigraphic section has been subdivided into the quantou qingshankou yaojia nenjiang sifangtai and mingshui formations in ascending order late cretaceous microfossils are diverse and abundant a detailed biostratigraphic study has subdivided the sequence into high precision biozones 21 ostracode assemblages 10 phytoplankton assemblages 7 palynological zones and 4 charophyta assemblages respectively in addition marine foraminifera were first discovered from the basin three 206pb 238u ages and one 40ar 39ar age were analysed ten local magnetozones have been recognised in the sk1 north and two magnetozones have been indicated in the sk1 south based on biostratigraphy high resolution magnetostratigraphy and sims u pb zircon analyses the sk1 stratigraphy is correlated with upper cretaceous stages in the international geologic time scale the upper part of the quantou formation is the lower turonian the qingshankou formation is the upper turonian lower coniacian the yaojia formation is from the upper coniacian to middle santonian the nenjiang formation is the upper santonian to middle campanian the sifangtai formation is limited to the upper campanian and the mingshui formation is the uppermost campanian to maastrichtian it is likely that the upper part of the mingshui formation belongs to the paleocene and the k pg boundary is within the member 2 of the mingshui formation around the depth of 328 m by new micropalaeontologic and magnetostratigraphic data

mineralogical and geochemical evidence for biogenic and petroleum related uranium mineralization in the qianjiadian deposit ne china abstract the sandstone hosted qianjiadian uranium deposit hosted in the upper cretaceous yaojia formation in the qianjiadian area songliao basin ne china has been studied for over twenty years however there exists debate on whether mineralization fluid is low temperature groundwater in favor of biogenic mineralization or diabase related magmatic hydrothermal fluid for this deposit and other adjacent geologically linked sandstone hosted uranium deposits baixingtu baolongshan and huitianzhao deposits in the north china this study provided new data from petrographic and geochemical analyses geochronology of uranium minerals the empa chemical dating method and petroleum hydrocarbon biomarkers in host sandstones two types of host sandstone were recognized in calcareous sandstones pitchblende coexists with colloform pyrite and poikilitic calcite cement while quartz and feldspars were extensively corroded in non calcareous sandstones coffinite coexists with colloform pyrite and only feldspars were slightly corroded this suggests that pitchblende formed in high ph ph 9 fluid while the ph of ore forming fluid for coffinite was lower ph 7 9 besides empa chemical dating revealed two stages of uranium mineralization stage a occurred in 43 28 ma with pitchblende as the only uranium mineral species stage b occurred in 19 3 ma with the formation of both pitchblende and coffinite the uranium mineralization was biogenic under low temperature groundwater condition and thus not from a diabase related mafic magmatic hydrothermal fluid based on the following lines of evidence i some coffinite occurs as phosphorus rich microorganism like microspherules structure ii pyrite aggregates were generated from bacterial sulfate reduction as indicated by the 34s values as low as 41 4 iii calcite cement in calcareous sandstone contains only single phase aqueous inclusions and have 13c values as low as 11 2 indicating that part of the carbon was derived from organic matter oxidation iv the organic matter oxidation is further supported by hydrocarbons extracted from petroleum inclusions within calcite cement showing occurrence of c26 c31 17 21 25 norhopanes typically resulting from heavy biodegradation

late variscan fluid migration at the variscan thrust front of eastern belgium numerical modelling of the palaeothermal and fluid flow field modelling of the palaeothermal field at the variscan thrust front in eastern belgium indicates significant temperature modifications by late variscan palaeofluids migrating from internal to peripheral parts of the orogen a detailed set of calibration data chlorite geothermometry microthermometry organic rank gives evidence of temporary palaeotemperature variations at the variscan thrust front obviously connected to the migration of hot low saline palaeofluids these thermal events likely enhanced organic maturation vitrinite reflectance conodont alteration of devonian and carboniferous sediments which accumulated long before the variscan orogeny occurred numerical simulation 2d finite element method of the palaeothermal field includes coupled heat transport by thermal conduction and fluid flow palaeothermal scenarios yield successive palaeotemperatures 200 300 c which are indicated by the control data due to relatively short term fluid ascent along the detachment and the imbricate thrust front the simulated flow velocities are up to tens of metre per year lasting several thousand years non steady state solution in the scenarios modelled these thermal events occur in a realm of enhanced bulk temperatures due to elevated basal heat flow densities 90 mw m 2 and an additional burial depth of some kilometres the simulated temperature enhancement due to fluids ascending at the variscan thrust front is several tens degrees the scenarios demonstrate long distance fluid migration during or after deformation of the palaeozoic basin and its effect on the palaeothermal field

cenozoic tectonics on the hautes fagnes plateau belgium abstract morphological features under which deformations of oligocene surfaces are included demonstrate the varied tectonic activity of the hautes fagnes plateau during cenozoic times beyond the general uplift of the region a local movement raised the baraque michel massif by about 100 m above the nearby crest of la vecquee moreover several zones of radial nw se faulting are active on the plateau they are related to the opening of the lower rhine embayment and represent the ultimate sw extension of the fault system associated with this opening

superheavy pyrite in the upper cretaceous mudstone of the songliao basin ne china and its implication for paleolimnological environments abstract the widely developed dark mudstone in the upper cretaceous nenjiang formation of the songliao basin is a natural archive for reconstructing the palaeoenvironment a time series sulfur isotope study on the nenjiang formation reveals that authigenic pyrite from the paleo lake is enriched in 34s relative to coeval marine sulfate in the lower nenjiang member i and basal nenjiang member ii the occurrence of 34s enriched pyrite must be explained to understand the paleolimnological environment and the sulfur cycling during this period for which several explanations can be advanced based on a comparison of various mechanisms for superheavy pyrite formation we consider the presence of an anaerobic sulfate minimum zone smz in the paleo lake as the most likely scenario in this zone sulfate was enriched in 34s through microbial sulfate reduction msr and this heavy sulfate became the source for pore water or bottom water from which superheavy pyrite was produced the conceptual model for formation of the superheavy pyrite in the nenjiang formation indicates that the distribution range of the smz was variable in the different sedimentary stages of the nenjiang formation these variations were likely related to successive inputs of sulfate from continental weathering which led to partial mixing of sulfate and attenuation of the smz in the basal nenjiang member ii