complex concentric granitoid intrusions in the coastal mobile belt espirito santo brazil the santa angelica pluton an example the brazilian coastal mobile belt in southern espirito santo consists of archean to upper proterozoic units which have been metamorphosed and deformed to a gneiss migmatite and granulite facies rock assemblage during archean and proterozoic tectono thermal events

the fluid dynamics of a basaltic magma chamber replenished by influx of hot dense ultrabasic magma this paper describes a fluid dynamical investigation of the influx of hot dense ultrabasic magma into a reservoir containing lighter fractionated basaltic magma this situation is compared with that which develops when hot salty water is introduced under cold fresh water theoretical and empirical models for salt water systems are adapted to develop a model for magmatic systems a feature of the model is that the ultrabasic melt does not immediately mix with the basalt but spreads out over the floor of the chamber forming an independent layer a non turbulent interface forms between this layer and the overlying magma layer across which heat and mass are transferred by the process of molecular diffusion both layers convect vigorously as heat is transferred to the upper layer at a rate which greatly exceeds the heat lost to the surrounding country rock the convection continues until the two layers have almost the same temperature the compositions of the layers remain distinct due to the low diffusivity of mass compared to heat the temperatures of the layers as functions of time and their cooling rate depend on their viscosities their thermal properties the density difference between the layers and their thicknesses for a layer of ultrabasic melt 18 mgo a few tens of metres thick at the base of a basaltic 10 mgo magma chamber a few kilometres thick the temperature of the layers will become nearly identical over a period of between a few months and a few years during this time the turbulent convective velocities in the ultrabasic layer are far larger than the settling velocity of olivines which crystallise within the layer during cooling olivines only settle after the two layers have nearly reached thermal equilibrium at this stage residual basaltic melt segregates as the olivines sediment in the lower layer depending on its density the released basalt can either mix convectively with the overlying basalt layer or can continue as a separate layer the model provides an explanation for large scale cyclic layering in basic and ultrabasic intrusions the model also suggests reasons for the restriction of erupted basaltic liquids to compositions with mgo 10 and the formation of some quench textures in layered igneous rocks

significance of ferrodioritic liquids in magma mixing processes a general model to explain the various igneous associations found in mixed magma intrusives and extrusives belonging to high level volcanic centres is presented this model is based on detailed mapping in the british tertiary volcanic centre on skye which suggests that basic and acid magmas were continually available throughout its development new major and trace element data from these rocks indicate that they were co genetic and that the basic magmas which combined with acid magmas to produce hybrid magmas were ferrodioritic in composition and not basaltic as had previously been thought

mesozoic cenozoic tectonic relationships between the kuqa subbasin and tian shan northwest china constraints from depositional records abstract stratigraphic profiles in the kuqa subbasin located along the southern flank of the tian shan northwest china display similar mesozoic cenozoic evolutionary sequences of compositional maturity exist in conglomerate clasts sandstone framework grains and detrital heavy minerals the similarity of these time series profiles resulted from orogenesis and intracontinental deformation of the provenance area the ancestral tian shan mineralogical maturities of conglomerates and sandstones increase from triassic to middle jurassic and decrease from upper jurassic lower cretaceous to tertiary this trend parallels a similar decrease in maturity in detrital heavy minerals zircon rutile and tourmaline dominate in middle upper triassic to middle jurassic sandstone whereas unstable hornblende and pyroxene dominate the heavy mineral suites in the tertiary especially in miocene and pliocene strata these compositional trends are coeval with gradual southward migration of alluvial depositional fronts and depositional depocenters from cretaceous to miocene since the pliocene large scale southward migration of alluvial depositional systems occurred while depositional depocenters migrated northward based on the mesozoic cenozoic depositional records the tectonic evolution of the tian shan kuqa subbasin may be divided into five phases 1 in early triassic following compression and uplift since permian gravelly braided river alluvial plain depositional systems developing in the kuqa subbasin characterized by sands of mixed orogenic provenance type derived from the ancestral tian shan 2 from middle triassic to middle jurassic sediment composition of the kuqa subbasin reflects arc orogen and mixed orogenic sand types with extensive planation of the ancestral tian shan and the development of relatively stable coal bearing depositional environments 3 renewed compression uplift of the tian shan occurred in late mesozoic especially in cretaceous with most detrital modes of the kuqa subbasin indicating provenance attributes akin to the south tian shan 4 further intensive compression uplift and probably southward basinward propagation of the south tian shan occurred during miocene and 5 supracrustal gravity gliding and collapse occurred in the tian shan kuqa subbasin probably due to intensive deep compression with rejuvenated uplift and probable southward basinward structural propagation of the south tian shan developing since pliocene observed changes in sediment composition and depositional environment since pliocene time were also controlled by frequent and abrupt climate changes in addition to intensive uplift of the tian shan moreover all depositional records in the kuqa subbasin seem to reflect west to east differences in provenance along the tian shan probably indicating greater exhumation depth in the western tian shan than that in the eastern tian shan since early cretaceous

tectonic significance of paleobotanically estimated climate and altitude of the late eocene erosion surface colorado erosion beveled the laramide front range uplift in colorado to a surface of low relief by the end of the eocene this study uses j a wolfe s new multivariate climate analysis techniques to determine the paleoelevation of this regional surface by examining the overlying 35 ma florissant flora a multiple regression model explaining 93 3 of the variance in mean annual temperature was developed using wolfe s dataset of 31 leaf physiognomic character states for 86 modern vegetation sites these character states were scored on 29 species collected from one facies of the florissant lake beds the paleotemperature estimate of mean annual temperature 10 7 plus minus 1 5c derived from these data when combined with sea level temperature and terrestrial lapse rate implies a late eocene paleoelevation of 2 4 2 7 km pliocene uplift is thus not required to explain the present elevation of 2 5 km it is unclear when and why the southern rocky mountains achieved this elevation magmatic crustal thickening can explain the late eocene high elevation of the southern rockies but neither this mechanism nor compressive thickening explains why the great plains which are tied to the florissant elevation by the wall mountain tuff were also high this paleoelevation estimate indicates that regional surfacesmore of planation could be formed at high elevation in the eocene probably because of peculiarities of the eocene climate less

organic geochemistry of oil and gas in the kuqa depression tarim basin nw china abstract the kuqa depression in the tarim basin nw china contains significant natural gas and condensate resources with only small amounts of black oil this study demonstrates that the primary reason for the accumulation of large natural gas reserves in the kuqa depression is the high maturity level of the jurassic coal bearing sequence that is currently at the peak stage of dry gas generation from the combined stable carbon isotopes and molecular biomarker data it is possible to identify two separate source rocks for the discovered hydrocarbon fluids the gases were primarily from the middle lower jurassic coals and associated clastic rocks and the oils were from the upper triassic lacustrine mudstones peak oil generation from the triassic source rocks occurred during the early miocene 23 12 ma b p these oils migrated laterally over relatively long distances 20 50 km reaching the outer periphery of the depression peak gas generation took place more recently perhaps during the past 5 ma the gases migrated mainly along faults over relatively short lateral distances resulting in accumulations adjacent to the over matured source kitchens different timings for the trap formation along the north and south margins and a late injection of gas into early oil accumulations provided favorable conditions for the formation of evaporative condensates and the preservation of gas pools in the more down dip reservoirs and oil pools in the more up dip locations

megaflora and palaeoclimate of a late oligocene tropical delta makum coalfield assam evidence for the early development of the south asia monsoon abstract the fossil megaflora from the late oligocene deltaic sediments exposed in the tirap coal mine assam india 27 17 20 n 95 46 15 e laid down at a palaeolatitude of 10 15 n records the composition and climate of tropical vegetation during the last episode of pronounced global warmth before the progressive overall cooling to present day conditions using a new calibration of the climate leaf analysis multivariate program clamp that includes 18 sites from modern vegetation in india the analysis of 80 fossil leaf morphotypes from the tirap mine indicates a mean annual temperature mat of 26 1 2 7 c a warm month mean temperature wmmt of 27 9 3 3 c and a cmmt of 20 1 4 3 c with adjustments for evapotranspirational cooling and underestimation of the wmmt at high temperatures these can be revised upwards to a minimum mat of 28 3 3 7 c a cmmt of 23 5 5 c and a wmmt of 33 6 5 2 c maximum estimates based on evaporative cooling seen in a modern analogue of the tirap environment yield an mat of 32 9 3 8 c a cmmt of 26 8 6 c and a wmmt of 39 7 1 c all uncertainties are 2 sigma precipitation estimates reveal a marked annual variation in rainfall showing a wet season with 20 times the rainfall of the dry season this is a similar regime to that seen in the sunderbans in the modern ganges brahmaputra meghna delta we interpret this to suggest that the south asian monsoon was already established by late oligocene times at an intensity similar to that of today

constraining tectonic compression processes by reservoir pressure evolution overpressure generation and evolution in the kelasu thrust belt of kuqa foreland basin nw china abstract the kuqa foreland basin kfb immediately south of the south tianshan mountains is a major hydrocarbon producing basin in west china the kelasu thrust belt in the basin is the most favorable zone for hydrocarbon accumulations widespread overpressures are present in both the cretaceous and paleogene reservoirs with pressure coefficients up to 2 1 the tectonic compression process in kfb resulted from the south tianshan mountains uplift is examined from the viewpoint of the overpressure generation and evolution in the kelasu thrust belt the overpressure evolution in the reservoir sandstones were reconstructed through fluid inclusion analysis combined with pvt and basin modeling overpressures at present day in the mudstone units in the kelasu thrust belt and reservoir sandstones of the dabei gas field and the keshen zone are believed to have been generated by horizontal tectonic compression both disequilibrium compaction and horizontal tectonic compression are thought to contribute to the overpressure development at present day in the reservoir of the kela 2 gas field with the reservoir sandstones showing anomalously high primary porosities and low densities from wireline log and core data the overpressure evolution for the cretaceous reservoir sandstone in the kelasu thrust belt evolved through four stages a normal hydrostatic pressure 12 5 ma a rapidly increasing overpressure 5 3 ma an overpressure release 3 1 64 ma and overpressure preservation 1 64 0 ma overpressure developed in the second stage 5 3 ma was generated by disequilibrium compaction as tectonic compression due to the uplift of the tianshan mountains acted at the northern monocline of kfb from 5 ma to 3 ma which provided abundant sediments for the kfb and caused the anomalously high sedimentation rate during the n2k deposition from 3 ma to 1 64 ma the action of tectonic compression extended from the northern monocline to the kelasu thrust belt and returned to the northern monocline of kfb from 1 64 ma to present day therefore the horizontal tectonic compression was the dominant overpressure mechanism for the overpressure generation in the third stage 3 1 64 ma and overpressure caused by disequilibrium compaction from 5 ma to 3 ma was only preserved in the kela 2 gas field until present day

palaeoaltimetry from energy conservation principles a knowledge of past changes in the mean elevations of large continental areas is important for understanding both dynamic processes in the earth s mantle 1 and the evolution of the global climate 2 but virtually all methods for determining palaeoelevations are problematic in part because changes in either elevation or climate can give rise to the same observed geological phenomena 4 ideally palaeoelevations would be inferred directly from estimates of palaeopressure and it has recently been shown 5 that vesicles in basaltic lava flows preserve a record of atmospheric pressure at the altitude of emplacement however the elevations thus obtained have large errors 1 4 km and the method can at present be applied only to lavas that have had a simple emplacement history 5 palaeobotanical methods for estimating palaeoelevation have received much attention 6 12 but they rely on empirical temperature elevation relationships the uncertainties in which are difficult to evaluate for past climates here we describe an alternative palaeobotanical approach based on energy conservation in the atmosphere in which fossil leaf assemblages are used to infer enthalpy rather than temperature this approach is relatively insensitive to palaeoclimate with an expected error in palaeoelevation of 700 m

petrogenesis of a basalt rhyolite tephra from the west central afar ethiopia the cindery tuff is an unusual tephra fall deposit that contains evidence for the mixing of basaltic and rhyolitic liquids prior to eruption it contains clear rhyolitic glass shards together with brown basaltic glass spheres and a broadly bimodal phenocryst assemblage brown glasses are ferrobasaltic in composition and are similar to the voluminous pliocene tholeiites of the surrounding west central afar volcanic field both are enriched in the light rare earth and incompatible elements and possess higher 87sr 86sr and lower 143nd 144nd than morb rhyolitic glasses are subalkaline and compared to the basaltic glasses are strongly depleted in the compatible elements and enriched in the incompatible elements both glass types have similar incompatible element and isotopic ratios and with the rhyolite glass showing a 2 fold parallel enrichment in rare earth element abundances over the basaltic glass these observations suggest that the two glasses are genetically related

provenance signatures recorded in transgressive sandstones of the upper cretaceous iberian seaway abstract maximum mesozoic transgressions flooded many continental areas worldwide forming a wide and shallow seaway on the iberian microplate during the late cretaceous several siliciclastic and mixed siliciclastic carbonate units developed along the iberian massif cratonic area while at the same time epeiric carbonate platforms spanned iberia these siliciclastic deposits unconformably cover the variscan basement as well as the permian and triassic deposits this study focuses on sandstone provenance in central spain in a transgressive relatively quiet tectonic setting with a wide rock variety in the potential source areas results shown in this paper can be applied in analogue systems transgressive sandstones often form important hydrocarbon reservoirs due to their high primary porosity the cretaceous siliciclastic deposits are included in four formations ranging in age from the cenomanian to the early coniacian the deposits were initially of fluvial origin followed by a coastal tidal setting quantitative petrographic analysis of sandstones from these formations reveals compositional variations related to provenance and weathering degree the oldest formation utrillas fm was deposited on a paleorelief surface sandstone composition changes from arkosic sandstones in the depressed area petrofacies p1a to younger quartzarenites when sediments were deposited on top of the paleotopographic high petrofacies p1b quartz grains in both sub petrofacies are angular to subangular and the framework is poorly sorted intense weathering conditions are deduced for petrofacies p1b manifested by grain infiltration clay coatings and the absence of plagioclase grains and alteration features on k feldspars all these observations have been related to wetter conditions during p1b deposition main source areas of the utrillas fm were ordovician metasediments and orthogneisses permian volcanic rocks and triassic buntsandstein facies petrofacies 2 encompasses the three coastal tidal formations constituted mainly by subarkoses generally showing a subangular and poorly sorted framework the deduced source areas are mainly associated with variscan granitoids pre ordovician schists and paragneisses and ordovician metasediments glauconite and carbonate grains support intrabasinal inputs the low degree of sorting of this petrofacies related to a low energy sedimentary environment produced lower values of original porosity compared to transgressive sandstone hydrocarbon reservoirs also intrabasinal inputs promoted carbonate cementation and contribute to almost occlude the porosity

a laboratory model of a replenished magma chamber abstract it has recently been suggested that periodic influxes of hot but heavy magma into the base of a basaltic magma chamber can remain isolated from the rest of the chamber while the new magma cools and crystallization proceeds when thermal equilibrium is almost complete the suspended crystals settle out and the residual less dense liquid can then mix with the fluid above in the present paper the basic fluid dynamical processes underlying this model have been investigated in laboratory experiments using aqueous solutions the lower layer was hot kno3 solution for which saturated solutions become less dense as the temperature decreases with a cold deeper layer of less dense nano3 or k2co3 above the lower layer there was strong convective transfer of heat through a sharp interface separating the layers at a rate which is predicted here drawing on previous studies carried out with oceanographic applications in mind once crystallization began non equilibrium effects became important and the observed temperatures differ somewhat from those predicted in the experiments crystals grew mainly from the bottom rather than while in suspension but this is not an essential aspect of the model the important fact is that the density of the residual liquid in the lower layer decreased until it became equal to that of the upper layer and then the interface broke down so that the two layers mixed thoroughly together leaving a layer of kno3 crystals at the base no crystallization at all occurred when the hot input liquid was forced to mix initially with the cold solution already in the chamber

interaction between coeval mafic and felsic melts in the st francois terrane of missouri usa abstract in the eastern st francois mountains of missouri a 1 48 ga subvolcanic ring pluton known as the silvermine granite hosts swarms of dark pillow shaped enclaves exhibiting classical features of mafic melt globules trapped in granitic magma the pillows formed by turbulent injection of near liquidus mafic melt into a resident visco plastic granitic magma exchange of crystals fluids and ions between the two melts produced a hybrid tonalite granite enclave series and modified host granite composition several lines of evidence suggest interaction between granitic melt that produced the granophyric cap of the pluton and basaltic melt that formed dikes in the area rapid cooling of the pillows re melted the host creating back veins in many enclaves mineral chemistry indicates the hybrid rocks have undergone extensive subsolidus re equilibration

a numerical model for porosity modification at a sandstone mudstone boundary by quartz pressure dissolution and diffusive mass transfer in many sandstones quartz cements significantly reduce porosity the origin of these cements is often unclear this paper investigates a possible mechanism for the generation of silica for quartz cement by pressure dissolution in interbedded mudstones theoretical models of quartz pressure dissolution including the effects of silica precipitation kinetics show that the concentration of dissolved silica in the pore fluids of a compacting sediment increases with decreasing grain size and silica precipitation constant quartz precipitation is strongly inhibited by the presence of small amounts of clay within a sediment suggesting that siltstones and quartz rich mudstones which are undergoing pressure dissolution may act as a source of dissolved silica for export to nearby coarser sediments a computational model for the diagenetic modification of a sandstone mudstone interface due to pressure dissolution is described both sandstone and mudstone layers are assumed to be actively compacting by pressure dissolution and mass transport by molecular diffusion is considered as quartz precipitation in the mudstone layer is relatively slow compared to that in the sandstone significant amounts of dissolved silica become available in the mudstone and may be exported into the adjacent sandstone in the absence of pore fluid advection this may result in the formation of extensive secondary quartz within the sandstone close to the interface the volume of silica exported from the mudstone is limited by the length scale over which diffusion through the mudstone is effective this is typically 3 5 m the volume of silica available therefore suggests that extensive porosity modification within the adjacent sandstone can only occur close to the mudstone thus it is possible that thin sandstones could become cemented by slow diffusive transfer of silica but that in thicker sandstones the silica may become dispersed by pore fluid advection

interactions between basaltic and granitic magmas in a svecofennian postorogenic granitoid intrusion aland southwest finland abstract the lemland intrusion is one of four postorogenic 1815 1770 ma granitoid intrusions occurring in southwestern finland the intrusions are dominated by porphyritic granite and basic intermediate rocks they show features of a bimodal magmatism causing net veining and formation of mixed rocks the current investigation of the southern part of the lemland intrusion reveals that the basic intermediate rocks form a ring like structure in which the rocks can be divided in three tentative units 1 fine grained mafic pillows in porphyritic granite 2 mixed rocks with mafic inclusions in a hybrid matrix and 3 medium grained mafic rock it is suggested that the ring like structure with the different units was emplaced from a disrupted zoned magma chamber and the different rock units were created due to differences in chemical and physical properties of the magmas the process started with the intrusion of basic magma into overlying acid magma creating basic pillows within it during the upward movement the basic magma left behind an area where the basic and the acid magma were intimately commingled and mixed this mixed magma intruded into the area inside the mafic pillows which formed an isolated barrier against the cooler acid magma the medium grained mafic rock in the middle of the ring structure is regarded as the same rock as the fine grained mafic rock the coarser grain size depending on the longer time for crystallization this rock was back veined and brecciated by the mixed magma creating a mega breccia when this process ended the acid magma was still active and formed cutting dykes in the mafic and mixed rocks

origin of hybrid ferrolatite lavas from magic reservoir eruptive center snake river plain idaho the mineralogy and geochemical characteristics of intermediate composition ferrolatites and related lavas from the magic reservoir eruptive center central snake river plain have been investigated to evaluate the origin and petrologic significance of these hybrid lavas the ferrolatites are chemically uniform but contain a disequilibrium phenocryst xenocryst assemblage derived in part from mixed rhyolitic and basaltic magmas that are closely represented by extrusive units in the area the hybrid lavas also contain xenoliths of archean granulites and have high 87sr 86sr and low 143nd 144nd ratios all of which suggest significant magma crust interaction quantitative models including magma mixing minor crystal fractionation and crustal contamination very closely reproduce the observed compositions of these ferrolatites closed system fractionation and or simple bulk contamination models are not as successful and can be ruled out it appears that preexisting mafic and silicic magmas from distinct sources e g mantle and crust encounter one another in crustal level magma chambers under conditions where intimate mixing may occur despite wide differences in the physical properties of these liquids

petrogenetic interpretation of granitoid rock series using multicationic parameters abstract granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la roche and his coworkers this shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors these suggest that most granitoid series result from a two stage process first fractional crystallisation of clinopyroxene olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition this magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series

the use of a resemblance function in the measurement of climatic parameters from the physiognomy of woody dicotyledons abstract wolfe compiled a data set clamp of the physiognomy of woody dicotyledon leaves with a view to using it to extract climatic information from fossil floras attempts made using these data to identify and describe the relationship between plant physiognomy and climate have all searched for a global relationship applicable throughout data space we investigate the possibility that the relation between climate and physiognomy is so non linear that only local relationships should be sought we use a resemblance function to select sites that are physiognomically similar to each unknown site these similar sites alone yield a climatic estimate for the unknown site data collected from new zealand and australia are then added to wolfe s data set in order to test this new method we show that the use of a resemblance function enables us to produce mean annual temperature estimates for all modern sites that lie within 2 6 c of meteorological data for 90 of the sites this method also allows the objective identification of outliers based on their distance in physiognomic space from their nearest neighbours when a method is used that searches for a global relationship between physiognomy and climate the misfit of estimated mean annual temperature for the combined southern hemisphere and clamp sites is almost twice as great 5 c as that to the clamp sites alone in contrast when the resemblance function is used the rms misfit of estimated mean annual temperature increases by only 0 2 c this result demonstrates the robustness of the new method

thrust and fold tectonics and the role of evaporites in deformation in the western kuqa foreland of tarim basin northwest china the kuqa foreland between the tarim basin and the tianshan mountains is rich in oil and gas based on field work and seismic profiles the structural styles and their formation mechanisms were determined and the role of evaporites in the deformation was demonstrated the main structural styles in the overburden are detachment folds large scale nappes triangle zones gentle and wide synclines fault propagation folds and pop ups the main structures in the substrate are small scale thrust faults duplexes pop ups and fault bend and fault propagation folds and formed mainly at the end of the pliocene under north south compression the evaporite layer in the lower section of the paleogene is the decollement zone for the disharmonic deformations in the overburden and in the substrate the detachment along the evaporite layer made it possible for compressive stresses to be transmitted farther in the overburden than in the substrate deformation in the overburden is more extensive than in the substrate at the leading edge of deformation at the trailing edge of deformation the structural highs in the overburden closely correspond to those in the substrate which is of significance for petroleum exploration in the western kuqa foreland

a late miocene subtropical dry flora from the northern altiplano bolivia abstract a variety of evidence suggests that the altiplano of the central andes the second highest and largest plateau on earth underwent significant uplift in the late miocene pliocene the most important datum supporting recent uplift is a collection of the 10 66 0 06 ma jakokkota flora from west central bolivia which implies a paleoelevation no more than 1600 1200 m today the site has an elevation of almost 4000 m in order to test the reliability of this estimate the present study analyzes a new collection of the jakokkota flora from a lacustrine unit that is 0 2 0 5 myr younger than the previously analyzed collection from a fluvial unit climate estimates based on leaf morphology for the two collections are statistically indistinguishable the combined flora has a mean annual temperature of 21 5 2 0 c and a mean annual precipitation of 550 180 mm the similarity of the climate estimates for the two floras suggests that there was not a significant climate change between them nor a significant bias in the leaf morphology due to differing taphonomic processes the climate estimate for the combined flora thus presents a representative picture of the late miocene climate of the northern altiplano if one assumes that the climate of the tropics has not changed significantly since the late miocene as is suggested by marine isotopic data then the paleoclimate of the jakokkota flora implies a paleoelevation of 1160 600 m thus the jakokkota flora supports the hypothesis of a young age for the altiplano

composite minor intrusions as windows into subvolcanic magma reservoir processes mineralogical and geochemical evidence for complex magmatic plumbing systems in the british tertiary igneous province the rudh a chromain sill is a composite minor intrusion emplaced into jurassic sandstones on the south coast of the ross of mull nw scotland and is part of a suite of basic silicic sheets associated with the early development of the 58 56 ma mull central igneous complex new whole rock major and trace element data combined with sr nd pb isotope data indicate that two distinct magma end members were involved in the formation of the sill a tholeiitic basaltic andesite magma generated by contamination and fractional crystallization of regionally available olivine tholeiite basaltic magma and a rhyolitic magma produced predominantly through crustal melting of basement metasediments intermediate compositions at the gradational boundaries between the basic margins and silicic interior of the sill formed by high temperature diffusive hybridization within a compositionally zoned magma reservoir prior to sheet emplacement the basic portions of the sheet are replete with a large variety of crustal xenoliths as well as numerous gabbroic and noritic cumulate fragments the rudh a chromain sill therefore preserves evidence for the complex interplay between a number of magmatic processes which when combined with data from the remainder of the suite suggests that the magmatic plumbing system which fed the sill complex was not simply one large long lived magma chamber but rather a plexus of variably connected sheet like magma reservoirs

impact of regional variation in detrital mineral composition on reservoir quality in deep to ultradeep lower miocene sandstones western gulf of mexico abstract future exploration in lower miocene sandstones in the gulf of mexico will focus increasingly at depths greater than 4 5 km and reservoir quality will be a critical risk factor in these deep to ultradeep reservoirs the goal of this study was to understand the variation in reservoir quality of lower miocene sandstones across the western gulf of mexico to do this we examined regional variation in detrital mineral composition diagenesis and reservoir quality in five areas 1 louisiana 2 upper texas coast 3 lower texas coast 4 burgos basin mexico and 5 veracruz basin mexico using petrographic and petrophysical data from depths of 0 9 7 2 km there are strong variations in mineralogical composition within the study area lower miocene sandstones from offshore louisiana have an average composition of quartz 86 feldspar 12 and rock fragments 2 q 86 f 12 r 2 feldspar and rock fragment content increase southward as source areas shifted to include volcanic and carbonate rocks composition of samples from offshore texas ranges from q 67 f 24 r 9 in the upper texas coast to q 58 f 24 r 19 in the lower texas coast lower miocene sandstones from the onshore burgos basin northern mexico have an average composition of q 54 f 22 r 23 whereas sandstones from the veracruz basin southern mexico contain the highest proportion of rock fragments q 33 f 12 r 55 main diagenetic events in quartz rich lower miocene sandstones in louisiana were mechanical compaction and precipitation of quartz cement compactional porosity loss increased to the south with increasing rock fragment content calcite is the most abundant cement in the south and is strongly related to reservoir quality loss at moderate burial depths the best reservoir quality occurs in quartz rich sandstones in louisiana and decreases with increasing lithic content in texas and mexico porosity is higher in louisiana and upper texas than in lower texas and mexico at all depths and temperatures but at depths 5 km and temperatures 175 c porosity differences are lessened the lower miocene sandstone trend in the western gulf of mexico from louisiana to mexico is an example of the importance of variation in detrital mineralogy as a control on diagenesis and reservoir quality

the effect of grain coating microquartz on preservation of reservoir porosity clay coatings have been widely accepted by many workers as an explanation for preserving high porosity in deeply buried sandstones but few workers have realized that similar effects can be produced by microcrystalline quartz coatings this phenomenon can be expected only under special circumstances but in such cases it can have profound consequences for exploration in the central graben area of the southern north sea unusually high porosity 20 27 and permeability 100 1000 md are found in certain zones in upper jurassic sandstones at depths of 3 4 4 4 km the porosity in these zones is 5 15 higher than expected based on average porosity depth trends from brent and haltenbanken sandstones we propose that the high porosity is due to continuous grain coatings of euhedral microcrystalline quartz crystals that are 0 1 2 m thick the distribution of microcrystalline quartz coatings is controlled by the presence of siliceous sponge spicules rhaxella which implies a sedimentological control on the reservoir quality we present a thermodynamic model showing how continuous microcrystalline quartz coatings inhibit development of no mal macrocrystalline quartz overgrowths sourced mainly from stylolites high porosities in parts of various upper jurassic oil fields ula and gyda have previously been explained by inhibition of quartz cementation by early hydrocarbon charge we suggest that the microcrystalline quartz coatings provide a more plausible explanation

magmatic evolution of the skye igneous centre western scotland modelling of assimilation recharge and fractional crystallization the skye igneous centre forming part of the british tertiary magmatic province developed over a 7 myr period 61 54 ma and is characterized by a complex suite of lavas hypabyssal and intrusive rocks of picritic to granitic composition the intrusion of magma from mantle to crust at 2 10 3 km 3 yr 6 mt yr advected magmatic heat of roughly 0 2 gw averaged over the period of magmatism supporting an excess heat flux of about 130 mw m 2 or about twice the present day average continental heat flow the volume of new crust generated at skye 15 000 km 3 spread over the present day area of skye corresponds to 9 km of new crust the geochemical evolution of the skye magmatic system is constrained using the energy constrained recharge assimilation and fractional crystallization ecrafc model to understand variations in the sr and pb isotopic and sr trace element composition of the exposed magmatic rocks with time the character composition and specific enthalpy of both assimilant and recharge magma appears to change systematically up section suggesting that the magma reservoirs migrated to progressively shallower levels as the system matured the model of the magma transport system that emerges is one in which magma batches are stored initially at lower crustal levels where they undergo rafc evolution residual magma from this stage then migrates to shallower levels where mid crustal wall rock is assimilated the recharge magma at this level is characterized by an increasingly crustal signature for some of the stratigraphically youngest rocks the data suggest that the magma reservoirs ascended into and interacted with upper crustal torridonian metasediments

the loch scridain xenolithic sill complex isle of mull scotland fractional crystallization assimilation magma mixing and crustal anatexis in subvolcanic conduits

artificial neural networks reveal a high resolution climatic signal in leaf physiognomy the relationship linking leaf physiognomy and climate has long been used in paleoclimatic reconstructions but current models lose precision when worldwide data sets are considered because of the broader range of physiognomies that occur under the wider range of climate types represented our aim is to improve the predictive power of leaf physiognomy to yield climate signals and here we explore the use of an algorithm based on the general regression neural network grnn which we refer to as climate leaf analysis with neural networks clann we then test our algorithm on climate leaf analysis multivariate program clamp data sets and digital leaf physiognomy dlp data sets and compare our results with those obtained from other computation methods we explore the contribution of different physiognomic characters and test fossil sites from north america the clann algorithm introduced here gives high predictive precision for all tested climatic parameters in both data sets for the clamp data set neural network analysis improves the predictive capability as measured by r 2 to 0 86 for mat on a worldwide basis compared to 0 71 using the vector based approach used in the standard analysis such a high resolution is attained due to the nonlinearity of the method but at the cost of being susceptible to 39 noise 39 in the calibration data tests show that the predictions are repeatable and robust to information loss and applicable to fossil leaf data the clann neural network algorithm used here confirms and better resolves the global leaf form climate relationship opening new approaches to paleoclimatic reconstruction and understanding the evolution of complex leaf function

sr isotope variations in a composite sill crystal liquid processes and the origin of the skye granites sr isotope data from the rubh an eireannaich sill one of a suite of composite mafic silicic minor intrusions associated with the 59 ma skye intrusive centre nw scotland indicate that both crystal liquid fractionation and magma mixing processes have played important roles in its genesis the data indicate that two distinct magmas were involved in the formation of the sill a ferrobasaltic andesite magma generated by contamination and fractional crystallization of regionally available basaltic magma and a rhyolite magma which has a significant crustal component hybrid intermediate compositions at the gradational boundaries between the mafic and silicic components of the sill formed by mixing prior to or during emplacement whilst fractional crystallization of the unmixed silicic magma occurred almost exclusively after mixing the identification of a significant crustal component within the silicic portion of the sill suggests that the compositionally related granites of the skye intrusive centre have a similar origin

geochemical evidence for coal derived hydrocarbons and their charge history in the dabei gas field kuqa thrust belt tarim basin nw china abstract large to middle scale thrust structures are important reservoir plays for coal derived hydrocarbons in the foreland basins of nw china with both gas and some accompanying oil in the dabei gas field of the kuqa thrust however the oil and gas pools are vertically distributed in a quite unique way 1 liquid oil and some dissolved gas are present in the dawanqi anticline with the reservoir at 300 700 m depth forming the only oil field in the kuqa thrust 2 gas and minor accompanying oil are found in the deep reservoir of the dabei 1 and dabei 2 thrust traps around 5000 6000 m depth 3 an extremely dry gas pool is found in the dabei 3 thrust trap where the depth of the reservoir is over 7000 m geochemical data suggest that the hydrocarbons in the dawanqi anticline and the dabei thrust traps originated from a similar source i e the underlying jurassic coal measures with some contribution from jurassic lacustrine shales the jurassic source rocks did not start to generate oil until the miocene around the kangcun stage and extended into the pliocene the kuche stage with the main gas generation period in the pliocene the kuche stage and the quaternary because the traps formed relatively early the dabei 1 and dabei 2 thrusts could trap some of the early generated oils but most of the early charged oil was redistributed to the shallower dawanqi anticline during the kuche stage the dabei 3 thrust trap formed concurrently with major gas generation and thus could not trap liquid hydrocarbons the difference in the vertical distribution of the hydrocarbon accumulations in the dabei gas field resulted from a complex interplay of source variability structural evolution of the basin and thermal maturation

petroleum geology of kela 2 the most productive gas field in china abstract the kela 2 gas field located in the kuqa depression of tarim basin is the most productive gas field in china based on per unit surface acreage the gas trap is a subsurface anticline formed along an e w trending thrust belt in front of the southern tianshan mountains the gas pay zones are located in fine grained sandstones of a fan delta front facies in the lower cretaceous bashijiqik formation k l bs and eogene evaporitic rocks serve as regional cap rocks the gases were derived primarily from over mature jurassic coal measures peak gas generation and final shaping of the kela 2 structure occurred relatively late in the late himalayan orogeny 5 0 ma thrust faulting appears to have played a significant role in the hydrocarbon generation migration accumulation and preservation in this foreland basin detailed delineation of the kela 2 gas field indicates that high quality regional cap rocks are essential for the formation of the super rich abnormally pressured giant gas fields while buried anticlines under the overthrust zone are the favorable gas habitat late gas accumulation is considered to be decisive for the conservation of the giant gas fields

salt structures and hydrocarbon accumulations in the tarim basin northwest china the tarim basin is one of the most important hydrocabon bearing evaporite basins in china four salt bearing sequences the middle and lower cambrian the mississippian the paleogene and the neogene have various thickness and areal distribution they are important detachment layers and intensely affect the structural deformation in the basin the kuqa depression is a subordinate structural unit with abundant salt structures in the tarim basin salt overthrusts salt pillows salt anticlines salt diapirs and salt withdrawal basins are predominant in the depression contraction that resulted from orogeny played a key function on the formation of salt structures growth strata reveal that intense salt structural deformation in the kuqa depression occurred during the himalayan movement from oligocene to holocene with early structural deformation in the north and late deformation in the south growth sequences also record at least two phases of salt tectonism in the yingmaili tahe and tazhong areas low amplitude salt pillows are the most common salt structures and these structures are commonly accompanied by thrust faults the faulting and uplifting of basement blocks controlled the location of salt structures the differences in the geometries of salt structures in different regions show that the thickness of the salt sequences has an important influence on the development of salt cored detachment folds and related thrust faults in the tarim basin salt sequences and salt structures in the tarim basin are closely linked to hydrocarbon accumulations oil and gas fields have been discovered in the subsalt intrasalt and suprasalt strata salt deformation has created numerous potential traps and salt sequences have provided a good seal for the preservation of hydrocarbon accumulations large and small scale faults related with salt structures have also given favorable migration pathways for oil and gas when interpreting seismic profiles special attention needs to be paid to the clastic and carbonate interbeds within the salt sequences because they may lead to incorrect structural interpretation in the tarim basin the subsalt anticlinal traps are good targets for hydrocarbon exploration

quantitative palaeoclimate estimates from late cretaceous and paleocene leaf floras in the northwest of the south island new zealand three new plant macrofossil assemblages were collected from late cretaceous and paleocene fluvio lacustrine sediments of the pakawau and kapuni groups in the northwest of the south island new zealand palaeoenvironmental interpretations were made from each locality and palaeoclimate was deduced from the dicotyledonous angiosperm leaf component of each flora a latest cretaceous pakawau bush road locality flora yielded 58 different dicotyledonous leaf forms the two paleocene collections ian s tip and pillar point track included 23 and 28 dicotyledonous leaf forms respectively quantitative palaeoclimate estimates were obtained using both leaf margin analysis lma and the climate leaf analysis multivariate program clamp temperature estimates suggest that there was a slight cooling from the latest cretaceous into the early paleocene in the northwest nelson region of new zealand supporting similar southern hemisphere palaeoclimate findings from antarctic data consistency in temperature estimates using different methods including lma multivariate leaf morphological analysis clamp oxygen isotope data regional versus local studies and global palaeoclimate models suggests that the mean annual temperature for the pakawau region in the latest cretaceous was between 12 and 15 c lma produced temperature estimates between 6 5 and 8 c for the two paleocene assemblages whereas clamp produced estimates were slightly higher between 9 and 12 5 c 2002 elsevier science b v all rights reserved

cenozoic uplift of the central andes in northern chile and bolivia reconciling paleoaltimetry with the geological evolution the cenozoic geological evolution of the central andes along two transects between 17 5 s and 21 s is compared with paleo topography determined from published paleo altimetry studies surface and rock uplift are quantified using simple 2 d models of crustal shortening and thickening together with estimates of sedimentation erosion and magmatic addition prior to 25 ma during a phase of amagmatic flat slab subduction thick skinned crustal shortening and thickening nominal age of initiation 40 ma was focused in the eastern and western cordilleras separated by a broad basin up to 300 km wide and close to sea level which today comprises the high altiplano surface topography at this time in the altiplano and the western margin of the eastern cordillera appears to be 1 km lower than anticipated from crustal thickening which may be due to the pull down effect of the subducted slab coupled to the overlying lithosphere by a cold mantle wedge oligocene steepening of the subducted slab is indicat

why do foliar physiognomic climate estimates sometimes differ from those observed insights from taphonomic information loss and a clamp case study from the ganges delta abstract palaeoclimate estimates derived from plant based proxies are potentially subject to uncertainties arising from taphonomic filtering in any given fossil assemblage it is possible to identify the kinds of likely taphonomic influences but virtually impossible to quantify the uncertainties they introduce because filtering removes information because that information is missing it cannot be measured an alternative approach is to measure the maximum uncertainty possible due to specific information loss within recognised analytical protocols in respect of the multivariate foliar physiognomic technique known as clamp climate leaf analysis multivariate program we have attempted to do this by experimentally degrading both the character state scores and the number and composition of taxa as subsets of the full range of character states and taxonomic diversity in the source vegetation in this study a stand of protected vegetation on green island 23 08 58 n 88 26 59 19 e within the ganges delta was sampled following standard clamp protocols the island is subject to annual flooding during the monsoon season and is typical of the kinds of naturally disturbed vegetation likely to be represented in ancient delta floodplain assemblages a total of 56 woody dicot taxa were scored in the living vegetation from this complete sample leaf character states for lobing margin size apex base length to width ratio and shape were removed in turn from all 56 taxa to give 7 analyses simulating worst case taphonomic loss of physiognomic data ten subsets of 20 randomly selected taxa were also analysed to simulate taphonomic diversity loss of almost two thirds of the potentially available taxa in the source vegetation in all cases the completeness statistic remained above the clamp recommended minimum of 0 66 the results show that in all cases the uncertainties arising from taphonomic processes either through taphonomic diversity or character state filtering were not significantly different from the statistical clamp uncertainties associated with the most commonly used calibration dataset physg3brc and gave similar climatic estimates as the source vegetation in its entirety this suggests that stratigraphically well constrained museum collections lacking detailed sedimentary or taphonomic context can still be used with confidence for clamp analyses leaf margin analysis displayed a greater sensitivity to diversity loss the green island estimates suggested a cooler moister climate than that indicated by the observed regional climate as derived from a 0 5 0 5 gridded data set used in climate modelling evaluation the likely cause for this disparity is the prevalence of a sub canopy microclimate signal developed by the vegetation itself and this is strongly dependant on the temperature and humidity characteristics of the regional climate as well as the proximity to water bodies within the sample size limitations of this study this disparity is larger than that introduced by taphonomic processes but potentially can be corrected for

differential uplift of the chinese tianshan since the cretaceous constraints from sedimentary petrography and apatite fission track dating the chinese tianshan is one of the important international natural laboratories for studying continental geodynamics but its uplift time kinematics and mechanism of formation are key unresolved questions in order to constrain the timing kinematics and mechanism of uplift of the chinese tianshan we applied sedimentary petrography and apatite fission track dating to cretaceous tertiary series from the northern tarim basin and the tianshan mountains we collected and analyzed 79 sandstone samples and 75 detrital heavy mineral samples from the kezilenuer kuqa profile northern tarim basin with a well defined magnetostratigraphy our data indicate that detrital mineral maturity abruptly decreased at the disconformity between the upper and lower cretaceous and decreased again after 15 12 ma the sediments in the northern tarim basin changed their provenance at 124 ma 26 24 ma and 15 12 ma respectively in addition we collected and analyzed 36 primary apatite samples from the south central and north tianshan our results show that the chinese tianshan underwent three phases of differential uplift the first phase of uplift started at the southern central tianshan during the early cretaceous and propagated southward the second phase of uplift started at the northern central tianshan during the late cretaceous and propagated also southward the third phase of uplift started at the northern central tianshan during the eocene and propagated both northward and southward these differential uplifts have caused development of disconformity and drops in mineral maturity of detrital sediments in the northern tarim basin such a differential and heterogeneous uplift process might have been trigged by collisions of different microcontinents i e lhasa kohistan dras and india at the southern margin of asia these collisions reactivated the south tianshan fault and then the north tianshan suture and uplifted the chinese tianshan step by step

geochemical evolution of the tertiary mull volcano western scotland the early tertiary mull volcano western scotland is one of the most dissected and best exposed igneous complexes of the north atlantic province the new and published geochemical data enable us to chart the magmatic evolution of the mull volcano from the oldest lavas through the intrusive rocks of three overlapping igneous centres to the youngest dykes in this study we identify four successive magma types within the remnant volcano the earliest type the mull plateau group comprises mildly alkaline basaltic rocks with steep chondrite normalized rare earth element ree patterns this type is succeeded within the lava succession and dyke swarm by the coire gorm magma type with essentially flat chondrite normalized ree patterns a third magma type represented within the lava and dykes the central mull tholeiites is more depleted in incompatible trace elements than the preceding types and has flat to lree depleted chondrite normalized patterns the major intrusions and cone sheets of mull centre 1 and early centre 2 belong to this magma type midway through the igneous activity associated with centre 2 the magma type changed to become more alkalic and more enriched in incompatible trace elements this magma type the late mull type is found to persist through the cone sheets and major intrusions of centre 3 to the youngest dykes these changes in magma composition were related to variations in the mantle source and depth of partial melting beneath mull and or differences in the efficiency of melt pooling before ascent through the lithosphere with the exception of the early staffa magma sub type part of the mull plateau group the location of magma chambers in which the bulk of contamination occurred changed with time from deep lower crustal lewisian gneiss to shallow upper crustal moine schist intermediate members of the plateau group and the late mull magma type are enriched in fe ti and p relative to the central mull tholeiites we attribute this difference to the more alkalic nature of these suites lower fo2 and the formation of fe3 p complexes in the magma the intermediate rocks were important in magma mixing processes with two types of mixing identified on mull 1 cryptic mixing between basalts and low fe intermediate magmas typified by lavas and early basic cone sheets of the central mull tholeiite magma type 2 observable mingling between rhyolitic magmas and high fe intermediate magmas of the late mull type shown by the mixed magma bodies of the glen more and loch ba ring dykes the main factor in determining which type of mixing occurred appears to have been the density contrast between the various magmas it may safely be maintained that mull includes the most complicated igneous centre as yet accorded detailed examination anywhere in the world bailey et al 1924 memoir of the geological survey of great britain scotland hmso edinburgh 1924

magma mixing the marsco suite isle of skye scotland magma mixing has been proposed as a major mechanism for the origin of a wide variety of rock suites in mid ocean basalts there are few obstacles to mixing because of the similarities in chemical and physical properties of the proposed end members however in calc alkaline rocks the proposed end members have disparate properties and these present obstacles to mixing

mean annual temperature estimation based on leaf morphology a test from tropical south america abstract are models that predict mean annual temperature mat from leaf morphology applicable globally fifteen models that predict mat from leaf morphology were tested on thirty floral samples from tropical south america to determine the degree to which models based on published data that are primarily from other regions are applicable to floras from tropical south america the models included are based on regional data from north america south america and asia of the fifteen models tested five are simple linear regressions six are multiple linear regressions two are canonical correspondence analyses and two are correspondence analyses followed by nearest neighbor analyses for the seven modern floras with mat 21 c every model overestimates mat for the 23 modern floras with mat 21 c all models produce variable results without a systematic error the range of average model errors is 2 7 7 3 c while the absolute extremes of error are 0 and 15 1 c average 95 predictive confidence intervals range from 1 6 to 6 9 c predicted mat falls within the published standard error of the model for 0 67 of the south american test floras evaluating the seven sites with mat 21 c separately from the 23 sites with mat 21 c shows that no equation accurately estimates mat of the majority of low temperature sites but that four equations accurately estimate 50 of high temperature sites the results suggest that at least for sites of unknown or high elevation mean annual temperature of fossil floras from tropical south america may be better predicted from models based on the leaf morphology of tropical south american floras

sedimentary and volcano tectonic processes in the british paleocene igneous province a review research on the british paleocene igneous province bpip has historically focused on the emplacement chemistry and chronology of its elaborate central intrusive complexes and lava fields however the bpip has also been dramatically shaped by numerous erosion sedimentation and volcano tectonic events the significance of which becomes ever clearer as localities in the bpip are re investigated and our understanding of volcano sedimentary processes advances the resultant deposits provide important palaeo environmental palaeo geographical and stratigraphical information and highlight the wide range of processes and events that occur in ancient volcanic settings such as the bpip in this paper we review the sedimentary and volcano tectonic processes that can be distinguished in the bpip and conceptualize them within a generalized framework model we identify and describe the sedimentary responses to four broadly chronological stages in the history of the bpip volcanoes 1 the development of the lava fields 2 early intrusion induced uplift 3 caldera collapse and 4 post volcano denudation and exhumation of central complexes we highlight and illustrate the range of sedimentary processes that were active in the bpip these operated on and helped shape a dynamic landscape of uplands and lowlands of alluvial fans braided rivers lakes and swamps and of volcanoes torn apart by catastrophic mass wasting events and or caldera collapse

pre eruptive magma mixing in ash flow deposits of the tertiary rum igneous centre scotland the northern marginal zone of the rum igneous centre is a remnant of an early caldera and its infill it is composed of intra caldera breccias and various small volume pyroclastic deposits overlain by prominent rhyodacite ash flow sheets of up to 100 m thickness the ash flows were fed from a feeder system near the caldera ring fault and intrusive rhyodacite can locally be seen grading into extrusive deposits a variety of features suggest that the ash flows were erupted from a magma chamber that contemporaneously hosted felsic and mafic magmas i chilled basaltic inclusions in rhyodacite ii formerly glassy basaltic to andesitic enclaves with fluid fluid relationships iii feldspars with thick reaction rims enclosed in the basaltic to andesitic inclusions yet with cores chemically resembling those of the rhyodacite iv trace element compositions of the rhyodacite and the mafic enclaves form a mixing line between the end member rhyodacite and basalt compositions additionally textural and chemical features in the rhyodacite feldspar phenocrysts are consistent with magma mixing v feldspars with resorption embayments cutting through internal zonation of the crystals vi complexly zoned crystals with sieve textured zones that are overgrown with euhedral zones vii oscillatory zonation of feldspar phenocrysts in the rhyodacite showing sharp increases in anorthite an 10 followed by gradual decrease in an content an 4 this evidence points to eruption of ash flows from a felsic magma chamber that was periodically replenished by injection of mafic magma diffusional mixing between the two magmas was permitted by temperature and compositional differences but was slow due to the contrast in viscosities and densities the fe ti p enriched basic magma that replenished the chamber was degassing on entering the lower temperature environment and soon equilibrated thermally followed by chemical exchange between the two end member magmas this process formed hybrid andesite enclaves enriched in trace elements beyond that caused by simple mixing implying trace element diffusion in addition to bulk mixing eruption was caused by replenishment with and degassing of the basic magma and the chamber partially evacuated while the process of hybridisation was underway the erupted products record magma mixing by chamber replenishment blending of two magmas and elemental exchange in the magma chamber and also physical mingling in the eruptive conduit

molecular organic geochemistry of the tarim basin northwest china we conducted organic geochemical analyses on the largest suite of oils and source rock extracts from the tarim basin northwest china currently available statistical cluster analysis of the entire suite of tarim oils distinguishes at least seven genetic groups of oils the largest group of oils was collected from the tazhong and tabei uplifts and originated from marine middle upper ordovician anoxic marls that mark slope facies at the margins of structural uplifts two other genetic groups most likely originated from marine middle upper ordovician source rocks but of distinct facies with one an oxic shale rich source west of the bachu uplift and the other an anoxic shale source at tazhong

fracture detection in oil based drilling mud using a combination of borehole image and sonic logs abstract the deeply buried 5 5 7 1 km lower cretaceous bashijiqike sandstones are important fractured reservoirs in the kuqa depression in these high temperature high pressure drilling environments oil based muds are used to limit drilling risks and improve efficiency making facture detection using resistivity based image logs difficult the maximum horizontal stress sh max trends close to north south 0 10 based on orientations of the drilling induced fractures and borehole breakouts core descriptions thin sections and image logs used to describe the fractures in the bashijiqike sandstone reservoirs show that opening mode natural fractures are common and the fractures range from fully open to sealed by calcite and clay minerals the open fractures are dominantly steeply dipping or vertical and primarily strike north south locally horizontal fractures or fractures with low angle dip are detected we compare fracture visibility on image logs acquired in the same ks 2 2 12 key well in oil based mud and water based mud fmi hd logs successfully detect large 0 1 mm aperture vertical fractures in oil based mud better than obmi image logs and the two imaging tools have a similar ability in detecting the high dip angle fractures since the ubi tool is not affected by oil based muds most of the fractures can be picked out on ubi images minor negative deviations of bulk density could be observed in fractured zones and the presence of fractures obviously causes an increase in sonic transit time full waveforms from dsi tools combined with electrical image logs detect fractured zones both the velocity and amplitude of the sonic waves are sensitive to fractures and the fractured zones could be identified according to the attenuation of stoneley waves the combination of cores image logs and full wave sonic logs offers comprehensive detection of fractures in oil based mud environments

the relationship between leaf physiognomy and climate based on a large modern dataset implications for palaeoclimate reconstructions in china abstract in this paper correlation between modern leaf physiognomy and climate in china are examined to optimize the use of leaf characters as a palaeoclimate proxy a large dataset was compiled recording the distribution of leaf physiognomic characters among 3166 native dicot trees species across 732 calibration grids on a county level grids span a range of ecological environments tropical rainforests to alpine shrubs across humid areas thirteen climatic parameters were included for each grid and 22 leaf physiognomic characters were scored for each tree species the correlation between leaf physiognomic characters and climatic parameters were calculated based on single linear regressions slr and multiple linear regressions mlr results indicate clear spatial distribution patterns linked to latitude exist for all leaf characters with temperature coldest month mean temperature cmmt and precipitation growing season precipitation gsp being the main climate controls moreover because leaf characters are more closely correlated with precipitation during the three wettest consecutive months p3wet rather than with precipitation during the three driest consecutive months p3dry seasonal variations in rainfall associated with the asian monsoon might especially influence leaf physiognomic characters closer correlations between leaf physiognomy and climate are seen using mlr compared with slr therefore mean annual temperature mat and mean annual precipitation map based on mlr equations provide the most promising basis for palaeoclimate reconstructions in china

deriving temperature estimates from southern hemisphere leaves abstract the percentage of woody dicots with entire margined leaves in a flora is known to be positively correlated with mean annual temperature leaf margin analysis lma but this relationship is not globally uniform in particular the floras of australia and new zealand have been regarded as displaying a different physiognomic relationship to climate than floras seen in the northern hemisphere this difference is more marked in new zealand where the lma relationship appears entirely absent here we amass data for both northern and southern hemispheres using standard protocols and show that regional variations in the leaf margin mean annual temperature relationship are real but become less significant when other characters are included even new zealand falls into line and most of the mean annual temperature signal in new zealand floras is encoded in non margin features we introduce a new clamp climate leaf analysis multivariate program calibration dataset for the southern hemisphere comprising leaf physiognomic data from argentina bolivia south africa australia new zealand and other pacific islands that offers comparable precision for climate prediction to similar datasets derived from the northern hemisphere

refining clamp investigations towards improving the climate leaf analysis multivariate program clamp climate leaf analysis multivariate program has been used for the past 17 years to estimate palaeoclimatic conditions the reliability and applicability of this method based on leaf physiognomic characters of fossil woody dicots has been widely discussed over the same period the present study focuses on some technical aspects of clamp mainly on its robustness in the context of the theoretical unimodal requirements of canonical correspondence analysis and introduces correction coefficients for these aspects of the statistical approach as a new way of interpreting and improving on clamp estimates this tool was tested on datasets derived from 17 european fossil floras ranging in age from the late oligocene to the pliocene additionally an objective statistical method for the selection of the best suited modern vegetation dataset from 144 site physg3br or 173 physg3ar extant biotopes is proposed

replenished magma chambers effects of compositional zonation and input rates several recent publications have reported investigations of the dynamical effects and geological consequences of the replenishment of a homogeneous magma chamber by the rapidinjection of hot relatively dense fresh magma the new magmaforms a separate layer at the base of the chamber whereit cools and crystallizes until the density of the residual liquid in the lower layer becomes equal to that of the upperlayer at which time the fluid in the two layers becomes intimately mixed the fluid dynamical aspects of this modelwere confirmed by laboratory experiments using aqueous solutions this paper reports three experimental variations on the basic theme which examine the effects of the rate of injection into homogeneous and compositionally stratified chambers first the rapid injection of a hot dense layer beneath a fluid with a lower temperature and a vertical compositional gradient is considered a series of layers gradually builds up from the base of the upper gradient region while the lower layer cools crystallizes and finally overturns in this situation however the rise of the lower layer fluid is restrained by the density gradient and mixing takes place with only part of the upper fluid second the slow influx of a hot dense liquid beneath a cold less dense homogeneous layer is considered a considerable quantity of the input fluid coolsand crystallizes immediately releasing some lighter fluid to mix with the fluid in the homogeneous layer with time some dense input fluid spreads along the bottom so that locally the situation is the same as the one considered in the previous studies with a local overturning occurring when the density of the lower fluid has decreased sufficiently the deposition of crystals continues and some rather fine chimney like structures can develop which bear a resemblance to the black smokers recently discovered on the sea floor third a combination of the first two variations is studied by the consideration of the slow influx of hot dense liquid beneath a uniformly cooler fluid with a vertical compositional gradient the input fluid is constrained in its rise by the density gradient as the influx continues the additional thermal energy is also confined and causes the crystals to redissolve and build up a lower layer as was observed in the case of a rapid injection beneath a compositional gradient

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

paleoclimatic estimates from tertiary leaf assemblages a primary obstacle to evaluating numerical modeling of tertiary nonmarine climates has been the significance and reliability of proxy data sloan barron 1990 lacking direct measurements of paleoclimatic parameters inferred paleoclimatic values are based on substitute proxy sources such as fossils or isotopes are proxy data significant that is have they been calibrated in modern environments and to what level is the calibration this is the problem of accuracy validity in the statistical sense second are the proxy data reliable can two workers or even the same worker consistently arrive at the same estimates using the same data set this is the problem of precision repeatability can these two problems be resolved quaternary palynologists have used the concept of transfer functions a methodology originally developed for foraminifera imbrie kipp 1971 applied in palynology a response surface for each palynomorph taxon is constructed for the environmental variables under consideration these transformations can then be subjected to a number of different kinds of multivariate analyses including ordination methodologies bartlein et al 1986 webb bryson 1972 these transfer functions can work for quaternary and especially the lateand post glacial of the last 20 to 30 thousand years pollen assemblages because in most regions where the methodology has been applied the flora is of known diversity and the equivalency of a given palynomorph species to one or a few extant species can be reasonably assumed even in the late neogene 1 5 to 10 million years ago however this assumption can no longer be made we know that the palynomorph assemblages contain exotic genera mccartan et al 1990 and the presence of exotic and or extinct species

sources of quartz grains influencing quartz cementation and reservoir quality in ultra deeply buried sandstones in keshen 2 gas field north west china abstract quartz cementation is a critical factor in the reservoir quality of ultra deeply buried sandstones because of the high temperature and high pressure at great depths therefore determining the main influences retarding the growth of the quartz overgrowths is important for predicting the sweet spots of tight gas sandstones the vast keshen 2 gas field in kuqa depression is typical of such ultra deep gas fields despite the porosity and permeability of the target sandstones in the lower cretaceous bashijiqike formation being less than 10 and 0 5 md respectively the main gas reservoirs had been buried previously to a depth of 7000 m with the maximum fluid temperature approaching 160 c in which authigenic quartz cements are extremely common the heterogeneity of the physical properties and quartz cementation was investigated using core analysis log interpretation thin sections and scanning electron microscopy sem the findings indicated that the bashijiqike formation could be stratified into upper porous and lower tight zones the porosity of the sandstones in the upper zone is generally higher than 5 and abundant polycrystalline quartz grains are present however the reservoirs in the lower zone with low overall porosity values below 5 contain high contents of monocrystalline quartz grains the polycrystalline quartz grains show brown cathodoluminescence that indicates mainly a metamorphic source from the southern tianshan provenance which is located to the north of keshen 2 the monocrystalline quartz grains display primarily blue to violet luminescence colours suggesting an origin from volcanic or plutonic mother rocks of the wensu and kuluketage provenance areas situated to the southwest and southeast respectively the monocrystalline quartz grains are surrounded commonly by quartz overgrowths whereas the polycrystalline quartz grains are cemented slightly the presence of polycrystalline quartz grains hampers potential quartz overgrowths the critical reason preserving the intergranular pores in the ultra deeply buried sandstones of this gas field accordingly we propose that the metamorphic quartz grain content is the main factor inhibiting quartz cementation which preserves reservoir quality this knowledge is conducive to determining the growing mechanism of high quality reservoirs and predicting the sweet spots of gas production in the ultra deeply buried sandstones

responses of two lithosomes of lower cretaceous coarse clastic rocks to tectonism in kuqa foreland sub basin northern tarim basin northwest china abstract coarse clastic rocks developed widely at foredeep adjacent to orogene were usually regarded as the mark of renewed thrusting action however a good example from the lower cretaceous in kuqa foreland sub basin illustrated that the coarse clastic rocks developed not only in initial thrusting stage but in early quiescence stage the kuqa foreland sub basin adjacent to the south tianshan orogene lies to the north of tarim basin northwest china the lower cretaceous outcrop in the front of south tianshan orogene was identified as a filling sequence of foredeep which includes two depositional cycles of kapushaliang group and bashijiqike formation each of them presents fining upwards and then coarsening upwards sequences two lithosomes of coarse clastic rocks developed in the lower of yageliemu formation of kapushaliang group and bashijiqike formation respectively both of them are mainly composed of thick bedded massive and chaotic conglomerate with debris flow microfacies of fan delta plain the analyses on stratigraphic and depositional records for tectonism revealed abrupt sedimentary change from delta facies to fan delta facies stratal geometry transformation and reflection termination migration of truncation and top lap between the kapushaliang group and the bashijiqike formation these records indicated that foredeep subsided rapidly while forebulge uplifted in the development of kapushaliang group which coincided perfectly with lithosphere deformation during thrusting stage foredeep uplifted rapidly while forebulge subsided in the later development of bashijiqike formation which coincided with lithosphere deformation during quiescence stage of foreland basin development therefore the lower cretaceous recorded a whole episode of foreland basin evolution from earlier thrusting to later quiescence the underfilled cycle of kapushaliang group corresponding to the thrusting stage is much thick with mainly muddy and silty sediments the overfilled cycle of bashijiqike formation corresponding to the quiescence stage is thin with mainly sandy sediments the two lithosomes of coarse clastic rocks were very similar with each other in the lithology and sedimentology however the one from lower yageliemu formation is responded to the renewed thrusting but the other from the lower bashijiqike formation is responded to the lithosphere rebounding during primary quiescence stage therefore cannot only coarse clastic rocks indicated a renewed thrusting

geochemistry origin and accumulation of continental condensate in the ultra deep buried cretaceous sandstone reservoir kuqa depression tarim basin china abstract a continental condensate field with the deepest burial depth 7084 m so far in china was recently discovered from the cretaceous sandstone reservoir in the bozi area of the kuqa depression tarim basin in this paper we report general features of this field including geochemistry of the condensates their origin and migration and accumulation general geochemistry of the condensate reflects that it is an over pressured condensate reservoir analytical results by newly developed high resolution gc gc tofms method indicate that the condensate is rich in n alkanes from nc 3 to nc 34 and in diamondoid hydrocarbons with a high content of adamantanes the condensate has a high abundance of aromatic hydrocarbons the gas 13 c 2 values in these are 23 3 which is characteristic of coal derived gases compared with the contents of conventional condensate oils the bz1 well has a high content of aromatic hydrocarbons suggesting that the condensate is in a stage of highly mature cracking analyses of oil biomarkers carbon isotopes gas compositions etc revealed that the condensate is dominantly sourced from the highly mature coals of the jurassic qiakemake formation in the western kuqa depression this set of coal source sequences has generated large quantities of condensate since 3 ma when the study area was subjected to a rapid subsidence with sediments over 2000 m and consequently attained at the condensate generating stage such condensates then migrated vertically into the cretaceous traps along faults therefore the bozi condensate field is a typical case of large scale oil gas field characterized by late stage accumulation multiple elements favor the formation of this large scale condensate field the timing of trap formation accords with that of the condensate generation since 3 ma the traps and source rocks are stacked vertically faults connect the source rock sequences and the reservoirs the hydrocarbon charge is strong and efficient thick paleogene gypsum beds act as an excellent cap rock favoring the accumulation and preservation of the condensate

deep burial diagenesis and reservoir quality evolution of high temperature high pressure sandstones examples from lower cretaceous bashijiqike formation in keshen area kuqa depression tarim basin of china the deep high temperature high pressure lower cretaceous bashijiqike sandstone buried to depths as great as 6 5 7 1km is an important natural gas reservoir in keshen gas field kuqa depression of the tarim basin reservoir quality is a critical risk factor in the development of these ultradeep reservoirs integrated approaches incorporating routine core analyses mineralogical petrographic and geochemical analyses have been used to investigate the diagenetic history of these rocks and their impact on reservoir quality with the aim to unravel the mechanisms for maintaining anomalously high porosities in sandstones that are buried to such a great depth these sandstones are dominantly fine to medium grained moderately to good sorted lithic arkoses and feldspathic litharenite most primary pores have been lost by mechanical compaction or carbonate cementation and the reduction of porosity by mechanical compaction was more significant than by cementation dissolution of framework grains contributed to the enhancement of reservoir quality eogenetic diagenetic alterations mainly include mechanical compaction precipitation of calcite cements and grain coating clays mesogenetic diagenesis is characterized by dissolution of framework grain by organic acids and subsequent precipitation of clay minerals and quartz infiltration of meteoric water related to teleodiagenesis would result in dissolution of the framework grains the meteoric leaching events during teleodiagenesis are of great importance for the bashijiqike sandstones grain coating clay minerals mixed layer illite smectite clays help to preserve porosity at depth by retarding quartz cementation and pressure solution the unique burial regime as early stage shallow burial with late stage rapid deep burial contributes to porosity preservation in eodiagenesis fluid overpressure caused by intense structural compression in the middle himalayan movement retarded compaction and helped preserve porosity in the late rapid deep burial stage anomalously high porosities are mainly found in medium grained good sorted sandstones with grain coating clays but with low clay and carbonate cement content of which the porosity is preserved primarily and enhanced secondarily the lowest porosities are associated with sandstones that are tightly compacted or cemented with carbonates or rich in detrital matrix porosity depth trends may vary significantly with lithofacies due to its differences in textural and compositional attributes five lithofacies are defined in terms of detrital composition and texture type and degree of diagenesis the reservoir quality prediction models of various lithofacies are constructed and the results of this study provide insights into mechanisms for maintaining anomalously high porosity and permeability in high temperature high pressure sandstone reservoirs and may help explain hydrocarbon distribution

effects of tectonic compression on petroleum accumulation in the kelasu thrust belt of the kuqa sub basin tarim basin nw china abstract the kelasu thrust belt is a favorable hydrocarbon accumulation zone in the kuqa sub basin with several known giant gas fields including the dabei and kela 2 gas fields as well as the dawanqi oil field the origin and accumulation process of the hydrocarbons were investigated through an integrated petroleum geochemistry and fluid inclusion analysis and basin modeling geochemical parameters indicate that the light oils from the dawanqi oil field and dabei gas field were generated from different sources as compared with light oils from the kela 2 gas field light oils from the dawanqi oil field and dabei gas field are primarily derived from the terrestrial mudstones in the jurassic qiakemake j2q formation with a maturity level of 1 4 1 6 ro whereas light oils from the kela 2 gas field are mainly derived from the terrestrial mudstones in the triassic huangshanjie t3h with a maturity level of 1 6 1 8 ro gases in the kelasu thrust belt are dominated by coal type gas and are primarily generated from the jurassic coal measures carbon isotope ratios suggest that gases in the dawanqi oil field and dabei gas field were generated at a thermal maturity level of 1 6 2 3 ro while gas in the kela 2 gas field was generated at a thermal maturity level of 2 1 2 5 ro two episodes of oil and one episode of gas charge were delineated in the dabei gas field the second episode of oil charge occurred around 5 4 ma while gas charge occurred around 3 2 ma three episodes of oil and one episode of gas charge were identified in the kela 2 gas field the latter two episodes of oil charge occurred around 5 5 4 5 ma and the gas charge occurred around 3 2 ma the timing of the petroleum charge was also confirmed by the correlation between the maturity of the source rocks during the times of charge and the maturity levels of the light oil and gas in the reservoirs the later oil and gas charge occurred at the same period in both the dabei and kela 2 gas fields possibly relating to structural reactivation caused by regional tectonic compression because intense tectonic compression and rapid uplift of the tianshan mountains occurred during the same period which may have caused thrust fault activation and opening hydrocarbon expulsion from the source rocks during the period was possibly also related to the regional tectonic movement providing hydrocarbon sources for the reservoirs