strain heating as a mechanism for partial melting and ultrahigh temperature metamorphism in convergent orogens implications of temperature dependent thermal diffusivity and rheology 1 we explore the importance of strain heating in ductile shear zones for production of leucogranites and high temperature metamorphism in collisional orogens with temperature dependent thermal diffusivity d and rock rheology new measurements on metamorphic rocks from the bohemian massif show that d is 1 3 mm2 s at 25 c and decreases exponentially to as low as 0 4 mm2 s at 600 c this temperature dependence causes model lithospheric geotherms to be straighter compared to geotherms calculated with a constant d using power law parameters for rheology we show that deformation of quartzite at strain rate of 3 10 13 s 1 produces 100 w m3 at 550 c and 7 w m3 at 800 c deformation of stronger clinopyroxenite at this strain rate produces 8 w m3 even at 1050 c when strain heating is introduced by a 3 km thick ductile shear zone with quartz rheology at the depth of 35 km in a lithosphere that has 70 km thick crust and 60 km thick lithospheric mantle the schist solidus is reached by 8 myr in the vicinity of the shear zone deforming at the strain rate of 3 10 13 s 1 for clinopyroxenite rheology ultrahigh temperature uht metamorphic conditions are reached in 40 myr after initiation of strain heating two dimensional models that replicate the exhumation of the greater himalaya crystalline rocks above the main central thrust produce extensive partial melting and an inverted metamorphic field gradient occurrences of leucogranites within crustal shear zone systems may be evidence of the coupling between deformation and heat production in the crust

controls on reservoir quality of lower cretaceous tight sandstones in the laiyang sag jiaolai basin eastern china integrated sedimentologic diagenetic and microfracturing data abstract the jiaolai basin fig 1 is an under explored rift basin that has produced minor oil from lower cretaceous lacustrine deltaic sandstones the reservoir quality is highly heterogeneous and is an important exploratory unknown in the basin this study investigates how reservoir porosity and permeability vary with diagenetic minerals and burial history particularly the effects of fracturing on the diagenesis and reservoir deliverability the laiyang sandstones are tight reservoirs with low porosity and permeability

exceptionally fast growth rate of 100 yr old tufa big soda lake nevada implications for using tufa as a paleoclimate proxy large tufa mounds 3 m tall with a basal circumference of 5 m have been discovered on the margin of big soda lake nevada usa these tufa mounds are rooted at a maximum of 4 m below the current lake surface and are actively forming from groundwater seepage which can be seen emanating from the top of the tufa mounds big soda lake is a volcanic crater lake whose water level is maintained exclusively by groundwater the age of the tufa mounds is well constrained because prior to the development of the newlands irrigation project in 1907 the water level was 18 m lower than the current lake level the vertical columnar nature of the tufa mounds indicates that they formed under the lake and not subaerially thus the tufa mounds are 100 yr old and have grown at a rate 30 mm yr stable oxygen and carbon isotope analyses of tufa carbonate compared to isotopic analyses of groundwater and lake water and hydrochemical data indicate that the fluids responsible for their precipitation are a simple mixture of modern groundwater and lake water and do not reflect a recent climate signature the exceptionally fast growth of the tufa mounds indicates that large tufa deposits may form almost instantaneously in geologic time given this potential for rapid growth and the fact that variations in isotopic compositions of tufa deposits have been interpreted in terms of changes in paleoclimate and changes in the composition of recharge water over thousands of years care should be taken when trying to determine the significance of variations in isotopic or chemical compositions of tufas that may have been caused by mixing with groundwater

hydrocarbon generation and expulsion characteristics of eocene source rocks in the huilu area northern pearl river mouth basin south china sea implications for tight oil potential abstract in recent years new oil reservoirs have been discovered in the eocene tight sandstone of the huilu area northern part of the pearl river mouth basin south china sea indicating good prospects for tight oil exploration in the area exploration has shown that the huilu area contains two main sets of source rocks the eocene wenchang e2w and enping e2e formations to satisfy the requirements for further exploration in the huilu area particularly for tight oil in eocene sand reservoirs it is necessary to re examine and analyze the hydrocarbon generation and expulsion characteristics based on mass balance this study investigated the hydrocarbon generation and expulsion characteristics as well as the tight oil resource potential using geological and geochemical data and a modified conceptual model for generation and expulsion the results show that the threshold and peak expulsion of the e2w source rocks are at 0 6 vitrinite reflectance and 0 9 vitrinite reflectance respectively there were five hydrocarbon expulsion centers located in the western eastern and northern huizhou sag and the southern and northern lufeng sag the hydrocarbon yields attributed to e2w source rocks are 2 4 1011 tons and 1 6 1011 tons respectively with an expulsion efficiency of 65 the e2e source rock threshold and peak expulsion are at 0 65 vitrinite reflectance and 0 93 vitrinite reflectance respectively with hydrocarbon expulsion centers located in the centers of the huizhou and lufeng sags the yields attributed to e2e source rocks are 1 1 1011 tons and 0 2 1011 tons respectively with an expulsion efficiency of 20 using an accumulation coefficient of 7 13 the eocene tight reservoirs could contain approximately 1 3 1010 tons to 2 3 1010 tons with an average of 1 8 1010 tons of in place tight oil resources highest recoverable coefficient can reach 17 18 indicating that there is significant tight oil potential in the eocene strata of the huilu area

brittle deformation during alpine basal accretion and the origin of seismicity nests above the subduction interface geophysical observations on active subduction zones have evidenced high seismicity clusters at 20 40 km depth in the fore arc region whose origin remains controversial we report here field observations of pervasive pseudotachylyte networks interpreted as evidence for paleo seismicity in the now exhumed valpelline continental unit dent blanche complex nw alps italy a tectonic sliver accreted to the upper plate at c 30 km depth during the paleocene alpine subduction pre alpine granulite facies paragneiss from the core of the valpelline unit are crosscut by widespread mm to cm thick pseudotachylyte veins co seismic heating and subsequent cooling led to the formation of ti rich garnet rims ilmenite needles ca rich plagioclase biotite microliths and hercynite micro crystals 39ar 40ar dating yields a 51 54 ma age range for these veins thus suggesting that frictional melting events occurred near peak burial conditions while the valpelline unit was already inserted inside the duplex structure in contrast the base of the valpelline unit underwent synchronous ductile and brittle seismic deformation under water bearing conditions followed by a re equilibration at c 40 ma 39ar 40ar on retrograded pseudotachylyte veins during exhumation related deformation calculated rheological profiles suggest that pseudotachylyte veins from the dry core of the granulite unit record upper plate micro seismicity mw 2 3 formed under very high differential stresses 500 mpa while the sheared base of the unit underwent repeated brittle ductile deformation at much lower differential stresses 40 mpa in a fluid saturated environment these results demonstrate that some of the seismicity clusters nested along and above the plate interface may reflect the presence of stiff tectonic slivers rheologically analogous to the valpelline unit acting as repeatedly breaking asperities in the basal accretion region of active subduction zones

growth rate and stable isotopic character of modern stromatolites from san salvador bahamas abstract 14 c 18 o and 13 c stratigraphies were measured on the successive carbonate crusts within large mushroom shaped stromatolitic heads from hypersaline storrs lake san salvador bahamas and also on the finely laminated soft sediment that enclose them 14 c dates show that the carbonate layers in these stromatolites range in age from 2310 70 years b p at the base to modern at the surface this suggests that the heads develop at an overall rate of 16 cm 1000 yr because there are 1 5 macroscopic laminae per cm less than one crustose layer is preserved in the heads per decade thin section examination of the crusts reveals numerous discontinuous micro unconformities which suggest multiple intervals of accretion and erosion these factor complicate any history of slow growth that may occur values of 18 o in the carbonates suggest that the heads were formed in waters with isotopic and temperature conditions similar to those that presently exist in the lake however carbonate 13 c values from the heads and sediments vary over 7 5 1 2 0 pdb and are significantly out of equilibrium with atmospheric co 2 the fluctuations in the 13 c values within the heads could not be correlated between adjacent heads nor with adjacent sediment on the basis of 14 c ages thus the sampled macroscopic layers mm cm in these calcified stromatolites do not appear to be recording simultaneous basin wide events but rather local diagenetic effects and micro environmental conditions in or under the microbial mats these data do not encourage basin wide interpretations of isotopic stratigraphies observed within ancient stromatolites where independent chronologies like 14 c are not available

reservoir quality natural fractures and gas productivity of upper triassic xujiahe tight gas sandstones in western sichuan basin china abstract the main target for hydrocarbon exploration in the western sichuan basin in china is the tight gas sandstone reservoir of the upper triassic xujiahe formation sandstones of the xujiahe formation are characterized as tight with ultralow porosity ultralow permeability and intensive heterogeneity in this study various techniques such as scanning electron microscopy x ray diffraction cathodoluminescence microscopy casting thin section and fluid inclusion thermometry were employed to investigate the composition sedimentary facies diagenesis history diagenetic intensity natural fracture characteristics and their impact on reservoir quality the results showed that subaqueous distributary channels and mouth bars with low rock fragment content are favorable for pore preservation and secondary pore development except for the medium to strong dissolution intensity chlorite rim growth is also important for the development of high quality reservoirs intraformational shear fractures and horizontal shear fractures associated with tectonic movement increase pore space and improve the capability of transmitting fluids differences in gas productivity could be attributed to differences in reservoir quality which were controlled by the sedimentary environment diagenetic intensity and fracture characteristics a significantly positive correlation was found between total porosity and gas productivity of the tight sandstones the high density fracture distribution was found owing to the fault system and structural deformation zone which resulted in high gas productivity the research results were successfully applied to improve production efficiency in the xujiahe tight gas sandstones and could be applicable to other similar fields involving tight gas

a preliminary study of the present day in situ stress state in the ahe tight gas reservoir dibei gasfield kuqa depression abstract knowledge of the present day in situ stress state has significant applications in the exploration and development of tight gas reservoirs the ahe formation is an important tight gas reservoir in the dibei gasfield of kuqa depression however prior to this study little attention has been paid to the present day in situ stress field within the formation in the present study the in situ stress orientation and magnitudes were investigated based on well log calculations and geomechanical modeling the horizontal maximum principal stress shmax orientation was determined from interpretations of drilling induced tensile fractures ditfs and borehole breakouts in imaging logs which showed variations between nnw sse trending and nne ssw trending in the dibei gasfield the in situ stress magnitudes were calculated in four wells based on well logs the results indicated a normal faulting stress regime within the ahe tight gas reservoir numerical simulation of the present day in situ stresses showed that the magnitudes of vertical stress sv shmax and horizontal minimum principal stress shmin were 105 5 mpa 191 0 mpa 88 9 mpa 142 9 mpa and 79 1 mpa 127 7 mpa within the ahe formation respectively in addition considering the present day in situ stress state in the ahe formation of dibei gasfield natural fractures in directions parallel sub parallel to the shmax orientation with high fracture angles showed great contributions to subsurface fluid flow borehole instability may become a potentially significant problem when drilling vertical wells and horizontal wells deviated toward the shmax orientation in the ahe tight gas reservoir of dibei gasfield

charging of the penglai 9 1 oil field bohai bay basin china functions of the delta on accumulating petroleum abstract the penglai 9 1 pl9 1 oil field which contains china s third largest offshore oil accumulation in place reserves greater than 2 28 10 8 ton or 1 49 10 9 bbl was found in shallow reservoirs 700 1700 m 2297 5577 ft within the most active fault zone in east china the pl9 1 field contains two oil bearing series the granite intrusions in mesozoic mz and both the sandstone reservoirs in neogene guantao ng and neogene minghuazhen nm formation the origins of the pl9 1 field both in terms of source rock intervals and generative kitchens were determined by analyzing biomarker distributions for 61 source rock samples and 33 oil samples the mesozoic granite intrusions which hold more than 80 of the oil reserves in the field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression the neogene reservoirs of the pl9 1 field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression and in the south by oil generated from the first member es 1 of the shahejie formation in the miaoxibei depression interactive contact between the large fan delta and the mature source rocks residing in the es 3 formation of the bodong depression resulted in a high expulsion efficiency from the source rocks and rapid oil accumulation in the pl9 1 field which probably explains how can this large oil field accumulate and preserve within the largest and most active fault zone in east china

extreme 13c depletions in seawater derived brines and their implications for the past geochemical carbon cycle extreme depletions in the 13c content of the total dissolved inorganic carbon ct were found in brines overlying microbial mat communities total alkalinity at and ct in the brines suggest that intense photosynthetic activity of the microbial mat communities depletes the ct from the brine we suggest that this depletion drives a large kinetic negative fractionation of carbon isotopes similar to that observed in highly alkaline solutions in brines of extreme salinity where microbial mat communities no longer exist the 13c content of the ct increases probably because photosynthesis no longer dominates the gas exchange processes this mechanism explains light carbon isotope compositions of carbonate rocks from evaporitic sections and bears on the interpretation of 13c values in bedded stromatolitic limestones that are ca 3 5 b y old

early cenozoic two phase extension and late cenozoic thermal subsidence and inversion of the bohai basin northern china abstract the bohai basin is one of a family of early cenozoic extensional basins that lie along the eastern margin of asia from russia to vietnam initial extension was probably triggered by subduction roll back of the oceanic pacific plate from the asian continent there were two phases in the bohai basin s rift history the earlier paleocene early eocene phase resulted in the deposition of the kongdian formation and the fourth lowest member of the shahejie formation in a series of elongate half grabens these half grabens have master faults with a nne ssw orientation secondary normal faults are typically clockwise oblique to the master faults indicating a component of dextral transtension deposition was focused in the west and south of the present basin these rocks are mainly alluvial fan and fluvial red beds the architecture of the basin underwent an important change at ca 43 45 ma middle eocene beginning with the deposition of the third member of the shahejie formation in part these sediments were deposited in the same half grabens as the kongdian formation but the bozhong depression in the central part of the basin originated at this time and became the major depocentre the bozhong depression superficially resembles a pull apart basin it formed when continued transtension of the earlier tertiary fault systems to the east and west created an extensional overlap between them during this phase the basin as a whole had a geometry with elements typical of both pull apart and transtensional basins regional extension in many east asian basins ended at the end of the oligocene probably because of the onset of transpression within eastern asia caused by the collision of australia with the philippine sea plate dextral transpression caused minor inversion of some of the earlier normal faults in bohai but as a whole the basin began to subside in a post rift phase of thermal subsidence that has lasted until the present day

from permo triassic lithospheric thinning to jurassic rifting at the adriatic margin petrological and geochronological record in valtournenche western italian alps abstract slices of polycyclic metasediments marbles and meta cherts are tectonically amalgamated with the polydeformed basement of the dent blanche tectonic system along a major alpine shear zone in the western alps becca di sale area valtournenche valley a combination of techniques structural analysis at various scales metamorphic petrology geochronology and trace element geochemistry was applied to determine the age and composition of accessory phases titanite allanite and zircon and their relation to major minerals the results are used to reconstruct the polyphase structural and metamorphic histories comprising both pre alpine and alpine cycles the pre alpine evolution is associated with low pressure high temperature metamorphism related to permo triassic lithospheric thinning in meta cherts microtextural relations indicate coeval growth of allanite and garnet during this stage at 300 ma textures of zircon also indicate crystallisation at ht conditions ages scatter from 263 to 294 ma with a major cluster of data at 276 ma in impure marble u pb analyses of titanite domains with variable al and f contents yield apparent 206pb 238u dates range from permian to jurassic chemical and isotopic data suggest that titanite formed at permian times and was then affected by extension related fluid circulation during the triassic and jurassic which redistributed major elements al and f and partially opened the u pb system the alpine cycle lead to early blueschist facies assemblages which were partly overprinted under greenschist facies conditions the strong alpine compressional overprint disrupted the pre alpine structural imprint and or reactivated earlier structures the pre alpine metamorphic record preserved in these slices of metasediments reflects the onset of the permo triassic lithospheric extension to jurassic rifting

brittle precursors of plastic deformation in a granite an example from the mont blanc massif helvetic western alps abstract in the mont blanc helvetic massif granites record mesoscale alpine structures which include joints veins cataclastic to mylonitic shear zones and foliated granites a detailed structural analysis indicates that brittle deformation predates plastic strain joints never pass through and veins are offset by cataclastic shear zones and mylonites the mylonites progressively develop by plastic reactivation of cataclastic shear zones during greenschist facies metamorphic conditions plastic deformation is first localized in the brittle discontinuities and the fine grained matrix of cataclasites then it involves the granite within brittle shear zones and this is initially accomplished mainly by flow of reaction softened aggregates of sericite widely replacing the strain supporting magmatic plagioclase the brittle to plastic evolution has resulted in highly localized discontinuous plastic shear zones with high lateral continuity and these characteristics are derived from reactivation of and focusing along pre existing brittle discontinuities in addition mylonites may inherit high angles of intersection and may contain granite porphyroclasts these features may allow the inference of a precursor brittle deformation where the plastic overprint has completely erased the initial brittle fabrics

enhanced development of lacustrine microbialites on gravity flow deposits great salt lake utah usa the great salt lake utah usa is a shallow hypersaline intracontinental lake hosting extensive microbial deposits at a large spatial scale the distribution of these deposits is driven by environmental and geodynamical factors i e water level fluctuations and a fault related framework a detailed mapping of the buffalo point area in the north western part of antelope island indicates the presence of an anomalous concentration of microbial deposits dated ca 5 8 ka bp and distributed along a lobe shaped geometry this uncommon microbial deposit geometry results from an extensive colonization of a conglomerate substrate exhibiting an accumulation of m sized rounded cambrian quartzite boulders we suggest that this conglomerate substrate provides a stable nucleation point that promotes the development and preservation of the lobe shaped microbial deposits microbial deposits may also have protected the conglomerate substrate from erosional processes and thereby increased the preservation potential of the lobe shaped structure based on the characteristics of the conglomerate e g grain size texture and its location i e 200 m beyond the average shoreline this lobe shaped structure likely results from subaqueous debris or a hyperconcentrated density flow that transports sedimentary material from the buffalo point slopes downward to the shore we estimate the age of the conglomerate deposition to be between 21 and 12 ka bp the initiation of the flow may have been triggered by various mechanisms but the existence of a major active normal fault in the vicinity of these deposits suggests that an earthquake could have destabilized the accumulated sediments and resulted in conglomerate emplacement the catastrophic 15 ka bp bonneville flood which led to a drop in the lake level approximately 110 m may also provide an explanation for the initiation of the flow

external controls on the distribution fabrics and mineralization of modern microbial mats in a coastal hypersaline lagoon cayo coco cuba active carbonate mineralizing microbial mats flourish in a tropical highly evaporative marine fed lagoonal network to the south of cayo coco island cuba hypersaline conditions support the development of a complex sedimentary microbial ecosystem with diverse morphologies a variable intensity of mineralization and a potential for preservation in this study the role of intrinsic i e microbial and extrinsic i e physicochemical controls on microbial mat development mineralization and preservation was investigated the network consists of lagoons forming in the interdune depressions of a pleistocene aeolian substratum they developed due to a progressive increase in sea level since the holocene the hydrological budget in the cayo coco lagoonal network changes from west to east increasing the salinity this change progressively excludes grazers and increases the saturation index of carbonate minerals favouring the development and mineralization of microbial mats in the easternmost lagoons detailed mapping of the easternmost lagoon shows four zones with different flooding regimes the microbial activity in the mats was recorded using light dark shifts in conjunction with microelectrode o2 and hs profiles high rates of o2 production and consumption in addition to substantial amounts of exopolymeric substances are indicative of a potentially strong intrinsic control on mineralization seasonal climate driven water fluctuations are key for mat development mineralization morphology and distribution microbial mats show no mineralization in the permanently submersed zone and moderate mineralization in zones with alternating immersion and exposure it is suggested that mineralization is also driven by water level fluctuations and evaporation mineralized mats are laminated and consist of alternating trapping and binding of grains and microbially induced magnesium calcite and dolomite precipitation the macrofabrics of the mats evolve from early colonizing flat mats to complex cerebroid or terrace structures the macrofabrics are influenced by the hydrodynamic regime wind driven waves inducing relief terraces in windward areas and flat morphologies on the leeward side of the lagoon other external drivers include i storm events that either promote for example by bioclasts covering or prevent for example by causing erosion microbial mat preservation and ii subsurface degassing through mangrove roots and desiccation cracks covered by flat mats i e forming hemispheroids and cerebroidal structures these findings provide in depth insights into understanding fossil microbialite morphologies that formed in lagoonal settings

fine grained agglutinated elongate columnar stromatolites tieling formation ca 1420 ma north china the mesoproterozoic tieling formation near jixian northern china contains thick beds of vertically branched laterally elongate columnar stromatolites carbonate mud is the primary component of both the stromatolites and their intervening matrix its abundance is attributed to water column whiting precipitation stimulated by cyanobacterial photosynthesis neomorphic microspar gives the stromatolites a streaky microfabric and small mud flakes are common in the matrix the columns consist of low relief mainly non enveloping laminae that show erosive truncation and well defined repetitive lamination in plan view the columns form disjunct elongate ridges 10 cm wide separated by narrow matrix filled runnels the stromatolite surfaces were initially cohesive rather than rigid and prone to scour and are interpreted as current aligned microbial mats that trapped carbonate mud the pervasive ridge runnel system suggests scale dependent biophysical feedback between i carbonate mud supply ii current duration strength and direction and iii growth and trapping by prolific mat growth together these factors determined the size morphology and arrangement of the stromatolite columns and their laminae as well as their branching patterns alignment and ridge runnel spacing ridge runnel surfaces resemble ripple mark patterns but whether currents were parallel and or normal to stromatolite alignment remains unclear the formation and preservation of tieling columns required plentiful supply of carbonate mud mat building microbes well adapted to cope with this abundant sediment and absence of both significant early lithification and bioturbation these factors were time limited and tieling stromatolites closely resemble coeval examples in the belt purcell supergroup of laurentia the dynamic interactions between mat growth currents and sediment supply that determined the shape of tieling columns contributed to the morphotypical diversity that characterizes mid late proterozoic branched stromatolites this article is protected by copyright all rights reserved

depositional environment and geochemical characteristics of the lower carboniferous source rocks in the marsel area chu sarysu basin southern kazakhstan abstract there are two sets of carbonate source rocks in the lower carboniferous layers in marsel the visean c1v and serpukhovian c1sr however their geochemical and geological characteristics have not been studied systematically to assess the source rocks and reveal the hydrocarbon generation potential the depositional paleoenvironment and distribution of c1v and c1sr source rocks were studied using total organic carbon toc content rock eval pyrolysis and vitrinite reflectance ro data stable carbon isotope data gas chromatography gc and gas chromatography mass spectrometry gc ms analysis data the data were then compared with well logging data to understand the distribution of high quality source rocks the data were also incorporated into basin models to reveal the burial and thermal histories and timing of hydrocarbon generation the results illustrated that the average residual toc contents of c1v and c1sr were 0 79 and 0 5 respectively which were higher than the threshold of effective carbonate source rocks dominated by type iii kerogen the c1v and c1sr source rocks tended to be gas bearing the two source rocks were generally mature to highly mature the average ro was 1 51 and 1 23 in c1v and c1sr respectively the source rocks were deposited in strongly reducing to weakly oxidizing marine terrigenous environments with most organic material originating from higher terrigenous plants and a few aquatic organisms during the permian the deep burial depth and high heat flow caused a quick and high maturation of the source rocks which were subsequently uplifted and eroded stopping the generation and expulsion of hydrocarbons in the c1v and c1sr source rocks the initial toc fitted by the logr method was recovered and it suggests that high quality source rocks toc 1 are mainly distributed in the northern and central local structural belt

key factors controlling hydrocarbon enrichment in a deep petroleum system in a terrestrial rift basin a case study of the uppermost member of the upper paleogene shahejie formation nanpu sag bohai bay basin ne china abstract mineralogical petrographical geochemical analyses and fluid inclusions petrography and microthermometry were combined to investigate the basic properties of the source rock organic matter content kerogen type and thermal maturity and sandstone reservoirs composition pore systems porosity and permeability the hydrocarbon origin and the formation mechanisms of the deep 3 5 km petroleum system in the upper paleogene es1 the uppermost member of the shahejie formation in the no 3 structural belt in the nanpu sag bohai bay basin the results indicate that the es1 source rock is primarily composed of dark gray mudstone and presents a set of high quality source rocks 500 m average total organic carbon toc 1 38 in a mature stage maximum pyrolysis yield of 430 c 460 c the es1 sandstone is composed of lithic arkose formed in a braided river delta and has low porosity average 13 4 but moderate high permeability average 184 9 md the hydrocarbons originated from the es1 source rocks in the caofeidian subsag during two charging periods 10 ma and 3 ma the key factors controlling the formation of the deep petroleum system are as follows a high quality hydrocarbon supply b medium high permeability reservoirs c a favorable configuration of the source rock and reservoirs self generated and self accumulated and d late hydrocarbon charging the second factor is the most important the medium high permeability reservoirs are attributed to a high energy depositional environment distributary channels of braid delta front a high content of rigid detrital grains mainly quartz and metamorphic rock fragments provided by the archean granite provenance and the secondary pores formed by feldspar dissolution this study provides a new example for revealing the formation mechanisms of deep 3 5 km petroleum systems in the terrestrial rift basin across the bohai bay basin

strain insensitive preferred orientation of porphyroclasts in mont mary mylonites abstract the shape preferred orientation spo of porphyroclasts was determined in high temperature mylonites the porphyroclasts approach rhomboidal sillimanite or elliptical garnet plagioclase sillimanite shapes and exhibit aspect ratios r as high as 11 particles with r 3 are dominantly rhomboidal the long axis of the best fit ellipse defines a very strong spo inclined at 5 10 to the mylonitic foliation in an antithetic sense with respect to the shear direction this angle is independent of r the inclination of the long sides of rhomboidal sillimanite increases from 10 to 20 with decreasing r in contrast the short sides have a constant orientation of 15 to 17 irrespective of r and are parallel to extensional crenulation cleavage low aspect ratio mainly elliptical objects show low intensity spo close to the shear plane the two spos appear strain insensitive in the case of r r 3 a stable position is acquired this is not explained by any of the current theoretical and experimental models of spo

how fast does tufa grow very high resolution measurement of the tufa growth rate on artificial substrates by the development of a contactless image based modelling device

deformation of granitoids at low metamorphic grade i reactions and grain size reduction abstract deformation and chemical reaction in granitoids at greenschist facies conditions were investigated in samples from three shear zones two from the alps corvatsch granodiorite and aiguilles rouges granite switzerland and one from eastern australia wyangala granite when examined by light and electron microscopy all show similar features of deformation that progressed from coarse parent rock through to fine grained mylonite quartz deformed plastically while both k feldspar and plagioclase fractured and recrystallized in conjunction with chemical change which had as its end point an assemblage albite quartz white mica caal silicates k feldspar and calcic plagioclase depending on fluid chemistry from the parent rock were unstable at low metamorphic grades in the presence of aqueous fluid since ca bearing plagioclase was not stable in these environments myrmekite did not replace k feldspar in any of the rocks examined recrystallization of feldspar which should perhaps be termed neocrystallization was initiated predominantly at clast margins or along microfractures that are marked by fluid inclusions and twin offsets in old feldspar grains particularly in plagioclases dislocations exist in wall like structures that are commonly associated with voids suggesting origins in microfractures these dislocations had severely limited mobility and subgrain rotation does not appear to have contributed to recrystallization we conclude that recrystallization mainly occurred via a classical nucleation mechanism with minor contributions from twin boundary migration we argue that the 450 550 c lower limit for recrystallization of feldspar referenced throughout the literature is not applicable to the rock systems under investigation and should be discarded as a universal limit microfracturing microboudinage and reaction are seen as the prerequisites for mylonite formation from coarse grained granitic rocks at low metamorphic grades see part ii of this paper neocrystallization fluid access and nucleation appear to have accompanied or immediately followed the first deformation increments and were primarily responsible for continued grain size reduction transgranular fracture was comparatively important only at the onset of deformation since the formation of shear zones in granitoids commonly takes place under conditions of low metamorphic grade in the presence of aqueous fluids in the earth s crust breakdown reactions and nucleation recrystallization in feldspars may be important influences upon localization of deformation in granitoids

synthetic saline aqueous and hydrocarbon fluid inclusions trapped in calcite at temperatures and pressures relevant to hydrocarbon basins a reconnaissance study abstract we conducted reconnaissance experiments to synthesize aqueous and hydrocarbon inclusions trapped in calcite at conditions relevant to petroleum basins and characterize the microthermometric properties of such inclusions fluid inclusions fis were synthesized in a system of saline aqueous solution 5 or 20 wt nacl coexisting with either heavy crude oil or gasoline under gas undersaturated conditions from 90 to 210 c and 200 550 bar the synthetic inclusions are not representative of gas bearing systems and methane ch 4 was not detected in any aqueous inclusions the fis are mainly distributed along planar healed cracks indicating that the inclusions formed by fracture healing in the calcite crystal microthermometric measurements were conducted on coeval aqueous and hydrocarbon inclusions and raman spectroscopic analyses were done on aqueous inclusions to determine the properties of fis trapped at these conditions homogenization temperatures of synthetic fis are mostly lower than the experimental trapping temperature although the fis show high variability in measured homogenization temperature results allow comparison of t h values for each sample with the expected t h isochores and pressure corrections calculated for the system h 2 o nacl the latter parameters are broadly consistent with the known pvtx properties of h 2 o nacl fluids suggesting little effect of hydrocarbons on the homogenization behavior although the low precision of the t h data limits this assessment nevertheless this result is not unexpected considering that light hydrocarbons gas is not present in the experiments as corroborated by raman spectroscopy a consequence of using dead oil in the experiments simulation of gas bearing petroleum basins will require additional protocols for producing gas either by in situ cracking of the starting hydrocarbon material or by other means the reconnaissance experiments documented here provide a basis for such future experiments

geochemical effects of primary migration of petroleum in kimmeridge source rocks from brae field area north sea i gross composition of c15 soluble organic matter and molecular composition of c15 saturated hydrocarbons in mature oil prone source rocks of the upper jurassic kimmeridge clay in the brae field area north sea the yield and the gross composition of solvent extractabte pctroleum likc compounds as well as the molecular proportions of c15 saturated hydrocarbons are primarily controlled by the effects of hydrocarbon expulsion during primary migration within sample series extending from shale centres towards adjacent reservoir sandstones regular and pronounced yield decreases have been documented as well as marked compositional changes for c15 soluble organic matter and its compound class fractions saturated hydrocarbons aromatic hydrocarbons nso compounds and for normal and isoprenoid alkanes relative migration losses indicating relative expulsion efficiencies were determined for the c15 alkanes throughout the outer five meters of thick shales relative expulsion efficiencies increase regularly and drastically for all compounds considered e g exceeding 90 for the c15 n alkanes in the outermost shale samples samples from thin 5 50 cm shale layers interbedded between reservoir sandstones reveal similarly high expulsion efficiencies for n alkanes the degree of depletion remains uniform throughout the molecular range c15 to c30i e no compositional fractionation occurred during primary migration which is interpreted to reflect expulsion of oil as a single phase fluid a simple conceptual model is proposed to explain the mechanisms and relationships of generation and expulsion processes in time and space a geochemically relevant conclusion is that the c15 soluble organic matter recovered by solvent extraction of mature source rocks represents only a portion of the total non volatile petroleum like material originally generated

carbon isotope record of late cambrian to early ordovician carbonates of the argentine precordillera a more than 2000 m thick cambrian ordovician carbonate platform succession developed on the exotic argentine precordillera terrane during rifting from laurentia and drifting towards gondwana on base of these carbonates a carbon isotope curve could be developed for the cambrian ordovician we measured 13ccarb and 13corg values on bulk rocks selected components and diagenetic cements whereas the carbon isotope signals of intertidal and supratidal rocks are altered by diagenesis most subtidal carbonates exhibit primary marine values we can report reliable curves for the middle late cambrian transition and for the latest cambrian to earliest middle ordovician the 13c curve matches well with the published data from global cambrian ordovician boundary sections excursions and shifts in the carbon isotope curve correspond to events in sequence stratigraphy this indicates the interdependence on sea level which rules the productivity and or preservation of organic carbon and therefore the partition between corg and ccarb burial

habit of bacterially induced precipitates of calcium carbonate and the influence of medium viscosity on mineralogy abstract marine bacteria can and do induce the precipitation of calcium carbonate in the laboratory and in nature which results in single crystals and aggregates of crystals crystal bundles the end member forms of the crystal bundles observed are rods and spheres with numerous variations in between these forms the most common of which is the dumbbell rounded dumbbells and single crystals resembling brushes appear to be unique to bacterially induced precipitates and consequently may serve to identify bacterially induced precipitates in the rock record viscosity of the growth medium is the single most important control over the mineral precipitated in the experiments conducted the medium viscosity controls the ion diffusion rate and thus the rate of precipitation and consequently the mineral precipitated in a liquid medium circulation and the ion diffusion rate are both high precipitation is rapid and aragonite forms in a gelatinous medium there is little circulation the ion diffusion rate is slow the rate of precipitation is slow and calcite is precipitated the overall form of the resultant precipitate rods or spheres was the same regardless of the mineral composition

diagenetic influence on reservoir quality evolution examples from triassic conglomerates arenites in the edvard grieg field norwegian north sea abstract the utsira high southern norwegian north sea has been a petroleum exploration target since the late 1960s the southwestern part of the utsira high complex haugaland high attracted new interest when in 2007 lundin norway as and partners revus energy asa and rwe dea norge as discovered commercial hydrocarbon reservoirs in triassic to early cretaceous formations edvard grieg field in the present study four siliciclastic cores from the edvard grieg field have been investigated sedimentologically including core logging optical mineralogy x ray powder diffraction xrd and scanning electron microscope sem quantification and characterization of the different mineralogical phases in thin section have been executed to better understand porosity evolution through time intergranular volume igv and cement volume were also compared in order to estimate the most important factors effecting porosity loss within the studied samples the results show that through time the various diagenetic events and phases such as dissolution of unstable grains and precipitation of clay minerals and cements strongly influenced reservoir quality in the edvard grieg field two main lithology groups are identified within the cored intervals conglomerates and sandstones these two groups can further be sub divided into four units 1 sandy conglomerate 2 silty conglomerate 3 interbedded sandstone 4 large scale cross bedded sandstone most of the reservoir quality reduction in the conglomerate matrix can be related to poor sorting carbonate cement and pore filling pore lining authigenic clay minerals better reservoir quality characterizes the sandstone dominated alluvial fan intervals which generally are associated with a greater degree of sorting that led to higher intergranular porosities large scale cross stratified sandstone units interpreted to be of aeolian origin have the highest reservoir quality these deposits are moderately to well sorted with only minor occurrences of patchy carbonate cement and generally low proportions of authigenic minerals however locally abundant kaolinite has been observed filling the pore space and reducing the porosity predominantly by blocking interconnected primary pores

diagenetic characteristics and reservoir quality of the lower cretaceous biyadh sandstones at kharir oilfield in the western central masila basin yemen the lower cretaceous biyadh formation in the masila basin is an important hydrocarbon reservoir however in spite of its importance as a reservoir published studies on the biyadh formation more specifically on the diagenesis and relate with reservoir quality are limited based on core samples from one well in the kharir oilfield western central masila basin this study reports the lithologic and diagenetic characteristics of this reservoir the biyadh sandstones are very fine to very coarse grained moderate to well sorted quartzarenite and quartzwacke the diagenetic processes recognized include mechanical compaction cementation carbonate clay minerals quartz overgrowths and a minor amount of pyrite and dissolution of the calcite cement and feldspar grains the widespread occurrences of early calcite cement suggest that the biyadh sandstones lost a significant amount of primary porosity at a very early stage of its diagenetic history based on the framework grain cement relationships precipitation of the early calcite cement was either accompanied or followed by the development of part of the pore lining and pore filling clay cements secondary porosity development occurred due to partial to complete dissolution of early calcite cement and feldspar grains in addition to calcite several different clay minerals including kaolinite and chlorite occur as pore filling and pore lining cements kaolinite largely occurs as vermiform and accelerated the minor porosity loss due to pore occlusion chlorite coating grains helps to retain primary porosity a by retarding the envelopment of quartz overgrowths porosity and permeability data exhibit good inverse correlation with cement thus reservoir quality is controlled by pore occluding cement diagenetic history of the biyadh sandstones as established here is expected to help better understanding and exploitation of this reservoir the relation between diagenesis and reservoir quality is as follows the initial porosity was decreased by compaction and cementation and then increased by dissolution of early calcite cement and feldspar grains the reservoir quality is also affected by depositional environment controls of grain size sorting and matrix thus best good quality reservoir rocks were deposited in braided river channels environment where no inhibited authigenic clays and high percentages of detrital quartz

nucleation and growth of retrograde shear zones an example from the needle mountains colorado u s a abstract brittle and ductile deformation features are heterogeneously developed in late proterozoic retrograde normal slip shear zones that cross cut amphibolites and quartzo feldspathic gneisses in the needle mountains replacement of amphibolite grade minerals by greenschist facies assemblages is spatially related to transgranular fractures that cross cut the older gneissosity steeply dipping chlorite lined slip surfaces are associated with chlorite quartz muscovite filled dilational jogs and narrow breccia zones arrays of slip surfaces are transitional into similarly oriented phyllonite zones within which the foliation locally overprints early cataclastic zones the nucleation of these shear zones under greenschist facies conditions involved fluid infiltration along early transgranular fractures and hydration of fe mg bearing minerals initial displacement occurred by slip along these fractures and local cataclasite development fluids were episodically drawn into dilatant sites along these slip surfaces a transition to plastic deformation resulted directly from the metamorphic breakdown of feldspars and amphiboles to phyllosilicates which allowed strain localization into narrow phyllonite zones thus dilatancy produced by early brittle deformation appears to be the main process by which fluids infiltrate into developing greenschist grade retrograde shear zones reaction softening via hydration reactions causes a brittle to plastic transition and results in strain localization

combined use of confocal laser scanning microscopyand pvt simulation for estimating the composition andphysical properties of petroleum in fluid inclusions we present a method to determine the composition and pvt properties of petroleum inindividual petroleum fluid inclusions confocal laser scanning microscopy is used to generatethree dimensional images of single petroleum inclusions because liquid petroleum fluorescesunder the laser the images readily distinguish the liquid and vapour within the inclusion and canbe used to determine the inclusions volumetric liquid vapour ratio using pvt modellingsoftware the liquid vapour ratio is used along with the homogenisation temperature to determinethe bulk composition phase envelope isochore and a range of physical properties of the includedpetroleum this is done using an iterative series of pvt calculations which match twoparameters 1 the molar volume of the petroleum at room and homogenisation temperatures 2 the liquid vapour ratio of the inclusion at room temperature key uncertainties in the methodare explored including the accuracy with which the liquid vapour ratio can be determined thecomposition of the titrant gas used in the iterative procedure and the composition of thepetroleum chosen to model the physical properties of the included petroleum data from coevalinclusions suggest that the saturation pressure gas oil ratio viscosity molar volume densityand surface tension of included petroleum are determined with a precision of a few percent confirmation of the accuracy of the method awaits tests using inclusions grown in the laboratoryunder carefully controlled pvtx conditions however it is likely that the physical properties ofincluded petroleums are more accurately modelled by fluids which are genetically related tothem if proven to be accurate the method will provide a routine method for determiningpalaeopressure in petroleum systems finally we present data from a central north sea examplewhich are geologically realistic and which for the first time record the evolution of fluid pressureand petroleum composition in a petroleum reservoir

study of an ordovician carbonate with alternating dolomite calcite laminations and its implication for catalytic effects of microbes on the formation of sedimentary dolomite

experimental observations on the effect of interface slip on rotation and stabilisation of rigid particles in simple shear and a comparison with natural mylonites for axial ratios r not vert similar3 porphyroclasts from three mylonites all show a very strong spo with the long axis of the best fit ellipse at an antithetic angle of 5 10 to the shear direction this is more consistent with a stable end orientation than with the transient fabrics predicted by theory for elliptical rigid particles in simple shear the cause of this divergence is investigated in a series of high simple shear strain 15 analogue experiments performed in a ring shear machine couette flow using a linear viscous matrix pdms the rotational behaviour of elongate r not vert similar5 rigid particles with elliptical and rhomboidal shapes comparable with the natural examples is modelled for both coherent and slipping particle matrix interfaces interface slip causes a dramatic reduction in the rotation rate of the elliptical particle compared with theory when the long axis is close to the shear direction but not stabilisation interface slip does result in stabilisation of the rhomboidal particle with the long diagonal oriented at a small antithetic angle to the shear direction for monoclinic particles mirror image shapes referred to here as types 1 and 2 show different rotational behaviour for the type 1 particle with a shape comparable to porphyroclast systems and mica fish the long side rotates asymptotically into parallelism with the shear direction natural examples of type 1 particles such as hornblende and olivine porphyroclasts measured from the finero mylonites southern alps show a very strong preferred orientation for r not vert similar3 with the long side parallel or at a small 5 antithetic angle to the mylonitic foliation for type 2 particles the short side stabilises close to the shear direction or at a small synthetic angle as also observed for sillimanite porphyroclasts from the mont mary mylonites western alps in this natural case stabilisation of the short sides is against an extensional crenulation cleavage rather than the mylonitic foliation the analogue experiments establish that interface slip is one mechanism for stabilisation of elongate rhomboidal particles in natural examples decoupling from the matrix may be affected by extensional crenulation cleavage or c planes in s c fabrics

ductile brittle transition in pre alpine amphibolite facies mylonites during evolution from water present to water deficient conditions mont mary nappe italian western alps in the austroalpine mont mary nappe italian western alps discrete zones of mylonites ultramylonites developed from coarse grained upper amphibolite facies metapelites of pre alpine age the syn mylonitic mineral assemblage is quartz biotite muscovite plagioclase garnet sillimanite ilmenite graphite and formed via the model hydration reaction grt 1 kfs h 2 o bt 2 ilm 2 qtz ms sil grain size reduction of about three orders of magnitude was accompanied by extensive recrystallization of all minerals except sillimanite and by compositional changes of garnet and biotite deformation took place at temperatures of 510 580 c under low pressure conditions 0 25 0 45 gpa and corresponds to the latest stages of pre alpine metamorphic evolution the pre alpine mylonitization conditions were close to the brittle ductile transition as indicated by syn mylonitic generation of pseudotachylytes and high diverential stress inferred from quartz grain size piezometry the brittle ductile behaviour at a relatively high temperature and the absence of annealing textures in quartz aggregates are suggestive of water deficient conditions during mylonitization these were accomplished through progressive consump tion of water by syn kinematic hydration reaction and by adsorption onto the greatly increased grain boundary area resulting from dynamic recrystallization

natural gas constituent and carbon isotopic composition in petroliferous basins china abstract there are abundant gas resources in petroliferous basins of china large to midsize gas fields are found in eastern central and western of china however origin constituents and isotopic composition of natural gas in different gas fields are varied distinctly and some present strong chemical secondary alteration and show variation both in age and space based on the systematic analysis of constituents and carbon isotope of a large number of gas samples combined with the geological characteristics this paper classifies the origins of the gases explores the gas isotope characteristics and evolutionary regulation with the variation time and space and further discusses the distinctive geochemistry of the gases in china these gases are dominated by dry gas its methane carbon isotope values range from 10 to 70 ethane from 16 to 52 propane from 13 to 43 and butane from 18 to 34 the carbon isotopes of most gases show the characteristics of humic derived gas and crude oil cracked gas in addition large primary biogenic gas fields have been discovered in the qaidam basin inorganic derived alkane gases have been discovered in deep of the songliao basin half of these gas fields are characterized by the alkane carbon isotope reversal in different degrees research indicates there are several reasons can result in carbon isotope reversal firstly gas charge of different genetic types or different source in one gas reservoir may cause carbon isotope reversal besides high over mature evolution of gas can also lead to the carbon isotopic reversal of alkanes thirdly secondary alteration of hydrocarbons may also result in abnormal distribution of carbon isotope isotope transforms to unusual light and heavy

petroleum resources in the nanpu sag bohai bay basin eastern china the nanpu sag is an important secondary tectonic division of the bohai bay basin and has an area of 1532 km2 591 mi2 of which 1000 km2 386 mi2 has been explored near bohai recently exploration has gradually shifted from continental to beach to shallow marine settings with significant exploration breakthroughs having occurred in the nanpu 1 2 and 3 tectonic belts indicating good resource potential however a systematic resource assessment has yet to be performed which strongly restricts the exploration progress in this study we improved upon the pareto model and reevaluated the area s resource potential using two new methods in one method the traps are divided into several types including structural stratigraphic and buried hill traps to predict their individual resource potential and total resources of this area in the other method the normalized fluid potential is used to divide the area into several accumulation systems to calculate the resource potential the nanpu sag resources are estimated at 1 45 109 t 10 6 109 bbl which represents an increase of approximately 2 70 108 t 19 8 108 bbl compared with previous evaluations because of the increase in exploration maturity and information validation the main residual resource is distributed in beach to shallow marine settings the stratigraphic and buried hill traps present better resource potential using the trap type method such information can guide the direction of exploration and selection of potential traps

fluid infiltration into fault zones chemical isotopic and mechanical effects fluid infiltration into fault zones and their deeper level counterparts brittle ductile shear zones is examined in diverse tectonic environments in the 2 7 ga abitibi greenstone belt major tectonic discontinuities with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism during reverse motion on the structures accommodating shortening of the belt these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids such fluids were characterised by 18o 6 2 d 50 20 13c 4 4 and temperatures of 270 to 450 c probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism hydrothermal fluids were more radiogenic 87sr 86sr 0 7010 to 0 7040 and possessed higher than did contemporaneous mantle komatiites or tholeiites and thus carried a contribution from older sialic basement a provinciality of87sr 86sr and 13c is evident signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres mineralised faults possess enrichments of large ion lithophile lil lil elements including k rb ba cs b and co2 and rare elements such as au ag as sb se te bi and w fluids were characterised by xco2 0 1 neutral to slightly acidic ph low salinity 3 wt k na 0 1 they carried minor ch4 co and n2 and they underwent transient effervescence of co2 during decompression clastic sediments occupy graben developed at fault flexures the40ar 39ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years

an improved hydrocarbon generation potential method for quantifying hydrocarbon generation and expulsion characteristics with application example of paleogene shahejie formation nanpu sag bohai bay basin abstract to evaluate petroleum resources it is important to quantify the hydrocarbon generation and expulsion characteristics of source rock the hydrocarbon generation potential method is an efficient model for calculating the characteristics of source rocks and evaluating the resource potential the previous hydrocarbon generation potential model was mainly established by measured rock eval pyrolysis data and due to inappropriate preservation measures an important component volatile hydrocarbon content of source rock may be significantly reduced prior methods may therefore not objectively reflect the properties of a source rock and cause unacceptable errors in the resource assessment this study proposes an improved hydrocarbon generation potential method the new method considers the initial hydrogen index hi0 and transformation ratio tr during the evolution of source rocks which can more realistically reflect the hydrocarbon generation and expulsion history of source rocks therefore the hydrocarbon evaporative loss qloss is calibrated and the hydrocarbon generation and expulsion features of source rocks are more accurately evaluated the proposed method is used to examine the effectiveness of the third member of the upper paleogene shahejie formation es3 in nanpu sag by utilizing the improved hydrocarbon generation potential model the hydrocarbon expulsion threshold of the es3 source rock is positioned at ro 0 875 the maximum hydrocarbon generation and expulsion potential qg and qe are 593 78 and 323 78 mg hc g toc respectively and the maximum hydrocarbon expulsion efficiency is 54 the maximum hydrocarbon generation and expulsion intensities are 500 104 t km2 and 250 104 t km2 respectively which locate source rock at the laoyemiao and gaoshangpu structural belts the amounts of generated and expelled hydrocarbon are 13 7 108 t and 6 9 108 t respectively and the resource potential of the tight oil of the es3 in the nanpu sag is 0 69 104 t compared with the previous method the improved hydrocarbon generation potential method limits the maximum qg and calibrates the qloss therefore the new method more objectively reflects the hydrocarbon generation and expulsion characteristics and resource prospect of the source rock

diagenesis porosity evolution and petroleum emplacement in tight gas reservoirs taranaki basin new zealand abstract tight gas reservoirs have become popular targets in petroleum exploration in recent years due largely to the increasing market demand for gas and also to technology advances used in extraction reservoir quality is typically poor due to deep burial diagenesis resulting in significant compaction cementation and illitization however analysis of tight reservoirs using integrated techniques can improve our understanding about the controls on reservoir quality and these results can potentially be used to help predict reservoir quality at other sites the use of integrated analysis of diagenetic and burial history is here shown for the eocene k3e kapuni group reservoir in cardiff 1 taranaki basin new zealand the k3e belongs to a deep gas play that was considered uncommercial in the early 1990 s due to poor reservoir quality associated with extensive authigenic illite potassium argon dating has shown that destruction of the reservoir through illitization occurred in the pliocene associated with a late stage heating and or fluid flow event timing of illite authigenesis in the k3e reservoir postdates the likely circulation of co2 rich fluids that caused reaction of feldspar to form kaolinite and quartz homogenization temperatures from two phase aqueous fluid inclusions within quartz cements together with 1d basin models of co2 expulsion from coaly source rocks indicate that feldspar reactions may have started in the mid miocene the co2 rich fluids are thought to have been generated by thermal decarboxylation of intraformational paleocene eocene coals at the same time oil was being expelled from older cretaceous coals and migrated into the mid late eocene reservoirs evidence for oil migration is demonstrated by the presence of residual oil and by the local occurrence of abundant oil bearing fluid inclusions the products of feldspar dissolution appear to be in reasonable balance with the amount of dissolved feldspar suggesting a relatively closed diagenetic system with little improvement in reservoir quality despite the large volume of feldspar dissolved petrographic evidence of reservoir sandstones at cardiff 1 demonstrates the presence of some illite free secondary macropores lined by residual oil this local preservation of porosity may be replicating the original distribution of oil saturated pores in the pliocene at the time when authigenic kaolinite underwent reaction to form illite remobilization of the oil probably occurred by gas flushing after the main phase of illitization at c 5 ma the data presented in this study are consistent with redistributed liquid petroleum into up dip traps and represent the potential for a new exploration play the eocene reservoir at cardiff 1 is currently gas charged with the pore system composed of approximately one third large macropores connected by a tortuous microporous network however it is possible that with the currently buoyant gas market and modern hydraulic fracturing techniques it may now be economic to flow gas from the locally large pores identified in the k3e reservoir

how ductile are ductile shear zones three premises of ductile deformation in the middle and lower crust are widely accepted 1 rocks flow with power law viscous rheology 2 localization in ductile shear zones involves strain softening and 3 fluid flows into and is channelized within ductile shear zones ductile viscous shear zones should therefore initially develop along planes of maximum shear stress strain soften and rotate as material planes into the field of progressive extension however the mean stress or pressure within a weak elongate viscous band being stretched is higher than the surrounding matrix and this is difficult to reconcile with premise 3 in contrast mohr coulomb brittle faults always have lower pressure within the fault zone flow of fluid and melt into high temperature shear zones therefore implies that ductile shear zones are not perfectly viscous but have a pressure dependent viscoplastic rheology the continued pressure dependence may reflect significant microcracking on the grain scale even when localized deformation does not produce larger scale discrete fractures

the potential of detrital garnet as a provenance proxy in the central swiss alps abstract detrital garnet is a promising candidate to reliably fingerprint sediment sources in the alps which has so far been complicated by the wide range and similarity of some of the lithologies garnet is present in most alpine sediments is easy to identify is fairly stable and most importantly reflects the type and the metamorphic grade of its source rock in its chemical composition this study aims to establish fingerprints based on detrital garnet composition for the most important tectonic units of the central alps including european penninic and adriatic basement rocks and their respective metasedimentary covers sediments collected from modern rivers which drain representative portions of the individual tectonic units contain a natural mixture of the various garnet populations present in each unit we selected six catchments in southwestern switzerland draining the external massifs helvetic sediments and the penninic nappe stack at the transition of alpine greenschist to amphibolite facies metamorphism in order to test the variability of alpine garnets and the role of inherited pre alpine garnets extraordinary grossular and spessartine rich garnets of the external massifs which experienced greenschist facies metamorphism are clearly distinguishable from generally almandine rich garnets supplied by the higher grade metamorphic penninic nappe stack the variable pyrope grossular and spessartine components of these almandine rich garnets can be used to further distinguish pre alpine alpine eclogite facies and low grade metasedimentary garnets this provenance proxy has the potential to be used for reconstructing sediment sources transport and dispersal patterns in a variety of settings throughout the alpine sedimentary record

deformation and ultrafine dynamic recrystallization of quartz in pseudotachylyte bearing brittle faults a matter of a few seconds abstract tectonic pseudotachylytes i e quenched friction induced silicate melts record coseismic slip along faults and are mainly reported from the brittle crust in association with cataclasites in this study we document the occurrence of recrystallization of quartz to ultrafine grained grain size 1 2 m aggregates along microshear zones 50 150 m thick in the host rock adjacent to pseudotachylytes from two different faults within quartzite schneeberg normal fault zone eastern alps and tonalite adamello fault southern alps in the brittle crust the transition from the host quartz to microshear zone interior includes i formation of high dislocation densities ii fine 0 3 0 5 m polygonization to subgrains defined by disordered to well ordered dislocation walls iii development of a mosaic aggregate of dislocation free new grains the crystallographic preferred orientation cpo of quartz towards the microshear zone shows a progressive misorientation from the host grain by subgrain rotation recrystallization to a nearly random cpo possibly related to grain boundary sliding these ultrafine aggregates appear to be typically associated with pseudotachylytes in nature we refer the crystal plastic deformation of quartz accompanied by dramatic grain size refinement to the coseismic stages of fault slip due to high differential stress and temperature transients induced by frictional heating microshear zones localized on precursory fractures developed during the stages of earthquake rupture propagation and the very initial stages of fault slip thermal models indicate that the process of recrystallization including recovery processes occurred in a time lapse of a few tens of seconds

dislocation creep of dry quartz small scale shear zones within the permian truzzo meta granite developed during the alpine orogeny at amphibolite facies conditions in these shear zones magmatic quartz deformed by dislocation creep and recrystallized dynamically by grain boundary migration with minor subgrain rotation recrystallization to a grain size of around 250 750 m consistent with flow at low differential stresses fourier transform infrared ftir spectroscopy reveals very low water contents in the interior of recrystallized grains in the form of discrete oh peaks 20 h 10 6 si and very little broad band absorption 100 h 10 6 si the spectral characteristics are comparable to those of dry brazil quartz in ftir spectra magmatic quartz grains show a broad absorption band related with high water concentrations only in those areas where fluid inclusions are present while other areas are dry drainage of fluid inclusions and synkinematic growth of hydrous minerals indicates that a hydrous fluid has been available during deformation loss of intragranular water during grain boundary migration recrystallization did not result in a microstructure indicative of hardening these ftir measurements provide the first evidence that quartz with extremely low intragranular water contents can deform in nature by dislocation creep at low differential stresses low intragranular water contents in naturally deformed quartz may not be necessarily indicative of a high strength and the results are contrary to implications taken from deformation experiments where very high water contents are required to allow dislocation creep in quartz it is suggested that dislocation creep of quartz in the truzzo meta granite is possible to occur at low differential stresses because sufficient amounts of intergranular water ensure a high recovery rate by grain boundary migration while the absence of significant amounts of intragranular water is not crucial at natural conditions

ultrafine grained quartz mylonites from high grade shear zones evidence for strong dry middle to lower crust creep strength of the crust depends upon the rheology of the most common mineral usually quartz recrystallized quartz grains in many high grade shear zones from the middle to lower crust are typically large millimeter sized implying active grain boundary migration but equivalents from old polymetamorphic and water deficient basement sheared at similar crustal depths can be very small for the latter strong crystallographic preferred orientation cpo of quartz with c axes aligned close to y progressive misorientation of crystals subgrain and dislocation development and core mantle structures with recrystallized grains of 2 8 m size all point to dislocation glide dominantly on the prism a system with recrystallization by subgrain rotation recrystallized grain size piezometry of such quartz indicates high flow stress in fine grained shear zones while the synkinematic metamorphic mineral assemblage and the cpo are typical of amphibolite facies conditions this is evidence that middle to lower crust is not inevitably weak due to its high temperature water content also has an important influence

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

amphibolite facies pseudotachylytes in premosello metagabbro and felsic mylonites ivrea zone italy abstract pseudotachylytes solidified friction induced melts produced during seismic slip that formed under high temperature ambient conditions might retain information on earthquake mechanics beneath the brittle ductile elasto frictional viscous plastic transition in the crust thin sharply bounded pseudotachylytes and ultramylonites occur together inside the granulite facies premosello metagabbro and inside country felsic mylonites of the ivrea zone italian southern alps petrographic and microstructural data indicate that the studied pseudotachylytes and ultramylonites are coeval and developed under amphibolite facies 500 650 c metamorphic conditions the occurrence of foliated pseudotachylytes and of local remnants of cataclastic microstructures within ultramylonites suggests that pseudotachylytes might have represented planar heterogeneities for nucleation of ultramylonites the association of coeval pseudotachylyte and mylonites is interpreted as caused by cyclic stages of coseismic high strain rate transients related to downward propagation of seismic ruptures from the upper brittle crust followed by post seismic stress relaxation by ductile flow