sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

the origin of the kupferschiefer type mineralization in the richelsdorf hills germany as deduced from stable isotope and organic geochemical studies abstract the kupferschiefer horizon in the richelsdorf section federal republic of germany acted as a geochemical trap by accumulating metals from ascending brines chemical composition of the extracted bitumens reflects a drastic change in the degree of oxidation of the organic matter towards rote faule this alteration pattern corresponds with regular changes in the isotopic composition of organic carbon and carbonate as well as with the base metal zonation around rote faule the enrichment of the organic material in 13c suggests the preferential release of isotopically light hydrogen equivalents through progressive degradation and oxidation of organic matter the opposite tendency towards lower 13c and 18o values of carbonate minerals provides evidence for isotopic reequilibration between carbonate and isotopically light oxidizing solutions the occurrence of isotopically heavy organic carbon together with low 13c and 18o values of carbonate suggests that 12c rich co2 generated due to oxidation of organic material may have been a source of carbonate the results reveal a post sedimentary formation of high grade mineralization and associated rote faule by ascending oxidizing brines they are in agreement with the results of mineralogical and geochemical studies which provided evidence for metal precipitation from basinal brines enriched in na and sulphate s the organic geochemical and isotopic data suggest that metal precipitation was caused by thermochemical sulphate reduction with organic matter acting as a reducing agent and proton donor

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

re os age of non mineralized black shale from the kupferschiefer poland and implications for metal enrichment six samples of non mineralized black shale from a kupferschiefer section in the northern part of the polish zechstein basin zdrada ig 8 drill hole 1026 16 1026 90 m were studied for re os isotopes and selected major and trace elements these black shales averaging 5 82 wt corg and 1 69 wt stot display very low base metal values up to 106 ppb cu 792 ppb pb and 144 ppb zn and have abundances of 64 1376 ppb re and 0 37 1 25 ppb os with a 187os 188os ratio of 6 95 22 5 the regression of all re os data yields an age of 247 20 ma which is within the range of uncertainties of previous rb sr and k ar geochronological studies the scatter in the re os data can be explained in terms of fluctuations in sedimentary conditions i e restricted basin with terrestrial influence

book review preferred orientation in deformed metals and rocks an introduction to modern texture analysis han rudolf wenk editor academic press inc new york 1985 xix 610 pp 50 50 59 50 hardback

palaeoceanography of the early zechstein sea during kupferschiefer deposition in the lower rhine basin germany a reappraisal from stable isotope and organic geochemical investigations abstract in the study area of the lower rhine basin the permian kupferschiefer was deposited in a shallow water environment water exchange from this marginal basin with the zechstein sea was restricted by palaeohighs the burial depth of the shale did not exceed 1000 m during the depositional history of most parts of the basin maturation of the organic matter was governed only by the geothermal gradient not exceeding 68 c km during the late carboniferous due to minor thermal alteration of organic matter diagenetic effects on the biomarker composition and the light stable isotope ratios c h o n of organic matter and carbonates are of minor importance in the present study isotopic and organic geochemical data are interpreted with respect to palaeoceanographic aspects the data provide information about salinity variations the nature of organisms living in the water column and the importance of bacterial activity in the sediment during deposition from the degree of methylation of 2 methyl 2 trimethyl tridecylchromans mttc an euhaline to mesohaline 30 40 sea water salinity during kupferschiefer sedimentation can be inferred the high abundance of biomarkers derived from green purple sulphur bacteria suggests h2s saturation of the bottom waters and maximum water depths below 100 m in the basin because these organisms live near the boundary between the photic zone and the anoxic euxinic bottom water at a depth of 10 30 m primary production in the upper water column was dominated by photosynthetic cyanobacteria or green algae in the sediment sulphate reduction occurred due to the availability of abundant sulphate and organic detritus from the overlying water column furthermore methanogenesis was active mostly during early kupferschiefer deposition this is reflected by the light carbon isotopic composition of organic matter originating from recycling of co2 generated by methane oxidizing bacteria in the water column saccate pollen are the only morphologically preserved organic matter in the sediment

simultaneous pure and simple shear the unifying deformation matrix abstract any simultaneous combination of finite simple shear and finite pure shear is a linear transformation which can be expressed as a single transformation matrix for two dimensions the matrix is upper triangular with an off diagonal term called the effective shear strain is a simple function of the pure and simple shear components for three dimensions a simultaneous combination of thrusting in the x direction thrusting in the y direction and a wrench in the x direction in addition to 3 orthogonal components of coaxial strain can also be represented by a 3 3 upper triangular matrix here three off diagonal terms xy x y and y z occur xy is a simple function of the horizontal coaxial strain values and thrusting in the x direction yz depends on the coaxial strain components in the y and z directions and the thrusting in the y direction while xz is related to all six strain components the matrix also allows for volume change either homogeneously or preferentially in a single direction a method of decomposing the deformation matrix into a series of incremental deformation matrices where each incremental deformation records the same kinematic vorticity number as the finite deformation is shown the orientation and magnitude of the finite strain ellipsoid ellipse is easily and accurately found at any increment during the deformation

sequence stratigraphy of carbonate evaporite basins models and application to the upper permian zechstein of northeast england and adjoining north sea the successions of carbonate evaporite basins which are periodically cut off from the world ocean are considered in terms of their sequence stratigraphy two basin types are distinguished those where incomplete drawdown takes place and those showing complete drawdown and wholesale basin desiccation it is argued that following relative sea level falls sequences begin with the evaporites precipitated as marginal lowstand gypsum wedges in the first basin type and as lowstand basin centre halite fills in the second the evaporites pass up into carbonate sediments which are mainly deposited on shallow water platforms around the basin during transgressive and highstand systems tracts the concepts and models developed are applied to the zechstein upper permian strata of northeast england and adjoining north sea seven sequences are proposed with some containing thin parasequences the sequence approach to carbonate evaporite basins which considers both basin margin and basin centre facies gives a more encompassing perspective of sedimentation than the traditional cycle concept with its emphasis on the basin centre

north south extension within the convergent himalayan region recent work by burg et al 1984 indicates the presence of east west striking gently north dipping normal faults in the higher himalayas and southern tibet that formed during postcollisional convergence of india and tibet these faults extend for at least 800 km along strike we interpret these normal faults as probable late miocene extensional features with perhaps several tens of kilometres of down to the north displacement a simple elastic model suggests that these normal faults may have formed during gravitational collapse of the miocene topographic front between india and tibet in this interpretation gravitational collapse occurred by southward motion relative to india and tibet of a wedge of crustal rocks bounded above by gently north dipping normal faults and below by thrust faults that probably dip north north south extension produced in this way is probably confined to upper crustal levels only and does not reflect regional extension of the entire lithosphere

combined isotopic and biomarker investigations of temperature and facies dependent variations in the kupferschiefer of the lower rhine basin northwestern germany abstract organic material in selected kupferschiefer samples from the lower rhine basin of nw germany has been studied using gas chromatography gc coupled gas chromatography mass spectrometry gc ms as well as c and h isotopic analyses of the organic matter o and c isotope compositions of carbonates have also been investigated the study area is located at the southwest shore of the ancient zechstein ocean the permian kupferschiefer was deposited here under anoxic lagoonal conditions five closely sampled profiles were analysed covering a total depth range of 350 760 m in order to detect temperature sensitive variations and compositional changes during kupferschiefer deposition variations in isotopic and molecular compositions of organic material as well as in calcite 13c within the kupferschiefer section in proximity of the basic intrusion that forms the krefeld high are the result of post sedimentary thermal degradation of organic matter variations in the 18o values of carbonates are governed primarily by the mineralogical composition cao mgo ratios outside this area the isotopic data point toward a slightly increasing salinity of the seawater during kupferschiefer sedimentation an input of terrigenous organic matter is indicated by the occurrence of the ring a degraded pentacyclic triterpenoid des a arborene the compound is thought to be generated from the related pentacyclic precursor by anaerobic bacteria the significant decrease of the compound towards the top of the kupferschiefer correlates with decreasing anoxic conditions during kupferschiefer sedimentation

simultaneous miocene extension and shortening in the himalayan orogen the south tibetan detachment system separates the high grade metamorphic core of the himalayan orogen from its weakly metamorphosed suprastructure it is thought to have developed in response to differences in gravitational potential energy produced by crustal thickening across the mountain front geochronologic data from the rongbuk valley north of qomolangma mount everest in southern tibet demonstrate that at least one segment of the detachment system was active between 19 and 22 million years ago an interval characterized by large scale crustal thickening at lower structural levels these data suggest that decoupling between an extending upper crust and a converging lower crust was an important aspect of himalayan tectonics in miocene time

multiproxy reconstruction of oceanographic conditions in the southern epeiric kupferschiefer sea late permian based on redox sensitive trace elements molybdenum isotopes and biomarkers abstract the key drivers controlling the redox state of seawater and sediment pore waters in low energy environments can be inferred from redox sensitive trace elements rste molecular biomarkers and trace metal isotopes here we apply a combination of these tools to the upper permian kupferschiefer t1 from the thuringian basin deposited in the southern part of the semi enclosed kupferschiefer sea enrichment patterns of the rstes molybdenum mo and uranium u as well as biomarker data attest to the rapid development of euxinic conditions in basin settings during early t1 times which became progressively less extreme during t1 deposition the evolution of redox conditions in basinal settings and the associated delay in the onset of euxinia at more shallow marginal sites can be attributed to the interaction of sea level change with basin paleogeography euxinia in the southern kupferschiefer sea did not lead to near quantitative depletion of aqueous mo possibly due to short deepwater renewal times in the thuringian basin low aqueous h 2 s concentrations the continuous resupply of rste during transgression and declining burial rates of rstes throughout t1 times drawdown of rste is however indicated for euxinic lagoon environments moreover admixture of freshwater supplied to these lagoons by rivers strongly impacted local seawater chemistry the highest mo isotope compositions of 1 70 in basin sediments allow a minimum kupferschiefer sea seawater composition of 2 40 to be estimated this composition is similar to the 2 30 estimate for the late permian open ocean and confirms a strong hydrographic connection between the epeiric kupferschiefer sea and the global ocean the substantial variation in mo isotope signatures is paralleled by diagnostic shifts in biomarkers responding to oxygenation in different parts of the water column water column chemistry has been affected by variation in sea level hydrodynamic restriction riverine freshwater influx and evaporitic conditions in shallow lagoons elucidation of the relative role of each driving factor by a single geochemical proxy is not feasible but the complex scenario can be disentangled by a multiproxy approach

patterns of stretch trajectories and strain rates within spreading gliding nappes abstract stretch trajectories in vertical flow planes through superficial nappes are thought to be specific for some classical mechanical models so that their recognition in the field is of particular interest in order to find a pattern of stretch trajectories related to a gravitational process a strain factorization is attempted from experimental scale models of nappes where spreading and gliding are combined the strain within this type of nappes is schematically considered as the simultaneous combination of two components a simple shearing component and a pure shearing component spatial and time distribution of these two components is computed from both time and spatial evolution of the strain pattern within the scale models a better understanding of stretch trajectories in spreading gliding nappes is consequently provided strain rates are also computed from scale models and the sudden increase of strain rate from top to bottom is explained finally a mechanical model of spreading gliding nappe is briefly discussed

the composition of brines in the early diagenetic mineralization of the permian kupferschiefer in germany the kupferschiefer is an approximately 0 5 m thick black marly shale of lower zechstein age in germany if one includes some of its footwall and hanging wall it contains 300 mt cu 800 mt zn and 300 mt pb the regional pattern of metal distribution demonstrates its relationship to variscan and permian tectonic structures faults and the topographic relief of the basement apparently controlled the uprise and lateral migration of reducing and slightly acid hot brines from deeper crustal levels to supply the metals for the mineralization of the proto kupferschiefer deep fluids are mainly richer in zn than pb and richer in pb than cu mixing of such slightly acid fluids with slightly alkaline formation waters seawater caused a gradient in ph from about three to eight and in sulfide concentration most of the sulfide came from dissolved pyrite which was very light in sulfur isotopes this gradient controlled the sequential precipitation of bornite chalcopyrite chalcocite galena and sphalerite which is observed in a lateral and vertical zoning of these sulfides the fluids experienced a fractionation of the metals during migration over meter to kilometer distances from the tectonically controlled vents within the unconsolidated proto kupferschiefer close to the vents the sulfide deposits attained concentrations up to 2 zn pb cu the migration of the metals over large distances took place in unconsolidated sediment thus the major mineralization of the kupferschiefer has to be classed as an early diagenetic process

asymmetric quartz c axis fabrics and flow vorticity a study using rotated garnets abstract the development of a type i crossed girdle c axis fabric with an asymmetric density distribution and an internally asymmetrical skeletal outline is examined in a specimen of garnet bearing mylonitic quartzite from the betic movement zone in southern spain the garnets are pre mylonitic skeletal porphyroblasts that rotated during mylonitic deformation but preserved a strain free equilibrium microstructure and a random c axis fabric it follows that the asymmetry of the density distribution must result from the deformation history itself the sense of asymmetry of the c axis population and that of the skeletal outline are consistent with the sense of vorticity inferred from extensional crenulations and asymmetric microboudinage and also with the sense of rotation of the garnets analysis of the rotation angles with aspect ratio of the garnet porphyroblasts demonstrates that a pure shear component was involved in an essentially non coaxial flow this may explain the internal asymmetry of the fabric skeleton and confirms the idea that a spectrum exists of type i fabrics intermediate between the theoretically predicted fabrics for pure and simple shear a tentative reconstruction of the kinematic framework suggests that the central segment of the fabric skeleton is linked to the extensional apophysis of the flow

the marl slate a model for the precipitation of calcite dolomite and sulphides in a newly formed anoxic sea detailed studies of a new complete marl slate core in south yorkshire have provided information on isotopic 13c 18o 34s and geochemical variations trace elements and c s ratio which enable the formulation of a model for carbonate and sulphide precipitation in the late permian zechstein sea calcite and dolomite are intimately associated the fine lamination organic character and absence of benthos in the sediments are indicative of anoxic conditions lithologically the core can be divided into a lower predominantly sapropelic marl slate 2 m and an upper transition zone 0 65 m of alternating sapropel and calcite rich and dolomite rich carbonates c s ratios are 2 22 for the marl slate and 1 72 for the transition zone respectively both characteristic of anoxic environments 18o in the carbonates shows a large and systematic variation closely mirrored by variations in calcite dolomite ratio the results suggest a fractionation factor equivalent to a depletion of 3 8 for 18o and 1 5 for 13c in calcite the 34s values of pyrite are isotopically light mean value 32 7 suggesting a fractionation factor for the marl slate of almost 44 typical of anoxic basins the results are related to stratification in the early zechstein sea calcite was precipitated in oxic upper layers above the halocline below the oxic anoxic boundary framboidal pyrite was precipitated resulting in lower sulphate concentration and elevated mg ca ratio due to calcite precipitation as a result of this dolomite formation occurred below the oxic anoxic interface within the anoxic water column and in bottom sediments variations in calcite dolomite ratios and isotopic variations are thus explained by fluctuations in the relative level of the oxic anoxic boundary in the zechstein sea

isotope shifts in the late permian of the delaware basin texas precisely timed by varved sediments closely spaced samples 285 in number of varved sediments from the upper permian in delaware basin texas have been analyzed for 13ccarb 13corg 18ocarb corg ccarb and calcite dolomite 13c records a dramatic rise from 2 8 to 5 7 in only 4400 years detected in three sections across the basin extrapolating smoothly through a 600 year interruption by a local west side of the basin fresh water inflow evidenced by low 18o this continuity and low corg within the basin both indicate that the excess net deposition of corg necessary to generate the rise in 13c took place in the ocean external to the delaware basin correlation with similar records from the zechstein basin suggest that the event was world wide although this poses obvious difficulties for the carbon cycle the rate of rise of 13c and its sustained high level must imply conversions of oxidized carbon to reduced carbon that are very large depending on which reservoirs were involved

quantitative kinematic flow analysis from the main central thrust zone nw himalaya india implications for a decelerating strain path and the extrusion of orogenic wedges quantitative kinematic indicators from the main central thrust zone mctz in the nw himalaya have been used to characterize the type of flow during deformation different generations of tension gashes have been rotated by variable angles with respect to the mylonitic foliation forming associated fringe folds these record the late stage brittle ductile flow and reveal that a strong pure shear component of deformation occurred throughout the mctz to characterize earlier deformation increments fabrics from highly deformed quartz ribbons were analyzed well developed shape and lattice preferred orientation patterns show a systematic change of the glide systems and suggest inverted palaeotemperatures within the mctz investigations of the c axes patterns reveal a strong asymmetry at the top of the mctz whereas the samples from the base of the mctz show almost perfectly symmetrical type i crossed girdles deformation within the mctz probably started close to simple shear flow at higher temperatures which progressively became a more general shear during cooling and ended in a pure shear dominated flow during the final stages of brittle ductile deformation i e a decelerating strain path using the higher himalaya crystalline as an example a kinematic model for the extrusion of crustal wedges above major thrust zones is suggested

reconstruction of deformation and flow parameters from deformed vein sets abstract in any homogeneously deformed material sets of material lines with a similar stretch history occupy sectors with a scale and orientation that depend on finite strain area change rate and vorticity of the parent flow if the size and shape of these material line sectors are known they can be used to determine the sense of shear and to calculate deformation and flow parameters even if actual stretches along material lines are unknown in rocks which have undergone near homogeneous deformation on a large scale the orientation of sets of boudinaged folded and folded boudinaged or boudinaged folded veins can be used for such calculations a general theoretical background to the problem is presented and a mohr circle construction to carry out the deformation and flow analysis is introduced among other statements the theory predicts that shortened or folded boudins must develop in non coaxial monophase deformation with considerable area change in the plane of observation or in polyphase deformation

occurrence of subtidal dolomite in a hypersaline lagoon kuwait we report here the discovery of subtidal dolomite in a shallow hypersaline lagoon during a study of recent carbonate and evaporite sediments in the al khiran region of southern kuwait in the northern part of the arabian gulf fig 1 diagenetic dolomites are known from a variety of geographical locations and a spectrum of environmental conditions1 6 although many occurrences of subaqueous dolomite have been documented1 4 none has been reported from the subtidal areas of extensive recent marine carbonate environments the al khiran dolomites show complex polyhedral crystal habits and a composition which ranges from ca51mg49 to ca56mg44 we postulate that a partial removal of dissolved sulphate ions by bacterial reduction from the interstitial waters of the sediments the moderate mg2 ca2 ratios of the hypersaline waters and the occasional near schizohaline conditions in the lagoon may be responsible for the formation of this dolomite

organic geochemistry and mineralogy i characterisation of organic matter associated with metal deposits abstract as geochemical appraisals of mineral regions of commercial prospectivity evolve the organic matter associated with metal rich ores has attracted greater attention petroleum basin and modern seafloor hydrothermal vent studies have suggested that organic matter can have a significant influence on the behaviour of mineralising fluids there have been many isolated reports of certain organic compositional or morphological e g pyrobitumen features showing an apparent relationships with hydrothermal fluids or minerals raising expectations that organic based parameters might be useful to mineral exploration however the understanding of organic inorganic relationships in earth systems is far from complete for example the detailed mechanics of the interaction of organics with hydrothermal fluids over geological time remain largely undefined organic geochemistry studies have traditionally involved the measurement and interpretation of the hydrocarbon composition of sedimentary rocks here we review the types of aliphatic hydrocarbons aromatic hydrocarbons and metalloporphyrins often detected from organic geochemical investigations in mineral rich regions such molecular data can be particularly diagnostic of biochemical sources and the palaeo environments at the time mineral associated organic matter was deposited sub surface trends of hydrocarbon alteration may also reflect major biogeochemical processes such as thermal maturity and biodegradation organic geochemistry data can also occasionally provide information about the nature e g origin composition temperatures and migration pathways of hydrothermal fluids and can make a contribution to holistic ore genesis models the well preserved organic matter associated with the economic here s your chance pb zn ag mine paleoproterozoic barney creek formation mcarthur basin australia and the transition metal rich early permian kupferschiefer formation germany poland have attracted significant attention a more detailed summary of the organic character of these deposits is provided to highlight the contribution organic geochemistry can make to understanding mineralisation processes most organic geochemical studies of highly mineralised regions however have not adequately addressed the significance of organic matter to mineralisation a slightly different analytical focus than traditionally used for exploration appraisal of petroleum hydrocarbons may be required to properly evaluate the significance of organic species to the mobilisation transport and deposition of ore metals the characterisation and subsequent thermodynamic modeling of organic substances and complexes within metalliferous hydrothermal systems will contribute to a better understanding of the nature and role of organic inorganic fluids or other affiliated organics in ore systems

carbon cycle changes of the zechstein sea isotopic transition zone in the marl slate the carbon isotope composition of carbonate rocks is one parameter used to study the carbon sulphur and oxygen cycles through geological time1 2 the understanding of these interrelated cycles is important in quantitative flux modelling of sedimentary rocks the carbon isotope composition in the large reservoir of dissolved carbonate in ocean water is a result of mass balance between the amount of carbon in the reduced organic reservoir and the oxidized carbonate reservoir at any given stage the reduced carbon reservoir preferentially sequesters 12c owing to biological fractionation processes any change in the removal ratio of oxidized reduced carbon will be reflected by the change of the 13c value of the oceanic carbonate system here we present a detailed study of the change in 13c which took place at the base of the upper permian zechstein sequence

marine hydrocarbon source rocks of the upper permian longtan formation and their contribution to gas accumulation in the northeastern sichuan basin southwest china abstract identification of the main hydrocarbon source rocks of the large puguang gas field northeastern sichuan basin southwest china has been the subject of much discussion in recent years a key aspect has been the lack of a comprehensive understanding of the development of hydrocarbon source rocks of the upper permian longtan formation which had been thought to contain mainly coal seams and thick carbonate layers in this paper based on geological data from more than ten wells and outcrops and their related mineralogy and geochemistry we investigated the depositional environment and main factors controlling organic matter enrichment in the longtan formation we propose a model which combines information on the geological environment and biological changes over time in the model organic matter from prolific phytoplankton blooms was deposited in quiescent platform interior sags with rising sea levels during the longtan period the area from bazhong to dazhou was a platform interior sag with relatively deep water and a closed environment which was controlled by multiple factors including syngenetic fault settling isolation of submarine uplifts and rising sea levels leading to water column stratification although the bottom water was anoxic the phytoplankton were able to bloom in the well lit upper euphotic zone thus giving rise to a set of sapropelic black shales and marlstones containing mostly algal organic matter with minor terrestrial contributions as a consequence these rocks have a high hydrocarbon generation potentials and can be classified as high quality source rocks the area from bazhong to dazhou is a center of hydrocarbon generation being the main source of reservoired paleo oils and presently discovered as pyrobitumen in the puguang gas field the identification of these source rocks is very important to guide future petroleum exploration in the northeastern sichuan basin

on the origin of copper mineralization in the kupferschiefer a suiphur isotope study sulphur isotopic compositions of copper and iron sulphides dispersed and vein mineralization from the polish part of the kupferschiefer were determined and compared with data from the literature most of the 34s values of sulphides range from about 40 to 25 indicating sulphide precipitation during bacterial sulphate reduction in an open system which gradually chanes into a closed system sulphides from veins are usually enriched in 34s compared to finely dispersed mineralization and were probably formed in a more closed system copper sulphides are generally a few permil heavier than pyrite coupled with detailed microscopical observations the isotope data suggest that the mineralization is either syngenetic or early diagenetic

towards determining the thermal state of old ocean lithosphere heat flow measurements from the blake bahama outer ridge north westem atlantic summary detailed suites of heat flow measurements have been completed at four sites on and to the east of the southern end of the blake bahama outer ridge in the north west atlantic on ocean crust which ranges in age from roughly 115 to 155 ma the principal purpose of these measurements was to compare instrumental techniques and to examine the decay of heat flow with age on old ocean floor multi penetration gradient measurements were made at the youngest site with a 2 5 m outrigger probe and multipenetration heat flow measurements at the other three sites with a new 3 5 m violin bow type instrument in addition at all four sites the gradient was measured using outriggers on a 9 m piston or gravity corer and conductivities were measured on the sediment recovered the average of thermal conductivities measured on cored sediments agreed to better than 2 per cent with the average of conductivities measured in situ at the oldest three sites such good agreement is surprising given the problems associated with making measurements on sediments recovered in cores the greatest measurement errors in determining heat flow were found to be caused by temperature disturbances generated by the piston coring process gravity coring reduced these disturbances but provided a less representative section for measuring thermal conductivity the violin bow probe which measures average interval conductivities in situ provided the most reliable heat flow determinations the accuracy of these determinations was limited primarily by the presence of thermal disturbances due to bottom water temperature variations the heat flow averages at all four sites are virtually identical they range from 47mw m 2 1 12 cal cm 2s 1 to 49mw m 2 1 17 cal cm 2s 1 with standard errors of less than 2 mw m 2 0 05 cal cm 2s 1 the constancy and the value of heat flow over lithosphere of this age and the local shallowing of depth with increasing age in the region containing the heat flow sites cannot be explained by either a simple plate or a boundary layer lithosphere cooling model the unexpectedly high heat flow and shallow depths may result from lithospheric thinning and perhaps dynamic forces associated with a thermal perturbation beneath the plate

strain and kinematic analysis in general shear zones we present a unifying theory for the development and distribution of strain markers and kinematic indicators in zones of general shear and thus provide a framework in which data previously considered contradictory may be understood rigid and deformable porphyroclast systems including and complex grains are potential indicators of both strain and flow the shapes and distribution of such porphyroclast systems may be used to distinguish among different tectonic regimes general shear is divided into two fields sub simple shear in which the rotational component of the strain is less than that for simple shear and super simple shear in which the rotational component is greater than for simple shear sub simple shear may involve narrowing or broadening of shear zones super simple shear regimes are possible in local regions such as the vicinities of deformable porphyroclasts but must be enclosed by regimes of sub simple shear the polar mohr constructions for finite deformation and flow are useful to analyze general shear in theory the hyperbolic net is employed for practical plotting of real data and derivation of the kinematic vorticity number wn this number represents the relative contributions of pure and simple shear in steady flow in nature deformation is thought to build up and decay by processes that may invalidate the assumption of constant flow regime we therefore introduce the concept of accelerating deformation and analyze the implications of non steady flow for the shearing histories of deformed objects