mineralogical and geochemical characteristics of the paleozoic source rocks akkas gas field western desert of iraq implications for their origin maturation and ordovician silurian transition abstract ordovician silurian black shales are the source rocks in the palaeozoic petroleum system in iraq however their source and depositional conditions from their mineralogy and inorganic geochemistry are quite lacking in previous works these shales also provide an opportunity to examine the changes in paleoenvironment paleoclimate and paleoredox conditions across the ordovician silurian transition the ordovician black shales comprise of kaolinite illite chlorite quartz dolomite calcite and traces of feldspars and siderite while the silurian black shales comprise of illite quartz calcite dolomite and pyrite calculated sio2 wt and al2o3 tio2 ratios suggest felsic source rocks for the ordovician black shales and intermediate source rocks for silurian hot shales the shallow marine setting for the ordovician black shales that changed to a deeper environment during the silurian time was interpreted from the v p2o5 and al2o3 diagrams is consistent with the abundance of trace fossils monocraterion sp cruziana problematica diplichnites sp and skolithos sp which refer to proximal shallow marine conditions and abundance of graptolites monograptus in the silurian black shales which refer to an open marine environment paleoredox indicators such as toc and mn contents as well as ni co v ni u th and v cr ratios prove fluctuation of redox conditions from oxic in the ordovician shales to anoxic in the silurian black shales late ordovician glaciation in iraq can be indicated from the low values of chemical index of weathering cia 52 58 in the samples from the upper part of the upper part of the khabour formation that refer to cold and arid climate conditions that prevailed during the late ordovician time abundance of extrabasinal and poor sorted mud clasts in this interval might support the glaciogenic origin of this part the black shales in the khabour formation is considered as fair source rock average toc 0 9 wt while that in the akkas formation is an excellent source rock average toc 13 2 wt for hydrocarbon generation kerogen in the ordovician and silurian black shales were derived from marine organic matter as indicated by the binary plot and total c1 c15 n c6 n c14 n c15 ternary diagram organic matter in the ordovician black shales is highly matured compared to that in the silurian black shales due to higher illite crystallinity ic values in the ordovician 0 61 0 75 d2 relative to that in the silurian 0 45 0 55 d2 black shales

carbon isotopes and event stratigraphy near the ordovician silurian boundary yichang south china abstract the organic carbon isotope data through the unweathered ordovician silurian boundary strata at the wangjiawan riverside section which is c 180 m southeast of the wangjiawan north section the gssp for the base of the hirnantian stage upper ordovician show that a positive 13 c org excursion begins just below the base of the hirnantian stage and peaks in the lower part of the n extraordinarius biozone this is followed by an interval of slightly reduced 13 c values and a second peak of 2 above pre hirnantian values which occurs in the lower part of the n persculptus biozone upper hirnantian the peaks in 13 c org values can be correlated well with episodes of glacial expansion described from africa and peri gondwanan europe evidence from sedimentological faunal and geochemical data from south china as well as the evidence of glacial sediments in north africa all suggests a short lived glaciation of 1 ma in the ordovician south pole region consisting of at least two major pulses the first phase of gradual glacial expansion began just before the hirnantian epoch and the second phase ended with rapid melting in the late hirnantian early n persculptus biozone

making methane down deep the global ocean is earth s largest biome which extends into the sediments and igneous crust below the oceans the abundance of microbial life beneath the sea floor is at least comparable to that in the oceans 1 but this biome remains poorly understood the ramifications of a massive buried biosphere are important on a global scale with sub sea floor microbes playing a crucial role in carbon sequestration element cycles and earth s evolution and likely encompassing staggering metabolic and genetic diversity on page 420 of this issue inagaki et al 2 report that even at almost 2 5 km beneath the sea floor microbial life is not only present and compositionally distinct from that in shallower sediments but also producing methane

optical characteristics of graptolite bearing sediments and its implication for thermal maturity assessment abstract graptolite reflectance was thought to be one of the most useful thermal maturity indicators for graptolite bearing sediments however the relationship between graptolite reflectance and vitrinite reflectance is not well established graptolites especially in the wufeng longmaxi formations from the ordovician to silurian of south china have been mistaken for vitrinite like particles or solid bitumen which results in inconsistent data on the thermal maturity in this paper we have employed optical microscope techniques to describe the detailed optical characteristics of graptolites and solid bitumen in the wufeng longmaxi formations laboratory simulation of maturation was used to determine the relationship between graptolite reflectance and vitrinite reflectance the organic constituents in the wufeng longmaxi formations are mainly composed of graptolites and solid bitumen granular and non granular graptolites were observed in the wufeng longmaxi formations with non granular as the most common texture solid bitumen can be distinguished from non granular graptolites by its coarse surface weaker anisotropy and lower random reflectance the combination of non polarized and polarized light is very helpful to distinguish solid bitumen from graptolite for comparison organic material from the early ordovician alum shale formation of sweden and estonia was also studied the macerals of the alum shales are mainly composed of lamalginites mineral bituminous groundmasses graptolites and solid bitumen the major textures of the graptolites in the sweden and estonia sediments are non granular and granular respectively both non granular graptolite and vitrinite reflectances display a systematic increase with the increase of heating temperature and time the granular graptolites in the estonian sample were gradually changed to non granular graptolites following laboratory simulated maturation indicating that granular graptolites can transform into non granular graptolites with maturation solid bitumen in the wufeng longmaxi formations was derived from the solid residue of kerogen and or post oil bitumen the graptolite random reflectance is a better thermal maturity indicator than graptolite maximum reflectance and is more precise due to the smaller standard deviation several equations are proposed to determine the thermal maturity of the graptolite bearing sediments based on graptolite random reflectance graptolite maximum reflectance and solid bitumen random reflectance

paleozoic cambrian through devonian anoxitropic biotopes berry w b n wilde p and quinby hunt m s 1989 paleozoic cambrian through devonian anoxitropic biotopes palaeogeogr palaeoclimatol palaeoecol 74 3 13 the oxygen poor to denitrified waters of modern oceans provide an analog for open ocean conditions which contained the early paleozoic graptolite biotope certain euphausiids other zooplankton and fish as demonstrated in the eastern tropical pacific are found concentrated in and about denitrified waters the boundary zone between oxic and denitrified waters show intense organismal growth due to the increased chemical availability of nutrients as reduced nitrogen compounds such waters are areally limited in the present cold and well ventilated modern ocean the distribution patterns showing attraction to low or oxygen depleted waters anoxitropy in these modern open marine faunas suggest that early paleozoic plankton and nekton preserved in lithofacies formed under low oxygen or anoxic coditions could have been similarly attracted to the more extensive ancient denitrified and anoxic waters the major paleozoic faunal groups in order of their occupation of the niche include agnostid and olenid trilobites graptoloid graptolites styliolinids thin shelled bivalves small orthocone nautiloids and early ammonoids the expansion of low oxygen to anoxic waters across the shelves during warm climates in the early paleozoic may be correlated with major evolutionary radiations in the graptolites and possibly in the early ammonites

lithofacies and depositional mechanisms of the ordovician silurian wufeng longmaxi organic rich shales in the upper yangtze area southern china the ordovician silurian organic rich shales in the wufeng and longmaxi formations are widespread in southern china and are the most important shale gas producers in china the shales display varying total organic carbon content ranging from 0 2 to 6 and are composed of black siliceous mudstone shelly limestone siliceous clay rich mudstone gray silty shaly interlaminated mudstone gray argillaceous mudstone and calcareous or dolomitic mudstone detailed stratigraphic correlation of these formations was achieved and a high resolution sequence stratigraphy was constructed based on the integration of well log data mineralogical geochemical and petrophysical analyses the wufeng formation and the guanyinqiao bed were interpreted to be a condensed section with four cycles of sea level fluctuation the longmaxi formation consists of three members the long 1 member was interpreted to be a third order depositional sequence that can be subdivided into a transgressive systems tract an early highstand systems tract and a late highstand systems tract within the constructed isochronal stratigraphic framework the characteristics and genetic mechanism of different shale lithofacies were studied the deposition of black siliceous mudstone of high total organic carbon in the wufeng formation and the long 1 transgressive systems tract was likely influenced by volcanic activity the guanyinqiao shelly limestone or calcareous mudstone was associated with the ordovician silurian transition when glaciation and mass extinction took place the gray silty shaly interlaminated mudstone of moderate total organic carbon in the long 1 early highstand systems tract was the product of bottom flow intrusion the deposition of gray argillaceous mudstone and calcareous or dolomitic mudstone with low total organic carbon in the long 1 late highstand systems tract resulted from enhanced terrigenous input from peripheral uplifts the distribution pattern of different lithofacies varies greatly in the upper yangtze area and this difference is a result of dissimilar sediment provenances and variable hydraulic restriction levels that were controlled by basin geometry a better understanding of the distribution pattern and depositional history of the wufeng and longmaxi formations might provide guidance for future profitable shale gas exploration

fracture development in paleozoic shale of chongqing area south china part two numerical simulation of tectonic stress field and prediction of fractures distribution abstract a tectonics sedimentation evolution has been researched in southeast chongqing and the reasonable longmaxi shale highstand system tract hst and transgressive system tract tst geological model were built respectively based on the rock mechanical test and acoustic emission experiment which the samples are from field outcrop and the yuye 1 well the longmaxi shale two dimension tectonic stress field during the cenozoic was simulated by the finite element method and the distribution of fractures was predicted the research results show that the tectonic stress field and the distribution of fractures were controlled by lithology and structure as a result of cretaceous movement there are trough like folds wide spaced synclines battlement like folds similar spaces between synclines and anticlines and ejective folds wide spaced anticlines which are regularly distributed from southeast to northwest in the study area since the strain rate and other physical factors such as the viscosity are not taken into account and the stress intensity is the main factor that determines the tectonic strength therefore the stronger tectonic strength leads the higher stress intensity in the eastern and southeastern study area than in the northwest the fracture zones are mainly concentrated in the fold axis transition locations of faults and folds the regions where are adjacent to faults the fragile mineral contents such as siliceous rock carbonate rock and feldspar in the shelf facies shale from south of the study area are higher than in the bathyal facies and abyssal facies shale from center of the study area the shales characterized by low poisson s ratio and high elastic modulus from south of the study area are easily broken during cenozoic orogenic movement

temporal variations in parameters reflecting terminal electron accepting processes in an aquifer contaminated with waste fuel and chlorinated solvents abstract a fundamental issue in aquifer biogeochemistry is the means by which solute transport geochemical processes and microbiological activity combine to produce spatial and temporal variations in redox zonation in this paper we describe the temporal variability of teap conditions in shallow groundwater contaminated with both waste fuel and chlorinated solvents teap parameters including methane dissolved iron and dissolved hydrogen were measured to characterize the contaminant plume over a 3 year period we observed that concentrations of teap parameters changed on different time scales and appear to be related in part to recharge events changes in all teap parameters were observed on short time scales months and over a longer 3 year period the results indicate that 1 interpretations of teap conditions in aquifers contaminated with a variety of organic chemicals such as those with petroleum hydrocarbons and chlorinated solvents must consider additional hydrogen consuming reactions e g dehalogenation 2 interpretations must consider the roles of both in situ at the sampling point biogeochemical and solute transport processes and 3 determinations of microbial communities are often necessary to confirm the interpretations made from geochemical and hydrogeological measurements on these processes

ordovician reef hosted jiaodingshan mn co deposit and dawashan mn deposit sichuan province china abstract the jiaodingshan mn co and dawashan mn deposits are located in the approximately 2 m thick daduhe unit of the wufengian strata of late ordovician ashgill age paleogeographic reconstruction places the deposits at the time of their formation in a gulf between chengdu submarine rise and the kangdian continent the jiaodingshan and dawashan deposits occur in algal reef facies the former in an atoll like structure and the latter in a pinnacle reef ores are mainly composed of rhodochrosite kutnahorite hausmannite braunite manganosite and bementite dark red yellowish pink brown green gray and black ores are massive banded laminated spheroidal and cryptalgal oncolite stromatolite algal filaments boundstones blue green and red algal fossils show in situ growth positions samples of high grade jiaodingshan and dawashan ores assay as much as 66 7 mno jiaodingshan mn carbonate ores have mean contents of ba co and pb somewhat higher than in dawashan ores cobalt is widely distributed and strongly enriched in all rock types as compared to its crustal mean content cobalt is correlated with cu ni and mgo in both deposits and additionally with ba and zn in the dawashan deposit the 13 c pdb values of mn carbonate ores 7 8 to 16 3 indicate contributions of carbon from both seawater bicarbonate and the bacterial degradation of organic matter the latter being 33 to 68 assuming about 24 for the 13 c pdb of the organic matter host limestones derived carbon predominantly from seawater bicarbonate 13 c pdb of 0 2 to 7 nw trending fault zones controlled development of lithofacies whereas ne trending fault zones provided pathways for movement of fluids the source of co ni and cu was mainly from weathering of mafic and ultramafic rocks on the kangdian continent whereas contemporaneous volcanic eruptions were of secondary importance the reefs were likely mineralized during early diagenesis under shallow burial the reefs were highly porous and acted as the locus for metasomatic replacement by mn that combined with co 2 produced during oxidation of organic matter in the zone of sulfate reduction and seawater bicarbonate that metasomatic replacement formed the rhodochrosite ores

establishing baseline water quality for household wells within the marcellus shale gas region susquehanna county pennsylvania u s a abstract flowback fluids associated with hydraulic fracturing shale gas extraction are a potential source of contamination for shallow aquifers in the marcellus shale region of northeastern pennsylvania certified water tests have been used to establish baseline water chemistry of private drinking water wells this study investigates whether a single certified multiparameter water test is sufficient for establishing baseline water chemistry from which possible future contamination by flowback waters could be reliably recognized we analyzed the water chemistry major and minor inorganic elements and stable isotopic composition of multiple samples collected from lake spring and well water from 35 houses around fiddle lake susquehanna county pa that were collected over approximately a two year period statistical models estimated variance of results within and between households and tested for significant differences between means of our repeated measurements and prior certified water tests overall groundwater chemistry varies more spatially due to heterogeneity of minerals within the bedrock aquifer and due to varying inputs of road salt runoff from paved roads than it does temporally at a single location for wells located within road salt runoff zones na and cl concentrations although elevated are generally consistent through repeated measurements high acid neutralizing capacity anc and base cation concentrations in well water sourced from mineral weathering reactions and a uniform stable isotopic composition for well water suggests long flowpaths for groundwater that dampen seasonal variability of most elements exceptions occur for two wells within road salt runoff zones that show the greatest range of concentrations for na and cl suggesting that these wells have a faster pathway to surficial recharge additionally sampling protocols can induce variability for fe mn and pb making other elements identified in flowback fluids ba br ca cl mg na sr more dependable indicators of contamination although there is general concordance between our repeated measurements and the certified test results characterizing baseline chemistry is strengthened when results from multiple households are combined to establish regional upper baseline limits that will have a low probability of being exceeded by future samples unless conditions have changed

geochemical characteristics in the longmaxi formation early silurian of south china implications for organic matter accumulation abstract the organic rich early silurian sediments longmaxi formation on the yangtze platform are considered to be one of the main source rocks in south china in order to investigate the mechanism of organic accumulation multiple geochemical proxies including redox parameters s c and trace element ratios productivity indices p and ba contents and clastic influx indicator ti al ratios are presented here from the hehua section yichang hubei province the longmaxi sediments have high toc contents 3 00 10 85 avg 5 63 low pyrite sulfur contents 0 42 1 14 avg 0 59 high p 0 02 0 44 avg 0 12 and ba contents 576 65 2542 43 ppm avg 1592 17 ppm calculated s c th u ni co v cr and v v ni ratios are 0 05 0 24 avg 0 12 0 23 9 86 avg 2 30 2 65 46 24 avg 15 46 0 27 14 42 avg 3 75 and 0 36 0 96 avg 0 75 respectively s c and trace element ratios together with pyrite morphology suggest dysoxic anoxic conditions prevailed during deposition of the longmaxi intervals which was mainly caused by a worldwide marine transgression after the melting of gondwana glaciation productivity proxies indicate that the organic rich longmaxi sediments were deposited in moderate to high primary productivity water columns the consistent ti al ratios suggest a rather homogeneous nature for the detrital supply geochemical data provide a good constraint on the accumulation of organic matter and relevant oceanic environment anoxic conditions together with relatively high productivity were likely responsible for the accumulation of organic rich sediments during the longmaxi interval

sponge dominated offshore benthic ecosystems across south china in the aftermath of the end ordovician mass extinction abstract offshore benthic communities were sparse after the end ordovician mass extinction the recent discovery of diverse abundant sponges in south eastern china anhui and zhejiang provinces that flourished during the hirnantian late ordovician post extinction interval raises questions over the extent and ecological significance of the sponge community at that time this paper dramatically expands the scale of the hirnantian sponge fauna within south china with seven new occurrences across 2000 km these occurrences cross the ordovician silurian boundary interval in the marginal and submerged platform areas of the yangtze sea in jiangsu hubei hunan chongqing and sichuan provinces in condensed sections platform margin facies the occurrences are normally represented by extensive spiculite layers but several sites yield entire exceptionally preserved body fossils at ganggangshan near nanjing jiangsu province such preservation is abundant the new occurrences are combined with palaeogeographic and tectonic reconstructions to produce a model for the distribution and preservation of the sponge fauna we argue that the exceptional preservation was due largely to nepheloid layers that were generated during rapid post glacial transgression that flooded the weathered land surface of the uplifted cathaysia block nepheloid layer collapse led to rapid deposition of suspended sediment within the deeper parts of the intra plate restricted basin and on adjacent platform margins and slopes the suspended sediment influx also introduced abundant nutrients to the water column as indicated by a significant 13c excursion during the sponge bearing mudstone interval at ganggangshan the combined sponge assemblage was dominant over large areas of the hirnantian offshore sea floor across south china we predict that similar occurrences with exceptional preservation will also be found in other continental blocks abundant articulated sponges may be encountered particularly in restricted basin successions containing rapidly deposited graptolitic mudstones near the ordovician silurian boundary

geochemical characteristics of organic rich shale upper yangtze basin implications for the late ordovician early silurian orogeny in south china abstract the tectonic sedimentary environment of the upper yangtze basin in china underwent significant changes from the late ordovician to early silurian the widely distributed shale formed during this interval has recorded key information about paleo ocean conditions analysis of major trace and rare earth elements was conducted on 135 shale samples collected from five wells in the study area the covariation of the mo u enrichment factors indicates that the upper yangtze basin in the wufeng stage was characterized by sedimentary differentiation the southern basin was dominated by a reducing bottom water environment under euxinic conditions the northern and central basins were dominated by a suboxic anoxic environment up to the early longmaxi stage the upper yangtze basin formed a relatively uniform sedimentary environment with gradually increasing oxygen content in the bottom water the paleoproductivity index indicates that marine organisms flourished in the wufeng to early longmaxi stages making an important contribution to the siliceous content in organic rich shale subsequently terrestrial siliciclastics gradually dominated analysis of paleogeography rare earth elements and weathering indicates that chuanzhong and qianzhong uplifts in the wufeng stage were the provenance area of the upper yangtze basin with a relatively high weathering degree weathering decreased in the beginning of the longmaxi stage and then gradually increased with the xuefeng uplift becoming the main provenance areas after the early longmaxi stage controlled by stress transfer from the continuous syn caledonian kwangsian orogeny in eastern south china the upper yangtze basin and xiangzhong basin were squeezed and pushed up successively the uplift separated the open shallow sea and formed a relatively limited deep water shelf environment resulting in a relatively euxinic bottom water environment which was favorable for organic matter accumulation the tectonic sedimentary evolution of the upper yangtze basin in the late ordovician to early silurian proposed in this study indicates that the formation of organic enriched shale was not only related to glacio eustatic change but also strongly controlled by tectonic activities in south china

structural evolution of organic matter and implications for graphitization in over mature marine shales south china abstract to characterize the degree of organic matter graphitization in the over mature lower paleozoic marine shales from south china a suite of kerogen samples covering different maturity ro ranging from 1 2 to 4 2 were analyzed by laser raman microprobe lrm transmission electron microscope tem and fourier transform infrared spectroscopy ftir techniques chemical structures and related major changes caused by thermal evolution history were systematically discussed the results indicate that with the thermal maturity increasing the aliphatic side chains fall off gradually and the aromatic rings increase continuously the ordered structure of shales continues to enhance leading to the increasing of graphitization degree the parameters of lrm i e position of g and d bands peak position difference rbs full width at half maximum fwhm and intensity ratio id ig highlight the turning point at maturity level around rmcro 3 5 which represents the chemical structure jump of the kerogen this chemical structure jump can be characterized by the continuous decreasing of amorphous carbon before the rmcro exceeded 3 5 and the sharp increasing degree of aromatic conjugation after that point tem analysis indicates that the carbon layers of shale samples with rmcro exceeds 3 5 show better ordering and continuity than that of low maturity shale samples the ftir analysis suggests that there are relatively high aromatics c c chains and very few aromatic c h chains in the high maturity samples this critical chemical structure jump at rmcro 3 5 could be interpreted as the structure of organic matter begins to transform from amorphous carbon to crystalline graphite in shales due to the increasing degree of graphitization graphitized shale is characterized by stable chemical structure condensed and orderly carbon layer constructure and ultra low resistivity

constraints on the accumulation of organic matter in upper ordovician lower silurian black shales from the lower yangtze region south china abstract the late ordovician to early silurian o s was an important period in which many significant geological events occurred during the o s transition organic rich black shales were widely deposited and became important unconventional energy sources paleoproductivity detrital input and redox conditions are the three major factors controlling organic matter om accumulation although the effect of each factor is relatively clear the complex influences of these factors remain poorly understood specifically the evolution of these factors and the corresponding influence on the accumulation of om during the o s transition has not yet been systematically investigated this paper investigates the constraints on om accumulation in o s transition black shales from the lower yangtze region based on graptolite fossil identification zircon u pb dating and geochemical analyses of a well sequenced drilling profile the results show that i the sy 1 core sequence was well constrained from graptolite zones wf2 447 62 ma to lm5 441 57 ma across the o s boundary with decreasing sedimentation rates srs in the upper katian wf2 to wf3 and increasing srs in the lower rhuddanian ii complementary volcanic inputs katian and rhuddanian and upwelling events hirnantian exerted strong control over paleoproductivity iii orogenic processes in south china controlled detrital inputs and redox conditions iv om accumulation in the lower yangtze area across the o s transition occurred in three stages in stage 1 wf2 wf3 strong volcanism boosted productivity whereas om preservation was not favored in the oxic environment in stage 2 wf4 lm3 upwelling and volcanism resulted in high productivity and provided the optimal configurations for om enrichment in stage 3 lm4 and later rare om was preserved due to terrestrial dilution and unfavorable preservation conditions eventually wf4 lm3 became the prominent om rich biozones due to the effective coordination of the controlling factors namely upwelling volcanism and redox conditions

new evidence for compaction driven vertical fluid migration into the upper ordovician hirnantian guanyinqiao bed of south china abstract the late ordovician was a time of major climatic and sea level changes linked to the hirnantian glaciation marked by large positive excursions of 13ccarb and 13corg globally known as the hirnantian carbon isotopic excursion hice however some upper ordovician sections in south china exhibit negative 13ccarb shifts within the hirnantian age guanyinqiao bed we hypothesize that these unusual carbon isotope patterns were due to influx of 13c depleted dissolved inorganic carbon dic from the underlying wufeng and overlying longmaxi black shales as a result of greater compaction of these fine grained siliciclastic units compared to the coarse grained carbonate guanyinqiao bed the isotopically light dic was generated through oxidation of organic matter by either microbial sulfate reduction msr or methanogenesis with subsequent anaerobic oxidation of methane aom in the black shales this hypothesis is supported by petrographic and geochemical evidence of vertical fluid migration within the guanyinqiao bed and across its contacts in the shiqiao drillcore the guanyinqiao bed exhibits a v shaped depression at its top that is connected to vertical channels filled with secondary carbonate cements having low 13c values in the huanggexi section both the base and top of the guanyinqiao bed are characterized by strong u enrichments despite unambiguously oxic depositional conditions as inferred from other proxies fe speciation mo and v concentrations these anomalous u enrichments resulted from oxidative remobilization of u along the guanyinqiao black shale contacts and subsequent transport into the guanyinqiao bed through compactional flow this finding demonstrates the importance of recognizing remobilized trace metals in sedimentary successions in order to avoid potential errors in redox interpretations

temporal geophysical signatures from contaminant mass remediation we have previously documented changes in bulk electrical conductivity self potential sp and ground penetrating radar gpr reflections in a field setting caused by biogeochemical transformations of hydrocarbon contaminated media these transformations are associated with hydrocarbon biodegradation the results of surface geophysical surveys acquired in 1996 2003 and 2007 document changes in geophysical signatures associated with removing hydrocarbon mass in the contaminated zone initial investigations in 1996 showed that relative to background the contaminated area was characterized by higher bulk electrical conductivity positive sp anomaly and attenuated gpr reflections repeated surveys in 2003 and 2007 over the contaminated area showed that in 2007 the bulk electrical conductivityhad reverted to near background conditions the positive sp anomaly became more negative and the zone of attenuated gpr reflections showed increased signal strength removal of hydrocarbon mass in the vadose zone o

presence of oxygen and aerobic communities from sea floor to basement in deep sea sediments the depth of oxygen penetration and microbial activity in marine sediments varies by region sediment cores from the south pacific gyre host oxygen and aerobic microbial communities to at least 75 metres below the sea floor

climatic and oceanic controlled deposition of late ordovician early silurian black shales on the north yangtze platform south china abstract black shales deposited across the late ordovician and early silurian transition are considered to be the most important source rock and shale gas reservoirs in the yangtze region of south china however the origin of these sediments remains contentious in this study we investigated the systematic changes in total organic carbon toc organic carbon isotopes 13corg major elements and trace elements on the ordovician silurian boundary strata from qiaoting north yangtze sea to reconstruct the climatic conditions redox changes primary productivity and other factors there promoting the understanding for the formation mechanism of the organic rich black shales element compositions and their ratios suggest that the black shales studied here were dominantly sourced by the felsic igneous rock which is similar to granodiorite in composition paleoclimatic proxies cia ciw 13corg suggest that the global climate system experienced significant changes from warm humid to cold dry and then to warm humid climates during the ordovician silurian transition paleoredox indices s c u th ni co and v v ni ratios also demonstrate fluctuating redox variations from anoxic to oxygenated and then to anoxic states during this interval in the yangtze sea which describe an oxygenated guanyinqiao strata sandwiched between the stagnant and anoxic wufeng and longmaxi black shales paleoproductivity parameters toc babio contents and p al ratio suggest that the organic rich wufeng and longmaxi black shales were deposited with a high biological productivity while the organic lean guanyinqiao sediments were deposited with a low biological productivity these data demonstrate large climatic and oceanic fluctuations during the ordovician silurian transition providing essential controlling factors on the oceanic anoxia primary productivity and subsequent organic rich black shale depositions in the yangtze region during the late ordovician and early silurian intervals

conodont biostratigraphy and astronomical tuning of the lower middle ordovician liangjiashan north china and huanghuachang south china marine sections abstract in this study systematic conodont biostratigraphy and cyclostratigraphy are carried out on ordovician sections from the north china and south china blocks the liangjiashan section situated on the north china block margin accumulated shallow marine carbonate during the early ordovician the huanghuachang section gssp for the dapingian stage situated on the south china block margin accumulated thinly bedded carbonates and minor clastics in a deep shelf environment conodont biostratigraphy and 405 kyr long eccentricity cycles interpreted from the liangjiashan and huanghuachang sections are used to establish an astronomical time scale ats for the early middle ordovician period the ats indicates that the duration of the floian stage is 7 08 0 405 myr the temporal ranges of lower middle ordovician conodont biozones are also estimated the durations of the serratognathus bilobatus serratognathus extensus oepikodus communis oepikodus evae and baltoniodus triangularis zones are 1 0 myr 5 1 myr 0 2 myr 0 8 myr and 0 2 myr respectively the evolution of the ratio of obliquity to total power and short eccentricity power to total power depicts periodicities of 1 myr for the s4 s3 term and 1 9 myr shifting to 1 myr for the g4 g3 term the shift in the g4 g3 term may indicate a chaotic transition in the mars and earth orbital motions from a s4 s3 2 g4 g3 to s4 s3 g4 g3 resonance state during the early ordovician

deducing the distribution of terminal electron accepting processes in hydrologically diverse groundwater systems the distribution of microbially mediated terminal electron accepting processes teaps was investigated in four hydrologically diverse groundwater systems by considering patterns of electron acceptor nitrate sulfate consumption intermediate product hydrogen h sub 2 concentrations and final product ferrous ion sulfide and methane production in each hydrologic system a determination of predominant teaps could be arrived at but the level of confidence appropriate for each determination differed in a portion of the lacustrine aquifer of the san joaquin valley for example all three indicators sulfate concentrations decreasing h sub 2 concentrations in the 1 2 nmol range and sulfide concentrations increasing along flow paths identified sulfate reduction as the predominant teap leading to a high degree of confidence in the determination in portions of the floridan aquifer and a petroleum hydrocarbon contaminated aquifer sulfate reduction and methanogenesis are indicated by production of sulfide and methane and hydrogen concentrations in the 1 4 nmol and 5 14 nmol range respectively however because electron acceptor consumption could not be documented in these systems less confidence is warranted in the teap determination in the black creek aquifer no pattern of sulfate consumption and sulfide production were observed but h sub 2 concentrations indicated sulfate reduction as the predominant teap in this case more where just a single line of evidence is available the least confidence in the teap diagnosis is justified because this methodology is based on measurable water chemistry parameters and upon the physiology of microbial electron transfer processes it provides a better description of predominant redox processes in groundwater systems than more traditional eh based methods less

effect of sedimentary environment on the formation of organic rich marine shale insights from major trace elements and shale composition abstract sedimentary environment and redox conditions play a significant role in the formation of organic rich shale the vertical variations of major trace elements toc total organic carbon and mineral compositions were investigated for the lower silurian longmaxi typical marine shale in the upper yangtze platform south china to decipher sedimentary environment redox conditions detrital input sedimentation rate sr paleoproductivity and watermass restriction this gives insight to the effects of variations in sedimentary environment on the formation of organic rich shale the results show that the lower longmaxi formation is composed of three systems tracts tst transgressive systems tract ehst early highstand systems tract and lhst late highstand systems tract from tst to lhst the contents of toc quartz and pyrite decline steadily whereas clay minerals and carbonate show an increasing trend thus organic rich siliceous orss organic moderate mixed omms and organic lean argillaceous olas shales are dominant for tst ehst and lhst respectively due to a continues fall of the relative sea level a deep water shelf environment with anoxic condition high paleoproductivity and low detrital input in tst gradually evolves into a semi deep water environment with dysoxic oxic conditions moderate paleoproductivity and moderate detrital influx in ehst further to an environment of oxic condition low paleoproductivity and high detrital flux in lhst as evidenced by mo toc and mo u patterns orss was deposited in a moderately restricted watermass weaker than black sea which progressively evolved into an enhanced restriction degree during the deposition of omms and olas due to a fall of relative sea level major trace elements and excess silica ex sio2 concentrations illustrate that origins of quartz in the lower longmaxi shale are primarily terrigenous biogenic and authigenic smectite illitization the average proportions of ex sio2 biogenic and authigenic quartz are 52 34 24 86 and 6 57 for orss omms and olas respectively biogenic quartz is the dominant contributor to ex sio2 while the contribution of authigenic quartz is limited and the formation of the former is earlier than the latter according to the diagenetic transformation temperature as both biogenic quartz and organic matter are firmly related to the abundance and preservation of paleoorganisms anoxic condition high paleoproductivity low detrital flux and moderate restriction collectively control the high enrichment and preservation of organic matter and biogenic quartz while oxic condition low paleoproductivity high detrital flux and stronger watermass restriction are unfavorable for the enrichment of biogenic quartz and organic matter

different formation mechanism of quartz in siliceous and argillaceous shales a case study of longmaxi formation in south china abstract brittle mineral especially quartz exert significant effect on the development of shale gas however the formation mechanism of quartz in shale is still unclear here we present x ray diffraction data scanning electron microscopy sem determination cathodoluminescence and geochemical data to investigate longmaxi formation which is a key target for shale gas exploration and development in china recently siliceous and argillaceous mudstones were recognized from 5 outcrops of longmaxi formation which were examined with respect to the formation mechamism of quartz three different types of quartz silt size detrital grain with bright luminescence micro sized grains and quartz overgrowths with bright luminescence were identified by sem eds cl both in the argillaceous and siliceous shale siliceous shale deposited by suspension sediment settling with high sea level because of anoxia condition indicated by lower th u and higher v cr ratios the quartz in siliceous shale display a positive covariation with babio as well as a good correlation between toc and quartz suggesting biogenic quartz is an important constituents argillaceous shale was likely dominated by suspension alternate with gravity current in consideration of the mixing of clay and silt laminae there is no correlation between quartz and toc and positive correlation between excess silica and zr indicating terrestrial quartz in argillaceous is more important relative to siliceous shale additionally reorientation of phyllosilicate particles and positive correlation between ki and quartz contents r2 0 57 suggest the indispensable diagenetic quartz illitization of smectite near or far from the clay minerals both in siliceous and argillaceous shales this process also result in high quartz saturation in silt rich laminae thus that quartz overgrowths encased in dolomite cements is common in argillaceous shale based on the geochemical analysis the argillaceous shale contains 86 detrital silica 14 digenetic silica however the siliceous shale approximately contains 33 detrital silica 11 digenetic silica and 56 biogenic silica occurrence and origin of quartz are of great significance for physical properties of shale and hydraulic fracturing during the development of shale gas

oriented graptolites in the uppermost ordovician wufeng black shale in southern china graptolites are elongated fossils that can be used to decipher the current direction to evaluate paleocurrent conditions abundant graptolite fossils are well preserved and clearly exhibit strong alignment in the black shales of the upper ordovician wufeng formation on the southern edge of the upper yangtze sea south china the orientations of these graptolites indicate that the remains of graptolites were deposited on the seafloor under the influence of currents instead of under calm water conditions based on the measurements of the long axis directions of graptolites the distributions of graptolites preserved on the bedding planes display discernable orientations and exhibit systematic changes throughout the stratigraphic section in the western region of the study area the paleocurrent directions in the stratigraphic sections gradually change from ne sw in the dicellograptus complexus biozone to n s in the paraorthograptus pacificus and normalograptus extraordinarius n ojsuensis biozones however in the eastern region of the study area the paleocurrent directions are more variable ranging from multi directional nne ssw and nnw sse in the p pacificus biozone to nw se in the n extraordinarius n ojsuensis biozone the changes in the orientations of graptolites in the d complexus and the p pacificus biozones are consistent with the southern configuration of the upper yangtze sea and indicate that a coastal current existed in addition some of the contemporaneous deformation structures were caused by tectonic forces observed in the lower graptolite shale member of the wufeng formation in the eastern region of the study area some of the changes in the orientations of graptolites in the n extraordinarius n ojsuensis biozone can be interpreted to have resulted from a change in tectonic activity the caledonian orogeny before the n extraordinarius n ojsuensis biozone furthermore lingula brachiopods which live on the seafloor in shallow water have been reported in the black shale of the wufeng formation which indicates that the paleoenvironment was at least partially oxic this supported the growth development and reproduction of planktonic graptolites and other organisms these results support the interpretation that the remains of organisms were quickly buried and that the amount of exchange between pore water and the water column gradually decreased h2s gas generated by the decay of organisms during deposition consequently generated a strongly reducing environment in these sediments which resulted in the formation of black shales

large perturbations of the carbon and sulfur cycle associated with the late ordovician mass extinction in south china high resolution 13 c data of organic carbon from a continuous section of the late ordovician early silurian reveal two positive 13 c excursions that are associated with the mass extinction in south china the fi rst stratigraphic 34 s measurements on pyrite tied to well established biostratigraphy indicate a large perturbation of the sulfur cycle consistent with major sea level changes related to the glaciation the elevated 34 s values of pyrites and a large short lived negative 34 s excursion of 20 associated with the decay of the glaciation suggest deep water anoxia during the hirnantian stage in contrast to the conventional view that the global oceans were oxygenated we suggest that deep water anoxia may have contributed to the late ordovician mass extinction in south china and possibly elsewhere

model for transgressive black shales many black shales in thick epicontinental basinal successions formed beneath an oxygen restricted puddle of deep water other black shales formed during rapid transgression when basinal deposition expanded to cover basin margin areas normally characterized by shallow water deposition an expanding puddle model is developed from the early jurassic of england wherein rapid sea level rise leads to marine sediment starvation due to sediment entrapment in flooded river valleys subsidence sea level rise and decreased sediment supply during early transgression are suggested to lead to rapid deepening and therefore the expansion of the are of the puddle such that in previously shallow water areas black shales rest on condensed basal transgressive lags or unconformities that in turn rest on shallow water facies reestablishment of sediment influx and aggradation in excess of any continued sea level rise cause shallowing throughout the basin and the cessation of black shale formation

spatial variation of carbon isotopic compositions of carbonate and organic matter from the late ordovician sedimentary succession in the yangtze platform south china implications for sea level eustacy and shoaling of marine chemocline abstract spatial correlation of isotopic chemostratigraphy across ancient epeiric basins is of particular interest in the field of geology this study examines the carbon isotopic compositions of carbonate and organic matter from the late ordovician sedimentary succession in the yangtze platform including the linxiang lx formation deposited in the bottom and the tiezufeike tzfk daduhe ddh wufeng wf formations in the top paired 13ccarb and 13corg analyses of the upper ordovician strata on the yangtze platform were recorded and the results show that the rocks in the lx formation have high 13ccarb and 13corg values relative to those in the ddf tzfk wf formations additionally a variation of 2 was found between shallow and deep water settings during the late ordovician heavier 13ccarb and 13corg values are observed at the wukemuchang wkmc and wanhe wh sections representing the shallow regions of the yangtze platform relative to the tianjiawan tjw and tianba tb sections representing the deeper margin of the yangtze platform we suggest that the variations of 13c in carbonate and organic matter are related to the sea level eustacy and shoaling of marine chemocline 1 sea level rise driven decrease in local scale carbonate weathering 2 decreased decomposition of organic matter under anoxic conditions and 3 incorporation of non photosynthetic chemoautorophic bacteria living in deeper waters the 13c 13c 13ccarb 13corg values in both the wh and wkmc sections display an increasing trend upward from the lx formation to the overlying strata varying from 27 8 to 31 2 and from 28 1 to 31 1 respectively these increased 13c values are related to the enhanced nutrients and correspondingly high primary productivity and thus that the anoxic water conditions and high primary productivity may be the significant factors in the deposition of late ordovician black shales

facies patterns and geography of the yangtze region south china through the ordovician and silurian transition abstract lithofacies and biofacies changes through the ordovician and silurian transition on the yangtze platform are coincident with stepwise mass extinctions recovery events global sea level changes and regional palaeogeographic configurations facies patterns through three intervals the late mid ashgill hirnantian and early rhuddanian indicate that black shale occupied most of the yangtze platform region during the late mid ashgill and early rhuddanian while the hirnantian possesses more diverse facies types the black shale was replaced by carbonate facies during the hirnantian coincident with a global sea level low stand biofacies changes from the late mid ashgill graptolitic to the hirnantian shelly facies were apparently signalled by gradual and diachronous existence of a mixed facies the manosia facies in the yangtze region however the biofacies change was abrupt from the hirnantian to the early rhuddanian when graptolitic facies occupied most areas on the yangtze platform leaving only a very narrow limited belt of shelly facies along the southern margin of the platform in northern guizhou the early rhuddanian unified biofacies pattern is a result of a global sea level rise which may be synchronized with a recovery bioevent of graptolites after hirnantian mass extinction

paleo environmental cyclicity in the early silurian yangtze sea south china tectonic or glacio eustatic control abstract the yangtze sea of the south china craton experienced strong environmental perturbations during the first 5 6 myr of the silurian the lower silurian lungmachi formation in the jiaoye 1 drillcore chongqing china records three sea level cycles stratigraphic sequences characterized by rapid deepening at the base of each cycle followed by slow shallowing each deepening event was associated with shifts toward higher marine productivity more intensely reducing bottomwater conditions reduced watermass restriction lower detrital input and enhanced siliciclastic weathering intensity we infer control by glacio eustasy in which deglacial sea level rises and concurrent climatic warming triggered the observed environmental changes shallowing was associated with renewed glaciation and characterized by the opposite set of conditions the results of this study thus provide evidence in support of continued continental glaciation during the early silurian i e following the termination of the major end ordovician hirnantian glaciation the study core also exhibits a long term shallowing trend through the entire lower silurian the origin of which may have been tectono epeirogenic uplift of the south china craton during the kwangsian orogeny

non uniform subsidence and its control on the temporal spatial evolution of the black shale of the early silurian longmaxi formation in the western yangtze block south china abstract the ordovician silurian transition was a significant period when an obvious variation occurred worldwide in terms of tectonics climate oceans paleontology and sedimentology here we use stratigraphic forward modeling constrained by paleobiota paleobathymetry sedimentology and geochemistry to study the tectonic subsidence history of the early silurian in the western yangtze block south china numerical modeling suggests that the tectonic subsidence was not uniform during the deposition of the early silurian black shale of the longmaxi formation with acceleration of tectonic subsidence during the later regression period furthermore the subsidence rate at this time was at least three times that during the early transgression period this acceleration resulted from the collision between the yangtze block and the southeastern cathaysia block which affected the tectonic subsidence and the heterogeneity of the black shale the results may provide quantitative implications for the reconstruction of the paleoenvironment the evolution of paleobiota the temporal spatial distribution of the black shale and the mechanism of block assemblage in south china

source and seal coupling mechanism for shale gas enrichment in upper ordovician wufeng formation lower silurian longmaxi formation in sichuan basin and its periphery abstract in recent years theoretical geologic research has made important progress in shale gas exploration and development and new discoveries such as the jiaoshiba weiyuan and changning shale gas fields provide geological cases to define key controls on shale gas accumulation in wufeng formation longmaxi formation marine shale strata a mechanism coupling source and seal development for shale gas enrichment is proposed in this study based on detailed research results of isochronous stratigraphic distribution of source rock and seals and source seal dynamic evolution great thickness wide distribution and high total organic carbon content toc of sources are key controls on the shale gas content and storage capacity in organic matter hosted pores micro cracks and bedding fissures is intensively developed the wufeng formation and the lower part of the first member of the longmaxi formation wf2 lm4 graptolitic zone are favorable sources that feature a slow deposition rate well graptolitic zone favorable organic organism type and high toc the organic matter type is benefit to the development of organic matter pores because the planktonic algae tends to generate and expulse large amounts of hydrocarbon and form many organic matter pores both high biogenic quartz and high toc ensure development of abundant organic matter hosted pores and result in a three dimensional network of interconnected organic matter pores that allows shale gas storage and flow the seal can be divided into direct and indirect seals the direct seal refers to the middle and upper parts of the first member of the longmaxi formation lm5 and higher graptolitic zone that are characterized by low toc and low porosity the indirect seal refers to the regionally distributed lower middle triassic gypsum layer s and mudstone that maintain regional geopressure systems the shale gas fields of jiaoshiba fushun yongchuan and changning have high geopressure coefficient factors 1 5 2 0 and 1 5 respectively in the absence of the lower middle triassic gypsum layer s and mudstone regional seals the high pressure system was destroyed and resulted in low normal geopressure shale gas reservoirs for instance the pengshui and zhaotong wells the static match and dynamic match of source and seal constrain the location of shale gas reservoirs and the degree of shale gas enrichment the model of a mechanism coupling source and seal for shale gas enrichment provides new ideas and methods for the assessment of shale gas this model promotes the evaluation of shale gas from the static parameters approach to the source and seal dynamic approach in the sichuan basin and its peripheral areas the promising areas for shale gas accumulation are those with favorable sources in the wf2 lm4 graptolitic zone and the presence of the lower middle triassic gypsum layer s and mudstone regional seal

k bentonites in ordovician silurian transition from south china implications for tectonic evolution in the northern margin of gondwana numerous k bentonites from the ordovician silurian o s transition in south china record important information about the geodynamics of volcanic activity in the northern margin of gondwana a series of k bentonite beds have been identified in the zhoujiaxi group early silurian in foreland basins from central hunan province china they are dominantly composed of illite with minor kaolinite volcanogenic minerals include quartz feldspar biotite and lesser apatite and zircon u pb zircon ages from three beds 442 8 1 8 442 2 1 9 and 441 6 2 0 ma are compatible with the age of the o s global boundary geochemical results indicate calc alkaline felsic magmas derived from continental crust and erupted in a subduction related collisional environment isopach schemes and grain size reveal that the volcanic ashes were sourced from a volcanic event likely with a volcanic explosivity index of 8 and transported 300 1000 km away from the palaeo sse the volcanism was associated with northwestern subduction of the zhenghe dapu ocean beneath the southeastern south china block scb on the northern margin of gondwana the zhenghe dapu fault might be a suture zone implying the consumption of the zhenghe dapu ocean during collision between the nanhai terrane and the scb this study supports that the wuyi yunkai orogenic belt is a collision type orogen rather than an intraplate belt supplementary material plots and geochemical data are available at https doi org 10 6084 m9 figshare c 5027096

the geochemistry of the sedimentary rocks from the huadi no 1 well in the wufeng longmaxi formations upper ordovician lower silurian south china with implications for paleoweathering provenance tectonic setting and paleoclimate abstract the late ordovician early silurian transition was a critical interval in earth s history marked by mass extinction the gondwana glaciation and volcanic events here we present mineralogical and geochemical characteristics across the ordovician silurian boundary wufeng guanyinqiao and longmaxi formations from the huadi no 1 well in the sichuan basin in order to explore the paleoweathering provenance tectonic setting and paleoclimatic conditions of the source area thin sections xrd x ray diffraction data and major element results reveal that the rocks were abundant in clay minerals quartz minor feldspar pyrite and carbonate minerals the samples have similar chondrite normalized ree patterns to those of paas which are characterized by slight lree enrichments and accompanied by flat hree trends with weakly negative eu anomalies paleoweathering indices cia and pia suggest that the sediments experienced weak to moderate chemical weathering in the source area cia values in the lower wufeng formation range from 67 11 to 72 17 indicating a warm and humid climate the cia values in the upper wufeng formation decrease from 70 35 to 66 15 and the cia values in the guanyinqiao and lower longmaxi formation are persistently low 56 64 62 87 suggesting a cold and dry climate which is consistent with the widespread presence of glaciation in the hirnantian period further upward in the upper longmaxi formation the cia returns to a high value 65 59 which may reflect that the climate started getting warm and glaciation had finished fluctuations in cia values reflect that the climate shifted from warm to cold and then to warm again during the end ordovician early silurian time period the a cn k triangular diagram and sio2 al2o3 tio2 tio2 zr and la th hf bivariate diagrams indicate that the provenance of the rocks from the three formations was primarily felsic igneous rocks discriminant function diagrams and la th sc th co zr 10 and th sc zr 10 triangular diagrams show that the clastic sediments of the wufeng longmaxi formations were derived most likely from an active continental margin finally across the late ordovician early silurian tectonic activity and the end of the ordovician glaciation dominantly controlled the deposition of black shales and siltstones in the wufeng longmaxi formations of south china

global distribution of microbial abundance and biomass in subseafloor sediment the global geographic distribution of subseafloor sedimentary microbes and the cause s of that distribution are largely unexplored here we show that total microbial cell abundance in subseafloor sediment varies between sites by ca five orders of magnitude this variation is strongly correlated with mean sedimentation rate and distance from land based on these correlations we estimate global subseafloor sedimentary microbial abundance to be 2 9 1029 cells corresponding to 4 1 petagram pg c and 0 6 of earth s total living biomass this estimate of subseafloor sedimentary microbial abundance is roughly equal to previous estimates of total microbial abundance in seawater and total microbial abundance in soil it is much lower than previous estimates of subseafloor sedimentary microbial abundance in consequence we estimate earth s total number of microbes and total living biomass to be respectively 50 78 and 10 45 lower than previous estimates

organic matter accumulation of the wufeng longmaxi shales in southern sichuan basin evidence and insight from volcanism abstract the wufeng longmaxi formations wf lm fms in the sichuan basin are sets of graptolite bearing shale strata containing high frequency bentonite layers in order to investigate the influence of volcanism on the organic matter om accumulation in shales detailed observations of several typical profiles and wells were performed also analyses including total organic carbon toc contents and mineral compositions were conducted on 126 shale and 5 bentonite core samples major and trace element analyses were conducted on the selected 25 shale and 5 bentonite samples in the wf lm fms of well lu a results show that wf and lm1 4 members are the bentonites concentrated sections while lm5 6 are the bentonites relatively concentrated sections and no bentonite is found in lm7 9 members the high potassium k content of bentonites have the typical characteristics of intermediate acid calcium alkaline volcanic rocks such as andesite and dacite which probably originated from intraplate collision or volcanic arc structural backgrounds related to the collision belt of the cathaysia block to the yangtze block productivity indicators p content excess si p al cu al and ni al in the wf and lm1 3 members are all significantly higher than those in the lingxiang lx and lm4 5 members the higher biological productivity during the ordovician silurian o s transition was attributed to the massive and intensive volcanism the fertilization by volcanic ash brought abundant biologically relevant nutrient elements n p si fe and al into the ocean thus triggering the phytoplankton bloom and enhancing primary biological productivity all the redox condition indexes moef uef nief vef mo toc corg p and u th positively correlate with toc content during the o s transition the intensive and massive volcanic eruptions triggered global cooling sea level changes late ordovician mass extinction and primary productivity increases thus promoting anoxic and possibly intermittently euxinic bottom conditions in addition the deposited bentonite layers had a strong capacity for oxygen isolation volcanism should be considered when modeling the om accumulation of the wf lm shales

dynamics of cyclic carbonate deposition and biotic recovery on platforms during the famennian of late devonian in guangxi south china constraints from high resolution cycle and sequence stratigraphy to better understand the dynamics of platform carbonate deposition evolution and biotic recovery during the famennian high resolution cycle and sequence stratigraphic analyses were carried out upon three platform sections one in ramp and two in rimmed platforms along with a biostratigraphically well constrained basinal section in guangxi south china four main facies and fourteen lithofacies are identified in the three isolated platforms these are vertically arranged into decimetre to metre scale shallowing upward peritidal and subtidal cycles or parasequces in which the peritidal cycles predominate over the lower middle famennian six third order sequences s1 to s6 are identified based on the cycle stacking patterns as illustrated by fischer plots and vertical facies changes these sequences are temporally calibrated through correlation with basinal sequences constrained with conodont zonation and match well the six main famennian transgressive regressive cycles t1 to t6 in euramerica and elsewhere indicating a eustatic control however an opposite longer term trend in accommodation change s3 to s4 between platform interior and deeper open shelf to basin settings during the middle famennian suggests a differential subsidence across the platform basin section likely driven by block tilting thus both eustatic fluctuations and local tectonism had played an important role in platform development and evolution after the frasnian famennian biotic crisis main marine benthos preferentially recovered in the normal marine niches on the nearshore open shelves and radiated gradually into offshore restricted platforms brachiopods notably rhychonellides were the taxa recovering the earliest s1 in the normal or near normal marine conditions then echinoderms s3 stromatoporoids upper s3 and corals s5 stepped in episodically however these benthos generally appeared later in the restricted platform interiors only as if the ecological conditions were improved well enough for their colonization therefore the biotic recovery processes were diachronous both taxonomically and ecologically specified

predominance of stratified anoxic yangtze sea interrupted by short term oxygenation during the ordo silurian transition abstract the ordo silurian transition was a critical interval in geological history during which profound biotic climatic and oceanic changes occurred in order to explore the oceanic palaeoredox changes multiple geochemical proxies including ratios of s c fehr fet fep fehr and dop values are presented here from three sections wangjiawan western hubei sanjiaguan northern hunan and nanbazi northern guizhou across the ordo silurian boundary on the yangtze platform these palaeoredox data indicate a predominance of stratified anoxic ferruginous ocean on the yangtze block during this transition which was interrupted by a brief episode of oceanic oxygenation in the early hirnantian this oxygenation temporally coinciding with the end ordovician glaciation and global glacio eustatic sea level fall likely resulted from enhanced circulation of polar cold dense oxygen rich water onto the low latitude shelf the prior and subsequent longer term episodes of anoxic ocean particularly the later one which started in the late hirnantian occurred in parallel with the rapid climatic warming and sea level rise which could have slowed down oceanic circulation thereby enhancing oceanic stratification anoxia and organic preservation oceanic redox changes together with rapid climatic and sea level fluctuations were likely responsible for the stepwise massive demise of the ordo silurian biotic crisis

heterogeneity characterization of the lower silurian longmaxi marine shale in the pengshui area south china abstract the heterogeneity of shale is significant for the evaluation and sweet spot prediction of a shale gas reservoir core observations thin sections field emission scanning electron microscopy fe sem nitrogen gas adsorption n2ga and geochemical analyses were performed on shale samples from the lower longmaxi formation in the pengshui area of south china in this study the macroscopic and microscopic heterogeneities of the longmaxi shale are revealed and their origins and inner link are also discussed the results show that three systems tracts were developed in the lower longmaxi formation a transgressive systems tract tst early highstand systems tract ehst and late highstand systems tract lhst from tst to lhst toc total organic carbon siliceous minerals quartz feldspar and pyrite show an upward decreasing trend in weight content while the clay minerals and carbonate contents increase upward hence the tst ehst and lhst shales are generally characterized by organic rich shale lithofacies organic moderate shale lithofacies and organic lean shale lithofacies respectively the in situ gas content decreases from tst to lhst and primarily depends on toc content the sedimentary environment of the tst shale is an anoxic environment with high paleoproductivity which then evolves to a dysoxic oxic environment in the ehst shale and an oxic environment in the lhst shale with relatively low paleoproductivity organic matter pores are the primary contributors to the total pore volume in the tst shale and then the pore content and role in porosity decrease upward from ehst to lhst however the proportions of clay related pores and brittle mineral related pores gradually elevate from the tst shale to the lhst shale the sedimentary environment including water depth redox conditions paleoproductivity terrigenous input and hydrodynamics etc control the development of organic matter mineral composition lithofacies association color bedding and palaeobios in the lower longmaxi shales which constitute the macroscopic heterogeneity nevertheless the microscopic heterogeneity of shale originates from diagenesis catagenesis specifically shales are primarily composed of interparticle pores and clay related pores during deposition and the porosity is reduced primarily under mechanical compaction and chemical cementation as the burial depth and diagenetic degree increase a large number of organic matter pores and dissolution pores begin to appear which are associated with the hydrocarbon generation process moreover macroscopic shale composition plays a crucial role in development levels of microscopic shale pores

late ordovician to earliest silurian graptolite and brachiopod biozonation from the yangtze region south china with a global correlation late ordovician to earliest silurian is an important geological period marked by large geological and biological events however the strata and fossils of this interval are not complete in many parts of the world based on studies of 43 sites in south china in particular the continuous sections on the yangtze platform we recognize a complete succession including seven graptolite zones and two shelly faunas in ascending order the graptolite zones are the dicellograptus complanatus dicellograptus complexus paraorthograptus pacificus including lower subzone tangyagraptus typicus subzone and diceratograptus mirus subzone normalograptus extraordinarius normalograptus ojsuensis normalograptus persculptus akidograptus ascensus and parakidograptus acuminatus zones the shelly faunas are the foliomena nankinolithus and hirnantia faunas which may be correlated with d complanatus zone and n extraordinarius n ojsuensis to part of n persculptus zones respectively the biozonation through this interval from the yangtze region can be correlated with that of other parts of the world such as dob s linn in scotland spain and portugal thuringia saxonia bavaria bohemia poland kazakhstan kolyma malaya peninsula yukon canadian arctic islands nevada argentina niger and victoria australia the hirnantian substage which has been proposed by us recently includes the n extraordinarius n ojsuensis zone hirnantia fauna and n persculptus zone the base of the hirnantian substage is marked by the first appearance data fads of n extraordinarius and n ojsuensis which have been determined to be synchronous on a global scale

quantitative stratigraphy of the wufeng and lungmachi black shales and graptolite evolution during and after the late ordovician mass extinction article i nfo graptolite bearing black shales are widely distributed on the yangtze platform in south china based on 19 sec tions systematically studied recently we conducted a quantitative stratigraphic analysis of the graptolite biodi versity change during and after the late ordovician mass extinction the combination of graphic correlation and rarefaction methods make it possible to evaluate the effect of sampling intensity on biodiversity estimates graptolite diversity reached its peak in the dicellograptus complexus chron and then a gradual decline to the p pacificus chron it was followed by a two step mass extinction the first and major phase occurred in the metabolograptus extraordinarius chron and the second and minor phase in the latest m persculptus chron the second phase of the extinction was mostly represented by the elimination of the diplograptina survivors from the major extinction event but did not show significant decline in standardized diversity curve thereafter a moderate increase in richness appeared in the early and mid parakidograptus acuminatus chron which was followd by a considerable decrease of graptolite richness in the late p acuminatus chron and early c vesiculosus chron the present study also indicates slow and uneven sedimentation rates in the studied sections from mid katian to early rhuddanian including a relatively slower sedimentation rate during the hirnantian epoch the latter andthehiatusatthe honghuayuanandguanwusections probablyreflecttheeffectsofthe hirnantian glaciation and regional tectonic movements

large scale natural gradient tracer test in sand and gravel cape cod massachusetts 3 hydraulic conductivity variability and calculated macrodispersivities hydraulic conductivity k variability in a sand and gravel aquifer on cape cod massachusetts was measured and subsequently used in stochastic transport theories to estimate macrodispersivities nearly 1500 k measurements were obtained by borehole flowmeter tests and permeameter analyses of cores the geometric mean for the flowmeter tests 0 11 cm s is similar to that estimated from other field tests the mean for the permeameter tests 0 035 cm s is significantly lower possibly because of compaction of the cores the variance for the flowmeter 0 24 is also greater than that for the permeameter 0 14 geostatistical analyses applying negative exponential models with and without nuggets reveal similar spatial correlation structures for the two data sets estimated correlation scales range from 2 9 to 8 m in the horizontal and from 0 18 to 0 38 m in the vertical estimates of asymptotic longitudinal dispersivity b 35 0 78 m are similar in magnitude to that observed in the natural gradient tracer test 0 96 m previously conducted at this site

crude oil in a shallow sand and gravel aquifer iii biogeochemical reactions and mass balance modeling in anoxic groundwater abstract crude oil floating on the water table in a sand and gravel aquifer provides a constant source of hydrocarbons to the groundwater at a site near bemidji minnesota the degradation of hydrocarbons affects the concentrations of oxidized and reduced aqueous species in the anoxic part of the contaminant plume that developed downgradient from the oil body the concentrations of fe2 mn2 and ch4 eh measurements and the 13c ratios of the total inorganic c indicate that the plume became more reducing ver a 5 a period however the size of the contaminant plume remained stable during this time field data coupled with laboratory microcosm experiments indicate that benzene and the alkylbenzenes are degraded in an anoxic environment in anaerobic microcosm experiments conducted under field conditions almost complete degradation 98 was observed for benzene in 125 d and for toluene in 45 d concentrations of aqueous fe2 and mn2 increased in these experiments indicating that the primary reactions were hydrocarbon degradation coupled with fe and mn reduction mass transfer calculations on a 40 m flowpath in the anoxic zone downgradient from the oil body indicated that the primary reactions in the anoxic zone are oxidation of organic compounds precipitation of siderite and a ferroan calcite dissolution of iron oxide and outgassing of ch4 and co2 the major difference in the two models presented is the ratio of co2 and ch4 that outgasses both models indicate quantitatively that large amounts of fe are dissolved and reprecipitated as ferrous iron in the anoxic zone of the contaminant plume

large scale natural gradient tracer test in sand and gravel cape cod massachusetts 1 experimental design and observed tracer movement a large scale natural gradient tracer experiment was conducted on cape cod massachusetts to examine the transport and dispersion of solutes in a sand and gravel aquifer the nonreactive tracer bromide and the reactive tracers lithium and molybdate were injected as a pulse in july 1985 and monitored in three dimensions as they moved as far as 280 m down gradient through an array of multilevel samplers the bromide cloud moved horizontally at a rate of 0 42 m per day it also moved downward about 4 m because of density induced sinking early in the test and accretion of areal recharge from precipitation after 200 m of transport the bromide cloud had spread more than 80 m in the direction of flow but was only 14 m wide and 4 6 m thick the lithium and molybdate clouds followed the same path as the bromide cloud but their rates of movement were retarded about 50 relative to bromide movement because of sorption onto the sediments

geochemistry of dissolved inorganic carbon in a coastal plain aquifer 1 sulfate from confining beds as an oxidant in microbial co2 production a primary source of dissolved inorganic carbon dic in the black creek aquifer of south carolina is carbon dioxide produced by microbially mediated oxidation of sedimentary organic matter groundwater chemistry data indicate however that the available mass of inorganic electron acceptors oxygen fe iii and sulfate and observed methane production is inadequate to account for observed co2 production although sulfate concentrations are low approximately 0 05 0 10 mm in aquifer water throughout the flow system sulfate concentrations are greater in confining bed pore water 0 4 20 mm the distribution of culturable sulfate reducing bacteria in these sediments suggests that this concentration gradient is maintained by greater sulfate reducing activity in sands than in clays calculations based on fick s law indicate that possible rates of sulfate diffusion to aquifer sediments are sufficient to explain observed rates of co2 production about 10 5 mmoll 1 year 1 thus eliminating the apparent electron acceptor deficit furthermore concentrations of dissolved hydrogen in aquifer water are in the range characteristic of sulfate reduction 2 6 nm which provides independent evidence that sulfate reduction is the predominant terminal electron accepting process in this system the observed accumulation of pyrite and calcite cemented sandstones at sand clay interfaces is direct physical evidence that these processes have been continuing over the history of these sediments