hydrocarbon biomarkers of neoproterozoic to lower cambrian oils from eastern siberia the neoproterozoic era is of widespread geobiological interest because it marks the critical transition from a world of microbes to one where animals become an established feature of the landscape much research into this time period has focused on the ventilation of the oceans as this is widely considered a primary factor driving the diversification of complex multicellular life in this study proterozoic to cambrian aged oils from eastern siberia were analyzed for their hydrocarbon biomarker contents and compound specific carbon isotopes in order to further our understanding of the prevailing environment and its microbial and metazoan communities geochemically these oils are broadly comparable to those of the ediacaran cambrian sedimentary rocks and oils of the south oman salt basin organic matter in the source sedimentary rocks included significant contributions from green algae demosponges and bacteria including cyanobacteria and methanotrophic proteobacteria although the ages of the siberian oils and putative parent source rock intervals are poorly constrained the geochemical similarities between the ediacaran oman huqf and nepa botuoba katanga family of siberian oil samples are impressive leading to the inference that their source rocks are coeval on the other hand oils from the baykit high are distinctive likely older and possibly of cryogenian age

paired carbon isotopic analysis of ordovician bulk carbonate δ 13 c carb and organic matter δ 13 c org spanning the great ordovician biodiversification event abstract paired measurements of bulk carbonate 13ccarb organic matter 13corg and their difference 13c can be used to estimate changes in isotopic fractionation through time as a function of o2 co2 in the atmosphere however because local scale processes can also affect 13c it is essential to compare sections from widely separated water masses here we present new 13corg data from ordovician carbonate rocks from the great basin oklahoma and appalachian basin and compare with published 13ccarb records from these sections and paired 13c values from other carbonate successions around north america these new data complement previous studies that focused on upper ordovician 13ccarb excursions and now provide a composite ordovician 13corg record new lower ordovician tremadocian stage 13corg data range from ca 26 to 28 decreasing throughout the lower middle ordovician floian dapingian stages to ca 29 to 31 13corg values remain at their lowest throughout the sandbian and are similar to other published upper ordovician sandbian katian 13corg data from north america 13c values from well preserved intervals generally vary between 26 to 28 throughout the lower to middle ordovician tremadocian to early darriwilian but increase to 31 during the mid late darriwilian and mid sandbian similar to published data from younger late ordovician positive 13c excursions known as the guttenberg gice and hirnantian hice events the overall 13c trend shows a 3 increase throughout the early middle ordovician and coincides with a previously interpreted period of ocean cooling and some of the earliest pulses of global biodiversity of marine invertebrates and planktonic organisms modeling studies predict that pco2 decreased during this time suggesting that the effect of pco2 on 13c may have been overwhelmed by other controls such as an in increase in po2 or a higher o2 co2 ratio during this biodiversification event

how landscape heterogeneity governs stream water concentration discharge behavior in carbonate terrains konza prairie usa abstract mounting evidence suggests ecosystem changes that alter subsurface water fluxes and carbon dioxide concentrations in carbonate terrains may drive measurable changes in chemical weathering rates stream water chemistry and flow path evolution on human timescales we test this idea by exploring if the encroachment of woody vegetation into grasslands in a carbonate terrain landscape at the konza prairie ks usa has resulted in differences in landscape stream connectivity and thus the behavior of stream water solutes woody encroachment up to 60 cover at konza has been observed on watersheds particularly those that experience a fire return interval of four years or greater we focus on three headwater catchments two grassland and one woody encroached and a downstream confluence and analyze stream water discharge and chemistry major anions cations and dissolved nutrients measured from 2015 to 2016 we observe that the woody encroached watershed exhibits a greater area normalized solute flux and greater degree of chemodynamic behavior for most geogenic species compared to the less encroached grassland watersheds the downstream confluence exhibits the most chemostatic behavior for these same solutes compared to the low order watersheds we interpret the chemodynamic behavior of the woody encroached watersheds to arise from a greater diversity of flow paths and solute sources that contribute to this stream end member mixing analysis emma supports this hypothesis but also indicates a possible missing end member which we interpret to be solutes likely derived from clay weathering along limestone mudstone boundaries we invoke differences in rooting systems between grass and woody species to explain the differences in flow paths and solute generation between these headwater sites given that they sit adjacent to each other dissect the same nearly horizontal dip 0 1 0 21 nw lithologic units and experience the same climate if these processes hold true at other sites then the globally observed encroachment of woody vegetation into grasslands may deepen flow paths and enhance chemical weathering fluxes from ecosystems and over long time periods alter the trajectory of soil development and landscape evolution

frequency domain finite element simulations of 2d sonic wireline borehole measurements acquired in fractured and thinly bedded formations we simulated wireline borehole sonic waveforms to appraise modal frequency dispersions across fractured and thinly bedded formations simulations included monopole and dipole sources of excitation and explicitly took into account the borehole the mandrel tool and casing whenever present calculations were performed in the frequency domain with a highly accurate finite element method that automatically generates optimal grids for each problem frequency combination the method guarantees solutions at significantly reduced computational time with relative energy errors below 0 5 even in the presence of singularities in the solution that can originate from complex geometries high material contrasts and simultaneous presence of large and fine structures such a high accuracy in the simulation of sonic waveforms is necessary to accurately quantify the effects of fractures and thin beds on acoustic logs simulations indicate that fractures mainly influence propagation modes related to the formation shear velocity in slow thinly bedded formations effective properties are similar to those of average layer properties as predicted by the reuss lower bound however presence of intralayer interfaces gives rise to multiple reflections that can deleteriously affect the estimation of elastic properties with dispersion processing casing effectively functions as a low pass frequency filter of sonic waveforms significantly distorting the original borehole modes hence the estimation of elastic properties

chemostratigraphy of the posidonia black shale sw germany ii assessment of extent and persistence of photic zone anoxia using aryl isoprenoid distributions aquatic depositional environments where anoxic conditions extend from bottom waters into the photic zone occurred frequently during the geologic past periods of photic zone anoxia pza can be recognized by the presence of specific lipids produced exclusively by the green sulphur bacteria chlorobiaceae that are preserved in the sedimentary record chlorobiaceae perform anoxygenic photosynthesis that requires light penetration into h2s saturated waters sediment samples integrate paleoenvironmental conditions over time intervals ranging from at best a few decades to more commonly several millennia photic zone anoxia recognized in paleoenvironmental analyses is thus defined as episodic with no further interpretation on the duration and persistence of the anoxic events we provide here a high resolution multiproxy chemostratigraphy study for the toarcian posidonia black shale from the dotternhausen section in sw germany in order to assess duration and seasonal fluctuation of photic zone anoxia based on the relative abundance of derivatives of chlorobiaceae lipids we assess the variability in the degree and persistence of photic zone anoxia using an aryl isoprenoid ratio air obtained by calculating the proportion of the short chain c13 17 versus the intermediate chain c18 22 aryl isoprenoids higher relative abundance of the short chain analogues is interpreted as indicating more intensive aerobic degradation of aryl isoprenoids air varies between values of 0 5 indicative of persistent pza phases and 3 0 for short termed episodic pza events absolute concentration of aryl isoprenoids is negatively correlated with the air which is in agreement with a progressive diagenetic breakdown of aryl isoprenoids the air decreases are validated using independent palecological and geochemical redox indicators for the posidonia shale in sw germany d 2004 elsevier b v all rights reserved

sources of weathering derived solutes in two granitic catchments with contrasting forest growth chemical weathering is one of the controlling factors for landform evolution here we present deductions about the location and rate of chemical weathering within catchments based on chemical observations of soil water groundwater springs and streams in two granitic catchments with contrasting forest growth conditions forested and non vegetated and soil development the two catchments are located in the tanakami mountains of central japan and share the same climate in both catchments sio2 and na are the dominant weathering derived solutes in the first order stream using hydrological evidence the contribution to the sio2 and na fluxes from soil and bedrock were partitioned despite the difference in mean soil depth net fluxes of sio2 and na from the soil profile do not differ much between the two catchments suggesting low levels of easily weatherable minerals in the forest soil net sio2 and na fluxes from bedrock are about three times greater in the forested catchment than in the bare catchment and these differences contribute largely to the difference in net fluxes from the catchments net fluxes of sio2 and na from the forested catchment are about twice those from the bare catchment part of this increase may be related to the greater proton production in forested catchment consequently about 60 to 70 of the net sio2 and na fluxes from the non vegetated catchment and 70 to 90 from the forested catchment are derived from bedrock suggesting that the contribution of bedrock to the export of these weathering products increased with forest growth and soil formation copyright 2004 john wiley sons ltd

lipid biomarker and stable isotopic profiles through early middle ordovician carbonates from spitsbergen norway abstract one of the most dramatic episodes of sustained diversification of marine ecosystems in earth history took place during the early to middle ordovician period changes in climate oceanographic conditions and trophic structure are hypothesised to have been major drivers of these biotic events but relatively little is known about the composition and stability of marine microbial communities controlling biogeochemical cycles at the base of the food chain this study examines well preserved carbonate rich strata spanning the tremadocian through upper dapingian stages from the oslobreen group in spitsbergen norway abundant bacterial lipid markers elevated hopane sterane ratios average 4 8 maximum of 13 1 detection of chlorobi markers in organic rich strata and bulk nitrogen isotopes 15ntotal averaging 0 to 1 for the open marine facies suggest episodes of water column redox stratification and that primary production was likely limited by fixed nitrogen availability in the photic zone near absence of the c30 sterane marine algal biomarker 24 n propylcholestane 24 npc in most samples supports and extends the previously observed hiatus of 24 npc in early paleozoic late cambrian to early silurian marine environments very high abundances of 3 methylhopanes average 9 9 maximum of 16 8 extends this biomarker characteristic to early ordovician strata for the first time and may reflect enhanced and sustained marine methane cycling during this interval of fluctuating climatic and low sulfate marine conditions olenid trilobite fossils are prominent in strata deposited during an interval of marine transgression with biomarker evidence for episodic euxinia anoxia extending into the photic zone of the water column

fast ground water mixing and basal recharge in an unconfined alluvial aquifer konza lter site northeastern kansas abstract ground water chemistry and water levels at three levels in a well nest were monitored biweekly for two and a half years in a shallow unconfined floodplain aquifer in order to study the dynamics of such shallow aquifers the aquifer in northeastern kansas consists of high porosity low hydraulic conductivity fine grained sediments dominated by silt and bounded by fractured limestone and shale bedrock results show that the aquifer underwent chemical stratification followed by homogenization three times during the study period the length of time between maximum stratification and complete homogenization was 3 5 months the chemical parameters most useful for demonstrating the mixing trends were dissolved nitrate and sulfate higher nitrate concentrations were typical of unsaturated zone water and were sourced from fertilizer applied to the cultivated fields on the floodplain variations in sulfate concentrations are attributed to dissolution of rare gypsum in limestone bedrock and variable evapoconcentration in the unsaturated zone the mixing of three chemically different waters entrained unsaturated zone water water entering the base of the floodplain aquifer and water in residence before each mixing event was simulated the resident water component for each mixing event was a fixed composition based on measured water chemistry in the intermediate part of the aquifer the entrained water composition was calculated using a measured composition of the shallow part of the aquifer and measurements of soil water content in the unsaturated zone the incoming basal water composition and the fractions of each mixing component were fitted to match the measured chemistry at the three levels in the aquifer a conceptual model for this site explains 1 rapid water level rises 2 water chemistry changes at all levels in the aquifer coincident with the water level rises 3 low measured hydraulic conductivity of the valley fill and apparent lack of preferential flow pathways 4 minuscule amounts of unsaturated zone recharge and 5 dissolved oxygen peaks in the saturated zone lagging water level peaks we postulate that rainfall enters fractures in bedrock adjacent to the floodplain this recharge water moves rapidly through the fractured bedrock into the base of the floodplain aquifer the recharge event through the bedrock causes a rapid rise in water level in the floodplain aquifer and the chemistry of the deepest water in the floodplain aquifer changes at that time the rising water also entrains slow moving nitrate rich unsaturated zone water altering the chemistry of water in the shallow part of the aquifer vertical chemical stratification in the aquifer is thus created by the change in water chemistry in the upper and lower parts of the saturated zone as the water level begins to decline the aquifer undergoes mixing that eventually results in homogeneous water chemistry the rise in water level from the recharge event also displaces gas from the unsaturated zone that is then replaced as the water level declines following the recharge event this new oxygen rich vadose zone air equilibrates rapidly with saturated zone water resulting in a dissolved oxygen pulse in the ground water that peaks one half to 2 months after the water level peak this oxygen pulse subsequently declines over a period of 2 6 months

methylhopanoids molecular indicators of ancient bacteria and a petroleum correlation tool abstract methylhopanoids are organic compounds synthesized by certain bacteria that when preserved in sediments act as molecular fossils or biomarkers for organic matter inputs from specific bacterial sources two series of methylhopanoids occur each mainly deriving from a distinct bacterial source cyanobacteria 2 methyl and methanotrophic bacteria 3 methyl the abundance and composition of methylhopanoids within sediments of modern depositional environments varies widely apparently due to different bacterial communities contributing to the sedimentary organic matter comparable molecular characteristics are found in oils and their source rocks consequently methylhopanoids are valuable in oil oil and oil source rock correlations distinguishing between samples related to different depositional environments in particular abundant 3 methylhopanoids from methanotrophic bacteria or an additional unknown bacterial source are characteristic of some modern alkaline saline lake environments comparable compositional features in the methylhopanes of oils allow the assignment of lacustrine oils offshore west africa to two distinct lacustrine source rock facies and to distinguish between different marine source facies thus refining oil source rock correlation

distribution and structure of hydrocarbons in four organic rich ordovician rocks abstract organic matter in four north american rocks of ordovician age has been analysed using geochemical and optical techniques including reflected light and fluorescence microscopy rock eval pyrolysis elemental analysis of isolated kerogens gas chromatography gc and gas chromatography mass spectrometry gc ms of hydrocarbons in the solvent extracted bitumens the samples analysed were guttenberg oil rock and black shales from the vinini womble and big fork formations in the united states the origin of some of the biomarkers found in the bitumen and the vitrinite particles observed in reflected light are discussed briefly with reference to possible algal and bacterial precursors the results indicate that the four samples are potentially excellent oil source rocks although the guttenberg oil rock is too immature to have generated a substantial quantity of hydrocarbons

watershed scale chemical weathering in a merokarst terrain northeastern kansas usa abstract carbonate weathering in the merokarst landscape at the konza prairie near manhattan ks is governed by kinetically rapid reaction rates similar to other carbonate settings the geology of the site consists of repeating couplets of shale and limestone mantled by pleistocene loess on which most soils are built the headwater stream that is the subject of this study is intermittent and well connected to the secondary porosity in the limestone aquifers such that the water chemistry is groundwater dominated despite increasing in situ weathering rates shown by increasing solute concentrations long term 21 of 24 years decline in stream water discharge has reduced chemical denudation the current chemical denudation rate is 0 02 mm yr 1 limestone bedrock thickness 26 6 m is 38 of total bedrock thickness 70 m the present landscape would have taken 1 4 million years to dissolve at current weathering rates despite paleogeographic reconstructions suggesting exposure for the past 260 ma estimates of the time to erode younger strata using current physical and chemical denudation rates are 80 159 ma still much less than the age of the rocks an alternate source of material dust is proposed that may slow limestone weathering which in turn protects shales from physical erosion thereby slowing landscape evolution

organic matter source variation and the expression of a late middle ordovician carbon isotope excursion the carbon isotopic composition of organic matter is a powerful tool in the study of organic carbon burial and p co 2 through the geologic record however the organic matter source can affect total organic carbon 13 c values and may complicate interpretation of environmental conditions we examined the influence of organic matter source variations on a late middle ordovician positive 13 c excursion in strata of the united states midcontinent in a core from iowa the magnitude of the excursion recorded by carbonate carbon is 2 5 whereas the excursion recorded by total organic carbon is nearly 8 although this difference could arise from a profound decrease in surface water co 2 concentrations association of the organic walled microfossil gloeocapsomorpha prisca with 13 c enriched total organic carbon toc in this interval suggests that the excursion could also record a shift from normal marine to g prisca dominated organic matter carbon isotope analyses of individual biomarkers indicate that both of these explanations are required to explain the data compounds inferred to be of g prisca origin are enriched in 13 c by 7 relative to compounds derived from other algal sources furthermore compounds exclusively from either g prisca or other sources exhibit a positive shift of only 3 5 thus the large excursion recorded by toc reflects in part a change in the proportional contribution of g prisca to toc that all compounds exhibit a positive carbon isotopic shift indicates that independent of contributions from g prisca a positive organic 13 c excursion occurred and records a change in environmental conditions such as co 2 aq concentrations the 3 5 shift is similar in magnitude to that observed for toc in correlative units from pennsylvania suggesting that this event has broad geographic significance this work illustrates that organic matter source variations as well as environmental conditions govern the toc 13 c values and shows how compound specific isotope analyses can resolve these multiple controls

ecosystem controlled soil rock pco2 and carbonate weathering constraints by temperature and soil water content carbonate dissolution in soil groundwater systems depends dominantly on ph temperature and the saturation state of the solution with respect to abundant minerals the ph of the solution is in general controlled by partial pressure of co2 pco 2 produced by ecosystem respiration which is controlled by temperature and water availability in order to better understand the control of land temperature on carbonate weathering a database of published spring water hydrogeochemistry was built and analysed assuming that spring water is in equilibrium with the soil water rock atmosphere the soil pco 2 can be back calculated based on a database of spring water chemistry the average soil rock co2 was calculated by an inverse model framework and a strong relationship with temperature was observed the identified relationship suggests a temperature control on carbonate weathering as a result of variations in soil rock pco 2 which is itself controlled by ecosystem respiration processes the findings are relevant for global scale analysis of carbonate weathering and carbon fluxes to the ocean because concentration of weathering products from the soil rock system into the river system in humid high temperature regions are suggested to be larger than in low temperature regions furthermore results suggest that in specific spring samples the hydrochemical evolution of rain water percolating through the soil rock complex can best be described by an open system with pco 2 controlled by the ecosystem abundance of evaporites and pyrite sources influence significantly the chemistry of spring water and corrections must be taken into account in order to implement the inverse model framework presented in this study annual surface temperature and soil water content were identified as suitable variables to develop the parameterization of soil rock pco 2 mechanistically consistent with soil respiration rate findings

key factors controlling hydrocarbon accumulations in ordovician carbonate reservoirs in the tazhong area tarim basin western china abstract the tazhong area at the center of the tarim basin western china contains abundant hydrocarbon resources principally in ordovician carbonate reservoirs the geological conditions for hydrocarbon accumulation in the area are quite complicated and are characterized by multiple stages of hydrocarbon generation accumulation adjustment and alteration despite decades of exploration and production in the region the mechanisms of hydrocarbon accumulation and their controlling factors are still not well established the geological setting and the distribution characteristics of the reservoir have been used to investigate the mechanisms of accumulation to quantitatively describe the main controlling factors and to predict potential favorable hydrocarbon accumulation zones in ordovician carbonate rocks of tazhong our results show that the hydrocarbons in the ordovician reservoirs came from mixed sources including middle lower cambrian and middle upper ordovician source rocks within the majiaer sag four stages of accumulation are recognized and hydrocarbons migrated into the tazhong area along six intersections of ne and nw fault sets principally from the northeast to the southwest but then locally from the northwest to the southeast the ordovician carbonate reservoirs are typically lithologically defined and the dynamic force of hydrocarbon accumulation is primarily reflects differential capillary forces the accumulation and distribution of hydrocarbons was controlled by the petrophysical properties of the reservoir and by hydrocarbon supply charge energy the petrophysical properties of the reservoir controlled the hydrocarbon accumulation threshold with the maximum differential capillary pressure force on average approximately 13 mpa the supply or charge energy of the hydrocarbons controls the accumulation distribution range the daily production of individual wells decreases with increasing distance from the fault intersections and the maximum hydrocarbon migration distance is about 35 km reservoir properties and the hydrocarbon supply charge energy coupling index rei appear to control hydrocarbon accumulation and distribution accumulation does not occur when the value of rei is 0 6 but is favored when values are higher

dust impure calcite and phytoliths modeled alternative sources of chemical weathering solutes in shallow groundwater abstract in highly reactive carbonate terrains that constitute more than one fifth of critical zone landscapes quantifying bedrock weathering processes may require understanding the realities of carbonate mineral impurity on solubility biotically produced minerals as an integral part of leaky biogeochemical cycles and dust deposited minerals as important high surface area first contact solute sources the potential impact of these processes has not been thoroughly investigated as groundwater solutes are mostly thought to be sourced from chemical reactions with soil and bedrock although dust is often viewed as an important delivery mechanism of nutrients to other ecosystems including those in mountain and tropical settings we present results of computer and hand calculated manual inverse modeling of two years of stream water chemistry spanning a dry and a wet year for a groundwater fed headwater stream at the konza tallgrass prairie long term ecological research site in northeastern kansas weathering of the limestone and shale bedrock at the site provide a possible source of solutes to the groundwater fed stream but our modeling suggests an alternate source considering the pathway of groundwater recharge likely encounters highly reactive phases before encountering bedrock we used the mineralogy and geochemistry of local dust collected previously estimates of a possible chemical composition of phytolith containing potassium and an impure calcite representing measured limestone bedrock chemistry to show that chemical reactions with the current dust flux are adequate to account for the groundwater chemistry average annual amounts were about 1 380 kg ha 1 yr 1 dust dissolved 2 80 kg ha 1 yr 1 bedrock carbonate dissolved and 3 320 kg ha 1 yr 1 phytoliths precipitated small amounts of cation exchange were also required to balance the models there were only small differences between the computer and manual inverse models both methods resulted in up to 4 6 times more mass of dust dissolved than bedrock we suggest that dust weathering may be a process that occurs widely considering the ubiquitous dust flux in continental regions significance of research solutes in groundwater and in streams fed by groundwater are thought to be mostly derived from aquifer bedrock and soil water recharging the aquifer this paradigm may fail for landscapes that have been subaerially exposed for 10 s to 100 s of millions of years in terrains where relatively rapid dissolution of minerals dominates such as carbonate mineral dominated rocks like limestone here we test whether dust having high surface area and being the first inorganic solid encountered by meteoric precipitation could provide enough solutes water to reduce the amount of bedrock that dissolves extending the timeframe of landscape evolution we found through inverse modeling with phreeqc that dust can provide 4 6 times as much mass to stream water in merokarst than calcite and that the mass of dust dissolved was the same order of magnitude as local dust deposition these results give permissive evidence that dust is important to understanding groundwater chemistry

high resolution isotope stratigraphy of the lower ordovician st george group of western newfoundland canada implications for global correlation the lower ordovician st george group of western newfoundland consists mainly of shallow marine platform carbonates 500 m thick it is formed from bottom to top of the watts bight boat harbour catoche and aguathuna formations the top boundary of the group is marked by the regional st george unconformity outcrops and a few cores from western newfoundland were sampled at high resolution and the extracted micritic materials were investigated for their petrographic and geochemical criteria to evaluate their degree of preservation the d13c and d18o values of wellpreserved micrite microsamples range from 4 2 to 0 vpdb and from 11 3 to 2 9 vpdb respectively the d13ccarb profile of the st george group carbonates reveals several negative shifts which vary between 2 and 3 and are generally associated with unconformities disconformities or thin shale interbeds thus reflecting the effect of or link with significant sea level changes the st george unconformity is associated with a negative d13ccarb shift 2 on the profile and correlated with major lowstand around the end of arenig on the local sea level reconstruction and also on those from the baltic region and central australia thus suggesting that the st george group unconformity might have likely had an eustatic component that contributed to the development enhancement of the paleomargin other similar d13ccarb shifts have been recorded on the st george profile but it is hard to evaluate their global extension due to the low resolution of the documented global lower ordovician tremadoc middle arenig d13ccarb profile

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

chemical and isotopic properties of kukersites from iowa and estonia abstract kukersite samples from estonia and iowa were analyzed for elemental composition functional group distribution and carbon and hydrogen stable isotope ratios the elemental and hydrogen isotope values together with other analytical data suggest a higher thermal maturity for the iowa kukersite the wide carbon isotopic range of 9 3 among kukersites with unusually negative 13c values reaching 33 2 indicates isotopically variable carbon sources for production of biomass and thus major paleoceanographic differences between the environments supporting biosynthesis

distinguishing cambrian from upper ordovician source rocks evidence from sulfur isotopes and biomarkers in the tarim basin abstract the reported source rocks for the abundant petroleum in the tarim basin china range from cambrian to lower ordovician and or upper ordovician in age however the difference between the two groups of source rocks is not well characterized in this study pyrite was removed from eleven mature to over mature kerogen samples from source rocks using the method of crcl 2 reduction and grinding the kerogen and coexisting pyrite samples were then analyzed for 34 s values results show that the kerogen samples from the cambrian have 34 s values between 10 4 and 19 4 the values are significantly higher than those from the lower ordovician kerogen 34 s of between 6 7 and 8 7 which in turn are generally higher than from the upper ordovician kerogen samples 34 s of between 15 3 and 6 8 the associated pyrite shows a similar trend but with much lower 34 s values this stratigraphically controlled sulfur isotope variation parallels the evolving contemporary marine sulfate and dated oil 34 s values from other basins suggesting that seawater sulfate and source rock age have an important influence on kerogen and pyrite 34 s values the relatively high 34 s values in the cambrian to lower ordovician source rocks are associated with abundant aryl isoprenoids gammacerane and c 35 homohopanes in the extractable organic matter indicating that these source rocks were deposited in a bottom water euxinic environment with water stratification compared with the upper ordovician the cambrian to lower ordovician source rocks show abundance in c 28 20r sterane c 23 tricyclic terpanes 4 23 24 trimethyl triaromatic dinosteroids and depletion in c 24 tetracyclic terpane c 29 hopane thus 34 s values and biomarkers of source rock organic matter can be used for distinguishing the cambrian and upper ordovician source rocks in the tarim basin

hydrogeology of thin limestones the konza prairie long term ecological research site northeastern kansas abstract the konza prairie research natural area and national science foundation long term ecological research lter site is a dissected tallgrass prairie upland located in northeastern kansas it is underlain by nearly horizontal alternating thin limestones and shales of permian age and by discontinuous quaternary alluvium shallow aquifers which interact with surface water in this region are an important steady source of water to the biota because of sporadic precipitation this study provides a summary of the shallow hydrogeology in a typical watershed on the konza prairie including an overview of directions of ground water movement inferred from water level data and of ground water chemistry measurements made every 4 to 6 weeks for over 2 5 years provide information on spatial and temporal variability in water chemistry and in directions of ground water flow during the end of a drought first year during a period of average rainfall second year and through a period of exceptionally high summer rainfall third year well yields from the limestones each cut by the ephemeral stream draining the watershed are variable and depend upon secondary porosity development potential for vertical flow is downward in all units and lateral flow directions are sometimes toward and sometimes away from the stream in addition water levels are sometimes above and sometimes below the tops of the aquifers indicating that aquifers behave sometimes as confined and sometimes as unconfined aquifers the stratigraphically and topographically lowest unit monitored morrill limestone is the highest yield aquifer and appears to be hydraulically linked to the stream the uppermost unit studied upper eiss limestone has water chemistry and well yield somewhat similar to the morrill although there is insufficient well control to establish that it too is closely linked to the stream the middle unit lower eiss limestone is characterized by lower hydraulic conductivity steady water chemistry and higher total dissolved solids than the upper and lower units despite the differing hydraulic behavior of the limestones concentration ranges of the major elements in water samples from the aquifers overlap with the exception of consistently higher dissolved magnesium in the lower eiss limestone water variability in hardness alkalinity and sulfate the principal components of the dissolved solids do not clearly distinguish between high and low permeability aquifers or parts of aquifers occasional easily identified sulfate spikes are the result of dissolution of pockets of gypsum or anhydrite in the limestones relatively long term progressive depression of sulfate concentrations is probably the result of steady recharge during relatively long et periods and is a good indicator of flushing of the aquifers even though water levels are not elevated calcium and alkalinity variations at this site reflect variations in recharge as modified by seasonal variations in below ground p co 2 calcium magnesium ratios are not constant indicating that either there is a non carbonate mineral source for magnesium or that more than one carbonate mineral with different magnesium contents contributes calcium to the water the time series sampling used in this study revealed information about the complicated chemical and hydraulic response of these shallow thin limestone aquifers to variable recharge

formation of phreatic caves in an eogenetic karst aquifer by co2 enrichment at lower water tables and subsequent flooding by sea level rise formation of extensive phreatic caves in eogenetic karst aquifers is widely believed to require mixing of fresh and saltwater extensive phreatic caves also occur however in eogenetic karst aquifers where fresh and saltwater do not mix for example in the upper floridan aquifer these caves are thought to have formed in their modern settings by dissolution from sinking streams or by convergence of groundwater flow paths on springs alternatively these caves have been hypothesized to have formed at lower water tables during sea level low stands these hypotheses have not previously been tested against one another analyzing morphological data and water chemistry from caves in the suwannee river basin in north central florida and water chemistry from wells in the central florida carbonate platform indicates that phreatic caves within the suwannee river basin most likely formed at lower water tables during lower sea levels consideration of the hydrological and geochemical constraints posed by the upper floridan aquifer leads to the conclusion that cave formation was most likely driven by dissolution of vadose co2 gas into the groundwater sea level rise and a wetter climate during the mid holocene lifted the water table above the elevation of the caves and placed the caves tens of meters below the modern water table when rising water tables reached the land surface surface streams formed incision of surface streams breached the pre existing caves to form modern springs which provide access to the phreatic caves phreatic caves in the suwannee river basin are thus relict and have no causal relationship with modern surficial drainage systems neither mixing dissolution nor sinking streams are necessary to form laterally extensive phreatic caves in eogenetic karst aquifers dissolution at water tables potentially driven by vadose co2 gas offers an underappreciated mechanism to form cavernous porosity in eogenetic carbonate rocks copyright 2012 john wiley sons ltd

the end ordovician glaciation and the hirnantian stage a global review and questions about late ordovician event stratigraphy abstract this paper proposes a global review of hirnantian event stratigraphy the hirnantian gssp in south china is tentatively correlated with latest ordovician strata from the peri gondwanan glacial regions problems of biostratigraphical correlation are highlighted at a worldwide scale the major biostratigraphically useful fossil groups graptolites chitinozoans brachiopods conodonts acritarchs are analysed and their limits for global correlation of the uppermost ordovician are discussed palaeobiogeographical disparities are invoked as the primary cause of the difficulty in establishing an effective late ordovician global biostratigraphical scheme as an alternative correlative tool the hice hirnantian isotopic curve excursion event is often put forward in the literature however carbon isotope chemostratigraphy shows like biostratigraphy some limits to the present state of knowledge no good independent biostratigraphical control of the hice exists in both shallow carbonate deposits and deeper shaly ones recent studies have also demonstrated inconsistencies between carbon isotopic signals obtained from organic 13corg and inorganic 13ccarb carbon species further complicating the use of the hice as an isochronous benchmark all of these difficulties for hirnantian event stratigraphy are discussed in detail in order to enable them to be overcome in the future precise late ordovician and early silurian event stratigraphies are essential for the understanding of the mechanisms linked to the first of the big five extinctions

high resolution carbon isotopic records from the ordovician of south china links to climatic cooling and the great ordovician biodiversification event gobe abstract the great ordovician biodiversification event gobe represented the largest increase in diversity in the marine biosphere during the phanerozoic eon yet its causes and consequences remain poorly understood patterns of isotopic variation in high resolution 13ccarb and 13corg records from a well exposed section at honghuayuan in south china may provide important insights regarding the gobe the honghuayuan isotopic profiles which can be correlated with c isotopic records from contemporaneous sections globally reveal large perturbations to the global carbon cycle during the ordovician a 8 increase in 13corg values in the floian implies a large albeit transient increase in the burial rate of organic matter during the mid early ordovician that may have contributed to climatic cooling and played an important role in triggering the gobe a 4 increase in 13ccarb and high frequency variation in 13corg in the darriwilian to sandbian suggest a second episode of elevated organic carbon burial rates accompanied by substantial instability in the global carbon cycle during the late middle and early late ordovician this pattern may mark the onset of climate changes culminating in the end ordovician hirnantian glaciation and mass extinction event that terminated the gobe

simulation and interpretation of sonic waveforms in high angle and horizontal wells abstractwe have developed a new method to process and interpret sonic waveforms acquired in high angle ha and horizontal hz wells in the vicinity of layer boundaries numerical simulations are examined for ha hz fluid filled borehole models in which sonic tools with monopole and dipole sources operate across a horizontal bed boundary in hard and soft formations simulations are performed with a 3d time domain finite difference method assuming a sonic logging tool in which each receiver station consists of eight azimuthal receivers instead of conventional processing for monopole and dipole waveforms which takes the average and difference respectively of waveforms acquired with azimuthal receivers we analyze the waveforms acquired individually by each azimuthal receiver for dipole sources we refer to the dispersive signals recorded by individual receivers as pseudo flexural waves and we first process them with a weighted spectral semblance method to obtain the frequency dispersion curves we t

multipole sources in boreholes penetrating anisotropic formations numerical and experimental results a 2 5 d velocity stress finite difference code is described that models acoustic propagation in a borehole penetrating a generally anisotropic formation the excitation may be a dilatation monopole or a point force dipole in an arbitrary direction the anisotropic formation is homogeneous along the axis of the borehole but may be inhomogeneous in the transverse plane the borehole cross section and location of the source in the borehole are arbitrary synthetic time domain waveforms are displayed for arrays of monopole and dipole receivers deployed along the borehole axis in both fast and slow anisotropic formations the specific anisotropy model employed for the numerical results is a transversely isotropic ti formation with its axis of symmetry inclined with respect to the borehole axis by an arbitrary angle flexural shear and stoneley wave slowness and attenuation estimates are extracted from the synthetic waveforms using a variant of prony s method for a range of borehole inclinations relative

hydrologically driven variations in the karst related carbon sink fluxes insights from high resolution monitoring of three karst catchments in southwest china summary rainfall p discharge q water temperature ph and specific electrical conductivity ec of the three karst catchments banzhai huanghou and houzhai with different land uses and carbonate lithologies but similar subtropical monsoonal climate in guizhou province southwest china were monitored with ctdp 300 high resolution multi parameter data loggers during the period of may 2007 october 2013 in addition hco3 and calcium concentrations were titrated in the field and the other major ions determined in the laboratory once every one or two months simple linear regression models were used to link the continuous chemical data to in situ measured data to estimate the concentration of hco3 the co2 partial pressures and the calcite saturation indices on the high resolution logger data continuous karst related carbon sink fluxes csfs were also estimated with the continuous q and hco3 concentrations in each catchment area the primary goal of this study is to understand how discharge and hco3 concentration determine the csfs at the storm scale seasonal scale and annual scale and to estimate the csfs for the three studied catchments results show that the variation in runoff river discharge played a more important role in controlling the csfs than the variation in hco3 for all the karst catchments because of the chemostatic behavior of hco3 in the catchments soil coverage vegetation and bedrock lithology determined the csfs by controlling the proportion of precipitation that recharges groundwater and thus q and controlling the soil co2 productivity and thus hco3 the average csfs in the banzhai huanghou and houzhai karst catchments were 29 3 33 5 and 39 8 t co2 km 2 a 1 respectively which are 15 times higher than those csfs by silicate weathering in the silicate rock catchments with similar hydrology showing the dominant role of carbonate weathering in the rock weathering related carbon sink the interannual change in csfs was large 1 7 2 5 fold for this study depending mainly on the variations of catchment river discharge e g high flow year vs low flow year this suggests that the conventional view that pre and post anthropogenic riverine carbon fluxes are equal is problematic in that large changes in river hydrology caused by global climate and land use and land cover changes have already been documented

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

sterane biomarkers as indicators of palaeozoic algal evolution and extinction events abstract algae are among the oldest organisms known to inhabit the earth s biosphere with a record dating back some 2 7 ga only few marine algae produce hard parts that can be preserved over geologic time and consequently their fossil record is incomplete molecular fossils or biomarkers add complementary information to the fossil palynomorph record steroids are important constituents of eukaryotic cell membranes and are preserved in sediments as steranes c28 and c29 steranes are indicators for the presence of green and c27 steranes for the presence of red algae respectively the relative abundance of steranes allows the investigation of the fossil record for palaeozoic algal diversification and evolution in this study 500 palaeozoic rock samples representing a broad facies variety from the upper ordovician to the p t boundary were investigated for sterane compositions in addition three profiles covering the hirnantian the f f and the hangenberg event were analyzed for possible shifts in the sterane distribution associated with extinction events a sharp increase of the c28 c29 sterane ratio from 0 70 at the devonian carboniferous boundary implies a fundamental change in the green algae assemblage from more primitive mainly c29 sterane producing algae to modern c28 sterane producing algae for all investigated extinction events a pronounced but short lived rise in the c28 sterane content occurs that is attributed to an episodic increase in prasinophytes the gradual radiation of algae may have been triggered by frequent mass extinctions in the upper devonian culminating with the massive decline of acritarchs at the d c boundary the coeval rise in the c28 c29 sterane ratio indicates the presence of an non encysting algal group and coincides with the global augmentation of numerous filamentous codiacea siphonales and the rise of euspondyle and metaspondyle dasycladales

compound specific isotopic variability in uinta basin native bitumens paleoenvironmental implications abstract we have analyzed the solvent extracts from three different types of native bitumens from the uinta basin in northeastern utah by a variety of analytical techniques including gc irms to evaluate variations in the paleodepositional environment during two periods of lake uinta deposition the gilsonite and tabbyite bitumens are associated with parachute creek member sediments deposited during a major expansion of ancient lake uinta compound specific isotopic analyses of s carotane and phytane 13 c 32 6 to 32 1 0 from these bitumens reflect input from primary photosynthetic producers such as cyanobacteria sterane 13c values 34 5 to 29 2 0 refflect contributions from lacustrine algae while extremely depleted 13c values for methylhopanes 58 1 to 61 5 0 suggest input from methanotrophic bacteria variations in the 13c values of the hopanes 51 4 to 37 7 0 imply additional input from other bacterial sources the wurtzilite bitumen was generated from the saline facies of the green river formation deposited during a later regression of lake uinta compound specific isotopic analyses of phytane 13 c 30 1 0 and steranes 13 c 29 6 to 26 7 0 from this bitumen indicate continued input from primary producers and eukaryotes the higher relative concentrations of gammacerane 13 c 26 9 0 indicate increasing input from aerobic protozoa we observed a slight enrichment in 13c in the wurtzilite extract and several biomarkers and suggest that this is a result of sulfate reducing bacteria outcompeting methanogens thereby eliminating the influence of methanotrophs in this later saline stage of deposition

perturbation of the marine nitrogen cycle during the late ordovician glaciation and mass extinction abstract the late ordovician was a critical interval in geologic history during which both the biosphere and marine environments underwent severe perturbations including one of the big five phanerozoic mass extinctions and the massive but short term 0 5 myr hirnantian glaciation the onset and termination of the hirnantian glaciation have been widely accepted as the triggers for the two extinction pulses that comprise the late ordovician biocrisis but the mechanisms that caused the hirnantian glaciation itself remain poorly known here we analyze the nitrogen isotope composition 15 n of two sections in south china wangjiawan and nanbazi in order to better understand nitrogen cycle perturbations in the late ordovician ocean and their relationship to contemporaneous climatic and biogeochemical changes low 15 n 1 in the upper katian and lower rhuddanian of both sections suggests intensive i e near quantitative denitrification and thus nitrogen fixation as the main source of biologically available nitrogen for primary producers a positive 15 n excursion in both sections during the hirnantian indicates weaker i e non quantitative denitrification possibly as a result of more vigorous thermohaline circulation and improved ocean ventilation weaker denitrification would have reduced the flux of n 2 o an intermediate product of denitrification to the atmosphere n 2 o is a potent greenhouse gas and a major decline in its production would have led to cooler climatic conditions and ultimately the hirnantian glaciation a global survey of published nitrogen isotope records suggests that similar processes operated broadly within the late ordovician global ocean

origin of petroleum in the neoproterozoic cambrian south oman salt basin abstract the south oman salt basin sosb is host to the world s oldest known commercial deposits most of the south oman oils have been proven to be associated with the source rocks of the neoproterozoic to cambrian huqf supergroup but the assignment of oils to specific huqf intervals or facies has been hampered by the geochemical similarity of the organic matter across the entire huqf sequence possibly as a consequence of limited change in the local palaeoenvironment and biota over the time of its deposition this study was conducted to establish improved correlations between organic rich rock units and reservoir fluids in the sosb through detailed molecular and isotopic analysis of the huqf supergroup with special emphasis directed towards understanding the ara carbonate stringer play unusual biomarkers tentatively identified as a norsteranes show distinctive patterns among carbonate stringer oils and rocks different from those observed in nafun sediments and ara rocks from the athel basin these putative a norsteranes form the basis for new oil source correlations in the sosb and provide for the first time geochemical evidence of a self charging mechanism for the carbonate stringer play the paucity of markers specific to the nafun group shuram buah and masirah bay formations confounds attempts to quantify their respective contributions to huqf oil accumulations nafun inputs can only be determined on the basis of subtle differences between nafun and ara biomarker ratios the most useful geochemical characteristics delineating nafun group organic matter from ara group intra salt source rocks included low relative abundance of mid chain monomethyl alkanes x compounds low relative abundance of gammacerane 28 30 dinorhopane 25 28 30 trinorhopane and 2 methylhopanes low c 22 t c 21 t and high c 23 t c 24 t cheilanthanes ratio values based on these parameters molecular evidence for major contributions of liquid hydrocarbons from nafun group sediments shuram buah and masirah bay formations is lacking our results suggest that the majority of sosb hydrocarbon accumulations originate from within the ara group either from the carbonate stringers or from the package of sediments that comprises the thuleilat athel silicilyte and u shale formations subtle aspects of the composition of some carbonate stringer and post salt huqf oils could suggest some degree of sourcing from the nafun rocks but stronger evidence is needed to confirm this

mechanisms for chemostatic behavior in catchments implications for co2 consumption by mineral weathering a r t i c l e i n f o article history concentrations of weathering products in streams often show relatively little variation compared to changes in discharge both at event and annual scales in this study several hypothesized mechanisms for this chemostatic behavior were evaluated and the potential for those mechanisms to in uence relations between climate weathering uxes and co2 consumption via mineral weathering was assessed data from loch vale an alpine catchment in the colorado rocky mountains indicates that cation exchange and seasonal precipitation and dissolution of amorphous or poorly crystalline aluminosilicates are important processes that help regulate solute concentrations in the stream however those processes have no direct effect on co2 consumption in catchments hydrograph separation analyses indicate that old water stored in the subsurface over the winter accounts for about one quarter of annual stream ow and almost one half of annual uxes of na and sio2 in the stream thus ushing of old water by new water snowmelt is an important component of chemostatic behavior hydrologic ushing of subsurface materials further induces chemostatic behavior by reducing mineral saturation indices and increasing reactive mineral surface area which stimulate mineral weathering rates co2 consumption by carbonic acid mediated mineral weathering was quanti ed using mass balance calculations results indicated that silicate mineral weathering was responsible for approximately two thirds of annual co2 consumption and carbonate weathering was responsible for the remaining one third co2 consumption was strongly dependent on annual precipitation and temperature these relations were captured in a simple statistical model that accounted for 71 of the annual variation in co2 consumption via mineral weathering in loch vale published by elsevier b v

the controls on the major and trace element variation of shales siltstones and sandstones of pennsylvanian permian age from uplifted continental blocks in colorado to platform sediment in kansas usa shales siltstones and sandstones of pennsylvanian permian age from near the source in colorado to those in the platform in eastern colorado and kansas have been analyzed for major elements and a number of trace elements including the rees the near source sandstones are significantly more enriched student t test at better than the 99 confidence level in sio2 and na2o concentrations and more depleted in al2o3 fe2o3 total tio2 th hf sc cr cs rees y and ni concentrations and laco and lani ratios than the near source shales and siltstones most likely due to more plagioclase and quartz and less clay minerals in the sandstones than in the shales and siltstones there are no significant differences in k2o and sr concentrations and eueu lalu lase thsc thco and crth ratios between the near source sandstones and the near source shales and siltstones samples of the molas hermosa and cutler formations near the source that were formed in different environments in the same area contain no significant difference in eueu lalu lasc thsc thco and crth ratios so a generally silicic source and not the environment of deposition was most important in producing these elemental ratios for example crth ratios of near source shales siltstones and sandstones range from 2 5 to 17 5 and eueu range from 0 48 to 0 78 which are in the range of sources of sediments derived from mainly silicic and not basic sources near source shales and siltstones contain significantly higher student t test and more varied concentrations of most elements al2o3 fe2o3 mno tio2 ba th hf ta co sc rees nb y but significantly lower concentrations of na2o and eueu than platform shales and siltstones in kansas e g la 65 7 40 and eueu 0 55 0 07 in near source shales and siltstones and la 23 7 8 7 and eueu 0 64 0 08 in platform shales and siltstones the sio2 and cao concentrations are not significantly different in platform shales and siltstones compared to the near source shales and siltstones so dilution of other minerals by quartz and calcite is not the main reason for the lower concentration of most elements in the platform relative to the near source shales and siltstones rather the lesser concentrations of most elements in clay minerals of the platform shales and siltstones can account for the lower concentration of most elements compared to corresponding near source shales and siltstones the lower concentrations of many elements in clay minerals in the platform shales and siltstones may be a result of having been derived from recycling of clay minerals from older rocks the greater homogeneity of elemental concentrations of the platform shales and siltstones compared to those in the source is also consistent with homogeneous mixing of such recycled material also there is no significant difference in thsc laco thco lani and crth ratios of the near source sedimentary rocks in colorado to the platform shales and siltstones in kansas and the latter are also consistent with derivation from mostly silicic source rocks

first plants cooled the ordovician the late ordovician period ending 444 million years ago was marked by the onset of glaciations the expansion of non vascular land plants accelerated chemical weathering and may have drawn down enough atmospheric carbon dioxide to trigger the growth of ice sheets

massive expansion of marine archaea during a mid cretaceous oceanic anoxic event biogeochemical and stable carbon isotopic analysis of black shale sequences deposited during an albian oceanic anoxic event 112 million years ago indicate that up to 80 weight percent of sedimentary organic carbon is derived from marine nonthermophilic archaea the carbon 13 content of archaeal molecular fossils indicates that these archaea were living chemoautotrophically their massive expansion may have been a response to the strong stratification of the ocean during this anoxic event indeed the sedimentary record of archaeal membrane lipids suggests that this anoxic event marks a time in earth history at which certain hyperthermophilic archaea adapted to low temperature environments

molecular indicators of redox and marine photoautotroph composition in the late middle ordovician of iowa u s a abstract saturated and aromatic hydrocarbons were used to evaluate depositional redox conditions and marine photoautotroph contributions to middle caradocian strata of the central united states ia at the base of the spechts ferry member of the decorah formation 13c enriched aryl isoprenoids derivatives of green sulfur bacteria become abundant indicating the development of photic zone anoxia this is coincident with the disappearance of the organic walled microfossil gloeocapsomorpha prisca and a marked decrease in the relative abundances of cyanobacterial biomarkers the development of dysoxic to anoxic conditions and or associated changes in basin circulation potentially affected the distributions and abundances of these organisms in the overlying guttenberg member g prisca derived organic matter becomes dominant but relative cyanobacteria abundances remain low in addition the percentage total organic carbon is greater than 20 even though selected biomarker ratios pristane phytane ratios greater than 3 and homohopane indices less than 0 5 and the presence of bioturbation indicate that bottom waters were oxygenated it is suggested that deposition of g prisca affected both organic matter preservation and depositional redox conditions observed variations in redox indicators and marine photoautotroph contributions are associated with changes in siliciclastic deposition reported macrofauna turnover and with evidence for oceanic cooling and a change in circulation patterns documented in the eastern united states

migrated hydrocarbons in outcrop samples revised petroleum exploration directions in the tarim basin abstract the application of age specific biomarker distributions established from mature exploration areas of the tarim basin northwestern china indicates that most carboniferous permian outcrop samples in the eastern segment of the southwest depression previously believed to have significant petroleum source potential in fact contain migrated hydrocarbons derived from cambrian lower ordovician strata new geochemical results have led to a major revision of petroleum exploration directions in this area

possible late middle ordovician organic carbon isotope excursion evidence from ordovician oils and hydrocarbon source rocks mid continent and east central united states oils generated by middle ordovician rocks are found throughout the mid continent and east central regions of the united states gas chromatographic characteristics of these oils include a relatively high abundance of n alkanes with carbon numbers less than 20 a strong predominance of odd numbered n alkanes between c10 and c20 and relatively small amounts of branched and cyclic alkanes saturated and aromatic hydrocarbon fractions of 43 ordovician oils from the anadarko ardmore forest city illinois michigan salina sedgwick and williston basins and the iowa shelf demonstrate a wide range in carbon isotope composition dgr13csat 24 9 pmil to 33 9 pmil dgr13carom 24 3 pmil to 33 7 pmil saturated and aromatic hydrocarbons extracted from late middle ordovician shales 17 core samples show ranges in dgr13c similar to that of the oils the wide ranges in dgr13c for oils and rock extracts reflect a major positive excursion s 6 9 per pmil in organic matter dgr13c in late middle ordovician rocks this excursion has at least a regional significance in that it can be documented in sections 480 mi 770 km apart in south central kansas and eastern iowa the distance may be as much as 930 mi 1 500 km if the carbon isotope variations observed in michigan basin ordovician oils and in organic matter from late middle ordovician rocks in southwestern ontario are related to the same carbon isotope excursion organic matter dgr13c in core samples from south central kansas and eastern iowa is not directly related to variations in quantity or quality of organic matter or maceral compositi n the positive excursion in organic matter dgr13c is a possible result of increased organic matter productivity and or preservation the parallel shifts in organic and carbonate dgr13c in core samples from 1 e m greene well washington county iowa imply changes in the isotope composition of the ocean atmosphere carbon reservoir differences in the magnitude of the carbon isotope shifts between organic matter 8 8 pmil and carbonate 4 2 pmil in this core suggest a decrease either locally or regionally in available dissolved co2 possibly a result of high organic matter productivity and or limited circulation in the late middle ordovician seas

multipole acoustic waveforms in fluid filled boreholes in biaxially stressed formations a finite difference method a finite difference method is developed to simulate elastic wave propagation in a borehole surrounded by a biaxially stressed solid formation the linear elastic formation is altered by such tectonic stresses that cause significant changes in the characteristics of wave propagation in a borehole the 2 5 dimensional problem addressed in this work concerns the three dimensional wave propagation in a medium inhomogeneous in two spatial coordinates transverse to the borehole axis a second order finite difference method is developed to solve the partial differential equations arising from a published acoustoelastic model for borehole acoustic wave propagation in prestressed formations the algorithm is validated and applied to model both the borehole flexural and axisymmetric stoneley waves the computed waveforms are processed by a variation of prony s algorithm that yields dispersion curves for flexural waves polarized both parallel and perpendicular to the stress direction the flexural dispersion crossover in a uniaxially stressed formation is quantitatively confirmed the stoneley dispersion in the presence of such stresses exhibits approximately a uniform shift toward lower slownesses over the entire bandwidth of interest this implies that azimuthal averaging of formation stiffnesses approximately yields the same effective stoneley stiffness at different radial positions

new evidence for land plants from the lower middle ordovician of saudi arabia macerations of middle ordovician llanvirnian shales from saudi arabia yield an assemblage of spores of probable land plants cryptospores acritarchs and chitinozoa the production of sporopollenin containing sporelike tetrads is considered a fundamental character of the embryophytes because no extant algae produce spores of this type no trilete spores were found at this horizon reinforcing previous assertions that obligate meiotic tetrads predate the earliest trilete spores sporomorph tetrads and dyads in conjunction with cuticlelike fragments were probably derived from terrestrial plants at a bryophyte grade although there are reports of possibly older cryptospores the hanadir assemblage described herein clearly establishes their presence by llanvirnian time

increasing shallow groundwater co2 and limestone weathering konza prairie usa in a mid continental north american grassland solute concentrations in shallow limestone hosted groundwater and adjacent surface water cycle annually and have increased steadily over the 15 year study period 1991 2005 inclusive modeled groundwater co2 verified by measurements of recent samples increased from 10 2 05 atm to 10 1 94 atm about a 20 increase from 1991 to 2005 the measured groundwater alkalinity and alkaline earth element concentrations also increased over that time period we propose that carbonate minerals dissolve in response to lowered ph that occurs during an annual carbonate mineral saturation cycle the cycle starts with low saturation during late summer and autumn when dissolved co2 is high as dissolved co2 decreases in the spring and early summer carbonates become oversaturated but oversaturation does not exceed the threshold for precipitation we propose that groundwater is a co2 sink through weathering of limestone soil generated co2 is transformed to alkalinity through dissolution of calcite or dolomite the annual cycle and long term increase in shallow groundwater co2 is similar to but greater than atmospheric co2 2008 elsevier ltd all rights reserved

simulation of borehole sonic waveforms in dipping anisotropic and invaded formations a numerical simulation study has been made of borehole sonic measurements that examined shoulder bed anisotropy and mud filtrate invasion effects on frequency dispersion curves of flexural and stoneley waves numerical simulations were considered for a range of models for fast and slow formations computations are performed with a cartesian 3d finite difference time domain code simulations show that presence of transverse isotropy ti alters the dispersion of flexural and stoneley waves in slow formations the flexural wave becomes less dispersive when the shear modulus c44 governing wave propagation parallel to the ti symmetry axis is lower than the shear modulus c66 governing wave propagation normal to the ti symmetry axis conversely the flexural wave becomes more dispersive when c44 c66 dispersion decreases by as much as 30 at higher frequencies for the considered case where c44 c66 and decrease

fast and slow flexural waves in a deviated borehole in homogeneous and layered anisotropic formations summary dipole acoustic fields in an arbitrarily deviated well penetrating a homogeneous as well as a stratified transversely isotropic formation are simulated using a 3 d finite difference timedomain algorithm in cylindrical coordinates the modelling results show that a dipole source can excite a fast and a slow flexural mode due to the shear wave anisotropy when the borehole is inclined with respect to the symmetry axis of transverse isotropy both flexural slownesses change with the wellbore deviation angle the splitting of flexural modes is prominent in full wave arrays when the shear anisotropy is strong enough it is revealed that the dipole orientation influences the relative amplitudes of the fast and slow flexural waves but it has no effect on their slownesses or phases in a vertical well parallel to the symmetry axis the two flexural waves degenerate and propagate at the same speed the degenerated flexural wave travels approximately at the shear speed along the borehole wall except in a few formations our study shows for example that it is about 10 per cent slower than the shear wave in mesaverde clayshale 5501 even in that kind of formations however extraction of the fastand slow shear velocities from the flexural modes is still possible if the borehole deviation is large enough to examine the effect of layering we modelled the full waves in a formation with a sandwich when the well is perpendicular to the layer interfaces reflection is obvious and can be recognized it becomes weaker or even invisible as the deviation angle increases so it is difficult to detect a thin layer embedded in a formation directly from reflected waves the sandwich can instead be recognized from the irregularity in the spectra of the full waveforms displayed versus depth

organic geochemical characteristics of black shales across the ordovician silurian boundary in the holy cross mountains central poland abstract black shales in the holy cross mountains area of poland provide a record of environmental change across the ordovician silurian boundary the changing depositional conditions have generated a variation in organic matter contents above and below the boundary investigating the organic constitution of these black shales has the potential to reveal how their organic matter contents were generated and how suitable these rocks and their lateral equivalents may be for exploitation as shale gas reservoirs one outcrop at the holy cross mountains with a continuous section across the ordovician silurian boundary occurs near the village of bardo stawy in the kielce region and contains sandy silty mudstones as well as grey and black shales organic geochemical analyses of samples at bardo stawy reveals low total organic carbon toc contents for ordovician samples and higher toc values for silurian samples organic biomarkers indicate that the ordovician rocks were deposited in a shallow marine shelf setting while the silurian rocks were deposited in a deeper marine environment the progressive increase in toc from the uppermost ordovician to the lowermost silurian rocks reflects increasingly oxygen poor depositional conditions during the post glacial transgression following the deposition and preservation of organic matter in the ordovician and silurian rocks these rocks were buried and subjected to thermal maturation rock eval and biomarker thermal maturity parameters all indicate that the organic matter is mature and lies within the oil window the ordovician and silurian shales have direct relevance to recent attempts to discover and exploit shale gas reservoirs in poland our data and interpretations suggest that the relatively low toc values

molecular isotopic evidence of environmental and ecological changes across the cenomanian turonian boundary in the levant platform of central jordan abstract we evaluated the structure of planktonic communities and paleoenvironmental conditions throughout the cenomanian turonian oceanic anoxic event oae2 by studying bulk geochemical properties and the molecular isotopic composition of source specific hydrocarbons from organic rich sediments deposited in an intrashelf basin at the levant platform central jordan high concentrations of desmethyl and 4 methylsteranes as well as dinosteranes indicate that marine algae including dinoflagellates were the main primary producing organisms the presence of 2 methylhopanes and 13 c enriched hopanes in addition to isotopically enriched aryl isoprenoids evidenced the contribution of cyanobacteria and green sulfur bacteria respectively additionally variable but fairly low 15 n values during oae2 suggest the occurrence of diazotrophy as a likely important process fueling primary production during oae2 in this stratified anoxic continental platform variations in the relative contribution of biomarkers revealed changes in planktonic communities associated with sea level change and water column stratification oae2 was characterized by strong stratification anoxic bottom waters and a deep chemocline as evidenced by high gammacerane and homohopane indices and the absence of photic zone euxinia pze markers respectively however the presence of isorenieratane and its derivatives in post oae black shales points to a shoaling of the chemocline and to pze this interval was also characterized by an exceptionally high abundance of chlorophyll derived pristane and phytane up to 2 mg g 1 toc likely as a result of highly enhanced primary production and organic matter preservation remarkably this high productivity event co occurs with an exceptionally high abundance of calcispheres reported elsewhere to be part of a global bio event

evolution of carbonate and karst critical zones abstract carbonate terrains ct underlie one fifth of terrestrial ice free land and are an important supply of potable water to the world s population and yet processes endemic to ct critical zones cz and responses of these processes to climatic and anthropogenic pressures are not well understood given the rapid dissolution rates and ability to generate well developed networks of secondary porosity these landscapes can be highly sensitive to impacts from climate change e g modifications of temperature precipitation sea level and human disturbance e g water withdrawal diversions changes in land use land cover this special issue includes 16 papers focused on ct cz processes and potential responses to climatic and human perturbations five major themes emerge from these papers namely 1 anthropogenic climate and land use changes alter ct cz weathering rate and diagenesis 2 metal and carbon fluxes in ct cz will respond to increasing hydrologic variance caused by climate change 3 endogenous and exogenous processes operating over short time periods

perennial flow through convergent hillslopes explains chemodynamic solute behavior in a shale headwater catchment abstract stream chemistry reflects the mixture of complex biogeochemical reactions that vary across space and time within watersheds for example streams experience changing hydrologic connectivity to heterogeneous water sources under different flow regimes however it remains unclear how seasonal flow paths link these different sources and regulate concentration discharge behavior i e changes in stream solute concentration as a function of discharge at the susquehanna shale hills critical zone observatory sshczo in central pennsylvania usa concentrations of chemostatic solutes k mg na si cl vary little across a wide range of discharge values while concentrations of chemodynamic solutes fe mn ca decrease sharply with increasing stream discharge to elucidate controls on chemodynamic solute behavior we investigated the chemistry of surface water and shallow subsurface water at the sshczo in early autumn when discharge was negligible and concentrations of chemodynamic solutes were high dissolved ions colloids and micron sized particles were extracted from hillslope soils and stream sediments to evaluate how elements were mobilized into pore waters and transported from hillslopes to the stream during the study period when flow was intermittent the stream consisted of isolated puddles that were chemically variable along the length of the channel inputs of subsurface water to the stream were limited to an area of upwelling near the stream headwaters and the water table remained over a meter below the stream bed along the rest of the channel chemodynamic elements fe and mn were preferentially mobilized from organic rich soils as a mixture of dissolved ions colloids and micron sized particles consequently subsurface water draining organic rich soils in the upper catchment was enriched in fe and mn conversely ca increased towards the catchment outlet and was primarily mobilized from stream sediments as ca2 concentrations of chemostatic solutes were relatively invariable throughout the catchment we conclude that chemodynamic behavior at sshczo is driven by seasonally variable connectivity between the stream and hillslope soils during the dry season stream water derives from a shallow perched water table interflow that upwells to generate metal rich stream headwaters high concentrations of soluble fe and mn at low discharge occur when metal rich headwaters are flushed to the catchment outlet during periodic rain events interflow during the dry season originates from water that infiltrates through organic rich swales thus metals in the stream at low flow are ultimately derived from convergent hillslopes where biological processes have concentrated and or mobilized these chemodynamic elements in contrast high concentrations of ca2 at low discharge are likely mobilized from stream sediments that contain secondary calcite precipitates we infer that chemodynamic solutes are diluted at high discharge primarily due to increased flow through planar hillslopes this study highlights how spatially heterogeneous biogeochemistry and seasonally variable flow paths regulate concentration discharge behavior within catchments

carbon isotopes support the presence of extensive land floras pre dating the origin of vascular plants abstract multiple lines of evidence indicate that earth s land masses became green some 2 7 ga ago about 1 billion years after the advent of life about 2 2 billion years later land plants abruptly appear in the fossil record and diversify marking the onset of ecologically complex terrestrial communities that persist to the present day given this long history of land colonization surprisingly few studies report direct fossil evidence of emergent vegetation prior to the continuous record of life on land that starts in the mid silurian ca 420 425 ma ago here we compare stable carbon isotope signatures of fossils from seven ordovician silurian 450 420 ma old appalachian biotas with signatures of coeval marine organic matter and with stable carbon isotope values predicted for ordovician and silurian liverworts bryocarb model the comparisons support a terrestrial origin for fossils in six of the biotas analyzed and indicate that some of the fossils represent bryophyte grade plants our results demonstrate that extensive land floras pre dated the advent of vascular plants by at least 25 ma the appalachian fossils represent the oldest direct evidence of widespread colonization of continents these findings provide a new search image for macrofossil assemblages that contain the earliest stages of land plant evolution we anticipate they will fuel renewed efforts to search for direct fossil evidence to track the origin of land plants and eukaryotic life on continents further back in geologic time

association of orogenic activity with the ordovician radiation of marine life the ordovician radiation of marine life was among the most substantial pulses of diversification in earth history and coincided in time with a major increase in the global level of orogenic activity to investigate a possible causal link between these two patterns the geographic distributions of 6576 individual appearances of ordovician vician genera around the world were evaluated with respect to their proximity to probable centers of orogeny foreland basins results indicate that these genera which belonged to an array of higher taxa that diversified in the middle and late ordovician trilobites brachiopods bivalves gastropods monoplacophorans were far more diverse in and adjacent to foreland basins than they were in areas farther removed from orogenic activity carbonate platforms this suggests an association of orogeny with diversification at that time

lipid taphonomy in the proterozoic and the effect of microbial mats on biomarker preservation the pre ediacaran biomarker record has several characteristic features that distinguish it from its phanerozoic counterpart including high concentrations of unresolved complex mixture ucm low concentrations or absence of eukaryotic steranes and a conspicuous carbon isotopic enrichment of n alkyl lipids relative to bulk sedimentary carbon we propose that these derive from a common non actualistic taphonomy based on the pervasive presence of microbial mats prior to the cambrian substrate revolution such mats would have formed a significant mechanical and biochemical barrier to in falling plankton leaving a biomarker record dominated by benthic microbial lipids most of which would have originated from the lower heterotrophically reworked layers of the mat most proterozoic biomarker assemblages studied in this work derive from shallow water sediments where cyanobacteria dominated upper mats represent a focused source of corrosive molecular oxygen this mat seal effect was broken with the onset of bioturbation in the ediacaran and early cambrian at which point the primary source of fossil biomarkers switched from the benthos to the plankton

organic geochemistry of the early toarcian oceanic anoxic event in hawsker bottoms yorkshire england a comprehensive organic geochemical investigation of the hawsker bottoms outcrop section in yorkshire england has provided new insights about environmental conditions leading into and during the toarcian oceanic anoxic event t oae 183 ma rock eval and molecular analyses demonstrate that the section is uniformly within the early oil window hydrogen index hi organic petrography polycyclic aromatic hydrocarbon pah distributions and tricyclic terpane ratios mark a shift to a lower relative abundance of terrigenous organic matter supplied to the sampling locality during the onset of the t oae and across a lithological transition unlike other ancient intervals of anoxia and extinction biomarker indices of planktonic community structure do not display major changes or anomalous values depositional environment and redox indicators support a shift towards more reducing conditions in the sediment porewaters and the development of a seasonally stratified water column during the t oae in addition to carotenoid biomarkers for green sulfur bacteria gsb we report the first occurrence of okenane a marker of purple sulfur bacteria psb in marine samples younger than 1 64 ga based on modern observations a planktonic source of okenane s precursor okenone would require extremely shallow photic zone euxinia pze and a highly restricted depositional environment however due to coastal vertical mixing the lack of planktonic okenone production in modern marine sulfidic environments and building evidence of okenone production in mat dwelling chromatiaceae we propose a sedimentary source of okenone as an alternative lastly we report the first parallel compound specific c13 record in marine and terrestrial derived biomarkers across the t oae the c13 records of short chain n alkanes acyclic isoprenoids and long chain n alkanes all encode negative carbon isotope excursions cies and together they support an injection of isotopically light carbon that impacted both the atmospheric and marine carbon reservoirs to date molecular c13 records of the t oae display a negative cie that is smaller in magnitude compared to the bulk organic c13 excursion although multiple mechanisms could explain this observation our molecular petrographic and rock eval data suggest that variable mixing of terrigenous and marine organic matter is an important factor affecting the bulk organic c13 records of the t oae

biomarkers of black shales formed by microbial mats late mesoproterozoic 1 1 ga taoudeni basin mauritania a b s t r a c t hydrocarbon biomarkers in late mesoproterozoic black shales from the taoudeni basin mauritania northwestern africa were analysed for palaeoenvironmental reconstruction within the atar group touirist formation shales showed the highest content of organic carbon 20 at very low maturity rc less than 0 6 microfacies and biomarker data indicate a shallow marine high productivity low oxygen setting with benthic mats as key players for the accumulation of organic matter both high c s ratios and the occurrence of rearranged hopanes indicate that euxinic conditions were not prevalent likely reflecting the shallow depositional environment steranes were not observed indicating only a minor importance of modern eukaryotic algae although low in abundance a palynological survey however reveals the presence of simple ornamented acritarchs input of highly aromatic biopolymers typical of mesoproterozoic acritarchs or microbial exopolymeric substances may be the origin of an unusually high aromaticity observed for the biomarker extracts high amounts of hopanes suggest that the benthic mats were dominated by cyano bacteria furthermore the presence of 2 3 6 trimethyl aryl isoprenoids points at contributions of organic matter from anoxygenic phototrophic bacteria however low concentrations of these compounds argue against major photic zone anoxia in the overlying water column and rather suggest a role of anoxygenic phototrophs as part of the benthic microbial mat community the high abundances of hopanes in these samples suggest that nitrogen limited conditions may have been common in the taoudeni basin at 1 1 ga these results are consistent with ideas of widespread nitrogen deficiency that emerged in mesoproterozoic oceans due to high denitrification rates in anoxic deep waters cyano and other phototrophic bacteria as well as a limited number of acritarch species were able to cope with such conditions much better than modern algae with their higher nitrogen and trace metal demands 2011 elsevier b v all rights reserved

biogeochemical evidence for euxinic oceans and ecological disturbance presaging the end permian mass extinction event article i nfo the permian triassic boundary event at 252 2 ma marks the largest extinction of marine fauna in the phanerozoic and there is a wide consensus that the extinction coincided with an intense oceanic anoxic event thestratotypeofthechanghsingianstage preciselyconstrainedbytheptbglobalstratotypesectionandpoint gssp and the gssp for the wuchiapingian changhsingian boundary both at meishan in southern china is well documented in respect to geochronology and the pattern of extinction here we report secular trends in bulk isotopic parameters and lipid biomarkers in a core spanning 214 m of stratigraphic section across the ptb and through the entire changhsingian interval our analysis of these data viewed in the context of relative sea level change and strontium isotopes reveals distinct shifts in paleoenvironmental conditions and profound changes in plankton ecology well before and following the biological extinction event specifically patterns of steroids and triterpenoids indicate a marine plankton community that was heavily dominated by bacteria during the late wuchiapingian middle changhsingian and early griesbachian stages secular trends in aromatic hydrocarbons diagnostic for anoxygenic green sulphur bacteria chlorobiaceae identify periods when euxinic conditions extended into the photic zone during the entire changhsingian stage here also the 15

vadose co2 gas drives dissolution at water tables in eogenetic karst aquifers more than mixing dissolution most models of cave formation in limestone that remains near its depositional environment and has not been deeply buried i e eogenetic limestone invoke dissolution from mixing of waters that have different ionic strengths or have equilibrated with calcite at different pco2 values in eogenetic karst aquifers lacking saline water mixing of vadose and phreatic waters is thought to form caves we show here calcite dissolution in a cave in eogenetic limestone occurred due to increases in vadose co2 gas concentrations and subsequent dissolution of co2 into groundwater not by mixing dissolution we collected high resolution time series measurements 1 year of specific conductivity spc temperature meteorological data and synoptic water chemical composition from a water table cave in central florida briar cave we found spc pco2 and calcite undersaturation increased through late summer when briar cave experienced little ventilation by outside air and decreased through winter when increased ventilation lowered cave co2 g concentrations we hypothesize dissolution occurred when water flowed from aquifer regions with low pco2 into the cave which had elevated pco2 elevated pco2 would be promoted by fractures connecting the soil to the water table simple geochemical models demonstrate that changes in pco2 of less than 1 along flow paths are an order of magnitude more efficient at dissolving limestone than mixing of vadose and phreatic water we conclude that spatially or temporally variable vadose co2 g concentrations are responsible for cave formation because mixing is too slow to generate observed cave sizes in the time available for formation while this study emphasized dissolution gas exchange between the atmosphere and karst aquifer vadose zones that is facilitated by conduits likely exerts important controls on other geochemical processes in limestone critical zones by transporting oxygen deep into vadose zones creating redox boundaries that would not exist in the absence of caves copyright 2014 john wiley sons ltd