is late quaternary climate change governed by self sustained oscillations in atmospheric co2 a simple earth system model is developed to simulate global carbon and phosphorus cycling over the late quaternary it is focused on the geological cycling of c and p via continental weathering volcanic and metamorphic degassing hydrothermal processes and burial at the seabed a simple ocean model is embedded in this geological model where the global ocean is represented by surface water thermocline and deep water boxes concentrations of dissolved phosphorus dissolved inorganic carbon and total alkalinity are calculated for each box the partial pressure of co2 in the atmosphere pco 2a is determined by exchange processes with the surface ocean and the continents it serves as key prognostic model variable and is assumed to govern surface temperatures and global sea level the model is formulated as autonomous system in which the governing equations have no explicit time dependence for certain parameter values the model does not converge towards a steady state but develops stable self sustained oscillations these free oscillations feature pco 2a minima and maxima consistent with the ice core record when vertical mixing in the ocean is allowed to vary in response to pco 2a controlled temperature change a stable 100 kyr cycle with a rapid transition from glacial to interglacial conditions is obtained when additional non linear equations are applied to calculate deep ocean mixing iron fertilization and the depth of organic matter degradation as function of pco 2a controlled surface temperature the delta c 13 value of carbon in the ocean atmosphere system calculated in these model runs is consistent with the benthic delta c 13 record however the simulated c 13 depletion in the glacial ocean is not driven by the decline in terrestrial carbon stocks but by sea level change controlling the rates of organic carbon burial and weathering at continental margins the pco 2a and delta c 13 oscillations develop without any form of external milankovitch forcing they are induced and maintained by sea level change generating persistent imbalances in the marine carbon and phosphorus budgets stable oscillations are also obtained when sea level change is allowed to lag temperature with a realistic time scale for ice sheet adjustment

regulation of atmospheric oxygen during the proterozoic abstract many studies suggest that oxygen has remained near modern levels throughout the phanerozoic but was much less abundant from the great oxygenation event around 2 4 ga until the late neoproterozoic around 600 ma kump 2008 using a simple model we show that the maintenance of atmospheric po2 at 1 of present atmospheric levels pal is inconsistent with modern biogeochemical cycling of carbon sulfur and iron unless new feedbacks are included low oxygen conditions are stable in our model if the flux of phosphorus to the oceans was greatly reduced during the proterozoic we propose a mechanism to reduce this flux through the scavenging of phosphate ions with an iron trap driven by greater surface mobility of ferrous iron in a low po2 world incorporating this feedback leads to two stable equilibria for atmospheric oxygen the first quantitative hypothesis to explain both proterozoic and phanerozoic o2 concentrations

reply to comments by h d holland on the oxygen geochemical cycle dynamics and stability geochim cosmochim acta 66 361 381 2002

organic and carbonate rich soil formation 2 6 billion years ago at schagen east transvaal district south africa abstract a 17 m paleosol sequence at schagen south africa which developed on a serpentinized dunite intrusion in a granite gneiss terrain 2 6 ga ago is characterized by an alternating succession of thick 1 3 m carbonate rich dolomite and calcite zones and silicate rich serpentines talc and quartz zones the upper 8 m section is especially rich in organic c up to 1 4 wt petrologic and geochemical data suggest the upper 8 m section is composed of at least three soil profiles that developed on i silicate rich rock fragments and minerals that were transported from local sources serpentinite and granite by fluvial and or eolian processes and ii dolomite and calcite zones that formed by locally discharged groundwater the mg and fe in the paleosol sequence were largely supplied from local sources mostly serpentinite but the ca sr and hco3 were supplied by groundwater that originated from a surrounding granite gneiss terrain in the uppermost soil profile the fe is retained the fe3 fe2 ratio increases and ferri stilpnomelane is abundant these data suggest the atmospheric po2 was much greater than 10 3 7 atm 0 1 present atmospheric level pal the carbonaceous matter in the soils is intimately associated with clays talc chlorite and ferri stilpnomelane and occurs mostly as seams 20 m to 1 mm thick that parallel the soil horizons these occurrences crystallographic structures h c ratios and 13corg values 17 4 to 14 4 pdb suggest that the carbonaceous matter is a remnant of in situ microbial mats originally 1 to 20 mm thick the microbial mats developed a mostly on soil surfaces during the formation of silicate rich soils and b at the bottom of an evaporating anoxic alkaline pond during the precipitation of the fe rich dolomite these 13corg values are difficult to be explained by a current popular idea of a methane and organic haze rich archean atmosphere pavlov et al 2001 these values however can be easily explained if the microbial mats were composed of cyanobacteria and heterotrophs that utilized the remnants of cyanobacteria in a strongly evaporating environment

efficient transport of fossil organic carbon to the ocean by steep mountain rivers an orogenic carbon sequestration mechanism mountain building exposes fossil organic carbon oc fossil in exhumed sedimentary rocks oxidation of this material releases carbon dioxide from long term geological storage to the atmosphere oc fossil is mobilized on hillslopes by mass wasting and transferred to the particu late load of rivers in large fl uvial systems it is thought to be oxidised in transit but in short steep rivers that drain mountain islands oc fossil may escape oxidation and re enter geological storage due to rapid fl uvial transfer to the ocean in these settings the rates of oc fossil transfer and their controls remain poorly constrained here we quantify the erosion of oc fossil from the taiwan mountain belt combining discharge statistics with measurements of particulate organic carbon load and source in 11 rivers annual oc fossil yields in taiwan vary from 12 1 to 246 22 tc km 2 yr 1 controlled by the high physical erosion rates that accompany rapid crustal shortening and frequent typhoon impacts effi cient transfer of this material ensures that 1 3 0 1 10 6 tc yr 1 of oc fossil exhumed in taiwan is delivered to the ocean with 15 loss due to weathering in transit our fi ndings suggest that erosion of coastal mountain ranges can force effi cient transfer and long term re accumulation of oc fossil in marine sediments further enhancing the role of mountain building in the long term storage of carbon in the lithosphere

coal weathering and the geochemical carbon cycle abstract the weathering rate of sedimentary organic matter in the continental surficial environment is poorly constrained despite its importance to the geochemical carbon cycle during this weathering complete oxidation to carbon dioxide is normally assumed but there is little proof that this actually occurs knowledge of the rate and mechanisms of sedimentary organic matter weathering is important because it is one of the major controls on atmospheric oxygen level through geologic time we have determined the aqueous oxidation rates of pyrite free bituminous coal at 24 and 50 c by using a dual cell flow through method coal was used as an example of sedimentary organic matter because of the difficulty in obtaining pyrite free kerogen for laboratory study the aqueous oxidation rate obtained in the present study for air saturated water 270 m o2 was found to be on the order of 2 10 12 mol o2 m2 s at 25 c which is fast compared to other geologic processes such as tectonic uplift and exposure through erosion the reaction order with respect to oxygen level is 0 5 on a several thousand hour time scale for both 24 and 50 c experiments activation energies determined under 24 and 50 c conditions were 40 kj mol o2 indicating that the oxidation reaction is surface reaction controlled the oxygen consumption rate obtained in this study is two to three orders of magnitude smaller than that for pyrite oxidation in water but still rapid on a geologic time scale aqueous coal oxidation results in the formation of dissolved co2 dissolved organic carbon doc and solid oxidation products which are all quantitatively significant reaction products

influence of hydrogeology microbiology and landscape history on the geochemistry of acid hypersaline waters n w victoria abstract there is now evidence that naturally occurring acid water is more abundant than previously thought and that it has been important in the geologic past understanding the processes leading to the formation of such systems is required to appreciate the role of acid systems in geologic processes and to develop indicators for recognizing the geologic environmental importance of these systems in the past this paper characterizes the hydrogeology hydrogeochemistry microbial biogeochemistry and landscape attributes of acid groundwater surface water systems in australia with an emphasis on a well studied playa lake system lake tyrrell murray valley a model for the origin of these acid brines is presented and the importance of acid brine producing systems is speculated upon data include porewater and groundwater geochemical measurements collected during a 10 day field campaign and results from geochemical modeling and graphics e g piper diagrams and x y plots of seawater evaporation trajectories key characteristics of the system are 1 aquifer materials have low acid buffering capacities 2 saline groundwater flowing onto playa surfaces is an oxic h2so4 solution 3 authigenic minerals include combinations of jarosite kfe3 so4 2 oh 6 alunite kal3 so4 2 oh 6 and fe oxides that can form as evaporite minerals 4 a source for solutes can be marine aerosols and 5 the formation of ironstones groundwater acidification by various processes including sulfide oxidation and ferrolysis and at many different times are the unique aspects for evolution of these acid brines and they can be considered another end member of the eugster jones hardie model for the evolution of brines in closed basins acid hypersaline groundwater and playa systems such as lake tyrrell may be an example of expected changes in the hydrogeochemistry of terrestrial water during late stage continental denudation under arid conditions historically these systems may have been integral to the formation of opal bauxite some low temperature ore deposits of authigenic k feldspars and continental redbeds natural acid saline systems such as those in australia may also be representative of acid saline systems on mars

biogeochemical effects of atmospheric oxygen concentration phosphorus weathering and sea level stand on oceanic redox chemistry implications for greenhouse climates abstract understanding the key factors influencing the global oceanic redox system is crucial to fully explaining the variations in oceanic chemical dynamics that have occurred throughout the earth s history in order to elucidate the mechanisms behind these variations on geological timescales numerical sensitivity experiments were conducted with respect to the partial pressure of atmospheric molecular oxygen p o 2 the continental shelf area a cs and the riverine input rate of reactive phosphorus to the oceans r p the sensitivity experiment for atmospheric p o 2 indicates that pervasive oceanic anoxia and euxinia appear when p o 2 p o 2 are higher than a previous estimate of 50 pal present atmospheric level due to redox dependent phosphorus cycling the sensitivity experiment regarding the shelf area demonstrates that changes in the shelf area during the phanerozoic significantly affected oceanic oxygenation states by changing marine biogeochemical cycling a large continental shelf acts as an efficient buffer against oceanic eutrophication and prevents the appearance of ocean anoxia euxinia we also found that an enhanced r p is an important mechanism for generation of widespread anoxia euxinia via expansion of both the oxygen minimum zone and coastal deoxygenation although the critical r p value depends significantly on p o 2 a cs and the redox dependent burial efficiency of phosphorus at the sediment water interface our systematic examination of the oceanic redox state under cretaceous greenhouse climatic conditions also supports the above results

tracing dissolved o2 and dissolved inorganic carbon stable isotope dynamics in the nyack aquifer middle fork flathead river montana usa abstract the geochemistry and microbiology of shallow groundwater aquifers is greatly influenced by the concentration of dissolved oxygen gas do however the mechanisms that consume do in groundwater e g biotic or abiotic are often ambiguous the use of stable isotopes of molecular o 2 18 o do in conjunction with stable isotopes of dissolved inorganic carbon 13 c dic has potential to discriminate between the various mechanisms causing do depletion in subsurface waters here we report the results of spatial and seasonal changes in 18 o do and 13 c dic at the nyack floodplain aquifer along the middle fork of the flathead river near west glacier montana usa over a short well constrained flow path 100 m near a main recharge zone of the floodplain the 18 o do consistently increased as do concentrations decreased with distance from the recharge source concurrently dic concentrations increased and 13 c dic values decreased these observations are explained by community respiration coupled with dissolution of calcite from cobbles in the aquifer matrix when these results are compared to data from wells distributed over the entire floodplain several km a much less predictable relationship was observed between do concentration and 18 o do many wells with low do concentrations e g 1 or 4 mg l 1 had anomalously low 18 o do values e g 2 may be contributed to the aquifer by diffusion from the vadose zone and by advection from the river recharge calculations presented here suggest that diffusion across a narrow air water interface can contribute isotopically light 18 o do to the saturated zone possible contributions of light 18 o do from other processes such as isotopic exchange and radial oxygen loss from plant roots in or near the water table are compared and evaluated

pyrite enhanced chemical weathering in karkevagge swedish lapland conventional wisdom once held that weathering in cold climates was overwhelmingly due to physical processes however that convention was challenged when chemical weathering was identified but unexplained as the dominant landscape denudation process in karkevagge an alpine valley in swedish lap land the research reported here involved scanning electron microscopy and energy dispersive x ray fluorescence of rock coatings to investigate chemical weathering in karkevagge analyses revealed that white coatings associated with streams emerging on the valley cliff face are commonly an amorphous aluminum oxyhydroxide sulfate such as basaluminite al 4 so 4 oh 10 h 2 o efflorescence on seasonal vegetation in stream channels demonstrates that this is an active process the white coating chemistry exhibited no systematic spatial patterns along the valley axis or with position on the cliff face although the white coatings were not crystalline and did not contain appreciable amounts of fe or ca in sheltered overhangs among boulders on the valley floor there were other well crystallized secondary sulfate minerals commonly associated with pyrite oxidation including gypsum jarosite and amorphous fe compounds this difference is due presumably to the ph of the associated waters because fe compounds tend to precipitate only at ph 5 which is the ph of the stream water pyrite oxidation may be an important early weathering process in this and in many other environments however it largely goes unrecognized because it occurs relatively rapidly in a geological sense and typically is only identified in recently disturbed landscapes associated with mining or other large scale earth moving activities karkevagge demonstrates that subarctic conditions do not preclude intense chemical weathering where conditions are favorable but it does not establish that strong chemical weathering is a widespread attribute of subarctic conditions

cretaceous shales from the western interior of north america sulfur carbon ratios and sulfur isotope composition carbon and sulfur abundance and 34 s of pyrite sulfur were studied in cores of selected cretaceous marine shales from the western interior of north america sulfur carbon ratios average 0 67 a value greater than that observed in recent marine sediments and much higher than global values calculated for the cretaceous increased s c ratios probably result from generally low levels of bioturbation and enhanced efficiency of sulfate reduction due to low oxygen levels in the cretaceous seaway isotopic compositions of pyrite sulfur vary systematically with the level of oxygenation of the depositional environment and therefore with organic carbon abundance and type of organic matter samples with organic carbon in excess of 4 wt contain disseminated pyrite that is extremely depleted in 34 s mean 34 s 31 these samples are laminated clay shales that contain hydrogen rich type ii organic matter samples containing less than 1 5 organic carbon display relatively heavy but wide ranging 34 s values 34 s 34 6 to 16 8 mean 34 s 12 4 these samples are highly bioturbated and contain only type iii hydrogen poor organic matter samples containing intermediate amounts of organic carbon contain pyrite with 34 s values averaging 25 9 and contain mixed type ii and type iii organic matter the higher organic carbon content and the preservation of hydrogen rich organic matter generally correlate with slow sedimentation samples rich in organic carbon and containing isotopically light sulfide sulfur accumulated beneath anoxic and perhaps sulfidic bottom waters samples with intermediate organic matter content and intermediate sulfur isotopic compositions accumulated under mainly dysaerobic bottom waters samples with relatively low amounts of organic carbon and wide ranging but less negative sulfur isotopic values were deposited beneath oxygenated bottom waters sulfur isotope data are apparently a sensitive indicator of diagenetic or depositional facies of fine grained cretaceous rocks in the western interior

paradigm shift in determining neoproterozoic atmospheric oxygen acknowledgments we thank the geological survey of australia for permission to sample the empress 1a and lancer 1 cores the natural sciences and engineering research council of canada for financial support grant 7961 15 of u brand and the national natural science foundation of china for support of f meng and p ni grants 41473039 and 4151101015 we thank m lozon brock university for drafting and constructing the figures we thank the editor brendan murphy as well as three reviewers steve kesler erik sperling and an anonymous reviewer for improving the manuscript into its final form

biotic enhancement of weathering atmospheric oxygen and carbon dioxide in the neoproterozoic 1 it has been suggested that biological colonization of the land surface began in the neoproterozoic 1000 544 million years ago ma we hypothesize that this colonization involved selective weathering of p from rocks as well as an amplification of overall weathering rates we show that two recent models despite differences in the feedback mechanisms represented predict that an increase in the weathering flux of p to the ocean would have caused a rise in atmospheric o2 in the neoproterozoic this in turn may have provided a necessary condition for the evolution of animals with hard skeletons seen in the cambrian explosion increased weathering of silicate rocks would also have caused a decline in atmospheric co2 which could have been a causal factor in the neoproterozoic glaciations

organic matter production and preservation and evolution of anoxia in the holocene black sea dating of sediments collected in gravity cores during leg 1 of the 1988 r v knorr expedition to the black sea suggests that the onset of water column anoxia at 7 5 ka was virtually synchronous across the basin over a depth range of 200 2250 m a finely laminated organic carbon oc rich sapropel unit ii was produced as a result of this anoxia the trigger for increased oc production and development of anoxia was the spillover of saline waters through the bosporus that probably began at 9 0 ka and peaked between 7 0 and 5 5 ka this spillover enhanced vertical mixing and nutrient cycling and caused a short term 2 3 kyr burst in surface water productivity during the early part of unit ii deposition continued incursion of saline waters enhanced vertical stability and inhibited mixing of nutrients into surface waters thus limiting primary production and decreasing the oc flux to sediments beginning 5 5 ka concentration accumulation rate and degree of preservation of organic matter all decreased in the upper part of unit ii as a result of decreasing productivity but anoxia persisted throughout most of the water column the end of unit ii sapropel deposition was synchronous across the black sea as the result of the first blooms of the coccolith emiliania huxleyi which presumably marked an increase in surface water salinity above 11 and the beginning of unit i deposition the high coccolith carbonate fluxes that occurred during deposition of unit i diluted the oc concentration in the sediments but oc accumulation rates are about the same as those in upper part of unit ii

varve calibrated records of carbonate and organic carbon accumulation over the last 2000 years in the black sea sedimentologic and geochemical studies of box and gravity cores recovered from the black sea during the first leg of a multileg international black sea expedition in 1988 allow reconstruction of the basinwide holocene environmental history of the black sea in the deeper parts of the basin box cores typically recovered a flocculent surface layer fluff laminated coccolith marls of unit i 25 45 cm thick and the upper 5 10 cm of finely laminated dark colored sapropels of unit ii fine grained homogeneous mud turbidites are interbedded with units i and ii over much of the basin but the stratigraphie position of these turbidites differs from site to site the deposition of individual turbidites up to 15 cm thick does not appear to have significantly disturbed underlying laminae sediment trap deployments in the black sea suggest that light and dark laminae couplets represent annual increments of sedimentation i e varves we have therefore constructed a varve chronology for the sequence in order to correlate and date distinctive sedimentation and paleoenvironmental events distinctive groups of laminae in unit i can be correlated across the entire deeper basin a distance of more than 1000 km this implies a remarkable homogeneity in production accumulation and preservation of biogenic material over much of the black sea during deposition of unit i the change from deposition of finely laminated organic carbon rich sapropels unit ii to laminated more calcareous coccolith rich marls unit i is thought to represent the crossing of a salinity threshold for emiliania huxleyi the varve chronology sets this change at about 1 63 ka 1633 100 yr b p but the record of magnetic secular variation measured in several cores produces an age estimate of about 2 0 ka for the base of unit i or about 1 2 times the varve age the average of six calibrated accelerator mass spectrometry radiocarbon ages for the base of unit i is 2 7 ka or about 1 7 times the varve age following the initial change to coccolith dominated sedimentation deposition of sapropel resumed for at least one significant period 1 56 1 25 ka since 1 25 ka cycles of carbonate deposition with quasi decadal periodicities have produced characteristic darker and lighter assemblages of laminae these cycles may have been climatically driven geochemical analyses coupled with the varve ages adopted herein indicate that accumulation rates of carbonate are nearly an order of magnitude higher in unit i averaging 35 45 g m 2 yr 1 than in sapropelic unit ii which contains primarily detrital carbonate the accumulation of lithogenic components in parts of unit i is only 1 5 times the rate in unit ii deepwater organic carbon accumulation rates are somewhat higher in unit i 3 5 4 5 g m 2 yr 1 than in the upper part of unit ii organic carbon accumulation rates in unit i are somewhat antithetic to those of carbonate and on the basis of this and additional constraints placed by pyrolysis and carbon isotopic analyses of organic material it appears that terrestrial organic matter is an important component perhaps 25 of total organic carbon burial in the basin unit i in the western part of the black sea has a higher terrestrial organic component and higher accumulation rates of terrigenous clastic material than unit i in the eastern part this difference between eastern and western black sea is to be expected because of the major rivers that empty into the western black sea from eastern europe ukraine and russia shallow slope sites but still within euxinic bottom waters have lower organic carbon accumulation rates and lower pyrolysis hydrogen indices than deepwater basinal sites suggesting selective resuspension and oxidation of organic matter at basin margins and focusing of organic matter deposition toward the basin center a comparison of the black sea data with those from several open ocean sites with similar water depths showed no significant difference between organic carbon accumulation rates under oxic and anoxic conditions for a given bulk accumulation rate the organic carbon accumulation rates normalized to primary productivity are about the same in both settings

the oxygen geochemical cycle dynamics and stability abstract the first and possibly only major rise of atmospheric oxygen from p o 2 0 1 pal the present atmospheric level to p o 2 10 pal appears to have occurred sometime before 2 ga ago although the exact time of and the cause s for the rise have been hotly debated equally important questions on the atmospheric oxygen concern its stability especially the mechanisms regulating the atmospheric p o 2 level and the causes and magnitude of p o 2 variations since the first major rise of atmospheric oxygen previous efforts to model the p o 2 variation during the phanerozoic time have typically relied on secondary information such as the carbon and sulfur isotopic records of sedimentary rocks and on simple dynamics of the geochemical cycles of o c s and p based on box type models as a result many kinetic questions about the variation and stability of atmospheric oxygen could not have been answered here we quantitatively evaluate the dynamics and stability of atmospheric o 2 and co 2 using recent experimental data field observations and a new model for the c o coupled geochemical cycles we examine the change with time in the fluxes of various compounds o 2 co 2 phosphate organic c carbonate c c bearing reduced volcanic gases and c free reduced volcanic gases among the various reservoirs atmosphere soil surface ocean deep ocean the lower crust and mantle and upper crust under a variety of scenarios our model does not assume steady state fluxes for any of the reservoirs rather the model incorporates the kinetic experimental data on oxidation of coal a proxy for kerogen the dynamics of soil formation and erosion the kinetics of decomposition of organic matter in the oceans by aerobic and anaerobic bacteria the equilibrium ocean atmosphere carbonate model the observed relationships among the organic burial flux dissolved o 2 content of deep ocean and sedimentation rates and the three box model ocean the important parameters that strongly influence the dynamics of atmospheric o 2 are found to be a the total area of soil formation on earth b the average soil depth c the average rate of physical erosion of soils which is linked to the average rate of accumulation of clastic sediments in the oceans d the composition and flux of volcanic gas and e the level of atmospheric co 2 we develop kinetic equations linking these parameters to the production and consumption fluxes of atmospheric oxygen and also to stable p o 2 values considering the likely ranges of variations in these parameters in geologic history we suggest that the atmospheric p o 2 level is likely to have stayed within a very narrow range of 0 6 2 pal and that the entire ocean except for local euxinic basins is likely to have been basically oxygenated since the first major rise of atmospheric oxygen more than 2 ga ago

age and depositional environment of the draa sfar massive sulfide deposit morocco the draa sfar mineralization consists of two main stratabound orebodies sidi m barek and tazacourt located north and south of the tensift river oued tessift respectively each orebody is comprised by at least two massive sulfide lenses the hosting rocks are predominantly black shales although minor rhyolitic rocks are also present in the footwall to the southern orebody shales rhyolitic volcanic rocks and massive sulfides are all included into the sarhlef series which is recognized as one of the main stratigraphic units of the moroccan variscan meseta hydrothermal activity related with an anomalous thermal gradient together with a high sedimentation rate in a tectonically driven pull apart marine basin favored the accumulation of organic rich mud in the deepest parts of the basin and the sedimentary environment suitable for massive sulfide deposition and preservation this took place by replacement of the hosting unlithified wet mud below the sediment water interface geochemical data suggest a sedimentary environment characterized by oxic water column and anoxic sediment pile with the redox boundary below the sediment water interface the low oxygen availability within the sediment pile inhibited oxidation and pyritization of pyrrhotite biostratigraphic analysis based on the palynological content of the hosting black shales restricts the age of the sulfides to the asbian substage mid mississippian this age is consistent with earlier geochronological constraints

agricultural land degradation by piping erosion in chaco plain northwestern argentina abstract soil piping has been pointed out as an important water erosion agent in a wide range of climatic regions it is responsible for high soil losses in loess derived soils the goal of this study is to evaluate the factors that are acting in the generation of piping processes and explain the mechanism of pipe collapse initiation the study was carried out in loess derived soils located in a rural area of the chaco plain between tucuman and santiago del estero provinces in northwestern argentina pipe collapse types were described and soil loss estimation was performed factors influencing the process were studied under six different categories i e physico chemical and soil mechanical soil mineralogical microstructural biological and land use properties in the study area pipes took place in agricultural fields principally in pastures with slope gradients between 1 and 3 soil pipe collapse occurred in the area as a consequence of sudden wetting of the collapsible soils during summer storms pipe collapse forms vertical pipes or macropores that provide pathways for runoff directly into the soil pipe network in addition tension cracks adjacent to pipe collapses can provide pathways for preferential flow from the surface to the soil pipe network with successive water infiltration the size of the pipes tends to increase and evolves to advanced stages of the process by internal erosion and eventually more pipe collapse blind gully formation is the final step of the piping process after the pipes roof collapse

geochemistry and mineralogy of the 2 45 ga pronto paleosols ontario canada abstract the ontario canada pronto paleosols which formed around 2 45 ga on archean granite were studied through field observation mineralogical study by microscope and microprobe and chemical analyses of major and 45 trace elements including rare earth elements rees since the first full description of its mineralogy and chemistry of major elements by gay and grandstaff gay a l grandstaff d e 1980 chemistry and mineralogy of precambrian paleosols at elliot lake ontario canada precambrian res 12 349 373 the pronto paleosols are among the most cited paleosols of the archean early proterozoic era though several questions have been raised as to whether they are true in place ancient soils results of this study show that the studied section meets the criteria for being in place paleosols furthermore the profile has no explicit traces of being strongly affected by hydrothermal alteration the ree containing accessory minerals were destroyed through weathering and secondary phosphate minerals with rees formed all of these observations support the weathering origin of the pronto paleosols however the profile should be identified as a saprolith rather than paleosol as even the uppermost samples exhibit the granitic texture of the parent rock the samples in this study were collected mainly from two sites site i and site ii saprolith samples from site i show the retention of fe and increases of the fe iii fe ii ratios and the chemical index of alteration cia values toward the unconformity as for the site ii samples the fe ti ratios show slight decreases with increasing cia values in the upper part of section whereas these samples also show the same trend of increasing fe iii fe ii ratios as the samples from site i microprobe analyses show that fe from the parent rock distributes mainly in mafic minerals as hornblende biotite or chlorite which were completely destroyed during the early stages of weathering in the saprolith section fe is present in sericite aggregates in the form of obscure patches of iron oxide tens of micrometers in size all these characteristics indicate that i the fe was not lost during soil formation at site i and slight amount of fe was lost at site ii and ii ferrous fe was quantitatively transformed to ferric fe i e oxidation during soil formation in the samples from both sites the ratios of al ti and si ti decrease toward the top of the profile together with the destruction of minerals toward the unconformity such as apatite biotite and chlorite the depletion of al and si suggests that the parental granite was weathered by an acidic weathering solution during the archean early proterozoic era the high atmospheric partial pressure of co 2 p co 2 is the most probable candidate for producing the acidic weathering solution

possible evidence for episodic epeiric marine and fluvial sedimentation and implications for palaeoclimatic conditions c 2 3 1 8 ga kaapvaal craton south africa abstract the debate on palaeoproterozoic atmospheric composition climate and the timing and nature of the postulated great oxidation event possibly at c 2 3 ga remain matters of debate within precambrian geology this paper contributes to the debate through examination of physical sedimentary structures preserved within two separate groups of sedimentary deposits from the central and northern portions of the kaapvaal craton south africa within the c 2 3 2 1 ga pretoria group study of epeiric marine sandstones and mudrocks magaliesberg and silverton formations c 2 1 ga suggests that fluvial input was predominant over low energy reworking by waves winds and tides this together with extensive evidence for microbial mat growth within the littoral sandstones of the magaliesberg formation points to strongly episodic sedimentation by both marine and fluvial processes within two younger basins belonging to the c 2 05 1 8 ga waterberg group anomalously high palaeoslopes calculated according to standard palaeohydrological methods combined with direct field evidence for sediment gravity flows and sheetflood deposition within an overall braided fluvial setting again suggest episodic sedimentation strongly episodic sedimentation can most easily be reconciled with a greenhouse palaeoclimate at least for that part of kaapvaal at that time taken together these data sets point to the postulate that the generally accepted change from a palaeoproterozoic greenhouse through a great oxidation event c 2 3 ga to less extreme climatic conditions may have been gradational and even diachronous across the earth s cratons at that time

new mineral names the following new minerals are discussed in this issue langbanshyttanite pseudolyonsite and yangzhumingite these new minerals have been described in the european journal of mineralogy and are reported here n v chukanov i v pekov e jonsson n v zubkova y e filinchuk d i belakovskiy and d yu pushcharovsky 2011 langbanshyttanite a new low temperature arsenate mineral with a novel structure from langban sweden eur j mineral 23 675 681 the new mineral langbanshyttanite was discovered in a specimen from the langban mine filipstad district varmland county bergslagen ore province sweden the carbonate hosted langban deposit 59 86 n 14 27 e is together with related occurrences in the western part of the palaeoproterozoic bergslagen ore province in south central sweden characterized by anomalously pb as ba be sb rich metamorphosed stratabound fe and mn oxide ores with associated skarn units sulfide assemblages as well as abundant vein and fissure hosted mineral assemblages the name is for langbanshyttan which is the old name of both the mine mining village and smelter that in more recent times has been known plainly as langban langbanshyttan actually means langban s smelter or langban s furnace langbanshyttanite occurs as a very late low temperature species in the deposit it crystallized during the last stage of hydrothermal activity involving metal remobilization in the langban system post dating regional metamorphism of the volcanic hydrothermal ores and their host rocks based on existing evidence these minerals formed at very low temperature and pressure in this case most likely below 70 c the mineral formed in fractures and corrosion veinlets post dating calcite in a mn oxide bearing mn silicate rich rock associated late stage minerals are calcite antigorite sparse euhedral trigonite and a few microscopic aggregates of a so far unidentified as bearing mineral typically both calcite and antigorite exhibit evidence of being partly corroded away prior to langbanshyttanite formation trigonite coeval with langbanshyttanite occurs as sparse euhedral crystals the groundmass to the veinlets or fractures mainly consists

dam triggered organic carbon sequestration makes the changjiang yangtze river basin china a significant carbon sink worldwide dam building in large river basins has substantially altered the carbon cycle by trapping much of the riverine transported particulate organic carbon poc in terrestrial reservoirs here we take the changjiang yangtze river basin in which 50 000 dams were built over the past 50 years as an example to evaluate the effect of dam building on poc sequestration we report the characteristics elemental composition radiocarbon and stable carbon isotopic compositions and raman spectra of bulk poc in the lower changjiang from october 2007 to september 2008 and we estimate the poc sequestration induced by dam building since the 1950s for the changjiang basin using radiocarbon measurements we quantify the fraction of biospheric poc pocbio and petrogenic poc pocpetro in changjiang poc over the study period around 25 of the changjiang poc is radiocarbon dead pocpetro the remaining is pocbio with a mean radiocarbon age of 3 5 kyr studies on the east china sea ecs shelf along with an oxidation experiment suggest that prior to dam building the changjiang pocbio was significantly oxidized in the ecs margin in contrast high preservation of poc is observed in changjiang reservoirs combining our poc data with hydrometric data sets our study indicates that over the past five decades dam building may have largely shifted the changjiang poc burial site from the ecs margin to terrestrial reservoirs this shift in burial site preserved labile pocbio that would have been oxidized suggesting a new temporary carbon sink we estimate that dam building in the changjiang has sequestered 4 9 1 9 megatons pocbio every year since 2003 approximately 10 of the global riverine poc burial flux to the oceans

theoretical constraints on oxygen and carbon dioxide concentrations in the precambrian atmosphere simple one dimensional climate models suggest that carbon dioxide concentrations during the archean must have been at least 100 1000 times the present level to keep the earth s surface temperature above freezing in the face of decreased solar luminosity such models provide only lower bounds on co2 so it is possible that co2 levels were substantially higher than this and that the archean climate was much warmer than today periods of extensive glaciation during the early and late proterozoic on the other hand indicate that the climate at these times was relatively cool to be consistent with climate models co2 partial pressures must have declined from approximately 0 03 to 0 3 bar around 2 5 ga ago to between 10 3 and 10 2 bar at 0 8 ga ago this steep decrease in carbon dioxide concentrations may be inconsistent with paleosol data which implies that pco2 did not change appreciably during that time oxygen was essentially absent from the earth s atmosphere and oceans prior to the emergence of a photosynthetic source probably during the late archean during the early proterozoic the atmosphere and surface ocean were apparently oxidizing while the deep ocean remained reducing an upper limit of 6 x 10 3 bar for po2 at this time can be derived by balancing the burial rate of organic carbon with the rate of oxidation of ferrous iron in the deep ocean the establishment of oxidizing conditions in the deep ocean marked by the disappearance of banded iron formations approximately 1 7 ga ago permitted atmospheric oxygen to climb to its present level o2 concentrations may have remained substantially lower than today however until well into the phanerozoic

spatial distribution of pipe collapses in goodwin creek watershed mississippi the internal erosion of soil pipes can induce pipe collapses that affect soil erosion processes and landform evolution the objective of this study was to determine the spatial distribution of pipe collapses in agricultural fields of goodwin creek watershed ground survey was carried out to detect pipe collapses and the location size and surface elevation was measured with differential gps a total of 143 of the 145 pipe collapses were found in cropland and the density was approximately 0 58 collapses per hectare the spatial distribution of pipe collapses was not uniform as pipe collapses were concentrated in the flat alluvial plains where the land use was dominated by cropland one of the four parcels had 90 of the pipe collapses with a density of 7 7 collapses per hectare the mean depth area and volume of these pipe collapses were 0 12 m 0 34 m2 and 0 02 m3 respectively and all these properties exhibited a skewed distribution the drainage area slope gradient equation which has been widely used for erosion phenomenon prediction did not represent pipe collapses in this study as the coefficient of determination was 0 01 this is clear evidence that subsurface flow is not represented by surface topographic characteristics the pipe collapses were found to intercept runoff thereby reducing the slope length factor by 6 and the drainage area by 7 both of these factors can reduce the sheet and rill erosion however the increased subsurface flow could enhance ephemeral gully erosion published 2012 this article is a u s government work and is in the public domain in the usa

modeling atmospheric o2 over phanerozoic time a carbon and sulfur isotope mass balance model has been constructed for calculating the variation of atmospheric o2 over phanerozoic time in order to obtain realistic o2 levels rapid sediment recycling and o2 dependent isotope fractionation have been employed by the modelling the dependence of isotope fractionation on o2 is based for carbon on the results of laboratory photosynthesis experiments and for sulfur on the observed relation between oxidation reduction recycling and s isotope fractionation during early diagenetic pyrite formation the range of fractionations used in the modeling agree with measurements of phanerozoic sediments by others results derived from extensive sensitivity analysis suggest that there was a positive excursion of o2 to levels as high as 35 during the permo carboniferous high o2 at this time agrees with independent modeling based on the abundances of organic matter and pyrite in sediments and with the occurrence of giant insects during this period the cause of the excursion is believed to be the rise of vascular land plants and the consequent increased production of o2 by the burial in sediments of lignin rich organic matter that was resistant to biological decomposition

a model for atmospheric co 2 over phanerozoic time a new model has been constructed for calculating the level of atmospheric co sub 2 over phanerozoic time which is much simpler mathematically than the blag model but more complex geologically and biologically results suggest that there has been a notable pattern of varying atmospheric co sub 2 level over the past 570 my with high levels during the mesozoic and early paleozoic and low levels during the permo carboniferous and late cenozoic sensitivity analysis shows that within reasonable limits of the principal governing parameters this qualitative trend of varying co sub 2 is relatively insensitive to the actual values chosen for these parameters causes of the co sub 2 variation are multiple and no single geological or biological process can be called upon to explain all co sub 2 variation for all time the calculated trend of co sub 2 over time agrees well with independent estimations of paleoclimates thus the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study

reactivity of micas and cap rock in wet supercritical co2 with so2 and o2 at co2 storage conditions abstract seal or cap rock integrity is a safety issue during geological carbon dioxide capture and storage ccs industrial impurities such as so2 o2 and nox may be present in co2 streams from coal combustion sources so2 and o2 have been shown recently to influence rock reactivity when dissolved in formation water buoyant water saturated supercritical co2 fluid may also come into contact with the base of cap rock after co2 injection supercritical fluid rock reactions have the potential to result in corrosion of reactive minerals in rock with impurity gases additionally present there is the potential for enhanced reactivity but also favourable mineral precipitation the first observation of mineral dissolution and precipitation on phyllosilicates and co2 storage cap rock siliciclastic reservoir core during water saturated supercritical co2 reactions with industrial impurities so2 and o2 at simulated reservoir conditions is presented phyllosilicates biotite phlogopite and muscovite were reacted in contact with a water saturated supercritical co2 containing so2 or so2 and o2 and were also immersed in the gas saturated bulk water secondary precipitated sulfate minerals were formed on mineral surfaces concentrated at sheet edges so2 dissolution and oxidation resulted in solution ph decreasing to 0 74 through sulfuric acid formation phyllosilicate dissolution released elements to solution with 50 fe mobilized geochemical modelling was in good agreement with experimental water chemistry new minerals nontronite smectite hematite jarosite and goethite were saturated in models a cap rock core siltstone sample from the surat basin australia was also reacted in water saturated supercritical co2 containing so2 or in pure supercritical co2 in the presence of so2 siderite and ankerite were corroded and fe chlorite altered by the leaching of mainly fe and al corrosion of micas in the cap rock was however not observed as the ph was buffered by carbonate dissolution ca sulfate and fe bearing precipitates were observed post so2 co2 reaction mainly centered on surface cracks and an illite rich illite smectite precipitate quantified water saturated impure supercritical co2 was observed to have reactivity to rock forming biotite muscovite and phlogopite mineral separates in the cap rock core however carbonates and chlorite were the main reacting minerals showing the importance of assessing actual whole core

release of biodegradable dissolved organic matter from ancient sedimentary rocks 1 sedimentary rocks contain the largest mass of organic carbon on earth yet these reservoirs are not well integrated into modern carbon budgets here we describe the release of dissolved organic matter dom from om rich sedimentary rocks under simulated weathering conditions results from column experiments demonstrate slow sustained release of dom from ancient sedimentary rocks under simulated weathering conditions 1h nmr analysis of shale derived dom reveals a highly aliphatic carbohydrate poor material distinct from other natural dom pools shale derived dom is rapidly assimilated and biodegraded by aerobic heterotrophic bacteria consequently no compositional signature of shale derived dom other than 14c depletion is likely to persist in rivers or other surface reservoirs combined these efforts show that dissolution provides a mechanism for the conversion of refractory kerogen into labile biomass linking rock weathering with sedimentary om oxidation and the delivery of aged om to rivers and ocean margins

evidence for the submarine weathering of silicate minerals in black sea sediments possible implications for the marine li and b cycles 1 the role of sediment diagenesis in the marine cycles of li and b is poorly understood because li and b are easily mobilized during burial and are consumed in authigenic clay mineral formation their abundance in marine pore waters varies considerably exchange with the overlying ocean through diffusive fluxes should thus be common nevertheless only a minor li sink associated with the low temperature alteration of volcanic ash has been observed we describe a low temperature diagenetic environment in the black sea dominated by the alteration of detrital plagioclase feldspars fluids expelled from the odessa mud volcano in the sorokin trough originate from shallow 100 400 m deep sediments which are poor in volcanic materials but rich in anorthite these fluids are depleted in na k li b and 18o and enriched in ca2 and sr2 indicating that anorthite is dissolving and authigenic clays are forming using a simple chemical model we calculate the ph and the partial pressure of co2 pco2 in fluids associated with this alteration process our results show that the ph of these fluids is up to 1 5 ph units lower than in most deep marine sediments and that pco2 levels are up to several hundred times higher than in the atmosphere these conditions are similar to those which favor the weathering of silicate minerals in subaerial soil environments we propose that in black sea sediments enhanced organic matter preservation favors co2 production through methanogenesis and results in a low pore water ph compared to most deep sea sediments as a result silicate mineral weathering which is a sluggish process in most marine diagenetic environments proceeds rapidly in black sea sediments there is a potential for organic matter rich continental shelf environments to host this type of diagenesis should such environments be widespread this new li and b sink could help balance the marine li and li isotope budgets but would imply an apparent imbalance in the b cycle

sulfate mineral crusts from pyrite weathering and acid rock drainage in the dakota formation and graneros shale jefferson county nebraska pyrite weathering in the uppermost dakota formation and lower graneros shale cretaceous near fairbury nebraska produces acid materials and soils typically ph 6 acid rock drainage ph 2 5 and surface crusts of gypsum and the hydrated fe3 and al sulfate minerals copiapite alunogen metahohmannite coquimbite paracoquimbite and meta alunogen the fe and al minerals produced by acid sulfate weathering are relatively rare heretofore undocumented from nebraska and form in quantity only during episodes of dry weather lasting up to several weeks the maturation of mineral crusts on the dakota formation involves the dehydration of hydrous fe3 and al minerals precursor fe2 sulfates as found in many other cases of pyrite weathering were not observed in surface crusts during the study period surficial mineral crusts on the graneros shale consist only of gypsum with included clay minerals and quartz derived from the underlying shale the processes described herein are noteworthy in a regional geochemical and hydrogeological context and also by virtue of their apparent dependency on weather conditions the acid sulfate weathering sites described herein seem to be relatively unique in the surrounding region nonetheless the study of these sites suggests that there are potentially widespread effects of natural acid sulfate weathering associated with the dakota formation and other pyritiferous cretaceous strata in the region and that the localized effects of anthropogenically induced acid sulfate weathering in roadcuts quarries and other excavations can present engineering problems acid sulfate weathering is likely to have influenced the development of regional groundwater chemistry during the quaternary and may create adverse engineering and environmental conditions such as the retardation of vegetation cover encouragement of subsoil gypsum growth acceleration of shale slaking and possibly even the corrosion of roadbed materials

the land plant δ13c record and plant evolution in the late palaeozoic abstract based on the evaluation of 1323 carbon isotope values for silurian to permian terrestrial organic carbon measured on plant fossils cuticules humic coals and bulk terrestrial organic matter tom we conclude that the temporal trend in 13ctom records variations in the global carbon cycle notably an increase in the fractional burial of light terrestrial organic matter in late palaeozoic sediments 13ctom values suggest that the late palaeozoic po2 peak could have been restricted to a time frame of 40 ma carbon isotope data from four taxonomic groups reveal small differences that could be a consequence of habitat conditions no significant differences in organic carbon isotopic composition in relation to variable climatic conditions are discernible the carbon isotopic composition solely reflects c3 plant metabolism

dynamic model constraints on oxygen 17 depletion in atmospheric o2 after a snowball earth a large perturbation in atmospheric co2 and o2 or bioproductivity will result in a drastic pulse of 17o change in atmospheric o2 as seen in the marinoan oxygen 17 depletion mosd event in the immediate aftermath of a global deglaciation 635 mya the exact nature of the perturbation however is debated here we constructed a coupled four box and quick response biosphere atmosphere model to examine both the steady state and dynamics of the mosd event our model shows that the ultra high co2 concentrations proposed by the snowball earth hypothesis produce a typical mosd duration of less than 106 y and a magnitude of 17o depletion reaching approximately 35 both numbers are in remarkable agreement with geological constraints from south china and svalbard moderate co2 and low o2 concentration e g 3 200 parts per million by volume and 0 01 bar respectively could produce distinct sulfate 17o depletion only if postglacial marine bioproductivity was impossibly low our dynamic model also suggests that a snowball in which the ocean is isolated from the atmosphere by a continuous ice cover may be distinguished from one in which cracks in the ice permit ocean atmosphere exchange only if partial pressure of atmospheric o2 is larger than 0 02 bar during the snowball period and records of weathering derived sulfate are available for the very first few tens of thousands of years after the onset of the meltdown in any case a snowball earth is a precondition for the observed mosd event

secondary minerals from extrapedogenic per latus acidic weathering environments at geomorphic edges eastern nebraska usa abstract acidic weathering of the sulfidic upper cretaceous carlile and pierre shales in nebraska has led to the precipitation of the al sulfate hydroxide minerals aluminite alunite basaluminite felsobanyaite e g the aluminum hydroxides gibbsite and bayerite and the rare al phosphate hydroxide vashegyite kaolinite has also been produced as a result of this acidic weathering these minerals do not appear as neoformed constituents in any extant soils in the region and their existence underscores the ability of pyrite oxidation to produce major changes in mineralogy on a holocene to recent time scale jarosite hydronium jarosite gypsum halotrichite and melanterite also appear as secondary minerals in the weathered shales acidic weathering and the formation of new minerals is extrapedogenic because it occurs well below the limit of modern soil sola these processes also occur at the edges of major landscape elements and can be considered to have a strong lateral component processes making them per latus processes in our usage

methane and climate during the precambrian era abstract the sun was substantially less bright in the distant past yet earth s surface temperature remained above freezing higher concentrations of the greenhouse gases co 2 and ch 4 were likely responsible for keeping the early climate warm ch 4 concentrations of 1000 ppm or higher are predicted for the late archean paleoproterozoic atmosphere prior to the rise of o 2 photolysis of this ch 4 may have created an optically thin organic haze during much of this time the rise of o 2 at 2 3 ga eliminated most of the methane and probably triggered the paleoproterozoic glaciations ch 4 concentrations could have remained elevated throughout much of the proterozoic however as a consequence of low concentrations of dissolved o 2 and sulfate in the deep oceans and a corresponding increase in organic matter recycling by fermentation and methanogenesis

geocarbsulf a combined model for phanerozoic atmospheric o2 and co2 abstract a model for the combined long term cycles of carbon and sulfur has been constructed which combines all the factors modifying weathering and degassing of the geocarb iii model berner r a kothavala z 2001 geocarb iii a revised model of atmospheric co2 over phanerozoic time am j sci 301 182 204 for co2 with rapid recycling and oxygen dependent carbon and sulfur isotope fractionation of an isotope mass balance model for o2 berner r a 2001 modeling atmospheric o2 over phanerozoic time geochim cosmochim acta 65 685 694 new isotopic data for both carbon and sulfur are used and new feedbacks are created by combining the models sensitivity analysis is done by determining 1 the effect on weathering rates of using rapid recycling rapid recycling treats carbon and sulfur weathering in terms of young rapidly weathering rocks and older more slowly weathering rocks 2 the effect on o2 of using different initial starting conditions 3 the effect on o2 of using different data for carbon isotope fractionation during photosynthesis and alternative values of oceanic 13c for the past 200 million years 4 the effect on sulfur isotope fractionation and on o2 of varying the size of o2 feedback during sedimentary pyrite formation 5 the effect on o2 of varying the dependence of organic matter and pyrite weathering on tectonic uplift plus erosion and the degree of exposure of coastal lands by sea level change 6 the effect on co2 of adding the variability of volcanic rock weathering over time berner r a 2006 inclusion of the weathering of volcanic rocks in the geocarbsulf model am j sci 306 in press results show a similar trend of atmospheric co2 over the phanerozoic to the results of geocarb iii but with some differences during the early paleozoic and for variable volcanic rock weathering lower co2 values during the mesozoic atmospheric oxygen shows a major broad late paleozoic peak with a maximum value of about 30 o2 in the permian a secondary less broad peak centered near the silurian devonian boundary variation between 15 and 20 o2 during the cambrian and ordovician a very sharp drop from 30 to 15 o2 at the permo triassic boundary and a more or less continuous rise in o2 from the late triassic to the present

trace sulfate in mid proterozoic carbonates and the sulfur isotope record of biospheric evolution concentrations of oceanic and atmospheric oxygen have varied over geologic time as a function of sulfur and carbon cycling at or near the earth s surface this balance is expressed in the sulfur isotope composition of seawater sulfate given the near absence of gypsum in pre phanerozoic sediments trace amounts of carbonate associated sulfate cas within limestones or dolostones provide the best available constraints on the isotopic composition of sulfate in precambrian seawater although absolute cas concen trations which range from those below detection to 120 ppm sulfate in this study may be compromised by diagenesis the sulfur isotope compositions can be buffered sufficiently to retain primary values stratigraphically controlled 34 s measurements for cas from three mid proterozoic carbonate successions 1 2 ga mescal limestone apache group arizona usa 1 45 1 47 ga helena and newland formations belt supergroup montana usa and 1 65 ga paradise creek formation mcnamara group nw queens land australia show large isotopic variability 9 1 to 18 9 1 1 to 27 3 and 14 1 to 37 3 respectively over stratigraphic intervals of 50 to 450 m this rapid variability ranging from scattered to highly systematic and overall low cas abundances can be linked to sulfate concentrations in the mid proterozoic ocean that were substantially lower than those of the phanerozoic but higher than values inferred for the archean results from the belt supergroup specifically corroborate previous arguments for seawater contributions to the basin limited sulfate availability that tracks the oxygenation history of the early atmosphere is also consistent with the possibility of extensive deep ocean sulfate reduction the scarcity of bedded gypsum and the stratigraphic 34 s trends and 34 s enrichments commonly observed for iron sulfides of mid proterozoic age copyright 2005 elsevier ltd

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

patterns of sedimentation in the precambrian abstract the principle of uniformitarianism may be applied to precambrian basin evolution and to the sedimentary record as a whole the major difference in the precambrian eon lay in variability of rates and intensities of processes controlling weathering erosion transport deposition lithification and diagenesis this paper examines precambrian sedimentation patterns within the larger framework of earth evolution pre rock record sedimentation probably comprised deep water oceanic realms within which meteoritic and cometary impact events generated very large tsunamis resulting in very coarse volcaniclastic detritus combined with fine dust settling out of suspension all reworked by marine current systems and localised turbidites from c 4 to 3 2 ga greenstone belts provided the predominant settings for the thin passive margin carbonates bif stromatolitic evaporites pelites and quartzites and lesser synorogenic turbidites conglomerates and sandstones that accompanied the volcanic and volcaniclastic rocks typical of these settings common palaeoenvironments were high gradient alluvial fans low sinuosity braided rivers and relatively shallow marine settings subject to wave and tidal action and turbidity currents although continental crustal growth continued largely through greenstone belts until c 2 7 ga the witwatersrand basin c 3 0 2 7 ga kaapvaal craton south africa reflects initial stabilisation of the oldest craton with an epeiric sea accumulating largely fluvial detritus subject to tidal inland and storm wave craton marginal reworking within a retroarc foreland basin setting neoarchaean palaeoproterozoic sedimentation is discussed within a framework of two global superevents at c 2 7 ga and 2 2 1 8 ga each encompassing major changes in earth s evolution related to the supercontinent cycle mantle superplumes peaks in crustal growth rates and significant biochemical changes within the atmosphere hydrosphere system concomitant globally raised sea levels led to chemical and clastic epeiric seas within which the first giant carbonate platforms developed and deposition of iron formation peaked globally at c 2 5 ga the first global glaciation at c 2 4 2 2 ga provides little support for the snowball earth theory but does suggest a negative feedback loop model whereby intraglacial co 2 related warming and synglacial decreases in weathering alternated up to three times models for palaeo atmospheric and oceanic evolution are mutually exclusive but by c 1 8 ga the existence of large landmasses and free oxygen in earth s atmosphere enabled erg development and red bed sedimentation globally the full spectrum of phanerozoic modern sedimentary environments was thus present on earth a third postulated superevent at c 0 8 0 6 ga essentially recreated conditions experienced at c 2 2 1 8 ga with additionally at least three global refrigeration events

weathering of sulfidic shale and copper mine waste secondary minerals and metal cycling in great smoky mountains national park tennessee and north carolina usa metal cycling via physical and chemical weathering of discrete sources copper mines and regional non point sources sulfide rich shale is evaluated by examining the mineralogy and chemistry of weathering products in great smoky mountains national park tennessee and north carolina usa the elements in copper mine waste secondary minerals stream sediments and waters that are most likely to have negative impacts on aquatic ecosystems are aluminum copper zinc and arsenic because these elements locally exceed toxicity guidelines for surface waters or for stream sediments acid mine drainage has not developed in streams draining inactive copper mines acid rock drainage and chemical weathering processes that accompany debris flows or human disturbances of sulfidic rocks are comparable to processes that develop acid mine drainage elsewhere despite the high rainfall in the mountain range sheltered areas and intermittent dry spells provide local venues for development of secondary weathering products that can impact aquatic ecosystems