late holocene paleoenvironmental changes inferred from manasbal lake sediments kashmir valley india abstract paleoclimate investigations and reconstruction using the lake sediment cores of kashmir valley have been rarely attempted the basin is influenced by indian summer monsoon westerlies and the local katabatic winds in the present study an 80 cm undisturbed sediment core was retrieved from the manasbal lake situated in north western himalaya sediments were dated using 14c method and the age depth model indicated a depositional history extending from 3345 yrs bp to the present grain size major and trace elements toc om contents c n ratio and diatom assemblages were applied to reconstruct the paleoenvironmental changes around the area the a cn k diagram displays that the weathering intensity of the manasbal lake sediments are moderate to highly weathered and the sediments have been derived from nearby and mixed source origin several wet and cold phases were identified during 3300 yrs bp to 2500 yrs bp and 1800 yrs bp to 1300 yrs bp due to intense precipitation reflect high lake level these wet phases are marked by higher sand and silt content c n ratio and high allochthonous input with less abundance of diatom species clay om toc contents and high cia values consequently low lake level and dry and cold period from 3345 yrs bp to 3300 yrs bp and 2500 yrs bp to 1800 yrs bp is observed these inferences are corroborated with the trace elemental ratios cia and cwi data our data indicate that the westerlies and localised katabtic winds rather than the indian summer monsoons played a major role in controlling the past climate around the manasbal lake kashmir valley

palaeoecology of macroneuropteris scheuchzeri and its implications for resolving the paradox of xeromorphic plants in pennsylvanian wetlands abstract the medullosan pteridosperm macroneuropteris scheuchzeri hoffmann cleal shute zodrow was widespread and abundant in the middle to late pennsylvanian forests of tropical pangaea on the basis of its thick cuticles few adaxial stomata sunken stomata and dense trichomes it has been inferred to be a xeromorphic plant here we test that hypothesis by analyzing its facies distribution especially in relation to coals at 273 site collections from 45 stratigraphic horizons accessioned in the smithsonian national museum of natural history washington d c u s a the collections represent mostly par autochthonous assemblages and cover the taxon s complete known temporal range west of the appalachians in west central pangaea chi square analysis of facies occurrence data indicates that m scheuchzeri had a strong preference for mineral enriched wetlands that immediately preceded and followed the development of peat swamps and mires coals particularly during the late middle pennsylvanian late moscovian times coincident with a period of reduced polar ice volume in the late pennsylvanian following an interval of global warming and tropical wetland reorganization palaeoequatorial climate shifted to an overall drier mode this was accompanied by the disappearance of m scheuchzeri from europe and its limitation west of the appalachians to the wettest available habitats on the landscape thus our data falsify the hypothesis that m scheuchzeri was a conventional xerophyte but highlight the paradox of a plant with apparent xeromorphic features confined to a wetland habitat we consider several possible explanations for this association 1 response to nutrient deficiency 2 response to substrate salinity due to growth in coastal mangrove habitats 3 response to the composition of the palaeozoic atmosphere 4 return on investment long leaf lifespan and 5 phylogenetic constraint reflecting ancestral conditions our findings have broader implications for interpreting a wide variety of other pennsylvanian wetland plants which similarly show xermorphic features

geochemistry of sediments of the peninsular rivers of the ganga basin and its implication to weathering sedimentary processes and provenance abstract geochemistry of the himalayan rivers has been a major point of contention in sedimentary geochemistry because of its global impact on ocean chemistry and climate among the himalayan rivers the ganga and its himalayan catchment have been studied extensively however the peninsular rivers constituting a significant part of the ganga basin have not received much attention heretofore in the present geochemical study of the peninsular river s sediments we have found that the initial chemical weathering of rocks in the catchment produces texturally mineralogically and geochemically diverse sediments and fluvial processes further segregate them into the geochemically contrasting coarse channel and fine grained suspended sediments the overbank sediments possess an intermediate texture and geochemistry but more towards the suspended sediments the sediment geochemistry data indicates that the peninsular river s sediments show an increase in the weathering intensity from the west banas river to the east son river along the climate gradient i e from the arid semiarid to the sub tropical condition the higher chemical index of alteration cia values of the peninsular river s sediments than the yamuna and ganga river sediments reflect the control of weatherable lithology in the tectonically stable low relief and subtropical climate condition the yamuna and ganga river sediments with lower cia values show more physical weathering in the tectonically active himalaya the suspended and overbank sediments of the yamuna and ganga rivers show an increase in their cia values after the confluence of the peninsular rivers indicating the contribution of more weathered materials by the peninsular rivers it has been found that there is a geochemical split between the channel and suspended sediments of the peninsular rivers for sharing different sources i e the dominant contribution of felsic sources to the channel and mafic sources to the suspended sediments the weathering geochemistry trace element systematics and ree patterns suggest that the dominant sources of the channel sediments of the peninsular rivers are the felsic crystallines and sedimentary lithologies of the aravalli range bundelkhand and chhotanagpur granite and gneisses and vindhyan sandstones whereas the mafic lithologies such as the deccan traps and mafic components of the felsic lithologies appear to be the major sources of the suspended sediments within the range of intermediate composition the overbank sediment chemistry reflects more contribution of the mafic sources except for the ken which shows a higher contribution of the felsic sources the geochemical split between the channel and suspended sediments of the peninsular river s sediments for the different provenances indicates differential weathering of the deccan basalts bundelkhand crystalline and vindhyan sedimentary rocks and also the hydrodynamic control of the peninsular rivers during erosion transport and deposition however the himalayan rivers do not show such contrast between the channel and suspended sediments because of the higher physical weathering and sediment mixing in the high gradient topography of the himalayan catchment

ordovician cyanobacterial calcification a marine fossil proxy for atmospheric co2 abstract ordovician atmospheric co2 level was an important influence on climate and life however modelled estimates of ordovician co2 differ widely and in contrast to much of the subsequent phanerozoic they lack fossil proxy constraints in vivo cyanobacterial sheath calcification promoted by carbon dioxide concentrating mechanisms ccms creates distinctive microfossils these provide a direct ecophysiological link to ambient concentrations of co2 and to a lesser extent o2 cyanobacteria do not calcify at high co2 concentrations experiments show that ccms can be induced in present day cyanobacteria at co2 levels below 10 times present atmospheric level pal and that this promotes sheath calcification we compiled a global database of cyanobacterial calcification in marine environments throughout the ordovician 485 443 myr ago and compared it with modelled estimates of atmospheric co2 and o2 these data show that many genera of marine calcified cyanobacteria reappeared from cambrian series 2 or first appeared globally during the late middle to late upper ordovician late darriwilian to late katian in carbonate platform facies resulting in a previously unrecognized ten fold increase in global diversity such a large increase in calcification suggests widespread induction of ccm expression in cyanobacteria consistent with sustained decline in external co2 concentrations below 10 pal together with increase in dissolved o2 level during the late darriwilian sandbian and katian stages 460 445 myr ago these cyanobacterial calcification fossil proxy data provide a first order constraint on modelled estimates of atmospheric co2 for the ordovician estimated co2 outputs from copse and recent geocarb based models are broadly consistent with this cyanobacterial calcification proxy for the ordovician in view of the long history of cyanobacteria the calcified cyanobacterial proxy offers potential to assist interpretation of co2 deeper into geological time

geochemistry of shales from the archean 3 0 ga buhwa greenstone belt zimbabwe implications for provenance and source area weathering abstract phyllites from the archean 3 0 ga buhwa greenstone belt zimbabwe were deposited on a stable cratonic platform analyses of the phyllites generally define a single geochemical group based on major and trace element abundances the phyllites are strongly depleted in cao na2o and sr with respect to average archean upper crust by contrast k2o ba and rb are enriched several times relative to average archean upper crust reflecting basin scale k metasomatism transition metals are somewhat depleted whereas high field strength elements are typically enriched relative to average archean upper crust samples generally have fractionated lree patterns average cen smn 2 4 with small negative eu anomalies average eu eu 0 78 and generally flat hrees average gdn ybn 1 3 such geochemical characteristics suggest that the source dominantly consisted of tonalite with less common occurrences mafic volcanic rocks and granite mixing calculations which massbalance the rees and th sc suggest 70 tonalite 15 mafic volcanic rocks and 15 granite as possible proportions for the source of the phyllites a nearby early archean 3 5 ga continental nucleus preserves similar lithologies and is the probable source intense chemical weathering of the source terrane is indicated by premetasomatized chemical index of alteration values of 95 100 nearly complete depletion of cao and na2o and high al2o3 na2o ratios fine grained sediments of comparable age and presumed tectonic setting elsewhere in southern africa show similar geochemical characteristics implying that source area compositions and weathering intensities were similar these mature platformal deposits suggest a tectonically stable environment where intense chemical weathering took place at 3 0 ga across southern africa

early paleogene wildfires in peat forming environments at schoningen germany wildfire activity in early paleogene greenhouse conditions can be used as an analogue to gauge the effect of future warming trends on wildfire in the current climate system inertinite fossil charcoal in coal from 11 autochthonous early paleogene lignite seams from the schoningen mine germany was quantified using macerations in situ pillars and industry standard crushed samples a new three transect method was developed to quantify in situ charcoal the combination of in situ pillars and crushed samples accounts for temporal and spatial variation in charcoal through a stratigraphically oriented pillar whilst maintaining comparability with industry standards and previous work charcoal occurs as a range of randomly distributed particle sizes indicating that fires were burning locally in the schoningen peat forming environment and in the surrounding areas but according to petrological data not in an episodic or periodic pattern although charcoal abundance is low relative to previous high fire worlds such as the cretaceous three quantitative and semi quantitative methods show increased wildfire activity relative to the modern world in the warmest parts of the early paleogene as atmospheric oxygen levels stabilised to modern values and precipitation and humidity became the main control on wildfire increased rainfall followed by drier intervals would have created an environment rich in dry fuel in which wildfires could easily propagate if humidity was low enough in the later part of the early eocene ypresian charcoal abundance fell to levels similar to those found in modern peats this indicates that the transition to the modern low fire world occurred within the early eocene earlier than previous records suggest

compositional evolution of siliciclastic sediments recording the tectonic stability of a pericratonic rift mesozoic kutch basin western india abstract this study presents a combined petrographical and geochemical investigation to track the compositional changes in the mesozoic sedimentary record during the evolution of the pericratonic rift basin of kutch the mesozoic sequence of the proven petroliferous basin of kutch representing 3000 m thick siliciclastic and carbonate deposition within a time frame of 70 ma consists of jhurio jhumara jhuran and bhuj formations in ascending order of succession the dominance of arkosic sandstones and the abundance of zircon and monazite indicate predominantly felsic source rocks the concentration of individual trace elements such as th sc zr v ni and ratios like th sc cr v y ni th co la sc support the predominantly felsic source rock the lree enrichment and the negative eu anomaly corroborate the predominantly felsic source however concentrations of v ni and ti reveal the mafic input in older stratigraphic units while gdn ybn indicates dominant post archean source across the mesozoic succession younger stratigraphic units reveal contributions from the archean rocks from nagar parkar and aravalli highland regions the cia values suggest intermediate to intense weathering while the icv data record a shift from immature sediments in the older formations to mature and recycled types in the younger formations the high value of zr sc as well a high content of hf reflects the addition of zircon by recycling or by erosional unroofing of older continental rocks major oxide sio2 na2o and k2o and trace elements la th and hf bear the passive margin setting for the kutch basin during the mesozoic the decrease in feldspar content in sandstones increase in the concentration of zr and hf in shale and a decrease in values of icv from older to younger stratigraphic units corresponds to the compositional evolution related to increased stability of the kutch basin during the transition from early syn rift to post rift

carbon isotope evidence implying high o2 co2 ratios in the permo carboniferous atmosphere abstract theoretical models predict a marked increase in atmospheric o2 to 35 during the permo carboniferous 300 ma occurring against a low 0 03 co2 level an upper o2 value of 35 however remains disputed because ignition data indicate that excessive global forest fires would have ensued this uncertainty limits interpretation of the role played by atmospheric oxygen in late paleozoic biotic evolution here we describe new results from laboratory experiments with vascular land plants that establish that a rise in o2 to 35 increases isotopic fractionation 13c during growth relative to control plants grown at 21 o2 despite some effect of the background atmospheric co2 level on the magnitude of the increase we hypothesize that a substantial permo carboniferous rise in o2 could have imprinted a detectable geochemical signature in the plant fossil record over 50 carbon isotope measurements on intact carbon from four fossil plant clades with differing physiological ecologies and ranging in age from devonian to cretaceous reveal a substantial 13c anomaly 5 occurring between 300 and 250 ma the timing and direction of the 13c excursion is consistent with the effects of a high o2 atmosphere on plants as predicted from photosynthetic theory and observed in our experiments preliminary calibration of the fossil 13c record against experimental data yields a predicted o2 co2 mixing ratio of the ancient atmosphere consistent with that calculated from long term models of the global carbon and oxygen cycles we conclude that further work on the effects of o2 in the combustion of plant materials and the spread of wildfire is necessary before existing data can be used to reliably set the upper limit for paleo o2 levels

the composition of shales from the ordos basin china effects of source weathering and diagenesis abstract the ordos basin situated in northwestern china is the biggest mesozoic terrigenous sedimentary basin developed on the north china platform the geochemical data imply that shales from the ordos basin were mainly derived from a source area with an average archaean granite composition high na2o contents very limited variation of ti zr and ratios of gd yb n higher than 2 0 indicate that ordos shales are less mature than typical post archaean shales such as nasc and paas highly variable cia values chemical index of weathering indicate that most ordos shales are less weathered than nasc and paas ratios of la sm n and total ree contents for the ordos shales are positively correlated with cia whereas those of gd yb n inversely vary with cia these suggest that the weathering of source rocks is responsible for the ree fractionation in the shales of the ordos basin depletion of eu in clay sized fractions of the ordos shales decreases with enhanced crystallinity of illite considering that ratios of fe 3 fe 2 in the shales decrease with the increase of crystallinity of chlorites we propose that eu anomalies are directly related to the reduction of iron during burial diagenesis

glaciation aridification and carbon sequestration in the permo carboniferous the isotopic record from low latitudes to evaluate the isotopic record of climate change and carbon sequestration in the late paleozoic we have compiled new and published oxygen and carbon isotopic measurements of more than 2000 brachiopod shells from carboniferous through middle permian 359 260 ma strata we focus on the isotopic records from the u s midcontinent and the russian platform because these two regions provide well preserved marine fossils spanning a broad time interval both regions show a 18o increase at the mid carboniferous boundary ca 318 ma that roughly correlates with geologic evidence for an expansion of gondwanan glaciers only the russian platform record shows a 18o maximum during the glacial maximum in the asselian in contrast to a previous study korte c jasper t kozur h w and veizer j 2005 18o and 13c of permian brachiopods a record of seawater evolution and continental glaciation palaeogeogr palaeoclimatol palaeoecol 224 333 351 our data show no oxygen isotope evidence for glacial retreat in the early permian but instead show increasing 18o values related to aridification dissimilarity in the 18o trends for the epicontinental seas of north american and the russian platform suggests that at least one region experienced periodic restriction that altered regional salinities and seawater 18o values these results highlight the need for complementary proxies to identify restricted circulation in epicontinental seas carbon isotopic compositions of carbonates exhibit substantial regional variation with low values in western north america intermediate values in the midcontinent and high values in the sverdrup basin russian platform and northern spain nevertheless both u s midcontinent and russian platform records show a late serpukhovian minimum a sharp increase across the mid carboniferous boundary and a minimum centered on the kasimovian the correlative increase in brachiopod 13c and 18o values at the mid carboniferous boundary is our best isotopic evidence for a link between the carbon burial and glaciation in the permo carboniferous

the evolution of respiratory systems in theropoda and paracrocodylomorpha the end triassic extinction and the role of late triassic atmospheric o2 and co2 abstract during the late triassic period 235 201 3 ma paracrocodylomorpha and theropoda switched predatory roles with the former filling the subsidiary predator niche and the latter filling the top predator niche at the end triassic extinction reasons for the transition in predator guilds remain unknown but atmospheric conditions during this time which involved high co2 and low o2 concentration levels may be associated with the event evidence of bird like pneumatic post crania present in both groups as foramina and fossae correlates with an avian like respiratory system this may have allowed organisms to cope with declining atmospheric o2 environments of the late triassic this study estimated po2 throughout the late triassic using organic carbon isotope measurements from newark hartford basin paleosols and examined the morphological change in skeletal remains of theropoda focusing on pneumatic bones compared with paracrocodylomorpha during the late triassic and across the triassic jurassic boundary with data compiled from the paleobiology database and published anatomical literature the change of pneumaticity in taxa is quantified by a pneumatic index pi in which the number of pneumatized units is divided by the total number of bones examined patterns of pneumaticity are individually scored for the presence or absence of pneumatic bones morphological data are compared to corresponding femur length estimated atmospheric o2 and co2 level reconstructions and an ancestral state reconstruction depicting how pi values change throughout various clades our results suggest that pi values in theropoda and paracrocodylomorpha correspond with the vacillating po2 and pco2 throughout the late triassic and into the jurassic high pi values are prevalent in advanced theropod taxa while paracrocodylomorpha pi values vary by clade with a generally negative trend throughout the triassic ancestral state reconstruction analysis highlights the increasing pi values within theropoda and clade dependent trends in paracrocodylomorpha this study is instrumental in reconstructing how theropoda became evolutionarily successful and perhaps how and why the avian like respiratory system originated

a modeling case for high atmospheric oxygen concentrations during the mesozoic and cenozoic changes in atmospheric oxygen concentration over earth history are commonly related to the evolution of animals and plants but there is no direct geochemical proxy for o2 levels meaning that estimations rely heavily on modeling approaches the results of such studies differ greatly to the extent that today s atmospheric mixing ratio of 21 might be either the highest or lowest level during the past 200 m y long term oxygen sources such as the burial in sediments of reduced carbon and sulfur species are calculated in models by representation of nutrient cycling and estimation of productivity or by isotope mass balance imb a technique in which burial rates are inferred in order to match known isotope records studies utilizing these different techniques produce conflicting estimates for paleoatmospheric o2 with nutrient weathering models estimating concentrations close to or above that of the present day and imb models estimating low o2 especially during the mesozoic here we re assess the imb technique using the copse biogeochemical model imb modelling is confirmed to be highly sensitive to assumed carbonate 13c and when this input is defined following recent compilations predicted o2 is significantly higher and in reasonable agreement with that of non imb techniques we conclude that there is no model based support for low atmospheric oxygen concentrations during the past 200 m y high mesozoic o2 is consistent with wildfire records and the development of plant fire adaptions but links between o2 and mammal evolution appear more tenuous

recognition of diagenetic contribution to the formation of limestone marl alternations a case study from permian of south china abstract limestone marl alternations lmas have been extensively used in studies of sedimentology cyclostratigraphy and paleoclimatology however it has long been debated whether lmas are derived from primary sedimentation or from diagenetic alteration and the markers to distinguish one source from the other remain ambiguous in this study we investigate widespread permian lmas from various depositional settings in south china using traditional petrographic mineralogical and major element al2o3 vs tio2 methods as well as emerging trace and rare earth element ree analyses performed using solution based and in situ techniques the original depositional differences of the limestone and its coupled marl beds can be identified based on 1 the high volumes of siliciclastic minerals in the marls 2 unremarkable differential compaction 3 the recognizable signatures of the detrital admixture i e the al zr and th characteristics and 4 flattened shale normalized ree patterns diagenetic lmas are characterized by the compaction of fossils rare aragonite skeletons and abundant diagenetic clays sepiolite and talc preserved in the marl beds we also identified fully diagenetic lmas originating from primary carbonate sedimentation based on two almost completely consistent seawater like ree patterns with diagnostic positive la and negative ce anomalies la la sn 1 64 0 17 ce ce sn 0 73 0 05 superchondritic y ho 47 4 and depleted light rees relative to high rees pr yb sn 0 39 0 09 diagenesis also dominates the formation of lmas with limited terrigenous input in shallow water carbonate depositional environments it is likely that both the active metabolic processes in early diagenesis especially aerobic sulfide oxidation and the temporal palaeoceanographic conditions e g high levels of dissolved oxygen and sulfate play crucial roles in the genesis of the diagenetic lmas in the permian strata of south china

the record of triassic charcoal and other evidence for palaeo wildfires signal for atmospheric oxygen levels taphonomic biases or lack of fuel abstract as wildfires are today important sources of disturbance in many terrestrial ecosystems it is of great interest to understand how different environmental parameters and fire activity interacted during past periods of the earth history fossil charcoal inertinites and pyrogenic polycyclic aromatic hydrocarbons pahs represent the only direct evidence for the occurrence of such palaeo wildfires in the present study a review of published data together with new data on the occurrence of fossil charcoal for the permian and the triassic is presented for a long time it has been speculated that an assumed lack of evidence for palaeo wildfires during the triassic should be explained by a large drop in atmospheric oxygen concentration following or during the end permian mass extinction event preventing the occurrence of wildfires however evidence for palaeo wildfires is relatively common in many middle and late triassic strata whereas such evidence is almost totally lacking from early triassic sediments the interpretation of this charcoal gap or depression is difficult as many factors e g atmospheric oxygen concentration taphonomical biases lack of sediments suitable for the preservation of macroscopic charcoal lack of fuel and ignorance of scientists may have influenced not only the production but also the preservation and recovery of evidence for palaeo wildfires during this period thus it is not clear whether this early triassic charcoal gap can also be seen as evidence for an assumed wildfire gap or not without any doubt further investigations on the early triassic record of charcoal and other evidence for palaeo wildfires will be necessary before this problem can be solved in fact it can be expected that the number of published records of early triassic evidence for palaeo wildfires will increase in the future as more and more scientist working on sediments of this age may become aware of the interest in fires from this time this will certainly make it possible to give a much better picture of the temporal and regional distribution of wildfires during this period in the future

trace elements in shale as indicators of crustal provenance and terrane accretion in the southern canadian cordillera in this study the trace element geochemistry of shale is used to infer the nature of adjacent crustal blocks during terrane amalgamation and accretion in southern british columbia the geochemistry of about fifty shale samples from one of the best dated stratigraphic sections in the north america cordillera is used to 1 infer proximity to source regions characterized by juvenile ocean arcs continental arcs and ophiolites and 2 address a controversy concerning the timing of terrane amalgamation and accretion this study includes analyses of shale from the entire mesozoic stratigraphic section of the cadwallader terrane and overlying tyaughton basin as well as argillites from the structurally adjacent bridge river complex the mid cretaceous albian strata of the upper taylor creek group show light rare earth lree enrichment la n sm n of 3 0 and anomalously high cr and ni older units upper triassic lower cretaceous that stratigraphically underlie the upper taylor creek group have less lree enrichment high ba n la n ratios and no cr or ni anomaly the mid cretaceous strata were probably derived from a continental arc during a period of uplift and erosion of ultramafic rocks probably ophiolites and the co extensive nature of these sediments suggests accretion of many basement terranes to the edge of a continent the trace element geochemistry of the older strata is similar to that of sediment derived from an oceanic arc however lower cretaceous strata of the relay mountain group may record the incipient collision and progressive closure of this ocean basin the bridge river complex which is dominated by oceanic rocks and is interpreted to be an accretionary complex contains two suites of argillites one of which shows significant lree enrichment and isotopic data suggest a jurassic cretaceous age for these argillites that compose the matrix in this complex leitch et al 1991 we suggest that the bridge river complex was a jurassic cretaceous accretionary complex that formed outboard of the methow section of rocks and was not juxtaposed with the cadwallader terrane and tyaughton basin until the albian when these terranes were accreted to north america paleomagnetic data from these rocks maxson et al 1993 indicate that accretion took place at the latitude of central mexico and that subsequent strike slip faulting brought these terranes to their present position by eocene time

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

phanerozoic atmospheric oxygen new results using the geocarbsulf model modifications of the geocarbsulf model for phanerozoic atmospheric oxygen have been made to account for new carbon isotopic data reconsideration of the fractionation of carbon isotopes between carbonate and organic matter deposited in sediments and different rates of weathering of volcanic rocks versus granitic rocks results indicate distinctly higher o2 values than geocarbsulf for the mesozoic and cenozoic lack of an appreciable drop in o2 below 15 percent at any time and a small late cenozoic decline of o2 to the present

petrological and geochemical evidence of the paleoproterozoic and the meso neoproterozoic sedimentary rocks of the bastar craton indian peninsula implications on paleoweathering and proterozoic crustal evolution the petrology and geochemistry of the sandstones and shales of the meso neoproterozoic chattisgarh and indravati basins and the pelites and quartzites of the paleoproterozoic sakoli and sausar basins of the bastar craton have been studied for the paleoweathering tectonic setting and to delineate sediment source components and finally to trace the proterozoic crustal evolution in the bastar craton indian peninsula the geochemical data shows decrease in the abundance of mafic major elements and transition elements and an increase in the large ion lithophile elements liles from the paleoproterozoic pelites to the meso neoproterozoic shales this suggests partial exposure of granitoids in the paleoproterozoic and unroofing of the granitoids by the complete removal of mafic rocks in the provenance as the meso neoproterozoic sedimentation progressed overall the study of the meso neoproterozoic sandstones and shales show homogeneity in the source rock composition with strong felsic component however the paleoproterozoic pelites and quartzites show heterogeneity in the source rock composition with mixture of the felsic and mafic components geological geochemical and petrographic evidences indicate that the sediments in the paleoproterozoic sakoli and sausar basins and the meso neoproterozoic chattisgarh and indravati basins have been deposited in passive margin tectonic settings cratonic basins or intra cratonic rifts the relationship among alkali and alkaline earth elements cia pia and the th u ratio indicate that the source area was affected by moderate to intense weathering history

diagenetic history and provenance of devonian terrestrial sandstones at the margin of gondwana padeha formation eastern alborz iran abstract the northern margin of gondwana in iran rifted in the devonian forming a passive continental margin to the paleotethys ocean the details of which are obscured by later collision a record of the early phase of opening of paleotethys is preserved in the 600 m thick padeha formation a middle devonian terrestrial rift basin succession the sandstones are quartz arenite sub arkose and arkose and contain minimal detrital matrix 1 bulk rock geochemistry according to major elements suggests a source to the sandstones that was dominated by i type granite but also based on trace elements included small amounts of intermediate or mafic rocks low zr and hree contents suggest little or no sandstone in the source area and thus low abundance of fine grained heavy minerals

constraints on carbon accumulation rate and net primary production in the lopingian late permian tropical peatland in sw china article i nfo during the permian peatland as represented in extensive coal deposits was a major component of the global carbon cycle carbon storage in peatland is a balance between decay and net primary production npp which in turn are sensitive to variations in the concentration of atmospheric co2 and o2 to evaluate peatland carbon storage and npp during the lopingian a period thought to be characterised by higher atmospheric o2 and co2 than modern levels spectral analyses of geophysical data from a 15 1 m thick lopingian upper permian coal in southwestern china were conducted to define the time frame of temporal carbon accumulation in tropical peatland the result shows that the mineral matter content ash yield of the coal was possibly influenced by 123 ka eccentricity 35 6 ka obliquity and 21 2 ka precession milankovitch periodicities using this timeframe and an understanding of carbon loss during coalification the lopingian tropical peatland carbon accumulation rate is calculated to be 61 1 73 0 g c m 2 yr which is expected to correspond to a npp of 611 1460 g c m 2 yr respectively a comparison between the predicted pennsylvanian late carboniferous npp and modern values indicates that the permian npp calculated is consistent with geochemical and paleobotanical models supporting a proposal that productivity was mainly controlled by temporal atmospheric o2 and co2 levels

weathering and sediment generation in the archean an integrated study of the evolution of siliciclastic sedimentary rocks of the 3 2ga moodies group barberton greenstone belt south africa abstract alluvial and braided fluvial deposits of the 3 2 ga moodies group in the barberton greenstone belt south africa are analyzed petrographically and geochemically to identify their source rocks provenance and assess the degree and type s of weathering required to produce the observed moodies sediment compositions conglomerate sandstone and shale data give somewhat differing pictures of provenance and weathering due to derivation from different components within the source terrane and size and compositional fractionation during transport the results suggest that shale geochemistry provides the most accurate estimate provenance although both rare earth element and trace element th sc zr cr and ti data must be used in combination to give the best results the source area for moodies group sediments was dominated by tonalite felsic volcanic rock komatiite basalt and granite based on mineralogical and major element divergence from estimated source area composition the moodies group sediments are remnants of an aggressive weathering environment labile materials such as komatiite basalt and coarse plagioclase grains decomposed almost entirely to clays and solutes and the chemical index of alteration for moodies shale is well above the global average an aggressive weathering environment in the archean may have been achieved by increased rainfall higher temperatures and or higher atmospheric p c o 2 more likely a combination of these conditions worked to offset the inhibitory weathering effects of a plant free environment

impacts of global warming on permo triassic terrestrial ecosystems geologists and palaeontologists have expressed mixed views about the effects of the end permian mass extinction on continental habitats and on terrestrial life current work suggests that the effects on land were substantial with massive erosion following the stripping of vegetation associated with long term aridification and short term bursts of warming and acid rain wildfires at the permo triassic boundary contributed to the removal of forests and the prolonged absence of forests from the earth s surface for up to 10 myr these physical crises on land impinged on the oceans suggesting tight interlocking of terrestrial and marine crises levels of extinction on land may well have been as high as in the sea and this is certainly the case for tetrapods the mass extinction seems to have been less profound for plants and insects but it is hard at present to disentangle issues of data quality from reductions in abundance and diversity several killing agents have been proposed and of these tetrapods may have succumbed primarily to acid rain mass wasting and aridification plants may have been more affected by the sudden effects of heating and wildfires and the crisis for insects has yet to be explored

severe selenium depletion in the phanerozoic oceans as a factor in three global mass extinction events abstract selenium se is one of the key trace elements required by all animal and most plant life and se deficiencies in the food chain cause pathologies or death here we show from new geochemical analyses of trace elements in phanerozoic marine pyrite that sustained periods of severe se depletion in the past oceans correlate closely with three major mass extinction events at the end of the ordovician devonian and triassic periods these represent periods of se depletion 1 5 2 orders of magnitude lower than current ocean abundances being within the range to cause severe pathological damage in extant se reliant organisms se depletion may have been one of several factors in these complex extinction scenarios recovery from the depletion extinction events is likely part of a natural marine cycle although rapid rises in global oxygen from sudden major increases in marine productivity and plant biomass after each extinction event may also have played a crucial role

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

from greenhouse to icehouse nitrogen biogeochemistry of an epeiric sea in the context of the oxygenation of the late devonian atmosphere ocean system abstract the late devonian emergence of extensive arborescent terrestrial ecosystems produced changes in the earth s atmosphere and climate that resulted in substantial changes to the biogeochemistry of marine ecosystems the biogeochemistry of nitrogen in epeiric seas was particularly susceptible to alteration because of its dependence upon the series of redox mediated reactions that comprise the marine n cycle in order to explore the impact of climate change on n biogeochemistry in a late devonian epeiric sea we sampled a core from the appalachian basin that spans the interval from the greenhouse climate at the base of the famennian period to glacial conditions near its conclusion based upon stable isotope analysis of n c and s as well as elemental analysis of n c p s and fe we contend that two distinct biogeochemical regimes obtained during the contrasting climates the greenhouse regime featured low seawater o2 and ph that served to significantly curtail the oxidation of ammonia i e nitrification resulting in an ammonium dominated water column and low sediment 15n values the greenhouse also featured more extensive recycling of c n and p in contrast the higher seawater o2 and ph of the icehouse regime permitted nitrification in the water column resulting in a nitrate dominated system and higher sediment 15n values we conclude that nitrification was the key component of the n cycle that differentiated the two climate biogeochemical regimes

phanerozoic concentrations of atmospheric oxygen reconstructed from sedimentary charcoal varying concentrations of atmospheric oxygen have affected the development of animals and the role of wildfire in ecosystems reconstructions of past oxygen concentrations from fossil charcoal constrain atmospheric oxygenation over the past 400 million years variations of the earth s atmospheric oxygen concentration po2 are thought to be closely tied to the evolution of life with strong feedbacks between uni and multicellular life and oxygen1 2 on the geologic timescale po2 is regulated by the burial of organic carbon and sulphur as well as by weathering3 reconstructions of atmospheric o2 for the past 400 million years have therefore been based on geochemical models of carbon and sulphur cycling4 5 6 however these reconstructions vary widely4 5 6 7 8 9 10 particularly for the mesozoic and early cenozoic eras here we show that the abundance of charcoal in mire settings is controlled by po2 and use this proxy to reconstruct the concentration of atmospheric oxygen for the past 400 million years we estimate that po2 was continuously above 26 during the carboniferous and permian periods and that it declined abruptly around the time of the permian triassic mass extinction during the triassic and jurassic periods po2 fluctuated cyclically with amplitudes up to 10 and a frequency of 20 30 million years atmospheric oxygen concentrations have declined steadily from the middle of the cretaceous period to present day values of about 21 we conclude however that variation in po2 was not the main driver of the loss of faunal diversity during the permo triassic and triassic jurassic mass extinction events

use of multi proxy approaches to determine the origin and depositional processes in modern lacustrine sediments carajas plateau southeastern amazon brazil abstract geochemical and isotopic compositions of surficial sediments from a plateau lake in carajas southeastern amazon region were investigated to understand the spatial distribution of major and trace elements 13 c 15 n and c n ratio depositional processes and the origin of inorganic and organic fractions the 13 c 15 n and c n ratio indicate mainly an autochthonous source with siliceous sponge spicules and algae being the major source of organic matter in the center of the lake sector 3 while an allochthonous source mainly derived from c3 vascular forest plants dominates in the shallowest portion of the lake sector 1 consequently there was an apparent dilution of c4 plants montane savanna in the sediment water interface among major elements fe 2 o 3 is highly enriched in sector 3 which is controlled by the erosion of catchment laterites and underwater topography while al 2 o 3 and p 2 o 5 enrichment near the northern border of the lake is controlled by the weathering of mafic rocks similar spatial distribution of sio 2 with total organic carbon toc and isotopic evidence indicate that si distribution is partially controlled by organic components such as siliceous sponge spicules and algae the occurrence of most of the trace and rare earth elements ree is independent of fe 2 o 3 and toc but controlled by detrital aluminum silicates and heavy minerals indicating a lack of post depositional diagenetic control on their distribution the distribution of as and mo are possibly controlled by organic matter mineralization during early diagenesis and subsequently precipitation of fe phases the values of the chemical index of alteration cia in the sediments are very high 94 99 and similar to those of the source rocks suggesting that sediment composition is mainly controlled by mechanical weathering rather than chemical weathering geochemical indices al k ti k al ti la th ti zr zr hf hf nb la al co th ba sr and th sc together with the a cn k plot suggest that the provenance of the inorganic sediments remained relatively uniform or constant during the depositional period and that they were mainly derived from laterite crusts and subordinately from mafic soils this inference was further substantiated by the chondrite normalized ree patterns and discrimination plots geochemical indices such as u th authigenic u mo al and v cr indicate that the sediments were deposited under an oxic environment

overview of the meso to neoproterozoic evolution of the vindhyan basin central india abstract despite its origin in a stable intracratonic basin the vindhyan supergroup central india embodies tectonic driven depositional cycles of various orders a marked change in sedimentation pattern was coupled with a transient plate margin compression in the otherwise extensional regime an unconformity laterally correlatable with a conformity that divides the supergroup in two sequences arose in consequence maximum flooding surfaces mfs within the sequences can generally be correlated with intrabasinal volcanism that drastically diminished through the initial rift to later sag stage of basin evolution concomitantly with the change in tectonic milieu paleoseismic deformation structures and related deposits also became drastically reduced in scale nevertheless metre and decametre scale depositional cycles correlate well with the subtle record of paleoseismicity intermittent tilting of the depositional substratum is demonstrable in systematic bed dip changes in metre scale fining upward depositional cycles in the rift stage in the sag stage it is reflected merely in consistent deflection of paleocurrent directions at the top of the decametre scale parasequence sets towards the top of the supergroup progressive thickening and decreasing frequency of parasequences indicates a declining rate of basin subsidence progradation despite punctuation thus resulted in basin filling

geochemical records of qionghai lake sediments in southwestern china linked to late quaternary climate changes abstract knowledge of the chemical weathering history under the subtropical monsoonal climate will help to resolve the discrepancies regarding how climate conditions constrain chemical weathering major element and rare earth element ree compositions of the qionghai lake sediments in sichuan province southwestern china were analyzed aiming to provide information on sediment source discrimination and history of chemical weathering intensities and its responses to variations of indian summer monsoon ism and paleoclimate conditions as revealed by the a cn k diagram and other provenance proxies including tio2 zr ratio th sc vs zr sc and la th vs hf diagrams as well as the ree characteristics the source of qionghai lake sediments was felsic rocks additionally these sediments were subjected to small changes in provenance sedimentary sorting and recycling and weak diagenesis after deposition and or metasomatism indicating original signals were maintained on the intensity of chemical weathering of source area the chemical weathering intensities inferred from cia chemical index of alteration values have significantly fluctuated over the past 28 kyr reflecting three stages of paleoclimate evolution which is consistent with grain size characteristics carbonate contents low frequency magnetic susceptibilities toc and biomarker proxy paq the cia values changed significantly during the typical warm and cold climate events including the last glacial maximum heinrich 1 cold event younger dryas and holocene climatic optimum and generally exhibited an increasing trend in amplitude correspondingly in concert with the climate shifting from cold and dry to warm and humid conditions generally warm and humid climate conditions suggest enhanced chemical weathering intensity whereas weak chemical weathering denotes cold and dry climate in the ism region in addition sequential variations of the cia values during the past 28 kyr may reflect changing chemical weathering processes in responses to the varying intensities of indian summer monsoon and the climate conditions forced by the northern hemisphere solar insolation

pb pb age of earliest megascopic eukaryotic alga bearing rohtas formation vindhyan supergroup india implications for precambrian atmospheric oxygen evolution abstract though considered to be the earliest known well preserved megascopic body fossil of an eukaryotic alga grypania spiralis has not yet been dated directly and reliably in any of its four known locations in the world we report a pb pb isochron age of 1599 48 ma for the grypania bearing rohtas formation of the vindhyan supergroup central india besides being about 500 myears older than the previously inferred age for this formation this pb pb age together with close age constraints on the same fossil bearing horizons in jixian china and montana usa indicates that grypania bloomed on a global scale between 1 6 and 1 5 ga being an obligate aerobe the appearance of a much older grypania within one of the principal bif deposits near michigan usa has been linked to a significant jump in atmospheric oxygen between 2200 and 1900 ma inferred from geochemical evidence the long gap of 400 myears between the older and younger grypania occurrences could be due to reduction of atmospheric oxygen below the grypania survival threshold as a result of extensive bifs between about 1950 and 1850 ma

addendum to inclusion of the weathering of volcanic rocks in the geocarbsulf model r a berner 2006 v 306 p 295 302 in the paper by berner 2006a 1 the compiled data presented by dessert and others 2001 2 for different values of the relative weathering rates of basalts versus granites was missed the term granite is used here to refer to all granitoid rocks including gneisses it is the primary

geochemistry and sedimentary petrology of archean clastic sedimentary rocks at mt goldsworthy pilbara craton western australia evidence for the early evolution of continental crust and hydrothermal alteration abstract geochemical and petrological analyses of archean clastic metasedimentary rocks at mt goldsworthy in the pilbara craton western australia reveal the early evolution of continental crust and the earth s surface environment the succession correlative to the ca 3 4 ga strelley pool chert is composed dominantly of silicified medium grained to very coarse grained sandstone siltstone and shale with minor chert and precipitative beds of nahcolite and barite the sandstone is generally rich in detrital quartz with the coarse grained sandstone containing abundant very well rounded mono crystalline quartz that is assumed to be derived from older sedimentary rocks the recycled detritus is mixed with first cycle detrital material such as feldspar and barite that is sourced from reworked precipitative beds the sandstone also contains zircon fe ti oxides sulfides and lithic fragments of various origins including mafic ultramafic volcanic rocks sedimentary and possibly metamorphic rocks al ti zr systematics indicates that the source area for the mt goldsworthy clastic metasedimentary rocks was locally subjected to hydrothermal alteration reaction with the acid solution resulted in al dissolution and the formation of zr and ti enriched residual detrital material the enrichment in heavy rare earth elements and low al 2 o 3 tio 2 values of mt goldsworthy samples reflects the inflow of the residual zircon and ti oxides enriched detritus th sc la sc and eu eu ratios that are unaffected by contamination by the residual detritus indicate a mixed provenance with a significant contribution from granitoid rocks the presence of detrital zircon older than 3 5 ga was also demonstrated in this study

provenance studies and mudrocks abstract provenance studies based on the mineralogy of sandstones seem to be falling rapidly into disrepute as a result of the increasing emphasis on the effects of diagenesis on the original detrital mineral composition feldspars in sandstones commonly are dissolved altered to clay minerals and albitized by widely occurring diagenetic processes accessory minerals all too frequently are confined in ancient sandstones to ztr mudrocks in contrast have the potential of greater preservation of feldspars and accessory minerals because of their lesser permeabilities few studies have attempted to use the nonclay mineralogy of mudrocks for provenance work and these few have had promising but mixed results mudrocks deserve more attention in provenance studies than they have received

paleoclimatic control on the composition of the paleoproterozoic serpent formation huronian supergroup canada a greenhouse to icehouse transition unlike other feldspathic arenites in the 12 km thick huronian supergroup strata of the 250 350 m thick serpent formation contain abundant plagioclase deposited in a distal alluvial setting the serpent formation consists of arenites with minor shale and siltstone the plagioclase abundance could reflect unroofing of a unique source relative to other huronian units or could be due to less intense chemical weathering major trace and rare earth element ree geochemistry of the serpent formation are used to evaluate these two possibilities serpent formation source rocks form part of the archean superior province which mainly consists of tonalitic granitic and supracrustal assemblages and their metamorphosed equivalents in al2o3cao na2ok2o acnk space shales define a linear array which indicates that the unweathered source contained plagioclase and k feldspar in the ratio of 5 1 this particular array indicates that serpent fluvial systems tapped a variably weathered carapace developed on the superior province rather than purely fresh bedrock a modelled mixture of 80 tonalite and 20 granite group rocks reproduces ree and trace element characteristics of the serpent formation sandstones and shales average eu eu 0 87 lan smn 4 4 gdnybn 1 8 and th sc 1 65 mass balance considerations indicate that less than 5 supracrustal group rocks can be added at the expense of the granite group a unique source for serpent detritus is rejected because underlying and overlying units have approximately the same provenance composition plagioclase k feldspar ratios in serpent sandstones range from 2 1 to 1 2 which achieves mass balance among source mudstone and sandstone compositions when plotted in acnk space achievement of mass balance implies that sandstones and mudstones were derived from the same weathering profiles these findings indicate that plagioclase preservation in the serpent formation is related to less intense compared with other huronian arenites paleoweathering conditions probably a harbinger of the widespread continental glaciation recorded in the overlying gowganda formation

mesoproterozoic neoproterozoic transition geochemistry provenance and tectonic setting of clastic sedimentary rocks on the se margin of the yangtze block south china abstract the se margin of the yangtze block south china is composed of the mesoproterozoic lengjiaxi group and the neoproterozoic banxi group with sinian and post sinian cover a geochemical study was undertaken on the mesoproterozoic neoproterozoic clastic sediments in order to delineate the characteristics of the sediment source and to constrain the tectonic development and crustal evolution of south china our results show that the mesoproterozoic clastic sediments have a dominant component derived from a metavolcanic plutonic terrane with a large of mafic component there is a minor contribution of mafic rocks and older upper crustal rocks to the provenance strong chemical weathering in the source area occurred before transport and deposition the provenance for the neoproterozoic clastic sediments was most likely old upper continental crust composed of tonalite granodiorite dominated tonalite granodiorite granite source rocks which had undergone strong weathering and or recycling a minor component of older k rich granitic plutonic rocks and younger volcanogenic bimodal rocks is also indicated based on the regional geology the geochemical data and the inferred provenance the mesoproterozoic group is interpreted as a successive sedimentary sequence deposited in an extensional rifting back arc basin adjacent to a 1 80 ga continental margin arc terrane the progressive extension rifting of the back arc basin was followed by increasing subsidence and regional uplift during continental marginal arc continent the cathaysian block collision at 1 0 ga caused the deposition of the neoproterozoic group into back arc to retro arc foreland basin therefore the depositional setting of the proterozoic clastic sediments and associated volcanic rocks within the back arc basin reflected basin development from an active continental margin back arc basin with extension or rifting of the back arc basin to a passive continental margin

petrography and geochemistry of lower carboniferous greywacke and mudstones in northeast junggar china implications for provenance source weathering and tectonic setting abstract northeast junggar occupies an important position that links east junggar and chinese altai numerous magmatic and sedimentary rocks of the paleozoic in this area recorded the final amalgamation processes of east junggar and chinese altai this study analyzes the petrological and geochemical characteristics of sandstones and mudstones from the early carboniferous nanmingshui formation in northeast junggar the provenance and tectonic setting of these clastic rocks are discussed petrography indicates that the composition and texture maturity of the sandstones are low the components of the sandstones are mainly volcanic fragments 61 87 feldspars 9 30 and monocrystalline quartz 2 18 with a few polycrystalline quartz and other minerals slice observation indicates that the majority of the volcanic fragments of sandstones are basic intermediate volcanic rocks with a few dacite and felsic plutonic fragments the detrital modes of the sandstones reflect that these sandstones are derived from undissected arcs a low to moderate chemical index of alteration and the al2o3 cao na2o k2o diagram reflect a low to moderate weathering degree in the source area trace and rare earth element e g la th hf sc cr co and eu contents and their ratios suggest that the source rocks of the clastic rocks are intermediate basic rocks with some felsic rocks compared with sandstones the source rocks for mudstones are more felsic the petrography and geochemistry characteristics of the clastic rocks suggest that the proximal dulate arc should be the primary source area mixing calculations based on ree data suggest that approximately two thirds of the sandstone fragments are intermediate basic volcanic rocks the contents of the major and trace elements as well as the stratum features of the clastic rocks manifest that these clastic rocks resemble sedimentary rocks in a back arc basin the formation of this back arc basin is caused by the southward subduction of the zaysan erqis ocean

secular distribution of highly metalliferous black shales corresponds with peaks in past atmosphere oxygenation highly metalliferous black shales hmbs are enriched in organic carbon and a suite of metals including ni se mo ag au zn cu pb v as sb se p cr and u pge compared to common black shales and are distributed at particular times through earth history they constitute an important future source of metals hmbs are relatively thin units within thicker packages of regionally extensive continental margin or intra continental marine shales that are rich in organic matter and bio essential trace elements accumulation and preservation of black shales and the metals contained within them usually require low oxygen or euxinic bottom waters however whole rock redox proxies particularly mo suggest that hmbs may have formed during periods of elevated atmosphere po2 this interpretation is supported by high levels of nutrient trace elements within these rocks and secular patterns of se and se co ratios in sedimentary pyrite through earth history with peaks occurring in the middle paleoproterozoic early cambrian to early ordovician middle devonian middle to late carboniferous middle permian and middle to late cretaceous all corresponding with time periods of hmbs deposition this counter intuitive relationship of strongly anoxic to euxinic localized seafloor conditions forming under an atmosphere of peak oxygen concentrations is proposed as key to the genesis of hmbs the secular peaks and shoulders of enriched se in sedimentary pyrite through time correlate with periods of tectonic plate collision which resulted in high nutrient supply to the oceans and consequently maximum productivity accompanying severe drawdown into seafloor muds of c s p and nutrient trace metals the focused burial of c and s over extensive areas of the seafloor during these anoxic to euxinic periods likely resulted in an o2 increase in the atmosphere causing short lived peaks in po2 that coincide with the deposition of hmbs as metals become scarce particularly mo ni se ag and u the geological times of these narrow hmbs horizons will become a future focus for exploration

the burning of gondwana permian fires on the southern continent a palaeobotanical approach abstract fossil charcoal has widely been accepted as a direct indicator for the occurrence of palaeo wildfires in upper palaeozoic sediments of euramerica and cathaysia records of these remains are relatively common and regionally and stratigraphically more or less homogeneously distributed in terrestrial sequences on the other hand just a few records have been published for the permian of gondwana and only recently has it been demonstrated that macroscopic charcoals are also common here most permian macroscopic charcoal from gondwana is gymnospermous and has been reported from coal bearing strata macroscopic charcoal occurrences are spread out in different sequences and also in distinct stratigraphic intervals in the permian e g parana basin sakmarian artinskian of brazil karoo basin artinskian of south africa damodar basin lopingian of india and dead sea area changhsingian of jordan they range from peri glacial post glacial to warm temperate climatic systems throughout the permian macro and micro charcoal occurrences are compared to inertinite incidences to support the pyrogenic origin for these coal macerals and to provide an up to date overview on the known evidences of permian wildfires on gondwana in space and time

uranium isotopes distinguish two geochemically distinct stages during the later cambrian spice event a b s t r a c t anoxic marine zones were common in early paleozoic oceans 542 400 ma and present a potential link to atmospheric po2 via feedbacks linking global marine phosphorous recycling primary production and organic carbon burial uranium u isotopes in carbonate rocks track the extent of ocean anoxia whereas carbon c and sulfur s isotopes track the burial of organic carbon and pyrite sulfur primary long term sources of atmospheric oxygen in combination these proxies therefore reveal the comparative dynamics of ocean anoxia and oxygen liberation to the atmosphere over million year time scales here we report high precision uranium isotopic data in marine carbonates deposited during the late cambrian spice event at ca 499 ma documenting a well defined 0 18 negative 238 u excursion that occurs at the onset of the spice event s positive 13

reversal of the middle upper songhua river in the late early pleistocene northeast china abstract the study of drainage evolution in the songnen plain northeast china is essential for understanding the interactions between tectonics topography climate drainage evolution in the region despite this it remains unclear whether the paleo songhua river upper middle reaches of the songhua river once flowed westward into the songnen plain and what forcings influenced the drainage development of the songnen plain in this contribution we provide insight into drainage development on the songnen plain using an integrated approach of magnetic susceptibility geochemical elemental and sr nd isotopic and heavy mineral composition recovered from a 102 m sediment core sediments extracted from the eastern edge of the songnen plain with sedimentological and topographic archives our results show that a dramatic provenance shift occurred at the depth of 62 2 m 0 94 ma in the core sediments it is proposed that the songhua river was separated by the jia yi jiamushi yilan divide into two segments before 0 94 ma the west flowing proto songhua river and the east flowing proto sanjiang river lower reach of the songhua river however the proto songhua river reversed direction at 0 94 ma when the jia yi divide was cut through by headward erosion of the proto sanjiang river marking the birth of the songhua river as a single eastward flowing river system tectonics is suggested as the first order control on the evolution of the songhua river before 1 20 ma whereas climate changes may be responsible after 1 20 ma

geochemistry of loess paleosol sediments of kashmir valley india provenance and weathering abstract middle to late pleistocene loess paleosol sediments of kashmir valley india were analyzed for major trace and ree elements in order to determine their chemical composition provenance and intensity of palaeo weathering of the source rocks these sediments are generally enriched with fe 2 o 3 mgo mno tio 2 y ni cu zn th u sc v and co while contents of sio 2 k 2 o na 2 o p 2 o 5 sr nb and hf are lower than the ucc chondrite normalized ree patterns are characterized by moderate enrichment of lrees relatively flat hree pattern gd cn yb cn 1 93 2 31 and lack of prominent negative eu anomaly eu eu 0 73 1 01 average 0 81 paas normalized ree are characterized by slightly higher lree depleted hree and positive eu anomaly various provenance discrimination diagrams reveal that the kashmir loess paleosol sediments are derived from the mixed source rocks suggesting large provenance with variable geological settings which apparently have undergone weak to moderate recycling processes weathering indices such as cia ciw and pia values 71 87 83 83 and 80 57 respectively and a cn k diagram imply weak to moderate weathering of the source material

provenance and tectonic setting of late carboniferous clastic rocks in west junggar xinjiang china a case from the hala alat mountains abstract the late carboniferous palaeo tectonic setting of the west junggar region is comprised of arcs alternating with basins geochemical analysis of the sedimentary rocks associated with these arc related basins was conducted to better constrain the provenance and tectonic setting major and trace element geochemistry data of late carboniferous mudstones and sandstones in the hala alat mountains suggest that these sedimentary rocks and their source areas are characterized by the following four features 1 sediments experienced a simple recycling process 2 a low degree weathering conditions in the source areas 3 compositional immature of the sedimentary rocks 4 dominated by intermediate to felsic provenance with a few intermediate to mafic sediments integrated with the palaeo flow data and previous authors works a fore arc basin model is proposed for the tectonic setting of the sedimentary rocks the sawur arc is the primary provenance and supplies the major intermediate to felsic detrital fragments the bozchekul chingiz arc and kexia oceanic island arc are the other two secondary sources

geochemistry of archean shales from the witwatersrand supergroup south africa source area weathering and provenance with a few exceptions shales from the archean witwatersrand supergroup 2800 ma in south africa are depleted in na ca lile ree and hfse compared to phanerozoic shales cr co and ni are enriched in all witwatersrand shales and fe and mg are high in shales from the west rand groups wrg and lower central rand group crg shales from the crg and uppermost wrg are enriched in na al lile ree hfse and transition metals relative to shales from the lower wrg chondrite normalized ree patterns for all witwatersrand shales are enriched in light ree and exhibit small to moderate negative eu anomalies a positive correlation of ree and al2o3 contents in the shales suggests that ree are contained principally in clay minerals relative to shales from the crg shales from the wrg exhibit depletions of na ca and sr a feature probably reflecting intense chemical weathering of their source rocks cia indices in witwatersrand shales are variable chiefly 70 98 even within the same shale unit such variations reflect chiefly variable climatic zones or rates of tectonic uplift in source areas with perhaps some contribution from provenance and element remobilization during metamorphism compared to present day upper continental crust all but the orange grove roodepoort and k8 shales appear to have been derived from continental sources depleted in lile ree and hfse and enriched in transition metals computer mixing models based on six relatively immobile elements th hf yb la sc co and four source rocks indicate that the relative proportions of granite basalt and komatiite increased with time in sediment source areas at the expense of tonalite the contributions of basalt and komatiite appear to reach a maximum during deposition of the booysens shale and granite during deposition of the k8 shales and possibly during deposition of the orange grove shales

magnitude and significance of carbon burial in lakes reservoirs and peatlands globally lakes are currently accumulating organic carbon oc at an estimated annual rate of about 42 tg yr 1 most of the oc in all but the most oligotrophic of these lakes is autochthonous produced by primary production in the lakes the sediments of reservoirs accumulate an additional 160 tg annually and peatlands contribute 96 tg annually these three carbon pools collectively cover less than 2 of the earth9s surface and constitute a carbon sink of about 300 tg yr 1 although the oceans cover 71 of the earth9s surface they accumulate oc at a rate of only about 100 tg yr 1

evaluating the use of amber in palaeoatmospheric reconstructions the carbon isotope variability of modern and cretaceous conifer resins abstract stable carbon isotope geochemistry of fossilized tree resin amber potentially could be a very useful tool to infer the composition of past atmospheres to test the reliability of amber as a proxy for the atmosphere we studied the variability of modern resin 13 c at both local and global scales an amber 13 c curve was then built for the cretaceous a period of abundant resin production and interpreted in light of data from modern resins our data show that hardening changes the pristine 13 c value by causing a 13 c depletion in solid resin when compared to fresh liquid viscous resin probably due to the loss of 13 c enriched volatiles modern resin 13 c values vary as a function of physiological and environmental parameters in ways that are similar to those described for leaves and wood resin 13 c varies between plant species and localities within the same tree and between different plant tissues by up to 6 and in general increases with increasing altitudes of the plant growing site we show that as is the case with modern resin cretaceous amber 13 c has a high variability generally higher than that of other fossil material despite the high natural variability amber shows a negative 2 5 3 13 c trend from the middle early cretaceous to the maastrichtian that parallels published terrestrial 13 c records this trend mirrors changes in the atmospheric 13 c calculated from the 13 c and 18 o of benthic foraminiferal tests although the magnitude of the shift is larger in plant material than in the atmosphere increasing mean annual precipitation and p o 2 could have enhanced plant carbon isotope fractionation during the late cretaceous whereas changing p co 2 levels seem to have had no effect on plant carbon isotope fractionation the results of this study suggest that amber is a powerful fossil plant material for palaeoenvironmental and palaeoclimatic reconstructions improvement of the resolution of the existing data coupled with more detailed information about botanical source and environmental growing conditions of the fossil plant material will probably allow a more faithful interpretation of amber 13 c records and a wider understanding of the composition of the past atmosphere

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

a new model for atmospheric oxygen over phanerozoic time a mathematical model has been constructed that enables calculation of the level of atmospheric o2 over the past 570 my from rates of burial and weathering of organic carbon c and pyrite sulfur s burial rates as a function of time are calculated from an assumed constant worldwide clastic sedimentation rate and the relative abundance and c and s contents of the three rock types marine sandstones and shales coal basin sediments and other non marine clastics red beds arkoses by our model values of o2 versus time using a constant total sedimentation rate agree with those for variable sedimentation derived from present day rock abundances and estimates of erosional losses since deposition this agreement is the result of our reliance on the idea that any increase in total worldwide sediment burial with consequently faster burial of c and s and greater o2 production must be accompanied by a corresponding increase in erosion and increased exposure of c and s on the continents to o2 consumption via weathering it is the redistribution of sediment between the three different rock types and not total sedimentation rate that is important in o2 control to add stability to the system negative feedback against excessive o2 fluctuation was provided in the modeling by the geologically reasonable assignment of higher weathering rates to younger rocks resulting in rapid recycling of c and s we did not use direct o2 negative feedback on either weathering of c and s or burial of c because weathering rates are assumed to be limited by uplift and erosion and the burial rate of c limited by the rate of sediment deposition the latter assumption is the result of modern sediment studies which show that marine organic matter burial occurs mainly in oxygenated shallow water and is limited by the rate of supply of nutrients to the oceans by rivers results of the modeling indicate that atmospheric o2 probably has varied appreciably over phanerozoic time during the late carboniferous and permian periods o2 was higher than previously because of the rise of vascular land plants and the widespread burial of organic matter in vast coal swamps a large decrease in o2 during the late permian was due probably to the drying up of the coal swamps and deposition of a large proportion of total sediment in c and s free continental red beds sensitivity study shows that major parameters affecting results are the mean c concentration in coal basins and the relative sizes of the reservoirs of young rapidly recycled versus old rocks less sensitivity was found for changes over time in total land area undergoing weathering and the use of direct o2 negative feedback on marine carbon burial good agreement for rates of c burial calculated via our model and via independent models which are based on the use of stable carbon isotopes indicates that the dominant factor that has brought about changes in atmospheric o2 level and the isotopic composition of dissolved inorganic carbon in seawater over phanerozoic time is sedimentation and not weathering or higher temperature phenomena such as basalt seawater reaction

palaeomagnetism of vendian early cambrian sedimentary rocks from e finnmark norway abstract a palaeomagnetic study has been made on vendian early cambrian rocks of the tanafjord and vestertana groups from the varanger peninsula northernmost norway magnetic components of probably primary origin were isolated at two sites apparently unaffected by the finnmarkian scandian events of the caledonian orogeny sites situated in the caledonian gaissa nappe or close to its front were remagnetized and comparison with a tentative ordovician to devonian apparent polar wander path indicates that the remagnetization occurred during these periods

evidence for wildfire in the meishan section and implications for permian triassic events polynuclear aromatic hydrocarbons pahs and black carbon bc in sediments are powerful tools in the identification of the combustion process throughout geologic history in this study combustion derived pahs and bc were carefully investigated in sediments from the global stratotype section and point of the permian triassic p tr boundary in meishan china quantitative analyses of combustion derived pahs and bc demonstrate anomalously high concentrations in the boundary event beds that coincide with the mass extinction horizon the prevalence of parent polynuclear aromatics e g phenanthrene in pahs together with non metric multidimensional scaling analysis confirms that the pahs are mainly derived from vegetation burning instead of having a coal and or oil origin bc detected in sediment occurs in various forms from large irregular charcoal particles to fine aciniform soot with an equivalent reflectance of up to 3 5 the results strongly suggest that a wildfire occurred during the p tr boundary which served as one of the possible triggers of mass extinction on land the wildfire occurrence indicates that the o2 concentration of the atmosphere during or before the p tr mass extinction was probably 17 the temporal coincidence of the mass extinction with intensive volcanic eruption marine anoxia and wildfire events in the region of the meishan section provides new insight into the mechanisms of the p tr biotic crisis our results show that wildfires could have played an important role in the collapse of the ecosystem in the meishan p tr events

c o sr and pb isotope systematics of carbonate sequences of the vindhyan supergroup india age diagenesis correlations and implications for global events abstract the vindhyan supergroup of central india records a substantial portion of proterozoic time and contains some of the most disputed precambrian cambrian fossil discoveries despite the significance of these fossil finds many issues including reliable geochronology remained unresolved similarly the geochemical aspects of the sedimentary sequences and their implications to the evolution of proterozoic oceans have been studied only at a reconnaissance level here we report the results of the pb pb dating for the rohtasgarh limestone from the lower vindhyan supergroup giving an age of 1601 130 ma an estimate that is in accord with the recent u pb zircon dating of the lower vindhyan supergroup by rasmussen et al geology 30 2002 103 and ray et al geology 30 2002 131 sr isotope stratigraphy of carbonates from the upper vindhyan supergroup suggests a mid neoproterozoic 750 650 ma age for these formations this in turn argues for a long hiatus between the deposition of the lower and upper vindhyan supergroups our results conflict with the reports of cambrian age small shelly fossils and ediacaran fossils from the upper vindhyan rocks at the same time they suggest that the alleged trace fossils in the lower vindhyan rocks must be of paleoproterozoic age the most common 18 o values for calcitic components from limestone formations of the supergroup range from 10 to 7 similar to paleo neoproterozoic carbonates worldwide the modes of 13 c in the lower and upper vindhyan supergroups are 0 2 and 3 2 respectively again consistent with the worldwide dataset the secular patterns of carbon isotope trends do not support the earlier assumptions that the carbonate sequences at the southern margin correlate with those at the western or northern margins of the vindhyan basin c and sr isotope data provide new calibration points for the seawater evolutionary curves particularly for the paleoproterozoic for strontium isotopes the data from the lower vindhyan supergroup suggest that seawater departed probably less rapidly from mantle values than was previously believed

paleoclimatology and provenance of the glaciogenic gowganda formation paleoproterozoic ontario canada a chemostratigraphic approach the gowganda formation dated as about 2 3 ga is widely but not universally interpreted as glaciogenic and our chemostratigraphic study supports such an interpretation the bulk compositions of diamictite matrix materials and associated argillites are considered to have resulted from the mixture of two detrital components one is glacial flour similar in composition to the unweathered archean upper crust whereas the other is chemically weathered detritus resembling average proterozoic shale in composition the first component has a chemical index of alteration cia value of 50 reflecting the abundance of feldspar and dearth of aluminous clay minerals the second component has a cia value of 70 and was produced primarily in weathering profiles by chemical weathering typical of temperate climatic regimes diamictite matrix materials 92 samples have an average cia value of 57 the argillites have higher values the average is 62 97 samples the lower cia values of the diamictites reflect a higher proportion of glacial flour suggesting a stronger influence of frigid climatic conditions than that which prevailed during deposition of the argillites systematic trends in cia values are developed across diamictite argillite boundaries and within a thick argillite between two major diamictite units these values reflect climatic variations with maximum amelioration during deposition of the middle section of the argillite rare earth element data and th sc and ti al ratios from the diamictite matrix materials all suggest a provenance that included a large supracrustal component 45 together with lesser amounts of tonalite trondhjemite granite and granite the proportion of supracrustal materials such as volcanic rocks and shales may have been exaggerated by selective comminution during glacial transport the matrix materials of the gowganda diamictites are severely depleted in ca and proportionally enriched in na relative to the source the anorthitic component of plagioclase has been selectively replaced by an albitic component during diagenesis and metamorphism a chemostratigraphic approach provides high resolution data for reconstruction of paleoclimatic conditions and valuable information concerning provenance and metasomatic processes

slope controlled seismic deformation and tectonic framework of deposition koldaha shale india abstract penecontemporaneous deformations with remarkable lateral continuity at selected stratigraphic levels record frequent seismicity in the meso proterozoic koldaha shale vindhyan supergroup central india their consistent bipolar orientation reflects the master control of basinal tectonics boudinage small scale conjugate faults and bidirectional joint planes indicate east northeast west southwest basinal extension detailed study of a 27 km strike parallel stretch between chorhat and shikarganj against a broader perspective reveals existence of multiple nw se elongated subbasins stratigraphic and sedimentologic criteria point to inheritance and subsequent sustenance of steep western and gentler eastern flanks of the sub basins it is also indicated that the perennial supply of sediment took place from the east while the western slope contributed only during tectonic seiches the relatively large scale faults are correlatable with the steeper and the smaller deformation structures to the gentler flank the nnw oriented half graben structures that were reactivated time and again is elicited previous geophysical studies inferred roughly e w elongated rift valley in the granitic basement and the present observations indicate that the rifting continued at least up to the time of koldaha shale deposition the half graben could then be guided by cross faults resulted from dextral shear it is imperative then the basin interior sedimentation and deformation patterns were more closely controlled by the cross faults rather than by the basin margin faults only a set of slump folds in a 10 m thick interval indicates that the northern margin of the main basin was relatively steeper this is further corroborated by concentration of large fans in mineralogically immature sediments and southerly paleocurrent at the northern fringe of the basin in contrast the vindhyan sediments commonly belong to orthoquartzite carbonate association a regional northerly slope of the vindhyan basin floor towards the relatively steeper flank provides an explanation for the general northwesterly paleocurrent even though the eastern flank of the sub basins sloped wsw this integrated study of the physical aspects of the sedimentary pile against the background information of basement tectonics recognize rifting with a dextral shear component as the overriding factor controlling the early part of evolution of the vindhyan basin

oceanic environment changes caused the late ordovician extinction evidence from geochemical and nd isotopic composition in the yangtze area south china the ordovician silurian o s transition was a critical interval in geological history multiple geochemical methods are used to explore the changes in oceanic environment the nd isotopic compositions in the yangtze sea are controlled by two sources the continental erosion and the panthalassa ocean high end t values during the katian late hirnantian and rhuddanian intervals are associated with the high sea level which resulted in less terrestrial input based on the low ti al and zr al ratios in contrast low end t values during the early hirnantian interval are related to the sea level fall in this case the exposure of submarine highs and the growth of yangtze oldlands could lead to more continental materials being transported into the yangtze sea based on high ti al and zr al ratios in addition the negative end t excursion can also be attributed to the weak circulation between the yangtze sea and panthalassa ocean when sea level was low furthermore the sea level eustacy plays a significant role in the changes in redox water conditions the redox indices mainly uef ce ce and corg pt across the o s transition show a predominance of anoxic ocean over the yangtze sea during the katian late hirnantian and rhuddanian intervals and an oxygenated episode was briefly introduced during the early hirnantian period because of the fall in sea level the late ordovician biotic crisis was marked by two phase extinction events and the change in sea level and redox chemistry may be the important kill mechanisms

linking the acadian orogeny with organic rich black shale deposition evidence from the marcellus shale abstract the trace and rare earth elements ree analyses were conducted on samples collected from a 30 m core of the marcellus shale obtained from greene county southwestern pennsylvania our results suggest that organic matter enrichment trends in the marcellus shale can be directly linked with the acadian orogeny the acadian orogeny has been recognized as a main sediment source for the marcellus shale synthesis of tectonic history and recent ash bed geochronology reveals that deposition of the organic carbon rich or zone characterized by toc 4 located between 2393 m and 2406 5 m core depth in the studied marcellus shale core was coincident with tectonically active and magmatic quiescent period of the acadian orogeny ca 395 380 ma this time period also corresponds to the highest rate of mountain building in the acadian orogeny the light rare earth lree and selected trace elemental e g ta cs composition of the or zone sediments is similar to that of the bulk continental crust supporting the lack of magmatic activity in the source area i e acadian orogeny in contrast subsequent deposition of the organic carbon poor op sediments characterized by toc

protracted development of bioturbation through the early palaeozoic era mobile organisms first appeared in the fossil record prior to the precambrian cambrian transition sediment textures indicate that the degree of sediment mixing by animal activity remained low for 120 million years following the transition

inclusion of the weathering of volcanic rocks in the geocarbsulf model the carbon cycle model geocarbsulf is extended by dividing the weathering of silicates into volcanic and non volcanic rocks the proportion of volcanic weathering is calculated as a function of time from the oceanic record of 87sr 86sr the volcanic proportion is then used to modify the equations for calculating atmospheric co2 by the addition of a new non dimensional volcanic weathering factor the effect of uplift and physical erosion on weathering is also modified by using only the distribution over time of the abundance of sandstones and shales and not sr isotopic data that had been used previously results indicate moderate change from geocarbsulf in the distribution of atmospheric co2 over phanerozoic time this includes an increased minimum in co2 during the late ordovician in agreement with the presence of a continental glaciation at that time and a shift of maximum mesozoic values from the jurassic to the early cretaceous

a combined petrographical geochemical provenance study of the newland formation mid proterozoic of montana a provenance study was conducted on the mid proterozoic newland formation in which petrographical features of sandstones and geochemical characteristics of shales were integrated to arrive at an internally consistent interpretation sandstones of the newland formation are typically arkosic sands and arkoses with very well rounded quartz and feldspar grains and only minor amounts of extrabasinal rock fragments the predominant feldspar types are k spar and microcline feldspar grains are smaller than quartz grains and feldspars show little alteration due to weathering detrital modes of newland sandstones qfl diagrams indicate that they were derived from a stable cratonic source these petrographical features imply a source area dominated by granites and granitoid gneisses semi arid to arid climate tectonic quiescence and overall peneplain conditions shales of the newland formation are dominated by illite quartz silt and fine crystalline dolomite they have small la th rations relatively large hf contents and small contents of cr co and ni all indicative of derivation from crust of granitic composition small tio 2 al 2 o 3 ratios also suggest source rocks of granitic composition the average chemical index of alteration cia for newland shales is 71 8 which in light of the probable granitoid source indicates modest amounts of chemical weathering relatively large sio 2 contents and large k 2 o na 2 o ratios reflect derivation from stable cratonic areas and tectonic quiescence thus in general the petrography of sandstones and geochemistry of shales provides the same provenance clues for the newland formation one notable discrepancy between the two approaches is that the sandstones indicate an arid to semi arid climate with very minor chemical weathering whereas the cia of the shales indicates at least modest amounts of chemical weathering this indicates on one hand the need to better calibrate the cia with a large variety of muds from modern climatic settings and on the other hand the possibility that this discrepancy is due to transport segregation

provenance and paleoweathering reconstruction of the mesoproterozoic hongshuizhuang formation 1 4 ga northern north china this is the first study presenting major and trace elemental data from the mesoproterozoic hongshuizhuang formation shales in yanshan basin north china in order to reconstruct its provenance and chemical weathering history the shales are strongly depleted in na2o and sr and enriched in y and transition metal elements relative to upper continental crust low zr concentrations and various discriminant plots e g th sc zr sc and al2o3 tio2 zr indicate insignificant mineral sorting or recycling of these shales the rocks show light rare earth element ree enrichment la ybcn 3 99 6 92 flat heavy ree and significantly negative eu anomalies euan 0 57 0 68 in chondrite normalized ree patterns similar to post archean australian average shales the fairly uniform ree patterns and trace element ratios indicate that the hongshuizhuang formation shales were derived from a felsic source area with granodiorite as the dominant contributor mixing calculations suggest a mixture of 30 granite porphyry 5 basalt and 65 granodiorite as the possible source of the shales also supporting that granodiorite was the predominant source intense chemical weathering of the source terrain is indicated by high values of the premetasomatized chemical index of alteration plagioclase index of alteration rb sr a strong positive correlation between tio2 and al2o3 depletion of cao na2o and sr and mineral compositions such strong chemical weathering suggests a warm and wet paleoclimate perhaps due to high atmospheric co2 and ch4 concentrations and a near equatorial location of the north china craton in the columbia supercontinent at 1 4 ga

terrestrial sedimentation and the carbon cycle coupling weathering and erosion to carbon burial this paper examines the linkages between the carbon cycle and sedimentary processes on land available data suggest that sedimentation on land can bury vast quantities of organic carbon roughly 1015 g c yr 1 to evaluate the relative roles of various classes of processes in the burial of carbon on land terrestrial sedimentation was modeled as a series of 864 scenarios each scenario represents a unique choice of intensities for seven classes of processes and two different global wetland distributions comparison was made with presumed preagricultural conditions the classes of processes were divided into two major component parts clastic sedimentation of soil derived carbon and organic sedimentation of autochthonous carbon for clastic sedimentation masses of sediment were considered for burial as reservoir sediment lake sediment and combined colluvium alluvium and aeolian deposits when the ensemble of models is examined the human induced burial of 0 6 1 5 1015 g yr 1 of carbon on land is entirely plausible this sink reaches its maximum strength between 30 and 50 n paddy lands stand out as a type of land use that warrants future study but the many faces of rice agriculture limit generalization in an extreme scenario paddy lands alone could be made to bury about 1 1015 g c yr 1 arguing that terrestrial sedimentation processes could be much of the sink for the so called missing carbon is reasonable such a hypothesis however requires major redesign of how the carbon cycle is modeled unlike ecosystem processes that are amenable to satellite monitoring and parallel modeling many aspects of terrestrial sedimentation are hidden from space

sediment chemistry and detrital zircon record in the bosque and paseo del mar coastal areas from the southwestern gulf of mexico abstract in this study we analyzed the mineralogy and bulk chemical composition of 20 sediment samples as well as trace rare earth element ree concentrations and u pb ages of 400 detrital zircons retrieved from the bosque pb and paseo del mar pm coastal sediments southwestern gulf of mexico to investigate the provenance the xrd study revealed that the pb sediments are associated with quartz muscovite cordierite albite and anorthite the pm sediments are associated with calcite aragonite and biogenic materials which derived probably within the coastal environment the weathering indices like chemical index of alteration cia chemical index of weathering ciw and plagioclase index of alteration pia revealed a moderate intensity of weathering for the pb sediments the chondrite normalized ree patterns of the pb and pm sediments are with negative and positive europium anomalies eu eu suggesting that the sediments were derived by the combination of felsic and mafic source rocks the th u ratios 0 3 of the pb and pm zircons indicated an igneous origin the chondrite normalized ree patterns of the pb and pm zircons are depleted in low ree lree and enriched in heavy ree hree with positive cerium and negative europium anomalies a wide variation in chondrite normalized ree patterns of zircons with respect to ages was observed the pb is dominated by proterozoic 551 2500 ma and paleozoic zircons 445 480 ma ordovician whereas pm is dominated by cenozoic zircons 5 21 ma miocene indicating that the zircons were derived from different source terranes the chiapas massif cmc and chuacus complexes are identified as the potential source areas which contributed proterozoic zircons to pb on the other hand cuicateco terrane cui and tuxtla volcanic field tvf are considered as the potential source areas which supplied significant number of cenozoic zircons to the pm coastal area the zircon u pb ages and the bulk sediment geochemistry together indicate that the source terranes which supplied sediments to the pb and pm coastal areas consist of mafic and felsic rocks the results of this study further illustrated the importance of littoral currents in distributing sediments although rivers are considered as a carrier and agent of distributing sediments along the coastal areas

geochemistry of quaternary sediments of the jeongokri archaeological site korea implications for provenance and palaeoenvironments during the late pleistocene the geochemical characteristics of an approximately 6 m long sediment core collected from the jeongokri archaeological site hantan river korea were examined to determine the provenance of the sediments and to reconstruct the palaeoenvironment of the study area during the late pleistocene 200 127 ka the core sediments were subdivided into two parts based on grain size an upper 0 380 cm depth and lower part 380 cm depth the lower part was deposited primarily by fluvial processes during an interglacial period marine isotope stage mis 7 with warm and humid conditions conversely the upper part was mainly deposited by aeolian processes during a cold and dry glacial period mis 6 geochemical characteristics represented by major trace and rare earth element ree compositions and textures of the jeongokri core sediments show distinct differences between the upper and lower parts the mineralogy and major trace and ree compositions indicate that the influence of felsic source rocks e g granite was dominant in the lower sediments which were derived from the hantan river in contrast increased quartz content and the very fine and homogeneous grain size in the upper sediments indicate an aeolian origin ree ratios and distribution patterns and geochemical signatures indicate that these sediments were derived predominantly from chinese loess deposits and partially from local sediments from the korean peninsula the possible source area of the upper sediments is the northern part of the yellow sea basin the yellow sea basin having mixed geochemical signatures between chinese loess and korean derived sediments was exposed because of low sea levels during mis 6 the exposed yellow sea basin was located in the path of winter monsoon winds which may have carried a great deal of airborne sediments from the basin to the jeongokri area copyright 2011 john wiley sons ltd

anomalously low al2o3 tio2 values for archean cherts from the pilbara block western australia possible evidence for extensive chemical weathering on the early earth geochemical sedimentological and mineralogical features of 3 0 ga archean cherts and intercalated bifs from the pilbara block western australia were studied chert layers that are well exposed at point samson 20 km north northeast of roebourne consist of various types of chert white light gray chert brownish yellow chert gray chert dark gray chert massive black chert and light gray chert the cherts other than brownish yellow chert consist mostly of microcrystalline quartz with a minor amount of fine silicate minerals and carbonates the brownish yellow chert is characterized by a high concentration of goethite most cherts contain thin layers characterized by high concentrations of ti bearing minerals such as rutile anatase fe ti aggregates and fine tio2 grains accordingly al2o3 tio2 values in some samples are very low 1 0 indicating that these samples contain more tio2 than al2o3 this geochemical feature is attributed mainly to the supply of detrital materials with high ti bearing minerals to the site of deposition because the ti bearing minerals are generally associated with detrital quartz and zircon ti enriched detrital materials are possibly formed by al ti fractionation during 1 extensive chemical weathering or 2 hydrothermal alteration of the source rocks in the first hypothesis which we prefer it is suggested that low ph values 4 of meteoric waters accelerated the decomposition of rock forming minerals and prevented precipitation of dissolved al3 such low ph values of meteoric waters could have been attributed to more violent volcanic activities issuing acid materials e g h2s and hcl and or a higher concentration of atmospheric co2 in the archean than today

depositional environments provenance and paleoclimatic implications of ordovician siliciclastic rocks of the thango formation spiti valley tethys himalaya northern india abstract recently published findings indicate that the ordovician period has been much more dynamic than previously anticipated thus making this period significant in geological time the ordovician of india can best be studied in the spiti region because the spiti basin records the complete uninterrupted history of excellent marine sedimentary rocks starting from cambrian to paleogene which were deposited along the northern margin of india due to these reasons the geochemical data on the ordovician rocks from the spiti region is uncommon the present geochemical study on the ordovician thango formation sanugba group is mainly aimed to understand the provenance and the paleoclimatic conditions the sandstones are the dominant lithology of the thango formation with intercalations of minor amount of shales detailed petrographic and sedimentological analysis of these rocks suggest that three major depositional environments viz fluvial transitional and marine prevailed in the basin representing transgressive and regressive phases the major and trace element ratios such as sio2 al2o3 k2o na2o and la th sc discrimination diagram suggest that these rocks were deposited in passive margin tectonic settings various geochemical discriminants and elemental ratios such as k2o na2o al2o3 tio2 la sc th sc cr th zr sc gd yb n and pronounced negative eu anomalies indicate the rocks to be the product of weathering of post archean granites the striking similarities of the multi elemental spider diagrams of the studied sediments and the himalayan granitoids indicate that sediments are sourced from the proterozoic orogenic belts of the himalayan region chemical index of alteration cia values of the studied sediments 55 72 suggest that the source rocks underwent low to moderate degree of chemical weathering the span of the cia values 55 72 recorded in the sediments from the spiti region may have resulted from varying degrees of weathering conditions in the source area this in turn reflects variable climatic conditions prevailing during the ordovician period which is consistent with the global studies the high cia values observed by numerous studies on siliciclastic sediments may imply warm paleoclimate attributed to an increase in atmospheric carbon dioxide and or methane levels inducing an acidic weathering environment and enhanced silicate weathering while the low cia values indicates prevalence of arid glacial conditions where negligible chemical alteration is possible this study documents the noteworthy events like fluctuating rise and fall atmospheric co2 and sea levels during the ordovician period a conclusion which is consistent with the other such studies on the phanerozoic glaciation or mass extinction events on gondwana supercontinent

the rare earth element compositions of sediments from the loess tableland in the liyang plain southern china implications for provenance and weathering intensity to identify the weathering intensity and to deduce the provenance of sediments black brown soil and loess from the loess tableland in the liyang plain is of great importance for understanding the development and origin of civilization of this critical region in china the geochemical results show similar ree distribution patterns among sediments sampled from the yc profile in the liyang plain reticulated red soils from the dongting lake area xiashu loess in zhenjiang and loess from the loess plateau in china these similarities imply a single provenance from dust storms rees especially the lree hree ratio and eu anomaly can trace weathering intensity higher lree hree ratios and remarkably eu anomalies are present in the top loess l0 lower lree hree ratios and insignificant eu anomalies are present in black brown soil s0 from the liyang plain these demonstrate that the black brown soils have undergone a lower intensity of weathering than the loess of yc profile moreover cia values for sediments from the yc profile provide powerful evidence to support the above result comparisons of analyses of the ree contents of sediments from the yc profile of reticulated red soils from the dongting lake area xiashu loess from the yangtze river and loess from the loess plateau clearly show the weathering intensity decreases according to the following sequence reticulated red soil from the dongting lake area sediments of yc profile from the liyang plain which formed from dust storms xiashu loess from lower reach of the yangtze river loess from the loess plateau

geochemistry of shales from the paleoproterozoic to neoproterozoic vindhyan supergroup implications on provenance tectonics and paleoweathering abstract major trace and rare earth element ree concentrations were measured for 88 shale samples from the paleoproterozoic to neoproterozoic vindhyan supergroup in central india the major and trace element data of the vindhyan shales are compared with north american shale composite upper crust mid oceanic ridge basalts and many other shale standards of archean proterozoic and phanerozoic age ree concentrations of the vindhyan shales are comparable to the upper continental crust various discriminant diagrams were used to reveal the inferred provenance tectonics and paleoweathering conditions a predominantly granitic source rock is inferred for the lower vindhyan shales whereas partial contribution from basaltic source is evident during deposition of the upper vindhyan shales existing paleocurrent data and the present geochemical investigations together suggest archean paleoproterozoic basement rocks exposed beyond the southern basin margin of the vindhyan outcrops as the possible source rocks the deposition of the vindhyan shales took place in an intracratonic basin where sediments were primarily derived from stable continental areas moderate climatic conditions are inferred during the deposition of the shales the upper vindhyan shales however reflect more intense weathering compared to the lower vindhyan shales which may be attributed to relative tectonic stability and more humid conditions during deposition of upper vindhyan shales

geochemical evidence for the paleoproterozoic arc back arc basin association and its importance in understanding the evolution of the central indian tectonic zone abstract the central indian tectonic zone citz is considered to be one sector in a series of paleoproterozoic orogens that stitched together the supercontinent columbia the paleoproterozoic mahakoshal belt forms the foundation of the citz metabasalts and metaclastic rocks of the mahakoshal belt have been studied for major elements and trace elements including the rare earth elements ree metabasalts of the lower saleemanabad formation are grouped into two types however both types of metabasalt depict a back arc basalt character by showing enrichments in large ion lithophile elements liles like k rb cs and ba and light rare earth elements lrees but show depletions in high field strength elements hfses like nb ta y and ti and hree heavy rare earth elements in comparison to the n morb this is further supported by some key elemental ratios like ba nb nb ta la nb eu eu nb nb and ree patterns the geochemistry of the metaclastic rocks of the lower saleemanabad middle parsoi and upper dudhmaniya formations of the mahakoshal belt show an arc signature rather than the cratonic signature in the bundlekhand ttg and n morb normalised diagrams the arc signature calc alkaline series of metaclastic rocks is further supported by various tectonic discrimination diagrams the overall study indicates that the mahakoshal belt was formed as a back arc rift basin very close to continental arcs on the hinterland of the bundelkhand craton at the initial stage of subduction as a result of trench rollback followed by thermal relaxation and basin inversion the sediment supply started from the continental arcs lying south of the mahakoshal basin furthermore the present study strengthens the mechanism of subduction related outgrowth of columbia along its continental margins and implies that the citz is a major precambrian crustal boundary that began as a mahakoshal back arc rift by northward subduction

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

oxygenation as a driver of the great ordovician biodiversification event the largest radiation of phanerozoic marine animal life quadrupled genus level diversity towards the end of the ordovician period about 450 million years ago a leading hypothesis for this great ordovician biodiversification event is that cooling of the ordovician climate lowered sea surface temperatures into the thermal tolerance window of many animal groups such as corals a complementary role for oxygenation of subsurface environments has been inferred based on the increasing abundance of skeletal carbonate but direct constraints on atmospheric o2 levels remain elusive here we use high resolution paired bulk carbonate and organic carbon isotope records to determine the changes in isotopic fractionation between these phases throughout the ordovician radiation these results can be used to reconstruct atmospheric o2 levels based on the o2 dependent fractionation of carbon isotopes by photosynthesis we find a strong temporal link between the great ordovician biodiversification event and rising o2 concentrations a pattern that is corroborated by o2 models that use traditional carbon sulfur mass balance we conclude that that oxygen levels probably played an important role in regulating early palaeozoic biodiversity levels even after the cambrian explosion an increase in biodiversity 450 million years ago coincided with a rise in atmospheric oxygen concentrations suggests a geochemical analysis oxygen availability may have thus helped spur the radiation alongside climatic cooling

the diversification of paleozoic fire systems and fluctuations in atmospheric oxygen concentration by comparing silurian through end permian 250 million years myr charcoal abundance with contemporaneous macroecological changes in vegetation and climate we aim to demonstrate that long term variations in fire occurrence and fire system diversification are related to fluctuations in late paleozoic atmospheric oxygen concentration charcoal a proxy for fire occurs in the fossil record from the late silurian 420 myr to the present its presence at any interval in the fossil record is already taken to constrain atmospheric oxygen within the range of 13 to 35 the fire window herein we observe that as predicted atmospheric oxygen levels rise from 13 in the late devonian to 30 in the late permian so too fires progressively occur in an increasing diversity of ecosystems sequentially data of note include the occurrence of charcoal in the late silurian early devonian indicating the burning of a diminutive dominantly rhyniophytoid vegetation an apparent paucity of charcoal in the middle to late devonian that coincides with a predicted atmospheric oxygen low and the subsequent diversification of fire systems throughout the remainder of the late paleozoic first fires become widespread during the early mississippian they then become commonplace in mire systems in the middle mississippian in the pennsylvanian they are first recorded in upland settings and finally based on coal petrology become extremely important in many permian mire settings these trends conform well to changes in atmospheric oxygen concentration as predicted by modeling and indicate oxygen levels are a significant control on long term fire occurrence

geochemistry of mesoproterozoic sedimentary rocks of upper vindhyan group southeastern rajasthan and implications for weathering history composition and tectonic setting of continental crust in the northern part of indian shield abstract the upper vindhyan succession of southeastern rajasthan is divisible into kaimur rewa and bhander groups the major and trace element including rare earth elements data of the upper vindhyan shales and sandstones are investigated to determine the weathering history composition and tectonic setting of mesoproterozoic continental crust cia chemical index of alteration values a cn k plot a al2o3 cn cao na2o k k2o and depletion in u na2o cao sr and ba suggest that the source area experienced moderate to high degree of chemical weathering under warm and humid conditions provenance modeling indicates that the kaimur sandstones are best modeled with a mixture having 40 granitic gneiss 20 tonalite trondhjemite granodiorite ttg 20 mafic enclaves and 20 berach granite of the banded gneissic complex bgc a mixture of 60 granitic gneiss 20 mafic enclaves and 20 berach granite of the bgc can model the rewa and bhander groups it is suggested that the upper vindhyan sedimentation commenced at the time of delhi sausar orogeny at about 1100 1000 ma the orogenic movements uplifted the parts of old continental crust in the bgc terrain creating positive areas which exposed older crustal blocks containing ttg as important component the debris of kaimur sandstone probably derived from these uplifted blocks as indicated by palaeocurrent data the rewa and bhander formations were derived from bundelkhand granitic gneiss complex bggc occurring to the north of the basin and or the chotanagpur granitic gneiss complex cggc of eastern indian shield the derivation of lower and upper groups of vindhyan succession from different source terrains of identical composition suggests that at the time of vindhyan sedimentation the bgc of rajasthan the bggc of central india and the cggc of eastern india had similar lithological composition this implies that well before the origin of the vindhyan basin these discrete terrains evolved as a single unit that existed as a mesoarchaean nucleus in the northern part of the indian shield

mo ni and organic carbon isotope signatures of the mid late mesoproterozoic oxygenation abstract this study performed a redox sensitive trace element rste and organic carbon isotope investigation on the shallow section of 1 2 ga bijaigarh shale kaimur group vindhyan supergroup the results demonstrate that unlike the coeval deeper section in which mo and ni concentrations are several folds higher compared to the upper continental crust ucc the shallow section contains mo and ni equivalent to the upper continental crust ucc this spatially heterogeneous burial of mo and ni is very similar to the modern stratified basins i e black sea and cariaco basin where ni and mo composition of the sediments underlying a shallow oxic water column is comparable to the ucc however the deeper sediments underlying the anoxic euxinic contains several folds higher mo and ni compared to the ucc bulk precipitation of mo in a hydrosphere is mainly controlled by sulphide present in the anoxic euxinic layers of the water column on the other hand ni precipitation is generally controlled by oxygenic primary productivity though the shallow section of the bijaigarh shale is depleted in ni a significant correlation between ni and toc is still relevant and indicates an oxygen rich surface water layer for the respective palaeohydrosphere furthermore 13c org values between 32 0 and 30 4 from the shallow section suggests that the organic carbon exported into the sediments during the bijaigarh shale deposition was primarily derived from oxygenic photosynthesis in the concurrent surface water layers

evidence of wildfires and elevated atmospheric oxygen at the frasnian famennian boundary in new york usa implications for the late devonian mass extinction the devonian period experienced significant fluctuations of atmospheric oxygen o2 levels 25 13 for which the extent and timing are debated also characteristic of the devonian period at the frasnian famennian f f boundary is one of the big five mass extinction events of the phanerozoic fossilized charcoal inertinite provides a record of wildfire events which in turn can provide insight into the evolution of terrestrial ecosystems and the atmospheric composition here we report organic petrology programmed pyrolysis analysis major and trace element analyses and initial osmium isotope osi stratigraphy from five sections of upper devonian f f interval from western new york usa these data are discussed to infer evidence of a wildfire event at the f f boundary based on the evidence for a wildfire at the f f boundary we also provide an estimate of atmospheric o2 levels of 23 25 at this interval which is in agreement with the models that predict elevated po2 levels during the late devonian this coupled with our os isotope records support the currently published osi data that lacks any evidence for an extra terrestrial impact or volcanic event at the f f interval and therefore to act as a trigger for the f f mass extinction the elevated o2 level at the f f interval inferred from this study supports the hypothesis that pco2 drawdown and associated climate cooling may have acted as a driving mechanism of the f f mass extinction

study of the west gondwana floras during the late paleozoic a paleogeographic approach in the parana basin brazil abstract the late paleozoic in west gondwana was a period of significant climatic changes ranging from a glacial climate in the late carboniferous to a semi arid climate in the late permian the floristic province of gondwana in the parana basin was directly affected by such changes and underwent a transformation regarding composition and geographic distribution thus the climatic phases were divided into three intervals phase a containing interglacially developed flora phase b containing floras of immediate post glacial temperate climates and phase c identified with floras related to the decline of dryness regarding their geographical distribution the floras were concentrated in the far northern and far southern portions of the basin during the glacial interval and with a gradual increase in temperature went on to occupy the entire basin finally we can see that the floras located in the argentinean portion of west gondwana are older and have greater species diversity than those present in the parana basin and africa during phase a in phase b there is a decline of argentinean flora species a large increase in the parana basin floras and an average increase in african floras in the final stage the floristic province no longer exists in argentina the flora of the parana basin also suffers a decrease of specimens and the african flora undergoes its moment of greatest development such diversity change also reflects a west to east migration throughout the late carboniferous

re os depositional age for black shales from the kaimur group upper vindhyan india abstract proterozoic sedimentary deposits from the vindhyan supergroup central india are excellent archives of paleo environmental conditions meaningful interpretation of these geological signatures and their global correlation requires depositional age information for the sediments data on which are limited for the upper vindhyan sediments in this work re os isotopic study of the bijaigarh shale kaimur group from the upper vindhyan has been carried out to infer their depositional age and paleo hydrological conditions the re os isochron for the bijaigarh shale a lagoonal deposit with an open ocean connection provides a depositional age of 1210 52 ma model 3 mswd 69 n 15 2 this age for the kaimur group is younger by 400 ma than the underlying semri group age 1600 ma confirming existence of a long sedimentary hiatus between the two groups the isochron derived initial 187os 188os osi ratio for these shales 0 6 is higher than those reported for mesoproterozoic marine shales 0 3 from other global margins osi ratios of shales could be regulated by regional paleo hydrological conditions osmium mass balance calculations for the restricted basin of the bijaigarh shale show that a minor increase in freshwater influx as low as 2 4 i e salinity change by 0 8 psu to the euxinic deep water of the basin is sufficient to elevate osi ratio from 0 3 marine value to 0 6 osi ratio of the lagoonal shale in contrast to lagoonal shales the osi ratios of marine shales seem to mimic the seawater 187os 188os during their deposition period compilation of marine osi ratios shows coarse synchrony between temporal changes in osi during the proterozoic eon and the atmospheric oxygen level pointing to the dominant role of oxidative continental weathering on paleo seawater 187os 188os ratio