controls of eustasy and diagenesis on the 238u 235u of carbonates and evolution of the seawater 234u 238u during the last 1 4 myr using a leaching protocol designed for the study of u isotopes in recent carbonates we measured the u isotope composition both 238 u 235 u and 234 u 238 u of modern and ancient corals n 6 a limestone and a dolostone as well as 43 shallow water carbonate sediments from the odp leg 166 site 1009 drill core on the slope of the bahamas platform although bulk corals record the seawater 238 u value within 0 02 differences of up to 0 30 in the 238 u of individual leachates suggest a control of the coral structure and a more positive 238 u 235 u ratio in the centers of calcification the drill core 238 u data shows that the 238 u 235 u ratio of shallow water carbonates is controlled mainly by 1 variations in sea level through the mixing of different amounts of platform derived sediments with 238 u 0 50 0 60 heavier than seawater and pelagic sediments with seawater like 238 u values 2 authigenic u enrichment via pore watercirculation and u reduction both on the platform and down to 5 m below the surface mbsf after deposition of the sediment and to a lesser extent by 3 early diagenetic processes i e carbonate dissolution and or recrystallization during sediment burial the global effect of these processes leaves the 238 u values of shallow water carbonates offset relative to that of seawater by carbonates sw 0 24 0 06 95 ci including all samples this shift can be used in seawater paleoredox reconstructions based on carbonates deposited on shallow water platform shelf and slope environments i e most of the carbonate sedimentary record prior to the mesozoic to account for the average effect of carbonate diagenesis assuming that the 238 u 235 u ratio of carbonate platform sediments directly records the seawater 238 u 235 u ratio would underestimate the extent of ocean seafloor anoxia by at least a factor 10 the rapid fluctuations in 238 u values due to sea level changes i is a factor that should be considered before interpreting 238 u variations as reflecting changes in oceanic paleoredox conditions and ii reinforces the need for statistically meaningful data sets the 234 u data suggest that the 234 u 238 u ratio of the seawater has remained within 20 of the modern seawater value during the last 1 1 4 myr furthermore we find that small scale 1 15 variations in seawater 234 u mirror sea level changes during the penultimate glacial interglacial period 140 to 200 ka thus confirming the record of lower 234 u sw during periods of low sea level stand and expanding it to at least the last two glacial interglacial events i e 0 23 ma such fluctuations in 234 u initial values should be taken into account when screening carbonate sediments u th ages on the basis of the initial 234 u 238 u ratios of the samples

uranium stable isotope fractionation in the black sea modern calibration of the 238 u 235 u paleo redox proxy abstract the isotopic compositions of redox sensitive metals including uranium u in marine sediments have recently emerged as powerful diagnostic tracers of the redox state of the ancient ocean atmosphere system reliable interpretation of sedimentary isotopic information requires a thorough understanding of the environmental controls on isotopic fractionation in modern anoxic environments before being applied to the paleo record in this study the relationship between ocean anoxia and the isotopic fractionation of u was investigated in the water column and sediments of the black sea the world s largest anoxic basin paired measurements of 238 u 235 u and u concentration supported by other redox parameters were obtained for water column and sediment samples collected during the 2013 ga04n geotraces expedition to the black sea removal of u from the water column occurs during the redox transition of soluble u vi to relatively insoluble u iv resulting in up to 43 of u being removed from solution in euxinic bottom waters uranium reduction and removal is accompanied by a progressive shift in 238 u 235 u towards isotopically light values in the water column as heavier 238 u is preferentially exported to sediments over lighter 235 u this gives rise to apparent isotope enrichment factors of e 0 63 0 09 and e 0 84 0 11 when u removal is modelled by rayleigh and closed system equilibrium isotope fractionation respectively these e values fall within the range determined for bacterial u reduction experiments and together with a striking correlation between the distributions of u and h 2 s implicate microbially mediated u vi u iv reduction as the primary mechanism controlling u isotopic shifts in the black sea the 238 u 235 u of underlying sediments is related to the the 238 u 235 u of black sea bottom waters through the isotope enrichment factor of the u reduction reaction but the relationship between sedimentary and water column 238 u 235 u is complicated by mass transport processes and the modelled e values may underestimate the true isotope enrichment factors these new results for the black sea provide important constraints on the use of 238 u 235 u as a proxy of the redox state of ancient oceans

timing of recovery from the end permian extinction geochronologic and biostratigraphic constraints from south china four volcanic ash beds bracket the early middle triassic boundary as defined by conodont biostratigraphy in a stratigraphic section in south china high precision u pb dates of single zircons allow us to place the early to middle triassic olenekian anisian boundary at 247 2 ma magnetic reversal stratigraphy allows global correlation the new dates constrain the early triassic interval characterized by delayed biotic recovery and carbon cycle instability to 5 m y this time constraint must be considered in any model for the end permian extinction and subsequent recovery

oceanic redox evolution across the end permian mass extinction at shangsi south china abstract the end permian mass extinction epme was the most severe extinction event of the phanerozoic to investigate oceanic redox conditions around the epme we conducted a series of geochemical analyses including iron speciation trace element geochemistry total organic carbon toc and nitrogen isotopes of kerogen 15nkero around the epme at the shangsi section south china three intervals with different redox conditions can be distinguished based on iron speciation during the first interval early and middle changhsingian bottom waters were pervasively euxinic in the second interval late changhsingian and the epme bottom water fluctuated between oxic and anoxic but non sulfidic conditions with the oxic mode becoming increasingly predominant over time during the third interval following the epme bottom waters appeared to have been consistently anoxic although again not pervasively euxinic this redox history is supported by enrichments in the authigenic fraction of redox sensitive elements these relatively high 15nkero values 1 0 corresponding with changhsingian euxinia suggest reducing bottom waters did not impinge on the photic zone the shift to values near 0 within and above the epme indicates an ecological expansion of diazotrophs stratigraphic trends of nixs cdxs pxs and toc indicate that primary productivity was highest in the first interval coinciding with euxinic bottom water then decreased during the lower part of interval 2 and remained at low level through the remainder of the studied section the temporal relationship between redox condition and primary productivity suggests that euxinia was supported by high productivity and carbon export in the early changhsingian the expansion of n2 fixation coincides closely with the previously documented warming of the ocean surface at shangsi and may be related to reduced oceanic circulation and suppressed vertical mixing the temporal distribution of deepwater anoxia and euxinia suggests that they were not primary causes for the extinction of benthos at shangsi

early triassic seawater sulfate drawdown abstract the marine sulfur cycle is intimately linked to global carbon fluxes atmospheric composition and climate yet relatively little is known about how it responded to the end permian biocrisis the largest mass extinction of the phanerozoic here we analyze carbonate associated sulfate cas from three permo triassic sections in south china in order to document the behavior of the c s cycle and its relationship to marine environmental changes during the mass extinction and its aftermath we find that 34 s cas varied from 9 to 44 at rates up to 100 myr 1 during the griesbachian smithian substages of the early triassic we model the marine sulfur cycle to demonstrate that such rapid variation required drawdown of seawater sulfate concentrations to 4 mm and a reduction in its residence time to 200 kyr this shorter residence time resulted in positive covariation with 13 c carb due to strong coupling of the organic carbon and pyrite burial fluxes carbon and sulfur isotopic shifts were associated with contemporaneous changes in climate marine productivity and microbial sulfate reduction rates with negative shifts in 13 c carb and 34 s cas linked to warming decreased productivity and reduced sulfate reduction sustained cooling during the spathian re invigorated oceanic overturning circulation reduced marine anoxia and limited pyrite burial as seawater sulfate built to higher concentrations during the spathian the coupling of the marine c and s cycles came to an end and a general amelioration of marine environmental conditions set the stage for a recovery of invertebrate faunas variation in seawater sulfate during the early triassic was probably controlled by climate change possibly linked to major eruptive phases of the siberian traps

biogeomorphology revisited looking towards the future although biogeomorphological research is well established with many studies on a range of two way interrelations between organisms and geomorphology in different environments there is little consensus over what constitutes biogeomorphology why it might be useful and where it is heading starting with definitions of core biogeomorphic processes we consider the need for future biogeomorphological studies to evaluate the crucial links between bioprocesses biological community dynamics and inorganic earth surface processes five key applications of biogeomorphological research are identified the roles of organisms in environmental reconstruction trace fossil analysis extraterrestrial geomorphology environmental engineering and the built environment some key research directions and methodological challenges for future biogeomorphological research include expanding the spatial and temporal coverage of datasets investigating the role of bioprocesses in landform development tackling scale issues investigating the relevance of nonlinear dynamical ideas to biogeomorphology and developing better sampling and monitoring techniques for bioprocesses

stress transfer during three sequential moderate earthquakes along the central calaveras fault california seismic and geodetic information on three sequential moderate earthquakes the 1979 m5 9 coyote lake the 1984 m6 2 morgan hill and the 1988 m5 1 alum rock along the central calaveras fault is used to examine how tractions on fault segments are transferred from one fault segment to the other geodetic data obtained before and after each earthquake are inverted for slip at depth the perturbed stress field induced by each earthquake is calculated using 3 d elastic dislocation theory although only long wavelength features of the slip distributions are well resolved the model suggests that the distribution of slip is nonuniform the largest slips tend to occur in regions having relatively few aftershocks or near the hypocenter according to the model the coyote lake earthquake induced 0 1 1 bar 0 01 0 1 mpa shear stress across the northern part of the morgan hill segment and only about 0 1 bar at the hypocenter of the morgan hill mainshock a shear stress of 0 5 bar was induced by the morgan hill earthquake at the hypocenter of the alum rock mainshock the average stress drops for the coyote lake morgan hill and alum rock earthquakes are estimated to be 30 25 and 15 bars respectively thus the earthquake induced shear stress of 0 1 0 5 bar at the hypocenter of the next earthquake is only a few percent of the total stress drop and cannot be solely responsible for the occurrence of the sequential earthquakes however the induced shear stress can trigger the adjacent earthquakes in the sense that adjacent earthquakes would have occurred at a later time if there was no such coseismic stress transfer it is inferred that fault geometry may influence the local stress field thereby initiation and termination of the rupture but not the regional stress accumulation

size variation of conodonts during the smithian spathian early triassic global warming event the early triassic smithian spathian boundary ssb crisis coincided with an episode of extreme warmth a high resolution stratigraphic framework comprising six conodont zones is provided in the jiarong section nanpanjiang basin in south china detailed size measurements of 441 conodont elements of the closely related genera neospathodus triassospathodus and novispathodus show for the first time that this clade suffered a temporary but significant size reduction during the ssb crisis the size reduction of conodonts was probably caused by an episode of global warming

meteoric burial diagenesis of middle pennsylvanian limestones in the orogrande basin new mexico water rock interactions and basin geothermics abstract stable isotopic compositions of cyclic middle pennsylvanian gobbler formation limestones record two stages of alteration early open system meteoric diagenesis during episodic subaerial exposure stabilized cycle top carbonate in the presence of meteoric fluid at high water rock ratios 400 4000 subsequent closed system burial diagenesis stabilized meteoric and residual marine carbonate in the presence of connate pore fluids at elevated temperatures to 150 c and low water rock ratios 1 0 10 present 18o distributions record normal to high geothermal gradients 27 86 c km during burial stabilization high basin center geothermal gradients probably resulted from elevated heat flow due to rapid crustal extens on and subsidence of the orogrande basin during the late pennsylvanian a dike injection lithospheric extension model with 40 oceanization best accounts for subsidence and geothermal patterns of the orogrande basin

lower triassic carbonate δ238u record demonstrates expanded oceanic anoxia during smithian thermal maximum and improved ventilation during smithian spathian boundary cooling event abstract the smithian spathian boundary ssb transition was recently identified as a major biocrisis on the road to marine ecosystem recovery following the end permian mass extinction marine anoxia is hypothesized to have played an important role in the ssb biocrisis however an understanding of the relationship of this biocrisis to contemporaneous marine redox conditions has been hampered by limited knowledge of the timing duration and extent of anoxia during the smithian spathian s s transition here we present a high resolution carbonate u isotope record from the jiarong section of south china that spans the mid smithian to mid spathian interval this record shows persistent negative 238u values averaging 0 56 in the late smithian followed by a rapid positive shift from 0 78 to 0 10 across the ssb and then a more gradual shift back to lower 238u values in the early to mid spathian u isotope mass balance modeling suggests that the global area of anoxic seafloor expanded strongly during the late smithian and the early to mid spathian but contracted sharply during the s s transition this redox pattern shows an excellent correspondence to previously published tropical sea surface temperature sst records with peak oceanic anoxia coinciding with the smithian thermal maximum stm and diminished anoxia during a pronounced global cooling event at the ssb although paleontological records commonly do not distinguish between terminations during the late smithian and ssb we hypothesize that the ssb biocrisis which was marked by sharp diversity losses among conodonts ammonoids and other marine invertebrates was primarily associated with the stm in which case oceanic anoxia is likely to have been a major stressor of mid olenekian marine biotas

timing of the early triassic carbon cycle perturbations inferred from new u pb ages and ammonoid biochronozones based on analyses of single thermally annealed and chemically abraded zircons a new high precision u pb age of 251 22 0 20 ma is established for a volcanic ash layer within the kashmirites densistriatus beds of early smithian age early triassic from the luolou formation northwestern guangxi south china this new date together with recalculated uncertainties of previous u pb ages from the same section m ovtcharova h bucher u schaltegger t galfetti a brayard j guex new early to middle triassic u pb ages from south china calibration with ammonoid biochronozones and implications for the timing of the triassic biotic recovery earth planet sci lett 243 2006 463 475 allows constraining the time framework of the early triassic and leads to an estimated duration of i ca 0 7 0 6 my for the smithian and ii a maximal duration of ca 1 4 0 4 my for the griesbachian dienerian time interval the new u pb age considerably reduces the absolute age gap comprised between the permian triassic boundary and the spathian late early triassic the new age framework provides the basis for the calibration of a new carbonate carbon isotope and ammonoid records of the early triassic luolou fm which in turn are of high significance for global correlations and for carbon cycle modeling this calibration indicates that the most significant and fastest early triassic carbon isotope perturbations occur between the earliest smithian and the early spathian thus spanning a time interval of about 1 my whatever caused these carbon cycle shifts of high intensity and short duration there is evidence for connections between these fluctuations the pulsate recovery of ammonoids and conodonts as well as climate changes

uranium isotope evidence for an expansion of marine anoxia during the end triassic extinction the end triassic extinction coincided with an increase in marine black shale deposition and biomarkers for photic zone euxinia suggesting that anoxia played a role in suppressing marine biodiversity however global changes in ocean anoxia are difficult to quantify using proxies for local anoxia uranium isotopes 238u in caco3 sediments deposited under locally well oxygenated bottom waters can passively track seawater 238u which is sensitive to the global areal extent of seafloor anoxia due to preferential reduction of 238u vi relative to 235u vi in anoxic marine sediments we measured 238u in shallow marine limestones from two stratigraphic sections in the lombardy basin northern italy spanning over 400 m we observe a 0 7 negative excursion in 238u beginning in the lowermost jurassic coeval with the onset of the initial negative 13c excursion and persisting for the duration of subsequent high 13c values in the lower middle hettangian stage the 238u excursion cannot be realistically explained by local mixing of uranium in primary marine carbonate and reduced authigenic uranium based on output from a forward model of the uranium cycle the excursion is consistent with a 40 100 fold increase in the extent of anoxic deposition occurring worldwide additionally relatively constant uranium concentrations point toward increased uranium delivery to the oceans from continental weathering which is consistent with weathering induced eutrophication following the rapid increase in pco2 during emplacement of the central atlantic magmatic province the relative timing and duration of the excursion in 238u implies that anoxia could have delayed biotic recovery well into the hettangian stage

global ocean redox variations across the smithian spathian boundary linked to concurrent climatic and biotic changes abstract the smithian spathian boundary ssb was an interval characterized by a major global carbon cycle perturbation climatic cooling from a middle late smithian boundary hyperthermal condition and a major setback in the recovery of marine necto pelagic faunas from the end permian mass extinction although the ssb has been linked to changes in oceanic redox conditions key aspects of this redox variation e g duration extent and triggering mechanisms and its relationship to coeval climatic and biotic changes remain unresolved here we report a high resolution middle smithian to middle spathian u isotope 238u record based on marine carbonates of the zuodeng south china and jesmond british columbia sections to investigate the timing and global extent of ocean redox variation across the ssb our 238u record reveals values similar to or slightly heavier than modern seawater 0 39 during the middle smithian a rapid negative shift to highly negative values during the early late smithian a positive shift at the ssb and a rapid shift back to more negative values in the early middle spathian a simple u isotope mass balance modeling suggests that the global area of anoxic seafloor expanded strongly during the late smithian and the early middle spathian covering 11 of total seafloor area but that it contracted sharply during the ssb 2 the redox pattern documented by our 238u record shows a good first order correspondence to tropical sea surface temperature sst data for the smithian spathian in particular peak anoxia coincided with the middle late smithian boundary hyperthermal event and diminished anoxia with a pronounced decline in ssts at the ssb the temporal correlation between anoxia and low biodiversity levels of many marine clades e g conodonts and ammonoids during the late smithian indicates that oceanic anoxia may have played a role in the ssb biocrisis

uranium isotope fractionation in saanich inlet a modern analog study of a paleoredox tracer abstract uranium isotope fractionation was studied in the sediment and water of saanich inlet a seasonally anoxic fjord on the east coast of vancouver island the concentration of dissolved u is the same above and below the redoxcline at 120 m depth with an average 238u value of 0 45 0 06 2 s e which is indistinguishable from seawater values reported in other studies this finding is consistent with water renewal times for the inlet that are roughly seasonal in frequency thus hiding the impact of the u losses to the anoxic sediment of the inlet complete digests of the anoxic sediment yielded higher 238u values than seawater 0 21 0 11 2 s e by contrast complete digests of the sediment trap samples yielded lower 238u values than seawater 0 52 0 10 2 s e and marine plankton from the inlet yielded the lowest 238u value of 1 24 0 17 2 cross plots of 238u and 234u vs th u reveal strong correlations indicative of two component mixing when the data from traps and anoxic inlet sediment are combined one mixing end member is fractionated uranium of seawater origin with a 238u value of 0 17 0 14 2 the other is detrital uranium with a 238u value of 0 83 0 12 2 the detrital end member is lower than the range of 238u values reported in the literature for granitoid igneous rocks 0 44 to 0 17 2 telus et al 2012 suggesting that continental weathering fractionates uranium isotopes with preferential release of 238u development and application of u isotopes as a paleoredox proxy has its basis in the nuclear volume fractionation the data from saanich inlet meets this expectation with a positive fractionation factor aq vi sed iv of 0 62 0 17 2 calculated as the difference in 238u between authigenic u in anoxic sediments and sediment traps 0 17 and u dissolved in seawater 0 45 however it is widely believed that u vi reduction in the marine environment occurs on the surfaces of particles and that the negative isotope effect associated with u vi sorption to plankton seawater plankton 0 79 0 17 2 opens up the possibility that the particulate pool of seawater derived u vi is fractionated from the dissolved pool accordingly the reduction of u vi in the marine environment might involve two steps 1 u vi sorption to particles with a negative fractionation and 2 reduction to u iv on particles with a positive fractionation environmental factors that are not yet well understood may influence the relative reaction rates for the two steps thus affecting the magnitude and sign of the overall fractionation this has the potential to explain conflicting results reported for u vi reduction experiments in the literature laboratory and field where both positive and negative fractionations have been observed and in some instances no fractionation at all variation in the fractionation factor has the potential to complicate application of u isotopes as a paleoredox proxy but this study and a study of the black sea romaniello 2012 give the same results within their respective uncertainties suggesting that 0 62 0 17 2 is a robust assessment of the apparent u isotope fractionation factor associated with reductive deposition of seawater u vi in both anoxic and euxinic marine sediments of the present day

latest permian to middle triassic redox condition variations in ramp settings south china pyrite framboid evidence a detailed 10 m y redox history of changhsingian to anisian latest permian to middle triassic oceans in ramp settings is reconstructed based on framboidal pyrite analysis from south china the result shows that the well established phenomenon of intense ocean euxinia anoxia is faithfully recorded in pyrite framboid data three major euxinia anoxia episodes namely the end changhsingian to end smithian middle to late spathian and early to middle anisian have been recognized from the ramp successions the first reducing episode is subdivided into four subepisodes permian triassic boundary griesbachian dienerian boundary earliest smithian and end smithian redox variations broadly track other oceanographic proxies euxinia anoxia episodes coincide with positive excursions of conodont ce anomalies negative excursions of 34scas carbonate associated sulfate increases in sea surface temperature and negative excursions of 13c in most cases however euxinia anoxia near the dienerian smithian boundary coincided with positive excursions of 13c and a general cooling period this exception may be the result of locally developed water column anoxia the permian triassic boundary subepisode witnessed two ephemeral euxinia anoxia events separated by a dysoxic to oxic period the former together with a rapid increase in sea surface temperature up to 8 c may have been responsible for the biodiversity crisis while the latter anoxic event destroyed ecosystem trophic structures in addition to the permian triassic boundary euxinia anoxia event which spread over habitats in all oceans the spathian and anisian euxinia anoxia episodes also prevailed in global oceans variation of the oxygen minimum zone are suggested as the driving mechanism that facilitated the movement of oxygen poor water columns in various paleogeographic settings over this critical period

transient and stepwise ocean oxygenation during the late ediacaran shuram excursion insights from carbonate δ238u of northwestern mexico abstract the ediacaran shuram excursion se was a key episode in the history of atmospheric and oceanic oxygenation that has also been linked to contemporaneous bioevolutionary events however key aspects of the redox state of ediacaran oceans during the se remain in doubt here the uranium isotope compositions 238u of marine carbonates from sonora northwestern mexico were measured to investigate ocean oxygenation during the se we found that the se in sonora is characterized by a shift toward higher 238u values from 0 7 to 0 3 consistent with a major oxygenation event that has now been documented in widely separated coeval upper ediacaran sections including the doushantuo formation in south china the bol shoy patom formation in siberia and the johnnie formation in california in the sonora succession this 238u shift exhibits a 0 8 myr lag relative to the 13ccarb excursion that defines the se to account for these observations we propose a two step oceanic oxygenation model for the se 1 initial oxidation of an aqueous reductant e g dissolved organic carbon that resulted only in a shift of 13ccarb from 5 to 3 and 2 subsequent oxidation of methane or particulate organic matter that caused a continuation of the negative shift in 13ccarb from 3 to 12 as well as a positive excursion of 238u due to progressive oceanic oxygenation this transient period of enhanced oceanic oxygenation of the late ediacaran ocean which may have promoted the evolution of early metazoans terminated after 5 0 to 6 5 myr

global seawater redox trends during the late devonian mass extinction detected using u isotopes of marine limestones abstract the late devonian extinction ranks as one of the big five phanerozoic extinctions affecting up to 80 of marine species and is characterized by two major extinction events that are separated by 238 u across a 7 my interval of well dated upper devonian marine limestones from the devil s gate formation in nevada usa the measured 238 u curve shows no co variation with local sediment derived redox trends water depth dependent facies changes redox sensitive metals toc or diagnostic elemental ratios from these relationships we infer that the 238 u curve represents global seawater redox conditions two negative 238 u excursions indicating more reducing seawater are observed with durations of 3 8 my late frasnian and 1 1 my early famennian respectively steady state modeling of the observed 0 2 to 0 3 shifts in 238 u points to a 5 15 increase in the total area of anoxic seafloor during these excursions the late frasnian negative excursion is broadly coincident with the first extinction event late rhenana zone or lower kellwasser event whereas the early famennian negative excursion lower middle triangularis zones occurs after the most intense frasnian famennian boundary f f extinction event upper kellwasser event compilations of local sediment redox conditions from upper devonian marine deposits with conodont zone level age control indicates that the extinction events were coincident with widespread anoxic deposits accumulating in subtropical epeiric sea and some open ocean settings supporting previous interpretations that widespread marine anoxia had an important influence on the late devonian extinctions the temporal relationships between global ocean redox trends represented by the 238 u curve and the newly compiled subtropical marine redox sediment trends indicates that local epeiric seawaters carried a similar u isotopic composition as the open ocean for the majority of the studied interval except for a brief interval

a cenozoic seawater redox record derived from 238u 235u in ferromanganese crusts oceanic oxygen levels are projected to drop in certain areas due to warming climate but the net effect to the overall ocean redox state is difficult to predict here we measured the stable uranium isotope composition 238u 235u in globally representative hydrogenous ferromanganese crusts in order to reconstruct the redox evolution of the global ocean throughout the cenozoic samples averaging 3 myr intervals have analytically indistinguishable 238u 235u throughout the cenozoic combined with a u isotope mass balance model we suggest that the overall ocean redox state has remained remarkably stable on million year time scales throughout the cenozoic despite large surface temperature fluctuations during this time this suggests that stabilizing feedbacks for example nutrient limitation in low oxygen zones may have prevented dramatic large scale shifts in oxygen levels in the ocean however the fe mn crust record will be unlikely to reflect rapid perturbations in ocean redox state to investigate these events sediment archives with faster accumulation rates and redox proxies with faster response time must be explored

redox conditions through the permian triassic transition in the upper khuff formation saudi arabia abstract the permian triassic boundary interval was identified in an outcrop in central saudi arabia within a 32 m thick succession of mixed carbonate and siliciclastic sediments this stratigraphic section was deposited in a coastal to shallow marine environment on the southern margin of the tethys ocean an area that has not previously been the focus of rare earth element ree and redox sensitive trace element studies geochemical data from this region may potentially inform ongoing discussions about redox conditions along the tethys margin during the permian triassic transition to better understand redox conditions on the southern tethyan margin we analyzed a total of 33 samples from the ptb interval in the upper part of the khuff formation for major and trace elements and rees the thorium uranium ratio th u uranium u and vanadium v content and cerium ce anomaly all serve as potential redox indicators multivariate analysis principal component analysis and linear regression of the elemental composition of the samples suggests that these redox indicators are predominantly associated with the detrital fraction th u ratios were generally 2 u and v concentrations do not show any significant authigenic enrichment and ce anomalies fluctuates around 1 0 collectively these results indicate that the distribution of redox indicators in this section is mainly controlled by the detrital composition and that shallow marine waters at the time of deposition were oxic comparing our results with data from other tethys sections reveals that redox conditions in shallow marine environments were heterogeneous in the aftermath of the permian triassic extinction and may reflect primarily local controls

uppermost permian to lower triassic conodont successions from the enshi area western hubei province south china abstract we present recent study results of the lower triassic conodont succession from the ganxi and jianshi areas of enshi city western hubei province south china which were situated on a carbonate ramp at the northeastern margin of the upper yangtze platform therein the uppermost permian to lower triassic succession is well exposed and yielded abundant conodonts a total of nine conodont zones are differentiated 1 clarkina yini zone 2 clarkina meishanensis zone 3 hindeodus changxingensis zone 4 hindeodus parvus zone 5 hindeodus postparvus zone 6 clarkina planata zone 7 neoclarkina aff discreta zone 8 neospathodus dieneri zone and 9 novispathodus waageni zone the ns dieneri m1 ns dieneri m2 and ns dieneri m3 subzones have also been distinguished within the ns dieneri zone and the nv waageni eowaageni and nv waageni waageni subzones are recognizable within the nv waageni zone in jianshi most of the zones occur in succession but the c planata zone is a local ecozone reflecting deeper water biofacies during h postparvus zone time in the jianshi section the permian triassic boundary is placed at bed 136 2 based on the appearance of hindeodus parvus immediately above the disappearance of changhsingian taxa while the induan olenekian boundary iob is drawn at bed 225 40 cm based on the first appearance of nv waageni eowaageni within the upper range of the ns dieneri zone indices the enshi conodont zones overall correlate well with those recognized elsewhere in south china and worldwide

high sediment input and possible oceanic anoxia in the pelagic panthalassa during the latest olenekian and early anisian insights from a new deep sea section in ogama tochigi japan abstract ecosystem recovery from the end permian mass extinction took around 5 million years of the early triassic in the pelagic deep sea of the superocean panthalassa deposition of bedded chert ceased during this period and instead siliceous claystone lithofacies with minor chert beds was deposited the reappearance of bedded chert around the early middle triassic olenekian anisian boundary oab was assumed to be related to recovery of radiolarian production in the pelagic realm this study reports a new pelagic deep sea section covering the transition from siliceous claystone lithofacies to bedded chert from ogama in tochigi prefecture japan based on conodont and radiolarian biostratigraphy and carbon isotope stratigraphy the ogama section was dated as uppermost olenekian to middle anisian the oab was recognised by the occurrence of the conodont chiosella timorensis while the radiolarian based oab adopted by previous studies on bedded chert in japan was revealed to be within the middle anisian in the ogama section the transition from siliceous claystone lithofacies to bedded chert is in the middle anisian the oab is characterised by black organic rich siliceous claystone which implies oceanic oxygen depletion importantly the linear sedimentation rate of the siliceous claystone lithofacies was found to be higher than that of middle triassic and jurassic bedded chert this shows that increased accumulation of clastic material was an important factor that caused the deposition of siliceous claystone in the pelagic panthalassa at the oab hence the deposition of black siliceous claystone at the oab may have occurred under different conditions from that at the end permian mass extinction which is thought to be a result of diminished biogenic silica production

deriving indicators of soil degradation from soil aggregation studies in southeastern spain and southern france soil degradation is perceived as a major threat in the mediterranean region due to changes in land use and possible future climate change soil aggregation parameters are used here to demonstrate their potential as a key indicator for land degradation studies the monitoring of these indicators offers a means of establishing the vulnerability and resilience of geo ecosystems soil aggregation stability and distribution were studied on soils with an open shrubby vegetation cover from several places in southeastern spain and southern france by applying drop tests and determining aggregate size distributions aspect and vegetation cover were incorporated in the soil sampling several indices were derived from these analyses to indicate the degree of soil aggregation this was done by referencing to a base level of aggregation bare soil aggregation it was found that soil aggregates were more stable and were often coarser under vegetation when compared to their immediate surrounding bare areas a similar slightly less clear effect was noted on n facing exposed slopes when compared to s facing exposed slopes long term changes were found by studying cultivated land abandoned fields and land covered by semi natural vegetation on comparable substrate and comparable land units it is clear that soil aggregation and aggregate stability increases with time years it is argued that soil aggregation indices can be used as a key indicator for degradation processes at a fine scale with implications for runoff and sediment generating processes at the hillslope scale

the early triassic ammonoid recovery paleoclimatic significance of diversity gradients ammonoids recovered much faster than other marine shelly invertebrates after the end permian mass extinction based on a refined global data set at the basin level we investigate the paleobiogeographical global latitudinal and longitudinal diversity patterns in terms of climatic changes during the early triassic such analysis differs from already published qualitative or quantitative studies in that it estimates faunal patterns and endemicity at an ecologically meaningful level of spatial resolution i e at the basin level during the early triassic the global first order trend in increasing ammonoid diversity was accompanied by a progressive change from cosmopolitan to latitudinally restricted distributions this led to the emergence of a clear latitudinal diversity gradient during most of the smithian and spathian stages which entails increased steepness of the sea surface temperature gradient during the late early triassic however two brief episodes of ammonoid cosmopolitanism combined with low global diversity interrupted the first order increasing trend at the very beginning of the smithian and at its very end the longitudinal analysis of smithian distributions indicates a westward decrease of diversity within the tethys which faded away during the spathian analysis of endemicity indicates a rapid biogeographical maturing and structuring of faunas concomitant with the edification of the latitudinal diversity gradient

proterozoic ocean redox and biogeochemical stasis the partial pressure of oxygen in earth s atmosphere has increased dramatically through time and this increase is thought to have occurred in two rapid steps at both ends of the proterozoic eon 2 5 0 543 ga however the trajectory and mechanisms of earth s oxygenation are still poorly constrained and little is known regarding attendant changes in ocean ventilation and seafloor redox we have a particularly poor understanding of ocean chemistry during the mid proterozoic 1 8 0 8 ga given the coupling between redox sensitive trace element cycles and planktonic productivity various models for mid proterozoic ocean chemistry imply different effects on the biogeochemical cycling of major and trace nutrients with potential ecological constraints on emerging eukaryotic life here we exploit the differing redox behavior of molybdenum and chromium to provide constraints on seafloor redox evolution by coupling a large database of sedimentary metal enrichments to a mass balance model that includes spatially variant metal burial rates we find that the metal enrichment record implies a proterozoic deep ocean characterized by pervasive anoxia relative to the phanerozoic at least 30 40 of modern seafloor area but a relatively small extent of euxinic anoxic and sulfidic seafloor less than 1 10 of modern seafloor area our model suggests that the oceanic mo reservoir is extremely sensitive to perturbations in the extent of sulfidic seafloor and that the record of mo and chromium enrichments through time is consistent with the possibility of a mo n colimited marine biosphere during many periods of earth s history

carbon oxygen and strontium isotopes in paleozoic carbonate components an evaluation of original seawater chemistry proxies abstract brachiopods trilobites cements and whole rock matrix material were evaluated for their reliability as proxies of original seawater carbon oxygen and strontium isotope chemistry in this process coeval material was evaluated from individual horizons of formations spanning the permian to cambrian unaltered shells of low mg calcite articulated brachiopods retain original seawater oxygen carbon and strontium isotope compositions as old as late ordovician assessments of older specimens are hampered by a lack of suitable material coeval brachiopod whole rock sets a definitive assessment of cement marine chemistry is difficult due to the paucity of material but despite this caveat cements hold some promise for retaining original carbon and possibly strontium isotope seawater values in contrast the potential of whole rock material as a proxy of original seawater chemistry is quite complex in some but not all instances the carbon isotopic composition of whole rock after detailed scrutiny and evaluation appears to represent an original seawater chemistry signal in a few instances their oxygen isotope compositions reflect original seawater values unlike the stable isotope compositions the strontium isotopes of all studied whole rock material permian to upper cambrian appear not to reflect original seawater chemistry values thus the potential for retaining original seawater isotope chemistry and serving as specific proxies in order of decreasing reliability are 1 unaltered low mg calcite brachiopods c o and sr isotopes 2 pristine marine cements c and sr isotopes and 3 whole rock material c isotopes carbon oxygen and strontium isotope compositions of ordovician trilobites mirror those of coeval unaltered brachiopods cambrian trilobites hold significant promise as an important proxy of original seawater isotope chemistry but further studies are needed to ascertain their full potential the survey of isotopes in some ordovician and cambrian intermediate low mg calcite trilobites demonstrates their potential as an important proxy of original seawater chemistry

conodont diversity and evolution through the latest permian and early triassic upheavals abstract a study of latest permian and early triassic multielement conodonts identifies eight steps in their evolutionary history during an interval when earth s biosphere was highly stressed these steps are 1 gradual decline of families and genera through the changhsingian up to the late griesbachian 2 conodont biofacies change and extinction of tethyan endemic species close to the permian triassic boundary ptb 3 faunal turnover with extinction and origination in the late griesbachian 4 initial radiation in gondolellids and diversification in apparatuses during the dienerian 5 explosive radiation in the early middle smithian 6 major extinction in the late smithian 7 major radiation early in the spathian 8 gradual turnover and decline in the late spathian through early anisian conodontophorids were reduced from five families at the beginning of the changhsingian to three by the ptb and to two late in the griesbachian from the changhsingian to the late griesbachian there was a single multielement apparatus represented in the gondolellidae whereas by the olenekian there were at least twelve given absolute age constraints the conodont recovery in the aftermath of the ptb was extraordinary conodont evolution during the dienerian remains obscure but was very significant in terms of changes in multielement apparatuses in spite of induan extinctions generic diversity generally increased from the ptb up to the late smithian in terms of species genera and multielement apparatuses the acme of triassic conodonts was in the middle smithian and the biggest extinction was in the late smithian after this extinction generic and apparatus diversity quickly returned to high levels marking a significant spathian recovery gradual decline characterized the late spathian and persisted into the early anisian a synthetic summary of the temporal distribution and proposed relationships amongst all known lower triassic conodonts provide an improved foundation for biostratigraphic and biochronologic studies extinction and radiation trends correlate well with sea level changes and sequence boundaries faunal turnovers correspond to lowstands in the late griesbachian late smithian and late spathian and radiations correspond to transgressions in the early griesbachian early smithian and early spathian the trends also correlate with perturbations in the carbon cycle with lower triassic 13c minima corresponding to extinction and faunal turnover and positive values generally occurring during radiations however middle triassic recovery of marine benthos follows a positive maxima and an overall decline in conodont diversity new taxa borinella chowadensis b megacuspa neogondolella griesbachensis and n mongeri are described

physical processes that enhance nutrient transport and primary productivity in the coastal and open ocean of the subarctic ne pacific abstract in comparison to the open ocean several additional processes including coastal upwelling river discharge tidal mixing estuarine circulation and benthic remineralization enhance nutrient supply to the surface waters of the continental shelf in general coastal waters become nitrate limited during the phytoplankton growing season whereas iron and dissolved silicate limit phytoplankton growth in the less productive oceanic waters of the gulf of alaska if coastal processes supply ample amounts of macro and micro nutrients during the growing season diatom communities dominated by species such as skeletomema costatum chaetoceros spp and thalassiosira spp will bloom growth rates of these bloom populations typically range from 0 5 to 1 5 doublings per day which place a high demand on nutrients any transport of coastal waters away from the shelf will enhance productivity in oceanic waters the general circulation of the eastern subarctic pacific does not allow for offshore transport except in special circumstances these include anticyclonic mesoscale eddy formation which can export as much as 5000 km 3 of nutrient rich waters from the shelf in a single eddy and recirculation of waters away from southwestern alaska due to the cyclonic circulation around the western edge of the alaskan gyre recirculation can carry nutrient rich water from the coast to the vicinity of ocean station papa 50 n 145 w within a few months for both eddies and gyre recirculation much of the water being carried into the open ocean lies below the euphotic zone iron enrichment occurs to a depth of at least 1000 m in the gulf of alaska as a result periods of enhanced eddy formation or recirculation may supply iron that enriches the open ocean for several years damming of the columbia river and human uses of its waters have resulted in more winter and less summer discharge of fresh water and dissolved si coastal currents in this area flow north in winter and south in summer as a consequence there has been a net temporal change in si inputs to the ocean since the mid 1970s with about 4 10 9 mol more si flowing north in winter and 9 10 9 mol less si flowing south in summer compared with the early 1900s since silicate limits diatom growth and diatoms are responsible for most carbon export in phytoplankton implications for ocean productivity are significant

large perturbations of the carbon cycle during recovery from the end permian extinction high resolution carbon isotope measurements of multiple stratigraphic sections in south china demonstrate that the pronounced carbon isotopic excursion at the permian triassic boundary was not an isolated event but the first in a series of large fluctuations that continued throughout the early triassic before ending abruptly early in the middle triassic the unusual behavior of the carbon cycle coincides with the delayed recovery from end permian extinction recorded by fossils suggesting a direct relationship between earth system function and biological rediversification in the aftermath of earth s most devastating mass extinction

the smithian spathian boundary late early triassic a review of ammonoid conodont and carbon isotopic criteria abstract the transition from the smithian substage to the spathian substage of the olenekian stage of the late early triassic was a critical time marked by a series of biological and environmental changes during the multimillion year recovery interval following the end permian mass extinction however the smithian spathian boundary ssb does not yet have an agreed definition a shortcoming that complicates high resolution analysis of events during the smithian spathian transition here we review key biostratigraphic i e ammonoid and conodont studies of the smithian and spathian substages in historically important regions e g the canadian arctic for the boreal realm western north america for the eastern panthalassic ocean and more recently re studied locations e g pakistan and india in the southern tethys south china in the eastern tethys as well as the carbon isotope chemostratigraphy of 29 major smithian spathian sections globally key ammonoid genera e g wasatchites anasibirites glyptophiceras and xenoceltites of the late smithian and bajarunia tirolites and columbites of the early spathian conodont species e g scythogondolella milleri novispathodus waageni and borinella buurensis of the late smithian and triassospathodus hungaricus neogondolella aff sweeti and icriospathodus spp of the early spathian and carbonate carbon isotope excursions provide appropriate markers for constraining the ssb use of the first occurrence of the conodont novispathodus pingdingshanensis as a potential marker of the ssb is also discussed based on correlations of biostratigraphic and carbon isotope data globally we propose to revise previous placements of the ssb transition in some sections finally we show that the smithian thermal maximum stm herein named was middle smithian in age and not correlative with the ssb as inferred in some earlier studies and that the ssb coincided with a subsequent major global cooling event

critical stress difference fault orientation and slip direction in anisotropic rocks under non andersonian stress systems abstract the coulomb navier failure criterion is applied to geological faulting in the general three dimensional case of rocks containing arbitrarily oriented strength anisotropies and subject to non andersonian stress systems i e with none of the principal stresses acting in a vertical direction general expressions for the critical stress difference necessary to cause failure as a function of depth are given in terms of material parameters pore fluid pressure orientation of the stress field and orientation of the strength anisotropy the range of angles between a plane of anisotropy and the maximum principal stress direction for which slip occurs along the pre existing anisotropy rather than along a new fault is calculated as a function of depth for different stress regimes when the stress field is non andersonian and or strength anisotropies not containing the intermediate stress direction occur in the rock faulting generally is oblique slip a kinematic classification of faulting is given on the basis of the angle between the strike direction and the slip direction on the fault plane triangular diagrams analogous to those used in petrology are introduced to describe i faulting in isotropic rock subject to arbitrarily oriented stress fields and ii faulting in anisotropic rock when one principal stress direction is vertical the type of faulting as a function of stress field and anisotropy orientation can be read off directly from these diagrams

smithian and spathian early triassic ammonoid assemblages from terranes paleoceanographic and paleogeographic implications early triassic paleobiogeography is characterised by the stable supercontinental assembly of pangea however at that time several terranes such as the south kitakami massif sk south primorye sp and chulitna respectively and presently located in japan eastern russia and alaska straddled the vast oceans surrounding pangea by means of quantitative biogeographical methods including cluster analysis non metric multidimensional scaling and bootstrapped spanning network applied to smithian and spathian early triassic ammonoid assemblages we analyze similarity relationships between faunas and suggest paleopositions for the above cited terranes taxonomic similarities between faunas indicate that primary drivers of the ammonoid distribution were sea surface temperature and currents possible connections due to current controlled faunal exchanges between both sides of the panthalassa are shown and terranes such as sk sp and chulitna played an important role as stepping stones in the dispersal of ammonoids sk and sp terranes show strong sub equatorial affinities during the smithian thus suggesting a location close to south china at the same time the chulitna terrane shows strong affinities with equatorial faunas of the eastern panthalassa this paleoceanographic pattern was markedly altered during the spathian possibly indicating significant modifications of oceanic circulation at that time as illustrated by the development of a marked intertropical faunal belt across tethys and panthalassa

hydropedology of a mildly arid loess covered area southern israel extensive loess covered areas characterize the mildly arid areas of western israel where average annual rainfall is 280 mm hydrological data point to a peculiar hydrological behavior of the ephemeral streams the frequency of sporadic flash floods is very high however even in extreme rain events peak discharges are extremely low hydrographs are usually characterized by very steep rising and falling limbs representative of saturated areas extending over a limited part of the watershed following this observation we advanced the hypothesis that storm channel runoff originated in the channel itself with negligible contribution from the adjoining hillslopes the study was based on two complementary approaches the hydrological approach was based on the detailed analysis of rainfall runoff relationships in a small watershed 11 km2 and on the analysis of the hydrological characteristics of the drainage network the second approach was based on the toposequence concept several boreholes were dug along a hillslope 400 m long chemical data obtained show no significant difference in the downslope direction similar results were also obtained for the particle size distribution and soil moisture content data obtained perfectly fit the concept of partial area contribution as it presents an extreme case of hydrological discontinuity at the hillslope channel interface the lack of pedological trends in the downslope direction is an additional indication of the limited connectivity between the hillslopes and the adjoining channel the limited connectivity is attributed to the prevalence of low rain intensities in the study area the present study is also relevant to our understanding of pedological processes in dry land areas the high frequency of intermittent low intensity rainstorms limits runoff generation and flow distances and casts doubt on the general application of the toposequence approach this article is protected by copyright all rights reserved

new early triassic ammonoid faunas from the dienerian smithian boundary beds at the induan olenekian gssp candidate at mud spiti northern india new collections at the induan olenekian boundary gssp candidate at mud himachal pradesh northern india lead to the recognition of several well preserved ammonoid faunas that significantly improve the biostratigraphic resolution in the beds underlying the proposed gssp level in ascending order the new biostratigraphical sequence comprises the ambites lilangense beds the fuchsites markhami beds the kingites lens beds the prionolobus rotundatus beds the flemingites bhargavai beds the kashmiritidae gen nov a beds and the vercherites cf pulchrum beds the faunas from bed 10 located about 1 m below the proposed gssp level contain certain ammonoids with typical early smithian affinity flemingitidae kashmiritidae and thus reflect the beginning of the early smithian evolutionary radiation seen from an evolutionary point of view the dienerian smithian boundary can therefore be placed just below bed 10 ideally the stage boundary should also be intercalibrated with other biological chemical or physical proxies as additional tools for world wide correlations four new species flemingites bhargavai kingites korni kingites parkashi and xenodiscoides variocostatus and two new genera mudiceras vercherites are described

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

uranium isotope fractionation during coprecipitation with aragonite and calcite abstract natural variations in 238u 235u of marine calcium carbonates might provide a useful way of constraining redox conditions of ancient environments in order to evaluate the reliability of this proxy we conducted aragonite and calcite coprecipitation experiments at ph 7 5 and 8 5 to study possible u isotope fractionation during incorporation into these minerals small but significant u isotope fractionation was observed in aragonite experiments at ph 8 5 with heavier u isotopes preferentially enriched in the solid phase 238u 235u of dissolved u in these experiments can be fit by rayleigh fractionation curves with fractionation factors of 1 00007 0 00002 0 00003 1 00005 0 00001 and 1 00003 0 00001 in contrast no resolvable u isotope fractionation was observed in an aragonite experiment at ph 7 5 or in calcite experiments at either ph equilibrium isotope fractionation among different aqueous u species is the most likely explanation for these findings certain charged u species are preferentially incorporated into calcium carbonate relative to the uncharged u species ca2uo2 co3 3 aq which we hypothesize has a lighter equilibrium u isotope composition than most of the charged species according to this hypothesis the magnitude of u isotope fractionation should scale with the fraction of dissolved u that is present as ca2uo2 co3 3 aq this expectation is confirmed by equilibrium speciation modeling of our experiments theoretical calculation of the u isotope fractionation factors between different u species could further test this hypothesis and our proposed fractionation mechanism these findings suggest that u isotope variations in ancient carbonates could be controlled by changes in the aqueous speciation of seawater u particularly changes in seawater ph p co 2 ca2 or mg2 concentrations in general these effects are likely to be small

a co2 decrease driven cooling and increased latitudinal temperature gradient during the mid cretaceous oceanic anoxic event 2 article i nfo the mid cretaceous is thought to be a greenhouse world with significantly higher atmospheric pco2 and sea surface temperatures as well as a much flatter latitudinal thermal gradient compared to the present this time interval was punctuated by the cenomanian turonian oceanic anoxic event oae 2 93 5 myr ago an episode of global massive organic carbon burial that likely resulted in a large and abrupt pco2 decline however the climatic consequences of this pco2 drop are yet poorly constrained we determined the first high resolution sea surface temperature sst record across oae 2 from a deep marine sedimentary sequence at ocean drilling program odp site 1276 in the mid latitudinal newfoundland basin nw atlantic by employing the organic palaeothermometer tex86 we found that ssts across the oae 2 interval were extremely high but were punctuated by a remarkably large cooling 5 11 c which is synchronous with the 2 5 5 5 c cooling in sst records from equatorial atlantic sites and the plenus cold event because this global cooling event is concurrent with increased organic carbon burial it likely acted in response to the associated pco2 drop our findings imply a substantial increase in the latitudinal sst gradient in the proto north atlantic during this period of global cooling and reduced atmospheric pco2 suggesting a strong coupling between pco2 and latitudinal thermal gradients under greenhouse climate conditions

some aspects of the regional variation in the amount of available sediment produced by isopods and porcupines northern negev israel a recent study conducted in the sde boqer experimental site drew the attention to the possible influence of the burrowing and digging activity of some desert animals on the spatial variation of erosion rates over arid limestone slopes such activity provides loose soil aggregates which are easier to remove by shallow overland flows than is the compacted and crusted loessial soil in order to study the regional extent of available sediment amounts produced by the biological activity six plots were selected in the northern negev in the range of 65 mm to 310 mm average annual rainfall amount all plots had the same north facing aspect and the same lithologic composition their size varied from 1110 m2 to 5470 m2 available sediment produced was found to vary from 3 g to 70 g m2 increasing with rainfall amount the distribution of available sediment within each plot was not spatially uniform depending greatly on the spatial distribution of bedrock surfaces and soil cover the overall possible influence of the biotic activity on short term cycles of soil erosion over limestone arid slopes in the negev is discussed

lower triassic conodont sequence in chaohu anhui province china and its global correlation abstract the early triassic paleogeographical setting of the chaohu section in china was in a deep part of the yangtze platform and this has resulted in a rather complete lower triassic sequence with rich ammonoid and conodont successions three lower triassic sections west pingdingshan north pingdingshan and south majiashan have been sampled in detail for a systematic conodont study eight conodont zones are recognized in ascending order these are the zones of hindeodus typicalis neogondolella krystyni neospathodus kummeli neospathodus dieneri neospathodus waageni neospathodus pingdingshanensis neospathodus homeri and neospathodus anhuinensis these are correlated with the sequences in north america and other areas of the world the succession provides a good basis for the definition of the global stratotype of the induan olenekian boundary gssp which has been proposed at the base of the neospathodus waageni zone in west pingdingshan seven new species are introduced neospathodus chaohuensis n chii n concavus n eotriangularis n pingdingshanensis n posterolongatus n tongi a new subspecies n waageni eowaageni and three morphotypes of n dieneri

geochemical evidence from bio apatite for multiple oceanic anoxic events during permian triassic transition and the link with end permian extinction and recovery abstract a detailed 20 myr redox history of permian to triassic oceans changhsingian to carnian stages has been constructed using ce anomaly ce and th u ratios from conodont albid crown apatite material the results show that the well established phenomenon of intense ocean anoxia coincident with the end permian mass extinction is faithfully recorded in conodont ce and th u data extending this conodont redox record shows that end permian anoxia persisted possibly into the earliest dienerian stage and that two intense oceanic anoxic events also occurred later in the early triassic earliest smithian earliest spathian and middle spathian followed by a weaker manifestation of anoxia in the anisian stage seen in ce data marine benthic radiation following the end permian mass extinction began after the smithian earliest spathian anoxic event suggesting a suppression of evolution prior to this due to these inimical conditions the failure of the middle spathian anoxic event to retard the evolutionary rebound implies shallow shelf seas remained well ventilated at this time even if the oceans did not other attributes of the early triassic record also closely coincide with redox fluctuations phases of anoxia intensification saw the proliferation of microbial carbonates and major negative carbon isotope swings that can be attributed to chemocline shallowing causing alkalinity pulses and enrichment in light remineralised carbon and or indicate a trigger meachnaims related to increased fluxes of light c from siberian volcanic sources

marine anoxia and delayed earth system recovery after the end permian extinction delayed earth system recovery following the end permian mass extinction is often attributed to severe ocean anoxia however the extent and duration of early triassic anoxia remains poorly constrained here we use paired records of uranium concentrations u and 238u 235u isotopic compositions 238u of upper permian upper triassic marine limestones from china and turkey to quantify variations in global seafloor redox conditions we observe abrupt decreases in u and 238u across the end permian extinction horizon from 3 ppm and 0 15 to 0 3 ppm and 0 77 followed by a gradual return to preextinction values over the subsequent 5 million years these trends imply a factor of 100 increase in the extent of seafloor anoxia and suggest the presence of a shallow oxygen minimum zone omz that inhibited the recovery of benthic animal diversity and marine ecosystem function we hypothesize that in the early triassic oceans characterized by prolonged shallow anoxia that may have impinged onto continental shelves global biogeochemical cycles and marine ecosystem structure became more sensitive to variation in the position of the omz under this hypothesis the middle triassic decline in bottom water anoxia stabilization of biogeochemical cycles and diversification of marine animals together reflect the development of a deeper and less extensive omz which regulated earth system recovery following the end permian catastrophe

uranium isotope evidence for temporary ocean oxygenation in the aftermath of the sturtian snowball earth abstract the appearance and radiation of animals are commonly attributed to neoproterozoic oceanic oxygenation yet independent geochemical evidence for such an event remains equivocal strata deposited between the sturtian and marinoan snowball earth glaciations 660 to 640 ma contain the earliest animal biomarkers and possible body fossils to quantify the extent of seafloor oxygenation during this critical interval we present uranium isotope ratios 238u 235u denoted as 238 u from limestone of the taishir formation in mongolia through two stratigraphic sections that are separated by 75 km within the same depositional basin above the sturtian glacial deposits through 150 m of stratigraphy 238 u compositions have a mean value of 0 47 this interval is followed by a 0 3 decrease in 238 u coincident with the taishir negative carbon isotope excursion thereafter 238 u values remain relatively low until the erosional unconformity at the base of the marinoan glacial deposits using a box model we show that the best explanation for the higher 238 u values of the post sturtian limestones is extensive but temporary oxygenation of the seafloor and is inconsistent with a scenario involving only increased delivery of uranium to the oceans due to post snowball weathering the decline in 238 u in overlying strata coincident with the taishir negative 13 c excursion indicates a subsequent decrease in seafloor oxygenation the u isotopic data combined with modeling results challenge the notion of a simple unidirectional oxygenation of neoproterozoic oceans

congruent permian triassic δ238u records at panthalassic and tethyan sites confirmation of global oceanic anoxia and validation of the u isotope paleoredox proxy

anomalous marine calcium cycle linked to carbonate factory change after the smithian thermal maximum early triassic abstract extreme greenhouse warming in the latest permian played a key role in the largest animal extinction event ever recorded in earth history the extinction was likely triggered by volcanic eruptions that dramatically increased atmospheric co2 levels and pushed the earth system into a lethally hot greenhouse state with stratified anoxic and more acidic oceans these conditions intensified a few million years later during the middle late smithian thermal maximum stm and a further biodiversity loss occurred during the subsequent cooling across the smithian spathian boundary ssb the marine carbonate factory is expected to have changed during this period but relevant studies are still lacking here we report calcium isotopic data of bulk carbonate rocks 44 40cacarb from two marine carbonate sections jiarong and shitouzhai in south china showing 0 5 0 7 positive shift of 44 40cacarb coupled to a 4 6 positive shift of 13ccarb from the middle smithian to the early spathian box modeling of the marine ca cycle yielded two scenarios i e constant and variable 44 40caseawater that can produce a 0 5 positive shift of 44 40cacarb 1 a local mineralogical shift in primary carbonate mineralogy at both sites from 80 aragonite to 80 calcite or 2 a 10 increase of global carbonate burial flux the former is consistent with a 20 50 fold rise of ca mg ratios and 10 50 fold decrease of sr ca ratios in the study sections and the latter fits well with massive carbonate deposition globally during the early spathian oceanic overturn and upwelling of alkaline deep waters during ssb climatic cooling is proposed as the main reason for the increase in carbonate burial flux thus the ssb transition marks an important step in the recovery of the marine fauna after the end permian mass extinction triggered by climatic cooling ocean ventilation and a pronounced rise in marine carbonate deposition on continental shelves

climatic and biotic upheavals following the end permian mass extinction the recovery from the end permian mass extinction was slow and prolonged a temperature reconstruction shows that further biotic crises during the recovery were associated with extreme warmth

smithian spathian boundary event evidence for global climatic change in the wake of the end permian biotic crisis one of the most important carbon cycle perturbations following the end permian mass extinction event straddles the smithian spathian boundary ssb olenekian early triassic this anomaly is characterized by a prominent positive carbon isotope excursion known from tethyan marine rocks its global signifi cance is established here by a new high paleolatitude record spitsbergen paleontological evidence such as boreal palynological data barents sea norway and global patterns of ammonoid distribution indicates a synchronous major change in terrestrial and marine ecosystems near the ssb the reestablishment of highly diverse plant ecosystems including the rise of woody gymnosperms and decline of the formerly dominating lycopods is interpreted as an effect of a major climate change this hypothesis is supported by modeling of ammonoid paleobiogeography the distribution patterns of which are interpreted as a proxy for sea surface temperatures sst the latest smithian thus appears to have been a time of a warm and equable climate as expressed by an almost fl at pole to equator sst gradient in contrast the steep spathian sst gradient suggests latitudinally differentiated climatic conditions we propose that this drastic climate change and the global carbon cycle perturbation were triggered by a massive end smithian co2 injection the ssb event could therefore represent one of the causes for stepwise and delayed recovery of marine and terrestrial biotas in the wake of the end permian biotic crisis

high amplitude redox changes in the late early triassic of south china and the smithian spathian extinction abstract the early triassic was a time of remarkably high temperatures large carbon cycle perturbations and episodes of widespread ocean anoxia the sediments in the nanpanjiang basin of south china provide superb opportunities to examine the sedimentary response to these extreme conditions especially during the crisis interval at the smithian spathian s s boundary we have investigated a deep water section at jiarong and a shallower water section at mingtang these contain a range of facies including black shales micritic limestone units and rudaceous carbonate event beds that include flat pebble conglomerates and breccia debrites that bear similarities to the hybrid event beds seen in clastic turbidite successions redox proxies pyrite framboids and trace metals reveal that widespread anoxia in the late smithian persisted into the novispathodus pingdingshanensis zone of the early spathian before a sharp transition to highly oxygenated griotte facies red marine strata in the icriospathodus collinsoni zone that records an oxic rebound benthic faunas are locally common but of low diversity and dominated by thin shelled bivalves and ostracodes with small foraminifers and exceptionally rare fish remains bioturbation was intense only in the early middle spathian i collinsoni conodont zone griotte facies anoxia and extremely high temperatures probably played a role in severely restricting the abundance of fish and the small sizes of marine invertebrates at this time the presence of ooids and seafloor fan cements in our study sections indicates highly saturated conditions rather than acidification at the end of the smithian

palaeoenvironments flora and organic carbon and nitrogen isotope changes across the non marine permian triassic boundary at wybung head australia abstract the permian triassic boundary section at wybung head eastern australia shows a rapid change from humid coal bearing lowland braided stream through a thin clay and coal breccia and paleosols to semi arid silty floodplain deposits identifiable plant remains and total organic matter disappear above the coal and clay breccia three characteristic palynofacies accumulated in a range from oxic to sub oxic to anoxic conditions the dominance of opaque phytoclasts in the entire sequence reflects deposition under oxic conditions especially in the sequence lying above the birdie coal the result of fluctuating water tables high energy and desiccating conditions in the birdie coal however at certain horizons a water saturated environment favored the preservation of organic matter such as pollen spores and structured organic matter this latest permian paleovegetation was dominated by opportunistic understory spore bearing plants with a canopy of pollen bearing glossopterids conifers and cordaitales total organic carbon drops from 30 in the coal through

diagenetic uptake of rare earth elements by bioapatite with an example from lower triassic conodonts of south china abstract the distribution patterns of rare earth elements rees are frequently used as proxies for ancient seawater chemistry or paleomarine environmental conditions however recent work has shown that diagenesis can lead to remobilization and inter elemental fractionation of rees and that these effects often occur in conjunction with redox reactions in sediment porewaters here we review existing literature on the diagenetic fluxes of rees in marine sediments and porewaters in order to systematize existing knowledge on this subject rees undergo significant redistribution among sediment phases during both early and late diagenesis as a consequence of adsorption and desorption processes remobilization of rees commonly leads to inter elemental fractionation variously leading to enrichment or depletion of the light middle or heavy ree fractions further ree remobilization can be facilitated by redox changes e g through reductive dissolution of host phases in suboxic and anoxic porewaters characteristic ree distribution patterns develop through these processes 1 a flat distribution signifying predominantly terrigenous siliciclastic influence 2 a middle ree bulge probably due to adsorption of light and heavy rees to mn and fe oxyhydroxides respectively and 3 heavy ree enrichment indicative of hydrogenous seawater influence note all patterns in this paper are normalized to the ree composition of average upper continental crust or ucc in the second part of this study we undertake an analysis of the ree distributions in conodonts and whole rock samples from west pingdingshan a permian triassic boundary section in south china using ree th and y ho ratios we show that almost all of the conodont samples have a strong diagenetic overprint and that the hydrogenous ree fraction is small and not isolatable furthermore the conodonts contain two diagenetic ree components one characterized by low ree 100 300 ppm high ree th ratios 1000 strong middle ree enrichment and eu eu ratios of 1 5 2 0 and the second by high ree 300 2000 ppm low ree th ratios 20 30 little or no middle ree enrichment and eu eu ratios of 1 0 the first component exhibits a pronounced middle ree bulge that represents an early diagenetic signature associated with suboxic conditions possibly related to adsorption of rees onto fe mn oxyhydroxides in the shallow subsurface environment the second component shows a flat ree distribution that is similar to both our whole rock samples and average ucc indicating derivation from rees released from detrital siliciclastics e g clay minerals probably at a range of burial depths from shallow to deep failure of the conodont samples to yield an isolatable hydrogenous component demonstrates that bioapatite does not always preserve a primary marine ree signature given that bioapatite rees have been widely used for this purpose often on the assumption of minimal or no diagenetic influence our findings are likely to necessitate a re evaluation of the results of many earlier studies in general we counsel caution in inferring a hydrogenous origin for rees in bioapatite owing to frequent diagenetic alteration of ree distributions

rapid expansion of oceanic anoxia immediately before the end permian mass extinction tive of an expansion of oceanic anoxia and higher th u ratios from 0 06 to 0 42 indicative of drawdown of u concentrations in seawater using a mass balance model we estimate that this isotopic shift represents a sixfold increase in the flux of u to anoxic facies implying a corresponding increase in the extent of oceanic anoxia the intensification of oceanic anoxia coincided with or slightly preceded the eh and persisted for an interval of at least 40 000 to 50 000 y following the eh these findings challenge previous hypotheses of an extended period of whole ocean anoxia prior to the end permian extinction

the july 1986 oceanside ml 5 3 earthquake sequence in the continental borderland southern california an earthquake of m l 5 3 occurred at 32 58 7 n 117 51 5 w southwest of oceanside in san diego county at 13 47 13 july 1986 ut this main shock was followed by an extensive aftershock sequence with 55 events of m l 3 0 during july 1986 the epicenters of the main shock and aftershocks are located at the northern end of the san diego trough bahia soledad fault zone sdt bs where it changes strike from northwest to a more westerly direction through a left offset or a bend in the fault the northwest striking sdt bs is one of three strike slip fault systems that constitute the offshore agua blanca fault system the spatial distribution of the aftershocks indicates a unilateral 7 to 9 km long rupture to the east southeast away from the epicenter of the main shock the focal mechanism of the main shock also has an east southeast striking and south dipping plane with mostly reverse movement on it focal mechanisms of the m l 3 0 aftershocks show both reverse and strike slip movement the reverse focal mechanisms indicate that this sequence may have occurred on a thrust fault that provides for a left stepping offset or a bend in the san diego trough fault as movement is transferred to the west along the santa cruz catalina island escarpment some of the aftershocks that are located to the southeast of the main shock and have strike slip focal mechanisms suggest activation of the northwest trending san diego trough fault a stress inversion of the focal mechanism data shows that the maximum principal stress determined from the focal mechanisms of the main shock and 22 aftershocks that occurred within 36 hours of the main shock has an azimuth of s30 w plunging 18 the maximum principal stress determined from 30 aftershocks that occurred from 15 july to 2 october 1986 has an azimuth of s20 w plunging 18 the values the measure of the relative sizes of the principal stresses are approximately 0 07 and 0 1 respectively indicating that the intermediate and minimum principal stress are of similar magnitude the results of the stress inversion and the focal mechanisms that showed reverse faulting suggest that the inner continental borderland offshore from oceanside is not currently a pure strike slip tectonic regime but rather a strike slip mixed with reverse faulting regime when the 52 aftershock focal mechanisms are divided into four groups and the stress inversion is repeated the change in stress can be described as a progressive counter clockwise rotation of 14 of the orientation of the maximum principal stress to a more southerly direction with the greatest change in stress orientation observed shortly after the main shock the abundance of aftershocks may be related to the large temporal variation in stress orientation that in turn may have resulted from the small stress drop of the main shock

fluid flow through carbonate platforms constraints from 234u 238u and cl in bahamas pore waters the geometry timing and rate of fluid flow through carbonate margins and platforms is not well constrained in this study we use u concentrations and isotope ratios measured on small volumes of pore water from bahamas slope sediment coupled with existing chlorinity data to place constraints on the fluid flow in this region and by implication other carbonate platforms these data also allow an assessment of the behaviour of u isotopes in an unusually well constrained water rock system we report pore water u concentrations which are controlled by dissolution of high u organic material at shallow depths in the sediment and by reduction of u to its insoluble 4c state at greater depths the dominant process influencing pore water 234 u 238 u is alpha recoil in holocene sediments the increase of pore water 234 u 238 u due to recoil provides an estimate of the horizontal flow rate of 11 cm year but with considerable uncertainty at depths in the sediment where conditions are reducing features in the u concentration and 234 u 238 u profiles are offset from one another which constrains the effective diffusivity for u in these sediments to be1 2 10 8 cm 2 s 1 at depths between the holocene and these reducing sediments pore water 234 u 238 u values are unusually low due to a recent increase in the dissolution rate of grain surfaces this suggests a strengthening of fluid flow probably due to the flooding of the banks at the last deglaciation and the re initiation of thermally driven venting of fluid on the bank top and accompanying recharge on the slopes interpretation of existing chlorinity data in the light of this change in flow rate constrain the recent horizontal flow rate to be 10 6 3 4 cm year estimates of flow rate from 234 u 238 u and cl are therefore in agreement and suggest flow rates close to those predicted by thermally driven models of fluid flow this agreement supports the idea that flow within the bahamas banks is mostly thermally driven and suggests that flow rates on the order of 10 cm year are typical for carbonate platforms where such flow occurs 1999 elsevier science b v all rights reserved

rotation of the principal stress directions due to earthquake faulting and its seismological implications earthquake faulting results in stress drop over the rupture area because the stress drop is only in the shear stress and there is no or little stress drop in the normal stress on the fault the principal stress directions must rotate to adapt such a change of the state of stress using two constraints i e the normal stress on the fault and the vertical stress the overburden pressure which do not change before and after the earthquake we derive simple expressions for the rotation angle in the 1 axis for a dip slip earthquake the rotation angle is only a function of the stress drop ratio defined as the ratio of the stress drop to the initial shear stress and the angle between the 1 axis and the fault plane but for a strike slip earthquake the rotation angle is also a function of the stress ratio depending on the faulting regimes the 1 axis can either rotate toward the direction of fault normal or rotate away from the direction of fault normal the rotation of the stress field has several important seismological implications it may play a significant role in the generation of heterogeneous stresses and in the occurrence and distribution of aftershocks the rotation angle can be used to estimate the stress drop ratio which has been a long lasting topic of debate in seismology

diagenetic effects on uranium isotope fractionation in carbonate sediments from the bahamas abstract uranium isotope variations 238u recorded in sedimentary carbonate rocks are a promising new proxy for the extent of oceanic anoxia through geological time however the effects of diagenetic alteration on the u isotopic composition in carbonate sediments which are crucial to understand the accurate reconstruction of marine 238u are currently poorly constrained here we examine the effects of the aragonite to calcite transition in the pleistocene key largo limestone of south florida and assess the effects of vadose meteoric phreatic meteoric and phreatic marine diagenesis on u isotope fractionation in carbonate sediments from the bahamas transect including the well studied clino unda and odp site 1006 drill cores our results suggest that early diagenetic processes in bahamas carbonate sediments fractionate u isotopes by an average of 0 27 0 14 1 sd heavier than contemporaneous seawater downcore variations of 238u in slope and basin sediments display little if any correlation with u concentration and common geochemical indicators of diagenesis 13c 18o mn sr mg ca sr ca enrichments of redox sensitive elements or rare earth elements anomalies we propose two possible mechanisms to interpret the positive change in the 238u during carbonate diagenesis authigenic enrichment of isotopically positive u iv in carbonates and preferential incorporation of isotopically positive aqueous u vi species into carbonates these processes likely operate during early syndepositional diagenesis on the banktop further diagenesis during deeper burial is limited by the low solubility of u iv under reducing pore water conditions the early diagenetic behavior of u isotopes in bahamas carbonate sediments is likely broadly representative of carbonate diagenesis in the geological past we suggest that the mean diagenetic offset determined in this study be applied when reconstructing seawater 238u from ancient carbonates furthermore early diagenesis induces significant statistical variability in sediment 238u values pointing to the need for large high resolution data sets in order to average out stochastic variations in individual bulk sediment samples

early triassic conodonts of jiarong nanpanjiang basin southern guizhou province south china abstract jiarong huishui county guizhou province south china is a key locality for the study of the early triassic recovery after the end permian mass extinction the size reduction of conodonts at the smithian spathian transition was first documented in jiarong and it is also a locality that contributes to the documentation of the early triassic paleo seawater temperatures in the jiarong sections thirteen conodont zones were identified for the early triassic in ascending order they are hindeodus parvus zone hindeodus sosioensis zone clarkina krystyni zone neoclarkina discreta zone neospathodus cristagalli eurygnathodus costatus assemblage zone novispathodus waageni eowaageni zone novispathodus waageni waageni zone discretella discreta zone pachycladina parachirognathus assemblage zone novispathodus pingdingshanensis zone icriospathodus collinsoni zone triassospathodus homeri zone triassospathodus triangularis zone these conodont zones in the jiarong sections improve the global correlation of early triassic sections and also provide better regional age constraints in an area that is important for studies of recovery from the extinction based on the first appearance of nv waageni eowaageni the induan olenekian boundary is recognized at 3 6 m above the base of the jiarong iii section the dominance of blade shaped segminate conodonts was replaced by gondola shaped segminiplanate conodonts twice the first time was in the late griesbachian and the second time was in the early spathian the dominance of segminiplanate conodonts probably indicates that the deeper seawater environment became more oxygenated during the late griesbachian and early spathian for short time intervals as it is believed that the griesbachian segminiplanate conodonts favored deeper oxygenated water habitats a new genus spathogondolella gen nov and a new species spathogondolella jiarongensis sp nov have been recognized

chemostratigraphy of the late mesoproterozoic atar group taoudeni basin mauritania muted isotopic variability facies correlation and global isotopic trends a b s t r a c t sedimentary strata of the atar el mreiti groups taoudeni basin mauritania are characterized by car bon isotope values that fall largely between 2 5 and 4 0 and contain stratigraphic trends that are strikingly similar to those recorded worldwide in strata with depositional ages from 1 2 ga to 1 1 ga chemostratigraphic results are consistent with recent re os dates of 1 1 ga for atar el mreiti group strata rooney et al 2010 and support an emerging dataset that identifies the late mesoproterozoic as an isotopically distinctive interval in earth history the relatively low amplitude carbon isotope variabil ity limits the use of chemostratigraphy in detailed correlation during this time interval in this study we combine chemostratigraphic data with key chronostratigraphic horizons and detailed analysis of deposi tional facies to construct a rigorous and testable model for the intrabasinal correlation of atar and el mreiti group strata data support a depositional model that results in broadly uniform stratigraphic thicknesses across the west african craton with predominantly stromatolitic facies of the atar group mauritania and the hank and dar cheikh groups algeria representing deposition on shallow water craton margins and clayey carbonate and shale facies of the el mreiti group mauritania representing deposition on a broad shallow water epicratonic platform within this stratigraphic framework regional differences in carbon isotope composition are interpreted to reflect spatial differences in water chemistry likely asso ciated with local carbon cycle dynamics in cratonic environments that have limited exchange with the open ocean similarly distinct differences in trace element composition recorded in multilayered marine cements within deeper water stromatolitic reef facies are interpreted to reflect vertical differences in water chemistry associated with redox gradients in the water column we use this multifaceted approach to test a recent hypothesis that suggests correlation of atar el mreiti group strata with glaciogenic strata of the vazante group sao francisco craton critically preservation of shallow water carbonate and evaporite strata across more than 1200 km of the predominantly epicra tonic taoudeni basin with minimal evidence for high amplitude sea level change is consistent with inferences of late mesoproterozoic highstand conditions in a global greenhouse climate such charac teristics are inconsistent with suggestions of a time equivalency with glaciogenic strata of the vazante group sao francisco craton despite broad similarities in re os geochronology and carbon isotope com position together these results emphasize both the utility and limitations of carbon isotope stratigraphy to inform hypotheses regarding global correlation and biospheric evolution 2012 elsevier b v all rights reserved

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

short and long term effects of bioturbation on soil erosion water resources and soil development in an arid environment the importance of vegetal cover on soil erosion processes has been recognized for a long time however the short and long term effects of faunal activity on soil erosion and soil development had been largely overlooked by geomorphologists the study of runoff and erosion processes in the negev desert indicated pronounced systematic differences in sediment concentration and soil erosion rates between rocky and colluvial surfaces erosion rates were always higher on the former than on the latter field observations drew attention to an intense burrowing and digging activity conducted mainly by isopods and porcupines the monitoring of this activity based on a grid system which consists of rows 5 m wide lasted ten consecutive years data obtained suggest the existence of a strong link between the spatial pattern of bioturbation and that of soil erosion the study also examines through feedback processes the regulatory role of bioturbation on the spatial distribution of water availability soil moisture and soil forming processes due to bioturbation two distinct environments were recognised the rocky environment which is characterized by a positive feedback with a high water availability and low soil salinity and the soil covered areas where a negative feedback results in low water availability and a high soil salinity

high resolution stratigraphic correlation of benthic oxygen isotopic records spanning the last 300 000 years abstract in order to compare the response of different oceanographic regions to global climate change very detailed stratigraphic techniques are required the global signal of ice volume changes recorded in the oxygen isotopic composition of foraminifera can provide the tool for developing the necessary high resolution stratigraphy in order to evaluate the resolution of a stratigraphy based on detailed isotopic records two techniques are used to correlate a set of benthic oxygen isotope records from seven piston cores taken in the north and south atlantic the indian and the equatorial and north pacific oceans the first technique was modified from the graphic correlation procedure of shaw 1964 this procedure requires the identification of isotopic events that are correlated from core to core detailed correlations for intervals of the cores between events are provided by a series of straight line segments connecting all common events the second technique developed by martinson et al 1982 uses inverse procedures to define a continuous non linear mapping function that correlates the isotopic records the mapping function maximizes the correlation coefficient between data sets being compared the techniques are independent in that they rely on different criteria for correlating the data series stratigraphic correlations obtained by these procedures are in excellent agreement the mean difference between the correlations is on the order of the sampling intervals of each core and when corrected for sedimentation rates suggests that benthic isotope records from the suite of seven cores can be correlated to a resolution of 2000 to 4000 yrs

a new high resolution δ13c record for the early triassic insights from the arabian platform a new carbon isotope record with conodont biostratigraphy is presented for the entire early triassic from the musandam peninsula united arab emirates uae this is a near continuous and exclusively shallow marine carbonate succession that allows analysis of a high resolution primary carbon cycling signature in the absence of significant depth dependent or lithologic controls the musandam carbon isotope record can be broadly correlated with global isotopic events but also resolves additional features including the presence of significant negative events during the previously identified positive excursions at both the dienerian smithian and smithian spathian boundaries a further positive event is revealed during the development of the mid spathian negative excursion a feature not previously reported in any other section these new short lived events are probably related to the occurrence of the more widely recognized early triassic excursions and may represent fluctuations in the driving mechanisms superimposed on the continued instability of the global carbon cycle in the aftermath of the end permian extinction together these features highlight additional complexities to the early triassic carbon cycle perturbations than previously documented

recurrent early triassic ocean anoxia the early triassic record from the smithian stratotype shows that the organic carbon isotope record from northwest pangea closely corresponds to major fluctuations in the inorganic carbon records from the tethys indicating truly global perturbations of the carbon cycle occurred during this time geochemical proxies for anoxia are strongly correlated with carbon isotopes whereby negative shifts in 13 c org are associated with shifts to more anoxic to euxinic conditions and positive shifts are related to return to more oxic conditions rather than by a delayed or prolonged recovery the early triassic is better characterized by a series of aborted biotic recoveries related to shifts back to ocean anoxia potentially driven by recurrent volcanism

impact of differential tectonic subsidence on isolated carbonate platform evolution triassic of the nanpanjiang basin south china the nanpanjiang basin of south china contains four exceptionally well exposed isolated triassic carbonate platforms detailed mapping of two dimensional transects and description of stratigraphic sections allow the reconstruction of facies architecture sequence stratigraphy and evolution of the platforms biostratigraphy magnetic susceptibility profiles and volcanic ash horizons allow chronostratigraphic correlation and thus a basinwide evaluation of mechanisms controlling platform evolution a comparison of platform architecture demonstrates that southerly platforms have substantially greater thickness backstepping geometry pinnacle development and earlier drowning that resulted from greater tectonic subsidence proximal to a probable convergent margin along the southern perimeter of the basin felsic volcanics thicken southward and contributed to the termination of the southernmost platform indicating the development of a volcanic arc along the southern margin of the south china tectonic block the northernmost isolated platform had greater longevity and lesser accumulation and lacks backstepping and pinnacle phases of development basin margin intertonguing relationships or lack thereof demonstrate that earlier siliciclastic influx into the basin to the south and concurrent starved basin conditions to the north impacted the evolution of platform margin geometries comparative analysis of platform evolution shows that the timing and rates of tectonic subsidence controlled the timing of platform termination by drowning backstep geometries pinnacle development and overall platform thickness the timing of siliciclastic basin fill dictated differences in platform margin geometries such as slope angle relief above basin floor and the presence or absence of basinward platform progradation despite the dramatic differences in platform architecture eustatic sea level fluctuations imparted a basinwide sequence stratigraphic signal

the timing and pattern of biotic recovery following the end permian mass extinction the aftermath of the great end permian period mass extinction 252 myr ago shows how life can recover from the loss of 90 species globally the crisis was triggered by a number of physical environmental shocks global warming acid rain ocean acidification and ocean anoxia and some of these were repeated over the next 5 6 myr ammonoids and some other groups diversified rapidly within 1 3 myr but extinctions continued through the early triassic period triassic ecosystems were rebuilt stepwise from low to high trophic levels through the early to middle triassic and a stable complex ecosystem did not re emerge until the beginning of the middle triassic 8 9 myr after the crisis a positive aspect of the recovery was the emergence of entirely new groups such as marine reptiles and decapod crustaceans as well as new tetrapods on land including eventually dinosaurs the stepwise recovery of life in the triassic could have been delayed either by biotic drivers complex multispecies interactions or physical perturbations or a combination of both this is an example of the wider debate about the relative roles of intrinsic and extrinsic drivers of large scale evolution from a much more devastated planet and biota than the others with only some 10 of species surviving the epme was much harsher than the other mass extinctions during which global species diversity reduced to only about 50 of the pre extinction total 1 2 24 26 this means that the triassic recovery has two profound implications first it may show qualitative as well as quantitative differences from the other post extinction recoveries and second it can act as an exemplar of what to expect at its most extreme when global biodiversity is pushed to the brink there are obvious implications for current concerns about biodiversity loss and recovery resulting from human impacts 27 28 in the past ten years attention has focused on the sedimentary successions in south china these are enormously laterally extensive with some formations extending more than 2 000 km from the zhejiang to yunnan provinces the huge exposures length of the sections and improving dating open up the opportunity to explore physical environmental and biotic changes through the extinction and recovery times in varied marine habitats and compare these with patterns elsewhere in the world fig 1 a fine scale forensic analysis of this extraordinary time in earth s history now becomes possible the end permian mass extinction the epme killed 80 96 of marine animal species and 70 of terrestrial vertebrate species

uranium isotope systematics of ferromanganese crusts in the pacific ocean implications for the marine 238u 235u isotope system abstract variations of 238u 235u ratio 238u in sedimentary rocks have been proposed as a possible proxy for the paleo oceanic redox conditions although the marine 238u system is not fully understood here we investigate the spatial variation of 238u in modern ferromanganese fe mn crusts by analyzing u isotopes in the surface 0 3 mm depth layer of 19 fe mn crusts collected from 6 seamounts in the pacific ocean 238u values in the surface layers show little variation and range from 0 59 to 0 69 the uniformity of 238u values is consistent with the long residence time of u in modern seawater although the 238u values are lighter than that of present day seawater by 0 24 the light 238u values are consistent with the isotope offset observed in previously reported adsorption experiment of u to mn oxide these results indicate that removal of u from seawater to mn oxide is responsible for the second largest u isotope fractionation in the modern marine system and could contribute to isotopically heavy u to seawater depth profiles of u isotopes 234u and 238u in two fe mn crusts mr12 03 d06 r01 and mc10 cb07 b dated by os isotope stratigraphy were investigated to reconstruct the evolution of the oceanic redox state during the cenozoic the 238u depth profiles show very limited ranges 0 57 to 0 67 for mr12 03 d06 r01 and 0 56 to 0 69 for mc10 cb07 b and have values that are similar to those of the surface layers of fe mn crusts the absence of any resolvable variation in the 238u depth profiles may suggest that the relative amounts of oxic and reducing u sinks have not varied significantly over the past 45 myr however the 234u depth profiles of the same samples show evidence for the possible redistribution of 234u after deposition therefore the depth profile of 238u in fe mn crusts may have been also overprinted by later chemical exchange with pore water or seawater and may not reflect the paleo oceanic environmental changes to assess the potential role of u removal by mn oxides on seawater 238u we calculated seawater 238u with different u sink fluxes into mn oxides using a simple mass balance model the results of these calculations suggest that seawater 238u could have varied significantly throughout earth s history due to changes in the accumulation rate of mn oxides

global ocean redox variation during the middle late permian through early triassic based on uranium isotope and th u trends of marine carbonates uranium isotopes 238u 235u in carbonates a proxy for global ocean redox conditions owing to their redox sensitivity and long residence time in seawater exhibit substantial variability in the daxiakou section of south china from the upper middle permian through the mid lower triassic 9 m y middle and late permian ocean redox conditions were similar to that of the modern ocean and were characterized by improving oxygenation in the 2 m y prior to the latest permian mass extinction lpme countering earlier interpretations of sustained or gradually expanding anoxia during this interval the lpme coincided with an abrupt negative shift of 0 5 in 238u that signifies a rapid expansion of oceanic anoxia intensely anoxic conditions persisted for at least 700 k y griesbachian lessening somewhat during the dienerian th u concentration ratios vary inversely with 238u during the early triassic with higher ratios reflecting reduced u concentrations in global seawater as a consequence of large scale removal to anoxic facies modeling suggests that 70 100 of marine u was removed to anoxic sinks during the early triassic resulting in seawater u concentrations of 5 that of the modern ocean rapid intensification of anoxia concurrent with the lpme implies that ocean redox changes played an important role in the largest mass extinction event in earth history

high resolution biochronology and diversity dynamics of the early triassic ammonoid recovery the smithian faunas of the northern indian margin a new high resolution biozonation based on the unitary association ua method is constructed for the dienerian ammonoid succession of the northern indian margin it includes 12 ua zones and leads to the subdivision of the dienerian into three parts early middle and late the corresponding diversity analyses coupled with results previously obtained for the early smithian ammonoids of the same regions highlight the four following phases 1 a first modest peak of diversity in the early dienerian 2 a very low diversity persisting throughout the middle dienerian 3 a slow increase of diversity during the late dienerian and 4 a marked diversification in the early smithian turnover rates are very high during this entire time interval and the boundaries between early middle and middle late dienerian are emphasised by complete renewals of the ammonoid faunas the low diversity values in the middle and early late dienerian are concomitant with an anoxic event on outer continental shelves and coincide with warmer temperatures than those of the early dienerian and early smithian this diversity pattern stands in strong contrast with the credo of a protracted or stepwise recovery following the end permian mass extinction together with the end smithian extinction the middle and early late dienerian diversity crises were likely both radical setbacks in the recovery of early triassic ammonoids however these two diversity crises do not necessarily imply identical environmental triggers that ultimately led to anoxic bottom waters on outer continental platforms in both cases

cooling driven oceanic anoxia across the smithian spathian boundary mid early triassic abstract the smithian spathian boundary ssb represents a major climatic oceanic biotic event within the 5 myr long recovery interval of the early triassic following the end permian mass extinction the ssb was associated with pronounced cooling following the middle smithian hyper greenhouse a 2 to 8 positive carbon isotope excursion and a second order mass extinction yet its underlying cause s remain poorly understood here we review oceanic environmental changes during the middle smithian to early spathian interval and their potential mechanisms in addition we undertook an analysis of the carbon sulfur iron c s fe systematics of the south majiashan section which was located on the paleo western margin of the south china craton during the early triassic to better understand the causation of these environmental changes this analysis revealed low 13ccarb i e the n3 minimum in the middle smithian but rapidly rising 13ccarb i e to the p3 maximum and 34scas within the ssb interval i e late smithian earliest spathian both the middle smithian and ssb intervals are marked by development of marine euxinia which we hypothesize had fundamentally different causes the middle smithian was associated with hyperwarming the smithian thermal maximum which was probably triggered by a peak in magmatic activity of the siberian traps lip in contrast the ssb interval was associated with global climatic cooling which may have stimulated oceanic overturning circulation and upwelling on continental margins leading to transient local increases in marine productivity and expansion of oceanic oxygen minimum zones omzs the concurrent positive excursions in 13ccarb and 34scas at south majiashan and other sections worldwide are evidence of enhanced burial of organic carbon and pyrite on a regional or global scale as well as of a concurrent decline in atmospheric pco2 that may have positively re enforced the ssb cooling event

onset of biotic and environmental recovery from the end permian mass extinction within 1 2 million years a case study of the lower triassic of the meishan section south china abstract paleontological sedimentary and geochemical data obtained from the lower triassic strata of the meishan section south china suggest that onset of biotic recovery coincided with amelioration of paleoceanographic conditions and an increase in ocean productivity the griesbachian meishanorhynchia association from meishan indicates biotic recovery between the recovery stages 1 and 2 both the initial biotic recovery and palaeoceanic environmental amelioration occurred within 1 2 myr after the end permian mass extinction in the late griesbachian