paleobotanical evidence for near present day levels of atmospheric co2 during part of the tertiary understanding the link between the greenhouse gas carbon dioxide co 2 and earth9s temperature underpins much of paleoclimatology and our predictions of future global warming here we use the inverse relationship between leaf stomatal indices and the partial pressure of co 2 in modern ginkgo biloba and metasequoia glyptostroboides to develop a co 2 reconstruction based on fossil ginkgo and metasequoia cuticles for the middle paleocene to early eocene and middle miocene our reconstruction indicates that co 2 remained between 300 and 450 parts per million by volume for these intervals with the exception of a single high estimate near the paleocene eocene boundary these results suggest that factors in addition to co 2 are required to explain these past intervals of global warmth

petrography palynology and depositional environments of the early miocene oberdorf lignite seam styrian basin austria abstract an early miocene ottnangian lignite seam up to 36 m thick occurs in the oberdorf trough at the northwestern margin of the styrian basin it forms part of the fluvial koflach voitsberg formation petrographic and palynologic data together with ash yield and sulphur content of samples from two boreholes and two surface profiles have been used to study vertical and horizontal coal facies variations numerous partings and a high ash yield show that the lignite originated in a topogenous mire petrographic indices and palynological data suggest a wet forest swamp paleo environment a fluvial main parting with channel sediments at the eastern margin of the oberdorf trough and overbank sediments in its central part splits the lignite into a lower and an upper seam the lower seam consists of a lower high ash part with frequent splittings and a higher low ash part the upward decrease in number and thickness of silty clayey partings interpreted as crevasse splay deposits reflects the withdrawal of the fluvial sediment source coal composition is characterized by an upward increase in detro xylitic coal and in tissue preservation a good correlation between tissue preservation and percentages of taxodiaceae cupressaceae pollen suggests that this is mainly a result of an increasing contribution of decay resistant gymnosperms conifers the upper seam is also ash rich abundant inertinite at the eastern margin of the oberdorf trough is related to fire episodes inside or outside the mire main features of the upper seam in the central basin are an upward increase in tissue preservation and in percentages of taxodiaceae cupressaceae pollen high sulphur contents in the fresh water lignite are a result of a concentration of sulphate rich waters above the impermeable floors of the lower and upper seams carbonate rich surface waters from the graz palaeozoic and raasberg sequence raised the ph value and controlled sulphur and ash contents in those parts of the lower seam which are uninfluenced by the basal sulphur enrichment palynomorph spectra are dominated by taxodiaceae cupressaceae pollen and pollen from plants living in a mixed mesophytic forest pollen from aquatic and reed plants are rare the ratio between arctotertiary and paleotropic pollen is close to one and supports the early miocene age of the lignite the detected pollen spectra point to warm temperate subtropic and humid conditions

probabilistic forecasting of earthquakes we present long term and short term forecasts for magnitude 5 8 and larger earthquakes we discuss a method for optimizing both procedures and testing their forecasting effectiveness using the likelihood function our forecasts are expressed as the rate density that is the probability per unit area and time anywhere on the earth our forecasts are for scientific testing only they are not to be construed as earthquake predictions or warnings and they carry no official endorsement for our long term forecast we assume that the rate density is proportional to a smoothed version of past seismicity using the harvard cmt catalogue this is in some ways antithetical to the seismic gap model which assumes that recent earthquakes deter future ones the estimated rate density depends linearly on the magnitude of past earthquakes and approximately on a negative power of the epicentral distance out to a few hundred kilometres we assume no explicit time dependence although the estimated rate density will vary slightly from day to day as earthquakes enter the catalogue the forecast applies to the ensemble of earthquakes during the test period it is not meant to predict any single earthquake and no single earthquake or lack of one is adequate to evaluate such a hypothesis we assume that 1 per cent of all earthquakes are surprises assumed uniformly likely to occur in those areas with no earthquakes since 1977 we have made specific forecasts for the calendar year 1999 for the northwest pacific and southwest pacific regions and we plan to expand the forecast to the whole earth we test the forecast against the earthquake catalogue using a likelihood test and present the results our short term forecast updated daily makes explicit use of statistical models describing earthquake clustering like the long term forecast the short term version is expressed as a rate density in location magnitude and time however the short term forecasts will change significantly from day to day in response to recent earthquakes the forecast applies to main shocks aftershocks aftershocks of aftershocks and main shocks preceded by foreshocks however there is no need to label each event and the method is completely automatic according to the model nearly 10 per cent of moderately sized earthquakes will be followed by larger ones within a few weeks

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

the 87sr 86sr ratios of lacustrine carbonates and lake level history of the bonneville paleolake system lakes in the bonneville basin have fluctuated dramatically in response to changes in rainfall temperature and drainage diversion during the quaternary we analyzed tufas and shells from shorelines of known ages in orderto develop a relation between 8 7 sr 8 6 sr ratio of carbonates and lake level which then can be used as a basis for constraining lake level from similar analyses on carbonates in cores carbonates from the late quaternary shorelines yield the following average 8 7 sr 8 6 sr ratios 0 71173 for the stansbury shoreline 22 20 1 4 c ka 1350 m 0 71153 for the bonneville shoreline 15 5 14 5 1 4 c ka 1550 m 0 71175 for the provo shoreline 14 4 14 0 1 4 c ka 1450 m 0 71244 for the gilbert shoreline 10 3 10 9 1 4 c ka 1300 m and 0 71469 for the modern great salt lake 1280 m these analyses show that the 8 7 sr 8 6 sr ratio of lacustrine carbonates changes substantially at low to mid lake levels but is invariant at mid to high lake levels sr isotope mixing models of great salt lake and the bonneville paleolake system were constructed to explain these variations in 8 7 sr 8 6 sr ratios with change in lake level our model of the bonneville system produced a 8 7 sr 8 6 sr ratio of 0 71193 very close to the observed ratios from high shoreline tufa and shell the model verifies that the integration of the southern sevier and beaver rivers with the bear and others rivers in the north is responsible for the lower 8 7 sr 8 6 sr ratios in lake bonneville compared to the modern great salt lake we also modeled the 8 7 sr 8 6 sr ratio of lake bonneville with the upper bear river diverted into the snake river basin and obtained an 8 7 sr 8 6 sr ratio of 0 71414 coincidentally this ratio is close to the observed ratio for great salt lake of 0 71469 this means that 8 7 sr 8 6 sr ratios of 0 714 for carbonate can be produced by climatically induced low lake conditions or by diversion of the upper bear river out of the bonneville basin this model result also demonstrates that the upper bear river had to be flowing into the bonneville basin during highstands of other late quaternary lake cycles carbonates from the little valley 130 160 ka and cutler dam 59 5 ka lake cycles returned 8 7 sr 8 6 sr ratios of 0 71166 and 0 71207 respectively and are too low to be produced by a lake without the upper bear river input

new evidence for persistent impact generated hydrothermal activity in the miocene ries impact structure germany the extent of impact generated hydrothermal activity in the 24 km sized ries impact structure has been controversially discussed to date mineralogical and isotopic investigations point to a restriction of hydrothermal activity to the impact melt bearing breccias specifically the crater fill suevite here we present new petrographic geochemical and isotopic data of postimpact carbonate deposits which indicate a hydrothermal activity more extended than previously assumed specifically carbonates of the erbisberg a spring mound located upon the inner crystalline ring of the crater show travertine facies types not seen in any of the previously investigated sublacustrine soda lake spring mounds of the ries basin in particular the streamer carbonates which result from the encrustation of microbial filaments in subaerial spring effluents between 60 and 70 c are characteristic of a hydrothermal origin while much of the primary geochemical and isotopic signatures in the mound carbonates have been obliterated by diagenesis a postimpact calcite vein from brecciated gneiss of the subsurface crater floor revealed a flat rare earth element pattern with a clear positive eu anomaly indicating a hydrothermal fluid convection in the crater basement finally the strontium isotope stratigraphic correlation of the travertine mound with the crater basin succession suggests a hydrothermal activity for about 250 000 yr after the impact which would be much longer than previously assumed

a prospective earthquake forecast experiment in the western pacific summary since the beginning of 2009 the collaboratory for the study of earthquake predictability csep has been conducting an earthquake forecast experiment in the western pacific this experiment is an extension of the kagan jackson experiments begun 15 years earlier and is a prototype for future global earthquake predictability experiments at the beginning of each year seismicity models make a spatially gridded forecast of the number of mw 5 8 earthquakes expected in the next year for the three participating statistical models we analyse the first two years of this experiment we use likelihood based metrics to evaluate the consistency of the forecasts with the observed target earthquakes and we apply measures based on student s t test and the wilcoxon signed rank test to compare the forecasts overall a simple smoothed seismicity model triples performs the best but there are some exceptions that indicate continued experiments are vital to fully understand the stability of these models the robustness of model selection and more generally earthquake predictability in this region we also estimate uncertainties in our results that are caused by uncertainties in earthquake location and seismic moment our uncertainty estimates are relatively small and suggest that the evaluation metrics are relatively robust finally we consider the implications of our results for a global earthquake forecast experiment

chlorophyll a and pheopigments as tracers of labile organic carbon at the central equatorial pacific seafloor high rates of primary production and fast sinking rates lead to the deposition of phytodetritus and highly reactive organic matter to the sediments of the central equatorial pacific these substances are responsible for driving important chemical fluxes and fueling benthic organisms chloropigments have proven useful as tracers of similar highly reactive organic carbon components in lacustrine and nearshore marine sediments in this study we investigate the degradation of chlorophyll a and pheopigments a at four abyssal sites on the jgofs equatorial pacific transect along 140 w and explore the usefulness of these chloropigments as tracers of the most reactive component of the deep sea particulate organic carbon poc rain first order reaction rate constants k 1 75 yr 1 half life 3 250 d and relative reactivities chlorophyll a allomer and pheophorbide a pheophytin a derived from most of the sedimentary profiles are similar to those found in laboratory and other field lake and coastal marine studies however in some profiles the rate constants determined by fitting data below 0 5 cm are slower by up to 3 orders of magnitude despite an apparent abundance of bacteria macrofauna and porewater oxygen model results assuming multi g kinetics suggest that these chloropigments degrade as two components one which accounts for at least 99 of the degradation and 11 57 of the sediment inventory degrades with a half life of 4 120 days the other component degrades with a half life of up to 440 years these results suggest that some otherwise labile poc may be protected and escape rapid degradation near the sediment water interface if phytodetritus is deposited continuously throughout the year our model calculated chlorophyll a fluxes indicate that it could account for 25 100 of the annual poc flux at sites close to the equator

stable isotope composition of bentonites from the swiss and bavarian freshwater molasse as a proxy for paleoprecipitation abstract the hydrogen and oxygen isotope compositions of bentonites and smectite rich tuffs from the north alpine foreland basin were measured for samples dated between 9 and 21 ma assuming clay mineral formation shortly after the deposition of the volcanic ash layers and at surface temperatures estimated from paleoclimatic studies the h and o isotope composition of water in equilibrium with the clay minerals can be calculated a comparison with values derived from other proxies of paleoprecipitation in the molasse basin such as pedogenic carbonates and mammal remains and 18 o values of carbonate in the bentonite beds suggests that the 18 o values of water estimated by this method are typical for foreland precipitation at this time and for this region therefore the 18 o value of smectite in bentonites and altered tuff layers can be a useful tool for studies of paleoclimate and topography there are however indications that the clay minerals did not retain their initial hydrogen isotopic composition but that a postformational exchange of h isotopes has occurred

watershed reconstruction of a paleocene eocene lake basin using sr isotopes in carbonate rocks provenance studies have used sr isotopes 87 sr 86 sr of silicate source rocks as a link to their eroded basinal equivalents this technique however cannot identify the proportional inputs from different watersheds or define more precisely sedimentation events due to tectonic or climatic change erosion of carbonate rocks dominates the sr input within basin drainage and potentially can be used through 87 sr 86 sr ratios to reconstruct paleohydrology of the entire basin and trace watershed inputs and depositional patterns in continental basins the sr isotopic ratios from waters of the source area allowing for the mixing of shallow groundwater and surface water along the transport path are homogenized in the basinal carbonate sediments mineralogy and diagenesis of carbonate rocks generally do not affect the sr isotopic signal in a near surface system lacking external influence by volcanism eolian dust or deep geothermal waters the 87 sr 86 sr ratios from the source area are directly comparable to those in the receiving continental basin the sr isotopic signal of the paleocene eocene flagstaff formation central utah a carbonate lake deposit in a foreland basin is compared to that of projected source waters draining its thrust front the sevier fold thrust belt freshwater carbonates compose a large portion of the lowermost ferron mountain and uppermost musinia peak members of the formation whereas gypsum and carbonates predominate in the middle cove mountain member previous research had attributed gypsum deposition to the deposition of the middle cove mountain member to either climatic change or unroofing of diapirs of jurassic gypsiferous carbonates to examine more closely the influence of climate versus tectonics on flagstaff sedimentation as well as the efficacy of provenance studies using carbonates we collected rock samples from the three members of the formation on the wasatch plateau of central utah in addition to sampling stream water associated with pennsylvanian permian and jurassic carbonate terrains from the nearby thrust front the 87 sr 86 sr ratios in carbonates and gyprock belonging to the flagstaff formation remained unchanged during deposition the average sr isotope composition of the flagstaff rocks being identical to that of sampled waters draining the projected provenance area there was little change in source rock weathering as the thrust front evolved deposition of gypsum occurred in the basinal lake only during the deposition of the middle cove mountain member despite its constant exposure in the drainage area suggesting a changing balance of tectonic and climatic controls during lake sedimentation the 87 sr 86 sr isotopic studies targeting carbonate rocks and their presumed source waters are a simple but accurate method for reconstructing the paleohydrology of lake basins

geochemical studies of the subo 18 enkingen drill core and other impact breccias from the ries crater germany suevite and melt breccia compositions in the boreholes enkingen and polsingen are compared with compositions of suevites from other ries boreholes and surface locations and discussed in terms of implications for impact breccia genesis no significant differences in average chemical compositions for the various drill cores or surface samples are noted compositions of suevite and melt breccia from southern and northeastern sectors of the ries crater do not significantly differ this is in stark contrast to the published variations between within crater and out of crater suevites from northern and southern sectors of the bosumtwi impact structure ghana locally occurring alteration overprint on drill cores especially strong on the carbonate impregnated suevite specimens of the enkingen borehole does affect the average compositions overall the composition of the analyzed impact breccias from ries are characterized by very little macroscopically or microscopically recognized sediment clast component the clast populations of suevite and impact melt breccia are dominated consistently by granitic and intermediate granitoid components the polsingen breccia is significantly enriched in a dioritic clast component overall chemical compositions are of intermediate composition as well with dioritic granodioritic silica contents and relatively small contributions from mafic target components selected suevite samples from the enkingen core have elevated ni co cr and ir contents compared with previously analyzed suevites from the ries crater which suggest a small meteoritic component platinum group element pge concentrations for some of the enriched samples indicate somewhat elevated concentrations and near chondritic ratios of the most immobile pge consistent with an extraterrestrial contribution of 0 1 0 2 chondrite equivalent

distribution petrography and shock metamorphism of the ejecta of the ries crater in germany a review abstract the lithologies and distribution of the various ejecta formations from the ries crater germany are described they may be subdivided into 1 low shock level 10 gpa represented by polymict crystalline breccias fall out suevites crater suevite and tektites moldavites the ejecta from the mesozoic sedimentary column do not show effects of shock pressures exceeding 10 gpa and only basement gneisses were shock melted to yield suevite glasses it is therefore concluded that the maximum impact energy was transferred from the impactor to the target rocks at a depth of at least 1000 m below ground level where a complex of gneisses underlies shallower granitic intrusions the estimated depth of the transient crater was about 2700 m and its diameter was 12 13 km bunte breccia megablocks of sedimentary rocks and crystalline breccias and megablocks were ejected in ballistic trajectories and form the earliest ejecta deposits extending up to a radius of 22 km fall out suevites are understood to have been lofted from the transient crater by an expanding plume of vaporized rocks and deposited outside the crater as fluidized turbulent masses on top of the earlier ejecta in contrast the crater suevite never left the crater cavity it represents the main mass of suevite moldavites are understood to have been formed during the first encounter of the impactor with the ground by condensation from vaporized and ionizised tertiary sands covering the surface of the target area

establishing a 14 6 0 2 ma age for the nordlinger ries impact germany a prime example for concordant isotopic ages from various dating materials abstract 40ar 39ar dating of recrystallized k feldspar melt particles separated from partially molten biotite granite in impact melt rocks from the approximately 24 km nordlinger ries crater southern germany yielded a plateau age of 14 37 0 30 0 32 ma 2 this new age for the nordlinger ries is the first age obtained from 1 monomineralic melt 2 separated from an impact metamorphosed target rock clast within 3 ries melt rocks and therewith extends the extensive isotopic age data set for this long time studied impact structure the new age goes very well with the 40ar 39ar step heating and laser probe dating results achieved from mixed glass samples suevite glass and tektites and is slightly younger than the previously obtained fission track and k ar and ages of about 15 ma as well as the k ar and 40ar 39ar age data obtained in the early 1990s taking all the 40ar 39ar age data obtained from ries impact melt lithologies into account data from the literature and this study we suggest an age of 14 59 0 20 ma 2 as best value for the ries impact event

evidence for a spatially extensive hydrothermal system at the ries impact structure germany the 15 ma 26 km diameter ries impact structure in south central germany was one of the first terrestrial impact structures where evidence of impact associated hydrothermal alteration was recognized previous studies suggested that pervasive high temperature hydrothermal activity was restricted to the area within the inner ring i e the crater fill impactite units here we present mineralogical evidence for localized hydrothermal activity in the ejecta beyond the crater rim in two previously unstudied settings a pervasively altered lens of suevite ejecta directly overlying the bunte breccia at the aumuhle quarry and suevite ejecta at depth overlain by 20 m of lacustrine sediments sampled by the wornitzostheim 1965 drill core a comprehensive set of x ray diffraction analyses indicates five distinct alteration regimes 1 surficial ambient weathering characterized by smectite and a minor illitic component 2 locally restricted hydrothermal activity characterized by an illitic component and minor smectite 3 hydrothermal activity at depth characterized by smectite a minor illitic component and calcite 4 hydrothermal activity at depth characterized by smectite a minor illitic component calcite zeolites and clinochlore and 5 pervasive hydrothermal activity at depth characterized by smectite a minor illitic component and minor clinochlore these data spatially extend the ries postimpact hydrothermal system suggesting a much more extensive complex and dynamic system than previously thought constraining the mineralogical alteration regimes at the ries impact structure may also further our understanding of impact associated phyllosilicate formation on mars with implications for climate models and habitability

carbon isotopic compositions of prokaryotic lipids as tracers of carbon cycling in diverse settings recent work has highlighted the ubiquity of bacteria and archaea and continues to affirm their significance in diverse biogeochemical processes the 13c values and distributions of diagnostic lipids derived from such microorganisms can provide insights into prokaryotic processes in modern settings and are one of the few means by which past prokaryotic processes in depositional settings can be elucidated here we present a brief review of prokaryotic lipids commonly observed in sediments and the controls on their carbon isotopic compositions we then present two case studies one of mediterranean cold seeps at which anaerobic oxidation of methane occurs and one of a holocene peat deposit in which a variety of aerobic and anaerobic microorganisms govern the degradation of organic matter these two studies illustrate the potential utility of compound specific carbon isotope analyses to deconvolute pathways of carbon flow in microbial communities

ries crater and suevite revisited observations and modeling part i observations we report results of an interdisciplinary project devoted to the 26 km diameter ries crater and to the genesis of suevite recent laboratory analyses of crater suevite occurring within the central crater basin and of outer suevite on top of the continuous ejecta blanket as well as data accumulated during the past 50 years are interpreted within the boundary conditions imposed by a comprehensive new effort to model the crater formation and its ejecta deposits by computer code calculations artemieva et al 2013 the properties of suevite are considered on all scales from megascopic to submicroscopic in the context of its geological setting in a new approach we reconstruct the minimum maximum volumes of all allochthonous impact formations 108 116 km3 of suevite 14 22 km3 and the total volume of impact melt 4 9 8 0 km3 produced by the ries impact event prior to erosion these volumes are reasonably compatible with corresponding values obtained by numerical modeling taking all data on modal composition texture chemistry and shock metamorphism of suevite and the results of modeling into account we arrive at a new empirical model implying five main consecutive phases of crater formation and ejecta emplacement numerical modeling indicates that only a very small fraction of suevite can be derived from the primary ejecta plume which is possibly represented by the fine grained basal layer of outer suevite the main mass of suevite was deposited from a secondary plume induced by an explosive reaction fuel coolant interaction of impact melt with water and volatile rich sedimentary rocks within a clast laden temporary melt pool both melt pool and plume appear to be heterogeneous in space and time outer suevite appears to be derived from an early formed melt rich and clast poor plume region rich in strongly shocked components melt clasts and originating from an upper more marginal zone of the melt pool crater suevite is obviously deposited from later formed clast rich and melt poor plumes dominated by unshocked and weakly shocked clasts and derived from a deeper central zone of the melt pool genetically we distinguish between primary suevite which includes dike suevite the lower sublayer of crater suevite and possibly a basal layer of outer suevite and secondary suevite represented by the massive upper sublayer of crater suevite and the main mass of outer suevite

interpretation of earthquake epicenter and cmt centroid locations in terms of rupture length and direction abstract a comparison is made between hypocenter and centroid estimates of shallow earthquakes to investigate whether the difference between these two quantities contains useful information on fault rupture length and direction an initial comparison of international seismological centre isc and harvard centroid moment tensor cmt catalog locations suggests that for earthquakes below mw 6 5 the difference in location is dominated by location errors whilst larger earthquakes appear to show the effect of increasing spatial rupture however for this data set combined location errors greater than 25 km are observed for a majority of earthquakes imposing a limit on interpretation we use these constraints to investigate this approach using a consistent earth model in the re analysis of eight previously well studied events new hypocenter estimates based on teleseismic p wave arrivals from the isc bulletin and a 3 d velocity model of the mantle s p12 wm13 are compared with new centroid locations obtained using the same 3 d model and waveform data from international deployment of accelerometers ida global digital seismic network gdsn and re calibrated high gain long period hglp stations the distance between our new hypocenter and centroid locations is shown to provide reliable information on both the rupture length and direction the rupture lengths and azimuths generally agree with the most recent previous results from other methods and provide an absolute estimate of the location of the rupture

synorogenic evolution of large scale drainage patterns isotope paleohydrology of sequential laramide basins in the past decade we and others have compiled an extensive dataset of o c and sr isotope stratigraphies from sedimentary basins throughout the paleogene north american cordillera in this study we present new results from the piceance creek basin of northwest colorado which record the evolving hydrology of the eocene green river lake system we then place the new data in the context of the broader cordilleran dataset and summarize implications for understanding the synorogenic evolution of large scale drainage patterns the combined data reflect 1 a period of throughgoing foreland rivers heading in the sevier fold and thrust belt and flowing east 2 ponding of freshwater lakes in the foredeep as laramide uplifts blocked drainage 3 hydrologic closure that led to both intensive evaporation in the terminal sink of the piceance creek basin and integration of catchments over length scales 1000 km 4 infilling of basin accommodation by southward migrating magmatism in distal catchments leading to the freshening and demise of intraforeland lakes that also stepped south over time

palaeoenvironmental and diagenetic reconstruction of a closed lacustrine carbonate system the challenging marginal setting of the miocene ries crater lake germany chemostratigraphic studies on lacustrine sedimentary sequences provide essential insights on past cyclic climatic events on their repetition and prediction through time diagenetic overprint of primary features often hinders the use of such studies for palaeoenvironmental reconstruction here the potential of integrated geochemical and petrographic methods is evaluated to record freshwater to saline oscillations within the ancient marginal lacustrine carbonates of the miocene ries crater lake germany this area is critical as it represents the transition from shoreline to proximal domains of a hydrologically closed system affected by recurrent emergent events representing the boundaries of successive sedimentary cycles chemostratigraphy targets shifts related to subaerial exposure and or climatic fluctuations methods combine facies changes with 13c 18o chemostratigraphy from matrix carbonates across five closely spaced temporally equivalent stratigraphic sections isotope composition of ostracod shells gastropods and cements is provided for comparison cathodoluminescence and back scatter electron microscopy were performed to discriminate primary syn depositional from secondary diagenetic features meteoric diagenesis is expressed by substantial early dissolution and dark blue luminescent sparry cements carrying negative 13c and 18o sedimentary cycles are not correlated by isotope chemostratigraphy both matrix 13c and 18o range from ca 7 5 to 4 0 and show clear positive covariance r 0 97 whose nature differs from that of previous basin oriented studies on the lake negative values are here unconnected to original freshwater lacustrine conditions but reflect extensive meteoric diagenesis while positive values likely represent primary saline lake water chemistry noisy geochemical curves relate to heterogeneities in primary porosity resulting in selective carbonate diagenesis this study exemplifies that ancient lacustrine carbonates despite extensive meteoric weathering are capable to retain key information for both palaeoenvironmental reconstruction and the understanding of diagenetic processes in relation with those primary conditions also it emphasizes the limitation of chemostratigraphy in fossil carbonates and specifically in settings that are sensitive for the preservation of primary environmental signals such as lake margins prone to meteoric diagenesis this article is protected by copyright all rights reserved

the determination of platinum group elements pge in target rocks and fall back material of the nordlinger ries impact crater germany abstract the nature of the impactor for the nordlinger ries has so far remained elusive suggestions have been made for a chondritic or an aubritic proctile but all studies had difficulties to establish beyond doubt the meteoritic parental material the majority of the ries samples so far analyzed derived from the present surface which may have lead to some bias therefore we analyzed fifty five drill core samples from the research borehole nordlingen 1973 to characterize the indigenous ir concentrations of the target rocks and to search for any enrichments of pt group elements in the suevite and the so called graded unit we found that ultramafic rocks in the crystalline basement at a depth of 826 m far below the current crater bottom contain up to 0 5 ng g ir the highest concentrations ever measured in the target rocks these rocks comprise about 8 of the crystalline basement and thus form a substantial indigenous source of pt group elements taking this into account one has to consider ir concentrations of up to about 0 060 ng g as indigenous although the median concentration is 0 013 ng g close to earlier estimates our results show that there is no indication of unequivocal extraterrestrial contamination in the cored materials of the crater ejecta it is surprising that this also holds for the current crater bottom and the graded unit which have previously been suspected to contain meteoritic contamination it seems that a chondritic projectile can be ruled out but a clear geochemical association of any of the known meteorite types with the ries bolide is not possible

the occurrence of calcified planktonic green algae in freshwater carbonates phacotus and coccomonas two carbonate secreting non marine planktonic chlorophyte genera are important sediment contributors mainly in hard water lakes the calcite loricae of these flagellate algae exhibit characteristic features easily recognizable under the microscope making phacotus and coccomonas important facies fossils for the recognition of ancient non marine environments the fossil record of phacotus can be traced back to the miocene and it is probable that further research could extend this record into pre tertiary periods

petrography of the impact breccias of the enkingen subo 18 drill core southern ries crater germany new estimate of impact melt volume a new drill core subo 18 that intersects a continuous sequence of impact breccias has been obtained at the town of enkingen at the southern edge of the ries inner crater detailed petrographic analysis of this core provides important new information regarding the nature and origin of within crater suevite which is not only relevant for the understanding of the formation of the ries impact structure but has strong implications for impact breccia deposition in general in the enkingen core below 21 m of crater sediment 90 m of impact breccia have been sampled most of this material is what in the past has been referred to as suevite defined as groundmass of clastic material entraining cogenetic melt fragments and target rock clasts only the bottommost 10 m of core are melt dominated impact breccia any relatively thick melt rock intersection along this core is revealed to be composed of individual centimeter to decimeter sized melt bodies best described as agglomerate due to its close resemblance to volcaniclastics of that type detailed macro meso and microscopic petrographic analysis has established that the subo 18 impact breccias cannot be divided into distinct units the groundmass is extensively altered to phyllosilicate smectite or chlorite or carbonate minerals results of a detailed scanning electron microscopic investigation of the groundmasses of samples from all parts of this sequence emphatically support the traditional definition of suevite irrespective of scale modal analysis at macroscopic to submicroscopic scales has shown that the overall average melt content of enkingen suevite is on the order of 48 vol this exceeds by far previous estimates and brings the ries crater melt volume in line with values traditionally suggested from crater and melt volume scaling for similar sized impact structures in crystalline and mixed targets

fresh water carbonates from the lower freshwater molasse oligocene western switzerland sedimentology and stable isotopes abstract the lower freshwater molasse of western switzerland comprises a thick series of continental deposits of late oligocene early miocene age fresh water carbonates occur at two main horizons within this succession lower chattian palustrine carbonates calcaires inferieurs show a shallow fresh water fauna flora of ostracods and charophytes but display clear evidence of subaerial exposure in the form of glaebule pisoid formation circumgranular cracking rhizoliths and microkarstic cavities repeated desiccation led to locally intense modification by pedogenesis these horizons record the development of shallow ephemeral lakes at the northern margin of the swiss molasse basin stable isotope analyses were carried out on 46 calcite samples data from matrix and intraclasts reveal typical fresh water compositions 13c 5 to 7 5 18o 5 5 to 9 a weak co variant trend suggests deposition in hydrologically closed lakes although the range of 13c values recorded is also consistent with pedogenetic overprinting associated with subaerial exposure spar cements and vadose crystal silts display 13c compositions from 6 to 7 but show light 18o values from 10 to 11 recording formation from meteoric waters upper chattian carbonates calcaires d eau douce et dolomie include algal ostracodal laminites interpreted as profundal lake deposits as well as bioturbated shallow lake charophyte ostracod mudstones and wackestones sandy wackestones and white dolomite stable isotope analyses 20 calcites 2 dolomites show 13c values from 2 to 6 and 18o from 6 to 11 data for laminites and biomicrites plot in different fields variations in carbon isotopic composition may be attributable to higher organic productivity during high lake stands the laminites show heavier 13c values or to areal differences in the proportions of biogenic authigenic and detrital carbonate 13c values are generally higher in areas of greater detrital carbonate supply the heavier 18o values shown by the dolomites 13 c 3 18 o 0 to 1 suggest formation from evolved evaporitic lake waters these carbonates record deposition in an extensive possibly deeper lake complex subject to clastic input from the alps in the south

earthquake forecasting in diverse tectonic zones of the globe we present a simple method for long and short term earthquake forecasting estimating earthquake rate per unit area time and magnitude for illustration we apply the method to the pacific plate boundary region and the mediterranean area surrounding italy and greece our ultimate goal is to develop forecasting and testing methods to validate or falsify common assumptions regarding earthquake potential our immediate purpose is to extend the forecasts we made starting in 1999 for the northwest and southwest pacific to include somewhat smaller earthquakes and then adapt the methods to apply in other areas the previous forecasts used the cmt earthquake catalog to forecast magnitude 5 8 and larger earthquakes like our previous forecasts the new ones here are based on smoothed maps of past seismicity and assume spatial clustering our short term forecasts also assume temporal clustering an important adaptation in the new forecasts is to abandon the use of tensor focal mechanisms this permits use of earthquake catalogs that reliably report many smaller quakes with no such mechanism estimates the result is that we can forecast earthquakes at higher spatial resolution and down to a magnitude threshold of 4 7 the new forecasts can be tested far more quickly because smaller events are considerably more frequent also our previous method used the focal mechanisms of past earthquakes to estimate the preferred directions of earthquake clustering however the method made assumptions that generally hold in subduction zones only the new approach escapes those assumptions in the northwest pacific the new method gives estimated earthquake rate density very similar to that of the previous forecast

new 40ar 39ar dating of the clearwater lake impact structures quebec canada not the binary asteroid impact it seems abstract the two clearwater lake impact structures quebec canada are generally interpreted as a crater doublet formed by the impact of a binary asteroid here arguments are presented that raise important questions about the proposed double impact scenario new 40 ar 39 ar dating of two virtually fresh impact melt rock samples from the 36 km west clearwater lake impact structure yielded two statistically robust early permian plateau ages with a weighted mean of 286 2 2 2 2 6 ma 2 mswd 0 33 p 0 57 in contrast 40 ar 39 ar results for two chloritized melt rocks from the 26 km east clearwater lake impact structure produced disturbed age spectra suggestive of a distinct extraneous argon component although individually weakly robust age spectra corrected for the trapped argon component and inverse isochron plots for the east clearwater melt rocks consistently yielded apparent ages around 460 470 ma no permian signal was found in either of these melt aliquots our new 40 ar 39 ar results reproduce earlier 40 ar 39 ar plateau ages 283 ma and 465 ma respectively for the two impact structures by bottomley et al 1990 and are in conflict with a previous statistically non robust rb sr age of 287 293 26 ma for east clearwater the combined cluster of apparent ages of 460 470 ma derived from four different samples across the impact melt sheet is very unlikely to represent a false age effect due to the incorporation of extraneous argon into the melt instead it strongly favors a middle ordovician age for the east clearwater impact and impact induced hydrothermal chloritization moreover the clearwater impact structures are characterized by different natural remanent magnetizations testifying to separate geologic histories an effect unexpected in the case of a permian double impact whereas the west clearwater impact affected ordovician carbonates incorporated into the impact breccia drill core reports from the 1960s concluded that clasts of ordovician sedimentary rocks are seemingly absent in the impact breccia lens of the east clearwater lake impact structure which is overlain by 100 m of post impact sandstones shales and carbonates no resolvable impactor contamination has so far been detected in the west clearwater impact melt rocks whereas east clearwater carries a distinct ordinary possibly l chondritic impactor signature in its melt rocks east clearwater lake might thus represent one among a long list of ordovician impact structures in north america and northern europe that were presumably formed in response to the l chondrite asteroid breakup event 470 ma ago paleogeographic reconstructions show that the ordovician east clearwater impact probably occurred in a near coastal to shallow marine setting while the permian west clearwater impact hit continental pangaea along with the new 40 ar 39 ar data the paleomagnetic sedimentologic and geochemical findings suggest that the close spatial arrangement of the two clearwater lakes is most likely pure coincidence the two impact structures seem to represent a false doublet struck by impacts separated by 180 million years in time the new results for the clearwater lake impact structures have major implications for the reliable identification of doublet impact craters and the rate of binary asteroid impacts on earth and on other planetary bodies in the inner solar system

statistical model for standard seismicity and detection of anomalies by residual analysis abstract a statistical point process model is derived to describe the standard activity of earthquake occurrences by assuming that general seismicity is given by the superposition of aftershock sequences the parameters are estimated ty the maximum likelihood method using the estimated model the residual point process of the data is defined and used to find the anomalies which are included in the data set but not captured in the considered model for the standard seismicity for instance seismic quiescences can be measured quantitatively by using the residual process some examples are provided to illustrate such analyses furthermore a time series of the magnitudes on the residual point process is considered to investigate its dependence either on the time or on the history of the seismicity by assuming the exponential distribution at each time and modelling of the b value we can examine such dependences and estimate them two practical examples are shown

the geochemistry of lake bosumtwi a hydrologically closed basin in the humid zone of tropical ghana lake bosumtwi lies in an isolated hydrologically closed basin formed by a meteor impact 1 x 10 6 yr ago comparison of lake water samples taken in 1993 with one from 1934 shows a decrease in the concentrations of dissolved solutes most likely owing to an estimated 13 increase in lake volume a mass balance calculation that uses an estimate of the average chloride composition of the rainfall shows that the most recent overflow of the lake occurred within the last 3 000 yr evaluation of the sources and sinks of major solutes suggests that deposition of harmattan dust may be an important component of the influx of ions into the lake although the lake is homogeneous with respect to major ion composition it is stratified into an upper oxygenated layer and a lower anoxic layer and there is an abrupt change in the concentration profiles of ph nh 4 po 4 3 no 3 and mn at a depth of 16 m this chemical stratification is apparently caused by photosynthesis in the upper layer and respiration and reducing conditions below the stable isotopic composition of the lake water is reasonably well simulated by a simple isotope balance model for the lake the model is used to show that the 18 o composition of the lake is relatively insensitive to changes in the water balance but is highly sensitive to relative humidity and the isotopic composition of atmospheric moisture

long term probabilistic forecasting of earthquakes we estimate long term worldwide earthquake probabilities by extrapolating catalogs of seismic moment solutions we base the forecast on correlations of seismic moment tensor solutions the forecast is expressed as a map showing predicted rate densities for earthquake occurrence and for focal mechanism orientation focal mechanisms are used first to smooth seismicity maps to obtain expected hazard maps and then to forecast mechanisms for future earthquakes several types of smoothing kernels are used in space domain we use the 1 distance kernel for the distribution of seismicity around any epicenter the kernel is parameterized using two adjustable parameters maximum distance and directivity distribution of seismicity around an epicenter with regard to the focal mechanism of an earthquake for temporal prediction we use the poisson hypothesis of earthquake temporal behavior we test these forecasts we use the first half of a catalog to smooth seismicity level and the second half of the catalog is used to validate and optimize the prediction to illustrate the technique we use available data in the harvard catalog of seismic moment solutions to evaluate seismicity maps for several seismic regions the method can be used with similar catalogs the technique is completely formal and does not require human operator intervention hence the prediction results can be objectively tested moreover the maps can be used as the poisson null hypothesis for testing by the likelihood method against any other prediction model which shares the same sample space the same zones time window and acceptance criteria

short term fluctuations in vegetation and phytoplankton during the middle eocene greenhouse climate a 640 kyr record from the messel oil shale germany the palaeogene was the most recent greenhouse period on earth especially for the late palaeocene and early eocene several superimposed short term hyperthermal events have been described including extremes such as the palaeocene eocene thermal maximum major faunal and floral turnovers in the marine and terrestrial realms were recorded in association with these events high resolution palynological analysis of the early middle eocene maar lake sediments at messel near darmstadt germany provides an insight into the dynamics of a climax vegetation during the middle eocene greenhouse climate in a time span without significant climatic excursions numerical techniques like detrended correspondence analysis and wavelet analysis have been applied to recognize cyclic fluctuations and long term trends in the vegetation through a time interval of approximately 640 kyr based on the numerical zoning of the pollen diagram three phases in the development of the vegetation may be distinguished throughout these phases the climax vegetation did not change substantially in qualitative composition but a trend towards noticeably less humid conditions probably in combination with a drop of the water level in the lake may be recognized a shift in algal population from the freshwater dinoflagellate cyst messelodinium thielepfeifferae to a dominance of botryococcus in the uppermost part of the core is interpreted as a response to changes in acidity and nutrient availability within the lake time series analyses of pollen assemblages show that variations in the milankovitch range of eccentricity obliquity and precession can be distinguished in addition fluctuations in the sub milankovitch range are indicated this demonstrates that floral changes during steady depositional conditions in the middle eocene of messel were controlled by orbital forcing

what do we really know about early diagenesis of non marine carbonates abstract non marine carbonate rocks including cave spring stream calcrete and lacustrine palustrine sediments are susceptible to early diagenetic processes these can profoundly alter the carbonate fabric and affect paleoclimatic proxies this review integrates recent insights into diagenesis of non marine carbonates and in particular the variety of early diagenetic processes and presents a conceptual framework to address them with ability to study at smaller and smaller scales down to nanometers one can now observe diagenesis taking place the moment initial precipitates have formed and continuing thereafter diagenesis may affect whole rocks but it typically starts in nano and micro environments the potential for diagenetic alteration depends on the reactivity of the initial precipitate commonly being metastable phases like vaterite ca oxalates hydrous mg carbonates and aragonite with regard to the ambient fluid furthermore organic compounds commonly play a crucial role in hosting these early transformations processes like neomorphism inversion and recrystallization cementation and replacement generally result in an overall coarsening of the fabric and homogenization of the wide range of complex primary microtextures if early diagenetic modifications are completed in a short time span compared to the annual to millennial time scale of interest then recorded paleoenvironmental signals and trends could still acceptably reflect original depositional conditions however even compact non marine carbonate deposits may behave locally and temporarily as open systems to crystal fluid exchange and overprinting of one or more geochemical proxies is not unexpected looking to the future relatively few studies have examined the behaviour of promising geochemical records such as clumped isotope thermometry and non conventional stable isotopes in well constrained diagenetic settings ongoing and future in vitro and in situ experimental approaches will help to investigate and detangle sequences of intermediate diagenetic products processes and controls and to quantify rates of early diagenesis bridging a gap between nanoscale molecular lab studies and the fossil field rock record of non marine carbonates

dolomite formation in the dynamic deep biosphere results from the peru margin early diagenetic dolomite beds were sampled during the ocean drilling programme odp leg 201 at four reoccupied odp leg 112 sites on the peru continental margin sites 1227 684 1228 680 1229 681 and 1230 685 and analysed for petrography mineralogy 13c 18o and 87sr 86sr values the results are compared with the chemistry and 13c and 87sr 86sr values of the associated porewater petrographic relationships indicate that dolomite forms as a primary precipitate in porous diatom ooze and siliciclastic sediment and is not replacing the small amounts of precursor carbonate dolomite precipitation often pre dates the formation of framboidal pyrite most dolomite layers show 87sr 86sr ratios similar to the composition of quaternary seawater and do not indicate a contribution from the hypersaline brine which is present at a greater burial depth also the 13c values of the dolomite are not in equilibrium with the 13c values of the dissolved inorganic carbon in the associated modern porewater both petrography and 87sr 86sr ratios suggest a shallow depth of dolomite formation in the uppermost sediment 30 m below the seafloor a significant depletion in the dissolved mg and ca in the porewater constrains the present site of dolomite precipitation which co occurs with a sharp increase in alkalinity and microbial cell concentration at the sulphate methane interface it has been hypothesized that microbial hot spots such as the sulphate methane interface may act as focused sites of dolomite precipitation varying 13c values from 15 to 15 for the dolomite are consistent with precipitation at a dynamic sulphate methane interface where 13c of the dissolved inorganic carbon would likewise be variable a dynamic deep biosphere with upward and downward migration of the sulphate methane interface can be simulated using a simple numerical diffusion model for sulphate concentration in a sedimentary sequence with variable input of organic matter thus the study of dolomite layers in ancient organic carbon rich sedimentary sequences can provide a useful window into the palaeo dynamics of the deep biosphere

distribution classification and ages of martian impact crater lakes paleolakes in impact craters on mars are characterized at global scale using the viking orbiter data we identified 179 paleolakes in impact structures formed by the influx of water and sediment derived from valley networks and channels that can be classified into three different fluviolacustrine systems closed open and lake chain systems we show the hydrogeologic implications for each of the three systems and their significance in terms of duration of fluviolacustrine activity this study provides a catalog of areographic physical and physiographic data for each of the studied impact crater lakes associated with the description of the sedimentary structures observed it also identifies environments where life and or precursors to life could have found favorable conditions to evolve

chemical and ecological evolution of the miocene ries impact crater lake germany a reinterpretation based on the enkingen subo 18 drill core scientific drilling conducted at the inner slope of the miocene central ries impact crater recovered a partial section of crater lake sediments four sequences were recovered composed of suevite derived sandstones thin lignite seams bituminous shales and marlstones to claystones these flooding evaporation sequences reflect the impact of short term climatic fluctuations on a hydrologically closed basin the superimposed trend from sequences rich in bituminous shales in the lower parts of the section to sequences dominated by organic poor claystones and intercalated lignites in the upper parts of the section resembles that of the 300 m thick central crater basin succession which has previously been considered to reflect a climate controlled development from an alkaline saline lake to a freshwater lake with temporary coal swamps in the sediment core of enkingen however the change from bituminous shales to organic poor claystones with intercalated lignites is associated with a general increase in salinity as indicated by 1 palynomorphs 2 increase in 13c of the lipid biomarker archaeol bis o phytanylglycerol and 3 the occurrence of 13c enriched c20 c25 archaeol o phytanyl o sesterterpanylglycerol specific to halophilic archaea in addition the unidirectional trend in 87sr 86sr of carbonates declining from ratios of variscan basement rocks toward marine ratios indicates a change from 1 weathering of crystalline rocks and suevite to 2 ejected jurassic sediments bunte breccia in the catchment area as the major source of ion influx to the lake from that trend a change in lake water composition and a general increase in ion concentrations are inferred these new results can be applied to a reassessment of major parts of the lacustrine succession of the ries crater we use these data to propose a new hypothetical model for the chemical and ecological evolution of the ries crater lake 1 after the establishment of a stratified brackish eutrophic soda lake due to silicate weathering and evaporation the increasing influx of waters from the bunte breccia carbonate and authigenic silicate precipitation led to a mesotrophic halite lake with marine like ion ratios and concentrations 2 further increase in ions among them mg2 and sr2 resulted in hypersaline conditions with gypsum precipitation low primary production and phreatic sr rich dolomitization in marginal carbonates 3 the final sudden change to oligotrophic freshwater conditions is explained by the formation of an outlet late in the lake history we conclude that the chemical and ecological evolution of the ries lake therefore appears to have been mainly controlled by the weathering history of the catchment area with climate fluctuations causing superimposed cycles similarly changes in terrestrial palynomorph associations may at least partly reflect a change in soil types in the catchment area from fertile moist soils on suevite to dry karst soils and soils on bunte breccia these interpretations imply that the initial suevite blanket of the ries crater was much more continuous and widespread than previously assumed

molecular proxies for paleoclimatology we summarize the applications of molecular proxies in paleoclimatology marine molecular records especially are proving to be of value but certain environmentally persistent compounds can also be measured in lake sediments loess deposits and ice cores the fundamentals of this approach are the molecular parameters the compound abundances and carbon hydrogen nitrogen and oxygen isotopic contents which can be derived by the analysis of sediment extracts these afford proxy measures which can be interpreted in terms of the conditions which control climate and also reflect its operation we discuss two types of proxy those of terrigenous and those of aquatic origin and exemplify their application in the study of marine sediments through the medium of ten case studies based in the atlantic mediterranean and pacific oceans and in antarctica the studies are mainly for periods in the present the holocene and particularly the last glacial interglacial but they also include one study from the cretaceous the terrigenous proxies which are measures of continental vegetation are based on higher plant leaf wax compounds i e long chain circa c30 hydrocarbons alcohols and acids they register the relative contributions of c3 vs c4 type plants to the vegetation in the source areas the two marine proxies are measures of sea surface temperatures sst the longer established one u37k is based on the relative abundances of c37 alkenones photosynthesized by unicellular algae members of the haptophyta the newest proxy tex86 is based on c86 glycerol tetraethers gdgts synthesized in the water column by some of the archaeal microbiota the crenarchaeota

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

the effect of uncertainties on estimates of background seismicity rate abstract identifying changes in the rate of background earthquakes is a common method to detect transients in seismic activity rates and these transients can often be linked to changes in physical properties of the crust or to the recording homogeneity of seismic networks in this article we consider the effect that various sources of uncertainty have on seismicity rate estimation and we describe a monte carlo method to compute the statistical significance of seismicity rate changes we consider real earthquake catalogs and synthetic catalogs that represent poissonian background seismicity we find that the choice of declustering algorithm and the variation in the related parameter values have the greatest impact on seismicity rate change calculations this sensitivity is a direct consequence of the fact that there is no unique or universally applied approach to separate aftershocks and foreshocks from background events hypocenter location uncertainty also influences the statistical significance of seismicity rate changes its relevance depends on the ratio of the location uncertainty to the extension of the seismicity rate anomaly we find that magnitude uncertainty and edge effects associated with seismicity declustering have less impact than the other factors but their influence is not negligible in an example application we suggest that when uncertainties are considered the reported seismicity rate changes prior to the 1992 landers and big bear mainshocks decrease significantly

rbsr systematics of rocks related to the ries crater germany abstract rb sr whole rock biotite ages of crystalline basement rocks from ries crater are 323 8ma initial 87 sr 86 sr rat are 0 7081 0 0007 these values compare perfectly with those for moldanubian rocks exposed in the bayerischer wald and schwarzwald it is demonstrated that impact related shock pressures up to 15 gpa and temperatures as high as 300 c did not disturb the rb sr isotopic systems of the rocks comparison of sr isotopic compositions of tertiary upper freshwater molasse sediments with those of moldavites suggests that such sediments can be regarded as source material of these tektites our data for components of the sediments show that a mixture of clay weathered crystalline rocks and secondary carbonates in addition to detrital quartz can explain the observed range of 87 sr 86 sr ratios in moldavites a similar comparison of moldavites with bentonites from the tertiary molasse definitely rules out a genetical relationship between these two materials we regard liquid gas filled bubbles in bentonite glasses as proof of their volcanic nature

salinity control on long chain alkenone distributions in lake surface waters and sediments of the northern qinghai tibetan plateau china abstract long chain alkenones in lacustrine settings are potentially excellent biomarkers for the reconstruction of past terrestrial environmental conditions and have been found in many different types of lakes around the globe a wider range of factors influence the occurrence and distribution of alkenones in lake sediments and waters when compared to marine systems lake environmental conditions such as temperature in particular and salinity are among the key factors controlling alkenone distributions in lacustrine settings here we investigated alkenone distribution patterns in lakes of the northern qinghai tibetan plateau china and their possible relationship with environmental conditions by analyzing paired samples of suspended particulate matter in surface waters and surface sediments salinity of investigated lake waters ranges from almost 0 to 100 g l while temperature variation among the lakes is minimal effectively eliminating temperature effects on the alkenone distribution patterns observed here we show that 1 alkenone concentrations vary substantially between the lakes yet controlling mechanisms remain elusive 2 c37 c38 ratios are substantially lower in the lakes of the qaidam basin than in the lake qinghai region probably indicating different alkenone producers in the two regions and 3 large variations in c37 4 the percentage of the c37 4 alkenone determined from both surface waters and sediments are negatively correlated with salinity we suggest that the c37 4 index could be used as a salinity indicator at least on a regional scale with careful considerations of other potentially complicating factors however potential reasons for why salinity could significantly affect c37 4 values need further investigation

an international and multidisciplinary drilling project into a young complex impact structure the 2004 icdp bosumtwi crater drilling project an overview the bosumtwi impact crater in ghana arguably the best preserved complex young impact structure known on earth displays a pronounced rim and is almost completely filled by lake bosumtwi a hydrologically closed basin it is the source crater of the ivory coast tektites the structure was excavated in 2 1 2 2 gyr old metasediments and metavolcanics of the birimian supergroup a drilling project was conceived that would combine two major scientific interests in this crater 1 to obtain a complete paleoenvironmental record from the time of crater formation about one million years ago at a near equatorial location in africa for which very few data are available so far and 2 to obtain a complete record of impactites at the central uplift and in the crater moat for ground truthing and comparison with other structures within the framework of an international and multidisciplinary drilling project led by the international continental scientific drilling program icdp 16 drill cores were obtained from june to october 2004 at six locations within lake bosumtwi which is 8 5 km in diameter the 14 sediment cores are currently being investigated for paleoenvironmental indicators the two impactite cores lb 07a and lb 08a were drilled into the deepest section of the annular moat 540 m and the flank of the central uplift 450 m respectively they are the main subject of this special issue of meteoritics planetary science which represents the first detailed presentations of results from the deep drilling into the bosumtwi impactite sequence drilling progressed in both cases through the impact breccia layer into fractured bedrock lb 07a comprises lithic in the uppermost part and suevitic impact breccias with appreciable amounts of impact melt fragments the lithic clast content is dominated by graywacke besides various metapelites quartzite and a carbonate target component shock deformation in the form of quartz grains with planar microdeformations is abundant first chemical results indicate a number of suevite samples that are strongly enriched in siderophile elements and mg but the presence of a definite meteoritic component in these samples cannot be confirmed due to high indigenous values core lb 08a comprises suevitic breccia in the uppermost part followed with depth by a thick sequence of graywacke dominated metasediment with suevite and a few granitoid dike intercalations it is assumed that the metasediment package represents bedrock intersected in the