translation and docking of an arc terrane geological and geochemical evidence from the southern zambales ophiolite complex philippines abstract the zambales ophiolite complex is made up of three massifs the masinloc cabangan and san antonio massifs field petrographic and geochemical analyses show that the cabangan and san antonio massifs are genetically related to the coto transitional mid ocean ridge island arc and acoje island arc blocks of the masinloc massif respectively the subic bay fault zone a left lateral fault zone separates the san antonio massif island arc terrane from the transitional mid ocean ridge island arc like sheeted diabase dikes pillow basalts of the cabangan massif the san antonio massif is a rifted terrane from the acoje block which was translated southward to its present position through the west luzon shear subic bay fault zone tectonized clinopyroxenite and gabbronorite hills which mimic the physical and geochemical characteristics of the acoje block and the san antonio massif ultramafic mafic cumulate rocks were left behind along the western side of the cabangan massif during the translation of the arc massif southward this scenario can account for the present day configuration of the zambales ophiolite complex

isotopic evidence of c4 grasses in southwestern europe during the early oligocene middle miocene c 4 plants are widely successful in the grass dominated ecosystems of tropical subtropical and warm temperate regions largely as a result of their ability to limit photorespiration and improve water use efficiency a widely held paradigm is that low 2 concentrations were an important factor selecting for the origin of c 4 plants although support in geological records is limited we determined the carbon isotopic composition of 686 individual grass pollen grains preserved in eight samples of lacustrine and shallow marine sediments from three basins spanning the early oligocene to middle miocene in southwestern europe grasses composed 4 grasses thus c 4 grasses occurred on the landscape as early as the earliest oligocene 14 m y earlier than previous isotopic evidence of first c 4 plants and before p co 2 fell during the oligocene

c4 expansion in the central inner mongolia during the latest miocene and early pliocene abstract the emergence of c4 photosynthesis in plants as a significant component of terrestrial ecosystems is thought to be an adaptive response to changes in atmospheric co 2 concentration and or climate during neogene times and has had a profound effect on the global terrestrial biosphere although expansion of c4 grasses in the latest miocene and pliocene has been widely documented around the world the spatial and temporal variations in the c4 expansion are still not well understood and its driving mechanisms remain a contentious issue here we present the results of carbon and oxygen isotope analyses of fossil and modern mammalian tooth enamel samples from the central inner mongolia our samples represent a diverse group of herbivorous mammals including deer elephants rhinos horses and giraffes ranging in age from the late oligocene to modern the 13 c values of 91 tooth enamel samples of early late miocene age or older with the exception of two 13 ma rhino samples 7 8 and 7 6 and one 8 5 ma suspected rhino sample 7 6 were all less than 8 0 vpdb indicating that there were no c4 grasses present in their diets and thus probably few or no c4 grasses in the ecosystems of the central inner mongolia prior to 8 ma however 12 out of 26 tooth enamel samples of younger ages 7 5 ma to 3 9 ma have 13 c values higher than 8 0 up to 2 4 indicating that herbivores in the area had variable diets ranging from pure c3 to mixed c3 c4 vegetation during that time interval the presence of c4 grasses in herbivores diets up to 76 c4 suggests that c4 grasses were a significant component of the local ecosystems in the latest miocene and early pliocene consistent with the hypothesis of a global factor as the driving mechanism of the late miocene c4 expansion today c3 grasses dominate grasslands in the central inner mongolia area the retreat of c4 grasses from this area after the early pliocene may have been driven by regional climate change associated with tectonic processes in central asia as well as global climate change

sedimentology stratigraphy and geochronology of the proterozoic mazatzal group central arizona quartzite conglomerate and shale of the mazatzal group record the filling of a prot erozoic intra arc basin in central arizona u pb ages of zircons from rhyolite ash flow tuff indicate that deposition began at 1701 2 ma basal deposits of the newly defined pine creek conglomerate formed in an alluvial fan setting synchronous with the final phase of extrusive rhyolite volcanism and active faulting after volcanic activity ceased shallower slope braided stream environments developed in early deadman quartzite time subsequent marine transgression produced shallow subaqueous deposits of the upper part of the deadman quartzite these were overlain by prodelta sediments of the maverick shale indicating a phase of basin deepening finally the mazatzal peak quartzite was deposited as the basin shoaled again first to shallow marine and subsequently to fluvial conditions the quartzite is diagenetic quartz arenite originally deposited as lithic arenite and lithic arkose the provenance was initially restricted and earliest sediment was derived mainly from the subjacent red rock group when tectonic activity ceased how ever the surrounding highlands were planed down by erosion and detritus from a wider variety of source rocks was funneled into the basin this included contributions from arc related supracrustal rocks of the payson ophiolite and east verde river formation and finally a granitic basement input detrital quartz in the lower part of the mazatzal group is largely monocrystalline and volcanic in origin polycrystalline quartz associated with detrital feldspar and of probable continental affinity is concentrated in the uppermost parts of the sequence the life span of the intra arc basin was on the order of 30 m y from the formation of the payson ophiolite at 1 73 ga to the deposition of the upper mazatzal peak quartzite sometime after 1 70 ga the pre mazatzal red rock group represents the last stages of volcanic arc activity and the mazatzal group records the transition from orogenic to nonorogenic sedimentation in central arizona

representational bias in phytoliths from modern soils of central north america implications for paleovegetation reconstructions abstract understanding localized patterns and community compositions of vegetation in an environment is critical to the reconstruction of climatic and ecological conditions across all spatiotemporal scales one of the most accurate and useful ways to characterize vegetation and therefore to describe the climatic and ecological conditions of a location is through the plant fossil record phytoliths plant silica microfossils are often preserved in the absence of other paleobotanical data and are becoming more widely used for deep time vegetation reconstructions significant work has been done to standardize the analytical methodology of phytolith extraction statistical analysis and interpretation but more detailed investigations are needed to understand how well a given soil assemblage represents the actual aboveground plant biomass for a given ecosystem we present results from paired soil phytolith assemblages and local vegetation assemblages across the central united states including temperate forest grassland and rangeland scrubland ecosystems phytolith assemblages obtained via extractions from soil a horizons were compared to percent cover of species and plant biomass estimates obtained via in situ field observations and aerial estimates of tree cover to analyze differences in the relative abundance of forest woody vegetation vs grasses soil phytolith assemblages from all sites average a 29 bias toward the grass morphotypes as compared to actual aboveground biomass observations and comparisons to percent cover yielded broadly comparable bias figures percent bias estimates do not show significant correlations to most environmental factors temperature precipitation local elevation however an extremely strong correlation p

the origin and spread of grass dominated ecosystems in the late tertiary of north america preliminary results concerning the evolution of hypsodonty abstract sediment samples were collected in northwestern nebraska from the following lithologic units 1 the upper oligocene monroe creek formation the lower miocene harrison formation and upper harrison beds of the arikaree group and 2 the lower miocene runningwater formation and the dawes clay member box butte formation of the ogallala group the samples were processed using heavy liquid extraction and analyzed for siliceous plant microfossils phytoliths all samples yielded well preserved and diverse assemblages dominated by grass phytoliths but included phytoliths produced by woody and herbaceous dicotyledons palms and sedges the abundance of woody dicotyledons and palms decreased up section the grass assemblages consisted mainly of festucoid c3 phytolith morphotypes an index assessing the amount of tree cover d p the ratio of dicotyledon phytoliths to grass phytoliths was employed to interpret the data according to this analysis there was open c3 dominated grassland in the study area between 25 and 17 ma at least 7 ma before supposed adaptations to grasslands in ungulates hypsodonty originate

the occurrence and significance of biogenic opal in the regolith abstract biogenic opal produced by vascular plants diatoms and siliceous sponges have been found in soils and terrestrial sediments of all continents except antarctica since the middle of the 19th century the opal particles range in size from fine silt to fine sand almost all soils contain detectable opal up to levels of 2 3 and a significant number contain values in excess of 5 even higher values have been found from soils and sediments of all continents in a wide range of soil types the most important factor is poor soil drainage and seasonal to permanent water logging this encourages the proliferation of silica producing organisms such conditions have been found in the soils and aquatic sediments of the monsoonal tropics tropical rain forests temperate forests tropical savanna tropical islands semi arid grasslands and savanna and temperate woodland and grassland the presence of a volcanic substrate also appears favourable in some cases but is not necessary biogenic opal preferentially collects in the a horizon of soils and to a lesser extent in the b horizon this preferential distribution facilitates identification of palaeosols in stacked soil sequences biogenic opal is also a component of windblown dust even in arid environments biogenic opal is significant to regolith processes in a number of ways firstly as in the case in marine environments it is likely to be important in silica cycling and storage because of its greater lability compared to quartz secondly dissolution and reprecipitation of opal a as opal ct or micro quartz may play a role in cementation and silicification of regolith to form silica hardpans and silcrete thirdly the organisms that form biogenic opal can have considerable palaeoenvironmental significance and be valuable in reconstructing regolith evolution finally some forms of biogenic silica in particular sponge spicules can present a health hazard their high abundance in some soils and sediments needs to be considered when assessing the health implications of airborne dust

model uncertainty quantification in seismic tomography method and applications uncertainty is inherent in every stage of the oil and gas exploration and production e p business and understanding uncertainty enables mitigation of e p risks therefore quantification of uncertainty is beneficial for decision making and uncertainty should be managed along with other aspects of business for example decisions on well positioning should take into account the structural uncertainty related to the non uniqueness of a velocity model used to create a seismic depth image moreover recent advances in seismic acquisition technology such as full azimuth long offset techniques combined with high accuracy migration algorithms such as reverse time migration can greatly enhance images even in highly complex structural settings provided that an earth velocity model with sufficient resolution is available modern practices often use non seismic observation to better constrain velocity model building however even with additional information there is still ambiguity in our velocity models caused by the inherent non uniqueness of the seismic experiment many different earth velocity models exist that match the observed seismic and well data and this ambiguity grows rapidly away from well controls the result is uncertainty in the seismic velocity model and the true positions of events in our images tracking these uncertainties can lead to significant improvement in the quantification of exploration risk e g trap failure when well logging data are not representative drilling risk e g dry wells and abnormal pore pressure and volumetric uncertainties whilst the underlying ambiguity can never be fully eradicated a quantified measure of these uncertainties provides a valuable tool for understanding and evaluating the risks and for development of better risk mitigation plans and decision making strategies

a high resolution stable isotopic record from the junggar basin nw china implications for the paleotopographic evolution of the tianshan mountains this study presents high resolution oxygen and carbon isotopic records of paleosol carbonates from fluvial sediments and lacustrine carbonates sampled from the jingou he and kuitun he stratigraphic sections located in the northern tianshan piedmont these sections expose remarkable outcrops of junggar foreland basin sediments that have been previously dated by high resolution magnetostratigraphy to between 23 6 and 1 ma and 10 5 and 3 1 ma a total of 216 samples of fluvio lacustrine sediments were collected from which isotopic analyses yield 18o smow values that range from 13 7 to 29 9 in the jingou he section and 16 3 to 21 0 in the kuitun he section 13c pdb values range from 12 9 to 3 0 in the jingou he section and from 7 8 to 4 0 in the kuitun he section 18o values decrease between 25 and 23 ma and then remain relatively steady with the exception of one period that contains samples with higher oxygen isotope values at 16 ma during the periods when there are samples that overlap in time from the kuitun he and jingou he sections we observe a difference of 1 7 between values from the two locales the 13c values also decrease between 25 and 23 ma and then remain relatively steady until 10 ma with again one short period of higher values at 16 ma then between 10 and 3 1 ma carbon isotope values progressively increase we interpret that 18o and 13c isotopic values during lacustrine periods 25 23 ma and 16 ma as largely controlled by evaporation and opening closing of the lake to external inputs we interpret the 18o values of paleosol carbonate in the junggar basin to be influenced by the hypsometry of the high tianshan range while the 13c values may record the uplift history of the depositional area in the foreland basin itself as well as the isotopic composition of plants consequently we conclude that the jingou he and kuitun he drainage basins in the central tianshan have remained at relatively unchanged elevations for the past 20 ma we also suggest that the elevation of the southern part of the foreland basin increased between 10 and 3 1 ma probably as a result of tectonic deformation in the piedmont and sedimentary filling of the sedimentary basin the carbon isotope record remains relatively stable through time and isotopic values suggest that there was little or no expansion of c4 plants in this region in the late miocene

the structure and rate of late miocene expansion of c4 plants evidence from lateral variation in stable isotopes in paleosols of the siwalik group northern pakistan this study uses stable isotope variation within individual mio pliocene paleosols to investigate subkilometer scale phytogeography of late miocene vegetation change in southeast asia between ca 8 1 and 5 ma a time interval that coincides with dramatic global vegetation change we examine trends through time in the distribution of low latitude grasses c4 plants and forest c3 plants on indo gangetic floodplains using carbon 13c and oxygen isotopic 18o values in buried soil carbonates in siwalik series sediments exposed in the rohtas anticline north central pakistan revised high resolution magnetostratigraphy and a new 40ar 39ar date provide improved age control for the 2020 m rohtas section carbon isotope results capture lateral variability of c3 versus c4 plants at five stratigraphic levels r11 8 0 ma r15 6 74 6 78 ma r23 5 78 ma r29 4 8 4 9 ma and upper boundary tuff ubt 2 4 ma using detailed sampling of paleosols traceable laterally over hundreds of meters paleosols and the contained isotopic results can be assigned to three different depositional contexts within the fluvial sediments channel fill crevassesplay and floodplain environments 13c results show that near the beginning 8 0 ma and after 4 0 ma the period of major ecological change vegetation was homogeneously c3 or c4 respectively regardless of paleo landscape position in the intervening period there is a wide range of values overall with c4 grasses first invading the drier portions of the system floodplain surfaces and c3 plants persisting in moister settings such as topographically lower channel swales although abrupt on a geologic timescale changes in abundance of c4 plants are modest 2 per 100 000 yr compared to rates of vegetation turnover in response to glacial and interglacial climate changes in the quaternary earlier research documented a sharply defined c3 to c4 transition in pakistan between 8 1 and 5 0 ma based on vertical sampling but this higher resolution study reveals a more gradual transition between 8 0 and 4 5 ma in which c3 and c4 plants occupied different subenvironments of the siwalik alluvial plain 18o values as well as 13c values of soil carbonate increase up section at rohtas similar to isotope trends in other paleosol records from the region spatially however there is no correlation between 13c and 18o values at most stratigraphic levels this implies that the changes in soil hydrology brought about by the shift from forest to grassland i e an increase in average soil evaporation did not produce the shift through time in 18o values we interpret the trend toward heavier soil carbonate 18o values as a response to changes in external climatic factors such as a net decrease in rainfall over the past 9 ma

diets and environments of late cenozoic mammals in the qaidam basin tibetan plateau evidence from stable isotopes the timing history and driving mechanisms of c4 expansion and tibetan uplift are hotly debated issues paleoenvironmental evidence from within the tibetan plateau is essential to help resolve these issues here we report results of stable c and o isotope analyses of tooth enamel samples from a variety of late cenozoic mammals including deer giraffe horse rhino and elephant from the qaidam basin in the northeastern tibetan plateau the enamel delta c 13 values are 89 parts per thousand for modern samples and 7 parts per thousand for fossils except for one late miocene rhino cd0722 with delta c 13 values up to 4 1 parts per thousand if the qaidam basin was as arid as today in the mio pliocene these data would indicate that the majority of the animals had c3 diets and only a few individuals besides the exceptional rhino cd0722 may have consumed some c4 plants based on geological evidence however the qaidam basin was probably warmer and more humid during the late miocene and early pliocene than today thus these delta c 13 values likely indicate that many individuals had significant dietary intakes of c4 plants and the qaidam basin had more c4 plants in the late miocene and early pliocene than today moreover the qaidam basin likely had much denser vegetation at those times in order to support such large mammals as rhinos and elephants while the delta o 18 values did not increase monotonously with time the range of variation seems to have increased considerably since the early pliocene indicating increased aridification in the basin the mean delta o 18 values of large mammals and those reconstructed for local meteoric waters display a significant negative shift in the late miocene consistent with the marine delta o 18 record which shows a cooling trend in the same period taken together the isotope data suggest a warmer wetter and perhaps lower qaidam basin during the late miocene and early pliocene increased aridification after the early pliocene is likely due to a combined effect of regional tectonism which resulted in a more effective barrier preventing moisture from the indian ocean or bay of bengal from reaching the basin and global cooling c 2012 elsevier b v all rights reserved

miocene to pliocene changes in south african hydrology and vegetation in relation to the expansion of c4 plants the miocene expansion of c4 plants mainly tropical grasses between 8 and 4 million years ma remains an enigma since regional differences in the timing of the expansion rules out decreased co2 pco2 as a dominant forcing e g tipple and pagani 2007 the early origins of terrestrial c4 photosynthesis annu rev earth planet sci 35 435 461 other environmental factors such as low latitude aridity and seasonality have been proposed to explain the low tree versus grass ratio found in savannahs and tropical grasslands of the world but conclusive evidence is missing here we use pollen and stable carbon 13c and hydrogen d isotope ratios of terrestrial plant wax from a south atlantic sediment core odp site 1085 to reconstruct miocene to pliocene changes of vegetation and rainfall regime of western southern africa our results reveal changes in the relative amount of precipitation and indicate a shift of the main moisture source from the atlantic to the indian ocean during the onset of a major aridification 8 ma ago we emphasize the importance of declining precipitation during the expansion of c4 and cam mainly succulent vegetation in south africa we suggest that the c4 plant expansion resulted from an increased equator pole temperature gradient caused by the initiation of strong atlantic meridional overturning circulation following the shoaling of the central american seaway during the late miocene

pseudostratigraphy and origin of the early proterozoic payson ophiolite central arizona the payson ophiolite ca 1 73 ga exposed within the early proterozoic orogenic belt of central arizona is a shallow dipping pseudostratigraphic sequence of gabbro sheeted dikes and submarine volcanic rocks partly disjointed by later intrusion and deformation an older basement complex occurs as roof pendants in the gabbro and screens in the sheeted dike complex and was tilted and eroded prior to development of the ophiolite gabbro dike mingling and mutual intrusion in the transition from gabbro to sheeted dikes indicates that the dikes are rooted in the gabbro analysis of detailed measured sections of well exposed sheeted dikes 600 m reveals 90 100 dikes with lateral variations in the proportions of tonalitic or dacitic dikes and basement screens the transition from sheeted dikes to submarine basalts is abrupt and marked by a stratigraphically continuous zone of intensely altered rocks the sheeted dike complex pseudostratigraphic structure and synmagmatic hydrothermal alteration of the payson ophiolite are diagnostic of a crustal section formed by sea floor spreading the payson ophiolite intrudes and is intruded by arc granitoids and is overlain by arc derived volcanic and sedimentary rocks a model of an intra arc basin formed along an arc parallel strike slip fault is proposed to account for 1 screens of older arc crust 2 inferred arc parallel extension and 3 juxtaposition of the ophiolite with a distinct arc terrane prior to regional convergent deformation and accretion of the arc to north america during the yavapai orogeny ca 1 70 ga

high resolution isotopic record of c4 photosynthesis in a miocene grassland abstract the origin and spread of grasslands is one of the key evolutionary events in the cenozoic which is characterized by long term cooling and drying climatic conditions one way to examine the relationship between vegetation and climate is to study the isotopic composition of organic carbon preserved in paleosols paleosols that preserve organic matter in the form of carbonaceous root traces provide direct evidence of the proportion of c3 to c4 biomass that grew in the soil in contrast with pedogenic carbonate 13c values which may also reflect complicating factors including mixing from atmospheric 13c in low productivity ecosystems a high temporal and spatial resolution reconstruction of past ecosystems was derived from thirty five paleosols in a thirty four meter section of the sixmile creek formation at timber hills montana usa that was deposited during the miocene 10 2 8 9 ma ago phytoliths were extracted from paleosol samples to compare vegetation assemblages to inferences based on isotopic compositions with both proxies giving similar results isotopic results from organic matter indicate both a small component of c4 photosynthetic plants locally prior to their regional expansion to dominance in the late miocene through the early pleistocene and large variation in the abundance of c4 plants 0 25 in this ecosystem both laterally and on a 100 kyr timescale in contrast pedogenic carbonate 13c values from this site indicate a high proportion of c4 photosynthesis that is at odds with both phytolith and 13corg results suggesting that the carbonate values are biased by diagenesis or diffusion of atmospheric co2 and that a similar issue may impact previous paleovegetation reconstructions based on pedogenic carbonates quantitative reconstructions of mean annual temperature and mean annual precipitation indicate little local variability through time and that the fluctuations in c4 proportion were not climatically driven instead the variable proportion of c4 photosynthesis is best explained by ecosystem scale variables such as succession fluvial avulsion and fire regime

tectonics or climate what drove the miocene global expansion of c4 grasslands investigations into the most plausible causes which triggered the late miocene global expansion of c4 grasslands have reached no consensus and are still being debated the global decline in co2 levels in the late miocene has been thought to be the most common driver although c4 grassland expansion was largely confined to the late miocene their first appearance varied significantly in different parts of the old and new world and therefore emphasizes role of local and or regional factors may or may not be in combination with one or more global factors the dynamic himalayan orogen constitutes a significant global tectonic event that is believed to have affected global climate hence a study of the himalayan foreland basin sediments could help in gleaning out possible causes behind this major paleoecologic event which could perhaps be directly or indirectly related stable carbon isotope analyses of a total of 141 pedogenic carbonates in the mio pleistocene siwalik paleosols of the ramnagar sub basin are coherent providing a better insight into paleovegetational changes across the sub basin on temporal and spatial scales furthermore paleovegetational history during oligocene is reconstructed from dagshai paleosols exposed in the subathu sub basin the isotopic results show dominance of c3 vegetation pre 7 ma and dominance of c4 vegetation post 5 ma percentage abundance of c4 vegetation was less than 20 pre 7 ma but increased to more than 40 post 5 ma reaching up to 100 in the youngest analyzed sediments there is exclusive dominance of c3 vegetation during oligocene these results conform to the pattern of change in vegetation documented in other parts of the himalayan belt the global expansion of c4 grasslands largely during late miocene have long been linked with then climate changes particularly brought by declining atmospheric co2 level large scale fires intensification of monsoon seasonality and aridity as demonstrated by various researchers these major hypotheses explaining expansion of c4 grasslands during late miocene are not very convincing due to significant shortcomings associated with them for example expansion of c4 grasslands in non monsoonal regions put serious constraints on the monsoonal intensification hypothesis likewise aridity as being the primary driver of c4 grassland expansion seems hard to support since there is no substantial evidence that could suggest global onset of arid conditions at about same geologic time and some most arid periods like the triassic show no evidence of c4 plants we suggest that the initial lowering of co2 below 450 ppmv created an environment for the beginning of c4 vegetation but the persistence of this threshold value for a considerable time during late miocene appears to be the probable cause of the late miocene global expansion of c4 grasslands irrespective of their time of first appearance it has been deduced through the correlation of himalayan tectonic events with atmospheric co2 levels and paleovegetational changes since upper miocene times that it was indeed the late miocene continuous intense tectonic instability of the himalayas that significantly decreased atmospheric co2 levels and which perhaps played a key role in changing the nature of photosynthetic pathways

pre drill pore pressure modelling and post well analysis using seismic interval velocity and seismic frequency based methodologies a deepwater well case study from mississippi canyon gulf of mexico managing and identifying risk and uncertainly involved in drilling operations in unconventional geologic settings starts with improving and correctly applying pore pressure modelling a relatively new approach which predicts pore pressure by way of seismic frequencies has addressed some of the short comings seen in seismic interval velocity applications with the overall goal of reducing operational drilling risk by utilizing multiple pore pressure modelling strategies a case study will be presented for a near salt field in deepwater gulf of mexico this study will outline the pre drill pore pressure modeling which includes petrophysical seismic interval velocity and seismic frequency based approaches the accuracy of these three approaches will be analyzed both qualitatively and quantitatively for currently existing wells and from a pre drill and post drill standpoint for one prospect well

reconnaissance of upper jurassic morrison formation ichnofossils rocky mountain region usa paleoenvironmental stratigraphic and paleoclimatic significance of terrestrial and freshwater ichnocoenoses seventy five types of ichnofossils documented during a four year reconnaissance study in the upper jurassic morrison formation demonstrate that highly diverse and abundant plants invertebrates and vertebrates occur throughout most of the morrison or equivalent strata invertebrate ichnofossils preserving the most environmentally and climatically sensitive in situ behavior of morrison organisms are in nearly all outcrops terrestrial ichnofossils record biotic processes in soil formation indicating soil moisture and water table levels freshwater ichnofossils preserve evidence of water depth salinity and seasonality of water bodies ichnofossils categorized as epiterraphilic terraphilic hygrophilic and hydrophilic new terms reflect the moisture regime where they were constructed the ichnofossils are vertically zoned with respect to physical chemical and biological factors in the environment that controlled their distribution and abundance and are expressed as surficial shallow intermediate and deep the sedimentologic stratigraphic and geographic distribution of morrison ichnofossils reflects the environmental and climatic variations across the basin through time marginal marine tidal to brackish water ichnofossils are mainly restricted to the windy hill member very large to small termite nests dominate the salt wash member similar size ranges of ant nests dominate the brushy basin member soil bee nests dominate in the salt wash decreasing in abundance through the brushy basin deeper and larger insect nests indicate more seasonal distribution of precipitation and rainfall shallower and smaller insect nests indicate either dry or wet substrate conditions depending on the nest architecture and paleopedogenic and sedimentologic character of the substrate trace fossil indicators of flowing or standing water conditions are dominant in the tidwell member and in fluvial sandstones of the salt wash and brushy basin members large communities of perennial freshwater bivalve traces are abundant in the tidwell and brushy basin members but to a lesser extent in the salt wash member shallow crayfish burrows indicating a water table level close to the surface 1 m are restricted to channel bank and proximal alluvial deposits in the salt wash recapture and brushy basin members sauropod theropod pterosaur and other vertebrate tracks occur throughout the morrison formation associated with alluvial lacustrine and transitional marine shoreline deposits ichnofossils and co occurring paleosols in the morrison reflect the local and regional paleohydrologic settings which record the annual soil moisture budget and were largely controlled by the climate in the basin contributions to near surface biologic systems by groundwater from distant sources were minor except where the water table perennially seasonally or ephemerally intersected the ground surface the jurassic morrison formation in the southern portion of the basin experienced a mosaic of seasonal climates that varied from a drier tidwell windy hill deposition to a wetter lower and middle salt wash deposition and slightly drier upper salt wash deposition tropical wet dry climate returning to a wetter tropical wet dry climate near the end of morrison deposition brushy basin deposition the northern part of the basin experienced similar trends across a mosaic of mediterranean climate types the range and mosaic pattern of wet dry morrison climates is analogous to the range of climates and their seasonal variability that dominates the african savanna today

predrill pore pressure prediction using seismic data 1a predrill estimate of pore pressure can be obtained from seismic velocities using a velocity to pore pressure transform but the seismic velocities need to be derived using methods having sufficient resolution for well planning purposes for a deepwater gulf of mexico example significant differences are found between the velocity field obtained using reflection tomography and that obtained using a conventional method based on the dix equation these lead to significant differences in the predicted pore pressure parameters in the velocity to pore pressure transform are estimated using seismic interval velocities and pressure data from nearby calibration wells the uncertainty in the pore pressure prediction is analyzed by examining the spread in the predicted pore pressure obtained using parameter combinations which sample the region of parameter space consistent with the available well data if calibration wells are not available the ideas proposed in this paper can be used with measurements made whi

rayleigh distillation and the depth profile of 13c 12c ratios of soil organic carbon from soils of disparate texture in iron range national park far north queensland australia a depth and particle size specific analysis of soil organic carbon soc and its isotopic composition was undertaken to investigate the effects of soil texture or particle size on the depth profile of stable carbon isotopic composition of soc 13csoc in two tropical soils depth specific samples from two soil profiles of markedly different texture coarse grained and fine grained were separated into particle size classes and analyzed for the mass mass concentration of soc c and 13csoc within 1 m of the soil surface 13csoc in the coarse textured soil increases by 1 3 to 1 6 while 13csoc from the fine textured soil increase by as much as 3 8 to 5 5 this increasing depth trend in the coarse textured soil is approximately linear with respect to normalized c while the increase in the fine textured soil follows a logarithmic function with respect to normalized c a model of rayleigh distillation describing isotope fractionation during decomposition of soil organic matter som accounts for the depth profile of 13csoc in the fine textured soil but does not account for the depth profile observed in the coarse textured soil despite their similar climate vegetation and topographic position these results suggest that kinetic fractionation during humification of som leads to preferential accumulation of 13c in association with fine mineral particles or aggregates of fine mineral particles in fine textured soils in contrast the coarse textured soil shows very little applicability of the rayleigh distillation model rather the depth profile of 13csoc in the coarse textured soil can be accounted for by mixing of soil carbon with different isotopic ratios

does the arc accretion model adequately explain the paleoproterozoic evolution of southern laurentia an expanded interpretation comment and reply comment assembly of lithosphere in southern laurentia is best interpreted to have taken place along a long lived 1 8 1 0 ga active margin via subduction accretion processes broadly analogous to present day convergence between australia and indonesia karlstrom and bowring 1988 1 karlstrom et al

mojave yavapai boundary zone southwestern united states a rifting model for the formation of an isotopically mixed crustal boundary zone the boundary between the paleoproterozoic mojave and yavapai crustal provinces in the southwestern united states is a 75 km wide zone characterized by complex isotopically mixed pb crust similar to other transitional crustal and lithospheric boundaries worldwide mojave crust is more isotopically evolved than the juvenile crust of the yavapai province indicating an older crustal component several areas of isotopically juvenile rocks within and near the boundary zone correspond to exposures of coeval 1 73 ga supracrustal rocks that contain pillow basalts and bimodal metavolcanic sequences we suggest that regions of juvenile crust within the mojave province and its boundary zone represent rift basins produced by extension or transtension near the eastern margin of the province into which primitive basaltic lavas and bimodal volcanic sequences were erupted the largest region of juvenile material within the boundary zone is bound to the west by a series of coincident n trending isotopic geochemical metamorphic and geophysical discontinuities that may represent a fundamental buried crustal structure perhaps a rift margin we propose that the distinct isotopic signature of the boundary zone persisted through subsequent deformational events including the one that juxtaposed the two provinces if our model for the formation of the boundary zone is correct its isotopically mixed character is at least partly an artifact of the precollision history of the eastern mojave province and may not solely reflect the processes that juxtaposed the two provinces formation of new crust by rifting may represent an underappreciated form of crustal growth during the paleoproterozoic that is distinct from arc accretion models for the formation of complex crustal boundary zones must consider the early prejuxtaposition history of terranes in interpreting their geochemical and geophysical characteristics

tertiary history of c4 biomass in the great plains usa we use the carbon isotope composition of paleosols to reconstruct the history of c4 biomass on the great plains from ca 23 to 1 ma the proportion of c4 biomass was uniform and moderate 12 34 throughout the miocene increased between 6 4 and 4 0 ma and reached modern levels by 2 5 ma ecological changes in great plains ungulates preceded the increase in c4 biomass the contrasts in the paleosol and ungulate records may indicate initial development of c3 grasslands after the middle miocene or a greater role for ecological interactions within communities in structuring ungulate faunas contrasts in paleosol records from different continents point to regional rather than global controls on the evolution of c4 grasslands

carbon isotope ratio of cenozoic co2 a comparative evaluation of available geochemical proxies 1 the carbon isotope ratio 13c of plant material is commonly used to reconstruct the relative distribution of c3 and c4 plants in ancient ecosystems however such estimates depend on the 13c of atmospheric co2 13cco2 at the time which likely varied throughout earth history for this study we use benthic and planktonic 13c and 18o records to reconstruct a long term record of cenozoic 13cco2 confidence intervals for 13cco2 values are assigned after careful consideration of equilibrium and non equilibrium isotope effects and processes as well as resolution of the data we find that benthic foraminifera better constrain 13cco2 compared to planktonic foraminiferal records which are influenced by photosymbiotes depth of production seasonal variability and preservation furthermore sensitivity analyses designed to quantify the effects of temperature uncertainty and diagenesis on benthic foraminifera 13c and 18o values indicate that these factors act to offset one another our reconstruction suggests that cenozoic 13cco2 averaged 6 1 0 6 1 while only 11 2 million of the last 65 5 million years correspond to the pre industrial value of 6 5 with 90 confidence here 13cco2 also displays significant variations throughout the record at times departing from the pre industrial value by more than 2 thus the observed variability in 13cco2 should be considered in isotopic reconstructions of ancient terrestrial plant ecosystems especially during the late and middle miocene times of presumed c4 grassland expansion

multi proxy evidence for tectonic control on the expansion of c4 grasses in northwest argentina the timing of the rise of c4 grasses and the climatic conditions driving their expansion are widely debated with recent studies suggesting that the expansion was more complex than previously thought proxy reconstructions from northwestern argentina record multiple increases and decreases in c4 abundance throughout the late miocene to early pliocene as well as variations in the timing of the spread of c4 grasses into the region here we present a multi proxy paleovegetation reconstruction of the proportions of c3 and c4 vegetation using organic carbon and phytoliths preserved in paleosols at entre rios in the santa maria basin of catamarca argentina between 6 2 and 3 3 ma both corg13 and phytolith assemblages indicate a c3 dominated ecosystem with no evidence for substantial amounts of c4 vegetation from the late miocene through mid pliocene despite their rise to dominance elsewhere during this time these data suggest that by 6 2 ma the santa maria basin floor was at an elevation high enough to create locally cool conditions that allowed c3 vegetation to outcompete c4 grasses phytolith assemblages show that later uplift of the sierra calchaquies and sierra aconquija ranges through the pliocene increased aridity and drove the expansion of c3 grasses at the expense of palms and other forest indicators this multi proxy paleovegetation reconstruction demonstrates that tectonics played an important role in controlling the late miocene expansion c4 grasses by suppressing their spread into northwest argentina

large scale hydrological change drove the late miocene c4 plant expansion in the himalayan foreland and arabian peninsula carbon isotope changes in paleosols from siwalik pakistan and marine sediments from the bengal fan indicate a major c 4 plant expansion in the himalayan foreland during the late miocene however the timing and mechanisms behind the c 4 plant expansion remain enigmatic here we present high resolution 60 k y biomarker and compound specific isotope data spanning the past 11 m y from ocean drilling program site 722 in the arabian sea an 5 6 increase in leaf wax 13 c values indicates a marked rise of c 4 plants from 10 to 5 5 ma with accelerated expansion from 7 9 to 5 5 ma a concurrent 50 rise in leaf wax d values is attributed to a combined effect of changes in precipitation amount and evaporation indicating that source regions for the plant waxes became progressively drier from 10 to 5 5 ma in contrast to earlier reports our isotope records biomarker abundances alkenone u k 37 and globigerina bulloides abundance data do not suggest enhanced summer monsoon circulation during this time interval rather our results suggest that large scale hydrological changes drove the late miocene expansion of c 4 plants in the himalayan foreland and arabian peninsula

regional scale variability in the spread of grasslands in the late miocene abstract a new paleovegetation reconstruction based on both phytolith and paleosol carbon isotopic data is presented for the middle late miocene 11 2 9 5 ma of southwestern montana both sources of data indicate an open habitat c3 grassland ecosystem with a small c4 component

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

cenozoic paleoclimate on land in north america abstract paleotemperature and paleoprecipitation over the past 40 m yr can be inferred from the degree of chemical weathering and depth of carbonate nodules in paleosols of oregon montana and nebraska paleosol records show that late eocene 35 ma middle miocene 16 ma late miocene 7 ma and early pliocene 4 ma warm climatic episodes were also times of a wet climate in oregon montana and nebraska oregon and nebraska were humid during warm wet times but montana was no wetter than subhumid within the rain shadow of intermontane basins global warm wet paleoclimatic spikes steepened rather than flattened geographic gradients of rocky mountain rain shadows long lived mountain barriers created dusty dry basins with sedimentation rates high enough to preserve milankovitch scale 100 41 kyr global paleoclimatic variation in some sequences of paleosols greenhouse warm wet climates indicated by paleosols were also peaks of diversity for north american plants and animals and coincided with advance

sequence stratigraphy of cenozoic continental rocks southwestern montana because the presently used bozeman group lithostratigraphy is difficult to apply to cenozoic basin fill rocks in the jefferson beaverhead melrose and divide valleys southwestern montana we advocate the use of sequence stratigraphy surface sequence boundaries are in many cases marked by calcic paleosol zones these zones can be projected into the subsurface and tied to seismic reflection data density velocity contrasts between calcic paleosol zones and overlying nonpedogenic rocks generate bright reflectors that define sequence boundaries sequence boundary delineation is further enhanced by reflection termination patterns similar to those found in marine strata sequence age calibration is based upon vertebrate fossil and radiometric age data five sequences separated by basin wide unconformities are recognized most sequence bounding unconformities are marked by paleosols an occurrence not previously reported for cenozoic strata of southwestern montana the sequences and their age ranges are 1 bridgerian uintan approximately 50 to 44 ma calc alkaline volcanic flows and interstratified sedimentary rocks 2 duchesnian to whitneyan approximately 42 to 30 ma terrestrial sedimentary and volcanic rocks 3 arikareean approximately 27 to 21 ma terrestrial sedimentary and volcanic rocks 4 barstovian to blancan approximately 16 to 4 ma terrestrial sedimentary and volcanic rocks and 5 early quaternary approximately 1 8 ma to holocene terrestrial sedimentary and volcanic rocks

stable isotopic results from paleosol carbonate in south asia paleoenvironmental reconstructions and selective alteration article i nfo we measured 18 o and 13 c values of paleosol carbonate nodules from a variety of sedimentary units in southern asia in order to reconstruct paleoenvironmental conditions and to evaluate for possible diagenetic alteration paleosol carbonate nodules were collected from lower to upper cretaceous strata exposed in two locations in southern tibet and from lower to middle miocene strata in northern india and nepal additional samples were collected from stratigraphically adjacent marine carbonate units to test for possible resetting of stable isotope values based on the implausibly low 18 o values 13 of most of the marine carbonate samples we interpret the 18 o values of the associated paleosol carbonate nodules as being reset and therefore unreliable for paleoenvironmental or paleoelevation reconstruction importantly the 18 o values of 13 c values of marine carbonate rocks fall within the expected primary

phytolith and carbon isotope evidence for late quaternary vegetation and climate change in the southern black hills south dakota abstract analyses of phytoliths and carbon isotopes document change in late quaternary grasslands in the red valley of the southern black hills late pleistocene grassland composition was equivalent to the c3grass parklands of modern central alberta the rise of mixed grassland occurred rapidly between 11 000 and 9000 yr b p early holocene mixed grasslands included both short and tall c4grasses a mid holocene erosional unconformity ca 8000 to 4500 yr b p precludes phytolith or isotope analysis but suggests lack of vegetation and landscape denudation caused by a drier climatic basin wide stability and soil development followed the erosional episode ca 4500 to 3600 yr b p mesic adapted c4panicoid grasses increased during this period of soil development low magnitude fluctuation in the c4 dominated mixed grassland occurred throughout the late holocene 3600 yr b p to present rise in 13c values during the last 1000 yr without corresponding change in phytoliths may indicate a decrease in woodlands caused by increased fire frequency

miocene climate evolution of northern europe a palynological investigation from denmark a palynological investigation has been conducted on lower upper miocene sediments from jylland denmark corresponding to the time interval of about 19 to 8 ma the sediments derived from the sdr vium drill core were deposited in marine to marginal marine environments as shown by the relatively high abundance of dinoflagellate cysts in all samples nevertheless rich and diverse pollen assemblages occur throughout the succession and the palynological analysis reveals that coastal areas of the study area were during the miocene dominated by taxodium swamp forests that also hosted terrestrial angiosperms such as nyssa betula alms and elements of the myricaceae further inland a mixed deciduous evergreen forest prevailed in areas with better drained soils or on elevated areas gymnospermous conifer forests prevailed including taxa such as pinus sequoia and sciadopitys overall the climate in the study area was warm temperate during major parts of the miocene with mean annual temperatures between 15 5 and 20 degrees c by employing the coexistence approach combined with the method of allocating taxa into standardized climatic groups four different climatic miocene events are detected within the studied succession correlated to the coeval climate record of northwestern europe the oldest event is a cooling during the earlier burdigalian at approximately 19 ma coinciding with the mbi 1 oxygen isotope excursion at ca 18 5 ma in mid burdigalian a warming phase is reconstructed characterized by the highest precipitation rates observed in the sedimentary succession a warming trend starting in the latest burdigalian corresponds to the globally recognized middle miocene climatic optimum mmco while a longer term late neogene cooling was initiated in the mid serravallian about 13 ma c 2011 elsevier b v all rights reserved less

late miocene atmospheric co2 concentrations and the expansion of c4 grasses the global expansion of c4 grasslands in the late miocene has been attributed to a large scale decrease in atmospheric carbon dioxide co2 concentrations this triggering mechanism is controversial in part because of a lack of direct evidence for change in the partial pressure of co2 pco2 and because other factors are also important determinants in controlling plant type distributions alkenone based pco2 estimates for the late miocene indicate that pco2 increased from 14 to 9 million years ago and stabilized at preindustrial values by 9 million years ago the estimates presented here provide no evidence for major changes in pco2 during the late miocene thus c4 plant expansion was likely driven by additional factors possibly a tectonically related episode of enhanced low latitude aridity or changes in seasonal precipitation patterns on a global scale or both

using phytolith assemblages to reconstruct the origin and spread of grass dominated habitats in the great plains of north america during the late eocene to early miocene abstract this paper outlines a general approach for analyzing siliceous microfossils from plants phytoliths in geologic sediments and uses this method to reconstruct the evolution of grasslands in the central great plains during the late tertiary phytolith assemblage analysis is widely employed for reconstructing vegetation types in pleistocene holocene paleoecology and archaeology but no standardized methodology is currently available published phytolith studies are often system specific and tailored after specific modern analogues as a result they vary in extraction technique classification scheme and method of inference for ancient phytolith assemblages whose modern analogues are not well understood a more general analytic approach is necessary this analytic approach includes studying all size fractions 2 250 mm using a classification scheme based on the available literature and a comprehensive modern phytolith reference collection and comparing relative frequencies through time of all diagnostic phytoliths to interpret changes in habitat structure this general method was applied to late eocene to early miocene sediment samples from northwestern nebraska to deduce vegetation history and the results were compared to those obtained using a more specific technique stromberg paleogeogr paleoclimatol paleoecol 177 2002 59 in both studies phytoliths were extracted by means of heavy liquid separation from the following lithostratigraphic units 1 the late eocene chadron formation and the early oligocene brule formation white river group 2 the late oligocene early miocene monroe creek formation the early miocene harrison formation and anderson ranch formation arikaree group and 3 the early miocene runningwater formation and box butte formation ogallala group the two techniques general vs specific produced results that differ markedly data from the general approach indicate the presence of relatively closed habitats in late eocene to early oligocene typified by the presence of phytoliths from bambusoid grasses woody and herbaceous dicotyledons and palms the introduction and spread of modern open habitat grasses such as pooids arundinoids and panicoids occurred between the late oligocene and early miocene this resulted in a savanna or woodland type habitat by the early miocene in contrast analysis using the specific method suggested the presence of open habitats in northwestern nebraska from the late eocene onward the difference in interpretation based on the two approaches is principally due to inclusion of phytoliths 50 mm and the use of an expanded reference collection in the current study general analytic approach these results point to the importance of methodological choices in phytolith analysis and emphasize the usefulness of phytoliths as paleoecological indicators in the fossil record

environmental change in the great plains an isotopic record from fossil horses abstract carbon and oxygen isotope ratios of fossil horse tooth enamel from nebraska and texas show evidence for late neogene environmental changes in the great plains the earliest unambiguous c4 dietary signal among texas equids coincides with the age of the classic late hemphillian age coffee ranch fauna which we suggest is 6 6 ma based on volcanic ash correlations c4 vegetation was present in the diets of a small fraction of late hemphillian equids in nebraska and was thereafter ordinary in the diets of both nebraska and texas equids there is no unequivocal evidence for abundant c4 vegetation in the diets of pre late hemphillian equids and we suggest that the ensuing dietary change reflects c4 biomass expansion in the latest miocene carbon isotope ratios of post hemphillian horses in nebraska can be divided into two statistically distinct populations on the basis of whether tortoise remains co occur with horse remains indicating that the two proxies carbon isotopes and presence absence of tort

a 35 myr north american leaf wax compound specific carbon and hydrogen isotope record implications for c4 grasslands and hydrologic cycle dynamics article i nfo hydrology source region and timing of precipitation are important controls on the climate of the great plains of north america and the composition of terrestrial ecosystems moisture delivered to the great plains varies seasonally and predominately derives from the gulf of mexico atlantic ocean with minor contributions from the pacific ocean and arctic region for this work we evaluate long term relationships for the past 35 million years between north american hydrology climate and floral change using isotopic records and average carbon chain lengths of higher plant n alkanes from gulf of mexico sediments dsdp site 94 we find that carbon isotope values 13 c of n alkanes corrected for variations in the 13 c value of atmospheric co2 provide minor evidence for contributions of c4 plants prior to the middle miocene a sharp spike in c4 input is identified during the middle miocene climatic optimum and the influence of c4 plants steadily increased during the late miocene into the pleistocene consistent with other north american records chain length distributions of n alkanes indicative of the composition of higher plant communities remained remarkably constant from 33 to 4 ma however a trend toward longer chain lengths occurred during the past 4 million years concurrent with an increase in 13 c values indicating increased c4 plant influence and potentially aridity the hydrogen isotope values d of n alkanes are relatively invariant between 33 and 9 ma and then become substantially more negative 75 from 9 to 2 ma changes in the plant community and temperature of precipitation can solely account for the observed variations in d from 33 to 5 ma but cannot account for plio pleistocene d variations and imply substantial changes in the source region of precipitation and seasonality of moisture delivery we posit that hydrological changes were linked to tectonic and oceanographic processes including the shoaling and closure of the panamanian seaway amplification of north atlantic deep water production and an associated increase of meridional winds the southerly movement of the intertropical convergence zone near 4 ma allowed for the development of a near modern pressure storm track system driving increased aridity and changes in seasonality within the north american interior

a proxy for humidity and floral province from paleosols abstractwe develop a proxy to infer humidity from the geochemistry of paleosols in order to enhance reconstructions of ancient paleoclimate beyond trends in mean annual precipitation geochemical transfer functions developed herein are used to estimate net primary production and evapotranspiration along three latitudinal transects of modern soils in the coterminous united states mean annual precipitation and the degree of chemical weathering are estimated from the major element concentrations in soils the ratio of evapotranspiration estimated from our proxy and mean annual precipitation provides a method of determining the humidity province of ancient climates that is more robust and meaningful than previous methods and our approach differs from existing methods since both the influx and efflux of moisture are explicitly determined the required input parameters for application of this proxy are 1 the soil morphology 2 accurate and complete major element concentration data for the active soil

carbon isotope fractionation during decomposition of organic matter in soils and paleosols implications for paleoecological interpretations of paleosols abstract stable isotope ratios reported as 13c of organic carbon preserved in paleosols have potential utility as a valuable paleoecological indicator if the isotopic composition of paleobiomass is preserved in the paleosol organic carbon without fractionation however soil organic matter is in a constant state of decomposition in an open system and frequently decomposes further during alteration after burial of the paleosol during this decomposition kinetic fractionation of 13c 12c in an open system results in concentration of 13c in the residual organic matter preserved in the soil and paleosol this paper summarizes studies of modern soils which show that this 13c enrichment follows a rayleigh distillation process whereby the 13c 12c ratio is a function of the natural logarithm of the fraction of remaining soil organic carbon leaving soil organic carbon 13c enriched by up to 6 with respect to the original biomass if the fraction of original biomass carbon remaining during these decomposition processes deviates significantly from 1 the soil organic carbon can be 13c enriched by several per mil and thus not a good paleoecological indicator of the 13c value of the original biomass therefore effective paleoecological studies of 13c preserved in paleosol organic carbon must therefore demonstrate that the measured concentration of organic carbon in the paleosol is near its maximum concentration during soil formation or that the paleosol organic matter does not include the 13c enriched products of microbial decomposition suggestions are made for interpreting the effects of carbon isotope fractionation of organic matter and for materials and methods most useful for paleoecological studies from bulk paleosol organic carbon

aeolian n alkane isotopic evidence from north pacific for a late miocene decline of c4 plant in the arid asian interior abstract aeolian deposition in the central north pacific has been well recognized to originate from arid asian interior while there is no doubt about the transport of organic matters along with the mineral dust from the source region little is known about the nature and changes of the terrestrial organic compounds preserved in the deep sea sediments in this study higher plant leaf wax n alkanes from odp site 1208 and site 886 in the north pacific since the middle miocene were analyzed to explore long term changes in vegetation and climate in the source region accumulation rates of leaf wax n alkanes show an increasing trend consistent with the documented climatic drying of the asian interior since the late miocene the records of carbon isotopic enrichment factors of c29 n alkane relative to atmospheric co2 ec29 co2 show a prominent decrease from 12 to 8 ma the average ec29 co2 value prior to 8 ma is 0 8 heavier than after 8 ma although almost all values of ec29 co2 25 3 to 21 3 are well within the range of c3 plants adjustment of isotope discrimination by c3 plants is not considered as the main cause of the observed variations instead changes in relative abundance of c3 vs c4 plants are invoked to interpret the ec29 co2 records higher c4 contribution 17 7 5 3 to the local vegetation is inferred for the period prior to 8 ma implying a slightly warmer climate in the source region a marked decline in c4 plants from 12 to 8 ma interpreted as a result of regional temperature drop coincides with the prominent growth of northern tibetan plateau around 8 ma along with the global cooling climate our results therefore point to apparently close links among plateau uplift development of drying and cooling climates and vegetation changes in the asian interior

ungulate diets reveal patterns of grassland evolution in north america abstract equids from the late miocene hemphillian north american land mammal age of texas evolved c4 dominated diets earlier than their nebraska counterparts leading researchers to hypothesize a northward expansion of c4 grasses between 8 and 6 ma however competing hypotheses from multiple paleoecological proxies support one of three hypotheses that northward c4 expansion occurred at the expense of c3 woodlands c3 grasslands or was not occurring during the hemphillian we test these alternative hypotheses by comparing the ecosystems of hemphillian texas and nebraska 6 3 7 5 ma using hoofed mammal dietary reconstruction hypsodonty and digestive strategy and by incorporating published tooth enamel isotopes paleosol isotopes and phytolith assemblage data we also use hypsodonty mesowear and microwear in a detailed comparison of two localities that are roughly contemporary cambridge nebraska at 7 ma and coffee ranch texas at 6 6 ma to rule out time averaging as an explanatory variable through analogy with modern african communities we reconstruct texas and nebraska ecosystems as bushland and woodland respectively using the proportions of hypsodont taxa we estimate mean annual precipitation values of 1217 mm year for nebraska and 1368 mm year for texas using rarefaction we also do not find differences in the richness of brachydont hypsodont and hindgut fermenting taxa we therefore conclude that both ecosystems were largely similar in hoofed mammal faunal structure during the late miocene when compared to published paleosol and phytolith data which show no differences in c3 c4 biomass among latitudes our results allow us to reject hypotheses of northward c4 expansion during the late miocene we therefore suggest that the equid enamel isotopes may have been biased by two potential factors the primary reliance on a single locality of appropriate age and possible behavioural lag in c4 feeding among nebraska equids these results suggest that the formation of a modern c3 c4 latitudinal gradient occurred later than is previously suggested by equid enamel carbon isotopes

well constrained seismic estimation of pore pressure with uncertainty the safe drilling of wells for hydrocarbon exploration or production requires that the wellbore pressure be maintained between the formation pore pressure and the maximum pressure the formation can withstand without fracturing this task is made more difficult when drilling in overpressured areas which require a quantitative predrill prediction of pore pressure with uncertainty to be made a predrill estimate of pore pressure can be obtained from seismic velocities using a velocity to pore pressure transform calibrated by offset well data however the uncertainty in velocity is often not quantified this example from the gulf of mexico uses seismic velocities with uncertainty derived by combining seismic velocities with well data den boer et al 2006 parameters in the velocity to pore pressure transform are estimated using seismic velocities density logs pressure information and well velocities derived by inverting time depth pairs from check shots in the area pore pressure and associated uncer

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

branching sheeted dikes and seafloor spreading within an early proterozoic intra arc basin the payson ophiolite 1 73 ga is exposed as a shallow dipping pseudostratigraphic sequence of gabbro sheeted dikes and submarine volcanic rocks with screens and roof pendants of older arc crust the sheeted dike complex is particularly well exposed and analysis of measured sections reveals a threefold increase in the average dike width with depth in the complex magmatic temperatures and slow cooling at the base of the sheeted dike complex indicated by gabbro dike mingling and mutual intrusion and coarse textures may have facilitated the growth of wide dikes in contrast extreme alteration of the top of the sheeted dike complex suggests that hydrothermal circulation dominated and caused rapid cooling as thin dikes the connection between wide dikes at depth with thinner dikes toward the top requires a new model where dikes branch upward in response to the strong vertical gradient in the rate of cooling and solidification the branching dike model has important implications for the timing and spatial distribution of seafloor phenomena in the neovolcanic zone of spreading centers

stable isotope analysis of the tooth enamel of chaingzauk mammalian fauna late neogene myanmar and its implication to paleoenvironment and paleogeography abstract the tooth enamel of a mammalian fauna from the uppermost miocene lower pliocene irrawaddy sediments at chaingzauk west central myanmar were analyzed using stable carbon and oxygen isotopes the 13 c values of porcupines tragulids rhinocerotids suids and proboscideans show that these mammals preferentially consumed c 3 plants in a wooded environment whereas the 13 c values of bovids and hippopotamids indicate that they were grassland adapted grazers to mixed feeders in contrast to the thorn scrub grassland and shrubland vegetation of present day central myanmar stable carbon isotope results of the chaingzauk fauna suggest a presence of wooded environment in the chaingzauk area at that time present day arid conditions are likely to have been caused by the uplift of the indo burman ranges due to the himalayan orogeny during the late miocene to pliocene resulting in a rainshadow effect in central myanmar furthermore southward marine regression due to the rapid influx of sediments from the indo burman ranges eastern himalayan ranges and sino burman ranges into the central myanmar basin in the miocene to pliocene might have played an important role in the aridification of this region since the lower pliocene

small mammal carbon isotope ecology across the miocene pliocene boundary northwestern argentina abstract the late miocene expansion of plants using the c 4 photosynthetic pathway in south america has been documented by tooth enamel carbon isotope ratios 13 c en however a more detailed understanding of this ecological event is hampered by poor chronological control on the widespread fossil localities from which isotopic data are derived this study develops a 13 c en record from a single 2500 m thick stratigraphic section in subtropical south america strata at puerta de corral quemado pcq northwestern argentina span 9 to 3 5 ma in age and existing paleosol carbonate data 13 c pc document c 4 expansion across the miocene pliocene boundary comparison of 13 c en data with 13 c pc data at high stratigraphic resolution refines understanding of this ecological event in south america small mammal 13 c en data in particular are complementary to that of large mammal and paleosol 13 c data small mammal teeth integrate isotopic data over much shorter temporal and spatial scales than large mammal teeth providing a sensitive measure of local vegetation and placing constraints on the landscape distribution of c 3 and c 4 plants explicit consideration of the distinctive carbon isotope enrichment factor between enamel and diet for rodents e en diet 11 as opposed to 14 for large mammals allows for unequivocal inference of c 4 vegetation 1 ma prior to that inferred from large mammal 13 c en data and 2 ma prior to 13 c pc data this multiproxy record demonstrates that c 4 plants were a stable component of the ecosystem hundreds of thousands of years prior to their major ecological expansion and that the expansion of c 4 plants was pulsed at pcq two periods of ecological change are demonstrated by 13 c and 18 o data at 7 ma and 5 3 ma coincident with the miocene pliocene boundary development of small mammal 13 c en records on other continents may provide similar insight into the early stages of the global c 4 event

pakistan mammal tooth stable isotopes show paleoclimatic and paleoenvironmental changes since the early oligocene abstract this research presents an isotopic study of three large mammal groups elephantoid proboscideans hyracodontid and rhinocerotid rhinocerotoids equids of the hipparion group from the bugti hills sequence eastern balochistan pakistan combined with published data from the miocene siwalik group northern central pakistan these two exceptional fossil records from pakistan provide an unambiguous source of biotic information from the early oligocene up to the late miocene the 13 c c and 18 o c results from the same herbivore groups show several significant variations in environmental and climatic conditions throughout the 30 to 7 5 myr period in this region first from 30 to 22 myr the environment is characterized by a relatively dry but dense forest existing under a temperate to subtropical climate with a more closed tropical environment at 23 myr oligocene 18 o of the terrestrial herbivore teeth agrees with the marine foraminifera 18 o and mg ca trends suggesting that the pakistan region was affected by global climate rather than regional conditions after 22 myr the 18 o c mammal enamel results show a long term decreasing trend until 15 myr toward a wetter environment with the appearance of tropical forests in response to the probable onset of the asian monsoon this is a period of high tectonic activity with the india asia collision leading to uplift of the tibetan plateau and shrinkage of the epicontinental paratethys sea this activity modified the land sea distribution and the thermal contrast between ocean and continent the driving force of the monsoon climate the middle miocene environment in pakistan experienced moist conditions under an intense monsoon system with relatively closed rainforest after 12 myr the 18 o c enamel values record a positive shift until 9 3 myr toward a drier environment with an increase of seasonality as suggested by higher 18 o c variability after 9 3 myr these late miocene drier climatic conditions and the asian monsoon intensification could potentially favour the c 4 photosynthetic pathway and hence the development of grassland to the detriment of subtropical forests resulting in the higher enamel 13 c values recorded after 9 3 myr

some effects of velocity variation on avo and its interpretation in recent years interest has increased in the interpretation of the amplitude variation of reflected signals as a function of offset avo a more meaningful relationship for interpreting reflection coefficients at the target horizon is amplitude variation with incident angle ava the challenge is to convert from avo to ava the effects of velocity variation in the overburden on amplitude variation with offset avo and on the final inversion of avo data into velocity density and poisson s ratio can be significant examples are given here for subsurface medium with a vertical velocity gradient range of 0 2s 1 to 0 8s 1 when the medium is treated as homogeneous in the conversion from avo to ava this velocity variation causes significant errors about 10 percent in both the gradient of ava and in the normal incident reflection coefficient such errors produce errors of similar magnitude in the inversion of ava data into the elastic parameters of velocity poisson s ratio and density the errors dep