early jurassic late pliensbachian co2 concentrations based on stomatal analysis of fossil conifer leaves from eastern australia the stomatal index a measure of stomatal density of an extinct australian early jurassic araucariacean conifer species allocladus helgei jansson is used to reconstruct the atmospheric carbon dioxide concentration pco 2 in the early jurassic the fossil leaves are preserved in a single bed palynologically dated to late pliensbachian similar to 185 183 mya atmospheric pco 2 is estimated from the ratios between the stomatal index of a helgei and the stomatal indices of three modern analogs nearest living equivalent plants co2 concentration in the range of similar to 750 975 ppm was calibrated from the fossil material with a best estimated mean of similar to 900 ppm the new average pco 2 determined for the late pliensbachian is thus similar to although similar to 10 lower than previously inferred minimum concentrations of similar to 1000 based on data from the northern hemisphere but may help constrain pco 2 during this period our results are the first pco 2 estimates produced using jurassic leaves from the southern hemisphere and show that i paleo atmospheric pco 2 estimates are consistent at a global scale though more investigations of southern hemisphere material are required and ii the stomatal proxy method can now be used without the context of relative change in pco 2 when applying the correct methodology c 2014 the authors published by elsevier b v on behalf of international association for gondwana research less

the posidonia shale lower toarcian of sw germany an oxygen depleted ecosystem controlled by sea level and palaeoclimate abstract the lower toarcian posidonia shale is famous for its excellently preserved fossils and its high amount of organic matter up to 16 both quality of preservation and accumulation of organic matter have been explained by permanent anoxic bottom water conditions high resolution geochemical sedimentological and palaeoecological investigations of various sections of the posidonia shale in sw germany however indicate that oxygen availability was variable and ranged from short oxygenated periods to longer term anoxia the benthic macrofauna consists of nine fossil communities and was used in combination with geochemical data to reconstruct a time averaged oxygen curve anoxic conditions prevailed during the deposition of the toarcian black shales they were however punctuated by various short periods weeks to years with oxygenated bottom water conditions sedimentological e g distinctiveness of microlamination siliciclastic content and geochemical parameters e g organic matter content isotopic signatures 18o and 13c molecular redox parameters pristane phytane ratio arylisoprenoids exhibit a remarkable covariation and seem to be controlled by sea level fluctuations maximum oxygen depletion and an extreme negative shift of 13corg values 34 occurred during the early falciferum zone this is explained by the recycling of 12c enriched carbon derived from remineralization of organic matter on and within the substrate during low sea level stand and a highly elevated redox boundary including photic zone anoxia the subsequent transgression permitted enhanced water exchange with the tethyan ocean and caused improvement of living conditions at the end of the falciferum zone other important factors controlling the depositional environment are the overall palaeogeographic situation and climate the early jurassic is the latest period before break up of pangaea and probably was ruled by a strong meridional atmospheric circulation system with pronounced seasonal changes of prevailing trade and monsoon wind systems an estuarine circulation with a positive water balance and surface water with slightly reduced salinity in the summer alternated with an anti estuarine circulation and a negative water balance in the winter during the summer months a stratified water column with anoxic conditions below the halocline developed 18o data indicate low salinity in the surface water during the monsoon influenced summer high productivity was then located in the photic zone and the corresponding isotopically light 18o signal was fixed in the calcareous nannoplankton during the winter months a saline circulation system brought oxygen to the benthic environment favouring temporary benthic colonization especially during times of relative sea level high stand

radiation damage halos in quartz radiation damage halos are present in quartz that surrounds or is adjacent to accessory minerals such as zircon these halos are not visible in transmitted light but are revealed by cathodoluminescence cl they extend up to 45 m away from the source of radioactivity some halos show concentric rings similar to those previously reported in pleochroic halos in biotite radiation damage halos occur in three main settings surrounding inclusions within quartz grains penetrating into quartz from adjacent radionuclide bearing grains and in quartz cement near such grains halos are more common in pre paleozoic rocks than in younger rocks except in cases of unusual enrichment in radioactive elements halos result from damage to quartz crystal structure identical to the process forming pleochroic halos in biotite damage is caused by alpha particles emitted by radioactive elements within mineral grains and is a partial function of time consequently radiation damage halos may have potential uses in geochronology

stable carbon isotope signatures preserved in authigenic gibbsite from a forested granitic regolith panola mt georgia usa six samples selected from a weathering profile developed on a granite in the panola mountain research watershed in the georgia piedmont were studied for their stable carbon isotopic properties the purpose was to understand the relationship between the stable carbon isotopic composition of the organic matter pool and the preservation of carbon in the authigenic soil minerals the method for yielding carbon from authigenic phases is based on that of yapp and

rise and fall of the southern santa cruz mountains california from fission tracks geomorphology and geodesy the santa cruz mountains are closely associated with a left bend along the right lateral san andreas fault the loma prieta area on the northeast side of the san andreas consists of fault bounded blocks that rise along active deeply rooted reverse and oblique slip faults six samples from a transect across this area yield concordant apatite fission track ages averaging 4 6 0 5 ma these ages date the time of cooling below 110 c and suggest that about 3 km of unroofing has occurred over the last 4 6 m y allowing for current elevations of about 1 km this suggests an average uplift rate of the order of 0 8 mm yr over the last 4 6 m y to further define the extent and distribution of this young uplift we used morphometric analyses of the youthful topography of the area steep drainage slopes and high local relief indicate that the area northeast of the san andreas forms a well defined zone of high uplift in contrast the region on the southwest side of the san andreas is characterized by broad upwarping and folding more subdued topography old fission track ages and mean quaternary uplift rates of 0 1 0 4 mm yr geodetic data 1906 san francisco earthquake and subsequent strain transients 20 years of interseismic deformation 1989 loma prieta earthquake and 2 years of post loma prieta earthquake strain show that the southern santa cruz mountains repeatedly rise and subside through a complex sequence of bay area deformation events an additional deformation element that involves reverse slip averaging 2 3 mm yr along the foothills thrust system must occur to explain the longer term uplift pattern in the loma prieta area since the late pliocene the asymmetry in deformation on opposite sides of the san andreas probably reflects the contrasting rock types on opposite sides of the fault the influence of preexisting structures and the interaction with neighboring faults of the san andreas system

groundwater dolocretes from the upper triassic of the paris basin france a case study of an arid continental diagenetic facies thick dolomite cemented horizons dolocretes occur within a fluvial sandstone mudstone sequence of late triassic age in the western part of the paris basin france two types of dolomites can be distinguished a nodular dolomitic beds less than a few metres thick which formed within mottled overbank siltstones and mudstones and b massive dolomite up to 16 m thick which occurs in coarse grained channel sandstones and conglomerates the majority of the dolomite consists of a finely crystalline groundmass of dolomicrospar and less commonly dolomicrite glaebules irregular spar filled cracks spheroidal dolomite silicification and vuggy porosity are locally abundant in the massive dolomite in contrast biologically induced micromorphological features such as rhizocretions and alveolar septal fabrics were observed in the thin nodular dolomite beds the dolomite is near stoichiometric well ordered and non ferroan 18o values range from 7 7 to 0 4 o pdb and 18o values range from 5 1 to 1 8 0 pdb and no obvious difference in the stable isotopic composition between both types of dolomites was observed sr isotope ratios range from 0 7101 to 0 7126 and are invariably higher than the contemporary triassic sea water a vadose pedogenic origin for the thin dolocrete layers is indicated by the occurrence of rhizocretions and other biological structures several features however argue against a pedogenic origin for the massive carbonates most notably the absence of biologically induced structures the occurrence in coarse grained channel and not overbank deposits and the great thickness these units are thus interpreted as groundwater in origin phreatic calcretes of quaternary age widespread in inland australia are regarded as a modern analogue for the triassic paris basin dolocretes petrographic observations argue in favour of primary proto dolomite precipitation although early diagenetic replacement of calcite by proto dolomite cannot be ruled out strontium and carbon isotope data of early diagenetic dolocrete cements and oxygen isotope data of early diagenetic silica indicate an entirely non marine continental origin for the groundwaters the poorly ordered and non stoichiometric protodolomite probably underwent stabilization upon further burial resulting in a near stoichiometric well ordered dolomite that clearly lacks evidence for pervasive recrystallization

estimating paleoatmospheric pco2 during the early eocene climatic optimum from stomatal frequency of ginkgo okanagan highlands british columbia canada abstract estimates of p co 2 for the early paleogene vary widely from near modern day levels to an order of magnitude greater based on various proxy measures resolving the relationship between climate and p co 2 during this globally warm period is a key task in understanding climate dynamics in a warmer world here we use the stomatal frequency of fossil ginkgo adiantoides from the okanagan highlands of british columbia canada to estimate p co 2 during the early eocene climatic optimum eeco the interval of peak warmth in the cenozoic we also examine a dataset of modern ginkgo biloba leaves to critically assess the accuracy and precision of stomatal frequency as a proxy indicator of p co 2 early eocene fossil g adiantoides has significantly lower stomatal frequency than modern g biloba suggesting p co 2 levels 2 modern pre industrial values this result is in contrast to earlier studies using stomatal frequency of ginkgo that indicated near modern day levels of p co 2 in the early paleogene though not including samples from the eeco we also find that levels of p co 2 as indicated by stomatal frequency are correlated with trends in climate mean annual temperature over time at the falkland fossil locality suggesting that climate and p co 2 were coupled during the eeco hyperthermal

a paleoclimate interpretation derived from pedogenic clay minerals from the piedmont province virginia abstract oxygen isotope ratios of pedogenic kaolinites were measured to estimate the ambient climate conditions during the formation of a saprolite in the piedmont province woodbridge va kaolinite is the predominant pedogenic clay mineral in this saprolite it is formed mostly from weathering of muscovite and to a lesser extent from weathering of microcline a dioctahedral smectite vermiculite phase formed by weathering muscovite is present in minor amounts the 18o 16o ratios indicate that most if not all the kaolinite formed in a cooler climatic regime in which meteoric waters were more depleted in 18o than most present meteoric waters it is possible that the pedogenic kaolinite formed shortly after or during the pleistocene glacial stage in north america this interpretation is consistent with the age of this saprolite derived from 10be dating methods the oxygen isotopic signatures of these kaolinites are not consistent with an older middle or early miocene age for this saprolite

ecological distribution of cenomanian terrestrial plants based on 13c 12c ratios the cenomanian lagoonal member of the argiles du baugeois anjou france yielded a rich and exceptionally well preserved fossil leaf flora stable carbon isotope ratios of fossil plants were measured in order to investigate the presence of a palaeoenvironmental signal the small intraspecies variations of 13c values observed for most of the fossil leaves suggested that the isotopic signal had not been significantly altered hence an isotopic approach was used as an attempt to assist in reconstructing the ecological distribution of the flora the 13c enrichment of the fossil leaves suggested that the plants underwent water or salt stress the occurrence of the conifer frenelopsis suggested at least locally a saline environment such as a lagoon according to their decreasing 13c values all the plants collected could have been distributed along a decreasing salinity transect from the lagoon to a flood plain the predominant species eretmophyllum andegavense a fossil ginkgo exhibited a wide range of 13c values this could indicate that this taxon grew in a wide range of habitats with varying salinities the origin of the organic matter appeared to be terrestrial with a major contribution from water stressed plants such as frenelopsis as suggested by the similarity between 13c values of the conifer and the sedimentary organic matter 13c values of the sediment indicated stable palaeoenvironmental conditions during the deposition of the argiles du baugeois member hence while detailed palaeovegetation reconstructions are generally limited to the few deposits which present in situ palaeoflora the contribution of isotope geochemistry could allow reconstructions for a wider range of fossil plant deposits

palustrine lacustrine and alluvial facies of the norian owl rock formation chinle group four corners region southwestern u s a implications for late triassic paleoclimate abstract the upper triassic norian owl rock formation was deposited in a low gradient floodbasin at a subtropical paleolatitude the lower part of the formation consists predominantly of fine grained siliciclastic lithofacies deposited by sheetflood and sinuous streams on a muddy floodplain during a period of continuous basin aggradation nodular calcretes are increasingly mature higher in the formation suggesting increasingly episodic depositional conditions the upper part of the formation consists mostly of interbedded fine grained siliciclastic facies and laterally continuous ledges of limestone and sandstone the predominant limestone facies has brecciated to peloidal fabrics spar filled circumgranular cracks and root channeling the subordinate limestone facies displays wavy to irregular argillaceous lamination desiccation cracks and oscillation ripples and is vertically and laterally gradational with the brecciated facies the upper owl rock formation records deposition of aggrading sequences of alluvial sediments deposited during base level rise capped by highstand carbonates deposited in small perennial and ephemeral carbonate lakes and ponds base level lowstand in an overall semiarid climate resulted in extensive pedogenesis of the limestone and laterally equivalent alluvial facies basin wide variations in base level are interpreted as resulting from climatic fluctuations this depositional model is consistent with an interpreted trend towards aridification on the colorado plateau during the late triassic as pangea drifted northward from one climate zone to another

preliminary velocity and resistivity models of the loma prieta earthquake region a preliminary three dimensional velocity model of the loma prieta epicentral region in the santa cruz mountains of california has been derived using raypaths from aftershocks recorded by the u s g s seismic network in addition a magnetotelluric sounding profile was completed prior to the earthquake and a two dimensional resistivity model computed the velocity and resistivity models include a low resistivity 3 10 ohm m low velocity 3 3 5 8 km s wedge of material between the zayante and san andreas faults that extends to depths of over 8 km and is interpreted to be largely tertiary marine sedimentary rocks a high resistivity 1000 ohm m high velocity 6 4 6 7 km s zone between the san andreas and sargent faults may represent largely mafic intrusive rocks

positive feedback drives carbon release from soils to atmosphere during paleocene eocene warming the paleocene eocene thermal maximum petm is the most rapid climatic warming event in the cenozoic and informs us how the earth system responds to large scale changes to the carbon cycle warming was triggered by a massive release of 13c depleted carbon to the atmosphere evidenced by negative carbon isotope excursions cie in nearly every carbon pool on earth differences in these cies can give insight into the response of different ecosystems to perturbations in the carbon cycle here we present records of 13ccc of pedogenic carbonates and 13corg from preserved soil organic matter in corresponding paleosols to understand changes to soil carbon during the petm cies during the event are larger in pedogenic carbonates than preserved organic matter for corresponding paleosols at three sites across two continents the difference in the cies within soil carbon pools can be explained by increased respiration and carbon turnover rates of near surface labile soil carbon increased rates of labile carbon cycling combined with decreases in the amount of preserved organic carbon in soils during the petm suggests a decrease in the size of the soil carbon pool resulting in a potential increase in atmospheric pco2 and a positive feedback with warming the petm is a model for how the earth system responds to warming and this mechanism would suggest that soils might serve as a large source for atmospheric co2 during warming events

paleoatmospheric pco2 fluctuations across the cretaceous tertiary boundary recorded from paleosol carbonates in ne china abstract a dramatic change in atmospheric composition has been postulated because of global carbon cycle disruption during the cretaceous k tertiary t transition following the chicxulub impact and deccan trap eruptions here pedogenic carbonates were collected from drill core of a borehole sk 1 n straddling the late cretaceous and early paleocene strata in the songliao basin northeast china to reconstruct atmospheric co 2 concentrations using a paleosol paleobarometer our estimates for atmospheric pco 2 from paleosol carbonates range between 277 115 ppmv and 837 164 ppmv between 67 8 ma and 63 1 ma one large 66 65 5 ma and several small co 2 spikes 64 7 64 2 ma during the latest maastrichtian to earliest danian are reported here and incorporated with previously published pco 2 estimates also estimated from paleosol carbonates these co 2 spikes are attributed to one million year long emplacement of the large deccan flood basalts along with the extraterrestrial impact at the k t boundary

seismotectonics of the loma prieta california region determined from three dimensional v p v p v s and seismicity three dimensional vp and vp vs velocity models for the loma prieta region were developed from the inversion of local travel time data 21 925 p arrivals and 1 116 s arrivals from earthquakes refraction shots and blasts recorded on 1700 stations from the northern california seismic network and numerous portable seismograph deployments the velocity and density models and microearthquake hypocenters reveal a complex structure that includes a san andreas fault extending to the base of the seismogenic layer a body with high vp extends the length of the rupture and fills the 5 km wide volume between the loma prieta mainshock rupture and the san andreas and sargent faults we suggest that this body controls both the pattern of background seismicity on the san andreas and sargent faults and the extent of rupture during the mainshock thus explaining how the background seismicity outlined the along strike and depth extent of the mainshock rupture on a different fault plane 5 km away new aftershock focal mechanisms based on three dimensional ray tracing through the velocity model support a heterogeneous postseismic stress field and can not resolve a uniform fault normal compression the subvertical or steeply dipping san andreas fault and the fault surfaces that ruptured in the 1989 loma prieta earthquake are both parts of the san andreas fault zone and this section of the fault zone does not have a single type of characteristic event

a middle late pleistocene palustrine lacustrine travertine system borj edouane unit nw tunisia sedimentology stable isotopes and palaeohydrological implications the carbonate borj edouane unit represents the northernmost documented middle late pleistocene continental carbonate deposits in tunisia the unit consists of two main facies associations asymmetrically distributed 1 calcrete palustrine laminar crust 2 microbialites the first accumulated carbonate formed in the distal zone of alluvial fans calcretes and in shallow lakes subjected to periodic exposure palustrine facies that occupied the westernmost strip of the basin the second association formed in permanent lakes stromatolites oncoids and planar stromatolites located in the central areas of the basin fed by springs associated with a concentration of vertical faults in the eastern area of the basin travertine facies at time of deposition these facies communicated with the lake via a transitional lacustrine travertine environment transitional travertine stromatolite facies all facies show a restricted range of 18o values around 5 8 0 5 suggesting formation from paleoprecipitation largely of atlantic derivation brought about by westerly winds as for the 13c values these show a wide range 6 4 to 11 7 overall relatively high values for all facies with the lower values corresponding to the calcrete palustrine association and the higher ones linked to the microbialite facies the trend in travertines probably mimics an increasing influence of carbon derived from dissolution of carbonate bedrock of the cretaceous substrate while that of palustrine samples records increasing respired c contribution the sedimentological and isotopic characteristics of the borj edouane unit reflect wetter conditions at the time of deposition and point to a humid period at the middle late pleistocene transition

seismic images of the deep structure of the san andreas fault system central coast ranges california three dimensional inversion of teleseimic p wave travel time residuals recorded at the u s geological survey central california array has resolved small scale approx tens of kilometers crustal and upper mantle heterogeneity down to depths of 90 km beneath the california coast ranges upper crustal lateral velocity variations of 8 correlate closely with surface geology lower than average velocities are associated with thick tertiary sedimentary fill and higher than average velocities with basement exposures lower crustal velocity heterogeneity of 4 appear to reflect crustal thickness variations a thinner crust is indicated southwest of the san andreas fault and northwest of san pablo bay a linear zone of low velocities 0 to 40 subparallel to the san andreas fault was resolved in the upper mantle the preferred interpretation is that the low velocities indicate a narrow upwarp of asthenosphere to unusually shallow depths approx 45 km beneath the coast ranges such an unusual upper mantle structure may have been produced by the northwestward migration along the california coast of a transiently unstable mendocino triple junction the inversion results also indicate the possibility of partial decoupling of the crust from the upper mantle

radiation damage rims in quartz from uranium bearing sandstones abstract using cathodoluminescence cl mode of a scanning electron microscope sem radiation damage in quartz is made visible in uranium vanadium bearing sandstones located in the salt wash member of the morrison formation jurassic from the colorado plateau u s a detrital quartz grains surrounded by uranium minerals display radiation damage rims three concentric rims with thicknesses of 37 m 24 m and 16 m have been observed the rims are similar to halos surrounding uranium and thorium rich accessory minerals observed by owen 1988 they are due to alpha particles which create damage when penetrating a medium the width of the rims agrees well with the bragg kleeman rule and corresponds to the most energetic alpha particles in the 238u decay series sandstones entirely cemented by vanadium clays also exhibit radioactive rims which demonstrates that uranium has been removed during diagenesis these results have important implications for the uranium ore genesis in the salt wash sandstones because they imply an ancient episode of uranium leaching prior to recent weathering therefore cathodoluminescence in sandstones may be useful in recognizing ancient zones or episodes of accumulation and leaching of alpha emitting nuclides from the uranium series

early to middle jurassic vegetation and climatic events in the qaidam basin northwest china abstract jurassic deposits are well exposed in the qaidam basin qinghai province northwest china and are regarded as one of the most completely developed early middle jurassic plant bearing sequences in northern china the early to middle jurassic palynoflora in this basin shows a high diversity of spores and pollen grains which are characterized by four palynological assemblage zones corresponding to the pliensbachian toarcian aalenian bajocian and bathonian in age vegetation reconstruction demonstrates four vegetation types upland coniferous forest in the pliensbachian coastal cheirolepidiacean forest in the toarcian lowland fern forest in the aalenian bajocian and a mixed forest in the bathonian nearest living relative analysis of the major plant groups shows that the early to middle jurassic vegetation in the qaidam basin not only consists of plants with tropical subtropical climate requirements but also those indicating temperate climatic conditions in addition bryophytes and fungi as well as cheirolepidiaceae which are generally considered to indicate warmer and or drier conditions are also documented in the palynofloras it is suggested that a temperate to subtropical climate generally prevailed during the early to middle jurassic in this basin however the vegetation features and the sedimentary data signify that an overall humid to semi humid phase was punctuated by warmer and locally dry and or arid episodes the two higher temperature and aridity events occurred in the toarcian and bathonian callovian periods in the qaidam basin these climatic events can be inferred by increase of relative abundance of classopollis pollen some tropical subtropical fern spores and the occurrences of variegated red beds and evaporite rocks these events may either be associated in some way with a transient global warming phenomenon due to an enhanced greenhouse effect or be linked with intensification of a potential monsoonal circulation such events finally caused a weakening and even arrested coal accumulation in the qaidam basin during the toarcian and the bathonian callovian intervals

biogeochemical constraints on the triassic jurassic boundary carbon cycle event 1 the end triassic mass extinctions represent one of the five most severe biotic crises in earth history yet remain one of the most enigmatic ongoing debate concerns the environmental effects of the central atlantic magmatic province camp eruptions and their linkage with the mass extinction event across the triassic jurassic boundary there is conflicting paleo evidence for changes in atmospheric pco2 during the extrusion of the camp basalts studies on sediments from european and pacific localities have however identified a substantial negative isotopic anomaly up to 3 5 across the tr j boundary providing an important indicator of changes in the operation of the ancient global carbon cycle we sought to explain the paleo evidence by utilizing a carbon cycle model for the hothouse world of the end triassic that emphasizes the chemical weathering of silicate and carbonate rocks and the ocean carbonate chemistry we find that volcanic co2 outgassing fails to fully account for either a sufficient rise in atmospheric pco2 indicated by the stomata of fossil leaves or the sedimentary isotopic fingerprint instead the scenario that best fits all of the geologic evidence is a positive feedback loop in which warming due to a buildup of volcanically derived co2 triggers destabilization of seafloor methane hydrates and the catastrophic release of ch4 palfy et al 2001 we calculate that this carbon cycle perturbation was huge involving the release of 8000 9000 gt c as co2 during the camp basaltic eruptions and 5000 gt c as ch4 in the model the initial isotopic excursion is assumed to take place over 70 kyr while complete reequilibration of the ocean atmosphere system with respect to co2 is accomplished over 700 1000 kyr our results thus provide a preliminary theoretical explanation for the bioevents estimated pco2 changes and isotopic excursions observed in marine and continental sediments at this time

prolonged carbonate diagenesis under an evolving late cenozoic climate nullarbor plain southern australia abstract the nullarbor plain in southern australia the largest areal karst on the globe is a 240 000 km2 uplifted succession of cenozoic marine carbonates whose surface has been exposed for 14 to 15 m y the middle miocene nullarbor limestone forms the upper surface of the plain and hosts a complex and prolonged record of meteoric diagenesis such a complete record offers unique insights into the effects of climate tectonics sea level topography and hydrology on the style and placement of numerous diagenetic events in flat low lying carbonate plains alteration took place during three broad phases comprising eight stages that are interpreted to have formed against a background of dramatic climate change middle miocene phase one diagenesis took place under a humid climate and resulted in rapid mineral equilibration calcite cementation extensive karst development and finally widespread lacustrine and palustrine sedimentation resultant palustrine sediments especially terrestrial ooids are now preserved at the surface and in underlying karst cavities latest middle miocene to middle pliocene phase two diagenesis occurred during a prolonged period 8 m y of temperate climate and resulted in initial deep cave dissolution during low sea levels and later shallow cave development in the course of a high sea level onset of a somewhat more arid climate in the latest pliocene led to the development of the modern desolate landscape of the plain this final phase of diagenesis involved creation of solution pits filled with black limestone pebbles open and closed dolines with associated colluvium fill and pervasive pedogenic calcrete the nullarbor plain demonstrates that low lying carbonate plains can have low surficial erosion rates precisely record relative sea level positions be able to have extensive caves with extended periods of arrested calcite precipitation and finally host extensive terrestrial ooid deposits the importance of this comprehensive paragenetic record is its applicability to not only recognize unconformities in the rock record but to better appreciate the climate in which they formed

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

co2 drawdown and cooling at the onset of the great oxidation event recorded in 2 45 ga paleoweathering crust abstract the archean atmosphere is thought to have been devoid of oxygen but instead containing high concentrations of greenhouse gases such as co2 and possibly ch4 that were required to keep the earth surface environments warm enough for maintenance of liquid water under faint young sun conditions earlier studies have suggested that the co2 concentrations must have been as high as over 1000 times present atmospheric levels pal to overcome the effects of weaker solar luminosity however more recent studies of precambrian paleosols imply existence of at least tenfold lower but still high pco2 levels the appearance of minute amounts of atmospheric o2 at the transition of archean and proterozoic is well documented however the bulk composition of the atmosphere and its dynamics at this crucial time is still widely debated different paleoclimate proxies of the 2 45 ga kuksha paleoweathering crust suggest its formation in a cool temperate climate paleoatmospheric pco2 estimates by geochemical and isotopic mass balance models suggest remarkably low paleoatmospheric co2 levels with the best guess estimates of atmospheric co2 between 1 and 10 pal we speculate that the kuksha paleoweathering crust either predates or partly overlaps with the onset of huronian glaciation and corresponds to a time interval of low co2 level during the first recorded large glaciation in earth history

transition from arid to hyper arid environment in the southern levant deserts as recorded by early pleistocene cummulic aridisols abstract the time at which deserts established their current arid or hyper arid conditions remains a fundamental question regarding the history of earth cosmogenic isotope exposure ages of desert pavement and welded calcic gypsic salic reg soils that developed on relatively flat alluvial surfaces 2 ma ago in the negev desert indicate long geomorphic stability under extremely dry conditions over a short interval during their initial stage of development between 1 2 ma these cumulative soils are characterized by calcic soils reaching maximum stage iii of carbonate morphology this interval is the only period when calcic soil horizons formed on stable abandoned alluvial surfaces in the southern negev desert since 1 ma pedogenesis changed toward more arid soil environment and the formation of gypsic salic soil horizons that were later followed by dust accumulation the dichotomy of only moderately developed calcic soil stages ii iii during a relatively long time interval 105 106 years indicates an arid environment that does not support continuous development but only occasional calcic soil formation the very low 18o and relatively high 13c values of these early pedogenic carbonates support soil formation under arid climatic conditions such an environment was probably characterized by rare and relatively longer duration rainstorms which occasionally allowed deeper infiltration of rainwater and longer retention of soil moisture this in turn enabled the growth of sparse vegetation that enhanced deposition of pedogenic carbonate at 1 ma these rare events of slightly wetter conditions ceased and less atmospheric moisture reached the southern negev desert leading to deposition of soluble salts and dust deposited in the soils the combination of long term hyperaridity scarcity of vegetation and lack of bioturbation salts cementation dust accumulation and tight desert pavement cover has protected the surfaces from erosion forming one of the most remarkably stable landscapes on earth a landscape that essentially has not eroded but accumulated salt and dust for more than 106 yr

teleseismic tomography of the loma prieta earthquake region california implications for strain partitioning from teleseismic travel times we derive three dimensional velocity models of the upper 71 km in the 1989 loma prieta earthquake region central california shallow crustal structure is consistent with local earthquake tomography horizontal velocity gradients at all depths suggest that the san andreas fault was a deep shear locus at least at one time a large low velocity feature near the moho beneath loma prieta probably is caused by a crustal root two low velocity features at about 45 70 km depth are offset right laterally along the san andreas by about 45 km cooling of this portion of the upper mantle furlong et al 1989 could have frozen in displacements in this region within a few million years after passage of the mendocino triple junction these results are consistent with furlong et al s model

palustrine deposits on a late devonian coastal plain sedimentary attributes and implications for concepts of carbonate sequence stratigraphy abstract palustrine deposits in coastal environments can cover thousands of square kilometers and are stratigraphically important palustrine deposits that originated in supratidal marshes can be used to track shifts in the shoreline position whereas palustrine deposits that formed in marshes above the peritidal realm are indicative of subaerial unconformities despite the importance of these deposits there are few documented examples of ancient coastal palustrine deposits and their sedimentary attributes remain poorly understood misinterpretation of coastal palustrine deposits as marine deposits or calcrete may partly explain this situation the upper devonian alexandra formation exposed in the northwest territories of canada is formed of two reef complexes that are separated by a type i sequence boundary at the landward part of the platform this boundary is marked by a succession of coastal plain deposits that is 50 cm thick the most distinct aspect of this succession are palustrine deposits characterized by charophytes skeletal rivularia stromatolites and various pedogenic features including complex crack networks root traces and authigenic kaolinite karst features and calcrete generally regarded as typical indicators of subaerial exposure are not found this study highlights the sedimentary attributes that can be used to identify ancient palustrine deposits in marine coastal regions distinguish these deposits from calcrete and demonstrates their sequence stratigraphic significance when found in marine limestone successions it clearly demonstrates that palustrine deposits like those found in the alexandra formation should be considered indicative of subaerial unconformities and sequence boundaries in the same manner as karst and calcrete

early oligocene paleosols of the dagshai formation india a record of the oldest tropical weathering in the himalayan foreland abstract this study reports paleopedological features of the fossil soils that formed during the earliest phase of continental sedimentation in the himalayan foreland the fluvial sequence of the dagshai formation 31 6 3 9 ma to 30 3 3 9 ma exposed along the koshaliya river nw himalaya contains four pedofacies named pedofacies a d of ferruginous paleosol sequences contained within overbank sediments the dagshai formation unconformably overlies the marine subathu formation pedofacies a consists of 3 4 well developed ferruginous paleosols overlain by gray sandstone beds pedofacies b d are marked by a progressive decrease in pedogenesis these paleosols occur as 0 5 m to 1 5 m thick bw bt btk bk bss horizons that are marked by extensive development of rhizoliths pedogenic carbonate and iron rich clay pedofeatures that correspond to modern entisols inceptisols alfisols and vertisols based on early oligocene paleogeographic position of the northward drifting indian plate it is inferred that these paleosols were formed at 18 n paleolatitude in the dagshai sub basin in the himalayan foreland micromorphology geochemical analyses weathering indices and stable isotope composition of paleosols indicate tropical climate paleoprecipitation of 947 1256 mm and paleotemperature of 25 c with an initial phase of monsoonal conditions during pedogenesis these paleoclimatic conditions favored c3 paleovegetation immediately after the transition from greenhouse to icehouse conditions

palaeogeographic significance of black pebbles lower cretaceous prebetic southern spain abstract the presence of black pebbles in carbonate stratigraphic sections constitutes a criterion for identifying emergence episodes which are significant to palaeographic reconstructions and to location of sedimentary cycle boundaries three genetic models can be inferred from the stratigraphic petrologic and geochemical study of black pebbles that occur in sediments of the lower cretaceous of the prebetic southern spain in the first model black pebbles are the product of redeposition in tidal and lacustrine environments from layers rich in organic matter carbonaceous layers in the second model blackening takes place as a result of very mature organic matter mainly generated from terrestrial plants possibly burnt ones selectively staining some of the intraclasts of the storm layers in intertidal environmnts in the third model applicable only to pedogenic and lacustrine environments black pebbles to a large extent originate from a redeposition of pedogenic carbonate materials affected by natural forest fires where blackening was caused by a sudden and rapid increase in temperature the third hypothesis is supported by data obtained from an experiment in which samples underwent progressive heating to monitor the blackening process and accompanying change in isotopic composition in all cases the effects of storms and or currents and waves caused erosion and redeposition

recent movements of the juan de fuca plate system analysis of the magnetic anomalies of the juan de fuca plate system allows instantaneous poles of rotation relative to the pacific plate to be calculated from 7 ma to the present by combining these with global solutions for pacific america and absolute relative to hot spot motions a plate motion sequence can be constructed this sequence shows that both absolute motions and motions relative to america are characterized by slower velocities where younger and more buoyant material enters the convergence zone pivoting subduction the resistance provided by the youngest portion of the juan de fuca plate apparently resulted in its detachment at 4 ma as the independent explorer plate in relation to the hot spot framework this plate almost immediately began to rotate clockwise around a pole close to itself such that its translational movement into the mantle virtually ceased after 4 ma the remainder of the juan de fuca plate adjusted its motion in response to the fact that the youngest material entering the subduction zone was now to the south differences in seismicity and recent uplift between northern and southern vancouver island may reflect a distinction in tectonic style between the normal subduction of the juan de fuca plate to the south and a complex underplating occurring as the explorer plate is overridden by the continent the history of the explorer plate may exemplify the conditions under which the self driving forces of small subducting plates are overcome by the influence of larger adjacent plates the recent rapid migration of the absolute pole of rotation of the juan de fuca plate toward the plate suggests that it too may be nearing this condition

water mass circulation on demerara rise during the late cretaceous based on nd isotopes abstract circulation in the north atlantic during the late cretaceous has implications for poleward heat transport and nutrient distribution during an extreme greenhouse interval with episodes of ocean anoxia nd isotopes of fossil fish teeth and debris represent one of the few water mass tracers that can be used to reconstruct deep ocean circulation we present nd isotopic data interpreted as bottom water values for 290 samples from three ocean drilling program sites on demerara rise sites 1258 1260 and 1261 along with 102 analyses from four other north atlantic sites cape verde goban spur bermuda rise and blake nose that provide additional geographic and bathymetric control our results confirm the presence of a water mass with low end values 14 to 17 that are believed to be influenced by continental material during local water mass formation at low latitudes this demerara bottom water dbw is the primary water mass in the region from the cenomanian to coniacian and from the late campanian through early maastrichtian following a hiatus of 10 my a positive 8 end unit excursion occurs during ocean anoxic event 2 oae2 that cannot be explained by changes in weathering inputs diagenesis or magmatic sources of nd instead it appears to represent an influx of bottom waters sourced from the tethys or north atlantic this replacement of dbw during oae2 argues for decreased production of dbw or enhanced production of tethys north atlantic waters during peak greenhouse conditions from the late campanian through early maastrichtian dbw becomes the only water mass recorded at demerara rise and it appears to expand to abyssal depths at cape verde in the campanian this water mass is ultimately replaced by waters that appear to be sourced from the north atlantic starting in the late maastrichtian observed variations in circulation in the tropical north atlantic during the late cretaceous can account for extensive deposition of black shales in the region prior to the hiatus as well as local warming during a global cooling event in the maastrichtian

the cyclic hierarchy of the purbeckian sierra del pozo section lower cretaceous berriasian southern spain the lowermost cretaceous berriasian sierra del pozo formation is divisible into metre scale cycles that are bundled in a four tiered hierarchy of cycles and cyclic sequences at the smallest scale sixth order cycles thought to be the product of precessionally forced sea level fluctuations c 20 ka average less than a metre in thickness shallow upward and are bounded by surfaces where deeper facies abruptly overlie shallower facies bundles of sixth order cycles called fifth order sequences are recognized by two types of asymmetric patterns in facies distribution first more pronounced facies changes occur at sixth order cycle boundaries lower in a sequence whereas smaller facies changes occur at cycle boundaries higher in a sequence secondly subtidal marine limestones i e biomicrites and biosparites are the dominant facies lower in a cyclic sequence whereas more restricted or shallower water facies i e mud cracked microbial laminites dolomites shale and clay are more predominant higher in a cyclic sequence the bundling of sixth order cycles is explained as a product of periodic change 100 ka in the eccentricity of the earth s orbit the degree of orbital eccentricity modulates the magnitude of precessional sea level fluctuations which in turn determine the relative facies contrasts at sixth order cycle boundaries larger scale fourth and third order sequences are defined by similar patterns in facies contrast at successive sequence boundaries and by a change in predominant facies type from bottom to top these patterns are explained as the product of 400 ka and 2 ma periodic variations in the eccentricity of the earth s orbit in summary the strength of the precessional signal varies in consort with periodic changes in orbital eccentricity at three time scales producing a stacked hierarchy of cycles and sequences of cycles change in obliquity of the earth s axis may modulate the effects of the precessional signal and thereby modify patterns of preserved cyclic structure this interpretation of cyclicity in the sierra del pozo section is markedly different from that of

growth rates of pedogenic carbonate coatings on coarse clasts abstract growth rates of pedogenic carbonate coatings on clasts can be used as a simple quantitative index of soil and sediment age as well as a chronological framework for palaeoecological reconstructions they are also probably connected with general intensity of formation of bk horizons in soils previously data on coating growth rates were restricted ecologically and geographically to desert regions of north america this paper presents growth rates of holocene pedogenic carbonate coatings on clasts within an extended range of environments calculated on the basis of archaeological and radiocarbon dating the rates in this study are higher than in earlier reports carbonate coatings can thicken with rates up to 1 mm 1000 years or higher in semi arid and semi humid climates at least five factors are likely to control growth rates 1 climate 2 lithology of carbonate parent material 3 depth under the soil surface 4 clast size 5 bulk density and composition of cutans favorable factors for comparatively rapid coating thickening seems to be climatic conditions ranging from semi arid to semi humid high carbonate content of parent material and large size of clasts there is also an optimal depth of carbonate coating growth in a soil profile little information on bulk density and composition of cutans is available but they appear to play an important role as one of the factors governing growth rates of pedogenic carbonate coatings on clasts

three dimensional vp and vp vs structure at loma prieta california from local earthquake tomography p and s p times from local earthquakes and p times from explosions at seismic stations in the vicinity of the 1989 loma prieta earthquake are inverted simultaneously to produce three dimensional images of vp and vp vs structure along the rupture zone the results confirm the presence of the major heterogeneities identified in previous studies using p waves only including high vp along the rupture in areas of significant slip and a low velocity wedge along the san andreas at the se edge of the rupture a change in rock properties evidenced by a significant vp vs increase equal to a 30 poisson s ratio increase from the middle crust to the upper crust may have been responsible for the upward termination of the main shock rupture we speculate that the deep high vp body that lies along the se portion of the rupture zone consists of two bodies based on model results indicating that the sw part of the body has relatively high vp vs while the ne part has relatively low vp vs

how relevant is the role of macrophytic vegetation in controlling peritidal carbonate facies clues from the upper jurassic of portugal abstract stratigraphic variability in peritidal carbonates is generally interpreted in terms of sea level changes but little consideration is given to the effects of vegetation and of how long term changes in macrophyte evolution have affected carbonate sedimentation in such settings many present day low energy tropical carbonate shorelines are dominated by macrophyte vegetation although several pre jurassic macrophytes have been interpreted to have lived in brackish water zones records of macrophyte dominated carbonate shorelines in the stratigraphic record are apparently rare or even absent which thus is an enigma we use upper jurassic platform interior carbonates from central portugal to emphasize these issues these successions contain both classical tidal flat bearing cyclothems and ones capped by marsh facies with evidence of macrophytes the former having developed in more restricted settings although these late jurassic shorelines were not affected by true mangroves we propose that tidal flat deposits were not developed because the shorelines at least locally were dominated by macrophytes we speculate that the paucity of classical tidal flat bearing peritidal cyclothems in the cainozoic may have been due at least partially to the spread of major macrophyte dominated mangrove communities during the paleogene

late cenozoic tectonic evolution of southwestern california we synthesize available geologic and geophysical data from southern california and adjoining areas in order to develop a reconstruction of the tectonic evolution of the southern coast ranges western transverse ranges and borderland regions of california since 30 ma premises include specified relative plate motions for times prior to 10 5 ma and after 3 ma a mid tertiary bight in the continental margin of southern california midcrustal detachment faults under much of california and adjoining regions rotation of the western transverse ranges about an eastern pivot and specified fault displacement histories prior to 18 ma about 90 of the tangential component of pacific north america relative motion was accommodated on an offshore dextral fault system near the toe of the continental slope from 18 ma to 5 5 ma dextral slip was accommodated predominantly on the offshore system but also on a second inboard system that included the san andreas fault fault bounded crustal blocks between the offshore and inboard fault systems underwent translation rotation and extension from 18 ma to 11 5 ma but not from 11 5 ma to 5 5 ma since 5 5 ma dextral slip has been accommodated predominantly on the inboard fault system dextral slip ceased on the offshore fault system north of the transverse ranges but continues on faults west of or within baja california the san gregorio san simeon hosgri fault system has accommodated less than 5 km of the late cenozoic dextral slip the distribution of dextral displacement in the plate boundary zone has been controlled by abrupt jumps of the position of a southern triple junction and to a lesser degree changes in magnitude of pacific north america relative motion based on our reconstuction the tangential component of pacific north america relative motion was 90mm yr for the period 10 5 ma to 5 5 ma and 60mm yr for the period 5 5 ma to 3 ma

late tertiary tectonic evolution of the seafloor spreading system off the coast of california between the mendocino and murray fracture zones a forward modeling program of two plate spreading on a sphere was utilized to reconstruct the late tertiary tectonic evolutionary history of the seafloor spreading system off the coast of california between the mendocino and murray fracture zones this analytical technique was applied to a unique set of magnetic anomaly data consisting principally of a new digital data set the original raff mason data from one of the most significant marine geophysical surveys the 1955 1956 uscgs pioneer survey all the data critical for the development of seafloor spreading and plate tectonic theory were digitized 32 to 52 n however only the southern half was analyzed in this study investigation of the raff mason data supplemented by additional magnetic anomaly data indicates that the primary mechanism for reorganization of this part of the pacific farallon ridge as the spreading center migrated toward and arrived at the north american trench was rift propagation the model presented here containing a total of 21 propagation episodes from 36 ma to 19 8 ma initiation time of the last propagator shows generally excellent agreement with the isochrons identified from the magnetic anomaly pattern although minor exceptions exist locally in complex areas a step by step evolution of the model is presented in a series of reconstructions documenting the history of spreading between the pacific plate and five smaller plates created from the breakup of the large ancestral farallon plate these plates include the vancouver plate north of the pioneer the farallon plate existing between the murray and pioneer transforms prior to the major reorganization at chron 10 30 33 ma and the arguello monterey and reyes microplates with northwest southeast spreading existing after chron 10

tomographic p wave velocity images of the loma prieta earthquake asperity tomographic inversion is applied to delay times from local earthquakes to image 3 d velocity variations surrounding the main rupture of the 1989 loma prieta earthquake the 55 times 45 square km region is represented by blocks of 1 km per side laterally and by 8 layers of varying thickness to 18 km depth high quality p wave arrival times recorded on the usgs calnet array from 549 crustal earthquakes with depths of 0 to 25 km were used as sources preliminary results note several velocity variations 5 12 that correlate with specific characteristics of the 1989 rupture these include prominent high velocity anomalies near the mainshock hypocenter and prominent low velocity anomalies where the dip of the san andreas fault appears to change significantly the termination of prominent low velocity features existing primarily in the hanging wall to depths of 7 9 km correlates with the top of the rupture zone high velocity variations along the fault dominate where aftershock activity is high the high velocity anomaly located at depth along the fault is interpreted as imaging the asperity on which the loma prieta earthquake occurred

stable isotope geochemistry of vertisols formed on marine limestone and implications for deep time paleoenvironmental reconstructions abstract carbon and oxygen isotope compositions of pedogenic carbonate preserved in paleosols have been used extensively to reconstruct ancient environmental conditions one concern is that pedogenic carbonate precipitated in association with a limestone parent material may include a contribution from inherited detrital lithogenic marine calcite thus compromising interpretations of stable isotope compositions to investigate the impact of lithogenic calcite on environmental interpretations using paleosols we measured stable isotope ratios in pedogenic carbonates and coexisting soil organic matter som in modern vertisols fine smectitic thermic udic haplusterts from riesel texas heiden series and zabcikville texas houston black series forming on cretaceous chalk deposits the pedogenic and lithogenic components in the heiden series soil at riesel were identified using micromorphology and cathodoluminescence cl which showed incorporation of luminescent marine allochems i e foraminifera mollusks into hard nodules and soft powdery pedogenic masses additionally micromorphology showed evidence of meteoric recrystallization of the allochems despite the presence of these inherited carbonates into hard nodules and soft powdery masses the stable isotope compositions recorded a partial pedogenic signal recrystallization of the marine allochems resulted in overprinting of primary marine isotope ratios with ratios that are more similar to those expected for pedogenic carbonates in these soils this study demonstrates that incorporation of parent material into pedogenic carbonates does not necessarily compromise the pedogenic signal that is useful for paleoenvironmental reconstructions however overprinting of marine allochems if present can be important and needs to be identified using micromorphology and cathodoluminescence before using stable isotope ratios of pedogenic carbonates for paleoenvironmental reconstructions

calcretes from a palaeosinkhole in jurassic palaeokarst subbetic southern spain abstract calcretes have been recognized in the bottom of a palaeokarstic sinkhole etched into early jurassic carbonates from the subbetic southern spain these are 3 to 10 cm thick and they show an internal structure in which three units can be distinguished the lower unit is composed of alternate irregular bands of unfossiliferous micrite and sparry calcite in the micrite several features point out the activity of endolithic microorganisms as fungi and bacteria the middle unit which has a laminated structure with palisade calcite spar and some vadose silt is interpreted as a speleothem and finally the upper unit shows calcrete pisoids and rhizocretions the isotope ratio analysis gives results in which 13 c ranges from 10 1 to 10 9 and 18 o ranges from 5 7 to 7 0 these values are very similar to those from palaeosols of other ages and localities which is an important argument favouring emersion stages with continental deposition in an island with an arid or semi arid climate nevertheless these calcretes outcrop in association with a palaeokarstic relief reflecting wet climate before the calcrete formation

geometry and evolution of the san andreas fault zone in northern california the evolution of the san andreas fault system is controlled by thermal mechanical processes associated with the development and evolution of a narrow slabless window formed beneath the western edge of north america this fault zone evolution begins after initiation of transform motion along the plate boundary with the northward migration of the mendocino triple junction as a consequence of initial lithospheric structure and the shallow emplacement of asthenospheric mantle the plate boundary separating the north american and pacific plates follows a complex three dimensional geometry which varies through time seismic velocity structure heat flow seismicity surface deformation uplift and fault development are controlled by the evolving thermal structure in the region after triple junction passage thermal mechanical models have been used to evaluate the fault system s time varying three dimensional dynamical behavior simulating the principal processes involved in the thermal mechanical evolution of the san andreas fault system results from this modeling indicate that the fault system has essentially a three stage history 1 in the vicinity of the mendocino triple junction the san andreas fault maps the eastern edge of the pacific plate with a broad 100 km zone of asthenospheric mantle separating the pacific and north american plates in the 25 to 90 km depth range 2 between 37 n and 39 n the plate boundary within the mantle separating the pacific and north american plates has developed approximately 40 60 km east of the surface trace of the san andreas fault and lies beneath the hayward calaveras faults and associated faults the surface trace of the plate boundary appears to be connected to the mantle segment via a lower crust subhorizontal detachment surface this fault zone orientation produces the surface deformations observed geodetically in the region 3 south of 37 n the surface fault again overlies the deeper plate boundary apparently as a result of an eastward jump in the surface fault

climate change on tectonic time scales abstract observational and modeling studies relevant to climate change on tectonic time scales are reviewed probably the most significant climate result from this time scale involves inferences about nearly ice free conditions for some intervals of earth history some additional results suggest relatively rapid transitions between climate states modeling studies indicate that although tectonic changes significantly modify the atmosphere and ocean circulation in most cases such modifications do not appear to be sufficient to explain ice free climates increased atmospheric co2 levels 5 10 presentvalues may be needed to completely reconcile models and data although the co2 paradigm has received widespread attention in the last few years the results summarized herein indicate that co2 is only one of several important factors influencing climate i believe the time is appropriate for contemplating climate change on tectonic time scales in terms of a post co2 synthesis in which direct tectonic factors are approximately equal in importance to co2 fluctuations in the last few years modeling studies have progressed from a state of virtually no work on the topic to one where the models are in some respect ahead of the observations in the sense that data have not been compiled to test even some of the most basic model predictions in particular information is needed on past atmospheric co2 levels tropical sea surface temperatures seasonality of continental interiors and locations and production rates of deep waters initial steps are being taken to integrate observational and modeling activities on tectonic time scales and some of these shortcomings may be rectified over the next few years

stability of atmospheric co2 levels across the triassic jurassic boundary the triassic jurassic boundary 208 million years ago is associated with widespread extinctions in both the marine and terrestrial biota the cause of these extinctions has been widely attributed to the eruption of flood basalts of the central atlantic magmatic province this volcanic event is thought to have released significant amounts of co2 into the atmosphere which could have led to catastrophic greenhouse warming but the evidence for co2 induced extinction remains equivocal here we present the carbon isotope compositions of pedogenic calcite from palaeosol formations spanning a 20 myr period across the triassic jurassic boundary using a standard diffusion model we interpret these isotopic data to represent a rise in atmospheric co2 concentrations of about 250 p p m across the boundary as compared with previous estimates of a 2 000 4 000 p p m increase the relative stability of atmospheric co2 across this boundary suggests that environmental degradation and extinctions during the early jurassic were not caused by volcanic outgassing of co2 other volcanic effects such as the release of atmospheric aerosols or tectonically driven sea level change may have been responsible for this event

a liassic isolated platform controlled by tectonics south iberian margin southeast spain the middle and upper members of the gavilan formation near velez rubio almeria province southeast spain are interpreted as carbonate platform deposits the studied outcrops form geologically part of the external zones of the betic cordillera south iberian palaeomargin a genetic unit limited by intra sinemurian and intra upper carixian sedimentary breaks is defined the evolution of the parasequence sets in the area and the development of deeper sedimentation in its northern outcrops suggest that this platform was isolated with regard to the south iberian margin three distinct parasequence sets are proposed progradational parasequence set only locally present retrogradational parasequence set middle member of the gavilan formation and aggradational parasequence set basically composed of the upper member of the gavilan formation sedimentary features such as neptunian dykes sharp lithological changes thickness variations the presence of palaeofaults and the subsidence history all lead to the conclusion of a significant regional tectonic influence in the genetic unit evolution normal extensional faulting has been proposed as a major control on sedimentation on this isolated platform this regional factor has completely distorted the effect of the eustatic fluctuations for this period of time

the relative mobility of u th and ra isotopes in the weathered zones of the eye dashwa lakes granite pluton northwestern ontario canada radioisotope activity ratios of weathered surface rocks from the eye dashwa lakes granite pluton show that in the 238u decay series 226ra has been leached more rapidly than the grandparent 234u and 238u isotopes the observation of 238th232th disequilibria in the 232th decay series shows that either 228th half life of 1 9 yrs or 228ra half life of 5 75 yrs have been removed from these rocks very rapidly indeed isotope ratios of separated mineral fractions appear to show that whereas uranium tends to be removed from all mineral fractions ra is strongly readsorbed onto feldspars presumably as these undergo alteration to clay minerals this necessitates making a distinction between intermineral mobility of u or ra and the net loss of u or ra from the whole rock an attempt has been made to model quantitatively the transport rate of ra though with little success failure of the modelling appears to indicate that the mobility of 228ra is higher than might be predicted by the mobility of 226ra that is the two isotopes are not strict analogues of one another in their response to initial weathering

high resolution image of uppermost mantle beneath ne iran continental collision zone we invert 3775 relative p wave arrival times using the ach damped least square method of aki et al 1977 to study upper mantle structure beneath the ne iran continental collision zone the data for this study were recorded by 17 three component broad band stations operated from august 2006 to february 2008 along a profile from the center of iranian plateau near yazd to the northeastern part of iran on the turan platform just north of the kopeh dagh mountains the results confirm the previously known low velocity upper mantle beneath central iran our tomographic model reveals a deep high velocity anomaly the surficial expressions of this anomaly are between the ashkabad and doruneh faults where the resolution and ray coverage are good a transition zone in uppermost mantle is recognized under the binalud foreland that we interpreted as suture zone between iran and turan platform our results indicate that atrak valley which is the boundary between the binalud and kopeh dagh mountains can be considered as the northeastern suture of the iranian plateau where eurasia and turan platform under thrust beneath the binalud range and central iran

the coupled δ13c radiocarbon systematics of three late glacial early holocene speleothems insights into soil and cave processes at climatic transitions abstract the coupled 13 c radiocarbon systematics of three european stalagmites deposited during the late glacial and early holocene were investigated to understand better how the carbon isotope systematics of speleothems respond to climate transitions the emphasis is on understanding how speleothems may record climate driven changes in the proportions of biogenic soil carbon and limestone bedrock derived carbon at two of the three sites the combined 13 c and 14 c data argue against greater inputs of limestone carbon as the sole cause of the observed shift to higher 13 c during the cold younger dryas in these stalagmites gar 01 from la garma cave n spain and so 1 from sofular cave turkey the combined changes in 13 c and initial 14 c activities suggest enhanced decomposition of old stored more recalcitrant soil carbon at the onset of the warmer early holocene alternative explanations involving gradual temporal changes between open and closed system behaviour during the late glacial are difficult to reconcile with observed changes in speleothem 13 c and the growth rates in contrast a stalagmite from pindal cave n spain indicates an abrupt change in carbon inputs linked to local hydrological and disequilibrium isotope fractionation effects rather than climate change for the first time it is shown that while the initial 14 c activities of all three stalagmites broadly follow the contemporaneous atmospheric 14 c trends the younger dryas atmospheric 14 c anomaly can be clearly discerned subtle changes in speleothem initial 14 c activities are linked to climate driven changes in soil carbon turnover at a climate transition

seawater ph and isotopic paleotemperatures of cretaceous oceans abstract stable oxygen isotope ratios 18 o of foraminifera are widely used to reconstruct the climatic history of earth it is well known that temperature reconstructions based on 18 o are complicated by factors such as the unknown isotopic composition of the ocean in addition recent experimental and theoretical work has shown that the seawater ph has a marked effect on the 18 o of foraminifera here i employ this effect to demonstrate that reconstructions based on 18 o of foraminifera may underestimate sea surface temperatures in the geological past ocean surface temperatures for the mid cretaceous are estimated to have been 2 3 5 c higher than previously thought

new constraints on using paleosols to reconstruct atmospheric pco2 ecosystem and climatic changes due to anthro po genic emissions of co 2 are of increasing importance to society one way to predict these changes in the future is to study warming events in the geologic past the main control of earth s temperature over geologic time is the concentration of atmospheric co 2 however the precise relationship between co 2 and temperature is not fully understood therefore it is essential to be able to quantify atmospheric co 2 concentrations in the geologic past especially at times of rapid climate change analogous to current atmospheric changes one widely applied proxy relates the carbon isotopic composition of pedogenic carbonates to atmospheric pco 2 but one of the key variables soil respired co 2 s z is not well constrained this study presents a new proxy where soil respired co 2 is related to mean annual precipitation map by the following equation s z 5 67 map 269 9 r 2 0 59 se 681 ppm this proxy validated for modern atmospheric pco 2 levels constrains the primary source of uncertainty in the soil carbonate paleobarometer we apply this proxy to make atmospheric pco 2 reconstructions for examples from the cenozoic mesozoic and paleozoic and calculate co 2 estimates that are in better agreement with estimates from other independent proxies and model results than previous pedogenic carbonate reconstructions the implications of the uncertainties attributed to pedogenic carbonate paleobarometry as well as guidelines for using this method are discussed by making individual measurements rather than assumptions for each isotopic value and combining those analyses with an s z estimate for each paleosol considered using our new proxy described herein we can obtain increased precision for atmospheric pco 2 reconstructions

the destruction of paleoclimatic isotopic signals in pleistocene carbonate soil nodules of western australia stable carbon and oxygen isotopic analyses were conducted on small 10 mm spherical pleistocene carbonate soil nodules from 53 different levels in a 9 15 m soil auger collected in northern western australia the 13c and 18o values range from 4 to 0 and 9 to 6 pee dee belemnite standard respectively comparison of these values to the 13c values of coexisting soil organic matter som reveals marked differences between the two records the som values record an enrichment of 16 through the section whereas the carbonate values record only a 4 variability application of a diffusion production model to the data indicates isotopic disequilibrium between the two carbon records one possible interpretation of the apparent isotopic disequilibrium is that the nodules formed at depths of 1 cm but this interpretation is not supported by field observations an alternative is that the soil organic matter currently in the profile was emplaced after nodule formation such a scenario would have to have occurred numerous times during the late pleistocene as the nodules grew below different soil zones through time a third explanation is that diagenetic alteration of the carbonates in the presence of dissolved inorganic groundwater carbon has occurred this interpretation is consistent with the widely fluctuating regional groundwater table it is also supported by petrographic fabrics and heterogeneous cathodoluminescence patterns indicative of initial pedogenic development of the nodules and then at least one dissolution event multiple precipitation events prolonged nodule growth by displacive spars and microspars cementation and recrystallization of some micrite the results illustrate potential problems for 1 the use of some pedogenic carbonate isotopic records as proxies for environmental change and 2 the use of altered 18o values and unaltered 13c values as screening tools for the presence or absence of diagenesis the results highlight the necessity of understanding regional environmental conditions and diagenetic histories prior to using pedogenic carbonates in paleoreconstructions

petrographic and geochemical features of sinkhole filling deposits associated with an erosional unconformity on grand cayman abstract on grand cayman exposures of dolostones belonging to the cayman formation miocene represent an erosional unconformity that has been developing since the late pliocene 3 6 ma sinkholes that developed during this time have remained open or become partly to fully filled with various combinations of rootcrete breccias loose limestone and dolostone lithoclasts and white red and orange limestones these sinkhole filling deposits have different geochemical attributes to the neogene and pleistocene marine carbonates that form the bedrock of the island the deposits in the sinkholes formed in response to the variations of sea level climate exposure and vegetation that developed during the period when the erosional unconformity was developing the rootcrete oncoids red and orange limestones are terrestrial in origin whereas the limestone and dolostone lithoclasts and white limestones are derived from marine deposits on the erosional unconformity intense root activity led to the formation of rootcrete and terrestrial oncoids but also selectively blackening reworked marine carbonates the red and orange limestone matrices which formed under more arid conditions contrast with the other sinkhole filling deposits that formed during periods when the climate was semi arid to humid the distinctive ree signatures of the sinkhole filling deposits which are different from those of the bedrock limestones and dolostones can probably be attributed to trace amount of terra rossa and or airborne saharan derived dust that are present in those deposits

high resolution body wave tomography beneath the svekalapko array i a priori three dimensional crustal model and associated traveltime effects on teleseismic wave fronts summary assessment of contributions from shallow lithosphere to teleseismic wave front distortion is a prerequisite for high resolution regional teleseismic tomography several methods have been proposed in the past for the correction of these effects e g application of station correction terms we propose an approach that is independent of the subsequent inversion and uses the available a priori knowledge of the crustal structure to calculate crustal traveltime effects of teleseismic wave fronts our approach involves the construction of a 3 d crustal model based on controlled source seismology data and calculation of the associated traveltime anomalies for incoming teleseismic wave fronts the model for central fennoscandia shows a maximum crustal thickness of 64 km and includes a high velocity lower crust as derived for parts of the study area by previous authors traveltimes calculated using finite differences for teleseismic waves travelling through this crustal model are compared with those from the standard reference model iasp91 and the residuals are used to correct observed teleseismic arrival times at the svekalapko array to test the performance of this approach in a second part of the study a synthetic traveltime data set is obtained by tracing wave fronts through a mantle structure with known velocity anomalies and the 3 d crustal model this data set is inverted with and without correction for crustal effects the 3 d crustal effects alone with a homogeneous mantle are also inverted and the results show that the crustal effects propagate down to 450 km the comparison of the inversion results demonstrates the need to apply appropriate 3 d crustal corrections in high resolution regional tomography for upper mantle structure beneath the baltic shield

waveform tomography of crustal structure in the south san francisco bay region 1 we utilize a scattering based seismic tomography technique to constrain crustal structure around the southern san francisco bay region sfbr this technique is based on coupled traveling wave scattering theory which has usually been applied to the interpretation of surface waves in large regional scale studies using fully three dimensional kernels this technique is here applied to observed p s and surface waves of intermediate period 3 4 s dominant period observed following eight selected regional events we use a total of 73 seismograms recorded by a u s geological survey short period seismic array in the western santa clara valley the berkeley digital seismic network and the northern california seismic network modifications of observed waveforms due to scattering from crustal structure include positive or negative amplification delay and generation of coda waves the derived crustal structure explains many of the observed signals which cannot be explained with a simple layered structure there is sufficient sensitivity to both deep and shallow crustal structure that even with the few sources employed in the present study we obtain shallow velocity structure which is reasonably consistent with previous p wave tomography results we find a depth dependent lateral velocity contrast across the san andreas fault saf with higher velocities southwest of the saf in the shallow crust and higher velocities northeast of the saf in the midcrust the method does not have the resolution to identify very slow sediment velocities in the upper approximately 3 km since the tomographic models are smooth at a vertical scale of about 5 km

quasi static eocene oligocene climate in patagonia promotes slow faunal evolution and mid cenozoic global cooling abstract new local regional climatic data were compared with floral and faunal records from central patagonia to investigate how faunas evolve in the context of local and global climates oxygen isotope compositions of mammal fossils between c 43 and 21 ma suggest a nearly constant mean annual temperature of 16 3 c consistent with leaf physiognomic and sea surface studies that imply temperatures of 16 18 c carbon isotopes in tooth enamel track atmospheric 13 c but with a positive deviation at 27 2 ma and a strong negative deviation at 21 ma combined with paleosol characteristics and reconstructed leaf area indices rlais these trends suggest aridification from 45 ma c 1200 mm yr to 43 ma c 450 mm yr quasi constant map until at least 31 ma and an increase to 800 mm yr by 21 ma comparable map through most of the sequence is consistent with relatively constant floral compositions rlai and leaf physiognomy abundance of palms reflects relatively dry adapted lineages and greater drought tolerance under higher p co2 pedogenic carbonate isotopes imply low p co2 430 300 ppmv at the initiation of the eocene oligocene climatic transition arid conditions in patagonia during the late eocene through oligocene provided dust to the southern ocean enhancing productivity of silicifiers drawdown of atmospheric co 2 and protracted global cooling as the antarctic circumpolar current formed and earth cooled wind speeds increased across patagonia providing more dust in a positive climate feedback high tooth crowns hypsodonty and ever growing teeth hypselodonty in notoungulates evolved slowly and progressively over 20 ma after initiation of relatively dry environments through natural selection in response to dust ingestion a ratchet evolutionary model may explain protracted evolution of hypsodonty in which small variations in climate or dust delivery in an otherwise static environment drive small morphological shifts that accumulate slowly over geologic time

black pebble occurrence and genesis in holocene carbonate sediments florida keys bahamas and tunisia abstract black carbonate lithoclasts along with blackened peloids ooids skeletal fragments and entire limestone beds are found in the shallow subtidal intertidal and supratidal zones of modern and ancient carbonate environments they are often associated with pedogenic features such as root traces or caliche the blackening is due to impregnation of the sediment by dissolved colloidal or finely particulate organic substances in an anoxic and alkaline environment or microenvironment the organic matter is derived from decayed algae and or decayed or burnt higher terrestrial plants iron sulfides contribute to the blackening especially in samples containing algal matter a complex interplay of adsorption of organic matter on carbonate crystal surfaces neomorphism and microcrystalline cementation in the vadose or freshwater phreatic zones is thought to fix the organic matter and make the black coloration relatively resistant to oxidation black pebbles form through reworking of the preferentially cemented and blackened sediment by coastal erosion they are mostly relics because the less consolidated host sediment is washed away black pebbles may thus be valuable indicators of ancient coastal and terrestrial environments

birdseyes fenestrae shrinkage pores and loferites a reevaluation abstract birdseyes birdseye limestone fenestrae fenestral fabric shrinkage pores and loferites are considered similar if not synonymous when occurring in lime mudstone or syndepositional dolomite especially in association with mudcracks and stromatolites compaction experiments indicate however that in the absence of early cementation these rugs can be completely obliterated whereas mudcracks and stromatolites remain relatively unchanged lumping of burrows and root tubes under the general terms birdseyes or fenestrae such as for example tubular fenestrae burrow fenestrae or root tube fenestrae is discouraged they should be called burrows or root tubes because the birdseyes fenestrae and shrinkage pores are so intimately associated with tidal flats in the minds of most geologists submarine cementation of pelletal and oolitic botryoidal grainstone under 5 to 6 m of water on the bahama banks has resulted in rugs provocatively similar to many birdseyes and fenestrae generally attributed to peritidal conditions in the literature birdseyes and fenestrae in ancient grainstones cannot therefore be reliably identified without consideration of the sedimentary sequence and assoc ated sedimentary structures

cementation and blackening of holocene sands by peat derived humates a case study from the great dune of pilat landes des gascogne southwestern france abstract the base sand layers of the aeolian great dune of pilat which stretches along the coast of arcachon bay have been locally impregnated with a dark brown to black amorphous organic substance of humate composition the humate cemented sand forms a well indurated horizon 40 50 cm in thickness that developed immediately beneath the holocene peaty layer p1 paleosoil the humate identified by means of ft ir and raman micro spectroscopy acted both as a cementing agent and as a coloring agent it formed thin coats and meniscus cements between individual sandstone grains which in turn caused the dark asphaltic like appearance of the sandstone field observations combined with geochemical analyses and the presence of identical geochemical compounds recognized in the peat and sandstone humate cement suggest that the peat containing low coalified rr 0 2 fragments of higher submerged and floating plants and marine algae deposited in a saline and reducing environment served as an obvious source rock for the humate the humate derived from decaying organic remains that descended from the peat into the permeable sand where it indurated irreversibly over a period shorter than 3500 years the present day actions of waves and tides contribute to the erosion of the frontal parts of the humate impregnated sandstone horizon resulting in the formation of the dark rounded sandstone slabs and pebbles that are deposited on nearby beaches this process provides a fine example of recent black pebble formation that derived from pre existing organic matter impregnated source rocks in contrast to their tropical carbonate counterparts however the humate induced blackening of the sandstone pebbles appears to be relatively unstable as the impregnated fragments bleach when exposed to air and seawater for a few seasons

time evolving seismic tomography the method and its application to the 1989 loma prieta and 2014 south napa earthquake area california we propose a time evolving approach to conduct traveltime seismic tomography in the 1989 mw 6 9 loma prieta earthquake and 2014 mw 6 0 south napa earthquake area california the recording period of the chosen seismic data between january 1 1967 and the day before the 2014 south napa earthquake is divided into two time windows separated by the 1989 loma prieta earthquake in each time window the subsurface velocity structure is iteratively updated starting from the final model of the first time window the velocity model has been successively improved throughout iterations in the second time window indicating that the traveltime data of later time windows have provided extra information to refine the subsurface images strong heterogeneities are observed in the final p wave velocity model both of the two large earthquakes occurred at transition zones in between high vp and low vp anomalies in all this study shows the effectiveness of the time evolving seismic tomography method

stable isotope record in mollusca and pedogenic carbonate from late pliocene soils of central italy abstract the late pliocene younger than 2 5 ma alluvial fan succession of toppetti quarry near todi umbria central italy includes many palaeosols pedogenic carbonate concretions and mollusc remains were separated from 73 palaeosols collected along 150 m of exposure and analysed for their oxygen and carbon stable isotope content 13c and 18o of the pedogenic carbonate and land snail shells suggest that no dramatic change in local climate took place values of the pedogenic carbonates are similar to other data reported for the mediterranean region 18o data suggest a mean annual temperature and or 18o similar to modern climatic conditions carbon isotope data from both land snails and pedogenic carbonate are consistent with a prevailing type c3 vegetation a mixture of forest and c3 grassland sustained by a mean annual precipitation between 300 and 1000 mm mainly in the cool periods of the year seems to be the most likely scenario the limited variation shown by the isotope composition of the biogenic and inorganically precipitated carbonate indicates that the environmental variations are referable mainly to change of humidity rather than temperature

late ordovician glaciation initiated by early land plant evolution and punctuated by greenhouse mass extinctions abstractlate ordovician hirnantian glaciation indicated by periglacial paleosols tillites and glacial pavements in saharan africa has been attributed to advances in weathering and carbon sequestration due to evolution of early land plants in the same way that devonian permian glaciation has been attributed to evolution of forests and quaternary glaciations to evolution of grasslands two problems for carbon cycle explanations of this glaciation are an hirnantian co2 greenhouse estimated at 4035 ppmv from mass balance models and possibly related hirnantian mass extinctions this estimate of high co2 is a 10 m yr average here evaluated against high resolution sequences of paleosols that give estimates not only of co2 but also of paleoclimate and vegetation through the late ordovician katian paleosols of the eastern united states show increases in depth and in degree of carbon consumption and storage comparable with those preceding glaciation of the devonian permian and quaternary early thalloid l

w and m type tetrad effects in ree patterns for water rock systems in the tono uranium deposit central japan abstract abundances of rare earth elements plus y ree were determined for granitic rocks tertiary sedimentary rocks and related groundwater in the tono area central japan tetrad effects concave curves in ree patterns were found for these rocks and groundwater samples conjugate m and w types of tetrad effects were simultaneously observed in these specimens which constitute the water rock system the granitic rocks show the m type tetrad effects while the groundwater and the sedimentary rocks exhibit the w type tetrad effects non chondritic y ho ratios were found especially in the groundwater y ho ratios showed larger values than the chondritic value for the samples showing w type tetrad effects and vice versa these results suggest that 1 preference of the groundwater for a w type tetrad effect and larger y ho ratio than chondrite produces an m type tetrad effects and lower y ho ratios in the granitic rocks during weathering processes 2 the w type tetrad effect and larger y ho ratio for the sedimentary rocks is brought about by the fixation of groundwater ree onto the sedimentary rocks the variation of the tetrad effect and y ho ratio was confirmed by laboratory experiments on the leaching of ree from the granitic rocks the w type tetrad effect and large y ho ratio in the u mineralization zone in the sedimentary rocks were also found by sims analysis which is consistent with the w type tetrad effect and larger y ho ratio in the whole rock abundances of the sedimentary rocks disequilibrium of the u series 234 u 238 u analyzed by sims in the u mineralization zone suggests that the u bearing minerals were formed through precipitation from groundwater as it became reducing these results suggest that the ree in the sedimentary rocks were transported by the groundwater from the granitic rocks in the tono area based on this study it is implied that the degree of the tetrad effects and the variation of y ho ratio can be valuable tools to investigate the migration of ree during water rock interactions in natural systems

genesis of blackened limestone clasts at late cenozoic subaerial exposure surfaces southern australia abstract black limestone clasts are present across the globe at modern and ancient subaerial exposure surfaces and in intertidal and supratidal environments these problematic clasts are particularly abundant at multiple subaerial exposure surfaces across southern australia the genesis of such exceptionally preserved clasts can be interpreted through universal fabrics across wide geographic regions and geologic ages regardless of location or age all south australian blackened clasts studied have a similar microstructure that is dominated by porous micritic laminae and chambered tubules such laminae are interpreted to represent calcified root cells and occur in two different varieties 1 micrite walled tubules with hollow centers that are thought to represent calcification in the rhizosphere or outer surfaces of the root and 2 tubules consistent with calcification of both the medulla and cortex which preserved medulla cortex and parenchymatic cells along with xylem vessels preserved root fabrics are present only in the blackest clasts and are consequently thought to be the main mechanism driving limestone blackening the dark coloration in southern australian clasts is derived from the impregnation of partially decayed terrestrial organic substances these organic substances were trapped in the cellular structures of roots as they calcified and were subsequently prevented from further decay and oxidation a threshold of approximately 7 weight organic carbon is needed in the insoluble residue to produce the distinct black coloration in limestone this process occurs at the base of slightly organic rich humic soil profiles where they interact with underlying carbonate bedrock b c soil horizon roots both physically and chemically through acid secretion corrode the underlying limestone and provide the calcium bicarbonate needed in the root calcification process specific semiarid flora have the ability to calcify their cellular structures which could explain why blackened clasts occur at only some unconformities this result means that the formation of blackened clasts via root calcification and entrapment of organics relies upon specific conditions of semiarid plants and climate along with organic soils such conditions would be restricted to a specific climate regime and when combined with the new proposed blackening mechanism herein could help explain their limited distribution and occurrences worldwide

assessing the carbon dioxide content of ancient atmospheres using palaeocalcretes theoretical and empirical contraints recent suggestions that the 13 c composition of calcretes can be used to determine the p co 2 of ancient atmospheres is critically evaluated the problem of differentiating pedogenic calcretes from groundwater ones which could not be used for p co 2 determinations is considered a critical problem a basic tenet of the use of calcretes for assessing p co 2 is that plants using c 4 or cras sulacean acid metabolism photosynthetic pathways were unimportant until the miocene this view is questioned and evidence is presented from carboniferous calcified root mats that non c 3 plants were probably present at this time confirming speculations by palaeobotanists that crassulacean acid metabolism or c 4 photosynthesis may have arisen numerous times during the evolution of higher plants

latest permian paleosols from wapadsberg pass south africa implications for changhsingian climate terrestrial settings preceding the endpermian crisis are reported to trend toward increasingly dry and arid conditions resulting in landscape change and a shift in fl architectures and regimes much of the latest permian changhsingian stratigraphic record in the karoo basin south africa consists of paleosols which record the physical conditions across time and space preboundary sequences at wapadsberg pass eastern cape province provide insight into the climate regime that infl uenced paleosol formation at that time a high resolution sedimentological and geochemical study of two stacked aggradational paleosols in conjunction with stable isotope geochemical characterization of paleosol carbonate cemented concretions over a 90 m section at this locality demonstrates that these landscapes were predominantly wetland terrains without a demonstrable trend in increasing drying up to the permian triassic boundary as defi ned by vertebrates in the area two paleosols examined 70 m below the permian triassic boundary are identifi ed as protosols and the former soil air interface of each is marked by an autochthonous forestfl oor litter in which canopy leaves of glossopteris and groundcover plants of trizygia are preserved molecular weathering ratios e g base loss clayeyness chemical index of alteration minus potassium cia k etc determined from these horizons are indicative of immature soil development under watersaturated conditions assuming that paleosol matrix concentrations of trace elements are indicative of permian soil solution chemistries high concentrations of ni cu ba and cr may have been growth stress factors that may account for the small glossopterid leaf size in the megafl oras in contrast to current models that implicate stress in response to climate change stable isotope 18 o and 13 c values are presented for micritic and microspar 20 m calcite cements from carbonate nodules collected at 15 horizons through a 90 m stratigraphic interval up to and including the permian triassic boundary these isotopic ratios exhibit dissimilar trends no clear trend exists in 18 o peedee belemnite pdb values range from 14 7 to 21 8 in contrast a trend exists in 13 c values where carbonate cements almost certainly precipitated under well drained conditions in an interval that is 60 m below the permiantriassic boundary 5 3 while 13 c values as low as 16 9 indicative of water logged conditions begin 90 m below and continue up to the permian triassic boundary hence no evidence is found for a preboundary trend toward increasing aridity at this locality the fi rst estimates of the latest permian atmospheric pco2 from paleosols based on coexisting calcite and organic matter 13 c values from paleosols that developed under well drained conditions provide a range of values from 900 to 1900 and 500 to 1300 ppmv respectively which are signifi cantly lower than the latest early permian when terrestrial biome replacement is documented to have occurred

selective blackening of bioclasts via mixing zone aragonite neomorphism in late triassic limestone zlatibor mountains serbia a peculiar facies of the norian rhaetian dachstein type platform carbonates which contains large amounts of blackened bioclasts and dissolutional cavities filled by cements and internal sediments occurs in the zlatibor mountains serbia microfacies investigations revealed that the blackened bioclasts are predominantly solenoporaceae with a finely crystalline originally aragonite skeleton of fine cellular structure blackening of other bioclasts also occurs subordinately solenoporacean dominated reefs developed behind the platform margin patch reef tract were the main source of sand sized detritus the blackened and other non blackened bioclasts are incorporated in automicrite cement radiaxial fibrous calcite cements in the dissolutional cavities are also black dark grey or white reworked black pebbles were reported from many occurrences of peritidal deposits in those cases the blackening took place under pedogenic meteoric diagenetic conditions in contrast in the inner platform deposits of the ilidz ya limestone the blackening of bioclasts occurred in a marine meteoric mixing zone as indicated by petrographic features and geochemical data of the skeleton replacing calcite crystals attributes of mixingzone pore waters were controlled by mixing corrosion different solubility of carbonate minerals and microbial decomposition of organic matter in the moderate energy inner platform environment large amounts of microbial organic tissue were accumulated and subsequently decomposed triggering selective blackening in the course of early shallow burial diagenesis the d 18 o and d 13 c values of the mixing zone precipitates and replacive calcite do not produce a linear mixing trend variation mainly resulted from microbial decomposition of organic matter that occurred under mixing zone conditions the paragenetic sequence implies cyclic diagenetic conditions that were determined by marine meteoric and mixing zone pore fluids the diagenetic cycles were controlled by sea level fluctuations of moderate amplitude under a semi arid to semi humid climate

relation between u series nuclide migration and microstructural properties of sedimentary rocks abstract natural radionuclide migration in miocene sedimentary rocks has been studied at the tono u deposit in japan which is a potentially useful analogue of radioactive waste isolation in geological environments uranium series disequilibrium studies have revealed that natural radionuclides have been redistributed during the past 3 5 105 a in the u mineralized zone permeability tests using core samples of the u mineralized zone have shown that the microfabrics of sedimentary rocks such as the connectivity of pores which control the groundwater movement directly influence the redistribution of nuclides detailed observations using cathodoluminescence cl and electron probe microanalysis epma were carried out after a dye impregnation test in order to improve the understanding of the importance of microfabrics in relation to nuclide migration results of the observations show that u has migrated within detrital grains such as biotite and quartz as well as between these grains uranium series disequilibrium studies of each detrital quartz and biotite grain have been shown that these detrital minerals behave differently in respect of the migration of u owing to their different textural properties the detrital biotite flakes especially along the 001 cleavage planes appear to have fixed u for a long period of time whereas the u has remained mobile within the microfractures in detrital quartz grains

milankovitch cyclicity in purbeck peritidal limestones of the prebetic berriasian southern spain peritidal carbonate rinks purbeck facies of the uppermost portlandian to berriasian in the type section of the sierra del pozo formation in the prebetic zone southern spain are divisible into 141 shallowing upward cycles averaging 2 m in thickness the subtidal facies in these cycles consist of micritic or marly limestones with dasycladacean algae and lituolids the intertidal facies are micritic limestones containing birdseyes and miliolids the supratidal facies comprise laminated algal limestones the tops of which display desiccation cracks and rhizocretions or more locally palaeosols calcretes or palaeokarst surfaces a statistical study using power spectra of the fast fourier transform demonstrates that the periodicity of these cycles is in the milankovitch frequency band

the paleozoic to mesozoic carbon cycle revisited the carbon isotopic composition of terrestrial organic matter 1 two thousand one hundred forty eight carbon isotope values for terrestrial organic matter plant fossils coal bulk terrestrial organic matter provide a proxy record for temporal changes in the global carbon cycle 13ctom 13ccarb and 13cco2 allow a full evaluation of carbon transfer in the atmosphere ocean system as well as between the marine and the terrestrial realm the temporal evolution of 13ctom parallels respective data sets from marine carbonate carbon thus reflecting the linkage between both reservoirs via atmospheric carbon dioxide on the basis of a comparison between measured and predicted isotope records for 13ctom changes in the carbon isotopic fractionation associated with plant metabolism are discernible this contradicts the notion of an invariable carbon isotopic fractionation associated with c3 plant metabolism in light of results from current plant growth experiments these changes are viewed as dependent on the atmospheric o2 co2 hence 13ctom might serve as a proxy signal for atmospheric composition

the use of autoradiography in determining the distribution of radionuclides sorbed on thin sections of plutonic rocks from the canadian shield abstract autoradiography coupled with classical petrographic techniques has been used to determine the distribution of radionuclides sorbed under oxic conditions onto rock thin sections representative of the four major types of plutons in the canadian shield to determine which minerals are most effective in removing radionuclides from aqueous solutions kodak spectroscopic and ilford k 5 nuclear emulsion plates were investigated the ilford film was found to give higher resolution and required a shorter exposure time than the kodak film sorption was found to be negligible on quartz and strongest on the mafic minerals the pyroxenes micas hornblende and opaques and on alteration minerals chlorite and sphene precipitation of am and pm was observed indicating that for actinides and rare earths experimentally obtained static sorption coefficients may reflect precipitation as well as sorption and must be used with caution in modelling studies

deciphering the history of hydrologic and climatic changes on carbonate lowstand surfaces calcrete and organic matter evaporite facies association on a palimpsest middle jurassic landscape from portugal abstract the unusual occurrence of calcretes and prominent organic matter in the middle jurassic lower bathonian serra de aire formation of the lusitanian basin of western portugal western iberian margin revealed a complex palimpsest exposure record here interpreted as reflecting hydrological changes caused by phases of emergence and immersion it serves as a potential model for understanding stratigraphic development at lowstand surfaces in carbonate successions the exposure dominated facies association grades upwards into peritidal and lagoonal limestones and the interval is assigned to the regressive peak of a transgressive regressive facies cycle 2nd order of the thick middle jurassic carbonate ramp succession the galinha quarry fatima region ne of lisbon a type section for this lowstand assemblage exhibits varied calcretes with black clasts interbedded with and grading into organic rich marly clayey seams and lenses locally with carbonate nodules carbonates with evaporite traces microbial laminites black clast and fenestral limestones some lithofacies are dolomitized the palynofacies contains phytoclasts associated with less refractory more prone to degradation components which suggests natural combustion pyrolysis wild fires the lowstand surface represents a low relief landscape with small depressions ponds bordering a more distal marginal littoral setting the partly subaerial and partly subaqueous settings were subjected to lengthy exposure and to fluctuating very shallow water bodies and water table coeval climatic regime was a seasonally dry wet one with dry semi arid phases dominating over the sub humid as shown by the combined record of intense calcrete development rhizogenic structures microbial mats brecciation desiccation evaporites and wild fire evidence however sea level rise caused changes to shallow sea water influenced restricted lagoonal peritidal settings comparisons and differences with modern and ancient coast marginal carbonates are made to provide a guide to the variability in such lowstand deposystems in the stratigraphic record

the depositional evolution of diapir and fault bounded rift basins examples from the lusitanian basin of west iberia new data on the evolution of rift basins is presented after analysing the late jurassic stratigraphy of the central lusitanian basin west iberia well outcrop and regional 2d seismic reflection profiles are used to investigate the differences in stratigraphic signature between diapir and fault bounded sub basins during the late jurassic syn rift phase surface rupturing in fault bounded sub basins resulted in the formation of tectonic scarps from which footwall derived gravity flows were sourced in contrast the diapir bounded bombarral alcobaca sub basin evolved as a distal bowl shaped depocentre with an axis located up to 10 km away from its basin margins low gradient marginal slopes developed in the bombarral alcobaca sub basin during the late jurassic rifting while growing salt pillows limited the vertical propagation of basement normal faults differences in tectonic evolution basin physiography and sediment input are the main factors responsible for the distinct sedimentary evolutions recorded in the study area 1 transverse footwall derived sediment fans predominant in fault bounded regions give place to axial southwards prograding fluvial to shallow marine units in the diapir bounded sub basins 2 growing salt pillows absent in the fault bounded sub basins formed barriers to and limited the development of transverse drainage systems