paleoclimatic and paleomagnetic constraints on the paleozoic reconstructions of south china north china and tarim abstract paleomagnetic and paleoclimatic data provide the most useful latitudinal constraints for plate reconstructions distributions through the paleozoic of five types of climatically sensitive sediments coals evaporites reefs dolomites and limestones for south china north china and tarim are shown on 15 maps that include 1578 reliable data points these paleoclimatic data agree reasonably well with available paleomagnetic directions although significant divergence between the two exists for the early paleozoic these data indicate the following 1 1 south china was in low latitudes during the entire paleozoic with a subtropical position in the cambrian 2 2 north china also remained near the equator in the early and late paleozoic except for the ordovian and the late permian when extensive evaporites suggest slightly higher latitudinal positions while its middle paleozoic position is uncertain due to the missing stratigraphie record 3 3 in south china local tectonics appears to have played a dominant role in determining paleogeography and therefore marine sedimentation especially after the late ordovician early silurian because the areal coverage of marine sediments through time is distinctly different from what would be expected from published global sea level curves 4 4 paleoclimatic and paleomagnetic data are compatible with biogeographic data which suggest that south china was part of eastern gondwana in the early paleozoic but was widely separated from gondwana in the late paleozoic and the split between the two probably happened in the devonian giving rise to a major break up unconformity in central south china

palaeolatitudinal distribution of lithologic indicators of climate in a palaeogeographic framework whether the latitudinal distribution of climate sensitive lithologies is stable through greenhouse and icehouse regimes remains unclear previous studies suggest that the palaeolatitudinal distribution of palaeoclimate indicators including coals evaporites reefs and carbonates has remained broadly similar since the permian period leading to the conclusion that atmospheric and oceanic circulation control their distribution rather than the latitudinal temperature gradient here we revisit a global scale compilation of lithologic indicators of climate including coals evaporites and glacial deposits back to the devonian period we test the sensitivity of their latitudinal distributions to the uneven distribution of continental areas through time and to global tectonic models correct the latitudinal distributions of lithologies for sampling and continental area bias and use statistical methods to fit these distributions with probability density functions and estimate their high density latitudinal ranges with 50 and 95 confidence intervals the results suggest that the palaeolatitudinal distributions of lithologies have changed through deep geological time notably a pronounced poleward shift in the distribution of coals at the beginning of the permian the distribution of evaporites indicates a clearly bimodal distribution over the past 400 ma except for early devonian early carboniferous the earliest permian and middle and late jurassic times we discuss how the patterns indicated by these lithologies change through time in response to plate motion orography evolution and greenhouse icehouse conditions this study highlights that combining tectonic reconstructions with a comprehensive lithologic database and novel data analysis approaches provide insights into the nature and causes of shifting climatic zones through deep time

taphonomy and palaeoecology in the upper barremian of the sw iberian chain spain a model to compare taxonomy and diversity of biotas from different coeval basins abstract a detailed study of the floral and faunal diversity of an upper barremian lentic ecosystem was performed by examining 50 000 microfossils the study provides an assemblage of 41 species of charophytes spermatophytes ostracods molluscs and vertebrates including eggshells the main goal of this study is to reconstruct the palaeoecology of a fluvio lacustrine and associated carbonate depositional system by integrating the sedimentology taphonomy and diversity from twelve horizons cropping out in the buenache de la sierra and the las hoyas basins the studied area corresponds to the lowermost succession of the tragacete formation serrania de cuenca iberian chain four facies associations polymictic alluvial carbonate palustrine and lacustrine eutrophic lacustrine and calcarenitic drainage facies were correlated to the composition of the fossil assemblages which have yielded a set of taphofacies confirmed by the non metric multidimensional scaling ordination test of all the horizons the taphofacies are dominated by bones and plant leaves by charophytes ostracods bivalves and eggshells and by coal leaves and bones the tragacete depositional system consists of demic and mostly autochthonous non catastrophic fossil associations a mixture of aquatic and terrestrial plants freshwater molluscs and ostracods coupled with aquatic and terrestrial vertebrate species fosters a biodiversity typical of depositional environments that are congruent with modern floodplain wetland systems these floodplain wetlands are characterised by a combination of periodically inundated ponds small lakes and floodplain areas with terrestrial habitats as such they provide suitable environments for the diversification and colonisation of charophytes ostracods gastropods fish and an ample herpetofauna the abundance and diversity of eggshells also suggest the development of nesting areas whereas the occurrence of charred cheirolepidiacean conifer would indicate intermittent wild fires linked to drought events the taxonomic breadth of this ecosystem is characterised by the taxonomic distinctness index which in turn becomes a referential model to which other lower cretaceous microfossil sites may be compared

late paleoproterozoic geon 18 and 17 reactivation of the neoarchean great lakes tectonic zone northern michigan usa evidence from kinematic analysis thermobarometry and 40ar 39ar geochronology abstract the neoarchean great lakes tectonic zone in the midcontinent of north america exerted a strong control during the proterozoic stabilization of the superior craton in northern michigan this zone underlies the paleoproterozoic marquette synclinorium a penokean compressional feature that was reactivated during post penokean orogenic collapse and gneiss dome formation early north side up motion along steep reverse faults under lower greenschist facies conditions was related to basin inversion of the marquette trough sediments during penokean orogenesis in the western portion of the marquette synclinorium these early penokean fabrics are overprinted by a high grade event recorded by synkinematic mineral growth in high grade shear zones these late shear zones accommodate s side up motion with archean basement uplifted relative to proterozoic supracrustal sequences activity related to the emplacement of the ca 1800 ma humboldt granite metamorphic amphiboles from the center of a circular pattern of metamorphic isograds the republic node record plateau ages of 1730 ma with progressively older ages across the marquette synclinorium away from the central metamorphic high model archean ages are preserved in the most distal amphibole samples north of the marquette syncline reflecting the preservation of amphibole crystallization in the biotite zone mica ages record complete resetting and a similar age progression with the youngest ages 1715 ma in the central metamorphic high and older ages 1806 ma towards the margin thermobarometry indicates peak temperatures of 620 c for the central sillimanite zone decreasing to 500 c for the garnet zone and maximum pressures of 300 400 mpa gasp and grips assemblages collectively these characteristics are interpreted to reflect two separate reactivation episodes of the gltz during penokean accretion marquette syncline formation and post penokean formation of granite cored gneiss domes collapse

the mid valanginian weissert event as recorded by calcareous nannoplankton in the vocontian basin the mid valanginian weissert event represents one of the most significant paleoceanographic events of the early cretaceous and is characterized by a major perturbation of the carbon cycle testified by a positive carbon isotope shift a crisis of both neritic and pelagic carbonate producers and climatic fluctuations here we propose a paleoreconstruction of paleoenvironmental changes that occurred in the reference vergol and la charce sections vocontian basin se france during the weissert event based on the analysis of calcareous nannofossil absolute abundance and assemblages these latter are compared to newly acquired and already published sedimentological and organic geochemical analyses our approach is novel for the time interval considered indeed principal component analysis was applied for the first time to the entire nannofossil assemblage to reconstruct environmental conditions instead of using paleoecological preferences of single species the comparison of calcareous nannofossils and biomarker analyses indicates that a phase of severe sea water stratification occurred prior to the carbon positive excursion of the weissert event in the vocontian basin this was followed by a raise in fertility of surface waters as attested by increased nannofossil abundances in particular of meso eutrophic taxa and biomarkers likely produced by dinoflagellates this increase in fertility was likely triggered by a humid climate and enhanced continental input of clays and nutrients to surface oceanic waters calcareous nannofossils also proved to react to sea level changes that occurred in the valanginian as inferred by previous works species likely inhabiting proximal areas were recorded in higher proportions during a major sea level drop in the peregrinus ammonite zone late valanginian the results of this study also permit to revise previously proposed paleoecological affinities of some nannofossil species we suggest that watznaueria barnesiae one of the most widely used species in the literature should be used cautiously because of its high plasticity with respect to environmental conditions also nannoconids that are usually regrouped in papers with paleoceanographic purposes should be analyzed separately because they show distinct species specific ecological preferences

tectonic implications of finite strain variations in baraboo interval quartzites ca 1700 ma mazatzal orogen wisconsin and minnesota usa abstract variably deformed baraboo interval quartzites 1750 1630 ma are now correlated by detrital zircon ages holm d schneider d coath c d 1998 age and deformation of early proterozoic quartzites in the southern lake superior region implications for extent of foreland deformation during final assembly of laurentia geology 26 907 910 and were analyzed using finite strain techniques which document a se nw tectonic shortening orientation from the baraboo syncline south to the flambeau syncline north fabric interpretations using bedding and the principal strain axis orientations indicate there was a mix of layer parallel and layer normal synfolding shortening in the plane of tectonic transport se nw in the thrust belt finite strain magnitudes increase from the foreland barron sioux quartzites south toward the baraboo syncline electron backscatter device ebsd fabric diagrams pole figures of quartz optic axes also demonstrate an increasingly penetrative strain to the south anisotropy of low field ac magnetic susceptibility ams as a strain proxy preserve kmin measurements in the baraboo syncline quartzites that are sub horizontal e w and intersect bedding ams measurements in underlying rhyolite on opposite limbs of the baraboo syncline are clean appear to be primary magmatic as kmax intersects bedding but require a complex folding interpretation that is inconsistent with field kinematic indicators the flat lying foreland barron and sioux quartzites preserve a mix of results quartzites with no strain finite strain and ebsd measurements or small strains that preserve vertical shortening ams measurements in the foreland preserve kmin axes that are sub horizontal and parallel to the regional shortening orientation in the adjacent thrust belt the mazatzal orogen produced a thrust belt that is orders of magnitude wider 500 km and of higher metamorphic grade than most thrust belts where both the thrust belt and foreland are quartzites

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

the fujita ziegler model a new semi quantitative technique for estimating paleoclimate from paleogeographic maps abstract the fujita ziegler model combines approaches developed by t t fujita and a m ziegler of the university of chicago to produce semi quantitative retrodictions of paleoclimates based on paleogeographic maps that include the sizes and positions of land and sea areas and the positions and extents of upland areas based on such paleogeographic maps the fujita model extrapolates past values of surface air pressure from present day relationships among air pressure land area latitude and season zonal mean air pressure for each latitude and season is hypothesized to depend on the amount of land area at that latitude and deviations from this mean over major bodies of land or water are hypothesized to depend on the area of the relevant body at that latitude fujita diagrams both illustrate these hypottheses and permit application of the model to paleogeographic maps surface air pressure maps based on these diagrams can be used to qualitatively retrodict seasonal windflow patterns and ocean currents tests of the fujita model on the recent geography suggest that most major air pressure cells are positioned accurately and that the values at the centers of cells are within 2 3 mb of measured values at low and middle latitudes and within 5 mb at the poles because the fujita model extrapolates from a partly glaciated world its retrodictions for ice free times are suspect particularly near the poles the ziegler model infers the areal and seasonal distribution of precipitation from reconstructed patterns of winds and ocean currents on paleogeographic maps retrodictions are based on 1 mechanisms that lift air including global patterns of atmospheric circulation intertropical convergence zone regional storm systems extratropical cyclones and relatively local lifting mechanisms orographic effects land sea breezes and summer convective thunderstorms 2 sources of moist air i e bodies of warm water upwind and 3 mechanisms that interfere with convection e g upwelling zones and trade wind inversions tests of the ziegler model on the recent geography accurately retrodicted seasonal precipitation at low and middle latitudes but did less well near the poles comparison with maps of the seasonality of precipitation in the recent shows that the model accurately retrodicted most ever dry and ever dry regions results emphasize the importance of accurately retrodicting the effects of orography moisture source and upwelling zones on precipitation

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

reply to n van wyck s comment on two paleoproterozoic statherian siliciclastic metasedimentary sequences in central wisconsin the end of the penokean orogeny and cratonic stabilization of the southern lake superior region precambrian res 157 2007 188 202

epeirogenic motions of africa as inferred from cretaceous shoreline deposits epeirogenic motions can be quantified if paleodatum planes can be recognized these motions have been determined for the time interval mid cretaceous cenomanian to recent in continental africa using the vertical displacement of ancient shoreline sediments and other nearshore or low elevation deposits that are inferred to represent a cenomanian sea level datum plane the cretaceous trans saharan seaway brought shoreline sediments deep into the african continental interior and additional data suggest that most of the remaining terrestrial regions were also low lying during the cenomanian the present elevations of the sea level sediments indicate that large portions of africa have undergone epeirogenic uplift since the cenomanian the character of the motions in north africa can be described as small scale high amplitude 3 km doming separated by relatively flat lying areas of deposition the largest single epeirogenic feature is the uplift associated with red sea and east african rift development the timing of post cenomanian epeirogenic motions can be further constrained using paleontologic k ar faulting paleodrainage and sedimentary data the most likely causal mechanism for african epeirogeny may be hot spot activity reflective of the mantle convection regime underlying the african lithosphere

the uranium mineralization potential of the paleoproterozoic sioux basin and its relationship to other basins in the southern lake superior region abstract the paleoproterozoic sioux basin and the baraboo barron flambeau mccaslin and waterloo quartzites in northcentral usa are all supermature quartz arenites that are among the world s oldest redbeds these quartzites were deposited on a stable craton at ca 1750 ma following exhumation and uplift of penokean crust and major orogenic activity related to the amalgamation of archean microcontinents at ca 2 0 1 8 ga to form laurentia 40ar 39ar ages of 1615 1543 ma from diagenetic muscovite in the sioux basin provide the first geochronological evidence for mazatzal related deformation and low grade metamorphism of the quartzites during subsequent convergence on the southern margin of laurentia one muscovite sample from the sioux basin has a 40ar 39ar age of 1465 ma that likely corresponds with fluid and thermal resetting due to felsic magmatism in the region and is similar to 40ar 39ar ages for muscovite from the baraboo and waterloo quartzites thus the sioux basin and other quartzites in the region have experienced a similar tectonic and fluid history the sioux basin has similar sedimentologic characteristics as other paleoproterozoic basins in north america including the uranium rich athabasca basin canada that is host to some of the world s largest and highest grade unconformity type uranium deposits we compared key characteristics such as the stratigraphy character of diagenetic fluids paleoaquifer characteristics and composition of leachable pb in the sandstones from the sioux basin with the athabasca basin in order to evaluate the fluid history of the basin and the potential of the sioux basin to host unconformity type uranium mineralization based on the hydrogen and oxygen isotopic composition of muscovite m1 that formed during diagenesis at 150 200 c the pore fluids that were present during peak diagenesis in the sioux basin had 18o and d values of 0 5 to 5 2 and 32 to 46 respectively similar to those of the fluids associated with uranium mineralization and alteration in the athabasca basin however fluid flow in the sioux basin was likely restricted to relatively thin and discontinous proximal fluvial facies that could have been diagenetic paleoaquifers in contrast to the extensive paleoaquifers in the athabasca basin that promoted large scale diagenetic reactions and alteration that led to the formation of unconformity type uranium mineralization in addition the non radiogenic isotopic composition of leachable pb in the sioux basin sandstones indicates that the majority of the pb is from a normal crustal source inconsistent with mobilization of radiogenic pb from a uranium rich source such as a uranium deposit although the sioux basin shares similar general characteristics to the athabasca basin the results of this study suggest that it has a lower potential than the athabasca basin to host significant high grade unconformity type deposits

controls on permo carboniferous precipitation over tropical pangaea a gcm sensitivity study abstract a series of late paleozoic climate model simulations was developed using the genesis atmospheric general circulation model to investigate the independent roles of gondwanan deglaciation atmospheric co 2 rise and regional tectonism on the long term 10 6 yr evolution of continental precipitation over tropical pangaea the model results indicate that either deglaciation or a co 2 increase from 1 to 8 present atmospheric levels could have caused substantial drying and warming at low latitudes a result that is consistent with late paleozoic proxy records yet the atmospheric processes that led to drying differ between these cases the deglaciation of gondwana reduces low latitude temperature gradients in the southern hemisphere decreasing by as much as 60 the meridional overturning in the southern hemisphere winter cell of the hadley circulation the decline in overturning reduces convective precipitation over equatorial pangaea in contrast high levels of co 2 have little effect on the large scale meridional overturning circulation but increase continental temperatures leading to high evaporation rates and reduced available soil moisture the source of convective precipitation on land in comparison to deglaciation and p co 2 regional uplift erosion of the central pangaean mountains cpms has a secondary effect on tropical precipitation in genesis and cannot explain the long term aridification and warming of western pangaea we suggest that the deglaciation of gondwana and a concomitant rise in atmospheric p co 2 could explain much of the late paleozoic climate change over low latitude pangaea

palaeo digital elevation models for use as boundary conditions in coupled ocean atmosphere gcm experiments a maastrichtian late cretaceous example abstract palaeogeography specifically palaeotopography and palaeobathymetry provides an essential boundary condition for computer based atmosphere and ocean modelling it also provides the geographic context for understanding surface processes palaeodrainage palaeoweathering and biotic interactions palaeoecology palaeobiogeography with increased model resolution coupled ocean atmosphere general circulation models gcms and the addition of vegetation soil weathering ice and chemical modules there is now a need for more robust detailed palaeotopographies and palaeobathymetries that are fully integrated with the processes being modelled especially the hydrological system here we present a new geographic information system gis based hydrologically correct palaeo digital elevation model dem for the maastrichtian late cretaceous we describe the methods and concepts used to construct the map and draw attention to the limits imposed by scale and uncertainty and how these factors must be considered as part of the error analysis of derived model results the underlying palaeogeography is one of a series of 27 global maps that represent the stages of the cretaceous and sub epochs of the cenozoic each map is generated at a scale of 1 30 million in arcview gis and arcinfo using data from the lead author s own databases of lithologic tectonic and fossil information the lithologic databases of the paleogeographic atlas project the university of chicago a survey of published literature and dsdp odp data interpretations of elevation are derived following the methods outlined in ziegler et al ziegler a m rowley d b lottes a l sahagian d l hulver m l gierlowski t c 1985 paleogeographic interpretation with an example from the mid cretaceous annual review of earth and planetary sciences 13 385 425 an understanding of the tectonic regime and evolution of each feature and the age depth relationship for the ocean the global palaeo dem was derived using the elevation contours from the paleogeography and the suite of hydrological tools available in arcinfo grid the palaeo dem has been constrained by defining areas of internal palaeodrainage palaeoriver mouths and known palaeoriver courses the maastrichtian has been completed first to provide the boundary conditions for a series of coupled atmosphere ocean experiments when integrated with the results of the coupled ocean atmosphere model the result is a powerful tool for understanding surface processes and an important step towards the development of a continuous series representing a fully evolving palaeolandscape

revisiting the paleogene climate pattern of east asia a synthetic review abstract east asian paleogene climates have long been regarded as controlled by the planetary wind system which might result in a climate pattern with three latitudinally distributed zones two humid zones located separately in the north and south were lithologically designated by coals and oil shales while an arid zone in the middle was represented by red beds and evaporites because the middle arid zone was located along 30 n paleolatitude its presence had been further linked with a then subtropical high however this long standing model has recently been challenged by growing evidence from petrology sedimentology paleontology paleobiogeography paleoclimatology and climate modeling here we review the primary data from these disciplines and reinterpret their climate significances to revisit the east asian climate pattern during the paleogene petrologically while the occurrence of coals and or oil shales is accepted as an indicator for overall humid climates that of red beds and or evaporites is highly equivocal to exclusively indicate perennial arid climates unless their origins are carefully investigated in reality generic red beds merely represent an oxidizing environment not essentially associated with a single specific climate type meanwhile evaporites although typically precipitated in arid environments may be deposited in either perennial dry or seasonal monsoonal climates there is no solid evidence so far to convincingly support that the landscape of the so called middle arid zone was dominated by desert and or steppe under a then subtropical high during most of the paleogene the plant function type study additionally suggests that the middle arid zone appears to be lack of xerophytic vegetation even though some xerophytic or sclerophyllous plant taxa did sporadically occur interestingly paleozoological data show that the paleogene mammalian faunas were somewhat equably distributed over east asia strongly suggesting the evident absence of a critical biogeographical or climatic barrier stretched across the middle arid zone as the planetary wind model implied in contrast to the planetary wind model monsoonal or monsoon like paleogene climates have been broadly reported from the northern middle and southern east asia as well as adjacent regions of russia and kazakhstan if only the indicators for humid climates are considered simply due to the uncertainty of those for perennial arid climates east asia must have had a relatively dry region in the continental interior during the late eocene to oligocene transition likely caused by the continentality and or the rain shadow effect along with the global cooling the monsoonal interpretation is highly in agreement with the evidence from floras faunas basin analyses and modeling experiments and well explicates the paleogene climate distribution and seasonal dynamics of east asia however further studies will be largely needed to verify whether uniformly according to the modern criteria the paleogene climates of the east asia interior can be accurately attributed to the arid category

tropical mountains and coal formation a climate model study of the westphalian 306 ma a global climate model has been used to study the seasonal sensitivity of tropical rainfall and soil moisture to the presence of himalayan scale mountains at tropical latitudes during the westphalian these mountains act to retard the northward progression of the intertropical convergence zone in their vicinity during the northern hemisphere summer such that there is converging low level flow from both the eastern and western panthalassa ocean and an eight fold enhancement of precipitation over the mountains the computed annual cycle of soil moisture for these tropical regions concurs with geologic evidence of extensive coal deposits formed in a broad area at tropical latitudes and only small seasonality in either temperature or precipitation in these areas

the formation of inertinite rich peats in the mid cretaceous gates formation implications for the interpretation of mid albian history of paleowildfire abstract image analysis and standard point count petrographic data are used to interpret the amount source and variation of inertinite in coal seams of the mid cretaceous gates formation rocky mountain foothills northeastern british columbia inertinite on average is abundant between 40 60 by seam by volume and higher in some zones and within seams fluctuates cyclically the inertinite is interpreted to be almost exclusively fire derived suggesting that fire was a relatively common occurrence in the original peat forming wetlands inertinite enrichment in the gates coals appears to have resulted from preferential destruction of vitrinite precursors by either low temperature decomposition processes or burning rather than by formation of inertinite by a microbial process the position of the gates formation depositional setting east of the rising canadian cordillera is interpreted to have resulted in overall drier conditions in the region and periodic drought in the wetland settings cyclic variation in inertinite vitrinite composition within some of the seams is primarily attributed to climatic variations although variation in subsidence rates could also have been responsible

strain variations across the proterozoic penokean orogen usa and canada abstract strata in the huron 2 5 2 0 ga and animikie 2 2 1 85 ga basins were deposited on the southern margin of the archean superior province these rocks were deformed during the penokean orogeny 1850 ma followed by subsequent accretionary orogens to the south at 1750 ma yavapai and 1630 ma mazatzal strain patterns are unique to each orogenic belt with no far field effect archean wawa terrane rocks in the penokean foreland preserve deformation associated with archean accretion with no younger penokean yavapai or mazatzal strain overprint the penokean orogeny deformed huron animikie basin sediments into a north vergent fold and thrust belt with no yavapai or mazatzal strain overprint yavapai orogen strains sw ne margin parallel shortening are unique when compared to the younger mazatzal shortening n20 w shortening with no strain overprint penokean deformation is characterized by shortening from the south including uplifted archean gneisses and a northerly thin skinned fold and thrust belt with north vergent nappes and a gently dipping foreland our study of finite and calcite twinning strains n 60 along 1500 km and across 200 km the penokean belt indicate that this orogeny was collisional as layer parallel shortening axes are parallel across the belt or parallel to the tectonic transport direction n s penokean nappe burial near the margin resulted in vertical shortening strain overprints some of which are layer normal the sudbury impact layer 1850 ma is found across the animikie basin and provides a widespread deformation marker with many local unique strain observations we also report new geochronology u pb zircon and apatite for the gneiss mafic dike rocks at wissota chippewa falls wi and arbutus black river falls wi dams respectively which bears on penokean yavapai deformation in the archean marshfield terrane which was accreted during the penokean orogen pseudotachylite formation was common in the superior province archean basement rocks especially along terrane boundaries reactivated by contemporaneous penokean trans hudson cape smith and new quebec deformation in the hinterland south the younger yavapai orogen 1750 ma n 8 deformation is preserved as margin parallel horizontal shortening sw ne in yavapai crust and up to 200 km to the north in the penokean thrust belt as a strain and barrovian metamorphic overprint mazatzal deformation 1630 ma n 16 is preserved in quartzites on yavapai and penokean crust with layer parallel and layer normal shortening strains oriented n20 w

an interpretation of cretaceous and tertiary biota in polar regions abstract rich fossil floras and vertebrate faunas lived within the arctic and atarctic circles during the cretaceous and paleogene these occurrences seem explicable by the nature of the thermal environments in polar regions and by the physiological responses of plants and animals allied to those that lived there there seems no need to invoke a lower tilt to the earth s axis to provide greater warmth and light in polar regions to account for these fossil records

climate of the supercontinent pangea numerous climate models predict that the geography of the supercontinent pangea was conducive to the establishment of a megamonsoonal circulation in general geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the triassic pangea in the late carboniferous had widespread peat formation in what is now central and eastern north america and europe and relatively dry conditions on the colorado plateau the equatorial region of the continent became drier through the end of the carboniferous by the permian the equatorial region of pangea was dry and indicators of aridity and rainfall seasonality became more widespread wind directions from colorado plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time in the triassic climate in the colorado plateau region became relatively wet though still seasonal and the few eolian sandstones indicate a major shift in wind direction at that time in addition sedimentation

in suspect terrane provenance of the late archean phantom lake metamorphic suite sierra madre wyoming the 2 68 ga phantom lake metamorphic suite of the sierra madre is a volcanogenic volcaniclastic and siliciclastic sequence that may have been deposited on or near the margin of the wyoming province or alternatively it may represent part of an exotic block accreted onto the southern margin of the wyoming province the metamorphosed supracrustal rocks of the phantom lake metamorphic suite along with quartzofeldspathic gneisses and granitoids of similar age have light rare earth element lree enriched ree patterns with little to no eu anomaly these patterns are comparable to those of modern oceanic arc rocks and sediments both supracrustal and metaigneous rocks have radiogenic initial end from 4 5 to 2 5 and nd crustal residence ages between 2 7 and 3 0 ga it is proposed that these juvenile rocks were part of an intra oceanic arc system formed beyond the influence of detritus from the wyoming province and subsequently were accreted onto the southern wyoming province following intrusion of grani

plant taphonomy and palaeoecology in the lacustrine una delta late barremian iberian ranges spain abstract plant cuticle compressions and sporomorphs were studied in coaly clays belonging to the upper barremian la huerguina formation in una south western iberian ranges cuenca spain cuticle assemblages are extremely monotonous and formed by the genera frenelopsis schenk emend watson classostrobus alvin et al and glenrosa watson and fisher sporomorphs are dominated by classopollis pflug emend srivastava the genus glenrosa is described for the first time in europe sedimentological and taphonomical analyses show that these assemblages originated by fragmentation and size selection during residence in the leaf litter and by fluvial transport final deposition occurred in crevasse splay deltaic front and pro deltaic environments our results indicate that the una delta was fed almost exclusively by remains of cheirolepidiaceous conifers living in the upper deltaic plain of a lacustrine delta a comparison with the flora found in the open lacustrine facies of las hoyas which is laterally equivalent of the beds studied shows that land plant assemblages of las hoyas are more diverse the parautochthonous matoniaceous tree fern weichselia reticulata dominated the lakeshore vegetation of las hoyas in contrast to the vegetation of the upper delta plain of una which was dominated by frenelopsis the habitats of frenelopsis and glenrosa from the upper barremian oligohaline basin of una las hoyas contrast with the habitats commonly hypothesized for both taxa in coastal marine environments or on saline edaphic profiles in conclusion frenelopsis appears to have a wider tolerance to salinities than previously thought and their adaptations to saline edaphic conditions should be considered species specific rather than genus specific

the influence of vegetation cover on soil organic matter preservation in antarctica during the mesozoic a possible biological component of the explanation for the lack of substantial coal formation on antarctica between the late jurassic and late cretaceous is hypothesised forcing a process based terrestrial biogeochemistry model with climate model simulations for three successive intervals of the mesozoic late jurassic 150 ma mid cretaceous 100 ma and late cretaceous 65 ma predicts the establishment of productive terrestrial ecosystems with substantial soil carbon pools throughout the land surface of antarctica between 150 and 65 million years ago sensitivity analyses indicate the annual land surface hydrological budget of antarctica 150 65 ma was largely balanced due to the effects of canopy transpiration on soil moisture post depositional erosion and tectonic setting must have played an important role in determining coal preservation on the continent however the model results indicate that an active vegetated land surface precluded the preservation of the substantial soil organic carbon inputs by minimising the potential for anaerobic preservation i e water logging

controls on the accumulation of coal and on the development of anastomosed fluvial systems in the cretaceous dakota formation of southern utah alluvial strata of the cretaceous dakota formation of southern utah are part of a transgressive systems tract associated with a foreland basin developed adjacent to the sevier orogenic belt these strata contain valley fill deposits anastomosed channel systems and widespread coals the coals constitute a relatively minor part of the dakota formation in terms of sediment volume but may represent a substantial amount of the time represented by the formation the coals are separated by clastic units up to 20 m thick the stratigraphically lowest clastic unit of the dakota formation lies above an unconformity cut into jurassic rocks incised valleys associated with the unconformity are up to 12 m deep two discrete episodes of valley fill sedimentation are recognized including a lower sandstone unit with conglomerate layers and an upper discontinuous coal bearing unit after the valleys filled the area became one of low relief where extensive mires formed peat accumulation was interrupted at least three times by deposition of clastic sediment derived from the west the clastic units consist of sandstone mudstone or heterolithic ribbon bodies stacked tabular sandstones and laminated mudstones and contain minor coal beds less than 0 35 m thick ribbon bodies are 1 9 m thick and 15 160 m wide have pronounced basal scours and are filled with both lateral and vertical accretion deposits an anastomosed channel complex is suggested by the large number of coeval channels of varying dimensions the variation in the structure and grain size of channel fills and the presence of abundant tabular sandstones interpreted as crevasse splays although some sandstone bodies have well developed lateral accretion surfaces the overall ribbon geometry indicates that mature meandering streams were not well developed this is in contrast to modern anastomosed systems which are commonly thought to be a transitional morphology caused by avulsion of a meander belt to a new position on its floodplain rather than being a transitional channel pattern related to river avulsion the anastomosed channels of the dakota formation may have formed part of a large inland delta that episodically invaded widespread mires the mires developed during periods when clastic influx was reduced either by high rates of subsidence close to the thrust belt or by deflection of rivers by emergent thrusts

iron formations a global record of neoarchaean to palaeoproterozoic environmental history abstract iron formations if represent an iron rich rock type that typifies many archaean and proterozoic supracrustal successions and are chemical archives of precambrian seawater chemistry and post depositional iron cycling given that if accumulated on the seafloor for over two billion years of earth s early history changes in their chemical mineralogical and isotopic compositions offer a unique glimpse into environmental changes that took place on the evolving earth perhaps one of the most significant events was the transition from an anoxic planet to one where oxygen was persistently present within the marine water column and atmosphere linked to this progressive global oxygenation was the evolution of aerobic microbial metabolisms that fundamentally influenced continental weathering processes the supply of nutrients to the oceans and ultimately diversification of the biosphere and complex life forms many of the key recent innovations in understanding if genesis are linked to geobiology since biologically assisted fe ii oxidation either directly through photoferrotrophy or indirectly through oxygenic photosynthesis provides a process for if deposition from mineral precursors the abundance and isotope composition of fe ii bearing minerals in if additionally suggests microbial fe iii reduction a metabolism that is deeply rooted in the archaea and bacteria linkages among geobiology hydrothermal systems and deposition of if have been traditionally overlooked but now form a coherent model for this unique rock type this paper reviews the defining features of if and their distribution through the neoarchaean and palaeoproterozoic this paper is an update of previous reviews by bekker et al 2010 2014 that will improve the quantitative framework we use to interpret if deposition in this work we also discuss how recent discoveries have provided new insights into the processes underpinning the global rise in atmospheric oxygen and the geochemical evolution of the oceans

facies and genesis of carboniferous coal seams of northwest germany abstract in order to get detailed information about the facies and genesis of upper carboniferous coal seams of northwest germany maceral analyses of complete seam profiles westphalian b d mainly westphalian c were carried out four main facies and twelve subfacies could be distinguished the main facies are 1 1 the sapropelic coal facies consisting of fine grained inertinite and liptinite which forms from organic sediments deposited at the bottom of moor lakes 2 2 the densosporinite facies which is high in inertinite and liptinite and low in vitrinite syngenetic pyrites clastic layers thick vitrains and fusains do not occur this facies originates from peats of open mires with higher groundwater table and herbaceous vegetation the open mire was situated in the centre of extensive swamps consequently clastic sedimentation did not affect this swamp type and nutrient supply and ph values were low 3 3 the vitrinite fusinite facies which is high in vitrinite this is the result of abundant vitrains under the microscope fusains were mostly identified as fusinite the vitrinite fusinite facies originates from a forest mire more or less abundant seam splits and clastic layers show that rivers flowed in the neighbourhood of this area 4 4 the shaly coal facies which represents the most marginal part of the former swamp frequently affected by clastic sedimentation within the carboniferous of the ruhr region it seems unlikely that the thin coal seams of the namurian c and westphalian a1 contain a densosporinite facies the swamps were situated in the lower delta plain where they were often affected by marine influences consequently coals are high in minerals and sulfur and they are thin and discontinous the best conditions for the formation of extensive swamps with open mires densosporinite facies in their central parts prevailed during westphalian a2 and b1 times low contents of sulfur and minerals and high content of inertinite are typical for these coals sedimentation mainly took place in the transitional zone from the lower to the upper delta plain during the westphalian b2 and c fluvial sedimentation dominated within the coal seams minerals sulfur and pseudovitrinite increase while inertinite decreases this is the consequence of coal of the densosporinite facies occurring with increased rarity the coal seams of the westphalian c2 contain no densosporinite facies because peat formation was restricted by increasing fluvial sedimentation and by a better drainage as a consequence extensive swamps with open mires in the centre were no longer formed after the formation of the odin seams above the odin seams coal of the vitrinite fusinite facies contains thick walled torisporinites variations and lowering of the groundwater table caused mild oxidative influences during peat formation this is documented by an increase in pseudovitrinite the occurrence of torisporinites and the absence of spheroidal sideritic concretions sulfur content increases in the absence of the low ash and low sulfur coal of the densosporinite facies in upper carboniferous coal seams of the ibbenburen region the inertinite and telocollinite contents are higher than in those of the ruhr region therefore variations of the groundwater table have been more pronounced and resulting oxidative influences must have been more severe seldom occurring marine and brackish horizons and a higher fusinite fusain content indicate a slight elevation of this area from early westphalian d times onward peat formation was no longer possible because of the better drainage this resulted in severe oxidative conditions which excluded peat formation

cretaceous climate a comparison of atmospheric simulations with the geologic record abstract atmospheric simulations using realistic cretaceous geography 100 million years ago suggest that paleography is an important factor governing the nature of the circulation the simulated cretaceous atmospheric circulations are markedly different both from the present day atmospheric circulation and from the classical hypotheses of a weaker circulation and poleward displacement of circulation features e g the subtropical high therefore they pose specific questions which can be tested against the geologic record aspects of the cretaceous simulations are verified in comparisons with the geologic record the simulations serve to guide areas of future paleoclimatic research and to formulate better the nature of the problem of warm equable climates

persistence of late carboniferous tropical vegetation during glacially driven climatic and sea level fluctuations abstract the late carboniferous glaciation reached its peak during the latter part of the westphalian late desmoinesian in the tropical illinois basin this was the time of deposition of the carbondale and lower modesto formations characterized by the cyclic repetition of major coal deposits black shales limestones gray shales and sandstones these lithological changes evidence repeated major fluctuations in climate and sealevel fossil floras from the tropical ever wet to seasonally wet terrestrial lithofacies coals and shales above coals remain compositionally similar throughout the 1 1 5 m y time interval floras from coals known from coal balls and palynology characteristically were composed of three major plant communities the wettest sites were dominated by monocarpic lycopsids intermediate sites were dominated by polycarpic lycopsids and areas subject to fires and intermittent flooding were dominated by medullosans and the small lycopsid paralycopodites clastic substrate environments were dominated by ferns and pteridosperms and conform to a single biozone indicating their compositional unity and distinctness from earlier and later assemblages the composition of lowland floras is poorly known from times between the deposition of coals and associated terrestrial rocks intervals during which most of the lowlands were flooded and marine rocks were being deposited consequently the temporally intermittent recurrence of lowland floras despite repeated widespread environmental disruption may be explained either by vegetational persistence and migration of floras or repeated disruption and reassembly several lines of evidence suggest persistence as a likely explanation

rainfall patterns and the distribution of coals and evaporites in the mesozoic and cenozoic abstract paleoclimatologists have adequately demonstrated over the last twenty years that the distribution of climatically sensitive sediments can be related to present day climatic zones that are roughly parallel to latitude for example coals were deposited at paleolatitudes that correspond to the present day rainy zones at the equator and at about 55 n and 55 s indicating that those zones were present in the past from this it can be concluded that atmospheric circulation has not been radically different from its present configuration despite some apparently great differences in some climatic parameters such as the equator to pole temperature gradient nevertheless the zonal model for predicting the distribution of climatically sensitive sediments is not wholly adequate although general atmospheric circulation may not have been radically altered from its present pattern it would have differed in some respects because the paleogeography was different from the present geography therefore we have constructed what we believe are more realistic maps of the distribution of rainfall through time these maps are based on maps of atmospheric circulation that have been successfully used to predict the distribution of some petroleum source beds and phosphorites we have compared the predicted distribution of rainfall to the distribution of coals and evaporites for each of seven geologic stages the circulation rainfall maps were more successful than the zonal model for predicting the distribution of evaporites and coals for times when the paleogeography would have maximized the development of a monsoonal circulation which most effectively disrupts the general zonal pattern for times when a monsoonal circulation would not have been important the zonal model adequately predicted the distribution of these rocks

glacier fed sandstone sheets in the weller coal measures permian allan hills antarctica abstract the upper member of the weller coal measures permian at allan hills victoria land antarctica consists of repetitive coal layers separated by sheetlike bodies of predominantly sandstone and subordinate siltstone and conglomerate all of fluvial origin investigation of the lowermost inter coal sheet wc1 reveals abrupt planar basal contacts persistent upward fining and a strong westward palaeocurrent trend three lithofacies are recognized in the wc1 sheet a small scale cross bedded pebbly sandstone which occupies most of the basal portions of the sheet b large scale cross bedded medium coarse sandstone confined to a linear ne sw belt overlying or locally replacing facies a and c siltstone and rippled fine grained sandstone which drapes and overlaps facies a and b and contains glossopteris leaves and vertebraria root traces facies distribution patterns indicate the wc1 body initiated as an abrupt sheetlike incursion of coarse sediment over a low lying mire facies a followed by entrenchment and confinement of flow as the sheet extended distally facies b facies c represents low energy floodplain sedimentation co existing with and later succeeding facies b as deposition evolved toward abandonment and eventual renewal of peat deposition relatively rapid deposition of the sandstone sheet is implied by the lack of any significant hiatus markers outsized clasts up to 45 cm in diameter one observed to display prominent striations occur sporadically throughout the wc1 including within siltstone beds of facies c these are inferred to be ice rafted deposits which together with other evidence suggest meltwater influence possibly glacial on sediment transport and deposition preliminary examination of other sandstone sheets in the upper weller indicates attributes similar to the wc1 including abrupt bases upward fining character and predominantly westward palaeocurrent patterns the allan hills exposures are believed to represent a succession of low lying mire complexes interrupted by abrupt but infrequent incursions of coarse sediment possibly by extreme meltwater floods

revisiting the paleoproterozoic baraboo interval in southern wisconsin evidence for syn depositional tectonism along the south central margin of laurentia abstract the statherian baraboo quartzite 1710 1650 ma is present in the baraboo ranges wisconsin usa it is one of several isolated quartzites outcropping across the southern lake superior region collectively these quartzites are known as baraboo interval quartzites and they record a history of basin development followed by regional deformation along the south central laurentian margin baraboo interval stratigraphy above the baraboo quartzite in the baraboo ranges is unresolved limiting understanding of the style and history of basin formation sedimentation and deformation as well as correlation between regional quartzites new precambrian geologic mapping within the core of the baraboo syncline baraboo ranges wi confirms early interpretations of local stratigraphy the baraboo interval section includes two upward fining sequences separated by an angular unconformity the lower sequence comprises the baraboo quartzite seeley slate and freedom formation the upper sequence comprises the dake quartzite and rowley creek slate the depositional age of the upper sequence is poorly constrained but could be nearly 200 million years younger than the underlying units u pb detrital zircon ages for the lower conglomeratic baraboo quartzite and the dake quartzite are dominated by nearby basement ages between 1800 and 1750 ma and 1900 1835 ma suggesting a restricted drainage system tapping proximal basement sources subsidence modeling of the lower sequence demonstrates at least 1 28 km of subsidence is required to generate the accommodation necessary to deposit the baraboo quartzite seeley slate and freedom formation these results support a model where deposition of the lower sequence between ca 1710 1650 ma occurred along a tectonically active plate margin the lack of coeval magmatism in the baraboo interval suggests deposition did not occur in a convergent arc setting however coeval orthoquartzite deposition in colorado arizona and new mexico along the southwestern margin of laurentia 1700 1650 ma occurred synchronous with arc volcanism requiring a component of plate margin convergence to the southwest to reconcile these differences a model where the entire southern margin of laurentia between 1710 and 1650 ma was dominated by strike slip motion is favored varying from highly oblique convergence in the southwest to dominantly strike slip motion in the southern lake superior region

phytogeography and paleoclimatic interpretation of the maestrichtian abstract insight into the true nature of cretaceous climate can best be grained through a worldwide study of the preserved climatic indicators this study focuses on reconstructing the climate of the maestrichtian latest cretaceous based on the abundant published information from the geologic record specifically the approach taken was to reconstruct the general patterns of the terrestrial ecological biomes based on the fossil megaflora and pollen record once the biomes were delineated the climatic constraints on the present counterparts of these biomes were used to determine the prevailing climate of each region biome boundaries were recognized by discontinuities in the phytogeographic distributions of a variety of fossil plant groups detailed comparisons of fossil plant assemblages with present day climatic preferences of nearest living relatives allowed each region to be assigned to a modern biome further comparisons with fossil leaf physiognomic studies and tree ring studies integrated with an extensive database of climatically important sediments helped to refine the biomal and climatic assignments altogether 12 climatic zones corresponding to 7 major biome types have been recognized for the late cretaceous period

paleoenvironmental conditions of puertollano coals spain petrological and geochemical study abstract in the present work petrographic geochemical and mineralogical data have been combined with results from prior paleobotanical studies in order to determine the sedimentary and postsedimentary diagenetic factors responsible for the physicochemical properties of coal seams and associated sediments from the puertollano stephanian coal basin although the coal seams 4 originated under similar lacustrine conditions the highest coal seams 1 and 1 bis show higher production preservation of structured tissues telinite and collotelinite than the lowest coal seams 2 and 3 where destruction of the cell tissues collodetrinite is predominant differences in degree of preservation as a result of changes in the environmental sedimentary conditions in the water table ph redox may explain the different maceral distribution this feature may also be due to the increase in degree of humification from the highest seams 1 and 1 bis to the lowest seams 2 and 3 however the gentle thermal maturation undergone by these stephanian coals only produced a slight modification in the physicochemical properties of the organic matter in general alkaline synsedimentary conditions could be deduced from the dominance of organic sulphur with respect to pyritic sulphur reducing conditions for seam 1 1 bis and 2 and more oxidant conditions for seam 3 can be deduced from maceral sulphur and carbonate distribution other diagenetic processes involved organic and inorganic sediments for example a kaolinitisation process with a different intensity for the early diagenetic stages suggests the occurrence of leaching processes which affected both organic and inorganic sediments

rise and demise of the bahama grand banks gigaplatform northern margin of the jurassic proto atlantic seaway abstract an extinct 5000 km long jurassic carbonate platform and barrier reef system lies buried beneath the atlantic continental shelf and slope of the united states a revised stratigraphic framework a series of regional isopach maps and paleogeographic reconstructions are used to illustrate the 42 m y history of this bahama grand banks gigaplatform from its inception in aalenian early middle jurassic time to its demise and burial in berriasian valanginian time early early cretaceous aggradation progradation rates for the gigaplatform are comparable to those of the familiar capitan shelf margin permian and are closely correlated with volumetric rates of siliciclastic sediment accumulation and depocenter migration siliciclastic encroachment behind the carbonate tracts appears to have been an important impetus for shelf edge progradation during the early cretaceous sea level changes combined with eutrophication due to landward soil development and seaward upwelling and the presence of cooler upwelled waters along the outer shelf appear to have decimated the carbonate producers from the carolina trough to the grand banks this allowed advancing siliciclastic deltas to overrun the shelf edge despite a notable reduction in siliciclastic accumulation rates however upwelling did not extend southward to the blake bahama megabank so platform carbonate production proceeded there well into the cretaceous subsequent stepwise carbonate abatement characterized the blake plateau basin whereas the bahamas have maintained production to the present the demise of carbonate production on the northern segments of the gigaplatform helped to escalate deep water carbonate deposition in the early cretaceous but the sudden augmentation of deep water carbonate reservoirs in the late jurassic was triggered by other agents such as global expansion of nannoplankton communities

cretaceous tertiary palynofloral perturbations and extinctions within the aquilapollenites phytogeographic province a combination of detailed intermediate and large scale stratigraphic perspectives is necessary to understand the driving mechanisms for floral change across the cretaceous tertiary k t boundary because short term physical and biotic events occur within longer term trends most maastrichtian palynofloral extinctions have been identified within the northern circumpolar supra continental aquilapollenites province in mid continental north america the presence of a physically defined k t boundary provides opportunities to examine contemporaneous terrestrial palynofloras over a latitudinal also approximately paleolatitudinal distance of 3200 km seventy five percent of last appearances occur before the k t boundary at high latitudes and must have been caused by ongoing terrestrial processes palynofloral events directly associated with the k t boundary include both local last appearances and inferred extinctions and synchronous and diachronous changes in relative abundances two different styles of factors are reflected in these events the first possibly attributable to chemical or other profound atmospheric perturbations associated with the worldwide distribution of the fireball layer of the k t claystone resulted in extinctions of angiosperm with a zoophilous pollination strategy the second factor possibly reflecting energy released during the deposition of ballistically transported impact debris or hackly ejecta layer of the boundary claystone resulted in the selective northward attenuating removal of the canopy vegetation best documented for southwestern canada which was succeeded by a fern dominated vegetation in mid continental north america these consequences of the boundary event were mediated by independent preexisting circumstances climate regional and through time local depositional environment and ongoing background extinctions and origins

cretaceous palaeopositions of the falkland plateau relative to southern africa using mesozoic seafloor spreading anomalies summary mesozoic seafloor spreading anomalies mo m10 have been identified in the natal valley between the south eastern african margin and the mozambique ridge these identifications confirm that seafloor spreading north and south of the falkland agulhas fracture zone fafz began simultaneously the natal valley anomalies are offset 1300km by the fafz from their equivalents in the southern cape basin their positions confirm that the tugela ridge marks the continent ocean boundary cob in the natal valley we have computed successive falkland plateau palaeopositions using natal valley and georgia basin anomalies these show that the offset in spreading ridges at the fafz remained 1300km long from m10 to mo time by anomaly 34 time the offset was 1270 km therefore no major ridge jumps had occurred by then dating mo as 108 myr bp and anomaly 34 as 80 myr bp the average halfspreading rate immediately south of the fafz for the cretaceous normal polarity epoch is 4 2 cm yr using this we date a the change in early pole of rotation at 105 myr b a reconstruction which juxtaposes salt boundaries in the brazil and angolan basins at 103 7 myr c final separation of the falkland plateau from southern africa at 98 3 myr d the formation of the oceanic northern part of the agulhas plateau at 97 3 90 7 myr comparison of magnetic data with implied cob positions in the southernmost cape and argentine basins and the georgia basin suggests continental separation began 122 1 27 myr bp with undeformed magnetic anomalies dating from 122 myr m10 these dates are consistent with micropalaeontological and sedimentological data around southern africa

two paleoproterozoic statherian siliciclastic metasedimentary sequences in central wisconsin the end of the penokean orogeny and cratonic stabilization of the southern lake superior region abstract statherian siliciclastic sedimentary rocks in the southern lake superior region are key to understanding the evolution and stabilization of paleoproterozoic crust in the midcontinent deposited during an important period of significant crustal growth controversy exists regarding the conditions of sandstone deposition and the relations between magmatism and sedimentation in central wisconsin the hamilton mounds inlier although restricted in areal extent is significant in that it reveals the existence of two separate statherian units an 1800 1760 ma immature meta arkose and a post 1760 ma baraboo interval supermature quartzite the meta arkose is crosscut by 1762 ma granite and contains abundant penokean age detrital monazite grains the younger quartzite contains detrital monazite as young as 1750 ma and was deposited unconformably upon these older units all units experienced 1630 ma low grade recrystallization and isotopic disturbance associated with the mazatzal orogeny in addition the supermature quartzite experienced k metasomatism and brecciation at 1470 ma ascribed to regional scale hydrothermal alteration related to the influence of the nearby 1470 ma wolf river batholith collectively these data suggest an early statherian episode of arkosic deposition and magmatism during yavapai orogenesis followed by a longer interval of deposition of supermature quartz arenite associated with crustal stabilization the existence of two separate statherian units reconciles apparent conflicts in depositional models and provides a greater understanding of the paleoproterozoic evolution of the midcontinent

authigenic chromium enrichments in proterozoic ironstones abstract chromium isotopes have recently emerged as a proxy for atmospheric oxygen levels in the precambrian chromium cr enrichments along with a suite of other redox sensitive metals have also been used as marine redox proxies for decades despite significant interest and growing use of this system which has been used to argue for low oxygen levels through the mid proterozoic leading up to the rise of animals there is a poor understanding of the host phases of cr in the sedimentary record without this context interpretation of measured isotopic signatures and concentrations of cr in various sedimentary archives can be ambiguous in order to shed light on this problem we have used electron microprobe elemental mapping to identify authigenic and detrital cr phases we have examined a range of ironstone samples that have been previously analyzed for cr isotopes and find that cr is predominantly associated with iron rich allochems instead of detrital cr mineral phases we did not find evidence for detrital chromite or other cr rich detrital minerals additionally we find evidence for authigenic ti enrichments and decoupling of al and ti elements traditionally used as detrital tracers similar to what has been reported in other slowly accumulating metal rich sediments e g iron manganese nodules lastly we have explored a range of possible sedimentary cr isotope signals that could result from changes in the percentage of detrital versus authigenic cr incorporated into a sample providing clear evidence for the ambiguity in interpretations of this isotope system without petrographic context

the valanginian δ13c excursion may not be an expression of a global oceanic anoxic event abstract marine and terrestrial sediments of the valanginian age display a distinct positive 13 c excursion which has recently been interpreted as the expression of an oceanic anoxic episode oae of global importance here we evaluate the extent of anaerobic conditions in marine bottom waters and explore the mechanisms involved in changing carbon storage on a global scale during this time interval we asses redox sensitive trace element distributions rste uranium vanadium cobalt arsenic and molybdenum and the quality and quantity of preserved organic matter om in representative sections along a shelf basin transect in the western tethys in the polish basin and on shatsky rise om rich layers corresponding in time to the 13 c shift are generally rare in the tethyan sections and if present the layers are not thicker than several centimetres and total organic carbon toc contents do not surpass 1 68 wt palynological observations and geochemical properties of the preserved om suggest a mixed marine and terrestrial origin and deposition in an oxic environment in the polish basin om rich layers show evidence for an important continental component rste exhibit no major enrichments during the 13 c excursion in all studied tethyan sections rste enrichments are however observed in the pre 13 c excursion om rich barrande levels of the vocontian trough in addition all tethyan sections record higher mn contents during the 13 c shift indicating rather well oxygenated bottom waters in the western tethys and the presence of anoxic basins elsewhere such as the restricted basins of the north atlantic and weddell sea we propose that the valanginian 13 c shift is the consequence of a combination of increased om storage in marginal seas and on continents as a sink of 12 c enriched organic carbon coupled with the demise of shallow water carbonate platforms diminishing the storage capacity of 13 c enriched carbonate carbon as such the valanginian provides a more faithful natural analogue to present day environmental change than most other mesozoic oaes which are characterized by the development of ocean wide dysaerobic to anaerobic conditions

the structure of the guinean continental margin implications for the connection between the central and the south atlantic oceans the results of a recent geological geophysical survey conducted off guinea are combined with previous data to establish a preliminary stratigraphy and provide a structural sketch of this portion of the west african continental margin three sectors are distinguished a northwestern portion of the margin comprises a wide and deeply submerged plateau the guinean marginal plateau underlain by a thick sedimentary sequence and facing westward toward the gambia abyssal plain scismic stratigraphy and structures show clear analogies to the jurassic margins of the central atlantic including the presence of a cretaceous paleoslope covered by cenozoic deposits a southern area of the margin comprises a series of aligned w e trending acoustic basement features extending along the slope and bounding the guinean plateau to the south these features basement ridges and volcanic piles are related to a fracture zone system also documented by magnetic anomalies and gravity data the bordering deep sierra leone abyssal plain also dissected by e w trending oceanic fracture zones contains a sedimentary cover apparently not older than middle cretaceous between both sectors and between two nw se trending scarps lies an intermediate area the seismic profiles show that here the margin is dissected by faults creating a series of asymmetric horst and graben features progressively narrowing towards the s e and covered by untectonized but partly eroded upper cretaceous to cenozoic sediments

palaeoclimate sedimentation and continental accretion climate has a pervasive effect on sedimentation today and the same climatic patterns are reflected in the distribution of lithofacies through the palaeozoic as the continents migrate beneath the climatic zones the low latitude hot wet zone is represented by thick elastics coals and carbonates and is best developed along east coasts where prevailing winds bring moisture and heated surface waters toward the continent the desert zones occur on the west sides of continents centred at 20 north and south and these dry belts are represented in the geological record by evaporites tillites thick elastics and coals occur in the temperate rainy belts especially on the windward west sides of continents above 40 latitude continental accretion occurs where subduction zones coincide with rainy zones such that the products of erosion are transported to the trench and thus thrust back extending the margin of the continent the opposite process of tectonic erosion wherein the descending oceanic slab continually rasps away the margin of the continental crust may occur in areas where rainfall and surface run off is insufficient to provide trench sediments this process has been operating adjacent to the atacama desert in south america during the past 200 ma to judge by the eastward migration of the calc alkaline intrusive foci about 250 km of the margin of south america have been transported down the subduction zone during this period

fossil crocodilians as indicators of late cretaceous and cenozoic climates implications for using palaeontological data in reconstructing palaeoclimate abstract that the earth s climate has cooled over the last 100 million years has been recognized since the early nineteenth century the transition from the hot house world of the cretaceous a time interval without significant polar icesheets to the ice house world in which we now live today the dynamics process responsible for this change are being examined using computer models especially general circulation models gcm s through such work our understanding of the dynamics of the earth system improves and our ability to predict future trends is enhanced but the success of modelling experiments can only be assessed by comparing results with observations the pattern which for palaeoclimate are drawn exclusively from the geological record palaeoclimate interpreted from geological data is invariably based on analogy with the recent the validity of which depends on corroboration from multiple lines of evidence this requires the compilation and investigation of large global datasets of well constrained geological climate proxies this study uses the palaeodistribution of fossil crocodilians to examine the spatial distribution of palaeoclimate during this transition fossil crocodilians have a relatively good fossil record and are climatically limited in the recent they also provide a manageable global dataset with which to investigate other issues that impinge on the use of geologic data for reconstructing palaeoclimate taphonomy sampling effects time averaging tectonics and for fossils palaeobiogeography and evolution as such this study provides a possible template for examining other climate proxies in order to validate and hone palaeoclimatic interpretations an analysis of modern crocodilians indicates that temperature is the principal influence on their global distribution with the coldest month mean temperature cmm of 5 5 c marking the minimum thermal limit for the group corresponding today to a minimum mean annual temperature mat of 14 2 c the duration of warmth during the year partly indicated by the mean annual range of temperature mart is also important as this affects early juvenile development and survival the presence of standing water provides an essential thermal buffer against temperature extremes by analogy the palaeodistribution of fossil crocodilians suggests the following during the late cretaceous and early palaeogene mat s in excess of 14 2 c cmm s 5 5 c permeated throughout mid latitudes and coastal regions in high latitudes during the oligocene the restriction of fossil crocodilians to low latitudes suggests high latitude cooling as indicated by numerous other lines of evidence coeval restriction of crocodilians to coastal regions in mid latitude north america and much of asia consistent with increased seasonality and aridification in continental interiors may reflect local orographic changes as well as global climate change during the miocene fossil crocodilians return to the great plains of north america but do not reoccupy the continental interior of asia by the pliocene crocodilians are again restricted to low latitudes and coastal regions in mid latitudes coincident with further high latitude cooling and aridification and cooling of mid latitude continental interiors minor distributional changes during the holocene may reflect human effects

a hierarchical tectonic model of the gulf of mexico and caribbean region abstract a quantitative computer graphic methodology hierarchical tectonic analysis has been used to model the tectonic evolution of the gulf of mexico and caribbean region this method employs a highly structured hierarchical description of the relative motions of pairs of tectonic elements in order to quantify the timing and style of plate interactions the main features described in this model are 1 1 a revised fit of pangea 2 2 the opening of the gulf of mexico in the middle late jurassic 3 3 the formation of a proto caribbean ocean due to the separation of north and south america during the early cretaceous 4 4 the formation of the greater antilles arc along the western margin of the proto caribbean ocean 5 5 the insertion of the farallon plate between north and south america during the middle cretaceous resulting in the northeastward advance of the greater antilles arc and the subduction of proto caribbean oceanic crust 6 6 the complete subduction of the proto caribbean ocean and the collision of the greater antilles arc with the bahamas platform in the late cretaceous 7 7 the truncation of the caribbean section of the farallon plate from its pacific counterpart and the formation of the panama arc latest cretaceous and 8 8 the westward movement of north and south america with respect to the caribbean plate resulting in the opening of the yucatan basin paleocene and subsequently in the evolution of the cayman trough and e w zone of strike slip

急速風化と成熟石英アレナイト堆積を支持する ウイスコンシン州 原生代初期珪岩の砕屑ジルコン年代

extensional tectonics in neogene and quaternary sequences at the western margin of the axios basin northern greece neogene and quaternary sequences close to the western margin of the axios basin northern greece have been studied to investigate the nature and extent of their neotectonic deformation synsedimentary deformation is indicated by conjugate growth faults and shear zones and by multiple angular unconformities where possible palaeo stress analysis has been carried out and the majority of the synsedimentary faults are shown to be dynamically controlled and to have developed in response to horizontal nne ssw extension this result which is consistent with recent earthquake focal mechanism studies in the region suggests a similarity in the neotectonic evolution of the northern and southern aegean areas during late cenozoic times

migration origination and extinction of southern hemisphere brachiopods during the middle carboniferous abstract the migration patterns and latitudinal diversity gradients of early and middle carboniferous articulate brachiopod genera from the paleoequatorial zone and southern hemisphere are consistent with the paleoclimatic history of these intervals interpreted from the study of paleoequatorial and northern hemisphere forms both poles apparently became warmer between the middle and late visean south polar cooling associated with glaciation probably began in the late visean at this time 44 of 92 southern hemisphere nonequatorial genera migrated toward the equator the north pole remained warm into the namurian a and cooled during the namurian a to b both northern and southern hemisphere non equatorial genera reacted to high latitude warming with significant increases in percent origination genera from all latitudinal zones responded to high latitude cooling with significant increases in percent extinction during the namurian a to b when both poles were cool a small but statistically significant number of equatorial genera 8 out of 70 migrated out of the equatorial zone into the non equatorial northern hemisphere no similar migration into the southern hemisphere occurred at this time perhaps due to the steep latitudinal temperature gradient several lines of evidence suggest that the latitudinal temperature gradient was steeper in the southern hemisphere than in the northern hemisphere whereas percent origination in northern non equatorial latitudes rose significantly following north polar cooling origination rates in southern non equatorial latitudes did not rise significantly following south polar cooling southern hemisphere non equatorial brachiopods suffered a greater loss of diversity during the interval of polar cooling than either equatorial or northern hemisphere non equatorial brachiopods and there may be namurian tillites within 20 s of the paleoequator veevers and powell 1987

age provenance and tectonic setting of paleoproterozoic quartzite successions in the southwestern united states new field studies combined with u pb zircon geochronology constrain the ages of deposition and sedimentary provenance of paleoproterozoic quartzite successions exposed in the southwestern united states orthoquartzites were deposited in short lived basins at two times ca 1 70 and 1 65 ga during crustal assembly of southern laurentia the more voluminous ca 1 70 ga successions occur in southern colorado northern new mexico and central arizona and are interpreted here to be time correlative though not necessarily deposited in the same basins detrital zircon from quartzites and metaconglomerates exposed in southern colorado and northern new mexico is characterized by a single population with a relatively narrow range of ages 1 80 1 70 ga and minimal archean input 5 of grains analyzed peak detrital zircon ages 1 76 1 70 ga vary slightly from location to location and mimic the age of underlying basement unimodal detrital populations suggest local sources and a first cycle origin of the orthoquartzites within a short time interval 1 70 1 68 ga during unroofing of local underlying basement the maximum age of quartzite exposed at blue ridge colorado is constrained by the 1705 1698 ma coarse grained granitoid basement on which quartzite was deposited unconformably the minimum age of ortega formation quartzite new mexico is constrained by ca 1680 1670 ma metamorphic monazite overgrowths these dates agree with direct ages on the lower mazatzal group arizona and suggest that orthoquartzite deposition occurred over a wide region during and soon after the ca 1 70 ga yavapai orogeny regional structural arguments and the thrust style of quartzite deformation suggest that the metasedimentary successions were deformed during the ca 1 66 1 60 ga mazatzal orogeny thus making them important time markers separating the yavapai and mazatzal orogenic events our model for syntectonic deposition involves extensional basin development followed by thrust closure possibly due to opening and closing of slab rollback basins related to outboard subduction the first cycle origin of orthoquartzites near the end of the arc collisions of the yavapai orogeny seems to contrast sharply with their extreme compositional maturity this can be explained in terms of protracted extreme diagenesis and or special environmental influences that enhanced chemical weathering but were unique to the transitional atmosphere and ocean chemistry of the proterozoic similarities among quartzites exposed throughout the southwestern united states and along the laurentian margin suggest that they represent a widespread regional and perhaps global episode of sedimentation involving a distinctive syntectonic setting and unique climatic conditions a combination that might make these units a signature lithology for paleoproterozoic time

a cretaceous and jurassic geochronology an integrated geomagnetic polarity and geologic time scale for the jurassic and cretaceous periods is presented based on various methods according to the availability of definitive isotopic ages an age calibrated sea floor spreading model is used to interpolate the ages of the kimmeridgian to barremian and the campanian to maestrichtian stages numerical age estimates for the aptian to santonian stage boundaries follow published isotopic age determinations the hypothesis of equal duration of ammonite zones is employed as a vernier to apportion time for the hettangian to oxfordian stages the new scale results in ages of 208 ma for the base of the jurassic 144 ma for the jurassic cretaceous boundary and 66 5 ma for the top of the cretaceous the integrated biostratigraphic magnetostratigraphic and geochronometric record serves as a working hypothesis for geologic correlation of jurassic and cretaceous strata

coal more than a resource critical data for understanding a variety of earth science concepts abstract coal is one of the world s primary energy sources and it is critical for making coke used in steel making and is used for a multitude of chemical products aside from its significance as a fuel or product however coal and data derived from the exploration or mining of coal have also provided the foundation and testing ground for diverse geologic concepts because of coal s economic importance and common variability in thickness distribution and quality it has been critical to collect and correlate a wide variety of surface and subsurface data sets at relatively high spatial frequency which varies from the mine to basinal scale also because many coal beds occur in most coal basins the collection of coal data from multiple beds creates relatively high temporal frequency data sets at scales from laminae to bed to larger unit scale these data have been important for the development and expansion of many earth science concepts including aspects of basin analyses paleogeography paleoclimatology paleontology stratigraphy sedimentology structural geology and tectonics

oxygen and hydrogen isotope compositions of paleosol phyllosilicates differential burial histories and determination of middle late pennsylvanian low latitude terrestrial paleotemperatures abstract the clay mineralogy chemistry and stable hydrogen and oxygen isotope compositions were measured from 20 phyllosilicate samples representing 11 pennsylvanian age paleosol profiles taken from three cores in the illinois basin in order to assess their utility as proxies of low latitude terrestrial paleotemperatures the majority of the samples are mineralogical mixtures of illite smectite i s kaolinite and rarely discrete illite samples from a shallowly buried locality in the northern part of the basin are dominantly composed of smectite rich i s with variable amounts of kaolinite and no discrete illite samples from deeply buried interior parts of the basin are composed of illite rich i s variable amounts of kaolinite and discrete illite these phyllosilicate mixtures have 18 o v smow and d v smow values that range from 17 2 to 23 0 and 56 to 27 respectively assuming that the phyllosilicates preserve a record of isotopic equilibrium with pennsylvanian meteoric waters these oxygen and hydrogen isotope values correspond to crystallization temperatures ranging from 22 3 c to 55 3 c the clay mineralogy phyllosilicate 18 o and d values and calculated crystallization temperatures of 44 c to 55 c from deeply buried localities in the interior of the basin are not consistent with a pedogenic origin instead these trends are considered to be the result of diagenetic recrystallization of pedogenic minerals in response to greater depths of burial by 1 5 to 3 km in the southerly basin center localities as well as an interval of middle permian elevated heat flow associated with magmatic intrusions in the southern part of the basin phyllosilicate mineralogy 18 o and d values and calculated phyllosilicate crystallization temperatures from a shallowly buried northern locality in the illinois basin are consistent with a pedogenic origin and reveal a long term warming trend from an average temperature of 23 3 c in the lower desmoinesian to an average temperature of 32 3 c in the missourian this temperature change is coincident with a significant change in the composition of wetland vegetation in euramerica which has been attributed to a shift in low latitude pennsylvanian climate towards warmer and drier conditions in the late pennsylvanian this study reveals the presence of a dynamic late paleozoic paleoequatorial icehouse climate characterized by significant low latitude temperature variability unprecedented on modern earth

palaeovalleys and protozoan assemblages in a late carboniferous cyclothem sydney basin nova scotia the early stephanian bonar cyclothem of the sydney basin nova scotia contains an erosional surface cut through coastal plain strata with economic coals and distributary channel bodies the erosion surface is interpreted as a palaeovalley 20 m deep and at least 7 km wide that marks a sequence boundary formed during relative fall in sea level the palaeovalley is filled with stacked alluvial channel bodies which become more isolated as the valley fill passes upward into red alluvial plain deposits probably laid down in an anastomosed river system in an adjacent interfluve area calcretes and red vertic palaeosols cap coastal strata assemblage analysis of agglutinated foraminifera and thecamoebians indicates that the palaeovalley was filled with freshwater sediments before an initial marine transgression flooded the alluvial surface and adjacent interfluve valley incision probably reflects glacioeustatic sea level fall however the alluvial nature of the valley deposits suggests that valley filling reflects an abundant sediment supply during lowstand and or transgressive stages and was not a direct consequence of sea level rise during the subsequent transgression phase aggradation was rapid as sediment supply apparently kept pace with rising sea level features of both channel and extra channel facies suggest that seasonality intensified during the transition from coastal plain to palaeovalley and alluvial plain deposition

southern polar forests the early cretaceous floras of victoria and their palaeoclimatic significance abstract a diverse fossil flora including cryptogams pteridosperms cycadales bennettitales ginkgoales coniferales and angiosperms occurs in early cretaceous fluvial and lacustrine strata in the otway and gippsland basins in southern victoria both evergreens e g araucarians cycads ferns and deciduous or semi deciduous forms e g certain pteridosperms and ginkgoales seem to have been represented certain ferns ginkgos and conifers grew to a large size overall the assemblages are typical of early cretaceous floras the associated fauna includes dinosaurs hypsilophodontids allosaurs lepidosaurs chelonians birds fish including the lungfish ceratodus and insects the evidence of the biota as a whole suggests a warm to cool temperate relatively equable climate of moderate seasonality with no widespread winter freezing the complex mesozoic apparent polar wander path apw indicated for australia places victoria in high to polar palaeolatitudes ca 70 85 s during the early cretaceous this apw path is supported by paths for other gondwana continents the existence of the victorian early cretaceous forest and biotic communities through polar nights of about two to five months duration is difficult to accept evergreen species would have required relative equability of light whatever the temperature the dinosaurs foliage throughout the year and the lungfish warm to temperate conditions without freezing in view of the consistency of mesozoic palaeomagnetic results for gondwanaland and the enigmatic presence of mesozoic and early cenozoic fossil floras and faunas in very high northern palaeolatitudes the possibility of a reduced obliquity of the ecliptic in mesozoic early cenozoic time should be considered

continental humid and arid zones during the jurassic and cretaceous abstract the global distribution of climatically significant criteria is surveyed for six successive time intervals hettangian toarcian aalenian callovian oxfordian tithonian berriasian barremian aptian cenomanian and turonian maastrichtian the criteria are primarily mineralogical evaporites coals bauxites ironstones and kaolinite but include sedimentological and palaeontological aspects of facies e g aeolian sands fossil ferns and xerophytes fresh water invertebrates in early and mid jurassic times an arid zone can be distinguished in low to mid latitudes in western pangaea with humid zones elsewhere in the late jurassic this arid zone spread northwards to embrace much of southern eurasia there followed in the early cretaceous a sharp reversal to more humid conditions over a large area extending from the eastern margin of north america to the middle east a major consequence of which was the widespread replacement of carbonates by coarse siliciclastic facies by late cretaceous times humid conditions were well established also in north america and the south atlantic margins and the tropical arid zone had contracted to a minimum the 87 sr 86 sr ratio of marine carbonates provides an independent monitor of continental runoff which is related to a area and b extent of aridity changes in the ratio confirm that taking sea level stand into account the late cretaceous was appreciably more humid than the late jurassic these climatic changes are related primarily to the progressive breakup of pangaea in the late jurassic and cretaceous which together with sea level rise in the mid to late cretaceous caused a significant increase in maritime influence this implies that monsoonal winds probably had a major role in promoting higher precipitation rates a puzzle remains as to why there was a spread of aridity in the late jurassic finally some implications for terrestrial plant evolution are noted

depositional environments of the early cretaceous kurnub hathira sandstones north jordan abstract the kurnub hathira sandstones in north jordan which are most probably of early cretaceous age are about 300 m thick varicoloured friable quartz arenitic sandstones based on grain size analysis sedimentary structures palaeocurrent fossil content and petrography these sandstones are postulated to be dominantly of fluvial origin with a few interfingering shallow marine horizons a southward displacement of jordan by at least 100 km would bring these sandstones opposite to similar rocks west of the jordan araba rift with jordan being higher during the early cretaceous

age constraints on a neogene tropical rainforest in china and its relation to the middle miocene climatic optimum abstract tropical rainforests have strongly influenced earth systems throughout their evolutionary history plant taxa found in the fotan group of fujian province indicate that an asian tropical rainforest prevailed in southeastern china during the miocene abundant insect bearing ambers co occur with diagnostic plant fossils in outcrop fotan group fossils demonstrate that highly diverse tropical ecosystems existed during the early neogene in southeastern china this study reports a robust 40ar 39ar age of 14 7 0 4 ma for the fotan fossils this age constrains interpretations of 1 when tropical rainforest ecosystems developed in china 2 whether the fotan flora temporally overlapped with the asian tropical forest in india and 3 whether the middle miocene climatic optimum triggered expansion of tropical rainforests in asia a precise age for fotan units provides important constraints on the biogeographic history of the field area and paleographic models linking asian and indian biota

world peat occurrence and the seasonality of climate and vegetation abstract the climatic controls on present day peat formation are examined in order to develop a uniformitarian tool for refining paleoclimate studies and to create a retrodictive model for the coals of the geologic record a peat database has been compiled for the world and the resulting patterns are compared with aspects of precipitation and temperature drawn from a gridded data set precipitation continuity through the annual cycle is important for biologic productivity in the terrestrial realm it is expressed in terms of the number of months with average precipitation above 40 mm temperature is limiting at higher latitudes where the potential growing season may be defined by the number of months with mean temperature exceeding 10 c a map predicting the growing season has been constructed from these rainfall and temperature statistics which compares very well with actual vegetation persistence through the year as measured directly from satellite instruments however biologic production will not result in peat accumulation unless groundwater levels are maintained through the growing season our peat prediction map therefore shows the percentage of time that precipitation occurs during the potential growing season present day peat accumulations are well predicted by this map

the influence of continental ice sheets on the climate of an ice age the climate influence of the land ice that existed 18 000 years before present 18k b p is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean simulated climates are obtained from two versions of the model one with the land ice distribution of the present and the other with that of 18k b p in the northern hemisphere the tropospheric flow field is strongly influenced by the laurentide ice sheet and features a split flow straddling the ice sheet with a strong jet stream forming the southern branch the northern branch of the flow brings very cold air over the north atlantic ocean where thick sea ice is maintained the distribution of sea surface temperature sst difference between the two experiments in the northern hemisphere resembles the difference between the sst at 18k b p and at present as estimated by the climap project 1981 the 18k b p ice sheets have very little influence upon atmospheric temperature and sst in the southern hemisphere this is because the interhemispheric heat transport hardly changes as the loss of heat energy due to the reflection of solar radiation by continental ice sheets in the northern hemisphere is almost completely counterbalanced by the in situ reduction of upward terrestrial radiation hydrologic changes in the model climate are also found with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in north america and eurasia these findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum

yangquanoxylon miscellum gen nov et sp nov a gymnospermous wood from the upper pennsylvanian lower permian taiyuan formation of yangquan city shanxi province with reference to the palaeoclimate in north china a silicified gymnospermous wood yangquanoxylon miscellum gen nov et sp nov is described from the upper pennsylvanian lower permian taiyuan formation yangquan city shanxi province north china the pycnoxylic wood is composed of thick walled tracheids and thin walled rays it is characterized by mixed radial tracheid pits uniseriate and homogeneous rays occurrence of scalariform radial pitting and various types of cross field pitting there are four types of cross field pitting in y miscellum gen nov et sp nov including simple taxodioid phyllocladoid and araucarioid the absence of growth rings within fossil woods described here and reported previously from north china suggests a humid climate with minimal precipitation variations during the late pennsylvanian early permian

continental brackish and marine carbonates from the lower cretaceous of kolone barbariga istria croatia stratigraphy sedimentology and geochemistry abstract during the early cretaceous wide areas of the dinaric adriatic carbonate platform emerged for long periods the hauterivian barremian carbonates from kolone barbariga show a few typical examples of lacustrine facies with dinosaur bones and brackish palustrine facies the sequence of the platform is made for the most part by subtidal and intertidal limestones the bone levels are located in a large depression few meters deep in the uppermost hauterivian marine limestones the filling facies of this depression are made by oncolitic rudstones and algal boundstones which represent marginal lacustrine facies and by laminated limestones thin stromatolitic levels and distal fringes of rudstones which represent relatively open lacustrine facies the fossil content is characterized by rare charophyte stems ostracods gastropods and plant remains while typical marine fauna is absent at the hauterivian barremian boundary a major emersion event has been observed then a slow transgressive phase occurred the transgressive facies are primarily made by mudstones with ostracods charophytes and spirillina brackish and probably freshwater facies wackestones with ophtalmidiidae and rare dasyclad algae storm layers with gastropods and miliolids and breccia like dinoturbated beds wackstones packstones and very rich in dasyclad grainstones outcrop at the top of the section representing the maximum of the transgression trace elements content carbon and oxygen stable isotope analyses have been performed to aid the palaeoenvironmental interpretation in this geological setting barium seems to discriminate between brackish and freshwater facies the isotopic values of the marine carbonates appear to depend on early diagenetic processes meanwhile lacustrine facies seem to show a weak signal of the depositional environment

remote sensing and gis investigation of glacial features in the region of devil s lake state park south central wisconsin usa abstract this study utilizes landsat tm aster and synthetic aperture radar sar derived dems in conjunction with geographic information systems gis in order to reevaluate previously published interpretations of glacial landforms in and around devil s lake state park south central wisconsin usa devil s lake sits in a gorge carved into the southern flank of a doubly plunging syncline known as the baraboo hills through which the wisconsin or some other river flowed prior to the last ice age during the last glacial maximum about 18 000 b p an outlet glacier of the laurentide ice sheet called the green bay lobe extended southward into south central wisconsin and left behind extensive glacial landforms such as moraines drumlins and eskers during advance of the green bay lobe into the region devil s lake gorge was plugged at both ends by glacial deposits and resulted in formation of devil s lake the wisconsin river if it originally flowed through devil s lake gorge found a new course to the east of the baraboo hills syncline this study utilizes the aforementioned remote sensing data to spatially image the following features 1 original extent of the green bay lobe 2 moraines and streamlined glacial landforms as indicators of ice flow directions and 3 former path of the old wisconsin or some other river prior to being rerouted by the green bay lobe gis analysis is also performed in order to test published interpretations of the regional glacial history this study confirms that glacial features observed today are consistent with the former advance of the green bay lobe into the area formation of glacial lake wisconsin plugging of devil s lake gorge by a moraine to form devil s lake and subsequent glacial retreat leading to the breaching of an ice dam and catastrophic flooding by 14 000 years ago the large aerial coverage of satellite imagery with resolutions up to 15 m are valuable for reevaluating regional interpretations previously based on local field mapping and aerial photography of limited extent

application of the fujita ziegler paleoclimate model early permian and late cretaceous examples abstract the fujita ziegler model is a new semi quantitative technique for reconstructing atmospheric circulation and resulting rainfall patterns of the geological past using uniformitarian assumptions in this paper we evaluate the performance of the model when applied to geographic and climatic conditions that were significantly different from the recent a late cretaceous maastrichtian reconstruction permits a test of the performance of the technique during a time that apparently lacked polar ice caps and steep latitudinal temperature gradients an early permian sakmarian reconstruction is used to evaluate the performance of the technique when the equator to pole temperature gradient was steep more like today but all major land masses had merged to form one large supercontinent pangea for both the maastrichtian and sakmarian the model produced more detailed retrodictions of surface air pressure and precipitation continuity than previously published paleoclimate reconstructions the results compare favorably with the known distribution of climatically sensitive sediments such as coals evaporites and phosphorites although the model considers complex relationships among land and sea distribution air pressure surface winds ocean currents and specific precipitation mechanisms it is still relatively simple and easy to apply therefore it is an excellent learning tool for the student of paleoclimate and should be an important technique to complement other methods of paleoclimate reconstruction

three growth in the mesozoic and early tertiary and the reconstruction of palaeoclimates abstract evidence from the distribution and characteristics of fossil wood in the mesozoic and early tertiary indicates that a much warmer global climate prevailed in those times there appears to have been a broad zone of largely non seasonal climate stretching from about 32 n to 32 s palaeolatitudes in addition to this low latitude zone forest growth extended into very high palaeolatitudes where trees cannot grow at the present day a number of theories have been proposed to account for the palaeoclimate responsible for this distribution of forests most notable have been those involving changes in the amount of carbon dioxide in the atmosphere in the positions of the continents or in the obliquity of the earth s axis of rotation evidence from fossil forests indicates that a combination of the effects of an increased quantity of carbon dioxide in the atmosphere and the palaeopositions of the continents in the mesozoic and early tertiary appears at the moment to be the simplest explanation for the climate of those geological times without the need to invoke axial movement

a global palaeoclimatic reconstruction for the valanginian based on clay mineralogical and geochemical data abstract high resolution clay mineral and 18ocarb analyses have been performed on three sections of valanginian age early cretaceous from northwestern 20 30 n and southern 53 s tethyan realms the data have been integrated in a large set of published mineralogical clays and geochemical 18ocarb 18obivalve 18olenticulina 18obelemnite and tex86 data from 17 sections situated between 45 n and 53 s based on this data set we provide new insights into valanginian climate conditions from a wide range of palaeolatitudes we highlight climate trends within specific areas and identify main climate belts in the proto north atlantic realm 15 17 n large amounts of smectite together with the occurrence of palygorskite testify for a semi arid climate belt throughout the valanginian significant variations in kaolinite content in the northwestern tethyan realm 20 to 30 n suggest that this realm has been more sensitive to changes in hydrological cycling and subsequent erosion and runoff processes during the early to early late valanginian transition interval this time interval that is coincident with the pronounced positive and globally recognized carbon isotope excursion cie the weissert episode documents the wet conditions of a humid subtropical climate belt temperature ranges derived from 18o records suggest climate warming by about 3 5 0 9 c in the northern hemisphere during the weissert episode this is followed by a global cooling of about ca 1 5 0 9 c in both hemispheres during the late valanginian we postulate that these patterns were due to interplays between tectonic and orbital factors which have controlled the distribution of regional palaeoclimate belts during the valanginian the semi arid belt expressed in the proto north atlantic realm has probably been induced by its specific palaeogeographic configuration and the existence of isolated basins which were each characterized by strong and continuous thermohaline circulation an eccentricity paced monsoon like system might have played a significant role in maintaining the subtropical belt around the northwestern tethyan realm up to the mid latitudes 35 45 n superimposed on these regional processes a widespread magmatic pulse in parana etendeka volcanic activity might have stimulated greenhouse conditions impacting marine biota and favouring the development of a dense vegetation cover on the continent an increase in sedimentary burial of 13c depleted organic carbon on the continents may have contributed to the progressive global positive carbon isotope excursion in the medium term it has also probably led to a significant decrease in atmospheric co2 as testified by the global cooling recorded during the late valanginian in both hemispheres and the probable concomitant extension of polar ice caps

conservatism of late pennsylvanian vegetational patterns during short term cyclic and long term directional environmental change western equatorial pangea the fossil record offers a unique opportunity to track species pools through time and to examine their responses to long term directional changes in physical conditions the ability to estimate environmental variables such as temperature rainfall amount and its seasonal distribution and atmospheric co2 is improving continuously links between proxy measures of such physical factors and quantitative data on changes in ecosystem composition and dynamics formerly the purview of pleistocene palaeoecology are now available even in the deep past for both terrestrial e g wing et al 2005 falcon lang et al 2006 montanez et al 2007 secord et al 2008 currano et al 2008 tabor et al 2011 and marine palaeozoic examples olszewski erwin 2009 ivany et al 2009 fall olszewski 2010 bonelli patzkowsky 2011 holland zaffos 2011 systems plant fossils themselves can be especially useful as palaeoclimate proxies even in the distant world of the palaeozoic e g falcon lang et al 2009 because of the strong sensitivities of plants to habitat and regional climate as sessile organisms plants are directly and inextricably linked to climate at the level of individual population local community and biome quantitative floristic studies of vegetation from the late palaeozoic are numerous e g scott 1978 pfefferkorn thomson 1982 bartram 1987 eble et al 1994 2006 pryor gastaldo 2000 dimichele et al 2007 oplustil et al 2007 sim nek martinek 2009 libertin et al 2009 bashforth et al 2010 although few have had a framework with which to link plants and their associated environments to changing global climate e g phillips peppers 1984 falcon lang 2004 it is a particular challenge to find a long relatively uninterrupted stratigraphic section that contains both a common species pool or pools and a clear signal of an overall directional and interpretable environmental change the latest pennsylvanian earliest permian markley formation of north central texas provides such an opportunity the markley fm was positioned in the western pangean tropics during the pennsylvanian permian transition a time of global climate change that accompanied the onset of permian glaciation fielding et al 2008 within the markley fm its partial equivalent the harpersville fm and into the base of its successor the archer city fm there are distinct packets of lithofacies that repeat in the stratigraphic section each lithofacies contains a distinctive fossil plant assemblage characterized and described by romanchock et al in press which can be followed through the markley fm the goal of this paper is to go beyond such a qualitative flora to facies correlation and to examine quantitatively the floristic similarity within and among these facies in space and through time in order to investigate and in this instance document the coherence of species assemblages in the face of short term and long term environmental changes and to evaluate spatio temporal scales on which niche versus neutral biological community assembly patterns may operate e g alonso et al 2006 weiher et al 2011 in addition we wish to examine the conformance of the markley fm data with interpretive models that call for climate change as the controlling variable on repeating patterns of lithofacies and plant distribution through time in the short and long term allocyclicity v models that call for changes in sedimentary environments as the driver of temporally recurrent floristic change under a relatively constant background climate autocyclicity

dispersed angiosperm cuticles their history preparation and application to the rise of angiosperms in cretaceous and paleocene coals southern western interior of north america abstract cuticle the decay resistant outer layer of leaves and young stems provides a reliable means of identifying fossil plant remains and reflects the vegetative adaptations of plants to climate and other environmental parameters the study of dispersed angiosperm cuticles originated prior to world war ii and has focused on the origin and paleoecology of coal activity in dispersed cuticles reached a high point during the 1950s and 1960s with the study of tertiary lignites in central europe then subsided in central europe as workers from other regions expanded the technique to other time periods and geographic regions data from dispersed cuticles augment data from palynomorphs because dispersed cuticles originate from a different generation of the vascular plant life cycle and have different taphonomic histories because the analysis of dispersed angiosperm cuticles is unfamiliar to many geologists methods for the analysis and preparation of dispersed angiosperm cuticles are detailed in an appendix dispersed cuticle assemblages from coals in the upper albian longford member of the kiowa formation and the maastrichtian paleocene raton formation of the southern western interior provide new constraints on the times that angiosperms entered coal swamps and rose to dominance the kiowa assemblages indicate that angiosperms first entered coal swamp environments by the late albian while the raton assemblages indicate that angiosperms dominated primary productivity in some subtropical coal swamps by the late maastrichtian angiosperms in kiowa coals probably comprised pioneer species in conifer dominated vegetation the most common family of angiosperms was chloranthaceae angiosperms in upper maastrichtian raton coals comprised the dominant seed plants to the exclusion of conifers magnoliid dicots and monocots were the dominant taxa and comprised diverse genera and families evidence from palynology and types of preserved cuticle indicates that ferns were subordinate to seed plants in biomass in raton coals in contrast to some described assemblages from the northern western interior paleocene coals from the raton basin show the loss of many cretaceous angiosperm taxa as well as the appearance of new taxa including conifers belonging to taxodiaceae however these taxodiaceae were evergreen and subordinate in abundance to angiosperms vegetational patterns shown by cretaceous paleocene coals of the southern western interior contrast with those of more northerly regions and indicate a poleward gradient in the timing of angiosperm dominance in coal swamps