oxygen isotopic composition of fossil horse tooth phosphate as a record of continental paleoclimate abstract oxygen isotopic elemental and x ray data are presented for a suite of 24 fossil horse teeth from nebraska ranging in age from 18 2 to 8 5 ma to test the use of 18o of enamel phosphate 18op04 as a quantitative record of continental climate modern equid teeth were analyzed to estimate a relationship between 8op04 and environment water multiple samples of seven different fossil species from burge quarry a 12 ma attritional fossil deposit indicate the diagenetic overprints exist but can be detected by decreased p concentration and increased crystallinity relative to modern enamel isotopic variation for the pristine samples from burge quarry is 1 5 1 n 9 which may represent the resolution of the procedure within a stratigraphic horizon there are no apparent correlations with body size hypsodonty or phylogeny a range of 7 0 in 18op04 occurs over the 10 m y interval a trend towards depleted 18op04 of about 4 corresponds to a depletion of up to 6 0 in 18o of precipitation between 18 2 and 8 5 ma but the range of variation of burge is large relative to the climate signal our results demonstrate that 18op04 should be useful in quantitatively reconstructing cenozoic continental paleoclimate on 106 year timescales isotopic variation due to taphonomic bias and the terrestrial rock record will likely obscure higher order climate signals

syntectonic carbonate veins from the barbados accretionary prism odp leg 110 record of palaeohydrology syntectonic carbonate veins were found along the decollement zone between the atlantic and caribbean plates and in two sites 12 and 17 km landward of the deformation front of the barbados accretionary prism odp leg 110 both calcite and lesser amounts of rhodochrosite mnco3 occur in microcrystalline fibrous and blocky mosaic forms in veins deposited along scaly shear zones descriptions of the occurrences textures mineralogy and stable isotope geochemistry of these veins presented herein help trace the hydrological evolution of the barbados accretionary prism which has seen the impact of more deeply derived fluids on elevated sediment temperatures and altered geochemistry of interstitial fluids at one site for example vein forming fluids have been as much as 10 c warmer and 1 more enriched in 18o than expected carbon isotope ratios of veins indicate a mixture of carbon derived from seawater and from oxidized organic matter during sulphate reduction although dissolution of calcareous skeletons may be an additional component the presence of methane is recorded in one vein sample in the accretionary prism indicating that either the plumbing of the prism has changed with time allowing more fluid to leak into the prism in the past or that materials currently 1 km above the decollement zone were once deformed in the decollement using oxygen isotope analyses of rhodochrosite samples from two sites in conjunction with measurements of fluid temperature and 18o values of interstitial fluids it is proposed that the fractionation of oxygen isotopes between rhodochrosite and water 1000 1n 38 at 25 c 10 greater than the fractionation between calcite and water however it appears that substitution of 10 20 mol ca into rhodochrosite reduces the fractionation factor by 2 9 so impure diagenetic rhodochrosite samples from the deep ocean will rarely be this enriched in 18o

in situ fossil forest from the upper fremouw formation triassic of antarctica paleoenvironmental setting and paleoclimate analysis abstract a structural and ecological study of a standing triassic forest containing 99 silicified trunks from the fremouw formation of antarctica is detailed utilizing quantitative methods forest density total forest cover per hectare mean separation of trees and basal area per stump were obtained this information integrated with sedimentologic taxonomic fossil wood and biomechanical data has allowed the reconstruction of a plant community that grew at very high paleolatitudes 70 75 s the paleoforest grew along river banks levees and within proximal floodplain environments where a taphocoenosis of permineralized stumps and compression impression foliage of the dicroidium type has been preserved in particular the intimate association of this leaf type with dense conifer like wood provides additional confirmation that the dicroidium foliage morphotype was attached to several types of stems this riparian forest stand was apparently in a mature stage prior to the beginning of preservation tree ring analysis as well as additional indirect evidence indicates that this middle triassic ecosystem in antarctica experienced a season very suitable for plant growth resulting from an overall favorable climatic regime this conclusion contrasts with earlier paleoclimate models based on physical parameters in which temperature ranges would make plant or animal growth at these latitudes almost impossible finally antarctic climatic change from latest permian through late triassic is considered in the context of tectonic and paleogeographic reconstructions of the east antarctic craton

biota and palaeoenvironment of a high middle latitude late triassic peat forming ecosystem from hopen svalbard archipelago a siliceous permineralized peat block recovered from hopen in the svalbard archipelago hosts a low diversity late triassic flora dominated by autochthonous roots and stems of bennettitaleans and lycophytes and parautochthonous leaves sporangia spores and pollen from a small range of pteridophytes and gymnosperms some parenchymatous bennettitalean root cells show interactions with chytrid fungi and bacteria the remains of other fungi and fungi like organisms are dispersed within the peat s detrital matrix cavities excavated through some roots and compacted detritus contain abundant coprolites probably derived from sapro xylophagous oribatid mites although no body fossils have yet been identified sparse larger coprolites containing leaf fragments attest to the presence of invertebrate folivores in the ancient ecosystem the low diversity flora relatively few trophic levels and simple nutritional web together with sedimentological aspects of the host formation and the peat structure collectively favour accumulation of the organic mass as a fibric root dominated peat within a temperate high middle latitude well aerated mire

reply to the discussion by danziger and jannuzzi on development of global correlation models between in situ stress normalized shear wave velocity and soil unit weight for plastic soils 1

late pliocene pleistocene high resolution pollen sequence of colombia an overview of climatic change two long continental pollen records funza i 357 m and funza ii 586 m from the high plain of bogota colombia at 2550 m elevation have been studied palynologically fission track dates on zircon from intercalated volcanic ashes provided a chronological framework and showed the pollen records which correlate with high precision to be continuous over the interval from ca 3 2 ma to ca 27 ka the late pliocene pleistocene history of the montane forests and open alpine paramo vegetation is documented with a temporal resolution of ca 6 5 ka and for the upper 1 1 ma with a resolution of ca 1 2 ka the immigration of the northern hemisphere elements alnus at ca 1 ma and quercus at ca 0 33 ma which travelled along the panamanian landbridge caused significant changes in the composition of the andean montane forests the successive pleistocene glaciations forced the andean vegetation belts to an almost continuous altitudinal movement the upper forest line at present at ca 3200 m shifted between 1800 m glacials and ca 3500 m interglacials corresponding to a variation in temperature between ca 5 and 15 c at 2550 m altitude a provisional land sea correlation funza pollen odp site 677 18o is shown for the upper 1 2 ma stages 3 35 frequency analysis of several time series showed significant periods of the eccentricity 100 ka and precession 23 and 19 ka bands showing orbital forcing and a strong change in climatic variability around 800 ka at ca 2 7 ma a significant cooling of ca 5 c is documented reflecting the classical terrestrial pliocene pleistocene boundary which correlates to the reuverian praetiglian boundary of the nw european stratigraphical climatic subdivision

microbial processes controls on the shape and composition of carbonate concretions abstract shape size and mineralogical chemical compositions of carbonate concretions vary considerably the questions to be answered are why do they form at all what processes are involved why do they so often form as regular spheroids why do they sometimes form laterally extensive bands what controls whether the mineral composition is calcite dolomite rhodochrosite or siderite or mixtures of them the questions are addressed and the answers illustrated by selected examples carbonate precipitation is the result of the sedimentary system exploiting the potential energy provided by juxtaposing oxidised detrital input with reducing agents organic matter microbes take advantage of the energy source and are believed to be involved in most of the various processes pore waters in steadily accumulated sediments show a depth related succession of chemical and carbon stable isotope compositions this results from degradation of organic matter proceeding via an orderly succession of processes during burial each mediated by a specific microbial group aerobic oxidation using dissolved oxygen occurs first followed by mn iv reduced to mn ii as the oxidant fe iii reduction and sulphate reduction are probably more significant methanogenesis is the final deepest microbial process the common product of all these reactions is co 2 or dissolved hco 3 which can result in carbonate supersaturation the specific process controls the chemical and isotopic compositions of pore water and leads to a characteristic mineralogy of any carbonate precipitated however the processes may not proceed successively and localised micro environments occur recent work on siderite concretions in very young salt marsh sediments norfolk u k has shown that microbial populations are not homogeneously distributed and that these localise and control concretionary growth concretions in ancient rocks can be described in terms of the same processes observed in modern sediments laterally extensive siderite bands in bullhouse quarry westphalian u k resulted from interaction of two sets of complementary processes shallow manganese and iron reduction coupled with deeper methanogenesis and decarboxylation the model is supported by a mass and charge balance calculation similar complementary processes formed spheroidal concretions gammon shale usa but there is evidence that the outer shell of the concretion formed before the inner core and in the absence of a core the shell was crushed by burial compaction the spheroidal form resulted from diffusion of reactive components controlled by the relative rates of the contributory processes calcite or dolomite analogues of the siderite concretions are formed by similar processes but inhibition of carbonate precipitation makes it impossible to use an equilibrium mass balance model kimmeridge bay uk dolomite ledges are marine analogues to the bullhouse examples for the pyrite rimmed calcite jet rock concretions early jurassic yorkshire u k the rate of production of sulphide from sulphate reduction locally exceeded availability of fe ii to precipitate pyrite outward diffusion of sulphide produced the characteristic spheroidal shape of the concretion because of their developmental pattern bedded concretions are more likely to preserve a sequence of diagenetic cements which record the history of pore water evolution however all represent an expression in ancient rocks of microbiological processes similar to those operating today

depositional setting and paleobotany of permian and triassic permineralized peat from the central transantarctic mountains antarctica abstract silicified peat is known from two sites in the central transantarctic mountains both are within a 2 km thick permo triassic sandstone shale sequence that was deposited by braided streams in a rapidly subsiding foreland basin along the paleo pacific margin of antarctica upper permian permineralized peat occurs as scattered boulders just above a channel form sandstone in the upper part of the buckley formation on skaar ridge overlooking the beardmore glacier these boulders are erosional remnants of fine grained deposits that accumulated in shallow lakes or swamps on a flood plain at fremouw peak the peat occurs near the top of the fremouw formation in strata that are probably middle to late triassic in age the peat consists of large blocks that were rafted into a sandy braided stream channel during a flood and then stranded and buried as flood waters receded both sites are characterized by exceptionally well preserved plant material although the composition and diversity of the two floras are very different permineralization apparently took place rapidly and was enhanced by the dissolution of siliceous volcanic detritus that is abundant in both formations

the geochemistry of concretions from the kimmeridge clay formation of southern and eastern england concretions from the kimmeridge clay formation are of three types calcareous concretions septarian calcareous concretions and pyrite calcite concretions and nodules which occur within different mudstone facies isotopic and chemical analysis of the concretionary carbonates indicate growth in the fe reduction sulphate reduction and decarboxylation zones the septarian concretions show a long and complex history with early initiation of growth and development spanning several phases of burial each often resulting in the formation of septaria growth apparently ceased in the transitional zone between the sulphate reduction and the methanogenesis zones very early growth in the fe reduction zones is also seen in one sample the non septarian concretions began growth later within the sulphate reduction zone and have had a simpler burial history while the pyrite calcite concretions show carbonate cementation in the sulphate reduction methanogenesis transition zone a ferroan dolomite calcite septarian nodule with decarboxylation zone characteristics also occurs development of concretions appears to be indirectly controlled by the sedimentation rate and depositional environment the latter determining the organic matter input to the sediments calcareous concretions predominate in swell areas and during periods of low sedimentation rate in the basins with poor organic matter preservation and deposition of calcareous mudstones pyrite calcite concretions occur in organic rich mudstones deposited under higher sedimentation rates in the basins while the ferroan dolomite nodule grew under very high sedimentation rates

petrographic changes induced by artificial coalification of peat comparison of two planar facies rhizophora and cladium from the everglades mangrove complex of florida and a domed facies cyrilla from the okefenokee swamp of georgia abstract petrographic changes during coalification of three peat samples were investigated by artificial coalification experiments using a semi open reactor system compressions of from 83 to 88 produced dark brown to black shiny flattened pellets exhibiting microscopic banding overall amounts of compression inversely correlated with the framework to matrix ratios f m although certain tissue fragments remained relatively uncompressed due to the presence of tanniniferous cell fillings and also hypothetically to the presence of colorless plant secretions or gelified wall materials that were present in the cells but only recognizable after a change in color during coalification the most distinct microscopic banding longest and widest bands developed in samples of the dome formed peat facies which had the highest framework to matrix ratios of any type and the greatest contents of surface litter composing the framework i e highest s n ratio the planar root dominated rhizophora facies showed the greatest change in microbanding character during coalification in that the numerous lens like bands produced by the compressed roots were very distinct at the 60 2100 psi 121 4 kg cm 2 stage but nearly disappeared at the 175 5000 psi 289 1 kg cm 2 stage this is explained as a result of differences in rates of coalification of the different telinitic precursors in the roots multilinear vitrinization and could explain why roots are significant components of many modern peats and ancient coal ball concretions but are difficult to recognize in bituminous coals similarly separation of cuticles from leaves in modern peat forming environments due to irreversible shriveling and subsequent enhanced microbiological decay partially explains why leaf remains are also difficult to recognize in most coals even those with abundant cutinites microcracks developed in all pellets with dominant orientations of cracks being either perpendicular to induced banding or horizontal to it minute vertical microcracks interpreted as dewatering features were observed primarily in gelinitic bands especially in the most fire prone cladium coal facies but these rarely extended into juxtaposed microlithotypes as did most of the larger vertical cracks horizontal cracks tended to form at microband boundaries almost all humotelinitic and humocollinitic precursors showed some changes in color during artificial coalification with humotelinites exhibiting less or slower changes than humocolinites or humodetrinites finer grained matrix material additionally nearly all dark brown degraded tissues in the peats became dark orange or red during coalification but many of these tissue masses were observed to contain significant amounts of minute inertinite derived from microorganisms pseudomicrinite that only became prominent after coalification and subsequent change in color of surrounding macerals fusinite precursors were only found in the fire prone cladium facies and although the coalified doming generated cyrilla facies exhibited evidence of significant drying events i e occasional bands or parts of bands containing significant pseudomicrinites macrinites and sclerotinites it was dominated by huminitic vitrinitic components liptinites were most common in the coalified dome formed cyrilla facies and displayed a slight qualitative increase in red green fluorescence during coalification and some possible flow of components into nearby cracks changes in mean random reflectance of huminitic macerals although still requiring more data and only measured to the 60 c 2100 psi 121 4 kg cm 2 level indicated increasing directions of change during artificial coalification with humocollinitic macerals progressing from an average of about 0 21 to 0 32 and humotelinitic macerals which consistently had lower inherent reflectances in the peats progressing from 0 15 to 0 25 the above petrographic results along with previously reported chemical results all suggest that the methods that we have used in these experiments have produced changes that might reasonably be expected to occur during natural coalification despite the fact that we have speeded up the process although more work needs to be done to verify and refine these results and to establish a correlation between these artificial coalification steps and true coalification the new observations and conclusions from these studies might still be helpful in constructing models to predict or interpret coal seam characteristics and to establish the timing and release potential of gaseous or liquid hydrocarbons from coals

the micromorphology of younger dryas aged black mats from nevada arizona texas and new mexico abstract black mats are organic rich sediments and soils that form in wet environments associated with spring discharge micromorphological and geochemical analyses of 25 black mats dating to the younger dryas chronozone 12 9 11 7 ka and early holocene were conducted to determine their composition and depositional environment samples were collected from arizona new mexico texas and nevada micromorphological analyses were conducted on thin sections using polarized and blue fluorescent light these analyses determined that black mats contain humic acids fine 5 20 m plant fragments diatoms phytoliths and gastropods the dominant type of organic matter in black mats is derived from herbaceous plants contradicting previous studies that supported algal or charcoal sources differences in the micromorphological characteristics of the samples revealed that black mats formed as three different types organic horizons moist soils and ponded sediments depending on their topographic position in relation to the water table the microscopic evidence found in black mats supports the presence of widespread wet environments in nevada and arizona during the younger dryas chronozone clearly indicating a sustained period of greater effective moisture optimal for spring discharge and black mat formation

organic matter in a coal ball peat or coal chemical analyses of morphologically preserved organic matter in a carboniferous coal ball reveal that the material is coalified to a rank approximately equal to that of the surrounding coal hence the plant tissues in the coal ball were chemically altered by coalification processes and were not preserved as peat

middle pleistocene age of the fossiliferous sedimentary sequence from tarija bolivia abstract the highly fossiliferous sediments of the tolomosa formation from tarija southern bolivia represent one of the most important localities in south america that documents the great american biotic interchange over the past several decades chronostratigraphic studies have indicated a middle pleistocene age for the tolomosa formation from 1 1 to 0 7 ma this interval correlates to the ensenadan south american land mammal age as it is characterized from classic localities in argentina recently however a new interpretation based on ams 14c ages indicates that the fossiliferous sediments from tarija are latest pleistocene i e

changing patterns of pennsylvanian coal swamp vegetation and implications of climatic control on coal occurrence abstract improved regional and interregional stratigraphic correlations of pennsylvanian strata permit comparisons of vegetational changes in euramerican coal swamps the coal swamp vegetation is known directly from in situ coal ball peat deposits from more than 65 coals in the united states and europe interpretations of coal swamp floras on the basis of coal ball peat studies are extended to broader regional and stratigraphic patterns by use of coal palynology objectives of the quantitative analyses of the vegetation in relation to coal are to determine the botanical constituents at the peat stage and their environmental implications for plant growth and peat accumulation morphological and paleoecological analyses provide a basis for deducing freshwater regimes of coal swamps changes in composition of pennsylvanian coal swamp vegetation are quire similar from one paralic coal region to another and show synchrony that is attributable to climate paleobotany and paleogeography of the euramerican province indicate a moist tropical paleoclimate rainfall runoff and evapotranspiration were the variable climatic controls in the distribution of coal swamp vegetation peat accumulation and coal resources in relative terms of climatic wetness the pennsylvanian period is divisible into five intervals which include two relatively drier intervals that developed during the lower middle and middle upper pennsylvanian transitions the climate during early pennsylvanian time was moderately wet and the median in moisture availability early middle pennsylvanian was drier probably seasonally dry wet late middle pennsylvanian was the wettest in the midcontinent early late pennsylvanian was the driest and late late pennsylvanian was probably the wettest in the dunkard basin the five climatic intervals represent a general means of dividing coal resources within each region into groups with similar botanical constituents and environments of peat accumulation regional differences in basinal geology and climate were significant variables but the synchronous control of paleoclimate was of primary importance

occurrence and morphology of carbonate concretions in the beulah zap coal bed williston basin north dakota carbonate concretionary bodies were encountered during mining of the beulah zap lignite seam in the coteau properties freedom mine mercer county north dakota preliminary studies show that areal and vertical distribution of the concretions are variable all concretions examined are composed almost entirely of calcite they occur as thin tabular bodies as more or less elliptical forms or as tear shaped bodies and may occur individually or as clusters of buff colored poorly consolidated to solidly crystalline material the carbonate masses vary in size from a few millimeters to tens of centimeters bedding in the lignite may display some compactional folding over dense spheroidal to elliptical concretions indicating formation of the concretions prior to compaction internal morphology of the concretions is complex and includes cone in cone structure cross cutting calcite veinlets and multiple generations of calcite carbon isotope values suggest the concretions are composed of biogenic carbonate probably related to early diagenesis and decomposition of organic matter peat oxygen isotope values are light and consistent with a freshwater origin

middle pleistocene climate change recorded in fossil mammal teeth from tarija bolivia and upper limit of the ensenadan land mammal age fossiliferous middle pleistocene sediments of the tarija basin of southern bolivia contain a classic ensenadan land mammal fauna new carbon isotopic data reported here for 50 specimens of the grazing mammals equus horse and cuvieronius mastodon documented from eight stratigraphic levels at tarija vary significantly in the 13c values of their teeth the pattern of variation appears to reflect the proportion of c3 and c4 grasses eaten during colder more c3 and warmer more c4 times within age limits set by associated magnetostratigraphy the cold periods can be correlated with particular even numbered stages in the marine oxygen isotope record and the warm periods can be correlated with odd numbered stages the oldest fossil teeth analyzed from the tarija section can thereby be assigned to stage 29 and the youngest to stages 17 or 15 that is the teeth range in age from about 1 1 myr to as young as 0 7 myr based on correlation of the upper part of the tarija beds to the isotopic stages the upper limit of the ensenadan land mammal age is between 0 7 and 0 6 myr which is younger than stated in most previous studies

behavior of inorganic constituents during early diagenesis of peats abstract extensive diagenetic changes occurring in peat during burial to approximately 1 5 km may result in the formation of lignite or medium brown coal examination of available literature indicates very little research dealing specifically with the behavior of inorganic non carbon based compounds during this early postburial diagenesis because these inorganic constituents determine both the quantity and quality of ash in coals and may act as potential diagenetic agents in associated rocks their behavior throughout the peat to lignite transformation is potentially important in several areas of study laboratory simulations of the early postburial diagenesis of peat offer a new approach for the study of such processes in the present research laboratory simulations have been used to study diagenesis of several well characterized peats during the experimental runs approximately 80 g of peat were compressed and heated in a ptfe lined reaction cell from atmospheric conditions to 2100 psi and 60 c thus approximately simulating conditions necessary for the formation of lignite pressure and temperature were increased on a stepwise pattern and prior to each increase expelled solution from the previous interval was collected following completion of each experimental run the residual solid plug was extracted from the cell intact extensive reorganization of organic compounds in the produced residual solids during laboratory simulations was documented by rollins et al 1991 in addition extensive petrographic changes can be observed including increases in gelatinous material darkening of colors and increases in reflectance concentrations of major inorganic constituents na k ca and mg released in solution are typically constant or decrease with increasing pressure and temperature for high ash peats whereas minor inorganic concentrations fe cu zn mn and al increase occasionally reaching a maximum and then decreasing with low ash peats concentrations generally are much lower than high ash peats and both major and minor inorganic concentrations typically increase throughout the experimental runs for all peats the ratio of major to minor inorganics decreases the general behavior of inorganics during the diagenesis of these peats is strongly related to the composition of the original peat and to the stage of alteration in addition organic acids including acetic and others are present within the solutions these organic acids may act as organic complexors and thus contribute to the mobilization of inorganic constituents

stable carbon and oxygen isotopic evidence for late cenozoic environmental change in northern china abstract stable carbon and oxygen isotope ratios of 311 enamel samples from a diverse group of herbivorous mammals including equidae rhinocerotidae bovidae rodentia and ochotonidaewere were analyzed in order to reconstruct the late cenozoic history of vegetation and environmental change in the yushe basin in north china the 13c values of bulk and serial enamel samples from large mammals show a wide range of variation from 13 3 to 1 4 with a mean of 7 4 3 5 n 294 this indicates that large herbivorous mammals in the area had a variety of diets since 6 5 ma ranging from pure c3 to mixed c3 c4 and pure c4 diets in contrast the 13c values of small mammals vary from 11 9 to 7 6 with a mean of 9 7 1 1 n 17 indicating that rodents and ochotonids were feeding mostly on c3 plants variations in 13c values within and between species reflect the variations in the habitat and the vegetation consumed by the animals in general horses had higher amounts of c4 grasses in their diets than other contemporary taxa such as bovids rhinos rodents and deer suggesting that horses exploited more open habitats such as grasslands while deer rhinos and rodents may have preferred more c3 vegetation which is more indicative of forested environments the carbon isotope data show that c4 grasses have been an important component of horses diets and of local ecosystems since 6 5 ma confirming that the late miocene c4 expansion occurred in north china as it did in africa indian subcontinent and the americas this supports a global factor as a main driver of the late miocene c4 expansion the combined carbon and oxygen isotope data reveal major shifts in climate to drier and or warmer conditions after 5 8 4 1 3 3 and 2 5 ma and significant shifts to relatively wetter and or cooler conditions after 6 4 5 3 5 ma the shifts to drier and or warmer climate after 5 8 ma and 2 5 ma coincide with two major fauna turnover events intra tooth 13c and 18o values are negatively correlated within individual modern teeth and some fossil teeth displaying the characteristic pattern of the summer monsoon regime and confirming a strong monsoon influence in the area since at least the early pliocene the data also suggest that the c4 abundance in the area has fluctuated over the past 6 5 ma in response to changes in climate with more c4 grasses during warmer and or drier periods and a reduced c4 component at cooler and or wetter times

stable isotopes in pocket gopher teeth as evidence of a late matuyama climate shift in the southern rocky mountains abstract previous work in the san luis valley of south central colorado and northern new mexico at the hansen bluff and sam cave localities has allowed reconstruction of the paleoclimate in the region during the interval from 0 6 myr to 2 6 myr surface exposures at hansen bluff have been correlated to deep sea oxygen isotope core stages 18 23 and one of the glacial periods contained therein to the oldest nebraskan till in southwestern iowa deposits in sam cave correlate to hansen bluff on the basis of paleomagnetics climate interpretation and microtine rodent biochronology in this paper carbon and oxygen stable isotope data of herbivorous rodent teeth are used as indicators of change in the predominance of c3 c4 and cam plants and of changes in temperature and precipitation taken together with other previously analyzed data from these localities the evidence indicates a shift in the severity of glacial events that is mainly related to the hydrologic characteristics of the climate this shift may have been caused by broad regional uplift that may have been instrumental in shifting global climate cycles from the 41 000 yr matuyama cycles to the brunhes 100 000 yr dominated cycles

stable carbon and oxygen isotope analysis of fossil tooth enamel using laser ablation abstract a technique is described whereby the 13c and 18o values of fossil tooth enamel can be measured in situ using laser ablation techniques the laser heats the sample and forms co2 from structural carbonate apatite the 18o values obtained with this method are equal to those of the phosphate oxygen due to the high temperature of reaction during ablation analytical precision is approximately 0 5 for both 13c and 18o the spatial resolution is 200 m or less which may be reduced as the technical modifications are made this method allows the analysis of samples that previously could not be analyzed due to difficulty with sample preparation size or rare nature the apparent oxygen isotope fractionation between the carbonate and laser derived oxygen co3 laser is 1 0071 for biogenic apatite at 38 c determined using the in situ laser comparison of 18o co3 and 18o laser analyses with 18o laser and 18o po4 results suggest a fractionation factor co3 po4 of 1 0083 variations in the 18o and 13c values of single teeth can be easily determined with the in situ technique this will allow the study of changes in diets or water sources during the period of tooth growth which for larger mammals can be several years for the tooth row the 13c and 18o values are important in paleodiet and paleoecology studies they can be used to study resource partitioning within an ecosystem and can shed light on the life history strategies within living and extinct species

shifting of the kosi river northern india the kosi river shifts laterally over the himalaya foreland plain by continual minor cutoffs and bank cutting and by episodic major shifts across watersheds by moving into and then out of preexisting adjacent less actively aggrading streams migration is unidirectional because after a channel is filled to instability floodwater will drain preferentially into a new adjacent low rather than across it to the next watershed or back to the last abandoned channel major shifts seem stochastic and autocyclic they do not correlate with the many severe quakes and floods that undoubtedly helped prime the system for shifts

preliminar correlation of the pleistocene sequences of the tarija valley bolivia with the pampean chronological standard most of the mammal collections of the pleistocene from the tarija valley bolivia lack precise stratigraphic data some fossil collections were made under stratigraphic control but have not been described however mammals were used for correlation and comparison with the pattern established for the pampean region of argentina the bearing units have been referred either to the ensenadan and bonaerian stages the belgranan the ensenadan or the lujanian in a broad sense corresponding to the middle upper pleistocene or the upper pleistocene studies during the last twenty five years accomplished by american authors and based on magnetostratigraphy and absolute dating suggest that the tarija sequence corresponds to the ensenadan early middle pleistocene of the pampean standard recently italian scientists based on radiometric dating discarded this age and considered that the whole sequence belongs to the late pleistocene new biostratigraphic and systematic studies allowed the recognition of glyptodon munizi arctotherium angustidens and hippidion devillei exclusive taxa of the mesotherium cristatum biozone the biostratigraphic base for the ensenadan of the pampean region however collections include mostly putative endemic species or those characteristic of the equus amerhippus neogaeus biozone the biostratigraphic base for the lujanian of the pampean area in sum from a biostratigraphic point of view the tarija sequence has taxa from the lower to middle pleistocene ensenadan and the upper pleistocene lower holocene lujanian of the pampean area from a paleofaunistic standpoint the association recovered from the tarija valley shows significant differences with the typical pampean association the high frequency of remains of gomphotheriidae and equidae and in lower proportion of hydrochoeriidae and tapiridae are noteworthy members of these two latter families are restricted today to warm and wet climates most glyptodontidae records belong to glyptodon and in the pampean region this family is much more diversified

cold climate fluvial to paralic coal forming environments in the permian collinsville coal measures bowen basin australia abstract the middle permian collinsville coal measures of the northern bowen basin illustrate a range of cold to cold temperate coal forming environments cold climate is indicated by glossopteris flora in the coal measures and by restricted marine fauna dominated by brachiopods and bryozoa in correlative marine sequences of the back creek group which contains also abundant lonestones dropstones sedimentation was characterised by an overall transgression interrupted by local fluvial and coastal progradation in a shallow epicontinental sea during a relatively quiescent tectonic period six sedimentary environments are represented fluvial fluvio paralic barrier strandplain back barrier tidal flat and open marine the basal coal formed from peat of swamps of abandoned areas of gravelly braided streams and is massive dull and with high ash 20 low sulphur 1 contents overlying coals developed from peats formed in fluvio paralic and paralic environments and thicker seams are generally brighter with low to moderate ash 8 17 and moderate to high total sulphur 1 6 contents seams associated with fluvial influence show splits and high ash yield while seams associated with coastal deposits show high sulphur levels up to 21 in contrast to reported models of coal forming environments no clearly defined deltaic or inter distributary bay fill sequences were identified in the area studied rather vast freshwater wetlands backed low gradient progradational coasts locally having bars and barriers the barriers were not prerequisites for substantial peat accumulation although may have locally assisted peatland development by raising the profile of coastal equilibrium

some observations regarding the potential effects of doming of tropical peat deposits on the composition of coal beds abstract several important concepts relative to the origin of coal beds can be gleaned from studies of modern domed and planar peat deposits in tropical subtropical settings these are 1 laterally some portions of a single continuous peat deposit may be domed and some portions may be planar 2 domed deposits are most often found to have begun as planar deposits 3 domed formed peat facies may be overridden by planar formed peat facies due to such factors as sea level rise and or increased rate of local and basinal subsidence 4 domed peat facies tend to have less mineral matter and contain fewer inorganic splits than planar facies 5 sulfur intrusion from marine waters can be retarded by doming allowing low sulfur peats to form relatively near to the coastline 6 marine transgression can cause high sulfur marine influenced planar peat facies to override freshwater domed or planar facies resulting in enrichment of the upper parts of these underlying facies in sulfur and ash 7 dome formed peat facies tend to be thicker and more uniform in composition than planar formed facies with dome formed peat facies having the potential to produce the more uniform bright coal types clarains and vitrains and planar formed peat facies often producing duller coal types and or alternating durainic inertinite rich and vitrainic wood derived bands 8 actively developing peat domes in wet settings often exhibit no appreciable increase in inertinitic material toward their tops although the tops of either domed or planar peat deposits can be enriched in inertinitic material if the water table is lowered by either local or regional changes in hydrology or climate

magnetic polarity stratigraphy of the middle pleistocene ensenadan tarija formation of southern bolivia abstract the tarija formation of southern bolivia which is well known for its classic vertebrate faunas is of prime importance in understanding of the chronology of the ensenadan land mammal age this formation consists of well exposed and relatively fossiliferous sections of clays clayey silts sands gravels and tuffs which were deposited in a predominately fluviatile regime in a pleistocene structural basin four stratigraphic sections each measuring 110 m or less were studied to establish a magnetic polarity stratigraphy paleomagnetic samples were collected from the finer grained sediments at 100 sites spaced at stratigraphic intervals of 5 m or less all paleomagnetic specimens were demagnetized in alternating fields of least 250 oersteds oe some specimens were also thermally demagnetized at 200 c or more of the 100 sites 77 were ultimately used to determine the magnetic polarity zonation based on the four sections sampled the tarija formation spans a time interval from about 1 my to about 0 7 my b p or perhaps younger the lower half of the composite section is of reversed polarity punctuated by a short normal event this sequence probably represents the late matuyama chron with the jaramillo subchron the upper part of the section is of normal polarity and represents early brunhes time a tuffaceous unit 43 m above the brunhes matuyama boundary yielded a fission track zircon age of 0 7 0 2 by b p these data indicate that the classic tarija fauna is middle pleistocene ensendan in age

climate and humans set the place and time of proboscidean extinction in late quaternary of south america abstract the late quaternary extinctions have been widely debated for a long time but the varying magnitude of human vs climate change impacts across time and space is still an unresolved question here we assess the geographic range shifts in response to climate change based on ecological niche models enms and modeled the timing for extinction under human hunting scenario and both variables were used to explain the extinction dynamics of proboscideans during a full interglacial glacial cycle from 126 ka to 6 ka in south america we found a large contraction in the geographic range size of two proboscidean species studied cuvieronius hyodon and notiomastodon platensis across time the largest contractions of their geographical ranges occurred in the northern part of south america where we previously reported no evidence of coexistence among earliest humans and non sloth megafauna including proboscideans our results herein support a strong effect of climatic changes on geographical range dynamics of proboscideans throughout late quaternary although this does not fully support climate change as the single cause of their extinctions we show that both proboscideans were narrowly distributed on scattered patches of suitable habitats i e refugia around 11 ka period in which the earliest humans potentially arrived in south america increasing the population density thereafter under this overall unsuitable climatic condition at 11 ka both proboscideans would be extinct after around 550 years of human hunting but if climatic conditions were suitable like in last glacial maximum lgm the time for extinction would be at least 3 times longer under the same human hunting pressures thus our findings support the broken zig zag model and show that south american proboscideans might have been completely extinct due to human impacts during periods of climate crisis we conclude in agreement with an increasing body of evidence in the recent literature that the late quaternary megafaunal extinction event was the result of additive effects from different stressors and that the relative magnitude of these impacts vary across space and time indeed climate changes set the place where the proboscideans were extinct in south america whereas the humans set the time of these extinctions

middle triassic paleosols and paleoclimate of antarctica abstract the lashly formation in the allan hills of southern victoria land antarctica is now at a latitude of 76 s and during the middle triassic was at least 70 s the combined evidence of fossil roots and soils indicates a paleoclimate unusual for such a high latitude temperate paleotemperature is indicated by roots logs and leaves of woody plants and the degree of chemical weathering and clay formation within the paleosols paleosols of the lashly formation are more like soils of southern sweden than those of either finland or southern europe silt infiltration structures around root traces and in cracks within the paleosols are evidence for a seasonally snowy climate but there is no evidence of ice wedges or other permafrost features in the paleosols other evidence of climatic seasonality includes well defined growth rings in fossil wood and abscission scars at the base of fossil leaves diverse broadleaf plants and noncalcareous paleosols indicate a humid climate with mean annual precipitation of about 1200 mm such a wet climate is anomalous for the interior of the supercontinent of pangea and such a warm and mildly seasonal climate is anomalous for such high latitudes this paleoclimatic anomaly may be a lingering effect of global greenhouse initiated at the permian triassic boundary paleoclimatic variables calculated here may be useful for recalibrating global paleoclimatic models for the middle triassic

geological geotechnical characterisation of sarapui ii clay abstract the paper presents the geological geotechnical characterisation of the very soft organic plastic slightly overconsolidated sarapui ii clay dissipation tests showed no artesian pressure in the deposit the organic content is in the range 5 18 the higher values to 3 m depth nacl content increases almost linearly with depth from 7 g l at 1 m depth to 24 26 g l at 6 m depth kaolinite is predominant throughout the profile increasing almost linearly with depth however smectite has almost the same percentage until 3 5 m depth the plasticity index varies in the range 60 170 and may be directly related to the clay minerals g o values decrease with depth from 14 28 mpa to 1 mpa at 3 m depth then increase with depth reaching 5 mpa at the bottom of the very soft material vane test results indicated two regions of s u versus depth the first from 1 m to 5 m depth with s u in the range 8 12 kpa the second from 6 m to 8 m depth with s u in the range 16 18 kpa there is a trend of linear increase in sensitivity with depth from 4 5 at 1 m depth to 7 9 at 7 m depth salt content does not seem to play a major role in the sensitivity of sarapui ii clay

palaeomagnetism of late cenozoic fossiliferous sediments from barranca de los lobos buenos aires province argentina the magnetic age of the south american land mammal ages abstract palaeomagnetic data for a sequence of late cenozoic sediments exposed at bajada martinez de hoz and el muelle barranca de los lobos atlantic coastal area buenos aires province are reported the sequence comprises sediments assigned to the chapadmalal formation montehermosense land mammal age barranca de los lobos vorohue and san andres formations uquiense land mammal age miramar formation ensenadense land mammal age and arroyo seco and arroyo loberia formations lujanense land mammal age the magnetostratigraphy recorded in the sequence suggests a brunhes magnetic age 3 15 ma for the chapadmalal formation it also suggests a brunhes to late matuyama magnetic age for the lujanense land mammal age a matuyama magnetic age for the ensenadense land mammal age a gauss magnetic age for the uquiense land mammal age and an early gauss to gilbert magnetic age for the montehermosense land mammal age finally the results obtained suggest that the panama isthmus was formed at an age earlier than 3 0 ma possibly 4 0 3 5 ma ago

a ground water mixing model for the origin of the imini manganese deposit cretaceous of morocco the imini deposit just south of the atlas mountains of morocco consists of three beds of manganese oxide ore in a slightly deformed dolomite unit about 10 m thick of cenomanian turonian late cretaceous age the dolomite host is sugary textured massive and permeable dolomite occurs as nearly euhedral rhombs each ore bed is about a meter thick and consists almost entirely of intergrowths of pyrolusite and hollandite family minerals bao up to 11 and pbo up to 28 with a flattened geode structure overlying the ore beds are solution collapse breccias with dolomite clasts janggunite mn fe oxide and dolomite matrix and pyrolusite hollandite calcite cement the ore solution collapse breccia and coarsely recrystallized pure dolomite are coextensive a zone only 400 to 1 000 m wide but 25 km long and elongate east northeast west southwest diagenetic features of the deposit are recrystallized texture of the dolomite flattened geode structure of the ore solution collapse breccia and associated draped laminae of the insoluble residues fossil replacement by mn oxides and zoned chert nodules with inclusions a mineralogic paragenesis shown independently in each of these features from older to younger is 1 precursor carbonates 2 dolomite janggunite and 3 hollandite pyrolusite chert calcite diagenesis probably occurred during the late cretaceous in a mixing zone of fresh and saline ground water as similar diagenetic sequences without manganese deposits are widely reported to have formed in such environments carbon and oxygen isotope compositions of carbonates and oxygen isotope compositions of chert show that an increasing component of fresh meteoric ground water was present as diagenesis proceeded falling sea level allowed the mixing zone to occupy various positions within the carbonate unit and convert the primary calcareous carbonate rocks to dolomite with chert nodules anoxic seawater is known both worldwide and from the local depositional basin atlas gulf in the cenomanian turonian this is believed to be the key to manganese deposition because anoxic conditions greatly enhance manganese solubility two specific versions of the mixing zone model are presented for manganese deposition one in which a primary sedimentary manganese precipitate formed along margins of the anoxic basin and was recrystallized during diagenesis in the mixing zone and the other in which anoxic saline ground water brought manganese into the mixing zone where it precipitated

correlation of late cenozoic sequences of southeastern buenos aires province biostratigraphy and magnetostratigraphy abstract correlations among stratigraphic sequences of the continental late cenozoic of southeastern buenos aires province have been historically based on lithostratigraphy and paleontological content recent magnetostratigraphic studies supplied new evidence which together with biostratigraphy allowed improvement of the chronostratigraphic framework recent studies were conducted at four localities of southeastern buenos aires province playa santa elena punta hermengo mar del sur and centinela del mar the studied sequences at santa elena and mar del sur show normal magnetic polarity while punta hermengo and centinela del mar display levels of reverse polarity discontinuities in the sequence of mar del sur might explain the absence of sediments of reverse polarity thus some units the lower ones could correspond to the normal magnetic events c1r1n and or c2n as the fossil fauna collected here has no typical pliocene components that could suggest an age older than the gauss matuyama boundary i e 2 58 ma the basal levels of the profile at punta hermengo with reverse polarity display ensenadan fauna this may be the most recent section of c1r c1r1r 0 90 0 78 ma which took place after the normal jaramillo event c1r1n the lower unit of playa santa elena of normal polarity c1n bears mammal remains suggesting a late ensenadan age

tree growth at polar latitudes based on fossil tree ring analysis permineralized trunks and mature wood samples with well preserved growth rings are described and analyzed from the upper permian and middle triassic of the central transantarctic mountains this fossil wood is unique in that the plants lived in an environment with no modern analogue and exhibited luxuriant tree growth above 75 s paleolatitude ring width averages 1 69 2 3 mm with maximum width of 6 83 9 9 mm an order of magnitude larger than ring widths produced at near polar latitudes today tree rings in both the permian and triassic woods show similar structure consisting almost entirely of earlywood spring wood with between 0 12 of each ring classified as latewood summer wood the small amount of latewood 0 6 cells indicates a very rapid transition to seasonal dormancy probably in response to decreasing light levels at these paleolatitudes in order to accurately delimit the earlywood latewood boundary a comparison was done of classical dendroclimatological techniques and alternative techniques utilized primarily by paleobotanists analyzing fossil woods we found that classical wood anatomy techniques provided a more accurate explanation of wood development and tree growth for these high latitude samples the suggested cool temperate late permian glossopteris flora from this area differs substantially from the warm temperate middle triassic corystosperm flora leaf type dicroidium and very different paleoclimates have been reconstructed for these two time periods ring structure and wood growth from both sites however are very similar indicating that these plants were responding to the environment in very similar ways the structure of the tree rings including a large number of earlywood tracheids and a very low number of latewood cells provides evidence that growth at these polar latitudes was limited by light levels rather than water and temperature as occurs in modern high latitude forests these fossil tree rings have important implications for understanding woody shoot growth and cambial function at high latitudes during periods of global warmth 2007 elsevier b v all rights reserved