antarctic continental weathering changes during eocene oligocene cryosphere expansion clay mineral and oxygen isotope evidence we have analyzed clay minerals and oxygen isotopes over the eocene oligocene climate transition 33 8 32 5 ma in ocean drilling program site 689 maud rise antarctica distinct changes in clay mineral assemblages suggest major instability in the east antarctic climate for 0 7 m y during this time of general expansion of the antarctic cryosphere and cooling of the southern ocean increased illite abundance reflects enhanced physical weathering associated with cryospheric development nevertheless continued dominance of smectite indicates that chemical weathering continued to prevail during the early oligocene weathering was much more intense than in modern deglaciated areas the clay mineral data support evidence from marine sediments suggesting that continental and marine climatic conditions during the early oligocene were intermediate between relative eocene warmth and intense neogene cold the clay mineral variations during the transition reflect major changes in continental precipitation and related continental ice accumulation

depth to pedogenic carbonate horizon as a paleoprecipitation indicator comment and reply royer 1999 1 has recently used a large data set from the u s natural resources conservation service nrcs to reexamine the relationship between mean annual precipitation and depth to the calcic horizon in soils the extremely poor correlation between these variables in his nrcs data r2 0

chemistry of modern soils as a guide to interpreting precambrian paleosols precambrian paleosols are potentially one of our best sources of information about the composition of the atmosphere early in earth s history to be used this way however an alteration profile must be shown to be an in situ product of vadose processes data from modern soils show that the ratios of less mobile elements such as zr ti and al can be used as a preliminary screen to test for the in situ nature of a profile if the ti zr ratio departs from that of the host rock by more than 40 or the ti al ratio departs by more than 50 for moderate degrees of weathering then a significant allochthonous contribution to the profile is indicated this technique correctly separates in place from allochthonous horizons when applied to independent data from two modern profiles a review of published precambrian profiles identifies two often cited examples denison and pronto as suspect based on these criteria in the interpretation of paleoatmospheres it is also necessary to show that fe is controlled not b

the multiple impacts hypothesis for mass extinction a comparison of the late devonian and the late eocene abstract application of the lag time multiple impacts hypothesis poag 1997b palaios 12 582 590 poag et al 2001 columbia univ press to the late devonian leads to the prediction that the frasnian famennian pulsed extinctions were triggered by a rapid drop in global temperature that followed an impact produced anomalous warm interval which interrupted the global cooling trend from the middle devonian greenhouse to the early carboniferous icehouse in actualistic comparison with the late eocene the lag time multiple impacts hypothesis would predict that a frasnian interval of multiple impacts should have occurred between 367 7 and 366 7 ma the fact that three impacts the alamo siljan and flynn creek do occur either within this predicted interval or close to it in time is corroborative evidence that the lag time multiple impacts hypothesis may indeed provide the causal mechanism for the frasnian famennian mass extinction based on the application of the lag time multiple impacts hypothesis to the frasnian famennian mass extinction it is here suggested that future searches for evidence of impact events in the late devonian be concentrated in strata that occur in the frasnian transitans to early hassi zonal interval and not in strata immediately below or above the frasnian famennian boundary

equation for compaction of paleosols due to burial existing empirically derived compaction curves for marine sediments fail to estimate the compaction of paleosols flood plain sediments and peats as indicated by deformation of clastic dikes dinosaur footprints and sandstone paleochannels yet compaction estimates are vital to reconstructing paleoclimate and geochemical profiles of paleosols to modeling sediment accumulation rates of nonmarine rocks and to tectonic flexural modeling of molasse facies this paper presents a compaction equation and physically derived constants that make geologically realistic estimates of compaction of paleosols and other nonmarine sediments a protocol for the application of the equation is suggested that would allow the following equation to solve for burial compaction c as a fraction of original thickness given depth of burial d in km as c s i f e d k 1 this equation can be applied to nonmarine sedimentary rocks or paleosols given appropriate empirical data on the physical constants in the equation such as initial solidity s i initial porosity f and the corresponding curve fitting constant k data on physical constants useful for this equation are compiled here for a range of paleosol and nonmarine sediment types

investigation of the clay minerals composition of soils derived from basalt parent materials in the early miocene to early pleistocene on the arabian shield using multiple techniques implications for paleoclimatic conditions knowledge of clay minerals composition can be used to understand paleoenvironmental and or paleoclimatic conditions particularly for soils derived from volcanic parent materials that were subjected to diverse climatic conditions during pedogenesis in this study the clay minerals composition in soils developed from basaltic parent materials during the cenozoic mostly during the early miocene to early pleistocene in the harrats region of the arabian shield in saudi arabia were investigated forty seven clay samples were examined using selective dissolution analyses x ray diffraction xrd thermogravimetric analysis tg fourier transform infrared spectroscopy atr ft ir scanning electron microscopy sem and transmission electron microscopy tem to obtain a better understanding of the clay minerals developed in basaltic parent materials particularly under a dry hot environment the xrd results revealed that the clay mineralogy was dominated by smectite kaolin kaolinite halloysite and interstratified vermiculite chlorite vm ch with mica pseudo chlorite palygorskite and ca zeolites as minor components the tem provided strong evidence for the presence of allophane and imogolite which is in line with numerous previous studies on soils formed from basaltic parent materials the existence of poorly crystalline minerals in these soils was strongly supported by the selective dissolution analysis results the combined influence of paleoclimates and parent material is evidenced in the clay minerals in the studied soils the formation of smectite vm ch and chlorite minerals in the harrats soils could be attributed to the simultaneous effect of temperate paleoclimates that dominated the pliocene and the wet transition periods that occurred through the pleistocene into the mid holocene while the minor palygorskite and ca zeolites could be related to the dry conditions that started in the late holocene and persist to the present day additional studies regarding the clay mineral assemblages in similar geoenvironmental settings are highly recommend and should account for paleoclimatic conditions to provide a better understanding of the relationship between clay minerals and paleoclimates

the structure of the baltic shield region on the basis of dss and earthquake data the lithospheric models obtained for the baltic shield by using deep seismic soundings are discussed and results from different parts of the shield are compared with models achieved by the investigation of surface waves and of p to s converted waves the results are found to agree rather well with each other particularly with regard to the first interface at a depth of 10 15 km and the whole thickness of the crust c 40 km the macroseismic focal depth determinations of regional earthquakes are correlated with lithospheric structure the main maximum in the focal depth distributions of finnish earthquakes occur at a depth of 10 12 km the geographical distribution of the earthquake epicentres suggests several seismo active zones in the northern baltic shield one new finding in this field concerns the lapland zone which runs in a north westerly direction

depth to pedogenic carbonate horizon as a paleoprecipitation indicator an analysis of 1168 modern soil profiles from the u s natural resources conservation service yields no correlation between mean annual precipitation and depth to the top of the carbonate horizon r 2 0 03 p 0 001 parent material and soil texture both play negligible roles in this regression when combined with similar published studies n 1481 r 2 improves slightly r 2 0 31 p 0 001 caution is therefore advised in using this or any previously published regression for inferring paleoprecipitation from paleosols however in the combined data set carbonate horizon bearing soils correlate with a mean annual precipitation of 760 mm p 0 05 thus the presence vs absence of pedogenic calcium carbonate is a good indicator of paleoprecipitation above or below this value

cooler winters as a possible cause of mass extinctions at the eocene oligocene boundary the eocene oligocene boundary at about 33 7 myr ago marks one of the largest extinctions of marine invertebrates in the cenozoic period1 for example turnover of mollusc species in the us gulf coastal plain was over 90 at this time2 3 a temperature change across this boundary from warm eocene climates to cooler conditions in the oligocene has been suggested as a cause of this extinction event4 but climate reconstructions have not provided support for this hypothesis here we report stable oxygen isotope measurements of aragonite in fish otoliths ear stones collected across the eocene oligocene boundary palaeotemperatures reconstructed from mean otolith oxygen isotope values show little change through this interval in agreement with previous studies5 6 from incremental microsampling of otoliths however we can resolve the seasonal variation in temperature recorded as the otoliths continue to accrete new material over the life of the fish these seasonal data suggest that winters became about 4 c colder across the eocene oligocene boundary we suggest that temperature variability rather than change in mean annual temperature helped to cause faunal turnover during this transition

eocene vegetation and ecosystem fluctuations inferred from a high resolution phytolith record a thorough understanding of the ecosystem factors that can act as drivers of vegetation change an important factor for projecting impacts of future climate change requires adequately distinguishing between plant community changes that occur on the local scale or over ecological time scales and long term trends phytolith assemblages have the potential to provide this information but little work has been done so far to test their ability to do so in deep time we examined vegetation patterns inferred from phytoliths plant silica microfossils from a single section of the renova formation timberhills region montana dated to 39 2 3 ma late middle eocene the section is composed of fl uvial sediments overprinted by paleosols including alfi sols entisols inceptisols and composite paleosols phytolith assemblages from 27 paleosol samples were used to reconstruct a high resolution vegetation history for the area and were compared with paleosol data phytoliths are predominantly from forest plants and include tropical elements such as palms arecaceae and gingers zingiberales suggesting a paratropical forest the high resolution sampling records heterogeneous vegetation including shifts among closed forest moderately open forest forest gaps edges and woodland and grass dominated habitats grasses are interpreted as early open habitat plants tolerant of drier conditions but they appear to be replaced by forest vegetation with time resulting in poor correspondence between paleosol type and phytolith assemblage at some stratigraphic levels where paleosol morphology indicates a forest ecosystem and the phytolith assemblages indicate a changing grass forest mixture as a function of depth within the profi les this is the fi rst study that has used phytoliths to construct a high resolution record of vegetation from deep time and we demonstrate that dense sampling and multiproxy approaches to paleo environmental reconstruction are necessary to capture vegetation heterogeneity in time and across microhabitats

pedogenesis of spatially associated red and black soils in purna valley from semi arid region of central india abstract eight representatives spatially associated red and black soils in purna valley from the semi arid region of central india were studied through mineralogical micromorphological and geochemical investigations to infer pedogenic transformations during changing climatic phase the morphology of soils showed that dissected alluvial plains over the basaltic landforms consists predominantly of dark reddish brown to dark yellowish brown soils with iron calcium carbonate nodules typic haplustepts and lithological discontinuities typic ustifluvents whereas pediplains and alluvial plains have clayey dark brown sodic slickensided bss horizons enriched with caco3 nodules typic haplusterts buried natrustalf on alluvial fans and floodplains has strong brown natric btn horizons with distinct ferriargillans and abundant caco3 nodules ferriargillans in alfisols indicates prevalence of humid climatic phase in the past during which alteration of plagioclase feldspars to smectites could have occurred thereafter termination of humid phase and an onset of semi arid climatic phase had favored drier non leaching environment which has resulted in the preservation of smectites in vertisols the randomness in soils are expressed as entropy index which showed that physical mixing in subgroups of vertisols and sodium enriched argrillic horizons in alfisols were the indicators of altered pedogenesis at steady state the formation of caco3 pedogenic carbonates and the concomitant development of sodicity during arid climatic phase were indicators of strong alkalinity and base accumulation in soils as a mark of aridity in red and black soils of the valley the chemical index of alteration weathering index and entropy index were served as good indicators for assessing intensity of chemical weathering rate with respect to hydrology and topography the study demonstrates that how the morphological physical chemical mineralogical and micromorphological data were useful in assessing pedogenetic processes in spatially associated red and black soils of purna valley

paleopedology of the chadron formation of northwestern nebraska implications for paleoclimatic change in the north american midcontinent across the eocene oligocene boundary abstract the big cottonwood creek member is a newly recognized lithostratigraphic unit of the chadron formation of northwestern nebraska i measured 23 superimposed paleosol profiles within 29 m of strata exposed 0 4 km 0 25 mile east of the type section of the big cottonwood creek member at toadstool park in northwestern nebraska and recognized four main types of paleosols the paleosols are all well drained moderately alkaline to alkaline oxidized and range from weakly developed azonal ustifluvents to moderately and well developed paleustalfs and argiustolls with argillic and petrocalcic horizons based on changes in soil structure horizons root traces and geochemical trends these paleosols record a gradual change from humid forested conditions of the late eocene to more seasonal semi arid open range conditions leading up to the global climatic deterioration event of the early oligocene at 33 2 ma this interpretation is supported by associated changes in sedimentology fluvial architecture floras and faunas over this period of time the section at toadstool park is significant in that it establishes a link between the big badlands of south dakota and correlative deposits of wyoming the contact of the chadron and brule formations in the big badlands of south dakota is marked by an unconformity that is in part correlative to the earliest oligocene sediments that elsewhere record the global climatic deterioration event at 33 2 ma the paleosols of the big cottonwood creek member of northwestern nebraska fill in a significant part of this gap and record paleoclimatic conditions of the late eocene leading up to the global climatic deterioration event of the early oligocene using the latest lithostratigraphic biostratigraphic magnetostratigraphic and tephrostratigraphic data for the white river group this change to more arid conditions in the midcontinent appears to have progressed from west to east over time

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

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

coupling of marine and continental oxygen isotope records during the eocene oligocene transition while marine records of the eocene oligocene transition indicate a generally coherent response to global cooling and the growth of continental ice on antarctica continental records indicate substantial spatial variability marine eocene oligocene transition records are marked by an 1 1 foraminiferal 18o shift but continental records rarely record the same geochemical signature making both correlation and linking of causal mechanisms between marine and continental records challenging here a new high resolution continental 18o record derived from the freshwater gill breathing gastropod viviparus lentus is presented from the hampshire basin uk the solent group records marine incursions and has an established magnetostratigraphy making it possible to correlate the succession directly with marine records the v lentus 18o record indicates a penecontemporaneous higher magnitude shift 1 4 than marine records which reflects both cooling and a source moisture compositional shift consistent with the growth of antarctic ice when combined with clumped isotope measurements from the same succession about half of the isotopic shift can be attributed to cooling and about half to source moisture change proportions similar to marine foraminiferal records thus the new record indicates strong hydrological cycle connections between marine and marginal continental environments during the eocene oligocene transition not observed in continental interior records

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

cenozoic expansion of grasslands and climatic cooling abstract mountains ocean currents forests and swamps have played an important role in regulating global climate for hundreds of millions of years but the truly novel event of the cenozoic was the evolution and expansion of grasslands with their uniquely coevolved grasses and grazers neogene expansion of the climatic and geographic range of grasslands at the expense of woodlands is now revealed by recent studies of paleosols fossils and their stable isotopic compositions grasslands and their soils can be considered sinks for atmospheric co2 ch4 and water vapor and their cenozoic evolution a contribution to long term global climatic cooling grassland soils are richer in organic matter than are woodland and desert soils of comparable climates and when eroded their crumb clods form sediment unusually rich in organic matter grasslands also promote export of bicarbonate and nutrient cations to lakes and to the oceans where they stimulate productivity and c burial this increased productivity and

faunal stability during the early oligocene climatic crash abstract traditional neo darwinism views species as highly flexible entities which adapt to climatic change by gradually evolving new morphologies of the 177 species of mammals from the upper eocene lower oligocene 37 30 ma white river group in the high plains most species are static for 2 4 million years on average and some persist much longer only three examples of gradualism can be documented in the entire fauna and these are mostly size changes contrary to expectations most mammalian species show no change during the earliest oligocene climatic crash 33 2 ma in spite of the fact that the vegetation changed from dense forests to open forested grassland mean annual temperatures dropped 13 c and conditions got much drier and more seasonal only a few mammalian lineages speciated a few more went extinct and the vast majority 62 out of 70 persisted through this climatic event with no observable response whatsoever this evidence shows that organisms are much less responsive to the environment than short term neontological studies suggest

global aridity during the early miocene a terrestrial paleoclimate record from the ebro basin spain abstract paleosols are an important tool in the paleoclimatic and paleoenvironmental interpretation of continental deposits and can provide a high resolution proxy for paleoclimate results from geochemical climofunctions applied to early miocene strata exposed in the ebro basin spain demonstrate that mean annual precipitation was the dominant control on paleosol type and indicate that the paleoclimate was considerably wetter during the early miocene by up to 1150 mm yr 1 in comparison to modern values placing it in a subhumid climatic regime rather than an arid semiarid regime as previously suggested by sedimentological and paleontological approaches by making comparisons with published data on paleoclimate during the early miocene this article stresses the importance of regional climatic changes in global paleoclimatic interpretation

linking the wasatchian bridgerian boundary to the cenozoic global climate optimum new magnetostratigraphic and isotopic results from south pass wyoming new paleomagnetic and stable isotopic results from the northeastern margin of the greater green river basin south pass wyoming provide a refined geochronological context for the wasatchian bridgerian land mammal age boundary and suggest the existence of large amplitude milankovich scale carbon and oxygen isotopic oscillations in this area during the early eocene analysis of 55 paleomagnetic sites through a 310 m section of wasatch green river and bridger formations indicates several reversals that can be correlated to the geomagnetic polarity time scale using radiometric age constraints this correlation places the wasatchian bridgerian boundary in chron c23r at about 52 ma approximately two million years older than previous estimates this new correlation suggests that the mammalian turnover which characterizes the wasatchian bridgerian boundary is coincident with the onset of the cenozoic global climate optimum the warmest interval of the entire cenozoic intrabasinal magnetostratigraphic correlation supports earlier claims that community composition and biostratigraphic datums of basinmargin faunas can differ significantly from coeval basin center faunas oxygen and carbon isotopic composition of paleosol carbonates show in phase cyclic variations on the order of 6 and 3 5 respectively based on the preferred magnetostratigraphic correlation the four best defined cycles represent 397 thousand years indicating potential forcing by variations in orbital eccentricity oxygen isotopic variations may be tracking wet dry cycles amplified by adjacent changes in levels of paleolake gosuite carbon isotopic variations may be tracking the vegetative response to these climate variations alternative interpretations involve cyclic changes in pedogenesis driving correlated variations in isotopic inheritance from parent paleozoic carbonate material and the possibility that c4 plants existed in marginal habitats earlier in geological time than previously thought q 2001 elsevier science b v all rights reserved

evolution of cenozoic seaways in the circum antarctic region abstract a complete circum antarctic seaway did not open until both the south tasman rise cleared the oates land coast of east antarctica and drake passage opened between the southern tip of south america and the northern end of the antarctic peninsula major plate motions based on dated seafloor spreading anomalies and distinct fracture zone lineations constrain the age of the opening of a seaway between the south tasman rise and antarctica as very close to the eocene oligocene boundary with an unrestricted opening deeper than 2000 m dating from 32 ma timing of the opening of drake passage is more circumstantial because the exact motions of certain micro continental fragments are not known the motion of africa with respect to south america as well as the motion of east antarctica with respect to africa are well constrained for the cenozoic these major plate motions are used with the reasonable assumption of no cenozoic motion of the antarctic peninsula with respect to east antarctica to constrain the location of the antarctic peninsula with respect to the southern tip of south america for the critical period of late eocene to late oligocene uncertainty of motion of the south georgia and south orkney microcontinents and other possible continental fragments make an exact time for opening of drake passage difficult to ascertain even so the early oligocene position of the antarctic peninsula with respect to south america requires a through going deep water seaway to have been open at drake passage prior to 28 ma even given the unconstrained motion of various high standing crustal fragments in the scotia sea with reasonable assumptions concerning motion of the crustal fragments in the western and central scotia sea it is likely that drake passage or passage through powell basin was open to deep water circulation by 31 2 ma

temporal variations in plate convergence and eruption rates in the western cascades oregon new k ar age determinations on basalts basaltic andesites and ash flow tuffs from the central western cascades in oregon range in age from 32 to 3 ma the ages decrease from west to east and with increasing elevation volcanism has been continuous throughout the evolution of the western cascades with some periods of greater activity 13 16 ma 22 26 ma and 29 31 ma relative volume estimates indicate that eruption rates decreased by a factor of 6 from 35 ma to the present the eruption rates during formation of the western cascades volcanic arc were influenced by changes in the direction and rate of convergence between the farallon and north american plates we have developed a model of the tertiary convergence of these two plates based on the mantle fixed hotspot reference frame which indicates a factor of 5 decrease in convergence rate 16 0 to 3 2 cm a clockwise rotation of the western margin of the north american plate led to a decrease in the convergence angle since about 35 ma apparently slower more oblique subduction resulted in a decrease in the volume of erupted magmas

late oligocene bunch grassland and early miocene sod grassland paleosols from central oregon usa abstract fossil soils burrows and mammals of the upper john day formation in central oregon are evidence of bunch grasses and open semiarid vegetation as old as late oligocene earliest arikareean 30 ma root traces in these paleosols include both stout tapering tubes like roots of trees as well as sinuous filamentous tubes similar to roots of grasses paleosol structure is fine subangular blocky with patchy distribution of grass like roots as in wooded grassland and sagebrush steppe with bunch grasses cursoriality in horses mesohippus miohippus and hypsodonty in rhinos diceratherium is also evidence for open grassy vegetation trace fossils of pallichnus dung beetle boli and edaphichnium earthworm chimneys are characteristic of wooded grassland paleosols whereas taenidium cicada burrows dominates desert shrubland paleosols as has also been found in quaternary paleosols and soils of eastern washington in both oligocene and quaternary paleosol sequences arid shrubland and semiarid grassland paleosols alternate on milankovitch frequencies 23 41 100 ka the oldest known paleosols in oregon with crumb structure and abundant fine fossil root traces characteristic of sod grasslands are dated by mammalian biostratigraphy as hemingfordian early miocene ca 19 ma wooded grassland habitats are indicated by scattered chalcedony calcite rhizoconcretions from large woody plants and by fossil chalicotheres moropus camels gentilicamelus paratylopus and horses parahippus silty texture and silcrete horizons are evidence of semiarid to arid paleoclimate and are in striking contrast to highly calcareous and clayey underlying paleosols of the john day formation these silcrete paleosols may represent the miocene onset of summer dry mediterranean seasonality as opposed to a summer wet monsoonal pattern of seasonality found in this region during the oligocene oregon s early rangelands can be compared with those in the north american great plains granular structured calcareous paleosols of the brule formation of south dakota are evidence of dry bunch grasslands as old as 33 ma early orellan early oligocene and crumb structured paleosols of the anderson ranch formation of nebraska are evidence of sod grasslands as old as 19 ma late arikareean early miocene although grasses were a conspicuous part of dry rangelands well back into the oligocene early and middle miocene sod grasslands in north america were restricted to regions estimated to have had less than 400 mm mean annual precipitation

regional paleoprecipitation records from the late eocene and oligocene of north america abstract the marine 18o record indicates precipitous cooling or significant expansion of antarctic ice volume across the eocene oligocene epoch boundary at 33 7 ma this climatic step is also found in estimates of decreased paleoprecipitation from paleosols in oregon montana and nebraska but is only a part of a long term decline across the eocene oligocene transition rather than a sudden shift this suggests that climate was driven by a gradual process rather than a single perturbation paleoprecipitation levels stabilized during the oligocene coincident with a stabilization in 18o values possibly indicating a new climatic steady state

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

paleoclimatic estimates from tertiary leaf assemblages a primary obstacle to evaluating numerical modeling of tertiary nonmarine climates has been the significance and reliability of proxy data sloan barron 1990 lacking direct measurements of paleoclimatic parameters inferred paleoclimatic values are based on substitute proxy sources such as fossils or isotopes are proxy data significant that is have they been calibrated in modern environments and to what level is the calibration this is the problem of accuracy validity in the statistical sense second are the proxy data reliable can two workers or even the same worker consistently arrive at the same estimates using the same data set this is the problem of precision repeatability can these two problems be resolved quaternary palynologists have used the concept of transfer functions a methodology originally developed for foraminifera imbrie kipp 1971 applied in palynology a response surface for each palynomorph taxon is constructed for the environmental variables under consideration these transformations can then be subjected to a number of different kinds of multivariate analyses including ordination methodologies bartlein et al 1986 webb bryson 1972 these transfer functions can work for quaternary and especially the lateand post glacial of the last 20 to 30 thousand years pollen assemblages because in most regions where the methodology has been applied the flora is of known diversity and the equivalency of a given palynomorph species to one or a few extant species can be reasonably assumed even in the late neogene 1 5 to 10 million years ago however this assumption can no longer be made we know that the palynomorph assemblages contain exotic genera mccartan et al 1990 and the presence of exotic and or extinct species

a high resolution micromorphological record of the late quaternary paleosols from ganga yamuna interfluve stratigraphic and paleoclimatic implications abstract this study reports the micromorphological record of a continuous set of samples from paleosol bearing intervals of two subsurface cores of 50 m depth representing typical pedosedimentary sequences of the ganga yamuna interfluve in the western ganga plains micromorphology microstructures rhizocretes fe mn features pedogenic carbonate illuvial clay coatings and relict pedofeatures was used to characterize pedogenic processes in the 13 paleosols in the iitk core and the 10 paleosols in the bhognipur core formation of these paleosols took place through incipient to moderate weathering on relatively stable surfaces of the ganga yamuna interfluve over the last 100 ka these paleosols range in character from simple ones having weakly developed pedofeatures to mature paleosols with strongly developed pedofeatures and are similar to modern entisols inceptisols alfisols and vertisols of the ganga plains pedosedimentary evolution in the two interfluve successions differs in terms of stratigraphic stacking of paleosols types of paleosols and heterogeneous nature of sediments in the northern part the iitk interfluve core is marked by a thick mature paleosol with a strongly developed argillic bt horizon at 41 45 m depth and weakly developed paleosols in the remaining part of the core the mature paleosol represents a major discontinuity when prolonged pedogenic activity took place on stable surfaces with little or no deposition on the other hand thin simple thick cumulic paleosols with weakly developed pedogenic features even with some preservation of sedimentary laminations indicate short stratigraphic breaks in rapidly aggrading sediments in the southern part the bhognipur core is marked by the heterogeneous nature of sediments with a predominance of cratonic sediments in the lower part and the himalayan sediments in the upper parts in contrast the iitk core shows a himalayan source throughout the entire interfluve succession in the bhognipur region is marked by rapid sedimentation and short pedogenic intervals of weakly developed paleosols excepting one mature paleosol with well developed argillic bt and vertic bss horizons at 10 14 m depth this mature paleosol possibly formed synchronously with a mature paleosol from the northern part of this interfluve the mature paleosol in both the cores represents a major stratigraphic break of 8000 10 000 years when prolonged pedogenesis occurred over large areas of the ganga yamuna interfluve following regional degradation and local gullying in response to climate change from sub humid to semi arid conditions during the mis 5 4 transition

petrography and stable isotope geochemistry of oligocene miocene continental carbonates in south texas implications for paleoclimate and paleoenvironment near sea level abstract cenozoic sedimentary rocks in the southern texas gulf coastal plains contain abundant continental carbonates that are useful for reconstructing terrestrial paleoclimate and paleoenvironment in a region near sea level our field observations and thin section characterizations of the oligocene and miocene continental carbonates in south texas identified three types of pedogenic carbonates including rhizoliths carbonate nodules and platy horizons and two types of groundwater carbonates including carbonate cemented beds and carbonate concretions with distinctive macromorphologic and micromorphologic features based on preservations of authigenic microfabrics and variations of carbon and oxygen isotopic compositions we suggest these carbonates experienced minimal diagenesis and their stable isotopic compositions reflect paleoclimate and paleoenvironment in south texas our oligocene and miocene carbonate clumped isotope temperatures t 47 are 23 28 c slightly less than or comparable to the range of modern mean annual and mean warm season air temperature 21 27 c in the study area these t 47 values do not show any dependency on carbonate type or trends through time suggesting that groundwater carbonates were formed at shallow depths these data could indicate that air temperature in south texas was relatively stable since the early oligocene the reconstructed paleo surface water 18o values are similar to modern surface water which could indicate that meteoric water 18o values also remained stable since the early oligocene mean pedogenic carbonate 13c values increased 4 6 during the late miocene most likely reflecting an expansion of c4 grassland in south texas this study provides the first mid and late cenozoic continental records of paleoclimate and paleoecology in a low latitude near sea level region

the source and fate of massive carbon input during the latest paleocene thermal maximum lithologic faunal seismic and isotopic evidence from the blake nose subtropical western north atlantic links a massive release of biogenic methane 55 5 million years ago to a warming of deep ocean and high latitude surface waters a large perturbation in the combined ocean atmosphere carbon cycle the largest of the past 90 million years a mass extinction event in benthic faunas and a radiation of mammalian orders the deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming massive carbon input to the global exogenic carbon cycle pelagic carbonate dissolution a decrease in dissolved oxygen and a benthic foraminiferal extinction event these events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the blake nose as a site of methane release

possible regional tectonic controls on mammalian evolution in western north america abstract previous work has suggested that tectonically active regions act as speciation pumps for mammals and plant species but little is known about how fast or widespread tectonism must be in order to directly influence evolution here we use oxygen and hydrogen isotopic data from miocene sedimentary deposits to characterize the topographic evolution of the southern columbia plateau snake river plain and northern rocky mountain regions during the yellowstone hotspot passage with the ultimate goal of understanding whether topographic changes caused by the hotspot influenced mammalian evolution within those regions we conducted oxygen isotope analyses of 130 samples of lacustrine and paleosol carbonate from miocene stratigraphic sections that span much of the northern rocky mountain region and combined these data with previously published isotopic records collectively these isotopic data show that caldera formation associated with the yellowstone hotspot has modified regional topography and rearranged drainages along the track of the hotspot and that the hotspot has left a topographic depression in its wake we explore the extent to which these topographic changes influenced or are decoupled from diversity changes exhibited by the local mammal faunas and conclude that the passage of the hotspot and consequent surface uplift created rainshadows in the lee of high elevation calderas and or generated large volumes of volcanic materials influencing soils and vegetation collectively that may explain a possible rise in mammal diversity in the cp srp region at 14 ma coincident with a drop in diversity in the nrm it is still unclear however how different taphonomic pathways and sample standardization problems are influencing apparent diversity peaks at this temporal and geographic resolution

weathering flux and co2 consumption determined from palaeosol sequences across the eocene oligocene transition abstract rates of base cation depletion are determined for late eocene and early oligocene alluvial palaeosols pacific northwest of north america from pedogenic mass balance geochemistry and time estimates of palaeosol sequences pedogenic strain volume change and mass transfer of base cations silica and other pertinent elements are calculated from the geochemical differences between palaeosol horizons and parent material parent material compositions are determined by identification of the least altered alluvial strata in the sequence time spans of sequences of palaeosols are estimated from 40ar 39ar age dates of interbedded tuff beds and from time of formation estimates of palaeosols based on their degree of development palaeosol sequences from the mid latitude setting of central oregon document a significant decrease in the degree of weathering of individual palaeosols across the eocene oligocene transition as the climate became cooler and drier this decrease in the degree of weathering is accompanied by an increase in the accumulation rate of alluvial soils as indicated by sedimentation rates of stratigraphic packages according to these calculations and estimates the weathering flux of base cations in the john day basin measured in grams per 1000 years per square centimetre increased across the eocene oligocene transition these results when attributed to climate change indicate that weathering flux at this local increased as climate changed from warm humid late eocene conditions to cooler drier oligocene conditions furthermore the extrapolation of these weathering flux results to other mid latitude settings with similar climate change history may help to explain the severe climate change of the eocene oligocene boundary it is proposed that in some mid latitude settings greater quantities of less weathered silicate material were exposed during the early oligocene than during the late eocene thus causing an increase in flux of weathered product increased weathering flux during this time in certain regions of the mid latitudes may have increased both co2 consumption and bicarbonate transport to the ocean and contributed to atmospheric pco2 drawdown and global cooling

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

gradients in seasonality and seawater oxygen isotopic composition along the early permian gondwanan coast se australia abstract oxygen isotope compositions of marine carbonates are commonly employed for understanding ancient temperatures but this approach is complicated in the very distant past due to uncertainties about the effects of diagenesis and the isotopic composition of seawater both locally and globally microsampled accretionary calcite from two species of the fossil bivalve eurydesma sowerby and morris 1845 collected from sediments of cisuralian age in high latitude marine sediments along the se coast of australia records cyclic seasonal fluctuations in shell 18 o values during growth demonstrating the primary nature of the isotope signal and thus allowing investigation of early permian seawater isotopic composition and water temperature in the high southern latitudes the mean and seasonal range of 18 o carb decreases poleward across about 10 of paleolatitude 67 s 77 s the presence of co occurring dropstones and stratigraphically associated glendonites constrains winter temperatures across the region to near freezing thus permitting calculation of realistic estimates of water composition and summer temperatures summer 18 o carb values indicate water temperatures between 5 c and 12 c with warmer values at lower latitudes the decrease in both mean sea surface temperature and seasonal amplitude with increasing latitude on the gondwanan coast is much like that observed along high latitude coastlines today calculated 18 o water decreases toward the pole likely associated with an increasing contribution of isotopically light fresh water derived from summer snow melt the gradient in 18 o water is similar to that documented over a similar span of latitude on the modern se greenland coast we infer the presence of a north flowing coastal current of cold o 18 depleted water that entrains progressively greater amounts of more typical seawater as it moves away from the pole 18 o values in se australia however are about 3 lower than those off greenland suggesting comparatively lower salinity water or more o 18 depleted glacial ice runoff in the permian gondwanan high latitudes perhaps augmented by more depleted negative global average seawater conditions in southeastern australia during the largest of the permian deglaciations were warmer than present day antarctica at similar latitudes but may approximate those of early mid miocene antarctica with frozen winters but summers closer to 10 c