assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures though many studies on the mg contents in the calcitic tests of foraminifers exist the processes controlling its uptake are still a matter of debate laboratory cultures offer an excellent opportunity to reveal these mechanisms the mg concentrations within single chambers of the planktic foraminifer globigerinoides sacculifer brady maintained under controlled laboratory conditions were measured 1 at variable temperatures 19 5 29 5 c and constant salinity and 2 at variable salinity 22 45 and constant temperature the experimental results suggest that under natural conditions temperature is the leading mechanism controlling the mg ca ratio temperature and magnesium are related proportionally a temperature increase of ca 10 c gives rise to an increase of the magnesium concentrations of ca 130 drastic unnatural salinity changes dominate the effects of temperature a 110 change in the mg ca ratio was observed when salinity was elevated or reduced by more than ca 10 specimens which underwent gametogenesis reveal significantly higher mg concentrations than specimens that did not release gametes partition coefficients for mg in foraminiferal calcite are orders of magnitude lower than values from inorganically precipitated calcite when comparing observed mg ca ratios of foraminiferal tests with predicted mg ca ratios calculated according to empirical equations it becomes evident that foraminiferal tests are undersaturated with respect to mg for the water temperature they have experienced apparently foraminifers are capable of controlling their mg concentration the physiological processes presumably responsible for such depressed mg ca ratios appear to be temperature controlled as deduced from the close relationship of the observed mg ca ratios and water temperature this study demonstrates that variations in temperature and salinity are definitely reflected in the mg content of foraminiferal tests magnesium may thus serve as a paleo proxy for past surface water temperatures as long as postdepositional changes and salinity variations are of subordinate importance or can be excluded

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

quantitative reconstruction of middle and late eocene paleoclimate based on palynological records from the huadian basin northeastern china evidence for monsoonal influence on oil shale formation abstract the eocene was an interval of climate evolution when the extreme high temperatures of the earliest cenozoic gave way to a global cooling trend fine grained lacustrine sediments of eocene age from northeastern china represent an excellent archive to study long term environmental and climatic changes at high resolution the huadian basin is a cenozoic fault bounded basin in jilin province northeastern china though small in area it contains numerous oil shale and coal bearing layers which provide an abundant middle to late eocene palynoflora eighty five palynomorph genera and one hundred palynomorph species were identified in the huadian formation allowing to distinguish 4 palynozones the nearest living relatives of the recovered palynomorph taxa suggest the presence of subtropical evergreen and deciduous broad leaved forests during deposition of the huadian formation using the coexistence approach ca we calculated seven paleoclimatic parameters which indicate a subtropical warm and humid climate with a mean annual temperature above 13 6 c and a mean annual precipitation of at least 887 mm however the climate became cooler and drier during the transition from the lower oil shale member to the upper carbonaceous shale member palaeoclimatic data from the various middle and late eocene basins of northeastern china i e the huadian fushun yilan hunchun and jishu basins were compared with data from north american and european basins middle eocene climate in the northern hemisphere was generally warm and humid and the mean annual temperature and precipitation in northeastern china were similar to those in north america though slightly lower than those of europe similar trends in temperature and precipitation on different continents support the existence of a global mid eocene cooling event this paper is the first systematic study of middle to late eocene seasonality in the huadian basin our results show an apparent differentiation in both temperature and precipitation between summer and winter supporting the view that the east asian monsoon was established in northeastern china already during the middle to late eocene this middle and late eocene monsoon was likely driven by the development of pacific trade winds and an alternating seasonal high and low pressure system over siberia the climatic changes observed in our dataset especially the precipitation changes appear to have played an important role in controlling oil shale formation in the huadian basin a warmer and more humid climate with abundant precipitation and high subsidence rates formed a deeper huadian depositional lake high productivity and stable stratification provided the abundant organic matter and favorable preservation conditions necessary for oil shale accumulation

deformation pattern in a massive ponded lava flow at odp iodp site 1256 a core and log approach 1 a complete in situ section of upper oceanic crust from extrusive lavas through dikes into gabbros has been recently drilled for the first time in 15 ma old crust created at the superfast spreading east pacific rise epr the upper igneous basement cored at ocean drilling program odp integrated ocean drilling program iodp holes 1256c and 1256d consists of sheet flows and massive flows including a ponded lava flow unit lava pond interpreted as a thick lava flow delivered off axis and accumulated in a topographic depression fine scale structural analysis shows that the lava pond is much less fractured than the deeper lavas probably as the effect of structure spacing that is larger than in the underlying lava flows in hole 1256d structures are mainly subhorizontal in the lava pond and become steeper downhole toward the sheeted dike complex this reflects the distance of the lava pond from the stress field produced by the intrusion of dikes at depth inducing mostly subvertical eruptive fractures and fracture network and the distance of the site from active rifting at the epr contrasting structural patterns in the lava pond and in the deeper parts of the drilled section are reflected in contrasting physical properties patterns as obtained by shipboard and downhole logging data electrical resistivity compressional velocity and bulk density are generally higher whereas natural radioactivity and neutron porosity are lower in the lava pond than in the deeper hole the occurrence of a thick massive lava flow at the top part of the volcanic section affects the deformation pattern of the entire drilled crust and consequently its permeability regime which in turn controls the geometry and distribution of hydrothermal circulation and basalt alteration

late eocene palaeogeography of the proto paratethys sea in central asia nw china southern kyrgyzstan and sw tajikistan

stable isotopic evidence for relative and eustatic sea level changes in eocene to oligocene carbonates baldwin county alabama eocene to oligocene marine carbonate shelf deposits in a continuous core in baldwin county alabama were evaluated within a sequence stratigraphic framework to determine characteristic stable isotopic responses to inferred fluctuations in sea level due to a greater sampling density per unit of time stable isotopes in this core reveal more defined trends than have previously been reported from dsdp odp deep sea drilling project ocean drilling project records and from more land ward sections that have undergone intense sub aerial alteration or erosion the 18 o signature records eustatic sea level 18 o becomes heavier as eustatic sea level falls and lighter as eustatic sea level rises 18 o records a secular shift to heavy from the early eocene to oligocene of 3 0 the 13 c signature records relative sea level change paleobathymetry 13 c generally becomes heavier in shallower water deposits and lighter in deeper water deposits however in planktonic oozes 13 c may shift to heavy 13 c also records a secular shift to heavy from the early eocene to the oligocene of 3 5 although minor diagenetic perturbations in the stable isotopes are present the depositional signal dominates the isotopic signal spar cements generally result in lighter 18 o and 13 c if the dolomite is 20 dolomitization results in heavier 18 o and 13 c

cenozoic crustal shortening between the pamir and tien shan and a reconstruction of the pamir tien shan transition zone for the cretaceous and palaeogene the magnitude of the late cenozoic crustal shortening during convergence of the pamir and tien shan was determined using a contemporary pattern consisting of facies zones palaeomagnetic data regarding the rotation of tectonic units and data on the structure of the tadjik depression by late cenozoic cretaceous and palaeogene facies zones were cut by the vakhsh trans alay overthrust and darvaz strike slip faults and a significant part of the cretaceous palaeogene tadjik basin was overthrust by the pamir massif the sediments of easternmost part of the basin are preserved in the tarim depression the facies zones of the southern slope of the afghan tadjik basin were deformed and moved northward a pattern of facies zones indicates a convergence between the pamir and tien shan over a distance of 300 400 km a number of cross sections through the tadjik depression were used to establish the structure before folding a rotation of tectonic units indicated by structural data conforms to the angles of rotation as determined in palaeomagnetic studies the data suggest 300 km of convergence between the pamir and tien shan stratigraphic lithological structural and palaeomagnetic data formed the basis for the construction of the palinspastically restored palaeogeographic and sedimentologic environments for the tadjik shallow sea basin which was situated between the pamir and tien shan before their convergence in the late cenozoic the maps were constructed for the eight stratigraphic levels of the cretaceous and palaeogene the tadjik sea was a bay in the enormous turan sea in the early aptian this bay was located in what is now the afghan tadjik basin in late cretaceous the eastern shore of the bay lay 600 700 km further eastward and in the eocene marine environments extended even further eastward but after the rupelian continental environments occupied all of this region 2000 elsevier science b v all rights reserved

assessing the reliability of holocene relative palaeointensity estimates a case study from swedish varved lake sediments we present palaeomagnetic secular variation and relative palaeointensity estimates from multiple sediment cores recovered from a varved lake sediment sequence in kalksjon a lake in central west sweden alternating field demagnetization of discrete samples reveals natural remanent magnetizations dominated by a stable single component magnetic grain size indicators which include day plots and first order reversal curves indicate that the main carrier of the natural remanence is single domain magnetite throughout the varved sequence which extends to similar to 9200 cal yr bp the millennial scale features of the kalksjon relative palaeointensity inclination and declination data are well matched against the fennoscandian master curves fennorpis and fennostack and a global dipole moment reconstruction curve there is evidence however of environmental bias in the relative palaeointensity estimates during specific time intervals we find that bias is particularly pronounced during the early holocene specifically between similar to 9000 and 7800 cal yr bp during this period the bias is apparent as a series of relative palaeointensity cycles with a wavelength of similar to 300 years some bias is also evident between 7800 and 3200 cal yr bp by comparing kalksjon s smoothed relative palaeointensity data with the reconstructed geomagnetic field intensity from c 14 on timescales longer than 500 years thereby removing the effect of relatively high frequency environmental bias in the early holocene we suggest that a distinct peak in intensity at centred on similar to 8700 cal yr bp is a true feature of the geomagnetic field a minimum at similar to 7400 cal yr bp and a maximum at similar to 2500 cal yr bp are also robust features our main conclusion is that sedimentary based relative palaeointensity reconstructions must be carefully assessed if short term centennial variations are to be examined less

stepwise palaeoclimate change across the eocene oligocene transition recorded in continental nw europe by mineralogical assemblages and d 15 n org rennes basin france the eocene oligocene transition eot 34 ma is the largest global cooling of the cenozoic era and led the earth s climatic system to change from a greenhouse to an icehouse mode although it is well documented in marine settings the few studies focusing on continental environments have demonstrated regional heterogeneities the study core cdb1 located in the rennes basin western france is a unique terrestrial lacustrine palustrine record comprising well preserved and terrestrial derived organic rich sediments encompassing the eot clay minerals and the first organic nitrogen isotope record d 15 n org of terrestrial origin for this period are used to reconstruct palaeoclimate changes across this key interval as suggested in worldwide marine and a few continental records a stepwise transition from warm humid conditions in the late eocene to cooler drier conditions in the early oligocene is confirmed in the area in addition an episode of drier conditions in the late eocene and humid dry cycles in the early oligocene are suggested terra nova 00 1 9 2016

convection and crystallization in magma cooled from above calculations are presented for the cooling from above of melts in the di an system in which the kinetics of crystallization are incorporated and play a dominant role the results indicate that even with no initial superheat whatsoever convection plays an important role in the cooling of magma chambers and allows substantial internal cooling crystallization and differentiation the calculations show in agreement with observations that in magma bodies hundreds of meters thick crystallization occurs predominantly in the interior or at the floor even though heat is lost only from the roof the ratio of the final thickness of the layer formed at the floor to that formed at the roof increases as the overall size of the chamber increases owing to the effects of convection

fracture and surface crust development in a holocene pahoehoe lava flow on the island of tenerife canaries abstract an almost horizontal pahoehoe surface in a holocene plagioclase basanite lava on tenerife displays three scales of fracture within the surface crust an early formed set of large scale fractures divides up the surface into an orthogonal set of rectangular slabs with dimensions of several metres and depths of 10 12 cm the shortest slab dimension is parallel to the flow emplacement direction inferred from a strong surface lineation the slabs are domed with the centre an average of 9 6 cm with range 4 19 6 cm above the edges of the slabs profiles of the slabs normal and perpendicular to the margins and through the crest indicate that they can be described by a power law in which the deflection of the slab h is related to the distance from the crest x with an exponent between 2 and 3 analysis of joints within the slabs indicates two smaller scale networks an intermediate scale joint network bounds blocks with rectilinear to polygonal shapes in plan view and has a characteristic mean spacing of 24 2 cm range 10 5 48 cm the major fractures in this set are normal and parallel to the slab margins a smaller scale joint network bounds polygonal equant blocks in plan view and has characteristic spacing of 6 4 cm range 3 7 10 5 cm a model of cooling from the pahoehoe surface is used to constrain the growth of the crust and timing of fracture development the large scale slabs are attributed to localised accumulation of gas beneath the growing crust causing buoyant forces the tensile stresses caused by uplift are sufficient to form the large scale fractures after 2 or 3 h of cooling the intermediate scale fracture network is attributed to the flexure of the slab crust the smaller scale polygonal joint network is related to the build up of isotropic tensile stresses in the cooling slab crust due to thermal contraction with fracture development being promoted by the flexure of the slabs an analysis of the slab deformation indicates that lava crust is weak the weakness is explained by division of the crust into three zones an outer zone with small scale joints that cause negligible strength a middle zone of elastic behaviour in which stress can build up and a lower zone of plastic deformation the crustal slabs display profiles similar to that expected in a bending elastic plate the deformation of the 10 cm thick crust can be explained if the elastic zone was about 2 cm thick this result agrees with an independent calculation of elastic zone thickness based on the position of the brittle ductile transition being located at the 600 c isotherm at a depth of about 2 cm when the crustal slabs were rifted apart

chemical labelling of oyster shells used for time calibrated high resolution mg ca ratios a tool for estimation of past seasonal temperature variations abstract the geochemical compositions of biogenic carbonates are increasingly used for palaeoenvironmental reconstructions the skeletal 18o temperature relationship is dependent on water salinity so many recent studies have focused on the mg ca and sr ca ratios because those ratios in water do not change significantly on short time scales thus those elemental ratios are considered to be good palaeotemperature proxies in many biominerals although their use remains ambiguous in bivalve shells here we present the high resolution mg ca ratios of two modern species of juvenile and adult oyster shells crassostrea gigas and ostrea edulis these specimens were grown in controlled conditions for over one year in two different locations in situ monthly mn marking of the shells has been used for day calibration the daily mg ca ratios in the shell have been measured with an electron microprobe the high frequency mg ca variation of all specimens displays good synchronism with lunar cycles suggesting that tides strongly influence the incorporation of mg ca into the shells highly significant correlation coefficients 0 70

mn2 activated luminescence in dolomite calcite and magnesite quantitative determination of manganese and site distribution by epr and cl spectroscopy abstract dolomite calcite and magnesite were studied by epr and cl spectroscopy mn2 activated luminescence in calcite and magnesite is characterized by single gaussian peaks at 16 250 cm 1 615 nm and at 15 300 cm 1 654 nm respectively in calcite the mn2 content and the normalized epr area are linearly correlated when the mn2 content is deconvolution of corrected cl spectra from dolomite shows two overlapping peaks at 17 315 cm 1 578 nm and 15 270 cm 1 655 nm in rare cases only the 15 270 cm 1 655 nm gaussian peak is present the cl peak at 17 315 cm 1 578 nm ia is due to mn2 in the ca site and the peak at 15 270 cm 1 655 nm ib to mn2 in the mg position the mn2 content in dolomite is linearly correlated with the normalized epr areas of the two sites the distribution ratio kd of mn2 in the two sites of dolomite i e the ca and the mg position was determined by epr and cl spectroscopy a linear correlation exists between kd from epr and the intensity ratio i b i a from cl cl spectroscopy is thus an appropriate method to determine kd in dolomite evaporitic dolomites may be differentiated from non evaporitic dolomites by their kd values

eocene seasonality and seawater alkaline earth reconstruction using shallow dwelling large benthic foraminifera abstract intra test variability in mg ca and other trace elements within large benthic foraminifera lbf of the family nummulitidae have been investigated using laser ablation inductively coupled plasma mass spectrometry la icpms these foraminifera have a longevity and size facilitating seasonal proxy retrieval and a depth distribution similar to surface dwelling planktic foraminifera coupled with their abundance in climatically important periods such as the paleogene this means that this family of foraminifera are an important but under utilised source of palaeoclimatic information we have calibrated the relationship between mg ca and temperature in modern operculina ammonoides and observe a 2 increase in mg ca c 1 o ammonoides is the nearest living relative of the abundant eocene genus nummulites enabling us to reconstruct mid eocene tropical sea surface temperature seasonality by applying our calibration to fossil nummulites djokdjokartae from java our results indicate a 5 6 c annual temperature range implying greater than modern seasonality in the mid eocene bartonian this is consistent with seasonal surface ocean cooling facilitated by enhanced eocene tropical cyclone induced upper ocean mixing as suggested by recent modelling results analyses of fossil n djokdjokartae and operculina sp from the same stratigraphic interval demonstrate that environmental controls on proxy distribution coefficients are the same for these two genera within error using previously published test seawater alkaline earth metal distribution coefficients derived from an lbf of the same family raitzsch et al 2010 and inorganic calcite with appropriate correction systematics for secular mg casw variation evans and muller 2012 we use our fossil data to produce a more accurate foraminifera based mg casw reconstruction and an estimate of seawater sr ca we demonstrate that mid eocene mg casw was 2 mol mol 1 which is in contrast to the model most commonly used to correct deep time mg ca data from foraminifera but in agreement with most other paleogene proxy and model data this indicates that mg casw has undergone a substantial 3 4 rise over the last 40 ma

a high resolution study of trace elements and stable isotopes in oyster shells to estimate central asian middle eocene seasonality modern asian climate is characterized by strong seasonality caused by the duality between monsoon dominated conditions in southeastern asia and semi arid to arid conditions in central asia eocene high resolution proxy records which enable the reconstruction of the onset and magnitude of changes in seasonality are lacking to understand in details how and when this climatic turnover pattern occurred here we propose an original method to estimate inter and intra annual variabilities in seawater temperature and salinity recorded by carbonate shell growth increments of the fossil oyster sokolowia buhsii grewingk collected from late lutetian marine strata of the proto paratethys in the southwestern tarim basin western china elemental ratio mg ca mn ca and carbonate stable isotope composition 18o were determined perpendicular to the growth lines of foliated calcite accumulated in the ligamental area during the oyster s lifetime we use temperature dependant mg incorporation to estimate seasonal temperature contrast in the past results suggest a warm annual average temperature 27 28 c with large offset between summer and winter temperatures until t 19 c combining these temperature estimates with stable oxygen isotope analyses from the same growth increments we deconvolve seawater 18osw as a proxy for salinity this suggests an average annual salinity about 34 35 increasing strongly during summer months and decreasing in winter based on these data we conclude that during the middle eocene central asian climate was characterized by a strong intra seasonal variability in both temperature and salinity although the subtidal setting might have contributed to the strong seasonal offsets this still suggests that semi arid to arid conditions prevailed during summer whereas winter was characterized by enhanced rainfall these results are consistent with previous regional palaeoenvironmental data and climate modelling experiments they thus attest for the reliability of the method developed here as a seasonal palaeoclimatic indicator

how old is the asian monsoon system palaeobotanical records from china the recent discovery of monsoon records in early miocene raised a question of the time when the east asian monsoon system initiated a distinguishing feature of the modern monsoon system is its geographic distribution which disturbs the zonal pattern indigenous to the planetary climate system and the appearance of the monsoonal climate pattern in the geological records should signify the onset of the monsoon system here we present the results of a compilation of palaeobotanical and lithological data from 125 sites over china that has revealed two completely different patterns of climate zones the palaeogene pattern with a broad belt of aridity stretched across china from west to east and the neogene pattern with the arid zone restricted to northwest of china which has persisted until today the reorganization of the climate system around the oligocene miocene boundary provides evidence for the establishment of the modern east asian monsoon since then the neogene has witnessed significant variations of the monsoon system including enhancement of aridity and monsoon intensity at about 15 13 my around 8 my and 3 my the new data do not support the onset of the asian monsoon system around 8 my rather the new data led to a hypothesis that the transition to the monsoon climate system in east asia occurred in the latest oligocene

a complete terrestrial oligocene magnetobiostratigraphy from the ebro basin spain abstract the integrated litho bio and magnetostratigraphic cross correlation of 11 continuous and correlatable sections in the southeastern ebro basin ne spain produced a complete oligocene magnetic polarity stratigraphy ranging from latest eocene to earliest miocene the magnetic polarity zonation of the different alluvial and shallow lacustrine sections has been correlated to the gpts using fossil mammals and the distinct sequence and pattern of polarity reversals the composite magnetic polarity sequence defines a continuous sequence from chron c15n to chron 6cn 2n from 34 8 to 23 7 ma late eocene early miocene in addition a few short normal and reverse polarity events that correlate to cryptochrons in the gpts are found i e in c11n 1r and c8n 1r the resulting regional magneto biostratigraphic framework based on fossil mammals is proposed to refine the dating of the european oligocene biochronological mammal paleogene units and correlate them with the standard oligocene marine stages and the north american land mammal ages the magnetochronology now established enables more precise dating of the late eocene and oligocene paleofloristic and paleofaunistic changes in southwestern europe which were coeval to ongoing global paleoclimatic and paleoceanographic changes on earth caused by high latitude cooling and ice sheet development in eastern antarctica

asian monsoons and aridification response to paleogene sea retreat and neogene westerly shielding indicated by seasonality in paratethys oysters asian climate patterns characterised by highly seasonal monsoons and continentality are thought to originate in the eocene epoch 56 to 34 million years ago ma in response to global climate tibetan plateau uplift and the disappearance of the giant proto paratethys sea formerly extending over eurasia the influence of this sea on asian climate has hitherto not been constrained by proxy records despite being recognised as a major driver by climate models we report here strongly seasonal records preserved in annual lamina of eocene oysters from the proto paratethys with sedimentological and numerical data showing that monsoons were not dampened by the sea and that aridification was modulated by westerly moisture sourced from the sea hot and arid summers despite the presence of the sea suggest a strong anticyclonic zone at central asian latitudes and an orographic effect from the emerging tibetan plateau westerly moisture precipitating during cold and wetter winters appear to have decreased in two steps first in response to the late eocene 34 37 ma sea retreat second by the orogeny of the tian shan and pamir ranges shielding the westerlies after 25 ma paleogene sea retreat and neogene westerly shielding thus provide two successive mechanisms forcing coeval asian desertification and biotic crises

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 monsoon prevalence over china a paleobotanical perspective abstract proxy based quantitative estimates of eocene climates can be made from marine isotope records for ocean conditions or fossil plants for terrestrial environment however our understanding about eocene terrestrial climates is derived mainly from north america and europe and little is known about east asia previous qualitative paleoclimate studies briefly revealed three climatic regimes across china during the eocene with a planetary wind dominated subtropical to tropical arid zone in the central part i e the subtropical highs which was flanked by the subtropical climate zone in the north and tropical climate zone in the south but such a pattern of paleoclimatic zonation still requires a test from quantitative study based on analyses of 66 plant assemblages carefully selected from 37 fossil sites throughout china we here report the first large scale quantitative climatic results and discuss the eocene climatic patterns in china our results demonstrate that the eocene monsoonal climate must have been more or less developed over china judging from the presence of apparent seasonality of both temperature and precipitation revealed by our quantitative estimation this appears not to support the previously claimed eocene planetary wind dominated climate system at least in the region of eastern china in addition the research indicates that with a slight declining trend of mat during the eocene the winter temperature substantially dropped in tropical southern china during the middle to late eocene interval this might be related to the development of a weak eocene kuroshio current in the southwestern pacific and or a significantly enhanced paleo winter monsoon from siberia

clamr a statistical evaluation of isotopic and temperature records in sclerochronologic studies abstract isotope sclerochronology has been widely used to reconstruct paleoclimate from the hard part remains of a broad range of taxa from many different environmental settings and geological and cultural contexts oxygen isotope 18o time series derived from these ultra high resolution daily seasonal annual records have been used to estimate annual averages seasonal ranges and seasonal extremes these time series however inherently include uncertainties such as unconstrained environmental noise changes in seasonal growth rates resulting in weighting annual temperature estimates toward seasons of maximum growth growth cessation and reliance on the most extreme 18o values in the time series to estimate seasonal temperature range etc to better quantify uncertainties in paleoclimate reconstructions using sclerochronologic data we developed an open source r package clamr the clamr evaluation tool improves upon the previous best fit sinusoid approach by introducing additional statistical computation and analysis including discrete fourier transform to initialize parameters for the sinusoidal function nelder mead method to optimize parameters jackknife error estimation and window size calculation for sinusoidal smoothing it can automatically calculate and plot statistical errors for oxygen isotope or temperature data series and provide statistical estimation of temperature and isotopic variables such as annual averages seasonal ranges and seasonal extremes moreover it allows evaluation of the influence of environmental and or physiological noise added to the climate signal therefore clamr enables more comprehensive and justified comparison between paleoclimate reconstructions and modern instrument records and ultimately advances our interpretation of seasonal isotope records from biogenic hard parts

deep time foraminifera mg ca paleothermometry nonlinear correction for secular change in seawater mg ca 1 the mg ca ratio of foraminifera tests is increasingly being utilized as a paleotemperature proxy deep time pre pleistocene mg ca paleothermometry is complicated by the fact that the mg ca ratio of seawater mg casw has undergone considerable secular variation over the cenozoic previous studies have corrected for this by assuming an invariant mg distribution coefficient dmg with mg casw more recent laboratory culturing has shown that this is not the case demonstrating that a power relationship best describes the variation in test mg ca mg catest with mg casw therefore previous corrections are likely to have led to inaccurate temperature reconstructions here we show how the systematics of such a correction should be applied and demonstrate why this provides good evidence that the mg ca ratio of paleogene seawater was lower than previously implied by foraminiferal constraints in agreement with the majority of the proxy mg casw evidence we also demonstrate how it is indirectly possible to constrain the value of h the power component of a mg catest mg casw calibration potentially enabling the appropriate correction of results derived from species where this relationship has not been calibrated however this technique should not be treated as a substitute for culturing the previous erroneous assumptions regarding both 1 the relationship between mg catest and mg caswand 2 the mg ca ratio of seawater at a given time in the past may counteract each other to differing extents as a result previous absolute pre pleistocene paleotemperature estimates derived from mg ca ratios in foraminifera should be treated with caution although relative temperature changes over short 1 ma timescales are likely to be reliable

calculated effect of vesicles on the thermal properties of cooling basaltic lava flows abstract this paper investigates the effects of porosity in the form of vesicles and bubbles on the transfer of heat within basaltic lava this study was undertaken to provide input for realistic cooling models of basaltic lava flows and to help explain some recent field measurements by jones 1992 1993 these field observations indicate that the surfaces of vesicular pahoehoe flows cool significantly more rapidly than that of dense flows it has been suggested that thermal radiation across vesicles is responsible for this enhanced cooling rate it is shown here that for vesicles in typical pahoehoe flows radiation across vesicles may enhance the effective thermal conductivity and thermal diffusivity but only at high temperatures t 800 c and high vesicularities 40 it is also found that convection of the gas phase within bubbles will not occur unless the cavities are larger than about 1 cm furthermore previous work has demonstrated that porosity greatly reduces the thermal conductivity and thermal inertia of cold lava it is shown here that this should also be true at high temperatures examining only radiation across vesicles severely understates the effect of porosity on the cooling of the surface of lava flows thermal inertia developed to describe diurnal surface temperature variations is the most appropriate thermal parameter in this case thermal inertia is a measure of how quickly surface temperature responds to heating or cooling with low thermal inertia materials responding more quickly it is shown here that porosity greatly reduces thermal inertia at all temperatures and that this provides a more general explanation for the field observation

mg ca sr ca and stable isotope δ18o and δ13c ratio profiles from the fan mussel pinna nobilis seasonal records and temperature relationships 1 we present new annually resolved 18o 13c mg ca and sr ca ratio records for two shells of the fast growing mediterranean fan mussel pinna nobilis collected from proximal spanish coast sea grass meadows the relationship between the potential geochemical proxies and ontogenetic and environmental controlling factors is investigated specifically the use of shell mg ca and sr ca ratios as potential calcification temperature proxies the latter calculated from measured shell 18o values has been assessed the 18o cycles along the growth axis indicate that our p nobilis specimens are 10 5 and 4 5 years old shell sr ca ratios do not exhibit any consistent interannual cyclicity and are not correlated to temperature a subtle ontogenetic effect on shell mg ca ratios was observed during the first 4 5 years of recorded growth but was highly evident during the organism s later growth years in p nobilis shells different mechanisms influence ontogenetic variation in shell mg ca and 18o records shell mg ca ratios from the first 4 5 years of growth correlate significantly to temperature in a best fit relationship described by the equation mg ca 17 16 1 95 exp 0 022 0 004 t p nobilis shell mg ca records therefore are a valid temperature proxy only during an early growth phase for the same range of temperatures shell mg ca ratios in p nobilis are approximately 1 3 lower than those reported for inorganic calcite but 3 to 4 times higher than in another bivalve species mytilus trossulus and 4 to 16 times higher than in foraminifera we suggest these offsets are due to a higher degree of similarity between seawater and calcification fluid composition in p nobilis than in other bivalves and foraminifera the observed shell mg ca ratio change per c of 2 2 also is lower than that observed for inorganic and other biogenic calcites our findings strongly support taxon and species specific mg ca temperature relationships for bivalves and other calcifying organisms an appreciation of the physiology and calcification mechanisms of any biogenic carbonate archive therefore is paramount prior to the application of stable isotope and element ca ratio proxies for paleotemperature reconstructions

seawater paleotemperature and paleosalinity evolution in neritic environments of the mediterranean margin insights from isotope analysis of bivalve shells the first step of ice sheet build up on antarctica at the eocene oligocene boundary was followed by a phase of climate instability culminating during the miocene with a warming event called the middle miocene climate optimum mmco that ended with a marked cooling phase identified as the middle miocene climate transition mmct while numerous benthic foraminifera 18o and mg ca data have been used to capture the global climate evolution during this interval of climate and ice sheet instability geochemical records from shallow water carbonates still remain scarce yet such records are crucial to capture the diversity of regional environmental responses to global climate changes and thus to better understand the behavior of our climate system during this critical interval in this work we test the potential of a multi proxy approach 18o clumped isotope 47 strontium isotopes 87sr 86sr applied to bivalves recovered from the liguro provencal basin and rhodano provencal basin northwestern of the mediterranean sea to reconstruct the evolution of shallow seawater temperature and salinity in this region over the latest oligocene to middle miocene interval 10 myrs our results highlight a local cooling in the northwestern mediterranean sea during the mmco that contrasts with the warming observed in other regions with seawater temperatures inferred from 47 analyses in the 13 18 c range these cool seawater temperatures recorded in the studied region during the mmco are much cooler than those recorded in the open oceans but are in agreement with the proliferation of bryozoan observed in the castillon du gard area during this interval low bivalve 18o values 3 24 in average are recorded during this episode are interpreted to reflect enhanced freshwater inputs lowering local salinity and seawater 18o such enhanced freshwater inputs point to a phase of enhanced hydrological cycle in the studied region possibly linked to the global mid miocene warming event bivalve 87sr 86sr data mostly fall within the global seawater sr isotope reference curve but remain compatible with enhanced freshwater inputs during the aquitanian and during the langhian as these inputs were probably not important enough to induce a large departure from the seawater curve at a regional scale

isotopic evidence for climate change during the vandal minimum from ariopsis felis otoliths and mercenaria campechiensis shells southwest florida usa archaeological evidence from coastal southwest florida suggests this region and its local inhabitants the calusa were affected by drought and cooling during the vandal minimum climate episode ad 500 800 to test this hypothesis we reconstructed seasonal scale climate conditions using stable oxygen and carbon isotope ratios 18o and 13c preserved in ariopsis felis otoliths and mercenaria campechiensis shells comparing 18o records from both species distinguishes between cool versus warm and wet versus dry conditions 18o values from four otoliths indicate cooling of winter temperatures occurred in the early vandal minimum ad 500 600 and late half of the middle vandal minimum ad 650 700 persistent dry summers punctuated by occasional years with wet summers throughout the vandal minimum were detected from 18o values of eight archaeological shells our climate reconstructions are in good agreement with archaeological observations and with the cool and dry conditions documented in europe

reconciling channel formation processes with the nature of elevated outflow systems at ophir and aurorae plana mars 1 many hesperian outflow channels head at elevations compatible with aquifer recharge beneath the martian south polar cap and such channels are widely interpreted as the products of this recharge some outflow channels head at greater elevations that are inconsistent with southern recharge including three systems located in aurorae planum and eastern ophir planum these three systems have previously been interpreted as having formed through aqueous outbursts from local aquifers recharged by the meltwaters of ancient upland glaciers to the west however the viability of this interpretation is weakened by the lack of a geomorphic record supportive of past meltwater flow from western uplands inconsistencies between hypothesized processes and the nature of regional topography and mineralogy and the absence of satisfactory analog processes for catastrophic aqueous flow from the subsurface in contrast a volcanic origin for the ophir and aurorae systems appears to be in accord with the basic characteristics of constituent channels and associated landforms the volcanotectonic nature of the valles marineris system and adjacent upland plains and the nature of available analog landforms and processes though numerous uncertainties remain a volcanic interpretation of these outflow systems can more simply account for the existence of component channels the attributes of other elevated outflow systems on mars similarly appear to be most consistent with volcanic origins if the ophir and aurorae systems formed volcanically thermal considerations imply minimum erupted lava volumes of 6 4 103 km3 for allegheny vallis and 6 2 104 km3 for elaver vallis

timing cause and impact of the late eocene stepwise sea retreat from the tarim basin west china abstract a vast shallow epicontinental sea extended across eurasia and was well connected to the western tethys before it retreated westward and became isolated as the paratethys sea however the palaeogeography and the timing of this westward retreat are too poorly constrained to determine potential wider environmental impacts let alone understanding underlying mechanisms of the retreat such as global eustasy and tectonism associated with the indo asia collision here an improved chronostratigraphic and palaeogeographic framework is provided for the onset of the proto paratethys sea retreat at its easternmost extent in the tarim basin in western china is provided five different third order sea level cycles can be recognised from the cretaceous palaeogene sedimentary record in the tarim basin of which the last two stepped successively westwards as the sea retreated after the maximum third incursion new biostratigraphic data from the fourth and fifth incursions at the westernmost margin of the tarim basin are compared to our recent integrated bio magneto stratigraphic results on the fourth incursion near the palaeodepocentre in the south western part of the basin while the fourth incursion extended throughout the basin and retreated at 41 ma base c18r the last and fifth incursion is restricted to the westernmost margin and its marine deposits are assigned a latest bartonian early priabonian age from 38 0 to 36 7 ma near top c17n 2n to base c16n 2n similar to the fourth the fossil assemblages of the fifth incursion are indicative of shallow marine near shore conditions and their widespread distribution across eurasia suggests that the marine connection to the western tethys was maintained the lack of diachronicity of the fourth incursion between the studied sections across the southwest tarim basin suggests that the sea entered and withdrew relatively rapidly as can be expected in the case of eustatic control on a shallow epicontinental basin however the westward palaeogeographic step between the fourth and fifth incursions separated by several millions of years rather suggests the combined long term effect of tectonism possibly associated with early uplift of the pamir kunlun shan thrust belt the fourth and fifth regressions are time equivalent with significant aridification steps recorded in the asian interior thus supporting climate modelling results showing that the stepwise sea retreat from central asia amplified the aridification of the asian interior

mg ca in fossil oyster shells as palaeotemperature proxy an example from the palaeogene of central asia fossil oyster shells are well suited to provide palaeotemperature proxies from geologic to seasonal timescales due to their ubiquitous occurrence from triassic to quaternary sediments the seasonal nature of their shell growth and their relative strong resistance to post mortem alteration however the common use to translate calcitic oxygen isotopes into palaeotemperatures is challenged by uncertainties in accounting for past seawater 18o especially in shallow coastal environment where oysters calcify in principle the mg ca ratio in oyster shells can provide an alternative palaeothermometer several studies provided temperature calibrations for this potential proxy based on modern species nevertheless their application to palaeo studies remains hitherto unexplored here we show that past temperature variability in seawater can be obtained from mg ca analyses from selected fossil oyster species and specimens high resolution mg ca profiles combined with 18o were obtained along 41 fossil oyster shells of seven different species from the palaeogene proto paratethys sea central asia found in similar as well as different depositional age and environments providing comparison suitable mg ca profiles defined by continuous cyclicity and reproducibility within one shell are found to be consistent for specimens of the same species but differ systematically between species implying a dominant species specific effect on the mg ca signal two species studied here ostrea turkostrea strictiplicata and sokolowia buhsii provide an excellent proxy for palaeoclimate reconstruction from china to europe in palaeogene marine sediments more generally the protocol developed here can be applied to identify other fossil oyster species suitable for palaeoclimate reconstructions

assessing the reproducibility and reliability of estuarine bivalve shells saxidomus giganteus for sea surface temperature reconstruction implications for paleoclimate studies studies using oxygen isotopes y 18 o of mollusk shells to determine paleotemperature need to assume water y 18 o values which could severely influence calculated temperatures we analyzed aragonitic shells of the butter clam saxidomus giganteus deshayes 1839 to determine the reproducibility of the isotopic signal between individuals and to assess how precisely temperature could be calculated given known salinity and temperature furthermore carbon isotopes are also investigated as an environmental proxy the abundance of well preserved s giganteus shells in archeological and geological deposits in northwestern north america makes them a particularly suitable species for paleoclimate studies seasonally resolved stable oxygen isotope profiles in three s giganteus shells collected from the same site in puget sound washington usa were well correlated 0 77br 2 b0 87 although there were differences up to 0 58x in high resolution y 18 o profiles of the three shells the difference between the average y 18 o of each shell was less than half of this 0 19x and half of what has been reported for between colony coral variability y 13 c profiles on the other hand were more complex with shell y 13 c being about 2 5x lower than expected equilibrium values however this roughly conforms to the idea that about 10 of the shell carbon originates from metabolic co2 both y 18 o and y 13 c indicate that s giganteus do not grow during periods of reduced salinity despite the excellent reproducibility of y 18 o between shells and the fact that salinity effects were duly considered calculated temperature still differed from instrumental temperature applying different salinity y 18 o water relationships to average shell y 18 o and considering salinity from the shell collection site and a nearby offshore station resulted in calculated average water temperatures ranging from 1 7 to 6 4 8c warmer than measured although we could not determine if s giganteus precipitate their shells in isotopic equilibrium we believe that the difficulty in predicting temperature arose from not being able to accurately determine

thermodynamic and rheological properties of rhyolite and andesite melts the heat capacities of a rhyolite and an andesite glass and liquid have been investigated from relative enthalpy measurements made between 400 and 1800 k for the glass phases the experimental data agree with empirical models of calculation of the heat capacity for the liquid phases the agreement is less good owing to strong interactions between alkali metals and aluminum which are not currently accounted for by empirical heat capacity models the viscosity of both liquids has been measured from the glass transition to 1800 k the temperature dependence of the viscosity is quantitatively related to the configurational heat capacity determined calorimetrically through the configurational entropy theory of relaxation processes for both rhyolite and andesite melts the heat capacity and viscosity do not differ markedly from those obtained by additive modeling from components with mineral compositions

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

columnar jointed bentonite below a doleritic sill tideswell dale derbyshire uk formation during prograde contact metamorphism columnar jointed tuffs bentonites are located below the lower carboniferous tideswell dale sill derbyshire in an abandoned quarry there are three zones of prismatic joints columnar joints 60 cm thick and mean column width of 4 1 cm and massive conchoidally fractured rock sequentially from the dolerite contact downwards the rocks are very fine grained 1 10 m and consist mainly of sanidine interlayered illite smectite and hematite with minor quartz apatite montmorillonite anatase and detrital minerals high k2o and fe2o3 low na2o and low mgo are interpreted as due to alteration of felsic volcanic ash the bentonite was contact metamorphosed by the sill to temperatures of c 300 c the progression of fracture geometries thermal considerations and application of theories of column formation indicate that columns formed downwards away from the sill due to prograde contact metamorphism of the originally clay rich bentonite the formation of columnar fracture networks by shrinkage due to igneous heating may have implications for the effectiveness of bentonite as a barrier for disposal of high level radioactive waste regional dimensions include documenting widespread felsic explosive volcanism and inferring a triassic oxidation event from palaeomagnetic data

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

the long lived mollusc arctica islandica a new paleoceanographic tool for the reconstruction of bottom temperatures for the continental shelves of the northern north atlantic ocean the carbonate shell of the bivalve arctica islandica has been recognized for more than a decade as a potentially important marine geochemical biorecorder owing to this species great longevity 200 years and wide geographic distribution throughout the northern north atlantic ocean a region vital to global climate and ocean circulation however until now this potential has not been realized owing to the difficulty of precisely sampling the shell of this slow growing species using newly available automated microsampling techniques combined with micromass stable isotope mass spectrometry a stable oxygen isotope record 1956 1957 and 1961 1970 has been obtained from a live captured 38 year old a islandica specimen collected near the former position of the nantucket shoals lightship 41 n 69 w the shell s 18o signal is compared with an expected signal derived from ambient bottom temperature and salinity data recorded at the lightship for the same period the results show that a islandica s 18o record 1 is in phase with its growth banding confirming the annual periodicity of this species growth bands 2 is in oxygen isotopic equilibrium with the ambient seawater 3 shows a consistent shell growth shutdown temperature of 6 c which translates into an 8 month may december shell growth period at this location and 4 records the ambient bottom temperature with a precision of 1 2 c these results add important information on the life history of this commercially important shellfish species and demonstrate that a islandica shells can be used to reconstruct inter and intra annual records of the continental shelf bottom temperature

preliminary evaluation of potential stable isotope and trace element productivity proxies in the oyster crassostrea gigas abstract as most bivalve mollusks are filter feeders or deposit feeders predatory septibranchs poromyacea being the notable exception they are closely linked with the activity of primary producers perhaps this is nowhere more evident than in shallow water habitats influenced by seasonal phytoplankton blooms in these systems photoautotrophs are capable of changing the physical and chemical properties of the water column in turn clams ingest large quantities of phytoplankton and precipitate their shells in these chemically altered waters thus clam shells likely archive valuable information about phytoplankton dynamics in shallow water habitats to better understand this relationship we investigated geochemical records from two potential productivity proxy systems archived in shells of the oyster crassostrea gigas that live in the san francisco bay estuary california usa here we present multi year records of shell carbon isotope 13ccarb and barium calcium ba cacarb variation these archives are compared with records of environmental variation using oxygen isotopes 18ocarb as a temporal marker we also present high resolution 13ccarb 18ocarb and ba ca profiles associated with the 2003 spring phytoplankton bloom our results suggest that the prominent positive 13ccarb excursion present in shell material deposited in the spring of 2003 most likely reflects photosynthetic enrichment of the dissolved inorganic carbon pool calibration of stable isotopes with calculated chlorophyll a concentrations measured during the bloom suggests that our 13ccarb sample variation reflects phytoplankton abundance with 3 to 4 day resolution these findings highlight the potential utility of stable isotope records as tools for reconstructing patterns of primary productivity elevated ba ca values are recorded each year in the spring thus like stable isotope profiles ba ca profiles from these specimens demarcate individual years of shell growth and establish ontogenetic age low and high resolution ba ca profiles do not however correlate with the 2003 spring phytoplankton bloom casting doubt on the relationship between ba ca ratios and phytoplankton blooms although the ba ca peak timing loosely correlates with freshwater discharge events peak amplitude does not leaving the environmental cause trigger of these peaks unknown nevertheless the san francisco bay estuary seems like an ideal environment in which to further investigate the relationship between skeletal geochemical variation and patterns of primary productivity

ghost of seagrasses past using sirenians as a proxy for historical distribution of seagrasses abstract seagrasses are a notable component of shallow marine habitats especially in tropical and subtropical regions their fossil record extends back to the mesozoic but it is relatively poor and fragmentary with large temporal and geographical gaps as a result very little is known about the paleobiogeography of these plants and how physical drivers such as climatic or oceanic events have affected their distribution one approach is to infer the past distribution of seagrasses using fossils of organisms dependent of seagrasses with more complete records as proxies seagrass consumers such as sirenians seacows manatees and dugongs are much better represented in the fossil record than seagrasses are the characteristically dense bones of sirenians together with the fact that they are usually found in marginal marine environments increases the potential for preservation and recognition of their fossils the long evolutionary history of sirenians extending throughout most of the last 50 ma together with their diet permits the use of their fossils as a proxy for inferring the paleobiogeography of seagrasses here i looked at the fossil record of sirenians and seagrasses from the eocene through the miocene epochs this comparison produced several inferences about seagrass paleobiogeography and how physical drivers such as climate change ocean currents and tectonic events have been influential in their distribution 1 seagrasses were well established in the western atlantic caribbean prior to the middle eocene making possible at least two instances of trans atlantic sirenian dispersal events either with the aid of tethyan currents or along the nearly continuous northern atlantic coastline that was present in the eocene 2 climatic cooling during the early oligocene seemed to have limited the extent of seagrasses and sirenians although these groups recovered and further diversified and expanded their distributions by the late oligocene in tandem with a climatic warming event 3 by the miocene seagrasses and sirenians reached the southern western atlantic and the eastern pacific aided by the presence of the central american seaway achieving a distribution similar to and sometimes surpassing that of today the fossil record of sirenians can provide a broad overview of seagrass paleobiogeography through time however several aspects such as when sirenians and seagrasses arrived to australia and the seemingly late arrival of seagrasses to south america and the eastern pacific still need further investigation

the potential of combined mg ca and δ18o measurements within the shell of the bivalve pecten maximus to estimate seawater δ18o composition the combined use of 18o and another independent palaeotemperature proxy from the same carbonate biomineral archive forms the basis of a much desired palaeosalinity proxy by circumventing the main source of uncertainty in interpreting 18o palaeorecords i e variations in the isotopic composition of seawater contrary to the 18o proxy transferring the mg ca temperature proxy to marine bivalves has proved problematic since a strong seawater temperature control on shell calcite mg ca has rarely been observed in this study a preliminary evaluation of the combined use of 18ocalcite and mg ca from pecten maximus inner shell calcite to estimate 18owater is reported new mg ca data obtained by milling the inner shell regions from p maximus specimens grown in laboratory aquaria under constant seawater temperatures between 10 and 20 c exhibit a strong relationship between mg ca and temperature mg ca 2 56 0 42 0 17 0 03 t r2 0 77 p 0 001 n 54 while the relationship between sr ca and temperature was not strong r2 0 30 p 0 001 n 54 using specimens grown in a separate aquaria validation experiment estimated mg ca derived seawater temperature was within 0 48 c of measured seawater temperature while estimated 18owater was within 0 05 to 0 15 of measured seawater 18o composition depending on the 18o temperature equation used and with uncertainty estimates of 0 63 and 0 35 such observations indicate the strongest potential to date for the development of valid temperature and 18owater salinity proxies in bivalves from the combined application of mg ca and 18ocalcite in the inner shell regions of p maximus further studies for a wide range of pectinid species ages and different natural environmental settings are needed to validate the observations of this study

isotopic evidence for partial geochemical decoupling between a jurassic epicontinental sea and the open ocean abstract we report stable isotope ratios 13c 18o minor and trace elements mn fe sr mg together with ca concentrations from bivalve shells and belemnites from the middle upper jurassic sundance seaway western united states we compare them with coeval open ocean tethyan data and reconstruct the palaeo circulation of seaway waters the sundance seaway was a 2000 km long epicontinental sea with a single entrance at mid latitudes 55 60 n which would have fostered substantial evolution of seawater chemistry relative to its open ocean source samples are distributed across the 13 million year marine history of the seaway and across a 540 km east west transect spanning wyoming delta13c values are in the same range as tethyan data and this suggests that they might record global changes in the carbon cycle with one exception in the oxfordian delta18o values from the seaway are in contrast highly depleted compared with tethyan data 2 to 6 and they indicate unrealistically high palaeotemperatures 20 40 c assuming an isotopic composition of seawater of 1 as generally used for the jurassic given more realistic temperature estimates from mg ca ratios of bivalve shells 10 25 c we explain such negative 18o values by the southward inflow of normal salinity isotopically depleted 3 4 arctic water into the seaway such water would become progressively more saline and denser as it flowed towards the southernmost portion of the seaway in the late jurassic characterised by wetter climate conditions less dense sundance waters may have instead exhibited a northward flow reducing the southward surface flow from the arctic the observed partial geochemical decoupling of sundance seaway water masses from the open ocean strongly recommends caution in interpreting the geochemical record of ancient shallow seas where local regional and global drivers of change all need to be considered

modelling the oxygen isotope distribution of ancient seawater using a coupled ocean atmosphere gcm implications for reconstructing early eocene climate one of the motivations for studying warm climates of the past such as the early eocene is the enhanced understanding this brings of possible future greenhouse conditions traditionally climate information deduced from biological or chemical proxies have been used to test computer model simulations of past climatic conditions and hence establish some of the uncertainties associated with model based predictions however extracting climate information from proxies is itself an interpretative process and discrepancies between climate information inferred from different types of proxy undermines the assumption that model data conflicts automatically mean that the model is inherently flawed a new approach which both acknowledges and reduces the uncertainties associated with both model and data is required although the oxygen isotopic ratio 18o preserved in calcareous marine fossils has been used to reconstruct past seawater temperature for several decades significant uncertainties associated with this method persist these include assumptions about past seawater 18o for which no proxy exists and which is a key control on the temperature inferred from fossil carbonate here we present the results of an early eocene simulation made using a state of the art general circulation model gcm hadcm3 with co2 set at six times pre industrial values and which has oxygen isotopes incorporated into the full hydrological cycle and hence simulates the 18o of past seawater this allows us to explore the implications of the different seawater 18o correction factors commonly used for 18o based temperature reconstruction it also allows us to focus model data comparison on 18o rather than interpret ocean temperature an approach that reduces uncertainties in model data comparison since the effects of both the temperature and the isotopic composition of ocean water on 18o of carbonate are accounted for the good agreement between model and data for both modern and well preserved early eocene carbonate increases confidence in climate reconstructions of this time

modelling the evolution of columnar joints abstract cooling cracks developing from the margins of solidifying lava flows or intrusive dykes or sills often propagate inward and divide the rock into prismatic columns it has been shown that 1 the initial crack pattern that forms at the surface of the body is not as regular as the pseudo hexagonal pattern which evolves later 2 columnar structures develop by repeated step wise crack advances forming cm to dm transverse bands on the column faces 3 even within well developed colonnades the polygonal outlines continue to shift slightly from one crack advance to the next we propose that each new crack should propagate parallel to the highest thermal gradient ahead of the current crack tip when adjacent columns are of unequal size the local asymmetry of the isotherms drives the new crack toward the biggest and hottest column we present a geometrical model and algorithm that follows this rule and mimics the successive crack advances as the cooling front migrates into the lava sheet or dyke the model polygonal pattern obtained consists of convex irregular polygons with a variable number of sides but in which pentagons and hexagons predominate the algorithm successfully reproduces the rapid evolution from an initial immature crack pattern to a pseudo hexagonal mature one in which the average number of sides approaches six it predicts also the predominance of y type crack junctions the rapid evolution toward columns of approximately equal sizes and the persistent changes in length and diverging orientation of growth steps observed along the sides of columns the model polygonal patterns exhibit geometrical properties which are very similar to those observed in well developed columnar jointed flows such as the giant s causeway

increased seasonality in middle east temperatures during the last interglacial period the last interglacial period about 125 000 years ago is thought to have been at least as warm as the present climate owing to changes in the earth s orbit around the sun it is thought that insolation in the northern hemisphere varied more strongly than today on seasonal timescales which would have led to corresponding changes in the seasonal temperature cycle here we present seasonally resolved proxy records using corals from the northernmost red sea which record climate during the last interglacial period the late holocene epoch and the present we find an increased seasonality in the temperature recorded in the last interglacial coral today climate in the northern red sea is sensitive to the north atlantic oscillation a climate oscillation that strongly influences winter temperatures and precipitation in the north atlantic region from our coral records and simulations with a coupled atmosphere ocean circulation model we conclude that a tendency towards the high index state of the north atlantic oscillation during the last interglacial period which is consistent with european proxy records contributed to the larger amplitude of the seasonal cycle in the middle east

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

early oligocene ice sheet expansion on antarctica stable isotope and sedimentological evidence from kerguelen plateau southern indian ocean sedimentological and stable isotope data from a pelagic sequence recovered from the southern indian ocean provide the most convincing evidence to date for short term expansion of a large ice sheet on antarctica during the earliest oligocene 36 ma terrigenous debris identified as ice rafted in origin on the basis of textural compositional and size criteria is present at the same stratigraphic level as the ubiquitous early oligocene oxygen isotope shift the highest benthic foraminiferal 18o values 3 0 of the paleogene occur in samples from within the ice rafted debris interval these values are similar to those recorded by holocene benthic foraminifera implying that the ice sheet may have attained a volume similar to that of the present day ice sheet on antarctica the stratigraphic distribution of ice rafted debris and high oxygen isotope values indicate that these conditions persisted for roughly 100 ka

structure and origin by injection of lava under surface crust of tumuli lava rises lava rise pits and lava inflation clefts in hawaii tumuli are positive topographic features that are common on hawaiian pahoehoe lava flow fields particularly on shallow slopes and 75 measured examples are presented here to document the size range tumuli form by up tilting of crustal plates without any crustal shortening and are thus distinguished from pressure ridges which are up buckled by laterally directed pressure the axial or star like systems of deep clefts that characterize tumuli are defined here as lava inflation clefts their tips advanced into red hot lava and they widened as uplift proceeded and while the lava crust was thickening flat surfaced uplifts formed like tumuli by injection of lava under a surface crust were previously called pressure plateaus but lava rise is proposed instead the pits that abound among lava rises previously attributed to collapse or subsidence are generally formed because the lava around them rose and the name lava rise pit is proposed unique examples of tumuli and lava rises from which lava drained out under a surface crust 1 5 to 2 5 m thick are described from kilauea caldera these examples show that in tumuli and lava rises the crust floats on considerable bodies of fluid lava and is able to do so because of its higher vesicle content the fluid lava loses many of its gas bubbles during residence beneath the crust the bulk densities of samples from tumuli show a general downward increase the form of the density profile is consistent with the relationship that for any given crustal thickness the density of fluid lava closely matched the average density of that crust suggesting that the lava was stably density stratified it is inferred that stable stratification was regulated by out flows of the more vesicular lava fractions loss of bubbles through the lava inflation clefts and entry of injected lava at its level of neutral buoyancy below the uppermost meter the downward decrease in vesicularity closely conforms with that expected by compression of a uniform mass of gas per unit mass of lava

quantitative temperature recovery from middle eocene halite fluid inclusions in the easternmost tethys realm middle eocene climatic reconstruction has long been the focus of geoscientists however quantitative temperature records for this interval remain lacking the easternmost tethys realm is especially problematic because the traditional climatic proxies are limited by the presence of widespread and thick evaporite deposits in this study we present the first quantitative seawater temperatures records revealed by homogenization temperatures th of primary halite fluid inclusions from the middle eocene xiaokuzibai formation of the kuqa basin in western china a total of 231 th data were obtained from two halite samples with values ranging from 12 8 to 37 3 c average th values of 22 4 c and 23 3 c are in good agreement with the previous studies of climatic proxies by combining our results with previously reported temperature records we infer that the entire tethys realm experienced similar climate conditions during the middle eocene including a maximum seawater temperature above 34 c which may be related to the middle eocene climatic optimum

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

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

characterization and evolution of fractures in low volume pahoehoe lava flows eastern snake river plain idaho we characterize fracture evolution in pahoehoe lava flows of the eastern snake river plain idaho and highlight significant differences to flood basalt sheet flows and implications for hydrologic models there are four distinct fracture types in east ern snake river plain flows 1 column bounding 2 column normal 3 entablature and 4 inflation fractures types 1 3 are driven by thermal stress whereas type 4 is induced by lava pressure from within the flow thermal stress distribution in a flow is dictated by its aspect ratio width height which controls the shape of isotherms isotherms control column bounding fracture orientations resulting in increasingly radial fracture patterns as the aspect ratio approaches unity column normal fractures form in response to thermal stress and fracture induced stress within basalt columns overlap in the timing of column bounding and column normal fracture growth has resulted in complex fracture relationships column normal fracture growth is strongly influenced by vesicular layers which act as mechanical heterogeneities creating preferential pathways for fracture growth as well as causing jogs or terminations along column bounding fractures eastern snake river plain entablatures which preserve the shape of the central lava core during the final stages of cooling have distinctly different origins and fracture styles compared to sheet flows entablatures formed by penetration of the edges of pressurized lava cores by inflation fractures causing rapid convective cooling in addition inflation fractures significantly perturb isotherm shapes in lava flows affecting flow scale fracture patterns and densities the overall effect of all these processes is a complex pattern of fracturing that attests to a strong impact by each fracture type on the growth behavior of all other fracture types

paleogene sea levels and climates u s a eastern gulf coastal plain abstract biostratigraphic zonation of the paleogene formations in the eastern gulf coastal plain of the u s a based on calcareous nannoplankton allows a reassessment of the timing and pattern of changing sea levels and climates in the region general similarity is recognizable between the gross pattern of paleogene transgressions regressions in the eastern gulf coastal plain and the recently published vail et al 1977 scheme of eustatic sea level changes local tectonism and sedimentation have however overprinted intra cycle shoreline fluctuations on the eustatic pattern a hiatus spanning at least calcareous nannoplankton zone np 11 exists between the early eocene hatchetigbee and tallahatta formations another significant hiatus representing most or all of np 23 exists between the early oligocene bucatunna clay and the late oligocene chickasawhay limestone nannoplankton assemblages suggest temperate sea surface waters during the early and early late paleocene followed by subtropical sea surface conditions from latest paleocene to earliest oligocene climatic conditions were cooler during the remainder of the early oligocene

a multiproxy record of holocene environmental changes in the central kola peninsula northwest russia a sediment core from chuna lake kola peninsula northwest russia was studied for pollen diatoms and sediment chemistry in order to infer post glacial environmental changes and to investigate responses of the lake ecosystem to these changes the past ph and dissolved organic carbon doc of the lake were inferred using diatom based transfer functions between 9000 and 4200 cal yr bp slow natural acidification and major changes in the diatom flora occurred in chuna lake these correlated with changes in regional pollen the arrival of trees in the catchment changes in erosion sediment organic content and doc during the past 4200 yr diatom based proxies showed no clear response to changes in vegetation and erosion as autochthonous ecological processes became more important than external climate influences during the late holocene the pollen stratigraphy reflects the major climate patterns of the central kola peninsula during the holocene i e a climate optimum between 9000 and 5400 5000 cal yr bp when climate was warm and dry and gradual climate cooling and an increase in moisture during the past 5400 5000 yr this agrees with the occurrence of the north south humidity gradient in fennoscandia during the holocene copyright 2002 john wiley sons ltd

quantitative reconstruction of holocene climate from the chuna lake pollen record kola peninsula northwest russia july mean temperatures and annual precipitation during the last 9000 years were inferred using the pollen record from chuna lake kola peninsula russia a quantitative pollen climate model was generated using the best modem analogues method from a training set of 99 surface pollen spectra from the kola peninsula northern fennoscandia and karelia according to the evidence from chuna lake the early and mid holocene c 9000 5000 cal bp was warm and dry in the central kola peninsula with july temperatures being 1 5 2c higher than at present the onset of warm and dry early to mid holocene occurred in the kola peninsula earlier than in the rest of northern fennoscandia july temperature started to decrease and annual precipitation increased from c 5000 cal yr bp and climate became cool and moist

asian monsoons in a late eocene greenhouse world the strong present day asian monsoons are thought to have originated between 25 and 22 million years myr ago driven by tibetan himalayan uplift however the existence of older asian monsoons and their response to enhanced greenhouse conditions such as those in theeocene period 55 34myrago are unknownbecause of the paucity of well dated records here we show late eocene climate records revealing marked monsoon like patterns in rainfall and wind south and north of the tibetan himalayan orogen this is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from myanmar and by aeolian dust deposition in northwest china our climate simulations support modern like eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhancedgreenhouse conditions counterbalanced the negative effect of lowertibetanrelief onprecipitation these strong monsoons later weakened with the global shift to icehouse conditions 34myr ago

inter annual climate variability in europe during the oligocene icehouse abstract new sclerochronological data suggest that a variability comparable to the north atlantic oscillation nao was already present during the middle oligocene about 20 myr earlier than formerly assumed annual increment width data of long lived marine bivalves of oligocene 30 25 ma strata from central europe revealed a distinct quasi decadal climate variability modulated on 2 12 mainly 3 7 year cycles as in many other modern bivalves these periodic changes in shell growth were most likely related to changes in primary productivity which in turn were coupled to atmospheric circulation patterns stable carbon isotope values of the shells 13 c shell further corroborated the link between shell growth and food availability sub decal oscillations in the 3 7 year band in other annually resolved fossil archives were often interpreted as el nino southern oscillation enso cycles this possibility is discussed in the present study however combined shell derived proxy and numerical climate model data lend support to the interpretation of a nao like variability according to numerical climate models winter sea level pressure wslp and precipitation rate wpr across central europe during the oligocene exhibited a pattern similar to the modern nao the simulated nao index for the oligocene shows periodicities coherent with those revealed by the proxy data 2 5 6 years yet on shorter wavelengths than the modern nao biennial and 6 10 year cycles likely the different paleogeography and elevated atmospheric co 2 concentrations not only influenced the sea level pressure pattern but also the temporal variability of the nao precursor the present study represents the first attempt to characterize the inter annual climate variability in central europe during the oligocene and sets the basis for future studies on the early phase of the cenozoic icehouse climate state

summer temperatures of late eocene to early oligocene freshwaters the marine foraminiferal isotope record displays a positive 18o shift early in the oligocene which has been identified as the onset of the antarctic oi 1 glaciation reported here are the first oxygen isotope derived summer paleotemperatures for continental freshwater in the northern hemisphere hampshire basin isle of wight uk leading up to and across this event these paleotemperatures are derived from multiple paleoproxies rodent tooth enamel gastropod shells charophyte gyrogonites and fish otoliths and are independent of freshwater evaporation effects and changes in ice volume we conclude that a fluctuating mesothermal climate existed but that there was no significant decrease in summer temperatures across the oi 1 glaciation this result is concordant with several other studies in suggesting that the majority of the isotopic shift in the marine realm across the oi 1 glaciation is linked to changes in antarctic ice volume and not to global temperature change our new approach has allowed us to derive numerical values for summer temperatures as well as to reconstruct relative temperature change across this key interval of the eocene oligocene transition

diagenesis and the reconstruction of paleoenvironments a method to restore original δ18o values of carbonate and phosphate from fossil tooth enamel abstract intra tooth 18 o variations within the carbonate 18 oc and phosphate 18 op components of tooth apatite were measured for miocene and pliocene hypsodont mammals from afghanistan greece and chad in order to evaluate the resistance of enamel to diagenetic alteration application of water apatite interaction models suggest that the different kinetic behaviours of the phosphate water and carbonate water systems can be used to detect subtle oxygen isotope disequilibria in fossil enamel when intra individual variations are considered selective alteration of the oxygen isotope composition from the carbonate component of afghan and greek enamels suggests inorganic isotopic exchange processes microbially induced isotopic exchange for phosphate is demonstrated for the first time in enamel samples from chad in association with extensive recrystallization in chad 18 op values were derived from partial isotopic exchange with fossil groundwater during early diagenesis mass balance calculations using average carbonate content in enamel as a proxy for recrystallization and the lowest 18 op value of dentine as a proxy for the isotopic composition of the diagenetic fluid indicate that diagenesis can alter 18 op by as much as 3 in some enamel samples this diagenetic alteration is also responsible for a decrease in intra individual variations of up to 1 in affected specimens the effects of diagenesis on 18 op values of fossil enamel are not systematic however and can only be estimated if sequential 18 op and 18 oc analyses are performed on fossil enamel and dentine reconstruction of large temporal or spatial scale paleoclimates based on 18 op analyses from mammalian teeth cannot be considered valid if enamel has been affected by bacterial activity or if the data cannot be corrected for diagenetic effects

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

continental ice in greenland during the eocene and oligocene the eocene and oligocene epochs approximately 55 to 23 million years ago comprise a critical phase in earth history an array of geological records supported by climate modelling indicates a profound shift in global climate during this interval from a state that was largely free of polar ice caps to one in which ice sheets on antarctica approached their modern size however the early glaciation history of the northern hemisphere is a subject of controversy here we report stratigraphically extensive ice rafted debris including macroscopic dropstones in late eocene to early oligocene sediments from the norwegian greenland sea that were deposited between about 38 and 30 million years ago our data indicate sediment rafting by glacial ice rather than sea ice and point to east greenland as the likely source records of this type from one site alone cannot be used to determine the extent of ice involved however our data suggest the existence of at least isolated glaciers on greenland about 20 million years earlier than previously documented at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher