pronounced zonal heterogeneity in eocene southern high latitude sea surface temperatures paleoclimate studies suggest that increased global warmth during the eocene epoch was greatly amplified at high latitudes a state that climate models cannot fully reproduce however proxy estimates of eocene near antarctic sea surface temperatures ssts have produced widely divergent results at similar latitudes with ssts above 20 c in the southwest pacific contrasting with ssts between 5 and 15 c in the south atlantic validation of this zonal temperature difference has been impeded by uncertainties inherent to the individual paleotemperature proxies applied at these sites here we present multiproxy data from seymour island near the antarctic peninsula that provides well constrained evidence for annual ssts of 10 17 c 1 sd during the middle and late eocene comparison of the same paleotemperature proxy at seymour island and at the east tasman plateau indicate the presence of a large and consistent middle to late eocene sst gradient of 7 c between these two sites located at similar paleolatitudes intermediate complexity climate model simulations suggest that enhanced oceanic heat transport in the south pacific driven by deep water formation in the ross sea was largely responsible for the observed sst gradient these results indicate that very warm ssts in excess of 18 c did not extend uniformly across the eocene southern high latitudes and suggest that thermohaline circulation may partially control the distribution of high latitude ocean temperatures in greenhouse climates the pronounced zonal sst heterogeneity evident in the eocene cautions against inferring past meridional temperature gradients using spatially limited data within given latitudinal bands

regional deformation of the sierra de san luis argentina implications for the paleozoic development of western gondwana 1 metamorphic and ductile deformation fabrics within the sierra de san luis central argentina provide evidence for the early to middle paleozoic development of the paleo pacific margin of gondwana presumed vendian aged metasedimentary rocks within both the sierra de san luis and the sierras de cordoba preserve early pressure solution cleavage development cambrian peak metamorphism in the sierras de cordoba and ordovician peak metamorphism in the sierra de san luis indicate that juxtaposition of these two terranes did not occur prior to the late ordovician peak metamorphism and regional folding of the sierra de san luis metasedimentary rocks is equated with early stages of the development and shortening of the famatinian magmatic arc along the western margin of gondwana extensive nne trending zones of upper greenschist to amphibolite facies ductile deformation within the sierra de san luis and along the western margin of the sierra de comechingones record the dextral oblique juxtaposition of the sierra de san luis terrane against the southwestern margin of the sierras de cordoba coincident with or closely followed by the suture of the exotic precordillera terrane to the western margin of gondwana by the early devonian middle to late devonian restricted lower greenschist grade reactivation of ductile faults may record the accretion of the chilenia terrane the final stage of paleozoic convergent tectonism along this segment of western gondwana

one kilometre thick ultramylonite sierra de quilmes sierras pampeanas nw argentina abstract we describe a 1 km thick ultramylonite forming the high strain base of the 3 5 km thick el pichao shear zone in the sierra de quilmes this shear zone thrusted granulite facies migmatites onto amphibolite facies rocks during the 470 ma famatinian orogeny strain grades upwards from ultramylonites to weakly sheared migmatites across the 3 5 km zone and the mylonitic rocks define a geochemical field narrower than the protolith suggesting they underwent mixing and homogenization through shearing ultramylonites this thick are uncommon the width of a shear zone in the absence of significant compositional rheological contrasts controlling strain localization is controlled by the balance between shear heat generation and diffusion under typical crustal conditions a strain rate of 10 12 s 1 is required to form a 1 km thick ultramylonite and this is achieved when large movement velocities are imposed across the shear zone we postulate that the el pichao shear zone and its thick ultramylonite accommodated a significant fraction of convergence velocities driving the orogeny and that the wide mylonitic shear zones characteristic of the cambrian ordovician deformation of the sierras pampeanas result from the convergent movement being taken up by only a few active major shear zones

ecological and biogeochemical change in an early paleogene peat forming environment linking biomarkers and palynology abstract sphagnum moss is the dominant plant type in modern boreal and sub arctic ombrotrophic bogs and is of particular interest due to its sensitivity to climate and its important role in wetland biogeochemistry here we reconstruct the occurrence of sphagnum moss and associated biogeochemical change within a thermally immature early paleogene 55 ma lignite from schoningen nw germany using a high resolution multi proxy approach changes in the abundance of sphagnum type spores and the c23 c31 n alkane ratio indicate the expansion of sphagnum moss within the top of the lignite seam this sphagnum moss expansion is associated with the development of waterlogged conditions analogous to what has been observed within modern ombrotrophic bogs the similarity between biomarkers and palynology also indicates that the c23 c31 n alkane ratio may be a reliable chemotaxonomic indicator for sphagnum during the early paleogene the 13c value of bacterial hopanes and mid chain n alkanes indicates that a rise in water table is not associated with a substantial increase in aerobic methanotrophy the absence of very low 13c values within the top of the seam could reflect either less methanogenesis or less efficient methane oxidation under waterlogged sulphate rich conditions

mid to late cambrian docking of the rio de la plata craton to southwestern gondwana age constraints from u pb shrimp detrital zircon ages from sierras de ambato and velasco sierras pampeanas argentina abstract the early palaeozoic stratigraphy and tectonic history of the eastern sierras pampeanas of central argentina are complicated by metamorphism and deformation resulting from the pampean 545 510 ma and famatinian 490 440 ma orogenies we report u pb sensitive high resolution ion microprobe dating of detrital zircons in two metasedimentary successions exposed at quebrada de la cebila c 28 459s 66 259w the ambato and the la cebila metamorphic complexes the ambato zircons record age peaks corresponding to pampean 530 10 ma brasiliano c 570 and c 640 ma grenville c 950 to c 1025 ma and minor neoarchaean ages similar peaks are also apparent in the la cebila sample but it additionally contains palaeoproterozoic zircons c 2 1 ga corresponding to the age of the rio de la plata craton from which they are considered to have been sourced our interpretation is that the protolith of the ambato complex was deposited prior to juxtaposition with the craton and is older than the early ordovician la cebila metamorphic complex we infer that the craton reached its current relative position in the mid to late cambrian after the main pampean tectonothermal event 530 520 ma and before deposition of the la cebila protolith and the achavil formation sierra de famatina which contain comparable detrital zircon populations

warm and wet conditions in the arctic region during eocene thermal maximum 2 several episodes of abrupt and transient warming each lasting between 50 000 and 200 000 years punctuated the long term warming during the late palaeocene and early eocene 58 to 51 myr ago epochs1 2 these hyperthermal events such as the eocene thermal maximum 2 emt2 that took place about 53 5 myr ago2 are associated with rapid increases in atmospheric co2 content however the impacts of most events are documented only locally86 here we show on the basis of estimates from the tex 86 proxy that sea surface temperatures rose by 3 5 c in the arctic ocean during the emt2 dinoflagellate fossils demonstrate a concomitant freshening and eutrophication of surface waters which resulted in euxinia in the photic zone the presence of palm pollen implies5 that coldest month mean temperatures over the arctic land masses were no less than 8 c in contradiction of model simulations that suggest hyperthermal winter temperatures were below freezing6 in light of our reconstructed temperature and hydrologic trends we conclude that the temperature and hydrographic responses to abruptly increased atmospheric co2 concentrations were similar for the etm2 and the better described palaeocene eocene thermal maximum7 8 55 5 myr ago 2009 macmillan publishers limited all rights reserved

climatic and environmental changes across the early eocene climatic optimum at mid waipara river canterbury basin new zealand abstract the cretaceous paleogene marine sedimentary succession exposed in the banks of the middle reaches of the waipara river referred to as mid waipara north canterbury new zealand has been the subject of several high profile studies of paleogene paleoclimate over the past decade it is one of relatively few sections globally where a multi proxy approach is possible due to the good preservation of microfossils and organic biomarkers the eocene section is also well dated by magnetostratigraphy and biostratigraphy based on planktic foraminifera calcareous nannofossils and dinoflagellate cysts dinocysts here we build on this previous work and undertake a comprehensive analysis of paleontological and geochemical indicators of climatic and environmental changes through the early middle eocene part of the section with particular focus on the early eocene climatic optimum eeco 53 26 49 14 ma we correlate a 33 5 m thick interval with the eeco based on biostratigraphy magnetostratigraphy tex86 paleothermometry and bulk carbonate 13c our new sea surface temperature sst record based on tex86 agrees with a previous lower resolution record based on tex86 and planktic foraminiferal 18o and mg ca ratios the eeco interval in this section extends from the upper part of the new zealand waipawan stage to the mangaorapan heretaungan stage boundary at 49 27 ma the eeco onset is not exposed but the termination is well constrained by a fall in sst and shift to more positive 13c values six negative carbon isotope excursions cies are recognised within the eeco and are tentatively correlated with cies j k m o q t and c22nh4 in the global 13c compilation the cies are associated with warmer ssts indicating that they represent hyperthermals the bayspar tex86 calibration indicates sst increased by as much as 12 c from the early eocene 55 ma to the eeco where sst peaked at 35 c sst gradually declined from mid eeco 51 ma into the middle eocene the marked warming in the early eeco is associated with the highest abundance of warm water taxa in calcareous nannofossil and dinocyst assemblages the highest proportion of planktic foraminifera and a coeval long term shift to abundant angiosperm vegetation primarily driven by a rise in casuarinaceae there is good agreement between tex86 and marine microfossil based proxies for temperature providing confidence that both approaches are useful guides to past water temperature warm water marine taxa are most abundant in the eeco but are not dominant comparison of the abundance of nannofossil warm water taxa between mid waipara and a low latitude site on shatsky rise suggests the latitudinal temperature gradient between mid and low latitudes in the eeco was greater than the tex86 proxy implies there is no clear evidence for enhanced sedimentation rates associated with the eeco in contrast to evidence from the nearby mead stream section superabundant homotryblium a euryhaline dinocyst in the early and middle eeco suggests elevated salinity and or stratified surface waters and there is no clear evidence of increased surface productivity associated with the eeco declining sst in the late eeco 50 ma corresponds with an increase in cool water taxa and terrigenous material this article highlights the importance of combining well calibrated paleontological and geochemical records to better constrain and understand past warm climate states

early paleogene evolution of terrestrial climate in the sw pacific southern new zealand 1 we present a long term record of terrestrial climate change for the early paleogene of the southern hemisphere that complements previously reported marine temperature records using the mbt cbt proxy based on the distribution of soil bacterial glycerol dialkyl glycerol tetraether lipids we reconstructed mean annual air temperature mat from the middle paleocene to middle eocene 62 42 ma for southern new zealand this record is consistent with temperature estimates derived from leaf fossils and palynology as well as previously published mbt cbt records which provides confidence in absolute temperature estimates our record indicates that through this interval temperatures were typically 5 c warmer than those of today at such latitudes with more pronounced warming during the early eocene climate optimum eeco 50 ma when mat was 20 c moreover the eeco mats are similar to those determined for antarctica with a weak high latitude terrestrial temperature gradient 5 c developing by the middle eocene we also document a short lived cooling episode in the early late paleocene when mat was comparable to present this record corroborates the trends documented by sea surface temperature sst proxies although absolute ssts are up to 6 c warmer than mats although the high calibration error of the mbt cbt proxy dictates caution the good match between our mat results and modeled temperatures supports the suggestion that sst records suffer from a warm summer bias particularly during times of peak warming

subtropical climate conditions and mangrove growth in arctic siberia during the early eocene the early eocene ca 56 47 8 ma was an interval of exceptional warmth with reduced pole to equator temperature gradients climate proxies indicate mean annual air temperatures mats and sea surface temperatures ssts exceeding 8 18 c and frost free mild winters in polar areas features that have proven difficult to reproduce with the most elaborate climate models a full appraisal of the early eocene polar climate has been however limited by possible seasonal biases associated with geochemical proxies and the lack of data from the vast eurasian arctic here we present multiproxy data from lower middle eocene coastal plain sediments of the new siberian islands russia showing that taxodioid cupressaceae palms and the mangrove avicennia grew in arctic siberia above 72 n under air temperatures averaging 16 21 c annually and 5 5 14 c in winter kaolinite contents are exceptionally high up to 60 of clay assemblages and comparable to those found in present day subtropical soils formed under high mean annual precipitation map 1000 mm and warm mat 15 c conditions the avicennia pollen records the northernmost mangrove growth ever documented and indicates early eocene ssts exceeding 13 c in winter and 18 c in summer considering the high map estimated for arctic siberia and other pan arctic landmasses we propose that the heat from warm river waters draining into the arctic might have amplified early eocene polar warmth our results provide the first climate constraints for the early eocene of arctic siberia and support the view that most climate models underestimate polar warming in greenhouse conditions

topography of the variscan orogen in europe failed not collapsed the variscan orogenic collage consists of three subduction collision systems rheno hercynian saxo thuringian and massif central moldanubian devonian to early carboniferous marine strata are widespread not only in the individual foreland fold and thrust belts but also in post tectonic basins within these foreland belts and on the cadomian crust of peri gondwanan microcontinental fragments which represent the upper plates of the subduction collision zones these marine basins preclude high elevations in the respective areas and also in their neighbourhood widespread late carboniferous intra montane basins with their coal bearing sequences are likewise incompatible with high and dry plateaus while narrow belts with high elevations remain possible along active margins within the orogen comparison of the variscides with the himalaya tibetan plateau is unfounded plausible reasons for the scarcity of high variscan relief include subduction of oceanic and even continental crust subduction erosion orogen parallel extension and most important lithospheric thinning accompanied by high heat flow and magmatism in many areas timing and areal array of magmatism and ht metamorphism are not compatible with a model of tectonic thickening and subsequent gravitational collapse it is suggested instead that lithospheric thinning and heating are due to mantle activities caused by the tethys rift the lower and middle crust were thermally softened and rendered unfit for stacking and isostatic uplift in terms of topography the variscides represent a failed orogen the ht regime also explains the abundance of granitoids and ht lp metamorphic rocks typical of the variscides melting in the ht regime extracted mafic components from variscan and cadomian crust as well as from cadomian metasomatized lithospheric mantle thus mimicking subduction related magmatism the onset of the ht regime at c 340 ma may also have triggered the final ascent of hp uhp felsic metamorphic rocks

reconstruction of atmospheric co2 during the early middle eocene by application of a gas exchange model to fossil plants from the messel formation germany abstract in this study atmospheric co 2 during the early middle eocene 47 ma is reconstructed using fossil plants from the messel formation close to darmstadt germany co 2 concentration is calculated using a mechanistic model of gas exchange which optimizes co 2 uptake by photosynthesis against water vapor loss by transpiration a strategy that is commonly realized in land plants input data for the model are stomatal data density and pore length paleoclimate data obtained by two different approaches and biochemical parameters of photosynthesis leaves from three taxa belonging to two different families were studied laurophyllum lanigeroides daphnogene crebrigranosa both lauraceae and rhodomyrtophyllum sinuatum myrtaceae the results suggest that co 2 was between 853 and 1033 ppm during the development of the messel formation stomatal data therefore indicate a co 2 concentration that was substantially higher than today the reconstructed range of co 2 concentration is close to data provided by geochemical modeling results and conforms to various data that indicate a warm and ice free climate during this time interval

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

isotopic studies on detrital zircons of silurian devonian siliciclastic sequences from argentinean north patagonia and sierra de la ventana regions comparative provenance the silurian devonian siliciclastic sedimentary units known as sierra grande formation and the upper part of the ventana group crop out in the eastern area of the north patagonian massif and in the ventania system toward the atlantic border of argentina both sequences show similar stratigraphical characteristics and were deposited in a shallow marine platform paleoenvironment previous contributions have provided evidence of an allochthonous patagonia terrane that amalgamate to gondwana during the permian triassic however other lines of research support a crustal continuity southward where the pampean and famatinian events extend into the northern patagonia in either case the detrital input to the eo mesopaleozoic basins generated along the passive margin tectonic setting should reflect the sedimentary sources in this contribution new age data on the sedimentary provenance of these units is provided by u pb and lu hf isotopic studies on detrital zircons using la icp ms and shrimp methodologies the main sedimentary sources of detrital zircons for both regions are of cambrian ordovician and neoproterozoic age while a secondary mode is mesoproterozoic zircons from older cratonic sources mesoarchean paleoproterozoic ages are scarcely recorded the sample from the upper section of the devonian lolen formation ventana group shows an important change in the sedimentary provenance with a main mode of mesoproterozoic detrital zircons detrital source areas considering the orogenic cycles known for southwest south america famatinian pampean brasiliano mesoproterozoic grenvillian and paleoproterozoic transamazonian are proposed

neoproterozoic to early palaeozoic events in the sierra de san luis implications for the famatinian geodynamics in the eastern sierras pampeanas argentina the application of the sensitive high resolution ion microprobe shrimp u pb dating technique to zircon and monazites of different rock types of the sierra de san luis provides an important insight into the provenance and timing of deposition of the sedimentary precursors as well as the metamorphic and igneous history of the various basement domains additional constraints on the famatinian metamorphic episode are provided by pb pb stepwise leaching experiments on one staurolite and two garnet separates the results indicate that the sedimentary precursors of the conlara metamorphic complex have a maximum age of c 590 ma whereas the pringles metamorphic complex metasediments appear to be sourced from the pampean orogen in the early cambrian folded xenoliths within the c 496 ma el penon pluton suggest that the host conlara metamorphic complex underwent a pampean compression from a 208 pb 232 th monazite age of 478 ma for a migmatite from the nogoli metamorphic complex the structural evolution of this basement complex appears to be entirely post pampean onset of the famatinian high grade metamorphism between c 500 ma and c 450 ma follows a period of crustal extension on the western outboard of gondwana and might not be related directly to a mid ordovician accretion of the cuyania terrane

ordovician back arc foreland and ocloyic thrust belt development on the western gondwana margin as a response to precordillera terrane accretion 1 the famatina belt southern central andes records a circa 470 m y shortening episode ocloyic orogeny affecting the peri gondwanan back arc basin in response to the accretion of the precordillera terrane collision created distinct features across and along the margin some of which persisted into the present andean structure from east to west the ocloyic deformation is recorded across the telescoped region of famatina represented by 1 an east vergent fold thrust belt evftb involving a major angular unconformity between early and middle ordovician rocks 2 a highly deformed volcano sedimentary belt and 3 an east vergent ductile shear zone affecting famatinian granites axis attitudes of ordovician refolded anticlines in the evftb show west east tectonic transport in agreement with kinematics of ocloyic high strain belts indicating shortening orthogonal to the present pacific margin eastward displacement of the ordovician volcanic arc at 27 s latitude together with a documented sinistral slip zone across the proto andean margin suggests tectonic indentation

las matras block central argentina 37 s 67 w the southernmost cuyania terrane and its relationship with the famatinian orogeny abstract the las matras block in central argentina constitutes the southernmost part of the cuyania terrane which was accreted to the southwestern margin of gondwana during the early to mid ordovician famatinian orogeny the grenville aged rocks of the las matras block are represented by the tonalitic to trondhjemitic las matras pluton a new u pb conventional zircon age of 1244 42 ma confirms previous sm nd and rb sr isochron ages of this pluton mineral composition data are consistent with the tonalitic trondhjemitic character of the pluton and constrain its emplacement level to 1 9 to 2 6 kb this shallow level of emplacement and the undeformed character of the pluton are distinctive features of this southernmost basement a regional comparison indicates that the igneous metamorphic evolution of the grenville aged basement rocks of the cuyania terrane occurred over a period of more than 200 million years with ages older than 1200 ma up to those close to 1000 ma the shallowest crustal level is found in las matras suggesting a southward shallowing of the exposed level of basement the deformation and metamorphism associated with the collisional famatinian orogeny affect both the cuyania terrane and the adjacent western margin of gondwana and the gondwana margin was also the locus of the related arc magmatism but the compressive effects of the collision decrease in intensity toward the south the famatinian metamorphism and magmatism continue even further south into the patagonia region but the southern continuity of the cuyania terrane into this region remains uncertain

cretaceous and paleogene saline lacustrine source rocks discovered in the southern junggar basin nw china abstract saline lacustrine source rocks in china provide the resource basis for many giant oil fields here we report the first discovery of such source rocks in the piedmont area of the northern tianshan mountains in the southern junggar basin of nw china these source rocks are cretaceous and paleogene in age organic geochemistry and trace element data suggest that these mudstones were formed in a brackish saline lacustrine environment characterized by deep water and reducing conditions and in a warm and dry paleoclimate evidence for this environment includes mudstone pr ph values of 0 4 and negative ce and eu anomalies the total organic carbon toc contents of these cretaceous and paleogene mudstones are typically 0 5 with maximum values of 1 45 and 2 22 respectively signifying moderate to high organic matter abundance rock eval and kerogen analyses suggest that the organic matter was dominated by type ii kerogen the mudstones are generally thermally mature suggesting favorable conditions for hydrocarbon particularly oil generation oil source correlation confirms the oil generation of these two sets of source rocks whose development are controlled mainly by reducing environments these cretaceous and paleogene mudstones should therefore be a target for regional exploration in the southern junggar basin in addition to the known gas producing jurassic rocks this oil bearing potential is unique amongst the early cretaceous and eocene oligocene central asian petroliferous basins as the eastern portion of this realm is considered to host predominantly jurassic coal based source rocks giving rise to numerous large gas fields rather than oil resources

neoproterozoic backarc basin sensitive high resolution ion microprobe u pb and sm nd isotopic evidence from the eastern pampean ranges argentina the eastern pampean ranges comprise high grade supracrustal sequences with linear belts of mafic ultramafic bodies representing ophiolite remnants new u pb and nd isotopic data suggest that the tectonic evolution of the pampean ranges started ca 640 ma with the deposition of supracrustal sequences in a backarc basin between a neoproterozoic magmatic arc to the east and the pampia terrane to the west ophiolite remnants of this backarc basin yielded a whole rock isochron indicating the age of 647 77 ma 2 and nd initial time t of 5 2 sensitive high resolution ion microprobe u pb data for detrital metasediments show provenance patterns with two main age populations the older 1 1 0 9 ga and the younger between ca 0 7 and 0 6 ga the neoproterozoic population is relatively more abundant in sediments of the easternmost units of the eastern pampean ranges and becomes less abundant toward the west depleted mantle ages show a similar pattern with ages generally increasing from east 1 42 ga to west 1 76 ga suggesting the presence of neo proterozoic sources to the east of the ranges the provenance data do not support previous evolution models for the eastern pampean ranges according to which the supracrustal sequence represents the passive margin of the rio de la plata craton early cambrian collision and high grade metamorphism mark the final stages of evolution of the belt and were shortly followed by calc alkaline metaluminous and peraluminous granitic magmatism ca 530 514 ma the results suggest that the geological evolution of the eastern pampean ranges took place between ca 640 and 514 ma coeval with other brasiliano orogens in brazil e g the paraguay and araguaia fold belts

warm arctic continents during the palaeocene eocene thermal maximum the palaeocene eocene thermal maximum petm 55 5 ma is a geologically relatively brief episode of extreme warmth both deep and surface ocean temperatures increased by up to 5 c in equatorial waters and up to 8 c in mid and high latitude waters from the continents the annual mean air temperature response during the petm is still largely unknown mainly due to a lack of quantitative temperature proxies and sufficient suitable continuous high resolution records recently a new proxy for continental temperature reconstructions has been proposed based on the distribution of membrane lipids of bacteria in present day soils j w h weijers s schouten j c van den donker e c hopmans j s sinninghe damste 2007 environmental controls on bacterial tetraether membrane lipid distribution in soils geochimica et cosmochimica acta 71 703 713 and shown to reconstruct annual mean air temperature in this study we applied this new proxy in an attempt to reconstruct the air temperature in high latitude continental areas during the petm by analysis of a marine sedimentary sequence obtained from the lomonosov ridge in the central arctic ocean integrated ocean drilling program expedition 302 site 004 hole a the results indicate a warming of 8 c above background values of 17 c this warming is coincident with a similar rise in sea surface temperatures documented earlier our results thus further confirm the warm conditions in the arctic and point to a strongly reduced latitudinal temperature gradient during the petm 2007 elsevier b v all rights reserved

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

the puncoviscana trough a large basin of late precambrian to early cambrian age on the pacific edge of the brazilian shield during the late precambrian to early cambrian a large basin with a homogeneous psammitic pelitic sediment fill existed in the area of the nw argentine andes it is now exposed in different tectonic levels this basin of meridional elongation was situated on a stable continental margin at the western edge of the brazilian shield it was underlain by segmented older continental crust according to the modal and chemical composition of the greywackes and subgreywackes a predominant metasedimentary source may be supposed four clastic facies types indicate a transport by gravity currents within a submarine fan system while massive red pelites represent cut off periods and rare carbonates deposition on rises the gravity currents derived from easterly directions the sedimentation age is proved by a rich ichnofauna and some medusoid impressions

climate sensitivity to arctic seaway restriction during the early paleogene abstract the opening and closing of ocean gateways affects the global distribution of heat salt and moisture potentially driving climatic change on regional to global scales between 65 and 45 million years ago ma during the early paleogene exchange between the arctic and global oceans occurred through two narrow and shallow seaways the greenland norway seaway and the turgai strait sediments from the arctic ocean suggest that during this interval the surface ocean was warm brackish and episodically enabled the freshwater fern azolla to bloom the precise mechanisms responsible for the development of these conditions in the paleogene arctic remain uncertain here we show results from an isotope enabled atmosphere ocean general circulation model which indicate that northern hemisphere climate would have been very sensitive to the degree of oceanic exchange through the arctic seaways we also present modelled estimates of seawater and calcite 18o for the paleogene by restricting these seaways we simulate freshening of the surface arctic ocean to 6 psu and warming of sea surface temperatures by 2 c in the north atlantic and 5 10 c in the labrador sea our results may help explain the occurrence of low salinity tolerant taxa in the arctic ocean during the eocene and provide a mechanism for enhanced warmth in the north western atlantic we propose that the formation of a volcanic land bridge between greenland and europe could have caused increased ocean convection and warming of intermediate waters in the atlantic if true this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates and supports a tectonic trigger hypothesis for the paleocene eocene thermal maximum petm

spatial heterogeneity of sources of branched tetraethers in shelf systems the geochemistry of tetraethers in the berau river delta kalimantan indonesia abstract the bulk organic matter composition total organic carbon toc content and 13ctoc and composition of isoprenoid and branched glycerol dialkyl glycerol tetraethers gdgt in surface sediments from 43 stations in the berau river delta east kalimantan indonesia including two coast shelf transects and stations within the river mouth were examined to reveal the spatial heterogeneity in these parameters in order to assess the impact of a tropical river loaded with suspended matter on the sedimentary organic matter in the shelf system the high resolution study showed that despite the extensive transport of eroded soil material by the river to the sea terrestrial organic matter and brgdgts are only deposited on a relatively small part of the shelf the concentrations of brgdgts are highest up to 120 g g 1 toc in sediments deposited in and close to the mouth of the berau river and their distribution indicates that they represent a mixture of soil derived and river in situ produced brgdgts crenarchaeol concentrations reach 700 g g 1 toc in sediments deposited on the outer shelf due to thaumarchaeotal production in shelf waters this results in a strong gradient 0 93 0 03 in the bit index with high values in the river mouth and low values on the shelf the decline in the bit index is caused by both decreasing concentrations of the brgdgts and increasing concentrations of crenarchaeol the bit index shows a highly significant but non linear relationship with 13ctoc on the shelf in the area not under the direct influence of the berau river cyclic brgdgts become relatively dominant most probably due to in situ production in the alkaline pore waters of the surface sediments the spatial heterogeneity of sources of brgdgts on the berau shelf complicates the use of brgdgts as temperature proxies application of the global soil calibration to sedimentary mixtures of brgdgts in the river influenced area of the shelf results in a severe underestimation of mean annual air temperature mat by 6 c this is due to the mixed origin of the brgdgts which are not only derived from soil erosion but likely also from riverine production as has been observed for other river systems comparison of the berau shelf other shelf systems indicates that in situ production of brgdgts in shelf sediments is a widespread phenomenon that is especially pronounced at water depths of ca 50 300 m it is hypothesized that this is so because benthic in situ production of heterotrophic brgdgt producing bacteria is fueled by the higher delivery of fresh organic matter to these sediments as the consequence of higher primary productivity in shelf waters and a decreased mineralization due to the relatively short settling times of particles on the shelf for palaeoclimatic studies of marine shelf sediments the application of brgdgts as proxies is severely complicated by the heterogeneity of sources of brgdgts comparison of the brgdgt composition of soils with those of shelf sediments may assist in deciding if sedimentary brgdgts are predominantly derived from soil erosion several methods to do so are discussed

early paleogene temperature history of the southwest pacific ocean reconciling proxies and models we present a new multiproxy tex86 18o and mg ca marine temperature history for canterbury basin eastern new zealand that extends from middle paleocene to middle eocene including the paleocene eocene thermal maximum petm and early eocene climatic optimum eeco in light of concerns that proxy based sea surface temperature sst estimates are untenably warm for the southwest pacific during the eocene we review the assumptions that underlie the proxies and develop a preliminary paleo calibration for tex86 that is based on four multiproxy eocene records that represent an sst range of 15 34 c for the southwest pacific paleogene we show that tex86l exhibits the best fit with the eocene paleo calibration ssts derived from related proxies tex86h 1 tex86 exhibit a systematic warm bias that increases as tex86 values decrease a warm bias of 4 7 c where tex86 0 7 the tex86l proxy indicates that southwest pacific sst increased by 10 c from middle paleocene to early eocene with sst maxima of 26 28 c tropical during the petm and eeco and an sst minimum of 13 16 c cool warm temperate at the middle late paleocene transition 58 7 ma the base of the eeco is poorly defined in these records but the top is well defined in canterbury basin by a 2 5 c decrease in sst and bottom water temperature bwt in the latest early eocene 49 3 ma bwt falls from a maximum of 18 20 c in the eeco to 12 14 c in the middle eocene overall cooler temperatures are recorded in the mid waipara section which may reflect a deeper 500 m water depth and less neritic depositional setting compared with hampden and odp 1172 200 m water depth the high ssts and bwts inferred for the petm and eeco can be reconciled with eocene coupled climate model results if the proxies are biased towards seasonal maxima and the likely effect of a proto east australian current is taken into account

provenance analysis and tectonic setting of the ordovician clastic deposits in the southern puna basin nw argentina provenance studies on early to middle ordovician clastic formations of the southern puna basin in north western argentina indicate that the sedimentary detritus is generally composed of reworked crustal material tremadocquartzrich turbidites tolar chico formation mean composition q t 89 f7 l4 are followed by volcaniclastic rocks and greywackes tolillar formation mean q t 33 f42 l25 these are in turn overlain by volcaniclastic deposits mean qt24 f30 l46 of the diablo formation late arenig early llanvirn that are intercalated by lava flows all units were deformed in the ocloyic orogeny during the middle and late ordovician sandstones of the tolar chico formation are characterized by th sc ratios 1 la sc ratios 10 whereas associated fine grained wackes show slightly lower values for both ratios lree light rare earth elements enrichment of the arenites is 50 chondrite eu eu values are between 0 72 and 0 92 and flat hree heavy rare earth elements patterns indicate a derivation from mostly felsic rocks of typical upper crustal composition the e n d t s e d values scatter around 11 to 9 the calculated nd t d m residence ages vary between 1 8 and 2 0 ga indicating contribution by a palaeoproterozoic crustal component the th sc and la sc ratios of the tolillar formation are lower than those of the tolar chico formation normalized ree rare earth elements patterns display a similar shape to paas post archaean average australian shale but with higher abundances of hrees eu eu values range between 0 44 and 1 17 where the higher values reflect the abundance of plagioclase and feldspar bearing volcanic lithoclasts average e n d t s e d values are less negative at 5 1 and nd t d m are lower at 1 6 ga this is consistent with characteristics of regional rocks of upper continental crust composition which most probably represent the sources of the studied detritus the rocks of the diablo formation have the lowest th sc and la sc ratios lower lree abundances than the average continental crust and are slightly enriched in hrees eu eu values are between 0 63 and 1 17 the nd isotopes e n d t s e d 3 to 1 t d m 1 2 ga indicate that one source component was less fractionated than both the underlying early ordovician and the overlying middle ordovician units synsedimentary vulcanites in the diablo formation show the same isotopic composition our data indicate that the sedimentary detritus is generally composed of reworked crustal material but that the diablo formation appears to contain 80 of a less fractionated component derived from a contemporaneous continental volcanic arc there are no data indicating an exotic detrital source or the accretion of an exotic block at this part of the gondwana margin during the ordovician

mid latitude continental temperatures through the early eocene in western europe branched glycerol dialkyl glycerol tetraethers brgdgts are increasingly used to reconstruct mean annual air temperature maat during the early paleogene however the application of this proxy in coal deposits is limited and brgdgts have only been detected in immature coals i e lignites using samples recovered from schoningen germany 48 n palaeolatitude we provide the first detailed study into the occurrence and distribution of brgdgts through a sequence of early eocene lignites and associated interbeds brgdgts are abundant and present in every sample in comparison to modern studies changes in vegetation type do not appear to significantly impact brgdgt distributions however there are subtle differences between lignites representing peat forming environments and siliciclastic nearshore marine interbed depositional environments using the most recent brgdgt temperature calibration matmr developed for soils we generate the first continental temperature record from central western continental europe through the early eocene lignite derived maat estimates range from 23 to 26 c while those derived from the nearshore marine interbeds exceed 20 c these estimates are consistent with other mid latitude environments and model simulations indicating enhanced mid latitude early eocene warmth in the basal part of the section studied warming is recorded in both the lignites 2 c and nearshore marine interbeds 2 3 c this culminates in a long term temperature maximum likely including the early eocene climatic optimum eeco although this long term warming trend is relatively well established in the marine realm it has rarely been shown in terrestrial settings using a suite of model simulations we show that the magnitude of warming at schoningen is broadly consistent with a doubling of co2 in agreement with late paleocene and early eocene pco2 estimates

co2 driven ocean circulation changes as an amplifier of paleocene eocene thermal maximum hydrate destabilization changes in ocean circulation have been proposed as a trigger mechanism for the large coupled climate and carbon cycle perturbations at the paleocene eocene thermal maximum petm ca 55 ma an abrupt warming of oceanic intermediate waters could have initiated the thermal destabilization of sediment hosted methane gas hydrates and potentially triggered sediment slumps and slides in an ensemble of fully coupled atmosphere ocean general circulation model aogcm simulations of the late paleocene and early eocene we identify such a circulation driven enhanced intermediate water warming critically we find an approximate twofold amplification of atlantic intermediate water warming when co2 levels are doubled from 2x to 4x preindustrial co2 compared to when they are doubled from 1x to 2x this warming is largely focused on the equatorial and south atlantic and is driven by a significant reduction in deep water formation from the southern ocean this scenario is consistent with altered petm circulation patterns inferred from benthic carbon isotope data and the intensity of deep sea carbonate dissolution in the south atlantic the linkage between intermediate water warming and gas hydrate destabilization could provide an important feedback in the establishment of peak petm warmth

petrogenesis of migmatites and leucogranites from sierra de molinos salta northwest argentina a petrologic and geochemical study abstract in sierra de molinos eastern cordillera nw argentina the relationship between different components of an anatectic system developed in high temperature and low pressure conditions we use petrological and geochemical variations to investigate the formation of granite magma from migmatites that derived from metasedimentary protoliths this provides evidence of the processes that occur during the evolution melting segregation and crystallization stages of partially molten terranes for which particular components protolith residuum and melt fractions are identified mass balance calculations are used to estimate the degree of partial melting and the degree of melt extraction in migmatites petrological and compositional data suggest that migmatites from this region are the result of open system processes and that fluid absent melting played a major role in the formation of migmatites and leucogranites the geochemical evidence suggests that the compositional variation within the anatectic rocks from molinos can be understood as a result of 1 variable degrees of melt residuum separation and 2 fractional crystallization of the anatectic melt compared to the protolith most of the migmatites have melt depleted compositions up to 0 25 of melt extraction in the same fashion most of the leucosomes represent cumulate products of fractional crystallization this means that they have lost some liquid of evolved composition and represent evidence of the melt extraction pathways and linkage to the magma ascent conduits

life at the top of the greenhouse eocene world a review of the eocene flora and vertebrate fauna from canada s high arctic early middle eocene ca 53 38 ma sediments of the eureka sound group in canada s arctic archipelago preserve evidence of lush mixed conifer broadleaf rain forests inhabited at times by alligators turtles and diverse mammals including primates tapirs brontotheres and hippo like coryphodon this biota reflects a greenhouse world offering a climatic and ecologic deep time analog of a mild ice free arctic that may be our best means to predict what is in store for the future arctic if current climate change goes unchecked in our review of the early middle eocene arctic flora and vertebrate fauna we place the arctic fossil localities in historic geographic and stratigraphic context and we provide an integrated synthesis and discussion of the paleobiology and paleoecology of these eocene arctic forests and their vertebrate inhabitants the abundance and diversity of tapirs and plagiomenids both rare elements in midlatitude faunas and the absence of artiodactyls early horses and the hyopsodontid condylarth hyopsodus well represented at midlatitude localities are peculiar to the eocene arctic the eocene arctic macrofloras reveal a forested landscape analogous to the swamp cypress and broadleaf floodplain forests of the modern southeastern united states multiple climate proxies indicate a mild temperate early middle eocene arctic with winter temperatures at or just above freezing and summer temperatures of 20 c or higher and high precipitation at times this high precipitation resulted in freshwater discharge into a nearly enclosed arctic ocean basin sufficient to cause surface freshening of the arctic ocean supporting mats of the floating fern azolla fluctuating arctic ocean sea level due to freshwater inputs as well as tectonics produced temporary land bridges allowing land plants and animals to disperse between north america and both europe and asia

the distribution of long chain n alkan 2 ones in peat can be used to infer past changes in ph abstract long chain c21 c33 n alkan 2 ones are biomarkers ubiquitous in peat deposits however their paleoenvironmental significance lacks constraints here we evaluate the influence ph exerts on the occurrence of long chain n alkan 2 ones in chinese peats a comparison of the distribution in a collection n 65 of modern peat samples with different ph ph values 4 4 8 6 from china demonstrates that their distribution is significantly different in acid compared to alkaline peat this difference can be explained by the ph control on the conversion of n alkan 2 one precursor compounds n alkanes and fatty acids transfer functions between ph and n alkan 2 one ratios were established using linear and logarithmic regression models we then applied these proxies to reconstruct variations of paleo ph in the dajiuhu peat sequence to identify the history of peatland acidification over the last 13 kyr we find significant changes in paleo ph during the deglaciation early holocene and relate these to times of dry climate in the region the drought induced peat acidification is supported by observations from modern drying events in the peatland we propose that long chain n alkan 2 ones in peats have potential to trace paleo ph changes across the deglaciation and holocene although further research from different peatlands and time periods is still needed

high temperatures in the terrestrial mid latitudes during the early palaeogene the early paleogene 56 48 myr provides valuable information about the earth s climate system in an equilibrium high p rm co 2 p co 2 world high ocean temperatures have been reconstructed for this greenhouse period but land temperature estimates have been cooler than expected this mismatch between marine and terrestrial temperatures has been difficult to reconcile here we present terrestrial temperature estimates from a newly calibrated branched glycerol dialkyl glycerol tetraether based palaeothermometer in ancient lignites fossilized peat our results suggest early palaeogene mid latitude mean annual air temperatures of 23 29 c with an uncertainty of 4 7 c 5 10 c higher than most previous estimates the identification of archaeal biomarkers in these same lignites previously observed only in thermophiles and hyperthermophilic settings support these high temperature estimates these mid latitude terrestrial temperature estimates are consistent with reconstructed ocean temperatures and indicate that the terrestrial realm was much warmer during the early palaeogene than previously thought

cenozoic foreland basin system in the central andes of northwestern argentina implications for andean geodynamics and modes of deformation 1 cenozoic strata in the central andes of northwestern argentina record the development and migration of a regional foreland basin system analogous to the modern chaco parana alluvial plain paleocene lower eocene fluvial and lacustrine deposits are overlain by middle upper eocene hypermature paleosols or an erosional disconformity representing 10 15 myr this supersol disconformity zone is traceable over a 200 000 km2 area in the andean thrust belt and is overlain by 2 6 km of upward coarsening eastward thinning upper eocene through lower miocene fluvial and eolian deposits middle miocene pliocene fluvial lacustrine and alluvial fan deposits occupy local depocenters with contractional growth structures paleocurrent and petrographic data demonstrate westerly provenance of quartzolithic and feldspatholithic sediments detrital zircon ages from cenozoic sandstones cluster at 470 491 522 544 555 994 and 1024 1096 ma proterozoic mesozoic clastic and igneous rocks in the puna and cordillera oriental yield similar age clusters and served as sources of the zircons in the cenozoic deposits arc derived zircons become prominent in oligo miocene deposits and provide new chronostratigraphic constraints sediment accumulation rate increased from 20 m myr during paleocene eocene time to 200 600 m myr during the middle to late miocene the new data suggest that a flexural foreland basin formed during paleocene time and migrated at least 600 km eastward at an unsteady pace dictated by periods of abrupt eastward propagation of the orogenic strain front despite differences in deformation style between bolivia and northwestern argentina lithosphere in these two regions flexed similarly in response to eastward encroachment of a comparable orogenic load beginning during late paleocene time

genesis of aluminous and intermediate granulites a case study in the eastern sierras pampeanas argentina abstract we report petrologic and geochemical features of anhydrous granulites from the eastern sierras pampeanas argentina aluminous grt crd bearing granulite is the most abundant rock type in the study region and hosts intermediate opx grt bearing granulites as interlayered lenses both granulite types crystallized under similar p t conditions of t 850 900 c and p c 7 5 kbar the formation of grt crd granulites by subsolidus dehydration conflicts with the absence of k feldspar in them moreover the aluminous granulites have an ree pattern that precludes postulating they derived by close system metamorphism of an extensively weathered protoliths comparing mineral and rock chemistry with experimental results in simple systems acfm akf and afm permits the mineralogical changes and the bulk composition evolution experienced by granulites during melting to be identified this work demonstrates that orthopyroxene is a primary phase in opx grt granulites however never crystallized within aluminous granulites the aluminous granulites have both mineral and chemical compositions matching those expected for a residuum derived from the partial melting of a greywacke like sedimentary precursor compared with the composition of the average continental crust aluminous granulites are depleted in most lithophile trace elements and lree have somewhat low k rb ratios and high contents of elements having high partition coefficients for garnet and or ilmenite hree y cr ni however aluminous granulites have initial sr isotope ratios 0 713 we discuss the possibility that an intense but short lived melting event led to isotopic disequilibrium during melting of biotite bearing protoliths leaving a granulitic residuum with lower initial sr isotope ratios in contrast opx grt granulites have trace element features e g high sr contents and ree patterns with marked positive eu anomalies that do not support the idea that they are simply residues left after biotite dehydration melting and melt extraction rather these rocks display several petrological major and trace element and isotopic features that suggest they formed through the interaction of mafic magmas and aluminous granulites

the evolution of latitudinal temperature gradients from the latest cretaceous through the present abstract latitudinal temperature gradients are a defining characteristic of the climate system using thermometric indicators including 18o plant and animal fossils glycerol dialkyl glycerol tetraether gdgt proxies and clumped isotope estimates we document marine and terrestrial temperature gradients for the latest cretaceous late paleocene early eocene early oligocene pliocene and recent the changes in gradients reflect the transition greenhouse to icehouse conditions the evolution of latitudinal temperature gradients in marine and terrestrial realms are similar but has some distinctive differences marine temperatures are generally warmer than those on land except for the late paleocene early eocene the marine records show distinct inflection points at 30 and 50 latitude indicating the existence of frontal systems in the ocean except for the late paleocene early eocene the marine records show an increasingly steeper trend from latest cretaceous through recent being most pronounced after the early oligocene greenhouse icehouse transition this trend reflects the increasing intensity of high latitude and polar cooling as the icehouse state developed during the late paleocene early eocene the oceans were characterized by slightly warmer tropics and much warmer higher latitudes than at present the continents have generally had tropical temperatures like those of today varying by

structural evolution of a composite middle to lower crustal section the sierra de pie de palo northwest argentina 1 the sierra de pie de palo of northwest argentina preserves middle to lower crustal metamorphic rocks that were penetratively deformed during ordovician accretion of the precordillera terrane to the gondwana margin new structural petrologic and geochronologic data from a 40 km structural transect reveals that the sierra de pie de palo preserves a middle to lower crustal ductile thrust complex consisting of individual structural units and not an intact ophiolite and cover sequence top to the west thrusting occurred intermittently on discrete ductile shear zones from 515 to 417 ma and generally propagated toward the foreland with progressive deformation ordovician crustal shortening and peak metamorphic temperatures in the central portion of the sierra de pie de palo were synchronous with retro arc shortening and magmatic flare up within the famatina arc accretion of the precordillera terrane resulted in the end of arc flare up and the onset of synconvergent extension by 439 ma continued synextensional to postextensional convergence was accommodated along progressively lower grade shear zones following terrane accretion and the establishment of a new plate margin west of the precordillera terrane the results support models of cordilleran orogens that link voluminous arc magmatism to periods of regional shortening the deformation metamorphic and magmatic history within the sierra de pie de palo is consistent with models placing the region adjacent to the famatina margin in the middle cambrian and not as basement to the precordillera terrane

the pacific gondwana margin in the late neoproterozoic early paleozoic detrital zircon u pb ages from metasediments in northwest argentina reveal their maximum age provenance and tectonic setting abstract u pb detrital zircon ages are reported from puncoviscana formation late neoproterozoic early cambrian and meson group late cambrian greywackes of northwest argentina to constrain provenance and depositional environment the new data are combined with previously published detrital zircon ages to show that puncoviscana formation age patterns contain two broad groups late mesoproterozoic early neoproterozoic 1150 850 ma and late neoproterozoic early cambrian 650 520 ma with their relative proportions varying inversely with youngest component age the 1150 850 ma age components are dominant in greywackes with oldest late neoproterozoic components 600 ma the former diminish considerably when late neoproteozoic components become dominant and younger to 520 ma a northernmost greywacke sample from purmamarca jujuy is distinctive whilst its zircon age pattern partly resembles other puncoviscana formation samples it contains no cambrian late neoproterozoic ages the youngest ages being early neoproterozoic this may reflect an early neoproterozoic passive margin depocentre for the formation or an older early neoproterozoic succession within it which may predate the brasiliano orogeny in brazil the youngest age components c 520 ma in a greywacke from rancagua cachi salta province dominate an almost unimodal pattern suggestive of contemporary volcanic sources at a late early cambrian depocentre detrital zircon age patterns of the meson group lizoite formation have major cambrian latest neoproterozoic components resembling those of the puncoviscana formation but its mesoproterozoic component is diminished and there are no significant age components of this age small youngest components at c 500 ma suggest a maximum late cambrian stratigraphic age the puncoviscana formation detrital zircon patterns suggest a provenance in a continental hinterland having a stabilised extensive late mesoproterozoic orogen with minor paleoproterozoic and archean precursors and a more variable late neoproterozoic orogen containing an evolving sequence of less extensive subcomponents a direct relationship with the brazilian shield is suggested with sediment supplies originating within active margin orogens of the interior and collisional orogens at the suture between african and south american cratons but ultimate deposition in passive margin environments of western gondwanaland

hot summers in the bighorn basin during the early paleogene during the early paleogene climate in continental interiors is thought to have been warmer and more equable than today but estimates of seasonal temperature variations during this period are limited global and regional climate models of the paleogene predict cooler temperatures for continental interiors than are implied by proxy data and predict a seasonal range of temperature that is similar to today here we present a record of summer temperatures derived from carbonate clumped isotope thermometry of paleosol carbonates from paleogene deposits in the bighorn basin wyoming united states our summer temperature estimates are 18 c greater than mean annual temperature estimated from analysis of fossil leaves when coupled these two records yield a seasonal range of temperature similar to that in the region today with winter temperatures that are near freezing these data are consistent with our high resolution climate model output for the early eocene in the bighorn basin we suggest that temperatures in continental interiors during the early paleogene greenhouse were warmer in all seasons but not more equable than today if generally true this removes one of the long standing paradoxes in our understanding of terrestrial climate dynamics under greenhouse conditions

tectono metamorphic evolution of a high to medium grade ductile deformed metagabbro metadiorite from the arenosa creek shear zone western sierras pampeanas argentina abstract textural and compositional changes affecting a quartzose metagabbro metadiorite in a ductile shear zone which is part of the early palaeozoic famatinian orogenic belt of the western sierras pampeanas argentina allow reconstruction of its tectono metamorphic evolution as well as the metamorphic conditions achieved on the basis of paragenetic associations and microfabrics three overprinted deformation events are differentiated a a relict ductile event developed within the granulite facies at temperatures exceeding 800 c and pressures 5 5 5 kbar b a two stage mylonitic deformation event under high to medium grade metamorphic conditions at temperatures 500 700 c and pressures between 6 and 7 kbar and c a brittle deformation event developed at low greenschist facies below 400 c evidence of the first event is preserved in the protolith although the subsequent deformation obliterated it partially slight modal and chemical changes were detected between the protolith and its mylonitic products deformation ages of the mylonites that vary from 441 9 1 9 ma to 438 7 1 9 ma are internally consistent and compatible with existing geological and geochronological data for the region suggesting that during the famatinian orogeny the western margin of gondwana was characterized by several episodes of ductile deformation that varied in time and space

oxygen isotope and paleobotanical estimates of temperature and δ18o latitude gradients over north america during the early eocene empirical estimates of climate parameters such as mean annual temperature mat are essential to describe both ancient climate and to ground truth climate model simulations of past climates in terrestrial settings no single proxy record is able to provide detailed temporal yet geographically widespread information and it thus becomes essential that paleoclimatic information obtained from different proxies be comparable as an example of how to compare estimates and to illustrate what can be learned by doing so we measured oxygen isotope ratios of phosphate in the tooth enamel of fossil mammals and the body scales of freshwater fish in order to estimate the mean annual temperature mat in which they lived the samples were collected from paleogene rocks of the bighorn green river and powder river basins of wyoming earliest eocene samples provide mat estimates that are similar to mat estimates for the same times and areas obtained from leaf margin analysis furthermore isotopic data from the paleocene eocene thermal maximum petm which has not yet yielded fossil floras indicate a significantly higher mat of 26 c we also used temperature estimates obtained by both methods to investigate paleoelevation and to reconstruct geographic patterns of mat over north america for the early eocene larger laramide basins have higher temperatures and lower inferred elevations compared to associated volcanic highlands where cooler temperatures are consistent with substantial elevations in turn latitudinal gradients in temperature indicate that warming centered on polar regions played an important role during the eocene hothouse lastly we show that the reconstructed eocene relation between oxygen isotope ratios of precipitation and mat is significantly different from the modern relation between these two variables because the relation has changed over time the modern correlation should not be used to estimate paleo mat from measurements of oxygen isotope ratios in fossil material

a mechanism to thin the continental lithosphere at magma poor margins crustal thinning where continental plates break apart can be accomplished by a system of conjugate concave downward faults instead of multiple normal faults through exhumation of mid crustal and mantle material where continental plates break apart slip along multiple normal faults provides the required space for the earth s crust to thin and subside1 after initial rifting however the displacement on normal faults observed at the sea floor seems not to match the inferred extension2 here we show that crustal thinning can be accomplished in such extensional environments by a system of conjugate concave downward faults instead of multiple normal faults our model predicts that these concave faults accumulate large amounts of extension and form a very thin crust 10 km by exhumation of mid crustal and mantle material this transitional crust is capped by sub horizontal detachment surfaces over distances exceeding 100 km with little visible deformation our rift model is based on numerical experiments constrained by geological and geophysical observations from the alpine tethys and iberia newfoundland margins3 4 5 6 7 8 9 furthermore we suggest that the observed transition from broadly distributed and symmetric extension to localized and asymmetric rifting is directly controlled by the existence of a strong gabbroic lower crust the presence of such lower crustal gabbros is well constrained for the alpine tethys system4 9 initial decoupling of upper crustal deformation from lower crustal and mantle deformation by progressive weakening of the middle crust is an essential requirement to reproduce the observed rift evolution this is achieved in our models by the formation of weak ductile shear zones

fast sediment underplating and essentially coeval juvenile magmatism in the ordovician margin of gondwana western sierras pampeanas argentina metasedimentary high pressure upper amphibolite facies gneisses 1 2 0 1 gpa and 780 45 c at las chacras sierra de valle fertil are tectonically juxtaposed to the westernmost parts outboard of the famatinian early ordovician magmatic arc which underwent syn plutonic middle crust high grade metamorphism at lower pressure u pb shrimp zircon data suggest that the gneisses contain famatinian igneous detritus so that their sedimentary protoliths were probably deposited in a forearc basin and then rapidly underthrust and accreted to the lower crust of the arc essentially coevally with arc magmatism at 468 4 ma chemically and isotopically juvenile garnetiferous amphibolites within the gneisses are recognised as representing the most primitive magmas so far observed in this belt which has often been considered to be a continental arc derived from isotopically mature sources this is consistent with the idea that at least part of the dominant famatinian magmatism originated in depleted mantle but was heavily contaminated by crustal components

eocene sea temperatures for the mid latitude southwest pacific from mg ca ratios in planktonic and benthic foraminifera abstract we have used laser ablation inductively coupled plasma mass spectrometry la icp ms to measure elemental mg ca al ca mn ca zn ca sr ca and ba ca ratios of 13 species of variably preserved early to middle eocene planktonic and benthic foraminifera from new zealand the foraminifera were obtained from ashley mudstone mid waipara river south island which was deposited at bathyal depth ca 1000 m on the northern margin of the east facing canterbury basin at a paleo latitude of ca 55 s la icp ms data yield trace element depth profiles through foraminifera test walls that can be used to identify and exclude zones of surficial contamination and infilling material resulting from diagenetic coatings mineralisation and detrital sediment screened mg ca ratios from 5 species of foraminifera are used to calculate sea temperatures from late early to early middle eocene ca 51 to 46 5 ma a time interval that spans the termination of the early eocene climatic optimum eeco during this time sea surface temperatures sst varied from 30 to 24 c and bottom water temperatures bwt from 21 to 14 c comparison of mg ca sea temperatures with published 18o and tex86 temperature data from the same samples hollis et al 2009 shows close correspondence indicating that la icp ms can provide reliable mg ca sea temperatures even where foraminiferal test preservation is variable agreement between the three proxies also implies that mg ca temperature calibrations for modern planktonic and benthic foraminifera can generally be applied to eocene species although some species e g v marshalli show significant calibration differences the mg ca ratio of the eocene ocean is constrained by our data to be 35 50 lower than the modern ocean depending on which tex86 temperature calibration kim et al 2008 liu et al 2009 is used to compare with the mg ca sea temperatures sea temperatures derived from 18o analysis of foraminifera from waipara show amplified variability relative to the mg ca and tex86 proxies this amplified variability is probably a diagenetic effect although it is possible that this eocene 18o record contains an ice volume component the amplification signalling that temperature changes may have been accompanied by growth and collapse of ephemeral polar ice sheets on timescales of ca 0 5 myr

puncoviscana folded belt in northwestern argentina testimony of late proterozoic rodinia fragmentation and pre gondwana collisional episodes stratigraphic correlations and tectonic analysis suggest that the puncoviscana fold belt of northwestern argentina was an intracontinental basin with bimodal igneous suites that formed in connection with the breakup of the rodinia supercontinent at 800 ma several lines of evidences point to an initial lithosphere rupture possibly induced by a rising mantle plume the earliest synrift igneous products are represented by ultra potassic dykes and alkaline lava flows of high lree hree and low zr nb y nb ratios the dyke emplacements and the initiation of rifting were probably synchronous they pass laterally and upwards middle part of the puncoviscana succession into basalts of alkaline transitional character oib like source the distinctive chemical feature of these lavas are very similar to the source of oceanic island basalts thus they are thought to represent a magmatism associated with the rift and rift drift transition stage during this stage of rifting probably true oceanic crust was formed the upper part of the puncoviscana sequence late precambrian lower cambrian in age comprises a thick and monotonous sequence of pillow lavas massive basaltic flows and minor volcanic breccias and hyaloclastites these lavas exhibit morb trace element characteristics with high feot and tio2 low k2o and p2o5 flat light ree spectra little or no depletion in nb and ta this volcanism consists of the major and latest effusive episode from the puncoviscana basin which was slightly modified by subduction processes the geodynamical model proposed for the generation of these volcanic rocks could have been developed in two stages in the first stage the volcanic event is compatible with a progressive opening of a continental rift leading to formation of a mature oceanic basin in contrast the second stage shows the effects of a completed wilson cycle including a primitive volcanic arc which continued until the accreted cuyania arequipa belen antofalla caba terrane against the proto gondwana western borderland of the amazonian shield 535 ma

changing atmospheric co2 concentration was the primary driver of early cenozoic climate the early eocene climate optimum eeco which occurred about 51 to 53 million years ago was the warmest interval of the past 65 million years with mean annual surface air temperature over ten degrees celsius warmer than during the pre industrial period subsequent global cooling in the middle and late eocene epoch especially at high latitudes eventually led to continental ice sheet development in antarctica in the early oligocene epoch about 33 6 million years ago however existing estimates place atmospheric carbon dioxide co2 levels during the eocene at 500 3 000 parts per million and in the absence of tighter constraints carbon climate interactions over this interval remain uncertain here we use recent analytical and methodological developments to generate a new high fidelity record of co2 concentrations using the boron isotope 11 b composition of well preserved planktonic foraminifera from the tanzania drilling project revising previous estimates although species level uncertainties make absolute values difficult to constrain co2 concentrations during the eeco were around 1 400 parts per million the relative decline in co2 concentration through the eocene is more robustly constrained at about fifty per cent with a further decline into the oligocene provided the latitudinal dependency of sea surface temperature change for a given climate forcing in the eocene was similar to that of the late quaternary period this co2 decline was sufficient to drive the well documented high and low latitude cooling that occurred through the eocene once the change in global temperature between the pre industrial period and the eocene caused by the action of all known slow feedbacks apart from those associated with the carbon cycle is removed both the eeco and the late eocene exhibit an equilibrium climate sensitivity relative to the pre industrial period of 2 1 to 4 6 degrees celsius per co2 doubling 66 per cent confidence which is similar to the canonical range 1 5 to 4 5 degrees celsius indicating that a large fraction of the warmth of the early eocene greenhouse was driven by increased co2 concentrations and that climate sensitivity was relatively constant throughout this period

terrestrial paleoenvironmental reconstructions indicate transient peak warming during the early eocene climatic optimum major changes in climate and ecology occurred during the early eocene climatic optimum sometime between 52 and 50 ma recent work suggests that the timing and duration of the event are characterized by different responses in the marine and terrestrial realms and that traditional causal mechanisms may not adequately explain such differences we applied high resolution paleopedology geochemical analysis and phytolith biostratigraphy techniques to paleosol suites within the well described wind river formation of western wyoming usa this multiproxy record indicates a short 1 m y peak period of carbon isotopic enrichment up to 2 higher and elevated pco2 high temperatures up to 8 c higher increased precipitation up to 500 mm yr 1 higher and shifts in fl oral composition up to 10 terrestrial climatic and ecological changes of this kind during the early eocene climatic optimum are consistent with changes in contemporaneous records that have been ascribed to high atmospheric pco2 but a transient peak interval suggests that the cause of high atmospheric pco2 during the early eocene was likely not increased volcanism or decreased silicate weathering which operate on longer timescales instead terrestrial records from across western north america agree that early eocene climatic optimum changes may have been caused by other sources such as a combination of increased ventilation of oceanic carbon and increased petroleum generation in sedimentary basins the climatic and environmental changes exhibited by this and other north american terrestrial records also defi ne a pattern of regional response that is relevant for understanding the impacts of global climate change events

asian eocene monsoons as revealed by leaf architectural signatures abstract the onset and development of the asian monsoon systems is a topic that has attracted considerable research effort but proxy data limitations coupled with a diversity of definitions and metrics characterizing monsoon phenomena have generated much debate failure of geological proxies to yield metrics capable of distinguishing between rainfall seasonality induced by migrations of the inter tropical convergence zone itcz from that attributable to topographically modified seasonal pressure reversals has frustrated attempts to understand mechanisms underpinning monsoon development and dynamics here we circumvent the use of such single climate parameter metrics in favor of detecting directly the distinctive attributes of different monsoon regimes encoded in leaf fossils leaf form adapts to the prevailing climate particularly under the extreme seasonal stresses imposed by monsoons so it is likely that fossil leaves carry a unique signature of past monsoon regimes leaf form trait spectra obtained from fossils from eocene basins in southern china were compared with those seen in modern leaves growing under known climate regimes the fossil leaf trait spectra including those derived from previously published fossil floras from northwestern india were most similar to those found in vegetation exposed to the modern indonesia australia monsoon i am which is largely a product of seasonal migrations of the itcz the presence of this distinctive leaf physiognomic signature suggests that although a monsoon climate existed in eocene time across southern asia the characteristics of the modern topographically enhanced south asia monsoon had yet to develop by the eocene leaves in south asia had become well adapted to an i am type regime across many taxa and points to the existence of a pervasive monsoon climate prior to the eocene no fossil trait spectra typical of exposure to the modern east asia monsoon were seen suggesting the effects of this system in southern china were a much later development

persistent near tropical warmth on the antarctic continent during the early eocene epoch the warmest global climates of the past 65 million years occurred during the early eocene epoch about 55 to 48 million years ago when the equator to pole temperature gradients were much smaller than today1 2 and atmospheric carbon dioxide levels were in excess of one thousand parts per million by volume3 4 recently the early eocene has received considerable interest because it may provide insight into the response of earth s climate and biosphere to the high atmospheric carbon dioxide levels that are expected in the near future5 as a consequence of unabated anthropogenic carbon emissions4 6 climatic conditions of the early eocene greenhouse world however are poorly constrained in critical regions particularly antarctica here we present a well dated record of early eocene climate on antarctica from an ocean sediment core recovered off the wilkes land coast of east antarctica the information from biotic climate proxies pollen and spores and independent organic geochemical climate proxies indices based on branched tetraether lipids yields quantitative seasonal temperature reconstructions for the early eocene greenhouse world on antarctica we show that the climate in lowland settings along the wilkes land coast at a palaeolatitude of about 70 south supported the growth of highly diverse near tropical forests characterized by mesothermal to megathermal floral elements including palms and bombacoideae notably winters were extremely mild warmer than 10 c and essentially frost free despite polar darkness which provides a critical new constraint for the validation of climate models and for understanding the response of high latitude terrestrial ecosystems to increased carbon dioxide forcing

the tectonic evolution of the transbrasiliano lineament in northern parana basin brazil as inferred from aeromagnetic data data from six airborne magnetic surveys were compiled and analyzed to develop a structural interpretation for the transbrasiliano lineament in northern parana basin brazil magnetic lineaments interpreted to reflect geologic contacts and structures at different depths were illuminated using the matched filter technique applied to aeromagnetic anomalies field based structural measurements generally support our magnetic analysis we estimated three primary magnetic zones i a zone of deep magnetic sources at 20 km depth ii an intermediate basement zone at 6 km depth and iii a shallow zone of near surface geological features at 1 5 km depth the deepest zone exhibits three major ne trending crustal discontinuities related to the transbrasiliano lineament dividing the region into four geotectonic blocks anomalies associated with the intermediate zone indicate directional divergence of subsidiary structures away from the main transbrasiliano fault which strikes n30 e the shallow magnetic zone includes near surface post brasiliano orogenic granites our analysis identified ne trending sigmoidal lineaments around these intrusions indicating intense zones of deformation associated with probable shear structures at the shallow depth zone magnetic anomalies caused by cretaceous alkaline intrusive bodies and basalts of the serra geral formation are enhanced by the matched filter method these igneous bodies are related to extensional nw striking lineaments and seismicity aligned along these lineaments suggests that they currently are reactivated prior to flexural subsidence of the parana basin reactivation processes along transcurrent elements of the transbrasiliano lineament promoted extensional processes and formed initial parana basin depocenters cretaceous and more recent sedimentation also correlate with reactivations of ne striking structures

timing of high grade metamorphism early palaeozoic u pb formation ages of titanite indicate long standing high t conditions at the western margin of gondwana argentina 26 29 s concordant u pb ages of c 530 510 ma and c 470 420 ma on titanite from calcsilicate orthogneiss and amphibolite rocks constrain the age of high t metamorphism in the early palaeozoic mobile belt at the western margin of proterozoic gondwana argentina 26 29 s the u pb ages document the time of titanite formation at high t conditions according to the stable mineral paragenesis and occurrence of titanite in the metamorphic fabric the presence of migmatite at all sample sites indicates temperatures were c 650 c titanite formed at similar metamorphic conditions at different times on the regional and on the outcrop scale the titanite crystals preserved their u pb isotopic signatures and chemical composition under ongoing upper amphibolite to granulite facies temperatures different thermal peaks or deformations are only detected by the different u pb ages and not by changes in the mineral paragenesis or metamorphic fabric of the samples the range of u pb ages e g in the ordovician and silurian c 470 460 440 430 420 ma is interpreted as the effect polyphase deformation with deformation enhanced recrystallization of titanite and or different thermal peaks during a long standing geographically fixed high t regime in the mid crust of a continental magmatic arc a clear correlation of the different ages with distinct tectonic events e g collision of terranes is not possible based on the present knowledge of the region

evolution of the sierras de cordoba argentina abstract located in the southeastern part of the sierras pampeanas argentina the pampean ranges of cordoba show the evolution at the western margin of the rio de la plata craton from extensional stages during neoproterozoic times to compressive stages during the pampean orogeny the cumbre de gaspar group represents distal deep sea clastic sedimentation deposited in a passive margin environment very possibly during a time of incipient oceanization the santa sabina group representing shelf sedimentation rests conformably on the cumbre de gaspar group stocks of granites and granodiorites of calc alkaline affinity intruded the cumbre de gaspar group during the early pampean or earlier the polyphase pampean orogeny involves several distinct metamorphic and orogenic events metamorphism is discussed using the chemical composition of minerals the major effect of the pampean orogeny was the formation of a pile of westward thrust blocks the rio de la plata craton thrust above its marginal basin forms the uppermost unit the intrusion of the el pilon granite dated at 520 5 ma post dates these tectonic and metamorphic events after this main orogenic event the domain remained permanently located on the cratonic side of younger famatinian and andean orogenic events the mermela group probably corresponds to the molasse of the pampean orogeny and to the base of a new sedimentary cycle it is difficult to distinguish famatinian tectonics in the sierras de cordoba because the main orogeny occurred further west however this orogenic cycle is marked by the intrusion of the large achala batholith during the late palaeozoic and mesozoic the sierras de cordoba remained a stable platform the whole region was rejuvenated by the andean orogeny which induced tilted blocks in its foreland and the pocho volcanics of shoshonitic affinities

origin and age of ultramafic rocks and gabbros in the southern puna of argentina an alleged ordovician suture revisited ultramafic rocks and gabbros are exposed in the southern puna nw argentina in tectonic association with continental arc related ordovician volcano sedimentary successions and granitoids the origin of this mafic rock suite has been debated for three decades as either representing an ordovician terrane suture primitive ordovician arc related rocks or relics of the pre ordovician basement in tectonic contact with the ordovician retro arc basin successions we present the first u pb ages of primary and inherited zircon from gabbros of this mafic ultramafic assemblage la icp ms analyses on cores and rims of these zircon grains yielded a concordia age of 543 4 7 2 ma for the gabbroic rocks other analysed zircons have mesoproterozoic and early ediacaran core and rim ages indicating that the magmas also assimilated meso and neoproterozoic crustal material prior to final crystallization the mafic rocks witnessed higher metamorphic grade than associated ordovician rocks which are unmetamorphosed or only affected by anchimetamorphism the gabbros are mostly tholeiitic and enriched in zr th as well as other incompatible elements and have end t 540ma ranging from 1 3 to 7 4 with most of the values between 5 and 7 147sm 144nd ratios show evidence of weak crustal contamination the mafic rocks do not reveal any affinity to mid ocean ridge basalts in their geochemistry but point instead to an emplacement in an active plate margin arc environment chromites from ultramafic rocks show typical ti al cr fe3 abundances found in magmatic arc rocks the formation of the gabbros and the associated ultramafic rocks in the southern argentine puna is related to the evolution of the margin of the pampia terrane including the puncoviscana basin during the late neoproterozoic and earliest cambrian in contrast to previous interpretations the rocks predate the ordovician evolution of the central proto andean active margin consequently interpretations assuming these rocks to represent an oceanic terrane suture of ordovician age have to be dismissed as much as all palaeotectonic models that define ordovician terranes in the central andes based on assumption that the ultramafic rocks and gabbros exposed in the southern puna mark plate boundaries

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

timing constraints on building an intermediate plutonic arc crustal section u pb zircon geochronology of the sierra valle fertil la huerta famatinian arc argentina 1 the sierra valle fertil range in northwestern argentina exposes a tilted crustal section through the ordovician famatinian arc from 25 km to shallow crustal paleodepths fourteen new u pb zircon crystallization ages of magmatic rocks from sierra valle fertil area show that this section of the arc was built over a short time interval during the ordovician between 485 and 465 ma zircon rim ages demonstrate that high grade metamorphism and migmatization were synchronous with magmatic emplacement inherited ages in some of the plutonic rocks as well as detrital zircons in the metasedimentary framework suggest that the famatinian arc was emplaced into a thick miogeoclinal cover to the thinned margin of the proto south american continent in the ordovician which represents a part of gondwana docking of the precordilleran terrane outboard of proto south america led to the cessation of arc magmatism in the valle fertil area and preservation of the arc in its early stages after 60 myr of subduction during the pampean and famatinian magmatic stages our age data from the sierra valle fertil indicate that wet mafic magmas were emplaced into the section at a rate typical for modern island arcs 30 km3 km 1 myr 1 the production of intermediate to felsic magmas in the upper plate was a result of partial melting of the metasedimentary framework and hybridization with mantle derived melts and resulted in the generation of tonalites granodiorites and granites in the upper crust at a rate of 100 km3 km 1 myr 1 similar to major magmatic flare ups in the mature arcs of north american cordillera the sierra valle fertil arc section is a type example of an immature cordilleran arc before major crustal thickening and crustal overturn takes place in the upper plate the famatinian arc section may also be an equivalent to the crustal architecture of more mature modern island arcs such as parts of the aleutians caribbean and japan

flat meridional temperature gradient in the early eocene in the subsurface rather than surface ocean sea surface temperature estimates from the early eocene indicate an unusually flat meridional temperature gradient a re evaluation of the proxy used to derive these temperatures argues against this interpretation

age constraints on the tectonic evolution and provenance of the pie de palo complex cuyania composite terrane and the famatinian orogeny in the sierra de pie de palo san juan argentina abstract new u pb age determinations confirm earlier interpretations that the strongly deformed and metamorphosed mafic and intermediate igneous rocks of the pie de palo complex represent a mesoproterozoic fragment of suprasubduction zone oceanic crust a gabbroic pegmatite interpreted to have formed during arc rifting or subsequent back arc spreading yielded a u pb age of 1204 5 3 4 7 ma highly tectonized ultramafic mafic cumulates occurring at the structural base of the pie de palo complex and previously interpreted to represent remnants of a primitive arc phase prior to rifting and back arc spreading could not be dated but should be older than 1204 ma if these inferences are correct tabular sill like bodies of leucogabbro diorite and calc alkaline tonalite granodiorite sills yielded ages of 1174 43 and 1169 8 7 ma respectively they may represent a younger more evolved arc phase established after arc rifting or a younger tectonically unrelated mesoproterozoic arc shrimp analysis of metamorphic zircon rims with low th u ratios in vvl 110 gave a 206pb 238u age of 455 10 ma similar to lower intercept dates determined by discordia lines combined these data indicate that the bulk of the amphibolite facies metamorphism present in the pie de palo complex was generated during the famatinian orogeny analysis of six single detrital zircon grains in a metasedimentary quartzofeldspathic garnet mica schist tectonically interleaved with the igneous rocks of the pie de palo complex and tentatively correlated with the difunta correa metasedimentary sequence of other workers yielded three age populations 1150 1160 ma 1050 1080 ma and 665 ma indicating that these sedimentary rocks were deposited during the late neoproterozoic or early paleozoic in addition they confirm structural evidence that intercalation of rocks of the pie de palo complex with isolated slivers of these sedimentary rocks is due to tectonic imbrications these ages are also consistent with a laurentian provenance and earlier interpretations that these rocks once represented a sedimentary cover to the pie de palo complex the zircon population of 1050 1080 ma could be derived from grenville age felsic plutons identified elsewhere in the pie de palo complex by other workers however no evidence has been found in our samples for a grenville age orogenic event invoked previously to explain accretion of the oceanic pie de palo complex to laurentia prior to the late neoproterozoic early cambrian rifting and drift of cuyania

ordovician metamorphism and plutonism in the sierra de quilmes metamorphic complex implications for the tectonic setting of the northern sierras pampeanas nw argentina towards unravelling the geodynamic setting of the northern sierras pampeanas nw argentina we describe the tectono metamorphic and geochronologic evolution of sub greenschist to granulite facies metamorphic sediments granitoid plutons and pegmatites in the ordovician sierra de quilmes metamorphic complex the protoliths of the metasediments are represented by a sequence of turbidites and minor calcsilicate rocks of the neoproterozoic to cambrian puncoviscana formation the metamorphic complex consists of four zones including the 1 chlorite 2 biotite muscovite 3 garnet cordierite sillimanite and 4 orthopyroxene zones zones 3 and 4 show an increasing degree of anatexis reaching large scale diatexis in the orthopyroxene zone at p t conditions exceeding 800 c and 600 mpa at or shortly after the metamorphic peak the granitic to tonalitic cafayate pluton intruded approximately along the boundary between anatectic and non anatectic rocks retrograde near isobaric cooling of the middle crust was accompanied by non penetrative ductile shearing at granulite to amphibolite facies p t conditions evidence for significant prograde deformation is absent in the sierra de quilmes metamorphic complex monazite and titanite u pb isotopic data constrain the metamorphic peak in migmatites and calcsilicate rocks to be at or slightly prior to 470 ma retrograde amphibolite facies mineral reactions led to continuous formation of monazite and titanite during slow cooling between 470 ma and 455 ma u pb data the composite cafayate pluton intruded over a time interval of several million years between 477 ma sm nd isochron and 460 ma monazite and titanite u pb isochron followed by pegmatites a younger group of pegmatites was emplaced in the country rocks at the end of the ordovician 440 ma rb sr mineral isochrons postdating most of the retrograde shear zones resetting of the muscovite k ar and 40ar 39ar system in weakly deformed pegmatites and crystallisation of new muscovite in low grade metamorphic sediments at 400 416 ma is attributed to minor late greenschist and sub greenschist facies metamorphism and deformation the massive early ordovician heat transfer the absence of major prograde deformation and subsequent prolonged phases of non penetrative deformation in the high grade metamorphic zones during slow near isobaric cooling contradict crustal thickening and continent collision models as have been proposed for the southern sierras pampeanas we suggest continuous or stepwise extensional tectonics in a back arc or a mobile belt tectonic environment for the ordovician sierra de quilmes and the northern sierras pampeanas in general an extensional setting of the northern sierras pampeanas in the ordovician is in agreement with the coeval formation of marine extensional sediment basins in vicinity of the sierras pampeanas in northwestern argentina and southern bolivia

evidence for seasonality in early eocene high latitude sea surface temperatures abstract specific challenges still exist in our understanding of past greenhouse climate states whilst climate model simulations using atmospheric co2 concentrations consistent with proxy estimates broadly align with lower latitude proxy temperature estimates they struggle to reproduce the warming implied by proxies at higher latitudes especially in the marine realm this inconsistency has often led to the conclusion that climate models are insufficiently sensitive here we analyse the distribution of photozoan and heterozoan carbonates which provide important constraints for latitudinal sea surface temperature sst gradients to assess data model mismatches for the early eocene climatic optimum the carbonate facies distribution is compared against quantitative geochemical proxy temperature estimates 18 o mg ca clumped isotopes and tex86 and a new hadcm3l climate simulation good correspondence exists between the simulated cold month ssts and photozoan carbonates indicating hadcm3l is effectively reconstructing meridional temperature gradients into mid latitudes whilst there is good agreement between simulated mean annual ssts and geochemical proxy estimates in low latitudes the 18 o mg ca and tex86 estimates instead align with warm month ssts at higher latitudes in light of the carbonate facies evidence and consistency between our simulation and available terrestrial proxy temperature estimates this study supports previous claims that a warm season bias exists in many middle and high latitude sst estimates this helps resolve the discrepancy between climate simulations and marine proxies and shows that climate models and data might be more closely aligned than is appreciated further we demonstrate that simple and widely available proxies can play a fundamental role in contextualising wider paleoclimate uncertainties

convergent cenozoic co2 history reconstructions of atmospheric carbon dioxide concentrations over the past 65 million years are heading towards consensus it is time for systematic testing of the proxies against measurements and against each other

seasonal variability in arctic temperatures during early eocene time abstract as a deep time analog for today s rapidly warming arctic region early eocene 52 53 ma rock on ellesmere island in canada s high arctic 79 n preserves evidence of lush swamp forests inhabited by turtles alligators primates tapirs and hippo like coryphodon although the rich flora and fauna of the early eocene arctic imply warmer wetter conditions than at present the quantification of eocene arctic climate has been more elusive by analyzing oxygen isotope ratios of biogenic phosphate from mammal fish and turtle fossils from a single locality on central ellesmere island we infer early eocene arctic temperatures including mean annual temperature mat of 8 c mean annual range in temperature of 16 5 19 c warm month mean temperature of 19 20 c and cold month mean temperature of 0 3 5 c our seasonal range in temperature is similar to the range in estimated mat obtained using different proxies in particular relatively high estimates of early eocene arctic mat and sst by others that are based upon the distribution of branched glycerol dialkyl glycerol tetraether gdgt membrane lipids in terrestrial soil bacteria and isoprenoid tetraether lipids in marine crenarchaeota fall close to our warm month temperature suggesting a bias towards summer values from a paleontologic perspective our temperature estimates verify that alligators and tortoises by way of nearest living relative based climatic inference are viable paleoclimate proxies for mild above freezing year round temperatures although for both of these reptilian groups past temperature tolerances probably were greater than in living descendants

cambrian to devonian geologic evolution of the sierra de comechingones eastern sierras pampeanas argentina evidence for the development and exhumation of continental crust on the proto pacific margin of gondwana abstract crystalline rocks from the sierra de comechingones eastern sierras pampeanas evolved through three distinct orogenic cycles during the eopalaeozoic 1 the first tectono thermal event named pampean orogeny 550 to 505 ma which peaked in the early cambrian was responsible for extensive metamorphism partial melting juvenile magmatism rapid decompression and persistent tectonic activity large part of the crustal section that was residing at middle levels c 27 km was heated above 800 c during the thermal peak stage of the pampean orogeny decompression of the pampean orogen s core took place at this high temperature the exhumation mechanism that assisted rapid uplifting combined the effects of ongoing tectonic forces with a buoyant instability created by a large amount of anatectic magmas in the middle to lower crust 2 beginning at the early ordovician the famatinian orogeny produced an overall shortening causing pervasive textural reworking of the cambrian metamorphic sequences under a high strain regime by being adjacent to the famatinian magmatic arc the western border of the cambrian crystalline package absorbed imposed deformation along a crustal scale ductile shear zone within this zone the high grade metamorphic rocks were reworked and re hydrated to lower temperature assemblages crystalline rocks currently exposed in the sierra de comechingones show that they crystallised and were exhumed in a setting where tectono thermal activity lasted even though it might have waned until the middle palaeozoic from the latest neoproterozoic c 550 ma until the late devonian c 360 ma tectonic activity was intermittently acting indicating continuous convergence along the proto pacific margin of gondwana

hot orogens tectonic switching and creation of continental crust many granulite terrains were too hot to have formed during continental collision rather along with many high grade metamorphic terrains that typify continental crust most formed in accretionary orogens during tectonic switching when prolonged lithospheric extension was interrupted by intermittent transient contraction based on modern and ancient examples tectonic switching occurs when slab retreat induces upper plate extension causing arc splitting formation of microcontinent slivers and backarc basins then intermittent arrival of buoyant oceanic plateaus induces transient flat subduction or slab flip and crustal thickening during slab retreat basaltic magmas produced from decompressed asthenosphere advect into the extending orogen causing granulite facies metamorphism and granite generation but subsequent thickening during flat subduction cools the region thickening is focused in the thermally softened backarc region and if sediment filled a hot short lived 10 m y narrow 50 100 km orogenic belt forms such thickening is often misleadingly ascribed to arc or microcontinent collision once slab retreat mode is reestablished lithospheric extension recommences and a new arc backarc system forms generally outboard arrival of another plateau will reverse the procedure and another short lived hot orogen will form within the orogenic system cycles of tectonic switching efficiently produce continental crust

revisiting the paleomires of western india an insight into the early paleogene lignite corridor abstract the paleocene eocene lignite sequences of western india occur in the bikaner nagaur barsingsar gurha and kasnau matasukh lignite seams and barmer kapurdi and giral lignite seams basins of rajasthan whereas those in the cambay vastan rajpardi and tadkeshwar lignite seams saurashtra bhavnagar upper and lower lignite seams and kachchh matanomadh and panandhro lignite seams basins are located in gujarat the position of the cambay basin gujarat being closer to the equator during the early eocene period makes it pertinent to understand the variations in petrographic and geochemical constituents of gujarat and rajasthan lignites in space and time floral growth which largely depends on the climate of the region and its geographical location has an important role in the formation of mire nevertheless the peat forming plant communities nutrient supply bacterial activity types of deposition temperature ph and redox potential impart various characteristics to coal and are reflected in macerals black bands in gujarat and rajasthan lignites are strongly gelified compared to brownish bands and are stratified in nature they are dominantly composed of huminite maceral group while liptinites and inertinites occur in subordinated amount these lignites of gujarat and rajasthan have high values of gelification index gi and low tissue preservation index tpi indicating thereby a continuous presence of wet condition in the basin and slow subsidence rate however due to fluctuating water level in the basins few sections experienced relatively oxic episodes indicated by relatively high inertinite content study of the ground water index gwi and vegetation index vi of these lignites indicates rheotrophic to mesotrophic hydrological condition the study revealed that the lignites of rajasthan and gujarat were formed during the transgressive phase under coastal marshy setting however there were intermittent episodes of fluvial activities which gave rise to supratidal flood plains

early paleozoic accretionary orogenies in nw argentina growth of west gondwana abstract two early paleozoic orogenic cycles in the gondwana margin of nw argentina were driven by subduction and interrupted by collision of continental ribbons of laurentian affinity subduction started at the passive margin of gondwana possibly in response to the end of amalgamation of the supercontinent the passive margin was underlain by a hyper extended continent ocean transition and low angle subduction gave rise to a wide and hot fore arc region during the pampean orogenic cycle the arrival of the first continent ribbon ended the pampean cycle steepened the subduction further heating the fore arc and restarting arc magmatism after a magmatic lull 250 300 km trenchwards initiating the famatinian orogenic cycle this cycle started with a 30 ma long period of extension and marine sedimentation followed by the arrival of the second continent ribbon and inversion the back arc initiating a 20 ma long shortening event culminating with the shutting down of the arc this event gave rise to a 300 km wide low topography hot orogeny thus the many peculiarities of the two paleozoic orogens of nw argentina result from a subduction history that efficiently transferred heat to a 300 400 km wide belt of turbidite dominated sediments that was first part of the pampean fore arc and then part of the famatinian retroarc developed at the extended continental margin of gondwana the two orogenies with continued high heat flux lasted 110 ma giving rise to two calc alkaline arcs separated by a 300 km belt of high t low p migmatites and peraluminous granites formed by anatexis of sediments deposited on the passive margin as well as those deposited in the wide pampean fore arc these turbidite dominated sequences were metamorphosed and melted to form a continental crystalline basement and accreted to the cratonic margin adding 500 km of crystalline rocks to the margin of gondwana at the same time that a similar process was happening in eastern australia along the same continental margin interestingly this wide accretionary orogen has now become the region where the andean system developed a wide orogeny above flat slab subduction