palynological analyses of eocene to oligocene sediments from dsdp site 338 outer voring plateau article i nfo against the background of the profound global climatic shift from greenhouse to icehouse conditions during the eocene oligocene transition major geographic and oceanographic changes were taking place in the norwegian greenland sea region the voring plateau was a prominent structural feature which influenced the evolution of water mass circulation in the nordic seas and we present detailed palaeoenvironmental reconstructions of this structure new palynological results suggest that shallow water inner neritic environments were developed across parts of the voring plateau during early eocene times with terrestrial and brackish water palynomorphs indicating that both basement highs to the north and the crestal part of the voring escarpment may have been emergent a transition from marginal marine to open marine conditions occurred around 44 ma ago with the complete subsidence of the voring plateau below sea level facilitating inter basinal surface water circulation and promoted a significant increase in photic zone fertility carbon sequestration associated with such enhanced productivity in the late eocene nordic seas may have contributed to declining cenozoic atmospheric carbon dioxide levels thence to declining global temperatures and the development of limited northern hemisphere continental ice on greenland in the latest eocene

cenozoic ice rafting history of the central arctic ocean terrigenous sands on the lomonosov ridge the cenozoic ice rafted debris ird history of the central arctic is reconstructed utilizing the terrigenous coarse sand fraction in iodp 302 cores from 0 to 273 meters composite depth this holocene middle eocene quantitative record of terrigenous sand accumulation on the lomonosov ridge along with qualitative information on grain texture and composition confirms the interpretation that ice initiation sea ice and glacial ice occurred 46 ma in the arctic and provides a long term pattern of arctic ice expansion and decay since the middle eocene ird mass accumulation rates range from 0 to 0 13 g cm2 ka in the middle eocene and from 0 to 0 36 g cm2 ka in the neogene ird mass accumulation rate mar maxima in the miocene and pliocene cooccur with either glacial initiation or intensification in the sub arctic the 46 25 ma ird onset in the central arctic slightly precedes the earliest evidence of ice in the antarctic and compares in timing with a 1000 ppm decrease in atmospheric concentrations of co2 the decline of pco2 in the middle eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface arctic ocean especially during times of low insolation

pollen distribution in marine sediments on the continental margin off northern california abstract pollen analysis of 84 samples from surface sediment of the continental margin off northern california between 38 and 39 n and 123 and 124 w shows that the composition of pollen assemblages in this part of the north pacific ocean reflects the regional vegetation of the russian river and other local drainage basins of the northern coast of california systematic trends in the quantitative and qualitative variations in these marine pollen assemblages show that fluvial and marine transport are important factors in determining the nature of pollen assemblages offshore these conclusions are supported by the analyses of pollen in rivers of the north coast of california and in particulate matter collected in a mid slope sediment trap

the roussillon basin s france a case study to distinguish local and regional events between 6 and 3 ma the roussillon basin is a non silled miocene sedimentary basin filling a late oligocene early miocene graben the basin was intensively impacted by the 2 messinian fluvial erosion as evidenced in exposed sections in seismic profiles and in deep boreholes drilled for hydrocarbon exploration as the basin was open to the mediterranean sea the huge drop in sea level at the peak of the messinian salinity crisis is clearly recorded along with the subsequent sudden marine reflooding and the resulting prograding sedimentary filling particularly in gilbert type fan deltas here the messinian erosional surface mes is accurately mapped in a high resolution document which corrects the confusion resulting from the set of 1 50 000 scale regional maps aim of the 3d reconstruction of the mes is to modernize geological mapping a crucial challenge for mediterranean and peripheral areas thanks to a reliable chronostratigraphy provided by planktonic foraminifers calcareous nannofossils micro and macro mammal remains paleomagnetism and a 10 be cosmogenic nuclide derived study our reconstruction is one of the most comprehensive models of changes in sea level from 6 to 3 ma after the marine reflooding of the mediterranean basin at 5 46 ma the fluctuations in sea level recorded in the roussillon basin were forced by global changes following reflooding the prades large olistostrome collapsed prepared by the previous exhumation along the canigou fault the olistostrome is a good example of a local accident resulting from messinian events the exceptional changes in sea level at the peak of the messinian salinity crisis deeply marked the roussillon basin momentarily overprinting the pyrenean orogenesis key words roussillon basin messinian subaerial erosion zanclean sedimentary filling prades olistostrome

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

coeval eocene blooms of the freshwater fern azolla in and around arctic and nordic seas abstract for a short time interval c 1 2 myr during the early middle eocene 49 myr the central arctic ocean was episodically densely covered by the freshwater fern azolla implying sustained freshening of surface waters coeval azolla fossils in neighboring nordic seas were thought to have been sourced from the arctic the recognition of a different azolla species in the north sea raised doubts about this hypothesis here we show that no less than five azolla species had coeval blooms and spread in the arctic and nw european regions a likely trigger for these unexpected azolla blooms is high precipitation prevailing by the end of the warmest climates of the early eocene climatic optimum eeco

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

late neoproterozoic cambrian granitic magmatism in the aracuai orogen brazil the eastern brazilian pegmatite province and related mineral resources

a suture related accretionary wedge formed in the neoproterozoic aracuai orogen se brazil during western gondwanaland assembly abstract the aracuai orogen represents a branch of the brasiliano orogenic system developed between the sao francisco and congo cratons in neoproterozoic time we conducted detailed studies on a complex schist belt located to the west of the rio doce magmatic arc along the assumed suture zone of the aracuai orogen this 30 km wide and 100 km long ns trending belt includes pelitic schists with intercalations of quartzites metaultramafic schists and diopsidites intruded by collisional granites u pb ages from detrital zircon grains point to distinct provenances for different portions of the schist belt the lower succession shows an age spectra and maximum depositional age 819 ma similar to passive margin deposits of the precursor basin the upper succession yielded a maximum deposition age around 600 ma pointing toward the rio doce arc as the main sediment source thrust to the west onto the guanhaes basement and separated on the east from the ediacaran rio doce magmatic arc by reverse dextral faults the schist belt exhibits the architecture of an asymmetric flower structure developed in transpressional regime the distribution of metamorphic assemblages across the schist belt characterizes a collisional barrovian type metamorphic zoning in which the sillimanite kyanite staurolite and garnet zones are locally duplicated by thrusts p t conditions range from 700 c at 7 5 kbar at the western base of the pile to 550 c at 5 5 kbar at the eastern top of the package zircon u pb ages record metamorphic overprinting on the sheared top of the basement at 560 20 ma and crystallization of collisional granites at 544 10 ma our results allow us to interpret the schist belt as a suture related accretionary wedge and suggest that basin closure during the assembly of west gondwanaland lasted to the ediacaran cambrian boundary in the aracuai orogen

the pan african west congo belt in the republic of congo congo brazzaville stratigraphy of the mayombe and west congo supergroups studied by detrital zircon geochronology abstract the african part of the neoproterozoic aracuai west congo orogen forms a more than 1400 km long belt running from gabon in the north to angola in the south parallel to the south atlantic coast it consists of the west congo fold belt in the west and a largely undeformed sedimentary foreland basin in the east in the republic of congo congo brazzaville these are known as respectively the mayombe fold belt and the niari basin the mayombe fold belt is largely made up of strongly deformed metasedimentary rocks of the mayombe supergroup and its reworked granitoid basement complex the niari basin comprises the sedimentary strata of the west congo supergroup which contain a unit of diamictite and associated cap carbonate related to the marinoan ca 635 ma glaciation in this paper detrital zircon u pb data are employed to investigate the relationships between the mayombe and west congo supergroups in congo brazzaville as well as the relationships with similar stratigraphic units in the democratic republic of congo dr congo unfortunately major differences in stratigraphical nomenclature exist between congo brazzaville and dr congo which together with geological differences complicate comparisons the terminology used in this paper follows the congo brazzaville tradition u pb data have been obtained by la icp ms on 1674 zircon grains from samples of the mayombe and west congo supergroups seven and eight samples respectively two of the samples have palaeoproterozoic ages the other samples are of neoproterozoic age zircons from the latter fall into four main age groups group 1 500 800 ma forming 8 of the total population group 2 900 1200 ma 29 group 3 1800 2300 ma 19 and group 4 2500 3100 ma 31 only ca 13 of the zircons fall outside of these groups most zircons of group 1 600 800 ma are interpreted to have been derived from late neoproterozoic magmatic arc rocks and syn to post collisional granites of the aracuai orogen in brazil since rocks of these ages are rare in the congo craton to the east most of group 2 zircons have probably been derived from early neoproterozoic 1000 900 ma rhyolitic and granitic rocks exposed in dr congo the palaeoproterozoic and archaean zircons of groups 3 and 4 may have been derived both from eastern and western source regions none of the stratigraphical units beneath the marinoan diamictite contain the 500 800 ma zircons of group 1 this is interpreted to indicate deposition of these units during the earlier neoproterozoic rift and drift phases in the history of the aracuai west congo orogen while the strata that do contain group 1 zircons were deposited during the collisional phases and post collisional uplift a significant hiatus is likely to be present beneath the marinoan diamictite based on these results a revision of the stratigraphy of the mayombe and west congo supergroups is recommended three granitoid rocks and two metasedimentary samples from the reworked basement complex have also been investigated yielding palaeoproterozoic ages 2050 2100 ma for the granites and palaeoproterozoic and archaean detrital zircon ages for the metasedimentary rocks sm nd isotope data have been obtained on a number of meta argilitic and siltstone samples all samples yielded palaeoproterozoic model ages indicating mixing of sediments of different ages as also observed in the zircon age distributions

extensional collapse in the neoproterozoic aracuai orogen eastern brazil a setting for reactivation of asymmetric crenulation cleavage the aracuao orogen of eastern brazil is one of many brasiliano pan african orogens formed during the neoproterozoic assembly of gondwana its western edge bordering the sao francisco craton is the serra do espinhaco fold thrust belt in which top up to the west reverse sense faults west verging folds f1 and east dipping spaced to phyllitic cleavage s1 developed we have found that the kinematics of deformation changes markedly at the hinterland margin of this fold thrust belt here beneath a plateau known as the chapada acaua metadiamictite and fine grained pelitic schist comprise an east dipping belt that contains an assemblage of structures indicative of top down to the east normal sense shear this assemblage includes a cascade of f2 folds that refold f1 folds and verge down the dip of the belt s enveloping surfaces vertical tension gashes and top down to the east rotated clasts based on the presence of these structures we propose that the plateau exposes a regional scale normal sense shear zone here called the chapada acauashear zone casz because f2 folds refold f1 folds normal sense shear in the casz occurred subsequent to initial west verging thrusting considering this timing of motion in the casz we suggest that the zone accommodated displacement of the internal zone of the aracuao orogen down relative to its foreland fold thrust belt and thus played a role in extensional collapse of the orogen the casz trends parallel to preserved thrusts to the west and thus may represent an inverted thrust fault notably throughout the casz s1 schistosity has been overprinted by a pervasive west dipping asymmetric crenulation cleavage s2 the sigmoid shape of s1 surfaces in s2 microlithons require that slip on each s2 surface was top down to the west s2 cleavage is axial planar to the down dip verging f2 folds based on its geometry we suggest that s2 cleavage initiated either as an antithetic extensional crenulation cleavage during reverse sense shear or as a near vertical asymmetric crenulation cleavage formed during east west shortening of a preexisting east dipping schistosity subsequent normal sense shear in the casz reactivated this cleavage causing clockwise rotation of s2 domains as viewed looking along strike to the north in a manner similar to that of rotational bookshelf faults such movement could have accommodated concomitant vertical flattening of the casz during extensional collapse

sequence stratigraphic framework of proterozoic successions in eastern brazil abstract first order regional unconformities separate proterozoic supracrustal rocks of the gas bearing sao francisco craton and surrounding thrust and fold belts eastern brazil into four genetic stratigraphic units which constitute 1st order basin fill sequences espinhaco canastra paranoa vazante macaubas and bambui sequences the espinhaco 1st order sequence ca 1 73 1 50 ga records a stage of aborted lithospheric stretching of the sao francisco congo continental mass the espinhaco basin displays a steer s head geometry where four 2nd order sequences are recognized prerift rift transitional and flexural third order rift propagation unconformities allowed the definition of three 3rd order synrift sequences within the rift 2nd order sequence the 2nd order flexural sequence of the espinhaco basin can be subdivided into three 3rd order transgressive regressive sequences the canastra paranoa vazante and macaubas 1st order sequences ca 1200 630 ma comprise rift to drift successions deposited during the breakup of the supercontinent rodinia and the opening of the brazilide and adamastor oceans respectively to the west and east of the sao francisco paleocontinent according to seismic data the passive margin canastra paranoa vazante 1st order sequence can be divided into two 2nd order sequences rift and passive margin the passive margin 2nd order sequence can be further subdivided into three 3rd order sequences the outcropping canastra paranoa vazante sequence consists mainly of shallow marine deposits which contain black shales marls with intervals showing high total organic carbon toc contents comprising one of the highest potential hydrocarbon source rocks of the sao francisco basin the bambui foreland 1st order sequence ca 750 550 ma formed as a consequence of thrust loading related to shortening in the brasilia fold belt on the western flank of the sao francisco craton during the closing of the brazilide ocean and the assembly of the west gondwana supercontinent the bambui sequence shows two distinct successions which reflect the main basin paleogeographic settings foredeep and flexural ramp three transgressive progradational 2nd order sequences can be recognized in the ramp succession of the bambui basin

rhyacian orosirian isotopic records from the basement of the aracuai ribeira orogenic system se brazil links in the congo sao francisco palaeocontinent abstract assembled during the rhyacian orosirian boundary the congo sao francisco palaeocontinent remained linked by a continental bridge from ca 2 ga to the atlantic ocean opening in the cretaceous to the south of that bridge precursor basins and orogenic outcomes encompassed by the neoproterozoic cambrian aracuai ribeira orogenic system aros and its african counterparts developed the aros discloses reworked basement units like the juiz de fora pocrane and quirino complexes which are key units to retrieve the palaeoproterozoic history of the congo sao francisco palaeocontinent this paper presents new u pb ages and the first lu hf in zircon signatures from those complexes all magmatic zircon grains show rhyacian and orosirian ages ranging from c 2250 ma to c 1850 ma the best concordia ages range from 2184 9 ma to 2080 19 ma hf in zircon and whole rock sm nd data disclose mantle related signatures for both the pocrane and juiz de fora complexes suggesting igneous protoliths with no or very few involvement of continental crust similarly to juvenile magmatic arcs conversely hf in zircon data for the quirino complex show an evolved signature compatible with a magmatic arc developed on a continental older crust with archaean components together with a thorough compilation on rhyacian orosirian orogenic systems roos our data allow us to envisage links within the congo sao francisco palaeocontinent comprising orogens characterised by mostly evolved isotopic signatures and zircon inheritance they are grouped into the i w roos including the mantiqueira complex the west segment of the eastern bahia belt intrusions in the south gaviao and porteirinha blocks and parts of the mineiro belt and ii e roos comprising the quirino complex basement rocks of the cabo frio tectonic domain the coastal eastern bahia belt and in africa eburnean and kimezian complexes as well as the western angola shield assembled between the w roos and e roos an orogenic system with prominent juvenile to moderately juvenile isotopic signature ju roos includes the juiz de fora and pocrane complexes and the buerarema complex at the central segment of the eastern bahia belt

neoproterozoic glacial deposits from the aracuai orogen brazil age provenance and correlations with the sao francisco craton and west congo belt article i nfo glacigenic diamictite successions of the macaubas group are widespread in the western domain of the aracuai orogen east of the sao francisco craton brazil diamictites also occur on this craton and in the african counterpart of the aracuai orogen the west congo belt detrital zircon grains from the matrix of diamictites and sandstones from the macaubas group were dated by the u pb shrimp technique the geochronological study sets the maximum depositional age of the glacial diamictites at 900 ma and indicates multiple sources for the macaubas basin with ages ranging from 900 to 2800 ma sm nd tdm model ages determined on whole rock samples range from 1 8 ga to 2 5 ga and get older up section comparison of our data with those from the cratonic area suggest that these glacial deposits can be correlated to the jequitai and carrancas diamictites in the sao francisco craton and to the lower mixtite formation of the west congolian group exposed in africa the 900 1000 ma source is most probably represented by the zadinian mayumbian volcanic rocks and related granites from the west congo belt however one of the most voluminous sources with ages in the 1 1 1 3 ga interval has not been detected in the sao francisco congo craton possible sources for these grains could occur elsewhere in africa or possibly from within the brasilia belt in western central brazil

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

tectono sedimentary evolution of sedimentary basins from late paleoproterozoic to late neoproterozoic in the sao francisco craton and aracuai fold belt eastern brazil abstract two first order regional unconformities separate proterozoic supracrustal rocks of the sao francisco craton and the aracuai fold belt eastern brazil into three genetic units these constitute three superimposed first order basin fill cycles the espinhaco macaubas salinas and bambui megasequences the paleo mesoproterozoic espinhaco megasequence ca 1730 1500 ma was deposited in an intracratonic rift sag basin in four stages pre rift rift transitional and flexural each of these stages is bounded by regional second order unconformities basin evolution was controlled primarily by tectonics although sea level variations were also important in the transitional and flexural stages after a hiatus of several hundred million years subsidence renewed during extension related to the early neoproterozoic breakup of the supercontinent rodinia with rift to passive margin sedimentation in the macaubas salinas basin ca 950 700 ma initial glaciogenic sedimentation possibly induced by uplift related to a mantle plume occurred in a rift setting subsequent a shelf slope deep sea passive margin deposits represent opening of a northern branch of the adamastor ocean tectonic magmatic climatic and eustatic processes all combined to control basin evolution the bambui megasequence ca 800 650 ma was deposited in a foreland basin during convergent and collisional tectonics related to closure of the brazilide ocean and generation of the brasilia fold belt west of the sao francisco paleocontinental region the evolution of the bambui basin whose fill is characterized by three transgressive progradational shallowing upward sequences was mainly controlled by tectonic processes

paleogene biomarker records from the central arctic ocean integrated ocean drilling program expedition 302 organic carbon sources anoxia and sea surface temperature 1 during integrated ocean drilling program expedition 302 arctic coring expedition acex a more than 200 m thick sequence of paleogene organic carbon oc rich black shale type sediments was drilled here we present new biomarker data determined in acex sediment samples to decipher processes controlling oc accumulation and their paleoenvironmental significance during periods of paleogene global warmth and proposed increased freshwater discharge in the early cenozoic specific source related biomarkers including n alkanes fatty acids isoprenoids carotenoids hopanes hopenes hopanoic acids aromatic terpenoids and long chain alkenones show a high variability of components derived from marine and terrestrial origin the distribution of hopanoic acid isomers is dominated by compounds with the biological 17 h 21 h configuration indicating a low level of maturity on the basis of the biomarker data the terrestrial oc supply was significantly enriched during the late paleocene and part of the earliest eocene whereas increased aquatic contributions and euxinic conditions of variable intensity were determined for the paleocene eocene thermal maximum and eocene thermal maximum 2 events as well as the middle eocene time interval furthermore samples from the middle eocene are characterized by the occurrence of long chain alkenones high proportions of lycopane and high ratios 0 6 of n c35 lycopane n c31 the occurrence of c37 alkenenones which were first determined toward the end of the azolla freshwater event indicates that the oc becomes more marine in origin during the middle eocene preliminary u37k based sea surface temperature sst values display a long term temperature decrease of about 15 c during the time interval 49 44 5 ma 25 to 10 c coinciding with the global benthic 18o cooling trend after the early eocene climatic optimum at about 46 ma parallel with onset of ice rafted debris sst interpreted as summer temperatures decreased to values 15 c for the late early miocene a sst of 11 15 c was determined most of the middle eocene acex sediments are characterized by a smooth short chain n alkane distribution which may point to natural oil type hydrocarbons from leakage of petroleum reservoirs or erosion of related source rocks and redeposition

subtropical mangrove and evergreen forest reveal paleogene terrestrial climate and physiography at the north pole sedimentological micropaleontological and geochemical studies of iodp leg 302 boreholes m0004a and m0002a drilled on the lomonosov ridge near the north pole are reported to construct chronostratigraphy and helped unravel paleogene palaeoclimatic these studies concluded to a mean annual temperature of sea surface waters ranging between 21 and 25 c during the paleocene eocene thermal maximum and to the occurrence of episodic ice on the arctic shelf in the earliest mid eocene pollen records are characterised by excellent preservation and identification of 112 taxa reveals a subtropical coastal vegetation comprising taxodium glyptostrobus swamps alternating with avicennia mangrove the hinterland was occupied by a subtropical evergreen forest including engelhardia and distylium occasionally replaced by rhodoleia and castanopsis lithocarpus climate was reconstructed using the climatic amplitude method resulting in the following temperature ranges for low elevations mean annual temperature 18 22 c mean temperature of the coldest month 10 14 5 c mean temperature of the warmest month 26 27 5 c and annual precipitation 1150 1400 mm palaeovegetation data allow us to establish climatostratigraphic relationships with the generalized oxygen isotope curve providing evidence for warm periods e g paleocene eocene thermal maximum petm early eocene climatic optimum eeco mid eocene climatic optimum meco alternating with cooler periods we date the latest record of avicennia mangrove in the arctic basin to the meco the azolla phase did not occur after the eeco but at 50 ma during a climatically unstable episode during the thermal optimum recurrence of rarely produced and weakly transported avicennia pollen the exceptional level of preservation of pollen grains and the high plant diversity indicate that lands of the lomonosov ridge were connected to north america in the ellesmere island region which in addition provided pollen grains of gymnosperms from high elevations these physiographic features suggesting the inflow of altitudinal cold waters into the sea may solve the apparent contradiction between possible sea ice and our reconstructed air temperatures during the middle eocene

magnetostratigraphic calibration of eocene oligocene dinoflagellate cyst biostratigraphy from the norwegian greenland sea the presence of abundant age diagnostic dinoflagellate cysts in ocean drilling program odp hole 913b leg 151 deep sea drilling project hole 338 leg 38 and odp hole 643a leg 104 has enabled the development of a new biostratigraphy for the eocene oligocene interval in the norwegian greenland sea this development is important because the calcareous microfossils usually used for biostratigraphy in this age interval are generally absent in high latitude sediments as a result of dissolution in parallel with this biostratigraphic analysis we developed a magnetic reversal stratigraphy for these norwegian greenland sea sequences this has allowed independent age determination and has enabled the dinocyst biostratigraphy to be firmly tied into the global geomagnetic polarity timescale gpts the relatively high resolution of this study has enabled identification of dinoflagellate cyst assemblages that have affinities with those from the north sea and the north atlantic which allows regional correlation correlation of each site with the gpts has also allowed comparison of the stratigraphic record preserved in each drill hole hole 913b is the most complete and is the best preserved record of the eocene and oligocene in the northern hemisphere high latitudes and can serve as a reference section for palaeoenvironmental reconstructions of this age interval

improved os isotope stratigraphy of the arctic ocean 1 the history of the arctic ocean remained poorly known until the 2004 iodp coring of lomonosov ridge sediments early studies of the recovered sequence demonstrated the existence of an eocene lake stage prior to the transition to marine conditions the marine stage onset was inferred to be 17 5 million years ma ago thus implying a nearly 26 ma gap between the lacustrine and marine episodes and an unusual tectonic history for lomonosov ridge in order to explain this gap more recently rhenium osmium re os isotope measurements of the transition from the lacustrine to marine sediments suggested a much earlier inception of marine conditions and the absence of any significant gap between both episodes here an improved osmium isotope stratigraphy and re os data concur to assign a late eocene age 36 ma to the marine invasion consistent with a relative change in sea level on top of lomonosov ridge either from tectonic origin or from another cause

sr and nd characteristics of brasiliano pan african granitoid plutons of the aracuai orogen southeastern brazil tectonic implications nd and sr isotope data were obtained for three plutonic suites 595 505 ma and distinct young granitoid intrusions 503 ma from the southern part of the neoproterozoic aracuai orogen the sr and nd isotopes 87sr 86sr end and tdm values from the plutons and distinct basement rocks are used to constrain the magma genesis of the granitoid plutons these isotopic parameters with end values ranging from 4 to 24 and tdm ages from 1 3 to 2 8 ga for the granitoid suites and 5 to 40 and 3 5 to 1 5 ga for the distinct archean and proterozoic basement complexes suggest that the jequitinhonha complex metasediments are the main crustal source for most of these plutons except for the youngest granitoid intrusions which may have a protolith similar to the mantiqueira and guanhaes complexes furthermore the isotope data indicate a minor but important participation of neoproterozoic oceanic lithosphere in the granite genesis which corroborates with a confined orogenic model and a narrow oceanic consumption b subduction for the aracuai orogen

arctic late paleocene early eocene paleoenvironments with special emphasis on the paleocene eocene thermal maximum lomonosov ridge integrated ocean drilling program expedition 302 we reconstruct the latest paleocene and early eocene 57 50 ma environmental trends in the arctic ocean and focus on the paleocene eocene thermal maximum petm 55 ma using strata recovered from the lomonosov ridge by the integrated ocean drilling program expedition 302 the lomonosov ridge was still partially subaerial during the latest paleocene and earliest eocene and gradually subsided during the early eocene organic dinoflagellate cyst dinocyst assemblages point to brackish and productive surface waters throughout the latest paleocene and early eocene dinocyst assemblages are cosmopolitan during this time interval suggesting warm conditions which is corroborated by tex86 reconstructed temperatures of 15 18 c inorganic geochemistry generally reflects reducing conditions within the sediment and euxinic conditions during the upper lower eocene spectral analysis reveals that the cyclicity recorded in x ray fluorescence scanning fe data from close to eocene thermal maximum 2 53 ma presence confirmed by dinocyst stratigraphy is related to precession within the lower part of the petm proxy records indicate enhanced weathering runoff anoxia and productivity along with sea level rise on the basis of total organic carbon content and variations in sediment accumulation rates excess organic carbon burial in the arctic ocean appears to have contributed significantly to the sequestration of injected carbon during the petm

a structural transect across the coastal mobile belt in the brazilian highlands latitude 20 s the roots of a precambrian transpressional orogen abstract we present results of a detailed structural analysis from a 250 km long east west trending transect crossing the coastal mobile belt a part of the precambrian orogen which lies between the eastern edge of the sao francisco craton and the atlantic coast the region exposes amphibolite granulite grade metamorphic rocks and migmatites which formed at mid lower crustal depths during the brasiliano orogeny 0 63 0 52 ga this event marked the closure of the northernmost adamastor ocean and collision between the sao francisco and congo cratons during west gondwana assembly brasiliano deformation resulted in w vergent structures including thrust faults which accommodated kilometer scale transport of crystalline basement overturned kilometer scale folds sheath folds and penetratively developed gneissosity and schistosity isolated relics of an older folded fabric occur locally and may represent transamazonian 2 2 2 0 ga deformation the orogen is kinematically partitioned with the eastern 175 km dominated by moderately to steeply dipping north trending dextral strike slip and oblique slip faults and associated flower structures whereas the western 75 km is dominated by w vergent shallowly to moderately east dipping thrust faults the boundary between these two provinces may mark a brasiliano suture throughout the transect quartzite and metasedimentary belts form strongly deformed zones between massive crystalline basement thrust sheets the granulite cored serra do caparau massif the highest mountains in south america outside of the andes and guyana shield occupies a restraining bend between two brasiliano dextral shear zones the w vergent coastal mobile belt formed contiguously with the e vergent pan african west congo orogen now exposed along the conjugate margin of africa thus an important late precambrian boundary between structurally linked but kinematically opposed structural provinces must lie hidden in the extended offshore continental margins of either continent cretaceous opening of the south atlantic and separation of the west congo belt from the coastal mobile belt may have been structurally influenced by this boundary

rhyacian evolution of subvolcanic and metasedimentary rocks of the southern segment of the mineiro belt sao francisco craton brazil abstract the tiradentes suite in conjunction with the coeval estacao tiradentes metasedimentary sequence makes up a distinct tectonic element within the paleoproterozoic framework of the mineiro accretionary belt in the southern sao francisco craton this suite is the second occurrence of volcanic and subvolcanic rocks in the mineiro belt and shows petrographic and geochemical similarities with the nearby serrinha suite 2 23 2 21 ga the first reported rhyacian volcanism in the mineiro accretionary belt the tiradentes suite is represented by mafic andesites dacites granophyres and tonalites and shows petrographic features of volcanic rocks such as spherulites amygdales granophyric intergrowths and porphyritic textures with plagioclase phenocrysts the rocks of this suite are metaluminous to peraluminous enriched in alkaline elements compatible with low al2o3 trondhjemites and show primary fractionation of plagioclase apatite hornblende biotite and ilmenite high hree content coupled with incipient negative eu anomaly and high y values are consistent with a garnet amphibolite protolith with plagioclase and hornblende as present in the residual phases the samples of the tiradentes suite show geochemical signatures of magmatic arcs which are also observed in rocks from the serrinha suite rocks of the tiradentes suite yield the following u pb zircon crystallization ages i mafic andesite 2217 23 ma ii dacitic dike 2204 11 ma iii subvolcanic tonalite 2213 9 ma the deposition of the estacao tiradentes metasedimentary sequence probably took place after ca 2088 12 ga although it may be as young as 1990 39 ma according to the u pb detrital zircon geochronology of selected samples diamictite ferruginous quartzite and carbonaceous phyllite the tiradentes rocks show three tdm model ages ranging between 2 4 and 2 3 ga indicating short crustal residence for the magmatic protoliths this inference is also supported by the nd 2 2 ga values 1 1 to 2 3 whereas the respective 87sr 86sr t ratios 0 7018 0 7032 are consistent with the involvement of low rb sr material in the magma genesis such as a paleoproterozoic oceanic lithosphere from a tectonic perspective the above data are consistent with the idea that a paleoproterozoic seafloor developed outboard of the archean siderian passive margin setting minas basin of the sao francisco proto craton the 2 23 2 21 ga volcanic subvolcanic rocks of the tiradentes and serrinha suites were associated with a rhyacian oceanic arc the estacao tiradentes metasedimentary sequence turbidites and distal phyllites probably formed in back arc setting concomitant with the tiradentes suite as indicated by detrital zircon geochronology

determination of the content and distribution of fixed ammonium in illite smectite by x ray diffraction application to north sea illite smectite a new x ray diffraction method for the determination of the amount and distribution of fixed nht in illite smectite has been developed illite smectite was saturated with k and heated at iso c the 002 and 005 reflections were recorded with steps of 0 01028 and the experimental d values and the values for full width at half height fwhh were determined using a peak profile fitting procedure peak profiles were calculated with the newmod program for illite structures having different amounts of nh and different patterns for the distribution of nh in interlayers for upper jurassic illite smectite from north sea oil source rocks the amount and the distribution of nh in illite interlayers were determined by comparing the experimental values for doo5 and fwhh with the values calculated for the selected illite structures the amounts of nh determined in this manner correlate well with the amounts determined by an isotopic dilution method the results demonstrate that these illite smectite samples have k end member illite and nh4 endmember illite tobelite layers and that the illite layers formed during diagenesis and oil generation actually are tobelite layers

unraveling complex 2 μm clay mineralogy from soils using x ray diffraction profile modeling on particle size sub fractions implications for soil pedogenesis and reactivity a specific methodology was developed to refine the complex clay mineralogy commonly encountered in soil environments the soil examined was a cambisol developed into a ferralitic paleosol the sample was split into four sub fractions of different particle sizes 0 05 0 05 0 1 0 1 0 2 and 0 2 2 mu m and their respective mass contributions to the overall 2 mu m clay fraction were determined for each sub fraction x ray diffraction xrd patterns were modeled using a trial and error approach based on the direct comparison of experimental and calculated profiles quantitative information derived from the fitting procedure for the different sub fractions allowed for the determination of the complex mineralogy of the 2 mu m clay fraction through the identification and quantification of eight clay phases the results show that the finest and most reactive clay fraction 0 05 pm was totally hidden in the xrd pattern of the 2 mu m fraction the fraction commonly considered in soil mineralogical analyses similarly this procedure revealed the presence of illite smectite chlorite and kaolinite illite mixed layer minerals seldom described in soil literature using classical methods the use of this methodology improved our understanding of the pedogenesis of this soil through the identification and quantification of clay phases structural properties the analysis of the evolution of structural parameters with particle size allowed for the detection of local modifications in the interlayer composition of expandable and hydroxy interlayered vermiculite layers following this approach key information can be derived to determine subtle changes in clay mineralogical composition that are related to microorganism and or plant activity

tectonics and sedimentation in a paleo mesoproterozoic rift sag basin espinhaco basin southeastern brazil abstract sedimentologic paleogeographic stratigraphic structural and tectonic studies in a paleo mesoproterozoic metasedimentary succession espinhaco megasequence southeastern brazil indicates deposition in a rift sag basin four basin evolution stages are recognized prerift rift transitional and flexural the four stages can be represented by six unconformity bounded tectonosequences the unconformities are recognized in the field and mappable even on a regional scale the prerift and rift stages of the espinhaco basin were filled by products of continental depositional systems the prerift stage probably represents the first product of the rifting process before the development of the half grabens that characterize the rift stage during the rift stage mechanical subsidence due to lithospheric stretching was predominant and led to episodic rising of the depositional base level as a result the basin fill is characterized by coarsening upward intervals paleocurrent patterns indicate that block tilting and half graben subsidence uplift controlled sediment dispersion the first marine incursion within the espinhaco basin marks the change in the subsidence regime of the basin the evolution of the transitional and flexural stages was probably controlled by thermal subsidence due to thermal contraction of the lithosphere during cooling the transitional stage was characterized by relatively low subsidence rates higher subsidence rates and a consequent sea level rise characterize the flexural stage of the espinhaco basin in which three second order transgressive progradational sequences can be recognized

the araa uaa west congo orogen in brazil an overview of a confined orogen formed during gondwanaland assembly abstract the neoproterozoic adamastor brazilide ocean was generated during the breakup of the rodinia supercontinent and remnants of its oceanic lithosphere have been found in the brasiliano pan african orogenic system that includes the aracuai west congo brasilia ribeira kaoko dom feliciano damara and gariep belts the aracuai and the west congo belts are counterparts of the same neoproterozoic orogen the first belt comprises two thirds of the aracuai west congo orogen this orogen is rather unique owing to its confined nature within the embayment outlined by the sao francisco and congo cratons in spite of this the presence of ophiolitic remnants and a calc alkaline magmatic arc indicate that the basin orogen evolution comprise both oceanic spreading and consumption it is assumed that coeval paramirim and sangha aulacogens played a key role by making room for the aracuai west congo basin sedimentary successions record all major stages of a basin that evolved from continental rift when glaciation related sedimentation was very significant to passive margin rifting started around 1 0 0 9 ga the oceanic stage is constrained by an ophiolitic remnant dated at 0 8 ga if the cratonic bridge that once linked the sao francisco and congo palaeocontinental regions did not hinder the opening of an ocean basin it certainly limited its width as a consequence only a narrow oceanic lithosphere was generated and it was subducted afterwards this is also suggested by orogenic calc alkaline granitoids occuping a small area of the orogen geochronological data for pre syn and late collisional granitoids indicate that the orogenic stage lasted from 625 ma to 570 ma a period of magmatic quiescence was followed by intrusion of postcollisional plutons at 535 500 ma the features of the aracuai west congo orogen suggest the development of a complete wilson cycle in a branch of the adamastor ocean which can be interpreted as a gulf with limited generation of oceanic lithosphere

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

light acidification in n fertilized loess soils along a climosequence affected chemical and mineralogical properties in the short term some evidences indicate that n fertilization of crops decreased ph values of loess soils of the argentinean pampas in the last decades we analyzed the a horizons of four n fertilized f and non fertilized nf paired soils developed on similar parent materials within a climatic sequence ustic to udic water regimes and measured 1 the extent of ph changes 2 how these changes affected chemical and mineralogical soil properties and 3 how the soils according to their h buffering substances can react in the future if n fertilization and acidification continue results indicated that all f and nf soils were lightly acidified differences between phw and phkcl higher than 1 0 and that fertilization produced ph decreases in all studied soils but particularly in those with udic water regimes in agreement with their longer n fertilization histories fertilized ustic soils showed less crystalline illites and kaolinites and higher contents of amorphous al oxides than nf soils it remains unclear if the higher contents of amorphous al are related with the dissolution of phyllosilicates the transformation of the abundant volcanic glasses of these soils or both processes at the same time the cation exchange capacity cec and the percent of base saturation v did not change between f and nf soils probably due to the large influence of soil organic matter som in the studied soils if n fertilization and consequently ph decreases continue soils placed in both the moistest argiudolls and the driest extremes of the climosequence haplustolls would be the less affected this is because udic soils contain high som as well as illitic clays and silts while ustic soils contain free lime and high density charged clay minerals which have high h neutralization capacity the most affected soils by acidification should be those placed in the intermediate zone of the climosequence hapludolls which have low amounts of substances with high buffer capacity

u pb la icp ms detrital zircon ages of the sao joao del rei and carandai basins new evidence of intermittent proterozoic rifting in the sao francisco paleocontinent abstract the tiradentes formation sao joao del rei basin is a shallow marine quartzite succession resting on the paleoproterozoic crust of the southern part of the sao francisco craton a regional angular unconformity separates the tiradentes strata from the younger carandai barroso and prados formations carandai basin the carandai formation is constituted of fault bounded diamictites containing lithoclasts derived from basement rocks and the tiradentes formation the barroso formation is a sag basin limestone succession whereas the prados formation is a pelitic succession that fills a ne sw trending aulacogen weak deformation and metamorphism 600 590 ma overprinted the sao joao del rei and carandai sequences due to the brasiliano orogen and likewise the overlying andrel ndia megasequence

responses of soil clay mineralogy in the rothamsted classical experiments in relation to management practice and changing land use abstract changes in the clay mineralogy of soil samples collected from the rothamsted classical experiments over the past 150 years were examined comparisons were undertaken to assess the impact of i different fertiliser practices on the top soil and sub soil of the park grass experiment and ii the effects of changing land use from agriculture to woodland where soil ph either remained close to ph 7 or became acidic analyses were undertaken on the 0 4 a are reported in both top soil 0 23 cm and sub soil 46 69 cm and are likely related to i changes in soil k or nh4 status and or ii increasing soil acidity the greatest change was found in the park grass experiment nh4 2so4 plot where soil ph fell below 3 7 it is believed that solubilisation of hydroxyl al in smectite interlayers enabled renewed access to k or nh4 ions leading to increased collapse in d 001 spacing however the results show that over a diverse range of soil conditions i s minerals of the batcombe series soils showed considerable resilience to major change this is considered to be a result of competition for sorption sites by i the presence of competing ions added as fertiliser or liming materials ii an increase in h ions as soil acidity increases iii the possible role of organic carbon in protecting i s minerals and iv the role of the i s minerals as k reservoirs however the impact of decreasing soil ph should be considered when land is re forested as this may lead to decreases in the d 001 spacing of i s minerals thus compromising useful clay properties such as cec

onset of long term cooling of greenland near the eocene oligocene boundary as revealed by branched tetraether lipids the eocene oligocene e o boundary interval is considered to be one of the major transitions in earth s climate witnessing the fi rst major expansion of the east antarctic ice sheet however the extent of the associated climatic cooling especially for high northern latitude continental landmasses is poorly constrained in this study we reconstruct the fi rst mean annual air temperature maat for the greenland landmass during the late eocene and early oligocene by applying a new proxy based on the distribution of branched tetraether lipids derived from soil bacteria preserved in a marine sediment core from the greenland basin the temperature estimates are compared with a composite continental temperature record based on bioclimatic analysis of pollen assemblages both proxies reveal comparable late eocene maats of 13 15 c and a gradual long term cooling of 3 5 c starting near the e o boundary these data are in agreement with other maat reconstructions from northern midlatitude continents and suggest a general cooling of the northern hemisphere during the e o transition

pan african rifting and orogenesis in southern to equatorial africa and eastern brazil abstract the upper proterozoic pan african belts of africa and brasiliano belts of south america are assumed to have evolved from an elaborate system of continental rifts which formed on the west gondwana continent 1100 1000 ma ago reviews of the damara belt kaoko belt gariep belt saldania belt west congolian belt lufilian arc and zambezi belt of southern and equatorial africa and the ribeira mantiqueira belt of brazil show the applicability of the continental rifting model to all these belts strict application of the rifting model describing the formation and further evolution of rift structures in the continental crust leads to the conclusion that the west congolian belt as traditionally described is incomplete and has to be supplemented by the mayumbian belt and a rift structure situated farther to the west the lufilian arc is assumed to have evolved from two rift structures separated from each other by the later domes region the golfe du katanga which branches off northeastwards from the lufilian arc is interpreted as an aulacogen shaba aulacogen the pan african brasiliano rift system is comparable to the mesozoic arctic north atlantic rift system with regard to size and distribution of rifts ocean floor spreading and opening of a proto south atlantic ocean most probably occurred along a main line of rifting situated between the west coast of africa and eastern brazil the wedge like ocean may have terminated at the sao francisco congo cratonic bridge between northeastern brazil and gabon cameroon there is no evidence of ocean floor spreading in the zambezi belt the lufilian arc and the traditional west congolian belt which are arranged along another major line of rifting closure of the pan african brasiliano rift system took place during two successive orogenic episodes the zambezi belt lufilian arc and west congolian belt underwent their main orogenic deformation with prevailing ene and wsw oriented tectonic transportation directions during the katangan episode at 900 750 ma the transcontinental sinistral mwembeshi shear zone adjusted opposite movement directions in the zambezi belt and lufilian arc and at its western prolongation concurrently supported opening of the khomas trough in the southern damara belt the proto south atlantic ocean still opening during the katangan episode was gradually closed during the damaran episode at 750 500 ma closure proceeded from north to south and was accompanied by northwest directed subduction underneath the brazilian plate and southeast directed tectonic transportation in the kaoko damara and gariep belts in the previously formed west congolian belt lufilian arc and zambezi belt a second deformation phase characterized by strike slip faulting and local emplacement of nappes occurred during this episode

architecture of late orogenic plutons in the aracuai ribeira fold belt southeast brazil abstract post collisional to late orogenic magmatism 580 to 480 ma in the aracuai ribeira fold belt se brazil is characterized by the predominance of high k metaluminous allanite titanite bearing granitoids small lenses of coronitic gabbro anorthosite pyroxenite and phlogopite peridotite are also common in deeper exposed areas of this fold belt in the region of southern espirito santo state the deep erosional level associated with a steep topography reveals the internal architecture of the intrusions a tendency to funnel shaped bodies with sub vertical hemi ellipsoidal conical roots changing upwards to shallow dipping tops associated stocks sills and dykes of basic and acid rocks generally intrude the enclosing gneisses along the foliation planes local ductile shear zones and parallel to fold hinges the contact between intrusions and the enclosing rocks is sharp in deeply eroded plutons e g santa angelica venda nova mimoso do sul and varzea alegre but at shallow levels e g castelo pedra azul and conceicao de muqui agmatic stoping zones occur along the borders a magmatic foliation within the granitoids is usually well marked but the schistosity in the surrounding gneisses wraps around the plutons the intrusions have a bimodal chemical distribution and generally are reversely zoned with mafic cores gabbro diorite to tonalite surrounded by a mingled marble cake zone where basic and acid rocks are interfingered and an external zone of syenomonzonite and granite widespread evidence of mingling and mixing between contrasting magmas of gabbroic and granitic and or syenomonzonitic compositions is characteristic for all intrusive complexes we suggest that replacement of lithospheric mantle by hot asthenospheric mantle induced partial melting of the crust the mantle exchange was due to lithospheric mantle delamination and slab breakoff following collisional orogenesis the bimodal plutons result from interaction among the contrasting magmas ascent and emplacement followed older regional structures such as regional fold hinges and ductile shear zones

was the arctic eocene rainforest monsoonal estimates of seasonal precipitation from early eocene megafloras from ellesmere island nunavut abstract the early eocene was the warmest interval of the cenozoic and included within it were several hyperthermal events with the paleocene eocene thermal maximum petm the most pronounced of these these globally warm climates extended into the arctic and substantive paleobotanical evidence for high arctic precipitation map 150 cm yr is indicative of an arctic rainforest which contradicts some climate models that show low arctic precipitation prior studies of arctic early eocene wood stable isotope chemistry however have shown a summer peak in precipitation which suggests modern analogs are best sought on the summer wet east coast of the asia e g china japan south korea not the winter wet west coasts of the pacific northwest of north america furthermore some prior modeling data suggest that highly seasonal monsoon type summer wet precipitation regimes i e summer map 55 characterized certain mid and lower latitude regions in the early to mid eocene presented here is a new analysis using leaf physiognomy of 3 leaf megafloras split lake stenkul fiord and strathcona fiord and palynofloral bioclimatic analysis from the margaret formation from ellesmere island placed stratigraphically as early eocene possibly occurring during or following one of the early eocene hyperthermals these new data indicate high summer precipitation in the arctic during the early eocene which in part corroborates the results from eocene wood chemistry nevertheless in contradiction to the wood analysis monsoonal conditions are not indicated by our analysis consistent with current modeling studies high summer light season and winter dark season precipitation in the eocene arctic during hyperthermals would have contributed to regional warmth

mid cenozoic tectonic and paleoenvironmental setting of the central arctic ocean drilling results from the integrated ocean drilling program s arctic coring expedition acex to the lomonosov ridge lr document a 26 million year hiatus that separates freshwater influenced biosilica rich deposits of the middle eocene from fossil poor glaciomarine silty clays of the early miocene detailed micropaleontological and sedimentological data from sediments surrounding this mid cenozoic hiatus describe a shallow water setting for the lr a finding that conflicts with predrilling seismic predictions and an initial postcruise assessment of its subsidence history that assumed smooth thermally controlled subsidence following rifting a review of cenozoic tectonic processes affecting the geodynamic evolution of the central arctic ocean highlights a prolonged phase of basin wide compression that ended in the early miocene the coincidence in timing between the end of compression and the start of rapid early miocene subsidence provides a compelling link between these observations and similarly accounts for the shallow water setting that persisted more than 30 million years after rifting ended however for much of the late paleogene and early neogene tectonic reconstructions of the arctic ocean describe a landlocked basin adding additional uncertainty to reconstructions of paleodepth estimates as the magnitude of regional sea level variations remains unknown

low temperature illitization of smectite in the late eocene and early oligocene of the isle of wight hampshire basin u k variegated palaeosols which formed from weathering of clays silts and brackish to freshwater limestones are present in the late eocene early oligocene solent group of the hampshire basin southern u k the detrital clay mineral suite is dominated by illite and illite smectite with minor kaolinite and chlorite in pedogenically modified palaeosol and evaporitic lacustrine clay rich sediments the proportion of illite in the illite smectite is greater than in the non pedogenically modified sediments and where alteration is most intense kaolinite and chlorite are absent the smectite to illite transition has been investigated in the 0 5 m fraction by xrd analysis powder and oriented mounts thermogravimetry tg analytical sem and chemical analysis of fe2 modeling of xrd data reveals that the illite smectite is a mixture of compositions overall 60 95 illite r 0 with high rotational stacking disorder dehydroxylation occurs mainly at 500 c but also at higher temperatures indicating heterogeneous octahedral cation composition analytical sem and chemical analysis of fe2 indicate that the illite to smectite transition occurs through fe reduction in octahedral sites leading to increased layer charge coupled with k fixation the driving mechanism for what appears to be irreversible fe3 reduction is wetting reducing and drying oxidizing cycles in gley soil in which reoxidation of reduced fe is never complete

a method for climatic reconstruction of the mediterranean pliocene using pollen data pollen data from numerous sites around the mediterranean sea indicate that several important vegetation and climatic changes occurred during the pliocene these data are in good agreement with pollen records from northwest europe and with 18o curves from mediterranean and atlantic deep sea cores quantitative palaeoclimatic reconstructions from pliocene pollen data of the mediterranean region cannot be based on conventional modern analogue techniques as individual pliocene pollen spectra contain taxa representing temperate warm temperate and subtropical plants that do not grow together today instead we propose a new method that uses a climatic amplitude method modified to take partially into account the relative abundances of the taxa we applied this method to the pliocene garraf 1 palynological sequence from catalonia which provides a long continuous record of climatic change from 5 3 ma to the early pleistocene we estimate that annual temperatures were 1 to 5 c higher than today and the annual precipitation 400 to 1000 mm higher than today prior to the beginning of the late cenozoic glacial interglacial cycles in contrast temperature and precipitation both fell sharply during the glacial phases of the earliest glacial interglacial cycles

proterozoic first order sedimentary sequences of the sao francisco craton eastern brazil abstract the sao francisco craton in eastern brazil hosts sedimentary sequences deposited between the paleoarchean 3300 ma and late neoproterozoic 580 ma proterozoic successions occurring in this region comprise five 1st order sedimentary sequences which besides episodes of global significance record major basin forming events the ca 8000 m thick minas itacolomi 1st order sequence exposed in the brazilian mining district of the quadrilatero ferrifero and containing as marker bed the lake superior type caue banded iron formation tracks the operation of a wilson cycle in the paleoproterozoic era the quartz arenite dominated espinhaco i and ii sequences record at least two major rift sag basin forming events which affected the host continent of the sao francisco craton at around 1 75 ga and 1 57 ga the macaubas sequence and its correlatives in the extracratonic domains witness the individualization of a sao francisco congo plate in synchronicity with the break up of rodinia in the cryogenian period the sao francisco congo plate together with various fragments derived from rodinia reassembled to form gondwana in the ediacaran period in the course of the gondwana amalgamation orogenic belts developed along the margins of the craton its interior converted into foreland basins received the shallow water carbonates and pelites of the bambui 1st order sequence and its correlatives

neoproterozoic oceanic remnants in eastern brazil further evidence and refutation of an exclusively ensialic evolution for the aracuai west congo orogen the aracuai eastern brazil and west congo southwestern africa belts are counterparts of the same neoproterozoic orogen located between the sao francisco and congo cratons the macaubas group represents a major passive margin sequence and is a key unit for interpreting the evolution of that orogen the salinas formation is the distal rock assemblage of the macaubas group and consists of a deep sea sand mud sequence and a volcanic sedimentary unit called the ribeirao da folha facies the latter includes metamorphosed volcanic exhalative sediments associated with ocean floor basalts amphibolites the magmatic protoliths of these amphibolites crystallized at about 816 72 ma sm nd whole rock isochron nd t 3 8 0 2 regional metamorphism reached the amphibolite facies at about 630 ma rb sr whole rock isochron when slabs of ultramafic rocks were tectonically emplaced over the ribeirao da folha facies we consider this volcanic sedimentary facies and the coeval slabs of ultramafic rocks to be remnants of a branch of the adamastor brazilide ocean the extensive occurrence of syntectonic to late tectonic calc alkalic granitoids along the internal domain of the aracuai belt implies that a reasonably large amount of ocean crust was consumed via an east dipping subduction zone during formation of the aracuai west congo orogen

late proterozoic glaciation in central eastern brazil synthesis and model abstract in the surroundings of the middle proterozoic sao francisco craton of central eastern brazil numerous traces of an ancient glaciation can be found almost all criterua necessary to prove an ancient glaciation occur including scratched and facetted pebbles a striated surface quarrying outwash plains eskers varvites dropstones decollement structures etc poorly sorted tillites with varying pebble composition are widely distributed continental tillites and glaciomarine sequences interfinger in the east and southeast of the craton traces of ice movement suggest flow directions of the ice towards the east and the southeast of the craton at the coast the wet base glaciers passed over to floating shelf ice in the northeast glaciers also came from the serrinha craton in northeastern bahia the glaciation covered an area of at least 1300 700 km the sequences containing traces of glaciation discordantly overlie archean to middle proterozoic rocks they in turn are overlain by late proterozoic calcareous and psammopelitic sediments of the bambui group present data indicate that glaciation took place around 1000 ma ago

evolution sedimentaire et tectonique du bassin proterozoique superieur de comba congo stratigraphie sequentielle du supergroupe ouest congolien et modele d amortissement sur decrochements dans le contexte de la tectogenese panafricaine abstract the comba trough infilled by the upper proterozoic west congolian supergroup trends n60 e and cuts across the congo zaire archean craton the trough is perpendicular to the nyanga niari basin which itself represents the foreland of the pan african mayombe belt moreover the comba trough was connected to other troughs extending further east beneath the mesozoic cenozoic of the congolian basin the tectono sedimentary evolution of the comba basin was initiated between 950 and 700 ma the trough was formed by a nw se extension it was filled up by periglacial fluvio lacustrine sediments which correspond to the deltaic formations of the bouenza group and the upper diamictite tillite superieurerd respectively then a general climatic warm up produced a rise of the eustatic sea level which flooded the lake of comba as well as the lakes and shelves of the congo zaire craton this marine sedimentation is represented by the schisto calcaire group which in terms of sequence stratigraphy we interpret as a transgressive system tract red marls of the lower part of the scia facies a condensed section pink dolomite of the upper part of the scia facies a highstand system tract deposited along a carbonate ramp the latter corresponds to a lateral facies variation and not a vertical facies succession as it was classically assumed this highstand system tract was composed of an external shelf scib facies a barrier scic facies a lagoon scii facies a beach kisantu oolithe of the sciiia facies and sciiib facies a tidal flat sciiic facies with fluvial sciv facies and tidal niari breccia facies channels between 700 and 600 ma a first compressive phase was responsible further west for the eastward pan african mayombian thrusting this phase was accompanied by the deposition of a thick molassic formation mpioka formation on the foreland belt and extending into the comba basin a late shortening phase of the mayombian belt propagated into the comba basin which was affected by strike slip deformation along its southern edge this strike slip deformation induced important disruptions of the regional mayombian tensor and a particular structural pattern of the comba basin characterized by strike slip damping structures sections of these structures are interpreted as positive negative and dual flowers this particular structural pattern provides an explanation of the combian structures as they reflect local deviation of the pan african shortening axes as a conclusion the evolutionary stages of the comba basin are discussed in the wider context of the upper proterozoic of the congo zaire craton

radiating 1 0 ga mafic dyke swarms of eastern brazil and western africa evidence of post assembly extension in the rodinia supercontinent abstract several mafic dyke swarms of similar composition and age tholeiite ca 1 0 ga occur on both sides of the atlantic ocean in eastern south america and western africa when assembled to their pre drift position in the mesozoic the brazilian coastal dyke province of bahia and the african dykes in cameroun ebolowa suite and congo comba and sembe ouesso provinces define a giant radiating pattern 1200 km 800 km similar to other dyke swarms elsewhere associated with large scale continental rifting magma flow indicators of the brazilian dykes and branching propagation styles of their african counterparts indicate that the dyke conduits were fed with magmas diverging from a source beneath the long axis of the meso neoproterozoic west congolian basin in africa there morb like metabasalts have been described in the la bikossi group of the mayombian supergroup whether the rifting event and intrusion of dyke swarms were triggered or not by a mantle plume beneath part of the rodinia subcontinental lithosphere remain to be confirmed

kinematic evolution of the aracuai west congo orogen in brazil and africa nutcracker tectonics during the neoproterozoic assembly of gondwana abstract the neoproterozoic aracuai west congo a wc orogen is one of many brasiliano pan african orogens that developed during the assembly of west gondwana this orogen was split apart in mesozoic time due to opening of the south atlantic the aracuai orogen now underlies eastern brazil whereas the west congo belt fringes central africa s atlantic coast significantly at the time it formed the a wc orogen was bounded on the west north and east by the sao francisco congo craton a crustal block that had the shape of a lopsided upside down u thus the orogen was partially confined during tectonism in that it occupied an enclave surrounded on three sides by cratonic crust formation of the a wc orogen resulted in kinematically complex deformation substantial crustal shortening and production of a large volume of magma how such features could develop in this particular setting has long been a mystery our field studies in the aracuai orogen together with published data on the west congo belt characterize the kinematic picture of the a wc orogen and lead to a tectonic model that addresses its evolution in our model the a wc orogen formed in response to closure of the macaubas basin this basin was underlain by oceanic crust in the south but tapered northward into a continental rift which terminated against the cratonic bridge linking the eastern and western arms of the sao francisco congo craton closure occurred when the western arm now the sao francisco craton rotated counterclockwise towards the eastern arm now the congo craton this closure may have been driven by collision of the paranapanema amazonian and kalahari cratons against the external margins of the sao francisco congo craton rather than by slab pull associated with subduction of the macaubas basin s floor thus the process of forming the a wc orogen resembled the process of crushing of a nut between two arms of a nutcracker such nutcracker tectonics led to a series of kinematically distinct deformation stages initially internal portions of the orogen flowed northwards then substantial crustal thickening occurred in the orogen s interior and the deformation front migrated outwards producing thrust belts that overlapped the internal margins of the craton with continued closure space in the enclave became restricted and the orogen s interior underwent lateral escape to the south late stage extensional collapse triggered both production of late to post collisional granites and exhumation of high grade rocks from mid crustal levels

evolution of polycyclic basement complexes in the aracuai orogen based on u pb shrimp data implications for brazil africa links in paleoproterozoic time paleoproterozoic basement of the aracuaorogen is composed of amphibolite and granulite facies orthogneiss units known as mantiqueira and juiz de fora complexes six u pb shrimp crystallization ages for the mantiqueira complex range from 2137 19 to 2041 7 ma studied samples are characterized by the abundance of inherited archean zircon grains tdm model ages ranging from 2 9 to 3 2 ga and strongly negative end t 9t o 13 gneiss protholits were mainly generated by partial melting of older continental material and the mantiqueira complex is related to active margin and syn collisional magmatism high grade gneiss samples of the juiz de fora complex yields crystallization ages of 2119 16 and 2084 13 and inherited zircon grains are absent this plutonic unit much probably evolved within an oceanic magmatic arc setting or on a very stretched continental crust the mantiqueira and juiz de fora complexes together with the kimezian basement of the west congo belt were parts of a paleoproterozoic orogenic system disrupted and deeply reworked during the evolution of the aracuacongo orogen neoproterozoic metamorphic overprint is dated at ca 590 574 ma 2007 elsevier b v all rights reserved

u pb geochronology of the granite magmatism in the embu terrane implications for the evolution of the central ribeira belt se brazil abstract the embu domain represents the central part of the ribeira fold belt in sao paulo brazil it hosts several granitic occurrences of varied composition ranging from small granitic bodies that outcrop in a domain bounded by the intersection of two major sutures taxaquara and guararema faults and batholitic masses outcropping to the east understanding the evolution of such granites is of vital importance to better constrain evolutionary models for the ribeira belt in the present study a set of samples from eleven main granite occurrences from the east of sao paulo state was selected for geochronological investigation using laser ablation multicollector inductively coupled plasma spectrometry la mc icp ms and thermal ionization mass spectrometry tims u pb dating of zircon and monazite crystals respectively the results indicate a remarkable cluster of ages around 590 ma with older events of granite magmatism between 660 and 600 ma registered for four plutons indicating a long history of crustal reworking and magma generation the ages of reworked sources were evaluated from inherited zircon cores although highly discordant these point to the predominance of paleoproterozoic 2 4 2 1 ga sources with minor contributions from mesoproterozoic 1 1 0 9 ga and archean sources 3 1 ga the new data bring important insights into the role played by the embu domain on the paleogeography and evolution of the ribeira belt

sm nd and sr isotope fingerprinting of iron mining tailing deposits spilled from the failed samarco fundao dam 2015 accident at mariana se brazil abstract this work presents the first sm nd and sr isotope tims data on the fine grained fraction 3 of a quartz and iron oxide rich slurry composed of water fine sand and silt that flowed into the gualaxo do norte and carmo rivers and eventually along the whole doce river samples were collected between 5 and 80 km downstream from the fundao dam along the santarem creek and the gualaxo do norte and carmo rivers xrd analyses show that samples are 90 composed of quartz and iron oxides hematite goethite and magnetite with minor phyllosilicates kaolinite and mica owing to sediment transport processes heavy hematite goethite magnetite to light quartz phyllosilicates mineral fractionation is observed as with xrd data major and trace element compositions also closely match those of the original paleoproterozoic caue formation bif iron ore the studied samples yielded nd between 17 0 and 19 7 pptt part per ten thousand with the exception of one sample with nd of 23 2 pptt strontium 87 sr 86 sr ratios show variability between 0 7351 and 0 7729 the t dm ages scatter between 1 94 ga and 2 75 ga with a negative correlation with phyllosilicate contents indicating that the latter has preferential provenance from younger more juvenile sources than the caue fm itabirites this interpretation is corroborated by two component mixing models of nd and sr isotope ratios where the nd sr isotopic signatures of the studied samples are compatible with 98 of the caue fm itabirite component mixed with a neoproterozoic juvenile mafic rocks component such as those from the ophiolitic assemblages of the distal macaubas group or tholeiitic mafic rocks of the pedro lessa suite the reported sm nd and sr isotope compositions closely match those of the original iron ore and contrast with either those of the upriver or downriver precambrian to ordovician bedrock units the firstly defined isotope signature can thus be potentially used as a proxy for ongoing suspended sediment dispersion studies farther downstream along the doce river and in adjacent marine environment

archean and paleoproterozoic crust of the sao francisco craton bahia brazil geodynamic features abstract recent geological geochronological and isotopic studies allow the identification of four important crustal segments in the basement of the sao francisco craton in bahia the oldest is the gaviao block in the wsw part of the studied area and comprises granitic granodioritic and migmatitic continental crust including remnants of 3 4 ga ttgs which are amongst the oldest rocks in south america and are associated with archean greenstone belts the youngest segment is exposed in the itabuna salvador curaca belt which extends from se bahia along the atlantic coast to salvador then northwards into ne bahia it is mainly composed of a low k calc alkaline plutonic suite and also contains strips of intercalated metasediments and ocean floor back arc basin gabbro and basalt in the ssw part of the area the jequie block comprises granulitic migmatites with inclusions of supracrustal rocks intruded by many charnockite plutons in the ne the serrinha block is composed of orthogneisses and migmatites which form the basement for paleoproterozoic greenstone belts during the paleoproterozoic transamazonian cycle these four crustal segments collided resulting in the formation of an important mountain belt the regional metamorphism resulting from the crustal thickening associated with the collision occurred at around 2 0 ga major mineralizations were formed during the evolution of the four archean blocks and also during and after the paleoproterozoic collision

the role of peri glacial active layer development in determining soil regolith thickness across a triassic sandstone outcrop in the uk this paper examines the weathering processes that have combined to produce the distribution of soil regolith sr thickness across the triassic sherwood sandstone group outcrop 750 km2 in nottinghamshire u k archive borehole logs n 282 taken across the outcrop showed that soil regolith thickness had mean and median depths of 1 8 and 1 5m respectively cores were taken from a forested site to depths 3m for geochemical analysis at this site the sr thickness was 1 7m analysis of the loss of elements compared to bedrock using mass balance calculations showed that all the calcite and gypsum cement had been removed to depths of 3m thus the major difference between the sr and the underlying saprolite was that the former exists as loose sand as opposed to a semi durable rock scanning electron microscopy sem analysis of core samples suggested that the non durable rock or saprolite had greater cementation of clay particles we propose that the mechanism through which the clay cement and other interlocking grain bonds were eased apart was through freeze thaw processes associated with the summer active layer development during the last glacial activity in the uk we tested this theory by developing a monte carlo simulation based on a simplified version of the stefan equation current arctic datasets of air and ground temperatures were obtained to provide reasonable starting conditions for input variables these were combined with known data for thermal conductivity bulk density and moisture content of the sherwood sandstone regolith model predictions n 1000 of the distribution of sr thickness accurately reflect the observed distribution thickness from the borehole logs this is strong evidence that freeze thaw and ald processes are major factors in determining the thickness of sr across this outcrop

evidence for a neoproterozoic carbonate ramp on the northern edge of the central african craton relations with late proterozoic intracratonic troughs during late proterozoic times the archaean central african craton was affected by trough faulting which led to the formation of grabens the sangha aulacogen being the main structure of this type in the studied area this transverse basin connects with other basins on the northern and south western borders of the craton during the cryogenian this network of basins was filled with fluvio deltaic and lacustrine periglacial deposits the glacio eustatic transgression in neoproterozoic iii end proterozoic times flooded extensive areas of shelf on the northern edge of the craton leading to the development of carbonate sedimentation in a broad outer shelf environment associated with nearshore barriers and evaporitic lagoons these facies are similar to those developed in the west congolian schisto calcaire shale limestone ramp succession the north central african ramp succession sediment slope contains an example of tidal rhythmites in vertical accretion which occurs beneath the barrier deposits on the subtidal outer shelf mathematical analysis of the bedding pattern yields a period of 29 30 days for the lunar month a result which is in agreement with astrophysical evidence for this epoch i e 650 ma ago major subsidence and seismic activity on this gently sloping platform associated with the proximity of the sangha aulacogen caused the triggering of carbonate turbidites and mass flow deposits the proliferation of microbial mats under euphotic conditions on an extensive shelf led to the build up of a carbonate platform during early neoproterozoic iii times the west congolian and north central african ramps prograded northwards and southwards respectively into the sangha aulacogen the sea at that time was restricted to a long graben like basin while a remaining area of marine sedimentation persisted into the palaeozoic thus the pattern of end proterozoic carbonate sedimentation on the borders of the central african craton can be interpreted in terms of an overall gently sloping ramp model with progradation converging towards the sangha aulacogen

changing provenance of late jurassic to early cretaceous rift related sedimentary rocks of the south atlantic margin la mc icpms u pb and lu hf isotopic study of detrital zircons from the camamu basin eastern brazil abstract the camamu basin is related to the breakup of gondwana and belongs to the group of sedimentary basins that are part of the eastern brazilian passive margin we have determined the provenance of the precursor sediments by investigating the petrography of fluvial and eolian units from the early rift brotas group and syn rift almada group coupled to in situ laser ablation mc icpms u pb and lu hf isotopic analyses of the detrital zircon grains detrital zircon grains from the sergi formation brotas group have a main population of u pb ages of 480 600 ma with smaller populations of ages of 900 1000 ma 1900 2100 ma 2500 2800 ma and 3000 3200 ma the almada group zircon grains are characterized by a distribution of ages predominantly in the paleoproterozoic and archean the hf t dm model ages of the brotas and almada group zircon grains range from ca 1 1 to 4 0 ga and the e hf t values vary from 31 4 to 9 6 providing evidence that some detrital zircon grains in the camamu basin were derived from juvenile sources but that the majority have reworked crustal sources or formed from juvenile magmatic rocks that were contaminated by older crustal material whole rock sm nd isotope data collected previously are largely consistent with the new u pb lu hf zircon data but do suggest that zircon poor detritus from the neoproterozoic to eopaleozoic brasiliano aracuai west congo belt contributed to particularly the brotas group sediments more than would be indicated by the zircon data alone thus integrated petrographic u pb lu hf zircon and sm nd whole rock studies provide very important clues to the provenance history of the initial sedimentation on camamu basin passive margin where the early rift phase is marked by the input of detritus from the aracuai west congo belt situated south of the basin whereas syn rift sedimentation received major contributions from paleoproterozoic transmazonian cycle to archean jequie cycle sao francisco craton units located to the west

tectonic implications of precambrian sm nd dates from the southern sao francisco craton and adjacent aracuai and ribeira belts brazil abstract the archean and paleoproterozoic sao francisco craton of eastern brazil is surrounded on all sides by brasiliano pan african orogens the n ne trending orogen that separates the eastern edge of the southern sao francisco craton from the atlantic coast can be divided into the largely greenschist and amphibolite facies aracuai belt on the west and the largely granulite facies ribeira belt on the east a pronounced linear gravity and magnetic anomaly the abre campo discontinuity defines the boundary between these two belts we obtained sm nd mineral ages and whole rock sm nd model ages for garnet bearing metamorphic rocks along an e w transect across the southern sao francisco craton the southern aracuai belt and the ribeira belt at about latitude 20 s a recrystallization age of 2 1 ga from metasediments recrystallized during the development of the classic dome and keel province of the southern sao francisco craton the quadrilatero ferrifero indicates that dome emplacement occurred during the waning stages extensional collapse of the transamazonian collisional orogeny seven mineral ages from the southern aracuai and ribeira belts date the thermal peak of metamorphism at between 538 and 589 ma confirming that these belts were pervasively remobilized during the brasiliano event samples from the aracuai belt yield either archean 2 6 ga or transamazonian 2 1 2 3 ga tdm model ages indicating that the protoliths were either fragments of the sao francisco craton crust or were sediments derived from that craton which presumably had been stretched to form a thinned continental margin during meso and neo proterozoic rifting events notably a mixed meta pelite and metabasite sequence in the southern aracuai belt the dom silverio group has transamazonian ancestry and thus may represent oceanic sediments deposited on or east of this stretched margin and then thrust back onto the continent to mark a collisional suture between the sao francisco block and an archean crustal sliver to the east the rocks of the ribeira belt i e the region east of the abre campo discontinuity have younger model ages tdm 1 6 2 0 ga indicating that this belt was not originally part of the sao francisco craton it may represent an accreted transamazonian terrane therefore the abre campo discontinuity marks an important crustal boundary possibly a suture brasiliano shear zones appear to steepen and root into the abre campo discontinuity suggesting that it formed in brasiliano time

chaotic flow patterns from a deep plutonic environment a case study on natural magma mixing this work focuses on the mixing between basalt and granite in a deep plutonic environment the description of mixing patterns and measurements of fractal dimensions and the evaluation of geochemical data from a cambro ordovician granitic pluton are summarized and discussed different morphologic domains within the pluton reveal concentric fragmented and or folded layers of granite in a gabbro granite mixed matrix this stands in contrast to two predominantly regular gabbroic regions these regular regions are separated by tightly stretched filament areas in which mixing is enhanced sharp and gradational contacts between granitic and gabbroic domains depict the interplay among frozen flows mingling and convection enhanced diffusion processes mixing measurements of fractal dimensions at different scales and analysis of normalized concentration variance for major elements point towards magma mixing the compositional variability and flow patterns of the studied pluton have been greatly controlled by a natural chaotic mixing process between a granitic and a basaltic end member during the mixing process coeval fractional crystallization no doubt contributed to increasing the complexity of the system however since flow and therefore mixing stops with temperature decrease flow patterns must have retained the predominant morphology and composition of the moment at which both contrasting magmas came together and froze flow patterns have been preserved with further temperature decrease fractional crystallization took over and hybrid rocks were generated from the fractionation of magmas previously mixed in different proportions

which 2 1 clay minerals are involved in the soil potassium reservoir insights from potassium addition or removal experiments on three temperate grassland soil clay assemblages field and laboratory observations based on x ray diffraction techniques suggest that 2 1 clay minerals behave as a k reservoir however 2 1 soil clay assemblages are most often composed of a mixture of different 2 1 clay mineral populations and the role of these different clay mineral populations in k absorption or k release are not fully understood this present work addressed this question through laboratory experiments by using an x ray pattern decomposition program to quantify peak area modifications of different clay mineral populations induced by k addition and k removal through plant action this study was performed on three typical temperate grassland soil clay assemblages containing illite interstratified illite smectite and soil vermiculite our results revealed that the quantities of well crystallized illite increased at the expense of soil vermiculite as a result of k absorption whereas the opposite trend was observed following k depletion this particular relationship between well crystallized illite and soil vermiculite suggests that they constitute a subgroup among 2 1 clay minerals poorly crystallized illite and interstratified clay minerals were also significantly affected by k absorption or removal indicating that they are also involved in soil k dynamics moreover we observed that these short term clay mineral modifications occurring at the day scale induced by root k extraction are reversible we also observed that the linear relationship between clay k content and the centre of gravity position of x ray diffraction patterns in the 2 1 clay mineral range seem to be a general property for soil clay assemblages dominated by illite and interstratified illite smectite materials our results support the view of 2 1 clay minerals as a k reservoir and specify the role of each of the 2 1 clay mineral populations in k absorption and release all the 2 1 clay minerals commonly found in temperate grassland soil clay assemblages take part in the soil k reservoir

basic magmatism and geotectonic evolution of the pan african belt in central africa evidence from the katangan and west congolian segments abstract in the west congolian and katangan pan african belts late proterozoic extensional tectonics related to the relaxation phase that followed the kibaran collision ca 1000 ma ago evolved to reach a mature rift stage characterized by the e morb from kimbungu bas zaire in the pan african west congolian belt and kibambale shaba zaire in the pan african katangan belt these mature rifts proto oceans closed during the pan african orogenic event in an embryonic collision between the kalahari craton to the south and the congo craton to the north this embryonic collisional belt differs from the classical ones in the lack of subduction and collision magmatic associations this difference is attributed to the limited extent of the collision slight crustal thickning and notably to the fact that it happened before the underthrust plate reached the minimum depth required to generate calc alkaline magmas through subduction

episodic fresh surface waters in the eocene arctic ocean it has been suggested on the basis of modern hydrology and fully coupled palaeoclimate simulations that the warm greenhouse conditions that characterized the early palaeogene period 55 45 myr ago probably induced an intensified hydrological cycle with precipitation exceeding evaporation at high latitudes little field evidence however has been available to constrain oceanic conditions in the arctic during this period here we analyse palaeogene sediments obtained during the arctic coring expedition showing that large quantities of the free floating fern azolla grew and reproduced in the arctic ocean by the onset of the middle eocene epoch approximately 50 myr ago the azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of arctic surface waters during an approximately 800 000 year interval the abundant remains of azolla that characterize basal middle eocene marine deposits of all nordic seas probably represent transported assemblages resulting from freshwater spills from the arctic ocean that reached as far south as the north sea the termination of the azolla phase in the arctic coincides with a local sea surface temperature rise from approximately 10 degrees c to 13 degrees c pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans we suggest that onset and termination of the azolla phase depended on the degree of oceanic exchange between arctic ocean and adjacent seas

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