comparison between the hot spot and geomagnetic field reference frames hot spots are located on the earth s surface and are caused by hot plumes of upwelling mantle material they manifest themselves by volcanic activity which changes its location in response to the movement of the lithosphere over the mantle plume it has been suggested1 3 that hot spots are relatively stationary with respect to each other and also that they represent a frame of reference with which to measure the absolute movement of the lithospheric plates over the surface of the earth another frame of reference can be partially defined by the position of the mean magnetic dipole field of the earth as the dipolar field is believed to be closely related to the spin axis this frame of reference automatically gives information about the palaeolatitude and orientation of the lithospheric plates but since the position of the ancient dipole field of the earth does not give any information about palaeolongitude and since in many cases the definition of the field is relatively poor due to less than adequate rock collections during the time of interest hot spot reference frames have been favoured by many people we now report a comparison of the two frames of reference and show that over the past 200 myr there has been relative movement between the two frames of reference of about 20 and that this motion has not been constant with time

a short term post lomagundi positive c isotope excursion at c 2 03 ga recorded by the wooly dolomite western australia it is generally accepted that carbon isotope variations in seawater were muted between c 2 06 ga after the end of the lomagundi carbon isotope excursion lcie and c 1 3 ga evidence is presented here that c 30 myr after the end of the lcie the biogeochemical cycle of carbon experienced a short term c 2 myr high amplitude up to 8 4 v pdb perturbation recorded in the horseshoe rift basin western australia the basin was initiated at c 2 03 ga with deposition of fluvial and shallow marine sandstones followed by the eruption of flood basalt and culminated with the deposition of platform carbonates and accompanying volcaniclastic and siliciclastic sediments wooly dolomite the horseshoe rift basin during deposition of the wooly dolomite was fault compartmentalized but connected to an ocean six depositional sequences make up the wooly dolomite sequence 1 records establishment of a carbonate platform conformably on basalt and coevally with volcaniclastic sedimentation all other sequences have dominant carbonate platform deposits and are unconformity bounded sequence 3 contains a c 57 m thick section with 13 c enriched carbonates bracketed between carbonates with close to 0 carbon isotope values further high resolution chemostratigraphic studies may reveal a more complex pattern of carbon isotope variations during the boring billion years but without precise geochronology similar short term carbon isotope excursions in carbonate successions could be incorrectly correlated to the lcie supplementary material table 2 including chemical and isotopic data sample locations and their position in figure 8 is available at https doi org 10 6084 m9 figshare c 2868055

precise u pb zircon ages for the molson dyke swarm and the fox river sill constraints for early proterozoic crustal evolution in northeastern manitoba canada precise u pb zircon ages have been obtained for samples from the molson dyke swarm and the fox river sill in ne manitoba canada the ages determined for the cross lake and cuthbert lake dykes are 1 883 7 1 5 1 7and 1 883 2 ma respectively and are in excellent agreement with the 1 882 9 1 4 1 5ma age obtained for the fox river sill these results support the contention that the emplacement of the fox river sill and the molson dyke swarm was contemporaneous and also demonstrate the potential for correlating mafic igneous activity in widely spaced localities the timing of early proterozoic mafic magmatism in the western superior province appears to be synchronous with igneous activity in other parts of the circum superior belt and in the trans hudson orogen to the west the emplacement of the molson dyke swarm at 1 883 ma indicates a 700 ma interval of quiescence between the final igneous activity that is recorded in the archean basement and dyke intrusion the presence of deformed equivalents of molson dykes in the thompson nickel belt indicates that the intense deformation in this belt occurred sometime after 1 883 ma

seismic imaging of complex structures by non linear traveltime inversion of dense wide angle data application to a thrust belt summary we have used a dense wide angle data set to test a two step procedure for the separate inversion of first arrival and reflection traveltimes data were collected in a complex thrust belt environment southern italy along a 14 km line with closely spaced sources 60 m and receivers 90 m we have applied a fully non linear tomographic technique specially designed to image complex structures to over 6400 first arrival traveltimes in order to determine a detailed velocity model a bi cubic spline velocity model parametrization is used the inversion strategy follows a multiscale approach and employs a non linear velocity optimization scheme the tomographic velocity model is adopted as the background reference medium for a subsequent interface inversion aimed at imaging a target upper crust reflector the interface inversion method is also based on a multiscale approach and uses a non linear technique for model parameters interface position nodes optimization we have applied the interface inversion method to over 1600 reflection traveltimes of a target event picked both in the near and in the wide angle offset range the retrieved interface is well resolved in the central part of the model where ray coverage mainly includes clear post critical reflections and the background velocity model is accurate in depth thanks to large offset deep turning rays the velocity and interface models thus determined are consistent with vertical seismic profiling data and correlate well with the geometry of known geological structures this study shows that the used inversion approach is efficient for target orientated investigations in complex geological environments

proterozoic continental volcanism in the belcher islands implications for the evolution of the circum ungava fold belt the belcher islands of eastern hudson bay expose a continuous sequence of early proterozoic volcanics and continental and shallow marine sedimentary rocks the volcanic rocks comprise two sequences of continental basalts the older eskimo formation and the younger flaherty formation the flows of both formations are composed of tholeiitic basalts mgo 9 wt which in each formation are divided into two groups based on the concentrations of high field strength elements both groups of eskimo flows have fractionated rare earth element ree patterns with negative nb anomalies relative to eskimo flows the flaherty flows have flatter ree profiles and higher nb contents the chemical variations observed in the eskimo flows are consistent with an assimilation fractional crystallization process involving a lower continental crust contaminant the major and most trace element trends of the flaherty flows are attributed to gabbroic crystal fractionation of two parental liquids which are interpreted to

terrestrial climate evolution in the southwest pacific over the past 30 million years abstract a reconstruction of terrestrial temperature and precipitation for the new zealand landmass over the past 30 million years is produced using pollen data from 2000 samples lodged in the new zealand fossil record electronic database and modern climate data of nearest living relatives the reconstruction reveals a warming trend through the late oligocene to early miocene peak warmth in the middle miocene and stepwise cooling through the late neogene whereas the regional signal in our reconstruction includes a 5 10 northward tectonic drift as well as an increase in high altitude biomes due to late neogene and pliocene uplift of the southern alps the pattern mimics inferred changes in global ice extent which suggests that global drivers played a major role in shaping local vegetation importantly seasonal temperature estimates indicate low seasonality during the middle miocene and that subsequent neogene cooling was largely due to cooler winters we suggest that this may reflect increased subantarctic influence on new zealand vegetation as the climate cooled

shifts in the intertropical convergence zone himalayan exhumation and late cenozoic climate the early miocene ca 23 16 ma was the time of peak himalayan exhumation and postulated mid crustal channel flow in the high himalayas a tectonic configuration not recognized before or after in the range previous models have correlated this rapid exhumation with the onset of the asian monsoon and or suggested that it contributed ultimately to mid miocene global cooling via silicate weathering and or organic carbon burial and consequent atmospheric co 2 drawdown based on published pacific ocean sedimentation records and india eurasia plate reconstructions we compare the position of the intertropical convergence zone itcz with the paleolatitude of the himalayas and show that these converged in the early miocene because the itcz is a zone of high precipitation we suggest that this convergence was an important driver of early miocene high himalayan exhumation and erosion continued northward motion of the indian plate took the himalayas north of the itcz which migrated south through the remainder of the miocene high himalayan exhumation and ductile shearing correspondingly decreased after the early miocene this mechanism for increased himalayan erosion is independent of the timing of the onset or enhancement of the asian monsoon which is debated

inversion of seismic refraction data using genetic algorithms the use of genetic algorithms in geophysical inverse problems is a relatively recent development and offers many advantages in dealing with the nonlinearity inherent in such applications however in their application to specific problems as with all algorithms problems of implementation arise after extensive numerical tests we implemented a genetic algorithm to efficiently invert several sets of synthetic seismic refraction data in particular we aimed at overcoming one of the main problems in the application of genetic algorithms to geophysical problems i e high dimensionality the addition of a pseudo subspace method to the genetic algorithm whereby the complexity and dimensionality of a problem is progressively increased during the inversion improves the convergence of the process the method allows the region of the solution space containing the global minimum to be quickly found the use of local optimization methods at the last stage of the search further improves the quality of the inversion the genetic algorithm has been tested on a field data set to determine the structure and base of the weathered layer regolith overlaying a basement of granite and greenstones in an archaean terrain of western australia

velocity interface model building in a thrust belt by tomographic inversion of global offset seismic data between september and november 1999 two test seismic lines were recorded in the southern apennine region of southern italy using the global offset technique which involves the acquisition of a wide offset range using two simultaneously active seismic spreads one consisted of a symmetrical spread moving along the line with geophone arrays every 30 m and a maximum offset of 3 6 km the other one consisted of fixed geophone arrays every 90 m with a maximum offset of 18 km this experimental acquisition project was carried out as part of the enhanced seismic in thrust belt esit research project funded by the european union enterprise oil and eni agip an iterative and interactive tomographic inversion of refraction reflection arrivals was carried out on the data from line esit700 to produce a velocity interface model in depth which used all the available offsets the tomographic models allowed the reconstruction of layer interface geometries and interval velocities for the target carbonate platform apula and the overburden sequence the value of this technique is highlighted by the fact that the standard approach based on near vertical reflection seismic and a conventional processing flow produced poor seismic images in both stack and migrated sections

late oligocene climatic changes evidence from calcareous nannofossils at kerguelen plateau site 748 southern ocean abstract palaeoecological changes in nannofossil assemblages in the southern ocean during oligocene times are examined through high resolution quantitative analyses of samples from ocean drilling program odp site 748 kerguelen plateau we quantitatively characterized the palaeoecological preference of groups of species and compared their general trends with those determined at maud rise odp sites 690 and 689 persico d villa g 2004 eocene oligocene calcareous nannofossils from maud rise and kerguelen plateau antarctica palaeoecological and palaeoceanographic implications marine micropaleontology 52 153 179 we then attempt a correlation between the main assemblage variation and sea surface temperature sst changes in the southern ocean at this time relatively stable cool conditions are interpreted to have persisted from earliest to late oligocene times when an increase in abundance of temperate water taxa is recorded both at maud rise and kerguelen plateau before the mi 1 event this reveals a climatic event that probably involved both sites and which is comparable to that indicated by the global oxygen isotope curve miller k g wright j d fairbanks r g 1991 unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion journal of geophysical research 96 6829 6848 zachos j pagani m sloan l thomas e billups k 2001 trends rhythms and aberrations in global climate 65 ma to present science 292 686 693 in the uppermost oligocene at site 689 the temperate water taxa index temperate temperate cool 100 increases from 25 2 ma similarly at site 748 the temperate water taxa index indicates an increase in sst in the late oligocene from about 26 5 ma at the base of chron c8n 2n which is offset by about 1 m y between the two areas the reason for this time difference can probably be found in the location of site 748 with respect to site 689 and in the palaeoceanographic setting taking into account that site 748 lies north of a deep water passage that separates kerguelen plateau from antarctica and north of the present day front of the antarctic circumpolar current the presence of warm water taxa exclusively at site 748 corroborates this hypothesis

diagenetic fluorapatite and aluminum phosphate sulphate in the paleoproterozoic thelon formation and hornby bay group northwestern canadian shield in the northwestern part of the canadian shield fluorapatite and a rare earth element bearing hydrated aluminum phosphate sulphate mineral aps occur as cements in continental successions near the base of the paleoproterozoic thelon formation thelon basin and hornby bay group hornby bay basin these minerals occupy interstitial sites form euhedral crystals display micro scale zonation make up part of an unmetamorphosed paragenetic assemblage and are distributed in correlative units across thousands of square kilometres suggesting a diagenetic origin stratigraphy geochronology and other lines of evidence suggest that the thelon formation and hornby bay group containing these phosphatic cements as well as the ellice formation and athabasca group are correlative and may have been originally interconnected the evidence suggests that the basal thelon formation and the hornby bay group underwent similar and approximately coeval diagenetic mineral paragenesis furthermore the diagenetic fluid

early partitioning of quebec microcontinent formation in the paleoproterozoic the distribution of allochthonous versus parautochthonous carbonate platforms combined with the timing of initial continental rift magmatism versus the timing of subsequent rifting of the continental margin provides tectonostratigraphic evidence for the formation and isolation of the oldest documented microcontinent perhaps as a consequence of the impingement of a mantle plume onto a cratonic margin during the paleoproterozoic initial rifting of the archean nucleus of north america in eastern canada is constrained to have been diachronous between 2 17 and 2 03 ga renewed rifting of a segment of the continental margin 292 to 120 m y later was accompanied by the emplacement of ultramafic layered sills the accumulation of komatiitic and alkalic basalts the deposition of banded iron formations and the isolation of a microcontinent and its 1 93 ga continental shelf succession subsequently accreted to the telescoped continental margin during collisional orogenesis

the coexistence approach a method for quantitative reconstructions of tertiary terrestrial palaeoclimate data using plant fossils abstract the coexistence approach is introduced as a method for quantitative terrestrial palaeoclimate reconstructions in the tertiary it is based on the assumption that tertiary plant taxa have similar climatic requirements to their nearest living relatives the aim of the coexistence approach is to find for a given fossil flora and a given climate parameter the climatic interval in which all nearest living relatives of the fossil flora can coexist for this purpose we have developed a data base climbot containing for over 800 tertiary plant taxa the nearest living relatives and their climatic requirements and an algorithm for analysis climst for all types of fossil floras the coexistence approach thus allows the rapid quantitative reconstruction of 10 different climate parameters including the mean annual temperature temperature of the warmest month temperature of the coldest month mean annual precipitation maximum monthly precipitation minimum monthly precipitation precipitation of the warmest month relative humidity potential evaporation as well as the ratio of mean annual precipitation over potential evaporation the reliability and resolution of the coexistence approach are tested with various techniques and proved to be reasonably good for instance the resolution with respect to the mean annual temperature can be up to 1 c applications to various modern and fossil floras are illustrated and the advantages and disadvantages of the coexistence approach are discussed

metallogenesis of an early proterozoic foreland sequence eastern hudson bay canada on the e side of hudson bay the nw margin of the archaean superior structural province is overlain by an unmetamorphosed little deformed early proterozoic supracrustal sequence the sequence is divisible into three parts possible tectosomes each characterized by a distinct style of mineralization the arkosic alluvial richmond gulf group was shed eastward from a thermal uplift and has been preserved only in a later aulacogen the richmond gulf graben it contains an apatite cemented redbed secondly a widespread post aulacogen carbonate rich w facing miogeocline blanketed the region a pyritic zone developed at its basal contact is particularly thick and hosts disseminated copper mineralization where formed on the arkose in the graben a pyritic brecciated stromatolite rich horizon within the carbonate contains galena and sphalerite thirdly widespread iron formation and a local 60 cm thick manganese carbonate bed overlying w derived basalt flows flysch and arkosic molasse all of uncertain tectonic affinity terminate the sequence

paleomagnetism and u pb geochronology of diabase dyke swarms of minto block superior province quebec canada in the first collaborative study of paleomagnetism and precise u pb geochronology in the minto block of the superior province mafic dyke swarms with three widely divergent paleomagnetic signatures and isotopic ages have been identified the 2505 2 ma ptarmigan dykes trend north to northeast and have a virtual geomagnetic pole at 42 s 220 e similar to that of 2473 2446 ma matachewan dykes of the southern superior province the ca 2230 ma maguire dykes trend west to northwest and yield a paleopole at 9 s 267 e similar to those for 2216 8 4 ma senneterre dykes and 2217 2210 ma nipissing sills of the southern superior and southern provinces respectively the 2209 1 ma klotz dykes trend west northwest but do not carry a consistent magnetization direction finally 1998 2 ma minto dykes of west northwest to northwest trend identical in age to the 1998 ma 2 ma purtuniq ophiolite of the cape smith belt have a paleopole at 38 n 174 e the similarity of paleopoles for the ca 2 23 2 21 ga maguire

fossil biotas from the okanagan highlands southern british columbia and northeastern washington state climates and ecosystems across an eocene landscape the late early to early middle eocene okanagan highlands fossil sites spanning 1000 km north south northeastern washington state southern british columbia provide an opportunity to reconstruct biotic communities across a broad upland landscape during the warmest part of the cenozoic plant taxa from these fossil sites are characteristic of the modern eastern north american deciduous forest zone principally the mixed mesophytic forest but also include extinct taxa taxa known only from eastern asian mesothermal forests and a small number of taxa restricted to the present day north american west coast coniferous biome in this preliminary report paleoclimates and forest types are reconstructed using collections from republic in washington state usa and princeton quilchena falkland mcabee hat creek horsefly and driftwood canyon in british columbia canada both leaf margin analysis lma and quantitative bioclimatic analysis of identified nearest living relatives of megaflora indicated uppe

the tectonic significance of some basic dyke swarms in the canadian superior province with special reference to the geochemistry and paleomagnetism of the mistassini swarm quebec canada the mistassini dykes extend northwest from the mistassini embayment and comprise both tholeiitic and komatiitic suites they are probably 2000 ma old and yield two major paleomagnetic components one of these with a pole at 131 w 13 s is thought to be an overprint related to the elsonian disturbance 1400 1500 ma ago a very steeply down and reversed component may be primary and has a pole at 080 w 50 n these spacial chemical and age relationships between the mistassini molson marathon and payne river dyke swarms and the aphebian supracrustal fold belts on the perimeter of the superior province suggest a genetic relationship between the dyke swarms and the fold belts the supracrustal belts are evidence of the opening and closing of oceans and the dyke swarms are evidence of early stage failed arms related to these openings more rarely for example the payne river dykes early stage dyke swarms are developed and preserved parallel to the edges of newly developed spreading plate boundaries

late miocene vegetation dynamics under monsoonal climate in southwestern china to better understand vegetation dynamics and the asian monsoonal climate in the neogene we reconstructed the vegetational succession and climate of wenshan basin in southwestern china during the late miocene 11 62 5 33 ma we used newly available palynological data and the results of a quantitative bioclimatic analysis the late miocene palynoflora in wenshan basin resembles that of modern evergreen broadleaf vegetation in subtropical east asia based on pollen elements and reconstructed palaeoclimates in 72 samples we found the composition of the vegetation in the wenshan basin fluctuated during the late miocene and was likely driven by natural climate variability quantitative estimates suggest that the mean annual temperature mat ranged from 16 6 to 17 5 degrees c the mean annual precipitation map was similar to 1500 mm and the monsoon intensity index msi ranged from 11 3 to 17 1 our results indicate that the wenshan basin experienced a warm wet and temperate to subtropical climate by comparison with other late miocene sites in yunnan we show that temperatures differed slightly from region to region and overall annual and seasonal precipitation levels were higher in the late miocene than at present but with a weaker monsoon intensity than in the wenshan basin today c 2015 elsevier b v all rights reserved

near tropical early eocene terrestrial temperatures at the australo antarctic margin western tasmania a worldwide greenhouse warm climate prevailed in the early eocene and nowhere was warming more dramatic than at high latitudes sea surface temperatures of 34 c have been estimated for a site at paleolatitude 65 s on the east tasman plateau of the southwest pacific ocean but these estimates require independent validation including from terrestrial proxies here we determine a near tropical terrestrial mean annual temperature estimate of 24 c at sea level for an early eocene site in tasmania australia using three proxies based on well dated estuarine plant fossils this estimate is lower than the nearby sea estimates to the east but similarly suggests that as in the southwest pacific early eocene climates in the eastern australo antarctic region were warmer than inferred elsewhere at high latitudes including on the antarctic peninsula such data are essential for improving our understanding of climatic and biotic evolution in the southern hemisphere

geochemistry of the metavolcanic rocks in the vicinity of the maclellan au ag deposit and an evaluation of the tectonic setting of the lynn lake greenstone belt canada evidence for a paleoproterozoic aged rifted continental margin abstract the paleoproterozoic ca 1900 ma lynn lake greenstone belt of northern manitoba canada has been previously characterized as comprising a series of tectonically juxtaposed intra oceanic derived metavolcanic rocks the results of more recent local and regional studies however support a significant contribution of continental crust during formation of the metasedimentary metavolcanic and intrusive igneous rocks that comprise the majority of the lynn lake greenstone belt the tectonic model previously proposed for the lynn lake greenstone belt however did not consider the geodynamics of the lynn lake greenstone belt in the context of all available data in this study we report the results of outcrop mapping and petrographic analysis as well as major minor and trace element geochemical analyses for 54 samples from the northern terrane and integrate and compare the results with data from previously published studies these data are used to recharacterize the metavolcanic rocks and to develop a new geodynamic model for the formation of the lynn lake greenstone belt ultramafic to intermediate rocks in the vicinity of the maclellan au ag deposit are characterized primarily by e morb like trace element characteristics and th nb la systematics which are interpreted to be the result of a primary plume derived melt interacting with continental lithosphere at a thinned i e rifted continental margin similarly the majority of the mafic to intermediate rocks that comprise the lynn lake greenstone belt are characterized by flat to e morb like trace element patterns and th nb la systematics which are consistent with mantle plume derived contaminated oceanic continental rift or rifted margin setting rocks this study suggests that the metavolcanic rocks of the lynn lake greenstone belt were derived via rifting between the superior and hearne cratons which resulted in the formation and growth of the manikewan ocean alternatively the metavolcanic rocks could have been derived from an upwelling plume generated from a back arc style subduction zone that formed between the rae and hearne cratons during the closure of the snowbird ocean which resulted in rifting of the passive hearne margin

a 9000 year oxygen and carbon isotope record of hydrological change in a small ethiopian crater lake the stable isotope composition of authigenic calcites in a core from lake tilo a small crater lake in the ethiopian rift valley provides a subcentury scale record of lake response to climatic change over the last 8850 14c yrs 9850 cal yrs an unusually high range of 18o and 13c values 15 is attributed in part to major changes in hydrothermal groundwater flux although hydrothermal groundwater influx to the lake was high during the early holocene its flow rate was relatively stable and thus climatically induced changes to the water budget can be inferred from variations in 18o and 13c ratios a major decline in hydrothermal groundwater input from 5500 14c yrs bp increased lakewater residence time and led to substantial increases in 18o and 13c before the mid holocene transition to more arid conditions during the last 2700 14c years diagenetic processes have resulted in extremely varied 18o and 13c values the holocene isotope record from lake tilo challenges the widely held assumpti

high frequency paleoclimate signals from foulden maar waipiata volcanic field southern new zealand an early miocene varved lacustrine diatomite deposit abstract a freshwater diatomite deposit near dunedin south island new zealand provides an exceptional archive of mid latitude seasonal climate variation during latest oligocene early early miocene time the diatomite accumulated in a small 1 5 km diameter maar floored lake that formed during basaltic volcanism except for exposures of basanite dated at 23 2 ma by 40 ar 39 ar and remnants of a paleogene sandstone and conglomerate cover the diatomite body is surrounded by otago schist geophysical profiles indicate that the total diatomaceous sediment thickness may exceed 100 m two depositional facies are described from 15 5 m of weakly consolidated fresh diatomite accessible in two pits a thinly laminated facies comprising 60 of the section consists of dark brown and white couplets of average thickness 0 5 mm both brown and white laminae are composed essentially of frustules of a single pennate diatom along with 1 2 of siliceous sponge spicules dark laminae also contain abundant 5 7 5 m diameter siliceous chrysophycean stomatocysts and organic matter decalcified complete skeletons of galaxias a southern hemisphere group of freshwater or diadromous fish are found throughout diverse well preserved leaves some with attached scale insects are dominated by lauraceae rare flowers are also present trace fossils preserved in the laminated comprise 1 1 5 mm wide pale diatomaceous strings of probable faecal origin and isolated 20 40 mm diameter sand lenses interpreted as faecal remains of swimming waterfowl the second diatomite facies group comprises dark brown speckled beds interpreted as sediment gravity flows up to 14 cm thick and interspersed throughout the study section they incorporate abundant laminated diatomite flecks and leaves and minor woody plant matter and terrigenous silt almost all are capped by 1 8 mm of white diatomite that is interpreted as post flow fall out of resuspended diatom frustules associated breccia and swirly beds up to 8 cm thick are composed of variably contorted clasts of laminated diatomite in a speckled matrix nodules spheroids and films of authigenic framboidal pyrite are commonly associated with plant and fish remains as in modern lakes white laminae likely formed from diatom blooms when light flux temperature or nutrients were optimal during spring early summer dark laminae accumulating during autumn winter months laterally continuous pinstripe lamination absence of bioturbation and excellent fish and plant preservation indicate that the profundal lake and floor were anoxic periodic variations in couplet thickness of 3 10 years compare with quaternary records of el nino southern oscillation variability and indicate that the early early miocene low altitude new zealand climate was seasonal and strongly ocean influenced as it is today

magnetic interpretation related to geo magnetic provinces the italian case history abstract a comparison of the results obtained from the geophysical interpretation with the available information regarding the italian geological situation permitted us to establish our so called geo magnetic provinces the relationship between the magnetic characteristics and the tectonic evolution permitted the identification of each of the four following provinces that exist inside the global tectonic confines 1 1 the sardo corso block which represents the eastern boundary of stable europe this province is characterized by medium wavelength low amplitude anomalies that originate in an outcropping basement hercynian granites s l 2 2 the orogenic belt which constitutes the double alps apennines system from a magnetic standpoint this system is characterized by short wavelength low amplitude anomalies that are due to a paleozoic outcropping and or buried acid crystalline basement these anomalies are found to overlie long wavelength medium amplitude regional anomalies that are related to a deep apenninic basement central northern apennines 3 3 the foreland area which occurs from sicily hyblean plateau and apulia northwards to ancona and the po plain this area is characterized by a crystalline basement which is typically differentiated from the standpoint of basicity 4 4 the rifting zone which is represented by the part of the tyrrhenian sea lying south of the 41st parallel discontinuity the ionian abyssal plain and the pantelleria and linosa troughs in the sicily channel the main characteristic of this province is its extreme basicity differentiation in the crystalline basement which is induced by the geochemical processes connected with the deep geodynamic events these phenomena do not permit the correlation of the semioceanic basement of the rifting zone with the continental basement by means of interactive modeling a structural tectonic picture of the basement of the various italian geo magnetic provinces has been obtained the main result was found to be that the orogenic belt basement is undergoing intense tectonic compression and overlies the structural highs of the foreland area which mainly show tensive events

depth and morphology of reflectors from the non linear inversion of arrival times and waveform semblance data part ii modelling and interpretation of real data acquired in southern apennines italy in order to retrieve a 2d background velocity model and to retrieve the geometry and depth of shallow crustal reflectors in the southern apennines thrust belt a separate inversion of first arrival traveltimes and reflected waveforms was performed data were collected during an active seismic experiment in 1999 by enterprise oil italiana and eni agip using a global offset acquisition geometry a total of 284 on land shots were recorded by 201 receivers deployed on an 18 km line oriented sw ne in the val d agri region southern apennines italy the two step procedure allows for the retrieval of a reliable velocity model by using a non linear tomographic inversion and reflected waveform semblance data inversion the tomographic model shows that the p wave velocity field varies vertically from approximately 3 km s to 6 km s within 4 km from the earth s surface moreover at a distance of approximately 11 km along the profile there is an abrupt increase in the velocity field in this zone indeed an ascent from 2 km depth to 0 km above sea level of the 5 2 km s iso velocity contour can be noted the retrieved velocity can be associated with plio pleistocene clastic deposits outcropping in the basin zone and with mesozoic limestone deposits the inversion of waveform semblance data shows that a p to p reflector is retrieved at a depth of approximately 2 km this interface is deeper in the north eastern part of the profile where it reaches 3 km depth and can be associated with a limestone horizon

paleoproterozoic stark formation athapuscow basin northwest canada record of cratonic scale salinity crisis abstract the paleoproterozoic stark formation a thick breccia unit formed during the transition from marine to non marine foreland basin fill in the athapuscow basin northwest territories canada four types of breccia occur in the stark formation 1 bedded breccias at the base of the unit overlying the basinal facies of the underlying pethei group are interpreted as debris flows 2 massive chaotic breccias occur in the lower part of the stark formation throughout the basin and these are interpreted to be evaporite collapse breccias 3 siltstone and mudstone breccia occurs in the upper part of the stark formation and is also interpreted as evaporite collapse breccia though much less evaporite was involved in its formation than the underlying chaotic breccia and 4 laminar accretionary breccia consisting of laminar carbonate clasts commonly with flat bottoms and convex up upper surface geometries these clasts occur in lenticular pods and are interpreted to form in caves following dissolution of evaporites or carbonates the widespread presence and abundance of evaporite pseudomorphs especially halite in all breccia types the stratigraphic restriction of the stark formation and irregular filling above this unit indicates that all but the bedded breccia formed by the dissolution and collapse of evaporites chaotic breccia directly above underlying pethei group shallow water and deep water carbonates indicates the evaporates formed across the platform and adjacent deep basin foundered megaclasts up to 1 5 km long and 40 m thick in basinal settings suggest cumulative evaporite thicknesses on the order of a few tens to a few hundreds of meters carbonate clasts in all the breccias contain abundant wave ripples planar laminations stromatolites and ooids these structures along with a paucity of subaerial exposure features indicates nearly all carbonate deposition in the stark was subaqueous thus by inference the evaporites in the stark formation were also partially subaqueous displacive halite pseudomorphs are common throughout all facies in the stark formation silicified and dolomite filled halite pseudomorphs are common along the contact between the evaporite collapse breccia and underlying carbonate platform pethei group and surrounding large clasts in basinal settings silicified hopper crystal casts within deep water rhythmites of the uppermost pethei group indicate precipitation of halite over deep waters gypsum pseudomorphs are exceedingly rare and anhydrite pseudomorphs were not observed the dominance of halite features in this basin and two penecontemporaneous basins kilihigok basin and wopmay orogen surrounding the slave craton suggests that relative to the present day seawater at 1 9 to 1 8 ga was oversaturated with respect to calcium carbonate had higher hco3 concentration and possibly was depleted in so42 the dearth of extensive thick bedded marine gypsum in the archean and early paleoproterozoic can be explained by low atmospheric oxygen content prior to 2 ga in conjunction with increased carbonate saturation before 1 6 ga

nanosims u pb dating of fossil associated apatite crystals from ediacaran 570 ma doushantuo formation abstract sedimentary rocks record a wealth of information on the evolution of lithosphere hydrosphere atmosphere and biosphere however uncertainty about the age of many precambrian sequences makes it very difficult to establish the accurate temporal framework which can dramatically improve our understanding of the scale and duration of geological and biological events the neoproterozoic doushantuo formation south china preserve unique assemblages of early multicellular fossils and records valuable paleoenvironmental information the age of these formations is thus critical for understanding the important biological and climatic events that occurred towards the end of the proterozoic eon in this study we used nanosims to date samples from the doushantuo formations by apatite u pb geochronology fossil associated precipitated apatite grains were identified using optical microscope and raman spectrometer the resultant age is 305 26 ma high common pb and low u concentration in those apatite specimens limit the precision of age determination while the yielded age suggests that the doushantuo formation may have experience a post depositional hydrothermal event

abrupt plant physiological changes in southern new zealand at the termination of the mi 1 event reflect shifts in hydroclimate and pco2 abstract a rise in atmospheric co2 is believed to be necessary for the termination of large scale glaciations although the antarctic ice sheet is estimated to have melted from 125 to 50 its modern size there is thus far no evidence for an increase in atmospheric co2 associated with the mi 1 glacial termination in the earliest miocene here we present evidence from a high resolution terrestrial record of leaf physiological change in southern new zealand for an abrupt increase in atmospheric co2 coincident with the termination of the mi 1 glaciation and lasting approximately 20 kyr quantitative p co 2 estimates made using a leaf gas exchange model suggest that atmospheric co2 levels may have doubled during this period from 516 111 ppm to 1144 410 ppm and subsequently returned back to 425 53 ppm the 20 kyr interval with high p co 2 estimates is also associated with a period of increased moisture supply to southern new zealand inferred from carbon and hydrogen isotopes of terrestrial leaf waxes the results provide the first high resolution record of terrestrial environmental change at the oligocene miocene boundary document a 20 kyr interval of elevated p co 2 and increased local moisture availability and provide insight into ecosystem response to a major orbitally driven climatic transition

u pb zircon and re os isotope geochronology of mineralized ultramafic intrusions and associated nickel ores from the thompson nickel belt manitoba canada a u pb zircon age 1880 5 ma has been obtained from a mineralized ultramafic body in the setting lake area of the thompson nickel belt this crucial new age for ultramafic magmatism in the thompson belt in conjunction with the precise age determinations established for the molson dike swarm cross lake dike 1883 7 1 7 1 5 ma cuthbert lake dike 1883 2 ma and the fox river sill 1882 9 1 5 1 4 ma by heaman et al 1986 provides the first direct evidence for the contemporaneous nature of mafic ultramafic magmatism along the northwest margin of the superior craton this magmatic event also appears to be synchronous with mafic magmatism in other parts of the circum superior belt and the trans hudson orogen re os isotope systematics of mineralized samples from seven deposits that span the length of the belt produce an age similar to the u pb zircon age but with a much larger error 1885 49 ma with an initial os of 4 6 the os isotope data demonstrate that the source of the thompson belt ores including those orebodies hosted in ultramafic rocks and those hosted in pelitic rocks was dominantly mantle derived establishing that thompson belt magmatism is synchronous with the molson dike swarm and the extensive fox river sill has important new exploration implications and requires modification of existing concepts which have presumed that thompson belt magmatism is significantly older than these other intrusive suites also it would appear that other important ni and ni cu deposits elsewhere in the circum superior belt and in the trans hudson orogen formed at or near 1 88 ga and thus this age could be considered an important and widespread nickel mineralizing metallogenic interval during the early proterozoic

diagenetic apatite character and in situ ion microprobe u pb age keeseville formation potsdam group new york state an occurrence of diagenetic fluorapatite cement is documented within the cambro ordovician keeseville formation potsdam group near chateaugay in new york state the fluorapatite cement occurs as stratiform layers within ephemeral fluvial quartz arenites which have been reworked by aeolian processes prior to burial the paragenetic sequence includes the following compaction of dust rimmed grains quartz cementation minor kaolinite fluorapatite cementation followed by secondary dissolution porosity and telogenetic hematite cementation mesogenetic illitization of kaolinite may have taken place prior to or following fluorapatite cementation the fluorapatite occurs as elongated bladed crystals that characteristically contain ladder like inclusion rich cores running parallel to crystal length surrounded by clearer rims and larger blocky crystals towards the middle of interstices in situ shrimp analyses of blocky fluorapatite crystals yield a u pb age of 486 29 ma indicating that the cement for

organic remains in late palaeoproterozoic granular iron formations and implications for the origin of granules toward the end of the palaeoproterozoic era over 109 billion tonnes of banded bif and granular gif iron formations were deposited on continental platforms granules in iron formations are typically sub spherical structures 0 2 to 10 mm in size whereas concretions are 10 mm both types of spheroids are preserved throughout the sedimentological record their formation has typically been interpreted to originate from reworked fe rich sediments in high energy wave agitated shallow marine environments new evidence from six different late palaeoproterozoic granular iron formations gif however suggests that some granules are the result of diagenetic reactions in addition to other features driven by microbial processes and mechanical movements characteristic coarse grain interiors and septarian type cracks inside granules akin to those features in decimetre to meter size concretions are interpreted as desiccation features from hydrated diagenetic environments where sulphate and or ferric iron were reduced while organic matter om was oxidised inside granules those granules derived from sulphate reduction preserve diagenetic pyrite rims whereas those formed via ferric iron reduction preserve diagenetic magnetite along their rims other diagenetic minerals including apatite mixed with om and various carbonate phases are commonly preserved within granules combined with systematically 13c depleted carbonate these diagenetic mineral assemblages point to the oxidative decay of om as a major process involved in the formation of granules spheroidal equidistant haematite laminations surround some granules and contain apatite associated with carbonate om and ferric ferrous silicates and oxides that further suggest these structures were not shaped by wave action along sediment water interfaces but rather by chemical wave fronts and biomineralisation our results demonstrate that the formation mechanisms of gif also involve microbial activity and chemically oscillating reactions as such granules have excellent potential to be considered as promising biosignatures for studying precambrian biogeochemistry as well as astrobiology

detailed study of the potentino seismic zone in the southern apennines italy abstract most relevant macroseismic and instrumental data concerning past and current seismic activity of the potentino southern italy have been collected in order to study the seismic behaviour of this area ten among the most important recent and historical earthquakes occurred in the area from 1826 to 1990 have been studied by means of macroseismic methodologies macroseismic fields for all the events indicate a general isoseismal lengthening in the direction of the apennines chain northwest southeast a rapid attenuation of intensity westward of the studied area and a strong propagation eastwards this configuration is strongly dependent on the source mechanisms of the seismic events and the geological dishomogeneities of the concerned areas as regards earthquakes which have been instrumentally recorded in the campania basilicata area from 1980 to 1991 more than 1300 accurate hypocentral locations have been computed for events with m d 2 5 using data from osservatorio vesuviano o v and istituto nazionale di geofisica i n g seismic networks special emphasis is put on the potenza may 5 1990 earthquake m s 5 4 neic national earthquake information center i vii msk which was the strongest recent event in the area and was felt in a large sector of southern italy as regards the seismic sequence following this event about 110 aftershocks with m d 1 9 have been located very close to the town of potenza northeast of it with a clustering type space distribution the occurrence of the events is strongly time concentrated in so defining a main shock aftershocks typical sequence moreover the macroseismic investigation of the main event has allowed to map out isoseismal lines bounding vii vi v and iv msk areas the isoseismals pattern shows that attenuation and amplification of intensity are observed in the same areas as for the previous events beginning from may 26 1991 an increase of seismicity initiated by an earthquake of m l 4 7 neic and i vi vii msk was observed nearly in the same area as the 1990 sequence accurate locations of 84 events with m d 1 9 have been computed however this sequence seems to have a slightly different character from the 1990 one in that events are scattered in time and seismic energy release is comparable to a swarm type seismic sequence as regards the previous sequences fault plane solutions for the highest magnitude events and for appropriate groups of events have been worked out the mechanisms indicate normal faulting motion with t axes oriented orthogonal to the apenninic chain in conclusion detailed analyses on the historical and recent seismicity of the potentino area and adjacent ones have allowed to identify at least four seismogenic zones which show activity with different features such zoning represents a contribution to the seismic hazard assessment in the southern apennines on a regional scale

inversion for crustal structure using reflections from the passcal ouachita experiment an interface inversion has been tested and applied to wide angle reflection data from the 1986 passcal ouachita experiment an interface corrugation with a relief of 10 km and a width of 30 km was successfully imaged in a test of the interface inversion velocity depth curves derived for shot points 14 19 using the tail sum method are similar to an average one dimensional velocity model from forward modeling using travel time correlations from southern profiles 14 19 the similarity of these velocity depth curves positioned over the southern half of the passcal experiment suggests that crustal structure in this region is approximately laterally homogeneous lower crustal velocities are not well resolved due to the recording on most profiles of only small segments of the travel time triplications a two dimensional velocity structure was derived by using the average one dimensional velocities for the deeper crustal layers and formally inverting for depth to interfaces the final inversion model is found to be consistent with previous refraction interpretations south of the ouachita orogenic trend and concurrent interpretations of the passcal data set inversion results for the central and southern portion of the passcal profile indicate a depth of 10 12 km for a midcrustal layer which thins southward from approximately 10 km to about 4 km a lower crustal layer with an average thickness of 12 km and a moho depth of approximately 29 5 km are also determined interface depths are in agreement with a normal moveout stack of the passcal data set in particular the shallowing of the moho to a depth of 30 km over the northern 50 km of the profile matches previous interpretations of the data set and has been interpreted here and in previous studies as the location of the paleozoic continental margin geophysical studies of the modern atlantic continental passive margin provide the simplest comparison to the crustal structure derived here the lower crustal layer found south of the shallowing of the moho to 30 km beneath the passcal profile is analogous in thickness and position to rift stage lower crust however other tectonic interpretations are possible given the uncertainties in velocity and lithology relationships

early proterozoic tectonics and metallogeny of the lake huron region of the canadian shield abstract deposition of the huronian supergroup dominantly fluvial clastic sediments with local basal volcanic accumulations began at 2 49 ga in a broad trough that extended far south of the present lake huron area atop a large archean continent that was assembled at 2 7 ga and broken up at 2 15 ga after intrusion of widespread gabbro sheets and dykes including nipissing diabase the wyoming province which contains sequences similar in age and stratigraphy to the distinctive huronian supergroup may be a fragment of this continent the superior province is a much larger fragment tectonic controls of deposition of the huronian and its paleoplacer uranium deposits and of the pre 2 2 ga deformation of these strata were probably unrelated to processes that controlled deposition of the animikie and marquette range sequences in the lake superior region at 2 0 ga the huronian animikie and marquette range sequences were deformed during the 1 85 ga penokean orogeny which occurred when an assembly of island arc terranes collided with the superior block the sudbury structure including the whitewater group and its contained sedex deposits and the sudbury igneous complex and its ni cu pge ores were also formed at 1 85 ga the elliot lake pyritic paleoplacer uranium ores myriad lenses of radioactive pyritic gravels were deposited by early huronian fluvial systems other endogenic huronian mineral deposits include disseminated ni cu sulphides in gabbros cu in red beds high in the huronian succession and silica in quartz arenites intrusions of nipissing gabbro near sudbury contain minor ni cu mineralization these intrusions also caused recycling of metals from archean and huronian rocks to form concentrations of cu au ag fe and w in veins and other epigenetic deposits most important of these are the unconformity related ag veins of the cobalt area which had particularly complex still undeciphered histories that probably included pre huronian weathering metallogenic patterns in the early proterozoic rocks were controlled by a complex interplay of factors including the distribution of mineral deposits in the archean basement tectonically controlled variations in huronian deposition and deformation and oxyatmoversion the transition from anoxic to oxygenic atmospheric conditions that occurred during deposition of the huronian supergroup

age of the richmond gulf group and implications for rifting in the trans hudson orogen canada abstract the aphebian richmond gulf group of the east coast of hudson bay is a fluvial sandstone sequence containing basalt flows it was shed eastward from a rifting related thermal dome situated in the present central part of hudson bay sandstone from the base of the group contains a uraniferous diagenetic apatite cement u pb and pb pb isochron analysis from this material show the age of the apatite haematite cement to be 2025 25 ma old these data provide an older age bracket for the deposition of the richmond gulf nastapoka and belcher groups they also date the formation of the richmond gulf graben an aulacogen related to the initial rifting of the trans hudson orogen

a 2169 ma u pb baddeleyite age for the otish gabbro quebec implications for correlation of proterozoic magmatic events and sedimentary sequences in the eastern superior province otish gabbro sills intrude sedimentary rocks in the otish basin of the southeastern superior province here deposition of otish supergroup sediments had previously been thought to be older than k ar and sm nd ages of ca 1750 1710 ma for otish gabbro sills and younger than ca 2515 2500 ma u pb ages of underlying mistassini dykes however a much older u pb baddeleyite age of 2169 0 1 4 ma is presented here for an otish sill indicating that they are coeval with and likely genetically related to the giant 2172 2167 ma biscotasing dyke swarm to the southwest and or the cramolet sills and payne river dykes to the north the new date also indicates that the age of the otish supergroup falls between ca 2515 ma and ca 2169 ma only a little different from the ca 2450 2217 ma bracket for the huronian supergroup of the southern province and is consistent with both supergroups spanning the oxy atmo inversion the otish supergroup could also be coeval with the sakami formation to the north but is like

contrasting palaeoenvironments of the mid late miocene dunedin volcano southern new zealand climate or topography abstract at the mid late miocene boundary a northward shift occurred in the subtropical front neighbouring the new zealand continental landmass the terrestrial palaeoenvironment of new zealand concurrently underwent a period of cooling the dunedin volcanic group in southern new zealand spans the mid late miocene boundary and the sedimentary deposits from kaikorai valley and double hill within this group contain diverse and well preserved floral assemblages we used terrestrial palaeoclimate proxies clamp climate leaf analysis multivariate program and ba bioclimatic analysis to determine the paleoenvironment at southern mid latitudes during the mid late miocene transition our results indicate that the mid late miocene climate of the dunedin volcano was warm temperate to subtropical mean annual temperature mat 17 19 c at double hill similar to modern coastal queensland and cool to warm temperate mat 12 14 c at kaikorai valley similar to modern northern new zealand winter temperatures at kaikorai valley were distinctly cooler 6 8 c differing aspect i e north vs south facing may have played a part in determining solar radiation particularly in an area of high relief such as the dunedin volcano because kaikorai valley was situated facing south and double hill facing north the two sites would have received differing radiative fluxes particularly in winter thereby possibly influencing the local environment biota and potentially also the palaeoclimate signal produced by floral proxies this study provides evidence for the temperature decline in terrestrial palaeoenvironments at mid latitudes caused by the northward movement of the subtropical front and strengthening of the antarctic circumpolar current during the mid late miocene

the significance of maar volcanoes for palaeoclimatic studies in china abstract the sediments of maar lakes often provide paleoenvironmental records which are highly suitable for palaeoclimatic studies the main advantages of the records from maar lakes compared with other lacustrine records are as follows first the presence of varves annually laminated layers and tephra layers as well as other materials like terrestrial plant macrofossils charcoals organic carbon organic shells suitable for isotopic dating like ams 14c 210pb 137cs 238u 230th 40ar 39ar provides the possibility of developing several independent chronologies enabling the development of robust high resolution chronologies second maars and maar lakes can provide continuous sedimentary records spanning tens of thousands of years tianyang maar in china is hosted the longest known record spanning at least 400 kyr bp that are ideal for the investigation of climate change on different timescales including orbital millennial centennial and annual decadal third recent studies of biomarkers based on long chain alkenones lcas and glycerol dialkyl glycerol tetraethers gdgts have demonstrated the potential of maar lakes for quantitative paleotemperature reconstruction in this study we review some of the more significant achievements of palaeoclimatic research based on maar lake sediment sequences from china with the focus on chronology multiple timescales and quantitative paleoclimatic reconstruction

conifer and angiosperm biomarkers in clay sediments and fossil plants from the miocene clarkia formation idaho usa the aliphatic lipids and terpenoids of conifer and angiosperm macrofossils and the clay sediment from a new site p 37 of the miocene clarkia formation idaho usa were analyzed to evaluate the preservation of characteristic conifer and angiosperm biomarkers in the sediment series of aliphatic lipids terpenoids and steroids similar to the biomarkers found in type locality clarkia p 33 were the predominant compounds in the sediment and in the fossils long chain aliphatic lipids were major compounds in the fossil plants and the sediment but a differentiation of angiosperm and conifer sources is not possible due to their common distribution among all vascular plants in addition to previously reported terpenoids diterpenoids of a conifer origin and several angiosperm derived polar triterpenoids of the oleanane lupane ursane and friedelane classes are reported here for the first time from the clarkia sediments the conifer shoots taxodium glyptostrobus calocedrus contained characteristic conifer biomarkers such as abietane type diterpenoids while characteristic angiosperm triterpenoids were predominant in the angiosperm leaves betula quercus lithocarpus the biomarker compositions of the taxodium and glyptostrobus shoots match the terpenoid patterns previously reported from fossil seed cones of the same genera although conifer macrofossils contribute about 45 to the flora of site p 37 characteristic conifer biomarkers occurred in the sediment in only low amounts while the angiosperm derived triterpenoids were present in comparatively higher abundances the results indicate that the conifers are under represented compared to the angiosperms according to the terpenoid composition of the sediment extract this may be due to the presence of small angiosperm derived particles leaf detritus wax in the sediment and or migration of leaf waxes from the angiosperm leaves into the sediment in contrast the diterpenoids are trapped in the resinous woody tissue of the conifers and are thus disseminated less into the sediment

a u pb age for mineralized nipissing diabase gowganda ontario concordant baddeleyite and rutile analyses from mineralized nipissing diabase at gowganda s castle mine yield a u pb age of baddeleyite is a primary phase of the diabase therefore the age dates the magmatic emplacement the genesis of rutile is less certain rutile could have formed during an episode of alteration veining and ag mineralization in which case the u pb age would also date the secondary event and demonstrate that ag mineralization was related to the nipissing magmatism however a primary magmatic origin of the rutile cannot be completely excluded for now thus the u pb age may not constrain the time of ag mineralization further research is needed to clarify this point

two billion year old isotopically heavy carbon evidence from the labrador trough canada forty eight samples of bulk carbonates were studied from the dunphy portage alder uve denault and abner formations and the undivided pistolet subgroup in the labrador trough quebec canada the carbonate units occur as a number of thick beds up to 300 m within 100 600 m thick formations they are interbedded with siliciclastic sediments and are composed of crystalline sparry micritic allochemical and stromatolitic dolostones the carbonate rocks are recrystallized and metamorphosed up to amphibolite grade they are chemically dolostones and include chemical or biochemical laminated and massive dolostones dolorudites dolarenites and dololitites which were deposited in shallow water dunphy denault and abner formations to relatively deep water uve formation marine environments reef facies are present in the denault and abner formations the dunphy portage alder and uve formations deposited between 2 17 and 2 14 ga yield isotopically heavy values of 13c pdb ranging from 5 3 to

quantitative palaeoclimate estimates for early miocene southern new zealand evidence from foulden maar abstract a rich and diverse plant macrofossil assemblage from an earliest miocene diatomite deposit in southern new zealand provides a detailed record of mid latitude southern hemisphere terrestrial climate in an oceanic setting quantitative palaeoclimate estimates for temperature and precipitation variables were obtained using the climate leaf analysis multivariate program clamp and the bioclimatic analysis approach in addition the surface area of fossil podocarpus travisiae leaves preserved at the site was used as a proxy for mean annual temperature clamp and bioclimatic analysis both estimated mean annual temperatures at 18 5 19 5 c with a moderate seasonal temperature range between summer and winter of 10 c and leaf size in podocarpus suggested a mat of about 21 c precipitation rates were high at around 1700 2000 mm per year clamp analysis suggested a 600 mm difference between the dry and wet season whereas bioclimatic analysis indicated a 200 250 mm difference between summer and winter when compared to clamp analysis on modern vegetation on subtropical oceanic islands it would seem that clamp overestimates seasonal precipitation differences

a unique annually laminated maar lake sediment record shows orbital control of southern hemisphere midlatitude climate across the oligocene miocene boundary the foulden maar deposit a finely laminated lacustrine diatomite from the south island of new zealand is the first high resolution oligocene miocene terrestrial climate record from the midlatitudes of the southern hemisphere we use the presence of orbital and solar cycles within the physical properties records from the deposit to infer that the laminations are annual varves and that the deposit spans 100 k y when combined with magnetostratigraphy and 40 ar 39 ar data we can assign the diatomite to chron c6cn 2n 23 033 22 931 ma coeval with the rapid deglaciation of antarctica during the second half of the mi 1 transient glaciation event both obliquity and precession cycles occur in the physical properties records from the site indicating a strong ocean atmosphere coupling in the southern hemisphere and influence from both low and high latitudes the appearance of a strong obliquity component in particular may indicate a transient incursion of the subtropical front onto the campbell plateau during the mi 1 deglaciation

seismic exploration in complex terrains a processing experience in the southern apennines we discuss a data processing sequence adopted to reprocess a seismic line that crosses the italian southern apennines from the tyrrhenian sea to the adriatic margin and investigate both the overthrust and foreland areas we first determine the main causes of the very low s n ratio in the field data and then propose a processing sequence aimed at exploiting the signal content also making use of a priori geological knowledge of this area our work indicates a combination of causes for the very low quality of the seismic data these include length of the spread about 20 km that is unfavorable because of the rapid variation in the near surface geology tectonic complexity crooked line acquisition and the rough topography associated with outcropping rocks characterized by highly variable velocities based on the outcome of this data analysis we present a processing sequence driven by knowledge of the regional tectonic setting and by knowledge of the shallow subsurface geology the main effort is in remov

deriving temperature estimates from southern hemisphere leaves abstract the percentage of woody dicots with entire margined leaves in a flora is known to be positively correlated with mean annual temperature leaf margin analysis lma but this relationship is not globally uniform in particular the floras of australia and new zealand have been regarded as displaying a different physiognomic relationship to climate than floras seen in the northern hemisphere this difference is more marked in new zealand where the lma relationship appears entirely absent here we amass data for both northern and southern hemispheres using standard protocols and show that regional variations in the leaf margin mean annual temperature relationship are real but become less significant when other characters are included even new zealand falls into line and most of the mean annual temperature signal in new zealand floras is encoded in non margin features we introduce a new clamp climate leaf analysis multivariate program calibration dataset for the southern hemisphere comprising leaf physiognomic data from argentina bolivia south africa australia new zealand and other pacific islands that offers comparable precision for climate prediction to similar datasets derived from the northern hemisphere

the characteristics and source of laminated mud at lake barrine northeast australia abstract in a small 1 km 2 crater lake in the australian upland tropics 17 15 s 145 38 e 721 m a s l laminated mud has accumulated throughout the past 5 ka it is limited to a central region below 50 67 m of water where it is protected by a monimolimnion the contents of the laminae e g total lake products organic detritus diatoms pollen grains vivianite crystals distinguish two contrasting types namely detritus rich and detritus poor judged against radiocarbon dates over long sequences these couplets are not annual gravimetric mineralogical and chemical observations on the mud and on suspended organic and inorganic matter caught through several periods indicate some diagenetic changes across the mud water interface diatom analyses do not assist in relating mud type to source or period of origin the most likely mechanism of lamination is that continuous deposition of clay with small and varied detrital accompaniment is periodically enhanced by greater detrital input this occurs in some but not all periods of winter isothermy when ground temperatures fall to zero and below on several consecutive nights this leads to the stirring of sediments in water shallower than 50 m and their relocation in the deeper meromictic zone fine variations in e g diatom content partly independent of lamination type probably contain a wealth of detail about the lake s environmental history

palaeoecological analyses of riversleigh s oligo miocene sites implications for oligo miocene climate change in australia during the cenozoic australian environments changed from being dominated by warm and humid rainforests to mainly arid semiarid habitats comparable to those found today northern australia s oligo miocene palaeoenvironment were analysed using mammalian assemblages from the riversleigh world heritage area northwestern queensland limitations of fossil assemblages were minimised using minimum sample richness and taxonomic distinctness analyses because these identify under sampled unrepresentative and taxonomically biased fossil assemblages which can then be removed from the overall analysis cenogram and body mass distribution methodologies were used to help determine the palaeohabitats of seventeen sites from riversleigh that span the late oligocene to early miocene middle miocene and early late miocene the results suggest a change of environment through time with the late oligocene of riversleigh represented by an open forest the early and middle miocene by rainforest and the early late miocene represented by open forest

upb geochronology of the western cape smith belt canada new insights on the age of initial rifting and arc magmatism abstract the cape smith belt of northern quebec is the foreland to hinterland transition of the ungava orogen a component of the paleoproterozoic trans hudson orogen of north america u pb ages for rift and volcanic arc related units from the cape smith belt are presented and used to evaluate models of its tectonic evolution a gabbroic sill intrusive into the rift related sediments near the base of the povungnituk group is 2038 2 4 ma old indicating that rifting of the superior province was initiated prior to that time 80 m y earlier than previously reported a granodiorite intrusive into the volcanic rocks of the povungnituk group is dated at 1991 2 ma indicating that magmatism associated with the rifting event was active at that time 30 m y earlier than formerly thought the age of parent group arc related magmatism ranges from 1874 3 4 ma the age of a diorite intrusion to 1860 2 ma the age of another diorite intrusion and of a rhyolite a granodiorite intrusive in the parent group yields an age of 1845 6 ma magmatism of the parent group is thought to be related to northward dipping subduction of the superior province margin below the watts group a gabbroic intrusion in the 2000 ma old watts group is dated at 1858 2 ma these ages are consistent with a tectonic model in which the rocks of the cape smith belt formed in a single continental rift to oceanic progression followed by subduction which led to an arc continent collision a comparison of u pb ages for similar events in different sectors of the trans hudson orogen in canada reveals that early events are diachronous and range from 2169 ma to 2038 ma the main collisional events are coeval in the ungava and new quebec orogens and in some of the western sectors at 1830 1860 ma younger ages of 1800 1820 ma are obtained for the late collisional stages throughout the trans hudson orogen

sm nd isochron age and provenance of the argillites of the gunflint iron formation in ontario canada abstract sm nd rb sr and k ar isotope analyses were made on argillaceous sediments from the gunflint iron formation in the lake superior region in order to provide new information on their sedimentation age and evolutionary history the investigations indicate that it might be possible to date the time of sedimentation by the sm nd method by studying specific material such as argillaceous whole rocks enriched in organic matter and clay fractions the spread in the sm nd ratios seems here to have been favoured by the incorporation of organic material in the argillites the sm nd isotope data yield an isochron age of 2 08 0 25 ga which seems to be a fair estimation of deposition age model calculations indicate that the main source supplying the animikie seawater with ree was located at the northern border of the basin the argillites and their clay minerals did not behave as closed systems with regard to the rb sr and k ar systems during further diagenetic evolution

tectonic history of the lagonegro domain and southern apennine thrust belt evolution abstract the tectonic history of the lagonegro domain in southern italy is an intriguing topic for the mesozoic mediterranean paleogeography and is important for reconstructions of the tethys previous interpretations postulate the paleogeographic position of a deep lagonegro molise sicilide basinal domain between the external apulia carbonate platform to the east and the internal apenninic carbonate platform i e the alburno cervati maddalena mountains to the west a second and separate deep basin more to the west was the home of the liguride units which cover extensive areas of the southern apennines following an extensive review of previously published concepts and on the base of the structural interpretation of the southern apennines thrust belt using additional subsurface data and extensive field mapping the authors now suggest that all deep basinal units of the southern apennines i e the ligurides the lagonegro units and the molise sicilide units derive from internal areas located to the west with respect to a coeval wide carbonate platform slope shallow basin complex which in its pre middle miocene reconstruction extended from apulia well beyond the present day tyrrhenian coast of southern italy the basinal units were first assembled as an accretionary wedge and overthrusted during the late miocene over the carbonate platform slope shallow basin complex the liguride lagonegro molise sicilide accretionary wedge was later cut by an envelopment thrust which overthrust the previously underlying platform complex over the previously emplaced complex accretionary wedge our hypothesis in part revives an old concept proposed by selli 1962 and requires further testing and research we conclude that paleogeographic reconstructions of the southern apennines and the mediterranean tethys are still in a state of flux

paleomagnetism u pb geochronology and geochemistry of lac esprit and other dyke swarms james bay area quebec and implications for paleoproterozoic deformation of the superior province an extensive set of north to northwest trending diabase dykes termed the lac esprit swarm is identified in the superior province east of james bay based on geological mapping and a distinctive paleomagnetic pole 61 7 n 169 1 e dm 7 7 dp 5 5 the lac esprit swarm yields a u pb baddeleyite age of 2069 1 ma similar to that of the 2076 5 4 ma fort frances swarm of the western superior province their paleomagnetic declinations differ by 23 12 after correction to a common reference locality the difference is likely due mainly to counterclockwise rotation about a vertical axis of the fort frances area relative to the lac esprit area differential rotation of 10 20 has been proposed more locally across the kapuskasing structural zone separating the eastern and western superior province in earlier paleomagnetic studies of ca 2450 ma matachewan and 2170 ma biscotasing dyke swarms thus relative rotation may have involved the entire eastern and western superior province perhaps in response

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

early proterozoic 1 88 1 87 ga tholeiitic magmatism in the new quebec orogen the new quebec orogen contains two volcano sedimentary sequences bounded by unconformities each sequence records a change from continental sedimentation and alkaline volcanism to marine sedimentation and tholeiitic volcanism the first sequence records 2 17 ga rifting and the development by 2 14 ga of a passive margin along the eastern part of the superior craton the second sequence developed between 1 88 and 1 87 ga in pull apart basins that reflect precollisional dextral transtension along the continental margin second sequence magmatism comprises i carbonatitic and lamprophyric intrusions and mildly alkaline mafic to felsic volcanic rocks ii widespread intrusion of tholeiitic gabbro sills and submarine extrusion of plagioclase glomeroporphyritic basalts and younger aphyric basalts and picrites and iii late stage mafic to felsic volcanism and intrusion of carbonatites crustal thinning allowed primitive tholeiitic magmas to equilibrate at progressively lower pressures before more buoyant

deep structure of the campanian lucanian arc southern apennine italy abstract recent exploration activities and successful discovery of large oil fields in the upper val d agri area southern apennine italy have encouraged the collection of large quantities of geological and geophysical data and their integration into comprehensive geological models here we present a series of structural profiles based on several hundred kilometres of seismic lines two and three dimensional and the results of many deep wells the best seismic lines have been extensively reprocessed and also tied to magnetotelluric data geological interpretations of those lines have been interactively tested and verified by gravity and magnetic modelling and structural balancing the wells and seismic data demonstrate that the fundamental tracts of the deep architecture of the orogen as it appears today were developed only at the end of the late pliocene the final closure of the ensialic shear zone responsible for the subduction of at least 150 km of continental lithosphere originally underlying the lagonegro basin can be dated as early pliocene the involvement of the inner apulian platform in the core of the belt and the activation of a new and more external left lateral oblique ensialic shear zone can be constrained to the late pliocene pleistocene the seismic profiles clearly show the underthrusting of the outer apulian platform unit beneath the inner apulian platform unit the thick skinned character of the plio pleistocene contractional structures is evident from the structural profiles this geometry is constrained by gravity magnetic data and structural considerations according to the relatively steep angle of dip about 10 of the apulian foreland beneath the chain the structural profiles depict the general architecture of the campanian lucanian arc the apennine platform and lagonegro unit are largely allochthonous and a part of the lagonegro basement could be buried below the apennine platform sole thrust the neogene plastic successions of the apennine platform and lagonegro basin were detached and now outcrop in the bradanic foredeep the inner apulian platform constitutes a huge thrust sheet structured as a wide antiform in the core of the belt its regional culmination roughly corresponds to the val d agri area extensional and transtensional structures cross cut the pre existing compressional structures as shown by the quaternary valleys of vallo di diano and val d agri the profiles shown also highlight the existing contrast between the deep structures in the core of the belt and the tectonic style of the lagonegro liguride and sicilide units these units were in fact subjected to brittle ductile deformation under metamorphic part of liguridi units and deep diagenetic to anchizonal conditions lagonegro units and were affected by a general overthrust shear directed towards the ne the inner apulian platform was on the contrary involved in the thrust belt together with its basement whereas the outer apulian platform affected by a subduction underwent a regional bending with associated normal faulting

geologic evidence for a mantle superplume event at 1 9 ga 1 both preserved and restored areal distributions of proterozoic marine intracratonic passive margin and platform sediments show a prominent peak at 1 9 ga indicating that shallow marine sediments were widespread on the continents and that sea level was high at this time the chemical index of alteration in shales deposited at this time was high suggesting warm climates possibly due to enhanced co2 levels in the atmosphere high sea level and warms climate may also explain an abundance of black shale banded iron formations and shallow marine phosphate deposits and an increase in the number of occurrences and diversity of stromatolites in general and microdigitate stromatolites at 1 9 ga all of these observations are consistent with a 1 9 ga superplume event the occurrence of only a minor positive carbon isotope shift in marine carbonates at 1 9 ga indicates that the relative rates of burial of organic and oxidized carbon remained about the same as at present slightly low 87sr 86sr isotopic ratios in seawater at 1 9 ga reflect increased mantle input of sr from the proposed superplume event whereas higher ratios at 1 85 1 75 ga may reflect increased input of continental sr from a growing supercontinent the first massive sulfate evaporites in the geologic record at 1 8 1 6 ga follow the possible 1 9 ga superplume event this may reflect an increase in both oxidation state and carbonate deposition in the oceans as plume related volcanism wanes

new developments in clamp calibration using global gridded meteorological data abstract climate leaf analysis multivariate program clamp is a versatile technique for obtaining quantitative estimates for multiple terrestrial palaeoclimate variables from woody dicot leaf assemblages to date it has been most widely applied to the late cretaceous and tertiary of the mid to high latitudes because of concerns over the relative dearth of calibration sites in modern low latitude warm climates and the loss of information associated with the lack of marginal teeth on leaves in paratropical to tropical vegetation this limits clamp s ability to quantify reliably climates at low latitudes in greenhouse worlds of the past one of the reasons for the lack of clamp calibration samples from warm environments is the paucity of climate stations close to potential calibration vegetation sites at low latitudes agriculture and urban development have destroyed most lowland sites and natural vegetation is now largely confined to mountainous areas where climate stations are few and climatic spatial variation is high due to topographic complexity to attempt to overcome this we have utilised a 0 5 0 5 grid of global interpolated climate data based on the data set of new et al 1999 supplemented by the era40 re analysis data for atmospheric temperature at upper levels for each location the 3 d climatology of temperature from the ecmwf re analysis project was used to calculate the mean lower tropospheric lapse rate for each month of the year the gridded data were then corrected to the altitude of the plant site using the monthly lapse rates corrections for humidity were also made from this the commonly returned clamp climate variables were calculated a bilinear interpolation scheme was then used to calculate the climate parameters at the exact lat long of the site when clamp analyses using the physg3br physiognomic data calibrated with the climate station based met3br were compared to analyses using the gridded data at the same locations gridmet3br the results were indistinguishable in that they fell within the range of statistical uncertainty determined for each analysis this opens the way to including natural vegetation anywhere in the world irrespective of the proximity of a meteorological station

early to middle miocene monsoon climate in australia the present day australian monsoon delivers substantial moisture to the northern regions of a predominantly arid continent however the pre quaternary history of the australian monsoon is poorly constrained due to sparse and often poorly dated paleoclimate proxy evidence sedimentological and paleontological data suggest that warm humid and seasonal environments prevailed in central and north australia during the miocene though it is unclear whether these were products of the australian monsoon we perform a series of sensitivity experiments using an atmospheric general circulation model combined with an offl ine equilibrium vegetation model to quantitatively constrain the areal extent of the miocene monsoon our results suggest a weaker than modern monsoon climate during the miocene this result is insensitive to atmospheric co 2 although somewhat sensitive to vegetation interactions and the presumed distribution of inland water bodies none of our miocene experiments exhibit precipitation rates greater than modern over north australia in disagreement with paleoclimate record interpretations vegetation modeling indicates that inferred precipitation values from fossil fl ora and fauna could only support miocene vegetation patterns if atmospheric co 2 was twice the modern concentration this suggests that elevated co 2 was critical for sustaining miocene vegetation

paleomagnetism structure and longitudinal correlation of middle precambrian dykes from northwestern ontario and minnesota a primary magnetization about 2 1 ga old is well preserved in the kenora kabetogama dyke swarm in minnesota and ontario its direction the mean for 12 dykes incorporating results from 30 paleomagnetic sites is 115 9 55 6 yielding a paleomagnetic pole position of latitude 42 7 s longitude 4 2 e dm 7 3 dp 5 2 the primary nature of the magnetization can be demonstrated using geochemistry to correlate individual dykes over distances that can exceed 300 km whereas the remanence direction varies between dykes it remains constant along a dyke sufficient proof that it was formed during initial cooling of the intrusion a weak longitudinal increase in hydrous alteration mgo content and degree of magnetic overprinting is observed as the swarm is followed to the south and may reflect increasing proximity to a precambrian continental margin that underwent rifting sedimentation and deformation during the time interval 2 2 1 6 ga bp although the cause of the longitudinal changes in terms of ma

paleomagnetism of the hearst dike swarm and implications for the tectonic history of the kapuskasing structural zone northern ontario prominent north to northwest trending dikes herein termed the hearst swarm west of the kapuskasing structural zone ksz in northern ontario yield a paleomagnetic pole position of 48 6 n 69 0 e dm 6 9 dp 3 6 60 samples from 12 dikes using paleomagnetic petrographic and structural criteria the hearst swarm is correlated with the 2 6 ga matachewan swarm east of the ksz a positive correlation is observed between the trend and paleomagnetic declination of hearst matachewan dikes and may result from an 15 post 2 6 ga rotation of terranes across the ksz paleomagnetic and structural data from the hearst dikes are consistent with the regional westward tilting of the crust near the southern ksz as first proposed in 1983 by percival and card

antarctic glaciation recorded in early miocene new zealand foraminifera abstract new zealand sedimentary sequences are important repositories of southern temperate palaeoenvironmental data as may be interpreted from biogenic chemical signals preserved in marine microfossils calibration curves for mg ca ratios versus water temperatures were established using modern benthic foraminifera notorotalia and cibicides notorotalia is a long ranged endemic benthic genus with a good record in shelf sediments while cibicides allows comparisons with similar studies elsewhere the resulting correlations were t c ln mg ca mmol mol 1 64 10 89 for cibicides spp and t c ln mg ca mmol mol 0 44 5 71 for notorotalia spp well preserved early miocene notorotalia and cibicides were collected for paired mg ca and 18 o analysis from a 3 6 m section of the mount harris formation spanning an estimated 60 ka and dating from about 17 7 ma globoconella zealandica zone roughly middle burdigalian early miocene within the local altonian stage 15 9 18 7 ma mg ca bottom water palaeotemperature estimates from cibicides and notorotalia gave concordant results 13 3 1 0 c for notorotalia spinosa 15 5 3 0 c for cibicides spp estimates of oxygen isotopic composition for altonian sea water 18 o palaeo sw were 0 4 0 4 suggesting the presence of small ice sheets on antarctica the method used to generate such results has far reaching implications for reconstructing 18 o palaeo sw and should allow antarctic ice volume history to be finely resolved from new zealand sequences

new insights on the orosirian carbon cycle early cyanobacteria and the assembly of laurentia from the paleoproterozoic belcher group abstract the orosirian period 2050 1800 ma of the paleoproterozoic era represents an interval between the great oxidation event and lomagundi jatuli excursion and the apparent environmental stability of the late paleoproterozoic to mid mesoproterozoic 1800 1300 ma here we present stratigraphic data carbon isotope chemostratigraphy element abundances and u pb zircon depositional ages from the belcher group in subarctic canada providing an unparallelled global reference section for the orosirian period u pb dates of 2018 5 1 0 ma and 2015 4 1 8 ma for two tuffs in the kasegalik formation lowest belcher group provide the first robust age constraints for earth s earliest unambiguous cyanobacterial fossil eoentophysalis belcherensis a tuffaceous shale 4 km stratigraphically higher at the contact of the flaherty and omarolluk formations 1854 2 1 6 ma provides an age for foreland basin development associated with the collision of the superior and hearne cratons carbonate carbon isotope data show smooth fluctuations ranging from 2 3 to 3 6 reaching a maximum near ca 1 88 ga this trend toward heavier carbon isotope values is interpreted as the result of global orogenesis during nuna assembly that elevated nutrient supply and sedimentation rates leading to an increase in the proportion of organic carbon burial relative to carbonate carbon burial

age and tectonic implications of paleoproterozoic mafic dyke swarms for the origin of 2 2 ga enriched lithosphere beneath the ungava peninsula canada abstract mafic dyke swarms represent short lived magmatic events that carry important temporal and chemical constraints for the evolution of the lithospheric mantle five baddeleyite u pb isotopic analyses of paleoproterozoic mafic dyke swarms intruding the ungava peninsula yielded ages of 2508 6 2220 1 2212 3 2199 5 and 2149 3 ma these ages fall within the 2 5 2 0 ga period previously defined by five other swarms which together comprise a magmatic record of more than 500 ma the similar age composition and surface area of two 2 51 ga swarms along with the lack of coeval supracrustal rocks suggest they correspond to failed rifts an important magmatic hiatus of 280 ma follows but ends with the intrusion of numerous dykes between 2 23 and 2 20 ga in the thinnest lithosphere of the northern ungava peninsula these dykes exhibit chemical signatures that vary from enriched older 2229 2212 ma dykes nd t 4 to relatively depleted 2209 2199 ma voluminous younger dykes nd t 1 4 la yb ca 2 21 2 20 ga later dykes emplaced ca 2 17 ga within a rejuvenated paleoproterozoic lithosphere also have depleted chemical compositions and map the extent of rifting coeval with the emplacement of early basalts in the labrador trough dykes emplaced in the 2 15 2 00 ga period further to the south are proximal to coeval continental basalts with which they share enriched isotopic compositions nd t 1 5 to 7 and a positive correlation between la yb and zr nb la yb 4 10 zr nb 7 20 that suggest assimilation of an archean crustal component a progressive decrease in the nd t values of these magmas with decreasing age further implies increasing contamination until the archean lithosphere failed ca 2 0 ga and permitted the eruption of isotopically depleted basalts the ca 2 2 ga depleted northern dykes and the 2 1 1 9 ga povungnituk basalts of the cape smith foldbelt share a negative correlation between zr nb and la yb that is expected for the incorporation of an enriched lithospheric component this component is represented by the alkaline rocks comprised in the circum ungava supracrustal belts carbonatites lamprophyric lavas alkaline basalts and by the lac aigneau lamprophyric dykes 1941 3 ma intruding the ungava peninsula these alkaline magmas collectively have 2 2 2 1 ga depleted mantle nd model ages t dm similar to a 2 15 ga sm nd isochron defined by the basaltic rocks of the supracrustal belts although these nd t dm ages and isochron are 100 300 ma older than magmatic ages they are identical with the ca 2 2 ga mafic dykes of the ungava peninsula this time correlation along with the similar chemical signature of the northern dykes and younger povungnituk basalts suggest that the composition of younger lavas and alkaline magmas was influenced by an enriched component associated with the pervasive metasomatism of the lithosphere coeval with the emplacement of the many ca 2 2 ga dykes

high resolution ice volume estimates for the early miocene evidence for a dynamic ice sheet in antarctica ice volume estimates for the early miocene 23 16 ma ats were determined by applying d 18 o to sea level calibrations to high resolution d 18 o records from odp sites 1090 and 1218 these calibrated records indicate that ice volume ranged between 50 and 125 of the present day east antarctic ice sheet eais during most of the early miocene 23 17 ma maximum icevolume occurred at each of the early miocene isotopic events i e mi events concomitant with bottom water temperatures generally between 1 and 2 8c rapid bb 1 myr and high amplitude ice volume changes also occurred intermittently during this period with some fluctuations ranging from a fully glaciated east antarctic continent to a partial collapse of the ice sheet equivalent to a 50 70 reduction in the eais these large scale ice volume changes often occurred at b100 kyr time scales suggesting an orbitally driven dynamic eais existed during the early miocene in contrast the calibrated d 18 o record from site 1090 indicates significantly less ice volume 25 70 of the present day eais was present between 17 and 16 ma these results are supported by numerical climate ice sheet modeling studies that show increased orbitally driven ice volume variability with elevated levels of atmospheric co2 the distribution of bottom water masses during the miocene was likely significantly different from today owing to variability in the production of deep water near the antarctic continent i e proto antarctic bottom water proto aabw weakening of proto aabw is suggested to have occurred during the early miocene especially during glacial minima resulting in it becoming more spatially restricted to the southern ocean and becoming entrained into a warmer deep water mass increased production of a warmer bottom water mass is also considered to have been important in the lighter isotopic values observed in the atlantic and indian oceans these changes are supported by evidence of a large dynamic eais based on strata cored on the antarctic margin and require a reevaluation of the view that antarctic ice volume was significantly reduced for most of the early miocene previous estimates have been constrained by the lack of deep water isotopic records proximal to antarctica and unduly influenced by the expansion of warmer deep water into most of the ocean basins at this time d 2005 elsevier b v all rights reserved

significant transient pco2 perturbation at the new zealand oligocene miocene transition recorded by fossil plant stomata abstract the reorganisation of earth s climate system from the oligocene to the miocene was influenced by complex interactions between tethyan tectonics orbital parameters oceanographic changes and carbon cycle feedbacks with climate modelling indicating that pco2 was an important factor oscillating episodes of climate change during the oligocene miocene transition omt have however been difficult to reconcile with existing pco2 records here we present a new pco2 record from the omt into the early miocene reconstructed using the stomatal proxy method with a database of fossil lauraceae leaves from new zealand the leaf database derives from three relatively well dated sites located in the south island of new zealand foulden maar mataura river and grey lake atmospheric pco2 values were obtained based on four separate calibrations with three nearest living equivalents using the stomatal ratio method as well as transfer functions our results based on the mean values of each of the four calibrations indicate pco2 ranging 582 732 ppm average 650 ppm at the omt falling precipitously to mean values of 430 538 ppm average 492 ppm for the earliest miocene and 454 542 ppm average 502 ppm in the early miocene the much higher values of pco2 at the omt indicate that pco played an important role in climate dynamics during this time potentially including the abrupt termination of glaciations

paleoclimate and paleoecology of the latest eocene florissant flora of central colorado u s a abstract the uppermost eocene florissant formation of central colorado u s a contains a diverse flora and fauna preserved in lacustrine facies and represents a key episode in earth history immediately preceding the eocene oligocene boundary laminated shales contain impressions of non monocot angiosperm leaves that were used to estimate paleoecological and paleoclimatic parameters using leaf physiognomic methods including leaf mass per area ma digital leaf physiognomy dilp leaf margin analysis lma and leaf area analysis laa the majority 58 of the morphotypes analyzed for ma suggested a semi evergreen leaf lifespan whereas another 27 indicated a deciduous habit and 15 an evergreen habit there was no significant relationship between ma and insect damage based on a small subset of florissant s leaves higher ma values 73 of leaves one year lifespan coupled with a tendency toward long and narrow leaf shapes and small leaf areas indicate the existence of sclerophyllous vegetation using the global regression for mean annual temperature mat the dilp estimate of mat was anomalously cold 5 5 4 c however using a northern hemisphere regression the dilp mat estimate of 11 6 3 3 c was more plausible using dilp mean annual precipitation map was estimated at 740 608 334 mm yr 1 which supports dry conditions estimates for mat and map using the univariate lma and laa methods overlapped within uncertainty of the dilp results in addition those taxa classified as growing in wet areas riparian had significantly more teeth than non riparian taxa these paleoclimatic and paleoecological results suggest that outside the riparian forest the florissant flora sampled a seasonally dry temperate sclerophyllous shrubland to woodland perhaps similar to modern chaparral forests in the western interior of the u s a just before the transition into the cooler oligocene

u pb geochronology in the trans hudson orogen northern saskatchewan canada we have obtained u pb ages on zircons from volcanic and plutonic units in several lithotectonic domains of the southern trans hudson orogen in northern saskatchewan these data constrain the timing of early proterozoic orogenic events in the region and enhance our understanding of both the relationships among local domains and the relationship of the trans hudson orogen to other early proterozoic orogens in north america with one exception all units studied so far yield zircon ages of 1890 1835 ma most of which are systematically earlier than previously reported rb sr isochron ages on the same or similar units suggesting open system behavior in the rb sr systems five metarhyolites from volcanic sequences in the la ronge domain glennie domain and hanson lake block give ages ranging from 1888 to 1876 ma most of the plutons we dated ranging from gneissic syntectonic tonalites and granodiorites to less deformed late intrusions such as the wathaman batholith and other smaller bodies yield ages of 18