magma types and the tectonic evolution of the swedish proterozoic information on tectonic evolution can be obtained from the succession of magmatic types represented i type and s type granitoids and volcanics basic dykes and alkali complexes the earliest proterozoic magmatic activity resulted in the formation of greenstone belts within the karelian continent area probably in the age range 2500 2100 ma this was followed by an event similar to andinotype orogeny at around 1900 ma with i type granitoids and calc alkaline volcanics this progressed to an event of hercynotype which was concluded by about 1750 ma subsequent magmatic activity i type granitoids and volcanics suggests a new phase of andino type orogeny until about 1630 ma s and c sweden or 1500 ma n sweden tension related magmatism at around 1550 ma basic dykes alkaline complexes and gabbro may relate to rifting prior to the independant evolution of sw sweden which includes intrusion of i s type granitoids metamorphism followed by continental rotation and collision with n america at about 1050 ma basic dykes and s type granites are related to subsequent uplift 950 850 ma ago

metallogeny and lead isotopic composition of base metal sulfide deposits in the rappen area northern sweden early proterozoic volcanic and sedimentary rocks of the rappen district in northern sweden were deposited at a destructive plate margin to the south of the archaean craton of the western baltic shield the volcano sedimentary suite was intruded by two generations of early proterozoic granites at ca 1 89 1 85 ga and ca 1 82 1 78 ga respectively and metamorphosed at upper amphibolite facies conditions small stratabound iron copper and zinc deposits occur in felsic to mafic tuffs and arkosic sediments small deposits of molybdenum tungsten and uranium formed during the emplacement of the younger granites the lead isotopic compositions of sulfide trace lead from the various deposits are highly heterogeneous in the 206pb 204pb 207pb 204pb diagram they fall on mixing arrays between little evolved early proterozoic lead and highly radiogenic caledonian lead the least radiogenic lead isotopic compositions from the various deposits have a wide range of 207pb 204pb ratios and thus indicate variable involvement of archaean crustal lead in the proterozoic deposits deposits hosted by siliciclastic rocks have higher 207pb 204pb ratios than deposits hosted in mafic to felsic tuffites the lead isotopic heterogeneity suggests that the lead in the various deposits was locally derived and furthermore that the sedimentary rocks in part originated from the archaean craton to the north lead mixing arrays in the 206pb 204pb 207pb 204pb diagram demonstrate that in paleozoic time radiogenic lead was mobilized and transported in the basement source ages calculated from the mixing arrays ca 1 9 ga and ca 1 8 ga correspond to the age of the early proterozoic volcanism and metamorphism respectively one group of deposits includes lead from at least three sources and illustrates that radiogenic lead was multiply mobilized and transported in the proterozoic basement it occurs in deposits that occur in zones that became permeable during the reactivations of the basement

lead mobilization during tectonic reactivation of the western baltic shield abstract lead isotope data from sulfide deposits of the western part of the baltic shield define mixing lines in the 206 pb 204 pb 207 pb 204 pb diagram lead from two types of sulfide deposits have been investigated 1 1 exhalative and volcanogenic deposits that are syngenetic with their host rocks 2 2 vein deposits the syngenetic deposits locally show a very wide range of lead isotopic compositions that reflect a variable addition of highly radiogenic lead while the vein deposits although they have radiogenic lead isotopic compositions exhibit only limited isotopic variations in different provinces of the shield both types of deposits fall on the same lead mixing array the slope of the lead mixing lines varies as a function of the age of basement rocks and the age of the tectonic event which produced the lead mobilization and therefore relates the source rock age with the age of lead mobilization calculated mixing ages fall into several short time periods that correspond either to orogenic events or to major phases of continental rifting the orogenic events are the ca 360 430 ma caledonian ca 900 1100 ma sveconorwegian and the ca 1800 1900 ma svecofennian orogenic cycles the rifting events correspond to the formation of the ca 280 ma oslo rift and the ordovician ca 450 ma graben system in the area of the present gulf of bothnia each mixing age indicates that lead was mobilized probably as a consequence of mild thermal disturbances and that the crust was permeable to lead migration the data show that the geographic distribution of sulfide deposits with highly radiogenic lead isotopic compositions coincides with old graben systems orogenic belts and orogenic forelands on the baltic shield the ages of vein deposits and their geographic distribution demonstrate multiple tectonic reactivation of the interior of the baltic shield in response to orogenic events at its margin

evolution of depleted mantle the lead perspective abstract isotopic data have established that compared to estimated bulk earth abundances the sources of oceanic basaltic lavas have been depleted in large ion lithophile elements for at least several billions of years various data on the tertiary mesozoic gorgona komatiite and cretaceous oka carbonatite show that those rocks also sample depleted mantle sources this information is used by analogy to compare pb isotopic data from 2 6 billion year old komatiite and carbonatite from the suomussalmi belt of eastern finland and munro township ontario that are with associated granitic rocks and ores that should contain marked crustal components within experimental error no differences are detected in the isotopic composition of initial pb in either of the rock suites these observations agree closely with sr and nd data from other laboratories showing that depleted mantle could not have originated in those areas more than a few tenths of billions of years before the rocks were emplaced on a world wide basis the pb isotope data are consistent with production of depleted mantle by continuous differentiation processes acting over approximately the past 3 billion years the data show that pb evolution is more complex than the simpler models derived from the rb sr and sm nd systems the nature of the complexity is still poorly understood

a high relative sea level stand in the middle holocene of southeastern tunisia abstract study of the marine holocene deposits in southeastern tunisia shows bioclastic beaches at elevations ranging between 0 and 100 cm above high tide level a h t l depending on the elevation of these fossilized shorelines the ages obtained are different the age of the older deposits ranges between 5900 and 4000 14cc yr b p 6400 4300 calendar yr b p there deposits consist of bioclastic beaches attaining an elevation of about 40 to 100 cm a h t l the younger deposit is dated at around 2100 14c years ago 1850 calendar yr b p and is found today at the same elevation as the present sea level this deposit also consists of bioclastic beach material and contains pottery fragments postglacial melting should not be responsible for this observed higher relative sea level stand because deglaciation ended about 7000 6000 14c years ago fairbanks 1989 furthermore the regularity of the paleobeach deposit elevation over a broad area in southeastern tunisia suggests that tectonics cannot explain the emergence the emergence of up to 1 m of marine deposits dating back to between 5900 and 4000 14c yr b p should rather be interpreted as the result in the region of a postglacial hydro isostatic rebound as predicted in the theological models of continental margins by for example clark et al 1978 and lambeck 1993 the present situation was reached 2100 14c years ago

chemistry of proterozoic orogenic processes at a continental margin in northern sweden abstract sm nd isotopic major trace and rare earth element data for two separate age groups of plutonic rocks have been used to characterize early proterozoic crust formation mechanisms in the vicinity of the exposed archaean of northern sweden the granitoid rocks of the older 1 89 1 87 ga group show calc alkaline trends diorite quartz monzonite adamellite and have negative nd values ranging from about 8 to 5 they represent variable contamination of isotopically juvenile mantle melts with archaean crustal material the younger 1 80 ga group of plutonic rocks are of true granitic composition they show a restricted range of nd values which is encompassed by those of the older group trace and major element data are consistent with the derivation of the younger group of rocks by remobilization of the earlier formed proterozoic continental crust this is in contrast to the temporally similar but isotopically more juvenile granitoids of the skellefte district to the south

tracking the sources of icebergs with lead isotopes the provenance of ice rafted debris in heinrich layer 2 the provenance of ice rafted debris ird deposited in the north atlantic before during and after heinrich event 2 has been determined through measuring the lead isotopic composition of single feldspar grains and multiple grain composites from the larger than 150 m size fraction from cores from the eastern and western north atlantic and from the labrador sea single grain analyses are used to identify the specific continental sources of the ird whereas composite samples are used to assess the relative ird contributions from different sources all single grains from heinrich layer 2 h 2 as well as h 2 composites plot along a correlation line on a 207pb 204pb versus 206pb 204pb diagram characteristic of the churchill province of the canadian shield this is yet another strong piece of evidence that this heinrich event was dominated by a massive iceberg discharge of the laurentide ice sheet lobe located over hudson bay in contrast single grains from the ambient glacial sediment above and below h 2 have multiple sources many of them also lie along the correlation line with h 2 grains but many others have pb signatures consistent with derivation from the grenville province and the appalachian range in north america and possibly from scandinavia and greenland composites from the ambient sediment generally lie well to the right of the h 2 reference line in agreement with the results of the single grain analyses the evidence provided by lead isotopes regarding the dominant role played by the hudson bay lobe of the laurentide ice sheet in the development of the heinrich events lends support to the binge purge model advanced by macayeal 1993a b that invokes trapping of geothermal heat by the base of the icecap and subsequent basal melting as the mechanism that triggered the heinrich events

sm nd and u pb dating of early proterozoic mafic felsic volcanism in northernmost sweden a sm nd mineral isochron of 1932 45 ma on a kiruna greenstone is defined by greenschist facies metamorphic minerals apparently older than the regional svecokarelian metamorphism 1880 ma however this age agrees within error with u pb zircon ages of 1909 1617 ma on quartz bearing prophyries which overlie but are in part intercalated with basic volcanics if these basic volcanics following previous studies are considered to be contemporary with the kiruna greenstones the present data suggest that eruption of both basic and acid volcanics and associated hydrothermal metamorphism took place over a short time interval close to 1 9 ga the greenstone sample is depleted in light rare earths and has high initial 145nd 144nd indicating a source in which such depletion has existed for a long time in contrast an albite diabase sample with a somewhat younger mineral age 1 80 0 08 ga is light rare earth enriched and has a correspondingly low initial nd isotopic composition

origin of granitic magma by crustal remobilisation rb sr and pb pb geochronology and isotope geochemistry of the late archaean qorqut granite complex of southern west greenland abstract rb sr and pb pb whole rock isochrons on the qorqut granite complex yield ages of 2530 30 myr initial 87 sr 86 sr 0 7081 0 0008 and 2580 80 myr respectively a model relating initial sr and pb isotopic compositions of the qorqut granites to the sr and pb isotopic compositions of the amitsoq gneisses ca 3700 myr and nuk gneisses ca 2900 myr at 2550 myr ago as well as sr and pb contents of the gneiss units suggests that between 40 and 50 of the qorqut granite magma was generated by partial melting of amitsoq gneisses and the remainder by partial melting of nuk gneisses

geochronology of an archaean tonalitic gneiss dome in northern finland and its relation with an unusual overlying volcanic conglomerate and komatiitic greenstone archaean gneiss greenstone relationships are still unresolved in many ancient cratonic terrains although there is growing evidence that most of the late archaean greenstone assemblages were deposited on older tonalitic crust

the late archaean to early proterozoic lead isotopic evolution of the northern baltic shield of norway sweden and finland abstract the late archaean rocks of the northern baltic shield comprise high grade gneiss terrains and granite greenstone terrains the high grade gneiss terrains consist mainly of older upper crustal material which became metamorphosed during the lopian orogeny ca 2 9 2 6 ga in contrast the 2 7 ga old granite greenstone terrains comprise mainly mantle derived materials at the southern and western edge the archaean craton became partially remobilized during the svecofennian orogeny 2 0 1 75 ga this orogeny represents a major crust forming event in the baltic shield during which mantle material was added to the crust and older material was remobilized whole rock galena and sulfide trace lead are used to outline lead provinces on the northern baltic shield the archaean lead from the baltic shield defines three secondary lead isochrons at 2 65 ga with different initial lead compositions which reflect average pre 2 65 ga 1 ratios of 8 0 8 1 and 8 3 respectively the variation of the initial lead composition of the high grade gneisses and tonalites lofoten and koitelainen area probably indicates 1 variable crustal residence time and or 2 different degrees of crustal contamination assimilation before the 2 65 ga metamorphic event and the lead from the eastern finland greenstone belts indicates a heterogeneous mantle with respect to u pb before 2 65 ga lead in proterozoic rocks of the different lead provinces defines sets of subparallel mixing fields which can be modelled by a 2 65 ga lead component and a 1 8 ga lead component the parallel offset of these fields reflects the pre 2 65 ga 1 ratio of these terrains i e it reveals the pre 2 65 ga 1 of the involved archaean rocks proterozoic terrains with involvement of archaean lower crustal lead show a poor correlation in the 206 pb 204 pb 208 pb 204 pb diagram whereas the other proterozoic terrains show a good correlation in the 206 pb 204 pb 208 pb 204 pb diagram

holocene development of the yellow river s subaqueous delta north yellow sea high resolution seismic profiles from the north yellow sea reveal a 20 40 m thick subaqueous clinoform delta that wraps around the eastern end of the shandong peninsula extending into the south yellow sea this complex sigmoidal oblique clinoform containing an estimated 400 km 3 of sediment overlies prominent relict transgressive surfaces the nearshore topset of the clinoform 50 m contain less than 1 m of holocene sediment with low sedimentation rates 1 mm year in contrast to other clinoforms the shandong clinoform appears to be a compound subaqueous deltaic system with what we interpret to be proximal and distal phases of clinoform development the underlying proximal sequence formed proximally between f11 and 9 2 ka in response to a temporary pause in the rapid postglacial sea level rise after the meltwater pulse 1b mwp 1b and increased discharge from the yellow river to the north yellow sea due to intensification of the summer monsoon a flooding surface appears to separate the proximal and distal phases corresponding to the next rapid sea level rise 9 5 9 2 ka bp mwp 1c since 9 2 ka bp an overlying distal sedimentary sequence has accumulated reflecting the backstepping and shifting river mouth westward to the gulf of bohai some inputs from coastal erosion and nearby small streams may be locally important along shore transport cross shelf advection and upwelling in the north yellow sea have reworked post lgm sediment and have helped maintain the morphology of the clinoform in the shandong mud wedge d 2004 elsevier b v all rights reserved

multiproxy assessment of holocene relative sea level changes in the western mediterranean sea level variability and improvements in the definition of the isostatic signal abstract a review of 917 relative sea level rsl data points has resulted in the first quality controlled database constraining the holocene sea level histories of the western mediterranean sea spain france italy slovenia croatia malta and tunisia we reviewed and standardized the geological rsl data points using a new multi proxy methodology based on 1 modern taxa assemblages in mediterranean lagoons and marshes 2 beachrock characteristics cement fabric and chemistry sedimentary structures and 3 the modern distribution of mediterranean fixed biological indicators these rsl data points were coupled with the large number of archaeological rsl indicators available for the western mediterranean we assessed the spatial variability of rsl histories for 22 regions and compared these with the ice 5g vm2 gia model in the western mediterranean rsl rose continuously for the whole holocene with a sudden slowdown at 7 5 ka bp and a further deceleration during the last 4 0 ka bp after which time observed rsl changes are mainly related to variability in isostatic adjustment the sole exception is southern tunisia where data show evidence of a mid holocene high stand compatible with the isostatic impacts of the melting history of the remote antarctic ice sheet our results indicate that late holocene sea level rise was significantly slower than the current one first estimates of gia contribution indicate that at least in the northwestern sector it accounts at least for the 25 30 of the ongoing sea level rise recorded by mediterranean tidal gauges such contribution is less constrained at lower latitudes due to the lower quality of the late holocene index points future applications of spatio temporal statistical techniques are required to better quantify the gradient of the isostatic contribution and to provide improved context for the assessment of 20th century acceleration of mediterranean sea level rise

isotopic data upb rbsr pbpb and smnd on mafic granulites from finnish lapland abstract a combined approach using several methods pb pb u pb rb sr sm nd on granulitic rocks selected from classic areas in northern finland is presented the results show that the emplacement of igneous rocks and the granulitic metamorphism occurred nearly coevally 1 9 2 0 ga this result which is supported by field observations means that these rocks are not ideal for comparing the response of the various parent daughter pairs to the high grade metamorphism or for checking the special geochronological possibilities of each method nevertheless because of the coherence of results from rocks of different origins a discussion is possible the bulk of the mafic granulite was certainly derived from upper mantle sources or short lived crustal mafic materials granulites of the granulitic belt and anorthosites are thought to have originated from two distinct mantle sources reflecting mantle heterogeneities at that time

on the age of the kiruna greenstones northern sweden abstract three types of zircons from an albite diabase sill within the kiruna greenstone group have been investigated to determine their age and order of crystallization the youngest pink and transparent zircons probably crystallized in late fissures and in association with a thermal event the intermediate white zircon populations could not be readily dated because of significant lead loss the lead 207 206 ages of both the pink and white zircons agree roughly with that of the sm nd isochron about 1 93 ga on secondary minerals from a kiruna greenstone skiold and cliff the oldest brown zircons indicate an age of about 2 2 ga and probably reflect the initial crystallization of the rock the formation of the early proterozoic greenstones in the kiruna area thus commenced about 2 2 ga ago or earlier these results are consistent with the proposed chronostratigraphy of the jatulian formations in finland e g simonen merilainen a time interval of at least 0 3 ga is assumed for the volcano sedimentary period which pre dates the svecokarelian orogeny of the kiruna area

lead isotope systematics of strata bound sulfide deposits in the higher nappe complexes of the swedish caledonides 55 galena samples from 18 deposits volcanite hosted deposits have a less radiogenic lead isotope composition than sediment hosted deposits while galena in quartz segregations and crack fillings shows the most pronounced radiogenic lead isotope composition application of the plumbotectonic model to the lead isotope data for the stratiform deposits suggests that the volcanite hosted deposits show the most significant influence of a mantle related source modified journal abstract

heat flow and thermal structure of the lithosphere across the baltic shield and northern tornquist zone abstract terrestrial heat flow data from archean and proterozoic provinces of the baltic shield its southwestern margin and the tectonic transition to the younger tectonic units of central europe northern segment of the european geotraverse are compiled and examined for local and regional variations a 2 d numerical lithospheric temperature and heat flux model is presented covering 1800 km of the deep seismic fennolora profile across the baltic shield and 500 km of eugeno s northern eugemi seismic lines across the northern tornquist zone and the danish and north german basins thermal lithosphere defined as the outer layer with relatively low temperatures t c in which heat transfer is dominantly by conduction is found to vary markedly in thickness from 85 110 km beneath basins and tornquist zone to about 150 km in central shield areas and 200 250 km in areas of low heat flow along the northern shield profile these results are in very good agreement with seismological information from surface wave dispersion analysis and the refraction wide angle seismic interpretation of fennolora data the combined thermal and seismologic evidence indicates that the uppermost mantle region stratified in seismic velocity is restricted to the upper relatively cold thermal layer which is interpreted to constitute shield lithosphere local and to some extent regional variations in surface heat flow are found to be closely related to variations in near surface radiogenic heat production for the southern baltic shield a heat flow heat production relationship of q 0 32 8 7 6 h 0 is derived regional increase in heat flow from northern and central shield provinces to the shield margin and the tornquist zone is interpreted to be related partly to differences in upper crustal heat generation partly and in southernmost areas mainly to an increased heat flux from the upper mantle upper mantle heat flux is estimated at 20 25 mw m 2 along the northern and central shield transect increasing to 30 40 mw m 2 beneath the shield margin basins and tornquist zone lithospheric thickness variations in this region of northern europe are found to be closely associated with variations in heat flux from the uppermost mantle and perhaps to a large extent controlled by geodynamically determined lateral differences in upper mantle heat flux earthquake focal depth data and information on crustal strength show baltic shield seismicity to be limited generally to the upper 20 25 km brittle part of the crust at temperatures less than 300 400 c maximum source depth of magnetic anomalies at temperatures near 600 c is in the deepest part of the crust near the crust mantle boundary in the southern region about 25 km depth along the tornquist zone and about 35 40 km in southern shield areas and in the uppermost mantle 60 70 km depth in the northern shield areas some petrologic implications are discussed the present deep crust is supposed to be at lower temperature pressure conditions than at early stages of formation however also the present deepest parts of the shield crust 35 40 km are within the stability field of eclogites the general absence of significant gravity anomalies in areas of marked crustal thickness variations indicate high density eclogites to be present in significant amounts in the deep shield crust

interpretation of lead isotope data from the uraniferous cu fe sulfide mineralizations in the proterozoic greenstone belt at kopparasen northern sweden the polymetamorphic early proterozoic basic metavolcanites of the kopparasen greenstone belt northern sweden contain u mineralizations which are confined to cu fe sulfide mineralizations in mylonitized zones within basic metatuffs and graphite bearing mica schists trace lead isotope data from sulfides indicate contamination of the sulfide lead with two different lead components at ca 430 ma one lead component was leached from rocks with a 232th 238u ratio of 3 0 3 2 while the other lead component had evolved in a environment with a lower 232th 238u ratio 0 0 0 05 the source for this latter lead component underwent a u th separation probably in relation to the formation of the u mineralizations if this lead component was leached from the u mineralizations these mineralizations have a 207pb 206pb model age of ca 1 780 ma which is less than the least radiogenic lead model age of the supracrustal belt ca 2 050 ma a possible genetic model for the uranium mineralizations includes the transport of u with an oxidized metamorphic fluid which was channelled into the permeable zones and the local reduction of the fluid by sulfides which caused the precipitation of u

holocene paleoclimate data from the arctic testing models of global climate change to evaluate the spatial variability of arctic climate change during the present interglacial cape project members compiled well dated terrestrial marine and ice core paleoenvironmental records spanning the past 10 12 thousand years ka six tundra biomes of increasing summer temperature requirements were defined based on regionally coherent pollen assemblages using a rule based approach pollen spectra were converted to tundra forest tundra or forest biomes ranked by their average growing season requirements marine sea surface reconstructions were based on proxy data following a similar rule based approach from these data based reconstructions departures in summer temperatures from modern normals were calculated in 1 ka time slices through the holocene to test predictive models data based summer temperature reconstructions were compared with general circulation model gcm simulations for 10 ka and 6 ka ago paleodata and model results both show that warming occurred earlier across beringia and asia relative to lands adjacent to the north atlantic and that late holocene cooling was most apparent in the north atlantic region however the gcm over predicts the magnitude of mid holocene warming over northern asia and underestimates the intensification of the north atlantic drift in the early holocene strong spatial variability in environmental response during the holocene despite symmetric insolation forcing suggests that any future changes whether caused by anthropogenic or natural factors are unlikely to result in a uniform change across the arctic adding additional complexity to forecasts of global impacts

structural diversity of biogenic carbonate particles in microbial mats non skeletal carbonate particles in microbial mats were studied using thin sections and scanning electron microscopy the microbial mats form biolaminated units so called potential stromatolites in salterns this study emphasizes the coexistence of different particle forms and makes a genetic connection between the heterogeneity of the organic substrate built by bacteria and diatoms and their extracellular polymeric substances eps whereas allochthonous particles are scarce lanzarote microbial mats provide various autochthonous surfaces for the attachment of cells and eps including sheaths and capsules of cyanobacteria frustules of diatoms metabolic products such as gas bubbles liquid globules and faecal pellets as well as the carbonate precipitates themselves morphologically different carbonate precipitates are i calcified organic clumps peloids ii particles composed of concentric aragonite and biofilm laminae ooids and oncoids hi isolated particles floating in gel supported mats and coated by rims of fibrous cement cortoids iv particles bound by cryptocrystalline matrices or cement resulting in aggregate grains and v lobate cement which fills out spaces and pores and fixes the particles peloids are suggested to represent faecal pellets although microbial systems also generate cell clumps by non faecal processes ooid and oncoid constructions clearly record alternating processes of biofilm accumulation and aragonite encrustation further characteristic features of carbonate particles generated within a microbial mat are i an irregular distribution ranging from isolated particles floating within the gel like matrix to closely packed particles ii the amalgamation of different particle types e g peloids and ooids in aggregate grains iii the heterogeneous nature of nuclei comprising bacterial clumps intraclasts individual cells cell colonies and bubbles iv the enrichment of remains casts and imprints of cells within precipitates and v deformation e g truncated cortices of particles

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

carbonate cements in holocene beachrock example from bahiret et biban southeastern tunisia abstract holocene beachrock has been studied on the northern and western shores of bahiret el biban a shallow restricted lagoon in southeastern tunisia the beachrock consists of horizontal cemented layers which are 2 15 cm thick early cementation took place at the water table below beach ridges where geochemical hydrodynamic and possibly also microbiological conditions favored rapid precipitation of aragonite and or high mg calcite locally superimposed low mg calcite cements point to subsequent freshwater influence at one site six vertically stacked beachrock beds are found total rock 14c dating shows that the highest beachrock bed is older than the one of the same petrographic composition situated at the present groundwater level this implies a downward progression of cementation which probably monitored the sea level fall following a local highstand about 3000 years ago

interglacial and holocene temperature reconstructions based on midge remains in sediments of two lakes from baffin island nunavut arctic canada abstract midge remains insecta diptera chironomidae and chaoboridae from two upland lake basins on the cumberland peninsula of baffin island were analyzed and the results used in a transfer function to reconstruct paleotemperatures this upland region remained ice free throughout the last glacial cycle and the two lake basins retain sediments deposited during the previous interglacial period as well as during the holocene period but they did not accumulate sediment during most of the glacial period midge remains are abundant and well preserved at both sites midge inferred summer surface water temperatures and mean july air temperatures were estimated using an inference model built on modern samples spanning a geographic range extending from devon island canada to maine usa data from twenty nine new surface samples from baffin island were added to an existing inference model the new weighted averaging wa model for summer surface water temperature yields r 2 jack 0 88 and rmsep 2 22 c for summer water temperatures and r 2 jack 0 88 and rmsep 1 53 c for mean july air temperatures reconstructions at both sites indicate that summer temperatures during the last interglacial were higher than at any time in the holocene and 5 to 10 c higher than present peak holocene temperatures occurred in the first half of the period and have decreased since about the mid holocene

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

multi chronometric ages and origin of archaean tonalitic gneisses in finnish lapland a case for long crustal residence time the tojottamanselka gneisses of the koitelainen region northern finland have been dated by the sm nd and the common pb methods the sm nd data of seven samples from a small area 100 m 100 m define an isochron oft 3 06 0 12 2 ga with correspondingind 0 50848 9 2 orend t 3 7 1 8 this age is in good agreement with the zircon u pb discordia age 3 1 ga reported by kroner et al 1981 and is interpreted as the time of magmatic emplacement the distinctly negativeend t value is found for the first time for archean tonalitic gneisses and implies derivation of these magmas by remelting of continental material with a long 200 500 ma crustal residence time a few samples on the other hand possessend t values close to zero hence they are thought to be derived by partial melting of basaltic sources with nearchondritic ree distribution patterns

granites and early proterozoic crustal evolution in sweden evidence from smnd upb and o isotope systematics abstract u pb zircon and whole rock rb sr sm nd and o isotope results are reported for granitoids from three proterozoic provinces in sweden that represent different crustal environments the radiometric ages span the period 1 89 1 65 ga and record events ranging from original igneous crystallisation to late metamorphic resetting these events occurred at different times in the crustal segments the o isotope ratios identify different crustal source materials for the granitoids the sm nd results indicate that the major crustal source components common to most of the granitoids formed shortly before 1 9 ga close in time to the formation of the earliest granitoids contributions from recycled archaean basement are minimal the geographically widespread occurrence of such crustal sources indicates that the period around 2 ga was of great importance for the growth of new continental crust in sweden

spiny ooids early subaerial deformation as opposed to late burial compaction a new type of ooid has been found in southeastern tunisia in holocene sands cemented in a vadose environment the sands are associated with serpulid and stromatolite bioherms and correspond to undisturbed relict lagoonal beaches they contain ooids that have cortical spines located near the points of contact between grains these coated grains resemble ooids that have been deformed by burial compaction although the geologic context and 14 c dates clearly indicate that they have never been subjected to lithostatic pressure the location of the spines and the evidence of vadose diagenesis point to postdepositional deformation and suggest that residual capillary waters control this phenomenon the spines may be related to the compressive effect of aragonite crystal growth which remained active in the external cortices after ooid deposition deformation due to burial compaction and deformation related to early diagenetic processes can be differentiated on the basis of the specific location of the compressive deformations such a distinction is important when interpreting the diagenetic history and porosity evolution of oolitic sands

nd isotope data on 1 9 1 2 ga old basic rocks and metasediments from the bothnian basin central sweden abstract sm nd data are presented for basic rocks and metagreywackes from the early proterozoic bothnian basin in central sweden the basic rocks include synsedimentary metabasalts early orogenic intrusions and anorogenic dolerites covering the age range 1 9 1 2 ga the samples thus span the entire period from the early part of the svecokarelian thermo tectonic episode to the time when this region of the baltic shield had been a stable craton for about 0 4 ga all these samples have slightly positive nd values up to 2 for synorogenic rocks and up to 3 5 for anorogenic dolerites if these values are representative for the contemporaneous mantle they suggest a less depleted character for this mantle than that shown for several other proterozoic shield areas three metagreywacke samples have nd values of 2 4 to 3 1 indicating a significant influx of detrital older crustal material into the bothnian basin

characteristics and geological setting of synkinematic svecokarelian granitoids in southern finland abstract synkinematic granitoids are the predominant component of the svecokarelian crust their zircon u pb ages vary from 1900 to 1860 ma mainly 1890 1870 ma being roughly similar to those of mafic plutonic rocks and metavolcanic rocks synkinematic granitoids occur as distinct plutons in schist belts and also form the granitold complex of central finland with a total area in excess of 35 000 km2 the granitoids in schist belts occur as concordant plutons although locally they have cross cutting contacts and they crystallized soon after the peak of major regional deformation and metamorphism but before younger deformation phases they are composed of granodiorites tonalites and trondhjemites composite plutons are often zoned with gabbro diorite tonalite and or trondhjemite at their margins and with granodiorite and less commonly granite at their centres the granitoid complex of central finland is composed of a vast number of intrusions ranging in composition from gabbro to granite the granite intrusions comprising large parts of the complex coarse grained granitoids and polyphase deformation are common major minerals of the synkinematic granitoids are plagioclase potassium feldspar quartz biotite and hornblende typical accessories are sphene apatite magnetite and zircon whole rock analyses of 143 granitoids from throughout southern finland show calc alkaline characteristics with variable sio2 high na2o k2o and a cnk below 1 1 initial 87sr 86sr ratios are low the granitoid complex of central finland has higher feo mgo and k2o na2o than the granitoids in schist belts irrespective of silica content the synkinematic granitoids have the geological and geochemical characteristics of phanerozoic i type granitoids and are cogenetic with mafic plutonic rocks intrusion of these latter evidently caused major remelting in the lower crust giving rise to granitoid magmas so that a variable mixing of mantle derived and crustal magmas is probable according to nd isotopes studies archaean material was insignificant in the source of the granitoids except near the border zone of the archaean craton this indicates rapid recycling of material newly derived from the mantle geochemical features of the granitoid complex may also reflect a thicker crust in central finland than in surrounding areas during the generation of the granitoids many characteristics of the synkinematic granitoids strongly suggest a subduction related origin however the similarity in isotopic ages and lack of obvious linear trends in distribution of rock types combined with evidence for a minor older crustal component in their source indicates that the processes were not identical to those operating at modern continental margins

origin of continental crust of 1 9 1 7 ga age nd isotopes in the svecofennian orogenic terrains of sweden initial nd isotopic ratios are reported for 57 samples representing all crustal components in the central and southern parts of the 1 9 1 7 ga old svecofennian orogenic terrains of sweden and the 1 8 1 7 ga old transscandinavian granite porphyry belt transscandinavian igneous belt u pb zircon ages are determined where the magmatic ages were not sufficiently constrained the nd isotopic results show that there are no archaean crustal blocks within the studied 1 9 1 7 ga old crustal segment this is consistent with results from finland the main input of recycled archaean crust to the svecofennian was in the form of sediments which are concentrated in the central svecofennian subprovince of north central sweden this is consistent with the vicinity of this subprovince to the archaean craton of the baltic shield these turbidite sediments contain up to 40 archaean material but s type granitoids associated with them have a smaller archaean component around 20 most of the quantitatively predominant i type granitoids and volcanics as well as all the basaltic rocks studied have nd from 1 to 3 and consist of 90 material newly derived from the mantle 1 9 1 7 ga ago we argue that the archaean material was introduced in the form of sediments but we cannot distinguish between pelagic sediments delivered on subducting oceanic crust and turbidite accumulations like the ones seen in north central sweden in either case an overall 15 archaean contribution for the swedish svecofennian was reasonably well homogenized with mantle derived magmatic products for this to occur an active near surface tectonic environment such as a complex of subduction zones must have been necessary

tracing sea level changes during the mid holocene in the southern mediterranean coast an example from the gulf of gabes abstract mid holocene sea level emergence was recorded along a mid latitude coastal site in the gulf of gabes tunisia in beach rock deposits however the post emergence sea level curve and associated hydro sedimentary processes have rarely been documented this study presents new records of sea level changes along the tunisian coast since the mid holocene each phase of the sea level curve was evidenced and supported by lithostratigraphic morphological and archaeologic markers post emergence sea level fall due to postglacial isostatic rebound was recognized in regressive sequences which vary depending on available accommodation space from a small pocket beach to a well developed dune system sea level stabilization following isostatic rebound has promoted the end phase deposits of the regressive sequences however this stability was interrupted during the late holocene by a high energy storm event that accumulated a transgressive boulder unit at 2 m above present shape and disposition of the boulder ridge behind a prograding modern shoreline suggests that sea level has not changed during the late holocene the existence of a roman fish pond on the upper foreshore confirms stability of sea level during the last two millennia the combination of lithostratigraphic morphological and archaeologic markers represents a tool for improving the accuracy of dating of erosional and depositional periods in mid coastal sections

a mediterranean holocene restricted coastal lagoon under arid climate case of the sedimentary record of sabkha boujmel se tunisia abstract the holocene sedimentary record of sabkha boujmel se tunisia is expressed by a shallowing upward carbonate lagoon tidal flat cycle 2 3 m thick unconformably overlying continental silt sandy sediment late wurmian in age the sedimentary package of this cycle starts with transgressive marginal shallow marine intertidal to subtidal bioclastic sands grading upwards to black mudstone rich in organic matter t o c up to 1 3 deposited within a lagoon protected from the sea by upper pleistocene lithified sand spits the uppermost part of the cycle is represented by oobioclastic carbonate sands covered with dead biodegraded microbial mats and or reddish sands of aeolian origin deposited in intertidal to supratidal environments the facies arrangement particularly the spatial distribution of the ancient and the more recent microbial mats records the progressive infilling of the lagoon as well as the progradation of the shoreline during the last 2000 years the organic rich facies which provide an age varying between 4130 and 6800 yr b p were deposited when the boujmel lagoon started to be progressively separated from the mediterranean sea the main factors controlling the facies and the thickness variation are the local topographic sea floor irregularities most likely controlled by the inheritance morphology resulting from an important fluviatile digging that occurred during the last glacial maximum the relative sea level fluctuations the hydro isostatic rebound and the climate

zircon upb versus rbsr whole rock age data from eastern finland a critical comment on the papers of barbey martin and martin precambrian research vol 35 1987 discussion et reponse sur les articles the role of komatiites in plate tectonics evidence from the archean and early proterozoic crust in the eastern baltic shield precambrien par barbey p et martin h 1987 35 p 1 14 et evolution and composition of granitic rocks controlled by time dependent changes in petrogenetic processes examples from the archean of eastern finland par martin h 1987 35 p 257 276

isotopic composition of phanerozoic ore leads from the swedish segment of the fennoscandian shield 95 analyses of ore lead isotope ratios from 23 phanerozoic ore deposits from the swedish segment of the fennoscandian shield form a marked linear trend on a 207pb 204pb versus 206pb 204pb diagram the line may be interpreted in a two stage model the lead being derived from 1 8 0 15 ga old svecokarelian basement and mineralization occurring at 0 4 0 15 ga the initial composition of the svecokarelian rock lead was similar to the lead in early proterozoic volcanogenic sulfide ores in sweden the large spread in the isotope ratios was caused by a combination of selective leaching of different minerals in the source rocks mixing with less radiogenic caledonian lead and local or regional variations in the u th and pb contents of the basement as a consequence conventional methods of identifying source rocks from lead isotopic data e g mu values th u ratios may not be directly applicable phanerozoic ore lead development in the swedish section of the fennoscandian shield was ensialic that is the ore lead was almost entirely derived from the precambrian basement although this basement does not appear to be anomalously enriched in pb no juvenile or mantle lead was apparently contributed to this section of the crust after the precambrian except for that mechanically transported onto the western edge of the shield by the caledonian nappes however some of europe s largest lead deposits are included in these swedish phanerozoic mineralizations suggesting that it was the nature of the processes involved rather than the richness of the source that determined their formation

evaporite carbonate and siliciclastic transitions in the jurassic sequences of southeastern tunisia abstract evaporite carbonate and siliciclastic transitions occur within the jurassic deposits of southeastern tunisia these facies are grouped into four major transgressive regressive sequences corresponding to various environments of deposition the latter include sabkha subaqueous evaporite basin carbonate tidal flats to shallow marine platform bioherms and mixed siliciclastic ramp rapid lateral and vertical variations in thicknesses and facies are controlled by tectonic climatic and eustatic factors east west and nw se fault systems generated a down faulted graben tataouine basin bordered by two uplifted horsts tebaga mole and libyan craton and have acted as an evaporite depocenter or as a siliciclastic trap eustatic related transgressions occurring during late lias bajocian early middle callovian and probable upper callovian oxfordian have led to opening and or deepening of the marine basin accompanied by carbonate sedimentation rapidly replacing evaporite or siliciclastic deposition this jurassic example not only confirms that tectonics and to a lesser extent climate largely controlled evaporite carbonate and siliciclastic transitions it also demonstrates that sea level changes may be another factor controlling such transitions in these ancient deposits

late caledonian extension in the ofoten area northern norway abstract structural observations along the base of the caledonian nappe pile in the ofoten region of northern norway demonstrate a complex interaction of compressional and extensional structures top to the west extensional structures are consistently superimposed on top to the east southeast compressional structures and control the basement cover relationships across the orogen extensional shear zones offsetting the basement cover contact appear to be restricted to the area east of the ofoten synform the eastern flank of the synform is an approximately 1 km wide w dipping shear zone with more than 30 km of dip slip offset the basement culimination roll over west of the synform is most likely controlled by the listric geometry of this shear zone at depth this major shear zone and other minor extensional shear zones within the rombak window have a ductile shear fabric with post kinematic recovery fabrics developed under middle to upper greenschist facies conditions suggesting that the footwall and hanging wall rocks were still at a mid crustal level some time after the extensional event the extensional shear zone flattens upsection and splays into a network of anastomosing detachment zones eastwards cutting both upsection and downsection in the direction of westward tectonic transport development of steeply dipping extensional basement faults and subhorizontal detachment faults in the cover have resulted in a complex basement cover relationship and reworking of the nappe stratigraphy established during the preceeding compressional event these relationships make restoration of the caledonian nappe pile to a pre orogenic configuration uncertain and shortening estimates difficult the recognition of the extensional event as a distinct post contractional tectonic event suggests a link with the devonian extensional collapse in southern norway a major difference between southern and northern norway however is the lack of brittle extensional features in the often area suggesting different amounts of extension and basement uplift in the two regions

evolution of the archean continental crust some 20 years of plate tectonic theory combined with new insights into the fine structure of the lithosphere the application of multielement geo chemical and isotopic studies paleomagnetism and geophysical modeling of mantle processes have profoundly influenced present thinking on the origin and evolution of the earth s early continental crust previously our knowledge of the continental crust was based almost exclusively on field geological observations although there is now general agreement on how the earth worked for the last 200 m y because of observable evidence in the oceans and continents e g bird 1980 condie 1982 it has proved difficult to extend this history into more ancient times in view of the lost oceanic record and the ambiguity and complexity of the pre mesozoic rock relationships in the continents dewey 1982 however preserved characteristic rock as semblages uniquely identifying modern type wilson cycle processes i e opening and closure of oceans underlain by oceanic crust have now been recognized in continental terranes as old as 900 m y and these assemblages provide strong evidence for the conclusion that the present global tectonic regime has governed the evolution of the lithosphere at least since the late precambrian kroner 1977 1981a b goodwin 1981 profound disagreement on the older crustal history however prevails to the present day since typical features characterizing phanerozoic accretionary terranes such as obducted ophiolites blueschists and franciscan type melanges have not been found in more ancient regions thus two types of evolutionary models have been developed one type postulates uniformitarian development back to the earliest archean burke

aspects of the proterozoic geochronology of northern sweden abstract it has been proved that u pb zircon dating provides reliable formation ages for magmatic rocks affected by medium or lower grade metamorphism the timing of the main volcanic plutonic and metamorphic episodes of the early to mid proterozoic evolution of northern sweden has therefore been verified a preliminary and schematic chronology of these events is presented archaean ortho and para gneisses 2 70 ga supracrustal rocks affected by the svecokarelian orogeny mafic volcanic phase 2 20 1 93 ga felsic volcanic phase 1 91 1 86 ga svecokarelian orogeny 1 88 1 80 ga post orogenic migmatization 1 80 ga

u series evidence for two high last interglacial sea levels in southeastern tunisia abstract pleistocene raised marine deposits in southeastern tunisia consist of a siliciclastic unit that culminates at 3 m asl overlain by a carbonate rich unit with strombus bubonius that culminates at 5 m asl 234 u 238 u ratios on fossil ostraea shells from both units are compatible with a marine origin from the uranium incorporated into the shells and show narrowly clustered 230 th ages respectively between 147 and 110 ka and 141 and 100 ka the two units were therefore developed during marine isotopic substage 5e miss 5e last interglacial their heights are comparable to those of contemporaneous marine deposits found in many tectonically stable areas of the world such as in the bahamas and in bermuda and can therefore be used as indicators of eustatic changes during the last interglacial it is argued that on the basis of this evidence the last interglacial was characterised by two eustatic maxima

the sm nd age of kambalda volcanics is 500 ma too old although sm nd isotopic analyses of volcanics from kambalda western australia form a 3 2 ga linear array pb pb analyses of the same suite give an isochron age of 2 73 0 03 ga and a 2 7 ga model age for the associated sulphides we suggest that the 3 2 ga age is incorrect and that the sm nd array results from mixing between depleted mantle and either older continental crust or enriched mantle

the age of the kambalda greenstones resolved by ion microprobe implications for archaean dating methods abstract a chert horizon within the archaean basalt pile at kambalda western australia contains zircons from air fall tuffs erupted as the sediment was laid down ion microprobe analyses of these magmatic zircons constrain the long sought age of the kambalda lavas to 2692 4ma 2 and show that regional metamorphism and deformation of the greenstone pile occurred within 30 ma of deposition rare zircon xenocrysts are evidence of pre greenstone crust as old as 3450 ma exposed remnants of which are yet to be identified subsets of both the magmatic and xenocryst zircons show evidence of hitherto unsuspected low temperature u and or pb mobility in the proterozoic long after stabilisation of the craton the ion microprobe data unravel complexities of isotopic inheritance and alteration illustrating the hazards of using bulk or whole rock samples in archaean isotopic investigations identification of interflow cherts as a precisely dateable rock type opens the way to direct ion probe dating of mafic ultramafic piles and close numerical age control of the complex but ill exposed stratigraphic and structural relations in this richly mineralised greenstone belt

some new lead isotope determinations from the proterozoic sulfide ores of central sweden lead isotope determinations were made on galenas from three strata bound sulfide ores in the early proterozoic svecokarelian bergslagen district of central sweden and four epigenetic deposits in the alvdalen and vansbro districts in the early to middle proterozoic post svecokarelian belt the leads from the strata bound bergslagen deposits show exceptional isotopic homogeneity over large areas their isotopic composition suggests the existence of a pre svecokarelian crust in the district and is consistent with exhalative sedimentary ore formation in an active continental margin environment the vansbro and alvdalen leads display constant compositions within each district but marked divergence between the districts their compositions preclude derivation exclusively from recycled svecokarelian lead and suggest a substantial lead contribution from a mantle like source the difference between model ages and geologic ages for many of the deposits with a small but significant excess of radiogenic lead suggests a significant deviation of the fennoscandian shield from conventional global lead evolution models

bounds on the time history and holocene mass budget of antarctica from sea level records in se tunisia solving the sea level equation for a maxwell earth we analyze the sensitivity of holocene sea level records in se tunisia to the time history of remote ice sheets assuming that mantle viscosity increases moderately with depth we find that in this region the sea level variations driven by the northern hemisphere ice sheets cancel so that the late holocene sea level high stand suggested by the geological record merely reflects the melting history of antarctica new insight into the history of this ice sheet is obtained analyzing the information contained in a revised set of relative sea level observations for sites across the mediterranean covering the last 8 kyrs from a trial and error misfit analysis it holds true that in this region the match between model predictions and observations improves when the volume of water released from antarctica is well below the value imposed by the ice3g chronology and when a sudden meltwater pulse is allowed between 8 and 7 kyrs before present corresponding to the epoch of the catastrophic rise event known as cre3

geochronologic significance of lead lines from old cratons abstract lead isotope data from geologically mixed suites of archaean gneisses often yield secondary isochrons that have statistically better fits than might be expected from the geological constraints on the range of samples used accepted as true isochrons these pb pb lines are commonly used both to determine the age of the rock suite and as evidence that all the rocks that yield data points within error of the isochron were formed at the same time from the same source using within geologically reasonable limits random data for initial lead and secondary lead growth we demonstrate that heterogeneous sample sets may yield statistically valid secondary isochrons this implies that the fit to a common secondary isochron does not necessarily mean that the samples used have the same age or an isotopically similar source numerical modelling of artificial data sets suggests that high correlation between 1 and 2 values is the single most important factor that enhances the statistical fit of the samples about a lead line and smoothes the initial scatter in contrast initial scatter will be preserved in data sets with a random relation between 1 and 2 values the 1 value estimated from the lead line will be biased towards the sample with the lowest 2 value

ore lead isotope variations in the proterozoic massive pyrite deposit at nasliden skellefte district sweden the ore lead isotope ratios from the nasliden deposit are mantle like in terms of the idealized plumbotectonics model they suggest that the nasliden deposit was formed in the proterozoic equivalent of a phanerozoic primitive island arc the mantle like nature of the lead and its homogeneity indicate that crustal lead does not constitute the major component of the ore lead crustal lead contamination is suggested to be the cause of divergences in ore lead isotopic compositions associated with later veins in the deposit

accretion tectonism in the proterozoic svecokarelides of the baltic shield the duality of early middle proterozoic terranes in the baltic shield reflects fundamental differences in history between coeval mobile belts and the manner of their interaction the karelides formed on a continent ocean transcurrent margin in which offsets developed as arcs and back arc basins on stretched continental crust at least one back arc basin was obducted onto the continental margin preserved as an allochthonous terrane in the karelian nappe pile remnant arc fragments form accreted exotic terrane in pohjanmaa the svecofennides developed as a succession of island arcs while the site of subduction moved south and successive extinct arcs were accreted onto the archean craton arc terrane impingement affected deformation style in the karelides which changed from one of major horizontal translation to one dominated by major dextral wrench faults analogies can be drawn with the phanerozoic evolution of the northeast pacific margin

pleistocene terrace deposition related to tectonically controlled surface uplift an example of the kyrenia range lineament in the northern part of cyprus abstract in this study we consider how surface uplift of a narrow mountain range has interacted with glacial related sea level cyclicity and climatic change to produce a series of marine and non marine terrace systems the terrace deposits of the kyrenia range record rapid surface uplift of a long lived tectonic lineament during the early pleistocene followed by continued surface uplift at a reduced rate during mid late pleistocene six terrace depositional systems are distinguished and correlated along the northern and southern flanks of the range termed k0 to k5 the oldest and highest k0 terrace system is present only within the central part of the range the k2 k5 terrace systems formed later at sequentially lower levels away from the range the earliest stage of surface uplift k0 terrace system comprises lacustrine carbonates interbedded with mass flow facies early pleistocene the subsequent terrace system k1 is made up of colluvial conglomerate and aeolian dune facies on both flanks of the range the later terrace systems k2 to k5 each begin with a basal marine deposit interpreted as a marine transgression deltaic conglomerates prograded during inferred global interglacial stages overlying aeolian dune facies represent marine regressions probably related to global glacial stages each terrace depositional system was uplifted and preserved followed by subsequent deposits at progressively lower topographic levels climatic variation during interglacial glacial cycles and autocyclic processes also exerted an influence on deposition particularly on short period fluvial and aeolian deposition

provenance of early proterozoic and archaean metasediments in finland a smnd isotopic study abstract sm nd isotopic analyses of early proterozoic and archaean clastic metasediments from finland are presented they have been used to calculate crustal residence ages and to constrain the sedimentary provenance the mean crustal residence age t dm for the svecofennian metagreywackes in the tampere schist belt is 2 22 ga which is about 0 3 ga in excess of the assumed stratigraphic age this indicates that the bulk of the sediments were eroded from newly formed crust their major source was most likely svecofennian orogenic material mixed with a small amount of archaean derived detritus the precursors of many granitoids in the svecofennian terrain also had similar short crustal residence times the kalevian metasediments which were deposited 2 05 1 9 ga ago on the edge of the archaean craton in eastern and northern finland have a mean t dm of 2 41 ga which is 0 4 0 5 ga more than the inferred stratigraphic age hence their source was on average older than that of the svecofennian metasediments investigated but definitely not purely archaean neither could crust similar to the bulk of the 1 9 ga old svecofennian terrain have been the only source various sources contributed at least locally but the bulk of the sedimentary material probably had a common provenance major sources consistent with existing isotopic data could have been 2 1 ga old jatulian rocks the c 2 0 ga old granulite belt in northern finland and or the svecokarelian early orogenic arc terrain mixed with archaean derived nd the method and data do not allow a distinction to be made between the possible alternatives the t dm model ages for two analysed archaean metasediments are slightly over 3 ga which is about 0 3 ga in excess of their assumed stratigraphic age thus providing no evidence for crust much older than 3 ga in this area

holocene stromatolites and microbial laminites associated with lenticular gypsum in a marine dominated environment ras el shetan area gulf of aqaba egypt field and petrographic investigations of holocene evaporites in the ras el shetan area gulf of aqaba egypt indicate the presence of microbial mats either in the form of laminites or stromatolites the morphology of microbial mats and gypsum crystal size characterize the following lithofacies 1 slump stromatolitic gypsarenite 2 random gypsrudite 3 stromatolitic gypsarenite and 4 microbially laminated gypsrudite these evaporite lithofacies are formed above pre evaporitic mudstones rich in disrupted cyanobacterial filaments burrows and cerithid gastropods the morphology of the gypsum crystals is mainly lenticular indicating enrichment of dissolved organic compounds in the depositional environment the difference in size of the lenticular gypsum crystals is related to minor changes in salinity and temperature of the parent brine fluid inclusions in gypsum crystals indicate their formation at low temperature 50 c in a seawater sourced brine that evaporated to gypsum saturation or higher the brine salinities range from 10 62 to 12 99 equivalent wt nacl and the brine densities range from 1 08 to 1 11 g cm3 the change in morphology of the microbial mats stromatolites and laminites is related mainly to changes in water depth from a very shallow salina to a coastal sabkha lenticular gypsum nucleated displacively in the microbial mats from saline oxygenated groundwater that seeped from the sea through a barrier

late holocene high resolution palaeoclimatic reconstruction inferred from sebkha mhabeul southeast tunisia relations between climate change and landscape evolution during the last two millennia in southeastern coastal tunisia have been documented using high resolution reconstruction of flood history and fire activity in the sebkha mhabeul core the age model based on tephrochronology indicates that the core extends from roman to modern times and encompasses the well defined climatic periods of the last two millennia this record provides a first palaeoecological palaeoclimatic high resolution reconstruction in north africa using a cross disciplinary approach with both physical grey scale intensity quartz particles and biological charcoal and pollen indicators the flood history shows four wet dry cycles ca ad 550 950 950 1300 1300 1570 and 1570 1870 of different duration major hydrological instabilities are concentrated during the medieval climate anomalies and the early little ice age between ad 1000 and 1550 direct correlation between climate and fire cannot be established suggesting that the fire history of the sebkha environment is mainly influenced by human activity this study demonstrates the great value of sebkhas as palaeoenvironmental archives

thorium uranium ratio of the earth through the study of komatiites and ophiolites remnants of the old mantle we review the evolution of the lead system in the depleted mantle through time using the 230th232th vs 208pb 206pb diagram 208pb 206pb radiogenic lead ratio we constrain the th u ratio of the bulk silicate earth to 4 2 this value is also in full agreement with ratios inferred from the study of the various types of meteorites using this value in the 208pb 206pb 143nd144nd diagram bulk earth plots on the oceanic basalt correlation line as previously guessed a comparison with sr and nd data shows that the th u fractionation correlates with that of rb sr and nd sm whereas the u pb fractionation is independent of other ratios

palaeogeographical and palaeoenvironmental reconstruction of the medjerda delta tunisia during the holocene abstract the progradation of the medjerda delta has been the subject of many studies since the 19th century the scale and the rapidity of this phenomenon interested researchers in various fields early on such as geomorphology geology palaeogeography history archaeology or geoarchaeology indeed the delta prograded by around 10 km over 3 millennia at the time of its foundation supposedly at the end of the 12th century bc the phoenician city of utica was located on a promontory bathed by the sea but the sediments carried by the medjerda progressively sealed the bay leaving the tip of the utica promontory now 10 km inland this area is therefore an exception to the general pattern along the tunisian coast since as over the same period everywhere else there is a regression of the coastline owing to a sea level rise of several decimeters based on multi proxy analyses of two coring transects this paper aims to reconstruct the palaeoenvironments and the palaeogeography of the medjerda delta s progradation since the mid holocene some aspects of which are described in ancient sources the results highlight in particular an episode of high intensity flooding around the 4th century ad which is consistent with episodes of high floods and an increase in sedimentation rates recorded in the watershed at the end of the roman period the gradual abandonment of the city of utica can certainly be related to the activity of the medjerda river but our results show that it is because of an increase of fluvial sediment contribution in connection with an erosive crisis in the headwaters and not because of the change of course of the river which had occurred long before

the western border of the archaean province of the baltic shield evidence from northern sweden restricted areas of acid to intermediate gneisses in northernmost sweden are known to be archaean and several other gneissic granodioritic to tonalitic massifs have been suggested to be of this age to delimit the western border of the archaean province of the baltic shield and to characterize the swedish archaean we have studied the 2 83 ga old soppero gneiss and 8 of the proposed archaean massifs in northern sweden by sm nd isotopic analyses u pb zircon dating in two cases and geochemistry

microbial signatures in peritidal siliciclastic sediments a catalogue a catalogue of microbial structural signatures is presented based upon the coupling of fundamental biogeochemical microbial processes and local morphogenetic determinants it summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones temperate humid mellum island southern north sea subtropical arid coast of southern tunisia textural geometries reveal a high structural diversity but their determinants are primarily based upon six major parameters 1 intrinsic biofactors structural diversification of sedimentary microbial films and mats inherent in the organisms i e their construction morphology growth taxis and behaviour and local abundance of specific morphotypes most prominent are the ensheathed filamentous cyanobacteria microcoleus chthonoplastes and lyngbya aestuarii and the sheathless filamentous cyanobacterium oscillatoria limosa 2 biological response to physical disturbances sediment supply erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats 3 trapping binding effects physicobiological processes give rise to grain orientations and wavy to lenticular lamina lamina specific grain arrangements and sucrose calcium carbonate accumulations 4 secondary physical deformation of biogenic build ups mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures 5 post burial processes textural fabrics that evolve from mechanical effects of gas formation from decaying mats and features related to the formation of authigenic minerals calcium carbonates calcium sulphates pyrite 6 bioturbation and grazing post depositional structures such as skolithos type dwellings traces of burrowing insects gastropod grazing traces and faecal pellets in synopsis the catalogue firstly comprises a sound set of ubiquitous signatures this uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings the catalogue secondly documents signatures that are extremely sensitive to tidal position hydrodynamic regime and overall climatic conditions these kinds of signature indicate narrow facies zones which often coincide with the activity or dominance zones of certain organisms an overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings

genesis of the lower triassic bonebeds from gogolin s poland the impact of microbial mats on trapping of vertebrate remains abstract three bone bearing horizons consisting of seven bone bearing beds with fish and reptile remains were recently discovered in the uppermost rot buntsandstein lower triassic peritidal and shallow marine carbonates in the vicinity of gogolin s poland the aim of this study is to recognize the genesis and depositional environments of the bonebeds detailed fieldwork microfacies analysis and sem eds analysis reveal that the vertebrate remains occur to a great extent alongside evidence for former microbial activity the reptile remains represent at least dactylosaurus and nothosaurus sauropterygia genera while the fish remains belong to the chondrichthyes and actinopterygii the vertebrate remains were deposited in a transitional zone between the costal sabkha and the epicontinental sea the first bone bearing horizon originated in the most landward setting in the uppermost intertidal zone likely at the margins of a pond or coastal lagoon the second bone bearing horizon was formed in the upper intertidal zone the vertebrate remains of the third bone bearing horizon were accumulated in two different settings in the lower intertidal zone in a small palaeopond and in the subtidal zone in a protected back shoal lagoon three bone accumulations occur within planar stromatolites while the other bone bearing beds reveal more indirect evidence for former microbial activity in our opinion the presence of the sticky microbial mats in the intertidal settings was the crucial factor that allowed the establishment of and controlled these accumulations of vertebrate remains the soft gluey substrates trapped vertebrate remains that were transported across them once trapped the vertebrate bioclasts were efficiently immobilized and thus protected against damage due to sedimentological agents the lack of any orderly arrangement of the vertebrate bioclasts suggests that they may have been delivered to the individual mat surfaces by diverse media from various directions and also at different times

the depositional evolution of the svecofennian supracrustal sequence in finland and sweden abstract on the basis of six new zircon ages from metavolcanic rocks together with other isotopic geophysical and geological data the chronological and tectono stratigraphic evolution of the early proterozoic svecofennian supracrustal rocks in finland and sweden are discussed these data suggest that a nw se displacement from the bothnian bay to lake ladoga and a sinking of the southwestern block was initiated 1950 2000 ma ago accumulation of pelitic sediments and greywackes on the subsiding archaean basement continued until about 1860 ma in south central and northern sweden shallow submarine and subaerial volcanics were extruded 1880 1890 ma ago the thick sedimentary piles and volcanic rocks were subsequently intruded by plutonic rocks forming large batholiths 1860 1890 ma ago

rb sr and sm nd ages and isotopic geochemistry of archaean granodioritic gneisses from eastern finland martin h chauvel c jahn b m and vidal p 1983 rb sr and sm nd ages and isotopic geochemistry of archaean granodioritic gneisses from eastern finland precambrian res 20 79 91 twenty granodioritic rocks and one amphibolitic enclave of the basement of the suomussalmi kuh mo archaean 2 65 ga greenstone belts central eastern finland have been chosen together with one greenstone sample for rb sr and sm nd geochronological and isotopic studies the granito id rocks are subdivided into three groups two generations of grey gneisses and a post belt augen gneiss the rb sr ages of the first and second generation of grey gneisses are 2 86 0 09 and 2 62 0 07 ga respectively these results are corroborated by sm nd data the post belt augen gneiss gives an age of 2 51 0 11 ga the results show that the two generations of grey gneisses the greenstone belts and the post greenstone augen gneiss were developed over a period 350 ma the two generations of grey gneisses show identical isr values 0 7023 8 and 0 7024 6 which contrast with that of the augen gneiss 0 7049 8 the low isr and the near chondritic ecthur values indicate that the grey gneisses cannot be derived from much older continental materials trace element studies suggest that these grey gneisses have had a multi stage development the augen gneiss with a moderately high isr is likely to be derived from a granodiorite originated by partial melting of older sialic crust the more probable parent rock seems to be the first generation grey gneisses the isr and average rb sr values preclude the greenstone belt and the second generation of grey gneisses as the protolith

lead isotope composition of caledonian sulfide bearing veins in sweden linear trend in the 207 pb 204 pb vs 206 pb 204 pb diagram extending from a normal caledonian lead composition 206 pb 204 pb nearly equal 17 9 to highly radiogenic values 206 pb 204 pb nearly equal 26 0 early proterozoic svecokarelian basement as source of the radiogenic component selective leaching of different minerals in the svecokarelian rocks and mixing with various proportions of nonradiogenic caledonian magmatic lead modified journal abstract

signatures of multiple mineralization processes in the archean orogenic gold deposit of the pampalo mine hattu schist belt eastern finland the hattu schist belt is an emerging gold producing ore district in the western part of the archean karelian province of the fennoscandian shield the belt consists of 2 76 to 2 70 ga tonalite granodiorite and leucogranite intruded into a mafic felsic epiclastic volcanic sequence of an only slightly older age complex and successive folding shearing and hydrothermal processes affected these rocks prior to the lower amphibolites facies peak metamorphism 550 50 c 3 5 kbar at ca 2 70 ga orogenic gold deposits are hosted by the highly strained zones that developed during the archean deformation of the belt however previous k ar and rb sr geochronological studies indicated that a second tectonothermal overprint affected the hattu schist belt between 1 7 and 1 8 ga during the svecofennian orogeny results of our field mineralogical textural and pb isotope studies suggest that ore deposition at pampalo was initiated by hydrothermal processes at the time of the emplacement of feldspar porphyry and tonalite intrusions and dikes at around 2 72 ga albitization and quartz tourmaline biotite muscovite veining characterize this hydrothermal activity the major stage of gold ore deposition can be confined to the subsequent development of high strain zones in an intermediate felsic tuffaceous unit mafic schist characterized by biotite carbonate pyrite alteration ar ar studies revealed the complete resetting of the ar ar system in muscovite and biotite due to the svecofennian orogeny with closure of the isotopic system at 1 81 ga results of pb isotope studies of hydrothermal k feldspar galena and altaite by laser ablation inductively coupled plasma mass spectrometry indicate that k feldspar alteration and remobilization of metals also took place during the svecofennian reactivation of high strain zones the petrographic manifestation of this process is the replacement of albite by hydrothermal k feldspar fluid inclusion data from hydrothermal k feldspar suggest that carbonic aqueous low salinity fluids interacted with the archean ore at 350 to 400 c and 1 8 to 2 4 kbar during the svecofennian overprint results of mass transfer calculations indicate that potassium gain correlates with increase of gold concentrations in the mafic schist and feldspar porphyry units therefore the svecofennian overprint locally also enhanced the grade of gold mineralization mostly along competency differences of the mafic schist and feldspar porphyry blocks dikes later percolation of relatively low temperature 300 c saline basin fluids in some fractures of the crystalline basement also left their pb isotope and fluid inclusion signatures on the mineralization while further modifying the composition of the ore occurrences of hydrothermal proto ores as well as fluid flow events along structures reactivated by overprinting orogenic processes are not exceptional features in archean orogenic gold provinces this study shows that the combination of in situ pb isotope studies of u poor alteration minerals and pb rich ore minerals together with evaluation of relationships between gold enrichment and hydrothermal alteration and fluid inclusion studies can be very useful in determining the significance and conditions of overprinting processes as well as their potential implications for genetic and exploration models

repeated syn and post orogenic gold mineralization events between 1 92 and 1 76 ga along the kiistala shear zone in the central lapland greenstone belt northern finland abstract the central lapland greenstone belt clgb is well endowed with orogenic gold deposits along major shear zones and structural lineaments in the northern part of the belt the kiistala shear zone kisz hosts the suurikuusikko gold deposit kittila mine currently the largest gold producer in europe the iso kuotko deposit is located 10 km to the north of suurikuusikko along the same shear zone gold mineralization at iso kuotko formed in two major stages an early stage refractory gold mineralization with auriferous arsenopyrite with similarities to the ore at suurikuusikko and a late main stage mineralization with free gold in carbonate quartz veins with abundant pyrrhotite native bismuth and other sulphide minerals this latter ore is absent at suurikuusikko based on u pb dating as well as re os and pb isotope systematics of rock forming and hydrothermal minerals we evaluate the relationships between tectonic evolution and formation of gold deposits throughout the late palaeoproterozoic in the northern part of the clgb results from in situ u pb dating of zircon and petrographically well constrained hydrothermal monazite and xenotime by la icpms and model age calculations using re os isotopic data for arsenopyrite and in situ pb isotope data for galena from the iso kuotko deposit provide evidence for multiple episodes of hydrothermal activity along the kisz data suggest coincident felsic magmatism and structurally controlled fluid flow events during wrench fault dominated n s shearing associated with early micro continent accretion ushering in the svecofennian orogeny this includes the formation of refractory gold ores at suurikuusikko 1916 19 ma and iso kuotko 1868 15 ma subordinate barren veining took place at 1830 ma during transient extension between the accretion and final collision stage xenotime in late stage veins with visible gold at iso kuotko yield u pb ages between 1761 9 and 1770 7 ma this time interval is concurrent with widespread granitoid emplacement at the close of the svecofennian orogeny disturbance of the re os system in the early auriferous arsenopyrite can be connected to the late stage mineralizing processes pb isotope data suggest a mixed mantle and lower crust origin for fluids in the post orogenic hydrothermal system in situ u pb dating in polished thin sections in tandem with electron microprobe analyses of mineral compositions and detailed textural observations highlights the utility of xenotime and monazite as robust geochronometers capable of recording repeated hydrothermal events in paleoproterozoic orogenic systems results provide precise temporal constraints for orogenic gold mineralization and vital information to refine the tectonic evolution of the central lapland greenstone belt

implications of new upb zircon chronology to early proterozoic crustal accretion in northern sweden abstract u pb ages ranging from 1 89 to 1 78 ga are reported for zircon populations formed during major magmatic events in the proterozoic development of northern sweden the studied area includes parts of the continental and the marine svecokarelian domains of the baltic shield the ages record crustal accretion and reactivation off the margin of an exposed archaean craton and show that magmatism was broadly coeval throughout the entire north swedish portion of the svecokarelian province irrespective of regions involved a detailed chronostratigraphy is presented for the skellefte district of northern sweden and comparisons are made with the evolution in other parts of the svecokarelian province two main magmatic phases commencing at 1 89 and 1 79 ga ago are recognized the first represents large scale volcanism and plutonism which in the skellefte district was characterized by the introduction of mainly mantle derived magmas or by magmas formed from rocks with short crustal residence time in the vicinity of the archaean craton some distance to the north the crust generating processes included the mobilization of archaean sources and appear to have continued until c 1 85 ga ago a relatively long period of consolidation and denudation separates this magmatic phase from the one at c 1 79 ga ago the generation of these later migmatite associated granites in the svecokarelian province coincided in time and was possibly associated with those processes which gave rise to the initial plutonism in the neighbouring transscandinavian granite porphyry belt