early carboniferous carbonate systems an alternative to the cainozoic paradigm abstract an alternative model for carbonate deposition is offered for the early carboniferous the major features of this interval are not explained using late cainozoic analogues early carboniferous low latitude shallow seas were apparently strongly influenced by upwelling and high nutrient levels these conditions favoured highly carbonate productive offshore systems but also resulted in the formation of extensive abiogenic carbonates as muds and ooids if correct the carboniferous serves to illustrate the dangers in extrapolating from present day systems to the geological record

late paleozoic glacial episodes in gondwanaland reflected in transgressive regressive depositional sequences in euramerica the late paleozoic glaciation of gondwanaland comprised two short episodes in the famennian i and visean ii confined to brazil and adjacent northwest africa and a long episode that started in the namurian iiia of eastern australia and bolivia argentina expanded to cover much of gondwanaland in the stephanian asselian iiib and collapsed in the early sakmarian iiic dropstones in eastern australia indicate that small ice centers lingered to the kazanian across the belt of low latitudes north of gondwanaland short ranging fossils in widespread shallow marine and paralic deposits indicate synchronous deposition of transgressive regressive sequences in different parts of euramerica these sequences correlate with glacial events in gondwanaland at three levels a four major regressions in euramerica in the famennian 1 visean 2 namurian 3 stephanian 4 and the tastubian transgression that preceded the sterlitamakian regression 5 also recorded in gondwanaland correlate with glacial episodes i ii and iiia iiib and iiic b the time interval of cyclothemic deposition in euramerica brigantian or latest visean to sterlitamakian correlates with that of glacial episode iii and c the dominant period of the euramerican cyclothems as estimated from the middle and late pennsylvanian deposits of the mid continent of north america and of the thickest known gondwanaland glacigenic sediment the earliest permian lyons group of western australia is 0 4 ma equivalent in turn to the long orbital eccentricity period of the quaternary ice age and the dominant period of fluctuation of the late miocene antarctic ice cap the three levels of correlations confirm wanless and shepard9s 1936 hypothesis that the late paleozoic cyclothems are controlled largely by sea level fluctuations related to the gondwanaland glaciation

mississippian early carboniferous stromatolite mounds in a fore reef slope setting laibin guangxi south china the mississippian early carboniferous is generally a period of scarce carbonate buildups in south china this study documents outcrops of stromatolite mounds at mengcun and helv villages in laibin city guangxi province south china the stromatolite mounds contain various stromatolite morphologies including laminar wavy laminar domal or hemispheroidal bulbous and flabellate growth columns intramound rocks are brachiopod floatstone and dark thin bedded laminated micrite limestone individual stromatolites at mengcun village are generally 3 6 cm thick and morphologically represent relatively shallow water laminar planar and wavy undulated stromatolites and deeper water domal bulbous and columnar forms where mounds were formed the stromatolites continued growing upward up to 60 cm thick thrombolitic fabrics also occur but are not common stromatolite microscopic structure shows the bulk of the lamination to consist of wavy microbialite and discrete thin micritic laminae these mounds are intercalated in deep water fore reef talus breccia packstone formed as a bioclastic debris flow and thin bedded limestone containing common chert layers of the tatang formation late visean further evidence supporting the deep water setting of the stromatolite mounds are 1 a laterally thinning horizon of brachiopod floatstone containing deep water small thin shelled brachiopods peloidal micritic sediments and low diversity mixed fauna e g thin shelled brachiopods tube like worms and algae that have been interpreted as storm deposits 2 common fore reef talus breccias 3 lack of sedimentary structures indicating current action 4 preservation of lamination with sponge spicules and 5 lack of bioturbation suggesting that the stromatolites grew in a relatively low energy deep water setting the stromatolite mounds are the first described stromatolite mounds in mississippian strata of south china and contain evidence that supports interpretations of 1 growth history of mississippian microbial buildups and 2 environmental controls on stromatolite growth and lithification

carbon and oxygen isotope stratigraphy of the lower mississippian kinderhookian lower osagean western united states implications for seawater chemistry and glaciation a positive carbon isotope 1 3 c excursion has been recognized in upper kinderhookian and early osagean carbonates in three sections in southeast idaho and nevada the oldest 1 3 c peak 7 is dated to the isostichaconodont zone and a younger peak occurs in the typicus zone the shifts are recorded in a range of carbonate lithofacies representing various water depths along the shelf lithofacies sampled for 1 3 c and 1 8 o at the samaria mountain section in southeast idaho record the shallowest water conditions indicated by cross bedded skeletal and peloidal grainstones the deepest water conditions are present in the pahranagat range section in eastern nevada which consists mainly of bioturbated lime mudstone and skeletal wackestone the 1 3 c values from these widely separated sedimentary basins show a consistent trend that correlates with early mississippian curves generated from brachiopod calcite in western europe and the midcontinent of north america as well as dolomites in utah and wyoming 1 8 o values become more positive up section generally paralleling the positive trend in 1 3 c during the late kinderhookian no subaerial exposure surfaces are recognized in the sections examined in southeast idaho and nevada and at least the 1 3 c trends are interpreted as primary seawater fluctuations sea level changes occurred near the beginning of the late kinderhookian 1 3 c shift early to middle parts of the isosticha zone and within the peak of the 1 3 c excursion kinderhookian osagean boundary although tectonic changes associated with the antler orogeny have likely modified the eustatic signature

pennsylvanian early triassic stratigraphy in the alborz mountains iran new fieldwork was carried out in the central and eastern alborz addressing the sedimentary succession from the pennsylvanian to the early triassic a regional synthesis is proposed based on sedimentary analysis and a wide collection of new palaeontological data the moscovian qezelqaleh formation deposited in a mixed coastal marine and alluvial setting is present in a restricted area of the eastern alborz transgressing on the lower carboniferous mobarak and dozdehband formations the late gzhelian early sakmarian dorud group is instead distributed over most of the studied area being absent only in a narrow belt to the se the dorud group is typically tripartite with a terrigenous unit in the lower part toyeh formation a carbonate intermediate part emarat and ghosnavi formations the former particularly rich in fusulinids and a terrigenous upper unit shah zeid formation which however seems to be confined to the central alborz a major gap in sedimentation occurred before the deposition of the overlying ruteh limestone a thick package of packstone wackestone interpreted as a carbonate ramp of middle permian age wordian capitanian the ruteh limestone is absent in the eastern part of the range and everywhere ends with an emersion surface that may be karstified or covered by a lateritic soil the late permian transgression was directed southwards in the central alborz where marine facies nesen formation are more common time equivalent alluvial fans with marsh intercalations and lateritic soils qeshlaq formation are present in the east towards the end of the permian most of the alborz emerged the marine facies being restricted to a small area on the caspian side of the central alborz there the permo triassic boundary interval is somewhat similar to the abadeh shahreza belt in central iran and contains oolites flat microbialites and domal stromatolites forming the base of the elikah formation the p t boundary is established on the basis of conodonts small foraminifera and stable isotope data the development of the lower and middle part of the elikah formation still early triassic in age contains vermicular bioturbated mudstone wackestone and anachronostic facies like gastropod oolites and flat pebble conglomerates three major factors control the sedimentary evolution the succession is in phase with global sea level curve in the moscovian and from the middle permian upwards it is out of phase around the carboniferous permian boundary when the dorud group was deposited during a global lowstand of sealevel when the global deglaciation started in the sakmarian sedimentation stopped in the alborz and the area emerged therefore there is a consistent geodynamic control from the middle permian upwards passive margin conditions control the sedimentary evolution of the basin which had its depocentre s to the north climate also had a significant role as the alborz drifted quickly northwards with other central iran blocks towards the turan active margin it passed from a southern latitude through the aridity belt in the middle permian across the equatorial humid belt in the late permian and reached the northern arid tropical belt in the triassic

millennial scale cyclicity in the geodynamo inferred from a dipole tilt reconstruction constraining past changes in the strength and configuration of the geomagnetic field provides a valuable perspective on the processes that govern the geodynamo here we update a modelled dipole tilt reconstruction for the last 9000 years by using palaeomagnetic records that originate from globally well distributed sites some features predicted by earlier dipole models become more distinct due to added data sets we identify a dominant 1350 year cycle in the dipole tilt variations and two preferred states of the dipole axis with north geomagnetic pole longitudes confined to either c 120 degrees west or c 30 degrees east the dipole tilt reconstruction is shown to be consistent with independent geomagnetic field intensity data from western eurasia which show generally higher intensities when the dipole is tilted towards this region our study implies that vadm reconstructions that are constrained by a biased spatial distribution of data can show variations resulting from dipole tilt instead of true dipole moment the preferred states of the modelled dipole axis can be related to the four semi stationary high latitude flux lobes that have been observed at the core mantle boundary in long term time averaged palaeomagnetic field models the tilt episodes towards 30 degrees east in the northern hemisphere are perhaps related to the appearance of a high intensity flux lobe beneath western eurasia the dipole tilt reconstruction is highly correlated to millennial scale variations in the length of day that have been reconstructed from ancient records of eclipses which indicates that the cyclicity may constitute an important component in core flow dynamics c 2011 elsevier b v all rights reserved less

tectonics and magmatism in turkey and the surrounding area this volume contains 23 papers from a range of international contributors describing recent research into the tectonics and magmatism of turkey and its surroundings this region is sited at the collision zone between eurasia and afro arabia and as such provides an extraordinarily complete and well exposed record of the staged tectonic evolution of this sector of the alpine himalayan orogen the geological history of this area involves separation of continental fragments from the margin of gondwana their migration across the tethyan oceans the subsequent closure of these oceans and finally the development of the neotectonic regime which continues to evolve to the present day such a comprehensive record is relevant to the understanding of collisional zones worldwide the volume is divided into five sections tethyan evolution neotethyan ophiolites post tethyan basin evolution neotectonics and igneous activity the first two sections deal with tethyan oceans whose growth and subsequent closure dominated the geodynamic framework in the mesozoic and cenozoic the subsequent sections deal with more recent geological developments from the balkan peninsula in the west to the transcaucasus in the east that followed consumption of the tethyan oceans there is a broad mix of papers throughout the volume wide ranging review papers on ocean development and extensional tectonics are followed by detailed descriptions of petrology and geochemistry and geographically focused studies on basin evolution specific aspects of extensional and strike slip tectonics and discussions of the relationship of magmatic activity to the tectonic development of the area tectonics and magmatism in turkey and the surrounding area presents up to date results and ideas from a large number of international contributors on a wide range of current research activity in this region it is essential reading for all geoscientists with an interest in both academic and applied aspects of eastern mediterranean geology

the anarak jandaq and posht e badam metamorphic complexes in central iran new geological data relationships and tectonic implications abstract the anarak jandaq and posht e badam metamorphic complexes occupy the nw part of the central east iranian microcontinent and are juxtaposed with the great kavir block and sanandaj sirjan zone our recent findings redefine the origin of these complexes so far attributed to the precambrian early paleozoic orogenic episodes and now directly related to the tectonic evolution of the paleo tethys ocean this tectonic evolution was initiated by late ordovician early devonian rifting events and terminated in the triassic by the eocimmerian collision event due to the docking of the cimmerian blocks with the asiatic turan block the variscan accretionary complex is a new name we proposed for the most widely distributed metamorphic rocks connected to the anarak and jandaq complexes this accretionary complex exposed from sw of jandaq to the anarak and kabudan areas is a thick and fine grain siliciclastic sequence accompanied by marginal sea ophiolitic remnants including gabbro basalts with a supra subduction geochemical signature new 40ar 39ar ages are obtained as 333 320 ma for the metamorphism of this sequence under greenschist to amphibolite facies moreover the limy intercalations in the volcano sedimentary part of this complex in godar e siah yielded upper devonian tournaisian conodonts the northeastern part of this complex in the jandaq area was intruded by 215 15 ma arc to collisional granite and pegmatites dated by id tims and its metamorphic rocks are characterized by some 40ar 39ar radiometric ages of 163 156 ma the variscan accretionary complex was northwardly accreted to the airekan granitic terrane dated at 549 15 ma later from the late carboniferous to triassic huge amounts of oceanic material were accreted to its southern side and penetrated by several seamounts such as the anarak and kabudan this new period of accretion is supported by the 280 230 ma 40ar 39ar ages for the anarak mild high pressure metamorphic rocks and a 262 ma u pb age for the trondhjemite rhyolite association of that area the triassic bayazeh flysch filled the foreland basin during the final closure of the paleo tethys ocean and was partly deposited and or thrusted onto the cimmerian yazd block the paleo tethys magmatic arc products have been well preserved in the late devonian carboniferous godar e siah intra arc deposits and the triassic nakhlak fore arc succession on the passive margin of the cimmerian block in the yazd region the nearly continuous upper paleozoic platform type deposition was totally interrupted during the middle to late triassic local erosion down to lower paleozoic levels may be related to flexural bulge erosion the platform was finally unconformably covered by liassic continental molassic deposits of the shemshak one of the extensional periods related to neo tethyan back arc rifting in late cretaceous time finally separated parts of the eocimmerian collisional domain from the eurasian turan domain the opening and closing of this new ocean characterized by the nain and sabzevar ophiolitic melanges finally transported the anarak jandaq composite terrane to central iran accompanied by large scale rotation of the central east iranian microcontinent ceim due to many similarities between the posht e badam metamorphic complex and the anarak jandaq composite terrane the former could be part of the latter if it was transported further south during tertiary time

the importance of changing oceanography in controlling late quaternary carbonate sedimentation on a high energy tropical oceanic ramp north western australia the north west shelf is an ocean facing carbonate ramp that lies in a warm water setting adjacent to an arid hinterland of moderate to low relief the sea floor is strongly affected by cyclonic storms long period swells and large internal tides resulting in preferentially accumulating coarse grained sediments circulation is dominated by the south flowing low salinity leeuwin current upwelling associated with the indian ocean gyre seaward flowing saline bottom waters generated by seasonal evaporation and flashy fluvial discharge sediments are palimpsest a variable mixture of relict stranded and holocene grains relict intraclasts both skeletal and lithic interpreted as having formed during sea level highstands of marine isotope stages mis 3 and 4 are now localized to the mid ramp the most conspicuous stranded particles are ooids and peloids which 14c dating shows formed at 15 4 12 7 ka in somewhat saline waters during initial stages of post last glacial maximum lgm sea level rise it appears that initiation of leeuwin current flow with its relatively less saline but oceanic waters arrested ooid formation such that subsequent benthic holocene sediment is principally biofragmental with sedimentation localized to the inner ramp and a ridge of planktic foraminifera offshore inner ramp deposits are a mixture of heterozoan and photozoan elements depositional facies reflect episodic environmental perturbation by riverine derived sediments and nutrients resulting in a mixed habitat of oligotrophic coral reefs and large benthic foraminifera and mesotrophic macroalgae and bryozoans indicators holocene mid ramp sediment is heterozoan in character but sparse most probably because of the periodic seaward flow of saline bottom waters generated by coastal evaporation holocene outer ramp sediment is mainly pelagic veneering shallow water sediments of marine isotope stage 2 including lgm deposits phosphate accumulations at 200 m water depth suggest periodic upwelling or fe redox pumping whereas enhanced near surface productivity probably associated with the interaction between the leeuwin current and indian ocean surface water results in a linear ridge of pelagic sediment at 140 m water depth this ramp depositional system in an arid climate has important applications for the geological record inner ramp sediments can contain important heterozoan elements mid ramp sediments with bedforms created by internal tides can form in water depths exceeding 50 m saline outflow can arrest or dramatically slow mid ramp sedimentation mimicking maximum flooding intervals and outer ramp planktic productivity can generate locally important fine grained carbonate sediment bodies changing oceanography during sea level rise can profoundly affect sediment composition sedimentation rate and packaging

the time dependence of intense archeomagnetic flux patches 1 the long term temporal behavior of intense geomagnetic flux patches at the core mantle boundary and the relation with lower mantle lateral heterogeneity are under debate we apply an algorithm to detect centers of intense flux patches and track their time evolution in a recent archeomagnetic field model in order to study the kinematics of such intense magnetic flux patches on millennial timescale we find that most intense flux patches appear near the edge of the tangent cylinder quasi stationary periods with small oscillations of patches occur more than drifts detailed comparison of the archeomagnetic patches behavior with that seen in numerical dynamos with tomographic heat flux boundary conditions suggests that core mantle thermal coupling could be the cause of a statistical preference for some longitudes on the long term which does not exclude significant time spent away from the preferred longitudes this could explain the roughly coincident locations of high latitude patches in the historical geomagnetic field with that of the time average paleomagnetic field together with the much weaker patches intensity in the latter alternating eastward and westward drifts are also observed the drifts are more westward than eastward especially in the southern hemisphere indicating that the time average zonal core flow may also be driven by core mantle thermal coupling an average patch lifetime of 300 years is found which we hypothesize may indicate the vortex lifetime in the outer core

application of chlorite sulfide oxide equilibria to metamorphosed massive sulfide ores snow lake area manitoba the stall lake and anderson lake massive cu zn sulfide deposits situated in the snow lake area of northern manitoba occur in hydrothermally altered felsic volcanic rocks which have been subjected to amphibolite grade metamorphism mineral assemblages from the two deposits contain in addition to chlorite the f sub o 2 f sub s 2 buffer assemblage of pyrite pyrrhotite and magnetite as well as quartz aluminosilicate and sphalerite in p t space the mole fraction of daphnite in a chlorite solid solution may be represented by a series of isopleths of fe sigma r super 2 calculated at p sub h 2 o p total for f sub o 2 and f sub s 2 buffered by pyrite pyrrhotite and magnetite calculations were based on an ideal ionic solution model for the daphnite component in chlorite i e a daphnite fe super 2 sigma r super 2 x daphnite and the free energy data for daphnite from bryndzia and scott 1987 chlorite isopleths are very sensitive to changes in ambient oxygen and sulfur fugacity conditions the very small deviations from average values of daphnite mole fractions in chlorite from the pyrite pyrrhotite magnetite bearing assemblages x 0 41 or 0 03 n 3 at anderson lake and 0 35 or 0 02 n 8 at stall lake demonstrates that fugacities of both oxygen and sulfur were buffered by pyrite pyrrhotite and magnetite intersection of chlorite and sphalerite isopleths gives peak metamorphic conditions of 6 5 to 7 0 kb and 580 degrees to 600 degrees c such high pressures are incompatible with metamorphic assemblages the intersection of chlorite isopleths with holdaway9s 1971 sillimanite kyanite phase boundary indicates peak metamorphic pressure and temperature to be 5 6 kb and 580 degrees c in excellent agreement with a previous estimate of 5 5 kb and 600 degrees c by froese and gasparrini 1975 chlorite isopleths in p t space are very steep and therefore sensitive to variations in temperature p t x daphnite diagrams have potential for geothermometry particularly when combined with other experimentally reversed equilibria defining reactions on a petrogenetic grid

a late quaternary geomagnetic secular variation record from lake waiau hawaii and the question of the pacific nondipole low a continuous paleomagnetic record for the last 13 000 years was obtained from the sediments of lake waiau located near the summit of mauna kea volcano on the island of hawaii the secular variation sv of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector the hypothesis that there has been anomalously low geomagnetic sv in the central pacific was tested using angular dispersion analysis the inclination record has a mean value of 27 that is much lower than the 35 predicted by the geocentric axial dipole hypothesis the spectrum obtained from spectral analysis shows major inclination peaks at periodicities of approximately 3600 and 7900 years and major declination peaks at periodicities of approximately 1100 2000 3300 and 7800 years the approximately 8000 and 3500 year periodicities shown in both inclination and declination spectrums may represent the dipole and nondipole variation respectively the approximately 1100 and 2000 year periodicities are probably derived from either the sources that affect declination only or the offsets between the core sections in addition bauer plots of the magnetic vector are dominated by clockwise motion the angular dispersion calculated from lake sediments is 5 9 with respect to the mean virtual geomagnetic pole vgp and 9 1 with respect to the geographic pole both values are much lower than the 13 5 expected from paleosecular variation model g which separates the angular dispersion into components from the dipole and the quadruple families our results support the hypothesis that an anomalously low secular variation is a characteristic feature of the central pacific furthermore this geomagnetic behavior persists on time scales of 104 years regional anomalies in temperature topography or electrical conductivity at the core mantle boundary are inferred to cause the low sv

tethyan oceanic currents and climate gradients 300 m y ago we reconstruct the oceanic circulation pattern of the tethys ocean 300 m y ago by placing late carboniferous early permian climate sensitive biotic associations from gondwana and laurasia on a pangea paleogeography constrained by selected paleomagnetic data warm climate fossils and facies from iran located at that time along the gondwanan margin of arabia are compatible with the existence in the tethys ocean of a warm subtropical surface current gyre whereas cold surface currents swept the glaciated gondwanan margin at higher southern latitudes redistributing cold biota toward the tropics this tethyan surface current system and the associated narrow zonal barrier show similarities to recent glacial climate patterns when placed on a large scale paleogeographic reconstruction of pangea of the b type it neatly explains the otherwise problematic observation that the carboniferous permian biota of iran and northern arabia is dominated by warm euramerican and or russian taxa that are strikingly different from typical cold gondwanan associations

terrane specific rock magnetic characteristics preserved in glacimarine sediment from southern coastal alaska sediments deposited in three fjord systems latitudinally spanning the northeast gulf of alaska coastline have distinctive rock magnetic characteristics that are derived from glacially eroded accreted terranes ideal conditions exist in coastal alaska to preserve primary rock magnetic properties within the sediment record because of the dominance of glacial erosion and rapid sediment transportation and burial in temperate glacially dominated marine settings terrigenous sediment is not diluted by biogenic material and diagenetic alteration is minimal the juxtaposition of temperate glaciers on the northwest trending accreted terranes of the southern alaska continental margin provides magnetic provenance tracers of sediment derived from this region that can aid in the interpretation of glacial paleoclimate and tectonic proxy records from marine sediment holocene sediment deposited in glacier bay is eroded from the craig subterrane of the alexander terrane it is characterized by high volume magnetic susceptibility and coarse grained pseudosingle domain psd and multidomain md magnetite in yakutat and disenchantment bays farther to the north glaciers also erode the yakutat and chugach terranes there sediment contains slightly finer grained psd and md magnetite which is chemically distinct from that of glacier bay in the northern most sector sediment is eroded from the chugach terrrane in harriman and college fiords adjacent to prince william sound these sediments have low magnetic susceptibility and contain micron size pyrrhotite

thresholds for paleozoic ice sheet initiation continental drift and atmospheric greenhouse gas concentrations have each in turn been proposed to explain the evolution of paleozoic climate from early era ice free conditions to late era continental scale glaciation despite continually increasing solar luminosity to assess the relative roles of continental configuration and atmospheric p co 2 on the formation of continental scale ice sheets we use a coupled ice sheet climate model to simulate ice sheet initiation at eight different paleozoic time slices using uniform topography for each time slice we simulate the climate at three atmospheric pco 2 levels 560 840 and 1120 ppm and both constant 97 5 of modern and time appropriate solar luminosity values under constant luminosity our results indicate that continental configurations favor ice sheet initiation in the mid paleozoic 400 340 ma after accounting for solar brightening ice sheet initiation is favored in the early paleozoic 480 370 ma simulations neither of these results is consistent with geological evidence of continental scale glaciation changes in atmospheric pco 2 can reconcile these differences sufficiently high 1120 ppm or low 560 ppm pco 2 overcomes paleogeographic and luminosity predispositions to ice free or ice age conditions based on our simulations and geological evidence of glaciation and atmospheric composition we conclude that atmospheric pco 2 was the primary control on paleozoic continental scale glaciation while paleogeographic configurations and solar irradiance were of secondary importance

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

late permian to late triassic palaeomagnetic data from iran constraints on the migration of the iranian block through the tethyan ocean and initial destruction of pangaea summary a palaeomagnetic study of late permian to early jurassic rocks from the alborz and sanandaj sirjan zones in iran and a compilation of selected palaeopoles from the carboniferous to the present provide an updated history of the motion of the iranian block within the tethys ocean the iran assemblage part of gondwana during the palaeozoic rifted away by the end of the permian we ascertain the southernhemisphere palaeoposition of iran at that time using magnetostratigraphy and show that it was situated close to arabia near to its relative position today a northward transit of this block during the triassic is shown with an estimated expansion rate of the neotethyan ridge of 100 140 km myr 1 the northward convergence with respect to eurasia ended during the ladinian middle triassic and is marked by a collision in the northern hemisphere with the turan platform which was the southern margin of the eurasian continent at that time no north south component of shortening is evidenced north of iran afterwards an analysis of the declinations from the late permian to the present shows diverent large rotations emphasizing the important tectonic phases suvered since the triassic finally we propose palaeomagnetic reconstructions of the tethys area during the late permian and the late triassic showing that the palaeotethys ocean was narrower than previously thought and did not widen its gate to the panthalassa before the triassic period

environmental gradients in carbonate sediments and rocks detected by correspondence analysis examples from the recent of norway and the dinantian of southwest england continuous sedimentary gradients are only crudely expressed by standard facies and microfacies methods which are more appropriate to situations where changes occur in relatively discrete steps in carbonate sediments and rocks continuous gradients are often represented by the arrangement of component grain types in a relay that is a systematic shifting of the relative importance of the components subdivision of such relays into micro facies can only be arbitrary correspondence analysis is shown to be useful for detecting isolating and describing relays particular use is made of the arch effect in which samples and components from data sets with a strong unidimensional structure a relay plot in the form of an arch in the plane of the first two factor axes a relay index indicating the position of samples in the relay can be extracted from the analysis and plotted on maps and stratigraphic logs to reveal details of the sedimentary gradient in areal and or stratigraphic context examples are given from i recent shallow marine carbonate sediments from northern norway illustrating a relatively simple depositional setting where surface sediments are viewed in plan and ii lower carboniferous carbonates of southwest england representing a more complex regional study of a particular stratigraphic interval viewed in cross section in both examples the relays can be related to identifiable environmental gradients

the margins of laurussia in central and southeast europe and southwest asia the continuation of the laurussian margin into central and southeast europe and southwest asia is defined by the rheic suture which becomes harder to trace to the southeast because of complex post variscan strike slip displacements and tectonic stacking linked to the cimmerian and alpine cycles the uncertain extent of the neoproterozoic baikalian orogeny fringing baltica ambiguous early paleozoic paleobiogeographic data and strike slip activity complicate the distinction of the tornquist suture from the transeuropean suture zone there is growing evidence for the incorporation of the brunovistulian malopolska and west moesian terranes into the late neoproterozoic cambrian baltican margin the istanbul zonguldak terrane along with the bitesh and east moesia terranes may have been part of the avalonian terrane assemblage although an arabian nubian shield or baltica provenance cannot be excluded the terranes of the armorica terrane assemblage bordering the rheic suture include the outer carpathian tatra getic and balkan terranes in southeast europe and sakarya and the anatolide tauride terrane in turkey further east the rheic suture may be present in the caucasus in all probability between the greater caucasus and the scythian platform or alternatively between the greater caucasus and transcaucasia alborz in northern iran is interpreted as a distal part of transcaucasia the location of the rheic suture in the southeast part of the turan domain of central asia is poorly constrained

incised valley fill interpretation for mississippian black hand sandstone appalachian basin usa implications for glacial eustasy at kinderhookian osagean tn2 tn3 boundary abstract lower mississippian strata of east central ohio are predominantly fine grained marine deposits of the cuyahoga and logan formations within these sediments is the black hand sandstone of the cuyahoga formation the black hand sandstone is a multistory crossbedded coarse grained conglomeratic sandstone the contact between the black hand sandstone and the subjacent cuyahoga formation is sharp and scoured with intraclasts of the cuyahoga formation incorporated into the basal black hand sandstone the black hand sandstone was previously thought to represent a distributary channel deposit however the combination of lithofacies and architectural elements indicates deposition in a braided stream setting the cuyahoga formation was deposited in a shallow marine setting the erosional basal contact of the black hand sandstone and the juxtaposition of fluvial and marine sediments suggests a sequence boundary the geographic distribution of the black hand sandstone combined with the evidence for a sequence boundary suggests deposition in an incised valley the age of the black hand sandstone is key to inferring the causes of valley incision the black hand sandstone is nearly devoid of body fossils necessitating a biostratigraphic analysis of the surrounding cuyahoga and logan formations analysis indicates the logan formation is early osagean age data from the cuyahoga formation suggest a kinderhookian age with a possible transition to the osagean in the uppermost cuyahoga formation this constrains the age of the black hand sandstone to the transition at the kinderhookian osagean boundary recent reports indicate late kinderhookian tournaisian tn2 gondwanan glaciation based upon tillites and sharp excursions in stable isotope curves a glacio eustatic fall in sea level is inferred to have caused incision of the cuyahoga formation followed by deposition of the black hand sandstone and logan formation during the subsequent sea level rise the associated unconformity correlates to the sequence boundary at the kinderhookian osagean boundary in the stratotype area of north america and the correlative tn2 tn3 boundary worldwide supporting the hypothesis of a global eustatic event at this time

warm water carbonates in proximity to gondwanan ice sheets a record from the upper paleozoic of iran abstract sedimentologic and paleontologic proxies recovered from the alborz basin the sanandaj sirjan zone and additional iranian peri gondwanan continental blocks near the arabian margin of northeastern gondwana record the formation of warm water shallow marine carbonates throughout the late pennsylvanian earliest permian this reflects a prevailing favorable climatic and environmental regime that contrasts with the cold conditions of slightly more southerly gondwanan regions that experienced profound glaciations the sedimentologic and paleobiologic properties of these iranian carbonates also differ greatly from coeval cool water carbonates of bolivia that developed at equivalent paleolatitudes along the northwestern margin of gondwana the complex climatic patterns reflected in the dispersal of marine taxa and their colonization of ecosystems relatively remote to their customary habitats and climate zones are interpreted to record the influence of ocean circulation based on these sedimentologic and paleobiologic data we utilized a climate model community climate system model version 3 ccsm3 to help resolve the mechanisms responsible for enabling transport of warm water to higher latitudes in northeastern gondwana these simulations reveal that spatial variations in sea surface temperatures exerted a strong forcing on paleo tethyan oceanic circulation and thereby governed the distribution diversity and abundance of taxa in late paleozoic marine ecosystems based on this outcome we conclude that the climatic contrasts registered across upper pennsylvanian lower permian carbonate platforms of the paleo tethys and panthalassic ocean originated through oceanic circulation driven by geographic differences in sea surface temperature

global paleobiogeography of brachiopods during the mississippian response to the global tectonic reconfiguration ocean circulation and climate changes abstract changes in mississippian global paleogeography derived from the reconfiguration of the continents a reversal in ocean currents and global cooling although the tectonic and climatic changes are well documented their effects on the distribution of brachiopod fauna are poorly documented here we present systematic quantitative analyses on global paleobiogeography based on a global brachiopod database from the mississippian i e tournaisian visean and serpukhovian the dataset consists of 2123 species of 344 brachiopod genera from 1156 localities our results reveal that global provincialism was not evident during the tournaisian and visean stages two realms i e the gondwanan and paleoequatorial realms are recognized during the tournaisian the paleoequatorial realm dominates during the visean stage whereas the gondwanan realm is not documented due to the absence of data points in contrast to the early and middle mississippian stages faunal provincialism is greatly enhanced in the serpukhovian stage with paleotethyan and north american realms easily distinguished this indicates that the rheic ocean was closed before the serpukhovian due to the collision between gondwana and laurussia that disrupted faunal interchange between the paleotethys and north america in addition the paleolatitude related thermal gradient was enhanced and the boreal realm was distinguished from the paleotethyan realm during the onset of the late palaeozoic ice age lpia in the serpukhovian the paleolatitude diversity gradient pattern further shows a distinct shift of diversity center from the southern tropic zone in the tournaisian and visean to the northern tropic zone in the serpukhovian

simulated circulation of an idealized ocean for pangaean time an eight level dynamical ocean model driven by prescribed surface forcing wind stress temperature precipitation minus evaporation from a previously published pangaean time climate simulation is used to study possible features of ocean circulation temperature and salinity for the early mesozoic the simulations are sensitivity experiments rather than estimates of the actual circulation because many simplifying assumptions are made concerning the prescribed surface forcing and the ocean basin s shape and depth simulated features include relatively warm water in high latitudes warm deep water a westward flowing equatorial current across panthalassa and into the tethys sea poleward and eastward flowing currents along the tethys coasts and relatively vigorous meridional and longitudinal vertical overturning cells cool relatively fresh polar water combines with warm saline tethys water to produce the relatively warm deep water there are few geological estimates of early mesozoic pangaean time ocean circulation available for comparison with the simulated circulation

variations of the trace fossil zoophycos with respect to paleoenvironment and sequence stratigraphy in the mississippian mobarak formation northern iran abstract zoophycos in the mississippian mobarak formation central alborz iran shows its potential in interpreting depositional settings ecological features and sequence stratigraphy zoophycos a zoa zoophycos b zob zoophycos phycosiphon zo phy and phycosiphon phy ichnocoenoses are identified in the middle and outer ramp facies of the mobarak formation on the basis of shape ichnodensity ichnocomplexity degree and size of zoophycos and other trace fossils zoophycos portrays a proximal to distal trend in the storm dominated ramp sequence in deeper parts of the ramp with long term stable conditions and organic enrichment zoophycos producers selected equilibrium strategies k selected whereas into the shallower parts they opted for opportunistic behavior r selected due to short term stable conditions with low food flux the feeding behavior proposed in this study is based on general morphology as well as mode of sediment exploiting and includes deposit feeding and the caching model moreover this study confirms that the distribution pattern of the paleozoic zoophycos producers within a sequence stratigraphic framework that was totally different from that of the mesozoic and cenozoic during the late transgressive systems tract tst and early highstand systems tract hst the excess of benthic food and the environmental stability together with the prevalence of dysaerobic conditions caused intense burrowing by the zoophycos producer in proximal outer ramp to distal middle ramp its ethology paleoecologic strategies and taphonomic signatures suggest that erosionally exhumed dewatered muddy beds firmground were not able to provide appropriate conditions for deposit feeding zoophycos producers as a consequence of their lower environmental stability therefore zoophycos as a standard component of the resident fair weather community cannot be a good representative of the distal expression of the glossifungites ichnofacies

facies and petrophysical signature of the tournaisian visean lower carboniferous sea level cycle in carbonate ramp to basinal settings of the wales brabant massif british isles we studied the relationships between stratigraphic distribution of outcrop spectral gamma ray magnetic susceptibility and carbonate facies stacking patterns across the regionally significant transgressive regressive cycle at the tournaisian visean boundary tn v early carboniferous in southern great britain and ireland south wales north staffordshire and dublin basin the tn v boundary coincides with a prominent climatic pulse connected with the late paleozoic glaciation of gondwana the aim was to correlate the gamma ray and magnetic susceptibility log patterns in carbonate ramp and basin settings and discuss the global regional nature and magnitude of this transgressive regressive cycle a robust ramp to basin correlation was produced based on the log patterns facies stacking patterns and foraminifer biostratigraphy the concentrations of k and th the clay gamma ray values and partly magnetic susceptibility are dependent on facies and show systematic changes along the inferred bathymetric profile from inner ramp to outer ramp and basin a model of carbonate productivity driven dilution of fine grained siliciclastics in caco3 as the major control on the petrophysical patterns is discussed the cleaning up and cleaning down petrophysical trends are related to down dip and up dip shifts of the carbonate factory with changing relative sea level in middle to outer ramp and basin settings this generates petrophysical trends just opposite to paleozoic carbonate shelves where peaks in magnetic susceptibility are known to be associated with peak regressions a distinct late tournaisian to early visean regressive to transgressive cycle with a prominent sequence boundary located close to the tn v stage boundary can be seen in the sections glacioeustatic origin of the sequence boundary is inferred from its correlation with tn v boundary sections from europe carbon isotope data from south china and the glacial deposits in the southern hemisphere mentioned by previous authors

archeomagnetic dating in western north america an updated reference curve based on paleomagnetic and archeomagnetic data sets 1 a robust database of paleomagnetic pm and archeomagnetic am data for western north america covering the past 4 millennia is assembled from three data sets 1 published pm data for dated lava flows 2 recently published am data generated by r l dubois and 3 published am data generated by j l eighmy chronologic information for the am data sets has been reassessed and the data points have been assigned to age ranges depending on their archeological contexts we have selected the computer program archeocourbe available from m le goff http www ipgp fr legoff or the auxiliary material see also http earthref org to construct am reference curves and to quantitatively estimate am dates for archeological and geological samples the updated curve provides a more detailed record of prehistoric secular variation for western north america than was previously available and shows a short interval of rapid secular variation sv in the 10th or 11th centuries at near excursional rates similar and coeval features in the hawaiian and to a lesser extent arkansan sv data sets possibly indicate a rapid amplitudinal shift in the regional nondipole field at that time

tectonics versus eustatic control on supersequences of the zagros mountains of iran abstract at least 12 km of strata ranging in age from the latest precambrian to the recent are exposed in the zagros mountains of iran this sedimentary cover is characterized by distinct stratal packages separated by major unconformities forming twelve supersequences they are informally named as 1 late precambrian cambrian hakhamanesh supersequence 2 ordovician kourosh supersequence 3 silurian camboojiyeh supersequence 4 devonian darioush supersequence 5 mississippian pennsylvanian khashayar supersequence 6 permian triassic ashk supersequence 7 jurassic farhad supersequence 8 early cretaceous mehrdad supersequence 9 late cretaceous ardavan supersequence 10 paleocene oligocene sassan supersequence 11 oligocene miocene ardeshir supersequence and 12 miocene pleistocene shapour supersequence these supersequences and their correlatives in neighboring areas have been used to infer tectonic events the dominant interpretation has been that local or regional epeirogenic movements were responsible for the formation of these supersequences unconformities are considered as indications that epeirogenic movements associated with tectonic events affected the area the present investigation provides an alternative to the established view of the phanerozoic supersequences of the zagros mountains a good correlation exists between the lithofacies of supersequences in the zagros mountains and the second order eustatic sea level changes deposition of deep water marine shales occurred during periods of eustatic sea level rise platform wide unconformities coincided with eustatic sea level lows in fact supersequences of the zagros mountains are nearly identical to those described from the north american craton and the russian platform suggesting that these stratal packages are global these observations suggest that supersequences of the zagros mountains formed by second order eustatic sea level changes and not by local or regional epeirogenic movements although tectonic events did not produce supersequences of the zagros mountains they influenced regional lithofacies patterns through the formation of intrashelf depressions such as the hormoz salt basin during the precambrian and the dezful embayment and the lorestan basin during the mesozoic tectonic events also affected sedimentation during the tertiary collision of arabia and the central iran microplate through uplift erosion and the formation of the zagros foreland basin the results of this investigation necessitate a re evaluation of the role and the significance of pre tertiary tectonic events commonly used to interpret the geological evolution of the zagros mountains

sedimentologic and paleoclimatic reconstructions of carbonate factory evolution in the alborz basin northern iran indicate a global response to early carboniferous tournaisian glaciations the lower carboniferous mobarak formation records the development of a storm sensitive pervasive carbonate factory on the southern paleo tethyan passive margin following the opening of the paleo tethys ocean into the alborz basin along the northern margin of gondwana its depositional facies encompass inner ramp peritidal environments peloidal to crinoidal shoals storm to fair weather influenced mid ramps proximal to distal shell beds and low energy outer ramps sedimentological analyses and foraminiferal biostratigraphy reveal four events affecting carbonate platform evolution in the alborz basin during the lower carboniferous 1 a transgression following global temperature rise in the early tournaisian middle hastarian caused the formation of thick bedded argillaceous limestones this interval correlates with early tournaisian nodular to argillaceous limestones in the moravia basin lisen formation czech republic the dinant basin pont d arcole formation belgium and at the rhenish slate mountains lower alum shale germany 2 late hastarian early ivorian glaciations previously identified in southern gondwana but had not yet recognized in northern gondwana were recorded through a sequence boundary 3 during the late tournaisian early visean a differential block faulting regime along the basin s margin caused uplift of the westernmost parts of the alborz basin and resulted in subsidence in the eastern part of the central basin this tectonically controlled shift in depositional regime caused vast sub aerial exposure and brecciation preserved in the top of the mobarak formation in the western portion of the central alborz basin 4 tectonic activity coinciding with a progressive multiphase sea level drop caused indirectly by the visean and serpukhovian glaciations phases ultimately led to the stagnation of the carbonate factory paleothermometry proxies the presence of foraminiferal taxa with a northern paleo tethyan affinity and evidence for arid conditions in the terrestrial hinterland place the alborz basin at lower latitudes than the approximately 45 50 southern paleolatitude reported thus far

lower carboniferous ramp sedimentation of the central alborz basin northern iran integrated sedimentological and rock magnetic studies the lower carboniferous mobarak formation in the alborz basin northern iran was deposited along the northeastern margin of gondwana in a carbonate ramp setting this paper focuses on the tournaisian stratigraphic interval of this formation that crops out at the jaban section in the southwestern central alborz basin the following facies associations representing different ramp palaeoenvironments have been identified 1 mudstone wackestone outer ramp facies 2 crinoidal to skeletal grainstone packstone mid ramp facies 3 peloidal to crinoidal grainstone packstone inner ramp facies and 4 coastal facies which include a variety of microbial laminated to oncoidal grainstones and mudstones with evaporitic pseudomorphs this ramp profile was affected by frequent storms that were responsible for the formation of several skeletal to non skeletal shoals in the distal mid ramp to the most proximal inner ramp areas the development of the skeletal to non skeletal shoals along the sea side of the ramp formed a semi enclosed lagoon sensitive to the influence of both high tides and storm surges the magnetic susceptibility xin of all the samples was measured and compared with that of the facies from which the sample was taken there is a clear link between xin and the facies the average xin values were higher for the distal facies than for the proximal facies the xin profile of this lower carboniferous carbonate sequence reflects stratigraphic variations in response to relative changes in sea level and the input of detrital materials in the context of the sequence stratigraphic framework the average xin values for lowstand and transgressive systems tract deposits are higher than for the highstand systems tract deposits the clear link between xin and facies indicates at least a partly preserved primary xin signal related to the detrital inputs however to obtain a better understanding of the nature and origin of the minerals carrying the xin we performed hyster esis measurements on selected samples it appears that the xin signal is mainly carried by low coercivity ferromagnetic minerals such as magnetite with a mixture of relatively coarse grains detrital fraction and ultra fine grains probably formed during diagenesis

paleoreef maps evaluation of a comprehensive database on phanerozoic reefs to get a better understanding of controls on reef development through time we created a comprehensive database on phanerozoic reefs the database currently comprises 2470 reefs and contains information about geographic position paleoposition age reef type dimensions environmental setting paleontological and petrographical features and reservoir quality of each buildup reef data were analyzed in two qualitatively different ways the first type of analysis was by visualization of paleogeographic reef distribution maps five examples late devonian early permian late triassic late jurassic middle miocene are presented to show the potential of paleoreef maps for paleogeographic and paleoclimatological reconstructions the second type of analysis was a numerical processing of coded reef characteristics to realize major trends in reef evolution and properties of reef carbonates the analysis of paleolatitudinal reef distributions through time shows pronounced asymmetries in some time slices probably related to climatic asymmetries rather than controlled by plate tectonic evolution alone the dominance of particular reef builders through time suggests that there are seven cycles of phanerozoic reef development first curves for the phanerozoic distribution of bioerosion in reefs bathymetric setting and debris potential of reefs are presented the observed pattern in the temporal and spatial distribution of reefs with reservoir quality may assist in hydrocarbon exploration statistical tests on the dependencies of reefal reservoir quality suggest that large size high debris potential low paleolatitude high amount of marine aragonite cement and a platform shelf edge setting favor reservoir quality reefal reservoirs are significantly enhanced in times of high evaporite sedimentation elevated burial of organic carbon low oceanic crust production low atmospheric co2 content and cool paleoclimate as well as when they are present in aragonite oceans

searching for single domain magnetite in the pseudo single domain sedimentary haystack implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations 1 magnetic hysteresis measurements of sediments have resulted in widespread reporting of pseudo single domain like magnetic properties in contrast the ideal single domain sd properties that would be expected to be responsible for high quality paleomagnetic records are rare determining whether sd particles are rare or common in sediments requires application of techniques that enable discrimination among different magnetic components in a sediment we apply a range of such techniques and find that sd particles are much more common than has been reported in the literature and that magnetite magnetofossils the inorganic remains of magnetotactic bacteria are widely preserved at depth in a range of sediment types including biogenic pelagic carbonates lacustrine and marine clays and possibly even in glaci marine sediments thus instead of being rarely preserved in the geological record we find that magnetofossils are widespread this observation has important implications for our understanding of how sediments become magnetized and highlights the need to develop a more robust basis for understanding how biogenic magnetite contributes to the magnetization of sediments magnetofossils also have grain sizes that are substantially smaller than the 1 15 m size range for which there is reasonable empirical support for relative paleointensity studies the different magnetic response of coexisting fine biogenic and coarser lithogenic particles is likely to complicate relative paleointensity studies this issue needs much closer attention despite the fact that sediments have been subjected to paleomagnetic investigation for over 60 years much remains to be understood about how they become magnetized

a comparison of holocene paleomagnetic secular variation records from north america the comparison of nine holocene 0 12 000 years b p records of paleomagnetic field secular variation psv obtained from across north america indicates that distinctive field features in inclination and declination often can be traced for more than 4000 km without significant change in pattern independent age determinations corroborate these correlations while also suggesting that westward or eastward drift is not significant on the other hand northward drift may be a significant process at least between 1500 and 5500 years b p several methods of analyzing the overall psv character point to circularity vector looping as a preferred means of defining coherent space time vector variations which are termed waveforms a few distinctive waveforms each discernible for about 1400 years dominate psv across north america during the holocene 4 5 loops and 2 loops being associated with clockwise and counterclockwise circularity respectively the clockwise loops appear to be periodic occurring every 2400 years and most likely result from the recurrence of a distinctive regional dynamo source in the outer core the pattern of circularity noted in north america during the last 3000 years correlates in time with similar circularity changes seen globally this may indicate that there is some degree of coupling between different regional dynamo sources within the outer core the fact that some north american waveforms are almost identical to waveforms observed elsewhere around the world at different times may indicate that similar distinctive regional dynamo sources recur randomly throughout the outer core

a 17 000 yr paleomagnetic secular variation record from the southeast alaskan margin regional and global correlations high resolution sedimentary records on two cores from the gulf of alaska margin allow development of a 17 400 yr reconstruction of paleomagnetic secular variation psv general agreement between the two records on their independent chronologies confirms that local psv is recorded demonstrating that such archives notwithstanding complexities due to variable sedimentary regimes deposition rates and diagenetic conditions provide meaningful information on past changes of the geomagnetic field comparisons with other independently dated sedimentary paleomagnetic records from the ne pacific indicate largely coherent inclination records that in combination create a ne pacific sedimentary inclination anomaly stack nepsias capturing the common signal over an area spanning 30 longitude and latitude from alaska through oregon to hawaii comparisons of nepsias with high quality declination records from the northern north atlantic nna show that negative shallow inclination anomalies in nepsias are associated with eastward nna declinations while positive steep inclination anomalies in nepsias are associated with westward nna declinations comparison of these directional records to regional geomagnetic intensities over the past 3000 yrs in north america and back nearly 8000 yrs in the euro mediterranean region are consistent with a driving mechanism of oscillations in the relative strength of the north american and euro mediterranean flux lobes the persistence of these dynamics through the holocene implicates a long lived organizing structure likely imposed on the geomagnetic field by the lower mantle and or inner core these observations underscore a fundamental connection between directional psv in the north pacific with that of the north atlantic supporting the potential for long distance correlation of directional psv as a chronostratigraphic tool

unusually large subsidence and sea level events during middle paleozoic time new evidence supporting mantle convection models for supercontinent assembly new evidence from basin modeling documents a nearly synchronous episode of rapid subsidence between middle devonian and earliest mississippian time in almost all preexisting margins and interior basins of north america the subsidence events appear to have been accompanied by a large sea level rise relative to the stable cratonic platform herein we suggest that the timing and magnitude of basin subsidence and sea level change are compatible with predictions by recent mantle convection models for the assembly of supercontinents if so the sea level and subsidence events were consequences of the onset of accretion of pangea above a major zone of mantle downwelling

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

geochemistry of brachiopods oxygen and carbon isotopic records of paleozoic oceans abstract combined trace element and isotope studies of 319 brachiopods covering the ordovician to permian time span show that 13c and 18o in well preserved specimens varied during the paleozoic the overall 13c secular trend is in accord with the previously published observations but its details are obscured by vital isotopic fractionation effects at generic level nonetheless the results suggest that the negative correlation between marine 13ccarbonate and 34ssulphate deteriorates at time scales of 106 years due to the long residence time and thus slow response of so42 in the ocean for oxygen isotopes all devonian and older specimens have 18o of 4 while the well preserved permian samples have near present day 18o of about 1 pdb this isotopic dichotomy is probably not due to post depositional phenomena salinity or biogenic fractionation effects this leaves open the perennial arguments for a change in 18 o 16 o of sea water versus warmer ancient oceans the present data are difficult to explain solely by the temperature alternative the coincidence of the proposed shift in 18o with the large late paleozoic changes in marine 87 sr 86 sr 13 c 12 c 34 s 32 s and sea level stands argues for a tectonic cause and for a change in 18 o 16 o of sea water although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites whatever the precise cause or combination of causes the implications for tectonism and or paleoclimatology are of first order significance

palynology and correlation of carboniferous permian glacigene rocks in oman yemen and pakistan palynological assemblages from sections in yemen and pakistan are similar enough to allow the application of biozones based on the pennsylvanian glacigene sediments of interior oman thirty four samples from the upper 84 m of a 125 m thick section of the tobra formation at zaluch nala western salt range pakistan yielded palynomorph taxa including microbaculispora tentula abundant monosaccate pollen including cannanoropollis janakii and plicatipollenites malabarensis converrucosisporites grandegranulatus horriditriletes ramosus and horriditriletes tereteangulatus indicating the late pennsylvanian oman 2165b biozone eleven samples from the yemen kuhlan formation and 22 samples from the underlying akbarah formation from approximately 300 m of a section near kuhlan in northwest yemen suggest a 2165a biozone age also late pennsylvanian this correlation indicates the widespread nature of glacial sediments of a narrow biostratigraphic late pennsylvanian age range the oman p5 unit in basins across part of the north gondwana margin new data from three samples from the tobra formation at the choa road section near khewra in the eastern salt range pakistan are assignable to the earliest permian 2141b biozone indicating a possible correlation between the tobra shale and the rahab shale member of oman which is considered to mark the final deglaciation sequence in oman

the deglacial transition on the southeastern alaska margin meltwater input sea level rise marine productivity and sedimentary anoxia 1 oxygen isotope data from planktonic and benthic foraminifera on a high resolution age model 44 14c dates spanning 17 400 years document deglacial environmental change on the southeast alaska margin 59 33 32 n 144 9 21 w 682 m water depth surface freshening i e 18o reduction of 0 8 began at 16 650 170 cal years b p during an interval of ice proximal sedimentation likely due to freshwater input from melting glaciers a sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14 790 380 cal years b p abrupt warming and or freshening of the surface ocean i e additional 18o reduction of 0 9 coincides with the bolling interstade of northern europe and greenland cooling and or higher salinities returned during the allerod interval coincident with the antarctic cold reversal and continue until 11 740 200 cal years b p when onset of warming coincides with the end of the younger dryas an abrupt 1 reduction in benthic 18o at 14 250 290 cal years b p likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater a regional megaflood event or brine formation associated with sea ice two laminated opal rich intervals record discrete episodes of high productivity during the last deglaciation these events precisely dated here at 14 790 380 to 12 990 190 cal years b p and 11 160 130 to 10 750 220 cal years b p likely correlate to similar features observed elsewhere on the margins of the north pacific and are coeval with episodes of rapid sea level rise remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia

after the collapse of stromatoporid coral reefs the famennian and dinantian reefs of belgium much more than waulsortian mounds

global time scale and regional stratigraphic reference scales of central and west europe east europe tethys south china and north america as used in the devonian carboniferous permian correlation chart 2003 dcp 2003 the boundaries of the devonian carboniferous and permian stages of the global stratigraphic reference scale abbreviated to global stratigraphic scale gss are described in relation to the biostratigraphic and or lithostratigraphic units of the regional stratigraphic reference scales abbreviated to regional stratigraphic scales rss of central and west europe east europe tethys south china eastern tethys and north america in their type regions the boundaries of gss units rarely coincide with those of homonymous rss units moreover the definitions of some rss units have changed several times over the last decades and subsequent misunderstanding of the stratigraphical significance of these changes has often introduced errors into proposed global correlation charts the stratigraphic framework proposed in our global devonian carboniferous permian correlation chart 2003 dcp 2003 devonian carboniferous permian correlation chart 2003 menning m schneider j w alekseev a s amon e o becker g von bitter p h boardman d r bogoslovskaya m braun a brocke r chernykh v chuvashov b i clayton g dusar m davydov v i dybova jachowicz s forke h c gibling m gilmour e h goretzki j grunt t a hance l heckel p h izokh n g jansen u jin y g jones p kading k ch kerp h kiersnowski h klets a klug ch korn d kossovaya o kotlyar g v kozur h w laveine j p martens th nemyrovska t l nigmadganov a l paech h j peryt t m rohn r roscher m rubidge b schiappa t a schindler e skompski s ueno k utting j vdovenko m v villa e voigt s wahlman g p wardlaw b r warrington g weddige k werneburg r weyer d wilde v winkler prins c f work d m 2004 abschlusskolloquium dfg schwerpunktprogramm 1054 evolution des systems erde wahrend des jungeren palaozoikums im spiegel der sedimentgeochemie abstracts univ erlangen germany 2004 p 43 herein abbreviated to dcp 2003 and cited as dcp 2003 in references is an attempt to reduce these errors the dcp 2003 is the stratigraphic base for project 1054 of the deutsche forschungsgemeinschaft dfg the evolution of the late palaeozoic in the light of sedimentary geochemistry this composite time scale has been carefully balanced as far as data allows to remove unnecessary artificial compression and expansion of time intervals biozonations and depositional events the ages selected in dcp 2003 are markedly different to those in the geologic time scale 1989 gts 1989 harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge pp 1 263 and in gradstein and ogg gradstein f m ogg j 1996 a phanerozoic time scale episodes 19 1 2 3 4 insert whereas they are closer to those of the geologic time scale 2004 gts 2004 gradstein f m ogg j g smith a g 2004 a geologic time scale 2004 cambridge univ press cambridge pp 1 589 mostly the ages are rounded to the nearest 0 5 ma in order to avoid estimates of questionable accuracy whereas ages of 0 1 ma in the gts 2004 and their error bars of 0 4 ma to 2 8 ma for the devonian to permian stage boundaries suggest an improved accuracy in contrast in the dcp 2003 questionable ages and positions of stratigraphic boundaries are marked by arrows c 2006 elsevier b v all rights reserved

carbon oxygen isotope signal of mississippian slope carbonates appalachians usa a complex response to climate driven fourth order glacio eustasy abstract mississippian chesterian ramp slope muds in virginia deposited on the margin of a rapidly subsiding foreland basin were not significantly reset isotopically by regional meteoric aquifer systems that affected units on the adjacent platform carbon and oxygen isotopic ratios of these muds tend to covary at the scale of the twelve 4th order sequences that dominate the platform succession the 13 c values of the slope muds range from 0 5 to 4 pdb and lie in the range of least altered contemporaneous brachiopods from north america indicating little resetting of carbon isotopes by diagenesis there is an approximately 1 to 2 decrease in 13 c in the maximum flooding zone relative to the lowstand followed by a positive shift upward in the highstand before becoming more negative toward 4th order correlative conformities meteoric diagenesis might have reset some sediments just beneath a sequence boundary to lighter values it cannot account for the observed shifts evident throughout the sequences the 13 c enriched values in 13 c profiles could be due to increased productivity during glacial stages the increased productivity during glacial stages was probably due to increased ocean circulation coupled with shallowing which brought the ramp top into waters with more 13 c enriched dissolved inorganic carbon with the opposite effects occurring during deglaciation the 18 o values of muds range from about 2 2 to about 4 6 pdb falling within and beyond the lighter part of the range of contemporaneous north american brachiopods mii h s grossman e l yancey t e 1999 carboniferous isotope stratigraphies of north america implications for carboniferous paleoceanography and mississippian glaciation geol soc am bull 111 960 973 these values likely have been reset by burial diagenesis and perhaps by some meteoric diagenesis just beneath correlative conformities the sequences show negative excursions of 1 to 2 in 18 o in the maximum flooding zone relative to the lowstand and then become more positive upward in the highstand then decrease toward the correlative conformities some of the preserved signal could reflect ice volume changes although this would account for only 0 5 to 1 change the ice volume effect during lowstands plus cooling of ramp top waters and small increases in salinity due to increased aridity in the appalachian basin could account for the remaining 0 5 to 1 5 of oxygen isotope excursions with the opposite effect occurring during high sea levels the 18 o and 13 c of the appalachian ramp slope facies lack the strong 3rd order trends of the mid continental united states and europe the remnant 4th order carbon and oxygen isotope signal is similar in structure to cenozoic deep sea isotope profiles that are due in large part to 4th order glacio eustasy this would be compatible with onset of late paleozoic glaciation of gondwana

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

the drift history of iran from the ordovician to the triassic new late ordovician and triassic palaeomagnetic data from iran are presented these data in conjunction with data from the literature provide insights on the drift history of iran as part of cimmeria during the ordovician triassic a robust agreement of palaeomagnetic poles of iran and west gondwana is observed for the late ordovician earliest carboniferous indicat ing that iran was part of gondwana during that time data for the late permian early early tri assic indicate that iran resided on subequatorial palaeolatitudes clearly disengaged from the parental gondwanan margin in the southern hemisphere since the late early triassic iran has been located in the northern hemisphere close to the eurasian margin this northward drift brought iran to cover much of the palaeotethys in approximately 35 ma at an average plate speed ofc 7 8 cm year 21 and was in part coeval to the transformation of pangaea from an irvin gian b to a wegenerian a type configuration

the formation of pangea abstract the making of pangea is the result of large scale amalgamation of continents and micro continents which started at the end of the neoproterozoic with the formation of gondwana as pieces were added to gondwana on its south american antarctica and australia side ribbon like micro continents were detached from its african and south chinese side cadomia in the late neoproterozoic avalonia and hunia in the ordovician galatia in the devonian and cimmeria in the permian cadomia was re accreted to gondwana but the other ribbon continents were accreted to baltica north china laurussia or laurasia finding the origin of these numerous terranes is a major geological challenge recently a global plate tectonic model was developed together with a large geological geodynamic database at the lausanne university covering the last 600 ma of the earth s history special attention was given to the placing of gondwana derived terranes in their original position using all possible constraints we propose here a solution for the variscan terranes another paper deals with the altaids the galatian super terrane was detached from gondwana in the devonian during the opening of paleotethys and was quickly separated into four sub terranes that started to by pass each other the leading terranes collided at the end of the devonian with the hanseatic terrane detached from laurussia in the carboniferous gondwana started to impinge onto the amalgamated terranes creating the variscan chain and the pangean super continent east of spain paleotethys remained opened until the triassic subducting northward under laurasia roll back of the paleotethyan slab triggered the collapse of most of the european variscan orogen which was replaced by series of permian rifts some of them becoming oceanized back arc basins during the triassic major force changes at the pangean plate limits at the end of the triassic provoked its break up through the opening of the proto caribbean central atlantic alpine tethys oceanic seaways

the birth of the rheic ocean early palaeozoic subsidence patterns and subsequent tectonic plate scenarios abstract new plate tectonic reconstructions of the gondwana margin suggest that the location of gondwana derived terranes should not only be guided by the models but should also consider the possible detrital input from some asian blocks hunia supposed to have been located along the cambrian gondwana margin and accreted in the silurian to the north chinese block consequently the gondwana margin has to be subdivided into a more western domain where the future avalonian blocks will be separated from gondwana by the opening rheic ocean whereas in its eastern continuation hosting the future basement areas of central europe different periods of crustal extension should be distinguished instead of applying a rather cylindrical model it is supposed that crustal extension follows a much more complex pattern where local back arcs or intra continental rifts are involved guided by the age data of magmatic rocks and the pattern of subsidence curves the following extensional events can be distinguished during the early to middle cambrian a back arc setting guided the evolution at the gondwana margin contemporaneous intra continental rift basins developed at other places related to a general post pan african extensional phase affecting africa upper cambrian formation of oceanic crust is manifested in the chamrousse area and may have lateral cryptic relics preserved in other places this is regarded as the oceanisation of some marginal basins in a context of back arc rifting these basins were closed in a mid ordovician tectonic phase related to the subduction of buoyant material mid ocean ridge since the early ordovician a new phase of extension is observed accompanied by a large scale volcanic activity erosion of the rift shoulders generated detritus armorican quartzite and the rift basins collected detrital zircons from a wide hinterland this phase heralded the opening of palaeotethys but it failed due to the silurian collision eo variscan phase of an intra oceanic arc with the gondwana margin during this time period at the eastern wing of the gondwana margin begins the drift of the future hunia microcontinents through the opening of an eastern prolongation of the already existing rheic ocean the passive margin of the remaining gondwana was composed of the galatian superterranes constituents of the future variscan basement areas remaining under the influence of crustal extension they will start their drift to laurussia since the earliest devonian during the opening of the palaeotethys ocean

upper devonian and mississippian foraminiferal and rugose coral zonations of belgium and northern france a tool for eurasian correlations the radiation of early carboniferous foraminifers and rugose corals following the devonian carboniferous crisis offers the best tool for high resolution correlations in the mississippian together with the conodonts in the tournaisian notably in the namur dinant basin however some of the guides are facies controlled and an integrated approach combining biostratigraphy sedimentology and sequence stratigraphy is critical to identify delayed entries potential stratigraphic gaps and to avoid diachronous correlations the main difficulty is in correlating shallow and deeper water facies at any given time in existing zonations the visean part of the scheme is always more detailed reflecting the widespread development of shallow water platforms in the early visean which created conditions more suitable for foraminifers and rugose corals over large areas in contrast the tournaisian zones less well documented reflect unfavourable environmental conditions in the lower ramp dinant sedimentation area and pervasive dolomitization of the inner ramp condroz and namur sedimentation areas recent progress in understanding the belgian early carboniferous sequence stratigraphy and lithostratigraphy and revision of the biostratigraphy of the key sections strongly modify former biostratigraphic interpretations improvements mainly concern the latest devonian the late tournaisian and the early visean the late devonian and the tournaisian are equated with foraminifer zones dfz1 to dfz8 and mfz1 to mfz8 respectively the visean correlates with zones mfz9 to mfz14 zone mfz15 straddles the visean namurian boundary and zone mfz16 is the youngest mississippian zone the rugose corals allow the recognition of ten zones rc0 to rc9 covering the strunian late famennian to serpukhovian interval discrepancies with former zonations are discussed the moliniacian stage is emended to restore the coincidence between its base and that of the visean

the magnitude of late paleozoic glacioeustatic fluctuations a synthesis a comprehensive literature review shows that the magnitude of eustatic fluctuations varied throughout the carboniferous and permian and that at least eight distinct phases can be recognized facies juxtapositions in carbonate successions and erosional relief in clastic successions indicate that glacioeustatic fluctuations of 20 25 m and occasionally as much as 60 m took place throughout the early mississippian tournaisian a widely recognized glacial period middle mississippian mid chadian through holkerian shallow marine carbonate and clastic successions indicate that eustatic fluctuations were 10 25 m a decrease that matches well with the paucity of coeval glacial deposits late visean asbian through mid brigantian glacioeustatic fluctuations of 10 50 m record the initial phases of ice accumulation in advance of the widespread mid carboniferous glacial event the latest mississippian earliest pennsylvanian mid brigantian through langsettian was a time of widespread glaciation and strata of this age commonly exhibit evidence of glacioeustatic fluctuations of as much as 40 100 m although middle pennsylvanian duckmantian through asturian glacial deposits are present in eastern australia paleovalley depths suggest that coeval glacioeustatic fluctuations were less than 40 m glacioeustatic fluctuations of as much as 100 120 m have been widely reported from late pennsylvanian earliest permian stephanian through mid sakmarian successions in north america an increase that corresponds to the growth of large ice sheets across much of gondwana and the accumulation of ice in the northern hemisphere incision and facies juxtaposition in early middle permian mid sakmarian through kungurian successions in eastern australia indicate that glacioeustatic fluctuations of 30 70 m occurred during the waning stages of major glaciation erosional relief in paleoequatorial carbonates and the presence of coeval glacial deposits in australia suggests that eustatic fluctuations of 10 60 m occurred during the final stages of glaciation in the middle to late permian roadian through capitanian but the modest size of most of these fluctuations makes it difficult to isolate the glacioeustatic signature this review demonstrates that far field cyclic successions record changing glacial conditions in gondwana that the magnitude of glacioeustatic fluctuations was directly related to the volume of glacial ice that carboniferous permian glacioeustasy was more variable than previously recognized and that generalizations from short temporal intervals are probably not representative of the late paleozoic ice age as a whole although any attempt to quantify the magnitude of ancient eustatic changes is based on caveats and assumptions this review incorporates the results of over 100 published papers on the topic in an attempt to minimize the errors inherent in any one study

petrology and depositional evolution of the paleozoic rocks of iraq abstract the study integrates petrographical and lithological data from deep exploration wells and outcrops in northern iraq to better understand the sedimentary environments present in the basin and to evaluate the depositional evolution of the paleozoic rocks in iraq the studied paleozoic successions are represented by five sedimentary cycles of intracratonic sequences these are dominated mainly by siliciclastic and mixed sedimentary packages and are separated by major and minor unconformity surfaces these cycles are as follow the ordovician cycle represented by the khabour formation the silurian cycle represented by the akkas formation the middle late devonian to early carboniferous cycle represented by the chalki pirispiki kaista ora and harur formations the permian carboniferous cycle represented by the ga ara formation and late permian cycle represented by the chia zairi formation generally the cycles are characterized by siliciclastic and mixed carbonate clastic facies with abrupt changes during late paleozoic reflecting the environmental and tectonic events during this period the ordovician khabour formation is suggested to be of shallow marine environment of deposition with stacked transgressive and regressive cycles that are eustatically controlled the shale of silurian akkas formation was deposited in open marine environment depositional regimes in the late devonian to early carboniferous are considered as a continuation of deposition in the subsiding basin with a wide geographic distribution that reflect the epicontinental or epeiric seas in a homoclinic ramp setting the permo carboniferous ga ara formation was deposited in continental to paralic environment while the late permian chia zairi formation represents the carbonate platform deposition the study revealed that potential source rocks may include some shale beds of the khabour formation hot shales of akkas formation and the shales of ora formation the sandstones of the khabour akkas and kaista formations have good reservoir potential the late permian carbonates of chia zairi formation may be self sourcing and contain multiple reservoirs the occurrence of shale as source rocks and limestone as reservoir rocks and some evaporates as sealing horizons make the formation as a reservoir in its own right

demise of a devonian carboniferous carbonate ramp by eutrophication the occurrence of organic rich mudrocks overlying carbonate deposits in the rock record has typically been ascribed to changes in relative sea level we propose alternatively that progressive eutrophication of the euphotic zone caused the ecological demise of a late devonian marine carbonate ramp system in alberta and its subsequent burial in organic rich mudrocks similar lithologic transitions elsewhere in the stratigraphic record may also reflect eutrophication rather than major shifts in sea level the transition from upper devonian carbonates to devonian carboniferous black mudrocks in alberta is characterized by a gradual decrease in net carbonate accumulation as indicated by 1 an upward increase in mud phosphate and glauconite 2 the existence of firmground surfaces and 3 a change from a dominantly phototrophic to heterotrophic benthic assemblage an upward trend to lower bulk 13 c organic and 15 n values reflects the eutrophication of surface waters by upwelling of nutrient laden deeper waters resultant primary production propelled higher organic matter flux to the sea floor caused the demise of carbonate producing benthic organisms and promoted burial of carbonate deposits by organic rich mudrocks

a holocene paleosecular variation record from 14c dated volcanic rocks in western north america 1 a paleosecular variation psv curve for western north america is presented on the basis of 94 virtual geomagnetic poles vgps from dated volcanic rocks sampled at 446 sites approximately 60 of the paleomagnetic database has been previously published a curve defined by spherical smoothed splines is fitted to the vgps ranked by the quality of the age determinations where the data density is highest between 3690 and 30 years before present b p a d 1950 between 7800 and 7050 years b p and between 14 060 and 12 700 years b p the younger segments of the curve derived from volcanic rocks are similar but less complex than other high resolution psv curves derived from lacustrine sediments particularly the record at fish lake oregon the psv record from lava flows psvl however is perhaps more reliable in its general shape and chronology because of the higher fidelity of volcanic rocks as magnetic field recorders and because of the greater density of 14c dates the new psvl record provides a partial holocene master curve for western north america and will be of particular value in dating geological and archeological materials using paleomagnetic directions