reflectance of dispersed vitrinite in palaeozoic rocks with and without cleavage implications for burial and thermal history modeling in the devonian of rursee area northern rhenish massif germany abstract vitrinite reflectance is used as coalification parameter in coals and as maturity and palaeotemperature indicator in sedimentary rocks in high grade diagenetic rocks i e rocks at the boundary between diagenesis and metamorphism vitrinites become increasingly anisotropic therefore it has been suggested to study maximum minimum reflectance instead of mean reflectance for rocks which reached this stage in the present study vitrinite reflectance data from a folded sequence of the northern rhenish massif germany are combined with microtectonic study of thin sections in samples in which both bedding and cleavage are present we show that vitrinites in different microtectonic domains cleavage domains and microlithons show significant differences in both maximum vitrinite reflectance and vitrinite reflectance anisotropy this behaviour is due to a strong partitioning of deformation in cleavage domains as compared to microlithons so that vitrinite reflectance is controlled by the thermal and deformation history accordingly estimation of maximum palaeotemperatures during burial should be based on vitrinite reflectance measurements in microlithons unaffected by deformation after maximum burial based on this finding burial and temperature history of the rursee area in the eastern rhenish massif is reconstructed numerical simulations indicate a maximum burial at the siegen ems boundary of about 5000 m and a maximum burial temperature of about 220 c

the east siberian basin in the silurian evidence for no large scale sea level changes according to conventional ideas numerous eustatic sea level changes occurred during the phanerozoic with amplitudes 20 100 m and periods t 1 3 myr third order cycles at the same time it is widely recognized that tectonic factors have an important role in such water depth changes rapid large scale sea level changes have been suggested for the silurian for which detailed and continuous stratigraphic successions are available in the east siberian sedimentary basin v2u10 6 km 2 in size these show slow deposition at depths 95 10 m proceeded for 10 20 myr in many regions and enable the mathematical analysis of maximum eustatic sea level changes with periods of t 1 3 myr third order that could have occurred during the silurian the amplitudes of such events could not exceed v20 30 m and for some epochs could not be larger than 8 10 m at the same time rapid water depth changes of up to v100 m occurred in some other cratonic areas as the silurian had a relatively stable sea level these must be attributed to rapid crustal uplift and subsidence the absence of third order eustatic fluctuations with amplitudes v10 20 m has also been demonstrated for the cambrian and earliest ordovician it is probable that no significant sea level changes also occurred at many other epochs while rapid changes in water depth resulted from large scale vertical crustal movements fl 2001 published by elsevier science b v

plate tectonic history basin development and petroleum source rock deposition onshore china abstract china comprises a mosaic of distinct continental fragments separated by fold belts these fold belts are suture zones resulting from the accretion of various fragments formerly separated by intervening areas of oceanic crust the major sedimentary basins onshore china can be classified into four groups those in western china are flexural developing as a result of north south compression in contrast those in the east are extensional and related to development of the pacific oceanic margin in central china basins have a more problematic origin those of north central china ordos sichuan are flexural basins controlled by eastward directed thrusting along their western margin in contrast basins further south chuxiong shiwandashan are predominantly extensional and related to major strike slip movements by synthesizing basin stratigraphies across china in tectonostratigraphic terms and in particular comparing the nature and timing of unconformities it is possible to formulate a coherent model for the palaeoreconstruction of china we identify five major tectonostratigraphic breaks which equate with the collision of the following continental fragments tarim north china carboniferous permian south china block permian triassic qiantang late triassic early jurassic lhasa block late jurassic early cretaceous and india early tertiary prior to permian times the southern margin of eurasia ran approximately along the northern border of modern china the late carboniferous collision of tarim north china with eurasia resulted in the development of a flexural basin junggar and deposition of non marine clastics to the south of the suture shallow marine deposition continued in the late permian early triassic the progressive collision from east to west of the south china block with the north china block resulted in a change to fluvial lacutrine sedimentation across the entire north china tarim block open marine carbonate deposition in the north of the south china block passed southward into a deeper marine clastic sequence deposited in a backarc basin further south a subduction zone existed along the southeastern margin of the south china block in western china northward subduction throughout the triassic resulted in the development of the songban ganzi accretionary prism with retroarc thrusting resulting in flexure and the first development of the tarim basin oblique collision of the qiantang block in the late triassic along the east of the south china block resulted in east west directed thrusting which initiated the suchuan and ordos basins continued strike slip deformation along the south western margin of the south china block resulted in the development of basins with a significant extensional component such as chuxiong the collision of the qiantang block with the southern edge of the tarim basin early jurassic resulted in a renewed clastic influx in both the tarim and junggar basins along the eastern pacific margin a compressional arc and retroarc basin in the south passed northwards into an extensional arc system subduction rollback of the extensional arc initiated rifting in the late jurassic in the eren and songliao basins the late jurassic early cretaceous collision of the lhasa block in the west rejuvenated the thrust systems bordering the western basin and resulted in a renewed clastic influx in the southeast the compressional arc phase culminated in widespread thrusting and folding of early cretaceous age in the northeast extension continued with the progressive migration of the rift system southward with time the arrival of the indian block in the early tertiary rejuvenated the bounding thrust belts of all the western basins in the east the change in convergence of the pacific plate to a more westerly direction is marked by extension and widespread rifting along the entire length of eastern china throughout most of china mesozoic and cenozoic deposition occurred in predominantly non marine environments source rocks in such settings comprise principally mudstones deposited in lakes organic rich mudstones these can accumulate in both deep and shallow lakes in order to accumulate substantial volumes the lake must be significant in space and time in china lacustrine orms occur in both rift and flexural basins lacustrine orms deposited under humid climatic conditions are restricted to the period of maximum tectonic subsidence in the flexural basins of western china source rock deposition follows basin initiation by 20 30 ma in the extensional basins of eastern china source rock deposition takes place 5 15 ma after basin initiation by contrast semi arid and arid climate lacustrine orms whilst being best developed during the period of maximum tectonic subsidence occur at all stages in the basin history

palaeoecology of transported brachiopod assemblages embedded in black shale cape phillips formation silurian arctic canada abstract brachiopod communities have been widely used for palaeoecological studies and reconstruction of sea level changes in earth history previous studies of brachiopod communities emphasised sampling benthic shelly fossils preserved in situ to avoid preservation bias silurian wenlock brachiopod assemblages are well preserved as debris turbidity flows including calcareous concretions embedded in thick sequences of black shale of the cape phillips formation with a mixture of deep water brachiopods and transported shallow water forms in this study the first attempt is made to use the transported assemblages to reconstruct silurian brachiopod communities that once lived along a palaeogradient from the shallow water arctic platform to the deep water franklinian basin seven transported brachiopod assemblages were recognised using multivariate analyses cluster analysis and principal components analysis with varying ratios of shallow versus deep water shells segregated according to their known palaeobathymetric ranges in other regions the wenlock early ludlow sea level fluctuations in the study area reconstructed using the percentage values of shallow and deep water brachiopod specimens as a proxy have a high degree of agreement with the arctic silurian sea level curve and moderate agreements with global sea level histories of other regions such as the british isles and gotland interpreted from graptolite abundance and diversity changes and sequence and event stratigraphical methods respectively

basin modeling meets rift analysis a numerical modeling study from the jeanne d arc basin offshore newfoundland canada abstract the jeanne d arc basin on the grand banks offshore newfoundland is a confined failed rift basin its initial development and burial history were controlled by crustal stretching and thinning this study provides a detailed analysis of the heat flow tectonic subsidence stretching factor maturation and temperature history based on 44 1d models and one full 4d space and time model in basin models the heat flow history is usually calculated from vitrinite reflectance vrr data however this causes uncertainties and reflects only the periods of sedimentation which where penetrated by wells therefore other methods should be used to reconstruct the early heat flow history not recorded by sediments in this study a discontinuous pure shear stretching model including radioactive heat production reflecting the timing and magnitude of stretching factors of crust and lithospheric mantle was applied to a 4d numerical model for the jeanne d arc basin it is the first time that this new technique is shown on a real case scenario and it gives new insights into the regional geodynamics results show that to understand the thermal evolution of the jeanne d arc sedimentary basin completely it is crucial to consider the triassic rift system this first rift generated the structural framework of the basin where most of the sediments were deposited the second extension in the cretaceous represents most likely an ultra slow extension phase with a heat impulse too weak to leave any thermal record this study demonstrates that the entire evolution of the jeanne d arc basin can be reconstructed assuming just one single triassic thermal rift additionally it shows the effects of a lateral heat transfer on the determination of stretching factors and thus on tectonic subsidence and the resulting heat flow history

fission track analysis of basement apatites at the western margin of the gulf of suez rift egypt evidence for synchroneity of uplift and subsidence fifty six apatite fission track ages and 52 horizontal confined track length measurements are reported from precambrian crystalline rocks along the western margin of the gulf of suez egypt ages fall in the range of ca 11 385 m y and older ages often occur within very close geographic proximity to younger ones indicating non uniform uplift the wide range in ages is accompanied by a systematic variation in the distribution of horizontal confined fission track lengths on the basis of apatite fission track ages and their length distributions data fall into three distinct groups group i ages ranging from 43 to 385 m y length distributions are all positively skewed and with decreasing age become progressively broader with shorter mean track length group ii ages ranging from 23 to 31 m y length distributions are negatively skewed with either a distinct tail or a small peak of short tracks group iii ages ranging from 11 to 20 5 m y length distributions are al unimodal narrow negatively skewed and have the longest mean lengths among samples studied apatite ages from groups i and ii are interpreted as mixed ages as a result of cooling during uplift from different levels within the apatite partial track annealing zone ages from group iii are interpreted as cooling ages due to uplift from the apatite total track annealing zone with minor partial annealing correcting the ages of the two oldest samples in this group for track length reduction yields ages of21 2 2and23 1 5m y it is proposed that the onset of rift flank uplift in the gulf of suez northern red sea area occurred between 21 and 23 m y ago fission track analysis in combination with subsidence data from the gulf of suez basin indicate that commencement of basement uplift postdate the start of rifting and is interpreted as evidence for passive rifting at the gulf of suez furthermore this uplift is contemporaneous with and is directly related to the process of extension and subsidence at the gulf of suez

cretaceous and cenozoic non marine deposits of the northern south yellow sea basin offshore western korea palynostratigraphy and palaeoenvironments abstract palynological analyses of two wells haema 1 and kachi 1 located in two sub basins of the northern south yellow sea basin have been carried out in order to establish a palynostratigraphic breakdown of the sedimentary succession and to determine environments of deposition seven assemblage zones and two assemblage subzones have been erected on the basis of frequency variations in and occurrences of biostratigraphically significant palynomorphs as follows classopollis ephedripites assemblage zone az barremian albian alisporites aquilapollenites penetetrapites az which is subdivided into an alisporites rugubivesiculites assemblage subzone cenomanian lower maastrichtian and an aquilapollenites penetetrapites assemblage subzone upper maastrichtian momipites coryluspollenites az paleocene caryapollenites inaperturopollenites az lower middle eocene quercoidites pinuspollenites az upper eocene liquidambarpollenites fupingopollenites magnastriatites az lower middle miocene graminidites persicarioipollis az pliocene the depositional environments represented by the well sections are considered to have been generally fluvio lacustrine and the climate to have varied between semi arid and wet and subtropical and warm temperate except during the late eocene and pliocene when a cool temperate climate prevailed six stages in the development of the sub basins are recognised these are 1 initial stage of rift or pull apart basin formation during the late jurassic cretaceous 2 subsidence from the paleocene to middle eocene 3 alternation of uplift and subsidence in the late eocene 4 synrift inversion and erosion through the oligocene 5 uplift during the early miocene and 6 widespread subsidence from the middle miocene onwards apart from during the early pliocene when the region was subjected to uplift once more

a flexural isostatic model of lithosphere shortening and foreland basin formation application to the eastern cordillera and subandean belt of nw argentina a numerical model of lithosphere shortening has been developed to combine flexural isostatic and structural balancing this allows us to quantitatively reconcile lithosphere shortening thrust sheet emplacement and foreland basin formation lithosphere shortening is accommodated by thrusting in the upper crust and by distributed deformation in the lower crust and the lithospheric mantle this leads to loading by thrust sheet emplacement crustal thickening and thermal perturbation additional loading and unloading are generated by sedimentation and erosion respectively the model is kinematically controlled each fault having its position geometry and movement prescribed the model is applied to the subandean late oligocene to recent foreland fold and thrust belt of nw argentina at 22 15 s the subandean belt of nw argentina contains three major stratigraphic units the lower middle and upper terciario subandino formations by modelling these formations we attempt to determine whether the terciario subandino group can be explained as a foredeep fill in response to thrust sheet loading and if so what is the required effective elastic thickness a successful model must predict not only foreland stratigraphy but also exhumation topography and crustal thickness we see a change in the wavelength of sedimentary deposition in the subandean basin through time that can be accounted for by a change in flexural rigidity accommodation space for the lower terciario subandino formation can be generated using an elastic thickness of 70 km for the middle upper terciario an elastic thickness of 15 km produces the correct basin geometries shortening estimates of 110 km have proved sufficient to generate the observed foreland stratigraphy bouguer anomaly and topography across the subandean belt and eastern cordillera however an additional 140 km of shortening is required to generate the observed bouguer anomaly and topography across the western andes this discrepancy could be due to earlier shortening in the western andes or to crustal thickening by magma addition

fluid inclusion technique for determining maximum temperature in calcite and its comparison to the vitrinite reflectance geothermometer theory laboratory experiments and empirical observation suggest that many aqueous fluid inclusions in calcite reequilibrate during overheating and therefore some homogenization temperatures t h record a temperature close to the maximum reached by the rock this characteristic suggests that aqueous fluid inclusions in calcite can be used to establish maximum temperature t peak to test this hypothesis we have compiled fluid inclusion t peak mean random vitrinite reflectance r m and present day t peak from 46 diverse geologic systems that have been at t peak from 10 4 to 10 6 yr present t peak ranged from 65 to 345 c t h modes and means ranged from 59 to 350 c and r m data ranged from 0 4 to 4 6 spanning the temperature and thermal maturity range associated with burial diagenesis hydrothermal alteration and low grade metamorphism plots of t h and t peak data for systems thought to be currently at maximum temperature demonstrate close agreement between t h and present t peak in sedimentary basins although caution should be applied the relation suggests that t h of aqueous fluid inclusions in calcite may be a useful measure of maximum temperature this study also compares t h to mean random vitrinite reflectance r m to offer further support for the use of t h as a measure of t peak and to provide a better understanding of r m t h correlates well with r m and results in a curve similar to r m vs t peak calibrations determined by other workers the strong correlation correlation coefficient r 0 93 between t peak and r m in these systems suggests that maximum temperature is the major control on thermal maturation

apatite fission track analysis apatite fission track aft analysis has been widely used during the past 30 years to constrain the low temperature thermal histories of many igneous metamorphic and sedimentary rocks in a wide range of geological settings applicable geological settings include orogenic belts rifted margins faults sedimentary basins cratons and mineral deposits the types of geologic problems that can be addressed include the timing and rates of tectonic events sedimentary basin evolution the timing of hydrocarbon generation and ore mineralization the absolute age of volcanic deposits the effects of major climatic changes on the near surface geothermal gradient and long term landscape evolution early work by naeser 1967 and wagner 1968 1969 first established the basic procedures that enabled the fission track dating method to be applied routinely to these geologic problems fleischer et al 1975 summarized the early studies of the broader discipline of nuclear track detection in different solid state materials more recent comprehensive overviews of fission track applications have been provided by naeser and mcculloh 1989 wagner and van den haute 1992 gallagher et al 1998 van den haute and de corte 1998 dumitru 2000 and gleadow et al 2002 etched natural fission tracks in several apatite grains are shown in figure 1 successful aft analysis is limited by the following 1 the availability of apatite from which useful aft data can be obtained often due to a lack of apatite of sufficient grain size and quality within available rock types or alternatively the lack of available rock samples due to minimal outcrop exposure or other reasons 2 economic considerations in terms of the time and money required to obtain sufficient aft data 3 the inherent limitations of aft data to resolve geological thermal history information often related to limited numbers of accumulated spontaneous fission tracks due to

early silurian sea level changes global sea level fluctuated markedly during the early silurian probably as a result of the waxing and waning of ice sheets in the south american portion of gondwana the highest sea levels of the silurian are recorded by the telychian upper crispus lower griestoniensis and spiralis lower lapworthi biozones other highstands occurred in the early aeronian during the convolutus zone mid aeronian guerichi zone and late turriculatus zone early telychian and early sheinwoodian low sea levels characterized much of the argenteus and sedgwickii zones aeronian the utilis subzone late guerichi early turriculatus zones early telychian the late telychian commencing in the mid lapworthi zone and after a period of apparently only small amplitude sea level fluctuations in the late sheinwoodian and earliest homerian the mid late homerian in particular the early nassa zone facies and faunal changes in the lower silurian do not support the p and s model of jeppsson and others but are consistent with the sea level changes proposed herein mid telychian marine red beds appear to have been deposited during a minor sea level fall immediately after a period of very high sea levels rather than during a transgressive episode as previously suggested comparison of the sea level curve presented herein with those constructed in the past is hampered by the lack of precision currently possible in the correlation of early silurian deep water graptolitic and shallow water shelly sequences improving the precision of this correlation should be a priority for future research

an overview of pre devonian petroleum systems unique characteristics and elevated risks abstract the radiation of land plants at the onset of the devonian resulted in a change in the character of available biomass which in turn introduced changes to the nature of petroleum systems this study examines the nature of pre devonian petroleum systems prior to this significant evolutionary event conventional hydrocarbon resources have been associated with pre devonian petroleum systems across the globe including the neoproterozoic infracambrian huqf supergroup of the oman basin the riphean vendian sequences of east siberia the cambrian of the murzuq basin the ordovician of the tarim basin and the silurian qusaiba of saudi arabia although individual accumulations can be quite significant e g hassi messaoud has ultimate recoverable reserves of 10 billion barrels the relative importance of pre devonian derived oils is thought to be limited compared to the global conventional resource base with growing interest in unconventional resources the relative importance of these systems is expected to increase as resource plays such as the ordovician utica shale of the appalachian basin the cambrian of china and possibly the silurian of central and eastern europe develop the advanced ages of these systems result in some unique properties and amplify risks that exist in younger petroleum systems differences in the nature of the biomass contributing to pre devonian source rocks may give rise to oils that display unique geochemical characteristics for example there are some precambrian oils where c 29 steranes dominate even though land plants were absent there are also ordovician source rocks dominated by gloeocapsamorpha prisca a primitive prokaryote which yield oils containing limited amounts of c 20 components and nearly lack pristane and phytane the potential for unconventional reservoirs in pre devonian systems may also be highly dependent upon the age of the system as biological evolution influences the availability and nature of biogenic silica an important factor controlling brittleness and fracability literature has shown that biogenic silica from different sources displays varying degrees of resistance to diagenesis which allows the formation of a silica network and influences brittleness for example radiolaria present during the cambrian are more resistant to diagenesis than diatoms which did not evolve until the jurassic risks associated with preservation of hydrocarbons are also amplified in pre devonian petroleum systems many such systems have been exposed to significant thermal stresses resulting in the cracking of oil and wet gas others have had complex tectonic histories potentially resulting in the breaching of seals or changes in pvt conditions that can result in gas loss gas loss may also occur through diffusion from these older reservoirs as a result of long residence times

the silurian dicoelosia communities temporal stability within an ecologic evolutionary unit abstract dicoelosia communities were a widely distributed high diversity type of brachiopod association that inhabited bioturbated muds in outer shelf settings benthic assemblage 4 5 a database from avalonia baltica and laurentia for the early silurian to early devonian shows that brachiopod species diversity in this major community type remained stable for a 30 million years interval during a single ecologic evolutionary unit eeu brachiopod species richness in local communities ranges mainly from 20 to 35 and shannon indices h per sample are mainly 1 5 2 5 with a maximum of 2 8 neither value shows any long term trend of stratigraphic increase or decrease stability in diversity is accompanied by persistence of the same functional morphotypes of brachiopods some genera particularly among orthida and strophomenida are present in the communities through all or most of their stratigraphic range while other genera particularly among smooth biconvex recliners show a pattern of temporal replacement within a morphotype dicoelosia communities appear and disappear in local areas as a consequence of changes in depositional facies but on the large scale of the three sampled plates they show no apparent changes related to silurian eustatic or other global oceanic events in general the history of dicoelosia communities corresponds to the model of ecologic stasis within an eeu this stasis is shown by species diversity and morphotype content and not by precise generic and specific composition data for the dicoelosia communities do not suggest a locked highly interactive ecologic structure and they are more compatible with a model of environmentally related recruitment in local areas from a widely distributed pool of offshore larvae

mesozoic cenozoic denudation and thermal history in the central uplift of the south yellow sea basin and the implications for hydrocarbon systems constraints from the csdp 2 borehole abstract this study focuses on the mesozoic cenozoic tectono thermal events in the central uplift of the south yellow sea basin sysb based on the csdp 2 borehole csdp 2 is the first borehole to penetrate the integrated paleozoic mesozoic sedimentary strata and recovered approximately 2736 m of core the drilling results confirm a significant stratigraphic hiatus i e indosinian unconformity between the neogene quaternary and the underlying lower triassic the eroded thickness estimated from sonic log and vitrinite reflectance data range from 1200 to 1400 m multiple paleo thermometer data from the csdp 2 cores including vitrinite reflectance apatite zircon fission track aft zft and fluid inclusions were used to reconstruct the mesozoic cenozoic thermal history in the study area there was a continuous heating process during the early mesozoic the peak paleo temperature may have reached up to 160 c base permian during the late jurassic with the highest paleo geothermal gradient of approximately 58 8 c km 1 the tectono thermal evolution was dominated by the mesozoic intracontinental collision between the yangtze craton and the sino korean platform the heating process was mainly caused by rapid burial on the passive continental margin and igneous activities the paleo temperature significantly decreased following the late jurassic two rapid cooling processes ca 100 65 ma and ca 35 ma are suggested by the aft modeling results cooling history indicates that the tectonic uplift and denudation likely occurred from the early cretaceous to the miocene the reconstruction results of thermal evolution confirm that the mesozoic paleozoic source rocks are mature or even highly mature and hydrocarbon generation migration and charge undoubtedly occurred in the central uplift showing substantial hydrocarbon potential moreover the reconstruction of the tectono thermal history provides important constraints for regional tectonic studies

early silurian glaciations in brazil abstract the opening of the brazilian paleozoic basins during the late ordovician was followed by a tectonic stabilization in the silurian at the time of the early silurian glaciations deposition of continental sandstones prevailed in the basins offshore environments were present in the amazonas basin and to a smaller extent in the parana basin the ice sheets advanced over fluviatile and littoral sediments except for the south margin of the amazonas basin where the glacial diamictites immediately overlie marine facies the ice produced much meltwater even when advancing and this was probably climatically controlled the ice movements were from the northwest at the northern margin of the amazonas basin and towards the northeast at the southern margin in the parnaiba basin and its outliers the jatoba basin and cariri valley the ice came from southeast and probably also from east further to the south in the parana basin it came from the north and northeast four glaciations have been dated to the early silurian the oldest is dated as latest ashgill and or earliest llandovery in the parana basin as evidenced from tillites in the upper rio ivai and lower vila maria formations including the former iapo formation it is contemporaneous with a glaciation in the cape basin south africa the next glaciation is dated as early middle llandovery gregarius graptolite zone and is present in the amazonas basin and the andean belt and probably also in the parnaiba basin and its outliers the two youngest tillites were widespread in the northern brazilian basins amazonas parnaiba and jatoba basins and cariri valley as well as in the andean belt and are dated as early late llandovery possibly starting already in the late middle llandovery and latest llandovery to earliest wenlock the latter tillite is the most widespread one assuming these glaciations are related to polar positions the apparent migration of the south pole ice cap must have been quite rapid from central north africa in late ashgill towards central brazil in the middle late llandovery the glaciation in the parana basin took place up to 45 from the late ashgillian south pole the cool climate continued during the silurian but no new glaciations are known before latest devonian

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

quantitative constraints on the rate of landform evolution derived from low temperature thermochronology in recent years the nature of the complex interactions between the solid earth and the overlying atmosphere has been the subject of much debate england and molnar 1990 whipple et al 1999 braun et al 1999 does erosion play an important role in the dynamics of mountain building is there a strong feedback into the balance of forces at the crustal scale from mass transport by erosional and depositional processes at the earth s surface or does erosion passively react to changes in the earth s surface topography to shape mountains with tectonic forces originating in the underlying convecting mantle dominating the dynamics of plate interactions and crustal deformation at convergent plate margins the answers to these fundamental questions lie in our ability to determine the rate at which surface processes can react to tectonic forcing whipple et al 1999 where erosion is efficient the coupling will be strong as the rate of change of surface loading by mass transport will be similar to the rate of creation of topography by crustal deformation this may lead to a concentration of deformation and thus exhumation in regions of intense erosion koons 1990 willett et al 1993 beaumont et al 2001 koons et al 2002 2003 braun and pauselli 2004 where erosion is relatively inefficient mountain building is the result of a balance between internal driving forces and those originating from the deflection of an upper free surface there is no feedback from erosional processes low temperature thermochronology such as u th he he or fission track ft dating in apatite and zircon provides information on the rate at which rocks cool as they are exhumed towards the cold earth surface duddy et al 1988 warnock et al 1997 farley 2000 reiners and farley 1999 because the

component concept for the study of the paleocommunities with an example from the early carboniferous of southern indiana u s a abstract predominantly suspension feeding faunas of three contemporaneous laterally contignous early carboniferous early mississippian facies are studied from exposures in southern indiana u s a each major taxonomic group is examined for the primary limiting factors controlling its distribution the paleoecology of the entire fauna is more easily evaluated from a component viewpoint five components are recognized with important limiting factors listed for each component as follows 1 organisms that lived at the sediment water interface which are influenced by sediment mobility and grain size including brachiopods bryozoans etc 2 organisms controlled by prevalent energy conditions such as crinoids 3 organisms controlled by turbidity such as sponges 4 commensal parasitic or predaceous organisms that are dependent upon the distribution of other organisms and 5 nektonic and planktonic organisms whose distribution and abundance are not only controlled by their original biological distribution but also by the depositional rate including fish and conodonts the distributions of different community components are independent however community integrity within a component is maintained from place to place at any time within a paleogeographic province

reproducibility of apatite fission track length data and thermal history reconstruction abstract the ability to derive detailed thermal history information from apatite fission track analysis is predicated on the reliability of track length measurements however insufficient attention has been given to whether and how these measurements should be standardized in conjunction with a fission track workshop we conducted an experiment in which 11 volunteers measured 50 track lengths on one or two samples one mount contained durango apatite with unannealed induced tracks and one contained apatite from a crystalline rock containing spontaneous tracks with a broad length distribution caused by partial resetting results for both mounts showed scatter indicative of differences in measurement technique among the individual analysts the effects of this variability on thermal history inversion were tested using the hefty computer program to model the spontaneous track measurements a cooling only scenario and a reheating scenario more consistent with the sample s geological history were posed when a uniform initial length value from the literature was used results among analysts were very inconsistent in both scenarios although normalizing for track angle by projecting all lengths to a c axis parallel crystallographic orientation improved some aspects of congruency when the induced track measurement was used as the basis for thermal history inversion congruency among analysts and agreement with inversions based on data previously collected was significantly improved further improvement was obtained by using c axis projection differences among inversions that persisted could be traced to differential sampling of long and short track populations among analysts the results of this study while demonstrating the robustness of apatite fission track thermal history inversion nevertheless point to the necessity for a standardized length calibration schema that accounts for analyst variation

post extinction recovery and diversification of reef dwelling brachiopod communities examples from the lower silurian of hudson bay basin canada abstract ziegler s 1965 early silurian brachiopod community zones and boucot s 1975 benthic assemblages have been instrumental in determining the community structures of early middle paleozoic level bottom communities but are difficult to apply to reef ecosystems due to the mixing of level bottom community assemblages in these systems in this study shannon and simpson diversity levels were calculated for reef dwelling brachiopod faunas from several north american and one european localities reef dwelling brachiopod diversity collapsed at the end of the ordovician and did not recover until the mid aeronian when modest diversity reef faunas appeared in the higher tropics reef dwelling brachiopods did not achieve high diversity levels until the telychian when reefs invaded the paleoequatorially located hudson bay and moose river basins the attawapiskat formation telychian contains the earliest known coral stromatoporoid reef complex with associated high diversity brachiopod faunas these faunas were separated into nine community associations through clustering and principal component analyses these associations can be further grouped into a level bottom type and a cryptic type based on dominant brachiopod taxa diversity levels average shell size and substrate type surprisingly the large species pentameroides septentrionalis was able to thrive in the relatively flat and open spaces of inter reef areas and among frame building corals and stromatoporoids within reef cores the absence of stricklandia within the attawapiskat formation is due to the high water temperature of the equatorial seas which were too warm to be invaded by this cool water dependent genus in addition the presence of deep water clorinda and gypidula in the shallow water attawapiskat reefs is explained by the lack of hurricane grade storms in the equatorial region which would be comparable to the quiet water conditions below storm wave base in higher latitudes

migration of igneous activities related to ridge subduction in southwest japan and the east asian continental margin from the mesozoic to the paleogene abstract in the inner zone of southwest japan the northern part of the median tectonic line mtl granites and their volcanic equivalents were formed in large quantities during the late cretaceous to early tertiary migration of magmatic activity related to ridge subduction is proposed to explain the widely distributed magmatism and its tectonics for this purpose the ages of granitic rocks were carefully inspected according to the criteria of the dating methods and procedures concerned and compiled with the sampling localities they clearly show a trend in rock ages along the mtl in agreement with the general direction of strikes in southwest japan from the trend of the ages and the cooling histories of the bodies it was concluded that the magmatism migrated eastward along the mtl with a rate of 30 km m y this migration concept is extended to the mesozoic igneous rocks of the east asian continental margin there two magmatic belts ranging in age from mesozoic to paleogene are found to become younger northeastward along the margins which is ascribed to the subduction of the farallon izanagi and kula pacific ridges

annealing kinetics of fission tracks in zircon an experimental study a series of laboratory annealing experiments on zircon fission tracks has been carried out under heating conditions of 350 750 c for 10 1 103 hr i e 4 5 min 40 days variation in the confined lengths of spontaneous fission tracks was determined using zircon grains from nisatai dacite the fading contours of normalized mean track length r on the arrhenius diagram showed as sets of straight lines we performed a series of model fittings called the parallel and fanning models in order to describe the decrease in r with increasing temperature or heating time the lowest temperature limit of the zircon partial annealing zone zpaz was defined as r 0 95 and the highest as r 0 4 which approximately corresponded to the total fading of surface tracks extrapolation of the results of the laboratory experiments to the geological timescale gives for a heating duration of 106 yr estimated values of the zpaz of 210 320 c 60 c 2 with the parallel model 190 350 c 50 c 2 with the fanning model critical temperature t0 and 170 390 c 50 c 2 with the fanning model t0 the temperatures of the zpaz decrease by 20 c for an annealing duration that is an order of magnitude longer because the estimated closure temperature of zircon fission track analysis approximately corresponds to the middle of the zpaz these results support the previously estimated closure temperature of 240 c by varying the etching time it was revealed that significant removal of radiation damage occurs at r 0 93

mesozoic tertiary exhumation history of the altai mountains northern xinjiang china new constraints from apatite fission track data abstract this study uses apatite fission track ft analysis to constrain the exhumation history of bedrock samples collected from the altai mountains in northern xinjiang china samples were collected as transects across the main structures related to palaeozoic crustal accretion events ft results and modeling identify three stages in sample cooling history spanning the mesozoic and tertiary stage one records rapid cooling to the low temperature part of the fission track partial annealing zone circa 70 10 c stage two records a period of relative stability with little if any cooling taking place between 75 and 25 20 ma suggesting the altai region had been reduced to an area of low relief support for this can be found in the adjacent junngar basin that received little if any sediment during this interval final stage cooling took place in the miocene at an accelerated rate bringing the sampled rocks to the earth s surface this last stage linked to the far field effects of the himalayan collision most likely generated the surface uplift and relief that define the present day altai mountains

a field based estimate of the zircon fission track closure temperature abstract a field based estimate of the zircon fission track closure temperature is proposed from 13 zircon fission track cooling ages of the gold butte block se nevada using previously published and new thermochronological data the thermal history of the gold butte block is re evaluated resulting in a geothermal gradient estimate of 20 3 c km and a slow cooling rate of 0 55 0 02 c m y from the late jurassic to the early miocene before onset of rapid miocene cooling the rapidly cooled part of the gold butte block provides a slip rate of 10 5 km m y of the hanging wall that caused the miocene exhumation of this crustal section assuming these thermal conditions are correct the closure temperature of the zircon fission track system is determined at 205 18 c which is in good agreement with previous field based estimates because of the variation in zircon fission track annealing behavior with radiation damage field studies are a suitable way to calibrate the closure temperature of the zircon fission track system

communities and paleoecology of eifelian mid devonian brachiopods from the bird fiord formation of arctic canada the carbonate siliciclastic strata in the bird fiord formation of arctic canada contain a diverse brachiopod dominated biota a collection of 46 381 brachiopods from 126 sites at 35 localities on ellesmere island north kent island grinnell peninsula devon island and bathurst island includes 22 species assigned to 21 genera many of these taxa are endemic to arctic canada each collection of brachiopods is typically dominated by only one or two taxa cluster analysis based on binary data shows that the brachiopods can be divided into an atrypa elythyna community group and a spinatrypina desquamatia community group the former encompasses the atrypa elythyna and atrypa elythyna perryspirifer communities and the latter includes the spinatrypina desquamatia and spinatrypina desquamatia cranaena communities the distribution of these communities was primarily related to water depth thus the atrypa elythyna community group which belongs to benthic assemblage 3 lived in a shallow proximal shelf envi

silurian thalassinoides in an offshore carbonate community wisconsin usa abstract silicified boxwork of the ichnogenus thalassinoides in the silurian wenlockian racine formation milwaukee wisconsin usa represents open burrow systems that extended decimeters below the sediment surface in offshore carbonate muds of an intracratonic basin the most completely silicified burrows contain a core of organic rich spiculitic chert a surrounding zone of chert and an outer zone of mixed chert and dolomite burrows reach 3 cm in diameter and include larger turning chambers they were probably produced by an arthropod bioturbation affected the epibenthic fauna by extensive vertical mixing of skeletal material and possibly by construction of small mounds at the sediment surface the same skeletal fauna of siliceous sponge spicules silicified crinozoan ossicles and a diverse array of other groups occurs in both burrows and surrounding dolomite matrix brachiopods including dicoelosia and skenidioides indicate silurian benthic assemblage 5 which represents an outer shelf setting trilobite sclerites are more common within thalassioides burrows than in the surrounding matrix two enrolled calymenid individuals and one molted calymenid exoskeleton occur within thalassinoides suggesting that commensal trilobites occupied the burrow systems

structural development and tectonic evolution of gunsan basin cretaceous tertiary in the central yellow sea abstract this study analyzes the structural development of the gunsan basin in the central yellow sea based on multi channel seismic reflection profiles and exploratory well data the basin comprises three depressions the western central and eastern subbasins filled with a thick ca 6000 m cretaceous to paleogene nonmarine succession it was initiated in the early cretaceous due to intracontinental extension caused by oblique subduction of the izanagi plate under the eurasian plate and sinistral movement of the tan lu fault the basin appears to have undergone transtension in the late cretaceous eocene caused by dextral movement of the tan lu and its branching faults the transtension was accommodated by oblique intra basinal normal faults and strike slip or oblique slip movement of a ne trending bounding fault in the northern margin of the central subbasin the entire basin was deformed ne sw contraction in the oligocene when tectonic inversion occurred possibly due to the changes in strike slip motion from right to left lateral of the tan lu fault during the early miocene extension resumed by reactivation of the pre existing normal and transpressional faults a combination of extension uplift and erosion resulted in differential preservation of the early miocene succession at the end of the early miocene extension ceased with mild contraction and then the basin thermally subsided with ensued rise in sea level

initial constraints on the timing of granitic magmatism in north korea using u pb zircon geochronology abstract the geology of north korea is very poorly known in this paper twenty seven granitic samples from the tumangang belt and the rangnim massif including diorite granodiorite and monzogranite were selected for in situ zircon u pb isotopic dating in the tumangang belt granites formed mainly in the jurassic with one sample giving a triassic age this is contrary to previous views that considered the granites to be permian to triassic in age in the rangnim massif precambrian granitic magmatism mainly took place at 2 1 and 1 9 1 8 ga no archean emplacement ages have been documented in this study although some inherited discordant zircon may be of this age mesozoic magmatism in this area can be divided into three stages with ages of 234 213 173 and 114 109 ma the triassic granites are mostly exposed in the north and the early cretaceous ones in the west the distribution of jurassic granites is less well documented and only one sample was identified in this study however previous data indicate they are more widely distributed in the area the 2 1 and 1 9 1 8 ga precambrian ages are comparable to paleoproterozoic magmatism in northeastern china indicating that the rangnim massif was most likely part of the north china craton during that time however the absence of 2 5 ga granites and the occurrence of 1 2 ga granites indicate that the rangnim massif was probably at the margin of the north china craton and affected by mesoproterozoic magmatism the similarity in age patterns of the mesozoic granites in north korea to surrounding areas of south korea and the liaodong peninsula of northeastern china indicate that they were controlled by subduction of the pacific ocean under eastern asia however roll back or retreat of the subduction zone resulted in a younging trend from northwest to southeast during the cretaceous

magnetostratigraphy and luminescence dating on a sedimentary sequence from northern east china sea constraints on evolutionary history of eastern marginal seas of china since the early pleistocene owing to the large and increasing population density in low lying coastal regions even small changes in sea level can have substantial societal and economic impacts alternations of terrestrial and marine sediments deposited in coastal areas or continental shelves are important and effective indicators of sea level changes and thus have been widely studied in the marginal seas of china over the past 30 years however sea level change results from not only eustatic factors but also tectonic activity the zhe min or zhejiang fujian uplift zmu was such an important factor in geomorphology and formed a barrier preventing entry of sea water into the northern marginal seas of china but its quaternary history is poorly known

onshore offshore structure and hydrocarbon potential of the south yellow sea abstract recent high resolution airborne gravity data taken over the south yellow sea and its western onshore offshore transition zone combined with ground gravity data taken over the onshore area subei basin china show that the south basin of the south yellow sea and the subei basin correspond to the same gravity low anomaly magnetic data also support our interpretations both areas have similar strata structures and hydrocarbon potential and form a large cenozoic terrestrial sedimentary basin controlled by the tanlu fault cenozoic terrestrial strata are well developed in the south basin of the south yellow sea and thick meso paleozoic marine strata are preserved in the central uplift area future hydrocarbon exploration in the south yellow sea should focus on the cenozoic continental sequence especially the paleogene in the south basin as well as the meso paleozoic marine rocks in the central uplift area the western part of the middle depression and middle and western parts of the north depression in the south basin of the south yellow sea have the greatest potential for hydrocarbon accumulation

mantle dynamics of western pacific and east asia insight from seismic tomography and mineral physics abstract recent results of high resolution seismic tomography and mineral physics experiments are used to study mantle dynamics of western pacific and east asia the most important processes in subduction zones are the shallow and deep slab dehydration and the convective circulation corner flow processes in the mantle wedge the combination of the two processes may have caused the back arc spreading in the lau basin affected the morphology of the subducting philippine sea slab and its seismicity under southwest japan and contributed to the formation of the continental rift system and intraplate volcanism in northeast asia which are clearly visible in our tomographic images slow anomalies are also found in the mantle under the subducting pacific slab which may represent a small mantle plumes b upwellings associated with the slab collapsing down to the lower mantle or c sub slab dehydration associated with deep earthquakes caused by the reactivation of large faults preserved in the slab combining tomographic images and earthquake hypocenters with phase diagrams in the systems of peridotite water we proposed a petrologic model for arc volcanism arc magmas are caused by the dehydration reactions of hydrated slab peridotite that supply water rich fluids to the mantle wedge and cause partial melting of the convecting mantle wedge a large amount of fluids can be released from hydrated morb at depths shallower than 55 km which move upwards to hydrate the wedge corner under the fore arc and never drag down to the deeper mantle along the slab surface slab dehydration reactions at 120 km depth are the antigorite related 5 reactions which supply water rich fluids for forming the volcanic front phase a and mg surssasite breakdown reactions at 200 and 300 km depths below 700 c cause the second and third arcs respectively moreover the dehydration reactions of super hydrous phase b phases d and e at 500 660 km depths cause the fluid transportation to the mantle boundary layer mbl 410 660 km depth the stagnant slabs extend from japan to beijing china for over 1000 km long indicating that the arc trench system covers the entire region from the japan trench to east asia we propose a big mantle wedge bmw model herein where hydrous plumes originating from 410 km depth cause a series of intra continental hot regions fluids derived from mbl accumulated by the double sided subduction zones rather than the india asia collision and the subsequent indentation into asia are the major cause for the active tectonics and mantle dynamics in this broad region

thermal control on post orogenic extension in collision belts abstract intracontinental extension develops in two different ways in the rhine graben the baikal or the east african rifts it is localized in a long and narrow zone along a few normal faults which often delineate a single graben in contrast in the basin and range province or the tibetan plateau it is distributed over a much broader area up to more than 1000 km across this difference arises from differences in rheology and applied forces widespread extension probably reflects the thinning of a previously thickened crust geological observations indicate that only wide orogenic belts undergo late or post orogenic thinning a related fact is that anatectic granites seem to be most abundant in wide orogenic belts the general correlation between belt width and occurrence of both extension and anatectic granites suggest that it reflects in part the characteristics of horizontal heat transfer between thickened crust and surroundings in wide orogenic plateaux the large amount of heat produced in the crust by radioactive decay and lack of erosion leads to high temperatures in narrow mountain belts horizontal heat transfer and high erosion rates concur to prevent temperatures from rising to values at which the crust may yield in extension we have tested this hypothesis using transient two dimensional numerical models of orogenic belts focussing on the effects of the shortening rate the final width of the belt and the rate of crustal radiogenic heat production in the range of geological values the shortening rate has little influence on the results crustal temperatures increase as a function of belt width we find that the sensitivity of crustal temperatures to belt width is most pronounced in the 100 300 km width range and for large values of crustal heat generation the pressure temperature paths followed by geological formations depend on the belt width which is consistent with available data the integrated shear strength of the lithosphere decreases with time as the belt is being built and then eroded this evolution is sensitive to belt width if extension occurs when the integrated shear strength drops below a critical value our results yield a framework for comparing different orogenic belts we predict that extension starts late in the history of wide belts and never occurs in narrow belts a final implication of this study is that the average rate of crustal heat production is probably close to 1 1 10 6 w m 3 which is in the upper range of possible values we present a simple and convenient diagram summarizing the thermal characteristics of orogenic belts as a function of width and shortening rate