wetlands at the last glacial maximum distribution and methane emissions the global distribution of potential wetlands and their methane ch4 emissions at the present day and the last glacial maximum lgm are estimated using a gcm simulation of lgm climate a vegetation model and simple algorithms for determining wetland area based on topography and soil moisture and ch4 emissions based on ecosystem carbon turnover in wet soils lgm wetland area was 15 larger than present but ch4 emissions were 24 less extensive wetlands were simulated on the exposed continental shelves the soil ch4 sink was simulated as 14 tg now but 0 5 tg at the lgm ch4 emissions at lgm were limited by substrate availability in turn due to low atmospheric co2 the glacial interglacial change in atmospheric ch4 concentration cannot be completely attributed to changes in the wetland source

late cenozoic bending of the bolivian andes new paleomagnetic and kinematic constraints 1 new paleomagnetic measurements of essentially undeformed late cenozoic volcanic rocks in the bolivian andes south america constrain rigid body rotations about vertical axes during the last 13 myr on both limbs of the bolivian orocline in the eastern cordillera thermal and alternating field demagnetization was carried out on samples from 52 sites in three major volcanic complexes 1 13 2 ma los frailes ignimbritic volcanics outcropping at 19 5 s 2 9 5 ma morococala ignimbritic volcanics outcropping at 18 s and 3 13 5 ma shoshonitic to acidic lavas and intrusives outcropping at 17 5 s well defined magnetic components were isolated which are interpreted to represent the earth s magnetic field at the time of volcanic activity the mean magnetic vector for site groupings suggests regional tectonic rotations about vertical axes with respect to stable south america of 10 8 clockwise for the 13 2 ma los frailes volcanic complex 8 9 clockwise for only the miocene 13 5 ma los frailes volcanics and 1 18 anticlockwise for the combined 13 5 ma morococala and eucalyptus volcanic complexes these data are consistent with observed shortening gradients on the eastern margin of the bolivian andes in the sub andean zone suggesting rotation and shortening are synchronous a joint inversion for both tectonic rotation and the amount of shortening assuming a linear variation in the amount of rotation along the length of the southern limb of the bolivian orocline shows that rotation of the eastern cordillera in the last 10 15 myr relative to stable south america varies from zero at the oroclinal hinge at 18 s to a maximum of 13 5 clockwise at 22 s decreasing to zero south of 23 s with an average rotation in the range 5 to 10 clockwise concomitant with this shortening in the sub andean zone decreases from a maximum of 86 km at the oroclinal hinge to 47 km at 22 s and then 33 km at 23 s the lack of evidence for large scale internal faulting in the eastern cordillera since 9 ma suggests either bending of the eastern cordillera was accommodated by more distributed small scale faulting or that relative rotation here mainly occurred prior to 9 ma the small average rotation of the eastern cordillera on the southern limb of the orocline is consistent with only very small rotation 10 of the forearc region in northern chile during the last 20 myr rotation of the northern limb is less well constrained but it is also likely to be small 5 and anticlockwise

an integrated ams structural palaeo and rock magnetic study of eocene marine marls from the jaca pamplona basin pyrenees n spain new insights into the timing of magnetic fabric acquisition in weakly deformed mudrocks

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

a note on the relationship between ice core methane concentrations and insolation 1 we re examine the link between july 30 n insolation and methane in the vostok ice core based on this link ruddiman 2003 suggested that an anthropogenic source of methane must have been present after 5 kyr bp in order to prevent concentrations from declining as insolation decreased through the holocene we conclude however that since precessional forcing does not explain the large glacial interglacial excursions the component of methane variability associated with precession is significantly smaller than assumed by ruddiman 2003 the implied decrease from 10 kyr bp to the present associated with precession alone is 60 ppbv or less we argue that increased emissions controlled by northern wetlands and river delta development likely contributed to the observed increase consistent with similar stable ch4 levels at mis 11 in the vostok and dome c records therefore a significant anthropogenic input is not obviously required to explain the late holocene record

palaeomagnetism petrology and geochronology of tertiary magmatic and sedimentary units from iran abstract an amount of 160 samples from igneous and sedimentary formations of palaeocene or eocene age was collected in iran northeast of the zagros belt palaeomagnetic analyses petrological studies and k ar dating indicate palaeocene and eocene palaeomagnetic directions in the zabol baluch region east iranian range and show that the area remained approximately stable with respect to the eurasian and african plates from the beginning of the cainozoic era conversely large post eocene deformations occurred in central iran these large rotations are both clockwise and anti clockwise they might have resulted from lateral shears between arabia and northeast iran the central elburz underwent a large clockwise rotation which is probably late oligocene in age as a whole our results show that the so called persian plate did not exist during the cainozoic era

atmospheric methane variability centennial scale signals in the last glacial period in order to understand atmospheric methane ch4 biogeochemistry now and in the future we must apprehend its natural variability without anthropogenic influence samples of ancient air trapped within ice cores provide the means to do this here we analyze the ultrahigh resolution ch4 record of the west antarctic ice sheet divide ice core 67 2 9 8 ka and find novel atmospheric ch4 variability at centennial time scales throughout the record this signal is characterized by recurrence intervals within a broad 80 500 year range but we find that age scale uncertainties complicate the possible isolation of any periodic frequency lower signal amplitudes in the last glacial relative to the holocene may be related to incongruent effects of firn based signal smoothing processes within interstadial and stadial periods the peak to peak signal amplitudes vary in proportion to the underlying millennial scale oscillations in ch4 concentration the relative amplitude change is constant we propose that the centennial ch4 signal is related to tropical climate variability that influences predominantly low latitude wetland ch4 emissions

on the origin and timing of rapid changes in atmospheric methane during the last glacial period we present high resolution records of atmospheric methane from the gisp2 greenland ice sheet project 2 ice core for four rapid climate transitions that occurred during the past 50 ka the end of the younger dryas at 11 8 ka the beginning of the bolling allerod period at 14 8 ka the beginning of interstadial 8 at 38 2 ka and the beginning of interstadial 12 at 45 5 ka during these events atmospheric methane concentrations increased by 200 300 ppb over time periods of 100 300 years significantly more slowly than associated temperature and snow accumulation changes recorded in the ice core record we suggest that the slower rise in methane concentration may reflect the timescale of terrestrial ecosystem response to rapid climate change we find no evidence for rapid massive methane emissions that might be associated with large scale decomposition of methane hydrates in sediments with additional results from the taylor dome ice core antarctica we also reconstruct changes in the interpolar methane gradient an indicator of the geographical distribution of methane sources associated with some of the rapid changes in atmospheric methane the results indicate that the rise in methane at the beginning of the bolling allerod period and the later rise at the end of the younger dryas were driven by increases in both tropical and boreal methane sources during the younger dryas a 1 3 ka cold period during the last deglaciation the relative contribution from boreal sources was reduced relative to the early and middle holocene periods

responses to rapid warming at termination 1a at gerzensee central europe primary succession albedo soils lake development and ecological interactions the transition from the oldest dryas to the bolling around 14 685 cal yr bp was a period of extremely rapid climatic warming from a single core of lake marl taken at gerzensee switzerland we studied the transition in stable isotopes of oxygen and carbon on bulk sediment and charophyte remains as well as on monospecific samples of ostracods after pisidium a in addition pollen chironomids and cladocera were analyzed the 18o record serves as an estimate of mean air temperature and by correlation to the one from ngrip in greenland it provides a timescale the timing of responses the statistically significant zone boundaries of the biostratigraphies are telescoped at the rapid increase of about 3 in 18o at the onset of bolling biotic responses may have occurred within sampling resolution 8 to 16 years although younger zone boundaries are less synchronous gradual and longer lasting responses include complex processes such as primary or secular succession during the late glacial interstadial of bolling and allerod two stronger and two weaker cool phases were found biological processes involved in the responses occurred on levels of individuals e g pollen productivity of populations increases or decreases immigration or extinction and on the ecosystem level species interactions such as facilitation or competition abiotic and biotic interactions include pedogenesis nitrogen fixation nutrient cycling catchment hydrology water chemistry of the lake and albedo controlled by the transition from tundra to forest for the swiss plateau this major change in vegetation induced a change in the mammal fauna which in turn led to changes in the tool making by paleolithic people

subglacial methanogenesis a potential climatic amplifier 1 subglacial environments are a previously neglected component of the earth s global carbon cycle a reflection of the view held until recently that they are dominated by abiotic and oxic conditions here we provide a realistic assessment of the theory that the basal regions of the ice sheets that formed over north america and europe during glaciations were host to significant populations of anaerobic microorganisms including methanogens able to metabolize organic carbon sequestered during interglacials and overridden during quaternary glacials in doing so we review the current evidence for subglacial methane release during deglaciation estimate the size of the subglacial reservoir of organic carbon soc and assess the amount of soc available to subglacial microbes and the likely pathways and rates of carbon turnover we then discuss the fate of subglacial methane and the potential impact of its release on atmospheric methane concentrations we calculate that the soc equates to 418 610 pg c and includes carbon from terrestrial soils vegetation peatlands lake and marine sediments the soc that is potentially available for microbial conversion to methane is smaller than this estimate due to 1 glacial erosion 2 accumulation of recalcitrant organic carbon compounds over time 3 conversion to carbon dioxide by aerobic anaerobic respiration and 4 incomplete conversion of labile organic matter to methane we estimate that the total soc available for conversion to methane is 63 pg c our estimates of methane production potentials span a wide range because of the current uncertainty surrounding subglacial metabolic rates we believe however that there is a strong likelihood that subglacial microbes could convert 63 pg of soc to methane during a glacial cycle if this were the case release of this methane from the ice sheet margins during retreat would need to be episodic in order to significantly impact atmospheric methane concentrations our findings suggest that it may well be important to consider subglacial environments as active components of the earth s carbon cycle conclusive determination of the potential impact of subglacial methane production on atmospheric methane concentrations during deglaciation however awaits more precise determination of the ability of subglacial microbes to degrade organic carbon components and their associated rates of metabolism under in situ conditions

magnetic fabric of clay sediments from the external northern apennines italy abstract we report on the anisotropy of magnetic susceptibility ams analyses of fine grained sediments deposited during the messinian in foredeep basins at the front of the northern apenninic chain the data refer to 32 sampling sites mostly distributed in the fine grained intervals of the laga and colombacci formations extending along the belt for a total length of about 300 km rock magnetism analyses indicate that the magnetic susceptibility and its anisotropy are in most cases dominated by the paramagnetic minerals of the clay matrix in order to delineate the contribution of the ferrimagnetic fraction to the overall susceptibility fabric the anisotropy of the anhysteretic remanent magnetisation was investigated at some representative sites the magnetic fabric of the studied sediments mostly reflects the effects of compaction showing a predominant magnetic foliation parallel to the bedding plane at all the sites a well distinct magnetic lineation was also found which is parallel to the fold axes and thrust fronts both at local and regional scales this feature is maintained in sequences that differ for sedimentological character and age implying that the magnetic lineation was produced by a mild tectonic overprint of the primary sedimentary compactional fabric the relationship between the magnetic lineation trends and the vertical axis rotations detected by speranza et al speranza f sagnotti l mattei m 1997 j geophys res 102 3153 3166 indicates that the magnetic lineation formed during the compressive phases of the messinian early pliocene when the apenninic front was almost rectilinear and oriented n320

onset of subduction as the cause of rapid pliocene quaternary subsidence in the south caspian basin backstripping a representative stratigraphic column from the northwest of the south caspian basin shows that 2 4 km of tectonic subsidence has occurred since ca 5 5 ma at 1 5 10 times the rate recorded in typical foreland basins roughly half the basin s sedimentary thickness of 20 km has accumulated in this time while the upper part of the succession has begun to deform by buckle folding the south caspian basement appears to be either thick oceanic crust or thinned high velocity continental crust seismicity and gravity data indicate that the basement is in the initial stages of subduction under the middle caspian region to the north we propose that basement subduction began ca 5 5 ma to create the major pliocene quaternary subsidence subduction may have been triggered by a regional reorganization in the arabia eurasia collision at that time possibly following the construction of the turkish iranian plateau

kinematic links between the eastern mosha fault and the north tehran fault alborz range northern iran kinematic interaction of faults is an important issue for detailed seismic hazard assessments in seismically active regions the eastern mosha fault emf and the north tehran fault ntf are two major active faults of the southern central alborz mountains located in proximity of tehran population similar to 9 million we used field geomorphological and paleoseismological data to explore the kinematic transition between the faults and compare their short term and long term history of activity we introduce the niknamdeh segment of the ntf along which the strike slip kinematics of emf is transferred onto the ntf and which is also responsible for the development of a pull apart basin between the eastern segments of the ntf the ira trench site at the linkage zone between the two faults reveals the history of interaction between rock avalanches active faulting and sag pond development the kinematic continuity between the emf and ntf requires updating of seismic hazard models for the ntf the most active fault adjacent to the tehran metropolis study of offsets of large scale morphological features along the emf and comparison with estimated slip rates along the fault indicates that the emf has started its left lateral kinematics between 3 2 and 4 7 ma according to our paleoseismological data and the morphology of the nearby emf and ntf we suggest minimum and maximum values of about 1 8 and 3 0 mm year for the left lateral kinematics on the two faults in their linkage zone averaged over holocene time scales our study provides a partial interpretation based on available data for the fault activity in northeastern tehran region which may be completed with studies of other active faults of the region to evaluate a more realistic seismic hazard analysis for this heavily populated major city c 2014 elsevier b v all rights reserved

n2o and ch4 variations during the last glacial epoch insight into global processes 1 greenhouse gas measurements along polar ice cores provide important insight into the former composition of the atmosphere its natural variations and the responses to fast climatic changes in the past we present high resolution nitrous oxide n2o and methane ch4 records measured along two ice cores from central greenland covering part of marine isotope stages 3 and 4 in the last glacial epoch the n2o data confirm the hypothesis that n2o shows variations in phase to fast climatic changes observed in the northern hemisphere the so called dansgaard oeschger d o events variations exist not only for events with a long duration 1500 years and more but also for the shorter ones the comparison with ch4 unveils interesting differences between the response of ch4 and n2o to d o events while the average amplitudes of ch4 oscillations associated with d o events are similar to those of the northern hemisphere summer insolation the magnitude of the n2o concentration change instead correlates with the duration of the d o events the records give further insight into the timing of concentration changes at the beginning of d o events they show that for long lasting events the n2o concentration starts to increase before both the sharp increase in the ch4 concentration and the temperature reconstructed for greenland

groundwater in the earth s critical zone relevance to large scale patterns and processes although we have an intuitive understanding of the behavior and functions of groundwater in the earth s critical zone at the scales of a column atmosphere plant soil bedrock along a toposequence ridge to valley and across a small catchment up to third order streams this paper attempts to assess the relevance of groundwater to understanding large scale patterns and processes such as represented in global climate and earth system models through observation syntheses and conceptual models evidence are presented that groundwater influence is globally prevalent it forms an environmental gradient not fully captured by the climate and it can profoundly shape critical zone evolution at continental to global scales four examples are used to illustrate these ideas 1 groundwater as a water source for plants in rainless periods 2 water table depth as a driver of plant rooting depth 3 the accessibility of groundwater as an ecological niche separator and 4 groundwater as the lower boundary of land drainage and a global driver of wetlands the implications to understanding past and future global environmental change are briefly discussed as well as critical discipline scale and data gaps that must be bridged in order for us to translate what we learn in the field at column hillslope and catchment scales to what we must predict at regional continental and global scales

changes in the atmospheric ch4 gradient between greenland and antarctica during the last glacial and the transition to the holocene significant variations in the interpolar difference of atmospheric ch4 concentration over the holocene period were observed by chappellaz et al 1997 here we extend this study to the last glacial and the transition to the holocene we observe a gradient of 3 4 parts per billion by volume ppbv during the last glacial maximum it increases to 26 10 ppbv during the bolling allerod and remains at 26 9 ppbv during the younger dryas cold period on average we find an interpolar difference of 14 4 ppbv during the cold phases and of 37 10 ppbv during the warm periods of the last glacial with a three box model we derive from the measured gradients the contributions of methane from the tropics and the mid to high latitudes of the northern hemisphere the tropics have been the largest source in all glacial epochs the contribution by the northern latitudes have been very small during the last glacial maximum but surprisingly large during the earlier part of the glacial epoch the model result suggests completely unexpected that the higher atmospheric ch4 concentration during the warm dansgaard oeschger events are caused by a higher source strength of the northern latitudes and not of the tropics

bending the bolivian orocline in real time global positioning system gps data from the central andes record vertical axis rotations that are consistently counterclockwise in peru and bolivia north of the bend in the mountain belt and clockwise to the south in southern bolivia argentina and chile these geologically instantaneous rotations have the same sense as rotations that have accrued over millions of years and are recorded by paleomagnetic and geologic indicators the change in sign of the rotation at both decadal and million year time scales occurs across the axis of topographic symmetry that defines the bolivian orocline when extrapolated to a common time interval the magnitudes of rotation from geologic features and from gps are surprisingly similar given that a significant part of the instantaneous deformation field is probably elastic and due to interseismic locking of the plate boundary some of the interseismic deformation field must reflect permanent deformation and or some of the current elastic deformation will be converted to upper plate permanent deformation over time rather than be recovered by elastic rebound during interplate earthquakes we suggest that the spatial patterns of the elastic and the permanent modes of bending are similar because they are driven by the same stress field

the origin of tectonic lineation in extensional basins combined neutron texture and magnetic analyses on undeformed clays abstract in extensional sedimentary basins fine grained sediments that appear undeformed at the outcrop scale can carry a magnetic fabric consistent with the regional deformation pattern the origin of the magnetic lineation which is often found in extensional basins is not yet well understood in clays from extensional basins in southern italy the magnetic lineation is tectonically controlled and oriented perpendicular to the main normal faults a combined analysis of magnetic and mineral fabrics was made to gain insight into the processes that lead to a lineation in extensional settings low field high field and low temperature susceptibility measurements were used to distinguish the ferrimagnetic and paramagnetic contributions to the magnetic susceptibility and its anisotropy the magnetic anisotropy of the sediments is predominantly carried by paramagnetic phyllosilicates neutron texture analysis was used to evaluate the spatial distribution of chlorite basal planes results demonstrate that the orientation of the magnetic lineation is related to the spatial distribution of chlorite lying parallel to the common axis of differently oriented basal planes a quantitative correlation between the magnetic and rock fabric was made comparing the low and high field magnetic anisotropy ams hfa to the theoretical anisotropy calculated from the chlorite preferred orientation a good linear correlation is found between the degree of theoretical anisotropy and the ams and hfa results show that the integrated approach of magnetic and mineral fabric investigations represents a valid alternative tool for detecting grain scale and regional deformation patterns in weakly deformed extensional basins where macroscopic evidence of deformation is often not visible

sea level induced variations in clay mineral composition in the southwestern south china sea over the past 17 000 yr variations in clay mineral composition of sediment cores from the margin and continental slope of the sunda shelf southern south china sea se asia covering the past 17 000 yr reflect changing influences of sediment sources together with clay mineral partitioning processes in shallow waters we identify the deglacial sea level rise as the principal factor driving these changes during the late glacial high values of kaolinite are interpreted to reflect a higher contribution of clays from soils that have formed on the exposed sunda shelf and in the southern archipelagos of indonesia at this time core sites were located in close proximity to the mouths of the sunda shelf palaeo drainage systems on the emerged shelf sundaland the progressive landward displacement of the coastline and breakdown of these vast drainage systems during deglaciation led to a decrease in influence of the kaolinite rich southern sources when the coastline had retreated closely to its present day position in mid holocene times the former dominance of southern sources was replaced by a stronger influence of illite rich sources e g borneo the overriding control of sea level changes on the clay mineral distribution patterns precludes a definite climatic interpretation of clay mineral data in terms of climatic monsoonal changes in such highly dynamic sedimentary environment

glacial interglacial wetland biomass burning and geologic methane emissions constrained by dual stable isotopic ch4 ice core records atmospheric methane ch4 records reconstructed from polar ice cores represent an integrated view on processes predominantly taking place in the terrestrial biogeosphere here we present dual stable isotopic methane records 13ch4 and d ch4 from four antarctic ice cores which provide improved constraints on past changes in natural methane sources our isotope data show that tropical wetlands and seasonally inundated floodplains are most likely the controlling sources of atmospheric methane variations for the current and two older interglacials and their preceding glacial maxima the changes in these sources are steered by variations in temperature precipitation and the water table as modulated by insolation local sea level and monsoon intensity based on our d ch4 constraint it seems that geologic emissions of methane may play a steady but only minor role in atmospheric ch4 changes and that the glacial budget is not dominated by these sources superimposed on the glacial interglacial variations is a marked difference in both isotope records with systematically higher values during the last 25 000 y compared with older time periods this shift cannot be explained by climatic changes rather our isotopic methane budget points to a marked increase in fire activity possibly caused by biome changes and accumulation of fuel related to the late pleistocene megafauna extinction which took place in the course of the last glacial

the qs problem sediment volumetric balance of proximal foreland basin systems although the stratigraphy of sedimentary basins depends on the balance between the magnitude and grain size characteristics of the sediment supply qs and the spatial distribution of tectonic subsidence generating accommodation x qs is problematical to measure in present day sediment routing systems and formidably difficult to predict in their ancient counterparts this challenge was tackled by treating the sediment discharge from the outlet of mountain catchments as the result of incision by a drainage network with a bulk diffusivity based on the length over which the mean annual rainfall is concentrated the size relief and slope of palaeo catchments acting as feeders for sediment routing systems are used to run simulations of sediment discharge and bulk diffusivity for a range of annual precipitation values a wide range of observable geological phenomena can be used to converge on the most likely solutions for qs including depositional volumes in the basin and bedrock thermochronology and detrital cosmogenic nuclide dating to constrain catchment erosion rates modelled sediment discharges can be checked with estimates derived from global regressions the sediment efflux of mountain catchments serves as a boundary condition for down system sediment transport and deposition variations in the volumetric ratio of sediment supply to available accommodation qs x determines patterns of transverse versus longitudinal axial sediment dispersal the volumetric ratio may change as a result of variations in climatic parameters tectonic uplift rate and catchment expansion an abrupt climate change to higher precipitation values promotes higher qs x but transient landscape response causes a return to values close to the baseline generating a distinctive down system extension of a gravel spike catchment expansion has a similar but more prolonged effect on gravel progradation in contrast a change in tectonic forcing such as an increase in slip rate on a border fault causes little change in qs x because increased subsidence compensates for the increased sediment supply studies of mid eocene oligocene sediment routing systems in the south central pyrenees allow the discrimination of different types of proximal wedge top sedimentary systems on the basis of the volumetric ratio of qs to accommodation x i small steep local fan systems in tectonically ponded underfilled basins supplied by low sediment discharges ii tectonically guided long range axial systems fed by large sediment discharges from widely spaced palaeovalleys and iii large shallow sloping transverse megafans burying underlying defunct or active tectonic structures supplied by high to very high sediment discharges understanding the role of variations in qs helps to explain the syntectonic evolution of proximal foreland basin systems the oligocene miocene north alpine foreland basin switzerland is qualitatively identified as a high qs example the miocene recent northern apennines of italy as a low qs example and the eocene oligocene southern pyrenees of spain as intermediate in character

post cimmerian jurassic cenozoic paleogeography and vertical axis tectonic rotations of central iran and the alborz mountains according to previous paleomagnetic analyses the northward latitudinal drift of iran related to the closure of the paleo tethys ocean resulted in the late triassic collision of iran with the eurasian plate and cimmerian orogeny the post cimmerian paleogeographic and tectonic evolution of iran is instead less well known here we present new paleomagnetic data from the upper jurassic bidou formation of central iran which we used in conjunction with published paleomagnetic data to reconstruct the history of paleomagnetic rotations and latitudinal drift of iran during the mesozoic and cenozoic paleomagnetic inclination values indicate that during the late jurassic the central east iranian microcontinent ceim consisting of the yazd tabas and lut continental blocks was located at low latitudes close to the eurasian margin in agreement with the position expected from apparent polar wander paths apwp incorporating the so called jurassic massive polar shift a major event of plate motion occurring in the late jurassic from 160 ma to 145 140 ma at these times the ceim was oriented wsw ene with the lut block bordered to the south by the neo tethys ocean and to the southeast by the neo sistan oceanic seaway subsequently the ceim underwent significant counter clockwise ccw rotation during the early cretaceous this rotation may have resulted from the northward propagation of the sistan rifting spreading axis during late jurassic early cretaceous or to the subsequent late early cretaceous eastward subduction and closure of the sistan oceanic seaway underneath the continental margin of the afghan block no rotations of or within the ceim occurred during the late cretaceous oligocene whereas a second phase of ccw rotation occurred after the middle late miocene both the late jurassic early cretaceous and post miocene ccw rotations are confined to the ceim and do not seem to extend to other tectonic regions of iran finally an oroclinal bending mechanism is proposed for the origin of the curved alborz mountains which acquired most of its curvature in the last 8 myr

synchronous deformation on orogenic plateau margins insights from the arabia eurasia collision abstract the temporal and spatial distribution of deformation during the early phases of plateau formation is poorly known the iranian plateau is developing in response to arabia eurasia convergence and is a potential analog to the early phases of tibetan plateau deformation previous studies document the onset of the iranian plateau growth based on the kinematic history of the zagros to the south and the alborz mountains to the north here we present new detrital apatite fission track aft data from 13 modern rivers of the talesh mountains northwestern iranian plateau these mountains lie immediately south west of the rigid south caspian block a total of 1233 single grain cooling ages were measured and range between 185 and 4 ma deconvolution of grain age data documents three main phases of exhumation including the oligocene 30 23 ma early to middle miocene 18 12 ma and early pliocene 5 ma comparison between cooling ages from the talesh mountains and elsewhere across the iranian plateau indicates widespread plateau formation in the oligocene earlier than previously suggested for the northwestern plateau margin these results highlight deformation on both the northern and southern margins of the plateau over almost the entire history of iranian plateau formation a similar pattern of synchronous deformation on the north northeastern and southern margins of the tibetan plateau has recently been documented and highlights the significance of rigid basement blocks focusing far field deformation for both plateaus

cenozoic exhumation history of the alborz mountains iran new constraints from low temperature chronometry the alborz mountains in the north of the turkish iranian plateau mainly developed in the cenozoic as a consequence of the closure of neo tethys and continental collision between arabia and eurasia cenozoic growth of the fold and thrust belt exploited an older palaezoic mesozoic crustal fabric but the extent to which this governed the overall form of the mountain belt is unclear to determine when and how the alborz mountain belt has grown apatite fission track aft and u th he ahe thermochronometry were performed on 46 bedrock samples collected along 8 transects across the range aft central ages range from 157 24 ma to 10 1 ma with most ages falling between 40 ma and 10 ma ahe ages range from 17 2 ma to 6 1 ma the data revealed enhanced exhumation ca 35 5 ma minor exhumation between ca 30 20 ma and an increase in exhumation thereafter this pattern matches the tripartite mid cenozoic stratigraphy of central iran where upper oligocene lower miocene carbonates are sandwiched between terrestrial clastic formations the most intriguing thermochronometric signal found is a major acceleration of exhumation that initiated in the late miocene to early pliocene recorded by the ahe data there does not appear to be a direct tectonic cause for pliocene intensified erosion as convergence rates between arabia and eurasia have remained relatively constant enhanced exhumation at this time may reflect a climatically induced intensification of erosion during caspian isolation and base level fall or a regional tectonic re organization of the arabia eurasia collision or both

a tectonic origin of magnetic fabric in the shemshak group from alborz mts northern iran abstract the magnetic lineation observed in undeformed sedimentary units has been interpreted either as an indication of paleoflow direction or as a result of tectonic overprint which progressively modifies the original sedimentary fabric related to compactional processes distinguishing between the two processes is not always easy in fact most studies of the anistropy of magnetic susceptibility ams of undeformed sequences have been carried out in fine grained sediments from foredeep sequences which are characterized by sedimentary flow directions which are almost parallel to the main deformation structures like thrust faults and folds in the alborz mts the upper triassic lower jurassic shemshak group was deposited in a foreland to molassic basin of the eo cimmerian orogen and now outcrops in several folds which are oriented parallel to the curved chain paleoflow directions are generally oblique to the main tectonic structures being directed ssw to sse and showing negligible changes in their orientation along the alborz mountains we have therefore the opportunity to distinguish between tectonic or sedimentary related origins of the magnetic lineation the ams results show that magnetic lineations of the shemshak group are oriented almost parallel to the main fold axes and thrust structures which follow the alborz mts curved trend suggesting that magnetic lineation is of tectonic origin in fine to medium grained mostly massive sandstones and confirming that ams is a valuable tool to study deformation processes in sedimentary rocks

retrodeforming the arabia eurasia collision zone age of collision versus magnitude of continental subduction the arabia eurasia collision has been linked to global cooling the slowing of africa mediterranean extension the rifting of the red sea an increase in exhumation and sedimentation on the eurasian plate and the slowing and deformation of the arabian plate collision age estimates range from the late cretaceous to pliocene with most estimates between 35 and 20 ma we assess the consequences of these collision ages on the magnitude and location of continental consumption by compiling all documented shortening within the region and integrating this with plate kinematic reconstructions shortening estimates across the orogen allow for 350 km of neogene upper crustal contraction necessitating collision by 20 ma a 35 ma collision requires additional subduction of 400 600 km of arabian continental crust using the oman ophiolite as an analogue ophiolitic fragments preserved along the zagros suture zone permit 180 km of subduction of the arabian continental margin plus overlying ophiolites wholesale subduction of this more dense continental margin plus ophiolites would reconstruct 400 500 km of postcollisional arabia eurasia convergence consistent with a ca 27 ma initial collision age this younger arabia eurasia collision suggests a noncollisional mechanism for the slowing of africa and associated extension

thermal histories from the central alborz mountains northern iran implications for the spatial and temporal distribution of deformation in northern iran we integrate new and existing thermochronological geochronological and geologic data from the western and central alborz mountains of iran to better constrain the late cenozoic tectonic evolution of northern iran in the context of the arabia eurasia collision new data are presented for two granitic plutons north of the alborz range crest additional new apatite u th he data are also presented for volcanic intrusive and detrital apatite grains from two transects south of the range crest our most definitive results include zircon and apatite u th he and limited k feldspar 40 ar 39 ar thermal history data from the cretaceous ca 98 ma nusha pluton that reveal that the alborz basement underwent generally slow denudation 0 1 km m y as late as 12 ma with more accelerated exhumation 0 45 km m y that likely began shortly after 12 ma the lahijan pluton a late neoproterozoic cambrian basement exposure near the caspian shore records apatite u th he closure at 17 13 ma additional u th he results from detrital apatites sampled along two separate horizontal transects all consistently yielded latest miocene to pliocene apparent ages that imply that even supracrustal cover rocks within the alborz have undergone significant regionally extensive exhumation overall our data are consistent with 5 km of regionally extensive denudation since ca 12 ma the onset of rapid exhumation in the alborz at ca 12 ma appears to be consistent with other timing estimates that place the onset of the arabia eurasia collision between 14 and 10 ma

oroclinal bending distributed thrust and strike slip faulting and the accommodation of arabia eurasia convergence in ne iran since the oligocene regional shortening is accommodated across ne iran in response to the collision of arabia with eurasia we examine how n s shortening is achieved on major thrust systems bounding the eastern branch of the alborz east of 57 e sabzevar and kuh e sorkh mountain ranges which lie south of the kopeh dagh mountains in ne iran although these ranges have experienced relatively few large earthquakes over the last 50 yr they have been subject to a number of devastating historical events at neyshabur esfarayen and sabzevar a significant change in the tectonics of the eastern alborz occurs directly south of the central kopeh dagh near 57 e to the east shortening occurs on major thrust faults which bound the southern margin of the range resulting in significant crustal thickening and forming peaks up to 3000 m high active shortening dies out eastward into afghanistan which is thought to belong to stable eurasia the rate of shortening across thrust faults bounding the south side of the eastern alborz north of neyshabur is determined using optically stimulated luminescence dating of displaced river deposits and is likely to be 0 4 1 7 mm yr 1 shortening across the sabzevar range 150 km west of neyshabur has previously been determined at 0 4 0 6 mm yr 1 although reassessment of the rate here suggests it may be as high as 1 mm yr 1 migration of thrust faulting into foreland basins is common across ne iran especially in the esfarayen region near 57 e where the northward deflection of the east alborz range reaches a maximum of 200 20 km from its presumed linear e w strike at the beginning of the oligocene west of 57 e the tectonics of the alborz are affected by the westward motion of the south caspian region which results in the partitioning of shortening onto separate thrust and left lateral strike slip faults north and south of the range at the longitude of 59 e published gps velocities indicate that 50 per cent of the overall shortening across ne iran is accommodated in the kopeh dagh the remaining 50 per cent regional shortening must therefore be accommodated south of the kopeh dagh in the eastern alborz and kuh e sorkh ranges assuming present day rates of slip and the fault kinematics are representative of the late cenozoic deformation in ne iran the total 200 20 km n s shortening across the eastern alborz and kopeh dagh mountains since the beginning of uplift of the kopeh dagh basin would be accommodated in 30 8 ma although this extrapolation may be inappropriate over such a long timescale the age is nevertheless consistent with geological estimates of post early to middle oligocene 30 ma for the onset of kopeh dagh uplift

the crustal structure of the southern caspian region the south caspian basin appears to behave as a relatively rigid aseismic block within the otherwise deforming alpine himalayan orogenic belt this anomalous character suggests that there is a fundamental compositional difference between the crust of the south caspian basin and that of the surrounding region five new estimates of crustal velocity structure beneath the southern caspian region are determined by the teleseismic receiver function method these models show that the crust in turkmenia along the trend of the apshceron balkhan sill kopet dag mountains is 50 km thick in the southwestern part of the caspian basin the crust is 33 km thick and consists of a 13 km thick sedimentary section lying on a high velocity vp 7 1 km s 1 lower crustal section in the southeastern part of the basin the crust is 30 km thick and consists of a 10 km thick sedimentary section overlying a 20 km thick low velocity vp 5 8 km s 1 crystalline crust the receiver function models are combined with velocity models from previous russian deep seismic sounding studies into a 1800 km long ese wnw trending crustal cross section across the kura depression the south caspian basin and the kopet dag mountains the most significant features of this crustal model are the 20 km variation in thickness of cenozoic sedimentary basin deposits the absence of a granitic vp 5 8 6 5 km s 1 crustal layer in the central part of the south caspian basin and 20 km of crustal thinning beneath the central part of the basin the moho beneath the south caspian basin has a broad arch like structure whose western boundary is a relatively narrow zone across which the crust thins rapidly 20 km thinning over a 100 km zone and whose eastern boundary has a more gradual change in crustal thickness 20 km thinning over a 400 km zone the velocity depth profiles derived from the receiver functions are compared to laboratory velocity estimates made at pressures and temperatures appropriate for the lower crust in turkmenia but the seismic p wave data alone do not permit differentiation between the various possible rock types the crustal model developed for the south caspian basin is consistent with the hypothesis that the crystalline crust of the basin is a section of oceanic crust that is being overthrust by the continental crust around much of its margins however we cannot rule out the possibility that the crystalline crust beneath the basin is a section of lower continental crust whose upper crustal section has been removed by erosion or faulting

the relationship of strain and preferred orientation of phyllosilicate grains in rocks a review abstract the calculation of strain from the preferred orientation of platy phyllosilicate grains taking strain to be homogeneous is surprisingly often successful from a pragmatic point of view although numerous theoretical objections to this procedure can be and have been raised for the calculation to succeed the original distribution of mica or clay mineral grains must be known or assumed the usual assumption that the starting distribution was random and therefore nearly uniform implies that the strain history of pelitic sediments is taken to start when the watery sediment was last stirred by waves or bioturbation or if it was laid down in still anoxic waters from the moment of first deposition it therefore includes compaction as part of the strain history which is usually neglected by structural geologists originally random distribution of clay flake orientations has been observed in recently deposited sediments in many instances and has been theoretically explained in various ways exceptions probably exist but their frequency has not been estimated biologically disturbed sediments may be brought nearer to a state of random orientation of clay flakes than they were at deposition with the exception of whole beds or concretions in which pores are early filled with cement mudrocks are almost always compacted by the weight of later deposits the strain so induced is axially symmetric about the vertical and thus about the pole of the bedding planes compaction acts on soft unconsolidated rocks but may continue with increasing overburden on rocks strengthened by cementation and by increasing interlocking of grains tectonic deformation may start early before the rock is fully compacted or it may begin only much later and the mechanisms of deformation increase in complexity with the increasing temperature and hydrostatic stress of deeper burial up to a certain level of mild metamorphism however phyllosilicate grains seem to be rather permanent if not as mineral species then at least by preservation of their constituent sheets of silica tetrahedra given this permanence the mechanisms of rock deformation whether intergranular slip cataclasis or dissolution and reprecipitation and various intragranular processes in the non phyllosilicate matrix hardly matter as far as the recording of strain is concerned even a certain amount of stress solution at especially heavily loaded points of the phyllosilicate grains themselves does not destroy their value as strain markers as long as the dissolved material is disposed of mainly by crystallographically continuous overgrowth on existing grains the same holds for local dissolution of phyllosilicates in portions of old grains that have become thermodynamically unstable by bending widespread irregular or random nucleation and growth of newly nucleated phyllosilicate grains at intermediate or high grades of metamorphism can reduce the reliability of the strain record and so can domainal structure of the deformed rock if both the volume fraction of phyllosilicate grains and the intensity of total strain differ sharply from one domain to another if distinct domains are not equant and have themselves a strong preferred orientation of shape nevertheless rocks containing an anastomosing network of zones rich in phyllosilicate grains as slates and other deformed mudrocks commonly do have in many cases been found to have average preferred orientations of mica or chlorite which if used to estimate the strain give results similar to those obtained from independent strain markers in the same rocks thus the most significant verification of the usefulness of strain estimates by measurement of preferred orientation is the mutual confirmation with independently determined strain the limit to such verification is the rarity of strain markers so that the coexistence of two independent ones is exceptionally rare for this reason however it is important to make full use of the orientation of phyllosilicate grains where they are available the alternative to have no strain measurements at all causes structural geologists to miss potential information

glacial interglacial water cycle global monsoon and atmospheric methane changes the causes of atmospheric methane ch4 changes are still a major contention in particular with regards to the relative contributions of glacial interglacial cycles monsoons in both hemispheres and the late holocene human intervention here we explore the ch4 signals in the antarctic epica dome c and vostok ice records using the methods of timeseries analyses and correlate them with insolation and geological records to address these issues the results parse out three distinct groups of ch4 signals attributable to different drivers the first group 80 variance well tracking the marine 18o record is attributable to glacial interglacial modulation on the global water cycle with the effects shared by wetlands at all latitudes from monsoonal and non monsoonal regions in both hemispheres the second group 15 variance centered at the 10 kyr semi precession frequency is linkable with insolation driven tropical monsoon changes in both hemispheres the third group 5 variance marked by millennial frequencies is seemingly related with the combined effect of ice volume and bi hemispheric insolation changes at the precession bands these results indicate that bi hemispheric monsoon changes have been a constant driver of atmospheric ch4 this mechanism also partially explains the holocene ch4 reversal since 5 kyr bp besides the human intervention in the light of these results we propose that global monsoon can be regarded as a system consisting of two main integrated components one primarily driven by the oscillations of inter tropical convergence zone itcz in response to the low latitude summer insolation changes anti phase between the two hemispheres i e the itcz monsoon component and another modulated by the glacial interglacial cycles mostly synchronous at the global scale i e the glacial interglacial monsoon component although atmospheric ch4 record integrates all wetland processes including significant non monsoonal contributions it is the only and probably the best proxy available to reflect the past changes of global monsoon however the utility of ch4 as a proxy of monsoon changes at any specific location is compromised by its bi hemispheric nature

tectonic control on sedimentary facies pattern and sediment accumulation rates in the miocene foreland basin of the southern alborz mountains northern iran 1 the southern alborz mountains of northern iran are an integral part of the arabia eurasia collision zone a magnetostratigraphic and rock magnetic investigation of the eyvanekey stratigraphic section in the southern alborz mountains reveals the spatiotemporal character of sedimentary facies migration in the alborz foreland basin the section constitutes three coarsening upward units units 1 2 and 3 comprising the upper red and hezardarreh formations our data reveal that the upper red formation was deposited between 17 5 and 7 5 ma while the depositional age of the top of the hezardarreh formation can be extrapolated to 6 2 ma slow sediment accumulation rates correlate with sedimentary facies comprising prograding coarsening upward units this is likely the result of intraforeland uplift units 1 and 2 and basin inversion probably associated with a growth syncline located in the proximal foreland unit 3 in contrast fine grained strata at the bottom of each cycle are associated with faster sediment accumulation rates testifying to enhanced flexural basin subsidence in the course of thrust loading progradation of coarse grained facies also occurred during relatively fast sediment accumulation top of unit 2 suggesting that the influx of coarse grained sediment outpaced the storage capacity of the proximal foreland thus despite an overall southward propagation of deformation into the southern alborz foreland the locus of active deformation must have migrated back and forth on a time scale of circa 0 7 to 2 ma

atmospheric methane ratio and environmental change in the sahara an sahel during the last 130 kyrs abstract the comparison of the vostok ch 4 curve over the last 130 ka with the dated succession of humid arid phases in the 6 500 000 km 2 area between 13 n and 27 n in africa shows that they roughly co vary we propose those past ecological changes in vast tropical areas as one of the factors that contributted to the global increase decrease of the methane production

physiological significance of low atmospheric co2 for plant climate interactions abstract methods of palaeoclimate reconstruction from pollen are built upon the assumption that plant climate interactions remain the same through time or that these interactions are independent of changes in atmospheric co 2 the latter may be problematic because air trapped in polar ice caps indicates that atmospheric co 2 has fluctuated significantly over at least the past 400 000 yr and likely the last 1 6 million yr three other points indicate potential biases for vegetation based climate proxies first c 3 plant physiological research shows that the processes that determine growth optima in plants photosynthesis mitochondrial respiration photorespiration are all highly co 2 dependent and thus were likely affected by the lower co 2 levels of the last glacial maximum second the ratio of carbon assimilation per unit transpiration called water use efficiency is sensitive to changes in atmospheric co 2 through effects on stomatal conductance and may have altered c 3 plant responses to drought third leaf gas exchange experiments indicate that the response of plants to carbon depleting environmental stresses are strengthened under low co 2 relative to today this paper reviews the scope of research addressing the consequences of low atmospheric co 2 for plant and ecosystem processes and highlights why consideration of the physiological effects of low atmospheric co 2 on plant function is recommended for any future refinements to pollen based palaeoclimatic reconstructions

modelling aeolian sand transport using a dynamic mass balancing approach abstract knowledge of the changing rate of sediment flux in space and time is essential for quantifying surface erosion and deposition in desert landscapes whilst many aeolian studies have relied on time averaged parameters such as wind velocity u and wind shear velocity u to determine sediment flux there is increasing field evidence that high frequency turbulence is an important driving force behind the entrainment and transport of sand at this scale of analysis inertia in the saltation system causes changes in sediment transport to lag behind de accelerations in flow however saltation inertia has yet to be incorporated into a functional sand transport model that can be used for predictive purposes in this study we present a new transport model that dynamically balances the sand mass being transported in the wind flow the dynamic mass balance dmb model we present accounts for high frequency variations in the horizontal u component of wind flow as saltation is most strongly associated with the positive u component of the wind the performance of the dmb model is tested by fitting it to two field derived namibia s skeleton coast datasets of wind velocity and sediment transport i a 10 min 10 hz measurement resolution dataset ii a 2 h 1 hz measurement resolution dataset the dmb model is shown to outperform two existing models that rely on time averaged wind velocity data e g radok 1977 dong et al 2003 when predicting sand transport over the two experiments for all measurement averaging intervals presented in this study 10 hz 10 min the dmb model predicted total saltation count to within at least 0 48 whereas the radok and dong models over or underestimated total count by up to 5 50 and 20 53 respectively the dmb model also produced more realistic less peaky time series of sand flux than the other two models and a more accurate distribution of sand flux data the best predictions of total sand transport are achieved using our dmb model at a temporal resolution of 4 s in cases where the temporal scale of investigation is relatively short on the order of minutes and at a resolution of 1 min for longer wind and transport datasets on the order of hours the proposed new sand transport model could prove to be significant for integrating turbulence scale transport processes into longer term macro scale landscape modelling of drylands

inversion tectonics in central alborz iran abstract structural analyses carried out in the southern central alborz iran have shown that the evolution of this belt has been strongly conditioned by the inversion of pre existent extensional faults inversion tectonics has been identified especially in the southern part of the belt and it is related to the reactivation of grabens formed in the foreland of the late triassic eo cimmerian orogen resulting from the accretion of the iranian block to eurasia three main associations of structures active during the late cenozoic have been distinguished 1 e w thrust faults and folds followed by the activation of 2 e w right lateral strike slip faults associated to large ene wsw trending en echelon folds and finally 3 ese wnw to se nw thrust faults and left lateral strike slip faults inverting in some cases previous e w right lateral faults central alborz is strongly controlled by the geometry of pre existing tectonic discontinuities which are responsible for strain partitioning between strike slip and reverse faults during convergence these results provide new insights on the style and evolution of this complex intracontinental belt which can be considered a significant example of transpressive tectonics

tectonic magnetic lineation and oroclinal bending of the alborz range implications on the iran southern caspian geodynamics in this study we use the anisotropy of magnetic susceptibility ams and paleomagnetic data for deciphering the origin of magnetic lineation in weakly deformed sedimentary rocks and for evaluating oroclinal processes within the arabia eurasia collision zone in particular we have analyzed the miocene upper red formation urf from the outer curved front of the southern central alborz mountains of north iran to test for the first time with paleomagnetic data the origin primary versus secondary of this orogenic arc ams data document the existence of a magnetic lineation parallel to the orientation of the major tectonic structures which vary along strike from wnw to ene these directions are highly oblique to the paleoflow directions and hence suggest that the magnetic lineation in the urf was produced by compressional deformation during layer parallel shortening in addition our paleomagnetic data document clockwise and anticlockwise rotations along vertical axis for the western and eastern sectors of the central alborz mountains respectively combined our results suggest that the orogen represents an orocline which formed not earlier than circa 7 6 ma most likely through bending processes caused by the relative motion between the rigid crustal blocks of the collision zone moreover our study provides new insights into the iran southern caspian basin kinematic evolution suggesting that the present day sw motion of the south caspian basin with respect to central iran postdates oroclinal bending and hence cannot be as old as late miocene to early pliocene but a rather recent configuration i e 3 to 1 ma

accommodation of transpressional strain in the arabia eurasia collision zone new constraints from u th he thermochronology in the alborz mountains north iran the alborz range of n iran provides key information on the spatiotemporal evolution and characteristics of the arabia eurasia continental collision zone the southwestern alborz range constitutes a transpressional duplex which accommodates oblique shortening between central iran and the south caspian basin the duplex comprises nw striking frontal ramps that are kinematically linked to inherited e w striking right stepping lateral to obliquely oriented ramps new zircon and apatite u th he data provide a high resolution framework to unravel the evolution of collisional tectonics in this region our data record two pulses of fast cooling associated with sw directed thrusting across the frontal ramps at 18 14 and 9 5 7 5 ma resulting in the tectonic repetition of a fossil zircon partial retention zone and a cooling pattern with a half u shaped geometry uniform cooling ages of 7 6 ma along the southernmost e w striking oblique ramp and across its associated nw striking frontal ramps suggests that the ramp was reactivated as a master throughgoing n dipping thrust we interpret this major change in fault kinematics and deformation style to be related to a change in the shortening direction from ne to n nne the reduction in the obliquity of thrusting may indicate the termination of strike slip faulting and possibly thrusting across the iranian plateau which could have been triggered by an increase in elevation furthermore we suggest that 7 6 m y old s directed thrusting predated inception of the westward motion of the south caspian basin

ams fabric and tectonic evolution of quaternary intramontane extensional basins in the picentini mountains southern apennines italy in this work we report the results of combined geological structural and anisotropy of magnetic susceptibility ams studies carried out on quaternary deposits in the picentini mountains southern apennines italy the study concerns four small continental basins acerno tizzano iumaiano and piano del gaudo related to fluvial lacustrine depositional environments ranging in altitude from 600 to 1 200 m a s l and strongly incised during recent time stratigraphic and structural analyses integrated by low and high field anisotropy of magnetic susceptibility ams show that the formation of these basins has been controlled by extensional and transtensional tectonics most of the ams sites exhibit a well defined magnetic foliation parallel to the bedding planes a well defined magnetic lineation has also been measured within the foliation planes in the iumaiano tizzano and piano del gaudo basins magnetic lineations cluster around nne ssw trend and are parallel to the stretching directions inferred by structural analysis of faults and fractures on the basis of structural sedimentological and high field ams data we suggest a tectonic origin for the magnetic lineation analogously to what has been observed in other weakly deformed sediments from neogene and quaternary extensional basins of the mediterranean region our results demonstrate that onset and the evolution of the investigated basins have been mainly controlled since lower pleistocene by nw se normal and transtensional faults this deformation pattern is consistent with a prevalent ne sw extensional tectonic regime still active in southern apennines as revealed by seismological and geodetic data

palaeomagnetic rotations in the eastern betic cordillera southern spain palaeomagnetic declinations from the external zones of the eastern betic cordillera southern spain and an adjacent area of the internal zone indicate variable and locally very large clockwise rotations the rotations occurred after latest oligocene times and probably before the late miocene this overlaps a period of dextrally oblique convergence during the early to middle miocene along the internal external zone boundary and within the external zone rotations in the external zone are recorded by palaeomagnetic results from 27 sites in upper jurassic ammonitico rosso facies limestones from the subbetic zone and one site of a similar age from the prebetic the sites show either two or three component behaviour the low temperature component is coincident with the present field direction the intermediate temperature component was probably acquired during miocene folding the high temperature component passes fold tests miocene age and a conglomerate test eocene early oligocene age palaeomagnetic declinations from individual tectonic blocks in the subbetic are consistent but indicate large differential rotations between blocks these blocks are underlain by low angle thrust faults which probably accommodated much of the rotation the largest rotations occur on relatively small isolated blocks of jurassic carbonates in a highly deformed triassic evaporite sequence the single site in the prebetic has not rotated significantly relative to stable iberia in malaguide rocks of the sierra espun a in the adjacent internal zone stable palaeomagnetic components were measured at one site in upper miocene sedimentary rocks at three sites in upper oligocene lower miocene red marls at one site in oligocene marls at one site in jurassic limestones and at two sites in permo triassic red beds the palaeomagnetic results suggest that about 60 of clockwise rotation occurred in the latest oligocene earliest miocene and a further 140 of clockwise rotation subsequently one site in late miocene sedimentary rocks yields unrotated declinations which if not representing an overprinted direction indicate that the rotation was complete by the end of the miocene

gas hydrate destabilization and methane release events in the krishna godavari basin bay of bengal abstract methane release events have been linked to global warming alteration of the carbon cycle and influence on biota however unequivocal evidence of paleomethane release events are limited we report several negative carbon stable isotope excursions in planktic and benthic foraminifera in a core md161 8 from the krishna godavari k g basin bay of bengal the most negative 13 c spikes are recorded during the marine isotope stages mis 4 and at the transition of mis 5 to 4 occurrence of highly 13 c depleted average 13 c 48 2 4 vpdb authigenic high magnesian calcite are also reported within this time window from the core md161 8 in the present work an unequivocal explanation for the observed 13 c depletion in the marine planktic and benthic foraminifera is difficult to achieve solely from the optical electron microscopy or c o stable isotope ratio analyses due to possible influence of diagenetic alteration we attribute the observed episodic methane expulsion events as inferred from the negative 13 c excursions and earlier reports on the occurrence chemosynthetic bivalves and mo concentration anomaly to the destabilization of the base of gas hydrate stability zone bghsz sea level drop and shale tectonics induced focused fluid flow are the two possible causes of hydrate destabilization discussed here shale tectonics were possibly responsible for creating fault systems which acted as the conduit for gas flow through the sediment column and subsequent seepage shale and salt tectonics in the passive continental margins being a globally observed phenomenon its role as an important driving force for enhanced methane emission needs detailed investigation to understand the climatic perturbations through geologic time additional evidence of methane emission from site md161 15 further supports the link between shale tectonics and methane emission

the ice age methane budget 1 accounting for the natural 40 reduction in methane during the last glacial maximum lgm represents one of the most challenging problems posed by polar ice core studies inverse modelling constrained by observations suggest it is driven by a decline in wetland sources but this is not supported by forward modelling using a comprehensive earth system model we show that closure of the methane budget requires reduced emissions and an amplified sink caused by reduction in emissions of volatile organic compounds vocs from lgm forests our study emphasizes a key role for the terrestrial biosphere in the methane budget during the quaternary

paleocurrent patterns of the sedimentary sequence of the taitao ophiolite constrained by anisotropy of magnetic susceptibility and paleomagnetic analyses abstract determination of paleocurrent directions is a robust approach to establish the mechanism of sediment transport and of deposition however in tectonically controlled or affected basins where rotations are suspected it is of critical importance to correct previously calculated paleocurrent directions to establish the original pre tectonic transport and deposition patterns in order to illustrate this we determined the orientations of the anisotropy of magnetic susceptibility ams fabrics from 14 sites distributed along the sedimentary deposits interbedded within the late miocene main volcanic unit mvu of the taitao ophiolite southern chile data were used to estimate characteristics directions and relative velocities of the sediment transporting paleocurrents and orientations of the depositional slope sedimentary deposits consist of a rhythmic sequence of conglomerate base sandstone and mudstone top beds that present a systematic decrease in grain size up sequence as a whole and within individual beds sedimentary deposits of the mvu as well as overlaying effusive volcanic products are disrupted by small and discrete dextral normal brittle faults the distribution of fault planes and their kinematic characteristics suggest the development of a dextral negative flower like fault zone in the area previously reported nw ward paleocurrent directions obtained from the orientations of sedimentary structures roughly agree with our calculations based on the orientations of ams fabrics calculated paleocurrent directions are sub parallel to the nw se trend of estero cono channel the main lineament in the area the spatial distribution of ams axes between and within sites suggest that coarse grain deposits were transported by relatively high velocity flows whereas fine grained deposits were by low to nearly null velocity flows previously reported paleomagnetic analyses indicate that counterclockwise rotations affected the whole taitao ophiolite including the mvu by applying the necessary corrections we obtained paleocurrent directions yielding mostly nnw ward directions restoration of the orientations of beddings indicates that the depositional surface dipped steeply at its easternmost edge and shallowly at the westernmost end we propose here that sediments were transported by turbidite flows generated by slope instabilities in the innermost part of the estero cono these turbidites followed the estero cono lineament while they filled the channel and transported sedimentary material eroded from the upper portions of the ophiolite and nearby units towards the pacific ocean sediments were deposited on a nw to w facing slope and sorted in decreasing grain size along the channel the instability of the slope was most probably triggered by the activity of a transtensional fault zone developed along the mid axis of the estero cono channel

deciphering oblique shortening of central alborz in iran using geodetic data the alborz is a narrow 100 km and elevated 3000 m mountain belt which accommodates the differential motion between the sanandaj sirjan zone in central iran and the south caspian basin gps measurements of 12 geodetic sites in central alborz between 2000 and 2002 allow to constrain the motion of the belt with respect to western eurasia one site velocity on the caspian shoreline suggests that the south caspian basin moves northwest at a rate of 6 2 mm year with respect to western eurasia north south shortening across the alborz occurs at 5 2 mm year to the south deformation seems to extend beyond the piedmont area probably due to active thrusting on the pishva fault we also observe a left lateral shear of the overall belt at a rate of 4 2 mm year consistent with the geological motion observed along e w active strike slip faults inside the belt e g the mosha fault

insights from the talysh of azerbaijan into the paleogene evolution of the south caspian region the age and mode of formation of the south caspian basin are disputed an 10 km thick predominantly middle eocene clastic and volcanic succession is exposed in the talysh mountains of azerbaijan at its western margin here high k alkali basalts pass laterally to the east and southeast into volcanogenic sandstone dominated turbidity current and debris flow deposits these southeasterly directed depositional systems accumulated in water depths generally greater than 200 m and fed directly into the western south caspian basin new ar ar ages cluster around 39 ma with an upper 1400 m thick volcanic interval being deposited in 2 2 0 2 m y we interpret that this rapid deposition and magmatism records a major back arc extensional transtensional event in the talysh north of the north dipping neotethyan subduction zone this event is recognized across much of southwest asia and may indicate a period of significant basin formation within the adjacent south caspian basin a transition into upper eocene lower oligocene strata dominated by fine grained turbidity current and hemipelagic sediments with slope instability features is interpreted to mark the end of rifting and volcanism in the talysh and the start of the arabia eurasia collision overlying oligocene coarse clastic rocks are interpreted as the erosional products of localized topography created by the further propagation of compressional deformation into the talysh region