compartmentalization of the coso east flank geothermal field imaged by 3 d full tensor mt inversion author s lindsey nj kaven jo davatzes n newman ga abstract the authors 2016 published by oxford university press on behalf of the royal astronomical society previous magnetotelluric mt studies of the high temperature coso geothermal system in california identified a subvertical feature of lowresistivity 2 5ohmm and appreciable lateral extent g1 km in the producing zone of the east flank field however these models could not reproduce gross 3 d effects in the recorded data we perform 3 d full tensor inversion and retrieve a resistivity model that out performs previous 2 d and 3 d off diagonal models in terms of its fit to the complete 3 d mt data set as well as the degree of modelling bias inclusion of secondary zxx and zyy data components leads to a robust east dip 60 to the previously identified conductive east flank reservoir feature which correlates strongly with recently mapped surface faults downhole well temperatures 3 d seismic reflection data and local microseismicity we perform synthetic forward modelling to test the best fit dip of this conductor using the response at a nearby mt station we interpret the dipping conductor as a fractured and fluidized compartment which is structurally controlled by an unmapped blind east flank fault zone

sedimentary impacts from landslides in the tachia river basin taiwan abstract a case study of coseismic landslides and post seismic sedimentary impacts of landslides due to rainfall events was conducted in the tachia river basin taichung county central taiwan about 3000 coseismic landslides occurred in the basin during the ml 7 3 chi chi earthquake in 1999 the deposits from these landslides provided material for numerous debris flows induced by subsequent rainfall events the estimated 4 1 107 m3 of landslide debris produced in the upland area caused sediment deposition in riverbeds and flash floods inundated downstream areas with sediment during torrential rains the landslide frequency size distributions for the coseismic landslides and the subsequent rainfall induced landslides were analyzed to determine the sediment budgets of the post seismic geomorphic response in the landslide dominated basin both the coseismic and the rainfall induced landslides show a power law frequency size distribution with a rollover it was found that the rainfall induced landslide magnitude was smaller than the coseismic one and that both have comparable negative scaling exponents in cumulative form of about 2 0 for larger landslides 10 2 km2 this may be attributed to ongoing movement or reactivation of old landslides and a natural stabilisation of small landslides between 10 4 and 10 2 km2 it is proposed that the characteristics of geological formations and rainfall as well as changes in landslide area are reflected in the power law distribution

distribution pattern of earthquake induced landslides triggered by the 12 may 2008 wenchuan earthquake abstract this paper presents the preliminary results of an extensive study of the mapping the distribution of landslides triggered by the wenchuan earthquake in sichuan province china on 12 may 2008 an extensive landslide interpretation was carried out using a large set of optical high resolution satellite images e g aster alos cartosat 1 spot 5 and ikonos as well as air photos for both the pre and post earthquake situation landslide scarps were mapped as points using multi temporal visual image interpretation taking into account shape tone texture pattern elevation and ridge and valley orientation nearly 60 000 individual landslide scarps were mapped the landslide distribution map was compared with the inventory map that was prepared directly after the earthquake which contains about 11 000 individual landslide points through the calculation of normalized landslide isopleths maps remarkable differences were observed as the earlier inventory mapping did not consider the pre earthquake situation and did not consider all individual landslides as part of the landslide inventory landslides were identified that had blocked the drainage and had formed landslide dams the landslide distribution was compared with a number of aspects such as the seismic parameters distance to epicenter distance to fault rupture co seismic fault geometry and co seismic slip distribution and geology the most remarkable correlation found was with the co seismic slip distribution and the fault geometry landslide distribution in the section of the fault that had mainly a thrust component with low angle fault plane was found to be much higher than the sections that had steeper fault angles and a major strike slip component

geological characteristics of tulargen magmatic cu ni co deposit in eastern xinjiang and its exploration direction the tulargen cu ni deposit a great breakthrough in cu ni exploration in xinjiang in the past ten years is obviously controlled by secondary fractures in the kangguer huangshan regional ductile sheer zone similar to things of the known huangshan and xiangshan cu ni deposits ore bodies are hosted in ultramafic complexes which consist of hornblende peridotite pyroxene peridotite hornblende pyroxenite and gabbro the proved nickel 125000 tons and cobalt reserves 10 000 tons have reached large size and copper reserves have reached medium size the richest massive ore body with an average grade of ni 4 56 and cu 2 52 can reach 37 98 m in thickness in no 1503 drill hole the ore district remains under prospecting now the deposit was formed through deep seated magma segregation and is characterized by bulk mineralization it has experienced a single intrusion with multiple pulsant inburst the m f values are between 3 1 and 4 8 falling into the category of ferrous ultramafic rocks the intrusion has low ti total alkali and al2o3 and contains high sulfur usually higher than 1 suggesting a good ore forming potential ore minerals consist of pyrrhotite pyrite pentlandite chalcopyrite and violarite ni and co elements occur as isolated sulfides and sulfur arsenic mineral components geochemical exploration reveals that the deposit is located in a cu ni co anomaly area with the ni peak value of 133 10 6 and cu value of 83 10 6 geophysical characteristics of this district show that high gravity high polarization and high magnetic anomalies are associated with low electric resistance the exploration direction is also pointed out in this paper new ore bearing ultramafic intrusions will be possibly found along the central weak shear zone between the strong shear zones on both sides and the southwestern extension of no i intrusion with well developed hornblende peridotite is the pipe center for magma upwelling and may be a mineralization enrichment center

palaeozoic collisional tectonics and magmatism of the chinese tien shan central asia abstract the chinese tien shan range is a palaeozoic orogenic belt which contains two collision zones the older southern collision accreted a north facing passive continental margin on the north side of the tarim block to an active continental margin on the south side of an elongate continental tract the central tien shan collision occurred along the qinbulak qawabulak fault southern tien shan suture the time of the collision is poorly constrained but was probably in in the late devonian early carboniferous we propose this age because of a major disconformity at this time along the north side of the tarim block and because the youshugou ophiolite is imbricated with middle devonian sediments a younger probably late carboniferous early permian collision along the north tien shan fault northern tien shan suture accreted the northern side of the central tien shan to an island arc which lay to its north the north tien shan arc this collision is bracketed by the middle carboniferous termination of arc magmatism and the appearance of late carboniferous or early permian elastics in a foreland basin developed over the extinct arc thrust sheets generated by the collision are proposed as the tectonic load responsible for the subsidence of this basin post collisional but palaeozoic dextral shear occurred along the northern suture zone this was accompanied by the intrusion of basic and acidic magmas in the central tien shan late palaeozoic basic igneous rocks from all three lithospheric blocks represented in the tien shan possess chemical characteristics associated with generation in supra subduction zone environments even though many post date one or both collisions rocks from each block also possess distinctive trace element chemistries which supports the three fold structural division of the orogenic belt it is unclear whether the chemical differences represent different source characteristics or are due to different episodes of magmatism being juxtaposed by later dextral strike slip fault motions because the southern collision zone in the tien shan is the older of the two the tarim block sensu stricto collided not with the eurasian landmass but with a continental block which was itself separated from eurasia by at least one ocean the destruction of this ocean in late carboniferous early permian times represented the final elimination of all oceanic basins from this part of central asia

late cenozoic slip on the talas ferghana fault the tien shan central asia although cenozoic crustal shortening and thickening by thrust faulting have built the present tien shan active right lateral shear on the northwest trending talas ferghana fault appears to be the most rapid localized deformation in the belt ephemeral stream valleys have been offset right laterally tens of metres new and published radiocarbon dates of organic material deposited in depressions blocked by offset ridges place upper bounds on the average holocene slip rate at 18 localities uncertainties allow 14 upper bounds to overlap the range of 8 16 mm yr and 95 confidence limits on such bounds at 11 sites are entirely within this range we infer that the rate of 10 mm yr is not simply an upper bound but applies to the late holocene epoch although the bounds on rates permit more rapid slip in the northwest than the southeast they do not place a useful constraint on variations in slip rate along the fault offsets of paleozoic facies boundaries imply a total right lateral shear of 180 250 km but early cretaceous sedimentary rock appears to have been offset only 60 10 km published paleomagnetic declinations of cretaceous miocene rock demonstrate 20 30 of counterclockwise rotation of the ferghana valley which lies just west of the talas ferghana fault with respect to stable parts of eurasia and 20 11 with respect to the central tien shan east of the fault these declinations are consistent with a maximum northwestward translation of 70 210 km of the ferghana valley at the talas ferghana fault and therefore with a similar maximum horizontal shortening across the chatkal ranges which lie between the ferghana valley and the kazakh platform estimates of crustal thickness beneath the chatkal ranges however permit only 60 100 km of cenozoic shortening if 100 km of slip on the talas ferghana fault accumulated at a constant rate of 10 mm yr it would imply an initiation of slip more recently than ca 10 ma long after india collided with the rest of eurasia

on two dimensional interpretation of magnetotelluric soundings summary the paper presents the views of the 2 d interpretation of magnetotelluric mt data that are characteristic of the russian magnetotelluric school discussing the strategy of 2 d interpretation of mt data we have to answer three questions in decreasing order of importance these questions are as follows 1 which field mode is more sensitive to the near surface and deep structures that are the targets of mt surveys 2 which field mode is more robust to the 3 d evects caused by real geological bodies 3 which field mode is more susceptible to the static shift induced by nearsurface inhomogeneities we examine the transverse magnetic tm and transverse electric te modes of the 2 d magnetotelluric field and show that they satisfy the principle of information complementarity 1 while the tm mode is more sensitive to the near surface structures the te mode may be more sensitive to the deep structures 2 while the tm mode is more robust to the 3 d evects caused by conductive structures the te mode may be more robust to the 3 d evects caused by resistive structures and 3 while the tm mode is more susceptible to the static shift the te mode may be almost undistorted thus the gaps left by one mode can be filled by another mode if so the most comprehensive and reliable information on the conductivity of the earth s interior can be obtained using both modes i e the transverse and longitudinal mt curves the general scheme of this bimodal mt inversion is rather simple the transverse curves provide details of near surface structures e g in the sediments and allow one to evaluate the lithosphere resistance and outline the deep conductive faults while the longitudinal curves help one to detect the conductive zones in deep layers of the lithosphere and in the asthenosphere an eycient two level algorithm for the bimodal mt inversion realizing this scheme is suggested as an illustration the paper presents the geoelectrical model of the kirghiz tien shan constructed by means of the bimodal mt inversion

landslides triggered by the 8 october 2005 kashmir earthquake abstract the 8 october 2005 kashmir earthquake triggered several thousand landslides these were mainly rock falls and debris falls although translational rock and debris slides also occurred in addition a sturzstrom debris avalanche comprising 80 million m3 buried four villages and blocked streams to create two lakes although landsliding occurred throughout the region covering an area of 7500 km2 the failures were highly concentrated associated with six geomorphic geologic anthropogenic settings including natural failures in 1 highly fractured carbonate rocks comprising the lowest beds in the hanging wall of the likely earthquake fault 2 tertiary siliciclastic rocks along antecedent drainages that traverse the hazara kashmir syntaxis 3 steep 50 slopes comprising precambrian and lower paleozoic rocks 4 very steep 50 lower slopes of fluvially undercut quaternary valley fills and 5 ridges and spur crests the sixth setting was associated with road construction extensive fissuring in many of the valley slopes together with the freshly mobilized landslide debris constitutes a potential hazard in the coming snowmelt and monsoon seasons this study supports the view that earthquake triggered landslides are highly concentrated in specific zones associated with the lithology structure geomorphology topography and human presence

sedimentary basins and crustal thickening abstract we consider the development of sedimentary basins in a tectonic context dominated by horizontal shortening and vertical thickening of the crust well known examples are foreland basins others are ramp basins and buckle basins we have reproduced various styles of compressional basins in experiments properly scaled for gravity a multilayered model lithosphere with brittle and ductile layers floats on a model asthenosphere a computer driven piston provides shortening and thickening synchronous with erosion and sedimentation after a first stage of lithospheric buckling thrust faults appear mainly at inflection points slip on an isolated reverse fault is accompanied by flexure footwall flexure results in a foreland basin and becomes accentuated by sedimentation hangingwall flexure is less marked but may become accentuated by erosion motion on a fault leads to hangingwall collapse at the surface either footwall sedimentation or hangingwall erosion tends to prolong the active life of a reverse fault slip on any pair of closely spaced reverse faults of opposite vergence results in a ramp basin simultaneous slip produces a symmetric ramp basin whereas alternating slip results in a butterfly shaped basin with superposed foredeeps some well developed ramp basins become pushed down until bounding faults meet at the surface and the basin disappears from view at this stage the basin depth is equivalent to 15 km or more slip on any pair of widely spaced reverse faults of opposite vergence results in a pronounced central anticline between two distinct foredeeps in central asia and in western europe cenozoic crustal thickening is due to continental collision for central asia western china kyrgyzstan uzbekistan tajikistan we have compiled a regional structure contour map on the base of the tertiary as well as 4 regional sections foreland basins and ramp basins are numerous and associated with cenozoic thrusts large basins tarim junggar fergana tajik occur around and between mountain ranges but smaller basins issyk kul naryn occur within them in western europe the alps and pyrenees are surrounded by foreland basins ramp basins or intermediate styles in the andes and its foreland neogene thrusts and compressional basins are due to subduction of oceanic lithosphere in colombia they account for much of the cordillera oriental in nw argentina for the altiplano in west central argentina for the sierras pampeanas compressional basins are also common in other areas of older crustal thickening

gradient analysis of faunal distributions associated with rapid transgression and low accommodation space in a late pennsylvanian marine embayment biofacies of the ames member glenshaw formation conemaugh group in the northern appalachian basin usa abstract the ames sea situated in a shallow marine embayment in the appalachian basin was the result of the most extensive marine transgression of the pennsylvanian in this region gradient analysis of the proportional abundance of taxa reveals an environmental continuum across the ames embayment along which four biofacies were distributed biofacies distribution is interpreted to be controlled by salinity turbidity and oxygen gradients associated with the geometry of the ames depositional basin and relative sea level change the eastern portion of the ames sea resembled a foredeep trough located on the detrital slope of the recently uplifted appalachian highlands biofacies 1 and 2 occur exclusively in the eastern part of the ames depositional basin and are dominated by eurytopic molluscs tolerant of terrigenous influx biofacies 3 occurs in both the eastern and western portions of the ames depositional basin this biofacies is dominated by the opportunistic brachiopod neochonetes which would quickly colonize the seafloor in the wake of transgression d biofacies 4 occurs exclusively in the western part of the ames depositional basin and is composed primarily of stenotopic crinoids bryozoans brachiopods and epifaunal bivalves that inhabited a clear water cratonic ramp on the eastern flank of the cincinnati arch vertical variations of faunal assemblages in the ames member were the result of variations in relative sea level associated with glacio eustatic cycles biofacies 3 dominated by neochonetes was deposited at the base of the ames member during the initial rapid transgression in a mostly dysoxic environment with low turbidity and marine salinity during the first regression low density surface water from eastern sources restricted vertical circulation established a stratified water column and promoted estuarine conditions in the ames embayment well oxygenated surface waters were unable to circulate to the benthic habitat which led to periodically dysoxic conditions and the establishment of biofacies 1 and 2 composed of diminutive eurytopic molluscs a second stratigraphically higher occurrence of biofacies 3 is interpreted to represent a second transgression however unlike the first transgression lithologic and faunal data suggest that the benthic habitat was well oxygenated above the mid ames marine zone occurrence of biofacies 3 biofacies 1 and 2 were deposited in the final regressive phase as local terrigenous source areas brought increasing turbidity and fluctuating salinity to the ames embayment previous paleoecological research on the ames member cited freshwater and or clastic influx as the major controls on biotic distribution but the results of the present study suggest that oxygen availability was also a major control stratification of the water column during the ames sea level cycle promoted estuarine circulation that prevented well oxygenated surface waters from reaching the benthic habitat this led to the deposition of dark gray to black fissile shales that contain fossil assemblages dominated by diminutive molluscs and brachiopods that were tolerant of low oxygen conditions

a magnetotelluric study of mount ruapehu volcano new zealand summary mt ruapehu is an active andesite cone volcano which marks the southern termination of the kermadec volcanic arc results from 40 broad band magnetotelluric soundings have been analysed using the phase tensor this approach provides a way of determining dimensionality allowing for distortion removal and visualizing data in a 3 d situation the phase tensor analysis suggests that the shallow resistivity structure is largely 1 d in character but that the deeper structure requires a 3 d interpretation 1 d inversions show that at sites on ruapehu a shallow conductive layer lies between a high resistivity layer of a few hundred metres thickness and higher resistivity layer corresponding to basement greywacke the low resistivity layer is contiguous with the waters of the highly acidic crater lake and thus is believed to be the hydraulically controlled upper limit of a zone of acid alteration overlain by dry volcanic rock and ash to the southwest of the volcano the conductive layer merges with a surface conductor associated with tertiary sediments following initial 2 d inversions the deep resistivity structure has been derived through 3 d inversion of data from 38 sites this indicates the existence of a dyke like low resistivity zone that persists to at least 10 km depth and extends from beneath the summit of ruapehu to the northeast where it appears to connect to a poorly constrained region of high conductivity which lies outside the network of measurement sites the low resistivity dyke like feature may be identified with a volcanic feeder system which also supplies the other volcanoes of the tongariro volcanic centre and marks the conduit by which hot gases and occasionally magma reach the surface

application of the 3d magnetotelluric inversion code in a geologically complex area the wsinv3dmt code makes the implementation of 3d inversion of magnetotelluric data feasible using a single pc audio magnetotelluric data were collected along two profiles in a cu ni mining area in xinjiang china where the apparent resistivity and phase curves the phase tensors and the magnetic induction vectors indicate a complex 3d conductivity structure 3d inversions were carried out to reveal the electrical structure of the area the final 3d model is selected from the inversion results using different initial lagrange values and steps the relatively low root mean square rms misfit and model norm indicate a reliable electrical model the final model includes four types of low resistivity areas the first ones coincide with the known location of an orebody and further forward modelling indicates that they are not in full connectivity to form a low resistivity zone the second ones are not controlled by magnetotelluric sites and embody little information of the observed data they are considered as tedious structures the third one is near to the regional kangguer fault and should be treated carefully considering the effect of the fault the last ones are isolated and existing at a limited level as the first ones they should be paid more attention to

electrical resistivity structures between the northern qilian mountains and beishan block nw china and tectonic implications abstract controversies exist on the tectonic models at the northern margin of the qinghai tibetan plateau new magnetotelluric mt data with a bandwidth of 0 001 5827 5 s were collected along one profile starting from the northern qilian mountains in the southern end crossing the hexi corridor the kuantan shan hei shan uplift the huahai basin and coming into the beishan block two dimensional 2d and three dimensional 3d resistivity models of the data are derived using magnetotelluric inversion codes the 2d models and the electrical structures along the profile extracted from the 3d models are comparable and complementary in defining reliable scales and shapes of anomalies in electrical resistivity the crust upper mantle structures beneath the northern plateau are characterized by two imbricated southward underthrusted blocks of continental crust or lithosphere the northern qilian fault is interpreted as a gently south dipping decollement in the upper crust along the top of a high resistivity body below the northern qilian mountains the two high resistivity bodies below the kuantan shan hei shan uplift are disconnected the upper crustal one may connect with the high resistivity basement below the northern qilian mountains in that the attitudes and deformations of the strata at these areas are coherent whereas the lower crust upper mantle one may be the cold lithospheric materials of the block north to the hexi corridor and that forms a south dipping boundary between the hexi corridor and its northern neighbors the observed high electrical resistivity beneath the beishan block provides further support for the notion that the beishan block should be rigid as a whole only in this manner could it transfer stress from south to north the northern boundary of the qinghai tibetan plateau is below the kuantan shan hei shan fault and underthrusting of continental crust or lithosphere is the main cause for the thickening of the plateau crust in the north

relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates the tien shan a high seismically active intracontinental mountain belt 1 000 2 000 km north of the himalaya has grown as a result of india s collision with asia1 the crustal shortening 200 50 km refs 2 3 and thickening that gave rise to the tien shan accommodates only a small fraction of india s total penetration into asia 2 000 3 000km and the temporal relationship of deformation in this belt to the india asia collision remains unclear here we report geodetic measurements of the tien shan using the global positioning system gps that indicate that the current crustal shortening rate is nearly half of india s convergence rate with eurasia in this area4 we infer a total shortening rate for the tien shan of 20 mm yr 1 which is approximately twice that inferred previously from the extrapolation of slip rates in the holocene3 and earthquake induced displacements during this century5 suggesting that the rate of mountain building in this region has accelerated several fold since the onset of collision 50 55 myr ago6 7 if as we argue the current shortening rate can be extrapolated to geological timescales then our results suggest that most of the tien shan has been constructed during the past 10 myr perhaps in response to an increased horizontal force following an abrupt rise of the tibetan plateau8 9

evaluation of factors controlling earthquake induced landslides caused by chi chi earthquake and comparison with the northridge and loma prieta events over 10 000 landslides were triggered by the september 21 1999 chi chi earthquake a large number of these landslides have been mapped from spot images and a smaller number were described in a detailed field investigation geographic information systems gis was used to conduct a spatial characterization of the slope failures including distribution of type size slope angle bedrock geology ground motion and distance from earthquake source the most abundant landslides were shallow disaggregated rock and soil slides landslides occurred primarily in tertiary sedimentary rocks which are well known for their susceptibility to landsliding in many parts of the world landslide concentration values diminish beyond epicentral distances of 40 and 70 km from the epicenter and the surface projection of the fault plane respectively ground motion was found to be the most significant factor in triggering the shallow landslides in the chi chi earthquake overall 74 of all slope failures occurred in regions with vertical ground motions greater than 0 2g and 81 of all slope failures occurred in the region with mean horizontal peak ground accelerations pga greater than 0 15g these factors were used to compare landslides generated by the chi chi earthquake to the landslides triggered by the 1989 loma prieta earthquake and the 1994 northridge earthquake the major difference in distribution of landslides between the chi chi earthquake and the two california earthquakes was the distribution of slope angles in the chi chi earthquake 90 of the failures occurred on slopes steeper than 45 while more than 80 of failures occurred on slopes less than 50 in california apparently reflecting much steeper and tectonically more active geologic setting in taiwan

tien shan geohazards database earthquakes and landslides abstract in this paper we present new and review already existing landslide and earthquake data for a large part of the tien shan central asia for the same area only partial databases for sub regions have been presented previously they were compiled and new data were added to fill the gaps between the databases major new inputs are products of the central asia seismic risk initiative casri a tentative digital map of active faults even with indication of characteristic or possible maximum magnitude and the earthquake catalogue of central asia until 2009 that was now updated with usgs data to may 2014 the new compiled landslide inventory contains existing records of 1600 previously mapped mass movements and more than 1800 new landslide data considering presently available seismo tectonic and landslide data a target region of 1200 km e w by 600 km n s was defined for the production of more or less continuous geohazards information this target region includes the entire kyrgyz tien shan the south western tien shan in tajikistan the fergana basin kyrgyzstan tajikistan and uzbekistan as well as the western part in uzbekistan the north easternmost part in kazakhstan and a small part of the eastern chinese tien shan for the zones outside kyrgyzstan and tajikistan only limited information was available and compiled on the basis of the new landslide inventory and the updated earthquake catalogue the link between landslide and earthquake activity is analysed first size frequency relationships are studied for both types of geohazards in terms of gutenberg richter law for the earthquakes and in terms of probability density function for the landslides for several regions and major earthquake events case histories are presented to outline further the close connection between earthquake and landslide hazards in the tien shan from this study we concluded first that a major hazard component is still now insufficiently known for both types of geohazards and even totally unknown for most giant landslides the time information thus dating rockslides and any large mass movement is a crucial factor in order to better constrain related hazards second we highlight the role of coupled hazards in the tien shan inside the mountain range the largest disasters were caused by earthquake triggered landslides and massive earth flows therefore it is of prime importance for these mountain regions to complement single hazard assessment by coupled hazard scenarios on the basis of these scenarios risk evaluations may then be completed considering direct impacts on artificial dams hydropower schemes mining and road infrastructure as well as remote effects from possible dam breaches and mobilisation of mining and nuclear waste storages basic hazard and risk components are partly analysed in this paper and partly in a companion paper tien shan geohazards database landslide susceptibility and impacts

brachiopod geochemical records from across the carboniferous seas of north america evidence for salinity gradients stratification and circulation patterns abstract stable isotopic analyses of 100 well preserved carboniferous brachiopod shells representing two time slices from across north america reveal systematic regional changes in environmental conditions for both of the time slices studied the chesterian latest mississippian and the virgilian latest pennsylvanian 18o and 13c show a stepwise decrease moving across the continent from modern day west to east higher 18o in the west reflects greater water depths less freshwater input and more direct upwelling influence from cool open marine waters than in the east modelling based on these regional isotopic data indicates salinity reductions on the order of 1 4 psu in the appalachian basin relative to the midcontinent basin for the virgilian time interval over a range of reasonable thermal gradient and 18ofw assumptions the magnitude of this gradient is similar to those of modern day hudson bay and the panama bight which exhibit permanent haloclines driven by freshwater discharge considering existing paleoecological evidence for freshening the lack of more dramatic benthic freshening suggests that the depth of a regional halocline was shallower than the depths inhabited by thick shelled stenotopic brachiopods although other lines of evidence are necessary to verify the strength of the halocline estimated 18o temperatures for appalachian basin brachiopods are 3 5 c cooler than those of coeval conodonts due to either slightly warmer fresher surface waters or uncertainty in the phosphate 18o paleothermometer despite discrepancies in calculated temperatures the magnitude of the regional isotopic gradient derived from brachiopod and conodont proxies is similar after making appropriate glacioisotopic and water depth corrections a decreasing 13c trend toward the east southern paleolatitude likely reflects greater restriction and terrestrial influence near the sea s tropical shoreline trace element trends are less consistent and are affected by species and metabolism erratic variations in mg ca concentrations even among pristine samples of the same genera with similar 18o values and unrealistic mg ca derived temperatures justify continued caution in applying existing mg ca thermometer equations to paleozoic brachiopods

two dimensional interpretation of three dimensional magnetotelluric data an example of limitations and resolution summary interpretation of magnetotelluric mt data for three dimensional 3 d regional conductivity structures remains uncommon and two dimensional 2 d models are often considered an adequate approach in this paper we examine 2 d interpretation of 3 d data by considering the synthetic responses of a 3 d structure chosen specifically to highlight the advantages and limitations of 2 d interpretation 2 d models were obtained from inversion of the synthetic 3 d data set with different conditions noise and distortion applied to the data we demonstrate the importance of understanding galvanic distortion of the data and show how 2 d inversion is improved when the regional data are corrected prior to modelling when the 3 d conductive structure is located below the profile the models obtained suggest that the effects of finite strike are not significant if the structure has a strike extent greater than about one half of a skin depth in this case the use of only tm mode data determined better the horizontal extent of the 3 d anomaly when the profiles are located away from the 3 d conductive structure the use of only tm mode data can imagine phantom conductive structures below the profile in this case the use of both polarizations produced a better determination of the subsurface structures it is important to note that the main structures are identified in all the cases considered here although in some cases the large data misfit would cause scepticism about features of the models

tien shan geohazards database landslide susceptibility analysis abstract this paper is the second part of a new geohazards analysis applied to a large part of the tien shan central asia focused on landslide susceptibility computations that are based on recently compiled geographic geological and geomorphological data the core data are a digital elevation model an updated earthquake catalogue an active fault map as well as a new landslide inventory the most recently added digital data are a new simplified geological map an annual precipitation map as well as river and road network maps that were produced for the kyrgyz and tajik parts of the tien shan on the basis of these records we determine landslide densities with respect to morphological m geological g river distance r precipitation p earthquake e and fault f distance factors correlations were also established between scarp locations and the slope angle distance to rivers curvature these correlations show that scarps tend to be located on steeper slopes farther from rivers and on more convex terrain than the entire landslides on the basis of the landslide density values computed for each class of the aforementioned factors two landslide susceptibility maps are created according to the landslide factor analysis the first one considers correlations between the landslide occurrences and the first four factors mgrp the second one is based on the first map mgrp combined with the seismo tectonic influence e f on landslide distributions from the comparison of these two maps with actual landslide distributions we infer that the distances to rivers as well as to faults and past earthquakes most strongly constrain the susceptibility of slopes to landslides we highlight several zones where the landslide susceptibilities computed for the mgrp e f factors fit better the observed concentration of landslides than those computed for the mgrp factors alone for a few zones both maps produce high landslide susceptibilities that do not well reflect the observed low sub regional landslide activity for some cases we consider that some influencing factors must not have been well taken into consideration for others we show that we simply had missed landslide detections at the scale of the mountain range the computed landslide susceptibility maps fit the observed landslide distributions relatively well but these maps only represent the spatial component of landslide hazards temporal aspects are not considered by this analysis

study of the 1920 haiyuan earthquake induced landslides in loess china many large scale landslides induced by earthquakes have been reported in loess soils they often cause catastrophes because they travel long distances at high velocity to clarify the mechanism of these landslides field survey was performed on the landslides triggered by the haiyuan earthquake china 1920 and a series of ring shear tests was conducted on the loess soils collected from a landslide the field surveys revealed that most of the loess landslides triggered by the haiyuan earthquake occurred on concave slopes gentler than 15 with long runout distance showing very small equivalent friction angle cyclic ring shear tests on saturated specimens in the undrained condition showed that when cyclic shear stress was applied to a loose loess specimen pore pressure was built up gradually before the failure and after that large pore pressure was quickly generated due to the failure of loess soil structure meanwhile to investigate the mechanism that produces the high mobility of loess landslides ring shear tests were conducted on loess specimens with large shear displacement of up to several meters under the undrained condition and it was found that the initial normal stress has no effects and overconsolidation ratio has little if any effects on the apparent friction angle in the steady state for loess soils results of tests on soils at different saturation degrees revealed that the reduction in shear strength results more likely from the generation of pore water pressure not of pore air pressure

paleoenvironments of the upper pennsylvanian ames limestone and associated rocks near pittsburgh pennsylvania paleoenvironmental analysis of the upper pennsylvanian ames limestone and associated rocks east of pittsburgh pennsylvania reveals a range of depositional environments from shallow marine to deltaic the depositional history began with paludal sedimentation followed by eastward transgression of a clastic lagoon dominated by abundant molluscs and mud lloater brachiopods especially thin shelled neochonetes this period was followed by the eastward transgression of a tidal belt and a shoreward low energy carbonate lagoon tidal belt sediments were derived from 1 shoreward transportation of offshore shelf sediments carbonate mud and fine sand fine crinoid debris and trilobites by tidal currents and 2 erosion and transportation of underlying clastic lagoon sediments molluscs neochonetes and clay minerals in tidal channels the carbonate lagoon contained abundant neochonetes in carbonate mud abandonment of the tidal belt allowed the eastward transgression of open circulation offshore shelf carbonate sediments the far offshore sediments were dominated by crinoids whereas near offshore shelf sediments had a sparse fauna of crurithyris and crinoids in the final stage of deposition deltaic progradation from the east established the following offshore to onshore sequence of environments offshore carbonate shelf near shore clay miner shelf prodelta and delta front nearshore clay mineral shelf deposits were dominated by crurithyris a robust thick shelled brachiopod indicative of higher energy conditions than were existent for the thin shelled neochonetes

eastern termination of the altyn tagh fault western china constraints from a magnetotelluric survey the left lateral altyn tagh fault forms the northern boundary of the tibetan plateau the strike slip rate of the active altyn tagh fault decreases northeastward and reduces close to zero as it passes north of the qilian shan this geometry raises controversies on whether and how the fault terminates or extends further east to address these controversies wide band magnetotelluric data were collected along four profiles across the altyn tagh fault ranging from 135 to 261 km in length all four profiles are located in the foreland of the qilian shan ranges and are oriented perpendicular to the inferred fault zone that could be the continuation of altyn tagh fault both the two dimensional and three dimensional electrical resistivity models derived from our magnetotelluric data show that the hexi corridor crust is generally of low resistivity whereas the crust of the huahai jinta basin is in general of high resistivity with a local and isolated low resistivity anomaly within the mid lower crust the generally high resistivity crust of the huahai jinta basin may be rheologically unfavorable for the altyn tagh fault passing through the basin toward the northeast the entirely different electrical structure between the hexi corridor and its northern neighbors indicates the existence of a tectonic boundary that coincides with the altyn tagh fault in the west and reverse faults in the east the two dimensional electrical conductivity models suggest that the altyn tagh fault transfers from a single fault in the west to a branching set of mainly dip slip faults in the east

two dimensional topographic responses in magnetotellurics modeled using finite elements we simulate the magnetotelluric response to two dimensional earth topography using finite elements linear interpolation of the secondary field parallel to strike over triangular elements allows accurate modeling of inclined resistivity boundaries including topographic surfaces to avoid discontinuities in field derivatives or resistivity care must be taken that the nodal values of the field parallal to strike used to obtain the auxiliary secondary fields are kept within uniform earth media the nodal locations may be shifted but the derivatives still are evaluated at the field points of interest correct values may be returned at gentle breaks in slope as well as along straight surfaces the finite element program is verified by comparison with the analytic transverse magnetic response of a hemicylindrical depression and with rayleigh scattering and transmission surface results for transverse electric and transverse magnetic polarization agreement with the other methods generally is excellent with t

landslides triggered by the 1949 khait earthquake tajikistan and associated loss of life abstract earthquake triggered landslides are a major geological hazard in central asia in july 1949 the m7 4 khait earthquake triggered many hundreds of landslides in a mountainous region near the southern limit of the tien shan mountains central tajikistan these landslides involved widespread rock slope failure as well as large numbers of flowslides in loess that mantles the steep slopes of the region in the yasman valley hundreds of loess landslides coalesced to form a massive loess flow est vol 245 mm 3 that travelled up to 20 km on a slope of only 2 in an adjacent valley the khait landslide involved transformation of an earthquake triggered rockslide into a very rapid flow by the entrainment of saturated loess into its movement it travelled 7 41 km over a vertical distance of 1421 m with an estimated average velocity of 30 m s we estimate its volume as 75 mm 3 an order of magnitude less that previously published estimates the khait landslide was simulated using dan the number of casualties due to earthquake triggered landslides in the epicentral region was considerable approximately 4000 people were killed in the yasman valley loess flow as 20 villages kishlaks were overwhelmed in the khait landslide alone we estimate ca 800 people lost their lives when the villages of khait and khisorak were overrun by rapidly moving debris our data indicates that a total of approximately 7200 people were killed by earthquake triggered landslides in the epicentral region of the khait earthquake and that in terms of loss of life the 1949 yasman valley loess flow was one of the most destructive landslides in recent history

complex rupture mechanism and topography control symmetry of mass wasting pattern 2010 haiti earthquake the 12 january 2010 mw 7 0 haiti earthquake occurred in a complex deformation zone at the boundary between the north american and caribbean plates combined geodetic geological and seismological data posited that surface deformation was driven by rupture on the leog ne blind thrust fault while part of the rupture occurred as deep lateral slip on the enriquillo plantain garden fault epgf the earthquake triggered 4490 landslides mainly shallow disrupted rock falls debris soil falls and slides and a few lateral spreads over an area of 2150 km2 the regional distribution of these slope failures defies those of most similar earthquake triggered landslide episodes reported previously most of the coseismic landslides did not proliferate in the hanging wall of the main rupture but clustered instead at the junction of the blind leog ne and epgf ruptures where topographic relief and hillslope steepness are above average also low relief areas subjected to high coseismic uplift were prone to lesser hanging wall slope instability than previous studies would suggest we argue that a combined effect of complex rupture dynamics and topography primarily control this previously rarely documented landslide pattern compared to recent thrust fault earthquakes of similar magnitudes elsewhere we conclude that lower static stress drop mean fault displacement and blind ruptures of the 2010 haiti earthquake resulted in fewer smaller and more symmetrically distributed landslides than previous studies would suggest our findings caution against overly relying on across the board models of slope stability response to seismic ground shaking

identifying hierarchical spatial patterns within paleocommunities an example from the upper pennsylvanian ames limestone of the appalachian basin abstract identifying ecological mechanisms that produce hierarchically arrayed spatial variation in community structure can be difficult in the fossil record due to conflation of spatial and temporal patterns however this difficulty can be mediated by minimizing the temporal duration of deposition within the unit examined in this study the fauna of the upper pennsylvanian ames limestone conemaugh group was analyzed to explore whether ames paleocommunities exhibited hierarchical structure in a spatial dimension this widespread carbonate unit was deposited during the maximum flooding interval of a glacio eustatically influenced fifth order sea level cycle and preserved taxa are contemporaneous within only a few thousand years paleocommunity structure and variability was assessed at multiple spatial scales using samples collected from seven outcrops of the ames limestone throughout southeastern ohio which form a northeast to southwest trending transect parallel to the paleoshoreline abundance data were collected using quadrat sampling for brachiopods bivalves gastropods bryozoa corals crinoids echinoids trilobites and foraminifera paleocommunity structure was analyzed via cluster ordination guild and abundance analyses at multiple spatial scales within a single locality among localities and within the total study area to provide insight on geographic partitioning of paleocommunity variation multiple levels of paleocommunity organization were recovered within the ames fauna all levels exhibited spatial partitioning but the inferred proximate controls shifted from abiotic environmental controls at higher hierarchical levels to biotic controls at the lowest level at the highest level differentiation into a northern and southern regional paleocommunity was controlled primarily by substrate consistency and habitat heterogeneity related to variation in fluvial input within the basin local paleocommunity differentiation reflects biotic responses to topographic and environmental conditions that were geographically distributed within the region whereas within outcrop variation was due largely to biotic feedback mechanisms

a paleopedologic and ichnologic perspective of the terrestrial pennsylvanian landscape in the distal appalachian basin u s a abstract the conemaugh group of southeastern ohio contains numerous ichnofossil bearing paleosols in both the lower glenshaw and upper casselman formations which were deposited during the kasimovian and gzhelian 305 301 ma along the distal edge of the appalachian basin this study examined the small scale twenty four stratigraphic sections were measured from ten sites in athens county ohio from which thirty paleosols were identified and described detailed field descriptions allowed differentiation of four distinct pedotypes one in the glenshaw formation and three in the casselman formation the glenshaw pedotype gpt is a vertisol that formed on a proximal to distal floodplain the three casselman pedotypes represent entisols inceptisols cpti alfisols cptii and vertisols cptiii all four types contain evidence of alteration by post pedogenic processes such as drowning by migrating river channels or rising sea level or a gradual transition from one alluvial subenvironment to another as a result of channel migration eight morphologically distinct ichnofossils were observed in the conemaugh group paleosols including three types of rhizoliths lined and unlined vertical to subhorizontal shafts chambers sinuous burrows with and without bioglyphs and general burrow mottling these ichnofossils occur in distinct assemblages that form unique ichnocoenoses within each of the four pedotypes they were produced by various plants arthropod detritivores carnivores and herbivores as well as amphibians and early reptiles as temporary to permanent members of complex soil ecosystems pedogenic properties combined with ichnofossil diversity abundance and distribution increase the understanding of the complexity of late pennsylvanian soil ecosystems and provide details on the small scale variations in paleosols due to short term autogenic changes in alluvial environments although broad regional studies across 10 2 10 3 of kilometers are important small scale variations over less than 1 km are needed to understand the effects of localized changes in hydrology topography organisms and sedimentary processes on soil formation and soil biodiversity consideration of these types of localized studies is also vital when attempting to interpret regional to global scale aspects of environment such as climate from paleosols

earthquake triggered increase in sediment delivery from an active mountain belt in tectonically active mountain belts earthquake triggered landslides deliver large amounts of sediment to rivers we quantify the geomorphic impact of the 1999 mw 7 6 chi chi earthquake in taiwan which triggered 20 000 landslides coseismic weakening of substrate material caused increased landsliding during subsequent typhoons most coseismic landslides remained confined to hillslopes downslope transport of sediment into the channel network occurred during later storms the sequential processes have led to a factor of four increase in unit sediment concentration in rivers draining the epicentral area and increased the magnitude and frequency of hyperpycnal sediment delivery to the ocean four years after the earthquake rates of hillslope mass wasting remain elevated in the epicentral area

inversion of magnetotelluric data for 2d structure with sharp resistivity contrasts we have developed a linearized algorithm to invert noisy 2 d magnetotelluric data for subsurface conductivity structures represented by smooth boundaries defining sharp resistivity contrasts we solve for both a fixed number of subsurface resistivities and for the boundary locations between adjacent units the boundary depths are forced to be discrete values defined by the mesh used in the forward modeling code the algorithm employs a lagrange multiplier approach in a manner similar to the widely used occam method the main difference is that we penalize variations in the boundary depths rather than in resistivity contrasts between a large number of adjacent blocks to reduce instabilities resulting from the breakdown of the linear approximation we allow an option to penalize contrasts in the resistivities of adjacent units we compare this boundary inversion method to the smooth occam inversion for two synthetic models one that includes a conductive wedge between two resistors and another that includes a resistive wedge between two conductors the two methods give good agreement for the conductive wedge but the solutions differ for the more poorly resolved resistive wedge with the boundary inversion method giving a more geologically realistic result application of the boundary inversion method to the resistive gemini subsalt petroleum prospect in the gulf of mexico indicates that the shape of this salt feature is accurately imaged by this method and that the method remains stable when applied to real data

an interpretation technique for superimposed induction anomalies summary a salt dome in a trough region of the north german basin was investigated with electromagnetic methods a full set of excellent magnetovariational and gnetotelluric sites by robust statistical frequency analysis in the period range d pulsations the transfer functions are related to a fixed reference site at a great distance from the salt dome the results are presented using induction arrows and principal axes of the magnetic or telluric field they show the superimposed influence of additional conductivity anomalies in the surrounding area the north german conductivity anomaly the gifhorn jurassic trough and two neighbouring salt domes wesendorf and vorhop assuming that the mutual inductive couplings between these anomalies are not too strong which is demonstrated each anomaly was interpreted individually to obtain a suitable data set belonging to a single anomaly the transfer functions of the others had to be subtracted from the field data this was carried out in four steps 1 the transfer functions belonging to preliminary salt dome models were derived with 3 d numerical model calculations 2 after the subtraction of this 3 d model data from the anomalous field data 2 d numerical model calculations were used for finding the model of the gifhorn trough 3 the salt domes were modelled again in 3 d using a 2 d reduced data set which was derived by subtracting the 2 d model data from the anomalous field data 4 the anomalous transfer functions of all the induction models were subtracted from the anomalous field data for interpreting the remaining data an interpretation procedure was developed for explaining induction data belonging to weakly coupled induction anomalies this procedure may also be useful in the case of strong inductive couplings providing an initial 3 d model for more sophisticated and time intensive model calculations that take all the anomalies into account

electrical resistivity structure at the northern margin of the tibetan plateau and tectonic implications 1 the ene wsw striking altyn tagh fault atf and the wnw ese trending western qilian mountains define the northern margin of the tibetan plateau new magnetotelluric data were collected along three profiles crossing the eastern section of the atf and the southern qilian mountains the basic sounding bandwidth ranged from 0 003 to 7000 s the transverse electric and transverse magnetic mode data sets were inverted into resistivity sections using a conventional two dimensional 2d inversion code and data at periods of 0 3333 5464 s were inverted using a commonly employed three dimensional 3d code the 3d results constrain the interpretation of the 2d models and the final interpretative resistivity models show that lithospheric structures are spatially variable along the atf and across southern qilian in profiles across the atf the main fault is imaged as a vertical resistivity boundary and the high resistivity body in the western profile extends about 15 km deeper than the corresponding body in the eastern profile positive flower structures are apparent in the western profile but are only weakly visible in the eastern profile these observations suggest that the depth of the atf is spatially variable mantle resistivity images indicate a relatively cold and rigid tarim lithosphere which is consistent with a geodynamic model of oblique subduction of the tarim basin below the atf a high resistivity body in the crust of southernmost qilian indicates a huge thick skinned structure low resistivity bodies at the crust mantle boundary south of the main atf are presumed to form a weak layer beneath northern tibet

evidence of a changing size frequency distribution of landslides in the kyrgyz tien shan central asia there is a strong possibility that environmental change whether climate or land use will be manifest as changes in the size frequency distribution of landslides here evidence is presented for this from western kyrgyzstan central asia remote sensing and spatial analysis have been applied to map mass movements in the central part of the maily say valley and to detect recent landslide activations the evolution of landslide activity over the past 50 years has been analysed on the basis of pre existing landslide maps and new analyses of aerial photographs as well as quickbird images five inventories were produced for the years 1962 based on the existing map of 1962 and aerial photographs of 1962 1984 based on the existing map of 1977 and aerial photographs of 1984 1996 based on aerial photographs of 1996 2002 based on the existing map of 2003 and quickbird imagery of 2002 and 2007 based on quickbird imagery of 2007 the geomorphologic features contained in the catalogues represent the landslide bodies observed from remote imagery of the corresponding year mapped landslides are generally considered as the result of a series of slope failure events size frequency analyses applied to the five landslide inventories show that both the number and size of unstable slopes increased from 1962 162 objects to 2007 208 objects and the power law exponent decreased over time this changing power law exponent may indicate that landslide related hazards are increasing this tendency is documented in more detail for two active landslide zones one in the main valley and one located to the west of it landslide detection methods were used to assist the evolution of slope instabilities choosing appropriate thresholds the image subtraction method based on normalized difference vegetation index ndvi allowed accurate detection of new sliding activation in these two zones this confirmed the results of the more extensive survey that there is a systematic shift in power law exponents and size frequency distributions for central asian landslides copyright 2011 john wiley sons ltd

statistical analysis of factors affecting landslide distribution in the new madrid seismic zone tennessee and kentucky abstract more than 220 large landslides along the bluffs bordering the mississippi alluvial plain between cairo ill and memphis tenn are analyzed by discriminant analysis and multiple linear regression to determine the relative effects of slope height and steepness stratigraphic variation slope aspect and proximity to the hypocenters of the 1811 12 new madrid mo earthquakes on the distribution of these landslides three types of landslides are analyzed 1 old coherent slumps and block slides which have eroded and revegetated features and no active analogs in the area 2 old earth flows which are also eroded and revegetated and 3 young rotational slumps which are present only along near river bluffs and which are the only young active landslides in the area discriminant analysis shows that only one characteristic differs significantly between bluffs with and without young rotational slumps failed bluffs tend to have sand and clay at their base which may render them more susceptible to fluvial erosion bluffs having old coherent slides are significantly higher steeper and closer to the hypocenters of the 1811 12 earthquakes than bluffs without these slides bluffs having old earth flows are likewise higher and closer to the earthquake hypocenters multiple regression analysis indicates that the distribution of young rotational slumps is affected most strongly by slope steepness about one third of the variation in the distribution is explained by variations in slope steepness the distribution of old coherent slides and earth flows is affected most strongly by slope height but the proximity to the hypocenters of the 1811 12 earthquakes also significantly affects the distribution the results of the statistical analyses indicate that the only recently active landsliding in the area is along actively eroding river banks where rotational slumps formed as bluffs are undercut by the river the analyses further indicate that the old coherent slides and earth flows in the area are spatially related to the 1811 12 earthquake hypocenters and were thus probably triggered by those earthquakes these results are consistent with findings of other recent investigations of landslides in the area that presented field historical and analytical evidence to demonstrate that old landslides in the area formed during the 1811 12 new madrid earthquakes results of the multiple linear regression can also be used to approximate the relative susceptibility of the bluffs in the study area to seismically induced landsliding

lithospheric and sublithospheric anisotropy beneath central southeastern brazil constrained by long period magnetotelluric data abstract electric anisotropy calculated from geoelectric strikes of magnetotelluric mt data and seismic anisotropy derived from shear wave splitting parameters are jointly analyzed to estimate the degree and orientation of strain in the subcontinental mantle of central southeastern brazil high quality long period mt soundings are available at 90 sites concentrated along four profiles at the southwestern and southern borders of the paleoproterozoic archean sao francisco craton this data set is complemented by a previous study of sks and skks splitting measurements available at more than 40 sites covering a slightly wider region for this study the mt data were processed with modern techniques including recovery of the undistorted em field polarizations through correction of static shift and phase mixing due to galvanic distortions three dimensional forward modelling of mt and gds geomagnetic depth soundings transfer functions supports interpretation of deep electrical anisotropy in the region magnetotelluric phase responses of orthogonal propagation modes present slight splitting at long periods for most of the sites indicative of overall electrically low mantle anisotropy to depths greater than 250 km the electrical strike azimuths are parallel to the fast nw directions of shear wave splitting along the southern borders of the sao francisco craton suggesting that the seismic anisotropy also resides within the same depth range since this direction is very different from that of present day south american westward absolute plate motion it is inferred that no significant lateral mantle flow or deformation related to the plate motion is observed under the study area either because it is absent or the rigid lithosphere is much thicker than expected to explain the prevailing electric and seismic common direction it is suggested that a mechanical coupling between lithospheric and sublithospheric mantle exists a relic strain possibly resulting from ancient continental collision processes is interpreted to have induced a general alignment of olivine down to mantle depths beneath the continental rigid plate the observed slightly enhanced conductive texture could be associated with hydrogen diffusion along the aligned olivine a axis especially within mantle patches subjected to metasomatic processes the coincidence of mantle strikes with the trend of surface deformation pattern also suggests that crust lithospheric and sublithospheric upper mantle have deformed and translated coherently preserving the regional nw direction since the tectono thermal event responsible for the deformation distinct electric azimuths from the general nw trend are observed in regions probably perturbed by cretaceous rift related intraplate magmatism and in zones of complex deep structures produced by superposed nearly simultaneous oblique neoproterozoic collisions in the southeast of the sao francisco craton

low seasonality in central equatorial pangea during a late carboniferous highstand based on high resolution isotopic records of brachiopod shells the relationship between permian carboniferous glacial cycles and low latitude climate remains a subject of vigorous debate this study investigated seasonality and regional environmental variability in a portion of central equatorial pangea during a late pennsylvanian highstand using stable isotope and trace element analyses of brachiopod shells from the virgilian ames member of the conemaugh group in the appalachian basin u s a well preserved thick shelled neospirifer dunbari specimens were serially sampled across growth bands to elucidate a record of seasonal variability during the life of the organisms because neospirifer only colonized this marginal basin during near maximum highstands when stable near marine salinities were established these data are a direct proxy for intra annual climate fluctuations during interglacial times neospirifer specimens show remarkably little internal chemical variability with 18 o generally fluctuating by 0 4 or less and 13 c fluctuating by less than 1 5 within a single specimen moreover total 18 o variability between all specimens is only 1 5 this lack of variation reflects a homogeneous nonseasonal to weakly seasonal climate during the ames highstand both 18 o and 13 c are 1 5 lower than those of other virgilian specimens from regions with a more proximal connection to the open ocean suggesting at least moderate freshwater influence in the appalachian basin during this time although salinities remained close enough to marine levels to maintain stenohaline fauna thus brachiopod seasonal records indicate normal moist tropical conditions during this penultimate carboniferous interglacial with no evidence for strong monsoonal variations in temperature or rainfall

the chromite deposits of the troodos complex cyprus evidence for the role of a fluid phase accompanying chromite formation the troodos ophiolite of cyprus hosts chromite deposits both as podiform bodies within the basal harzburgite and as lesser layers and schlieren within the overlying dunites and clinopyroxene dunites of the metacumulate sequence all chromitite types have been studied from both field and mineralogical aspects with particular emphasis on the chemistry of the ubiquitous silicate inclusions within chromite grains two distinct inclusion assemblages have been documented chromites from podiform bodies contain abundant hornblende serpentine ortho and clinopyroxene and lesser olivine while those from the metacumulates host pargasite albite serpentine and rare pyroxenes this implies that no single silicate inclusion assemblage in chromite can be considered typically ophiolitic the presence of an alkalirich fluid phase during chromite crystallization as evidenced by the unusual mineralogy of these inclusions has already been widely discussed in the literature however the marked stratigraphic control of inclusion types in chromite as reported here enables more complete modelling of the evolution of this phase to be made