positive inversion tectonics in foreland fold and thrust belts a reappraisal of the umbria marche northern apennines central italy by integrating geological and geophysical data abstract unraveling the tectonic style in the outer zones of fold and thrust belts is generally puzzling because the basement cover relationships are often hidden in the subsurface as in the outer northern apennines of italy this study aims to reconstruct the deep setting of the northern apennine foreland thrust belt by integrating surface structural geological and subsurface seismic reflection profile and well data corroborated by a gravity magnetic modeling a remarkable mountain ridge the umbria marche apennine ridge umar which corresponds to a prominent area of structural and topographic elevation characterizes the morphology of the northern apennines this mountain ridge is constituted by meso cenozoic carbonates involved in neogene compressive structures and is surrounded by wide exposures of foredeep deposits the basement cover relationships are poorly constrained and both thin and thick skinned tectonic styles have been applied the interpretation of subsurface data allowed recognizing a thick pre jurassic sedimentary sequence filling a late paleozoic triassic symmetric fault bounded extensional basin lying directly below the umar this deep rooted basin underwent positive inversion during the neogene compression and thrust fold development the reconstructed thick skinned inversion tectonic model is consistent with both the modest amount of shortening and the remarkable structural elevation of the umar the outcomes of this study reveal that prominent mountain ridges occurring in foreland thrust belts are most likely related to the deep rooted basement involved positive inversion of pre existing extensional basins

the fracture patterns of the tin tin anticline fracturing process during the foreland evolution in the calchaqui valley northwestern argentina abstract we present a field based work which illustrates the fracture patterns of the carbonate silicoclastic yacoraite formation in the tin tin anticline a basement fault related fold located in southern part of the eastern cordillera northwestern argentina the fracture patterns include small scale strike slip faults vertical shear fractures and en echelon arrays thrust faults extension fractures joints veins and normal faults and stylolites extensional mesostructures were formed by along foreland stretching prior to the contractional ones that were formed by the layer parallel shortening mechanism furthermore all fractures are interpreted to be formed before or at the early stages of folding and thrusting during the andean contraction all of them belonging to the eocene thrust belt foreland system at the calchaqui valley of northwestern argentina

the development of antarctic glaciation and the neogene paleoenvironment of the maurice ewing bank abstract a micropaleontologic magnetostratigraphic and sedimentologic analysis of 56 piston cores provides the basis of a geologic study of the late miocene to holocene depositional and erosional history of the intermediate depth maurice ewing bank meb located at the eastern extremity of the falkland malvinas plateau southwest atlantic ocean sedimentation on the meb is controlled presently by the position of the polar front and strong bottom currents beneath the axis of the antarctic circumpolar current acc fluctuations in the position of the polar front and in the intensity of the acc are inferred to have largely controlled deposition on the meb since the initiation of acc flow over the bank in the miocene the sedimentary record of the meb is used to infer the late miocene to holocene oceanographic and climatic conditions in the south atlantic sector of the southern ocean the meb suffered major erosion by intense acc flow during late miocene time which exposed cretaceous miocene sediment near the surface and shaped the present configuration of the bank this erosional event is inferred to have occurred during late miocene to early pliocene time 7 2 4 7 m y b p with the major phase of erosion occurring between middle magnetostratigraphic chron 7 and late chron 6 7 2 6 2 m y b p we suggest that the miocene sedimentary record of the meb and other paleoenvironmental evidence from the circum antarctic region precludes the existence of a west antarctic ice sheet or extensive ice shelves along the antarctic margin prior to the late miocene during the late miocene a west antarctic ice shelf formed in the former west antarctic sea and rapidly thickened until it grounded below sea level to form the west antarctic ice sheet formation of this ice sheet with floating and partially grounded extensions ice shelves in the ross and weddell embayments led to the first major production of true antarctic bottom water formed in a manner similar to today which permanently altered global abyssal circulation late miocene changes in oceanic ccd levels and a permanent shift in the oceanic 13 c 12 c composition may be attributed to this major change in abyssal circulation a decrease in acc velocity during an early pliocene amelioration of climate led to resumption of deposition on the bank from 4 7 to 3 9 m y b p intensification of the acc during the late gilbert and early gauss chrons again resulted in limited deposition and widespread erosion and or non deposition over most of the meb from 4 0 to 3 2 m y b p acc velocity apparently began to wane during the middle of the gauss chron and allowed widespread deposition on the bank during late gauss time 2 9 2 48 m y b p and over more limited areas during earliest matuyama time 2 48 to about 2 2 m y b p during middle to late matuyama time bottom current intensity reached its greatest post miocene level forming a regional disconformity between sediments of about 2 0 and 1 0 m y in age this increased circumpolar circulation and associated erosion is inferred to have peaked during the late matuyama chron 1 2 1 0 m y b p and is approximately the same age as the tentatively dated greatest patagonian glaciation in nearby southern argentina between 1 0 and 0 7 m y b p the bank was blanketed with a coarse erosion resistant layer of ice rafted detritus which armored the older sediment thereby protecting it from major subsequent erosion sedimentation on the meb during the bruhnes chron 720 000 yr b p present was intermittent and finally culminated with the deposition of a veneer of carbonate ooze during or since latest pleistocene time

plio quaternary uplift rates in the outer zone of the central apennines fold and thrust belt italy abstract geological seismic and borehole data permitted the reconstruction of the plio quaternary uplift subsidence and erosion sedimentation history for the outer sector of the central apennines during the latest contractional stages middle late pliocene the frontal sector of the belt experienced a net subsidence locally compensated by the growth of the fold and thrust system this tectonic uplift was localized at the axial culmination of the anticlines and particularly for the major structures was responsible for exhumation and erosion of the neogene succession and for near flat planation surfaces development on meso cenozoic carbonate rocks at the crest of the anticlines since the early middle pleistocene a regional doming involved the outer part of the belt peri adriatic domain this process interacted with quaternary eustatic sea level fluctuations and caused the basinward migration of shallow marine deposits forming an overall prograding system quaternary shoreline retreat base level drop and climatic changes were mainly associated with valley deepening and fluvial terrace formation the present study outlines that fold thrust growth and regional doming driving processes characterized by different amplitude wavelength and uplift rate amounts are both responsible for the morphological setting of the central apennines external zones

evidence for pre folding vein development in the oligo miocene asmari formation in the central zagros fold belt iran in order to understand the interplay between vein development and folding in the carbonates of the oligo miocene asmari formation one of the main hydrocarbon reservoir rocks in iran several anticlines have been investigated in the central part of the zagros folded belt combining observations of relative chronology between veins based on calcite filling phases and crosscutting abutting relationships as well as aerial satellite image interpretation on several anticlines allowed proposing a tectonic model highlighting the widespread development of veins and other extensional micro meso structures in the central zagros folded belt our data suggest that most of the veins affecting the asmari formation predated the main miocene pliocene folding episode an early regional vein set striking n50 marked the onset of collisional stress build up in the region then n150 and n20 trending vein sets were initiated in response to local extension caused by large scale flexure drape folds above n s and n140 basement faults reactivated under the regional ne compression at the onset and during miocene pliocene folding of the sedimentary cover the early formed veins were reactivated reopened and or sheared while duplexes low angle reverse faults and thrusts formed beyond regional implications this study puts emphasis on the need of carefully considering regional local vein development predating folding as well as influence of underlying basement faults in models of folded fractured reservoirs in fold thrust belts

contrasting styles of fault reactivation in curved orogenic belts examples from the central apennines italy the geometry of the apennine fold and thrust belt has been strongly influenced by the original architecture of the adria paleomargin in the central apennines pre thrusting normal faults pre orogenic permian triassic jurassic and synorogenic neogene were reactivated with compressional kinematics during the neogene quaternary orogenesis we present a study of the control of preexisting extensional faults on thrust tectonics in the central apennines we describe positive inversion geometries of some salient fold and thrust structures from the central apennines setteporte the sabini mountains the sibillini mountains montagna dei fiori the gran sasso range maiella mountain and casoli bomba by integrating surface geological data and seismic line interpretation in these structures different styles of fault reactivation depend on their orientation with respect to the subsequent compressional ne sw trending stress field the nw se and wnw ese trending pre thrusting normal faults in the backlimbs of the anticlines were displaced and passively translated in the hanging wall blocks of the thrust planes thus exhibiting a classical shortcut geometry shortcut anticlines differently pre orogenic normal faults in the n s trending anticlines were reactivated in a transpressive deformational context as documented by the mainly dip slip and strike slip kinematics along the thrusts and back thrusts respectively reactivation anticlines the cases studied document differences in geometry in fold and thrust structures related to the trend of preexisting extensional faults showing that different reactivation geometries linked to the same inversion event can coexist at regional scale in curved fold and thrust belts the proposed inversion tectonic model and the resulting geometry of the fold and thrust belt could possibly be applied to analogous orogenic belts

the effects of pre existing normal faults on thrust ramp development an example from the northern apennines italy the umbria marche foreland fold and thrust belt in the northern apennines of italy provides excellent evidence to test the hypothesis of synsedimentary structural control on thrust ramp development this orogenic belt consists of platform and pelagic carbonates late triassic to miocene in age whose deposition was controlled by significant synsedimentary extension normal faulting mainly active from jurassic through late cretaceous paleogene time resulted in significant lateral thickness variability within the related stratigraphic sequences by late miocene time the sedimentary cover was detached from the underlying basement and was deformed by east verging folds and west dipping thrusts two restored balanced cross sections through the southernmost part of the belt show a coincidence between the early synsedimentary normal faults and the late thrust fault ramps these evidences suggest that synsedimentary tectonic structures such as faults and the related lithological lateral changes can be regarded as mechanically important controlling factors in the process of thrust ramp development during positive tectonic inversion processes

beryllium 10 in hydrothermal vent deposits from the east pacific ridges role of sediments in the hydrothermal processes beryllium 10 concentrations were determined for 31 handpicked hydrothermal sulfides six oxyhydroxides seven basalts and five sediments collected from the hydrothermally active areas of the east pacific ridges the samples include specimens from the east pacific rise epr at 21 n and 13 n the galapagos rift the guaymas basin and the gorda and the juan de fuca ridges additional samples from massive sulfides associated with the oman ophiolites were studied in all samples we obtained values ranging from 0 04 106 atoms g to 125 106 atoms g with the lowest values being very close to our blank 0 015 106 atoms g the data show systematic variations with sample location and type the 10be concentrations measured for the mid ocean basalts are of the order of 0 3 10 atoms g and reach 3800 106 atoms g for the pelagic deep sea sediments collected near the epr 21 n based on their 10be concentrations we can clearly distinguish two categories of sulfides sulfides containing low 10be concentration 106 atoms g located atop of a thick pile of young sediments guaymas basin or gorda ridge the oxy hydroxides collected on some of the juan de fuca chimneys are always very rich in 10be with concentrations reaching 125 106 atoms g we propose three mechanisms to explain these data 1 mechanical entrapment of sediments in the hydrothermal chimneys as observed in the gorda ridge sulfides 2 leaching of 10be from the ocean crust sediments transport by hydrothermal fluids and coprecipitation with heavy metals as hypothesized to explain the be concentrations observed in the guaymas basin and 3 passive adsorption of 10be from seawater preferred hypothesis oxy hydroxides of the areas with no sediment cover

from mesozoic rifting to apennine orogeny the gran sasso range italy the apennines are a low temperature accretionary prism generated by the west directed subduction of the adriatic ionian plate whose structural origin is still to be fully understood the highest and best exposed seg ment of the apennines the gran sasso range is here documented to unravel the tectonic history of the northern tip of gondwana it is located along a ne verging salient of thrust sheets decoupling the sedimentary cover of the subducting adriatic lithosphere field mapping and structural analysis along the e w trending left lateral transpressive segment of the salient highlight the interplay of the inherited mesozoic passive margin stratigraph ic and tectonic framework with the neogene contraction the rheological differences between the massive carbonate platform and the well bedded turbiditic and pelagic limestones determined along strike undulations of the thrusts geometries and fold styles during shortening heterogeneities are due to inherited syn and post rift mesozoic tectonics the gran sasso overturned anticline shows a backlimb anomalously tilted toward the foreland and we infer this dip as being related to a deeper back thrust of a triangle zone the pinching out of the foredeep sequence on the growth anticline forelimb dates the contractional phases of the region to the late messinian from the late pliocene to present the area has been uplifted and extended about 2 km by oblique normal faults cross cutting the accretionary prism some of them are seismically active as shown by the 2009 mw 6 3 l aquila earthquake

10be and36cl depth profiles in an apollo 15 drill core cosmic ray produced10be t1 2 1 6 106 years and36cl t1 2 3 0 105 years have been measured in the apollo 15 long core for study of galactic cosmic ray production profiles using tandem accelerator mass spectrometry from these experiments the half attenuation length for10be production and36cl production were calculated to be 120 g cm2 and 132 g cm2 150 400 g cm2 region the measured half attenuation length for10be is slightly longer than that predicted by the reedy arnold theoretical model the flatter and somewhat deeper maximum seen in the36cl profile compared to the10be 26al and53mn profiles can be explained by production from secondary thermal neutrons on35cl

10be distribution in soils from merced river terraces california abstract the distribution and residence time of cosmogenic 10 be in clay rich soil horizons is fundamental to understanding and modelling the migration of 10 be on terrestrial sediments and in groundwater solutions we have analyzed seven profiles of clay rich soils developed from terrace sediments of the merced river california the terraces and soils of increasing age are used to compare the 10 be inventory with a simple model of accumulation decay and erosion the data show that the distribution of 10 be varies with soil horizon clay content that the residence time of 10 be in these horizons exceeds 10 5 years and that to a rough approximation the inventory of 10 be in a thoroughly sampled soil profile fits the equation n q em 1 e where q is delivery rate e is erosion rate m is the concentration of 10 be in the eroding surface layer is the decay constant and t is the age of the depositional unit from which the soil has developed the general applicability of this model is uncertain and warrants further testing in well calibrated terrace sequences

fingerprinting stress stylolite and calcite twinning paleopiezometry revealing the complexity of progressive stress patterns during folding the case of the monte nero anticline in the apennines italy in this study we show for the first time how quantitative stress estimates can be derived by combining calcite twinning and stylolite roughness stress fingerprinting techniques in a fold and thrust belt first we present a new method that gives access to stress inversion using tectonic stylolites without access to the stylolite surface and compare results with calcite twin inversion second we use our new approach to present a high resolution deformation and stress history that affected meso cenozoic limestone strata in the monte nero anticline during its late miocene pliocene growth in the umbria marche arcuate ridge northern apennines italy in this area an extensive stylolite joint vein network developed during layer parallel shortening lps as well as during and after folding stress fingerprinting illustrates how stress in the sedimentary strata did build up prior to folding during lps the stress regime oscillated between strike slip and compressional during lps before ultimately becoming strike slip again during late stage fold tightening our case study shows that high resolution stress fingerprinting is possible and that this novel method can be used to unravel temporal relationships that relate to local variations of regional orogenic stresses beyond regional implications this study validates our approach as a new powerful toolbox to high resolution stress fingerprinting in basins and orogens combining joint and vein analysis with sedimentary and tectonic stylolite and calcite twin inversion techniques

syn contractional overprinting between extension and shortening along the montagna dei fiori fault during plio pleistocene antiformal stacking at the central apennines thrust wedge toe

ancient synsedimentary structural control on thrust ramp development an example from the northern apennines italy the umbria marche sabina foreland fold and thrust belt northern apennines italy provides excellent test cases for the hypothesis of ancient syndepositional structural features controlling thrust ramp development the sedimentary cover late triassic to miocene in age is made of platform and pelagic carbonates whose deposition was controlled by significant synsedimentary extension normal faulting mainly during the jurassic and the late cretaceous palaeogene determined sensible lateral thickness variations within the relative sequences by late miocene the sedimentary cover was detached from its basement along a mainly evaporitic horizon and was deformed by means of eastward verging folds and thrusts in order to locate the points where thrust ramps branch off the basal detachment both line length and equal area techniques were used in the construction of a balanced cross section through three major fault related folds in southeastern umbria the nucleation of thrust ramps was controlled by the occurrence of jurassic and cretaceous palaeogene synsedimentary normal faults these interrupted the lateral continuity of the evaporitic unit the late triassic anidriti di burano fm at the base of the sedimentary cover and acted as obstacles to the eastward propagation of the thrust system giving rise to major folds which originated from tip line folding processes therefore the inferred relationships between ancient normal faults and late thrusts indicate that synsedimentary tectonic structures and the related lateral stratigraphic variations can be envisaged as mechanically important perturbations which effectively control the nucleation and development of thrust ramps

coalescence of fault bend and fault propagation folding in curved thrust systems an insight from the central apennines italy the coalescence and spatial variability of different thrust related folding mechanisms involving the same mechanical multilayer along a curved thrust system are documented in this study the field based analysis of thrust related folds spectacularly exposed in the gran sasso thrust system central apennines of italy allowed us to reconstruct the interference fold pattern between fault bend and fault propagation folding these two thrust related folding mechanisms exhibit spatial variability along the differently oriented ramps of the curved gran sasso thrust system passing from one style to the other their selective development is controlled by contrasting styles of compressional normal fault reactivation related to positive tectonic inversion fault bend and fault propagation folding interact with a characteristic interference fold pattern in the salient apex zone of the curved thrust system due to their synchronous in sequence growth this interference fold pattern might be helpful and predictive when reconstructing lateral variations in different thrust related folds in similar subaerial or submarine thrust belts

coexistence of fault propagation and fault bend folding in curve shaped foreland fold and thrust belts examples from the northern apennines italy terra nova 24 396 406 2012 abstract fault bend and fault propagation folds have unique profiles in foreland fold and thrust belts that are caused by different fault related folding models and controlled by the mechanical characteristic of the multilayer and or by reactivation of normal faults in a positive inversion tectonics context in this work nne ssw and nw se trending anticlines related to the neogene curve shaped olevano antrodoco sibillini thrust northern apennines italy are investigated to reconstruct fault related folding mechanisms geological and structural analysis allows us to interpret the nne ssw trending anticlines as fault bend reactivation folds and the nw se trending anticlines as fault propagation shortcut anticlines the coexistence of fault bend and fault propagation folding processes involving the same multi layered succession in different arms of a curve shaped thrust is explained in an inversion tectonics context this along strike variation of different folding mechanisms might be recognised in similar curve shaped orogenic thrust belts controlled by structural inheritance

revitalising exploration and re development of deep carbonate targets in the southern apennines thrust belt southern italy reappraising vintage data with modern approaches

macro and meso scale structural criteria for identifying pre thrusting normal faults within foreland fold and thrust belts insights from the central northern apennines italy

the khaviz anticline an outcrop analogue to giant fractured asmari formation reservoirs in sw iran the carbonate reservoirs in the late oligocene early miocene asmari formation in the dezful embayment of sw iran are characterized by low matrix permeability and effective drainage is dependent on the occurrence of open fractures limited information on fracture orien tation and fracture density is available from core and borehole image data and high quality high resolution three dimensional seismic is often lacking in this area well and core data do not contain information on important fracture parameters like length distribution crosscutting relationships fracture density v lithology and bed thickness the understanding of fracture distri bution and formation in the region and their effects on fluid flow has been greatly improved by the use of outcrop analogue data exposures of the asmari formation in the khaviz anticline are in close vicinity to the giant hydrocarbon fields the khaviz anticline has a similar geometry and structural history to the major hydrocarbon fields in the area and represents an excellent analogue for these two types of fracture features were observed diffuse fracturing and fracture swarms the diffuse fractures form networks and comprise structures grouped into four fractures sets which are the typical for this type of anticline two orthogonal fracture sets are oriented parallel and perpendicular to the fold axis and two conjugate fracture sets are oblique to the fold axis with their obtuse angle intersecting the trend of the fold axis the fractures are typically stratabound sub perpendicular to bedding and commonly about the bounding stratigraphic surfaces to a large extent the density and height of fractures in the asmari formation are controlled by the mechan ical stratigraphy which is controlled by the depositional environment and cycles these outcrop data have been essential in the generation of discrete fracture network dfn models and the population of the fracture properties in the reservoir models

the fracture network a proxy for mesoscale deformation constraints on layer parallel shortening history from the malargue fold and thrust belt argentina an analysis was performed of the fracture networks in the n s trending thick skinned malargue fold and thrust belt mftb a total of 2000 planar structures including joints and veins were measured in different structural domains ranging from surficial thin skinned systems detached in the cover to large scale structures such as basement cored folds the investigated stratigraphic section ranges from the middle jurassic cuyo group to the paleocene malargue group including sandstones siltstones shales and limestones four main fracture sets are identified trending e w nw se ne sw and n s the abutting relationships provide a reliable chronology between the four fracture sets which are ubiquitously found in the mftb throughout the various structural domains due to this observation we assume the fracture signal to be regional and developed in response to both large scale processes and folding in particular based on a fold test and the characteristics of data dispersion the fracture sets i ii and iii exhibit a prefolding origin while set iv shows a synfolding origin a regional interpretation of the various fractures is proposed involving several stages of fracture formation from compaction to folding including prefolding layer parallel shortening the fracture signal yields useful insights about the structural history of the mftb and the spatiotemporal evolution of the foreland tectonic regime since late cretaceous times we then place the various identified fracture sets into the known pattern of geodynamic evolution since the late cretaceous

melting history of antarctica during the past 60 000 years marked changes in the surface water hydrology of the southern ocean during the past 60 kyr are revealed by a detailed comparison of the oxygen isotopic composition of planktonic and benthic foraminifera from sediment cores and the surface water temperature estimated by a transfer function derived from the distribution of diatoms in the same sediments from 35 to 17 kyr bp the southern ocean polar front was covered by a melt water lid containing a significant contribution from melting icebergs calved from antarctic ice shelves these icebergs may have originated from a succession of surges of the ice shelves

beryllium 10 in continental sediments abstract the concentration of 10 be has been measured in 10 samples taken from a transect of surface sediments beginning in the atchafalaya river and extending across the bay 136 km into the gulf of mexico if corrected for a lower retentivity of sand for be they have a concentration that is constant within 13 this concentration is about an order of magnitude smaller than that of deep ocean sediments for comparison measurements of 10 be in rainwater in a sample of soil and in a deep ocean core were made

structural evolution of a foreland fold and thrust belt the umbria marche apennines italy abstract outcrop scale structures that record a progressive sequence of deformation can be used to clarify the kinematic evolution of an entire fold and thrust belt the temporal progression of the compressional deformation as reconstructed by means of a mesoscopic structural analysis provides a key for unraveling the kinematic history of the umbria marche apennines central italy overprinting relationships at outcrop scale allow for the recognition of three distinct structural stages which are in sequence a layer parallel shortening b folding c thrusting individual stages are explained in the framework of a progressive deformation model where shortening of the sedimentary cover was continuous and occurred during a single contractional episode as a consequence of tip line folding processes a comparison of this history with those reported from other fold and thrust belts shows that layer parallel shortening folding and thrusting are sequentially dominant processes in areas which have experienced compressional deformation

fracture controlled paleohydrogeology in a basement cored fault related fold sheep mountain anticline wyoming united states new geochemical and microstructural data constrain the origins and pathways of paleofluids during the growth of sheep mountain anticline wyoming united states oxygen carbon and strontium isotope studies were performed on prefolding and fold related calcite veins and their sedimentary host rocks and combined to fluid inclusion microthermometry results we show that most of the cements precipitated from paleogene meteoric fluid stable isotopes and fluid inclusion homogenization temperatures further indicate that most veins were mineralized from upward moving fluids after these fluids were heated at depth t 110 c this implies that fluids migrated along the basement thrust underlying the fold and or at the base of the cover above the fault tip the fluids circulated rapidly in the diffuse synfolding and early folding fracture network the zone of preferential migration of the warm fluids is currently located in the backlimb of the fold which supports some of the previously published structural interpretation of the subsurface this study also highlights the potential of combined fracture analysis and geochemical analyses of paleofluid flows in fractures to constrain both the deformation history and the fluid flow during basement involved shortening in laramide style forelands

combining outcrop data and three dimensional structural models to characterize fractured reservoirs an example from wyoming combining a detailed outcrop characterization of fracture and fault occurrence with attributes from a three dimensional model of an anticlinally folded clastic reservoir body we determine which characteristics of the structural form and evolution are most closely related to the development of important reservoir scale structures our example reservoir body studied is the frontier formation 1 sandstone in oil mountain an asymmetric anticline on the western flank of casper arch in central wyoming the three dimensional model of the structure was constructed using an iterative scheme designed to maximize interpretation accuracy and precision the model was analyzed to determine the spatial variance in morphologic and kinematic attributes using a quantitative testing approach we found that the intensity of tectonically produced fractures is closely related spatially to rate of dip change and total curvature with the former having the strongest correlation this folding is a low strain process compared to tear faulting which has the strongest spatial correlation to larger strains the location and magnitude of these higher strain areas can be adequately predicted by three dimensional restoration and forward modeling of the upper bounding surface of the reservoir body we use these results to build a predictive model for fault and fracture distribution at oil mountain and to discuss how this approach can aid in the exploitation of analogous producing reservoirs

the geochemical cycle of 9be a reconnaissance an initial survey has been made of the geochemistry of 9be in natural waters with a view to utilizing the isotope with the cosmogenic species 10be t1 2 1 5 m y in geochronological studies of sedimentary accumulation the mobility of9be in continental waters is a strong function of ph with acid streams ph 6 being strongly enriched as compared to alkaline carbonate rivers large scale scavenging of beryllium occurs in the estuaries of rivers containing more than about 200 pm of the element in alkaline systems of lower concentration the element appears to behave conservatively the net flux of beryllium to the ocean is estimated as that equivalent to an average effective river concentration of about 150 pm beryllium is strongly enriched in ridge crest hydrothermal solutions over ambient seawater the flux is approximately 70 of that from the continents the deep water concentrations of 9be vary by only 20 between the north atlantic and north pacific demonstrating that the chemical saltation produced by scavenging from the deep water column and release from the sediments predominates over simple advective concentration along flow lines isotopic homogenization of 10be and 9be is probably achieved in the ocean the situation in continental waters appears much less promising

beryllium systematics in young volcanic rocks implications for 10 be beryllium is an incompatible trace element that closely parallels neodymium in its geochemical behavior be analyses conducted on well characterized oceanic and arc volcanic rock suites as well as on marine sediments suggest a bulk solid liquid distribution coefficient of 0 03 0 06 for melting of the mantle and crystallization of basalts the be nd ratio for many volcanic rocks from diverse tectonic environments is approximately 05 similar to the ratio in chondrites be data for samples from volcanic arcs show that there are significant variations in 10be 9be among different arcs and that variations in 10be are not due to variations in be concentration alone for at least one volcano bogoslof the 10be 9be ratio is constant for samples that vary by a factor of three in both their be and 10be concentrations suggesting that 10be is an inherited magmatic signature and not simply a result of contamination near the surface in addition the be nd and pb isotope systems for this volcano are all consistent with a model in which small amounts of sediment were incorporated into the bogoslof source region provided the mantle wedge has the isotopic characteristics of depleted morb since 10be exists only in the uppermost tens of meters of oceanic sediments the data suggest an efficient return flux of sediment to the mantle at subduction zones

the role of fractures in the structural interpretation of sheep mountain anticline wyoming the development of fractures in the sedimentary layers of sheep mountain anticline a laramide asymmetric fault cored fold of the bighorn basin is documented and interpreted to constrain the kinematic evolution of the fold the fracture pattern is interpreted to identify five main fracture sets a fracture set striking 110 set i oblique to the future fold trend is interpreted as a regional fracture set that predates laramide compression a joint set set ii striking 045 and present in the hinge and backlimb is related to the ne oriented laramide compression just prior to and during initial anticline growth joints striking 135 set iii parallel to the fold trend are found within the hinge and are interpreted to have developed in response to the bending of layers the two youngest fracture sets are attributed to a late stage of fold growth a joint set set iv in the backlimb striking parallel to the set i fractures but vertical and a fracture set in the forelimb consisting of set i fractures reactivated as reverse faults the relative chronology mode of formation opening vs shearing and structural locations of these fractures suggest the following kinematics of folding at sheep mountain anticline little or no lateral fold propagation no hinge migration and limb rotation with only minor limb flexure and stretching

interactions between mantle upwelling drainage evolution and active normal faulting an example from the central apennines italy summary in this paper we show that the processes that have shaped the quaternary surface development of the apennines in central italy are all consequences of a single subcrustal process the upwelling of the mantle the relationship between gravity and topography shows that mantle convection is responsible for a long wavelength 150 200 km topographic bulge over the central apennines and stratigraphic evidence suggests this bulge developed in the quaternary active normal faulting is localized at the crest of this bulge and produces internally draining fault bounded basins these basins have been progressively captured by the aggressive headward erosion of major streams that cut down to the sea on the flanks of the regional bulge the only surviving closed basins are those on the apennine watershed most distant from the marine base level where continued normal faulting is still able to provide local subsidence that defeats their capture by the regional drainage network understanding the competition between regional capture and local fault related subsidence of intermontane basins is crucial for recognizing potentially hazardous active faults in the landscape and also for interpreting the sediment supply to adjacent offshore regions central italy provides a good modern analogue for processes that are probably common in the geological record particularly on rifted margins and intracontinental rifts but may not have been fully appreciated

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

a review of deformation pattern templates in foreland basin systems and fold and thrust belts implications for the state of stress in the frontal regions of thrust wedges aesthetically appealing thrust systems and related large scale anticlines in both active and fossil foreland fold and thrust belts and the economic potential associated with the m have captured the interest of structural geologists for many decades as a consequence a large amount of data on sub seismic deformation patterns from thrust related an ticlines is available in the literature we provide a review of deformation pattern templates from fi eld data in foreland fold and thrust belts and show that the most frequent tre nds of sub seismic syn orogenic deformation structures hosted in km scale thrust related folds frequently and pa radoxically indicate a syn th rusting strike slip stress fi eld con fi guration with a near vertical 2 and a sub horizontal 3 rather than a contractional one where the latter is expected to be the vertical principal axis of the stress ellipsoid this a pparent inconsistency between sub seismic syn orogenic deformation structures and stress fi eld orientation is here named the 2 paradox field data support a possible expla nation of the paradox provided by the major role played by i nherited early orogenic extensional deformation struc tures on thrust fault nucleation nucleation of major thru sts and their propagation is facilitated and driven by the positive inversion and linkage of the early orogenic sub s eismic extensional inheritance developed in the foreland basin this process eventually leads to the development of l argereversefaultzonesandcanoccurbothincontractional and strike slip stress fi eld con fi gurations

10be and 9be in marine sediments and their potential for dating using sequential leaching experiments we have measured the fraction of the cosmogenic isotope 10be half life 1 5 my and its stable isotope 9be co extracted with the following phases in marine sediments exchangeable calcium carbonate fe and mn oxyhydroxides organic opal and detrital the extraction of the authigenic phases typically release 70 of the 10be but only 40 of the 9be in order to test its potential for dating marine sediments we have measured the authigeniccally associated 10be 9be in 17 surface sediment samples from different ocean basins the observed spatial variability which appears to be influenced by proximity to continental input of 9be precludes the general and precise applications of leached 10be 9be for dating however the relatively constant value observed in surface sediments over large areas of the pacific indian and southern atlantic oceans shows considerable promise for approximate dating of open oceans sediments in order to test temporal variability a profile of the authigenically associated 10be 9be ratio has been measured in the independently dated central pacific core rc12 65 the observed variation in 10be 9be over the past nine my is approximately twice that expected on the basis of 10be decay alone several possible explanations for such behavior and their potential consequences for the use of leached 10be 9be for dating are discussed

beryllium 10 in australasian tektites evidence for a sedimentary precursor each of seven australasian tektites contains about 1 x 10 sup 8 atoms of beryllium 10 half life 1 53 x 10 sup 6 years per gram cosmic ray bombardment of the australites cannot have produced the measured amounts of beryllium 10 either at the earth s surface or in space the beryllium 10 contents of these australites are consistent with a sedimentary precursor that adsorbed from precipitation beryllium 10 produced in the atmosphere the sediments must have spent several thousand years at the earth s surface within a few million years of the tektite producing event

structural and microstructural evolution of the rattlesnake mountain anticline wyoming usa new insights into the sevier and laramide orogenic stress build up in the bighorn basin the rocky mountains in western us provide among the best examples of thick skinned tectonics following a period of thin skinned tectonics related to the sevier orogeny the compressional reactivation of basement faults gave birth to the so called laramide uplifts arches the bighorn basin located in wyoming is therefore a key place to study the transition from thin to thick skinned tectonics in orogenic forelands especially in terms of microstructural and stress strain evolution our study focuses on a classic laramide structure the rattlesnake mountain anticline rma wyoming usa a basement cored anticline located in the western part of the bighorn basin stress and strain evolution analysis in folded sedimentary layers and underlying faulted basement rocks were performed on the basis of combined analyses of fractures fault slip data and calcite twinning paleopiezometry most of the fractures are related to three main tectonic events the sevier thin skinned contraction the laramide thick skinned contraction and the basin and range extension serial balanced cross sections of rma and displacement profiles suggest that all thrust faults were coeval evidencing strain distribution in the basement during faulting the comparison of rma with another structure located in the eastern edge of the bighorn basin i e the sheep mountain anticline sma allows to propose a conceptual model for the geometric and kinematic evolution of laramide related basement cored anticlines finally the stress evolution is reconstructed at both the fold scale and the basin scale we show that the evolution of stress trends and magnitudes was quite similar in both structures rma and sma during laramide times thick skinned tectonics in spite of different stress regimes during sevier thin skinned tectonics and post laramide times stress trends and fracture patterns were different in these two structures these results suggest that the distance to the orogenic front influenced the fracture patterns but not the foreland stress magnitudes which were likely controlled by the structural style

book review the techniques of modern structural geology volume 2 folds and fractures john g ramsay and martin i huber academic press london 1987 xi 309 398 pp price stg17 50 us 34 50 paperback

distribution of joints in the hinge line culmination of foreland verging overturned anticlines an example from the montagna dei fiori structure in the central apennines of italym francioni et al distribution of joints in overturned anticlines the distribution of joints veins and shear fractures in the montagna dei fiori overturned anticline is here reported two joint sets longitudinal and transverse to the nnw sse anticline axial trend and a conjugate system of shear fractures are recognized the transverse and longitudinal joint sets have a pre folding development likely related to the foreland foredeep flexure the transverse joints were reopened during layer parallel shortening along with the development of the shear fractures then during syn folding outer arc extension and hinge line culmination fold axial parallel extension both the longitudinal and transverse joints were enhanced and reactivated respectively

10be study of rapid erosion in taiwan cosmogenic 10be was measured using accelerator mass spectrometry in soils and sediments to study the erosion of taiwan which has the highest denudation rate in the world the river sediments in taiwan have very low 10be concentrations around 5 million atoms per gram about 145 the world wide average this is the direct consequence of its high sediment yield of more than 1000 mg cm2 yr 70 times the world average combining these values we found that for taiwan as a whole the 10be output to the sea only slightly exceeds the input from the rain a situation typical of many areas around the world therefore even in this example of extremely rapid erosion 10be seems to remain a useful indicator for erosion status the total 10be inventory found in a soil profile from a geologically stable area is at least 18 of the maximum possible inventory the minimum age thus estimated for the soil is 0 11 ma in reasonable agreement with estimates from other means the maximum erosion rate for this area thus estimated is at most 0 14 mg cm2 yr four orders of magnitude slower than the average value observed for taiwan we also demonstrate that the shelf sediments around taiwan have received the admixing of a 10be rich component from the ocean and would give a poor estimate for material eroded from taiwan

from extension to contraction in syn orogenic foredeep basins the contessa section umbria marche apennines italy syn orogenic deposits that occupy foredeep basins commonly experience contraction related to the migration of fold and thrust systems toward the foreland this contraction may overprint the earlier extensional deformation that is related to the initiation of the basin although predicted by models for foredeep development evidence for extension predating contraction at different scales is not extensively recorded in syn orogenic deposits mesoscopic structures from the contessa section in the umbria marche apennines italy reveal a complex history characterized by extension soon before the contractional deformation normal faults predate the folds and thrusts that are related to the miocene age orogenic event responsible for the development of the apennines extensional deformation may have resulted from flexuring of a lithospheric plate induced by the load of a stacking thrust pile the transition from extension to contraction could play an important role in the evolution of belt foredeep foreland systems as it could reflect the migration of advancing thrust fronts toward the foreland

greenland ice10be concentrations and average precipitation rates north of 40 n to 45 n abstract a model of 10 be deposition within the subarctic and arctic is developed based on the behavior of 90 sr in the troposphere measured 10 be fluxes based on analyses of 10 be in one year s snow fall 1979 1980 from the dye 3 site in southwest greenland and on published data and predicted 10 be fluxes based on the 10 be deposition model agree these results indicate that with regard to 10 be the troposphere north of 40 n to 45 n presently behaves as if it is well mixed and that the average precipitation rate within that reservoir controls in large part the concentration of 10 be in greenland ice inversion of the greenland ice core 10 be concentration record with the aid of the model indicates 1 that the average precipitation rate in the subarctic and arctic was lower than the present rate during the maunder minimum of solar activity and higher than the present rate during the wolf and sporer solar activity minimums and 2 that during the wisconsin holocene transition the average precipitation rate in the subarctic and arctic was about one third the present precipitation rate

influence of structural position on fracture networks in the torridon group achnashellach fold and thrust belt nw scotland abstract in fold and thrust belts rocks undergo deformation as fold geometries evolve deformation may be accommodated by brittle fracturing which can vary depending on structural position we use 2d forward modelling and 3d restorations to determine strain distributions throughout folds of the achnashellach culmination moine thrust belt nw scotland fracture data is taken from the torridon group a thick coarse grained fluviatile sandstone deposited during the proterozoic modelling infers a correlation between strain and simple curvature we use simple curvature to infer how structural position and strain control fracture attribute variations in a fold and thrust belt in high curvature regions such as forelimbs fracture intensities are high and fractures are short and oriented parallel to fold hinges in low curvature regions fractures have variable intensities and are longer fracture orientations in these regions are scattered and vary over short distances these variations do not relate to strain data suggests lithology may influence fracturing the strain history of fold structures also influences fracturing structures with longer deformation histories exhibit consistent fracture attributes due to moderate high strain during folding despite present day low curvature this is in contrast to younger folds with similar curvatures but shorter deformation histories we suggest in high strain regions fracturing is influenced by structural controls whereas in low strain regions lithology becomes more important in influencing fracturing

the interaction of extensional and contractional deformations in the outer zones of the central apennines italy abstract the relationships among normal faults and thrusts in the apennines of italy are often unclear and the local absence of syn tectonic stratigraphic controls have led to contrasting interpretations on the relative chronology for both classes of structures the activity of normal faults has been variously regarded as due to pre syn or post orogenic extension and the contrasting evidence from different sites has produced an ongoing debate on the normal fault thrust interaction the results of a kinematic analysis on selected composite structures of the outer zones of the central apennines make it possible to unequivocally establish a relative chronology of extensional and contractional deformations detailed mapping outcrop scale observations and structural overprinting relationships support a positive inversion tectonic history where normal faults and fault controlled escarpments formed first and were later deformed by thrusts and related folds all normal faults control the distribution of foredeep deposits thus indicating that the recognised episode of positive inversion is related to the incipient stages of construction of the apennine thrust belt the systematic collection of structural data may help to unravel the evolution of adjacent sectors of the apennine chain as well as of other belt foredeep foreland systems whose extension contraction relationships are poorly constrained

fracture patterns in the zagros simply folded belt fars iran constraints on early collisional tectonic history and role of basement faults pre early folding fracture patterns were recognized in several anticlines from three structural domains in the simply folded belt of the fars arc these fracture sets were characterized in terms of opening mode and relative chronology and used to reconstruct the main compressional trends related to the early zagros collisional history the palaeostress reconstructions based on these fracture sets were further refined by combination with newly collected or already available fault slip and calcite twin data as an alternative to previous models of rigid block rotations or regional stress rotation we propose that the complex pattern of pre folding fractures and the contrasting palaeostress orientations through time in the different domains investigated are related to the presence of basement faults with n s and wnw trends above which basement and cover were variably coupled during stress build up and early deformation of the arabian margin beyond regional implications this study draws attention to the need to carefully consider pre existing fractures possibly unrelated to folding to build more realistic conceptual fold fracture models

provenance and earthquake signature of the last deglacial xinmocun lacustrine sediments at diexi east tibet abstract well preserved lacustrine sediments are found in some areas in east tibet this region is characterized by a windy and semi arid climate alpine valleys and frequent earthquakes measurements of rare earth elements observations from a scanning electron microscope and a high resolution record of grain size measurements allowed us to compare fine sediments from the xinmocun section in the diexi lake with loess from the chinese loess plateau and south china results indicate that fine grains of the xinmocun lacustrine sediments were transported by wind and trapped in the lake whereas the 16 m fraction was likely from local sources the grain size changes within the section repeatedly show abrupt coarsening and upward fining probably due to palaeoearthquake events large earthquakes in the study area often caused rockfalls and landslides exposing fine sediments that had accumulated on mountains slopes the fine grains were then retransported by wind to the diexi lake optically stimulated luminescence dating of the xinmocun section indicates continuous deposition from 18 65 to 10 63 ka these results indicate that palaeoearthquakes in the study area had a mean recurrence interval of 0 32 ka therefore we propose that lacustrine sediments in a tectonically active region have the potential to record a continuous history of palaeoearthquakes palaeoearthquakes probably produced numerous rockfalls and landslides in alpine valleys and provided significant sources of regional eolian dust

implications of heterogeneous fracture distribution on reservoir quality an analogue from the torridon group sandstone moine thrust belt nw scotland abstract understanding fracture network variation is fundamental in characterising fractured reservoirs simple relationships between fractures stress and strain are commonly assumed in fold thrust structures inferring relatively homogeneous fracture patterns in reality fractures are more complex commonly appearing as heterogeneous networks at outcrop we use the achnashellach culmination nw scotland as an outcrop analogue to a folded tight sandstone reservoir in a thrust belt we present fracture data is collected from four fold thrust structures to determine how fracture connectivity orientation permeability anisotropy and fill vary at different structural positions we use a 3d model of the field area constructed using field observations and bedding data and geomechanically restored using move software to determine how factors such as fold curvature and strain influence fracture variation fracture patterns in the torridon group are consistent and predictable in high strain forelimbs however in low strain backlimbs fracture patterns are inconsistent heterogeneities in fracture connectivity and orientation in low strain regions do not correspond to fluctuations in strain or fold curvature we infer that where strain is low other factors such as lithology have a greater control on fracture formation despite unpredictable fracture attributes in low strain regions fractured reservoir quality would be highest here because fractures in high strain forelimbs are infilled with quartz heterogeneities in fracture attribute data on fold backlimbs mean that fractured reservoir quality and reservoir potential is difficult to predict

10 be and delta 2 h in polar ice cores as a probe of the solar variability s influence on climate and discussion by using the technique of accelerator mass spectrometry it is now possible to measure detailed profiles of cosmogenic cosmic ray produced 10 be in polar ice cores recent work has demonstrated that these profiles contain information on solar activity via its influence on the intensity of galactic cosmic rays arriving in the earth s atmosphere it has been known for some time that as a result of temperature dependent fractionation effects the stable isotope profiles delta 2 o and delta 2 h in polar ice cores contain palaeoclimate information thus by comparing the 10 be and stable isotope profiles in the same ice core one can test the influence of solar variability on climate and this independent of possible uncertainties in the absolute chronology of the records we present here the results of such a comparison for two antarctic ice cores one from the south pole covering the past ca 1000 years and one from dome c covering the past ca 3000 years

stress and strain patterns kinematics and deformation mechanisms in a basement cored anticline sheep mountain anticline wyoming 1 in order to characterize and compare the stress strain record prior to during and just after folding at the macroscopic and the microscopic scales and to provide insights into stress levels sustained by folded rocks we investigate the relationship between the stress strain distribution in folded strata derived from fractures striated microfaults and calcite twins and the development of the laramide basement cored sheep mountain anticline wyoming tectonic data were mainly collected in lower carboniferous to permian carbonates and sandstones in both rock matrix and veins calcite twins recorded three different tectonic stages the first stage is a pre laramide sevier layer parallel shortening lps parallel to fold axis the second one is a laramide lps perpendicular to the fold axis and the third stage corresponds to laramide late fold tightening with compression also perpendicular to the fold axis stress and strain orientations and regimes at the microscale agree with the polyphase stress evolution revealed by populations of fractures and striated microfaults testifying for the homogeneity of stress record at different scales through time calcite twin analysis additionally reveals significant variations of differential stress magnitudes between fold limbs our results especially point to an increase of differential stress magnitudes related to laramide lps from the backlimb to the forelimb of the fold possibly in relation with motion of an underlying basement thrust fault that likely induced stress concentrations at its upper tip this result is confirmed by a simple numerical model beyond regional implications this study highlights the potential of calcite twin analyses to yield a representative quantitative picture of stress and strain patterns related to folding

relationships between thrusts and normal faults in curved belts new insight in the inversion tectonics of the central northern apennines italy abstract the relationships between thrusts and normal faults represent primary constraints in the reconstruction of the modes and timing of pre syn and post orogenic deformation events in fold and thrust belts such relationships are well exposed in curved orogenic belts where the thrusts are oblique to the trend of normal faults we study the nne ssw trending olevano antrodoco sibillini oblique thrust and its crosscutting relationships with nw se trending normal faults in order to constrain the neogene quaternary deformation history of the central northern apennine italy the analysis of structural and geological data allowed us to reconstruct the geometric and kinematic constraints of two inversion events 1 during the pliocene positive inversion reactivated the nne ssw trending pre existing ancona anzio normal fault as the olevano antrodoco sibillini oblique thrust ramp and caused the shortcut of nw se oriented normal faults 2 during the quaternary negative inversion reactivated nw se trending pre thrusting normal faults the growth of the nw se quaternary normal faults causes seismicity and is responsible of the development of wide quaternary intramontane basins their distribution and the related seismicity have been controlled and compartmentalized by nne ssw trending oblique thrusts thus the crosscutting relationships between thrusts and normal faults are crucial in seismic hazard assessment

foreland directed gravitational collapse along curved thrust fronts insights from a minor thrust related shear zone in the umbria marche belt central northern italy gravitational collapse occurs during the mature evolution of orogenic belts but its signature is difficult to discriminate in macroscopic structures from that of pre syn or late post orogenic extension so reliable mesoscopic examples are particularly useful a composite fabric developed along a lateral thrust ramp in the apennines reveals mesoscopic normal faults that truncate the thrust surface overprint the s fabric and merge downwards in a foreland directed splay leaving the thrust footwall undeformed these relationships indicate syn late thrusting extension which we interpret as induced by hanging wall gravitational collapse our study provides critical constraints for reconstructing the kinematic evolution of collapsing thrust fronts