a new cretaceous tertiary boundary site at flaxbourne river new zealand biostratigraphy and geochemistry abstract an exceptionally complete rock sequence across the cretaceous tertiary k t boundary has been discovered near the flaxboume river marlborough province south island new zealand the boundary is marked by a large ir anomaly 21 ng g on a decalcified basis with an integrated abundance of 134 ng cm2 after correction for background above the boundary there is a 30 cm transition zone in which a few cretaceous foraminiferal taxa such as hedbergella monmouthensis and guembelitria cretacea survived though with reduced abundance and size only ca 1 2 to 1 4 of normal apparently reflecting environmental stresses inaa and icp analyses show that in addition to ir the boundary clay is also enriched in cr and ni mainly from meteoritic material and as co cu sb and zn from terrestrial sources volcanic sources even when scaled to the 10 7 km 3 volume of the deccan basalts fail by three orders of magnitude to account for the ir and as at the k t boundary and by even larger factors for sb zn cu etc comparison of our data with those from six other k t boundary sites shows that the zn sb as sb and zn as ratios generally fall between crustal and oceanic values suggesting contributions from both sources mass balance calculations show that as and sb could be derived from only 300 500 m of ocean water or also from modest amounts 20 36 g cm 2 of average crustal rock copper and zn on the other hand can only be derived from crustal or mantle rock 5 15 g cm 2 presumably impact ejecta such an amount of ejecta is fairly close to the global fallout of boundary clay 2 5 g cm 2

duplex style and triangle zone formation insights from physical modeling duplexes are a common feature in thrust belts at many scales their geometries vary significantly from antiformal stacks with significant forethrusting in the cover e g southern pyrennes spain to triangle zones e g foreland canadian rockies to low displacement individually spaced ramp anticlines e g sub andean thrust belt bolivia we present a series of physical experiments demonstrating that the strength of the decollements relative to that of the intervening and overlying rock layers plays a significant role in controlling the duplex style the models comprise brittle layers made of dry quartz sand and decollements made of two types of viscous silicone polymers the strength of the decollements in the models is a function of the shortening rate applied to the model the relative strength of the decollements and surrounding rocks affects the development of active or passive roof duplexes triangle zones it also affects the amount of translation of individual thrust blocks and the spacing of thrust ramps which in turn determine if a duplex evolves into an antiformal stack or into individually spaced ramp anticlines model results indicate that specific associations of structural features form systematically under similar rheological and boundary conditions the presence of relatively strong decollements promotes local underthrusting of the cover individual ramp anticlines internal deformation of thrust sheets low early layer parallel shortening and sequential towards the foreland propagation of structures weak decollements promote forethrusting of the cover antiformal stacks coeval growth of structures and low internal strain with the exception of significant early layer parallel shortening no underthrusting at a regional scale occurred in any model

groundwater recharge and discharge in a hyperarid alluvial plain akesu taklimakan desert china groundwater recharge and discharge in the akesu alluvial plain were estimated using a water balance method the akesu alluvial plain 4842 km2 is an oasis located in the hyperarid tarim river basin of central asia the land along the akesu river has a long history of agricultural development and the irrigation area is highly dependent on water withdrawals from the river we present a water balance methodology to describe a surface water and groundwater interaction and b groundwater interaction between irrigated and non irrigated areas groundwater is recharged from the irrigation system and discharged in the non irrigated area uncultivated vegetation and wetlands are supplied from groundwater in the hyperarid environment results show that about 90 of groundwater recharge came from canal loss and field infiltration the groundwater flow from irrigated to non irrigated areas was about 70 of non irrigated area recharge and acted as subsurface drainage for the irrigation area this desalinated the irrigation area and supplied water to the non irrigated area salt moved to the non irrigation area following subsurface drainage we conclude that the flooding of the akesu river is a supplemental groundwater replenishment mechanism the river desalinates the alluvial plain by recharging fresh water in summer and draining saline regeneration water in winter copyright 2007 john wiley sons ltd

structural analysis and interpretation of the surface deformations of the el asnam earthquake of october 10 1980 the el asnam earthquake of october 10 1980 represents the major seismotectonic event of these last decades in the west mediterranean area it has induced a large amount of surface breaks this earthquake reveals the importance of compressional phenomena that characterize nowadays the tectonics of north africa the tectonic analysis of surface rupture shows the complexity of the deformation mechanism the principal mechanism consists of the activation of a nw se trending thrust fault accompanied with a left lateral motion and with an intense deformation of the northwestern overthrusting block an accurate description of these deformations shows that for a large part the breaks geometry depends closely on the substratum structure finally the analysis of the dislocations on irrigation ducts just above the fault traces allowed a quantitative study of the deformation

ru ir ratios at the cretaceous tertiary boundary implications for pge source and fractionation within the ejecta cloud abstract ruthenium and ir are the least mobile platinum group elements pges within the cretaceous tertiary k t boundary clay the ru ir ratio is therefore the most useful pge interelement parameter for distinguishing terrestrial and extraterrestrial contributions to the boundary clay the ru ir ratio of european marine k t sections 1 67 0 38 is statistically different from that of the north american continental sections 0 76 0 26 it is unlikely that this difference is due to secondary pge remobilization pge input to the boundary clay during multiple impacts or volcanic emissions the global difference in ru ir ratios in the boundary clay may therefore be primary the positive correlation between distance from the chicxulub impact structure yucatan mexico and ru ir ratio and the more than 1000 c difference in the condensation temperatures of these elements lead us to propose that fractionation of ru from ir during condensation from the ejecta cloud may have occurred resulting in the global difference in ru ir ratios

large earthquakes at the ibero maghrebian region basis for an eews large earthquakes mw 6 imax viii occur at the ibero maghrebian region extending from a point 12ow southwest of cape st vincent to tunisia with different characteristics depending on their location which cause considerable damage and casualties seismic activity at this region is associated with the boundary between the lithospheric plates of eurasia and africa which extends from the azores islands to tunisia the boundary at cape st vincent which has a clear oceanic nature in the westernmost part experiences a transition from an oceanic to a continental boundary with the interaction of the southern border of the iberian peninsula the northern border of africa and the alboran basin between them corresponding to a wide area of deformation further to the east the plate boundary recovers its oceanic nature following the northern coast of algeria and tunisia the region has been divided into four zones with different seismic characteristics from west to east large earthquake occurrence focal depth total seismic moment tensor and average seismic slip velocities for each zone along the region show the differences in seismic release of deformation this must be taken into account in developing an eews for the region

early cretaceous rifts of western and central africa an overview abstract the structure and evolution of early cretaceous rift basins in western and central africa are described two stages of rift development and fracturing have been identified 1 from neocomian to early aptian roughly e w and nw trending troughs upper benue n cameroon s chad sudan etc opened in response to a submeridian extensional regime in central africa while in western africa the n s trending transsaharian fault zone acted as a sinistral wrench 2 from middle aptian to late albian large northwest trending troughs e niger sudan sirte etc opened in response to a northeast extensional regime while the central african fault zone from benue to sudan exhibited strike slip movements generating pull apart basins these rift and fracture systems delimit three large blocks within the african plate a western block an arabian nubian block and an austral block the arabian nubian block tends to separate from the two other blocks migrating towards the north during the first stage of basin development and then towards the ne during the second stage the opening of the atlantic ocean was the dominant driving force for the western and austral blocks while the arabian nubian block probably moved in response to the opening of the indian ocean and to the evolution of the tethyan margin

geologic structure and neotectonics of the north african continental margin south of sicily abstract marine geological and geophysical data together with drilling information indicate that the north african passive continental margin has been subjected to extension and wrenching after it collided with the northern part of sicily the area of the tripolitania basin jarrafa trough melita and medina bank and the ragusa malta plateau has formed part of a sinking passive margin since the dispersal of gondwanaland at about 180 my ago as observed from geohistory diagrams a record of rifting in a nw se direction accompanied by dextral shear along the southern troughs is observed in seismic reflection data the rifting started during the neocomian and lasted until the eocene when activity became minor a pre middle miocene period of northward subduction of oceanic crust is inferred from the geology in ne sicily uplift of the northern part of the african margin after collision in the middle miocene is seen in wells in southern sicily after the messinian a rift and dextral shear zone established itself across the african margin from the strait of sicily to the medina ridge in the lonian basin the zone is marked by up to 1 7 km deep grabens narrow active wrench faulted channels volcanic fissures and local uplifted keilhorsts such as malta this zone which varies in width from 100 to 35 km forms the southern boundary of a microplate which includes sicily we speculate that the present motion of this microplate is partly due to the eastward movement of the calabrian arc with the sicilian block over the last remaining oceanic lithosphere in the eastern mediterranean

style of atlassic tectonic deformation and geodynamic evolution of the southern tethyan margin tunisia the structure of the southern atlas fold and thrust belt of tunisia was investigated using new geologic mapping seismic reflection data together with the construction of a balanced cross section the structural architecture of the tunisian foreland consists in a mixed tectonic style with deep seated basement faults shallower decollements within sedimentary cover and salt diapirism the restoration of the cross section shows a surface shortening of 8 1 km similar to 7 3 sequential restoration of the balanced cross section has been permitted to decipher the structure and evolution of the southern tethyan margin of tunisia structural geometry and orientation of the pre existing permian to cretaceous extensional structures controlled subsequent contractional deformation within the sedimentary cover during the shortening this inherited tectonic framework controlled the development of ene trending thrust related anticlines such as the orbata and chemsi structures nw trending lateral ramp such as the gafsa and fejej faults and diapir structures as the beidha anticline the inversion of the margin can be correlated with the onset of the convergence between africa and eurasia the first phase of the orbata thrusting growth might occur in late cretaceous continuous inversion of the margin occurred during the eocene and mainly during the late miocene to present day this study underlines the predominant role of inherited basement structures acquired during the evolution of the southern tethyan margin and their influence on the geometry of the atlassic thrust belt this structural analysis provides new perspectives for future hydrocarbon exploration in this poorly explored region c 2015 elsevier ltd all rights reserved

tectonic inheritance crustal architecture and contrasting structural styles in the venezuela andes surface and subsurface data image contrasting structural styles for the two flanks of the venezuela andes in the north a flexural basin developed in neogene times between the andes and the lake maracaibo north verging thrusts are mainly detached in the pre cretaceous substratum and form a deeply buried antiformal stack secondary decollement levels occur both in the upper cretaceous and tertiary strata accounting for the passive roof thrust of a conventional frontal triangle zone in the south the barinas basin hardly compares with a flexural basin it is largely dominated by both north and south verging basement involving structures paleogene normal faults are locally inverted and caribbean nappes are frequently reactivated or refolded by younger oblique neogene andean structures seismic profiles in this area also attest to the strong neogene structural inversion of upper jurassic lower cretaceous grabens hercynian or more likely early paleozoic structures account for local preexisting crustal heterogeneities reactivated during both the tethyan rifting and the andean deformations two trans andean regional profiles have been balanced and constrained by an inversion of the gravimetric data they imply a progressive deepening of the northern moho and a south dipping subduction of the infracontinental lithospheric mantle of the maracaibo block the shortening for both sections averages 60 km palinspastic restorations assume a relative cylindricity for the deep crustal architecture of the andes and minimize the possible effects of a progressive right lateral escape of the maracaibo block with respect to stable south america along the bocono fault strain partitioning during neogene oblique convergence induced surficial thrust fronts parallel to the plate boundary strike slip motion in the allochthon along the bocono fault and an asymmetric subduction wedging at depth

petroleum geology of tunisia recent discoveries and important oil shows have proven the existence of hydrocarbons in newly identified depocenters and reservoirs in general except for some areas around the producing fields tunisia is largely underdrilled the national company etap has decided to release data and to publish a synthesis on the petroleum geology of tunisia the geology of tunisia provides a fine example of the contrast between alpine folding which typifies northern tunisia and the african craton area of the saharan part eastern tunisia corresponds to an unstable platform forming plains or low hills and extending eastwards to the shallow pelagian sea there are a wide variety of basins central and northern tunisia represents a front basin the saharan ghadames basin or the chott trough are sag basins the gulf of gabes was formed as a distension margin the gulf of hammamet is a composite basin and several transversal grabens cut across the country including offshore and are rift type basins all these features are known to be oil prolific throughout the world two large fields and many modest size pools are known in tunisia oil and gas fields in the surrounding countries namely the saharan fields of algeria and libya the large bouri fieldmore offshore tripolitania and discoveries in the italian part of the straits of sicily suggest a corresponding potential in tunisia exposed paleogeographic and structural maps balanced sections and examples of fields and traps will support an optimistic evaluation of the future oil exploration in tunisia less

the southernmost margin of the tethys realm during the mesozoic and cenozoic initial geometry and timing of the inversion processes 1 along the northern border of africa pangea breakup has been diachronic during the jurassic the alpine tethys propagated northeastward from the atlantic to the alps during the permian the neo tethys propagated westward from oman to northwestern arabia then a secondary and late branch of neo tethys gave birth to the east mediterranean basin finally the two oceans connected at end of jurassic times achieving the development of africa northern plate boundary by the late cretaceous convergence between africa and eurasia led to the progressive closure of the tethys realm the continental collision is not completely achieved and the different segments of the confrontation zone maghreb central and east mediterranean zagros and oman expose different stages of the process however we emphasize the existence of synchronous geodynamic events from one end of the system to the other although they do not have the same meaning two of them are particularly important the campanian santonian c s event corresponds to 1 obduction and exhumation of high pressure low temperature metamorphic rocks around the arabian promontory 2 inversion along the margins of the east mediterranean basins and 3 lithosphere buckling in the atlas system maghreb and adjacent sahara platform the middle late eocene mle event corresponds to 1 the onset of collision at the northern corner of arabia 2 the onset of slab retreat in the mediterranean and 3 inversion along the margin of the east mediterranean as well as in the atlas the c s event coincides with a change in plate kinematics resulting in an abrupt increase of convergence velocity the mle event coincides with a period of strong coupling between the africa and eurasia plates and an abrupt decrease of convergence velocity in the middle of the system the central mediterranean seems to escape to the effects of convergence and is the site of quite permanent extensional movements since the triassic

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

halokinesis and structural evolution of the major features in eastern and southern tunisian atlas abstract the eastern and southern tunisian atlas is marked by the presence of three major faults the n s axis fault the nw se gafsa fault and the e w northern chott fault seismic lines crossing these structures show the existence of significant halokinetics that began in the early jurassic the aim of this paper is to study and better understand the triassic salt movements which are mainly linked to periods when the major basement faults were reactivated resulting in extension compression transtension or and transpression analysis of the seismic data allows us to conclude that the triassic salt migration started in the early jurassic and continued during the late jurassic and the early cretaceous although these periods are characterized by an extensional tectonic regime the synsedimentary halokinesis is accompanied by thickening and thinning of the overlying series salt remobilization was accentuated during the compressional deformation which occurred from the late tertiary to quaternary and resulted in local diapiric extrusions along the major structural features

recent spatial and temporal changes in the stress regime along the southern tunisian atlas front and the gulf of gabes new insights from fault kinematics analysis and seismic profiles tectonic deformations in the southern atlassic front of tunisia saft and the gulf of gabes result from the nubia eurasia convergence this study based on the inversion of geologically determined fault slip vectors presents evidences for spatial and temporal changes in the stress state fault kinematics analyses reveal a temporal change in states of stress during the late cenozoic a paleostress miocene pliocene state is characterized by a regional compressional tectonic regime with a mean n134 09 e trending horizontal maximum stress axis 1 a modern quaternary to present day state of stress also corresponds to compressional tectonic regime with a regionally mean n05 10 e trending horizontal 1 the saft corresponds to two distinct domains a far foreland atlassic front related to contractional deformation associated with southward propagate thrusting and eastward the gulf of gabes characterized by normal component nw to wnw trending faults at the crustal margin scale probably related with a transtensional tectonic regime we propose that the spatial and temporal changes in the stress during the miocene pliocene and quaternary may result from the geodynamic evolution of the tunisian atlas in relation to the rotation of corsica sardinia blocks and the separation of the sicilian continental lithosphere from the ionian oceanic lithosphere these temporal and spatial stress changes along the saft and the gulf of gabes are probably the engine behind the moderate seismicity leading at the same time to a reactivation of the inherited major structures created during the evolution of the southern tethyan margin

latest cretaceous to late paleocene radiolarian biostratigraphy a new zonation from the new zealand region the scarcity of records of early paleocene radiolarians has meant that while radiolarian biostratigraphy is firmly established as an important tool for correlation there has been a long standing gap between established zonations for the cretaceous and from latest paleocene to recent it has also led to considerable speculation over the level of faunal change across the cretaceous tertiary k t boundary consequently the discovery of rich and diverse radiolarian assemblages in well delineated k t boundary sections within siliceous limestones of the amuri limestone group in eastern marlborough new zealand is of great significance for biostratigraphy and k t boundary research this initial report is restricted to introducing a new latest cretaceous to mid late paleocene zonation based on the radiolarian succession at four of these sections and a re examination of faunas from coeval sediments at dsdp site 208 lord howe rise three new paleocene species are described amphisphaera aotea amphisphaera kina andstichomitra wero six new interval zones are defined by the first appearances of the nominate species in ascending order these are lithomelissa hoplites foreman zone rk9 cretaceous amphisphaera aotea n sp zone rp1 paleocene amphisphaera kina n sp rp2 stichomitra granulata petrushevskaya rp3 buryella foremanae petrushevskaya rp4 andburyella tetradica rp5 good age control from foraminifera and calcareous nannofossils permits close correlation with established microfossil zonations where age control is less reliable radiolarian events are used to substantially improve correlation between the sections no evidence is found for mass extinction of radiolarians at the end of the cretaceous however the k t boundary does mark a change from nassellarian to spumellarian dominance due to a sudden influx of actinommids which effectively reduces the relative abundance of many cretaceous survivors an accompanying influx of diatoms in the basal paleocene of marlborough together with evidence for an increase of total radiolarian abundance suggests siliceous plankton productivity increased across the k t boundary possible causes for this apparently localised phenomenon are briefly discussed

tectonic evolution of the northern african margin in tunisia from paleostress data and sedimentary record abstract a reconstruction of the tectonic evolution of the northern african margin in tunisia since the late permian combining paleostress tectonic stratigraphic and sedimentary approaches allows the characterization of several major periods corresponding to consistent stress patterns the extension lasting from the late permian to the middle triassic is contemporaneous of the rifting related to the break up of pangea during liassic times regional extensional tectonics originated the dislocation of the initial continental platform in northern tunisia the evolution of the liassic ne sw rifting led during dogger times to the north african passive continental margin whereas in southern tunisia a n s extension associated with e w trending subsiding basins lasted from the jurassic until the early cretaceous after an upper aptian early albian transpressional event ne sw to ene wsw trending extensions prevailed during late cretaceous in relationship with the general tectonic evolution of the northeastern african plate the inversions started in the late maastrichtian paleocene in northern tunisia probably as a consequence of the africa eurasia convergence two major nw se trending compressions occurred in the late eocene and in the middle late miocene alternating with extensional periods in the eocene oligocene early middle miocene and pliocene the latter compressional event led to the complete inversion of the basins of the northwestern african plate originating the maghrebide chain such a study supported by a high density of paleostress data and including complementary structural and stratigraphic approaches provides a reliable way of determining the regional tectonic evolution

groundwater recharge environments and hydrogeochemical evolution in the jiuquan basin northwest china the groundwater recharge environments and hydrogeochemical characteristics in the quaternary aquifer of jiuquan basin was investigated using a combination of chemical indicators stable isotopes and radiocarbon dating the d excess values of winter precipitation and surface water revealed that the meltwater from snow and ice played the dominant role in the basin s surface water supply the unconfined groundwater showed gradual enrichment of heavy isotopes along the flow path but delta o 18 and delta h 2 values were similar to those of surface water suggesting recent recharge as a result of rapid seepage along rivers combined with the effects of high evaporation the c 14 pmc values of unconfined groundwater was between 71 5 and 90 9 and since 80 modern carbon probably represents the upper limit of initial c 14 activity this suggests that the groundwater is relatively young the confined groundwater was depleted in heavy isotopes coupled with low c 14 values similar to 20 53 indicating that the groundwater was mainly recharged as palaeowater during the late pleistocene and holocene epochs under a cold climate the surface water and most groundwater samples were fresh rather than saline with tds 490 and 1000 mg l 1 respectively the chemistry of unconfined groundwater changed from hco3 dominated to no dominant ions and then to so42 dominated moving along the flow path from the jiuquan jiayuguan basin to the jinta basin and the confined water was so42 dominated the results have important implications for groundwater management in the basin where a high proportion of the water being used is in effect being mined i e extracted faster than its replacement rate thus significant changes are urgently needed in the regional water use strategy c 2012 elsevier ltd all rights reserved

flexural behaviour of the north algerian margin and tectonic implications the algerian margin formed through back arc opening of the algerian basin mediterranean sea resulting from the roll back of the tethyan slab recent geophysical data acquired along the algerian margin showed evidence of active or recent compressive deformation in the basin due to the ongoing africa eurasia convergence published data from four wide angle seismic profiles have allowed imaging the deep structure of the algerian margin and its adjacent basins in this study we converted these velocity models into density models then into isostatic anomalies this allowed us to image an isostatic disequilibrium relative to a local isostasy model reaching a maximum amplitude at the margin toe converting isostatic anomalies into moho depth variations shows that the moho extracted from wide angle seismic data is deeper than the one predicted by a local isostasy model in the oceanic domain and shallower than it in the continental domain these anomalies can be interpreted by opposite flexures of two plates separated by a plate boundary located close to the margin toe we use a finite element model to simulate the lithospheric flexure the amplitude of the equivalent vertical moho deflection is larger in the central part of the study area 6 7 km than on the easternmost and westernmost profiles 3 km the effective elastic thickness used to best match the computed deflection is always extremely low always less than 10 km and probably reflects the relatively low strength of the lithosphere close to the plate boundary comparison with other wide angle seismic profiles across an active and a passive margin show that the north algerian margin displays isostatic anomalies close to that of an active margin finally plate flexure is highest at the southern tip of the ocean continent transition possibly indicating that a former passive margin detachment is reactivated as a crustal scale reverse fault pre dating a future subduction

a new technique for measuring ir concentrations via icp ms abstract impact ejecta deposits have the potential for being ideal stratigraphic markers identifying impact horizons however is done by the identification of shock metamorphic minerals however such work is time consuming often requiring searching through hundreds of grains and is therefore not feasible when searching through extensive stratigraphic sections alternatively impact horizons are frequently identified by the presence of ir anomalies this is typically done through either ni fire assay and column chemistry or by instrumental neutron activation analyses both of which are time consuming and or require specialized training here we present results of our new technique for measuring ir without fire assay or inaa 90 mg of sample is dissolved in hf nitric followed by a mixture of hcl and nitric analyses are conducted on a quadrupole mass spectrometer using indium to correct for instrumental drift and standard addition to avoid matrix complication we have tested this technique with a mix of both cody shale doped with known amounts of ir and with naturally ir rich samples this technique is capable of identifying anomalies as low as 1 ppb while other geochemical techniques can provide more precise concentrations particularly at lower concentration the ease of this technique is well suited as a first pass screening tool for identifying impact horizons in large stratigraphic sections

multiproxy analysis of a new terrestrial and a marine cretaceous paleogene k pg boundary site from new zealand an integrated study of palynology mossbauer spectroscopy mineralogy and osmium isotopes has led to the detection of the first k pg boundary clay layer in a southern hemisphere terrestrial setting the k pg boundary layer was independently identified at centimetre resolution by all the above mentioned methods at the marine k pg boundary site of mid waipara and the terrestrial site of compressor creek greymouth coal field new zealand mossbauer spectroscopy shows an anomaly of fe containing particles in both k pg boundary sections jarosite at mid waipara and goethite at compressor creek this anomaly coincides with a turnover in vegetation indicated by an interval dominated by fern spores and extinction of key pollen species in both sections in addition to the terrestrial floristic changes the mid waipara section reveals a turnover in the dinoflagellate assemblages and the appearance of global earliest danian index species geochemical data reveal relatively small iridium enrichments in the boundary layers of 321 pg g at mid waipara and 176 pg g at compressor creek unradiogenic os 187 os 188 values of the boundary clay reveal the presence of a significant extraterrestrial component we interpret the accumulation of fe nano phases at the boundary as originating from both the impactor and the crystalline basement target rock the goethite and jarosite are interpreted as secondary phases formed by weathering and diagenesis the primary phases were probably controlled by the initial composition of the vapor plume and condensation kinetics rather than condensation thermodynamics this investigation indicates that identification of fe in nano phases by mossbauer spectroscopy is an accurate and cost effective method for identifying impact event horizons and it efficiently complements widely used biostratigraphic and geochemical methods c 2010 elsevier ltd all rights reserved less

south pacific evidence for the long term climate impact of the cretaceous paleogene boundary event abstract the cretaceous paleogene k pg boundary is well represented across a range of depositional settings in new zealand trends in fossil assemblages and marine lithofacies indicate that the k pg event was followed by a pronounced and long term 1 myr perturbation in climate and ocean conditions these findings are supported by a tex86 derived sea surface temperature sst reconstruction across the k pg boundary at mid waipara river north canterbury the bayspar calibration indicates that sst was very stable in the uppermost cretaceous 20 c but abruptly warmed by 4 c in a 25 cm thick lowermost paleocene interval this interval is overlain by a 2 m thick interval in which sst abruptly cooled by 10 c and then progressively returned to 20 c the basal paleocene warm interval is associated with an acme in the dinoflagellate species trithyrodinium evittii and the succeeding cool interval is associated with an acme in palaeoperidinium pyrophorum biostratigraphic correlation of the shelfal mid waipara section to the pelagic k pg sections in marlborough reveals that a significant unconformity separates these two acme events with the t acme event occurring in the earliest paleocene and the p pyrophorum acme occurring 1 myr later and lasting 200 kyr a succession of dinoflagellate acme events within the intervening interval in the marlborough sections implies unstable climatic and environmental conditions in the lead up to the p pyrophorum acme and cooling event at 65 ma this event also coincides with a peak in biogenic silica accumulation in the marlborough sections we suggest that disruption to biogeochemical pathways at the k pg boundary caused long term climatic cooling in the southern pacific region

fold accommodation faults fold accommodation faults are secondary faults that accommodate strain variations related to structural and stratigraphic position during fold evolution four main types of fold accommodation faults are commonly found out of syncline and into anticline thrusts form primarily because of an increase in bed curvature within fold cores although differential layer parallel strain at different scales also contributes to fault slip depending on the kinematic evolution of the major fold the thrusts may propagate along the steep or gentle limb of an asymmetric fold or along the hinge of symmetric folds wedge thrusts are primarily formed in competent units because of variations in penetrative layer parallel strain between adjacent units limb wedges occur as hanging wall and or footwall fault bend and fault tip folds whereas hinge wedges occur as multiple nested faults that tend to thicken the more competent units forelimb and backlimb thrusts form by a variety of mechanisms forelimb space accommodation thrusts are low displacement thrusts that resolve strain discontinuities resulting from increased curvature in fold cores forelimb shear thrusts form in the late stages of folding because of rotation and layer parallel extension on the steep forelimbs of folds most backlimb thrusts originate as out of syncline thrusts they may eventually link with forelimb thrusts to form forelimb backlimb thrusts back thrusts accommodate hanging wall strain during the formation of fault related folds they either form selectively in competent units or propagate through the section at the same rate as the main thrust although fold accommodation faults are secondary features they are important elements that define the geometry and size of structural traps in fold thrust structures accurate mapping of these structures is therefore critical in interpreting the structural geometry of fold and thrust belts shankar mitra holds the monnett chair and professorship of energy resources at the university of oklahoma he received his ph d in structural geology from johns hopkins university in 1977 he spent 19 years at arco research and exploration as senior and principal research geologist director of structural geology manager of geological research and senior exploration research advisor his primary research interests are in the development of structural concepts and methods and their application to exploration and production problems he is a recipient of aapg s wallace pratt and cam sproule awards

evidence for late devonian vertical movements and extensional deformation in northern africa and arabia integration in the geodynamics of the devonian world 1 the upper paleozoic geodynamic evolution is discussed at the scale of a wide part of gondwana from north africa to arabia with the aim of giving an integrated tectonic scenario for the study domain we revisit six key areas namely the anti atlas belt morocco the bechar basin west algeria the hassi r mel high central algeria the talemezane arch south tunisia the western desert egypt and finally the high zagros belt iran below the so called hercynian unconformity which is in reality a highly composite discontinuity surface and subsurface data display a well known arch and basin geometry with basement highs and intervening paleozoic basins we show that this major feature results mainly from a late devonian event and can no longer be interpreted as a far effect of the variscan orogeny this event is characterized by a more or less diffuse extensional deformation and accompanied either by subsidence in the western part of the system or by an important uplift of probable thermal origin followed by erosion and peneplanation by the end of the devonian the whole region suffered a general subsidence governed by the progressive cooling of the lithosphere such a primary configuration is preserved in arabia with typical sag geometry of the carboniferous and permian deposits but strongly disturbed elsewhere by the conjugated effects of the variscan orogeny during the carboniferous and or by subsequent uplifts linked to the central atlantic and neo tethys rifting episodes in conclusion we try to integrate this new understanding in the geodynamics of the late devonian which at world scale is characterized by the onset of the variscan orogeny on the one hand and by magmatism rifting and basement uplift on the other hand

neogene to quaternary broken foreland formation and sedimentation dynamics in the andes of nw argentina 25 s 1 the northwest argentine andes constitute a premier natural laboratory to assess the complex interactions between isolated uplifts orographic precipitation gradients and related erosion and sedimentation patterns here we present new stratigraphic observations and age information from intermontane basin sediments to elucidate the neogene to quaternary shortening history and associated sediment dynamics of the broken salta foreland this part of the andean orogen which comprises an array of basement cored range uplifts is located at 25 s and lies to the east of the arid intraorogenic altiplano puna plateau in the salta foreland spatially and temporally disparate range uplift along steeply dipping inherited faults has resulted in foreland compartmentalization with steep basin to basin precipitation gradients sediment architecture and facies associations record a three phase 10 5 and 2 ma east directed yet unsystematic evolution of shortening foreland fragmentation and ensuing changes in precipitation and sediment transport the provenance signatures of these deposits reflect the trapping of sediments in the intermontane basins of the andean hinterland as well as the evolution of a severed fluvial network present day moisture supply to the hinterland is determined by range relief and basin elevation the conspiring effects of range uplift and low rainfall help the entrapment and long term storage of sediments ultimately raising basin elevation in the hinterland which may amplify aridification in the orogen interior

active oblique ramp faulting in the southern tunisian atlas abstract the gafsa fault is the longest and most active structure of the fold and thrust belt achieving southeastward propagation of the atlas belt of eastern north africa onto the saharan platform the gafsa fault is a 75 km long dextral oblique basement fault ramp that poses a sizable challenge in earthquake hazard assessment because the post paleozoic sedimentary cover is decoupled from its basement above the basement fault in this study we combine seismic lines interpretation tectonic geomorphology and paleoseismological investigations to assess the level of seismic hazard of this fault and evaluate its role in the geodynamic framework of the central mediterranean we show that despite a moderate instrumental and historical seismicity the fault has produced m 6 earthquakes with a return period of ca 500 5000 years during the late quaternary the latest large event having produced a surface rupture on the fault occurred around 8000 yr bp suggesting an m 6 earthquake is overdue on the fault the fault has a minimum reverse component of slip rate of 0 21 0 34 mm yr over the past 50 ka the occurrence of m 7 paleoearthquakes on the fault may be suspected but not established such very strong earthquakes would require transient coseismic linkage of the buried basement fault with the overlying listric fault ramping off the decollement layer the level of seismic hazard may be underestimated on the gafsa fault indeed given the geometry of the basement cover fault system a number of earthquakes generated in the basement would have led to coseismic surface folding instead of to surface rupture the gafsa fault is a major structure accommodating eastward extrusion spreading of the atlas belt onto the saharan and pelagian plateforms above the retreating ionian lithospheric slab

chemostratigraphy across the cretaceous tertiary boundary and a critical assessment of the iridium anomaly the elevated concentration of iridium one of the platinum group elements pge at the cretaceous tertiary boundary is still the most generally accepted evidence that a large bolide struck the earth at the time of the end cretaceous mass extinctions new chemostratigraphic data for cross boundary sections from both hemispheres are not easily explained in terms of such an impact event for example the observation that the pge patterns show marked differences between the hemispheres the new constraints indicate that models of mantle derived pge should be seriously considered and that pge anomalies might not be as useful as previously thought as unambiguous identifiers of large impact events in the earth s history

structural evolution and tectonic style of the tunisian central atlas role of inherited faults in compressive tectonics ghoualguia anticline abstract geological mapping field cross sections structural analyses and new subsurface data were used to characterize the geometry and tectonic setting of the ghoualguia structure which is an e w trending anticline located between the kalaa khasba and rouhia troughs of the central tunisian atlas the results show an important ne sw extensional phase during the mesozoic as demonstrated by synsedimentary normal faults nw se and e w and thickness variations in the aouled mdoua area the absence of paleocene eocene rocks indicates that the eastern and western parts of the ghoualguia structure were separated by high topography in addition the angular unconformity observed between the upper cretaceous unit abiod fm and the upper eocene series souar fm provide evidence of a tilted block structure delineated by north south faults a major compressional phase during the middle to late miocene created various detachment levels that originated mainly in the triassic and cretaceous deposits faults were reactivated as thrust and strike slip faults creating fault related fold structures in the core of the ghoualguia fold an original s dipping normal fault underwent reverse movement as a back thrust fault slip data indicate that the area records a major ne sw extensional phase that took place during the late miocene and pliocene a balanced cross section provides insight into the existence of two main detachment levels rooted in the triassic depth 6 km and the lower cretaceous depth 2 5 km the balanced cross section highlights a shortening of about 2 5 km along cross section and 1 5 km in the central part of the ghoualguia anticline this work underlines the predominant role of the inherited mesozoic structures during the evolution of the atlassic range and their influence on the geometry of the central tunisian atlas

geophysical constraints on the location and nature of the north saharan flexure in southern tunisia gravity data integrated with seismic refraction reflection data well data and geological investigations were used to determine the location of the paleogeographic boundary between the precambrian saharan domain and the younger tunisian atlas domain this boundary north saharan flexure or nsf has not been as clearly defined as it has been to the west in algeria and morocco the gravity data analysis which included the construction of complete bouguer and residual gravity anomaly maps revealed that the atlasic domain is characterized by relative negative gravity anomalies and numerous linear gravity trends implying a thick and deformed sediment cover the saharan domain is characterized by relatively positive gravity anomalies with few gravity trends implying a thin and relatively undeformed sediment cover an edge enhancement analysis of the residual gravity anomalies revealed that the nsf is characterized by a series of discontinuous east and northwest trending linear anomalies south of 34 n that are not related to the well known faults within the gafsa and accident de medenine regions based on the continuity of the amplitudes of seismic reflection data and the trends of the residual gravity anomalies the nsf is not an abrupt discontinuity but a series of step faults dipping toward the atlasic domain to obtain a more quantitative representation of the southern edge of tunisian atlas a regional gravity model constrained by two wells and seismic reflection refraction data was constructed along a north south trending profile which confirms the presence of thicker sediments north of the nsf our analysis shows that the nsf has controlled the depositional environment of the sedimentary rocks within the region since at least triassic time and has acted as a barrier to atlasic deformation south of the nsf the nsf is considered an important tectonic feature that has controlled the paleogeographic evolution of the southern margin of the tethys ocean and it continues to be active today based on seismicity hazard studies

petrography mineralogy and geochemistry of the late eocene oolitic ironstones of the jebel ank southern tunisian atlas abstract the oolitic ironstones ore deposit of jebel ank central tunisia is a simply folded stratiform ore body of about 2 5 8 m thickness located in the upper part of the epicontinental souar formation late eocene and is covered by the continental segui formation mio pliocene the deposit contains about 20 mt of ore with an average grade of 50 fe generally oolitic iron deposition occurs in shallow water lagoonal environments the jebel ank deposit lies between two regional disconformities late eocene and miocene and is evidence of a transitional stage at the end of regional regression before renewed transgression the footwall of the oolitic iron ore bearing bed consists of a fine grained sandstone bed 10 20 cm thick pinching out laterally westward into green clays the hanging wall is composed of thin bedded limestone and clay alternations 2 3 5 m thick iron occurs in the form of cryptocrystalline goethite with limited al fe substitution the goethite contains around 48 fe 5 al and up to 1 5 p jarosite alunite and manganese minerals cryptomelane psilomelane and manjiorite are supergene secondary minerals probably related to descending surface fluids these manganese minerals occur as accessory minerals with the goethite and are most abundant at the lowermost part of the succession showing varied morphologies local cement space filling and free centimeter sized nodules fe oolites in the deposit are similar to those documented in many other oolitic ironstone deposits the dominant fe oolite type 90 has a concentrically laminated cortex with no nucleus the nuclei of the oolites that do have a nucleus are most commonly detrital quartz grains major elements in high grade samples fe 2 o 3 65 vary within a limited range and show higher concentrations of sio 2 average 7 85 and al 2 o 3 average 5 1 with minor tio 2 mno mgo na 2 o k 2 o and so 3 less than 1 paas normalized trace elements of bulk samples and fe oolite generally show similar behavior both are enriched in v co ni mo as zn and y and are depleted in cu rb zr nb ba and hf anomalous v cr ni zn and ree y are correlated with goethite paas normalized ree y patterns of both bulk samples and fe oolite show slight hree enrichment positive ce with negative y anomalies the mineralogy goethite and cryptomelane along with the geochemistry si vs al as cu mo pb v zn vs ni co binary plots zn ni co triangular diagram ree y content and patterns and ce ce vs nd and ce ce vs y n ho n binary plots of the studied oolitic ironstone are congruent with a hydrogenetic type while two possible sources of iron for jebel ank ironstone can be proposed i submarine weathering of glauconite rich sandstone and ii detrital iron from adjacent continental hinterland the later is the more plausible source of iron based on paleogeographic setting the occurrence of fine sandstone underlying the iron level occurrence of mn ores in the lower part of the fe ores succession high phosphorous zinc ree y concentrations and y ho ratios and low la ce ratios

identification of sequence stratigraphy in the dongying formation of the liaoxi low uplift bohai bay basin china a change in sea level or lake level causes a change in accommodation space and sediment compensation which then controls the formation and evolution of sequences a multidisciplinary approach ba

senonian basin inversion and rejuvenation of rifting in africa and arabia synthesis and implications to plate scale tectonics abstract the late paleozoic to tertiary stratigraphic record of much of the african plate reflects the effects of continental rifting and passive margin development several short lived but widespread and tectonically important compressional or wrench dominated events occurred however during the permian to recent evolution of africa we focus here on the best documented of these events which occurred during the late santonian at that time older sedimentary basins mostly ene wsw trending were folded and inverted including some basins along the tethyan margin from morocco to the syrian arc and the intraplate benue southern chad basins and the lugh mandera basin in oman ophiolites were obducted following the santonian tectonism an extensive phase of rifting occurred in central and north africa and northern arabia spanning from campanian to maastrichtian or paleocene times rejuvenation or acceleration of subsidence occurred in several basins located along the tethyan margin along the atlantic and indian ocean margins as well as within the intraplate domain rifting was sometimes accompanied by magmatic activity especially in offshore northern libya and along the indian ocean margin compressional deformations rejuvenated or developed by latest maastrichtian times along the tethyan margin and locally within the intraplate domain one of the most remarkable attributes of the santonian tectonic event which we consider representative of the major trans african stress field changes is the rapidity with which the change was reflected stratigraphically across north and central africa and its short duration the cause of the santonian compressional event is directly linked to the change in poles of rotation for the opening of the atlantic at 83 85 ma the end of the cretaceous normal magnetic quiet zone this was also synchronous with the obduction of ophiolites along the northeast margin of arabia oman the onset of separation between india and madagascar with formation of the mascarene oceanic basin and the development of the european alpine chain we interpret these phenomena as causally related aspects of a global tectonic event the santonian compressional event as well as the campanian maastrichtian rifting event and the end cretaceous compressional event illustrate the critical connection between intraplate tectonic histories and processes occurring at sometimes very distant plate boundaries

towards sustainable development of the environmentally degraded arid rivers of china a case study from tarim river increases in water resources development and utilization over the last 30 years have led to significant environmental and hydrological degradation of the tarim river basin water discharge in the lower reaches has been seriously compromised a total of 300 km of the lower reach has been drained between the 1950s and 1970s the water table fell from 2 3 to 4 10 m between the years 1960 and 1980 and the annual rate of fall of the water table was 20 cm from 1980 to the present the area populated by populus euphtatica has declined by two thirds and the biomass has decreased by half between the years 1958 and 1978 in the tarim river basin from the 1950s to the 1990s the area of p euphtatica e angustifolia forest the main tree species of the region declined by 3 820 km2 in the lower reaches of the tarim river basin while the shrub and meadow area declined by 200 km2 such hydrological changes have resulted in a marked degradation of aquatic habitats and have caused substantial land desertification a total of 12 300 km2 of desertified lands formed between the 1960s and 1990s during the past 30 years the salt content of the tarim river has increased gradually according to observational data from the alar hydrological station the maximum salt content in 1960 was 1 28 g l 1 but in 1981 1984 it reached 4 0 g l 1 and in 1998 was 7 8 g l 1 based on the present organic carbon content in desertified lands total emissions of c into the atmosphere in the last 30 years have been 112 2 tg representing 28 3 of organic carbon in the 0 1 0 m soil layer due to the hydrological degradation among factors contributing to these problems human activities are fore most solving these problems will require raising the level of scientific and technological expertise in the monitoring conservation protection and rehabilitation of water resources and associated habitats presently the greatest priority is to expand and improve water conservation studies

structure paleogeographic inheritance and deformation history of the southern atlas foreland fold and thrust belt of tunisia 1 structural analysis of the southern tunisian atlas was carried out using field observation seismic interpretation and cross section balancing it shows a mix of thick skinned and thin skinned tectonics with lateral variations in regional structural geometry and amounts of shortening controlled by nw se oblique ramps and tear faults it confirms the role of the late triassic early jurassic rifting inheritance in the structuring of the active foreland fold and thrust belt of the southern tunisian atlas in particular in the development of nw se oblique structures such as the gafsa fault the late triassic early jurassic structural pattern is characterized by a family of first order nw se trending normal faults dipping to the east and by second order e w trending normal faults limiting a complex system of grabens and horsts these faults have been inverted during two contractional tectonic events the first event occurred between the middle turonian and the late maastrichtian and can be correlated with the onset of the convergence between africa and eurasia the second event corresponding to the principal shortening tectonic event in the southern atlas started in the serravalian tortonian and is still active during the neogene the southern atlas foreland fold and thrust belt propagated on the evaporitic decollement level infilling the late triassic early jurassic rift the major eocene atlas event described in hinterland domains and in eastern tunisia did not deform significantly the southern tunisian atlas which corresponded in this period to a backbulge broad depozone

further research on the historical seismicity of tunisia a first report on the historical seismicity of tunisia was read at the joint egs esc cec symposium bologna 1988 subsequently further research has revealed new information and confirmed previous doubts careful discussion of sources definitely throws out the famous 408 utica earthquake and increasingly the effects of the 306 310 and 365 events seem dubious on the other hand several sequences 981 1735 1835 1872 1881 1887 are better known although the location of most epicentres still remains vague while catalogues underestimate the frequency of events in northern as well as in southern tunisia where there is a zelzel legend they continue to overestimate the intensities of modern earthquakes

geological and biological consequences of giant impacts it seems inescapable that large impacts have been an ongoing phenomenon throughout geological time in the phanerozoic the estimated frequency of impact by bodies of 5 km diameter or more is on the order of 1 0 every 1 00 myr the 5 km lower limit is chosen arbitrarily but it is shown in this review that such a body is certainly large enough to cause very large terrestrial effects a small decrease in this size limit would lead to a large increase in the frequency of occurrence it may be claimed that bodies of a size likely to have drastic and sudden effects on niany physical and biological features of the earth have arrived with a frequency comparable to the average duration of a biostratigraphic stage nothing is said of the interval between arrivals which may be random i e stochastic currently there is not enough geological evidence to allow recognition of other than random spacing between a few positively identified events during the phanerozoic since impacts by extraterrestrial bodies have been clearly established it is reasonable to postulate that they must leave a record in the stratigraphic column why then do we currently have so few horizons that have been claimed to contain evidence of a global impact event since the effects we are considering are unquestionably global in this paper we bring together evidence from several disciplines that

mechanics and erosion of basement cored uplift provinces 1 basement cored uplift provinces are often characterized by high angle reverse faulting along preexisting crustal heterogeneities which may greatly affect the mechanics of deformation and the coupling between erosion and orogenic structure herein we construct a coupled deformation erosion model to understand the mechanics and erosion of mountain belts in which the spatial distribution of deformation is largely influenced by the presence of preexisting high angle faults in this case deformation is accommodated along and topography is built above these structures this topographic loading leads to increasing lithostatic stresses beneath these regions as a result active deformation may migrate to frictionally stronger structures in adjacent regions where lithostatic loading is lower the migration of deformation to such nearby structures depends on the hubbert rubey pore fluid pressure ratio of the crust the orientations of the frictionally weaker and stronger preexisting faults 1 and 2 respectively the friction coefficients b1 and b2 and hubbert rubey fluid pressure ratios b1 and b2 of these faults and the surface slope of the topography above the frictionally weaker structure assuming zero surface slope above the frictionally stronger structure in general we found that for a given and 1 as b1 increases b1 b2 increases and 2 decreases the value of b2 required to force deformation to migrate increases however as erosional processes lead to decreasing surface slopes deformation will be inhibited from migrating to frictionally stronger structures in adjacent regions our model results may help to explain some aspects of the deformation observed and the possible correlation between precipitation and the migration of deformation within these tectonic provinces

salt tectonics driven by sediment progradation part i mechanics and kinematics using conceptual reasoning and results from physical models we describe the mechanical and kinematic characteristics of sediment wedges spreading seaward above a viscous evaporitic layer spreading can occur if the distal sediment overburden is thin and weak or if it comprises preexisting salt bodies spreading is accommodated by proximal extension and an associated rise of diapiric ridges by midslope seaward translation and by distal shortening rapid sediment progradation can lead to the reactivation of older distal folds by later extension either retrogradation or renewed sedimentation following a long depositional hiatus can reactivate older grabens and diapirs in shortening

fires at the k t boundary carbon at the sumbar turkmenia site abstract we have measured carbon at the marine k t boundary site sm 4 at the sumbar river in turkmenia ussr which has an undisturbed ir profile and the largest known ir anomaly 580 ng cm 2 twenty samples ranging from 100 to 100 cm were analyzed to determine the concentration and 13 c of elemental carbon and kerogen using a cr 2 o 7 oxidation method wolbach and anders 1989 to resolve these components the samples were unusually complex containing 3 kerogen components of distinctive ir spectra and half lives in cr 2 o 7 200 100 and 60 h in addition to soot and charcoal from the k t fire the elemental c has 13 c 25 96 0 6 l o close to the mean for 11 k t sites 25 8 0 6 11 mg cm 2 the first of the 2 kerogen components 13 c 22 8 which dominates in the cretaceous appears to come from detrital carbonaceous shale the second 13 c 27 7 o occurs only in the boundary clay and may come from land plant material swept to sea or phytoplankton grown in the presence of excess light co 2 from fires on land the great thickness of the boundary clay 10 5 cm permits determination of the compositional profiles with unprecedented spatial resolution ir and shocked quartz both representing impact ejecta rise sharply at the boundary peak in the basal layer and then decline soot and total elemental c show a similar spike in the basal layer but then rise rather than fall peaking at 7 cm apparently fires started before the basal layer had settled implying that ignition and spreading of major fires became possible if not immediately then very soon after the impact there is no basis for claims by hansen et al 1987 that k t carbon black first occurs 3 5 m below the danish k t boundary and has 13 c of 27 4 to 27 8 o reexamination of a sample from nye klov shows that these authors confused kerogen with carbon black

the geomorphologic responses to hinge migration in the fault related folds in the southern tunisian atlas in kinematic models of fault related folds hinges must be mobile during fold growth yet hinge migration has been rarely demonstrated in nature several complementary and independent geomorphological responses are presented here that indicate fold hinge migration in the southern tunisian atlas the deformation of the overlying quaternary pediment suggests recent migration of the forelimb synclinal hinge as predicted by the rafini and mercier model the uplift of the first order transverse drainage network the poor maturation and shallow incision features of limb drainage networks toward the base of the limb slope suggest that new and un eroded material was regularly uplifted from the down slope flat plains as predicted by the fault propagation fold model

cenozoic contractional reactivation of mesozoic extensional structures in the eastern cordillera of colombia 1 the eastern cordillera of colombia is key to understanding the role of inherited basement anisotropies in the evolution of active noncollisional mountain belts in particular the rio blanco guatiquia region of the eastern cordillera is exemplary in displaying a variety of phenomena that document the importance of the orientation geometry and segmentation of preorogenic anisotropies we document the first unambiguous evidence that extensional basement structures played an important role in determining the locus of deformation during contractional reactivation in the eastern cordillera detailed structural field mapping and analysis of industry seismic reflection profiles have helped to identify the inherited san juanito naranjal and servita normal faults and associated transfer faults as important structures that were inverted during the cenozoic andean orogeny apparently the more internal faults in the former rift basin were not properly oriented for an efficient reactivation in contraction however these faults have a fundamental role as strain risers as folding is concentrated west of them in contrast reactivated normal faults such as the more external servita fault are responsible for uplifting the eastern flank of the eastern cordillera in addition these structures are adjacent and intimately linked to the development of thin skinned faults farther east in part the superimposed compression in this prestrained extensional region is compensated by lateral escape the dominant presence of basement involved buckling and thrusting and the restricted development of thin skinned thrusting in this inversion orogen makes the eastern cordillera a close analog to the intraplate atlas mountains of morocco and other inverted sectors of the andean orogen farther south

platform collapse and pelagic seamount facies jurassic development of central tunisia abstract in central tunisia the lower liassic facies consists of peritidal carbonates deposited on a wide platform which has been broken into irregular tilted blocks in the early pliensbachian black shale was deposited in some of the down faulted blocks during the early toarcian oceanic anoxic event the bajocian bathonian deposits are represented by ironstones and hemipelagic ammonite and zoophycos rich marl limestones the upper jurassic is composed by pelagic limestones and debris flow deposits the middle jurassic deep marine sedimentation was frequently associated with condensed sections submarine erosion leading to stratigraphic hiatuses the latter results from the interaction between global sea level fluctuations and regional tectonic activity generating an uplifted block in central tunisia in relation with early mesozoic rifting and associated distensional drifting of the north african tethyan margin this horst block has acted as a starved pelagic shoal on which sedimentation has been recorded especially during retrogradational and the aggradational phases

syn to post rift diapirism and minibasins of the central high atlas morocco the changing face of a mountain belt the atlas mountains are classically regarded as a failed mesozoic rift arm subject to alpine inversion folding and thrusting here we present new integrated structural and sedimentological studies that have revealed numerous early middle jurassic diapiric ridges and minibasins characterized by distinctive halokinetic structures diachroneity in halokinesis is observed across the central high atlas waning first in the sw during the early middle jurassic jbel azourki and tazoult ridges and continuing to late middle jurassic towards the ne imilchil region the halokinetic structures are readily differentiated from the effects of later alpine deformation allowing a new picture of the central high atlas to emerge the most pervasive deformation in the central high atlas is associated with early middle jurassic diapirism whereas the impact of alpine inversion is mostly focused at the basin margins this new understanding helps explain previously problematic aspects of the atlas mountains which we now recognize as an exceptionally well exposed natural laboratory for understanding the interactions between halokinesis tectonics and sedimentation

inversion tectonics and the evolution of the high atlas mountains morocco based on a geological geophysical transect an edited version of this paper was published by the american geophysical union agu copyright 1998 agu see also http www agu org pubs crossref 1999 1998tc900015 shtml http atlas geo cornell edu morocco publications beauchamp1999 htm

effect of overburden thickness on thrust belt geometry and development laboratory sand models simulating development of thrust belts indicate that 1 distance between the backstop and the first formed thrust is a linear function of initial sand layer thickness 2 spacing between the first two thrusts is most likely a nonlinear function of initial sand layer thickness 3 initial dip of successive ramps decreases progressively toward the foreland because of variations in principal stress directions with depth and or changes of mechanical properties of sand with increasing overburden 4 faults to the hinterland steepen and become less active as hinterland thrust sheets undergo penetrative shear during sand wedge growth and 5 new ramp initiation occurs to the hinterland of the basal detachment tip line these observations can be interpreted both in context of area balance considerations and soil mechanics theory if initial sand layer thicknesses in our models represent syntectonic overburden in natural thrust belts i e distance between the ground surface and the detachment then our results suggest that locations of some thrust belt salients are controlled by along strike variations in stratigraphic thicknesses and that initial thrust spacing decreases progressively to the foreland if the thrust belt involves a foreland tapering basin furthermore our sand model observations suggest that the concept of a fixed rigid backstop in the hinterland of thrust belts may be misleading as a consequence of thickening the hinterland portion of the thrust belt becomes stabilized and effectively becomes the backstop itself

an overview of the late cretaceous eocene positive inversions and oligo miocene subsidence events in the foreland of the tunisian atlas structural style and implications for the tectonic agenda of the maghrebian atlas system abstract structural interpretation of surface and subsurface data in the eastern foreland basins of tunisia allows us to recognize positive inversion structures i e related to compressional events expressed and recorded in the paleogene sedimentary pile of the atlas domain these episodes are followed by a period of relative tectonic quiescence during oligocene early miocene with development of extensional structures with slightly tilted panels grabens and locally the development of listric normal faults branched at depth on decollement levels comparison of the seismic interpretations and field data collected along the south atlas front as well as in the atlas belt allows us to propose a tectonic scenario at the scale of eastern tunisia atlas in particular we emphasise the role of the so called atlas event middle late eocene which was initially defined in algeria but poorly outlined in tunisia we will show that the tectonic agenda defined in eastern tunisia is consistent with the one proposed elsewhere in the maghreb allowing us to propose a unified view of the geodynamic evolution of the whole atlas system during this period the negative inversion recorded during oligocene early miocene along with the occurrence of synsedimentary normal faults are related to an increase of the subsidence rate in the frame of continuous shortening coeval to basin formation in the front of the atlas the whole oligo miocene evolution results from two different mechanisms flexuration in the front of the atlas and the onset of the extension of the pantelleria linosa malta rift system of central mediterranean which attained a climax stage later during pliocene quaternary

closure of the africa eurasia north america plate motion circuit and tectonics of the gloria fault we examine the closure of the current plate motion circuit between the african north american and eurasian plates to test whether these plates are rigid and whether the gloria fault is an active transform fault we also investigate the possible existence of microplates that have been previously proposed to lie along these plate boundaries and compare the predicted direction of motion along the african eurasian plate boundary in the mediterranean with the direction of slip observed in earthquakes from marine geophysical data we obtain 13 transform fault azimuths and 40 3 m y average spreading rates 34 of which are determined from comparison of synthetic magnetic anomaly profiles to 140 observed profiles slip vectors from 32 earthquake focal mechanisms further describe plate motion detailed magnetic surveys north of iceland provide 11 rates in a region where prior plate motion models had few data magnetic profiles north of the azores triple junction record a rate of 24 mm yr 4 mm yr slower than used by prior models gloria and sea beam surveys accurately measure the azimuths of seven transform faults our plate motion model fits six of the seven within 2 two transform faults surveyed by gloria side scan sonar lie near famous area transform faults a and b and give azimuths 13 clockwise of them because recent studies show that short offset transforms such as transforms a and b are in many places oblique to the direction of plate motion we exclude azimuths from transforms with less than 35 km offset the best fitting and closure enforced vectors fit the data well except for a small systematic misfit to the slip vectors on right lateral slipping transforms slip vectors tend to be a few degrees clockwise of plate motion and mapped fault azimuths whereas on left lateral slipping transforms slip vectors tend to be a few degrees counterclockwise of plate motion and mapped fault azimuths we search the long eurasia north america boundary for evidence of an additional plate but find no systematic misfits to the data in particular if a spitsbergen plate exists and moves relative to eurasia its motion is less than 3 mm yr an africa eurasia euler vector determined by adding the eurasia north america and africa north america euler vectors is consistent with the gloria fault trend and with slip vectors from eastern azores gibraltar ridge focal mechanisms a small circle centered at the africa eurasia closure enforced pole fits the trace of the gloria fault the model in which closure was enforced predicts 4 mm yr slip across the azores gibraltar ridge and west northwest convergence near gibraltar 45 more oblique than suggested by a recent model based on compressive axes of focal mechanisms moreover our model predicts directions of plate motion that agree well with northwest trending slip vectors from thrust earthquakes between gibraltar and sicily because closure enforced vectors fit the data nearly as well as the best fitting vectors we conclude that the data are consistent with a rigid plate model and with the gloria fault being a transform fault

fractionation of ruthenium from iridium at the cretaceous tertiary boundary new data on ru ir abundance ratios are presented for nonmarine hell creek montana frenchman river saskatchewan and marine cretaceous tertiary boundary sites brazos river texas beloc haiti dsdp 577 and dsdp 596 the ru ir ratio varies from 0 5 to 1 within 4000 km of chicxulub and increases to 2 3 at paleodistances 65 ma of up to 12 000 km from the impact site for ci chondrites ru ir 1 5 a ballistic model of ejecta cloud cooling and expansion which employs the available vapor pressure versus temperature data for ru and ir predicts qualitatively similar global variation in the ru ir ratio but by only a factor of 1 5 we infer that several other factors such as remobilization of pge during diagenesis preferential oxidation of ru condensation kinetics and atmospheric chemical and circulation processes may account for the observed larger ru ir variation

stratigraphic occurrences of iridium anomalies at four cretaceous tertiary boundary sites in new zealand three new iridium anomaly sites have been discovered in cretaceous tertiary boundary sequences in new zealand these are at needles point chancet rocks and waipara where integrated iridium deposition values were 165 211 and 7 ng cm2 respectively in contrast to the previously reported woodside creek stratigraphic sequence that had an iridium anomaly of 187 ng cm2 a ferruginous boundary clay is absent in the three new sites though the base of the tertiary is marked by limonite staining the relatively weak anomaly at the waipara section is probably due to extensive bioturbation coupled with a high sedimentation rate at the time of deposition the discovery of these additional boundary rock sequences in new zealand negates suggestions that the woodside creek iridium anomaly was a fortuitous occurrence caused by unusual weathering conditions the integrated iridium deposition values at these three new sites of somewhat different geology support the previously reported high iridium level for woodside creek which until now was the only iridium anomaly on land in the southern hemisphere

geometry and kinematics of the south atlas front algeria and tunisia abstract the south atlas front is the structural boundary between the sahara platform and the atlas mountains it is frequently indicated as a foreland dipping monocline known as the sahara flexure earlier work generally considered that such a cover structure resulted from direct inversion of basement faults this assumption is not applicable to the studied area which is situated close to the algeria tunisia border our study demonstrates a thin skinned style characterised by ramp related folds ten parallel balanced cross sections give an interpretation for the south atlas front from negrine to gafsa about 100 km along strike the geometry at depth of each cross section is defined by forward modelling of each individual anticline the depth to detachment is defined using the geometric characteristics of the fault propagation folds well exposed along the deformation front in all sections the modelling is consistent with basal decollements located within cretaceous stratigraphic levels lateral changes of the tectonic style accommodated by tear faults are observed they seem related to lateral variations in the efficiency of the based decollement faults inducing either a jump of the decollement to another level or the development of en echelon folds the modelling predicts small rotations of cover sheets separated by large scale tear faults

cretaceous tertiary boundary problem on shallow carbonate platform carbon and oxygen excursions biota and microfacies at the k t boundary sections dolenja vas and sopada in sw slovenia adria cp abstract the transition of maastrichtian to danian in sw slovenia was studied in two shallow marine carbonate successions apart from the extinction of some biota the k t boundary is reflected also in carbonate isotopic composition and in geochemistry the k t boundary is characterized by 20 cm to 1 m thick sedimentary breccia of intertidal origin extreme depletion in the 13 c content up to 8 was found in dolenja vas section just at this boundary it related to global climatic changes caused by impact of extraterrestrial body followed by the destruction and combustion of terrestrial plants slight enrichment in 13 c content up to 2 is evident at danian selandian boundary too

deformation styles related to intraplate strike slip fault systems of the saharan tunisian southern atlas north africa new kinematic models the complex geometry and tectonic evolution of the saharan tunisian southern atlas strike slip fault systems north africa have not been investigated comprehensively to date this paper proposes new conceptual models to better understand the structural styles along these intraplate fault zones we use a multidisciplinary approach including field observations geological mapping stress analysis and seismic data to investigate the development and interaction of major strike slip fault segments the regional fault system is dominated by the e w trending biskra alima orbata bouhedma and chotts basement faults that constitute the principal displacement zones pdzs our analyses and interpretations reveal that each pdz has a typical dextral strike slip architecture comprising multi scale fault segments that are linked through extensional and contractional stepovers bends during mesozoic times under ne sw shmin the transtensional fault segments of biskra and alima formed the boundaries of the khanguet sidi neji gafsa ksg basin which developed as a z shaped dextral releasing stepover in cenozoic the ksg basin was inverted in response to the africa eurasia convergence when there was a regional nw se orientation for maximum horizontal stress this inversion occurred mainly along basin sidewalls by reactivation of the pre existing normal oblique faults as right lateral transpressional shears further east the e w dextral strike slip faults of orbata and bouhedma are connected via a ne sw restraining stepover finally all e w dextral strike slip fault segments are associated with ene right stepping en echelon folds and riedel shear patterns of different scales in response to basement wrenching currently most fault zones are still active with deep strike slip earthquakes

the origin of intraplate deformation in the atlas system of western and central algeria from jurassic rifting to cenozoic quaternary inversion abstract analysis of petroleum exploration data supplemented by paleostress data enabled discussion of the origin of the deformation in the western and central saharan atlas algeria this intraplate area has recorded the breakup of pangea late triassic the opening of the maghrebian tethys since the dogger and subsequently its closure oligocene to present however the two periods of strong coupling between europe and africa late lutetian and pleistocene which correspond to rapid uplifts of the atlas system and important deformations are not collision related they can be correlated to the beginning and the end of the development of the western mediterranean sea

structural inheritance in mountain belts an alpine apennine perspective abstract the geological structure of continental lithosphere shows complex variety that is inherited into orogenic belts and influences the localization and amplification of contractional structures during mountain building in the alpine apennine sector together with other sectors of the tethyan orogenic system the pre orogenic crustal template can include arrays of extensional faults other faults can form adjacent to the evolving mountain belt and subsequently become incorporated as the thrust belts migrate into their forelands while in some areas these inherited features may simply reactivate under inversion more commonly faults show complex partial reactivation structures in volumes of distributed strain faults may serve to nucleate large scale buckle folds for example along basement cover interfaces these different patterns of basement reactivation may reflect spatially varying strength depth profiles in continental lithosphere that are themselves inherited from spatially distinct geological histories even when not themselves reactivating basement faults can control deformation in the overlying sedimentary cover by offsetting otherwise regionally extensive detachment horizons the 3d form of thrust systems can be strongly compartmentalized by pre existing cross faults such as the oblique lineaments of the apennines on a large scale the distribution of pre existing faults and other weaknesses may affect the propensity for orogenic contraction in basement and therefore directly control larger scale tectonic processes in the central mediterranean the evolution of slab roll back and the related growth of overlying extensional basins e g tyrrhenian sea may be strongly modulated by the distribution of rift related weak zones in the adjacent continental crust the subduction of continental crust will strongly depend on the inherited structure of this crust specifically the distribution of deep crust of basic composition this develops relatively higher densities associated with eclogite metamorphism which act in turn to reduce the buoyancy of thickened continental crust that otherwise serves to inhibit further shortening investigating all these aspects from the scale of bulk crustal compositions to the geometry timing and strength of earlier fault zones preserved in orogenic belts requires the integration of substantial multidisciplinary geological data sets the extent to which continental orogenic belts represent the amplification of inherited geological heterogeneities as opposed to self ordered phenomena modulated by the syntectonic environment remains unclear

subsurface mesozoic basins in the central atlas of tunisia tectonics sequence deposit distribution and hydrocarbon potential the mesozoic and cenozoic outcrops of the central and meridional atlas of tunisia have been studied by structural biostratigraphic and sedimentologic approaches we extend these studies to the subsurface employing seismic and well data addressing structures sequence stratigraphy and hydrocarbon potential the basin structures are related to strike slip fault systems associated with triassic evaporites mesozoic sedimentary sections in the areas of the gafsa sidi ali ben oun sidi aich and majoura blocks were studied by an integrated seismic sequence stratigraphic and tectonic approach calibrated to wells and surface geologic controls we identified tectonic corridors where upper triassic evaporites intruded younger mesozoic rocks beginning in the jurassic the organization of the tectonic blocks is characterized by the distribution of subsiding basin zones of graben and rim synclines and resistant areas of platforms triassic intrusions induced by the strike slip movements formed salt pillows and domes that accentuate the border elevations between the rim syncline depocenters and the platforms mesozoic sequence deposits are distributed along the flanks of the basin platform borders according to lowstand prograding downlap systems tracts overlapped by aggrading and retrograding onlap and toplap deposits the time space distribution of the systems tract deposits indicates the possibility of formation of triassic jurassic and cretaceous carbonate and sandstone prograding turbidites reefs structural and stratigraphic pinch outs and unconformities in the flanks of salt domes and basins the geometry and distribution of reservoir and seal systems tracts permit the consideration of new triassic jurassic and cretaceous combined stratigraphic and structural hydrocarbon traps around the basins and the platforms this begin page 886 is a new tectonic model of the central atlas of tunisia that shows new potential objectives and traps

the hammamet gabes and chotts basins tunisia a review of the subsidence history abstract we modeled the subsidence of three mesozoic basins in tunisia by using well data seismic lines and field data the results are presented here with an attempt to relate the succession of events deduced from the subsidence evolution analysis to the geodynamic evolution of the northern african margin the mesozoic and cenozoic geological history of tunisia has been broken down into two major periods separated by a transition period the first period from trias to aptian was characterized by a constant subsidence of variable intensity spread over most of tunisia and over all the studied basins this period was dominated by extension accompanying the tethyan rifting during trias lias the transition period during the upper cretaceous was characterized by extension and by the weak effects of far seated compressional events it is coeval with the first appearance of salt mobilization the last period in tertiary marked the appearance of the major collisional events mostly during neogene during this last period basins were characterized by very different behaviour depending on their location east or west of the north south axis and close or not to the tellian nappes among the three basins we studied we paid special attention to the southernmost gabes basin located south of the present eastern margin of tunisia the first order evolution of its subsidence is similar to that we infer for most of the tunisian basins we emphasize the role of the structuration of the gabes basin in the partition of the subsidence through time

fault related folding in sandbox analogue models of thrust wedges abstract the nucleation and growth of thrust fault related folds has been simulated using high resolution sandbox coulomb wedge type analogue models thrust related anticlines grew progressively from initial layerparallel shortening to decollement folding thrust tip folding and eventually thrust ramp folding thrust ramps nucleated in the central sector of the overturned forelimb of decollement folds as a consequence of limb thinning thrust tip folding occurred during outward migration of the ramp tips the fault propagation rate was greater at the lower ramp tip which quickly joined the basal thrust flat while folding continued beyond the upper tip the development of the analogue model thrust fault related folds by progressive changes in kinematics from decollement folding to thrust tip folding and finally thrust ramp folding compares well with analyses of naturally occurring thrust fault related folds

palaeogeographical and palaeoenvironmental reconstruction of the medjerda delta tunisia during the holocene abstract the progradation of the medjerda delta has been the subject of many studies since the 19th century the scale and the rapidity of this phenomenon interested researchers in various fields early on such as geomorphology geology palaeogeography history archaeology or geoarchaeology indeed the delta prograded by around 10 km over 3 millennia at the time of its foundation supposedly at the end of the 12th century bc the phoenician city of utica was located on a promontory bathed by the sea but the sediments carried by the medjerda progressively sealed the bay leaving the tip of the utica promontory now 10 km inland this area is therefore an exception to the general pattern along the tunisian coast since as over the same period everywhere else there is a regression of the coastline owing to a sea level rise of several decimeters based on multi proxy analyses of two coring transects this paper aims to reconstruct the palaeoenvironments and the palaeogeography of the medjerda delta s progradation since the mid holocene some aspects of which are described in ancient sources the results highlight in particular an episode of high intensity flooding around the 4th century ad which is consistent with episodes of high floods and an increase in sedimentation rates recorded in the watershed at the end of the roman period the gradual abandonment of the city of utica can certainly be related to the activity of the medjerda river but our results show that it is because of an increase of fluvial sediment contribution in connection with an erosive crisis in the headwaters and not because of the change of course of the river which had occurred long before

thick skinned tectonics within the intracontinental easternmost atlas foreland and thrust belt tunisia meso cenozoic kinematics and implications for regional geodynamics the transition zone between western and central mediterranean domains presents a key area to investigate kinematic interactions within the adjacent orogen systems such as the easternmost atlas foreland and thrust belt analysis of gravity and seismic data revealed a highly structured basement characterizing a series of structural highs and lows delimited by high angle n s e w and nw se extensional faults this basement architecture is inherited from successive extensional events related to the openings of the triassic early cretaceous tethys oceans i e alpine tethys ligurian tethys and mesogea throughout this period this mosaic of continental blocks significantly controlled the thickness and facies distributions early stages of diapirism took place along these basement faults and allowed maximum subsidence in minibasins revealed by the development of growth strata in response to the late cretaceous eocene shortenings these extensional faults have been reactivated as trasnpressional shear zones giving rise to narrow popup structures in addition gravity modeling indicates crustal thinning and deep rooted faults affecting the crust south of the zaghouan thrust and along e w transfer zones from the late miocene a drastic change in the stress regime is attributed to the effect of the adjacent sicily channel on the study area this promotes crustal thinning basin subsidence and channeling up of mantle derived helium along lithospheric scale weak zones our results give rise to new insights into the reactivation of inherited weakness zones of southern tethys margin in response to the complex interaction between african and eurasian plates accommodated by subduction rollback collision and slab segmentation

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

active thrust faulting offshore boumerdes algeria and its relations to the 2003 mw 6 9 earthquake 1 we investigate the active seismogenic fault system in the area of the 2003 mw 6 9 boumerdes earthquake algeria from a high resolution swath bathymetry and seismic survey a series of 5 main fault propagation folds 20 35 km long leave prominent cumulative escarpments on the steep slope and in the deep basin fault activity creates plio quaternary growth strata within uplifted areas such as a rollover basin on the slope and piggyback basins in the deep ocean most thrusts turn to fault propagation folds at the sub surface and depict ramp flat trajectories we find that the two main slip patches of the 2003 mw 6 9 boumerdes earthquake are spatially correlated to two segmented cumulative scarps recognized on the slope and at the foot of the margin the overall geometry indicates the predominance of back thrusts implying underthrusting of the neogene oceanic crust

structures and tectonics of tunisia abstract in the tunisian atlas nothing is known about the nature of the acoustic basement and in the saharan cratonic part only a few deep exploration wells have reached the precambrian below a thick unfolded palaeozoic sequence north of the craton a major set of faults w e or wnw ese represents the southern limit of palaeo tethys thick sequences of marine late carboniferous and permian were developed below the jeffara and chott jerid triassic evaporites are thick below the tunisian atlas which has enabled detachment of the cover from the basement and folding into plis de couverture structures large diapiric intrusions are known especially in the northwestern sillon tunisien tunisian trough from east to west there is a progressive variation from the stable platform on the eastern side to the unstable shelf of western tunisia between these a zone of tectonic instability named the north south axis corresponds to a deep fault system that acted as a positive suture characterized by tilted blocks gaps in sedimentation and reduced or condensed sequences in the north the unstable shelf of western tunisia grades to the deep furrows where the sediments now forming the tellian and numidian nappes were deposited these nappes overthrust the autochthonous foreland during the miocene orogeny the main folding took place in the pliocene and early pleistocene recent tectonic activity occurs along the main fault zones

the structure and kinematics of the southeastern zagros fold thrust belt iran from thin skinned to thick skinned tectonics 1 we present the first complete balanced cross section across the southeastern zagros fold thrust belt zftb the following main structural features emerge from this section 1 in the south of the zftb the proterozoic to recent sedimentary sequence has been decoupled from its panafrican basement along the ductile basal evaporites and folded into a series of large detachment anticlines ongoing shortening of these structures has resulted in migration of the basal salt layers into the cores of the anticlines and propagation of forelimb thrusts 2 in the north of the zftb deep seated ramps have folded the hanging wall rocks and produced imbrications and duplex structures within the higher levels of the sedimentary sequence 3 out of sequence thrusts linked to major seismogenic basement faults have cut through the structures in the cover of the zftb a three step incremental restoration of the section shows that two main phases of deformation can be separated in the tectonic evolution of the zftb a mio pliocene thin skinned phase in the course of which most of the structures in the cover were generated followed by a pliocene to recent thick skinned phase expressed as out of sequence faulting in the cover which is currently underlined by the seismicity within the basement in plan view the initial structures of the southeastern zftb developed with a curved shape essentially controlled by the shape and thickness of the underlying proterozoic salt basin i e the jura style in the following basement involved phase out of sequence thrusts cut at oblique angles through the preexisting structures of the cover the total shortening absorbed in the cover amounts to at least 45 km corresponding to a ratio of 22

late stage evolution of fault propagation folds principles and example abstract fault propagation folding commonly occurs near the fronts of mountain belts this type of folding may even represent in some thrust systems the major mode of deformation however fault propagation folds are frequently altered by two kinds of late stage evolution breakthrough thrusting or transport on the flat we model the geometric features of these kinds of fold in particular the late stage modification and present the algorithms and equations used in an original program an application based on an example from the atlas mountains of algeria illustrates the main features of the model

controls on the geometry of fold thrust belt salients salients convex to the foreland curves in the map traces of orogens typically involve fold thrust belts formed along the foreland margin of orogens an examination of the map view shape degree of asymmetry dimensions and structural trend line patterns i e the variation in fold trend and fault strike along the length of the belt of 20 fold thrust belt salients worldwide illustrates relationships between salient geometry and the geologic setting in which the salient formed in order to understand these relationships we used simple sandbox models to simulate the formation of three of the several types of salients specifically we examined indenter controlled salients the geometry of which reflects interaction of a fold thrust belt with a hinterland indenter basin controlled salients the geometry of which reflects lateral variations in the thickness of predeformational basin fill and detachment controlled salients the geometry of which reflects lateral variations in the strength of a detachment surface our models demonstrate that thrusts in these three types of salients initiate with a curved shape and that rocks within thrust sheets on the limbs of salients can undergo a vertical axis rotation in response to simple shear without requiring major rotation of the fault trace furthermore trend line patterns distinguish basin controlled from indenter controlled salients specifically structural trend lines in basin controlled salients converge at the end points of the curve while in indenter controlled salients they diverge at the end points of the curve the asymmetry of a salient correlates with the asymmetry of the predeformational basin and or of the indenter and with the convergence direction thus our results explain geometric characteristics of individual salients and address controversies concerning paleomagnetic data in salients they also may help prioritize petroleum exploration targets in salients foreland basin oil fields concentrate at the apex of basin controlled salients because the geologic factors that generate the salient also contribute to localizing oil fields

superposed folding in the neogene series of the northeastern tunisia precision of the upper miocene compression and geodynamic significance new field observations carried out in northeastern tunisia kechabta neogene basin allowed us to clarify and pinpoint the chronology of the folding phases which had been the subject of contradictions in previous studies to better understand the folding in the study area a set of structural lithostratigraphic and cartographic arguments are given in order to confirm the atlassic folding phase upper tortonian affecting rheologically weak and incompetent materials of the neogene layers in the kechabta neogene basin the upper tortonian folding is materialized by an unconformity between the kechabta tortonian and the oued bel khedim messinian formations the highlight of this event allows us to identify the current fold structure of the study area as a superposition of two major folding episodes the first one occurred during the upper tortonian and the second in the early quaternary post villafranchian the chronological consistency of the upper tortonian folding in the kechabta basin with the rest of the tunisian chains allows for a better understanding of the collision context miocene to the quaternary which dominated the western mediterranean sea and steered the structural evolution of tunisia

triassic palaeogeography of tunisia abstract a stratigraphic palaeogeographic and palinspastic synthesis of the triassic successions in tunisia is herein documented from a sse nnn oriented profile saharan platform gulf of gabes offshore tunisian atlas tellian units across the northern boundary of the gondwana plate and the future south tethyan margin it is principally based on a reinvestigation of old data and on recent results particularly related to new lithostratigraphic subdivisions and palaeontologic datings obtained from assemblages of benthic foraminifera algae palynomorphs ammonites and brachiopods the various triassic successions of tunisia are compared at the scale of the formations and sequences in the most possible precise biochronologic framework the corresponding chart is used as reference to seven maps of the dominating depositional environments during the following time intervals induan olenekian anisian lower ladinian middle upper carnian norian lowermost part of rhaetian and uppermost part of rhaetian in a peri tethyan domain controlled both by eustasy and extensional tectonics the proposed maps show the alternation of regressions marked by fluvio deltaic siliciclastics and paralic sebkha type evaporites and transgressions marked by foraminifera bearing limestones dolomites of internal proximal platform sometimes open to pelagic influences the transgressions were particularly widespread during carnian and rhaetian times and probably came from a deeper trough situated towards ene during a first rifting phase the motion of normal crustal faults strongly inclined towards the north induced well marked differential subsidences in conclusion a new palinspastic reconstruction along a south north sse nnw oriented profile is proposed it shows a succession of shoals flanked by lateral steps such as the tebaga of medenine shoal sub basins atlas and tilted blocks hairech ichkeul heralding the structuring of the south tethyan margin during jurassic times

architecture and neogene to recent evolution of the western calabrian continental margin an upper plate perspective to the ionian subduction system central mediterranean the western calabria continental margin forms the transition between the pliocene to recent marsili spreading center and continental calabria all parts of the upper plate of the ionian subduction zone integrating high resolution and crustal seismic images constrained by gravity modeling we provide a detailed reconstruction of the architecture of the margin and develop a new scheme for its miocene to present evolution this time span encompasses the continent continent collision between africa and eurasia subsequent orogenic collapse and rifting apart between the two continental masses and the pliocene to recent emplacement of oceanic crust in the vavilov and marsili basins the crust of the margin thins from the calabria coast 25 km to the marsili continent ocean transition 12 km on the whole upper and lower crusts thin proportionally with pure shear geometry the continental margin is covered by an oligocene to present sedimentary succession reaching a maximum thickness of 6 0 km in the paola basin during the miocene the continental margin experienced regional shortening accommodated by a large number of mainly west vergent thrusts possibly associated with the late stages of the kabilo calabrian chain shortening continued through pliocene to recent but was accommodated by a limited number of west vergent thrust faults located in the western part of the margin and by a few tens of kilometers wide syncline located in the eastern part of the profile the accommodation space created in the syncline core hosted a 4 5 km thick plio quaternary sedimentary succession the paola basin no significant extensional fault is observed along the profile miocene to recent subsidence was controlled by 1 a short wavelength component related to shortening and responsible for the formation of the paola basin syncline and possibly contributing to the uplift of onshore calabria and 2 a long wavelength component responsible for the regional subsidence and oceanward tilting of the calabria margin short wavelength subsidence ended in the late pliocene but long wavelength downward movements persisted and even accelerated during late pliocene to quaternary times when the present day bathymetry was achieved both horizontal deformations and vertical movements are difficult to explain in the context of a normal back arc basin without taking into consideration patterns of secondary mantle flow generated by the retreat of the subducting slab

global fire at the cretaceous tertiary boundary cretaceous tertiary k t boundary clays from five sites in europe and new zealand are 102 104 fold enriched in elemental c mainly soot which is isotopically uniform and apparently comes from a single global fire the soot layer coincides with the ir layer suggesting that the fire was triggered by meteorite impact and began before the ejecta had settled