fault reactivation in brittle viscous wrench systems dynamically scaled analogue models and application to the rhine bresse transfer zone abstract analogue experiments on oblique rifting and subsequent transpressional reactivation were performed with two layer slabs of sand and silicone in this brittle viscous system transtensional and transpressional wrench faulting was induced by movements of a basal rigid plate the dynamically scaled analogue models are confronted with the structural evolution of the rhine bresse transfer zone rbtz that linked palaeogene rifting in the upper rhine and bresse grabens and that appears to have been transpressively reactivated in neogene to recent times fault patterns produced in the sand layer above the basal silicone layer are compared with structural elements in the sedimentary cover separated from the basement by an evaporitic decollement layer in order to investigate strain rate dependence of fault reactivation and graben inversion transpressional shortening was performed under different displacement rates experimental results suggest that the reactivation of pre existing structures in a brittle cover above a viscous decollement is strongly dependent on the strain rate within the viscous layer under low to intermediate displacement rates 2 6 cm h 1 deformation concentrates within the basal viscous layer and former normal faults within the cover are not reactivated the reactivation at higher displacement rates 5 cm h 1 results in a complete inversion of graben structures within the cover ongoing shortening produces lobed thrust fronts which crosscut pre existing normal faults late pliocene to recent en echelon aligned folds and isolated thrust faults in the cover of the rbtz are attributed to thick skinned reactivation of basement faults a comparison of natural and experimentally obtained structures suggests that fault reactivation occurred under low displacement rates

evolution of a fold thrust belt deforming a unit with pre existing linear asperities insights from analog models abstract heterogeneity whether geometric or rheologic in crustal material undergoing compression affects the geometry of the structures produced this study documents the thrust fault geometries produced when discrete linear asperities are introduced into an analog model scaled to represent bulk upper crustal properties and compressed varying obliquities of the asperities are used relative to the imposed compression and the resultant development of thrust fault traces and branch lines in map view is tracked once the model runs are completed cross sections are created and analyzed the models show that asperities confined to the base layer promote the clustering of branch lines in the surface thrusts strong clustering in branch lines is also noted where several asperities are in close proximity or cross slight reverse sense reactivation of asperities cut through the sedimentary sequence is noted in cross section where the asperity and the subsequent thrust belt interact the model results are comparable to the situation in the dinaric alps where pre existing faults to the sw of the ne adriatic fault zone contribute to the clustering of branch lines developed in the surface fold thrust belt these results can therefore be used to evaluate the evolution of other basement involved fold thrust belts worldwide

analogue modelling of reverse fault reactivation in strike slip and transpressive regimes application to the giudicarie fault system italian eastern alps abstract sandbox analogue models were used to study the reactivation of a reverse fault in strike slip and transpressive regimes for comparison with the evolution of the giudicarie fault system in the central eastern alps the giudicarie system is interpreted as resulting from late miocene sinistral transpressive reactivation of an older late oligocene reverse fault the old reverse fault was reproduced as a pre cut dilatant surface obtained by pulling a stiff metal wire through the model sand layer the position of the pre existing fault with respect to the base plate fault accommodating the strike slip and transpressive faulting phase controlled the extent and geometry of reactivation the clearest reactivation in a pure strike slip regime was achieved in experiments where the basal strike slip fault was immediately below the pre existing fault plane this strong reactivation involved lateral extrusion and lateral stepping of secondary faults from the basal fault to the pre existing reverse fault in the case of transpression the most spectacular reactivation was achieved for a convergence angle of 10 strongly asymmetric structures developed on either side of the pre cut dilatant zone the analogue experiments reproduced very closely the structural features of the giudicarie fault system supporting a model involving a twofold tectonic evolution for the giudicarie fault system with later reactivation in sinistral transpression of an older reverse fault

fault reactivation control on normal fault growth an experimental study field studies frequently emphasize how fault reactivation is involved in the deformation of the upper crust however this phenomenon is generally neglected except in inversion models in analogue and numerical models performed to study fault network growth using sand silicon analogue models we show how pre existing discontinuities can control the geometry and evolution of a younger fault network the models show that the reactivation of pre existing discontinuities and their orientation control i the evolution of the main fault orientation distribution through time ii the geometry of relay fault zones iii the geometry of small scale faulting and iv the geometry and location of fault controlled basins and depocenters these results are in good agreement with natural fault networks observed in both the gulf of suez and lake tanganyika they demonstrate that heterogeneities such as pre existing faults should be included in models designed to understand the behavior and the tectonic evolution of sedimentary basins

eocene to present subduction of southern adria mantle lithosphere beneath the dinarides we modeled global positioning system measurements of crustal velocity along a n13 e profile across the southern adria microplate and south central dinarides mountain belt using a one dimensional elastic dislocation model we assumed a n77 w fault strike orthogonal to the average azimuth of the measured velocities but we used a constrained random search algorithm minimizing misfit to the velocities to determine all other parameters of the model the model fault plane reaches the surface seaward of mapped sw verging thrusts of eocene and perhaps neogene age along the coastal areas of southern dalmatia consistent with sw migrating deformation in an active fold and thrust belt p wave tomography shows a ne dipping high velocity slab to 160 km depth which reaches the surface as adria dips gently beneath the foreland and becomes steep beneath the dinarides topographic high the thrust plane is located directly above the shallowly dipping part of the slab the pattern of precisely located seismicity is broadly consistent with both the tomography and geodesy deeper earthquakes down to 70 km correlate spatially with the slab and shallower earthquakes are broadly clustered around the geodetically inferred thrust plane the model fault geometry and loading rate ages of subaerially exposed thrusts in the fold and thrust belt and the length of subducted slab are all consistent with adria eurasia collision involving uninterrupted subduction of southern adria mantle lithosphere beneath eurasia since eocene time

multiple monsoon controlled breakdown of oxygen minimum conditions during the past 30 000 years documented in laminated sediments off pakistan abstract late holocene laminated sediments from a core transect centred in the oxygen minimum zone omz impinging at the continental slope off pakistan indicate stable oxygen minimum conditions for the past 7000 calendar years high sw monsoon controlled biological productivity and enhanced organic matter preservation during this period is reflected in high contents of total organic carbon toc and redox sensitive elements ni v as well as by a low diversity high abundance benthic foraminiferal buliminacea association and high abundance of the planktonic species globigerina bulloides indicative of upwelling conditions surface water productivity was strongest during sw monsoon maxima stable omz conditions reflected by laminated sediments were found also during warm interstadial events preboreal bolling allerod and dansgaard oeschger events as well as during peak glacial times 17 22 5 ka all ages in calendar years sediment mass accumulation rates were at a maximum during the preboreal and younger dryas periods due to strong riverine input and mobilisation of fine grained sediment coinciding with rapid deglacial sea level rise whereas eolian input generally decreased from glacial to interglacial times in contrast the occurrence of bioturbated intervals from 7 to 10 5 ka early holocene in the younger dryas 11 7 13 ka from 15 to 17 ka heinrich event 1 and from 22 5 to 25 ka heinrich event 2 suggests completely different conditions of oxygen rich bottom waters extremely low mass and organic carbon accumulation rates a high diversity benthic fauna all indicating lowered surface water productivity during these intervals the omz was very poorly developed or absent and a sharp fall of the aragonite compensation depth favoured the preservation of pteropods the abundance of lithogenic proxies suggests aridity and wind transport by northwesterly or northeasterly winds during these periods coinciding with the north atlantic heinrich events and dust peaks in the tibetan loess records the correlation of the monsoon driven omz variability in the arabian sea with the rapid climatic fluctuations in the high northern latitudes suggests a close coupling between the climates of the high and low latitudes at a global scale

new insights into the tectonic evolution of the andaman basin northeast indian ocean multibeam swath bathymetry data acquired over an area of about 30 000 km2 together with magnetic and single channel seismic data have been analyzed to understand the tectonic evolution of the andaman basin northeast indian ocean swath bathymetry data revealed several morphotectonic features that divide the basin into a complex western part comprising arc parallel seamount chains and n s trending fault systems and a relatively smooth eastern part a sw ne trending spreading ridge bisects the basin an offset of about 11 8 km at 94 21 e longitude divides the spreading ridge into sw and ne segments high resolution bathymetry and magnetic data enabled us to identify two finer scale segments over the sw part of the ridge that display distinct topographic fabric compared to the ne segment thin sediment cover and presence of axial seamounts characterize sw segments of the ridge whereas the ne segment has thick sediment cover and well maintained rift valley kinematics of basin evolution derived from the identification of the seafloor spreading magnetic anomalies suggest very slow initial opening rates of about 1 6 cm yr and an increase in the spreading rate to about 3 8 cm yr from anomaly 2 to present although this interpretation relies only on magnetic anomalies in the two westernmost segments it is suggested that the true seafloor spreading started about 4 ma in the andaman backarc basin rather than the 11 ma postulated previously we infer based on the integrated analysis of swath bathymetry magnetic and seismological data that the basin has evolved as a consequence of extrusive tectonics that prompted extension and rifting along the plane joining the sagaing and semengko fault systems extension by seafloor spreading during the past 4 myr resulted in the formation of the deep andaman backarc basin this phase has also experienced westward propagation of the spreading center

normal fault development during two phases of non coaxial extension an experimental study we use scaled experimental analog models to study the effect of a pre existing fault fabric on fault development during extension in our models a homogeneous layer of wet clay undergoes two noncoaxial phases of extension whose directions differ by up to 45 the normal faults that develop during the first phase create a pronounced fault fabric that influences normal fault development during the second phase in all models the pre existing faults are reactivated during the second phase of extension their sense of slip depends on the angle between the first and second phase extension directions specifically the component of dip slip relative to strike slip decreases as the angle between the first and second phase extension directions increases new normal faults also form during the second phase of extension in all models the number of new fault segments increases as the angle between the first and second phase extension directions increases the orientations of the new normal fault segments are both orthogonal and oblique to the second phase extension direction indicating that both the secondphase extension direction and the pre existing fault fabric control the orientation of new fault segments some of the new normal faults cut and offset the pre existing faults whereas others terminate against them producing complex fault patterns and interactions the modeling results explain fault interactions observed in the jeanne d arc rift basin of offshore newfoundland canada and the reactivation of abyssal hill normal faults at outer highs near subduction zones

a review of brittle compressional wedge models abstract fold and thrust belts and accretionary wedges form by compression of sedimentary sequences and basement rocks into forward and backward thrusts folds nappes and duplexes for over a century models have been used to investigate the essential characteristics of such brittle wedges here i review model studies of brittle thrust wedges in orthogonal compression focussing on critical taper theory analogue and numerical techniques for modelling brittle behaviour and the most commonly investigated variations in wedge model studies those in basal dip basal strength internal strength and surface processes many model results can be placed in the context of critical taper theory which provides analytical solutions for wedge taper angle and slip line orientations for a homogeneous material on the verge of failure throughout dynamic forward models have confirmed critical taper predictions of decreasing surface dip for increasing basal dip wider wedges with steeper forward thrusts and shallower backward thrusts for decreasing basal strength narrower wedges and enhanced exhumation for surface erosion and decreasing surface dip for increasing internal strength but analogue and numerical models have been able to take these results a step further by investigating the evolution of non critical thrust wedges and the effects of non homogeneous materials with decollement layers and strain weakening shear zones these results have highlighted the strong impact of heterogeneous materials on the internal structures of thrust wedges and raise the question whether the complexity of structures that are observed in many natural fold and thrust belts requires that lithological layering inherited faults or a wide range of rheologies need to be included in forward models of brittle thrust wedges

a 25 ka indian ocean monsoon variability record from the andaman sea recent paleoclimatic work on terrestrial and marine deposits from asia and the indian ocean has indicated abrupt changes in the strength of the asian monsoon during the last deglaciation comparison of marine paleoclimate records that track salinity changes from asian rivers can help evaluate the coherence of the indian ocean monsoon iom with the larger asian monsoon here we present paired mg ca and d 18 o data on the planktic foraminifer globigerinoides ruber white from andaman sea core rc12 344 that provide records of sea surface temperature sst and d 18 o of seawater d 18 osw over the past 25 000 years ka before present bp age control is based on nine accelerator mass spectrometry ams dates on mixed planktic foraminifera mg ca sst data indicate that sst was 31c cooler during the last glacial maximum lgm than the late holocene andaman sea d 18 osw exhibited higher than present values during the lateglacial interval ca 19 15 ka bp and briefly during the younger dryas ca 12 ka bp lower than present d 18 osw values during the bolling allerod ca 14 5 12 6 ka bp and during the early holocene ca 10 8 5 5 ka bp are interpreted to indicate lower salinity reflect some combination of decreased evaporation precipitation e p over the andaman sea and increased irrawaddy river outflow our results are consistent with the suggestion that iom intensity was stronger than present during the bolling allerod and early holocene and weaker during the late glaciation younger dryas and the late holocene these findings support the hypothesis that rapid climate change during the last deglaciation and holocene included substantial hydrologic changes in the iom system that were coherent with the larger asian monsoon r 2007 elsevier ltd all rights reserved

an intriguing middle sized horse from coste san giacomo anagni basin central italy various species and ecomorphotypes of the genus equus are recorded in several southern european early pleistocene local faunal assemblages lfas though their taxonomy phylogenetic relationships and chronological distribution are still a matter of debate this article aims to increase knowledge on the european pre olduvai stenonoid horses by describing and discussing the equid sample from the middle villafranchian gelasian italian site of coste san giacomo csg anagni although horse remains from csg are scanty the morphological traits dimensions and proportions of teeth and some limb bones suggest some affinities with middle sized european stenonoid horses in particular with equus senezensis as supported by statistical analysis this opens a new window on the possible phylogenetic relationships of the middle sized slender middle villafranchian horses although some questions about their actual taxonomic rank cannot be firmly answered based on available data the complex relationship among environment structure of the accompanying mammalian fauna and the presence in the early pleistocene lfas of only one equid large or middle sized or even of more horse species with different size is briefly discussed

carbonate preservation and climatic changes in the central red sea during the last 380 kyr as recorded by pteropods abstract numerical abundances of pteropods and planktic foraminifera and the mode of pteropod preservation were determined in core kl 11 taken from the central part of the red sea the abundance of pteropods shells g dry sediment was compared to that of planktic foraminifera pt pf pt a technique that permits detection of changes in carbonate preservation for the last 380 kyr the numerical abundance of pteropods is influenced by the properties of the water column and preservation is influenced by the bottom water during the last 200 kyr except during isotope stage 5 5 carbonates are in general well preserved during this period the abundance pattern of the pteropods and planktic foraminifera is very similar and follows the climatic signal of the red sea with high numbers during the interglacial stages changing to very low numbers during glacial maximum conditions the similar abundance trends of the two groups and between them and the 18o curve indicates abundance is strongly linked to salinity from isotope stage 6 to the bottom of the core the pteropods occur in low numbers unlike the planktic foraminifera which continue to display the high amplitude glacial interglacial cyclicity the deviations mainly during interglacial stages between the abundance pattern of the two groups and the low pt pf pt values indicate a significant change in carbonate preservation distinctive carbonate dissolution intervals are recognized in the red sea correlating to large scale deep water dissolution events of the mid brunhes dissolution cycle in the indian ocean the anti estuarine circulation pattern of the red sea prevents a direct connection between the deep water masses of the two oceans and rules out the likelihood that changes in the deep water circulation caused these carbonate dissolution events the numerical variations between nonmigratory epipelagic and migratory mesopelagic pteropods were used to evaluate changes in the structure of the water column abundance maxima of mesopelagic pteropods as in the recent red sea indicate an aerated water column with 0 5 ml o2 l oxygen concentrations at the minimum zone mesopelagic abundance maxima coincide commonly with negative monsoonal index values indicating a more aerated water column connected to increasing aridity in the red sea region abundance maxima of epipelagic pteropods indicate a strongly stratified water column at times causing severe depletion in oxygen at intermediate water depths epipelagic peak events coincide often with positive monsoon index values implying an overall milder and more humid climate in the red sea probably associated with enhanced precessional controlled southwest monsoon activity

the impact of analogue material properties on the geometry kinematics and dynamics of convergent sand wedges abstract simulation of geodynamic processes in sandbox experiments requires analogue materials with a deformation behaviour that reproduces the deformation mechanisms of typical crustal rocks we present data on the frictional strength of different sand types employing static and dynamic shear tests the sand types analysed are characterised by an elastic frictional plastic mechanical behaviour with a transient strain hardening and strain softening phase prior to transition to stable sliding this is in conflict with the standard assumption of an ideal cohesionless coulomb material with constant frictional properties the influence of the identified transient material properties on the kinematics growth mechanisms and internal deformation patterns of convergent sand wedges results in characteristic wedge segments which vary depending on material compaction between wedges with well defined segments i e frontal deformation zone frontal imbrication zone and internal accumulation zone with straight slopes and wedges with a continuous convex topographic profile for most materials only the frontal part of the wedge is critical during experimental runs taper and strength of the wedge segments can be shown to be controlled by the frictional properties of active faults wedge segmentation is controlled by a bulk strength increase toward the rear of the wedge due to fault rotation in mechanically less favourable orientations and plastic material hardening the limit between the frontal critical parts of a wedge and internal stable parts is largely controlled by a critical state of stress upon which either renewed failure or fault inactivation occurs on this basis we suggest that critical taper analysis of wedges must be restricted to specific kinematic segments comparison of the experimental results with the nankai accretionary wedge suggests that our interpretation also applies to natural convergent wedges moreover we provide constraints for the selection of adequate granular analogue materials to simulate typical crustal rocks in natural convergent wedges

dietary response of early pleistocene ungulate communities to the climate oscillations of the gelasian calabrian transition in central italy abstract climatic oscillations at the gelasian calabrian transition modified terrestrial palaeoenvironmental settings in the european region a gradual drop in global temperatures beginning about 2 7 ma led to drier conditions and to a reduction in and subsequent disappearance of sub tropical vegetation in the central mediterranean area by ca 1 2 ma large ungulates are sensitive to vegetation changes and faced with harsher environmental settings may shift their feeding strategies to exploit available food resources in different ecosystems in fossil assemblages such dietary adaptations are reflected by tooth morphology a phylogenetic signal and tooth wear degree a direct signal of the species diet in this paper we investigate how large herbivores responded to palaeoenvironmental changes that occurred at the passage between the gelasian and calabrian ages in the italian peninsula analysing the dental wear patterns and hypsodonty of the early pleistocene fossil ungulates assemblage of olivola aulla central italy we found that while ungulate feeding behaviours during the gelasian spanned from browsers to grazers in the locality of olivola this group of herbivores display a narrower range of diet types with many taxa adopting a mixed feeding behaviour cervids in particular whose fossils are often associated only with wooded environments as a response to the reduction of covered sub tropical vegetation shifted from a strict browsing diet in mostly closed habitats to a more abrasive one taking advantage of the spread of open landscapes we also provide new data on the feeding behaviour of the rare fossil caprines procamptoceras and gallogoral meneghinii suggesting a grass rich mixed diet for the former and a certain degree of dietary plasticity for the latter our research thus contributes to the better understanding of how ungulates adapted in the past to exploit different resource types during pivotal climatic changes and how environments changed in central italy on the onset of colder and more arid conditions

sea surface temperature and productivity records for the past 240 kyr in the arabian sea abstract deep sea sediments of two cores from the western ty93 929 p and the southeastern md900963 arabian sea were used to study the variations of the indian monsoon during previous climatic cycles core ty93 929 p was located between the sw monsoon driven upwelling centres off somalia and oman which are characterized by large seasonal sea surface temperature sst and particle flux changes by contrast core md900963 was situated near the maldives platform an equatorial ocean site with a rather small sst seasonality less than 2 c for both cores we have reconstructed sst variations by means of the unsaturation ratio of c37 alkenones which is compared with the 18o records established on planktonic foraminifera in general the sst records follow the 18o variations with an sst maximum during oxygen isotope stage 5 5 the last interglacial at about 120 130 kyr and a broad sst minimum during isotope stage 4 and 3 3 approximately 40 50 kyr the sst difference between the holocene and the last glacial maximum lgm is of the order of 2 c in both cores the ssts during isotope stage 6 are distinctly higher by 1 2 c than the cold sst minima during the last glacial cycle lgm and stage 3 to reconstruct qualitatively the past productivity variations for the two cores we used the concentrations and fluxes of alkenones and organic carbon together with a productivity index based on coccolith species florisphaera profunda relative abundance within each core there is a general agreement between the different palaeoproductivity proxies in the southeastern arabian sea core md900963 glacial stages correspond to relatively high productivity whereas warm interstadials coincide with low productivity all time series of productivity proxies are dominated by a cyclicity of about 21 23 kyr which corresponds to the insolation precessional cycle a hypothesis could be that the ne monsoon winds were stronger during the glacial stages which induced deepening of the surface mixed layer and injection of nutrients to the euphotic zone by contrast the records are more complicated in the upwelling region of the western arabian sea core ty93 929 p this is partly due to large changes in the sedimentation rates which were higher during specific periods isotope stages 6 5 4 5 2 3 and 2 unlike core md900963 no simple relationship emerges from the comparison between the 18o stratigraphy and productivity records the greater complexity observed for core ty93 929 p could be the result of the superimposition of different patterns of productivity fluctuations for the two monsoon seasons the sw monsoon being enhanced during interglacial periods whereas the ne monsoon was increased during glacial intervals a similar line of reasoning also could help explain the sst records by the superimposition of variations of three components global atmospheric temperature and sw and ne monsoon dynamics

paleozoic tectonostratigraphic units of the northwest and central dinarides and the adjoining south tisia in the central dinarides and south tisia different paleozoic complexes occur in four geotectonic zones 1 comparatively autochthonous units located in the cores of disrupted anticlines of the external dinarides 2 allochthonous disrupted units accompanied by more predominant triassic formations in the sava nappe which is thrust onto the northeastern margin of the external dinarides 3 allochthonous disrupted units also together with triassic formations in the pannonian and durmitor nappes of the internal dinarides and 4 polymetamorphic sequences in basement of the pannonian basin and south tisia respectively this paper presents basic geological features for the main paleozoic areas included in these four zones the tectonostratigraphic units of the first two zones were related to the gondwana passive continental margin those of the third zone to the paleotethyan oceanic realm and those of tisia to the active laurussia margin geodynamic evolution of all these paleozoic complexes was related to opening and closure of the rheic and paleotethys oceans rifting processes along north gondwana started in the silurian locally in the cambrian ordovician and were followed by the late silurian devonian opening of the paleotethys subduction processes were active by the end of the devonian and at the beginning of the carboniferous along the laurussia margin they were followed during the westphalian by main variscan deformation during collision of gondwana and laurussia associated metamorphism was very low grade in the paleozoic units of the sava nappe low grade to epidote amphibolite grade within the paleozoic complexes of the pannonian and durmitor nappes in the internal dinarides and poly metamorphic with migmatites and granitoids in south tisia these processes gave rise to a pangea stage with the variscan basement disconformably overlain by late carboniferous and permian sediments

temporal variability in the northern arabian sea oxygen minimum zone omz during the last 225 000 years the northern arabian sea is one of the few regions in the open ocean where thermocline water is severely depleted in oxygen the intensity of this oxygen minimum zone omz has been reconstructed over the past 225 000 years using proxies for surface water productivity water column denitrification winter mixing and the aragonite compensation depth acd changes in omz intensity occurred on orbital and suborbital timescales lowest o2 levels correlate with productivity maxima and shallow winter mixing precession related productivity maxima lag early summer insolation maxima by 6 kyr which we attribute to a prolonged summer monsoon season related to higher insolation at the end of the summer periods with a weakened or even non existent omz are characterized by low productivity conditions and deep winter mixing attributed to strong and cold winter monsoonal winds the timing of deep winter mixing events corresponds with that of periods of climatic cooling in the north atlantic region

analogue modelling of fault reactivation tectonic inversion and oblique remobilisation of grabens abstract analogue models of sand above a silicone layer were examined to determine the effects of normal fault reactivation models were first subjected to extension which lead to the formation of two linear grabens each model was then subjected to a second phase deformation either parallel or oblique to the previous initial extension and either extensional or contractional the influence of sedimentation has been evaluated using experiments with and without sedimentation in cases of oblique secondary deformation all newly formed faults were parallel to the older grabens thus they were oblique to the direction of the principal stress directions during the second deformation phase in experiments without sedimentation all older faults were reactivated whereas in experiments with sedimentation some of the older faults were not reactivated in the case of an oblique compressional secondary deformation phase with post rift sedimentation strain partitioning occurred between reactivated older normal faults and new reverse faults 2 was vertical on reactivated normal fault planes whereas 3 was vertical on reverse fault planes in the case of oblique compressional secondary deformation phase without post rift sedimentation no strain partitioning was observed in this model 3 was vertical on every fault plane it is therefore concluded that sedimentation within grabens induces a variation of stress orientation and strain partitioning

lithospheric scale analogue modelling of collision zones with a pre existing weak zone lithospheric scale analogue experiments have been conducted to investigate the influence of strength heterogeneities on the distribution and mode of crustal scale deformation on the resulting geometry of the deformed area and on its topographic expression strength heterogeneities were incorporated by varying the strength of the crust and upper mantle analogue layers and by implementing a weak plate or part of a plate between two stronger ones three brittle crust viscous crust strong viscous upper mantle and four brittle crust viscous crust brittle upper mantle strong viscous upper mantle layer models were confined by a weak silicone layer on one side in order to contain but not oppose lateral extrusion experimental results show that relative strength contrasts between converging plates and intervening weak plates control the location and the shape of deformation sites taken as collision orogens if the contrast is small internal deformation of the strong plates through fore and backthrusting occurs early in the deformation history however the bulk system is dominated by buckling that nucleates on the weak plate whose antiformal topography is highest model moho of the bordering stronger plates is deepest under these conditions if the contrast is large deformation remains localized within the weak plate for a larger amount of shortening and develops a root zone below a narrow deformation belt which coincides with the locus of maximum topography implementing a buoyant low viscosity layer above the model moho of the weak plate favours the development of asymmetric model orogens notwithstanding the initial symmetric setup once the asymmetry is established strain remains localized in thrust faults and ductile shear zones documenting foreland directed displacement of the model orogen such laterally and vertically irregular configurations have applications in continent continent collision settings such as the eastern alps first order mechanical boundary conditions recognized from modelling to be favourable to the post early oligocene tectonics of the eastern alps include 1 subtle rather than high strength contrasts between the adriatic indentor and the strongly deformed region comprising penninic and austroalpine units to the north of it 2 decoupling of penninic continental upper crust from its substratum to allow for crustal scale buckling of the tauern window 3 weak mechanical behaviour of the european lower crust during collision to account for its constant thickness along the transalp deep seismic transect and 4 the direct continuation of the basal detachment underlying the fold and thrust belt in the hangingwall of the european plate with a wide ductile shear zone in the core of the orogen which separates the european from the adriatic plate the geological society of london 2005

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

the influence of the ne winter monsoon on productivity changes in the gulf of aden nw arabian sea during the last 530ka as recorded by foraminifera abstract benthic and selected planktic foraminifera and stable isotope records were determined in a piston core from the gulf of aden nw arabian sea that spans the last 530 ka the benthic foraminifera were grouped into four principal assemblages using q mode principal component analyses comparison of each of these assemblages with the fauna of the nearby regions enabled us to identify their specific environmental requirements as a function of variability in food supply and strength of the oxygen minimum zone and by that to use them as indicators of surface water productivity the benthic foraminiferal productivity indicators coupled with the record of globigerina bulloides a planktic foraminifer known to be sensitive to productivity changes in the region all indicate higher productivity during glacial intervals and productivity similar to present or even reduced during interglacial stages this trend is opposite to the productivity pattern related to the sw summer monsoon of the arabian sea and indicates the role of the ne winter monsoon on the productivity of the gulf of aden a period of exceptionally enhanced productivity is recognized in the gulf of aden region between 60 and 13 kyr indicating the intensification of the ne winter monsoon to its maximal activity contemporaneous indication of increased productivity in other parts of the arabian sea unexplained so far by the sw summer monsoon variability might be related to the intensification of the ne winter monsoon another prominent event of high productivity second in its extent to the last glacial productivity event is recognized between 430 and 460 kyr these two events seem to correspond to periods of similar orbital positioning of rather low precession and eccentricity amplitude for a relatively long period glacial boundary conditions seem to control to a large extent the ne winter monsoon variability as also indicated by the dominance of the 100 ka cycle in the investigated time series secondary in their importance are the 23 and 41 ka cycles which seem also to contribute to the ne monsoonal variability following the identification of productivity events related to the ne winter monsoon in the gulf of aden it is possible now to extend this observation to other parts of the arabian sea and consider the contribution of this monsoonal system to the productivity fluctuations preserved in the sedimentary records

orogenic evolution of the external dinarides in the ne adriatic region a model constrained by tectonostratigraphy of upper cretaceous to paleogene carbonates abstract mesozoic to cenozoic evolution of the central part of the adriatic plate external dinarides and adriatic foreland is still a matter of debate this is expressed by opposing paleogeographic models single carbonate platform adriatic or adriatic dinaridic versus two carbonate platforms adriatic and dinaridic separated by the inter platform budva cukali basin estimates of shortening during adria ne subduction that resulted in the development of the dinaric alps differ substantially the single platform model involves minor shortening achieved by folding and faulting along steep reverse faults the two platform model involves significant shortening achieved mainly by thrust stacking which resulted in almost complete underthrusting of the intervening basinal deposits analysis of upper cretaceous to paleogene stratigraphical data from both outcrops and boreholes allows regional correlation and the interpretation of major lithostratigraphic units as a result a few tectonostratigraphic units are recognized the tectonostratigraphy is used as a basis for a new model on the late mesozoic to cenozoic evolution of the region generally adriatic and dinaridic segments acted as major regional crustal entities of adria the upper portions of the sedimentary cover were differentially affected by progressive southwestward verging thin skinned deformations during the paleocene to eocene miocene the adriatic foreland stayed out of the deformations and is characterized predominantly by wrench and salt tectonics the regional tectonic map shows arcuate thrust fronts of the external dinarides they could be a consequence of both differential propagation of early orogenic thin skinned deformations over crustal fragments separated by transversal faults and or differential isostatic movements of the fragments the collision zone of the adriatic and dinaridic segments is characterized by late orogenic oligocene to miocene thick skinned compressional uplift exhumation related gravity gliding and still active escape tectonics wrenching these processes masked primary thin skinned deformations a significant amount of shortening within and between the thin skinned sedimentary covers is proposed therefore the question of the general paleogeography of the region and the original nw extent of the budva cukali basin ne adriatic trough remains open

sandbox experiments on basin inversion testing the influence of basin orientation and basin fill analogue modelling experiments using brittle materials are performed to study the inversion of extensional structures asymmetric grabens of two different orientations are first created during a phase of extension and progressively filled they are subsequently shortened in the same direction the aim of our experiments is to determine factors affecting the style of deformation during inversion we specifically investigate variations in thickness and distribution of strong and weak layers constituting the graben fill and in initial basin orientation the main advantage of our experimental set up is that we have a complete control on graben location width infill and orientation before inversion the experiments show that shortening results only in limited reactivation of pre existing normal faults in general forward thrusts and backthrusts cut across normal faults into the footwall of the graben the forward thrusts either propagate parallel to the enveloping surface of faulted blocks or they cut across basin limiting normal faults at various angles the graben fill is mechanically extruded by displacement along forward thrusts that accommodate most of the shortening both pre existing faults and weak graben fill act as zones of weakness during inversion and determine the orientation and location of both backthrusts and forward thrusts the results of our experiments conform well to natural examples of inverted graben structures

mechanical behaviour of granular materials used in analogue modelling insights from grain characterisation ring shear tests and analogue experiments abstract the mechanical behaviour of several dry granular materials is investigated through ring shear tests grain characterisation and simple analogue experiments analysed by x ray computed tomography an improved knowledge of granular materials is essential to determine their suitability as analogues for upper crustal rocks in experimental models and to compare analogue and numerical experiments the ring shear tests show that the granular materials have an elastic frictional plastic behaviour with strain hardening preceding failure at peak strength followed by strain softening until a dynamic stable value is reached this is similar to the behaviour exhibited by experimentally deformed rocks the physical characteristics of the grains determine the amount of diffuse deformation before failure the percentage of strain softening and act on the thickness of the shear zones before broadening initial shear zone width in extensional and contractional experiments is between 11 and 16 times the mean grain size the angle of internal friction defining one of the mechanical properties of granular materials and thus fault dip is not only related to physical characteristics of the grains and to the handling technique used e g sieving or pouring but also to the overburden and to the experimental setup used

shear test results for cohesion and friction coefficients for different granular materials scaling implications for their usage in analogue modelling abstract laboratory tests have been carried out on dry granular materials such as quartz sand glass microspheres and sugar with different grain size rounding and sphericity the measurements have been made with a simple shear test machine for different values of normal stress 50 900 pa shear stress has been plotted against normal stress in order to determine the cohesion and coefficient of internal friction for the investigated materials resulting values of cohesion and coefficient of internal friction are mainly dependent on rounding and sphericity while grain size has a less significant influence further the behaviour of the materials for very small normal stresses 0 400 pa is more complex than previously assumed the fracture envelopes for all materials investigated are convex outward for this small range and converge towards a straight failure envelope with increasing normal stress finally in extensional faulting experiments there is no significant change in fault dip with increasing depth therefore the non linear behaviour for small normal stresses is best described as a dependence of the cohesion on the normal stress and not as a dependence of the coefficient of internal friction on the normal stress values for cohesion increase from 0 pa 15 pa at zero normal stress to 137 247 pa 15 pa for normal stresses greater than 250 400 pa the results show that well rounded spherical material is better suited to model brittle behaviour of rocks in crustal and lithospheric scale analogue models than less well rounded material since it has a smaller cohesion and a coefficient of internal friction which is closer to values of natural rocks

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

formation of dabashan arcuate structures constraints from mesozoic basement deformation in south qinling orogen china abstract the dabashan arcuate structures are composed of the nw striking northern dabashan belt belonging to the southern margin of the south qinling orogen and the curved southern dabashan belt located in the northern margin of the yangtze block with the arcuate chengkou fangxiang fault as their boundary the deep understanding of the orogenesis is indispensable to unravel the mechanism of the dabashan arcuate structures as the basement preserves important clues on the deformational characteristics as well as the timing and orogenic processes here we report integrated field investigation structural analysis and 40 ar 39 ar thermochronological data in the wudang and ankang uplifts in the south qinling orogen to decipher the forming processes and mechanisms of the dabashan arcuate structures the field and microscopic observations reveal a dominantly top to south southwest shear sense at low to medium temperatures the basement deformation expanded southward southwestward in the form of duplex during the continued shortening the basement was uplifted due to thrust stacking within duplex systems according to the deformation temperatures and the new and published 40 ar 39 ar thermochronological data the basement recorded the ca 248 212 ma orogenesis for the wudang uplift and the ca 222 161 ma orogenesis for the ankang uplift based on the tectonic evolution of the study area the formation of composite dabashan arcuate structures included three stages firstly the arcuate master fault accompanied by a series of nw striking faults came into being at ca 450 400 ma based on previous studies secondly the scissor like convergence between the south china block and north china block reactivated the extensional structures and formed the general features of the northern dabashan belt at ca 250 160 ma finally the deformation expanded toward the foreland and formed the curved southern dabashan belt with obstruction by the hannan uplift and shennongjia huangling uplift in the front at ca 160 100 ma

quaternary paleo oceanography pteropod preservation and stable isotope record of the red sea abstract an abundance of pteropod species their mode of preservation and stable isotope ratios of carbon and oxygen in benthic and planktic foraminifera have been determined in core md76 140 from the northern red sea isotopic data and benthic foraminiferal species indicate changes in o2 concentration in the bottom sediments the glacial stages are characterized by an almost anoxic bottom while the interglacial bottom was generally well ventilated in general very well preserved pteropod shells occur in glacial oxygen depleted intervals and also on recent well ventilated bottoms in the interglacial stages the preservation deteriorates and in the most extreme cases there is a complete dissolution of the aragonitic shells in these cases most of the assemblage is lost and the only traces of the original shells are their internal molds these are cemented with high magnesium calcite hmc which is a more stable carbonate phase in bottom sediments of the interglacial dissolution of aragonite discriminates between large and small shells the latter tend to be removed completely while the larger ones may be preserved as internal hmc molds limacina inflata is more readily molded than l trochiformis and thus its relative abundance increases in poorly preserved assemblages the state of aragonitic shell preservation depends on the degree of organic matter combustion in the sediments well preserved shells occur in sediments where the supply of organic matter is limited and o2 levels are high preservation deteriorates with increasing supply of organic carbon o2 consumption and increasing production of co2 in this case the dissolved carbonate is reprecipitated as hmc cement with further increase in organic matter supply and reduced ventilation nearly all oxygen is consumed and no3 and subsequently so42 become the oxidizing agents this is followed by an increasing carbonate alkalinity and excellent aragonitic shell preservation

deep transverse basement structural control of mineral systems in the southeastern canadian cordillera1geological survey of canada contribution 20110294 intermittent reactivation of deep paleoproterozoic and archean aged transverse structures in the north american cratonic basement beneath the southeastern canadian cordillera exerted an important influence on the subsequent sedimentary intrusive deformation and mineralization history two regional crossbelt transverse structural corridors recognized by recurrent episodic changes in sediment thickness and facies and anomalous transverse structural trends occur within the thrust and fold belt palinspastic restoration of the exposed transported structural corridors showed that the northern and southern structural corridors are cover expressions of the red deer zone and vulcan low structures in the cratonic basement respectively transverse basement controlled structural corridors enhanced the mineral potential and mineralization systems along them by localization of sedimentary facies favourable for mineralization hydrothermal flow intrusions and favourable structures for mineralization greatest enhancement of hydrothermal flow and mineralization occurred near the intersection of basin parallel and transverse structures greater opportunity for mineralization and intrusion occurred not only along the exposed corridors but also in the west above their undeformed root in the basement the processes that intensified mineralization and localized intrusions along transverse basement controlled structural corridors in the southeastern canadian cordillera should have occurred in thrust and fold belts elsewhere the niobium bearing aley carbonatite complex in the eastern cordillera of northeastern british columbia may be an example of this

late quaternary record of pteropod preservation from the andaman sea abstract in order to understand the glacial to interglacial fluctuations in pteropod preservation and productivity during the late quaternary 54 ka bp to present we investigated pteropod organic carbon corg and globigerina bulloides abundance in a deep sea core from the western andaman sea pteropod abundance and preservation is similar to the indo pacific carbonate preservation type showing better preservation during glacial and poor preservation during interglacial periods the core site appears to have remained below the aragonite compensation depth acd throughout the holocene indicated by the total absence of pteropods maximum abundance and good preservation of pteropods was observed during stadials such as younger dryas yd heinrich events hes and last glacial maxima lgm indicating weaker oxygen minimum zone omz and deeper acd furthermore the high relative abundance of mesopelagic pteropods over epipelagic forms suggests a well ventilated water column with weak omz particularly during lgm apparently driven by intense winter monsoon increased monsoon driven productivity was observed during 45 40 ka of early marine isotope stage 2 mis 2 24 22 ka bolling allerod b a 15 13 5 ka yd and late holocene as evidenced by corg content and g bulloides enhanced pteropod preservation of h1 associated with low corg content and g bulloides suggests that reduced monsoonal driven productivity might have influenced pteropod preservation deglacial preservation spike in the andaman sea is consistent with other northern indian ocean records and elsewhere outside the indian ocean implying the event is global in nature marked by deepening of acd probably driven by enhancement of winter monsoon on local and changes in intermediate water circulation on regional scale

measurements of friction coefficients and cohesion for faulting and fault reactivation in laboratory models using sand and sand mixtures abstract simple laboratory tests have been made on dry quartz sand and on mixtures of sand and clay and sand and cement tests were made on both low and high density specimens of each mixture as determined by physical handling techniques the tests included measurements of density estimates of the coefficient of internal friction based on fault orientation and estimates of the friction coefficients and cohesion values for fault initiation and reactivation in a shear frame apparatus which was also used to test artificial fault zones made from pure clay glass microspheres and wheat flour the results suggest that density is determined more by handling technique than by composition and that friction coefficients and perhaps cohesion both increase with increasing density the shear testing revealed a consistent drop in cohesion for fault reactivation in all densely packed mixtures tested although small this drop may be significant for some types of laboratory models

impact of short term climatic events on latest pliocene land settings and communities in central italy upper valdarno basin abstract the upper valdarno italy plio pleistocene continental deposits record the latest uniform subtropical humid conditions and the successive climatic signature of glacial interglacial cycling the palynological and sedimentological analyses on the poggio rosso alluvial plain sediments reveal two major climatic fluctuations correlated to a glacial interglacial cycle just before the plio pleistocene boundary the glacial phase indicated by the expansion of herbs as well as by ephemeral streams associated with calcareous palaeosols extends from the base of the succession and culminates close to an impressive mammalian bone accumulation dated at 1 87 ma the associated increasing aridity had severe consequences on the faunal communities inducing the migration of open plain dwellers and the trapping of other residents around a few residual shrinking water bodies a cooperative pachycrocuta brevirostris clan acted as regulator of game populations debilitated by drought previous research indicates that hyenas were also the major bone accumulators the following moister and warmer interglacial phase ca 1 83 ma is documented by arboreal taxa and hydromorphic palaeosols in a floodplain crossed by migrating perennial sinuous streams the climatic amplitude method calculated mean annual temperatures around 12 5 14 c and mean annual precipitation around 800 mm with a minimum of 400 mm during the glacial phase and 15 16 19 c and 750 1200 mm during the interglacial phase the reconstruction reveals higher mean annual temperatures and precipitation during the interglacial as compared to the present day climate during the glacial conditions were similar to today s in all but lower precipitation values were reached during the acme drought phase just above the fossiliferous bed poggio rosso documents the ecological consequences the buildup of the apennine chain had under the effects of the latest pliocene global climatic changes it therefore represents one of the first signals of the patchiness that since then gradually increased leading to the eventual habitat fragmentation typical of the late pleistocene landscapes

late orogenic strike slip faulting and escape tectonics in frontal dinarides hellenides croatia yugoslavia albania and greece the frontal zone of the dinarides and its foreland are characterized by the presence of major late orogenic northwest southeast faults trending parallel to and locally dissecting the leading edge of the thin skinned thrust belt on the basis of their geometry and regional distribution these structures are interpreted as right lateral strike slip faults and are related to the formation of en echelon compres sional structures in the split dubrovnik area of the central adriatic region and to the opening of the post messinian pull apart albanian foredeep south adriatic basin in the pliocene holocene these strike slip faults represent the last stage of the mountain building process in the pliocene and holocene when the forelandward prop agation of the dinaric thrust belt was inhibited by stacking of thrust sheets and by overall thickening of the colliding continental crust in that respect the dinaric side of the apulia adria differs from the apenninic side where the thin skinned thrusting progressed normally toward the foreland until the pliocene on a regional scale these northwest southeast trending strike slip faults in the frontal dinarides and their apparent continuation to the hellenides of western greece as well as the dextral vardar fault system indicate the existence of escape tectonics in the di naric hellenic region during the last stage of orogeny the strike slip faults provided a means of tectonic transport from the collision zone of apulia with europe toward the subduction zone of the hellenic trench in southern greece the southeastward moving dinaric hellenic blocks apparently interfered with the westward moving anatolian plate and deflected it southwestward the albanian foredeep in terms of tectonic setting resembles the pull apart vienna basin which formed within the attenuated southwest northeast trending transfer zone of the west carpathi ans during the last stages of the alpine orogeny the late orogenic strike slip faulting may have breached seals and thus negatively affected the hydrocarbon potential of the dinaric hellenic side of the peri adriatic region as contrasted with that of the more prolific apenninic side which was not significantly disrupted by the late orogenic strike slip faulting

evidence of late gelasian dispersal of african fauna at coste san giacomo anagni basin central italy early pleistocene environments and the background of early human occupation in europe since the late 70s the early pleistocene gelasian site of coste san giacomo anagni basin central italy has been known amongst palaeontologists for its diverse vertebrate fauna during the last 5 years new excavations and the drilling of a 46 m deep core have provided novel pieces of information palaeomagnetic data pollen and small vertebrates analyses are presented here for the first time and combined with the updated list of the large vertebrates and ostracod analysis in a multidisciplinary perspective large and small mammals pollen and ostracod analyses have allowed an integrated palaeoenvironmental reconstruction of the sedimentary sequence depicting the evolution of the alluvial plain in the surrounding landscape moreover magnetostratigraphy pollen and small mammal biochronological data have confirmed the position of the coste san giacomo faunal unit focusing the possible age of the mammal assemblage around 2 1 ma in a reversed phase before the base of the olduvai chron in particular the occurrence of the large vole mimomys pliocaenicus has important biochronological significance the coste san giacomo site offers a unique opportunity to investigate the faunal and environmental changes that occurred in mediterranean europe during the early pleistocene coinciding with major climatic changes at a global scale the occurrence of taxa such as hippopotamus sp in the assemblage provides evidence of early dispersal events of african taxa prior to the early homo diffusion into europe

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

area length and thickness conservation dogma or reality abstract the basic assumption of quantitative structural geology is the preservation of material during deformation however the hypothesis of volume conservation alone does not help to predict past or future geometries and so this assumption is usually translated into bed length in 2d or area in 3d and thickness conservation when subsurface data are missing geologists may extrapolate surface data to depth using the kink band approach these extrapolations preserving both thicknesses and dips lead to geometries which are restorable but often erroneous due to both disharmonic deformation and internal deformation of layers first the bolivian sub andean zone case is presented to highlight the evolution of the concepts on which balancing is based and the important role played by a decoupling level in enhancing disharmony second analogue models are analyzed to test the validity of the balancing techniques chamberlin s excess area approach is shown to be on average valid however neither the length nor the thicknesses are preserved we propose that in real cases the length preservation hypothesis during shortening could also be a wrong assumption if the data are good enough to image the decollement level the chamberlin excess area method could be used to compute the bed length changes

the site of coste san giacomo early pleistocene central italy palaeoenvironmental analysis and biochronological overview abstract facies and ostracod analyses have been performed on a continental core drilled at coste san giacomo anagni central italy where a middle villafranchian faunal assemblage was first discovered in 1978 the core intercepted the palaeontological level and penetrated the underlying sedimentary succession previously largely unknown for a total sediment recovery of 40 m in addition new field surveys led to the discovery of hippopotamus sp remains at the faunal site thus pre dating the dispersal of this large ungulate into europe to the middle villafranchian the new sedimentological and palaeoecological data allowed to define a palaeoenvironment mainly ascribable to an alluvial plain characterized by a marsh evolving into a floodplain with overbank deposits and a sand bed fluvial channel this scenario is supported by the reassessed coste san giacomo faunal assemblage consistent with running and or clear waters as well as prairies and grasslands under mild climatic conditions

effect of spatial distribution of hormuz salt on deformation style in the zagros fold and thrust belt an analogue modelling approach scaled analogue models of thin skinned simultaneous shortening above adjacent viscous and frictional decollements simulate the effect of hormuz salt on the shortening in the zagros fold and thrust belt the models consisted of sand layers that partly overlay a viscous layer of silicone and were shortened from one end spatial distribution of the viscous decollement varied along strike and dip as occurs in part of the zagros fold and thrust belt in this belt phanerozoic sedimentary cover was shortened partly above the hormuz salt lying on the precambrian crystalline basement behaving as a basal viscous decollement model results display how the nature of the decollement affects the evolution of an orogenic belt using model results we explain the development of deflection zones and discuss strain partitioning formation of different topographic wedges and differential sedimentation along the zagros fold and thrust belt model results suggest the formation of a gentle taper consisting of both foreward and backward thrusts above a viscous decollement and a relatively steeper taper consisting only of forward vergent imbricates above a frictional decollement however in our models the steepest wedge with the highest topography formed where the viscous substrate had a limited extent with a transitional boundary pinch out perpendicular to the shortening direction shortening of this boundary led to development of frontal ramps associated with significant uplift of the area behind the deformation front

basin inversion and fault reactivation in laboratory experiments abstract a series of analogue models have been performed to get insights into the relationships between the reactivation of pre existing normal faults and the orientation of a successive compressive stress field the models were deformed in two phases 1 a first extension phase h 3 generating a graben and 2 a successive compressive phase with the orientation of the shortening direction h 1 trending between 0 and 90 obliquity angle to the faults bounding the graben the deepening of this graben was accompanied by syn tectonic sedimentation that included a basal ductile layer simulating salt in nature overlain by a brittle sand pack the experimental results suggest that the development of compressive structures is strongly controlled by the pre existing normal faults and by the obliquity angle the experiments have invariably shown that the extensional faults were reactivated during shortening whatever the value of the angle whereas strike slip reactivation of major normal faults is favoured by low obliquity angles mostly dip slip reactivation of pre existing structures is instead promoted for high obliquity angles the analysis of model results highlights the important role played by a ductile layer at the base of the basin fill and the obliquity angle in controlling both strain partitioning and brittle ductile decoupling

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

paleomagnetic and geochronologic constraints on the geodynamic evolution of the central dinarides the geodynamic evolution of the dinaride mountains of southeastern europe is relatively poorly understood especially in comparison with the neighboring alps and carpathians here we construct a new chronostratigraphy for the post orogenic intra montane basins of the central dinarides based on paleomagnetic and 40ar 39ar age data a first phase of basin formation occurred in the late oligocene a second phase of basin formation took place between 18 and 13 ma concurrent with profound extension in the neighboring pannonian basin our paleomagnetic results further indicate that the dinarides have not experienced any significant tectonic rotation since the late oligocene this implies that the dinarides were decoupled from the adjacent adria and the tisza dacia mega units that both underwent major rotation during the miocene the dinaride orogen must consequently have accommodated significant shortening this is corroborated by our ams data that indicate post middle miocene shortening in the frontal zone wrenching in the central part of the orogen and compression in the hinterland a review of paleomagnetic data from the adria plate which plays a major role in the evolution of the dinarides as well as the alps constrains rotation since the early cretaceous to 48 10 counterclockwise and indicates 20 of this rotation took place since the miocene it also shows that adria behaved as an independent plate from the late jurassic to the eocene from the eocene onwards coupling between adria and africa was stronger than between adria and europe adria continued to behave as an independent plate the amount of rotation within the adria dinarides collision zone increases with age and proximity of the sampled sediments to undeformed adria these results significantly improve our insight in the post orogenic evolution of the dinarides and resolve an apparent controversy between structural geological and paleomagnetic rotation estimates for the dinarides as well as adria

how do the properties of a pre existing normal fault population influence fault development during a subsequent phase of extension abstract we use scaled experimental analog models to investigate how the properties of a population of pre existing normal faults influence fault development during a subsequent phase of extension in the models a homogeneous layer of wet clay undergoes two phases of extension whose extension directions differ by 45 to vary the properties of the first phase fault population we vary the magnitude of the first phase extension as the magnitude of the first phase extension increases the number average and maximum length and average and maximum displacement of the first phase normal faults increase for a poorly developed first phase fault population new normal faults which strike perpendicular to the second phase extension direction form during the second phase for a well developed first phase fault population many first phase normal faults are reactivated as oblique slip faults during the second phase new normal faults also form these second phase normal faults are shorter and have displacement maxima adjacent to the reactivated first phase faults they are less likely to cut the pre existing first phase faults than second phase normal faults that form in models with a less developed first phase fault population in all models pre existing faults serve as nucleation sites for new faults in models with a well developed first phase fault population the pre existing faults also act as obstacles to the propagation of the second phase normal faults fault geometries in the models vary considerably parallel zig zag or intersecting fault geometries develop depending on whether the first phase fault population is poorly moderately or well developed respectively

microfossil evidence for changing salinity patterns in the bay of bengal over the last 20 000 years the monsson climate characterizing the northern indian ocean produces salinity gradients that are large compared with those in other open ocean areas these gradients are substantially independent of thermal and other ecologically important gradients this situation makes it possible not only to isolate the effect of salinity on sea bed distribution patterns of planktonic foraminifera but also to investigate past salinity changes along a north south transect of piston cores in the bay of bengal analysis of 152 surface sediment samples reveals that at least three factors other than salinity are important in controlling foraminiferal distribution sea bed dissolution surface productivity and surface temperature of these dissolution is the most important therefore in order to reconstruct past salinity patterns in the bay of bengal faunal indices need to be developed that isolate the effect of salinity we have developed two independent approaches the first uses ternary diagrams of the three dominant dissolution resistant species globoquadrina dutertrei globorotalia menardii pulleniatina obliquiloculata high values of g dutertrei are associated with low surface salinities the second approach uses dissolution buffered salinity transfer functions based on the total foraminiferal fauna in the 152 surface samples from the northern indian ocean applied to downcore samples these methods show the same basic historical pattern of salinity variation which is in turn consistent with independent inferences based on preliminary oxygen isotope data duplessy 1980 historical changes in the bay of bengal salinity are reconstructed along a north south transect of seven cores at 90 e the stratigraphy of the transect is controlled by oxygen isotope profiles that are similar to the generalized patterns observed in other areas over the past 20 000 yr salinity gradients are reconstructed for three time intervals 1 the last glacial maximum lgm 2 the mid termination mt and 3 the holocene during the lgm interval salinity was highger in the bay of bengal particularly in the north thus reducing the north south salinity gradient during the mt the middle of the transition from glacial to interglacial global climatic regimes northern bay of bengal surface salinity was considerably reduced while salinity to the south was generally similar to today thus the salinity gradient between 10 n and 15 n was considerably steeper than today in contrast the holocene gradient was approximately the same as the modern gradient with absolute values along the transect being slightly but uniformly higher these changes in the pattern of salinity are explained in terms of changes in the local patterns of precipitation and river run off during the lgm the salinity pattern probably results from decreased precipitation and decreased run off by the ganges brahmaputra river system during the mt decreased salinity in the northern bay of bengal is caused by increased precipitation and run off rather than by the influx of glacial meltwater the steeper mt salinity gradient in the central bay of bengal suggests increased eastward advection of equatorial surface waters by a southwest monsoon current somewhat more vigorous than today these patterns can be correlated with faunal evidence from the western arabian sea that suggest decreased upwelling during the lgm and increased upwelling during the mt this coupling of events may be associated with changes in the pattern or intensity of circulation during the southwest monsoon decreased intensity at the lgm 18 000 b p and increased intensity at the mt 10 500 to 12 500 b p