a history of cleavage and folding an example from the goldenville formation nova scotia temporal relationships between cleavage formation and folding in sedimentary rock sequences can vary from either phenomena preceding the other to both occurring simultaneously knowledge of this relationship however is required to understand fully the relationship of cleavage orientation to finite strain and the origin of cleavage refraction across competent incompetent layers evidence from the goldenville formation provides an example of cleavage formed before folding by 50 pressure solution removal of material resulting in cleavage planes normal to bedding during active folding this layer parallel shortening was accompanied by excess pore pressure that in some cases exceeded lithostatic pressure causing formation of bedding parallel quartz veins with crack seal textures folds developed by a mechanism of differential flexural flow with no loss of coherence across bedding surfaces en echelon veins formed sequentially across some beds during active folding and subsequently were deformed by various increments of bedding parallel shear after folds reached 80 limb dips continued horizontal shortening was accommodated by additional pressure solution but no recognizable new cleavage was formed because cleavage in the goldenville formation formed perpendicular to bedding before folding and was passively rotated and extended by bedding parallel simple shear during fold amplification the resulting cleavage planes cannot lie in the xy plane of the finite strain ellipsoid differential shear between metagray wacke and slate beds accounts for the observed cleavage refraction and the bedding cleavage angle provides a good estimate of the shearing across these beds during active folding if cleavage can be shown to postdate folding in other examples it is possible that cleavage planes will lie in the xy plane of the finite strain ellipsoid

estimating relative ages from iron oxide total iron ratios of soils in the western po valley italy abstract nineteen samples were collected from deeper layers of as many terraces forming agesequences in five basins most samples were collected at depths of 1 m or more with some below 3 m soils at the sample sites were tentatively identified as alfisols entisols or inceptisols total amounts of iron and the amounts extractable by dithionite and by oxalate were determined for the 19 samples redness ratings were calculated from sample colors and related to amounts of extractable iron by regression mineralogies of the fine sand silt and clay fractions were also determined the percentage of the total iron fe t extracted by dithionite fe d minus the amount extracted by oxalate fe o increased gradually with ages of the terraces which range from early middle pleistocene to upper pleistocene holocene these percentages are independent of the total amounts of iron in the samples and of the general lithology of a basin such ratios thus promise to be useful in estimating relative ages especially where time sequences exist mineralogies of the samples were consistent with relative ages of terraces as estimated from the ratios of iron in different forms so were the redness ratings the regression of extracted iron on redness ratings suggests that colors can be used as preliminary field indicators of relative ages of terraces without time sequences

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

cleavage fold relationships and their implications for transected folds an example from southwest virginia u s a abstract a non coaxial deformation involving pre folding initiation of cleavage perpendicular to bedding is proposed to explain non axial planar cleavage associated with mesoscopic folds in part of the appalachian foreland thrust belt of southwest virginia folds are gently plunging asymmetric upright to slightly inclined sinusoidal forms with non axial fanning cleavage they show extreme local variations in type and degree of transection and the consistency of transection direction these relations are further complicated by hinge migration cleavage fan angles bedding cleavage angles and transection values appear influenced by fold tightness and in part by fold flattening strain fold flattening increments are considered simultaneous with folding axial surface traces and not cleavage traces coincide with the principal extension direction in fold profiles geometric modelling of cleavage fanning and bedding cleavage angle variations for various theoretical folding modes suggest that folding in limestone and sandstone layers was by tangential longitudinal strain significant shape modification and change in bedding cleavage relations occurred after limb dips of 40 and 50 were attained in limestone and sandstone respectively mud rock class 1c folds with convergent cleavage fans show features transitional between buckling and flexural flow initiation of cleavage fabrics during layer parallel shortening prior to significant folding may be important for cleavage evolution in some deformed rocks

geometry and kinematics of the north monagas thrust belt venezuela abstract the complex geometry and structural evolution of the north monagas thrust belt were investigated and new exploration trends in this part of eastern venezuela considered the pirital thrust and related structures of the maturin basin are used to discuss the sequence of thrusting and to illustrate the constant balance between erosion and thrust reactivation in a recent fold and thrust belt a careful analysis of the chronostratigraphy and the internal geometry of the foredeep and piggy back syntectonic deposits has been used to constrain balanced cross sections and to establish the kinematics of each individual structure basement involvement is postulated for the pirital thrust which remobilizes previously emplaced cover structures such as the el furrial or orocual structural units it thus probably relates to the pinch out of a shallow decollement level coal measures of the barranquin formation older late jurassic to lower cretaceous evaporites or other mesozoic plastic horizons and to the reactivation of a deeper basement fault the westward emergence of the pirital and el furrial thrusts in a complex transfer area the urica fault is also analysed according to transverse profiles the surficial urica fault does not connect directly to a basement fault but instead acts as a lateral ramp for the el furrial cover unit and as a tear fault for the pirital thrust reactivation of ancient thrust faults also occurs at the rear of the pirital thrust in the west in areas where the topographic profile of the eastern venezuelan ranges has recently been modified by the pirital thrust emplacement these out of sequence thrusts resulting from fault reactivation in the inner parts of the prism are discussed in terms of the preservation of the critical taper they effectively relate directly to erosional processes which significantly decrease the load applied on this portion of the wedge the influence of the sequence of thrusting on the potential plays is considered

the role of sulphate reducing bacteria and cyanobacteria in dolomite formation in distal ephemeral lakes of the coorong region south australia abstract the dolomitic distal ephemeral lakes of the coorong region of south australia are dynamic systems in which the concentrations of solutes generally increase during late spring and summer when the rate of evaporation greatly exceeds aqueous input during late evaporation active bacterial sulphate reduction occurs in uppermost anoxic lake sediments as rising salinity and then h2s toxicity kills off the macrobiota these hypersaline lakewaters are characterised by high ph and elevated concentrations of carbonate and sulphate ions magnesium concentrated in cyanobacterial cells and sheaths is released into the strongly electrolytic alkaline lake brines from lake margin stromatolites and mats during desiccation and may explain the remarkable increase in mg levels recorded at this time continued evaporation of the lakewaters produces a halite crust overlying the dolomite sulphate free residual puddles and the absence of gypsum indicates that all sulphate is removed by sulphate reducing bacteria dolomite forms in situ as a primary precipitate from these microbially mediated lake porewaters and both the morphology and size distribution of dolomite grains is identical to bacterial cells it is not proven exactly when dolomite precipitation occurs but the submicron sized grains and multiple defects in a disordered lattice indicate that precipitation is rapid and follows bacterial removal of sulphate which is known to inhibit dolomite formation bacterial sulphate reduction and cyanobacterial degradation may thus lead to the removal of all kinetic inhibitors to dolomite formation and provide a mechanism for dolomite precipitation around bacterial cells in shallow subsurface sediments during the late stages of evaporation in adjacent non dolomitic lakes sulphate is present throughout evaporation so that other minerals principally aragonite and hydromagnesite are precipitated

thrust fault mechanics and origin of a frontal ramp several features of thrust sheets in nonmetamorphic and relatively low grade metamorphic terrains indicate that the modes of faulting included both gradual and stick slip types of motion a first order quantitative analysis is made of the mechanics of this type of faulting in the analysis part of a wedge shaped thrust belt slips forward over a fault area of length l and unit width w producing a strain concentration in subhorizontal strata at the front of the growing thrust where a frontal ramp develops by shear fracturing equations for net slip x and the conditions for ramping are evaluated with limit equilibrium principles and coupled oscillator theory the quantitative analysis takes into account anisotropy resulting from contrasts in competency and facies changes a special case solution for maximum net slip associated with stick slip is lw ki 1 cos ot o 12 1 cos 1t where is the stress drop ki are spring constants of the strata 0 and 1 are natural frequencies of the system and t evaluated from another equation is the time for net slip the spring constants and natural frequencies can be evaluated from seismic and stratigraphic data a preliminary solution for piggy back thrusting indicates that ramp spacing can be systematic and that it depends upon the thickness of the deforming package the elastic parameters of the deforming package the slope of the topographic surface and the stresses along the trailing edge of the package

cover deformation above a blind duplex an example from west virginia u s a abstract pretectonic cover above blind thrust systems responds to underlying thrusting by combinations of forethrusting backthrusting and coupling the role of these responses was examined in the hanging rock cacapon mountain anticlinorium of the central appalachians this cover fold consists of middle ordovician and younger sedimentary rocks above a blind horse of cambro ordovician carbonates the cover has abundant folding and subsidiary faulting cover cleavage in carbonate and fine grained clastic rocks formed before regional folding in response to layer parallel shortening lps this 15 lps also produced grain suturing and fluid inclusion trails in quartzarenites the lps formed during cover forethrusting accommodating older blind horses in the hinterland with the formation of the underlying horse cover coupling occurred with bending folding additional secondary buckling and cleavage rotation by flexural flow with perhaps minor flattening this cover coupling was insufficient to accommodate horse formation no evidence exists for backthrusting but forelandwards abundant subsurface evidence exists for cover forethrusting with imbricate thrusting this thrusting accommodates horse formation and differs in style from the lps of the older forethrusting event so for this blind system the cover responded with a combination of coupling and forethrusting

vertical strain variations in the osen roa thrust sheet north western oslo fjord norway abstract vertical variations in deformation style and shortening within the osen roa thrust sheet are examined on the north western side of the oslo fjord using thrust distribution diagrams and graphs of throw against height in the stratigraphy particular formations are identified in which thrusts are either created or destroyed many thrusts are killed by a combination of 1 dissipation of slip by splaying of thrusts in shales and 2 the presence of a thick competent unit that requires a thrust to attain a specific displacement value in order to propagate through the unit in one jerk the upper didymograptus shales and ampyx limestone make an effective combination that kills thrusts with less than 50 m of throw within the thrust sheet deformation styles change vertically from imbricate slices pop up and triangle zones with tip line folds in the cambro ordovician shales and limestones to buckle folds in the silurian limestones sandstones and shales this change is accompanied by a decrease in shortening from 34 in the former to 17 in the latter hence one or several higher bedding parallel detachment horizons need to be invoked to separate areas of varying deformation character

experimental and field study of the effects of lithological contrasts on thrust related deformation 1 the influence of mechanical contrasts related to stratigraphy on thrust related deformation are investigated by sandbox modeling using combinations of granular materials possessing different mechanical properties and by structural analysis of a natural example from the spanish pyrenees the models used in this study consist of loose sand and glass microbeads in varied stratigraphic thicknesses and sequences and the natural example consists of a weakening upward sequence of sandstones and carbonates in both cases layers of different composition had a mechanical significance and accommodated shortening differently model sand and natural sandstone exhibited most shortening by thrust imbrication irrespective of stratigraphic position whereas glass microbeads and carbonates exhibited wider deformation zones and enhanced folding accompanied by displacement reduction along thrust surfaces cutting them transitions of structural style were guided by the stratigraphy rather than by a simple unidirectional propagation from a step up layer parallel shortening was accommodated by diverse mechanisms but did not vary significantly in layers which had different properties the magnitude with which mechanical contrasts were expressed in the models was influenced by the strength at the decollement zone the effect of mechanical contrast was more profound in models shortened above a low friction decollement

recent developments in centrifuge modelling of tectonic processes equipment model construction techniques and rheology of model materials abstract the experimental tectonics laboratory at queen s university is equipped with a large capacity centrifuge that is capable of subjecting tectonic models measuring 127 76 mm in plan and up to 51 mm in depth to accelerations as high as 20 000 g this high capacity greatly extends the range of potential model materials and permits the use of relatively stiff and or brittle substances a number of new techniques of model construction have been devised that permit internal and surface strain patterns and kinematic evolution to be monitored in detail one particularly useful technique which will find application in non centrifuged experiments as well allows the preparation of highly uniform anisotropic multilayers composed of alternating layers of plasticine and silicone putty with individual layer thicknesses as low as 20 m and with controllable ratio between thicknesses of the relatively competent and incompetent units examples of models constructed using these new techniques are illustrated one particular type of the commonly used model material silicone putty has been subjected to a series of rheological test the results indicate that at strain rates in the range 10 6 10 3 s 1 applicable to the centrifuge experiments the silicone putty exhibits power law rheology with n 7 2 at higher strain rates the material appears to tend towards linear behaviour available rheological data and dimensional analysis using standard scaling laws and appropriate model ratios suggest that the microlaminated plasticine silicone putty multilayer is a suitable analogue in centrifuged experiments for interbedded sequences of indurate limestone and incompetent shale the excellent degree of dynamic similitude attained is demonstrated by the realistic form of fold and fault structures developed in models constructed of this material

interrelations of mesoscopic structures and strain across a small regional fold virginia appalachians abstract small regional folds such as the clover hollow anticline of the narrows thrust sheet in southwest virginia u s a are considered to be large buckle folds expressing lateral shortening above a subsurface decollement cleavage mesoscopic and regional folds and contraction faults have developed in these rocks under anchimetamorphic conditions in a single protracted deformation during thrust sheet emplacement the contraction faults dominate the structure at all scales three fault associations isolated contraction faults contraction faults in series and complex fault zones with intense folding determine the pattern and intensity of local structures regional displacement transfer of strain along and across faults has produced local variations in structural style duplex like systems of second order faults terminate laterally into zones of intense folding and third order faulting fold tightness cleavage intensity strain magnitude and total longitudinal strain e t are maximum in these regions contraction faults in this thrust sheet have propagated along zones of high strain rate associated with mesoscopic folding and intense cleavage regional hinge migration and greater structural complexity along the southeast limb of the clover hollow anticline are considered to be due to emplacement of the adjacent thrust sheet

fold generated imbricates examples from the caledonides of southern norway abstract the cambro silurian sequence of the oslo region contains fold trains and closely spaced imbricate thrust faults the imbricates could be interpreted as having ramped off the sole detachment and generated fault propagation folds several imbricate thrusts however appear to die out both downwards and upwards into folds this suggests that the thrusts were generated within the cambro silurian sequence and propagated down to the sole thrust rather than propagating upwards from the sole thrust the mechanical stratigraphy is apparently responsible for this style where during folding relatively brittle limestone members faulted in the highly strained fold forelimbs prior to through going faulting developing in the shales understanding the origin of such imbricates is important when choosing a method of section restoration

centrifuge modelling of thrust faulting structural variation along strike in fold thrust belts abstract the three dimensional geometry and the kinematic evolution of fold thrust structures are investigated by analog modelling using the centrifuge technique we focus on along strike structural variation and transfer of displacement between faults and folds the total horizontal shortening across the model fold thrust belts is constant yet there are systematic variations in shortening by the mechanisms of thrusting folding and layer parallel shortening these along strike changes in structural geometry and strain mechanism are manifestations of displacement transfer the model thrust faults have different amounts of thrust displacement at different points along strike the variation is accommodated by transfer of displacement to over or underlying faults or to en echelon faults by transfer of shortening into folding or by transfer of displacement into layer parallel shortening in the models it is clear that faults nucleate at points that are localized by earlier folding of competent units faults nucleated at different points along a single fold may propagate along the fold and link together to form major thrusts the thrust displacement in such cases varies from smaller values at linkage points to larger values at nucleation points the models have a stratigraphie succession like that of the central appalachian valley and ridge province after an equivalent amount of structural shortening the models exhibit structural features analogous to those of the valley and ridge the lowest competent unit equivalent to the cambro ordovician lithotectonic unit forms a large scale duplex like that of the waynesboro sheet the middle competent unit equivalent to the siluro devonian clastic units forms anticlinoria and synclinoria like those of the martinsburg sheet these structures are spatially associated with underlying culminations and depressions that reflect respectively large and small displacements on thrusts that ramp through the lowest competent unit however in the models it appears that the amplitude of buckling of the middle unit controls the amount of displacement on underlying thrusts whereas in the appalachians the structural culminations of the middle unit are interpreted to have been caused by large displacement on underlying faults

centrifuge modelling of fold thrust structures in a tripartite stratigraphic succession abstract analog models measuring 127 76 mm in plan were deformed at 2500 4000 g in a centrifuge scaled stratigraphic sequences were constructed of anisotropic multilayers with individual layers of plasticine and silicone putty as thin as 40 m the plasticine silicone putty multilayers are analogs for interbedded competent carbonates and clastics and incompetent pelites given the model ratios of acceleration 2500 g length 5 10 6 specific gravity 0 6 time 10 10 modelling of fold thrust tectonics emphasizes the influence of stratigraphic succession on structural evolution the models are constructed with a tripartite stratigraphic succession comprising basal and upper well laminated and incompetent units and a middle somewhat more isotropic and competent unit the models deform by three mechanisms layer parallel shortening folding and thrust faulting they reproduce a number of fold thrust relationships that have been observed in nature folds are typically periclinal in en echelon arrays folds and thrusts are arcuate in plan reflecting differential shortening fold attitudes grade from upright at high levels to overturned at deeper levels within a structural panel reflecting drag against the basal decollement fold axial surfaces and thrust faults are listric while competent units may be offset by localized displacement on thrust faults the discrete faults may die out both upwards and downwards into regions of ductile strain in less competent units thrust faults appear to follow staircase trajectories through the strata transecting incompetent units at shallow angles to bedding and competent units at steeper angles however the apparent staircase pattern results from propagation of a fault along a relatively straight trajectory through previously folded strata foreland verging thrusts are more common than back thrusts the latter have steeper dips the models suggest a mechanism of thrust ramp nucleation following detachment folding long wavelength buckling of a competent unit can initiate localized strain folding and layer parallel shear in an underlying incompetent unit beneath the anticlines of the competent unit thrust faults propagate up section from these high strain zones through the foreland dipping limbs of buckle folds in the competent unit this mechanism may explain the commonly observed spatial periodicity of thrust ramps the model results bear similarities to natural fold thrust belts in which the stratigraphic succession consists of three mechanical units for example the asiak foreland and bear creek hills fold thrust belts of the slave province northwest territories canada

three dimensional geometry and kinematics of experimental piggyback thrusting the three dimensional geometry and kinematics of piggyback stacks of imbricate thrust sheets are illustrated and discussed using a single model shortened in a squeeze box strike parallel geometric elements simulated include lateral ramps eyed sheath folds splays and thrust thrust interference fine details of these structures were exposed by eroding a shortened wedge of sand using a newly developed vacuum eroding technique a kinematic analysis of the model shows a stepwise increase in imbricate thrust spacing and or a decrease in rate of nucleation of imbricate thrusts in the direction of thrust transport despite the steady forward advance of a rear wall the piggyback wedge accreted episodically recording different strain domains in longitudinal cross sections strain partitioning in single layers by bed length balancing showed an increase in layer shortening with volume loss and a corresponding decrease in imbricate thrusting and ramp folding with depth

modelling the geometry of coulomb thrust wedges internal geometry and detachment of coulomb thrust wedges is examined in a combined gravity and pressure force field under various boundary conditions and coulomb parameters frontally buttressed sand wedges accreted with narrow tapers above soles with negligible friction in these models serial imbricates stepped up in conjugate sets which operated synchronously or serially with increases in sole friction model coulomb wedges accreted in piggyback style with enhanced taper but narrower spacing of imbricates in this mode flat topped box fold anticlines nucleated at the frontal tip of a sole thrust prior to the fore limb failing as a ramp the initial ramp thrusts subsequently rotated and steepened to acquire concave upwards listric geometry when cohesion was a significant component of strength and the sand grains interlocked thoroughly ramp climb during piggyback thrusting occurred through the generation of a stack of backthrusts the taper of cohesionless sand wedges which lack any length scale was consistent with the critical cohesionless coulomb wedge taper in contrast the taper of experimental cohesive sand wedges which are scale dependent was consistent with the theoretical cohesive coulomb narrow taper only when the cohesive length scale was lr sr rar 10 6 this was constrained by comparing geometry of cohesive sand wedges shortened at different body force per unit mass

hydrologic framework of a sabkha along arabian gulf during the last 4 000 to 5 000 years sedimentary offlap and a relative fall in sea level have resulted in the development of broad gently seaward sloping about 1 3 000 planar areas or sabkhas along much of the south shore of the arabian persian gulf the depth of the water table below the sabkha surface increases with distance from the sea until it reaches 1 0 to 1 5 m after which it remains constant when the water table depth is in the range of 1 0 to 1 5 m the sabkha surface has reached a state of deflational equilibrium the water table beneath the sabkha always slopes seaward indicating that the direction of ground water flow is toward the sea the subsurface flow system beneath the sabkha is part of a regional seaward flowing groundwater regime in the seaward part of the sabkha a downward flow component is superimposed on the general seaward ground water flow pattern as a result of the infiltration and percolation of water from shallow bodies of seawater that are propelled inland over the sabkha surface by strong onshore winds farther inland where marine flooding does not occur the vertical flow component is directed upward in response to evaporative losses at the sabkha surface the net rate of evaporation from the central parts of the sabkha is on the order of 6 cm factor of 2 of ground water per year a regional ground water flow system which causes the water table level to rise as the sabkha progrades appears to be a requirement for the development and the preservation of broad sabkhas fluctuations in sea level during sabkha development influence the rate of progradation and the thickness of sedimentary facies the refluxing of sabkha brines beneath the lagoons in the abu dhabi area indicates a mechanism for preserving anhydrite during marine transgressions thus permitting the development of stacked sabkha successions which are common in the rock record

alternative model of thrust fault propagation a widely accepted explanation for the geometry of thrust faults is that initial failures occur on deeply buried planes of weak rock and that thrust faults propagate toward the surface along a staircase trajectory we propose an alternative model that applies gretener s beam failure mechanism to a multilayered sequence invoking compatibility conditions which demand that a thrust propagate both upsection and downsection we suggest that ramps form first at shallow levels and are subsequently connected by flat faults this hypothesis also explains the formation of many minor structures associated with thrusts such as backthrusts wedge structures pop ups and duplexes and provides a unified conceptual framework in which to evaluate field observations

two phase diagenesis of quaternary carbonates arabian gulf insights from delta 13 c and delta 18 o data abstract samples from a linear transect of borings in the shallow marine waters offshore of al jubayl saudi arabia represent dolomitic deposits dolomitic facies overlain by low magnesium calcitic deposits calcitic facies and topped by a veneer of aragonitic sediments aragonitic facies the dolomitic fades with its associated evaporites accumulated and was diagenetically altered as part of pleistocene sabkha complexes the calcitic facies is composed of a wide variety of shallow marine pleistocene carbonates and is petrographically indicative of diagenesis in a meteoric phreatic realm the aragonitic sediments are holocene and have undergone only minor shallow marine diagenetic alteration whole rock stable isotope data 26 aragonitic and 112 calcitic samples show that the calcitic deposits have undergone two distinct episodes of diagenesis 1 during pleistocene sea level lowstand s diagenesis in the meteoric vadose realm altered these originally aragonitic and high magnesium calcitic sediments with estimated mean 18o and 13c values of 0 0 and 3 3 pdb respectively to low magnesium calcites with mean 18o and 13c values of 3 5 and 2 0 pdb respectively 2 under the present sedimentological regime sabkha derived evaporative waters with relatively high 18o values descended from the modern coast mixed with the regional groundwater and flowed laterally gulfward within a confined phreatic aquifer i e the calcitic facies beneath the marine waters of the arabian gulf although the calcitic samples display diagenetic trends because of the descent and concomitant lateral migration of waters beneath an exposure surface these trends differ from those recognized in similar studies the subsequent diagenetic overprinting by the sabkha derived surface waters has increased the 18o values as much as 4 additionally an overprint of the waters path can be recognized to the seaward end of the sample transect almost 10 km from the shoreline by a gradual decrease gulfward in the mean whole rock 18o values within the calcitic facies in contrast to analogous studies diagenesis of the al jubayl carbonates due to the sabkha derived waters resulted in 18o values that are widely distributed whereas the 13c values are narrowly distributed and the sediments show the highest 18o values where the water had the greatest influence in the water rock interaction these trends are opposite to those of most other diagenetic sequences

plio quaternary continental deposits of the castellamonte area between orco and dora baltea basins torino province italy abstract new geologic mapping of the area near castellamonte torino province describes a wide plio quaternary continental succession up to about 100 m thick this sequence is distinguished according to allostratigraphic criteria altitude degree of pedogenesis and sediment supply from different basins are also used within a single alloformation several lithofacies are described fine grained fan delta sediments vespia alloformation are described in the lower part of the continental succession the fossil plant remains indicate an early middle pliocene age these sediments show an evident deformation and fill ancient lacustrine basins likely associated with the canavese line trend their wide distribution and considerable thickness suggest subsidence coarse grained glacial outwash and fluvial sediments colleretto castelnuovo s defendente case musso pagliero serra and piverone alloformations are described in the upper part of the continental succession they consist of undeformed sediments deposited during middle to late pleistocene these sediments indicate the presence of small local glaciers along the current valley trends the terracing ratios among the different units and their small thicknesses indicate subsequent differential uplift

structure and tectonics of central and southern appalachian valley and ridge and plateau provinces west virginian and virginia the valley and ridge and eastern allegheny plateau from pennsylvania into tennessee is subdivided into distinct allochthonous sheets emplaced over an essentially featureless precambrian basement surface sheet development is related to variations in stratigraphic thickness and lithology as well as regional basement configuration three sheets control central appalachian structural style the massanutten blue ridge sheet is easternmost and is bounded on the west by the little north mountain pulaski fault system continuing westward into the plateau the martinsburg sheet contains anticlinoria and synclinoria uncut by major thrust faults both massanutten blue ridge and martinsburg sheets are seated in upper ordovician martinsburg reedsville shales the underlying waynesboro sheet is rooted in lower cambrian waynesboro rome shales and its imbrication has controlled the locations of major anticlinoria and synclinoria in the upper sheet within the southern appalachians greater imbrication of the lower sheet and increased thrust fault displacement at longitudinal ramps have destroyed the lateral continuity along strike of the central appalachian waynesboro and overlying martinsburg sheets there imbrication to the surface has formed the saltville sheet continuous into alabama as well as the st clair narrows copper creek cove mountain and st paul honaker sheets southwest of the trend change the holston stone mountain sheet adjacent to the blue ridge is rooted primarily in lower and middle cambrian strata and is underlain by the pulaski sheet in the westernmost sector of this region the pine mountain and richlands sheets are seated in devonian shales the pulaski and massanutten blue ridge sheets rooted primarily in upper ordovician shales form a continuous structural unit and include blue ridge and piedmont rocks

impact of erosion and decollements on large scale faulting and folding in orogenic wedges analogue models and case studies deformation mechanisms long term kinematics and evolution of fold and thrust belts subjected to erosion are studied through 2d analogue experiments involving large convergence first order parameters tested include 1 decollements and or plastic layers interbedded at different locations within analogue materials and 2 synconvergence surface erosion weak layers depending on their location in the model favour deformation partitioning characterized by the simultaneous development of underplating domains in the inner part of the wedge basal accretion and frontal accretion where the wedge grows forward interaction between tectonics and surface processes influences this behaviour development of antiformal thrust stacks controlled by underplating shows small and large scale cyclicity thin plastic layers induce folding processes which are studied at wedge scale recumbent and overturned folds with large inverted limbs develop in a shear induced asymmetric deformation regime via progressive unrolling of synclinal hinges surface erosion and underplating at depth induce further rotation passive tilting and horizontalization of fold limbs model results give insights to discuss the mechanisms responsible for the large scale structures i e antiformal nappe stacks klippen and kilometre scale recumbent fold nappes encountered in several mountain belts such as the montagne noire french massif central the galicia variscan belt spain and the northern apennines italy supplementary material raw data of the experiments are available at www geolsoc org uk sup18658

the pindos fold and thrust belt greece inversion kinematics of a passive continental margin continuous exposure in the pindos mountain chain greece and the detailed stratigraphic measurements in the area enable us to construct eight balanced cross sections across the pindos fold and thrust belt pftb and to approach quantitatively some parameters which controlled foreland evolution the 160 km wide passive continental margin of the apulian continent in greece was progressively shortened from east to west at rates of 6 mm year between the early oligocene and late eocene from the rear to the frontal part of the wedge fault bend folds duplexes and imbricates were formed while strain was partitioned into faulting 34 layer parallel shortening 23 and buckling 9 foreland subsidence and internal deformation of the orogenic wedge are strongly affected by two parameters of equal importance the thrust load of the overthrusted microcontinents and the rigidity of the underthrusted apulian passive margin changes in the thickness of the pre orogenic sediments and reactivated transform faults induced salients during the lower miocene the orogenic wedge in the peloponnese suffered additional uplift and westward gravitational gliding induced by the intracontinental subduction of the palaeozoic rift zone of the phyllite quartzite series which was reactivated and returned to the earth s surface during the hellenic orogeny

mechanics of triangle zones and passive roof duplexes implications of finite element models abstract finite element models of passive roof duplexes simulate the evolution and distribution of fault slip and deformation as functions of boundary conditions friction on the roof fault cover strength and amount of overburden a foreland buttress is essential for backthrust displacement in the models this foreland buttress is analogous to a pin line between the cover and footwall forelandward of the triangle zone in a balanced cross section and could be caused by a stratigraphic pinchout of the upper detachment or a strong cover in the foreland with boundary conditions that prevent the cover from slipping toward the hinterland relative to the wedge incipient forethrust and backthrust ramps zones of high equivalent plastic strain cut through the cover in the models there is more backthrust displacement with a lower friction coefficient on the upper detachment and with a stronger cover because of pressure dependence both fault strength and material strength increase with increasing overburden therefore the effect of overburden on backthrust displacement is determined by the nature of the pressure dependencies for fault friction and material strength in models with multiple imbricate faults the distribution of equivalent plastic strain adjacent to each fault is similar to that in single fault models with differences resulting from bending strains in the wedge and cover the strain distribution in the cover of the models is similar to that above natural passive roof duplexes characterized by layer parallel shortening above the tip of each horse in the duplex

sequence architecture of the bighorn dolomite wyoming usa transition to the late ordovician icehouse abstract although major late ordovician glaciation was confined to the terminal ordovician hirnantian stage lasting less than 2 million years recent isotopic evidence suggests a prolonged interval of slow growth in polar ice caps tropical carbonate platforms from passive margins and epicontinental seas offer the opportunity to monitor changes in eustatic sea level changes that accompanied this transition from a greenhouse towards an icehouse climate the late ordovician bighorn dolomite of northern wyoming and adjacent states preserves such a transition the bighorn dolomite was deposited on a northeastward facing subequatorial platform and it consists of three third order depositional sequences each is bounded by a regional erosional surface commonly with erosional truncation visible at outcrop scale and commonly mantled by a distinctive brecciated horizon the bighorn dolomite is dominated by highly bioturbated and fossiliferous open marine shallow subtidal facies but portions also contain dolomitic bioturbated restricted marine shallow subtidal and laminated peritidal facies as well as thin bedded argillaceous and fossiliferous deep subtidal limestone the three depositional sequences preserve a transition in their internal cyclicity that is consistent with computer modeling of the stratigraphic signal of increasing period and amplitude of eustatic sea level changes the lowermost sequence which spans the lander and steamboat point members consists of homogeneous acyclic shallow subtidal facies with a few meter scale peritidal parasequences near its top the middle sequence which corresponds to the leigh member contains acyclic to weakly cyclic restricted shallow subtidal and peritidal facies the uppermost sequence consisting of the horseshoe mountain member is dominated by five decameter scale parasequences composed of open marine shallow subtidal restricted shallow subtidal and peritidal facies overall the bighorn dolomite is interpreted to represent deposition during a shift from low amplitude a few meters short period 20 kyr cyclicity to moderate amplitude 10 m long period 100 kyr cyclicity indicating a shift from greenhouse conditions towards icehouse conditions a shift that agrees with recent isotopic evidence for changing late ordovician climate

reconstructing plant community scenarios by means of palaeocarpological data from the cenofita database with an example from the ca viettone site pliocene northern italy abstract cenofita 1 2 is a database containing published and unpublished information about 70 late cenozoic italian sites with plant macrofossils taxonomy stratigraphy geography qualitative and quantitative carpological data plant ecology and habitus literature citations it provides a supporting tool for an easy retrieval of palaeofloristic data also accessible to non specialist users which are useful to study italian phytodiversity of the last 6 myr and to contribute in reconstructing palaeovegetation and palaeoenvironment as an example this paper presents a first attempt towards the definition of a standardized reconstruction of selected aspects of late cenozoic plant communities on the basis of data mainly concerning fruits and seeds extracted from cenofita 1 2 which regard the pliocene ca viettone site we obtained five alternative plant community scenarios pcss each one containing fifty sketchy plant symbols which represent several categories of growth forms e g evergreen tree deciduous shrub etc the number of plant symbols of each type in a pcs has been determined on the basis of percent abundance x in sediment samples of plant macrofossils referred to a definite category of growth form we also introduced tentative corrections for taphonomical biases induced by different size and production rate of plant parts thanks to data integration from a wide sedimentation area pcss based on several roughly contemporaneous plant assemblages have been considered definitely more accurate representations of the ancient mesic plant communities than those based on a single plant assemblage this type of pcs suggests in agreement with former reconstructions that the generalized mesic plant community of the ca viettone site would be a forest vegetation highly diverse and dominated by evergreen angiosperms and conifers

high diversity european palaeoflora favoured by early pliocene warmth new chronological constraints from the ca viettone section nw italy abstract we present new chronological constraints for a reference european palaeoflora based on integrated stratigraphic palaeobotanical palaeomagnetic and micropalaeontological analysis carried out on the pliocene section of ca viettone northwestern italy this site is characterized by rich fossil plant records of high taxonomic diversity good preservation and varied taphonomic mode palaeofloral analysis shows that the ca viettone assemblage reflects a chronologically delimited and distinguishable stage of vegetation development in northern italy called ca viettone florenkomplex palaeomagnetic analyses show a dominant normal polarity that however seems to be the result of a remagnetization process due to secondary oxidation layers with no evidence of oxidation have registered a reverse polarity which likely represents the original magnetization of the sediments these results in combination with biochronological indications suggest that deposition of the succession preceded the gilbert gauss reversal and took place during the final part of the gilbert chron this confirms a late zanclean age for the rich ca viettone palaeoflora and allows us to propose this locality both as reference for a regional florenkomplex and as a representative example of terrestrial vegetation in europe during the early pliocene warm interval

deformation behavior during blind thrust translation as a function of fault strength deformation partitioning between translation and distortion for a thrust sheet and for the roof sequence above a moving thrust horse were analyzed in terms of the role of fault strength using finite element models greater frictional resistance on the thrust decollement decreased fault translation increased distortion of the thrust sheet and roof sequence and increased the ratio of backthrusting to forethrusting for the roof sequence in all models with weak decollements 0 35 the ratio of tip line propagation to thrust displacement is very high during initial thrust movement but decreases significantly during later fault motion this observation supports interpretations in natural thrust systems where thrust faults propagate large distances before accumulating significant displacements the tip lines for weak decollements also propagated into the foreland well in advance of the distortion front in the overlying thrust sheet or roof sequence this result does not support interpretations from natural systems for the existence of ductile beads in front of propagating thrusts but rather suggests that recent models for fault arrest or displacement gradient folds may be mechanically valid in addition no model for roof sequences yielded a simple end member response of only backthrusting or forethrusting suggesting that the many blind thrust belts where only one response has been interpreted may need to be re examined finally in those cases where more than one thrust flat moves simultaneously in the models partitioning of displacement and distortion in space and time changes significantly this result supports interpretations from natural systems where more than one thrust is thought to move at once

models of strain variation in nappes and thrust sheets a review abstract strain within nappes and thrust sheets can be modelled using simple boundary conditions an original rectangular prism of material resting on a thrust plane is considered to be subject to various pure and simple shear components operating parallel to the thrust deformation gradient tensors are determined for the models and solutions found for the principal strains a two dimensional model considers heterogeneous simple shear combined with a stretch in the direction of shear simple shear zones arise as a special case where 1 recumbent fold nappes characteristic of gravitational collapse can be modelled with 1 and thrust sheets with layer parallel shortening and folding with differential transport of nappes gives rise to additional wrench type shears solutions for the principal strains in this type of model are found and used to interpret side wall ramps and steep zones parallel to nappe movements by including a stretch in the transport direction these differential transport models produce prolate strains 1 and oblate strains finally a brief consideration of bending strains produced in a sheet passing over a ramp indicates reversals in the shear direction during the strain history these predict possible crenulation of early thrust fabrics at ramps

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

pencil structure and strain in weakly deformed mudstone and siltstone abstract weakly deformed mudstone and siltstone middle ordovician knobs formation of the appalachian valley and ridge province south western virginia u s a show strain dependent transitions between bedding fissility pencil structure and cleavage pencil structures are associated with a bulk inhomogeneous shortening deformation where minimum principal strain z ranges between 9 and 26 shortening assuming a plane strain and constant volume where strains are less bedding fissility dominates pencil fragments are defined by intersecting fracture sets subparallel to the pre existing bedding fissility and cleavage their long axes are both parallel to the bedding cleavage intersection and to the inferred y axis of the tectonic strain ellipsoid pencil development is considered to result from fracturing along both fabric anisotropies during weathering and post tectonic stress relaxation pencils show variations in size and shape depending on lithology grain size and composition degree of initial clay preferred orientation degree of cleavage development type of cleavage total bulk strain and degree of strain homogeneity their shape l w however is a direct measure of total y z strain since strain determinations from chlorite pressure fringes on framboidal pyrite within the pencil fragments give y z 0 913 0 019 l w pencil structure is therefore a potential strain marker in weakly deformed rocks

physical analog centrifuge model investigation of contrasting structural styles in the salt range and potwar plateau northern pakistan abstract we use scaled physical analog centrifuge modeling to investigate along and across strike structural variations in the salt range and potwar plateau of the himalayan foreland fold thrust belt of pakistan the models composed of interlayered plasticine and silicone putty laminae comprise four mechanical units representing the neoproterozoic salt range formation basal detachment cambrian eocene carapace sequence and rawalpindi and siwalik groups neogene molasse on a rigid base representing the indian craton pre cut ramps simulate basement faults with various structural geometries a pre existing north dipping basement normal fault under the model foreland induces a frontal ramp and a prominent fault bend fold culmination simulating the salt range the ramp localizes displacement on a frontal thrust that occurs out of sequence with respect to other foreland folds and thrusts with a frontal basement fault terminating to the east against a right stepping east dipping lateral ramp deformation propagates further south in the east strata to the east of the lateral ramp are telescoped in ene trending detachment folds fault propagation folds and pop up structures above a thick basal detachment salt range formation in contrast to translated but less deformed strata with e w trending salt range structures to the west the models are consistent with salt range potwar plateau structural style contrasts being due to basement fault geometry and variation in detachment thickness

comparison of sequences formed in marine sabkha subaerial and salina subaqueous settings modern and ancient marine evaporites occurring in modern subaqueous salina settings and subaerial sabkha settings are different subaqueous holocene evaporites occur as shoaling upward lacustrine sequences up to 10 m thick they are evaporite dominated and are composed primarily of bottom nucleated crystals that may be deposited as massive laminated or rippled units each coastal lake is dominated by laminated evaporites with subordinate carbonate sediments in plan view they show a well developed bull s eye pattern with a sulfate center and a carbonate rim in contrast subaerial sabkha evaporites occur as part of a laterally prograding shoaling upward peritidal sequence in which the supratidal unit is usually no more than 1 m thick sabkha sequences are matrix dominated not ev porite dominated with the bulk of the sulfate phase occurring as diagenetic nodules enteroliths or diapirlike structures these sulfates were formed during syndepositional diagenesis by replacement and displacement processes the various facies of the sequence tend to accumulate in belts parallel with the shoreline relative to the sea level or the brine level sabkhas tend to form over paleotopographic highs whereas salinas tend to occur in paleotopographic lows some of the characteristics that distinguish holocene subaerial and subaqueous evaporite sequences can be used to do the same for similar ancient facies even when gypsum has been converted to nodular anhydrite the distinction is important for it can be used by explorationists in the oil industry to define the paleotopography of the associated underlying porous and nonporous carbonates

kinematic evolution of thrusts wedge and erratic line length balancing insights from deformed sandbox models kinematic evolution of fold thrust structures has been investigated by analogue models that include syntectonic sedimentation different decollement dips and basement thicknesses produced different wedge geometries and propagating characteristics a model with one decollement level was characterized by a closely spaced thrust system during early stages of shortening as compared to the late stages the frequency of fault nucleation was rapid during the early stages of deformation conversely the frequency of fault nucleation was low and thrust spacing was significantly wider in a model with two decollement levels individual faults became locked at steep dips and deformation stepped forward as a new fault nucleated in sequence in front of the older locked structure once the thrust system was established up to 27 overall shortening an overlying bed was introduced to simulate syntectonic deformation model sand wedge did not grow self similarly but rather its length and height increased episodically with deformation restoration of deformed models show that layer parallel shortening accommodated for approximately half of the total model shortening across the multilayers calculated error in apparent layer shortening from the restored layers revealed a direct relation with depth of the layers in the models the experimental results are comparable to a natural example from the northern apennines fold and thrust belts

mechanisms of thrust propagation some examples and implications for the analysis of overthrust terranes abstract evidence is presented for the existence of three fundamental mechanisms by which thrust sheets move the mechanisms are 1 failure of a stiff layer to form ramp flat geometry imbricated thrust sheets 2 detachment of a layer by folding decollement thrust sheets 3 differential layer parallel shortening lps thrust sheets the mechanisms are independent but may operate interactively to form families of hybrid thrust sheets since lps thrust sheets have not been previously described or documented data from the new york plateau deformed almost exclusively by differential lps is presented to demonstrate the physical characteristics of this thrust mechanism information from the plateau indicates that finite strain behavior closely reflects the geometric boundary conditions and is independent of temperature and depth of burial finite strain data are used to construct a set of iso strain maps in both the deformed and undeformed states the iso strain maps are in turn used to determine the displacement field for the thrust sheet the displacement field allows visualization of the effects of both lagrangian and eulerian transformations on an initially orthogonal grid utilizing sections from a number of overthrust belts it is shown that the three mechanisms occur universally although in various proportions lps is regionally developed throughout the central and northern appalachians the presence of the lps thrust sheets probably accounts for the failure of structural cross sections to bed length balance in these blind thrust terranes finally a series of examples drawn from the field as well as the literature are used to illustrate both the characteristics of hybrid thrust sheet families as well as to indicate how knowledge of their behavior can be utilized in developing strategies for the construction and balancing of structural cross sections

passive roof duplex geometry in the frontal structures of the kirthar and sulaiman mountain belts pakistan abstract exploration for hydrocarbons over the past few years has greatly improved our understanding of the geometry of frontal mountain belt structures in this study we introduce and discuss the concept of the passive roof duplex using as the main example the kirthar and sulaiman ranges in the baluchistan province of pakistan structures similar to those described here have been recognized previously in other mountain belts and they appear to exist as a common feature in many more frontal regions of mountain belts our example of a passive roof duplex which we describe from pakistan is compared briefly with similar structures reported by others the passive roof duplex is here defined as a duplex whose roof thrust has backthrust sense passive roof thrust and whose roof sequence those rocks lying above the roof thrust remains relatively stationary during foreland directed piggy back style propagation of horses within the duplex