introduction to journal of structural geology special issue on deformation processes in lithospheric high strain zones the past two decades have seen many advances in both numerical modeling and practical field and laboratory studies on deformation structures and fabrics in earth s lithosphere a topical session on deformation processes in lithospheric high strain zones at the 2012 geological society of america annual meeting in charlotte north carolina successfully facilitated communication between modelers and field based structural and tectonic geologists this special volume under the same title as the session captures the theme of the discussion the six papers in this special volume cover new advances in theoretical numerical and field methods as well as applications of these and existing methods to specific field areas jiang highlights the significance of rheological heterogeneities in earth s lithosphere and the necessity of a multiscale approach toward natural deformation he reviews and further develops a micromechanical approach capable of integrating multiscale deformations the proposed self consistent multiorder power law approach is based on continuum micromechanics and considers the rheological evolution with time in the deforming rock mass as a result of fabric buildup this approach is applied to the cascade

the motion of rigid ellipsoidal particles in slow flows abstract preferred orientations of fabric elements in tectonites are usually interpreted with reference to two continuum models namely those of march 1932 and jeffrey 1922 it is argued that the first of these is usually inappropriate if the fabric elements are rigid inhomogeneities embedded in a deformable matrix jeffrey s model is more applicable but until recently its use has been limited to problems involving axisymmetric particles and simple flow geometries in this paper jeffrey s equations have been solved numerically in order to investigate the behaviour of more general systems the motions of two particle shapes one a prolate spheroid the other a triaxial ellipsoid are considered in parallel for four specified flow geometries which involve pure or simple shear and combinations of both any departures from particle axisymmetry or from simple flow geometries have a significant effect on particle behaviour compared with that predicted by spheroid simple flow solutions

the rigid grain net rgn an alternative method for estimating mean kinematic vorticity number wm the use of porphyroclasts rotating in a flowing matrix to estimate mean kinematic vorticity number wm is important for quantifying the relative contributions of pure and simple shear in penetratively deformed rocks the most common methods broadly grouped into those that use tailed and tailless porphyroclasts have been applied to many different tectonic settings however attempts have not been made to unify the various methods here we propose the rigid grain net rgn as an alternative graphical method for estimating wm the rgn contains hyperbolas that are the mathematical equivalents to the hyperbolic net used for the porphyroclast hyperbolic distribution phd method we use the rgn to unify the most commonly used wm plots by comparing the distribution of theoretical and natural tailless porphyroclasts within a flowing matrix test samples from the south tibetan detachment tibet yield indistinguishable results when the rgn is compared with existing methods because of its ease of use ability for comparing natural data sets to theoretical curves potential to standardize future investigations and ability to limit ambiguity in estimating wm the rgn makes an important new contribution that advances the current methods for quantifying flow in shear zones 2006 elsevier ltd all rights reserved

short lived polyphase deformation during crustal thickening and exhumation of a collisional orogen ribeira belt brazil abstract the ribeira belt brazil is a neoproterozoic collisional related feature that was located in a south central position in west gondwana we present quantitative data on finite strain flow vorticity and deformation temperatures for the curitiba terrane a major segment of the southern ribeira belt six deformation phases d 1 d 6 related with crustal thickening and exhumation were recognized d 1 and d 2 related microstructures are preserved exclusively within porphyroblasts in part grown during stages of high pressure 9 12 kbar isobaric heating after crustal thickening d 3 phase was active from peak metamorphism attained in contrasting crustal levels 810 400 c to the early stage of exhumation 500 400 c as indicated by petrological microstructural and quartz c axis fabric evidence kinematic vorticity results indicate that the sl 3 mylonitic fabric resulted from a simple shear dominated deformation related with westward thrusting north verging overturned d 4 folds with e w trending subhorizontal axes derived from a pure shear dominated deformation regional d 5 open folds with subvertical axes and nne ssw trending traces were produced by indentation tectonics d 6 phase comprises retrograde orogen parallel transcurrent shear zones related with scape tectonics geochronological data indicate that d 3 d 6 phases occurred between 584 and 580 ma suggesting a fast exhumation rate of 8 mm year for the deepest rocks from the southern ribeira belt

effect of finite strain on clast based vorticity gauges abstract clast based vorticity gauges utilize orientations of grains assumed to have behaved as isolated rigid particles suspended in a flowing viscous matrix a fundamental assumption behind use of the method is that sufficient strain has accumulated for high aspect ratio grains to rotate into positions approaching their stable sink orientation and that clasts below a critical aspect ratio may be observed in any orientation relative to the flow plane we constructed a numerical model to explore the effect of variable finite strain on development of the orientation distribution of a large population of rigid clasts embedded in a viscous medium for end member pure and simple shear and for several distinct general shear flows our model predicts the technique will tend to produce vorticity overestimates for lower vorticity flows for a wide range of finite strain the model also indicates that clast populations in moderate to high vortical flows tend to develop shape preferred orientations that closely resemble those expected for flows of lower vorticity we conclude that clast based methods are not effective for extracting detailed kinematic information from a mylonite deformed in a flow with arbitrary boundary conditions in fact it appears that most general shear flows continued long enough to develop moderate high finite strains will tend to produce a clast orientation distribution that will yield a visual estimate of the critical aspect ratio that suggests approximately equal contributions of pure and simple shear components

kinematics strain pattern and geochronology of the salem attur shear zone tectonic implications for the multiple sheared salem namakkal blocks of the southern granulite terrane india abstract structural mapping strain analysis and a variety of geochronological studies were carried out to determine the tectonothermal evolution of the salem attur shear zone in the southern granulite terrane of south india the salem namakkal blocks containing the shear zone consisted of quartzofeldspathic gneiss charnockite and mafic granulite and had undergone multiple phases of magmatism spanning over a period of 3 2 0 5 ga the rocks were deformed by four phases of deformation d1 d4 the d1 deformation was characterized by isoclinal and recumbent ne sw trending f1 fold with a pervasive subhorizontal axial planar granulitic fabric s1 and associated quartzofeldspathic leucosomes granulite metamorphism was dated at ca 2 5 2 3 ga the f1 fold and s1 fabric were coaxially refolded by tight to isoclinal upright to steeply inclined ne sw trending f2 folds during d2 deformation the d2 deformation was associated with f2 axial planar shear zones crenulations and leucosomes s2 fabric large scale d2 shear zones characterized by high temperature ductile shear fabric with a vertical flow host syntectonic syenite pluton which was dated at ca 2 5 2 4 ga a p t condition of 7 kb 600 c was inferred for the d2 deformation the d3 deformation was characterized by nw se to e w trending f3 folds and the salem attur shear zone the shear zone was a greenschist to amphibolite facies shear zone being characterized by mylonitic foliation and dominantly down dip stretching lineation defined by quartz biotite and hornblende minerals and dated at ca 2 0 ga it indicated n nne vergence of thrusting with the mean kinematic vorticity number wm as 0 7 suggesting general simple shear strain with 50 pure shear component the d4 deformation was manifested as nne ssw striking strike slip faults and nw se striking extensional normal faults pseudotachylite veins having an age of 1 9 ga injected during strike slip faulting and granite pegmatite veins showing age of 0 8 0 5 ga intruded during normal faulting the salem namakkal blocks thus recorded a long lived shearing history we suggest that the salem attur shear zone and other shear zones such as palghat cauvery moyar bhavani karur kambam painavu trichur and achankovil shear zones were paleoproterozoic intraterrane shear zones which were overprinted by meso neoproterozoic cambrian ductile and brittle deformations

strain memory of 2d and 3d rigid inclusion populations in viscous flows what is clast spo telling us abstract we model the development of shape preferred orientation spo of a large population of two and three dimensional 2d and 3d rigid clasts suspended in a linear viscous matrix deformed by superposed steady and continuously non steady plane strain flows to investigate the sensitivity of clasts to changing boundary conditions during a single or superposed deformation events resultant clast spos are compared to one developed by an identical initial population that experienced a steady flow history of constant kinematic vorticity and reached an identical finite strain state allowing examination of spo sensitivity to deformation path rotation paths of individual triaxial inclusions are complex even for steady plane strain flow histories it has been suggested that the 3d nature of the system renders predictions based on 2d models inadequate for applied clast based kinematic vorticity gauges we demonstrate that for a large population of clasts simplification to a 2d model does provide a good approximation to the spo predicted by full 3d analysis for steady and non steady plane strain deformation paths predictions of shape fabric development from 2d models are not only qualitatively similar to the more complex 3d analysis but they display the same limitations of techniques based on clast spo commonly used as a quantitative kinematic vorticity gauge our model results from steady superposed and non steady flow histories with a significant pure shearing component at a wide range of finite strain resemble predictions for an identical initial population that experienced a single steady simple shearing deformation we conclude that individual 2d and 3d clasts respond instantaneously to changes in boundary conditions however in aggregate the spo of a population of rigid inclusions does not reflect the late stage kinematics of deformation nor is it an indicator of the unique mean kinematic vorticity experienced by a deformed rock volume

vorticity analysis in calcite tectonites an example from the attico cycladic massif attica greece abstract although calcite tectonites are widespread in nature their use to quantify flow vorticity is limited we use new micro structural petrofabric and vorticity data to analyse the kinematics of flow in outcrop scale calcite mylonite zones these zones are genetically related to a crustal scale ne directed ductile thrust basal thrust that emplaced the blueschist over the basal unit during the exhumation of the attico cycladic massif calcite microstructures reveal that the last stage of deformation occurred at temperatures 200 300 c achieved by mild heating which is possibly related with the reburial of the basal thrust s footwall vorticity analyses were based on the degree of asymmetry of calcite c axis fabrics as well as on the assumption that the orientation of the long axes of calcite neoblasts within an oblique foliation delineates the direction of instantaneous stretching axis both methodological approaches provide consistent estimates with a simple shear component between 55 and 82 w n 0 76 0 96 the use of the stress axis 1 orientation recorded by twin c axis pairs to quantify vorticity generally gives significantly lower simple shear component comparison of our vorticity estimates with previous estimates inferred from quartz fabrics and rigid porphyroclasts reveals that exhumation related deformation in the nappe pile was steady state

the use of jadammina macrescens brady and balticammina pseudomacrescens bronnimann lutze and whittaker protozoa foraminiferida as sea level indicators in studies of foraminiferal distributions in saltmarshes in new england and atlantic canada balticammina pseudomacrescens and jadammina macrescens have formerly been grouped as trochammina macrescens this study recognises them as distinct species and shows that they have significantly different distributions on the surface of saltmarshes in maine here relative abundances of j macrescens correlate with tidal elevation r2 0 55 p 0 00 whereas those of b pseudomacrescens do not r2 0 03 p 0 34 therefore j macrescens is a better sea level indicator in maine marshes than b pseudomacrescens in menunketesuck river marsh connecticut a clear vertical zonation of saltmarsh foraminifera is absent which hinders interpretation of fossil data this study shows that in maine separating b pseudomacrescens and j macrescens in counts of fossil data facilitates the detection of transgressional and regressional events in the biostratigraphical record and hence the reconstruction of local sea level histories regional variability between northern and southern new england saltmarshes necessitates the establishment of local reference sets of modern analogue data to aid palaeoecological interpretations

deformation temperatures and flow vorticities near the base of the greater himalayan series sutlej valley and shimla klippe nw india abstract we report new deformation temperature and flow vorticity data from the base of the greater himalayan series ghs exposed in the sutlej valley and shimla klippe of nw india we focus on three groups of transects across the hanging wall of the main central thrust mct in order of relative foreland hinterland positions they are the shimla klippe western and eastern sutlej transects deformation temperatures indicated by quartz c axis fabric opening angles increase both from foreland to hinterland at a given structural distance above the mct and up structural section from the mct within individual transects deformation temperatures in the immediate hanging wall to the mct are estimated at 510 535 535 550 and 610 c on the shimla western sutlej and eastern sutlej transects respectively the steepest inferred field gradients in deformation temperatures are recorded adjacent to the mct and progressively decrease up structural section following a power law relationship comparison with temperature estimates based on multi mineral phase equilibria data suggests that penetrative shearing occurred at close to peak metamorphic conditions vorticity analyses indicate that shearing along the base of the ghs occurred under sub simple shear conditions wm values of 0 9 1 0 with a minor component of pure shear

a kinematic model for deformation within brittle shear zones textural analysis of fault gouge indicates that displacement of particles within brittle shear zones occurs by three diaerent modes synthetic riedel shears antithetic riedel shears and shearing particulate flow a kinematic model is developed which incorporates these three slip modes and constrains the combined deformation to be simple shear parallel to the shear zone boundaries penetrative fabric p foliation and shape preferred orientation of survivor grains commonly observed in foliated fault gouge is assumed to be a result of the shearing particulate flow only the model which relates penetrative fabric orientation to the relative shear rates on riedel shears and shearing particulate flow reconciles inclined p foliation and high g 10 shear strain 1999 elsevier science ltd all rights reserved

taphonomic processes affecting late quaternary molluscs along the coastal area of buenos aires province argentina southwestern atlantic molluscan concentrations were abundantly deposited along the coastal area of buenos aires province argentina southwestern atlantic by different sea level episodes during the late quaternary most of them represent holocene ridges highly energetic depositional environments subparallel to the modern shore where the main associations preserved are parautochthonous and others mainly autochthonous associations occurring in tidal flats seaward of the ridges or coastal lagoon deposits accumulated behind them low energetic analysis of three physical taphonomic signatures disarticulation fragmentation and abrasion of the molluscan skeletons of four bivalve species tagelus plebeius mactra isabelleana pitar rostratus brachidontes rodriguezi which exhibit different shell shape and thickness conditions habitats and life habits and represent the most widely distributed and palaeoecologically significant taxa along the area of study support the distinction of both palaeoenvironments characterized by low and high taphonomic grades respectively the taphonomic alteration breakage and abrasion of most shells seems to have been a direct consequence of the amount of reworking of the material especially during periods of exposure along an extensive beach zone more than a consequence of transport from a distant original habitat abrasion signatures are the only probably correlated with after death time span shells showing a near modern aspect and original luster being most probably younger than those with chalky or polished appearance the infaunal species analysed typically living on clays and silts or fine sandy bottoms of the infralittoral or intertidal t plebeius m isabelleana are better preserved less fragmented and abraded than shells of the epibyssate b rodriguezi which lives on hard bottoms of the intertidal and supralittoral areas more exposed to highly unstable conditions with longer episodes of exposure although these nearshore concentrations may represent a time averaging of 1000 yr b p taking into account the ecological requirements of the most constant and dominant taxa together with the taphonomic analysis of shells from parautochthonous and autochthonous associations they still represent valid indicators of past marginal marine conditions in the area but are only reliable to establish long term palaeoenvironmental variations

flow in natural shear zones the consequences of spinning flow regimes abstract the ancient flow regime in natural shear zones is often considered to have followed a deformation path comparable to that in theoretical shear zones i e progressive simple shear between rigid wall rocks with a persistent flow plane orientation parallel to the edges of the zone this is often based on the presence of monoclinic fabric elements in the zones which indicate a dominantly non coaxial flow regime though not necessarily persistent simple shear the deformation fabric of a shear zone from the pyrenees illustrates that even at a kinematic vorticity number of w 1 simple shear along the entire deformation path obliqueness of the flow planes with the edges of the zone is possible for some time if incremental stretching axes were rotating with respect to zone edges this implies that ductile deformation must have taken place in the wall rock of the zone such a flow regime may be difficult to recognize with the fabric criteria used at present but leads to an unusual kinematic significance of the shear zone involved in extreme cases the zone may have acted as a passive marker in a ductilely deforming medium it also means that not only w must be known to reconstruct the ancient flow regime in natural shear zones but at least also the time dependence of the orientation of the incremental stretching axes

simultaneous pure and simple shear the unifying deformation matrix abstract any simultaneous combination of finite simple shear and finite pure shear is a linear transformation which can be expressed as a single transformation matrix for two dimensions the matrix is upper triangular with an off diagonal term called the effective shear strain is a simple function of the pure and simple shear components for three dimensions a simultaneous combination of thrusting in the x direction thrusting in the y direction and a wrench in the x direction in addition to 3 orthogonal components of coaxial strain can also be represented by a 3 3 upper triangular matrix here three off diagonal terms xy x y and y z occur xy is a simple function of the horizontal coaxial strain values and thrusting in the x direction yz depends on the coaxial strain components in the y and z directions and the thrusting in the y direction while xz is related to all six strain components the matrix also allows for volume change either homogeneously or preferentially in a single direction a method of decomposing the deformation matrix into a series of incremental deformation matrices where each incremental deformation records the same kinematic vorticity number as the finite deformation is shown the orientation and magnitude of the finite strain ellipsoid ellipse is easily and accurately found at any increment during the deformation

the dilemma of asymmetric porphyroclast systems and sense of shear abstract asymmetric porphyroclast systems have long been used as independent shear sense indicators based on their clast tail asymmetry and or stair stepping tail geometry over the last two decades advances in exploring the mechanical behavior of rigid clasts in a viscous flow has shed new light on understanding the formation of porphyroclast systems embedded in noncoaxial viscous flow and subsequently quantifying many aspects of flow kinematics using examples from naturally deformed rocks combined with results from recent advances our study indicates that 1 in general only porphyroclast systems composed of equant shaped clasts can be treated as independent shear sense indicators 2 special attention should be given to type porphyroclast systems composed of high angle intermediate aspect ratio clasts which may contain meaningful information on bulk flow kinematics 3 bookshelf structures cannot serve as independent shear sense indicators multi criteria and thorough three dimensional shape analyses are suggested for a proper interpretation of flow kinematics in ductile shear zones

kinematics nature of deformation and tectonic setting of the taxaquara shear zone a major transpressional zone of the ribeira belt se brazil abstract in this paper we have investigated the taxaquara shear zone tsz a major strike slip structure within the ribeira belt rb se brazil in order to assess its kinematics the nature of deformation of rocks affected by the tsz and its tectonic setting the tsz presents a vertical ne trending mylonitic foliation and ene to wsw stretching lineation with variable plunge granitic rocks are intensely deformed giving rise to mylonites with newformed matrix assemblage quartz oligoclase k feldspar biotite muscovite rutile magnetite this assemblage within a pseudosection couple with muscovite biotite thermometer helps to constrain a metamorphic condition during deformation which spans 513 525 c and 3 9 4 4 kbar with mean peak at 520 c and 4 0 kbar quartz accommodates deformation through dislocation creep achieving subgrain rotation with minor contribution of grain boundary migration at a mean strain rate of 10 13 10 12 s 1 feldspar porphyroclasts record brittle deformation microfaults and evidences of dislocation creep e g kink twinning the cpos for monomineralic quartz ribbons display monoclinic pattern and activation of basal rhomb slip systems during deformation however the cpos for quartz and feldspar from fine grained polyphase matrix show a switch in deformation mechanism from dislocation creep to diffusion creep the vorticity and three dimensional finite strain data results suggest that the tsz was developed under a moderate to high strain conditions and a transpressional sub simple shear environment with predominance of simple over pure shear regional correlation with other structures from the ribeira belt and african belts based on finite strain quantification support that a major transpressional system was mainly responsible for the shear zones development during late stages of braziliano pan african orogeny

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

significance of transport parallel strain variations in part of the raft river shear zone raft river mountains utah usa this paper examines part of the raft river shear zone rrsz in northwestern utah that exhibits an extreme transport parallel increase in strain intensity coupled with a transition from flattening to constrictional strain detailed geologic mapping and finite strain quartz c axis fabric and kinematic vorticity analyses demonstrate local necking of the shear zone associated with an increase in transport parallel elongation accommodated by a stretching fault at the base of the shear zone the domain of intense deformation and necking of the shear zone is localized where the basal stretching fault cuts rheologically weak rocks this domain is characterized by strain in the constrictional field caused by transport perpendicular flow into the area of high transport parallel elongation where rocks cut by the stretching fault are rheologically strong the rrsz locally records flattening strain and lower strain intensities limiting the amount of stretching needed at the base of the shear zone in any one direction and or recording transport perpendicular flow into adjacent highly extended domains the rheology of rocks cut by the stretching fault directly controlled the amount and style of zone normal shortening and transport parallel elongation and these observations provide an example of deformation partitioning in a crustal scale structure driven by local rheological transitions

coast line evolution in portugal since the last glacial maximum until present a synthesis abstract an effort has been made to assemble a data set on the evolution of coastal morphology of the west iberian continental margin in portugal which has occurred since the last glacial maximum in this integrated review a particular attention was given to the analyses of coastline shaping phenomena on different time scales several overlapping processes such as shore erosion local sediment supply rate climatic changes anthropic impacts and mean sea level rise mslr were identified and their combined effects assessed the eustatic see level rise appears as a principal factor in shaping the shore line contour until mid holocene since then the non eustatic factors namely the terrigenous sediment supply rate and the dynamics of barriers and spits systems became dominant in the evolution of the near shore morphology since the 15th century ad the anthropogenic activities namely deforestation and land cultivation contributed decisively to the positive sedimentary balance in the portuguese coastal zone finally the multiple damming of the major rivers in 20th century and exploitation of sand and gravel from the river beds led to the sediment starving of the coastal zone and generalized shore line retreat

forward modeling of non steady state deformations and the minimum strain path reply structural analyses of shear zones often rely on an assumption of steady state behavior i e that the ratio of pure shear strain rate s to simple shear strain rate s remains fixed throughout deformation however geological deformations are not necessarily steady state non steady state deformation paths can be theoretically modeled if certain deformation parameters such as strain or offset are specified we have analyzed a two dimensional case of specified offset and geometry termed the minimum strain path the minimum finite strain needed to produce a fixed offset across a shear zone is neither simple shear nor pure shear but a combination of the two the minimum strain path if this deformation accumulates with a steady state deformation the kinematic vorticity number w of the minimum strain path varies with the amount of finite offset although w approaches 0 7 at high offset values because of this relation between w and finite offset the minimum strain path is better modeled as a non steady state deformation in which case deformation history starts close to simple shear but rapidly changes to a more pure shear dominated deformation it is expected that the minimum strain path is applicable to geological deformation zones with relaxed boundary conditions such as basal parts of spreading nappes or extensional detachment systems 0 1997 elsevier science ltd

evolution and facies architecture of the mesotidal guadiana river delta s w spain portugal abstract the guadiana river estuary and delta is one of the most important mesotidal fluvio marine systems of the southwestern iberian peninsula the river mouth was formed as a narrow channel excavated by fluvial incision during the pleistocene lowstand and then flooded 6500 yr ago during the flandrian transgression holocene the estuary is in an advanced state of sediment infilling in its proximal part due to its narrow morphology which prevents passage of sediment through to the open coast consequently sediment is accumulating in the river mouth causing progradation as response of the interaction between coastal and fluvial processes sedimentation is controlled by the interaction of sediment load delivered by the guadiana river and the active longshore current which also supplies sand eroded from barrier islands and friable cliffs in the portuguese algarve to the west tidal range is mesotidal 2 0 m and mean significant wave height is 0 6 m with an average period of 3 6 s morphological differences exist between the two sides of the river mouth the western side has a large spit separated from the mainland by a marsh and the eastern side shows an array of old barrier islands separated by salt marsh areas a vibracore study allows us to distinguish 12 different depositional facies in the system fluvial delta tidal inlet flood tidal delta washover beach dune estuarine channel lagoon tidal creek channel margin tidal flat and salt marsh furthermore a different architectural scheme of these facies is present on each side to the east there is a longitudinal repetition of the sandy facies corresponding to the barrier islands on the west side there is a transverse growth of a single spit containing eolian dunes these differences result from asymmetric interaction between the tidal and fluvial currents at the river s mouth and the waves and tidal currents of the open coastal zone

kinematic vorticity and strain rate patterns associated with ductile extrusion in the chelmos shear zone external hellenides greece abstract kinematic vorticity strain rate finite strain and structural data have been used to describe the heterogeneous nature of ductile deformation in an extruding crustal scale shear zone the chelmos shear zone csz of the external hellenides the csz has a curved shape which is marked by a frontal flat and a steep zone the spatial variation in the kinematic vorticity number is strongly correlated with the geometry and the structural depth of the shear zone the pure shear component of deformation decreases from back to front and from top to bottom the ductile thinning normal to the shear zone s boundaries is higher in the steep zone and decreases westwards quartz grain size and strain rate in the csz is distributed into two approximately homogeneous domains the higher strain rate is recorded in the steep zone and the base of the frontal flat zone with lower rates in the upper parts of the frontal flat zone based on mesoscopic structural data and the spatial distribution of the shear strain rate the existence of a west dipping back flow zone in the boarder zone between these two domains is inferred the overall pattern of deformation in the csz implies that tectonic extrusion from the steep zone occurred at the final stages of ductile deformation and was associated with the formation of the backflow zone in the front of the shear zone ductile deformation of rocks probably started close to simple shear on a planar low angle shear zone progressively became penetrative and more general shear occurred as the csz steepened up this progressive increase in pure shearing may have occurred in a heterogeneous manner and was higher close to both the eastern margin of the steep zone and the top of the frontal flat zone solid state extrusion in the csz was also associated with a heterogeneous and progressive increase in strain rate

applications of inclusion behaviour models to a major shear zone system the nordfjord sogn detachment zone in western norway rigid inclusion models have reached a stage where one should be able to use them to obtain quantitative values from ductile shear zones we used natural data collected in three sites and combined analogue and theoretical modelling to assess vorticity strain nature of rigid inclusion matrix interface and confinement in the large scale ductile nordfjord sogn detachment zone nsdz of the caledonides of western norway our study shows that 1 the observed shape preferred orientation spo at higher structural levels of the nsdz at site 1 gjervika can be explained by simple shear pure shear simple shear ratio sr 0 associated with a slipping inclusion matrix interface 2 the observed spo at deeper structural levels of the nsdz at site 2 near sandane can be produced by simple shear associated with a significant amount of shortening across the shear zone sr z 1 acting upon rigid inclusions in slipping contact with the enclosing matrix 3 observed back rotated boudins deeper in the nsdz at site 3 biskjelneset can form in confined flow associated with a considerable amount of shortening across the shear zone sr 0 4 4 the observed tails of porphyroclasts indicate a minimum at least local strain of ca g z 20 5 the clasts in the studied shear zones strongly depart from jeffery s model jeffery g b 1922 the motion of ellipsoidal particles immersed in a viscous fluid proceedings of the royal society of london a102 161e179 the large scale extensional nsdz under investigation shows evidence of strain partitioning rocks vary from protomylonites to ultramylonites and the simple shear and pure shear components are heterogeneously distributed therefore we conclude that flow in the nsdz was very heterogeneous both at the kilometre and the metre scale however the present study suggests that the amount of shortening across the shear plane throughout the nsdz increases with depth and the flattening component contributes to exhumation of the eclogite facies rocks in its footwall 2007 elsevier ltd all rights reserved

clast fabric development in a shearing granular material implications for subglacial till and fault gouge elongate clasts in subglacial till and in fault gouge align during shearing but the relation between clast fabric strength and cumulative shear strain for such materials is effectively unknown this relation was explored in experiments with a large ring shear device in which a till and a viscous putty that contained isolated clasts were sheared to high strains as expected rotation of clasts in the putty is closely approximated by the theory of g b jeffery who derived the orbits of rigid ellipsoids in a slowly shearing fluid clast rotation in the till however is strikingly different rather than orbiting through the shear plane as predicted by jeffery most clasts rotate into the shear plane and remain there resulting in strong fabrics regardless of the aspect ratios and initial orientations of clasts this divergent behavior is likely due to slip of the till matrix along the surfaces of clasts which is a natural expectation in a granular material but violates the no slip condition of jeffery9s model these results do not support the widespread belief that subglacial till deformation results in weak clast fabrics thus many tills with weak fabrics thought to have been sheared subglacially to high strains like many basal tills of the laurentide ice sheet may have been sheared only slightly with little effect on either ice sheet dynamics or sediment transport in addition these results indicate that in simple shear the rotation of clasts in till and in fault gouge is best analyzed with the model of a march who treated inclusions as passive markers

fabric evolution of rigid inclusions during mixed coaxial and simple shear flows abstract in a slowly moving viscous fluid a population of non interacting rigid inclusions evolves in an oscillatory fashion or creates a stable fabric depending on the flow geometry and the shape of the inclusions using jeffery s equations for the motion of a rigid ellipsoidal inclusion a mixed coaxial and simple shear flow was investigated both analytically and by numerical modeling exact results were obtained for spheroidal inclusions depending on the axial ratio of the inclusion and the amount of the coaxial component of flow individual inclusions can move cyclically or rotate to a stable orientation in one of two mutually orthogonal directions equations were found which allow us to distinguish between these types of motion and to determine the stable inclusion orientation the relative motions of individual inclusions determine the preferred orientation in a population of inclusions in a heterogeneous population with diverse axial ratios the fabric evolves as the superposition of subfabrics corresponding to subsets with different axial ratios the orientations of stable subfabrics depend on axial ratios and could thus be used as kinematic indicators in cases of a sufficiently large coaxial component of flow the fabric created by a heterogeneous population may comprise two stable mutually orthogonal subfabrics no exact results are available for general i e non spheroidal ellipsoidal inclusions and numerical modeling must be used if the coaxial component of flow is sufficiently strong the non spheroidal inclusions move much like the spheroidal ones orthogonal subfabrics may appear as transient features in the evolution of a homogeneous population of non spheroidal ellipsoidal inclusions

holocene alluviation in the algarve southern portugal the case for an anthropogenic cause abstract finding a causal mechanism to account for observed phases of valley alluviation in the mediterranean region and southern europe during the holocene has been a subject of debate for more than 20 years three possible causes have been suggested regional climatic change anthropogenic induced erosion and the crossing of intrinsic thresholds within fluvial systems so that deposition rather than erosion is favoured in this paper we report investigations carried out in the algarve region southern portugal where past research is interpreted as suggesting a climatic cause mapping and sedimentological investigations of holocene sediments within three major valleys in this region are reported together with the association of these deposits with artifacts a roman moorish mill and bands of charcoal chemical as well as physical sedimentological interpretation was carried out on the deposits we also report the results of a detailed investigation and reconstruction of the land use and settlement history of the area and show that episodes of valley alluviation coincide in time with phases of intensive agriculture and clearance within the catchments of these valleys whereas episodes of valley erosion coincide with episodes of relative stability whilst recognizing that temporal correlations are not necessarily causal we argue that in this area anthropogenic forcing of phases of holocene alluviation is the preferred mechanism

reference frame angular momentum and porphyroblast rotation abstract rotation of small rigid objects in a deforming ductile matrix can produce two different types of microstructure a shape fabric due to alignment of the principal axes of a population of elongate objects and the inclusion trail microstructure preserved in syntectonic porphyroblasts we use numerical modeling to show that inclusion trails of elongate porphyroblasts are expected to be extremely complex in contrast snowball garnets are readily interpretable but misuse of reference frame and kinematic misconceptions have obfuscated the discussion on the formation of porphyroblast inclusion trails in general and snowball garnet inclusion trails in particular we clarify this point models for snowball garnet formation that are based on the notion of garnets being irrotational with respect to the earth can be rejected on a geometrical and kinematic basis further the notion that rigid objects embedded in a deforming ductile matrix generally do not rotate is unsound it violates the fundamental physical law of balance of angular momentum

clast based kinematic vorticity gauges the effects of slip at matrix clast interfaces clast based methods for estimating the mean kinematic vorticity number wm are compromised by strain localization at the clast margins localization increases with modal matrix mica content as determined with samples from the sandhill corner mylonite zone a crustal scale high strain strike slip shear zone in maine using these samples we estimate wm with the oblique quartz shape preferred orientation and rigid clast rotation methods the rigid clast rotation method yields much lower values for wm than the quartz method to investigate whether or not slip at the matrix clast interface can explain the discrepancy in calculated wm we conducted numerical modeling of rigid clasts enveloped by a low viscosity layer both embedded within a shearing viscous matrix within this dynamic framework we carried out numerical sensitivity analyses in which we varied the viscosity ratio between the lubricating layer and the surrounding matrix the thickness of the lubricating layer and the kinematic vorticity number of the bulk flow our data and numerical results succeed in explaining why wm estimates from clast based rotational methods are typically lower than estimates from other methods and this has implications for testing hypotheses related for example to vorticity partitioning in oblique convergent settings crustal scale extrusion or channel flow and exhumation of ultra high pressure rocks all of which rely on robust estimates of wm the relation between the shape preferred orientations of clasts and modal mica content lead to the hypothesis that mica is the cause of the lubrication at clast matrix interfaces if so then we surmise that mica fish should be self lubricating and would therefore form an end member shape preferred orientation regardless of matrix modal mica content the unique role of mica allows us to speculate about the bounds on viscosity contrast between the matrix and lubricated clast interfaces

asymmetric quartz c axis fabrics and flow vorticity a study using rotated garnets abstract the development of a type i crossed girdle c axis fabric with an asymmetric density distribution and an internally asymmetrical skeletal outline is examined in a specimen of garnet bearing mylonitic quartzite from the betic movement zone in southern spain the garnets are pre mylonitic skeletal porphyroblasts that rotated during mylonitic deformation but preserved a strain free equilibrium microstructure and a random c axis fabric it follows that the asymmetry of the density distribution must result from the deformation history itself the sense of asymmetry of the c axis population and that of the skeletal outline are consistent with the sense of vorticity inferred from extensional crenulations and asymmetric microboudinage and also with the sense of rotation of the garnets analysis of the rotation angles with aspect ratio of the garnet porphyroblasts demonstrates that a pure shear component was involved in an essentially non coaxial flow this may explain the internal asymmetry of the fabric skeleton and confirms the idea that a spectrum exists of type i fabrics intermediate between the theoretically predicted fabrics for pure and simple shear a tentative reconstruction of the kinematic framework suggests that the central segment of the fabric skeleton is linked to the extensional apophysis of the flow

are isolated stable rigid clasts in shear zones equivalent to voids abstract particles in shear enclose important information about a rock s past and can potentially be used to decipher the kinematic history and mechanical behavior of a certain outcrop or region isolated rigid clasts in shear zones often exhibit systematic inclinations with respect to the shear plane at small angles tending towards the instantaneous stretching direction of the shear zone this shape preferred orientation cannot be easily explained by any of the analytical theories used in geology it was recently recognized that a weak mantle surrounding the clast or a slipping clast matrix interface might be responsible for the development of the observed inclinations physical considerations lead us to conjecture that such mantled rigid clasts can be effectively treated as voids that are not allowed to change their shape the resulting equivalent void conjecture agrees well with numerical and field data and has the following important geological implications i clasts in shear zones can have stable positions in simple shear without the requirement of an additional pure shear component ii the stable orientation can be approached either syn or antithetically hence the clast can rotate against the applied shear sense iii the strain needed to develop a strong shape preferred orientation is small 1 and therefore evaluations based on other theories may overestimate strain by orders of magnitude iv the reconstruction of far field shear flow conditions and kinematic vorticity analysis must be modified to incorporate these new findings

2 d shape preferred orientations of rigid particles in transtensional viscous flow ghosh and ramberg tectonophysics 34 1976 1 70 studied the two dimensional 2 d rotational behaviour of individual rigid particles embedded in a viscous medium subject to simple shear and transpression sr 0 at low medium shear strains we now extend this theoretical study to transtension sr 0 by deriving a new analytical solution to non interacting populations of rigid particles and to high shear strains we used different initial orientations of particles in the same graph to simulate populations of particles in an originally isotropic rock our results show that 1 shape preferred orientations spos developed in viscous simple shear flow are transient and cyclical except for particles with aspect ratio or material lines which tend to the shear direction 2 stable spos can develop in transpression they dip towards the shear sense but when defining an s c structure with the shear foliation this composite fabric is always antithetic and thus indicates the wrong sense of shear 3 stable spos can also develop in transtension they dip opposite to the shear sense but when defining an s c structure with the shear foliation this composite fabric is always synthetic and thus indicates the correct sense of shear 4 spos produced in transpression or transtension can be used as vorticity gauges only when they represent stable orientations which must be demonstrated a priori

stable positions of rigid objects in non coaxial flow a study in vorticity analysis abstract distortions of a homogeneous fabric which occur around rigid objects in rocks deformed by non coaxial ductile flow are useful to determine the sense of shear but also contain information on other aspects of the flow rigid objects in a non coaxial flow fall into two categories those which are permanently rotating and those which can reach stable positions at high finite strain the orientation of such immobilized objects with respect to eigenvectors of instantaneous flow is a function of the vorticity number of the flow the ratio of instantaneous stretches and the axial ratio of the object in naturally deformed rocks immobilized rigid objects may be recognized from the geometry of the surrounding fabric tails of recrystallized material around porphyroclasts in a mylonite rotate towards parallellism with the extensional eigenvector of the flow and the shape of tails reflects the rotational behaviour of the porphyroclast the axial ratio of immobilized porphyroclasts and their orientation with respect to the tails can theoretically be used to determine the vorticity number of the flow and deviations from isochoric plane strain in practice such an analysis is as yet difficult but a tentative example is given of the way in which the vorticity number can be calculated from a population of feldspar porphyroclasts in a quartzite mylonite from the french pyrenees

a critique of vorticity analysis using rigid clasts abstract estimating the kinematic vorticity numbers from rock fabrics presents many problems in this paper we use numerical modeling to investigate the reliability of those widely used vorticity analysis methods using rigid clasts we use very simple flows steady state homogeneous and having monoclinic symmetry to represent plane straining zones and transpressional zones and assume that the rotation of rigid clasts perfectly obeys the theory of jeffery 1922 proceedings of the royal society of london a102 161 179 these are assumptions made in current vorticity analysis using rigid clasts even with these simple assumptions our modeling shows that the current methods have intrinsic uncertainties so large that it is pointless to use the estimated vorticity numbers to constrain shear zone boundary conditions and kinematics it is perfectly consistent with numerical modeling results if the currently reported vorticity numbers estimated from rigid clasts in the range of 0 50 0 85 are all interpreted as being from natural shear zones with close to simple shearing flows the large uncertainties arise because the motion of rigid clasts is intrinsically a three dimensional problem

depositional history of estuarine infill during the last postglacial transgression gulf of cadiz southern spain abstract the late pleistocene and holocene evolution of the estuaries in the gulf of cadiz is interpreted for the first time using drill cores logs trenches and 38 new radiocarbon data and the results compared with the shelf the odiel tinto and guadalete rivers deposited conglomerates during a highstand that did not reach the present sea level dated at ca 25 30 ka isotopic stage is 3 corresponding to a relatively humid period in the area rivers incised these coarse grained deposits during the last main lowstand at ca 18 ka when sea level dropped to 120 m and the coastline lay 14 km seawards from the present the erosional surface is a sequence boundary and the flooding surface of the postglacial eustatic rise overlain by the valley fill deposits of the transgressive and highstand phases of the last fourth and fifth order depositional sequences recognised in the shelf the first marine influence in the estuaries during the transgression occurs at 25 30 m at ca 10 000 years bp according to fossil assemblages the transgressed basins changed from brackish to more open marine as the sea rose until ca 6500 years bp when it reached the maximum flooding and the sandy estuarine barriers ceased to retrograde toward the muddy central basins then the rate of eustatic rise decreased drastically and the estuarine filling followed a two fold pattern governed by the progressive change from vertical accretion to lateral centripetal progradation at ca 4000 years bp the fluvial input surpassed the already negligible rate of rise causing partial emergence of tidal flats and spit barriers in the largely filled estuarine basins prevalence of coastal progradation upon vertical accretion at ca 2400 years bp caused accelerated expansion of tidal flats and rapid growth of the sandy barriers further changes since the 16th century reflect widespread anthropic impacts

postglacial sea level rise and sedimentary response in the guadiana estuary portugal spain border abstract the study of sedimentological features foraminifera and molluscan fauna in samples recovered from four rotary boreholes permitted after 14 c dating the first assessment of the post glacial transgression in guadiana river estuary the holocene sequence is underlain by coarse sediments from delta fan enclosing continental swamp deposits dated 16 980 year bp the holocene sedimentary sequence was deposited either directly on this delta fan gravels or on top of fluvial sands deposited probably between 11 000 and 10 000 yr bp an accelerated phase of the estuary infilling by clayey sediments containing the salt marsh foraminifer trochammina began ca 9800 year bp when sea level was about 39 m below present between 7500 and 7000 year bp the central part of the estuary started to accommodate coarser sediments partially introduced from the continental shelf the first phase of holocene sea level rise at a rate of 0 85 m century terminated ca 6500 year bp since then lagoonal sediments in the vicinity of the estuary have been enclosed behind sand spits and predominantly sandy sedimentation was initiated within the estuary after a second phase of slower rise at the rate of 0 3 m century which lasted until ca 5000 year bp the sea approached the present level

quantitative kinematic flow analysis from the main central thrust zone nw himalaya india implications for a decelerating strain path and the extrusion of orogenic wedges quantitative kinematic indicators from the main central thrust zone mctz in the nw himalaya have been used to characterize the type of flow during deformation different generations of tension gashes have been rotated by variable angles with respect to the mylonitic foliation forming associated fringe folds these record the late stage brittle ductile flow and reveal that a strong pure shear component of deformation occurred throughout the mctz to characterize earlier deformation increments fabrics from highly deformed quartz ribbons were analyzed well developed shape and lattice preferred orientation patterns show a systematic change of the glide systems and suggest inverted palaeotemperatures within the mctz investigations of the c axes patterns reveal a strong asymmetry at the top of the mctz whereas the samples from the base of the mctz show almost perfectly symmetrical type i crossed girdles deformation within the mctz probably started close to simple shear flow at higher temperatures which progressively became a more general shear during cooling and ended in a pure shear dominated flow during the final stages of brittle ductile deformation i e a decelerating strain path using the higher himalaya crystalline as an example a kinematic model for the extrusion of crustal wedges above major thrust zones is suggested

sand dynamics at the mouth of a rock bound tide dominated estuary abstract the lowermost kennebec river is a relatively narrow deep bedrock cut estuary situated along the highly indented central coast of maine a large tidal prism and strong tidal currents control bedload sediment transport at the estuary mouth riverine sediment is introduced to the estuary during spring freshets when freshwater discharge may increase by an order of magnitude during the same time some of the existing estuarine sediment is exported to the nearshore a barrier adjacent to the estuary is the product of an abundant riverine sand supply and numerous bedrock ridges which anchor this sand deposit a variety of sedimentologic geomorphic and hydraulic data collected over a 14 year period document a clockwise sand circulation cell that involves the exchange of bedload among the entrance channel to the estuary adjacent beaches nearshore and offshore region tidal currents transport sand from the estuary through a subsidiary channel bordered on both sides by bedrock islands to an offshore subtidal bar northeast storm waves breaking along this outer bar move sand westward and landward toward the beach leading to the development of large bar complexes the welding of a bar complex to the western end of hunnewell beach occurs every 6 9 years and adds 2 300 000 m3 of sand to the shoreline sediment transport calculations along the outer bar are consistent with this volume of sand the sediment gyre is completed as beach sands are moved eastward along the beach and dumped into the estuarine channel this movement of sand is produced by wave action and tidal currents that enter the estuary peripherally during the flooding tide during the ebb cycle strong tidal currents flowing seaward through the subsidiary channel advect water from along the beach which enhances sand transport into the estuary thirteen years of beach profile surveys demonstrate a good correspondence between bar welding events and short term 1 4 years accretionary shoreline changes however the volumetric changes of hunnewell beach cannot be accounted for by bar welding alone the apparent movement of sand between hunnewell beach and other sand is further evidenced by the 135 year record of historical shoreline changes that reveal up to 200 m of shoreline excursions over a 26 year period these data suggest that erosional depositional trends along hunnewell beach are complex and the result of the exchange of sand among the adjacent beaches nearshore zone fox and wood island tombolos kennebec river channel and offshore region the effects of major spring floods and strong bedrock influences produce patterns of sedimentation and a distribution of sand bodies at the mouth of kennebec river that differ markedly from accepted estuarine models that are based on the relative importance of wave and tidal energy this study demonstrates the need to consider structural controls when using these models

sedimentology and stratigraphy of a tidal sand bank in the southern north sea abstract a set of 125 vibrocores collected on the basis of a dense grid of high and very high resolution seismic coverage over a tidal sand bank the middelkerke bank provides a unique opportunity to reconstruct the stratigraphy and sedimentary facies succession of such a large tidal sand body five sedimentary facies are distinguished they range from clay to pebble and display various types of bedding and lithologies corresponding to different depositional environments a succession of four late quaternary units are defined on the basis of the stratigraphic framework given by the seismic grid the first unit represents the infill of a palaeovalley system by tidally influenced sedimentary facies it is followed by extensive and thick lagoonal or sub tidal deposits the third unit reveals the development of a landward prograding storm dominated sand bar this unit is dominated by clean fine sand the last unit corresponds to the present day tidal sand bank it shows the typical offshore tidal sand bank facies cross bedded sand prograding in an offshore direction like other banks located in a more offshore position the middelkerke bank is a composite bank incorporating facies which do not occur in classic tidal sand banks

the accommodation concept in sequence stratigraphy some dimensional problems and possible redefinition abstract a debate is provoked here as to what is meant exactly by the term accommodation and how well this concept as it presently stands serves the conceptual and quantitative framework of sequence stratigraphy accommodation in terms of its original definition contains some conceptual flaws it represents a space that has three dimensional extent associated with a certain availability of sediment and thus is not really independent of sedimentation however this space is fairly unspecifiable because of the inherent difficulty of distinguishing real accommodation from the space which is very unlikely to be filled by sediment anti accommodation the accommodation concept cannot be extended to subaerial environments because the equilibrium profile of streams which is sometimes used for this purpose is difficult to recognize even if it existed a possible redefinition of accommodation is suggested as the thickness measured at a specified site and time of a space which becomes filled with sediments during a specified time interval this accommodation is not a space but the thickness of a space not something potential but an objective result not specifiable from the graded profile or geomorphic base level but from stratigraphic base level and not separated from sedimentation but partly dependent from it potential accommodation may be used to describe the maximum of possible accommodation at a specified site and time which can substantially coincide with the height of a water column at a given site and time

variation in vorticity of flow during exhumation of lower crustal rocks neoproterozoic ambaji granulite nw india abstract the exhumation of the neoproterozoic ambaji granulite in the aravalli delhi mobile belt nw india took place along nnw sse trending d2 shear zones the shear zones evolved from a high temperature 700 c thrust slip shearing event in the lower middle crust to a low temperature 450 c retrograde sinistral top to nw shearing event at the brittle ductile transition bdt the vorticity of flow wm along the shear zones is estimated with the rigid grain net and strain ratio orientation techniques the wm estimates of 0 32 0 40 and 0 60 coincide with the high temperature event and suggests pure shear dominated deformation the low temperature phase coincides with wm estimates of 0 64 0 87 and 1 0 implying two flow regimes the shear zone was first affected by general non coaxial deformation and gradually became dominated by simple shearing we interpreted that the high temperature event happened in a compressive tectonic regime which led to horizontal shortening and vertical displacement of the granulite to the bdt the low temperature event occurred in a transpressive tectonic setting that caused the lateral displacement of the granulite body at bdt depth the wm values indicate a non steady strain during exhumation of granulite this tectonic evolution is comparable with that of the himalayas

a sensitive vorticity gauge using rotated porphyroblasts and its application to rocks adjacent to the alpine fault new zealand variable aspect ratio porphyroblasts deformed in non coaxial flow and internally containing rotated relicts of an external foliation can be used to characterise plane strain flow regimes the distribution obtained by plotting the orientation of the long axis of such grains classified by aspect ratio against the orientation of the internal foliation is potentially a sensitive gauge of both the bulk shear strain as previously suggested and kinematic vorticity number we illustrate the method using rotated biotite porphyroblasts in the alpine schist a sequence of mid crustal rocks that have been ramped to the surface along the alpine fault a major transpressional plate boundary results indicate that at distances greater than or equal to similar to1 km from the fault the rocks have undergone a combination of irrotational fattening and dextral oblique normal sense shear with a bulk shear strain of similar to0 6 and kinematic vorticity number of similar to0 2 the vorticity analysis is compatible with estimates of strongly oblate bulk strain of similar to 75 maximum shortening dextral reverse transpressional flow characterises higher strain s tectonite mylonite within similar to1 km of the alpine fault these relationships provide insight into the kinematics of flow and distribution of strain in the hangingwall of the alpine fault and place constraints on numerical mechanical models for the exhumation of these mid crustal rocks c 2001 elsevier science ltd all rights reserved

interglacial sea levels abstract isotopic curves have been used as approximative estimators of global sea level calculations of the amplitude of sea level variations during interglacials especially for the last interglacial are based on the study of emerged coral terraces the application of different dating methods shows great uncertainty about the length of each interglacial and also about the number chronology and altitude of the different highstands that occur during each interglacial data of raised marine terraces from areas with different geodynamic behaviour bermudas bahamas peru chile italy and spain are summarized in order to analyze the relationships between sea level and interglacial stages two interglacials have been identified for the early pleistocene represented by two marine terraces with different highstands during the early middle pleistocene an interglacial with several highstands is recorded in uplifted areas during isotopic stage 11 at least one highstand with sea level equal or higher than present has been recorded similar sea level behaviour can be suggested for isotopic stage 9 all the analyzed areas record two highstands during isotopic stage 7 when warm equatorial fauna migrate into the mediterranean during isotopic substage 5e at least two highstands took place with evidence of lowstands between them and at least one highstand during substage 5c with similar sea level height above present msl except in barbados and bermuda during substage 5a at least one highstand has been recorded

at the land s end marine resources and the importance of fluctuations in the coastline in the prehistoric hunter gatherer economy of portugal abstract this paper focuses on the importance of aquatic resources in economy and subsistence strategies during the middle and upper palaeolithic of portugal modern theoretical biases in archaeology have led to a marginalization of marine resources and a dismissal of their use by palaeolithic hunter gatherers geological and archaeological data show that changes in the position of the coastline had a direct impact on the visibility of marine resources in the archaeological record marine regressions and transgressions have significantly altered the record of pleistocene coastal settlement using recent studies on changes in upwelling intensity during the last glacial we offer a new perspective on palaeolithic hunter gatherer economy that emphasizes the importance of the coast as a focus of subsistence and settlement

an analytical solution in 2d for the motion of rigid elliptical particles with a slipping interface under a general deformation a mathematical model for rigid inclusions with a slipping interface immersed in a general 2d homogeneous deformation is developed under bulk pure shear inclusions are expected to rapidly approach the stretching axis when compared to the behaviour of inclusions with no slip at the interface the derived model predicts synthetic and antithetic motion into a stable orientation under simple shear and thereafter the inclusion makes an antithetic angle with the shear direction under simple shear rotation rates can be higher or lower than those of no slip inclusions depending on orientation a direct relationship between object inclination to the shear direction and the vorticity of the bulk flow is predicted the model compares well with published analogue and numerical experiments

global and regional factors controlling changes of coastlines in southern iberia spain during the holocene the interaction between global glacio eustatic sea level rise and regional factors oceanographic and tectonic has controlled the evolution of coastline during the holocene in southem iberia at ca 10 000 14c years bp a deceleration of relative sea level rise took place both in the atlantic and mediterranean littorals with a maximum transgression at 6450 14c years bp in subsiding areas present tidal flats estuaries illustrate a clear marine influence recorded both in sediments and the fauna while in uplifting areas prograding spit bar systems developed two phases of major progradation are distinguished in these systems the first one between 6450 and 3000 14c years bp with a sedimentary gap at ca 4000 14c years bp and the second one from 2750 14c years bp up to present with an intervening gap between 1200 and 1050 14c years bp these progradation phases develop during stillstands followed by relative sea level fall while the sedimentary gaps represent relative high sea level in the mediterranean areas with a higher uplift rate marine terraces almost coeval to those gaps occur the most pronounced modifications in littoral dynamics occurred at between 3000 and 2750 14c years bp represented by changes in the direction of longshore drift and prevailing winds and in the predominance of progradation over aggradation processes at ca 1000 14c years bp the estuaries record a greater fluvial than marine influence and at 500 years ago an extraordinary increase in coastal progradation took place in all littoral zones the european medieval warm period is characterized at least during its initial phase by low pressure climate conditions while during the little ice age anticyclonic conditions gave rise to a strong coastal progradation

numerical modeling of the motion of rigid ellipsoidal objects in slow viscous flows a new approach abstract a simple algorithm for modeling the rotation of rigid ellipsoidal objects in viscous flows based on jeffery s 1922 proceedings of the royal society of london a102 161 179 theory is presented and is implemented in a fully graphic mathematics application mathcad http www mathsoft com the orientation of ellipsoidal objects is specified in terms of polar coordinate angles that can be easily converted to the trend and plunge angles of the three principal axes rather than the euler angles with the mathcad worksheets presented in the supplementary data associated with this paper modeling the rotation paths of individual rigid objects the development of inclusion trail geometry within syn kinematic porphyroblasts and the development of preferred orientation and shape fabrics for a population of rigid objects becomes as easy a task as using a spreadsheet the shape and preferred orientation fabrics for a population of rigid objects can be presented in both a three dimensional form and a two dimensional form allowing easy comparison between field data and model predictions the modeler can customize the type and format of the output to best fit the purpose of the investigation and to facilitate the comparison of model predictions with geological observations application examples are presented for various types of modeling involving rigid objects

porosity depth saturation pds model quantification of porosity preservation with burial in carbonate oil reservoirs and application to infer oil charging time abstract oil saturated carbonate reservoirs typically display anomalously high porosities compared to their water filled counterparts and this has been largely documented in the literature nevertheless no porosity model has been proposed yet to quantify the evolution of porosity preservation by oil under burial this paper presents a porosity depth saturation model pds model for carbonate reservoirs that quantifies for the first time the evolution of porosity with depth and oil saturation for a given charging time the pds model formulation decouples compaction from porosity preservation the mechanical and chemical compaction is defined phenomenologically from the schmoker and halley 1982 compaction trend but applied to the water domain only the computation of the porosity preservation is based on 2 new concepts the porosity preservation potential that is solely a function of time of charge and the porosity preservation factor that is a function of fluid saturation the work focuses on a large and laterally homogeneous carbonate reservoir the relations between porosity oil saturation and depth are extracted from the associated reservoir geomodel and analyzed to define the porosity preservation factor the pds model is tested on a specific reservoir facies and provides the porosity evolution with depth and saturation at any time of charge it indicates that even at a low water saturation such as irreducible water condition of an oil reservoir a reduced amount of water still suffice to reduce somewhat the porosity with burial from the current reservoir condition it is shown that the pds model solely based on porosity depth and residual water saturation can back calculate the time of charge of a reservoir not only the pds model proposes an initial time of charge in line with the findings of an independent study but it can also provide relative and quantified charging time for the various zones within the reservoir offering a level of granularity never achieved before

strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab everest massif tibet this paper presents quantitative data on strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab the data were collected from the tibetan side of the everest massif where two low angle normal faults bound the upper surface of the greater himalayan slab the earlier and structurally lower lhotse detachment and the later and structurally higher qomolangma detachment greenschist to sillimanite grade quartz rich metasedimentary rocks exposed in the rongbuk to north col region of the everest massif are characterized by cross girdle quartz c axis fabrics indicating approximate plane strain conditions fabric opening angles progressively increase with depth beneath the overlying lhotse detachment and indicate progressively rising deformation temperatures of 525 625 50 c at depths of 300 600 m beneath the detachment deformation temperatures of c 450 c are indicated by fabric opening angles in epidote amphibolite facies mylonites located closer to the overlying detachment a top down to the north normal shear sense is indicated by the asymmetry of microstructures and c axis fabrics but the degree of asymmetry is low at distances greater than 400 m beneath the detachment and sillimanite grains are drawn into adjacent conjugate shear bands but still appear pristine indicating that deformation occurred at close to peak metamorphic temperatures these quenched fabrics and microstructures indicate rapid exhumation in agreement with previous isotopic dating studies mean kinematic vorticity numbers w m were independently calculated by three analytical methods calculated w m values range between 0 67 and 0 98 and indicate that although a simple shear component is generally dominant particularly in greenschist facies mylonites located between the lhotse and overlying qomolangma detachments there is also a major component of pure shear in samples located at 400 600 m beneath the lhotse detachment pure and simple shear make equal contributions at w k 0 71 our integrated strain and vorticity data indicate a shortening of 10 30 perpendicular to the upper surface of the greater himalayan slab and confirm that the upper surface of the slab is a stretching fault with estimated down dip stretches of 10 40 assuming plane strain deformation measured parallel to the flow plane transport direction

strain and kinematic analysis in general shear zones we present a unifying theory for the development and distribution of strain markers and kinematic indicators in zones of general shear and thus provide a framework in which data previously considered contradictory may be understood rigid and deformable porphyroclast systems including and complex grains are potential indicators of both strain and flow the shapes and distribution of such porphyroclast systems may be used to distinguish among different tectonic regimes general shear is divided into two fields sub simple shear in which the rotational component of the strain is less than that for simple shear and super simple shear in which the rotational component is greater than for simple shear sub simple shear may involve narrowing or broadening of shear zones super simple shear regimes are possible in local regions such as the vicinities of deformable porphyroclasts but must be enclosed by regimes of sub simple shear the polar mohr constructions for finite deformation and flow are useful to analyze general shear in theory the hyperbolic net is employed for practical plotting of real data and derivation of the kinematic vorticity number wn this number represents the relative contributions of pure and simple shear in steady flow in nature deformation is thought to build up and decay by processes that may invalidate the assumption of constant flow regime we therefore introduce the concept of accelerating deformation and analyze the implications of non steady flow for the shearing histories of deformed objects

telescoping of isotherms beneath the south tibetan detachment system mount everest massif abstract petrologic and microstructural crystal fabric data indicate that isotherms recorded in greater himalayan series ghs schists and gneisses in the footwall to the south tibetan detachment system stds have undergone extreme telescoping during penetrative flow associated with southward extrusion of the ghs in the rongbuk valley to the north of mount everest we have made three vertical sampling traverses from the stds down into the ghs and estimated temperatures associated with penetrative deformation using the opening angles of quartz c axis fabrics measured on dynamically recrystallized grains from north to south the deformation temperature data indicate apparent thermal field gradients of 369 385 and 420 c per km for our three traverses traced over a maximum vertical sampling distance of 0 5 km adopting a differential flow path model simple geometric analysis using sections drawn parallel to the local transport direction indicates that detachment parallel transport magnitudes of 25 170 km are needed to explain the extreme telescoping of isotherms in the immediate footwall to the stds depending on assumed original geothermal gradient dip of detachment etc these particle transport estimates are similar to those previously calculated from barometry data of ghs rocks in the everest region and are compatible with channel flow models for extrusion and exhumation of the ghs

rotation of long tectonic clasts in transpressional shear zones abstract the two dimensional analysis of rotation of rigid ellipsoidal inclusions is not applicable to situations in which either the bulk deformation deviates from plane strain or one of the principal axes of the inclusion is at an angle to the vorticity vector both these situations may occur in certain types of transpressional ductile shear zones the model presented here shows how long cylindrical or ellipsoidal tectonic clasts with the longest axis parallel to the walls of the shear zone but at an angle to the vorticity vector rotate in transpressional shear zones long clasts initially at a low angle to the vorticity vector and at a large angle to the stretching lineation will rotate and tend to become subparallel to the stretching lineation the rotation of the principal axes of the elliptical cross section around the cylinder axis cannot be unlimited for any inclusion including the inclusion with circular cross section r 1 if the deformation is sufficiently large there is always a stable position of orientation the model explains simultaneous occurrence of monoclinic rolling structures in sections parallel and perpendicular to the vorticity vector depending upon the initial orientation the long axes of different clasts in the foliation plane may rotate clockwise and counterclockwise consequently opposite senses of asymmetry of rolling structures may appear in sections parallel to the vorticity vector

analysis of deformation paths in shear zones the geometry of ductile shear zones can be used to solve problems of regional tectonics if the deformation path of material in the zones is sufficiently understood flow in many shear zones may have deviated from simple shear and consequently data on the final deformation state such as finite strain and volume change are insufficient for reconstruction of the deformation path even if flow parameters were constant during progressive deformation additional information on the flow vorticity number is also needed and can be obtained from fabric elements such as sets of folded boudinaged veins rotated porphyroblasts and blocked rigid objects mohr circle constructions are presented as a tool to calculate deformation parameters from fabric data to represent the deformation path graphically and to reconstruct flow parameters from the shape of this path if the vorticity number or the volume change rate changed during progressive deformation the deformation path can be partly reconstructed using sets of fabric elements which register mean and final values of these parameters

late pleistocene holocene sediments on the spanish continental shelves model for very high resolution sequence stratigraphy abstract sequence stratigraphy analysis of high resolution seismic profiles geopulse uniboom and 3 5 khz of late pleistocene holocene sediments has been carried out on five sectors of the spanish continental margin four types of depositional settings are distinguished in these sectors 1 low subsident ramps alboran margin cadiz gulf 2 high subsident 2m kyr ramps alicante valencia 3 ria type morphology on the atlantic passive margin ria de muros and 4 fault scarp morphology systems with subsidence balearic margin a type 1 sequence is interpreted in all these sectors being composed of lowstand systems tract transgressive systems tract and highstand systems tract this conforms to the basic concepts of sequence stratigraphy and each systems tract correlates with a particular part of the last eustatic hemicycle characteristic shelf features such as terraces terraces with beach deposits and progradational sediment wedges evidence a complex stacking of lesser sub sequences in all the systems tracts which must be related to very short period sea level stillstands and fall we propose a very high resolution sequence stratigraphy model in which the last sea level hemicycle is punctuated by p cycles 4500 years which give rise to the neo glacial events h cycles 2200 950 years and c cycles 500 50 years these cycles interact with each other thus establishing the placing of the high and low sea levels this attention to detail 1 explains sedimentary evolution on both the shelf and upper slope during late pleistocene holocene time 2 illustrates some departures from the classical sequence stratigraphy model and 3 also demonstrates that the late pleistocene holocene eustatic curve is not one simple transgression but is modulated by three differing period cycle groups below the milankovitch band our model is delimited by fluctuating sea level during pleistocene holocene times such features should be identifiable on any continental margin however localized features occur due to subsidence and continental shelf morphology which determ ine the location and depth of sedimentary bodies generated in each eustatic cycle

experimental stabilization of carbonate sediments to calcite insights into the depositional and diagenetic controls on calcite microcrystal texture abstract aragonite and high magnesium calcite are abundant constituents of modern shallow marine carbonate sediments but are rare in ancient carbonate rocks because these minerals are metastable they tend to stabilize to microcrystalline calcite which is ubiquitous in most phanerozoic marine and lacustrine limestones calcite microcrystals exhibit a range of textures that have been classified in terms of crystal size morphology and contact geometry these textures have the potential to reveal information about the precursor sediments as well as the diagenetic conditions of stabilization and thus may serve as a proxy for paleoenvironmental conditions however despite their ubiquity and importance the origin of these textures is controversial hypotheses regarding the origin of calcite microcrystal textures typically involve inferences regarding the precursor depositional sediments diagenetic conditions of stabilization or diagenetic processes here hundreds of laboratory experiments were conducted in which metastable carbonate sediments were stabilized to calcite the goal of these experiments was to investigate the depositional and diagenetic controls on calcite microcrystal textures the depositional variables investigated were precursor mineralogy type and size and the diagenetic variables were temperature fluid chemical composition and fluid solid ratio our results show that experimental stabilization of carbonate sediments produces calcite with a wide variety of textures depending on the various depositional and diagenetic parameters these textures are remarkably similar to those commonly observed in the rock record calcite microcrystal morphology is controlled by fluid chemistry fluid solid ratio and reactant type calcite microcrystal size is controlled by temperature fluid chemistry fluid solid ratio and reactant size the degree to which calcite microcrystals are fitted together is controlled by reactant size and reactant microstructure our findings challenge most of the existing hypotheses regarding the origin of calcite microcrystal textures we specifically show that textures that have been interpreted to indicate late diagenetic processes such as dissolution and cementation may be the result of the early diagenetic processes of stabilization

taphonomic tiering experimental field taphonomy of molluscs and foraminifera above and below the sediment water interface abstract a review and synthesis of field based taphonomic experiments using molluscs and foraminiferans in marine systems reveal differing patterns of hardpart accumulation and destruction for these two major groups of fossil organisms for benthic molluscs most destruction appears to occur at the sediment water interface in siliciclastic settings mollusc preservation is suggested to be high once the shell is buried below the taphonomically active zone although this observation has not been experimentally addressed foraminiferal preservation however depends on microhabitat biogeochemical conditions within the sediments and test composition the taphonomically active zone for foraminiferans appears to be the upper 10 cm in most depositional settings from shallow to deep sea the preservation of tests or shells however has not been examined below the sediment water interface using field based experiments pore water geochemistry and associated microbial processes may be the most important factors in which to examine subsurface taphonomy the term taphonomic tiering is applied to variations in taphonomic activity within the sediments that differentially affect hard parts in essence the subsurface region where hardparts are presumed to be preserved is one of the new frontiers in experimental field taphonomy

the palaeogeography of mesolithic settlement subsistence and shell midden formation in the muge valley lower tagus basin portugal this paper reports the first detailed palaeogeographical analysis of the environmental context of late mesolithic shell midden sites in the lower tagus area and focuses on the lower muge valley which contains an internationally significant mesolithic record the lower muge valley fill comprises buried estuarine and fluvial environments contemporary with mesolithic settlement holocene environmental and palaeogeographic changes influenced mesolithic settlement subsistence and midden accumulation the sudden appearance of large late mesolithic shell middens throughout portugal represents a process of increased visibility and preferential preservation of the archaeological record prior to 6100 cal bc aggrading valley floor environments did not occupy the entire width of the present lower tagus floodplain and any sites located in the early holocene valley are currently deeply buried shell midden occupation on terrace levels followed the establishment of aggrading estuarine environments containing produ

discussion of microfacies diagenesis and oil emplacement of the upper jurassic arab d carbonate reservoir in an oil field in central saudi arabia khurais complex by rosales et al 2018

quantitative microstructural analysis of mylonites formed during alpine tectonics in the western mediterranean realm abstract quantitative microstructural investigations involving new gis based tools are applied to three different types of mylonitic rocks these techniques enable mineral shape distribution maps to be produced thereby allowing the nature and relative percentage of the weakening vs hardening layers as well as their kinematics to be obtained within a statistically meaningful dataset selected rock types are derived from shearing associated with the meso alpine strike slip tectonics of the western mediterranean realm which since the paleocene has involved skarn migmatitic paragneiss and tonalites these rocks belong to a deep seated portion of the original southern european variscan chain known as the calabrian pelortani orogen microstructural maps reveal porphyroclastic domains represented alternatively by feldspar amphibole pyroxene or scapolite that can be distinguished from weakening phase areas characterised by quartz biotite plus quartz or alternatively by calcite when the weakening layer is controlled predominantly by skarns image elaboration of porphyroclastic domains was employed to estimate the dominant shear type with rigid grain analysis indicating a pure shear component of 66 68 for the mylonitic tonalites 62 66 for the mylonitic paragneisses and 58 62 for the mylonitic skarn grain boundary mapping of the quartz rich domains also permits an estimate of shear strain rate which ranges from 1 14 10 12 1 s for mylonitic paragneiss to 5 91 10 12 1 s for mylonitic tonalite and is in accord with high strain zones in natural settings finally our results opened up new perspectives in the interpretation of the kinematics and rheology of this exhumed sector of the southern european variscan chain reflecting the deep seated meso alpine strike slip tectonics of the western mediterranean realm