subglacial bedrock welding associated with glacial earthquakes a c 635 ma glacial striations on a neoproterozoic sandstone pavement is documented only instantaneous solidification could have preserved the breccia in situ glacier speeds of c 0 3 m s 1 would have induced peak flash temperatures sufficient 1130 c to cause partial frictional welding of the deformed quartzitic bedrock beneath an ice loaded clast these results support suggestions that glacial seismicity is due to episodic very rapid shifts of large ice masses over the substrate stick slip movement they also indicate that significant effective normal stresses occur at the base of glaciers

structure and evolution of the northern potwar deformed zone pakistan the northern potwar deformed zone npdz is part of the active foreland fold and thrust belt of the salt range and potwar plateau in northern pakistan about 500 km of seismic reflection profiles are integrated with surface geologic and drilling data to examine the deformation style and structure of the npdz with particular emphasis on history of deformation of the dhurnal oil field the seismic lines suggest that the overall structure of the eastern npdz is a duplex structure developed beneath a passive roof thrust the roof thrust is generated from a tipline in the miocene murree formation and the sole thrust is initiated from the same eocambrian evaporite zone that extends 80 km southward beneath the soan syncline and salt range the dhurnal oil field structure is a pop up at the southern margin of the npdz and developed beneath the passive roof thrust the passive roof thrust crops out just north of dhurnal on the steep northern limb of the soan syncline an overstep passive roof thrust sakhwal fault is interpreted west of dhurnal this fault developed due to

late precambrian glacially related grooved and striated surfaces in the tillite group of central east greenland abstract the tillite group of central east greenland comprises five formations of which two are dominantly glacigenic the ulveso formation formerly lower tillite and the storeelv formation formerly upper tillite both of which embrace a wide range of facies including glaciomarine nearshore and terrestrial glacial sediments evidence of periodic terrestrial conditions is indicated especially by a variety of grooved and striated surfaces on the island ella o in the ulveso formation grooves of complex geometry 0 4 m wide and 0 3 m deep were cut into a cemented conglomerate horizon they are interpreted as having formed as a result of subglacial meltwater cavitation at the base of the storeelv formation boulders thought to have been dropped into partially cemented sandstone by floating glacier ice were largely planed off by a subsequent advance of grounded ice in the middle of the storeelv formation a striated boulder pavement occurs within diamictite on the basis of stone fabric striation orientation and cross bedding data this pavement is inferred to have formed by the packing of stones along a shear surface within an accumulating lodgement till such features have rarely been observed in pre pleistocene glacigenic sequences they imply that each glacigenic formation accumulated during a complex series of advances and retreats rather than just one

development of the himalayan frontal thrust zone salt range pakistan the salt range is the active frontal thrust zone of the himalaya in pakistan seismic reflection data show that a 1 km offset of the basement acted as a buttress that caused the central salt range potwar plateau thrust sheet to ramp to the surface exposing mesozoic and paleozoic strata the frontal part of the thrust sheet was folded passively as it overrode the subthrust surface on a ductile layer of eocambrian salt lack of internal deformation of the rear part of the thrust sheet is due to decoupling of sediments from the basement along this salt layer early to middle pliocene 4 5 ma conglomerate deposition in the southern potwar plateau previously interpreted in terms of compressional deformation may instead document uplift related to basement normal faulting stratigraphic evidence paleomagnetic dating of unconformities and sediment accumulation rates suggest that the thrust sheet began to override the basement offset from 2 1 to 1 6 ma cross section balancing demonstrates at least 20 to 23 km of shortening across the ramp the rate of himalayan convergence that can be attributed to underthrusting of indian basement beneath sediments in the pakistan foreland is therefore at least 9 14 mm yr about 20 35 of the total plate convergence rate

short paper palaeocurrent evidence of a northern structural high to the welsh basin during the late llandovery palaeocurrents from the northernmost aberystwyth grits formation are consistently from the north which is at variance with the generally accepted southerly source area for the rest of the formation the anomalous directions appear to indicate a structural high and possible sediment source to the north

the effect of decollement dip on geometry and kinematics of model accretionary wedges we conducted a series of sand box models shortened asymmetrically above a frictional plastic decollement to study the influence of amount and sense of the decollement dip on the geometry and kinematics of accretionary wedges model results illustrate that the amount and direction of decollement dip strongly influence the geometry and mode of deformation of the resulting wedge in general for models having similar decollement frictional parameters the resulting wedge is steeper grows higher and is shorter when shortened above a decollement that dips toward the hinterland at 42 bulk shortening the length height ratio of wedges formed above a 5 dipping decollement was equal to 2 4 whereas this ratio was equal to 3 for wedges shortened above a horizontal decollement moreover models with a hinterland dipping decollement undergo larger amounts of layer parallel compaction lpc and area loss than models shortened above a non dipping decollement the effect of decollement dip on wedge deformation is most pronounced when basal friction is relatively high b 0 55 whereas its effect is less significant in models where the basal decollement has a lower friction b 0 37 model results also show that increasing basal slope has a similar effect to that of increasing basal friction the wedge grows taller and its critical taper steepens

centrifuged models of gulf of mexico profiles abstract physical models dynamically scaled in a centrifuge are used to explore the importance of slope progradation in driving internal salt structures much further horizontally than they rise large increments of ductile plastic overburden added at normal gravity values simulated primary clastic sedimentary progradation of a clastic slope over a layer of buoyant fluid simulating salt during load increments at a nominal 800 g in a centrifuge this ductile topographic slope spread over the ductile decollement except for down to basin growth faults all the structures considered to be distinctive in the northern gulf of mexico are simulated in the models that are scaled such that 1 mm and 60 s in the model correspond to 1 1 5 km and 2 6 ma in the prototype ratios of the rate of advance to the rate of rise of the shelf break compared with the rate of advance and increase in relief of salt structures control how much of the deep autochthonous salt is squeezed ahead of the advancing shelf and the paths this salt takes to shallow structural levels the few three dimensional diapiric stocks which developed from many two dimensional mullions in the models spread stock canopies which advanced huge distances before some became tongue canopies by climbing over clastic sediments already aggraded in front of them the models emphasize the significance of ductile spreading of the clastic sediments now being discerned by backstripping

active tectonics of western potwar plateau salt range northern pakistan from insar observations and seismic imaging abstract the foreland fold and thrust belt of northern pakistan is located at the western end of the himalayan arc where salt tectonics is responsible for structural styles hydrocarbon source areas and seismicity three sub regions of fold and thrust belt are the potwar plateau salt range kohat plateau surghar range and the bannu basin khisor range the difference in deformation intensity between these regions is mainly attributed to the presence or absence of an infra cambrian salt layer this study investigates the active tectonics of the potwar plateau and salt range region emphasizing the role of salt using the small baseline subset interferometry sbas technique and 2 d seismic interpretations ten palsar images and four seismic profiles from western potwar plateau salt range region were used sbas results derived from palsar images spanning from 2007 to 2010 suggest that the potwar plateau salt range is active with the western portion of the region experiencing an uplift at an average rate of around 10 mm year two uplift anomalies were observed which were interpreted as zones of transpression and salt diapirism time migrated seismic profiles show that the salt layer acts as a detachment our results show that salt has different roles in different regions of the fold and thrust belt in the potwar plateau region the salt layer acts as a detachment while in salt range salt flow induced structures are prominent the integration of sbas and 2d seismic interpretation reveals that the deformation of western potwar plateau salt range is influenced by two main faults the dextral kalabagh fault and the main frontal thrust finally this work was compared to the kuqa fold and thrust belt in western china due to their structural similarities

lateral structural variation along the kalabagh fault zone nw himalayan foreland fold and thrust belt pakistan abstract the nw himalayan fold and thrust belt in pakistan is of gentler regional slope and wider extent than the other parts of the convergent plate boundary between india and the rest of asia large scale structural re entrants typify the main frontal thrust mft of the nw himalayan fold and thrust belt in pakistan understanding dynamics of the formation of these structural variations has been hampered by the lack of information about the lateral structures bounding the re entrants our mapping of the kalabagh fault zone a lateral ramp linking the salt and the surghar ranges advanced spaceborne thermal emission and reflection radiometer aster data field investigations and the interpreted reprocessed 2d seismic data this integration of surface and subsurface geology provides new insights on the geometry and evolution of the kalabagh fault zone by showing that it forms an oblique ramp to the main frontal thrust and at north a lateral ramp with right lateral strike slip movement our results indicate that the presence and areal extent of the evaporates is the dominant factor controlling lateral structural variation in the nw himalayan fold and thrust belt of pakistan the kalabagh fault zone acts as a zone that accommodates differential shortening and structural variation along the orogenic trend

polyphase deformation of diapiric areas in models and in the eastern prebetics spain fingerlike bodies of evaporite rocks have been observed in many regions affected by multiple tectonic phases such as the atlas the pyrenees or the zagros mountains where they have been interpreted as fault plane diapiric injections or collapse related salt welds in this article we suggest a new interpretation of these structures as squeezed diapirs based on detailed structural and sedimentological field data of the bicorb quesa diapir eastern prebetics and offer five analog models which simulate the polyphase deformation of the eastern prebetics in this area diapirs formed from the oligocene to langhian during an extensional phase related to the opening of the valencia trough these diapirs were later affected by a serravallian contractional phase which inverted the preexisting grabens and created new folds and thrusts the preexisting diapirs were necked and or squeezed forming secondary welds with a fingerlike geometry that isolated the diapir bulbs from their source layer extrusion of diapiric material was also accelerated during this phase but no new diapirs formed finally the area was again affected by an extensional phase during the tortonian which reactivated the normal faults and created a new set of diapirs the new diapirs formed where the overburden was thinner that is at the toe of the major reactivated faults commonly these faults coincide with the bounding faults of the major grabens formed during the first extensional phase and therefore the new diapirs grow close to the location of the squeezed diapirs the models also show that the faults created during the initial extension prevailed as the main focus for deformation during the polyphase history deformation in the overburden and the viscous layer was mainly accommodated along the major grabens formed during the first extensional stage during shortening the initial major grabens deformed as complex anticlines and during the subsequent extensional phase most deformation occurred by the collapse of these anticlines along preexisting faults fault welds and the flank of the squeezed diapirs the source layer is compartmentalized accumulating and withdrawing material in the same locations the initial grabens and horst as a result the source layer is easily depleted beneath the initial horst forming primary welds

an evaporite bearing accretionary complex in the northern front of the betic rif orogen the guadalquivir accretionary complex forms a largely oblique prism at the northern edge of the betic rif orogen where miocene sediments plus allochthonous evaporite bearing units were accreted during the displacement of the alboran domain towards the west traditional interpretations end the tectonic structuring of the betic cordillera at the present topographic front beyond which gravitational and or diapiric processes would predominate however this study shows pervasive tectonic deformation in the outer prism with coherent oblique shortening kinematics which is achieved through an alternation of roughly n s arcuate thrust systems connected by e w transfer fault zones these structures accord well with the geophysical models that propose westward rollback subduction the main stage of tectonic activity occurred in the early middle miocene but deformation lasted until the quaternary with the same kinematics evaporite rocks played a leading role in the deformation as evidenced by the suite of ductile structures in gypsum distributed throughout the area s and l gypsum tectonites scaly clay fabrics and brittle fabrics coexist and consistently indicate westward motion top to 290 with subordinate n s contraction almost perpendicular to the transfer zones this work reveals ductile tectonic fabrics in gypsum as a valuable tool to elucidate the structure and deformational history of complex tectonic melanges involving evaporites above the decollement level of accretionary wedges

glacial and rocky shore dynamics of the karlebotn monadnocks late neoproterozoic of northern norway located near the village of karlebotn in east finnmark norway a cluster of six gneissic monadnocks is unconformably surrounded by weakly metamorphosed sandstone strata of late neoproterozoic age in the smalfjord formation differentiated by faults the monadnocks were further sculpted by a glacier that flowed through a coastal valley concordant with the present day varangerfjorden the largest of the monadnocks is 337 m long and 167 m wide there remains ample evidence of glacial activity associated with this feature relict lodgement tillites are preserved on the west side of the monadnock flowtillites on the steep surfaces of the north and southwest sides and a small esker directly on top the valley was later inundated due to glacial eustacy and the karlebotn monadnocks became an archipelago in a shallow estuary of a broad fjord interpretation of exposed versus sheltered rocky shores on opposite sides of the largest monadnock island is supported by mineralogical variations in basal strata along t

sandbox experiments of inverted listric and planar fault systems abstract the kinematic and geometric evolution of basement controlled inversion structures has been analyzed using a plane strain sandbox apparatus the results of two representative scaled analogue models comprising rigid listric and planar detachment faults that both have cut off angles of 60 to the horizontal are described in detail the hangingwall above these detachment geometries was constructed from alternate layers of sand and mica in order to simulate an anisotropic sedimentary sequence in both experiments initial shortening at the onset of inversion was accommodated by bulk strain this was followed by reactivation of the basal detachment together with the main basin controlling planar and listric faults which propagate upwards through the post rift sequence at approximately the same angle as the upper part of the detachment fault i e 60 reactivation of relatively steep intra basinal extensional faults within the cover was restricted to nucleation of reserve faults and thrusts in the region of the tips during approximately the first 10 to 15 contraction this resulted in gently dipping thrusts that propagated upwards through the post rift sequence to produce harpoon shaped structures later in the inversion phase after approximately 15 contraction backthrusts cut through and displaced the original antithetic extensional graben faults producing downward tapering wedge shaped structures at the margins of the basin although deformation in these experiments was limited to purely dip slip displacement the nature of the original extensional faults and their reactivated tip regions resulted in cross sectional geometries that have a marked resemblance to strike slip induced flower structures uplift was asymmetric and centred above the upper part of the main detachment above the listric fault but was more symmetrical and centred above the soling out point of the detachment in the case of the planar fault geometry the results of these experiments show distinct similarities to structures seen on seismic sections form the southern north sea and other inverted sedimentary basins

the paleoclimatic significance of deformation structures in neoproterozoic successions abstract this paper reviews the different types of soft sediment deformation structures that can form in glacial and non glacial settings and explores the potential use of these structures in resolving long standing debates in paleoenvironmental reconstructions of neoproterozoic glacigenic successions soft sediment deformation structures are created when compressional gravitational or shear stress is applied to unlithified sediments during or shortly after deposition in subglacial or ice marginal glacial settings shear and compressional stress imparted by ice moving on top of a deformable substrate or advancing ice buldozing unlithified ice marginal sediments can result in a wide range of folding faulting and shear structures in glaciofluvial or stagnant ice marginal setting gravitational collapse and remobilization of sediments associated with the melting of buried ice can result in normal faulting and broad folding in glaciolacustrine or glaciomarine settings compressional shear and gravitational types of deformation structures can occur as a result of grounding ice or icebergs rapid sedimentation and reworking downslope associated with high sedimentation rates in non glacial settings similar deformation structures can form as a result of slope instability and reworking of sediments downslope rapid sedimentation seismic shaking wave induced shearing or loading in this context two case studies are presented to demonstrate the type of paleoenvironmental information that an analysis of deformation structures can provide in the first case study analysis of deformation in the port askaig formation scotland reveals a distinctive stratigraphic distribution of deformation structures the types of deformation observed together with their recurrence over several 100s of meters and their basinal context are used to infer a seismic origin for the deformation which in turn suggests a significant tectonic control on sedimentation atop a record of ice margin fluctuations in a glaciomarine setting in the second example analysis of deformation in the smalfjord formation northern norway provides strong evidence for deformation by active ice overriding glaciofluvial deposits the types of deformation in this example together with its complexity scale and associated facies provide the strongest case for ice marginal deformation in sum analysis of deformation structures together with analysis of structural geology stratigraphy facies and facies associations can provide additional constraints on paleoenvironmental conditions at the time of deposition which can help us refine or test paleoenvironmental models proposed for this critical time period in earth history

loophole for snowball earth the snowball earth hypothesis posits an ice covered planet new climate simulations of snowball conditions allow ice free equatorial oceans that may be crucial for a theory about early animal evolution

the role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

a model for striated boulder pavement formation on glaciated shallow marine shelves an example from the yakataga formation alaska abstract laterally extensive striated boulder pavements crop out within glaciomarine diamicts of the early pleistocene yakataga formation on middleton island alaska boulder pavements consist of planes of one clast thickness with faceted upper surfaces showing consistently oriented striation directions cropping out over several kilometers along strike clasts do not have the preferred long axis alignment nor the characteristic bullet shape of boulders transported at a glacier base and deposited by lodgement processes in most cases pavements identify the planar bounding surfaces of thick up to 100 m tabular units of fossiliferous muddy diamict deposited by the settling of fine grained sands and muds from suspension together with ice rafted debris in water depths between 20 and 250 m diamict facies both underlying and overlying the pavements contain abundant unabraded macro and microfossils and show no evidence of deformation by subglacial shear processes pavements appear to have originated as boulder lag surfaces produced by wave and tidal current winnowing of diamict on relatively shallow bank areas during episodes of relative sea level lowering lags were subsequently overridden and abraded by a grounding ice shelf the glacially abraded pavements are thought to record the repeated expansion of a partially floating ice shelf to the edge of the gulf of alaska continental shelf during the early pleistocene recognition of boulder pavements formed in this manner may help establish the former presence of ice shelves whose depositional record remains enigmatic

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

the influence of an embedded viscoelastic plastic layer on kinematics and mass transport pattern within accretionary wedges abstract the major aim of this study was to examine the influence of an embedded viscoelastic plastic layer at different viscosity values on accretionary wedges at subduction zones to quantify the effects of the layer viscosity we analysed the wedge geometry accretion mode thrust systems and mass transport pattern therefore we developed a numerical 2d sandbox model utilising the discrete element method starting with a simple pure mohr coulomb sequence we added an embedded viscoelastic plastic layer within the brittle undeformed sediment package this layer followed burger s rheology which simulates the creep behaviour of natural rocks such as evaporites this layer got thrusted and folded during the subduction process the testing of different bulk viscosity values from 1 1013 to 1 1014 pa s revealed a certain range where an active detachment evolved within the viscoelastic plastic layer that decoupled the over and the underlying brittle strata this mid level detachment caused the evolution of a frontally accreted wedge above it and a long underthrusted and subsequently basally accreted sequence beneath it both sequences were characterised by specific mass transport patterns depending on the used viscosity value with decreasing bulk viscosities thrust systems above this weak mid level detachment became increasingly symmetrical and the particle uplift was reduced as would be expected for a salt controlled forearc in nature simultaneously antiformal stacking was favoured over hinterland dipping in the lower brittle layer and overturning of the uplifted material increased hence we validated that the viscosity of an embedded detachment strongly influences the whole wedge mechanics both the respective lower slope and the upper slope duplex shown by e g the mass transport pattern

evidence for a glacial origin of neoproterozoic iii striations at oaibaccannjar ga finnmark northern norway the origin of the famous late precambrian striated pavement at oaibaccannjar ga bigganjargga northern norway remains controversial most investigators have accepted a glacial formation but some prefer a soft sediment mechanism however a newly discovered c 2 5 mm thick zone of brecciation under rare polished striations indicates a hard substrate during formation and thus a glacial origin for the striations other points indicating that the striations formed in a hard substrate are 1 the striated platform in the veidnesbotn formation is c 150 ma older than the overlying diamictite smalfjord formation having been buried to c 2 5 km depth cementation should have started before smalfjord times 2 the marked irregularity of the sub smalfjord formation palaeotopography on skjaholmen 3 the presence of rounded veidnesbotn formation boulders in the diamictite above the striations imprints of clasts appearing to lie across the striations are re interpreted as relicts of mud flakes within the veidnesbotn formation which were cut across and quarried out during pavement formation the origin of the overlying diamictite tillite vs debris flow is not constrained by the presence of glacial striations and most probably was deposited some time after striation formation

the formation of convolute lamination in mud rich turbidites convolute lamination is a common fold structure within turbidite beds attributed to the deformation of sediment during or soon after deposition of the host bed despite the prevalence of this feature the formational processes are still not well understood possible mechanisms are investigated here through redescription and analysis of convolute lamination from the aberystwyth grits group silurian west wales uk in which convolute bedding was first defined internal bed structures have been studied in clean coastal exposures and on high resolution optical scans of cut surfaces convolute lamination occurs in intervals 2 10 cm thick spanning the top of the very fine sand bouma c division through the d division of interlaminated silt and clay observed growth geometries confirm that the structure formed during sedimentation of the host graded bed folds show a down flow asymmetry and doubly vergent diapiric geometries mushroom shaped structures grain size measurements from a modern turbidite icod bed 165 ka mor occan turbidite system suggest there is an optimal window of average grain size and mud content parameter space within which convolute lamination develops it is proposed that this window coincides with a bed density inversion created during deposition of a graded bed as clean sand with pore spaces infilled by water fines upwards into mud rich sand with pores infilled by an increasing proportion of mud porosity decreases and bulk bed density correspondingly increases the resulting unstable density gradient may lead to vertical buoyancy driven overturn manifest as growing folds subsequent amplification of the folds due to density differences and modification due to horizontal shear imposed by the depositing turbidity current may then occur the bed density gradient stabilises with deposition of low permeability mud suppressing further fold development quantitatively both rayleigh taylor instability and kelvin helmholtz instability are theoretically possible in forming folds in this context

active transfer faulting in the nw sub himalaya india observed by space borne topographic analyses abstract the results of surface morphology and insar analyses carried out along a nne ssw oriented 7 km long transfer fault are presented this structure actively accommodates differential motion across two blocks in the western sub himalayan belt of india segmentation is most pronounced in this sector of the accretionary wedge where minimal climatic variations and a three fold sub division kangra renetrant nahan salient dehradun reentrant are well recognized segmentation is here clearly elucidated by variation in surface topography geologic structure and recorded seismicity over the last few decades however the transition from one segment to another is poorly documented and understood this article primarily documents surface topography and drainage anomalies within the transition zone between the kangra reentrant and the nahan salient through the study of space imageries spanning nearly six decades i e early 1960 s to present geomorphic observations and insar analyses demonstrate that the segmentation is largely governed by lateral variation in geological structure deformation patterns and mechanical stratigraphy and accommodated by transverse movement along the transfer fault it should be noted that transfer faults commonly represent a privileged pathway for the major drainage and therefore surface manifestations are rarely preserved e g yamuna tear ganga tear etc a rare instance of preserved surface topography associated with the recent activity along the sabilpur transfer fault at the transition between the kangra renetrant and the nahan salient is documented here our investigations demonstrate that the sabilpur active fault saf accommodates differential tectonic convergence between the two blocks predominantly by left lateral strike slip kinematics with a component of uplift related to thrusting at hft

modeling of thrust fronts above ductile and frictional detachments application to structures in the salt range and potwar plateau pakistan series of scaled sandbox models are used to simulate the development of thin skinned simultaneous shortening above adjacent ductile and frictional substrates these models simulate the evolution of the potwar plateau and salt range in pakistan where pale

glacial or non glacial origin for the bigganjargga tillite finnmark northern norway bigganjargga is the classic locality for the varangian ice age in northern scandinavia the presence of two sets of striations on the underlying quartzite basement has been taken as evidence for a glacial origin of the bigganjargga diamictite however soft sediment surface structures on the underlying sandstone indicate that it was not consolidated when the diamictite was emplaced together with structures in the diamictite this shows that the deposit formed as a debris flow moving northwestwards over an unconsolidated substrate there is no evidence for glacial origin or contribution for the diamictite material

the role of syntectonic sedimentation in the evolution of doubly vergent thrust wedges and foreland folds this paper shows the evolution of time constrained two dimensional scaled analogue models of doubly vergent thrust systems in the presence of syntectonic sedimentation two sets of experiments were considered 1 the addition of a syntectonic layer composed of a polymer and overlying sand in the prowedge and 2 the addition to the previous condition of a progradational sedimentary load results from the first set of experiments indicate that the foreland fold and thrust belt has a strong relationship with the competence of the syntectonic layers when the competence is low the deformation produces tight asymmetric detachment folds as the competence increases the fold and thrust belt shows break trough folds with longer and better defined foreland vergence results from the second set of experiments indicate that structural vergence is determined by the sense of progradation of the syntectonic layers and in the case of strong aggradation at the prowedge extension and reactive diapirism form contemporaneously with the contraction three end members are proposed for mountain front thrust systems formed in the presence of syntectonic polymer and sand sedimentation 1 outcropping fold and thrust belt sequence in the case of no syntectonic sedimentation 2 long displacement blind thrust sheets in the case of under filled basins and 3 short displacement blind thrust sheets in the case of over filled basins all results indicate that ductile units at the base of syntectonic layers increase the displacement of the underlying frontal thrusts at the prowedge and reduce the critical taper results also indicate that at very high sedimentary rates and hyper critical taper conditions the prowedge collapses conclusions drawn from this research may be applied as an analogue to foreland evolution and to evaluate hydrocarbon generation migration and entrapment in thrust belts in areas where seismic imaging is generally poor

role of lateral thickness variations on the development of oblique structures at the western end of the south pyrenean central unit abstract the montsec unit is one of the most important detached south verging nappes within the south pyrenean central unit spcu southern pyrenees a n s cross section of its western sector based on seismic reflection profiles shows a hangingwall ramp geometry in mesozoic strata overlain by a syntectonic series of lower eocene sediments with growth geometry the geometry of growth strata constrains the age of its movement between the paleocene and the middle eocene the geometry of the western oblique ramp of the south pyrenean central unit is defined by a series of n s folds in some cases associated with underlying west verging thrusts as indicated by seismic reflection profiles and field data in this paper we propose that the geometry of the thrust wedge of mesozoic units progressively thinning from east to west strongly contributed to constrain the location and geometry of the western termination of the montsec thrust the hypothesis proposed is checked by a series of experimental wedges developed in a sandpack with lateral and three dimensional thickness variations oblique structures form as thrusting progresses at the tip of the sand wedge

experimental modeling of role of gravity and lateral shortening in zagros mountain belt dynamically scaled analogs of the geologic structures of the zagros mountain belt are used to argue that different parts of the zagros mountains of iran record different combinations of the effects of a gravity driven overturn and a southwest northeast lateral shortening superimposed on the zagros overturn partially scaled material models have been used to simulate the zagros geodynamics which involve layer parallel compression of a 6 to 7 km thick phanerozoic carbonate cover containing a pattern of preshortening diapirs the folds in the zagros form rapidly 1 5 mm yr in a 20 to 30 km wide zone reactive some of the preshortening diapirs and generate new synshortening listric diapirs a third set of postshortening diapirs rises from the hormuz decollement behind the fold thrust front model buckle folds superimposed on diapirs or pillows tend to avoid and curve around preshortening diapirs which flatten in the synclines model profiles show that lateral shortening induces residual salt at depth to flow toward and rise through the anticlinal cores as synshortening or postshortening diapirs i suggest that any salt pillows in currently diapir free zones of the zagros fold thrust belt may surface as diapirs through the anticlines in the future in the absence of well data seismic and field observations i have used only three map pattern criteria to recognize the timing of diapirs these are locally obscured by extrusive salt sheets preshortening diapirs are generally small and elongate parallel to fold axes and are restricted to synclines synshortening diapirs are elongate perpendicular to the fold axes and are restricted to anticlines postshortening diapirs can be the same size as synshortening diapirs or larger and can be circular they are more common in the anticlines

eye and sheath folds in turbidite convolute lamination aberystwyth grits group wales eye and sheath folds are described from the turbidites of the aberystwyth group in the silurian of west wales they have been studied at outcrop and on high resolution optical scans of cut surfaces the folds are not tectonic in origin they occur as part of the convolute laminated interval of each sand mud turbidite bed the thickness of this interval is most commonly between 20 and 100 mm lamination patterns confirm previous interpretations that convolute lamination nucleated on ripples and grew during continued sedimentation of the bed the folds amplified vertically and were sheared horizontally by continuing turbidity flow but only to average values of about 1 the strongly curvilinear fold hinges are due not to high shear strains but to nucleation on sinuous or linguoid ripples the aberystwyth group structures provide a warning that not all eye folds in sedimentary or metasedimentary rocks should be interpreted as sections through high shear strain sheath folds highlights eye folds occur in turbidite convolute lamination viewed down the palaeoflow direction the convolutions formed during bed deposition and are overturned down flow by current shear the eye folds are sections through non cylindrical sheath folds due to this shear average shear strains are less than 1 0 lower than generally necessary to generate sheath folds instead sheath folds nucleate on already sinuous current ripples lower in the turbidite bed

displacement fields and finite strains in a sandbox model simulating a fold thrust belt this thesis uses geodetic satellite data to measure present day crustal deformation in the zagros fold thrust belt sw iran geodetic type measurements are also used in down scaled models that simulate the surface deformations seen in convergent settings like the zagros fold thrust belt global positioning system gps measurements of three surveys between 1998 and 2001 indicate 9 3 mm yr and 5 3 mm yr shortening across the se and nw zagros respectively gps results show that in addition to the different rates and directions of shortening on either side of the ns trending kazerun fault local along belt extension occurs to the east differential sar interferograms of ers1 2 images between 1992 and 1999 detect 8 4 mm yr uplift rate across a newly recognized fault in sw qeshm island this can be attributed to a steep imbricate thrust that may still represent the local zagros deformation front the salt diapirs in the zagros rise from a source layer that acts as a low frictional decollement that decouples the deformation of the cover sediments from their basement in the eastern zagros whereas the cover to the west deforms above a high friction decollement physical models were prepared to simulate cover deformation in the zagros by shortening a sand pack above adjacent high and low frictional decollements represented by a ductile layer the strain distributions differed above the two types of decollements it was more heterogeneous above the salt where local extension in the shortening direction was dominant a separate work also investigated systematically the role of basal friction on cover deformation in convergent settings accurate height measurements of the model surface by laser scanner indicated a deformation front more distal than usual particularly in the low basal frictional models the volume reduction in our shortened sand models correlated directly with their basal friction

influence of basement faults on the development of salt structures in the danish basin scaled centrifuged models based on interpreted seismic profiles were used to simulate the salt structures in the danish basin the models consisted of a viscous layer simulating rock salt overlain by layers of cohesive sand that mimic brittle failure in natural overburdens model results support the hypothesis that basement faults trigger the growth of many salt diapirs in the danish basin in plan view model diapirs are localized as buoyant walls along faults in the overburden which collapsed due to basement fault movement with further burial single diapirs rose from these buoyant walls some of the diapirs surfaced through the faulted overburden a few were trapped beneath the competent cretaceous units and others were starved due to lack of supply from below in section model diapirs were asymmetric and were rooted on the tip of the faults or located on the rotated footwall blocks model diapirs not located over faults were triggered by differential loading and collapsing of overburden layers due to basement block rotation models show that the presence of fewer salt structures in the northern than the southern part of the basin is due to differential subsidence and flow of buoyant material from north to south where they rise diapirically in the model the pressure due to loading by overburden layers changed from 1 3 102 pa in the south to 2 3 102 pa in the northern part of the basin in general the model results illustrate that basement faults influence diapirs by accumulating buoyant material in half grabens and introducing a slope and steps at the base of the buoyant layer weakening its overburden and causing differential loading and compaction the spreading overhangs of salt diapirs beneath the cretaceous chalk in the danish basin would seal any potential pre cretaceous reservoir rocks

global and continental scale glaciations on the precambrian earth abstract earth s climate during the proterozoic eon was marked by major glacial events with evidence for large continental ice sheets on many cratons and with sedimentological data indicating that glaciers had extended to sea level this paper emphasizes the sedimentological and sequence stratigraphic responses to glaciations and evaluates the major driving forces of glaciations during the precambrian first and second order sequences are recognized related to continental scale fragmentation and formation of marine rift basins wherein sedimentary rocks indicate glacial influences and pronounced tectonic climatic linkages coarse syn rift deposits are typically characterized by mass flow diamictites and conglomerates it is important to undertake sedimentological facies and sequence stratigraphic analysis of these syn rift and capping passive margin sequences as well as of slope turbidite deposits which formed if enhanced subsidence of the basins was occurring more generally latitude and syn rift tectonic uplift can cause formation of glacial ice and enhance distinctive glacial influences on extensional basin sedimentation thus supporting a causal relationship between thermal subsidence and the formation of glacier ice on inland areas during the precambrian however it is suggested that long lived marine terminated glaciers also situated at low paleolatitudes were related to an extensional tectonic setting in such settings glacial deposits associated with sedimentary sequences of distinctively different origin e g carbonate and chemically mature siliciclastic sequences can well be used to detect the prominent sequence boundaries to verify depositional systems tracts internal sediment stacking patterns in sequences are indicative of dynamic processes along glaciated continental margins and without always having the need for global synchroneity in glacially influenced rift basins and continental margins it is important to recognize the sequence boundaries of significant subaerial unconformities and their correlative conformities a sequence boundary is a chronostratigraphically significant surface always produced as a consequence of a change in relative sea level these can then be well related to initiation and decay of glaciations however on land glacial deposits in a very few cases are prevented from later erosion attenuation of continental crust during rifting and breakup of the continent raises relative sea level and also many of the shallow intra cratonic basins subsided below sea level in favourable conditions being affected by major continental glaciations paleoproterozoic and neoproterozoic glacial deposits are known in north and south america south africa india western australia and fennoscandia against this background continental scale to global glaciations in the precambrian appear to be possible however views on the causes and timing of these glaciations as well as on planetary extent of ice cover are still contradictory there is a need to continue detailed sedimentological studies of pre glacial and post glacial deposits as well as to interpret syn glacial lithofacies for their inferred transportation and depositional processes pre glacial deposits especially should provide a new target to help us understand the processes that initiated these precambrian glaciations the sequence stratigraphic approach with understanding of the stacking pattern of depositional systems could prevent oversimplification and use of just single events to explain the complexity of evolution of glacially influenced precambrian continental margin sediments

are some tillites impact related debris flow deposits abstracta number of ancient glacial deposits or tillites are currently interpreted as originating by subaqueous debris flow processes at glacial termini problems in identifying the glacial origin of such deposits can arise because some criteria commonly used for establishing glaciation especially outsize clasts interpreted as dropstones from icebergs can apparently be produced by nonglacial debris flows and debris falls could some of these debris flow diamictite deposits be related to large body impacts especially those that occurred at times other than established glacial periods debris flow ejecta of known impacts seem to be marked by mildly shocked clasts showing evidence of plastic behavior with brittle failure commonly resulting in multiple partially displaced fractures grading into crushed and brecciated clasts these deformation features entail brief periods of high confining pressures in accord with a hypervelocity impact origin i report here several debris flow diamictites currently

control of cambrian evaporites on fracturing in fault related anticlines in the zagros fold and thrust belt orientation and distribution of fractures in the oligocene early miocene asmari formation a major reservoir rock of the zagros petroleum system were investigated in two anticlines of the zagros fold and thrust belt the sim and kuh e asmari anticlines developed in the areas of the zagros characterized by the occurrence and absence of cambrian evaporites at the bottom of the stratigraphic pile respectively the aim was to outline major differences in terms of fracture spacing and saturation organic matter maturity and clay minerals based geothermometers suggest that the depth of deformation for the top of the asmari formation in the kuh e asmari anticline was in the range of 1 5 2 7 km assuming a geothermal gradient of 22 5 c km the asmari formation in the sim anticline probably experienced a slightly deeper sedimentary burial maximum 3 km with a geothermal gradient of 20 c km the spacing of fractures is generally 2 3 times larger i e strain accommodated by fracturing is smaller in the sim anticline than in the kuh e asmari anticline this is consistent with regional geological studies analogue and numerical models that suggest that thrust faults geometry and related folds are markedly different in the absence or presence of a weak decollement evaporites the larger spacing in the sim anticline is also consistent with higher temperature predicted for the asmari formation in this area by contrast the orientation of fractures with respect to the fold axes is the same in both anticlines the fracture systems are rather immature in both anticlines the amount and density of fractures in the twofolds are controlled by regional occurrence absence of salt and probably different burial rather than local features fold geometry

glacial influence on neoproterozoic sedimentation the smalfjord formation northern norway there is much debate regarding the intensity and geographic extent of glaciation during the neoproterozoic particularly in response to recent geochemical work suggesting that the neoproterozoic earth was at times ice covered from equator to poles the snowball earth hypothesis a detailed sedimentological analysis of the neoproterozoic smalfjord formation of northern norway was conducted in order to determine the extent and intensity of glacial influence on sedimentation in the tarmfjorden area the smalfjord formation consists of a stacked succession of diamictites interbedded with fine grained laminated mudstones containing rare outsized clasts diamictites and interbedded mudstones are interpreted as the product of subaqueous mass flows generated along the basin margin in the varangerfjorden area chaotically interbedded diamictites conglomerates and sandstones are overlain by a thick succession of stacked sandstone beds one diamictite unit at bigganjargga overlies a striated pavement the varangerfjorden outcrops appear to record deposition on a subaqueous debris apron although diamictites contain rare striated and faceted clasts suggesting a glacial sediment source their origin as subaqueous mass flows prevents the interpretation of ice mass form or distribution rare lonestones may be associated with floating ice in the basin which may be of glacial or seasonal origin glacial ice may have contributed poorly sorted glacial debris to the basin margin either directly or through fluvioglacial systems but there is no evidence of direct deposition by ice at varangerfjorden or tarmfjorden the overall fining upward trend identified in the smalfjord formation and overlying nyborg formation is consistent with depositional models of rift basin settings this fining upward trend the predominance of mass flow facies including breccias associated with scarps and the evidence for extensional tectonic activity in the region suggest that tectonic activity may have played an important role in the development of this neoproterozoic succession the smalfjord formation at tarmfjorden and varangerfjorden does not exhibit sedimentological characteristics consistent with severe glacial conditions suggested by the snowball earth hypothesis

subglacial deformation and water pressure cycles as a key for understanding ice stream dynamics evidence from the late ordovician succession of the djado basin niger subglacial deformation is crucial to reconstructing glacier dynamics sediments associated with the late ordovician ice sheet in the djado basin niger exhibit detailed structures of the subglacial shear zone three main types of subglacial shear zones ssz are discriminated the lowermost ssz developed on sandstones displays riedel macrostructures and cataclastic microstructures these resulted from brittle deformation associated with strong glacier bed coupling and low pore water pressure where they developed on a clay rich bed the overlying ssz display s c to s c fabrics sheath folds and dewatering structures these features indicate high ductile shear strain and water overpressure on fine grained sand beds the ssz exhibit homogenized sand units with sand stringers interpreted as fluidized sliding beds the succession of subglacial deformation processes depends on fluid pressure behavior in relation to subglacial sediment permeability fluid overpressure allows subglacial sediment shear strength and ice bed coupling to be lowered leading to ice streaming

salt flow by aggrading and prograding overburdens the mechanisms responsible for segmentation of salt sheets and their emplacement into higher stratigraphic levels are not separable and act simultaneously three sets of centrifuge models with strongly planar anisotropic anisotropy the ratio between the effective viscosities in pure and simple shear ranging between 4 8 and 16 4 microlaminate overburdens are used to study the effect of aggradation and progradation on segmentation and emplacement of allochthonous salt sheets in the first set of models a tabular buoyant source layer was overlain by tabular anisotropic overburden simulating aggradation during centrifuging the underlying ductile source layer was segmented into individual wall like diapirs by the subsiding blocks formed due to extension and faulting of the overburden the extensional zone in these models started at the spreading edge free face of the model and migrated backwards in the second set of models a tabular buoyant source layer was overlain successively by wedges of anisotropic overburdens simulating progradation during centrifuging the buoyant layer was displaced from the back of the model where loading was higher towards the free face in the front of the model where overburden units were thinner overburden units extended at the back and the middle of the model while contractional structures dominated at the front where asymmetric diapirs formed overhangs that spread basinward to form salt sheets in the third set of models a wedge shaped buoyant source layer was overlain successively by wedges of anisotropic overburden simulating progradation the overburden wedge created a lateral pressure gradient ranging from 144 pa at the back of the model to 80 pa at the front when deformed in the centrifuge in these models as in the second set of models the underlying buoyant mass was displaced basinward by the subsiding thicker overburden units at the back of the model contractional structures dominated the deformation at the leading edge of the wedge comparison of model results suggests that progradation as in the second and third sets of models loads underlying salt differentially displaces it downdip and segments it as it segments at the back the salt flows laterally to areas of lower loading by intruding through the thinner overburden units and forming secondary salt sheets at the front on the other hand aggradation of uniform overburden segments a buoyant sheet into two dimensional salt walls or stocks as in the first set of models

contained reflected turbidity currents from the middle ordovician cloridorme formation quebec canada an alternative to the antidune hypothesis the parautochthonous cloridorme formation is a syn orogenic flysch succession that was deposited in an elongate foredeep basin as mainly lower middle fan outer fan and basin floor deposits the basin floor deposits about 1 5 km thick are confined to members 1 2 and 1 and are characterized by graded thick 1 10 m mud rich calcareous greywacke beds previously interpreted as deposits of concentrated muddy unidirectional turbidity currents that locally generated backset antidune lamination in internally stratified flows the dominant flow directions were from east to west but west to east transport also occurred as seen in the orientation of ripples climbing ripples flutes consistently overturned flames and grain imbrication we believe that the flows that deposited these thick calcareous greywacke beds reversed by roughly 180 one or more times during deposition of the lower sandy part of the beds flow reversals are consistent with the sharp grain size breaks and mud partings within sandy divisions measurement of grain fabric relative to stratification in the most celebrated antidune bedforms indicates flow from west to east thus the bedforms were produced by west to east migration of megaripples not by the upcurrent migration of antidunes the thick muddy beds were deposited by large volume muddy flows that were deflected and reflected from the side slopes and internal topographic highs of a confined basin floor much like the contessa and similar beds of the italian apennines large quantities of suspended mud were ponded above the irregular basin floor and settled to produce the thick silty mudstone caps seen on each bed because of their mode of emplacement we propose that these beds be called contained turbidites

deformation style and controlling geodynamic processes at the eastern guadalquivir foreland basin southern spain the tectonic structure of the guadalquivir foreland basin becomes complex eastwards evolving from a single depocenter to a compartmented basin the deformation pattern within the eastern guadalquivir foreland basin has been characterized by combining seismic reflection profiles boreholes and structural field data to output a 3d model high dipping nne ssw to ne sw trending normal and reverse fault arrays deform the variscan basement of the basin these faults generally affect tortonian sediments which show syntectonic features sealed by the latest miocene units curved and s shaped fault traces are abundant and caused by the linkage of nearby fault segments during lateral fault propagation preexisting faults were reactivated either as normal or reverse faults depending on their position within the foreland at tortonian time reverse faults deformed the basin forebulge while normal faults predominated within the backbulge along strike variation of the betic foreland basin geometry is supported by an increasing mechanical coupling of the two plates alboran domain and variscan basement towards the eastern part of the cordillera thus subduction would have progressed in the western betics while it would have failed in the eastern one there the initially subducted iberian paleomargin nevado filabride complex was incorporated into the upper plate promoting the transmission of collision related compressional stresses into the foreland since the middle miocene nowadays compression is still active and produces low magnitude earthquakes likely linked to nne ssw to ne sw pre exiting faults reactivated with reverse oblique slip kinematics seismicity is mostly concentrated around fault tips that are frequently curved in overstepping zones