sediment dewatering and pore fluid migration along thrust faults in a foreland basin inferred from isotopic and elemental geochemical analyses eocene southern pyrenees spain abstract the lower eocene ainsa basin was formed during the first stages of the south pyrenean foreland basin evolution due to southwestward migration of imbricated thrust folds isotopic and elemental geochemistry of syn kinematic veins calcite and celestite and their marly host rock sampled in three thrust fault zones and one footwall syncline allows us to characterize the origin of pore fluids and the early stages of their evolution and circulation during the early deformation of the basin fill the isotopic composition of sulfur and the 87 sr 86 sr ratios of calcites and celestites from the veins in the footwall syncline show that the original fluid had the isotopic composition of eocene seawater the different 87 sr 86 sr ratio in veins from the thrust fault zones compared with the same ratio in the marly host rock of the footwall syncline indicates that the thrust fault zones acted as conduits for advective fluids the relatively high 87 sr 86 sr ratio in the veins related to the thrust fault zones indicates that the fluid originated from the interaction of seawater with an external fluid coming from deeper sources or from the meteoric weathering of the emerged part of the belt 18o and 13c values of calcites show that the isotopic composition of the calcite cements in veins was controlled by the isotopic composition of the marly host sediment depletion of both 18o and 13c with respect to eocene seawater composition together with elemental geochemistry of calcite cements in the veins points to burial transformations of a seawater derived fluid to a formation water composition the distribution of 18o and 13c values of the marly host rock and calcite cements in veins of the four outcrops probably resulted from differences in the meteoric water influences the hydrogeological regime at the toe of the submarine thrust system was dominated by tectonically induced dewatering of the foreland basin sediments the thrust fault zones were the channelizing paths for migration of fluids expelled from the surrounding sediments as well as fluids derived from more internal parts of the belt

ten million year history of a thrust sheet the final deformed state of a fold and thrust belt may be reached by an infinite number of kinematic paths two end member kinematic paths are due to continuous or discontinuous rates of deformation we have used a new magnetostratigraphic section from the spanish pyrenees to calibrate the emplacement history over 10 m y of a major thrust sheet the sierras marginales thrust sheet and the deformation of both its hanging wall and footwall six time windows from before 36 5 ma until after 24 7 ma were recognized on the basis of structural and stratigraphic relationships between syntectonic strata and major structures footwall deformation of the sierras marginales thrust sheet occurred continuously on a detachment within the foreland basin sequence 4 5 km net shortening shortening rates steadily increased from 0 14 to 1 5 mm yr with time although the detachments at the base of the foreland and the detachment at the base of the sierras marginales thrust sheet were active coevally the rate of displacement on the sierras marginales detachment decayed with time and shows considerable variability emplacement of the thrust sheet may be divided into three distinct periods a rapid 13 8 km translation from 37 0 to 36 5 ma 27 6 mm yr a gradual climb of the toe of the thrust sheet up a 4 3 km long ramp across the foreland basin succession from 36 5 to 32 0 ma 0 95 mm yr and a final 8 9 km translation from 32 0 to 29 5 ma 3 56 mm yr internal deformation of the thrust sheet occurred only after it reached its present position at some time before 29 5 ma shortening rates steadily decreased from 0 6 mm yr between 29 5 and 27 8 ma to 0 26 mm yr from 27 8 until after 24 7 ma only 1 km of shortening accumulated during each of the two periods the last shortening localized on the most northerly thrust in the study area folding and subsequent faulting above the detachment beneath the foreland suggest that slip was transmitted to its tip point continuously throughout the deformation in contrast translation followed by internal deformation on the hinterland side of the toe of the sierras marginales thrust sheet indicates a successive deactivation of the southern parts of the detachment with time rate of deformation on both detachments was discontinuous and shows substantial variability about the mean in general the spatial and temporal pattern of deformation was distributed and continuous in detail however shortening was spatially and temporally discontinuous above each detachment and structures related to each one display distinctly different deformational patterns rates and styles

widespread chemical remagnetization orogenic fluids or burial diagenesis of clays paleomagnetic rock magnetic and geochemical results from mesozoic carbonates in the vocontian trough in southeast france support a hypothesized acquisition of a chemical remanent magnetization crm during burial diagenesis of smectite and are inconsistent with an orogenic fluid remagnetization mechanism the geographic and vertical distribution of a widespread crm which resides in magnetite is parallel to the degree of burial diagenesis of clays the crm is absent only where there is no evidence for clay diagenesis the crm is poorly developed where significant smectite is still present and is well developed with higher natural and anhysteretic remanent intensities where smectite has completely altered to illite strontium isotope results do not support alteration by orogenic type fluids a commonly invoked mechanism for similar crms the results suggest that the burial diagenesis of clays is a viable remagnetization mechanism for limestones in the vocontian trough

synfolding remagnetization and deformation results from palaeozoic sedimentary rocks in west virginia summary palaeomagnetic analysis was conducted at 27 sites from two stratigraphically adjacent palaeozoic units along two transects meldey and rig of the patterson creek anticline in the appalachian orogen of west virginia to better understand the relationship between deformation and remagnetization while no primary directions were observed we isolated identical well defined secondary late palaeozoic magnetizations in carbonates from the late silurian tonoloway formation and the early devonian helderberg group standard application of conventional palaeomagnetic fold tests suggests that the magnetizations are synfolding in the helderberg group and pre folding to early synfolding in the tonoloway formation a fold test on all data combined indicates a synfolding magnetization best grouping at 60 65 per cent unfolding but the resulting distributions are not circular an alternative interpretation based on optimal differential unfolding at the site mean level yields one group with a nearly pre folding or early synfolding magnetization 70 per cent unfolding that is both circular and concordant with north america s apparent polar wander path the second group has a variable synfolding magnetization that is elliptical at the optimum unfolding level and falls off the path differences in either the age of remagnetization or viscous partial thermoremanent magnetization contamination cannot account for this result the sites falling into the pre folding group are biased towards the tonoloway formation the medley transect the northwest limb away from small folds and lower dip angle relative to the sites in the synfolding group the two groups defined by the fold test results also have a relationship with both total strain and strain partitioning the rocks containing the early synfolding remanence exhibit less total strain and in particular less pressure solution strain relative to grain boundary sliding and calcite twinning it is likely that the remagnetization in the entire area was coincident and occurred prior to folding even though some sites reveal synfolding directions the variation in the behaviour of the remagnetization relative to folding is unclear at present but it indicates that pressure solution and stylolite formation are important processes in remagnetization in any event the relationship between deformation and magnetization is not simple apparently identical magnetizations from adjacent sites may have very different histories and or responses to deformation while the exact relationship between remagnetization and deformation remains elusive this study demonstrates that significant variation in behaviour can exist at a very local scale

diagenetic sources of stable remanence in remagnetized paleozoic cratonic carbonates a rock magnetic study hysteresis measurements lowrie fuller tests cisowski tests and low temperature demagnetization experiments on samples of the knox dolomite trenton limestone and onondaga limestone indicate that the remanence in these remagnetized carbonate units resides principally in single domain magnetite in contrast to previous interpretations volumetrically however a significant fraction of the magnetite is coarser grained as previous scanning electron microscopic work on magnetic extracts has shown these conclusions are based mainly on the characteristic wasp waisted shape of the hysteresis loops and on the anomalously high ratios of remanent coercivity to bulk coercivity both of which clearly indicate a bimodal distribution of coercivities grain sizes the magnetization is controlled mainly by cubic magnetocrystalline anisotropy consistent with the spheroidal particles commonly observed in extracts hysteresis trends show that especially the finest particles lack shape anisotropy in view of these conclusions the two components of natural remanence in these rocks are interpreted as 1 a late paleozoic kiaman chemical remanence carried by single domain diagenetic magnetite and 2 a cenozoic thermoviscous overprint residing principally in coarser pseudosingle domain and multidomain magnetite also of late paleozoic diagenetic origin

multidisciplinary approach to constrain kinematics of fault zones at shallow depths a case study from the cameros demanda thrust north spain thrusting at shallow depths often precludes analysis by means of structural indicators effective in other geological contexts e g mylonites sheath folds shear bands in this paper a combination of techniques including structural analysis magnetic methods as anisotropy of magnetic susceptibility and paleomagnetism and paleothermometry is used to define thrusting conditions deformation and transport directions in the cameros demanda thrust north spain three outcrops were analyzed along this intraplate large scale major structure having 150 km of outcropping length 30 km of maximum horizontal displacement and 5 km of vertical throw results obtained by means of the different techniques are compared with data derived from cross sections and stratigraphic analysis mixed layer illite smectite and vitrinite reflectance indicating deep diagenetic conditions and mature stage of hydrocarbon generation suggests shallow depths during deformation thus confirming that the protolith for most of the fault rocks is the footwall of the main thrust kinematic indicators foliation s c structures and slickenside striations indicate altogether a dominant nnw movement of the hanging wall in the western zone and ne in the eastern zone of the thrust thus implying strain partitioning between different branches of the main thrust the study of ams in fault rocks nearly 400 samples of fault gouge breccia and microbreccia indicates that the strike of magnetic foliation is oblique to the transport direction and that the magnetic lineation parallelizes the projection of the transport direction onto the k max k int plane in sites with strong shear deformation paleomagnetism applied to fault rocks indicates the existence of remagnetizations linked to thrusting in spite of the shallow depth for deformation and a strong deformation or scattering of the magnetic remanence vectors in the fault zone the application of the described techniques and consistency of results indicate that the proposed multidisciplinary approach is useful when dealing with thrusts at shallow crustal levels

cleavage development within a foreland fold and thrust belt southern pyrenees spain abstract in the southern pyrenees lithologically distinct cleavage fronts are each parallel to bedding and dip 20 towards the foreland pressure solution was the dominant mechanism of cleavage development the mudstone cleavage front is coincident with the 195 c paleoisotherm and is associated with a pressure solution strain of 5 a mechanical twin strain of 4 and a deviatoric stress magnitude of 65 mpa illite crystallinity measurements define a geothermal gradient of 15 c km 1 and indicate that the paleoisotherms are bedding parallel deviatoric stress magnitudes from calcite twins were regionally constant at 65 mpa and principal stress axes were perpendicular to cleavage temperature was the primary control on deformation micromechanisms and the position and orientation of the cleavage front within the foreland thrust wedge deformation below the cleavage front occurs predominantly by pressure solution which in conjunction with mechanical twinning and microfracturing produces a quasi plastic rheology stress magnitudes determined from mechanical twinning of carbonate grains and long term 10 6 10 76 y strain rates determined for regional folds and faults suggest an apparent macroscopic viscosity of 9 8 10 18 to 7 2 10 19 pa s for the lower thrust wedge above the cleavage front temperature pressure solution strain total strain and mesoscale deformation diminish the region of the thrust wedge above the 100 c paleoisotherm is characterized by large brittle faults with cataclastic fault zones and negligible grain scale deformation indicating an elastico frictional rheology

an integrated paleomagnetic rock magnetic and geochemical study of the marcellus shale in the valley and ridge province in pennsylvania and west virginia an integrated paleomagnetic rock magnetic and diagenetic study of the devonian marcellus subgroup from threefolds in the valley and ridge province in pennsylvania and west virginia indicates that the unit contains an intermediate temperature chemical remanent magnetization crm with south southeast declinations and shallow negative inclinations residing in pyrrhotite and a crm with more southerly declinations and shallow positive inclinations residing in magnetite rock magnetic results confirm the presence of pyrrhotite and magnetite tilt tests indicate that pyrrhotite and magnetite crms are syntilting to posttilting and paleopoles for both crms are similar and plot on the permian part of the apparent polar wander path for north america the marcellus subgroup has a complex paragenetic sequence which includes bitumen deposition and vein formation the magnetite and pyrrhotite crms formed in the permian probably due to burial diagenetic processes and not orogenic fluids the base of the unit contains the highest total organic content toc values and highest magnetic intensities both of which decrease up section this connection between toc and magnetic intensity suggests that the magnetite formed as a result of the maturation of the organic matter although more work is needed to test this hypothesis the pyrrhotite may have formed as a result of thermochemical sulfate reduction involving organic matter during the production of methane in this gas reservoir the similar permian crm ages may be explained by thrusting which resulted in rapid burial of the marcellus subgroup as it passed through the oil window and into the gas window quickly producing magnetite and pyrrhotite respectively

fluid control of localized mineral domains in limestone pressure solution structures grain to grain and stylolitic solution structures in two central appalachian siluro devonian limestone macroscale folds contain one of four distinct mineral assemblages that are characterized by the dominant iron phase mineral present 1 chloritegillitegpyritegcalciteg quartzgtio2ggoethite 2 chloritegillitegpyrite altered to iron oxide hydroxidegcalcite gquartzgtio2 3 chloritegilliteg magnetitegcalcitegquartz and 4 chloritegilliteggoethitegcalcitegquartzgtio2 optical reflectance microscopy and sem eds was used to characterize the mineralogy and mineral morphology of these structures geochemical modeling was used to constrain the conditions of formation and preservation the primary control on solution structure mineral assemblage was the redox conditions present in the solution structures during burial and deformation the redox conditions on the microscale may have been controlled by the local fluid chemistry and the presence absence of hydrocarbons and organic acids within the formation fluids and the influx of externally derived fluids by fracture formation during the folding process the wide variation in mineralogy of the solution structures shows that they were chemical factories where a variety of chemical reactions took place during rock dissolution in particular the formation of authigenic magnetite in solution structures has significant implications for paleomagnetic applications and use of anisotropy of anhysteretic remanent magnetization and anisotropy of magnetic susceptibility fabrics q 2005 elsevier ltd all rights reserved

new and revisited paleomagnetic data from permian triassic red beds two kinematic domains in the west central pyrenees abstract new paleomagnetic results of permian triassic red beds from bielsa aure and somport anayet sectors in the pyrenean axial zone are presented and combined with revisited and reviewed paleomagnetic data from the west central pyrenees the paleomagnetic data from the red beds vary between different sectors that share similar structural position i e whilst all sectors share the existence of a characteristic prefolding component a cenozoic postfolding component is found only in one area but not in other areas with similar structural position and kinematics previous paleomagnetic data to the west of the studied zone reveal a pre turonian remagnetization component but this secondary component is not found in an area that shares a similar structural position aure this variability suggests that the paleomagnetic behavior is the result of a series of factors related to the particular tectonic history of the region sedimentation burial and deformation during basin inversion and therefore paleomagnetic data demands careful assessment in order to unravel the kinematics of areas with equivalent structural positions in orogens however important kinematic implications that hold in the pyrenees can be inferred from the restoration of the permian triassic characteristic magnetizations to positions previous to the paleomagnetic rotations recorded by cretaceous or cenozoic paleomagnetic data the restoration reveals on one hand the lack of large rotations in the south pyrenenan zone except in the nogueras area according to bates 1989 and on the other hand the contrasting rotations recorded to the west of the studied zone in the paleozoic basque massifs pbm and the south pyrenean zone indicating the existence of two different tectonic domains in the west central sector of the pyrenees the strong clockwise rotations postdating the early cretaceous remagnetization that are recorded in the pbm and in the north pyreneean zone suggest a late dextral shear deformation affecting areas near the north pyrenean fault zone

evolution of a turbiditic foreland basin and analogy with an accretionary prism example of the eocene south pyrenean basin the south pyrenean tertiary basin was an east west trending foreland trough which developed from early eocene to miocene times in a north south trending compressive regime a turbiditic series of lower and middle eocene age hecho group enables us to define the typical features of the tectono sedimentary evolution of the basin 1 slope and shelf derived carbonate turbidites and megaturbidites bear witness to the seismic activity of the basin borders 2 the southern basin border evidenced by the onlap of the turbidites onto slope and shelf deposits migrated progressively southwards in time and 3 the deformation pattern is characterized in the meso cenozoic sediments by a complex thrust fold system of thin skinned tectonics style its specific geometry and kinematics were influenced by the pre deformation geometry onlap this thrust fold system is related to south directed basement nappes and its front advanced progressively southwards in time from this data we infer an evolutionary model for this highly mobile basin it was a flexural basin linked to the northward bending of the lithosphere in the foreland of a south directed crustal accretionary prism as the nappes advanced the basin migrated progressively southwards in the foreland direction as for the actual basin evolution many analogies with accretionary prism trench systems of active margins exist

remagnetization of lower cretaceous limestones from the southern pyrenees and relation to the iberian plate geodynamic evolution paleomagnetic study 34 sites of thick cretaceous 5000 m marine carbonate strata from the organya basin ob in the southern pyrenees reveals a uniformly normal polarity characteristic remanence with varying declination d berriasian barremian d 295 o aptian albian d 348 o upper cretaceous d 354 o that resides in magnetite and predates late cretaceous tertiary folding the lack of reverse polarity magnetizations in the berriasian barremian series together with their distinct hysteresis properties that are typical of remagnetized carbonates elsewhere are taken as evidence for a secondary overprint in the lower part of the succession a hypothesized age of remagnetization near the barremian aptian boundary fits with a major tectosedimentary event in the basin that changed deposition from platform to basinal conditions and increased subsidence during the aptian the angular difference 53 o between declination from the remagnetized strata and the mean for aptian albian strata indicates that a counterclockwise rotation occurred between the two acquisition times part of this rotation is interpreted to be local and due to slip variation along strike of a normal fault that bounded the basin and tilted the pre aptian series this cretaceous extensive phase is framed in the rift evolution of the northern margin of the iberian plate the inferred remagnetization age within the ob falls within the range of previously inferred widespread cretaceous remagnetization events affecting the iberian plate in the ob remagnetization is speculated to have taken place through chemical burial diagenetic origin rather than simple thermoviscous resetting

conical folds and apparent rotations in paleomagnetism a case study in the southern pyrenees abstract the so called apparent rotation was defined as the angular deviation between a local paleomagnetic direction after the standard bedding correction and their corresponding paleomagnetic reference j geophys res 85 1980 3659 in this paper we make a theoretical exploration on this concept and we conclude that depending on the number sequence orientation and magnitude of the deformation axes that have affected to the rock volume the apparent rotation may be the addition of a vertical axis rotation plus a spurious rotation the later is an error whose origin is the inappropriate application of the bedding correction during the restoration which does not fit the reverse sequence of deformations then apparent rot s l spurious rot vertical axis rot conical folds are complex geometries that cannot be restored by using the bedding correction however appearance of apparent and spurious rotations has not been studied even though the presence of this kind of folds is very common in fold and thrust belts in this paper we show a way to restore these structures and its associated paleomagnetic data by means of forward modelling on a stereographic projection the modelling has to be based on a good characterization of the geometry fold axis orientation and understanding of the kinematics of the fold general modelling has also allowed us to predict the apparent rotation in conical synclines its magnitude depends on the semiapical angle and on the degree of development of the fold the sense of the rotation clockwise or counter clockwise will depend on the sense of rotation the fold axis the western external sierras provide an excellent case study of apparent rotations due to the presence of a conical fold in the footwall ebro foreland basin of the south pyrenean sole thrust in addition a vertical axis clockwise rotation up to 47 32 in average has been detected in the hagingwall an apparent rotation up to 28 20 in average is observed in the footwall of the structure when a simple bedding correction is used this deviation does not fit with the expected ebro basin direction reference and is caused by the effect of the riglos conical syncline developed by the flexure of the foot wall ramp of the south pyrenean sole thrust the forward modelling carried out considering the geometry and kinematics non significant rotations in the autochthonous foot wall of this structure predicts very well the paleomagnetic observations in the field geographic coordinates with angular departures of only 5 in average the only application of the bedding correction would introduce errors spurious rotations up to 21 12 in average related to the conical geometry that would not allow the differentiation of these distinct structural units

the chronology of the eocene tectonic and stratigraphic development of the eastern pyrenean foreland basin northeast spain abundant and clearly exposed relationships between structures and syntectonic sedimentary rocks in the southern pyrenees make this area particularly suitable for detailed studies of the sequential development of a collisional orogenic belt during the pyrenean orogeny major shortening occurred in the eastern pyrenees in eocene and early oligocene times until now individual tectonic and depositional events have been only loosely defined temporally by biostratigraphic data in order to provide a more precise chronological framework four new magnetostratigraphic sections spanning 8 km of eocene strata and encompassing 18 m y have been developed in the eastern pyrenees of northern spain the ages of nine major depositional sequences in the eastern pyrenean foreland have been specified within the context of these chronologic data beginning with the early eocene transgression that commenced at 58 ma the timing of numerous tectonic events that occurred during the subsequent 16 m y can also be delineated including the initial emplacement of the pedraforca thrust sheet 58 54 ma the development of the pedraforca breakback thrusts 47 5 40 ma at a mean shortening rate of 2 4 mm yr rotation of the pedraforca footwall three intervals of motion along the vallfogona thrust 42 5 44 0 40 5 41 5 and

triassic paleomagnetism from the western pyrenees revisited implications for the iberian eurasian mesozoic plate boundary since the pioneering studies of van der voo tectonophysics 7 1969 5 and van der voo and boessenkool j geophys res 78 1973 5118 paleomagnetism of permo triassic redbeds and volcanics from the western pyrenees has furnished important contributions for delineating the mesozoic boundary between the iberian and eurasian plates in this paper we present a new paleomagnetic study focussed on triassic red beds 23 sites of the paleozoic basque massifs pbm the aim of this study is to complement previous studies done in those massifs to better constrain the complex kinematics of the western pyrenees two stable magnetic components have been isolated 1 a dual polarity pre folding magnetisation carried by specular hematite and 2 a secondary normal polarity component also carried by hematite our data confirm both the origin and the rotation pattern of the primary remanence described in previous works nevertheless field tests performed on the secondary component do not confirm the earlier interpretations by schott and peres tectonophysics 156 1988 75 as they indicate a synfolding nature of the remagnetisation instead of a post folding origin we consider that the secondary component is better explained if a cretaceous age is considered the presence of such remagnetisation in the western pyrenees strengthens the widespread occurrence of similar remagnetisation events reported in northern iberia in connection with the extensional tectonic events that occurred during cretaceous times a comparison of the rotations recorded by the triassic component and by the remagnetisation indicate that the paleozoic units underwent variable tectonic rotations before the remagnetisation was acquired most likely in connection with the counterclockwise rotation of iberia with respect to eurasia these results favour that the mesozoic plate boundary between the iberian and eurasian plates was a wide domain of distributed deformation and therefore contradict previous interpretations claiming for a discrete plate boundary

evaluation of paleomagnetic and finite strain relationships due to the alleghanian orogeny in the mississippian mauch chunk formation pennsylvania 1 three localities of the mississippian mauch chunk formation around the pennsylvania salient broad top synclinorium minersville syncline and a sublocality in the minersville syncline were sampled for detailed paleomagnetic and strain analysis paleomagnetic analysis showed three magnetization components an intermediate temperature b component t b 620 c and an sw component unblocked over a wide range of temperatures and observed only on the northern segment of the salient normalized fry strain and r f strain were measured in three dimensions and correlated to the paleomagnetic results at one site jtsf locality a clear correlation between the amount of strain e s and remanence direction indicates that axial planar cleavage formation has caused remanence rotation the correlations at the minersville syncline and broad top synclinorium are not definitive but suggest that different mechanisms are operating the observed heterogeneity in paleomagnetic response to strain indicates that the effects will be strongly dependent on the strain history at a particular site

fluid mixing and recycling during pyrenean thrusting evidence from fluid inclusion halogen ratios abstract syntectonic fluids have been sampled through fluid inclusion microthermometry and crush leach analyses cations and halogens from a 50 km n s transect through the central southern pyrenees the fluid inclusions are contained in syntectonic quartz veins in triassic redbeds cretaceous carbonates and hercynian basement rocks with some calcite and dolomite data from limestones and evaporites in more external parts of the belt the main datasets come from 1 alpine shear zones cutting the neouvielle granodiorite in the hercynian axial zone at the north end of the transect 2 an imbricate zone beneath the alpine gavarnie thrust at the pic de port vieux 3 several localities in the footwall and hangingwall of the gavarnie thrust on the southern margin of the axial zone the inclusion fluids generally decrease in salinity from 27 35 at the northern end of the transect to 7 22 on the southern margin of the axial zone the majority of the inclusions have cl br ratios lower than seawater and are interpreted as relict fluids after seawater evaporation and halite precipitation in the upper trias this interpretation is supported by cl br na systematics which are consistent with a change from halite to halite sylvite precipitation with progressive evaporation fluids in the basement shear zones are interpreted to have essentially the same evaporitic origin as those still contained in sedimentary formations although it is possible that final concentration of brines in the neouvielle massif involved retrograde hydration reactions with removal of water by precipitation of hydrous minerals the fluids are also very similar in salinity and halogen chemistry to those found in veins associated with mesozoic pb zn f deposits which predate the thrusting the lower salinities seen at the southern margin of the axial zone are interpreted to reflect mixing of the brines with a higher level fluid connate or meteoric water circulating within the mesozoic carbonates of the higher thrust sheets at one locality where triassic evaporites are still present high cl br ratios at relatively low salinities are present in inclusions within the underlying triassic redbeds but low cl br ratios at higher salinities are seen lower in the sequence this is consistent with dissolution of halite by a dilute fluid but with limited penetration downwards we suggest that the fluid history of the pyrenees evolved through a series of stages 1 upper triassic evaporite formation with sinking of brines into underlying redbeds and fractured basement rocks 2 circulation of brines with formation of pb zn deposits along faults at some time between the triassic and the upper cretaceous 3 renewed extension with erosion of triassic rocks in many areas and further drawing down of triassic brines into the basement 4 deposition of u cretaceous and palaeocene carbonates containing connate waters of marine origin 5 formation of the pyrenean thrust belt with overpressuring and expulsion of the brines along shear zones and faults 6 creation of topography with a high level circulation system in the mesozoic thrust sheets driven largely by topography at the southern margin of the axial zone there was limited mixing of the deeper overpressured brines with these more dilute hydrostatically pressured fluids an important point is that because of their density hypersaline brines are difficult to expel from the upper crust and may be involved in a succession of alteration and mineralisation events in the same general area over hundreds of millions of years

shallow water carbonates record marginal to open ocean quaternary paleoceanographic evolution 1 the oxygen and carbon isotopic composition of shallow water carbonates and their fossil components can be important tools for understanding quaternary paleoceanographic conditions of marginal seas including coral reef regions however most previous paleoceanographic studies using isotopes have been based on pelagic or hemipelagic sediments because the original 1 8 o and 1 3 c values of shallow water carbonates are normally altered by postdepositional diagenesis this study shows that marginal to open ocean isotopic signals can be preserved in carefully cleaned low mg calcitic planktic foraminifers of shallow water carbonates even when the isotopic values of the carbonate host rock have been altered by meteoric fluids and subaerial exposure the two studied core sections were collected from the mid quaternary ryukyu group southwestern japan which consists mainly of bioclastic grainstone packstone rhodolith floatstone rudstone and large foraminiferal floatstone corresponding to open shelf to shelf slope facies from the southwest ryukyu islands japan down core 1 8 o records of planktic foraminifers in the ryukyu group imply that sea surface temperatures sst in the northwestern pacific increased 2 0 c at the beginning of oxygen isotope stage 19 post mid pleistocene revolution mpr this warming may have triggered the expansion of reef complex deposits as large as those now in the ryukyu islands and was approximately coeval with the lower section of the australian great barrier reef sst warming due to the expansion of the western pacific warm pool wpwp toward the north and south subtropical regions is a possible mechanism for reef expansion and initiation of the coral reefs of the western pacific region

the occurrence and origin of late paleozoic remagnetization in the sedimentary rocks of north america although it has been known for 25 years that some paleozoic sedimentary rock units in europe and north america were remagnetized during pennsylvanian or permian time it is only very recently that the complex and widespread nature of the late paleozoic remagnetization phenomenon has been generally acknowledged it is now recognized that many paleozoic paleomagnetic poles for north america that were once considered reliable are in fact the result of remagnetization and as a consequence the paleomagnetic data base for the paleozoic is undergoing rapid and drastic revision the causes of late paleozoic remagnetization in north america are currently the focus of much interest and active research the remagnetization can reside in either hematite or magnetite and different remagnetization mechanisms have been important in different settings chemical remagnetization processes some related to specific diagenetic events are dominant in hematite bearing sandstones and carbonates in magnetite bearing carbonates both chemical and thermoviscous remagnetization processes appear to have been important but it is difficult to determine which process is the dominant one in some settings some of the observed remagnetizations can be linked to the migration of chemically active and perhaps hot fluids during the mountain building events that affected much of the continent during the late paleozoic paleomagnetic studies promise to be important in assessing the role of orogeny in driving fluid migrations within sedimentary basins and in constraining the age of the migrations and the nature of the fluids

rotation velocity of a thrust a paleomagnetic study in the external sierras southern pyrenees abstract an accurate calibration of chronologic and geologic data biostratigraphic and magnetostratigraphic with gpts has been performed for the middle and upper eocene syntectonic deposits in the surrounding areas of the pico del aguila anticline south pyrenean external sierras this calibration shows a variable sedimentation rate that changes from 4 8 cm ka at the bottom to 34 cm ka at the top with a maximum of 58 6 cm ka in the upper part of the studied stratigraphic section and gives a fine and continuous chronologic frame to understand the rotational kinematics of the infrajacent thrust system at the same time a detailed paleomagnetic study has been carried out 14 sites and a total of 157 thermally demagnetised samples to know the amount of rotation in the area taking advantage the tape recording effect of the syntectonic materials these samples display a chrm between 250 and 400 c both polarities that agree very well with the sequence of magnetostratigraphic zones and consistency with the magnetic reference due to the decreasing value of the magnetic declination from 46 to 3 of the primary components checked by fold and reversal test the calibration has been useful to assign an absolute age to every rotation value from 40 32 to 37 05 ma a time versus rotation curve does not show significant differences of rotation between the flanks of the pico del aguila anticline less than 8 thus the clockwise rotations detected in the study area result from the kinematics of the imbricate basal thrust system which is also responsible for the development of detachment folds e g pico del aguila anticline in a time against rotation graph the simplest fit for the overall rotation values is given by a linear segment rotation velocity of 10 ma however the best fit is given by a segment of a parabolic curve this pattern implies that there were changes of the rotation velocities between 21 ma and 5 3 ma that in this segment of the external sierras were caused by an acceleration of the rotational movement between 9 ma2 and 5 5 ma2 the thrust sheet shows maximum values of at least 40 of clockwise rotation

magnetite dissolution and neocrystallization during cleavage formation paleomagnetic study of the martinsburg formation lehigh gap pennsylvania paleomagnetic study of the shale to slate transition in the ordovician martinsburg formation at lehigh gap pennsylvania reveals that the remanence of the relatively undeformed shales predates cleavage formation and that the slates were remagnetized during cleavage development the shales display two components of remanence component 1 c1 was the only magnetization direction in the majority of the shales and the first removed component in 10 shale specimens component 2 c2 is observed as a single component remanence with a low 300 400 c unblocking temperature range in samples from one shale station and as a second removed component in 10 shale specimens the mean directions are declination inclination 347 04 346 47 in situ tilt corrected for c1 and 80 63 135 40 for c2 the pencil slates and well cleaved slates both display single component remanences the mean directions are 198 12 201 26 for the pencil slates and 199 24 225 54 for the well cleaved slates using the relationship between cleavage development and remagnetization in the slates the timing of cleavage development and folding and the regional geology we can constrain the relative ages of the remanences as follows 1 the shale c1 direction is most likely prefolding and represents a primary upper ordovician direction 2 the slate directions are younger in age than the shale directions and are probably of permo carboniferous alleghenian age these results show that remagnetization occurred during development of slaty cleavage in these rocks we interpret the mechanism for this remagnetization to have been strain induced dissolution and neocrystallization of magnetite the additional difference in the characteristic directions of the pencil slates and well cleaved slates may be attributed to strain reorientation of the pencil slate remanence after new growth of magnetite the unknown temporal relationship between dissolution and neocrystallization and strain precludes any quantitative attempt to correct remanence for strain in these samples our study shows that paleomagnetic studies of deformed sediments must consider the possibility of dissolution and neocrystallization of remanence carriers in addition to strain induced rotation

magnetic reorientation induced by pressure solution a potential mechanism for orogenic scale remagnetizations abstract new paleomagnetic analyses of triassic cretaceous and eocene strata in the south central pyrenees show evidence for a widespread remagnetization located along the southern border of the axial zone the internal sierras and the northern part of the jaca pamplona basin this remagnetization always reversed in polarity was acquired after an extensive period of late eocene early oligocene folding and tilting in the area and affects limestones sandstones marls and red beds in addition a characteristic prefolding component was identified in 30 of upper cretaceous and triassic red beds these results together with a revaluation of previously published paleomagnetic data from the central pyrenees indicate that the spatial distribution of the postfolding remagnetization coincides with that of a domain of pressure solution cleavage a relationship between the intensity of the remagnetization and the characteristic prefolding component with respect to the density of cleavage surfaces leads us to propose a mechanism for the remagnetization related to the development of pressure solution cleavage that is framed within the tectonic evolution of the central pyrenees partial dissolution of rock under tectonic compression leads to the liberation and subsequent accumulation of insoluble minerals in cleavage planes magnetic grains are part of the relatively insoluble residue and they reorient in the presence of the ambient field after they are freed during dissolution of the rock matrix chemical reequilibrium dissolution and or neoformation of magnetic carriers during this process cannot be excluded the remagnetization mechanism we propose can help to explain widespread remagnetizations in low to moderately deformed rocks without the need of large scale migration of orogenic fluids

paleomagnetic structural and stratigraphic constraints on transverse fault kinematics during basin inversion the pamplona fault pyrenees north spain 1 the pamplona fault in the pyrenees is a major transverse structure that has been classically interpreted as a strike slip fault however lack of consensus concerning the sense of movement casts doubt on its actual kinematics and as a consequence its role in the cenozoic evolution of the pyrenees remains controversial in order to assess its kinematics we have conducted a paleomagnetic structural and stratigraphic study focused on the mesozoic and tertiary sedimentary rocks that outcrop around the southern segment of the fault restoration of balanced cross sections allows us to examine the present day spatial relationship of the sedimentary sequences on both sides of the fault and to reconstruct the geometry of the extensional basins formed during mesozoic rifting episodes in the bay of biscay and pyrenean domains paleomagnetic results indicate that no significant tectonic rotations occurred around the fault during tertiary inversion of the pyrenees the lack of tectonic rotations and revaluation of previous hypotheses argues against a strike slip movement of the fault we propose a new model in which the pamplona fault is treated as a large scale hanging wall drop fault whose kinematics was determined by variations in the geometry and thickness of mesozoic sequences on both sides of the fault these variations influenced the geometry of the thrust sheet developed during tertiary compression we are unaware of any other transverse fault that has been interpreted in this fashion thus the pamplona fault serves as a case study for the evolution of transverse faults involved in basin inversion processes

reanalysis of the cocorp deep seismic reflection profile across the san andreas fault parkfield california in 1977 cocorp recorded a short seismic reflection test line across the san andreas fault through parkfield california where the salinian crustal block is juxtaposed against a contrasting terrane of franciscan and overlying material although analysis of this seismic line has been limited by crooked geometry lack of cross lines complex terrain possible recording noise and perhaps most of all its short length gross crustal features are discernible after extensive reprocessing and reanalysis the salinian block southwest of the san andreas consists of a maximum of 2 km of relatively underformed sediments overlying a reflective and inhomogeneous basement which exhibits deep subhorizontal layering at 8 to 10 km depth density and amplitude of reflections markedly decay perhaps corresponding to the base of a salinian granitic crust which overlies franciscan or other contrasting material northeast of the san andreas subhorizontal reflections suggest that franciscan material may extend as deeply as 13 km below which is a nonreflective zone which might represent relict oceanic crust reflections from moho depths differ across the san andreas fault beneath the salinian block is a thick zone of reflections beginning at about 22 km depth while less layered and weaker reflections seem to define the moho discontinuity at 29 km beneath the franciscan terrane the san andreas fault zone appears to be traceable as a distinct feature on the reflection section throughout the entire crust forming a near vertical zone about 3 km wide in the seismogenic upper crust down to 15 km the fault zone is marked by sharp structural truncations and short reflection or diffraction segments at depth it seems to be distinguished by a nonreflective column this vertical change in reflection character may correspond to the transition from a brittle to a ductile deformation regime

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget