palaeoseismology review of the state of the art abstract historical seismicity provides only a partial indication of the seismotectonic character i e earthquake potential of a given region even in italy where a relatively long historical record exists available catalogues are generally unsatisfactory for this purpose fortunately strong earthquakes often leave geological evidence herein referred to as seismites that are mainly related to surface faulting folding or other deformation and occasionally to secondary ground failures e g landslides liquefaction features etc these features may be preserved and therefore palaeoseismological studies may detect and date them thereby permitting extension of knowledge beyond the local historical threshold up to 2000 years in the most fortunate cases this paper provides a summary of criteria which may aid in the identification of areas suitable for palaeo earthquake investigation historical seismicity and the presence of well developed tectonic geomorphic features are recognized as the most reliable criteria for identifying active faulting however lack of these characteristics cannot be considered conclusive evidence for lack of activity palaeoseismological techniques aim at identifying not only the obvious effects of surface faulting such as offset of young geologic units but also the more subtle tectonic or non tectonic features including liquefaction structures gravity features and coseismic uplift and or subsidence finally we discuss some questions that pertain to palaeoseismicity evaluation techniques among these are the reliability of the quaternary dating techniques the evaluation of the seismic energy released minimum magnitude and principally the unequivocal identification of a seismic origin for the considered geological structures

sedimentary structures tentatively attributed to seismic events abstract fingerprints of earthquakes in the sedimentary record are as yet difficult to identify this is particularly true for failure phenomena dewatering slumping fault graded and turbidite structures that could have been triggered also by other kinds of energy input other promising candidates are strange biostratinomic features convex down stacking of shells current orientation in wave ripple accumulations as well as certain preservational features found in geosynclinal pelagic limestones but in every case verification of the seismic origin is still needed

magnetic fabrics and fluid flow directions in hydrothermal systems a case study in the chaillac ba f fe deposits france this study presents a possible use of anisotropy of magnetic susceptibility ams to describe the mineralizing process in hydrothermal systems ba f fe rich deposits within the chaillac basin are on the southern border of the paris basin in these deposits hydrothermal textures and tectonic structures have been described in veins sinters and sandstone cemented by hydrothermal goethite 278 oriented cores from 24 sites have been collected in these formations in addition a lateritic duricrust superimposed on the hydrothermal formation has been sampled rock magnetic investigations show that the principal magnetic carrier is goethite for the hydrothermal mineralization and for the laterite level the ams measurements show distinguishable behaviors in the different mineralogical and geological contexts the k1 magnetic lineation maximum axis is strongly inclined for the vertical veins for the horizontally mineralized sinters the magnetic lineation is almost horizontal with an azimuth similar to the sedimentary flow direction the ams of goethite rich sandstone close to the veins shows strongly inclined k1 as they are probably influenced by the vertical veins however when the distance from the vein is larger than 1 m the ams presents rather horizontal k1 directions parallel to the sedimentary flow the laterite has a foliation dominance of ams with vertically well grouped k3 axes and scattered k1 and k2 axes field structural observations suggest that the ore deposit is mainly controlled by ew extension tectonics associated with ns trending normal faults combining the ams results on the deposit with vein textures and field data a model is proposed in which ams results are interpreted in terms of hydrothermal fluid flow this work opens a new investigation field to constrain hydrodynamic models using the ams method textural study combined with efficient ams fabric measurements should be used for systematic investigation to trace flow direction in fissures and in sand porosity

plate and intraplate processes of hercynian europe during the late paleozoic abstract it is speculated that until late carboniferous time the region of hercynian europe was occupied by an elongated island arc system underlain by a segment of continental crust in the upper carboniferous two subduction zones are assumed to have extended from the north and south beneath hercynian europe an extensive zone of hot partially molten upper mantle lay above and between these and diapiric uprise of portions of this material led to separation of mafic magmas widespread partial melting in the lower and middle crust high temperature low pressure metamorphism in crustal rocks and regional uplift and extension of the crust as indicated by intermontane troughs and their associated volcanic rocks in visean to westphalian time hercynian europe collided with both the large neighbouring plates north america europe and africa during these diachronous collisions and owing to reduced rigidity of the relatively hot island arc crust the irregular continental margins of the larger and thicker continental plates induced oroclinal bending of hercynian europe after the collision processes had been terminated processes of upper mantle activity continued causing further crustal uplift and even enhanced crustal extension for several tens of million years into the lower permian decline of the upper mantle activity beneath hercynian europe is indicated by crustal subsidence and formation of a peneplain in permian time followed by the upper permian transgression of both the zechstein sea and the tethys sea which mark the end of the hercynian geodynamic cycle

geochemistry tectonomagmatic origin and chemical correlation of altered carboniferous permian fallout ash tuffs in southwestern germany thin but laterally widespread fallout ash tuff layers interbedded with complex fluvio lacustrine successions of the carboniferous permian late variscan intermontane saar nahe basin in southwestern germany provide important tephrostratigraphic markers in the purely continental depositional setting the tuffs are rhyolitic to rhyodacitic and indicate geochemical affinities to moldanubian variscan s type granitoids the volcanic ashes are suggested to have been derived from the general region of the central and northern black forest southwestern germany and the northern vosges eastern france at 100 150 km distance south of the saar nahe basin six tuff beds from the jeckenbach and odernheim subformations meisenheim formation glan group have been correlated within the basin over a distance of 50 km by mapping and whole rock geochemical fingerprinting in each subformation three tuffs can be well distinguished using geochemical discriminant function analysis additional comparisons of trace and rare earth element contents provide further criteria for the differentiation of individual tuff beds these discriminations show that the tuffs have unique chemical fingerprints probably reflecting differences in the original composition of the parent volcanic tephra thus chemical differences between the tephrostratigraphic markers are geologically significant and provide a powerful tool for establishing tuff layer identification and correlation within the complex sedimentary sequence of the saar nahe basin they also provide clues to the tectonomagmatic settings of the source volcanoes

volcanic rocks as discriminants in evaluating tectonic versus climatic control on depositional sequences permo carboniferous continental saar nahe basin the third and fourth order sequential arrangement of continental sedimentary strata in the permo carboniferous saar nahe basin preserves a detailed record of contemporaneous faulting and volcanism transgressive lacustrine facies of the upper carboniferous coincide with the stratigraphic position of extrabasinally derived pyroclastic fallout layers and features of synsedimentary tectonism such as unconformities thickness and facies changes across faults and seismogenic deformation structures the tectonic imprint on fourth order cycle initiation is further documented by abrupt vertical facies transitions during lake transgression implying rapid and episodic rather than gradual basin subsidence this interaction becomes much more pronounced within the fluvially dominated lower permian when tectonism controlled both the ascent of large volumes of magma within the basin as well as episodic enlargement of accommodation space and depositional area major extrusive volcanic units are preferentially associated with sequences recording transgression that are only preserved in fault bounded hanging wall traps starved from clastic sediment input it is suggested that the stratigraphic position of pyroclastic fallout within the sequential framework of basins elsewhere provides an important analytical tool for the identification of contemporaneous tectonic events and as such form a discriminant between purely climatically induced milankovitch band cycles versus those involving a tectonic control

coalification pattern and thermal modelling of the permo carboniferous saar basin sw germany abstract palaeo heat flow values and thicknesses of eroded permo carboniferous sediments in the saar basin were evaluated using one dimensional thermal modelling techniques thermal burial and erosion histories for 16 wells were calibrated by comparing measured and calculated vitrinite reflectance using the kinetic easy r o algorithm and by comparing measured and calculated temperature data on the basis of 37 wells coalification maps were constructed revealing a syn kinematic coalification pattern thermal maturity of the sediments can only be explained by deep burial and moderate heat flows during time of maximum burial i e in the permo carboniferous calculated heat flow data range between 50 and 75 mw m 2 which implies a crustal thickness between 30 and 40 km during the time of maximum burial these values are in accordance with the geodynamic setting of the basin the influence of the permo carboniferous volcanism on the palaeo temperature distribution was overwhelmed by the subsequent deep burial during permian times between 1800 and 3000 m of permo carboniferous sediments were eroded different sedimentation and erosion histories are characteristic for anticlines and synclines respectively

on the reactivation of extensional fault systems in terranes that have undergone substantial extension three sets of faults dominate a shallow to steep dipping commonly rotational normal faults b a really extensive shallow dipping normal detachment faults and c steep dipping transfer faults that strike at high angles to the normal faults these fault systems may extend through a large fraction of the crust reactivation of these fault systems will depend primarily on the relative strengths of the faults shear zones and their host rock and their orientation in the prevailing stress field it is concluded that reactivation is generally mechanically favoured but that it will probably only take place when the fault shear zones are in near ideal orientations consideration of the tectonic setting of extended terranes and of the limited number of well described examples suggests that reverse thrust reactivation of the normal and detachment faults and wrench reactivation of transfer faults are the most likely styles examples of these styles are described from the bass strait basins of southeastern australia because extended terranes commonly underlie sedimentary basins for example on passive continental margins reactivation of extensional faults may be a key control on the tectonic evolution of such basins i e basin inversion

kinematic significance of sediment filled fissures in the north mountain basalt fundy rift basin nova scotia canada abstract numerous sediment filled fissures are present near the upper surface of the north mountain basalt 202 ma of the fundy basin which formed during triassic jurassic rifting the fissures are infilled with the same clastic material comprising the basal parts of the overlying earliest jurassic age sedimentary formations which accumulated less than 200 k y after the cooling of the basalt nearly all of the 1368 fissures measured in this study are planar to sub planar and are sub vertical after correcting the basalt flows to paleo horizontal the fissures typically formed along preexisting columnar joints within the basalt northeast striking fissures generally define a preferred orientation and commonly are wider than other fissures the sediment filled fissures therefore indicate earliest jurassic age nw se extension this extension direction is consistent with that indicated by the ne striking shelburne diabase dike the attitude of mesoscopic faults and the geometry of the fundy rift basin thus sediment filled fissures by themselves can serve as useful kinematic indicators and place tight constraints on the relative timing of extension

geological interpretation of dekorp deep seismic reflection profiles 1c and 9n across the variscan saar nahe basin southwest germany abstract deep seismic reflection results across the variscan saar nahe basin in southwest germany recorded as parts of dekorp lines 1c and 9n provide excellent images of the geometry of the basin and also of the structures in the underlying basement this basement consists of several discrete units some of which are highly reflective whereas others are essentially non reflective two of these units consist of well layered dipping reflectors that are interpreted as having been telescoped by thrusting adjacent to the south hunsruck fault the sedimentary pile within the saar nahe basin is over 8 km thick but it thins dramatically towards the southeast and east the position of continuous reflectors both in the basin and the basement indicate that the south hunsruck fault is subvertical and not a listric normal fault as proposed in several earlier interpretations this implies that the basin did not form by normal extension but that it is transtensional in character its geometry predominantly being controlled by strike slip movements on the south hunsruck fault

geologic evidence for a large prehistoric earthquake in eastern connecticut postglacial wedges cutting stratified late quaternary glacial deposits have been widely reported throughout the northeastern us previous interpretations of these features as periglacial ice wedge casts have proved untenable for at least several of the reported localities this conclusion is also reached in the detailed study of 29 such wedges at a gravel quarry in eastern connecticut the wedges there are found to be planar vertical zones that widen upward from a few centimeters to as much as 150 cm and that contain material injected from below as well as collapsed from the sides these zones are interpreted as extension and collapse fissures that served as conduits for water and liquefied sediment during one or more prehistoric liquefaction events seismic excitation seems the most likely cause for the episode s of liquefaction and violent dewatering similar phenomena were reported to accompany large eighteenth century earthquakes in new england if the relation between large earthquakes and wedges is substantiated at their study locality and other localities these possibly contemporaneous features may provide an opportunity to determine the felt area magnitude of prehistoric earthquakes in the northeastern us 18 references 3 figures

deciphering the sedimentological imprint of paleoseismic events an example from the aptian codo formation northern brazil abstract a stratigraphic horizon bearing several styles of soft sediment structures occurs sandwiched within entirely undisturbed deposits in the lacustrine codo formation aptian located in the eastern part of the grajau basin northern brazil these deposits show a variety of sedimentary features distinguished according to their deformation style as follows from bottom to top a zone 1 consisting of widespread molar tooth structures i e fine grained spar filled cracks that are interconnected with small scale faults fissures and stylolites inclined at a high angle to bedding b zone 2 represented by complex convolute folds with lateral gradation of smooth synclines and anticlines into isoclinic folds and internal layers that retain the normal bedding features recumbent folds nappe folds with associated thrust faults pseudonodules and mound and sag structures c zone 3 consisting of normal faults and fissures that are vertical to near vertical show ragged morphology with small delicate peaks taper both downward and upward after a few centimeters and are associated with large up to 2 5 m long collapsed boulders and d zone 4 characterized by shales with irregular convolute folds these deformation zones are interpreted to reflect sediment rheology and alternating periods of sediment accumulation and deformation under the influence of synsedimentary seismic events as suggested mostly by 1 occurrence between undeformed deposits 2 lateral correlation for several kilometers of distance 3 similarity with other features formed in areas affected by seismic activity 4 presence of structures attesting to sediment deformation in an unconsolidated to semi consolidated state and 5 complex association of brittle and ductile deformation structures hence zone 1 records small scale cracking and faulting of early cemented cohesive deposits zone 2 is dominated by ductile deformation structures formed on water saturated unconsolidated sediments probably as a reflex of compressional stress zone 3 records a change in tectonic style to dominantly distension as evidenced by the horizon with normal faults finally zone 4 shows structures attributed to ductile deformation of water saturated muds which was probably formed during the same episode of deformation responsible for the faults and fissures in zone 3 this succession of deformation events appears to be consistent with transtensional and compressional shear stresses during the sedimentary evolution of the grajau basin

paleo earthquakes in passive margin settings an example from the paleocene of the golfo san jorge basin argentina abstract paleocene sedimentary rocks in the golfo san jorge basin include the marine salamanca formation and the continental rio chico formation both units contain soft sediment deformation features and evidence of contemporary tectonics which include 1 sediment filled fissures hosted in muddy marine sediments of the salamanca formation fragmentosa section where the sandy infill of the fissures took place from above 2 synsedimentary normal faults in the uppermost levels of the salamanca formation with vertical throws rarely exceeding 1 m 3 fault graded beds in the banco negro inferior marine continental transition which show a deformed sequence with small scale normal faults at the bottom and intraformational breccias on top and 4 liquefaction and or fluidization pillars v or funnel shaped with vertical extension of up to 5 m and preserved into fluvial channels of the rio chico formation deformed strata are bounded by undisturbed horizons and some of these features can be correlated along 60 km of exposures the suite of soft sediment deformation structures is considered a secondary evidence of synsedimentary paleo earthquakes seismites in this portion of the south american passive margin this work shows new evidence of syndepositional tectonic activity in the lowermost paleogene of the golfo san jorge basin

late paleozoic volcanism in the central part of the southern permian basin ne germany w poland facies distribution and volcano topographic hiati based on facies analysis of more than 5 500 m cores of 45 deep wells three large sub provinces have been defined for the lower rotliegend volcanic rocks in the central southern permian basin spb in northeastern germany and western poland additional data came from unpublished descriptions of more than 200 wells the three sub provinces are a the mecklenburg vorpommern sub province mvsp dominated by silica rich lava domes and subvolcanic intrusions b the eastern brandenburg sub province ebsp dominated by a mg andesite shield volcano complex which extends into western poland and c the flechtingen altmark sub province fasp with prominent ignimbrite sheets punctuated by lava domes and flows whereas in ne germany thickness of up to 2 300 m have been found in places in western poland ignimbrites and other pyroclastic deposits as well as andesitic and silica rich lava complexes accumulated successions of a few hundreds of meters a hiatus of up to 30 ma occurs between the lower rotliegend volcanic and sedimentary rocks asselian sakmarian and upper rotliegend ii sediments upper wordian capitanian upper rotliegend i deposits are known from a few wells and outcrops only previous studies postulated solely intrabasinal tectonics to account for this major unconformity however under semiarid to arid conditions as assumed for the rotliegend of the spb both sio2 rich lava complexes and silica poor shield volcanoes can be expected as being extremely resistant to weathering and erosion most probably these bodies drowned in a regolith formed by physical weathering rarely removed by torrential rain thus the silica rich lava complexes and the shield volcanoes in the central european basin system cebs can be viewed as long living morphological highs with intervolcanic depressions in between in these intervolcanic depressions syn to postvolcanic successions of conglomeratic to sandy alluvial fan sediments and lake to mud flat deposits accumulated during the upper rotliegend i they show numerous pedogenic horizons representing times of non deposition during the upper rotliegend ii the remaining volcano topography was filled up with alluvial eolian and playa deposits in some places in western poland covering was not complete until the zechstein latest permian at the same time soil formation and or erosion in the upper part of sio2 rich complexes and shield volcanoes remained subordinate consequently the volcano topographic hiatus on top of the volcanic complexes comprises the maximum period of time whereas in the intervolcanic depressions this time splits into periods of deposition and numerous minor intraformational hiati intrabasinal tectonic activity cannot be ruled out as one major control of the rotliegend depositional evolution in the subsiding spb however the presence of weathering resistant volcanic edifices led to the formation of long lasting depositional gaps in many regions of the central spb

filling sequence in late paleozoic continental basins a chimera of climate change a new light shed given by the graissessac lodeve basin se france abstract the characteristics of sedimentary deposits in continental basins especially those controlled by extension are often used to infer global climatic changes we question the relevance of such an approach because the stratigraphic pattern of those basins are mostly similar whatever their latitudes paleolatitudes i e their general climatic conditions namely the transition from 1 an ancestral drainage network to 2 deep lake with a dominance of black and grey shale deposits 3 shallow oxic lake with a dominance of red pelites deposits and to eventually 4 a new drainage network such transitions observed in late palaeozoic continental basins throughout laurasia and gondwana are generally interpreted as evidence of global change from a wet climate to an arid climate from the sedimentological and structural analysis of a late palaeozoic basin the graissessac lodeve basin in the south of the variscan french massif central we proposed a new tectono stratigraphic sequence of this basin from the late carboniferous to the early trias we estimate the paleo area from 295 450 km 2 to 880 1150 km 2 of the basin and we deduce a subsidence curve from the late carboniferous to the late permian from 600 200 m my to 100 10 m my we conclude that the graissessac lodeve basin stratigraphic pattern corresponds to a classical continental rift sequence controlled by tectonics in order to assess a possible control of the stratigraphic sequence by the climate we have reconstructed the paleo depth of the lake with 1 the morphometric analysis of the wave ripples and 2 with an estimation of the lacustrine slope considering the tectonic origin of the lake we find that the maximum lacustrine depth has evolved from a range of 80 300 m during the late carboniferous to 40 45 m during the late permian from our estimates of the different configurations of the basin we show that the volume of the water in the lake has remained nearly constant between 10 and 30 km 3 from the late carboniferous 300 my to the late permian 250 my eventually we conclude that the sedimentological indicators of shallowing and episodic drying observed from the late carboniferous to late permian in this basin and probably in all the pangea basins of the same type are the consequence of the basin enlargement by tectonics and its sedimentary filling rather than climatic change

geophysical greenfield exploration in the permo carboniferous saar nahe basin the wiesbaden geothermal project germany structurally bound upwelling and outflowing hot fluids in the city of wiesbaden suggest an interesting geothermal potential at the northern margin of the permo carboniferous saar nahe basin snb germany the snb in the wiesbaden area was previously not a target for intensive geophysical prospecting of the deeper underground we present new geophysical exploration data of the snb to investigate potential geothermal reservoirs near wiesbaden for heat and power production the main goal was to explore the local geometry and internal structure of the snb exploration encompasses analysis of lidar data a dense grid gravity survey as well as 2d and 3d seismic surveys the geophysical data revealed for the first time the deep structure of the mainz and saar nahe basins near wiesbaden down to a depth of c 4000m the snb is strongly segmented and comprises deep reaching active faults an essential element of the exploration concept was the definition of those structures as geothermal drilling targets which promise high permeability at a low risk of induced or triggered seismicity for this reason numerical simulations of the local stress field were used to evaluate the geomechanical characteristics of the identified faults zones and their fault reactivation tendency geomechanical ensemble modelling helped to characterise the influence of uncertain input parameters and boundary conditions the results of the geomechanical simulations together with temperature estimates and the reservoir characterization were used to identify a number of promising drilling targets this article is protected by copyright all rights reserved

joint hypocentre determination of intermediate depth earthquakes in fiordland new zealand abstract relocation of well observed intermediate depth earthquakes in the fiordland region by the method of joint hypocentre determination has revealed some fine structure in the benioff zone the earthquakes occur in three groups the central group is the largest and occupies a planar volume less than 15 km thick striking n40 e and dipping at 80 the deepest events in the region at depths of 150 km occur at the northeast end of this group the two smaller groups lie to the northeast and to the south of the main group the focal mechanism of the majority of the main group is that of thrust faulting we suggest that the main group lies within a section of indian plate lithosphere which has been broken off and rotated into its observed position and that the northern edge of the unbroken subducted indian plate is indicated by the southern group we suggest that the small northeastern group has quite a different tectonic origin and is similar to a group of earthquakes further north which are at a similar distance from and presumably related to the alpine fault use has also been made of the travel time information which is a by product of the joint hypocentre method to construct upper mantle velocity models for p and s waves in the south island the features of this model are a high velocity region in the vicinity of the benioff zone and a subcrustal zone of high seismic velocities running east west across the center of the south island in an otherwise normal mantle

seismites in the fluviatile bima sandstones identification of paleoseisms and discussion of their magnitudes in a cretaceous synsedimentary strike slip basin upper benue nigeria abstract the upper benue basin northeastern nigeria is interpreted as a complex strike slip basin which consists of a set of sub basins controlled by synsedimentary n60 c e trending strike slip faults which were active during early cretaceous times the oblique planar cross beds made of the medium to fine grained sandstones of the upper member of the bima sandstone formation are affected by various soft sediment i e early diagenetic but soft sediment deformational structures these are present not only close to the synsedimentary faults but also on a larger regional scale three main types of structures undulated and recumbent folded cross bedded lamination dislocated convolutions and concordant microbreccias discordant fluidised intrusions are described these are related to processes of sediment deformation favored by sand hydroplasticity liquefaction and fluidization the local organization of these soft sediment intrastratal deformational structures their spatial distribution with respect to synsedimentary faults and their independance with respect to marginal paleoslopes suggest that they cannot be explained by slumping or current drag all the deformations are related to pore water expulsion and it is proposed that the required sand reorganization was triggered by seismic waves the spatial and chronologic distribution and intensity of the various types of deformation structures suggest that they were produced around different epicenters repeated by earthquakes of varying magnitudes associated with the synsedimentary strike slip tectonics

lithospheric instability beneath the transverse ranges of california recent high resolution seismic experiments reveal that the crust beneath the san gabriel mountains portion of the transverse ranges thickens by 10 15 km contrary to earlier studies associated with the transverse ranges there is an anomalous ridge of seismically fast upper mantle material extending at least 200 km into the mantle this high velocity anomaly has previously been interpreted as a lithospheric downwelling both lithospheric downwelling and crustal thickening are associated with the oblique convergence of pacific and north america plates across the san andreas fault though it seems likely that the lithospheric downwelling is driven at least partly by gravitational instability of the cold lithospheric mantle we show by means of numerical experiment that the balance between buoyancy forces that drive deformation and viscous stresses that resist deformation determines the geometry of crustal thickening and mantle downwelling we use a simple two layered lithospheric model in which dense lithospheric mantle overlies relatively inviscid and less dense asthenosphere and is overlain by buoyant crust external plate motion drives convergence which is constrained by boundary conditions to occur within a central convergent zone of specified width a fundamental transition in the geometry of downwelling is revealed by our experiments for slow convergence or low crustal viscosity downwelling occurs as multiple sheets on the margins of the convergent zone for fast convergence or crust that is stronger than mantle lithosphere a single downwelling occurs beneath the center of the convergent zone this complexity in the evolution of the system is attributed to the interaction of crustal buoyancy with the evolving gravitational instability in order for a narrow downwelling slab to have formed beneath the transverse ranges within the last 5 myr the effective lithospheric viscosity of the convergent region is at most about 10 20 pa s

using quantitative textural analysis to understand the emplacement of shallow level rhyolitic laccoliths a case study from the halle volcanic complex germany received february 1 2002 accepted november 8 2002in qualitatively homogeneous magmatic bodies quantitativetextural analysis such as crystal size distribution modalabundance and spatial distribution pattern analyses allowstheir internal heterogeneity to be measured and interpreted inthis study these methods are applied to samples from a 300mdrill core through one of the porphyritic rhyolitic laccoliths petersberg unit of the 300ma halle volcanic complex germany qualitatively thegeochemicallyhomogeneouspetersbergunit does not show much textural variation quantitatively however the crystal size distributions of the three most commonphenocryst phases orthoclase plagioclase and quartz suggestcontinuouscrystalgrowthduringmagmaascentandemplacement but different growth histories of the phenocryst phases throughoutthe genesis of the laccolith in situ cooling did not affect thephenocryst population size distributions of the phenocrysts varyon a centimetre to decimetre scale but are similar on the scale ofthe laccolith the modal abundance of the phenocryst phases isvery similar throughout the drill core quantification of thespatial distribution of phenocrysts however reveals a trend forclusteringtowardstheinteriororupperpartofthelaccolith whichis attributed to flow and shear processes during emplacement anddiscontinuities in the interior relating to the intrusion of differentmagmapulses circularstatisticsoftheorientationoflongaxesofcrystals reveala weakalignment oftheorthoclaseand plagioclasephenocrystsonthesamplescaleasaresultofflowinthemagmainspite of little acicularity in general laccoliths can be fedby several pulses of magma without major cooling betweenbatches

late orogenic basin evolution in the variscan internides the saar nahe basin southwest germany abstract the late variscan evolution of the saar nahe basin in southwest germany is closely controlled by the kinematics of the hunsruck boundary fault which also separates two main tectonostratigraphic units of the variscides the saar nahe basin comprises a half graben structure which formed due to extensional reactivation of a variscan thrust between the early westphalian and late rotliegend about 8 5 km of alluvial fan fluvial and lacustrine sediments accumulated during the permo carboniferous w e oriented extension was accommodated by a system of nw se trending transfer faults and orthogonal normal faults balanced cross section construction and subsidence analyses suggest a 35 extension of the previously thickened crust in the late stage of the orogeny the subsidence analyses show discontinuous depth dependent extension with laterally varying extension factors in the crust and mantle the offset between syn and post rift depocentres is explained by a mantle stretching zone shifted laterally with respect to the area of maximum crustal extension finally a geodynamic model for the evolution of the saar nahe basin with special reference to the earlier variscan development and the general evolution of permo carboniferous basins in central europe is presented

facies architecture variations and seismogenic structures in the carboniferous permian saar nahe basin sw germany evidence for extension related transfer fault activity abstract sedimentary and volcanic strata in the late orogenic intermontane saar nahe basin preserve a record of sedimentary responses to motion on contemporaneously active faults studies of such deposits can constrain both concepts for lateral and vertical sedimentary facies development and geometric and kinematic models of intrabasinal extension during carboniferous permian syn rift development the saar nahe basin underwent a marked intrabasinal segmentation generated by the offsets of longitudinal normal faults and dextral oblique strike slip faults which were developed perpendicular to the sw ne basin elongation the latter are interpreted as transtensional transfer faults which compartmentalized the basin into segments of differing structural style bed thickness and facies development the fault zones themselves bound an assemblage of variously sized uplifted and downthrown blocks showing variable magnitudes and senses of displacement their activities are recorded by the contrasting depositional histories of tephrostratigraphically constrained sedimentary units occupying footwall and hanging wall block positions during basin filling the influence of faults on the depositional system is seen in their effect as topographic barriers thus restricting free dispersal and mixing of sediment particular sedimentary facies such as coals and biogenic limestones are confined to the immediate vicinity of the fault zones indicating the isolation of sediment starved areas near downthrown hanging walls other fault generated depressions acted as depositional traps favouring considerable accumulations of basaltic lavas volcaniclastic mass flows and fluvial channel deposits in contrast uplifted footwalls are characterized by the formation of unconformities and pedogenic features the abundance of syn tectonic deformation structures such as sediment filled fissures intraformational breccias series of micro faults clastic dykes and other water escape features within syn rift strata and their distinct spatial linkage to fault zones implies considerable seismically triggered processes associated with faulting the combined occurrence of abrupt variations in facies architecture across faults and seismotectonic structures suggests that the basin subsidence history involved a series of events rather than gradual change

upper mantle anisotropy in the new zealand region shear wave splitting parameters of fast polarization direction and delay time t are determined using data from the southern alps passive seismic experiment sapse on the south island of new zealand and in the surrounding region our results clearly show that are subparallel to trends of the alpine and marlborough faults and to the pacific australian plate boundary the t values range from 0 6 2 2 s with an average value of 1 6 s the largest values are from the central south island the main source of the observed shear wave splitting is an anisotropic region between 40 400 km the width of the zone is approximately 200 km we attribute the coincidence of surface structural trends with the measured and the large t values to significant shear deformation in a 200 km thick zone along the plate boundary extending from the surface to deep within the upper mantle

the evolution of the south hunsruck and taunus borderzone abstract the main fabric development of the south hunsruck and taunus borderzone htb occurred during late variscan homoaxial backfolding of an early variscan stack of thrust sheets in a narrow wsw ene trending zone several hundred kilometres long rotation and uplift of the southern rhenohercynian zone was accompanied by the subsidence of the southward adjacent northernmost parts of the saxothuringian zone and the development of the saar nahe basin during the latest carboniferous changing stress conditions gave rise to the development of normal faults along the htb and an extensive tholeiitic and rhyolitic volcanism contemporaneous uplift of the hunsruck is reflected by coarse elastics in the saar nahe basin subsequently the htb became covered by latest carboniferous early permian and mesozoic sediments cretaceous uplift of the rhenish shield caused their erosion the faultzone separating the rhenohercynian hunsruck and taunus from the permo carboniferous saar nahe basin is characterised by reverse and normal faults conjugate shear indicated by slickensides on steep oblique fracture planes as well as slight folding and small scale thrusting in post variscan sediments may be attributed to compressional foreland deformation reactivating variscan joint fabrics and fault systems timing of these deformations is ambiguous and could partly be related to dextral shear during the cenozoic subsidence of the rhine graben cenozoic sediments of the upper rhine graben overstep the northeastern parts of the htb seismic investigations indicate that the htb is associated with a system of southeast hading listric planes extending beneath the moho occasional dip slip earthquakes occur along these fractures

subsidenz und tektonik des saar nahe beckens sw deutschland the saar nahe basin in sw germany is one of the largest permo carboniferous basins in the internal zone of the variscides its evolution is closely related to movements along the hunsruck boundary fault which separates the rhenohercynian and the saxothuringian zones recent deep seismic surveys indicate that the saar nahe basin formed in the hanging wall of a major detachment which soles out at lower crustal levels at about 16 km depth oblique extension along an inverted variscan thrust resulted in the formation of a half graben within more than 8 km of entirely continental strata accumulated the structural style within the basin is characterized by normal faults parallel to the basin axis and orthogonal transfer fault zones balanced cross section construction and subsidence analysis indicate extension of the orogenically thickened lithosphere by 35 subsidence modeling shows discontinuous depth dependent extension with laterally varying extension factors for crust and mantle lithosphere thus the offset between maximum rift and thermal subsidence can be explained by a zone of mantle extension shifted laterally with respect to the zone of maximum crustal extension

sediment deformation structures and the palaeotectonic analysis of sedimentary basins with a case study from the carboniferous of northern england

a global study of pn anisotropy beneath continents we apply a two station method of velocity determination to p n arrival times reported in the international seismological centre bulletin during the period 1964 1993 the azimuthal variation of these velocities provides evidence of p n anisotropy as large as 9 6 anisotropic regions are identified by examination of the azimuthal variation of the p n velocities within circular caps of radius 1 5 and 3 spaced at 1 intervals across the earth this procedure leads to 255 geographically distributed estimates of anisotropy the length scale over which the anisotropy varies indicates that uppermost mantle anisotropy beneath continents is controlled by regional orogenic strains and is inconsistent with a general interpretation in terms of plate scale mantle flow in addition the correlation between p n anisotropy and surficial tectonic features indicates that the anisotropy is primarily the result of the most recent deformation event we compare our p n anisotropy results fast directions and magnitudes with those of sks splitting studies to attempt to constrain the depth extent of the anisotropy this comparison suggests that in some areas where the fast directions agree sks splitting observations may arise from a layer beginning just below the moho whereas in others it must have a deeper origin in these areas the relative magnitudes of the measured anisotropy are consistent with a thin 100 150 km lithospheric layer of anisotropy

subduction zone retreat and recent tectonics of the south island of new zealand the central south island of new zealand is a zone of recent oblique continent continent convergence between the australian and pacific plates convergence is localized on the alpine fault and its broader expression has created the southern alps we propose that many of the strike variations in orogenic style of this zone e g physical extent and style of crustal shortening argon release patterns and fission track observations can be explained by differential amounts of subduction zone retreat beneath the orogen the observed patterns suggest greater eastward retreat of the subducting pacific plate in the south than in the north to support this hypothesis we compare geodynamic models having varying amounts of subduction zone retreat with geological and geophysical observations incorporating subduction zone retreat not only creates tectonic variations similar to those observed but also provides a geodynamically consistent explanation for the size shape and location of the broad negative bouguer gravity anomaly associated with the orogen in addition these geodynamic models suggest that subduction zone retreat may result in local topographic lows which may serve as preferential locations for the formation of intermontane basins and associated lakes possibly explaining the chain of south island lakes our preferred interpretation of the geologic history of the central south island convergence has an initial phase of pacific plate lower crust and mantle subduction underthrusting with no retreat followed by a second phase of subduction zone retreat in the southern part of the zone this retreat may be a consequence of oblique convergence which creates interference beneath fiordland between the south east dipping australian plate and the underthrust west dipping pacific plate to the north and forces retreat

continental crust under compression a seismic refraction study of south island geophysical transect i south island new zealand 1 the 1996 south island geophysical transect sight active source seismic survey was designed to show the style of lithospheric thickening due to late cenozoic oblique convergence across the australian pacific plate boundary in new zealand as part of this study two seismic refraction lines were shot across central south island and offshore extensions of the continental crust in the tasman sea and pacific ocean we present the data and a 603 km long seismic velocity profile of the crust and uppermost mantle along one of these seismic transects a tomographic inversion of 62 563 travel times from crustal and upper mantle refractions and wide angle reflections resulted in a model with a two layer crust upper crustal velocities were between 5 9 and 6 3 km s and lower crustal velocities were between 6 5 and 7 0 km s continental compression has locally reduced the seismic velocities in the pacific plate crust by 0 2 0 3 km s a possible effect of high strain and fluids in the crust the thickening of the crust from 28 km at the east coast of south island to 37 km beneath the southern alps can account for about 25 of the 80 110 km shortening of pacific plate crust while the rest must be accounted for by rapid erosion of mesozoic sedimentary rocks on the west side of the orogen in our model the lower crust forms a continuous 2 6 km thick layer beneath central south island the asymmetric topography of the southern alps is reflected in the crustal root which has a steeper flank at the west coast this observation is consistent with westward underthrusting of pacific lower lithosphere beneath south island that has been suggested in earlier studies

the continental collision zone south island new zealand comparison of geodynamical models and observations the south island zone of oblique continent continent convergence occurs along a 400 km long section of the modern australia pacific plate boundary zone across which about 50 km of shortening has been accommodated since about 10 ma the orogen comprises a central mountain range southern alps flanked on both sides by what are interpreted to be foreland basins two essential features that characterize the orogen are 1 the degree of denudation that accompanied deformation and 2 a fundamental structural asymmetry the architectural asymmetry of the orogen can be explained by plane strain finite element models of continental convergence incorporating mantle subduction comparison of model and orogen polarity implies that pacific plate mantle subducts the models predict two crustal scale dipping shear zones that form above the point where the pacific mantle subducts the localized one more distant from the incoming plate retro step up shear zone corresponds to the alpine fault whereas its conjugate pro step up shear zone corresponds to the distributed strain and thrusting along the eastern margin of the mountain belt parameters that modify the model boundary conditions top surface degree of denudation basal zone subduction load crust mantle velocity discontinuity subduction of lower crust mantle retreat and distributed decrease in mantle velocity and the internal strength of the crust two layer crust with moderate coupling temperature distribution strain weakening are varied in a series of numerical model calculations that establish the combination of material properties and boundary conditions that lead to different cross sectional architectures of the modeled collision zone in turn these are compared with observations about the south island orogen the calculations show how the style and extent of deformation across the whole orogen depend on the rheological properties of the crustal layer and on the balance between its internal strength and the combined effects of the boundary and gravitational stresses north to south along strike differences in the width and two dimensional architecture of the orogen simulated in the experiments by varying the model parameters can be explained by a combination of southward increases in preconvergent crustal thickness geothermal gradient convergence and potentially subduction retreat with the added possibility of a southward decrease in the component of lower crustal subduction

compression and right lateral strike slip movement at the southern hunsruck borderfault southwest germany abstract compressional tectonic structures have been known from the southern hunsruck borderzone since the end of the last century in the western part of the borderzone the saar nahe syncline is upthrown whereas in the eastern part the hunsruck is upthrown against the saar nahe syncline folds with axes parallel and oblique to the 60 trending fault zone have been described in the past in the area between idar oberstein and kirn permian lava sheets are displaced in such a way that their recent distribution can be explained by a right lateral strike slip movement of 5 8 km the block of the saar nahe basin between the southern hunsruck borderfault and the saarbrucken anticline has been tilted to the ene since the late palaeozoic the transcurrent movement can only be related to the opening of the upper rhine graben ne sw and nne ssw trending folds in the rotliegend sediments are considered to be transpression structures related to strike slip movement in early tertiary times recent seismicity along the southern hunsruck borderzone indicates that this zone is still active

the permo carboniferous saar nahe basin south west germany and north east france basin formation and deformation in a strike slip regime the permo carboniferous saar nahe basin in south west germany and north east france formed at the boundary between the rhenohercynian and saxothuringian zones within the variscan orogen where non marine sediments were deposited in a narrow structurally controlled basin the basin has an asymmetrical geometry perpendicular to the south hunsruck fault however there is a lack of growth of the sediment pile into the fault and isopach maps show the depocentre always located adjacent to the south hunsruck fault but migrating towards the north east with time this pattern is typical of a strike slip basin indicating that the south hunsruck fault was a dextral strike slip fault during sedimentation tectonic subsidence curves indicate that during the middle devonian to early carboniferous the basin subsided due to thermal relaxation of the lithosphere a change to very rapid subsidence at the start of the westphalian continued until late in the autunian this was due to mechanical subsidence associated with strike slip movement on the south hunsruck fault towards the end of subsidence in the saar nahe basin the grenzlager volcanics introduced a thermal pulse into the crust leading to thermal cooling and relaxation of the lithosphere

eocene paleoseismic record of the green river formation fossil basin wyoming u s a implications of synsedimentary deformation structures in lacustrine carbonate mudstones abstract laterally extensive intervals containing sedimentary deformation features are identified in outcrops of lacustrine deposits of the eocene 52 51 ma green river formation in fossil basin southwestern wyoming fossil basin is the smallest of the paleo lakes in the green river system and is located in the sevier fold and thrust belt which was tectonically active during deposition deformation structures include convolute lamination load structures hybrid brittle ductile features sedimentary dikes microfaults fluid escape features such as cusps and pipes oil shale breccias and mass transport deposits in most cases these structures are hosted by finely laminated variably organic rich carbonate mudstones that accumulated in a low energy profundal lacustrine environment deformed intervals range from a few centimeters to 5 m in thickness and are bound above and below by undeformed strata of the same facies which demonstrates the early post depositional timing of deformation the distribution of these features indicates a primary control exerted by sediment rheology resulting from variation in grain size clay and organic content and degree of lithification which in turn were governed by the depositional environment and early diagenesis based on their morphological attributes lateral extent and recurrence at different stratigraphic levels along with their sedimentary environment and the tectonic setting of the basin the deformation structures are interpreted to be seismites i e the result of stresses induced by syndepositional earthquakes and other potential trigger agents are rejected moreover stratigraphic relationships indicate that these small scale deformation features as well as the mass transport deposits formed on a virtually flat lake floor ruling out instability caused by the gravitational regime syndepositional deformation in fossil basin points to tectonic activity along the nearby absaroka and or hogsback thrusts and related fault systems seismites point to possible tectonic forcing as a mechanism for changes in bathymetry and sedimentation in the green river formation and consequently demonstrate their potential for elucidating the tectonic history of other lacustrine and marine basins

rock mechanical analysis of a m1 4 0 seismic event induced by mining in the saar district germany summary on 2008 february 23 a 4 0 magnitude seismic event occurred in close proximity to a deep underground longwall coal mine in the german saar mining district preceding this event was a series of smaller seismic events which can be traced back to geological structures a seismic network was installed to observe and analyse the seismic events underground core drilling was performed to obtain rock samples for rock mechanical testing possible causes for the events failure of rock mass or slip on unknown faults are evaluated by numerical methods failure of rock mass is excluded as a cause since the stresses are well below the strength of the rock mass seismic events are of similar fault plane strike and are organized in several clusters associated with local and regional tectonic elements it was found from backcalculation that fault planes with friction angles as low as 8 must have been present the role of pore pressure on the fault stability is discussed and found to play no role in generating the seismic events finally the question of mining in a rock mass obviously close to failure is addressed and it was concluded that any mining activity would lead to a significant seismic response

lower rotliegend fluvio lacustrine sequences in the saar nahe basin the rotliegend beds of the middle of the kusel group to the middle of the lebach group in the saar nahe basin are characterized by sedimentary sequences which developed in streams deltas and lakes

carbonate lake deposits associated with distal siliciclastic perennial river systems abstract the genesis of thick accumulations of carbonate lake deposits on the siliciclastic floodplains of perennial rivers situated below the regional spring line requires 1 a significant source for calcium in the watershed and 2 a protected area to accumulate calcite the phanerozoic record of fluvial deposits shows that anastomosing rivers with carbonate rich provenance situated in distal areas below the spring line are the best environments for floodplain accumulation of significant carbonate lake deposits anastomosing rivers exist below the regional spring line and have isolated flood basins generally protected from bedload by high levees receiving suspended and dissolved load during flooding events numerical modeling to test the rate of accumulation for these carbonate sediments was performed using stratigraphic data from the pennsylvanian succession containing floodplain limestones of the stewart quadrangle of athens county in ohio usa limestone volumes for six limestone units upper pittsburgh fishpot sewickley benwood arnoldsburg uniontown and waynesburg limestones were calculated with the assumption of overland input of dissolved calcite from carbonate source areas in comparing the calcium input rate to the amount of calcium calculated from limestone unit volumes overland transport of calcium ions not spring input can supply sufficient ions to accumulate thick carbonates over the short lifetime of floodplain lakes within anastomosing river systems

linked fault families in basin formation abstract recent models of faulting tectonics in basins and passive margins have emphasized the linked nature of faults in a way that is analogous to that developed for thrust regimes a linked fault system requires three components ramps flats and sidewalls or transfers basins that are the result of other processes are not considered in this contribution and the examples used are drawn from the midland valley and northumberland basins of the u k where existing mapping by the british geological survey as well as field work undertaken by the author indicate that such models are appropriate this paper summarizes the geometric features and constraints of such models and emphasizes the role of each of the three critical components of a linked system for large deformations that result in the formation of major extensional and strike slip basins the principal geometries can be understood by reference to regionally and locally balanced fault models that involve detachment ramp and sidewall or transfer elements tip strains and both lateral and vertical accommodation zones are included in the general model but these probably account for less than 10 of the total upper crustal strain the basic analysis of a linked basin system requires the transfer of displacement on and between the fault and shear zone components the geometry of the stratigraphic units is used to deduce the active linkage on the fault system in oblique slip systems and where the dominant extensional ramp is connected to oblique transfer and detachment systems lateral and sidewall sub basins and intra basin uplifts occur as part of continuing slip on the fault system these control facies distribution and depocentre evolution the existence of a basin forming linked system frequently controls later deformation of basins and margins and an appreciation of basin growth faults and stratigraphic geometry is essential in the interpretation of inverted basins and orogenic belts involving supracrustal formations

sedimentary structures exposed in bar tops in the brahmaputra river bangladesh the brahmaputra river is one of the world s largest sand bed braided rivers with a channel belt up to 15 km wide a mean channel depth of 5 m and maximum scour depths of up to 40 m the recorded discharge varies by around 60 000 cumecs every year following the annual monsoon producing dramatic stage fluctuations with the water level falling between 7 and 8 m from bankfull to low flow stage in the dry season large areas of bar top and channel bed are exposed and low flow channels cut natural sections through bar tops exposing the internal stratification elements of upstream downstream and lateral accretion are identified although the high width depth ratio of channels up to 500 1 results in extremely low depositional dips on bed bounding surfaces within the accretionary elements vertical and lateral changes in sedimentary structures are ubiquitous and varied but some patterns can be discerned channel deposits are dominated by sinuous crested dunes and trough cross stratification upper stage plane bed lamination often with a very low angle depositional dip has been observed in beds up to 4 m thick and is generally found at the base of the exposed bar top sections trough cross stratification in bar tops occurs in sets from 0 1 m to 3 m thick with rapid vertical and lateral changes in set thickness very large sets of trough cross stratification 3 m thick do not occur in the bar top sections current ripple lamination is most abundant on the tops of bars with very high rates of climb associated with high rates of sediment deposition from these observations a generalised vertical sequence of bar top origin might include trough cross stratification overlain by upper stage plane bed lamination isolated sets of trough cross stratification truncated and capped by current ripple lamination this sequence which is considered to represent the deposits of a single flood may occur within the upstream downstream or lateral accretion elements however it should be noted that vertical and lateral changes in facies are extremely abundant with many changes in sedimentary structures and reactivation surfaces within each depositional episode

upper carboniferous and lower permian tectonostratigraphy on the southern margin of the central north sea hydrocarbon exploration in uk licence blocks 31 26 and 39 2 on the southern margin of the central north sea in 1996 and 1997 proved the presence of a palaeozoic sedimentary succession previously undescribed in the area biostratigraphic data from the sediments and radiometric dating of interbedded basaltic lavas indicate that the succession spans the upper carboniferous westphalian b to lower permian asselian interval this has been informally split into three sedimentary units the lower flora sandstone is of westphalian b c age this clastic interval is overlain by the first of two main lavas which is in turn overlain by the westphalian c d to stephanian upper flora sandstone the flora sandstones are interpreted to be lithostratigraphic equivalents to the schooner formation of the southern north sea the flora sandstones are separated from the grensen formation by an angular unconformity possibly related to variscan asturic inversion the grensen formation is in turn overlain by a second basaltic lava flow both basaltic units are assigned to the inge volcanics formation rotliegend group petrographic data indicate that the grensen formation also forms part of the rotliegend group a major extensional event of permian age post dates all of these strata extensional faults are planed by a regional unconformity saalian unconformity that is overstepped by permian to cretaceous strata

tectonic and volcanic controls on early jurassic rift valley lake deposition during emplacement of karoo flood basalts southern namibia abstract the karoo igneous province of southern africa is one of the classic mesozoic flood basalt provinces of the world in the case of the early jurassic kalkrand formation of namibia the succession comprises three major flood basalt units that are separated by two stratigraphically important fluvio lacustrine interlayers these horizons preserve a record of the complex interplay between sedimentation effusion of karoo flood basalts and extensional tectonics that predated and accompanied the break up of gondwanaland both sediment layers start with the dominantly local derivation of weathered and eroded lava debris followed by the emplacement of subaqueous mass flows and subsequent deposition of chemical sediments the latter are characterised by interbedded stromatolitic carbonates grass like structured gypsum and plane bedded sandstones and mudstones containing euhedral displacive gypsum crystals that grew in the subsurface as well as rosettes which nucleated on the sediment surface the central parts of the lacustrine units are overlain by thin deltaic sandstones showing bottomset foreset and topset layering and finally braided fluvial trough cross bedded sandstones evidence of subsidence synchronous with the formation of lake bodies can be explained by two principal mechanisms the first acted in localised areas only and is reflected by the development of small centrally subsiding basins from the repeated occurrence of onlapping geometries within such a pool a multiphase history of sagging is deduced being most likely related to periodic magma withdrawal and reduction in magmatic pressures in subsurface lava feeders beneath the basin floor abundant syn subsident fracture features at lava sediment contacts such as sediment hydrothermal calcite and sometimes basic lava filled fissure systems indicate the pronounced interaction between the underlying volcanics and these small areas of pronounced subsidence fluids passing through the volcanic pile exhaled into the lake giving it the characteristics of alkaline lake systems described from more recent flood basalt areas associated with the modern african rift system on the regional scale however northerly trending extensional fault systems controlled half graben basin geometries and both facies and thickness variations across faults indicate that tectonism operated contemporaneously with volcanism and lacustrine sedimentation the analysis of faults and associated structures such as regularly aligned sediment filled fissures sets of micro faults folds and basaltic dykes constrains the extensional opening direction for the karoo graben structures in this area that heralded the opening of the south atlantic and thus provides a basis to discuss the extensional history of the namibian coastal margin within the regional tectonic framework

quaternary tectonics in a passive margin marajo island northern brazil marajoisland is located in a passive continental margin that evolved from rifting associated with the opening of the equatorial south atlantic ocean in the late jurassic early cretaceous period this study based on remote sensing integrated with sedimentology as well as subsurface and seismographic data available from the literature allows discussion of the significance of tectonics during the quaternary history of marginal basins results show that eastern marajoisland contains channels with evidence of tectonic control mapping of straight channels defined four main groups of lineaments i e nne ssw ne sw nw se and e w that parallel main normal and strike slip fault zones recorded for the amazon region additionally sedimentological studies of late quaternary and holocene deposits indicate numerous ductile and brittle structures within strati graphic horizons bounded by undeformed strata related to seismogenic deformation during or shortly after sediment deposition this conclusion is consistent with subsurface bouguer mapping suggestive of eastern marajoisland being still part of the marajograben system where important fault reactivation is recorded up to the quaternary together with the recognition of several phases of fault reactivation these data suggest that faults developed in association with rift basins might remain active in passive margins imposing important control on development of depositional systems copyright 2007 john wiley sons ltd

variscan molasse in the saar nahe basin w germany upper carboniferous and lower permian the saar nahe basin is a permocarboniferous molasse basin within the variscan orogenic chains surface access is possible in an area of 100 40 km just south of the rheinisches schiefergebirge below a thick mesozoic cover the basin has a total extension of about 300 100 km 4 1 km upper carboniferous and 1 6 km lower rotliegend grey fluviolacustrine deposits and additional 1 8 km upper rotliegend red alluvial deposits were accumulated

experiments on strike slip faulting and block rotation analogue model experiments investigating strike slip faulting in zones of distributed shear deformation show that fault orientations and fault evolution indicate modifications of the stress field with increasing bulk shear strain dextral bulk shear deformation at low strain is accommodated dominantly by synthetic strike slip faults riedel shears at higher strain secondary antithetic and synthetic faults develop mostly between earlier formed major riedel shears closely spaced parallel antithetic faults cross faults delimit domains that rotate about vertical axes with continuing shear deformation rotation of fault bounded domains results in sigmoidal antithetic faults that have a dip slip component and a dip direction that changes along strike there is good agreement between models and natural examples of distributed shear zones where block rotations about vertical axes have been documented

crust and mantle thickening beneath the southern portion of the southern alps new zealand summary an 8 54 0 20 km s 1pn speed is estimated on a line oriented ca n5 e from the alpine fault beneath the southern alps of south island based on a refraction experiment that uses the fiordland earthquake of august 2003 as a source this high pn speed results from both strong anisotropy in the mantle lid of 7 13 per cent and a high pn speed average of 8 3 0 3 km s 1 a maximum crustal thickness of 48 4 km is calculated for the southern south island near the town of wanaka this represents a crustal root of about 18 km compared to measured crustal thicknesses at the east and west coasts of the south island the average topography in the southern southern alps is of the order of 1000 m which is less than half that predicted by airy isostasy for an 18 km crustal root as recently proposed for the central south island 120 km to the north we propose that thickened cold and therefore more dense mantle lithosphere exists beneath southern south island and that this excess of mass is an effective load that pulls down the overlying crust the load is similar to that beneath the central southern alps despite the predicted convergence across the alpine fault there being nearly twice that at wanaka gravity modelling of crustal structure along a profile through wanaka suggests that this mass excess has a minimum density contrast of 35 5 kg m 3 between thickened mantle and asthenosphere assuming an across moho density contrast of 300 kg m 3 we speculate that the reason for the enhanced thickening beneath wanaka is that the subducted australian plate at the southwestern corner of the south island acts like a backstop onto which pacific mantle collides at 26 mm yr 1 ca 3 4 the full plate speed

facies and basin architecture of the late carboniferous salvan dorenaz continental basin western alps switzerland france the salvan dorenaz basin formed during the late palaeozoic within the aiguilles rouges crystalline basement western alps as an asymmetric intramontane graben elongated in a ne sw direction and bounded by active faults at least 1700 m of fluvial alluvial fan and volcanic deposits provide evidence for a strong tectonic influence on deposition with long term average subsidence rates of 0ae 2m m yr 1 the early basin fill was associated with coarse grained alluvial fans that were dominated by braided channels unit i these issued from the south western margin of the basin the fans then retreated to a marginal position and were overlain by muddy floodplain deposits of an anastomosed fluvial system unit ii that drained towards the ne deposition of thick muds resulted from a reduction in the axial fluvial gradient caused by accelerated tectonic subsidence overlying sand rich meandering river deposits unit iii document a reversal in the drainage direction from the ne to the sw caused by synsedimentary tectonism reflecting large scale topographic reorganization in this part of the variscides with subsidence now preferentially in the w and sw and uplift in the e and ne coarse grained alluvial fan deposits unit iv repeatedly prograded into and retreated from the basin as documented by coarsening upward cycles tens of metres thick reflecting smaller scale tectonic cycles volcanism was active throughout the evolution of the basin and u pb isotopic dating of the volcanic deposits restricts the time of basin development to the late carboniferous 308 295 ma 40 ar 39 ar ages of detrital white mica indicate rapid tectonic movements and exhumation of the nearby basement in unit i youngest ages are close to that of the host sediment but the age spectrum is wide in unit ii high subsidence and or sedimentation rates coincide with very narrow age spectra indicating small homogeneous catchment areas in unit iii age spectra became wider again and indicate growing catchment areas

paleozoic lake faunas establishing aquatic life on land abstract lakes are important archives for continental records of paleoenvironmental as well as paleoclimatic change they also record a unique macroevolutionary pattern that occurred when faunas invaded the continental realm in order to document that pattern we compiled a database of over one hundred and six lake basins from the neoproterozoic to permian looking at this critical time in lacustrine evolution several patterns emerge for the neoproterozoic through silurian time there is a paucity of documented lake deposits and lake faunal records however the records that are available indicate that lakes were oligotrophic and their nutrient cycling regimes primitive it is not until the establishment of land plants in the silurian that lakes began to respond with higher diversities and more complex physical and chemical conditions during the devonian carboniferous periods diversity was on the rise as trophic structure became more complex most lakes of the devonian and carboniferous formed along continental margins or in tectonic basins with occasional connection to the marine realm the faunas from these types of lakes were commonly comprised of mixed marine and freshwater elements and were far more diverse than other more inland lakes this estuary effect created a gateway or filter through which faunas invaded the continental realm the early history of lake faunas is one of opportunity and amelioration the feedback loops created by the establishment of vascular plants altered the nutrient cycle on land and in lakes all trophic levels were established early but became increasingly complex throughout the paleozoic as roles changed and faunal elements became established groups invading the continents via the estuary effect did so numerous times before establishing themselves permanently this was linked with the episodic re establishment in marine freshwater connections along these continental margins

climate variability in the stephanian b based on environmental record of the msec lake deposits kladno rakovnik basin czech republic abstract in the stephanian b in eastern equatorial pangaea a large freshwater lake was formed in the continental basins of the west central and northeast bohemia czech republic with a total area estimated at 5000 10 000 km 2 and a lifetime of 50 to 500 ky its size exceeded that of any permian carboniferous lake in the european basins of that period so far described continual sedimentation of organic rich seasonally laminated clayey silty lake deposits produced a unique high resolution record of part of the stephanian b climate in the studied region an extraordinarily large trophic web of fish assemblages also proves the temporal stability of this meromictic oligotrophic lake the lake hydrology was inferred from the chemical and isotopic analyses of the autochthonous carbonates particularly siderite and analysis of organic matter the environmental and weathering conditions in the lake watershed were inferred from analysis of palynospectra and detrital clay minerals the lake passed through several stages of development including an initial highstand with peak productivity a stepwise increase in mineralization accompanying gradual lake regression a lowstand in the middle part of its lifetime a partial lake recovery and then a final transition to a shallow lacustrine deltaic system lake regression was triggered by a long term decrease in the p e ratio coupled with increasing seasonality and accompanied by a decrease in intensity of chemical weathering in the drainage basin considerable vegetation response to fluctuating lake levels suggests complex environmental changes during the initial lake highstand abundant and diversified assemblages of xerophilous elements prevailed spores of ferns prevailed during the regressive episode and spores of lycopsids abruptly increased at the lowstand and remained dominant in the palynospectra of the second lake highstand final transition to a lacustrine deltaic system was associated with pronounced increase in sphenopsids and ferns these changes can be attributed to milankovitch like climate change from warm wet to warm seasonal dry and may be inferred to have been responsible for stephanian continental cyclothems the entire stephanian b period was more humid than the preceding barruelian and subsequent stephanian c in the czech basins thus revealing a climate cycle at a timescale of several million years which is discussed in relation to southern gondwana ice sheet stability

tidal modulation of estuarine plumes abstract off an estuary mouth the nonlinear transfer of vorticity from the oscillating onshore offshore tidal currents to the mean field generates a pair of counter rotating eddies that flows seaward near the center axis of the inlet and landward on both sides the coriolis deflection strengthens the anticyclonic eddy but weakens the cyclonic one a seaward sloping shelf enhances these eddies but a seaward sloping estuary weakens them these tidal residual eddies strengthen and hasten the expansion of a river forced plume off an estuary mouth but weaken and retard the development of the coastal jet farther downcoast to lowest order this is the primary effect of tides on an estuarine plume in a coupled estuary shelf system tidal effects on the subtidal river forced circulation inside the estuary are secondary