high resolution sequence stratigraphic analysis of late quaternary deposits of the changhua coastal plain in the frontal arc continent collision belt of central taiwan abstract detailed analysis of the sequence stratigraphy in 30 cores from the late quaternary deposits of the changhua coastal plain provides a 25 ka record of the depositional history of a region situated in the frontal arc continent collision belt of taiwan twenty five lithofacies and nine facies associations are recognized an alluvial plain was the dominant feature during a pronounced sea level fall at 25 20 ka ago between 20 and 10 ka alluvial fans were deposited along the western front of the pakua tableland during movement along the changhua fault and a local sag basin was produced no other deposits in the seaward area are recognized between 20 and 16 ka or in the landward area between 20 and 10 ka between 16 and 6 ka the changhua coastal plain experienced rising sea level and retrogradational deposition from 16 to 10 ka estuarine deposits lower transgressive systems tract were deposited and the base of these deposits defines the last glacial maximum lgm unconformity sequence boundary now preserved in four regions to the east of the plain from 10 to 6 ka shelf shoreface and lagoonal deposits upper transgressive systems tract were laid either on top of the estuarine deposits or directly on the lgm unconformity surface by about 7 6 ka sea level had reached its peak maximum flooding surface and shelf and marginal marine sediments covered most of the study area after 6 ka the highstand was dominated by progradation of offshore transition shoreface lagoonal tidal channel tidal flat and alluvial plain deposits one thousand year old fluvial deposits in incised channels are preserved in the central part of the changhua coastal plain since then fluvial channels shifted southward to the present day chuoshuei river the depositional patterns in this tectonically active area during the last interglacial period reflect the complex interplay between high frequency sea level fluctuations tectonics subsidence and uplift and autocyclic processes in the seaward area however fluctuations in sea level were clearly the dominant factor in controlling the nature of depositional facies

present day interseismic surface deformation along the longitudinal valley eastern taiwan from a ps insar analysis of the ers satellite archives 1 in taiwan about one third of the lithospheric plate convergence between eurasia and the philippine sea plate is accommodated on the eastern coast across the narrow longitudinal valley lv the longitudinal valley fault lvf is the main seismically active fault zone in this region however the spatial distribution of ground deformation due to interseismic loading on locked fault segments remains widely unknown to address this problem we use a permanent scatterer ps interferometric synthetic aperture radar insar approach for processing the ers satellite archives the ps mean velocity maps allow accurately mapping and quantifying the ground deformation all along the lv assuming that close to the surface the fault plane along the central lvf creeping segment dips 55 to the east we derive a slip vector at the surface of 25 mm yr with a mean rake of 70 in agreement with our ps observations shallow seismicity indicates a clear change in the fault mechanical behavior of the creeping segment around fuli town finally we propose a combination of the ps velocity fields for estimating a 3 d map of ground deformation in the southern part of the lv the vertical component reveals an uplift of the coastal range with respect to the lv of 10 mm yr moreover between taitung and luyeh the vertical deformation is essentially accommodated along the luyeh strand finally north of rueisuei the coastal range uniformly subsides at 15 mm yr relative to the western side of the lv however a local uplift pattern is detected around latitude 23 42

estimates of the amount and rate of sea level change across the rhaetian hettangian and pliensbachian toarcian boundaries latest triassic to early jurassic an attempt is made to determine the amount and rate of sea level change for two major events in the latest triassic to early jurassic both of which are associated with mass extinctions using the best available facies evidence and time scale the amount of marine deepening across the pliensbachian toarcian boundary based on analysis of the excellent yorkshire coast section is likely to have been a few tens of metres at a rate of between 1cm 1 2 ka 1 and 1cm 0 4 ka 1 the change across the rhaetian hettangian triassic jurassic boundary was different in that the sea level rise was immediately preceded by a sea level fall effectively a 9regression transgression9 couplet the earliest jurassic sea level rise is likely to have been much more rapid than that across the pliensbachian toarcian boundary at a rate of at least 1 cm 0 2 ka 1 whereas the speed of pliensbachian toarcian change is consistent with the growth of oceanic ridges the appreciably more rapid triassic jurassic change is suggestive of a different tectonoeustatic mechanism involving stress induced changes in plate density

an interpretation of the active deformation of southern taiwan based on numerical simulation and gps studies abstract the fold and thrust belt of taiwan results from oblique convergence between the eurasia and the philippine sea plate and its front structures are strongly influenced by the presence of large horsts and basins in the foreland using a 2 d numerical modelling finite element and distinct element methods we evaluate the influences on the active deformation of southern taiwan of 1 the foreland structural highs 2 the major fault zones in the belt and 3 the presence of a subduction zone to the south to constrain our models we take into account for the first time the present day velocity field of southern taiwan estimated based on new geodetic data obtained through the global positioning system gps particular attention is paid to the role of geological discontinuities through an evaluation of the presence and role of mechanical decoupling along major faults which plays an important role in the distribution of the regional and local velocity and stress patterns this particular analysis of the behaviour and influence of weak shear zones in taiwan is carried out by using for the first time the distinct element method additional 3 d distinct element modelling allows better consideration of oblique shearing such as for the longitudinal valley fault of eastern taiwan we conclude that the active velocity field and tectonic stress pattern in southwestern taiwan strongly depend on 1 the presence and shape of the peikang high 2 the presence of the major active regional discontinuities the longitudinal valley fault and the major thrusts of western taiwan and 3 the neighbouring weakness zone of the accretionary prism of the northern manila subduction zone and cannot be explained by any of these factors taken solely

crustal deformation at the southernmost part of the ryukyu subduction east taiwan as revealed by new marine seismic experiments abstract the southernmost part of the ryukyu subduction where the philippine sea plate is subducting under the eurasian plate is known to be a very seismically active region of transition from a north dipping subduction along the ryukyu subduction to an se nw collision along the taiwanese orogenic wedge in this paper we will focus on the ryukyu forearc area close to taiwan where the deformation is paroxysmal in order to decipher the nature of the seismic deformation in this region a three month passive experiment combining 22 ocean bottom seismometers and 51 onland stations has been led starting from an a priori heterogeneous model we have obtained 801 well located earthquake hypocenters a precise p wave tomography model and 14 focal mechanisms the seismicity along the ryukyu forearc is mainly located not only in the vicinity of the interplate seismogenic zone isz but also within both the subducting psp and the overriding plate seismicity within the upper plate is essentially localized east of nanao basin where nw se extension occurs and northwest of the hoping basin where strike slip dominates as revealed by both the p wave velocity structure and the newly derived seismicity we argue that a sub vertical step offsetting the subducting psp around 10 km may support the presence of a trench parallel tear the psp also undergoes extension in its upper part that is probably caused by buckling and slab pull the p wave velocity structure reveals three other major features 1 a continuity between the central range and the ryukyu arc with a shallower moho 30 km depth between 122 3 n and 122 5 n along the ryukyu arc 2 high p wave velocities along the eastern side of the central range and 3 two bodies with similar high crustal velocities 6 5 7 0 km s at 12 18 km depths embedded within the ryukyu arc basement just north of hoping basin and north of the nanao basin

north sea rift system abstract the mesozoic north sea rift forms an integral part of the arctic north atlantic rift system rifting activity in the north sea commenced during the earliest triassic during the mid jurassic the central north sea underwent a temporary doming stage crustal extension peaked during the late jurassic earliest cretaceous abated subsequently and terminated altogether during the paleocene the saucer shaped cenozoic post rift basin straddles the axis of the viking and central grabens this speaks for the applicability of a depth dependent pure shear model rather than a simple shear model geophysical data indicate an important discrepancy between upper and lower crustal attenuation across the north sea rift suggesting that during rifting processes the mono discontinuity was seriously destabilized this requires a basic modification of currently favoured crustal stretching models

tectonics of short lived intra arc basins in the arc continent collision terrane of the coastal range eastern taiwan the coastal range in eastern taiwan was originated from an oblique collision between the luzon volcanic arc and asian continent since the late neogene in this collision terrane two intra arc basins the pliocene chingpu and pleistocene chengkung basins were developed on the eastern part of the neogene chimei and chengkuangao volcanic islands respectively prior to their accretion to eastern taiwan the tectonic evolution of these neogene volcanic islands and associated intra arc basins is reconstructed by stratigraphic and sedimentological analysis igneous rock geochemistry and comparison with observations in modern collision zone in the regions off southeastern taiwan in the coastal range the intra arc basin sequences are 1 5 10 km wide and 40 km long comparable in size to their modern analogues in the active collision zone the basin axis trends subparallel to the volcanic ridge in both basins deepwater flysch overlies shallow marine reef carbonates which in turn rest on volcanic basement indicating rapid arc collapse minimum rate of 1 km m y soon after the arc continent collision the arc collapse occurred earlier in the north chimei between 5 1 and 3 5 ma and later in the south chengkuangao between 2 9 and 1 8 ma in concert with a southward propagation of the oblique collision sedimentation ended about 2 ma and 1 ma in the chingpu and chengkung basins respectively coeval with rotation of the neogene volcanic islands this suggests that the rotation inverted the intra arc basin into thrusting uplifting and final emergence thus the duration of sedimentation for the intra arc basins spanned only about 0 8 3 1 m y on the basis of land geology offshore observations and a clay model experiment simulating oblique arc continent collision a model for the intra arc basin evolution in eastern taiwan is proposed during the collision strike slip faults would have been developed in the eastern part of volcanic islands to induce transtension movements thus forming pull apart intra arc basins on the collapsed volcanic island this mechanism is believed to be responsible for the formation of the pliocene chingpu and pleistocene chengkung basins as well as the present day offshore intra arc basins found on the lutao and lanhsu volcanic islands the two intra arc basins on lutao and lanhsu are predicted to be short lived as collision continues these two basins together with their underlying northern part of the luzon arc will be rotated thrust and uplifted in the next 1 m y and finally will become part of the southern extension of the coastal range

ice age at the middle late jurassic transition a detailed record of sea surface temperatures in the northern hemisphere based on migration of marine invertebrate fauna ammonites and isotopic thermometry 18o values of shark tooth enamel indicates a severe cooling at the middle late jurassic transition mljt about 160 ma ago the magnitude of refrigeration 1 3 c for lower middle latitudes and its coincidence in time with an abrupt global scale fall of sea level documented through sequence stratigraphy are both suggestive of continental ice formation at this time ice sheets may have developed over the high latitude mountainous regions of far east russia the drastic cooling just post dated the middle late callovian widespread deposition of organic rich marine sediments e g northwestern europe central atlantic and arabian peninsula this thermal deterioration can thus be ascribed to a downdraw in atmospheric co2 via enhanced organic carbon burial which acted as a negative feedback effect i e the inverse greenhouse effect the glacial episode of the mljt climaxed in the late callovian lasted about 2 6 myr and had a pronounced asymmetrical pattern composed of an abrupt 0 8 myr temperature fall opposed to a long term 1 8 myr stepwise recovery the glacial conditions at the mljt reveal that atmospheric co2 levels could have dropped temporarily to values lower than 500 ppmv during mesozoic times

supply and removal of sediment in a landslide dominated mountain belt central range taiwan abstract a strong coupling between hillslope and valley systems is often inferred for mountain landscapes dominated by bedrock landsliding we reveal the nature of this link using data sets on landsliding and sediment transport from two montane catchments draining the eastern central range of taiwan here the magnitude frequency distribution of landslides can be modeled by a robust power law but this scale invariance is not mirrored in the sediment discharge at the mountain front instead downstream sediment loads reflect a complex response to both sediment supply and ambient hydraulic conditions the rivers do not transport significant amounts of sediment unless it is provided by hillslope mass wasting in the catchment removal of landslide debris is a function of the transport capacity of the stream at the site of entry thus there is a dual supply and transport control on sediment loads in bedrock floored streams over a monitoring period of 25 yr the bulk of the sediment leaving the mountain bel

collision and stress trajectories in taiwan a finite element model abstract field analyses of plio quaternary compressional deformations in taiwan have enabled us to reconstruct the paleostress trajectories resulting from the collision of the luzon arc philippine sea plate with the chinese continental margin eurasian plate the direction of the maximum compressional stress 1 shows a fan shaped pattern that we interpret as resulting from the collision of a rigid body the luzon arc indenting a more deformable material the thick sediments of the chinese continental margin simple analytical models qualitatively explain the fan shaped pattern but the influence of various parameters such as boundary conditions and rheology cannot be quantitatively accounted for by this approach consequently we have used a finite element technique to compute the stresses and strains induced by the push of a rigid body against a two dimensional viscous material the boundary conditions are the velocities based on plate kinematics a motion in the n300 e direction best explains the stress trajectories observed in central taiwan viscosity contrasts as well as small changes in the shape of the northern edge of the indenter have little influence on the computed stress pattern the most important parameter is the direction of convergence our model quantitatively explains the general pattern of the stress trajectories observed in the collision zone of taiwan between the philippine sea plate and eurasia

sedimentology of early pliocene sandstones in the south western taiwan foreland implications for basin physiography in the early stages of collision abstract this work presents sedimentological observations and interpretations on three detailed sections of the pliocene yutengping ailiaochiao formations deposited in the early stages of collision in taiwan seven facies associations record paleoenvironments of deposition ranging from nearshore to lower offshore with a strong influence of tidal reworking even in shelfal sub tidal environments and a pro delta setting characterized by mass flows the association of shallow facies of the upper offshore to lower shoreface with pro delta turbidite facies sourced in the orogen to the east suggests a peculiar setting in which turbidite deposition occurred below wave base but on the shelf in water depths of probably less than 100 m this adds to the examples of shallow turbidites increasingly commonly found in foreland basins and challenges the classical view of a deep early underfilled foreland basin time series analysis on tidal rhythmites allow us to identify a yearly signal in the form of periodic changes of sand supply energy and bioturbation that suggests a marked seasonality possibly affecting precipitation and sediment delivery as well as temperature the taiwan foreland basin may also present a potentially high resolution record in shallow sediments of the early installation of monsoonal circulation patterns in east asia we confirm partly the paleogeography during the early stages of collision in taiwan the chinese margin displayed a pronounced non cylindrical geometry with a large basement promontory to the west in place of the modern taiwan mountain range collision in taiwan may have happened at once along the whole length of the modern mountain range instead of progressively from north to south as classically considered

structure of the 1999 chi chi earthquake rupture and interaction of thrust faults in the active fold belt of western taiwan abstract we summarize the structural characteristics of the surface ruptures of the 1999 mw 7 6 chi chi earthquake in western taiwan and discuss the geological interaction of the chelungpu fault with adjacent faults based on geological investigations seismological analyses and gps measurements of surface co seismic displacements we describe the regional 3 d fault plane and slip distribution of the chi chi earthquake and compare these to the geological features of the chelungpu fault we find that one key feature of the chelungpu fault is the stratigraphy controlled slip surface at the level of the uppermost few kilometers the chelungpu fault slip plane generally follows the bedding plane of the pliocene chinshui shale the second key feature of the chelungpu fault is the difference in structurally geometric configuration between its northern and southern segments the northern fengyuan segment shows a bedding parallel thrust fault within east dipping strata in both footwall and hanging wall in contrast the southern tsaotun segment exhibits east dipping strata are overthrust onto flat lying recent alluvial deposits these two features not only explain a hinterland imbricate thrusting on the hanging wall of the fengyuan segment but also explain the change in strike of the chi chi surface ruptures at the northern end the southern end of the 1999 chi chi rupture is interpreted to be linked to a series of nw trending strike slip faults in particular we propose that the luliao strike slip fault served as the lateral ramp of the chelungpu fault and the gukeng strike slip fault acted as a barrier to end the southern propagation of the 1999 rupture geomorphic features and paleoseismological data indicate that the range front chelungpu fault has generated large earthquakes during the last several thousand years alternatively in the miaoli area to the north and the chiayi area to south historical earthquakes as well as active geomorphic features are not restricted on the range front thrust faults instead more complicated structures including tightly spaced folds duplex structures and strike slip faults are involved in seismogenic processes a more detailed investigation of regional structural characteristics is needed for mitigation against the seismic hazards in the 300 km long active fold belt in western taiwan where several damaging large earthquakes have been documented during the last century

seismogenic patterns in the taiwan region insights from source parameter inversion of bats data abstract we systematically invert source parameters of 96 earthquakes that occurred in the taiwan region between july 1995 and june 1998 using waveforms recorded by the newly established broadband array in taiwan for seismology bats the results are utilized to delineate the seismogenic patterns associated with the regional tectonic processes between the eurasia and philippine sea plates in general high seismicity is observed at five locations including the nan ao basin 24 n 122 4 e near the hualien area 24 2 n 121 7 e east of the longitudinal valley and within the philippine sea plate the forearc region to the west of lanshu and the okinawa trough events with focal depths less than 25 km scatter across a wide region from the taiwan strait to the ryukyu and luzon arcs whereas events between 25 and 50 km concentrate offshore east of taiwan most earthquakes that occurred beneath the nan ao basin are consistent with the northward subduction of the philippine sea plate along the plate interface events offshore east of the longitudinal valley and within the philippine sea plate are dominated by a compressional regime along the nw nww directions whereas the lanshu lutao forearc is characterized by e w compression normal faults showing n s extension are observed in the okinawa trough where we observed a successive rotation of t axes from n s to nw se as the epicenters approach taiwan indicating a possible interaction between the extensional and compressional strain regimes there most events between 50 and 65 km depth within the subducted philippine sea plate beneath ryukyu are in downdip extension with lateral compression approximately parallel to the strike of the slab the depth where the state of strain switches from downdip extension to downdip compression is constrained at 110 125 km for the southernmost ryukyu slab based on our results we propose that the subducted philippine sea plate beneath ne taiwan plays a significant role in the overall orogenic process of taiwan the lithospheric collision in taiwan should consist of two major components one is the well recognized arc continent collision that dominates the central and southern taiwan and another the slab continent collision that reigns in northern taiwan a cluster of earthquakes near hualien suggests that an incipient west or northwestward subduction of the philippine sea plate is currently taking place there alternatively they can be interpreted to suggest that the steeply east dipping longitudinal valley fault may have transformed near hualien into a diffuse thrust zone which eventually connects itself to the plate interplate beneath the southernmost ryukyu arc earthquakes beneath taiwan and the taiwan strait are compatible with the overall collision convergence and lateral extrusion nonetheless the lateral extrusion is probably only a secondary feature in the tectonic processes of taiwan

a study on the background and clustering seismicity in the taiwan region by using point process models 1 this paper investigates the shallow seismicity occurring in the taiwan region during the 20th century using a stochastic declustering method that has been developed on the basis of the theory of the epidemic type aftershock sequence model it provides a probability based tool to objectively separate the space time occurrences of earthquakes into a background and a clustering component on the basis of the background and clustering seismicity rates we discuss the correlation between the distribution of the cluster ratio and the regional seismotectonic structures specifically we find that the areas of the highest clustering ratio correspond to the major strike slip fault traces in and around taiwan additionally in the taiwan inland region during the period 1960 1990 the outputs for the stochastically declustered catalogue show a clear quiescence in background seismicity preceding the recovery of activation and the occurrences of the 1999 chi chi earthquake of ml7 3 while the other active regions show stationary background activity this could be interpreted as an effect of the aseismic slip in the chi chi rupture fault whereby the inland region around the chi chi source becomes a stress shadow

probabilistic seismic risk analysis in the taiwan area based on pga and spectral amplitude attenuation formulas abstract a method for conducting a seismic hazard analysis of active faults using a fault rupture model and a point source model is presented based on a peak ground acceleration pga attenuation formula the annual probability of exceedance at a specific site is calculated the uniform hazard spectrum is also determined based on a spectral amplitude attenuation formula to improve the reliability of the seismic hazard analysis a detailed study of hazard parameters is conducted and discussed a specific site in taiwan is chosen to illustrate the hazard analysis

continuous monitoring of an active fault in a plate suture zone a creepmeter study of the chihshang fault eastern taiwan abstract data from continuously monitored creepmeters across the active chihshang fault in eastern taiwan are presented the chihshang fault is an active segment of the longitudinal valley fault the main suture between the converging philippine and eurasian plates in taiwan since the 1951 earthquake mw 7 0 no earthquake larger than magnitude 6 0 occurred in the chihshang area at least during the last 20 years the chihshang fault underwent a steady creep movement resulting in numerous fractures at the surface five creepmeters were installed in 1998 at two sites tapo and chinyuan within the chihshang active fault zone one year results from august 1998 to july 1999 show a horizontal shortening of 19 4 0 3 mm and 17 3 0 7 mm at tapo and chinyuan respectively these annual shortening rates are in a good agreement with other estimates of strain rate independently obtained from geodetic measurements and geological site investigation the creepmeter measurements were made on a daily basis providing accurate information on the previously unknown evolution of creep during the year the records of fault creep at the tapo site thus revealed close seasonal correlation with average rainfall the period of high creep rate coincides with the wet season whereas that of low creep rate coincides with the dry season also in comparison with the tapo site the creep behaviour as a function of time is complex at the chinyuan site possible factors of irregularity are under investigation thermal effect acting on the concrete basement of the creepmeters earth tide effect water table variations in a nearby rice field and rainfall the comparison between gps measurements across the longitudinal valley 31 mm year of horizontal displacement and the creepmeter measurement across the chihshang fault zone 17 19 mm year of horizontal displacement suggests that there exists other shortening deformation across the active fault zone in addition to those we have measured from the creepmeters

structure and quantification of processes controlling the evolution of the inverted ne german basin abstract a ne sw reflection seismic transect crossing the entire ne german basin negb was investigated in detail to study the interaction between tectonics and sedimentation during the multiphase evolution of the region by restoring a geological section across the post rotliegend the kinematic evolution was reconstructed and rates of important geological processes such as erosion or basin shortening were quantified the present day structural style of the negb is the result of several major deformation events 1 regional subsidence accompanied by local thin skinned e w extension during the permo triassic jurassic was followed by basin inversions at the 2 jurassic cretaceous and at the 3 cretaceous tertiary boundary zechstein salt played an important role since mobile zechstein evaporites decoupled the supra salt from the sub salt succession and allowed the transmission of deformation over a large distance of major significance to the late cretaceous structural development was the crustal scale upthrusting of the calfoerde block along the gardelegen fault at the southern basin margin the accompanying horizontal shortening has a minimum value of 9 km and led to the development of thrusts and folds within the post zechstein succession

seismogenic faults along the major suture of the plate boundary deduced by dislocation modeling of coseismic displacements of the 1951 m7 3 hualien taitung earthquake sequence in eastern taiwan abstract research at plate boundaries generally focuses on the kinematics of plate motions the genesis of large earthquake and natural resources however often the present state of knowledge is still insufficient to reveal the details of such dynamic systems to define in more detail the dynamics of a major plate boundary fault the coastal range fault eastern taiwan we use seismologic and geodetic data to unravel its subsurface geometry and relevant fault behavior by recomputing the archive triangulation datasets 1917 1978 and using a dislocation algorithm we determine that it consists of three segments our model results are consistent with the observation of the 1951 m7 3 hualien taitung earthquake sequence that the southern two segments are both oblique slip faults with significant thrust components while the northern segment is a pure strike slip fault according to our model each segment has the potential to produce an earthquake larger than m7 however based on gps observations and seismic records slip on the southern segment may take the form of aseismic creep and multiple moderate earthquakes rather than large events with long recurrence interval as occur on the two more northerly segments with regard to the central segment the epicenter distribution of catalogued earthquakes occurring after 1951 reveals the presence of a seismic gap indicating that slip on this segment is predominantly coseismic with a correspondingly higher potential for large earthquakes in the future

disentangling the control of tectonics eustasy trophic conditions and climate on shallow marine carbonate production during the aalenian oxfordian interval from the western france platform to the western tethyan domain the objective of this work is to improve our understanding of the processes controlling changes in the architecture and facies of intracontinental carbonate platforms we examined the facies and sequence stratigraphy of aalenian to oxfordian limestones of western france seventy seven outcrop sections were studied and thirty one sedimentary facies identified in five depositional environments ranging from lower offshore to backshore platform evolution was reconstructed along a 500 km cross section twenty two depositional sequences were identified on the entire western france platform and correlated with european third order sequences at the biozone level demonstrating that eustasy was the major factor controlling the cyclic trend of accommodation the tectonic subsidence rate was computed from accommodation measurements from the aalenian to the oxfordian in key localities tectonism controlled the sedimentation rate and platform architecture at a longer time scale tectonic subsidence triggered the demise of carbonate production at the bathonian callovian boundary while the uplift made possible the recovery of carbonate platform from caen to le mans during the mid oxfordian topography of the paleozoic basement mainly controlled lateral variations of paleodepth within the western france platform until the mid bathonian a synthesis of carbonate production in the western tethyan domain at that time was conducted stages of high carbonate production during the bajocian bathonian and the middle to late oxfordian are synchronous with low 13c high eccentricity intervals and rather dry climate promoting 1 evaporation and carbonate supersaturation and 2 oligotrophic conditions periods of low carbonate production during the aalenian and from the middle callovian to early oxfordian correlate with high 13c and low eccentricity intervals characterized by wet climate and less oligotrophic conditions such conditions tend to diminish growth potential of carbonate platforms this work highlights the importance of climate control on carbonate growth and demise at large scale in western tethyan epicontinental seas

tectonic subsidence modelling of the polish basin in the light of new data on crustal structure and magnitude of inversion abstract the polish basin pb is one of a set of basins developed on the paleozoic platform of western europe in the late paleozoic between the variscan orogen and the east european craton eec its main depocentral axis the mid polish trough mpt was active during most of the basin development as a maximum subsidence zone with almost uninterrupted sedimentation the present base of the permian in the mpt ranges in depth from ca 3000 to 3500 m near the baltic coast to up to 8000 m to the southeast the mpt lies parallel and adjacent to the edge of the eec and appears to be related to a distinct structural zone within the crust the tornquist teisseyre zone ttz subsidence of the mpt can be explained in terms of crustal extension transtension and related lithosphere cooling coupled with the structural predetermination of the underlying ttz tectonic subsidence analysis of the preserved and reconstructed stratigraphic record suggests the occurrence of a late permian early triassic rifting phase however there is a deficit of geologically observable extensional features faulting of this age implying an important relationship between this phase of apparent basin subsidence and earlier post variscan late carboniferous early permian tectonism the match between crustal structure implied by basin modelling studies and available deep seismic sounding dds data is not always clear this is probably related to the heterogeneous basement which comprises the outer zone of the variscan belt in the southwest eec crust in the northeast and a complex of caledonian reworked precambrian crustal blocks in the central part of the basin changes to crustal architecture as a result of alpine tectonics may also play a role increased tectonic subsidence rates during oxfordian kimmeridgian times late jurassic correlate with intensified rifting and wrench activity within the arctic north atlantic rift system and along the northern tethyan margin in contrast accelerating tectonic subsidence beginning in the cenomanian is a precursor of compressional deformations in the basin that culminated in alpine related basin inversion during the latest late cretaceous and earliest tertiary taking inversion into account the maximum depth of the base zechstein structural surface at the end of the cretaceous is estimated to have been as much as 5000 m near the baltic sea to more than 10 000 m in the southeasternmost part of the basin because of the erosion of these sediments however constraints on cretaceous subsidence and in turn the magnitude and exact timing of late cretaceous paleogene inversion are poor

basin evolution of the northern part of the northeast german basin insights from a 3d structural model abstract a 3d structural model for the entire southwestern baltic sea and the adjacent onshore areas was created with the purpose to analyse the structural framework and the sediment distribution in the area the model was compiled with information from several geological time isochore maps and digital depth maps from the area and consists of six post rotliegend successions the upper permian zechstein lower triassic middle triassic upper triassic jurassic cretaceous and cenozoic this structural model was the basis for a 3d backstripping approach considering salt flow as a consequence of spatially changing overburden load distribution isostatic rebound and sedimentary compaction for each backstripping step in order to reconstruct the subsidence history in the region this method allows determination of the amount of tectonic subsidence or uplifting as a consequence of the regional stress field acting on the basin and was followed by a correlation with periods of active salt movement in general the successions above the highly deformed zechstein evaporites reveal a thickening trend towards the gluckstadt graben which also experienced the highest amount of tectonic subsidence during the mesozoic and cenozoic two periods of accelerating salt movement in the area has been correlated with the e w directed extension during the late triassic early jurassic and later by the late cretaceous early cenozoic inversion suggesting that the regional stress field plays a key role in halokinesis the final part of this work dealt with a neotectonic forward modelling in an attempt to predict the future topography when the system is in a tectonic equilibrium the result reveals that many of the salt structures in the region are still active and that future coastline will run with a wnw ese trend arguing that the compressional stresses related to the alpine collision are the prime factor for the present day landscape evolution

palaeoenvironments of the late triassic rhaetian sea implications from oxygen and strontium isotopes of hybodont shark teeth the oxygen and strontium isotopic composition of 125 teeth of the hybodont sharks lissodus and hybodus from various late triassic rhaetian bone bed localities in the central european basin are used as environmental and ecological tracers for the shallow epicontinental rhaetian sea the preservation of tooth enameloid was ascertained by cathodoluminescence microscopy mean 18op values differ regionally across the rhaetian sea with values of 18 6 0 6 near the western gate 16 1 0 8 in the east 15 4 0 6 in the southeast and 17 7 0 9 in the south the 18op values in the eastern rhaetian sea are 4 5 lower relative to tethyan seawater while teeth from the southern and western parts close to the marine gates are less fractionated the strontium isotopic composition of teeth from most localities is more radiogenic in comparison to late triassic seawater the observed spatial 18op trend in the rhaetian sea indicates a shift from marine to brackish conditions in the south and west towards extensively brackish conditions with salinities of less than 16 in the east thus confirming the existence of two marine gates brackish conditions persisted throughout early rhaetian times and were maintained by increased fluvial discharge from the vindelician bohemian and fennoscandian highs as a result of enhanced atmospheric moisture availability in the course of the rhaetian transgression the 18op values of lissodus and hybodus indicate euryhaline behaviour of rhaetian hybodonts by exceeding modern shark intraspecific variability the lack of accordance in 18op values between different isotopically conspicuous localities in the rhaetian sea contradicts a basin wide migration pattern differences between co site taxa might indicate some degree of niche partitioning

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

b values of shallow earthquakes in taiwan abstract in taiwan the b values of earthquakes with focal depths of less than 35 km are smaller offshore than on land on land except for the coastal range the b value correlates to the degree of metamorphism of rocks which decreases inland from east to west small b values appear at the leading edge of the subducting slab of the philippine sea plate that plunges underneath northern taiwan possibly indicating high stress due to a bending of the slab large b values in an area including the volcano groups in northern taiwan may be due to the remnant geothermal effect after past volcanic activities besides small b values on land are mainly associated with low bouguer gravity anomalies offshore small b values are related to high bouguer gravity anomalies particularly in regions with a large gravity gradient

eustatically controlled sedimentation in the hettangian sinemurian early jurassic of poland and sweden in earliest jurassic times terrigenous continental and marginal marine deposition occurred in a large epeiric basin along the tornquist line in europe detailed sedimentological studies allow recognition of palaeoenvironmental fluctuations in space and time the main earliest jurassic transgressions occurred in the early hettangian early sinemurian mid sinemurian and latest sinemurian and formed bounding discontinuities transgressive surfaces of considerable correlative significance there is a step wise trend of increasing marine extension and influence during the early hettangian early sinemurian mid sinemurian and latest sinemurian earliest pliensbachian transgressions four sequences four transgressive systems tracts three highstand systems tracts and three levels regarded as equivalents of maximum flooding surfaces are distinguished in the case of type 2 sequences when incised valley fill deposits are not developed and regional erosion is less common it may be rather difficult to define the sequence boundaries which are often concealed within the amalgamated fluvial deposits occurring in the neighbouring parts of two adjacent sequences fluvial deltaic sediments terminate the highstand systems tracts and in this setting the transgressive systems tracts start with continental deposits prior to the transgressive surfaces generally an exact correlation can be achieved between the sequence stratigraphy of the northeast and northwest european lower jurassic and the eustatic curve proposed by epr assuming some changes proposed by a hallam the establishment of this correlation hopefully will stimulate future studies of the sequence stratigraphy of poorly dated siliciclastic deposits of marginal basins in this setting even minor changes in sea level may cause major changes in facies development over large areas

sequence stratigraphic framework of the lower and middle jurassic in the north german basin epicontinental sequences controlled by boreal cycles in the early jurassic the epicontinental central european basin ceb including the north german basin ngb was covered with a semi enclosed inland sea that was in the late middle jurassic transferred to a continental shelf sea connected with the boreal and the tethyan oceans the pronounced facies architectures of lower to middle jurassic coastal deltaic and basinal deposits challenged many workers to apply sequence stratigraphic methods however resulting regional schemes are in places contradicting which is caused by both common problems with precise dating and processes of regional to local scale obliterating the sea level signal such as tectonically enhanced subsidence enhanced sediment supply thermal doming or salt diapirism this paper proposes a lower to middle jurassic sequence stratigraphic framework of the ngb the application of a multi method approach including intensive macro and micropalaeontological dating as well as mapping of biofacies and lithofacies architecture to an extensive data set of cored and logged wells resulted in a hierarchical framework of 2nd 3rd and 4th order epicontinental sequences this approach enabled the identification and exclusion of areas and locations where subordinated controls such as salt diapirism superimposed the signature of sea level fluctuations within stratal pattern architectures the proposed sequence stratigraphic framework correlates well with the boreal standard but to much lesser extent with the tethyan standard and thus demonstrates the principle control of boreal cycles on epicontinental stratal pattern architectures of the ngb this coincides with more significant faunal exchanges between the boreal and subboreal provinces in particular the opening of a marine strait via the russian platform in the late middle jurassic enabled the immigration of boreal ammonites and ostracods into the ngb and the northern ceb and illustrates the change from a semi enclosed inland sea to a continental shelf sea furthermore the recognition of lower and middle jurassic 4th order sequences supports suggestions of glacio eustatic sea level changes in the jurassic

crust mantle boundaries in the taiwan luzon arc continent collision system determined from local earthquake tomography and 1d models implications for the mode of subduction polarity reversal abstract in order to better understand the mode of subduction polarity reversal in the taiwan luzon arc continent collision zone we mapped its crust mantle boundaries using local earthquake tomography by contouring surfaces of constant vp 7 5 km s 1 we identified three moho discontinuities and the plate interface that juxtaposes eurasian lower crust against mantle lithosphere of the philippine sea plate the plate interface dips to the east under southeastern taiwan and steepens progressively towards north until it becomes vertical at 23 7 n from there it continues northward in a vertical orientation until the limit of the tomographic model inhibited further mapping for the moho additional depth constraints were derived from 1d models using p wave arrivals of local earthquakes the mohos of the eurasian and philippine sea plates are disconnected across the plate interface beneath southern taiwan the eurasian moho dips to the east at 50 60 following the orientation of the plate boundary and continuous with the benioff zone towards north the eurasian moho steepens into subvertical again together with the plate boundary the philippine sea plate moho exhibits a synform like crustal root interpreted as the base of the magmatic luzon arc towards the north this root deepens from 30 to 70 km underneath the ryukyu trench in northernmost taiwan the hinge of the vertically subducting eurasian slab steps westward out of the thrust belt leaving the deformation front to the east inactive and giving way to the north dipping philippine sea plate a subhorizontal moho at 30 35 km depth overlies the north dipping philippine sea slab and is interpreted as a newly formed moho established after westward rollback and delamination of the subducting eurasian slab in combination these data support a model of progressive subduction polarity reversal in which a tear within the eurasian lithosphere propagated southwestward deactivating the deformation front

taiwan orogeny thin skinned or lithospheric collision abstract the taiwan orogeny is young and presently very active it provides an excellent environment for studying ongoing orogenic processes especially since the region is monitored intensively with dense seismological and geodetic networks and new studies aiming at deciphering shallow and deep structures in and around taiwan have been recently conducted or are being planned the available data can be used continually to test critically hypotheses of the taiwan orogeny hypotheses dealing with the mechanics of mountain building are basic to the understanding of taiwan orogeny and are particularly amenable to testing the widely cited thin skinned tectonics hypothesis was formulated to explain mainly the geologic and relatively shallow

structure and holocene evolution of an active creeping thrust fault the chihshang fault at chinyuan taiwan abstract we conducted a variety of measurements and analyses at chihshang active fault observatory in eastern taiwan including surface rupture mapping three shallow borehole core analysis and kinematic analysis of geodetic measurements we found that the chihshang fault exhibits a three branch fault system in the chinyuan alluvial fan which is composed of at least 100 m thick gravel deposits outside of the chinyuan river the chihshang fault shows a single fault system with a sharp lithological contact combining the leveling results and trench excavation we interpret that the three fault branches are coupled with a 50 60 m wide pop up structure in the hangingwall based on the ratio between vertical and horizontal displacements we obtained dip angles of 38 62 and 16 for two west vergent thrusts and an east vergent backthrust respectively this pop up was estimated to develop at the uppermost 30 40 m unconsolidated gravels during the last few thousand years above the main fault with a dip angle of 42 by compiling the available ages data we obtained an uplift rate of 2 3 cm yr of the chihshang fault and an alluvial sedimentation rate of 1 1 cm yr during the past thousands years consequently the individual uplift rate for each fault branch at the chihshang observatory was slightly less than the deposition rate of the chinyuan river no geomorphic fault scarp can thus be observed in the three branch fault system area

palaeoceanographic and palaeoclimatic reorganization around the middle late jurassic transition abstract a middle to upper jurassic succession of submarine hardgrounds overlain by nodular limestones is exposed in the jura mountains and in the helvetic of the swiss alps these sediments were accumulated along the northern shelf of the east west trending tethys seaway submarine hardgrounds and nodular limestones were also formed on the brianconnais high today outcropping in the middle penninic nappe pile of the alps hardgrounds record strong and persistent current activity along the northern tethys shelf and on the brianconnais high during the callovian and early oxfordian the transition from hardgrounds to nodular limestones corresponds to a major reorganization of tethys oceanography the change occurred in plicatilis ammonite zone middle oxfordian carbon isotope stratigraphy calibrated against an ammonite dated reference section in the french subalpine basin serves as a correlation tool between ammonite dated sections and successions with poor biostratigraphic resolution correlation demonstrates that the end of hardground formation was synchronous over wide parts of the northern tethys the change in shelf sedimentation coincides with a positive carbon isotope excursion with an amplitude of 1 5 the change in c isotope stratigraphy indicates that observed reorganization of current patterns along the northern tethys shelf was coupled with global change in oceanography and climate we propose that the change in northern tethys sedimentation was caused by opening of new seaways at a time of progressive collapse of pangaea

on the unsteady separation intrusion of the gaspe current and variability in baie des chaleurs modeling studies a numerical model has been used to study separation intrusion of an unsteady baroclinic coastal jet the gaspe current gc and its impact on dynamics and thermodynamics of the baie des chaleurs bdc gulf st lawrence canada the model has 2 layers with primitive equation dynamics and an embedded bulk mixed layer ml model it is forced with observed atmospheric fluxes as well as the gc the simulations show that the variability in the baie des chaleurs is controlled by the characteristics of the unsteady gc separation intrusion on the basis of the dynamic and vorticity balance analyses it is found that the separation is related to the adverse pressure gradient force which is induced by the ageostrophic terms in the momentum equations and to local vorticity intensification due to the inertial effect in the flow the simulations demonstrate characteristics of unsteady separation the presence of separation in an accelerating current as well as in a linear current with strong deceleration when momentum advection is neglected gives new insight into the mechanisms of unsteady boundary current separation unsteady separation or intrusion occurrence depends on the magnitude of the gc transport as well as its rate and duration of deceleration or acceleration the gc intrusion generates cyclonic circulation in the bdc prevailing westerly winds reduce the cyclonic circulation inside the bay but have little effect on separation intrusion near the entrance the gc either intrudes along the coastline attachment or after separation reattachment increasing vertical shear of the gc and offshore movement of the gc axis reduces the tendency to separate the finding of an asymmetric response of gc separation intrusion to symmetric gc forcing explains the monthly mean features seen in observations taken in the bay

upper triassic lower cretaceous seismic sequence stratigraphy and basin tectonics at bornholm denmark tornquist zone nw europe abstract an integrated analysis of seismic sequence stratigraphy and structural evolution of a dynamic intraplate fault basin was conducted along a segment of the tornquist zone at the boundary between the northwest european craton and the baltic shield east european platform high quality regional seismic reflection lines document the late triassic through early late cretaceous tectonic history and depositional sequence architecture the stratigraphic package was divided into three major transgressive regressive cycles 1st order sub cycles the upper upper triassic through lower cretaceous siliciclastic cycles i and ii are divided into 2nd order transgressive regressive facies cycles composed of higher frequency 3rd order sequences the lowstand basin fill comprises stacked successions of lowstand systems tracts produced by relative sea level rises and falls during the 3rd order regressive intervals highstand dominated depositional conditions prevailed to the northwest while lowstand dominated conditions occurred to the southeast cycle iii records an upper cretaceous major siliciclastic chalk cycle the magnitude of the relative sea level highs and lows increased up through the studied interval a two dimensional structural evolution analysis is based on the variation of the sediment thickness across the fault blocks up through the sedimentary column basin subsidence can be divided into successive structural tectonic regimes fault block rotation and structural inversion characterized the early subsidence of the basin floor during the second interval inversion ceased while fault block rotation continued in the third interval the rotation also stopped and no deformation of the basin is recognized the three major transgressive regressive facies cycles and associated relative sea level cycles are linked with the structural regimes contemporaneous deposition of 3rd order highstand and lowstand dominated complexes related to differential subsidence and uplift is also evidence of basin tectonics as the controlling factor on relative sea level changes comparison of the relative sea level curve developed for the study area with eustatic sea level curves shows that they follow different trends the deviations between these curves and the correlation of sequence boundaries with changes of the tectonic regime support the conclusion that tectonics was a major control on relative sea level fluctuations in the study area the 2nd order cycles linked with deformation episodes along the tornqist zone correlate with lower middle jurassic 2nd order cycles in england deformation along the tornquist zone may thus have influenced the sequence stratigraphy across the entire northwest european craton

new results from physical modelling of arc continent collision in taiwan evolutionary model abstract both the analysis of the geological data and the results from 2d and 3d experimental modelling of arc continent collision in taiwan reveal the following major stages in this process 1 failure and thickening of the subducting crust of the chinese continental margin under the frontal part accretionary prism of the philippine sea plate psp since ca 6 7 ma 2 uplift squeezing and exhumation of the subducted crustal slice of the chinese margin and initiation of the central range about 5 ma ago 3 flexural buckling subsidence of the luzon arc fore arc under strong horizontal compression and sedimentary infilling of this area by the material shed from the growing and exhuming central range 4 failure of the psp along the west vergent longitudinal valley fault dipping beneath the arc and closure of the fore arc 5 subduction reversal and stoppage of continental subduction which has already occurred in northern taiwan and propagates to the south the southward propagation of the collision is not stationary currently occurring initial collision in southern taiwan and offshore to the south does not follow the same described above evolution as in central and northern taiwan the evolution of the collision in time and space should be considered in the framework of a 3d model where the psp rupture is preparing in the central and northern taiwan during a long time passing through a number of evolutionary stages once it has occurred the rupture longitudinal valley fault rapidly propagates to the south into the domain which did not undergo the pre rupture evolution the rupture front is currently located near 21 30 n

geomorphic evidence for an active pop up zone associated with the chelungpu fault in central taiwan abstract the destructive chi chi earthquake mw 7 6 ml 7 3 occurred in central taiwan on september 21 1999 the surface ruptures extend more than 100 km mainly along the chelungpu fault the northerly striking ruptures however branch and turn northeast from shihgang to neiwan in this vicinity a group of unpaired and polycyclic terraces along the tachia river known as hsinshe river terraces is situated on the hanging wall of the chelungpu fault many of the terraces were tilted and the younger ones and the river beds popped up during the chi chi earthquake the geomorphic evidence suggests that the terraces in the western group have been continually deformed by a pop up structure with a hinge coincident with that of the 1999 pop up deformation it suggests that the pop up structure of the chi chi earthquake has developed since the late pleistocene and has migrated northward along with tectonic activity of the chelungpu fault however the early deformation of this pop up structure shows a kink fold style as this structure propagates northward the tachia river has been diverted around its plunging nose four cycles of tectonic uplift channel migration point bar formation have been recognized in the hsinshe river terraces and serve as a model for river response to growing tectonics furthermore this study tentatively estimates the rate of 4 75 0 62 m ka for tectonic uplift in the pop up zone and 2 73 0 35 m ka for the regional rate of uplift because the pop up structure is a secondary structure associated with the main thrust the chelungpu fault the rates estimated in this study give the lower bound of the vertical slip rate in this region

polarity reversal of active plate boundary and elevated oceanic upper mantle beneath the collision suture in central eastern taiwan the active collision between the eurasia and philippine sea plates in eastern taiwan has been explored from the recently determined 3d velocity images and relocated hypocenters a north northeast south southwest trending high velocity zone corresponding to the oceanic upper mantle is narrowly defined under neath the collision suture from hualien to taitung this elevated and hot oceanic upper mantle must have played an important role in the tectonic evolution mountain building process of the adjacent continental crust a northwest dipping seismic zone can be identified in the northern collision zone extending from the surface to 30 km depth which can be correlated with the northern longitudinal valley fault lvf this zone marks a transitional plate boundary separating the high vp and high vp vs oceanic crust to the east and the high vp and vs upper crust and low vp and low vp vs mid to lower continental crust to the west a significant amount of plate con vergence along the suture has been accommodated by the high angle thrusting along the northern lvf in contrast a southeast dipping seismic zone can be identified extending from the surface to 25 km depth near taitung in the southern collision zone this zone coincides with a region of high vp and high vp vs suggesting that earthquakes occurred within a highly fractured or fluid rich zone the reverse polarity of active plate boundary faults marks two distinguished transition boundaries one from eastward subduction in southern taiwan to east west collision in the southern collision zone corresponding to the early phase of plate collision and the other from east west collision to northwest subduction in the northern collision zone corre sponding to the advanced phase of plate collision the central collision zone is creep ing and aseismic which can be attributed to the high heat flow and geothermal activity during an interseismic period since the 1951 taitung earthquake

more than one event in the late triassic mass extinction the recent hypothesis that mass extinctions are discrete phenomena that have occurred with great regularity during the history of life1 2 is testable in several ways two essential elements of the hypothesis are 1 that each extinction event represents a significant departure from normal or background rates of extinction and 2 that such mass extinction events are spaced equally in time the analyses of the cyclicity of mass extinctions so far have concentrated on the past 250 myr with the first event occuring at the permian triassic boundary 245 myr ago1 5 the second event followed 26 33 myr later1 6 in the late triassic here i present a detailed analysis of the fossil record of marine and non marine life during the late triassic which suggests that there were at least two phases of mass extinction during that time separated by 12 17 myr

shear concentration in a collision zone kinematics of the chihshang fault as revealed by outcrop scale quantification of active faulting longitudinal valley eastern taiwan abstract repeated measurements of active deformation were carried out at three sites along the active chihshang fault a segment of the longitudinal valley fault zone of eastern taiwan the present day plate boundary between the philippine sea plate and eurasia reliable annual records of displacement along an active fault were obtained based on detailed surveys of faulted concrete structures along the active chihshang fault striking n18 e we determined average motion vectors trending n37 w with an average shortening of 2 2 cm yr thus the transverse component of motion related to westward thrusting is 1 8 cm yr whereas the left lateral strike slip component of motion is 1 3 cm yr the fault dips 39 45 to the east so that the vertical displacement is 1 5 3 cm yr and the actual oblique offset of the fault increases at a rate of 2 7 3 7 cm yr this is in good agreement with the results of regional geodetic and tectonic analyses in taiwan and consistent with the n54 w trend of convergence between the northernmost luzon arc and south china revealed by gps studies our study provides an example of extreme shear concentration in an oblique collision zone at chihshang the whole horizontal shortening of the longitudinal valley fault 2 2 cm yr on average occurs across a single narrow fault zone so that the whole reverse slip about 2 7 3 7 cm yr depending on fault dip was entirely recorded by walls 20 200 m long where faults are tightly localized this active faulting accounts for more than one fourth 27 of the total shortening between the luzon arc and south china recorded through gps analyses further surveys should indicate whether the decreasing shortening velocity across the fault is significant revealing increasing earthquake risk due to stress accumulation or not revealing continuing fault creep and weak behaviour of the chihshang fault

triassic rifts and facies patterns in western and central europe the triassic evolution of western and central europe was governed by regional crustal extension that induced the subsidence of a complex network of grabens and troughs these formed an integral part of the arctic north atlantic and the tethys central atlantic gulf of mexico rift and rift wrench systems which in the course of the mesozoic and cenozoic developed into major break up axes of pangea

the toarcian bajocian deltaic system in the north german basin subsurface mapping of ancient deltas morphology evolution and controls research focussing on the morphology and morphodynamics of modern river deltas has contributed much to the understanding of reservoir geometry and prediction of hydrocarbon splays and deep geothermal aquifers the interplay of allogenic and autogenic controls results in complex histories of modern river deltas comprising subsequent regressive and transgressive stages of delta formation the application to ancient examples is still ambiguous and in particular the detailed morphological description of ancient deltas is often hampered by limited subsurface data this basin scale study employs a data set of 15 cored wells and more than 450 logged wells in combination with lithofacies biofacies and architectural analysis to reconstruct high resolution subsurface facies and sand thickness maps of the toarcian bajocian deltaic system in the north german basin the results of this study show the evolution from smaller elongate river dominated delta types in the lower and upper toarcian 15 000 to 20 000 km and a larger lobate river dominated delta in the upper aalenian 40 000 km to a cuspate mixed river dominated and wave modified delta in the upper bajocian 25 000 km the river dominated parts are composed of subsequently formed of distributary deltaic channel belts and associated sheetsands of the delta plain and distributary mouth bar complexes with bar finger sand architectures of the delta front increasing marine processes in the bajocian resulted in modification of delta complexes forming a shoreface setting with foreshoals arc like chains of ooid bearing barrier shoals and back barrier lagoons the complex history of the toarcian bajocian deltaic system was mainly controlled by allogenic sea level fluctuations that triggered the delta progradation and subordinately by allogenic basin reorganisation autogenic process change of channel avulsion led to locally reduced sediment flux and culminated in lobe abandonment and transgressive shorelines differential compaction of underlying deltaic deposits result in strong differences in accommodation space and contributed to much to large scale delta shifts 300 km this article is protected by copyright all rights reserved

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

marine and terrestrial sedimentation across the t j transition in the north german basin abstract the global mesozoic sea level rise contributed to the stepwise flooding of the central european basin ceb across the t j transition and transformed the ceb from a late triassic inland playa to an early jurassic semi enclosed inland sea the calibration of sections from north germany and thuringia using high resolution palynomorph and ammonite biostratigraphy contributes to the improved temporal and spatial resolution of this decisive period the herein proposed deltoidospora concavisporites dc zone placed between the rhaetian ricciisporites polypodiisporites rp zone and the hettangian pinuspollenites trachysporites zone marks the transitional zone of overlapping rhaetian and hettangian palynomorphs in brackish marine brackish and terrestrial environments of the north german basin ngb thus the dc zone enables the identification of the t j transition in the ngb following a short term ingression in the late norian corollina porcellispora subzone the first rhaetian transgression contributed to substantial marine terrestrial facies shifts the diachronous transgressive onlap of brackish marine strata culminated in a first rhaetian maximum flooding in the upper corollina enzonalasporites zone to lower rhaetipollis limbosporites rl zone after a regressive maximum in the middle rl zone the next transgression culminated in a second rhaetian maximum flooding in the upper rl zone following the end triassic regression herein assigned to the upper rp zone the diachronous transgressive onlap of marine shales marks the change to marine jurassic environments the herein proposed deltoidospora concavisporites dc zone placed between the rhaetian ricciisporites polypodiisporites rp zone and the hettangian pinuspollenites trachysporites zone marks the transitional zone of overlapping rhaetian and hettangian palynomorphs in brackish marine brackish and terrestrial environments of the north german basin ngb thus the dc zone enables the identification of the t j transition in the ngb at the western gate of the ceb the onset of marine hettangian strata with ammonites dated as the p erugatum biohorizon at st audrie s bay postdates the base hettangian gssp by 250 kyr from there to thuringia the diachronous onlap of marine hettangian strata with ammonites herein dated as the p plicatulum biohorizon took place over 100 kyr the first jurassic maximum flooding is dated as the interval of the p psilonotum to p plicatulum biohorizons lower planorbis zone rhaetian hettangian 3rd order sequences of the ceb correlate with contemporaneous sequences described from tethyan and peri tethyan basins pointing to circum tethyan eustatic cycles the 4th order sequences are evident in the rhaetian hettangian but only a set of rhaetian 4th order sequences can be correlated in the ngb so far

the evidence and implications of polar ice during the mesozoic abstract the mesozoic perhaps representing the longest period of warmth during phanerozoic earth history contains in general sparse and frequently equivocal evidence for polar ice although this time is undoubtedly punctuated by oscillations in climate whether sufficient to lead to polar cooling and the formation of polar ice an inviting mechanism to account for faunal and floral distribution patterns and large scale sea level change has been widely debated mesozoic evidence for glacial conditions includes abraded rock surfaces generally unsorted stone rich beds and the presence of dropstones rafted by ice within a finer grained host sediment faunal and floral evidence has also been utilised to determine the presence or absence of cold or sub freezing polar conditions together with more indirect evidence for glacial conditions derived from general circulation model gcm simulations of climate the analysis of clay mineral distributions glendonite abundance and palaeontological and sedimentological evidence for globally synchronous sea level change the extent of possible glacial environments during the mesozoic has been established by plotting published reports of glacial sediments on palaeogeographic reconstructions the general clustering of evidence at high palaeolatitudes suggests that the extent of polar ice during the mesozoic is likely to have been approximately one third the size of the present day based on such evidence a number of episodes of cold or sub freezing polar climates during the bajocian bathonian tithonian volgian valanginian and aptian are recognised evidence exists possibly also for a cold episode during the early jurassic pliensbachian although poorly constrained owing to limited biostratigraphical control the longevity of these events may be represented by a cold snap within a stage although undoubtedly the possible smearing of ages may have had the effect of lengthening and hence promoting the importance of these proposed events the climate regime of the earth during these times may be hypothesised to be characterised by a relatively steep pole to equator temperature gradient where low latitude regions are as warm or warmer than today the evidence to support such reasoning includes sharp increases in the areal distribution of both glendonites and deposits with affinities to glacial tillites and dropstones for these times coincidental falls of sea level arid events and an increased bipolarity of faunas at these times imparts further confidence that these events were of a magnitude to effect the earth as a whole

a simple criterion for gyre formation by the surface outflow from a strait with application to the alboran sea a survey of relevant numerical laboratory and observational studies combined with our own laboratory experiments suggests that the surface outflow from a strait generally forms a gyre in the adjacent sea if the exit corner is sharp the gyre grows from an initial separation bubble of radius u f where u is the current speed and f the coriolis frequency the criterion for the maintenance of a coastal jet along a curved coast instead of separation and gyre formation seems to be that the rossby number u frw 1 1 with rw the radius of curvature of the exit corner so that the coriolis force can hold the current to the coast this synthesis disregards factors such as the variation of u across the current but applied to the flow through the strait of gibraltar into the alboran sea suggests that a gyre should always form as the exit corner is sharp we suggest though that the relevant curvature is that where the interface between the two layers intersects the seafloor rather than where the sea surface meets the coast if this is the case supercritical flow or some subcritical flows at the eastern end of the strait should still always lead to gyre formation but the observed replacement of the gyre by a coastal jet along the moroccan coast could be related to subcritical flow that is reduced below its normal value by a barotropic fluctuation or by changes in the interface depth in the mediterranean

ten second love wave propagation and strong ground motions in taiwan applying the surface wave gaussian beam method to a three dimensional 3 d structure of taiwan we have studied the generation and propagation of short period 10 s surface waves in a region of pronounced crustal heterogeneity especially in a region defined to be at an epicentral distance larger than a few focal depths away where high frequency near field motions are largely attenuated and surface waves are adequately developed by perturbing the source model as well as the crustal model in an iterative inversion process we have achieved an excellent fit to the recent strong motion observations recorded during the tung ao earthquake june 5 1994 ml 6 0 in taiwan this allows us to 1 obtain a refined 3 d crustal model of taiwan from an initial model that was derived from recent tomographic results and more important 2 explain the distribution patterns of the strong shaking reported in terms of intensity maps for historical large earthquakes and predict the long period strong motion distribution patterns for future large earthquakes in taiwan with an improved 3 d structure we have gained better insight into short period surface wave propagations as they are modified by crustal lateral heterogeneity focusing and defocusing are clearly demonstrated of particular interest is the central mountain range a massive tertiary metamorphic body forming the backbone of taiwan that seems to serve as a divergent lens for the propagating surface waves whereas the large sedimentary basin in southwestern taiwan seems to focus the wavefronts instead the computed distortions of the propagating surface wave field due to lateral heterogeneity are correctly reflected by the observations

the crustal deformation of the ilan plain acted as a westernmost extension of the okinawa trough abstract we analyze the current deformation in ilan plain of northeastern taiwan considered as the western extension of okinawa trough based on 34 geodetic sites observed between 2002 and 2006 the station velocities are between 1 9 mm yr and 43 0 mm yr in a direction between 38 and 143 relative to stable continent margin of eurasian plate this largest velocity is moving southeastward 143 at a rate of 43 mm yr was enhanced by a seismic doublet that occurred on march 6 2005 the station velocities at the northern margin of ilan plain are insignificant with a magnitude of 1 9 mm yr to 7 5 mm yr on the contrary the station velocities increase approximately southward along the southern margin of ilan plain the stations are moving roughly e w with a magnitude of 5 8 mm yr to 21 8 mm yr further southward the station velocities increase to a value of 43 0 mm yr in a direction of 143 the most prominent feature of the strain distribution patterns in ilan plain are the remarkable extensional strain rates observed in central and southern flank of the ilan plain the largest extensional rate is found 2 66 strain yr in 147 with a shortening rate in the perpendicular direction 1 28 strain yr in 57 indicating transtensional deformation mode in the northeastern flank of ilan plain insignificant or minor deformations are observed overall the extensional rates in this area clearly increase from north to south the extension directions in study area mostly trend e w to nw se directions using the velocity field of 34 gps stations and its strain rate filed we suggest the lateral extrusion process towards mechanically weak domain adjacent ryukyu subduction zone the lateral extrusion is facilitated by the opening of the okinawa trough we conclude that the northeast taiwan is subjected to both the compressional force exerted by the indentation of philippine sea plate and the tensile force induced by trench retreat related to the suction force at the ryukyu trench due to the interaction of two forces the stress regime rapidly changes from pure compression in the taiwan collision belt to transtension near ilan plain and its offshore area

a sensitivity study of reduced gravity channel flows with application to the alboran sea abstract the reduced gravity response of an hydraulically forced flow in a rectangular channel is examined numerically the model parameters were set by observed features of the circulation in the westernmost basin of the mediterranean sea the alboran sea numerical experiments reveal that the solution depends critically on the inclusion of the momentum advection terms and on the form of the boundary condition on the domain s sidewalls in particular while free slip conditions show a coastally trapped current on the model s southern boundary no slip conditions cause the formation of an anticyclonic gyre upon the flow s entry into the basin

paleoseismology of the rueisuei segment of the longitudinal valley fault eastern taiwan paleoseismic trench excavations in the dafu area of eastern taiwan have provided data on the rupture history of the rueisuei segment of the longitudinal valley fault during the late holocene the 1951 taitung earthquake ruptured the dafu site which is characterized by several terrace raises with late holocene sediments uplifted by the westward thrust fault trenches across the northwest facing fault scarp exposed fluvial and alluvial deposit sediments although nearly all of the 23 radiocarbon ages vary somewhat within each layer the overall age determined for each layer is in good accord with the stratigraphic ordering of these layers based on stratigraphic ordering and a statistical comparison of radiocarbon dates using the oxcal program we estimate that two pre 1951 earthquake surface ruptures at the dafu site occurred in the periods a d 1736 1898 and a d 1564 1680 the same oxcal model constrains the past two recurrence intervals to about 165 and 140 yr although with sizable uncertainties 55 215 and 90 260 yr respectively which are 95 ranges through the correlation of three trenches across the longitudinal valley fault we are able to identify evidence for at least three earthquakes with moment magnitudes of about 7 0 7 2 that occurred up to 390 yr prior to and during 1951 furthermore based on the radiocarbon dates the mean recurrence interval is roughly 150 yr uncertainty is indeterminate with a minimum vertical uplift rate of 8 5 12 2 mm yr

an explanation for the curvature of the atlantic jet past the strait of gibraltar abstract a consistent explanation for the anticyclonic curvature of the atlantic jet as it passes through the strait of gibraltar and flows into the mediterranean sea eastern side of the strait is provided the anticyclonic curvature of the atlantic jet which is the key feature to understand the upper layer circulation in the western alboran sea is simply related to the positive net evaporation over the mediterranean the result of this positive net evaporation that mainly occurs in areas of the mediterranean far from the strait of gibraltar is a net inflow transport through the strait it is proposed that the positive net evaporation is able to produce such a net inflow in the strait because of an anomalous large scale pressure gradient this anomalous pressure gradient is found to be approximately collinear to the strait orientation the time averaged inflow of atlantic water at the eastern side of the strait of gibraltar must therefore be supergeostrophic and hence it must have anticyclonic curv

azimuthal variation of coda q in northern taiwan seismograms of local earthquakes recorded on the short period sensor of the tato station one of the sro stations near taipei northern taiwan are used to determine values of coda q qc results show the azimuthal dependence of the values of qc a correlation between the values of qc and the tectonics of the region is determined the value of qc is small in the oceanic lithosphere intermediate in the plate boundaries and large in the continental lithosphere

lake mire deposition earthquakes and wildfires along a basin margin fault ronne graben middle jurassic denmark abstract regional uplift of structural highs took place in the greater north sea region in early middle jurassic times resulting in a change from marine shelf deposition in the early jurassic to widespread emergence erosion and localized deposition in grabens the middle jurassic baga formation exposed on the island of bornholm in the baltic sea was deposited in the ronne graben which forms a dog leg pull apart basin linking the northern and southern branches of the tornquist zone the studied succession is situated on the hanging wall immediately adjacent to the main eastern graben margin fault and the footwall consists of deeply weathered granite it is the only locality along the northern branch of the tornquist zone where active tectonic influence on middle jurassic deposition can be demonstrated in outcrop small alluvial fans composed of poorly sorted washout sands and muddy debris flows with weathered granite boulders fringed the footwall scarp syn depositional soft sediment deformation and chaotic bedding structures interpreted as seismites caused by earthquake shocks are characteristic at several levels on the hanging wall further away from the active fault the depositional environment was dominated by shallow freshwater lakes with deposition of clay lake deposition outpaced subsidence and open oxygen deficient freshwater mires were formed during periods of no or only incremental fault movement the mires were only occasionally isolated from clastic input due to doming and dense vegetation resulting in accumulation of pure peat beds the content of spores and pollen shows that the mires were covered by a vegetation of arborescent and herbaceous filicopsida ferns lycopsida club mosses cycadales bennettitales ginkgoales caytoniales taxodiaceae or cupressaceae and araucariaceae wildfires were common in the mires and also on the footwall probably followed by episodes of increased run off and erosion of the upland the presence of common washout sands debrites seismites and abundant lacustrine flooding surfaces indicating sudden drowning of the mires was caused by abrupt movements on the fault with associated earthquakes the succession thus provides an example of temporal changes in deposition in response to changes in tectonic conditions the study illustrates how regional uplift of structural highs caused a restriction of deposition to narrow grabens like the ronne graben facies patterns changed dramatically from laterally extensive uniform packages controlled by sea level changes in the early jurassic to strongly localized deposition with marked facies changes controlled by faulting and earthquakes in the middle jurassic the succession thus serves as an excellent example of tectonically controlled deposition under humid conditions in a continental graben

three dimensional p and s wave velocity structures beneath taiwan deep structure beneath an arc continent collision the island of taiwan is a byproduct of one of the few active collisions between a continent represented by the eurasian continental shelf and an island arc represented by the northern extension of the luzon arc on the philippine sea plate to understand better the evolution and current tectonics of this collision we selected 1260 well recorded earthquakes from an initial set of 50 000 located by the taiwan telemetered seismograph network for the determination of one and three dimensional p and s wave velocity structures beneath the island the results for both structures and earthquake relocations reveal that the island is divided tectonically into three distinct zones in the east the philippine oceanic plate is underthrusting the eurasian plate east of a north south boundary that is well defined by both seismic activity and a region of high velocity in the south the eurasian continental plate is underthrusting the philippine sea plate south of an east west boundary at about 23 n that is sharply defined by both subcrustal seismicity and a zone of relatively low velocities the dip of the subducted continent is shallow until it reaches the luzon island arc 50 km east of the main island structure under the main part of the island north of 230n reveals a shallow dipping zone of low velocities in the west above 25 km depth that narrows and steepens below that depth to at least 50 km beneath the central range the dip of this low velocity region is outlined by a narrow zone of seismicity that extends to depths of 100 km this seismic zone lies in a velocity saddle and marks an apparent offset in the central low velocity region at 24 n evidence for the subduction of the eurasian continent beneath taiwan therefore exists everywhere beneath the island and the low velocity regions in the mantle support but do not require the subduction of some 6 16 km of lower continental crust to depths of at least 50 km the distinct change in both the velocity structure and the seismic activity at 23 n and the offset of the low velocity regions at 24 n argue for abrupt changes in the nature of subduction across these latitudes these changes may be caused by an interaction of the luzon island arc with the subducted continental shelf that mimics a similar interaction evident at the surface finally the velocity structure of the subducting philippine sea plate suggests that the earthquakes beneath 70 km depth are not occurring within the highest velocity regions of the plate but are probably located near the upper edge of the plate there is also evidence from earthquake locations and velocity structure that suggests that the subducting plate is segmented and that subduction is presently occurring as far south as 22 n

tectonic evolution of the mid polish trough modelling implications and significance for central european geology abstract the polish basin forms the easternmost part of the permian mesozoic northwest european basin the depocentral axis of the polish basin the mid polish trough mpt is superimposed on the boundary between the west european phanerozoic and east european proterozoic crustal domains within the trans european suture zone the presence of this fundamental crustal boundary may be paramount in structurally controlling the position of the mpt concentrating stresses during post variscan wrench and extensional tectonics in central europe tectonic subsidence analysis of the preserved and reconstructed stratigraphic record of the polish basin indicates the occurrence of an initial late permian early triassic 255 241 ma rifting phase that was followed by subsequent episodes of increased tectonic subsidence during the oxfordian kimmeridgian 157 152 ma and beginning in the cenomanian 97 ma the oxfordian kimmeridgian episode is interpreted as corresponding to a second extensional event which correlated with intersified rifting and wrench activity within the arctic north atlantic rift system and along the northern tethyan margin while the cenomanian may be considered a precursor of compressional deformations in the basin which culminated in basin inversion in the latest cretaceous and paleocene forward modelling results in view of existing geophysical interpretations which show the presence of a deep moho and a very velocity lower crustal layer beneath thempt suggest that permo mesozoic basic development may be related at least in part to the intrusion of mantle material into and densification of the lower crust rather than exclusively to crustal extension and thinning

two dimensional crustal structures of taiwan from gravity data to delineate the tectonic character of taiwan an island wide gravity survey of taiwan was conducted between 1980 and 1987 the bouguer anomaly map shows that in general isogals trend nne in consonance with the overall structural trend of the island with seismic and other geophysical data as constraints the subsurface density structures were modeled along three profiles across the major structural trends the gravity data are consistent with average continental moho depths of 26 km in the coastal plain and the western foothills 28 km underneath the coastal range in eastern taiwan and 33 km under the central range a lack of significant correlation of the bouguer anomalies with the topography implies dynamic rather than isostatic support of topography in the taiwan region

vertical crustal movements in eastern taiwan and their tectonic implications abstract leveling surveys along several routes and tidal observations at various points in eastern taiwan demonstrate rapid vertical crustal movements and they provide an effective means for monitoring the effects of collision between the philippine sea plate and the eurasian plate rapid elevation changes were detected in the southern section of the longitudinal valley repeated releveling along three routes since 1984 reveals that the coastal range was uplifted with respect to the longitudinal valley floor at a rate of about 3 0 cm yr this deformation is found to be confined within a very narrow zone along the east coast of taiwan two surveys 1984 and 1987 revealed that the coast is also undergoing uplift but at different rates from 0 cm yr to 3 5 cm yr the point of the most rapid uplift is located near 23 n and the rate generally diminishes towards the north the changes in rates may be controlled by the movements across faults tidal observations while providing a local datum show that uplift of the tidal station has occurred significant horizontal creep has been observed across many faults but rapid vertical creep as observed in the longitudinal valley is not very common

the chiuhsiungken fault a candidate to trigger a hazardous earthquake in western taiwan abstract the chiuhsiungken fault located along the boundary between the western foothills fold and thrust belt and the coastal plain in the chiayi yunlin area of taiwan has been identified as an active thrust through geological and geomorphic investigations young geomorphic features provided by shortening across the chiuhsiungken fault are well preserved and provide excellent examples to illustrate features provided by active thrust faulting historic seismicity records show that the deformation front in the chiayi yunlin area is very active and the fault slips at a rate of mm yr based on tectonic geomorphic investigation the chiuhsiungken fault has the potential to produce large earthquakes in the future the fault with a length about 15 km can be traced northward to the sinistral kuken transfer fault and southward to near the sinistral chuchi transfer fault the maximum potential magnitude of an earthquake triggered by the chiuhsiungken fault is estimated to be a m w 6 4 however the magnitude of the earthquake could be larger than expected if the adjacent faults rupture together with the chiuhsiungken fault

high resolution sequence stratigraphy of a hettangian sinemurian paralic succession bornholm denmark sequence stratigraphic interpretation of paralic successions is complicated by the complex interfingering of marine and continental strata the successions may also include terrestrial extensions of marine parasequences and completely independent lacustrine parasequence analogues failure in recognizing the possible interbeddding of these two independent parasequence types may lead to construction of sequence stratigraphic schemes based on incompatible data sets we have studied a lower jurassic paralic section from the baltic island of bornholm situated in the tornquist zone which demarcates the transition from the stable precambrian baltic shield to the subsiding danish basin and danish polish trough the hettangian sinemurian sose bugt member ronne formation of bornholm includes lacustrine fluvial and restricted marine estuarine deposits reflecting the basin margin position biostatigraphic resolution is poor and a sequence stratigraphic interpretation of the paralic succession is far from straightforward a multidisciplinary approach including facies analysis recognition and lateral trading of key surfaces palynostratigraphy palynofacies coal petrography palaeopedology clay mineralogy and source rock geochemistry is applied in order to obtain a high degree of precision in the interpretation of the paralic facies in this way four sequences are recognized in the overall backstepping lacustrine to estuarine succession marine and marginal marine parasequences are distinguished from their purely lacustrine analogues and an internally consistent sequence stratigraphic scheme is proposed this is compared and tentatively correlated with fossiliferous marine sediments in the danish basin and with published eustatic cycle charts

application of sar interferometry to a large thrust deformation the 1999 mw 7 6 chichi earthquake in central taiwan summary application of the interferometric method to four ers2 sar images acquired before and after the 1999 chichi earthquake has allowed determination of the coseismic surface displacement in the footwall area of the chelungpu fault the interferometric results revealed a relative shortening in the round trip distance between the radar antenna and the ground of the footwall side of chelungpu fault during the earthquake this shortening progressively increased from the west to the east and reaches the maximum amount of approximately 26 cm near the central segment of the chelungpu fault our interferometric results have been precisely examined using a dense gps network in the investigated area we mapped the gps coseismic measurements into the radar line of sight and implemented a forward simulation of sar interferogram from this synthesized result to control our unwrapping performance in this study these two observations are compared with a 3 d dislocation model of the fault finally a deformation analysis based on our interferometric result has indicated that a segment with irregular deformation behaviour can be distinguished in the footwall area of the chelungpu fault this segment may result from either the influence of inherited basement faults or the presence of a structural terrace that provide local opportunities for superficial deformation

present day surface deformation and tectonic insights of the extensional ilan plain ne taiwan abstract taiwan s mountain belt is an ideal location to address major questions regarding mechanisms of lithospheric deformation in convergent settings mountain building processes from oceanic subduction to continental subduction and post orogenic extension in the northeast of this belt the ilan plain is a triangular deltaic plain characterized by a flat topography close to the sea level and surrounded by the high mountains of the hsuehshan range to the northwest and the central range to the southeast its eastern coast faces the western tip of the okinawa trough the back arc basin of the ryukyu subduction zone in this study we analyzed the present day surface deformation of the ilan plain aiming at deciphering its relationships with basement faults and the regional geodynamic setting our approach is mainly based on surface vertical displacements revealed by persistent scatterer interferometry synthetic aperture radar psi which indicate that there is an area of active subsidence 18 mm yr located in the southern part of the plain in probable connection with active basement faults and in agreement with previous geodetic measurements and existing geophysical data our psi results also suggest that the subsidence occurring in the ilan plain has moved from north to south during quaternary in relation with extrusion of the belt due to the westward propagation of the okinawa trough through the taiwan mountains

vertical crustal motion of active plate convergence in taiwan derived from tide gauge altimetry and gps data abstract located at the converging junction between the eurasian and philippine sea plates the island of taiwan is subject to an active lithospheric deformation as well as seismicity taking the difference between the satellite altimetry data alt that give the absolute sea level variation and the tide gauge data tg that record the relative sea level variation we obtain the absolute vertical crustal motion of the tide gauge sites we use 20 tg stations along the west and east coasts of taiwan along with the alt measurements from the topex poseidon jason satellites in the nearby waters the alt tg results are compared with vertical gps measurements in discussing vertical motion we find a general subsidence of the entire taiwan coast during the past two decades the west coast sees no prominent vertical motion but with a severe local subsidence due to the over withdrawal of groundwater on the east coast the alt tg results in the northern section demonstrate a northward dipping motion the elastic thickness of the neighboring oceanic lithosphere modeled as an elastic plate with the flexure of the subducting plate shows that the adjacent philippine sea plate should be an old thick oceanic plate which could drag the slab into the mantle as manifested in a gentle northward subsidence in the northeast taiwan in the southern section of the east coast the alt tg results reveal a segmented or undulating pattern in the vertical motion rates judging from the different behaviors between the co seismic and interseismic vertical motions marked by the major earthquakes during the studied period we postulate a temporal saw tooth scenario for the deformation in phases it demonstrates the opposite motions under different mechanisms in the frontal sections of the subduction zone which can be understood with lateral collision and slab dragging subject to varied temporal and spatial dependences

seismicity and tectonics of a continent island arc collision zone at the island of taiwan a collision between the eurasian plate continental margin and a volcanic island arc on the philippine sea plate about 4 m y ago uplifted the island of taiwan many lines of geological and geophysical evidence suggest that the collision is still active today and is currently propagating southward due to plate interaction geological and tectonic settings have become more complicated since the onset of the collision the collision suture is along the longitudinal valley lv in eastern taiwan seismic studies including earthquake monitoring and seismic refraction lines conducted in 1985 in eastern taiwan and its offshore area using land seismic stations and ocean bottom seismographs have generated results that better constrain the present day plate interaction both the crustal velocity structure and earthquake hypocenter distribution suggest that the subduction of the philippine sea plate along the ryukyu trench extends to the east coast of taiwan near about 23 5 n very high seismicity with dominant right lateral strike slip faulting is found in the back arc region behind the ryukyu trench this seismic activity is interpreted as a result of plate convergence and back arc wrenching due to the relative motion between the okinawa platelet and the eurasian plate the region close to the lv in eastern taiwan showed only shallow and a relatively low level of seismicity during this experiment with higher seismicity to the east of the lv the lack of intermediate depth events suggests that subduction is no longer active along the collision zone and the difference in seismicity between the regions east and west of the lv reflects the difference in strength of the adjacent continental and island arc crusts to the south of the lv seismicity continued southward with intermediate depth events distributed mainly to the east of taiwan along a nearly vertical benioff zone this supports the argument that convergence and collision are still active south of taiwan

slip distribution on a thrust fault at a plate boundary the 2003 chengkung earthquake taiwan summary the 2003 chengkung earthquake mw 6 8 occurred on the east dipping chihshang fault of eastern taiwan a listric fault with dominant reverse motion a joint inversion taking into account geodetic gps and seismological accelerometric and teleseismic data is performed this modelling highlights the rupture process behaviour on the fault plane at depth the coseismic rupture developed essentially between 12 and 26 km depth expanding laterally by about 30 km towards the ssw two slip patches dominated with slip values exceeding 1 5 m during the 30 s of the whole process the rupture propagation decelerated with time starting at 3 4 0 3 km s 1 in the two main slip patches and ending with velocities below 1 6 0 1 km s 1 the 48 hr of aftershocks that followed the main shock are distributed essentially inside the coseismic slip patches on the fault surface except in the deepest southern part of the fault where slip is less resolved the results of our modelling illustrate the particular behaviour of the 2003 chengkung earthquake where the coseismic slip rapidly diminished towards the surface in good agreement with the observation of fast post seismic slip followed by interseismic creep along the chihshang fault

sedimentological palynological and geochemical studies of the terrestrial triassic jurassic boundary in northwestern poland the kamien pomorski ig 1 borehole pomerania nw poland yields a profile through the triassic jurassic t j transition in continental deposits an integrated study of the sedimentology sequence stratigraphy palynology biostratigraphy and geochemistry of these deposits has been carried out on the boundary interval which represents a time of major environmental change two lithological units within the transitional section are distinguished the lower middle rhaetian wielichowo beds of alluvial plain facies which shows evidence of a semi arid climate and the upper rhaetian to lower hettangian zagaje formation lying above a marked erosional sequence boundary composed of mudstone claystone and sandstone deposited in a fluvial lacustrine environment carbon isotope values obtained from palynomaceral separates and thus reflecting isotopic changes in atmospheric co 2 show significant fluctuations through the rhaetian the most conspicuous negative 13 c org excursion is correlated with the rhaetian initial excursion and shows two sub peaks pointing to short term carbon cycle disturbances of lesser magnitude above the initial negative excursion there is a positive excursion followed again by more negative values representing subordinate fluctuation within a positive excursion and is correlated with the t j boundary seventy two miospore taxa have been determined from the studied t j transitional section two major palynological assemblages have been distinguished the lower one typically rhaetian named the cingulizonates rhaeticus limbosporites lundblandii association which corresponds to the rhaetipollis ricciisporites rhaetipollis limbosporites zone and the upper one typically hettangian named the conbaculatisporites mesozoicus dictyophyllidites mortoni cerebropollenites thiergartii association with the age diagnostic pollen c thiergartii which corresponds to the pinuspollenites trachysporites trachysporites heliosporites zone the t j palynofloral turnover occurred in a humid period and is more conspicuous then palynofloral changes observed in greenland the tethyan domain or other parts of ne europe the osmium isotope system is studied herein for the first time from t j continental deposits and shows marked disturbances similar to those measured in marine deposits and attributed to volcanic fallout carbon and osmium isotope correlation and coeval increase in polycyclic aromatic hydrocarbon pah content and darkening of miospores confirm that eruptions of the central atlantic magmatic province camp contributed to the perturbances in climate and crisis in the terrestrial biosphere a series of periodical atmospheric loading by co 2 ch 4 or alternatively by so 2 sulphate aerosols and toxic compounds is inferred to have caused a series of rapid climatic reversals directly influencing the ecosystem and causing the triassic floral crisis a floral turnover period commenced at the initial 13 c excursion with the onset of camp volcanism obtained values of initial 187 os 186 os between 2 905 and 4 873 and very low iridium content about 5 ppt lend no support to a role for an extraterrestrial impact at the t j boundary event the position of the initial negative carbon isotope excursion about 12 m below the t j boundary position of sequence boundaries emergence surfaces and other isotope excursions allow reliable correlation with marine profiles including st audrie9s bay uk csovar hungary and the gssp profile at kuhjoch austria

the early toarcian jurassic anoxic event stratigraphic sedimentary and geochemical evidence detailed paleogeographic studies in the southern alps suggest that an oxygen minimum model is appropriate for interpreting conditions on tethyan continental margins advection of manganese in this low oxygen layer may explain the local occurrence of carbonate ores of this element carbon sulfur and iron sulfur ratios although showing considerable scatter suggest that bottom waters at this time were locally euxinic containing free hydrogen sulfide this oceanic anoxic event was preceded by significant faunal turnover of ammonites in tethys and accompanied by widespread extinction of benthos in northern europe in response to the lateral spread of anoxic bottom waters during transgression similar changes may be recognized in other parts of the world other anoxic events may have taken place during the jurassic but documentation is as yet meagre furthermore models for such phenomena remain largely speculative although upwelling and increased planktonic productivity commencing in pre toarcian time are favored for the falciferum zone event documented here from author

stepwise atmospheric carbon isotope excursion during the toarcian oceanic anoxic event early jurassic polish basin abstract during the mesozoic 250 64 ma intervals of about 0 5 myr were subject to severe environmental changes including high sea surface temperature and very low oxygen content of marine water these oceanic anoxic events or oaes occurred simultaneously with profound disturbance to the carbon cycle the carbon isotope anomaly in the early jurassic that marks the toarcian oceanic anoxic event t oae at 182 ma is characterized in marine sections by a series of dramatic steps towards lighter values herein we present new carbon isotope data from terrestrial organic matter phytoclast separates collected through a late pliensbachian middle toarcian coastal and marginal marine succession in the polish basin a setting where hinterland climate and sea level change are well recorded the results show that the shift to light carbon isotope values in the woody organic matter and therefore also in atmospheric carbon dioxide similarly occurred in major steps the steps are here correlated with those identified from marine organic matter where they have previously been attributed to 100 kyr eccentricity forcing of climate the results provide strong support for orbitally and climatically controlled release of isotopically light carbon from gas hydrates into the ocean atmosphere system in a series of rapid bursts additionally a link between the carbon isotope steps and shoreline movements can be demonstrated individual peaks of the negative excursion are mostly associated with facies indicative of sea level rise flooding surfaces however at the same time inferred higher atmospheric carbon dioxide content may be expected to have resulted in increased rainfall and temperature leading to accelerated weathering and erosion and consequently increased sediment supply progradation and regression causing some mismatches between isotope shifts and inferred sea level changes enhanced abundance of megaspores derived from hydrophilic plant groups and marked increase in kaolinite are coincident with the overall development of the negative isotope excursion the combined data suggest that each 100 kyr cycle in carbon isotope values was characterized by increasingly severe palaeoclimatic change culminating in extremely hot and humid conditions co incident with the peak of the final most negative carbon isotope excursion the chemostratigraphic correlation allows very precise dating of the late pliensbachian middle toarcian coastal and marginal marine sedimentary succession in the polish basin

plate collision and paleostress trajectories in a fold thrust belt the foothills of taiwan abstract field analyses of compressional faulting and folding in the foothills of western taiwan enable us to reconstruct paleostress trajectories over a large area and to establish the relative chronology of tectonic events two main compressional events have contributed to the present structure of the fold thrust belt stratigraphic data show that these events are plio pliocene in age older normal faulting indicates nnw sse extension across the chinesse passive continental margin during the neogene the two main compressional events of the taiwan collision correspond to similar fan shaped distributions of maximum compressive stress trajectories with a counterclockwise shift of 30 50 between the two events using the relationship between recent stress trajectories and the direction of recent plate motion as a guide we reconstruct the direction of plate convergence for the older event we suspect that the relative motion philippine sea plate eurasia has rotated counterclockwise of at least 35 45 in taiwan during collision this conclusion is in agreement with independent plate tectonic reconstructions several problems provide objectives to further tectonic and paleomagnetic studies including the duration and diachronism of compressional events as well as possible clockwise rotation of northernmost taiwan

baroclinic eddy generation at a sharp corner in a rotating system laboratory experiments were conducted to investigate the generation of anticyclonic gyres by separation of a surface current from a coast in a rotating two layer system the experiments were motivated by the hypothesis that the flow of coastal currents around capes can generate oceanic eddies as well as by the observation of gyres at the mouths of various straits in the experiments the gyre is formed when the current which flows with the coast to its right if one is oriented in the downstream direction encounters a sharp convex corner the current overshoots the corner loops to the right and reattaches to the coast downstream of the corner between the current loop and the coast is an anticyclone whose width grows with time if a countercurrent flows under the surface current a similar separation in the lower layer results in the generation of a cyclone as well under some circumstances the cyclone and anticyclone advect each other away from the coast as a heton previous studies on related systems found that the corner must be sufficiently sharp for a gyre to form i show that for a very sharp corner the angle made by the corner must be above a critical value of between 40 and 45 for a gyre to form this is in contrast to nonrotating flows of comparable rayleigh number which will separate from a sharp corner at virtually any angle for angles below the critical value the current profile downstream of the corner changes as a function of corner angle indicating that it is the stagnation of the flow nearest the wall which causes the anticyclone to form this stagnation is reminiscent of the two dimensional nonrotating picture of viscous boundary layer dynamics forcing separation of a boundary current however the gyre grows more slowly when the lower layer is much thicker than the upper layer indicating that baroclinic processes are at least quantitatively important in the generation of the gyre by varying the initial condition of the current it is shown that the gyre formation is not a product of the interaction of the nose of the current with the corner in conclusion the experiments indicate that the basic mechanism of gyre formation may be viscous boundary effects as in nonrotating systems but that rotation tends to inhibit eddy generation while baroclinic effects tend to enhance it

sequential thrusting model for mountain building constraints from geology and heat flow of taiwan in this study we analyze the thermal evolution of the taiwan fold and thrust belt based on the available geological information a finite element program is used to simulate the complex kinematics of the observed sequential thrusting and the interplay of uplift erosion and sedimentation processes the discrete sequential thrusting model successfully reproduces the observed decrease in heat flow at the deformation front in northern taiwan this reveals that the heat flow drop may be due to the recent stacking of cold thrust sheets at the deformation front this inference is consistent with the high seismicity and dense quaternary fault distribution in western taiwan the model also successfully reproduces the observed high heat flow in the central ranges suggesting that the observed high heat flow may be a result of tectonic unroofing due to active underplating uplift and erosion these conclusions are insensitive to uncertainties in the frictional coefficient on the thrust plane

pedogenic approach to resolving the geomorphic evolution of the pakua river terraces in central taiwan abstract the southern part of the pakua tableland in taiwan comprises a series of wide unpaired river terraces that have as many as six altitude levels from pk 1 highest to pk 6 lowest the terrace surfaces are covered with lateritic soils this study described sampled and analyzed the soils from each terrace soil taxonomies are oxisol ultisol and inceptisol soil morphological characteristics were quantified as a profile development index pdi to determine the degree of soil development the chemical analyses included cation exchange capacity cec and selected extraction of fe in soils based on the degree of soil development surface deposits on terrace flights form the post incisive soil chronosequence supporting the hypothesis of terrace formation by fluvial processes soil ages were estimated based on iron crystallinity fed feo fet analytical results indicate that river terraces in the pakua tableland are aged 40 400 ka the long term uplift rate of the tableland can be estimated using terrace ages and folding geometry the variation of uplift rates demonstrates that the landscape underwent increased shortening of frontal thrusting by the changhua fault running beneath the tableland

seismotectonics of taiwan abstract high quality seismicity data and focal mechanism solutions obtained during 1973 1983 by the permanent taiwan telemetered seismographic network and several temporary local seismographic networks are used for a detailed study of the seismotectonics of the taiwan area seismicity distribution in southern taiwan clearly reveals an east dipping benioff zone which has a thickness of about 30 km and begins to deepen along 121 e at a dip angle of 55 60 the leading edge of this benioff zone reaches a depth of about 180 km between 21 n and 22 n but tapers off to a shallower depth of about 100 km from 22 n to 23 n the presence of this seismic zone implies that subduction of the south china sea plate under the philippine sea plate extends from luzon northward to about 23 n the position of the northern boundary of the south china sea plate as tentatively defined according to the seismicity distribution passes through southern taiwan from the offshore area in the taiwan strait west of kaohsiung in an east northeast direction to the taitung area where a triple junction probably lies seismicity is found to disappear abruptly below a certain depth in many parts of taiwan this phenomenon may be attributed to the frictional to quasiplastic transition in the crust or upper mantle comparison of shallow seismicity with surface faults and fractures shows that all areas of active shallow seismicity are marked by densely developed faults and fractures however the converse is not necessarily true this may be partly due to the relatively short duration of seismicity data and partly due to excessive weakening of some of the severely faulted and fractured areas finally focal mechanism solutions for west central taiwan and the kuangfu fuli area in eastern taiwan predominantly show a maximum horizontal compression in the se nw direction which can be related to collision between the eurasian and philippine sea plates however focal mechanism solutions for both the hualien area in eastern taiwan and the tainan area in southwestern taiwan show remarkable irregularities which may result from local tectonic complexities

glendonites from an early jurassic methane seep climate or methane indicators abstract an early jurassic late pliensbachian section margaritatus to spinatum ammonite zone northeast of cremlingen germany revealed three horizons with abundant glendonites calcite pseudomorphs after ikaite caco3 6h2o as well as authigenic carbonates these pseudomorphs have previously been used as indicators for organic and phosphate rich paleoenvironments with near freezing bottom water temperatures stable isotope measurements clearly show that the ikaite glendonite was precipitated at a methane seep location with methanotrophic sulfate reduction as the triggering geochemical process for ikaite formation at the sulfate methane interface the termination of methane seepage probably led to the disintegration of the primary mineral ikaite and successive pseudomorph formation reconstructed paleo bottom water temperatures ca 10 c from belemnites and ostracods indicate temperatures well above the previously observed range of ikaite stability near freezing raising the question if methane seeps are distinct geochemical sites promoting ikaite formation at higher temperatures