mesozoic and cenozoic reconstructions of the south atlantic abstract the movement of antarctica with respect to south america has a number of implications for paleocirculation as well as for the reconstructions of gondwanaland recent papers on the southwest indian ridge have published new or revised poles of opening for africa and antarctica which can be combined with the poles of opening between south america and africa to give resultant motions between south america and antarctica the first indication of a complete closure between south america and the antarctic peninsula is at anomaly 28 time 64 ma as the two continents are now configured between anomaly 28 time 64 ma and anomaly m0 time 119 ma the amount of closure does not change greatly and the small computed overlap can be explained by minor uncertainties in the rotation poles used for the reconstructions or some slight extension between east and west antarctica by 135 ma some rotation or translation of the antarctic peninsula with respect to east antarctica must be postulated in addition to any presumed extension between east and west antarctica in order to avoid an overlap of south america with the antarctic peninsula having determined what we feel to be a viable reconstruction of western gondwanaland and holding south america fixed we rotated africa and antarctica with respect to south america for eight different times during the past africa moved away from south america in a more or less consistent manner throughout the time period closure to present while antarctica moved away from africa in a consistent manner only between 160 ma and 64 ma at 64 ma its motion changed abruptly it slowed its north south motion with respect to africa and began slow east west extension with respect to south america this change supports the hypothesis that a major reorganization of the triple junction between africa antarctica and south america occurred between 60 and 65 ma the triple junction changed from ridge ridge ridge to ridge fault fault at the time of the major westward jump of the mid atlantic ridge just south of the falkland agulhas fracture zone the mesozoic opening of the somali basin moved madagascar from its presumed original position with africa in gondwanaland the closure of sri lanka with india produces a unique fit for india and sri lanka with respect to africa madagascar and antarctica this fit juxtaposes geological localities in southeast india against similar localities in enderhy land east antarctica the late jurassic opening in the somali basin is tied to opening of the same age in the mozambique basin since this late jurassic movement represents the initial break up of gondwanaland it is assumed that similar movement must have occurred in what is now the western weddell sea and may also explain the opening evidenced by the rocas verdes region of southern south america

double ridge subduction recorded in the shimanto accretionary complex japan and plate reconstruction combining a quantitative model relating ridge subduction and radiolarian biostratigraphical data from the shimanto belt including accreted midocean ridge basalt the plate configuration for the western north pacific since 83 ma can be reconstructed the kula north new guinea and north new guinea pacific ridges passed along the japan are assuming a constant plate motion the half spreading rates angles at which ridges entered the trench convergent rates and angles and migration rates of triple junctions can be calculated

major and minor structural features of a bedding shear zone along a coal seam and related gas outburst pingdingshan coalfield northern china abstract a fractured coal band traditionally called a soft coal band or structurally referred to as a bedding shear zone within the wu coal seam in the pingdingshan coalfield northern china was structurally studied based on field examination and observations by reflectance microscopy and scanning electron microscopy sem the bedding shear zone is not consistent with a simple bedding fault defined by pioneering geologists but rather a complexly deformed band locally overprinted by ductile shearing fabrics dominant small scale structures within the bedding shear zone are thrusts folds cleavage duplexes and related structures but local refolded folds kink bands and s c band structures also indicate ductile shear deformation typically developed in areas of steep dip such as within the limb of a subordinate fold bed parallel shearing within the coal seam has been considered a serious influence on gas outburst in underground mining production in addition to thickening the seam and reducing the quality of coal locally abnormal thickening of a shear zone and extensive compressive structures where ductile fabrics frequently occur are closely related with the site of an outburst thickening of a shear zone increases the capacity of methane storage and compressive structures within a shear zone may act as a tectonic screen blocking methane migration which can result in a pocket of high methane pressure a potential risk of outburst is indicated as a working face approaches an area of high methane pressure three abnormal phenomena encountered during a mining operation presage methane outburst for seams with a bedding shear zone

plate reconstruction based upon age data of japanese accretionary complexes the ages of the oceanic plates for the japanese accretionary complexes are plotted against time of accretion the plots show that early cretaceous transform faulting modified the arrangement of the pre middle cretaceous accretionary complexes and that three or four mid ocean ridges have collided with the japan arc since permian time the plate configuration for the western north pacific is reconstructed

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

field pumping experiments and numerical simulations of shield tunnel dewatering under the yangtze river the water conveyance tunnel for the changshu power plant is located under the riverbed of the yangtze river the tunnel passes through muddy silty clay and silty clay because quicksand and water bursting occurred in the tunnel due to confined water and biogas in layers and it can be concluded that the tunnel is intensely affected by the confined aquifer layer to obtain more accurate hydrogeological parameters of the aquifers in situ pumping tests were carried out the tests were divided into five stages and during the test process the flux and drawdown were monitored based on the measured data the permeability coefficients of the confined aquifers were calculated by the formula and numerical methods the calculated results indicate that the parameters derived from the two methods are very similar the hydraulic connections of the confined aquifers were also inversed from the pumping tests the dewatering schedule for tunnel recovery was simulated using modflow based on the numerical simulation 21 wells whose screens were installed in layer were designed for the dewatering operation during pumping the water levels declined to the drawdown requirement the results indicate that the dewatering approach is feasible for tunnel recovery and can provide solutions for similar projects

revised history of early tertiary plate motion in the south west pacific reanalysis of early tertiary magnetic anomalies on the pacific plate south of the campbell plateau indicates that in early tertiary time there was a previously unrecognized triple junction of the pacific the antarctic and a third plate now beneath the bellingshausen sea corresponding revised parameters for pacific antarctica motion do not require early tertiary displacements within antarctica or new zealand but suggest a change in direction of the pacific plate over the hotspots of approximately the same sense and timing as the hawaiian emperor bend

mesozoic cenozoic rift drift sequence of asian fragments from gondwanaland abstract the university of cambridge atlas map plotting computer program has been used to plot a reconstruction of the dispersal of continental blocks from eastern gondwanaland from the late jurassic 160 ma until the late miocene 10 ma the geological basis for the reconstruction rests on the concept of south tibet burma western thailand malaya and sumatra having been part of the eastern gondwana continent during the late palaeozoic and early mesozoic the reconstruction is also based on the view that these asian continental blocks were rifted from eastern gondwanaland in the late jurassic this rifting episode gave rise to the continental margin of central new guinea and northern australia it was associated with the sea floor spreading anomalies preserved in the floor of the northeastern indian ocean the model considers the indication of crustal uplift in the middle jurassic followed by profound subsidence in the cretaceous and palaeogene exposed in the islands of the outer banda arc from seram to timor and the similar jurassic cretaceous facies in eastern sulawesi implies that these areas formed part of this rifted northern margin of australia in the jurassic subsequent tectonic collision and associated major strike slip movements have deformed and disrupted these rock sequences during the cainozoic the date of the rifting that removed south tibet burma western thailand and malaya from gondwanaland is controversial the indications in favour of the rifting episode having occurred in the jurassic rather than in the permo triassic are stratigraphie structural observations on the northwestern australian shelf in the banda arc and in central new guinea the identification of the continental blocks removed by this rifting is based partly on stratigraphie correlation with the banda arc and new guinea and partly on indications that the age of collision of tibet burma western thailand and malaya with asia was a late cretaceous event and not triassic jurassic as is generally held there are very few reliable land based palaeomagnetic measurements to constrain the movements of these dispersed continental fragments from gondwanaland the computer generated map reconstructions put forward here fit the available indian ocean sea floor spreading data although they are not unique solutions much of the critical ocean floor data associated with the rifting and dispersal of these continental fragments has been destroyed in the tectonic collision processes that occurred at the asian continental margin

pre breakup continental extension in east gondwanaland and the early opening of the eastern indian ocean abstract extension of continental crust by up to 360 km on a north northeast azimuth in the great australian bight occurred prior to the middle cretaceous 96 ma onset of seafloor spreading between australia and antarctica this large amount of continental extension is constrained to the late jurassic 160 ma middle cretaceous interval about a pole estimated to lie about 40 southeastward of southeastern australia using bathymetric data combined with seismic and magnetic determinations of the continent ocean boundaries off australia india and antarctica we determine a revised fit of east gondwanaland prior to continental extension and at various stages thereafter in the first stage from 160 to 132 5 ma m11 india australia rotated from antarctica with continental crustal extension between australia and antarctica and largely transform motion between the coromandel coast margin of india and the kron prins olav kyst margin of antarctica in the second stage from 132 5 to 96 ma india rotated northwestward away from australia antarctica producing m10 and younger magnetic anomalies along the western margin of australia continental extension was greatest between australia and antarctica during this stage the newly determined 132 5 96 ma rotation between india and australia provides an improved fit between the orientation of observed m10 m0 magnetic anomalies and the southward decrease in spreading rate off the western australian margin together with bathymetry the new rotation parameters lead to identification of the abandoned 96 ma spreading ridge along the lost dutchmen and dirck hartog ridges the naturaliste fracture zone is found to lie nearly parallel to the early cretaceous transform direction between india and antarctica suggesting that slow seafloor spreading required between australia and antarctica to accommodate the continental extension further east occurred between naturaliste fracture zone and the m4 m0 anomalies adjacent to the naturaliste plateau the revised fit of india in east gondwanaland reduces the eastward extent of greater india to 95 e but does not change its extent as far north as the cape range fracture zone the new pole determined for the early cretaceous rotation between india and australia antarctica lies within 15 of the southern tip of india significantly closer than in previous determinations thereby reducing the amount of seafloor spreading generated between africa and antarctica by the india antarctica rotation and thus offering a possible solution to the perceived spreading rate problems between m11 and m0 in the somali mozambique and antarctic basins

paleogene history of the kula plate offshore evidence and onshore implications paleocene to middle eocene magnetic anomalies were mapped over oceanic crust that accreted at the kula pacific spreading center and is now obliquely entering the western aleutian trench between 179 e and 168 e the strike of anomalies and the pattern of abyssal hills and fracture zones changed abruptly during 56 55 ma when north south spreading veered to northwest southeast 310 130 kula pacific spreading ceased in 43 ma a 75 km long section of the fossil kula rift axis has avoided subduction although it now intersects the trench axis almost orthogonally near 171 5 e a narrow remnant of the former kula plate northwest of this fossil spreading center is bounded by a fossil kula pacific transform with a high transverse ridge alongside a sediment filled transform valley anomalies on this remnant show that eocene kula pacific spreading was highly asymmetric 2 1 the 56 55 ma change in kula plate rotation inferred from the change in spreading direction coincided with birth of the aleutian subduction zone and was probably a consequence of the resulting change in slab pull stresses on the oceanic lithosphere the change in direction of kula north american motion is a plausible explanation for the detachment of continental terranes from the pacific northwest and their migration around the gulf of alaska and for the early eocene demise of alaska range are volcanism the cessation of kula pacific spreading coincides with a major change in pacific plate rotation and the subsequent direction of convergence of the pacific plate with the aleutian arc was similar to the 55 43 ma direction of kula plate convergence

composition and spatial organization of a cold seep community on the south barbados accretionary prism tectonic geochemical and sedimentary context abstract deep faunal assemblages were observed on cold seeps between 1000 and 2000m depth along the southern termination of the barbados accretionary prism during the caracolante ii and diapicar cruises faunal composition and microdistribution of a cold seep community were analyzed at one site using deep sea photographs and seismic 3 5 kz profiles the community is dominated by large mussels up to 20cm long possibly related to the genus bathymodiolus tiny vesicomyid clams and vestimentiferan clusters in which animals are up to 2m long there is a high density of sponges three species bryozoans and gorgonians other taxa occasionally associated with this assemblage include galatheid crabs anemones holothurians and possibly pennatulaceans which are numerous at boundaries of the site a typical deep sea fauna of fish asteroids and ophiuroids is also scattered about the vicinity this seep community is distributed as a band of discontinuous colonies 40 50m in width and more than 10km in length living colonies alternate with accumulations shells and bare areas the substratum is hard mud covered by a ferrugineous crust and cemented by carbonates the early diagenetic character of the bottom and the occurrence of biological assemblages indicate that seepages of sulphur and or methane which have been revealed along the decollement zone of the barbados prism must diffuse through the sea floor these biological and geological features are located on the crests of ne sw anticlinal ridges and mud volcanoes which have been built by diaprism

deep sea hydrothermal communities in southwestern pacific back arc basins the north fiji and lau basins composition microdistribution and food web abstract during the year 1989 two diving cruises of the french deep sea submersible nautile were devoted to the study of hydrothermal vent biology in spreading centers of two southwestern pacific back arc basins lau basin and north fiji basin in both cases two major active sites were visited white lady and mussel valley in the north fiji basin and hine hina and vai lili in lau basin the faunal associations clustered around active vents are dominated by two species of snails ifremeria nautilei and alviniconcha hessleri and one or two species of mytilids belonging to bathymodiolus these species are associated with chemoautolithotrophic bacteria in intracellular symbiosis as detected by the activity of the calvin benson cycle diagnostic enzyme rubpcase pedunculate and sessile barnacles dominated the outer rim of the site and are analogs of the fiter feeding serpulids living in the epr sites the hot extremes of the sites are poorly or not colonized by alvinellids or other taxa in the lau basin cold seep sites are found at the periphery of active hot or warm ventsand are dominated by vestimentiferans and pogonophorans no major differences were seen between associations of the two back arc basins at the generic level with the exeption of the abundance of synaptid holothurians associated with bathymodiolus in side the mussel valley site

plate tectonic evolution of the mediterranean middle east region abstract an interpretive model for the mesozoic cenozoic plate tectonic evolution of the mediterranean and adjacent areas is illustrated by a series of paleoposition maps at selected intervals between the late triassic and recent this interval witnessed an important period of tensional development during the triassic and jurassic that fragmented pangea after its late paleozoic consolidation a number of oceanic areas evolved through jurassic time all of which have since been consumed during the alpine orogeny during the cretaceous and tertiary sea floor spreading geometry in the north and south atlantic resulted in convergence between africa and eurasia that controlled the evolution of the mediterranean and adjacent middle east areas from the late mesozoic to recent the interpretation departs from several previous ones in the following respects 1 1 the eastern mediterranean and adjacent middle east area are interpreted to have developed as two seaways with an intervening continental sliver derived from africa that now comprises central turkey and west iran these seaways persisted from the late triassic to late cretaceous by which time they were largely consumed by northward subduction 2 2 spreading that produced the present eastern mediterranean sea developed during the late cretaceous driving the tripolitza eratosthenes iskenderun continental fragments northward from africa to collision with central turkey as the preceding southern arm of the mesozoic tethys sea floor was entirely consumed initial block faulting in this zone occurred during the jurassic and early cretaceous but without subsidence reaching clearly bathyal depths until the cenomanian turonian this differs from the timing of events in the ionian sequence of the pindic nappe of crete which shows a change from shallow carbonate shelf in the triassic to deep basin in the liassic to the north of equivalent platform facies of the tripolitza nappe 3 3 moesia and rhodope are concluded to have been a single plate until a rifting event that started during the late jurassic the balkan mountains are interpreted to represent an alpine inversion of this mesozoic rift system that extended west from the black sea basin 4 4 the eastern carpathian microcontinental sliver is concluded as continuing southward as the serbo macedonian massif that separates rhodope from the vardar zone rather than as rhodope itself 5 5 the scutari pec lineament is considered as representing a major discontinuity between the apulia pannonian plate and adjacent greece and turkey ophiolites to the northwest of this lineament originated in a single oceanic area the vardar zone ophiolites to the southeast of this lineament evolved from two oceanic areas those of interior greece and northern anatolia and the associated ankara melange relating to the vardar zone the former north arm of tethys and the pindos southern anatolia zagros oman ophiolites relating to a former south arm of mesozoic tethys 6 6 based on the history of development of various elements of the alpine system there is a strong suggestion that important dextral movement took place along a major strike slip fault system reaching from the middle east to the central alps between late cretaceous and middle eocene times

tunnel boring machine collision with an ancient boulder beach during the excavation of the barcelona city subway l10 line a case of adverse geology and resulting engineering solutions the existence of a layer of hard boulders up to 1 m in size within the soft sediments of the holocene llobregat delta in the sw of barcelona city caused the damage and stoppage of the epb type tunnel boring machine that excavated the subway l10 line this layer constitutes a detrital deposit of exceptionally large grain size developed in the base of the delta it originated as an alluvial fan in the northern margin of the delta during the last fall of the mediterranean sea level at the end of the pleistocene period the subsequent sea level rise holocene transgression caused the flooding of this alluvial fan and the reworking of its materials by sea waves thereby a retrogradant boulder beach developed in which the largest rock fragments of the former alluvial fan remained densely packed the tunnel boring machine precisely collided with the main boulder concentration area of this ancient beach the cutter tools and the structure of the cutterhead were seriously affected the repair tasks required the excavation of a mine in the tunnel face under atmospheric pressure and a sealing and stable environment to get these conditions a jet grouting block from the surface was performed to consolidate the deltaic sediments around the tunnel face additional tam injections were carried out to improve some deficiencies in the sealing of the block subsequently the shield of the tunnel boring machine was embedded into the block and the water table was depressed by pumping wells after 13 months of complicated works the tunnel boring machine resumed the excavation encountering further problems although the layer of boulders was early identified by the geological and geotechnical studies of the l10 constructive project its precise geological characteristics and potential adverse influence on tunnelling was then not valued in depth a better knowledge of the geology of this layer would have been helpful in order to foresee the incident and propose alternatives

tectonic setting of western pacific marginal basins abstract global kinematics as well as magnetic anomalies of marginal basins with continental geology and paleomagnetic data as additional constraints are used to present a set of reconstructions of the western pacific marginal basins between 56 ma and the present at key periods 56 43 32 20 12 and 3 ma our model accounts for the rapid motion of exotic terranes along the whole of the western pacific convergent zone marginal basins appear to open in a great variety of tectonic settings the two extreme examples being the mariana trough where trench suction may be the predominant driving force and the south china sea where intracontinental deformation appears to be the major mechanism the study of marginal basins is a 3 d problem which must take into account the whole tectonic context subduction related tectonics in cross section and upper plate deformation in map view and not only a 2 d problem the classical trench arc back arc problem

origin and evolution of the west philippine basin a new interpretation abstract combined analyses of the magnetic lineations and seafloor structures of the west philippine basin show that it was formed by spreading from the central basin spreading center in two distinctly different spreading phases before and after subduction was initiated along the palau kyushu trend at 45 ma b p these episodes are recognized by differences in the strike of the magnetic lineations spreading rates density and strike of fracture zones and basement relief from 60 45 ma b p spreading was ne sw relative to present orientations at a half rate of 44 mm a at about 45 ma b p the spreading direction changed to a more n s direction with a reconfiguration of the central basin spreading center into numerous short e w segments offset by closely spaced n s transform faults spreading slowed to a half rate of 18 mm a and ceased at 35 ma b p thus the west philippine basin originated at 45 ma b p by the trapping of normal ocean crust west of the initial subduction along the palau kyushu trend the 45 35 ma b p period represents the dying phase of spreading on the central basin spreading center following isolation of the west philippine basin from the plate driving forces of the pacific

pre pliocene extension around the gulf of california and the transfer of baja california to the pacific plate late miocene 12 5 ma extension around the edges of the gulf of california has been alternatively attributed to basin and range extension back arc extension or development of the pacific north america plate boundary this extension was ene directed and similar in structural style to extension in the basin and range province timing constraints permit nearly synchronous onset of this deformation in a belt extending sse from northernmost baja california to the mouth of the gulf where this extensional faulting continued through pliocene time to the present synchronous with motion on the modern transform plate boundary in the gulf of california no change in direction of extension can be resolved revised constraints on pacific north america plate motion support the development of this late miocene extension as a component of pacific north america displacement that could not be accommodated by strike slip displacement along the existing plate boundary west of the baja california peninsula this scenario implies that transfer of baja california from the north america plate to the pacific plate was a gradual process beginning about 12 10 ma when motion of the pacific plate relative to north america was partitioned into separate regimes of strike slip and dip slip displacement on opposite sides of baja california

a case history of tunnel boring machine jamming in an inter layer shear zone at the yellow river diversion project in china this is a case study of a tunnel boring machine tbm jamming in a section of the connection works no 7 tunnel of the yellow river diversion project yrdp in china analysis of tunnel lithology rock convergence by shearing rock strength and ground stress indicates that a high rate of convergence within an inter layer shear zone in the lower part of an anticline was a dominant factor in the jamming in addition the shield encountered unfavorable tunnelling conditions in the form of wet clay groundwater inflow and cavities coincident with tensile stresses in the lower part of an adjacent syncline based on these diagnoses economical and quick measures were adopted including additional excavation outside of the shield leaving free space to release the tbm after 9 days of being jammed the tbm was totally released and resumed normal excavation this example highlights lessons learned from folding and inter layer shear zone in tbm tunnelling

evidence of a carbonate platform beneath georges bank abstract the subsurface of the new england continental margin beneath georges bank contains a jurassic and cretaceous carbonate platform that interfingers landward into and is stratigraphically sandwiched between clastic wedges of deltaic origin the seaward edge of the platform is a presently buried precipitous up to 5 km high wall that resembles the modern bahama escarpment the platform edge and its younger cover have been sampled by submersible and dredging where they outcrop locally in submarine canyons there is no evidence of a major vertical tectonic displacement beneath the continental slope and the ocean subsidence has been continuous and regional commencing with listric faults in stretched brittle continental lithosphere and diminishing in rate with the square root of time primarily in respond to thermal cooling and flexure from the sedimentary overburden

spatial distribution of inter layer shear zones at gaobazhou dam site qingjiang river china abstract the spatial distribution of inter layer shear zones is studied based on the fully mapped inter layer shear zones at the gaobazhou dam site on the qingjiang river in hubei province china the field observations revealed that two types of inter layer shear zone under developed and well developed are distributed differently the former are associated with the incompetent rock layers and the latter are controlled by the inter bed folds and lithological properties of the strata to represent their lithological properties geomechanically data on strength by the schmidt hammer test and thickness of each field identified rock layer were collected to form strength sequences and thickness sequences the adjacent rock layers of similar strength are then grouped and two grouped sequences are combined into a single sequence whose individual term is the strength weighted by the exponential function value of the centralized thickness sct the rescaled range r s analysis results of sct sct r s taking into account the presence of inter bed folds are in good agreement with r s analysis results of the spacing sequence of the well developed inter layer shear zones thus the sct r s model has the potential to predict their spatial distributions