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

neptunic dikes and their relation to the hydrodynamic circulation of submarine hydrothermal systems neptunic dikes in lower jurassic sedimentary rocks of the tethyan margins consist of internal sediment in cavities and submarine cement the textures of the infilling sediment indicate downward and lateral movements of seawater beneath what was probably a deep sea floor this circulation probably was part of the hydrodynamic circulation that supplied hot ore bearing solutions to hydrothermal vents near a spreading ridge system this working hypothesis is being tested by stable isotope studies now in progress

stratigraphic record of the early mesozoic breakup of pangea in the laurasia gondwana rift system rift basins of the central atlantic margins cam of north america and morocco preserve largely continental sequences of sedimentary strata and less important minor basalt flows spanning much of the early mesozoic the best known is the newark basin of new jersey new york and pennsylvania where an astronomically calibrated magnetic polarity time scale is developed lacustrine cycles of milankovitch origin are commonly present in cam basins with the period changing from 10 ky paleoequator with coals to 20 ky 4 10n to perhaps 40 ky northward with evaporites cycles of100 ky 413 ky and2 my are also important four mostly unconformity bounded tectonostratigraphic sequences are present the anisian ts i is fluvial and eolian ts ii ts iv late triassic to early jurassic consist of tripartite lacustrine sequences caused by extension pulses the newark basin accumulation rate history allows comparison with quantitative rift basin models the north american plate s slow northward drift resulted in a relative shift of climate although the rapid humidification during the latest triassic and early jurassic is associated with a sea level rise the triassic jurassic mass extinction is of independent origin plausibly impact related

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

isolated stationary carbonate platforms the middle triassic ladinian of the marmolada area dolomites italy as a result of a phase of extensional tectonics in the western tethyan region a horst and graben topography formed during the middle triassic ladinian in northern italy horsts were sites of shallow water carbonate sedimentation while pelagic and volcaniclastic sediments were deposited in the grabens two carbonate platforms approximately 500 m thick can be distinguished in the marmolada area of the dolomites the marmolada platform proper which covered an area of 6 km2 and the costabella platform which extended for about 12 km in a nw se direction and was about 3 km across the facies of these isolated platforms reflect the influence of storms from the sw windward platform margins were characterized by a marine sand belt of skeletal and aggregate grainstones with a dominant platform directed cross stratification the central portions of the platforms were occupied by supratidal sand cays which are made up of storm washovers leeward parts of the platforms are composed of shallow subtidal sand flat deposits laterally discontinuous reefs chiefly composed of various calcareous algae are developed at the outer margins of the platforms along windward margins reefs may form a belt several hundred metres wide along leeward margins their width is commonly reduced to some tens of metres foreslope talus breccias surround the platforms clinoform bedding showing basinward dips of 30 40 is typical of this facies belt which is approximately 2 km wide basinal sediments only some tens of metres thick are radiolarian micrites abundant sediment gravity flow deposits expand the basinal sequence at the toes of windward margins and were probably triggered by storm return flows synsedimentary faults striking both nne ssw and nw se separate the bedded platform limestones from flank deposits and reefs they account for the stationary nature of the platforms neptunian dykes show preferred nne ssw and e w trends sinistral displacements are associated with nw se trending faults depressions in the basins filled with red turbiditic pelagic sediments show n s trends and are probably compressional in origin the structural pattern may have resulted from oblique nw se oriented extension of the e w trending middle triassic graben zone of the dolomites in the ladinian of the dolomites the stationary platform type can be distinguished from a retrograding type whereas continuously prograding platforms apparently did not develop

an experimental study of the secondary deformation produced by oblique slip normal faulting we have used scaled clay models to define the secondary deformation produced by oblique slip normal faulting in the models the master fault beneath the clay layer dips 45 degrees and strikes at a 45 degrees angle relative to the heave direction i e the horizontal component of the displacement direction thus the master fault has both normal dip slip and strike slip components of displacement the modeling results show the following 1 the fault patterns produced by oblique slip normal faulting vary significantly with depth secondary faults that strike obliquely to the master fault trend are more abundant near the top of the clay layer whereas secondary faults that are subparallel to the master fault trend are more abundant at depth 2 a single episode of oblique slip normal faulting produces two populations of secondary faults that have different trends and ages secondary faults that strike obliquely to the master fault trend are more abundant during the early stages of the experiments whereas secondary faults that strike subparallel to the master fault trend are more abundant during the later stages of the experiments 3 relay ramps between overlapping secondary synthetic normal faults are wide and temporally persistent in oblique slip models the ramps are cut by numerous small scale normal faults that are subparallel to the ramp bounding faults cross faults are uncommon and begin to develop only during the final stages of the experiments 4 both map and cross section data are necessary to distinguish among the deformation patterns produced by strike slip oblique slip and dip slip faulting the map views of oblique slip models closely resemble those of strike slip models in both models many of the secondary faults strike obliquely to the master fault trend these map views however differ considerably from those of dip slip models in which most of the secondary faults strike subparallel to the master fault trend alternatively the cross sectional views of oblique slip models are similar to those of dip slip models in both models a highly faulted extensional forced fold develops these cross sectional views are dissimilar to those of strike slip models which show no appreciable folding and no change of regional level

relations between submarine fissures internal breccias and mass flows during triassic and earlier rifting periods deep fissures in shallow water limestones filled with deep water sediments are described from many places especially in the triassic and jurassic of the tethys and in the middle to upper devonian of the variscian mountains mass flows occur in the same formations and areas on the island of hydra greece it was possible to show that both phenomena are linked by internal breccias of well fitted limestone fragments they are indicative of slope or near slope positions and are very probably caused by flexure like deformations of shallow burial limestones seismic shocks producing overpressure may be instrumental in the disintegration of the semi lithified limestones thus providing the material for mass flows these events are associated with a tectonical subsidence as shown by deep water matrix in the brecciated shallow water limestones they occur in areas and periods of submarine rifting especially in late devonian and triassic time at least four triassic brecciation events can be traced from greece to the alps and correspond presumably to major transgressions in the cratonic basin of middle europe

sand injectites at the base of the coconino sandstone grand canyon arizona usa abstract in the grand canyon large tabular and wedge shaped sand filled cracks commonly occur at the base of the coconino sandstone penetrating downward into the coarse siltstones of the hermit formation all previous workers have casually identified the vertical sand filled cracks as desiccation cracks until now they have never been studied cracks and their associated features were found and examined at thirty locations and it was found that they have characteristics difficult to explain using desiccation mud cracks or large playa cracks as a model instead it was found the cracks have features commonly found in clastic dikes and sand injectites some lateral sand bodies associated with the cracks have clastic sill like characteristics liquefaction and injection of the basal coconino into the hermit is indicated by 1 macroscopic and microscopic banding flow structures within the cracks 2 bedded sandstone clast breccias in structureless sandstone lenses at the base of the coconino 3 lateral sand bodies which are connected to the vertical cracks 4 a zoned depth distribution of cracks about the bright angel fault zone 5 insufficient clay mineralogy and particle size for the hermit to crack by desiccation 6 preferred orientation of the cracks roughly perpendicular to the bright angel fault zone and several other features caution should be exercised when interpreting sand filled cracks as desiccation features i e mud cracks even if the interpretation fits well with accepted paleoenvironmental models

the effects of strike slip motion along the cobequid chedabucto southwest grand banks fault system on the cretaceous tertiary evolution of atlantic canada the newfoundland fracture zone the southwest grand banks transform and the cobequid chedabucto fault zone form a linked strike slip fault system from the atlantic ocean to southeastern canada this paper suggests that several large scale geological features in southeastern canada are the result of a small amount of strike slip motion on the system during the mid cretaceous and oligocene regional extension features developed in the releasing bend in the laurentian sub basin during the mid cretaceous but the same area experienced oligocene compression this tectonic model accounts for the distribution of mid cretaceous volcanism fault bounded basins and regional unconformities as well as mid to late cretaceous subsidence of the scotian basin and oligocene uplift of the eastern scotian shelf

transtensional arm of the early mesozoic fundy rift basin penecontemporaneous faulting and sedimentation formed as a major right lateral fault zone during paleozoic collisional orogenies and reactivated as a left oblique system during the early mesozoic the east striking minas fault zone of atlantic canada controlled adjacent sedimentation in the fundy rift basin producing a series of synsedimentary microbasins northeast striking boundary faults of the fundy basin underwent mostly early mesozoic normal slip and are reactivated paleozoic thrusts the adjacent basin has a much thicker section transverse folds and synthetic rider blocks contrasts in structural and stratigraphic styles are a response to local deformation controlled by reactivated fault zones of differing orientation under consistent northwest southeast early mesozoic extension rather than responses to a sequence of changing stress patterns

paleomagnetism and k ar isochron dates of early jurassic basaltic flows and dikes of atlantic canada k ar isochron dates of 193 2 189 3 and 191 2 ma are reported for the shelburne dike of nova scotia the avalon dike of newfoundland and the caraquet dike of new brunswick respectively these major tholeiitic dikes agree in radiometric date with the north mountain basalt of nova scotia and with other tholeiitic flows of the newark supergroup that have been paleontologically assigned to the hettangian however further work is needed to resolve the discrepancy between the triassic jurassic boundary date of 193 6 ma suggested by the newark supergroup flows and the boundary dates of 204 213 ma adopted in recent time scales the north mountain basalt flows at nine sites on the north shore of the bay of fundy are shown to have likely magnetized during initial cooling yielding an hettangian virtual paleopole at 66 n 72 e dp 9 dm 14 new paleomagnetic results are also reported for the caraquet and avalon dikes the virtual paleopoles from hettangian flows and dikes of atlantic canada lie on a

mapping subtle structures with light detection and ranging lidar flow units and phreatomagmatic rootless cones in the north mountain basalt nova scotia light detection and ranging lidar is an emerging technology to generate high resolution digital elevation models dems subtle topographical differences among three flow units of the jurassic north mountain basalt eastern canada are visible on a lidar derived dem the boundaries were verified by field mapping and allow a simple projection of the contact planes through the terrain model to provide a three dimensional visualization of the flow units several ring structures in the lower flow unit distinguishable only in the lidar data are interpreted to be the remnants of rootless phreatomagmatic cones glacial erosion has since excavated the highly fractured cone material leaving the more resistant dike and quenched melt to form protruding ring structures the ability to detect subtle variations in topography using lidar may identify previously undetected landscape elements

a detailed subduction structure in the kuril trench deduced from ocean bottom seismographic refraction studies abstract in 1983 we conducted an ocean bottom seismograph obs experiment in the southernmost part of the kuril trench beneath which the pacific plate is subducting under hokkaido island japan the aim of this experiment was to determine crust and upper mantle structure from the oceanic basin to the continental slope by dense seismic refraction profiling using explosives and airguns the total length of the profiles was 560 km along which ten obs s were deployed the observed data were of good quality which enabled us to obtain a detailed velocity structure of the active margin down to 20 30 km we constructed a velocity structure model by ray tracing and amplitude modeling in the oceanic basin the crust has a typical oceanic structure characterized by three layers with p wave velocities of 1 8 3 8 6 5 and 6 5 7 0 km s the velocity gradient in layer 3 increases downward from 0 075 to 0 10 s 1 the moho discontinuity was well constrained by clearly observed p n and p m p phases the total thickness of the oceanic crust was determined to be 8 km and almost constant in the oceanic basin the p wave velocity is 7 9 km s beneath the moho discontinuity which increases downward with a rather small velocity gradient 0 015 0 03 s 1 beneath the continental slope we found relatively low velocity 2 5 to 5 5 5 8 km s material the oceanic moho discontinuity associated with the subducting plate was traced down to a depth of 25 km our seismic data strongly suggest that oceanic layer 2 is smoothly subducting and does not break up to form a wedge structure this result is in remarkable contrast with the velocity structure in the active margin of the ryukyu trench area about 1000 km south of the present experimental area where we found a 12 km thick prominent low velocity wedge is situated 50 150 km landward from the trench axis on the seaward side of the wedge the surface of the igneous basement undulates severely the wedge was probably formed by materials of oceanic origin such a difference in velocity structure suggests that the subduction mechanism in the trench area differs from region to region in the northwestern pacific

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

tectonic evolution of the fundy rift basin canada evidence of extension and shortening during passive margin development seismic and field data show that the fundy rift basin of southeastern canada experienced two distinct episodes of deformation during mesozoic time the first episode during middle triassic to early jurassic time was extensional rifting associated with nw se extension reactivated ne trending paleozoic compressional structures as normal faults forming the northwestern boundary faults of the fundy basin displacements on the low angle boundary faults locally exceeded 10 km rifting also reactivated east trending paleozoic compressional structures as oblique slip faults with normal and sinistral strike slip components forming the northern boundary faults of the fundy basin several kilometers of sediments and lava flows filled the basin during rifting the second deformational episode occurred during or after early jurassic time and probably before or during early cretaceous time inversion associated with nw se shortening occurred along all faulted margins of the fundy basin the northwestern boundary faults experienced several kilometers of reverse displacement broad anticlines developed within their hanging walls and the fundy basin acquired its synclinal form the northern boundary faults of the fundy basin became oblique slip faults with reverse and dextral strike slip components gentle synclines tight anticlines and faults with reverse separation deformed the synrift strata near the northern margin of the fundy basin neither collision nor subduction zones existed near the fundy basin during mesozoic time hence we believe that tectonic processes associated with seafloor spreading e g incipient ridge push forces continental resistance to plate motion produced the shortening in the fundy basin shortening occurred during the transition from rifting to drifting as north america separated from northern africa and or during the early stages of drifting as the seafloor spreading centers of the north atlantic propagated northward

oriented clastic dike swarms as indicators of paleoslope an example from the upper cretaceous nanaimo group canada abstract an impressive oriented clastic dike swarm 165 dikes occurs within 3 25 m of strata of a submarine fan turbidite succession of the upper cretaceous nanaimo group british columbia the dikes are remarkably parallel in orientation are consistently subvertical and strike southwest slump fold vergence paleocurrent indicators and other evidence indicate that local paleoslope strike was northwest with a downslope direction to the southwest thus the clastic dikes strike downslope indicating that extension occurred perpendicular to the regional downslope direction not parallel as generally expected two possible models are proposed 1 rapid downslope compression caused by sudden loading perhaps due to slumping events or deposition of thick turbidity current beds this downslope compression caused minor extension perpendicular to the downslope direction resulting in small extensional joints that accommodated clastic injection from buried overpressured sands 2 chaotic sedimentary breccias laterally adjacent to the dike swarm formed as part of a large slumping event which created a local slump channel minor slumping into the main channel from the sides caused extension parallel to the channel margin slope and formation of the clastic dikes parallel to the channel margin but perpendicular to the regional slope oriented clastic dike swarms may represent a new type of paleoslope indicator but they may be created by a number of processes and should therefore be used only in conjunction with supporting evidence

depth of seismic coupling along subduction zones underthrusting at subduction zones can cause large earthquakes at shallow depths but it is always accommodated by aseismic deformation below a certain depth the maximum depth of the seismically coupled zone or seismogenic zone is a transition from unstable to stable sliding along the plate interface we have determined the depth of this stability transition for the circurn pacific subduction zones of honshu kuriles kamchatka aleutians alaska mexico and chile these subduction zones have experienced great interplate earthquakes and the aftershock regions are well located depth estimates of interplate events that are located at the downdip edge of the aftershock regions are used to determine the maximum depth of seismic coupling for an average p wave velocity of 6 7 km s 1 above the plate interface we find that for most subduction zones the stability transition occurs at 40 5 km depth there are however several exceptions at the hokkaido trench junction where the japan trench and the kurile trench intersect seismic coupling is deep and extends down to 52 55 km deep coupling was also found in the coquimbo region in central chile the mexico subduction zone has shallow coupling the transition occurs at 20 30 km depth previous studies of micro earthquakes in honshu hokkaido the aleutians and alaska show that earthquakes within the upper plate extend no deeper than the downdip edge of the coupled zone that we find given our measurements of seismic coupling depth we then explore the mechanism that may determine coupling depth the concept of critical temperature has been used to explain the depth of seismic coupling in other tectonic environments thus we first test whether a critical temperature can explain our results temperatures at the plate interface are dependent on many variables but two that are poorly determined are shear stress and radiogenic heat generation shear stress has been constrained by inversion of heat flow data assuming a crustal radiogenic heat production rate of 3 1 exp z 8 5 wm 3 and a constant coefficient of friction we find two critical temperatures of about 400 c and 550 c the lower critical temperature may be characteristic of regions with a relatively thick continental crust and the higher temperature of regions with a relatively thin continental crust on the other hand one single critical temperature of about 250 c can explain the coupling depths if shear stresses are constant with depth

new early jurassic tetrapod assemblages constrain triassic jurassic tetrapod extinction event the discovery of the first definitively correlated earliest jurassic 200 million years before present tetrapod assemblage fundy basin newark supergroup nova scotia allows reevaluation of the duration of the triassic jurassic tetrapod extinction event present are tritheledont and mammal like reptiles prosauropod theropod and ornithischian dinosaurs protosuchian and sphenosuchian crocodylomorphs sphenodontids and hybodont semionotid and palaeonisciform fishes all of the families are known from late triassic and jurassic strata from elsewhere however pollen and spore radiometric and geochemical correlation indicate an early hettangian age for these assemblages because all typical triassic forms are absent from these assemblages most triassic jurassic tetrapod extinctions occurred before this time and without the introduction of new families as was previously suggested by studies of marine invertebrates this pattern is consistent with a global extinction event at the triassic jurassic boundary the manicouagan impact structure of quebec provides dates broadly compatible with the triassic jurassic boundary and following the impact theory of mass extinctions may be implicated in the cause

a new attenuation relation for peak horizontal acceleration of strong earthquake ground motion in japan abstract a new attenuation relation for peak horizontal acceleration applicable to the near source region in japan is developed the data base consists of 1372 horizontal components of peak ground acceleration from 28 earthquakes in japan and 15 earthquakes in the united states and other countries coefficients describing the decrease in acceleration with increasing distance found by most previous studies of japanese data are significantly smaller than those found by analyzing individual earthquakes this phenomenon is examined and found to result from use of general nonstratified multiple regression analyses the present analysis uses a two step stratified regression procedure and an attenuation model that accounts for geometrical spreading and anelastic attenuation but has magnitude independent shape at very short distances the resulting relation in japan is log 10 a 0 41 m log 10 r 0 032 10 0 41 m 0 0034 r 1 30 where a is the mean of the peak acceleration from two horizontal components at each site cm sec 2 r the shortest distance between site and fault rupture km and m the surface wave magnitude the median estimate of peak horizontal acceleration at the source region is 620 cm sec 2 independent of earthquake magnitude effects of four different ground condition rock hard medium and soft soils on the attenuation relation are also examined average peak horizontal accelerations for the rock and the soft soil sites are 60 and 140 per cent respectively of the value predicted from the equation

structural and sedimentary history of the quaco head area southern new brunswick remapping of the quaco head area of southern new brunswick has revealed a more complex structure than had been previously documented the structure is dominated by two major thrust faults that dip to the south and southeast at between 35 and 45 the lower younger thrust emplaces precambrian basalts and tuffaceous siltstones coldbrook group over alluvial sediments of the boss point and tynemouth creek formations westphalian a b resting unconformably on the upper surface of the basalt is a thin layer 10 m of marine basal windsor group limestone disconformably overlain by alluvial conglomerates of inferred hopewell group age this sequence is truncated by an older southeast dipping thrust fault to the southeast of which lie hopewell conglomerates overturned towards the west and northwest the latter sequence probably forms the lower limb of a large recumbent fold folding and thrusting in the quaco head area may have begun during westphalian b times although major movement was probably post westphalian c and occurred contemporaneously with dextral strike slip movement on the minas geofracture following this alleghenian variscan deformation the area underwent deep erosion prior to the deposition of a thick sequence of triassic alluvial sediments the more southerly reverse fault was reactivated as a normal fault during a phase of late triassic or jurassic faulting along the bay of fundy that was probably related to early atlantic rifting

neptunian dykes along a drowned carbonate platform margin an indication for recurrent extensional tectonic activity three successive mesozoic neptunian dyke generations and related unconformities suggest recurrent extensional fracturing and periods of relative sea level rise along the nw trento plateau margin in the southern alps italy the first neptunian dyke generation was induced by nnw sse directed extension of early jurassic skeletal oolitic periplatform deposits generating micritic early middle liassic neptunian dykes with orthogonal orientation the second generation of neptunian dykes was possibly caused by marginal extension at the drowned platform edge penetrating late jurassic red pelagic limestones with a pelagic matrix of albian cenomanian age and nearly orthogonal fracture orientation the third generation of neptunian dykes occurred after a prolonged period of submarine exposure and erosion aptian albian to late maastrichtian during the rapid burial of the submarine trento plateau margin relief the late maastrichtian neptunian dykes were caused by extension of early to middle jurassic oolitic periplatform limestones along steep inclination 10 submarine slopes generally successive neptunian dyke generations along drowned carbonate platform margins could be caused by repeated extensional brittle fracturing of lithified periplatform deposits and the filling of micritic matrix derived from overlying pelagic sediment sequences under substantial hydrostatic pressure this would suggest that recurrent extensional fracturing is continuously recorded by neptunian dyke formation which could be used to indicate extensional tectonic activity at a foundering deep marine carbonate platform edge

coseismic crustal deformation from the 1994 hokkaido toho oki earthquake monitored by a nationwide continuous gps array in japan using a brand new nationwide continuous gps array we monitored coseismic displacements from the october 4 1994 hokkaido toho oki kurile islands earthquake mjma 8 1 based on 2 week time series of site coordinates of 21 gps stations we present a coseismic deformation field of whole hokkaido within 1 cm precision for example the station at nemuro 170 km west of the epicenter moved 44 cm to the east and subsided 10 cm even stations in southern hokkaido 600 km apart from the epicenter moved a few cm horizontally toward the epicenter we compare the gps result with displacements calculated from two preliminary models assuming fault planes parallel or perpendicular to the kurile trench since the observed were far field displacements on land both models can explain the gps result

thermal metamorphic signature of an impact event in the vredefort dome south africa pseudotachylitic breccias and shock deformation features related to the 2 02 ga formation of the vredefort dome by meteorite impact were overprinted by a static metamorphic event the intensity of which decreased from granulite facies t 700 c in the center of the dome to greenschist facies t 400 c around its margins geobarometric estimates of 0 2 0 3 gpa for the metamorphic parageneses indicate some 8 11 km of erosion since the impact event the strong lateral thermal gradient implied by these p t results is attributed to the combined effects of differential uplift of mid crustal rocks heated along a pre impact geotherm and increased shock heating of the target crust toward the center of the impact structure we suggest that the exceptionally high grade of metamorphism in the center of the dome may in part reflect an elevated regional geothermal gradient of 25 c km in the target crust due to lingering thermal effects related to the 2 05 2 06 ga bushveld magmatic event

the nature and significance of rift related near surface fissure fill networks in fractured carbonates below regional unconformities fissure fill networks are a widely recognized but relatively little described near surface phenomenon supplementary material appendix a is available at https doi org 10 6084 m9 figshare c 5023103

asperity distribution and earthquake occurrence in the southern kurile islands arc the seismicity in the southern kurile islands arc is characterized by a complex overlapping of aftershock zones of a few great and many large earthquakes ms 7 0 the spatial relationships of these aftershock zones can be explained in terms of a simple pattern of fault plane heterogeneity the four largest earthquakes in this region are from north to south the 1963 kurile islands mw 8 5 the 1958 etorofu mw 8 3 the 1969 kurile islands mw 8 2 and the 1973 nemuro oki mw 7 8 events detailed body wave studies indicate that the moment release associated with each event is concentrated in a small portion of the aftershock area with scale lengths 100 km these regions of high moment release are the largest asperities the areas that surround the large asperities slip in two modes 1 coseismically during the great events and 2 as distinct large ms 7 0 earthquakes both before and after the great events the second mode involves either rupture of relatively weak regions which results in low stress drop events or rupture of smaller asperities the earthquakes produced by failure of small asperities tend to repeatedly rupture the same regions and they have impulsive source time functions indicating rupture of highly stressed regions of the fault surface by analysis of all ms 7 0 events since 1946 in this region we find a segmentation of the southern kurile islands thrust zone into strongly coupled regions with two scale lengths dominant and secondary asperities and weakly coupled regions the surrounding areas generating the low stress drop events the largest earthquakes and the smaller asperity earthquakes occur at the down dip portion of the lithospheric interface while the low stress drop events occur much closer to the trench axis this implies a difference in the degree of mechanical coupling between the subducting and overriding plates with the deeper portions having greater strength than the shallower parts

cephalopod limestone deposition on a shallow pelagic ridge the tafilalt platform upper devonian eastern anti atlas morocco as a result of early variscan tectonic movements and of differential subsidence a platform and basin topography was created along the northern margin of the sahara craton during the late devonian in the moroccan anti atlas mountains the tafilalt platform is an approximately n s running ridge which developed since the late middle devonian it separated a slowly subsiding shallow basin in the east tafilalt basin from a rapidly subsiding furrow in the west mader basin platform deposits are characterized by highly reduced thicknesses shallow subtidal to supratidal deposits in the late frasnian and by unconformities at the lower upper frasnian and the frasnian famennian boundaries after a local transgression over emergent areas in the north water depth probably never reached more than several tens to about 100 m in the lower famennian cephalopod limestones of this age deposited on the platform represent a very diverse facies pattern comprising quartz rich brachiopod coquinas crinoidal limestones thick bedded cephalopod limestones and nodular limestones sedimentation rates ranged from 1 to 5 mm 1000 yr in the late famennian more uniform marl and nodular limestone facies suggest slightly deeper environments platform margins are characterized by higher rates of subsidence debris flow deposits and slump structures in the relatively shallow tafilalt basin marls with intercalated nodular limestones were deposited in the mader basin sandy and calcareous turbidites suggest deeper water conditions in the late devonian during the strunian tournaisian the whole area was overwhelmed by a thick deltaic sequence the general facies distribution is in agreement with depositional models of other upper devonian and lower carboniferous cephalopod limestones in the european variscan orogenic belts in all these cases condensed cephalopod limestones occupy a distinct palaeogeographic position in predictable facies sequences that reflect pre orogenic phases in the variscan geodynamic cycle moreover close parallels exist with condensed sequences in the triassic and jurassic that occur in a very similar position within the alpine orogenic cycle

on the edge of camp geology and volcanology of the jurassic north mountain basalt nova scotia abstract the north mountain basalt nmb is a sequence of continental tholeiitc basalts that are part of the larger 200 ma central atlantic magmatic province camp the nmb occur within the fundy basin one of several mesozoic extensional basins that formed during the incipient rupture of pangea in addition to the nmb the fundy basin was also filled by fluvial alluvial playa lacustrine and aeolian sediments under arid to semi arid conditions mapping of a 200 km long segment of the nmb along the southern coast of the bay of fundy indicates for the first time the lateral continuity of the three recognized lava units the east ferry margaretsville and brier island members efm mm bim respectively that comprise the nmb the efm 150 m are massive and characterized by pervasive development of columnar jointing both colonnade and entablature in addition whereas the efm contains abundant layers of mafic pegmatite the bim is characterized by abundant mesostasis possibly reflecting widespread quenching of this flow and locally abundant segregation pipes due to mobilization of a late stage felsic liquid these two units represent expansive eruption of low viscoity flows onto a low slope surface which encouraged uniform thickness and their massive nature but the role of faulted basins cannot be ruled out in contrast the mm 170 m consists of numerous 16 inflated pahoehoe sheet flow lobes evidence that these flows formed as pahoehoe flows is represented by exceptional development of the vesicle zonation i e upper crust vesicle sheets vesicle cylinders pipe vesicles as observed in modern hawaiian flows historical icelandic flows and ancient flows of the columbia river basalt group the thickness of upper crust zones indicates that the individual flows formed over months to years whereas inclined basal pipe vesicles indicate the mm and bim flowed to the south the similar age and nature of the nmb to other basalt sequences in camp suggest that similar processes operated throughout this lip thereby having implications for such phenomena as atmospheric contamination and extinction events caused by eruption of these voluminous basaltic lava flows

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

platform slope transition during rifting the mid cretaceous succession of the amasya region northern anatolia turkey abstract the mid cretaceous rocks of the amasya region north central anatolia record the geological processes that occurred during the break up of the eastern pontide carbonate platform which existed from mid jurassic to early cretaceous the mid cretaceous sedimentary rocks consists of benthic foraminiferal packstones grainstones of ferhatkaya formation and limestone breccias turbidites pelagic foraminiferal wackestones packstones and radiolarites of sarilar formation corresponding to platform and slope apron environments respectively the lithological development of these units was controlled mainly by active subsidence due to block faulting affecting the eastern pontide carbonate platform due to the break up of the platform during late barremian early aptian times slope and basin sediments were deposited on the deeper parts of the platform re deposited sediments such as limestone breccias and calciturbidites document the infilling of asymmetric grabens during the mid cretaceous rifting phase re deposited sequences which were formed as a fault slope apron sedimentary prism related to this rifting were deposited during thinning and fining upward megacycles a typical megacycle commences with breccias deposited at the base of a fault scarp association in addition the upper part of the platform carbonates ferhatkaya formation includes neptunian dykes composed of red mudstones with pelagic fossils indicating a period of extension

the great kurile earthquake of october 4 1994 tore the slab the fault geometry depth and slip distribution of the kurile earthquake of oct 4 1994 are estimated using seismic waveforms aftershock distribution geodetic measurements and tsunami waveforms previous large earthquakes in the kurile arc had typical underthrusting focal mechanisms due to the local subduction seismic wave inversions of the 1994 event indicate a thrust type mechanism with a large strike slip component this does not represent an underthrust event at the subduction interface the focal depth is estimated at 50 kin just beneath the previously estimated subduction interface we calculate crustal deformation and tsunami waveforms from the two possible fault planes of the focal mechanism solution and find that both fault planes explain the observations we choose the north south striking plane because of the occurrence of a large m w 7 8 intermediate depth earthquake on dec 6 1978 northwest of the 1994 rupture area the lineation of aftershock distributions of these two events suggests that both earthquakes were due to a tearing of the slab perpendicular to the trench the joint inversion of geodetic and tsunami data shows that the largest slip about 17 m occurred at the upper end of the slab

role of synsedimentary strike slip faults in the formation of moroccan triassic basins upper triassic sandstone and siltstone infilled basins in the massif ancien of the high atlas morocco are distributed along a complex east northeast trough at the boundary between the hercynian orogen and the west african craton the formation of these basins involved a dense pattern of pre existing faults hydroplastic slickensides which affect nonlithified sediments help identify not only dip slip but also strike slip faults together with other tectonic and sedimentary structures the directional distribution of these faults leads to a model in which extension varies from north northwest during lower unit sandstone infilling to northwest during upper unit siltstone infilling the latter direction is compatible with the formation of the lower liassic intrusional doleritic dikes of the anti atlas

the 1994 hokkaido toho oki earthquake sequence the complex activity of intra slab and plate boundary earthquakes abstract we study the complex activity of the 1994 hokkaido toho oki earthquake sequence based on strong motion records and teleseismic data first we examine s wave acceleration spectra of the aftershocks by comparison with that of the main shock the main shock m w 8 2 an intra slab earthquake has been characterized by strong radiation of high frequency seismic waves from different shapes of the spectral ratios of the aftershocks to the main shock the aftershocks can be classified into three types next we redetermine the source parameters focal depth seismic moment and source duration for larger events by waveform modeling of teleseismic p waves the hypocentral locations and stress drops estimated from these parameters show that the three aftershock types fall into different categories of subduction zone earthquakes intra slab relatively deep plate boundary and shallow plate boundary earthquakes finally we estimate source spectra for three different earthquake categories after correcting s wave acceleration spectra for the attenuation effect the source spectrum at high frequencies is modeled by using a high cut filter whose parameters are a cut off frequency f max and a decay rate the source spectrum of intra slab earthquakes has high f max and small decay rate due to this feature and the high stress drop intra slab earthquakes radiate strong high frequency seismic waves through this study we demonstrate that the 1994 hokkaido toho oki earthquake sequence has the complex activity of intra slab and plate boundary earthquakes

influence of preexisting fault fabric on inversion related deformation a case study of the inverted fundy rift basin southeastern canada 1 preexisting zones of weakness significantly influenced the structural development of the fundy basin during rifting and subsequent basin inversion the preexisting fabric consisting of ne striking faults with gentle dips and east striking faults with steeply dipping upper segments and gently dipping lower segments formed during paleozoic and older orogenic activity during mesozoic rifting the preexisting fabric was reactivated creating a border fault system composed of linked ne and east striking extensional fault zones with anomalous dips gentle and steep compared to those of newly formed normal faults during inversion the preexisting fabric was again reactivated as the hanging wall of the composite border fault system moved nne relative to the footwall inversion was highly oblique on the ne striking fault zones producing gentle fault parallel buttress folds and fault perpendicular detachment folds above the low angle fault zones inversion was moderately oblique on the east striking fault zone producing relatively tight fault parallel buttress and detachment folds above the gently dipping lower fault segments and reactivating the steeply dipping upper fault segments as left lateral strike slip faults thus inversion related deformation on the east striking fault zone was partitioned at shallow levels i e partitioned updip our work shows that the geometry of preexisting extensional faults and their obliquity relative to the shortening direction profoundly affect deformation style during basin inversion namely the type of inversion related faults the type and shape of inversion related folds and the distribution of deformation e g updip partitioning depend in part on the geometry of the preexisting extensional faults and the variations in these geometries with depth and along strike

aftershock distribution of the october 4 1994 mw8 3 kurile islands earthquake determined by a local seismic network in hokkaido japan on october 4 1994 an earthquake with magnitude mw8 3 occurred in the western part of kurile islands at 43 42 n 146 81 e and 33 km in depth the hypocenter parameters were determined by hokkaido university in japan aftershocks following this remarkable event were located using data from a local seismic network operated by hokkaido university we found that most of the aftershocks occurred 1 on the fault plane of the mainshock 2 in the subducting plate around the fault plane of the mainshock and 3 in the focal area of the largest aftershock which occurred on october 9 with mw7 3 both 2 and 3 were not active immediately after the mainshock considering the time sequence of the aftershock activity we identified one of the nodal planes of the harvard quick cmt solutions as the fault plane of the mainshock the strike is almost parallel to the trench axis and the dip angle is near vertical it is obvious that this event is different from a low angle thrust type interplate earthquake the distribution of aftershocks strongly suggests that it is an intraplate event