synsedimentary collapse of portions of the lower blomidon formation late triassic fundy rift basin nova scotia a chaotic mudstone unit within the lower blomidon formation late triassic has been traced for 35 km in the mesozoic fundy rift basin of nova scotia this unit is characterized by highly disrupted bedding that is commonly cut by small 0 5 m domino style synsedimentary normal faults downward movement of material geopetal structures variable thickness and an irregular partially faulted contact with the overlying unit the chaotic unit is locally overlain by a fluvial sandstone which is overlain conformably by mudstone although the thickness of the sandstone is highly variable the overlying mudstone unit exhibits only gentle regional dip the sandstone unit exhibits numerous soft sediment deformation features including dewatering structures convoluted bedding kink bands and convergent fault fans the frequency and intensity of these features increase dramatically above low points at the base of the sandstone unit these stratigraphic relations suggest buried interstratal karst the subsurface

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

searching for distal ejecta on the craton the sedimentary effects of meteorite impact abstractdistal ejecta from meteorite impacts are rare and hard to spot in the field because of their thinness 5 mm diameter sediments and produce high flow regime bedforms megaripples dunes upper plane beds and possi

large scale alluvial architecture and correlation in a triassic pebbly braided river system lower wolfville formation fundy basin nova scotia canada abstract determining what the controls are on the large scale 10 km horizontal architecture of coarse grained fluvial deposits is important for understanding subsurface fluid distribution and extraction from these important aquifers and hydrocarbon reservoirs this contribution describes the architecture of coarse grained fluvial sediments from an almost continuous lateral profile 27 km long by 115 m high in the upper triassic wolfville formation fundy basin nova scotia the lateral extent and quality of exposure allows development of a high resolution correlation scheme and definition of architectural elements the lower wolfville formation lithofacies composed of breccias conglomerates sandstones mudstones and paleosols comprises alluvial fan fluvial and ephemeral lake margin facies associations alluvial fan deposits form 15 of the studied section and are developed locally between the overlying fluvial facies and the unconformity with carboniferous strata where they infill remnant topography the succession is dominated 80 by pebbly sandstones deposited as part of a gravelly braided fluvial system and ends abruptly with a thin ephemeral lake margin facies association 5 the large scale architecture and sedimentology of the pebbly sandstone succession is documented with particular attention focussed on bounding surfaces and stacking patterns in the fluvial facies association two scales of development of erosion surface and cycles can be recognized the s surfaces can be correlated across the profile 27 km and show evidence of up to 10 m of erosion a significant facies or grain size change onlap and association with mature calcic paleosols the e surfaces can be correlated between 5 and 17 km display erosion of the regional extent of the e and s surfaces indicate that the gravelly fluvial system has a large scale sheet like geometry which comprises a series of stacked erosion dominated multi story bodies high resolution architectural elements are poorly defined in this coarse fluvial system and make it difficult to constrain the scale of the depositional system an individual high resolution cycle records braid plain development and is interpreted as a multi story channel belt the braid plain width is estimated at 19 km but the width of individual active channels is unknown the sediments were deposited in a proximal fluvial setting disconnected from marine influences we interpret the high resolution cycles and bounding e surfaces to record a progressive decrease in runoff and fluvial transport capacity indicative of a drying upward climatically driven signal the origin of the s surface bounded packages is more difficult to determine a variety of mechanisms are considered including changes in discharge driven by climatic fluctuations changes in stream power related to drainage capture within the source area and tectonic tilting an important aspect of the study is that the s surfaces can be identified and correlated for 27 km and provide an example of a robust high resolution correlation framework in coarse grained braided fluvial deposits that could be applied elsewhere in contrast the e surfaces do not display any significant changes in facies or grain size across them such that many of the smaller scale cycles could potentially be miscorrelated

uniquely extensive soft sediment deformation in the rhaetian of the uk evidence for earthquake or impact the lower part of the cotham member in the penarth group latest triassic rhaetian of the uk incorporates a uniquely extensive metre scale horizon of soft sediment deformation interpreted as a seismite it shows evidence for only a single seismic event even at its thickest development it is recorded from more than forty sites across at least eight discrete sedimentary basins covering n250 000 km 2 and originally must have covered a still larger area such a widespread horizon of soft sediment deformation unique for the uk phanerozoic and implying a seismic event of exceptional magnitude is difficult to account for by conventional terrestrial mechanisms contemporaneous volcanism in the central atlantic magmatic province camp was too far distant to cause the deformation and the tectonic setting of the region was not conducive to earthquakes on this scale slump fold long axes suggest an epicentre broadly in the southern irish sea or st george s channel impact of a km scale asteroid here potentially could produce the observed sedimentological effects across the uk but any late triassic impact structure would now be concealed by a km or more of younger strata at its thickest development in northern ireland the seismite is succeeded by a rip up breccia and hummocky and wave rippled cross stratification these facies and their position immediately above the seismite are consistent with the effects of a tsunami arising directly from the seismic event tentative evidence for a tsunamite of this age has also been reported from southern france the putative tsunamite in northern ireland is succeeded by a desiccation cracked hiatus which may correlate with a similar hiatus truncating the seismite at sites in southern england the hiatus in southern england correlates closely with a 13 c isotope excursion that has been traced from eastern europe across to western north america and is associated with significant biotic changes the ultimate cause of the seismite and associated tsunamite remains unclear no impact crater of appropriate age or location is currently known and other evidence for impact at this time is at best equivocal it is considered here that impact of a km scale asteroid may have caused the observed sedimentological effects in the lilstock formation across the uk area but was not necessarily a significant contributory factor in the generation of either the isotope excursion or of the biotic changes through the triassic jurassic boundary interval

basalt breccias and conglomerates in the lower jurassic mccoy brook formation fundy basin nova scotia differentiation of talus and debris flow deposits abstract basalt talus breccias and debris flow conglomerates are interbedded with terrestrial redbeds in the lower jurassic mccoy brook formation in the synrift fundy basin the redbeds formed in a semiarid to arid climate in alluvial fan eolian fluvial playa and lacustrine environments the basalt talus breccias formed adjacent to cliffs of north mountain basalt produced by synsedimentary faulting on the northern side of the basin the breccias lack bedding planes contain basalt boulders up to 8 m in length and are interstratified with fluvial playa eolian and lacustrine sandstones and mudstones at wasson bluff 24 m of talus breccia with a matrix of sandy mud comprise a sequence that is matrix supported at the base and rapidly grades upward to the typical clast supported fabric the matrix of clast supported breccia locally contains horizontal to inclined sandy gravel layers and in a few places abundant bones of small reptiles that lived within the talus indicating that matrix infiltrated open spaces around the boulders a slope of 34 to the southeast f the paleosurface of the talus is inferred from the orientations of the lower surfaces of discoidal and plate shaped boulders the basalt debris flow conglomerates total 21 m in thickness and comprise 51 beds some beds are separated by centimeter scale sandstone layers deposited by streamflows the conglomerates have a sandy mud matrix and a fabric that varies from matrix supported to clast supported the mean orientation of discoidal clasts is subhorizontal with substantial scatter of individual clasts the base of each flow is non erosional and many boulder project above flow surfaces we attribute the debris flows to remobilization of debris during heavy rainstorms in the semiarid to arid climate

thrust faults and extensional detachment faults in cretan tectono stratigraphy implications for middle miocene extension abstract the revised tectono stratigraphy of crete and especially of the phyllites quartzites complex demonstrated the distinction of the probable paleozoic low medium grade metamorphic rocks of the arna unit from the underlying permo triassic phyllites and associated carbonate sediments trypali facies of western crete unit as well as the overlying permo triassic phyllites and associated sediments of the tyros ravdoucha beds at the base of the tripolis unit the pre existing mixture of the above tectono stratigaphic units in a single complex created a number of misinterpretations as far as stratigraphy metamorphism and interpretation of low angle faults as thrusts or detachments especially in cases where the inferred tectonic contact concerns the transition between the tyros beds and the base of the tripolis carbonate platform there is no structural omission and therefore the contact represents a minor disharmonic sliding surface and not a detachment based on the revised tectono stratigraphic analysis the determination of the structural omission for each tectonic contact was possible and several detachments were described for the first time footwall rocks of the detachments comprised several tectonic units usually from the lower nappes and hanging wall rocks comprised several tectonic units usually from the upper nappes the detachment may separate not only metamorphosed units in the footwall mani western crete arna from non metamorphosed units in the hanging wall tripolis pindos and higher nappes but also all other possible combinations from the cretan nappe pile extension in crete started in the middle late miocene with the formation of extensional detachment faults the reported extensional structures of oligocene to early miocene age do not correspond to crustal extension of crete but to localized shear zones related to nappe stacking and the exhumation of metamorphic rocks extensional detachments in crete form a tectonic horst through two oppositely dipping e w trending zones one dipping north related to the opening of the cretan basin and the other dipping south related to the formation of the messara supra detachment basin the deformation history of units within crete can be summarized as i compressional deformation producing arc parallel east west trending south directed thrust faults in oligocene to early miocene time ii extensional deformation along arc parallel east west trending detachment faults in middle miocene time with hanging wall motion to the north and south and iii late miocene quaternary transtensional deformation along high angle normal and oblique normal faults that disrupt the older arc parallel structures

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

p wave attenuation structure in the fault area of the 1995 kobe earthquake the three dimensional 3 d p wave attenuation structure in the kobe epicentral area is determined using aftershock records from the 1995 kobe hyogo ken nanbu earthquake waveform data from both permanent seismic networks and portable stations set up following the kobe mainshock were used the observed p wave amplitude spectra were inverted for the spectral plateau value the source corner frequency and a frequency independent t operator assuming an 2 type source model the calculated t operators were subsequently used for the computation of the 3 d absorption structure using a 3 d velocity model only high quality amplitude spectra were used for the estimation of reliable attenuation parameters resulting in a final data set of 4100 t operators two regions of high absorption were found in the upper part of the crust one is below the northern part of awaji island and reaches down to a depth of 5 km the other region northeast of kobe city is along the arima takatsuki tectonic line and extends along the rokko kashiodani and yamada faults it extends northward to the hokusetsu sanchi area in both regions a high density of fault lineations is mapped and high poisson ratios are known this suggests that partially saturated cracks cause the observed high attenuation

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

estimating slab earthquake response spectra from a 3d q model the problem of estimating response spectra for a heterogeneous lithosphere can be addressed by directly computing attenuation from physical models in a subduction zone slab earthquakes will have different attenuation through the mantle wedge than the slab this article is primarily concerned with very high loss paths through the attenuating mantle underlying the volcanic zone of the north island new zealand where low q requires modification of the standard new zealand engineering response spectrum model a lack of strong motion data prevents a standard regression analysis for paths from deep slab earthquakes through the highly attenuating mantle zone instead modifications have been derived using a 3d frequency independent q model that has been developed for the north island subduction zone from 2 20 hz local earthquake t data by calibrating the t crustal results to the standard new zealand model amplitudes can be compared between the standard model and the 3d q model additional path averaged attenuation rate coefficients cq for each source and station pair are determined this results in simple expressions for cq as a function of centroid depth for modifying the standard model this modification reduces the model spectra by a factor of approximately 2 4 for mantle wedge paths below the volcanic region this reduction is similar to the observed variation in response spectra at periods below 0 4 sec for a 160 km deep m w 6 0 earthquake for shallow earthquakes propagating through the shallow volcanic region the new model gives results that are similar to a volcanic path attenuation term derived by regression analysis manuscript received 24 february 2003

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

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

geologic evidence for recurrent moderate to large earthquakes near charleston south carolina multiple generations of earthquake induced sand blows in quaternary sediments and soils near charleston south carolina are evidence of recurrent moderate to large earthquakes in that area the large 1886 earthquake the only historic earthquake known to have produced sand blows at charleston probably caused the youngest observed blows older late quaternary sand blows in the charleston area indicate at least two prehistoric earthquakes with shaking severities comparable to the 1886 event

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

a genetic classification of sinkholes illustrated from evaporite paleokarst exposures in spain this contribution analyses the processes involved in the generation of sinkholes from the study of paleokarst features exposed in four spanish tertiary basins bedrock strata are subhorizontal evaporites and in three of the basins they include halite and glauberite in the subsurface our studies suggest that formation of dolines in these areas results from a wider range of subsidence processes than those included in the most recently published sinkhole classifications a new genetic classification of sinkholes applicable to both carbonate and evaporite karst areas is thus proposed with the exception of solution dolines it defines the main sinkhole types by use of two terms that refer to the material affected by downward gravitational movements cover bedrock or caprock and the main type of process involved collapse suffosion or sagging sinkholes that result from the combination of several subsidence processes and affect more than one type of material are described by combinations of the different terms with the dominant material or process followed by the secondary one e g bedrock sagging and collapse sinkhole the mechanism of collapse includes any brittle gravitational deformation of cover and bedrock material such as upward stoping of cavities by roof failure development of well defined failure planes and rock brecciation suffosion is the downward migration of cover deposits through dissolutional conduits accompanied with ductile settling sagging is the ductile flexure of sediments caused by differential corrosional lowering of the rockhead or interstratal karstification of the soluble bedrock the paleokarsts we analysed suggest that the sagging mechanism not included in previous genetic classifications plays an important role in the generation of sinkholes in evaporites moreover collapse processes are more significant in extent and rate in areas underlain by evaporites than in carbonate karst primarily due to the greater solubility of the evaporites and the lower mechanical strength and ductile rheology of gypsum and salt rocks

sheet flow deposits of graded beds and mudstones on an alluvial sandflat playa system upper triassic blomidon redbeds st mary s bay nova scotia the 400 m of blomidon redbeds accumulated in a semi arid rift valley in the subtropics at st mary s bay these redbeds are 64 sandy mudstone playa mudflats 25 graded beds sandflats at the toes of alluvial fans 10 fissile claystone playa lakes and 1 channel sandstone stream channels flash floods in mountains south of the valley flowed down alluvial fans to spread out to the north east as sheet flows on sandflats and playa mudflats deceleration of the sheet flows deposited graded beds 2 83 cm in thickness on the sandflats and thin layers of mud on the playas nine sequences consisting of arrangements of six lithologies compose 90 of the graded beds in order of decreasing abundance these are ripple cross laminated siltstone horizontally laminated mudstone fining upward ripple cross laminated siltstone ripple cross laminated sandstone horizontally laminated mudstone cross bedded sandstone horizontally laminated mudstone ripple cross laminated sandstone ripple cross laminated siltstone rippledrift cross laminated siltstone horizontally laminated mudstone fining upward ripple drift cross laminated siltstone cross bedded sandstone ripple cross laminated siltstone and cross bedded sandstone ripple cross laminated siltstone horizontally laminated mudstone the sheet flows perhaps up to 1 m in depth had a high concentration of suspended load deposition was dominantly during lower flow regime conditions and moderate to rapid flow deceleration there are 32 thinning and fining up cycles where a sandflat package of graded beds is transitionally followed by a playa package of sandy mudstone the cycles range in thickness from 1 3 to 13 3 m averaging 4 6 m each cycle is initiated by avulsion to a new active channel network on a fan gradual abandonment of the channel network produces the thinning and fining up cycle the cycles are grouped in three 60 70 m fining up megacycles upwards within each megacycle the packages of sandy mudstone compose a progressively larger proportion of the cycles each megacycle evidently was initiated by a brief period of tectonic movement on the border faults that produced greater relief of the highlands relative to the valley floor subsequent erosion gradually lowered the relief to yield a fining up megacycle

three dimensional attenuation model of the shallow hikurangi subduction zone in the raukumara peninsula new zealand 1 the material properties of the shallow subduction zone are imaged with data from a passive seismic deployment in the raukumara peninsula attenuation images are obtained using t values measured from 2848 spectra of p wave arrivals the t values are inverted for frequency independent three dimensional 3 d qp using a 3 d velocity model linked nodes in a preliminary 2 d inversion are used to obtain the most reliable initial model for 3 d inversions the results show the benefits of obtaining 3 d q in addition to 3 d vp and vp vs q is related to localized permeability and heterogeneity and thus 3 d q is an important tool for interpreting active tectonic regions qp in the shallow overlying plate generally corresponds to the mapped geology two high qp features 600 represent subducted seamounts or cretaceous volcanics within the overlying plate the gradient above the subducting plate is the strongest feature in the qp model with the slab having high qp 600 900 below 20 km depth and above the plate interface there is a zone of 50 decrease in qp and high vp vs about 10 km thick which represents actively subducting sediment and has distributed microearthquake activity associated with active underplating

constraints on synrift intrabasinal horst development from alluvial fan and aeolian deposits triassic fundy basin nova scotia the authors would like to acknowledge shell e and p for funding this study rob raeside at the acadia university and liz kosters for their support during the field seasons we also would like to thank brian p j williams for enthusiastic discussions in the field

structural stratigraphic and sedimentological characterisation of a wide rift system the triassic rift system of the central atlantic domain abstract the extension driven break up of the pangean supercontinent in the present day central and north atlantic domains commenced during permo triassic times permian rift processes in this region are generally attributed to crustal collapse during the latter part of the hercynian variscan orogeny but the triassic rifting style is more complex and the presence of a single over riding first order control is equivocal basement terrane structures and boundaries provide pre existing zones of weakness that had significant influences on the location timing orientation and extent of triassic rifting the 201 ma central atlantic magmatic province camp a large igneous province lip increased lithospheric heat flow at the end of rifting produced uplift and doming and also contributed to deformation and subsequent continental breakup analysis of the triassic basin structures in the central atlantic and north atlantic domains respectively georgia to nova scotia and conjugate margin and newfoundland iberia shows that four main basin types are geographically distributed 1 southern basins georgia to virginia small to medium size with limited growth structures 2 basins in the central east domain new jersey nova scotia wide basins with growth structures along long lived inherited bounding faults 3 basins in the central west domain offshore ns and morocco that comprise numerous half graben sub basins in a lower unit and an upper very wide tabular unit and 4 northern basins newfoundland portugal that are tabular and extremely wide basin architectures suggest that subsidence was regional in extent and not necessarily controlled by main faults variations in crustal characteristics are considered to have led to the development of the four main basin types stratigraphic data show that the onset of deposition in the central and southern north atlantic domain was restricted to a central segment between two main structural lineaments overall crustal rheology and inheritance exhibited first order controls on subsidence and basin development triassic basins in the central and north atlantic domain were all filled by continental deposits in various palaeo environments such as alluvial fan mega fluvial systems terminal fluvial systems fan delta fluvial systems permanent oxic and anoxic lakes playa lakes and saline lakes some of them interbedded with aeolian and volcanic deposits most basins were far from any marine domain but marine ingressions from the tethys domain are inferred from dolomite and marine fauna in portugal and from thick salt deposits in morocco and offshore canada during the late rhaetian a series of palaeogeographic maps are presented utilising plate reconstructions based on sahabi et al 2004 in order to summarize continental scale palaeo environment distribution our tectono stratigraphic model suggests that initial strain was accommodated in a central segment by inherited faults during the early and middle triassic during the carnian the rift domain was increasingly extended with the development of half graben basins in the central segment and some in the northern segment in both segments the initial strain re activated inherited faults and later the rift zones evolved towards significantly wider basins marked by the presence of a major erosional truncation surface across the basins and followed by lacustrine sedimentation that eventually overlapped paleo topographic highs subsidence of such regional extent is likely driven by thermal processes following a phase of extreme lithospheric thinning and lower crustal removal associated with mantle uplift the architecture of the triassic rifting has the characteristics of the wide rift mode very large basins with some active faults for which subsidence is driven by lower crustal flow within a high heat flow region nevertheless some faults were active during late triassic sedimentation but accounted for a relatively minor part of the overall subsidence pulses of active subsidence and topographic rejuvenation led to fluvial dominated deposition within basins non rejuvenation of hinterland led to more lacustrine dominated sedimentation and eventual connection of basins across topographic highs due to regional thermal subsidence during the latest rhaetian basins with the lowest elevations were possibly flooded by marine waters resulting in precipitation of thick salt deposits

stress strain changes and triggered seismicity following the mw 7 3 landers california earthquake calculations of dynamic stresses and strains constrained by broadband seismograms are used to investigate their role in generating the remotely triggered seismicity that followed the june 28 1992 mw7 3 landers california earthquake i compare straingrams and dynamic coulomb failure functions calculated for the landers earthquake at sites that did experience triggered seismicity with those at sites that did not bounds on triggering thresholds are obtained from analysis of dynamic strain spectra calculated for the landers and mw6 1 joshua tree california earthquakes at various sites combined with results of static strain investigations by others i interpret three principal results of this study with those of a companion study by gomberg and davis this issue first the dynamic elastic stress changes themselves cannot explain the spatial distribution of triggered seismicity particularly the lack of triggered activity along the san andreas fault system in addition to the requirement to exceed a coulomb failure stress level this result implies the need to invoke and satisfy the requirements of appropriate slip instability theory second results of this study are consistent with the existence of frequency or rate dependent stress strain triggering thresholds inferred from the companion study and interpreted in terms of earthquake initiation involving a competition of processes one promoting failure and the other inhibiting it such competition is also part of relevant instability theories third the triggering threshold must vary from site to site suggesting that the potential for triggering strongly depends on site characteristics and response the lack of triggering along the san andreas fault system may be correlated with the advanced maturity of its fault gouge zone the strains from the landers earthquake were either insufficient to exceed its larger critical slip distance or some other critical failure parameter or the faults failed stably as aseismic creep events variations in the triggering threshold at sites of triggered seismicity may be attributed to variations in gouge zone development and properties finally these interpretations provide ready explanations for the time delays between the landers earthquake and the triggered events

isotopic imprint of climate and hydrogeochemistry on terrestrial strata of the triassic jurassic hartford and fundy rift basins abstract late triassic to early jurassic terrestrial sequences in the hartford and fundy rift basins have distinctive carbon and oxygen isotopic compositions of calcite and dolomite the isotopic data mostly reflect paleoclimatic fluctuations and hydrogeochemistry of the lacustrine playa and fluvial environments dolomites from laminae in three sequences of playa red mudstones and lacustrine gray to black mudstones in the hartford basin have variable isotopic compositions 13c 5 8 to 1 8 pdb 18o 7 2 to 0 7 pdb within any single symmetrical cycle of playa red mudstone lacustrine gray black gray mudstone playa red mudstone there is a systematic change to relatively enriched 13c compositions in dolomite in the grayish black and black mudstones in the center of the cycle these carbon isotopic data suggest that the lacustrine sequences formed as the lakes changed from well mixed with anoxic bottom waters to stratified with anoxic bottom waters where 13c depleted carbon was concentrated in organic matter that was then buried calcites from lacustrine micritic and biomicritic limestones of the scots bay formation of the fundy basin have stable isotopic compositions 13c 4 6 to 2 2 pdb 18o 6 1 to 3 0 pdb that become more enriched in 18o and 13c upward in shallowing depositional sequences these isotopic data reflect initial calcite precipitation when a high inflow of fresh water produced high lake levels followed by progressively lower inflow resulting in lower lake stands and higher salinity due to continuing evaporative loss of surface wat r the lake waters were well oxygenated at all times in the hartford basin caliche calcites in fluvial mudstones and sandstones have isotopic compositions 13c 7 3 to 3 8 pdb 18o 8 0 to 5 6 pdb that reflect paleosol processes during climatic conditions that varied from warm and dry in late triassic time to relatively cooler and probably wetter in the early jurassic isotopic compositions of caliche calcites in redbeds in the fundy basin indicate a parallel climate change from late triassic to early jurassic time but also that the climate was relatively hotter and probably drier over the entir interval as compared to the hartford basin

eolian sandstones in upper triassic lower jurassic red beds of the fundy basin nova scotia abstract eolian sandstones occur interbedded with alluvial fan and braided river red beds in the upper triassic wolfville formation and at the base of the lower jurassic mccoy brook formation in nova scotia extensive semiaridity and aridity in the subtropical rift valley favored deposition of eolian sandstones caliche paleosols alluvial fan conglomerates braided river alluvium and playa mudstones in postdrift configuration paleowinds blew to the southwest west and northwest down the valley reflecting the direction of trade winds at 25 n paleolatitude a three step hierarchy of surfaces truncates cross beds first order bedding planes of low relief extend for at least hundreds of meters truncating all eolian structures these surfaces were sculptured by desert flash floods and then deflated to ventifact bearing bimodal regs second order surfaces bound cross bed sets and are mostly concave up and dip downwind recording shifts in migration direction of individual dunes or dunes superimposed on larger dune structures third order surfaces within cross bed sets formed on the lee sides of dunes due to fluctuations in wind direction and strength barchans initially developed on the alluvial fan and braided river alluvium later coalescing into barchanoid transverse ridges as evidenced by the internal geometry of the eolian sandstones p

controls on the stratigraphic development of the triassic fundy basin nova scotia implications for the tectonostratigraphic evolution of triassic atlantic rift basins abstract the late triassic synrift succession of the minas sub basin bay of fundy nova scotia includes a fluvio alluvial fan dominated unit lower and middle wolfville formation a transitional fluvio playa unit upper wolfville formation and an upper playa dominated package blomidon formation we describe the facies development in the 240 m thick upper wolfville formation examine vertical facies stacking patterns and develop a depositional model for this succession the unit comprises channelized and unconfined fluvial deposits interbedded with aeolian and playa sediments that grade upward into playa deposits the succession comprises progradational and retrogradational fluvial packages and thin aggradational playa claystones comparison with 11 other atlantic margin continental triassic rift basins allows an assessment of the controls that govern rift basin development the transition from fluvial to playa or lacustrine conditions occurs in all basins at different times the lack of synchronicity indicates that global climate change was not a controlling factor we suggest that the fluvial to lacustrine or playa transition was due to a decrease in source area relief related to a decline in regional tectonic activity and that the basin was hydrologically closed throughout sedimentation this tectonostratigraphic model may be appropriate for other triassic basins developed along the atlantic margin

grain contact adhesion hysteresis a mechanism for attenuation of seismic waves we propose a new mechanism for attenuation of seismic waves in rocks it is shown that grain contact adhesion hysteresis leads to energy dissipation without having to invoke frictional sliding at grain contacts adhesion hysteresis gives rise to frequency independent attenuation that increases with strain amplitude for large strains and decreases with overburden stress we can obtain qualitatively correct trends that show the effect of fluid saturation pore structure and grain size through simple models for granular sedimentary rocks

paleoseismic evidence for recurrence of earthquakes near charleston south carolina a destructive earthquake that occurred in 1886 near charleston south carolina was associated with widespread liquefaction of shallow sand structures and their extravasation to the surface several seismically induced paleoliquefaction structures preserved within the shallow sediments in the meizoseismal area of the 1886 event were identified field evidence and radiocarbon dates suggest that at least two earthquakes of magnitudes greater than 6 2 preceded the 1886 event in the past 3000 to 3700 years the evidence yielded an initial estimate of about 1500 to 1800 years for the maximum recurrence of destructive intraplate earthquakes in the charleston region

cycles of sand flat sandstone and playa lacustrine mudstone in thetriassic jurassic blomidon redbeds fundy rift basin nova scotia implications for tectonic and climatic controls the redbeds of the 220 m blomidon formation comprise more than 100 pairs of i sand flat sandstone distal alluvial fan and ii playa sandy mudstone and or lacustrine claystone these pairs are tectonic autocycles generated by rift basin subsidence and sagging along the glooscap fault zone that shifted loci of active fan sedimentation toward and away from the playa surface as fan lobes migrated into topographically low areas intervals of intense and prolonged aridity are recorded in many of the sand flat sandstones and playa sandy mudstones by evaporite minerals principally gypsum precipitated by subsurface evolution of a caso4 nacl brine aridity is further demonstrated by intense disruption of sediment fabrics beneath evaporite crusts deep mudcracks eolian sandstone layers and patches and the presence of authigenic ca mg rich illite smectite and analcime during relatively wetter intervals claystone beds accumulated in shallow lakes that filled the playa depression lapping onto the sand flat