cessation reactivation of polygonal faulting and effects on fluid flow in the voring basin norwegian margin polygonal faults mainly oriented n50 n110 and n170 are abundant in the upper part of the mud dominated kai formation upper miocene lower pliocene of the voring basin a second less developed tier of polygonal faults oriented n20 n80 and n140 exists at the base of the overlying naust formation upper pliocene present the faults abruptly terminate upward below a thick interval of debris flows we propose a dynamic model in which 1 the development of polygonal faults discontinues temporarily as a result of a change in regional sedimentation leading to inactive polygonal faults 2 rapid emplacement of debris flows in the late pleistocene creates a new interval of polygonal faults in the lower part of the naust formation immediately beneath the debris flow and some faults penetrate into the underlying kai formation 3 some polygonal faults within the kai formation are reactivated and propagated upward into the base of the naust formation the high interconnectivity between faulted layers allows the fluids to reach shallower depths forming well expressed pipes and pockmarks on the sea floor the model of cessation reactivation of polygonal faults constrains the sealing capacity of sedimentary cover over the reservoirs and helps to reconstruct the fluid migration history through the sedimentary column

chemical alteration and mineral growth under high pco2 conditions insights from the mineral chemistry of carbonate phases in the caprese reservoir northern apennines central italy abstract carbon cycle is one of the most complex geochemical cycles of the earth as it involves atmosphere hydrosphere biosphere and lithosphere among these different geochemical spheres mechanisms and reaction rates governing migration and fixation of carbon i e fluxes such as the stability of the different carbonates minerals under specific conditions in crustal reservoirs are still matter of detailed studies in this work sem and xrd investigations and emp analyses were combined to study the mineralogical and chemical compositions of carbonate phases occurring in strongly altered triassic volcanic rocks hosting a co 2 reservoir namely the caprese reservoir located in eastern tuscany central italy the caprese crustal fluid reservoir lying at 3300 m depth beneath the quaternary san cassiano basin hosts a supercritical co 2 n 2 rich phase and a na cl rich saline up to 81 5 g l brine the mineralogical assemblage consists of authigenic microcrystalline quartz ca fe mg carbonates na k clay minerals and fe oxides the primary minerals being almost completely chemically altered by secondary processes scanning electron microscope images and cation ca fe mg contents in carbonates highlighted that zoned ankerite was re grown on calcite crystals due to interactions processes with co 2 rich fluids the geochemical and mineralogical data provided useful insights for understanding both the processes that formed the c bearing minerals and their growth in deep saline reservoirs

depositional systems composition and geochemistry of triassic rifted continental margin redbeds of the internal rif chain morocco the middle to upper triassic redbeds at the base of the ghomaride and internal dorsale calcaire nappes in the rifian sector of the maghrebian chain have been studied for their sedimentological petrographic mineralogical and chemical features redbeds lie unconformably on a variscan low grade metamorphic basement in a 300 m thick upward fining and thinning megasequence successions are composed of predominantly fluvial red sandstones with many intercalations of quartzose conglomerates in the lower part that pass upwards into fine grained micaceous siltstones and massive mudstones with some carbonate and evaporite beds this suite of sediments suggests that palaeoenvironments evolved from mostly arenaceous alluvial systems middle triassic to muddy flood and coastal plain deposits the successions are characterized by local carbonate and evaporite episodes in the late triassic the growth of carbonate platforms is related to the increasing subsidence norian rhaetian during the break up of pangea and the earliest stages of the western tethys opening carbonate platforms became widespread in the sinemurian sandstones are quartzose to quartzolithic in composition testifying a recycled orogenic provenance from low grade palaeozoic metasedimentary rocks palaeoweathering indices chemical index of alteration chemical index of weathering and plagioclase index of alteration suggest both a k enrichment during the burial history and a source area that experienced intense weathering and recycling processes these processes were favoured by seasonal climatic alternations characterized by hot episodically humid conditions with a prolonged dry season these climatic alternations produced illitization of silicate minerals iron oxidation and quartz rich red sediments in alluvial systems the estimated burial temperature for the continental redbeds is in the range of 100 to 160 c with lithostatic tectonic loading of ca 4 to 6 km these redbeds can be considered as regional petrofacies that mark the onset of the continental rift valley stage in the western pangea middle triassic before the opening of the western part of tethys in the middle jurassic the studied redbeds and the coeval redbeds of many alpine successions betic tellian and apenninic orogens show a quite similar history they identify a mesomediterranean continental block originating from the break up of pangea which then played an important role in the post triassic evolution of the western mediterranean region

the erris ridge a major geological feature in the nw irish offshore basins the erris ridge is a narrow structural high that separates the erris and rockall troughs it has a composite internal character and its orientation is thought to be controlled by a pre caledonian structural fabric which was frequently reactivated during caledonian to cenozoic time in the north it is fault bounded and probably contains rocks of palaeozoic and older age it formed a positive topographic feature which was progressively onlapped during permo triassic to cretaceous times fault reactivation occurred along its western boundary in tertiary times and it was submerged by approximately latest miocene times further south the ridge is more complex the palaeozoic and older core is flanked to the se by interpreted permo triassic to lower jurassic strata which constitute a fault controlled uplifted remnant of a half graben basin this composite structure was probably inverted during late jurassic times and remained as a topographic feature until cretaceous times it was progressively onlapped during cretaceous and tertiary times with a minor phase of fault reactivation during the early tertiary the ridge acted as a rigid block which facilitated the focusing of several phases of crustal extension in the erris trough and in the rockall trough

the drainage of africa since the cretaceous much of the drainage of africa is relatively youthful many of its major rivers have shown substantial changes in their courses since the break up of gondwanaland in the cretaceous in addition many of the rivers have distinctive morphological characteristics such as inland deltas cataracts and elbows of capture tectonic and climatic changes including the development of the east african rift system and the aridification of the quaternary help to explain the nature of these rivers the history of the saharan rivers the niger the nile the congo the cunene the zambezi the limpopo and the orange is reviewed

syntectonic sedimentation in a middle triassic rift northern apennines italy abstract the anatomy of the sedimentary and volcanic fill of a middle triassic continental rift at the western margin of the tethys is illustrated by the study of a 250 m thick sequence on the tyrrhenian coasts of the northern apennines this sequence contains two cycles of sedimentation 1 a the lower cycle comprises a basal transgressive sequence from continental alluvial fans to shallow marine carbonates and an upper sequence which correspond to an increasing tectonic activity submarine syntectonic facies assemblage the lower part of the last assemblage is characterized by a thick 22 m rapidly deposited sequence of coarse carbonate breccias with minor calcareous sandy turbidites this is overlain by channelized red beds of submarine fans composed of close interstratification and juxtaposition of carbonate breccias with red clastic matrix and red sandy quartz pebble conglomerates and silty sands interbedded alkaline pillow lava record penecontemporaneous submarine eruptions the lavas are capped by thin red cherty diaspri crusts the lower cycle of sedimentation ends with a karstic surface on relatively deep marine carbonate layers this suggests a rapid emersion due to the arrest and reversal of the downsinking of the initial aborted or failed rift 2 b the upper cycle of sedimentation starts with more mature fluvial red beds and changes upward into shallow marine sands and carbonates this upper cycle represents an early stage of evolution of a new major rift this second major rift led in jurassic times to the opening of an oceanic area between europe and western italy

the spatial and temporal distribution of pipe formation offshore namibia a group of nearly 400 pipe structures from the continental slope of northern namibia are analysed for their spatial and temporal distribution the pipes most likely formed as a result of highly focused fluid venting and understanding the factors controlling their distribution in space and time is key to their genesis we analysed their spatio temporal distribution using an arbitrary chronostratigraphic timescale from which it is concluded that the pipes did not form at the same time pipe formation is shown to be intermittent and persistent with 2 29 pipes forming in each of the 20 arbitrary time intervals that are considered to span the neogene period the spatial distribution of these pipes is clustered to dispersed spatial statistics conducted on the distribution of pipe formation timings have shown that two statistically significant groups of pipes exist within the population 1 in the north and west and 2 in the south with the former occurring prior to the latter locally pipe formation is sporadic with clusters and outliers occurring during the same time period a conceptual model is proposed whereby pipe formation in specific locations is the result of localised breaching of the seals for isolated pressure cells which are locally independent yet broadly controlled an inferred basinal fluid source is thought to determine the broader patterns of pipe formation and the focus of this fluid source shifts from north to south with time at a local scale multiple local factors interact producing a sporadic pipe formation distribution through a prolonged period of highly focused fluid migration once formed the pipes continued to focus fluids intermittently leading in some cases to later pockmark formation

eocene fan delta submarine fan deposition in the wagwater trough east central jamaica the wagwater trough is a fault bounded basin which cuts across east central jamaica the basin formed during the late palaeocene or early eocene and the earliest sediments deposited in the trough were the wagwater and richmond formations of the wagwater group these formations are composed of up to 7000 m of conglomerates sandstones and shales six facies have been recognized in the wagwater group facies i unfossiliferous massive conglomerates facies ii channelized non marine conglomerates sandstones and shales facies iii interbedded fossiliferous conglomerates and sandstones facies iv fossiliferous muddy conglomerates facies v channelized marine conglomerates sandstones and shales and facies vi thin bedded sheet sandstones and shales the wagwater and richmond formations are interpreted as fan delta submarine fan deposits facies associations suggest that humid region fan deltas prograded into the basin from the adjacent highlands and discharged very coarse sediments on to a steep submarine slope at the coast waves reworked the braided fluvial deposits of the subaerial fan delta into coarse sand and gravel beaches sediments deposited on the delta front slope were frequently remobilized and moved downslope as slumps debris flows and turbidity currents at the slope basin break submarine fans were deposited the submarine fans are characterized by coarse inner and mid fan deposits which grade laterally into thin bedded turbidites of the outer fan and basin floor

breccia hosted manganese rich minerals of alpi apuane italy a marine redox generated deposit mn rich beds occur within the brecce di seravezza formation bsfm intercalated between norian metadolostone megalodontic marble and hettangian marble in the alpi apuane italy the bsfm is a rockfall talus deposit that accumulates at the base of the footwall scarp of normal faults bordering extensional marine coastal basins the type sequence of metabreccia ends with a bed of chloritoid schist interpreted as the metamorphic equivalent of lateritic soils the four main types of mn mineral assemblages are 1 braunite piemontite and rare hausmannite 2 piemontite braunite hollandite and minor rhodochrosite and kutnahorite 3 braunite hollandite and rare piemontite the other minerals are quartz calcite muscovite phlogopite baryte and minor hematite rutile and apatite during the alpine orogeny pressures of 4 6 kb and temperatures of 350 380 c were attained mn assemblages with hematite and phlogopite indicate o2 10 8 for t 350 c and o2 10 6 when braunite appears on the mn rich rocks ti fe nb sn ta hf th ga rb pr k na nd were identified as detrital in origin and are positively correlated with al u is positively correlated with co pb bi mo the rare earth element patterns normalized to seawater show a negative slope towards the heavy rare earth elements with positive ce anomalies in some samples positive ce and eu anomalies in other samples and negative ce and positive eu anomalies in a third group the eu concentrations are nearly constant and the eu anomalies reflect differences in the concentration of other rare earth elements for ce a positive correlation with al2o3 sio2 indicate that a detrital signature prevails on that produced by duration of seawater exposure but a significant good correlation of la tm lu with mg could indicate at least for these elements a seawater signature only in some samples ba eu sr show anomalously high concentrations likely of hydrothermal origin however generally in all the chemical variation diagrams the bsfm samples fall outside the field of hydrothermal and hydrogenous deposits as defined in the literature for other mn deposits in addition metabasites and metavolcaniclastic beds are absent from the bsfm sequence and bsfm coastal basins were for the most part separated from the open ocean and related streams that must be excluded as possible mn sources owing to the arid climate of late triassic the runoff was negligible and the groundwater oxidizing and alkaline were unable to mobilize mn the bsfm basins are then the most suitable depositional environment for mn the water column was stagnant and stratified only where bottom of the basin was deeper than the oxic anoxic boundary reducing marine bottom waters percolated within the fractured basement and leached mn from disseminated minerals of metamorphic rocks and then rising along fault and fractures supplied mn to the bottom waters afterwards when tectonic uplift and sealevel drop brought the bottom into the oxic field mn precipitated and formed the mn rich matrix of the bsfm deposits

surface and subsurface signatures of gas seepage in the st lawrence estuary canada significance to hydrocarbon exploration abstract the seabed of the st lawrence estuary is characterized by many fluid releasing features on multibeam bathymetric images these features correspond to crater like depression pockmarks predominantly found on the northwestern shoulder of the 300 m deep laurentian channel as well as on the channel floor aligned pockmarks which define segments up to 12 km long are frequent in the laurentian channel whereas they are preferentially associated with submarine landslides on the northwestern shoulder of the channel on high resolution seismic profiles pockmarks found in the laurentian channel are characterized by seismic chimneys that may be traced down to the autochthonous paleozoic rocks st lawrence platform suggesting a thermogenic origin for the gas on the northwest shoulder of the laurentian channel the seismic signature of pockmarks does not extend downward to the reflector that corresponds to bedrock st lawrence platform and or grenvillian province suggesting together with high sedimentation rate a biogenic origin for the gas these results are discussed in the light of the data collected in the onshore parts of the st lawrence platform and suggest the presence of a mature hydrocarbon source the conclusions are supportive arguments for the hydrocarbon prospectivity of both the onshore and offshore segments of the paleozoic autochthonous domain st lawrence platform

sedimentology of a middle cambrian outer shelf margin with evidence for syndepositional faulting eastern california and western nevada abstract the middle to upper cambrian emigrant formation at horse thief canyon california is a transitional section between the outer shelf bonanza king formation and the basin facies represented by the emigrant formation in nevada at horse thief canyon the emigrant is subdivided into four members the limestone siltstone member the papoose lake tongue the megabreccia member and the limestone chert member for a portion of middle cambrian time the shelf structure was that of a ramp bedded and burrowed pelletal dolostones were deposited in the deeper waters of the outer shelf sediment for the outer shelf may have been derived from a mid shelf shallow subtidal to peritidal zone cycle patterns of burrowed and bedded dolostones are probably related to periods of little sediment input accompanied by intense burrowing of the bottom followed by periods of heightened current activity and bedded dolostone deposition later in the middle cambrian the shelf structure changed to a platform megabreccia and breccia beds representing debris flow deposits and interbedded allodapic calcarenite and calcisiltite are evidence for the existence of a significant slope between shelf and basin this slope may have been caused by syndepositional faulting and collapse of a portion of the outer shelf the fault hypothesis is based on a rust colored marker unit recognized in the emigrant at horse thief canyon and in the outer shelf bonanze king section 13 km to the south along with the presence of distinctive algal boundstone clasts in the megabreccia member the megabreccia beds lie above the marker unit but all known source rocks for the algal boundstone occur stratigraphically well below the marker uncertainty egarding the syndepositional fault hypothesis centers on whether the horse thief and last chance range sections are in the same or different allocthons

post variscan verrucano like deposits in italy and the onset of the alpine tectono sedimentary cycle abstract in the italian regions the stratigraphic successions of the verrucano s l consist essentially of continental alluvial plain to coastal neritic siliciclastic redbeds deposited at different times in the alps mid late permian the northern apennines mid late triassic p p locally in southern tuscany also followed by the jurassic pseudoverrucano complex and the calabro peloritani arc mid late triassic exceptionally reaching earliest jurassic whereas in sardinia the recognition of the verrucano succession is still a topic of discussion the most typical metamorphic lithofacies in the pisan mts of tuscany is represented by the verrucano s s conglomerates and breccias including quartz clasts and minor metamorphic and volcanic lithics grading laterally and vertically to quartzitic sandstones and pelites in the pisa symposium the term verrucano was suggested only for those detrital deposits laid down in the alpine mediterranean areas after the final act of the variscan orogeny and also to use local geographical names consequently the typical terms verrucano toscano the verrucano lombardo the verrucano brianconnais and other similar deposits being linked to the variscan belt were generally accepted the ages of these verrucanos since they are devoid of fossils can only be interpreted indirectly the verrucano lombardo of central southern alps was recently ascribed to a mid late permian interval late guadalupian lopingian p p taking into account that the connected val gardena sandstones of the nearby venetian region are interdigitated with the late permian bellerophon fm the verrucano brianconnais of the maritime alps is again mostly related to late permian being covered by the lower triassic alluvial deltaic quartzites in the easternmost ligurian apennines near la spezia the mesozoic section of punta bianca which begins with a fluvial conglomerate transgressive and unconformable on a metamorphosed paleozoic variscan basement is composed of two main cycles of which the upper one correlates to the typical pisan verrucano s s and the overlying mt serra quartzites the latter yielding carnian pelecypods and vertebrate footprints the verrucano from the mid tuscan ridge to mt leoni and in the argentario promontory is delimited above by the tocchi formation and presumably developed from middle late ladinian up to late triassic carnian times in contrast in calabria e g the longobucco unit of sila grande and in sicily e g the taormina longi unit of peloritani mts the so called pseudo verrucano deposits pertain to mid late triassic and are capped by a basal jurassic succession determined by the discovery of an early hettangian palynoflora all over their distribution areas the above mentioned alpine verrucanos rest through an unconformity marked by a gap of varying and imprecise duration on late paleozoic volcanic sedimentary successions or directly on the underlying variscan metamorphic basement schematically the post variscan succession in italy can be subdivided into three main tectono sedimentary megacycles the first generally ranges from the late carboniferous to or slightly above the early permian the second from mid late permian to middle triassic while the third cycle begins with the mid late triassic p p attaining the jurassic in some parts of southern tuscany and the calabro peloritani arc after the late carboniferous and early permian transtensional tectonics represented by many strike slip continental basins cycle i widespread middle permian geodynamic reorganization mid permian episode auctt led to the development of a dominant extensional regime and the birth of tectonic plates and oceans neotethys meliata maliak etc between africa and europe the erosion of the variscan relief was followed by ingression from s e sectors of shallow marine branches of neotethys cycle ii the major rifting events that led to the jurassic birth of the ligurian piedmont ocean started during the middle late triassic and were related to the eastern opening of the atlantic ocean these rifting events gave rise to the development of the adria and europe corsica sardinia conjugate passive margins characterized by an asymmetric structural and sedimentary evolution in this geological context the verrucano like deposits of italy can be interpreted as a discontinuous and asynchronous tectofacies that marks the final dismantling of the se border of the variscan chain

inheritance of jurassic rifted margin architecture into the apennines neogene mountain building a case history from the lucretili mts latium central italy the western lucretili mts in the central apennines latium italy have been recently re mapped in great detail and are the subject of combined stratigraphic sedimentological and structural investigations in this paper we present a new stratigraphic interpretation of the jurassic paleogeography of western lucretili mts where a rift derived intrabasinal paleo high of the alpine tethys has been identified for the first time by means of facies analysis and biostratigraphic dating recognised facies associations combined with dated stratigraphic sections allow to define the morphology of the structural paleo high and to identify the associated gravity driven deposits olistoliths accumulated in the surrounding basin furthermore we investigated the modes of interaction between jurassic extensional structures and the subsequent contractional patterns developed during the tertiary mountain building in detail the role played during apennines tectonics by the paleo escarpments bounding the paleo high and by the surrounding olistoliths has been analysed the paleo escarpments either acted as focussing features for ene directed frontal thrust ramp localisation and were offset with small shortening amounts or reactivated as nne striking high angle transpressional faults or preserved the original geometries as a result of variable orientation of paleo escarpments with respect to the neogene compressive stress field with ene oriented sigma1 newly formed ene striking tear faults connect these either inherited or neo formed discontinuities this complex stratigraphic and structural pattern is substantially different from the previous interpretations of this portion of the central apennines based on a hypothesised layer cake stratigraphy deformed by neo formed neogene thrusts this contribution strengthens the importance of integrating facies analyses and structural investigations to detect the influence of pre orogenic structures on compressive structural patterns in an area where commercial seismic lines are not available and cannot help in reconstructing the subsurface geometries

gas seepage as an indicator of deeper prospective reservoirs a study based on exploration 3d seismic data three periods of sustained gas seepage in geological time have been revealed in danish block 5604 26 in the north sea by the use of exploration 3d seismic data the most recent period is indicated by a cluster of seismic chimneys which ties in to buried craters near the seabed and possible present gas escape through the seabed along with amplitude anomalies indicating a shallow gas sand charged by gas migrating from a deeper level the cluster of seismic chimneys indicative of vertical gas migration is visible down to 1 5 s twt 1500 ms and therefore the gas is interpreted as migrating from a deeper stratigraphic horizon below this level it becomes difficult to see the chimneys due to complex faulting the faults may work as gas migration pathways the geometry of the cluster of seismic chimneys indicates that the gas has been migrating from one point the nearest possible source of the gas is an underlying prospect where an oil and gas discovery has been made two earlier periods of gas seepage are indicated by mounds possibly carbonate buildups over gas seepages in pliocene time and similarly buried craters formed by gas seepages in an earlier period in pliocene time the results of this study are that gas seepage is a periodical process in geological time and that its presence and associated features can be used as an indicator of deeper prospective reservoirs

1000 m long gas blow out pipes abstract this study presents seismic observation of pipe anomalies from offshore nigeria outcrops of blow out pipes from rhodes greece and geophysical modelling of an acoustic pipe the studies give insight into how pipes form their internal structure the seismic image and geophysical artefacts related to the pipes over one hundred seafloor craters 100 m 700 m wide and up to 30 m deep have been observed on the seafloor offshore nigeria they are underlain by interpreted cones and seismic pipe anomalies that can be traced down to reservoir zones at 1000 m 1300 m below the seafloor the seismic pipe anomalies are 50 m 150 m wide and almost vertical they are interpreted as up scaled pipes found in outcrops on rhodes greece the outcrops show pipe related structures at three levels lowest the reservoir rock contains metre sized cavities which are filled with a mixture of clay derived from the overlying cap rock in the middle several circular to oval structures in plane view of pipes are observed in the lowest part of the cap rock highest 15 m into the clay cap rock strongly sheared country rock forms circular structures with a core of structureless clay based on outcrop observation on rhodes we constructed an acoustic model of a 50 m wide and 1000 m long pipe seismic modelling proves that such pipes would be expressed in seismic data that they are similar to the seismic pipe anomalies offshore nigeria but this study also revealed that prominent intra pipe reflections are artefacts a formation model for the pipes is suggested high fluid overpressure in the reservoir generated hydro fractures from the reservoir to seafloor where a mixture of gas and fluid flowed at high speed to form pipes cones and seafloor craters after hours to weeks of gas and fluid flow through the pipe the pore pressure in the reservoir dropped and the blow out terminated muddy slurry fell back and plugged the cavity in the reservoir and the pipe

fault stability perturbation by thermal pressurization and stress transfer around a deep geological repository in a clay formation author s urpi l rinaldi ap rutqvist j wiemer s abstract 2019 american geophysical union all rights reserved the increase of temperature of a low permeability fluid saturated media may trigger significant thermal pressurization where the expansion of pore fluid cannot be accommodated by the thermal expansion of the pore space with the aid of a coupled thermohydromechanical numerical simulator we investigate the possible impact of thermal pressurization during the life of a deep geological repository dgr for high level radioactive waste characterized by the emplacement of radioactive material filled canisters in a series of parallel tunnels excavated in a low permeability clay formation we represent the fault as a planar structure embedded in a thermoporoelastic material and shear activation evaluated by a strain softening mohr coulomb failure criterion the results show that stress changes caused by temperature and thermal pressurization of a rock mass around the emplacement tunnels may trigger a slip event on a fault plane in proximity of the geological disposal site rupture nucleates at depth hundreds of meters below the dgr stress transfer plays a key role while a direct hydraulic connection between the repository and the nucleation zone is not necessary in order to trigger rupture a low stress ratio may favor the occurrence of slip up to a distance of 600 m of the fault from the outermost tunnel these results highlight the need of investigating hydromechanical properties and local stress conditions at depth to characterize the geomechanical response of weak planes located in the surroundings of a high level radioactive waste repository and to provide sufficient knowledge for the safe development of the dgr site

triassic continental rifting of pangaea direct evidence from the alpujarride carbonates betic cordillera se spain abstract evidence is presented for triassic rift related palaeo structures from the alpujarride complex carbonates of the betic cordillera se spain direct evidence of synsedimentary extensional tectonics is provided by macro to meso scale normal faults overstepped by younger strata most faults define domino like horst and graben structures the faults are associated with an expanded synrift sedimentary prism in which soft sediment deformation gravity flow deposits and unconformities are widely developed syntectonic mafic igneous intrusions also occur the age of this phase of extension is constrained as ladinian carnian c 237 216 ma from a palaeogeographical standpoint the thick triassic carbonates of the betic internal zone together with comparable successions in northern calabria southern apennines occupied a belt with elevated subsidence connecting the neo tethys to the east with the eastern north american intracontinental rift system to the west their carbonate facies intermediate between classical alpine and germanic type triassic facies recorded the main episodes of rifting affecting central pangaea

total grain size distribution and volume of tephra fall deposits on 17 june 1996 ruapehu volcano new zealand produced a sustained andesitic sub plinian eruption which generated a narrow tephra fall deposit extending more than 200 km from the volcano the extremely detailed data set from this eruption allowed methods for the determination of total grain size distribution and volume of tephra fall deposits to be critically investigated calculated total grain size distributions of tephra fall deposits depend strongly on the method used and on the availability of data across the entire dispersal area the voronoi tessellation method was tested for the ruapehu deposit and gave the best results when applied to a data set extending out to isomass values of 1 g m 2 the total grain size distribution of a deposit is also strongly influenced by the very proximal samples and this can be shown by artificially constructing subsets from the ruapehu database unless the available data set is large all existing techniques for calculations of total grain size distribution give only apparent distributions the tephra fall deposit from ruapehu does not show a simple exponential thinning but can be approximated well by at least three straight line segments or by a power law fit on semi log plots of thickness vs area 1 2 integrations of both fits give similar volumes of about 4 106 m3 integration of at least three exponential segments and of a power law fit with at least ten isopach contours available can be considered as a good estimate of the actual volume of tephra fall integrations of smaller data sets are more problematic

the atlas east variscan elbe shear system and its role in the formation of the pull apart late palaeozoic basins the variscan orogeny occurred as a result of the late devonian to late carboniferous collision and accretion of gondwana derived microcontinents and continental masses with those of laurussia the irregular boundaries of the colliding continents caused isochronous transpressional and transtensional tectonics accompanied by a complex pattern of intracontinental shear zones at the scale of the southern european variscides these shear zones and their configuration controlled the subsequent evolution of permian to middle triassic paleogeography the geographic distribution from morocco to the eastern alps of the late carboniferous permian up to triassic basins most of which are considered as pull apart basins was related with the development of the late palaeozoic intracontinental shear network our analysis of the stratigraphic tectonic and volcanic features of the late carboniferous permian continental basins across the laurussia gondwana boundary reveals the role of the east variscan shear zone during this time as a precursory lineament for the development of the permian to triassic rifting of pangaea and the following opening of oceanic basins e g the neothetyan ocean

tectonics of the punta bianca promontory insights for the evolution of the northern apennines northern tyrrhenian sea basin the structural setting of the eastern headland of the la spezia gulf punta bianca promontory provides some constraints on the contractional and extensional framework of the northern apennines northern tyrrhenian sea basin geodynamic system and allows a detailed reconstruction of a complex evolutionary path out of sequence thrusting is supposed in the inner side of the chain two different extensional events are identified the older early middle miocene may be related to the imbrication of the deeper metamorphic units of the apenninic thrust wedge younger extension fits very well into an eastward asymmetrical faulting framework related to the opening of the northern tyrrhenian sea basin from the late miocene to the pliocene pleistocene well exposed low angle normal faults developed during this event extensional structures were then overprinted and reactivated by a mainly strike slip regime in the quaternary

the middle triassic magmatic tectonic arc development in the southern alps abstract the geodynamic meaning of the middle triassic magmatic and tectonic events in the southern alps is still uncertain the main problem is the significance of the compressional tectonic structures recognized in the central dolomites in fact these structures are incompatible with the extensional geodynamic interpretation crustal rifting assumed by several authors therefore the compressional tectonic elements of the dolomites have been mostly ignored or not seriously taken into account or considered as local phenomena due to the volcanic tectonic interplay other more modern interpretations are founded on regional transcurrent and or transpressive tectonics recent discovery of a middle triassic thrust system located in the piave river area some tens of kilometres east of the central dolomites lends more credence to the compressional middle triassic event the magmatic series of volcanic and plutonic middle triassic rocks display an orogenic character with typical calc alkaline trends recognized across the whole southern alps as well as in the dinaric and hellenic domains such a character is rather uncommon in the crustal evolution by rifting but is more in accord with a compressional geodynamic setting furthermore the time space distribution of the south alpine magmatic rocks coupled with their petrochemical affinity are close to the modern volcanic arcs nevertheless the general geodynamic context of the southern alps owing to their pronounced ensialic character does not fit the oceanic model

styles of tectonic inversion within syn orogenic basins examples from the central apennines italy the geometry of several thrust related folds in the central apennines of italy results from a switch in deformation regime from extension to contraction this switch in tectonic regime occurred during the deposition of syn orogenic sediments and the emplacement and migration of the thrust belt foredeep system towards the foreland in neogene time the styles of positive tectonic inversion result from normal faults that were steepened rotated and truncated by thrusts with local development of minor folds due to buttressing normal fault controlled escarpments are also locally preserved in the forelimbs and backlimbs of thrust related anticlines the location and amplitudes of contractional structures across the belt reflects the distribution of pre thrusting normal faults within precursor syn orogenic basins a result that may improve our understanding of the evolution of apennine as well as other thrust belt foredeep systems

the mesozoic continental rifting in the mediterranean area insights from the verrucano tectofacies of southern tuscany northern apennines italy in the alpine mediterranean region the continental redbeds and shallow marine siliciclastics related to the early depositional phases of the late permian mesozoic continental rifting are referred to as the most common representative of the verrucano tectofacies the verrucano type successions exposed in southern tuscany are diachronous spanning from triassic to earliest jurassic in age and accumulated within the tuscan domain a paleogeographic region of continental crust that due to the opening of the piedmont ligurian ocean formed part of the adria passive margin they belong to the metamorphic verrucano group and the non metamorphic pseudoverrucano fm viewed overall these verrucano type successions appear to manifest five episodes or pulses of an ongoing continental rifting with the exception of the first episode that developed entirely within a terrestrial setting each one is represented by basal verrucano type continental siliciclastics overlain by compositionally mixed marine deposits which resulted from four diachronous post middle triassic transgressions this suite of tectonic pulses produced the progressive westward widening backstepping of the tuscan domain in the rifting south tuscany area

on entropy and clustering in earthquake hypocentre distributions summary the degree of clustering or disorder within earthquake distributions may be measured using the concept of entropy a method for calculating the entropy of any 3 d point set e g earthquake foci is presented this makes use of voronoi cells convex polyhedra representing nearest neighbour regions to measure point density in three dimensions an estimate of event density can be determined directly from the size of voronoi cells normalizations are introduced to the definition of entropy that allow data sets containing different numbers of events and occupying different volumes to be compared quantitatively for example earthquake catalogues from different tectonic regimes our results show a clear correlation between earthquake entropy and tectonic regime the most ordered are the mid ocean ridges followed by the subduction zones and finally intraplate seismicity we show how entropy may be used to quantify the simplification of earthquake distributions for example due to relocation procedures a recently published algorithm called the collapsing method is used as an example of a technique that reduces entropy while respecting data fit modifications to this method are made that reduce artefacts and use additional temporal information in the earthquake distribution these methods are applied to a global catalogue of 85 000 events and a local catalogue from the sil network in iceland containing 43 300 events the entropy of both catalogues is reduced results from the hengill region within the sil network show lineations whose orientations agree with independent studies using relative location techniques and surface faulting

tertiary syntectonic carbonate platform development in indonesia cenozoic tropical carbonate sedimentation was strongly influenced by local and regional tectonics in se asia this paper outlines the evolution of the syntectonic eocene to middle miocene tonasa formation of south sulawesi evaluating controls on sedimentation facies distribution and sequence development development of a facies model for this cenozoic tropical carbonate platform provides a meaningful analogue for similar less well studied se asian carbonates which commonly comprise targets for hydrocarbon exploration this study also has considerable implications for the study of syntectonic carbonates controls on carbonate sedimentation carbonate platform development in backarc areas and se asian tectonics detailed facies mapping logging petrographic and biostratigraphic analyses indicate that the tonasa formation was deposited initially as part of a transgressive sequence in a backarc setting by late eocene times shallow water carbonates were being deposited over much of south sulawesi forming a widespread 100 km long platform area shallow water sedimentation continued unabated in some areas of the platform until the middle miocene elsewhere active normal faulting resulted in fault block platforms with local subaerial exposure of footwall blocks and the formation of basinal graben in adjacent hangingwall areas platform top facies were aggradational and dominated by larger benthic foraminifera low angle slopes particularly hangingwall dip slopes were characterized by the development of ramps faults controlled in part by pre existing structures were periodically active and formed steep escarpment margins variable regional subsidence strongly influenced the development of the tonasa carbonate platform whereas platform wide effects caused by regional eustacy have not been identified computer modelling of the tonasa platform confirms that the accommodation space and sedimentary geometries observed can be produced by block faulting and regional subsidence alone modelling also reveals that regional subsidence and extension oblique to the main stretching direction were low on the margins of the backarc basin shallow water accumulation rates for this foraminifera dominated tropical carbonate platform were an order of magnitude lower than those for modern warm water platforms dominated by corals or ooids

the interaction of extensional and contractional deformations in the outer zones of the central apennines italy abstract the relationships among normal faults and thrusts in the apennines of italy are often unclear and the local absence of syn tectonic stratigraphic controls have led to contrasting interpretations on the relative chronology for both classes of structures the activity of normal faults has been variously regarded as due to pre syn or post orogenic extension and the contrasting evidence from different sites has produced an ongoing debate on the normal fault thrust interaction the results of a kinematic analysis on selected composite structures of the outer zones of the central apennines make it possible to unequivocally establish a relative chronology of extensional and contractional deformations detailed mapping outcrop scale observations and structural overprinting relationships support a positive inversion tectonic history where normal faults and fault controlled escarpments formed first and were later deformed by thrusts and related folds all normal faults control the distribution of foredeep deposits thus indicating that the recognised episode of positive inversion is related to the incipient stages of construction of the apennine thrust belt the systematic collection of structural data may help to unravel the evolution of adjacent sectors of the apennine chain as well as of other belt foredeep foreland systems whose extension contraction relationships are poorly constrained

geochemical and geochronological data on triassic volcanism of the southern alps of lombardy italy genetic implications a widespread volcanism mainly consisting of pyroclastic products and lava flows is found in the southern alps of lombardy the volcanics are interbedded with anisian ladinian carbonatic sequences and continental terrigenous or transitional deposits of ladinian carnian age the petrographic and geochemical data for this volcanism indicate a calc alkaline affinity with characters similar to those of convergent continental margins in this sector of the alps the geological evidences show that in the middle triassic general extensional movements were the dominant deformation event and do not support the existence of a subduction zone during this period the apparent contrast between the tectonic environment and the type of magmas erupted in the anisian carnian is tentatively explained by partial melting during the early stage of rifting of an upper mantle deeply modified during the previous hercynian orogenesis and contaminated by crustal material this hypothesis is in agreement with the preliminary sr isotopic ratios 0 705 and 0 709 k ar and rb sr ages on biotites date the beginning of the volcanism at around 225 m y

rscm thermometry in the alpi apuane nw tuscany italy new constraints for the metamorphic and tectonic history of the inner northern apennines abstract in this study raman spectroscopy on carbonaceous material rscm is applied for the first time in the northern apennines with particular focus on the alpi apuane nw tuscany italy and surrounding areas in order to constrain peak metamorphic temperatures and their variability in the different continent derived units of the nappe stack peak temperatures in the range of 530 320 c were found in the alpi apuane whereas in the nearby metamorphic core of the monte pisano and punta bianca lower peak temperatures of 305 315 c and 350 c were found respectively the tuscan nappe in la spezia area west of alpi apuane shows temperatures in the range of 295 246 c whereas the same unit in the lima valley east of the alpi apuane shows temperatures lower than 230 c the collected data allowed refining the thermal architecture of the belt and the relationships between deformation early and late folds and low angle normal detachments and the metamorphic architecture of the alpi apuane core these results provide new contraints for the thermo mechanical evolution and exhumation history of the inner northern apennine and its geodynamic setting in particular our data support the interpretation of the alpi apuane as a cold metamorphic core complex in which the preserved paleothermal structure and part of the exhumation are related with crustal thickening while the final exhumation stages depth 15 km and at ambient crustal temperature 350 c are associated with crustal thinning still ongoing in the area

some examples of the middle triassic marine transgression in south western mediterranean europe in southwestern mediterranean europe ne spain sardinia and nw apennines e g monti pisani and punta bianca the middle triassic transgression on a margin of an intracratonic basin appears to be controlled by the different morphology and tectonic activity of the margin itself

the association of continental crust rocks with ophiolites in the northern apennines italy implications for the continent ocean transition in the western tethys abstract the late cretaceous sedimentary melanges from the external liguride units of the northern apennines include large slide blocks of ophiolites and lower and upper continental crust rocks representative of a continent ocean transition between the internal liguride oceanic domain and the thinned continental margin of the adria plate the slide blocks preserve a record of the long lived history of rifting which led to opening of the jurassic western tethys basin the external liguride ophiolites consist of 1 undepleted spinel peridoties partly re equilibrated under plagioclase facies conditions which were interpreted as unroofed subcontinental mantle 2 rare gabbroic rocks mainly troctolite to olivine bearing gabbro probably crystallised from n morb magmas and 3 basalts with n to t morb affinity covered by late callovian early oxfordian radiolarian cherts both gabbroic rocks and basalts locally intrude the mantle peridotites and postdate their re equilibration to plagioclase facies conditions the slide blocks of lower continental crust are composed of gabbro derived mafic granulites and felsic granulites the latter include quartzo feldspathic granulites and rare quartz poor to quartz free charnockitic rocks in both mafic and felsic granulites granulite facies re equilibration was followed by a retrograde metamorphic evolution to amphibolite greenschist and subgreenschist facies conditions retrogression is commonly accompanied by deformations progressively changing from plastic to brittle the upper crustal rocks occurring as slide blocks consist of hercynian granitoids with orogenic affinity mainly biotite bearing granodiorites and peraluminous two mica leucogranites locally the granitoids are intruded by basaltic dykes or capped by basaltic flows and radiolarian cherts the granitoids underwent polyphase brittle deformations under subgreenschist facies conditions which predated the basalt emplacement the tectono metamorphic evolution recorded by the slide blocks of the external liguride units started in the late carboniferous early permian about 290 ma with the emplacement at deep crustal levels of the gabbroic protoliths for the mafic granulites the associated felsic granulites likely represent the remnants of the lower continental crust intruded by the gabbro derived granulites mafic and felsic granulites subsequently underwent tectonic exhumation in permo triassic times as testified by the development of granulite to amphibolite facies ductile shear zones the granulites were finally exhumed to shallow levels probably in association with the subcontinental mantle in late triassic middle jurassic times the latter period was most likely characterized by extensive brittle faulting at shallow crustal levels thus giving rise to extensional allochthons formed by stretched slices of granitoids the western tethys opening is finally testified by the basalt intrusion and effusion in the late jurassic followed by deep sea pelagic sedimentation the external liguride crustal stratigraphy can be regarded as a fossil example of the transitional realm at the continent ocean boundary this reconstruction fits well with the available data on the present day continental margins derived from passive lithosphere stretching