stress magnitude and orientation in the potiguar basin brazil implications on faulting style and reactivation 1 we analyzed borehole breakout data and drilling induced tensile fractures derived from resistivity image logs run at 10 oil wells to derive the orientation of the maximum horizontal stress shmax from the potiguar basin in the continental margin of brazil stress magnitudes are derived from density logs for the vertical stress mini frac tests for the minimum horizontal stress shmin and rock strength laboratory analysis to estimate the shmax magnitudes we compared these results with the stress regime and shmax orientation derived from nine earthquake series located in the crystalline basement where seismicity is concentrated and previous breakout data from the basin in the basin the shmax gradient is 20 0 mpa km and the shmax shmin ratio is 1 154 indicating a normal tectonic stress regime from 0 5 to 2 0 km whereas the shmax gradient of 24 5 mpa km and shmax shmin ratio of 1 396 indicate a transition from a normal to strike slip stress regime at 2 5 to 4 0 km the deeper stress regime in the basin is similar to that in the basement at 1 12 km depth this transition of the tectonic stress regime is consistent with an incipient tectonic inversion in the basin we note that the shmax orientation rotates from nw se in the western part of the potiguar basin to e w in its central and eastern parts roughly following the shoreline geometry indicating that local features such as flexural stresses influence the local scale 100 km stress pattern we also conclude that the basement is critically stressed but not the basin

release fault a variety of cross fault in linked extensional fault systems in the sergipe alagoas basin ne brazil abstract two types of cross faults are herein recognized transfer faults and the newly termed release faults transfer faults form where cross faults connect distinct normal faults and horizontal displacements predominate over vertical ones in contrast release faults form where cross faults associated with individual normal faults die out within the hangingwall before connecting to other normal faults and have predominantly vertical displacements release faults are geometrically required to accommodate variable displacements along the strike of a normal fault thus they form to release the bending stresses in the hangingwall and do not cut normal fault planes nor detachment surfaces at depth release faults have maximum throws adjacent to normal faults and may be nearly perpendicular or obliquely oriented to the strike of the latter such geometry appears not to depend upon pre existing weaknesses but such variable orientation to normal faults is an inherent property of release faults release faults commonly appear as simple normal faults in seismic sections without implying extension along the strike of rift and basins three dimensional strain deformation occurs in the hangingwall only between the terminations of an individual normal fault but regionally release faulting is associated with plane strain deformation in linked extensional fault systems

effect of the altiplano puna plateau south america on the regional intraplate stresses abstract a previous compilation of stress data for the sub andean region of northwest argentina is complemented with eight additional earthquake focal mechanisms seven events 5 3 5 5 mb had their mechanisms determined by inversion of teleseismic body waves short period p waves and long period sh waves all events had predominantly reverse faulting mechanisms five had almost pure dip slip motion and two had a component of oblique motion the other mechanism was a composite fault plane solution of the hualfin catamarca series of july 1986 maximum 4 mb determined with data from a local temporary network and the permanent inpres regional network the local data shows that the hualfin events occurred on a single fault plane oriented nw se with predominantly strike slip motion the stress data in the sub andean region suggests a radial pattern around the altiplano puna plateau with compressional stresses tending to be perpendicular to the eastern front of the plateau this indicates that local spreading stresses due to lateral density variations crustal thickening or lithospheric thinning of the plateau may be comparable or even exceed the plate wide regional stresses at the southeastern border of the puna plateau where a stress rotation of about 30 may be detected preliminary order of magnitude calculations indicate that the local plateau induced compression can be about 1 2 times greater than the regional horizontal deviatoric stress the present predominance of the local stress over the regional stress is consistent with the decrease of the nazca south america convergence rate observed since about 10 20 ma

the northeast brazilian rift system the northeast brazilian rift basins provide important data critical to the understanding of continental rifting processes associated with the opening of the south atlantic these basins represent the locus of intersection of the southern and equatorial branches and some basins yield substantial chronostratigraphic data that constrain the temporal and spatial interaction of the rift phases similar data are not found in its counterpart in africa especially for the neocomian these early cretaceous rift basins of northeast brazil illustrate key three dimensional geometries of intracontinental rift systems mainly controlled by the basement structural framework during the main rift phase syn rift ii neocomian early barremian extensional deformation was distributed over three main rift axes 1 the gabon sergipe alagoas gsa trend 2 the reconcavo tucano jatoba rtj trend and 3 the cariri potiguar cp trend during this phase extensional deformation jumped west from the easternmost basins gsa trend to a series of ne trending intracratonic basins rtj and cp trends characterized by a set of asymmetric half grabens separated by basement highs transfer faults and or accommodation zones these basins are typically a few tens of kilometers wide and trend ne sw roughly perpendicular to the main extension direction during the neocomian preexisting upper crustal weakness zones like the dominantly ne sw trending shear zones of the brazilian pan african orogeny controlled the development of intracrustal listric normal faults internal transverse structures such as transfer faults and accommodation zones were also controlled by the local basement structural framework the megashear zones of pernambuco brazil and ngaundere africa seem to have behaved like a huge accommodation zone accommodating extensional deformation along the rtj gsa trends with simultaneous extension along the cp trend during the late barremian syn rift phase iii a significant change in rifting kinematics occurred when the cp trend was aborted and major rifting initiated at the equatorial branch during the aptian while the equatorial branch and benue trough africa experienced the main rift phase the rtj trend was aborted and the gsa trend developed a transitional phase between the rift and drift stage the gsa trend and the offshore potiguar basin represent the site of continued evolution into passive margin basins following the main rift episode

brazilian structural provinces an introduction abstract the territory of brazil coincides almost entirely with the south american platform the crystalline core of the continent its basement is composed of ancient metamorphic and igneous rocks and it has not suffered any tectonic regeneration since the beginning of the phanerozoic sedimentary rocks with almost horizontal bedding cover this crystalline basement this latter shows ages as old as early precambrian although ages between 500 and 1000 m y are conspicuously frequent the cratonic areas became consolidated more than 1700 m y ago whereas the fold belts formed essentially between 500 and 1700 m y ago the sedimentary cover accumulated from the early silurian in three large intracratonic basins until the platform became completely stabilized a late jurassic to early cretaceous reactivation caused by the break up of the ancient gondwana continent created another basin sequence chiefly along the atlantic continental margin based on the nature of the crystalline basement rocks and the sedimentary cover ten structural provinces can be distinguished 1 rio branco province in the north of the country occupied by the guyana shield and still only poorly known with an important fold belt developed during the so called transamazonian cycle 2000 200m y with high grade metamorphic rocks and only slight influence of later events 2 tapajos province in central brazil corresponding to the amazonas or guaporecraton showing chiefly precambrian crystalline rocks and behaving as an cratonic area during the phanerozoic 3 sa o francisco province located on the atlantic shield with its basement covered by rocks of different ages chiefly affected by the brasiliano cycle between 1000 and 500 m y and constituting another cratonic area 4 tocantins province between the amazonas and sa o francisco cratons with the oldest rocks in its centre ages over 2600 m y and at the eastern and western borders metamorphic sequences of various fold belts and almost no phanerozoic deposits 5 mantiqueira province located along the southern part of the atlantic coast affected chiefly by the brasiliano folding cycle 6 borborema province in the northeast brazilian fold belt affected by the brasiliano cycle in a very complex way and with important faulted zones it was reactivated in phanerozoic times when also sedimentary covers accumulated 7 amazonas province represented by the amazonas sedimentary basin syneclise and subdivided into four parts by three important arcs 8 parnaiba province coinciding with the piauf maranha o syneclise and filled with a rather thick sedimentary sequence 9 paranaprovince the sedimentary basin of southern brazil in which the well known late paleozoic glaciation features are found and which possesses an extensive cover of basaltic rocks of late jurassic to early cretaceous age 10 coastal province and continental margin the youngest structural unit developed during the separation of the continent and represented by rift valleys and coastal basins filled with mesozoic cenozoic deposits of various kinds

control of rheological stratification on rifting geometry a symmetric model resolving the upper plate paradox numerical experiments reproduce the fundamental architecture of magma poor rifted margins such as the iberian or alpine margins if the lithosphere has a weak mid crustal channel on top of strong lower crust and a horizontal thermal weakness in the rift center during model extension the upper crust undergoes distributed collapse into the rift center where the thermally weakened portion of the model tears among the features reproduced by the modeling we observe 1 an array of tilted upper crustal blocks resting directly on exhumed mantle at the distal margin 2 consistently oceanward dipping normal faults 3 a mid crustal high strain zone at the base of the crustal blocks s reflector 4 new ocean floor up against a low angle normal fault at the tip of the continent 5 shear zones consistent with continentward dipping reflectors in the mantle lithosphere 6 the mismatch frequently observed between stretching values inferred from surface extension and bulk crustal thinning at distal margins upper plate paradox rifting in the experiment is symmetric at a lithospheric scale and the above features develop on both sides of the rift center we discuss three controversial points in more detail 1 weak versus strong lower crust 2 the deformation pattern in the mantle and 3 the significance of detachment faults during continental breakup we argue that the transition from wide rifting towards narrow rifting with a pronounced polarity towards the rift center is associated with the advective growth of a thermal perturbation in the mantle lithosphere

rift kinematics during the incipient stages of continental extension evidence from the nascent okavango rift basin northwest botswana high resolution aeromagnetic data from the nascent okavango rift in northwest botswana provide an unprecedented view of rift kinematics during the incipient stages of continental extension crosscutting relationships between west northwest trending 180 ma karoo dikes and reactivated northeast trending proterozoic basement faults are used to document the kinematics of cenozoic faulting during the initial stages of rifting depth estimates to the top of the dikes using three dimensional euler deconvolution solutions have produced the following interpretations 1 the okavango rift is a half graben with a downthrow of 200 300 m 2 the width of the okavango rift 100 20 km is similar to that of more mature continental rifts such as the tanganyika and baikal rifts this suggests that the width of continental rifts is acquired early in their evolution and reflects neither the age and maturity of the rift basin nor the amount of extension it is suggested that the cumulative downthrow sediment infill included and subsidence may be a better indicator of the relative maturity of rift basins 3 preexisting basement faults exert a major control during rifting and reactivation processes do not occur synchronously along the entire length of preexisting faults 4 the okavango rift is defined by normal faults there is no evidence of major strike slip faults thus excluding a pull apart tectonic model for this nascent continental rift stage 5 the preexisting sekaka shear zone terminates the okavango rift to the south suggesting that such shear zones represent major barriers during longitudinal propagation of rifts this probably explains why such shear zones commonly evolve into accommodation or transfer zones during further evolution of continental rifts

coal maceral ratios as indicators of environment of deposition do they work for ombrogenous mires an example from the miocene of new zealand abstract maceral indices were applied to sub bituminous coals of the maryville coal measures as a means of interpreting environment of deposition very low amounts of inertinite and ubiquitous bituminite lead to difficulties in interpretation of the maceral ratios comparison with modern analogues suggests the theoretical basis for discrimination of mire type by maceral ratios is not well founded on the following grounds absence of well structured wood tissues does not imply the absence of arborescent vegetation inertinite formation may be unrelated to vegetation gelification is used in a geochemical sense and does not indicate groundwater table level as supposed for biochemical gelification detrital macerals often result from in situ fragmentation and not transportation

petrographical palynological and geochemical analyses of the hub and harbour seams sydney coalfield nova scotia canada implications for facies development abstract benched channel samples and continuous block samples of the hub and harbour seams from the sydney basin nova scotia were studied to define the variations in petrography geochemistry and palynology of the seams and to interpret the depositional environments of the precursor mires petrographic compositions of the seams are very similar with high vitrinite content low inertinite moderate liptinite and negligible clastic mineral content pyrite content is moderate there is little variation in petrographic composition between benches in either seam there are marked variations in petrographic compositions at the lithotype scale petrographic facies parameters indicate deposition of the bulk of both seams under fairly uniform conditions in relatively wet mires unusually wet or dry periods were rare the palynological assemblages of both seams indicate a middle to late westphalian d age the common to abundant palynomorphs are derived from arborescent and herbaceous lycopsids tree ferns and other ferns and sphenopsids the palynological assemblages support the petrographic interpretation of relatively wet mires cordaites pollen florinites is rare suggesting that there was little contribution from plants growing in dry or upland areas the absence of the densospore miospore phase and the petrographic data indicate there were no periods in which domed mires occurred the distinctive dull bands occurring in the hub and harbour seams are characterised by low vitrinite contents high inertinite content high liptinite and common detrital minerals sporinite showing varying degrees of degradation is commonly highly concentrated in thin bands the geochemistry is marked by much higher hi values than normally reported for coals but other indices are typical for coals of this rank the palynological assemblages of the dull bands are dominated by tree fern spores and other ferns with only a minor contribution by sphenopsid spores the dull bands were deposited during periods of inundation of mires relatively low mineral content indicates that the distributary channels which flooded the mires were quite distant from the depositional sites of the samples

tightening up ne brazil and nw africa connections new u pb lu hf zircon data of a complete plate tectonic cycle in the dahomey belt of the west gondwana orogen in togo and benin the dahomey belt in togo and benin is an important segment of the larger west gondwana orogen here we review the geodynamic evolution of the dahomey belt and discuss new u pb and lu hf zircon data in light of similar data previously acquired on the geologically related northern borborema province in ne brazil eighteen samples from different tectonic settings and regions within the belt were collected for zircon isotopic investigation passive margin deposits of the atacora structural unit and lower units of the volta basin have detrital zircon signatures compatible with the flanking west africa craton the arc related magmatism resulted from the east dipping subduction of the goias pharusian oceanic lithosphere and is represented by a variety of granitoids emplaced in the benino nigerian shield between 670 and 610 ma these granitoids were mainly sourced from crustal reservoirs with subordinate juvenile input detrital zircon ages from syn orogenic deposits in benino nigerian shield suggest that arc development could have started as early as 780 ma the main period of melting in the internal part of the belt the benino nigerian shield is related to crustal thickening and occurs only ca 30 m y after initiation of the continental collision marked by the ca 610 ma ultra high pressure uhp metamorphism recorded at lato hills foreland development represented by the upper units of the volta basin developed soon after continental collision and persisted with the development of the west verging thrust front synchronously with the main period of crustal melting due to collision at ca 580 ma the subvertical transbrasiliano lineament in south america that corresponds to the kandi lineament in africa provides a present day fit between nw africa and ne brazil restoration of the movement of the transbrasiliano kandi lineament strike slip plate boundary places the dahomey belt and borborema province ne brazil along the same section of the west gondwana orogen this configuration would explain some of the misfits previously discussed in the literature and aligns the uhp eclogites in togo and ne brazil

the genesis of coal from the viewpoint of coal petrology abstract the genesis of the microscopic constituents of coal macerals and of maceral associations microlithotypes representing various coal facies is discussed in the light of recent advances that have been made in the study of coals and modern peats peat microscopy especially promoted the understanding of humification and biological gelification both of which are decisive for the genesis of huminites vitrinites in brown coals and hard coals respectively microbial activity during peatification has been documented by chemists microbiologists and petrologists and recently by electron microscopical observations in coals this activity leads to the incorporation of lipid substances into the humic matter and later influences the chemical physical and technological properties of vitrinites geochemical gelification transforms the huminites of brown coals into the vitrinites of bituminous coals and is probably caused by the onset of bitumen generation in coal in this process the hydrogel brown coal is transformed to the bitumogel bituminous coal coal as a source rock for oil has become an important research subject for coal petrologists and oil exploration the formation of more or less liquid bitumen and its later cracking to gaseous hydrocarbons leads to the coalification jumps of the macerals especially liptinites and vitrinites and to the generation of secondary macerals like exsudatinite bitumen and micrinite dead carbon bituminization in coal has been revealed by the use of fluorescence microscopy which also found the presence of new liptinite macerals bituminite fluorinite and exsudatinite and suggests a higher proportion of algal material in coals than was thought earlier the genesis of various types of inertinite macerals will probably become an increasingly important subject of research especially with regard to rank inertinites that seem to attain their high inertinitic reflectance initially during coalification besides the origin of macerals the origin of various coal facies in terms of maceral associations is considered in relation to the palaeogeographic depositional milieu the peat forming vegetation palaeoclimate water and nutrient supply acidity marine and calcareous influence and fire with examples from euramerican carboniferous coals gondwana coals and tertiary brown coals vegetation water and oxygen supply eh conditions are most important for the generation of coal facies vegetation has been reconstructed with the help of palaeobotany including palynology cuticular analysis and wood anatomy in brown coals and with the study of petrified permineralized peats preserved in coal balls the microscopical investigations of botanically recognizable plant remains isolated from coals or accompanying rocks has been especially informative however the results of palynological and cuticular analyses should be evaluated with caution considering the varying resistance of palynomorphs and cuticles and in the case of palynomorphs their possible extrapaludal origin microscopical studies of modern peats that were derived from different types of vegetation growing in different hydrological environments have been very helpful in interpreting coal facies especially in brown coals the much disputed origin of brown coal lithotypes is considered in detail for hard coals there seems to be agreement that coal layers rich in vitrites and liptinite poor clarite were deposited in wet forest swamps that microlayered liptinite rich clarites are sub aquatic humic muds and that inertinite rich durites represent oxidized peats the origin of liptinite rich durites is controversial either subaquatic muds or oxidized peats the latter perhaps from raised bogs a recent trend in the literature is the assumption that many if not all mineable coal seams have been deposited in raised bogs under ombrogenous oligotrophic conditions although raised bogs with a dense arborescent vegetation are known from borneo it seems not probable that most seams which were deposited in foredeeps or steadily sinking graben zones are of ombrogenous origin although a succession from relatively wet and eutrophic to relatively dry and oligotrophic conditions may be true for occasional seams but as in modern peats striking changes of coal facies are commonly caused by hydrological events e g inundations as a consequences of crevasses or of fires that burned the peat the origin of the inertinite rich gondwana coals is discussed in relation to their specific climatic conditions and a comparison with sub arctic peats is recommended coals influenced by marine and calcareous conditions are characterized by high contents of sulfur and pyrite as well as by hydrogen rich vitrinites with a relatively low reflectance and high fluorescence all due to a strong bacterial activity in peats of low acidity proposals for further research are made in the conclusions

tectonic evolution of the sergipano fold belt ne brazil during the brasiliano orogeny abstract the sergipano fold belt sfb represents the southern segment of a brasiliano age 600 ma continental collision zone which extends over ne brazil and continues into central africa as the north equatorial fold belt major sinistral transcurrent fault shear zones and thrusts separate domains with individual lithological tectonometamorphic and magmatic characteristics the principal steeply dipping strike slip zones trend east west to wnw ese lithological correlations across the shears have not proved possible which suggests that displacements were probably large but as yet are unquantified major folding and thrusting affected all the domains folds have a southerly vergence with nw se to wnw ese trends consistent with a ne sw to nne ssw shortening direction although small differences in shortening trends exist between individual domains the southernmost allochthonous domain of carbonate to clastic shelf slope sediments was subject to a single phase of folding and thrusting onto the sao francisco craton accompanied by greenschist facies metamorphism north of this domain lies the macurure domain which is separated from the southernmost allochthonous domain by the major sao miguel do aleixo transpressive shear zone polyphase deformation amphibolite facies metamorphism and massive granitic intrusion characterize this domain north of the macurure domain lie the migmatites and granites of the poco redondo domain which represent a deeper crustal level they are separated from the macurure domain by the belo monte shear a late tectonic leucogranite in the poco redondo domain yields a 600 ma rb sr isochron finally the poco redondo domain was overthrust from the north by the caninde gabbroic complex associated with carbonates pelites and amphibolites metamorphosed to greenschist and upper amphibolite facies this has previously been interpreted as an ophiolite sequence although the relative movements or absolute ages of the domains are unknown their distinct geological differences suggest that they are separate crustal blocks which underwent large lateral movement during the brasiliano collision

upper crustal earthquake swarms in sao caetano reactivation of the pernambuco shear zone and trending branches in intraplate brazil abstract seismogenic fault reactivation of continental scale structures has been observed in a few intraplate areas but its cause is still a matter of debate the objective of the present study is to analyze two seismic swarms that occurred along the ew trending pernambuco ductile shear zone and in a ne trending branch in 2007 and 2010 in sao caetano county northeastern brazil we studied both epicentral areas using a nine and a seven station network during 180 and 54 days respectively the results indicate that the 2007 swarm correspond to a right lateral strike slip fault with a normal component of slip strike 74 dip 60 and rake 145 and the 2010 swarm corresponds to a normal fault strike 265 dip 79 and rake 91 the former reactivated a ne trending branch whereas the latter reactivated the main e w trending mylonitic belt of the pernambuco shear zone these results are consistent with seismogenic reactivation of this major structure generated by the present day ew trending compression and ns trending extension as observed by previous studies this shear zone was reactivated as rift faults in the cretaceous during the south america africa breakup however our study confirms that the basement fabric such as continental scale ductile shear zones show evidence of crustal weakness outside areas of previous rifting and it reveals the potential for large earthquakes along dormant rift segments associated with major basement shear belts

the northeastern brazil and gabon basins a double rifting system associated with multiple crustal detachment surfaces analysis of structural stratigraphic and gravimetric data from the reconcavo tucano and sergipe alagoas basins in northeastern brazil and the gabon basin in africa shows that these basins originated in a double rifting system associated with multiple crustal detachment surfaces and that the direction of dip of the detachment surfaces was reversed at the vaza barris fault system this geometry is in agreement with models and data from modern rifts but it requires the existence of a predominantly extensional stress regime in the northern part of the south atlantic during the early stages of oceanic evolution evidence for the existence of such a stress regime is given by application of kinematic constraints to early cretaceous reconstructions of the south atlantic ocean interpretation of the regional geologic setting suggests that the double rifting system and the point of final continental rupture were controlled by the preexisting structural orientation of the tectonic provinces in the precambrian basement

coal petrological and xylotomical characterization of miocene lignites and in situ fossil tree stumps and trunks from lusatia region germany palaeoenvironment and taphonomy assessment abstract the present paper investigates rank and composition of coal as well as depositional and hydrogeological settings persisting during the stage of peat accumulation and evaluates taphonomy and conditions for the in situ preservation of outstanding fossilized stump and trunks using coal petrological and xylotomical analyses the obtained results are further interpreted and compared with existing literature records lignite samples and fossil wood specimens were collected from the 2nd mfh 2nd miocene seam horizon or its equivalent present at meuro piskowitz and welzow sud open cast mines located in lusatia germany the examined lignite samples indicate low rank coals at lignite or subbituminous rank stage and are characterised by slight dominance of attrinite over textinite ulminite suberinite cutinite porigelinite resinite and corpohuminite macerals waterlogged conditions prevailing in the mire are associated with peat accumulation under anoxic conditions accompanied by low decomposition rates the determined facies indicators suggest a moderate to high as well as low gelification of the organic matter for the meuro and piskowitz open cast mines respectively in meuro open cast mine the prevalence of herbaceous plant in a mire or a bacterial fungal degradation of woody plant tissues can be envisaged whereas in the piskowitz open cast mine it is suggested that peat formed in a wet forest mire environment with a limited oxygen supply and a relatively low bacterial fungal degradation the studied fossil wood specimens revealed the presence of quasisequoioxylon piskowitzense preserved as an in situ fossilized stump as well as taxodioxylon cryptomerioides and sciadopityoxylon wettsteinii species preserved as fossilized trunks the examined species belong to the families of cupressacea sciadopityaceae and cupressaceae li sensu lato the taphonomy of the in situ fossilized stump and trunks can be explained by nutrient and oxygen poor oligotrophic mires distinguished as raised bogs and suggesting generally anoxic conditions during middle to late miocene climate transition

structural segmentation and the influence of basement structure on the namibian passive margin passive margins are segmented into discrete elements by segment boundaries exhibiting a variety of structural styles the namibian margin is bounded by a hinge line that is offset by segment boundaries the most important is the cape cross segment boundary here pre existing basement lineaments and karoo rift elements were reactivated during late mesozoic rifting it marks the northern limit of the earliest of three rift sequences and relates to a temporal change in break up and formation of the south atlantic a similar change occurs across other important segment boundaries but smaller examples lack this major segment boundaries with a temporal change in rifting and break up exhibit a strong connection to the basement province

basement fabric controls rift nucleation and postrift basin inversion in the continental margin of ne brazil abstract in passive continental margins the brittle reactivation of shear zones and their role in the deformation and deposition of sedimentary basins are still a matter of debate in this research we investigated the role of the brittle reactivation of precambrian shear zones in the nucleation of rift and postrift faults in the onshore portion of the sergipe alagoas and pernambuco basins in northeastern brazil we combine and interpret a dataset of aeromagnetic and topographic data associated with reflection seismic and borehole data to analyze the evolution of a portion of the atlantic continental margin of brazil our results indicate that in the crystalline basement the magnetic lineaments are correlated with ductile structures as shear zones and the continuity of these lineaments in the sergipe alagoas and pernambuco basins is interpreted as the shear zones below the sedimentary cover of these basins we document the following phases of the brittle reactivation of basement shear zones 1 the opening of the south atlantic ocean in the early cretaceous under an extensional stress regime and 2 tectonic inversion induced by the mid atlantic ridge push and the andean cordillera rise in the neogene quaternary under a predominantly strike slip stress regime during the rift phase the brittle reactivation of the shear zones controlled the locations and architectures of the rifts these structures acted as zones of weakness and were reactivated as normal faults the brittle reactivation of shear zones was still active during the postrift phase and was responsible for the development of compressional structures the reverse faulting and related folding pattern indicate tectonic inversion in the late cretaceous cenozoic the structures formed during the postrift phase under a strike slip regime are consistent with the present day stress field indicating that tectonic inversion is an active phase of the brazilian margin

neogene quaternary fault reactivation influences coastal basin sedimentation and landform in the continental margin of ne brazil we investigate the role of reactivation of precambrian basement fabric in the tectono sedimentary and geomorphological evolution of the paraiba basin continental margin of northeastern brazil during the cretaceous neogene and quaternary this basin represents part of the last bridge between south america and africa before the last breakup stage of the south atlantic rifting in the early cretaceous the paraiba basin infill is composed of siliciclastic and carbonate cretaceous units as well as aeolian fluvial and marine quaternary units we used shuttle radar imagery aeromagnetic wellbore and field data the reduced to the pole magnetic map rtp indicates the continuity of the steeply dipping precambrian basement shear zones beneath the paraiba basin the combined analysis of surface and subsurface data shows that ne sw and e w striking shear zones were subjected to brittle reactivation in the aptian middle albian during the basin opening and again in the neogene quaternary forming a system of horsts and grabens along the basin some of these structures such as the e w oriented pernambuco shear zone present modern day seismicity n s and mainly nw se striking transfer faults cut across aptian middle albian to neogene quaternary strata these four main fault directions control main river channels and alluvial valleys up to 2 km wide topographic breaks up to 50 m were created by late reactivation of rift faults which mark the boundary between horsts and grabens along the basin in addition structural data evidence syn tectonic faulting with vertical offsets up to 80 m in the cretaceous and up to 70 m in the neogene quaternary we conclude that shear zones across the study area are long lived structures that have behaved as weakness zones their neotectonic brittle reactivation has controlled sediment deposition and landform development which continued through the neogene quaternary

crustal detachment during south atlantic rifting and formation of tucano gabon basin system a series of major sedimentary basins of mesozoic to tertiary age are associated with the brazilian continental margin between 8 and 14 s fig 1 this passive continental margin formed when africa and south america split apart with the initiation of seafloor spreading in the aptian albian3 the offshore basins which border the continental margins on both sides of the atlantic show evidence of both rifting and crustal attenuation before break up and thermal subsidence after it in contrast a combined stratigraphical and gravity study of the brazilian onshore basins which are separated from the offshore basins by a northward widening strip of precambrian suggests that up to 7 km of non marine sediments were deposited during the rifting stage of the south atlantic with no apparent extension of the lower crust beneath these basins and no subsequent thermal subsidence a mechanism for the linked development of these onshore and offshore basins is proposed here along the lines suggested by wernicke4 5 in which upper crustal extension in the onshore region is connected to and balanced against deeper lithospheric extension beneath the incipient passive margin by intracrustal detachments

quaternary fault control on the coastal sedimentation and morphology of the sao francisco coastal plain brazil abstract the role of neotectonic faulting in shaping topography and controlling sediment deposition has been increasingly documented along the stable continental margin of south america but the level of the present day tectonic stability of this margin is still a matter of debate this paper presents an investigation of the effects of quaternary fault reactivation on the sao francisco coastal plain sfcp this feature is a 56 km long progradational coastal plain located in the sergipe alagoas basin along the continental margin of brazil the sfcp is bounded on the west by a system of normal faults striking n s to ne sw the horst that bounds this plain is capped by the miocene barreiras formation and quaternary debris flow and fluvial deposits whereas the graben is filled with braided stream deposits and sandy beach ridge sediments the faulting contributed to the generation of accommodation space for the deposition of coastal sediments on the plain these processes started with the reactivation of cretaceous faults during the miocene during the quaternary fault reactivation and associated soft sediment deformation occurred between 82 and 8 3 ka with minor pulses between 1700 and 60 cal yr bp several faults along this margin are tectonically active and may represent the onshore continuation of gravitational collapses that have been documented offshore along the continental shelf and slope

sediment deformation in miocene and post miocene strata northeastern brazil evidence for paleoseismicity in a passive margin abstract stratigraphic intervals characterized by varied and complex styles of soft sediment deformation structures are well preserved in miocene and late pleistocene to holocene deposits of a sedimentary basin located in northeastern brazil the miocene strata represented by the barreiras formation record only brittle structures including numerous faults and fractures with straight and high angle dipping planes that are often filled with sands derived from overlying beds folds consisting of broad anticlines and synclines are also present in this unit the late pleistocene to holocene deposits named post barreiras sediments contain an indurated sandy package with a large variety of ductile and brittle deformation structures i e massive sandstones with isolated sand fragments and breccias undulatory strata sand dykes and diapirs sinks and bowls pebbly pockets plunged sediment mixtures fitted sand masses cone shaped cracks fault grading and sedimentary enclaves these features confined to sharp based stratigraphic horizons that progressively grade downward into undisturbed deposits are related to seismic shocks of high surface wave magnitude i e ms 5 or 6 amalgamated seismites suggest that previously formed seismites were affected by subsequent seismic wave propagation seismic waves caused by activity along one or most likely several tectonic structures would have propagated throughout the depositional environment producing laterally extensive seismites the close proximity to earthquake epicenters would have promoted pervasive re sedimentation due to pore overpressure resulting high volumes of massive sandstones and breccia the similarity between deposits with correlatable strata from many other areas along the brazilian coast allows raise the hypothesis that the seismic episodes might have affected sedimentation patterns in a large i e extension of several hundreds of kilometers geographic area thus the modern seismicity recorded along northeastern brazil was recurrent during the quaternary and perhaps also in the pliocene the estimated high magnitude of the seismic events and the great regional extent of the affected area demonstrate that the brazilian coast experienced tectonic stress through the last geological episodes of its evolution which would have favored sediment accumulation and penecontemporaneous re sedimentation this geological context is unexpected in a passive margin inducing to revisit the debate on how active is a passive margin

styles of neotectonic fault reactivation within a formerly extended continental margin north west shelf australia we have investigated the locations and patterns of neotectonic deformation in the carnarvon basin along the mesozoic rifted margin of western australia to evaluate the characteristics of post neogene tectonic reactivation geological geophysical geotechnical and bathymetric data demonstrate that preferentially oriented rift era structures have been reactivated under the current neotectonic stress regime the most recent pulse of neotectonic reactivation initiated during the plio pleistocene 4 0 to 1 8 million years ago and is ongoing reactivated structures in the region demonstrate a variety of styles of deformation consistent with dextral transpression structural styles include both positive and negative flower structures restraining and releasing bends and hourglass structures barrow island lies within a broad kinematic restraining bend that appears to warp the mis 5e marine terrace on the island fold reconstructions of neogene strata on the cape range and barrow anticlines yield uplift rates consistent with uplift rates determined from folded late pleistocene units in the cape region although tectonic rates are low compared to interplate settings evidence for active tectonic deformation precludes this part of the australian plate from being classified as a stable continental region

new interpretations of the facies of the rhenish brown coal of west germany abstract new ideas concerning the understanding of the facies of the rhenish brown coal of west germany are discussed these new interpretations are based on a significantly larger number of samples and refined procedures for analysis within the field of paleobotany palynology coal petrology and organic geochemistry than were available to p w thomson and m teichmuller the light and dark bands in the coal are mainly the result of different degrees of plant decomposition the influence of the peat forming plant communities plays a subordinate role in the petrographical composition of these particular strata of the rhenish brown coal

sequence stratigraphic analysis and the origins of tertiary brown coal lithotypes latrobe valley gippsland basin australia abstract the methods of sequence analysis have been applied to the onshore gippsland basin and in particular to the latrobe valley group coal measures which include up to five coal seams each exceeding 100 m in thickness the methods appear to provide new depositional concepts to the evolution of these seams and the development of coal lithotypes in the eastern half of the latrobe valley evidence for marine transgressions into the coal measures are recorded in most of the interseam sediment splits by the presence of contained foraminifera and dinoflagellates to the west inland these splits pinch out into continuous coal however they can be followed westwards as enhanced organic sulphur levels along sharply defined boundaries between light coal lithotypes below and dark coal lithotypes above the dark lithotype immediately overlying each of these boundaries contains the highest sulphur value and warmer climate pollen assemblages sluiter et al 1995 this volume colorimeter and lithotype logging strongly supports an upwards lightening cyclicity to coal colour at 12 20 m intervals through the approx 100 m thick seams with cycle boundaries defined at sharp planar to undulating surfaces the lightening upward lithotype cycles together with their unique boundary conditions i e enhanced organic sulphur levels warm climatic indicators and laterally equivalent marine clay splits are interpreted as parasequences and parasequence boundaries respectively each major coal seam can comprise up to five parasequences and is interpreted to represent deposition during an outbuilding high stand systems tract at one of several maximum periods of tertiary coastal onlap the top of each major seam shows evidence of truncation erosion on a regional scale and these surfaces are interpreted to represent the sequence boundaries the major seams are usually conformably underlain by marine clays and extensive aquifer sands being deposits of the late transgressive systems tracts the low stands and early parts of the transgressive systems tracts appear not to be represented in the latrobe valley due to its more basin margin location but are probably present down dip in the equivalent marine facies of the seaspray group stratigraphic correlation of the sequence boundaries identified in the coal measures to the adjacent internationally dated marine seaspray group provides a basis for chronostratigraphic correlation of the coal successions to the coastal onlap charts of haq et al exon mesozoic cenozoic chronostratigraphic chart version january 1988 and august 1989 from this dating it appears that each major seam is confined to high stands of third order eustatic cycles it therefore follows that the lithotype cycles parasequences that comprise each seam are related to fourth order eustatic cycles by analogy all the coal cycles may have developed under subtropical conditions as ombrogenous forested peat swamps in a similar manner to the holocene though tropical swamps of indonesia

the unsteady post rift stage of the south american passive margin based on the tectono sedimentary evolution of the onshore paraiba basin ne brazil abstract the post rift tectono sedimentary history of passive margins has been an issue of increased interest after the perception of their unsteady nature during the neogene and quaternary the evolution of the eastern south america margin might be benefited from investigations of the sedimentary record in a number of marginal basins the paraiba basin is of particular interest to discuss the post rift evolution of the south american passive margin because it represents the last bridge with the african plate this work aims to analyze the post rift sedimentary record of the onshore paraiba basin as a contribution to discuss the neotectonic history of the south american passive margin surface and subsurface data were integrated from outcrops deep stratigraphic profiles airborne geophysical maps and remote sensing products the depositional and denudational processes in this basin were a result of tectonic subsidence and uplifting tectonics after the main rifting phase are indicated by abundant structures including normal reverse and strike slip faults as well as folds that affected the neogene and late pleistocene sedimentary deposits the ductile and brittle deformation resulted mainly from multiple reactivations of e w ne sw and nw se trending basement shear zones the deformation mechanism included distension and compression under a strike slip regime tectonic reactivations even during the late pleistocene support an unsteady south atlantic passive continental margin throughout the post rifting stage

neogene through quaternary tectonic reactivation of sw iberian passive margin southwest portugal the gulf of cadiz and morocco are under the potential threat of natural hazards linked to seismicity and tsunami generation we report the results of two multi channel seismic mcs surveys carried out in 1992 and 1998 along the continental margin and oceanic crust of sw iberia this mcs data set shows the evidence of the compressional deformation which involves both the continental and the oceanic crust of the study area the area of deformation extends from the southern border of the tagus abyssal plain to the seine abyssal plain encompassing the continental margin of sw portugal most of the structures observed are probably related to a mid miocene phase of africa europe plate convergence in this paper we discuss the recent advances on the identification of the tectonic structures that are still active and that may generate great earthquakes and tsunamis the tectonic structures identified are located respectively at the guadalquivir bank along the eastern border of the horseshoe abyssal plain and along the southern continental slope of sw portugal

topography growth drives stress rotations in the central andes observations and models 1 recent numerical models that couple global mantel circulation with lithosphere dynamics show that growth of the central andes controls the 30 reduction of convergence velocity between the nazca and south america plates observed over the past 10 ma the increase of gravitational potential energy due to topographic growth is also a major control on the stress pattern here we use numerical models which reproduce the nazca south america convergence history to predict the change of stress pattern in the central andes for the past 10 ma comparison of the modeled stress orientations at present day with the observed ones results in 23 9 mean deviation based on this good agreement we attempt to predict paleostress orientations 10 ma ago interestingly the modeled stress orientations 3 2 ma ago are very similar to the present day orientations from this result we infer that stress rotations occurred between 10 and 3 2 ma ago when topography was considerably lower

pre existing normal faults have limited control on the rift geometry of the northern north sea abstract many rifts develop in response to multiphase extension with numerical and physical models suggesting that reactivation of first phase normal faults and rift related variations in bulk crustal rheology control the evolution and final geometry of subsequent rifts however many natural multiphase rifts are deeply buried and thus poorly exposed in the field and poorly imaged in seismic reflection data making it difficult to test these models here we integrate recent 3d seismic reflection and borehole data across the entire east shetland basin northern north sea to constrain the long term regional development of this multiphase rift we document the following key stages of basin development i pre triassic to earliest triassic development of multiple sub basins controlled by widely distributed nnw to ne trending east and west dipping faults ii triassic activity on a single major ne trending west dipping fault located near the basins western margin and formation of a large half graben and iii jurassic development of a large e dipping n to ne trending half graben near the eastern margin of the basin which was associated with rift narrowing and strain focusing in the viking graben in contrast to previous studies which argue for two discrete periods of rifting during the permian triassic and late jurassic early cretaceous we find that rifting in the east shetland basin was protracted from pre triassic to cretaceous we find that during the jurassic most pre jurassic normal faults were buried and in some cases cross cut by newly formed faults with only a few being reactivated previously developed faults thus had only a limited control on the evolution and geometry of the later rift we instead argue that strain migration and rift narrowing was linked to the evolving thermal state of the lithosphere an interpretation supporting the predictions of lithosphere scale numerical models our study indicates that additional regional studies of natural rifts are required to test and refine the predictions of physical and numerical models more specifically our study suggests models not explicitly recognising or including thermal or rheological effects might over emphasise the role of discrete pre existing rift structures such as normal faults

marlies teichmuller 1914 2000 pioneering genetic coal petrologist some paleobotanical palynological and botanical influences on her research marlies teichmuller focused her career on genetic coal petrology in her investigations of the botanical components of coal and reconstructions of carboniferous and tertiary mires she was greatly influenced by eric stach walther gothan reinhardt thiessen rolf teichmuller paul thomson gilbert cady and william spackman jr some of these influences deal with paleobotany palynology and botany and these are set forth in this tribute

structural style and early stage growth of inversion structures 3d seismic insights from the egersund basin offshore norway abstract high quality three dimensional 3d seismic reflection and borehole data from the egersund basin offshore norway are used to characterise the structural style and determine the timing of growth of inversion related anticlines adjacent to a segmented normal fault system two thick skinned normal faults which offset permian clastics and evaporites delineate the north eastern margin of the basin these faults strike nnw sse have up to 1900 m of displacement and are separated by an ese dipping c 10 km wide relay ramp both of these faults display exclusively normal separation at all structural levels and tip out upwards into the upper part of the lower cretaceous succession at relatively shallow structural levels in the hangingwalls of these faults a series of open low amplitude fault parallel anticlines are developed these anticlines which are asymmetric and verge towards the footwalls of the adjacent faults are interpreted to have formed in response to mild inversion of the egersund basin the amplitude of and apparent shortening associated with the anticlines vary along strike and these variations mimic the along strike variations in throw observed on the adjacent fault segments we suggest that this relationship can be explained by along strike changes in the propensity of the normal faults to reactivate during shortening wider damage zones and lower angles of internal friction coupled with higher pore fluids pressures at the fault centre mean that reactivation is easier at this location than at the fault tips or in the undeformed country rock seismic stratigraphic analysis of growth strata indicate that the folds initiated in the latest turonian to earliest coniacian c 88 6 ma and santonian c 82 6 ma the control on this c 6 myr diachroneity in the initiation of fold growth is not clear but it may be related to strain partitioning during the early stages of shortening anticline growth ceased in the maastrichtian and the inversion event is therefore interpreted to have lasted at least c 20 myr this study indicates that 3d seismic reflection data is a key tool to investigate the role that normal fault segmentation can play in controlling the structural style and timing of inversion in sedimentary basins furthermore our results highlight the impact that this structural style variability may have on the development of structural and stratigraphic hydrocarbon traps in weakly inverted rifts

the role of precambrian mylonitic belts and present day stress field in the coseismic reactivation of the pernambuco lineament brazil abstract the pernambuco lineament is a steeply dipping continental scale ductile shear zone rooted within the precambrian lithosphere of intraplate northeastern brazil it was formed during the brasiliano orogeny 600 ma and reactivated during the pangea breakup in the cretaceous when it controlled fault propagation and sediment accumulation in several rift basins the region is now under an e w trending horizontal compression and n s trending extension and faulting occurs predominantly in a strike slip regime we investigated two aftershock sequences and the preexisting tectonic fabrics along the pernambuco lineament in order to evaluate the role of these fabrics in the coseismic reactivation of continental scale structures the lineaments consist of a main ene wsw trending mylonitic belt about 2 3 km wide and two secondary ne trending mylonitic belts about 100 m wide they both present steeply dipping mylonitic foliations and shallowing plunging stretching lineations the mylonites present granitoid protoliths and mineral parageneses that range from amphibolite to greenschist facies brittle deformation overprints the ductile fabric in all mylonitic belts in 1991 coseismic reactivation nucleated along the ene wsw striking 3 3 5 6 km deep normal fault of less than 1 km in length in the main mylonitic belt in 2002 seismicity migrated to a ne trending secondary mylonitic branch and moved as a right lateral strike slip 1 2 km long 3 8 4 9 km deep fault plane both fault segments reactivated the mylonitic foliation and form part of a major system we conclude that the interplay between the present day stress field and preexisting fabrics controls seismogenic fault location attitude and kinematics the pernambuco lineament is an example of a long lived continental scale structure where selective reactivation has occurred other shear zones in the region also show a long history of brittle reactivation and present similar orientation in relation to the present day stress axes they might be dormant structures prone for reactivation under the present day stress field

the recognition of reactivation during continental deformation reactivation involves the accommodation of geologically separable displacement events intervals 1 ma along pre existing structures the definition of a significant period of quiescence is central to this phenomenological definition and the duration of the interval chosen represents the resolution limit of reactivation criteria found in most ancient settings in neotectonic environments reactivation can be further defined as the accommodation of displacements along structures that formed prior to the onset of the current tectonic regime this mechanistic definition cannot always be applied to ancient settings due to the uncertainties in constraining relative plate motion vectors four sets of criteria may be used to recognize reactivation in the geological record stratigraphic structural geochronological and neotectonic some structural criteria may not be reliable if used in isolation to identify reactivated structures much of the previously published evidence cited to invoke structural inheritance is equivocal as it uses similarities in trend dip or three dimensional shape of structures numerous fault and shear zone processes can cause significant weakening both synchronously with deformation and in the long term and may be invoked to explain reactivation the collage of fault bounded blocks forming most continents therefore carries a long term architecture of inheritance which can explain much of the observed complexity of continental deformation zones

distribution timing and causes of andean deformation across south america the andean orogeny in south america has lasted over 100 ma it comprises the peruvian incaic and quechuan phases the nazca and south american plates have been converging at varying rates since the palaeocene the active tectonics of south america are relatively clear from seismological and global positioning system gps data horizontal shortening is responsible for a thick crust and high topography in the andes as well as in se brazil and patagonia we have integrated available data and have compiled four fault maps at the scale of south america for the mid cretaceous late cretaceous palaeogene and neogene periods andean compression has been widespread since the aptian the continental margins have registered more deformation than the interior for the peruvian phase not enough information is available to establish a tectonic context during the incaic phase strike slip faulting was common during the quechuan phase crustal thickening has been the dominant mode of deformation to investigate the mechanics of deformation we have carried out 10 properly scaled experiments on physical models of the lithosphere containing various plates the dominant response to plate motion was subduction of oceanic lithosphere beneath continental south america however the model continent also deformed internally especially at the margins and initial weaknesses

effect of relative lake level changes in mire lake system on the petrographic and floristic compositions of a coal seam in the most basin miocene czech republic abstract exposures in the bilina opencast mine provide a direct evidence that the 3 5 m thick upper bench of the main seam in the most basin passes over a distance of about a kilometre into a hundred metres thick equivalent of clastic deltaic sediments with gilbert type mouth bars and thus clearly corroborates the co existence of lacustrine delta mire system deposition of the delta and the upper bench of the main seam were affected by five short term lacustrine incursions possibly related to tectonic subsidence before final lacustrine transgression took place between the temporary lacustrine incursions delta mouth bars prograded into an extensive mire being separated only by a shallow compaction lake along mouth bars foreland however most clastics introduced from delta were caught by dense vegetation in a narrow proximal zone of mire and did not affect more distal parts of relatively dry woodland mire with water table fluctuating around the surface it is therefore characterised by low ash yield and increased resinite fusinite and inertodetrinite contents palynological data indicate that the peat forming vegetation of the upper bench of the main seam was dominated by taxodiaceae glyptostrobus athrotaxis and calamus palm accompanied by paludal species of the family pinaceae and rich undergrowth of ferns and vaccinium type ericaceae progradation of delta mouth bars to the proximity of the study section is documented by increasing proportion of allochthonous elements produced by plants colonizing the flood plain and delta plain areas nyssa taxodium parrotia ulmus pyramidalis and comptonia pinus oviformis associations in contrast during periods of temporary lacustrine transgressions the mire was replaced by open water environment which favoured deposition of clay rich coals or partings 30 of ash yield of the flooding horizons in spite of fact that delta body retreated to the basin margin and the clastics were introduced from a larger distance rare palynomorphs indicate only sparse vegetation cover of aquatic plants during this time clay content seems to be the best indicator of the water level fluctuations facies indices e g tpi and gi show only poor correlation to hydrological and floristic changes detected in the mire lake system

the role of pre existing precambrian structures in rift evolution the albertine and rhino grabens uganda abstract we integrated shuttle radar topography mission srtm digital elevation models dem airborne magnetic radiometric and three dimensional full tensor gravity gradiometry 3d ftg data to investigate the role of precambrian structures in the evolution of the largely amagmatic miocene recent aged albertine and rhino grabens in uganda these grabens represent the northern segment of the western branch of the east african rift system ears the two ne trending grabens are connected by a right stepping transfer zone and they extend within the archean paleoproterozoic northeast congo block which represents the northeastern extension of the congo craton our results show the following and highlight the importance of pre existing structures in the evolution of continental rift systems 1 the ne extent of the albertine full graben is controlled by ne trending precambrian fabric and the graben terminates at its northeastern end when it encounters a multiply folded precambrian basement terrain with poorly developed nw trending structural grain additionally the northeastern termination of the albertine graben coincides with the presence of nw trending right stepping high density bodies within the precambrian terrain 2 the transfer zone between the albertine and rhino grabens is controlled by ne trending precambrian structures which might have facilitated the development of relay ramp faults 3 strain localization within the better developed southeastern border fault of the rhino half graben is facilitated by the presence of precambrian structures better aligned in a ne direction in the southeastern part of the basin compared to its northwestern part 4 further to the northeast the rhino graben is segmented and transitions into a narrower ene trending half graben with a better developed border fault on its northwestern side this segmentation coincides with the presence of n trending precambrian structures 5 the rhino graben terminates farther northeast against the nw trending precambrian aswa shear zone a prominent structure with complex but generally nw trending fabric

proterozoic links between the borborema province ne brazil and the central african fold belt the congo cc and the sao francisco sfc cratons were joined at about 2 05 ga northern parts of palaeoproterozoic basement subsequently underwent extension at about 1 ga forming intracratonic basins neoproterozoic metasedimentary rocks in these basins yield detrital zircons as young as 630 ma the brasiliano and pan african c 620 580 ma assembly of west gondwana extensively altered this system the sergipano domain occurs north of the sfc and the comparable yaoundedomain occurs north of the cc crust north of the sergipano domain com prises the pernambuco alagoas peal domain the ne sw striking tchollire banyo fault in cameroon may extend southwestwards between the peal and sergipano domains defining northern limits of abundant sfc cc basement the adamawa yadedomain in africa does not appear to extend into brazil the transverse domain of brazil is a collage of palaeoproterozoic crustal blocks the 1 0 ga cariris velhos orogen cvo late neoproterozoic basins and brasi liano granites the cvo extends ene for more than 700 km in brazil but eastern continuation into africa has not been identified north of the transverse domain contiguous c 2 15 ga gneisses comprise basement of rio grande do norte and cearadomains which continue eastwards into western nigeria and western sahara

terrane boundary reactivation barriers to lateral fault propagation and reactivated fabrics rifting across the median batholith zone great south basin new zealand prominent pre existing structural heterogeneities within the lithosphere may localise or partition deformation during tectonic events the ne trending great south basin offshore new zealand formed perpendicular to a series of underlying crustal terranes including the dominantly granitic median batholith zone which along with the boundaries between individual terranes exert a strong control on rift physiography and kinematics we find that the crustal to lithospheric scale southern terrane boundary of the median batholith zone is associated with a crustal scale shear zone that was reactivated during late cretaceous extension between zealandia and australia this reactivated terrane boundary is oriented at a high angle to the faults defining the great south basin we identify a large granitic laccolith along the southern margin of the median batholith expressed as sub horizontal packages of reflectivity and acoustically transparent areas on seismic reflection data the presence of this strong granitic body inhibits the lateral south westward propagation of ne trending faults which segment into a series of splays that rotate to align along the margin as they approach further we also identify two e w and ne sw oriented basement fabrics likely corresponding to prominent foliations which are exploited by small scale faults across the basin we show that different mechanisms of structural inheritance are able to operate simultaneously and somewhat independently within rift systems at different scales of observation the presence of structural heterogeneities across all scales need to be incorporated into our understanding of the structural evolution of complex rift systems

inversion tectonics in central africa rift system evidence from the heglig field abstract the mesozoic cenozoic tectonic history of the muglad basin is dominated by extension and inversion tectonics but evidence of the inversion tectonics has not been well documented yet in some other rift basins of cars and wars the phase of the inversion tectonics is well documented by several authors this paper presents a structural study of the heglig field area located on the eastern flank of the muglad basin detailed 3d seismic interpretation allows a better understanding of the structural style of the heglig field the new structural analysis has shown that the heglig field has a complex structural framework reflected in the presence of a combination of two structural styles the extensional structure is influenced by inversion tectonics during the santonian time that creates four way dip anticline structure overprinted by the subsequent extensional movement that creates tilted fault block the presence of inversion tectonics has supported by different means including seismic reflection velocity and source rock maturity data the authors attributed the trapping of oil in the lower bentiu reservoir that requires a horizontal seal to the presence of the four way dip anticline structure created by the inversion tectonics the current interpretation of the heglig field 3d seismic data sheds new light on the development and evolution of a key structure in the muglad basin the results help to resolve long standing discussion concerning hydrocarbon accumulation of the lower part of bentiu formation that lacks horizontal sealing

ductile precambrian fabric control of seismic anisotropy in the acu dam area northeastern brazil 1 in the joao c mara area ne brazil seismic anisotropy has been interpreted as the result of either precambrian ductile fabric or stress aligned fluid filled grain boundary caused by high pore fluid pressures the first interpretation is based on the fact that the direction of the fastest s wave splitting agrees with the north south trending precambrian fabric the second interpretation related to the extensive dilatancy anisotropy eda is based on the stress field orientation and on the assumption that the pore fluid pressure in the region is high enough to modify microcrack distribution and cause s wave polarization to become parallel to the north south oriented minimum horizontal stress shmin here we address this question by investigating this ambiguity we have analyzed the seismicity in the acu dam area 150 km west of joao c mara over a 3 year period in the acu area the northeast southwest trending ductile precambrian fabric is not parallel or orthogonal to the east west trending maximum horizontal stress shmax we combined the interpretation of fastest s wave polarizations their time delays and fabric orientation measured in the field with side looking airborne radar imagery taken before the lake impoundment thus we discriminate between 1 stress aligned fluid filled cracks 2 high pore pressure fluids modifying the microcrack distribution and therefore causing 90 flips and 3 fabric or paleostrain as causes for the observed s wave anisotropy our main result indicates that the direction of the fastest s wave polarization in the acu dam area agrees with the northeast southwest trending fabric n40 e eda or 90 flips control of seismic anisotropy if occurring in acu have minor effects

pliocene lignites from apofysis mine amynteo basin northwestern greece petrographical characteristics and depositional environment coal petrological investigation along with proximate and elemental analyses were undertaken to determine the petrographic characteristics of the apofysis lignites amynteo basin northwestern greece and their depositional environment eight samples representing different lignite beds of the apofysis deposit were collected from a borehole the apofysis lignites have an eu ulminite b reflectance of rr 0 22 and in terms of lithotype belong to matrix soft brown coals huminite is the most abundant maceral group and consists mostly of humodetrinite inertinite has relatively low percentages whereas liptinite concentrations are low in the lower lignite beds and higher in the upper ones ternary plots and facies indices were employed in order to investigate the palaeoenvironment the depositional environment of the apofysis lignites is not definitely ascribed to a forest swamp or a reed marsh environment the high ash content of the analysed samples is a clear indication of a topogenous setting low tissue preservation index tpi and high gelification index gi values are observed high alkalinity and strongly reducing conditions may be inferred from the presence of syngenetic framboidal pyrite the low tpi values which indicate high bacterial activity and thus high ph conditions and the preservation of gastropod shells and chlorophyllinite high gi indicates a constant influx of calcium rich waters into the coal swamp the apofysis lignite deposit may be interpreted to be autochthonous to hypoautochthonous the peat accumulation was governed by a high groundwater level wet telmatic to limno telmatic facies and a moderate subsidence rate

reactivation of intrabasement structures during rifting a case study from offshore southern norway abstract pre existing structures within crystalline basement may exert a significant influence over the evolution of rifts however the exact manner in which these structures reactivate and thus their degree of influence over the overlying rift is poorly understood using borehole constrained 2d and 3d seismic reflection data from offshore southern norway we identify and constrain the three dimensional geometry of a series of enigmatic intrabasement reflections through 1d waveform modelling and 3d mapping of these reflection packages we correlate them to the onshore caledonian thrust belt and devonian shear zones based on the seismic stratigraphic architecture of the post basement succession we identify several phases of reactivation of the intrabasement structures associated with multiple tectonic events reactivation preferentially occurs along relatively thick c 1 km relatively steeply dipping c 30 structures with three main styles of interactions observed between them and overlying faults i faults exploiting intrabasement weaknesses represented by intra shear zone mylonites ii faults that initiate within the hangingwall of the shear zones inheriting their orientation and merging with said structure at depth or iii faults that initiate independently from and cross cut intrabasement structures we demonstrate that large scale discrete shear zones act as a long lived structural template for fault initiation during multiple phases of rifting

senonian basin inversion and rejuvenation of rifting in africa and arabia synthesis and implications to plate scale tectonics abstract the late paleozoic to tertiary stratigraphic record of much of the african plate reflects the effects of continental rifting and passive margin development several short lived but widespread and tectonically important compressional or wrench dominated events occurred however during the permian to recent evolution of africa we focus here on the best documented of these events which occurred during the late santonian at that time older sedimentary basins mostly ene wsw trending were folded and inverted including some basins along the tethyan margin from morocco to the syrian arc and the intraplate benue southern chad basins and the lugh mandera basin in oman ophiolites were obducted following the santonian tectonism an extensive phase of rifting occurred in central and north africa and northern arabia spanning from campanian to maastrichtian or paleocene times rejuvenation or acceleration of subsidence occurred in several basins located along the tethyan margin along the atlantic and indian ocean margins as well as within the intraplate domain rifting was sometimes accompanied by magmatic activity especially in offshore northern libya and along the indian ocean margin compressional deformations rejuvenated or developed by latest maastrichtian times along the tethyan margin and locally within the intraplate domain one of the most remarkable attributes of the santonian tectonic event which we consider representative of the major trans african stress field changes is the rapidity with which the change was reflected stratigraphically across north and central africa and its short duration the cause of the santonian compressional event is directly linked to the change in poles of rotation for the opening of the atlantic at 83 85 ma the end of the cretaceous normal magnetic quiet zone this was also synchronous with the obduction of ophiolites along the northeast margin of arabia oman the onset of separation between india and madagascar with formation of the mascarene oceanic basin and the development of the european alpine chain we interpret these phenomena as causally related aspects of a global tectonic event the santonian compressional event as well as the campanian maastrichtian rifting event and the end cretaceous compressional event illustrate the critical connection between intraplate tectonic histories and processes occurring at sometimes very distant plate boundaries

coal petrology and the origin of coal macerals a way ahead the development of coal petrology and the establishment of a nomenclatural system have proved of major use both for the industrial utilization of coal and for the development of a broad understanding of coal formation and diagenesis the development over the past 30 years however of nomenclature that includes aspects of plant origin and process is a retrograde step e g pyrofusinite degradofusinite and funginite equally problematic is the use of prescriptive formulae to indicate coal origins this paper reviews some of the problems involved with coal petrology as it is usually practiced in addition new advances in organic geochemical techniques have led to a fuller understanding of the relationship of plants and coal macerals recent research on the origin of coal macerals is presented and there is a discussion of the problems and challenges facing coal petrologists a holistic approach to studies of the origin of coal and coal macerals which includes not only petrographic but also chemical and biological studies is advocated d 2002 elsevier science b v all rights reserved

paleoenvironmental conditions of puertollano coals spain petrological and geochemical study abstract in the present work petrographic geochemical and mineralogical data have been combined with results from prior paleobotanical studies in order to determine the sedimentary and postsedimentary diagenetic factors responsible for the physicochemical properties of coal seams and associated sediments from the puertollano stephanian coal basin although the coal seams 4 originated under similar lacustrine conditions the highest coal seams 1 and 1 bis show higher production preservation of structured tissues telinite and collotelinite than the lowest coal seams 2 and 3 where destruction of the cell tissues collodetrinite is predominant differences in degree of preservation as a result of changes in the environmental sedimentary conditions in the water table ph redox may explain the different maceral distribution this feature may also be due to the increase in degree of humification from the highest seams 1 and 1 bis to the lowest seams 2 and 3 however the gentle thermal maturation undergone by these stephanian coals only produced a slight modification in the physicochemical properties of the organic matter in general alkaline synsedimentary conditions could be deduced from the dominance of organic sulphur with respect to pyritic sulphur reducing conditions for seam 1 1 bis and 2 and more oxidant conditions for seam 3 can be deduced from maceral sulphur and carbonate distribution other diagenetic processes involved organic and inorganic sediments for example a kaolinitisation process with a different intensity for the early diagenetic stages suggests the occurrence of leaching processes which affected both organic and inorganic sediments

reworking and discontinuities in holocene sedimentation in the nile delta documentation from amino acid racemization and stable isotopes in mollusk shells abstract the late holocene sedimentary history of the northwestern edge of the nile delta is reconstructed from amino acid racemization radiocarbon and stable isotope analysis of a series of bivalve shells from a core taken at the edge of lake maryut near alexandria amino acid racemization confirmed by radiocarbon and stable isotope analysis indicates that in many parts of the core mixed age mollusk assemblages are present dating of the time of sediment accumulation at various levels in the core is therefore based on the age of the youngest shells which are identified by amino acid racemization analysis lowest d l values ams radiocarbon analysis is used to determine the ages of the shells except for the most recent sediments last 100 yr for which aspartic acid racemization provides more precise ages amino acid racemization analysis of 59 shells from 21 levels in the 4 8 m holocene sequence in the core enabled identification of a large hiatus holocene sedimentation started at ca 2400 bc apparently corresponding to a westward shift of the course of the canopic nile distributary which lies to the east deposition continued at a rate of 1 4 mm per year ceasing at ca 550 bc at which time the canopic nile shifted eastward again and subsequently became defunct a marine connection during this period is indicated by stable isotope values of shells sediment accumulation began again only at the end of the 19th century when a series of irrigation canals was connected to the lake maryut basin stable isotope values indicate a strong freshwater influence deposition has continued to the present at a very high rate 19 mm per year due to supply of sediments by agricultural activity the relative ease with which racemization analyses can be carried out permits detailed analysis of core chronostratigraphy leading to more accurate reconstruction of core chronology hiatuses can be pinpointed and documented and age mixtures can be identified with appropriate individual shells being selected for ams radiocarbon analysis aspartic acid racemization analysis permits dating of samples from the last several hundred years a period for which radiocarbon analyses provide poor precision

the influence of structural inheritance and multiphase extension on rift development the northern north sea the northern north sea rift evolved through multiple rift phases within a highly heterogeneous crystalline basement the geometry and evolution of syn rift depocentres during this multiphase evolution and the mechanisms and extent to which they were influenced by pre existing structural heterogeneities remain elusive particularly at the regional scale using an extensive database of borehole constrained 2d seismic reflection data we examine how the physiography of the northern north sea rift evolved throughout late permian early triassic rp1 and late jurassic early cretaceous rp2 rift phases and assess the influence of basement structures related to the caledonian orogeny and subsequent devonian extension during rp1 the location of major depocentres the stord and east shetland basins was controlled by favorably oriented devonian shear zones rp2 shows a diminished influence from structural heterogeneities activity localises along the viking sogn graben system and the east shetland basin with negligible activity in the stord basin and horda platform the utsira high and the devonian lomre shear zone form the eastern barrier to rift activity during rp2 towards the end of rp2 rift activity migrated northwards as extension related to opening of the proto north atlantic becomes the dominant regional stress as rift activity in the northern north sea decreases through documenting the evolving syn rift depocentres of the northern north sea rift we show how structural heterogeneities and prior rift phases influence regional rift physiography and kinematics controlling the segmentation of depocentres as well as the locations styles and magnitude of fault activity and reactivation during subsequent events

polyphase faulting during the development of the west galicia rifted margin rifted margins are commonly characterised by an extension discrepancy the amount of extension measurable from the observed faulting is far less than that required to explain the crustal thinning it is shown here that polyphase faulting may provide a simple explanation for this paradox but can be very hard to recognise on seismic sections however at the west galicia rifted margin the galicia interior basin between the galicia bank and the mainland and the deep galicia margin to the west of the galicia bank a combination of high quality depth images seismic velocity information and stratigraphic control through odp drilling and submersible sampling provide complementary evidence for polyphase faulting berriasian hauterivian rifting in the galicia interior basin occurred along two sets of faults the first unroofed deep crustal rocks evidenced by high seismic velocities close to top basement the second cut and dismembered these early faults further rifting up until the aptian then focussed west of the galicia bank where two further phases of faulting can be inferred from the diachronous nature of seismostratigraphic units tilted within fault blocks removal of the latest phase of faulting aligns discontinuous reflections within the fault blocks into an anastomosing network of earlier faults restoration along these brings the crust back to its early hauterivian state similar to the present structure of the interior basin

botanical control on banding character in two new zealand coal beds abstract two new zealand coal beds were examined using a palaeobotanical approach to determine controls on banding characteristics the morley cretaceous coal is thickly 5 to 1 or 32 to 2 mm and well 25 banded whereas the brunner eocene coal is essentially non banded palynological analyses indicate that the morley was formed from a gymnosperm dominated vegetation with a secondary component of angiosperms in contrast the brunner was dominated by angiosperm vegetation with only a minor component of gymnosperms however it was found that any xylite vitrain bands 1 mm in either coal bed were comprised exclusively of secondary xylem of probable gymnosperm origin the presence of gymnosperm wood i e secondary xylem forming the larger bands in both coals can be related to the relative resistance of this material to chemical and physical decay as compared to all other plant tissues an absence of angiosperm wood in either the morley or brunner coal beds may be the result of the relative chemical degradability of angiosperm wood as compared to gymnosperm wood alternatively angiosperms in either of the two palaeo mires may have been shrubby and thus did not produce abundant woody tissue in either case the banded nature of the morley coal bed is the result of the presence of gymnosperm wood and the non banded nature of the brunner is the result of being dominated by a flora angiosperm which is easily degraded

structure and evolution of the demerara plateau offshore french guiana rifting tectonic inversion and post rift tilting at transform divergent margins intersection we present the structure and evolution of the eastern part of the demerara plateau offshore french guiana from the analysis of geophysical data collected during guyaplac cruise this area is located at the intersection of a transform segment and a divergent segment of a continental margin related to the early cretaceous opening of the equatorial atlantic the main structures are nne ssw to nnw sse trending normal faults on the eastern edge of the plateau and wnw ese to nw se trending acoustic basement ridges on its northern edge when replaced in their albian position these structures appear to be parallel to the coeval oceanic accretion axis and transform faults respectively the most striking structures are related to a post rift but syn transform tectonic inversion producing e w to wnw ese trending folds sealed by a regional unconformity this shortening can not be related to ridge push but is probably related to a plate kinematic change 105 my ago that modified the deformation in the vicinity of the transform fault late post rift evolution also includes a significant tertiary oceanward tilt of the edge of the demerara plateau the driving mechanism of this late tilt is unclear but may be related to a lithospheric flexure resulting from the loading of the abyssal plain by the orinoco and amazon deep sea fans

northeastern brazilian margin regional tectonic evolution based on integrated analysis of seismic reflection and potential field data and modelling abstract integration of regional seismic reflection and potential field data along the northeastern brazilian margin complemented by crustal scale gravity modelling is used to reveal and illustrate onshore offshore crustal structure correlation the character of the continent ocean boundary and the relationship of crustal structure to regional variation of potential field anomalies the study reveals distinct along margin structural and magmatic changes that are spatially related to a number of conjugate brazil west africa transfer systems governing the margin segmentation and evolution several conceptual tectonic models are invoked to explain the structural evolution of the different margin segments in a conjugate margin context furthermore the constructed transects the observed and modelled moho relief and the potential field anomalies indicate that the reconcavo tucano and jatoba rift system may reflect a polyphase deformation rifting mode associated with a complex time dependent thermal structure of the lithosphere the constructed transects and available seismic reflection profiles indicate that the northern part of the study area lacks major breakup related magmatic activity suggesting a rifted non volcanic margin affinity in contrast the southern part of the study area is characterized by abrupt crustal thinning and evidence for breakup magmatic activity suggesting that this region evolved partially with a rifted volcanic margin affinity and character

the origin of lithotype cycles in oligo miocene brown coals from australia and germany abstract brown coal colour lithotype cycles range from 10 to 30 m thick in oligo miocene coals of the latrobe valley gippsland basin australia similar colour lithotype cycles occur in the lusatia german miocene brown coals in both the latrobe valley and germany the cycles often display well developed colour lightening upward trends as defined by new colourimetry measurement the typical lithotype cycle boundary is abrupt between light below and dark lithotype above geological geochemical palynological and macrofossil evidence is consistent with a relative drying terrestrialisation upward depositional model for each cycle and the overlying dark lithotype represents renewed peat accretion the dark lithotype may include charcoal near the cycle base explained by the fire prone and highly flammable nature of the herbaceous reed wetlands in both the german and australian coals wetter darker lithotypes are characterized by a gymnosperm paleoflora while drier lighter lithotypes are characterized by angiosperms in the german rhenish miocene brown coal exposed in large open cut mines at garzweiler and hambach a 1 0 m spaced sampling and colourimetry measurement program shows lightening upwards cycles for the morken seam frimmersdorf a seam frimmersdorf b seam and for the garzweiler ii seam at hambach where the 60 m thick main seam includes amalgamations of frimmersdorf a frimmersdorf b and garzweiler i ii iii seams the lightening upwards trends provides a means of stratigraphic subdivision the palaeogeographic setting for latrobe valley and german brown coals is similar in latrobe valley the seams split and thin to the east into marine facies in the rhenish and lusatia brown coals they also split and thin to the north into marine facies the two rhenish mines at hambach and garzweiler respectively typify end members of this palaeogeography the hambach mine is located in a distal location where sulphur content is negligible the garzweiler mine is located in a proximal location to the marine boundary where sulphur content is higher the colourimetry and facies succession suggest german brown coal deposition followed a similar cyclic depositional succession to the latrobe valley and that this succession may be fundamental in all thick coal seams

crustal evolution of the pernambuco alagoas complex borborema province ne brazil nd isotopic data from neoproterozoic granitoids the borborema province in northeast brazil forms the western part of a major 600 ma brasiliano pan african mobile belt that extends from brazil through central africa in a pre drift reconstruction of gondwanaland the pernambuco alagoas peal complex is a large area within the borborema province and consists of high grade migmatitic gneisses and granitic batholiths although the peal complex has previously been called a massif or terrane in reality it comprises many different types of protoliths or plutons the protoliths for many of the migmatitic gneisses are difficult to decipher due to the varied deformation and metamorphism during the cariris velhos and brasiliano orogenies nd isotopic data discriminate two major crustal domains in the peal complex the garanhuns and the agua branca domains rocks of the garanhuns domain have nd tdm in the range of 1 8 to 2 4 ga indicating that most of it is underlain by paleoproterozoic crust and does not include significant mesoproterozoic or neoproterozoic crustal additions the marimbondo correntes batholith is inside the garanhuns domain but includes younger tdm ages similar to those found in the agua branca domain this batholith includes contributions from younger sources and may intrude a block of younger allocthonous crust thrust over the older crust of the garanhuns domain rocks of the agua branca domain show tdm within the range of 0 90 to 2 10 ga with most nd model ages between 1 5 and 1 0 ga the pre brasiliano crust in this domain thus includes substantial amounts of mesoproterozoic to neoproterozoic additions the presence of some older model ages suggests that the aguas belas domain may have some vertical crustal zonation with paleoproterozoic and neoproterozoic crustal segments tectonically interleaved during successive accretional or collisional episodes including the ultimate brasiliano collision at 600 ma the mesoproterozoic nd model ages therefore represent mixing of different crustal and mantle sources rather than a discrete episode of mesoproterozoic crustal formation various metaluminous or peraluminous granitoids of brasiliano age from the buique paulo afonso aguas belas caninde and marimbondo correntes batholiths show tdm ranging from 0 90 ga to 1 10 ga suggesting that they either were wholly derived from juvenile material of the 1 0 ga cariris velhos orogeny or contain substantial contributions of juvenile material from the 0 6 ga brasiliano cycle some high k to shoshonitic granitoids from the aguas belas domain show mesoproterozoic 1 4 ga tdm model ages the model ages recorded in these plutons could suggest either that the magma was derived from enriched lithospheric mantle associated with the cariris velhos orogeny or that it was a mixture between enriched lower crust of transamazonian age and juvenile material from the cariris velhos or brasiliano orogenies

neotectonic reactivation of shear zones and implications for faulting style and geometry in the continental margin of ne brazil abstract the eastern continental margin of south america comprises a series of rift basins developed during the breakup of pangea in the jurassic cretaceous we integrated high resolution aeromagnetic structural and stratigraphic data in order to evaluate the role of reactivation of ductile neoproterozoic shear zones in the deposition and deformation of post rift sedimentary deposits in one of these basins the paraiba basin in northeastern brazil this basin corresponds to the last part of the south american continent to be separated from africa during the pangea breakup sediment deposition in this basin occurred in the albian maastrichtian eocene miocene and in the late quaternary however our investigation concentrates on the miocene quaternary which we consider the neotectonic period because it encompasses the last stress field this consisted of an e w oriented compression and a n s oriented extension the basement of the basin forms a slightly seaward tilted ramp capped by a late cretaceous to quaternary sedimentary cover 100 400 m thick aeromagnetic lineaments mark the major steeply dipping ductile e w to ne striking shear zones in this basement the ductile shear zones mainly reactivated as strike slip normal and oblique slip faults resulting in a series of miocene quaternary depocenters controlled by ne e w and a few nw striking faults faulting produced subsidence and uplift that are largely responsible for the present day morphology of the valleys and tablelands in this margin we conclude that precambrian shear zone reactivation controlled geometry and orientation as well as deformation of sedimentary deposits until the neogene quaternary

the araripe basin in ne brazil an intracontinental graben inverted to a high standing horst abstract the mesozoic sediments of the araripe basin peak at ca 1000 m more than 500 m above the host precambrian basement this means that an intracontinental graben has been inverted to a topographically high standing horst which raises four fundamental questions 1 where are the inversion structures 2 what is the age of the inversion 3 how can inversion occur in a thick lithosphere 4 what forces are responsible for the inversion here we show that displacement on inverted normal faults increases towards the core of the horst and new reverse faults thrust basement over basin field observations indicate that inversion has occurred on faults striking between nne ssw and e w following the structure of the host basement inversion is reverse dextral in the nne ssw system and reverse sinistral in the ene wsw system this is consistent with the mid atlantic ridge and andean pushes from the tectonic analysis of topography and gravity anomaly the nw se faults seem critical to the inversion although not clearly recognized in the field the inversion of high angle normal faults occurred by oblique slip and injection of clay rich breccias which apparently reduced friction sufficiently to allow for major inversion fault scarps with a prominent topographic expression and faults cutting through colluvium indicate that the latest stage of inversion is quaternary although older inversion episodes are likely the new tectonic data the timing and the stress field altogether indicate that inversion was due to plate wide compression which preferentially concentrated along inherited shear zones and reactivated them to form the main inversion faults of the araripe basin the high degree of inversion in the araripe basin is most likely due to its position at a bend in the major patos shear zone which worked as a restraining bend under the maximum compressive stress acting in ne brazil

cyclic sedimentation in tertiary lower rhine basin germany the liegendrucken of the brown coal open cast fortuna mine abstract in the lower rhine basin at the northwestern headlands of the schiefergebirge in western germany the oligocene miocene koln formation once was splendidly exposed in the former fortuna mine one of the open cast mines of the regional brown coal mining industry there a complex 60 m thick clastic marine shoreline succession was studied coastal marine sediments were formed along a high energy coast in the basal sediment fill of the basin due to repeated ingressions of the tertiary north sea a number of subtidal to supratidal coastal onlap cycles developed this study provides first knowledge about cyclic sedimentation in the tertiary of the lower rhine basin

the coal bearing cenozoic as pontes basin northwestern spain geological influence on coal characteristics lignite deposits in the cenozoic as pontes strike slip basin northwestern spain were formed as a function of specific paleoclimatic conditions and tectonic evolution of the basin during the early evolutionary stages the presence of active normal faults and thrusts inside the basin resulted in two subbasins with distinct differences in sedimentary records with respect to lignite seam occurrence thickness area1 extent and lithotype development in contrast during the late evolutionary stages the basin was not split and a more homogeneous sedimentary record in terms of coal seam occurrence and lithotype characteristics developed a total of 26 lignite samples distributed along the basin infill were analyzed by organic petrography and geochemistry all are lignite b astm the lignites deposited during lower basin infill sedimentation units 1 and 2 are dark matrix rich mainly huminitic brown coals with minor bright liptinitic rich coal lithotypes the dark huminitic coals in these units show sedimentological and paleontological evidence of lacustrine influence persistent relatively moderate to low tissue preservation index tpi values and high average gelification index gi values are characteristic of these limno telmatic coals lignites in the upper basin infill unit 4 are almost exclusively matrix rich huminitic brown coals persistent widespread low tpi values and variable but low average gi values are also characteristic of these telmatic coals the overall coal petrological data trend tpi gi and widespread development or absence of liptiniteenriched lignite layers recorded from the lower to the upper basin infill units agrees with the stratigraphic and sedimentological data which show a trend of increasingly drier conditions development of bright liptinite enriched lignite layers was widespread during the early basin evolutionary stages and was influenced by punctuated water table oscillations sedimentological petrological and organic geochemical data point to the conclusion that although the paleoenvironments where peat deposition took place did not undergo dramatic changes they were affected by distinguishable

stress orientations in brazilian sedimentary basins from breakout analysis implications for force models in the south american plate summary regional patterns of crustal stresses in brazil were studied with a detailed breakout analysis performed in 541 wells distributed throughout the country 481 from basins along the continental margin and 60 from intracratonic basins a total of about 591 km of cumulative well length digitally sampled at 0 15 m intervals was analysed most intervals 80 per cent are confined between 400 and 4000 m only wells that deviate less than 10d from the vertical were considered for a given well 1 the mean orientation and the standard deviation of each interval with breakouts were calculated 2 all intervals with mean breakout orientations less than 10d from the orientation of the hole deviation were discarded 3 all intervals with standard deviations less than 12d were selected 4 the selected breakouts were weighted by their interval length to calculate the mean orientation and standard deviation of the whole well and 5 the final results were classified according to the world stress map criteria thus 16 wells were classified as a a total of 7 2 km of breakouts 42 as b 7 1 km 78 as c 7 4 km 205 as d 3 3 km 184 as e 0 7 km and 16 were discarded in most basins the breakout orientations from different wells were usually consistent for qualities a b and c allowing a good estimate of the regional maximum horizontal stress shmax wells classified as quality d showed a large scatter the regional shmax determined from breakouts is generally in good agreement with the available nearby focal mechanisms the main trends of shmax are 1 nw se parallel to the coast along the equatorial marginal basins 2 e w in the alagoas basin 3 nne ssw parallel to the coast in the sergipe and reconcavo basins and 4 nw se in the middle amazon basin in the equatorial and eastern continental margins north of 15ds breakouts and focal mechanism measurements indicate that the shmax orientation is remarkably parallel to the coastline following a 90d bend of the coast in northeastern brazil because the theoretically predicted intraplate stresses in northern brazil trend about wnw to ene e g meijer 1995 coblentz richardson 1996 we interpret our observations as indicating that local sources of stress at the continental margins e g flexural stresses and lateral density contrasts dominate the plate wide stresses and may have been underestimated in theoretical stress models of the south american plate the new stress data 136 a c quality out of a population of 541 wells cover a region of mid plate south america where only 23 data points had been compiled previously in the world stress map database the more detailed observed patterns of the intraplate stress field should be helpful in better constraining future models of the forces driving the south american plate

three dimensional reconstruction of an in situ miocene peat forest from the lower rhine embayment northwestern germany new methods in palaeovegetation analysis palaeovegetation reconstructions particularly of fossil forests are generally restricted to scant information on the taxonomic composition relative abundance of individual taxa or on tree density we have developed new techniques for the analysis of stump horizons that result in a relatively detailed three dimensional reconstruction of ancient forests in addition a rough estimate of their above ground standing biomass can be calculated these techniques are applied to an in situ miocene peat forest preserved in the lower rhine embayment northwestern germany in a study area of 2500 m2 476 stumps were mapped and used in the forest reconstruction additionally pollen samples and leaf remains have been analysed the peat forest consists primarily of conifers in particular taxodiaceae and pinaceae with sciadopitys being the most common genus the only angiosperms in the wood flora were palms but in the pollen flora evidence for the myricaceae mastixiaceae ericaceae and a few other angiosperms is also present the forest was relatively dense with 1904 trees ha and a basal area of 164 m2 mean trunk diameter was 28 cm while mean tree height is calculated to have been 9 9 m height diameter and density distribution are illustrated using contour and three dimensional surface plots estimated above ground biomass is 750 t ha but this value also includes dead or partly dead trees this peat forest does not closely compare with previous reconstructions of miocene peat forests its three dimensional structure and biomass differ from those of modern bald cypress swamps

environmental history of the german lower rhine embayment during the middle miocene as reflected by carbon isotopes in brown coal stable carbon isotope investigations have been carried out on miocene brown coal from the garzweiler seam of the german lower rhine embayment material studied included fossil wood from seven different taxa and brown coal matrix isotope results from macrofossil analysis show variations of more than 6 within individual samples and reveal a general isotopic difference between angiosperm and gymnosperm wood specimens according to mean carbon isotope values found for gymnosperms angiosperms and brown coal matrix 23 3 26 0 and 25 8 the peat forming vegetation of the garzweiler seam was dominated by angiosperm taxa results from brown coal matrix establish a continuous high resolution depth profile of carbon isotope variations during the late middle miocene they show a significant and characteristic isotope pattern with distinct medium and short term cycles high frequency variations in the two main units of garzweiler seam locally split into three units the medium term 13c variations are most likely caused by varying proportions of gymnosperms within the peat forming vegetation while high frequency oscillations seem to be a direct signal of environmental changes a long term decline of carbon isotope values observed within the complete garzweiler seam from base to top is presumably due to a cooling trend in the miocene

dynamic processes controlling evolution of rifted basins abstract the extension of the lithosphere controlling the development of rifted basins is driven by a combination of plate boundary forces frictional forces exerted on the base of the lithosphere by the convecting asthenosphere and deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system although mantle plumes are not a primary driving force of rifting they play an important secondary role by weakening the lithosphere and by controlling the level of rift related volcanic activity a distinction between active and passive rifting is only conditionally justified the extension of the lithosphere depending on its rate and magnitude and the potential temperature of the asthenosphere can cause by adiabatic decompression partial melting of the lower lithosphere and upper asthenosphere in rift systems the level and timing of volcanic activity is highly variable the lack of volcanic activity implies passive rifting an initial passive rifting stage can be followed by a more active one during which magmatism plays an increasingly important role magmatic destabilization of the moho may account for the frequently observed discrepancy between upper and lower crustal extension factors combined with evidence for thermal thinning of the mantle lithosphere this suggest that the volume of the lithosphere is not necessarily preserved during rifting as advocated by conventional stretching models the structural style of rifts is controlled by the rheological structure of the lithosphere the availability of crustal discontinuities that can be tensionally reactivated the mode orthogonal or oblique and amount of extension and the lithological composition of pre and syn rift sediments simple shear extension prevails in rifts that subparallel the structural grain of the basement pure shear extension is typical for rifts cross cutting the basement grain pre existing crustal and mantle lithospheric discontinuities contribute to the localization of rift systems the duration of the rifting stage of extensional basins is highly variable stress field changes can cause abrupt termination of rifting in major rift systems progressive strain concentration on the zone of future crustal separation entails abandonment of lateral rifts depending on constraints on lateral block movements crustal separation can be achieved after as little as 9 my and as much as 280 my of rifting activity syn rift basin subsidence is controlled by isostatic adjustment of the crust to mechanical stretching of the lithosphere its magmatic inflation and thermal attenuation of the mantle lithosphere post rift basin subsidence is governed by thermal reequilibration of the lithosphere asthenosphere system deep seated thermal anomalies related to syn rift pull up of the asthenosphere lithosphere boundary have decayed after 60 my by about 65 and after 180 my by about 95 the magnitude of post rift subsidence is a function of the rift induced thermal anomaly and crustal density changes the potential temperature of the asthenosphere and initial water depths intraplate stresses can have an overprinting effect on post rift subsidence stretching factors derived from post rift subsidence analyses must be corrected for such effects

parameters determining the carbon isotopic composition of coal and fossil wood in the early miocene oberdorf lignite seam styrian basin austria abstract petrographical and geochemical data of gelified and ungelified fossil wood from the early miocene oberdorf lignite seam styrian basin austria provide evidence that the early diagenetic aerobic degradation of wood by fungi may be followed by further decomposition under reducing conditions by the activity of anaerobic bacteria based on the molecular compositions of terpenoid hydrocarbons the wood fragments in the lignite are identified as gymnosperms this result is corroborated by the mean isotopic composition 13c 24 2 of the macrofossils the isotopic difference between fossil wood and extracted cellulose of most samples 3 9 2 5 is higher than in modern trees which can be explained by the smaller effect of 13c discrimination during decomposition of cellulose when compared with wood the mean carbon isotope values found for gymnosperms and coals 24 2 and 24 7 respectively confirm the results from biomarker analyses indicating that the peat forming vegetation of the oberdorf seam was dominated by gymnosperm taxa minor variation in the relative contributions of gymnosperms and angiosperms to coal deposition is of negligible influence on the isotopic composition of the coals cross correlations between 13c of the coals soluble organic matter yield and the proportions of liptinite macerals of higher plant origin imply that the carbon isotopic composition may be affected by the contents of plant lipids because of their 13c values ranging from 5 to 10 less than whole plant tissue values an isotopic shift of the coals towards more negative values due to the activity of prokaryotes i e anaerobic bacteria in organic matter degradation is proposed the results obtained from the early miocene oberdorf lignite indicate that the carbon isotope ratios of the coals are primarily affected by varying contributions of different parts of whole plant tissue due to their different isotopic and molecular compositions e g epicuticular leaf waxes resins wood and their different decay resistance against the early diagenetic changes involved in organic matter decomposition carbon cycling during anoxic decomposition of plant derived organic matter is assumed to affect the 13c values of coal 13c values of wood and extracted cellulose are affected only to a minor extent

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