late cretaceous and cenozoic tectonics of the malay peninsula constrained by thermochronology abstract new thermochronological analyses of granites from the malay peninsula record the region s thermal history during the late mesozoic and cenozoic 40 ar 39 ar and u th sm he analyses are combined with existing fission track data to provide a comprehensive set of temperature and time data fully and partially reset k feldspar and biotite mica 40 ar 39 ar analyses indicate a significant period of thermal perturbation between 100 and 90 ma and a second lesser perturbation between 51 and 43 ma zircon u th sm he analyses and existing fission track data indicate exhumation of the malay peninsula in the cretaceous and renewed localised exhumation in the early paleogene apatite u th sm he and fission track data indicate rapid exhumation of the region in the late eocene and oligocene late cretaceous tectonism is linked to the reversal of a regional dynamic topographic low following the cessation of subduction along the sundaland margin in the late cretaceous causing regional uplift and exhumation and the addition of significant heat into the crust via mantle upwelling early paleogene exhumation may reflect the continuation of cretaceous tectonism or a discrete phase of paleocene exhumation linked to localised transpressional tectonics eocene tectonism is coincident with major subsidence offshore of the malay peninsula interpreted to reflect regional block faulting in response to north south compression driven by the resumption of subduction along the southern margin of sundaland in the eocene

synchronous compressional pulses in extensional basins abstract such paradoxes as synchronous compression and tension in extensional sedimentary basins and synchronous deformation of intractonic basins and eustatic sea level falls can each be related to pulsed changes in curvature of the earth s surface australia is everywhere in a state of significant relatively uniform upper crustal horizontal compression approximately perpendicular to the continental margins and generally directed towards its centre the compression commenced in the pliocene but was absent in the late miocene during the evolution of the gippsland and bass basins under extensional stress from the late jurassic to recent seven pulses of similarly directed compression have been identified from the campanian to recent time equivalent compressional pulses can also be demonstrated in such widely separated areas as northwest and northeast australia northwest europe and central america nine earlier pulses of early triassic to albian age are similarly synchronous global events and another twenty three pulses inferred since the neoproterozoic 800 ma are probably similarly globally synchronous earth expansion with subduction can explain these observations since it causes the surface curvature to decrease resulting in flattening of the semi rigid crust flattening results in lower crustal extension which generates sedimentary basins while contemporaneous upper crustal compression inverts and folds the sediments since globally synchronous compressional pulses may reflect expansion in the ocean basins there is a correlation of such pulses with major eustatic sea level lowstands any site of expansion within the earth is transmitted to the semi rigid crust as a volume increase by the whole gravitating fluid oblate spheroid this results in ubiquitous synchronous compressional pulses in the upper crust detectable on seismic reflection data not only at basin scale but also in individual petroleum producing structures

prospect of hydrocarbon associated with fossil rift structures of the southern indus basin pakistan the southern indus basin 550 x 250 km is characterized by tectonic upwarping on the western margin of the indo pakistan subcontinent several hypotheses have so far been proposed to explain the origin of these crustal features but these basement upwarps remain puzzling aeromagnetic data have been analyzed and interpreted supplemented with seismicity and geological information from the integrated study we inferred basement configuration and developed models for tectonic evolution of these exotic crustal features and their impact on hydrocarbon potential associated with the southern indus basin the southern indus basin is identified as an extension basin resulting from an inferred fossil rift crustal feature overlain by a thick sedimentary sequence extension was a consequence of temporal divergence of the indo pakistan subcontinent from gondwanaland during the early paleozoic based on magnetic anomaly trends the indus basin fossil rift feature is characterized by horst and graben structures together with a system of transcurrent faults the association of seismicity events and basement crustal features suggests that tertiary reactivation of individual segments of the inferred rift structure has deformed overlying sequences of the indus basin and also the surrounding areas particularly the fold and thrust belt of pakistan on the western side of the basin the proposed geological models also illustrate the potential for appropriate environments for development of hydrocarbon source rocks sufficient heat for thermal maturity and structures for reservoirs and seals suggesting more bright prospects in the southern indus basin

sea level changes in a back arc foreland transition the late carboniferous permian karoo basin of south africa abstract the late carboniferous to early permian succession in the karoo basin consists in ascending stratigraphic order of diamictites mudrocks greywackes and immature sandstones the diamictites are interpreted as glacigene deposits laid down by a marine ice sheet on a shelf post glacial suspension settling of predominantly mud occurred on the basin floor during open marine and later brackish conditions basin floor fan deposits accumulated in the foredeep whereas deltaic mud silt and sand finally infilled the basin glacigene sedimentation occurred in a back arc basin during the late carboniferous and early permian the post glacial succession accumulated in a foreland basin in which the rising orogenic belt was the predominant sediment source relative sea levels following the major namurian regression apparently remained low during the extensive gondwana glaciation marine ice sheets are highly sensitive to sea level fluctuations and minor sea level rises probably climatically controlled were recorded as interglacials when parts of the marine ice sheet collapsed final collapse of the marine ice sheet was associated with a major transgression post glacial mudrock deposition was characterised by relatively high sea levels except for the period of basin floor fan deposition when there was a sea level lowstand final infilling of the basin by prograding deltas was accompanied by a major regression the late carboniferous to early permian sea level fluctuations in the karoo basin show correspondence with global eustatic cycles reflecting low tectonic interference with sea level patterns however late permian sea levels were predominantly tectonically controlled as a result of foreland basin evolution possible global eustatic events complemented apparent sea level changes within the basin during this period

the messina layered intrusion limpopo belt south africa an example of in situ contamination of an archean anorthosite complex by continental crust the messina layered intrusion was emplaced prior to 3 0 ga into supracrustal rocks presently comprising the central zone of the limpopo belt analyses of relict cumulate plagioclase megacrysts in the intrusion and its tectonic setting show that it was emplaced as a thick body of batholithic dimensions composed of varying proportions of bytownite an77 and hypersthene the magma giving rise to the intrustion was heterogeneous characterized by positive sr values neutral to negative nd values and high 207pb 204pb ratios relative to 206pb 204pb it also was light ree enriched these characteristics probably originated by the interaction of a magma derived from a depleted mantle source with crustal material similar in composition to the rocks of the enclosing beit bridge group and sand river gneisses as a result most of the characteristics of the intrusion are closer to those of proterozoic massif type anorthosite complexes than to those of archean complexes the messina layered intrustion was metamorphosed and deformed prior to 3 0 ga when its composition was changed to quartz hornblende plagioclase gneisses by the introduction of water pb sr and rb were also added to most of these rocks probably derived from the host rocks but the primary isotopic characteristics of relict plagioclase megacrysts and of partially assimilated xenoliths of metapelite were preserved more recently the intrusion was metamorphosed under granulite facies conditions at 2 0 ga prior to the joining of the rocks of the central zone with the zimbabwe and kaapvaal cratons the emplacement metamorphism and deformation of the intrusion had nothing to do with early evolutionary events on those cratons

the structural setting and deformation associated with pseudotachylite occurrences in the palala shear belt and sand river gneiss northern transvaal abstract two occurrences of shear related pseudotachylite from the limpopo metamorphic province are described in particular the structural setting as well as deformation textures in pseudotachylite inclusions and host rocks are presented for these occurrences in gabbroic anorthosite from the palala shear belt and dioritic to granodioritic rocks from the sand river gneiss locality the palala shear belt is a 13 km wide zone of intensely mylonitized rocks of the beit bridge and bushveld complexes situated at the southern boundary of the central zone of the limpopo metamorphic province the sand river gneiss comprises a bimodal suite of high grade dioritic and granodioritic rocks which were subjected to at least three periods of deformation in the context of comparisons between pseudotachylites from different geological settings i e cryptoexplosion structures meteorite craters and tectonic settings the major results are as follows 1 1 the deformation phenomena associated with pseudotachylite formation as recorded in quartz and feldspar occurring as inclusions or at the host rock contact are undulatory extinction in quartz brecciation mechanical twinning and kinking of plagioclase and characteristic formation of irregular and planar vredefort type fractures the latter occurring in quartz 2 2 frequency distributions of crystallographic orientations of planar fractures and their annealed manifestation planar fluid inclusion trails are very similar for the vredefort structure the sudbury structure the johannesburg dome the witwatersrand basin and the limpopo pseudotachylites it is therefore concluded that planar fractures in quartz are the typical microdeformation associated with pseudotachylite irrespective of the geological setting of the latter planar fractures alone do not provide unambiguous information on the genesis of the structure in which they are found

stratigraphy and reservoir potential of glacial deposits of the itarare group carboniferous permian parana basin brazil drilling in the parana basin of brazil in the mid 1980s discovered gas and condensate in the itarare group and showed that glacial deposits in brazil can contain hydrocarbons the reservoir potential of the carboniferous permian itarare group of the basin is analyzed using new subsurface data from 20 deep wells drilled in the early to middle 1980s central to the analysis was the construction of over 3000 km of cross sections based on more than 100 wells the description of more than 400 m of core and study of 95 thin sections subsurface exploration and mapping of the itarare are greatly aided by the recognition of three recently defined and described formations and four members which are traceable for hundreds of kilometers these units belong to three major glacial cycles in which the pebbly mudstones and shales are seals and glacially related sandstones are reservoirs the best sandstone reservoirs in the deep subsurface belong to the rio segredo member the uppermost sandy unit of the itarare the rio segredo member is the best petroleum target because it is overlain by thick seals and massive pebbly mudstones and shales and because it is shallower and less compacted than underlying more deeply buried sandstones this member has little detrital matrix and much of its porosity is secondary developed by carboxylic acid and co 2 generated when jurassic cretaceous basalts sills and dikes were intruded into the parana basin as gondwana broke up

relating petroleum system and play development to basin evolution west african south atlantic basins abstract sedimentary basins can be classified according to their structural genesis and evolutionary history and the latter can be linked to petroleum system and play development we propose an approach in which we use the established concepts in a new way breaking basins down into their natural basin cycle division then defining the characteristics of each basin cycle including the type of petroleum systems and plays they may contain and comparing them with similar basin cycles in other basins thereby providing a means to learn through a greater population of perhaps not immediately obvious analogues furthermore we introduce the use of the trajectory plot as a new tool in such an analysis this methodology has been applied to the west african south atlantic marginal basins between cameroon and angola and we demonstrate that the similar tectonostratigraphic evolution of the individual basins along this margin has led to the development of similar types of petroleum systems and play level s consequently we can make analogue comparisons among these basins in order to evaluate and predict the presence of potential yet undiscovered hydrocarbon accumulations in less well explored parts of the margin

hydrocarbon plays and global basin classification hydrocarbon plays and the global basin classification system have important connections after a basin has been classified its similarities or differences with other basins may be compared prolific hydrocarbon basins are categorized and the plays are compared to specific tectonic and depositional events some plays are controlled by basin initiating tectonic events such as interior fracture or interior sag and the type of sedimentation inherent in each basin type in more complex polyhistory basins oil and gas plays are commonly associated with combinations of various cycles or by basin modifying tectonics such as episodic wrenching subsidence foldbelts and basin tilt

tectonic evolution of south america during the late proterozoic abstract this paper discusses the evolution and the late proterozoic assembly of the south american continent i e the west gondwana under the light of global tectonics the northern portion of the continent the amazonian craton is a pre brasiliano domain it may be a fragment derived from laurentia this domain behaved as a large continental plate which was accreted to the central and southeastern portions of the continent brasiliano domain the brasiliano domain had a more complex history and composition during the brasiliano cycle middle proterozoic to early paleozoic in the brasiliano domain several late proterozoic continental plates have been identified sao luiz west africa congo kasai sao francisco rio de la plata arequipa antofalla which acted as forelands to the brasiliano orogenic belts that surround and amalgamate these plates smaller fragments of pre brasiliano continental lithosphere are common in the interior of the brasiliano orogenic belts and played diversified roles microplates microcontinents structural highs some of them have acted as true backlands hinterlands flanked by arc magmatism two principal types of brasiliano orogenic belts are recognized between the continental plates a marginal orogenies to the late proterozoic plates with pelitic carbonatic rocks and discrete volcanism which were thrust by collision onto the margin of the plates and which seem to represent final products of previous passive margin sequences b distal orogenics internal belts within the continental masses sometimes a branching system of orogenics that contain varied clastic and minor carbonate sedimentary rocks accompanied by important bimodal volcanism and calc alkaline plutonism for these orogenies a greater variety of basinal scenarios and tectonic settings may be visualized the amalgamation of the continent during the late proterozoic i e the formation of the brasiliano structures indicates the existence of practically synchronous multilateral stresses within lithospheric plates this can be produced by complementary adjustment of the continental plates as a response to major global events elsewhere analogous to modern continental collisions two large and important tectonic zones may be candidates to such a scenario the hijaz mozambique zone site of connection of east and west gondwana and the transbrasiliano lineament which cuts across south america and extends to north africa following the zone of connection between pre brasiliano and brasiliano domains other small ocean openings and closings inside the various brasiliano areas dom feliciano gariep for instance were minor events and complementary to the other two major tectonic zones mentioned above

basin superposition on the northern margin of the south china sea abstract basin superposition on the northern margin of the south china sea is a product of pulsed basin development with geometries which changed through space and time of changing strain fields and of tectonically inherited pre existing zones of crustal weakness this region of the south china sea was welded together or assembled prior to the cretaceous three distinct episodes of continental disassembly and accompanying basin evolution ensued each episode commencing with rifting and the formation of grabens or half grabens and each terminating with a gentle subsidence phase the major trends of the faults and basins varied from predominantly ne for the first episode through ne ew for the second to ew nw for the third the first episode occurred during the late cretaceous to paleocene as a back arc extensional domain induced by the dip steepening of a subducted oceanic slab the second basin episode of the late eocene to early oligocene was initiated by the collision of the indian plate with the eurasian plate the continued penetration of the former into the latter led to the tectonic escape and subsequent clockwise rotation of the indochina block creating regional transtension and left lateral motion along the red river fault the third episode of basin development occurred during the middle miocene as a reactivated product of this collision owing to the clockwise rotation of indochina the approximately e w trend of the simple shear principal displacement zone changed to northwest by the pliocene the eastward extrusion of south china had exceeded that of indochina reversing the sense of red river fault displacement to right lateral a clockwise rotation of the red river geosuture together with considerations of the influence of zones of inherited crustal weakness provides a model for the observed episodic changes in regional strain such a model best explains the post cretaceous evolution of superimposed basins on the northern margin of the south china sea

geodynamic mechanism and classification of basins in the earth system abstract the sedimentary basin is a basic geological unit in the earth system its formation and evolution are controlled mainly by plate tectonics and geodynamics which have produced a variety of basin types the development and evolution of various basins depend not only on the tectonic effect of lithospheric plate but also on sublithospheric and earth surface actions basin classification schemes based on the theories of platform geosyncline or plate tectonics could neither include all basin types nor reflect the complex processes of basin formation and evolution from the viewpoint of earth system we proposed a new basin classification scheme based on geodynamic mechanism that is lithospheric plate sublithospheric and earth surface actions in our geodynamic classification we employed a series of geodynamic settings of basin formation and evolution including the lithospheric plate sublithospheric and earth surface environments the dynamic regimes of basin formation and evolution such as tectonic setting extension compression and shearing the thermal processes and gravity effects the various natures of basin basement and crustal types continental oceanic or transitional crust and the history of basin sedimentary filling and tectonic paleogeography successively as the controlling factors for basin classification this new geodynamic classification scheme highlights both the role of the lithosphere and the effects of the sublithospheric and the earth surface actions on controlling the basin formation and evolution the basic dynamic types of basin classification include the prototype basin forming under a single tectonic thermal or gravity regime and the superimposed basin as well as residual basin forming under multistage thermal and or tectonic regimes thus this classification scheme could provide an evolving understanding of lithosphere crust mantle interaction and geodynamic processes as well as of hydrocarbon accumulation and metallogenic mechanisms in sedimentary basins and would help in the synthetic exploration of various resources

lithospheric structures and possible processes in phanerozoic eastern australia from deep seismic investigations abstract the eromanga basin in eastern australia developed during four major episodes on the rifted eastern margin of the australian precambrian craton seismic reflection profiling together with coincident wide angle reflection refraction profiling indicates structures and compositions in the crust which are dominant in various depth ranges some structural features seem to be limited to the upper crust other deep reflection events and high crustal velocities predominate in the lower crust with mafic intrusion from upper mantle sources being one preferred interpretation these features emphasize the difference in structures and composition between the upper and lower parts of the crust yet other structural and deep reflection features are interpreted as being truly lithospheric in scale because they seem to have seismic expression right from the surface to the upper mantle similar interpretations are made for other continental regions indicating that lithospheric processes affect different depth ranges of the crust and upper mantle in a variety of ways any modelling of such processes in the lithosphere must lead to these quite different end results at appropriate depth ranges

the structural framework of the southern margin of the limpopo belt south africa abstract the southern marginal zone is characterized by two prominent regional structural features i massive crustal wedges 20 km 50 km containing large oval shaped closed fold structures which are related to an early d 1 phase of deformation and which are bounded by ii major ductile shear zones that strike in a general e w direction the hout river shear zone forms the southern boundary of the southern marginal zone where granulites are juxtaposed against lower grade granite greenstones of the kaapvaal craton this fault system also acted as the sole thrust for the other high grade shear zones in the southern marginal zone and played a major role in the development of the zone of retrogression and the establishment of the orthoamphibole isograd in the southern marginal zone the hout river shear zone and related faults within the southern marginal zone clearly post date d 1 and a period of peak metamorphism m 1 they are composite structures showing dominantly reverse sense displacements and are responsible for the emplacement of the granulite terrane over and onto the kaapvaal craton in contrast to these older structures are the reactivated shear zones these structures clearly cross cut and displace the high grade shear zones in the southern marginal zone as well as the retrograde orthoamphibole isograd the fact that the hout river and related shear zones are in metamorphic equilibrium with the surrounding wall rocks suggests their age is that of the metamorphism i e 2670 ma barton and van reenen 1992

extensional model for the subsidence of the northern united states atlantic continental margin the simple extensional model for the subsidence of the northern united states atlantic continental margin attributes subsidence which results in sedimentary basin formation to extension and thinning of continental lithosphere the model is used to predict the tectonic subsidence histories that would be associated with various amounts of extension actual tectonic subsidence history curves are calculated from data collected in the continental offshore stratigraphic test cost wells b 2 b 3 g 1 and g 2 and are found to be consistent with the predictions

global geologic history and distribution of hydrocarbon reserves a review of global geologic history during seven major periods between the cambrian and the holocene reveals the principal factors influencing the distribution of world hydrocarbon reserves the paleozoic reserves located mainly in north america and europe are mostly related to stable platform environments the mesozoic and tertiary reserves are found in more diverse tectonic environments represented mainly by the mesogean tethyan realm passive margins and the western american mobile belts the mesogea tethys formed a latitudinal feature separating gondwana and laurasia the mesogean realm contains 69 of the world oil and gas reserves divided almost equally between the gondwana and laurasia areas the voluminous reserves in the mesogean realm reflect the history of repeated opening and closing of the mesogea ocean that resulted in several phases of basin development the comparative isolation of the basins from the global ocean circulation favored preservation f organic matter because of diagenesis the thermal history and migration the ultimate hydrocarbon reserves generally decrease as the ages of the reservoir and source rocks increase migration is usually directed toward the higher parts of the stratigraphic section concentrations of reserves within particular age ranges apparently reflect development of two major categories of basins 1 marine platform basins which were dominant in the devonian jurassic and cretaceous periods and 2 rapidly subsiding basins which were dominant in the late tertiary and probably during the late carboniferous pennsylvanian the middle east has an exceptional volume of sediments prolific source rocks and well preserved hydrocarbons and it is not likely that another hydrocarbon province of comparable importance will be found moreover these middle east reserves do not give any anomalous weight to the total reserves of the gondwanian areas when compared to those in the laurasian areas

a model for the formation of intracratonic sag basins summary intracratonic sag sedimentary basins occur in the middle of stable continental or cratonic blocks they are rarely fault bounded although strike slip faulting can occur within them a simple model for the development and evolution of these basins is proposed the mechanism is driven by mildly coupled convective down welling of the asthensophere beneath the lithosphere initially a rapid alteration of the mantle convective system causes a descending plume to develop a depression which can be of the order of 600 m can be formed at the earth s surface this depression when loaded with sediment will form a sedimentary basin of the order of 2 5 km thick if the convective downwelling remains a period of thermal cooling of the lithosphere occurs which is similar to the thermal cooling subsidence phase of passive continental margins this thermal cooling occurs because of the thermal anomaly temperature decrease beneath the lithosphere caused by the convective downwelling if a change of convective pattern occurs and the descending plume is removed the basin will undergo uplift and erosion whereby a significant thickness of the sedimentary basin can be removed the ordovician and silurian tectonic development of the canning basin western australia appears to be well explained by this model

current aspects of basin analysis abstract current research in basin analysis focuses on interdisciplinary integration of geodynamics mathematical and physical modelling and sedimentary geology these efforts are organized into a research framework emphasizing basin formation nature of the basin fill maturation diagenesis of the basin fill and timing of events research in geodynamics permits development of a proposed classification of sedimentary basins in which basin types are discriminated according to nature of the plate margin basin position on or within a tectonic plate nature of the crust and geodynamic models or known process of formation a summary of current research developments on sedimentary basin fills focuses on the interdisciplinary solutions developed to understanding carbonate distribution through time origin of black shales sea level history and global sedimentary cycles maturation of basin fills requires an understanding of both thermodynamic aspects of mineral phase changes and changing character of the chemistry of flow of water through porous sediments during basin evolution summary case histories from the illinois basin and the appalachian basin illustrate these approaches

pangea extravagant sedimentary resource formation during supercontinent configuration an overview abstract the pangea supercontinent stage the interval from the late carboniferous to earliest jurassic is known for its rich and diverse economic resources from sedimentary systems their uniqueness is not the abundance but the resource association on a global scale and even more the time space distributions the evolution of the supercontinent configuration in context of icehouse to coldhouse stages generated maximum coal evaporite and phosphate deposition furthermore important hydrocarbon uranium and sedimentary metal deposits sedimentary fe and al deposits are very rare also typical is the absence of resources from organic deposition during the early triassic the extravagant spatial distribution of these resource systems but also the timing of their occurrences is linked to the tectonic evolution of pangea during accretion zenith amalgamation and breakup as well as to the resulting paleogeographic climatic oceanographic and ecological reorganization of the biosphere the published data on pangean resources are reviewed and reveal a conspicuous pangean pattern these time space relationships are explained in the context of paleotectonic and ecological changes during the supercontinent stage

geochemical and organic petrological study of bituminous sediments from dahomey basin sw nigeria abstract the dahomey basin sw nigeria hosts a 3000 m thick sedimentary succession of cretaceous and cenozoic age of which the turonian maastrichtian afowo formation includes sandstones arkoses shales shelly limestones unconsolidated sand clay and most importantly bituminous tar sand strata eighteen samples were picked up from outcrops exposed by streams and channels and were examined applying sedimentological mineralogical petrographical geochemical inorganic and organic and radiological techniques with the aim of assessing the origin and the thermal maturity of the organic facies the samples represent mostly coarse grained sands and subordinately shales referred usually as tar sands they consist of mainly quartz and kaolinite with variable amounts of mixed clay layers of illite montmorillonite mica and pyrite probably derived from weathering of the migmatite gneiss complex exposed to the north of the basin this can also explain the relative enrichment in the natural radionuclides 40k 238u 226ra and 232th for some samples although the radioactivity falls within the range for world values for soils the clastic material of afowo formation was deposited in a rather oxic shallow marine environment the particulate organic matter of the bituminous sediments comprises solid hydrocarbons coalified huminite and partially oxidized inertinite remnants of terrestrial plants and minor amounts of both terrestrial and marine liptinite macerals the random reflectance values of the indigenous huminite population ranges between 0 40 and 0 45 pointing to an immature stage for oil generation the respective reflectance of the migrabitumens ranges from 0 49 to 0 59 corresponding to vitrinite equivalent reflectance values of 0 70 0 76 falling well within the oil window this study concludes that the hydrocarbons contained in the afowo formation are upwards migrating from parts of the basin where afowo formation has subsided at depths corresponding well within the oil window the source rock corresponds to the middle shale horizon whereas the sandy horizons act as migration paths and or reservoirs

comparing the spatial structure of variability in two datasets against each other on the basis of eof modes in analysis of climate variability or change it is often of interest how the spatial structure in modes of variability in two datasets differ from each other e g between past and future climate or between models and observations often such analysis is based on empirical orthogonal function eof analysis or other simple indices of large scale spatial structures the present analysis lays out a concept on how two datasets of multivariate climate variability can be compared against each other on basis of eof analysis and how the differences in the multivariate spatial structure between the two datasets can be quantified in terms of explained variance in the leading spatial patterns it is also illustrated how the patterns of largest differences between the two datasets can be defined and interpreted we illustrate this method on the basis of several well defined artificial examples and by comparing our approach with examples of climate change studies from the literature these literature examples include analysis of changes in the modes of variability under climate change for the sea level pressure slp of the north atlantic and europe the slp of the southern hemisphere the surface temperature of the northern hemisphere the sea surface temperature of the north pacific and for precipitation in the tropical indo pacific

main stages of the development of the sedimentary basins of south america and their relationship with the tectonics of supercontinents abstract twelve main stages of sedimentary basins of the south american platform have been identified as follows one neoarchean seven proterozoic and four phanerozoic basin forming tectonics are related to the accretion fusion and fission of the major continental landmasses of the earth s history such as atlantica nena rodinia gondwana pannotia and pangea the first proposed stage of basin development precedes the formation of these major landmasses and was developed on mesoarchean microcontinents the last stage succeeds the fission of pangea and is still in progress

tracing tectonic deformation using the sedimentary record an overview tectonic activity on a range of scales is a fundamental control on sedimentary activity the range of structural deformation within a region extends from the plate tectonic scale governing for example rift initiation to the basin scale with the formation of basin bounding faults internal basin configuration is also strongly influenced by tectonic activity however the relationship between tectonic activity and sedimentation is a complex one given the many additional factors which can also influence sedimentary activity including erosion sediment transport source area lithology groundwater chemistry range of depositional environments climate eustasy and the relative location of an area and its distality to marine influences in this paper we provide a selective overview of the issues associated with the interlinked themes of tectonics and sedimentation examining the main basin types forming in both extensional and compressional plate settings we then review the various models of sedimentation in the selected basins both on a local and a basinal scale finally we look to the future providing a series of possible research areas almost exclusively multidisciplinary which would help to improve existing models of interlinked sediment tectonics systems

rapid late quaternary denudation of the karacasu graben in response to subsidence in the buyuk menderes corridor insights from morphotectonics and archaeogeology abstract the timing and geomorphological consequences of high angle normal faulting in the buyuk menderes graben w anatolia is an essential yet poorly studied issue that has been evaluated mostly regarding detachment faulting in the central menderes core complex however this subject has direct concerns related to ongoing debates regarding the level of seismic risk and the response of surface process to active tectonics in the most rapidly extending region in the world to approach this problem an integrated scheme was followed that involves the study of late quaternary stratigraphy terraces and ancient and modern civic structures in the karacasu graben located on the southern uplifted block of the buyuk menderes graben our stratigraphic observations coupled with the existing micro mammalian fossils demonstrate the widespread occurrence of terrestrial coarse red clastics karacasu formation before the appearance of the narrow faulted corridor the onset of high angle normal faulting started with gradual denudation through the axial dandalas creek and its confluences southward while alluvial sedimentation remained active in the more southern areas of the karacasu graben ages from surface dating techniques mainly osl and cosmogenic radionuclides show that previous knickpoints determined by the incision accumulation threshold reached the vicinity of the antique greek city of aphrodisias 30 km from the buyuk menderes valley with a headward erosion rate of 75mky 1 by the end of last glacial maximum lgm incision rates derived from terraces and roman aqueducts in the middle and upper reaches of the basin increased from 1 mmy 1 background average geological rate for the last 65 ka to 3 mmy 1in the last 2 3 ka presumably due to increased population pressure in and around the vicinity of the city of aphrodisias at the centre of the graben modern civic structures such as aqueducts and bridges constructed after the 1970 s demonstrate the second wave of incision increased to as much as 10 mmy 1 likely due to increasing human pressure and the mechanisation of farming on the other hand inverse extrapolation of the knickpoint progression rate yields a surprisingly younger age of 400 ka for the birth of the new narrow tectonic corridor this morphotectonic transformation exposed large depositional areas such as karacasu and bozdogan grabens to erosion and should have resulted in a significant increase in the sediment supply to buyuk menderes river however seismic investigations in the aegean sea have yet to identify the sedimentary record of this tectonic transformation

regional geological setting of the limpopo belt abstract the 2 7 ga limpopo belt granulite terrane is situated between two lower grade granite greenstone cratons the kaapvaal craton in the south and the zimbabwe craton in the north this granulite facies terrane is subdivided into three zones each with a distinctive geological signature and separated from each other and from the adjacent cratons by well defined shear zones 1 the southern marginal zone composed of granite greenstone material very similar to that of the kaapvaal craton has retrogressed granulites on its southern margin in the hanging wall of the northward dipping terrane boundary hout river shear zone separating the granulite terrane from the adjacent kaapvaal craton 2 the northern marginal zone a granite greenstone terrane at granulite grade which is separated from the zimbabwe craton by a southward dipping terrane boundary and 3 the central zone a unique crustal element with distinctive carbonate platform lithologies and a metagabbroic layered complex which intruded before or at 3250 ma this zone cannot be related to the kaapvaal craton or to the zimbabwe craton it is separated from the two marginal zones by mylonitic shear zones with horizontal stretching lineations the entire limpopo belt is characterized by a distinctive deformational and metamorphic style which contrasts markedly from that of the adjacent granite greenstone terranes of the kaapvaal and zimbabwe cratons this distinctive pattern developed during the limpopo orogeny probably as a consequence of continental collision during the late archaean

unraveling the record of successive high grade events in the central zone of the limpopo belt using pb single phase dating of metamorphic minerals abstract dating of relic metamorphic assemblages can provide important information about the timing and character metamorphic grade and or pt evolution of early high grade episodes in polymetamorphic provinces using pb stepwise leaching of metamorphic silicates we have dated multiple granulite facies metamorphic episodes in the central zone cz of the limpopo belt ages of 2 52 ga were obtained from sillimanite and cogenetic garnet and ages of about 2 01 ga from titanite garnet and clinopyroxene together with new and published conventional age data from accessory phases and in the context of combined petrological and structural data these results lead us to a reinterpretation of the tectono metamorphic history of the cz three distinct high grade events at about 3 2 3 1 ga 2 65 2 52 ga and 2 0 0 05 ga are recognized each of these is suggested to correspond to a tectonic episode of distinct character a for the 3 2 ga event magmatic activity can mainly be identified best represented for example by the sand river gneisses or the messina layered intrusion the field relationships concerning the tectonometamorphic history of this early archean event are largely erased by at least two high grade metamorphic overprints b late archean 2 6 2 52 ga low pressure granulite facies metamorphism was associated with voluminous granitic and charnockitic plutonism the anticlockwise p t evolution of these granulites probably reflects deep crustal processes associated with magmatic underplating or in plating contemporaneous with vertical crustal growth of the zimbabwe craton around 2 6 ga c during the proterozoic event 2 05 1 95 ga tectonic thickening was caused by the collision of the kaapvaal and zimbabwe cratons the cz was squeezed between these two cratons and as a consequence underwent high pressure granulite facies metamorphism with a clockwise p t evolution the structural metamorphic and geochronological data can be best explained with a tectonic model that describes this final event as a dextral transpressive orogeny

mechanism of formation of hydrocarbon basins the west siberia volga urals timan pechora basins and the permian basin of texas abstract many authors suggest that a large role in the formation of hydrocarbon basins is played by stretching or thrust loading our previous analysis artyushkov and baer 1983 1984a b 1986 has revealed a large number of deep basins on continental crust in fold belts that were formed by rapid subsidence without significant stretching or thrust loading this paper shows that the hydrocarbon basins of west siberia volga urals timan pechora and the permian basin in texas pertain to the same basin type water loaded basins 0 3 0 5 km deep were produced in these regions by rapid subsidence in 1 ma shallow water and deeper water strata cover the same area in the basins which precludes significant stretching during the subsidence there was no folding in the adjacent regions ai the epochs of the subsidence which precludes thrust loading a short duration of the subsidence precludes a significant role of thermal relaxation rapid subsidence was commonly preceded by slight crustal uplift in the volga urals and timan pechora it was also preceded by slight volcanism we suggest destruction of the lower crust under asthenospheric upwelling to the base of the crust as a cause of rapid subsidence the asthenospheric upwelling strongly increases the heat flow which ensures hydrocarbon maturation at shallow depth activization of local tectonic movements from crustal heating occurs after rapid subsidence which produces numerous traps for hydrocarbons deposition of highly organic rocks good source rocks and the formation of reefs and or clinoforms good reservoirs commonly occur after rapid subsidence deposition of shales and evaporites good seals takes place in deeper water basins formed by rapid subsidence diapirism of the latter rocks produces additional hydrocarbon traps the combination of all the above effects associated with rapid subsidence produces very favourable conditions for the generation and preservation of hydrocarbons almost all large hydrocarbon fields in the basins considered are located in regions of rapid subsidence there are no large fields in the adjacent sedimentary basins formed by slow subsidence although the sediment thickness is commonly high

the significance of 3000 ma granulite facies mafic dikes in the central zone of the limpopo belt southern africa abstract structural petrographic and chemical relationships indicate that a suite of mafic dikes possibly 3000 ma old were emplaced at high crustal levels deformed and metamorphosed epicontinental supracrustal rocks of the central zone of the limpopo belt these dikes were subsequently metamorphosed at granulite grade conditions probably during the limpopo orogeny about 2700 ma ago the earlier metamorphism was under conditions of at least amphibolite grade and isotopic data suggest that it may have occurred between about 3200 ma and 3100 ma ago these relationships indicate that the rocks comprising the central zone did not follow a single p t time loop but instead were involved in two distinct orogenies the orogenies were separated by a period of crustal stability during which the supracrustal rocks presently and originally exposed at the surface were again moved near to the surface this tectonic history also implies that the supracrustal rocks of the central zone and the sand river gneisses are of great antiquity if the sand river gneisses with their unique suite of older mafic dikes form a previously deformed basement to the supracrustal rocks then the sand river gneisses have been involved in three orogenies pb isotopic data indicate that the mafic dikes were derived from a mantle source with a high average ratio at some stage in its evolution prior to 3200 ma all archean lithologic units within the central zone of the limpopo belt are characterized by having been derived from rocks that had a large mu ratio at some time in their history and this relationship suggests that a link existed between the crustal rocks of the central zone and this mantle source from at least 3200 ma ago until it was destroyed by or after the limpopo orogeny the tectonic history of the central zone is different from those of the lithologies forming the adjacent terranes and suggests that it evolved separately from these terranes until they were juxtaposed during the limpopo orogeny

deep crystal response to continental collision the limpopo belt of southern africa the limpopo belt is an example of an archean 2700 ma continental collisional zone in which the thickened crust 70 km has virtually attained equilibrium with the adjacent non thickened plates by a process of upward movement and lateral spreading of the underthrust high grade metamorphosed plates

the tectonic evolution of the north celtic sea and cardigan bay basins with special reference to basin inversion abstract the morphology and structural evolution of the north celtic sea basin ncsb and cardigan bay basin cbb are in large part controlled by reactivation of basement features of caledonian and possibly variscan origin from earliest triassic until maastrichtian times sedimentation was almost continuous initially in a rapidly subsiding rift system and finally in a progressive passive sag phase at the onset of the alpine orogeny both basins experienced spectacular inversion along readily identifiable axes the inversion takes the form of a compressive reactivation and reversal of the pre existing growth faults and a broad regional upwarping of the cretaceous depocentre the amount of inversion varies depending on the location within the basin but values in excess of 1000 m are possible by utilising regional seismic data the timing of inversion can be estimated as occurring between maastrichtian and eocene times which correlates with the so called laramide pulse of the alpine orogeny

comparative study of the eastern iberides spain and the western pyrenees france mesozoic basins abstract three main periods characterize the geodynamic evolution of the mesozoic basins located in the eastern iberides and the western pyrenees 1 1 from triassic to albian times the breakup of the hercynian basement led to the general formation of different sized half grabens the regional distensional stress which generated such basins was oriented northwest southeast triassic and jurassic then northeast southwest early cretaceous with a high activity in the early triassic the early lias the kimmeridgian the barremian and the late aptian during the early cretaceous period extensional tectonics induced block tilting as well as halokinetic movements of the triassic evaporites 2 2 the albian period put an end to this common evolution the rifting movements lessened considerably in the eastern iberian basin where continental to coastal sandstones were deposited whereas they accelerated in the west pyrenean basin leading to flysch accumulations related to the openning of the bay of biscay 3 3 the late cretaceous was characterized by the same opposed evolution of a shallow carbonate platform in the eastern iberides and a deep terrigenous flysch basin in the western pyrenees during mesozoic times both on the platforms and in the basins the depositional sequence organisation was closely linked to eustatic sealevel changes nevertheless the local extensional process generated important modifications in thickness particularly within the lower triassic the liassic the kimmerdigian and the aptian series as well as within the pyrenean middle and upper cretaceous deposits the structural framework of both eastern iberian and western pyrenean areas was induced by the deformation of the iberian plate related to relative sinistral movements of africa with respect to europe the later structural evolution tertiary tectogenesis was strongly influenced by the inherited mesozoic framework both in the eastern iberides where the extensional structures are preserved and in the western pyrenees where the important compressional stress led to generalized reversal tectonics

origin of thick first cycle quartz arenite successions evidence from the 1 7 ga ortega group northern new mexico abstract the 1700 ma old ortega group in northern new mexico represents a 1000 m thick succession of metamorphosed quartz arenites and subordinate pelites published ages of detrital zircon grains from the ortega group indicate that the sediments were derived mainly from 1760 1700 ma old volcano plutonic basement rocks and not from the archean wyoming province to the north evidence for recycling within the ortega group also is lacking consequently the ortega group quartz arenites are considered to be first cycle sediments the compositional and textural maturity of these sandstones is attributed to intense chemical and mechanical weathering abnormally high al contents of pelites within the ortega group imply intense chemical weathering in the provenance similar to present day low relief tropical regions quartz arenites in the ortega group were deposited exclusively within a shallow marine shelf environment influenced by tide storm and wave processes prolonged sediment transport especially on the tide dominated inner shelf in conjunction with inferred gradual subsidence optimized mechanical destruction of labile grains and rounding of quartz grains although the maturity of sediments in the ortega group can be accounted for the mode of origin of 850 m of quartz arenites remains enigmatic thick quartz arenite sequences of global distribution in the phanerozoic coincide with first order eustatic sea level rises world wide occurrences of 1700 ma old thick quartz arenite shelf successions suggest that the ortega group may have accumulated in response to a similar major eustatic sea level rise

identification of wrench faults using subsurface structural data criteria and pitfalls 1 many structures imaged with reflection seismic can resemble a wrench fault system because of the great structural diversity of strike slip faults and the wide range of contractional and extensional features associated with these faults because of these resemblances numerous faults are misidentified as wrench faults by workers using subsurface structural data credible identification requires combinations of profile and map criteria 1 narrow long straight throughgoing solitary master fault or zone of deformation 2 steep to moderate dip of the master fault at depth 3 offset of the top of basement 4 changes in relative upthrown side separation sense and or fault dip direction at depth or along the strike of the master fault 5 narrow fault slices within the master fault zone that steepen and join at depth negative and positive flower structures 6 different separation sense and orientation of relative upthrown side at these fault slices and 7 coeval en echelon flanking structures the identification should be confirmed with other criteria that refute alternative interpretations the main pitfalls to a reliable identification are not considering alternative structural styles and the misinterpretation of features or patterns that superficially resemble wrench systems the profile geometries of basement involved reverse or normal faults particularly those with structural inversion can resemble the single strand of convergent or divergent wrench faults profile geometries of flower structures can be mimicked by narrow contractional horsts or narrow extensional grabens complexly faulted anticlines or synclines splay faults fault zones intruded by salt or shale and overprinted structures pitfalls in interpreting map relationships are possible when structural patterns combine several tectonic influences are controlled by rock anisotropy or include elements hat are not coeval and if the patterns characteristic of other styles are misinterpreted many erroneous identifications of wrench faults can be eliminated by demonstrating that the investigated fault or feature lacks a straight trace lateral length or throughgoing continuity

the triangle shearzone zimbabwe revisited new data document an important event at 2 0 ga in the limpopo belt abstract the limpopo belt in southern africa has been used to demonstrate that modern style continent continent collision operated during the late archaean 2 6 2 7 ga we have studied the age and pt conditions of strike slip tectonism along the important right lateral triangle shearzone our results substantiate existing proterozoic metamorphic mineral age data of prior uncertain significance using the pb pb and sm nd garnet chronometers and the ar ar step heating technique for amphibole we have dated pre and syn tectonic metamorphic minerals at 2 2 and 2 0 ga thus the triangle shearzone can now be regarded as an important proterozoic suture examination of corresponding high grade pt conditions reaching 800 c at 9 kbar indicates a clockwise metamorphic evolution with pronounced isothermal uplift although the evidence that thrusting of the marginal zones of the limpopo belt over the adjoining cratons occurred during the late archaean clearly remains it is now very uncertain to which event the various pt paths obtained in the limpopo belt may be assigned therefore the question of whether the 2 6 2 7 ga tectonism fits on its own a modern style continental collision model remains open and has to be reassessed

development of the late proterozoic to mid paleozoic intracratonic amadeus basin in central australia a key to understanding tectonic forces in plate interiors the intracratonic amadeus basin in central australia is a complex composite basin covering 17 000 km with at least nine distinct episodes of evolution between 900 and 300 ma these have been identified in neighboring central australian basins and are characterized by intervals of renewed subsidence followed by intervals of erosion and changes in basin shape several unconformities separating the tectonostratigraphic sequences represent periods of mild regional uplifts and correlate with major episodes of compressive tectonism at the evolving margin of the early australian plate in the absence of direct geological evidence for thermal events in the amadeus basin after the initial period of subsidence ended possibly at about 800 ma the correlations found between events in the amadeus basin those in the neighboring interconnected basins and tectonic events at the continental or plate margins emphasize that regional horizontal stress fields contribute significantly to primary basin forming mechanisms this suggests that stresses generated at continental or plate margins may propagate to the plate interior with the lithosphere acting as a stress guide throughout the history of the amadeus basin both periods when compressional stresses were dominant and when extensional tectonics controlled subsidence can be identified there were also transitional periods when neither compression nor extension dominated so that other processes masked the effects of weak horizontal stresses the most recent compressional thrust belt concentrated at the northern margin between 300 and 400 ma and has partly obscured the record of earlier basin shape and size

classification of rifted sedimentary basins of the pannonian basin system according to the structural genesis evolutionary history and hydrocarbon maturation zones abstract we apply the concept that sedimentary basins can be classified according to their structural genesis and evolutionary history to the tertiary rifts of the pannonian basin of eastern europe we have approached the classification by breaking the basins down into the cycles or stages that they comprise this approach helps us to understand the basin evolution better and allows us to compare the basins more easily the drivers that define the cycles of basin history are 1 basin forming tectonics 2 sedimentary processes and 3 basin modifying tectonics we link common elements of petroleum systems and plays to these natural cycles or stages in basin evolution to improve the prediction of which plays could be expected to occur in a particular basin or region this concept is constructed through several steps these steps are 1 to identify standard evolutionary patterns related to geodynamic drivers 2 to group the basins with similar tectono stratigraphic evolution and correlate these with petroleum system development 3 to relate basin trap types to basin history and 4 to calculate characteristic hydrocarbon maturation zones by thermal modeling we present an application to the pannonian basin system of eastern europe an area formed by miocene back arc extension and affected by compressional reactivation during its late stage evolution the sub basins of the pannonian basin system appear to have experienced comparable magnitudes of deformation to have developed similar trap types and to have experienced a characteristic hydrocarbon maturation history in a way that supports play prospectivity

genetic classification of petroleum systems our genetic classification of petroleum systems is founded on a simple working nomenclature that consists of combining qualifiers from each of the following three categories 1 charge factor supercharged normally charged or undercharged 2 migration drainage style vertically drained or laterally drained and 3 entrapment style high impedance or low impedance the charge factor is estimated on the basis of the richness and volumetrics of mature source rocks the source potential index spi which combines source rock richness and thickness into a single parameter is a convenient shortcut for comparing the petroleum potential of diverse source rocks containing dissimilar kerogen types and for rapidly estimating regional charging capacity in extensively explored basins a positive correlation exists between the magnitude of spi and basin wide petroleum reserves the migration drainage style is determined from the structural and stratigraphic framework of a basin vertical migration drainage which occurs mainly through faults and fracture systems breaching a seal is characteristic of petroleum systems contained within rift basins deltaic sequences salt dome provinces wrench basins and fold and thrust belts in contrast lateral migration drainage is dominant wherever stratigraphically continuous seal reservoir doublets extend over a very large area in a tectonically stable province e g commonly foreland or intracratonic platform basins recognition of the dominant migration style helps to predict the location of zones of petroleum occurrence in relation to the hydrocarbon kitchens the entrapment style which is also dependent on the structural framework and the presence and effectiveness of seals describes the degree of resistance i e impedance working against dispersion of the petroleum charge application of these working concepts should help to significantly reduce geologic risk particularly in new ventures type exploration

episodic rifting and subsidence in the south china sea the south china sea experienced at least three stages of rifting and two intervening stages of sea floor spreading since the early cretaceous its evolution can be described by an episodic model of tectonism one of thermal cooling and subsidence pulsed by temporally and spatially confined heating events analysis of regional geologic and geophysical data suggests episodes of rifting and associated thermal activities initiated during the late cretaceous the late eocene and the late early miocene the rift system corresponding to the first episode trends northeast southwest whereas those of the second and third trend east west these two trends coincide with the orientations of the major tectonic lineations within the basin age estimates from heat flow and bathymetric data suggest the oceanic crust in the southwest subbasin is considerably older 55 ma than that in the northwest 35 36 ma or east 32 ma subbasins the episodic tectonic model is supported by basin subsidence analysis subsidence especially subsidence rate curves derived from the regional well data demonstrates that unlike a classic atlantic passive margin thermal subsidence in the south china sea was punctuated by rapid subsidence events which are chronologically consistent with the rifting episodes in terms of hydrocarbon potential the episodes of rifting and drifting would be conducive to the development of overprinted structures and the deposition of several discrete transgressive packages of source rocks and reservoirs separated by widespread unconformities the thermal maturity of sedimentary organic matter affected by episodic rifting and subsidence may be greater than expected on a purely passive margin of equivalent age that had not experienced repeated heating

himalayan tibetan analogies for the evolution of the zimbabwe craton and limpopo belt abstract the limpopo orogeny which lasted from 2700 to 2600 ma was characterised by nnw sse directed shortening this resulted in both crustal thickening accommodated by folding and nnw directed thrusting and associated crustal extrusion whereby a number of crustal blocks including the central zone of the limpopo belt was displaced to the west southwest along wsw ene trending shear zones this was part of a regionally distributed phase of orogenic deformation which affected the adjoining kaapvaal and zimbabwe cratons from the witwatersrand basin in the south to the harare greenstone belt in the north this deformation which migrated northwards with time postdated an earlier phase of crustal accretion during which the archaean crustal unit now marked by the kaapvaal and zimbabwe cratons and the limpopo belt grew towards the north northwest shortening of this unit during the limpopo orogeny may be regarded as the last stage of the crustal accretion process this tectonic process of continental growth by accretion followed by crustal shortening with associated crustal extrusion has many features in common with tibetan tectonics from the mesozoic to the present

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

petroleum geology and potential hydrocarbon plays in the gulf of suez rift basin egypt the gulf of suez in egypt has a north northwest south southeast orientation and is located at the junction of the african and arabian plates where it separates the northeast african continent from the sinai peninsula it has excellent hydrocarbon potential with the prospective sedimentary basin area measuring approximately 19 000 km 2 and it is considered as the most prolific oil province rift basin in africa and the middle east this basin contains more than 80 oil fields with reserves ranging from 1350 to less than 1 million bbl in reservoirs of precambrian to quaternary age the lithostratigraphic units in the gulf of suez can be subdivided into three megasequences a prerift succession pre miocene or paleozoic eocene a synrift succession oligocene miocene and a postrift succession post miocene or pliocene holocene these units vary in lithology thickness areal distribution depositional environment and hydrocarbon importance geological and geophysical data show that the northern and central gulf of suez consist of several narrow elongated depositional troughs whereas the southern part is dominated by a tilt block terrane containing numerous offset linear highs major prerift and synrift source rocks have potential to yield oil and or gas and are mature enough in the deep kitchens to generate hydrocarbons geochemical parameters sterane distribution and biomarker correlations are consistent with oils generated from marine source rocks oils in the gulf of suez were sourced from potential source rock intervals in the prerift succession that are typically oil prone type i and in places oil and gas prone type ii or are composites of more than one type multiple types i ii or iii for oil prone oil and gas prone or gas prone respectively the reservoirs can be classified into prerift reservoirs such as the precambrian granitic rocks paleozoic cretaceous nubian sandstones upper cretaceous nezzazat sandstones and the fractured eocene thebes limestone and synrift reservoirs such the miocene sandstones and carbonates of the nukhul rudeis kareem and belayim formations and the sandstones of south gharib zeit and

withdrawn 3d crustal architecture of a magma poor passive margin santos campos and espirito santo basins comparisons with a volcanic passive margin pelotas basin offshore brazil

the simplest enso recharge oscillator 1 eastern pacific sea surface temperature sst and mean equatorial pacific thermocline depth are key variables in el nino southern oscillation enso a linear fit to observations leads to a remarkably simple picture enso can be represented by a classical damped oscillator with sst and thermocline depth playing the roles of momentum and position respectively an independent fit of observed relationships between western and eastern thermocline depth central wind stress and eastern pacific sst yields the same picture and supports a recharge oscillator interpretation the oscillation arises from the interaction between the recharge time of the warm pool and the time delay between east and west pacific both finite kelvin wave speed and sst dynamics contribute to the time delay including seasonality in the description we find two periods of relative instability boreal spring with a large phase progression and autumn with nearly stationary phase

depositional sequences in a foreland basin north western domain of the continental duero basin spain abstract the cenozoic record of the north western domain of the duero basin is articulated at the surface through a set of continental depositional sequences called from base to top the vegaquemada sequence the candanedo sequence and the barrillos sequence these depositional sequences were deposited in continental sedimentary environments the deposition of the first sequence occurred through a fluvial system with floodplains cut by low sinuosity channels the vegaquemada sequence was developed between the middle eocene and the early agenian the second sequence was formed by a set of highly efficient transport alluvial fans that evolved laterally towards fluvial systems with low sinuosity fluvial channels and an extensive floodplain where several types of palaeosols were formed this sequence developed between the early agenian and the late vallesian the third unit the barrillos sequence between the late vallesian and the turolian ruscinian transition was generated by a set of highly efficient transport alluvial fans dominated by low sinuosity fluvial channels in subsurface geology seismic and well data are used to rebuild the stratigraphic architecture the two basal depositional sequences can be identified with two seismic units the palaeogene seismic unit pgsu and the neogene seismic unit ngsu respectively in the present work we obtained the isovelocity isochron and isobath maps for the top and base of the two cenozoic units the palaeozoic pzsu and mesozoic mzsu seismic units are found under these two units through study of the logs of the various boreholes it was only possible to analyse the upper 700 m of the candanedo sequence ngsu without encompassing the total thickness of the unit several middle order sequences were differentiated in general showing a sequential fining upwards evolutionary character additionally for the boreholes analysed two main types of electrofacies were identified both representing fluvial channels and floodplain deposits the north western domain of the duero basin is interpreted to have been formed in response to the tectonic uplifting of the cantabrian mountains since middle eocene times integration of the data concerning the surface and subsurface geology in this domain reveals that this basin edge behaved as a foreland basin during cenozoic stages the foredeep with a depth of 2800 m is oriented east west and has a sediment thickness of up to 3500 m the forebulge is located in the southwestern zone and represents an area of basement uplifting in which a minimum thickness of materials from the cenozoic depositional sequences has accumulated

enso dynamics and diversity resulting from the recharge oscillator interacting with the slab ocean el nino southern oscillation enso is the leading mode of interannual global climate variability which in its essence is often described by the equatorial dynamics of the recharge oscillator with a fixed pattern here we explore the idea that enso can be simulated in a model with a fixed pattern of sea surface temperature variability following the recharge oscillator mechanism which interacts with the thermodynamic red noise of a slab ocean this model is capable of simulating the leading modes of sea surface temperature variability in the tropical pacific in good agreement with the observations and most coupled general circulation models enso dynamics amplitude seasonality the structure of the leading patterns its meridional extension its variations in an eastern and central pacific pattern and associated positive feedbacks are all influenced and simulated well by including the interaction of recharge oscillator and the thermodynamic coupling to the slab ocean model we further point out that much of the enso diversity in the spatial structure is a reflection of this interaction however it also has to be noted that some equatorial dynamics are missing in this model and in coupled general circulation models that are important for the enso diversity

single mineral pbpb dating a new stepwise leaching procedure applied to ca bearing silicates enables the selective recovery of radiogenic and common pb from a mineral and thus makes single phase pbpb dating possible this permits independent dating of rock forming minerals within a paragenetic sequence and the direct combination of age data with petrological results furthermore the stepwise leaching technique has the advantage over multi phase pbpb dating in that it does not require initial pb isotope equilibrium among the phases but may be used to test it the presence of microscopic solid inclusions which complicate dating of single phases if they are not in equilibrium with the host can be traced via the behaviour of the 208pb 204pb ratio through the various leaching steps this constitutes a major advantage over conventional bulk phase pbpb dating in addition the precision of an isochron age can be improved relative to that of the bulk mineral approach since the 207pb 204pb and 206pb 204pb data spread is significantly enhanced therefore the technique may both be used to date younger phases and or minerals with less favourable u pb ratios and to extend the applicability of self consistent p t t modelling

models of glaciomarine sedimentation and their application to the interpretation of ancient glacial sequences abstract this paper argues that glaciomarine environments can be regarded as special glacially influenced types of continental margin environments e g continental shelf slope rise and basin plain knowledge of the stratigraphic architecture and typical sedimentary sequences of non glacial margins is becoming well known but remains limited for those that have been glacially modified the principal influences on sedimentation in these environments relate to the glacial sediment input controlled by relief of basin margin glacier thermal regime and ice flow dynamics and depositional environments influence of traction currents substrate relief and proximity to nearby ice margins typical ranges of sedimentation rates can be established for glacially influenced continental margin environments and these may provide a framework for ancient sequences starvation of sediment supply to glacially influenced continental margins is common the nature of sub ice shelf sedimentation a model that has been applied to many ancient glacial sequences is critically reviewed the significance of such sedimentation in the rock record has probably been exaggerated because of oversimplistic interpretations of diamictite sequences existing process models of glaciomarine sedimentation derived from study of modern environments are sometimes difficult to employ in investigation of ancient sedimentary sequences because simple lithofacies criteria and typical vertical profiles are not available to aid in interpretation in addition compositional data emphasized by many workers for distinguishing glaciomarine from continental glacial diamict ite s frequently fingerprint sediment source and not mode of deposition the importance of facies analysis methods for isolating depositional environments is illustrated by three examples of ancient glaciomarine sequences these are the early proterozoic gowganda formation 2 3 ga of northern ontario canada the late proterozoic port askaig formation 670 ma of scotland and ireland and the late cenozoic yakataga formation 20 ma to recent of the gulf of alaska these examples illustrate the significance of detailed genetic studies of ancient glacial rocks in the interpretation of palaeogeographic and tectonic settings diamictite units in ancient glaciomarine sequences cannot be easily interpreted in terms of climatic or ice advance retreat cycles because of the varied controls on diamict accumulation and diamictite preservation in marine basins

structural features of northern tarim basin implications for regional tectonics and petroleum traps the rhombus shaped tarim basin in northwestern china is controlled mainly by two left lateral strike slip systems the northeast trending altun fault zone along its southeastern side and the northeast trending aheqi fault zone along its northwestern side in this paper we discuss the northern tarim basin s structural features which include three main tectonic units the kalpin uplift the kuqa depression and the north tarim uplift along the northern margin of the tarim basin structural mapping in the kalpin uplift shows that a series of imbricated thrust sheets have been overprinted by strike slip faulting the amount of strike slip displacement is estimated to be 148 km by restoration of strike slip structures in the uplift the kuqa depression is a mesozoic cenozoic foredeep depression with well developed flat ramp structures and fault related folds the baicheng basin a quaternary pull apart basin developed at the center of the kuqa depression subsurface structures in the north tarim uplift can be divided into the mesozoic cenozoic and the paleozoic lithotectonic sequences in seismic profiles the paleozoic litho tectonic sequence exhibits the interference of earlier left lateral and later right lateral strike slip structures many normal faults in the mesozoic cenozoic litho tectonic sequence form the negative flower structures in the north tarim uplift these structures commonly directly overlie the positive flower structures in the paleozoic litho tectonic sequence the interference regions of the northwest trending and northeast trending folds in the paleozoic tectonic sequence have been identified to have the best trap structures our structural analysis indicates that the tarim basin is a transpressional foreland basin rejuvenated during the cenozoic

statistical evaluation and calibration of model predictions of the oil and gas field distributions in superimposed basins a case study of the cambrian longwangmiao formation in the sichuan basin china abstract superimposed basins are commonly characterized by a complex distribution of oil and gas accumulations because they have generally experienced multistage hydrocarbon accumulation and tectonic movement it is challenging to predict favorable exploration zones in these basins the exploration of the deep strata of the sichuan basin i e a typical superimposed basin west china has been unsatisfactory for petroleum prospectors therefore we chose the cambrian longwangmiao formation in the sichuan basin as an example to demonstrate the method i e combination of petroleum system elements to quantitatively predict the petroleum favorable exploration zones based on the detailed analysis of the hydrocarbon accumulation process the source rock s migration m reservoir depositional facies d and regional cap rock c are the most important elements controlling the formation and distribution of oil and gas accumulations in the studied basin by studying the functional relationships among these four elements and the distribution of the petroleum accumulations we determined the accumulation probability related to each element and quantitatively predicted the probability of a favorable hydrocarbon accumulation zone we built a quantitative model of the reservoir preservation probability based on the statistical relationship between the intensity of the tectonic movement and subsequent destruction of existing oil and gas accumulations favorable exploration zones can be determined by overlaying favorable accumulation zones with disturbances associated with the tectonic evolution the results suggest that the most favorable exploration zones of the longwangmiao formation in the sichuan basin are distributed in the regions west of weiyuan and east of gaoshiti moxi pengxi yilong and dazhou kaijiang the production data for existing fields in the sichuan basin show that 87 of the successful wells are in the predicted favorable exploration zones and that the success rate with respect to the prediction of failure wells is 67 this approach highlights the most prospective exploration areas in superimposed basins which in general is challenging and complex for traditional basin modeling tools

the significance of rb sr ages of biotite and phlogopite for the thermal history of the central and southern marginal zones of the limpopo belt of southern africa and the adjacent portions of the kaapvaal craton abstract generally rb sr biotite and phlogopite ages range from 2050 ma to 1950 ma between the murchison thabazimbi and triangle tuli sabi shear zones of southern africa in the rocks comprising the central and southern marginal zones of the limpopo belt and adjacent portions of the kaapvaal craton in some shear zones however similar ages ocurr as young as 800 ma in contrast within the kaapvaal craton south of the murchison thabazimbi shear zone rb sr biotite ages range between 3150 ma and 2100 ma and show no regular distribution in all cases the ages are interpreted to indicate the time elapsed since the biotite last cooled below its closure temperature approximately 320 c the regular pattern of 2050 ma to 1950 ma rb sr biotite ages north of the murchison thabazimbi shear zone suggests that the present erosional surface approximates a paleo isothermal surface this surface was exposed by uplift and erosion which was completed by 1900 ma to 1800 ma ago when the sedimentary and volcanic rocks of the soutpansberg group were deposited the regional uplift was accommodated by motion on the murchison thabazimbi and triangle tuli sabi shear zones and probably was related to tectonism associated with the emplacement of the anorogenic bushveld and phalaborwa complexes other anorogenic granitic magmatism accompanied uplift the depth represented by the paleo isothermal surface and the magnitude of the uplift that exhumed it cannot be constrained precisely it is suggested however that the majority of the 10 to 15 km by which crust in this area is thinner than that of the adjacent cratons is the manifestation of this uplift

revisiting morphological relationships of modern source to sink segments as a first order approach to scale ancient sedimentary systems abstract catchments provide water and sediment to downstream sedimentary systems and these form individual source to sink systems source to sink systems comprise adjacent linked segments commonly hinterland catchments alluvial and coastal plains the continental shelf continental slope and submarine fan the dimensions of the catchment and how it scales to downstream segments provides insight into the sedimentary and tectonic controls that influence the morphology and sedimentation patterns in a basins evolution in ancient sedimentary successions where the sedimentary routing system is buried and inaccessible for study or fragmented due to uplift and erosion using scaling relationships can provide a powerful tool to understand the complete sedimentary system observational data from modern sedimentary systems provide an opportunity to create morphological and sedimentological scaling relationships of segments on the entire source to sink system however previous studies on global modern source to sink systems have typically been based on a limited number of examples restricted by the data available at the time and the methodology used to analyze large datasets in the last decade the volume and quality of remotely sensed information has significantly improved so that it is now timely to revisit scaling relationships of modern source to sink systems segment morphologies and discuss the implications of those r esults for sedimentological parameters and applicability to ancient source to sink systems the results of this reanalysis show that dimensions of the catchment and submarine fan segments scale internally in terms of fan width length and area in addition fan area scales to its largest hinterland catchment area in agreement with previous studies however it is important to consider all catchments that contribute sediment to a basin floor region in paleogeographic settings where individual submarine fans are difficult to tie to a single catchment and where basin floor systems are amalgamated the contributing sediment discharge of all catchments may be significant and likely influence the scale of its submarine fan accommodation versus sediment supply in relation to relative sea level change are important controls on the position of the shoreline which vary considerably from system to system over time and space thus influencing morphological relationships between source to sink segments the continental shelf should therefore be viewed as a transient geomorphic feature rather than a segment of a source to sink system furthermore the continental slope length should not be used to scale other segments of the source to sink system which contradicts previous research the underlying tectonic and sedimentological control on the continental shelf and slope segments in addition to the subjective interpretation of their basinward boundaries may render those segments unsuitable for scaling the morphology of other segments the study highlights both the temporal variability and complexity of controls that influence the morphology and scaling relationships of internal and adjacent linked source to sink segments and the need to place this in a framework of both tectonic and sedimentological history

shear zones of the limpopo belt and adjacent granitoid greenstone terranes implications for late archaean collision tectonics in southern africa abstract granulite metamorphism in the 2 65 ga limpopo belt of southern africa is related to crustal thickening due to late archaean collision tectonics the central zone of the belt is a major thrust sheet of distinctive lithological structural and isotopic character separated from adjacent terranes by crustal scale shear zones and the northern and southern marginal zones are up thrust deep level granulite facies terranes of the adjacent cratons geometrically the marginal zones are mirror images and the limpopo belt is essentially symmetrical in n s section conventionally regarded as a n s collisional orogeny the gross structural and lithological differences between the central zone and the marginal zones kinematic data from shear zones and geophysical data showing the three dimensional geometry of the central zone are here used to suggest that the direction of emplacement of the central zone was also the collision direction this was from northeast to southwest with the upthrust outwardly directed marginal zones developing in mechanical response to this collision

atmospheric methane from organic carbon mobilization in sedimentary basins the sleeping giant abstract the mass of organic carbon in sedimentary basins amounts to a staggering 1016 t dwarfing the mass contained in coal oil gas and all living systems by ten thousand fold the evolution of this giant mass during subsidence and uplift via chemical physical and biological processes not only controls fossil energy resource occurrence worldwide but also has the capacity for driving global climate only a tiny change in the degree of leakage particularly if focused through the hydrate cycle can result in globally significant greenhouse gas emissions to date neither climate models nor atmospheric co2 budget estimates have quantitatively included methane from thermal or microbial cracking of sedimentary organic matter deep in sedimentary basins recent estimates of average low latitude eocene surface temperatures beyond 30 c require extreme levels of atmospheric co2 methane degassing from sedimentary basins may be a mechanism to explain increases of atmospheric co2 to values as much as 20 times higher than pre industrial values increased natural gas emission could have been set in motion either by global tectonic processes such as pulses of activity in the global alpine fold belt leading to increased basin subsidence and maturation rates in the prolific jurassic and cretaceous organic rich sediments or by increased magmatic activity such as observed in the northern atlantic around the paleocene eocene boundary increased natural gas emission would have led to global warming that was accentuated by long lasting positive feedback effects through temperature transfer from the surface into sedimentary basins massive gas hydrate dissociation may have been an additional positive feedback factor during hyperthermals superimposed on long term warming such as the paleocene eocene thermal maximum petm as geologic sources may have contributed over one third of global atmospheric methane in pre industrial time variability in methane flux from sedimentary basins may have driven global climate not only at time scales of millions of years but also over geologically short periods of time earth system models linking atmospheric ocean and earth surface processes at different timescales with the sedimentary organic carbon cycle are the tools that need to be developed in order to investigate the role of methane from sedimentary basins in earth s climate

analysis of the slab ocean el nino atmospheric feedbacks in observed and simulated enso dynamics in a recent study it was illustrated that the el nino southern oscillation enso mode can exist in the absence of any ocean dynamics this oscillating mode exists just due to the interaction between atmospheric heat fluxes and ocean heat capacity the primary purpose of this study is to further explore these atmospheric slab ocean enso dynamics and therefore the role of positive atmospheric feedbacks in model simulations and observations the positive solar radiation feedback to sea surface temperature sst due to reduced cloud cover for anomalous warm ssts is the main positive feedback in the slab ocean el nino dynamics the strength of this positive cloud feedback is strongly related to the strength of the equatorial cold tongue the combination of positive latent and sensible heat fluxes to the west and negative ones to the east of positive anomalies leads to the westward propagation of the sst anomalies which allows for oscillating behavior with a preferred period of 6 7 years several indications are found that parts of these dynamics are indeed observed and simulated in other atmospheric or coupled general circulation models agcms or cgcms the cmip3 agcm slab ensemble of 13 different agcm simulations shows unstable ocean atmosphere interactions along the equatorial pacific related to stronger cold tongues in observations and in the cmip3 and cmip5 cgcm model ensemble the strength and sign of the cloud feedback is a function of the strength of the cold tongue in summary this indicates that the slab ocean el nino dynamics are indeed a characteristic of the equatorial pacific climate that is only dominant or significantly contributing to the enso dynamics if the sst cold tongue is sufficiently strong in the observations this is only the case during strong la nina conditions the presence of the slab ocean enso atmospheric feedbacks in observations and cgcm model simulations implies that the family of physical enso modes does have another member which is entirely driven by atmospheric processes and does not need to have the same spatial pattern nor the same time scales as the main enso dynamics

the epicontinental subsiding margin of the triassic in northern israel north arabian plate abstract the triassic sedimentary pattern of the north arabian margin represents a transition from continental to deep marine we here present a transect part of this suite from southern to northern israel cuttings from the ramalla s and devora n boreholes were studied by petrographic and cathodoluminescence microscopy biotic and sedimentological components were grouped into microfacies upon which a carbonate evaporitic depositional facies model was based mid to inner ramp conditions persisted along the transect essentially following a s n depositional strike with outer ramp to basinal facies to the west five low order lo cycles were identified and integrated into a sequence stratigraphic model with eustatic tectonic and differential subsidence components lo cycle 1 is late anisian pelsonian cycle 2 is late anisian to longobardian cycle 3 is early carnian cycle 4 is late carnian and cycle 5 is at the carnian norian transition facies range from supratidal via lagoonal facies in late hst or lst to calcarenitic shoals and short term deepening to offshore at maximum flooding cycles 1 and 2 are non evaporitic with a clastic influx event in cycle 2 cycles 3 and 4 contain sabkha or salina evaporites in the lagoonal facies that end in the lower part of cycle 5 these facies group into a higher order cyclicity with discrete events that can be correlated between the boreholes depositional and burial history were correlated to alpine and arabian plate stratigraphy over 20 myr from the anisian pelsonian to the norian siliciclastic carbonate and evaporite dominated environments indicate climates ranging from relatively humid to extremely arid rapid subsidence in the late anisian is attributed to neotethyan rifting of northeastern gondwana from latest anisian to early carnian reduced subsidence took place in the face of eustatic sea level rise renewed subsidence in the carnian is attributed to further neotethyan rifting subsidence terminated in the norian with uplift to the north attributed to pre volcanic doming

is the present the key to the past a global characterization of modern sedimentary basins the stratigraphic record is heavily biased because it is uniquely composed of sediments that were laid down in basins whereas the majority of the present and historic land surface of the planet is composed of areas that are in net long term erosion with no preservation potential global mapping and quantification of the distribution of currently active sedimentary basins suggest that only 16 of earth s terrestrial land surface is within sedimentary basins the remainder of the land is in upland areas that will not be represented in the future rock record furthermore 60 of the modern basin area has an arid climate as opposed to 27 of the land surface tectonic classification of modern basins indicates that intracratonic and foreland basins cover the greatest area whereas forearc extensional and strike slip basins are the least represented by area while this modern snapshot does not account for differences in subsidence rate or basin longevity the mapping and quantification of modern basins highlight the incompleteness of the stratigraphic record and the importance of caution when assuming the present is the key to the past

maturation based geodynamic geochemical classification of sedimentary basins abstract geodynamic principles and processes are combined with continental margin type basin position on a plate and crustal type to classify sedimentary basins in a tectonic mode tectonic basin classifications however have not improved the rate of discovery of hydrocarbons or mineral deposits in sedimentary basins to improve prediction of commercial hydrocarbon occurrence and sedimentary hosted ore deposits it is recommended that the proposed geodynamic basin classification could be combined with organic petroleum or inorganic metals geochemical classification systems organic geochemical basin classification discriminates basin types using three criteria charge factors migration drainage factors and impedance factors demaison and huizinga 1989a b a similar approach is applicable to mineral deposits an inorganic geochemical classification is proposed that recognizes three criteria of inorganic maturation metal solubility factor migration drainage factor and environmental potential for mineral precipitation this combined geodynamic and geochemical maturation approach to basin classification should enhance resource exploration efficiency

influence of tectonics on permian coal rank patterns in australia abstract coal in the australian permian basins is dominantly subbituminous coal to medium volatile bituminous coal the subbituminous coal and higher rank bituminous coals are generally the result of burial diagenesis localized low volatile bituminous coal to anthracite is commonly associated with igneous activity extensive zones of high rank coal in the eastern part of the bowen basin are due to uplift of deeply buried coal measure sequences during late permian and triassic tectonism high rank coals in the sydney basin are due to uplift of deeply buried permian rocks preceding sea floor spreading in the tasman sea during the late cretaceous and early tertiary although this conclusion is controversial localized semianthracite and anthracite at depths greater than 2 500 m in the cooper basin were formed either by enhanced heat flow from radiogenic basement granites or by vertical movement of hot fluids through the fractured granitic bodies during the tertiary permian coals in the pedirka and arckaringa basins in the center of the continent and the perth carnarvon canning bonaparte and officer basins in the west are generally low in rank due to either shallow depths of burial or slight heat flow or both the fitzroy trough of the canning basin is an exception there significant tectonic activity has occurred since the permian

isotopic and ree characteristics of the intrusive charnoenderbite and enderbite geographically associated with the matok pluton limpopo belt southern africa abstract intrusive charnoenderbite and enderbite in the southern marginal zone of the limpopo belt are genetically linked with peak metamorphism m1 during the 2700 ma to 2650 ma limpopo orogeny they occur geographically associated with and are intruded by the granodiorite and granite of the matok pluton which were emplaced between the response phase m2 and the rehydration phase m3 of that orogeny rb sr pb ree and sm nd elemental and isotopic data for whole rock samples and u pb data for populations of zircon suggest that the charnoenderbite and enderbite were intruded 2671 ma ago and were derived from a crustal precursor the granodiorite and granite of the matok pluton were intruded at approximately the same time between 2667 ma and 2664 ma ago they also were derived from a crustal precursor nd model ages and ree patterns for the charnoenderbite and enderbite and the granodiorite are distinct this relationship may imply that they are not cogenetic alternatively these rock types could be cogenetic if the magma from which they were derived was assimilating older crustal material as it evolved nd isotopic data indicate that the magma giving rise to the charnoenderbite and enderbite formed by partial melting of rocks compositionally similar to some portions of the baviaanskloof gneiss data for the granodiorite are consistent with the possibility that this unit formed in a similar manner from rocks compositionally similar to other portions of the baviaanskloof gneiss the close temporal relationship between the emplacement of the charnoenderbite and enderbite and the granitic rocks of the matok pluton indicates that the retrograde portion of the limpopo orogeny beginning 2670 ma ago occurred rapidly perhaps over 7 ma

a new approach of relating petroleum system and play development to basin evolution an application to the conjugate margin gabon coastal and almada camamu basins sedimentary basins can be classified according to their structural genesis and evolutionary history and comprise tectonic and sedimentary cycles and stages to which common elements of petroleum systems and plays may be linked we describe a new method that allows easier and more efficient comparisons between petroliferous sedimentary basins with similar geologic characteristics using this method we can make predictions of potential petroleum systems and plays occurring in underexplored basins or regions in this article the methodology is applied to the well explored gabon coastal basin west african margin and the conjugate almada camamu basin brazilian margin which is a frontier basin the two basins experienced a similar tectonostratigraphic evolution and share many similarities we propose that petroleum systems and plays identified in the gabon coastal basin might potentially also be present in the almada camamu basin these could include a second lacustrine synrift petroleum system as well as a fluviomarine transitional petroleum system potential but not yet proven reservoirs in the almada camamu basin include coarse sandstones surrounding basement highs within the synrift synrift lacustrine carbonates fluviomarine sandstones at the base of the transitional cycle and early postrift ramp carbonates the methodology and newly developed figures are particularly useful to obtain a first impression of the tectonostratigraphy likely petroleum system and play development and exploration history of potentially analogous basins furthermore the approach allows for the recognition of important differences raising questions that can be answered by more direct techniques

structural styles and basin evolution in eromanga region eastern australia the eromanga region of eastern australia has undergone at least four major tectonic cycles the results of which are recognized in the structures seen on seismic sections the late proterozoic early phanerozoic cycle ended with the formation of the thomson foldbelt which forms basement in the region the subsequent reactivations of the fault systems within this basement and deeper lithosphere have produced the structural styles now important as exploration targets most reactivations are interpreted as resulting from crustal shortening events affecting sedimentary strata deposited in an epicontinental shallow water environment with small strike slip adjustments affecting some structures the dominant style of deformation evident from the seismic sections is that seen across high angle thrust faults in other parts of the world with the amount of overthrusting being comparatively small generally the maximum throw on faults in the devonian strata can be measured in thousands of meters whereas those in the permian triassic and jurassic cretaceous strata are a few hundred meters at most the devonian sequences of the adavale basin and associated troughs were deformed during two carboniferous events the first with crustal shortening in a north south direction and the second in an east west direction associated small strike slip movements were accommodated along a number of faults including the warrego grenfield warbreccan and canaway faults southwest of our study area in the permian triassic cooper basin other workers have interpreted a northwest southeast crustal shortening event during the late permian and another wrench induced northeast southwest crustal shortening during the triassic during the middle tertiary a crustal shortening event regionally affected the jurassic cretaceous eromanga basin sequence and older sedimentary rocks this event is seen pro inently in a deformation zone between the canaway and cunnavalla faults with the direction of crustal shortening being northeast southwest small strike slip movements are interpreted as partially decoupling events from neighboring provinces the adavale basin and cheepie shelf to the east and southeast and the cooper basin and warbreccan dome to the southwest and northwest respectively in this partial decoupling the canaway cunnavalla warrego and warbreccan faults are interpreted as playing an important role the basin modifying tectonic episodes within the lithosphere control structural style these relatively small scale events have resulted in structures that provide attractive petroleum prospects

delineation of saltwater intrusion into the freshwater aquifer of lekki peninsula lagos nigeria recently the deterioration of water quality in the coastal zones of lekki peninsula area of lagos due to saltwater infiltration into the freshwater aquifer has become a major concern with the aim of providing valuable information on the hydrogeologic system of the aquifers the subsurface lithology and delineating the groundwater salinity vertical electrical resistivity ves sounding survey was carried out utilizing surface schlumberger electrode arrays and electrode spacing varying between 1 and 150m the dc resistivity surveys revealed significant variations in subsurface resistivity also the ves resistivity curves showed a dominant trend of decreasing resistivity with depth thus increasing salinity in general the presence of four distinct resistivity zones were delineated viz the unconsolidated dry sand a having resistivity values ranging between 125 and 1 028 m represent the first layer the fresh water saturated soil zone b having resistivity values which correspond to 32 256 m is the second layer the third layer zone c is interpreted as the mixing transition zone of fresh with brackish groundwater the resistivity of this layer ranges from 4 to 32 m while layer four zone d is characterized with resistivities values generally below 4 m reflecting an aquifer possibly containing brine the rock matrix salinity and water saturation are the major factors controlling the resistivity of the formation moreover this investigation shows that saline water intrusion into the aquifers can be accurately mapped using surface dc resistivity method

global basin classification system a proposed system classifies sedimentary basins worldwide into specific as well as general categories the geologic history of each basin may be subdivided into cycles using three parameters basin forming tectonics depositional sequences and basin modifying tectonics sedimentary basins may be simple with one or two tectonic sedimentary cycles or they may be complex polyhistory basins with many different cycles and events there are eight simple cycle types in this classification which cover continental continental margin and oceanic areas the eight basic cycle types their depositional fills and tectonic modifiers have been given letter and number symbols so that the specific geologic history of each basin may be written as a formula these formulas may then e compared and similarities or differences between basins noted

petrology and microthermometry of aluminous rocks in the botswanan limpopo central zone evidence for isothermal decompression and isobaric cooling phase analysis in the model k2o poor aluminous rock system fmash illustrates the following sequence of reactions during retrograde metamorphism in the botswanan limpopo central zone opx sil qtz crd opx sil spr crd grt qtz opx crd opx crd w ged qtz grt opx crd w ged and grt qtz w ged crd a quantitative petrogenetic grid with phase relations shows that sapphirine results from nearly isothermal decompression in the quartz undersaturated portions of the grid and that gedrite formation by reactions 4 6 records isobaric cooling from high temperature c 800 c after the decompression conditions for hydration in the western part of the area were 700 800 c and c 6 kbar based on microthermometric data and the available garnet cordierite geothermometer on the basis of these conditions and predicted thermodynamic properties of gedrite phase relations in t xmg space were constructed to investigate the isobaric cooling event the results are in good agreement with the hydration p t path further the t xmg topologies show that hydration of orthopyroxene in the central part of the area reaction 4 occurred at about 800 c and c 5 kbar therefore we conclude that the botswanan limpopo central zone has suffered isothermal decompression similar to the central zone in south africa and zimbabwe followed by isobaric cooling the isobaric cooling event in the western at c 6 kbar and central at c 5 kbar parts of the area commenced at nearly the same temperature c 800 c and appear to be consistent with a tectonic model that involved westward movement thrusting of the central zone

investigating the stratigraphy and palaeoenvironments for a suite of newly discovered mid cretaceous vertebrate fossil localities in the winton formation queensland australia the winton formation of central queensland is recognized as a quintessential source of mid cretaceous terrestrial faunas and floras in australia however sedimentological investigations linking fossil assemblages and palaeoenvironments across this unit remain limited the intent of this study was to interpret depositional environments and improve stratigraphic correlations between multiple fossil localities within the preserved winton formation in the eromanga basin including isisford lark quarry and bladensburg national park twenty three facies and six repeated facies associations were documented indicating a mosaic of marginal marine to inland alluvial depositional environments these developed synchronously with the final regression of the eromanga seaway from central australia during the late albian early turonian investigations of regional and local scale structural features and outcrop core and well analysis were combined with detrital zircon provenance signatures to help correlate stratigraphy and vertebrate faunas across the basin significant palaeoenvironmental differences exist between the lower and upper portions of the preserved winton formation warranting informal subdivisions a lower tidally influenced fluvial deltaic member and an upper inland alluvial member this work further demonstrates that the isisford fauna is part of the lower member of the preserved winton formation whereas fossil localities around winton including lark quarry and bladensburg national park are part of the upper member of the winton formation these results permit a more meaningful framework for both regional and global comparisons of the winton flora and fauna

subsidence in intracontinental basins due to dynamic topography the origin of anomalous tectonic subsidence ats of large intracontinental basins long after their most recent phase of extension and last thermal perturbation is the subject of a long standing debate we show that deep earth processes may contribute to the subsidence of these tectonically stable basins by analysing the tertiary mantle convection driven topography history of a global set of more than 220 intracontinental basins integrated into a plate kinematic framework most basins are affected by increasing negative dynamic topography over the last 70 myr due to the motion of many continents away from large mantle upwellings and towards downwellings previously located along the perimeter of the supercontinent pangaea during continental dispersal increasing negative dynamic topography causes dynamic subsidence of the basins creating additional accommodation space we utilise a parameter from a global crustal analysis of intraplate basins termed anomalous tectonic subsidence to quantify sediment accumulation not related to crustal stretching we propose that dynamic subsidence due to plate motions relative to the underlying mantle as well as variations in the large scale convection patterns can significantly contribute to the creation and destruction of accommodation space in intraplate basins