tectono sedimentary evolution of the bowland basin n england during the dinantian the bowland basin is a ne sw trending sedimentary basin lying between the askrigg bowland high to the n and nw and the central pennine high to the se the basin was initiated in late devonian tournaisian times sediment thickness and facies variations within the dinantian succession show marked asymmetry on both a basin wide and intra basin scale as a result of approximate nw se to n s extension across normal faults thickening of the sedimentary sequence from ne to sw over much of the basin resulted from fault controlled extension along the se margin of the basin with downthrow to the nw giving the basin a half graben character extension occurred in two distinct episodes marked by basin wide debris flow and sedimentary slide slump deposits during the late chadian early arundian the simple half graben became modified by a series of ne sw trending antithetic and nw se trending transfer faults associated with local unconformities and marked lateral thickness and facies variations this interval marks the transition from carbonate ramp to slope sedimentation and a temporary halt in carbonate supply to the basin the second episode of extension the late asbian early brigantian marks the break up of the northern basin margin ending major carbonate deposition within the basin reactivation of these structures at the end of the carboniferous created the ribblesdale fold belt as a result of nw se to n s compression transpression application of this research to areas surrounding the bowland basin has led to the recognition of additional shelf basins the orientation of which suggests control by normal and transfer fault systems discussion and

sourcelands for the carboniferous pennine river system constraints from sedimentary evidence and u pb geochronology using zircon and monazite

the euramerican coal province controls on late paleozoic peat accumulation abstract the ancestral tropical peats and associated strata of the euramerican coal province record the interwoven effects of climate tectonism and eustasy during the late paleozoic many peats formed in foreland and intermontane basins associated with equatorial orogenic belts along the borderlands of euramerica and gondwana while other peats formed in adjacent cratonic basins the resolution of controls on euramerican peat formation requires testing against a well constrained temporal framework the late paleozoic coal age followed the evolution of vascular plants in the late silurian and was associated with assemblage of the pangean supercontinent devonian and early carboniferous peats developed locally the major phase of peat formation commenced in the namurian a and persisted to the end of the stephanian spanning 10 30 ma in different regions of euramerica it is ascribed in part to the residence of northward drifting euramerica within the equatorial rainy belt within individual depocenters basin hydrology was suitable for peatland formation during a period 10 6 10 7 years represented by the stratigraphic distribution of coal measures and termed here the basin fill coal window repeated successions cyclothems of coal siliciclastic and carbonate strata punctuate the coal window and typically represent 10 4 10 5 years these stratal successions are widely ascribed to orbitally driven glacioeustasy although cyclothems that lack marine strata may represent associated climatic shifts cyclothem groupings mesothems of 10 6 years duration are recognised locally and may have eustatic or tectonic causes cyclothems produced by autocyclic events such as delta switching should have durations in the order of 10 3 years the coal beds themselves represent autogenic processes of peat formation over periods of 10 3 10 4 years constrained by longer term allogenic effects recorded in the coal bed are tolerable allogenic events such as fires and floods caused by short term climatic excursions the termination of most mires probably occurred when single or combined allogenic effects surpassed the inherent ability of the ecosystem to adapt

modelling phase assemblage diagrams for magnesian metapelites in the system k2o feo mgo al2o3 sio2 h2o geodynamic consequences for the monte rosa nappe western alps magnesian metamorphic rocks with metapelitic mineral assemblage and composition are of great interest in metamorphic petrology for their ability to constrain p t conditions in terranes where metamorphism is not easily visible phase assemblage diagrams for natural and model magnesian metapelites in the system kfmash are presented to document how phase relationships respond to water activity bulk composition pressure and temperature the phase assemblages displayed on these phase diagrams are consistent with natural mineral assemblages occurring in magnesian metapelites it is shown that the equilibrium assemblages at high pressure conditions are very sensitive to a h2o specifically the appearance of the characteristic hp assemblage chloritoid talc phengite quartz with excess h2o in the magnesian metapelites of the monte rosa nappe western alps is due to the reduction of a h2o furthermore the mineral assemblages are determined by the whole rock feo feo mgo ratio and effective al content x a as well as p and t the predicted mineral associations for the low and high x a model bulk compositions of magnesian metapelites at high pressure are not dependent on the x a variations as they show a similar sequence of mineral assemblages above 20 kbar the prograde sequence of assemblages associated with phengite with excess sio2 and h2o for low and high x a bulk compositions of magnesian metapelites is carpholite chlorite chlorite chloritoid chloritoid talc chloritoid talc kyanite talc garnet kyanite garnet kyanite biotite at low to medium p t conditions a low x a stabilises the phengite bearing assemblages associated with chlorite chlorite k feldspar and chlorite biotite while a high x a results in the chlorite phengite bearing assemblages associated with pyrophyllite andalusite kyanite and carpholite a high x a magnesian metapelite with nearly iron free content stabilises the talc kyanite phengite assemblage at moderate to high p t conditions taking into account the effective bulk composition and a h2o involved in the metamorphic history the phase assemblage diagrams presented here may be applied to all magnesian metapelites that have compositions within the system kfmash and therefore may contribute to gaining insights into the metamorphic evolution of terranes as an example the magnesian metapelites of the monte rosa nappe have been investigated and an exhumation path with p t conditions for the western roof of the monte rosa nappe has been derived for the first time the exhumation shows first a near isothermal decompression from the alpine eclogite peak conditions around 24 kbar and 505 c down to approximately 8 kbar and 475 c followed by a second decompression with concomitant cooling

buried granites within the mid north sea high a gravity survey of the uk sector of the north sea reveals the presence of three gravity lows over the mid north sea high seismic data eliminate the possibility that these lows are due either to thicker sediments or to salt structures consequently the anomalies may be related to buried granites within the palaeozoic basement gravity modelling demonstrates that the amplitude and shape of the observed anomalies may be explained by buried batholith shaped bodies with densities appropriate for granites the tectonic influence of the buried granites may explain to some extent the continued stability of the mid north sea high throughout much of the development of the north sea basins

carboniferous stratigraphy sedimentation and correlation of well 48 3 3 in the southern north sea basin integrated use of palynology natural gamma sonic logs and carbon sulphur geochemistry a methodology for the correlation of offshore silesian upper carboniferous sequences is developed using an integrative approach based upon biostratigraphy downhole logging and geochemistry we develop the combined use of miospore zonation gamma ray spectrometry formation velocities and carbon sulphur ratios to determine the location of marine horizons and other lithofacies in a thick 1 km largely uncored silesian sequence in the southern north sea gas basin at least nine major marine horizons are recognized within a basin fill sequence of marsdenian yeadonian and langsettian ages namurian b c and westphalian a in the well these horizons help to provide a detailed subdivision of the offshore sequence although the correlations must remain tentative until further deep wells are drilled in the area the implications of the correlations for offshore palaeogeography are that the area of northern quadrant 48 was a deep periodically anoxic basin until infill by successive submarine fan lobes in late marsdenian times yeadonian delta front and coastal plain deposits pass upwards into fluvio deltaic wetland facies of the langsettian

new insights on subsurface energy resources in the southern north sea barrin area the southern north sea basin area stretching from the uk to the netherlands has a rich hydrocarbon exploration and production history the past present and expected future hydrocarbon and geothermal exploration trends in this area are discussed for eight key lithostratigraphic intervals ranging from the lower carboniferous to cenozoic in the period between 2007 and 2017 a total of 95 new hydrocarbon fields were discovered particularly in upper carboniferous rotliegend and triassic reservoirs nineteen geothermal systems were discovered in the netherlands onshore mainly targeting aquifers in the rotliegend and upper jurassic lower cretaceous formations although the southern north sea basin area is mature in terms of hydrocarbon exploration it is shown that with existing and new geological insights additional energy resources are still being proven in new plays such as the basal upper rotliegend ruby discovery for natural gas and a new chalk play for oil it is predicted that hydrocarbon exploration in the southern north sea basin area will probably experience a slight growth in the coming decade before slowing down as the energy transition further matures geothermal exploration is expected to continue growing in the netherlands onshore as well as gain more momentum in the uk

crust and upper mantle velocity structure in the appalachian orogenic belt implications for tectonic evolution the crust and upper mantle structure of the northeastern united states neus was studied by combining teleseismic and regional body wave observations with surface wave dispersion measurements the velocity models suggest that structures as much as 200 km deep and even deeper can be correlated with surficial geologic and tectonic features and that the grenville and appalachian orogenic belts show marked differences in crustal structure this has the important implication that major orogenic belts have effects that reach well into the lithosphere and are stable for extended periods of time perhaps as long as 1 b y regional travel times recorded across the neus seismic network indicate that the northern appalachians are characterized by a well defined two layer crust with a relatively high velocity lower layer the crust of the grenville province in new york state is slightly thinner than that of the new england appalachians and it is vertically homogeneous with nearly constant p and s velocities lateral variations in structure were studied using time term analysis and teleseismic p wave residuals the suture between the grenville and appalachian provinces in the northeastern united states probably occurs along a north northeast trending belt extending from northwestern vermont to southwestern connecticut high crustal velocities and or crustal thinning a linear gravity high a serpentinite belt precambrian uplifts and the taconic thrusts are found along much of this belt comparison of seismic velocities with resistivity measurements suggests that the lower crust of the grenville province may be composed of rocks with hydrous mineral phases resulting in lowered velocities and a higher poisson s ratio alternatively the rocks of the lower crust beneath the grenville province may be similar to those found on the surface while higher velocity mafic mineralogies are prevalent in the lower crust of the appalachians this is consistent with the hypothesis that the grenville crust underwent substantial reactivation thickened and became vertically uniform during the grenville orogeny in contrast the rocks of the appalachian belt probably were associated with a cycle of oceanic opening and closure which suggests an ensimatic origin of the lower crust in this region recent cocorp results indicate that the orogenic belt of the southern appalachians is allochthonous and is underlain by a basal decollement that extends eastward to the coastal plain however contrasts in structural style and tectonic evolution between the northern and southern appalachians suggest that it may not be possible to extrapolate the cocorp results to the northern appalachians north of about 41 latitude and that the suture between the grenville province and the appalachian orogenic belt in new england is located in the vicinity of or just east of the serpentinite belt

geothermobarometry in albite garnet orthogneisses a case study from the gran paradiso nappe western alps abstract the aim of this paper is to estimate syntectonic p t conditions within albite and garnet bearing orthogneisses these rocks are generally characterized by the assemblage quartz albite biotite phengite cafe garnet epidote titanite garnet contains up to 55 mole per cent of grossular k feldspar is a relict magmatic phase p t conditions are estimated using several independent methods first it is shown that exchange reactions based on the fe mg partitioning between garnet and biotite or garnet and phengite cannot be used to estimate temperatures in these rocks due to the high grossular content of garnet second maximum and minimum pressures are constrained respectively by the occurrence of albite instead of jadeite quartz and by the assemblage phengite biotite quartz third phase equilibria in albite and garnet bearing metagranites are modelled in the system k 2 o cao feo al 2 o 3 sio 2 h 2 o equilibrium curves are calculated for the observed phase compositions uncertainties in p t estimates mainly result from the choice of appropriate non ideal solution models for the garnet an application is developed for granites from the gran paradiso nappe western alps these granites show an heterogeneous deformation of alpine age expressed by mylonitic shear zones cutting across weakly deformed domains estimated p t conditions for the synkinematic assemblages are 10 16 kbar at 550 50 c

constraints on the late thermotectonic evolution of the western alps evidence for episodic rapid uplift forty two new apatite and zircon fission track ages are presented for samples from the western alps in southern switzerland northern italy and southeastern france measured ages plotted against assumed closure temperatures yield cooling patterns for the final cooling uplift and exhumation of the western alps similar fission track zircon ages in the penninic gran paradiso massif dent blanche nappe sesia lanzo zone and ivrea zone indicate cooling of all four units to 225 c by 33 ma differences in apatite ages reveal differential cooling of the four blocks between 33 ma and the present in the sesia lanzo zone similarity of apatite ages regardless of elevation together with near volcanic confined fission track length patterns suggest rapid cooling and uplift at 25 ma compared with slow cooling of other western alps units around 12 ma uplift is thus not continuous but episodic often over a short time interval beyond the resolution of other methods such episodes of uplift as revealed here in the sesia lanzo zone may be the rule rather than the exception

nucleation and growth of myrmekite during ductile shear deformation in metagranites myrmekite is extensively developed along strain gradients of continuous lower amphibolite facies shear zones in metagranites of the gran paradiso unit western alps to evaluate the role of stress strain energy and fluid phase in the formation of myrmekite we studied a sample suite consisting of weakly deformed porphyric granites wdgs foliated granites fgs representative of intermediate strains and mylonitic granites mgs in the protolith most k feldspar is microcline with different sets of perthite lamellae and fractures in the wdgs abundant quartz oligoclase myrmekite developed inside k feldspar only along preexisting perthite lamellae and fractures oriented at a high angle to the incremental shortening direction in the wdgs stress played a direct role in the nucleation of myrmekites along interfaces already characterized by high stored elastic strain because of lattice mismatch between k feldspar and albite in the fgs and mgs k feldspar was progressively dismembered along the growing network of microshear zones exploiting the fine grained recrystallized myrmekite and perthite aggregates this was accompanied by a more pervasive fluid influx into the reaction surfaces and myrmekite occurs more or less pervasively along all the differently oriented internal perthites and fractures independently of the kinematic framework of the shear zone in the mgs myrmekite forms complete rims along the outer boundary of the small k feldspar porphyroclasts which are almost completely free of internal reaction interfaces therefore we infer that the role of fluid in the nucleation of myrmekite became increasingly important as deformation progressed and outweighed that of stress mass balance calculations indicate that in al si conservative conditions myrmekite growth was associated with a volume loss of 8 5 this resulted in microporosity within myrmekite that enhanced the diffusion of chemical components to the reaction sites and hence the further development of myrmekite

lead isotopic evidence for distinct sources of granite and for distinct basements in the northern appalachians maine lead isotopic compositions of feldspars in plutons of the coastal lithotectonic block avalonian basement central maine merrimack synclinorium and connecticut valley gaspe synclinorium in northern maine granville basement indicate the presence of three fundamentally different sources of devonian granitic rocks in maine plutons in the coastal lithotectonic block have the most radiogenic values 206 pb 204 pb 18 25 19 25 207 pb 204 pb 15 59 15 67 208 pb 204 pb 38 00 38 60 plutons in northern maine are the least radiogenic 206 pb 204 pb 18 00 18 50 207 pb 204 pb 15 51 15 55 and 208 pb 204 pb 37 80 38 38 intermediate lead isotope values characterize the plutons in central maine 206 pb 204 pb 18 20 18 40 207 pb 204 pb 15 56 15 60 and 208 pb 204 pb 38 00 38 30 all plutons show relatively radiogenic lead values for their ages and suggest the imprint of continental crustal sources especially in the coastal block and in central maine plutons from the connecticut valley gaspe synclinorium allow for a more significant isotopic input from the subcontinental mantle the three distinct lead isotope groups probably identify plutons formed in different crustal fragments in a continental collisional environment that were juxtaposed after emplacement of the granites

excess 40ar free phengite in ultrahigh pressure metamorphic rocks from the lago di cignana area western alps abstract ar ar analyses of phengites and paragonites from the ultrahigh pressure metamorphic rocks zoisite clinozoisite schist garnet phengite schist and piemontite schist in the lago di cignana area western alps were carried out with a laser probe step heating method using single crystals and a spot dating method on thin sections eight phengite and two paragonite crystals give the plateau ages of 37 42 ma with 96 100 of 39 ar released each rock type also contains mica crystals showing discordant age spectra with age fractions 20 35 ma significantly younger than the plateau ages phengite inclusions in garnet give ages of 43 2 1 1 ma and 44 4 1 5 ma which are significantly older than the spot age 36 4 1 4 ma from the matrix phengites and the plateau ages from the step heating analyses inclusion ages 43 and 44 ma are consistent with a zircon shrimp age 44 1 ma in this area these results suggest that the oceanic materials that underwent a simple subduction related uhpm form excess 40 ar free phengite and that the peak metamorphism is ca 44 ma or little older we suggest that matrix phengites experienced a retrogression reaction changing their chemistry contemporaneously with deformation related to the exhumation of rocks releasing significant radiogenic 40 ar from the crystals this has lead to the apparent ages of the matrix phengites that are significantly younger than the inclusion age

alpine metamorphism of hercynian hornblende granodiorite beneath the blueschist faciesschistes lustresnappe of ne corsica the hercynian granitic basement which forms the tenda massif in ne corsica represents part of the leading edge of the european plate during middle to late cretaceous eoalpine high p metamorphism the metamorphism of this basement induced by the overthrusting of a blueschist facies schistes lustres nappe was confined to a major ductile shear zone c 1000m thick within which deformation increases upwards towards the overlying nappe metamorphism within the basement mostly records lower blueschist facies conditions crossite epidote except near the base of the shear zone where the greenschist facies assemblage albite actinolitic amphibole has developed instead of crossite study of the primary mafic phase breakdown reactions within hornblende granodiorite reveals the following metamorphic zonation zone 1 biotite to chlorite towards zone 2 biotite to phengite zone 2 hornblende to actinolitic ca amphibole albite sphene and biotite to actinolitic ca amphibole albite phengite ti ore epidote zone 3 hornblende to crossite low ti biotite phengite sphene and biotite to crossite low ti biotite phengite ti ore sphene epidote p t conditions at the base of the shear zone are estimated to have been 390 490 c at 600 900 m pa 6 9kbar and the corsican basement is therefore deduced to have been buried to 20 30 km during metamorphism this relatively shallow metamorphism contrasts with some other areas in the western alps where the eoalpine event apparently buried the european continental crust to depths of 80 km or more as there is no evidence for a long history of blueschist facies metamorphism prior to the involvement of the european continent it is deduced that the eoalpine blueschists were produced during the collision of the insubric plate with europe rather than during tethyan intraoceanic subduction coherent blueschist terrains such as the schistes lustres probably record buovant feature collision and obduction tectonics rather than any preceding oceanic subduction

critical evaluation of an upper carboniferous tight gas sandstone reservoir analog diagenesis and petrophysical aspects upper carboniferous sandstones are one of the most important tight gas reservoirs in central europe we present data from an outcrop reservoir analog piesberg quarry in the lower saxony basin of northern germany this field based study focuses on the diagenetic control on spatial reservoir quality distribution the investigated outcrop consists of fluvial 4th order cycles which originate from a braided river dominated depositional environment westphalian c d stratigraphy sedimentary thicknesses and exposed fault orientations nnw sse and w e reflect tight gas reservoir properties in the region further north diagenetic investigations revealed an early loss of primary porosity by pseudomatrix formation present day porosity 7 on average and matrix permeability 0 0003 md on average reflect a high temperature overprint during burial the entire remaining pore space is occluded with authigenic minerals predominantly quartz and illite this reduces reservoir quality and excludes exposed rocks as tight gas targets the correlation of petrographic and petrophysical data show that expected facies related reservoir quality trends were overprinted by high temperature diagenesis the present day secondary matrix porosity reflects the telogenetic dissolution of mesogenetic ankerite cements and unstable alumosilicates faults are associated with both sealed and partially sealed veins near the faults indicating localized mass transport around w e striking faults dissolution is higher in leached sandstones with matrix porosities of up to 26 3 and matrix permeabilities of up to 105 md the dissolution of ankerite and lithic fragments around the faults indicates focused fluid flow however a telogenetic origin cannot be ruled out the results of this work demonstrate the limits of outcrop analog studies with respect to actual subsurface reservoirs of the greater area whereas the investigated outcrop forms a suitable analog with respect to sedimentological stratigraphic and structural inventory actual reservoirs at depth generally lack telogenetic influences these alter absolute reservoir quality values at the surface however the temperature overprint and associated diagenetic modification which caused the unusually low permeability in the studied outcrop may pose a reservoir risk for tight gas exploration as a consequence of locally higher overburden or similar structural positions

metamorphic petrology of a high pressure low temperature subduction complex in west central baja california mexico the western baja terrane wbt of west central baja california is an uplifted subduction complex that is divided into smaller subterranes on the basis of bounding faults and petrological differences each subterrane contains coherent early jurassic to early cretaceous sedimentary and mafic volcanic rocks not melange that have been metamorphosed under blueschist facies conditions key phases in metabasites and metaturbidites include jadeitic to acmitic clinopyroxene sodic amphibole lawsonite aragonite chlorite titanite and white mica pressure indicators include the jadeite content of clinopyroxene and the presence of aragonite temperature indicators include the presence of lawsonite the absence of greenschist facies minerals and results from vitrinite reflectance studies conditions at the peak of metamorphism were 8 kbar 225 325 c for subterrane 1 7 8 kbar 170 220 c for subterrane 2 and 5 6 kbar 175 200 c for subterrane 3 these correspond to cold geothermal gradients 6 9 km vein assemblages that include aegerine jadeite and aegerine albite aragonite lawsonite and sodic amphibole indicate uplift during continued cold conditions probably during steady state subduction

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

on the periodicity and magnitude of late carboniferous glacio eustatie sea level changes data from sedimentary cycles in basins from northern england the appalachians and midcontinent us afford an insight into periodicities and controls of late carboniferous glacio eustatic sea level changes lithofacies with identifiable palaeobathymetry are used to assess the magnitude of sea level change in the pennine basin of northern england the method yields a minimum value of 42m walsh power spectral analysis is employed to resolve periodicities of about 120ka within the pennine basin of northern england 212 140 and 93 ka within the midcontinent us succession and 109 84 67 63 ka within the appalachian basin within the pennine basin periodicities and magnitudes are found to be independent of their position within the basin thus any tectonism can be assumed to have had a negligible effect on the transgressions a simplified modelled climatic curve is derived from milankovitch parameters and pleistocene 18 o data this is used in a basin fill model that simulates the thermally subsiding pennine basin the resulting distribution of marine deposits is seen to depend upon both the steady regional subsidence and the magnitude and extent of glacio eustatic transgressions

the extension of grenville basement beneath the northern appalachians results from the quebec maine seismic reflection and refraction surveys from 1983 to 1984 the united states geological survey and the geological survey of canada undertook a series of seismic experiments to determine the crustal structure of the appalachian mountain belt in maine and southeast quebec these experiments included four deep crustal seismic reflection profiles perpendicular to the strike of regional geological trends and several high resolution refraction wide angle reflection profiles both parallel and perpendicular to strike here the data recorded in quebec and the northwest part of maine are interpreted in conjunction with existing reflection profiles from quebec synthetic seismogram calculations in laterally varying media are used to model the refraction wide angle reflection data while reprocessing migration and attribute plotting are used in the interpretation of the reflection data a major zone of reflections extending over a distance exceeding 200 km can be traced from shallow depths beneath the st lawrence lowlands southeast to about 25 km depth beneath the southeast edge of the chain lakes massif this zone of reflections is interpreted as a master decollement separating autochthonous grenville basement from overlying allochthonous rocks of the appalachian orogen including foreshortened miogeoclinal rocks the remnants of one or more magmatic arcs the connecticut valley gaspe synclinorium and the chain lakes massif in the vicinity of the chain lakes massif extension has caused grenville basement to be thinned by as much as 40 reflections from the decollement show strong layering and evidence for basement faulting associated with the guadeloupe and other faults normal incidence and wide angle reflections are observed to be almost continuous beneath the baie verte brompton line and connecticut valley gaspe synclinorium indicating that the baie verte brompton line is confined to the upper crust the connecticut valley gaspe synclinorium is characterized by p wave velocities of about 5 3 km s 1 and is shown to be a shallow structure with a maximum depth of about 3 km rock velocities immediately below the connecticut valley gaspe synclinorium are typical of chain lakes material 6 1 km s 1 a new model for the tectonic development of the region is proposed in which all pre silurian units between the baie verte brompton line and the southeastern edge of the chain lakes massif are allochthonous and confined to the upper crust we infer that the chain lakes massif volcanics of the ascot weedon formation and associated deeper crustal rocks were thrust over grenvillian basement as a composite unit and may now underlie parts of the connecticut valley gaspe synclinorium

late yeadonian upper sandstone group incised valley supply and depositional systems in the south wales peripheral foreland basin implications for the evolution of the culm basin and for the silesian hydrocarbon plays of onshore and offshore uk abstract the upper sandstone group of south wales has previously been interpreted as a simple nnw sse trending incised valley that was filled during the late yeadonian namurian g1b data presented in this study indicate a far more complex scenario the group is well developed in the pembrokeshire sub basin but it is absent from the main part of the south wales basin located to the east of the penlan axis the principal source area for sediment flux was the forebulge of the basin located to the north in lower palaeozoic foreland strata variscan flexural uplift of this source area and an accompanying rapid high magnitude fall in sea level produced a very high sediment budget thus during the late yeadonian lowstand of sea level massive amounts of sediment were being generated and transported via an incised valley system across the western part of the south wales peripheral foreland basin the location and orientation of the incised supply system and its related interfluves were controlled by intrabasinal synsedimentary variscan structures many of which were reactivated caledonian extensional faults during the succeeding sea level rise the incised valley was filled initially by fluvio deltaic sands and later by estuarine argillaceous sediments the implications of this combined tectonic sedimentological high resolution sequence stratigraphic model for the evolution of the late namurian crackington formation turbidites of the culm basin are discussed examples of silesian incised valley fill sandstone reservoirs developed in the east midlands oilfield and the southern gas basin are briefly summarised and their spatial and temporal distributions are appraised data generated from these case studies are assessed in terms of their use for the modelling of incised valley fill sequences in foreland basins and other tectonic settings

inversion tectonics of the variscan foreland of the british isles late westphalian inversion structures on the variscan foreland display wide variations in orientation that are the product of the underlying basement grain the orientation of the major basement lineaments in relation to the direction of maximum shortening also determined the severity of deformation of the inverted basins ne sw trending faults were oriented roughly perpendicular to the nw se to nnw sse direction of maximum shortening determined from thrust transport directions in the variscan orogen to the south as a consequence ne sw trending basins in the variscan foreland have been strongly inverted the silesian post rift fill has commonly been expelled from the basins and the syn rift sediments have been deformed by chevron folds dublin and bowland basins in contrast the n s and nw se trending faults were oriented more obliquely to the direction of maximum shortening and as a consequence display a significant component of oblique slip this oblique slip component is manifested as en echelon periclines and flower structures in general the n s and nw se trending basins were less strongly inverted and the silesian post rift fill has been retained

processing and inversion of refraction and wide angle reflection data from the 1986 nevada passcal experiment we derive averaged one dimensional velocity models for the crust beneath the basin and range in western nevada by inverting p composites extracted from slant stacks of refraction and wide angle reflection data a combination of high cut filtering in the frequency domain with coherency filtering in the p domain has proved effective in smoothing severe static shifts due to lateral heterogeneities and suppressing artifacts due to spatial aliasing we supplement the low frequency information provided by the refraction records with higher frequency arrivals picked from the normal incidence and wide angle reflection sections generalized least squares inversion of data from eight shots for p and s wave velocity structure beneath two perpendicular profiles yields consistent estimates for total crustal thickness p wave 30 31 km s wave 30 32 km and average crustal velocity 6 2 km s 3 4 3 5 km s average poisson s ratio beneath the n s profile is 0 27 0 28 p wave velocities near the base of the crust 7 4 0 3 km s are estimated by inverting precritical reflections from the moho standard errors in depth for these models range from 1 to 3 km extremal depth bounds in general are about twice as large uncertainties in velocity estimated from resolving kernels range from 0 1 to 0 3 km s estimates of poisson1s ratio as a function of depth are characterized by large standard errors reflecting the poor resolution of shear wave velocities the combination of low average p and s wave velocities with a high average poisson s ratio in the upper half of the crust however is consistent with the presence of fluid filled cracks these results highlight the need for three component recording to better resolve shear wave velocity structure

diachronous variscan late orogenic collapse as a response to multiple detachments a view from the internides in france to the foreland in the irish sea

evaluation of a workflow to derive terrestrial light detection and ranging fracture statistics of a tight gas sandstone reservoir analog understanding natural fracture networks in the subsurface is highly challenging as direct one dimensional borehole data are unable to reflect their spatial complexity and three dimensional seismic data are limited in spatial resolution to resolve individual meter scale fractures here we present a prototype workflow for automated fracture detection along horizontal scan lines using terrestrial light detection and ranging t lidar data are derived from a kilometer scale pennsylvanian locally upper carboniferous reservoir outcrop analog in the lower saxony basin northwestern germany the workflow allows the t lidar data to be integrated into conventional reservoir modeling software for characterizing natural fracture networks with regard to orientation and spatial distribution the analysis outlines the lateral reorientation of fractures from a west southwest east northeast strike near a normal fault with approximately 600 m 1970 ft displacement toward an east west strike away from the fault fracture corridors 10 20 m 33 66 ft wide are present in unfaulted rocks with an average fracture density of 3 4 3 9 m 1 11 2 12 8 ft 1 a reservoir scale digital outcrop model was constructed as a basis for data integration the fracture detection and analysis serve as input for a stochastically modeled discrete fracture network demonstrating the transferability of the derived data into standard hydrocarbon exploration and production industry approaches the presented t lidar workflow provides a powerful tool for quantitative spatial analysis of outcrop analogs in terms of natural fracture network characterization and enriches classical outcrop investigation techniques this study may contribute to a better application of outcrop analog data to naturally fractured reservoirs in the subsurface reducing uncertainties in the characterization of this reservoir type at depth

dispersion of rg waves in southeastern maine evidence for lateral anisotropy in the shallow crust abstract group velocities of short period rayleigh waves rg are sensitive to variations in the velocity structure of the upper few kilometers of the crust in this study we analyzed dispersive properties of rg waves recorded from blasts detonated as part of the maine seismic refraction experiment conducted in 1984 by the u s geological survey the period range of the rg waves in this study is 0 4 to 1 6 sec group velocities in this period range are sensitive to the velocity structure at depths ranging from very near the surface to about 2 km group velocities were found to vary significantly from one path to the next a simple explanation of the observed pattern of group velocities is that higher velocities were observed for paths parallel to the structural grain of the appalachians than for paths transverse to the grain for example 1 sec rg waves have group velocities of about 3 0 to 3 2 km sec for paths parallel to the grain and about 2 6 to 2 7 km sec for paths transverse to the grain thus our results suggest that the shallow crust beneath the appalachians of southeastern maine is laterally anisotropic rg group velocities from this study were inverted to obtain shear wave velocity models of the upper 1 5 to 2 0 km of the crust underlying southeastern maine to compare our results with refraction and laboratory results v p was estimated from v s using a v p v s ratio of 1 78 inverting the average group velocities for all paths in this study resulted in a v p model with velocities ranging from 4 9 km sec in the upper 0 3 km to 6 2 km sec at 2 km depth the range in observed rg group velocities from one path to the next is evidence of a variation in shallow crustal structure depending on geographical location and or orientation of the paths in the upper 0 3 km v p appears to range from about 4 8 to 5 3 km sec and at 2 km depth v p appears to range from about 5 6 to 6 6 km sec

sequence stratigraphy of coastal alluvial plain westphalian b coal measures in northumberland and the southern north sea abstract westphalian b coastal alluvial plain coal measures of northumberland and the southern north sea are susceptible to stratigraphic base level fluctuations of various magnitudes which create a hierarchy of flooding surfaces 1 high magnitude third order maximum flooding surfaces corresponding to the anthracoceratites vanderbeckei and anthracoceras aegiranum marine bands defining the top and bottom of the succession when vast areas of the westphalian foreland basin were flooded by marine incursions 2 high frequency fluctuations promoting small scale fourth order flooding of the entire or large areas 100 s km 2 of the alluvial plain resulting in deposition of non marine bivalve beds or marine bands depending on their position on the third order base level curve and 3 small scale localised base level rises due to differential compaction and autocyclic switching of minor crevasse splays and distributary channels a regionally extensive third order tectonically induced sequence boundary is also recognised in the southern north sea slightly above the maximum stand in stratigraphic base level recorded by the vanderbeckei marine band this sequence boundary which represents the lowest point on the background eustatic base level curve between the two maximum flooding surfaces is overlain by the multilateral multistorey caister sandstone the lack of significant erosional relief beneath this channel sandstone suggests that accommodation space at this time was being created at a very low rate the succession above the caister sandstone sequence boundary up to the aegiranum marine band maximum flooding surface records an increasing rate of stratigraphic base level rise this equates to a third order transgressive systems tract or sequence set comprising a number of fourth order sequences which change upwards in response to the background low frequency rise the increasing rate of base level rise and increased accommodation space is accompanied by a change in fluvial style to more isolated channels enclosed within floodplain deposits

glaucophane chloritoid bearing assemblages from ne oman petrologic significance and a petrogenetic grid for high p metapelites pelitic layers and lenses interbedded with blueschists and eclogites in saih hatat ne oman contain chloritoid and sodic amphibole bearing mineral assemblages that are useful for reconstructing the p t history of the area textural and mineral chemical relations suggest that coexisting glaucophane gln and chloritoid ctd formed at the expense of chlorite chl paragonite pg and later broke down to garnet gt pg during prograde metamorphism according to the reaction gln ctd qz gt pg h2o during retrogression gln and chl first formed at the expense of gt and pg followed by the breakdown of ctd and gt to chl the final stages of retrogression are marked by the breakdown of gln to an aggregate of chl albite ab a projection from quartz qz h2o and phengite ph on the al2o3 fe2o3 feo mgo na2o plane in the system nfmash is best suited for the representation of the phase relations in high p metapelites petrogenetic grids for the model systems nmash and nfash were calculated using program geo calc berman et al 1987 and its database berman 1988 after the retrieval of s i o and h f o for gln and ctd by mathematical programming and calculating all possible reactions among gln ctd chl jadeite jd ab gt pg talc tc pyrophyllite prl and kyanite ky the calculated petrogenetic grid for the system nfash shows that fe ctd and ferroglaucophane coexist at p 6 5 kbar and t 6 kbar this grid is consistent with the p t estimates for high p metapelites from oman new caledonia seward peninsula ile de groix sifnos and peloponnese where gln ctd bearing units are interbedded with cofacial mafic blueschists and eclogites the grid also explains the observed textural relations in the metapelites of oman and is consistent with the clockwise p t path proposed for this area but differs from the grids of guiraud et al 1990 in showing a larger stability field for gln ctd that overlaps with the stability fields of jd qz as well as ab the petrogenetic grid calculated for the system nmash shows that mg ctd gln bearing assemblages require unusually low geothermal gradients to form in metapelites it also shows that mg rich ctd tc coexist at high pressures over a wider p t range than predicted by guiraud et al 1990 this grid can therefore be applied to high p metamorphic assemblages from the eastern and western alps

upper permian zechstein supergroup carbonate evaporite platform palaeomorphology in the uk southern north sea abstract seismic interpretation geological mapping and depth conversion of the zechstein supergroup z2 cycle using high quality well calibrated three dimensional 3 d seismic has revealed the complex palaeomorphology of a deeply buried ancient carbonate shelf margin on the southwestern margin of the southern permian basin the new mapping shows that the margin comprises a series of corrugated embayments and promontories which extend up to 5 km 3 mi into the basin and locally have a palaeobathymetric relief of 200 m 650 ft well calibration across the margin demonstrates a strongly bipartite lateral thickness distribution between a high velocity anhydrite dominated shelf and a lower velocity halite dominated basin strong lateral and vertical velocity variations in the upper permian zechstein supergroup are known to have major impacts upon seismic imaging and depth conversion in the spb the resulting uncertainty remains one of the major challenges when interpreting and assessing the prospectivity of the underlying upper permian rotliegend group leman sandstone formation reservoirs in the uk southern north sea an understanding of the zechstein shelf edge s 3 d physiography and its velocity variation has implications for the delineation of traps containing the prospective reservoirs that lie below recognition of the complexity and effects of this shelf margin contributed to the recent juliet discovery whose position outside of the presently defined rotliegend group play fairway suggests that prospectivity is more extensive along the basin margin than previously thought as such the work provides a means by which to identify and delineate new structures and extend the life of this mature yet prolific gas province

avalon terrane in eastern coastal maine seismic refraction wide angle reflection data a 145 km long seismic refraction line recorded parallel to the eastern coastline of maine within the avalon terrane provides information about the crustal velocity structure within the avalon block and its relation to other appalachian terranes a crustal velocity model for the upper 8 km determined by using two dimensional ray tracing accounts for all first arrivals on the traveltime curves for each of the shots recorded and shows that except for a thin surficial layer of velocity 5 0 5 3 km s upper crustal granites and country rocks have velocities in the range 6 0 6 3 km s and gabbros have a 6 5 km s velocity to determine the lower crustal structure deep reflections were analyzed by applying normal moveout corrections routinely used in reflection data processing major reflective boundaries at approximately 3 4 7 and 10 11 s two way traveltime are easily distinguished and are similar to those observed in a near vertical seismic reflection survey crossing the refraction profile at its southwestern end the deepest reflections correspond to the crust mantle boundary at a depth of 34 35 km

aberrations in the coalification patterns of the offshore coalfields of northumberland and durham united kingdom abstract the offshore extensions of the northumberland and durham westphalian coalfields are formed of continuous and linked sequences of sediments which lie in contrasting structural regimes respectively basin and block the coalfields have suffered different geothermal histories offshore northumberland basin sediments endured low heating rates and low maximum temperatures to give seams which even at the base of the succession hardly reached vitrinite reflectances of roil 0 60 apart from raised values due to igneous activity the offshore durham block succession was exposed to higher temperatures and heating rates due to the proximity of the lower devonian weardale granite underlying the block which was re activated during carboniferous times these geothermal conditions not only led to higher levels of reflectance and steeper maturation gradients offshore in the block succession than offshore in coals of the basin but also produced contrasting relationships between correlations of vitrinite oil reflectance and volatile matter yield of coals for the two structural zones and probably also for other property relationships as well reflectance profiles have been modified due to three circumstances first considerable variation locally in the raising of reflectance levels caused by igneous activity second lowering of vitrinite reflectance values due to arenaceous sediments being deposited immediately on top of vitrinite precursors within the coal forming organic matter and third possible interference from liptinite rich accumulations within coal seams or near to them in the succession which exuded aliphatic materials relatively early in coalification which were then absorbed by vitrinites or more likely deposition of the vitrinite precursors in a marine near marine and calcium rich environment so reducing reflectance values on coalification similar contrasting property relationships to those described here may have been produced by lower devonian granitoid bodies which have been identified on the north sea high if they also were re activated during the carboniferous

a buried granite batholith beneath the east midland shelf of the southern north sea basin published bgs gravity data of the uk southern north sea basin show the presence of a gravity low trending to the ese across the northern half of quadrant 47 two simplified geological cross sections have been constructed across this feature with sedimentary structure based upon well information and reflection seismic data gravity modelling of these sections demonstrates that the gravity anomaly is unlikely to be produced by the presence of thick low density sediments consequently the presence of a large buried granite batholith is postulated the buoyant influence of such a granite may have exerted considerable tectonic control during the development of the southern north sea basin in particular its presence may help to explain the development of the east midland shelf the associated complex fault movements along the flamborough head and dowsing fault zones and the areal distribution and thickness of the rotliegendes sand

seismic facies analysis of westphalian sequences of the southern north sea abstract differing seismic facies are observed from within the westphalian sequences of the southern north sea a review of published synthetic seismograms and seismic data from known coal bearing basins establishes seismic facies types and their relationships similar reflection character is recognized from westphalian sequences in the southern north sea and lithologies confirmed by borehole information probable sand silt or clastic prone upper coal measures westphalian c d stages and coal prone lower and middle coal measures westphalian a b and part c stages can be defined and mapped providing information on the regional distribution of source and reservoir rocks and stratigraphic plays it is suggested that sand prone channel complexes or clastic dominated areas within the mainly a b stages can be recognized and mapped providing information on migration pathways and stratigraphic plays

the crustal structure in central maine from coherency processed refraction data in 1984 the u s geological surcvey and the canadian department of energy mines and resources conducted an extensive seismic refraction experiment the quebec maine transect project as part of this project a 180 km long seismic refraction profile was recorded along the axis of the central maine synclinorium high near surface velocities of 6 0 6 2 km s made a conventional refraction analysis including first arrivals uninformative below about 10 km peak signal frequencies around 30 hz recorded at all offsets and a trace spacing of 800 m led to severe spatial aliasing effects for secondary arrivals on the record sections to allow a reliable deep structural interpretation a coherency processing technique was applied to the data to enhance phase coherent secondary arrivals in addition interpretation of a coincident wide angle reflection study provided constraints on the deep crustal velocities and structure the crust beneath the central maine synclinorium can be described by three major structural units the upper crust is interpreted as the metasedimentary rocks of the central maine synclinorium with velocities that range from 6 2 to 6 3 km s regions of relative lower velocity 6 0 6 1 km s within the upper crust are interpreted as granitic intrusions low velocity regions modeled at 2 7 km depth with velocities around 5 4 km s are interpreted as seismic evidence for folding and doubling within the upper crustal metasedimentary sequence at 12 15 km depth the base of the synclinorium appears alternately as a strong reflector indicating the presence of layering and also as a weak reflector especially ne of the sebago pluton a 4 km thick boundary layer at 24 km depth is interpreted as a major intracrustal shear zone in which the velocity increases from 6 4 to 6 8 km s the crust thickens from 36 to 40 km going from refraction experiment the quebec maine transect project as part of this project a 180 km long seismic refraction profile was recorded along the axis of the central maine synclinorium high near surf ace velocities of 6 0 6 2 km s made a conventional refraction analysis including first arrivals uninformative below about 10 km peak signal frequencies around 30 hz recorded at all offsets and a trace spacing of 800 m led to severe spatial aliasing effects for secondary arrivals on the record sections to allow a reliable deep structural interpretation a coherency processing technique was applied to the data to enhance phase coherent secondary arrivals in addition interpretation of a coincident wide angle reflection study provided constraints on the deep crustal velocities and structure the crust beneath the central maine synclinorium can be described by three major structural units the upper crust is interpreted as the metasedimentary rocks of the central maine synclinorium with velocities that range from 6 2 to 6 3 km s regions of relative lower velocity 6 0 6 1 km s within the upper crust are interpreted as granitic intrusions low velocity regions modeled at 2 7 km depth with velocities around 5 4 km s are interpreted as seismic evidence for folding and doubling within the upper crustal metasedimentary sequence at 12 15 km depth the base of the synclinorium appears alternately as a strong reflector indicating the presence of layering and also as a weak reflector especially ne of the sebago pluton a 4 km thick boundary layer at 24 km depth is interpreted as a major intracrustal shear zone in which the velocity increases from 6 4 to 6 8 km s the crust thickens from 36 to 40 km going from the ne to the sw end of the profile surface rocks at the sw end of the profile have a metamorphic depth of burial of at least 15 km indicating that the crust below the central maine synclinorium may have been thickened to at least 55 km during paleozoic collisions

high pressure low temperature metamorphism in the gran paradiso basement western alps the gran paradiso basement complex of the french and italian alps is composed of metasediments termed the gneiss minuti and metabasic rocks both of which are intruded by a late hercynian granite the bonneval gneiss which crops out at the western edge of the complex is composed of highly deformed metasediments volcanics and volcaniclastic rocks eclogites now highly altered occur in the metabasic rocks kyanite and blue green amphibole are locally present in the gneiss minuti and aegirine plus riebeckite occur in the bonneval gneiss a moderately high pressure low temperature metamorphic event of probable alpine age occurred in the basement complex this metamorphic event differs from that in the overlying sesia unit and ophiolites of the schistes lustres nappe in being at lower pressures below the ab jd100 qz transition and post dating the major d2a deformation the origin of the metamorphism is discussed and interpreted as a probable consequence of the overlying nappe pile which was emplaced during the d2a event subsequent greenschist facies metamorphism in the basement complex is a consequence of thermal relaxation during uplift

the silkstone rock westphalian a from the east pennines england implications for sand body genesis the silkstone rock westphalian a langsettian is a major multistorey channel sandstone formed in a delta plain environment with minimal marine influence it occupies up to three interseam intervals in the east pennine coalfield england and exceeds 50 m in thickness and 15 km in width at its maximum development which is larger than many westphalian channel sand bodies the high ash content of coal adjacent to the channel belt indicates that regional peat accumulation took place contemporaneously with the existence of the channel system the major channel system fed a number of minor channels during different interseam intervals and conducted sediment and water into nearby delta plain lakes via lacustrine delta and crevasse splay systems these minor channels which show a range of fills are sub parallel and show lateral offset stacking suggesting that differential compaction was an important control on their location the major channel belt acted as a long lived distributary system that flowed towards the east away from the overall basin depocentre with its position being controlled mainly by deltaic processes

a buried granite batholith and the origin of the sole pit basin uk southern north sea modelled gravity profiles based upon the post carboniferous geological structure revealed by reflection seismic data have been used to predict the gravity variation across part of the southern north sea basin when compared to the observed gravity field these calculated values reveal a significant residual gravity low located to the east of the sole pit axis this low may indicate the presence of a large buried granite body a sister to the granite previously proposed beneath the east midland shelf to the sw of the sole pit axis during periods of extensional tectonics major subsidence has occurred within the sole pit basin between these two granite cored stable areas

wide angle deep crustal reflections in the northern appalachians summary seismic refraction data collected in the northern appalachians provide an unusual opportunity to use wide angle reflections to examine the lower crust and upper mantle the pmp phase clearly identified on several hundred records has been used to construct an isopach map of the crust which shows a stepwise regional thickening of the crust beneath the axis of the appalachians the data have been examined to times of up to 40 s two way travel time to investigate the possibility of coherent upper mantle reflections such as those recently observed by birps on near vertical data northwest of britain although substantial coherent energy appears after the pmp phase synthetic seismogram modelling shows that all of these arrivals are explicable by s phases converted phases and multiples from within the crust we conclude that in this region of the northern appalachians we have not detected any significant regionally extensive reflecting horizons within the upper mantle

synthesis of salt tectonics in the southern north sea uk abstract a structural model encompassing the southern north sea basin west of the central graben has been developed this model consists of a rift system affecting the post salt section around the basin margin and a large area of detached compressional buckle folds within the basin this pattern is initially a response to gravity sliding of the post salt section on the salt within the basin during the late triassic to late jurassic a close relationship between the location and trend of the peripheral graben system and basement structures in the pre salt is noted pre jurassic extension across the peripheral graben systems was balanced by the sum of fault heaves at the pre salt rotliegend level and shortening across salt cored buckle folds in the post salt section salt pillows and swells passively infilled the cores of these gravity induced buckle folds cretaceous and tertiary inversion involved basin tilt and renewed movement on basin bounding basement faults notably reverse movements did not propagate from basement structures up into the peripheral graben systems the post salt sedimentary section experienced gravity spreading in response to inversion related uplift resulting in syn inversion extensional faulting in the sole pit high where the mesozoic section was thickest this extension combined with a loss of fault heave in the pre salt section was balanced by amplification of salt cored buckle folds in the centre of the basin in the context of the model described here salt pillows represent passive infill of thin skinned compressional buckle folds which later amplified during thick skinned basement shortening crestal collapse of such folds occurs via normal faulting accompanied by reactive diapirism such reactive diapirs establish conduits through which salt may leak leading to pillow deflation and ultimately conduit preservation as a salt wall flanked by rim synclines in areas where the buckle folds were emergent the salt structures described here are related to cover folds and faults which in turn reflect episodes of basin extension tilting and inversion hence individual salt structures can be said to be only remotely connected with regional intraplate stresses

upper carboniferous and lower permian tectonostratigraphy on the southern margin of the central north sea hydrocarbon exploration in uk licence blocks 31 26 and 39 2 on the southern margin of the central north sea in 1996 and 1997 proved the presence of a palaeozoic sedimentary succession previously undescribed in the area biostratigraphic data from the sediments and radiometric dating of interbedded basaltic lavas indicate that the succession spans the upper carboniferous westphalian b to lower permian asselian interval this has been informally split into three sedimentary units the lower flora sandstone is of westphalian b c age this clastic interval is overlain by the first of two main lavas which is in turn overlain by the westphalian c d to stephanian upper flora sandstone the flora sandstones are interpreted to be lithostratigraphic equivalents to the schooner formation of the southern north sea the flora sandstones are separated from the grensen formation by an angular unconformity possibly related to variscan asturic inversion the grensen formation is in turn overlain by a second basaltic lava flow both basaltic units are assigned to the inge volcanics formation rotliegend group petrographic data indicate that the grensen formation also forms part of the rotliegend group a major extensional event of permian age post dates all of these strata extensional faults are planed by a regional unconformity saalian unconformity that is overstepped by permian to cretaceous strata

active folding in the algerian earthquake of 10 october 1980 a fold controlling the form of the local topography near el asnam algeria increased in amplitude at the time of the earthquake of 10 october 1980 the deformation occurred rapidly in an elastic brittle manner and not in the gradual ductile fashion in which folds are normally thought to develop

alluvial fans and fluvial fans at the margins of continental sedimentary basins geomorphic and sedimentological distinction for geo energy exploration and development alluvial fans and fluvial fans are the most common depositional landforms along the margins of continental sedimentary basins their occurrence is determined by the area relief and hydrology of the catchment which ultimately control the relative ratios of sediment v flow discharge and runoff regimes fundamental morphological and process distinctions exist between these two kinds of deposystem which are seen as essentially different facies associations and internal architectures for the corresponding deposits alluvial fans commonly develop over short radial distances hundreds of metres to a few kilometres and are constructed by ephemeral flash flow events that lead to poor organization of the sedimentary facies and overall architecture of the corresponding deposits by contrast fluvial mega fans are fed by proper river systems which aggrade much larger volumes of clastic sediment over distances of up to a few hundred kilometres distinct channel belt and overbank domains are developed with a marked heterogeneity in the distribution of sedimentary facies represented by hierarchically well organized fluvial deposits the general properties of alluvial and fluvial fans reflect the different potentials for the corresponding successions to host economically attractive oil and gas resources and the different approaches required in exploration and prediction

a sequence stratigraphic model for the lower coal measures upper carboniferous of the ruhr district north west germany upper carboniferous coal measures strata have been interpreted traditionally in terms of cyclothems bounded by marine flooding surfaces marine bands and coal seams correlation of such cyclothems in an extensive grid of closely spaced coal exploration boreholes provides a robust stratigraphic framework in which to study the lower coal measures namurian c westphalian a of the ruhr district north west germany three distinct types of cyclothem are recognized based on their bounding surfaces and internal facies architecture 1 type 1 cyclothems are bounded by marine bands each cyclothem comprises a thick 30 80 m regionally extensive coarsening upward delta front succession of interbedded shales siltstones and sandstones which may be deeply incised by a major fluvial sandstone complex the delta front succession is capped by a thin 5 km wide 20 40 m thick steep sided multistorey fluvial sandstone complexes erode deeply into and in some cases through these successions and are overlain by the coal seam defining the cyclothem top 3 type 3 cyclothems are bounded by regionally extensive coal seam groups characterized by numerous seam splits on a local 0 1 10 km scale intervening strata vary in thickness 15 60 m and are characterized by strong local facies variability root penetrated aggradational floodplain heteroliths pass laterally into single storey fluvial channel fill sandstones and coarsening upward shallow lake infill successions of interbedded shales siltstones and sandstones over distances of several hundred metres to a few kilometres narrow 2 km but thick 20 50 m multistorey fluvial sandstone complexes are rare but occur in a few type 3 cyclothems several cyclothems are observed to change character from type 1 to type 2 and from type 2 to type 3 up the regional palaeoslope consequently we envisage a model in which each cyclothem type represents a different palaeogeographic belt within the same idealized delta system subject to the same allogenic and autogenic controls on facies architecture type 1 cyclothems are dominated by deltaic shorelines deposited during a falling stage and lowstand of sea level type 2 cyclothems represent the coeval lower delta plain which was deeply eroded by incised valleys that fed the falling stage and lowstand deltas type 3 cyclothems comprise mainly upper delta plain deposits in which the allogenic sea level control was secondary to autogenic controls on facies architecture the marine bands widespread coals and coal seam groups that bound these three cyclothem types record abandonment of the delta system during periods of rapid sea level rise the model suggests that the extant cyclothem paradigm does not adequately describe the detailed facies architecture of lower coal measures strata instead these architectures may be better understood within a high resolution stratigraphic framework incorporating sequence stratigraphic key surfaces integrated with depositional models derived from analogous pleistocene holocene fluvio deltaic strata

more seismic evidence on the location of grenville basement beneath the appalachians of quebec maine summary high quality multichannel seismic 133 fold and refraction wide angle reflection 1 to 3 km receiver spacing and 30 to 60 km shot spacing data have been collected across the northern appalachians in quebec and maine an integrated interpretation of the seismic data from the southeastern quebec western maine region provides strong evidence that the rocks of the predominantly oceanic dunnage zone are allochthonous having been thrust westwards over precambrian grenville basement during and subsequent to the closing of the iapetus ocean

early carboniferous extension in east avalonia 350 my record of lithospheric memory abstract despite reactivations during variscan and alpine orogenies and the opening of the northern atlantic avalonia is one of the few regions where the initial mid paleozoic basin structure is still recognisable largely intact and well studied its kinematics and dynamics remain however largely unknown in particular in view of the successive late paleozoic to recent evolution of the basin consequently the importance of the mid palaeozoic tectonic evolution and structural controls are often overlooked and poorly understood in basin studies in this paper we reassess the importance of mid palaeozoic tectonics on subsequent sedimentary basin evolution of north western europe to this end we analyse the dynamics of early variscan extension in avalonia based on the integration and re evaluation of available geophysical and geological data from lithosphere to basin scales based on a revised crustal map of the thor suture zone we present a new paleo tectonic reconstruction and tectonic scenario for the devonian carboniferous rifting these findings are key for a better understanding of long lived tectonic segmentation and post rifting deformation phases our findings indicate that the structural grain of many crustal fault dominated sedimentary basin structures such as the north sea central graben were created in the early carboniferous consequently the main basement structuration of northwest europe was completed before the variscan orogeny and successive post variscan extension and inversion phases reactivated the existing basement structures without creating major new fault groups incorporation of the paleozoic structural grain allows for a consistent tectonic framework for the mesozoic contributing to fundamental understanding of basin evolution from our tectonic framework analysis avalonia therefore stands out as a fine example of long lived lithosphere memory spanning over 350 my of structural control in geodynamic evolution

warwickshire group pennsylvanian red beds of the canonbie coalfield england scotland border and their regional palaeogeographical implications late carboniferous red beds 700 m thick at outcrop and in the subsurface of the canonbie coalfield can be assigned to the warwickshire group they are preserved within the axial part of the solway syncline and are divisible into the eskbank wood canonbie bridge sandstone and becklees sandstone formations sedimentation largely took place on a well drained alluvial plain characterized mainly by early primary oxidation of the strata large northerly flowing braided river systems were common with overbank and floodplain fines deposited lateral to the channels soils formed during intervals of low sediment aggradation the canonbie succession includes some of the youngest carboniferous rocks preserved in the uk correlation of the eskbank wood formation is equivocal but using petrographical heavy mineral zircon age dating and palaeocurrent data the canonbie bridge sandstone formation can be unambiguously correlated with the halesowen formation of warwickshire the pennant sandstone formation of south wales and the offshore boulton formation this suggests that southerly derived detritus travelled considerable distances from the variscan highlands of brittany and or central germany across the southern north sea and uk areas to a position some hundreds of kilometres north of that previously recognized the becklees sandstone formation has much in common with the salop formation of the english midlands it appears to have no preserved equivalent elsewhere in the uk or in the uk sector of the southern north sea but resembles stratigraphically higher parts of the southern north sea succession seen in the dutch sector

miocene to present differential exhumation in the western alps insights from fission track thermochronology 1 analysis of cooling age patterns yielded by low temperature thermochronometers provides key information about the role played by tectonic discontinuities during the late stages of exhumation of metamorphic belts in the western alps fission track data published so far are heterogeneously scattered and concentrated in few structural domains preventing analyses at the scale of the whole belt the new apatite fission track data reported in this work obtained with the external detector method as well as the population method in very low u content samples fill this gap they constrain the postmetamorphic evolution of the western alps along two transects from the foreland to the retroforeland unraveling the effective role played by some major faults during the exhumation of the belt at shallow crustal levels a clear regional pattern characterized by decreasing ages moving from the axial sector to the european external sector of the belt and by an along strike gradient with increasing ages from north to south has been unraveled evident breaks in this age pattern have been detected in correspondence of faults that are near parallel to the trend of the belt pointing to the occurrence of active tectonics during and after exhumation the most apparent breaks have been observed in the axial sector of the belt where the postmetamorphic deformation would have been negligible according to classic tectonic models faults located in the axial sector split the belt into two major blocks eastern and western since the miocene the western block experienced higher exhumation rates than the eastern one such differential exhumation was accommodated in the northern portion of the belt thanks to reverse motion along the internal houiller fault which occurred in a convergent transcurrent framework to the south it was accommodated instead by normal reactivation of the brianconnais front and by activity of the longitudinal fault system which occurred in a divergent transcurrent framework the tectonic activity affecting the axial sector of the belt in a context of regional dextral strike slip is coeval with the forward propagation of the external thrusts and of similar magnitude we suggest that the contrasting kinematic regimes i e convergent versus divergent transcurrence observed in the western alps moving along strike were responsible of the increasing exhumation rates toward the north revealed in both blocks by the along strike age gradient the higher exhumation rates recognized northward would be related to an increasing importance of crustal shortening that promoted erosion during the late stages of exhumation of the belt

dating deformation using rb sr in white mica greenschist facies deformation ages from the entrelor shear zone italian alps ages of deformation have been obtained by rb sr analysis of white micas whose microstructural and chemical characteristics indicate that they crystallized or recrystallized during shear fabric formation since white micas commonly define deformation fabrics in medium grade metamorphic rocks these ages can be directly related to structural geometries with regional context this direct method contrasts with estimates of midcrustal deformation ages derived from cooling histories because it does not rely on assumptions about the thermal structure of the crust it does require that the dated minerals attained isotopic equilibrium with the dominant sr reservoir at temperatures lower than the closure temperature this resetting was apparently achieved during dynamic recrystallization of white micas in greenschist facies metasediments and metagranitoid units in the western alps the results suggest that the sr isotopic composition of the new mica is buffered by the coexisting high sr phases calcite feldspar or epidote via the grain boundary network high strain rocks from the entrelor shear zone system of the western alps have yielded indistinguishable white mica rb sr ages along 30 km of individual and kinematically linked shear zones the age of the back thrusting event is constrained at 34 1ma the age yielded by the younger generation of synkinematically crystallized white micas this event was short lived involving at least 20 km of shortening in 1 m y or less an earlier variably overprinted component dating from 38 to 37 ma has been identified in the mica fabric but its kinematic significance is uncertain this method of dating strain fabrics offers a powerful tool for tectonic studies since isotopic resetting can be directly linked to structural geometries microstructural textures and pt conditions it allows testing of kinematic models in orogens and can provide important information on the rates of geological processes in the crust

tectonic interpretation of an inverse gradient of zircon fission track ages with respect to altitude alpine thermal history of the gran paradiso basement extensive sampling along vertical and north south cross sections in the gran paradiso basement internal crystalline massif western alps reveals an inverse gradient of zircon fission track ages with respect to altitude which is explained by an inverted metamorphism during eocene time subsequent to the obduction of the schistes lustres nappe high pressure eoalpine phase the gran paradiso massif cooled down 90 80 myrs ago the austro alpine nappe of monte emilius dent blanche overthrust the gran paradiso massif 38 40 myrs ago inducing in its basement an inverted metamorphism or more precisely a nappe emplacement metamorphism greenschist facies the last cooling below 100 c occurred as early as 35 40 myrs ago in the southern gran paradiso massif in the northern part this last cooling occurred 20 myrs ago accompanied by an important uplift phase 2 mm year

structural synthesis of s staffordshire uk implications for the variscan evolution of the pennine basin the presence of strata of westphalian a to possibly stephanian age in south staffordshire located at the southern margin of the pennine basin provides a rare control on the timing of late carboniferous deformation in central england during westphalian a c times sedimentation in south staffordshire was controlled by thermal subsidence with a superimposed influence of synsedimentary normal and reverse faulting alkaline basic igneous activity occurred during westphalian c times synchronous with uplift of the southern margin of the pennine basin uplift culminated during westphalian c d times in a phase of variscan inversion along basement lineaments and the development of a regional unconformity renewed subsidence and deposition of a relatively thick sedimentary sequence of westphalian d to possibly stephanian age was followed by a final phase of variscan deformation comprising possibly two pulses of uplift tilting and erosion observations presented for south staffordshire in conjunction with studies from other parts of the pennine basin indicate a complex interrelationship between rifting thermal subsidence and variscan basin inversion pulses of n s extension and e w to nw se compression are interpreted as the product of regional strike slip deformation superimposed upon a regime of thermal subsidence alkaline igneous activity is considered to be the product of mantle partial melting in response to limited decompression due to transtensional displacements on crustal thickness faults

tectono metamorphic evolution of the siliciclastic units in the middle tuscan range inner northern apennines mg carpholite bearing quartz veins related to syn metamorphic syn orogenic foliation abstract this paper accounts for a new finding of high pressure low temperature hp lt metamorphism documented in continental derived rocks exposed in the central part of the middle tuscan range representing the easternmost location in the tyrrhenian region where blueschist facies metamorphism has been documented it describes the development mechanism of mg carpholite bearing quartz veins in the framework of the deformational events described for the inner northern apennines the hp lt peak metamorphism can be estimated in p 1 1 gpa and t 370 420 c as supported by the mineralogical assemblage consisting of quartz muscovite chloritoid pyrophylite hematite chlorite paragonite ti oxides documented in the aluminous metasediments pelites and quartzose sandstones of the triassic verrucano succession this paragenesis defines the s 1 schistosity an axial planar tectonic foliation associated to map and mesoscale isoclinals folds f 1 s 1 schistosity is a composite foliation resulted from a non coaxial progressive deformation associated to the de 1 collisional event late oligocene early miocene mg carpholite bearing quartz veins developed as tension gashes in en echelon arrays within brittle ductile shear zones the development of quartz veins was guaranteed by the high volumes of si rich fluids produced by the dynamic recrystallization process on the siliciclastic rocks

devonian marine incursions into the orcadian basin scotland bp chevron well 14 6 1 drilled in the east orkney basin has penetrated devonian sedimentary rocks which can be dated palynologically as within the latest givetian to early frasnian interval this microflora contains the first substantiated record in western europe of archaeoperisaccus a spore hitherto regarded as restricted to northern laurasia three grey green intervals within the well contain marine microfossils which provide the first direct evidence for the movement of marine waters into the northern part of the old red sandstone continent onshore an eday marls section in the bay of berstane orkney contains a marine microfauna which demonstrates the presence of a marine incursion of mid late givetian age this is the first record of a devonian marine incursion in scotland combination of this palaeontological data with sedimentological studies of the eday marls and upper old red sandstone suggests that a wide flat sabkha plain extended eastwards from the onshore orcadian basin during the later stages of its infill and was subjected to episodic marine incursions these incursions are tentatively linked with marine transgressions into the argyll area of the central north sea two orders of cyclicity occur within the dated devonian interval of 14 6 1 and are interpreted as resulting from orbital cyclicity at periodicities of 39 5 and 413 9 ky this indicates that the control on the devonian sea level maxima may have been orbital cyclicity these marine incursions are speculatively correlated to high stands on the devonian sea level curve the bay of berstane marine incursion representing the taghanic onlap whilst those in 14 6 1 are the rhinestreet middlesex and genundewa transgressions reconsideration of the palaeogeography of the northern margin to the marine devonian indicates that the sea entered the orcadian basin from the east along the tornquist zone at the margin of the fenno scandian high