minas fault zone late paleozoic history of an intra continental orogenic transform fault in the canadian appalachians abstract the minas fault zone mfz defines the boundary between the avalon and meguma terranes in the canadian appalachians and is exposed in mainland nova scotia and southern new brunswick these terranes originated along the gondwanan margin but had accreted to laurentia by the middle devonian the surface trace of the mfz is adjacent to the southern margin of the latedevonian permian maritimes basin the late devonian late carboniferous evolution of the mfz involves several episodes of oblique dextral shear that resulted in basin formation and inversion and at various times the zone was the focus of magmatism regional fluid flow and mineralization in the late devonian early carboniferous asymmetric rifting accompanied by dextral shear produced two coeval sequences the horton group which is dominated by continental clastic strata and the fountain lake group which consists predominantly of bimodal volcanic rocks that overlie high level plutons emplaced along active shear zones the overall tectonic environment may have been dominated by dextral transtension along the southern margin of laurentia which corresponded with the northern flank of the rheic ocean a major change in the evolution of the minas fault zone occurred in the late mississippian early pennsylvanian and produced the e w chedabucto fault clockwise rotation of pre existing structures local zones of transtension and transpression as well as regional fluid flow and extensive mineralization this major change may reflect the onset of laurentia gondwana oblique collision the effects of which continued into the latest carboniferous with coeval development of flower structures and pull apart basins in zones of local transpression and transtension

orogenesis and basin development u pb detrital zircon age constraints on evolution of the late paleozoic st marys basin central mainland nova scotia abstract the st marys basin along the southern flank of the composite late paleozoic magdalen basin in the canadian appalachians and along the avalon meguma terrane boundary contains late devonian early carboniferous continental clastic rocks of the horton group that were deposited in fluvial and lacustrine environments after the peak of the acadian orogeny shrimp ii geological survey of canada data on approximately 100 detrital zircons from three samples of horton group rocks from the st marys basin show that most of the zircons have been involved in a multistage history recycled from clastic rocks in the adjacent meguma and avalonian terranes although there is a minor contribution from early silurian 411 ma and late devonian suites ca 380 370 ma neoproterozoic ca 700 550 ma and paleoproterozoic ca 2 0 2 2 ga zircon populations predominate with a minor contribution from ca 1 0 1 2 and 1 8 ga zircons published u pb single zircon analyses on clastic sedimentary rocks indicate th

post paleocene cooling in the southern canadian atlantic region evidence from apatite fission track models the traditional view of the geomorphic evolution of the southern canadian atlantic margin is one of gradual exhumation and peneplanation following triassic jurassic rifting thermal modelling of apatite fission track data from pre carboniferous granitic basement in nova scotia and from permian and triassic sandstones from nova scotia new brunswick and prince edward island suggest a more complex thermal evolution of the onshore part of the margin models clearly indicate significantly elevated regional paleotemperatures during jurassic time and as much as 30 c of post paleocene cooling model predicted paleogeothermal gradients for granitic samples from the digby d 1 well are normal ranging from 15 to 20 c km post paleocene cooling may be attributable to the combined effects of 13 c of exhumational cooling from erosion of approximately 700 m of post aptian sediments caused by decreased eustatic sea levels and 8 17 c of cooling from the propagation to depth of a 10 20 c decrease in paleo mean ann

the provenance of middle jurassic sandstones in the scotian basin petrographic evidence of passive margin tectonics the tectonic and geomorphological evolution of the scotian margin and its hinterland is poorly known between late triassic rifting and the early cretaceous progradation of major deltas this study determined sedimentary provenance of middle jurassic mohican formation sandstones from three wells using heavy minerals and mineral chemistry indicator minerals such as xenotime altered ilmenite and varietal types of garnet and tourmaline are similar to those in hauterivian barremian sandstones in the western scotian basin which are almost exclusively derived from the meguma terrane the wells adjacent to the canso ridge have more zircon and less ilmenite indicating a greater contribution of polycyclic reworking but with an ultimate source in the meguma terrane zircon and ilmenite were likely derived in part from carboniferous sandstones in eastern mainland nova scotia and cape breton island any river drainage from the inboard terranes of the appalachians either was diverted through the fundy basin or entered the easternmost scotian basin where the mohican formation is 5 5 km thick along the linear continuation of the southwest grand banks transform such sediment did not reach the canso ridge suggesting that the cobequid chedabucto fault zone in orpheus graben was not a significant physiographic feature this tectonically controlled paleogeography in the middle jurassic is quite different from that during active rifting in the late triassic early jurassic middle jurassic quiescence was followed in the tithonian early cretaceous by renewed tectonic uplift associated with rifting of grand banks from iberia and labrador from greenland

stratigraphic record of the early mesozoic breakup of pangea in the laurasia gondwana rift system rift basins of the central atlantic margins cam of north america and morocco preserve largely continental sequences of sedimentary strata and less important minor basalt flows spanning much of the early mesozoic the best known is the newark basin of new jersey new york and pennsylvania where an astronomically calibrated magnetic polarity time scale is developed lacustrine cycles of milankovitch origin are commonly present in cam basins with the period changing from 10 ky paleoequator with coals to 20 ky 4 10n to perhaps 40 ky northward with evaporites cycles of100 ky 413 ky and2 my are also important four mostly unconformity bounded tectonostratigraphic sequences are present the anisian ts i is fluvial and eolian ts ii ts iv late triassic to early jurassic consist of tripartite lacustrine sequences caused by extension pulses the newark basin accumulation rate history allows comparison with quantitative rift basin models the north american plate s slow northward drift resulted in a relative shift of climate although the rapid humidification during the latest triassic and early jurassic is associated with a sea level rise the triassic jurassic mass extinction is of independent origin plausibly impact related

a new paradigm for the predominance of standing central pacific warming after the late 1990s canonical el nino has a warming center in the eastern pacific ep but in recent decades el nino warming center tends to occur more frequently in the central pacific cp the definitions and names of this new type of el nino however have been notoriously diverse which makes it difficult to understand why the warming center shifts here we show that the new type of el nino events is characterized by 1 the maximum warming standing and persisting in the cp and 2 the warming extending to the ep only briefly during its peak phase for this reason we refer to it as standing cp warming cpw global warming has been blamed for the westward shift of maximum warming as well as more frequent occurrence of cpw however we find that since the late 1990s the standing cpw becomes a dominant mode in the pacific meanwhile the epochal mean trade winds have strengthened and the equatorial thermocline slope has increased contrary to the global warming induced weakening trades and flattening thermocline we propose that the recent predominance of standing cpw arises from a dramatic decadal change characterized by a grand la nina like background pattern and strong divergence in the cp atmospheric boundary layer after the late 1990s the anomalous mean cp wind divergence tends to weaken the anomalous convection and shift it westward from the underlying sst warming due to the suppressed low level convergence feedback this leads to a westward shift of anomalous westerly response and thus a zonally in phase sst tendency preventing eastward propagation of the sst anomaly we anticipate more cpw events will occur in the coming decade provided the grand la nina like background state persists

mesozoic stratigraphy and paleoenvironments of the georges bank basin a correlation of exploratory and cost wells abstract the exxon 975 1 conoco 145 1 and mobil 312 1 hydrocarbon exploratory wells and the continental offshore stratigraphic test cost g 1 and g 2 wells were drilled in the southeastern part of the georges bank basin we used drill cuttings and logs from these wells to describe and correlate the dominant lithostratigraphic units and to document lateral changes in the depositional environments the strata penetrated by the exxon 975 1 and cost g 1 wells are much more terrestrial than at the seaward downdip cost g 2 conoco 145 1 and mobil 312 1 wellsites oldest rocks penetrated by the exploratory wells represent a middle jurassic carbonate evaporite sequence that correlates to the iroquois formation the iroquois records nonmarine to marginal marine sabkha tidal flat and restricted lagoonal paleoenvironments in the exxon 975 1 and cost g 1 wells but progressively changes to inner neritic littoral and lagoonal paleoenvironments at the mobil 312 1 wellsite the nonmarine deltaic siliciclastics of the overlying mohican formation misaine shale and mic mac mohawk formations are thicker and the marine carbonates of the scatarie and bacarro limestones are usually thinner in the jurassic strata of the exxon 975 1 and cost g 1 wells than at the other wellsites similarly lower delta plain and delta front facies of the early cretaceous missisuaga and logan canyon formations at the exxon 975 1 and cost g 1 wellsites reflect a greater terrestrial influence than the laterally equivalent shallow marine to delta front facies present at the downdip wellsites

burial and exhumation of the long range inlier and its surroundings western newfoundland results of an apatite fission track study the long range inlier a steep sided plateau underlain mainly by grenvillian gneisses is the most prominent topographic feature of western newfoundland apatite fission track analysis of 31 samples from the long range inlier and its surroundings yielded measured apparent ages of 343 152 ma age versus elevation plots track length distributions and model thermal histories indicate that the region experienced slow cooling in the late paleozoic with apparent exhumation rates of 7 9 m ma 1 and cooling rates of 0 08 0 28 c ma 1 model thermal histories suggest that the present upper surface of the long range plateau cooled below 120 c in ordovician times the thermal histories are compatible with but do not require some exhumation of the long range inlier along acadian thrust faults results from early carboniferous sedimentary rocks of the deer lake basin are similar to long range inlier data from similar elevations implying that at some time between 350 and 300 ma the entire region was buried to

geochemical identification of clastic sediment provenance from known sources of similar geology the cretaceous scotian basin canada abstract this study tests the effectiveness of a geochemical approach in identifying provenance in a basin where different sources do not show strongly contrasting geology petrological studies indicate that at least three distinct rivers draining reactivated horsts of the appalachian orogen supplied sediment to the lower cretaceous deltaic sandstones and mudrocks in the offshore scotian basin ninety five samples mostly from conventional core were analyzed for 44 major and trace elements the data were first screened for variability unrelated to provenance including changes in elemental abundance due to weathering and diagenesis and the effects of grain size and sorting on element variation the effect of hydraulic sorting was distinguished from the effects of concentration of ultrastable heavy minerals from polycyclic sources multivariate statistical analysis by principal component analysis pca was used to test the hypothesis of three discrete sources suggested by the petrologic model major element pca on sandstones discriminated the sources but results from trace element pca required further investigation using element biplots to understand their significance only a few elements were found to be diagnostic of different sources namely k rb sr u th nb and ti with the latter two of value only for sandstones all of these are elements that are abundant in the granites of the appalachians most published geochemical discrimination diagrams did a poor job of distinguishing the three petrographically recognized sources in other basins with quite different hinterland geology other elements are known to be of value in discriminating provenance thus it is unlikely that a globally applicable set of elemental discriminants can identify terrigenous sediment sources rather systematic investigation is needed that evaluates processes such as diagenesis and sorting and then tests geographic and stratigraphic variability in bulk geochemistry informed by at least semiquantitative petrographic data

sediment sources and dispersion as revealed by single grain 40ar 39ar ages of detrital muscovite from carboniferous and cretaceous rocks in mainland nova scotiageological survey of canada contribution 20090289 single grain ages of detrital muscovite from 15 sand stone samples from the lower carboniferous horton group and the lower cretaceous chaswood formation of central nova scotia were used to infer the nature of the early carboniferous unroofing of the meguma terrane and the reworking of carboniferous rocks in the early cretaceous in the western windsor basin a sample from the oldest horton group rocks yielded ages principally between ca 400 and 380 ma suggesting that most of the muscovite present came from the metamorphic rocks of the meguma terrane but was variably reset by the intrusion of the south mountain batholith at ca 380 ma other samples in this part of the basin show partial post depositional resetting younger horton group metamorphic rocks in the eastern windsor basin contain many grains with ages of ca 370 360 ma suggesting derivation from the central core of the south mountain batholith or the musquodoboit pluton horton group sandstones from the western part of the st marys basin co

the effects of strike slip motion along the cobequid chedabucto southwest grand banks fault system on the cretaceous tertiary evolution of atlantic canada the newfoundland fracture zone the southwest grand banks transform and the cobequid chedabucto fault zone form a linked strike slip fault system from the atlantic ocean to southeastern canada this paper suggests that several large scale geological features in southeastern canada are the result of a small amount of strike slip motion on the system during the mid cretaceous and oligocene regional extension features developed in the releasing bend in the laurentian sub basin during the mid cretaceous but the same area experienced oligocene compression this tectonic model accounts for the distribution of mid cretaceous volcanism fault bounded basins and regional unconformities as well as mid to late cretaceous subsidence of the scotian basin and oligocene uplift of the eastern scotian shelf

the provenance of jurassic and lower cretaceous clastic sediments offshore southwestern nova scotia jurassic and cretaceous sandstones in the shelburne subbasin and fundy basin offshore nova scotia are poorly known but are of current interest for petroleum exploration the goal of this study is to determine the provenance of sandstones and shales which will contribute to a better understanding of regional tectonics and paleogeography in the study area mineral and lithic clast chemistry was determined from samples from conventional cores and cuttings from exploration wells using scanning electron microscopy and an electron microprobe whole rock geochemical composition of shales was used to test the hypotheses regarding provenance of mesozoic clastic sedimentary rocks in the sw scotian basin lower jurassic clastic sedimentary rocks in the fundy basin contain magnetite biotite and chlorite suggesting local supply from the north mountain basalt and meguma terrane whereas pyrope and anthophyllite suggest small supply from distant sources in the sw scotian basin detrital minerals lithic clasts and shale geochemistry from middle jurassic to early cretaceous indicate a predominant meguma terrane source and transport by local rivers rare spinel and garnet grains of meta ultramafic rocks only in the middle jurassic at the mohawk b 93 well suggest minor supply from the rising labrador rift via the same river that transported distant sediments to the fundy basin lower cretaceous sandstones from the mohican i 100 well contain minor garnet spinel and tourmaline from meta ultramafic rocks characteristic of sediment supplied to the central scotian basin at that time the dominant meguma terrane provenance precludes thick deep water sandstones in the eastern part of the shelburne subbasin but the evidence of middle jurassic distant river supply through the fundy basin is encouraging for deep water reservoir quality in the western part

late paleozoic to cenozoic history of the offshore sydney basin atlantic canada the sydney basin covers a large offshore area south of newfoundland with a well exposed outcrop belt on cape breton island the geological history of the poorly known offshore area is interpreted using an industry seismic grid and lithoprobe line 86 5 tied to outcrops and two wells the mid devonian to upper carboniferous permian basin fill is 6 7 km thick and represents three extensional phases with intervening and succeeding compressive phases the mid devonian mcadams lake formation was deposited in a local half graben during early post acadian extension following deformation a suite of early carboniferous extensional basins filled mainly with horton group conglomerates developed on northeast trending and southeast dipping master faults some faults developed along acadian terrane boundaries the windsor group extends over the master faults to onlap basement as a result of thermal sag and visean eustatic rise mid carboniferous deformation linked to the alleghanian orogeny reactivated faults an

paleoclimatic control on porosity occurrence in the tilston interval madison group williston basin area the tilston interval of the madison group in the williston basin area is sparsely well constrained by biostratigraphic data it is confined to the lower half of mamet foraminifer zone 8 in the upper tournaisian the distribution of lithologies relative to biozones and marker beds is used to define two equatorial shallow water paleoclimatic facies associations these are 1 a grain rich carbonate association that formed during a temperate humid climate in the lower tilston and 2 a mud rich carbonate and evaporite association that formed during a hot arid climate in the upper tilston skeletal oolitic grainstone and crinoid dominated grainstone and packstone of the lower tilston formed a near continuous sheet that extended more than 1500 km 930 mi parallel to the platform margin and more than 500 km 310 mi perpendicular to the platform margin compaction reduced primary interparticle porosity 5 15 with good permeability 10 to 100 md occurs widely in the williston basin however compaction and burial cements have occluded interparticle pore space in outcrop areas to the west dolomite intercrystal and fossil moldic porosity are the main porosity types in the strata that formed during the hot arid climate of the upper tilston dolomite developed as a replacement of the matrix in mudstone and wackestone porosity and permeability are as high as 38 and more than 100 md but average dolomite crystal size varies widely 5 90 m and controls porosity permeability relationships

diagenetic barite and sphalerite in middle mesozoic sandstones scotian basin as tracers for basin hydrology cementation of sandstone by minor late barite and sphalerite is widespread in the scotian basin at burial depths 2 km 1 mi providing information on fluid flow in the basin the texture and geochemistry of these minerals were analyzed by scanning electron microscopy and electron microprobe on samples from conventional core barite and sphalerite postdate silica and carbonate cementation occurring in veins or occupying secondary porosity they occur with diagenetic chlorite kaolinite pyrite titania minerals kutnohorite and mn siderite this study relates barite and sphalerite to the salt tectonic evolution of the basin based on seismic interpretation and the thermal history of the basin based on fluid inclusion studies barite is readily transported in basinal fluids 100 c 212 f yet is consistently a very late diagenetic mineral this implies that the source of ba is because of the late diagenetic breakdown of k feldspars at 2 3 km 1 2 mi depth which is confirmed by covariation of ba and rb in sandstones sulfur isotope data suggest that the was derived from argo formation evaporites that include 1 7 anhydrite sphalerite is mobile only in saline formation water 140 c 284 f and requires long distance transport through sandstones with zn rich fe ti oxides active detachment faults on salt welds provide potential pathways and a source of salt for migrating formation water the particularities of source and transport of both barite and sphalerite allow the pathways of basinal fluids and their relationship to active salt tectonics to be inferred providing indirect dating of the later stages of diagenetic paragenesis corresponding to times of hydrocarbon charge

deformation of upper carboniferous coal measures in the sydney basin evidence for late alleghanian tectonism in atlantic canada upper carboniferous stephanian coal measures of the sydney basin are deformed by reverse faults and folds with dips of up to 50 on the limbs these structures represent compressional or transpressional events donkin episode of unknown sequence and timing offshore swath bathymetry data indicate that northwest striking reverse faults are folded by prominent northeast trending folds vitrinite reflectance patterns of oriented coal samples from the fold limbs are uniaxial negative with minimum reflectance axes rmin near normal to bedding and fanning across fold axes this pattern implies that the bulk of coalification took place through burial compaction without directed horizontal stress prior to the deformation that produced the folds slight divergence between rmin axes and poles to bedding may reflect slight tilting associated with differential subsidence or early reverse faulting before or during coalification or may lie within analytical error one moderately biaxial sample suggests that some deformation accompanied coalification locally available apatite fission track data for the sydney basin indicate that cooling of the coal measures to below 100 20 c was underway by the middle to late triassic or earlier because cooling implies that coalification was largely complete the fission track results are compatible with latest paleozoic or early mesozoic deformation we infer that the donkin episode represents late alleghanian permian compression within the appalachian orogen if so the sydney structures are manifestations of a little known tectonic episode in atlantic canada however mesozoic cenozoic deformation cannot be ruled out resume les series houilleres du bassin de sydney carbonifere superieur stephanien sont deformees par des failles inverses et des plis deverses dont les flancs atteignent des pendages de 50o ces structures representent des evenements de compression ou de transpression episode donkin dont la sequence et la synchronisation sont inconnues les donnees de bathymetrie par secteurs au large indiquent que les failles inverses a direction nord ouest sont pliees par des plis proeminents a tendance nord est les patrons du facteur de reflexion de la vitrinite provenant d echantillons de charbon orientes preleves sur les flancs des plis sont uniaxes negatifs avec des axes de reflectance minimum rmin presque perpendiculaires au litage et se dispersant en travers des axes de plis ce patron implique que la plus grande part de la carbonisation a eu lieu par compaction d enfouissement sans contrainte horizontale directe avant la deformation qui a produit les plis la legere divergence entre les axes rmin et les poles du litage pourrait refleter un leger basculement associe a une subsidence differentielle ou a des failles inverses precoces avant ou durant la carbonisation ou encore cette divergence pourrait etre a l interieur de la fourchette de l erreur analytique notre echantillon moderement biaxe suggere qu une certaine deformation ait localement accompagne la carbonisation pour le bassin de sydney les donnees disponibles de datation par traces de fission sur l apatite indiquent que le refroidissement des series houilleres a des temperatures inferieures a 100 20 oc etait deja en cours au trias moyen a tardif ou plus tot puisque le refroidissement implique que la carbonisation etait presque terminee les resultats de datation par traces de fission concordent avec la deformation au paleozoique terminal ou au mesozoique precoce nous concluons que l episode donkin represente une compression a l alleghanien tardif permien a l interieur de l orogene des appalaches si tel est le cas les structures de sydney sont des evidences d un episode tectonique peu connu au canada atlantique cependant une deformation au mesozoique cenozoique ne peut etre rejetee d emblee

plate tectonic reconstructions and paleogeographic maps of the central and north atlantic oceans1 2 1this article is one of a series of papers published in this cjes special issue on the theme of mesozoic cenozoic geology of the scotian basin 2earth sciences sector contribution 20120172 we have established a new plate kinematic model of the central and north atlantic oceans between north america africa meseta iberia flemish cap and galicia bank from late triassic to late cretaceous to better understand the nature and timing of rifting of nova scotia and morocco conjugate continental margins since late triassic the maps of salt distributions at the sinemurian pliensbachian limit 190 ma after salt deposition and in middle bajocian 170 ma show that an area of the nova scotia margin is devoid of allochthonous salt and that an area of similar size located oceanward of the west african coast magnetic anomaly shows salt deposits suggesting that a portion of the nova scotia margin with its overlying salt deposits could have been transferred onto the moroccan side right after the formation of the conjugate east coast magnetic anomaly and west african coast magnetic anomaly seven paleogeographic maps from late triassic to late cretaceous are presented with structural elements and ma

authigenesis of titania minerals and the mobility of ti new evidence from pro deltaic sandstones cretaceous scotian basin canada titania tio2 minerals are minor diagenetic phases in many sandstone shale successions but the conditions of ti mobility and titania authigenesis are poorly known here new modes of occurrence of authigenic titania minerals filling pores and replacing phytodetritus are documented from lower cretaceous prodeltaic sandstones in the offshore scotian basin of southeastern canada textural relationships suggest that titania minerals formed at the same time as kaolinite most commonly below lowstand sequence boundaries related to flux of meteoric water such authigenic titania is most abundant in thin bedded sandstones interbedded with thick prodeltaic mudstone in which fine grained detrital ti rich minerals are concentrated textures in titania that has replaced uncompacted phytodetritus suggest microbial mediation in near surface eodiagenesis eogenetic titania is enriched in phosphorus 0 6 p2o5 and may co occur with authigenic fluorapatite and crandallite crystals such titania resulted from prolonged flow of meteoric water that dissolved p from apatite and feldspar thereby enhancing ti solubility in basins with supply of immature sediment from granitic terranes and important diagenesis by meteoric water the assumption that ti is an immobile element and that rutile or other titania minerals are exclusively of detrital origin may not be valid probable mesodiagenetic titania has low p content suggesting that ti mobility under these conditions was facilitated by some other agent probably organic acids the results of this study illustrate that even in cases where titania minerals are volumetrically insignificant their microtextures and trace element chemistry can provide important insights into the character of fluid flow during diagenesis of siliciclastic rocks

karst controlled diagenesis and reservoir development example from the ordovician main reservoir carbonate rocks on the eastern margin of the ordos basin china the ordovician majiagou formation contains the main reservoir of the ordos central gas field in the ordos basin the producing zone at the top of member 5 consists of carbonate rocks modified during a long period of subaerial exposure and karstification from the late ordovician to the middle carboniferous on the eastern margin of the ordos basin the porosity of the exposed carbonate rocks of this unit ranges from 0 5 to 15 1 and permeability ranges from 8 and permeability ranges from 0 1 to 5 md the main reservoir porosity is a dissolution enhanced vuggy porosity associated with dolomite the carbonate rocks show great heterogeneity reflecting the varying effects of karstification in creating and modifying porosity petrographic and geochemical analyses of various components in these carbonates provided evidence for depositional and diagenetic processes the reservoir carbonates were deposited in shallow and restricted hypersaline environments and were later modified by karstification and burial diagenesis dolomitization appears to have resulted from mixing of marine and meteoric waters and probably occurred in both shallow and deep burial settings cementation by calcite also occurred in both shallow and deep environments under different hydrodynamic conditions both depositional settings and diagenetic processes such as leaching by meteoric water paleokarstification dolomitization and cementation controlled reservoir development the outcrop and subsurface samples show similar petrographic features porosity types and geochemical characteristics but the exposed section of the formation shows evidence of more alteration by meteoric water

karst landforms revealed at various scales using lidar and uav in semi arid brazil consideration on karstification processes and methodological constraints abstract this paper analyzes different types of karst landforms and their relationships with fracture systems sedimentary bedding and fluvial processes we mapped karst features in the cretaceous carbonates of the jandaira formation in the potiguar basin brazil we used high resolution digital elevation models acquired using lidar and aerial orthophotographs acquired using an unmanned aerial vehicle uav we grouped and described karst evolution according to scale and degree of karstification these degrees of karst evolution are coeval fractures are opened by dissolution forming vertical fluid conduits whereas coeval dissolution occurs along horizontal layers this conduit system acts as pathways for water flow the enlargement of conduits contributes to the collapse of blocks in sinkholes and expansion of caves during an intermediate degree of karstification propagation of dissolution can cause the coalescence of sinkholes and the capture of small streams fluvial processes dominate karst dissolution at an advanced degree of karstification comparisons with previously published ground penetrating radar gpr borehole and seismic surveys in sedimentary basins indicate that these structures can be partially preserved during burial

characterization of reservoir lithologies within subunconformity pools pekisko formation medicine river field alberta canada the pekisko formation in western canada is a third order sequence comprised of an open marine grainstone through restricted carbonate mudstone succession truncation of the pekisko along an unconformity edge prior to the jurassic and several periods of incision from early jurassic early cretaceous have formed an intricately sculptured subcrop belt in the medicine river field oil is trapped in discrete pools close to the unconformity edge reservoir facies comprise three lithologies medium crystalline dolostone with intercrystalline and vuggy porosity forms the reservoir in an elongate dolostone body that has replaced grainstone fine crystalline dolostone is facies selective within a lime mudstone unit in which the common reservoir rock is bioturbated dolomudstone with intercrystalline porosity grainstones have secondary porosity formed though leaching of microcrystalline calcite allochems and intergranular cements reservoir quality is assessed from consideration of orthogonal permeability values kmax maximum horizontal permeability k90 horizontal permeability at 90 to the maximum and kv vertical permeability obtained from conventional whole core analyses sedimentary lamination primarily affects the kv and the presence of fine grained lamination dictates that kv 3k90 and kv k90 from this relationship the fracture density in all three lithologies appears to be similar low and variable porosity and permeability values in grainstones indicate that the fracture system is poorly connected to the matrix despite leaching and fracturing at the unconformity edge reservoir distribution closely follows patterns of facies that were susceptible to dolomitization future exploration potential lies in fine crystalline dolostone bodies that may form stratigraphic traps downdip from the unconformity edge

the relationship between the east asian summer monsoon and el nino southern oscillation revealed by reconstructions and a control simulation for millennium abstract proxy based reconstructions of the asian summer monsoon exhibit variability over multiple scales from inter annual to centennial the relationship between east asia summer monsoon easm variability and the el nino southern oscillation enso over the last millennium remains unclear and a focus of current research this study investigates this relationship using observations reanalysis data proxy based reconstructions and a control simulation using the community earth system model cesm the results derived from both the observation reanalysis proxy based reconstruction and the simulation show consistently that the relationship between easm strength and nino3 4 sst is divergent the observation reanalysis data illustrate strong negative correlations between nino3 4 sst and easm strength at an annual scale in the 1920s 1930s and 1980s 1990s with weak correlations during other periods the proxy based reconstruction demonstrates strong negative correlations at inter decadal scales from the 1360s to the 1530s with either weak correlations or positive correlations during other periods moreover the simulations reveal positive correlations in some periods and negative or weak correlations in other periods the simulations demonstrate that the divergent relationship may be derived from multi decadal variations in pacific sst caused by internal variability in the climate system likely due to the inter decadal pacific oscillation ipo the easm variation is usually in out of phase with nino3 4 sst during the positive negative phase of the ipo in the positive phase of the ipo there is a tripolar pattern expressed in a cyclone anticyclone cyclone arrangement at pressure level of 850 hpa from the tropics to mid latitudes over the northwest pacific warming of the nino3 4 strengthens the tropical cyclone by weakening the trade winds and subsequently strengthening the subtropical anticyclone leading to a strong meiyu front which suggests a strong easm however in the negative phase of the ipo a huge cyclone occupies the northwest pacific warming of the nino3 4 strengthens the cyclone by weakening the trade winds which leads to a weak meiyu front which suggests a weak easm these results may be helpful in further understanding the mechanisms through which the enso and ipo impact the atmospheric circulations in the asian pacific especially regarding the long term variations in easm at inter annual to inter decadal scales

two types of el nino events cold tongue el nino and warm pool el nino abstract in this study two types of el nino events are classified based on spatial patterns of the sea surface temperature sst anomaly one is the cold tongue ct el nino which can be regarded as the conventional el nino and the other the warm pool wp el nino the ct el nino is characterized by relatively large sst anomalies in the nino 3 region 5 s 5 n 150 90 w while the wp el nino is associated with sst anomalies mostly confined to the nino 4 region 5 s 5 n 160 e 150 w in addition spatial patterns of many atmospheric and oceanic variables are also distinctively different for the two types of el nino events furthermore the difference in the transition mechanism between the two types of el nino is clearly identified that is the discharge process of the equatorial heat content associated with the wp el nino is not efficient owing to the spatial structure of sst anomaly as a result it cannot trigger a cold event it is also demonstrated that zonal advective feedback i e zonal adve

the scotian basin offshore nova scotia thermal history and provenance of sandstones from apatite fission track and 40ar 39ar data apatite fission track and 40ar 39ar age spectrum data from sandstone drill core minerals taken from depths of 2 5 km in nine wells from the scotian basin are presented and interpreted in terms of the thermal history of the basin and the provenance of its sediments the focus of the study is a comparison of the data from these thermochronometers with each other and with previously published vitrinite reflectance and aromatization isomerization a i reactions in biomarker compounds from the same or nearby wells apatite fission track ages are generally in agreement with expectations in that they trend to zero at a depth of 4 km corrected bottom hole temperature 120 c shallower lower present temperature samples are partially annealed the degree of partial annealing correlates closely with the degree of a i reactions both thermal indicators are activated over the temperature range 60 120 c samples from two wells mic mac j 77 and erie d 26 are anomalous they are more annealed than present formati

integrated methodology for determining provenance of detrital quartz using optical petrographic microscopy and cathodoluminescence cl properties abstract the provenance of detrital quartz is a useful predictor in frontier basin sandstone reservoirs of the availability of coarse grained quartz grains of plutonic or high grade metamorphic origin the standard approach is to use scanning electron microscope sem panchromatic cathodoluminescence cl imagery and observations from an optical petrographic microscope we describe a work flow modified from previous literature proposals to determine quartz provenance in detrital grains using optical petrographic microscopy and cl properties from both a hot cathode cathodoluminescence microscope attachment hcma and panchromatic sem cl hcma analysis permits better discrimination of different types of metamorphic quartz this method is applied to a middle jurassic to lower cretaceous section in the bandol 1 wildcat well located in the laurentian sub basin south of newfoundland two types of high grade metamorphic quartz are distinguished one with low luminescence as described in previous literature and one with medium blue cl colour and a moderate colour shift that is also known from granulite in the hinterland three phases of detrital supply are identified suggesting progressive unroofing of higher grade metamorphic sources through the middle jurassic and major input of plutonic quartz in the early cretaceous

pore facies of smackover carbonate reservoirs in southwest alabama abstract pore facies are rock units that are defined by certain proportions of pore types contain specific pore throat size distributions and exhibit certain consequent fluid flow properties pore facies may contain only one pore type but more typically are characterized by a combination of several pore types data used in this study consist of point counts of thin sections that are plotted on ternary diagrams whose apices are pore types ternary pore plots commercial porosity and permeability data from core analyses qualitative thin section descriptions and qualitative core descriptions two distinct but partially intergrading pore facies are recognized in the smackover of southwestern alabama these pore facies are defined based on the two most common pore types in the smackover particle moldic including secondary intraparticle and intercrystalline pores which together account for greater than 85 of total porosity in the smackover rocks assigned to the moldic pore facies exhibit similar depositional fabrics and experienced similar diagenetic processes for example this pore facies is most commonly composed of peloid and ooid grainstone some fabric selectively dolomitized modified by early cementation and particle dissolution by contrast in the intercrystalline pore facies destruction of primary fabrics by nonfabric selective dolomitization is almost the sole determinant of pore system characteristics the moldic pore facies dominates to the northwest choctaw western clarke washington counties the updip area and the intercrystalline pore facies is dominant to the south and east mobile monroe baldwin escambia and conecuh counties the downdip area pore facies distributions overlap in some areas e g western monroe county indicating that multiple pore facies occur in many smackover fields the two pore facies exhibit substantially different petrophysical characteristics the mean slope of regression lines of porosity on ln natural log permeability for the intercrystalline pore facies is 0 47 with a range of 0 19 to 0 90 the mean slope for the moldic pore facies is 0 22 with a range of 0 18 to 0 27 the higher slopes for the intercrystalline pore facies mean that permeability values may be more precisely predicted from porosity data in this pore facies the mean maximum permeability for the intercrystalline pore facies is 130 md the corresponding value is 91 md for the moldic pore facies high permeability fluid conduits are more common in the intercrystalline pore facies than in the moldic pore facies in addition all high permeability examples of the moldic pore facies contain substantial amounts of interparticle porosity and are found near the smackover subcrop the remainder of the moldic pore facies is characterized by permeability values substantially less than those of the intercrystalline pore facies porosity values are commonly higher in the moldic pore facies which has a range of mean porosity of 10 2 to 28 0 compared to 9 6 to 20 5 for the intercrystalline pore facies greater hydrocarbon volumes can be stored in reservoirs dominated by the moldic pore facies but connectivity is better in the intercrystalline pore facies mixtures between the two pore facies are moderately common mixed pore systems commonly resemble the intercrys talline pore facies in the slope of the regression line of porosity on ln permeability in strata with mixed pore systems isolated particle moldic pores are commonly connected by networks of intercrystalline pores which control transport of fluids out of particle moldic pores

significance of gneissic rocks in the liscomb complex nova scotia the liscomb complex comprises late devonian intrusive rocks principally peraluminous granite and medium to high grade metamorphic rocks gneisses that collectively are hosted by low grade greenschist facies metasediments of the cambro ordovician meguma group the conventional view that these gneisses contain high grade mineral assemblages and represent basement rocks has recently been challenged and indeed some of the rocks previously mapped as gneisses particularly metapelites have isotopic compositions resembling the meguma group amphibole bearing enclaves in the liscomb plutons however are isotopically distinct and in this regard resemble xenoliths of basement gneisses in the popes harbour lamprophyre dyke south of the liscomb area metasedimentary enclaves with meguma isotopic signatures can contain garnets with unzoned cores implying high temperatures that host high grade minerals prismatic sillimanite spinel and or corundum and are enclosed by retrograde zoned rims these f

how sandstone porosity and permeability vary with diagenetic minerals in the scotian basin offshore eastern canada implications for reservoir quality abstract the scotian basin is an under explored offshore basin that has produced gas and minor oil from jurassic cretaceous deltaic sandstones reservoir quality is an important exploration risk in the basin this study evaluates whether there are systematic stratigraphic or geographic variations in diagenetic mineral assemblage control of reservoir porosity and permeability three data sets are used a compilation of all available core plug porosity and permeability measurements 3271 in total a subset of 577 corresponding to thin sections with lithofacies assignments and a subset of 35 thin sections principally from reservoir sandstones in which modal abundance of diagenetic minerals has been determined by image analysis of scanning electron microscope backscattered electron images abundances above a 4 threshold of diagenetic kaolinite calcite and ankerite correlate inversely with permeability but chlorite and possibly siderite correlate positively diagenetic assemblages show no systematic variation with stratigraphy or geography both of which may involve variable detrital supply permeability shows the well known variation with grain size and depth of burial but after correcting for these effects it is greatest in estuarine channel and river mouth turbidite sandstones this is because these facies preferentially develop chlorite rims on detrital quartz grains and are also the sites of enhanced flow of late basinal fluids resulting in secondary porosity local effects such as facies distribution architecture of channel sandstones fluid pathways related to complex salt tectonics and the effects of overpressure are more important than predictable basin wide effects in controlling sandstone reservoir quality

dolomitization and neomorphism of mississippian visean upper debolt formation blueberry field northeastern british columbia geologic petrologic and chemical evidence petrographic chemical and isotopic studies of the mississippian visean upper debolt formation in the blueberry field british columbia canada reveal that dolomitization was the result of several diagenetic events and that neomorphic alteration of these dolomites significantly modified their original chemical signatures these studies also demonstrate how tectonics play an important role in controlling and modifying reservoir dolomites in the area petrographic investigations have documented two early dolomite phases 1 early matrix dolomite and 2 pervasive dolomite and two later generations 3 coarse cement and 4 pseudomorphic replacement of crinoids early matrix dolomite occurs as small average 25 m subhedral to euhedral crystals that replace the matrix of carbonate mudstones wackestones and packstones petrographic evidence suggests that early matrix dolomite had a relatively early precompaction origin possibly from marine fluids however geochemical evidence indicates that later fluids have altered their original geochemical signatures copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received february 1 1996 revised manuscript received august 16 1996 final acceptance january 19 1997 2department of earth sciences university of windsor windsor ontario canada n9b 3p4 present address chauvco resources ltd 2900 255 5th avenue s w calgary alberta t2p 3g6 canada 3department of earth sciences university of windsor windsor ontario canada n9b 3p4 this research was supported by individual operating grants from canada s natural sciences and engineering research council nserc awarded to i s al aasm and additional funding from pancanadian petroleum resources limited and suncor inc s durocher acknowledges support from an ontario graduate scholarship s brame talisman energy l williams phillips petroleum resources ltd g burrowes and i mcllreath pancanadian petroleum ltd and j packard rhomb carbonate consulting ltd are thanked for the valuable information insights and ideas for tackling the complexities of the blueberry field thanks are also due to j veizer university of bochum and university of ottawa for strontium isotope analysis an earlier version of this paper benefited from critical reviews by m malone texas a m university c viau shell canada ltd s schutter j dravis dravis interest inc and an anonymous reviewer

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

tourmaline composition as a guide to mineral exploration a reconnaissance study from nova scotia using discriminant function analysis tourmaline has an extensive range of solid solution that can potentially reflect the nature of its coexisting phases including some minerals of economic interest in this study tourmaline compositions are considered in the framework of two hypothetical classes of mineral deposits to evaluate the use of tourmaline chemistry to assess economic potential tourmalines from 27 known mineralized and barren localities in nova scotia were analyzed by electron microprobe for their major elements and by inductively coupled plasma mass spectrometry for their boron isotope compositions linear discriminant function analysis of these data on a two group mineralized and barren basis correctly classified 85 to 89 percent of the tourmaline samples similarly linear discriminant function analysis on a three group nongranite mineralized granite related mineralized granite related barren basis correctly classified 72 to 85 percent of the tourmaline samples quadratic discriminant function analysis resulted in even better discrimination these preliminary results suggest that this type of geochemical statistical approach is promising for mineral exploration

post variscan evolution of the anti atlas belt of morocco constrained from low temperature geochronology the anti atlas belt of morocco extends ene wsw over more than 600 km from the atlantic margin in the west to the interior of the african plate in the east it exhibits precambrian rocks outcropping as basement inliers and surrounded by marine ediacaran cambrian sequences around the axis of the mountain range the belt which has for a long time been interpreted as of variscan age is now revealed to have experienced major vertical movements through mesozoic and cenozoic times thereby the anti atlas domain appears to be affected by two episodes of exhumation separated by an episode of subsidence the initial episode occurred in the late triassic and led to the exhumation of 7 5 10 5 km of crustal rocks by the end of the middle jurassic ca 160 150 ma the following phase resulted in 1 3 km of basement subsidence and occurred during the late jurassic and most of the early cretaceous the basement rocks were then slowly brought to the surface after experiencing 2 3 5 km of exhumation throughout the late cretaceous and the cenozoic the timing of these episodes of exhumation and subsidence coincides with major tectonic and thermal events in relation with the evolution of the atlantic and tethys oceans indicating that the effects of their rifting and drifting extended beyond their presumed margins

a revised biostratigraphic and well log sequence stratigraphic framework for the scotian margin offshore eastern canada12 1this article is one of a series of papers published in this cjes special issue on the theme of mesozoic cenozoic geology of the scotian basin 2earth sciences sector contribution 20120137 in this study we build on a foundation of previous biostratigraphic studies for the scotian basin offshore eastern canada by conducting new quantitative multidisciplinary biostratigraphic studies of the mesozoic sections in eight wells bonnet p 23 chebucto k 90 cohasset l 97 glenelg j 48 glooscap c 63 mohican i 100 south desbarres o 76 and south griffin j 13 these wells were chosen to provide good spatial coverage stratigraphic penetration and correlation with the seismic grid we have also evaluated pre existing biostratigraphic data and undertaken the well log sequence stratigraphic interpretation of upper triassic to cenozoic sediments in 16 additional wells using a consistent multidisciplinary event scheme derived from the new wells key to the dating of some horizons has been integration of the palynology and micropaleontology disciplines mostly used previously on the scotian margin with new nannofossil data simultaneously we have closely integrated the biostratigraphic results with

porosity permeability relationships in interlayered limestone dolostone reservoirs porosity and permeability data from five carbonate platform successions of different settings ages and burial depths are examined to identify overall similarities and differences in the reservoir quality of interlayered limestones and dolostones each succession consists mainly of limestone and dolostone with subordinate proportions of intermediate partly dolomitized compositions in the three deeply buried platforms the key features are that limestones have much lower average porosity than associated dolostones and that limestones and dolostones show little difference in average permeability for given porosity in contrast the shallowly buried platforms show little difference in average porosity between limestones and dolostones and also display higher average permeability for given porosity in dolostones than limestones these data suggest the following general guidelines for depositional and diagenetic controls on reservoir architecture in carbonates consisting of interlayered limestone and dolostone 1 reservoir compartmentalization by the formation of tight limestone barriers is largely a burial diagenetic process involving calcite cementation locally produced by chemical compaction 2 both the pattern of early dolomitization and the distribution of clay minerals because they influence the localization of chemical compaction are key factors that determine the distribution of tight limestone barriers separating flow units thus the pattern of eventual burial compartmentalization follows a template that is hardwired into the stratigraphic architecture by depositional mineralogy and early diagenesis 3 after burial 2 3 km 1 2 1 8 mi dolostones should not be expected to have higher permeability for given porosity than associated limestones these rules assume dolomitization to occur early relative to chemical compaction which will commonly be the case because of combined hydrologic and mass balance constraints dolomitization and concentration of clay appear linked to cycle and sequence architecture in the present examples and thus may have a useful degree of predictability at least in terms of statistical parameters such as net gross and probability of flow unit thickness distribution

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

a high resolved record of the asian summer monsoon from dongge cave china for the past 1200 years abstract two annually laminated and 230th dated stalagmite oxygen isotope 18o records from dongge cave china provided a high resolution asian summer monsoon asm history for the past 1200 years a close similarity between annual band thickness and stable isotope analyses 13c and 18o suggests the calcite 18o is most likely a proxy associated with asm precipitation the two duplicated stalagmite 18o records show that the asm varies at a periodicity of 220 years concordant with a dominant cycle of solar activity a period of strong asm activity occurred during the sporer minimum 1450 1550 a d followed by a striking drop circa 1580 a d potentially consistent with the social unrest in the final decades of china s ming dynasty 1368 1644 a d centennial scale changes in asm precipitation over the last millennium match well with changes in tropical atlantic sea surface temperatures ssts and south american summer monsoon precipitation our findings suggest that variations in low latitude monsoon precipitation are probably driven by shifts in the mean position of the intertropical convergence zone itcz which is further mediated by solar activity and tropical ssts

varietal heavy mineral analysis of sediment provenance lower cretaceous scotian basin eastern canada abstract the origin of a major increase in sand supply in the early cretaceous of the scotian basin offshore eastern canada has been investigated by analysis of heavy mineral varieties the chemistry of detrital minerals from the scotian basin was compared with that of minerals from potential source rocks sampled from older sedimentary successions river sands and glacial tills on land heavy mineral varieties were established based on 1000 high quality electron microprobe emp analyses and used to classify heavy mineral types by mineral liberation analysis mla which uses a rapid scanning electron microscope particle analyser heavy mineral varieties were compared between the cretaceous quartz arenites and subarkoses and samples from potential source areas different chemical varieties of the same mineral group have different grain size distributions so that their relative modal abundances may be influenced by hydraulic sorting but modal abundance of different varieties of tourmaline garnet and spinel provides useful information widely used provenance sensitive mineral ratios are difficult to interpret because of the abundance of polycyclic sources comparisons of the shape parameters of the individual mineral types are also useful for provenance identification aspect ratio in elongate grains such as tourmaline and zircon is a measure of polycyclic reworking but is influenced by the initial shapes of minerals from different source rocks uniformity of varietal heavy minerals over a large area and stratigraphic range and the covariance of spinel and zircon with quite different crystalline sources indicate predominance of polycyclic sources to the central scotian basin probably principally from carboniferous and lower paleozoic sandstones in part sourced from western newfoundland ophiolites heavy mineral varieties in the west scotian basin can be closely matched to sources in the adjacent meguma terrane of the appalachians all the data show that the sands of the scotian basin were derived from reworking of crystalline basement of the appalachian orogen and its paleozoic sandstone cover uplifted during rifting of iberia from the grand banks there is no evidence of a significant supply of sand to the scotian basin from a proto st lawrence river

tree ring precipitation reconstruction in the chifeng weichang region china and east asian summer monsoon variation since a d 1777 1 the total precipitation of previous august to current july was reconstructed on the basis of the pinus tabulaeformis ring widths from three sites in chifeng and weichang regions china for the past 236 years the explained variance of reconstruction is 47 4 the intervals with below average precipitation 1768 2003 comprise 1779 1806 1853 1883 1926 1972 and 1980 1989 the intervals with above average precipitation consist of 1807 1852 1884 1925 1973 1979 and 1990 1999 precipitation in the study area is dependent on the east asian summer monsoon strength the reconstructed series is significantly correlated with the average dryness wetness index series of datong and beijing as well as with previous results from baiyinaobao helan mountains and even the state of mongolia a significant negative correlation r 0 63 p 0 0001 is also found between the reconstruction and our previously reconstructed temperatures of weichang for the period 1884 2002 our result suggests that the variations of the east asian summer monsoon on a decadal scale are coincident with the other regions within the environmentally sensitive zone of northern china as well as mongolia for the past 236 years and our reconstruction is representative of regional climate patterns

pre mesozoic basement rocks offshore nova scotia canada new constraints on the accretion history of the meguma terrane basement samples from offshore wells and geophysical data show that the meguma terrane forms the basement of mesozoic cenozoic sedimentary basins as far as 200 km offshore nova scotia the data provide constraints on avalon meguma terrane interaction during middle to late paleozoic events in the appalachian orogen the basement consists of metasedimentary rocks intruded by late paleozoic granitoid plutons principally magnetite bearing granodiorites which contrast with more peraluminous ilmenite bearing devonian granodiorite and granite onshore offshore tonalites have a subduction related trace element signature that is similar to the signature in minor devonian gabbro and tonalite intrusions on land nd sr and pb isotopes suggest three sources for meguma terrane plutons 1 2 ga basement possibly saharan shield and sediments derived therefrom this basement may be present beneath the southwestern scotian shelf 2 late proterozoic underthrust avalonian basement and basement autochthonous to the meguma terrane and 3 melts from mantle last remobilized in the late proterozoic pan african orogeny seismic reflection profiles show meguma terrane thrust northward over a wedge of avalon basement extending 30 km south of the surface suture there is no evidence that the devonian tonalites are directly related to subduction the lack of either ophiolites or paleozoic pelagic sediment suggests that convergence of the avalon and meguma terranes was achieved principally by strike slip motion resulting from low angle continent continent convergence with only a minor thrust component the widespread devonian carboniferous igneous activity of the amalgamated meguma and avalon terranes was a consequence of regional extension which resulted in decompression melting of upper mantle and production of mafic magmas variably mixed with crustal material

tectonostratigraphic evolution of the labrador margin atlantic canada abstract the labrador continental margin provides a rich source of data with which to study the relationships between stratigraphy tectonics and paleoenvironment we have completed a regional seismic interpretation and integrated this with new biostratigraphic data based on analyses of palynomorphs from wells in the hopedale and saglek basins which occur on this margin our results are summarized in a tectonostratigraphic chart which displays new and consistent age control for the major lithostratigraphic units and provides more precise evaluation of their depositional and paleoenvironmental history we have identified and dated six regional unconformities in the wells and we can recognize several others on the seismic data the older unconformities cretaceous are related to the tectonics of rifting and seafloor spreading and may delineate the onset of different stages of the rift process in the paleocene early eocene unconformity development was influenced by episodic volcanism due to the passage of the proto iceland hotspot to the north and to a major change in spreading direction in the labrador sea many of these unconformities are also identified in offshore southwest greenland and the grand banks suggesting widespread controlling mechanisms during the post seafloor spreading stage the effects of mass wasting and slumping and of paleoenvironmental controls on the stratigraphy were more pronounced we discuss the petroleum potential of the hopedale basin in terms of the structures we see on the seismic data and highlight the bjarni formation which likely contains the most prospective source and reservoir rocks in this basin

northeastern extension and crustal expression of terranes from cape breton island nova scotia based on geophysical data the narrowest section of the appalachian orogen in atlantic canada from grenville age basement in the west to the avalon terrane in the east is preserved in cape breton island where components of four terranes display distinctive stratigraphic igneous metamorphic aeromagnetic and gravity characteristics the blair river complex of northwestern cape breton island is a fragment of grenvillian rocks that is similar to units in western newfoundland the aspy terrane is characterized by mid paleozoic granitic rocks and high pressure paragneisses and appears to continue across the cabot strait as the gander terrane of the hermitage flexure in newfoundland the bras d or terrane is composed of hadrynian to early cambrian low pressure metasedimentary units and dioritic to granitic plutonic rocks as indicated by aeromagnetic anomalies this terrane continues across the laurentian channel to the south coast of newfoundland where it may be terminated by the hermitage fault the avalon terrane of southeaster