comparative stratigraphy and subsidence history of mesozoic rift basins of north atlantic mesozoic rift basins around the north atlantic all possess many of the following upper jurassic to lower cretaceous oxfordian to albian stratigraphic elements 1 an early oxfordian hiatus 2 backfill deposits in upper jurassic paleovalleys 3 multiple tithonian transgressive regressive sequences 4 early berriasian regressive sequences 5 a sub valanginian unconformity overlain by coarse siliciclastic sandstones and conglomerates 6 valanginian to hauterivian fining upward sequences 7 condensed barremian sequences and 8 prominent aptian unconformities more local features include abrupt kimmeridgian deepening lusitanian basin portugal albian deepening cantabrian and aquitaine basins northern spain and southern france and late albian early cenom nian source rejuvenation cantabrian basin northern iberia decompaction and backstripping of sediments from well and outcrop sections in six basins also reveal broad similarities in trends of rates of apparent basement subsidence relatively high rates 50 100 m m y characterize onset of rift phases in the triassic and the kimmeridgian locally in the lusitanian basin of portugal kimmeridgian rates reach about 250 m m y in the cantabrian and aquitaine basins a third phase of rapid subsidence characterizes the aptian albian interval after the main phase of continental breakup around iberia this phase may be due to transtensional stresses as iberia continued to rotate relative to europe tensional intraplate stresses or gravity driven partial collapse of the new continental marg n the north atlantic mesozoic basins share many features because they had a common origin controlled by intracontinental rifting and subsequent separation of europe and north america pulses of extension generally are reflected in the stratigraphy of all of the basins superimposed on this record are the effects of eustatic sea level variations the main difference between the canadian jeanne d arc basin and iberian basins is the significantly greater early and middle jurassic basement subsidence rate in the former about 40 m m y vs 0 10 m m y this difference may result from prolonged extension on the canadian side perhaps due to northward transfer of shear stress from left lateral transform motion between the grand banks and northwestern africa

oolitic sandbody depositional models and geometries mississippian of southwest britain implications for petroleum exploration in carbonate ramp settings abstract a 1000 m thick early mississippian carbonate supersequence the carboniferous limestone of southwest britain consists of three third order depositional sequences these comprise parasequences in various configurations and the whole forms a carbonate ramp stack within this framework five major oolitic carbonate sandbodies developed a castell coch limestone b stowe oolite c brofiscin oolite d gully oolite and e high tor limestone the depositional regime was storm and wave dominated throughout and the major sandbodies represent a range of progradational carbonate beaches barriers and detached subtidal shoals analysis of the three dimensional shapes and distribution of these five examples shows that they evolved to produce three major carbonate sandbody geometries a strings b sheets and c wedges these geometries are characterised using the five field examples and offered as a template which may assist in the exploration and reservoir modelling of petroleum rich high energy ramp systems progradation for up to 40 km of barrier islands stowe oolite and beach ridge plains gully oolite formation generated strings and thick sheets individually up to 10 20 m thick thin shoreface retreat carbonate packstone grainstone sheets up to 5 m thick high tor limestone developed during transgressions as veneers across flooding surfaces these are comparable with sheet sands developed in siliciclastic shelf depositional systems progradation for up to 30 km and vertical aggradation of shoreline detached oolite shoals castell coch limestone brofiscin oolite generated basinwards expanding or thinning wedges up to 30 m thick tectonically controlled stacking of strandplain sheets produced a composite carbonate sandbody up to 80 m thick gully oolite the intrinsic sedimentary and extrinsic eustacy tectonism climate factors which controlled these sandbody geometries are addressed establishing the positions of the sandbodies accurately within depositional sequences allows them to be located within inferred seismic sequence geometries and provides one possible solution to the difficult problem of predicting carbonate facies distribution in subtle stratigraphic plays in this ramp system the most homogeneous sandbodies up to 30 m grainstones with greatest reservoir facies potential are represented by shoal belt wedges potential grainstone reservoir facies in the prograding shorelines are limited to the upper parts of individual shoreface sequences max 10 m grainstones for shoreline carbonate sandbodies the greatest reservoir and stratigraphic trapping potential exists in the earliest ramp parasequences where enveloping offshore sediments are siliciclastic mudstones in later stages potential seals are likely to be less reliable low porosity outer ramp carbonates

bioturbation influence on reservoir quality a case study from the cretaceous ben nevis formation jeanne d arc basin offshore newfoundland canada the delineation ben nevis l 55 well located in the hebron ben nevis field offshore newfoundland targeted the cretaceous ben nevis formation in the petroleum rich jeanne d arc basin this case study focuses on the bioturbated net pay horizons and assesses the importance of animal sediment interactions in controlling the porosity and permeability of sandstone reservoir intervals our data reveal that bioturbation can either reduce permeability and porosity by as much as approximately 33 or enhance it by up to 600 dependent on burrow type and behavior of the trace making organism the net pay interval in the cored interval of ben nevis l 55 is characterized by ophiomorpha dominated ichnofabrics the action of bioturbators can be classified in terms of sediment mixing sediment cleaning sediment packing and pipe work building strategies bioturbation has the potential to 1 increase isotropy or uniformity of grain size by destroying sedimentary laminae through burrow homogenization or 2 decrease isotropy by selectively sorting grains into burrow lining and fill by grain size and through creation of open burrow systems filled with later sediments of differing character to the host sediment the petrophysical characteristics of the reservoir facies are highly dependent on trace fossil morphology presence or absence of burrow linings nature of burrow fills burrow size and bioturbation intensity mudstone rich facies and ichnofabrics containing mudstone filled and or lined burrows e g ophiomorpha and clusters of chondrites have the net effect of permeability reduction in contrast permeability enhancement is documented from muddy sandstone facies with clean sand filled burrows e g thalassinoides and clean sandstones with burrow mottled or diffuse to massive textures

tectonism the dominant factor in mid cretaceous deposition in the jeanne d arc basin grand banks abstract the development of stratigraphic sequences has been demonstrated to be controlled by a set of factors including variations in subsidence sediment input eustatic sea level and physiography well and seismic data from the jeanne d arc basin grand banks indicate that mid cretaceous tectonism controls at least three of these factors namely subsidence sediment input and physiography north atlantic rift tectonism was therefore the dominant factor in controlling the migration of coastal to shallow marine environments and the development of sequence stratigraphy in this basin during the mid cretaceous the avalon formation respresents a mainly barremian to early aptian regressive phase of clastic marine to marginal marine sedimentation this followed the deposition of a thick sequence of mainly marine limestones and shales of the whiterose formation above a mid valanginian sequence bounding unconformity the increased clastic input and northward progradation of coastal environments represented by the avalon formation occurred during uplift of a basement arch to the south with subsidence of the basin increasing to the north accompanied by only relatively minor faulting these features indicate that a period of epeirogenesis was initiated during the barremian continuing uplift over an expanding area at the southern end of the basin is interpreted to have resulted in the development of an angular unconformity with incised valleys this mid aptian unconformity defines the top of the whiterose avalon sequence initiation of brittle fracturing of the sedimentary package and underlying basement i e rifting in mid aptian times resulted in rapid fault controlled subsidence and fragmentation of the jeanne d arc basin this great increase in subsidence rate caused retrogradation of coastal environments across the previously developed sequence bounding unconformity despite continuing high rates of sediment input from the uplifted basin margins the transgressive siliciclastic ben nevis formation comprises two separate but related facies associations a locally preserved basal association represents interfingering back barrier environments and is herein defined as the gambo member an upper ubiquitous facies association comprises tidal inlet channel shoreface and lower shoreface offshore transition sandstones this upper facies association onlapped marine ravinement diastems above the laterally equivalent back barrier facies the rapid fault controlled subsidence and high sediment input rate of this mid aptian to late albian rift period resulted in the accumulation and preservation of very thick shoreface sandstones the transgressive sandstones were buried by laterally equivalent offshore shales of the nautilus formation flooding of the basin margins induced by the onset of thermal subsidence in latest albian or early cenomanian times marks the top of the ben nevis nautilus syn rift sequence

age and significance of sequence boundaries on jurassic and early cretaceous rifted continental margins the age and significance of sequence boundaries on jurassic to early cretaceous rifted continental margins in three ocean basins have been documented the margins are the santos basin in the south atlantic the grand banks in the north atlantic and the beaufort sea in the arctic ocean large industry data bases were used for the interpretation of each area megasequence boundaries separate the major phases of basin evolution for example syn rift and post rift boundaries developed with an average periodicity of 49 m y sequence boundaries define the component parts of each megasequence and developed with a modal periodicity of 10 15 m y out of 27 total boundary ages most 16 are developed on just one margin only two possible age ranges overlap on all three margins ighty percent of the megasequence boundaries and 50 of the sequence boundaries show a direct causal connection with coeval faulting and or folding the rest of the boundaries appear as unstructured surfaces separating transgressive and or regressive sedimentary wedges and are interpreted to result from changes in the rate of basin subsidence sediment input and long term eustatic sea level these data do not support theories advocating synchronous worldwide boundary development resulting from periodic short term falls in global eustatic sea level only in like basins of the same age with identical subsidence and sediment input rates are boundaries likely to develop synchronously hence the concept of global synchroneity of sequence boundary development may well be an illusion creat d by the similarity in age of the majority of basins studied as a result of this study it seems wise discard the global approach to basin analysis

basin modeling meets rift analysis a numerical modeling study from the jeanne d arc basin offshore newfoundland canada abstract the jeanne d arc basin on the grand banks offshore newfoundland is a confined failed rift basin its initial development and burial history were controlled by crustal stretching and thinning this study provides a detailed analysis of the heat flow tectonic subsidence stretching factor maturation and temperature history based on 44 1d models and one full 4d space and time model in basin models the heat flow history is usually calculated from vitrinite reflectance vrr data however this causes uncertainties and reflects only the periods of sedimentation which where penetrated by wells therefore other methods should be used to reconstruct the early heat flow history not recorded by sediments in this study a discontinuous pure shear stretching model including radioactive heat production reflecting the timing and magnitude of stretching factors of crust and lithospheric mantle was applied to a 4d numerical model for the jeanne d arc basin it is the first time that this new technique is shown on a real case scenario and it gives new insights into the regional geodynamics results show that to understand the thermal evolution of the jeanne d arc sedimentary basin completely it is crucial to consider the triassic rift system this first rift generated the structural framework of the basin where most of the sediments were deposited the second extension in the cretaceous represents most likely an ultra slow extension phase with a heat impulse too weak to leave any thermal record this study demonstrates that the entire evolution of the jeanne d arc basin can be reconstructed assuming just one single triassic thermal rift additionally it shows the effects of a lateral heat transfer on the determination of stretching factors and thus on tectonic subsidence and the resulting heat flow history

geochemistry of the lower cretaceous chaswood formation nova scotia canada provenance and diagenesisgeological survey of canada contribution 20080004 the fluvial chaswood formation records a complex history of tectonic reactivation of basement horsts and shedding of clastic sediment previous mineralogical studies indicate sources from both local and more distant basement rocks of the appalachians because such mineralogical studies identify only particular source rocks the geochemistry of 60 samples from a complete section through the chaswood formation in borehole rr 97 23 was investigated to determine the character of bulk sediment supply the detrital signature is partially obscured by diagenetic processes that caused concentration of k p sr and u at three regional unconformities the elements ti in ilmenite and its alteration products zr in zircon th and y are largely controlled by the abundance of heavy minerals in the rocks ilmenite is the dominant first cycle heavy mineral whereas much of the zircon is of polycyclic origin therefore the ti zr ratio is a guide to the proportion of first cycle sediment supply from crystalline basem

emplacement of clay into sand by infiltration abstract laboratory experiments and examination of core samples from holocene sand bodies demonstrate that vadose infiltration of muddy water through sand is an effective mechanism by which clay can be emplaced into sand infiltrated clays form coatings on and bridges between sand sized framework grains clay particles are mostly oriented parallel to grain surfaces in coatings and perpendicular to grain surfaces in bridges the amount of clay emplaced as coatings and bridges is determined by complexly interacting variables that include sand grain size clay particle size clay particle shape concentration of suspended sediment and clay composition of these relatively coarse sand sizes and high concentrations of suspended sediment appear to promote the emplacement of the most infiltrated clay in holocene sands the formation of grain coatings and bridges is facies dependent infiltrated clays are most effectively emplaced in environments characterized by high suspended sediment concentrations fluctuating water levels and minimal sediment reworking e g point bar and delta plain in contrast virtually no infiltrated clay is emplaced in environments characterized by low suspended sediment concentration and continuous reworking e g beach and tidal delta

extensional tectonics and stratigraphy of hibernia oil field grand banks newfoundland the tectonic evolution of the grand banks involved several episodes of rifting and sequential development of the continental margin the dominant period of rifting and basin formation in the central grand banks was late callovian to aptian extensional failure of the central grand banks crust probably occurred along a shear zone that dipped gently to the west listric normal basin forming faults merge at depth with this detachment system the listric murre fault soles at 26 km 16 mi creating the very deep jeanne d arc basin cross basin transfer faults accommodated different amounts and rates of extension and resulted in the conspicuous offset pattern and funnel shaped geometry of the jeanne d arc basin the hibernia oil field is associated with one of these structural salients the stratigraphy of the jeanne d arc basin and the hibernia oil field is a direct response to this tectonic and structural framework large scale unconformity bounded sequences correspond to major plate reorganizations and zipper type opening of the atlantic ocean smaller scale adjustments to episodic extension are expressed in multiple stacking of depositional sequences the broad scale evolution of the synrift succession involved the early deposition of limestones and oil prone shales about 10 12 m y later rifting climaxed resulting in floods of coarse terrestrial material from the rift shoulders the characteristics of these depositional systems reflect a pervasive structural control affecting the distribution of facies tracts dip slip movement on basin bounding faults and c oss basin transfer fault trends were equally important a profound structural modification of the hibernia structure occurred in late barremian time when a major detachment developed within the basin fill this structural modification and associated antithetic and synthetic faulting in the hanging wall largely controlled reservoir distribution and the maturation migration and trapping of hydrocarbons

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

geological history of the flemish pass basin offshore newfoundland in this paper we present a seismic stratigraphic interpretation of the mesozoic and tertiary geologic history of the flemish pass basin offshore newfoundland based on seismic data and data from seven wells that were integrated on the bp subsurface integrated interpretation system siis four megasequences are identified megasequence 1 ms1 is triassic to lower berriasian and includes poorly known sediments associated with triassic early jurassic rifting prior to spreading between the north african and american continents the uppermost mappable unconformity bounded unit within ms1 contains major kimmeridgian to portlandian marine source rocks deposited in two east west trending subbasins in the baccalieu and gabriel areas during the early berriasian pronounced rif ing linked to the subsequent spreading of iberia from the grand banks barremian aptian led to regional deepening and deposition of clastic sediments ms2 in two northeast southwest trending fault bounded subbasins in the baccalieu and gabriel areas in the aptian early cretaceous subbasins were inverted due to strike slip movement as extension assumed a northeast southwest orientation prior to movement of greenland europe away from labrador albian ms3 sediments fill northwest southeast trending fault bounded depocenters typically located on areas that had formed highs during the early cretaceous postrift sedimentation continued from the albian to the present with upper cretaceous pelagic limestone and later clastic sediment deposition

variations in mixed layer illite smectite diagenesis in the rift and post rift sediments of the jeanne d arc basin grand banks offshore newfoundland canada mixed layer illite smectite i s clays were analyzed from 22 deep exploration wells from the jeanne d arc basin on the grand banks offshore newfoundland the host of large commercial hydrocarbon accumulations discovered in the last two and a half decades the fine fraction of the clays 0 1 m consists mainly of mixed layer i s with minor amounts of kaolinite illite and chlorite smectite and or smectite rich i s clays were supplied to the jeanne d arc basin from upper jurassic to tertiary times smectite rich i s clays occur only in shallow samples irrespective of geologic age the proportion of illite in i s mixed layers as well as the degree of ordering increase with depth and temperature indicating that smectite rich i s clays have been progressively illitized in both rift and post rift sediments of the jeanne d arc basin during burial the transition from random to r1 ordered i s occurs between subsurface depths of 1940 and 3720 m and crosses major stratigraphic boundaries the transition fr

tectonic controls on upper jurassic to lower cretaceous reservoir architecture in the jeanne d arc basin with some comparisons from the porcupine and moray firth basins

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

diagenesis and origin of calcite cement in the flemish pass basin sandstone reservoir upper jurassic implications for porosity development abstract the flemish pass basin is a deep water basin located offshore on the continental passive margin of the grand banks eastern newfoundland which is currently a hydrocarbon exploration target the current study investigates the petrographic characteristics and origin of carbonate cements in the ti 3 member a primary clastic reservoir interval of the bodhran formation upper jurassic in the flemish pass basin the ti 3 sandstones with average q 86 0 f 3 1 r 10 9 contain various diagenetic minerals including calcite pyrite quartz overgrowth dolomite and siderite based on the volume of calcite cement the investigated sandstones can be classified into 1 calcite cemented intervals 20 calcite and 2 poorly calcite cemented intervals porous petrographic analysis shows that the dominant cement is intergranular poikilotopic 300 500 m calcite which stared to form extensively at early diagenesis the precipitation of calcite occured after feldspar leaching and was followed by corrosion of quartz grains intergranular calcite cement hosts all liquid inclusions mainly in the crystal core but rare primary two phase liquid and vapor fluid inclusions in the rims with mean homogenization temperature t h of 70 2 4 9 c and salinity estimates of 8 8 1 2 eq wt nacl the mean 18 o and 13 c isotopic compositions of the intergranular calcite are 8 3 1 2 vpdb and 3 0 1 3 vpdb respectively whereas fracture filling calcite has more depleted 18 o but similar 13 c values the shale normalized rare earth element ree sn patterns of calcite are generally parallel and exhibit slightly negative ce anomalies and positive eu anomalies fluid inclusion gas ratios co 2 ch 4 and n 2 ar of calcite cement further confirms that diagenetic fluids originated from modified seawater combined evidence from petrographic microthermometric and geochemical analyses suggest that 1 the intergranular calcite cement precipitated from diagenetic fluids of mixed marine and meteoric riverine waters in suboxic conditions 2 the cement was sourced from the oxidation of organic matters and the dissolution of biogenic marine carbonates within sandstone beds or adjacent silty mudstones and 3 the late phases of the intergranular and fracture filling calcite cements were deposited from hot circulated basinal fluids calcite cementation acts as a main controlling factor on the reservoir quality in the flemish pass reservoir sandstones over 75 of initial porosity was lost due to the early calcite cementation the development of secondary porosity mostly enlarged moldic pores and throats by later calcite dissolution due to maturation of organic matters e g hydrocarbon and coals was the key process in improving the reservoir quality

provenance and paleodrainage patterns of upper jurassic and lower cretaceous synrift sandstones in the flemish pass basin offshore newfoundland east coast of canada upper jurassic to lower cretaceous synrift sandstones from two industry exploratory wells in the flemish pass basin were studied for provenance using heavy mineral proxies these sandstones were deposited during the north atlantic rifting stage at which time rifting intensified between iberia and the grand banks several heavy mineral methods were used including in situ u pb geochronology and morphological and chemical analysis of detrital zircons chemical discrimination of detrital tourmalines and heavy mineral ratios clastic bed load material entering the northern flemish pass basin during the tithonian to berriasian was connected to transport systems reaching west as far as 400 to 500 km 249 311 mi source areas to the west included igneous rocks and associated cover sequences of the avalon zone as well as the magmatic rocks metasedimentary rocks and associated cover sequences present in the central mobile belt the eastward directed input of bed load material into the basin is considered to have resulted in the concentration of sandstone units along its western margin with deteriorating reservoir grade toward the east given the regional extent of drainage systems it is likely that similar constraints apply to equivalent sandstones in the adjacent east orphan basin by the valanginian barremian paleodrainage orientations had switched and bed load material began to enter the flemish pass basin from more proximal areas to the southeast with the avalon zone basement overall no evidence exists to support sediment sourcing from the iberian margin or the flemish cap galicia bank continental fragment to the east and material from these areas is instead interpreted to have been shed into the incipient atlantic ocean or bay of biscay also no evidence exists to support sourcing from grenville basement farther to the west implying that a drainage divide may have existed somewhere between central and western newfoundland west of which material was presumably being transported to the south or southwest

sequence stratigraphic response to aptian albian rifting in conjugate margin basins a comparison of the jeanne d arc basin offshore newfoundland and the porcupine basin offshore ireland

sequence stratigraphic analysis of the aptian albian lower greensand in southern england abstract facies analysis and its use in sequence stratigraphy is described using the lower greensand of southern england as an example and the resulting interpretations are outlined this work forms an independent test of sequence stratigraphic techniques and the exxon cycle chart sequence stratigraphy is a very powerful tool in the analysis of problematic successions although some modification is made here in emphasizing the use of the transgressive surface changing palaeoenvironmental conditions and the effect that palaeoceanography has on the recognition of sequence boundaries are also discussed broad agreement is found between these results and the cycle chart although changing tidal conditions alter the criteria available for analysis of the aptian albian lower greensand succession comparison between this study and sequence stratigraphic analyses conducted in the more condensed type sections of england and france shows that further sequence boundaries are recognizable

revised upper cretaceous and lower paleogene lithostratigraphy and depositional history of the jeanne d arc basin offshore newfoundland canada the jeanne d arc basin is a relatively small passive margin rift basin that underlies what is now the northeastern corner of the grand banks of newfoundland in the late cretaceous and early paleogene the basin formed an elongated depression where sediment accumulated in and along the margins of a shallow shelf sea seismic and well data were used to examine the late cretaceous and paleogene evolution of the basin and to formally revise the existing stratigraphic classification scheme in the late cretaceous the western margin of the basin was characterized by a well developed shelf and slope system comprised of the sand prone otter bay and fox harbour members and the distally equivalent shale prone red island and bay bulls members respectively these members record two main progradational episodes that are separated by a regional unconformity and a thick shale interval corresponding to the bay bulls member east of the shelf slope system upper cretaceous shale and sparse sandstone of the dawson canyon formation and chalk of the petrel member and wyandot formation were deposited in a relatively condensed section in the early part of the paleogene two main sandstone units herein named the avondale and south mara members were deposited east of the well developed latest cretaceous slope in the lower part of the banquereau formation the avondale member corresponds to small sand prone submarine fans deposited on the basin floor in the early paleocene the submarine fans were fed primarily by two canyons that incised the western margin of the basin eroding the late cretaceous shelf and slope also in the paleocene siliceous shale and siltstone of the tilton member were deposited above bathymetric highs along the western and southern basin margins the exact temporal relationship between the tilton and avondale members is poorly understood the south mara member was deposited in the latest paleocene and early eocene in the southern parts of the basin it forms a regressive sandstone unit above the tilton member deposited during a period of renewed shelf slope progradation in the central and northern parts of the basin the south mara member corresponds to small sand prone submarine fans similar to those deposited in the early paleocene

dynamics of the north american ice sheet complex during its inception and build up to the last glacial maximum the north american ice sheet complex played a major role in global sea level fluctuations during the late quaternary but our knowledge of its dynamics is based mostly on its demise from the last glacial maximum lgm a period characterised by non linear behaviour in the form of punctuated ice margin recession episodic ice streaming and major shifts in the location of ice divides in comparison knowledge of the pre lgm ice complex is poorly constrained largely because of the fragmentary nature of the evidence relating to ice sheet build up in this paper we explore the inception and growth of ice 120 20 ka using a glacial systems model which has been calibrated against a large and diverse set of data relating to the deglacial interval we make use of calibration data prior to the lgm but its scarcity introduces greater uncertainty which is partly alleviated by our large ensemble analysis results suggest that following the last interglaciation oxygen isotope stage ois 5e the ice complex initiated over the north eastern canadian arctic and in the cordillera within a few thousand years it then underwent rapid growth to an ois 5 maximum at 110 ka 5d and covered 70 of the area occupied by the lgm ice cover although only 30 by volume an ois 5 minimum is modelled at 80 ka 5a before a second phase of rapid growth at the start of ois 4 which culminated in a large ice complex at 65 ka almost as large as at the lgm subsequent deglaciation was rapid maximum modelled sea level contribution of 16 cm per century and resulted in an ois 3 minimum between ca 55 60 ka thereafter the ice complex grew towards its lgm configuration interrupted by several phases of successively less significant mass loss our results support and extend previous inferences based on geological evidence and reinforce the notion of a highly dynamic pre lgm ice complex e g with episodes of 10 s m of eustatic sea level equivalent in 50 but even the thin ois 5 ice sheets exhibit fast flow features several 1000 m a 1 in major topographic troughs notwithstanding the severe limitations imposed by the use of the shallow ice approximation we note that most fast flow features generated prior to the lgm correspond to the location of known ice streams during deglaciation i e in major topographic troughs and over soft sediments at the southern and western margins moreover the modelled flux of these ice streams sensu lato appears to be non linearly scaled to ice sheet volume i e there is no evidence that decay phases were associated with significantly increased ice stream activity this hypothesis requires testing using a model with higher order physics and future modelling would also benefit from additional pre lgm constraints e g dated ice free margin positions to help reduce and quantify uncertainties

the influence of tectonics on early cretaceous sedimentation in bedfordshire england the lower cretaceous sediments of the bedfordshire area are aptian and albian in age during this time the area was situated within an extensional tectonic regime and the pattern of sedimentation in terms of lateral variation both in sediment type and thickness reflects the influence of normal faulting jurassic topography created by block faulting and erosion controlled the distribution of later facies largely by continued tectonic processes especially the reactivation of the jurassic fault block system which produced syn sedimentary faulting of the overlying sequence thus the traditional view of the infill of an erosional basin by the lower greensand is challenged

thermal diagenesis of clay minerals within volcanogenic material from the tonga convergent margin abstract clay minerals are examined in detail in the sediment from the tonga trench margin at site 841 leg 135 odp the changes in amount and nature of secondary clays with depth provide an alternative explanation for the intensive alteration of volcanogenic material at convergent margins a characteristic distribution of clay minerals with depth shows four distinct zones unexplainable by simple burial diagenesis processes these are named the upper reactive lower and rhyolitic zones the reactive zone is intercalated with numerous sills and is characterized by the dominant iron rich clays such as saponite corrensite and chlorite associated with analcime the occurrence of such iron rich clays mostly associated with a large amount of analcime yields chemical and mineralogical evidence for thermal diagenesis the required heat for the diagenetic process was transferred from recently intruded basaltic andesite sills in the vicinity of these intrusions the iron rich clay minerals may have formed at temperatures up to 200 c a zoning with respect to clay and zeolite minerals indicates that the influence of the palaeoheat flow decreased with the distance from the intrusion the formation of interlayered i s illite kaolinite and aluminous chlorite which are recognized as major secondary minerals within the rhyolitic complex was mainly controlled by both early diagenesis at moderately elevated temperatures and since the eocene by burial diagenesis at low temperatures the occurrence of a steam zone in an early stage of the intrusion is restricted to miocene tuffs and has overprinted the early alteration of the volcanogenic material within the tuffs and has changed the originally pristine composition of the pore fluids

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

active normal faulting beneath a salt layer an experimental study of deformation patterns in the cover sequence scaled experimental models show that the presence of a viscous layer such as salt facilitates the development of extensional forced folds above active normal faults the geometries of the extensional forced folds and their associated secondary fault patterns depend on the thickness and viscosity of the viscous layer the thickness of the cover sequence the strength and ductility of the cover sequence and the magnitude and rate of displacement on the underlying master normal fault increasing the thickness of the viscous layer and the cohesive strength and ductility of the overburden enhances the decoupling between the deep and shallow deformation alternatively increasing the viscosity of the viscous layer the thickness of the overburden and the magnitude and rate of displacement on the master normal fault reduces the decoupling between the deep and shallow deformation enhanced decoupling facilitates the formation of broad extensional forced folds and the development of detached secondary faults both near and far from the master normal faults the model predicted deformation patterns closely resemble those observed in the gulf of suez the haltenbanken area of offshore norway and the jeanne d arc basin of the grand banks offshore southeastern canada

variations of the sequence stratigraphic model past concepts present understandings and future directions the working hypothesis upon which the sequence concepts are based is that the relative sea level change results in changes in the capacity of a basin to accommodate sediment which in turn results in a succession of sequences the interplay between eustasy tectonics sediment flux and physiography yields a predictable geologic response in carbonate clastic as well as mixed carbonate clastic settings the criteria for recognition of sequence boundaries can be varied within a given basin as well as between basins they include but are not restricted to 1 a basinward shift of facies across a sharp bedding contact 2 onlapping stratal geometry and 3 truncation of strata the key to the correct utilization of these concepts is to recognize sequence stratigraphy as an approach or a tool rather than a rigid template observations from the upper albian cretaceous viking formation of the western canadian sedimentary basin are presented to illustrate the stratigraphic expression of clastic depositional sequences on a ramp margin in this setting forced regressions and lowstand shorelines commonly occur incised valleys sometimes occur and submarine fans rarely occur in response to fluctuations of relative sea level the base of the viking formation sometimes is characterized by relatively coarse grainedmore sediments sharply overlying fine grained offshore muds and is interpreted as a third order sequence boundary pebbles occasionally are observed at this contact subsequently a number of higher order sequences within the lower to middle viking are observed and are characterized by the occurrence of forced regressions and lowstand shorelines without associated incised valleys less