an 40ar 39ar thermochronology of the ofoten troms region implications for terrane amalgamation and extensional collapse of the northern scandinavian caledonides fifteen 40ar 39ar cooling ages are reported for metamorphic hornblende and muscovite from far traveled terranes constituting the ofoten nappe stack of northern norway eight cooling ages on hornblende range from 425 to 394 ma and seven muscovite ages from the same or nearby outcrops as the hornblendes range from 400 to 373 ma these data are compared with 40ar 39ar ages from over a large part of the northern caledonides to evaluate regional mineral cooling patterns results indicate that 1 scandian silurian devonian metamorphism was predominant 2 most of the nappes investigated contain some vestige of pre scandian tectonism and or metamorphism 3 hornblende and muscovite cooling ages are progressively younger to the west and south which suggests a hinged to the east mineral cooling pattern and 4 a late out of sequence thrust is the only disruption of this cooling pattern synmetamorphic amalgamation of the nappes resulted from scandian a type subduction the hinged to the east mineral cooling pattern implies isostatic adjustment and exhumation of the footwall of a west dipping crustal scale extensional fault located somewhere west of the present norwegian coast during late synorogenic gravitational collapse the late out of sequence fault formed contemporaneously with uplift in the hinterland implying a kinematic and temporal connection with east directed contractional faulting in the foreland

late quaternary climate change from δ18o records of multiple species of planktonic foraminifera high resolution records from the anoxic cariaco basin venezuela seasonal trade wind induced upwelling along the southern margin of the caribbean sea occurs in response to the annual migration of the intertropical convergence zone laminated high deposition rate sediments of the cariaco basin a small anoxic basin on the venezuelan continental shelf clearly record large changes in the past intensity of this upwelling because sediments of the cariaco basin are largely unbioturbated they offer a natural opportunity to study the stable isotopic records of multiple planktonic foraminiferal taxa and to evaluate their sensitivity to both the modern hydrography and temporal changes in upwelling intensity and climate oxygen isotope data 18o from four dominant foraminiferal taxa are presented for the time period covering the last 28 kyr the 18o data from globigerina bulloides after correction for nonequilibrium precipitation are used as a monitor of sea surface conditions during the winter spring upwelling season the 18o data from white globigerinoides ruber are used as a measure of annual average conditions in the near surface while pink g ruber data are consistent with use as an index of endmember conditions during the summer fall nonupwelling season data from the deeper dwelling neogloboquadrina dutertrei yield information on conditions near the base of the local thermocline during the last glacial 18o data from g ruber and generally reduced interspecific differences indicate cooling of surface waters over the cariaco basin by up to 4 c this longer term cooling does not appear to be related to changes in upwelling intensity along the coast but may instead reflect more regional cooling of the larger caribbean superimposed on this pattern between 12 6 and 10 ka is a convergence of 18o data between g bulloides and n dutertrei implying much stronger upwelling during the last deglaciation this scenario is consistent with other evidence for high productivity at this time at 14 ka a sharp 18o depletion event observed in all taxa seems to have been produced by increased freshwater discharge to the southern caribbean suggesting either higher regional rainfall or the influence of glacial melting in the andes minimum 18o values of pink g ruber around 6 7 ka record warmer summer sea surface temperatures and or decreased salinity in the mid holocene

subduction and eduction of continental crust major mechanisms during continent continent collision and orogenic extensional collapse a model based on the south norwegian caledonides during continental collision in the middle silurian the thickness of the lithosphere under the caledonides of s norway was doubled by subduction of the western margin of baltica including the western gneiss region under laurentia crustal rocks of the baltic plate reached sub moho depths of near 100 km or more as inferred from the presence of coesite in eclogites isostatic calculations indicate an average elevation of the mountain chain of about 3 km at this stage the subducted lithosphere experienced vertical constrictional strains as a result of slab pull by its heavy and cold root eduction of the deeply buried crustal material was initiated by decoupling of the thermal boundary layer in the subducted lithosphere isostatic rebound resulted in very rapid uplift 1 2 mm yr 1 and the deep crust was exhumed mainly by tectonic extensional stripping over a period of 30 40 myr the eduction was probably related to a rolling hinge footwall uplift mechanism and the early high pressure coaxial fabrics were overprinted by extensional simple shear as the deep crust reached middle and upper crustal levels the model explains the present day normal crustal thickness under the exhumed deep rocks without necessarily invoking large scale lateral flow of material in the lower crust or igneous underplating

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

subsidence in late paleozoic basins in the northern appalachians during the interval between continental collision in the devonian and continental breakup in the triassic the northern appalachians became the site of a wide plate boundary zone of dominantly right lateral strike slip as is typical of intracontinental transforms tectonism was both diachronous and rapidly variable along strike through regimes of pure strike slip transpressional deformation and rapid subsidence of extensional basins up to 9 km of mainly nonmarine clastic sediments accumulated in these local depocenters which subsided episodically in two stages 1 an initial phase of stretching and thinning of the lithosphere when subsidence was rapid fault controlled and often accompanied by volcanism and 2 a subsequent phase of gradual thermal subsidence during which the depositional basins expanded to bury the earlier border faults and progressively younger sedimentary units onlapped basement the largest depocenter the magdalen basin opened as a pull apart between strike slip faults in newfoundland and new brunswick from late devonian to early carboniferous subsequent thermal subsidence affected a large area during medial and late carboniferous a phenomenon that is well recorded to the north and west where no later tectonism occurred in areas to the south and east of the basin strike slip on other faults continued into the time of thermal subsidence introducing complications such as localized transpressional deformation and rapid subsidence in smaller pull aparts

accurate estimation of sea surface temperatures using dissolution corrected calibrations for mg ca paleothermometry 1 paired 18o and mg ca measurements on the same foraminiferal shells offer the ability to independently estimate sea surface temperature sst changes and assess their temporal relationship to the growth and decay of continental ice sheets the accuracy of this method is confounded however by the absence of a quantitative method to correct mg ca records for alteration by dissolution here we describe dissolution corrected calibrations for mg ca paleothermometry in which the preexponent constant is a function of size normalized shell weight 1 for g ruber 212 300 m mg ca ruber 0 025 wt 0 11 e0 095t and b for g sacculifer 355 425 m mg ca sacc 0 0032 wt 0 181 e0 095t the new calibrations improve the accuracy of sst estimates and are globally applicable with this correction eastern equatorial atlantic sst during the last glacial maximum is estimated to be 2 9 0 4 c colder than today

thermal history of the southwestern meguma zone nova scotia from an 40ar 39ar and fission track dating study of intrusive rocks two geologically distinct regions within the meguma terrane have been studied in detail and are shown to have contrasting thermal histories this conclusion is based on 31 new 40ar 39ar age spectra on micas k feldspars and hornblendes from several of the plutons in southern nova scotia which are satellites to the much larger south mountain batholith smb in addition we report four k feldspar age spectra from a locality in the northeastern part of the smb and seven fission track ages from both the southern and northern areas the complex age spectrum of hornblende from a mafic phase associated with the bamngton passage pluton suggests a minimum intrusive age of 385 ma a result consistent with geologic evidence that this pluton represents an early less evolved magmatic pulse later intrusive activity appears to have been coeval with the intrusion of the smb at ca 370 ma ago in the southern region argon clocks in feldspars were completely reset and mica clocks variably reset by a later thermal event the cumulative geochronologic and geologic evidence constrains this event to 300 320 ma ago in the smb this alleghanianl hercynian thermal disturbance is much less pronounced and appears to be localized to small areas that are often associated with economic mineralization k feldspars from the southern plutons record an episode of argon loss 220 230 ma ago which is less evident in the smb to the north upper triassic dike injection in the southern region associated with the initial rifting phase of the canadian atlantic margin accompanied this milder thermal pulse apatites in the two regions record a mean fission track age of ca 180 ma which we attribute to the final cooling of the terrane below about 100 c the timing of this event coincides with regional uplift recorded in sedimentary sequences along much of the maritime continental shelf deux kgions gtologiques distinctes inttgkes au terrane de meguma ont ctt ctudites en dctai1 et leurs histoires thermales

deglacial changes in ocean circulation from an extended radiocarbon calibration temporal variations in the atmospheric concentration of radiocarbon sometimes result in radiocarbon based age estimates of biogenic material that do not agree with true calendar age this problem is particularly severe beyond the limit of the high resolution radiocarbon calibration based on tree ring data which stretches back only to1 2 about 11 8 kyr before present bp near the termination of the younger dryas cold period if a wide range of palaeoclimate records are to be exploited for better understanding the rates and patterns of environmental change during the last deglaciation extending the well calibrated radiocarbon timescale back further in time is crucial several studies attempting such an extension using uranium thorium dated corals3 4 5 and laminae counts in varved sediments6 7 8 9 show conflicting results here we use radiocarbon data from varved sediments in the cariaco basin in the southern caribbean sea to construct an accurate and continuous radiocarbon calibration for the period 9 to 14 5 kyr bp nearly 3 000 years beyond the tree ring based calibration a simple model compared to the calculated atmospheric radiocarbon concentration and palaeoclimate data from the same sediment core suggests that north atlantic deep water formation shut down during the younger dryas period but was gradually replaced by an alternative mode of convection possibly via the formation of north atlantic intermediate water

thermochronologic constraints on ore formation at the gays river pb zn deposit nova scotia canada from apatite fission track analysis fission tracks in detrital apatites from the cambro ordovician metasedimentary basement in the vicinity of the carboniferous hosted gays river pb zn deposit nova scotia provide a record of final

geologic fluid inclusion and stable isotope studies of the gays river lead zinc deposit nova scotia canada the gays river deposit is the largest carbonate hosted lead zinc deposit known in the mississippian windsor group of atlantic canada the orebody mainly occupies one flank of a porous dolomitized carbonate bank that unconformably overlies a basement ridge of the metasedimentary lower paleozoic megurea group the orebody consists of stratiform disseminated sulfides as open space fillings in primary and secondary pores of the dolomite and fault controlled veinlike bodies of high grade massive sphalerite and galena the carbonate bank is overlain by evaporite deposits of mississippian age underground mapping and laboratory studies suggest four main stages of evolution for gays river 1 deposition of the visean carbonate bank preore evaporite deposition pervasive dolomitization and growth of diagenetic marcasite 2 deposition of sphalerite galena chalcopyrite and calcite as a result of influx of hydrothermal metal rich saline brines into fractures and porous dolomite 3 postore deposition of calcite fluorite barite marcasite pyrite and selenite and 4 uplift localized dedolomitization of the mineralized carbonates and exposure by erosion in cretaceous times microthermometry of fluid inclusions yields the following mean homogenization temperatures sphalerite 215oc ore stage calcite 173oc postore calcite 142oc fluorite 142oc and barite 137oc pressure corrections should be minimal for these temperatures no evidence of boiling was observed in the inclusions salinity determinations from the ice melting temperatures of inclusions in postore fluorite and calcite yield a value of ca 20 4 equivalent wt percent naci for the hydrothermal fluid during the waning stages of mineralization isotopic analyses indicate that anhydrite and gypsum in the overlying evaporites and barite within the orebody are enriched in heavy sulfur t 34s 13 1 16 5 0 suggesting a mississippian seawater source ore stage sphalerite galena and chalcopyrite probably derived their sulfur b34s 8 0 13 65 0 from sulfates or possibly a homogenized basement source postore marcasite and pyrite are characterized by light probably biogenic sulfur ba4s 9 7 to 46 0 mineralized carbonates are significantly depleted in the heavier isotopes of oxygen and carbon with respect to their unmineralized equivalents preliminary lead isotope data for galena suggest that the metasedimentary basement was a source of lead this study disputes an earlier interpretation that the stratiform lead zinc ores are an early low temperature diagenetic cement of the carbonate bank the high grade zones are not residual concentrations related to sinkholes as originally thought instead both disseminated and massive ores are probably the result of the same mineralizing episode involving deeply convecting brines or brines expelled during basin dewatering under high geothermal gradients in the late paleozoic

nature of palaeozoic extension in lofoten north norwegian continental shelf insights from 3 d seismic analysis of a cordilleran style metamorphic core complex analyses of 3 d seismic data reveal that pre triassic basins are present underneath the mesozoic north traena basin lofoten margin norway these are linked to a cordilleran style metamorphic core complex that developed in palaeozoic times including rotated fault blocks with hanging wall growth wedges bounded by listric faults that sole into a sub horizontal detachment on the basis of similarity in age structural style and transport direction we propose a kinematic link with a permian mylonitic detachment documented onshore this study presents the first offshore evidence for palaeozoic detachment faulting elucidating the mechanisms behind the long lived exhumation history of the lofoten basement

the roles of pedogenesis and diagenesis in clay mineral assemblages lower cretaceous fluvial mudrocks nova scotia canada abstract clay mineral assemblages in alluvial mudrocks are important for paleoclimatic interpretation and for understanding burial diagenetic cementation in sandstones but it is commonly difficult to unravel the relative importance of source weathering pedogenesis and diagenesis in their origin the clay mineral assemblages in fluvial overbank mudrocks from the lower cretaceous chaswood formation in central nova scotia investigated by x ray diffraction analysis of the

ductile and brittle extension in the southern lofoten archipelago north norway implications for differences in tectonic style along an ancient collisional margin the lofoten archipelago north norway occupies the most inter nal position of the caledonian belt in northern scandinavia and rocks and structures exposed there are crucial to understanding processes of how the baltic basement and its cover allochthons responded to continental lithospheric subduc tion and subsequent continental separation relatively little is published about the structural and metamorphic development and especially the timing of these events consequently it is unknown how features exposed on these spatially isolated islands relate to those of the adjacent mainland rocks in lofoten were affected by caledonian regional metamorphism and structures record tops east contraction and later extension related to late to post caledonian basement exhumation tops west extension is preferentially developed in meter to km scale ductile shear zones containing west dipping extensional shear bands west verging rootless folds and asymmetric feldspar porphyroclasts west plunging sinistral oblique elongation lineations in the mylonitic foliation are interpreted to indicate the line of transport mesoscopic backfolds are locally developed within the tops west shear zones and further document west directed transport of structurally higher rocks the ductile extensional shear zones locally are cross cut by low angle tops west cataclastic normal faults reflecting progressive unroofing of the shear zones to shallower crustal levels during late and post caledonian extensional events northeast striking high angle brittle normal faults truncate all other fabrics and structures and juxtapose structurally deep undeformed precambrian basement with the caledonian nappe sequence 40 ar 39 ar data indicate that ductile extension in lofoten likely initiated soon after the caledo nian metamorphic peak at 430 ma and continued episodically until at least permian time rocks passed through the brittle ductile transition rapidly at 275 ma recent paleomagnetic data also point to later phases of brittle faulting in lofoten one in the jurassic cretaceous and one related to tertiary opening of the norwegian sea the magnitude and style of late to post caledonian exten sion and basement exhumation in lofoten differs markedly from the formation of phenomenal devonian basins and exposures of caledonian ultra high pressure assemblages in the western gneiss region wgr of southern norway differ ences in the styles of extension between northern and southern norway are interpreted to reflect inherited differences in crustal architecture that may have been enhanced during the caledonian orogeny

polyphase late paleozoic tectonothermal evolution of the southwestern meguma terrane nova scotia evidence from 40ar 39ar mineral ages 40ar 39ar incremental release ages of hornblende muscovite and biotite from a variety of granitic stocks and host metamorphic rocks suggest a complex late paleozoic tectonothermal evolution for the southwestern meguma terrane regional d1 folding with cleavage formation under greenschist lower amphibolite facies m1 metamorphic conditions occurred at ca 400 410 ma and was followed by emplacement of a series of granitic stocks ranging in age between ca 375 and 315 ma these were emplaced at relatively shallow crustal levels and developed contact metamorphic aureoles of variable grade these are locally superposed on m1 regional metamorphic assemblages and result in a complex isograd pattern 40ar 39ar mineral ages suggest episodes of contact metamorphism occurred at 1 360 375 ma possibly related to emplacement of the south mountain batholith or temporal equivalents 2 350 356 ma around the port mouton pluton and northeastern shelburne pluton 3 ca 315 325 ma near the wedgeport pluton and in

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

k ar and 40ar 39ar geochronology of granitoid rocks from southern nova scotia its bearing on the geological evolution of the meguma zone of the appalachians k ar and or 40ar 39ar apparent ages are reported for 28 samples of biotite and muscovite from nova scotia s south mountain batholith and associated northern satellite stocks in addition 14 mica samples from the southern satellite stocks were dated previous workers using primarily k ar and rb sr techniques have reported a spread of apparent ages ranging from 240 420 ma for these intrusive rocks the present data set is internally consistent and has been calibrated against accepted interlaboratory standards a mean age of 367 ma was obtained for the south mountain batholith and the northern stocks a value consistent with results recently obtained in an rb sr study by clarke and halliday no differences in apparent age among the various phases or clear geographic age distribution patterns were evident satellite stocks in the southern part of the province have in general younger apparent ages clustered in the range 300 320 ma we suggest that in southern areas mica argon systems record the effect

western caribbean sea surface temperatures during the late quaternary 1 mg ca ratios in the planktonic foraminifera globigerinoides ruber from colombian basin core odp 999a suggest that caribbean sea surface temperatures ssts were from 2 1 to 2 7 c colder than the present during the last three glacial maximums in comparison faunal derived ssts simmax method show that august ssts in the caribbean varied 2 c over the past 360 kyr whereas february ssts varied between 21 0 c and 26 5 c changes in the mg ca sst record contain a strong 23 kyr periodicity suggesting the mg ca sst record reflects a warm season weighted sst average rather than an annual mean sst combining several dissolution indices we identify brief periods of decreased carbonate preservation in our record and show that mis 11 stands out as the most intensive dissolution cycle in the caribbean over the last 460 kyr comparison of caribbean sst change with a similar estimate of tropical sst variability in the western pacific over the past 360 kyr reveals shifts in the east west tropical sst gradient that are coeval with glacial interglacial climate change and consistent both with a southward migration of the glacial itcz and with a glacial el nino like mode of tropical circulation

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

variability in the mean latitude of the atlantic intertropical convergence zone as recorded by riverine input of sediments to the cariaco basin venezuela abstract changes in the strength and position of the intertropical convergence zone itcz are an important component of climate variability in the tropical atlantic the cariaco basin located on the northern margin of venezuela is sensitive to tropical atlantic climate change and its sediments provide a record of past itcz behavior today the cariaco basin experiences two distinct seasons that reflect the annual migration of the atlantic itcz between january and march when the itcz lies south of the equator northeasterly trade winds sit directly over cariaco basin and strong coastal upwelling and dry conditions dominate beginning in june july as the itcz moves north local rainfall reaches a maximum and the upwelling diminishes or disappears here we summarize new and previously published data on the river derived terrigenous fraction of cariaco basin sediments as well as comparisons to other paleoclimate records which together suggest a coherent climatologic response in the tropical atlantic triggered by a pattern of itcz migration that mimics the seasonal cycle during periods of cooler north atlantic ssts on time scales ranging from the little ice age to the younger dryas to the cold stadials of the last glacial decreased detrital delivery to cariaco basin from local rivers suggests a southward shift in the mean latitudinal position of the itcz during warm interstadials and periods of holocene and deglacial warmth northward shifts in itcz position and its belt of convective rainfall are inferred from increased detrital delivery to the basin whether the rapid shifts in itcz position and precipitation recorded by cariaco basin sediments and other regional records reflect a response to forcing originating in the high latitude atlantic or to forcing potentially sourced in the tropics is a key question yet to be fully answered

multispecies approach to reconstructing eastern equatorial pacific thermocline hydrography during the past 360 kyr 1 stable isotope data from eastern equatorial pacific eep core tr163 19 2 15 n 90 57 w 2348 m are presented for the surface dwelling foraminifers globigerinoides ruber and g sacculifer and thermocline dwelling globorotalia menardii and neogloboquadrina dutertrei using species specific normalization factors derived from experimental and plankton tow data we reconstruct a 360 kyr record of water column hydrography across the past three glacial cycles we demonstrate that g ruber maintains a mixed layer habitat throughout the entire record while g sacculifer records a mixture of thermocline and mixed layer conditions and g menardii and n dutertrei record thermocline properties we conclude that g sacculifer is not appropriate for paleoceanographic applications in regions with steep vertical hydrographic gradients results suggest that this region of the eep had a thicker mixed layer and deeper 13cdic boundary between the surface and equatorial undercurrent during the last two glacial periods a shift in n dutertrei and g sacculifer geochemistry prior to 185 kyr suggests water column structure and chemocline gradients changed possibly due to a shift in the position of the undercurrent relative to this site the timing and magnitude of glacial interglacial 13c variations between species indicates that near surface carbon chemistry is controlled by changes in productivity atmospheric circulation and advected intermediate water sources north of the antarctic polar front these results demonstrate that when properly calibrated for species differences multispecies geochemical data sets can be invaluable for reconstructing water column structure and properties in the past

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

post breakup burial and exhumation of passive continental margins seven propositions to inform geodynamic models despite many years of study the processes involved in the post breakup development of passive margins remain poorly understood integration of apatite fission track analysis afta and stratigraph

millennial scale sea surface temperature variability in the western tropical north atlantic from planktonic foraminiferal census counts planktonic foraminiferal census counts are used to construct high resolution sea surface temperature sst and subsurface thermocline temperature records at a core site in the tobago basin lesser antilles the record is used to document climatic variability at this tropical site in comparison to middle and high latitude sites and to test current concepts of cross equatorial heat transports as a major player in interhemispheric climate variability temperatures are estimated using transfer function and modern analog techniques glacial maximum cooling of 2 5 3 c is indicated maximum cooling by 4 c is inferred for isotope stage 3 the sst record displays millennial scale variability with temperature jumps of up to 3 c and closely tracks the structure of ice core dansgaard oeschger cycles sst variations in part of the record run opposite to the sst evolution at high northern latitude sites pointing to thermohaline circulation and marine heat transport as an important factor driving sst in the tropical and high latitude atlantic both on orbital and suborbital timescales

timing of paleozoic orogeny and extension in the continental shelf of north central norway as indicated by laser 40ar 39ar muscovite dating metamorphic rocks of lofoten norway represent a leading edge of the baltic craton that was partly subducted beneath laurentia during caledonian orogeny we find that muscovite porphyroblasts in lofoten record a remarkably complete history of cooling and unroofing and yield data about lofoten9s tectonic evolution in the interval from 425 to 265 ma these data confirm that culminating metamorphism of basement and allochthonous rocks in lofoten occurred during the scandian phase of orogeny permian ages for muscovite are the youngest obtained for regional metamorphic rocks anywhere in scandinavia and appear to record significant basement unroofing during extensional evolution of the norwegian greenland seaway regional age variations of muscovite in lofoten can be related to present crustal thickness devonian to permian sedimentation in the norwegian seaway and extensional structures and they indicate the timing of multiple extension events in the evolution of norway9s passive margin the results of this study show that 40 ar closure profiles in porphyroblasts can form even in active tectonic settings characterized by rapid and episodic unroofing

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

evolution of a major segmented normal fault during multiphase rifting the origin of plan view zigzag geometry abstract this case study addresses fault reactivation and linkage between distinct extensional episodes with variable stretching direction using 2 d and 3 d seismic re ection data we demonstrate how the vesterdjupet fault zone one of the basin bounding normal fault zones of the lofoten margin north norway evolved over c 150 myr as part of the north atlantic rift this fault zone is composed of nne ssw and ne sw striking segments that exhibit a zigzag geometry the structure formed during late jurassic and early cretaceous rifting from selective reactivation and linkage of triassic faults a rotation of the overall stress field has previously been invoked to have taken place between the triassic and jurassic rift episodes along the lofoten margin a comparison to recent physical analogue models of non coaxial extension reveals that this suggested change in least principal stress for the lofoten margin may best explain the zigzag style linkage of the triassic faults although alternative models cannot be ruled out this study underlines the prediction from physical models that the location and orientation of early phase normal faults can play a pivotal role in the evolution of subsequent faults systems in multi rift systems

new insights into the cretaceous cenozoic tectono stratigraphic evolution of the southern lofoten margin offshore norway abstract the tectono stratigraphic evolution of the southern lofoten margin and its immediate transition towards the northern voring margin has been studied in detail utilizing 2d multi channel seismic reflection profiles available wells in addition to gravity and magnetic data new and better refined structural elements have been mapped within the study area including informally named the west rost high fault complex rost syncline and sandflesa high furthermore four main rift phases have been recognised and refined late jurassic earliest cretaceous rifting controlled the initial structuring of the main structural elements mid cretaceous rifting was responsible for initiation of faulting in the west rost high fault complex while a composite late cretaceous rift phase took place and led to westward propagation of fault activity paleocene rifting generated new faults and reactivated several earlier faults prior to continental breakup and seafloor spreading initiation at the paleocene eocene transition the bivrost lineament separating the southern lofoten and northern voring margins has exhibited a distinct morphological expression during cretaceous cenozoic and is recognised as a structural corridor which segments highs and basins sub basins furthermore two dome shaped features have been observed on the southern lofoten margin and have probably experienced several phases of growth from late cretaceous to miocene times the domes are located in close proximity to the outer voring margin and bivrost lineament that are believed to have facilitated the transfer of imposed compressional deformation on the ne atlantic margins finally a comparison of the study area to the conjugate northeast greenland margin provides valuable insights on the margin evolution in a regional and conjugate setting

short lived reheating events in the sommartuva shear zone hosted in cold crust ar diffusion modelling constraints for the exhumation of eclogites in flakstadoy lofoten islands norway abstract the exhumation of the norwegian lofoten eclogites formed during the continental collision of laurentia and baltica is mainly due to the reactivation of shear zones during the collapse of the caledonian orogen the current cooling history temperature time t t paths for the exhumation of these rocks as determined by 40 ar 39 ar dating and geothermometry involves a protracted period of slow cooling c 1 7 c ma 1 from high t the sommartuva shear zone hosted in a palaeoproterozoic anorthosite contains retrogressed eclogite and amphibolite facies lenses and served as an open system for ar with 40 ar rich and 40 ar poor hot fluid infiltration ca rich amphiboles from amphibolites contain excess ar and are mantled by phlogopites that yield ar diffusion loss profiles with plateau ages of 413 400 ma associated with an extensional event in lofoten locally the zone was intruded in its late stage history c 333 ma by a granitoid rock crystallizing annite and muscovite previously inferred to be injected synchronously with amphibolite facies metamorphism an alternative cooling path related to the exhumation of the eclogites was determined by a combination of i 40 ar 39 ar ages in minerals that grew during different thermal events ii thermal modelling of the ar systematics in these minerals and iii exploration of the thermal effects caused by the superposition of each event on pre existing mineral phases the best fit t t path as constrained by the ar data reveals that in order to preserve ar radiogenic and excess within the minerals the ambient t must have been relatively low 300 c over 80 ma 413 333 ma likewise the associated intrusion of the granitoid and the hot fluid that percolated the shear zone and crystallized the phlogopites were likely to have been short lived c 100 25 ka and at relatively moderate t 500 c in contrast to previous thermal models where the thermal events are represented as simple inflexions in a t t curve our cold crust model incorporates short lived thermal disturbances including estimates of the magnitude of their maximum temperature and duration superimposed on protracted periods of slow cooling from high t a new proposed t t path obtained for the exhumation of this terrane indicates that the eclogites resided for 80 ma 413 333 ma at relatively cool ambient temperatures c 300 c highlighting the enormous potential of coupling geochronological data from multiple isotopic systems with thermal modelling to identify and constrain the duration of short lived events

resolution of the age structure of the detrital zircon populations of two lower cretaceous sandstones from the weald of england by fission track dating modes in the frequency of distribution of fission track ages obtained from detrital zircon grains may prove characteristic of individual sandstone bodies supporting the identification of the sources from which a particular flow of sedimentary detritus was derived and thus allowing new inferences to be made concerning palaeogeography a computer program has been written and used to identify modes in the zircon fission track age distribution within two lower cretaceous sandstone samples from the weald of southern england pronounced modes appear in one rock around 119 ma 160 ma 243 ma and 309 ma and in the other around 141 ma 175 ma 257 to 277 ma and 394 to 453 ma the geological implications of these quite dissimilar zircon age spectra are discussed it is concluded that they support the palaeogeographical models of allen 1981 and indicate that the provenance of the first sample from the top ashdown sandstone member at dallington in east sussex was almost entirely southerly while that of the second from the netherside sand member at northchapel in west sussex was more varied but predominantly westerly and northerly

paleomagnetism of the gays river zinc lead deposit nova scotia pennsylvanian ore genesis the gays river zinc lead deposit is the largest known mississippi valley type deposit in the mississippian windsor group of atlantic canada thermal and af demagnetization show that both ore and host rock have very similar magnetic characteristics stability tests constrain the magnetization to be mid mississippian to late pennsylvanian the pole position from the ore and host rock sites falls next to the pennsylvanian apw path suggesting an 8 clockwise rotation of the meguma platform relative to the craton regional thermal history and geochemical evidence suggest that the zinc lead ore magnetization and host rock remagnetization are coeval

organic matter and clay anomalies associated with base metal sulfide deposits abstract organic matter and clay mineral anomalies surround the polaris gays river and gaspe mines base metal sulfide deposits the polaris mine in the canadian arctic is an mvt deposit formed by low temperature solutions homogenization temperatures t h 105 120 c and is characterized by a zone of pure illite above a kaolinite envelope surrounding the deposit these clay mineral assemblages are laterally replaced by kaolinite illite and chlorite corrensite zones while the background assemblage in the host rocks is illite interstratified illite smectite chlorite the organic matter reflectance r o shows two trends depending on the permeability and chemical reactivity of the host rock 1 an increase with depth above the ore zones in the overlying impermeable shaly cap rock r o reaches a maximum value of 1 3 above the ore compared to 0 8 in equivalent country rocks 2 an anomalous decrease with depth in the mineralized carbonate horizon that hosts the deposit the gays river mine nova scotia is a medium temperature t h 250 c carbonate hosted deposit associated with the replacement of well crystallized detrital illite and chlorite by smectite forming a halo around the main ore zone and by kaolinite and chlorite corrensite within the ore zone reflectance and its absolute variability increase in the host rocks toward the ore zone adjacent to the deposit 0 8 to 1 88 and shows a relatively low r o in the ore the economic mineralization at gaspe mines quebec is a typical high temperature skarn and porphyry copper deposit with the concomitant clay mineral alteration assemblages chlorite corrensite illite smectite chlorite illite and almost pure illite with traces of chlorite the first assemblage is observed within the ore zone and extends slightly outside the procellanite halo smectite is also found near the mineralization but its limit of occurrence is wider than the chlorite assemblage the illite assemblage is found outside the chlorite zone and is present as irregular tongues r o increases 1 2 to 15 approaching ore over a lateral distance of 60 km in the bleached zone the organic matter exhibits mosaic and degasification textures and isotropic alteration rims with very low r o these three deposits as well as others studied by the authors are centrally located within thermal aureoles whose size and intensity correlate directly with increasing temperature of formation the decreasing values of r o in the ore zones of these deposits and the associated authigenic clay minerals reflect changes in chemical conditions due to precipitation of sulfides and to reaction of the ore and post ore fluids with host rocks

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

early paleozoic orogenic collapse tectonic stability and late paleozoic continental rifting revealed through thermochronology of k feldspars southern norway southern norway was subjected to contractional orogenesis and subsequent extensional collapse during the early to middle paleozoic when baltica collided with laurentia resulting in the caledonian orogen the largely unknown post caledonian paleozoic thermal history of the crust in southern norway has been assessed through application of multiple diffusion domain thermal modeling of k feldspar 40ar 39ar data samples were collected along a 250 km e w traverse from the internides of the orogen along the western coast near bergen through a series of middle to upper crustal nappes to the east the k feldspar thermal models which complement published mica and hornblende 40ar 39ar data are consistent with rapid cooling at the end of the caledonian orogenic cycle when early devonian 400 ma extensional collapse resulted in exhumation through mainly midcrustal conditions following extensional collapse a period of relative tectonic and thermal stability may have prevailed until 300 ma the k feldspar modeling suggests that southern norway entered a new phase of relatively rapid cooling a few c ma in the permo carboniferous and that the increase in cooling rate was diachronous across the traverse the onset of this cooling phase occurs at about the time of the earliest faulting and magmatism in the oslo graben to the southeast the increase in cooling rate may also indirectly date the onset of the first important rift phase and associated sedimentation in the north sea graben system the distribution of permian and younger fission track ages in both southern continental norway and its marginal basin sediments is consistent with the permo carboniferous rapid cooling recorded in the k feldspars the simplest explanation for the late paleozoic increase in cooling rate is that rifting around the margin of southern norway has resulted in a decrease in the base level and an increase in the rate of erosional denudation resulting in essentially uniform exhumation of 2 4 km along the traverse

the silurian to permian history of a metamorphic core complex in lofoten northern scandinavian caledonides 1 the lofoten archipelago exposes precambrian baltic basement and caledonian allochthonous sequences within a 1000 km long chain of gravity and magnetic highs and structural culminations along the extended british and norwegian continental shelf previous regional geophysical studies indicate that post caledonian extension and development of the northern norwegian shelf occurred during broadly defined carboniferous permian cretaceous jurassic and early tertiary events structures related to these events are known to young westward we report field structural and 40ar 39ar thermochronologic data from rocks exposed in lofoten that further define the history and style of post caledonian extension the islands of southwest lofoten also represent the most outboard exposures of caledonian basement in northern norway that presumably formed the middle to deep crustal core of the orogen metasedimentary rocks and penetratively deformed basement in lofoten record high grade silurian devonian metamorphism and top to the east hereinafter tops east thrusting followed by episodes of late devonian to early carboniferous tops west ductile extension which progressed into oblique left slip movements the structural style and timing of silurian contraction in this area are remarkably similar to that determined for the more forelandward areas on the mainland 120 km to the east supporting the inference that distal parts of the baltic continental margin that were once deeply subducted are presently exposed in lofoten the timings of post devonian structural events that affected rocks in lofoten are partially constrained by the ages of unconformities and strata known to be preserved in graben flanking the lofoten culmination the radiometric age and structural data presented in this study in combination with stratigraphic constraints suggest a westward progression through time of extensional deformation over a protracted interval of silurian to permian time the latest permian extension in lofoten is largely characterized by brittle structures that formed at conditions substantially less than 300 c compared to the exhumation history of the southern western gneiss region the depth of caledonian continental a type subduction and subsequent unroofing of lofoten are of lesser magnitude and the present erosional level remained in the middle crust for a much longer interval of time the permian 40ar 39ar mineral ages documented in this study are the youngest such ages yet identified in scandinavia these ages relate to episodes of deformation and cooling in response to extensional tectonic events that occurred roughly 100 m y after comparable effects identified on the caledonian mainland our preferred explanation for the carboniferous permian radiometric ages structural evolution and stratigraphic data for lofoten is that they all developed in the context of a long lived cordilleran style metamorphic core complex

early cretaceous uplift and erosion of the northern appalachian basin new york based on apatite fission track analysis abstract the thermal history of outcropping devonian sediments of the northern appalachian basin new york has been investigated using fission track analysis of detrital apatites from 57 sandstone samples based on lengths and apparent age measurements using fission tracks in apatite it is concluded that lower devonian sediments presently at the surface in the catskill region were cooled rapidly from temperatures higher than about 110 c during early cretaceous times 120 140 ma ago in the western part of new york wellsville buffalo data from late devonian sediments are consistent with cooling at the same time as that identified for the catskill region but from lower temperatures in the range of approximately 80 110 c the maximum temperature these sediments experienced since deposition for a pre uplift paleogeothermal gradient of 25 35 c km the confined track length data indicates uplift and erosion of 2 3 km for western new york and greater than 3 4 km for the catskill region a differential uplift pattern which is consistent with the historical stratigraphic data from the region this conclusion is at variance with earlier interpretations put forth by others rapid broad scale uplift and erosion of the scale identified imply that large volumes of sediment could have been supplied from the northern appalachian basin during the early cretaceous this timing for the dominant post devonian cooling phase in the basin is not accounted for by recent models of the tectonic evolution of the appalachian orogen but is compatible with the change from carbonate to siliciclastic deposition in the atlantic coastal plain it is suggested that this style of broad regional uplift without significant deformation is characteristic of a tectonic regime associated with and subsequent to continental rifting apatite fission track analysis is shown to be a basic tool in providing fundamental limits for thermal history assessment in regional tectonic problems

late paleozoic collision delamination short lived magmatism and rapid denudation in the meguma terrane nova scotia canada constraints from 40ar 39ar isotopic data the meguma terrane consists of 8 15 km of early paleozoic stratified rocks deposited on a continental basement that were deformed and metamorphosed during the late paleozoic as a result of lithospheric plate collision the oldest cleavage previously published whole rock 40ar 39ar plateau ages of 415 395 ma dates the onset of crustal thickening which was followed by voluminous but short lived late devonian granitic and minor mafic magmatism 380 370 ma this magmatism may have been the product of delamination of the lower lithosphere and upwelling of asthenosphere which effected melting above the new moho and resulted in intrusion at depths of 5 12 km 40ar 39ar plateau ages of hornblende muscovite and biotite indicate that at the present erosion level most of the meguma terrane cooled through 300 c by 368 360 ma slightly earlier than for the southwestern meguma terrane ca 345 ma the present erosion level was exhumed by the latest devonian early carboniferous visean the age of the

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

lateral variations in tectono magmatic style along the lofoten vesteralen volcanic margin off norway abstract the 400 km long passive continental margin west of the lofoten vesteralen archipelago off northern norway links the volcanic rifted voring margin and the sheared w barents sea margin multi channel seismic reflection profiles supplemented with crustal velocity gravity and magnetic anomaly data are used to outline the regional setting and main tectono magmatic features a well defined along strike margin segmentation comprising three segments characterized by distinct crustal properties structural and magmatic styles sediment thickness and post opening history of vertical motion is revealed the margin segments are governed by changes in fault polarity on late jurassic early cretaceous border faults and are separated by coeval cross margin transfer zones which acted as persistent barriers to rupture propagation and reflect the trend and character of older structural heterogeneities the transfer zones spatially correlate to small offset early opening oceanic fracture zones implying a structural inheritance from one rift episode to another culminating with lithospheric breakup at the paleocene eocene transition the pre seafloor spreading margin structural evolution is governed by the older predominantly late jurassic early cretaceous structural framework however the margin also provides evidence for mid and late cretaceous extension events that are poorly understood elsewhere off norway furthermore the lofoten vesteralen post breakup subsidence history contrasts with the adjacent margins reflecting breakup in thicker crust and a diminishing volume of high velocity lower crust emplaced during breakup

sedimentary environment and diagenesis of the lower cretaceous chaswood formation southeastern canada the origin of kaolin rich mudstones abstract the lower cretaceous fluvial sandstone mudstone succession of the chaswood formation is the proximal equivalent of offshore deltaic rocks of the scotian basin that are reservoirs for producing gas fields this study interprets the mineralogical consequences of cretaceous weathering and early diagenesis in a 130 m core from the chaswood formation in order to better understand detrital and diagenetic minerals in equivalent rocks offshore mineralogy was determined by x ray diffraction electron microprobe analysis and scanning electron microscopy the rocks can be divided into five facies associations light gray mudstone dark gray mudstone silty mudstone and muddy sandstone sorted sandstone and conglomerate and paleosols facies transitions in coarser facies are related to deposition in and near fluvial channels in the mudstones they indicate an evolutionary progression from the dark gray mudstone facies association swamps and floodplain soils to mottled paleosols well drained oxisols and ultisols following syntectonic uplift facies transitions and regional distribution indicate that the light gray mudstone facies association formed from early diagenetic oxidation and alteration of the dark gray mudstone facies association probably by meteoric water principal minerals in mudstones are illite muscovite kaolinite vermiculite and quartz illite muscovite is of detrital origin but variations in abundance show that it has altered to kaolinite in the light gray mudstone facies association and in oxisols vermiculite developed from the weathering of biotite and is present in ultisols the earliest phase of sandstone cementation in reducing conditions in swamps and ponds produced siderite nodules and framboidal pyrite which were corroded and oxidized during subsequent development of paleosols kaolinite is an early cement coating quartz grains and as well crystallized pore filling booklets that was probably synchronous with the formation of the light gray mudstone facies association later illite and barite cement indicate a source of abundant k and ba from formation water this late diagenesis of sandstone took place when the chaswood formation was in continuity with the main scotian basin prior to oligocene uplift of the eastern scotian shelf findings of this study are applicable to other mid latitude cretaceous weathering and early diagenetic environments

hidden cretaceous basins in nova scotia early cretaceous unconsolidated quartz sand and kaolinitic clay deposits in the lowlands of nova scotia are preserved in narrow half grabens obscured by glacial drift the chaswood formation sediments can be subdivided into three members upper and lower members dominated by cyclical sand mud facies of fluvial origin and the middle member with lignitic clay of lacustrine origin ferruginous oxisols are common in the fine grained facies of the upper and lower members seismic data indicate that chaswood formation strata in the elmsvale basin are deformed into steeply dipping faults and fault related folds rutherford road fault zone an aptian albian age for this tectonic event is inferred from synsedimentary deformation and from the angular unconformity spanning the late cretaceous and tertiary that truncates the chaswood formation exhumation of a thick cover of mesozoic sediment 1 2 km is needed to account for the preservation of chaswood formation outliers after 80 ma of erosion the half grabens that host the chaswood formation were formed in the mesozoic and were antecedent to the present day structurally controlled lowlands