a new stratigraphic framework for the gaspe belt in southern quebec implications for the pre acadian appalachians of eastern canada the post taconian units in the quebec and northern new brunswick appalachians constitute the gaspe belt and geological studies have mostly focussed on its eastern quebec segment biostratigraphic data indicate that the succession in southern quebec is no older than late silurian and extends into the early devonian two distinct stratigraphic assemblages are present the first assemblage saint luc cranbourne and lac aylmer formations and glenbrooke group unconformably overlies the humber and dunnage zones the units show a basal alluvial conglomerate that passes progressively to deeper marine facies upsection which have recorded a post late silurian transgressive event the second assemblage saint francis group and frontenac formation is faulted against either dunnage units or autochthonous post taconian units it locally unconformably overlies units of the dunnage zone the succession shows progressively deeper marine conditions upsection and also has recorded a post late silurian transgressive ev

structural evolution of the laurentian margin revisited southern quebec appalachians implications for the salinian orogeny and successor basins the laurentian margin of the appalachians is divided into external and internal zones on the basis of metamorphic and structural contrasts in the southern quebec internal zone silurian to early devonian southeast verging structures are superimposed on northwest verging structures whereas most of the external zone lacks such overprints regional backthrust faults define a major upper plate lower plate boundary the external zone rocks are in the hanging wall and internal zone rocks are in the footwall metamorphic rocks with silurian early devonian 40 ar 39 ar ages 430 410 ma characterize the lower plate to the east the saint joseph fault and the baie verte brompton line are southeastdipping normal faults that crosscut the upper plate lower plate boundary metamorphic rocks with middle ordovician 40 ar 39 ar ages 469 461 ma and rocks of the external zone both occur in the downthrown side of the saint joseph fault and the baie verte brompton line u pb and 40 ar 39 ar ages suggest that the northwest verging structures are related to ophiolite obduction and crustal thickening during the taconian orogeny ca 480 445 ma whereas the southeast verging structures formed during silurian early devonian backthrusting and normal faulting the revised structural interpretation has implications for the salinian orogeny and involves 1 southeast directed transport of the taconian crustal wedge of the upper plate followed by normal faulting and juxtaposition with the lower plate along the saint joseph fault and the baie verte brompton line and 2 the forma

the red island road formation early devonian terrestrial fill in the anticosti foreland basin western newfoundland more than 100 m of nearly flat lying fluvially derived thick bedded and lensoid clast supported conglomerate and sandstone are found on red island off the coast of the port au port peninsula western newfoundland formally described herein and named red island road formation the strata represent a unique lithologic formation not exposed or known anywhere else in the region characteristic features include abundant rounded highly weathered and varnished cobbles and boulders derived from an unknown mixed volcanic and very low to low grade metamorphic terrane although the unit is largely unfossiliferous a thin sandstone bed near the top of the type section contains primitive dichotomously branched plant remains and biostratigraphically significant palynomorphs among more than 25 species of spores it is the diversity of emphanisporites dictyotriletes and dibolisporites and in particular dibolisporites echinaceus dictyotriletes canadensis emphanisporites annulatus e erraticus and e schultzi

late quaternary oceanography of the mouth of the gulf of california the polycystine connection the mouth of the gulf of california is a region where three principal water masses converge the equatorial water the water associated with the california current and the water from the gulf itself these water masses exhibit a complex interaction which has been recorded by the polycystine radiolarian distribution patterns defined in the underlying sediments the occurrence in the gulf of water associated with the california current is indicated by the distribution of cycladophora davisiana ehrenberg while the occurrence of the equatorial water is characterized by high abundance of tetrapyle octacantha muller where the california current meets the equatorial water a water mass boundary is formed and this is depicted by the distribution of druppatractus cf pyriformis bailey micropaleontological analysis of six sedimentary gravity cores located along the mouth of the gulf of california correlated through 18o stratigraphy show that from approximately 33 000 to 15 500 years ago the california current frequently invaded the mouth of the gulf displacing the water mass boundary system and the equatorial water southward these oceanographic events preceded the global climatic changes indicated by the 18o stratigraphy occurring first in the surface and subsurface water in the mouth of the gulf and then in the deep waters

integration and spatial analysis of high resolution geophysical and geological data eastern gaspe peninsula in the vicinity of the town of gaspe the relationships between the silurian devonian sedimentary succes sion of the gaspe belt and the humber and the dunnage zones are complex to unravel these relationships we used high resolution aeromagnetic data and regional gravimetric data coupled with field tectonostratigraphic information the magnetic vertical derivative located several magnetic anomalies associated with near surface features in the silurian devonian cover sequence in particular a conglomerate with magnetic fragments that overlies the late silurian salinic unconformity is clearly recognizable large ovoid anomalies of significant intensity located in the silurian devonian sedimentary cover area cannot be associated with any known geological feature the interpretation of the high pass and low pass filtered aeromagnetic survey indicates that the ovoid anomalies originate below the silurian devonian cover sequence the most significant of the ovoid anomalies is associated with a gravimetric anomaly it is proposed that these geophysical anomalies are probably associated with ultramafic and or volcanic rocks correlative in the subsurface with outcrops of the cambrian ordovician lithologies of the lady step complex and or the shickshock group resume dans la region de gaspe les relations entre la couverture sedimentaire siluro devonienne de la ceinture de gaspe et les zones de humber et de dunnage sont complexes pour mieux comprendre ces relations nous avons utilise des donnees aeromagnetiques de haute resolution et des donnees gravimetriques regionales appariees aux donnees tecto nostratigraphiques de terrain le gradient magnetique vertical a mis en evidence plusieurs signatures magnetiques peu profondes dans la couverture sedimentaire siluro devonienne en particulier un conglomerat a fragments magnetiques surmontant la discordance salinique du silurien tardif est aisement identifiable de grandes anomalies ovoides d intensite importante localisees dans la couverture siluro devonienne n ont pu etre associees a aucun element geologique connu le passage du leve magnetique dans des filtres passe haut et passe bas a permis de mieux cerner cer taines signatures magnetiques et de determiner que les anomalies ovoides prennent source sous la couverture siluro devonienne la plus grande des anomalies ovoides est associee a une anomalie gravimetrique il est propose que ces anomalies geophysiques soient vraisemblablement associees a des roches ultramafiques et ou volcaniques correlatives en profondeur a des lithologies affleurantes des unites cambro ordoviciennes du complexe de lady step et ou du groupe de shickshock

paleogeography and tectono sedimentary history at the margin of laurentia during silurian to earliest devonian time the gaspe belt quebec the silurian lower devonian sequence of the gaspe belt at the laurentia margin south of the quebec reentrant and st lawrence promontory was deposited during the period between the two main orogenies that created the northern appalachians the late ordovician taconian and the middle devonian acadian orogenies although this sequence is traditionally considered to have been deposited during a period of quiescence between both orogenies significant tectonic activity attributed to the salinic disturbance began during late llandoverian telychian time and persisted until the acadian orogeny this tectonic activity has profoundly influenced the composition and distribution of the silurian earliest devonian sedimentary facies the shelf and shelf edge history at the laurentia margin along the quebec reentrant st lawrence promontory is summarized according to four broad phases phase 1 is a llandoverian wenlockian regressive phase r1 related to post taconian successor basin filling that culminated with extensive carbonate platform development phase 2 is a late wenlockian ludlovian transgressive phase t1 phase 3 corresponds to a later ludlovian pridolian second regressive phase r2 phases 2 and 3 were accompanied by extensional tectonics that produced shelf faulting and block tilting on top of which block reefs and reef complexes settled and built a reef tract all the way along the gaspe temiscouata shelf phase 4 is an early devonian phase of accelerated subsidence transgression t2 affecting the northwestern part of the segment quebec reentrant area while the southeastern part st lawrence promontory area was already uplifted due to the ongoing collision between laurentia and the western margin of gondwana related terranes to the south composition and distribution of sedimentary facies were controlled by the interaction of tectonics sediment influx and sea level fluctuations construction of a post taconian pre acadian palinspastic map to plot facies has proven to be basic to obtaining a realistic picture of the paleogeography of the shelf and shelf edge of the gaspe temiscouata segment at the margin of the laurentia craton during the silurian earliest devonian time interval

contributions of la nina and el nino to middle holocene drought and late holocene moisture in the american southwest eolian landforms in estancia basin central new mexico record two episodes of extreme drought and low groundwater levels during the middle holocene 7000 5400 1 4 c yr b p followed by a rise in the water table throughthe late holocene blowouts and associated lunettes formed when water levels fell below the desiccated floor of pluvial lake estancia allowing widespread deflation elevation of the water table in the basin is regulated by a balance between evaporation from playas that occupy the blowouts and recharge of aquifers in the adjacent manzano mountains isotopic analyses of modern precipitation and groundwater reveal that recharge originates primarily as winter moisture which is amplified during el ninos and diminished during la ninas thus changes in the elevation of a reconstructed holocene water table may reflect systematic changes in el nino southern oscillation enso circulation

laminated sediments in the bay of la paz gulf of california a depositional cycle regulated by pluvial flux core bap96 cp sampled from the deepest part of the bay of la paz gulf of california has been analysed sedimentologically taking into account regional climate and oceanography laminated sediments at the bottom of the bay are essentially not bioturbated by benthic fauna a subanoxic condition o 2 0 2 ml l 1 inhibits the proliferation of benthic fauna within the bay the relative abundances of terrigenous and biogenic inputs change periodically the terrigenous input is greater than the biogenic input and apparently experiences larger fluctuations the terrigenous input dominates in dark laminae whereas the biogenic input mostly occurs in light laminae thus it is assumed that down the core the alternation of dark and light laminae represents cycles in the extent of dilution of the biogenic input by terrigenous input the terrigenous input into the bay of la paz is mostly regulated by pluvial runoff thus its temporal fluctuation follows the periods shown by the regional pluvial regime particularly the 11 2 year period this is equal to the frequency of sunspot cycles

taconian orogenesis sedimentation and magmatism in the southern quebec northern vermont appalachians stratigraphic and detrital mineral record of iapetan suturing cambrian ordovician units of the southern quebec appalachians oceanic domain include obducted ophiolites and an overlying syncollisional sedimentary basin represented by the saint daniel melange and flysch units of the magog group these terrains were thrust onto the laurentian continental margin during the taconian orogeny and are unconformably overlain by silurian devonian successor basins this contribution presents and discusses new stratigraphic data acquired in the oceanic domain as well as u pb and 40ar 39ar geochronological data on detrital zircons and muscovites sampled at various stratigraphic levels from the base of the sedimentary units of the oceanic domain and the silurian devonian units of the gaspe belt this work combined with the compilation of existing data for southern quebec and western new england allows a better definition of the tectono stratigraphic evolution of the area and are used to propose correlations with different rock units of the northern new england appalachians which represents a collage of laurentian margin and oceanic units it is shown that cambrian ordovician rocks of southern quebec and northern vermont have undergone a similar tectonic evolution the ophiolites were obducted onto the laurentian margin as a more or less coherent slab of oceanic lithosphere both the ophiolites and continental margin rocks were uplifted eroded and unconformably overlain by middle to late ordovician units of the saint daniel melange and magog group in a forearc setting the presence of mafic and felsic volcanic flows that are interstratified within the saint daniel melange can be correlated with an episode of delamination and slab breakoff during the final stages of obduction and exhumation of the orogenic wedge the magog group was deposited during the emplacement of the taconian nappes as the outboard volcanic arc was still active but progressively shutting down the provenances suggested by the age of the dated detrital minerals can be entirely reconciled with the peri laurentian context of the studied rock units and testify of the tectonic evolution and sedimentary recycling of the taconian orogen from ophiolite obduction onto the laurentian margin to the collapse of the orogenic belt and the formation of successor basins

mise a l evidence et cinematique de la faille de la guadeloupe appalaches du sud du quebec in the appalachians of southern quebec the contact between siluro devonian rocks of the connecticut valley gaspe synclinorium and the cambro ordovician rocks of the dunnage zone is marked by an important thrust fault striking northwest la guadeloupe fault this fault separates two stratigraphically distinct domains but the regional deformations are related to the same orogenic period in the sherbrooke and weedon areas different structural features show evidence of la guadeloupe fault and reveal its kinematics the exposed rocks near the fault exhibit structures that indicate a strong deformation zone the deformation includes well developed stretching lineations and shearing zones the ductile deformation is restricted to the cambro ordovician rocks macroscopic and microscopic studies of samples from the shear zones related to la guadeloupe fault reveal systematically a tectonic transport from southwest to northwest this interpretation is supported by the quartz crystallographic c axis orientat

silurian extension in the upper connecticut valley united states and the origin of middle paleozoic basins in the quebec embayment pre silurian strata of the bronson hill arch bha in the upper connecticut valley nh vt are host to the latest ludlow comerford intrusive suite consisting east to west of a mafic dike swarm with sheeted dikes and an intrusive complex the rocks are mostly mafic but with compositions ranging from gabbro to leucocratic tonalite the suite is truncated on the west by the monroe fault a late acadian thrust that carries rocks of the bha westward over silurian devonian strata of the connecticut valley gaspetrough cvgt dikes intrude folded strata with a pre intrusion metamorphic fabric taconian but they experienced acadian deforma tion twenty fractions of zircon and baddeleyite from three sample sites of gabbro diorite spanning nearly 40 km yield a weighted 207 pb 206 pb age of 419 1m a greenschist facies dikes sampled over a strike distance of 35 km were tholeiitic basalts formed by partial melting of asthenospheric mantle with little or no influence from mantle or crustal lithosphere the dike chemistry is similar to mid ocean ridge within plate and back arc basin basalts parent magmas originated in the astheno sphere and were erupted through severely thinned lithosphere adjacent to the cvgt extensive middle paleozoic basins in the internides of the appalachian orogen are restricted to the quebec embayment of the laurentian rifted margin and include the cvgt and the central maine trough cmt separated from the bha by a silurian tectonic hinge the ne trending comerford intrusions parallel the cvgt cmt and the tectonic hinge and indicate nw se extension during post taconian convergence the irregular margins of composite laurentia and avalon permitted continued colli sion in newfoundland st lawrence promontory and coeval extension in the quebec embayment extension may be related to hinge retreat of the northwest directed brunswick subduction complex and rise of the asthenosphere following slab break off an alternative hypothesis is that the basins originated as pull apart basins between northwest trending left stepping sinistral strike slip faults along the southern flanks of the new york and st lawrence promontories

tectonic evolution and significance of silurian early devonian hinterland directed deformation in the internal humber zone of the southern quebec appalachians in the southern quebec appalachians the early tectonic history of the laurentian margin humber zone comprises foreland propagating northwest directed thrust faulting nappe emplacement and regional prograde metamorphism in response to the obduction of large ophiolitic nappes during the taconian orogeny in the internal humber zone this event is dated at 462 3 ma late middle ordovician which is interpreted to represent the timing of near peak taconian metamorphism superimposed hinterland directed structures are accompanied by retrograde metamorphism and consist of back thrusts and normal faults which respectively delimit the northwestern and southeastern limbs of the sutton and notre dame mountains anticlinoria both salient structures of the internal humber zone of southern quebec geochronologic data on the timing of hinterland directed deformation vary from 431 to 411 ma two tectonic models are presented and discussed which may account for the silurian early devonian evolution of the la

climate and ocean variability during the middle and late holocene recorded in laminated sediments from alfonso basin gulf of california mexico a laminated sequence core bap96 cp 24 38 12 n 110 33 24 w 390 m depth from the alfonso basin in bay of la paz southern gulf of california contains a record of paleoceanographic and paleoclimatic changes of the past 7900 yr radiolarian assemblages and magnetic susceptibility are used as proxies of oceanographic and climatic variability the records provide a regional scenario of the middle and late holocene suggesting two major climatic regimes and several millennial scale events conditions relatively warmer and drier than today occurred from 7700 to 2500 cal yr bp promoting the intensification of evaporation processes and the prevalence of the gulf of california water in the basin these conditions correlate with strong droughts in the middle holocene of north america and with minimal incursion of tropical waters into the gulf of california proxies indicate a warm scenario and the dominance of the equatorial surface water in the alfonso basin from 2400 to 700 cal yr bp suggesting the intensification of enso cycles a climatic signal between 1038 and 963 cal yr bp may be correlated with global signal of the medieval warm period several cooling events are recognized at 5730 3360 2700 1280 and 820 cal yr bp and are associated with intensification of northwest winds leading to upwellings and enhanced productivity in the basin

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

late neoproterozoic to permian tectonic evolution of the quebec appalachians canada abstract due to the unique location of the quebec appalachians in a re entrant of the paleo north american margin and to the fact that the area largely escaped late paleozoic deformation this segment of the orogen preserves evidence of the early orogenic stages that are partly obscured elsewhere despite diachronicity both along and across strike of the orogen five tectonic events of regional significance are recognized 1 the earliest event is mainly recorded by neoproterozoic to early ordovician normal faults associated with extension of the laurentian craton and the establishment of a passive continental margin 2 the second event the ordovician taconian orogeny is marked by foreland directed deformation and corresponds to the principal deformational and metamorphic events recorded by the laurentian margin 3 the third event early salinic is early silurian it is restricted to the southern part of the quebec appalachians and consists of hinterland se directed thrusts folds and retrograde metamorphism 4 the fourth event late salinic is recorded by regional scale late silurian to early devonian normal or transtensional faults and is associated with the formation of the connecticut valley gaspe trough and 5 the last event the devonian acadian orogeny affects with variable intensity all the pre carboniferous lithologies this tectonic synthesis implies that the subdivision of the peri laurentian oceanic tracts proposed in other segments of the appalachians should be applied with caution in quebec and that the structural style the number of oceanic domains and possibly the vergence of subduction change along the strike of the orogen in particular the similarities of the thetford mines and boil mountain ophiolitic complexes and sedimentary covers and the lack of evidence for a major intervening suture are consistent with the maximum allochtony hypothesis i e the assumption that the southern quebec ophiolites are rooted east of the chain lake massif a geodynamic model involving the taconian obduction of a large ophiolitic nappe s the docking of a peri gondwanan gander medial new england terrane in early salinic the formation of large sedimentary basins connecticut valley gaspe and merrimack troughs due to trench rollback and or delamination during the late salinic event and collision at the outer margin of composite laurentia during the acadian orogeny can account for the protracted structural and metamorphic history of the quebec appalachians

high resolution paleoceanography of the guaymas basin gulf of california during the past 15 000 years abstract deep sea drilling project site 480 27 54 10 n 111 39 34 w 655 m water depth contains a high resolution record of paleoceanographic change of the past 15 000 years for the guaymas basin a region of very high diatom productivity within the central gulf of california analyses of diatoms and silicoflagellates were completed on samples spaced every 40 50 yr whereas icp aes geochemical analyses were completed on alternate samples sample spacing 80 100 yr the bolling allerod interval 14 6 12 9 ka note ka refers to 1000 calendar years bp throughout this report is characterized by an increase in biogenic silica and a decline in calcium carbonate relative to surrounding intervals suggesting conditions somewhat similar to those of today the younger dryas event 12 9 11 6 ka is marked by a major drop in biogenic silica and an increase in calcium carbonate increasing relative percentage contributions of azpeitia nodulifera and dictyocha perlaevis a tropical diatom and silicoflagellate respectively and reduced numbers of the silicoflagellate octactis pulchra are supportive of reduced upwelling of nutrient rich waters between 10 6 and 10 0 ka calcium carbonate and a nodulifera abruptly decline at dsdp 480 while roperia tesselata a diatom indicative of winter upwelling in the modern day gulf increases sharply in numbers a nearly coincident increase in the silicoflagellate dictyocha stapedia suggests that waters above dsdp 480 were more similar to the cooler and slightly more saline waters of the northern gulf during much of the early and middle parts of the holocene 10 to 3 2 ka at about 6 2 ka a stepwise increase in biogenic silica and the reappearance of the tropical diatom a nodulifera marks a major change in oceanographic conditions in the gulf a winter shift to more northwesterly winds may have occurred at this time along with the onset of periodic northward excursions el nino driven of the north equatorial countercurrent during the summer beginning between 2 8 and 2 4 ka the amplitude of biogenic silica and wt fe al and ti proxies of terrigenous input increase possibly reflecting intensification of enso cycles and the establishment of modern oceanographic conditions in the gulf increased numbers of o pulchra after 2 8 ka suggest enhanced spring upwelling

timing of peak metamorphism and deformation along the appalachian margin of laurentia in newfoundland silurian not ordovician u pb and ar ar isotopic age data from the corner brook lake region of the eastern appalachian humber zone in western newfoundland indicate that regional deformation and peak amphibolite facies metamorphism are early silurian a lower limit on deformation is provided by a u pb zircon age of 434 2 3 ma for a pegmatite that is affected by the regional foliation and is interpreted to be syntectonic monazite and rutile from a garnet kyanite staurolite schist which records peak metamorphic conditions and in which porphyroblasts have overgrown the regional foliation gave u pb ages of 430 2 ma and 437 6 ma respectively ar ar cooling ages for hornblende from amphibolites and muscovite from psammitic and pelitic schists range from 430 to 420 ma a silurian age for deformation and metamorphism of the laurentian margin is coincident with the timing of similar events along the newfound land gondwana margin and suggests that the silurian was a period of major continent continent collision

exploring laser ablation u pb dating of regional metamorphic garnet the straits schist connecticut usa abstract garnet is a prominent recorder of metamorphic processes and plays a pivotal role in deciphering the pressure temperature evolution of metamorphic rocks however the potential of regional metamorphic garnet for laser ablation u pb dating remains unexplored as variable and low u we applied la icp ms u pb dating to garnet and zircon monazite and xenotime from the straits schist western connecticut usa to constrain the timing of garnet growth within the overall acadian age metamorphic history recorded by this unit we assessed the effects of u rich inclusions on garnet u pb data using high resolution microbeam sampling grain size analysis and calculations assessing how inclusion size and abundance affect u concentrations measured in garnet when analysing garnet our results demonstrate that by scrutinizing the time resolved u signal u rich inclusions can be identified and effectively removed during data evaluation if u rich inclusions are unaccounted for garnet analyses have elevated u contents compared to pure garnet and in a tera wasserburg diagram data points are shifted to the left right or along the garnet regression line for inclusions older younger or of the same age as the garnet respectively garnet from two metapelitic samples yielded lower intercept ages of 409 10 ma and 406 15 ma and a combined u pb age of 406 1 8 3 ma metamorphic zircon yielded age clusters at 446 2 4 2 ma 413 3 3 0 ma and 382 9 2 8 ma monazite ages range between 390 and 355 ma and xenotime yielded 370 1 5 6 ma the 446 ma age peak is attributed to detrital zircon formed during the waning stages of the taconian orogeny early acadian metamorphism is recorded by garnet and 413 ma zircon whereas monazite and zircon ages of 390 to 383 ma coincide with peak metamorphic conditions early carboniferous monazite and xenotime ages could reflect the incursion of fluids into the straits schist during neo acadian metamorphism coeval plutonism in new england or breakdown of garnet during regional exhumation

how do radiolarian sediment assemblages represent surface ocean ecology in the central equatorial pacific ever since q mode factor analysis has been applied to microfossil data investigators have attempted to determine whether statistical groupings of species in deep sea sediments are ecologically meaningful we address this question for radiolaria using living death and sediment assemblages from the equatorial pacific of the seven sediment assemblages identified from a basin wide analysis four are important in the tropics eastern boundary and transitional sediment assemblages identify ecological environments similar to living assemblages the western pacific sediment assemblage does not appear to represent a natural grouping of species the dominant tropical sediment end member represents a combination of warm water species from subtropical and western pacific environments of the two the predominant signal in tropical sediments is that of the western pacific the implication of a sediment bias toward warm water species may be due to the lack of an important cold water indicator species lophophaena hispida in the sediment analysis

evidence for abrupt climate changes in annually laminated marine sediments annually laminated sediments from marine or lacustrine settings represent valuable high resolution archives of climate change that record variation due to changing precipitation and run off from land or variation in biological productivity and flux in the water column because of their annual resolution such sediments may capture abrupt changes of interannual to decadal scales rivaling corals and ice cores in resolution laminated sediments often occur intermittently in the sediment column and the onset and cessation of laminae commonly record the abrupt crossing of thresholds related to climate change for example in the degree of oxygenation of bottom waters such records from marginal basins and continental margins have been pivotal in demonstrating that abrupt changes hitherto documented only in high latitude ice cores are synchronous with climatic change at low latitudes these insights into global teleconnections have improved our understanding of the mechanisms of rapid climate change in deep sea settings the discovery of the episodic occurrence of laminated diatom rich sediments in the equatorial pacific and southern ocean provides evidence for massive climate related biogeochemical excursions tied to abrupt changes in the input distribution and availability of nutrients in the oceans

vertical water mass circulation and the distribution of radiolaria in surface sediments of the gulf of california abstract quantitative analysis of microfossils from sediment cores taken in the gulf of california shows that the distribution of radiolaria is controlled by both surface ocean conditions and vertical circulation patterns in this marginal sea fifty four surface sediment samples from intermediate water depths were used in this study samples were taken from surface scrapings of box cores or large diameter gravity cores to insure that the samples represented recent deposition q mode factor analysis was used to divide the radiolarian population found in the gulf of california into three assemblages the first is made up of species typical of the gulf these species are in general not a major part of the open ocean radiolarian fauna the general geographic distribution of this assemblage shows a maximum abundance in the north central part of the gulf where warmer high salinity water is found this assemblage is also important in areas of upwelling the second fauna is dominated by radiolaria typical of the subtropical pacific ocean this assemblage dominates in the southern part of the gulf the last assemblage is dominated by species commonly found in the eastern boundary of the north pacific and is found in areas of upwelling within the gulf of california analysis shows that the first two assemblages are strongly influenced by the vertical structure of the southern part of the gulf of california the gulf assemblage shows a maximum in samples taken between 600 and 800 m water depth the subtropical assemblage shows high values in shallow sites and in samples taken in water depths greater than 800 m and a distinct minimum at intermediate depths the fauna typical of the north pacific eastern boundary current shows no depth preference the maximum in the gulf assemblage coincides with the depth of strong southerly flow of warmer higher salinity water out of the gulf of california this suggests that the abundance of the gulf assemblage in the southern end of the gulf of california is in part controlled by advection and thus vertical circulation has an important part in controlling the distribution of radiolaria in the sediments of the gulf of california

preserved stable isotopic signature of subaerial diagenesis in the 1 2 b y mescal limestone central arizona implications for the timing and development of a terrestrial plant cover discussion and reply reply

radiolarian distribution in the water column southern gulf of california and its implication in thanatocoenose constitution abstract the geographical and depth distributions of five radiolarian plankton assemblages defined through q mode factor analysis of 24 plankton samples demonstrate a direct correspondence to the distribution of oceanographic water masses in the southern gulf of california two assemblages are associated exclusively with water masses of the mixed layer two represent only subsurface water masses and one is important in both surface and subsurface environments the lithomelissa thoracites group and peridium spinipes are predominant species in water that is formed at the surface of the guaymas basin and subsequently is subducted southward into the carmen basin plagiocantha panarium is the predominant species in upwelled surface water at the carmen basin while tetrapyle octhacanta and botryostrobus scutum follow the incursion of the subtropical water mass into the gulf of california through the pescadero and farallon basins druppatractus variabilis and porodiscus sp b occur conspicuously in the upper layer of the pacific intermediate water between approximately 400 and 700 m water depth statistical correlation between plankton and sediment assemblages supports previous evidence that the radiolarian thanatocoenose in the gulf of california is composed primarily of species from the surface mixed layer two exceptions to this are observed in the data first the upwelling plankton assemblage was not well correlated to the sediment assemblage and second input to the sediment during glacial stages appears to be dominated by subsurface forms

modeling climate shift of el nino variability in the holocene a coupled ocean atmosphere general circulation model is used to investigate climatic shift of el nino in the holocene the model simulates a reduced enso intensity in the early and mid holocene in agreement with paleoclimate record the enso reduction is proposed to be caused by both an intensified asian summer monsoon and a warm water subduction from the south pacific into the equatorial thermocline

carbonate botryoids in lower devonian amygdaloidal basalts evidence for precipitation of high magnesium calcite from heated and volcanic co 2 buffered marine waters abstract amygdaloidal basalts are found in the lower devonian upper gaspe limestones in the gaspe peninsula these basalts were extruded on a distal outer shelf as evidenced by field relationships embedded fragments of metazoans and high vacuole content the lava flows were fractured and brecciated the network of fractures allowed connections of some vesicles with seawater vesicles in the nonfractured basalt are filled by silicates whereas those opened to seawater are filled by carbonates the latter comprise in stratigraphic order geopetal micrite botryoidal calcite and coarse anhedral calcite petrographic attributes including microdolomite inclusions and trace element distribution in the botryoids indicate former high magnesium calcite mineralogy the d18opdb 9 2 to 10 0 and d13cpbd 3 0 to 5 3 ratios support botryoid precipitation from heated marine waters that were contaminated by magmatic co2 volatiles high radiogenic sr values originated from compaction waters expelled from the host succession submarine high magnesium calcite agrees with the aragonite inhibiting stage for the early devonian the botryoid fabric should be the norm for early calcite in such an odd diagenetic setting

stratigraphy and tectono sedimentary evolution of the late ordovician to middle devonian gaspe belt in northern new brunswick evidence from the restigouche area the gaspe belt in the restigouche area comprises three successions separated by a late silurian salinic disconformity and an early devonian angular unconformity the lower upper ordovician to lower silurian sequence consists of siliciclastic turbidites of the boland brook and whites brook formations grog brook group overlain by calcareous turbidites of the pabos and white head formations matapedia group and slope and shelf deposits of the upsalquitch and limestone point formations lower chaleurs group above the salinic disconformity the upper chaleurs group and the dalhousie group record a transgressive regressive cycle the former comprises pridolian carbonate rocks of the west point formation and overlying pridolian to lochkovian sedimentary rocks of the indian point formation the chaleurs group is conformably overlain by lochkovian to early emsian subaerial volcanic rocks of the dalhousie group val d amour formation which is unconformably overlain by alluvial lacustrine deposits of the late emsian campbellton formation acadian orogenesis began during the emsian and is characterized by open to closed folding heterogenous cleavage development and reverse and strike slip faults the salinic orogeny is manifested in extensional block faulting within plate volcanism and uplift and deep erosion of early silurian strata early devonian high level intrusion of the matapedia group white head clasts in indian point conglomerate and thermal maturation data all indicate an extended period of late silurian early devonian uplift in parts of the restigouche area thermal maturities of west point and indian point strata are within the oil and condensate windows and suggest potential for hydrocarbons in the study area

the dog bay liberty line and its significance for silurian tectonics of the northern appalachian orogen1this article is one of a series of papers published in this cjes special issue in honour of ward neale on the theme of appalachian and grenvillian geology 2geological survey of canada contribution 20100257 the dog bay line a silurian suture key to deciphering appalachian accretionary history was first recognized in newfoundland it marks where the ordovician tetagouch exploits ensimatic back arc basin teb which had opened within the leading peri gondwanan gander terrane finally closed here we extrapolate this suture into new england placing it between the liberty orrington miramichi inliers lom and the merrimack fredericton trough mft southeastward marine strata of the mft overlie the teb passive margin exposed in the ganderian st croix block and display southeast vergent structures transected by acadian cleavage they structurally underlie southeast vergent thrusts at the base of the lom northwestward the lom central maine matapedia trough cmmt and lower silurian igneous rocks record elements of the upper plate trench arc system respectively a subduction complex forearc basin and arc the cmmt forearc received detritus both from the northwesterly arc region and also from the

the lower devonian compton formation in southern quebec from delta front to pro delta sedimentation the lower devonian compton formation is the uppermost unit of the st francis group in the connecticut valley gaspe synclinorium of southern quebec the compton formation is composed of three informal members five distinct sedimentary facies have been recognized in the lower two members of the compton formation high energy shallow marine and channel sands dominate the milan member the overlying lac drolet member consists of below wave base mud and silt deposits with abundant turbidite sand the milan member is interpreted to represent deposits of a river dominated delta front environment whereas the lac drolet member is suggestive of below storm wave base pro delta deposits the transition from the milan member to the lac drolet member is correlated with the deepening event recognized in coeval succession in the gaspe peninsula and known as the t2 event there the coeval indian point formation is interpreted to represent pro delta sediments the new paleogeographic map for the lochkovian illustra

early devonian marine isotopic signatures brachiopods from the upper gaspe limestones gaspe peninsula quebec canada abstract brachiopods from the upper gaspe limestones gaspe peninsula eastern canada document the isotopic geochemistry 18o 13c and 87sr 86sr of marine calcites for the siegenian and emsian stages early devonian nonluminescent brachiopods nlb from five species of a deep water benthic community show a narrow range of 13c values 1 3 to 1 7 average 1 5 and a much wider range of 18o values 2 7 to 4 6 average 3 7 that partially overlaps the field of luminescent brachiopods this is probably related to retention of fabric during diagenesis despite oxygen isotope exchange the heaviest 18o values for nonluminescent brachiopods 3 3 siegenian 2 7 emsian are interpreted as the signature of marine low mg calcite the 18o values for the gas e brachiopods suggest a negative 18o shift at the end of the early devonian the heaviest 18o values documented by previous workers for late early devonian emsian brachiopods cluster around 4 5 a figure that differs by 1 8 from the heaviest value for gaspe brachiopods this difference is most likely related to the growth of the gaspe brachiopods in deeper and cooler seawater as suggested by independent sedimentologic and biologic evidence rather than a 7 c warming of ocean surface temperatures or a rapid 7 ma shift in the 18o of seawater in a period of nonglaciation the 87sr 86 data for early devonian brachiopods fill the early devonian gap in the burke et al 1982 curve for devonian seawater the siegenian value is slightly more radiogenic than the younger emsian ones and support a continuous decrease in 87sr 86sr values from latest silurian to middle devonian time

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

marine burial and meteoric diagenesis of early silurian carbonate ramps quebec appalachians canada the coeval early silurian platformal sayabec and la vieille formations covered 10 000 and 20 000 km 2 respectively in the gaspe basin in the appalachian orogenic belt field studies petrography and carbon and oxygen stable isotopes have been used to document the diagenetic evolution of the carbonate platforms significant diagenetic features included marine cements shallow burial marine to possible meteoric phreatic cements burial cements pressure solution stylolites fractures and minor fracture fill cements meteoric dissolution and meteoric vadose cements cementation started in the marine environment lf1 it was minor 18 o 5 3 per thousand delta 13 c 3 8 per thousand is taken as the best value for early silurian marine composition the upper part of the radiaxialoptic cement layers is composed of an initial non luminescent equant to prismatic spar lf2 passing into complexly banded luminescent scalenohedral spar lf3 these two cements constitute the bottom of cement successions in other lithofacies of both the sayabec and la vieille formations they are interpreted as likely shallow marine burial cements but a possible meteoric phreatic origin is not ruled out both hypotheses rely on cl petrographic similarities with known examples their depleted delta 18 o signature and wide range of delta 13 c values ferroan cements lf4 fill over 85 of the pore space occlusion of which was completed at burial depths of around 450 m lf4 cements are 18 o depleted delta 18 o 8 1 per thousand and 8 7 per thousand for sayabec and la vieille formations respectively when compared to lf2 delta nearly equal 2 3 per thousand and lf3 delta nearly equal 1 3 per thousand cements for both formations the delta 13 c values for the lf2 to lf4 la vieille cements are much higher than those of the sayabec this is explained by early methanogenesis related to the paleogeographic nature of the platform stylolitization fracturing and minor calcite cementation minor dolomitization and sulfatization occurred in the burial environment and postdate lf4 cements post initial burial lf5 gravitational and lf6 cements delta 18 o 10 7 per thousand and 10 1 per thousand delta 13 c 3 7 per thousand and 4 4 per thousand respectively are interpreted to be meteoric vadose cements filling solution vugs of the la vieille limestones in the western part of the ramp they are related to late silurian uplift in the gaspe belt

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

radiolaria as indicators of upwelling processes the peruvian connection abstract in the sediments along the coastal region of peru certain radiolarian species have preferences to waters associated with upwelling such is the case forpolysolenia murrayana in the upwelling areas fed by equatorial water and forcenosphaera sp in the upwelling areas fed by temperate subantarctic water cycladophora davisiana appears to frame the upwelling centers suggesting that it prefers regions near thermic fronts the down core records of these species as well as records of quartz and organic carbon are depicted in three14c and 18o dated cores located along the pacific coast of south america between 11 and 13 s they suggest that both the eolian and oceanic circulation were more intense during the last glacial stage approximately between 33 000 and 11 000 years ago than during the present postglacial at these latitudes the intensification in circulation was not only accompanied by an increased coastal upwelling and in turn by an increased primary productivity but also by a larger supply of temperate waters to the area

palinspastic restoration of a post taconian successor basin deformed within a transpressive regime northern appalachians restoration of transpressional orogens requires a three dimensional analysis of the strain state in order to take into account both the pure shear and simple shear components of the deformation and assess their relative contribution throughout the deformation history restoration of the post taconian successor basin the gaspe belt located within the external part of the acadian orogen in the canadian appalachians was performed by using a step by step method based on the successive removal of strain increments the pure shear component contributed 70 of the total strain during the first stages of the deformation whereas the simple shear component contributed 30 of the total strain during the last stages three retrodeformation steps are defined starting with restoration of the last deformation stage and working back to the first deformation stage the first step is to restore slip along acadian strike slip faults the second step is to restore shortening related to the horizontal extension during the acadian regional simple shear event finally the third step is to restore vertical extension related to the pure shear event by removing slip along the reverse faults unfolding and removing internal strain associated with cleavage development retrodeformation of the simple shear component of the transpressive deformation during the first two steps is performed on a horizontal view of the gaspe belt basin which contains the horizontal extension direction and which is perpendicular to the acadian nw se directed compression likewise restoration of the pure shear component is performed in vertical sections which contain the vertical extension and which are perpendicular to the acadian nw se directed compression the palinspastic map presented here is a much more appropriate base map for the basin and allows for a more realistic paleogeographic interpretation of the gaspe belt

varve formation in the gulf of california insights from time series sediment trap sampling and remote sensing the varved sediments that accumulate in the central gulf of california guaymas and carmen basins provide a record that allows for the resolution of annual to decadal scale climate variability in this region time series sediment trapping combined with remotely sensed observations of sea surface temperature avhrr and color czcs have been used to examine the mechanism of varve formation in the central gulf sst and surface pigment concentration records for both the mainland and baja sides of the gulf display similar seasonal trends high temperatures and low pigment concentrations occur synchronously on both sides of the central gulf from june through to october in association with the 1991 92 el nino warm temperatures persist in the central gulf until december low ssts typically occur from december through may with high pigment concentrations marking the period from november through april the summer early fall june october is a time of high terrigenous and biogenic sediment fluxes during this time of year the total flux is dominated by eolian transported lithogenic material and dark laminae are deposited during this period during el nino years high terrigenous fluxes may extend into winter light laminae represent deposition from november through may during which time biogenic material dominates the total sediment flux high opal fluxes beginning in november are attributed to seasonal cooling of surface water and upward mixing of nutrients true upwelling conditions do not develop in the gulf until late winter spring during this time the total flux is still dominated by opal but the magnitude of the flux is reduced this may be an artifact of phytoplankton grazing and not lower production rates

ordovician and silurian metamorphic cooling ages along the laurentian margin of the quebec appalachians bridging the gap between new england and newfoundland geochronological studies on the timing of deformation and metamorphism along the laurentian margin have shown that the ages of metamorphism events change along the strike of the newfoundland new england segment of the appalachian orogen the quebec appalachians represent a critical transition zone where new single grain laser 40 ar 39 ar plateau ages show that both middle ordovician and silurian deformation and metamorphism are recorded parts of the analyzed samples give 40 ar 39 ar muscovite ages ranging from 468 to 461 ma these samples were taken within structural windows of the eastern internal humber zone that are overlain by ophiolitic and melange rocks of the dunnage zone other analyzed samples yielded silurian 40 ar 39 ar muscovite ages clustering from 425 to 421 ma these samples were taken across the notre dame mountains anticlinorium which represents a structural and metamorphic dome within the internal humber zone the middle ordovician ages of southern quebec are coeval with data from western new england and are interpreted as representing cooling shortly after the peak taconian regional metamorphism the silurian ages which have never been previously documented in the quebec appalachians are comparable to those described in newfoundland however they are not attributed to tectonism that shows characteristics of an orogen scale continent continent collision salinian orogeny but rather those of late taconian backthrusting and normal faulting or a period of crustal extension that followed the main taconian crustal thickening

carbonate sedimentation in an extensional tectonic regime the lower devonian upper gaspe limestones quebec appalachians carbonate sedimentation occurred over most of eastern gaspe peninsula in early devonian time the resulting succession known as the upper gaspe limestones is a 500 1800 m thick unit outcropping in the connecticut valley gaspe synclinorium detailed stratigraphic and sedimentologic work allows recognition of important thickness and lithofacies variations in a north south oriented transect in the eastern part of the peninsula variations are spatially associated with acadian middle devonian dextral strike slip faults three lithotectonic domains are proposed and interpreted they are from north to south 1 a proximal outer shelf 2 a distal gently sloping outer shelf and 3 a slope or slope toe field mapping and reinterpretation of seismic profiles from this area have shown that the faults bounding the three domains are reactivated normal listric faults early devonian vertical movement along these faults caused accelerated subsidence of the central and southern segments of the sedimentary ba

hydrological changes and paleoproductivity in the gulf of california during middle and late holocene and their relationship with itcz and north american monsoon variability abstract this study investigates changes in precipitation patterns and variations in paleoproductivity in the tropical pacific region associated with the north american monsoon intertropical convergence zone itcz latitudinal migration and changes in insolation during the middle and late holocene major and trace element records al ba c k si and ti and zr al and ba al ratios in a core from alfonso basin southern gulf of california are used as proxies of terrigenous input and bio productivity records reveal an increase in precipitation and low bio productivity ca 6200 to 2400 cal yr bp associated with the strengthening of monsoonal precipitation and northward shift of the itcz mean position in the eastern tropical pacific a multi centennial drought from ca 2400 to 1900 cal yr bp and a dry and cold interval ca 700 and 500 cal yr bp are characterized by strong aeolian input and enhanced productivity associated with diminution of the summer monsoonal precipitation and reduced insolation in the northern hemisphere and more southerly itcz position correlation of alfonso basin records with other records in the gulf of california and the pigmy and cariaco basins in the gulf of mexico and central atlantic provides constraints on nam itcz migration and insolation driven changes

timing and distribution of alluvial fan sedimentation in response to strengthening of late holocene enso variability in the sonoran desert southwestern arizona usa abstract the integration of geomorphic mapping soil stratigraphy and radiocarbon dating of alluvial deposits offers insight to the timing magnitude and paleoclimatic context of holocene fan sedimentation near yuma arizona mapping of 3400 km2 indicates about 10 of the area aggraded in the late holocene and formed regionally extensive alluvial fan and alluvial plain cut and fill terraces fan deposits have weakly developed gravelly soils and yielded a date of 3200 2950 cal yr bp from carbonized wood alluvial plain deposits have weakly developed buried sandy soils and provided a date of 2460 2300 cal yr bp from a terrestrial snail shell precipitation records were analyzed to form historical analogues to the late holocene aggradation and to consider the role of climatic variability and extreme hydrologic events as drivers of the sedimentation the historical precipitation record indicates numerous above average events correlated to the southern oscillation index soi in the region but lacks any significant reactivation of alluvial fan surfaces the timing of aggradation from 3200 to 2300 cal yr bp correlates well with other paleoclimatic proxy records in the southwestern u s and eastern pacific region which indicate an intensification of the el nino southern oscillation enso climatic pattern and rapid climate change during this period

radiolarian assemblages from santa barbara basin sediments recent interdecadal variability santa barbara basin contains a sedimentary record ideal for high resolution paleoclimate studies because of the annual varves and regional to global scale climate signals preserved in the sediments lange et al 1990 kennett and ingram 1995 even though it does not lie directly in the path of the california current a nearly 100 year annual time series 1909 1991 of polycystine radiolarian assemblages from santa barbara basin sbb sediments was analyzed to the species level counts on a replicate sbb core dated 1870 1987 indicate that results are reproducible and the flux of a few representative species can be extrapolated to estimate fluxes of environmentally sensitive groups the frequency of species occurrences resembles a lognormal curve and year by year comparisons of species fluxes revealed only modest changes in the assemblages from 1909 1991 indicating that the assemblages represent a single oceanic province for paleoceanographic analysis of the radiolarian record species were combined into groups according to the water mass in which they occur to test this method temperature sensitive species were identified using t tests this generated warm and cool classes exhibiting trends in relative flux similar to those of the water mass groups both total flux and relative fluxes of water mass groups relate to low frequency decadal scale temperature fluctuations but not strongly to el nino southern oscillation events generally fluxes of species from different water masses covary suggesting changing carrying capacities and productivity through time while the consistent inverse relationship in relative fluxes indicate variability in climate the subtle decadal scale changes in assemblages diversity and increase in percent warm water fauna are consistent with a spin down of the california current system suggested by other records

assessments of swelling anisotropy of ankara clay determination of swelling pressure exerted by expansive soils is important for designing structures such as shallow foundations shallow tunnels retaining walls canal linings and underground conduits in such soils the axial deformation and swelling pressure under zero lateral deformation can be determined by conventional oedometer using two identical samples however this test doesn t permit a synchronized measurement of both the axial and lateral swelling pressures on the same sample the ankara clay which is an overconsolidated clay rich in smectite group clay minerals and partly covers the southern part of ankara the capital of turkey causes damage to light structures located at the surface and at shallow depths a comprehensive study was conducted i to determine the swelling parameters swelling pressure and swelling percentage of ankara clay both in vertical and lateral directions using a thin wall oedometer ring providing synchronized measurement of swelling parameters in both directions ii to compare lateral and vertical swelling parameters of the clay for the assessment of swelling anisotropy and iii to investigate the effect of microstructure of ankara clay on its swelling behavior using scanning electron microscope sem the experimental results revealed that the swelling parameters measured in vertical direction were greater than those measured in lateral direction the ratio between the swelling pressures in lateral and vertical directions was found between 0 34 and 0 98 the results of the sem analyses suggested that the clay minerals in ankara clay show horizontal and or nearly horizontal sheeting and have stepped face to face structure this arrangement indicates that the swelling parameters in vertical direction should be greater than those in lateral direction it also confirms the experimental results and shows the influence of the microstructure of the clay on swelling anisotropy

suppression of el nino during the mid holocene by changes in the earth s orbit a number of recent reports have interpreted paleoproxy data to describe the state of the tropical pacific especially changes in the behavior of the el nino southern oscillation enso over the holocene these interpretations are often contradictory especially for the eastern tropical pacific and adjacent areas of south america here we suggest a picture of the mid holocene tropical pacific region which reconciles the data enso variability was present throughout the holocene but underwent a steady increase from the mid holocene to the present in the mid holocene extreme warm el nino events were smaller in amplitude and occurred less frequently about a mean climate state with a cold eastern equatorial pacific and largely arid coastal regions as in the present climate this picture emerges from an experiment in which a simple numerical model of the coupled ocean atmosphere system in the tropical pacific was driven by orbital forcing we suggest that the observed behavior of the tropical pacific climate over the mid to late holocene is largely the response to orbitally driven changes in the seasonal cycle of solar radiation in the tropics which dominates extratropical influences

diatoms in the gulf of california seasonal flux patterns and the sediment record for the last 15 000 years flux and taxonomic composition of the diatom assemblage was determined for biweekly sediment traps in the central gulf of california over a 2 year period fluxes and relative abundance of taxa are not significantly different in traps from the eastern side of the guaymas basin and the western side of the carmen basin indicating that patterns of diatom production are uniform across the central gulf at all seasons of the year the annual maximum in diatom flux occurred during the winter season of both years either as a sustained event over many weeks 1990 or as a series of short blooms 1991 1992 of the most abundant taxa only hyalochaete chaetoceros species showed a clear seasonal cycle with a flux maximum in the spring of both years factor analysis defines five assemblages representing 1 summer and fall conditions of surface stratification and nutrient limitation 2 winter bloom triggered by onset of strong northwesterly winds 3 late spring to summer production probably related to sporadic events during periods of weak southeasterly winds 4 spring 1991 inferred to reflect the distal edge of a coastal upwelling phase 5 lateral advection of resuspended sediments from the continental shelf possibly resulting from trapped coastal waves during summer hurricanes and from storms during the 1991 1992 el nino southern oscillation enso the diatom data support the inference that subtropical pacific water penetrates deeper into the gulf during enso events in order to compare the sediment trap record to a sediment core a second factor analysis was done using only the taxa which are preserved in the sediment and omitting the most abundant taxa which showed little downcore variation this produces five factors representing 1 summer fall low production 2 early winter bloom 3 late winter spring upwelling 4 enso conditions and 5 a late spring summer assemblage of uncertain significance variation of species characterisic of each factor was examined in piston core atlantis ii 125 8 56jpc taken from the oxygen minimum zone in guaymas basin correlation to nearby deep sea drilling project hole 480 indicates that the core penetrates to about 15 ka with laminated sediments in the holocene 0 10 ka and late deglacial 11 13 ka and massive nonlaminated sediments around younger dryas time 10 11 ka and before 13 ka downcore variations in the diatom assemblage do not correspond directly to presence of laminations implying that the processes controlling bottom water oxygen content are not determined by conditions of surface water production presence of calcareous nannofossils downcore correlates inversely with two diatom assemblages enso and winter bloom indicators and not with occurrence of laminations suggesting that occurrence of calcareous nannofossils in the sediment is at least partly a function of surface water production prior to 12 ka production was lower than at present during all seasons implying weaker winds throughout the year subtropical waters extended to the midgulf as they do today during enso events between 11 and 12 ka conditions were similar to those of the present with relatively high winter and spring production resulting from northwesterly winds enso events were still common although less so than during the preceding period younger dryas time was one of transition with intermediate conditions a slackening of winter spring northwesterly winds and reduction of total annual production and increased occurrence of enso conditions in the early to middle holocene winter northwesterlies increased to a maximum resulting in very high production but apparently did not persist into spring subtropical waters mostly disappeared from the gulf in the late holocene northwesterly winds have supported high production during both winter and spring seasons

turbidite channel overbank deposition in a lower devonian orogenic shale basin fortin group of gaspe peninsula northern appalachians canada abstract the lower devonian fortin group one of the major stratigraphic units in connecticut valley gaspe synclinorium of the gaspe peninsula and its stratigraphic equivalent the temiscouata formation in northwestern new brunswick and southeastern quebec are interpreted as a base of slope to deep basin turbidite succession sandwiched between shallow marine to nonmarine siluro devonian sediments the deep water interpretation is based on a comparison with modern deep sea turbidite depositional environments and the lower slope to deep basinal settings established by previous investigators for equivalent rocks in new england the monotonous sequences of largely unfossiliferous well bedded dark slate phyllite and siltstone with intercalated sandstone packets of the fortin group and temiscou ta formation in the matapedia and madawaska st john valley regions respectively are interpreted as submarine overbank and channel fill facies associations seven lithofacies have been distinguished 1 associations of massive sandstone beds up to 13 m thick and 2 associations of sandstone beds of intermediate 0 5 2 0 m thickness forming isolated sandstone packets encased in slate and siltstone are the equivalent of modern deep channel fill deposits 3 5 laterally continuous largely nonbioturbated thin siltstone layers with climbing ripple lamination turbidite c division and parallel lamination turbidite d division followed by slate turbidite e division and hemipelagite are analogous to muddy spill over turbidites with interbedded hemipelagites on modern natural levees th t accompany deep channels among the fine grained sediments a proximal to distal facies succession with respect to presumed lateral distance from channels consists of 3 siltstone slate 4 banded slate and 5 laminated slate if found in lateral succession the same succession may reflect spill over from progressively deeper channels the channel levee interpretation is supported by field observations of i a partly exposed channel wall ii truncation of siltstone and slate layers at sandstone contacts iii lag material at the base of massive sandstone layers and iv the chevron pattern of nearly opposing paleocurrent directions in the spill over facies 6 syndepositionally deformed and diamictite facies comprise fine grained rocks of facies 3 5 7 volumetrically subor inate conglomerates are the coarsest of the redeposited sediments siegenian praguian emsian turbidite deposition occurred in a deep basin of the connecticut valley gaspe trough that developed in response either to wrench tectonics or back arc spreading related to a volcanic island arc piscataquis volcanic belt deep sea trench system merrimack fredericton trough

an enhanced role for the tropical pacific on the humid pleistocene holocene transition in southwestern north america abstract climate effects on landscape evolution during the late pleistocene holocene transition 14 6 8 ka in southwestern north america traditionally are linked to the activity of the north american monsoon and to vegetation change related to a decrease in winter precipitation acting in response to orbital cyclicity we performed an integrated analysis of regional alluvial fan lacustrine and paleobotanical records for the area comparing them with hemispheric and regional paleoclimate proxies our focus was on the potential role the tropical pacific has as a synoptic pattern modulator and moisture source for hydrogeomorphic activity in the region our analysis indicates that the onset of alluvial fan aggradation in most of the region at 13 5 ka could have been a response to semi permanent el nino like conditions in the tropical pacific which enhanced the frequency of winter frontal storms as well as increased penetration of tropical cyclones in the region the north american monsoon was restricted in extent and intensity until 7 ka and probably was not a major factor in alluvial fan aggradation a second stage of alluvial fan aggradation from 11 5 to 9 ka was dominated by hyper concentrated flows and sheet flood sedimentation along with deposition in fluvial settings storms were probably were linked to landfall of enhanced water vapor bands in the leading edge of winter extra tropical cyclones with moisture advected directly from the tropical pacific at 8 ka favorable conditions for the occurrence of these storms waned and storm tracks shifted northward analysis of modern analogs for storm types described above as prevalent during this period indicates that changes in circulation patterns across the tropical pacific can affect storm properties enough to explain the observed geomorphic effects regardless of other factors traditionally considered of large impact like vegetation change our results suggest that the tropical pacific plays a larger role than currently thought in landscape evolution of the region

ophiolite obduction in the quebec appalachians canada 40 ar 39 ar age constraints and evidence for syn tectonic erosion and sedimentation 1 2 3 detailed field work conducted in the dunnage zone of the quebec appalachians is herein combined with 40 ar 39 ar dating on a series of ophiolitic massifs crosscutting granites and associated metamorphic rocks occurring along the baie verte brompton line the taconian suture between laurentia and lower paleozoic peri laurentian oceanic terranes studied massifs are the lac brompton ophiolite and the riviere des plante ultramafic complex in southern quebec and the nadeau ophiolitic melange in the gaspe peninsula our work suggests that these massifs form remnants of eroded ophiolitic nappes which are unconformably overlain by the saint daniel and riviere port daniel melanges and correlate with the thetford mines and mont albert ophiolitic complexes our 40 ar 39 ar data and compiled regional age constraints indicate that ophiolite obduction was diachronous along the strike of the orogen the timing of obduction and melange formation varies according to the irregular geometry of the early paleozoic laurentian margin with earlier collision occurring along or at the margins of promontories obduction was initiated with the formation of infraophio litic metamorphic soles between ca 479 and 472 ma in southern quebec and the nadeau ophiolitic melange and pos sibly as late as ca 470 466 ma for the mont albert complex these sole rocks were later exhumed and translated onto the laurentian margin with the overlying ophiolites between 475 and 460 457 ma the uplifting and erosion of the orogenic wedge during the waning stages of obduction has resulted in the sedimentation of olistostromal melanges and onlapping flysch units above the ophiolitic nappes as well as foredeep flysch successions during the latest arenig to earliest caradoc