dry creek salt dome mississippi interior salt basin recent drilling of salt dome flanks in the mississippi salt basin has resulted in important new discoveries and the opening of a frontier play this play is focused on gas condensate reserves in several cretaceous formations most notably the upper cretaceous eutaw and lower tuscaloosa intervals and lower cretaceous paluxy and hosston formations as many as eight domes have been drilled thus far sandstones in the upper hosston formation comprise the primary target production has been as high as 3 5 mcf and 500 1200 bbl of condensate per day with estimated ultimate reserves in the range of 0 2 to 1 5 mboe million barrels oil equivalent per well as typified by discovery at dry creek salt dome traps are related to faulting unconformities and updip loss of permeability previous drilling at dry creek and in the basin generally avoided the flank areas of most domes due to geologic models that predicted late stage tertiary piercement and breached accumulations recent data from dry creek and other productive domes suggest that growth was episodic and that piercement of tertiary strata did not affect deeper reservoirs charged with hydrocarbons in the late cretaceous

geochemical relationships of petroleum in mesozoic reservoirs to carbonate source rocks of jurassic smackover formation southwestern alabama algal carbonate mudstones of the jurassic smackover formation are the main source rocks for oil and condensate in mesozoic reservoir rocks in southwestern alabama this interpretation is based on geochemical analyses of oils condensates and organic matter in selected samples of shale norphlet formation haynesville formation trinity group tuscaloosa group and carbonate smackover formation rocks potential and probable oil source rocks are present in the tuscaloosa group and smackover formation respectively extractable organic matter from smackover carbonates has molecular and isotopic similarities to jurassic oil although the jurassic oils and condensates in southwestern alabama have genetic similarities they show significant compositional variations due to differences in thermal maturity and organic facies lithofacies organic facies reflect different depositional conditions for source rocks in the various basins the mississippi interior salt basin was characterized by more continuous marine to hypersaline conditions whereas the manila and conecuh embayments periodically had lower salinity and greater input of clastic debris and terrestrial organic matter petroleum and organic matter in jurassic rocks of southwestern alabama show a range of thermal transformations the gas content of hydrocarbons in reservoirs increases with increasing depth and temperature in some reservoirs where the temperature is above 266 f 130 c gas condensate is enriched in isotopically heavy sulfur apparently derived from thermochemical reduction of jurassic evaporite sulfate this process also results in increased h2s and co2 in the gas and depletion of saturated hydrocarbons in the condensate liquids thermochemical sulfate reduction probably depends on the mineralogic composition of the reservoir rock as well as temperature because some deep 18 000 ft or 5 5 km and hot 320 f or 160 c smackover and norphlet reservoirs contain low sulfur petroleum

circulation and low frequency variability near the chilean coast remotely forced fluctuations during the 1991 92 el nino results are reported from the first long recording current meter observations over the slope off chile these observations at 308s during the 1991 92 el nino event are analyzed together with observations of currents at a local deep sea site local wind and sea level sea level from the peru and chile coasts and wind temperature and currents from the equatorial pacific mean poleward flow of 12 cm s21 was observed within the peru chile undercurrent over the slope mean flow in the depth range of antarctic intermediate water was not distinguishable from zero in the presence of strong low frequency lf variability which dominated slope currents at all depths the strongest lf fluctuations had periods of about 50 days but periods of 10 and about 5 days were also observed significant local wind forcing of slope currents was only found in the period band 6 10 days and may be related to coastal trapped waves in the atmosphere our analysis shows that free coastal trapped waves in the ocean arriving from the north dominated the lf variability over the shelf and slope off northern and central chile during the 1991 92 el nino event strong 50 day period fluctuations there started their journey about two months earlier and 15 000 km farther up the coastal equatorial waveguide near the date line in the equatorial pacific as equatorial kelvin waves forced by westerly wind events of similar period upon reaching the south american coast these waves forced coastal trapped waves which propagated along the peru coast into the study region likewise a scenario of equatorial trapped waves forcing coastal trapped waves may explain 10 day as well as 6 day and 4 5 day period coastal trapped waves off chile stemming from mixed rossby gravity and inertia gravity waves trapped at the equator since the large 50 day period coastal trapped waves may strongly modify coastal upwelling source water such remotely forced waves may have a significant influence on the pelagic ecosystem off chile at least during el nino events

impact of a coastal trapped wave on the near coastal circulation of the peru upwelling system from glider data alongshore velocity data from a glider repetitive section off the coast of peru 14 s are used to study the cross shore structure and temporal variability of the peru current system during a 5 week period in april may 2010 besides providing substantial information on the surface frontal jet associated with the peru coastal current and the surfacing peru chile undercurrent that flows poleward trapped on the continental shelf and slope the glider data reveal the presence of an intense deep equatorward current which transports up to 2 5 sv the dynamics of this current are investigated using an eddy resolving regional model the variability of the vertically sheared alongshore flow is shown to be related to the passage of a poleward propagating coastal trapped wave likely of equatorial origin solutions from a two dimensional linear coastal wave model suggest that the alongshore current observed vertical structure is associated with the second and third baroclinic modes of the coastal trapped wave

pressure solution in carbonate source rocks and its control on petroleum generation and migration abstract based on detailed geochemical and petrographic studies of conventional cores of a triassic age carbonate source rock formation from three well sites at increasing maturity stages it is shown that the effects of carbonate diagenesis especially pressure solution during relatively shallow burial stages exercise major controls on the processes of petroleum generation and migration during deeper burial pressure solution leads to an internal redistribution of organic matter within this source rock formation in the form of local concentrations as solution seams and stylolites they provide very favourable conditions for effective petroleum generation and migration due to their internal structure and composition three dimensional arrangement of kerogen surrounded by carbonate cemented rims as tight seals the geochemical and petrographic effects of petroleum generation and expulsion are documented e g the expulsion of petroleum occurred as a separate phase fluid at high efficiencies 60 80 for the normal and isoprenoid alkanes and was facilitated by fractures presumably resulting from pore fluid overpressuring a five stage conceptual model is proposed to explain how the effects of pressure solution achieved during relatively shallow burial stages exercised controls on the extent and efficiency of petroleum generation and expulsion during deeper burial stages

early mesozoic southward migration of cordilleran transpressional terranes oblique plate convergence can cause forearc arc and back arc regions of active margin orogenic belts to behave as semi independent terranes relative to bordering continental and oceanic lithospheric plates these terranes called here transpressional terranes are bound by the subduction zone on one side by arc parallel strike slip faults in the forearc in the volcanic arc or in the back arc region on the other and are underlain by throughgoing basal decollements these terranes undergo shortening in a direction perpendicular to the subduction zone and migrate as coherent structural bodies parallel to the subduction zone along bounding strike slip faults many terranes of the north american cordillera may have behaved in this manner and perhaps did not travel across the pacific basin but rather were always peripheral to north america we propose that during the triassic to mid cretaceous portions of the cordillera borderland generally were displaced southward with respect to the north american craton due to left oblique convergence since the mid cretaceous they moved northward due to right oblique subduction the proposed displacements are consistent with structural paleomagnetic and paleontologic data and with the relative and absolute motions of north america and the pacific basin plates based on hotspot reference frame models

mid crustal emplacement and deformation of plutons in an andean style continental arc along the northern margin of the north china block and tectonic implications abstract outcrop mapping and thermobarometrical thermochronological and microstructural analyses in five late carboniferous early permian arc plutons in the northern north china block ncb indicate a transition of tectonic regime from arc perpendicular contraction to transpression and successive uplift and exhumation of the crustal rocks during magma emplacement and construction of the continental arc system the early emplaced daguangding and boluonuo plutons 324 302 ma display well developed penetrative moderately to steeply dipping magmatic foliations and high temperature sub solidus foliations that are parallel to host rock foliation near the contact widespread high temperature sub solidus foliations in these plutons indicate that they are syn tectonic with n s arc perpendicular shortening and record arc construction at a convergent continental margin however the late emplaced tianqiao and xianghuangqi wudaoyingzi plutons 288 274 ma display relatively weak magmatic fabrics at their margins and lack sub solidus foliations and pluton related ductile deformation of the contact host rocks these structural differences likely reflect a kinematic transition from early arc perpendicular contraction to late sinistral transpression during continental arc formation aluminum in hornblende barometry shows that their estimated emplacement depths decrease gradually from the late carboniferous 18 7 0 8 km to early permian 13 8 0 9 km indicating successive exhumation of the crustal rocks at an average rate of ca 123 mm ka over 40 million years of arc formation 40 ar 39 ar thermochronological results show that cooling of the continental crust was very slow 4 9 c ma during arc construction in the late carboniferous late permian but increased significantly during the late permian middle triassic after arc termination the mid crust of the northern ncb remained very hot 530 c during arc construction and emplacement of the arc batholiths combined with emplacement depth estimated by aluminum in hornblende barometry paleogeothermal gradients of 42 8 46 5 c km were estimated in mid to upper crustal levels 0 19 km hot mid crust and high mid upper crust geothermal gradients resulted from magmatic advection are likely the most important reasons for crust thickening and uplift during construction of andean style continental arcs and largely influenced the rheological behavior of continental crust

transpressional shearing and strike slip partitioning in the late cretaceous sierra nevada magmatic arc california the rosy finch shear zone rfsz represents an example of synmagmatic strike slip tectonics in the east central sierra nevada and provides information on transpressional tectonics within magmatic arcs the rfsz 1 4 km wide and 80 km long is contained in late cretaceous granitoids 92 83 ma of the mono pass intrusive suite dextral strike slip deformation is indicated by a continuous band of orthogneiss mylonitic and cataclastic deformation characterized by subvertical foliations with subhorizontal lineations the style of dextral shearing in the rosy finch shear varies along strike from wide zones of ductile deformation in the youngest plutons to narrow zones of cataclastic deformation in the older plutons deformation of the youngest granitoids is synmagmatic as constrained by both field observations and isotopic studies dextral shearing occurs concurrently in contemporaneous intrusive suites to the north and south tuolumne and mount whitney suggesting strike slip movement along the axis of active plutonism field studies also suggest that contraction across the arc acted concurrently with strike slip movement consistent with a transpressional setting for the late cretaceous sierra nevada magmatic arc comparison of the field data with strain models of oblique plate convergence suggests that the rfsz is a preserved ductile signature of transcurrent motion of strike slip partitioning within a transpressional orogenic system recent plate reconstructions indicate a switch from sinistral to dextral oblique convergence at 95 ma which is consistent with the timing constraints on the dextral movement on the rfsz

propagation and forcing of high frequency sea level variability along the west coast of south america tide and wind data from coastal and island stations from buenaventura colombia 4 n to callao peru 12 s have been analyzed for the 1979 1984 time period to determine the propagation and forcing characteristics of coastal sea level variability at periods of days to weeks as well as how they vary either with season or between the 1982 1983 el nino southern oscillation enso period and non enso years during four non enso years the ensemble averaged cross spectra between coastal sea level height slh and local winds show weak evidence of local forcing during the whole year without significant differences between the austral summer and winter seasons other than a greater energy in the wind fluctuations at talara during summer cross spectra between slh series from neighboring stations show evidence of poleward phase propagation during winter seasons at speeds of about 2 0 m s 1 between la libertad and talara at periods of a week or more and about 2 7 m s 1 between talara and callao at periods of 5 11 days but no propagation is found during summers during the 1982 1983 enso there is a large increase in slh energy at most frequencies at all coastal stations but especially in the 8 to 11 day band where energies are enhanced by as much as an order of magnitude above non enso levels the cross spectra between adjacent slh stations indicate a nondispersive poleward propagation of events during the 1982 1983 enso with phase speeds of 2 2 3 5 m s 1 from la libertad to talara periods of a week or more and 3 4 3 6 m s 1 from talara to callao 3 5 days or more as with the slh energy the coherence and phase propagation were much stronger along the peru coast in 1982 1983 than during non enso periods especially in the 8 to 11 day band the one third increase in phase speeds during the enso over the non enso speeds is found to be consistent with the anomalous depression of the density structure during el nino comparisons between coastal slh and the local alongshore wind suggest that locally forced slh variability was obscured during the 1982 1983 enso by the noncoastally forced but energetic propagating fluctuations which probably originated in the equatorial waveguide

lower tertiary and upper cretaceous source rocks in louisiana and mississippi implications to gulf of mexico crude oil the lower tertiary sparta formation wilcox group and the midway group in southern louisiana include organic rich source facies that generate crude oil at relatively high thermal maturities the wilcox group is an important source of wilcox crude oil and regional kerogen variations explain two crude oil subfamilies wilcox crude oils in downdip areas of southern louisiana migrated short distances but long range lateral migration about 150 km best explains wilcox crude oils far updip from mature source rocks crude oils in oligocene and younger reservoirs in southern louisiana migrated vertically from deep lower tertiary source rocks some crude oils in upper cretaceous tuscaloosa reservoirs were emplaced by long range lateral migration from tuscaloosa source rocks g ven little evidence of upper tertiary source rocks and the overmaturity problems of mesozoic source rocks most crude oils in upper tertiary and pleistocene reservoirs of the gulf continental shelf are best explained by vertical migration from deep lower tertiary source rocks even so it is simplistic to assume an exclusive lower tertiary origin many tertiary and pleistocene crude oils of this study probably include an overprint of high maturity hydrocarbons from mesozoic sources

dynamics of remotely forced intraseasonal oscillations off the western coast of south america abstract six years of sea level observations at six locations along the south american coast from peru to chile were analyzed at intraseasonal frequencies periodicity 1 2 months a high resolution low frequency numerical coastal model having realistic shelf and slope topography and bottom friction and forced by an equatorial signal was used to analyze the intraseasonal coastal dynamics at these latitudes the following results were obtained lagged correlations between sea level stations imply a sea level poleward propagation of 250 km day 1 the frictionless vertical wall theory poleward phase speed was considerably less at 216 km day 1 model runs with realistic bottom friction and shelf and slope bottom topography gave poleward phase speeds much closer to that observed for typical parameters the phase speed was 253 km day 1 both bottom friction and topography significantly affect the propagation speed past work has shown that the sea level amplitude should grow alongshore like f f coriolis

the physical environment of the peruvian upwelling system abstract knowledge of the characteristics of the physical environment of the peru coastal upwelling zone has increased greatly during the past decade observations made during 1976 and 1977 many made as part of the coastal upwelling ecosystem analysis joint ii expedition provide the basis for an interpretative description of the physical processes and phenomena occurring in peru coastal waters four important phenomena are discussed wind driven upwelling the poleward undercurrent surface mixed layer deepening and low frequency coastal trapped waves the coastal winds were invariably favorable for coastal upwelling even during the 1976 el nino the agreement between the offshore transport in the relatively shallow 30 m surface layer and the ekman transport deduced from the local wind was good for both the mean and variable state the agreement with the deeper onshore transport was less good consistent with the marked three dimensionally and spatial variability of the upwelling the poleward undercurrent was apparently continuous from 5 s to at least 15 s flowing just below the surface layer over the continental shelf and slope and supplying the upwelling water the variability in the alongshore velocity field was dominated by baroclinic free coastal trapped waves with periods of 5 20 days although there is appreciable temporal and spatial variability in the peru coastal upwelling system the upwelling the undercurrent and the low frequency coastal trapped waves were ubiquitous

tectonic controls on mudrock geochemisry mesozoic rocks of eastern oregon and western idaho u s a implications for cordilleran tectonics abstract tectonic models for the mesozoic evolution of accreted island arcs and subduction complexes in the blue mountain province bmp of eastern oregon and western idaho vary widely the bmp is situated between coeval accreted terranes of southern british columbia and the western u s and is critical for interpreting mesozoic paleogeography of the u s cordillera in this study we interpret the triassic jurassic evolution of the bmp using geochemistry as a tool to evaluate the provenance of mudrocks in fine grained turbidites temporal and spatial variations in mudrock geochemistry indicate that during late triassic to early jurassic time the wallowa terrane was an intra oceanic island arc and the olds ferry terrane was a pericratonic continental fringing island arc subsequently a regionally extensive middle to late jurassic marine basin received input from continental sources and sediment may also have been derived from coeval terranes to the south comparison of provenance data from the bmp with similar data from accreted terranes to the north and south suggests that triassic jurassic basins of the western u s share a long term provenance history within a complex system of continent fringing and intra oceanic island arcs in contrast it appears that the quesnel terrane of southern british columbia had a distinct provenance with a more direct link to laurentia during triassic time early to middle jurassic sedimentary rocks from southern british columbia and the western u s show a high degree of geochemical provenance similarity this may indicate reorganization of formerly discrete tectonic regions into a nascent integrated western laurentian margin prior to complete development of a cretaceous andean type margin the results of this study demonstrate the utility of mudrock geochemistry in tectonic analyses and show that major and trace element geochemistry of mudrocks is useful for developing a comprehensive understanding of regional tectonic evolution

stretching lineations in transpressional shear zones an example from the sierra nevada batholith california abstract ductile shear zones and associated stretching lineations are generally considered to be the result of two dimensional simple shear deformations with stretching lineations interpreted to rotate into parallelism with the direction of tectonic transport with increasing deformation however stretching lineations perpendicular to the inferred tectonic transport direction are displayed by some shear zones field studies in the sierra nevada batholith have revealed a single shear zone the rosy finch gem lake shear zone that contains both steeply plunging stretching lineations in older metamorphosed sedimentary and granitic rocks and shallowly plunging stretching lineations in syntectonic granitoids dextral sense of shear indicators are found in all these units and deformation occurred simultaneously along the length of the shear zone theoretical strain modeling indicates that stretching lineations can be either horizontal or vertical within transpressional shear zones to investigate the kinematics of three dimensional deformation we examine the role of stretching lineations which form as a result of finite strain including the possibility of partitioning a component of the strike slip movement onto shear bands comparing the field data with the strain modeling we interpret the along strike variation in lineation behavior within the rosy finch gem lake shear zone to be a result of the differences in finite strain recorded by different units the older units showing steeply plunging lineation have recorded more finite strain across a narrower shear zone than the syntectonic granites which record shallowly plunging lineations we conclude that the orientation of the lineation within transpressional shear zones does not necessarily correlate with the transport direction but may reflect along strike variations in finite strain and or strain partitioning

further evidence for coastal trapped waves along the peru coast abstract time series of coastal sea level during 1976 77 from 2 12 s to 17 s along the west coast of south america show that low frequency 0 25 cycles per day cpd fluctuations propagate poleward with the phase speed of baroclinic kelvin waves 2 3 m s 1 the alongshore coherence is highest in the frequency band 0 1 0 2 cpd computing the frequency domain empirical orthogonal functions eof for alongshore current from an army of current meters extending from 5 s to 15 s during march may 1977 gives 70 of the variance in the 0 1 0 2 cpd frequency band to an eof mode with poleward phase propagation at 2 75 m s 1 the vertical structure of the alongshore current fluctuations 0 1 0 2 cpd over the continental slope at 5 s and 15 s is consistent with a first mode baroclinic kelvin wave the current and sea level fluctuations are coherent and propagate poleward through latitudes where their frequency equals the local inertial frequency the fluctuations are not significantly coherent with coastal

interpreting magmatic fabric patterns in plutons abstract most plutons have widespread magmatic fabrics the interpretation of which remains controversial we propose a method to constrain likely causes of fabric patterns the application of which indicates the following 1 preserved fabric patterns often form after chamber construction and only rarely provide information about ascent or emplacement 2 fabrics are poor recorders of total strain and are easily reset preserving only the last increment of strain during crystallization 3 in magmatic systems mechanically decoupled from host rocks patterns may result from strain during internally driven flow filter pressing or porous flow in relatively static chambers or by final increments of strain during emplacement 4 with greater emplacement depths fabric patterns increasingly reflect strain caused by regional deformation and 5 given that magmatic fabrics are easily reset and reflect only the last increment of strain of comparatively weak materials they may provide a relatively direct record of paleostress in orogenic belts

paleomagnetism and tectonic significance of albian and cenomanian turbidites ochoco basin mitchell inlier central oregon 1 understanding continental growth and convergent margin dynamics associated with terrane accretion and modification of the cordilleran margin of north america is prevented by conflicts in paleogeographic models for major terranes oceanic plates and the north american margin we present new paleomagnetic data suggesting that the blue mountains superterrane located at an inboard portion of the cordilleran margin has undergone substantial northward translation and clockwise rotation relative to north america since mid cretaceous time positive baked contact conglomerate and fold tests provide evidence that the magnetization of these rocks dates from their deposition these results yield a mean direction of d 10 8 i 58 5 k 127 95 4 1 and n 11 comparison of magnetic inclinations and magnetic fabrics shows no evidence for inclination error a paleolatitude of 39 2 4 8 4 3 n is obtained indicating a paleolatitude anomaly of 15 9 4 1 northward translation of 1760 460 km and cw rotation of 37 7 3 with respect to north america since circa 93 ma application of an ad hoc 5 inclination error yields translation of 1200 460 km through comparison with other units in the western cordillera we infer that the mitchell inlier was located adjacent to the sierra nevada arc during mid cretaceous time and that the blue mountains province may correlate with the intermontane superterrane in british columbia other interpretations such as large inclination errors or an independent displacement history for the mitchell inlier are possible but unlikely more work is needed to fully test these hypotheses and resolve major questions of cordilleran tectonics

application of wavelet transform in the study of coastal trapped waves off the west coast of south america 1 wavelet transform and cross wavelet transform were applied for analyzing long time series of sea level and alongshore wind stress to identify intraseasonal variability off western south america and the relations with remote and local forcings hydrographic data were used to estimate properties of coastal trapped waves with a theoretical model for el nino years we found the existence of intraseasonal oscillations with periods 20 90 days between 2s and 27s at the peak of 91 92 and 97 98 el ninos we found perturbations in the northern region probably associated with remotely forced internal kelvin waves with periods 6 11 days and phase velocities 160 260 km day between 12s and 15s during two el nino events our calculations show perturbations which appear to be barotropic shelf waves propagating southward with velocities between 110 and 150 km day and periods between 30 and 50 days

local and remote forcing of sea surface temperature in the coastal upwelling system off chile an analysis is presented of records of sea surface temperature sst sea level and winds collected during the period 1991 1995 along the coast of northern and central chile sea level also from the peru coast in 1991 1994 and of sst from remote sensing during the austral summers of 1991 and 1992 off northern chile large interannual fluctuations of sst and sea level off northern chile are linked to vertical displacements of the equatorial thermocline during el nino la nina events in the intraseasonal 50 day band sst and sea level are intimately related all along the coast whereby sst anomalies lag sea level perturbations by about 12 days such sea level fluctuations are due to free coastal trapped waves ultimately forced via equatorial kelvin waves by 50 day wind events in the western and central tropical pacific these results and those of the remote sensing analysis suggest significant remote forcing of sst fluctuations in the coastal zone off chile by the action of the coastal trapped waves off central chile sst is also related to local wind stress in the intraseasonal band simulations with a simple local wind driven upwelling entrainment model capture rather well observed synoptic and intraseasonal oscillations of sst there off northern chile however this simple model is not successful in simulating observed sst an attempt to include effects of coastal trapped waves into this simple one dimensional model did not improve model fit to data at either location an explanation for the apparent strong influence of these waves on sst along this coast should therefore be sought in other effects not considered by this model such as cross shelf and alongshore advection

illite polytype distribution as an inorganic indicator of thermal maturity in the smackover formation of the manila embayment southwest alabama abstract illite polytype distribution is compared to pyrolysis tmax values in the smackover formation in the manila embayment southwest alabama to determine its potential as an indicator of thermal maturity the percent 2m illite polytype 2m 1m 2m increases from 20 to 80 over the formation temperature interval 100 165 c and as tmax values increase from 432 to 461 c illite polytype distribution is considered a good qualitative indicator of thermal maturity in the smackover formation of the study area the correlation between the percentage of 2m illite and temperature and thermal maturity in the smackover formation is believed to be primarily the result of the diagenetic transition from the 1m to the 2m polytype depositional effects are manifested in four samples as anomalously high 2m polytype percentages this variation is interpreted to be the result of locally high concentrations of detrital 2m muscovite because original sediment composition and illite chemistry may vary significantly both locally and regionally illite polytype distribution is a useful thermal maturity indicator only within a particular basin and when calibrated with other thermal maturity indicators

the equatorial source of propagating variability along the peru coast during the 1982 1983 el nino using data obtained from tide gages in south america current meters along the equator and the peru coast and an array of pressure gages and inverted echo sounders within and around the galapagos archipelago we have analyzed the equatorial origin of coastal trapped waves observed by cornejo rodriquez and enfield this issue along the peru coast during the intense 1982 1983 el nino the propagating fluctuations along the coast were much stronger at that time than either before or after the el nino and the variability was not locally forced by coastal winds we find that the coastal variability was also more energetic during previous el nino occurrences at periods of 1 2 weeks the meridional component of currents on the equator is up to an order of magnitude more energetic than the zonal fluctuations and is consistently associated with sea level that fluctuates antisymmetrically between hemispheres at periods longer than 2 weeks the zonal velocity component is more energetic and the cross equatorial sea level variability is symmetric the meridional and zonal phase structures of cross spectra involving the currents and sea level establish the 1 to 2 week equatorial fluctuations as mixed rossby gravity yanai waves of low wave number with infinite phase speed standing oscillations in the middle of the band 10 days the corresponding structures for longer periods are consistent with nondispersive kelvin waves frequency domain eof modes of the sea level and current data establish the mixed rossby gravity waves as the principal source of the strong trapped wave variability in the 1 to 2 week band along the ecuador peru coast during the 1982 1983 el nino episode

paleomagnetism of the tertiary clarno formation of central oregon and its significance for the tectonic history of the pacific northwest the clarno formation a mostly eocene and partly early oligocene sequence of andesitic lavas and volcaniclastic rocks is the oldest tertiary formation exposed in north central oregon remanent magnetization directions at 46 sites in the lavas provide a paleomagnetic pole at 84 n 278 e with a 95 confidence cone of 7 comparison of this pole with the north american reference pole for eocene time indicates that the clarno formation has rotated 16 clockwise with an uncertainty of 10 but has undergone no significant latitudinal displacement further comparison with paleomagnetic data from the miocene columbia river basalt group and steens basalt shows that large scale block rotations in the eastern columbia embayment ceased sometime between 38 m y and 15 m y a paleogeographic reconstruction for 38 m y is offered which is consistent with the observed rotation of the clarno and with the other paleomagnetic data from the pacific northwest which are briefly reviewed this reconstruction shows that it is possible to account for virtually all of the paleomagnetically indicated rotations in pre miocene tertiary rocks of the pacific northwest by an extensional tectonic model as a consequence only part of the rotations in the pre tertiary rocks of the eastern columbia embayment need to be the result of accretionary tectonics the initiation of magmatism in the eastern columbia embayment that is represented by the clarno formation itself may have been contemporaneous with the beginning of crustal extension in the pacific northwest

the generation of high sr y plutons following late jurassic arc arc collision blue mountains province ne oregon abstract high sr y plutons sr y 40 occupy large areas in ancient and modern orogenic belts yet considerable controversy exists regarding mechanisms of their generation the tectonic settings in which they form and their relationship to contractional deformation through time in the blue mountains province ne oregon a suite of late jurassic 148 145 ma high sr y plutons intrude middle jurassic 162 157 ma low sr y 600 ppm and sr y values 40 and positive initial epsilon hf values 10 5 to 7 8 2 weighted average these geochemical and isotopic results are consistent with geochemical models suggesting derivation from partial melting of island arc crust in the presence of a plagioclase poor to absent clinopyroxene hornblende garnet bearing source depths 35 40 km we propose that the transition from low sr y to high sr y magmatism resulted from orogenic thickening of island arc crust in the dixie butte area during late jurassic arc arc collision between the olds ferry and wallowa island arcs at 159 154 ma this fundamental change in crustal structure influenced post orogenic magmatism and resulted in a relatively brief 3 myr 148 145 ma episode of high sr y magmatism other high sr y plutons occur throughout the us sector of the western north american cordillera e g salmon river suture zone klamath mountains peninsular ranges and closely follow major contractional events involving arc arc and arc continent collisions

analysis of the wallowa baker terrane boundary implications for tectonic accretion in the blue mountains province northeastern oregon the baker terrane exposed in the blue mountains province of northeastern oregon is a long lived ancient late paleozoic early mesozoic accretionary complex with an associated forearc this composite terrane lies between the partially coeval wallowa and olds ferry island arc terranes the northern margin of the baker terrane is a broad zone 25 km wide of fault bounded imbricated slabs and slices of meta igneous and metasedimentary rocks faulted into chert argillite melange of the elkhorn ridge argillite metaplutonic rocks within tectonic units in this zone crystallized between 231 and 226 ma and have low initial 87 sr 86 sr ratios 0 7033 0 7034 and positive initial e nd values 7 7 to 8 5 in contrast siliceous argillites from the chert argillite melange have initial 87 sr 86 sr values ranging from 0 7073 to 0 7094 and initial e nd values between 4 7 and 7 8 we interpret this broad imbricate fault zone as a fundamental tectonic boundary that separates the distal wallowa island arc terrane from the baker accretionary complex terrane we propose that this terrane boundary is an example of a broad zone of imbrication made up of slabs and slices of arc crust tectonically mixed within an accretionary complex providing an on land ancient analogue to the actualistic arc arc collisional zone developed along the margins of the molucca sea of the central equatorial indo pacific region

stratigraphic record of triassic jurassic collisional tectonics in the blue mountains province northeastern oregon sedimentary and volcanic rocks in the blue mountains province bmp of northeastern oregon preserve a well studied record of triassic jurassic magmatism basin evolution and terrane accretion terranes of the bmp represent two magmatic arcs wallowa and olds ferry terranes an intervening oceanic subduction and accretionary complex baker terrane and a complex thick succession of sedimentary rocks commonly known as the izee terrane we divide volcanic and sedimentary rocks into two regionally correlative unconformity bounded megasequences 1 ms 1 late triassic to early jurassic deposits that change up section from 1a older volcanic and volcaniclastic deposits of the wallowa and olds ferry arcs to 1b marine turbidites shale and argillite with chert clast conglomerate and olistostromes derived from the emergent baker terrane and 2 ms 2 early to late jurassic marine deposits that overlap older rocks and structures and record 20 to 40 m y of deep crustal subsidence in a large marine basin many of the known stratigraphic relationships in the blue mountains cannot be explained using the existing model for a middle triassic to late jurassic west facing non collisional volcanic arc and forearc basin we propose a new tectonic model for the bmp based on prior studies and comparison to modern analogues which includes 1 middle triassic magmatism in the wallowa and olds ferry arcs during subduction and progressive closure of an ocean basin 2 late triassic collision between facing accretionary wedges of the wallowa and olds ferry arcs and growth of marine basins on both sides of the emergent baker terrane thrust belt 3 early to middle jurassic terrane continent collision which resulted in closure of a wide back arc basin crustal thickening and loading in nevada and growth of a large marine collisional basin in the bmp and 4 late jurassic thrusting regional shortening and final accretion of the basin and underlying terranes to western north america this analysis suggests that collisional tectonics may have played a significant role in plate interactions that drove triassic jurassic crustal thickening mountain building and basin development in the western north american cordillera

the intraseasonal oscillation in eastern pacific sea levels how is it forced abstract daily sea level and surface winds at eastern pacific shore locations and equatorial islands together with gridded five day averages of 850 mb winds have been analyzed for the 1979 84 period to determine how the 40 60 day intraseasonal oscillation of eastern pacific sea levels is forced as described by spillane et al for 1971 75 the oscillation was also present in 1980 84 from callao peru to san francisco with maximum energy near 52 57 days and band limits of 43 and 65 days during 1980 84 there was no evidence for forcing of the large scale oscillation in the eastern pacific although a local contribution of forcing was superimposed on the remote signal at the california stations interannual fluctuations in amplitude were evident in the sea level time series consistent with those of the corresponding wind oscillation in the western equatorial pacific the oscillation was best developed in both variables in 1980 82 and became weak or nonexistent during the recovery phase of the 1982 83 e

gas souring by thermochemical sulfate reduction at 140 c discussion 814 the subject of the article gas souring by thermochemical sulfate reduction at 140 c by worden et al 1995 is closely related to our recent research we examined the origin of h2s and other organic sulfur compounds osc in produced gas from gas condensate filled stari gradac field in the drava depression in croatia based on results of numerous conventional and specific analyses of reservoir rocks gas condensate and formation water and data from fluid composition monitoring over a long period of time we concluded that sulfur compounds in the stari gradac reservoir permian triassic depths greater than 3700 m were formed by thermochemical reduction mechanism of sulfate rock anhydrite in the presence of

framework of hydrocarbon generation and destruction in eastern smackover trend laminated lime mudstones of the lower member of the jurassic smackover formation are significant source rocks for crude oil across mississippi alabama and florida the source facies was deposited in an anoxic and perhaps hypersaline environment that preserved algal derived kerogen the distribution of kerogen along laminations of depositional origin and along stylolites of diagenetic origin resulted in efficient expulsion of crude oil with increasing thermal maturity crude oil initially emplaced in reservoirs was cracked to yield gas condensate and then methane rich in nonhydrocarbon gases such as hydrogen sulfide carbon dioxide and nitrogen early destruction of methane was driven by thermochemical sulfate reduction the thermal maturity framework of the smackover rend explains the distribution of hydrocarbon discoveries and suggests areas previously overlooked by exploration

migration of crude oil from the smackover source rock to jurassic and cretaceous reservoirs of the northern gulf rim abstract migration of distinctive crude oils from the upper jurassic smackover source rock across the northern gulf rim began at various times during the cretaceous regional source rock differences resulted in two compositional subfamilies of smackover crude oils type i crude oils in upper smackover reservoirs of east texas arkansas louisiana and mississippi reflect an origin from algal derived kerogen deposited in an anoxic environment type ii crude oils in upper smackover reservoirs of alabama and florida reflected an origin from kerogen preserved in a less anoxic environment with a terrestrial component comparison of molecular and carbon isotopic compositions of crude oils suggests that vertical migration of type i smackover crude oils charged many overlying upper jurassic lower cretaceous and upper cretaceous reservoirs some lateral migration to cretaceous reservoirs north of the updip limit of the smackover formation also occurred both type i smackover crude oils and geochemically dissimilar cretaceous sourced oils are found in upper cretaceous tuscaloosa and woodbine reservoirs because of impermeable barriers to migration especially in alabama vertical migration of type ii crude oils was less significant

sterane and triterpane patterns as diagnostic tools in the mapping of oils condensates and source rocks of the gulf of mexico region abstract four hundred and eighty one gulf of mexico oils and condensates can be subdivided into nine major families based on their sterane m z 217 218 and triterpane m z 191 177 biomarker mass chromatogram patterns these families are 1 carbonate sourced oils reservoired in jurassic cretaceous reservoirs onshore and plio pleistocene reservoirs offshore 2 austin chalk reservoired oils 3 tuscaloosa oils 4 wilcox reservoired oils la 5 south texas palaeogene reservoired oils 6 mississippi delta oils 7 post mature oils of uncertain affinities 8 migration contaminated oils showing attributes of a mixing of immature and post mature sources and 9 oils and condensates lacking biomarkers each oil family is concentrated in specific age defined producing trends ranging in age from jurassic to pleistocene for tertiary reservoirs these producing trends shift geographically with time in a manner analogous to the clockwise migrating cenozoic depocenter model for the northern gulf of mexico at least six ages of marine source rock deposition may be implicated in the genesis of these oils 1 the kimmeridgian oxfordian including smackover and norphlet formations 2 the aptian including pine island bexar and sunniland formations 3 the albian paluxy formation 4 the cenomanian turonian including eagle ford and tuscaloosa formations 5 the coniacian santonian eagle ford and austin chalk and 6 the palaeocene wilcox midway sparta formations the jurassic and cretaceous source rocks correspond to described oceanic anoxic events of probable global significance this paper will concentrate on describing the biomarker patterns of the oils and postulated source rocks but due to reasons of space isotopic elemental and other data will only be briefly discussed

magnetic fabric in the biella and traversella stocks periadriatic line implications for the mode of emplacement abstract the biella and traversella stocks forming part of the intrusions along the periadriatic line intruded into the sesia lanzo zone italian western alps 30 ma ago samples were collected from 12 localities in the traversella massif diorites and 22 in the biella massif granites syenites monzonites in most localities the fabric is primarily planar with a distinct foliation of intermediate to subvertical dip the magnetic lineation is less developed its plunge is very variable marking a girdle pattern the mean foliations and lineations per locality are scattered this is probably due to the fact that the outcropping parts of the two stocks are summital i e nearer the roof and hence the magma movements may have been less regular in the structurally deepest part of the biella massif the magnetic foliation dips regularly to the northwest its direction could reflect the pattern of the deep fractures along which the magma rose the classic models of owens to describe the process of magnetic mineral orientation do not apply to the features of these two stocks a new model has been constructed to take account of the differences in viscosity contrast between the magnetic mineral crystals and the matrix referred to as the ductile model it offers a suitable representation of the typical situation of crystal mushes and is the most appropriate for the biella and traversella stocks

peru coastal currents during el nino 1976 and 1982 year long measurements of subsurface current and temperature on peru9s continental shelf included the onset of el nino in 1976 and 1982 the peru coastal undercurrent more than doubled in speed and advected anomalously warm water poleward el nino began in different seasons in 1976 and 1982 but the current and temperature responses were very similar acceleration of poleward flow at 10 s occurred several days after sea level rose at the galapagos islands in october 1982 suggesting the onset of el nino propagated as a kelvin wave

strain partitioning in an obliquely convergent orogen plutonism and synorogenic collapse coast mountains batholith british columbia canada 1 we describe the crustal structure of the coast mountains batholith between 54 and 55 n within the canadian cordillera with emphasis on emplacement of the 7 km thick kasiks sill complex ksc kinematic patterns that developed during emplacement of the ksc are the result of interactions between magma transport magma accumulation and regional deformation the sills were emplaced during nw directed normal shearing and flattening of country rocks that host the ksc a 2 km thick shallowly ne dipping mylonite zone cuts the eastern side of the ksc kinematic indicators within the mylonite zone record top to the east normal displacements structural analysis shows that mylonite formation occurred during subvertical shortening and east northeast subhorizontal extension u pb zircon age dates show that ene directed normal shearing along the eastern side of the ksc and wnw directed normal shearing within the ksc occurred contemporaneously between 54 and 51 ma indicating strong strain partitioning between the mylonite and the ksc this pattern of strain partitioning is interpreted to have been driven by return flow of melt laden crust in response to tectonic denudation of the upper crust seismic profiling shows that many of these structures extend to mid and lower crustal depths comparison of our results with other regions within the canadian cordillera indicates that orogen scale right lateral strike slip faults deformed synchronously with wide spread magmatism and formation of extensional gneiss domes thus the crustal structure of the coast mountains batholith was the result of early tertiary batholith construction during dextral oblique convergence and synorogenic collapse

paleomagnetism and mesozoic tectonics of the seven devils volcanic arc in northeastern oregon upper triassic volcanogenic rocks of the seven devils group and huntington formation of brooks 1979b in northeastern oregon record two episodes of magnetization the older magnetization which predates late jurassic deformation of the volcanic arc terrane comprising the seven devils group was probably acquired in late triassic time the inclinations of both normal and reversed polarity magnetizations indicate that the triassic rocks originated approximately 18 from the paleoequator the results are consistent with paleomagnetic data from similar triassic rock assemblages on vancouver island and in south central alaska we interpret these assemblages as displaced fragments of wrangellia a once coherent late paleozoic volcanic arc and early mesozoic volcanic plateau that was torn apart and carried north by plate motion along the continental margin we interpret the younger magnetization which fails the fold test as a widespread thermochemical overprint caused by late jurassic and early cretaceous plutonism this magnetization yields a paleomagnetic pole at 60 n 295 e 95 7 and is similar to the pole obtained from plutons that intrude the seven devils group the angular difference between the pole from the plutons and the late jurassic early cretaceous reference pole for stable north america suggests that the seven devils volcanic arc has undergone a large clockwise rotation 66 21 the rotation may reflect the last stages of the arc s accretion to the continental margin or later large scale block movements in the pacific northwest

an eolian facies within the upper jurassic smackover formation tchula lake field mississippi the late jurassic upper smackover formation in mississippi is primarily composed of an overall regressive sequence of marine carbonate ramp deposits in central mississippi however carbonate deposition was interrupted by a large influx of siliciclastic sediment tchula lake field is unique not only because it produces gas and condensate from dolomitic quartz sandstone deposited in a mixed siliciclastic carbonate environment but also because it produces from what we interpret to be an eolian dune sand facies throughout the gulf coast basin no previous literature has cited an eolian facies within the smackover formation several characteristics of the producing zone sandstones have led to interpretations of this unit as an eolian coastal dune facies deposited on and around a jurassic paleohigh facies and paleoenvironmental interpretations are based on compositions and textures described in cores and thin sections the eolian facies consists of fine grained dolomitic quartz sandstone with a mean porosity of 10 20 and permeability of 0 800 md the sand grains are rounded to subrounded and well sorted the sandstone exhibits a sequence of upward steepening planar laminations capped at the top by a set of small scale wedge planar cross laminations the sharply defined parallel lamina are less than 5 mm thick and are commonly inversely graded and contain probable vadose meniscus carbonate cements this facies is interpreted to have been deposited in a backshore coastal dune environment the unit is characterized by low angle 20 degrees dip climbing translatent strata commonly produced by the migration of wind ripples along a dune no fossils or trace fossils are found within this facies eolian deposited sandstone is a potential reservoir rock along the updip limit of the smackover formation in west central mississippi other paleohighs along the jurassic shoreline may have undergone similar eolian deposition during a regional sea level fall eolian deposited sandstones on these paleohighs should have begin page 486 similar reservoir properties as the sandstone at tchula lake field the updip smackover formation in west central mississippi is an underexplored horizon and eolian deposited reservoirs have strong potential as a new exploration target the sea level fluctuation event associated with deposition at tchula lake field also has implications for exploration in upper jurassic sedimentary rocks across the entire united states gulf coast basin and prompts a reevaluation of these reservoirs

simultaneous batholith emplacement terrane continent collision and oroclinal bending in the blue mountains province north american cordillera the north american cordillera is a classic example of accretionary orogen consisting of multiple oceanic terranes attached to the western margin of laurentia during the mesozoic times although the cordillera is linear for most parts terrane boundaries are at a high angle to the overall structural grain in several segments of the orogen which has been a matter of longstanding controversy as to how and when these orogenic curvatures formed this paper discusses mechanisms kinematics and timing of initiation of one of these major curvatures the blue mountains province in northeastern oregon here magmatic fabric patterns and anisotropy of magnetic susceptibility in the wallowa batholith record three phases of progressive deformation of the host wallowa terrane during early cretaceous first is terrane oblique ne sw shortening interpreted as recording attachment of the amalgamated oceanic and fringing terranes to the continental margin during dextral convergence at 140 ma deformation subsequently switched to pure shear dominated nne ssw shortening associated with crustal thickening caused by continued impingement of the amalgamated blue mountains superterrane into a presumed westward concave reentrant in the continental margin at 135 128 ma upon impingement at 126 ma the northern portion of the superterrane became locked leading to reorientation of the principal shortening direction to nnw sse while its still deformable southern portion rotated clockwise about a vertical axis we thus propose oblique bending as the main mechanism of the orocline formation whereby horizontal compressive forces resulting from plate convergence acted at an angle to the terrane boundaries

geochemical studies of crude oil generation migration and destruction in the mississippi salt basin abstract the main source for crude oil in the mississippi salt basin is the laminated lime mudstone facies of the lower smackover crude oil generation and migration commenced at a level of thermal maturity equivalent to about 0 55 vitrinite reflectance short range lateral migration of crude oil was focused to upper smackover and norphlet reservoirs but vertical migration also charged some overlying cotton valley rodessa lower tuscaloosa and eutaw reservoirs following migration from the lower smackover thermal maturity history of reservoir rocks controls the preservation of crude oil gas condensate and methane slow thermal cracking of crude oil occurred in deep upper smackover reservoirs resulting in formation of gas condensate and precipitation of solid bitumen the maximum thermal maturity for preservation of condensate is equivalent to about 1 3 vitrinite reflectance only methane pyrobitumen and nonhydrocarbon gases including hydrogen sulfide persist at higher levels of thermal maturity early destruction of methane in deep upper smackover reservoirs near the wiggins arch is driven by thermochemical sulfate reduction lesser availability of sulfate in norphlet reservoirs in lower mobile bay could account for methane preservation at higher levels of thermal maturity one basic geochemical strategy for further exploration of the mississippi salt basin is to focus exploration effort on traps with reservoirs in the thermal maturity window for hydrocarbon preservation another strategy is to avoid drilling traps with overmature reservoir rocks

biomarkers and carbon isotopes of oils in the jurassic smackover trend of the gulf coast states u s a abstract the geochemistry of 25 oils from 23 fields in alabama and the mississippi and louisiana arkansas jurassic salt basins was evaluated results show that the oils were generated by a carbonate source rock which was deposited under highly anoxic conditions and which contains mainly marine derived organic matter the mississippi and louisiana arkansas oils are geochemically similar indicating similar depositional environments for the source although the alabama oils were also derived from a carbonate source rock they are dissimilar to the mississippi and louisiana arkansas oils terpane biomarkers suggest that in addition to marine derived organic matter the source for the alabama oils had an organic input from a more near shore paralic environment i e with a component of terrestrially derived kerogen within each area the oils are similar therefore the norphlet and upper smackover oils in alabama share a common source and the upper smackover cotton valley and some of the lower tuscaloosa oils where production is from faulted structures in mississippi also share a common source maturities of the oils in the three areas vary from low in the updip mississippi salt basin high in the louisiana arkansas salt basin to very high in portions of alabama based on the maturity of oils in mississippi oil generation and migration commenced during the cretaceous when the source was at modest levels of thermal maturity oils migrated relatively short distances into nearby reservoir rocks some oils reached high maturities in the reservoirs resulting in abundant late forming bitumen and pyrobitumen deposition in pore spaces

magnetic fabric of late jurassic arc plutons and kinematics of terrane accretion in the blue mountains northeastern oregon abstract the blue mountains province of northeastern oregon western idaho and southeastern washington usa consists of the amalgamated wallowa distal island arc baker melange bearing accretionary wedge forearc and olds ferry fringing island arc terranes anisotropy of magnetic susceptibility ams and particularly the orientation of magnetic lineations in middle to late jurassic diorite tonalite granodiorite plutons intruding the baker terrane indicate a change in tectonic regime from flattening with principal stretching at a high angle to the local orientation of the terrane boundaries at around 160 ma to constriction with boundary subparallel subhorizontal stretching at ca 146 ma the former magnetic fabric is compatible with magnetic lineations recording strain related to top to the southwest back thrusting onto the olds ferry arc in contrast the 146 ma boundary parallel stretching may record strain partitioning whereby a part of the baker terrane was extruded laterally parallel to terrane boundaries after the terrane collision after restoration for the clockwise post mid cretaceous terrane rotation the 160 ma restored principal stretching directions are compatible with the overall left oblique subduction and convergence of the wallowa distal and olds ferry fringing arc terranes magnetic fabric data from the plutons thus support the interpretation that the early displacement of the blue mountains superterrane and perhaps also its possible correlative intermontane superterrane of the canadian cordillera was southward along the truncated north american continental margin during the late middle jurassic

contrasting structural histories of the salmon river belt and wallowa terrane implications for terrane accretion in northeastern oregon and west central idaho the salmon river belt is composed of metamorphic tectonites with poorly dated mesozoic and paleozoic protoliths that lie between volcanic arc assemblages of northeastern oregon and the western margin of the north american continent in west central idaho to the west the salmon river belt overlies late paleozoic and mesozoic volcanic arc rocks of the wallowa terrane on a shallowly east dipping fault to the east the belt is separated from north american rocks by the western idaho shear zone the salmon river belt is divided into western and eastern assemblages composed of greenschist and amphibolit facies metamorphic tectonites respectively and is deformed in three and locally four generations of penetrative structures first generation structures are synmetamorphic west vergent tight to isoclinal folds with a penetrative axial planar cleavage and downdip stretching lineation second and third phase structures are postmetamorphic and consist of open to close upright to slightly overturned folds with north south and east west trending penetrative axial planar cleavages respectively low angle faults truncate metamorphic structures within the salmon river belt and juxtapose rocks with different metamorphic grades the faults formed together with second generation structures and are deformed by third generation folds the age of metamorphic and postmetamorphic structures is constrained by deformed carbonate rocks of late triassic age and clastic rocks of late early jurassic age and by the ca 145 ma emplacement of an undeformed tonalitic pluton along the eastern margin of the salmon river belt structures are overprinted and transposed by a younger steeply east dipping mylonitic shear zone the mid cretaceous western idaho shear zone synmetamorphic structures within the salmon river belt formed before amalgamation of the wallowa terrane and the north american fringing arc complex and developed as part of a regional belt of intra arc metamorphic tectonites the pr cretaceous docking of the wallowa terrane is recorded within the salmon river belt by development of postmetamorphic structures and predates formation of the western idaho shear zone the western idaho shear zone formed after the amalgamation of the arc terranes and records the intraplate deformation associated with the collapse of the fringing arc and back arc basin system

fabric development in syn tectonic intrusive sheets as a consequence of melt dominated flow and thermal softening of the crust the temperature dependence of ductile deformational processes suggests that the thermal anomaly associated with a cooling syn tectonic intrusion will produce a crustal low viscosity horizon that will concentrate deformation in the vicinity of the pluton during cooling this effect should be most prominent when magma is present but should also occur after solidification of the magma when flow is by solid state processes this paper evaluates this hypothesis for sheet like intrusions using one dimensional time dependent thermal models and accompanying predictions of viscosity vs time history based on experimental flow laws these models predict that for systems with an initial normal geothermal gradient e g extensional systems strike slip systems or thrust systems with low displacement rates the base of a large plutonic sheet cools more slowly than the top and fabric development should be most pronounced on the floor of the pluton in contrast in megathrust systems where displacements are sufficiently rapid to produce temperature inversions cooling is also upside down and fabric development should preferentially occur along the top of plutonic sheets moreover when a pluton is emplaced within a zone of inverted isotherms the heat may be trapped within the inversion a natural system characterized by this history should show a sharp thermal front coincident with the top of a paleo temperature inversion if a pluton is weaker than its country rock it will form a weak horizon in the crust throughout its cooling history and the plutonic sheet should take up the bulk of the deformation throughout its cooling history if a pluton is stronger than its country rock under conditions of solid state flow however models predict a two phase deformational history prior to solidification the deformation should be concentrated in the pluton with the magma representing a weak horizon in the crust but upon crystallization the pluton should become relatively rigid with respect to its country rock and deformation should be concentrated in the wall rocks these two cases predict markedly different structural histories and the history could easily be misinterpreted in the first case static mineral growth might be prominent in the wall rocks and these textures could be misinterpreted as evidence for post tectonic emplacement in the second case the extensive high t deformation of the wall rocks could be readily ascribed to non tectonic emplacement related deformation rather than a consequence of syn tectonic emplacement the model predictions are tested with three examples of well exposed plutonic sheets a neogene extensional system in death valley california and two megathrust systems in southern alaska border ranges fault system and mclaren metamorphic belt structural observations from these systems are broadly consistent with the model predictions and lend support to first order characteristics of the models nonetheless more sophisticated 2 d models of the coupled thermal mechanical system are needed to thoroughly test the hypothesis

timing of hydrocarbon generation and accumulation in fault bounded compartments in the norphlet formation offshore alabama abstract analysis of the variation in depth of the gas water contacts in the bon secour bay and lower mobile bay mary ann fields of offshore mobile bay alabama together with fault seal analysis implies that some of the pre cretaceous faults in these fields must be sealing it is also likely that the large post cretaceous lower mobile bay fault is dip leaking the gas currently reservoired in the norphlet formation has most likely been produced by thermal degradation of oils generated in the overlying jurassic lower smackover formation for a range of heat flow models appropriate for this area of the gulf coast the onset of gas generation defined as the time at which 10 of the maximum possible amount of gas has been generated occurs at 104 5 10 ma the error bounds in this estimate are the 90 confidence limits which were calculated by assuming that the times of onset of gas generation are log normally distributed the time of onset of gas generation is younger than the age of the sealing faults in the area hence it is likely that gas generation occurred in situ in the norphlet formation with re migration occurring during the development of the post cretaceous lower mobile bay fault

stable isotope δ13ccarb and org δ15norg and trace element anomalies during the late devonian punctata event in the western canada sedimentary basin late devonian marine deposits in the western canada sedimentary basin were analyzed for 1 accumulations of bioproductivity and paleoredox trace element proxies and for 2 variations of 13c carb and org and 15norg in order to understand and interpret the regional history of the global yet short term punctata event geochemical perturbation statistical correlations suggest that changes in detrital input and associated micronutrient delivery were the main driver of a eutrophication event noted early and possibly also late in the punctata zone around the isolated miette platform manifested by increased toc positive 13c excursions and concurrent enrichments of all elemental proxies evaluation of data within a regional sequence stratigraphic perspective revealed a eustatic sea level influence with proxy accumulations associated mostly with early transgression iic1 deposition and preservation of organic matter rich facies occurred during conditions of enhanced primary production and facilitated bottom water suboxia anoxia following eutrophication lower 15norg and 13corg values predominated and persisted throughout much of the punctata zone before rebounding toward its close suggesting a time interval of environmental stagnation and lower overall productivity during which n2 fixing autotrophs may have had an ecological advantage under nitrate limited conditions the punctata event approximately coincided with the advent of archaeopterid forest expansion beginning around mid frasnian time which fundamentally altered the nature of continental weathering through extensive soil formation and increased nutrient delivery to the oceans this evolutionary event may have amplified the detrital influx already elevated by sea level lowstand and early transgression and increased denudation of rising mountain ranges in near equatorial regions

a comparison of long coastal trapped wave theory with observations off peru abstract the agreement between coastal trapped wave theory and observation is studied for the case of observations made off peru during the 1977 cuea joint ii experiment wave properties are calculated using a numerical model with realistic horizontally uniform stratification and realistic bottom topography these properties are then explored as a function of the ratio of the first internal rossby radius of deformation to the shelf slope width the agreement of observed and calculated first mode free wave phase speeds 230 cm s 1 is excellent while modal structures agree more poorly a forced wave calculation using observed winds and currents as input is used to hindcast alongshore currents and sea level in the frequency band where smith 1978 observed free coastal trapped waves during 1977 the model suggests that most of the observed sea level and alongshore velocity fluctuations in the 5 10 day period band are due to free waves originating equatorward of 5 deg s while winds between 5 deg s and

major late triassic strike slip displacement in the seven devils terrane oregon and idaho a result of left oblique plate convergence abstract the shortening direction in rocks deformed in collision or subduction zones is not directly related to the plate convergence vector rather it is perpendicular to the collision zone or subduction zone even in cases where plate convergence is oblique the component of convergence parallel to the subduction collision zone is expressed by strike slip displacement in the arc region behind the subduction zone such strike slip shear zones have been recognized in the seven devils terrane of northeastern oregon and adjacent idaho one of these the oxbow shear zone consisting of cataclasite mylonite and ultra mylonite trends northeasterly from oxbow oregon to cuprum idaho the original rock types of the shear zone were plagiogranite gabbro diabase bassalt and keratophyre the age of the mylonitization is constrained by 40ar 39ar dates as late triassic meso and microscopic structures textures and quartz c axes fabrics indicate that the shear zone was formed by left lateral strike slip motion a minimum left lateral displacement of 65 km has been estimated but the true displacement may have been much larger the oxbow shear zone is interpreted as an intra arc strike slip zone of the seven devils terrane related to left oblique plate convergence during the triassic

a record of crustal scale stress igneous foliation and lineation in the mount waldo pluton waldo county maine abstract the late devonian mount waldo pluton is a porphyritic granite that has a magmatic foliation and lineation foliation is defined by 1 preferred orientation of potassium feldspar phenocrysts and biotite crystals and 2 the anisotropy of magnetic susceptibility ams ams alone defines the lineation the carrier of the ams signal is multidomain magnetite confirmed by petrographic observation high bulk susceptibility generally 3 e3 si units of samples and results of isothermal remanent magnetization experiments ams data from 26 sites in the pluton consistently show a subhorizontal north south trending lineation defined by the orientation of the maximum axis of the ams ellipsoid and a subvertical north south striking foliation whose pole is the minimum axis of the ams ellipsoid at individual sites the feldspar and ams foliations are parallel the lack of evidence for significant solid state deformation in the pluton suggests that both the lineation and foliation are entirely magmatic in origin the pluton s relatively small size 15 km diameter and shallow emplacement depth 3 kbar suggest that it was in its magmatic state for a short time probably less than one million years the orientation of the lineation and foliation is consistent with their formation due to a small increment of crustal scale strain absorbed by the pluton in its geologically brief magmatic state if so these fabrics record a late devonian crustal scale strike slip stress regime that may also have driven dextral movement on the neighboring norumbega fault zone

large scale transpressive shear zone patterns and displacements within magmatic arcs the coast plutonic complex british columbia the coast plutonic complex is the largest magmatic arc of the north american cordillera extending from northwestern washington state to eastern alaska it forms the transition between two tectonic domains that are suspected to have undergone several phases of large several thousands of kilometers orogen parallel displacement during the mesozoic and early cenozoic a compilation of fabric data published isotopic ages and new structural observations shows that the western coast plutonic complex was affected by subvertical orogen parallel crustal scale shear zones these shear zones mainly reflect sinistral transpression and were sequentially active from 110 to 87 ma during the intrusion of voluminous batholiths sinistral shearing was roughly coeval with the development of the thrust belts flanking the coast plutonic complex between 101 and 85 ma suggesting plate scale transpression was a first order process in the construction of the coast mountains orogen these shear zones separate panels with distinct plutonic and cooling histories suggesting the sinistral displacements between crustal blocks were large greater than tens to hundreds of kilometers this transpressive shear system likely reflects the jurassic to early late cretaceous migration of outboard cordilleran terranes to the south suggested by paleomagnetic evidence and plate reconstruction models this example from the coast orogen shows how transpression is partitioned between a thermally weakened magmatic arc and outwardly vergent fold and thrust belts our analysis further shows that the 2000 km long late cretaceous to early tertiary coast shear zone has a minimum extent toward the south to at least 51 30 n

effects of elemental sulfur during programmed pyrolysis of kerogen abstract the effects of elemental sulfur during programmed pyrolysis of eocene green river shale and common rock matrix minerals were assessed experimentally mixtures of elemental sulfur and green river shale with calcium carbonate silicon dioxide calcium sulfate and zinc sulfide were analyzed with the weight fraction green river shale held at near constant values the addition of elemental sulfur resulted in substantial decreases in hydrogen index and substantial increases in oxygen index the effect is so significant that thermally immature type i kerogen can yield a pyrolysis response typical of type iii kerogen moreover elemental sulfur appears to influence estimations of thermal maturity during programmed pyrolysis only minor differences in pyrolysis response were noted for the different matrix compounds without elemental sulfur this study suggests that programmed pyrolysis results on rocks containing unusually high contents of elemental sulfur should be interpreted with caution