lower permian sediment gravity flow sequence eastern california abstract the lower permian middle wolfcampian zinc hill sequence a 65 to 110 m thick series of beds in the owens valley group in east central california comprises sediment gravity flow deposits consisting of carbonate sediment that originated on and siliciclastic sediment that may have been generally ponded behind a carbonate shelf to the east and northeast thickness patterns and paleocurrent indicators show that the sediment forming this sequence was transported primarily southeastward and deposited in a southeast trending lobe shaped body evidently the sediment was carried from the shelf by sediment gravity flows that travelled westward down the slope and then turned southeastward upon reaching a southeast trending basin at the base of the slope data derived from the study of this basin which paralleled the shelf edge and is thought to have formed parallel to a southeast oriented segment of the early permian continental margin constitute one of the most important arguments favoring a pennsylvanian to early permian age of truncation of the western north american continental margin

re evaluation of the middle miocene eagle mountain formation and its significance as a piercing point for the interpretation of extreme extension across the death valley region california u s a abstract the death valley area of eastern california and southern nevada has been highly influential in the development of ideas about extreme crustal extension one of the tightest constraints on death valley extension is apparently provided by clasts in inferred alluvial fan deposits of the eagle mountain formation 15 11 ma and their source in the hunter mountain batholith now located 100 km from some of the deposits because alluvial fans are usually less than 10 20 km in radius the remaining separation has been interpreted as tectonic new research reported here suggests that the eagle mountain formation at its type location was deposited in a fluvial lacustrine setting and provides no constraint on either the magnitude or the direction of tectonic transport and or crustal extension confidence in palinspastic reconstruction thus depends on resolving ambiguities in the correlation of pre extensional markers or on the recognition of demonstrably proximal facies tectonically distributed across the region the succession at eagle mountain comprises 1 diffusely stratified monolithologic carbonate breccia and sandstone 140 m onlapping cambrian carbonate rocks at an unconformity with 110 140 m of relief fluvial or fluvially influenced 2 10 m of tabular bedded siltstone diamictite and sandstone lacustrine 3 cross stratified and channelized sandstone and polymict conglomerate bearing hunter mountain clasts with minor siltstone and carbonate 110 m mostly fluvial and 4 tabular bedded sandstone siltstone and minor carbonate 140 m mostly lacustrine eight prominent stratigraphic discontinuities mapped within the third interval are characterized by up to 15 m of local erosional relief and by abrupt upward coarsening from siltstone or carbonate to conglomerate or sandstone a fluvial interpretation for the same critical part of the succession is based upon the existence of the mapped surfaces the ubiquitous development of channels trough cross stratification and upward fining trends particularly between the mapped surfaces and the abundance of well rounded clasts in conglomerate paleocurrents are generally directed between southward and eastward although with considerable dispersion and they shift from approximately southward or southeastward in the mostly fluvial deposits to approximately eastward in the upper lacustrine interval an unusual feature of the eagle mountain formation at eagle mountain is the presence of five crosscutting conglomerate bodies interpreted as vertically infilled fissures of tectonic origin numerous normal reversed normal and oblique slip faults with up to 34 m of stratigraphic separation are thought to postdate sedimentation and tilting of the eagle mountain formation after 11 ma

structure and evolution of the east sierran thrust system east central california 1 a belt of arc parallel northeast vergent contractional deformation the east sierran thrust system ests crops out for 150 km along the east side of the sierran continental margin arc the ests is nowhere wider than 20 km and it accommodated an estimated minimum of 9 3 km of horizontal shortening remarkably it experienced repeated episodes of broadly coaxial and coaxial planar contractional deformation beginning prior to 188 ma and continuing past 140 ma we postulate that the ests resulted primarily from episodic underthrusting of the back arc lithosphere beneath the east edge of the sierran arc facilitated by a buttressing effect of the arc as a result of this process rocks along the east flank of the batholith including the ests were episodically shortened against the arc buttress the ests experienced significant deformation during the nevadan orogeny indicating that contractional to transpressive deformation affiliated with this event affected the eastern wall rocks of the arc as well as its western wall rocks index terms 8102 tectonophysics continental contractional orogenic belts 9609 information related to geologic time mesozoic 8015 structural geology local crustal structure 9350 information related to geographic region north america keywords eastern california mesozoic structure cordilleran thrust system citation dunne g c and j d walker 2004 structure and evolution of the east sierran thrust system east central california tectonics 23 tc4012 doi 10 1029 2002tc001478

the butte valley and layton well thrusts of eastern california distribution and regional significance the butte valley and layton well thrusts are major structural features in two adjacent mountain ranges west of southern death valley the butte valley thrust in the southern panamint range underlies most of the range and emplaces proterozoic rocks over strata as young as jurassic in age the layton well thrust to the southwest in the slate range has been interpreted to have proterozoic rocks juxtaposed on rocks as young as jurassic suggesting that the butte valley thrust and the layton well thrust might be correlative new information indicates that the allochthonous rocks of the layton well thrust are mesozoic in age and are not likely part of the same allochthon as that above the butte valley thrust in addition the butte valley thrust cuts sharply downward to the north and west across lower plate paleozoic strata suggesting that the fault roots beneath the layton well thrust the layton well thrust probably belongs to the east sierran thrust system and thus would be in the upper plate of the butte valley thrust

early permian thrust faults in east central california one exposed and another inferred thrust fault in the southeastern inyo mountains of east central california are interpreted as early permian in age these faults both apparently of local extent are temporally and geographically related to a major episode of basin formation which occurred along a southeast trending segment of the permian north american plate margin the close relationship between basin formation and thrust faulting supports a previous interpretation by us that this segment of the margin was undergoing active wrench tectonism during the early permian resulting in the essentially simultaneous development of local extensional and compressional structures similar to those now forming in the california continental borderland

barotropic rossby wave radiation from a model gulf stream 1 the barotropic rossby wave field in the north atlantic ocean is studied in an eddy resolving ocean model simulation the meandering model gulf stream radiates barotropic rossby waves southward through preferred corridors defined by topographic features the smoother region between the bermuda rise and the mid atlantic ridge is a particularly striking corridor of barotropic wave radiation in the 20 50 day period band barotropic rossby waves are also preferentially excited at higher frequencies over the bermuda rise suggesting resonant excitation of topographic rossby normal modes the prevalence of these radiated waves suggests that they may be an important energy sink for the equilibrium state of the gulf stream

subinertial oscillations on the amundsen sea shelf antarctica abstractmooring data from the western flank of dotson trough amundsen sea shelf region show the presence of barotropic oscillations with a period of 40 80 h the oscillations are visible in velocity temperature salinity and pressure and are comparable to tides in magnitude the period of the oscillations corresponds to topographic rossby waves of low group velocity and a wavelength of about 40 km that is the half width of the channel it is suggested that these resonant topographic rossby waves cause the observed peak in the wave spectra the observations show that sparse ctd data from this region should be treated with caution and need to be complemented with moorings or yo yo stations in order to give a representative picture for the hydrography

circulation and thermohaline variability of the hanna shoal region on the northeastern chukchi sea shelf we analyzed velocity and hydrographic data from 23 moorings in the northeast chukchi sea from 2011 to 2014 in most years the eastern side of hanna shoal was strongly stratified year round while weakly stratified regions prevailed on the shelf south and west of the shoal stratification differences cause differential vertical mixing rates which in conjunction with advection of different bottom water properties resulted in seasonally varying along isobath density gradients in agreement with numerical models we find that bottom waters flow anticyclonically around the shoal whereas most of the shelf responded barotropically to wind forcing there was a strong baroclinic component to the flow field northeast of hanna shoal resulting in no net vertically integrated transport on average in contrast there is a net eastward transport from west of the shoal which implies convergence north of the shoal convergence and along isobath density gradients may foster cross shelf exchange north of hanna shoal modal analyses indicate that the shelf south of the shoal and barrow canyon responded coherently to local and remote winds whereas the wind current response around hanna shoal was less coherent barotropic topographic waves of 3 day period were generated episodically northeast of the shoal and propagate clockwise around hanna shoal but are blocked from entering barrow canyon and are possibly scattered by the horizontally sheared flow and converging isobaths on the western side of the shoal analysis of water properties on the western side of hanna shoal suggests that these include contributions from the western and southern portions of the chukchi sea

paired benthic foraminiferal cd ca and zn ca evidence for a greatly increased presence of southern ocean water in the glacial north atlantic benthic foraminiferal 13c and cd ca studies suggest that deep atlantic circulation during the last glacial maximum was very different from today with high nutrient low 13c high cd deep southern ocean water sow penetrating far into the north atlantic however if some glacial 13c values are biased by productivity artifacts and or air sea exchange processes then the existing 13c data may be consistent with the continual dominance of north atlantic deep water nadw cibicidoides wuellerstorfi cd ca results presented here indicate that the glacial north atlantic was strongly enriched in dissolved cd below 2500 m depth if nadw formation was still vigorous relative to sow formation these data could be explained by either increased preformed nutrient levels in the high latitude north atlantic or by increased organic matter remineralization within lower nadw high glacial zn ca values in the same samples however are best explained by a substantially increased mixing with zn rich sow the cause was most likely a partial replacement of nadw by less dense glacial north atlantic intermediate water this reorganization also lowered deep north atlantic co32 concentrations by perhaps 10 to 15 mol kg 1

a topographic rossby mode resonance over the iceland faeroe ridge abstract an array of current meter moorings along 12 w on the southern side of the lceland faeroe ridge reveals a narrowband barotropic oscillation with period 1 8 days in spectra of velocity the signal is coherent over at least 55 km scales and propagates phase with shallow water on the right toward the northwest velocity ellipses tend to be elongated crossing contours of f h and rotate anticyclonically solutions of the rigid lid barotropic shallow water equations predict the occurrence of a topographic rossby normal mode on the south side of the ridge with spatial scales exceeding 250 km and with intrinsic period near 1 84 days this fundamental mode of the south side of the ridge has predicted spatial structure phase propagation and velocity ellipses consistent with the observed oscillation the frictional amplitude e folding decay time for this normal mode is estimated from the observations to be 13 days the observed ocean currents are significantly coherent with zonal wind stress fluctuatio

a hydraulic box model study of the mediterranean response to postglacial sea level rise 1 this paper quantifies the role of changing sea level in affecting mediterranean stratification using a new model of the strait basin system which allows for explicit time dependence during the last deglaciation fairbank s meltwater peak 1b leads to rapidly rising global sea levels and a freshening of the oceans and hence increasing influx of ever freshening atlantic water into the mediterranean basin owing to long residence times the salinity of the deep and intermediate water reservoirs would have decreased more slowly so that the basin was more stably stratified for a period with possible implications for sapropel formation our model is used to estimate the size of this reservoir effect in comparison to the freshwater influx from the opening of the black sea at the bosphorus it is found that this mechanism affects the stratification to a similar degree as the black sea opening other climatic mechanisms have also affected the freshwater budget of the mediterranean at this time but their sizes are more difficult to quantify

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

multiple oscillatory modes of the argentine basin part ii the spectral origin of basin modes in this paper the spectrum of barotropic basin modes of the argentine basin is shown to be connected to the classical rossby basin modes of a flat bottom constant depth rectangular basin first the spectrum of basin modes is calculated for the argentine basin by performing a normal mode analysis of the barotropic shallow water equations then a homotopy transformation is performed that gradually morphs the full bathymetry geometry through a flat bottom configuration into a rectangular basin following the eigenmodes through this transition establishes a connection between most of the basin modes and the classical rossby basin modes of a rectangular geometry in particular the 20 day mode of the argentine basin is identified with the lowest order mode of classical theory sensitivity studies show that the decay rate of each mode is controlled by bottom friction but that it is insensitive to lateral friction lateral friction strongly impacts the oscillation frequency in addition the modes are found to be only slightly sensitive to the presence of a background flow

dansgaard oeschger cycles interactions between ocean and sea ice intrinsic to the nordic seas dansgaard oeschger d o cycles are the most dramatic frequent and wide reaching abrupt climate changes in the geologic record on greenland d o cycles are characterized by an abrupt warming of 10 5 c from a cold stadial to a warm interstadial phase followed by gradual cooling before a rapid return to stadial conditions the mechanisms responsible for these millennial cycles are not fully understood but are widely thought to involve abrupt changes in atlantic meridional overturning circulation due to freshwater perturbations here we present a new high resolution multiproxy marine sediment core monitoring changes in the warm atlantic inflow to the nordic seas as well as in local sea ice cover and influx of ice rafted debris in contrast to previous studies the freshwater input is found to be coincident with warm interstadials on greenland and has a fennoscandian rather than laurentide source furthermore the data suggest a different thermohaline structure for the nordic seas during cold stadials in which relatively warm atlantic water circulates beneath a fresh surface layer and the presence of sea ice is inferred from benthic oxygen isotopes this implies a delicate balance between the warm subsurface atlantic water and fresh surface layer with the possibility of abrupt changes in sea ice cover and suggests a novel mechanism for the abrupt d o events observed in greenland ice cores

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

north atlantic circulation and reservoir age changes over the past 41 000 years 1 constraints on the timing of atlantic meridional overturning circulation amoc changes during the last deglaciation are fundamental to understanding the climate s rapid response to insolation forcing however uncertainty about high latitude north atlantic hlna radiocarbon reservoir ages has previously precluded robust age model development for this critical region hlna reservoir ages also serve as a proxy for amoc strength we present regionally averaged hlna reservoir ages for 0 to 41 thousand years before the present kyr bp based on over 500 radiocarbon dates from 33 north atlantic cores an early deglacial increase to 1000 14c yr reservoir ages between 18 5 and 16 5 kyr bp suggests reduced amoc before peak heinrich stadial 1 hs1 ice rafted debris ird a rapid decrease in reservoir ages coincident with the ird maximum at 16 kyr bp indicates strong stratification of the upper water column caused by massive freshwater release

evolution of the northeast labrador sea during the last interglaciation 1 boreal summer insolation during the last interglaciation lig generally warmed the subpolar to polar northern hemisphere more than during the early holocene yet regional climate variations between the two periods remain we investigate northeast labrador sea subsurface temperature and hydrography across terminations t i and ii and during the lig to assess the impact of two different magnitudes of boreal summer insolation increase on the northeast labrador sea we use mg ca ratios in neogloboquadrina pachyderma sinistral as a proxy of calcification temperature to document changes in subsurface temperatures over eirik drift our corresponding record of d 18 o of seawater documents changes in water mass salinity mg ca calcification temperatures peak early in the holocene coincident with peak boreal summer insolation in contrast lig temperatures are relatively constant through the interglaciation and are no warmer than peak holocene temperatures during the first half of the lig d 18 o of seawater remains depleted likely from southern greenland ice sheet retreat and enhanced arctic freshwater and sea ice export to the labrador sea the consequent stratification of the labrador sea and attendant suppressed convection explains delayed deep ocean ventilation and a cooler subsurface in the northeast labrador sea during the lig

depositional framework and controls on mixed carbonate siliciclastic gravity flows pennsylvanian permian shelf to basin transect south western great basin usa mixed carbonate siliciclastic sediment gravity flow deposits of late pennsylvanian to early permian age are exposed in the death valley owens valley region of east central california the mexican spring unit constitutes the upper part of the keeler canyon formation and is characterized by turbidites debris flow deposits and megabreccias all of mixed carbonate siliciclastic composition the mixed composition of the keeler canyon formation provides an opportunity to link facies architecture to controls on depositional system development depositional relationships indicate that the deposits represent a non channellized base of slope carbonate apron system with inner outer and basinal facies associations these gravity flow deposits are characterized by repeated stacked small scale 100 m coarsening and thickening upward cycles contemporaneous outer shelf and upper slope deposits of the tippipah limestone are exposed at syncline ridge on the nevada test site the deposits consist of carbonate buildups directly overlain by cross bedded quartz rich sandstone and conglomerate which filled channels that traversed across the previously existing carbonate shelf detritus was transported to the west down the upper slope by gully systems that fed the temporally persistent base of slope apron of the upper part of the keeler canyon formation this style of deposition differs from point sourced siliciclastic submarine fan depositional systems however the keeler canyon system has lithofacies similar to some sandy siliciclastic turbidite systems such as the delta fed submarine ramp facies model which is a line sourced shelf fed system that is not supply limited the mixed clastic apron systems of the keeler canyon formation differ from classical carbonate aprons in that the former is characterized by an abundance of sedimentary cycles controls on the development of these cycles and of the facies distribution may have resulted from changes in type and rate of sediment supply relative sea level changes and or tectonic events interpretation of the data is focused on relative changes in sea level as the most significant control on development of the depositional system relative sea level changes serve two important functions 1 they provide a mechanism for bringing coarse siliciclastic and bioclastic grains together on the outer shelf and 2 shelf margin collapse may be initiated during relative lowstands allowing for transport of the sediment to the deep basin and development of deep basinal cycles therefore an abundance of mixed clastic gravity flow deposits such as these in the rock record may be an indicator of periods of high frequency changes in relative sea level which is a characteristic of late palaeozoic sea level history

the oquirrh basin revisited the upper paleozoic succession in the oquirrh basin is unusually thick up to 9300 m and consists mainly of a pennsylvanian middle permian sedimentary package located within the cordilleran miogeocline of northwestern utah previous workers have suggested a tectonic origin for the oquirrh basin that is incompatible with the basin location in both time and space there is no evidence for pennsylvanian and lower permian tectonism in the middle of the miogeocline thermal evidence from the mississippian mission canyon shale does not support the implied deep burial of the crustal sag models of basin formation stratigraphic and facies evidence indicates a growth fault origin for the basin regional isopach maps and facies maps are powerful tools in interpreting depositional environments and in reconstructing fold and thrust belts however the location of measured sections relative to the location of the growth fault needs special consideration for these tools to be effective in reconstructing a thrusted growth fault basin the charleston nebo thrust may have essentially reversed the movement on a growth fault thick oquirrh basin sedimentary rocks may not be required to balance structural sections across this thrust fault a thin skinned extensional growth fault origin for the oquirrh basin implies that the cordilleran miogeocline did not participate in the pennsylvanian north vergent uplifts of the ancestral rocky mountains

precession driven changes in iceland scotland overflow water penetration and bottom water circulation on gardar drift since 200 ka abstract benthic foraminiferal stable isotopic records from a transect of sediment cores south of the iceland scotland ridge reveal that the penetration depth of iceland scotland overflow water isow varied on orbital timescales with precessional pacing over the past 200 kyr similar higher benthic foraminiferal 13 c values 1 0 were recorded at all transect sites downstream of the iceland scotland ridge during interglacial periods marine isotope chrons 5 and 1 indicating a deeply penetrating isow during glacial periods marine isotope chrons 6 4 and 2 benthic foraminiferal 13 c values from the deeper 2700 3300 m southern sites within this transect were significantly lower 0 5 than values from the northern shallower portion of the transect 1 0 reflecting a shoaling of isow and greater influence of glacial southern component water scw in the deep northeast atlantic particularly during intermediate climate states isow strength is driven by precessional cycles superimposed on the large scale glacial interglacial isow variability millennial scale variability in the penetration of isow likely caused by high frequency heinrich and dansgaard oeschger events is most pronounced during intermediate climate states

ferromagnetic resonance characterization of greigite fe3s4 monoclinic pyrrhotite fe7s8 and non interacting titanomagnetite fe3 xtixo4 ferromagnetic resonance fmr spectroscopy has become an increasingly useful tool for studying the magnetic properties of natural samples magnetite fe3o4 is the only magnetic mineral that has been well characterized using fmr this limits the wider use of fmr in rock magnetism and paleomagnetism in this study we applied fmr analysis to a range of magnetic minerals including greigite fe3s4 monoclinic pyrrhotite fe7s8 magnetically non interacting titanomagnetite fe3 xtixo4 and synthetic magnetite chains to constrain interpretation of fmr analysis of natural samples and to explore applications of fmr spectroscopy we measured the fmr signatures of a wide range of well characterized samples at the x and q bands fmr spectra were also simulated numerically to compare with experimental results the effects of magnetic anisotropy mineralogy domain state and magnetostatic interactions on the fmr spectra are discussed for all studied minerals our experimental and theoretical analyses of magnetically non interacting tuff samples and magnetically interacting chains enable quantitative assessment of contributions of magnetostatic interactions and magnetic anisotropy to the fmr spectra our results also indicate that intact magnetosomes are a unique system with distinct fmr signatures while fmr analysis is useful for characterizing magnetic properties of natural samples care is needed when making interpretations because of overlaps in a range of fmr signatures of different magnetic minerals with different magnetic properties our analyses will help to constrain such interpretations in rock magnetic studies

triassic plutonism in southern california southward younging of arc initiation along a truncated continental margin earliest cordilleran magnatism in the southwestern united states is recorded by a belt of triassic plutons that inme protemzoic basemint of the mojave crustal province and its cratona miogeoclinal cover the belt extends from the western mojave desert through the trausverse ranges to the colorado river trough triassic plutons are predominantly alkali calcic fe and sr mriched quartz mzrdior tes and monzonites the northern part of the belt is comlx sed of two older plutonic mites 241 231 ma which are high k to shoshonitic the southern part of the belt is a younger 218 213 ma sodic alkalic suite the plutonic record in southern california suggests a short lived southward younging continental margin arc sang for eraplacement of triassic plutons sulim on a continental margin modified by s mistral tranqform faulting triassic plutonism in this region was followed by a magmatic lull prior to the onset of voluminous middle to late jurassic cordilleran arc magmatism

ventilation changes in intermediate water on millennial time scales in the se nordic seas 65 14 kyr bp 1 a glacial epibenthic 13c record from 773 m water depth in the se nordic seas reveals moderate but distinct changes in the ventilation 65 000 14 000 years ago the last glacial maximum the warm interstadials and the shorter stadials are characterized by high 13c values indicating well ventilated intermediate water masses in the nordic seas decreasing 13c values during the cold heinrich events signify a reduction in intermediate water ventilation we attribute the reduction to the development of a halocline causing a stop in convection and outflow from the nordic seas the well ventilated outflow water is replaced by warmer atlantic water which due to the stratification is isolated from the atmosphere its initial high 13c values are reduced due to ageing we ascribe the lack of response in the subsurface atlantic water during the stadials to the smaller geographical extent of these events as compared to the heinrich events

a speculative reconstruction of the middle paleozoic continental margin of southwestern north america geologic relations and data from strontium and oxygen isotopic studies are used together to speculate on the paleogeographic positions of various crustal blocks or terranes in southwestern north america with respect to the middle paleozoic continental margin the southwestern margin of the middle paleozoic continent based on these data is quite irregular in its present configuration but most of the irregularities can be accounted for by strike slip displacement of continental fragments during several post middle paleozoic tectonic events we conclude that large scale late paleozoic sinistral displacements and mesozoic and cenozoic dextral displacements have been the major events affecting the configuration of this margin our preferred model includes the following elements 1 500 km of left lateral displacement of a large part of the margin during a late paleozoic truncation 2 slivering of the margin by right lateral faulting during the mesozoic amounting to about 275 km of total displacement and 3 further deformation of the margin during the cenozoic primarily by right lateral faulting oroclinal bending and crustal extension

interpretation of the last chance thrust death valley region california as an early permian decollement in a previously undeformed shale basin abstract the last chance thrust discontinuously exposed over an area of at least 2500 km2 near the south end of the cordilleran foreland thrust belt in the death valley region of east central california is controversial because of its poorly constrained age and its uncertain original geometry and extent we interpret this thrust to be early permian in age to extend throughout a sedimentary basin in which deep water mississippian shale overlain by pennsylvanian and earliest permian limestone turbidites accumulated to represent about 30 km of eastward displacement and to be related to convergence on a northeast trending segment of the early permian continental margin last chance deformation occurred between the times of the antler and sonoma orogenies of late devonian early mississippian and late permian ages respectively and followed early to middle pennsylvanian truncation of the continental margin by transform faulting in the western part of the mississippian shale basin in east central california the originally recognized exposures of the last chance thrust show neoproterozoic and early paleozoic strata above lower plate mississippian shale farther east faults subparallel to bedding above below and within the mississippian shale are interpreted to mark the thrust zone and to represent a regional decollement at the eastern margin of the basin upper plate thrust slices of deep water late paleozoic strata are interpreted to have piled up against the margin of the mississippian carbonate shelf to form a large antiformal stack above the lee flat thrust which we regard as the easternmost exposure of the last chance thrust thrust loading depressed the western part of the shelf creating a new sedimentary basin in which about 3 5 km of younger early permian deep water strata were deposited against the antiformal stack later probably in the late permian other thrusts including the inyo crest thrust which was subsequently overlapped by early to middle triassic marine strata cut across the last chance thrust we interpret the last chance thrust as similar in many ways to appalachian type decollements in which the zone of thrusting is localized along a shale interval the last chance thrust however has been dismembered during later geologic events so that its original geometry has been obscured our model may have unrecognized analogs in other structurally complex shale basins in which the initial deformation was along a major shale unit

low frequency waves in the santa barbara channel observed by high frequency radar are antisymmetric with a mean propagation speed of 5k m d 1 and relative vorticity of order 0 1 f complex empirical orthogonal function decomposition in the 10 20 day passband partitions variance into two dominant modes the first mode represents the vortices with an average period of 14 4 days the second mode represents alongshore fluctuations with an average period of 13 3 days amplitude functions of the two modes correlate with in situ current time series at 5 and 45 m depths obtained from moorings at the east and west channel entrances suggesting coupling with the larger scale circulation of the northern southern california bight the observations support interpretation of mode 2 as a coastal trapped wave since the period and alongshore flow are consistent with previous observations and predictions we hypothesize that mode 1 is a resonant response of the santa barbara basin in the form of a trapped topographic rossby mode the spatial mode resembles the predicted pattern based on a simplified analytical model of the fundamental mode the amplitude of mode 1 is consistently large when the frequencies of modes 1 and 2 converge suggesting that the vortices are a basin scale resonant response to coastal trapped waves index terms 4520 oceanography physical eddies and mesoscale processes 4512 oceanography physical currents 4508 oceanography physical coriolis effects 4516 oceanography physical eastern boundary currents 4544 oceanography physical internal and inertial waves keywords propagating eddies santa barbara channel coastal trapped waves citation beckenbach e and l washburn 2004 low frequency waves in the santa barbara channel observed by high frequency radar j geophys res 109 c02010 doi 10 1029 2003jc001999

correlation of permian and triassic deformations in the western great basin and eastern sierra nevada evidence from the northern inyo mountains near tinemaha reservoir east central california geologic relationships exposed near tinemaha reservoir southeast of big pine east central california provide key chronological and structural constraints for linking permian and triassic deformational events recognized in the white and inyo mountains in the western great basin with those in the eastern sierra nevada particularly the mount morrison and saddlebag lake pendants permian to earliest triassic deformation in the tinemaha reservoir area produced a large north to northwest trending east vergent originally recumbent syncline mule spring syncline cut by an overriding thrust strange hill thrust we correlate this deformation with a middle permian to earliest triassic contractional deformation recognized in the southern inyo mountains and with a major episode of folding and thrust faulting in the eastern sierra nevada after a period of tectonic quiescence and marine sedimentation in the early triassic rocks in the tinemaha reservoir area were refolded twice producing distinctive sets of steeply plunging folds similar structures in the mount morrison pendant that formed prior to intrusion of a 225 16 ma dike along the laurel convict fault are correlated with those in the tinemaha reservoir area the timing of these folding events may be similar to that of displacement on the golconda and or lundy canyon thrusts in the saddlebag lake pendant close structural and stratigraphic ties suggest that rocks in the northeastern part of the mount morrison pendant and tinemaha reservoir area now separated by 65 km of dextral displacement along the cryptic tinemaha fault originally lay adjacent to one another this offset postdates triassic folding and is inferred to predate emplacement of the latest triassic wheeler crest granodiorite which crops out across the projected fault trace

changes in the strength of the nordic seas overflows over the past 3000 years the nordic seas overflows constitute the densest component of the deep limb of the atlantic meridional overturning circulation amoc changes in the vigour of the overflows may have had important climatic effects in the past and may also have in the future yet evidence for multidecadal to millennial changes in the deep limb of the amoc and their potential relationship to north atlantic climate variability during the holocene remains weakly constrained here we present grain size data as a proxy for near bottom current speed from sub decadal to decadally resolved sediment cores located in the direct pathway of the two nordic overflows east and west of iceland the iceland scotland overflow water isow and the denmark strait overflow water dsow respectively the results show no clear relationship between reconstructed changes in the vigour of the nordic overflows and the well known periods of centennial scale climate variability recorded in the north atlantic region however well defined millennial scale trends are found in both of the overflow strength records over the last 3000 years which were possibly related to hydrographic reorganizations in the nordic seas driven by the decrease in northern hemisphere summer insolation over the neoglacial period a comparison between the near bottom flow speed reconstructions from isow and dsow suggests an anti phased relationship between the nordic seas overflows east and west of iceland over the last 3000 years this feature has been observed in climate models potentially as a result of shifts in the deep water formation sites as a response to changes in atmospheric patterns over the nordic seas

millennial scale climate instability during the early pleistocene epoch climate proxy records of the past 100 000 years show that the earth s climate has varied significantly and continuously on timescales as short as a few thousand years 1 7 similar variability has also recently been observed for the interval 340 500 thousand years ago8 these dramatic climate shifts expressed most strongly in the north atlantic region may be linked to and possibly amplified by alterations in the mode of ocean thermohaline circulation4 5 6 7 8 9 here we use sediment records of past iceberg discharge and deep water chemistry to show that such millennial scale oscillations in climate occurred over one million years ago this was a time of significantly different climate boundary conditions not only was the early pleistocene epoch generally warmer but global climate variations were governed largely by changes in earth s orbital obliguity our results suggest that such millennial scale climate instability may be a pervasive and long term characteristic of earth s climate rather than just a feature of the strong glacial interglacial cycles of the past 800 000 years

glacial interglacial variability in deep sea ostracod assemblage composition at iodp site u1314 in the subpolar north atlantic abstract we present a detailed study of glacial interglacial deep sea benthic ostracod assemblage variability at iodp site u1314 subpolar north atlantic in relation to the history of ice rafting events and changes in deep ocean circulation over the past 170 ky our records of ostracod diversity abundance and dissolution and sediment properties ird and caco 3 show an excellent correspondence to high amplitude orbital and millennial variability observed in the climate records 13 c and 18 o from neighboring deep water sites suggesting that the benthic meiofauna fluctuates synchronously with the prevailing oceanographic conditions surface ocean conditions deep ocean circulation and water temperature and food flux krithe dominant argilloecia and cytheropteron are the most abundant and diverse genera in association with rockallia enigmatica three ostracod assemblages are recognized the genera pennyella argilloecia pelecocythere ambocythere pseudobosquetina bradleya and nannocythere are associated with interglacials and interstadials and possibly reflect increased flux of food to the sediments and more vigorous nadw formation a transitional assemblage composed of species of cytheropteron xestoleberis and eucythere is restricted to climatic transitions and indicate moderate environmental conditions and seasonal productivity a glacial stadial assemblage is characterized by a temporal predominance of either intermediate depth and shallow water arctic subarctic species belonging to cytheropteron polycope pedicythere swainocythere cluthia heterocyprideis elofsonella and finmarchinella or abyssal north atlantic ostracods bythocythere dutoitella bathycythere and bythocypris the influx of high latitude taxa can be partially explained by ice rafting but may also represent a shift of the location of intermediate and deep water convection to the area south of iceland therefore the combination of species characteristic of different watermasses during glacials may reflect shifts in the influence of high nutrient southern source water e g aabw vs low nutrient gnaiw during glacials