isopach pattern of the lower cambrian zabriskie quartzite death valley region california nevada how useful in tectonic reconstructions new thickness measurements of the lower cambrian zabriskie quartzite indicate an original isopach pattern much less regular than once supposed and thus less useful as an indicator of the magnitude of lateral slip on the death valley fault system but within a wide range of possible restorations the isopachs conform with the locations of proterozoic highlands and basins the zabriskie quartzite being mature laterally persistent and unlike the underlying formations devoid of evidence of rifting apparently records the beginning of the passive stage of the developing cordilleran miogeocline

mixed layer shear generated by wind stress in the central equatorial pacific abstract sixteen months of wind and current profile observations in the central equatorial pacific show the response of the upper ocean shear to local wind forcing the shear at the ocean surface is significantly correlated with the wind stress in direction but not in magnitude implying that the vertical eddy viscosity coefficient is proportional to the square of the wind speed or to the stress using this variable eddy viscosity coefficient in stommel s model of the equatorial undercurrent we calculate shears in the mixed layer that compare well with the observations the flow is downwind on the equator and tends toward and ekman spiral off the equator

glacial and syntectonic sedimentation the upper proterozoic kingston peak formation southern panamint range eastern california a sedimentological stratigraphic study of the upper proterozoic kingston peak formation in the southern panamint range shows that it was deposited under glacial conditions with contemporaneous volcanism and tectonic activity evidence for glaciation rests primarily upon 1 the homogeneity thickness and lateral extent of two diamictite units 2 the facies association of the diamictite and 3 presence of striated stones and dropstones within the formation elsewhere in the death valley area in the panamint range pillowed basalt interbedded with diamictite demonstrates synchronous subaqueous volcanism lower kingston peak units rest on a variable substrate and locally overlap faults indicating tectonism prior to deposition tectonism during kingston peak deposition is inferred from abrupt thickness changes and buried faults sedimentation was chiefly on a submerged continental platform and locally terrestrial during a period of incipient rifting two ice advances are recorded with associated sea level fluctuations the formation thickens northward from 40 to about 1 200 m over 40 km initial sediments were fine grained and in basins a few kilometres across nearby islands provided coarse debris overlying sandstone and conglomerate indicate regression predominantly massive diamictite as much as 450 m thick and interpreted as lodgment till or glacioma rine sediment records the first ice advance a northward increase in diamictite thickness decrease in clast size and facies change from diamictite to argillite and graywacke suggest a southern source overlying laminated limestone marks a transgression succeeding interbedded sandy limestone thick bedded graywacke and parallel laminated siltstone and sandstone double in thickness over a few kilometres demonstrating local subsidence and renewed terrigenous input trough cross laminated arkosic sandstone and conglomerate overlain by predominantly massive diamictite as much as 190 m thick with a locally erosive base represent glaciofluvial deposits and lodgment till and record the second ice advance

local atmospheric forcing during the coastal ocean dynamics experiment 1 a description of the marine boundary layer and atmospheric conditions over a northern california upwelling region as part of the coastal ocean dynamics experiment code meteorological instruments were deployed on buoys and at coastal stations and instrumented aircraft flights and coastal soundings were made to study the three dimensional structure of the marine boundary layer over the continental shelf off northern california during the 1981 and 1982 upwelling seasons these measurements show that after the atmospheric spring transition the airflow in the marine layer is dominated by the north pacific high and the surface wind field over the shelf is characterized by periods of strong 7 15 m s upwelling favorable alongshelf winds lasting for up to 30 days interrupted by shorter periods of much weaker winds directed either equatorward or poleward these periods of weak or reversed winds typically last several days and are called wind relaxations even though they are primarily associated with coastally trapped perturbations of the marine layer along the central and northern california coast and not with a large scale weakening of the north pacific high the atmospheric boundary layer measurements made in code suggest a simple conceptual model which can explain much of the physiology or structure of the marine layer and associated surface wind field during periods of persistent upwelling favorable winds during these periods which represent the quasi steady state regime during the upwelling season the inversion base of the marine layer drops eastward toward the coast until it intersects the coastal mountain range at a height of several hundred meters and the associated thermal wind produces an alongshelf wind jet which has a maximum speed just below the inversion base turbulent mixing tends to homogenize any stratification in the marine layer beneath the jet and couple the jet to the ocean surface producing strong upwelling favorable winds over the shelf day night heating cooling over the narrow coastal strip beneath the marine layer generates a weak cross coast secondary circulation which causes the core of the alongshelf jet to drop in elevation and shift onshore this diurnal change in the marine layer structure explains both the daytime acceleration of the surface winds observed over and near the coast and its offshore decay and the associated offshore increase in the subdiurnal alongshelf wind thus the quasi steady component of the wind stress has a significant curl over the inner shelf during periods of active upwelling this mean summer atmospheric boundary layer regime is occasionally interrupted by synoptic and or mesoscale events or anomalous conditions analysis of the code observations suggests five types of events two primarily synoptic scale conditions which lead to stronger than normal upwelling favorable winds over the shelf and three primarily mesoscale events which lead to wind relaxation about half of the wind relaxation events observed in 1981 and 1982 are believed to be associated with either coastal trapped gravity currents or internal kelvin waves which propagate north ward in the marine layer along the central and northern california coastal mountain range

neoproterozoic tectonics of australia antarctica and laurentia and the 560 ma birth of the pacific ocean reflect the 400 m y pangean supercycle unequivocal evidence for the proterozoic reconstruction of australia antarctica and laurentia remains elusive although various authors have interpreted sedimentary and igneous events in terms of initial neoproterozoic rifting and final neoproterozoic cambrian drifting the synchronous rifting and drifting reflect the tectonics of a late neoproterozoic pangea east gondwanaland and laurentia that amalgamated along the mozambiquean belt 720 ma and broke up at 560 ma by growth of the paleo pacific and lapetus oceans in this paper these events are interpreted as part of a 400 m y supercycle comparable to the 320 ma amalgamation of pangea a and its 160 ma breakup during supercycle a 320 ma to present events near the end of the cambrian 500 ma in east gondwanaland included epeirogenic uplift of cratons shown by widespread k ar and apatite fission track dates and the inception of quartz turbidite fans intense deformation and intrusion by granite of the antarctic and south eastern australian mar

direct evidence for an ekman balance in the california current moored acoustic doppler current profiler velocity estimates and buoy wind observations made during a period of moderate southward winds were used to test the ekman balance at a site in the california current as in prior studies the wind driven flow was separated from the total flow by subtraction of a deep reference current the wind driven flow was shown to be in an ekman balance on daily timescales over a period of several months the mean observed transport was to the right of the wind and agreed to within 3 in magnitude and 4 in phase with the predicted ekman transport although the error bar was about 20 the mean velocity profile was a smooth spiral qualitatively similar although flatter than the theoretical ekman spiral prom the observed mean momentum balance profiles of the turbulent stress and eddy viscosity were inferred eddy viscosity estimates within the wind mixed layer were o 100 cm2 s 1

forced oscillations near the critical latitude for diurnal inertial resonance abstract oscillations at or close to the inertial frequency are widely observed in shelf seas where frictional damping is weak in the vicinity of latitudes 30 n and s such motions may become significantly enhanced by a resonance in which the local inertial frequency coincides with that of diurnal forcing under these conditions regular daily variations in wind stress tend to produce large anticyclonic motions that may extend throughout the water column as shown in the analytical theory of craig here the authors examine new observations from a location close to the critical latitude on the namibian shelf in the southern hemisphere the measurements cover almost the full depth 175 m of the water column by using upward and downward looking adcps suspended in midwater the observed flow involves a steady drift to the north maximum 11 cm s 1 at 40 m but the kinetic energy budget is dominated by anticyclonic circular motions with speeds in the surface layers exceeding 40 cm s 1 at times comparably e

cap carbonate platform facies model noonday formation se california the neoproterozoic outcrop belt of the death valley region california preserves an oblique cross section of the noonday formation a mixed carbonate siliciclastic platform that hosts distinctive basal ediacaran cap carbonate affiliated sedimentary structures stromatolite textures and 13 c carb values the noonday platform encompasses two depositional sequences that reveal two cycles of relative sea level change within strata conventionally considered to record a single rapid postglacial sea level rise in updip localities facies of the first depositional sequence record the transition from a carbonate ramp to a stromatolite bearing tubestone textured reef rimmed platform downdip localities seaward of the reefal escarpment variably preserve a thin and condensed onlapping foreslope wedge base level fall exposed the reef crest to karstic dissolution and propagated submarine incised valleys into the seaward margin of the reef overlying strata record the backfilling of a submarine incised valley and reestablishment of a back stepping carbonate dominated ramp prior to a second subaerial exposure event that defines the contact between the noonday and johnnie formations we address the relative contributions of syndepositional tectonism and recovery from low latitude deglaciation in dictating noonday platform architecture and the intra noonday formation sequence boundary noonday formation deposition coincided with extension of the laurentian margin during disaggregation of the rodinian supercontinent within this framework previous work has suggested that the intra noonday formation sequence boundary records growth faulting that reinforced differential topography uplifting reef rimmed horsts exposing the reef crest to karstic dissolution and downdropping grabens however we trace the intra noonday formation sequence boundary seaward of the reef crest and demonstrate that for a time wave base was situated downdip of the reef escarpment on putatively downdropped fault blocks thus if the noonday margin were undergoing extension then the creation of the intra noonday formation sequence boundary required a concomitant decrease in accommodation due perhaps to postglacial isostatic uplift attendant with low latitude deglaciation we speculate that noonday formation sequence architecture records 1 immediate deglacial flooding 2 shoaling and exposure due to isostatic rebound induced by either a hiatus in meltwater flux or rapid ice sheet collapse against a background of global deglaciation and 3 resumed flooding following complete deglaciation as rift related tectonism could amplify or counter glacial isostasy inferences of the amplitude of local postglacial sea level change will require robust estimates of syndepositional extension across the noonday margin

diurnal variability in currents and temperature on the continental shelf between central and southern california 1 long time series are used to describe the diurnal variability in the meteorological and astronomical tidal forcing and the temperature and current response on the continental shelf of california between port san luis and port hueneme spectral characteristics are used to attribute the response to each of the forcing mechanisms the diurnal temperature field is decomposed into two dominant vertical modes a surface enhanced mode is coherent with the meteorological forcing suggesting that it is a direct response to local heating and wind forcing the amplitude of the second mode is maximum at middepth spectra of this mode exhibit multiple peaks at frequencies corresponding to the astronomical tidal forcing the phase difference between the middepth mode and the tidally dominated sea level is not consistent across the region we conclude that this mode is a localized baroclinic response to the astronomical tidal forcing the diurnal velocity field is dominated by a clockwise component at the surface this component is coherent across the study region and it is also coherent with the diurnal wind stress suggesting that it is a direct response to the diurnal heating and wind forcing coherence with the surface enhanced temperature mode further confirms this a weaker barotropic counterclockwise component is also present in the diurnal velocity field spectra of this component exhibit multiple peaks at periods corresponding to the astronomical tidal forcing the phase difference between this component and the surface elevation varies little between the observational sites we conclude that this velocity component represents a barotropic response to astronomical forcing that is coherent over the study area

braided fluvial to marine transition the basal lower cambrian wood canyon formation southern marble mountains mojave desert california abstract the lower cambrian wood canyon formation recognized over a 39 000 km2 belt through the southern great basin and mojave desert was examined in the southern marble mountains eastern mojave desert southeastern california there it crops out as a well exposed 90 130 m thick feldspathic sandstone nonconformably overlying proterozoic basement previous investigators have suggested a tide dominated nearshore shallow marine origin for the entire unit in the eastern mojave based on broad scale stratigraphic trends and localized fossil occurrences in the upper member of the formation in contrast to a regional approach the present study uses a detailed lithofacies analysis in a smaller study area to suggest that a fluvial to marine transition occurs within these strata the middle and upper members of the wood canyon formation are recognized in the southern marble mountains and are divisible into six distinct lithofacies that possess gradational contacts where exposed cross stratified sandstone facies a mediumpebble conglomerate facies b planar stratified sandstone facies c sandstone and thin mudstone facies d mudstone with intercalated sandstone facies e and horizontally laminated siltstone facies f facies a d contained within the middle member comprise the bulk of wood canyon sediments and record the depositional characteristics of a transition zone from a distal alluvial braid plain to a tidally influenced fluvial dominated braid delta complex cross stratification in the braid plain sediments displays a strongly unimodal pal ocurrent pattern suggestive of downstream migrating sinuous crested megaripples braid delta sediments however show a more dispersed paleocurrent pattern and contain a sparse trace fossil assemblage a change from fluvial dominated to marine dominated processes is recorded in upper member rocks facies e and f facies e contains many of the traits characteristic of a low to mid tidal flat sequence such as coarsely interlayered bedding flaser and lenticular bedding microripple marks and locally abundant rusophycus and planolites trace fossils facies f which dominantly consists of horizontally laminated siltstone is interpreted as the product of an estuarine lagoon that developed behind and within a discontinuous barrier of stranded braid bars

theory of radar imaging of internal waves radar images taken over ocean areas in particular those obtained by the synthetic aperture radar sar onboard the american seasat satellite in 19781 2 sometimes show features that seem to be surface manifestations of oceanic internal waves3 11 here i present a theory explaining the large radar signatures of internal waves in which the imaging is attributed to variations in the short scale surface roughness induced by current variations associated with internal waves

anisotropic response of surface circulation to wind forcing as inferred from high frequency radar currents in the southeastern bay of biscay the short term less than 20 days response of surface circulation to wind has been determined in waters of the southeastern bay of biscay using wind impulse response time domain and transfer frequency domain functions relating high frequency radar currents and reanalysis winds the response of surface currents is amplified at the near inertial frequency and the low frequency and it varies spatially the analysis indicates that the response of the ocean to the wind is slightly anisotropic likely due to pressure gradients and friction induced by the bottom and coastline boundaries in this region thus the transfer function at the near inertial frequency decreases onshore due to the coastline inhibition of circularly polarized near inertial motion in contrast the low frequency transfer function is enhanced toward the coast as a result of the geostrophic balance between the cross shore pressure gradient and the coriolis forces the transfer functions also vary with season in summer the current response to wind is expected to be stronger but shallower due to stratification in winter the larger mixed layer depth results in a weaker but deeper response the results obtained are consistent with the theoretical description of wind driven circulation and can be used to develop a statistical model with a broad range of applications including accurate oceanic forecasting and understanding of the coupled atmosphere ocean influence on marine ecosystems

anisotropic response of surface currents to the wind in a coastal region analysis of coastal surface currents measured off the coast of san diego for two years suggests an anisotropic and asymmetric response to the wind probably as a result of bottom coastline boundary effects including pressure gradients in a linear regression the statistically estimated anisotropic response explains approximately 20 more surface current variance than an isotropic wind ocean response model after steady wind forcing for three days the isotropic surface current response veers 42 86 28 to the right of the wind regardless of wind direction whereas the anisotropic analysis suggests that the upcoast onshore wind stress generates surface currents with 10 86 48 71 86 38 to the right of the wind direction the anisotropic response thus reflects the dominance of alongshore currents in this coastal region both analyses yield winddriven currents with 3 5 of the wind speed as expected in addition nonlinear isotropic and anisotropic response functions are considered and the asymmetric current responses to the wind are examined these results provide a comprehensive statistical model of the wind driven currents in the coastal region which has not been well identified in previous field studies but is qualitatively consistent with descriptions of the current response in coastal ocean models

west florida shelf response to upwelling favorable wind forcing kinematics the barotropic responses of the west florida continental shelf to idealized upwelling favorable alongshore and offshore wind stresses are studied using the three dimensional time dependent primitive equation princeton ocean model pom when forced with uniform winds the shelf circulation evolves quickly to a quasi steady state a southeastward alongshore wind lowers sea level along the coast and drives a southeastward coastal jet with a relatively weak northwestward return flow farther offshore a southwestward offshore wind lowers sea level along the west florida coast and raises sea level along the panhandle coast two independent circulation gyres are set up in association with these regionally different sea level distributions an anticyclonic gyre off the west florida coast consisting of a southeastward coastal jet and a broad return flow over the middle shelf and a cyclonic gyre off the panhandle coast consisting of a strong northwestward coastal jet and an adjacent narrow southeastward undercurrent these gyres are separated by the big bend region in both cases alongshore and offshore wind forcing the circulations are fully three dimensional with opposing surface and bottom boundary layer flows accounting for the across shelf transports the shapes of the coastline and the isobaths are important determinants of the shelf wide responses several locally maximum upwelling regions are identified for geometrical reasons these include the panhandle coast south of apalachicola bay the west florida coast south of tampa bay along the florida keys and at the shelf break where topographic rossby waves are evident

wind driven ocean currents and ekman transport oceanographic engineering of the woods hole oceanographic institution and the massachusetts institute of technology woods hole ma 02543 oceanographers have long sought to verify the theoretical ekman transport relation which predicts that a steady wind stress acting together with the coriolis force will produce a transport of water to the right of the wind in situ measurements of wind and ocean currents provide a detailed view of this phenomenon by separating the wind driven current from the measured total current and by averaging over a long record it is found that the observed transport is consistent with theoretical ekman transport to within about 10 percent in this case the wind driven transport is strongly surface trapped with 95 percent occurring in the upper 25 meters as a result of fair summer weather

active synsedimentary tectonism on a mixed carbonate siliciclastic continental margin third order sequence stratigraphy of a ramp to basin transition lower sekwi formation selwyn basin northwest territories canada the lower part of the early cambrian sekwi formation in the selwyn basin of the northwest territories canada is composed of two regional unconformity bounded sequences s0 and s1 which record the first widespread carbonate deposition during the initial palaeozoic transgression onto the western margin of laurentia these early cambrian sequences are unique to the western north american cordillera representing the only record of primarily deep water deposition on a tectonically active mixed carbonate siliciclastic ramp during this period more specifically the geometry of the sekwi ramp changed during deposition of s0 and s1 from a shallowly dipping homoclinal ramp during the s0 transgressive systems tract to a steeply dipping tectonically modified ramp during the early highstand systems tract of s0 the steeply dipping ramp profile of s0 was preserved into the early transgressive systems tract of s1 the sekwi ramp returned to a gently sloping ramp during the late highstand systems tract of s1 and remained so throughout the remainder of sekwi deposition the evolving shape of the sekwi ramp is attributed to syndepositional down to the basin faulting during deposition of both s0 and s1 and is recorded by i the westward thickening irregular geometries of s0 and s1 ii geographical restriction of deep water facies including sediment gravity flow deposits iii the presence of large allochthonous blocks and iv the clast composition of sediment gravity flow deposits sediment gravity flow deposits play an unusually important role in the sequence stratigraphic interpretation of the lower sekwi formation as they delineate depositional packages including the maximum flooding zone the transitions between portions of systems tracts and the inferred locations of syntectonic extensional faults syntectonic faults increased accommodation basinward of an extensive ooid shoal complex that developed along the sekwi ramp crest greatly influencing sequence geometry and initiating the downslope motion of sediment gravity flows the syndepositional faulting probably was a continuation of extension that began during the latest neoproterozoic rifting of western laurentia the composition of sediment gravity flow deposits track changing accommodation space on the lower sekwi ramp and can be used to differentiate systems tracts that probably were related more to tectonism than eustasy

stratigraphy sedimentology and isotopic geochemistry of australian neoproterozoic postglacial cap dolostones deglaciation delta 13 c excursions and carbonate precipitation abstract thin d13c excursions in the geologic record they are interpreted to record a brief postglacial anomaly in ocean chemistry in australia the marinoan varanger equivalent 600 ma cap dolostone units exhibit many of the characteristics displayed by such deposits elsewhere around the globe including fine grained dolomitic mineralogy lateral persistenc at basinal scales thin laminae graded beds intervals with abundant marine cements crystal fans and a distinctive negative d13c isotopic signature of up to 5 pdb on the basis of these features the australian examples are interpreted here to be deeper water deposits below storm wave base resulting from an anomalous flux of inorganic carbonate to the sea floor during postglacial transgression detailed isotopic analysis of australian cap dolostones indicates d13c values ranging from 1 to 5 and gen rally becoming more depleted in 13c upsection trace element data indicate some diagenetic stabilization but textural evidence and the presence of similar profiles in different basins argue against a pervasive recrystallization event the range in d13c values between sections as well as more negative 13c values appear to correlate with greater paleobathymetry within basins this implies either 1 only partial preservation of the complete oceanic variation of d13c or 2 precipitation of this peculiar facies owes its genesis to basinal specific oceanographic processes such as proximi y of a given section to a postglacial upwelling zone in the later case d13c values would not represent whole ocean values stratigraphic constraints and paleoenvironmental interpretations suggest that much of this excursion lies within the geologically brief period of postglacial transgression this implies that the cause s of d13c variation likely operated on time scales significantly less than the residence time of carbon in the oceans 105 yr the continent wide and perhaps global nature of cap dolostones indicates that large volumes of carbonate were precipitated during the postglacial transgressive period such large scale carbonate precipitation over the hypothesized short time interval of postglacial transgression must have caused or have been the product of profound changes in the carbon cycle and global climate at tha time similar evidence for transgression and increased carbonate deposition in the holocene are attributed to the changing basin shape and ph of the oceans the coral reef hypothesis of berger 1982 cap dolostones may record a proterozoic equivalent of this process with the substitution of abiotic carbonate precipitation for skeletal precipitation by reef organisms

integrated ediacaran chronostratigraphy wernecke mountains northwestern canada abstract terminal neoproterozoic ediacaran ca 600 543 ma strata of the upper part of the windermere supergroup are well exposed in the mackenzie mountains and the wernecke mountains of northwestern canada windermere strata in the mackenzie mountains contain an exceptional ediacaran biostratigraphic and isotopic c and sr record while the sequence stratigraphic record is subtle throughout this predominantly deep water succession coeval strata in the wernecke mountains can be correlated with the succession in the mackenzie mountains on a formational level in contrast to the deep water setting of the mackenzies succession the werneckes succession preserves a predominantly shallow water succession amenable to detailed sequence stratigraphy integrated lithostratigraphy chemostratigraphy biostratigraphy and sedimentology partitions the wernecke mountains succession into five depositional sequences and constrains correlation with strata in the mackenzie mountains the siliciclastic and carbonate sediments deposited along the margin of the proto pacific ocean record accumulation in continental slope neritic and terrestrial paleoenvironments distinctive temporal chemostratigraphic and biostratigraphic attributes allow these strata to be correlated with other ediacaran successions worldwide integrating sequence stratigraphy with these attributes is a robust yet under utilized correlation tool and is a step toward erecting a more detailed working neoproterozoic chronostratigraphy

lack of impact of hurricane michelle on tidal flats andros island bahamas integrated remote sensing and field observations abstract major storms commonly are cited as important geomorphic and sedimentologic agents and their significance is perhaps most emphatically noted in interpretations of modern and ancient tidal flats the purpose of this study was to assess the impact of hurricane michelle on the carbonate tidal flats of andros island bahamas by coupling remote sensing data and field observations although regional modis remote sensing data reveal that the passage of hurricane michelle suspended sediments across the shallow bank integrating ultra high resolution remote sensing data with field observations demonstrates that the hurricane had almost no impact on the andros island tidal flats this lack of impact is surprising because the storm still had hurricane force winds as it passed immediately over some of the focal areas with this hurricane storm strength and intra storm interval were probably not limiting factors instead several influences combined to minimize the storm s impact on both sedimentation and erosion including the low level of water on the bank resulting from ebb tides and in the northwestern area from offshore storm winds and the short duration of the storm resulting from its high forward velocity given the apparent prevalence of widespread storm effects on ancient tidal flats but the spatially limited major geomorphic impacts of storms on many modern systems we suggest that the geologic evolution and preservation of ancient tidal flat successions may have been shaped by mega storms that simply cannot form in the present global climate nonetheless understanding tidal flat dynamics and changes on human timescales will require continued monitoring and assessment of low impact storms such as michelle as well the more sensational hurricanes that produce widespread death destruction and deposition

gradual establishment of iapetan passive margin sedimentation stratigraphic consequences of cambrian episodic tectonism and eustasy southern appalachians the middle to upper cambrian conasauga group of the southern appalachians constitutes part of the thick pericratonic cambro ordovician sauk sequence that represents the interplay between an extensive carbonate platform to the east and a deeper water intrashelf shale basin to the west the conasauga group consists of a series of interfingering carbonate and shale formations the shales represent deeper water deposition 50 m and the carbonates show evidence for gradual shoaling through aggradation and progradation from deeper water to shallow water the upper parts of the craig limestone member rogersville shale and the maryville limestone both middle cambrian contain evidence for subaerial exposure of subtidal sediments followed by platform drowning following platform exposure that shot down carbonate production a large relative sea level rise driven by an increase in the rate of subsidence led to platform reinundation but was rapid enough to drown the carbonate platform flooding was sufficient to allow deeper water basinal shales to onlap the drowned platform changes in the rate of subsidence driven by thermal cooling of the lithosphere sediment loading and or regional extension were probably responsible for cyclic sedimentation even though burial curves suggest gradual thermal subsidence through this time lithofacies patterns and the regional tectonism reviewed herein suggests that the iapetan margin was not fully stabilized subsiding uniformly spatially and temporally a true passive margin until the late cambrian critical stratigraphic studies of other cambrian and younger passive margins may reveal comparable anomalies related to similar jerky subsidence patterns

near surface measurements of quasi lagrangian velocities in open water abstract near surface water velocities have been measured in the coastal zone of lake huron and cape cod bay by tracking drifters and drogues using acoustic travel time and compass sighting techniques the near surface current defined as the velocity of near surface drifters and drogues relative to a drogue set at 1 8 m varied on the depth scale on the order of 1 m and was directed nearly parallel to the wind and to predominant wave propagation velocity velocity profiles were logarithmic with depth to order 1 m depth and realistic values of stress were calculated using a law of the wall formula and a karman s constant of 0 4 inferred roughness lengths were of the order of 30 cm anomalously high values of wind stress were inferred from velocity profiles observed during conditions of light wind and steady swell these may be due to the similarity of stokes drift distribution to turbulent shear flow profiles

early opening of australia and antarctica new inferences and regional consequences abstract both continental margins of australia and antarctica exhibit a very clear gravity anomaly on the satellite free air gravity data the detailed sinuosity of these first order conjugate features matches perfectly suggesting that they are the signature of the initial continental breakup and mark the ocean continent boundary another weaker still clearly deciphered pair of symmetrical gravity anomalies is identified oceanward these anomalies are considered as pseudo isochrons f and g and tentatively dated 128 and 94 ma precise reconstructions of pseudo isochron f are achieved over three sections of the margin denoting the relative motion of australia and east antarctica the polda block and east antarctica and tasmania and west antarctica the polda block and tasmania are transient micro continents tasmania and australia are reconstructed to align their linear eastern margin the eastern margins of reconstructed australia tasmania and west antarctica on one hand the western margin of reconstructed lord howe rise and campbell plateau on the other hand fit a small circle of radius 15 which suggests a transform motion between 128 and 83 ma along this plate boundary the reconstruction predicts a gap between east and west antarctica probably filled by non cratonic continental crust compressively deformed and thickened by the sw motion of east antarctica and participating to the formation of the trans antarctic mountains the initial extension between australia and east antarctica may be related to the inception of the kerguelen hotspot 1000 km to the west the different rheology of cratons and orogenic terranes has played a role in the style and localization of both extensional and compressional deformations

deep valley incision in the terminal neoproterozoic ediacaran johnnie formation eastern california usa tectonically or glacially driven neoproterozoic sedimentary successions worldwide display evidence for multiple low latitude glacial events and continental rifting episodes related to the fragmentation of the supercontinent rodinia in death valley eastern california these events are represented by two intervals of glacial diamictite and two episodes of synsedimentary extensional faulting in the kingston peak formation deep incised valleys of uncertain origin in the upper johnnie formation approximately 1 km stratigraphically above the kingston peak formation may provide evidence either for a third glacial episode or for an additional tectonic event eleven measured sections indicate that one of these incised valleys is 120 m deep and approximately 2 5 km wide detailed mapping of the paleovalley has revealed the presence of numerous synsedimentary normal faults that offset underlying units but are capped by incised valley breccia abrupt incision occurs across buried normal fault scarps several large olistoliths up to 15 m in diameter are located near the fault scarps and the average clast size of the breccia decreases in general away from mapped normal faults incised valley clasts are derived exclusively from underlying neoproterozoic formations nearly entirely from the johnnie formation itself there is no evidence for direct glacial influence as no striated clasts or dropstones were observed the absence of glacial indicators coupled with the strong correlation between incision and synsedimentary normal faulting imply a primary tectonic control on valley formation the valley represents a significant tectonic reactivation of the neoproterozoic passive margin similar to early paleozoic extensional events in the northern cordillera of western north america 2005 elsevier b v all rights reserved

poleward propagating subinertial alongshore surface currents off the u s west coast 1 the network comprising 61 high frequency radar systems along the u s west coast uswc provides a unique high resolution and broad scale view of ocean surface circulation subinertial alongshore surface currents show poleward propagating signals with phase speeds of o 10 and o 100 300 km d 1 that are consistent with historical in situ observations off the uswc and that can be possibly interpreted as coastally trapped waves ctws the propagating signals in the slow mode are partly observed in southern california which may result from scattering and reflection of higher mode ctws due to curvature of shoreline and bathymetry near point conception california on the other hand considering the order of the phase speed in the slow mode the poleward propagating signals may be attributed to alongshore advection or pressure driven flows a statistical regression of coastal winds at national data buoy center buoys on the observed surface currents partitions locally and remotely wind forced components isolates footprints of the equatorward propagating storm events in winter off the uswc and shows the poleward propagating signals year round

observations of the velocity response to wind forcing in the upper ocean the response of the horizontal velocity field to forcing by the local wind was observed in the upper 150 m of the ocean by profiling with vector measuring current meters from the research platform flip as it drifted off the coast of california in january 1977 in the mixed layer approximately 50 m deep motion at frequencies lower than 0 1 cph was coherent with the wind stress rotary cross spectral analysis showed that the shear in the surface layer was related to the local wind stress and that the structure of the response at low frequencies was similar to but did not agree completely with the predictions of simple linear eddy viscosity models

decomposing observations of high frequency radar derived surface currents by their forcing mechanisms decomposition techniques and spatial structures of decomposed surface currents 1 surface current observations from a high frequency radar network deployed in southern san diego are decomposed according to their driving forces pure tides and their neighboring off band energy local winds and low frequency several superposed ocean responses are present as a result of the complicated bottom topography and relatively weak winds off southern san diego as opposed to coastal regions where circulation can be explained by a dominant forcing mechanism this necessitates an application of a statistical decomposition approach surface currents coherent with pure tides are calculated using harmonic analysis locally wind driven surface currents are estimated by regression of observed winds on observed surface currents the dewinded and detided surface currents are filtered by weighted least squares fitting assuming white noise and three colored signal bands low frequency band less than 0 4 cycles per day and near tidal peaks at the diurnal k1 and semidiurnal m2 frequencies the spatial and temporal variability of each part of the decomposed surface currents is investigated in terms of ocean response to the driving forces in addition the spatial correlations of individual components exhibit gaussian and exponential shapes with varying decorrelation length scales

three dimensional wind driven flow in an elongated rotating basin abstract the wind driven circulation in lakes lagoons estuaries or coastal embayments is described with a linear steady three dimensional barotropic model in an elongated basin of arbitrary depth distribution on an f plane with rotation the vertically averaged velocity scales with the ekman depth rather than the maximum depth h0 as in the case without rotation near the closed ends of the basin the flow turns in viscous boundary layers because the length of the turning areas depends on the sign of the bottom slope and on the ratio of the ekman depth to h0 there is a striking contrast between the turning areas on either side of an observer looking toward the end of the basin in the northern hemisphere the turning area on the left is broad of order 1b where b is the basin half width the turning area on the right is narrow of order b and dynamically equivalent to the western boundary current in models of the wind driven ocean circulation ekman solutions are used to describe the ve

earth s oldest jellyfish strandings a unique taphonomic window or just another day at the beach discoidal macrofossils reported herein from the lower cambrian zabriskie quartzite great basin western united states record the oldest phanerozoic medusozoan body fossils as well as the oldest medusozoan stranding event on record moreover these fossils provide evidence of a significant shift in the taphonomic mode characteristic of preservation of nonmineralized taxa in coarse grained siliciclastic successions near the onset of the phanerozoic taphonomic and sedimentological evidence recorded by these and younger examples of stranded cambrian medusae is consistent in suggesting that several of the requirements for preservation of these fossils were holdovers from the ediacaran period including the presence of microbial mats and a lack of carcass disturbance by scavenging and or bioturbating taxa to shed further light upon the taphonomic factors necessary for the preservation of cambrian medusae we compared the biostratinomy and sedimentology of cambrian medusa strandings to those of ediacara biota assemblages from lithologically similar successions we find key secular disparities in the taphonomic histories of these two types of fossil assemblage inconsistencies between the preservational styles characteristic of fossil assemblages preserved in sandstone lithofacies on each side of the precambrian cambrian boundary are explained by a considerable change in the preferred depositional setting in which these macrofossil assemblages are preserved thus rather than documenting a single taphonomic continuum through the precambrian cambrian transition the zabriskie and younger medusozoan body fossil assemblages record the advent of an entirely new yet still very rarely exploited taphonomic window exclusive to the cambrian period

late precambrian tectonism in the kingston range southern california speculation on the early history of the cordilleran geosyncline of north america has relied in part on interpretation of the tectonic setting of the precambrian pahrump group recent mapping in the kingston range resulted in new data to aid our speculation specifically precambrian tectonic events involving folding and later low angle normal faulting affected the crystal spring formation beck spring dolomite and lower part of the kingston peak formation unconformably overlying these units is a relatively undeformed conglomerate diamictite occurs both above and below the unconformity hence cordilleran wide correlations of the kingston peak formation based on diamictite require reassessment the nature of boundaries localized deformation and outcrop distribution of the pahrump group suggest that these rocks may be preserved in transtensional basins associated with strike slip faulting possibly occurring during development of the late precambrian continental margin

extending the western north american proterozoic and paleozoic continental crust through the mojave desert data supporting the existence of proterozoic basement in the central and western mojave desert include u pb zircon geochronology and nd sr and pb isotopic values of quartzofeldspathic gneisses detrital zircon provenance ages and the presence of basement clasts in paleozoic and mesozoic conglomerates these data corroborate existing isotopic data from mesozoic and tertiary intrusive rocks that suggest involvement of proterozoic crust in their genesis exposures of proterozoic basement and late proterozoic and paleozoic transitional miogeoclinal cratonal facies trends in the central and western mojave desert consistently imply that cratonal north america continues westward uninterrupted through this region to the san andreas fault these data place geographic limits on the position of several pre tertiary tectonic elements speculated to exist in the mojave desert

early cambrian metazoans in fluvial environments evidence of the non marine cambrian radiation davies and gibling 2012 1 raise concerns that sediments hosting trace fossils in the early cambrian middle member of the wood canyon formation which we have interpreted as fluvial may be marine in origin they suggest that in the absence of body fossils or specific minerals it may not be

modeling ice dynamics of coastal seas a coupled sea ice barotropic ocean model with a 1 km resolution and a seaward domain of 200 km quantifies three coastal processes coupling of ice motion to wind driven coastal currents ice thickness redistribution under compaction at the coast and formation of coastal shear zones the model consists of an ice momentum balance mass concentration and two parameter ice thickness distribution and equations for horizontal water motion and continuity using vertical structure functions an appropriate constitutive law appears to be a hardening plastic based on qualitative observations from alaskan continental shelves for first year sea ice strength is taken to be proportional to the square of ice thickness a north wind example of 10 m s with the coastline to the west shows the depth dependence of rotational shear in the sea ice ocean boundary layer and sea surface tilt which contributes an alongshore slope current there is slight convergence of sea ice over the shelf a coastal shear zone of 4 km and an alongshore ice speed seaward of the shear zone of 6 of the wind speed caused by the combination of an under ice shear layer and an alongshore slope current for an onshore wind ice is near free drift at 3 of the wind seaward of a ridging front which propagates seaward a square dependence of ice strength on thickness is required for the rubble field to approach a limiting thickness consistent with observations the hardening plastic interpretation of the rubble field has the stress state at the yield limit in contrast with a rigid plastic of high constant strength that yields only at the coast we conclude that 1 ice thickness motion feedback is important on scales less than 10 km 2 the observational base to discriminate between mesoscale constitutive laws is not yet available and 3 the relation of ice velocity to wind stress is variable because the ocean slope current responds only to the alongshore component of the wind

resonant ocean current responses driven by coastal winds near the critical latitude the currents forced by wind stress near the critical latitude 30 n or 30 s appear enhanced as a result of the combination of natural modes of ocean currents e g near inertial motions and diurnal land sea breeze driven currents here we assess the wind current transfer function derived from observations of coastal surface currents and surface winds off the u s west coast 32 n to 47 n as a function of the latitude alongshore direction and frequency we compare the transfer functions at the diurnal frequency derived from observations and two analytical models e g the ekman model and a near surface averaged ekman model the amplitude of the data derived transfer function decreases with increasing distance from the critical latitude and its argument varies nearly within the range estimated from two analytical models our results confirm that the resonant wind current responses near the critical latitude are 8 to 12 times stronger than the purely diurnal land sea breeze forced currents in other latitudes

combined flow origin of edgewise intraclast conglomerates sellick hill formation lower cambrian south australia unusually thick coarse grained edgewise intraclast conglomerates occur at eight or more horizons within subtidal nodular and ribbon bedded wackestones and packstones of the lower cambrian sellick hill formation south australia the intraclast beds are flat based and laterally discontinuous forming bar like structures that must have exhibited bathymetric relief of as much as 1 m the internal fabrics of these beds are variable thinner beds are dominated by flat lying intraclasts thicker beds contain both chaotic randomly oriented steeply inclined intraclasts and clusters of fan shaped vertically stacked edgewise intraclasts the sellick hill formation intraclast conglomerates are inferred to have been formed by intense storm generated combined flows on a broad subtidal carbonate ramp superimposition of wave induced oscillatory motions on geostrophic bottom flows during large storms generates short lived but exceptionally high instantaneous shear stresses in the bottom boundary layer entrainment of the relatively large intraclasts occurs through sliding rather than pivoting edgewise fabrics are a product of asymmetric acceleration and deceleration of intraclasts during passage of waves and the chaotic nature of collisions between intraclasts moving within the boundary layer collisions between intraclasts impart a rotating moment causing intraclasts to tip up during maximum fluid shear stress lodgement or packing of clasts in vertical or steeply inclined positions occurs within scours where intraclasts can wedge between other vertically inclined clasts or where intraclasts are pinned in steep orientations by collisions with shallowly inclined intraclasts differential erosional resistance of the intraclast deposits probably led to the development of sharp lateral changes in thickness the sellick hill formation intraclast conglomerates record erosion and reworking of subtidal subfairweather wave base environments by exceptionally intense and presumably rare storm flows the intraclast horizons represent a substantial loss in stratigraphic resolution due to widespread erosion of the ramp

high frequency response of wind driven currents measured by drifting buoys and altimetry over the world ocean 1 we investigate the wind driven current response over the world ocean using svp drifting buoys ers 1 and ers 2 and topex altimetry data and ecmwf wind stress fields wind driven ageostrophic currents are estimated from drifting buoys by removing altimetry deduced geostrophic currents from observed drifting velocities removing the geostrophic signal enhances the coherence with wind stress at periods longer than 10 days for superinertial periods lower than 20 days a two parameter i e angle and amplitude model is fitted to the isolated ageostrophic signal to study the upper ocean response to surface wind stress in that frequency band the model which can explain up to 30 of the variance in some areas indicates that the currents spiral to the right left of the wind with depth in the northern southern hemisphere in agreement with the ekman theory the absolute value of the angle parameter is found to exhibit significant spatial and seasonal variability the vertical eddy viscosity and the ekman layer depth as deduced from ekman theory are compared to previous results their seasonal variability is also studied model results are then used to compute the mean and standard deviation of ageostrophic currents in 5 boxes over the world ocean the equatorial divergence and the subpolar and subtropical convergence zones are well reproduced

the stratigraphic expression of a large negative carbon isotope excursion from the ediacaran johnnie formation death valley the rainstorm member of the ediacaran johnnie formation of the southern basin and range us records a large negative excursion in carbon isotope ratios of carbonate strata 13 c vpdb 6 the character of the excursion raises fundamental questions about whether this isotopic pattern is accurately capturing the time series behavior of marine dissolved inorganic carbon dic or is a product of diagenesis to explore this issue we examined the expression of this isotopic excursion within the johnnie oolite a 2 m thick marker bed which records the highest rate of change in 13 c sedimentologically the oolite unit is thought to be time transgressive if the isotopic excursion reflects time series behavior of the carbon cycle its expression in the oolite across the basin should systematically align the sections according to their slight diachroneity detailed carbon and oxygen isotopic stratigraphy of the oolite at seven different locations indicates the magnitude of the excursion at the base of the oolite is spatially variable such that after a palinspastic reconstruction the sections align along a systematic north to south gradient in the isotopic data the oolite preserved in the old dad mountains the most southerly section measured is an outlier to this trend and the most difficult to ordinate accurately in the reconstruction showing the largest isotopic range between the onset of carbonate deposition and top of the oolite several hypotheses are congruent with these data but the sum of observations is best explained by a scenario wherein the oolite is time transgressive and deposited in a north to south manner throughout the onset of the isotopic excursion if correct this implies that the stratigraphic 13 c pattern reflects time series behavior of marine dic

archaeocyathan buildups within an entirely siliciclastic succession new discovery in the toyonian lalun formation of northern iran the proto paleotethys passive margin of northern gondwana abstract meter scale buildups constructed exclusively by archaeocyaths have been recognized within the uppermost lower cambrian siliciclastic succession of eastern alborz in northern iran they are the only known toyonian reefs in iran and adjacent countries and occur in the lower part of the shale unit of the lalun formation the reefs are of limited lateral extent reach a maximum thickness of 2 5 m and consist of several reef complexes containing cabbage or sack shaped buildups surrounded by well bedded colored shale each reef complex in the main reef zone consists of meter scale individual and kalyptrate compound buildups that are overgrown by laminated stromatolite the individual buildups are 12 to 75 cm thick and 5 to 50 cm in diameter but the compound buildups are up to 2 m thick and their diameter ranges from 75 to 120 cm in contrast to most lower cambrian reefs these compound buildups demonstrate a complete ecological succession including pioneer and climax phases archaeocyaths in the buildups are solitary and colonial types showing great diversity of growth forms with vase bowl and cup shaped and cylindrical forms present the cups range from less than 1 mm to 1 5 cm in diameter and are up to 4 cm tall in the majority of the skeletons but they may reach up to 4 cm in diameter in the massive colonial forms or in the branching forms of the upper outer part of the compound bioherms the limited lateral extent of the reef horizons and lateral facies changes in the colored shale toward various reefs supports deposition in drowned tidal channels in an estuarine depositional environment a change of the individual bioherms to larger compound buildups suggests lateral depth variation of the tidal channels partial infilling of the primary inter biohermal cavities by large reef clasts and cross laminated siltstone to very fine sandstone suggests occasional disturbances by storms and periodic influx of coarse siliciclastics in striking contrast to other lower cambrian reefs the archaeocyathan buildups of the alborz flourished in a completely siliciclastic setting and lack the skeletal calcimicrobes which dominated the lower cambrian reefs abrupt lateral and vertical facies changes to colored shale and fluvial red beds the presence of infiltrated shale between the skeletons and in central cavities and the intervallum of the archaeocyaths suggest highly turbulent and turbid incoming water with abnormally high concentrations of fine siliciclastic material during reef development high concentrations of fine suspended siliciclastics could well have prevented the light penetration which was necessary for calcimicrobial growth in addition the relatively small size of the archaeocyaths and absence of reef dwellers is very likely a consequence of the high terrigenous mud content and perhaps below normal salinity of the ambient sea water in the absence of calcimicrobes and suspension feeder metazoans in the dark and muddy water of the mid estuarine setting archaeocyathans became the only bioconstructors of the iranian buildups abnormally high concentration of nutritious fine siliciclastics suggests that photosymbionts and oligotrophic conditions were not needed by archaeocyaths particular hydrodynamic conditions along with high nutrient flux rather than light were essential for archaeocyathan communities

poleward along shore current pulses on the inner shelf of the bay of biscay abstract we analyzed strong events of coastal poleward along shore currents above 10 cm s 1 and up to more than 50 cm s 1 on the inner shelf 50 80 m depth of the bay of biscay bob from the spanish coast to the brittany coast we used data from four acoustic doppler current profilers adcps deployed from july 2009 to august 2011 the goal of this study was to analyze current variability at meso and subinertial scales and its generation mechanism these currents occurred all year long and were classified into three types events occurring principally in the southern part of the bob were classified as southern events bay scale events were defined when strong poleward currents were detected over all the shelf typically stronger on the spanish and the southern brittany shelves strong events were characterized by depth averaged current velocities over 40 cm s 1 in the southern part of the bob at short time lags the along shore currents were clearly related to along shore wind stress at upstream locations an explanation is provided for longer time lags in terms of coastal trapped wave ctw dynamics the first ctw mode phase speeds were in agreement with the propagation speeds of the fastest events 5 m s 1 while inner shelf modes could explain the slowest events 1 3 m s 1 the cross shelf density gradient and the extension of the ipc were also associated with strong coastal poleward along shore currents the duration of the events the vertical structure of the currents and the associated coastal trapped waves were studied in relation with the stratification

palaeoecology of the archaeocyathan reefs from the lower cambrian harkless formation southern nevada western united states and carbon isotopic evidence for their demise abstract archaeocyath sponges the first group of reef building organisms have a globally distributed albeit restricted stratigraphic occurrence archaeocyathan reefs are well known from the western united states particularly in units like the montenegro poleta and harkless formations of the white inyo ranges and esmeralda county nevada while it is recognized that these organisms disappear at some time above the last occurrence of their reefs in the harkless formation the precise timing of their disappearance is unknown here we show that the last archaeocyathan reefs in the upper harkless formation near gold point nevada are overlain by 20 60 m of interbedded siltstone and carbonate that preserve a negative carbon isotopic excursion consistent with the aece event archaeocyath extinction carbon excursion point counts of reef thin sections and analysis of acid insoluble residues of reef and reef adjacent samples illustrate that these last reefs also harbor previously undescribed diversity and abundance of animals living in and among the reefs including an array of small shelly fossil taxa we confirm previous work that the reefs of the early cambrian were ecologically diverse and functioned in many ways like reefs of the later paleozoic even just prior to their global demise in the late early cambrian and that the extinction of archaeocyaths is recorded in strata of the harkless formation

field and modelling studies of cambrian carbonate cycles virginia appalachians reply abstract field studies coupled with computer modelling of carbonate cycles in the elbrook conococheague formations middle to upper cambrian in the appalachians have helped define the mechanisms of formation the sequence is up to 1 6 km thick and composed of cyclic peritidal carbonates these formed on an aggraded rimmed shelf on a mature passive continental margin the cycles 1 7 m thick have lower parts of subtidal intertidal carbonate and caps of dolomitic laminite containing minor quartz arenite shale and breccia sedimentation rates for these peritidal carbonate environments exceeded long term subsidence of the platform 0 01 to 0 1 m 1 000 yr thus the shelf stayed near to sea level i e was aggraded milankovitch 20 000 to 100 000 yr low amplitude sea level fluctuations few meters superimposed on 3rd order sea level fluctuation of 1 to 3 m y duration and less than 20 m amplitude caused periodic submergence of the gently sloping platform less than 0 02 m km slopes resulting in deposition of over 400 peritidal cycles in about 26 m y cycles that formed during 3rd order sea level rise are thick and limestone rich whereas those formed during 3rd order fall are thin quartzose and highly dolomitized the modelling suggests that fewer and thinner cycles formed during the long term falls compared to the rises reflecting decreased accommodation cycle frequency decreases into areas of lower subsidence rate open marine cycles typical of the outer shelf and cycles formed during 3rd order sea level rise contain digitate bioherms grainstone and ribbon carbonates in lower parts they reflect high subsidence rate and an open marine setting inner shelf cycles and cycles that formed during 3rd order sea level fall commonly are thrombolitic or have thin subtidal parts grainstone conglomerate or stromatolite and reflec the low subsidence rates interior areas of quaternary carbonate shelves are characterized by incipiently drowned facies and pinnacle reefs and are punctuated by soil caliche horizons and karst surface that reflect 100 m glacio eustatic sea level fluctuations in contrast many ancient shelves like the cambro ordovician shelf of the appalachians were flat topped and dominated by cyclic peritidal sequences lacking evidence of high amplitude sea level fluctuations such aggraded shelves may represent the typical state of mature carbonate shelves that formed in response to low amplitude milankovitch sea level fluctuations as opposed to the large scale fluctuations that typified the quaternary

the oldest zoophycos and implications for early cambrian deposit feeding zoophycos group burrows are prevalent elements of the post cambrian trace fossil record here we report the oldest specimens of zoophycos from lower cambrian strata of the lower member wood canyon formation in southeastern california in addition to these being the oldest examples of this well known trace fossil the discovery of these specimens also reveals the presence of deposit feeding considerably earlier than has been suggested for the advent of this feeding style this type of activity may have had a significant impact on sediment mixing during the precambrian cambrian transition though the rarity and shallow tier position of these specimens suggests otherwise

depositional and sequence stratigraphic framework of the lower cambrian zabriskie quartzite implications for regional correlations and the early cambrian paleogeography of the death valley region of california and nevada the lower cambrian zabriskie quartzite in the death valley region of california and nevada records deposition in both nearshore marine and terrestrial environments and represents two genetically distinct depositional units the lower unit defined by the resting springs member is a highstand systems tract in which sandy braidplain deposits prograded over storm influenced inner shelf mudstone and sandstone the top flooding surface of that systems tract is a sequence boundary type 2 the upper unit defined by the emigrant pass member is the lowermost deposit of a transgressive systems tract in which nearshore marine sediments progressively overstep onlap the sequence boundary cratonward it is herein suggested that in the death valley area the top of lower cambrian grand cycle b is coincident with this sequence boundary this work shows that nonmarine deposition characterized much of the southwestern margin of cratonic north america during early cambrian time bonnier olenellus zone the stable tectonic setting and consistently low latitudinal position of laurentia during this time preclude tectonism and climactic variation and associated changes in sediment flux as principal forcing mechanisms of relative sea level change consequently eustatic variation was the probable first order causative mechanism for systems tract and facies development the relative sea level changes indicated in this study can be used to further aid the construction of global sea level curves

alluvial facies evolution during the palaeozoic greening of the continents case studies conceptual models and modern analogues the palaeozoic greening of the continents the appearance and expansion of embryophytes land plants in terrestrial environments was arguably the most fundamental phanerozoic change to the earth system thirteen case studies of cambrian to devonian fluvial deposits from north america and europe are documented here to illustrate the evolution of fluvial style during this period during the cambro ordovician prior to the advent of terrestrial vegetation fluvial systems laid down relatively coarse sands with little mud resulting in self formed channels and an architecture dominated by broad sheets of trough cross beds sheet braided style similar deposits formed across a wide range of latitudes and passed basinward into sandy coastal deposits from the mid ordovician onwards an increase in floodplain mudstone corresponds broadly with the appearance of embryophytes which would have progressively enhanced upland weathering mud production and floodplain storage of fines during the late silurian small heterolithic channel bodies with lateral accretion sets provide the first evidence of meandering channels and floodplain mudstones contain more varied palaeosols especially calcretes which appear abundantly for the first time by the early devonian channel deposits comprise sandstone lenses channelled braided style probably due to the increased bank strength and cohesion and reduced potential for sediment sorting imparted by sand mud mixtures muddy coastal deposits are prominent by the upper devonian fluvial deposits commonly contain fossil trees and large mainstem meandering channels with lateral accretion sets indicating that rooted vegetation stabilized channels the advent of stable floodplains with levees crevasse splays and organic litter would have encouraged the diversification of terrestrial invertebrates which left alluvial ichnological signatures from the late silurian onwards

mesoscale surveys over the shelf and slope in the upwelling region near point arena california repeated mesoscale surveys of a 40 km wide 100 km long coastal region near point arena california were conducted during the upwelling season april august in 1981 and 1982 each survey included conventional conductivity temperature depth casts at standard locations over the continental shelf and slope between 38 n and 39 10 n and continuous operation of a doppler acoustic log to obtain velocity profiles in the 20 to 150 m depth range synoptic surveys covered the entire grid in 2 3 days winds were strongly favorable for upwelling during the three 1981 surveys and were weak or variable during the three 1982 surveys surface temperature and salinity fields reflect the influence of both the seasonal winds and day to day variations in the wind persistently low surface salinities offshore reflect the general southward advection of subarctic waters and sporadic low salinities over the inner shelf reflect north ward advection of local runoff through an intermittent narrow countercurrent along the coast circulation patterns during all but one of the surveys were very complex and included meandering equatorward flow cyclonic and anticyclonic eddies and inshore countercurrents the simple two dimensional equatorward baroclinic coastal jet usually associated with coastal upwelling was observed during only one of our surveys overall average fields are relatively simple they show broad equatorward surface flow a very weak inshore countercurrent and a definite poleward undercurrent at the shelf break average temperature salinity and density fields are generally congruent with the average flow pattern average isotherms and isohalines are not strictly parallel to the coastline south of the coastline bend at point arena they diverge gradually from the coast comparison of average sections calculated from 10 matched pairs of central and arena lines separated by 50 km shows there are systematic differences between them warmer fresher waters lie nearer shore and in shallower water off point arena than on the central line this suggests that the surface waters flowing past point arena have sufficient southward momentum to cross isobaths comparison of average velocity sections on these two lines shows some differences in structure since the variability is large these may not be significant comparison of the measured and geostrophic average shears suggests there is a significant ageostrophic component in the upper layers above 40 m it may be the signature of an average wind driven ekman spiral

structural geology of the montgomery mountains and the northern half of the nopah and resting spring ranges nevada and california more than 7 500 m of upper precambrian and paleozoic sedimentary rocks in the area of the montgomery mountains and the northern half of the nopah and resting spring ranges represent a typical cordilleran miogeosynclinal sequence during mesozoic time after a period of earlier mesozoic folding and high angle faulting these rocks were cut by thrust faults that divided the rock sequence into four structural units in the resting spring range and the montgomery mountains from the top down the units are 1 the montgomery thrust plate 2 the baxter thrust plate 3 the resting spring thrust plate and 4 the amargosa unit beneath the montgomery thrust fault in the montgomery mountains lies the six mile thrust plate which has limited extent but may be a major subunit of the baxter plate the montgomery thrust plate moved eastward along a single thrust but the resting spring thrust plate moved eastward along an anastomosing series of thrust faults which divided it into a series of lobes thrust faults in the resting spring range now dip east because cenozoic tilting has reversed their original subhorizontal or west dips in the nopah range there are three major structural units which are from the top down 1 the chicago pass thrust plate 2 the shaw thrust plate and 3 the nopah range unit structural units in the nopah range cannot be unequivocally correlated with those in the resting spring range and montgomery mountains and two hypotheses must be presented for correlation hypothesis 1 correlates the baxter thrust plate of the resting spring range with the shaw thrust plate of the nopah range and hypothesis 2 correlates the baxter thrust plate with the chicago pass thrust plate of the nopah range post thrusting structures are related to progressive west or northwest extension cenozoic folds around the north end of stewart valley are oblique and related to right slip on the northwest striking stewart valley fault these may be the oldest post thrusting structural features in the area right slip and high angle dip slip faults are probably contemporaneous forming ranges and valleys by pull aparts continued extension caused rotation of earlier high angle dip slip faults so that some of them are now subhorizontal some low angle faults are probably gravity slides and form gradations into more chaotic landslides

the fine structure of nearshore tidal and residual circulations revealed by h f radar surface current measurements abstract using the ocean surface current radar oscr developed by the rutherford appleton laboratory uk 30 days of synoptic hourly surface current vectors were obtained for 84 locations within a nearshore region some 18 kms square tidal analyses of these data show that the currents associated with the predominant m2 constituent sweep smoothly and regularly through the area unaffected by the finer topographic features moreover contours of the amplitude of the m2 semi major axis are mutually consistent to a precision of better than 0 5 cm s 1 statistical analyses of these data indicate that the standard error of oscr current measurements is less than 4 cm s 1 by contrast the major higher harmonic constituent m4 shows pronounced but ordered spatial variability relating the observed distributions for m4 and m2 is foreseen as an instructive modeling problem that should advance our knowledge of shallow water tidal interaction processes standard relationships between residual surface currents and

stratigraphy and tectonics of the virginia north carolina blue ridge evolution of a late proterozoic early paleozoic hinge zone late proterozoic 690 570 ma through ordovician rocks of the virginia north carolina blue ridge and valley and ridge record the evolution of an eastward facing passive margin and its subsequent deformation during continent arc collision taconic orogeny comparison of blue ridge stratigraphy with modern rifts and passive margins suggests that late proterozoic rifting involved substantial crustal attenuation in the eastern blue ridge the axial zone of the blue ridge from central virginia southward is occupied by a major fault system hayesville fries rock fish valley fault contrasts between rocks deposited east and west of this fault suggest that it is a reactivated hinge zone separating highly attenuated continental crust to the east from continental crust of more normal thickness to the west during rifting normal faulting and rapid subsidence of attenuating crust in the eastern blue ridge produced rift basins in which deep water clastic and volcanic rocks accumulated lynchburg group ashe formation landward of the hinge zone in the western blue ridge mainly terrestrial to shallow water clastic and volcanic rocks were deposited in a series of subaerial rift basins swift run catoctin grandfather mountain mount rogers formations the hinge zone not only controlled depositional patterns throughout the rift and passive margin history but it was also reactivated during the taconic collision when attenuated crust and its cover were thrust westward over the shelf edge turbidite dominated rift sequences of the eastern blue ridge are unlike typical rift deposits which are characterized by predominantly subaerial and shallow water sedimentation deep water rifts may be common on attenuated crust as in the bay of biscay however they are poorly known from the stratigraphic record because of their susceptibility to destruction during orogeny

cordilleran hingeline late precambrian rifted margin of the north american craton and its impact on the depositional and structural history utah and nevada the structural pattern set by late precambrian rifting and fragmentation of the north american continent is apparent in both sedimentary and tectonic trends in western utah and eastern nevada the late precambrian cratonic margin cordilleran hingeline displays several prominent structural features such as the wasatch and ancient ephraim faults fillmore arch and northeast trending lineaments which were repeatedly reactivated as structural uplifts ramps strike slip faults and extensional detachments the renewed activity affected among others the geometry of the late paleozoic ancestral rocky mountain uplifts and basins the extent of the jurassic arapien basin the sedimentary pattern of the cretaceous foreland basin the geometry of the sevier orogenic belt and the extent and type of basin and range extensional tectonics the rifted cratonic margin has thus remained a major influence on regional structures long after rifting has ceased

two from donegal neoproterozoic glacial episodes on the northeast margin of laurentia two glacial episodes the sturtian ca 720 ma and marinoan varangerian ca 590 ma characterize many neoproterozoic successions worldwide in contrast northeast laurentia is typically considered as containing only the latter in scotland and ireland this is represented by the port askaig tillite here we present evidence ice rafted debris for a second younger neoproterozoic glacial event in the dalradian southern highland group of donegal ireland these deposits overlie strata correlative to ca 595 ma rocks in scotland making this heretofore unrecognized glacial episode a marinoan varangerian equivalent in that the port askaig occurs 3 5 km stratigraphically below the southern highland group rocks it is most likely sturtian not marinoan varangerian in age thus the dalradian succession in the irish caledonides contains strata representing both the sturtian and marinoan varanger glaciations

fan deltas and braid deltas varieties of coarse grained deltas two types of coarse grained deltas are recognized fan deltas and braid deltas fan deltas are gravel rich deltas formed where an alluvial fan is deposited directly into a standing body of water from an adjacent highland they occupy a space between the highland usually a fault bounded margin and the standing body of water in contrast braid deltas here introduced are gravel rich deltas that form where a braided fluvial system progrades into a standing body of water braid deltas have no necessary relationship with alluvial fans as exemplified by fluvioglacial braid deltas braid deltas have previously been classified as fan deltas even though the geomorphic and sedimentologic settings of the two systems can be vastly different braid deltas are a common present day geomorphic feature and are abundant in the geological record fan deltas and braid deltas can be distinguished in the rock record by distinctive subaerial components of these depositional systems the shoreline and subaqueous components of both are similar fan delta sequences have a subaerial component that is an alluvial fan facies comprising interbedded sheetflood debris flow and braided channel deposits fan deltas produce small a few tens of square kilometres wedge shaped bodies of sediment commonly displaying high variability in paleocurrent patterns and abrupt changes in facies the deposits are generally very coarse grained with large out sized clasts very poorly sorted matrix rich polymictic heterolithic partially cemented by penecontemporaneous carbonate and have low porosity and permeability braid deltas in contrast have a subaerial component consisting entirely of braided river or braidplain facies their deposits display better sorting roundness and clast orientation than do fan delta sediments they lack a muddy matrix they display size grading and bar migration they commonly have a sheet geometry with high lateral continuity tens to hundreds of square kilometres and they exhibit moderate to high porosity and permeability valuable paleogeographic and tectonic information concerning the proximity of highlands and major fault zones may be misinterpreted or lost if these two coarse grained deltaic systems are not differentiated

west florida shelf response to local wind forcing april 1998 we compare west florida shelf velocity and sea level data with a model simulation for april 1998 responses for three upwelling and three downwelling favorable wind events are documented along shelf jets accompanied by oppositely directed upper and lower layer across shelf flows with connecting vertical velocity comprise the fully three dimensional inner shelf responses which are sensitive to stratification with an initial density field representative of april 1998 the model simulates velocity and sea level variations in general agreement with the observations whereas substantial mismatches occur without stratification despite the winds being the primary motive agent for the inner shelf the stratification dependence requires that model density fields be maintained through a combination of adequate initial conditions surface offshore and land derived buoyancy inputs and data assimilation dynamical analyses define the inner shelf as the region where the surface and bottom boundary layers are important in the momentum balance kinematically this is where surface ekman layer divergence fed by the bottom ekman layer convergence or conversely sets up the across shelf pressure gradient stratification causes a response asymmetry wherein the offshore scale and magnitude of the upwelling responses are larger than those for the downwelling responses this asymmetry is attributed to thermal wind effects across the bottom ekman layer buoyancy torque by isopycnals bending into the bottom adds constructively destructively with planetary vorticity tilting under upwelling downwelling favorable winds and this may have important implications for nutrients and other material property distributions on the shelf

mapping ocean outfall plumes and their mixing using autonomous underwater vehicles this paper reports on our experiences developing methods to survey an ocean outfall discharge plume using an autonomous underwater vehicle auv the mobility of an auv provides a significant advantage in surveying discharge plumes over traditional boat based methods and when combined with optical and oceanographic sensors provides a capability for both detecting plumes and assessing their mixing in both the near and far fields unique to this study is the optical sensing of of the presence of colored dissolved organic matter cdom in the discharge plume for quantitatively assessing the dilution ratio of the plume water this capability is demonstrated for two publicly operated treatment works potws located offshore san diego california that have significantly different environmental settings and operating parameters the first is the south bay ocean outfall sboo operated by the international boundary water commission ibwc whose discharge is located in approximately 30m deep water at a flow rate of 28 million gallons per day mgd the second discharge is the point loma ocean outfall ploo which discharges at approximately 90m with a nominal volume flow rate of 250 mgd the methodologies for planning the auv missions to sample the discharge plume characterizing the plume using the signals measured by the onboard oceanographic and optical sensors and use of those data in predictive models is outline the results suggest that even in variable oceanic conditions properly planned missions for auvs equipped with appropriate sensors can accurately characterize and track ocean outfall plumes with high spatial resolution more effectively than traditional methods

aeolian sand sheet deposits in the lower cambrian nekso sandstone formation bornholm denmark sedimentary architecture and genesis abstract the lower cambrian nekso sandstone formation which hitherto has been thought to be of pure fluvial origin locally contains a significant amount of aeolian deposits these aeolian sediments form relatively thin tabular sand sheet deposits separated by straight to somewhat irregular erosional bounding surfaces and associated pond deposits these bounding surfaces can be classified after rank of after genesis the aeolian bounding surfaces in the nekso sandstone formation are probably multugenetic and signify initial ground water controlled deflation of the sand sheets followed by a ground water rise or low energy flooding and pond sedimentation the sand sheets and intervening pond deposits form a multistorey succession 7 m thick that records systematic fluctuations in available sand supply in the source area air flow characteristics ground water level and aeolian accumulation rate apparently the recorded sedimentary pattern reflects episodic growth of a sand sheet deposit related to systematic climatic fluctuations

sedimentology and sequence stratigraphy of neoproterozoic and cambrian units across a craton margin hinge zone southeastern california and implications for the early evolution of the cordilleran margin abstract neoproterozoic basal cambrian strata exposed in eastern california represent the deposits of a craton margin hinge zone that formed in response to the fragmentation of the neoproterozoic supercontinent rodinia one unresolved question regarding the late neoproterozoic stratigraphy in the southwestern united states has been the interpretation of paleotectonic affinity for rocks deposited above the glaciogenic kingston peak formation of central concern has been attempts to identify the position in this stratigraphy where rift related sediments give way to passive margin deposits subsidence analyses suggest that rifting occurred near the start of the cambrian perhaps coincident with the feldspathic middle member wood canyon formation it rests on a disconformity that represents the base of the sauk supersequence and would likely represent the break up unconformity in subsidence analysis models middle member wood canyon and overlying lower middle cambrian strata extend far into the craton detailed sedimentary facies and sequence stratigraphic analysis of post kingston peak pre middle wood canyon rocks indicate that depositional facies in this succession distal alluvial through shallow subtidal are similar to units deposited on the stable craton further these pre sauk units which can be divided into multiple principally eustatically driven depositional sequences are correlated across long distances and even lap onto the edge of the stable craton we suggest the kingston peak formation is the principal rift generated deposit and the overlying thick predominantly siliciclastic section represents the basal deposits of the cordilleran passive margin kingston peak strata consist of thick coarse diamictites interbedded with turbidites such facies are unique in the overall stratigraphy but are similar to other known rift deposits although the age of the kingston peak formation is not well constrained and may be as young as 590 ma it may correlate with the rapitan sturtian glaciation 720 ma which would place middle wood canyon strata some 150 ma younger than the start of rifting

thin eolianites interbedded within a fluvial and marine succession early proterozoic whitworth formation mount isa inlier australia abstract the early proterozoic whitworth formation in the mount isa inlier australia contains the oldest known thinly bedded eolian dune and amalgamated interdune deposits and records the complex interplay of eolian fluvial and marginal marine depositional processes the whitworth formation accumulated during the waning phases of rifting in a north south trending trough that began between 1808 and 1790 ma and ended before 1740 ma three eolian facies are recognized 1 cosets of cross strata 2 sets of horizontal to low angle strata and 3 isolated sets of cross strata facies el records preservation of dunes with low angles of climb without intervening interdune deposits sets of facies e2 are interpreted as either sand sheet preserved dune plinths or amalgamated interdune deposits facies e3 is encased in facies e2 and consists of lenses of cross strata with irregular tops this association of facies is comparable to recent gypsum dune and interdune deposits at white sands new mexico facies e3 reflects limited dune preservation during migration and accumulation at or near the groundwater table vertical change from amalgamated interdune deposits to dune without interdune deposits records dunefield initiation or lateral migration from a peripheral to a more centralized position within the dunefield increased sedimentation rates promoted preservation of dune deposits represented by facies e1 decreased sedimentation rate and possible limited sediment bypassing resulted in amalgamation of interdune deposits on the dunefield periphery eolian facies e1 and e2 are interbedded with ephemeral river deposits three ephemeral river facies are recognized 1 cosets of horizontal strata 2 cosets of horizontal strata and overlying trough cross beds and 3 cosets of medium scale trough cross beds ephemeral river facies f3 often are preserved in channels incised into eolian facies e3 associated marginal marine facies consist of 1 thin bedded arenites of intertidal to supratidal origin and 2 trough and tabular planar cross bed sets and cosets that resulted from migration of subaqueous dunes within a tide dominated subtidal setting interbedded fluvial and eolian deposits reflect either autogenic processes such as reworking of fluvial sands by eolian processes or incursion of a fluvial system into a dunefield related to allogenic processes such as climatic change dune deposits in the whitworth formation probably developed under arid to semi arid conditions as indicated by extensive ephemeral river deposits presence of evaporite pseudomorphs and absence of wet interdune deposits interbedded eolian fluvial and marginal marine deposits resulted from relative sea level fluctuations related to a combination of eustasy and intrabasinal tectonics

two diamictites two cap carbonates two δ13c excursions two rifts the neoproterozoic kingston peak formation death valley california stratigraphic mapping of the neoproterozoic glaciogenic kingston peak formation death valley california provides evidence for two temporally discrete extensional deformation episodes these episodes are bracketed by the sourdough limestone and noonday dolomite the facies characteristics and 13 c data ranging between 2 15 and 2 56 and 1 88 and 4 86 respectively of which make them equivalent to sturtian and varangian age cap carbonates respectively this constrains the two extensional episodes along the southwestern margin of laurentia to ca 700 ma and ca 600 ma these observations and data show that the field evidence for mid neoproterozoic breakup and the predictions from tectonic subsidence curves for a latest neoproterozoic breakup are both correct thus neoproterozoic plate reconstructions must account for two discrete rift episodes separated by 100 m y or more confining rifting to within the kingston peak formation thereby places the younger proterozoic rocks of the southwestern great basin in the rift to drift tectonic phase

evidence for late rifting of the cordilleran margin outlined by stratigraphic division of the lower cambrian gog group rocky mountain main ranges british columbia and alberta the lower cambrian mcnaughton formation of the gog group occupies a stratigraphic position transitional between the rift related rocks of the underlying upper proterozoic miette group and the overlying paleozoic passive margin succession a major regional unconformity overlain by a distinctive orthoquartzite marker has been traced within the mcnaughton formation this unconformity has been shown to truncate normal faults active during the deposition of the lower mcnaughton formation the lower mcnaughton formation consists of mature coarse grained fluvial sediments accumulated in hanging wall half grabens of active normal faults these faults represent the final stage of rifting on the continental margin the unconformity on the footwall blocks of these faults can be traced into the hanging wall and is overlain by the shoreface sediments of the transgressive upper mcnaughton formation formal subdivision of the mcnaughton formation into four lithostratigraphic members is proposed in order to describ

stratigraphic investigations of carbon isotope anomalies and neoproterozoic ice ages in death valley california an unusual richness of biogeochemical events is recorded in neoproterozoic cambrian strata of the death valley region california united states eight negative carbon isotope d13c excursions are found in carbonate units between 1 08 ga and the precambrian cambrian boundary four of these excursions occur in carbonates that contain textural features similar to those found globally in postglacial cap carbonates including one or more of the following laminite with rollup structures apparent tube rocks seafloor precipitates and sheet crack cements however only two of these units the sourdough limestone member of the kingston peak formation and the noonday dolomite rest directly upon glacial strata the basal beck spring dolomite and the rainstorm member of the johnnie formation each contain negative excursions and cap carbonate like lithofacies but do not rest on known glacial deposits if the negative d13c excursions are assumed to record depositional processes two equally interesting hypotheses are possible 1 the death valley succession records four glacial pulses in neoproterozoic time but glacial units are not preserved at two stratigraphic levels 2 alternatively other global oceanographic processes can cause negative excursions and cap carbonate like facies in addition to or independent of glaciation

trends in oolite dolomitization across the neoproterozoic cambrian boundary a case study from death valley california abstract changes in dolomite fabric within the neoproterozoic cambrian stratigraphic succession in death valley california preserve evidence for a first order biogeochemical change in early diagenetic environments through the neoproterozoic cambrian transition oolite forms the primary focus of the study so that the general paleoenvironmental setting and presumed susceptibility to early diagenesis and fluid flow can be kept relatively constant across geologic time two key generalizations can be made 1 late neoproterozoic dolomitization in death valley occurred very early in the paragenetic sequence was volumetrically significant and preserved fine detail of the original aragonite or calcite precursor and 2 early cambrian dolomitization in death valley occurred late in the paragenetic sequence with burial was commonly incomplete and obliterated details of the calcite or aragonite precursor early diagenetic dolomitization of any kind was absent the dolomitization fabrics in death valley parallel the presumed pattern of seawater mg ca with respect to mimetic dolomitization in the paleozoic low mg ca little no mimetic dolomitization and cenozoic higher mg ca more common mimetic dolomitization however the volume of neoproterozoic mimetic dolomitization is immense compared to the cenozoic examples we speculate that a fundamental shift in the early diagenetic environment occurred in late neoproterozoic time perhaps in association with secular variation in the sulfate concentration of seawater and the advent and proliferation of penetrative bioturbation that destroyed sediment capping microbial mats an oscillatory trend in the fabric and volume of dolomite through the phanerozoic has been suggested but the termination of volumetrically significant mimetic dolomitization across the neoproterozoic cambrian transition a critical time in earth history for many reasons dwarfs the oscillatory trends noted in the phanerozoic

observations of seasonal variation in the ekman layer abstract the seasonal variation in the ekman layer is examined using observations from the long term upper ocean study lotus including surface meteorology current and temperature the near surface current is found to be coherent with the wind at low frequencies periods greater than one day using a wind relative averaging method the authors find the observed near surface volume transport to be consistent with ekman transport the mean current profile has a spiral shape that is flat compared to the classic ekman spiral in that it rotates less with depth than does the ekman spiral the mean current e folds over 12 m in the summer and 25 m in the winter with a decay in amplitude that implies eddy viscosities of 60 10 4 and 250 10 4 m2 s 1 respectively diurnal cycling is the dominant mode of variability in the summer and it determines the vertical structure of the spiral in the winter diurnal cycling is almost nonexistent due to greatly reduced solar insolation and stronger winds a persisten

timing of exhumation wheeler pass thrust sheet southern nevada and california late jurassic to middle cretaceous evolution of the southern sevier fold and thrust belt zircon u th he zhe thermochronologic data for 46 samples from the wheeler pass thrust sheet which carries thick passive margin strata and is discontinuously exposed across the southern part of the sevier fold and thrust belt record late jurassic cooling related to exhumation during early thrust slip and local middle cretaceous cooling related to footwall basement imbrication within the frontal part of the wheeler pass sheet exposed in the northwest spring mountains zhe ages decrease from ca 160 to 140 ma over a paleodepth interval of 6 to 9 km in devonian to lower cambrian strata interpreted to record exhumation and enhanced cooling above a frontal ramp followed by slow cooling a similar pattern of zhe ages occurs over a more limited paleodepth range exposed within the resting spring range to the south in the nopah range zhe ages of ca 140 ma in lower cambrian strata record early cooling followed by slow cooling until ca 100 ma zhe ages in underlying paleoproterozoic basement rocks decrease from ca 100 to 85 ma over a paleodepth interval of 9 to 12 km interpreted to record uplift exhumation and cooling during footwall basement imbrication as slip was transferred eastward onto the keystone thrust system late jurassic slip on the wheeler pass thrust overlapped with deformation along the nw trending east sierran thrust system early hinterland crustal thickening and growth of the sierra magmatic arc and may have been correlative with early deformation in the central nevada thrust belt slip on the wheeler pass thrust preceded major slip on other thrust sheets that carried thick passive margin strata in more northern parts of the sevier belt probably reflecting the influence of different initial widths and tapers of the passive margin sedimentary wedge

trilobite extinctions facies changes and the roece carbon isotope excursion at the cambrian series 2 3 boundary great basin western usa the mass extinction of the olenellid trilobites occurred around the cambrian series 2 series 3 boundary like many other crises it coincided with a negative carbon isotope excursion but the associated palaeoenvironmental changes remain unclear to investigate the causal mechanism for this event we report facies changes pyrite framboid petrography and carbon isotope values from cambrian series 2 series 3 traditionally early middle cambrian boundary strata of the carrara formation death valley region california and pioche formation nevada these data reveal regionally changing water depths from high energy nearshore facies oolitic grainstone to more offshore silty marl and finer grained carbonate mudstone in the carrara formation the series boundary occurs within a deepening succession transitioning from high energy nearshore facies oolitic grainstone and oncolitic packstone to offshore marl the latter of which contains pyrite framboid populations indicative of low oxygen dysoxic depositional conditions intermittent dysoxia persisted below sub wave base settings throughout the early and middle cambrian but did not intensify at the time of extinction arguing against anoxia as a primary cause in the olenellid trilobite extinction within both field areas the extinction interval coincided with a minimum in 13ccarb values which we interpret as the regional manifestation of the redlichiid olenellid extinction carbon isotope excursion roece the series 2 series 3 boundary is reported to closely coincide with a large amplitude sea level fall that produced the sauk i ii sequence boundary but the placement of the series 2 series 3 boundary within a transgressive interval of the carrara formation shows that this is not the case the main sequence boundary in the succession occurs much lower in the succession at the top of the zabriskie quartzite and therefore precedes the extinction of the olenellids and roece

patterns of sedimentation in the precambrian abstract the principle of uniformitarianism may be applied to precambrian basin evolution and to the sedimentary record as a whole the major difference in the precambrian eon lay in variability of rates and intensities of processes controlling weathering erosion transport deposition lithification and diagenesis this paper examines precambrian sedimentation patterns within the larger framework of earth evolution pre rock record sedimentation probably comprised deep water oceanic realms within which meteoritic and cometary impact events generated very large tsunamis resulting in very coarse volcaniclastic detritus combined with fine dust settling out of suspension all reworked by marine current systems and localised turbidites from c 4 to 3 2 ga greenstone belts provided the predominant settings for the thin passive margin carbonates bif stromatolitic evaporites pelites and quartzites and lesser synorogenic turbidites conglomerates and sandstones that accompanied the volcanic and volcaniclastic rocks typical of these settings common palaeoenvironments were high gradient alluvial fans low sinuosity braided rivers and relatively shallow marine settings subject to wave and tidal action and turbidity currents although continental crustal growth continued largely through greenstone belts until c 2 7 ga the witwatersrand basin c 3 0 2 7 ga kaapvaal craton south africa reflects initial stabilisation of the oldest craton with an epeiric sea accumulating largely fluvial detritus subject to tidal inland and storm wave craton marginal reworking within a retroarc foreland basin setting neoarchaean palaeoproterozoic sedimentation is discussed within a framework of two global superevents at c 2 7 ga and 2 2 1 8 ga each encompassing major changes in earth s evolution related to the supercontinent cycle mantle superplumes peaks in crustal growth rates and significant biochemical changes within the atmosphere hydrosphere system concomitant globally raised sea levels led to chemical and clastic epeiric seas within which the first giant carbonate platforms developed and deposition of iron formation peaked globally at c 2 5 ga the first global glaciation at c 2 4 2 2 ga provides little support for the snowball earth theory but does suggest a negative feedback loop model whereby intraglacial co 2 related warming and synglacial decreases in weathering alternated up to three times models for palaeo atmospheric and oceanic evolution are mutually exclusive but by c 1 8 ga the existence of large landmasses and free oxygen in earth s atmosphere enabled erg development and red bed sedimentation globally the full spectrum of phanerozoic modern sedimentary environments was thus present on earth a third postulated superevent at c 0 8 0 6 ga essentially recreated conditions experienced at c 2 2 1 8 ga with additionally at least three global refrigeration events

decomposing observations of high frequency radar derived surface currents by their forcing mechanisms locally wind driven surface currents 1 the wind impulse response function and transfer function for high frequency radar derived surface currents off southern san diego are calculated using several local wind observations the spatial map of the transfer function reflects the influence of the coast on wind current dynamics near the coast within 20 km from the shoreline the amplitudes of the transfer function at inertial and diurnal frequencies are reduced due to effects of coastline and bottom bathymetry meanwhile the amplitude of low frequency currents increases near the coast which is attributed to the local geostrophic balance between cross shore pressure gradients against the coast and currents locally wind driven surface currents are estimated from the data derived response function and their power spectrum shows a strong diurnal peak superposed on a red spectrum similar to the spectra of observed winds current magnitudes and veering angles to a quasi steady wind are typically 2 5 of the wind speed and vary 50 90 to the right of the wind respectively a wind skill map is introduced to present the fractional variance of surface currents explained by local winds as a verification tool for wind data quality and relevance moreover the transfer functions in summer and winter are presented to examine the seasonal variation in ocean surface current response to the wind associated with stratification change

tectonic subsidence of the early paleozoic passive continental margin in eastern california and southern nevada quantitative analysis of tectonic subsidence in cambrian and ordovician platform carbonates and associated strata exposed in the spring mountains nevada and the nopah funeral and inyo ranges california indicates that subsidence associated with this segment of the early paleozoic passive continental margin is exponential in form consistent with thermal contraction of the lithosphere following extension as in other parts of the north american cordillera continental separation in the southern great basin appears to have taken place between 590 and 545 ma these results are not sensitive to uncertainties in stratigraphic thickness biostratigraphic age control or paleobathymetry uncertainties in the cambrian time scale lead to predictable variations in the inferred time of onset of thermal subsidence but they have no effect on the inferred stratigraphic position of the rift to post rift transition a younger age for the base of the middle cambrian results in a younger inferred age of onset of thermal subsidence accompanied by greater rates of subsidence during the cambrian whereas a significantly older estimate of the onset of thermal subsidence can be obtained only if the base of the middle cambrian is substantially older than 540 ma a possibility that is inconsistent with available data results of the subsidence analysis are particularly significant because this is one of the few regions along the length of the north american cordillera where they can be compared directly to the geologic evidence for syn rift and post rift deposition basement involved faulting associated with the amargosa basin aulacogen ceased during deposition of the noonday dolomite which is thought to be older than 700 680 ma on the basis of stromatolites of late riphean affinity the overlying johnnie formation contains supposed vendian stromatolites younger than 700 680 ma if it is assumed that our results indicate the timing of the final rift to post rift transition then either the ages inferred from stromatolites are incorrect or the lithosphere was thinned regionally after deposition of the noonday the latter possibility is supported by limited geologic evidence for extension in latest proterozoic and early cambrian time the lack of appreciable physical evidence for crustal extension after deposition of the noonday however may imply that 1 a uniform extension model for lithospheric thinning is inappropriate for this part of the margin or that 2 some or all of the localities studied are continentward of the hinge zone and that the observed subsidence is exaggerated by flexural loading in a deeper basin to the west

measurements of upper ocean surface current shear with high frequency radar estimates of the variation with depth of both the speed and direction of near surface ocean currents within the top meter have been made using time series data collected from a dual frequency high frequency radar located on the california coast south of monterey long term averages derived from this data set over 3 different years consistently revealed an expected reduction in the speed of the near surface current as a function of depth consistent with a logarithmic vertical current profile an unexpected and previously unmeasured clockwise rotation with increasing depth of the near surface current was also observed hypotheses are suggested for the apparent rotation

recognition of interfluve sequence boundaries integrating paleopedology and sequence stratigraphy in shallow marine and coastal plain strata sequence boundaries are easily recognized at the base of incised valley fills between valleys however it is more difficult to recognize sequence boundaries where they are expressed as interfluve paleosols we suggest that interfluve paleosols can be most reliably identified using a combination of 1 stratigraphic position 2 field observations such as thickness structure color and degree of rooting and 3 micromorphological features such as bioturbation fabric clay coatings ferruginous features and siderite and barite only micromorphology permits recognition of temporal changes in drainage surface stability and protracted pauses in sedimentation that typify these surfaces this three part approach has been successfully employed to identify interfluve sequence bounding paleosols in the cenomanian dunvegan formation in alberta and british columbia canada

the effect of rising atmospheric oxygen on carbon and sulfur isotope anomalies in the neoproterozoic johnnie formation death valley usa abstract carbonates within the rainstorm member in the terminal neoproterozoic johnnie formation of death valley california record a remarkable negative carbon isotope anomaly to a nadir of near 11 that accompanies a dramatic rise in trace sulfate abundance and fall of carbonate associated sulfate 34 s values the carbonates including the laterally extensive johnnie oolite were deposited during marine flooding atop a sequence boundary best observed in cratonward sections the 12 c rich alkalinity delivered to the seawater pool was likely associated with a dramatic rise in atmospheric o 2 which resulted in 1 the oxidation of exposed continental shelf sediments rich in fossil organic matter and sulfides and 2 the ventilation of the oceans similar carbon isotope anomalies are recorded in broadly equivalent successions that post date known marinoan glacial deposits and pre date the precambrian cambrian boundary in oman india china australia and namibia supporting the view that the oxygenation event was global thus the biogeochemical anomaly post dates the last widely recognized neoproterozoic ice age but is nonetheless associated with sea level drawdown that is likely to be eustatic in origin the radiation of a high diversity microbiota and the first appearance of large metazoan fossils ediacaran animals follow this carbon isotope anomaly suggesting that a critical threshold with respect to atmospheric o 2 had been crossed by this time a negative excursion of similar magnitude occurs in overlying strata at the precambrian cambrian boundary which likely reflects similar processes

the shuram and subsequent ediacaran carbon isotope excursions from southwest laurentia and implications for environmental stability during the metazoan radiation current understanding of secular changes in the carbon isotopic composition of mid to late ediacaran carbonates suggests a relatively long steady recovery of the global ocean from the shuram negative excursion followed by a smaller negative excursion at the precambrian cambrian boundary new radiometric stratigraphic and carbon isotope data from thick exposures of the upper johnnie formation in the panamint range of eastern california combined with data from carbonate rich facies of the stirling quartzite in the funeral mountains confirm an ediacaran age for these strata and provide a more complete record of isotopic variations during this time interval than previously determined from sw laurentia and other key sections around the globe a siltstone in the lower part of the johnnie formation yielded a detrital zircon grain with an age of 640 33 0 09 ma lowering the maximum radiometric age constraint on the johnnie formation by 400 m y consistent with an ediacaran age based on chemo and biostratigraphic data in contrast to previous c isotope compilations from this region which were generally based on relatively thin portions of the cordilleran miogeocline near its depositional hinge the more basinward exposures exhibit a recovery from values near 12 to 0 within the upper part of the johnnie formation details in the shape of the chemostratigraphic profile through the upper johnnie formation closely match those in profiles through the wonoka formation in south australia which lies above the basal ediacaran global stratotype section and point and the shuram buah interval in oman confirming temporal correlation and suggesting genesis through changes in the isotopic composition of the global ocean the shuram excursion in sw laurentia is followed by at least three smaller ediacaran to earliest cambrian isotopic excursions recorded within from oldest to youngest the uppermost johnnie formation the middle stirling quartzite and the lower wood canyon formation these data indicate that the negative excursion associated with the base of the cambrian is not a unique post shuram event and that post shuram pre cambrian animal evolution occurred in an environment of repeated large magnitude fluctuations in the carbon isotopic composition of the global ocean

precambrian cambrian transition death valley united states the death valley region contains one of the best exposed and often visited precambrian cambrian successions in the world but the chronostratigraphic framework necessary for understanding the critical biologic and geologic events recorded in these sections has been inadequate the recent discovery of treptichnus phycodes pedum within the uppermost parasequence of the lower member of the wood canyon formation allows correlation of the precambrian cambrian boundary to this region and provides a necessary global tie point for the death valley section new carbon isotope chemostratigraphic profiles bracket this biostratigraphic datum and record the classic negative carbon isotope excursion at the boundary for the first time biostratigraphic chemostratigraphic and lithostratigraphic information from pretrilobite strata in this region can be directly compared with similar data from other key sections that record the precursors of the cambrian explosion few precambrian cambrian boundary sections contain both the facies restricted boundary fossil t pedum and carbon isotope data as found in death valley thus the death valley succession provides a critical link toward our understanding of the correlation between siliciclastic dominated and carbonate dominated precambrian cambrian transition sections