the evolution of oceanic and atmospheric anomalies in the northeast pacific during the el nino and la nina events of 1995 2001 abstract from late 1995 through early 2001 three major interannual climate events occurred in the tropical pacific the 1995 97 la nina ln 1997 98 el nino en and 1998 2001 ln we analyze atmospheric and upper oceanic anomalies in the northeast pacific nep during these events and compare them to anomalies both elsewhere in the north and tropical pacific and to typical en and ln anomaly patterns the atmospheric and oceanic anomalies varied strongly on intraseasonal and interannual scales during the 1995 97 ln and 1997 98 en the northeast pacific was dominated by negative slp and cyclonic wind anomalies and by upper ocean temperature and sea surface height ssh anomalies the latter were positive along the north american west coast and in the nep thermal anomaly pool between hawaii vancouver island and baja california and negative in the central north pacific this atmospheric oceanic anomaly pattern is typical of en an eastward shift in the atmospheric teleconnection from east asia created en like anomalies in the nep during the 1995 97 ln well before the 1997 98 en had begun the persistence of negative sea level pressure slp and cyclonic wind anomalies in the nep during the 1997 98 en intensified pre existing upper oceanic anomalies atmospheric anomalies were shifted eastward during late 1996 early 1998 leading to a similar onshore shift of oceanic anomalies this produced exceptionally strong positive upper ocean temperature and ssh anomalies along the west coast during the 1997 98 en and explains the unusual coastal occurrences of several species of large pelagic warm water fishes the growth and eastward shift of these pre existing anomalies does not appear to have been linked to tropical pacific en anomalies until late 1997 when a clear atmospheric teleconnection between the two regions developed prior to this remote atmospheric impacts on the nep were primarily from east asia as the 1998 2001 ln developed nep anomalies began reversing toward the typical ln pattern this led to predominantly negative slp and cyclonic wind anomalies in the nep and upper ocean temperature and ssh anomalies that were mainly negative along the west coast and positive in the central north pacific the persistence of these anomalies into mid 2001 and a number of concurrent biological changes in the nep suggest that a decadal climate shift may have occurred in late 1998 during 1995 2001 nep oceanic anomalies tracked the overlying atmospheric anomalies as indicated by the maintenance of a characteristic spatial relationship between these anomalies in particular wind stress curl and ssh anomalies in the nep maintained an inverse relationship that strengthened and shifted eastward toward the west coast during late 1996 early 1998 this consistent relationship indicates that anomalous ekman transport driven by regional atmospheric forcing was an important contributor to temperature and ssh anomalies in the nep and ccs during the 1997 98 en other studies have shown that coastal propagations originating from the tropical pacific also may have contributed to coastal nep anomalies during this en our results indicate that at least some of this coastal anomaly signal may have been generated by regional atmospheric forcing within the nep

flow directions in dikes from anisotropy of magnetic susceptibility data the bootstrap way one of the first applications of anisotropy of magnetic susceptibility ams was an attempt to determine flow directions from mafic dikes khan 1962 since the seminal work of knight and walker 1988 defining the expected behavior of ams in response to magma flow there has been increasing interest in using ams for this purpose here we present a quantitative method for interpretation of ams data from dikes using a parametric bootstrap first dikes must be sampled with at least five and preferrably more samples from within 10 cm of the dike margin the distributions of the eigenvalues and eigenvectors of the ams tensor are delineated by calculating eigenparameters of many bootstrapped paradata sets we generate paradata sets by first selecting a sample at random then calculating a replacement set of data by drawing tensor elements from normal distributions with the mean and standard deviation of the entire site the bounds containing 95 of the eigenparameters of the bootstrapped data serve as confidence limits for the parameter of interest classification of dikes proceeds as follows sites whose maximum and intermediate eigenvalues could not be distinguished are deemed uninterpretable in addition sites with principal eigenvectors with angles 45 away from the dike margin inverse or with markedly different directions on either side of the dike scissored are excluded the remaining dikes are classified as having unique flow direction information if the principal eigenvectors from at least one side are distinct from the dike plane based on the distribution of the bootstrapped principal eigenvectors if neither side has principal eigenvectors distinct from the dike plane the dikes are classified as having lineation information only a study comprising 251 dikes from the troodos ophiolite has 151 sites with directional data 38 sites with lineations only 7 inverse sites 5 scissored sites and 55 sites not fitting into any other category the flow directions interpreted from the data were generally southerly toward a fossil transform zone

laccolithic as opposed to cauldron subsidence emplacement of the eastern mourne pluton n ireland evidence from anisotropy of magnetic susceptibility the structural evolution and emplacement of the eastern mourne pluton was investigated using anisotropy of magnetic susceptibility ams measurements carried out on 112 oriented block samples and structural data from the host rocks from these new data cauldron subsidence as the emplacement mechanism is disputed and evidence for an alternative laccolithic style model involving inflation is presented this includes deflection and uplift of host rock bedding close to contacts and the magnetic fabric pattern which has a gentle dome geometry even close to contacts the magnetic lineations usually plunge down dip near the external margins but otherwise have a general ssw nne trend that diverges northward this suggests a northward directed inflow direction the model for the emplacement of the eastern mourne pluton is a laterally fed laccolith emplaced south to north the eastern margin is interpreted as a faulted contact facilitating the inflation of an asymmetrical breached laccolith

contributions of wind forcing waves and surface heating to sea surface height observations in the pacific ocean the dominant processes affecting sea surface height ssh variability observed by the topex poseidon altimeter vary regionally in the pacific baroclinic rossby waves equatorially trapped kelvin waves steric response to seasonal heating and the response to wind stress curl forcing are all important the steric response to surface heating dominates seasonal ssh variability in the subpolar gyre and the eastern subtropical gyre south of the kuroshio extension and south of 20 n in the eastern pacific the dominant contribution to ssh is from near annual period rossby waves to quantify the wave energy observed ssh was assimilated into a kinematic model of westward propagating waves these waves account for 70 of ssh variance between 10 s and 10 n but only 30 between 10 n and 30 n although wave energy in the eastern pacific is correlated with ssh anomalies at the equator the much larger wave energy in the western pacific is correlated with wind stress curl suggesting that the rossby waves there are locally forced in addition to these planetary waves the ocean response to wind forcing via ekman pumping is observed in several places specifically in the north equatorial current a quasi steady topographic sverdrup balance is detectable over most of the north pacific at latitudes as low as 10 15 n as well as in the south pacific where it is seen north of 50 s the decomposition of the ssh signal into propagating waves an ekman pumping response and sverdrup transport is consistent with the results from an isopycnal numerical model

interannual westward propagating baroclinic long wave activity on line p in the eastern midlatitude north pacific abstract for the period 1959 81 quasi zonal hydrographic sections have been made between the southern coast of vancouver island 49 n 126 w and ocean station p 50 n 145 w approximately every two months along this section called line p hydrographic std stations were repeated at nearly the same locations approximately 2 of longitude apart and at closer intervals near the coast as such 13 stations in all were made nearly every two months over the 23 year period thus the line p dataset has particular value in verifying the existence of interannual baroclinic long waves near 50 n in previous studies white kang and magaard and white and saur had found evidence of annual and interannual baroclinic long wave activity in the eastern midlatitude north pacific over the range 20 40 n but earlier attempts could not discover these westward traveling waves along line p in this study both spectral analysis and complex empirical orthogonal function analysis are used to do just that concentrating u

rossby waves and the variability of the north pacific current during 2002 03 abstracta numerical model the parallel ocean program pop with 0 25 horizontal spatial resolution and 28 vertical levels is used to simulate the circulation of the north pacific ocean for the time period 1960 2006 spectral nudging is used so that model drift of the mean state over the 46 yr time period of the simulation is prevented while allowing for the prognostic evolution of the circulation at time scales that are not nudged the simulation successfully reproduces a southward shift in the north pacific current in 2002 03 as calculated from scalar observations it is suggested that this calculated shift may not be solely due to meridional current drift but also a consequence of the shifting intensity of two eastward moving current bands separated by 300 500 km a distance consistent with the rhines scale the scale at which the 2d turbulence cascade tends to be arrested which implies an influence from rossby waves that are heavily affected by nonlinearities the simulation suggests that the nort

magnetic fabrics of dike swarms from se bahia state brazil their significance and implications for mesoproterozoic basic magmatism in the sao francisco craton abstract magnetic fabrics were determined by applying two techniques anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanence aar ams was performed in 81 dikes from ilheus olivenca and itaju do colonia swarms located in se bahia the dikes intrude high grade metamorphic terrains as old as 3 2 ga dikes are vertical or subvertical in dip and trend mainly e w they are tholeiitic in composition and are classified into two groups characterized by high tio 2 2 and incompatible elements contents and low tio 2 and incompatible elements contents respectively thicknesses vary from a few centimeters to ca 20 m average of 3 m 40 ar 39 ar data indicate ages of 1 012 ilheus dikes and 1 078 ga olivenca dikes rock magnetism shows that ti poor titanomagnetites up to pure magnetites pseudo single domain multidomain grain sizes carry the magnetic fabrics three types of ams fabric are recognized i normal fabric 64 dikes defined by the clustering of k 1 k 2 axes on the dike plane whereas k 3 axes are nearly perpendicular to it this fabric is interpreted as due to magma flow ii intermediate fabric seven dikes characterized by k 1 k 3 axes clustering close to dike plane and k 2 axes perpendicular to the dike wall it was interpreted as due to vertical compaction of a static magma column with the minimum stress along the dike direction and iii inverse fabric nine dikes defined by k 2 k 3 plane parallel to the dike plane and k 1 perpendicular to dike wall aar measurements were performed in three dikes two of them with inverse and one with normal ams fabrics aar was coaxial for normal ams fabric and it resulted in intermediate and normal for inverse ams fabrics a combination of ams and aar fabrics suggests that the magmatic fabric for these dikes that should be flow was overprinted by some local event probably related to brasiliano orogeny processes after dike emplacement inverse ams fabric would record this event normal fabric is the most important one found for the studied swarms the analysis of k 1 inclination permitted one to infer that the dikes from ilheus were fed dominantly by horizontal fluxes k 1 k 1 60 dikes from itaju do colonia region have the steepest k 1 suggesting that this region could be closer to a magma source on the other hand a magma source near to olivenca area could be also inferred since the majority of the dikes were fed by inclined flow the existence of more than one source is supported by geochemical geochronological and paleomagnetic data which have shown that contemporaneous dikes were fed by compositionally distinct magmas the ams data also suggest that the majority of dikes were fed from upward flow coming from west to east and only a few of them were fed from upward flow from east to west

signatures of climate vs sea level change within incised valley fill successions quaternary examples from the texas gulf coast abstract the passive margin texas gulf of mexico coastal plain consists of coalescing late pleistocene to holocene alluvial deltaic plains constructed by a series of medium to large fluvial systems alluvial deltaic plains consist of the pleistocene beaumont formation and post beaumont coastal plain incised valleys a variety of mapping outcrop core and geochronological data from the extrabasinal colorado river and the basin fringe trinity river show that beaumont and post beaumont strata consist of a series of coastal plain incised valley fills that represent 100 kyr climatic and glacio eustatic cycles valley fills contain a complex alluvial architecture falling stage to lowstand systems tracts consist of multiple laterally amalgamated sandy channelbelts that reflect deposition within a valley that was incised below highstand alluvial plains and extended across a subaerially exposed shelf the lower boundary to falling stage and lowstand units comprises a composite valley fill unconformity that is time transgressive in both cross and down valley directions coastal plain incised valleys began to fill with transgression and highstand and landward translation of the shoreline paleosols that define the top of falling stage and lowstand channelbelts were progressively onlapped and buried by heterolithic sandy channelbelt sandy and silty crevasse channel and splay and muddy floodbasin strata transgressive to highstand facies scale architecture reflects changes through time in dominant styles of avulsion and follows a predictable succession through different stages of valley filling complete valley filling promoted avulsion and the large scale relocation of valley axes before the next sea level fall such that successive 100 kyr valley fills show a distributary pattern basic elements within coastal plain valleys can be correlated with the record offshore where cross shelf valleys have been described from seismic data falling stage to lowstand channelbelts within coastal plain valleys were feeder systems for shelf phase and shelf margin deltas respectively and demonstrate that falling stage fluvial deposits are important valley fill components signatures of both upstream climate change vs downstream sea level controls are therefore interpreted to be present within incised valley fills signatures of climate change consist of the downstream continuity of major stratigraphic units and component facies which extends from the mixed bedrock alluvial valley of the eroding continental interior to the distal reaches wherever that may be at the time this continuity suggests the development of stratigraphic units and facies is strongly coupled to upstream controls on sediment supply and climate conditions within hinterland source regions signatures of sea level change are critical as well sea level fall below the elevation of highstand depositional shoreline breaks results in channel incision and extension across the newly emergent shelf which in turn results in partitioning of the 100 kyr coastal plain valleys moreover deposits and key surfaces can be traced from continental interiors to the coastal plain but there are downstream changes in geometric relations that correspond to the transition between the mixed bedrock alluvial valley and the coastal plain incised valley channel incision and extension during sea level fall and lowstand with channel shortening and delta backstepping during transgression controls the architecture of coastal plain and cross shelf incised valley fills

magma flow directions in dikes of the koolau complex oahu determined from magnetic fabric studies we compared the magnetic fabric with the macroscopic surface lineation direction previously assumed to be parallel with magma flow direction for 35 dikes of the koolau complex oahu anisotropy of magnetic susceptibility ams was determined for 530 samples from 59 dikes including a sill and a pluglike intrusive body and two filled lava tubes and statistically significant ams clusters were found in all but five dikes for the 35 lineated dikes the mean maximum ams direction 1 coincides with the macroscopic lineations to within 25 in 18 and to within 15 in eight the ams ellipsoid shape in about half of the samples is prolate cigar shaped and in about half is oblate pancake shaped we interpret the ams to be determined by shape anisotropy of ferromagnetic grains the mean total anisotropy is 2 2 and total anisotropy h ranges from 0 24 to as high as 14 12 the principal ams axes for samples from a dike are tightly grouped on equal area plots and for most of the dikes the minimum ams axes plot near to the pole of the dike our ams measurements enable us to infer absolute magma flow directions for half the dikes studied the maximum ams axes of samples from one side of the dike form a tight cluster on an equal area plot and those from the other side of the dike form another tight cluster the two clusters are close together separated by 10 30 for narrow dikes 100 cm wide and are farther apart 30 60 for wide dikes and are symmetrically disposed on either side of the plane of the dike we infer that these paired clusters are caused by imbrication of nonequant ferromagnetic crystals against each margin of the dike during deposition in a velocity gradient and hence indicate the flow azimuth i e the absolute magma flow direction nearly half of the dikes measured 25 gave paired ams plots in 12 the magma flowed up at low oblique angles 5 30 from the horizontal in five it flowed down at 5 20 in four it flowed horizontally 5 in three it flowed up at a steep angle 50 75 and in one it flowed down at a steep angle the magma flow in general was rarely vertical or horizontal

geomorphic effectiveness a linear concept in a non linear world geomorphic effectiveness has been an influential concept in geomorphology since its introduction by reds wolman and john miller in 1960 it provided a much needed framework to assess the significance of an event by comparing event magnitude to the resultant geomorphic effects initially this concept was applied primarily in river channels under the linear assumption that geomorphic responses to similarly sized flood events will be consistent numerous authors have since attempted to quantify a direct proportional relationship between event magnitude and different forms of geomorphic response in a variety of geomorphic settings in doing so these investigations applied an array of metrics that were difficult to compare across different spatiotemporal scales and physiographic and geomorphic environments critically the emergence of other geomorphic concepts such as sensitivity connectivity thresholds and recovery has shown that relationships between causes events and geomorphic effects responses are often complex and non linear this paper disentangles the complex historical development of the geomorphic effectiveness concept and reviews the utility of various metrics for quantifying effectiveness we propose that total energy joules is the most appropriate metric to use for quantifying the magnitude of disturbance events cause and volumetric sediment flux associated with landform modification is the most appropriate metric for quantifying geomorphic effects while both metrics are difficult to quantify they are the only ones which facilitate comparison across a range of spatiotemporal scales comparability in a variety of geomorphic environments flexibility the geomorphic effectiveness concept can continue to be useful provided that geomorphologists use flexible and comparable metrics today geomorphologists are better prepared to consider the influence of non linear processes on determinations of geomorphic effectiveness allowing investigators to not only determine if a disturbance event was effective but also to explain why or why not copyright

using morphospaces to understand tafoni development tafoni research has tended to focus on issues around definition and differences rather than trying to develop general concepts for understanding the nature of tafoni this paper uses the concepts of fitness landscapes and morphospaces to develop a standardized and dimensionless phase space within which to represent visualize and analyse a dataset of 800 tafoni collected from antarctica within this phase space it is possible to identify clustering of tafoni forms and to illustrate how tafoni development is constrained by a relational hierarchy of rock structure processes and geometry or form

the relation between climate and river processes landforms and deposits during the quaternary abstract the extent to which river processes and morphology are dependent on climate is an old question when looking at large time scales climatic cyclicity seems to coincide with alternating events in fluvial development however the shorter the time scales at which fluvial development is considered the more it is difficult to find a close correspondence with climate evolution ultimately it appears that the response time of river processes to climatic change may restrict the sensitivity of the fluvial systems to adapt to short climatic oscillations the impact of climate on fluvial systems is largely transferred to these systems by the climate determined soil cohesion and peak discharges the latter factors are especially related to vegetation cover and permafrost conditions finally a number of basin characteristics are discussed that demonstrate that fluvial systems are not completely controlled by climate

magma flow directions of shallow dykes from the east greenland volcanic margin inferred from magnetic fabric studies abstract the role played by plume generated crustal magmatic complexes in the segmentation of volcanic margins is highlighted by a preliminary study of magma flow directions in shallow intrusives from the east greenland volcanic margin we investigate the magmatic texture using anisotropy of magnetic susceptibility for eight dykes of tholeitic affinity belonging to a dyke swarm associated with the tertiary opening of the north atlantic ocean the thickness of the sampled dykes ranges from 3 to 37 m the dykes are of doleritic texture and contain up to 12 of opaque minerals and 35 of plagioclase laths dykes showing a magnetic foliation plane within the dyke plane i e a magnetic fabric usually attributed to magmatic processes represent 40 of the samples from the studied swarm these dykes have a low degree of anisotropy and their ellipsoid of magnetic susceptibility is strongly oblate inverse magnetic fabrics where the maximum principal susceptibility axis lies near the pole to the dyke account for 60 of the data we interpret these inverse fabrics either as alteration minerals with highly prolate ellipsoids of magnetic susceptibility or primary titanomagnetites with oblate ellipsoid of low anisotropy the flow direction is inferred for normal fabric dykes using the mirror imbrication of magnetic lineation analysis of thin sections shows a good agreement between magnetic fabric directions and phenocryst preferred orientations the inferred flow directions are predominantly horizontal throwing a new light on volcanic margin development

a quasi geostrophic circulation model of the northeast pacific part i a preliminary numerical experiment abstract a limited area quasi geostrophic numerical model with mesoscale resolution is developed to study the circulation in the northeast ne pacific ocean the model domain extends from the british columbia alaska coast out to 170 w and down to 45 n and incorporates the coastline geometry and bottom topography of the region a long term integration was conducted using a steady climatological wind stress curl field to drive the circulation several statistical properties of the solution are determined and compared with observations a cyclonic circulation develops in the model basin with a meandering alaska current feeding at the head of the gulf of alaska into an intense boundary current corresponding to the alaskan stream the head of the gulf is a region where anticyclonic closed streamline features are occasionally generated with characteristics resembling those of the sitka eddy in the downstream region the boundary current separates and is subject to lateral meandering due to topographic wave

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

the form distribution and anisotropy of magnetic susceptibility of jurassic dykes in h u sverdrupfjella dronning maud land antarctica implications for dyke swarm emplacement abstract the mesozoic dyke swarms of western dronning maud land antarctica form a minor intrusive component of the karoo large igneous province five hundred and sixty one dykes were recorded intruding neoproterozoic gneisses and middle jurassic syenite plutons 40 ar 39 ar geochronology data reveal two temporally distinct components the 178 175 ma alkaline straumsvola dyke swarm that predominantly intrudes a nepheline syenite pluton and the 206 204 ma tholeiitic jutulrora dyke swarm found throughout the study area the straumsvola swarm exhibits highly variably dyke trends that display a restricted opening direction interpreted to be the result of high magma pressure equal to the maximum principal stress the jutulrora swarm displays a fan of dyke trends with dyke thickness and spacing increasing away from the inferred point of fan convergence anisotropy of magnetic susceptibility measurements reveal vertical magma transport within both dyke swarms in the straumsvola area with the southern outer exposures of the jutulrora swarm exhibiting lateral magma transport although associated with a long lived local igneous centre comparison of palaeostress estimates for the straumsvola dyke swarm and contemporaneous dykes in ahlmannryggen and vestfjella indicates the presence of a regional scale radial stress system in western dronning maud land between 178 175 ma supporting a mantle plume origin for the karoo large igneous province

physical weathering in arid landscapes due to diurnal variation in the direction of solar heating despite the prominent role of physical weathering in arid and semi arid landscapes there has been little study of the specifi c processes responsible for the rapid breakdown of subaerially exposed rocks for example many boulders and cobbles in deserts exhibit fi ne near vertical cracks although workers have hypothesized that these and other cracks are initiated by diurnal heating and cooling no convincing specifi c mechanism for their formation has been proposed we have characterized these cracks at eight sites on surfaces of different ages in the mojave sonoran and chihuahuan deserts and the high desert of central new mexico our data reveal four basic types of cracks longitudinal surfaceparallel fabric related and meridional the orientations of the fi rst three types are associated with clast shape and rock fabric the azimuths of meridional cracks however are preferentially aligned north south typically with a nonrandom multimodal distribution we propose that these cracks are caused by tensile stresses that arise in the interior of clasts due to strong radial gradients in temperature that evolve and rotate in alignment with the sun s rays we suggest that the multimodal nature of crack orientations may be in part attributable to the seasonally varying latitude dependent solar elevation angle over millennial time scales we suggest that this thermal cracking is an effi cient weathering process that together with cumulic soil epipedon development creates the key attributes of most desert pavements in addition to individual clasts exposed on desert surfaces this mechanism of cracking is potentially signifi cant in other climates and on other planets as well as for rock outcrops and for man made structures

known and suggested quaternary faulting in the midcontinent united states abstract the midcontinent united states between the appalachian and rocky mountains contains 40 known faults or other potentially tectonic features for which published geologic information shows or suggests quaternary tectonic faulting we report results of a systematic evaluation of published and other publicly available geologic evidence of quaternary faulting these results benefit seismic hazard assessments by 1 providing some constraints on the recurrence intervals and magnitudes of large prehistoric earthquakes and 2 identifying features that warrant additional study for some features suggested quaternary tectonic faulting has been disproved whereas for others the suggested faulting remains questionable of the 40 features nine have clear geologic evidence of quaternary tectonic faulting associated with prehistoric earthquakes and another six features have evidence of nontectonic origins an additional 12 faults uplifts or historical seismic zones lack reported paleoseismological evidence of large quaternary earthquakes the remaining 13 features require further paleoseismological study to determine if they have had quaternary earthquakes that were larger than any known from local historical records seven of these 13 features are in or near urbanized areas where their study could affect urban hazard estimates these seven are 1 the belt of normal faults that rings the gulf of mexico from florida to texas 2 the northeast ohio seismic zone 3 the valmont and 4 goodpasture faults of colorado 5 the champlain lowlands normal faults of new york state and vermont and 6 the lexington and 7 kentucky river fault systems of eastern kentucky

holocene evolution of the east texas coast and inner continental shelf along strike variability in coastal retreat rates abstract the low gradient east texas coast and inner continental shelf from sabine lake at the texas louisiana border to the western end of galveston island experienced extreme along strike variations in rates of holocene coastal retreat around 7 7 ka a barrier shoreline was located approximately 55 km offshore toward the western end of galveston island the shoreline retreated 55 km occupying a position on the lagoon side of the island by about 5 3 ka toward the texas louisiana border the shoreline retreated more gradually occupying a position seaward of sabine bank by 5 3 ka between 4 7 ka and 2 8 ka the shoreline at sabine bank retreated 30 km while galveston island prograded seaward bolivar peninsula began to accrete around 1 5 ka heald and sabine banks located on the inner continental shelf above terraced fluvial deposits of the trinity sabine incised valley are the only preserved remnants of these former shoreline positions fluctuating rates of sea level rise were not the forcing mechanism behind episodes of rapid shoreline retreat because these events were localized rather along strike variations in the rate of transgression were caused by the variable inner shelf gradients which increase towards the west and the orientation of the sabine incised valley and associated terraced fluvial deposits which trend northeast southwest parallel to shore as shorelines retreated over fluvial deposits these served as local sand sources that enabled barrier islands to persist figure 1 map of the east texas inner shelf showing locations of sabine heald and shepard banks paleotopographic map of the pleistocene surface thin contours siringan 1993 delineates the trinity sabine incised valley which formed during the last lowstand of sea level thomas and anderson 1994 bathymetric contours are shown as thick lines with bold numbers dots are core locations end page 405 offshore out of equilibrium with sea level once these sand sources became depleted and or sea level reached some critical threshold barrier shorelines became stranded offshore as banks and new shorelines formed landward the geologic setting of coastal areas specifically antecedent topography plays a primary role in controlling coastal evolution to accurately forecast long term centennial to millennial coastal evolution it is essential that impacts associated with variations in the underlying geology of coastal areas be incorporated into coastal forecasting models

thickness and spatial distributions of clastic dykes northwest sacramento valley california abstract the geometry and distribution of the clastic dykes of the ono district north sacramento valley are examined within stream sections five traverses along dry stream beds provide good exposure allowing the spacing thickness and geometry of the dykes to be recorded the spatial and thickness distribution of the dykes are considered using cumulative frequency plots allowing a visual estimation of a best fit distribution dyke thickness conforms best to a log normal distribution there is also a characteristic minimum dyke thickness in a traverse and this is attributed to the minimum aperture that a fluid with sand clasts is able to exploit dyke spacing however shows a good correlation with a power law distribution for four traverses suggesting that there is a mechanistic control on the spatial distribution plotting dyke thickness against minimum dyke spacing reveals that thin dykes do not generally intrude in isolation unlike veins and igneous dykes clastic dykes continue to provide preferential pathways for fluid flow subsequent to their intrusion thus inhibiting intrusion in the area surrounding a pre existing dyke a combination of this process and dyke branching provides the best model for the observed spatial and thickness distribution of clastic dykes seen in the ono district california

the elusive feeders of the karoo large igneous province and their structural controls abstract dolerite sills in the central parts of the karoo large igneous province on the kalahari craton in south africa record the emplacement of magic magmas over 350 000 km2 but the feeders to the voluminous magmatism have yet to be identified extensive exploration and mining data across a 7400 km2 area and to a depth of 2 5 km in the northern karoo basin provide unprecedented access to the subsurface geometry of dolerite sills and their relationship to underlying basement strata the data show saucer shaped sills in the karoo supergroup with distinctly funnel shaped geometries along their base that are seated within basement rocks the funnel shaped dolerite structures are interpreted to represent the feeders to the overlying regional scale sill saucer complexes four distinct saucer geometries can be identified 1 cone shaped saucers that extend outwards from a single funnel shaped point type a 2 elongated saucers that dip towards multiple aligned funnel shaped points type b 3 the more commonly described elongated saucers with flat inner sills type c and 4 elongated saucers with a combination of type b and c geometries type d type a and c saucer geometries and point like contacts are consistent with analogue models of saucers for respective pipe like and linear feeders however the multiple pipe like feeders associated with type b and combination thereof with sheet like feeders type d represent saucer feeder relationships thus far not modelled notably the lower dolerite funnels are commonly rooted in older faults and or dykes within the basement rocks this spatial correlation emphasizes the significance of pre existing basement structures in the kalahari craton for the long range transfer of the magmas through the crust the distributed occurrence of numerous magma feeders across much of the craton is more consistent with thermal incubation of the sub lithospheric mantle beneath gondwana than the impact of a mantle plume

petrogenesis of peralkaline granite dykes of the straumsvola complex western dronning maud land antarctica peralkaline syenite and granite dykes cut the straumsvola nepheline syenite pluton in western dronning maud land antarctica the average peralkalinity index pi molecular al na k of the dykes is 1 20 n 29 and manifests itself in the presence of the zr silicates eudialyte dalyite and vlasovite and the na ti silicate narsarsukite the dykes appear to have intruded during slow cooling of the nepheline syenite pluton and the petrogenetic relationship of the dykes and the pluton cannot be related to closed system processes at low pressure given the thermal divide that exists between silica undersaturated and oversaturated magmas major and trace element variations in the dykes are consistent with a combination of fractional crystallization of parental peralkaline magma of quartz trachyte composition and internal mineral segregation prior to final solidification the distribution of accessory minerals is consistent with late stage crystallization of isolated melt pockets the dykes give an rb sr isochron age of 171 4 4 ma with variable initial 87sr 86sr ratio 0 7075 0 0032 and have an average e nd of 12 0 quartz phenocrysts have 18o values of 8 4 9 2 which are generally in o isotope equilibrium with bulk rock differences in the 18o values of quartz and aegirine average quartz aegirine 3 5 suggest aegirine formation temperatures around 500 c lower than expected for a felsic magma but consistent with poikilitic aegirine that indicates subsolidus growth the negative e nd 10 and magma 18o values averaging 8 6 assuming quartz magma 0 6 are inconsistent with a magma produced by closed system fractional crystallization of a mantle derived magma by contrast the nepheline syenite magma had mantle like 18o values and much less negative e nd average 3 1 n 3 the country rock has similar 18o values to the granite dykes average 8 0 n 108 this means that models for the petrogenesis of the granites by assimilation are unfeasible unless an unexposed high 18o contaminant is invoked instead it is proposed that the peralkaline syenite and granite dykes formed by partial melting of alkali metasomatised gneiss that surrounds the nepheline syenite followed by fractional crystallization

annual rossby wave characteristics in the california current region from the geosat exact repeat mission abstract examination of sea level variability in the california current region from 20 to 50 n and from the coast of north america to 140 w was made possible with altimetric observations obtained by the geosat exact repeat mission erm for the period november 1986 october 1987 during this period a time sequence of twenty one 17 day maps of altimetric sea level residuals over the califomia current region was constructed the rms distribution of these altimetric sea level residuals displayed local maxima at three locations adjacent to the coast of california i e off point eugenia at 27 n southwest of point conception at 32 n and between monterey and cape mendicino i e 37 40 n complex empirical orthogonal function ceof analysis reveals that 53 of the variance over this one year period was associated with the annual cycle with amplitude maximum in summer and minimum in winter the spatial distribution of amplitude displayed local maxima adjacent to the coast again at 27 n 32 n and from

aspects of jurassic magmatism and faulting in western dronning maud land antarctica implications for gondwana break up

applicability of ams technique as a flow fabric indicator in dykes insight from nandurbar dhule deccan dyke swarm determination of the nature of magma flow vertical or lateral from rock fabrics in a dyke swarm holds significant importance in deciphering its emplacement mechanism depth of magma chamber and its association with mantle plumes nandurbar dhule dyke swarm from western india consists of 210 mappable tholeiitic large linear dykes intruding the country rocks of deccan basalt we discuss here the development of flow controlled rock fabrics in these dykes as a function of their thicknesses magnetic fabric obtained from anisotropy of magnetic susceptibility ams analysis of the samples collected from these dykes was used as a proxy for rock flow fabric samples from the central parts of the thicker dykes strike perpendicular thickness 10 m show random and inconsistent development of magnetic fabrics than their marginal counterparts petrography suggests the development of relatively clear shape preferred orientations of the elongated mineral grains only at the margin of a thick dyke thinner dykes strike perpendicular thickness 10 m show both consistent magnetic fabrics and clear shape preferred orientations we propose that the center of a thick dyke fails to provide due to high flow velocity slower cooling rate lack of friction induced shearing and draining back of magma a favorable condition where a flow fabric can efficiently develop and b magnetic fabric can effectively mimic the flow fabric thinner dykes and the margins of the thicker dykes are hence better candidates for observing flow fabrics represented by magnetic fabrics this work is also motivated by the reservations expressed by earlier researchers in using the ams technique for magma flow characterization especially for giant dyke swarms we have critically evaluated their reservations in light of our results and commented on the applicability of the ams technique on such studies

pegmatite dyke emplacement and the state of stress during cratonization an example from the dharwar craton south india abstract in this study we measured orientations of 797 pegmatite dykes intruding the 2 5 ga koppal pluton dharwar craton south india and use the data to evaluate the state of stress prevalent during dyke emplacement we infer that the dykes were emplaced synchronously with late d3 regional deformation that was controlled by nw se directed shortening dykes within the koppal pluton kp have a restricted range of orientations which is indicative of fluid pressure pf

possible role of midcrustal igneous sheet intrusions in cratonic arch formation 1 factors controlling widespread cratonic arch formation across western north america from the early paleozoic to the middle mesozoic remain poorly understood while a number of causes such as mantle hot spots lithospheric contraction mantle flow and lithospheric flexure due to surface loading have been suggested to explain the localized uplift of basement blocks on otherwise tectonically quiescent margins a variety of mechanisms may be at work here we test the hypothesis that seismically detected packages of discrete midcrustal igneous sheet intrusions impart rheological contrasts within the crust which act as seeds for cratonic arch formation in the presence of weak intraplate compression using finite element modeling of intraplate deformation we find that the seismically resolved sills can generate significant surface uplift in the presence of modest strain rates over reasonable orogenic timescales cratonic arch formation would be enhanced in the presence of additional thin seismically unresolvable sills while midcrustal sheet intrusions may be just one of many factors influencing cratonic arch formation their presence in northern alberta canada can help explain the asymmetric configuration of the well studied peace river arch

low frequency isopycnal variability in the alaska gyre from argo abstract the deployment of a large number of argo floats in the northeast pacific ocean since 2001 has led to a great increase in the volume of data available to study the regional variability on interannual to decadal time scales in this paper gridded fields of hydrographic data from argo are used to examine the low frequency variability of representative isopycnal surfaces over the alaska gyre in the eastern subpolar north pacific anomalies in the depth of isopycnal surfaces and spice anomalies on these surfaces are considered over the 14 year period 2004 2017 an eof analysis is used to characterize the variability occurring at large scales over the region the leading mode of isopycnal depth anomalies through the upper 1000 m of the water column is found to be related to the pacific decadal oscillation the response of a stochastic climate model driven by local ekman pumping is shown to give a reasonable account of variability in the depth of the shallow main pycnocline over the alaska gyre although ocean dynamics must play a role in shaping the spatial response to the wind forcing evidence is presented for counter propagating isopycnal depth anomalies in the subarctic current at the depth of the main pycnocline propagation is dominated by disturbances that are advected eastward by the mean flow at greater depths isopycnal depth anomalies propagate westward at approximately twice the speed of first mode long baroclinic rossby waves consistent with the propagation of rossby waves seen in altimetric observations of sea surface height variability the eastward advection of spice anomalies is also evident in the upper ocean however the dominant signal in the record is a large scale positive spice anomaly that forms locally on subsurface isopycnals evidence is presented that this anomaly arises mainly from the downward diffusion across the pycnocline of heat associated with the marine heatwave of 2013 14 over the northeast pacific the extent to which anomalies are generated locally may limit the potential for decadal prediction of upper ocean conditions over the region

magnetic anisotropy produced by magma flow theoretical model and experimental data from ferrar dolerite sills antarctica summary volcanic rocks forming sills dykes or lava flows may display a magnetic anisotropy derived from the viscous flow during their emplacement we model a sill as a steadystate flow of a bingham fluid driven by a pressure gradient in a horizontal conduit the magma velocity as a function of depth is calculated from the motion and constitutive equations vorticity and strain rate are determined for a reference system moving with the fluid the angular velocity and the orientation of an ellipsoidal magnetic grain immersed in the fluid are calculated as functions of time or strain magnetic susceptibility is then calculated for a large number of grains with a uniform distribution of initial orientations it is shown that the magnetic lineation oscillates in the vertical plane through the magma flow direction and that the magnetic foliation plane changes periodically from horizontal to vertical the results are compared with the magnetic fabric of ferrar dolerite sills victoria land east antarctica derived from low field susceptibility measurements

is this magnetic fabric normal a review and case studies in volcanic formations abstract when studying weakly anisotropic rocks non standard relationships between magnetic and expected petrofabric axes are sometimes observed in particular the so called inverse or intermediate fabrics a review of possible explanations for these effects is presented and leads to the conclusion that a majority of abnormal magnetic fabrics often encountered in magnetite rich volcanic rocks are due to abnormal preferred orientations or distributions of magnetite grains through case studies in dikes from skye island yemen and the iberian peninsula and magma and ash flows from the ethiopian traps and southern corsica the various possible origins of such fabrics are examined it is possible to retrieve reliable magma flow directions from these sites provided proper data selection is performed leading to non unique interpretations

magma flow pattern of the 1 78 ga dyke swarm of the north china craton during the initial assembly of the supercontinent nuna columbia constraints from rock magnetic and anisotropy of magnetic susceptibility studies abstract the geodynamic origin of the 1 78 ga dyke swarm in the north china craton ncc is long debated it is considered either a post collision process or paleoplume related constraining its origin is essential for the reconstruction of the ncc position within the supercontinent nuna also referred to as columbia here we report on the rock magnetism and anisotropy of magnetic susceptibility ams of thirty three 1 78 ga dykes to constrain the magma center of the igneous event the samples were collected from the entire swarm across the ncc magnetite appears to be the dominant magnetic mineral in all the dykes occasionally with minor maghemite while the magnetite grain size within the dykes is generally increasing from south to north ams results of the dykes portray a magma flow related fabric over half of the studied dykes show a predominance of horizontal to subhorizontal magmatic flow while a few have been formed by vertical intrusion these observations imply that the 1 78 ga dyke swarm may have been generated by sustained magma flow from a magmatic source centered at the south margin of the ncc during dyke propagation some localized magma subchambers may have been formed they could be responsible for the less common vertically intruded dykes and the ew trending dykes therefore a plume related tectonic setting for the 1 78 ga dyke swarm is more compelling with the eruption center along the margin of the ncc it may serve as an essential criterion to search for possible counterparts in other tectonic units within nuna columbia to evaluate the proximity of the ncc with them

observation of mesoscale ocean features in the northeast pacific using geosat radar altimetry data in this paper geosat altimetry data from the northeast pacific are examined the data are 1 binned data on 1 latitude by 2 longitude blocks and 2 collinear track data the binned data cover the region from 20 n to 60 n from the north american coast westward to 150 w and span from december 15 1986 to june 1 1989 to examine the data for evidence of westward propagation of sea level anomalies three zonal transects 45 n 49 n and 57 n are made complex empirical orthogonal function analysis of the data transects at these latitudes reveals phase speed and amplitude information the first eigenmode at each latitude has a very strong annual signal two dimensional spectral analysis of the first eigenmode at 45 n and 57 n shows westward propagation of sea level anomalies at 45 n only the propagating features are annual in period and of order 1000 km in length at 57 n westward propagation is evident as at 45 n but there is also an eastward component to examine the variability of the coastal sea level signal collinear track data from three ascending tracks crossing the gulf of alaska are analyzed revealing mesoscale features of the order of 100 km that parallel the canadian and alaskan coast the most notable feature is the sitka eddy westward propagation of several of these features is observed the results from the analysis of both types of geosat data are compared with other observational data

origins and implications of soil layering abstract layering is common in soils due to a variety of pedologic and geologic processes and has important consequences for the interpretation of soils and landscapes layering can derive from original sedimentary layering depositional upbuilding episodic surface erosion deposition and stability soil production by weathering vertical or lateral translocation bioturbation and various combinations of these complex and polygenetic models incorporate both geogenic and pedogenic processes and allow for physical and biological processes as well as both vertical and horizontal movements we review these conceptual frameworks and synthesize them into a vertical contrast model vcm for interpreting layered surficial materials the vcm incorporates a variety of geologic and pedologic processes which may create destroy enhance or obscure vertical contrasts the model is illustrated via application to sites in the ouachita mountains usa and northwest saxonian lowlands germany the examples illustrate the importance of a comprehensive pedogeomorphic interpretation of layering since neither standard stratigraphic or top down pedogenetic principles necessarily apply the examples also show that the same process can sometimes contemporaneously both create and destroy vertical contrasts

dynamic topography and long term sea level variations there is no such thing as a stable continental platform abstract globally uniform i e eustatic sea level trends with time scales approaching 100 myr have been inferred from both seismic and backstripping stratigraphic analysis at a small set of geographic sites that are presumed to lie on stable continental platforms and passive continental margins characterized by simple thermal subsidence histories e g the new jersey margin the western african margin we demonstrate using mantle flow simulations based on high resolution seismic tomography that both the new jersey margin and the conjugate western african margin have been subject to orders of 100 m of dynamic i e flow induced topography change over the last 30 myr we also show that the changing pattern of downwelling mantle flow associated with plate subduction is a significant contributor to the background eustatic sea level trend which is also of order 100 m during the 30 myr time window therefore late cenozoic variations of dynamic topography on these passive margin sites are comparable to the eustatic sea level changes and can partially mask the latter furthermore even if the observed trend could be accurately corrected for local dynamic topography variation the residual eustatic signal does not merely reflect changes in mean spreading rates at mid ocean ridges we conclude that the observed long term sea level variations at so called stable sites cannot be interpreted as eustatic moreover previous analyses that have used long term sea level trends as a proxy for spreading rates and geochemical fluxes must be revisited

paleomagnetism and magnetic fabric of middle jurassic dykes from western patagonia argentina abstract jurassic volcanism in patagonia is widespread although associated dyke swarms are conspicuous they have been almost neglected in previous geologic studies of this region radiometric paleomagnetic and magnetic anisotropy studies are reported from a middle jurassic basic to intermediate dyke swarm exposed in the sierra de mamil choique western patagonia in an area of over 350 km2 two whole rock k ar determinations indicate that these dykes were intruded at around 170 ma an anisotropy of magnetic susceptibility ams study on 15 dykes 74 block samples shows that they carry different kinds of magnetic fabric both normal and inverse apparently governed by compositional differences a paleomagnetic study of these samples suggests that ti poor titanomagnetite is the probable carrier of the characteristic remanence mean site characteristic directions pass a reversal test grade c a paleomagnetic pole computed by averaging vgps from each individual dyke is situated at 70 2 s 190 4 e n 13 95 9 7 not substantially apart from other middle jurassic poles from south america further refinement of the jurassic south american apparent polar wander path is needed to establish whether or not the mamil choique dykes were affected by a small tectonic rotation

variation in the form and distribution of dykes in the mull swarm scotland the dykes of the mull swarm part of the british tertiary igneous province have been examined in a series of well exposed coastal sections traverses through the dyke swarm show systematic changes in the thickness and spacing of dykes both of which are typically log normally distributed both the geometric mean thickness and spacing of dykes increase with distance from the mull centre concordant with a decrease in crustal extension variations in the thickness and spacing result from changes in character of the magma flow it is inferred that the magma flux was fairly evenly distributed near the mull centre but farther away from the source it becomes focused into larger dykes the form orientation and opening direction are also observed to vary with distance away from the volcanic centre on mull the dykes intrude a range of pre existing fractures the range of fractures used decreases with distance from the centre this together with other features of the form of the dykes have been interpreted in terms of the varying magma pressure and regional stress which is expressed as the r ratio analysis of the variable strikes of fracture filled dykes is consistent with decreasing magma pressure with distance from the mull centre assuming that regional stresses were relatively invariant across the same distance

flow lobes in granite the determination of magma flow direction in the trawenagh bay granite northwestern ireland using anisotropy of magnetic susceptibility anisotropy of magnetic susceptibility ams has been determined from 152 sites over the 64 km2 trawenagh bay granite part of the 400 ma caledonian donegal batholith microscopic observations thermomagnetic analyses high field torque magnetometry and heating experiments demonstrate that the ams fabric is carried by biotite with varying amounts of mimetic magnetite in the biotite cleavage planes the ams fabric is interpreted as a flow fabric because microstructures indicate magmatic state deformation it defines large scale macroscopic flow features flow lobes in this weakly deformed granite at pluton scale the data set shows a gentle westward plunging lineation at a smaller scale many lobate magnetic foliation patterns can be discerned in which the magnetic lineation is usually symmetrically disposed about the long axes of the lobes in three dimensions the lobes are tongue like 1500 m wide subunit scale and elongated east west parallel with the general lineation they close consistently westward and younger lobes in the east appear to deflect older lobes in the west the trawenagh bay granite is west of a major synplutonic shear zone that hosts the main donegal granite pluton these structures are interpreted as frozen flow lobes and indicate that the magma flowed in a westward direction from within the active shear zone of the main donegal granite into the weakly deformed wall rock trawenagh bay granite intra unit pulses or surges have long been suspected in granite plutons however this study reports the most detailed description of such structures to date

the search for a topographic signature of life landscapes are shaped by the uplift deformation and breakdown of bedrock and the erosion transport and deposition of sediment life is important in all of these processes over short timescales the impact of life is quite apparent rock weathering soil formation and erosion slope stability and river dynamics are directly influenced by biotic processes that mediate chemical reactions dilate soil disrupt the ground surface and add strength with a weave of roots over geologic time biotic effects are less obvious but equally important biota affect climate and climatic conditions dictate the mechanisms and rates of erosion that control topographic evolution apart from the obvious influence of humans does the resulting landscape bear an unmistakable stamp of life the influence of life on topography is a topic that has remained largely unexplored erosion laws that explicitly include biotic effects are needed to explore how intrinsically small scale biotic processes can influence the form of entire landscapes and to determine whether these processes create a distinctive topography

laboratory drilling of field orientated block samples abstract corrections required to restore specimens to their field attitude are given for specimens cored in the laboratory from a block arbitrarily orientated on the drill table

the influence of valley aggradation and listric normal faulting on styles of river avulsion a case study of the brazos river texas usa abstract the holocene avulsion history of the lower brazos alluvial valley of east texas usa was studied using 10 drill cores 26 radiocarbon dates aerial photos and a digital elevation model this study shows that two long term processes aggradation and localized valley tilting along a normal listric fault are responsible for generating two styles of avulsion the first process precedes avulsion by progradation while the second process precedes avulsion by annexation as valley aggradation migrated updip over the last 7 5 ka three regional backstepping avulsions occurred along the lower 140 km of the valley and each generated sizable deposits a pattern emerges of landward stepping progradational avulsions tracking the locus of valley aggradation and of valley aggradation migrating inland even after the rate of sea level rise diminishes at the same time several local nodal avulsions occurred between 50 and 55 km updip of the current highstand shoreline but generated no observable deposits geomorphic evidence indicates that since the late pleistocene active movement along a previously undocumented normal listric fault has occurred at the location of the nodal avulsion these two long term processes do not operate mutually exclusive of each other to promote avulsions rather they operate concurrently only aggradation promotes avulsions that affect floodplain alluviation although the total volume of these deposits comprises a small portion of the valley fill

geology and petrogenesis of the straumsvola nepheline syenite complex dronning maud land antarctica the 170 ma straumsvola nepheline syenite complex in western dronning maud land antarctica is located on the eastern edge of the penck jutul trough a major tectonic feature which may be a palaeozoic mesozoic rift system the 5 km diameter pluton consists entirely of nepheline syenite and can be divided into two volumetrically important units a relatively structureless outer zone which is overlain by a layered zone the latter exhibits continuous rhythmic alternations of layers containing different proportions of alkali feldspar to amphibole na rich pyroxene biotite nepheline throughout its 350 m thickness the mafic zone is a volumetrically minor unit which unconformably overlies the layered zone and consists almost entirely of mafic minerals and nepheline the layered zone shows no systematic stratigraphic variation in major or trace composition or mineral chemistry which is interpreted as being due to a combination of migration of intercumulus liquid and action of deuteric fluids the remarkably constant thickness of successive layers throughout the layered zone suggests that layering resulted from an internally self regulating processes the layering is defined by changing proportions of alkali feldspar to mafic minerals nepheline which is consistent with layering being caused by differences in nucleation rate during eutectic crystallization dykes associated with the complex show wide ranging compositions and include both over and undersaturated types low s l9 o values of the nepheline syenites mean 5 9 o n 9 suggest that the magma from which the nepheline syenites crystallized was mantle derived peralkaline microgranite dykes have higher s n o values mean 7 3 n 4 and it is suggested that they are either undersaturated liquids contaminated by siliceous crust or derived by partial melting of partly fenitized gneiss oxygen isotope ratios of the surrounding gneiss indicate that the intrusion of the nepheline syenite did not cause extensive circulation of meteoric or magmatic hydrothermal fluids

subglacial imprints of early gondwana break up as identified from high resolution aerogeophysical data over western dronning maud land east antarctica determining the location and geometry of possible subglacial rifts in western dronning maud land is a key element to address processes leading to early gondwana break up however previous geophysical investigations did not lead to unambiguous delineation of rift structures over this region we interpret high resolution airborne radar and aerogravity data to image subglacial rift structures subglacial topography free air and bouguer gravity maps coupled with 3d inverse gravity models image a rift rift rift triple junction at the intersection of the jutulstraumen ice stream and the pencksokket glacier these continental rifts were associated with alkaline and tholeiitic intrusions minor dyke swarms and flood basalts of jurassic age but not with huge volumes of karoo magmatism such as that which characterizes the southern africa conjugate margin the western dronning maud land triple junction may be linked to the karoo mantle plume and represents an early stage of magmatism and rifting during gondwana break up

interdecadal variations in the alaska gyre abstract climatic dynamic topography variations in the alaska gyre during the period 1968 1990 are described with an objective analysis of more than 12000 std and xbt stations and coads wind stress data interannual dynamic height and sst variations were correlated and were consistent with recently described large scale climatic shifts in the north pacific the gyre was cantered more to the east circulation appeared stronger and sst was lower during the early to mid 1970s than during the 1980s the aleutian low np and pna indices intensified during the interim but the response did not appear as a gyre spinup instead the associated wind stress anomalies forced a slowly varying dynamic height anomaly across the eastern and northern part of the gyre through ekman convergence which had the effect of displacing the gyre s low somewhat to the wsw in the 1980s the wind curl spectrum was white and the slow oceanic response was modelled as stochastic forced climate variability with a simple first order m

on the thermal viability of dikes leaving magma chambers dikes beginning to propagate away from a magma source are thin and grow slowly and thus are susceptible to freezing a self similar solution is obtained for a dike propagating down a temperature gradient when the wallrock and magma temperatures are equal at the chamber wall the solution applies only to the special case of a single component magma intruded at the solidus temperature but provides insight into the case in which the magma temperature is above the solidus the dike propagation velocity relative to that in the absence of freezing is determined by a single dimensionless parameter for sufficiently large magma freezing chokes the dike faster than propagation can elastically widen it and the dike cannot grow if the magma intrudes at a temperature above the solidus there is some value of above which the dike will propagate a certain distance and freeze and below which it will propagate until depletion of the source or three dimensional elastic effects promote freezing for reasonable parameters this process can explain why basaltic dikes are found far from obvious source regions while granitic dikes are scarce except in the immediate vicinity of granitic plutons even if a rhyolite is 5 orders of magnitude more viscous than a basalt however this distinction can be offset if the rhyolite has an excess source pressure only 1 order of magnitude greater than that of the basalt

evidence from magnetic fabric for the flow pattern of magma in the mackenzie giant radiating dyke swarm continental flood basalts and their associated swarms of mafic dykes are thought to result from melting in mantle plumes1 3 but the processes by which the resulting magma makes its way from mantle to crust remain obscure here we use magnetic anisotropy measurements to reconstruct the pattern of magma flow in the proterozoic mackenzie dyke swarm our results indicate that magma was injected vertically within 500 km of the focal point of the dyke swarm and then travelled horizontally at all further distances out to at least 2 100 km the sharp transition from vertical to horizontal flow at between 500 and 600 km may correspond to the outer boundary of melt generation in the mantle plume believed to be responsible for the mackenzie igneous events

the anticyclonic baroclinic eddy off sitka alaska in the northeast pacific ocean abstract among the many mesoscale eddies found in the northeast pacific ocean is a well developed anticyclonic baroclinic eddy situated within a few hundred kilometers of sitka alaska 57 n 138 w it has definitely been observed during spring and summer 1958 summer 1960 and summer 1961 observations made at other times show some evidence of its occurrence also the trajectories of three norpax drifting buoys for april may 1977 also indicated the probable presence of an eddy there the eddy whose diameter ranges from 200 to 300 km and whose depth extends to 100 m and probably to as much as 2000 m recurs at the same location the center of the eddy is characterized by the following features the surface water is less saline and only somewhat warmer than at its periphery at depths within and below the halocline it is warmer less saline and contains more dissolved oxygen than at the periphery and a warm core is situated within the halocline the halocline is usually depressed by less than 100 m but

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

perfection and complexity in the lower brazos river abstract the perfect landscape concept is based on the notion that any specific geomorphic system represents the combined interacting effects of a set of generally applicable global laws and a set of geographically and historically contingent local controls because the joint probability of any specific combination of local and global controls is low and the local controls are inherently idiosyncratic the probability of existence of any given landscape is vanishingly small a perfect landscape approach to geomorphic complexity views landscapes as circumstantial contingent outcomes of deterministic laws operating in a specific environmental and historical context thus explaining evolution of complex landscapes requires the integration of global and local approaches because perfection in this sense is the most important and pervasive form of complexity the study of geomorphic complexity is not restricted to nonlinear dynamics self organization or any other aspects of complexity theory beyond what can be achieved via complexity theory the details of historical and geographic contexts must be addressed one way to approach this is via synoptic analyses where the relevant global laws are applied in specific situational contexts a study of non acute tributary junctions in the lower brazos river texas illustrates this strategy the application of generalizations about tributary junction angles and of relevant theories does not explain the unexpectedly high occurrence or the specific instances of barbed or straight junctions in the study area at least five different causes for the development of straight or obtuse junction angles are evident in the lower brazos the dominant mechanism however is associated with river bank erosion and lateral channel migration which encroaches on upstream oriented reaches of meandering tributaries because the tributaries are generally strongly incised in response to holocene incision of the brazos the junctions are not readily reoriented to the expected acute angle the findings are interpreted in the context of nonlinear divergent evolution geographical and historical contingency synoptic frameworks for generalizing results and applicability of the dominant processes concept in geomorphology

catena linking of landscape geochemical processes and reconstruction of pedosedimentogenesis a case study of defensive constructions of the mid 17th century south russia abstract the catena concept along with previously proposed meanings of this term has recently acquired a soil evolutionary content the prospects of wider special and chronological study of dated pedotopocatenas include the possibility of a more detailed analysis of the mutual dependence of soil geomorphological relationships through distinguishing relatively homogeneous climatic stages of pedogenesis and denudation with this purpose the present study comprised earthen defensive constructions which within the rampart ditch system combine erosive trans accumulative catenas and accumulators of pedolithosediments the goal was to develop a system of the most information rich pedogenetic indicators to reconstruct the dynamics of erosion accumulative processes on the basis of dated earthen defensive constructions of a historical period using the example of a frontier rampart within a ditch from the mid 17th century soil samples were collected within the limits of the erosion and trans accumulative catenas as well as in the closing alignment of the ditch over the vertical profile in eight strata of pedosediments of up to 1 m high the granulometric composition concentration of macroelements and trace elements 25 metals and oxides in soils and in particles with sizes 0 01 mm in size the content of organic carbon and its qualitative composition the sum of the elements accumulated in the soil p ca k mg mn cu as well as the geochemical ratios which reflect the processes of leaching can serve as palaeogeographic tracers of the climatic variability at the level of intra secular changes under forest steppe conditions the history of the formation of pedosediments over 3 5 centuries in the forest steppe zone of eastern europe comprises two wet periods 1890 1935 1976 2013 when the average annual rates of pedosedimentogenesis were similar 2 80 2 85 mm yr 1 and two periods of geomorphological lull and a xeromorphic climatic condition span 1821 1890 and 1666 1741 these periods correspond to diminution of the average rate of accumulation of sediments down to 2 47 mm yr 1 the results of the present study suggest the need for purposeful research and wide inclusion of dated sites of the anthropogenic relief formation with flow geochemical series over the topographic gradient into studies of soil geomorphologic interrelations and calibration of mathematic models of natural processes using on site data

magnetic fabrics and rock magnetism of the xiong er volcanic rocks and their implications for tectonic correlation of the north china craton with other crustal blocks in the nuna columbia supercontinent abstract the tectonic background of the paleoproterozoic xiong er volcanic rocks xvr is important for understanding the tectonic evolution of the north china craton ncc as well as its paleogeographic position during the assembly of the nuna columbia supercontinent here we report the results of the first anisotropy of magnetic susceptibility ams study of the xvr and use the interpreted flow directions to constrain the emplacement mechanism and to assess its geological significance for the reconstruction of the nuna columbia supercontinent thirty lavas were sampled from three sections in western henan province detailed rock magnetic analyses including measurements of hysteresis loops magnetization versus temperature curves and first order reverse curves were performed to identify the main magnetic phases and grain sizes the inferred directions from the ams results reveal a radial flow pattern with an eruption center probably located near xiong er mountain our data suggest that the xvr may have been emplaced in a triple conjugated continental rift on the south margin of the ncc probably initiated from a paleoplume based on this interpretation a comparison of geological and paleomagnetic results among the proposed crustal blocks in the nuna columbia supercontinent suggests a close linkage of the ncc with sao francisco congo rio de la plate and siberia

sandstone weathering a century of research and innovation abstract a review of sandstone weathering research particularly in the past 100 years reveals a trajectory of enquiry from early description and classification of features to development of process based explanations to decreasing scales of investigation and a disparity between understanding of process es and explanations of the genesis of sandstone weathering features developments in expositions on mesoscale weathering features on sandstone surfaces are discussed demonstrating a range of approaches to weathering phenomena field based and laboratory based that must be linked to provide an explanation of observed features on a landform scale throughout the twentieth century a thematic chronology highlights certain trends in research description of forms often in arid and semi arid environments single process form models an emphasis on experimentation difficulties in measuring weathering rates and a persistent emphasis on physical causes of breakdown a new research agenda is promoted in which biodeterioration and chemical processes gain parity a holistic approach based on conceptual modeling of weathering systems gains prominence and scale issues are addressed more rigorously

hindcast forecast of enso events based upon the redistribution of observed and model heat content in the western tropical pacific 1964 86 anomalous sea level anomalous observed dynamic height 0 400 db and anomalous model dynamic height are examined at the locations of 13 island sea level stations in the tropical pacific for each bimonth of the four year period 1979 to 1982 starting in 1981 the anomalous dynamic height data show off equatorial rossby waves propagated toward the w boundary of the pacific basin at the w boundary the model rossby wave activity was found to have excited coastally trapped kelvin munk waves which transmitted the anomalous dynamic height equatorward at the equator coastally trapped wave activity excited eastward propagating equatorial kelvin waves yielding a pair of anomalous peaks in dynamic height variability in the e equatorial pacific associated with the 1982 1983 enso event the evolution of the peaks in dynamic height associated with the rossby and kelvin wave activity reflects the redistribution of observed upper ocean heat content in the w tropical pacific providing a qualitative hindcast for the 1982 1983 enso event

significance of anisotropy of magnetic susceptibility fabrics in proterozoic mafic dykes hopedale block labrador abstract anisotropy of magnetic susceptibility fabrics have been studied in a suite of mafic early proterozoic kikkertavak dykes and two mid proterozoic kokkorvik sills in the hopedale block of labrador two sets of en echelon dyke arrays from the kikkertavak swarm are considered to represent two linear dyke intrusions at depth three main fabrics were revealed in the kikkertavak dykes in the first the maximum susceptibility axis is sub horizontal or gently inclined and parallel to the dyke walls and is interpreted as the primary magma flow direction a second fabric affects only dykes along strike from a much younger dyke and is interpreted as the result of local stress anisotropy the third fabric with significantly lower susceptibility is only locally developed in the southeast near the mid proterozoic kanairiktok shear zone and is also interpreted as the result of local superimposed tectonic stress the kokkorvik sheets preserve a single flow induced fabric sub parallel to the measured crack propagation lineation indicating that the magma flow was parallel to the crack propagation direction the gently inclined magma flow direction inferred for the kikkertavak dykes is believed to reflect later stage magmatic emplacement when consolidation had already commenced at this stage the buoyancy contrast between magma and host rock had been reduced to the point when the initially vertical magma flow was no longer sustainable and was replaced by lateral flow

landscape evolution space and the relative importance of geomorphic processes and controls abstract the concept of landscape evolution space les is introduced as a tool for assessing landscapes and geomorphic systems intended to be a systematic means for assessing the various factors that contribute to the potential for change in geomorphic systems the les conceptual model is based on the energy and mass available to drive and accommodate landscape evolution an n dimensional landscape evolution space is defined not only by spatial coordinates but also by the availability of mass and energy the les is thus a space or hypervolume representing the resources available for geomorphic evolution and landscape change an expression for les is derived based on elevation material density surface area and inputs of solar meteoric and biological energy and mass though primarily an heuristic device the les model can be used to address concrete problems two examples are given in one increased surface area due to topographic roughening and dissection of an incised plateau is found to only slightly offset erosional removals of mass in terms of the magnitude of the les in the other sensitivity of coastal plain rivers to several impacts of sea level and climate change is explored the les model also leads to the concept of a geomorphological niche representing the resources available to drive or support a specific process or suite of processes considerations of landscape evolution have traditionally focused on the interplay of endogenic vs exogenic processes uplift vs denudation or soil formation vs erosion the les model explicitly broadens the conceptual framework of landscape evolution beyond the traditional dialectics

eolian dunes computer simulations and attractor interpretation a simple computer simulation algorithm for the transport of sand by wind produces forms resembling barchan crescentic ridge linear and star natural dune classes sand is moved as slabs composed of many grains that are picked up at random transported in a specified direction and deposited 1 with a probability that depends on the local presence or absence of sand or 2 in shadow zones in the lee of dunes the simulated dune fields are interpreted as complex systems with sand dune classes being dynamical attractors of these systems the evolution of dunes once formed becomes decoupled from the details of eolian sand transport

biological energy in landscape evolution traditional conceptual models of landscape evolution view topography as an outcome of endogenic forces uplift working against exogenic forces of denudation the energy considerations of these concepts have focused on the conversion of the potential energy of landscape relief to kinetic energy the concept of the biosphere as a planetary membrane for capturing and converting solar energy coupled with the critical geomorphic role of biota call for a consideration of biotic contributions to geomorphic work a review of estimates of global rates of kinetic energy of denudation and uplift and net primary production npp indicates that the energy density of npp is on average three to seven orders of magnitude greater than the others if even a tiny fraction of npp is geologically significant then the biological subsidy to the energy of landscape evolution must be considered on a par with that of geophysical and geochemical phenomena a case study in eastern kentucky shows that even if only 0 1 percent of npp is geomorphically significant it still far exceeds the energy inputs from uplift and conversion of potential to kinetic energy by denudation this is unlikely to be unique though the relative importance of biological and geophysical processes must obviously vary with climate tectonic setting and other factors results indicate that particularly where biological activity is significant geomorphic work performed by biota may be greater than that associated with endogenic processes and with the kinetic energy of denudation

the mean sea surface height and geoid along the geosat subtrack from bermuda to cape cod measurements of near surface velocity and concurrent sea level along an ascending geosat subtrack were used to estimate the mean sea surface height and the earth s gravitational geoid velocity measurements were made on three traverses of a geosat subtrack within 10 days using an acoustic doppler current profiler adcp a small bias in the adcp velocity was removed by considering a mass balance for two pairs of triangles for which expendable bathythermograph measurements were also made because of the large curvature of the gulf stream the gradient wind balance was used to estimate the cross track component of geostrophic velocity from the adcp vectors this component was then integrated to obtain the sea surface height profile the mean sea surface height was estimated as the difference between the instantaneous sea surface height from adcp and the geosat residual sea level with mesoscale errors reduced by low pass filtering the error estimates were divided into a bias tilt and mesoscale residual the bias was ignored because profiles were only determined within a constant of integration the calculated mean sea surface height estimate agreed with an independent estimate of the mean sea surface height from geosat obtained by modeling the gulf stream as a gaussian jet within the expected errors in the estimates the tilt error was 0 10 m and the mesoscale error was 0 044 m to minimize mesoscale errors in the estimate the alongtrack geoid estimate was computed as the difference between the mean sea level from the geosat exact repeat mission and an estimate of the mean sea surface height rather than as the difference between instantaneous profiles of sea level and sea surface height in the critical region near the gulf stream the estimated error reduction using this method was about 0 07 m differences between the geoid estimate and a gravimetric geoid were not within the expected errors the rms mesoscale difference was 0 24 m rms

the influence of an alaskan stream eddy on flow through amchitka pass flow into the bering sea through amchitka pass in the central aleutian islands is shown to respond to the presence of a large meander eddy in the alaskan stream south of the pass maximum flow into the aleutian basin of the bering sea occurs when the eddy center lies nearest to the axis of amchitka pass a conceptual model of low frequency circulation variability within the bering sea based upon results of empirical orthogonal function analyses of sea surface height anomalies measured by the geosat radar altimeter is presented

magnetic fabric and its significance in the 1400 ma mealy diabase dykes of labrador canada an anistropy of magnetic susceptibility ams study of the relatively fresh mealy diabase dyke swarm indicates a correlation between the ams and the deformational effects in the rocks several ams components were revealed during experimental work on 211 samples that had been heated to 640 c during a paleomagnetic study and 22 fresh samples progressively treated in alternating fields seventeen sites with slight or no deformation have a magnetic fabric composed of two major components the stable component attributed to a primary shape anisotropy has minimum and maximum principal susceptibility directions preferentially oriented vertically and along dyke strike n 60 e respectively this configuration is consistent with an origin due to a post emplacement stress field whereby horizontal extension acted on a vertical sheet of partially crystallized magma the orientation of this component with respect to the present horizontal suggests that the dykes have not been tilted since their emplacement the unstable component removed by fields up to 250 mt is attributed to induced domain anisotropy produced by mild tectonic stress during the grenville orogeny the approximate orientation of its principal components as found by the method of substitutional ellipsoids suggests an east west directed maximum stress four other sites with noticeable deformation have magnetic fabric that could not be reliably analyzed but which may be largely composed of domain and stress induced anisotropies developed during the grenville orogeny

pre rift tectonic scenario of the eo cretaceous gondwana break up along se brazil sw africa insights from tholeiitic mafic dyke swarms

a new chronology for the age of appalachian erosional surfaces determined by cosmogenic nuclides in cave sediments the relative chronology of landscape evolution across the unglaciated appalachian plateaus of kentucky and tennessee is well documented for more than a century geomorphologists have carefully mapped and correlated upland erosional surfaces inset by wide valley straths and smaller terraces constraining the timing of river incision into the appalachian uplands was difficult in the past due to unsuitable dating methods and poorly preserved surface materials today burial dating using the differential decay of cosmogenic 26al and 10be in clastic cave sediments reveals more than five million years of landscape evolution preserved underground multilevel caves linked hydrologically to the incision history of the cumberland river contain in situ sediments equivalent to fluvial deposits found scattered across the eastern highland rim erosional surface cave sediments correlate with 1 thick lafayette type gravels on the eastern highland rim deposited between c 5 7 and c 3 5 ma 2 initial incision of the cumberland river into the eastern highland rim after c 3 5 ma 3 formation of the parker strath between c 3 5 ma and c 2 0 ma 4 incision into the parker strath at c 2 ma 5 formation of a major terrace between c 2 0 ma and c 1 5 ma 6 shorter cycles of accelerated incision and base level stability beginning at c 1 5 ma and 7 regional aggradation at c 0 85 ma initial incision into the appalachian uplands is interpreted as a response to eustasy at 3 2 3 1 ma incision of the parker strath is interpreted as a response to eustasy at 2 5 2 4 ma a third incision event at c 1 5 ma corresponds with glacial reorganization of the ohio river basin widespread aggradation of cave passages at c 0 85 ma is interpreted as the beginning of intense glacial interglacial cycling associated with global climate change copyright 2006 john wiley sons ltd

avulsion regimes in southeast texas rivers avulsions relatively sudden changes in course or establishment of new anabranches are an important process in alluvial rivers their key role in floodplain construction and alluvial architecture and the general conditions favouring avulsions are well known however avulsion processes and evolution and the factors controlling avulsion regimes are poorly understood in the southeast texas coastal plain where avulsions are common features of the river valleys avulsions were studied on the lower brazos navasota trinity neches and sabine rivers using a combination of aerial imagery digital elevation models and field surveys avulsions have important influences on the surface morphology and contemporary processes in all five rivers features associated with avulsions are active and distinct throughout the study area and all the rivers have experienced geologically if not historically recent avulsions however no two of the study rivers have the same contemporary avulsion regime first order differences in avulsion style are controlled by the stage of valley filling and within the three rivers characterized by an unfilled incised valley antecedent morphology associated with late quaternary and holocene coastal and fluvial deltaic processes accounts for the major differences in the navasota 27 avulsions in 185 km and neches 21 in 340 km rivers subchannels associated with avulsions exist in all stages of development from active to infilled and some have occurred in recent decades the other rivers have fewer avulsions but both the sabine and trinity have experienced historic channel shifts only the brazos river has experienced no avulsions within the past c 300 years results show that even within a region of similar environmental controls and geological history local variations in inherited morphology can result in different avulsion regimes copyright 2008 john wiley sons ltd