roll convection within an arctic cold air outbreak interpretation of in situ aircraft measurements and spaceborne sar imagery by a three dimensional atmospheric model abstract atmospheric roll convection within an arctic cold air outbreak was observed over the greenland sea during the arktis 1993 experiment on 24 march 1993 by in situ aircraft measurements and synthetic aperture radar sar imagery from the first european remote sensing satellite ers 1 inside a boundary layer heated from below two kinds of rolls were observed one aligned parallel and the other perpendicular to the mean wind direction the wind parallel rolls occupied the entire boundary layer whereas the wind perpendicular rolls were confined to a region around the top of the boundary layer where a strong vertical shear in the downstream wind component was observed a three dimensional numerical model has been applied to simulate the observed convective pattern it is shown that the model does not reproduce the observed pattern when using a height constant geostrophic wind profile however when adjusting the vertical wind profile to the one measured from the aircraft the model reproduces buoya

sea level changes in a back arc foreland transition the late carboniferous permian karoo basin of south africa abstract the late carboniferous to early permian succession in the karoo basin consists in ascending stratigraphic order of diamictites mudrocks greywackes and immature sandstones the diamictites are interpreted as glacigene deposits laid down by a marine ice sheet on a shelf post glacial suspension settling of predominantly mud occurred on the basin floor during open marine and later brackish conditions basin floor fan deposits accumulated in the foredeep whereas deltaic mud silt and sand finally infilled the basin glacigene sedimentation occurred in a back arc basin during the late carboniferous and early permian the post glacial succession accumulated in a foreland basin in which the rising orogenic belt was the predominant sediment source relative sea levels following the major namurian regression apparently remained low during the extensive gondwana glaciation marine ice sheets are highly sensitive to sea level fluctuations and minor sea level rises probably climatically controlled were recorded as interglacials when parts of the marine ice sheet collapsed final collapse of the marine ice sheet was associated with a major transgression post glacial mudrock deposition was characterised by relatively high sea levels except for the period of basin floor fan deposition when there was a sea level lowstand final infilling of the basin by prograding deltas was accompanied by a major regression the late carboniferous to early permian sea level fluctuations in the karoo basin show correspondence with global eustatic cycles reflecting low tectonic interference with sea level patterns however late permian sea levels were predominantly tectonically controlled as a result of foreland basin evolution possible global eustatic events complemented apparent sea level changes within the basin during this period

the record of the varanger glaciation at the rio de la plata craton vendian cambrian of uruguay abstract a sedimentary succession included in the lower section of the playa hermosa formation from the playa verde basin uruguay is described two facies associations one mainly coarse to medium grained and other one fine grained have been defined fa i ii in the first one breccias conglomerates sandstones and minor mudstones were deposited in a subaqueous depositional setting proximal suggesting slope instability and resedimentation processes the second one contains diamictites rhythmites sandstones and mudstones and presents abundant evidence of soft deformation also interpreted to be deposited in a subaqueous environment distal dropstones clast layers diamictites rhythmites and varve like deposits are interpreted as ice rafting processes generated during a glacial episode this glacial related succession constitutes the first record from the varanger glaciation at the rio de la plata craton of the late neoproterozoic age and also represents one of the oldest sedimentary records after the collision of the rio de la plata and kalahari cratons a combined interaction of extensional faulting and glaciation in a tectonically active basin with locally high subsidence rates resulted in high rates of sedimentation and resedimentation processes as a whole the sedimentary succession sets a relevant datum to be used in future paleogeographic reconstructions of the vendian glacial record in southern south america

use of spaceborne synthetic aperture radar imagery of the sea surface in detecting the presence and structure of the convective marine atmospheric boundary layer abstract two distinct backscatter regimes are seen on a european remote sensing satellite ers 1 c band 5 6 cm synthetic aperture radar sar image of the sea surface during a time of fair synoptic scale weather conditions one backscatter regime is mottled in contrast to that the second backscatter regime is marbled the authors hypothesize that the mottled backscatter pattern is a characteristic sar backscatter pattern linked to the presence of the convective i e statically unstable convective eddy containing marine atmospheric boundary layer cmabl and can be used to help determine cmabl structure convective eddy type cellular convection versus longitudinal rolls eddy wavelength and cmabl depth via mixed layer similarity theory for aspect ratio the hypothesis linking the presence and structure of the cmabl to the mottled backscatter pattern on sar imagery is validated by analyzing data from a number of sources gathered in the vicinity of the boundary between the mottled and marbled reg

the karoo igneous province a problem area for inferring tectonic setting from basalt geochemistry tholeiitic basalts and associated intrusives are the major component of the karoo igneous province they are of mesozoic age and constitute one of the world s classic continental flood basalt cfb provinces it has been argued that most karoo basalts have not undergone significant contamination with continental crust and that their lithospheric mantle source areas were enriched in incompatible minor and trace elements during the proterozoic the only exceptions to this are late stage morb like dolerites near the present day continental margins which are considered to be of asthenospheric origin when data for the southern karoo basalts are plotted on many of the geochemical discriminant diagrams which have been used to infer tectonic setting essentially all of them would be classified as calc alkali basalts cab s or low k tholeiites virtually none of them plot in the compositional fields designated as characteristic of within plate basalts there is little likelihood that the compositions of the karoo basalts can be controlled by active subduction at the time of their eruption and no convincing evidence that a subduction component has been added to the subcontinental lithospheric mantle under the entire area in which the basalts crop out it must be concluded that the mantle source areas for cab s and the southern karoo basalts have marked similarities in contrast the data for northern karoo basalts largely plot in the within plate field on geochemical discriminant diagrams available data suggest that the source composition and or the restite mineralogy and degree of partial melting are different for southern and northern karoo basalts there is no evidence for any difference in tectonic setting between the southern and northern karoo basalts at the time they were erupted this appears to be clear evidence that specific mantle source characteristics and or magmatic processes can vary within a single cfb province to an extent that renders at least some geochemical discriminant diagrams most unreliable for classifying tectonic environment with respect to continental volcanic rocks

viewing a cold air outbreak using satellite based synthetic aperture radar and advanced very high resolution radiometer imagery in this phenomenological study we compare nearly simultaneous visible wavelength advanced very high resolution radiometer avhrr and synthetic aperture radar sar images of a cold air outbreak that occurred off the ice pack in the bering sea the visible image shows the spatial evolution of the cloud structure from the ice edge to several hundred kilometers offshore near the ice edge the clouds form regular linear features known as cloud streets these streets are spaced about 5 km apart 5 times the depth of the boundary layer by 200 km offshore the visible image shows nascent closed cell mesoscale cellular convection mcc with connected disks and smears of white clouds surrounded by arcs and rings of dark cloud free regions the diameters of the disks range between 10 and 15 km the sar image shows the same broadly defined spatial pattern but with a substantial increase in detail uncorrelated with the avhrr image in the area of the cloud streets shown in the avhrr image are two dimensional elongated regions of enhanced radar backscatter called sar streaks with the same cross wind spacing as the cloud streets this suggests the presence of quasi two dimensional roll vortices in the atmospheric boundary layer downstream in the area of proto mcc are broadly spaced expanses of enhanced backscatter that form two dimensional patterns such as connected arcs that have structure and scales similar to the spaces between the clouds the spatial evolution of the streaks and streets broadly conforms to the patterns of downdrafts and updrafts respectively exhibited in modeling studies of cold air outbreaks however the comparison with modeling studies is more successful for the cloud streets than for the sar streaks we suggest that this difference is because the clouds in the avhrr images give a time integrated signal of large scale quasi two dimensional atmospheric turbulence whereas mesoscale radar patterns of surface roughness give a relatively instantaneous view of fundamentally three dimensional structure within the atmospheric boundary layer

glaciation and tectonics in an active intracratonic basin the late palaeozoic itarare group parana basin brazil the parana basin 1 600 000 km2 is the largest intracratonic basin in southern south america and contains a thick 1300 m permo carboniferous glacial succession the itarare group this paper describes over 1700 m of drill core recovered during recent exploration for oil and gas itarare group sediments consist of massive and stratified diamictites interbedded with massive and graded sandstones and massive and laminated mudstones facies are interpreted as the product of sediment gravity flows in a glacially influenced marine basin three stratigraphic formations can be defined across the basin each consisting of a lowermost sandstone rich member overlain by a diamictite rich member examination of itarare group rocks both in core and outcrop shows that depositional processes were influenced by active faulting and downslope resedimentation on relatively steep and unstable substrate slopes primary glacial deposits such as tillites and associated striated pavements occur along the present eastern outcrop belt which probably coincided with the eastern basin margin during deposition of the itarare group ice masses fringing the eastern southern african and western bolivian basin margins supplied sediment to the basin in the form of fluvio glacial deltas fans and floating ice tongues this sediment was then resedimented downslope as debris flows and turbidites both stratigraphic relationships and the regional distribution of facies types identify a clear pattern of basin subsidence and step wise expansion by outward faulting within late proterozoic mobile belts the position of successive basin margins can be related to specific lineament structures in the underlying basement asymmetric expansion of the parana basin occurred along the northern and southern basin margins during deposition of the itarare group this expansion probably reflects shallow crustal adjustments activated by collisional movements along the andean margin of south america during the hercynian orogeny

importance of peakedness in sea surface slope measurements and applications we recall the simple statistical concept that non gaussian distribution peakedness results from the compounding of random processes this idea is applied to observations and analysis of sea surface slopes as inferred using optical and microwave scattering measurements our study emphasizes the importance of identifying and quantifying the distribution variance and kurtosis from observations data are shown to indicate consistently non gaussian peakedness to indicate the need to report at least two parameters in an even order analysis and to indicate near equivalence between radar and optical data physical interpretation for observed infrequent steep slopes is given via compounding statistical processes where normally distributed short scale waves are modulated because of random fluctuations mainly associated with the underlying long wave field implications of non gaussian peakedness are provided for altimeter backscatter theory and for modeling wave breaking probability

measured changes in ocean surface roughness due to atmospheric boundary layer rolls a research aircraft was recently flown over the mid atlantic eight during a mild cold air outbreak to sample the planetary boundary layer at low levels of 15 20 m above the sea surface aircraft sensors measured near surface atmospheric turbulence and at the same time variations in sea surface roughness using laser and radar the aircraft turbulence observations indicate a coherent secondary flow consistent with boundary layer roll vortices of crosswind scale 1 5 2 0 km modulation in measured laser and radar inferred sea surface slope variance occurs at similar scales remarkable correlation is found between the radar backscatter and near surface wind speed data showing that the short wave slope variance is responsive to these large eddies associated small but periodic changes in wind direction do not appear to impact the short wave slope signature differentiation between short and intermediate scale wave roughness using aircraft laser and radar data leads us to conclude that observed fluctuations in intermediate scale wave slope were not directly linked to the local wind a synthetic aperture radar sar image was acquired by the canadian space agency s radarsat coincident with the aircraft measurements widespread streaking in the sar image suggests the surface impacts of atmospheric longitudinal rolls our aircraft results indicate that the dominant term dictating sar backscatter modulations at the eddy scale of 1 2 km is the fluctuation of the along wind velocity nominally associated with regions of near surface convergence or divergence wind speed fluctuations of 7 10 estimated from the sar and aircraft radar are consistent with the aircraft s measured variations in near surface wind speed

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

relations among subduction parameters clues to the dynamics of the subduction process are found in the many measurable parameters of modern subduction zones based on a critical appraisal of the geophysical and geological literature 26 parameters are estimated for each of 39 modern subduction zones to isolate causal relationships among these parameters multivariate analysis is applied to this data set this analysis yields empirical quantitative relations that predict strain regime and strike slip faulting in the overriding plate maximum earthquake magnitude benioff zone length slab dip arc trench gap and maximum trench depth excellent correlation is found between length of the benioff zone and the product of convergence rate and age of the downgoing slab this relationship is consistent with the conductive heating model of molnar et al 1979 if the model is modified in one respect the rate of heating of the slab is not constant it is substantially slower during passage of the slab beneath the accretionary prism and overriding plate the structural style in the overriding plate is determined by its stress state though the stress state of overriding plates cannot be quantified one can classify each individual subduction zone into one of seven semiquantitative strain classes that form a continuum from strongly extensional class 1 back arc spreading to strongly compressional class 7 active folding and thrusting this analysis indicates that strain class is probably determined by a linear combination of convergence rate slab age and shallow slab dip interplate coupling controlled by convergence rate and slab age is an important control on strain regime and the primary control on earthquake magnitude arc parallel strike slip faulting is a common feature of convergent margins forming a forearc sliver between the strike slip fault and trench optimum conditions for the development of forearc slivers are oblique convergence a compressional environment and a continental overriding plate the primary factor controlling presence of strike slip faulting is coupling strongly oblique convergence is not required the rate of strike slip faulting is affected by both convergence obliquity and convergence rate maximum trench depth is a response to flexure of the underthrusting plate the amount of flexural deflection at the trench depends on the vertical component of slab pull force which is very sensitive to slab age and shallow slab dip shallow slab dip conforms to the cross sectional shape of the overriding plate which is controlled by width of the accretionary prism and duration of subduction deep slab dip is affected by the mantle trajectory established at shallow depth but may be modified by mantle flow much of the structural complexity of convergent margins is probably attributable to terrane juxtaposition associated with temporal changes in both forearc strike slip faulting and strain regime empirical equations relating subduction parameters can provide both a focus for future theoretical studies and a conceptual and kinematic link between plate tectonics and the geology of subduction zones

sunglint images of current gradients at high resolution critical angle and directional observing strategy abstract high resolution satellite images of the ocean surface in and around the sunglint often provide unique observations of sub mesoscale upper ocean surface processes local anomalies of wind waves currents or surfactants appear on the images as local anomalies of brightness a quantitative interpretation of those brightness anomalies must relate them to slope properties of the wave field which are to the lowest order described by the mean square slope mss the prevailing paradigm for such interpretation is that of the critical zenith angle it states that for sub critical zenith view angle brightness and mss anomalies have opposite signs and this defines the so called inversion region this prevailing paradigm implicitly builds on the assumption that the mss decomposition between upwind and crosswind components is conserved the mss anomalies are then isotropic and can be reduced to a scalar i e one dimensional quantity in such a case one single sunglint image would be sufficient to retrieve the mss anomaly this isotropic case likely applies for surface wave changes induced by varying wind speed or by surfactants yet satellite and airborne observations at multiple view angles recently revealed anisotropic mss anomalies e g with mss increase in the upwind direction and decrease in the crosswind direction this anisotropic behavior likely characterizes wave modulations by anisotropic surface current gradients this paper details the expected properties of such anisotropic mss modulations it is shown that 1 the classical concept of critical angle does not systematically hold neither for frontal current shear nor for internal wave divergence 2 at least two sunglint images at different zenith and azimuth angles are needed to retrieve the mss anomalies and a single observation is not sufficient 3 a satellite with radiometers looking at multiple zenith angles is capable of providing a geometry favorable to retrieve mss anomalies an illustration is discussed with internal waves observed by the multi angle imaging spectroradiometer misr where the upwind and crosswind components of the retrieved mss anomalies are anisotropic those results provide guidelines to interpret available observations and to help refine strategy for future satellite missions

early permian to middle jurassic rifting and sedimentation in east africa and madagascar pre drift sediments of madagascar early permian middle jurassic have been studied palynologically these studies resulted in a more precise dating of individual stratigraphic units and the recognition of minor and major breaks in the succession palynostratigraphic and physical evidence of unconformities have been used to subdivide the pre drift sediments into depositional cycles and to infer rifting events a comparison with equivalent strata of mozambique tanzania kenya ethiopia and somalia shows a general correspondence and provides additional information for the construction of a generalized framework for the east african madagascan region which demonstrates the relationships between rifting and sedimentation and elucidates the prehistory of the break up of gondwana into a western and eastern fragment during the middle jurassic the predrift succession of east africa madagascar can be subdivided into two major sequences a karoo sequence cycles 1 5 asselian early smithian and a transitional sequence cycles 6 9 ladinian early bajocian the two sequences are separeted by a late scythian to anisian hiatus which indicates extensive uplift and erosion before a major rifting event initiated the resumption of sedimentation in the ladinian this middle triassic event marks the transition from the intracratonic rift stage to the pericratonic basin stage and correlates with a significant event in the pangaean history the transition from final coalescence to initial dispersal the onset of the southward drift of madagascar is believed to have occurred about 60 ma later near the aalenian bajocian boundary contemporaneous with or immediately after the deposition of syntectonic sediments of cycle 9

an assessment of marine atmospheric boundary layer roll detection using sentinel 1 sar data abstract the ability of high resolution synthetic aperture radar sar to detect marine atmospheric boundary layer mabl roll induced roughness modulation of the sea surface wave field is well known this study presents sar measurements of mabl rolls using global coverage data collected by the european space agency s c band sentinel 1a satellite in 2016 2017 an automated classifier is used to identify likely roll events from more than 1 3 million images that were acquired at two incidence angles of 23 and 36 5 in either vv or hh polarization characteristics of the detected rolls are examined for different wind speeds polarizations incidence and relative azimuth angles roll detection counts are much higher at the higher incidence angle and nearly equivalent for vv and hh polarizations detection depends strongly on the relative azimuth with roll detection rates at crosswind being 3 10 times lower than for up or downwind all data show a low wind speed threshold near 2 m s 1 and that rolls are most commonly observed at wind speeds near 9 m s 1 for all viewing configurations we find that rolls induce a wide range of mean surface wind speed modulation with the most frequent value being 8 3 5 roll detection at crosswind is associated with stronger roll induced surface wind enhancement dependencies of roll detection on the incidence and relative azimuth angles are consistent with rapid short scale wind wave adjustments to the roll induced surface wind gusts these cm scale waves are highly directional and provide limited crosswind backscatter at shallower incidence angles the same roll induced surface forcing is thus not equally detectable at all viewing geometries or polarizaions stronger and possibly longer duration wind forcing is likely needed to produce detectable roll induced modulations at crosswind

inferring multiscale structure in atmospheric turbulence using satellite based synthetic aperture radar imagery this paper describes the multiscale structure in synthetic aperture radar sar backscatter seen in an image of a cold air outbreak as being due to the influence on the surface of the ocean of three scales of interacting atmospheric turbulence a low resolution pixels have side lengths of 100 m sar image shows the first class of backscatter pattern to be broken lines of enhanced radar backscatter of order 1 db above the background with an average cross wind scale of 5 km and downwind lengths of many tens of kilometers these are associated with quasi two dimensional roll vortices the second class of radar backscatter pattern is two dimensional backscatter regions whose linear aggregrations constitute the lines of backscatter they are on average 1 km wide in the cross wind direction and are 2 5 km long in the downwind direction a higher resolution image pixels have side lengths of 12 5 m of the same area shows a third class of structure smaller scale regions of enhanced backscatter up to several hundred meters in length downwind and greater than 100 m across wind that are associated with 7 db variations in in the unaveraged image the modulated fine scale backscatter structure compares favorably in both scale and effect to observations of the modulation of microfronts in the atmospheric surface layer by kilometer scale inactive eddies the latter being of uncertain origin therefore the hypothesis offered here is that the fine scale sar structure is caused by the influence of atmospheric microfronts on the ocean surface while the two dimensional kilometer scale backscatter features are the signature of inactive eddies linearly aggregated by or possibly intrinsic to the roll vortices

volcanic rocks as discriminants in evaluating tectonic versus climatic control on depositional sequences permo carboniferous continental saar nahe basin the third and fourth order sequential arrangement of continental sedimentary strata in the permo carboniferous saar nahe basin preserves a detailed record of contemporaneous faulting and volcanism transgressive lacustrine facies of the upper carboniferous coincide with the stratigraphic position of extrabasinally derived pyroclastic fallout layers and features of synsedimentary tectonism such as unconformities thickness and facies changes across faults and seismogenic deformation structures the tectonic imprint on fourth order cycle initiation is further documented by abrupt vertical facies transitions during lake transgression implying rapid and episodic rather than gradual basin subsidence this interaction becomes much more pronounced within the fluvially dominated lower permian when tectonism controlled both the ascent of large volumes of magma within the basin as well as episodic enlargement of accommodation space and depositional area major extrusive volcanic units are preferentially associated with sequences recording transgression that are only preserved in fault bounded hanging wall traps starved from clastic sediment input it is suggested that the stratigraphic position of pyroclastic fallout within the sequential framework of basins elsewhere provides an important analytical tool for the identification of contemporaneous tectonic events and as such form a discriminant between purely climatically induced milankovitch band cycles versus those involving a tectonic control

sea surface wind streaks in spaceborne synthetic aperture radar imagery wind streaks are often observed in synthetic aperture radar sar images they are used to determine the sea surface wind direction for sea surface wind field retrievals it is generally understood that visible wind streaks are caused by roll vortices in the marine atmospheric boundary layer in this study 227 x band spaceborne sar terrasar x and tandem x images acquired from the three fino platforms in the north sea and baltic sea were thoroughly analyzed for a comprehensive understanding of the manifestation of wind streaks in sar images approximately 48 0 of the 227 sar images displayed wind streaks among which 67 3 20 0 and 12 7 occurred under unstable neutral stable atmospheric conditions respectively the proportions indicate that wind streaks are more likely to be generated from thermal convection further investigations suggest that the inflection point and the wind shear may be essential for the appearance of wind streaks in sar images under stable atmospheric conditions this article is protected by copyright all rights reserved

controls on early permian shelf deglaciation in the karoo basin of south africa abstract the late carboniferous to early permian glacigene dwyka group has at its top three types of transitions from diamictite to postglacial mudrock in the southern karoo the type 1 transition sequence consists of clast poor carbonate rich diamictite having a sharp contact with the overlying mudrocks this diamicton accumulated slowly by rain out and sediment gravity flow processes during sedimentation the polar ice front was stabilised by a possible ice shelf collapse of the ice shelf caused rapid ice margin retreat the type 2 transition sequence consists of clast poor diamictite with sandstone bodies overlain by mudrock with ice rafted debris or thin interbedded debris flow diamictites deposition of the diamictite facies occurred during oscillations of a subpolar ice front with short stable periods of surface melting of the ice resulting in the formation of small subaqueous outwash fans the type 3 transition sequence consists of bouldery diamictite interbedded with massive or sandstone bearing diamictite overlain by mudrock with ice rafted debris or thin interbedded debris flow diamictites the sequence represents highly unstable ice front conditions and fluctuating sea levels with periods of rapid deposition probably by collapsing ice streams climatic conditions may have alternated between polar and subpolar the type 1 transition sequence is predominant in the western part and the type 3 sequence in the eastern part of the karoo basin long term controls on deglaciation was climatic warming as gondwana drifted over the pole as well as changes in land sea configuration superimposed on these were local controls such as relative sea level changes presence of deformable substrate and meltwater production

ocean wave slope observations using radar backscatter and laser altimeters abstract combination of laser and radar aboard an aircraft is used to directly measure long gravity wave surface tilting simultaneously with nadir viewing microwave backscatter from the sea surface the presented dataset is extensive encompassing varied wind conditions over coastal and open ocean wave regimes laser derived slope statistics and ka band 36 ghz radar backscatter are detailed separately to document their respective variations versus near surface wind speed the slope statistics measured for 1 2 m show good agreement with cox and munk s oil slickened sea measurements a notable exception is elevated distribution peakedness and an observed wind dependence in this likely proxy for nonlinear wave wave interactions aircraft ka band radar data nearly mimic ku band satellite altimeter observations in their mean wind dependence the present calibrated radar data along with relevant observational and theoretical studies suggest a large 5 db bias in previous ka band results next wave

collision induced rifting the grenville orogeny and the keweenawan rift of north america abstract we propose that the keweenawan rift formed as a result of convergence related to the synchronous grenville orogeny this proposal is based on 1 1 isotopic ages in the keweenawan rift and the grenville province are similar according to the best u pb and rb sr dates the grenville orogeny existed from 1150 to 1100 ma and keweenawan rifting occurred 1120 1100 ma 2 2 a similar modern orogenic belt and rift relationship in the middle east serves as an actualistic model the red sea gulf of aden rift system has formed as a continuous series of coalesced pull apart basins and is opening parallel to the orogenic front of the zagros and bitlis mountains rifting began in the early miocene while the collision began in the eocene suggesting that rifting is related to the collision 3 3 many other ancient rift collision pairs have a similar age relationship and geometrical configuration based on comparisons of these tectonic regimes we have derived a model whereby these rifts formed as a result of strike slip faults forming in either the foreland or the hinterland of orogenic zones

paleomagnetism and geochronology of late paleozoic granitic rocks from the lake district of southern chile implications for accretionary tectonics k ar and sup 40 ar sup 39 ar dating shows that granite rocks in the central lake district southern chile are late paleozoic granitic rocks of similar age extend far up the coast of chile perhaps as much as 1800 km the authors have obtained paleomagnetic directions from seven sites near lago ranco these give a paleomagnetic pole at lat 57 4 degree s long 323 5 degree e with a circle of 95 confidence of 18 8 degree this is not significantly different from the mean late paleozoic reference pole for the south american craton if these results are characteristic of the late paleozoic belt as a whole it follows that post late plaeozoic accretion and terrane displacement are absent throughout much of the central andes

origin of the pennsylvanian coal bearing cyclothems of north america past controversy about the tectonic or eustatic origin of pennsylvanian cyclothems is resolved by regional basin subsidence analysis global paleoclimate paleogeography and plate tectonic evolution differences between marine carbonate kansas type cyclothems of the northern midcontinent and nonmarine clastic appalachian type cyclothems of the eastern united states are controlled by laterally changing flexural deformation during plate accretion into a supercontinent coupled with superposed glacial eustasy kansas type cyclothems accumulated on a relatively stable platform affected only moderately by collision tectonics of north american margins these cycles are eustatic characterized by a periodicity comparable to milankovitch orbital parameters appalachian type cyclothems accumulated in response to episodic thrust loading during plate collisions that developed a series of flexurally deformed wide and shallow resurgent foreland basins this resurgent foreland basin evolution during paleozoic time increased crustal rigidity in the appalachians thus yoking the appalachian and illinois basins during pennsylvanian time with each thrust load foreland basin deepening favored transgressive cyclothem facies which changed to a regressive facies because sediment yield increased as denudation rates increased off uplifted orogens illinois type cyclothems are intermediate between the two end member processes of flexural tectonics and glacial eustasy characterizing appalachian type and kansas type cyclothems respectively thus the pennsylvanian coal bearing cyclothems of north america owe their origin to the remarkable coincidence of supercontinent development concomitant glaciation and eustatic sea level change and associated episodic thrust loading and foreland basin subsidence of small magnitude on progressively more rigid crust

late middle miocene volcanism in northwest borneo southeast asia implications for tectonics paleoclimate and stratigraphic marker abstract explosive volcanic events often produce pyroclastic materials that can be recognized from the geological record these discrete pyroclastics form regional marker beds here we report the occurrence of a tephra layer interbedded within very thick coal beds near mukah sarawak borneo traceable for tens of kilometers in the mukah area of sarawak this tephra layer can be considered as regional stratigraphic marker with precise chronostratigraphic control systematic sedimentological mineralogical geochemical and zircon u pb geochronological studies have revealed a major effusive volcanic event during the latest middle miocene presumably contemporaneous and or related to a magmatic event of an earlier phase of the mt kinabalu pluton or magmatism in west sarawak or east sabah the volcanic event had promoted catastrophic flooding of coastal swamps and fall out from the ash clouds that formed a regionally monotonous tephra layer across the serravallian tortonian boundary in conjunction with the regional occurrences of trap rocks structural trends and known tectonic events we constrained the regional depositional environments and climate the tephra layer was deposited in a coastal plain swamp seasonal shallow high moderate energy fluvial channel lacustrine environmental setting wherein atmospheric fallout and eroded material from regoliths formed over older basement and volcanic rocks of the hinterland which were mixed to produce the tephra layer this tephra layer is sandwiched between the very thick coal beds a pre existent volcanic chamber that was active for a long time also experienced periodic explosive activity from probably the same magma chamber and conduit and including a major explosive activity that recycled early formed crystals and felsic magma rhyolite dacite during the major effusive event are also recognized our findings provide robust evidence for the prevalence of intensive chemical weathering under a wet humid climate and relative tectonic quiescence before the major effusive event and the existence of vast monotonously gently sloping coastal plains and luxuriant vegetation akin to the present

momentum transfer over the coastal zone spatial variations of surface stress over the coastal shoaling zone are studied offshore of duck north carolina by the longez research aircraft equipped to measure both atmospheric turbulence and oceanic waves we find that the spatial variation of the friction velocity with offshore distance is much larger with offshore flow than with onshore flow in general the mean square slope of the short waves wavelength shorter than 2 m decreases with offshore distance while the mean square slope of the long waves wavelength longer than 2 m increases with offshore distance with onshore flow the friction velocity is strongly correlated with surface waves in addition the variation of the neutral drag coefficient is well correlated with the atmospheric bulk richardson number with offshore flow the observed momentum flux significantly decreases with offshore distance within the first few kilometer offshore the relationship between the friction velocity and the mean square slope of the short waves and the relationship between the neutral drag coefficient and the atmospheric bulk richardson number are obscured by the direct influence of the upstream land surface on the measured turbulence these relationships for offshore flow agree well with those for onshore flow if the fetch is beyond the immediate influence of the land surface the results in this study suggests that the effects of the strong turbulence advected from over the nearby land surface in offshore flow may lead to ambiguous physical interpretation of the correlation between the momentum flux and the wave state

late paleozoic depositional sequences are synchronous and worldwide more than fifty transgressive regressive depositional sequences are present in carboniferous and permian shallow marine successions on stable cratonic shelves worldwide these were synchronous depositional events resulting from eustatic sea level changes that generally ranged from 100 to 200 m each transgressive regressive sequence is correlatable using current fossil knowledge they average about 2 m y and range from 1 2 to 4 m y in length the presence within these strata of numerous synchronous unconformities of considerable duration and worldwide extent suggests that the fossil record is very incomplete and that we are studying a punctuated fossil record and not a punctuated evolution based on a highly irregular mutation rate these late paleozoic transgressive regressive depositional sequences facilitate correlations because depositional histories of a rock succession can support interpretations of faunal assemblages and faunal similarities in evaluating age relationships

effect of large eddies on atmospheric surface layer turbulence and the underlying wave field to improve existing models for air sea interaction a better understanding of the energy transfer across the boundary layer and in particular of the coupling of large atmospheric eddies with the air sea interface is needed recent investigations have already shown a possible coupling of large structures in atmospheric turbulence and surface ripples this was done using synthetic aperture radar sar imagery of ocean surface and almost simultaneous advanced very high resolution radiometer avhrr imagery of cloud streets at a cold air outbreak the intent of our study is to further validate this hypothesis in a general case of coastal circulation for this purpose we analyze a suite of collocated simultaneous records of airflow radar return and surface elevations from a coastal platform we investigate the influence of large eddies 20 60 min on the turbulent properties of the airflow in the first 2 m above the ocean surface the analysis shows very prominent peaks in the magnitude of 12 to 16 min fluctuations which are further modulated in 20 to 40 min intervals these scales and modulations are characteristic for all variables of interest here the detected scales and their modulation suggest significant interaction of surface layer within the first 1 2 m with large eddies of scales of o 1 and o 10 km the intermittent structure of turbulence responds by alternating contributions from bursts and sweeps the frequency of occurrence of bursts and sweeps also reveals the influence of large structures the instantaneous cross correlation between the shorter scales of momentum flux and radar return corresponding to the individual burst events can be 4 times as strong as the overall cross correlation

surface roughness changes by finescale current gradients properties at multiple azimuth view angles abstractat times high resolution images of sea surface roughness can provide stunning details of submesoscale upper ocean dynamics as interpreted transformations of short scale wind waves by horizontal current gradients are responsible for those spectacular observations those observations could prove particularly useful to validate numerical ocean models that reach increasingly high resolutions focusing on surface roughness at optical wavelengths two steps have recently been performed in that direction first it was shown in a previous paper by rascle et al that surface roughness variations not only trace surface current divergence but also other characteristics of the current gradient tensor mainly the strain in the wind direction the wind direction with respect to the current gradient thus stands out as an important interpretative parameter the second step is the purpose of the present paper where the effect of the viewing direction is investigated to this end the authors discuss pairs of

phosphogenesis carbon isotope stratigraphy and carbonate platform evolution along the lower cretaceous northern tethyan margin we distinguish three different stages in the evolution of the tithonian late jurassic to aptian early cretaceous northern tethyan carbonate platform 1 carbonate production in the coral oolite mode late tithonian to early valanginian early barremian to early aptian 2 carbonate production in the crinoid bryozoan mode early valanginian haute rivian late aptian and 3 platform retrogradation and destruction condensation and phosphogenesis that is platform drowning early valanginian to early hauterivian middle hauterivian late hauterivian to early barremian early to early late aptian and latest aptian to earliest albian transitions from the coral oolite mode to the crinoid bryozoan mode and consequently to platform drowning may have been driven by increases in nutrient levels on the shelf phases of relative sea level rise in times of carbonate production in the coral oolite mode are named constructive because of the observed platform regeneration following phases of widespread emersion during late sea level highstands in contrast phases of relative sea level rise in times of platform drowning are termed destructive the 13 c stratigraphies obtained from valanginian hauterivian and aptian albian hemipelagic successions beyond the platform correlate well with the early cretaceous pelagic 13 c record positive excursions in the pelagic 13 c record correspond in time to episodes of platform drowning this suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning in our view the early cretaceous crises in carbonate platform growth were the consequence of reinforced greenhouse conditions which may have been triggered by episodes of extensive flood basalt volcanism strong greenhouse conditions may have induced the following chain of feedback mechanisms enabling the biosphere to return to normal conditions climate warming sea level rise accelerated water cycle intensified weathering nutrient mobilization platform destruction increased productivity increased phosphogenesis and carbon burial weakened greenhouse conditions

formation and deformation of subglacial intrusive clastic sheets in the dwyka formation of northern natal south africa abstract an arenaceous diamictite rests on fissile silty mudstone and argillaceous diamictite and is overlain by a laminated muddy siltstone east of helpmekaar in the dundee district of northern natal the argillaceous deposits originated either in the subglacial or proglacial zone of a partly grounded marine ice sheet where sediment was supplied by debris laden floating ice meltwater plumes and turbidity currents the arenaceous diamictite is the product of melt out debris released close to the grounding line of the ice sheet where it was subjected to overriding by the ice and slumping and redeposition by sediment gravity flow the laminated siltstone represents sediment that was deposited in a low energy setting by turbidity currents and suspension settling downslope from a retreating g ounding line dispersed ice rafted clasts occur in these fine grained deposits the upper surface of the arenaceous diamictite displays regularly spaced linear undulations that are parallel to the former iceflow direction as are corrugations in discrete subhorizontal slip planes in its upper part dike like bodies of this diamictite are found in the underlying mudstone and argillaceous diamictite these dikes or wedge shaped sheets of sandy diamictite are nearly vertical in their upper parts but at depth curl to the southeast to form sill like bodies these intrusive diamictites record a novel and previously undescribed form of subglacial bed shear by repeated hydraulic injections which shuffled the upper layers of the substrate to the south southeast bed compaction and shear beneath the grounded ice is recorded by folds in steepened portions of the clastic intrusive sheets and by pinch and swell and folded pinch and swell of the clastic sills displacement of steep folded sheet elements along subhorizontal slicken sided slip planes indicate that bed shear continued along spaced planes of slip during the process of compaction the corrugated and planar slip surfaces and the formation of the listric or spoon shaped intrusions are all shown to be different expressions of bed shear induced by traction from the overriding ice flowing to the southeast when it was temporarily grounded the base of an ice sheet flowing from land into the sea undergoes flow acceleration and forms a ramp where it decouples from the high friction substrate the arenaceous diamictite mound most likely to have developed beneath this ramp is inferred to have a structural core of sediments that have been squeezed and sheared and have slipped from beneath the ice in the tidal grounding zone

basin evolution in western newfoundland new insights from hydrocarbon exploration the humber zone is the most external zone of the appalachian orogen in western newfoundland it records multiphase deformation of the cambrian ordovician passive margin and of the ordovician to devonian foreland basins by the taconian salinian and acadian orogenic events the recent phase of exploration drilling has provided new evidence for structural stratigraphic reservoir and source rock maturation models of western newfoundland the first well port au port 1 supported the hypothesis that the round head thrust had an earlier extensional history prior to the acadian compressional inversion that created the present day structural high of the port au port peninsula the well tested a small anticline formed in a footwall shortcut fault of the round head thrust the second well long point m 16 was drilled at the northern tip of long point to test a triangle zone identified by previous workers this well demonstrates that the frontal monocline at the western edge of the triangle zone is elevated by a stack of imbricate thrusts composed of rocks of the taconian allochthon and compressional basement involved faults that have uplifted the cambrian ordovician carbonate platform the structural model developed in the port au port area with the aid of these wells has been extended throughout the humber zone in western newfoundland changes in structural style illustrated by regional cross sections suggest that prospective trap geometries are only developed in the southern and central parts of the region the reservoir model proposed invokes exposure and karsting of the footwalls of extensional faults formed as the carbonate platform collapsed during a middle ordovician hiatus the st george unconformity structural relief became more pronounced as extensional collapse continued through the middle ordovician begin page 394 these structurally high fault footwalls became the foci for dolomitizing and mineralizing fluids that used major faults as fluid conduits during the devonian fluids deposited sulphide ores and created zebra and sparry dolomite and some sucrosic hydrothermal dolomites in the st george group and the table point formation the reservoir model maturity and source rock data and the structural models have been combined with seismic and onshore surface geology this enables the prospectivity of the western newfoundland cambrian ordovician play trend to be evaluated for further exploration

sea level curve for pennsylvanian eustatic marine transgressive regressive depositional cycles along midcontinent outcrop belt north america at least 55 cycles of marine inundation and withdrawal are recognized in the mid desmoinesian to mid virgilian midcontinent outcrop sequence in north america they range from widespread major cycles classic cyclothems with deep water facies extending across the northern shelf through intermediate cycles persisting as marine horizons across the shelf to minor cycles developed on the lower shelf or as parts of major cycles biostratigraphic differentiation of the cycles should establish interbasinal correlation on a scale fine enough to allow evaluation of differential tectonics and sedimentation sequential groupings of cycles are more irregular than proposed megacyclothems or mesothems but they may be obscured by the distinctness of the major cyclothems estimates of cycle periods range from about 40 to 120 x 10 sup 3 yr for the minor cycles up to about 235 to 400 x 10 sup 3 yr for the major cyclothems the range for all cycles corresponds well to the range of periods of earth s orbital parameters that constitute the milankovitch insolation theory for the pleistocene ice ages and it further supports gondwanan glacial control for the pennsylvanian cycles even though the dominant period of the major pennsylvanian cyclothems is up to four times longer than the dominant 100 000 yr period inmore the pleistocene the shapes of both curves display rapid marine transgression rapid melting of ice caps and slow interrupted regression slow buildup of ice caps which suggest similar linkages between the climatic effects of the orbital parameters and ice cap formation and melting at the two different scales widely separated in time 28 references 3 figures less

atmospheric boundary layer rolls observed by the synthetic aperture radar aboard the ers 1 satellite two synthetic aperture radar sar images acquired by the european remote sensing satellite ers 1 over the jade weser estuary in the german bight of the north sea on january 2 and 20 1992 are analyzed the images show sea surface manifestations of atmospheric boundary layer rolls this is inferred from the orientation of the quasi periodic sea surface patterns which are aligned approximately with the wind direction from the ratio of the wavelength of the patterns to the height of the boundary layer and from the conditions encountered in the atmospheric boundary layer as measured quasi simultaneously by radiosondes the atmospheric boundary layer rolls were generated by a dynamic instability on january 2 and by a thermal instability on january 20 for the first time quantitative estimates of variations of the wind velocity at the sea surface associated with the atmospheric rolls are extracted from a spaceborne radar sar image it is shown that wind velocities derived from sar image intensity variations are in agreement with theoretical estimates

patterns of late palaeozoic deglaciation in the parana basin brazil abstract the itarare subgroup middle carboniferous early permian of the parana basin of southeastern brazil contains the thickest most extensive and one of the longest records of late palaeozoic glaciation in all of the gondwana supercontinent glacially controlled deposition started as early as the middle carboniferous when lobate termini of ice streams from the windhoek ice sheet wis and rio grande do sul and asuncion ice caps moved into the parana basin lobes reached sea level and advanced grounded at least as far as 200 km into the basin stabilizing as tidal intertidal margins glaciation and glacial sedimentation occurred penecontemporaneously with the transgressive phase of the late palaeozoic tectonic cycle of the parana basin while gondwana was gradually moving away from the south pole evolution involved complex interaction of tectonic palaeogeographic and palaeoclimatic factors initial flooding of the basin by an epicontinental sea in the middle carboniferous may have provided moisture necessary for the growth of glaciers conversely episodes of sea level rise probably affected the stability of marine glaciers the palaeoclimatic setting for the wis and other ice masses at the margins of the parana basin was mostly temperate multiple ice advances are evidenced by subglacial tillites resting on striated and or glaciotectonized basement and deformed glacigenic sediments identified at different stratigraphic levels in the itarare subgroup glaciation reached its maximum expansion sometime between the late carboniferous and early permian gradually diminishing and vanishing in the late early permian the reconstructed palaeogeographic evolution favors a model of irregular melt back of ice masses particularly along the eastern margin of the parana basin in analogy with the deglacial pattern of the pleistocene laurentide ice sheet in north america retreat of marine glaciers was mostly associated with relatively simple accumulations or complex build ups of ice contact proglacial facies associations in glacial estuarine embayments fast retreat was mainly controlled by decoupling associated with sea level rise and intense calving in the terrestrial environment more fragmentary evidence shows that retreat may have involved several mechanisms including downwasting of stagnant inactive ice margins and destabilization by surging of glaciers moving over deformable sediments highstand sea level following ice wastage is often marked by widespread deposition of relatively thin marine beds at least four stratigraphically different basinwide marine horizons are recognized isostatic rebound of deglaciated margins of the parana basin is recorded by transition from deep marine beds to shallowing coarsening upward prograding sequences of littoral fluvio deltaic facies basinwards sourced from raised basin margins eventually upon emersion these constituted platforms for interglacial and postglacial peat development although glaciation lasted for a long time glacial sedimentation alternated with relatively long periods of intense and widespread subaerial and subaquatic submarine reworking of previously deposited glacigenic sediments and deposition of normal non glacial sediments that comprise the bulk of the itarare subgroup sequence thin coal beds which locally rest on fossil soils denote climatic amelioration during these interglacial phases

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

an ers 1 synthetic aperture radar image of atmospheric lee waves an ers 1 synthetic aperture radar sar image of the island hopen shows a distinct 7 6 km wavelength wave phenomenon near the island this wave phenomenon is interpreted as the surface imprint on open water of atmospheric lee waves the pattern is visible in the sar image since the lee waves modulate the horizontal wind speed near the ocean surface which in turn modulates the surface roughness and the radar cross section the physical setting for the observation is presented and discussed the lower bound on horizontal wind speed modulation is estimated to range from 3 2 ms 1 for the wind speed minima to 12 2 ms 1 for the wind speed maxima based upon the observed radar cross section modulation and the ers 1 scatterometer wind retrieval model cmod4 the wavelength and wind speed modulation are consistent with linear lee wave model predications the model uses an atmosphere with an exponential profile of the scorer parameter ratio of buoyancy frequency to wind speed to represent a shallow ground based inversion layer observed at bear island and a bell shaped barrier to represent the forcing effects of hopen

controls of subduction geometry location of magmatic arcs and tectonics of arc and back arc regions most variation in geometry and angle of inclination of subducted oceanic lithosphere is caused by four interdependent factors combinations of 1 rapid absolute upper plate motion toward the trench and active overriding of the subducted plate 2 rapid relative plate convergence and 3 subduction of intraplate island seamount chains aseismic ridges and oceanic plateaus anomalously low density oceanic lithosphere cause low angle subduction under conditions of low angle subduction the upper surface of the subducted plate is in contact with the base of the overlying plate the wedge of low density asthenosphere is replaced by subducted lithosphere and the width of the arc trench gap either is significantly increased or a magmatic arc is not developed within the overlying plate the fourth factor is age of the subducting lithosphere subduction of young lithosphere produces two opposing tendencies 1 low angle subduction and increased arc trench distance owing to its low density and 2 decreased arc trench distance owing to its higher temperature two factors of secondary importance contribute to variation in subduction zone geometry and arc trench distance accretion of sediment in trenches depresses the upper portion of the subducting oceanic plate and causes the trench axis to migrate seaward prolonged subduction thickens the upper plate depresses the isotherms in the subducted plate and may create a broader arc both factors increase the arc trench gap the four primary factors also control development of other tectonic elements such as regional subsidence for example the amazon basin and a portion of the cretaceous interior seaway of western united states intra arc extension for example the basin and range province foreland fold and thrust belts and laramide style tectonics

structure of the surface wind field from the seasat sar an intensive analysis of the vector wind field of one seasat data set pass 1339 is described wind speed and direction signatures are found in seasat sar synthetic aperture radar images and the resulting estimates are compared with the seasat a scatterometer system sass and simultaneous noaa p 3 aircraft measurements a power law is presented to relate sar measured backscatter to sass estimated wind speed and the sar estimates are shown to agree with the sass estimates to within a standard error of 0 7 m s over a range of wind speeds from 3 m s to 13 m s the surface expressions of atmospheric roll vortices are apparent in several of the sar images and may be responsible for the wind direction signature in these cases wind field estimates averaged over regions of variable sizes are possible because of the high resolution of sar imagery a method for extracting low wave number directionality and its variability from sar spectra is described and sar direction estimates obtained from spectra of 6 4 km square images are shown to have a precision of approximately 10 although a comparison data set that could validate these higher resolution estimates is lacking averages over 40 km square regions are in good agreement with the other wind field information the sar wind direction estimates yield a more complete interpretation in a region with a turning wind field near a front that is ambiguous with only sass observations in this region the flow patterns of the high resolution estimates appear consistent with our knowledge of the overall circulation considering all the observations however in another region the small scale variability is too large and random to represent real wind variability although averages derived from these estimates are still reliable

the neoproterozoic of southwestern africa with emphasis on platform stratigraphy and paleontology abstract neoproterozoic sediments in southwestern africa occur in the pan african kaoko khomas gariep vanrhynsdorp and saldania belts they were deposited in response to rifting break up of a supercontinent formed at 1000 ma and subduction and collisions of the congo kalahari rio de la plata and malvinas plates these collisions led to the formation of a neoproterozoic cambrian supercontinent this paper deals with the geology of the platform successions of the kaoko khomas gariep and vanrhynsdorp belts deposition of the sediments occurring in these belts commenced 900 to 1000 ma ago and probably ended between 500 and 520 ma the sediments record wilson cycles that ended with the deposition of red beds palaeontological and carbon isotope studies on the damara sequence gariep complex nama group and vanrhynsdorp group make intra and inter basinal correlations possible prior to deposition of the nama group two or perhaps three glaciations took place over an extensive area in southwestern africa these being the kaigas chuos 725 700 ma numees 650 600 ma or 610 590 ma and possibly the varianto 745 725 ma glaciations the numees tillite is overlain by a stratigraphic unit containing pinkish dolomite during deposition of the nama group the minor vingerbreek 600 545 ma glaciation or cold water period occurred the major kaigas chuos and numees and minor vingerbreek glaciations correspond with low 13c isotope ratios and appear to have taken place at relatively low palaeolatitudes the riphean sediments were deposited predominantly during rifting and break up of a supercontinent during the late vendian to early cambrian deposition of the nama group in southern namibia and the penecontemporaneous vanrhynsdorp group in the republic of south africa took place in the nama foreland basin detrital micas indicate that deposition of the nama group took place between 635 and 530 ma the nama foreland basin which was connected to a major ocean to the south formed as a result of collisions between the congo kalahari and rio de la plata plates with the exception of the nama group little is known about the palaeontology of the neoproterozoic in southwestern africa the lower nama group is latest proterozoic in age it contains an ediacaran fauna a depauperate assemblage of organic walled microfossils and a relatively well diversified ichnofauna with brooksella diplocraterion and nereites which are atypical of vendian strata many trace fossils are exceptionally small the occurrence of the shelly fossil cloudina and probable calcified metaphytes in the lower nama group suggest that skeletalization in animals and metaphytes occurred almost simultaneously towards the end of the proterozoic the upper nama group is early cambrian in age as indicated by the occurrence of the trace fossil phycodes pedum the upper nama group dominated by red beds contains a low diversity ichnofauna with trace fossils of normal size bio and chemostratigraphy combined with sequence stratigraphy will probably establish how the prominent unconformities which occur in the neoproterozoic of southwestern africa are related to the periods of formation of the wonoka canyons in south australia

environmental impact of volcanic margin formation late rift stage uplift and subsequent massive transient volcanism during breakup of rifted volcanic continental margins constrain paleoenvironments by modifying basin geometry and the composition of the atmosphere hydrosphere and thus biosphere on regional and global scales the early tertiary north atlantic breakup history shows that lava emplacement was accompanied by regional ashfalls and that extrusive complexes influenced paleogene oceanic and continental margin circulation and sedimentation temporal correspondence with the terminal paleocene deep sea extinction event and the earliest eocene greenhouse suggests a global impact possibly by enhanced atmospheric co 2 levels leading to polar warming and thereby changing patterns of deep water formation in this context transient subaerial volcanism at continental margins should be considered with the much discussed continental flood basalt provinces and oceanic plateaus

direct influence of gravity waves on surface layer stress during a cold air outbreak as shown by synthetic aperture radar abstract synthetic aperture radar sar images of oceans and the great lakes have provided a highly detailed means of observing atmospheric boundary layer phenomena such as convection land breezes and internal gravity waves this is possible because the backscattered radiation detected by sar can be dominated by scattering from wind driven capillary waves whose spatial variation is visible as patterns in the sar images in this paper we present two case studies in which sar images taken over lake superior demonstrate spatial variability in the surface wind stress created over the lake by coincident gravity waves and boundary layer convection during cold air outbreaks of particular interest is the direct influence of the gravity waves on the lake surface stress despite the intervening highly convective atmosphere as well as the detailed view of the fetch dependence of that stress

investigation of multifrequency multipolarization radar signatures of rain cells over the ocean using sir c x sar data radar signatures of rain cells are investigated using multifrequency multipolarization synthetic aperture radar sar images acquired from the space shuttle endeavour during the spaceborne imaging radar c x band sar sir c x sar missions in april and october 1994 in sir c x sar images radar signatures of rain cells over the ocean usually consist of irregularly shaped bright and dark patches that strongly depend on radar frequency and polarization the radar signatures of rain cells observed in sir c x sar imagery of the ocean originate from 1 the scattering and attenuation of the microwaves by raindrops and ice particles in the atmosphere and 2 the modification of the sea surface roughness induced by the impact of raindrops and by wind gusts associated with rain cells raindrops impinging on the sea surface generate ring waves which enhance the sea surface roughness but they also generate turbulence in the upper water layer which reduces the sea surface roughness depending on the radar wavelength ocean areas struck by rain can have higher or lower normalized radar cross section nrcs than the surrounding rain free area in ocean areas where heavy rain is impinging on the sea surface the x and c band nrcs is usually enhanced and the l band nrcs is reduced from the phase difference between the horizontally and vertically copolarized signals estimates of the rain rate are obtained the present analysis shows further that the presently used wind speed retrieval algorithms for the scatterometers aboard the ers and adeos satellites may yield biased wind fields if several rain cells lie within a scatterometer resolution cell

deformation styles at the appalachian structural front western newfoundland implications of new industry seismic reflection data new seismic reflection data gathered during hydrocarbon exploration in and adjacent to the external humber zone western newfoundland have important implications for the interpretation of structural style at the appalachian front these new data indicate that the structural front is influenced by both thin skinned and thick skinned structures where the structural front is thin skinned it is characterized by a triangle zone or tectonic wedge similar to structures observed at the southeastern margin of the canadian cordillera and at other orogenic fronts the thin skinned tectonic wedge is overridden locally by thick skinned thrusts which are generally emergent but are locally blind forming a thick skinned tectonic wedge timing relationships indicate that although initial motion occurred during the early to middle ordovician taconian orogeny the thin skinned allochthonous slices in western newfoundland were not emplaced until devonian time the acadian orogeny thick skinned deformation which p

marine flooding surfaces recorded in permian black shales and coal deposits of the main karoo basin south africa implications for basin dynamics and cross basin correlation abstract the marine origin of black shales in the context of the permian postglacial development of the karoo basin south africa is subject of an ongoing controversial discussion here we present and discuss palynological and sedimentological data providing evidence of a transgressive event during the early guadalupian palynofacies assemblages of the black shales of the southern basin include marine phytoplankton that exhibit peak abundance within the whitehill shales and which also occur within siltstones and glauconitic sandstones on top of the no 5 coal seam of the north eastern basin palynostratigraphic control makes this marine signal a powerful tool for cross basin correlation moreover palynofacies analysis demonstrates a facies transition from terrestrial lacustrine and fluvio deltaic in the northeast to deep marine in the south western parts of the basin

structural and tectonic evolution of the humber zone western newfoundland 2 a regional model for acadian thrust tectonics the humber zone of the western newfoundland appalachians represents a cambrian ordovician passive continental margin which was deformed in taconian mid ordovician and acadian silurian devonian orogenic events a deformation front is imaged in seismic reflection data offshore of western newfoundland structures associated with this deformation front are exposed on port au port peninsula where silurian rocks are strongly deformed but mississippian strata are flat lying indicating that latest thrusting was acadian a gravity low in the gulf of st lawrence corresponds to a sediment filled acadian foreland basin previous models suggest that the on land shelf succession is autochthonous to parautochthonous however two lithoprobe seismic reflection transects show sub horizontal reflections between 2 and 5 s two way travel time which extend up to 85 km east of the thrust front these are interpreted as autochthonous platform and basement in this model shallower reflectors and outcropping units include both allochthonous platform and basement comprising the acadian port au port allochthon the taconian humber arm allochthon was carried westward as a high structural slice during thrusting of this allochthon no major structural discontinuity exists between grenville age crystalline rocks of the long range massif and platform rocks interpreted as allochthonous in the northern seismic line a monocline at the southern extremity of the long range probably represents an oblique or lateral hanging wall ramp above the basal detachment within the long range thrust zone at the western margin of the massif the long range thrust shows only a few kilometers of displacement however the parsons pond thrust which we interpret to run offshore at green point juxtaposes contrasting successions with different structural and thermal histories it probably carries a much larger amount of the total displacement the basal decollement of the port au port allochthon is therefore interpreted to pass beneath the southern part of the long range massif

tuffs tectonism and glacially related sea level changes carboniferous permian southern namibia abstract the carboniferous permian glacigene dwyka group in southern africa has been widely regarded as amagmatic only in the higher parts of the permian and subsequent younger strata has evidence of magmatism been recognised particularly in the form of pyroclastic fallout ash beds the source of these tuffs has been suggested to be patagonia and west antarctica forming part of an extensive volcanic arc which lay some 1500 to 2000 km to the south and west in their pre break up gondwana positions rhyolitic dacitic and basaltic andesitic tuff beds within the glaciomarine sediments of the dwyka group in namibia reveal new evidence for an early onset of proximal bimodal volcanic activity in southern africa contemporaneous tectonism is recorded by type 1 unconformities and systematic thickness changes across nw se trending extensional normal faults we suggest that this tectonomagmatic period marks initial extensional events in southern namibia and the carboniferous permian volcanic trend appears to coincide with the position of the eventual namibian continental margin significantly the stratigraphic positions of the tuff beds show a distinct association with enclosing marine transgressive depositional sequences most of them coincide with sharply defined flooding surfaces within relatively thick shaly successions reflecting their multiple transgressive nature widening the study context to the latest early permian in southern africa the main karoo basin of southern africa exhibits a similar coincidence of marine transgressions and extrusion of volcanics the relationship between tuff beds and transgressive depositional sequences is not only the result of enhanced preservational potential during transgression but of a genetic coupling between magmatism extensional tectonics and basin subsidence the latter accelerating a rise in relative sea level this interaction is significant not only for understanding potential controls on relative sea level change but also for understanding the early geodynamic evolution of the southern south atlantic continental margin

deglaciation sequences in the permo carboniferous karoo and kalahari basins of southern africa a tool in the analysis of cyclic glaciomarine basin fills the late westphalian to artinskian glaciomarine deposits of the karoo and kalahari basins of southern africa consist of massive and stratified diamictite mudrock with ice rafted material sandstone silty rhythmite shale and subordinate conglomerate forming a cyclic succession recognizable across both basins a complete cycle comprises a resistant basal unit of apparently massive diamictite overlain by softer bedded stratified diamictite sandstone and mudrock with a total thickness of as much as 350 m four major cycles are observed each separated by bounding surfaces lateral facies changes are present in some cycles the massive diamictites formed as aprons and fans in front of the ice grounding line whereas the stratified diamictites represent more distal debris flow fans the sandstones originated in different environments as turbidite sands small subaqueous outwash channel sands and delta front sands the rhythmites and mudrock represent blanket deposits derived from turbid meltwater plumes cycles represent deglaciation sequences which formed during ice retreat phases caused by eustatic changes in the karoo and kalahari basins evidence for shorter term fluctuation of the ice margin is present within the major advance retreat cycles hardly any sediment was deposited during lowstand ice sheet expansion whereas a deglaciation sequence was laid down during a sea level rise and ice margin retreat with the volume of meltwater and sediment input depending on temporary stillstands of the ice margin during the retreat phase the duration of the cycles is between 9 and 11 ma suggesting major global tectono eustatic events smaller cycles probably linked to orbital forcing were superimposed on the longer term events a sequence stratigraphic approach using the stacking of deglaciation sequences with the ice margin advance phases forming bounding surfaces can be a tool in the framework analysis of ancient glaciomarine basin fills

structure of the appalachian deformation front in western newfoundland implications of multichannel seismic reflection data petroleum industry multichannel marine seismic data in the public domain do not support the traditional interpretation of the acadian deformation front in the appalachians of western newfoundland they show that the late ordovician to latest silurian long point clam bank succession is folded in a northwest facing monocline whereas the underlying cambrian ordovician platform succession dips southeast we interpret the intervening region as a structural triangle zone similar to those at the foreland edges of other thrust belts the contact between the long point group and the underlying humber arm allochthon previously interpreted as unconformable on port au port peninsula is the southeast vergent upper detachment surface of the triangle zone the platform succession on the peninsula is probably within the triangle zone and is therefore allochthonous at least 30 km of acadian silurian devonian northwest transport is implied the triangle zone continues to the northeast offshore the bay of islands suggesting that grenvillian basement of the long range massif is also allochthonous

flexural modeling of paleozoic foreland basin subsidence offshore western newfoundland evidence for substantial post taconian thrust transport multichannel seismic reflection data gathered by the petroleum industry offshore of western newfoundland constrain the absolute thicknesses of the middle ordovician and post middle ordovician portions of the anticosti foreland basin immediately adjacent to the appalachian structural front these seismic lines which include 1970s vintage data in the public domain and recently acquired proprietary data indicate that the middle ordovician taconian portion of the foreland basin is more than an order of magnitude thinner than the preserved post middle ordovician salinian acadian portion the mechanical lithospheric coupling of foreland basins and their adjacent overthrust belts is a well understood phenomenon a thin taconian foreland succession and a thick salinian acadian succession imply that the overthrust loads responsible for flexural depression of the anticosti basin were much more distant and or much smaller during the middle ordovician taconian orogeny than they are today we quantify thi

late paleozoic paleofjord in the southernmost parana basin brazil geomorphology and sedimentary fill abstract in the southernmost part of the parana basin records of the late paleozoic glaciation occur in a discontinuous form preserved in paleovalley systems excavated in the crystalline basement this paper addresses one of these paleovalleys the mariana pimentel which extends over 60 km with nw se valley direction and a constant width of 2 5 km with the objective of demonstrating that the paleovalley worked as a fjord during the glaciation period its origin as well as sedimentary fill and morphology were analyzed the paleovalley morphology was obtained through electrical resistivity electrical sounding and lateral mapping and mathematical modeling in four transverse sections the morphology of the paleovalley documented by the u shape steady width and high depth reaching up to 400 m are typical features of modern glacial valleys the sedimentary facies that fill the base of the paleovalley such as rhythmites and dropstones with thickness up to 70 m and diamictites with faceted pebbles up to 5 m thick are signs of its glacial origin during the glaciation period the paleovalley had a connection to the epicontinental sea located to the northwest extended toward namibia and was excavated by glaciers from the highlands of this region thus the evidence attests that the mariana pimentel paleovalley was a fjord during the late paleozoic glaciation the duration of the late paleozoic glaciation which is longer than the quaternary glaciation the apatite fission track that suggests erosion up to 4 km thick in the study area and the lack of preserved hanging valleys in the mariana pimentel indicate that the paleovalley once featured a higher dimension furthermore the existence of paleofjords excavated in the border of the basement corroborates the idea of small ice centers controlled by topography during the late paleozoic glaciation

origin of the odd twins anomaly magnetic effect of a unique stratigraphic marker in the appalachian foreland basin gulf of st lawrence the odd twins magnetic anomaly is a pair of linear asymmetric positive anomalies located in the gulf of st lawrence over the post taconian pre acadian foreland basin fill related to the development of the appalachians a marine magnetic survey allowed the anomaly to be traced close to the coast of newfoundland and an on land survey identified both peaks within the area of outcrop of the late ordovician long point group sandstones of high susceptibility sampled from sparse outcrops close to the locations of the anomaly peaks contain up to 0 58 magnetite models involving dipping sheets of sandstone having similar and slightly higher susceptibility can explain both the onshore and offshore anomaly the magnetite is of detrital origin and represents a paleoplacer heavy mineral concentration formed in a marginal marine environment the anomaly provides a unique tie point between the known onshore stratigraphy and the succession in the foreland basin known only from industry seismic profiles this tie

mid paleozoic thrusting at the appalachian deformation front port au port peninsula western newfoundland structures exposed on port au port peninsula in western newfoundland record the nature of the appalachian deformation front which forms the western boundary of the humber tectono stratigraphic zone the major structures affect the late ordovician to late silurian long point clam bank succession but not the unconformably overlying carboniferous rocks they are probably of devonian age at the west coast of the peninsula long point and clam bank strata are affected by both east vergent and west vergent structures the basal surface of the succession is interpreted as an east vergent thrust forming the upper detachment of a triangle zone and correlates with a similarly located contact seen in offshore multichannel seismic profiles within the succession east vergent deformation zones locally duplicate the stratigraphy west vergent structures including a map scale overturned fold north of round head mountain are probably younger farther south middle ordovician foreland basin sediments are also af

tectonic and lithological constraints on the evolution of the karoo graben of northern malawi east africa the results of a lithostratigraphic tectonic and kinematic study of the karoo deposits of northern malawi are reported the objective of the lithostratigraphic study is to correlate the deposits of the karoo basins of northern malawi with the well known deposits of southern tanzania thus establishing a stratigraphic framework through which the timing of faulting can be constrained the kinematic analysis of faulting constrains the opening direction for the karoo graben in this area and provides basic data to discuss the karoo graben development within the regional tectonic framework of south eastern africa the studied adults are defined by moderately to steeply dipping cataclastic zones with a width of up to 15 m and are characterized by an array of slickensided fault surfaces with different orientations and slip directions in this study small faults offset 10 m but generally not exceeding 30 40 m have been distinguished methods used to analyse the kinematic data include the pressure tension pt method which estimates the principal axes for the bulk brittle strain and the internal rotation axis ira method which estimates the axis of bulk internal rotation and the overall sense of slip at the faults a mass balance calculation reveals a volume increase of up to 16 during cataclastic deformation in the fault zones the pt method shows an approximately east trending extension direction for faults that occur only in the latest carboniferous and early permian strata whereas the fault kinematics from faults that cut middle permian to early triassic rocks is characterized by a ese to se trending extension direction the small faults yield essentially the same kinematic results as the meso scale faults in a transport parallel cross sectional view the principal extension axes are at an acute angle of approximately 60 to the major fault planes given the moderate fault density the relatively high angle between the orientation of the principal extension axis and the fault planes suggest only a moderate amount of horizontal extension across the karoo graben of northern malawi riedel structures in the fault zones formed within two conjugate sets of localized shear zones slip on one set was top to the w nw and on the other top to the e se the two conjugate sets of riedel structures have an acute angle about the regional shortening axes implying that no pronounced rotation of the strain axes occurred the internal rotation axes for the riedel structures reveal a largely bimodal distribution and inferred weakly monoclinic to orthorhombic symmetry therefore the overall deformation during karoo rifting in northern malawi is interpreted to be close to a coaxial deformation with a limited amount of horizontal extension p

tectonic and volcanic controls on early jurassic rift valley lake deposition during emplacement of karoo flood basalts southern namibia abstract the karoo igneous province of southern africa is one of the classic mesozoic flood basalt provinces of the world in the case of the early jurassic kalkrand formation of namibia the succession comprises three major flood basalt units that are separated by two stratigraphically important fluvio lacustrine interlayers these horizons preserve a record of the complex interplay between sedimentation effusion of karoo flood basalts and extensional tectonics that predated and accompanied the break up of gondwanaland both sediment layers start with the dominantly local derivation of weathered and eroded lava debris followed by the emplacement of subaqueous mass flows and subsequent deposition of chemical sediments the latter are characterised by interbedded stromatolitic carbonates grass like structured gypsum and plane bedded sandstones and mudstones containing euhedral displacive gypsum crystals that grew in the subsurface as well as rosettes which nucleated on the sediment surface the central parts of the lacustrine units are overlain by thin deltaic sandstones showing bottomset foreset and topset layering and finally braided fluvial trough cross bedded sandstones evidence of subsidence synchronous with the formation of lake bodies can be explained by two principal mechanisms the first acted in localised areas only and is reflected by the development of small centrally subsiding basins from the repeated occurrence of onlapping geometries within such a pool a multiphase history of sagging is deduced being most likely related to periodic magma withdrawal and reduction in magmatic pressures in subsurface lava feeders beneath the basin floor abundant syn subsident fracture features at lava sediment contacts such as sediment hydrothermal calcite and sometimes basic lava filled fissure systems indicate the pronounced interaction between the underlying volcanics and these small areas of pronounced subsidence fluids passing through the volcanic pile exhaled into the lake giving it the characteristics of alkaline lake systems described from more recent flood basalt areas associated with the modern african rift system on the regional scale however northerly trending extensional fault systems controlled half graben basin geometries and both facies and thickness variations across faults indicate that tectonism operated contemporaneously with volcanism and lacustrine sedimentation the analysis of faults and associated structures such as regularly aligned sediment filled fissures sets of micro faults folds and basaltic dykes constrains the extensional opening direction for the karoo graben structures in this area that heralded the opening of the south atlantic and thus provides a basis to discuss the extensional history of the namibian coastal margin within the regional tectonic framework

the break up of east gondwana along the northeast coast of oman evidence from the batain basin recent detailed studies on the batain nappes northeast coast of oman which represent a special part of the so called oman exotics have led to a better understanding of the neotethyan geodynamic evolution the batain exotics bear witness to volcanic activity sea level changes tectonic instability rifting and oceanization along the eastern oman margin during late palaeozoic and mesozoic times they allow definition of the batain basin as an aborted permian branch of neotethys this marine basin was created in early permian times extending southward to the east african madagascar region and was linked to the karoo rift system the presented revised classification of the batain nappes considers the batain basin to be no longer a part of the hawasina basin and the neotethyan margin proper we attribute the batain basin to a mozambique somali masirah rift system somoma this system started in early permian times creating a marine basin between arabia and india madagascar rifting in the late triassic and oceanization during late jurassic times led to the separation of east gondwana

eurydesma lyonia fauna early permian from the itarare group parana basin brazil a paleobiogeographic w e trans gondwanan marine connection abstract here the biocorrelation of the marine invertebrate assemblages of the post glacial succession in the uppermost portion of the late paleozoic itarare group parana basin brazil is for the first time firmly constrained with other well dated gondwanan faunas the correlation and ages of these marine assemblages are among the main controversial issues related to brazilian gondwana geology in total 118 brachiopod specimens were analyzed and at least seven species were identified lyonia rochacamposi sp nov langella imbituvensis oliveira streptorhynchus sp cyrtella sp tomiopsis sp cf t harringtoni archbold and thomas quinquenella rionegrensis oliveira and biconvexiella roxoi oliveira the presence of tomiopsis sp cf t harringtoni and the bivalve atomodesma aphanaia orbirugata harrington in the teixeira soares beds plus myonia argentinensis harrington and heteropecten paranaensis neves et al both of which recorded in deposits in the teixeira soares and mafra beds butia suggests a biocorrelation with the eurydesma fauna from the bonete formation sauce grande colorado basin argentina furthermore the presence of lyonia archbold and praeundulomya cf subelongata dickins in the taciba formation indicates affinities with deposits in the lyons group carnarvon basin and the fossil cliff member perth basin western australia suggesting a late asselian early sakmarian age even more importantly the collected data suggest the existence of an w e trans gondwanan marine seaway between the parana brazil sauce grande colorado argentina huab hardap shale of the dwyka group aranos area namibia southwest africa the carnavon western australia basins and beyond eastward to the cimmerian region a v proto rift system through two major axes of extensional basin development facilitated the w e marine connection main axes formed by a north northwesterly trending axis paralleling the future south atlantic and a broadly north northeasterly trending line of separation related to the future indian ocean this proto rift system coupled with a sea level rise of at least 100 m favored the establishment of a long narrow shallow seaway allowing the exchange of eurydesma fauna between eastern and western gondwana

a latest carboniferous warming spike recorded by a fusulinid rich bioherm in timor leste implications for east gondwana deglaciation abstract during the late paleozoic and early mesozoic timor lay in the northern part of the north south east gondwana rift system along which the western margin of australia later developed discovery of a latest gzhelian bioherm in the central highlands of timor leste has implications for latest carboniferous earliest permian climate history and deglaciation in basins further south in the rift system limestone outcrop of the maubisse formation near the village of kulau is recognized as a bioherm with a massive lower unit including reef framework at the base and a bedded grainstone upper unit the bioherm developed on a basalt substrate in warm shallow water as indicated by photozoan assemblages in the massive lower unit foraminifera belonging to 17 genera are recorded from the bioherm these include representatives of the families biseriamminidae biwaellidae bradyinidae cornuspiridae lasiodiscidae palaeotextulariidae pseudotaxidae ozawainellidae schubertellidae schwagerinidae staffellidae and textrataxidae twenty one species have been referred to known types and 12 species are left in open nomenclature the assemblage probably belongs within the uppermost gzhelian schwagerina robusta ultradaixina bosbytauensis zone although a possible lowest asselian correlation cannot be excluded the bioherm is the oldest carbonate unit so far recorded from the maubisse formation and the oldest sedimentary unit biostratigraphically dated in timor the dominantly heterozoan composition of the skeletal component of the limestone except for the basal photozoan assemblage and the taxonomic diversity of the larger foraminifera suggest a subtropical environment consistent with a paleolatitude of about 40 s the late pennsylvanian was a time of glaciation that in australia is represented by a significant stratigraphic hiatus in basins to the south of timor in the east gondwana rift system the development of the kulau bioherm during the latest gzhelian may have coincided with a global warming spike that led to rapid melting of continental ice sheets and a substantial influx of glacigene sediment alternating diamictite and mudstone in the southern basins

basin development and inversion at the appalachian structural front port au port peninsula western newfoundland appalachians in the humber zone of the newfoundland appalachians cambro ordovician shelf and foreland basin successions are affected by middle ordovician taconian orogeny and devonian acadian orogeny deformation on port au port peninsula the presence of the late ordovician to late silurian long point clam bank succession allows these episodes to be separated the taconian foreland basin stratigraphy on port au port peninsula is highly variable on the west coast platform carbonates are overlain by megaconglomerates of the cape cormorant formation which record progressive exposure of 1 km of the platform succession the conglomerates are restricted to a narrow zone consistent with derivation from a fault scarp originally immediately west of the outcrops in palinspastic restoration farther east at victors brook the cape cormorant formation is absent but the overlying almost undeformed goose tickle group contains conglomerate derived both from the upper part of the platform succession and from the tacon

magmatic intervals transgression regression cycles and oceanic events in the cretaceous and tertiary of southern south america abstract the southern part of south america provides an excellent test area to analyse relationships between transgression regression cycles along a passive continental margin with magmatic activity and tectonic movements of the andean orogen most of the tectono eustatic sea level changes recognized are related to magmatic activity whether calc alkaline or alkaline the magmatic activity depends on whether tectonic convergence or extension forces are dominant

cold air outbreak during gale lidar observations and modeling of boundary layer dynamics abstract two cold air outbreaks were studied during the genesis of atlantic lows experiment a lidar system was operated to observe the boundary layer evolution and the development of clouds on the first day 30 january 1986 boundary layer rise was less than 50 of the value for the second day 2 march 1986 on the first day only a thin broken cloud cover formed while on the second day a thick solid cloud deck formed although the average moisture content was 60 of that on the first day a trajectory slab model was employed to simulate the evolution of the layer over the ocean near the cast atlantic shore the model allows for vertical gradients in conservative variables under neutrally buoyant conditions the primary effect of these assumptions which are based on observed thermodynamic profiles is to reduce cloudiness to be more in line with observations boundary layer depth was reasonably well predicted as was sensible and latent heat flux

shrimp u pb zircon dating and palynology of bentonitic layers from the permian irati formation parana basin brazil abstract this paper presents the first shrimp zircon age data from bentonitic ash fall layers intercalated with the irati sedimentary rocks as well as palynofossils retrieved from the petrobras six mine parana state southern brazil the permian irati formation is one the most important oil source horizons within the parana basin and consists mainly of siltstones gray claystones as well as organic rich claystones intercalated with limestones zircon morphology based on cathodoluminescence images includes two different populations a dominant population of euhedral prismatic elongate to acicular grains which are most likely related to an ash fall volcanism and a population of rounded to large prismatic grains that were interpreted as detrital grains shrimp analysis performed on the euhedral and prismatic grains revealed an age of ca 278 4 2 2 ma 7 points with 95 confidence interpreted as the crystallization age of the volcanic eruption based on this new dating the irati formation should be placed on the lower permian cisuralian artinskian in age modifying substantially the traditional ages previously attributed to this unit the palynofossils from this level include key species of the lueckisporites virkkiae zone such as l virkkiae l densicorpus l stenotaeniatus weylandites lucifer alisporites splendens typical species of this zone also occur in african and other south american argentina permian strata allowing stratigraphical correlations the origin of the ash falls is not clearly defined it may be related either to calc alkaline arc magmatism associated to the sanrafaelica orogeny 275 and 250 ma or to bimodal volcanic events associated to an early intracontinental rift developed within southwestern gondwana at ca 278 my the dating of this unit is significative to calibrate biostratigraphic schemes along the parana basin as well as equivalent zones in gondwana areas mainly in its occidental portion

mesozoic deposits of sw gondwana namibia unravelling gondwanan sedimentary dispersion drivers by detrital zircon the namibian mesozoic successions may be remnant of a high dynamic sedimentary system that is characterized by multiple stages of sediment accumulation and erosion with contemporaneous homogenization starting with the deposition of the permo carboniferous dwyka group strata and continues at least until the lower cretaceous the lower cretaceous sedimentary system is interpreted to have involved at least an area covering the whole sw gondwana documenting the sedimentary history during the evolution from an ice house environment to an arid desert to test the sediment homogenization hypothesis we applied a combination of isotopic and morphometric data on detrital zircon grains as well as whole rock geochemical data of selected mesozoic sandstones from namibia as a base for the interpretation of the detrital zircon age data we compiled a zircon age dataset with c 44 000 analyses for the southern african region all samples reveal a major detrital pan african zircon age peak of c 0 5 0 7 ga sourced from the pan african magmatic events occurring around the kalahari craton margin the lowermost triassic is characterized by the occurrence of additional mesoproterozoic and paleoproterozoic age peaks of c 1 0 1 2 ga and 1 8 2 0 ga with a majority of zircon grains showing angular shapes the protosource of these grains is interpreted to possibly be the namaqua metamorphic complex and other paleoproterozoic structural units deformed in course of the namaqua orogeny in contrast other samples show a prominent permo triassic age peak and completely rounded zircon grains putatively derived from within the gondwanides volcanic arc the disparity in the zircon age pattern may point towards a change in provenance and also a change in the whole system of zircon recycling during the mesozoic southern gondwana the lower triassic neu loore fm are constrained to more local bedrock sources and short zircon transport distance in contrast zircon grains of the middle triassic omingonde the jurassic etjo und the cretaceous twyfelfontein formations are an expression for a major recycling and sediment homogenization system the system was facilitated by an interplay between fluvial and eolian sedimentary transport systems

dynamics and early post tsunami evolution of floating marine debris near fukushima daiichi the devastating tsunami triggered by the t hoku oki earthquake of 11 march 2011 caused a crisis at the fukushima daiichi nuclear power station where it overtopped the seawall defences on retreating the tsunami carried loose debris and wreckage seaward and marshalled buoyant material into extensive plumes widespread concern over the fate of these and numerous other t hoku tsunami depositions prompted attempts to simulate debris dispersion throughout the wider pacific however the effects of locally perturbed wind and wave fields active langmuir circulation and current induced attrition determine a complex and poorly understood morphology for large floating agglomerations here we show that the early post tsunami evolution of marine debris plumes near fukushima daiichi was also shaped by near surface wind modifications that took place above relatively calm lower surface roughness waters covered by surface films derived from oil and other contaminants high spatial resolution satellite tracking reveals faster than expected floating debris motions and invigorated plume evolution within these regions while numerical modelling of turbulent air flow over the low drag film covered surface predicts typically metre per second wind strengthening at centimetric heights sufficient to explain the observed debris speed increases wind restructuring probably stimulates the dispersion of flotsam from both biological and anthropogenic sources throughout a global ocean of highly variable surface roughness the tsunami triggered by the 2011 t hoku oki earthquake carried debris seaward satellite data and numerical simulations suggest that small scale wind modifications over a smooth film covered sea surface affected debris motions

carboniferous permian palynostratigraphy of west australian marine rift basins resolving tectonic and eustatic controls during gondwanan glaciations abstract the longest interval of cold climate in earth s phanerozoic history spanned some 55 million years from the namurian late carboniferous to the kungurian early permian when glaciation affected much of high latitude gondwana uncertainty surrounds the timing of glaciation s and the frequency of interglacial episodes ice volumes and the location of ice centres this is because the glacial record is preserved predominantly within marine strata deposited in intracontinental rift basins marginal to onshore ice centres on uplifted basement highs the direct stratigraphic record of glaciation is meagre on adjoining basement highs and extremely difficult to date many basins contain broadly similar threefold lithostratigraphic successions of lowermost glaciomarine diamictite facies middle shales and uppermost carbonate and sandstone rich commonly coal bearing deltaic strata in the absence of absolute age control and infrequent presence of macrofossils such deglaciation sequences are widely assumed to be correlative from basin to basin recording gondwanan deglaciation s and a world wide glacioeustatic sea level rise a newly compiled biostratigraphic database for west australia using first appearance datums of spore pollen types allows correlation of late palaeozoic siliciclastic successions between seven basins bonaparte canning carnarvon collie gunbarrel northern and southern perth basins these extend some 3800 km along australia s western continental margin adjacent to the west australian shield all but the gunbarrel basin contain tripartite glacially influenced successions diamictite shale sandstone biostratigraphic data reveal sharp differences in ages and stratigraphic distributions and marked variations in the thickness of coeval units diamictite shale sandstone successions accumulated diachronously from basin to basin recording a dominant tectonic control on subsidence and relative sea level middle shale units are not exact correlatives between basins and thus are unlikely to simply represent widespread climatically controlled glacioeustatic events instead they are argued to record high relative sea levels during times of maximum synrift subsidence this tectonostratigraphic model can be applied to other intracontinental rift basin successions across gondwana