sedimentary record of a fluctuating ice margin from the pennsylvanian of western gondwana parana basin southern brazil abstract the parana basin is a key locality in the context of the late paleozoic ice age lpia because of its location east of the andean proto margin of gondwana and west of contiguous interior basins today found in western africa in this paper we document the sedimentary record associated with an ice margin that reached the eastern border of the parana basin during the pennsylvanian with the aim of interpreting the depositional environments and discussing paleogeographic implications the examined stratigraphic succession is divided in four stacked facies associations that record an upward transition from subglacial to glaciomarine environments deposition took place during deglaciation but was punctuated by minor readvances of the ice margin that deformed the sediment pile tillites well preserved landforms of subglacial erosion and glaciotectonic deformational structures indicate that the ice flowed to the north and northwest and that the ice margin did not advance far throughout the basin during the glacial maximum consequently time equivalent glacial deposits that crop out in other localities of eastern parana basin are better explained by assuming multiple smaller ice lobes instead of one single large glacier these ice lobes flowed from an ice cap covering uplifted lands now located in western namibia where glacial deposits are younger and occur confined within paleovalleys cut onto the precambrian basement this conclusion corroborates the idea of a topographically controlled ice spreading center in southwestern africa and does not support the view of a large polar ice sheet controlling deposition in the parana basin during the lpia

a conceptual model for glaciogenic reservoirs from landsystems to reservoir architecture abstract glaciogenic sediments are present in many hydrocarbon producing basins across the globe but their complex nature makes it difficult to characterise the reservoir quality sedimentary units despite this ordovician glacial deposits in north africa and carboniferous permian glaciogenic sequences in the middle east have been proven to host significant economical hydrocarbon accumulations additionally discoveries have been made in the shallow

late paleozoic glacial episodes in gondwanaland reflected in transgressive regressive depositional sequences in euramerica the late paleozoic glaciation of gondwanaland comprised two short episodes in the famennian i and visean ii confined to brazil and adjacent northwest africa and a long episode that started in the namurian iiia of eastern australia and bolivia argentina expanded to cover much of gondwanaland in the stephanian asselian iiib and collapsed in the early sakmarian iiic dropstones in eastern australia indicate that small ice centers lingered to the kazanian across the belt of low latitudes north of gondwanaland short ranging fossils in widespread shallow marine and paralic deposits indicate synchronous deposition of transgressive regressive sequences in different parts of euramerica these sequences correlate with glacial events in gondwanaland at three levels a four major regressions in euramerica in the famennian 1 visean 2 namurian 3 stephanian 4 and the tastubian transgression that preceded the sterlitamakian regression 5 also recorded in gondwanaland correlate with glacial episodes i ii and iiia iiib and iiic b the time interval of cyclothemic deposition in euramerica brigantian or latest visean to sterlitamakian correlates with that of glacial episode iii and c the dominant period of the euramerican cyclothems as estimated from the middle and late pennsylvanian deposits of the mid continent of north america and of the thickest known gondwanaland glacigenic sediment the earliest permian lyons group of western australia is 0 4 ma equivalent in turn to the long orbital eccentricity period of the quaternary ice age and the dominant period of fluctuation of the late miocene antarctic ice cap the three levels of correlations confirm wanless and shepard9s 1936 hypothesis that the late paleozoic cyclothems are controlled largely by sea level fluctuations related to the gondwanaland glaciation

a new high resolution unstructured grid finite volume arctic ocean model ao fvcom an application for tidal studies 1 a spherical coordinate version of the unstructured grid 3 d fvcom finite volume coastal ocean model has been applied to the arctic ocean to simulate tides with a horizontal resolution ranging from 1 km in the near coastal areas to 15 km in the deep ocean by accurately resolving the irregular coastlines and bathymetry in the arctic ocean coastal regions this model reproduces the diurnal k1 and o1 and semidiurnal m2 and s2 tidal wave dynamics and captures the complex tidal structure along the coast particularly in the narrow straits of the canadian archipelago the simulated tidal parameters harmonic constituents of sea surface elevation and currents agree well with the available observational data high resolution meshes over the continental shelf and slope capture the detailed spatial structure of topographic trapped shelf waves which are quite energetic along the greenland siberia and spitsbergen continental slope and shelf break areas water stratification influences the vertical distribution of tidal currents but not the water transport and thus tidal elevation the comparison with previous finite difference models suggests that horizontal resolution and geometric fitting are two prerequisites to simulate realistically the tidal energy flux in the arctic ocean particularly in the canadian archipelago

late palaeozoic glacial cycles and subcycles in western gondwana correlation of surface and subsurface data of the parana basin brazil the parana basin the largest basin in south america received glacially derived sediments during the late palaeozoic ice age lpia of the gondwana supercontinent despite the importance of this basin for understanding the continental development of the gondwana glaciation and the fact that ca 95 of this basin is not exposed at the surface few attempts have been made to connect the exposed glacial strata to the subsurface record in this paper exposures of glacial cycles in the upper itarare group in santa catarina state southern brazil are analyzed locally correlated and then linked to the three major glacial cycles previously described from subsurface studies along the basin together study areas doutor pedrinho and vidal ramos record five partially comparable shorter glacial subcycles relative to the major glacial cycles these series comprise coarse grained subaqueous outwash deposits turbidite sand sheets marine shales and diamictites the latter mostly derived from delta slope failure and ensuing resedimentation in addition to sedimentological and genetic stratigraphic description and analysis preliminary age determination based on the palynological content is also presented besides a regional correlation of the described succession to the subsurface record is proposed based on well logs and core information all the palynomorph associations identified from the exposed successions which represent the upper third part of the itarare group are related to the subzone protohaploxypinus goraiensis base of the vittatina costabilis zone this zone and correlated ones along the gondwana are considered early permian in age however a first isotopic age recently obtained for the upper itarare group and published elsewhere is considered within a regional stratigraphic framework once it leads to new insights in terms of the lpia time span recorded in the parana basin

reply to comment by dario bilardello on new late pennsylvanian paleomagnetic results from parana basin southern brazil is the recent giant gaussian process model valid for the kiaman superchron

pathways and modification of the upper and intermediate waters of the arctic ocean 1 the purpose of this study is to investigate the pathways and the ventilation of source water masses of the upper and intermediate waters of the arctic ocean for the arctic and subarctic domain a coupled ice ocean general circulation model is set up to be integrated for several decades it is driven by a climatological seasonal cycle of monthly mean atmospheric data from 1980 to 1989 and by restored sea surface salinities passive tracers are used to visualize and interpret the modeled flow and to compare it with observations the model is able to reproduce known features of the arctic ocean circulation like the inflow of two branches of atlantic origin via the fram strait and the barents sea and their subsequent passage at middepths in several cyclonic circulation cells the fate of these atlantic source water masses river water and bering strait inflow water in the model are studied the branch crossing the barents sea is subject to an intense heat loss and ice formation as a result water of this branch leaves the shelf toward the central part of the arctic ocean not only at the surface but also in denser varieties which finally feed the central arctic at halocline and middepths the lightest part turns northward and finally westward joining the transpolar drift the densest part 200 1000 m depth moves eastward along the continental slope a similar path is taken by the atlantic water branch from the fram strait the inflowing branch over the barents sea turns out to be the dominant source for the lower atlantic water layer in the arctic ocean in this investigation atlantic tracers starting in fram strait need 6 years to reach the northern laptev sea slope travel times to return to fram strait are 15 20 years along the lomonossov ridge and about 30 years along the continental slope of the canadian basin tracers that mark the pacific water or the mackenzie river water flow eastward and leave the arctic mainly via the canadian archipelago the siberian river water tracers at the surface penetrate far into the canadian basin before they join the transpolar drift the travel times of the river water from the river mouths are 2 3 years to the shelf edge and 12 14 years to fram strait

millennial scale climate cycles in permian carboniferous rhythmites permanent feature throughout geologic time two late paleozoic glacial rhythmite successions from the itarare group parana basin brazil were examined for paleoclimate variations paleomagnetic characteristic remanent magnetization chrm and magnetic susceptibility k z measurements taken from the rhythmites are interpreted as paleoclimatic proxies ratios of low frequency components in the k z variations suggest milankovitch periodicities this leads to recognition of other millennial scale variations reminiscent of abrupt climate changes during late quaternary time and are suggestive of bond cycles and the 2 4 k y solar cycle we infer from these patterns that millennial scale climate change is not restricted to the quaternary period and that millennial forcing mechanisms may have been prevalent throughout geologic time

catastrophic floods as a possible cause of organic matter accumulation giving rise to coal parana basin brazil abstract gondwana coals of the rio bonito formation parana basin in southern brazil have generally large ash yields so they could be better called coaly siltstones than coal in addition hummocky cross stratification hcs was found in several coal beds of the rio bonito formation throughout the basin in this formation the frequent and close relationship between facies involving rocks generated by subaqueous gravity flows diamictites and coal itself provides an excellent depositional model based on resedimentary processes acting during deposition as well as a stratigraphic rearrangement of the present units in the state of rio grande do sul southern part of parana basin coals are actually prodelta deposits related to delta front diamictite and conglomeratic sandstone with sigmoidal bedding coal forming organic sediments would come from trees plucked by the floods as indicated by the wood logs floating in the diamictite and reworking of previous peat accumulations every coal layer is covered generally by paleosoil siltstones which represent colonization at the top of the catastrophic flood deposit ending a sedimentary cycle in case of brazilian coal settings several authors recognized deltas fan deltas or braid deltas here is particularly considered the general environment as a salted interior sea lago mare hsu et al sense the present study will refer to three important lithostratigraphic units in the carboniferous early triassic cycle the itarare group the rio bonito formation and the palermo formation although the preferential mode of occurrence of hcs in shallow marine environments indicates a genesis attributed to storm action other causes such as catastrophic flooding have been advanced mutti et al mem sci geol 48 1996 233 described flood dominated deltaic systems with thick conglomerate sandstone and pelitic deposits derived from small to medium scale fluvial systems and mountain bordered drainage basins adjacent to the sea in such settings seaward sediment flow can increase dramatically when weather conditions can supply water in such amounts to produce catastrophic floods thick and laterally extensive sandstone lobes with hcs are the fundamental depositional elements of fan deltas and other river dominated delta systems diamictites and coal together could be a result from jokullhlaups an icelandic term for glacial outburst flood in case of catastrophic floods coming from a melting mountain glacier similar to the columbia river valley scablands 15 000 bp and in modern iceland examples

subaqueous mass flow origin for lower permian diamictites and associated facies of the grant group barbwire terrace canning basin western australia the intracratonic canning basin is western australia s largest sedimentary basin 400 000 km2 and has experienced repeated episodes of phanerozoic extension and subsidence resulting in deposition of a number of first order megasequences a major phase of basin extension and sedimentation grant group occurred in the late carboniferous early permian when australia lay at high palaeolatitudes facies analysis of 5000 m of drill core from 25 continuously cored wells in grant group strata on the fault bounded barbwire terrace in the northern canning basin identified three facies associations fas these record the predominance of fault generated subaqueous mass flow and sediment reworking the lowest association fa i up to 355 m thick rests unconformably on tilted older strata and consists of coarse grained subaqueously deposited sediment gravity flow facies these include fault generated breccias massive and graded sandstones and conglomerates deposited by turbidity currents and diamictites generated by mixing of different textural populations during downslope remobilization fa i is overlain abruptly by relatively fine grained deposits of fa ii up to 140 m thick which consist of laminated to thin bedded mudstone and sandstone turbidites recording an abrupt increase in relative water depths in turn these facies coarsen upwards and are transitional into shallow water swaley cross stratified and rippled sandstones of fa iii up to 125 m thick the overall stratigraphic succession probably records an initial phase of faulting and accommodation of coarse sediment fa i a subsequent phase of rapid subsidence increasing water depths and sediment underfilling fa ii and finally a regressive phase of shoreface progradation the occurrence of rare striated clasts in fa i suggests reworking of glacial sediment but no direct glacial influence on sedimentation can be identified

the paths and timing of late paleozoic ice revisited new stratigraphic and paleo ice flow interpretations from a glacial succession in the upper itarare group parana basin brazil abstract this paper examines a glacial diamictite bearing succession from the upper itarare group taciba formation in eastern parana basin brazil the object of study provides the opportunity to investigate in detail the late stages of glacial sedimentation during the late paleozoic ice age lpia in this sector of sw gondwana with implications for glacial cyclicity and regional paleo ice flow reconstructions sedimentology geological mapping and palynological analysis allowed the recognition of four facies associations comprising subaqueous outwash mass transport tide influenced delta front and tide influenced delta plain deposits the succession records at least two episodes of ice margin advance and retreat into a marine influenced environment and can be placed in the earliest permian based on the palynomorph assemblage cross stratification in outwash facies and deltaic deposits indicate sediment transport to the sw the same revealed by deformational structures in mass transport diamictites derived from downslope resedimentation of glaciomarine sediments during deglaciation a glacial source to ne is therefore indicated and is in agreement with paleo ice flow directions obtained from previously studied localities to the north this north derived early permian glaciation contrasts with glacial sources to the se recognized in the lower and middle intervals of the itarare group the scenario suggests a geometric reconfiguration of the parana basin during the lpia and the migration of ice centers with time during the late paleozoic ice age in sw gondwana

palaeoclimate implications from deep drilling of neoproterozoic strata in the officer basin and adelaide rift complex of australia a marine record of wet based glaciers abstract two prominent episodes of neoproterozoic glaciation in australia are recorded in the cryogenian sturtian

on improving the simulation of atlantic water circulation in the arctic ocean 1 we performed a set of numerical experiments in order to better simulate the circulation of atlantic water in the arctic ocean by employing a coupled ice ocean arctic regional model we found that the inflow of atlantic water via fram strait is weak in the case of high viscosity and diffusivity coefficients 1 108 cm2 s and 1 107 cm2 s and creates an anticyclonic circulation in the eurasian basin this flow increases significantly when both coefficients are scaled down to 1 107 cm2 s and 0 5 106 cm2 s but the current path is then unstable and it becomes mostly anticyclonic after about a decade of integration a further reduction of these coefficients leads to growing instabilities due to insufficient grid resolution short term integration of the model with doubled space resolution shows better agreement with observations but long term calculation is still restricted by simulation time alternatively a lower resolution version of this model benefits from parameterizations of subscale processes incorporation of the neptune parameterization of eddy topography interaction into the model intensifies the current steered by subsurface topography and results in cyclonic circulation of the atlantic water in every subbasin and in the whole arctic region in the absence of salinity restoring there was strong salinity drift at the surface resulting in a salinity increase in the central arctic by 3 units from 1960 to 2005 the arctic freshwater content is driven basically by year to year variations of convective mixing involving more saline water from lower layers after cooling and increasing in salinity through brine rejection the surface water becomes denser leading to even stronger convective mixing one dimensional model tests showed how model performance could be improved by implementing a lower vertical diffusion coefficient and higher vertical resolution

evaluation and control mechanisms of volume and freshwater export through the canadian arctic archipelago in a high resolution pan arctic ice ocean model 1 this study examined the 1979 2004 volume and freshwater fluxes through the canadian arctic archipelago caa and into the labrador sea using a high resolution 9 km coupled ice ocean model of the pan arctic region to provide a reference compare with limited observational estimates and investigate control mechanisms of this exchange the 26 year mean volume and freshwater fluxes through nares strait were 0 77 sv 0 17 sv and 10 38 msv 1 67 msv respectively while those through lancaster sound amounted to 0 76 sv 0 12 sv and 48 45 msv 7 83 msv respectively the 26 year mean volume and freshwater fluxes through davis strait were 1 55 sv 0 29 sv and 62 66 msv 11 67 msv while the modeled fram strait branch provided very little 2 freshwater into the labrador sea compared to the total caa input compared to available observations the model provides reasonable volume and freshwater fluxes as well as sea ice thickness and concentration in the caa in nares strait and lancaster sound volume flux anomalies were controlled by the sea surface height ssh gradient anomalies along the straits and freshwater anomalies were highly correlated with the volume anomalies at least half of the variance in the time series of ssh gradient anomaly was due to ssh anomalies in northern baffin bay the west greenland current wgc exhibits seasonality with cross shelf flow into the labrador sea peaking in january february march while reducing the northward flow across eastern davis strait we hypothesize that the eddy reduced northward flow of wgc results in the lower volume and ssh in baffin bay this maximizes the ssh gradients between the arctic ocean and baffin bay leading to maximum winter volume fluxes through nares strait and lancaster sound model limitations include the insufficient spatial resolution of atmospheric forcing especially to account for the effects of local topography the representation of river runoff into hudson bay and coastal buoyancy currents low mobility of modeled ice and incomplete depiction of ice arching many of these issues are expected to be resolved with increased model grid cell resolution improved sea ice and ocean models and more realistic atmospheric forcing

representing eddy stress in an arctic ocean model 1 experiences with a number of ocean models have shown arctic ocean circulation to be quite dependent upon assumptions about eddy stresses a key difference is between assuming that subgrid eddies act as friction and assuming that eddies act to generate entropy propelling mean flows sometimes called neptune fisheries and oceans canada is developing global ocean and sea ice modeling after nucleus for european modeling of the ocean nemo we have modified nemo to include neptune as an alternative to friction consistent with previous modeling studies our results show marked impacts neptune supports narrow cyclonic midwater and deepwater currents around the peripheries of arctic basins neptune also induces two way flows through channels in the canadian archipelago and limits the width of the ice tongue exiting at fram strait

late ordovician carbonate productivity and glaciomarine record under quiescent and active extensional tectonics in ne spain abstract carbonate productivity and glaciomarine deposits of the ordovician silurian transition display different sedimentary architectures in the iberian and hesperian chains of ne spain as a result of quiescent and active extensional tectonics on platforms fringing north gondwana the late katian carbonate productivity of the iberian platform reflects the onset of bryozoan pelmatozoan meadows and mud mound complexes throughout an intra shelf ramp whereas carbonate nucleation of prominent carbonate factories took place on the top of isolated palaeo highs in the hesperian platform in both cases the end of carbonate productivity is associated with glacioeustatic regression subaerial exposure and karstification predating widespread precipitation of iron ore deposits in the vicinity of palaeohighs the hirnantian glacioeustatic transgression is represented lithostratigraphically by the orea formation in the iberian platform the formation consists of two distinct depositional sequences bounded by the progradation of conglomeratic channels and is dominated by the record of massive and crudely stratified diamictites with tabular geometries and deposited subaqueously as rain out facies in contrast the hesperian platform is rich in disrupted diamictites which form strongly deformed units interpreted as submarine slumps associated with active synsedimentary faults in both cases the anomalous occurrence of massive diamictites rich in boulder to sand sized carbonate dropstones and displaying rapid variations in density and size suggests that distinct iceberg drift lanes existed indicating current activity in the open sea

atmospheric forcing on the canadian arctic archipelago freshwater outflow and implications for the labrador sea variability the variability of the freshwater export through the canadian arctic archipelago caa is analyzed using a hindcast simulation forced by surface atmospheric forcing from the era40 reanalysis 1958 2001 although the two channels representing the archipelago in the model are both sensitive to the along channel sea surface height ssh gradient they appear to have very distinct behaviors the outflow to lancaster sound is shown to be largely controlled by the magnitude of the upstream ssh gradient across mcclure strait the gradient shows a close link to the wind stress curl in the western arctic but also to a large scale ssh anomaly pattern which has a strong signal over the shelf to the south of mcclure strait the latter has however little statistical connection to the ssh variability in the beaufort gyre by contrast the outflow through nares strait responds preferentially to ssh variations in the northern baffin bay which are remotely forced by air sea heat exchanges in the labrador sea the variability is largely coherent between the two outflows and is controlled by a dipolar atmospheric pattern reminiscent of the north atlantic arctic oscillation when entering the subpolar gyre the caa freshwater outflow remains confined to the labrador shelf with little impact on the salinity of the interior labrador sea and potentially on the convection the latter is represented by a distinct mode of salinity variability in the western subpolar gyre which is rather influenced by the variability of the sea ice export through fram strait

study of the west gondwana floras during the late paleozoic a paleogeographic approach in the parana basin brazil abstract the late paleozoic in west gondwana was a period of significant climatic changes ranging from a glacial climate in the late carboniferous to a semi arid climate in the late permian the floristic province of gondwana in the parana basin was directly affected by such changes and underwent a transformation regarding composition and geographic distribution thus the climatic phases were divided into three intervals phase a containing interglacially developed flora phase b containing floras of immediate post glacial temperate climates and phase c identified with floras related to the decline of dryness regarding their geographical distribution the floras were concentrated in the far northern and far southern portions of the basin during the glacial interval and with a gradual increase in temperature went on to occupy the entire basin finally we can see that the floras located in the argentinean portion of west gondwana are older and have greater species diversity than those present in the parana basin and africa during phase a in phase b there is a decline of argentinean flora species a large increase in the parana basin floras and an average increase in african floras in the final stage the floristic province no longer exists in argentina the flora of the parana basin also suffers a decrease of specimens and the african flora undergoes its moment of greatest development such diversity change also reflects a west to east migration throughout the late carboniferous

bioerosion in shells from the early permian rio bonito formation brazil taphonomic paleobiological and paleoecological implications abstract we report the occurrence of sponge borings in composite molds of heteropectinid shells from early permian marine siliciclastic deposits of the parana basin of southern brazil sponge borings are preserved mainly as chambers entobia and channels entobia and clionolithes three preservational variations of entobia are present morphologically equivalent to the alpha beta and gamma ontogenetic stages of clionid sponges this equivalence suggests that the ontogenetic behavior in clionid sponges remains the same since early permian times and points to a conservative evolutionary trend for this group the pattern of bioerosion and other taphonomic signatures indicate rapid shell burial due to frequent and energetic storm events that might have limited the time available for bioerosion activity the new findings improve the paleozoic record of entobia and clionolithes and indicate that sponge borings have potential to be preserved in ancient siliciclastic rocks

sedimentary dynamics and evolutionary history of a late carboniferous gondwanic lake in north western argentina lacustrine deposits are well represented in the lower part of the late carboniferous agua colorada formation in the north west sierra de narvbez catamarca province argentina lake narvbez was one of the several water bodies formed in the region immediately after the gondwana glaciation shallow lake and deep lake delta progradation proceeded from the ese coarse grained delta plain and turbidite delta front deposits suggest that the delta was formed close to the headwaters short headed stream delta type during periods of high discharge river mouths acted as bypass zones and fine and very fine sands were transported further into the lake by underflow currents the clastic material supplied by the deltaic system was partially reworked by wave action sands accumulated in unstable conditions at the upper delta front as a consequence of delta progradation as a result of the addition of clastics in the steep delta front turbidity currents were formed spreading their load along the lower delta slope deep lacustrine deposits are typically stacked forming two different kinds of progradational turbidite lobe sequences type i lobes were formed in a basinal setting and were probably detached from their feeder systems as a result of sediment bypassing in a shallow lake during periods of low lake level these turbidite lobes are replaced upwards by type i1 lobes which were formed on the delta slope during periods of lake level rise that allowed the onset of delta progradation the presence of highly deformed sandstone bodies suggests rapid depositional rates in a high slope setting whereas the occurrence of hummocky cross stratified sandstones indicates wave reworking of the sands initially emplaced by turbidity currents therefore the inner part of type i1 lobes was formed above storm wave base the depositional history of lake narvaez can be traced through four evolutionary stages lake transgression formation of type i lobes formation of type i1 lobes and delta progradation tectonic activity was probably important at the early stage of lake evolution but the subsequent depositional history was mainly controlled by fluctuations of lake level the lacustrine transport system has been divided into three distinct zones delta

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

origin of late paleozoic multiple glacially striated surfaces in northern parana basin brazil some implications for the dynamics of the parana glacial lobe abstract four stratigraphically repeated closely spaced striated surfaces on late paleozoic sandstone at the base of the itarare subgroup in northern parana basin were generated by subglacial erosion during advances of the grounding zone of the tidewater terminus of the parana glacial lobe on unconsolidated sand the sandstone corresponds to a channelized sheet like proglacial outwash fan accumulated sub aquatically in front of the tidewater terminus of a temperate warm based glacier at the margin of the marine flooded parana basin sandy siltstone beds intercalated with the sandstone and resting on top of the striated surfaces represent aggradational mud deposited from settling of fine debris plumes overflows erosion was mostly by abrasion wear of the sand bed under a glacier sliding over an unfrozen substratum evidence of ploughing is minimal the glacier bed is thought to have behaved rheologically as a rigid essentially undeformable substratum discontinuities in the distribution of striations on the surfaces indicate that ice may have at places decoupled from its bed the section studied documents an upward fining and deepening deglacial sequence comprising four stratigraphic cycles of accumulation of sand formation of a striated surface followed by deposition of mud cycles are correlated with short lived probably fast seasonal advances of the tidewater terminus during general retreat of the parana lobe ice advances were not associated with deposition of subglacial diamicton or lodgement of clasts but to erosion of sand probably by ice protuberances under the sliding glacier

magnetostratigraphy and mid palaeolatitude vgp dispersion during the permo carboniferous superchron results from parana basin southern brazil rhythmites summary a detailed magnetostratigraphic and rock magnetism study of two late palaeozoic rhythmite exposures itu and rio do sul from the itarare group parana basin brazil is presented in this paper after stepwise alterning field procedures and thermal cleaning were performed samples from both collections show reversed characteristic magnetization components which is expected for late palaeozoic rocks however the itu rocks presented an odd flat inclination pattern that could not be corrected with mathematical methods based on the virtual geomagnetic pole vgp distributions correlation tests between the maximum anisotropy of the magnetic susceptibility axis k1 and the magnetic declination indicated a possible mechanical influence on the remanence acquisition the rio do sul sequence displayed medium to high inclinations and provided a high quality palaeomagnetic pole after shallowing corrections of f 0 8 of 347 5 e 63 2 s n 119 a95 3 3 k 31 which is in accordance with the palaeozoic apparent wander pole path of south america the angular dispersion sb for the distribution of the vgps calculated on the basis of both the 45 cut off angle and vandamme method was compared to the best fit model g for mid latitudes both of the sb results are in reasonable agreement with the predicted palaeo latitudinal s relationship during the cretaceous normal superchron cns although the sb value after the vandamme cut off has been applied is a little lower than expected this result in addition to those for low palaeolatitudes during the permo carboniferous reversed superchron pcrs previously reported indicates that the low secular variation regime for the geodynamo that has already been discovered in the cns might have also been predominant during the pcrs

a note on alongshore sediment transport on weakly curvilinear coasts and its implications abstract this paper presents a simple approximation for assessment of the alongshore sediment transport rate on dissipative weakly curvilinear coasts the approximation considers spatial variations in the wave angle and energy sediment size beach slope and type of wave breaking inside the surf zone similar approaches were employed in the past for coasts forced by high oblique waves where shoreline undulations frequently develop with our approach we can analyze more realistic situations i e alongshore relations between the sediment size and the beach slope the general expression for alongshore sediment transport is made explicit using a simple model for wave propagation the solution is used to examine the implications of the behavior of alongshore sediment transport on shoreline evolution after the analysis of the effects of variations in the wave conditions the alongshore beach slope distribution and the shoreline geometry three different shoreline tendencies were obtained for undulating shorelines migration for changes in deep water wave angle amplitude growth for increases in wave height or period and changes in shoreline geometry and wavelength changes and asymmetries for coasts with alongshore changes in beach slope our results also indicate that wave setup may enhance the formation of undulating shoreline features

geochemistry of metasedimentary rocks of uwet area oban massif southeastern nigeria metasediments comprising phyllites schists and gneisses constitute the predominant rock types in uwet area of the oban massif of southeastern nigeria these rocks which range from middle greenschist to uppermost amphibolite facies grade are products of barrovian type regional metamorphism they are of pan african age 600 100 ma

analysis of the physical integrity of earth dams from electrical resistivity tomography ert in brazil dams are structures that barrier rivers and streams for a variety of purposes the constant maintenance of these structures is essential since a possible accident can lead to damage of catastrophic proportions in november 2015 in the city of mariana minas gerais mg brazil a tailings dam burst and spilled 56 million cubic meters of tailings in addition to victimize 19 people the event caused material economic and environmental damage it is considered the largest environmental disaster of brazil this research presents a cheap and quickly applied alternative for investigation of seepage of water in earth dams built with distinct embankment materials one dam composed of predominantly silt and clay soil and the other predominantly composed of sandy soil the research methods used were geotechnical tests as gradation test permeability test with the guelph permeameter method and the application of the dc resistivity geophysical method from the electrical resistivity tomography ert technique in wenner array three ert lines were positioned parallel to the longitudinal axis at each dam the data are presented in 2d and 3d geophysical images with electrical resistivity values modeled based on the physical principle of electrolytic conduction i e decrease in electrical resistance in materials or siliceous minerals in moisture conditions compared to the material in the dry state the results revealed low resistivity zones restricted to some points associated with water infiltration in the transverse direction the results indicate saturation restricted to some points and low permeability at the present time an installation of piping processes

permian carboniferous tectono stratigraphic evolution and petroleum potential of the northern canning basin western australia the canning basin 400 000 km2 of western australia is one of the largest intracratonic basins to have been affected by cold climates as gondwana drifted across the south polar regions during the permian carboniferous this article describes the tectono stratigraphic setting and evolution of the permian carboniferous reeves formation and grant group of the northern part of the basin we employ seismic facies analysis downhole well log responses palynostratigraphy and sedimentary facies logs from 25 continuously cored wells the succession rests on a widespread erosional unconformity of middle carboniferous age this surface may have been modified by glacial erosion when a late carboniferous ice sheet expanded across the entire basin but no primary glacial deposits can be identified if present such sediments were likely reworked during subsequent basin faulting reeves formation and grant group strata are dominated by massive and deformed sandstones diamictites and conglomerates deposited subaqueously as sediment gravity flows close to active faults initial strata of late carboniferous age reeves formation are preserved in the deeper troughs fitzroy trough and in salt collapse subbasins on high standing structural blocks barbwire betty and balgo terraces crossland platform these areas later subsided and were blanketed by gravity flow deposits of early permian age hoya formation in turn a regional flooding surface and overlying bioturbated siltstone unit calytrix formation records an increase in relative water depths across the northern canning basin siltstones coarsen upward into lower shoreface storm influenced sandstones clianthus formation and the fluvial poole sandstone potential petroleum play types are principally associated with faults and channels

ocean drilling program leg 178 antarctic peninsula sedimentology of glacially influenced continental margin topsets and foresets abstract ocean drilling program leg 178 february april 1998 drilled two sites sites 1097 and 1103 on the outer antarctic peninsula pacific continental shelf recovered strata are no older than late miocene or early pliocene site 1097 lies on the outer shelf within marguerite trough which is a major outlet for ice expanding seaward from the antarctic peninsula and reached a maximum depth drilled of 436 6 m below the sea floor mbsf seismic stratigraphic data show flat lying upper strata resting on strata that dip gently seaward uppermost strata to a depth of 150 mbsf were poorly recovered but data suggest they consist of diamictites containing reworked and abraded marine microfauna this interval is interpreted as having been deposited largely as till produced by subglacial cannibalization of marine sediments deformation till recording ice sheet expansion across the shelf underlying gently dipping strata show massive stratified and graded diamictite facies with common bioturbation and slump stuctures that are interbedded with laminated and massive mudstones with dropstones the succession contains a well preserved in situ marine microfauna typical of open marine and proglacial marine environments the lower gently dipping succession at site 1097 is interpreted as a complex of sediment gravity flows formed of poorly sorted glacial debris site 1103 was drilled in that part of the continental margin that shows uppermost flat lying continental shelf topsets overlying steeper dipping slope foresets seaward of a structural mid shelf high drilling reached a depth of 363 mbsf with good recovery in steeply dipping continental slope foreset strata foreset strata are dominated by massive and chaotically stratified diamictites interbedded with massive and graded sandstones and mudstones the sedimentary record and seismic stratigraphy is consistent with deposition on a continental slope from debris flows and turbidity currents released from a glacial source data from sites 1097 and 1103 suggest the importance of aggradation of the antarctic peninsula continental shelf by till deposition and progradation of the slope by mass flow this may provide a model for the interpretation of palaeozoic and proterozoic glacial successions that accumulated on glacially influenced continental margins

ams and grain shape fabric of the late palaeozoic diamictites of the southeastern parana basin brazil diamictites interbedded with marine shales and turbidites onlap the eastern border of the parana basin southern brazil these poorly sorted sediments were deposited during the permo carboniferous glaciation and their matrix supported clasts show no preferred orientation these massive rocks have been studied using anisotropy of magnetic susceptibility ams and grain shape fabric hysteresis loops and thermomagnetic measurements show that ams depends mostly on the paramagnetic clays but fine ferromagnetic particles also contribute to the anisotropy the coarse silt to sand grain preferred orientation study supports the use of ams in describing the diamictite fabric at least regarding the orientation of the foliation ams and grain shape data reveal subhorizontal to weakly inclined magnetic and grain shape foliation parallel to the regional bedding the magnetic lineations are normally scattered within the foliation plane in agreement with the oblate ams ellipsoids found in these rocks both fabric patterns are consistent with deposition by subaqueous mudflows that were resedimented downslope with clastic supply from continental sources the off vertical grain shape foliation poles suggest that the deposition of diamictites was controlled by the depocentre topography of the rio do sul sub basin

permo carboniferous sequences of gondwana affinity in southwest china and their paleogeographic implications abstract in southwest china permo carboniferous depositional sequences of gondwana affinity were first discovered in the himalayan region by the expedition team of acadimia sinica in 1975 by 1983 gondwana affinity permo carboniferous sequences had been identified also in the lhasa block the south qiangtang block in tibet and the tengchong and baoshan blocks in yunnan these sequences are characterised by the presence of successions which are interpreted as glacio marine deposits and by the presence of gondwana affinity biota the distribution of gondwana affinity permo carboniferous indicates that basins whose remnants are now represented by the yarlung zangbo suture and the bangong nujiang suture did not exist at that time and the vast area south of the lungmu shuanghu jinshajiang zone in tibet and west of the changning menglian belt in yunnan formed a part of the northern margin of gondwana

representing topographic stress for large scale ocean models abstract interaction of eddies with seafloor topography can exert enormous systematic forces on the ocean circulation this interaction has been considered previously under idealized circumstances theoretical results are here simplified and extended toward practical application in large scale ocean circulation models among the suggestions is that coarse resolution models can correct a depth independent part of the velocity field toward a velocity given by z flh where z is the vertical unit vector f is coriolis form l is a length scale o 10 km and h is the total depth absence of this tendency may be implicated in a number of systematic defects that appear in present ocean models

making a homogenite an outcrop perspective into the evolution of deformation within mass transport deposits abstract mass transport deposits mtds may show a variety of deformation aspects from poorly deformed layers to highly deformed and homogenized deposits as a result of the different kinds of mass transport processes involved in their evolution previous studies indicate that the downslope flow transformation of mtds is characterized by increasing disaggregation mixing and homogenization of a non to poorly lithified protolith which may ultimately generate a homogenite we here explore the role of deformation processes in the disaggregation and mixing of sediments that tend to lead to sediment homogenization and so may also control the evolution of mtds using the itarare group of the parana basin southern brazil as our case study we examine several types of structures in mtds with varying degrees of mass disaggregation and discuss the role of deformation process in the continuum homogenization of the sediment three deformational facies df 1 df 2 and df 3 were identified and interpreted as recording varying stages of homogenization of sediments disaggregation and mixing within the incipient mature and evolved flows respectively these different stages show transitional aspects that indicate a continuum homogenization the comparison between structural assemblages and the amount of matrix in the three different deformational facies indicates a close relationship between styles of deformation and the homogenization expected for mass flows the processes that promoted disaggregation include boudinage faulting layer parallel shearing and marginal deformation of intrabasinal clasts while mixing processes that generate matrix include shearing and liquefaction fluidization of sediments

radiometric age determination of tonsteins and stratigraphic constraints for the lower permian coal succession in southern parana basin brazil abstract ion microprobe shrimp ii dating of zircons from tonsteins interbedded with coal seams from the candiota and faxinal coalfields early permian rio bonito formation parana basin brazil is presented the mean ages obtained 290 6 1 5 ma are more precise than previously published intervals calibrations of chronostratigraphic data with radiometric ages show that the main coal succession from the southern basin is constrained to the middle sakmarian the 2 ma time interval of deposition supports the hypothesis that the coal generating process was quite rapid in terms of geological time in a general context faxinal and candiota coals are assigned into the protohaploxypinus goraiensis subzone besides some paleocological differences evidenced by palynological studies this bio interval does not correspond to a consistent palynostratigraphic tool and more accurate biostratigraphic zonation for the carboniferous permian interval must be delineated the new results have far reaching significance for correlations of the basin with sequences of the argentinian paganzo basin 302 6 ma and 288 7 ma and also with the karoo basin with the lowermost ecca group 288 3 ma and 289 6 3 8 ma this new evidence supports the presence of an active and widespread lower permian explosive volcanic event in western gondwana which is interpreted as the same volcanism which produced the choiyoi group in western argentina according to this correlation the ash fall source is located about 1400 km to the southwest of their area of deposition

observing global ocean topostrophy 1 recent publications have evaluated topostrophy f v d where is f coriolis v is velocity and d is gradient of total depth as a means of comparing models circulations some results are striking comparing four global models two with modest grid size and two with fine grids merryfield and scott 2007 show that finer grid models are characterized by more positive especially at greater depths and higher latitudes among nine arctic ocean models holloway et al 2007 find in three of the models quite distinct from the other six a result shown to depend upon subgrid eddy parameterization from different choices of numerical method within the same model penduff et al 2007 show that improved numerical representations support more positive can these model results be compared with observations a global compilation has been prepared from 17120 current meter records spanning 83087 current meter months the compilation tends to confirm modeling progress achieved by finer resolution improved parameterizations and better representations a new characterization of global ocean circulation emerges with suggestive dynamical insights

a comparison of long coastal trapped wave theory with remote storm generated wave events in the gulf of california abstract moored pressure temperature and current observations of low frequency coastal trapped wave ctw events in the gulf of california are examined in the context of long wave ctw theory mode 1 ctws that are generated by summer tropical storms are consistent with the occurrences and propagation speeds of the observed wave events in the gulf the mode 1 ctw generation however occurs farther north than observed presumably due to insufficient wind data the mode 1 and observed across shelf wave structure in the gulf are similar in that alongshelf currents are nearly depth independent in 100 m water depth the pressure response is strongest at the coast with decay offshore and with depth and downwelling occurs over the shelf with the amplitude of the mode 1 density response within a factor of two of the observed response the main discrepancies between the mode 1 and observed wave structure are that the speed of the mode 1 alongshelf current increases toward the coast while the weakest observed sp

on the origin of the itarare group basal nonconformity and its implications for the late paleozoic glaciation in the parana basin brazil abstract outcrop studies of the itarare group in the alfredo wagner area along the eastern margin of the parana basin in brazil reveal a partially exhumed nnw sse oriented glacial paleovalley the carboniferous rio do sul formation represents the basal interval of the glacially influenced itarare group and rests directly on precambrian basement rocks this nonconformity is thought to represent an areal scouring surface as indicated by the series of glacially carved linear depressions that were incised into the glaciated bedrock during glacial advances these large scale erosional landforms differ in their extent by orders of magnitude and include wide deep troughs as well as narrower shallower gouges glacial troughs and gouges usually display smaller scale subglacial erosion landforms such as polished and grooved striations on their walls and floors these indicate the nnw motion of a warm based grounded glacier in addition large scale erosional features represent local topographic lows within the major glacial paleovalley these local lows are large enough to contain part of the succeeding deglacial deposits which thin toward and onlap the wall of these depressions we grouped these deglacial deposits into six genetic facies associations fa 1 to 6 within three fining upward glacial cycles fa 1 is composed of black shale and represents an initial marine flooding event it can be correlated with the regionally widespread lontras shale fa 2 is composed of sandstones and mudstones associated with flood derived hyperpycnal flows and occasionally with surge type turbidites fa 3 is represented by plastered or injected matrix supported conglomerates emplaced as lodgment tills fa 4 comprises matrix and clast supported conglomerates sandstones and mudstones attributed to ice rafting and concentrated flows in grounding line fan facies this unit also contains ice keel dragging features carved into soft substrate fa 5 is composed of dropstone bearing black shale related to a second major marine flooding event within the paleovalley fa 6 comprises sandstones associated with channelized surge type turbidites forming the second turbidite system in the succession as these deposits are confined to a paleovalley we infer that sedimentation was influenced by topographically controlled ice streams instead of non confined widespread ice lobes as previously suggested reconstructing south america and southern africa in their positions during the lpia suggests that the glacial valleys then present in the namibia area may have extended further into the eastern margin of the parana basin in this scenario confined outlet glaciers would have flowed out from the namibian windhoek ice cap and terminated along the eastern margin of the parana basin

flow dynamics of a wide arctic canyon we extend and interpret acoustic doppler current profiler and conductivity temperature depth data collected in the summer of 1993 over barrow canyon in order to implement a high resolution 1 5 to 5 km model of the beaufort and chukchi seas this paper addresses physical processes relevant to the barrow canyon region using common dynamical analyses of both field data and numerical results the field data reveal the dominant physical processes that guide the design of our numerical experiments the observed velocity field shows an intense and variable down canyon flow with transports ranging from 0 5 to 1 4 sv a momentum analysis reveals that the cross canyon dynamic balance for the barotropic component is primarily geostrophic conversely the baroclinic cross canyon momentum balance is ageostrophic and secondary flow results from a local imbalance between the vertically varying coriolis acceleration and the cross canyon pressure gradient in addition to the moderate influence of stratification froude number of 0 4 and burger number of 0 06 the barotropic pressure gradient component across the canyon inferred from the large magnitude and little vertical variability of the residuals is dynamically important for both upcanyon and downcanyon flows that occur at different locations concurrently the along canyon dynamic balance is ageostrophic since the time derivative and the coriolis term are of the same order of magnitude temporal rossby number is approximately 1 an analysis of the longitudinal density and velocity fields from the model reveals that the main driving mechanism for generating the observed upcanyon flow is the nonlinear interaction of the variable barotropic flow with the steep topography stratification is maintained by the downcanyon advection of fresh and warm water from the bering and chukchi seas and the upcanyon advection of saltier and colder water from the arctic

a three dimensional model of the mean and seasonal circulation of the gulf of california 1 the mean and seasonal circulation of the gulf of california is simulated with a three dimensional numerical model forced by the pacific ocean through specifying the sea level the temperature and the salinity fields at its entrance at the sea surface the wind and the heat and freshwater fluxes are specified the model reproduces the observed mean and seasonal variability of sea level of heat and salt balances and the sea surface temperature sst climatology it also reproduces the general surface circulation of the northern gulf which consists of a seasonally reversing basin wide gyre it is found that tides and heat fluxes are both indispensable to reproduce the spatial structure and temporal evolution of the sst tides provide the mixing to upwell the cooler subsurface waters in the large islands area and the heating from the surface raises the sst the general circulation of the southern part of the gulf is due to the wind and the pacific forcing in the ekman layer two periods of anticyclonic circulation and one cyclonic per year occur below this layer two cyclonic periods develop in the northern part the tides play an important role in producing mean residual currents and both tides and winds compete against the pacific forcing to produce a cyclonic and anticyclonic circulation once a year contrary to conclusions of previous studies the thermohaline circulation is found to be unimportant in the gulf

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

processes and products of grounding line fans from the permian pagoda formation antarctica insight into glacigenic conditions in polar gondwana abstract glacimarine grounding line fans are subaqueous depositional features that form due to the expulsion of sediment laden subglacial waters at the grounding lines of temperate tidewater glaciers few studies of ancient grounding line fans exist this study describes and interprets several ancient glacimarine grounding line fans and their physical characteristics using the lower permian pagoda formation along tillite glacier in the central transantarctic mountains antarctica as a deep time example wedge shaped sandstone bodies are used to identify major depositional processes and products that occurred during fan formation the depositing processes on these fans operated in tandem as tractive freshwater discharge from beneath the glacier s was progressively replaced down the fans in the direction of flow by buoyant upwelling and the development of overflow plumes tractive flow deposits are characterized by trough and climbing cross stratification while deposits resulting from settling from meltwater plumes consist of horizontal laminations and abundant soft sediment deformational structures load flame and diapiric structures secondary features such as thrust and normal faults resulted from advance and retreat dynamics of the ice front whereas mass flow deposits convolute bedding recumbent and s shaped folds slumps and slides resulted from resedimentation because glacimarine grounding line fans require specific depositional conditions to develop their identification is useful in constraining environmental conditions in the rock record for the pagoda formation the occurrence of grounding line fan deposits is significant as these strata were originally interpreted as deposits of a large terrestrial ice sheet centered over the location of the present transantarctic mountains that extended outward and covered much of gondwana for up to 90 million years however this study demonstrates that these rocks were deposited in a glacimarine setting results combined with other recent studies suggest that multiple small temperate ice sheets occurred in south polar antarctica during the late paleozoic ice age rather than a single massive ice sheet

structural orientations and precambrian deformational episodes of uwet area oban massif se nigeria abstract orientations of planar linear and micro structures are consistent with the results of isotopic data from the uwet area of southeastern nigeria which indicate that the area was subjected to polyphase deformation and polymetamorphism during the precambrian the dominant trends of the mesoscopic structures are n s to ne sw 0 50 with dips or plunges varying from 8 to 90 structures showing these attitudes represent imprints of penetrative pan african deformation and regional metamorphism that occurred in the uwet area 676 26 ma and 527 16 ma ago foliation trends of nw se 100 140 with dips of 25 60 towards 40 and fold axes plunging steeply 70 80 towards 70 are interpreted as representing relicts of a pre pan african deformation and metamorphism that also occurred in the uwet area 784 31 ma ago and possibly earlier during the kibaran orogeny

facies petrophysical and geochemical properties of gravity flow deposits in reservoir analogs from the itarare group late carboniferous parana basin brazil abstract since many reservoirs do not allow direct observation due to their depth and or difficulty of sampling studies of analogs have been commonly used as a tool to understand the spatial distribution of reservoir properties the parana basin is 1 6 million km2 large and has two known petroleum systems however there are only 124 irregularly distributed wells drilled in the basin among which 22 contain gas or oil shows and 10 have sub commercial accumulations the permo carboniferous itarare group due to the exploration history is the best exploratory target in the basin because it has thick intervals of sandstones with moderate to good reservoir quality and also because it often lies directly on gas prone source rocks of the devonian ponta grossa formation in order to increase knowledge about itarare group reservoirs as well as to better understand its heterogeneities this study aims to integrate petrophysical data with facies and facies associations using both outcrop and cores from shallow wells in southeastern parana basin by doing this it is expected to fill a gap of quantitative data in previous studies on reservoir analogs in the itarare group cores and outcrops were analyzed in sandstones in order to integrate surface and subsurface data and to understand the lateral continuity according to stratigraphic correlations equipment such as gamma ray spectrometer portable x ray fluorescence and a minipermeameter were used for the acquisition of quantitative data sedimentological description of cores and outcrops as well as thin section description were also carried out the facies with the greatest reservoir potential are medium to fine grained massive sm and normally graded sg sandstones in one outcrop locality rio dos cedros the sg facies presents the best reservoir properties such as secondary porosity of 32 and average permeability of 1439 md the geochemical data allowed evaluating the gamma ray variation in relation to chemical elements such as iron oxide in outcrop api radiation is higher in relation to the cores as well as al2o3 and fe2o3 these values are related to the large amount of intraclasts and cementation by iron oxides hydroxides despite in the great amount of iron presents in the rio dos cedros samples the porosity is mainly secondary generated by the feldspars dissolution the correlation between the cores and outcrops allowed the evaluation of the influences of mass transport deposits in the petrophysical properties of sandstones in cores sandstones interbedded with these deposits have high permeability but it is not possible to evaluate its lateral continuity in outcrops it was possible to observe that these deposits affect lateral continuity permeability and porosity we conclude that the best reservoir facies in the itarare group will be associated with sites within the basin that are away from the slope region and the influence of mass transport processes

an upper bound for the tidally rectified current at one location on the southern flank of georges bank abstract long term current observations at 45 and 75 m at one location on the southern flank of georges bank in water 85 m deep were examined for evidence of tidal rectification loder has shown analytically that rectification of the strong semidiurnal tidal current can cause a mean along bank flow and thus may partially drive the observed clockwise circulation around georges bank the amplitude of the tidally rectified along bank flow is proportional to the squared amplitude of the cross bank tidal current a simply extension of loder s model to include the weaker n2 and s2 tidal components suggests that fortnightly 354 h and monthly 661 h variations of the square of the cross bank tidal current should cause a modulation of the subtidal along bank flow the predicted ratio r of the fortnightly and monthly modulation of the along bank flow to the mean along bank flow on the southern flank was a function of position and ranged from 0 1 0 5 the amplitude of modulation of the along bank flow at 360

inviscid quasi geostrophic flow over topography testing statistical mechanical theory numerical simulations are employed in a detailed test of the statistical mechanical description of topographic turbulence predictions of steady flows correlated with topography are given particular attention agreement between numerical and statistical mechanical results is demonstrated for a large range of parameter values and over an ensemble of random choices of topography and initial conditions

ichnological signatures of shallow freshwater lakes in the glacial itarare group mafra formation upper carboniferous lower permian of parana basin s brazil abstract the upper carboniferous lower permian glacigenic deposits of the itarare group parana basin are widely known and cover an extensive area in the southern brazil these deposits consist of different arrangements of massive shales diamictites rhythmites and fine to medium grained sandstones with trough cross stratification five genetically distinct thickening locally coarsening upward successions of regular rhythmites can be distinguished in the mafra rio negro region santa catarina and parana states southern brazil representing the landward portion of an incised valley filled during deglaciation a low diversity invertebrate ichnofauna composed of a freshwater shallow burrow dominated suite and trackway dominated suite occurs in these rhythmites the freshwater shallow burrow dominated suite is composed of cochlichnus anguineus cruziana cf problematica gordia arcuata gordia marina hormosiroidea meandrica rusophycus cf carbonarius and treptichnus pollardi as well as undichnia consulca and intermittent rusophiciform traces it represents a mermia ichnocoenosis and occurs in the rhythmites of the upper sets commonly overlapped by d gouldi and d biformis in palimpsest preservation d gouldi and d biformis compose the trackway dominated suite which occur in all ichnofossiliferous paired mudstone siltstone of the basal sets of the rhythmite succession and in almost all of the upper sets it represents an atypical scoyenia ichnocoenosis and is generally preserved over microbially induced wrinkle structures the rhythmic deposition suggests distal underwater gravity flow deposits filling shallow lakes or ponds in depressed areas the siltstones deposited by melting currents and the mudstones by sediment fall out after the flux ceased the abundant wrinkle structures suggest quiet waters the overlying deposits bearing a brackish water ichnofauna and marine fossils suggest a coastal setting connected with the sea although atypical the occurrence of a scoyenia ichnocoenosis in almost all ichnofossiliferous rhythmite couplets preserved over wrinkle structures or overlapping mermia ichnocoenosis suggests that these shallow lakes were episodically dried up at least partially the present data allow interpreting the regular ichnofossiliferous rhythmites of the mafra formation as deposited in shallow lakes or ponds developed in outwash plains at the landward side of a fjord embayment during deglaciation

the vendian succession of northeastern spitsbergen petrogenesis of a dolomite tillite association abstract the sedimentary record of late precambrian time is magnificently displayed in the highland snowfields of northeastern spitsbergen svalbard vendian strata are represented essentially by the polarisbreen group which consists mostly of dolostone and includes two dolomitic glacial units the oldest sediments in the polarisbreen group compose the elbobreen formation c 400 m which is divided into four laterally persistent members the lower carbonate member e1 125 m contains a distinctive basal dark grey limestone with microspar filled synaeresis cracks suggested to be of lagoonal origin and associated with minor dolostone shale and chert higher parts of the member are dominantly dolostone partly stromatolitic with some shale and sandstone shallow subtidal to intertidal deposition is indicated by the dominance of intraclastic lithologies and relics of anhydrite penecontemporaneous dolomite is partially overprinted by microsparry dolomite thought to be of groundwater origin the redefined petrovbreen member e2 consists of diamictite and other detrital dolostone pronounced thickness variations 2 40 m are thought to be original depositional features the member represents the deposits of a short glacial period in which the following depositional processes are inferred lodgement massive diamictite subaqueous meltout massive and bedded diamictite ice rafting lithologies bearing dropstones and possibly also diamictite redeposition by sediment gravity flows some diamictite and conglomerate rhythmite and shale current winnowing thin tabular conglomerate subaerial or subaqueous meltwater action channelled conglomerate and sandstone periglacial shrinkage diamictite wedge fillings the macdonaldryggen member e3 230 m is a monotonous succession of shaly dolostone of lagoonal origin it grades up into the slangen member e4 25 m which consists of subtidal to intertidal dolarenite with anhydrite relics succeeded by fenestral dolostone that was fractured and cemented by saline groundwaters in an emergent environment the wilsonbreen formation 160 m represents a return to glacial deposition but this time longer lasting and with substantial extra basinal material represented the gropbreen member w1 28 107 m and the ormen member w3 44 139 m consist dominantly of dolomitic diamictite with subordinate conglomerate and sandstone and are separated by a middle carbonate member w2 3 30 m which contains distinctive rhythmitic and stromatolitic limestone as well as sandstone the same depositional processes can be recognised as in the petrovbreen member but the wilsonbreen formation is overall of somewhat more continental aspect lower proportion of rhythmite and dropstone structures in addition there are basal breccia and crack fillings formed by frost shattering of the underlying cemented dolostone tabular sandstone thought to be formed by wave reworking of outwash a striated terrestrial cobble pavement supraglacially derived breccia horizons periglacial wedges filled by sand and the w2 assemblage of possible lacustrine origin the dracoisen formation 525 m represents an abrupt return to non glacial conditions an upward deepening wave dominated succession of pure dolostone d1 20 m and impure dolostone d2 105 m is succeeded by offshore black shale d3 150 m and then by a very shallow water succession of evaporite lacustrine aspect with a dolostone containing evaporite relics d5 10 m separating dolomitic sandstone and shale d4 80 m and d6 150 m the contact with the transgressive cambrian sandstones above is poorly exposed deposition of the succession dominantly under marine conditions is inferred but it is difficult to rule out a lacustrine environment at any particular horizon this dolomite tillite association can be explained by penecontemporaneous and minor secondary dolomite formation in marginal environments with warm climatic indicators at some levels being sharply interrupted because of rapid climatic changes by glacial sediments containing abundant detrital dolomite since the latter sediments make up only 17 of the 1080m thick succession glacial conditions only occupied a small proportion of vendian time

dynamic metamorphism and oxidation of amphibolites of tegina area northwest nigeria abstract amphibolites of the tegina area are texturally distinct from most other amphibolites from the schist belts of nigeria thin sections and polished sections of samples are characterized by cataclastic features except for enhanced oxidation ratios of the tegina rocks overall chemical compositions are similar to those of other amphibolites and related rocks from the region and from other precambrian terranes it is considered here that the intense oxidation in the rocks may be linked to dynamic deformation this view is further supported by the fact that recent investigations show that the tegina rocks are related to a major n s shear belt

freshwater fluxes through the western fram strait two hydrographic and d18o transects across fram strait aug sept 1997 1998 are used to examine freshwater contributions to the east greenland current egc the egc featured up to 16 meteoric water in both years but was made comparatively more saline through the formation of up to 11 m of sea ice we derive meteoric water fluxes of 3680 km3yr 1 in aug sept 1997 and 2000 km3yr 1 in aug sept 1998 the 1997 and 1998 data show a long term me m sea ice flux through fram strait around half the long term mean meteoric water flux a 1991 d18o section bauch et al 1995 yielded a very similar ratio our 1998 section reveals fresh 1ow 6180 water on the east greenland shelf whose comparatively large volume constitutes a potentially significant contribution to the total freshwater flux through fram strait such fluxes are important to the regional and global thermohaline circulation we suggest that efforts towards monitoring both the egc and east greenland shelf waters are thus required

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

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

residual circulation and tidal stress in the gulf of california 1 results of a three dimensional nonlinear barotropic shelf model are used to study the effect of the m2 tidal stress on the residual current in the gulf of california the tidal stress summarizes the nonlinear interactions and forces the residual circulation it is calculated following the method developed by nihoul and ronday 1975 the vertical structure of the tidal stress reveals clearly the zones where the interaction between tidal currents and the basin geometry is strong the highest values of tidal stress were found over the salsipuedes sill and in the ballenas channel in the central archipelago and in the colorado river delta relatively high values of tidal stress were also found in deeper layers in the southern part the high tidal stress values coincide well with the anomalous cold water patches observed in the archipelago area attributed to tidal mixing the calculated residual currents show a maximum of about 15 cm s 1 in the upper layers in the archipelago area at subsurface layers an anticyclonic circulation is observed divergence patterns in the upper layers suggest that m2 tide residuals contribute to significant upward movements of water on the west side of tiburon island this barotropic process may contribute to the generation of the observed cold patches

high resolution sequence stratigraphy of clastic shelves iv high latitude settings abstract high frequency clastic shelf sequences deposited in high latitude settings display marked differences in term of facies and stratigraphic architecture with respect to their lower latitude counterparts this is due to the presence of ice which 1 leads to the accumulation of glacigenic and glacimarine deposits 2 provides an additional control on accommodation and 3 determines the position of the shoreline transgressions and regressions in glaciated settings are controlled respectively by the retreat and advance of the ice shoreline i e the water ice contact irrespective of relative sea level changes once the ice retreats across the land the traditional land shoreline is exposed and the control on sequence architecture is exerted by the interplay between relative sea level changes and sediment supply as in low and middle latitude settings a general model that includes both glacial and non glacial climatic regimes is provided by this paper in this frame the classic sequence stratigraphic model represents one ice free end member which is opposed to an ice permanent end member between these end members sequences may accumulate in part under ice free conditions and in part under conditions dominated by ice on the shelf the main implication of this is that the classic sequence stratigraphic model may be viewed as only a possible scenario in the stratigraphic record rather than the rule

volume and freshwater transports through the canadian arctic archipelago baffin bay system 1 baffin bay connects the arctic ocean and the labrador sea it receives polar water through the canadian arctic archipelago and by the west greenland current the polar water is after transformation exported through davis strait with control sections both upstream and downstream baffin bay invites the use of an idealized geostrophic approach to estimate transports the baroclinic transports driven by the density differences between the arctic ocean and baffin bay are first determined the density and upper layer depth are assumed the same in lancaster sound nares strait and the west greenland current once the baroclinic transports are estimated the sea level difference between the arctic ocean and baffin bay is computed next the upper layer depth in nares strait and the west greenland current is reduced while the sea level difference is kept constant this allows for deep inflows through nares strait and the west greenland current to establish a deep outflow through davis strait a barotropic sea level slope between the arctic ocean and the labrador sea is estimated from two ideal water columns the transports are computed for different salinities in the polar water and the salinity giving mass balance in the deeper layers is determined the effects of possible increased melting of the greenland icecap are examined if the meltwater is added directly to baffin bay the effects are small but if it is incorporated in the east and west greenland current a significant reduction of the outflow through the archipelago might occur

glacial geologic confirmation of an intraplate boundary in the parana basin of brazil the predrift fit of south america and africa remains problematic given the inability to match all parts of the coastlines simultaneously early opening of the south atlantic ocean may have been facilitated by intraplate deformation in either south america or africa but the location of such deformation is controversial and poorly constrained broad scale remote sensing has suggested an intraplate boundary in south america stretching from the cochabamba bend in the andes to the rio grande walvis rise but the inferred boundary crosses the paranaa basin of brazil where any evidence of deformation is obscured by late jurassic flood basalts a subsurface study of the upper paleozoic glaciogenic infill of the paranaa basin the 1300 m thick itarare group ca 300 260 ma identifies repeated episodes of intracratonic rifting on either side of an accommodation zone crossing the basin along the trend of the inferred intraplate boundary renewed influence of this zone during the opening of the south atlantic is suggested by the asymmetric distribution of successive magma units within the serra geral lava pile and by the trend of dike swarms the intraplate boundary identified within the paranaa basin may extend westward along the northern margin of the chaco basin in bolivia

geochemistry of the ilesha granite gneiss in the basement complex of southwestern nigeria abstract the ilesha granite gneiss comprises a varied series ranging from porphyroblastic alkali gneiss and granitic gneiss to banded and strongly foliated melanocratic rocks deformation is intense and the dominant structural trend is approximately n s chemical data show essentially a systematic variation reflecting the differences in the petrographic character of the outcrops sio 2 na 2 o k 2 o and related trace elements particularly rb are higher in the alkali and granitic varieties whereas the melanocratic types have lower contents of these elements the basic rocks are likewise significantly enhanced in tio 2 fe mgo cao cr and ni concentrations with some values being comparable to those of basaltic rocks

facies and allostratigraphy of high latitude glacially influenced marine strata of the early permian southern sydney basin australia the sydney basin of new south wales australia is a foreland basin containing a thick up to 10 km permo triassic succession the southern margin of the basin exposes strata deposited during late palaeozoic glaciation of south eastern gondwana the early permian wasp head pebbley beach snapper point formations and wandrawandian siltstone were deposited between 277 and 258 ma on a polar glacially influenced continental margin adjacent to ice sheets located over east antarctica and eastern australia sedimentary facies together with related ichnofacies and fauna can be grouped into six facies associations that record marine sub environments ranging from high energy storm dominated inner shelf to turbidite dominated upper slope settings cold marine conditions with near freezing bottom water temperatures are recorded by glendonites ice rafted debris most likely deposited by icebergs occurs in almost all facies associations an allostratigraphic approach emphasizing the recognition of bounding discontinuities i e erosion surfaces and marine flooding surfaces is used to subdivide the early permian stratigraphy into facies successions three types of succession can be identified and record changes in the relative influence of allocyclic controls such as basin tectonics sediment supply and glacio eustatic sea level variation together sedimentological and allostratigraphic data allow reconstruction of the depositional history of the south western margin of the sydney basin initial marine sedimentation characterized by sediment gravity flows and storm deposited sandstones of the lower wasp head formation occurred adjacent to a faulted basin margin overlying successions within the upper wasp head pebbley beach and snapper point formations record aggradation in inner to outer shelf settings along a storm and glacially influenced continental margin tectonic subsidence and basin flooding is recorded by deeper water turbidites of the wandrawandian siltstone

u pb dating of tonstein layers from a coal succession of the southern parana basin brazil a new geochronological approach abstract this paper presents new radiometric dating of zircons idtims u pb from tonsteins interbedded with coal seams from the candiota coalfield rio grande do sul state the ages obtained 296 9 1 65 ma and 296 4 2 ma are consistent within error and are quite different from a previously published age of 267 1 3 4 ma calibrations of palynostratigraphic data with numerical ages showed that the candiota coals from the southern parana basin related to the protohaploxypinus goraiensis subzone are constrained to the asselian consequently the basal part of the gondwana sequence in the southern part of the basin must belong to the carboniferous permian boundary and not to the sakmarian as it was previously considered the new results have far reaching significance for correlations of the parana basin with sequences of the argentinian paganzo basin 302 6 ma and 288 7 ma and also with the karoo basin with the top of the dwyka tillite 302 3 ma and 299 2 3 2 ma and with the lowermost ecca group 288 3 ma and 289 6 3 8 ma this new evidence supports the presence of an active and widespread upper carboniferous volcanism in western gondwana

anisotropy of magnetic susceptibility and sedimentary cycle data from permo carboniferous rhythmites parana basin brazil a multiple proxy record of astronomical and millennial scale palaeoclimate change in a glacial setting in this study we examine glaciogenic rhythmites from the late palaeozoic itarare group paranabasin brazil we conduct spectral analysis on lithological cycle couplet thick ness series and declination of maximum axis of anisotropy of magnetic susceptibility ellipsoidal tensor k1 data we tested the efficiency of k1 as a palaeoclimatic proxy to constrain the time scale of harmonic features in the data we analysed the couplet thickness spectra converting the spectra to the time domain using an astronomical calibration based on milankovitch frequency ratios comparison of the two rhythmites provides insights into their sedimentation rate evolution and cyclicity millennial scale mechanisms of climatic origin influenced the deposition of both rhythmites generating the lithological couplets and are consistent with millennial scale variations recognized as triggers for large scale climatic changes during the late pleistocene the common harmonic features in the couplet thickness and k1 spectra support the view that the azimuth of the k1 axis in sedimentary fabric is a useful palaeoclimatic proxy reflecting sedimentation processes that were directly influenced by flow induced sediment transport which is linked to external climate factors

an eddy parameterization based on maximum entropy production with application to modeling of the arctic ocean circulation abstract an eddy parameterization derived from statistical mechanics of potential vorticity is applied for inviscid shallow water equations the solution of a variational problem based on the maximum entropy production mep principle provides with some physical constraints several viscous terms along with the traditional laplacian operator mep parameterization includes the neptune effect which is similar to that described by holloway the neptune effect describes the interaction of eddies with seafloor topography mep parameterization is then incorporated into a high resolution tidal model of the arctic ocean mep viscosity does not substantially affect the distribution of amplitudes phases and tidal currents however residual tidal circulation is sensitive to employed parameterization in areas of maximum bottom slope the neptune effect is the main contributor among other viscosities the combined effect of the new viscous terms and nonlinear terms results in cyclonic residual tidal circulatio

effect of topographic stress on circulation in the western mediterranean the interaction of eddies with seafloor topography can exert large systematic forces on ocean circulation using a statistical mechanics approach it is possible to obtain a parametrization of this effect the neptune effect for application in large scale ocean circulation models circulation of the western mediterranean has been observed to follow a definite cyclonic path numerical models usually show good qualitative agreement for the large scale circulation but show systematic deficiencies at a subbasin scale we have tested the importance of the neptune effect on the circulation of the western mediterranean sea to perform this test different numerical experiments on western mediterranean circulation were done with and without eddy topography interaction as a first step we analyze the influence of the neptune effect in an ideal western mediterranean with closed straits after these experiments the more realistic case of open straits is studied all the experiments show that the neptune effect may be a significant factor in the basin and subbasin scale circulation in the western mediterranean sea

50 million year long record of glacial to postglacial marine environments preserved in a carboniferous lower permian graben northern perth basin western australia abstract the perth basin is an intracratonic rift in western australia and contains a carboniferous to cretaceous infill in excess of 12 km thick some 2 km of mid carboniferous to lower permian glacially influenced marine strata spanning the serpukhovian to kungurian about 50 my form one of the longest late paleozoic cold climate successions preserved anywhere in gondwana and record the transition from full glacial to postglacial conditions at high 70 paleolatitudes the great thickness of the succession reflects an abundant supply of glaciclastic sediment from the adjacent ice covered yilgarn craton and continued subsidence along the darling urella fault system the oldest part of the basin fill comprises a 1 5 km thick succession of massive and laminated marine mudstones with striated dropstones nangetty formation deposited in a fiord like environment from plumes of suspended sediment dilute turbidity currents and icebergs meltwater inputs are recorded by erosionally based multistory channels filled with coarse grained gravity flow facies wicherina member deposited on a fan delta along the steep faulted basin margin the nangetty formation passes upward into a regressive succession of postglacial mudstones holmwood shale with bioclastic calcarenites and marine macrofossils capped by sandstone and mudstone facies high cliff sandstone deposited in a storm influenced inner shelf setting on the outer margins of coalesced fan deltas along the basin margin the overlying irwin river coal measures contain a flora that indicates colonization of fan deltas and the yilgarn craton by ferns and lycopods an overlying thick transgressive shale with ice rafted debris carynginia formation records renewed subsidence but continuing seasonally cool climates where coarse debris was rafted by ice into a marine embayment the sedimentology of the perth basin highlights the key role of glacial meltwaters in transporting coarse and fine grained clastic sediment to marine basins rather than direct glacial processes per se the equivalent terrestrial record of glaciation and climate change across the yilgarn craton at this time is very limited

facies relationships recorded in a late paleozoic fluvio deltaic system parana basin brazil insights into the timing and triggers of subaqueous sediment gravity flows abstract this paper aims at documenting the spatial and genetic relationships between fluvial and subaqueous gravity flow deposits in an ancient fluvio deltaic system exposed in the eastern border of the parana basin southern brazil the examined interval comprises the pedra alta sandstone and associated deposits which are included in the glacially influenced late paleozoic itarare group five facies associations were identified and comprise the following coeval depositional settings from the more proximal to the more distal a braided fluvial delta plain b channel mouth zone c delta slope d distal marine glacially influenced and e non cohesive density flow deposits these facies associations form a conformable shallowing upward succession about 200 m thick whose stacking pattern is interpreted as a postglacial progradation the stratigraphic architecture suggests a genetic correlation between high energy fluvial discharges possibly related to meltwater release and coarse grained deposits non cohesive density flow deposits accumulated on the delta foreset and bottomset mass transport deposits were more likely triggered by sediment load increase on the delta slope due to high sediment supply rather than by relative sea level fall the stratigraphic evolution can be reconstructed considering an initial stage characterized by a grounded ice margin and the deposition of mudstones with ice rafted debris glacial stage this stage was succeeded by a second phase in which a fluvial system formed as a result of ice margin retreat farther to the se postglacial stage this glacial postglacial stratigraphic succession is different from that recognized by previous workers in the itarare group a conclusion that impacts greatly in reservoir prediction and modeling in the parana basin

effect of the topographic stress on the tide and wind induced residual currents in the gulf of california because eddy topography interactions topographic stress are difficult to resolve by numerical models a parameterization has been proposed by holloway 1992 based on the statistical mechanical equilibria tendencies neptune effect a vertically integrated numerical model is used to study the influence of neptune effect upon the tide and wind induced residual circulation of the gulf of california the model is forced at the mouth of the gulf by the tides and at the sea surface by the wind it is found that the parameterization induces mean currents in areas where the residuals produced by tides and winds are small tide and wind induced residuals are large along the mainland coast and from the archipelago to the north where the neptune effect parameterization is less important observations give some support to this parameterization

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

circulation characteristics in three eddy permitting models of the north atlantic a systematic intercomparison of three realistic eddy permitting models of the north atlantic circulation has been performed the models use different concepts for the discretization of the vertical coordinate namely geopotential levels isopycnal layers terrain following sigma coordinates respectively although these models were integrated under nearly identical conditions the resulting large scale model circulations show substantial differences the results demonstrate that the large scale thermohaline circulation is very sensitive to the model representation of certain localised processes in particular to the amount and water mass properties of the overflow across the greenland scotland region to the amount of mixing within a few hundred kilometers south of the sills and to several other processes at small or sub grid scales the different behaviour of the three models can to a large extent be explained as a consequence of the different model representation of these processes

spectral analysis and modeling of microcyclostratigraphy in late paleozoic glaciogenic rhythmites parana basin brazil we investigate the depositional time scale of lithological couplets fine sandstone siltstone siltstone mudstone from two distinctive outcrops of permo carboniferous glacial rhythmites in the itarare group parana basin brazil resolving the fundamental issue of time scale for these rhythmites is important in light of recent evidence for paleosecular variation measured in these sequences spectral analysis and tuning of high resolution gray scale scans of sediment core microstratigraphy which comprises pervasive laminations reveal a comparable spectral content at both localities with a frequency suite interpreted as that of short term climate variability of recent and modern times this evidence for decadal to centennial scale deposition of these lithological couplets is discussed in light of the varvic character i e annual time scale that was previously assumed for the rhythmites

a numerical investigation of the annual variability in the gulf of california the observations of sea level at the annual frequency in the gulf of california are reproduced both in amplitude and phase with a horizontal two dimensional linear two layer model the main forcing agents through which variability is explained are wind stress and the action of the pacific ocean which excites an internal wave in the mouth of the gulf the surface heating is shown to play a secondary role the response of the basin is qualitatively similar to that observed that is an energetic circulation in the upper layer cyclonic in summer and anticyclonic in winter compared to a weaker and opposite circulation in the bottom layer as well as a transversely averaged horizontal heat flux equal both in amplitude and phase to that calculated with historical hydrographic data the results of the simulation show that variability across the gulf is as important as the longitudinal variability

ice marginal environment and ecosystem prior to initial advance of the late palaeozoic ice sheet in the mount butters area of the central transantarctic mountains antarctica basal rocks of the upper carboniferous to lower permian pagoda formation at mount butters provide an unusual view of periglacial conditions in the central transantarctic mountains region prior to the initial advance of the gondwanide ice sheet these rocks were deposited on a high relief unconformity that developed on granite deposition within relief on the unconformity possibly in the lee of a granite buttress protected the rocks from erosion during subsequent overriding by the ice sheet the succession reflects deposition in a glacial fed to ice contact lake that contained a freshwater crustacean fauna centimetre to decimetre scale basal layers include breccia and coarse grained sandstone the occurrence of breccia resting on weathered granite suggests sedimentation as scree and as mass flow deposits overlying decimetre to metre scale stratified diamictites interbedded with metre scale coarsening upward successions of siltstone to cross laminated sandstone suggest lacustrine deposition by suspension settling rain out of ice rafted debris and deltaic progradation thin zones with abundant conchostracans and or with prolific trace fossils in addition to less common remains of other crustaceans attest to the presence of a low diversity benthic fauna conchostracans are concentrated in a series of thin beds that reflect moderately lengthy perhaps seasonal periods of free flowing water patchy vertical and lateral distribution of intense bioturbation and profuse trace fossils probably reflect repeated colonization events during times of favourable environmental conditions massive diamictite overlies the basal rocks and indicates that the ice marginal lake was subsequently overridden by the late palaeozoic ice sheet occurrences of lodgement till glacitectonite and deformation till suggest deposition from temperate or warm based ice whereas underlying lacustrine and deltaic deposits along with a crustacean and trace fossil fauna suggest temperate periglacial conditions previous studies have stressed that upper palaeozoic glacigenic deposits in antarctica and in gondwanaland record deglaciation events in contrast rocks at mt butters provide an unusual glimpse into an ice margin lake and its fauna just prior to ice sheet advance

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

model simulated volume fluxes through the canadian arctic archipelago and davis strait linking monthly variations to forcing in different seasons the solution of a 10 year simulation of the arctic ocean produced using a 6 km resolution coupled ocean and sea ice model is analyzed to understand the variability control and forcing mechanisms of the volume fluxes through the canadian arctic archipelago caa and davis strait ds the analysis focuses on variability at monthly time scales analysis confirms the control of volume fluxes through the caa proposed in previous studies by 1 variations of sea surface height ssh in the upstream regions and the relationship of this control to alongshore wind in the beaufort sea and 2 by ssh in the downstream region in baffin bay that may be related to wind stress in baffin bay and the northern labrador sea the effectiveness of these control and forcing mechanisms vary for fluxes through different sections and for different seasons variation of the southward flux through ds is directly influenced by fluxes through nares strait ns and barrow strait bs in summer fall and winter in spring variations of the southward and northward fluxes through ds are closely related to each other and correspond to changes in the ssh along pathways of the irminger current and the east and west greenland currents

iceberg rafting and scouring in the early permian shoalhaven group of new south wales australia evidence of heinrich like events abstract this paper describes multiple layers of ice rafted debris and an ice scour structure in early permian marine strata within the shoalhaven group of the sydney basin new south wales australia strata were deposited on a high latitude glacially influenced continental margin during the final stages of late palaeozoic glaciation between 277 and 260 ma poorly sorted ice rafted debris forming layers up to 1 25 m thick is common within inner to outer shelf and continental slope facies of the shoalhaven group more than 120 layers can be identified these are argued to record the enhanced delivery of debris by icebergs drifting north from marine based antarctic ice margins deformation structures in associated sediments are interpreted as iceberg scours and ice keel turbates associated glendonites record early diagenesis of organic rich sediment and bottom water temperatures close to freezing a speculative hypothesis relates layers of ice rafted debris within the shoalhaven group to multiple episodes of accelerated calving at the margins of a marine based early permian ice sheet in east antarctica these events may be analogous to late pleistocene heinrich events when huge armadas of icebergs were released from the marine based laurentide ice sheet and triggered abrupt changes in ocean circulation and climate similar forcing may have characterized the early permian ice ocean system regardless of the climatic significance of ice rafted layers this is the first time such facies have been documented in the pre pleistocene literature to date few ice scour structures and no ice keel turbates have been reported

subduction mega shear systems and late palaeozoic basin development in the african segment of gondwana basins within the african sector of gondwana contain a late palaeozoic to early mesozoic gondwana sequence unconformably overlying precambrian basement in the interior and mid palaeozoic strata along the palaeo pacific margin small sea board pacific basins form an exception in having a carboniferous to early permian fill overlying devonian metasediments and intrusives the late palaeozoic geographic and tectonic changes in the region followed four well defined consecutive events which can also be traced outside the study area during the late devonian to early carboniferous period up to 330 ma accretion of microplates along the patagonian margin of gondwana resulted in the evolution of the pacific basins thermal uplift of the gondwana crust and extensive erosion causing a break in the stratigraphic record characterised the period between 300 and 330 ma at the end of this period the gondwana ice sheet was well established over the uplands the period 260 300 ma evidenced the release of the gondwana heat and thermal subsidence caused widespread basin formation late carboniferous transpressive strike slip basins e g sierra australes colorado karoo falklands ellsworth central transantarctic mountains in which thick glacial deposits accumulated formed inboard of the palaeo pacific margin in the continental interior the formation of zambesi type rift and extensional strike slip basins were controlled by large mega shear systems whereas rare intracratonic thermal subsidence basins formed locally in the late permian the tectonic regime changed to compressional largely due to northwest directed subduction along the palaeo pacific margin the orogenic cycle between 240 and 260 ma resulted in the formation of the gondwana fold belt and overall north south crustal shortening with strike slip motions and regional uplift within the interior the gondwana fold belt developed along a probable weak crustal zone wedged in between the cratons and an overthickened marginal crustal belt subject to dextral transpressive motions associated with the orogenic cycle was the formation of mega shear systems one of which falklands east africa tethys shear split the supercontinent in the permo triassic into a west and an east gondwana by a slight clockwise rotation of east gondwana a supradetachment basin formed along the tethyan margin and northward displacement of madagascar west falkland and the gondwana fold belt occurred relative to a southward motion of africa

an investigation of the dynamics of the east greenland current in fram strait based on a simple analytical model abstract the east greenland current egc in fram strait is examined in summer based on the hydrographic data from the mizex 84 experiment and its dynamics is further analyzed using a simple analytical model from the observed density field the southward geostrophic transport relative to the bottom in the egc is estimated to be about 4 sv sv 106 m3 s 1 at 78 4 n which assuming a ratio 1 1 between the bottom and the relative transports as suggested in the literature allows one to postulate a 4 sv bottom transport the hydrographic data also reveal a northward gradient of potential energy along the east greenland slope between 77 5 n and 80 5 n such a gradient is the prerequisite for the existence of the joint effect of baroclinicity and relief jebar which is here proposed as a driving mechanism for the bottom transport in the egc a model with idealized topography and a density distribution prescribed from the above data is constructed based on a steady state vorticity equation in which the

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

sensitivity of a large scale ocean model to a parameterization of topographic stress abstract a conventional ocean model was revised to include a tendency for velocities to relax toward a maximum entropy solution that depends on the shape of topography the tendency called topographic stress generates poleward eastern boundary undercurrents strengthens equatorward deep western boundary currents sustains a deep alaska stream and contributes to deep water exchange although the influence of topographic stress is most clearly seen at depth surface expressions include reducing the overshoot of western boundary current separation thereby limiting implied air sea heat and freshwater fluxes near these separations

finger like plumes of suspended sediment in the colorado river delta gulf of california abstract the present investigation focused on solving the significance of tidal currents in the sediment resuspension process revealed by satellite imagery in the tidal basin of the colorado river delta located in the northernmost part of the gulf of california a depth integrated finite difference hydrodynamic model coupled with a suspended sediment transport module has been applied to calculate the velocity field and potential suspended sediment changes in the delta region prescribed values of tidal harmonics were used to force the model at the open boundary of the model domain the experiments revealed that sediment plumes are generated by the interaction of the tidal flow and the seabed exposing a remarkable agreement between the crest of sandbanks existing in the delta and the potential sediment resuspension close to spring tides the instantaneous potential transport of sediment in suspension reaches values up to 0 05 m3 integrated over each cell of 280 m 280 m the calculations showed that in the shallow coastal area at the gulf s head sandbank presence is critical for the energy dissipation processes the crests of sandbanks dissipate much of the energy the simulated processes are strong evidence that the frictional effect of tidal flow during the initial stages of the spring tides contributes significantly to the sediment s picking up from the seabed going into suspension these processes shape the plumes of suspended sediment which extended in the same direction as the sandbanks comparison between satellite imagery and modeled distribution of sediment revealed a good agreement between observed and modeled finger like plumes of sediment the undulating topography s effect is reflected in the horizontal distributions of energy dissipation current speed and kinetic energy

late paleozoic glaciotectonic structures in northern parana basin brazil abstract fluviatile deltaic sediments containing thin coal layers and glaciofluvial sediments of the itarare subgroup late paleozoic cropping out near cerquilho northern parana basin exhibit post depositional deformation such as recumbent and drag folds shear fractures faults and shear lamination the deformation occurs in an interval of 3 4 m thick and is confined between horizontal strata the deformed strata are directly overlain along a horizontal erosional tectonic contact surface by a silty sandy massive 1 m thick clast poor tillite deformation shows a consistent geometry indicating a predominant vergence toward the ssw having been developed under a horizontal stress oriented from nne to ssw the deformation is interpreted to be of glaciotectonic origin associated with an ice readvance in the area the glacier moved toward the ssw on relatively soft deformable sediments depositing the subglacial till on top of them the tillite shows parallel upglacier dipping shear fractures at its base and wedge like intrusions into the underlying sandstone probably formed during its subglacial deposition the tillite is overlain by cyclic braided stream fluviatile sandstone beds the top of these shows deformations small recumbent folds and reverse faults below another clast poor silty sandy tillite this could represent another glacial readvance with subglacial deposition of till occurrence of glaciotectonic deformation overlain by subglacially deposited tillites in the cerquilho area indicates glacier readvances and permanence of the glacial influence in the upper part of the itarare subgroup absence of incorporated material from the underlying deformed sediments in the tillite and the style of the deformations suggest an unfrozen water saturated mostly unconsolidated substratum these conditions may have generated instability and fast ice flow of the glacier they also suggest that the sediment may have most likely failed in this manner under rapidly applied stresses associated with a surging behavior of the retreating glacier

circulation in the arctic ocean results from a high resolution coupled ice sea nested global fvcom and arctic fvcom system abstract a high resolution unstructured grid global regional nested ice current coupled fvcom system was configured for the arctic ocean and used to examine the impact of model resolution and geometrical fitting on the basin coastal scale circulation and transport in the pan arctic with resolving steep bottom slope and irregular coastal geometry the model was capable of simulating the multi scale circulation and its spatial variability in the arctic basin and flow through the bering strait fram strait and canadian archipelago the model simulated annual mean velocities were in good agreement with observations within the measurement uncertainty and variability due to insufficient sampling the errors in the flow direction varied with the flow speed larger in the weak velocity zone and smaller as the velocity increased in the upper 50 m layer the annual mean circulation pattern was dominated by the wind and ice drifting induced anticyclonic circulation in the arctic basin and a relatively strong cyclonic slope current along the edge of the continental shelf in the deep 200 600 m layer a relatively permanent cyclonic circulation occurred along the steep bottom slope these annual mean circulations accounted for 85 of the total kinetic energy variance de trending the mean flow an empirical orthogonal function eof analysis showed that the semi annual and seasonal variability of the sub tidal flow was dominated by the first and second modes that accounted for 46 and 30 of the total variance in the upper 50 m layer and 58 and 20 in the deep 200 600 m layer consistent with observations the ao fvcom simulated cyclonic slope flow was characterized by a large positive topostrophy sensitivity experiment results with various grid configurations suggested that the currents over slopes narrow straits and water passages featured topographic and baroclinic frontal dynamical scales associated with bathymetric slope and internal rossby deformation radius over the arctic slope since these two scales are in the same order the along slope current could be captured as the cross isobath model resolution was refined to resolve the steep bottom topography under this condition there is no need to add neptune forcing into the momentum equations the accuracy of the estimation of the transport through the strait and narrow water passage was affected by the model resolution in fram strait where the flow is characterized by strong lateral current shear resulting from the atlantic inflow and arctic outflow the transport estimation could have a significant uncertainty due to both horizontal and vertical sampling resolutions