invariance and scaling properties in the distributions of contributing area and energy in drainage basins a the cumulative probability distributions for stream order stream length contributing area and energy dissipation per unit length of channel are derived for an ordered drainage system from horton s laws of network composition it is shown how these distributions can be related to the fractal nature of single rivers and river networks finally it is shown that the structure proposed here for these probability distributions is able to fit the observed frequency distri butions and their deviations from straight lines in a log log plot

vesicle distribution in basalt lava flow units in the mesozoic rift basins of northeast china and its application in gas reservoir prediction the mesozoic rift basins of northeast china are characterized by a significant proportion of basalt due to the progressive emplacement of basalt lava flows the objective of this study was to construct vesicle distribution models of the basalt lava flow units including conceptual geological models and thickness models to understand the architecture of the basalt and the gas reservoir distribution the conceptual geological models were constructed based on the characteristics of outcropping basalt lava flows with supplemental seismic data used to extrapolate the lateral extents of large scale basalt lava flows the thickness models were constructed using data on the thicknesses of basalt lava flow units and vesicle zones these data were obtained from 27 units in outcrop and 204 units interpreted from well logs in the basin the conceptual geological models revealed that the shapes of the basalt lava flow units change from braided to tabular with increasing thickness and that their inner structures can

basaltic lava flows covering active aeolian dunes in the parana basin in southern brazil features and emplacement aspects abstract burial of active aeolian dunes by lava flows can preserve the morphology of the dunes and generate diverse features related to interaction between unconsolidated sediments and lavas in the study area located in southern brazil burial of aeolian deposits by cretaceous basaltic lava flows completely preserved dunes and generate sand deformation features sand diapirs and peperite like breccia the preserved dunes are crescentic and linear at the main contact with basalts and smaller crescentic where interlayered with lavas the various feature types formed on sediment surfaces by the advance of the flows reflect the emplacement style of the lavas which are compound pahoehoe type four feature types can be recognized a type 1 features are related to the advance of sheet flows in dune interdune areas with slopes 5 b type 2 is formed where the lava flows advance in lobes and climb the stoss slope of crescentic dunes slopes 8 12 c type 3 is generated by toes that descend the face of linear dunes slopes 17 23 and d type 4 occurs when lava lobes descend the stoss slope of crescentic dunes slopes 10 15 the direction of the flows the disposition and morphology of the dunes and the ground slope are the main factors controlling formation of the features the injection of unconsolidated sand in lava lobes forms diapirs and peperite like breccias sand diapirs occur at the basal portion of lobes where the lava was more solidified peperite like breccias occur in the inner portion where lava was more plastic favoring the mingling of the components the generation of both features is related to a mechanical process the weight of the lava causes the injection of sand into the lava and the warming of the air in the pores of the sand facilitates this process the lava sediment interaction features presented here are consistent with previous reports of basalt lavas with unconsolidated arid sediments and additional new sand deformation features formed by lava breakouts and sand diapir injections are presented

scaling and elevation in river networks the analysis of large river networks obtained from digital elevation models has given insight into the variation of channel slope with scale investigators have recently suggested that channel slopes are self similar with magnitude or area as a scaling parameter our data indicates otherwise in particular the variance of channel slope is larger than that predicted by simple self similarity this suggests multiscaling the scaling exponent for the standard deviation is approximately half the corresponding exponent in the relationship of the slope mean to magnitude or area a model for channel slopes based on a point process of elevation drops along the channel is presented the model reproduces observed multiscaling properties when the density of elevation increments is related to area or magnitude as a

deriving river networks and catchments at the european scale from medium resolution digital elevation data abstract the extraction of drainage networks and catchment boundaries from digital elevation models dems has received considerable attention in recent years and is recognized as a viable alternative to traditional surveys and the manual evaluation of topographic maps however most studies have covered limited areas due to the lack of detailed information and or the lack of highly efficient algorithms in this paper we present an application that delineates river networks and catchment boundaries across the european continent from a medium resolution 250 m dem we exploit novel algorithms based on the concepts of mathematical morphology and implement a landscape stratification for drainage density a flow direction grid is computed using an efficient algorithm for the removal of spurious pits river networks are then derived by imposing a variable threshold for the minimum contributing area needed to form and maintain a channel this is achieved through a landscape stratification that reflects the ability of the terrain to develop different drainage densities it is shown that the analysis of environmental characteristics coupled with the analysis of local slope versus contributing area enables river network mapping with a spatially varying drainage density the result has been validated by comparing the derived data to digital river and catchment data from other sources and with varying scales of observation

the neoproterozoic cambrian paraguay belt central brazil part i new structural data and a new approach on the regional implications abstract together with the araguaia and brasilia belts the paraguay belt forms in central brazil the tocantins province that is one of the largest orogens of western gondwana the corumba area occupies the site where the northern and southern parts of the paraguay belt form together with the chiquitos tucavaca aulacogen stretching e w in the adjacent bolivian territory an r r r basin system opened filled in the 700 650 540 ma interval within the amazon rio apa paleo continent the sedimentary volcanic rocks of the jacadigo and corumba groups found around the corumba city record part of the neoproterozoic cambrian passive margin precursor of the paraguay belt our pioneer structural analysis reveals that these rocks experienced progressive deformation phases d 1 d 2 d 3 and low grade metamorphism during the brasiliano cycle 540 513 ma the crystalline basement was also involved according to structural data and k ar ages in the literature the paleo passive margin was thickened during the d 1 d 2 deformation and was lately shortened d 3 in two orthogonal directions se nw d 3p and sw ne d 3t developed co axially and verging to nw d 1 d 2 d 3p structures record the closure of the basin precursor of the paraguay belt whereas d 3t structures seem related to the inversion of the aulacogen although the tectonic transport to nw as observed in the corumba area matches the reported transport of paraguay belt s supracrustal rocks towards the eastern margin of the rio apa block and araguaia belt s rocks towards the amazon craton the transport direction is opposite in other parts of the paraguay belt our comprehensive discussion of these facts brings to light profound regional implications

spatial temporal evolution of the distribution pattern of river systems in the plain river network region of the taihu basin china abstract understanding the spatial temporal distribution characteristic and evolution tendency of river systems is important in integrated river basin management in this paper six indicators were adopted to describe the physical characteristic of river systems the spatial temporal evolution of the distribution pattern of river systems in the plain river network region of the taihu basin prnrtb during the 1960s 2000s was analyzed using exploratory spatial data analysis esda and the gravity centre model the impacts of urbanization were then investigated results indicated that the global distribution patterns of box dimension and river density were all statistically significant spatially clustered and river sinuosity was partially spatially clustered while water surface ratio main river area length ratio and river development coefficient were not spatially clustered moreover the water surface ratio was the most stable parameter box dimension was also relatively stable parameter but the others were unstable meanwhile the mutual transformations of hot and cold spots of river systems especially water surface ratio river development coefficient and river sinuosity were frequent the hot spot regions were mainly located in the northeast region in addition most gravity centres migrated gradually from southeast to northwest with low distance except those of river development coefficient and river density these aforementioned differences were caused by the rapid urbanization based on the integrated river basin management suggestions for prnrtb the river density box dimension and river sinuosity should be maintained and restored across the whole watershed and the river conservation and restoration should focus on countermeasures against the reduction of river development coefficient and main attention should be paid on the river systems conserving and restoring in haiyan and haining in southeast prnrtb

on the description of the basin effective drainage structure abstract the relationships between the local properties of the morphological elements of a drainage basin and its drainage structure are analysed two theoretical approaches are used for which hydro dynamics and basin morphology are respectively assumed to represent the lowest and the highest starting scale level the results show a convergence toward the idea of slope scaling with contributing area in river networks this concept is then used as an indicator of channel initiation and maintenance for the identification of the effective drainage structure of the basin on the basis of existing digital elevation models dems integral properties of the single dem pixel are finally introduced to reduce the noise owing to a possible dem low accuracy e g in the estimation of the local slope value from the elevation data set the resulting network is characterized by a non uniform drainage density as expected for natural river networks

textural evidence for high grade ignimbrites formed by low explosivity eruptions parana magmatic province southern brazil abstract the parana etendeka province is a lower cretaceous huge bimodal tholeiitic volcanic province 1 million km 3 that predated the gondwana breakup its silicic portion makes up a total volume of at least 20 000 km 3 and in southern brazil it comprises the chapeco porphyritic high ti trachydacites dacites and the palmas microporphyritic aphyric low ti dacites rhyolites the widespread silicic sheets are debated in the literature because they bear similarities between lavas and high grade ignimbrites here we provide new observations and interpretations for flow units with large dark and vesicle poor lens shaped blobs surrounded by a light colored matrix the textural features macro to micro scale of these blobs are different from typical pumice and or fiamme and support a low explosivity pyroclastic origin possibly low column fountain eruptions with discharge rates high enough to produce laterally extensive high grade ignimbrites such an interpretation combined with a conspicuous absence of lithic fragments in the deposits is aligned with a lack of identified calderas in the parana etendeka province maximum timescales of crystallization associated with the juvenile blobs and estimated from csd slopes are on the order of millennia for phenocryst populations and on the order of decades for microphenocryst populations

basin form characteristics causes and implications of the ten kongduis in the upper reaches of the yellow river the ten kongduis the transliteration of ephemeral flood gullies in mongolian are one of the main sediment sources of the upper reaches of the sediment laden yellow river in china the basin form characteristics and their causal factors and environmental effects of the kongduis are important knowledge for understanding the geomorphic processes and for managing the kongduis in this study we extracted the drainage networks and watersheds of the kongduis from the dem calculated the geometric and structural indices of the watersheds and networks investigated relations of the gully density with surface material composition vegetation coverage and topography and the relations of the sediment yield with gully density and other geometric indices of watersheds and associated the gully density with the evolution stage of landforms of the basins the results reveal that the ten kongduis are 5th 6th order streams and their watersheds are long and narrow with a circularity ratio of 0 16 0 26 an elongation ratio of 0 29 0 43 and a power of drainage area of 0 89 4 52 in the power function between mainstream length and drainage area yet the available data do not support the impacts of the geometric indices of watersheds on the sediment yield in the ten kongduis and the insignificant relation between the specific sediment yield and drainage area denies the existence of scale effect in sediment yield in the kongduis in contrast the gully density is found to be closely and positively related with the sediment yield the hypsometric integrals of the upstream reaches of the ten kongduis and the relation between gully density and hypsometric integral suggest that the kongduis are in the mature stage of landform evolution and the west five kongduis are in the early mature stage with a potential increase trend of gully density and a concomitant escalation of sediment yield in future

death of a sand sea an active aeolian erg systematically buried by the etendeka flood basalts of nw namibia here we report on a fossilized sand sea that was progressively engulfed by the basal etendeka flood basalts in nw namibia preserved relict aeolian landforms include transverse barchanoid dunes and isolated barchan dunes present day preferential erosion of the lava flows exhumes relict aeolian bedforms preserved in the position in which they were migrating at the time of burial c 133 ma a passive eruption style of inflated pahoehoe flows has preserved the bedforms without significant deformation the sediment interlayers record a decrease in sand supply and a change in palaeowind direction which may have been driven by the ongoing break up of west gondwana or may be a direct result of the widespread volcanism itself

long distance lava correlation in the parana volcanic province along the serra geral cuesta southeastern brazil the capability of determining the flow by flow stratigraphy and the long distance correlation of lava flows in large continental volcanic provinces leads to a considerable advance in the understanding of processes related to generation and evolution of the lavas the parana volcanic province is exposed along the serra geral cuesta of southern brazil in a steeply inclined 1 000 m high section starting 40 m above sea level each of the 10 20 pahoehoe flows and rhyodacite flow units has a unique chemical composition integrated with field stratigraphy and gamma spectrometric measurements this leads to the establishment of the correct stratigraphic sequence in each of three different vertical sections the number of flows integrating the three serras is 26 serra is a mountain range in portuguese each serra has basaltic andesites at the base whereas rhyodacites are intercalated with basaltic andesites at the top three basaltic andesite flows and one rhyodacite flow unit are correlated between serra umbu and serra boa vista 10 km in the serra faxinal a thick 170 m sill at the base correlates with flow 13f whereas a dike sill in the graxaim quarry 24 km distance correlates with flow 3f one basaltic andesite and two rhyodacite flow units correlate between serra faxinal and serra umbu 50 km the results are most significant for the understanding of large tracts of continental volcanic provinces with use of common geochemical and gamma spectrometric techniques

tectonic significance of the florianopolis dyke swarm parana etendeka magmatic province a reappraisal based on precise u pb dating abstract the first precise id tims u pb baddeleyite zircon dating of dykes representative of the main activity in the florianopolis dyke swarm parana etendeka magmatic province south brazil reveals a restricted age range 134 7 0 3 to 133 9 0 7 ma this is at least 5 ma older than indicated by previous 40 ar 39 ar stepwise heating dating and precludes a direct relationship with syn rifting magmatism connected with opening the south atlantic ocean instead as indicated by their age and geochemical signature these dykes are feeders to the nearby urubici lavas and coeval khumib lavas in etendeka these new geochronological results also cast doubt on a large 10 ma time span for the emplacement of the florianopolis dyke swarm implied by 40 ar 39 ar dates but the determination of its upper age limit still requires accurate dating of younger low volume fine grained dykes with distinct low ti chemistry crystals suitable to u pb dating were not obtained thus far from these dykes

channel initiation and the problem of landscape scale since the 1940s it has been proposed that landscape dissection into distinct valleys is limited by a threshold of channelization that sets a finite scale to the landscape this threshold is equal to the hillslope length that is just shorter than that necessary to support a channel head a field study supports this hypothesis by showing that an empirically defined topographic threshold associated with channel head locations also defines the border between essentially smooth undissected hillslopes and the valley bottoms to which they drain this finding contradicts assertions that landscapes are scale independent and suggests that landscape response to changes in climate or land use depends on the corresponding changes in the threshold of channelization

effusive silicic volcanism in the parana magmatic province south brazil evidence for locally fed lava flows and domes from detailed field work abstract lava flows and dome complexes of silicic composition were identified in the lower cretaceous parana magmatic province pmp at rio grande do sul state southern brazil detailed mapping and image analysis reveals significant volumes of effusive deposits aligned according to main lineaments likely representing the fissural systems that fed the three palmas type silicic units different structures indicative of effusive emplacement lava domes lobated flows sheet flows and autobreccias are very common in the study area and are probably also more abundant than previously thought in whole pmp silicic magmatism in fact effusive deposits seem predominant in the three distinct silicic units identified in the area since no remnants of pyroclastic components have been identified the vitreous dacites that make up the upper flows of the basaltic andesite to dacite barros cassal sequence are clearly effusive as indicated by their occurrence as thin sheet flows the much thicker early caxias do sul dacites occur mostly as lava flow lobes and pancake like of low to moderate viscosity and lava domes the younger high sio2 santa maria rhyolite unit shows unequivocal examples of effusive deposits at its lower portion as lobated flows formed by vesicle rich obsidian in spite of higher viscosities relative to the previous units 106 pa s it is probable that the very low h2o contents 1 wt of these rhyolite melts associated with high discharge rates resulted in an effusive nature in most to this unit

palaeowind patterns during the latest jurassic earliest cretaceous in gondwana evidence from aeolian cross strata of the botucatu formation brazil abstract the direction of sediment transport in the aeolian sandstones of the botucatu formation latest jurassic earliest cretaceous of the parana basin has been interpreted on the basis of cross strata dip directions which allowed the reconstruction of regional wind patterns in midwestern gondwana regionally cross strata dip directions indicate variations of palaeowind directions across the outcrop area of the botucatu palaeoerg the northern portion of the palaeoerg was characterized by palaeowinds blowing from the nne whereas the southern portion was under the influence of palaeowinds coming from the sw a wind convergence zone occurred at palaeolatitudes around 24 to 26 s the identified wind pattern agrees with general circulation models for the late jurassic which predict that during the summer months december through february strong monsoonal winds to the s existed at low latitudes in gondwana southerly winds converged at the itcz at around 24 s with winds blowing toward the northeast

stratigraphy and volcanic facies architecture of the torres syncline southern brazil and its role in understanding the parana etendeka continental flood basalt province abstract the torres syncline is a large structure that constitutes the eastmost outcrop of the parana etendeka cfb in south american side and this work focuses the stratigraphy and facies architecture of the volcanic pile in the syncline the volcanic sequence along the study area permits the division of three regions main valley intermediate zone and south hinge each of them with distinct stratigraphy which probably reflects the structural evolution of the syncline the stratigraphy of the torres syncline is composed by 1 botucatu palaeoerg 2 basic volcanic episode i 3 basic volcanic episode ii 4 acidic volcanic i 5 basic volcanic episode iii and 6 acidic volcanic episode ii the five volcanic episodes recognized in study area can be related to five volcanic facies architecture compound braided tabular classic tabular lobate escoriaceous dome field acidic lavas and tabular flows acidic lavas the basic episode i is composed by pahoehoe flows with a compound braided facies architecture that covered the botucatu palaeoerg the basic episode ii is a tabular classic facies architecture predominantly composed by simple flows 10 20 m thick reaching the total thickness of 500 m in main valley the acidic episode i is exposed in main valley and south hinge and is composed by acidic lavas forming lava dome field facies architecture with a thickness of 150 m the basic episode iii is predominantly constituted by a flows with tabular lobate escoriaceous facies architecture the acidic episode ii is constituted by tabular flow volcanic facies acidic flows and outcrops all along the study area the torres syncline constitute the eastmost on shore exposures of the parana etendeka cfb in south american side and detailed stratigraphic volcanological and structural studies in these area coupled with correlation with huab basin nw namibia africa will aim the understanding of the gondwana breakup process and the early stages of the south atlantic margin opening

the 3d facies architecture of flood basalt provinces and their internal heterogeneity examples from the palaeogene skye lava field quantifying the facies architecture of flood basalt provinces is important as it can be used to understand the physical volcanology and rock property variations throughout the lava sequence the 3d facies architecture and internal heterogeneity of the skye lava field for example provides important insights into the evolution of the british tertiary igneous province and valuable information to aid in the exploration of potential offshore reservoirs underlying significant flood lavas along the north atlantic margin the volcanic stratigraphy of the talisker bay area of skye comprises 1 lower compound braided lavas flow lobes 3 the transitional sequence 7 4 km 3 and the upper sequence 17 0 km 3 the lower sequence lavas formed on the flanks of a shield volcano and were sourced from the ne volcanological features such as lava feeder tubes pahoehoe textures and lobes indicate a scale of volcanism similar to that of present day hawaii the within flow heterogeneity of the basalts is characterized using an intrafacies scheme allowing comparison of variations in lithofacies with characteristic geophysical rock properties of compressional wave velocity and density

volcanic glass in cretaceous dacites and rhyolites of the parana magmatic province southern brazil characterization and quantification by xrd rietveld abstract acidic rocks are a significant component of the cretaceous parana magmatic province occurring in different stratigraphic positions and often forming deposits of complex and as yet poorly defined architecture vitrophyric varieties are surprisingly abundant for a volcanic sequence of this age and are composed of predominant glass plus plagioclase labradorite andesine pyroxenes augite pigeonite and orthopyroxene ti rich magnetite and traces of apatite hypocrystalline rocks largely derived from devitrification additionally contain sanidine cristobalite and quartz the negative correlation between the abundance of these minerals and the amount of glass suggests that these latter phases formed by devitrification modal analysis using a combined xrd rietveld rir method detected glass contents between 0 and 85 wt in a set of representative samples of palmas type acidic rocks from southern brazil with dacite to rhyolite composition modal compositions determined by xrd and by scanning electron microscope are in good agreement with each other and were checked against whole rock xrf chemical data water contents up to 4 wt show a positive linear correlation with the amount of glass and are inferred to be mostly secondary as original pre eruptive h2o dissolved in melts is inferred to have been

characterization of subaerial volcanic facies using acoustic image logs lithofacies and log facies of a lava flow deposit in the brazilian pre salt deepwater of santos basin abstract volcanic rock facies characterization in subsurface log data have always being challenging even though considerable types of well logs are acquired the results achieved on facies characterization with the conventional log suits are very limited conversely high resolution borehole image logs calibrated with side wall core samples can provide the necessary structural and textural information for facies definitions in this case study an integration of good quality acoustic image log data side wall core petrography and geochemical analyses provided a good understanding of volcanic facies and stratigraphic relationships additionally outcrop data from the analogous serra geral formation and other large igneous provinces were used for comparison in the studied well from santos basin brazil it was possible to identify several kinds of subaerial basaltic lava flow units such as compound pahoehoe sheet pahoehoe and rubbly pahoehoe lava flows vesicles amygdales vesicle cylinders sub horizontal vesicle sheets autobreccias and entablature are some of the structures described in this study as a result 2 image catalogues of subaerial volcanic rocks were produced characterizing facies and flow units along with a stratigraphic model of the history of this volcanism this is the first time that pahoehoe lava flow units could be characterized at an offshore brazilian basin the results achieved are important for the understanding of the cretaceous volcanism events in the pre salt layer and also provide support for the evaluation and geological modelling of the volcanic rocks in santos basin oil fields

morphologies and emplacement mechanisms of the lava flows of the faroe islands basalt group faroe islands ne atlantic ocean the palaeogene faroe islands basalt group fibg comprises three eruptive sequences or formations all emplaced into a subaerial environment during the development of the extensive continental flood basalt province that stretches from east greenland through the faroe islands and into the faroe shetland basin the beinisvor formation having a tabular classic facies architecture is composed of a sequence of simple flows each comprising a single sheet lobe the beinisvor formation is overlain by the distinctly contrasting malinstindur formation that has a compound braided facies architecture the enni formation occurs at the top of the sequence and consists of a mixture of simple and compound flows with tabular classic and compound braided facies architectures respectively surface and internal characteristics of the sheet lobes of the beinisvor and enni formations indicate emplacement through inflation which is more obvious for the tube fed compound flows of the malinstindur and enni formations the difference between the simple and compound flow sequences of the fibg is most likely linked to the manner in which the lava was supplied during the eruption and the eruptive style of the volcanic system the sheet lobes were erupted over laterally extensive areas from fissure systems which had a continuous supply of lava which contrasts with the tube fed compound flows which were erupted in a gradual piecemeal manner from point sourced low shield volcanoes with limited areal extents

integrating topography hydrology and rock structure in weathering rate models of spring watersheds weathering rate models designed for watersheds combine chemical data of discharging waters with morphologic and hydrologic parameters of the catchments at the spring watershed scale evaluation of morphologic parameters is subjective due to difficulties in conceiving the catchment geometry besides when springs emerge from crystalline massifs rock structure must be accounted in formulas describing the area of minerals exposed to the percolating fluids for a realistic evaluation of the rates these particular features are not included in the available approaches and for that reason a new model was developed coined throw model this is a lumped approach that integrates t opography h ydrology ro ck structure and w eathering in a single algorithm the study area comprises several stream watersheds and spring sites of the vouga river basin northern portugal shaped on granites firstly the throw model couples a terrain modeling analysis with hydrologic models based on discharge rates to determine hydraulic conductivities k effective porosities ne and annual recharges vr at the stream watershed scale subsequently these parameters are used in a water balance model to estimate concomitant groundwater travel times t the mean k 4 7 3 2 10 7 m s 1 and ne 2 0 1 3 10 2 values are adopted as proxies for the spring watersheds and a firm regression equation is defined between time and stream watershed area a secondly two more runs of terrain modeling analysis are executed to extrapolate morphologic parameters for the spring watersheds the first run hinges on scaling properties of the drainage networks known as horton laws and is used to scale watershed areas across stream orders i the scaling function is described by another regression equation the second run evaluates the order of a spring watershed defined as equivalent order ieq and equated to the mean order of the surrounding stream watersheds having calculated the ieq spring watershed areas and travel times were downscaled using the regression equations a 10 km2 and t 1 4 2 8 year standing on the physical and hydrologic parameters of the spring watersheds the throw model finally calculates plagioclase weathering rates in the vicinity of the spring sites the sib model pacheco and van der weijden 1996 was used before to estimate the contribution of plagioclase dissolution to the chemical composition of these springs van der weijden and pacheco 2006 the chemical data were now coupled with k ne and t in a rate equation to estimate chemical weathering rates of plagioclase in the basin in the throw model the rate equation describes the exposed surface area as a function of fracture spacings openings and porosities pacheco and alencoao 2006 the calculated rates wpl 2 5 1 2 10 14 mol m 2 s 1 are consistent with previous reports and with results of experimental kinetic models the sib results predict formation of halloysite and gibbsite along the flow path which were indeed close to equilibrium with the dissolved al and si activities o develop a weathering model that incorporates rock structure in the rate equation o conceive a weathering model especially designed for fracture artesian springs o create a model that integrates topography hydrology rock structure and weathering

quartz latite rheoignimbrite flows of the etendeka formation north western namibia the etendeka formation of north western namibia consists of a sequence of interbedded quartz latites and tholeiitic basalts and forms part of the karoo igneous province in southern africa the age of the etendeka formation is approximately 130 135 ma the quartz latites make up a significant proportion of the stratigraphic succession 25 of the total stratigraphic thickness and form as much as 60 of the outcrop area in the southern etendeka apart from some systematic differences between pitchstones and devitrified quartz latite largely explained by alteration processes individual quartz latite units exhibit remarkably uniform compositions with no significant vertical or lateral variation geochemistry can be used as a primary criterion for the correlation of major quartz latite units over much of the southern etendeka area enabling the reconstruction of the etendeka formation stratigraphy in this region individual quartz latite units occur as voluminous 400 2600 km3 widespread up to 8800 km2 sheet like deposits typically between 40 and 300 m thick each unit consists of basal main and upper zones the main zone generally constitutes over 70 of the thickness of the unit and typically consists of texturally featureless devitrified quartz latite in contrast the basal and upper zones of the flow are characterised by flow banding pitchstone lenses and breccia with rare occurrences of pyroclastic textures the quartz latites are sparsely porphyritic 10 phenocrysts with glassy or devitrified groundmass textures the phenocrysts consist of plagioclase pyroxene titanomagnetite and rare ilmenite pyroxene geothermometry indicates high 1000 1100 c temperatures of crystallisation which coupled with the absence or primary hydrous phases indicates that the quartz latites were relatively hot h2o undersaturated magmas the quartz latites display features common to both rhyolite lavas and ignimbrites and are clearly the products of an unusual eruption style the local preservation of pyroclastic textures and the broad areal extent of these units lead to the conclusion that the quartz latites are high temperature rheomorphic ignimbrites i e rheoignimbrites a combination of high eruption temperature and relatively low viscosity helps to explain the often completely welded and homogeneous textures observed in most quartz latite outcrops in the etendeka area

a revised chemo chrono stratigraphic 4 d model for the extrusive rocks of the parana igneous province abstract the statistical analysis of a lithogeochemical database from whole parana igneous province pip containing 5974 outcrop and drillhole samples stresses natural gaps separating sio2 zr tio2 and p2o5 in high and low values their combination delimits 16 chemical types which have been adopted to classify a sub set of extrusive rocks with

dividing the south american continent to fit a gondwana reconstruction a model based on continental geology abstract the south american continental plate has been affected by intraplate deformation since the start of west gondwana disruption in the lower cretaceous about 140 ma that the present shape of south america is not precisely the same as its shape in reassembled gondwana partly explains the imperfect fits of the conjugate margins of the south atlantic proposed since the first reconstruction models of the early 20th century several attempts at defining subplates within south america have been published but not all take account of existing knowledge of its continental geology here a subdivision into eight rigid subplates is proposed based primarily on geological and tectonic evidence our model is tested against three published models of a multi subplate africa as re shaped to the pre breakup outline of that continent by visual fitting and the use of piercing points the south america blocks were rotated and the euler poles calculated interactively in reconstruction software all three proposed fits had overlapping block margins within south america indicating post breakup rifting except for the transbrasiliano lineament this nne ssw crustal scale shear zone was used as a boundary for seven of the eight blocks it is clearly the main intraplate accommodation zone in south america and an important piercing point in relation to the kandi lineament in west africa the other block boundaries correspond to narrow zones with sedimentary basins and or dyke swarms that have developed since south atlantic opening each fit required a different configuration of the south america subplates since the pre rift disposition of the african subplates also differ from each other contributing to the uncertainty in any detailed reassembly

flow and fragmentation patterns in the silicic feeder system and related deposits in the parana etendeka magmatic province sao marcos south brazil voluminous silicic volcanic products from the paran etendeka magmatic province are exposed in the southern brazil a regional synformal structure torres syncline controls a tick sequence of these units in the region of sao marcos rio grande do sul parallel to the axis of torres syncline a nw se trending zone constituted by the alignment of complex structures was interpreted as the feeding system of silicic volcanism characterized as fissural through a combination of field mapping and determination of fractal dimension fd we have identified and described distinct intermingled morphological domains one related to flow processes and one related to fragmentation processes vertical flow directions in this zone exhibit two preferential directions nw ranging from n272 degrees to n 355 degrees and ne varying from n20 degrees to n85 degrees the systematic repetition and crosscutting relations of domains point towards a cydicity of flow and fragmentation processes in this zone this feeder system intrudes previous basaltic and silicic volcanic rocks the later being composed by banded deposits interpreted as rheoignimbrites and proximal volcanic breccias this set is overlapped by hybrid deposits lava flows and finally massive deposits the silicic volcanism can be summarized at an early pyrodastic stage characterized by rheoignimbrites and proximal volcanic breccias a transition between explosive and effusive events is suggested by the occurrence of hybrid deposits which gradually give place to lobated lavas local alternation with new possibly rheoignimbritic deposits suggests oscillatory fragmentation processes at the conduit related to decompression and volatiles ex solution in an effective permeable system

lava sediment interaction in desert settings are all peperite like textures the result of magma water interaction abstract this study reports on lava sediment interaction in dry depositional settings focusing on the early cretaceous volcano sedimentary sequence in the huab basin nw namibia as a detailed example here an active aeolian sand sea erg system was progressively engulfed by lavas of the etendeka flood basalt province 133 ma bp this volcanic flooding resulted in 1 the unprecedented preservation of large parts of the active dune system 2 the development of a variety of sediment interlayers and 3 a record of excellent examples of the dynamic interaction between lava and aeolian sand the lava sediment interaction happens on a variety of scales from simple sediment interbeds within the lavas at a large scale down to complex breccia horizons and bulbous lava sediment contacts at small scales peperite like textures are found where hot lava has dynamically interacted with unconsolidated aeolian sands such interaction could involve lava cascading down the front of dune faces or active aa style flow fronts bulldozing into and oversteepening dune faces causing rapid influx of sand into the active flow front resulting breccia horizons have been found up to 5 m thick locally the aeolian sand is baked to a quartzite by the hot lava in contrast on other surfaces the lava leaves striations in the sand as it flows across it indicating local flow directions and less pronounced interaction in places wind ripples and topset beds are preserved on the stoss side of the dune indicating the passive nature of emplacement for some of the lava flows peperites are often thought to form due to the presence of water within the unconsolidated sediments that the juvenile magma comes into contact with however examples from arid environments demonstrate that peperite forming processes are diverse and may not always require water therefore it is suggested that the term peperite should be used to describe deposits consisting of sediments mixed with juvenile magmatic components where it is clear that there has been a dynamic interaction between the two this leaves the presence or lack of water as an issue for interpreting the processes by which the peperite formed

formation mechanism of volcanic reservoirs within a volcanostratigraphic framework the case of the wangfu fault depression in the songliao basin china abstract we discuss the reservoir formation mechanisms in volcanic gas reservoirs within a volcanostratigraphic framework with a focus on the huoshiling formation of the wangfu fault depression in the songliao basin china the volcanic sequences are divided from large to small into the volcanic cycle vc cooling unit set cus and cooling unit cu the cu is the basic volcanogenic stratigraphic unit and the cus is a superposition of cooling units which may be recognized on seismic profiles the huoshiling formation consists of two volcanic cycles and one volcanic sedimentary cycle the formation mechanisms of volcanic reservoirs include three processes based on the strata s evolution first cus formed and primary pore spaces developed near cooling surfaces second cuss and vcs formed and parasyngenetic and secondary pore spaces developed around the crater or caldera especially near the weathering surface lastly numerous dissolved pores and structural fractures formed during burial and concentrated near the fault belt cus volcanic edifices and structural systems controlled the formation of volcanic reservoirs the overlapping crater proximal crater region and the faulted area were centres of reservoir formation in the huoshiling formation cus 6 cus 8 and cus 13 are the major horizons where volcanic reservoirs developed forming dissolution reservoirs and structurally fractured reservoirs for natural gas accumulation

preservation of aeolian genetic units by lava flows in the lower cretaceous of the parana basin southern brazil the lower cretaceous geological record of the intracratonic parana basin in southern brazil comprises a thick succession of aeolian sandstones and volcanic rocks the intercalation between aeolian sandstone and volcanic floods allowed the preservation of distinct aeolian genetic units each genetic unit represents an accumulation episode bounded by supersurfaces that coincides with the base of lava flood events the entire package can be subdivided into a lower genetic unit which corresponds to aeolian sandstones preserved below the initial lava flows botucatu formation and an upper set of genetic units which comprises interlayered aeolian deposits and lava floods serra geral formation the lower genetic unit is up to 100 m thick its base is composed of ephemeral stream and aeolian sand sheet deposits that are overlain by cross bedded sandstones whose origin is ascribed to simple locally composite crescentic and complex linear aeolian dunes aeolian accumulation of the lower unit was possible as a result of the existence of a wide topographic basin which caused wind deceleration and a large sand availability that promoted a positive net sediment flux the upper genetic units comprise isolated sand bodies that occur in two different styles 1 thin lenses 3 m thick formed by aeolian sand sheets and 2 thick sand lenses 3 15 m comprising cross bedded cosets generated by migration and climbing of simple to locally composite crescentic aeolian dunes accumulation of the aeolian strata was associated with wind deceleration within depressions on the irregular upper surface of the lava floods the interruption of sedimentation in the lower and upper genetic units and related development of supersurfaces occurred as a result of widespread effusions of basaltic lava preservation of both wind rippled topset deposits of the aeolian dunes and pahoehoe lava imprints indicates that lava floods covered active aeolian dunes and hence protected the aeolian deposits from erosion thus preserving the genetic units

morphology and emplacement of flows from the deccan volcanic province india the present study is probably the first of its kind in the deccan volcanic province dvp that deals in detail with the morphology and emplacement of the deccan trap flows and employs modern terminology and concepts of flow emplacement we describe in detail the two major types of flows that occur in this province compound pahoehoe flows similar to those in hawaii and the columbia river basalts crb constitute the older stratigraphic formations these are thick flows displaying the entire range of pahoehoe morphology including inflated sheets hummocky flows and tumuli in general they show the same three part structure associated with pahoehoe flows from other provinces however in contrast to the crb pahoehoe lobes in the dvp are smaller and hummocky flows are quite common simple flows occur in the younger formations and form extensive sheets capped by highly vesicular weathered crusts or flow top breccias these flows have few analogues in other provinces although considered to be a a flows by previous workers the present study clearly reveals that the simple flows differ considerably from typical a a flows especially those of the proximal variety this is very significant in the context of models of flood basalt emplacement at the same time they do not display direct evidence of endogenous growth understanding the emplacement of these flows will go a long way in determining whether all extensive flows are indeed inflated flows as has recently been postulated

an ams study of different silicic units from the southern parana etendeka magmatic province in brazil implications for the identification of flow directions and local sources abstract in the southern portion of the parana etendeka magmatic province in brazil extensive silicic dacite rhyolite deposits occur at the top of a sequence of low ti pahoehoe to rubbly basalts the internal architecture of the silicic deposits and their eruptive style as well as the location of their sources are still unsatisfactorily known in an attempt to provide independent evidence for flow directions in deposits previously characterized as effusive and test the hypothesis of local sources we carried out anisotropy of magnetic susceptibility ams studies on the two main silicic units caxias do sul dacites and santa maria rhyolites with the best exposures in an area previously mapped in detail magnetic anisotropies were determined on oriented cylindrical specimens from a total of 28 sites rock magnetism properties indicate that pseudo single domain magnetite carries the fabrics and the remanence magnetic fabrics were determined by applying anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanent magnetization aarm both ams and aarm tensors are coaxial indicating that the ams fabric is not affected by the effect of magnetite single domain grains magnetic data from several dacitic coulees caxias do sul unit indicate flows from se to nw the location and spatial distribution of these lavas support the hypothesis of local sources aligned along a ne sw trend these data are in agreement with the alignments of structures dome shaped hills observed in field work and dem images on the other hand magnetic data obtained in santa maria rhyolites indicate that flow directions in two different areas are distinct towards nw ne and w suggesting that they derived from different emission centers so regarding the silicic volcanism in the studied region our data do not support the model which classifies the entire silicic volcanism of the province as extensive rheomorphic pyroclastic deposits released from a central conduit in contrast we propose the occurrence of local volcanic events implying in the existence of different sources possibly characterized by local emission centers

the importance of pahoehoe abstract pahoehoe lava flows are common in every basaltic province and their submarine variants pillow lavas and sheet flows cover the bulk of the earth pahoehoe flows are emplaced by inflation the injection of molten lava underneath a solidified crust only in the past few years has an understanding of the inflation process and the ability to recognize ancient inflated lava flows been achieved all large terrestrial basaltic flow fields studied to date including flood basalts were emplaced as thermally efficient inflated compound pahoehoe sheet flows this leads us to propose that this is the standard way of emplacing large lavas the swell hypothesis the atmospheric impact of such flood basalt eruptions could have been protracted and severe providing a plausible link between flood basalt eruptions and mass extinctions

the mode of emplacement of neogene flood basalts in eastern iceland facies architecture and structure of the holmar and grjota olivine basalt groups abstract holmar and grjota are two stratigraphically distinct transitional alkaline olivine basalt lava groups within the westward dipping neogene flood basalts of eastern iceland the holmar olivine basalt group separated from the overlying grjota olivine basalt group by only a few tholeiite flows can be traced over 80 km north south with thicknesses varying from 250 m where thickest to 30 m where thinnest the grjota group can be traced over 50 km also north south reaching thicknesses of 250 m and thinning down dip to 10 m in contrast to other groups in eastern iceland that thicken down dip the studied olivine basalt groups thicken up dip the groups filled topographic confinements and formed aprons around central volcanoes we have estimated the minimum volumes to be 119 km 3 for holmar and 86 km 3 for grjota scoria cones are found in the holmar group and two thick olivine dolerite sills cross cut the holmar group and probably belong to the plumbing system that fed the grjota group the architecture of the lava groups are near identical the architecture is compound with lobes stacked horizontally and vertically varying from 1 15 m thick and 2 200 m long but do also encompass a number of thicker 15 20 m and more extensive 1 km long lava lobe in the stacks filled lava tubes are commonly observed within the lava flows the constituent lobes of the flows are often directly emplaced or welded together suggesting rapid buildup but are also found interbedded with redbeds and thicker tuff deposits and occasionally preserve tree molds the internal structure follows the characteristics for lava lobe morphology in general with an upper vesicular crust forming half to one third of the total thickness a massive core with abundant vesicle cylinders and a thin basal vesicular crust flow tops are of the pahoehoe type seldom found with scoria or clinker inflation structures such as tumuli and inflation clefts were identified in the flows the eruptions were dominantly fissure fed with a few vents evolving to short lived point source volcanism the pre existing topography exerted control on the advancement of the flows and influenced the final architecture of the groups at each location it is evident that the large and dense spatial distribution of these groups including numerous thick lava units suggests large volcanic episodes together the groups imply a period with higher production of olivine basalts in iceland and form well defined stratigraphic markers the transitional alkaline olivine basalt groups are interpreted to delineate a fossil southward propagating rift flank volcanic zone located east of a now extinct and buried mature rift zone

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

volcanic sedimentary features in the serra geral fm parana basin southern brazil examples of dynamic lava sediment interactions in an arid setting abstract the formation of volcanic sedimentary interaction features in extreme arid environments is not a commonly described process specifically the occurrence of dynamically mixed sediments and juvenile igneous clasts as peperites for water has been considered one major important factor in the processes of magma dismantling and mingling with unconsolidated sediment to form such deposits the study area located in south brazil shows a sequence of lava flows and intertrapic sandstone layers from the parana basin associated with the formation of clastic dykes flow striations peperite and peperite like breccias four processes are suggested for the genesis of the peperites a fragmentation of the flow front and base b sand injection c dune collapse d magma cascade downhill the continued flow of a lava while its outer crust is already cooling causes it to break especially in the front and base fragments falling in the sand and getting mixed with it generating the flow front peperite like breccia the weight of the lava flow associated to shear stress at the base cause sand to be injected inwards the flow forming injection clastic dykes in the cooled parts and injection peperite in the more plastic portions the lava flow may partially erode the dune causing the dune to collapse and forming the collapse peperite like breccia the shear stress at the base of a flowing lava striates the unconsolidated sand forming the flow striations the sand that migrates over a cooled jointed lava flow may get caught in the cavities and joints forming the filling clastic dykes these deposits are analogous to those found in the etendeka nw namibia and show that sediment lava interactions in arid settings are widespread throughout the parana etendeka province during the onset of flood volcanism

seismic volcanostratigraphy of large volume basaltic extrusive complexes on rifted margins large volume extrusive basaltic constructions have distinct morphologies and seismic properties depending on the eruption and emplacement environments the presence and amount of water is of main importance while local rift basin configuration erosion and resedimentation determine the overall geometry of the volcanic constructions we have developed the concept of seismic volcanostratigraphy a subset of seismic stratigraphy to analyze volcanic deposits imaged on seismic reflection data the method places special focus on identification and mapping of seismic facies units and the volcanological interpretation of these units interpretation of seismic reflection data along the atlantic and western australia rifted margins reveals six characteristic volcanic seismic facies units named 1 landward flows 2 lava delta 3 inner flows 4 inner seaward dipping reflectors inner sdr 5 outer high and 6 outer sdr these units are interpreted in terms of a five stage tectonomagmatic volcanic margin evolution model comprising 1 explosive volcanism in a wet sediment broad basin setting 2 subaerial effusive volcanism forming gilbert type lava deltas along paleoshorelines 3 subaerial effusive volcanism infilling a fairly narrow rift basin 4 shallow marine explosive volcanism as the injection axis is submerged below sea level and finally 5 deep marine sheet flow or pillow basalt volcanism further erosion and resedimentation processes are particularly important during the shallow marine stages seismic volcanostratigraphy provides important constraints on rifted margin development in particular on the prevolcanic basin configuration relative timing of tectonomagmatic events total amount of volcanic rocks location of paleoshorelines and margin subsidence history these parameters give key boundary conditions for understanding the processes forming volcanic margins and other large volume basaltic provinces

structures and lithofacies of inferred silicic conduits in the parana etendeka lip southernmost brazil abstract extensive silicic units in the parana etendeka lip have been long interpreted as pyroclastic density currents rheomorphic ignimbrites derived from the messum complex in namibia in recent literature however they have been characterized as effusive lava flows and domes in this paper we describe structures and lithofacies related to postulated silicic lava feeder conduits at mato perso sao marcos and jaquirana cambara do sul areas in southern brazil inferred conduits are at least 15 25 m in width and the lithofacies include variably vesicular monomictic welded and non welded breccias in the margins to poorly vesicular banded spherulitic and microfractured vitrophyres in the central parts flat lying coherent vitrophyres and massive obsidian are considered to be the subaerial equivalents of the conduits large scale regional tectonic structures in southern brazil include the ne sw aligned porto alegre suture leao and acotea faults besides the antas lineament a curved tectonic feature accompanying the bed of antas river south of the antas lineament smaller scale nw se lineaments limit the exposure areas of the inferred conduits ne sw and subordinate nw se structures within this smaller scale lineaments are represented by the main postulated conduit outcrops and are parallel to the dominant sub vertical banding in the widespread banded vitrophyre lithofacies upper lava flows display flat lying foliation pipe like and spherical vesicles and have better developed microlites petrographic characteristics of the silicic vitrophyres indicate that crystal poor magmas underwent distinct cooling paths for each inferred conduit area the vitrophyre chemical composition is defined by the evolution of trachydacitic dacitic vitrophyres with 62 65 wt sio 2 to rhyodacite and rhyolite with 66 68 wt sio 2 the more evolved rocks are assigned to the latest intrusive grey vitrophyre outcropping in the center of the conduits degassing pathways formed during fragmentation and fracturing episodes within the conduits may have helped to inhibit the explosivity of the eruptions based on the documented lithofacies architecture we attribute the source of the silicic lava flows in the studied localities to tectonic controlled local conduits rather than pyroclastic density currents from distant vent areas

the mode of emplacement of neogene flood basalts in eastern iceland facies architecture and structure of simple aphyric basalt groups simple flows tabular in the neogene flood basalt sections of iceland are described and their mode of emplacement assessed the flows belong to three aphyric basalt groups the kumlafell group the holmatindur group and the hjalmadalur group the groups can be traced over 50 km and originate in the brei dalur thingmuli volcanic zone the groups have flow fields that display mixed volcanic facies architecture and can be classified after dominating type morphology the kumlafell and the holmatindur groups have predominantly simple flows of p hoehoe and rubbly p hoehoe morphologies with minor compound or lobate p hoehoe flows the hjalmadalur group has simple flows of rubbly p hoehoe but also includes minor compound or lobate flows of rubble and a simple flows are most common in the distal and medial areas from the vents while more lobate flows in proximal areas the simple flows are formed by extensive sheet lobes that are several kilometers long with plane parallel contacts some reaching thicknesses of 40 m aspect ratios 0 01 they have overlapping contacts and are free of tubes and inflation structures their internal structure consists generally of a simple upper vesicular crust a dense core and a thin basal vesicular zone the brecciated flow top is formed by clinker and crustal rubble the clinker often welded or agglutinated the simple flows erupted from seemingly short lived fissures and have the characteristics of cooling limited flows we estimate the effusion rates to be 105 m3 s for the simple flows of the kumlafell and holmatindur groups and 104 m3 s for the hjalmadalur group the longest flows advanced 15 20 km from the fissures with lava streams of fast propagating flows inducing tearing and brecciation of the chilled crust compound or lobate areas appear to reflect areas of low effusion rates or the interaction of the lava with topographic barriers or wetlands resulting in chaotic flowage slowing lobes with brecciated flow tops developed into a flows the groups interdigitated with lava groups from the rey arfjor ur volcanic zone to the east and the exhumed brei dalur thingmuli volcanic zone which appear to have formed as a flank lineament parallel the main rift zone flood basalt volcanism in flank areas may support a mantle anomaly more pronounced and or perhaps more widespread in the neogene of iceland than today eruptions of simple flows have not been observed in modern times and are significant for models of crustal accretion in iceland and other large igneous provinces

lithofacies analysis of basic lava flows of the parana igneous province in the south hinge of torres syncline southern brazil abstract the parana igneous province records the volcanism of the earlier cretaceous that preceded the fragmentation of the gondwana supercontinent historically investigations of these rocks prioritized the acquisition of geochemical and isotopic data considering the volcanic pile as a monotonous succession of tabular flows this work provides a detailed analysis of the emplacement conditions of these basic volcanic rocks applying the facies analysis method integrated to petrographic and geochemical data the torres syncline is a nw se tectonic structure located in southern brazil where a thick sequence of the parana etendeka volcanic rocks is well preserved this study was performed in the south hinge of the syncline where the basaltic lava flows are divided into three lithofacies associations early compound pahoehoe early simple pahoehoe and late simple rubbly the first lavas that erupted were more primitive compound pahoehoe flow fields composed of olivine basalts with higher mgo contents and covered the sandstones of the botucatu formation the emplacement of compound pahoehoe flow fields is possibly related to intermittent low effusion rates whereas the emplacement of simple pahoehoe is related to sustained low effusion rates with continuous supply the thick simple rubbly lavas are associated with high effusion rates and were formed during the main phase of volcanism in the area the absence of paleosoils between the lavas and lithofacies associations suggests that the successive emplacement of the lava flows occurred in a relatively short time gap geochemically the lithofacies associations are low tio2 and belong to gramado magma type the lavas of the south hinge of the torres syncline have a similar evolution when compared to other continental basaltic provinces with earlier compound flows at the base and thicker simple flows in the upper portions

understanding the offshore flood basalt sequence using onshore volcanic facies analogues an example from the faroe shetland basin flood basalts in associated volcanic rifted margins such as the north atlantic igneous province have a significant component of lavas which are preserved in the present day in an offshore setting a close inspection of the internal facies architecture of flood basalts onshore provides a framework to interpret the offshore sequences imaged by remote techniques such as reflection seismology a geological interpretation of the offshore lava sequences in the faroe shetland basin using constraints from onshore analogues such as the faroe islands allows for the identification of a series of lava sequences which have characteristic properties so that they can be grouped these are tabular simple flows compound braided flows and sub aqueously deposited hyaloclastite facies the succession of volcanic rocks calculated in this study has a maximum thickness in excess of 6800 m down to the top of the sub volcanic sediments the offshore volcanic succession has a thickness of about 2700 m where it can be clearly identified across much of the area with a further 2700 m or more of volcanic rock estimated from the combined gravity and seismic modelling to the north and west of the region a large palaeo waterbody is identified on the basis of a hyaloclastite front apron consisting of a series of clinoforms prograding towards the eastern part of the basin this body was 500 m deep must have been present at the onset of volcanism into this region and parts of the water body would have been present during the continued stages of volcanism as indicated by the distribution of the hyaloclastite apron

hydrodynamic description of the erosional development of drainage patterns the erosional development of drainage networks is analyzed by modeling two dimensional flow of water and sediment over a bare slope deterministic equations of mass and momentum conservation are coupled with random fluctuations of sediment pickup and transportation processes acting at the hydrodynamic scale these fluctuations are then shown to be able to provide an active source of channelization at the hillslope scale controlled experiments are also carried out by simulation runs aimed at investigating model performance 1 to describe formation of natural drainage patterns 2 to account for different factors i e soil characteristics hillslope geometry and rainfall intensity which control network formation and development and 3 to reproduce differentiation of drainage patterns due to above factors

the onset of flood volcanism in the north western part of the siberian traps explosive volcanism versus effusive lava flows abstract the siberian traps large igneous province was formed during the end permian about 252 ma ago basaltic melt was injected into the organic and salt rich tunguska sedimentary basin forming interconnected sill complexes and associated hydrothermal vent complexes thick deposits of basaltic tuff and tephra covered the paleosurface before the onset of flood volcanism commonly taken as direct evidence for the explosive nature of the initial phase of volcanism the field work in this study revealed that tuffs are virtually absent along a 150 km long transect along the dyupkun lake and kureika river even though tuff is shown on available geological maps towards the south and west the transition between the end permian sediments and the flood basalts is either characterized by thin 2 5 m to no tephra deposits khantaika area hyaloclastites and associated lake deposited tephra kureika area or massive tephra deposits from local eruptive centers severnaya area the new results can be put into the context of other studies about volcanic tuff horizons in siberia and questions the notion of province scale explosive volcanism in siberia during the onset of flood volcanism moreover the main thicknesses of explosive tuff deposits up to 700 m are located in the central and southern parts of the province where the lip erupted through thick cambrian salt and carbonate sequences since numerous phreatomagmatic pipes are present in these areas we suggest a causal relationship between deep magma sediment interactions explosive eruptions and the resulting environmental stress that initiated the end permian mass extinction

radiogenic isotopic and clay mineralogical signatures of terrigenous particles as water mass tracers new insights into south atlantic deep circulation during the last termination abstract the past evolution of the southern ocean one of the major components of the climatic system is still a matter of debate this study provides new insights into the deep southern ocean circulation based on the radiogenic isotopes and clay mineralogical signature of the terrigenous fractions transported by the main deep water masses to sediments recovered in core md07 3076q from the central south atlantic this approach successfully permits 1 provenance identification of the various grain size fractions clay cohesive silt and sortable silt 2 assignment of each grain size fraction to a specific water mass 3 reconstruction of past changes in the main deep water mass pathways these data document the evolution of deep water masses in the south atlantic ocean during the last deglaciation the antarctic bottom water aabw speed and northward extension were maximum at the end of the last glacial maximum lgm associated with strong bottom water production in the weddell sea together with a vigorous lower circumpolar deep water lcdw in contrast the north atlantic deep water nadw circulation was weaker than today the onset of the deglaciation from 17 5 ka to 15 ka heinrich stadial 1 hs 1 was marked by weakening and southerly retreat of the aabw and by an increase of mixing between aabw and lcdw the speed of the aabw remained at its lowest during the bolling allerod b a and the younger dryas yd and the lcdw slowed and retreated to the south while the nadw progressively migrated southward deepened and strengthened between the beginning of the bolling allerod and the holocene from 15 to 10 ka

pahoehoe flows from the central parana continental flood basalts inflated and compound pahoehoe flows have been identified within the central parana continental flood basalts based upon their morphology surface features and internal zonation pahoehoe flow features have been studied at five localities in the western portion of parana state brazil ponte queimada toledo rio quiteria matel ndia and cascavel we have interpreted the newly recognized flow features using concepts of hawaiian pahoehoe formation and emplacement that have been previously applied to the columbia river basalt and deccan plateau surface features and or internal structure typical from pahoehoe lavas are observed in all studied areas and features like inflation clefts squeeze ups breakouts and p type lobes with two levels of pipe vesicles are indicative of inflation in these flows the thinner compound pahoehoe flows are predominantly composed of p type lobes and probably emerged at the end of large inflated flows on shallow slopes the presence of vesicular cores in the majority of compound lobes and the common occurrence of segregation structures suggests high water content in the pahoehoe lavas from the central pcfb more volcanological studies are necessary to determinate the rheology of lavas and refine emplacement models