correlations between the classic parana and cape karoo sequences of south america and southern africa and their basin infills flanking the gondwanides du toit revisited

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

holocene tectonic activity along kachchh mainland fault impact on late mature harappan civilization kachchh western india abstract paleoseismic and archaeological records of the kachchh rift basin krb of western india indicates that the region become tectonically active during the period of middle to late holocene to understand the relationship between strain accumulation earthquake genesis and landform development we analyzed uplifted late quaternary terraces and archaeological evidence along the kachchh mainland fault kmf zone dividing the elevation of the bedrock strath at each site by their ages yields vertical uplift rates of 0 29 1 17 mm y for the kmf zones archaeological data from the excavation of the kotada bhadli site suggest that the site was occupied during the late mature harappan 2300 2500 bce period and abandoned around 1900 bce the ruins of harappan civilization at kotada bhadli location are resting over the middle holocene fluvial sediments the oldest fluvial sediment is dated to 4 ka whereas the youngest sediment yielded an age of 3 ka the chronological constraints in geomorphic and archaeological records suggest that the area was hit by an earthquake around 2200 bc 3 5ka the geomorphic and chronologically constrained uplift rates reveal that the kmf zone of the intraplate region of the kachchh is geodynamically controlled by several fault segments which are consistent with the ambient tectonic stress field owing to the northward movement of the indian plate concerning the eurasian plate

a paleoclimatic review of southern south america during the late paleozoic a record from icehouse to extreme greenhouse conditions abstract this paper provides a review of the late mississippian to permian paleoclimatic history for southern south america based on lithologic indicators biostratigraphic information and chronostratigraphic data the region is divided into three major types of basins 1 eastern intraplate basins e g parana basin 2 western retroarc basins e g paganzo basin and 3 western arc related basins e g rio blanco basin four major types of paleoclimatic stages are recognized in these basins 1 glacial late visean early bashkirian 2 terminal glacial bashkirian earliest cisuralian 3 postglacial cisuralian early guadalupian and 4 semiarid arid late guadalupian lopingian the glacial stage began in the late visean and continued until the latest serpukhovian or early bashkirian in almost all of the basins in southern south america during the bashkirian earliest cisuralian terminal glacial stage glacial deposits disappeared almost completely in the western retroarc basins e g paganzo basin but glaciation persisted in the eastern basins e g parana and sauce grande basins a gradual climatic amelioration postglacial stage began to occur during the earliest permian when glacial deposits completely disappeared across all of south america during this interval glacial diamictites were replaced by thick coal beds in the parana basin while north south climatic belts began to be delineated in the western basins which were likely controlled by the distribution of mountain belts along the panthalassan margin of south america towards the late permian climatic belts became less evident and semiarid or arid conditions dominated in the southern south america basins eolian dunes playa lake deposits and mixed eolian fluvial sequences occur in the parana basin and in the western retroarc basins volcanism and volcaniclastic sedimentation dominated along the western margin of south america at that time the stratigraphic record obtained in southern south america supports a long duration transition from icehouse to extreme greenhouse conditions

numerical simulation of rock failure and earthquake process on mesoscopic scale on the basis of the lattice model of mora and place discrete element method and molecular dynamics approach another kind of numerical model is developed the model consists of a 2 d set of particles linked by three kinds of interactions and arranged into triangular lattice after the fracture criterion and rules of changes between linking states are given the particle positions velocities and accelerations at every time step are calculated using a finite difference scheme and the configuration of particles can be gained step by step using this model realistic fracture simulations of brittle solid especially under pressure and simulation of earthquake dynamics are made

simulations of permian climate and comparisons with climate sensitive sediments abstract we use a climate model to simulate two intervals of permian climate the sakmarian ca 280 ma at the end of the major permo carboniferous glaciation and the wordian ca 265 ma we explore the climate sensitivity to various levels of atmospheric co2 concentration and to changes in geography and topography between the two periods the model simulates large seasonality and high aridity in the continental interiors of both hemispheres for both periods the northern summer monsoon weakens and the southern monsoon strengthens between the sakmarian and the wordian owing to changes in geography and topography the northern middle and high latitudes cool in winter between the sakmarian and wordian associated with northward shift of the continents this high latitude cooling strengthens the winter westerlies and shifts the maximum storm track precipitation south in the southern hemisphere the winter westerlies weaken from the sakmarian to the wordian starting the simulations with no permanent i

evidence for palaeo wildfire in the late permian palaeotropics charcoal from the motuca formation in the parnaiba basin brazil abstract the permian deglaciation of gondwana caused a global icehouse greenhouse transition leading to increased aridity over large parts of this continent during the lopingian contributing to the overall scarcity of plant bearing localities despite a continuous increase of reports of fossil charcoal as direct evidence for palaeo wildfires from late palaeozoic deposits such records from low latitude and arid to semi arid areas are still rare in order to contribute to the discussion about palaeoenvironmental conditions that dominated low latitudinal portions of the globe during that period and especially the occurrence of wildfires the present contribution reports on charcoal recovered from sandstones from the andradina outcrop late permian lopingian motuca formation in the parnaiba basin northern brazil this locality is part of the northern tocantins petrified forest which is classified as one of the most important permian assemblages of permineralized plant remains from warm temperate palaeobiomes of the southern hemisphere the results presented here provide the first evidence for the occurrence of palaeo wildfires in the western part of the gondwanan palaeo tropics during the lopingian

permian phytogeographic patterns and climate data model comparisons abstract the most recent global icehouse hothouse climate transition in earth history began during the permian warmer polar conditions relative to today then persisted through the mesozoic and into the cenozoic we focus here on two permian stages the sakmarian 285 280 ma and the wordian 267 264 ma also known as the kazanian integrating floral with lithological data to determine their climates globally these stages postdate the permo carboniferous glaciation but retain a moderately steep equator to pole gradient judging by the level of floral and faunal differentiation floral data provide a particularly useful means of interpreting terrestrial paleoclimates often revealing information about climate gradations between dry and wet end member lithological indicators such as evaporites and coals we applied multivariate statistical analyses to the permian floral data to calibrate the nature of floral and geographical transitions as an aid to climate interpretation we then classified sakma

permian phytogeography in gondwana abstract phytogeographic patterns based on multivariate techniques multidimensional scaling are proposed for the permian vegetation of gondwana this approach requires a data set with broad geographic coverage based on generic composition and with good time control in general strong phytogeographic differentiation can be observed throughout the permian in order to identify short term phytogeographic patterns the permian period was informally divided into five time slices in the permian stage i earliest permian the vegetation was strongly influenced by glacial conditions a very impoverished vegetation is seen except in patagonia and parts of south america four units were identified patagonia nothosouthamerica australia and indo africa by far patagonia was the most diverse and had the most favourable climatic conditions perhaps as a result of palaeogeographic separation from western gondwana nothosouthamerica which included plant assemblages from nw argentina and brazil perhaps as two subunits is a mid latitude area with glacial influence in the brazilian sector indo africa had a much lower diversity occupying high latitudes whereas australia had the lowest diversity of all the vegetational regions in stage i the early permian stage ii shows a more diversified and expanded plant cover vegetation of eastern and western gondwana was differentiated patagonia and south america including a brazilian and nw argentinean unit had the richest plant assemblages whereas africa indo australia and antarctica as separate units are less diverse probably due to late glacial influence by the late early permian stage iii gondwana shows much more ameliorated climatic conditions basically due to drifting into more temperate latitudes as well as increased moisture resulting in expansion of peat forming areas this is immediately reflected in the vegetation as shown by diversified plant assemblages even in antarctica nonetheless a differentiation is again observed between eastern gondwana patagonian and south american units and the western sector indo australian and antarctic units whereas africa would probably represent an ecotone beginning in the late permian stage iv there was a decrease in the number of plant assemblages and diversity indicating a deterioration in climate resulting from generally drier conditions latitudinal differentiation can be observed with antarctica as a polar unit afro australia at high latitudes whereas the south american indian and patagonian units are located in middle latitudes finally in permian stage v latest permian a south american unit can be differentiated clearly from the rest africa and indo australia antarctica is interpreted again as a discrete unit in the stage v time slice eastern gondwana returns to more humid climatic conditions allowing the formation of extended peat swamps whereas the western sector is affected by seasonal and strong droughtness this kind of phytogeographic approach has proven useful for detecting some palaeogeographic problems such as those involving the patagonian subcontinent in this regard palaeogeographic reconstructions and palaeoclimatic models should be tested against these phytogeographic patterns

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

late paleozoic tropical climate response to gondwanan deglaciation coupled climate biome model simulations of the late paleozoic were developed to determine the response of pangean tropical climate to gondwanan deglaciation the model simulations predict substantial changes over equatorial pangea including continental drying a reversal of equatorial winds warming heavier 18 o values of meteoric precipitation and the expansion of deserts and the contraction of forests the magnitude of these tropical responses is sensi tive to the extent of gondwana continental ice and the deglacial rise in atmospheric pco 2 boundary conditions that are not well known for the late paleozoic nonetheless the model predictions are consistent with climatic and environmental trends determined from terrestrial proxy data implying that the deglaciation of gondwana was a transformational climate event in tropical pangea

venezuelan paleoflora of the pennsylvanian early permian paleobiogeographical relationships to central and western equatorial pangea abstract the flora of northwestern venezuela shows close links with the pennsylvanian flora of the northern hemisphere and northern africa in the early permian it also closely matches the flora reported in the southwestern and central united states the permian fossils from venezuela have various species and genera in common with that of this part of the usa not only flora but also warm water marine fauna the floristic data studied here provide evidence of a close relationship of the plants of the central portion of pangea with those of gondwanaland based on these similarities in the flora it is suggested that during the pennsylvanian early permian the northeastern part of gondwanaland which was one of the regions most affected by the formation of pangea had a progressively drier climate with the vegetation characteristic of such conditions moreover the relationship between the vegetation of this equatorial area and that of the cathaysian province during the early permian is discussed both showed the presence of gigantopterid genera although there were climatic differences furthermore the differences in the species of the group suggest that the two regions may have had quite different vegetation rather than the shared one traditionally proposed

extending the database of permian palaeo wildfire on gondwana charcoal remains from the rio do rasto formation parana basin middle permian rio grande do sul state brazil abstract macroscopic charcoal has been recovered from a bonebed from the barro alto outcrop middle permian guadalupian rio do rasto formation in the southernmost part of the parana basin brazil during this time a global biotic crisis was taking place and changes in the palaeofloristic composition can be observed records of palaeowildfires from the guadalupian period are scarce on a global scale in the parana basin low plant diversity compared to the entirety of gondwana persists and just a few plant bearing localities have so far been described from the northern part of the basin in the studied locality macroscopic charcoal could be detected in an outcropping bonebed and the occurrence of palaeo wildfires was confirmed besides representing the first palaeobotanical data for the guadalupian of the southern part of the parana basin the charcoal remains analyzed here are also a significant record of the local environmental conditions during the increase in aridity observed during the guadalupian and lopingian in gondwana this contributes to the understanding of regional changes that took place during this interval

numerical simulation of earthquake faults with gouge toward a comprehensive explanation for the heat flow paradox the particle based lattice solid model is used to simulate transform faults with and without fault gouge stick slip frictional behavior is observed in two dimensional numerical experiments of model faults both with and without gouge when no gouge is present the fault is strong and the heat generation and stress drops are correspondingly high in disaccord with observations surrounding the heat flow paradox in contrast when a gouge is specified the fault is weak and the heat generation as well as stress drops are low in quantitative agreement with observational constraints the heat flow is low on average and during short periods of aseismic creep seismic efficiencies are compatible with observationally based bounds counter intuitively the fault strength decreases as the intrinsic friction between particles is increased beyond a given threshold the mechanism for low fault strength and heat is rolling and jostling of fault gouge grains during slip this allows macroscopic movement of the fault with only minimal slip between surfaces of the gouge grains as this dynamical mechanism operates during seismic and aseismic slip it provides an explanation for the lack of a heat flow anomaly in both the seismic and creeping parts of the san andreas fault the simulation results provide the first comprehensive and quantitative possible explanation of the heat flow paradox and suggest that fault gouge plays a fundamental role on the dynamics of earthquake faults whether rolling and jostling of fault gouge particles provides the explanation for the heat flow paradox in nature remains to be validated by observation evidence

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

simulation of the frictional stick slip instability a lattice solid model capable of simulating rock friction fracture and the associated seismic wave radiation is developed in order to study the origin of the stick slip instability that is responsible for earthquakes the model consists of a lattice of interacting particles in order to study the effect of surface roughness on the frictional behavior of elastic blocks being rubbed past one another the simplest possible particle interactions were specified corresponding to radially dependent elastic brittle bonds the model material can therefore be considered as round elastic grains with negligible friction between their surfaces although breaking of the bonds can occur fracturing energy is not considered stick slip behavior is observed in a numerical experiment involving 2d blocks with rough surfaces being rubbed past one another at a constant rate slip is initiated when two interlocking asperities push past one another exciting a slip pulse the pulse fronts propagate with speeds ranging from the rayleigh wave speed up to a value between the shear and compressional wave speeds in agreement with field observations and theoretical analyses of mode ii rupture slip rates are comparable to seismic rates in the initial part of one slip pulse whose front propagates at the rayleigh wave speed however the slip rate is an order of magnitude higher in the main part of pulses possibly because of the simplified model description that neglected intrinsic friction and the high rates at which the blocks were driven or alternatively uncertainty in slip rates obtained through the inversion of seismograms particle trajectories during slip have motions normal to the fault indicating that the fault surfaces jump apart during the passage of the slip pulse normal motion is expected as the asperities on the two surfaces ride over one another the form of the particle trajectories is similar to those observed in stick slip experiments involving foam rubber blocks bruneet al 1993 additional work is required to determine whether the slip pulses relate to the interface waves proposed by brune and co workers to explain the heat flow paradox and whether they are capable of inducing a significant local reduction in the normal stress it is hoped that the progressive development of the lattice solid model will lead to realistic simulations of earthquake dynamics and ultimately provide clues as to whether or not earthquakes are predictable

phanerozoic atmospheric oxygen new results using the geocarbsulf model modifications of the geocarbsulf model for phanerozoic atmospheric oxygen have been made to account for new carbon isotopic data reconsideration of the fractionation of carbon isotopes between carbonate and organic matter deposited in sediments and different rates of weathering of volcanic rocks versus granitic rocks results indicate distinctly higher o2 values than geocarbsulf for the mesozoic and cenozoic lack of an appreciable drop in o2 below 15 percent at any time and a small late cenozoic decline of o2 to the present

numerical simulation of progressive rock failure and associated seismicity in this paper a numerical approach to modeling progressive failure leading to collapse in rock and associated seismicity is reported in the first part a newly developed numerical code rfpaz rock failure process analysis is introduced the program allows modeling of the observed evolution of damage and associated seismic events due to progressive failure leading to collapse in brittle rock there are three features distinguishing the approach from conventional numerical methods such as fem 1 by introducing heterogeneity of rock parameters into the model rfpaz can simulate non linear behavior in rock using a linear method 2 by introducing elastic modulus reduction for failed elements rfpa2d can process discontinuum mechanics problems by a continuum mechanics method and 3 by recording the event rate of failed elements the seismicities associated with the progressive failure in rock can be simulated in the second part of the paper the applications of rfpa2d in simulating geological process and in solving mining design problems are illustrated numerical simulation of a fault initiation process indicates that some of the important phenomena such as coalescence of microfracture the nucleation and growth of crack clusters fault initiation and development elastic rebound dilatation uplift and seismic behavior etc can be simulated with this numerical code the simulation of progressive failure leading to collapse in underground openings demonstrates the capacity of this code in solving mining design problems