crustal structure and nature of emplacement of the 85 e ridge in the mahanadi offshore based on constrained potential field modeling implications for intraplate plume emplaced volcanism abstract an integrated interpretation of multi channel seismic reflection gravity and magnetic datasets belonging to northern most part of the 85 e ridge in the mahanadi offshore is carried out to study the crustal structure and mode of its emplacement the basement structure map of the ridge reveals that it is 130 150 km wide and is composed of an eastern high which appears as a continuous broad and smooth topographyand the western high characterized by several steep isolated highs the seismic velocities reported for the first time over the ridge indicate several sedimentary sequences ranging in velocities between 1 6 and 4 0 km s above the acoustic basement top the salient aspects of the sedimentary velocities are a low velocity layer 2 6 3 2 km s within the cretaceous sequence in the intervening depressions encompassing the flank region and a regionally widespread higher velocity layer 3 5 3 8 km s belonging to the eocene oligocene section overlying the ridge a layer having a velocity of 4 2 4 7 km s probably made of volcanoclastic rocks is observed immediately below the acoustic basement the sediment isopach maps presented here for three major horizons are used to compute the 3 d sediment gravity effect to obtain a crustal bouguer anomaly map of the region detailed analysis of the gravity and magnetic anomaly maps clearly demonstrates the continuity of ridge up to the mahanadi coast at chilka lake seismically constrained gravity and magnetic models indicate that the ridge is composed of volcanic material that was emplaced on continental crust in the shelf slope areas and over the oceanic crust in the deep offshore areas the modeled crustal structure below the ridge further indicates volcanic emplacement of the ridge on a relatively younger lithosphere we propose two alternative models for the emplacement of the ridge

climate warming in the latest permian and the permian triassic mass extinction high resolution oxygen isotope records document the timing and magnitude of global warming across the permian triassic p tr boundary oxygen isotope ratios measured on phosphate bound oxygen in conodont apatite from the meishan and shangsi sections south china decrease by 2 in the latest permian translating into low latitude surface water warming of 8 c the oxygen isotope shift coincides with the negative shift in carbon isotope ratios of carbonates suggesting that the addition of isotopically light carbon to the ocean atmosphere system by siberian traps volcanism and related processes resulted in higher greenhouse gas levels and global warming the major temperature rise started immediately before the main extinction phase with maximum and harmful temperatures documented in the latest permian meishan bed 27 the coincidence of climate warming and the main pulse of extinction suggest that global warming was one of the causes of the collapse of the marine and terrestrial ecosystems in addition very warm climate conditions in the early triassic may have played a major role in the delayed recovery in the aftermath of the permian triassic crisis

new somali basin magnetic anomalies and a plate model for the early indian ocean abstract the oldest portions of the indian ocean formed via the breakup of gondwana and the subsequent fragmentation of east gondwana we present a constrained plate model for this early indian ocean development for the time period from gondwana breakup until the start of the cretaceous normal superchron the motions of the east gondwana terranes are determined using new geophysical observations in the somali basin and existing geophysical interpretations from other coeval indian ocean basins within the somali basin recent satellite gravity data clearly resolve traces of an east west trending extinct spreading ridge and north south oriented fracture zones a thorough compilation of somali basin ship track magnetic data allows us to interpret magnetic anomalies m24bn through m0r about this extinct ridge our magnetic interpretations from the somali basin are similar in age spreading rate and spreading directions to magnetic anomalies previously interpreted in the neighboring mozambique basin and riiser larsen sea the similarity between the two magnetic anomaly datasets allows us to match both basin s older magnetic anomaly picks by defining a pole of rotation for a single and cohesive east gondwana plate however following magnetic anomaly m15n we find it is no longer possible to match magnetic picks from both basins and maintain plausible plate motions in order to match the post m15n geophysical data we are forced to model the motions of madagascar india and east antarctica australia as independent plates the requirement to utilize two independent plates after anomaly m15n provides strong circumstantial evidence that suggests east gondwana breakup began around 135 ma

structure and isostatic compensation of the comorin ridge north central indian ocean summary bathymetry gravity and magnetic data about 9200 lkm of the comorin ridge north central indian ocean were investigated using the transfer function and forward model techniques to understand the mode of isostatic compensation and origin of the ridge the ridge extends for about 500 km in nnw sse direction and associates with low amplitude gravity anomalies ranging from 25 to 30 mgal compared to the ridge relief suggesting that the anomalies are compensated at deeper depths from admittance analysis an airy model or local compensation with an elastic plate thickness t e of about 3 km and crust thickness t of 15 20 km are suggested for the southern part of the comorin ridge south of 5 n whereas for the northern part a flexural plate model with an elastic thickness of about 15 km is obtained admittance analysis together with the results from gravity forward modelling reveal that the south part was emplaced on relatively weak oceanic crust with both surface and subsurface loading while the north part was emplaced on the continental crust based on present studies and published plate kinematic models we interpret that the comorin ridge was evolved at about 90 ma during the rift stage of madagascar from the southwest of india we have also demarcated the continent ocean boundary cob west of sri lanka and southern tip of india which runs across the strike of the ridge placing the northern part of the ridge on continent and southern part on oceanic crust on the southern part of the ridge eastern flank is steep faulted up to 0 6 km and is controlled by the 79 e fz and then by cob

new aeromagnetic data from the western enderby basin and consequences for antarctic india break up 1 in order to enhance our understanding of the continental break up between east india and antarctica a japanese german aerogeophysical survey was conducted off eastern dronning maud land and western enderby land antarctica the systematic survey with a line spacing of 20 km provides strong constraints on the timing of the initial break up of india antarctica compared to the conjugate margin south of sri lanka while the continent ocean transition is very well marked by pronounced positive and negative magnetic anomalies no hints on the existence of magnetic spreading anomalies north of this zone has been found in the new data set thus in contrast to most recently published models the data only support kinematic models which include a final break up of sri lanka india from our investigated area some 90 118 ma within the cretaceous normal superchron

triassic foraminifers of the lampang group northern thailand abstract triassic foraminifers are recognized for the first time in limestones from four localities of the lampang group northern thailand tectonically assigned to the sukhothai subterrane sukhothai folded belt which is located between western the sibumasu shan thai terrane and eastern indochina four foraminiferal associations are distinguished 1 glomospirella lampangensis n sp 2 pilammina densa 3 endothyroid foraminifers diplotremina astrofimbriata and 4 aulotortus sinuosus microfaunas based on comparison with the coeval european faunas they are thought to be 1 early triassic 2 anisian 3 ladinian and 4 carnian in age important taxa of these associations are common to those of south china and southeast asia most of them are closely similar to those of europe and show a remarkable contrast with those of middle and late permian foraminiferal assemblages having many provincial and endemic characters glomospirella lampangensis n sp is herein systematically described among the distinguished 41 species

griesbachian earliest triassic palaeoenvironmental changes in the salt range pakistan and southeast china and their bearing on the permo triassic mass extinction abstract facies and faunal analysis from pakistan and china show that the permo triassic mass extinction of marine invertebrate faunas was associated with a spectacularly rapid griesbachian transgression which lead to the widespread establishment of deep water anoxic and dysoxic conditions the extinction event was thus caused by habitat loss due to the extensive development of inhospitable conditions the initial griesbachian transgression in pakistan produced extensive shallow normal marine conditions in which permian holdover taxa were able to survive until the development of dysaerobic facies in the late griesbachian the exceptionally complete sections of china show a three phased deepening and extinction event beginning in the latest permia by the late griesbachian a variety of dysaerobic and anaerobic facies were developed in all the regions studied several of these contain evidence for minimal sulphate reducing activity suggesting that marine productivity and thus organic matter flux to the sediments was very low in early triassic seas

breakup and early seafloor spreading between india and antarctica summary we present a tectonic interpretation of the breakup and early seafloor spreading between india and antarctica based on improved coverage of potential field and seismic data off the east antarctic margin between the gunnerus ridge and the bruce rise we have identified a series of ene trending mesozoic magnetic anomalies from chron m9o 130 2 ma to m2o 124 1 ma in the enderby basin and m9o to m4o 126 7 ma in the princess elizabeth trough and davis sea basin indicating that india antarctica and india australia breakups were roughly contemporaneous we present evidence for an abandoned spreading centre south of the elan bank microcontinent the estimated timing of its extinction corresponds to the early surface expression of the kerguelen plume at the southern kerguelen plateau around 120 ma we observe an increase in spreading rate from west to east between chron m9 and m4 38 54 mm yr 1 along the antarctic margin and suggest the tectono magmatic segmentation of oceanic crust has been influenced by inherited crustal structure the kinematics of gondwanaland breakup and the proximity to the kerguelen hotspot a high amplitude e w oriented magnetic lineation named the mac robertson coast anomaly mca coinciding with a landwards step down in basement observed in seismic reflection data is tentatively interpreted as the boundary between continental transitional zone and oceanic crust the exposure of lower crustal rocks along the coast suggests that this margin formed in a metamorphic core complex extension mode with a high strength ratio between upper and lower crust which typically occurs above anomalously hot mantle together with the existence of the mca zone this observation suggests that a mantle temperature anomaly predated the early surface outpouring steady state magmatic production of the kerguelen lip an alternative model suggests that the northward ridge jump was limited to the elan bank region whereas seafloor spreading continued in the west enderby basin and its sri lankan conjugate margin in this case the mca magnetic anomaly could be interpreted as the southern arm of a ridge propagator that stopped around 120 ma

composition and structure of microbialite ecosystems following the end permian mass extinction in south china after the end permian mass extinction microbialites were widespread in the shallow marine environments in south china diverse microbialites are characteristic of the early triassic carbonate sequences their stratigraphic range is rather short just across the permian triassic p tr boundary and defined by conodonts n meishanensis h changxingensis and h parvus zones thus the p tr microbialites grew immediately after the first episode of the end permian mass extinction coinciding with the beginning of the conodont n meishanensis zone and ceased their growth at the beginning of the conodont i staeschei zone which occurred just before the second episode of the end permian crisis at meishan they include three main types stromatolites thrombolites and dendrites in south china the presence of abundant microbial remains of coccoid type and renalcis like microbes strengthens the previous view that the p tr microbialites are biogenic both cyanobacteria and other microbes have participated to construct the microbial ecosystems the thrombolite communities are dominated by the renalcis like microbes and foraminifers and also contain ostracods microgastropods and microconchids the stromatolite communities are dominated by coccoidal microbes with minor constituents of other undetermined microbes metazoans are rare the dendrolite assemblage contains few identifiable microfossils most of microbialite communities have a high abundance low diversity community structure characteristic of marine communities after the end permian mass extinction some metazoans of either opportunists or disaster forms dwelled in this special ecosystem the microbialite builders formed the primary producer communities and constructed the lowest level ecosystem structure the lower level ecosystem proliferated due to the collapse of the higher level of ecosystem structure characterized by benthic shelly and predator communities in the end permian crisis

estimation of the backscatter vertical profile of a pine forest using single baseline p band pol insar data the vertical backscatter profile of a pine forest constituted by stands of different height is inverted from a single baseline p band pol insar data in order to identify scatterers in the canopy the proposed approach uses the gaussian vertical backscatter profile model which associates an interferometric coherence expression to a vertical scatterers distribution characterized by relative standard deviation and elevation the methodology which uses in situ measurements of forest height and unbiased ground level estimation is applied to hv and vv channels providing accuracy given sufficiently low ground to canopy power ratios inverted backscatter profiles show maximum power converging toward the basis of the tree crown on highest forests where the largest branches are located indicating the high sensitivity of p band measurements to the forest structure and to the vertical biomass distribution over lower stands with larger tree densities the power peak is located in the upper part of the canopy which can be explained by a stronger attenuation in the canopy

transform marginal plateaus abstract numerous submarine plateaus form highstanding bathymetric highs at continent to ocean transitions due to their proximity to continents they have been frequently labelled marginal plateaus although this term has not been clearly defined or associated with a specific geology or geodynamic process until now these elevations have been interpreted as submerged thinned continental fragments detached from continents basaltic buildups formed by hotspots volcanic margins or oceanic plateaus many of these plateaus formed at transform margins connecting oceanic basins of contrasted ages we propose for the first time to define and review a class of marginal plateaus related to a specific tectonic setting transform marginal plateaus tmps based on a compilation of 20 tmps around the world we show that most of them have a polyphased history and have undergone at least one major volcanic phase our review highlights in particular a hitherto unrecognized close link between hotspots volcanic activity and transform margins we also propose that due to their polyphased history tmps may contain several successive basins and overlooked long lived sedimentary archives we finally highlight that because these tmps were transform plate boundaries perpendicular or oblique to surrounding rifts many of them were close to last contact points during final continental breakup and may have formed land bridges or bathymetric highs between continents therefore we discuss broader scientific issues such as the interest of tmps in recording and studying the onset and variations of oceanic currents or past biodiversity growth bio connectivity and lineage evolution

the tectonic origin of the bay of bengal and bangladesh we are able to decipher the tectonic evolution of the bay of bengal a puzzle which has not been satisfactorily solved in the past and we are also able to shed new light on origin of the buried 85 e ridge we do so by incorporating a number of disparate items into a unified solution these items are the marine magnetic anomalies in the western basin of the bay of bengal the rajmahal and sylhet traps and deep seismic sounding lines in india a prominent magnetic anomaly doublet and seismic seaward dipping reflectors in bangladesh and a new precise gravity map of the bay of bengal we identify seafloor spreading magnetic anomalies ranging in age from 132 ma m12n to 120 ma m0 in the western basin these anomalies are one sided the conjugate anomalies lie in the western enderby basin off east antarctica the direction of spreading was approximately nw se and the half spreading rates varied from 2 5 to 4 0 cm yr with the arrival of the kerguelen plume around m0 time seafloor spreading was reorganized and a new spreading axis opened at or close to the line joining the rajmahal and sylhet traps the prominent magnetic anomaly doublet connecting the rajmahal and sylhet traps indicates that these traps are not individual eruptions at about 118 ma but rather together define the new line of opening spreading started at this line and subsequently india changed direction from west to north the new oceanic crust thus generated underlies bangladesh and the eastern basin of the bay of bengal and is younger than 118 ma the western boundary of the new ocean floor is a transform fault which was generated by the spreading axis jump this transform fault appears as the 85 e ridge and further north on land as a negative free air gravity anomaly strip a unique feature of the northern boundary of the new oceanic crust is that due to the later deposition of enormous sediments derived from the himalayan orogeny it lies onshore bangladesh in contrast to most continent ocean boundaries in the world which lie offshore

advanced insights into magmatism and volcanism of the mozambique ridge and mozambique basin in the view of new potential field data summary a new plate tectonic model is presented which describes the emplacement of the mozambique ridge off southeast africa as the result of long lasting volcanic activity 140 122 ma during the initial opening between africa and antarctica thus an oceanic origin for the mozambique ridge is proposed this model is based on a new and systematic high resolution magnetic anomaly data set acquired across the mozambique ridge and throughout the mozambique basin data from the mozambique basin allow the identification of mesozoic magnetic anomalies from m0r to m26 124 61 155 3 ma with previously unmatched accuracy small scale fracture zones are recognized by offsets of magnetic anomalies in the westernmost part of the basin additionally a bend in the major fracture zones f and e between m17r and m18n 142 84 144 04 ma and a recognized sinusoidal change in spreading direction with an amplitude of about 15 indicate that the basin experienced several small scale changes in spreading direction through time a maximum change in spreading direction to almost 0 at around m11n 135 69 ma is followed by a short lived increase in spreading half rate from 23 5 km ma 1 to about 27 5 km ma 1 in the time frame from m10r to m9n 134 30 132 83 ma we propose that this is related to the initial opening of the south atlantic ocean represented by the onset of seafloor spreading between the falkland plateau and africa in the conjugate georgia and natal basins across the mozambique ridge high amplitude magnetic anomalies at major structural boundaries suggest that the different plateaus of the ridge were formed at different times a simple 2 d gravity and magnetic model for the ridge supports the hypothesis of multiple volcanic episodes which formed the ridge though long lasting volcanic activity between about 140 and 122 ma together with new and verified rotation parameters from the mozambique basin and its conjugate the riiser larsen sea antarctica a series of plate tectonic reconstructions are presented which demonstrate when and how the different parts of the ridge evolved through time

a foraminiferal assemblage as a bioevent marker of the main ladinian transgressive stage in the betic cordillera southern spain abstract the betic cordillera comprises the mountain range in the southern iberian peninsula that extends from cadiz to alicante which displays typical features of alpine cordilleras the betic cordillera includes two large geological tectonic domains namely an external zone and an internal zone the external zone is essentially composed of epicontinental triassic rocks that consist of the buntsandstein muschelkalk and keuper facies the buntsandstein facies rarely occur in outcrops whereas the keuper stratigraphic successions are truncated the muschelkalk facies frequently displays complete successions that are very useful for interpreting the ladinian stage palaeogeography the muschelkalk facies consists of a lower carbonate member formed by three thick massive limestone beds with intervals of thin bedded marly limestone and an upper marly member with intercalation of distinct beds of limestones and marls where tempestites predominate the first member has been interpreted as a transgressive systems track in which subtidal and ramp deposits can be identified the second member is related to a highstand systems track and consists of marine platform and coastal deposits which correspond to a shallowing upward sequence we describe and interpret a distinct bioclastic limestone bed with high concentrations of involutinidae benthic foraminifers that has been found in the muschelkalk of several distant sections this unusual bed is just above the third bed of massive muschelkalk limestone and consists of a bioclastic wackestone packstone up to 8 cm thick with many involutinidae of ladinian age the most abundant species are lamelliconus gr biconvexus ventroplanus lamelliconus cordevolicus and triadodiscus eomesozoicus these foraminiferal concentrations form a well defined marker bed that may be related to a bioevent the appearance of these foraminiferal taxa which are also very common in the triassic alpine realm coincides with the maximum flooding interval of a transgressive sequence we surmise that these tethyan foraminifers moved into newly developed coastal zones during maximum transgression and at times produced prolific shallow water communities which were reworked by storm currents that caused their unusual concentrations in deeper water these concentrations thus generated the marker beds of foraminiferal packstones that can be found over distant outcrops in the region similar involutinid foraminiferal assemblages occur in the upper muschelkalk of the iberian ranges and catalan coastal ranges as well as in the upper part of the transgressive systems track of the uaa 2 2 third order cycle identified in the muschelkalk of the pyrenees basin thus this foraminiferal assemblage can be considered as an extensive bioevent marker related to an important transgressive stage of ladinian age

seafloor spreading magnetic anomalies in the enderby basin east antarctica abstract the timing of the early separation of india from the contiguous antarctica australia is still an unresolved problem although it is well established that antarctica and india formed a single indo antarctic platform prior to the fragmentation of eastern gondwanaland inadequate age information either in the form of magnetic anomaly isochrons or dating of oceanic rocks from the conjugate margins of antarctica and india perhaps led several authors to propose incomplete plate reconstruction models particularly for the early separation of india from antarctica analysis of magnetic and satellite derived gravity data in the enderby basin east antarctica reveals the presence of seafloor spreading type linear magnetic anomalies and eight new fracture zones the observed magnetic anomalies can be interpreted as the younger sequence of mesozoic anomalies m11 m0 half spreading rates range from 6 5 to 2 8 cm yr and are comparable with those measured in the bay of bengal these similarities in the mesozoic magnetic anomaly sequence and in the spreading rates provide evidence that these two basins are conjugate and contemporary a consistent plate reconstruction model can be derived from the identified conjugate patterns of mesozoic magnetic anomalies and fracture zones the occurrence of the oldest magnetic anomaly m11 close to the coasts in these two offshore basins unequivocally suggests that the break up of india from antarctica occurred before 134 ma

mesozoic anomalies in the bay of bengal abstract the analysis of 8200 line km of total magnetic intensity data in the bay of bengal northeastern indian ocean revealed the presence of approximately n30 e trending seafloor spreading type magnetic anomalies these anomalies resemble the mesozoic anomaly series m11 m0 reported elsewhere the oldest anomaly m11 132 5 ma identified close to the east coast of india is followed by the younger series of mesozoic anomalies towards the offshore some of the anomalies are offset by 60 80 km the configuration of the offsets of the isochrons allowed us to propose approximately n120 e trending oceanic fracture zones the mesozoic crust of 132 5 118 ma is estimated to evolve with an average half spreading rate of 3 5 cm yr except for the ocean floor between the m9 and m4 magnetic isochrons this part of the crust appears to be affected by the buried subsurface 85 e ridge

a reassessment of paleogeographic reconstructions of eastern gondwana bringing geology back into the equation abstract in recent years several tectonic reconstructions have been presented for australia antarctica break up with each putting the australian plate in a different location with respect to antarctica these differences reflect the different datasets and techniques employed to create a particular reconstruction here we show that some of the more recent reconstructions proposed for australia antarctica break up are inconsistent with both our current knowledge of margin evolution as well as the inferred match in basement terranes on the two opposing conjugate margins we also show how these incorrect reconstructions influence the fit of the indian plate against antarctica if its movement is tied to the australian plate such errors can have a major influence on the tectonic models of other parts of the world in this case we show how the position of the australia plate can predetermine the extent of greater india which is rightly or wrongly used by many as a constraint in determining the timing of india asia or india island arc collisions during the closure of tethys we also discuss the timing of australia antarctica break up and which linear magnetic features are a product of symmetric sea floor spreading versus those linear magnetic features that result from rifting of a margin the 46 ma to 84 ma rotational poles previously proposed for australia antarctica break up and confined to transitional crust and the continent ocean transition zone more likely formed during earlier stages of rifting rather than during symmetric sea floor spreading of oceanic crust so rotation poles that have been derived from magnetic anomalies in such regions cannot be used as input in a plate reconstruction a new reconstruction of the australia antarctica margin is therefore proposed that remains faithful to the best available geological and geophysical data

controls on facies architecture of a large triassic carbonate platform the great bank of guizhou nanpanjiang basin south china abstract the great bank of guizhou gbg is an exceptionally well exposed isolated triassic platform in the nanpanjiang basin of south china the platform is exhumed with its depositional profile preserved and is dissected by a faulted syncline that exposes a complete and uncomplicated cross section providing a unique opportunity to evaluate mechanisms involved in its birth evolution and demise the gbg formed near the southern margin of the yangtze platform during a deepening event that expanded the nanpanjiang basin and drowned the region surrounding the gbg in the latest permian initial accumulation of the gbg began in the latest permian with small reef mounds and open marine skeletal packstones following the end permian extinction cyanobacterial boundstones grew over the bank top during the early triassic the gbg developed a low relief bank profile with mobile oolite shoals at the margin shallow subtidal and peritidal deposits in the interior and gentle slopes dominated by pelagics debris flow deposits and turbidites at the basin margin in the middle triassic anisian the gbg developed a progressively steepening profile rimmed with massive tubiphytes reefs the platform was flat topped with tidal flat deposits across the interior basin margin deposition was dominated by turbidites and debris flow deposits but eventually shifted to avalanche and rock fall deposits as the slopes steepened to the angle of repose in the middle triassic ladinian an erosional escarpment up to 1700 m high developed at the margin platform margin strata are bedded packstones similar to interior strata whereas breccias at the basin margin contain coral boundstone clasts suggesting erosion of reefs from the escarpment a restricted subtidal lagoon formed in the interior producing an atoll like morphology later a flat topped profile was restored as tidal flats spread across the interior in the beginning of the late triassic deepening contributed to termination of the gbg before siliciclastic turbidites and shales were deposited over the platform in contrast with the well known platforms of the dolomites of northern italy the gbg contains abundant muddy carbonates and a progressively steepening bank to reef rimmed and escarpment architecture the italian platforms contain little mud and have angle of repose pinnacle geometries the gbg s larger size increased mud production and protected it from extensive winnowing of mud which in turn resulted in off bank shedding of muddy sediments that were stable on relatively gentle basin margin slopes which progressively steepened and ultimately led to avalanche deposits and a high relief erosional escarpment in contrast the lesser mud content of the dolomites platforms forced avalanche and talus deposition to dominate throughout deposition of basin margins which in turn produced their angle of repose geometries

derivation of paleolongitude from the geometric parametrization of apparent polar wander path implication for absolute plate motion reconstruction obtaining ancient longitude position of continents in the past has always been a challenge for plate tectonic reconstructions paleomagnetism has been commonly used to reconstruct paleolatitudes and relative rotations but not paleolongitudes in this work we present a synthesized method to derive paleolongitude by geometrically parametrizing apparent polar wander path apwp great and small circle modeling are implemented concurrently to the identified apwp tracks to calculate the paleomagnetic euler parameters stage rotation pole and rotation angle from the euler parameters of the optimal fitting option the absolute motion history can be restored for the reference geometries using our method as well as the results from relative plate motion studies we reevaluate the dispersion history of east gondwana since 140 ma to further test the validity of our method we compare the predictions from four other absolute motion models mainly in paleolatitude movement longitudinal variation and great circle distance which suggest the most similarity with the global hybrid reference frame

the breakup of east gondwana assimilating constraints from cretaceous ocean basins around india into a best fit tectonic model published models for the cretaceous sea oor spreading history of east gondwana result in unlikely tectonic scenarios for at least one of the plate boundaries involved and or violate particular constraints from at least one of the associated ocean basins we link east gondwana spreading corridors by integrating magnetic and gravity anomaly data from the enderby basin off east antarctica within a regional plate kinematic framework to identify a conjugate series of east west trending magnetic anomalies m4 to m0 126 7 120 4 ma the mid ocean ridge that separated greater india from australia antarctica propagated from north to south starting at 136ma northwest of australia and reached the southern tip of india at 126 ma sea oor spreading in the enderby basin was abandoned at 115 ma when a ridge jump transferred the elan bank and south kerguelen plateau to the antarctic plate our revised plate kinematic model helps resolve the problem of successive two way strike slip motion between madagascar and india seen in many previously published reconstructions and also suggests that sea oor spreading between them progressed from south to north from 94 to 84 ma this timing is essential for tectonic ow lines to match the curved fracture zones of the wharton and enderby basins as greater india gradually began to unzip from madagascar from 100 ma in our model the 85 east ridge and kerguelen fracture zone formed as conjugate anks of a leaky transform fault following the 100ma spreading reorganization our model also identi es the afanasy nikitin seamounts as products of the conrad rise hotspot

foraminiferal fauna recovered after the late permian extinctions in iberia and the westernmost tethys area abstract the mass extinction at the end of the permian has long been recognized as the greatest in the history of life foraminifers were common throughout the permian triassic p t interval and provide one of the best and certainly the most informative fossil records of the p t crisis this study addresses the recovery of foraminiferal faunas during the triassic after the late permian extinction in the western tethys and particularly in iberia through the analysis of evolution rates both at the species and genus level for the tethys area in general a rapid recovery of these faunas during the olenekian is reflected by high rates of appearance of new taxa along with the reappearance of many lazarus taxa these taxa became stabilized throughout the anisian and ladinian with a reduction in the rates of origination of new taxa and the presence of associations that were highly diversified comprising large numbers of species the first foraminifers in the triassic of iberia can be observed at two different levels the first of these is in the upper anisian while the second level corresponds to the upper ladinian longobardian lower carnian the triassic associations of the basins of iberia show paleobiogeographic characteristics that are generally tethyan most of these associations being well known for the alpine triassic for the ladinian some associations from ne iberia ne iberian basin catalonian basin and pyrenean basin also show germanic affinities finally also for the ladinian there is some evidence of the possible southward movement of faunas from the sephardic domain to the betic basin this point however requires further investigation with the exception of faunas associated with the reefs of the ladinian catalonian basin communities are usually of low diversity and typical of unstable shallow marine facies

seismic evidence of continental margin influence on the ninetyeast ridge in the bay of bengal the ninetyeast ridge ner one of the most enigmatic features in the indian ocean is covered by thick bengal fan sediment north of 9 n we present seismic reflection data on the eastern flank of the ner at 10 n that show the presence of 4 5 km thick sediments beneath the bengal fan sediments these sediments can be imaged up to 60 km beneath the andaman fore arc accretionary wedge suggesting that the decollement lies above these sediments the presence of thick sediments above the northernmost segment of the ner suggests that this segment was close to a continental margin during its emplacement we propose that these sediments were deposited soon after the breakup of india and antarctica between 130 and 100 ma and might act as source rocks for oil and gas generation beneath recent bengal fan sediments furthermore subducting thick sediments can significantly change the seismogenic behavior of the andaman subduction zone

recovery tempo and pattern of marine ecosystems after the end permian mass extinction high resolution sampling of more than 10 000 microfossils from seven late permian middle triassic paleoequatorial sections in south china refutes claims for a 5 m y recovery delay after the end permian mass extinction we show that level bottom seafloor diversity began to recover in the early smithian little more than 1 m y after the mass extinction while recovery of reef building metazoans began 4 m y later in the anisian a further mass extinction in the late smithian identified in the pelagic fossil record is weakly manifest as a temporary pause in diversification among benthic communities in the early triassic of south china the offshore diversity increase began before then in shallower settings the recovery from the end permian mass extinction in south china was therefore significantly more rapid and environmentally more complex than hitherto known

early triassic disaster and opportunistic foraminifers in south china survival and recovery are important dynamic processes of biotic evolution during major geological transitions disaster and opportunistic taxa are two significant groups that dominate the ecosystem in the aftermath of mass extinction events disaster taxa appear immediately after such crises whilst opportunists pre date the crisis but also bloom in the aftermath this paper documents three disaster foraminiferal species and seven opportunistic foraminiferal species from lower triassic successions of south china they are characterized by extreme high abundance and low diversity and occurred occasionally in griesbachian smithian and spathian strata the characteristics small size simple morphology and stratigraphic ranges of these groups suggest that r selection is a commonly used strategy for survivors to cope with either harsh post extinction conditions and or environments lacking incumbents

new continental margin magnetic anomalies of east antarctica over the past decade australian norwegian and russian marine surveys have collected integrated seismic gravity and magnetic data in the southern indian ocean the more than 350 000 line km of new airborne and marine magnetic observations for the east antarctic continental margin have been compiled into an improved definition of crustal magnetic anomaly patterns this compilation provides important new constraints on the breakup processes and igneous activity related to the formation of the passive margin of east antarctica the eastern sector of the map from bruce rise in the west to the d urville sea in the east is largely dominated by seafloor spreading magnetic anomalies the adelie rift block of highly stretched and extensively faulted continental crust is associated with a smooth anomaly fabric abrupt magnetic anomaly changes along the oceanic continent transition in the cooperation sea including the enderby basin anomaly extend for more than 1680 km from the kerguelen plateau towards the cosmonaut sea three sectors of the east antarctic continental margin exhibit pronounced disparities in the anomaly patterns that strongly suggest different modes of seafloor formation strong positive seafloor magnetic anomalies mark the southern margin of the kerguelen plateau the maud rise and adjacent areas in the riiser larsen sea the new compilation suggests that at least 300 km of the enderby basin and shackleton basin may be part of the cretaceous kerguelen volcanic province and possibly maps an abandoned fossil spreading center in the central enderby basin the majority of the published age models for the enderby basin and australian sector of the east antarctic margin are not in agreement with the structural grain of magnetic anomalies in the newly compiled map

the initial gondwana break up a synthesis based on new potential field data of the africa antarctica corridor abstract the initial opening of the africa antarctica corridor in the heart of gondwana is still enigmatic due to missing information on the origin of major crustal features and the exact timing of the onset of the first oceanic crust in the jurassic therefore in 2014 new ship borne magnetic data were systematically acquired in the northern mozambique basin and across beira high which we merged with all accessible magnetic data in the mozambique basin herein distinct magnetic lineations are observed which allow a refined identification of a whole set of jurassic magnetic spreading anomalies constraining the timing of the onset of oceanization beginning at m38n 2n 164 1 ma in combination with high resolution potential field data from the conjugate antarctic margin well expressed fracture zones can be traced throughout the africa antarctica corridor and allow the precise rotation of antarctica back to africa the initial fit depicts striking continuations of onshore tectonic features across the plate boundaries taking onshore aeromagnetic data of both margins into account within a tight gondwana fit the beira high can be restored along the major sinistral namama orvin shear zone of the east african antarctic orogen the beira high represents a continental block which was detached from antarctica by 157 ma at the latest simultaneously the antarctic plate cleared the area of the mcp however the crustal nature of the southern mcp remains ambiguous the northern natal valley and the mozambique ridge consist of thick oceanic crust being emplaced between m26r m18n 157 1 144 ma and m18n m6n 144 131 7 ma respectively about the half of this crust was won from the antarctic plate by a series of southwards directed ridge jumps to the northern boundary of the explora wedge a refined kinematic break up model constrained by the most extensive magnetic dataset is presented describing consistently the initial opening of the africa antarctica corridor and the somali basin

olenekian early triassic foraminifers of the gorny mangyshlak eastern precaucasus and western caucasus a new early triassic olenekian foraminiferal assemblage has recently been discovered in the gorny mangyshlak in the caspian sea region the triassic foraminiferal assemblages of the western caucasus and eastern precaucasus are similar to those present in the gorny mangyshlak widely distributed species of foraminifers conodonts and ammonoids occur in the lower triassic of all three of those regions therefore it is possible to correlate the olenekian foraminiferal assemblage of the gorny mangyshlak to the meandrospira pusilla assemblage in other parts of the world and to the global stratigraphic scale the olenekian foraminiferal assemblage of the gorny mangyshlak mainly consists of primitive attached foraminifers and diverse nodosariids such a foraminiferal assemblage usually indicates adverse paleoenvironmental conditions for benthic fauna the taxonomic composition of the olenekian foraminiferal assemblages from the gorny mangyshlak and caucasus regions allows us to conclude that these faunas are similar to the foraminiferal assemblages from the carpathians and balkans it is possible that the paleobasins of these regions had good connections and foraminifers migrated between these regions the late olenekian transgression provided conditions for the existence of different groups of macrofaunas and foraminifers to develop in these basins the late olenekian transgression allowed the biota from the caucasus paleobasin to move into the paleobasin of central asia mangyshlak similarities of the early triassic biotic assemblages of the caucasus and gorny mangyshlak to coeval strata in europe are demonstrated

geochemical evidence from bio apatite for multiple oceanic anoxic events during permian triassic transition and the link with end permian extinction and recovery abstract a detailed 20 myr redox history of permian to triassic oceans changhsingian to carnian stages has been constructed using ce anomaly ce and th u ratios from conodont albid crown apatite material the results show that the well established phenomenon of intense ocean anoxia coincident with the end permian mass extinction is faithfully recorded in conodont ce and th u data extending this conodont redox record shows that end permian anoxia persisted possibly into the earliest dienerian stage and that two intense oceanic anoxic events also occurred later in the early triassic earliest smithian earliest spathian and middle spathian followed by a weaker manifestation of anoxia in the anisian stage seen in ce data marine benthic radiation following the end permian mass extinction began after the smithian earliest spathian anoxic event suggesting a suppression of evolution prior to this due to these inimical conditions the failure of the middle spathian anoxic event to retard the evolutionary rebound implies shallow shelf seas remained well ventilated at this time even if the oceans did not other attributes of the early triassic record also closely coincide with redox fluctuations phases of anoxia intensification saw the proliferation of microbial carbonates and major negative carbon isotope swings that can be attributed to chemocline shallowing causing alkalinity pulses and enrichment in light remineralised carbon and or indicate a trigger meachnaims related to increased fluxes of light c from siberian volcanic sources

middle cretaceous geomagnetic field anomalies in the eastern indian ocean and their implication to the tectonic evolution of the bay of bengal abstract the middle cretaceous period is largely known for its stable normal polarity in the earth s magnetic field a few reversals isea m 3r m 2r and m 1r have been postulated during this period but are yet to be accepted in total recently two anomalies q1 92 ma and q2 108 ma have been identified globally and proposed as internal time markers useful to trace the evolution of the world oceans while the evolutionary history of the indian ocean from late cretaceous to present is well established the older middle to early cretaceous record is still ambiguous the occurrence of a major plate reorganization during the middle cretaceous period has added to the dilemma in understanding the early evolution of the eastern indian ocean the detailed evolution of the bay of bengal and its conjugate enderby basin has remained speculative to date due to various constraints such as lack of good geophysical dataset and drill sites and the presence of thick sedimentary load in the present study an attempt is made to validate the occurrence of the middle cretaceous internal time markers in the eastern indian ocean these time markers are used to provide additional constraints for tracing the evolution of the eastern indian ocean since late jurassic identification of these markers aided to confirm the timing of spreading ridge extinction in the perth basin as 102 ma in the bay of bengal these markers facilitated to infer the evolution of the middle cretaceous crust east of the buried 85 e ridge the age of the oceanic crust increases from south to 115 ma at the northern tip of the bay of bengal seafloor spreading occurred in nne ssw direction between 115 ma and 102 ma and thereafter it changed its direction to n s half spreading rates ranging from 4 0 to 4 2 cm yr between 108 ma and 84 ma in the bay of bengal are higher than its conjugate enderby basin this spreading system belongs to the second rifting episode between antarctica and india and was caused by the kerguelen mantle plume activity the 85 e ridge south of 12 n is emplaced on a transform fault that constitutes the northern extension of the 86 e fracture zone and active since 102 ma the study suggests that excess crustal accretion occurred on the indian plate since the middle cretaceous

reconstruction of early triassic ocean redox conditions based on framboidal pyrite from the nanpanjiang basin south china abstract widespread oceanic anoxia has been implicated as an important factor in the ptb permian triassic boundary mass extinction and the delayed recovery of early triassic marine ecosystems an investigation of framboidal pyrite in the bianyang section nanpanjiang basin south china suggests that euxinia dysoxia peaked during the induan late smithian to earliest spathian and late spathian these anoxic episodes show a relationship albeit imperfect to major episodes of climatic warming during the early triassic that were associated with intensified oceanic stratification reduced marine productivity and organic carbon sinking fluxes as well as diminished burial fluxes of organic carbon and reduced sulfur in contrast intervals of better oxygenated marine conditions were associated with episodes of relative climatic cooling during the early to middle smithian and mid spathian the degree of ventilation of the thermocline region in particular had a profound effect on marine biotas with intervals of improved ventilation resulting in increased global diversity among ammonoids and conodonts and increased local abundance of foraminifera in the nanpanjiang basin these observations suggest that oceanic redox fluctuations played an important role in the delayed recovery of early triassic marine ecosystems and specifically that episodic expansion of oceanic oxygen minimum zones omzs resulted in repeated setbacks to the recovery process a pattern that persisted until the late spathian

3 1 ga tuff from the sholl belt in the west pilbara further evidence for d diachronous volcanism in the pilbara craton of western australia abstract an age of 3112 6 2 ma determined by conventional techniques on single zircons from a felsic volcanic rock from the sholl belt in the western part of the archaean pilbara craton of western australia is interpreted as the age of felsic volcanism this is about 100 ma older than felsic volcanic rocks in the nearby but unconnected whim creek belt and is significantly younger than felsic volcanism in the east pilbara which took place during two distinct episodes at 3450 ma and 3300 ma the present results rule out previous correlations between the felsic volcanic rocks of the sholt belt and the 3452 16 ma old duffer formation in the east pilbara

terrestrial marine teleconnections in the collapse and rebuilding of early triassic marine ecosystems abstract the latest permian mass extinction lpe just prior to the permian triassic boundary at 252 ma resulted in the disappearance of 90 of skeletonized marine taxa and the replacement of the paleozoic fauna by the modern fauna in the immediate aftermath of the extinction shallow marine ecosystems were dominated by microbial communities and diminutive disaster taxa lilliput faunas and the post crisis period in general was characterized by high abundance low diversity marine communities occupying a reduced ecological space the recovery of marine ecosystems was a protracted process lasting throughout the 5 myr long early triassic some clades failed to recover and subsequently went extinct dead clades walking while others recovered only to suffer secondary crises during the early triassic profound environmental changes accompanied these biotic developments deep oceans experienced sustained hypoxia or anoxia for at least several million years following the boundary event anoxia was also widespread in shallow marine areas especially at the time of the lpe but it was more episodic and abated more rapidly than in the deep ocean making it an unlikely factor in the delayed recovery of early triassic marine ecosystems the development of anoxia was due at least in part to a sharp temperature rise following the lpe but may have been stimulated by changes in marine nutrient inventories and productivity rates as well these conditions may have been the result of a concurrent increase in subaerial weathering rates that was sustained into the early triassic in addition to increasing nutrient fluxes to marine areas rapid weathering caused a massive influx of sediment to shallow marine systems subjecting marine biotas to siltation stress this scenario implies close teleconnections between terrestrial and marine environments during the permian triassic boundary crisis with perturbations of the terrestrial realm contributing to the marine crisis

early cretaceous fracture zones in the bay of bengal and their tectonic implications constraints from multi channel seismic reflection and potential field data abstract due to the lack of clearly discernible magnetic anomaly identifications and fracture zones in the bay of bengal bob the early cretaceous plate reconstruction history of eastern gondwanaland remains an unresolved issue with regard to the separation of the east coast of india from the conjugate enderby basin of antarctica based on the correlation of oceanic basement information obtained from a vast amount of deep reflection seismic data we identified 16 nw se trending fracture zones fz1 fz16 in the bob region the trends of these fracture zones at the ecmi indicate two distinctly different sets one set in the direction n25 w to n35 w in the southern part fz1 fz7 and the other set in n50 w fz8 fz15 direction along the northern part these two sets of fracture zones further support the earlier inferences about the segmented nature of the ecmi into southern sheared oblique rifted margin and the northern normal rifted margin while the southern part of the ecmi had formed under slow asymmetric spreading and mixed transform setting with its conjugate western enderby basin the northern part of the ecmi formed after the breakup of the elan bank from india at m2 considering this scenario we infer the presence of late mesozoic younger to m4 anomalies along the ecmi and the subdued nature of magnetic anomalies in the western bob can be explained by the obliquity of fracture zones with respect to the coast as observed in many marginal smooth zones of the world oceans the disposition of the 85 e ridge with respect to the pre evolved bob crust and early cretaceous volcanic episodes in the region together indicate an emplacement of the ridge from 105 ma onwards as a result of a hotspot source related to the kerguelen super plume during its intense eruption activity

unusual intraclastic limestones in lower triassic carbonates and their bearing on the aftermath of the end permian mass extinction flat pebble conglomerates were a common carbonate facies in cambrian to early ordovician open marine settings but they become extremely rare in these environments after this time however the early triassic witnessed an anachronistic reappearance of flat pebbles together with other intraclast types in a range of carbonate depositional settings in south china flat pebble conglomerates are encountered in storm dominated platform carbonates to deep basinal settings while prefossilized bivalve intraclasts and flat pebbles are common in mid ramp facies of northern italy the emplacement mechanisms of the intraclast bearing beds appear to have been diverse and to have included basinal turbidity flows and storm generated hyperconcentrated flows true storm beds deposited under combined flow conditions are rare the cause of the widespread early lithification implied by the early triassic intraclasts appears to have been twofold suppression of bioturbation allowing the preservation of thin beds and rapid submarine lithification both features appear to be a response to the widespread development of benthic dysoxia anoxia during and following the end permian mass extinction this event appears to have temporarily recreated the conditions that pertained in cambro ordovician shelf seas flat pebble conglomerates may therefore constitute a proxy indicator of stressed environmental conditions associated with global anoxic dysoxic events

evolutionary dynamics of the permian triassic foraminifer size evidence for lilliput effect in the end permian mass extinction and its aftermath abstract there is growing evidence of the lilliput effect in the end permian mass extinction and its aftermath however very little has been published on assessing the lilliput effect on protozoans in the early triassic based on quantitative analysis of a great quantity of samples from outcrop sections this study investigates foraminiferal test size variations through the changhsingian to the olenekian based on fossil records from three outcrop sections in south china the sharp reduction in foraminifer sizes coincides with the first or main episode of the end permian mass extinction foraminifers remained small in sizes in the early induan their body sizes increased slowly in the late induan to olenekian but never recovered to the pre extinction test size levels the lilliput effect on foraminifera in the aftermath of the end permian crisis is indicated by the extinction of large taxa decrease in size for surviving taxa and rise of small sized new forms physiological reactions of various foraminifer groups reveal that several defaunation events such as anoxia ocean acidification and global warming that prevailed through the permian triassic interval may be responsible for both the end permian crisis and the lilliput effect

the evolution of the geothermal gradient from lambert graben and mahanadi basin a contribution to the indo antarctic rift debate abstract the east antarctic lambert graben and the indian mahanadi basin are considered to represent segments of an intra gondwanan rift structure that was active at least since the paleozoic fission track analyses of apatites from a comprehensive data set across the shoulders of both grabens were used to compare their low temperature history and to estimate the paleo geothermal gradients before the onset of the last denudation rifting stage late jurassic the paleo geothermal gradients of both juxtaposed gondwana margins similarly increase from the basement towards the respective rift shoulder from 15 20 ckm 1 to 25 30 ckm 1 this trend of increasing paleo geothermal gradients together with a denudation episode commencing in the early cretaceous and coeval igneous activity indicates a common rifting stage accompanying the breakup of gondwana in the india antarctica sector

air and shipborne magnetic surveys of the antarctic into the 21st century the antarctic geomagnetics community remains very active in crustal anomaly mapping more than 1 5 million line km of new air and shipborne data have been acquired over the past decade by the international community in antarctica these new data together with surveys that previously were not in the public domain significantly upgrade the admap compilation aeromagnetic flights over east antarctica have been concentrated in the transantarctic mountains the prince charles mountains lambert glacier area and western dronning maud land dml coats land additionally surveys were conducted over lake vostok and the western part of marie byrd land by the us support office for aerogeophysical research projects and over the amundsen sea embayment during the austral summer of 2004 2005 by a collaborative us uk aerogeophysical campaign new aeromagnetic data over the gamburtsev subglacial mountains 120 000 line km acquired within the ipy antarctica s gamburtsev province project reveal fundamental geologic features beneath the east antarctic ice sheet critical to understanding precambrian continental growth processes roughly 100 000 line km of magnetic data obtained within the international collaboration for exploration of the cryosphere through aerogeophysical profiling promises to shed light on subglacial lithology and identify crustal boundaries for the central antarctic plate since the 1996 97 season the alfred wegener institute has collected 90 000 km of aeromagnetic data along a 1200 km long segment of the east antarctic coast over western dml recent cruises by australian german japanese russian british and american researchers have contributed to long standing studies of the antarctic continental margin along the continental margin of east antarctica west of maud rise to the george v coast of victoria land the russian polar marine geological research expedition and geoscience australia obtained 80 000 and 20 000 line km respectively of integrated seismic gravity and magnetic data additionally us expeditions collected 128 000 line km of shipborne magnetic data in the ross sea sector

triassic stratigraphy facies and evolution of the arabian shelf in the northern united arab emirates this study provides a reconstruction of the late permian and triassic depositional history of the arabian shelf in the northern united arab emirates based on facies analysis and foraminiferal biostratigraphy the presented data show that sedimentation occurred in three major sequences from the late permian to olenekian carbonates and evaporites were deposited in restricted lagoons and tidal flats after a hiatus sedimentation resumed and continued until the late ladinian carnian leading to the deposition of a carbonate platform dominated by peritidal dolostones a period of shelf exposure and erosion spanning from the carnian to norian was followed by the third major sequence with sedimentation into the early jurassic during this third depositional sequence sedimentation changed from pure carbonate into mixed carbonate siliciclastic deposits this transition reflects the global regression of the sea in the late triassic triasina hantkeni zone and the increased erosion of large parts of the arabian hinterland a comparison of the evolution of the arabian shelf in the study area with chronostratigraphic reference schemes for the arabian plate reveals remarkable differences in the distribution of middle and upper triassic sequences these are most likely the result of poor biostratigraphic control on previously studied formations in the region

signals of barremian 116 ma or younger oceanic crust beneath the bay of bengal along 14 n latitude between 81 e and 93 e abstract the magnetic profile along 14 n in the bay of bengal collected on board r v samudra manthan of the geological survey of india was processed in the frequency domain from the energy spectrum the computed average thickness of sediment cover comes to 6 km and the average geothermal gradient to 20 c km analysis of the vertical magnetic structure by a singular point method yields a pseudosection marked by four clear domains the eighty five east ridge appears as a pair of strong magnetic features between 84 e and 86 e whereas the ninety east ridge shows up as a narrow well defined vertical magnetic feature at 92 e by match filtering technique we extracted a magnetic profile of the basement which displays a number of polarity reversals the reversals between 81 e and 84 e appear to be records of barremian or younger seafloor spreading instead of m series reversals between 132 and 119 ma this is based on the fact that neither the basic lavas nor the marine sediments so far obtained from the basin margin are older than barremian 116 ma given the uncertainty in apwp of the indian landmass between 200 and 117 ma the rajmahal hot spot might have powered the rifting of india from antartica from 117 ma onwards initiation of rifting at 132 ma as reconstructed by earlier workers is not proved

the jurassic history of the africa antarctica corridor new constraints from magnetic data on the conjugate continental margins abstract finding the best fit for east and west gondwana requires a detailed knowledge of the initial jurassic movements between africa and antarctica this study presents results of systematic and densely spaced aeromagnetic measurements which have been conducted in 2009 2010 across the astrid ridge antarctica and in the western riiser larsen sea to provide constraints for the early seafloor spreading history between both continents the data reveal different magnetic signatures of the northern and southern parts of the astrid ridge which are separated by the astrid fracture zone the southern part is weakly magnetised corresponding to the low amplitude anomaly field of the southwestern riiser larsen sea in contrast the northern astrid ridge bears strong anomalies of positive value furthermore several sets of trends are visible in the data in the mozambique channel we extended the existing magnetic spreading anomaly identifications combined with the spreading anomalies in the conjugate riiser larsen sea they were used to establish a new model of the relative movements of africa and antarctica after the breakup of gondwana in jurassic times a detailed model for the emplacement of the mozambique ridge is now incorporated the model postulates a tight fit between africa and antarctica and two stages of breakup the first of which lasting until 159 ma m33n during this stage antarctica rotated anticlockwise with respect to africa the grunehogna craton cleared the coastal plains of mozambique to a position east of the mozambique fracture zone the southern astrid ridge is interpreted to consist of oceanic crust also formed during this first stage prior to the riiser larsen sea during the second stage antarctica moved southward with respect to africa forming the mozambique basin and the conjugate riiser larsen sea the mozambique ridge and the northern natal valley were formed at different spreading centres being active subsequently

two pulses of extinction during the permian triassic crisis over 90 of marine species were lost during the end permian extinction fossil data show that the crisis in china was marked by two distinct phases of marine extinction separated by a 180 000 year recovery period

seafloor spreading magnetic anomalies south off sri lanka abstract results obtained from compilation and reinterpretation of about 21 200 line km of bathymetry magnetic and satellite gravity data between 10 s to 10 n latitudes and 75 to 90 e longitudes south off sri lanka are presented here magnetic data and the synthetic seafloor spreading model reveal the presence of mesozoic anomaly sequence m11 through m0 south of sri lanka the oldest magnetic anomaly m11 134 ma occurs between 110 and 140 km away from the sri lankan coast the seafloor created during the early cretaceous is estimated to have evolved with variable half spreading rates ranging from 5 5 to 1 53 cm yr the trends of the fracture zones inferred from the offsets in the magnetic anomalies have been constrained using the satellite gravity mosaic the cretaceous magnetic quiet zone cmqz 121 84 ma crust between the isochrons m0 and a34 has an unequal width and widens from about 170 km in the west 80 e longitude to about 500 km towards east 85 e longitude plate reconstruction models for 160 fit 134 m11 121 m0 and 84 ma a34 are generated under the constraints of newly identified magnetic anomaly isochrons and fracture zones the mismatch in the a34 reconstruction is attributed to the emplacement of the ob lena and marion dufresne seamounts at the spreading ridge axis and or the frequent ridge jumps in the middle cretaceous during the major plate reorganization

diagenesis and its impact on the reservoir quality of miocene sandstones surma group from the bengal basin bangladesh abstract rapid supply and deposition of 1000 s of meters of miocene and pliocene sediment tend to lead to a different set of controls on reservoir quality than older more slowly buried sandstones here we have studied miocene fluvial deltaic bhuban formation sandstones from the surma group bengal basin buried to 3 000 m and 110 c using a combination of petrographic geochemical and petrophysical methods in order to understand the controls on miocene sandstone reservoir quality to facilitate improved prediction of porosity and permeability the main conclusions of the study are that mechanical compaction processes are the dominant control on porosity loss although early calcite growth has led to locally negligible porosity in some sandstones mechanical compaction occurred by grain rearrangement ductile grain compaction and brittle grain fracturing calcite cement occupying up to 41 intergranular volume was derived from a combination of dissolved and recrystallized bioclasts an influx of organic derived carbon dioxide and plagioclase alteration clay minerals present include smectite illite kaolinite and chlorite the smectitic clay was probably restricted to low energy depositional environments and it locally diminishes permeability disproportionate to the degree of porosity loss kaolinite is probably the result of feldspar alteration resulting from the influx of organic derived carbon dioxide quartz cement is present in small amounts despite the relatively high temperature due to a combination of limited time available in these young sandstones grain coating chlorite and low water saturations in these gas bearing reservoir sandstones reservoir quality can now be predicted by considering primary sediment supply and primary depositional environment the magnitude of the detrital bioclast fraction and the influx of organic derived carbon dioxide

geoid and gravity anomaly data of conjugate regions of bay of bengal and enderby basin new constraints on breakup and early spreading history between india and antarctica 1 timing of breakup of the indian continent from eastern gondwanaland and evolution of the lithosphere in the bay of bengal still remain as ambiguous issues geoid and free air gravity data of bay of bengal and enderby basin are integrated with shipborne geophysical data to investigate the early evolution of the eastern indian ocean geoid and gravity data of the bay of bengal reveal five n36 w fracture zones fzs and five isolated ne sw structural rises between the eastern continental margin of india ecmi and the 85 e ridge 86 e fz the fzs meet the 86 e fz at an angle of 39 the rises are associated with low gravity and geoid anomalies and are oriented nearly orthogonal to the fzs trend the geoid and gravity data of the western enderby basin reveal a major kerguelen fz and five n4 e fzs the fzs discretely converge to the kerguelen fz at an angle of 37 we interpret the fzs identified in bay of bengal and western enderby basin as conjugate fzs that trace the early cretaceous rifting of south ecmi from enderby land structural rises between the fzs of bay of bengal may either represent fossil ridge segments possibly have extinct during the early evolution of the bay of bengal lithosphere or may have formed later by the volcanic activity accreted the 85 e ridge two different gravity signatures short wavelength high amplitude negative gravity anomaly and relatively broader low amplitude negative gravity anomaly are observed on south and north segments of the ecmi respectively the location of continent ocean boundary cob is at relatively far distance 100 200 km from the coastline on north ecmi than that 50 100 km on the south segment on the basis of geoid gravity and seismic character and orientation of conjugate fzs in bay of bengal and western enderby basin we believe that transform motion occurred between south ecmi and enderby land at the time of breakup which might have facilitated the rifting process in the north between combined north ecmi elan bank and macrobertson land and in the south between southwest sri lanka and gunnerus ridge region of east antarctica approximately during the period between the anomalies m1 and m0 and soon after detachment of the elan bank from north ecmi the rifting process possibly had reorganized in order to establish the process along the entire eastern margins of india and sri lanka

aftermath of the permian triassic mass extinction event paleoecology of lower triassic carbonates in the western usa paleoecologic study of invertebrate faunas from three successive early triassic seaways reveals that biotic recovery from the end permian mass extinction event was slow and that full recovery did not occur until after the early triassic simple cosmopolitan opportunistic generalists and low diversity low complexity paleocommunities were characteristic of the entire early triassic in the western usa an increase in guild and taxonomic diversity was observed with the addition of several new higher taxa in the late early triassic spathian to the almost exclusively molluscan faunas of the earlier early triassic nammalian potential disaster forms the inarticulate brachiopod lingula and the paper pecten claraia dominated the earliest early triassic faunas griesbachian and even occurred in the late early triassic normal marine stromatolites comparison with data on faunas from the permian and triassic suggests that even the most diverse early triassic faunas in the spathian were rather low in guild diversity and species richness these characteristics of genera and paleocommunities in the early triassic may be typical of mass extinction aftermaths

triassic palaeogeography of tunisia abstract a stratigraphic palaeogeographic and palinspastic synthesis of the triassic successions in tunisia is herein documented from a sse nnn oriented profile saharan platform gulf of gabes offshore tunisian atlas tellian units across the northern boundary of the gondwana plate and the future south tethyan margin it is principally based on a reinvestigation of old data and on recent results particularly related to new lithostratigraphic subdivisions and palaeontologic datings obtained from assemblages of benthic foraminifera algae palynomorphs ammonites and brachiopods the various triassic successions of tunisia are compared at the scale of the formations and sequences in the most possible precise biochronologic framework the corresponding chart is used as reference to seven maps of the dominating depositional environments during the following time intervals induan olenekian anisian lower ladinian middle upper carnian norian lowermost part of rhaetian and uppermost part of rhaetian in a peri tethyan domain controlled both by eustasy and extensional tectonics the proposed maps show the alternation of regressions marked by fluvio deltaic siliciclastics and paralic sebkha type evaporites and transgressions marked by foraminifera bearing limestones dolomites of internal proximal platform sometimes open to pelagic influences the transgressions were particularly widespread during carnian and rhaetian times and probably came from a deeper trough situated towards ene during a first rifting phase the motion of normal crustal faults strongly inclined towards the north induced well marked differential subsidences in conclusion a new palinspastic reconstruction along a south north sse nnw oriented profile is proposed it shows a succession of shoals flanked by lateral steps such as the tebaga of medenine shoal sub basins atlas and tilted blocks hairech ichkeul heralding the structuring of the south tethyan margin during jurassic times