ophiolite emplacement by collision between the sula platform and the sulawesi island arc indonesia much of the tectonic complexity displayed in eastern indonesia results from a series of neogene collision events between island arcs continental fragments and the australian continent here we examine the emplacement of a large ophiolite belt resulting from the miocene collision between the sulawesi island arc and a continental fragment the sula platform we present the results of several marine geophysical expeditions to the sw molucca sea and the nw banda sea plus gravity and geology on the east arms of sulawesi the batui thrust separates the ophiolite from sedimentary rocks deformed along the leading edge of the sula platform we mapped this thrust eastward from sulawesi along the southern margin of the gorontalo basin the latter is floored by oceanic crust and its south edge is uplifted against the thrust thus the sulawesi ophiolite can be traced offshore to its origin as basement of the gorontalo basin the ophiolite is composed of harzburgite in the southeast arm and passes upward through a complex of gabbros and diabase dikes in the east arm ophiolite melange underlies the harzburgites on the southeast arm beneath low angle thrust contacts where seen our local observations show the melange to be composed of thrust packets of both serpentine and red shale matrix varieties the packets are several hundred meters thick and the melange where studied has a moderate north to northeast dipping foliation this orientation if regionally representative of the melange fabric is consistent with a significant northward component of movement of the lower plate probably the sula platform or its margin where the ophiolite is in contact with rocks of the central schist belt it dips under the schist but where it encounters melange or mesozoic or paleogene sedimentary rocks the ophiolite is thrust over them the tectonic overlap sequence from west to east is schist over ophiolite over older sediments or melange the ophiolite appears to have been emplaced by oblique convergence of the sula platform along the southern edge of the gorontalo basin we suggest that the gorontalo basin represents a forearc basin and the ophiolite is its basement analogous to a number of other forearc settings deformation of the ophiolite may have occurred in part on the seafloor prior to emplacement but we feel that much of the deformation occurred during emplacement the sulawesi ophiolite is only one of a number of ophiolites in the indonesian region each of which has a very different origin and tectonic history

high precision u pb geochronology and a new chronostratigraphy for the canadon asfalto basin chubut central patagonia implications for terrestrial faunal and floral evolution in jurassic abstract the fluvial lacustrine and tuffaceous sedimentary succession of the canadon asfalto continental basin exposed in the argentinean chubut province of central patagonia preserves an extraordinary record of jurassic fauna and flora that marks key events in the evolution of dinosauria early mammals and major south american plant groups however basin wide correlation of the fossiliferous units is complicated by fault displacements unconformities and repetitive lithofacies new u pb analyses of zircon ca tims method from five primary tuff beds interstratified with the lacustrine strata establish a new chronostratigraphic framework for the sedimentary and volcanic units of canadon asfalto basin constraining ca 33 m y of depositional history and biotic evolution that spans nearly all three epochs of the jurassic five major vertebrate and plant rich stratigraphic intervals have been identified and are being actively investigated that range in age from pliensbachian to kimmeridgian or younger our combined biostratigraphic and high precision geochronologic results indicate that the major faunal turnover of the sauropodomorph dinosaurs which led to the rise of the eusauropods took place in the early jurassic earlier than previously recognized similarly the first successful radiation of the ornithischian dinosaurs heterodontosaurids as well as the evolutionary diversifications of the araucarian conifers and the osmundaceous ferns all occurred before the end of the early jurassic the diverse palynofloral assemblage of the canadon calcareo formation that was once considered to be early cretaceous in age is now entirely constrained to the late jurassic

contribution of calcareous nannoplankton to carbonate deposition a new approach applied to the lower jurassic of central italy abstract the upper pliensbachian lower toarcian somma section central italy which displays alternation of limestone marl lithotypes was investigated for its calcareous nannofossil and caco3 contents in order to evaluate the contribution of calcareous phytoplankton to the carbonate fraction of rocks a new method was applied combining a recently developed technique for nannofossil absolute quantification and measurements of nannofossil size our study suggests that nannofossils did not produce the bulk of carbonate mud in the studied section although they contribute to different extents to the pelagic carbonate fraction the contribution of both coccoliths and mainly the incertae sedis schizosphaerella to the carbonate fraction was important only in periods of reduced accumulation rates and or during clay deposition the highest estimated carbonate production by nannofossils in the studied section is around 83 of the total carbonate content but in a sample containing only 12 8 wt caco3 the observed limestone marl alternations therefore result from cyclical export of carbonate mud from the shallow latium abruzzi carbonate platform to the umbria marche basin and only subordinately from changes in nannoplankton productivity

models of seismic anisotropy in the deep continental lithosphere seismological observations sks wave polarizations systematic p residual variations azimuthal dependence of pn and surface wave velocities or a dispersion of surface waves are not consistent with isotropic if laterally heterogeneous upper mantle structure therefore an anisotropy should be considered as an a priori aspect of future large scale studies of mantle structure most studies of anisotropy however have assumed horizontal or vertical axes of symmetry but such orientations cannot explain bipolar patterns of spatial variations of p residuals which we have observed at many seismological stations on the basis of the petrophysical properties of real upper mantle rocks we consider anisotropy formed either by hexagonal or by orthorhombic aggregates composed of olivine orthopyroxene and clinopyroxene rotations of the aggregates about vertical and horizontal axes allow us to find the three dimensional orientations of symmetry axes that fit combinations of both p and s seismological observations in central europe and in western north america the orientations with plunging symmetry axes velocity extremes seem to be consistent across large spatially uniform tectonic units and change abruptly at important suture zones

middle cretaceous calcareous nannofossil biogeography and preservation in the atlantic and indian oceans implications for paleoceanography abstract the quantitative study of calcareous nannofossil preservation and biogeographic distribution puts constraints on paleoceanographic models for the atlantic and indian oceans during the middle cretaceous we establish a dissolution ranking of middle cretaceous calcareous nannofossils based on susceptibility to dissolution a positive correlation of organic carbon content of the sediments and the relative abundance of watznaueria indicates that much of the carbonate dissolution was caused by the release of carbon dioxide during oxidation of organic matter the depth distribution of the most dissolution resistant species watznaueria barnesae shows relative abundance maxima at the deepest sites and a maximum where intermediate waters impinge on slopes this reflects stagnant oxygen poor bottom waters and possibly a mid water oxygen minimum zone with increased deposition and catabolic breakdown of organic matter factor analyses are performed on various data sets for three different time slices ranging in age from late aptian to early albian middle albian and late albian to cenomanian the resulting factors can be related to paleoceanographic conditions such as colder water at high latitudes high fertility upwelling conditions and neritic conditions for all three time intervals a wide tropical to subtropical zone was flanked by boreal and austral zones upwelling conditions probably existed along the north african margin and over the falkland plateau zonal upwelling is tentatively postulated for the northwestern and northeastern margin of the north atlantic in the middle albian and for the eastern margin of the north atlantic off western europe for the late albian to cenomanian we speculate on surface water current patterns location of upwelling regions and haline driven deep circulation for the middle cretaceous

tectonic role of ophiolite bearing terranes in the development of the southern apennines orogenic belt new data on ophiolite bearing terranes of the liguride complex together with some information on the terranes of the sicilide complex result in a better understanding of the role and tectonic significance of these units in the construction of the southern apennines orogenic belt the liguride complex is composed of two main tectonic units overlain by a thick turbiditic sequence of late oligocene middle miocene age the uppermost one frido unit is a polydeformed and polymetamorphosed sequence composed of two tectonic subunits of shales and calc schists respectively containing blocks of ophiolite garnet gneiss amphibolites and granitoids this unit is thrust over the un metamorphosed terranes calabro lucano flysch unit consisting of a broken formation with blocks of late jurassic ophiolite and their sedimentary cover cretaceous eocene pelagic sediments and late oligocene volcaniclastic deposits the frido unit underwent hp lt metamorphism p 8 10 kb t 400 500 c resulting in glaucophane and lawsonite assemblages in the ophiolitic rocks and aragonite in the meta limestones and calc schists followed by greenschist fades metamorphism p 4 kb t 300 350 c from a structural point of view units of the liguride complex comprise structures developed at different structural levels indicating progressive non coaxial deformation in response to tectonic transport towards the n ne the ophiolite bearing terranes of the liguride complex can be considered as a remnant of an accretionary complex in which the calabro lucano flysch unit represents the toe of the wedge where frontal accretion processes occur and the frido unit is a deeper portion emplacement of the frido unit is explained as being due to formation of a deep duplex structure during the early stage of continental collision processes the polarity of tectonic transport provides new evidence that the liguride complex represents a suture zone between the apulian and the calabrian blocks the age of collision appears to be not older than late oligocene the allochtonous terranes of the liguride and sicilide complexes therefore represent a complete accretionary wedge which records first subduction of the neotethys ocean beneath the calabrian europe continental margin and later continental collision with the african block

evolution of the san jorge basin argentina the san jorge basin although small is the most important hydrocarbon producing basin in argentina remaining untested potential is high because of the presence of good source rock favorable structural complexity and multiple reservoirs reservoir quality is commonly low because of the highly tuffaceous sandstones the sedimentary fill of the basin is closely related to its tectonic history northwest southeast trending grabens formed and filled during a triassic and early jurassic early rift phase climaxing with a pervasive middle jurassic volcanic episode continued growth and filling of the basin occurred during a late jurassic earliest cretaceous late rift phase and cretaceous early and late sag phases late cretaceous early tertiary extension set up many of the present day structural traps along normal faults middle tertiary andean compression produced the narrow north south san bernardo structural belt which exhibits reversed movement on older normal graben bounding faults and on local low angle thrust faults marked early to middle tertiary erosion produced a significant unconformi y within cretaceous beds around basin margins origin of upper jurassic and lowermost cretaceous sedimentary fill is primarily lacustrine or fluvial in origin lacustrine organic rich black shales are fringed by oolitic and other limestones and fluvial deltaic sandstones derived mostly from the north a significant southern source of sand existed during the valanginian interbedded marine shales occur mostly to the west toward a presumed marine seaway connection to the northern magallanes basin middle to upper cretaceous sedimentary rocks sourced mostly from the north are mainly fluvial sandstone shale successions with some minor lacustrine influence reservoir quality glauconitic sands were deposited during a late cretaceous early tertiary marine incursion from the atlantic after development of a lower tertiary regional unco formity relatively undisturbed younger tertiary sediments completed the basin fill lower cretaceous lacustrine shales of the d 129 formation are the best source rocks yet identified however most hydrocarbon production occurs above the source in middle and upper cretaceous sandstones along the basin flanks the most obvious hydrocarbon emplacement mechanism is vertical migration along reactivated graben faults

the emplacement of ophiolites by collision ophiolites recognized in most of the world s orogenic belts are generally interpreted to be oceanic crust and upper mantle lithosphere fragments that have been incorporated into continental margins at consuming plate boundaries we suggest that the mechanism for ophiolite emplacement is the same in both the alpine and andean type orogenes in both geological settings obduction of oceanic lithosphere onto the continental lithosphere is caused by the convergence of light buoyant bodies such as oceanic plateaus continental slivers island arcs or old hot spot traces for example the troodos ophiolite complex previously interpreted by some workers as resulting from continental collision may have been emplaced by the collision of cyprus with the eratosthenes plateau embedded in the oceanic eastern mediterranean crust on the other hand the upper jurassic coast range ophiolites of california previously interpreted as resulting from typical oceanic subduction may be the result of a continuous injection of thick nonsubductable packages of light continentally derived sedimentary rocks seamounts and plateaus into the subduction zones many other ophiolite complexes may be similarly related to accreted terranes

paleomagnetism of jurassic and cretaceous rocks in central patagonia a key to constrain the timing of rotations during the breakup of southwestern gondwana abstract a paleomagnetic study in jurassic and cretaceous rocks from the canadon asfalto basin central patagonia indicates the occurrence of about 25 30 clockwise rotation in upper jurassic lowermost cretaceous rocks whereas the overlying mid cretaceous rocks do not show evidence of rotation this constrains the tectonic rotation to be related to a major regional unconformity in patagonia which in turn seems to be close in time with the early opening of the south atlantic ocean the sense and probably the timing of this rotation are similar to those of other paleomagnetically detected rotations in different areas of southwestern gondwana suggesting a possible relationship between these and major tectonic processes related with fragmentation of the supercontinent on the other hand the mid cretaceous rocks in the region yield a paleopole located at lat 87 south long 159 east a95 3 8 this pole position is consistent with coeval high quality paleopoles of other plates when transferred to south american coordinates implying it is an accurate determination of the aptian circa 116 ma geomagnetic field in south america

gravity signatures of terrane accretion abstract in modern collisional environments accreted terranes are bracketed by forearc gravity lows a gravitational feature which results from the abandonment of the original trench and the initiation of a new trench seaward of the accreted terrane the size and shape of the gravity low depends on the type of accreted feature and the strength of the formerly subducting plate along the central american trench the accretion of gorgona island caused a seaward trench jump of 48 to 66 km the relict trench axes show up as gravity lows behind the trench with minimum values of 78 mgal n of gorgona and 49 mgal s of gorgona respectively these forearc gravity lows have little or no topographic expression the active trench immediately seaward of these forearc gravity lows has minimum gravity values of 59 mgal n of gorgona and 58 mgal s of gorgona respectively in the north the active trench has a less pronounced gravity low than the sediment covered forearc in the mariana arc two cretaceous seamounts have been accreted to the eocene arc the northern seamount is most likely a large block the southern seamount may be a thrust slice these more recent accretion events have produced modest forearc topographic and gravity lows in comparison with the topographic and gravity lows within the active trench however the minimum values of the mariana forearc gravity lows are modest only by comparison to the mariana trench 216 mgal their absolute values are more negative than at gorgona island 145 to 146 mgal we speculate that the forearc gravity lows and seaward trench jumps near gorgona island were produced by the accretion of a hotspot island from a strong plate the mariana gravity lows and seaward trench jumps or thrust slices were the result of breaking a relatively weak plate close to the seamount edifice these gravity lows resulting from accretion events should be preserved in older accreted terranes

large cretaceous sphenodontian from patagonia provides insight into lepidosaur evolution in gondwana sphenodontian reptiles successfully radiated during triassic and jurassic times but were driven almost to extinction during the cretaceous period1 the sparse early cretaceous record of sphenodontians has been interpreted as reflecting the decline of the group in favour of lizards their suspected ecological successors2 however recent discoveries in late cretaceous beds in patagonia partially modify this interpretation numerous skeletons of a new sphenodontian priosphenodon avelasi gen et sp nov were collected from a single locality in the cenomanian turonian candeleros formation where it is more abundant than any other tetrapod group recorded in the quarry for example crocodyliformes serpentes dinosauria and mammalia 3 4 adult specimens of priosphenodon reached one metre in length larger than any previously known terrestrial sphenodontian here we propose using available evidence that sphenodontians were not a minor component of the cretaceous terrestrial ecosystems of south america and that their ecological replacement by squamates was delayed until the early tertiary the new discovery helps to bridge the considerable gap in the fossil record around 120 million years that separates the early cretaceous sphenodontians5 6 7 from their living relatives sphenodon

tectonic evolution of the north patagonian andes 41 44 s through recognition of syntectonic strata abstract the north patagonian fold thrust belt 41 44 s is characterized by a low topography reduced crustal thickness and a broad lateral development determined by a broken foreland system in the retroarc zone this particular structural system has not been fully addressed in terms of the age and mechanisms that built this orogenic segment here new field and seismic evidence of syntectonic strata constrain the timing of the main deformational stages evaluating the prevailing crustal regime for the different mountain domains through time growth strata and progressive unconformities controlled by extensional or compressive structures were recognized in volcanic and sedimentary rocks from the cordilleran to the extra andean domain these data were used to construct a balanced cross section whose deep structure was investigated through a thermomechanical model that characterizes the upper plate rheology our results indicate two main compressive stages interrupted by an extensional relaxation period the first contractional stage in the mid cretaceous inverted jurassic lower cretaceous half graben systems reactivating the western canadon asfalto rift border 500 km away from the trench at a time of arc foreland expansion for this stage available thermochronological data reveal forearc cooling episodes and global tectonic reconstructions indicate mid ocean ridge collisions against the western edge of an upper plate with rapid trenchward displacement widespread synextensional volcanism is recognized throughout the paleogene during plate reorganization retroarc paleocene eocene flare up activity is interpreted as product of a slab rollback and fore to retroarc oligocene slab asthenospheric derived products as an expression of enhanced extension the second stage of mountain growth occurred in miocene time associated with nazca plate subduction reaching nearly the same amplitude than the first compressive stage extensional weakening of the upper plate predating the described contractional stages appears as a necessary condition for abnormal lateral propagation of deformation

the sauropod diversity of the la amarga formation barremian neuquen argentina abstract a study of the abundant and undescribed isolated and associated bones and teeth from the la amarga formation barremian of neuquen argentina permitted the recognition of additional clades of sauropod dinosaurs basal titanosauriforms both basal and derived titanosaurs and rebbachisauroid diplodocoids which are now added to the already known dicraeosaurids and a recently published basal diplodocoid these forms substantially increase the knowledge on the early cretaceous sauropod diversity in gondwana

origin and assembly of the tethyside orogenic collage at the expense of gondwana land abstract the tethysides are a superorogenic complex flanking the eurasian continent to the south and consisting of the cimmerides and alpides products of palaeo and neo tethys respectively we here review their evolution mainly on the basis of new maps showing the distribution of sutures magmatic rocks certain palaeobiogeographically and palaeoclimatologically significant taxa and facies and fragments of pan african 900 450 ma orogenic system forming the basement of many tethyside blocks these are supplemented by palaeomagnetic data reported in the literature a fundamental tenet of this paper is that major sutures which contain ophiolite fragments represent tectonic sections between continental blocks where oceanic crust has been subducted palaeo tethys came into existence largely in late carboniferous time coevally it began to be consumed by both internal and peripheral subduction zones which continued into the permian some of these had been inherited from pre tethyan times in the later permian rifting subparallel with the northern margin of gondwana land began between the zagros and malaysia separating a cimmerian continent from n gondwana land and thus heralding the opening of neo tethys and other smaller oceans that were back arc basins of palaeo tethys this rifting possibly also extended farther west into crete and mainland greece however the north china block yangtze block huanan block the eastern moity of the qangtang block north tibet and annamia all originally pieces of the end proterozoic early palaeozoic gondwana land had already separated from it in pre late carboniferous times possibly during the devonian all of these blocks and the cimmerian continent were characterized by cathaysian floral elements in late palaeozoic time palaeomagnetic and palaeontological data showing the original gondwana land affinity of these continental blocks are supplemented by correlating late proterozoic early palaeozoic pan african sutures orogenic belts and sedimentary basin fragments across tethyside sutures late permian foraminiferal provinces are related to this palaeogeographical interpretation by triassic times most cimmeride subduction zones were already in existence the cimmerian continent accelerated its separation from gondwana land and locally in the late permian began disintegrating internally along the waser rushan pshart banggong co nu jiang mandalay ocean by late triassic time all of the chinese blocks except lhasa and annamia had collided with each other and with laurasia the resulting enormous orogenic collage had a soft cushion between itself and laurasia in the form of the enormous accretionary complex of the songpan ganzi this connection enabled laurasian land vertebrates to reach south east asia by late triassic time in late triassic to middle jurassic times most major cimmeride collisions were completed widespread aridity in central asia occurred in late jurassic time probably in the rain shadow of the newly formed cimmeride mountain wall neo tethyan subduction systems formed along the s margin of the cimmerides or within neo tethyan oceanic lithosphere during the jurassic most if not all were north or east dipping they continued the northerly migration of the tethyside blocks evolution of the tethysides influenced the distribution of marine and terrestrial organisms and affected sea level changes and patterns of atmospheric circulation during much of the mesozoic and cainozoic it is likely to have reflected the surface expression of a persistent trend in the large scale convective circulation in the mantle that continuously transported material northward into the tethyan domain

processes of allochthonous terrane evolution mindoro island philippines on mindoro two tectonostratigraphic terranes the north palawan block and the mindoro block are separated by a steeply dipping shear zone the north palawan block was rifted off southern china in the oligocene and comprises most of the shallow southern end of the south china sea the eastern part of this terrane exposed on mindoro includes jurassic and paleogene strata probable rift basalts of oligocene age and oligo miocene graben fill deposits in the late oligocene and early miocene the eastern north palawan block underwent crustal stretching with grabens oriented at a high angle to synchronous spreading anomalies in the south china basin we hypothesize that grabens formed in an overall transtensional environment near a transform boundary at the eastern margin of the opening south china basin the mindoro block consists of a pre upper cretaceous low grade metamorphic basement overlain by upper cretaceous and upper eocene strata the mindoro block records several episodes of intense deformation of mesozoic and tertiary age and contrasts with the north palawan block both in terms of stratigraphy and structural evolution the mindoro suture which separates the mindoro and north palawan blocks is a complex structural boundary comprising slices of diverse lithologies separated by steeply dipping anastomosing faults deformed tectonic slices in the suture zone include serpentinized ultramafic rock amphibolite and rocks derived from both of the bounding terranes we interpret this suture as a zone of mostly transcurrent faulting that was active through much of mid tertiary time paleogeographic considerations for early and middle miocene time support the premise that the west side of the central philippine archipelago was a left lateral transform boundary the mindoro and north palawan blocks were initially juxtaposed along the transcurrent mindoro suture by late miocene time subsequent deformation on mindoro includes crustal shortening associated with the southern end of the manila trench which projects onshore on southwest mindoro the onset of shortening here probably reflects a late miocene change in philippine eurasian plate motion the mindoro suture zone is now locked and it acts as a rigid buttress against which strata of the north palawan block have been structurally stacked the mindoro suture zone is similar to other terrane boundaries in the northern philippines the history of terrane transport in this region was apparently dominated by strike parallel shuffling of terranes along major transcurrent boundaries within the philippine arc transcurrent motion has taken place in extensional and compressional regimes and it is ongoing today this may be a dominant process by which complex island arc systems are disrupted prior to accretion onto a continental margin

seismotectonics of the southern boundary of anatolia eastern mediterranean region subduction collision and arc jumping the pattern of seismicity and fault plane solutions of earthquakes are used to outline the tectonic features of the southern boundary of anatolia in the eastern mediterranean and southeastern turkey the results of this study show that this boundary is composed of two distinct parts one in southeastern turkey and syria is a wide and complex zone of continental collision the other in the levantine basin of the eastern mediterranean is a zone of oceanic subduction in the region of continental collision three zones of seismicity are observed most of the seismic activity in this region follows the bitlis zone and is associated with a zone of thrusting and mountain building this appears to be the zone of most active deformation and plate consumption in the plate boundary region between arabia and turkey a less active zone of seismicity to the north of the bitlis zone is interpreted to have been more active in the past whereas another active zone of seismicity to the south is interpreted to be a zone which may be more active in the future as the main zone of plate consumption jumps to the south in the subduction zone of the eastern mediterranean the depth of the subducted slab and the rate of seismicity generally increase from east to west the zone of present day convergence between africa and turkey in the levantine basin can be best outlined by the northern edge of the mediterranean ridge the subduction zone in this area sequentially jumps to the south as small continental fragments collide with existing zones of subduction deep seismic activity near the gulf of antalya is associated with a detached subducted slab north of the anaximander mountains that is distinctly different from the seismic trend which is associated with present day active subduction the plate boundary between africa and turkey at the center of the levantine basin appears to have shifted to the south of the anaximander mountains and florence rise most of the focal mechanisms of the earthquakes along the entire southern boundary of anatolia indicate that n to nnw thrusting is the dominant mode of seismic deformation the present set of data is inconsistent with a major transform fault in the cyprean arc east of cyprus and in southeastern turkey

high precision u pb zircon geochronology of the late triassic chinle formation petrified forest national park arizona usa temporal constraints on the early evolution of dinosaurs the triassic successions of the colorado plateau preserve an important record of vertebrate evolution and climate change but correlations to a global triassic framework are hampered by a lack of geochronological control tuffaceous sandstones and siltstones were collected from the upper triassic chinle formation exposed in the petrified forest national park arizona usa within a refined stratigraphic context of 31 detailed measured sections u pb analyses by the isotope dilution thermal ionization mass spectrometry id tims method constrain maximum depositional ages for nine tuffaceous beds and provide new insights into the depositional history of the chinle fluvial system the base of the blue mesa member of the chinle formation is placed at ca 225 ma and the top of the petrified forest member is placed at 208 ma or younger bracketing an 280 m thick section that spans nearly the entire norian stage of the late triassic estimated sediment accumulation rates throughout the section reflect extensive hiatuses and or sediment removal by channel erosion the new geochronology for the chinle formation underscores the potential pitfalls of correlation of fluvial units based solely on lithostratigraphic criteria a mid norian age ca 219 213 ma for the distinctive sonsela conglomeratic sandstone bed constrains the adamanian revueltian land vertebrate faunachron boundary our new data permit a significant time overlap between the lower chinle sequence and the dinosauromorph rich ischigualasto formation of northwestern argentina near contemporaneity of the trans american deposits and their faunal similarities imply that early dinosaur evolution occurred rapidly across the americas

ogasawara plateau multi beam sonar bathymetry and possible tectonic implications the ogasawara plateau bathymetry in the northwest pacific ocean is presented by u s naval oceanographic office multi beam sonar data the plateau is significant in that it separates the izu and bonin trenches and may be obducted onto the overriding plate and or jamming the subduction zone the high resolution bathymetry suggests morphologic evidence of faulting within and possible uplifting on the approximately 20 000 km 2 features

effects of co2 h2o and oblique collision on orogenesis the european hercynides as an example abstract the european hercynides are considered the collisional result of baltica and the microcontinents of southern europe after subduction destroyed the intervening rheic ocean during the early paleozoic their geotectonic development is assumed to consist of four overlapping stages 1 1 lithospheric thinning upwelling of hot asthenospheric material subsidence along listric faults and basinal and geosynclinal development on the opposing shelves of the rheic ocean starting in pre devonian time 2 2 intermittent subduction of the rheic ocean interspersed with episodes of fracturing volcanism local uplift and subsidence and basement reactivation as a result of compression with dextral megashear particularly since the earliest devonian 3 3 several phases of folding with a northward vergence and thrusting and overthrusting along listric surfaces the true orogenic stage 4 4 post orogenic stage of massive granite intrusions and subsequent volcanism in the permo triassic the high clastic content as opposed to carbonates of the sedimentary sequences involved in the subduction and folding processes and the consequent release of large amounts of meteoric water are held responsible for the synorogenic and post orogenic magma rise and for the wide zone of anatectic granites and migmatites the dominant dextral megashear the constant re adjustment of the microcontinents of southern europe oblique collision and the scarcity of back arc basins oceanic plateaus and microcontinents led to the poor preservation of ophiolites and ultrabasic rocks and to a wide over 1500 km hercynian foldbelt during the paleozoic the depositional center of the rhenish massif shifted from south polar latitudes in the early ordovician to tropical positions within a period of about 100 m y the sediment facies reflects this paleogeographic development

high resolution chronostratigraphy of the cerro barcino formation patagonia paleobiologic implications for the mid cretaceous dinosaur rich fauna of south america abstract the cretaceous cerro barcino formation chubut group of central patagonia argentina has yielded a remarkable fossil vertebrate fauna which form important components of the south american mid cretaceous fauna including titanosauriform sauropod dinosaurs theropod dinosaurs crocodyliforms turtles and lepidosauromorphs however a lack of robust chronostratigraphic framework for its fossil occurrences has so far hampered a full realization of their paleobiologic significance this contribution presents new stratigraphic sedimentologic and u pb isotopic age data from 11 localities throughout the patagonian somuncura canadon asfalto basin and analyzes the evolutionary characteristics of the cerro barcino fauna within the biostratigraphic context of the cretaceous of gondwana four new high precision 206pb 238u zircon dates by the ca id tims method range from 118 497 0 063 ma to 98 466 0 048 ma 2 internal errors and limits the puesto la paloma cerro castano and las plumas members of the cerro barcino formation largely to the aptian albian and cenomanian stages of the cretaceous respectively accordingly the majority of the cerro barcino vertebrates fall within a 118 110 ma time interval in the latest early cretaceous which makes them the oldest documented component of the mid cretaceous faunal assemblage of gondwana paleobiologic analyses of the latter assemblage suggests a 10 m y period of faunistic stability characterized by only minor evolutionary novelties or faunal turnovers

patagonian broken foreland and related synorogenic rifting the origin of the chubut group basin abstract the central patagonia is characterized by prominent continental deposits that belong to the cretaceous chubut group basin whose tectonic setting remains controversial it has been interpreted as a foreland basin an extensional basin and even as a sag stage of a rift event related deposits outcrop as part of the patagonian broken foreland east of the patagonian andes particulary the san bernardo fold and thrust belt between 42 and 48 s as the main sector of the broken foreland constitutes a nnw trending intraplate belt located 450 km away from the trench coincidentally at these latitudes 1200 km east of the trench intraplate deformation has caused tectonic inversion of mesozoic basins presently located at the atlantic offshore area additionally at the san jorge gulf area this orogenic system interferes with a conspicuous e w extensional system transversally disposed to the andean strike mainly active between the late early cretaceous and late paleocene we carried out an integrated analysis from structural 2 d and 3 d seismic data at the san bernardo ftb and the adjacent rio mayo basin studying sections of the chubut group basin to unravel the different evolutionary stages thus surface and subsurface evidence of syn compressional deposition indicate the development of a broken foreland basin related to the formation of the san bernardo ftb suggesting an initial growth during the late early cretaceous and probably up to the late paleocene our results imply that the cretaceous compression acted in concert with transversal foreland extension hence we propose a syncontractional rift reactivation of a potential lithospheric anisotropy triggered by regional contraction finally the origin of compression during this time is discussed in relation to multiple processes that go from high convergence between plates and trenchward motion of south america collision of mid ocean ridges to potential dip changes in the subducted slab as suggested by arc expansion

paleomagnetism and the motion of large and small plates the focus of paleomagnetic research during past decades has varied greatly the first generation in paleomagnetism might be defined as beginning with the pioneering studies aimed at discovering whether the geomagnetic field has been a reliable reference frame for measuring and timing continental displacements an enormous effort followed in the form of individual paleomagnetic studies of cratonic rocks culminating with the construction of apw apparent polar wander paths for the continents which could be used to test paleogeographic reconstructions coupled with parallel research in marine geophysics and geology the refined apwp which result from this effort have helped to develop a reasonable first order history of cenozoic mesozoic paleogeography for the major plates

oceanic plateaus the fragmentation of continents and mountain building many anomalous rises in today s oceans may be submerged continental fragments detached from previous continents ancient island arcs or basaltic piles formed by hot spots and spreading centers these rises are embedded in their respective moving oceanic plates and are fated to be consumed at active margins where such rises are being consumed at present e g the nazca ridge they cause cessation of volcanism disruption of the downgoing slab and possible shifts in plate boundary configuration many past rises including numerous continental fragments have been recognized within mountain belts as allochthonous terranes they constitute a large portion of the orogenic belts in the north pacific from mexico through western north america alaska east siberia japan and in new zealand the orogenic deformation in these belts is possibly the result of the accretion of the allochthonous terranes many terranes have been accreted with substantial deformation also in the alpine chain well before major continent continent collisions it is suggested therefore that the accretion of fragments may be the common process of the deformation phase of mountain building subduction of normal oceanic crust may be insufficient for deformation whereas full continent continent collision may not be necessary the general validity of this conclusion depends critically on whether allochthonous terranes caused orogenic deformation in the andes or not most of the accreted fragments with continental affinities in the mesozoic cenozoic orogenic belts of the world can be traced back to the breakup of gondwana beginning with a pacifica domain in the permian through a larger india domain in the early mesozoic and continuing through the separation of the somalia plate in the near future the reasons for this 250 million year breakup process are not known but some kind of thermal process possible of mantle wide scale is implied

an introductory overview to the concept of displaced terranes on land much of the pacific margin is composed of allochthonous terranes which are of continental and noncontinental origins in the oceans numerous oceanic rises some of which are submerged continental fragments are presently embedded in the oceanic plates these oceanic rises are probably future accreted terranes they thus represent one stage in the development of allochthonous terranes found in orogenic zones minerals found in these terranes were formed at locations that in the past could have been thousands of kilometres away this is because some oceanic terranes were split into several parts that moved with their respective plates in different directions also faulting at the continental margins caused large scale concurrent and post accretionary horizontal translations of hundreds of kilometres of the allochthonous terranes studying the allochthonous terranes may provide important information about the paleozoic and early mesozoic history of the pacific ocean because most of the oceanic crus

detrital zircon provenance from the neuquen basin south central andes cretaceous geodynamic evolution and sedimentary response in a retroarc foreland basin the surface response in terms of drainage pattern changes to the cretaceous geodynamic reorganization of the andean subduction zone between 36 s and 41 s is reconstructed through the geochronology based provenance study of alluvial detrital zircons the age spectra obtained by 500 spot u pb ages record an eastward provenance of detritus coming from the foreland during the early cretaceous backarc extensional stage followed by westward sourced clastics coming from the cordillera during the cenomanian this drainage pattern reversal fits the regional unconformity in the sedimentary record that is linked to the geodynamic reorganization of the continental margin from an extensional to a compressional regime forcing the neuquen basin to evolve from a retroarc to a foreland stage after this inversion the clastic systems progressively returned to be mainly fed by the foreland due to the uplift of the peripheral bulge as a consequence of the late cretaceous thrust front migration this tectonic evolution of the neuquen basin and the related response of the drainage pattern are thought to be the surface expression of the dip decrease of the benioff subduction zone

tectonostratigraphic evolution of cenozoic marginal basin and continental margin successions in the bone mountains southwest sulawesi indonesia abstract the bone mountains located in southwest sulawesi along the se margin of sundaland are composed of oligocene to possibly lower miocene marginal basin successions bone group that are juxtaposed against continental margin assemblages of eocene miocene age salokalupang group three distinct units make up the latter i middle upper eocene volcaniclastic sediments with volcanic and limestone intercalations in the upper part matajang formation reflecting a period of arc volcanism and carbonate development along the sundaland margin ii a well bedded series of oligocene calc arenites karopa formation deposited in a passive margin environment following cessation of volcanic activity and iii a series of lower middle miocene sedimentary rocks in part turbiditic which interfinger in the upper part with volcaniclastic and volcanic rocks of potassic affinity baco formation formed in an extensional regime without subduction the bone group consists of morb like volcanics showing weak to moderate subduction signatures kalamiseng formation and a series of interbedded hemipelagic mudstones and volcanics deko formation the deko volcanics are in part subduction related and in part formed from melting of a basaltic precursor in the overriding crust we postulate that the bone group rocks formed in a transtensional marginal basin bordered by a transform passive margin to the west sundaland and by a newly initiated westerly dipping subduction zone on its eastern side around 14 13 ma an extensional tectonic event began in sw sulawesi characterized by widespread block faulting and the onset of potassic volcanism it reached its peak about 1 ma year later with the juxtaposition of the bone group against the salokalupang group along a major strike slip fault walanae fault zone the latter group was sliced up in variously sized fragments tilted and locally folded potassic volcanism continued up to the end of the pliocene and locally into the quaternary

conditions for a crustal block to be sheared off from the subducted continental lithosphere what is an essential factor to cause features associated with collision 1 crustal blocks are detached from the subducting lithosphere at various depths i call such phenomena shearing off and investigate the mechanical conditions for shearing off to occur in the continental lithosphere the buoyancy of the crustal block does not work selectively as a driving force until it has been sheared off and i suppose that shearing off occurs when the shear traction at the thrust whose maximum value is calculated from the strength along the thrust overcomes the strength of the boundary faults of the block and determine the depth of the leading edge of the subducted crustal block when shearing off occurs the temperatures of the slab and at its surface are calculated by the steady state formula of molnar and england 1990 as a function of the surface heat flow dip angle and convergence velocity of the subducted continental plate as the shear stress and temperature at the ductile part of the thrust zone are consistent with the flow law the shear stress at the brittle part is a strong function of the pore fluid pressure ratio i show that shearing off of an upper crustal block is possible only for a small value of such as 0 4 when the surface heat flow value is 70 mw m2 i suggest that the essential factor to cause shallow offscraping of crustal blocks in collision zones is not a buoyancy of the continental crust but a low value of which would result from a little amount of dehydration from the subducted continental plate

south american reference pole for the mid cretaceous further constraints in the interpretation of andean paleomagnetic data a paleomagnetic study of the aptian cerro barcino formation in central patagonia showed the presence of a stable magnetization with a positive tilt test the obtained pole position lat 85 s long 181 e 95 5 6 n 11 differs from reliable early and late cretaceous south american cratonic poles the cerro barcino pole overlaps coeval poles from the chilean andean fore arc previously interpreted to record crustal block rotations this new result indicates that previously published andean tectonic models must be reviewed

new remains and new insights on the gondwanan meiolaniform turtle chubutemys copelloi from the lower cretaceous of patagonia argentina abstract new cranial and postcranial remains of the gondwanan meiolaniform turtle chubutemys copelloi gaffney rich vickers rich constantine vacca and kool 2007 from the lower cretaceous puesto la paloma member of the cerro barcino formation chubut province patagonia argentina are presented described and compared in this contribution carapace and plastral remains pectoral and pelvic girdle cervical and thoracic vertebrae and the left maxilla and jugal are the new recovered elements from c copelloi these new remains were found in 2008 in turtle town locality the same site where the holotype and referred specimens of c copelloi had been found in 1997 the facies analysis of the sedimentary succession in turtle town and surrounding areas suggests a paleoenvironment constituted by a broad alluvial plain with influx of volcanic ash falls whose deposits were disturbed by pedogenesis or reworked by current flows that supplied water and sediment in ponded areas the presence of a very thin shell broad vertebrals broader than pleurals the presence of a shallow nuchal notch with the vertebral 1 almost reaching the anterior border of the carapace the presence of costo peripheral fontanelles and the presence of an ectepicondylar canal in the humerus are the most notable features provided by the new remains a cladistic analysis has been performed to test the phylogenetic position of c copelloi this phylogeny corroborates the basal position of c copelloi among meiolaniformes the plausible phylogenetic relationships of the clade meiolaniidae with other gondwanan e g otwayemys cunicularius gaffney kool brinkman rich and vickers rich 1998 or laurasian lower cretaceous taxa e g sinochelyids are also discussed in this contribution taxa included in meiolaniformes have been mainly found in gondwana and as the most basal taxon was found in patagonia paleobiogeographic studies suggest this clade originated in south america due to the basal position of c copelloi among meiolaniformes the discovery of more and previously unknown remains of this species sheds light on the origin and early evolution of this curious clade

accreted terranes in the northern part of the philippine archipelago the philippine archipelago consists of a complex array of ophiolites continental fragments and island arc elements that can be identified as accreted terranes similar to those increasingly recognized as components of orogenic zones the northern philippines including luzon mindoro and nearby smaller islands can be divided into at least six of these tectonic elements from west to east across central luzon there are the neogene accretionary prism of the west luzon arc the eocene zambales ophiolite the cretaceous angat ophiolite and a late cretaceous early paleogene volcanic arc built on an older metamorphic basement this arc terrane is repeated by offset along the philippine fault to the south the western luzon terranes are juxtaposed against the metamorphic basement block of mindoro which itself is colliding with the north palawan microcontinental fragment the ophiolites appear to have originated in back arc basins rather than in oceanic plateaus and the metamorphic belts have protoliths indicating deformation along active margins perhaps deep within accretionary prisms the philippine terranes are interpreted as fragments that originated within the complex pacific eurasian plate boundary rather than as intra pacific basin units these terranes have been assembling at least since the oligocene by strike slip and convergent displacements strike slip displacement either along transcurrent faults or as a component of convergence played a very important if not dominant role in this assembly most terranes identified in the northern philippine appear to be plate fragments with attached crust and upper mantle their characteristics contrast with those usually interpreted for terranes in the north american cordillera where near orthogonal convergence and shallow dipping terrane sutures are favored

phytoplankton response and geochemical evidence of the lower toarcian relative sea level rise in the umbria marche basin central italy abstract quantitative and qualitative analyses have been carried out on the lower toarcian organic rich lithologies of the umbria marche domain marne di monte serrone formation with the aim to emphasize the potential of organic and geochemical parameters as palaeoenvironmental indices the organic matter and phytoplankton data suggest that the palaeoenvironmental evolution of this area was controlled by a third order cyclicity induced by climatic eustatic fluctuations during the early toarcian sea level rise two different phases have been recognized the phase of facies retrogradation referable to the transgressive system tract lying in the early and middle part of the d tenuicostatum zone this phase was characterized by a relative increase of basinal caco 3 a better fertility within the photic zone and a decrease of sea bottom oxygenation and of the micronutrients in surface waters the maximum flooding event at the top of the retrogradation phase corresponds with the maximum of palaeoenvironmental distality sedimentary starvation and total organic carbon toc values the phase of facies progradation corresponding to the high stand system tract occurred in the uppermost portion of the d tenuicostatum zone this phase induced a more efficient water circulation producing a re oxygenation at the sea bottom a better nutrient recycling and a reflourishing of nannoplakton the caco 3 in the basin was mainly extrabasinal because the carbonate platforms started producing and exporting the carbonate mud basinwards again this approach confirms that eustatic fluctuations strongly influenced the variations of phytoplankton total abundance and species diversity and the distribution of organic matter in the sediments it also regards a significant tool for the investigation of lithologies where the lack of significant sedimentary structures does not give detailed palaeoenvironmental information

accretionary nature of the crust of central and east java indonesia revealed by local earthquake travel time tomography abstract reassessment of travel time data from an exceptionally dense amphibious temporary seismic network on and offshore central and eastern java meramex confirms the accretionary nature of the crust in this segment of the sunda subduction zone 109 5 111 5e traveltime data of p and s waves of 244 local earthquakes were tomographically inverted following a staggered inversion approach the resolution of the inversion was inspected by utilizing synthetic recovery tests and analyzing the model resolution matrix the resulting images show a highly asymmetrical crustal structure the images can be interpreted to show a continental fragment of presumably gondwana origin in the coastal area east of 110e which has been accreted to the sundaland margin an interlaced anomaly of high seismic velocities indicating mafic material can be interpreted to be the mantle part of the continental fragment or part of obducted oceanic lithosphere lower than average crustal velocities of the java crust are likely to reflect ophiolitic and metamorphic rocks of a subduction melange

collisional processes in the eastern mediterranean in the eastern mediterranean the collision of the erastosthenes and the anaximander seamounts with the cyprus arc results in a unique tectonic setting due to the small size of the eastern mediterranean basin as a result of the collision some of the motion between the african plate and the eurasian plate is taking place by thrust faulting along the north african passive margin it seems that the stress at the plate boundary along the cyprus arc may be transmitted southward to cause the reactivation of a pre existing fault zone along the passive margin of eastern north africa

calibrating the guadalupian series middle permian of south china abstract the guadalupian epoch represents one of the most critical intervals during the earth history which is characterized by a series of global geological and biological events however it is poorly constrained by radioisotopic ages in comparison with the high precision dates from the lopingian and lowest triassic in south china and the cisuralian in southern urals russia in this study we report combined ca id tims and sims u pb zircon geochronology for three ash beds from the base and lower part of the kuhfeng formation in the chaohu area southeastern china zircons from ash beds a c and d were initially analyzed by sims and yielded weighted mean 206pb 238u dates of 269 0 1 4 ma mswd 1 03 n 31 266 3 2 2 ma mswd 2 2 n 29 and 262 2 1 7 ma mswd 1 0 n 20 in ascending order however high precion u pb geochronology of the same ash beds by the ca id tims method point to important inaccuracies in the sims results due to pb loss in zircons ash beds a and c yielded two tims weighted mean 206pb 238u dates of 272 95 0 11 ma mswd 1 9 n 7 and 271 038 0 097 ma mswd 2 2 n 8 respectively the depositional age of 272 95 0 11 ma for ash bed a is postulated as the traditional cisuralian guadalupian boundary cgb age in south china our new geochronology suggests that the guadalupian series in south china had a total duration of 13 85 0 52 myr given a guadalupian lopingian boundary glb age of 259 1 0 5 ma the new age calibration of the base of the guadalupian series is ca 0 65 0 51 myr older than and improves upon the previous estimates for the cgb age and the duration of the guadalupian epoch based on the 2016 international chronostratigraphic chart icc and the 2012 geologic time scale gts