development of a predictive model for defining subsurface sand bodies abstract numerous hazardous and toxic waste sites are underlain by sedimentary deposits the delineation of buried paleochannels is a prime concern during the characterization of these sites buried paleochannels often provide direct conduits for contamination to move rapidly in the subsurface historically the method used to define a discontinuous sand body was to grid the entire area of interest and start drilling closely spaced holes the grid pattern method is expensive and potentially hazardous geologists in the petroleum industry have developed techniques to predict the size shape and orientation of subsurface sedimentary deposits by defining local environments of deposition of geologic materials within regional settings based on the depositional history of the paleochannel deposits empirical equations have been developed which allow for the calculation of channel depths as well as channel and meander belt widths by combining geostatistics kriging paleogeomorphic studies and probability techniques a predictive model was developed which has application in both ground water investigations and in oil and gas exploration

stratigraphy composition and form of the deccan basalts western ghats india in the western ghats between latitudes 18 20 n and 19 15 n 7000 km2 of deccan basalt have been mapped with the primary objective of establishing a flow stratigraphy as a guide to the volcanic history of the flood basalts using over 70 measured vertical sections major and trace element analyses of nearly 1200 samples and rare earth and87sr 86sr determinations for over 60 samples we divide the basalt into three subgroups and ten formations in this paper we describe the seven principal formations in the area and the most prominent individual flows

interpreting avulsion process from ancient alluvial sequences guadalope matarranya system northern spain and wasatch formation western colorado alluvial deposits of the guadalope matarranya system oligocene ebro basin spain and the wasatch formation eocene western colorado provide time integrated records of the process of river channel avulsion these sequences consist of isolated channel belt sandstones incised into and abruptly overlain by flood plain siltstones indicating deposition by avulsive river systems the geometry and distribution of channel incisions suggest that avulsion was not controlled by tectonics climate or base level changes but formed by autocyclic processes measurements from 221 channel fills in the guadalope matarranya system and 38 from the wasatch formation allow us to statistically characterize channel geometries we infer to be associated with establishment and abandonment of individual river avulsions paleoflow depths in both systems average 1 4 to 1 6 m aggradation height superelevation of channel margin levees are on average 0 6 and 1 1 times paleoflow depth in the guadalope matarranya and wasatch systems respectively these results are consistent with values from recently avulsed modern rivers and suggest that 1 flow depth is the appropriate parameter against which to scale the critical superelevation necessary for channel avulsion and 2 the increase in potential energy due to channel perching drives the lateral instability that is needed for avulsion to be successful numerous stacked channel fills indicate repeated reoccupation of the same site by avulsing channels these reoccupation channels indicate that inherited flood plain topography here abandoned channel forms was an important control on the arrival site of newly avulsed channels comparison of our results to others suggests two end member types of avulsion can take place incisional avulsion seen here is characterized by an early incision phase followed by infilling by migrating bar forms aggradational avulsion begins with aggradation followed in time by stream integration into a single downcutting channel we suggest that the type of avulsion is strongly influenced by whether or not the adjacent flood plain is well or poorly drained in both cases subsequent aggradation and channel perching increase the chances that some triggering event will lead to avulsion

a geochemical clock in earliest paleogene pelagic carbonates based on the impact induced os isotope excursion at the cretaceous paleogene boundary 1 an impact induced osmium os isotope excursion provides a unique means of assessing the completeness of marine cretaceous paleogene k pg boundary sections and surmounting challenges associated with constraining the time scale of the earth system recovery from this extreme perturbation a model of the recovery of seawater187os 188os following the impact event allows independent estimates of the time elapsed since the impact which can be directly compared to time estimates derived from biostratigraphy magnetostratigraphy and cyclostratigraphy this approach is tested using data from three deep ocean sites cored by the ocean drilling program odp data from odp 1262b south atlantic and odp 690c southern ocean display the expected 187os 188os minimum very close to the biostratigraphically defined k pg boundary and yield os based accumulation rate estimates similar to those obtained from magnetostratigraphy and orbital tuning in contrast the187os 188os minimum in odp 1209c western pacific occurs 9 cm below the k pg boundary low os concentrations throughout the boundary interval and an implausibly rapid recovery to higher pre impact187os 188os ratios provide strong evidence for a previously unrecognized gap in the k pg interval of site 1209 results presented here provide strong empirical evidence that os isotope data are uniquely valuable in assessing the completeness and accumulation rates of earliest paleogene sediments from the deep sea they are of broad interest because they have implications for astronomical tuning of the geologic time scale and illustrate that whole ocean geochemical perturbations can provide an alternative to biostratigraphy for correlation and timekeeping during abrupt biotic events

tectono metamorphic evolution of syros and sifnos islands cyclades greece abstract miocene exhumation of metamorphic rocks in the aegean sea is partly a consequence of post orogenic extension if the post orogenic mechanism of exhumation is rather well understood the earlier syn orogenic eocene exhumation is still largely enigmatic previous authors have argued in terms of extension or compression new structural and petrological data on sifnos and syros islands show that exhumation of high pressure low temperature hp lt rocks involves crustal scale extensional ductile shear zones during the eocene we observe a continuum of top to the ne and e ductile shear from the eocene in the blueschist facies to the miocene in the greenschist facies this deformation is distributed in the eclogites and blueschists whereas it is rather localised along ductile shear zones in the greenschists eclogites which are preserved only at the top of the structural pile are exhumed with a cold retrograde p t path in the lower part of the structural pile we observe a progressive retrogression of eclogites in blueschist then greenschist facies this lower part of pile is subsequently exhumed with p t paths showing a nearly isothermal decompression before cooling p t t deformation data suggest that the cycladic blueschists are progressively exhumed by a continuum of accretion at the base of the orogenic wedge and by a partly non coaxial extensional deformation above distributed during the syn orogenic stage then localised during the post orogenic stage we then compare the mechanism of syn orogenic exhumation of crete and the cyclades and we discuss a simple geodynamic scenario for the aegean domain and the external hellenides which accounts for 1 the southward migration of the hellenic trench and arc during the cenozoic 2 the p t t deformation data for the cycladic blueschists and the phyllite quartzite nappe and 3 the transition from syn orogenic to post orogenic in the cyclades

a new method integrating high precision u pb geochronology with zircon trace element analysis u pb tims tea increased precision in isotope dilution thermal ionization mass spectrometry id tims u pb geochronology has revealed age complexities in zircon populations that require new tools for understanding how the growth of zircon is related to geologic processes u and pb are routinely separated from other elements in dated minerals by ion exchange separation prior to tims isotope measurement we develop a method in which trace elements in the exact same volume of zircon are redissolved and analyzed using solution nebulization inductively coupled plasma sector field mass spectrometry with matrix matched external liquid calibration using 0 5 ml solution resulting concentrations are between 1 ppt for elements such as ti nb and ta and tens of ppb for zr by analyzing a series of standard solutions zircons and procedural blanks we show that accurate measurements are performed on zr hf y sc and the hree while low concentration elements can be measured accurately to 5 ppt we performed combined u pb id tims geochronology with trace element analysis here called u pb tims tea on zircons from eight volcanic rocks comprising several volcanic systems and one metamorphic sample similar to previous in situ trace element analyses zircon geochemistry is distinct between different samples and records petrogenetic processes such as fractional crystallization assimilation and or magma mixing unique from in situ analysis u pb tims tea can trace geochemical evolution in accessory minerals with adequate age precision to resolve magmatic processes in rocks at least 200 million years old this provides a means to identify auto ante and xenocrystic zircon and lead to more robust age interpretations in id tims u pb geochronology one suite of cretaceous andesitic zircons shows correlations in geochemistry and absolute time that record evolution of a magmatic system over 250 ka prior to eruption future work will combine u pb tims tea with solution isotopic analysis of nd sr and hf and will be applied to a host of datable minerals such as monazite sphene apatite rutile xenotime and baddeleyite these combined tools will provide access to an improved understanding of a wide range of igneous and metamorphic processes as a function of time

application of an alluvial architecture model to better understand seepage risk in floodplains abstract the amount and distribution of coarse grained sediment e g sands and gravels relative to fine grained sediment e g clays and silts within a floodplain influences many of the floodplain geotechnical properties including the potential for groundwater seepage seepage is a primary driver of levee and dam failure and understanding its potential is of paramount concern to engineers and resource managers this paper reports the results of a computational modeling study that simulated alluvial floodplain construction using a suite of simple geomorphic process imitating rules a model aggrades a floodplain cross section within an alluvial basin creating floodplain architecture by differentiating between sediment deposited by channel processes sand and sediment deposited by overbank flood processes clay the evolution of two floodplain cross sections of the trinity river near dallas texas is simulated using five different experimental scenarios the study area is the site of large levee rehabilitation projects in which accurate characterization of the geologic environment has significant engineering importance study results predict that scenario components including the alluvial basin width the initial topography of the floodplain base level and the channel aggradation rate significantly affect the fraction of the floodplain width that contains channel deposits by influencing the avulsion frequency of the river during floodplain construction increased avulsion frequency equated to more numerous yet smaller channel deposits the dimensions of the channel deposits predicted by this study are similar to those typically observed in large fully meandering river systems the model devised for this study is relatively simple and can be run in multiple iterations to produce probabilistic outputs such as the likely range of channel deposit widths within a floodplain cross section this type of information is useful to engineers for a host of applications including predicting the data collection density necessary to characterize the geotechnical properties of a project site

first palaeomagnetic results from the cycladic massif greece and their implications for miocene extension directions and tectonic models in the aegean abstract the aegean region is characterised by major fault bound blocks with markedly contrasting structural trends recent models account for these variations either through differential block rotation or through a process of radial extension the cycladic massif in the back arc region to the hellenic trench represents a critical area where apparently divergent extension directions are observed this contribution provides the first palaeomagnetic results from this area magnetic remanence and ams data are presented for middle miocene granodiorites on the islands of mykonos and naxos these rocks are exposed in the footwalls of major extensional detachments within the metamorphic core complexes that characterise the cycladic massif a clear correlation between the orientation of an l s fabric developed within the intrusions and the magnetic fabric data is observed demonstrating the presence of a normal magnetic fabric of extensional origin the mean extension directions inferred from the orientations of the maximum axes of the magnetic susceptibility ellipsoids are markedly divergent at 064 mykonos and 351 naxos northeasterly in situ magnetic remanences are observed on mykonos whereas those on naxos are directed to the nnw neither direction corresponds to the appropriate palaeomagnetic reference direction for the miocene standard palaeomagnetic tilt corrections cannot be applied at these sites because of the lack of palaeohorizontal markers deviations of in situ remanences away from the reference direction are potentially due to rotation around any one of an infinite number of net tectonic rotation axes each of these may be arbitrarily decomposed into components of tilting and vertical axis rotation geologically realistic solutions which restore the in situ magnetisations back to the reference direction may be found by consideration of regional structural trends assuming that tilting is controlled by the major block bounding faults these solutions indicate significant components of differential vertical axis rotations across the cyclades mykonos is bound by nw se trending regional faults and is shown to have rotated clockwise by ca 22 in contrast naxos is bound by ene wsw trending structures and has rotated anticlockwise by ca 33 the apparent divergence of extension directions inferred from both the magnetic anisotropy and structural data is resolved by correcting the mean ams data for subsequent rotation using the rotation solutions derived from the magnetic remanence data the data imply that the primary middle miocene extension direction in the cycladic massif was nearly uniform along a nne ssw azimuth we consider that the uniform extension direction and opposing senses of block rotation determined for this portion of the cycladic massif are most consistent with a recent model describing deformation within the aegean in terms of a system of broken fault bounded slats within this scenario mykonos occupies a position on a clockwise rotating slat which continues northwest at least as far as evvia a major ene wsw trending fault between the islands previously identified on shallow seismic sections separates this domain from an anticlockwise rotating slat which includes naxos

cyclostratigraphy and astronomical tuning of the late maastrichtian at zumaia basque country northern spain the standard geological time scale for the cretaceous is still largely based on seafloor anomaly profiles combined with radio isotopic tie points the astronomical tuned time scale with its much higher resolution and accuracy has recently been extended to the k pg boundary and is being extended into the cretaceous to construct such a time scale for the cretaceous we selected the upper maastrichtian of the zumaia section in the basque country northern spain which contains a cyclic alternation of limestones and marls deposited in a hemipelagic setting the paleogene portion of the zumaia section has previously been studied for a joint cyclostratigraphic radioisotopic intercalibration of the age of the k pg boundary here we present a high resolution cyclostratigraphic framework for the upper maastrichtian latest cretaceous of the zumaia section in the basque country northern spain with new biostratigraphic and magnetostratigraphic data bed to bed correlation with the nearby sopelana section provides additional bio and magnetostratigraphic constraints the stacking pattern of the lithologies shows a hierarchy that reflects the combined influence of the orbital parameters of precession and eccentricity this is confirmed by time series analyses of lithological and geochemical data indicating a strong influence of eccentricity modulated precession on latest cretaceous climate the expression of the 405 kyr eccentricity cycle serves as primary signal for astronomical tuning we provide two tuning options depending on absolute k pg boundary ages of 65 56 and 65 97 ma the logged part of the section encompasses nine and a half 405 kyr cycles in total and spans 3 9 myr the acquired cyclostratigraphic framework provides ages for characteristic planktonic foraminiferal events magnetic reversals and carbon isotope excursions and resolves the late maastrichtian time scale in unprecedented detail with relative age uncertainties o 100 kyr the high resolution and large amplitude of shifts in d 13 c on the 405 kyr and 1 2 myr scales allow for global

the north cycladic detachment system and associated mineralization mykonos greece insights on the evolution of the aegean domain 1 in the aegean back arc domain some 30 35 ma ago an increase of the rate of slab retreat led to the initiation of post orogenic extension largely accommodated by large scale structures such as the north cycladic detachment system ncds although this extension is still active nowadays an e w compressional regime developed in the late miocene with the propagation of the north anatolian fault on mykonos island cyclades the ne sw back arc extension is particularly well expressed with the livada and mykonos detachments that belong to the ncds and that are associated with nw se barite veins emplaced during the synkinematic cooling of the mykonos intrusion this study shows that the formation of the mineralization occurred when the pluton crossed the ductile to brittle transition during its exhumation below the ncds at 11 10 ma in addition the kinematics of mineralized structures evolved with time 1 most of the displacement was accommodated by the top to the ne livada and mykonos detachments accompanied by the formation of mineralized normal faults that were 2 reworked in a strike slip regime with an e w direction of shortening and a persistent ne sw stretching and 3 a late post mineralization e w compressional stage with a minor reworking of shallow dipping faults locally including the detachments themselves we interpret this increase of the e w shortening component recorded during the mineral deposition as a consequence of the initiation of the westward motion of anatolia from 10 ma thus 4 ma before the propagation of the north anatolian fault in the dardanelles strait and the localization of the strain on the aegean sea margins

simplified process modeling of river avulsion and alluvial architecture connecting models and field data abstract modeling is an invaluable tool for studying sedimentary basin filling and for understanding depositional processes with long recurrence intervals including channel avulsion simplified modeling approaches such as cellular models and process analogue experiments are particularly useful for efficiently exploring alternative hypotheses and evaluating first order controls on river avulsion and alluvial architecture here we review the history and current state of the art in simplified avulsion and alluvial architecture models with a particular focus on how results and insights from these models can be incorporated into field and subsurface studies and vice versa simplified avulsion and alluvial architecture models have proliferated in the past decade providing a wide variety of models to serve as a basis for future coupled field modeling studies we compare features of leading models and discuss avenues for effectively pairing model capabilities with hypotheses and field data outstanding questions highlighted by recent modeling efforts include 1 what thresholds control avulsion initiation in different systems 2 how do floodplain processes and topography influence avulsion dynamics and alluvial architecture 3 what factors determine where avulsion channels stabilize answering these questions will require targeted modeling efforts coupled to data from ancient systems hence our model comparison emphasizes features that can be used to choose or design fit for purpose models and we outline how quantitative data useful for model selection and validation can be obtained from modern systems and ancient deposits matching model goals with targeted questions and model parameters and predictions with quantitative field data will help tighten communication between field and model oriented sedimentary geologists facilitating advances in our understanding of river avulsion and alluvial architecture

systematics of chlorite alteration at the phelps dodge massive sulfide deposit matagami quebec hydrothermal alteration at the phelps dodge archcan volcanogenic massive sulfide deposit has converted rhyodacite and rhyolite footwall rocks into the following mineral assemblages quartz chlorite albite epidote or sericite quartz chlorite or sericite chlorite or sericite and chlorite talc or stilpnomelane alteration at constant al was initiated by hydration addition of fe mg silicification and leaching of ca na which produced al saturated chlorites with a wide range of fe fe mg ratios within the assemblage quartz chlorite albite epidote or sericite with continued addition of fe and less mg combined with extensive leaching of quartz the chlorite became al undersaturated quartz chlorite talc assemblage and ultimately formed a rock composed essentially of chlorite the chlorite talc or stilpnomelane assemblage is stable in late crosscutting veinlets and in the ore zone chlorites in the si al mg fe system form a rectangular solid solution plane with limited substitution of al for si and extensive substitution of fe for mg in si al space the solid solution plane is outlined by al saturation presence of other al rich mineral and al undersaturation presence of al poor or al free mineral boundaries al iv substitution for si in the chlorites increases from 2 3 to 3 01 formula units based on 8 si al iv with fe fe mg whereas al iv occupancy decreases from 2 88 to 2 65 the valence charge balance is compensated by octahedral site vacancies or by the conversion of fe super 2 to fe super 3 the al iv content of chlorite also increases with temperature chlorites on the al saturated boundary of the solid solution field form a potentially useful geothermometer t degrees c 106 al iv 18 al iv is corrected for changes with the fe fe mg ratio as al iv corrected al iv 0 7 fe fe mg the fe fe mg ratios of bulk rock and contained chlorite correlate well birefringence colors of the chlorite change from green to brown violet and berlin blue as fe fe mg changes from 0 18 to 0 64 the fe fe mg variation apparently depends largely on the proportions of mg rich seawater and fe rich hydrothermal fluid in the altering brine

stratigraphy structure and volcanology of the se deccan continental flood basalt province implications for eruptive extent and volumes the deccan volcanic province is one of the world9s largest continental flood basalt provinces and derives additional importance because its eruptions 64 67 ma straddle the cretaceous tertiary boundary to better assess the environmental impact of deccan volcanism and its possible effect upon cretaceous tertiary boundary biota it is necessary to document the stratigraphy chronology and volume of the eruptions new chemostratigraphical data permit mapping of the se deccan these data strengthen the likelihood that the rajahmundry traps of eastern india were originally fed by long distance flows and are an extension of the main deccan volcanic province an east west cross section reveals a depression or moat around the se periphery of the deccan volcanic province this provided a site in which shallow lakes initially formed and along which later lava eruptions became channelled and confined published palaeomagnetic data indicate that the lavas of the se deccan were erupted during chron 29r coeval with the cretaceous tertiary boundary and the chemostratigraphic data place the associated lake sediments i e lameta group beneath and within lavas of the wai subgroup finally these new map data are combined with previous work to provide a quantitative estimate for the original deccan volcanic province eruptive volume of c 1 3 10 6 km 3

tectonics of the syros blueschists cyclades greece from subduction to aegean extension 1 on syros high pressure metamorphism affects a lithological pile that is composed of from base to top 1 the komito vari granitic basement 2 a margin sedimentary sequence that is predominantly made of marbles and schists the pyrgos and kastri units and 3 the kambos metaophiolitic melange the tectonic history occurred in three main stages during the first stage in the mid eocene the kambos oceanic unit was thrust southward on top of the sedimentary pile top to the south southwest ductile senses of shear are synchronous with prograde high pressure metamorphism and associated with this thrusting event the second stage corresponds to a top to the northeast ductile shear that affects the whole metamorphic pile and is synchronous with the metamorphic retrogression from eclogite to greenschist facies however the kambos oceanic unit remained partly undeformed as shown by significant volumes containing undeformed lawsonite pseudomorphs no major extensional detachment related to this exhumation event outcrops on the island the localized semibrittle to brittle deformation of the third stage is associated with the postmetamorphic development of 1 a ramp flat extensional system at the island scale whose southward minimum displacement is estimated at approximately 7 km and 2 two sets of steeply dipping strike slip faults with a normal component trending either east west or around north south indicating that the mean stretching and shortening directions are trending nne ssw and ese wnw respectively this sequence of major tectonic events and their relationship to metamorphism are interpreted within the framework of the subduction of the pindos ocean and then of the adria continental passive margin

astronomical calibration of the maastrichtian late cretaceous abstract recent improvements to astronomical modeling of the solar system have contributed to important refinements of the cenozoic time scale through astronomical calibration of sedimentary series we extend this astronomical calibration into the cretaceous on the base of the 405 ka orbital eccentricity variation thanks to the recovery of well preserved maastrichtian sedimentary series from odp ocean drilling program holes 1258a leg 207 equatorial atlantic 1267b leg 208 south atlantic 762c leg 122 indian ocean and dsdp deep sea drilling program hole 525a leg 74 south atlantic cyclostratigraphic analysis is performed on high resolution measurements of magnetic susceptibility on sediments cored during legs 207 and 208 and gray level variations of sediment color obtained from core photographs from legs 122 and 74 astronomical control on sedimentation is evident at every site with the presence of cycles corresponding to forcing by precession obliquity and orbital eccentricity variations identification of these cycles leads to the definition of a detailed cyclostratigraphic frame covering nearly 8 ma from the upper campanian to the cretaceous paleogene k pg boundary durations of each magnetochron from c32r 2r to c29n are inferred by cycle counting astronomical calibrations of maastrichtian sedimentary series are proposed based on the 405 ka eccentricity variation according to the most recent astronomical solution la2010a two different ages are suggested for the k pg boundary considering the uncertainty of the long term variation of the 405 ka eccentricity cycle the first proposal provides a cretaceous paleogene boundary age of 65 59 0 07 ma and the second an age of 66 0 07 ma which is coherent with the most recent radio isotopic datings magnetochron boundaries and the campanian maastrichtian boundary are dated relative to these numerical ages of the k pg boundary

from ductile to brittle evolution and localization of deformation below a crustal detachment tinos cyclades greece 1 the cycladic oligo miocene detachment of tinos island is an example of a flat lying extensional shear zone evolving into a low angle brittle detachment a clear continuum of extensional strain from ductile to brittle regime is observed in the footwall the main brittle structures marking extension are shallow and steeply dipping normal faults associated with subvertical extensional joints and veins the earliest brittle structures are low angle normal faults which commonly superimpose on and reactivate earlier precursory ductile shear bands but newly formed low angle normal faults could also be observed low angle normal faults are cut by late steeply dipping normal faults the inversion of fault slip data collected within and away from the main detachment zone shows that the direction of the minimum stress axis is strictly parallel to the ne sw stretching lineation and that the maximum principal stress axis remained subvertical during the whole brittle evolution in agreement with the subvertical attitude of veins throughout the island the high angle of 1 to the main detachment suggests that the detachment was weak this observation together with the presence of a thick layer of cataclasites below the main detachment and the kinematic continuum from ductile to brittle leads us to propose a kinematic model for the formation of the detachment boudinage at the crustal scale induces formation near the brittle ductile transition of ductile shear zones near the edges of boudins shear zones are progressively exhumed and replaced by shallow dipping cataclastic shear zones when they reached the brittle field most of the displacement is achieved through cataclastic flow in the upper crust and only the last increment of strain gives rise to the formation of brittle faults the formation of the low angle brittle detachment is thus prepared by the ductile shear zone and the cataclasites and favored by the circulation of surface derived fluids in the shear zone

volcanological and tectonic control of stratigraphy and structure in the western deccan traps many of the world s flood basalt provinces form elevated plateaux at the margins of continents although in most cases their present large elevation is not the result of mountain building processes several explanations have recently been put forward to explain such occurrences of epeirogeny the deccan trap basalt province forms one such elevated plateau and results are presented here showing how the epeirogenic uplift in this region combined with crustal subsidence probably associated with the rifting of the indian continental margin has affected the structure of the basalt sequence trace element analytical data are used for samples from numerous vertical sections through the deccan traps lava series along and around the western ghats ridge in india the results reinforce the previously defined stratigraphy of the mahabaleshwar area and extend it over a region covering some 36 000 km2 reaching as far south as belgaum and the trap basement contact these results show that the lava pile is not flat lying but forms a very low amplitude anticlinal fold structure plunging southwards by up to 0 3 over most of the area although in the south there is evidence of a reversal of this plunge the fold is interpreted as being the result of two tilting processes 1 westward tilting near the coast due to the foundering of the passive continental margin and 2 epeirogenic uplift along the whole west coast of india producing the observed topography and the peninsula wide drainage patterns and also the easterly component of dip variations in the magnitude of the latter effect along the western continental margin may also be important in generating the plunge of the fold although the possibility of some component of depositional dip may also be important this latter possibility can be modelled using a simple computer program the results of this modelling show that a migrating linear volcanic edifice fits the observations best

conditioning a process based model of sedimentary architecture to well data abstract prediction of sedimentary architecture for modeling of fluid flow in hydrocarbon reservoirs and aquifers is accomplished mainly using stochastic structure imitating models because these can be conditioned to data from wells seismic profiles and outcrop analogs conditioning implies that modeled architecture fits all available observations however the sedimentary architecture simulated by such models is commonly unrealistic process based forward models potentially provide more realistic prediction and understanding of sedimentary architecture but these models are not widely used because conditioning to well seismic or outcrop data is considered to be very difficult we show here that conditioning of process based models to well data is possible in principle using a 3d alluvial architecture model as an example this model considers the formation of alluvial deposits as a predominantly deterministic process with a single channel belt moving by avulsion over an aggrading floodplain however the initial floodplain topography is simulated by a random field thus yielding different model output for each run monte carlo simulation was used to produce model realizations that fit five hypothetical vertical wells within predetermined tolerance bands such simulation allows calculation of the probability of occurrence of channel belt deposits for each 3d cell in the 3d block of sediments generated by the model as well as the probability distributions of volumes of channel belt deposits and connectedness ratios adding more conditioning wells increases the precision of model predictions application of this approach in practice will require a major effort particularly in overcoming the anticipated large amounts of computing time

complexity in a cellular model of river avulsion abstract we propose a new model of river avulsion that emphasizes simplicity self organization and unprogrammed behavior rather than detailed simulation the model runs on a fixed cellular grid and tracks two elevations in each cell a high elevation representing the channel levee top and a low one representing the channel bottom the channel aggrades in place until a superelevation threshold for avulsion is met after an avulsion is triggered a new flow path is selected by steepest descent based on the low values of elevation flow path depends sensitively on floodplain topography particularly the presence of former abandoned channels several behavioral characteristics emerge consistently from this simple model 1 a tendency of the active flow to switch among a small number of channel paths which we term the active channel set over extended periods leading to clustering and formation of multistory sand bodies in the resulting deposits 2 a tendency for avulsed channels to return to their previous paths so that new channel length tends to be generated in relatively short segments and 3 avulsion related sediment storage and release leading to pulsed sediment output even for constant input each of these behaviors is consistent with observations from depositional river systems a single valued threshold produces a wide variety of avulsion sizes and styles larger nodal avulsions are rarer because pre existing floodplain topography acts to steer flow back to the active channel channel stacking pattern is very sensitive to floodplain deposition this work highlights the need to develop models of floodplain evolution at large time and space scales to complement the improving models of river channel evolution

conditions for branching in depositional rivers it is often taken for granted that rivers organize transport into a single active channel in some net depositional environments however flow of water and sediment is distributed in several stable channels such branching rivers may be confined in valleys anabranching or anastomosed or unconfined on deltas distributaries and their existence confronts us with the very basic question of what governs the spatial organization of channel patterns in sedimentary landscapes current models for equilibrium channel morphology cannot predict the occurrence of branching rivers because they do not consider dynamical processes such as avulsion i e the rapid abandonment of a channel in favor of a new path at lower elevation the requisite conditions for avulsion have been the subject of ongoing debate here we resolve the conditions leading to channel avulsion and show that branching rivers occur when avulsion is the dominant mechanism of lateral channel motion a compilation of field and laboratory data demonstrates that avulsion frequency scales with the time required for sedimentation on channel beds to produce a deposit equal to one channel depth from the relative rates of bank erosion and channel sedimentation we derive a dimensionless mobility number that accurately predicts the conditions under which anabranching and distributary channels occur results may be directly applied to modeling landscape evolution over human and geologic time scales and for inverting formative environmental conditions from channel deposits on earth and other planetary surfaces

underthrusting and exhumation a comparison between the external hellenides and the hot cycladic and cold south aegean core complexes greece 1 after their emplacement in the course of the late mesozoic and the cenozoic the hellenic nappes became fragmented during late orogenic extension since the late eocene here we focus on the transition of underthrusting during nappe emplacement to exhumation during late orogenic extension to this end we compared previously published data on the structural geological and metamorphic history of the underthrusted parts of the tripolitza and ionian nappes which were exhumed in the cycladic and south aegean windows with newly obtained data on the sedimentary stratigraphic and structural development of the part of these nappes in the foreland in front of the subduction thrust the results allow the identification of two major events event 1 took place around the eocene oligocene transition and marks the onset of underthrusting of the tripolitza nappe below the pindos nappe and the ionian nappe below the tripolitza nappe respectively this led to the uplift and erosion of the pindos unit and the onset of deposition of the tripolitza and ionian flysch in front of the pindos thrust together with the formation of mylonites at the base of the metamorphosed portions of the pindos unit related to the underthrusting of the tripolitza unit event 2 occurred in the latest oligocene to earliest miocene and marks the decoupling of the ionian unit from the underthrusting plate the accretion of the tripolitza and ionian units to the overriding plate and the onset of late orogenic extension and exhumation in the overriding plate this led to the formation of the south aegean and cycladic core complexes and the subsidence of the klematia paramythia half graben throughout the early miocene

significance of channel belt clustering in alluvial basins the distribution of channel deposits in alluvial basins is commonly used to interpret past changes in climate tectonics and sea level here we present preliminary evidence that longtime scale 10 3 10 5 yr self organization in fl uvial systems may generate structured stratigraphic patterns spontaneously in the absence of or independent from changing basin boundary conditions a physical experiment and an ancient alluvial succession ferris formation latest cretaceous paleogene south central wyoming both show stratigraphy where clusters of many closely spaced channel deposits are separated from each other by extensive intervals of overbank mudstones analysis using spatial point process methods shows that channel deposits in both basins are statistically clustered over intermediate basin length scales in the experiment external controls base level subsidence rate and sediment water supplies were not varied and therefore not factors in cluster formation likewise the ancient system lacks stratigraphic and sedimentologic evidence of external controls on channel clustering we propose that channel clusters as seen in this study refl ect a scale of flself organization that is not usually recognized in ancient deposits this type of internally generated stratigraphy should be considered when reconstructing tectonic climate and sea level changes from

magnetostratigraphy and 40ar 39ar geochronology of the malwa plateau region northern deccan traps central western india significance and correlation with the main deccan large igneous province sequences abstract basaltic lava flows of malwa plateau together with the mandla area and the toranmal section constitute the northern deccan province in central western india with the present outcrop area of 80 000 km2 the malwa flows form an extensive but relatively thin sequence we sampled deccan basalts along two 100 km each n s and e w transects along the western and southern rims of the malwa plateau the 67 12 0 44 ma 40ar 39ar age obtained in the present study clearly shows that the eruption of the malwa flows started during the magnetochron c30n by mapping the magnetic c30n c29r transition on the western and southern edge of the plateau the total volume and eruption rate can be calculated 42 000 km3 0 03 km3 a furthermore the results point towards the narmada tapi rift zone as the possible source area for the malwa lava flows the malwa sequence is older and partly synchronous with the thick sequences of the western ghats since their eruption centers are spatially independent they should not be correlated with younger although geochemically similar formations of the western ghats other northern deccan flows show clear similarities with the malwa flows and can be magnetostratigraphically and geochemically correlated we therefore suggest a new subgroup for the northern deccan province the narmada subgroup defined on the geochemical and magnetic characteristics of the malwa mandla and toranmal flows the introduction of this new subgroup clarifies the position of the northern deccan province in the deccan stratigraphy and is a step towards a better understanding of the deccan eruption history

layer parallel shortening and related structures in zones undergoing active regional horizontal extension folds and thrust faults formed by layer parallel shortening coaxial with extensional structures such as normal dip slip faults and ductile necking structures with orthorhombic fabric symmetry are usual but little recognised structures formed within normal dip slip shear zones bounding rifts they are generated because of the shear distribution in a zone of progressive deformation and may be later extended and disrupted depending on which part of the strain ellipsoid they may be located we here describe folds and thrust faults from the southern margin of the alasehir rift in western turkey as an opportunity to discuss the properties of pureextension related structures formed by layer parallel shortening such structures are more commonly generated during the early stages of rifting when deformation rates are slow and the shear zones broader than those forming later in the life of a rift when strain rates are usually higher such structures have commonly been mistaken for witnesses documenting regional episodes of shortening rather than as integral parts of the extensional structures forming rifts not all layer parallel shortening related structures therefore indicate regional shortening we plead that hasty statements concerning the meaning of geological structures at all scales be avoided before a thorough understanding of bulk strains that have affected a region are properly understood

a new high resolution chronology for the late maastrichtian warming event establishing robust temporal links with the onset of deccan volcanism the late maastrichtian warming event was defined by a global temperature increase of 2 5 5 c that occurred 150 300 k y before the cretaceous paleogene k pg mass extinction this transient warming event has traditionally been associated with a major pulse of deccan traps west central india volcanism however large uncertainties associated with radiogenic dating methods have long hampered a definitive correlation here we present a new high resolution single species benthic stable isotope record from the south atlantic calibrated to an updated orbitally tuned age model to provide a revised chronology of the event which we then correlate to the latest radiogenic dates of the main deccan traps eruption phases our data reveal that the initiation of deep sea warming coincides within uncertainty with the onset of the main phase of deccan volcanism strongly suggesting a causal link the onset of deep sea warming is synchronous with a 405 k y eccentricity minimum excluding a control by orbital forcing alone although amplified carbon cycle sensitivity to orbital precession is evident during the greenhouse warming a more precise understanding of deccan induced climate change paves the way for future work focusing on the fundamental role of these precursor climate shifts in the k pg mass extinction

abrupt deep sea warming at the end of the cretaceous climatic and oceanographic variations during the last 2 m y of the maastrichtian inferred from high resolution 10 k y stable isotope analysis of the mid latitude south atlantic deep sea drilling project site 525 reveal a major warm pulse followed by rapid cooling prior to the cretaceous tertiary boundary between 66 85 and 65 52 ma cool but fluctuating temperatures average 9 9 and 15 4 c in intermediate and surface waters respectively this interval is followed by an abrupt short term warming between 65 45 and 65 11 ma which increased temperatures by 2 3 c in intermediate waters and decreased the vertical thermal gradient to an average of 2 7 c this warm pulse may be linked to increased atmospheric pco 2 increased poleward heat transport and the switch of an intermediate water source from high to lowmiddle latitudes during the last 100 k y of the maastrichtian intermediate and surface temperatures decreased by an average of 2 1 and 1 4 c respectively compared to the maximum temperature between 65 32 and 65 24 ma

geometry and kinematics of mykonos detachment cyclades greece evidence for slip at shallow dip 1 the eastern part of mykonos island cyclades greece shows the detailed internal structure of a two branch shallow dipping extensional detachment system of miocene age this paper shows that the last stage of slip along the detachment during the deposition of syn rift sediments occurred with a very low dip and proposes that this geometry prevailed since the initiation of extension extensional deformation during and after a 13 ma old granite intrusion is taken up by two main shallow dipping shear zones 1 the lower livada detachment which extends laterally across tinos island is a ductile structure located at the interface between the granite and the upper cycladic nappe metabasites a pervasive top to the ne shearing deformation is observed throughout the granite in this island with a strong gradient toward the intrusive contact later brittle faults shallowly and steeply dipping rework the ductile deformation with the same overall shear sense 2 the upper mykonos detachment is brittle and separates the metabasites from late miocene sandstones and conglomerates the detachment fault dips 12 15 toward the nne and its sense of shear is consistent with that of the livada detachment soft sediment deformation during the time of detachment faulting and the presence of steep normal faults that root into the detachment gouge indicate a shallow depth of deformation rotations about vertical and horizontal axes can be reconstructed within and below the detachment zone indicating that the overall direction of extension is nne ssw with a sense of shear toward the nne and the dip of the fault is throughout very low the two detachments have accommodated several tens of kilometers of horizontal extension during the formation of the aegean sea which emphasizes the importance of low angle extensional faults and shear zones in extensional tectonics

constraining the long term evolution of the slip rate for a major extensional fault system in the central aegean greece using thermochronology the brittle ductile transition is a major rheologic boundary in the crust yet little is known about how or if rates of tectonic processes are influenced by this boundary in this study we examine the slip history of the large scale naxos paros extensional fault system npefs cyclades greece by comparing published slip rates for the ductile crust with new thermochronological constraints on slip rates in the brittle regime based on apatite and zircon fission track aft and zft and u th he dating we observe variable slip rates across the brittle ductile transition on naxos zft and aft ages range from 11 8 0 8 to 9 7 0 8 ma and 11 2 1 6 to 8 2 1 2 ma and u th he zircon and apatite ages are between 10 4 0 4 to 9 2 0 3 ma and 10 7 1 0 to 8 9 0 6 ma respectively on paros zft and aft ages range from 13 1 1 4 ma to 11 1 1 0 ma and 12 7 2 8 ma to 10 5 2 0 ma while the u th he zircon ages are slightly younger between 8 3 0 4 ma and 9 8 0 3 ma all ages consistently decrease northwards in the direction of hanging wall transport most of our new thermochronological results and associated thermal modeling more strongly support the scenario of an identical fault dip and a constant or slightly accelerating slip rate of 6 8 km myr 1 on the npefs across the brittle ductile transition even the intrusion of a large granodiorite body into the narrowing fault zone at 12 ma on naxos does not seem to have affected the thermal structure of the area in a way that would significantly disturb the slip rate the data also show that the npefs accomplished a minimum total offset of 50 km between 16 and 8 ma

direct high precision u pb geochronology of the end cretaceous extinction and calibration of paleocene astronomical timescales abstract the cretaceous paleogene k pg boundary is the best known and most widely recognized global time horizon in earth history and coincides with one of the two largest known mass extinctions we present a series of new high precision uranium lead u pb age determinations by the chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims method from volcanic ash deposits within a tightly constrained magnetobiostratigraphic framework across the k pg boundary in the denver basin colorado usa this new timeline provides a precise interpolated absolute age for the k pg boundary of 66 021 0 024 0 039 0 081 ma constrains the ages of magnetic polarity chrons c28 to c30 and offers a direct and independent test of early paleogene astronomical and 40ar 39ar based timescales temporal calibration of paleontological and palynological data from the same deposits shows that the interval between the extinction of the dinosaurs and the appearance of earliest cenozoic mammals in the denver basin lasted 185 ky and no more than 570 ky and the fern spike lasted 1 ky and no more than 71 ky after the k pg boundary layer was deposited indicating rapid rates of biotic extinction and initial recovery in the denver basin during this event

a comparison of geodetic and finite strain pattern in the aegean geodynamic implications abstract a comparison of the active strain pattern of the aegean constrained by global positioning system measurements and the oligo miocene finite strain field shows some striking similarities in terms of direction and rates of extension the geometry of extension at crustal scale is also very similar with north dipping normal faults connecting near the brittle ductile transition to shallow north dipping shear zones this pattern of extension is not significantly modified by the recent extrusion of the motion of anatolia and aegea the persistence over more than 25 myr of the same pattern of extension suggests that the cause for extension resides within the aegean lithosphere gravitational collapse allowed by extensional boundary conditions after 30 ma slab retreat is the primary cause for post orogenic extension in the aegean and western anatolia

on impact and volcanism across the cretaceous paleogene boundary the cause of the end cretaceous mass extinction is vigorously debated owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary disentangling their relative importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing impact and extinction we used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing we found support for major outgassing beginning and ending distinctly before the impact with only the impact coinciding with mass extinction and biologically amplified carbon cycle change our models show that these extinction related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide thus limiting the global warming otherwise expected from postextinction volcanism

a continuum mechanics approach to quantify brittle strain on weak faults application to the extensional reactivation of shallow dipping discontinuities a number of field observations suggest that sliding on fault planes may occur at very shallow dip in the brittle field the existence of active low angle normal faults is much debated because 1 the classical theory of fault mechanics implies that faults are locked when the dip is less than 30 and 2 shallow dipping fault planes do not produce large earthquakes m 5 5 to reconcile observations and theory we propose a new model for fault reactivation by introducing an elasto plastic frictional fault gouge as an alternative to the classical dislocation models with frictional properties contrary to the classical model which implies that the dilation angle equals the friction angle our model accounts for and permits 0 in the fault gouge as deduced from laboratory and field observations whilst the predicted locking angles differ in most cases by less than 10 from the classical model a significant amount of plastic strain strain occurring in elasto plastic regime is predicted to occur on badly oriented faults prior to locking in a strain hardening regime we describe four modes of reactivation which include complete partial reactivation with without tensile failure in the surrounding medium this paper presents analytical solutions to separate those four different modes as well as numerically computed estimates of the amount of plastic strain accumulated before locking we conclude that plastic strain on badly oriented faults is favoured by compaction of the fault gouge and that those faults are probably aseismic because this strain always occurs in a hardening regime

determination of widths of meander belt sandstone reservoirs from vertical downhole data mesaverde group piceance creek basin colorado paleohydrologic reconstructions have been applied to downhole measurements made in the u s department of energy s multi well experiment mwx wells in order to derive sand body widths for the nonmarine part of the mesaverde group cretaceous in the east central part of the piceance creek basin of northwestern colorado these sediments were deposited in a predominantly meandering fluvial system paleochannel depths recognized in the wells from the heights of fining upward trends in core can be converted to channel widths using a published formula the resulting channel widths are used to calculate meander belt amplitudes sand body widths from relationships derived from published empirical data the estimate of width derived from this technique can be compared with sa d body widths derived by three other methods these various techniques give compatible results indicating the validity of the downhole technique

westward propagation of the north anatolian fault into the northern aegean timing and kinematics we present new evidence for the propagation processes of the north anatolian fault folding in the dardanelles straits region allows us to document the timing of the deformation preceding and the finite displacement after the passage of the propagating tip of the fault the accuracy of the observations is due to interplay between deformation and the sea level changes in the mediterranean the well known messinian regression followed by the pliocene transgression the long term kinematics around the sea of marmara pull apart total displacement of about 85 km over the past 5 m y is similar to the present day kinematics deduced from space geodesy at a larger scale westward propagation of the north anatolian fault over nearly 2000 km in the past 10 m y appears to be associated with strain recovery suggesting that the continental lithosphere retains long term elasticity

quantitative models of sedimentary basin filling summary quantitative modelling of the filling of sedimentary basins was begun in earnest in the 1960s dozens of themes and variations have been proposed since then and have yielded an abundance of idealized stratigraphic patterns as functions of both imposed changes and basin properties post plate tectonic modelling began with rigid lid models which show the stratigraphic signature of subsidence variation this work introduced the connection between stratigraphy and the rheology of the lithosphere rigid lid models are the simplest type of geometric model in which the sediment surface is assigned prescribed geometries usually corresponding to different depositional environments these can reproduce many aspects of overall stratal geometry but are formally restricted to relatively long timescales for which quasi steady surface topography can be assumed so called dynamic models attempt to represent the morphodynamics of the sediment surface by abstracting and averaging short term transport processes most of the dynamic models proposed to date can be seen as special cases of a single general morpho dynamic equation the most important result of the first wave of quantitative basin filling models is that even relatively simple models can produce reasonable stratal patterns we now have a wide array of tools for exploring scenarios searching for general behaviours and effects and making initial quantitative predictions we have also learned that basin response to external forcing as recorded in stratigraphy can be as sensitive to the characteristics of the basin as to the forcing the main brake on the development of basin modelling is not computing power but lack of methods and data for testing the models we have already developed physical experiments which are only just beginning are one means of doing this experimental stratigraphy is a bridge to quantitative field tests which will require collaboration among academic researchers from a wide range of areas and between academia and industry on projects of greater scale and degree of integration than we have seen so far the advancement of quantitative sedimentary geology will also require significant changes in the way the subject is taught at all levels

the eruptive tempo of deccan volcanism in relation to the cretaceous paleogene boundary late cretaceous records of environmental change suggest that deccan traps dt volcanism contributed to the cretaceous paleogene boundary kpb ecosystem crisis however testing this hypothesis requires identification of the kpb in the dt we constrain the location of the kpb with high precision argon 40 argon 39 data to be coincident with changes in the magmatic plumbing system we also found that the dt did not erupt in three discrete large pulses and that 90 of dt volume erupted in 1 million years with 75 emplaced post kpb late cretaceous records of climate change coincide temporally with the eruption of the smallest dt phases suggesting that either the release of climate modifying gases is not directly related to eruptive volume or dt volcanism was not the source of late cretaceous climate change

three dimensional model of alluvial stratigraphy theory and applications abstract a three dimensional model of alluvial stratigraphy has been developed to simulate the spatial distribution proportion and connectedness of coarse grained channel belt deposits in alluvial strata as a function of channel belt width floodplain width bankfull channel depth channel belt and overbank sedimentation rates avulsion location and period compaction and tectonism tilting and faulting in this model a floodplain surface of variable width and length is occupied by a single channel belt changes in floodplain topography are produced by spatial and temporal variation of channel belt and floodplain deposition rates and by compaction and local or regional tectonism the location and timing of avulsions are determined by local changes in floodplain slope relative to channel b lt slope and by flood magnitude and frequency the diverted channel belt follows the locus of maximum floodplain slope at the end of each simulation architectural parameters are calculated including channel deposit proportion and connectedness and the dimensions of channel belt sandstone bodies three dimensional perspective diagrams mesh surfaces and two dimensional stratigraphic sections can be plotted to illustrate depositional surfaces time planes and the location and geometry of coarse grained channel belt deposits within finer grained overbank deposits the model predicts that channel belt proportion and connectedness and dimensions of sandstone bodies vary as a function of distance from avulsion points and cross section orientation upstream from avulsion points sandstone bodies have low width thickness ratios because of aggradation in a fixed channel belt immediately downstream from avulsion points channel belts tend to be connected resulting in sandstone bodies with high width thickness ratios avulsion sequences develop where points of avulsion shift up valley with a progressive decrease in avulsion period such sequences may produce successions in which channel belt proportion and connectedness vary vertically with a cyclic period of 103 to 105 years down valley increases in aggradation rate or down valley decreases in floodplain slope for example associated with a rise in base level may result in an increase in channel belt proportion and connectedness because of high avulsion frequencies in down valley regions of the floodplain down valley decreases in aggradation rate as in alluvial fans foreland basins and during base level fall may result in high avulsion frequencies in up valley parts of the floodplain tectonic tilting and faulting locally increase avulsion probabilities and channel belts generally shift toward areas of maximum subsidence under certain conditions however depositional topography may cause channels to shift away from areas of maximum subsidence channel deposit proportion and connectedness are gen rally high near downthrown areas of the floodplain but distribution clustering of channel belts may not be a reliable indicator of fault geometry or displacement models of alluvial architecture that consider only sediment accumulation rate as the main controlling factor are oversimplified the three dimensional model presented here predicts many of the features of channel behavior observed in modern rivers but there is a pressing need for better models and adequate natural data to test them

granite intrusion in a metamorphic core complex the example of the mykonos laccolith cyclades greece abstract the aegean domain is a well suited place to study the formation of metamorphic core complex mcc and to investigate the role of syn tectonic granites on their development in the northern cyclades the mykonos delos rhenia mcc is characterized by the intrusion of a kilometer scale late miocene pluton of i type granitoids within a migmatitic gneiss dome new combined ams anisotropy of magnetic susceptibility and microstructural studies on the mykonos granitoids together with recently published thermochronological data allow us to use the granitoids as strain markers the mykonos granitoids form a laccolith like intrusion with a n70 e long axis the laccolith is strongly asymmetric with an outlying root zone to the sw and a major body mainly developed to the ne the laccolith construction is due to successive pulses of more or less differentiated magma that intruded the cycladic blueschist unit the attitude of stretching markers suggests an important about 60 vertical axis local rotation phenomenon in the cycladic upper crust during the exhumation of the mykonos mcc structural data suggest a four stage evolution of the mykonos mcc i a first stage characterized by flat shearing toward the n ne and by the formation of a domal structure in migmatitic paragneisses with multi scale generation of folds with axes either perpendicular or parallel to the regional stretching as a result of the interplay between regional n20 e directed extension and ew shortening ii a second stage marked by the emplacement of the mykonos laccolith at 13 5 0 3 ma at the top of the migmatitic paragneisses iii the third stage corresponding to the development of protomylonitic foliations and lineations in the whole laccolith in high to medium temperature conditions and iv the late stage marked by an acceleration of the exhumation of the mykonos mcc this exhumation was accommodated by important rotations of upper crustal blocks during the end of the exhumation processes around 10 ma deformation localized at the top of the laccolith in semi ductile conditions and then in brittle conditions in the major detachment plane our study shows that the cycladic plutonism event had no role on the initiation of the mcc however the geometry of the mykonos intrusion supports that the magmas are sucked into the direction of regional extension and that the intrusion of magmas has caused an acceleration of the last stages of the mcc development this acceleration was marked by a very fast exhumation of the laccolith after its emplacement

causes of river avulsion insights from the late holocene avulsion history of the mississippi river u s a abstract the emphasis on gradient advantages in studies of avulsion is misleading while gradient advantages are necessary for an avulsion to occur the late holocene avulsion history of the mississippi river in louisiana suggests that factors such as substrate composition and floodplain channel distributions are more important cross valley to down valley slope ratios of the modern floodplain range from 16 to 110 and are typically 30 the slope ratio is 35 at the location of the mississippi atchafalaya diversion old river yet slope ratios are 83 to 110 immediately upvalley of old river all values of mississippi river floodplain slope ratios are significantly larger than values of avulsion threshold calculated by numerical models shallow floodplain cores 14c dating of organic remains and geologic mapping show that the mississippi river has avulsed only four times over the past 5 ky in the southern lower mississippi valley lmv gradient advantages are widespread yet avulsions are rare these observations indicate that factors other than gradient advantage control mississippi river avulsion several examples of mississippi and red river avulsion by channel reoccupation support the idea that channel distributions and substrate compositions are primary influences on avulsion incipient mississippi river avulsion and development of the atchafalaya river involved reoccupation of abandoned mississippi river channels and a red river crevasse splay complex the modern atchafalaya river also incises buried mississippi river channel belt sands abandoned channel belts and crevasse splay complexes consist of sandy substrates that facilitate scour and the development of channels capable of capturing the mississippi river abandoned channels provide ready made conduits for mississippi river flow that can efficiently develop into avulsive channels multi storied sheet sandstones in ancient fluvial deposits may provide additional support for the idea that erodible substrates and floodplain channel distributions are critical influences on avulsion these features record episodic reoccupation of channel belts which at least in some cases may simply reflect successive avulsions rather than major changes in aggradation rate or extrabasinal factors such as climate

first quantitative test of alluvial stratigraphic models southern rio grande rift new mexico since 1978 the results of computational architectural models have been widely used to aid interpretation of ancient alluvial successions here we present the first quantitative test of such models we parameterize variables from field and magnetostratigraphic data collected from the well exposed pliocene pleistocene camp rice and palomas formations of the rio grande rift in south central new mexico computational runs establish that the lab leeder allen and bridge model correctly predicts the gross architectural patterns of ancestral axial rio grande half grabens and full grabens convergence of tectonic subsidence rate and mean sedimentation rate over the studied interval suggests that the dynamic basis of the models is correct i e it is the tectonic drawdown of axially supplied sediment that controls the net preservation potential of alluvial successions

volatile fluxes during flood basalt eruptions and potential effects on the global environment a deccan perspective abstract we examine the role that flood basalt eruptions may have played during times of mass extinction through the release of volcanic gases continental flood basalt provinces have formed by numerous eruptions over a short period of geologic time characteristically a few million years within this period a short lived climactic phase that lasts about 1 ma typically emplaces a large proportion of the lava volume this phase consists of a series of huge eruptions each yielding 10 3 10 4 km 3 of magma each eruption lasted on the order of a decade or more and built an immense p hoehoe dominated lava flow field by eruptive activity along fissures tens to hundreds of km long high fire fountains emanating from vents along the fissures at times sustained eruption columns that lofted gas and ash into the upper troposphere and lower stratosphere while the lava flows covered huge areas the combination of large eruption magnitudes maintained high effusion rates during eruptions and the repeated nature of the characteristic large scale eruptive activity occurs in earth history only during periods of flood basalt volcanism based on recent analogs and determination of volatile contents of ancient flood basalt lavas we estimate that individual eruptions were capable of releasing 10 000 tg of so 2 resulting in atmospheric loadings of 1000 tg a 1 during a sustained decade long eruptive event we apply this model of flood basalt volcanism to estimate the potential mass of co 2 and so 2 released during formation of the 65 ma deccan province the deccan lava pile contains the record of hundreds of enormous p hoehoe flow fields erupted within a period of about 1 ma consequently atmospheric perturbations associated with so 2 emissions from just one of these long lasting eruptions were likely to have been severe and constantly augmented over a decade or longer by contrast the amounts of co 2 released would have been small compared with the mass already present in the atmosphere and thus much more limited in effect individual eruptions were followed by hiatuses of hundreds to thousands of years during which the gas contributions to the atmosphere would be recycled it is clear that the nature and potential atmospheric impact of a series of huge volume repeated long term degassing events requires further investigation in conjunction with appropriate climate models

high resolution chronostratigraphy of the terrestrial cretaceous paleogene transition and recovery interval in the hell creek region montana detailed understanding of ecosystem decline and recovery attending the cretaceous paleogene boundary kpb mass extinctions is hindered by limited constraints on the pace and tempo of environmental events near the boundary to mitigate this shortcoming high resolution 40ar 39ar geochronology was performed on tephras intercalated between fossiliferous terrestrial sediments of the upper hell creek and lower fort union formations in the western williston basin of northeastern montana usa tephra samples were collected from 10 stratigraphic sections spanning an area of 5000 km2 several distinctive tephras can be correlated between sections separated spatially by as much as 60 km the tephras are thin distal deposits generally preserved only in lignite beds which are interbedded with clastic deposits yielding vertebrate faunas of lancian late maastrichtian to torrejonian early danian north american land mammal ages sanidine from 15 tephra samples was analyzed in 1649 total fusion experiments 1597 on single crystals and 12 incremental heating analyses of multigrain aliquots ages were determined for 13 distinct tephras ranging from 66 289 0 051 to 64 866 0 023 ma including only analytical uncertainties this level of precision is sufficient to resolve the ages of all of the coal beds that have served as a basis for a regional stratigraphic framework the data confirm that the hell creek fort union formational contact is diachronous and further support the age of the kpb impact layer at 66 043 0 010 ma or 0 043 ma considering systematic uncertainties application of the new results to previous magnetostratigraphic data indicates an appreciably compressed time interval between the base of chron c29r and the top of chron c28r with a maximum duration estimate of 1 421 0 066 ma most notable is the implied brevity of chron c29r with a maximum estimate of 457 54 ka and possibly as brief as 345 38 ka compared to the 710 ka estimate from the geologic time scale 2012 gts2012 further application of new results to terrestrial biostratigraphy adds higher precision to the timing and tempo of biotic change before and after the kpb our results indicate that the timing of pre kpb ecological decline is constrained to the last 200 ka of the cretaceous adding further support to the press pulse extinction hypothesis additionally the duration of the depauperate basal paleogene puercan 1 disaster fauna is confined to a 70 ka interval faunal recovery in this region indicated by the appearance of primitive members of the placental mammal radiation and the restoration of taxonomic richness and evenness occurred within 900 ka after the kpb these results show that biotic recovery after the mass extinction in the terrestrial realm was more rapid than in the marine

crustal scale geometry and kinematics of late orogenic extension in the central aegean cyclades and ewia island abstract the aegean continental domain is known to be the site of widespread back arc extension since at least the middle miocene overprinting structures related to the mesozoic cenozoic hellenic orogeny features attributed to early thrusting include the overall ductile deformation within two broad belts that have suffered hp lt metamorphism across the aegean this study summarizes the results of a structural study in the central aegean area cyclades and evvia island examining in particular the relationship between ductile and brittle deformation on a regional scale extension appears to be responsible for most of the ductile deformation within hp rock units that have experienced penetrative greenschist facies and higher grade metamorphic overprinting on each island studied progressive extensional deformation has occurred through the development of a major normal sense detachment zone down to depths of about 18 25 km the geometry of the extensional system on the scale of the central aegean is described taking into account the characteristic features of the regional scale ductile strain field at least two probably three subparallel major north dipping detachment zones are identified trending nw se in the northwestern cyclades and e w in the southeastern cyclades both with initial dips estimated at around 30 45 the present geometry of the extensional system implies that these detachment zones and related metamorphic core complexes interfere with each other two main evolutionary models are considered which can account for such a kinematic link between parallel detachment zones structural data favour the sequential development of synthetic major detachments zones in a direction opposite to the sense of dip of the detachments early oligocene lower miocene detachment type extension in the area studied is related to a late orogenic post thickening back arc setting

ductile and brittle shortening extension parallel folds and maintenance of crustal thickness in the central aegean cyclades greece in contrast to previous studies that concentrated on the two dimensional crustal strain in the central aegean region cyclades it is shown that nne ssw extension via ductile and brittle stretching and low angle detachments was accompanied and or alternated with horizontal shortening perpendicular to the stretching direction since at least the early miocene roughly e w directed ductile shortening produced large scale overturned and upright folds having axes parallel or slightly oblique to the stretching lineation upright folding and arching of low angle normal faults occurred above the brittle ductile transition and brittle e w compression culminated with vertical axis block rotations strike slip faults and minor thrusts since at least the early miocene the structure of the cycladic massif evolved through alternating and or coeval increments of horizontal shortening and vertical thinning associated with an approximately constant nne ssw stretching exact magnitudes of the vertical and horizontal deformational components are difficult to assess nevertheless we note that extensional tectonics that affected the cyclades during the last 15 20 m y have produced no net crustal thinning we suggest that crustal thickness was maintained by extension parallel folds which represent true contractional structures and that crust was fed into the extended region from its margins

mechanisms controlling the clustering of fluvial channels and the compensational stacking of cluster belts abstract analysis of sand body distribution reveals that fluvial channel sands in the upper cretaceous lower williams fork formation in the central piceance basin colorado usa are not randomly distributed but are predictable in their spatial and stratigraphic position sand bodies are organized in channel belt clusters that are compensationally stacked on different temporal scales while channel clustering occurred over a shorter period channel and channel belt scale 10s ky to 100s ky compensational stacking occurred over a much longer time scale channel cluster belts 400 ky the lower williams fork formation consists of three distinct intervals of clustered channel belts each 400 ft 122 m thick topped by a thin coal layer the primary control on the cluster formation is autogenic channel avulsion during an overall aggradational phase short lived changes in in basin accommodation caused by either changes in tectonic subsidence or high frequency eustatic changes due to milankovitch band orbital forcing at the end of each cluster interval result in a distinct increase in channel thickness and coal formation towards the end of each cycle coals at the end of each sub cluster span the entire study area but their overall thickness is greater in the inter cluster floodplain prone areas the resulting differential early coal compaction is greatest in the inter cluster areas and has a significant control on the subsequent cluster belt position overlying the coal channel sands overlying the coals are concentrated in the previously low net gross floodplain prone inter cluster areas resulting in compensationally stacked cluster belts on the longest time scale 1 to 1 5 my which encompasses the entire lower williams fork changes in channel geometries and sand body thickness seem to be controlled mainly by long term changes in eustasy and autogenic processes are of lesser importance

u pb zircon age constraints on the earliest eruptions of the deccan large igneous province malwa plateau india abstract climate instability driven by emission of volatiles during emplacement of large igneous provinces lips is frequently invoked as a potential cause of mass extinctions however documenting this process in the geologic record requires a holistic understanding of eruption rates the location of eruptive centers and potential sources of climate changing volatiles we present new chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims u pb zircon geochronology from malwa plateau basalts on the northern margin of the deccan lip india these basalts have been previously interpreted as either an extension of the province s main volcanic stratigraphy or as an independent eruptive center active up to millions of years prior to the main eruptive phase our data instead demonstrate that the lower malwa plateau basalts are temporally correlative with the first pulse of deccan volcanism and provide new constraints on its initiation and duration paleomagnetic data further indicate that upper malwa plateau basalts may be age equivalent to the second third and fourth pulses of deccan volcanism the relative thicknesses of age equivalent packages of basalt are consistent with eruption of the deccan lip from a southward migrating eruptive center the first eruptive pulse is coeval with a 200 kyr late maastrichtian warming event preserved globally in contemporaneous stratigraphic sections we propose that the first pulse of deccan magmatism was more voluminous in the north where it erupted through organic rich sedimentary rocks of the narmada tapti rift basin thermal metamorphism of these sediments could have been a source of sufficient co2 to drive the late maastrichtian warming event which if true would reconcile the apparent dampened warming signals associated with later deccan eruptive pulses

hydrothermal venting of greenhouse gases triggering early jurassic global warming abstract the climate change in the toarcian early jurassic was characterized by a major perturbation of the global carbon cycle the event lasted for approximately 200 000 years and was manifested by a global warming of 6 c anoxic conditions in the oceans and extinction of marine species the triggering mechanisms for the perturbation and environmental change are however strongly debated here we present evidence for a rapid formation and transport of greenhouse gases from the deep sedimentary reservoirs in the karoo basin south africa magmatic sills were emplaced during the initial stages of formation of the early jurassic karoo large igneous province and had a profound influence on the fate of light elements in the organic rich sedimentary host rocks total organic carbon contents and vitrinite reflectivity data from contact aureoles around the sills show that organic carbon was lost from the country rocks during heating we present data from a new type of geological structures termed breccia pipes rooted in the aureoles within the shale of the western karoo basin the breccia pipes are cylindrical structures up to 150 meters in diameter and are mainly comprised of brecciated and baked black shale thousands of breccia pipes were formed due to gas pressure build up during metamorphism of the shales resulting in venting of greenhouse gases to the toarcian atmosphere mass balance calculations constrained by new aureole data show that up to 1800 gt of co2 was formed from organic material in the western karoo basin about 15 times this amount of co2 27 400 gt may have formed in the entire basin during the intrusive event u pb dating of zircons from a sill related to many of the pipes demonstrates that the magma was emplaced 182 5 0 4 million years ago this supports a causal relationship between the intrusive volcanism the gas venting and the toarcian global warming

source and differentiation of deccan trap lavas implications of geochemical and mineral chemical variations the basalt stratigraphy of the deccan trap between mahabaleshwar ghat and belgaum over steps the basement from north to south sr isotope and zr nb ratios and sr rb and ba concentrations correlate portions of the post poladpur stratigraphy over 250 km along the western ghats thereby confirming a southerly component of dip of 0 06 at the southwestern margin the stratigraphy extends upwards from the compositionally uniform ambenali formation cox hawkesworth 1984 into a sequence of grossly heterogeneous flow units which have been allocated to the mahabaleshwar and panhala formations lightfoot hawkesworth 1988 the mahabaleshwar formation is represented only by a sequence of highly fractionated flows termed the kolhapur unit with similar 87sr 86sr0 to the mahabaleshwar 0 7045 but with sr 2 25 succeeding the kolhapur unit are a series of flows with high 87sr 86sr0 0 7045 0 705 zr nb 13 and low sr 230 but trace element concentrations similar to the mahabaleshwar formation these have been allocated to the desur unit of the panhala geochemical variations in flows overlying the ambenali define two distinct trends one is attributed to gabbro fractionation and the other to variations in the compositions of the parental magmas and arguably their source regions there is little evidence for significant crustal contamination in these flows and the degree of fractionation and the composition of the phase extract are shown to vary along strike within the mahabaleshwar formation the high tio2 content of kolhapur unit flows is shown to be the result of shallow level gabbro fractionation rather than the presence of a primitive high ti magma mahabaleshwar formation basalts exhibit a broad negative correlation between the degree of fractionation and sr isotopic composition the endmember with lower 87sr 86sr0 has different zr y from the ambenali basalts and would appear to have been generated by lower degrees of melting of a similar source the other endmember has more radiogenic sr lower zr nb similar zr y but higher mg number the simplest interpretation is that these magmas were more primitive and hence hotter and more able to interact with the lithosphere en route to the surface and that they then mixed to produce the mahabaleshwar array the panhala formation basalts plot on the sr nd array defined by the mahabaleshwar formation and the desur unit basalts plot on an extension of this array this suggests that the source characteristics are also lithospheric the absolute elemental abundances may then be a function of melting and fractionation we are impressed by the apparent switch from crustal lithospheric contributions to mantle lithospheric contributions through the stratigraphy and suggest that this together with the more protracted fractionation of the magma reflects a change in the availability of the lithospheric components accompanying the southerly migration of the volcanic edifice

widespread silicic and alkaline magmatism synchronous with the deccan traps flood basalts india abstract deccan traps dt volcanism and the chicxulub bolide impact have been suggested as potential triggers of the cretaceous paleogene boundary kpb mass extinction recently published geochronology has established a timeline for the main basaltic sequence of the dt showing that the majority of eruptions occurred within 700 800 kyr spanning the kpb silicic to alkaline magmatism linked to the dt spatially associated with the narmada lineament in central india has been long known but not as well studied previous geochronology of some of the felsic magmatic centers has yielded dates that span many millions of years making their temporal relationship with dt volcanism uncertain we present zircon u pb ages from the alech barda girnar rajula and phenai mata silicic alkaline complexes in addition to a series of trachytes on the coastal plain near mumbai while the trachytes are 64 ma and mark the continental breakup of india 1 5 myr after the main phase of dt eruptions the silicic alkaline complexes were all emplaced coevally with the main phase of dt volcanism ca 66 2 65 7 ma initial ehf in zircons 10 to 20 whole rock 87sr 86sr 0 702439 0 760932 and end 1 11 to 35 7 for all five intrusive complexes suggest a hybrid origin involving juvenile sources as well as significant assimilation of older continental crust recognition that the silicic alkaline complexes are coeval with basaltic magmatism and associated with a significant thermal imprint on the crust in and near the narmada rift sedimentary strata supports the hypothesis that outgassing of organic rich sediments may have contributed to the end maastrichtian warming and biologic crisis

slab segmentation and late cenozoic disruption of the hellenic arc the hellenic subduction zone displays well defined temporal and spatial variations in subduction rate and offers an excellent natural laboratory for studying the interaction among slab buoyancy subduction rate and tectonic deformation in space the active hellenic subduction front is dextrally offset by 100 120 km across the kephalonia transform zone coinciding with the junction of a slowly subducting adriatic continental lithosphere in the north 5 10 mm yr and a rapidly subducting ionian oceanic lithosphere in the south 35 mm yr subduction rates can be shown to have decreased from late eocene time onward reaching 5 12 mm yr by late miocene time before increasing again along the southern portion of the subduction system geodynamic modeling demonstrates that the differing rates of subduction and the resultant trench offset arise naturally from subduction of oceanic pindos lithosphere until late eocene time followed by subduction of a broad tract of continental or transitional lithosphere hellenic external carbonate platform and then by miocene entry of high density oceanic ionian lithosphere into the southern hellenic trench model results yield an initiation age for the kephalonia transform of 6 8 ma in good agreement with observations consistency between geodynamic model results and geologic observations suggest that the middle miocene and younger deformation of the hellenic upper plate including formation of the central hellenic shear zone can be quantitatively understood as the result of spatial variations in the buoyancy of the subducting slab using this assumption we make late eocene middle miocene and pliocene reconstructions of the hellenic system that include quantitative constraints from subduction modeling and geologic constraints on the timing and mode of upper plate deformation

the dan c2 hyperthermal event at gubbio italy global implications environmental effects and cause s abstract the dan c2 event is an early danian transient 100 kyr hyperthermal episode centered at 65 2 ma which records shifts in carbon reservoirs and ocean warming in the northwestern and southeastern sectors of the atlantic ocean here we present and discuss high resolution biochronostratigraphic and magnetic susceptibility data and geochemical records from the western tethyan contessa highway section gubbio italy which provide the first direct evidence of the dan c2 event beyond the atlantic ocean and point to the supra regional possibly global significance thereof at contessa highway the dan c2 event exhibits stressed ecological responses among calcareous nannoplankton and foraminifera which highlight marked environmental perturbation affecting the geobiosphere and resulting in enhanced eutrophication of the sea surface waters and carbonate dissolution as well as lowered oxygen content along the water column and at the sea bottom as for other early paleogene hyperthermal events the cause of the dan c2 event might likely to be found in changes potentially astronomically paced in the distribution of carbon within surface biosphere reservoirs however the role played by the concurrent third and last phase of deccan volcanism with its huge release of greenhouse gases into the atmosphere would be also taken into account in addition here we provide first evidence of a further short lived 38 kyr hyperthermal event not known up to now and that we term the lower c29n event

thrust or detachment exhumation processes in the aegean insight from a field study on ios cyclades greece 1 whether back arc extension in the aegean is symmetric or asymmetric at the regional scale is a key question to the understanding of the dynamics of back arc extension new field observations structural analysis of finite and instantaneous strain and their relationship with metamorphism on ios island cyclades lead us to investigate the significance of the south cycladic shear zone scsz two successive tectonometamorphic events have been documented in the hanging wall and the footwall of the scsz first penetrative top to the south shearing is observed in the upper cycladic blueschists and the lower cycladic basement close to their contact it is expressed in the hanging wall by shear bands and pressure shadows associated to blueschist facies minerals contemporaneous with overthrusting of the cycladic blueschists over the basement unit second large extensional top to the north shear zones lately crosscut the whole stack these constraints allow us to reinterpret the kinematics of the aegean domain during synorogenic and postorogenic periods when replaced in the reconstructed geometry of the hellenic eocene orogenic wedge the observed top to the south thrusting is coeval with extensional shear zones observed in syros that could represent the roof of the cycladic blueschists an extrusion structure is then proposed for the exhumation of the cycladic blueschists in the subduction zone top to the north asymmetric extension together with the andros tinos mykonos and paros naxos detachments can be correlated to oligo miocene extension in the back arc domain

extensional faulting on tinos island aegean sea greece how many detachments zircon and apatite fission track zft and aft and u th he 40ar 39ar hornblende and u pb zircon ages from the granites of tinos island in the aegean sea greece suggest together with published zft data that there are three extensional detachments on tinos the tinos granites crosscut the tinos detachment cooling of the granites was controlled by the livadi detachment which occurs structurally above the tinos detachment our u pb zircon age is 14 6 0 2 ma and two 40ar 39ar hornblende ages are 14 4 0 4 and 13 7 0 4 ma zft and aft ages go from 14 4 1 2 to 12 2 1 0 ma and 12 8 2 4 to 11 9 2 0 ma u th he ages are from 10 4 0 2 to 9 9 0 2 ma zircon and 11 9 0 5 to 10 0 0 3 ma apatite all ages decrease northeastward in the direction of hanging wall transport on the livadi detachment and age distance relationships yield a slip rate of 2 6 3 3 1 0 km ma 1 this rate is smaller than a published slip rate of 6 5 km ma 1 for the vari detachment which is another detachment structurally above the tinos detachment because of the different rates and because published zft ages from the footwall of the vari detachment are 10 ma we propose that the vari detachment has to be distinguished from the older livadi detachment we discuss various models of how the extensional detachments may have evolved and prefer a scenario in which the vari detachment cut down into the footwall of the livadi detachment successively exhuming deeper structural units the thermochronologic ages demonstrate the importance of quantitative data for constraining localization processes during extensional deformation

a geological map of the southern deccan traps india and its structural implications a geological map of an area of over 125 000 km 2 within the southern deccan traps india is presented which is based upon variations in the basalt geochemistry it represents a synthesis of new data and earlier work the use of large data sets has allowed stratigraphic boundaries to be established with greater accuracy over a much larger area than before the geochemical sections demonstrate that the southward overstepping stratigraphic style encountered along the ghats ridge has an essentially north to south polarity and that there appears to be detectable overstep in an east to west sense however the stratigraphy defines a pronounced coastward dipping monoclinal flexure across the western ghats ridge between 16 n and 18 n the data are consistent with two models of eruption the first considers the deccan eruptive focus to have been fixed throughout the volcanic episode producing an essentially annular flow pattern the second considers the flow pattern to have been generated from a southerly migrating eruptive centre resulting from the northerly drift of india over a fixed hotspot both hypotheses are consistent with recent quantitative models which suggest that rapid and voluminous flood basalt eruptions are the result of continental rifting events associated with plume generated thermal 9highs9 until a causal link between established plume hotspot trails and impact sites can be satisfactorily demonstrated we find it unnecessary to invoke a cataclysmic impact event as an explanation for the deccan eruptions

structural development of high pressure metamorphic rocks on syros island cyclades greece abstract new data obtained during re mapping of the northern part of syros cyclades greece allow the refinement of existing concepts about the structural evolution of this island a metabasite belt and its metasedimentary envelope near kampos and san michali were mapped at a 1 5000 scale with special emphasis on the structural inventory the hp lt rocks p 1 5 gpa t 500 c at 50 ma exposed are intensely deformed by at least two isoclinal folding events relative age relations between deformation and peak metamorphism indicate that isoclinal folding took place before or during peak metamorphism later deformation stages include miocene non penetrative upright kink folding and crenulation transpressional strike slip faulting and open upright cylindrical folding followed by the development of steep normal faults taking into account recent zircon u pb geochronological constraints lithostratigraphic observations and published data on the neogene structural evolution of the aegean we present a history for the rocks of syros beginning with the formation of the oceanic crust represented by the metabasites to the present

paleosol barometer indicates extreme fluctuations in atmospheric co2 across the cretaceous tertiary boundary we present an atmospheric p co 2 p is partial pressure curve showing extreme fluctuations for the interval between ca 77 and 63 ma in southern alberta canada using a paleosol barometer paleosol carbonate nodules micrite were collected from 40 bk horizons among 6 stratigraphic sections for stable carbon isotope analysis based on results from the study area declining atmospheric p co 2 from 1200 ppmv v is volume in the campanian to 780 ppmv in the maastrichtian correlates with late cretaceous climate cooling and falling sea level as documented in global records the remarkable rise in atmospheric p co 2 near 65 5 ma 1440 ppmv correlates with volcanic activity associated with the deccan traps rising sea level and warmer global climates the decline in atmospheric p co 2 760 ppmv at the cretaceous tertiary boundary and subsequent sharp rise into the danian 1000 ppmv occurred during static terrestrial temperatures and sea level this work provides compelling evidence that atmospheric p co 2 curves modeled for the phanerozoic do not offer the resolution needed to understand environmental conditions during catastrophic events in earth9s history

fluvial channel and overbank deposits from the westphalian of the durham coalfield ne england the westphalian upper carboniferous coal measures of the durham coalfield in ne england were deposited in lower and upper delta plain environments distributary channels crossed the plain and were separated by shallow interdistributary lakes and bays detailed observation of three dimensional 3 d opencast surface mine exposures in collaboration with subsurface borehole analysis has revealed the existence of five varieties of channel deposits and two associated overbank facies within the durham coal measures major distributary channels were the major avenues of sediment transport across the coal measures plain were variably sinuous mostly 1 2 km wide and deposited elongate belts of sand mostly up to 5 km wide proximal major crevasse splay channels formed by the breaching of major channel banks during flood events were straight sand filled and up to 400 m wide minor distributary channels formed by the sustained operation of such crevasses varied from straight to highly sinuous and deposited shoestring sand mud belts up to a few hundred metres wide minor crevasse channels generally straight and up to 50 m wide were formed through bank breaching of minor and in a few cases major distributaries distal feeder channels formed down palaeocurrent extensions of minor distributaries which supplied interdistributary minor delta subsystems were generally straight and up to 200 m wide of the two types of channel overbank levee deposits recognized one comprising thinly interbedded fine grained sandstone and siltstone claystone is mostly though not exclusively associated with major distributary channels the other consisting of massive siltstones with regularly spaced thin claystone bands is uniquely developed at the margins of minor distributary channels the lower part of the westphalian a succession in the northern pennines records a change in the depositional environment upwards from a lower to upper delta plain through this transition major channel deposits show evidence of having evolved from being of dominantly low sinuosity to being more variable in morphology channel sedimentation was profoundly influenced by regular possibly seasonal variations in flow stage and sediment load

u pb constraints on pulsed eruption of the deccan traps across the end cretaceous mass extinction temporal correlation between some continental flood basalt eruptions and mass extinctions has been proposed to indicate causality with eruptive volatile release driving environmental degradation and extinction we tested this model for the deccan traps flood basalt province which along with the chicxulub bolide impact is implicated in the cretaceous paleogene k pg extinction approximately 66 million years ago we estimated deccan eruption rates with uranium lead u pb zircon geochronology and resolved four high volume eruptive periods according to this model maximum eruption rates occurred before and after the k pg extinction with one such pulse initiating tens of thousands of years prior to both the bolide impact and extinction these findings support extinction models that incorporate both catastrophic events as drivers of environmental deterioration associated with the k pg extinction and its aftermath

river and floodplain process simulation for subsurface characterization subsurface heterogeneity is characterized with a method based on facies delineation and process modeling a geologic process model is formulated to simulate the development of four facies channel fill levee splay and floodplain which commonly form in a meandering river and its floodplain the model accounts for meandering cutoff flooding and crevasse splay processes and links these formational processes to the statistical properties of the resulting facies the model is utilized in a case study to simulate the horizontal pattern of deposition and facies distributions of the stratton field part of the middle frio formation of southeast texas using known or estimated relationships and historical information for the stratton field region the simulated distributions of longitudinal and transverse facies dimensions and corresponding transition probabilities among facies are compared to those determined from sampling an observed section of the field yielding similar results though some differences similarities and differences are related to the model processes and sampling procedures model sensitivity is investigated by changing selected model variables and analyzing the change in the facies distributions the application of the geologic process model to the stratton field demonstrates the viability of linking process understanding and modeling of complex meandering stream processes to characterization of subsurface heterogeneity

a high resolution marine 187os 188os record for the late maastrichtian distinguishing the chemical fingerprints of deccan volcanism and the kp impact event abstract a composite late maastrichtian 65 5 to 68 5 ma marine osmium os isotope record based on samples from the southern ocean odp site 690 the tropical pacific ocean dsdp site 577 the south atlantic dsdp site 525 and the paleo tethys ocean demonstrates that subaerially exposed pelagic carbonates can record seawater os isotope variations with a fidelity comparable to sediments recovered from the seafloor new results provide robust evidence of a 20 decline in seawater 187os 188os over a period of about 200 kyr early in magnetochron c29r well below the cretaceous paleogene boundary kpb confirming previously reported low resolution data from the south atlantic ocean new results also confirm a second more rapid decline in 187os 188os associated with the kpb that is accompanied by a significant increase in os concentrations complementary platinum pt and iridium ir concentration data indicate that the length scale of diagenetic remobilization of platinum group elements from the kpb is less than 1 m and does not obscure the pre kpb decline in 187os 188os increases in bulk sediment ir concentrations and decreases in bulk carbonate content that coincide with the os isotope shift suggest that carbonate burial flux may have been lower during the initial decline in 187os 188os we speculate that diminished carbonate burial rate may have been the result of ocean acidification caused by deccan volcanism

nature of continental crust along the narmada son lineament inferred from gravity and deep seismic sounding data abstract the narmada son lineament nsl is a very prominent feature on the tectonic map of india and divides the indian peninsula into two parts the northern part characterised by lower elevations and more positive bouguer gravity anomalies as compared to the southern part the lineament is characterised by a gravity high practically all along its length four published deep seismic sounding dss profiles across the nsl give vital information concerning its origin an analysis of the bouguer gravity field along these profiles has been carried out using all available geological and velocity density information the analysis reveals that the areas immediately south of the nsl are characterised by higher density crust in comparison to the areas north of it this increase in density could have taken place during mesozoic to tertiary times when major tectonic volcanic activity took place over peninsular india the presence of deep seated faults sediments and anomalous crust shows that the lineament has some characteristics of a rift valley

spatial variation of overbank aggradation rate and its influence on avulsion frequency river avulsions are commonly considered to be driven by the aggradation and growth of alluvial ridges and the associated increase in cross valley slope relative to either the down channel slope or the down valley slope the latter is termed the slope ratio in the present paper therefore spatial patterns of overbank aggradation rate over stratigraphically relevant time scales are critical in avulsion dominated models of alluvial architecture detailed evidence on centennial to millennial scale floodplain deposition has to date been largely unavailable new data on such long term overbank aggradation rates from the rhine meuse and mississippi deltas demonstrate that the rate of decrease of overbank deposition away from the channel belt is much larger than has been supposed hitherto and can be similar to observations for single overbank floods this leads to more rapid growth of alluvial ridges and more rapid increase in slope ratios potentially resulting in increased avulsion frequencies a revised input parameter for overbank aggradation rate was used in a three dimensional model of alluvial architecture to study its effect on avulsion frequency realistic patterns of avulsion and interavulsion periods 1000 years were simulated with input data from the holocene rhine river with avulsions occurring when the slope ratio is in the range 3 5 however caution should be practised with respect to uncritical use of these numbers in different settings evidence from the two study areas suggests that the avulsion threshold cannot be represented by one single value irrespective of whether critical slope ratios are used as in the present study or superelevation as has been proposed by other investigators

experimental study of avulsion frequency and rate of deposition in existing models of alluvial architecture it is typically assumed that mean avulsion frequency is independent of sedimentation rate however if avulsion is driven by superelevation of a river bed above its surrounding flood plain one might expect avulsion rate to increase with sedimentation rate we have carried out a series of experiments with laboratory scale fluvial fans in which we measured the frequency of apical avulsions as a function of mean sedimentation rate on the fan avulsion frequency increased strongly with increasing sedimentation rate and then stabilized as mass flows began to influence deposition in the regime of increasing avulsion frequency the added volume of sediment needed to trigger an avulsion decreased with increasing sedimentation rate although our experimental results cannot simply be scaled up to natural rivers they suggest the possibility of coupling between avulsion frequency and sedimentation rate that would be strong enough to change qualitatively the results of existing models of alluvial architecture these models should be applied with caution until avulsion mechanics are better understood

astronomical calibration of upper campanian maastrichtian carbon isotope events and calcareous plankton biostratigraphy in the indian ocean odp hole 762c implication for the age of the campanian maastrichtian boundary abstract an integrated framework of magnetostratigraphy calcareous microfossil bio events cyclostratigraphy and 13c stratigraphy is established for the upper campanian maastrichtian of odp hole 762c exmouth plateau northwestern australian margin bulk carbonate 13c events and nannofossil bio events have been recorded and plotted against magnetostratigraphy and provided absolute ages using the results of the cyclostratigraphic study and the recent astronomical calibration of the maastrichtian thirteen carbon isotope events and 40 nannofossil bio events are recognized and calibrated with cyclostratigraphy as well as 14 previously published foraminifer events thus constituting a solid basis for large scale correlations results show that this site is characterized by a nearly continuous sedimentation from the upper campanian to the k pg boundary except for a 500 kyr gap in magnetochron c31n correlation of the age calibrated 13c profile of odp hole 762c to the 13c profile of the tercis les bains section global stratotype section and point of the campanian maastrichtian boundary cmb allowed a precise recognition and dating of this stage boundary at 72 15 0 05 ma this accounts for a total duration of 6 15 0 05 ma for the maastrichtian stage correlation of the boundary level with northwest germany shows that the cmb as defined at the gssp is 800 kyr younger than the cmb as defined by belemnite zonation in the boreal realm odp hole 762c is the first section to bear at the same time an excellent recovery of sediments throughout the upper campanian maastrichtian a precise and well defined magnetostratigraphy a high resolution record of carbon isotope events and calcareous plankton biostratigraphy and a cyclostratigraphic study tied to the la2010a astronomical solution this section is thus proposed as an excellent reference for the upper campanian maastrichtian in the indian ocean

the geochemistry of indian bole horizons palaeoenvironmental implications of deccan intravolcanic palaeosurfaces deccan intravolcanic bole horizons represent weathering products formed during major hiatuses of a major volcanic episode in these quiescent periods weathering processes pervasively altered the newly formed volcanic landscape and subsequent flows covered and effectively fossilized the resulting weathered palaeosurfaces the current work is a detailed geochemical study which examines patterns of element mobilization during these intravolcanic weathering events the bole horizons normally rest on top of altered basaltic lavas both boles and altered lavas represent a comparatively early stage in weathering because the content of chemically residual elements such as aluminium and iron are closer to fresh basalt than laterite nevertheless these is clear evidence for significant chemical alteration because the more mobile elements such as calcium and sodium have been substantially removed a chemically distinctive nature for some boles can be demonstrated from chondrite normalized ree plots and in these instances strontium and neodymium isotopic compositions demonstrate that the fine grained bole material is derived from a chemically distinct source in addition thin sections reveal that these fine grained portions commonly contains glass shards and occasionally fresh phenocrysts it is therefore suggested that many deccan boles are in fact weathered pyroclastic material and that the pyroclastic content of the basaltic succession may be greater than previously supposed a significant pyroclastic input during the deccan eruptions has important palaeoenvironmental implications for the fate of late cretaceous flora and fauna in peninsular india

siberian gas venting and the end permian environmental crisis abstract the end of the permian period is marked by global warming and the biggest known mass extinction on earth the crisis is commonly attributed to the formation of the siberian traps large igneous province although the causal mechanisms remain disputed we show that heating of tunguska basin sediments by the ascending magma played a key role in triggering the crisis our conclusions are based on extensive field work in siberia in 2004 and 2006 heating of organic rich shale and petroleum bearing evaporites around sill intrusions led to greenhouse gas and halocarbon generation in sufficient volumes to cause global warming and atmospheric ozone depletion basin scale gas production potential estimates show that metamorphism of organic matter and petroleum could have generated 100 000 gt co2 the gases were released to the end permian atmosphere partly through spectacular pipe structures with kilometre sized craters dating of a sill intrusion by the u pb method shows that the gas release occurred at 252 0 0 4 million years ago overlapping in time with the end permian global warming and mass extinction heating experiments to 275 c on petroleum bearing rock salt from siberia suggests that methyl chloride and methyl bromide were significant components of the erupted gases the results indicate that global warming and ozone depletion were the two main drivers for the end permian environmental crisis we demonstrate that the composition of the heated sedimentary rocks below the flood basalts is the most important factor in controlling whether a large igneous provinces causes an environmental crisis or not we propose that a similar mechanism could have been responsible for the triassic jurassic 200 ma global warming and mass extinction based on the presence of thick sill intrusions in the evaporite deposits of the amazon basin in brazil

variability of channel belt dimensions and the consequences for alluvial architecture observations from the holocene rhine meuse delta the netherlands and lower mississippi valley u s a abstract over the past decades many studies have focused on the dimensions of channel belt sand bodies referred to as channel belts in fluvial deposits because of their relevance for hydrocarbon exploration and production some field studies have revealed a significant downstream decrease of channel belt width and width thickness ratio along the length of the channel belt to verify whether this is a common feature in fluviodeltaic settings eight holocene channel belts in the rhine meuse delta the netherlands were selected and one in the lower mississippi valley u s a we determined channel belt geometry width or width thickness ratio using geological geomorphological maps and detailed cross sections based on borings it was found that the width of channel belts encased in cohesive deposits decreases by a factor of 4 to 6 5 in a downstream direction along the length of the channel belts the width thickness ratio decreases by a factor of 2 5 to 5 on the other hand the width of a channel belt incised in a noncohesive substrate remains constant along its entire course these observations are related to longitudinal changes in bank erodibility and stream power it is suggested that bank erodibility is the dominating factor determining the geometric properties of channel belts and the variability therein at least in the rhine meuse delta the currently available alluvial architecture models most likely overestimate sand quantities and connectedness in alluvial successions because channel belt dimensions are held constant in all models we therefore propose that the factors bank erodibility and stream power which influence width and width thickness ratio of channel belts should be incorporated in future alluvial architecture models in order to make more realistic estimates of sand quantities in river deltas

palaeoenvironments of the dinosaur bearing lameta beds maastrichtian narmada valley central india abstract the maastrichtian lameta beds of central india are intimately associated with the deccan lavas and are critical to determining upper cretaceous palaeoenvironments and palaeogeography of the area in the type jabalpur sub region four mappable units of the lameta beds are recognised the basal green sandstone is interpreted as a braided stream deposit the lower limestone characterised by brecciation and shrinkage cracks is interpreted as a sub aerially exposed palustrine flat with calcrete formation occurring on topographic highs of low relief plains the overlying mottled nodular beds exhibit a variable range of calcrete fabrics and morphologies including circum granular and linear cracks root casts and nodules these are interpreted as pedogenically modified sheet wash deposits of a semiarid alluvial plain the upper sandstone is a sheet flood deposit again pedogenically modified before arrival of the basal lava flows overall the lameta beds are considered to represent a regionally extensive maastrichtian regolith carbon and oxygen isotope analyses of calcareous components are entirely consistent with soil zone environments the 13c values are low typically 8 to 9 pdb demonstrating a strong input of carbon from the decay of terrestrial land plants calcrete 18o values are variable 5 to 10 pdb consistent with precipitation from meteoric water some of which was evaporatively modified in pools on the alluvial palustrine flat the lameta beds are well known for sauropod nesting sites and sedimentological analyses of these sites suggest that the animals selected topographic highs usually in marly or sandy soft sediment multiple nests with similar egg types probably indicate colonial nesting isotopic analyses of eggshell carbonate agree with earlier work suggesting that the sauropods ate a c3 plant food

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago