an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

orbital scale glacio eustasy in the middle devonian detected using oxygen isotopes of conodont apatite implications for long term greenhouse icehouse climatic transitions abstract results from previous paleoclimate studies indicate gondwanan glaciation marking the onset of middle paleozoic icehouse climate conditions began by the latest devonian famennian more recently 18o trends from conodont apatite suggest cooling middle devonian subtropical seasurface temperatures 20 my prior to famennian glaciation and high latitude temperatures cool enough to permit the growth of continental glaciers which controlled longer term my scale glacio eustasy this study evaluates the details and patterns of middle devonian high frequency thirteen complete middle devonian givetian subtidal cycles 0 5 3 m thick in the little cedar formation of southeastern iowa are characterized by oxygenated offshore facies transgression poorly oxygenated offshore facies maximum flooding a return to oxygenated facies and are capped by bioturbated lower shoreface facies regression lowstand which lack evidence of subaerial exposure across shelf cyclostratigraphic facies relationships suggest relatively subdued water depth changes were responsible for cycle development measured 18o values from conodont apatite range from 15 9 to 18 4 and repeated systematic intracycle trends are dominated by lower isotopic values in offshore facies and higher isotopic values in cycle capping lower shoreface facies which is consistent with glacio eustasy driving the water depth changes the average 0 6 magnitude of intracycle isotopic shift 0 2 to 1 0 total range suggests 15 23 m glacio eustatic oscillations were responsible for observed water depth changes the higher range of intracycle isotopic magnitudes may be the result of increased subtropical evaporation rates during glacial stages which locally enriched surface seawater 18o values orbital scale

controls on the basinwide architecture of late miocene messinian evaporites on the levant margin eastern mediterranean abstract interpretation of 2d and 3d seismic data from the levant margin eastern mediterranean has revealed the complex depositional and structural setting of the basinwide late miocene messinian evaporites the data set covers a total area of 20 000 km2 permitting a semi regional investigation of the thick up to 1 8 km evaporitic wedge the sequential analysis of time structure maps isochron maps and seismic cross sections highlighted the main morphological and structural features characterizing the pre syn and post evaporitic levant margin this approach provided insights on the impact of local vs regional factors in governing the distribution of the messinian salinity crisis in the region two regional features have been recognized as the most significant controlling factors for the architecture of the messinian evaporites firstly a series of anticlines of the syrian arc foldbelt acted as a structural barrier indirectly governing the overall landward extension of the evaporites secondly submarine canyons active in the area at least since the oligocene afiq el arish and ashdod canyons represented preferential sites of erosion and deposition of evaporites our results document therefore the importance of the deep seated structures and relict drainage for the architecture of the messinian evaporites on the levant margin the new insights provided can be additionally used to infer the original depositional geometry of the evaporites in the study area and as an analogue in other mediterranean areas where 3d seismic is not available yet and sub salt imaging is limited

marine geologic evidence for a levantine sinai plate a new piece of the mediterranean puzzle marine geophysical data recorded offshore egypt illustrate the presence of an active fault belt trending n145 e that obliquely transects the eastern nile deep sea fan this belt more than 150 km long consists of a series of linear transtensive faults with an apparent right lateral horizontal component these fault zones bound thick sediment filled grabens where linear salt ridges and diapirs represent likely messinian salt reactive response to regional transcurrent geodynamics we infer that this tectonic belt might correspond to an offshore extension of the gulf of suez rift system if our hypothesis is correct this fault belt might represent the western boundary of a levantine sinai microplate locked between the major arabia and africa plates and the anatolian aegean microplate

carbonate shale cycles in the middle devonian of new york an evaluation of models for the origin of limestones in terrigenous shelf sequences thin widespread carbonate beds in the predominantly siliciclastic hamilton group middle devonian of new york appear to represent biogenic accumulations of winnowed shallow normal to storm wave base shelf areas rather than products of transgression induced sediment starvation as frequently assumed in western new york these fossiliferous limestones form the centers of subsymmetrical marine cyclothems carbonates are overlain and underlain by calcareous gray to black laminated shales and they grade laterally into siltstones or sandstones that cap upward coarsening sequences in central new york thus the limestones appear to represent shallow water facies of regressive hemicycles instead of transgressive maxima as argued by earlier workers

a tale of shales the relative roles of production decomposition and dilution in the accumulation of organic rich strata middle upper devonian appalachian basin abstract a new consensus on the processes responsible for organic carbon burial in ancient epeiric seas has emerged more firmly grounded in the uniformitarian framework of modern oceanography and biogeochemistry this consensus recognizes the interdependent roles of sedimentation primary production and microbial metabolism in favor of earlier end member models e g production vs preservation in this study one of the classic stratigraphic sequences upon which the preservation end member was based is re interpreted in light of this new consensus the study employs an extensive new sedimentological biogeochemical database from cores drilled in western new york the database spans over 500 m and 15 my of devonian deposition in the appalachian basin and provides a framework for comparative study of organic matter burial the major conclusions are 1 few organic rich units were deposited under pervasive anoxic sulfidic water columns 2 establishment and breakdown of seasonal thermoclines on annual or longer timescales were the predominant mode of stratification and 3 under such conditions remineralization of bio limiting nutrients may have played a key role in organic matter burial by creating a eutrophication pump this pump may have augmented an already rising nutrient inventory such that productivity levels exceeded the threshold required for development of suboxic to anoxic conditions in sediments and episodically in bottom waters a final conclusion asserts that the master variable for organic matter accumulation was relative sea level change which exerted influence on clastic dilution preservation and production processes sea level rise events led to sediment starvation and organic carbon concentration in distal basin sediments as well as to decreased effectiveness of seasonal mixing and thus longer build up intervals for remineralized nutrients episodic mixing of nutrient enriched bottom waters led to enhanced production ultimately increased clastic sediment delivery and water column mixing during relative sea level fall diluted surface sediment organic content such that respiratory demand could be met by increased oxygen supply thus terminating deposition of strata enriched in organic carbon

symmetrical and upward shallowing cycles in the middle devonian of new york state and their implications for the punctuated aggradational cycle hypothesis the middle devonian eifelian and givetian hamilton group in western and central new york composed largely of fossil rich marine shelf and slope facies is subdivisible into repetitive facies sequences of varying thicknesses minor cycles include 1 to 3 m thick upward coarsening shale to siltstone hemicycles resembling sixth order punctuated aggradational cycles pacs in central new york probably correlative 0 5 1 0 m shale to argillaceous nodular limestone couplets occur in western areas major cycles in western new york include subsymmetrical 3 to 5 m thick packages with medial limestone beds analogous to upper limestones of pennsylvanian cyclothems the center of each cycle marks a regressive maximum and grades vertically above and below into black shale or dark gray mudstone corresponding in a facies sense to cyclothemic core shales in the midcontinent pennsylvanian these widespread units appear to be allocyclic in nature and approximate fifth order transgressive regressive cycles based upon average unit thickness relative to the encompassing well zoned hamilton sequence correlations show that most key regressive events marked by limestones in western new york are expressed by equivalent siltstone or fine sandstone units in central new york most cycles which are nearly symmetrical in western new york grade eastward into 5 to 20 m upward coarsening pac motif hemicycles these asymmetric cycles apparently reflect rapid sediment aggradation to limits imposed by wave energy in a region of abundant sediment supply further minor shallowing was accompanied by winnowing and bypass of fine grained sediments generating condensed capping deposits of coarser silt and sand reworked shells and commonly phosphatic nodules ensuing sea level rises were accompanied by initial sediment starvation followed by sedimentation in deeper water hence asymmetrical upward shallowing hemicycles pacs appear to grade offshore into thin but symmetrical cycles both pac and symmetrical motifs are local responses to the same probably allocyclic sea level fluctuations we suggest that the pac motif is partially facies controlled being largely restricted to shallow shelf settings with relatively high rates of sediment accumulation

crustal fabric in the tibetan plateau based on waveform inversions for seismic anisotropy parameters 1 the tibetan plateau has the thickest continental crust on earth and fabrics within the crust that are anisotropic to seismic waves may provide clues to how it reached such extreme proportions and how it is currently deforming waveform modeling using a global minimization inversion technique applied to receiver functions computed from 11 stations spanning the north south length of the eastern plateau has yielded a suite of crustal models that include anisotropy these models suggest that the tibetan crust contains 4 14 anisotropy at different depths that is likely a result of both fossil fabrics and more recent deformation all models contain anisotropy in the surface layer and for most stations the alignment of the slow symmetry axis suggests a relationship with crustal fabrics associated with e w trending thrust faults or sutures middle to lower crustal anisotropy is present at most stations with a fast axis trending n s to nw se in the south nearly e w in the central plateau and n s to ne sw in the northern plateau this pattern appears consistent with recent ductile deformation due to both topographically induced flow and to boundary forces from subducting lithosphere at the northern and southern margins of the plateau the orientations of crustal anisotropy determined for most stations in this study are significantly different from shear wave splitting fast polarization directions implying distinct deformation in the crust and mantle

the unique dynamics of the pacific hemisphere mantle and its signature on seismic anisotropy abstract the portion of earth s mantle lying below the hemispherical region occupied by the pacific ocean basin is characterized by a unique style of convection the unique dynamics below the pacific hemisphere are revealed by analyzing the mantle flow predicted on the basis of high resolution seismic images of mantle structure in the pacific hemisphere we find a dome like upwelling originating in the lower mantle which actively transports material into the upper mantle a unique aspect of this flow found only in the pacific hemisphere is a demi tour or u turn of the circulation which occurs in the shallow mantle west of the east pacific ridge this demi tour connects the westward movement of the pacific plate to the dome like upwelling below the central pacific ocean and it also provides an explanation for the asymmetric distribution of seismic anisotropy on either side of the ridge axis in a global analysis of the correlation between mantle flow and seismic anisotropy we find the strongest agreement occurs in the pacific hemisphere mantle

seismic anisotropy indicators in western tibet shear wave splitting and receiver function analysis abstract using recently collected data from western tibet we find significant variation in the strength vertical distribution and attributes of seismic wave speed anisotropy constrained through a joint application of teleseismic shear wave splitting techniques and a study of p s mode converted waves receiver functions we find that the crust of tibet is characterized by anisotropy on the order of 5 15 concentrated in layers 10 20 km in thickness and with relatively steep 30 45 from the vertical slow symmetry axes of anisotropy these layers contribute no more than 0 3 s to the birefringence in teleseismic shear waves significantly smaller than splitting in many of the observations and much smaller than birefringence predicted by models developed through group inversions of shear wave recordings consequently we interpret models constrained with shear wave observations in terms of structures in the upper mantle near the altyn tagh fault our data favor a two layer model with the upper layer fast polarization approximately aligned with the strike of the fault near the karakorum fault our data are well fit with a single layer of relatively modest 0 5 s delay anisotropy fast polarization in this layer is 60 ne similar to that of the lower layer in the model for the altyn tagh fault site assuming that layers of similar anisotropic properties at these two sites reflect a common cause our finding favors a scenario where indian lithosphere under thrusts a significant fraction of the plateau data from a site at the southern edge of the tarim basin appear to be inconsistent with a common model of seismic anisotropy distribution we suspect that thick sediments underlying the site significantly distort observed waveforms our ability to resolve features of anisotropic structure in the crust and the upper mantle of western tibet is limited by the small amount of data collected in a 6 month observing period we stress the importance of future teleseismic data collection in tibet over extended periods to insure better directional distribution of observed seismic sources

the nile deep sea fan an example of interacting sedimentation salt tectonics and inherited subsalt paleotopographic features abstract structural analysis of the nile deep sea fan ndsf indicates that post miocene deformation is largely controlled by down slope movement above a messinian salt layer in contrast to other similar systems the ndsf shows significant lateral asymmetry and three distinct provinces can be recognized regional variations in salt thickness and base salt geometry within the system have led to the presence of structures typical of both gravity gliding and gravity spreading trends of structures within the western and central parts of the ndsf are consistent with forming due to gravity gliding processes this pattern contrasts with that in the eastern ndsf that seem to be much more consistent with deformation due to gravity spreading observed differences in structural style across the ndsf can be related directly to the paleomorphological evolution of the nile cone during messinian time which is perhaps partly related to features that have been inherited from early mesozoic evolution of the north egypt passive margin in the east part of the ndsf the structural evolution has been significantly influenced by the proximity of eratosthenes seamount this large topographic buttress has served to both limit and deflect northeastward allochthonous advance of the messinian evaporites and has thus severely complicated deformation of the overlying plio quaternary sedimentary cover within the broad corridor that runs nnw sse and cuts obliquely across the modern bathymetry of the nile cone

three dimensional p wave azimuthal anisotropy in the lithosphere beneath china seismic anisotropy in the upper mantle beneath east asia has been studied extensively using shear wave sks splitting measurements which have provided important information on mantle dynamics in this region however sks measurements have poor vertical resolution and so their interpretations are usually not unique in this work we use a large number of traveltime data from 34 036 local earthquakes recorded by 1563 seismic stations to determine the first model of 3 d p wave azimuthal anisotropy in the lithosphere beneath china our results show that the fast velocity directions fvds are generally correlated with the surface geologic features such as the strikes of the orogens active faults and tectonic boundaries the fvds in the upper crust are normal to the maximal horizontal stress h in regions with extensive compression such as the tibetan plateau whereas they are subparallel to h in strike slip shear zones such as the western and eastern himalayan syntax the comparison of the fvds of p wave anisotropy with sks splitting measurements indicates that beneath the tibetan plateau the seismic anisotropy in the lithosphere contributes significantly to the sks splitting observations in contrast in east china the p wave fvds in the lithosphere are different from the sks splitting measurements suggesting that the sks splitting is mainly caused by the anisotropy in the deeper mantle such as the asthenosphere and the mantle transition zone under east china these novel results provide important new information on the lithospheric deformation and mantle dynamics in east asia

late paleozoic depositional sequences are synchronous and worldwide more than fifty transgressive regressive depositional sequences are present in carboniferous and permian shallow marine successions on stable cratonic shelves worldwide these were synchronous depositional events resulting from eustatic sea level changes that generally ranged from 100 to 200 m each transgressive regressive sequence is correlatable using current fossil knowledge they average about 2 m y and range from 1 2 to 4 m y in length the presence within these strata of numerous synchronous unconformities of considerable duration and worldwide extent suggests that the fossil record is very incomplete and that we are studying a punctuated fossil record and not a punctuated evolution based on a highly irregular mutation rate these late paleozoic transgressive regressive depositional sequences facilitate correlations because depositional histories of a rock succession can support interpretations of faunal assemblages and faunal similarities in evaluating age relationships

an undulatory discontinuity surface on a gently inclined muddy ramp possible evidence of secondary helical flow from the geological record an unusual somewhat cryptic undulatory discontinuity has been recognized near the basal contact of the wanakah shale member of the middle devonian ludlowville formation in western new york it is in part marked by undulating diagenetic limestone beds and concretionary horizons but can be traced continuously by subtle surfaces of fossil and pyritic lags this surface marks the top of parallel elongate mud ridges trending approximately n s perpendicular to the inferred e w depositional strike of the appalachian basin in western new york these ridges are observed in the field as irregularly spaced mud swells which have up to 1 5 m of relief and vary from 30 to 50 m or more in width the intervening broad flat channel floors are characterized by dense concentrations of diminutive brachiopods with gastropods and styliolinids which are gradually replaced by thin styliolinid horizons with abundant pyrite nodules and pyritized burrows over the tops of the swells traceable shelly horizons are observed to pinch out over the swells suggesting a period of relatively undisturbed sediment filling following the formation of the channellized surface the interval of nearly barren shale below this irregular surface however contains concretionary horizons and rare styliolinid pavements which are themselves irregular possibly indicating a changing topography for this surface through time previous taphonomic and palaeoecological studies of the lower wanakah shale member have disclosed a well defined regressive transgressive cycle with more subtle superimposed subcycles the undulatory surface described here occurs within the early regressive part of this cycle and appears to record an accentuated regressive kick of a lower order subcycle the formation of this surface is therefore interpreted to be a consequence of regressive submarine erosion and sediment bypass together with redeposition from suspension the development of the channels and parallel longitudinal mud ridges was probably controlled by helical flow cells within offshore directed bottom currents they may be the first recorded instance of sedimentary furrows described from the geological record taphonomic and biofacies data indicate relative depths below average storm wave base suggesting that sediment winnowing and redeposition occurred at depths only rarely affected by the direct impact of storm wave agitation

crustal thickness map of the chinese mainland from teleseismic receiver functions abstract we present a new crustal thickness map of the chinese mainland and adjacent areas based on a compilation of previously published data more than 1900 estimates of crustal thickness from receiver function studies were collected and the weighted averages were used to develop a contour map of crustal thickness beneath the chinese mainland the combined dataset provided good coverage especially over eastern and central china and our analysis revealed crustal thickness variations of the chinese mainland with considerably more detail than in previous models our crustal thickness map shows a large variation from a thickness of less than 30 km in the mesozoic basin of eastern china to over 80 km in the tibetan plateau the thickest crust was found in central tibet while the thinnest continental crust was observed beneath eastern china normal to slightly thick crust 38 51 km was found for the stable precambrian basins and orogenic belts comparison between our model and other models reveals that the models share similar large scale and smaller scale features over large portions of eastern china where the data coverage is good however large differences up to 25 km in crustal thickness occur in areas with complex crustal structure or poor data coverage we also evaluated the quality of previous models by comparing them with our newly compiled point observations of crustal thickness

newly recognized eastern extension of the nile deep sea fan a previously unreported easternmost segment of the nile river deep sea fan complex has been identified in the deep levant basin offshore israel based mainly on a recently released high quality three dimensional seismic data set this segment is characterized by densely spaced seabed and subseabed turbidite channel complexes generally fed from the region of the historically active northeastern damietta and pelusian branches of the nile this pattern suggests a previously unnoticeable symmetry in the modern channel distribution between the eastern and western branches of the deep sea fan the base of the nile9s eastern deep sea fan is determined by a nw trending system of pre nile turbidite slope channels at the top of the messinian evaporites the overlying pliocene holocene fan complex is further divided into two distinct stratigraphic units a lower stratified sand rich unit deposited in a basin floor setting and an upper heterogeneous mud rich unit consisting of downslope mass transport and hemipelagic sediments with encased slope channel complexes richer in sand due to gravity gliding and spreading above the underlying thick mobile messinian salt both stratigraphic units as well as the upper part of the messinian salt layer are faulted and folded

crust mantle coupling at the northern edge of the tibetan plateau evidence from focal mechanisms and observations of seismic anisotropy abstract the tarim basin is distinct from the tibetan plateau by the apparently low degree of internal deformation relative motion between the lithospheres of tibet and tarim likely results in coherent mantle deformation with a diagnostic signature of anisotropic seismic wave speed birefringence splitting in core refracted shear phases sks pks observed along the tibet tarim border is indicative of seismic anisotropy along their path the mantle deformation direction inferred from shear wave splitting under the assumption of a single source of anisotropy is approximately e w the size of the splitting delays inferred in our analysis suggests that most of the anisotropic signature is coming from the mantle furthermore our data suggest vertical stratification of rock fabric focal mechanisms of regional earthquakes both published and derived from new data provide evidence for nne ssw compression within the tarim basin north of the border with tibet this type of internal deformation in the lithosphere is consistent with its underthrusting subduction beneath tibet within the crust of the tibetan plateau we find a more complex pattern suggestive of the e w extension and generally consistent with the sense of motion on the altyn tagh fault that extends along the tibet tarim boundary therefore at the tibet tarim border we find close similarity between deformation directions within the crust of the plateau and within the upper mantle on both sides of the boundary a plausible explanation of such similarity would be the coupling of the crust and the upper mantle with no weak zone being present in the lower crust one scenario for such coupling would involve an extension of a deformation zone associated with the altyn tagh fault into the uppermost mantle making this fault zone very similar to a plate boundary

sea level curve for pennsylvanian eustatic marine transgressive regressive depositional cycles along midcontinent outcrop belt north america at least 55 cycles of marine inundation and withdrawal are recognized in the mid desmoinesian to mid virgilian midcontinent outcrop sequence in north america they range from widespread major cycles classic cyclothems with deep water facies extending across the northern shelf through intermediate cycles persisting as marine horizons across the shelf to minor cycles developed on the lower shelf or as parts of major cycles biostratigraphic differentiation of the cycles should establish interbasinal correlation on a scale fine enough to allow evaluation of differential tectonics and sedimentation sequential groupings of cycles are more irregular than proposed megacyclothems or mesothems but they may be obscured by the distinctness of the major cyclothems estimates of cycle periods range from about 40 to 120 x 10 sup 3 yr for the minor cycles up to about 235 to 400 x 10 sup 3 yr for the major cyclothems the range for all cycles corresponds well to the range of periods of earth s orbital parameters that constitute the milankovitch insolation theory for the pleistocene ice ages and it further supports gondwanan glacial control for the pennsylvanian cycles even though the dominant period of the major pennsylvanian cyclothems is up to four times longer than the dominant 100 000 yr period inmore the pleistocene the shapes of both curves display rapid marine transgression rapid melting of ice caps and slow interrupted regression slow buildup of ice caps which suggest similar linkages between the climatic effects of the orbital parameters and ice cap formation and melting at the two different scales widely separated in time 28 references 3 figures less

mantle flow pattern and geodynamic cause of the north china craton reactivation evidence from seismic anisotropy 1 we investigate the mantle flow pattern and geodynamic cause of north china craton ncc reactivation using shear wave splitting measurements from 140 broadband stations using a newly developed method for simulating wave propagation in a two dimensional anisotropic medium we first examined the influence of sedimentary structures on sks splitting measurements the simulations show that a sedimentary layer whether isotropic or anisotropic significantly influences the waveform however the shear wave splitting parameters can be retrieved with negligible errors as a result this study included new splitting measurements at stations which were deployed within basins and not used previously among 121 broadband stations that contribute valid splitting results 55 stations are newly added which were deployed within basins this significantly improved the sampling coverage on the ncc the complicated spatial patterns of the splitting parameters indicate that complex upper mantle deformation has occurred in the ncc to obtain both deep kinematic and geometric information we interpret our splitting measurements in the context of new high resolution tomographic results for the ncc by comparing our observations with three end member conceptual models upwelling wedge flow and lithospheric delamination we found that the observed anisotropy pattern beneath the ncc is not completely consistent with any of them thus we prefer a hybrid mantle flow model where the subduction of the pacific plate causes a mantle wedge flow beneath the eastern archean block and a regional upwelling beneath the central block which has been imaged as a low velocity anomaly in seismic tomography thus we speculate that the subduction of the pacific plate compared to the ncc yangtze craton amalgamation and the india eurasian collision is most likely the geodynamic cause of the reactivation of the ncc eastern block during the late mesozoic to cenozoic

scaling of stagnant lid convection with arrhenius rheology and the effects of mantle melting summary on the basis of numerical modelling and scaling analysis a few modifications are proposed for the scaling of stagnant lid convection in order to make it more applicable to the thermal evolution of terrestrial planets the effect of using arrhenius rheology as opposed to more popular linear exponential rheology is first investigated and the stability analysis of top thermal boundary layer is shown to be able to capture systematic differences caused by the different kinds of temperature dependent viscosity the local stability analysis is then extended to handle the effects of mantle melting such as dehydration stiffening and compositional buoyancy a new heat flow scaling law incorporating these effects suggests that mantle melting may reduce the conventional prediction of surface heat flux by up to a factor of 5 10 and its potential impact on our understanding of planetary evolution is briefly discussed

bathymetry of the levant basin interaction of salt tectonics and surficial mass movements abstract a new high resolution bathymetric map of the levant basin between israel and the eratosthenes seamount reveals previously undetected folds faults and channels the map facilitates a regional map view analysis of structures that were previously examined only in cross section the systematic mapping of morpho structural elements in the entire basin is followed by a kinematic interpretation that distinguished between two main processes sculpting the seabed from bottom and top salt tectonics and sediment transport we show that the contractional domain related to salt tectonics is far more complex than previously thought ridges previously interpreted as contractional folds are in fact surficial undulations of the seabed reminiscent of sediment waves moreover other folds previously interpreted as downdip contraction of the westward gliding plio quaternary section are in some parts of the basin caused by updip climbing of this section eastwards as a result of the regional pattern of salt flow away from the nile cone in the context of sediment transport we show that the northern sinai continental slope is covered by a dense net of turbidite channels whereas the levant slope has no channels at all particularly interesting is the levant turbidite channel described and named here for the first time this feature begins at the southeastern corner of the mediterranean at water depths of 1100 m continues along the valley between the sinai and levant slopes and reaches the deepest part of the basin in water depths of 2500 m northeast of the eratosthenes seamount however this prominent feature cannot be explained by the current drainage consisting of two minor rivers that enter the basin at that point and thus most likely reflects periods of wetter climate and or lower sea level when these rivers were more active and possibly connected to the submarine channel system

punctuated aggradational cycles implications for stratigraphic analysis application of the hypothesis of punctuated aggradational cycles pacs a model of episodic stratigraphic accumulation has yielded results fundamentally in conflict with those predicted and generated by gradualistic models the assumption that stratigraphic accumulation is controlled principally by rapid small scale base level fluctuations in the milankovitch band leads to the adoption of the pac a thin time stratigraphic unit as the fundamental unit of stratigraphic description and interpretation the thicker generally diachronous formation is inadequate for stratigraphic analysis because it is an artifact of stratigraphic gradualism correlation of stratigraphic sections is accomplished by matching patterns of facies change particularly the abrupt changes at the synchronous surfaces that mark pac boundaries this kind of physical event correlation is far more accurate than traditional biostratigraphic methods focus on synchronous pac boundaries separating environmentally disjunct facies reveals discontinuities that preclude application of walther s law across those surfaces when viewed from this episodic perspective the manlius formation of the helderberg group in new york state becomes a highly ordered set of time stratigraphic cycles rather than a disordered mosaic of facies representing short term autogenic processes in a single nearshore environment not only was manlius deposition episodic with no gradual upward deepening as is predicted by stratigraphic gradualism but also the manlius coeymans formational boundary is interpreted as a small scale unconformity rather than a paleoenvironmental boundary created by gradual transgression each of these interpretations is the direct result of assuming and applying a model of episodic stratigraphic accumulation

multiproxy late quaternary stratigraphy of the nile deep sea turbidite system towards a chronology of deep sea terrigeneous systems abstract understanding the recent formation of a sedimentary system such as a deep sea turbidite system dsts requires an accurate stratigraphic control on deposits due to the important terrigeneous input which disrupts the sedimentary record dsts is an environment where stratigraphic control is difficult to assess most of the time traditional stratigraphic tools are not accurate enough this has led to a rather limited number of studies concerning stratigraphy in dsts in this study we examine several hemipelagic long piston cores collected from the nile dsts eastern mediterranean in order to understand the recent evolution of the complex sedimentary system in this area the first aim of this study is to show how to obtain a reliable timeframe in dsts indeed we provided a detailed ecostratigraphical scheme based on planktonic foraminiferal distribution oxygen isotope records and lithostratigraphy sapropels and tephra of three cores where the sedimentation is least disturbed we have identified 29 foraminiferal ecozones during the last 250 000 years bp with an approximately 2000 year time resolution the time span of each ecozone was constrained by the oxygen isotope record 14 c ams radiometric data tephrochronology and the sapropel chronology these high resolution ecostratigraphical time subdivisions have been applied in discontinuous mixed hemipelagic turbiditic sequences of a levee record this example shows how to date gravity events formation and time periods of sedimentary accumulations

historical and pre historical tsunamis in the mediterranean and its connected seas geological signatures generation mechanisms and coastal impacts abstract the origin of tsunamis in the mediterranean region and its connected seas including the marmara sea the black sea and the sw iberian margin in the ne atlantic ocean is reviewed within the geological and seismotectonic settings of the region a variety of historical documentary sources combined with evidence from onshore and offshore geological signatures geomorphological imprints observations from selected coastal archeological sites as well as instrumental records eyewitnesses accounts and pictorial material clearly indicate that tsunami sources both seismic and non seismic e g volcanism landslides can be found in all the seas of the region with a variable tsunamigenic potential local regional and basin wide tsunamis have been documented an improved map of 22 main tsunamigenic zones and their relative potential for tsunami generation is presented from west to east the most important tsunamigenic zones are situated offshore sw iberia in the north algerian margin in the tyrrhenian calabria and messina straits in the western and eastern segments of the hellenic arc in the corinth gulf of central greece in the levantine sea offshore the dead sea transform fault and in the eastern side of the marmara sea important historical examples including destructive tsunamis associated with large earthquakes are presented the mean recurrence of strong tsunamis in the several basins varies greatly but the highest event frequency 1 96 years is observed in the east mediterranean basin for most of the historical events it is still unclear which was the causative seismic source and if the tsunami was caused by co seismic slip by earthquake triggered submarine landslides or by a combination of both mechanisms in pre historical times submarine volcanic eruptions i e caldera collapse massive pyroclastic flows volcanogenic landslides and large submarine landslides caused important tsunamis although little is known about their source mechanisms we conclude that further investigation of the tsunami generation mechanisms is of primary importance in the mediterranean region inputs from tsunami numerical modeling as well as from empirical discrimination criteria for characterizing tsunami sources have been proved particularly effective for recent well documented aseismic landslide tsunamis e g 1963 corinth gulf 1979 cote d azur 1999 izmit bay 2002 stromboli volcano since the tsunami generation mechanisms are controlled by a variety of factors and given that the knowledge of past tsunami activity is the cornerstone for undertaking tsunami risk mitigation action future interdisciplinary research efforts on past tsunamis are needed

shallowing upward sequences in purbeckian peritidal carbonates lowermost cretaceous swiss and french jura mountains purbeckian carbonates in the swiss and french jura goldberg formation lower berriasian comprise shallow subtidal intertidal supratidal low energy high energy marine brackish freshwater and hypersaline facies these facies are arranged in small 0 2 1 5 m thick sequences which display a dominant shallowing upward component and which form the fundamental units of the highly structured purbeckian sedimentary record six types of small scale sequences can be recognized a intertidal to supratidal overprinting of shallow lagoonal facies b algal marsh sequence with frequent dolomitization c sabkha sequence often associated with collapse breccia d tidal flat sequence with desiccation features e lacustrine sequence f terrestrial overprinting of subtidal or intertidal facies episodic event deposits such as tempestites are superimposed thin transgressive beds which rework elements of the underlying facies are frequently found at the base of the sequences green marls and black pebbles are common at the top and indicate long subaerial exposure the sequences are often incomplete as subtidal facies may be absent or their upper part can be eroded lateral facies changes are common which is due to the very shallow and partly emergent purbeckian platform where various depositional environments were juxtaposed however many sequence boundaries are well developed and can be correlated over large parts of the study area the purbeckian shallowing upward sequences were generated by climatically controlled sea level changes autocyclic processes occurred locally but were overprinted by drops of sea level affecting the entire platform the small scale sequences are most probably related to the 20 000 year cycle of the precession of the equinoxes larger sequences with usually well developed emersion surfaces are attributed to the 100 000 and 400 000 year eccentricity cycles of the earth s orbit identification and correlation of sequence boundaries makes it possible to set up a framework of isochronous surfaces which often cut across facies boundaries and thus to interpret in detail the palaeogeographic sedimentological and diagenetic evolution of the purbeckian peritidal carbonate environments

a depositional model for storm and tide influenced prograding siliciclastic shorelines from the middle devonian of the central appalachian foreland basin usa a stratigraphic motif observed in many foreland basins is the development of basinward tapering siliciclastic wedges characterized by various scales of depositional cycles the middle devonian givetian mahantango formation in the central appalachian foreland basin is such an example it consists of both small and large scale thickening and coarsening upward cycles the small scale cycles are typically less than 10 m thick whereas larger scale cycles are generally a few tens of metres thick and commonly contain several of the smaller scale cycles outcrop based facies analyses indicate that the depositional cyclicity resulted from episodic progradation of a regionally straight tide dominated shoreline onto a storm dominated shallow marine shelf the depositional model for this ancient shallow marine system consists of a vertical facies succession in which storm dominated offshore marine mudstone and fine sandstone pass gradationally upward into storm dominated nearshore marine shelf and shoreface sandstone overlain by in proximal sections tide dominated shoreline sandstone pebbly sandstone and mudstone transgressively reworked lag deposits cap most of the thickening and coarsening upward packets in this model coarse grained rocks rather than implying basinward shifts of facies are a consanguineous part of the stacked shoaling cycles lateral facies relationships show that the dominance of storm vs tide generated sedimentary features is simply a function of palaeogeographical position within the basin proximal sections contain tidally influenced sedimentary features whereas more distal sections only display evidence for storm influenced deposition these results suggest caution when inferring palaeoceanographic conditions from sedimentological datasets that do not contain preserved examples of palaeoshorelines

indian mantle corner flow at southern tibet revealed by shear wave splitting measurements 1 we constrain anistropic seismic structure in the southernmost tibet and the tethyan himalays using sks and skks phases recorded from a temporary seismic network operated from july 2004 to august 2005 in conjunction with the hi climb project shear wave splitting is not detected at 16 stations most of which are located near and to the north of the indus yalong suture iys for the first time anisotropy with an n s fast direction and 0 4 1 s delay times is observed to the region about 50 km south of the iys this weak anisotropy correlates with the flat part of the subducting indian lithosphere and could be caused by northward asthenospheric flow and shear at the base of the indian lithosphere the null measurements in the vicinity of the iys are most likely the result of a vertical asthenospheric flow the corner flow induced by the subvertical subduction of the indian lithosphere just south of the bangong nujiang suture bns observations of the systematic changes in mantle anisotropy from southern tibet to the central tibet provide evidence for different mantle flow fields between the indian and the eurasian asthenospheric mantle which are separated by a subvertical indian lithosphere at the bns

rapid strand plain accretion in the northeastern nile delta in the 9th century a d and the demise of the port of pelusium an unusually large 1 km 3 and rapid influx of nile river sediment in the early 800s a d resulted in accretion of an extensive strand plain 6 to 15 m thick 35 km long and as much as 12 km wide on the subsiding northeastern nile delta margin egypt this event is related to blockage of the pelusiac branch and breaking through of a new distributary to the west of present day port said probably representing initiation of the damietta branch the sand is of analytically identical age throughout the area and was deposited within less than 60 yr as indicated by 14 c and amino acid racemization analyses of donax shells from a series of cores radiocarbon dates in combination with historical accounts by al jakubi who found the strand plain already in existence when he visited the area in the late 800s place this event in the early 800s nilometer flood records suggest that the sequence of great floods of 813 816 and 820 may have been the triggering events this sudden displacement of sand caused pelusium then the principal port and fortified city of the northeastern nile delta located at the mouth of the pelusiac branch to be cut off from both the nile and the mediterranean and led to its decline and eventual abandonment by the 12th century when the crusaders arrived

seismic anisotropy across the kunlun fault and their implications for northward transforming lithospheric deformation in northeastern tibet abstract the northeastern tibet is produced by the far field effects of the india eurasia collision in late cenozoic as the southern boundary of the northeastern tibet the kunlun fault is a key to understand how the tibetan plateau transforms lithospheric deformation outward using a northeast southwest trending seismic array deployed in songpan ganzi qaidam kunlun and qilian blocks we measured sks skks wave splitting parameters at 15 broadband seismic stations to study the variation in anisotropy across the kunlun fault and among these blocks the average splitting parameters of the southern segment in songpan ganzi block are n132 3 e and 1 1 s respectively and those of the northern segment in qilian block are n103 8 e and 0 98 s interfered with the middle segment in qaidam kunlun block with a smaller average delay time 0 63 s a schematic geodynamic model is used to explain the distinct features among these blocks weak anisotropy suggests the strong lithosphere of qaidam kunlun block with negligible deformation a counterclockwise rotation of the fast polarization direction of about 30 from songpan ganzi block to qilian block is produced by a ladder shaped strong qaidam kunlun block

taphonomy and depositional dynamics of devonian shell rich mudstones abstract fossil preservation e g articulation of multi element skeletons provides important insights into depositional dynamics detailed taphonomic analysis of marine mudstones and associated shell beds from the middle devonian of western new york indicates that these beds record primarily episodic sediment deposition of short duration we propose a storm winnowing mud blanketing model to explain the variety of shell and mudstone beds observed and to explain apparent onshore offshore gradients of shell bed characteristics shell beds themselves appear to have accumulated during relatively long spans of time ranging up to perhaps thousands of years most are internally complex and exhibit evidence for multiple events of burial and exhumation by winnowing shell accumulation facilitated colonization of the seafloor by hard substrate encrusting organisms these contributed to increasingly complex communities that were ultimately destroyed and permanently blanketed by thick mud layers the sparsely fossiliferous mudstones which compose up to 85 of the hamilton stratigraphic section mainly record very abrupt inputs of sediment in some instances taphonomy of enclosed fossils indicates deposition of layers up to several centimeters thick prior to compaction within hours to a few days in turn some sequences of shell and mudstone beds were deposited within the life span of single colonial organisms and thus also record only relatively short spans of time overall this reinforces our conclusions that most time in mudstone sequences must be represented by discontinuities at sharp surfaces or thin condensed beds that bound more or less continuous bundles of shell and mudstone beds again these often subtle discontinuities can be recognized on the basis of taphonomic criteria many complex shell beds as well as simple shell beds can be traced along depositional strike for tens of kilometers condensed shell beds only a few centimeters thick can commonly be correlated for 100 to 200 km along and across depositional strike the correlatable nature of shell beds apparently reflects the temporal contrast between these beds and enclosing muds on a regional scale shell beds represent integrated accumulations that were deposited over spans of tens to thousands of years conversely the mud layers that blanketed and terminated shell bed accumulations may represent very rapid depositional events spanning hours to days which are locally isochronous thus the study of taphonomy of shell beds reveals a good deal of detail about their depositional history these studies imply that the stratigraphic record is even more episodic and discotinuous than commonly recognized episodic deposition implies that while the stratigraphic record of epeiric seas may be adequate for examining details of community succession and paleontology it probably can not generally be used for microevolutionary studies other than examination of patterns of stasis

initiation of gravitational collapse of an evaporite basin margin the messinian saline giant levant basin eastern mediterranean regional 2d and 3d seismic data from the levant basin reveal the updip extensional component of thin skinned gravity tectonics on this continental margin because of its youth 5 7 ma the earliest stages of deformation of this salt basin are preserved without the severe structural overprinting common on more mature giant salt tectonic systems extension detaches onto and within messinian evaporites up to 1800 m thick by structural restoration we reconstruct the tectonic evolution of the messinian evaporites using paleobathymetric constraints from wells and seismic profiles this analysis suggests that the mediterranean drawdown during the messinian salinity crisis was 800 m the 10 to 15 km wide extensional domain tracks the landward pinch out of the mobile messinian evaporites against an older late miocene scarp diachronous extension began in the center of the margin in the mid pliocene then spread northward in the late pliocene then finally southward in the early pleistocene extension continues today on many of the most landward faults extensional strain varies greatly along strike from 1 km to as much as 12 15 km comparing observations with four end member conceptual models we infer that both extension and seaward salt flow thinned the evaporite margin and its overburden both processes were triggered by a combination of uplift of the continental shoulder of the dead sea rift and subsidence in the mediterranean basin at least three factors controlled variations in extension 1 degree of tilting of the salt wedge related to the interplay of coastal uplift and basin subsidence 2 presence of pre messinian canyons overlain by landward salients of salt and 3 variations in evaporite facies and the proportion of siliciclastic admixture

geoframework coupling multiple models of mantle convection within a computational framework solver coupling can extend the capability of existing modeling software and provide a new venue to address previously intractable problems a software package has been developed to couple geophysical solvers demonstrating a method to accurately and efficiently solve multiscale geophysical problems with reengineered software using a computational framework pyre pyre is a modeling framework capable of handling all aspects of the specification and launching of numerical investigations we restructured and ported citcoms a finite element code for mantle convection into the pyre framework two citcoms solvers are coupled to investigate the interaction of a plume at high resolution with global mantle flow at low resolution a comparison of the coupled models with parameterized models demonstrates the accuracy and efficiency of the coupled models and illustrates the limitations and utility of parameterized models

kinematics and dynamics of the namche barwa syntaxis eastern himalaya constraints from deformation fabrics and geochronology abstract field observations deformation and fabric analyses and precise age data acquired by zircon shrimp la icp ms u pb and 40 ar 39 ar dating methods have yielded new constraints on the kinematics and dynamics of the namche barwa syntaxis nbs which is the eastern corner of the himalaya a two stage model has been established to explain the formation and evolution of the nbs the northward indentation of the indian plate beneath the lhasa terrane began at 55 40 ma and crustal materials at this corner were subducted to depths 70 km where they experienced hp uhp metamorphism since 40 ma large scale right lateral strike slip along the sagaing fault has accommodated the rapid northward movement of the eastern indian plate corner with respect to the indochina block this caused significant and progressive bending of the indus yarlung suture zone iysz such that it became the dongjiu milin left lateral strike slip shear zone dmsz in the west and the aniqiao motuo right lateral strike slip shear zone amsz in the east both zones underwent strong mylonitization meanwhile the hp uhp metamorphic rocks were rapidly exhumed first into the deep crust at 22 18 ma and then to the shallow crust to form an antiformal dome at 6 2 ma our model provides new insight into the processes of post collisional crustal thickening related to the formation of the himalayan orogenic belt

evidence of active mantle flow beneath south china 1 the india eurasia collision is responsible for producing the himalayan mountains and tibetan plateau and has been hypothesized to have significant far field influences including driving the baikal rift and the eastward extrusion of south china however quantification of lithospheric buoyancy forces and integrated effect of tractions acting at base of the lithosphere are unable to explain the observed surface motions within south china we present 198 new sks shear wave splitting observations beneath south china and invert these data along with published gps data to solve for the subasthenospheric flow field beneath south china to assess the role of small scale convection here we find a 15 20 mm yr southwestward directed mantle flow toward the burma slab this flow is consistent with the mantle response of slab retreat over the past 25 ma and counter flow due to subduction of burma sunda slabs demonstrating the importance of localized mantle convection on present day plate motions

correlation of carboniferous strata using a hierarchy of transgressive regressive units carboniferous strata can be described interpreted and correlated using six scales of allocyclic transgressive regressive t r units these t r units are inferred to be the net result of deposition during cycles of sea level change all pennsylvanian and lower permian strata constitute one second order t r unit or synthem the pennsylvanian system contains third fourth fifth and sixth order t r units that can be correlated across both marine and nonmarine facies in the appalachian basin this permits differentiation of allocyclic t r units from autocyclic t r units or fluvial autocyclic units the hierarchical approach is also useful for predicting the location of marine horizons coals claystones and various types of stratigraphic breaks a hierarchical scheme of allocyclic t r units could be combined with biostratigraphic radiometric and magnetostratigraphic data to form a practical chronostratigraphic framework for the carboniferous

significant and vertically coherent seismic anisotropy beneath eastern tibet 1 shear wave splitting measurements using teleseismic sks and skks phases recorded by the indepth iv arrays has revealed a strong upper mantle anisotropic fabric in northeastern tibet with large delay times of up to 2 2 s suggesting that anisotropy exists in both the lithospheric and asthenospheric mantle the coherence among fast polarization orientations of split core phases and the left lateral slip on eastern striking southern striking faults in eastern tibet and the surface deformation fields calculated from both gps observations and quaternary fault slip rates support the idea that left lateral shear strain is the predominant cause of the orientation of the upper mantle petrofabrics we suggest the bending of the eastern himalayan syntaxis around the foundering burma andaman sumatra slab also contributes to the observed seismic anisotropy in the eastern himalayan syntaxis region two plausible competing processes are proposed for the flow of asthenosphere in eastern tibet in the first the deforming lithosphere glides over the passive asthenosphere inducing flow in the asthenospheric mantle in the second the asthenosphere beneath northeastern tibet is squeezed between the advancing indian continental lithosphere and the thick tarim and qaidam lithospheric blocks to the north a westward retreat of the burma slab from eurasia may induce flow that is toroidal and located exclusively around the northern edge of the slab the rotation of fast orientations for stations in the eastern himalayan syntaxis region are consistent with the toroidal flow pattern as well as the rotational deformation of the overlying lithosphere

tomography based mantle flow beneath mongolia baikal area abstract recent progress in seismic tomography of asia allows us to explore and understand more clearly the mantle flow below the mongolia baikal area we present a tomography based model of mantle convection that provides a good match to the residual topography the model provides predictions on the present day mantle flow and flow induced asthenospheric deformation which give us new insights on the mantle dynamics in the mongolia baikal area the predicted mantle flow takes on a very similar pattern at the depths shallower or deeper than 400 km and almost opposite flow directions between the upper shallower than 400 km and lower deeper than 400 km parts the flow pattern could be divided into the simple eastern region and the complex western region in the mongolia the upwelling originating from about 350 km depth beneath baikal rift zone is an important possible drive force to the rifting the seismic anisotropy cannot be simply related with asthenospheric flow and flow induced deformation in the entire mongolia baikal area but they could be considered as an important contributor to the seismic anisotropy in the eastern region of mongolia and around and in sayan baikal orogenic belt

diversion and morphology of submarine channels in response to regional slopes and localized salt tectonics levant basin abstract in the levant basin submarine channels are abundant around the nile deep sea fan ndsf an area which is also affected by salt tectonics related to the messinian salt giant here we focus on the relationship between submarine channels and obstacles formed by salt tectonics initially we use methods developed for terrestrial morphological analysis and quantify channel sinuosity width and slope in search for consistent relationships between morphometric parameters and channel response to obstacles however this traditional analysis did not yield robust conclusions then we apply two new morphometric parameters suggested here to express the distortion of channels by obstacles incident angle defined as the acute angle between the regionally influenced channel direction and the strike of the tectonic obstacle and diversion angle defined as the angle between the direction of the regional bathymetric slope and the average direction of the channel these parameters illustrate the influence of the regional scale basin geometry and the superimposed tectonic influenced seabed patterns on channel development we found hyperbolic relationships between incident angle and diversion angle in which channels flowing approximately parallel 0 to tectonic folds are obviously not diverted channels nearly orthogonal 90 to obstacles crosscut them right through and again not diverted much in contrast channels with a general direction diagonal to the obstacles 40 are diverted by ten degrees 10 this diversion accumulates along large distances and significantly influences the regional development of channels around the ndsf noteworthy this phenomenon of channel diversion indirectly deteriorate normal slope sinuosity relationships known from terrestrial studies in light of these findings we suggest that these new parameters can be applied to other basins where submarine channels interact with seabed obstacles

architecture and formation of transgressive regressive cycles in marginal marine strata of the john henry member straight cliffs formation upper cretaceous of southern utah usa marginal marine deposits of the john henry member upper cretaceous straight cliffs formation were deposited within a moderately high accommodation and high sediment supply setting that facilitated preservation of both transgressive and regressive marginal marine deposits complete transgressive regressive cycles comprising barrier island lagoonal transgressive deposits interfingered with regressive shoreface facies are distinguished based on their internal facies architecture and bounding surfaces two main types of boundaries occur between the transgressive and regressive portions of each cycle i surfaces that record the maximum regression and onset of transgression bounding surface a and ii surfaces that place deeper facies on top of shallower facies bounding surface b the base of a transgressive facies bounding surface a is defined by a process change from wave dominated to tide dominated facies or a coaly shelly interval indicating a shift from a regressive to a transgressive regime the surface recording such a process change can be erosional or non erosive and conformable a shift to deeper facies occurs at the base of regressive shoreface deposits along both flooding surfaces and wave ravinement surfaces bounding surface b these two main bounding surfaces and their subtypes generate three distinct transgressive regressive cycle architectures i tabular shoaling upward marine parasequences that are bounded by flooding surfaces ii transgressive and regressive unit wedges that thin basinward and landward respectively and iii tabular transgressive lagoonal shales with intervening regressive coaly intervals the preservation of transgressive facies under moderately high accommodation and sediment supply conditions greatly affects stratigraphic architecture of transgressive regressive cycles acknowledging variation in transgressive regressive cycles and recognizing transgressive successions that correlate to flooding surfaces basinward are both critical to achieving an accurate sequence stratigraphic interpretation of high frequency cycles

influence of continental roots and asthenosphere on plate mantle coupling the shear tractions that mantle flow exerts on the base of earth s lithosphere contribute to plate driving forces and lithospheric stresses we investigate the sensitivity of these tractions to sub lithospheric viscosity variations by comparing shear tractions computed from a mantle flow model featuring laterally varying lithosphere and asthenosphere viscosity with those from a model with layered viscosity lateral viscosity variations generally do not change the direction of shear tractions but deeply penetrating continental roots increase traction magnitudes by a factor of 2 5 compared to 100 km thick lithosphere a low viscosity asthenosphere decreases traction magnitudes by a smaller amount and is important only if 100 km thick increased plate mantle coupling beneath thick continental lithosphere may increase plate driving forces surface deformation and mantle derived lithospheric stresses in these regions by contrast a low viscosity asthenosphere does not decouple the lithosphere from mantle flow highlighting the geological importance of mantle tractions on the lithosphere

carbonate platform lagoon and delta high frequency cycles from the carnian of lombardy southern alps italy abstract the early and middle carnian succession of the bergamasc alps southern alps italy was deposited in three different environments a deltaic depositional system passing seaward to a lagoon or bay and then to a carbonate platform the corresponding lithofacies sandstones and siltstones shales and limestones are organized in high frequency cycles fining upward trends are typical of the subaerial delta plain cycles and shallowing upward trends are widespread in the lagoon and platform cycles the genesis of the lagoonal and carbonate platform cycles is possibly accounted for by sea level changes mainly controlled by small scale eustatic oscillations sea level changes are interpreted as exerting a major control also in the development of the deltaic cycles

crinoid biofacies in upper carboniferous cyclothems midcontinent north america faunal tracking and the role of regional processes in biofacies recurrence abstract coordinated stasis is a pattern of long term multispecies evolutionary and ecological stability bounded by rapid turnover events one class of models proposed to explain the paleoecological pattern of biofacies stability typified by ecological locking states that biotas within habitats become integrated into ecological units that through population and community level processes rebound and persist through short term disturbances this high frequency community resilience allows the units to persist through geologic time tracking their preferred habitats during transgressions and regressions because species are tightly woven into the fabric of the ecosystem there is little opportunity for speciation this also buffers them against extinction this ecological locking by ecosystem homeostatic processes produces long intervals of regionally stable biofacies in the fossil record in these models the primary structuring mechanisms are at the local community level controlled by species autecology species interactions and local disturbance regime an opposing class of models states that species are fundamentally independent and that species interactions are not strong nor spatio temporally persistent enough to forge communities into integrated units with long term persistence community recurrence would be expected as long as the various habitat types recur in time and space species autecologies remain stable the pool of available species remains intact and the recruitment of species into local habitats is not interrupted the focus of these models is dominantly at the regional level controlled by biogeographic history and dispersal among as well as within communities the results of this study of crinoids from the upper carboniferous lansing group of midcontinent north america show that they are distributed among five recurrent paleocommunity types or biofacies which are generally arrayed along an onshore offshore gradient two of these biofacies are restricted to the offshore dysaerobic horizons of the most extensive cyclothem in the group the other three biofacies recur consistently among the cycles however this repeated pattern includes a regionally distributed offshore biofacies unique to late transgressive deposits that is not found in analogous regressive deposits while the distribution of the two shoreward biofacies is consistent with faunal tracking the recurrence of a biofacies unique to late transgressive horizons is not consistent with an integrated paleocommunity that tracks shifting habitats through transgression and regression these results favor the alternative models namely that biofacies develop in place via dispersal from a persistent species pool in response to prevailing environmental conditions the recurrence of apparently ephemeral biofacies through time underscores the importance of regional processes in controlling local paleocommunity composition the establishment of refuges or source populations during environmental bottlenecks i e lowstands is critical to maintaining the regional species pool through time for continued recruitment into local sink paleocommunities during more amenable times i e highstands metapopulation dynamics among habitats are equally important in maintaining species within a region through time conflicting observations of stochastic individualistic and deterministic integrated behaviors of the same ecological systems probably result from differences in the scales of analyses and therefore the processes being studied

recent depositional patterns of the nile deep sea fan from echo character mapping the nile deep sea fan was surveyed in 1998 using swath multibeam bathymetry backscatter imagery and 3 5 khz and seismic profiling on the basis of this new data set the fan has been divided into three main provinces western central and eastern recent sedimentary patterns as deduced from echo character mapping show that gravity induced sedimentary deposits are predominant and are expressed through either slides debris flows or turbidites turbidity processes are particularly active in the westernmost province through a well developed network of deep sea channels this network controls turbiditic flows that subsequently overflow levees mass wasting processes are extremely efficient all over the nile deep sea fan in the upper central province a broad allochthonous tongue of mass flow deposits generated by slope destabilizations may have led to channel avulsions and migrations in the eastern province a northwest southeast deformed belt resulting from combined deep seated and salt related tectonics contains large proportions of destabilized sediments i e originating from destabilization processes such as mass movements probably settled by recent tectonic activity this article highlights 1 the influence of both thin skinned and thick skinned tectonics on sedimentary distribution and 2 the predominance of gravity induced sediments turbidites slides and mass flows in such submarine fans the distribution of debris flows and sedimentary deposits settled by turbidity currents appears fundamental in predicting reservoir geometry and economic potential

late tertiary structure and stratigraphy of north sinai continental margin new seismic data provide information on the structural development and late tertiary stratigraphy of the continental slope and rise off northern sinai the upper continental slope is characterized by a marginal plateau composed of a series of platforms or steps the lower continental slope is smooth except for a low ridge paralleling the western part numerous diapiric structures along the continental margin north of the sinai peninsula emerge from an evaporitic layer of late tertiary age the diapirs usually are aligned along west northwest trending faults a salt ridge 90 km long produces a submarine ridge in the lower continental rise two main fault trends have been mapped in the western part of the continental margin they trend west northwest and in the eastern part northeast these trends parallel the continental slopes of northern sinai and southern israel respectively the structural grain of the sinai margin appears to be controlled by two main tectonic elements 1 rejuvenated basement faults of the continent ocean transition zone and 2 salt diapirism due to loading of messinian evaporites with nile derived upper tertiary clastics

sequence stratigraphy and a revised sea level curve for the middle devonian of eastern north america abstract the well exposed middle devonian rocks of the appalachian foreland basin onondaga formation hamilton group tully formation and the genesee group of new york state preserve one of the most detailed records of high order sea level oscillation cycles for this time period in the world detailed examination of coeval units in distal areas of the appalachian basin as well as portions of the michigan and illinois basins has revealed that the pattern of high order sea level oscillations documented in the new york pennsylvania section can be positively identified in all areas of eastern north america where coeval units are preserved the persistence of the pattern of high order sea level cycles across such a wide geographic area suggests that these cycles are allocyclic in nature with primary control on deposition being eustatic sea level oscillation as opposed to autocylic controls such as sediment supply which would be more local in their manifestation there is strong evidence from studies of cyclicity and spectral analysis that these cycles are also related to milankovitch orbital variations with the short and long term eccentricity cycles 100 kyr and 405 kyr being the dominant oscillations in many settings relative sea level oscillations of tens of meters are likely and raise considerable issues about the driving mechanism given that the middle devonian appears to record a greenhouse phase of phanerozoic history these new correlations lend strong support to a revised high resolution sea level oscillation curve for the middle devonian for the eastern portion of north america recognized third order sequences are eif 1 lower onondaga formation eif 2 upper onondaga and union springs formations eif giv oatka creek formation giv 1 skaneateles giv 2 ludlowville giv 3 lower moscow giv 4 upper moscow lower tully and giv 5 middle tully geneseo formations thus in contrast with the widely cited eustatic curve of johnson et al 1985 which recognizes just one major transgressive regressive t r cycle in the early mid givetian if prior to the major late givetian taghanic unconformity iia upper tully geneseo shale we recognize four t r cycles if restricted ig ih and ii we surmise that third order sequences record eustatic sea level fluctuations of tens of meters with periodicities of 0 8 2 myr while their medial scale fourth order subdivisions record lesser variations primarily of 405 kyr duration long term eccentricity this high resolution record of sea level change provides strong evidence for high order eustatic cycles with probable milankovitch periodicities despite the fact that no direct evidence for middle devonian glacial sediments has been found to date

episodic accumulation and the origin of formation boundaries in the helderberg group of new york state at any single locality in the helderberg group of new york state most formation and member boundaries coincide with boundaries of punctuated aggradational cycles in each case of coincidence the boundary is a discontinuity that was produced by a rapid rise of relative base level rather than a facies contact representing gradual migration of contiguous paleoenvironments apparently diachronous formation boundaries in the sequence are not single continuous surfaces instead each diachronous boundary is actually a stratigraphic series of isochronous surfaces that are separate punctuated aggradational cycles pac boundaries produced by distinct geologically instantaneous base level rises these conclusions about the origin of formation boundaries suggest that the concept of the formation as a fundamental unit of stratigraphic description and interpretation may need revision if the stratigraphic record accumulated episodically on a small scale

significant seismic anisotropy beneath the southern lhasa terrane tibetan plateau 1 shear wave splitting measurements using teleseismic pks skks and sks phases recorded by station lsa on the southern part of the lhasa terrane of the tibetan plateau reveal significant azimuthal anisotropy with a splitting time of up to 1 5 s a conclusion that is contradictory to previous studies which suggested isotropy or weak anisotropy in addition systematic variations of the splitting parameters fast polarization direction and splitting time with the arriving azimuth of the seismic ray path are observed suggesting a model of anisotropy that is more complicated than a single layer with horizontal axis of symmetry the measurements are consistent with a model with two layers of anisotropy the top layer has a ne sw fast direction which is consistent with gps revealed direction of surface movement and can be associated with lattice preferred orientation of middle lower crustal minerals such as amphibole the lower layer has a nearly e w fast direction and can be the consequence of either the n s directed compressional stress originated from the india eurasia collision or flow in the asthenosphere related to the absolute motion of eurasia this study underlines the importance of a long duration of deployment of seismic stations in resolving complex anisotropy

modeling olivine cpo evolution with complex deformation histories implications for the interpretation of seismic anisotropy in the mantle relating seismic anisotropy to mantle flow requires detailed understanding of the development and evolution of olivine crystallographic preferred orientation cpo recent experimental and field studies have shown that olivine cpo evolution depends strongly on the integrated deformation history which may lead to differences in how the corresponding seismic anisotropy should be interpreted in this study two widely used numerical models for cpo evolution d rex and vpsc are evaluated to further examine the effect of deformation history on olivine texture and seismic anisotropy building on previous experimental work models are initiated with several different cpos to simulate unique deformation histories significantly models initiated with a preexisting cpo evolve differently than the cpos generated without preexisting texture moreover the cpo in each model evolves differently as a function of strain numerical simulations are compared to laboratory experiments by boneh and skemer 2014 in general the d rex and vpsc models are able to reproduce the experimentally observed cpos although the models significantly over estimate the strength of the cpo and in some instances produce different cpo from what is observed experimentally based on comparison with experiments recommended parameters for d rex are m 10 5 and 0 3 and for vpsc 10 100 numerical modeling confirms that cpo evolution in olivine is highly sensitive to the details of the initial cpo even at strains greater than 2 these observations imply that there is a long transient interval of cpo realignment which must be considered carefully in the modeling or interpretation of seismic anisotropy in complex tectonic settings

vertical coherence of deformation in lithosphere in the eastern himalayan syntaxis using gps quaternary fault slip rates and shear wave splitting data we present 59 new sks skks and combine them with 69 previously published data to infer the mantle deformation field in se tibet the dense set of anisotropy measurements in the eastern himalayan syntaxis ehs are oriented along a ne sw azimuth and rotate clockwise in the surround regions we use gps measurements and geologic data to determine a continuous surface deformation field that is then used to predict shear wave spitting directions at each station comparison of splitting observations with predictions yields an average misfit of 11 7 illustrating that deformation is vertically coherent consistent with previous studies within the central ehs in areas directly surrounding the namche barwa metamorphic massif the average misfit of 11 stations increases to 60 8 and vertical coherence is no longer present the complexity of the mantle anisotropy and surface observations argues for local alteration of the strain fields here associated with recent rapid exhumation of the indian crust

sequences cycles and basin dynamics in the silurian of the appalachian foreland basin abstract field stratigraphic analysis of the early and medial silurian strata of ontario new york and pennsylvania permits recognition of six major sequences reflecting 3rd order cycles in the niagaran llandoverian ludlovian of new york and adjacent regions these sequences correspond approximately to the medina lower clinton middle clinton upper clinton two sequences and lockport groups each is bounded by widespread unconformities produced by the interplay of eustatic sea level drop and local tectonic uplift in general erosional sequence boundaries and transgressive surfaces are merged with no record of the lowstand wedge each sequence is subdivisible into two to five sub sequences that are marked by sharp though generally non erosional basal discontinuities investigation of the clinton and lockport groups corroborates earlier suggestions that carbonate and siliciclassic tongues extended basinward from opposite margins synchronously in response to sea level drops analysis of the thickness and basinward extent of the progradational tongues reveals the existence of multi scale sedimentary cycles sequences and component sub sequences are correlative basinwide and are synchronous within the resolution of bio and event stratigraphy major drops in relative sea level are represented by the sequence bounding discontinutiies these surfaces are overlain by siliciclastic wedges near terrigenous source areas or winnowed carbonate pack and grainstones on the tectonically passive margin overlying highstand deposits typically shales calcareous mudstones and limestones are separated from lowstand or transgressive deposits by thin condensed intervals commonly marked by phosphatic or glauconitic material and or surfaces of maximum sediment starvation the relative highstand deposits of sequences and sub sequences are developed in relatively deep water facies and are at most slightly progradational hence most sequences and sub sequences are sharply bounded roughly upward deepening to slightly shallowing successions of strata in turn sub sequences are further divisible into widespread minor parasequences and parasequence sets probably corresponding to 6th and 5th order cycles respectively the smaller scale units 0 2 5 mthick commonly display an upward shallowing motif the nested relationship of these cycles supports the hierarchical model of transgressive regressive allocycles proposed by busch and rollins 1984 niagaran cycles discussed herein are equivalent to third fourth and fifth order cycles and are traceable circumbasinally depocenters of successive sequences and sub sequences display a pattern of eastward westward eastward basin axis migration through the silurian during early llandoverian the taconic queenston deltaic complex began to subside and the basin axis depocenter and eastern shoreline shifted eastward approximately 200 km over a 6 million year period as the basin axis migrated eastward the western basin ramp forebulge was repeatedly upwarded and eroded resulting in the generation of regionally angular unconformities at the bases of sequences ii iv and vi the pattern of unconformity greatest to the west suggests rise of the algonquin arch concomitant with eastward basin axis migration during the late llandoverian to early wenlockian the algonquin arch subsided slightly concurrently with a reversal in direction of basin axis migration during deposition of upper clinton and lockport vernon strata sequences v vi the basin axis shifted approximately 300 km back to the west eastward migration of the basin axis corresponds with a time of tectonic quiescence and probable thrust load relaxation the abrupt reversal of migration in the late llandoverian may be a signal of renewed thrusting in the hinterland at the onset of the salinic disturbance

statistical testing of community patterns uppermost hamilton group middle devonian new york state usa abstract we present an extensive and rigorously controlled quantitative paleoecological study within an interval of inferred coordinated stasis this middle devonian hamilton group study completes a 20 yr project by providing data within the unresolved upper hamilton group section together with other rigorously controlled studies these data sets have the potential to address the larger question of coordinated stasis in the fossil record we collected data from the windom member moscow formation uppermost hamilton group to test different statistical approaches to define paleocommunities we evaluate various techniques including non parametric multidimensional scaling and agglomerative hierarchical clustering to decipher community patterns additionally we advocate regular use of cluster significance testing along with anosim i e analysis of similarities when examining ecological data together these techniques test the significance of sample groups more rigorously than conventional testing e g discriminant analysis or analysis of variance anova our results indicate that communities within this upper hamilton group interval exhibit variable taxonomic membership within a relatively stable ecological structure

thickness trends and sequence stratigraphy of the middle devonian marcellus formation appalachian basin implications for acadian foreland basin evolution analysis of more than 900 wireline logs indicates that the middle devonian marcellus formation encompasses two third order transgressive regressive t r sequences mss1 and mss2 in ascending order compositional elements of the marcellus formation crucial to the successful development of this emerging shale gas play including quartz clay carbonate pyrite and organic carbon vary predictably within the proposed sequence stratigraphic framework thickness trends of marcellus t r sequences and lithostratigraphic units reflect the interplay of acadian thrust load induced subsidence short term base level fluctuations and recurrent basement structures rapid thickening of both t r sequences especially mss2 toward the northeastern region of the basin preserves a record of greater accommodation space and proximity to clastic sources early in the acadian orogeny however local variations in t r sequence thickness in the western more distal area of the basin may reflect the reactivation of inherited eocambrian basement structures including the rome trough and northwest striking cross structural discontinuities induced by acadian plate convergence episodes of block displacement locally warped the basin into northeast southwest trending regions of starved sedimentation and or erosion adjacent to depocenters in which regressive systems tract deposits were ponded block movement appears to have initiated in late early devonian time resulting first in thinning and local erosion of the oriskany sandstone in northwest pennsylvania this study in addition to providing the basis for a predictive sequence stratigraphic model that can be used to further marcellus exploration tells of a foreland basin more tectonically complex than accounted for by simple flexural models

the shear wave splitting in the crust and the upper mantle around the bohai sea north china abstract in order to infer the distribution of local stress and the deep geodynamic process in north china this study detects seismic anisotropy in the crust and upper mantle beneath the bohai sea area a total of 535 local shear wave and 721 xks including sks pks and skks phases splitting measurements were obtained from stations in permanent regional seismograph networks and a temporary seismic network called zbnet e the dominant fast polarization orientation of local shear waves in the crust is nearly east west suggesting an east west direction of local maximum compressive stress in the area nearly north south fast orientation was obtained at some stations in the tan lu fault belt and the zhang bo seismic belt the average fast orientation from xks splitting analysis is 87 4 measured clockwise from the north the average time delays of xks splitting are range from 0 54 s to 1 92 s corresponding to a 60 210 km thick layer of anisotropy the measured results indicate that upper mantle anisotropy beneath bohai sea area even the eastern part of north china is mainly from asthenospheric mantle flow from the subduction of the pacific plate from the complicated anisotropic characteristics in this study we infer that there might be multiple mechanisms in the crust and upper mantle around the bohai sea area that led to the observed anisotropy

punctuated aggradational cycles a general hypothesis of episodic stratigraphic accumulation according to the hypothesis of punctuated aggradational cycles presented here the stratigraphic record consists of small scale 1 5 m thick shallowing upward cycles pacs separated by surfaces marked by abrupt change to deeper facies this motif pervasive in time and environment is produced by relatively long periods tens of thousands of years of base level stability punctuated by geologically instantaneous relative base level rises of at least basin wide extent as basin wide lithologic time stratigraphic units pacs are fundamental to all aspects of stratigraphic analysis including correlation paleoenvironmental interpretation and paleogeographic reconstruction of several possible allogenic mechanisms for a pervasively cyclic stratigraphic record glacial eustasy driven by orbital perturbations is preferred the pac hypothesis is presented as a comprehensive model to be tested and modified by examination of the stratigraphic record from an episodic perspective

defining the nature and location of a late devonian early mississippian pycnocline in eastern kentucky the pycnocline the intermediate layer in a tripartite density stratified water column is an important element in recent explanations of the origin of anaerobic sediments dysaerobic sediments deposited where the pycnocline intersects the bottom are distinct from overlying aerobic and underlying anaerobic sediments and were used to define the position of the paleopycnocline on a late devonian early mississippian sea bottom in eastern kentucky surface and subsurface mapping of the bedford berea sequence and equivalent parts of the new albany and chattanooga shales reveals approximately coeval aerobic dysaerobic and anaerobic facies that permitted mapping of the paleopycnocline apparently the first time the actual sea bottom position of a paleopycnocline has been defined the bedford berea devonian mississippian sequence is situated between the black ohio shale devonian below and the black sunbury shale mississippian above the black shales reflect deposition in a deepening transgressive sea where anaerobic conditions were easily established and maintained the intervening bedford berea sequence however represents deposition in aerobic and dysaerobic environments during a shallowing regressive episode as deltas prograded to the south and west in eastern kentucky the gray sandstones siltstones and shales of the bedford berea sequence have been interpreted as pinching out between the black shales above and below in east central kentucky each of the above units however has a distinctive signature on gamma ray logs comparison of gamma ray logs and radioactivity profiles with corresponding cores drillers9 logs and exposures indicates that black shale equivalents are present beyond the point where the gray bedford shale pinches out this also is supported by limited biostratigraphic data this transition from gray bedford shales to black shale equivalents marks the approximate position of the ancient pycnocline and has been mapped in the subsurface and on the outcrop in eastern kentucky the ancient pycnocline closely parallels the bedford berea delta front suggesting major control by the delta the continued influx of oxygen rich sediment laden waters from the delta apparently prevented the northward and eastward migration of the pycnocline up the delta front the introduced oxygen and sediment however were effective only in breaking up the pycnocline over a distance of 25 to 40 km from the active delta fronts stratigraphic paleontologic and geographic constraints indicate that the paleopycnocline was not horizontal but sloped northeastward from shallower waters near the cincinnati arch to deeper waters off the delta fronts

mudrock sequence stratigraphy a multi proxy sedimentological paleobiological and geochemical approach devonian appalachian basin abstract delineation of stratigraphic sequences and their component systems tracts in mudrock dominated facies is generally difficult due to the relatively homogenous fine grained nature of the strata in this study we apply a multi proxy analytical approach to a thick devonian mudrock dominated succession through detailed analysis of sedimentologic paleobiologic and geochemical data through 600 m of mudrock rich facies varied combinations of proxies prove to be most useful in delineating sequence development in anoxic dysoxic and oxic dominated mudrock settings and in mixed mudrock carbonate and mixed mudrock sandstone successions these interpretations are tested against an established sequence stratigraphic framework for 11 middle to upper devonian mid eifelian to lower famennian sequences in the appalachian basin the sequences presented here further detail and refine global devonian t r cycles id to iie of the well known johnson sandberg and klapper sea level curve the usefulness of proxies in delineating depositional sequences and systems tracts varies dependent on depositional paleoceanographic paleoecologic and early diagenetic conditions those proxies that show a range of variations in specific settings such as grain size degree of bioturbation and concentrations of toc and elements elemental ratios e g caco3 al ti mg sc si mo ni v si al and ti al may help delineate depositional dynamics related to redox conditions condensation dilution and clastic biologic and or authigenic sediment sources in fine grained anoxic dominated facies interpreted to represent basinal settings sequences and systems tracts are best delineated by anoxic related proxies toc and mo in intermediate dysoxic dominated settings toc mo bioturbation and al remain effective indicators of sequence development in relatively oxygenated mudrock rich and carbonate poor sequences bioturbation may function as the most effective proxy for recognizing systems tracts for mixed fine grained siliciclastic carbonate successions concentration and type of caco3 e g benthic macroskeletal pelagic styliolinid dacryoconarid and micritic calcisilt are useful in identifying position within cycles in more proximal carbonate poor successions fine and coarse grained fractions become increasingly differentiated these can be distinguished by relatively high si al ratios si al ca 5 elemental ratios indicative of coarser clastic input e g si al zr al and ti al are applicable to identifying position with a sequence but they may also be affected by input from eolian volcanogenic or biogenic sources in addition fluxes of siliciclastic carbonate and toc sediment types may dilute the concentration of the others multiple lines of evidence should be examined in interpreting relative depth and position within a sequence

environmental and physiological influences on isotopic and elemental compositions of brachiopod shell calcite implications for the isotopic evolution of paleozoic oceans abstract brachiopods from the demissa bed middle devonian hamilton group biologically regulated the incorporation of mg sr and na into their shell calcite significant taxonomic differences in the elemental contents of three species athyris spiriferoides mediospirifer audacula and mucrospirifer mucronatus may be related to differences in calcification processes in contrast no significant difference or vital effects were observed between the isotopic values of mediospirifer audacula and athyris spiriferoides from erie 18o 0 03 p 0 949 13c 0 76 p 0 083 and genessee counties 18o 0 39 p 0 471 13c 0 06 p 0 854 this suggests that these brachiopods did not exert a biological control over their isotopic compositions and that their shell calcites reflect ambient physicochemical conditions isotopic compositions in unaltered shell calcites of brachiopods from genessee county which was close to the basin depocentre are heavy for carbon 13c x 5 01 pdb and oxygen 18o x 2 85 pdb compared to the species sampled at the basin s edge erie county 13c x 2 79 pdb 18o x 3 83 pdb there is a significant separation in isotopic values between the deeper and shallower water brachiopods of the basin 18o 0 98 p 0 0005 13c 2 22 p 0 0005 the 18o variation suggests a temperature salinity change with water depth whereas the change in 13c composition probably records an enrichment depletion of organic matter with water depth this observation has significant implications for paleozoic ocean isotopic evolution studies because many global changes in marine 18o and 13c are based on isotopic shifts of similar magnitude