the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

andean tectonics as a cause for changing drainage patterns in miocene northern south america newdatafromneogenestratainnorthernsouthamericasuggestthatmiocenetectonisminthenortheasternandeswasresponsible for the genesis of the amazon river and changes in the drainage patterns of other major rivers such as the magdalena and the orinoco here we present a new model for the paleogeographic evolution of northern south america during the miocene in the early miocene a large part of the drainage of northwest amazonia was directed northward along the paleo orinoco river system to a deltainlakemaracaibo upliftoftheeasterncordillerainthelate middle miocene caused thefirst development of the amazon river however no connection with the atlantic was established and the amazon fed the paleo orinoco river system which drained toward the caribbean substantial andean uplift in the late miocene resultedinmajorchangesinpaleogeography theorinocochangedits course the amazon established a connection to the atlantic causing the drowning of carbonate platforms and the amazon caribbeanconnectionwasclosed thusthedrainageandpaleogeography ofnorthernsouthamericainthemiocenewerestronglycontrolled by tectonic movements in the northeastern andes

uplift history of the central and northern andes a review the elevation of the andean cordillera is a crucial boundary condition for both climatic and tectonic studies the andes affect climate because they form the only barrier to atmospheric circulation in the southern hemisphere and they intrigue geologists because they have the highest plateau on earth formed at a noncollisional plate margin the altiplano puna yet until recently few quantitative studies of their uplift history existed this study presents both 1 a review of the quantitative paleoelevation estimates that have been made for the central and colombian andes and 2 an examination of the source and magnitude of error for each estimate in the central andes paleobotanical evidence suggests that the altiplano puna had attained no more than a third of its modern elevation of 3700 m by 20 ma and no more than half its modern elevation by 10 7 ma these data imply surface uplift on the order of 2300 3400 m since the late miocene at uplift rates of 0 2 0 3 mm yr paleobotanical and geomorphological data suggest a similar uplift history for the eastern cordillera namely no more than half the modern elevation present by 10 ma no evidence exists for an exponential increase in uplift rate as has been interpreted from fissiontrack data these uplift rates mostly reflect mean surface uplift rather than rock uplift that is uplift of material points because little dissection of the western eastern cordillera has occurred south of lat 19 s and of the altiplano puna thus the central andean plateau appears to be young in the colombian andes paleobotanical data imply rapid uplift of the eastern cordillera between 2 and 5 ma at rates on the order of 0 6 3 mm yr however some of this uplift is likely rock uplift due to erosion driven isostatic rebound rather than mean surface uplift

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

forcing mechanisms for mid cretaceous black shale formation evidence from the upper aptian and lower albian of the vocontian basin se france calcareous nannoplankton palynomorph benthic foraminifera and oxygen isotope records from the supraregionally distributed niveau paquier early albian age oceanic anoxic event 1b and regionally distributed niveau kilian late aptian age black shales in the vocontian basin se france exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid cretaceous low latitudes to quantify surface water productivity and temperature changes nutrient and temperature indices based on calcareous nannofossils were developed the nutrient index strongly varies in the precessional band whereas variations of the temperature index reflect eccentricity since polar ice caps were not present during the mid cretaceous these variations probably result from feedback mechanisms within a monsoonal climate system of the mid cretaceous low latitudes involving warm humid and cool dry cycles a model is proposed that explains the formation of mid cretaceous black shales through monsoonally driven changes in temperature and evaporation precipitation patterns the lower albian niveau paquier which has a supraregional distribution formed under extremely warm and humid conditions when monsoonal intensity was strongest bottom water ventilation in the vocontian basin was diminished probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes surface water productivity in the vocontian basin was controlled by the strength of monsoonal winds the upper aptian niveau kilian which has a regional distribution only formed under a less warm and humid climate than the niveau paquier low latitude deep water formation was reduced to a lesser extent and or on regional scale only the threshold for the formation of a supraregional black shale was not reached the intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale at least in the vocontian basin the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity

sea level fluctuations driven by changes in global ocean basin volume following supercontinent break up abstract long term variations in eustatic sea level in an ice free world which existed through most of the mesozoic and early cenozoic eras are partly driven by changes in the volume of ocean basins previous studies have determined ocean basin volume changes from plate tectonic reconstructions since the mesozoic however these studies have not considered a number of important elements that contribute to ocean basin volume such as regional differences in sedimentation or uncertainties within the plate tectonic model itself such as spreading asymmetries and the incomplete representation of back arc basins in the mesozoic additionally studies on long term changes in sea level related to the extension and rifting of passive margins have not been performed on a global scale and likely significantly underestimated the influence of this process in order to improve reconstructions of sea level on geologic time scales and assess the uncertainty in deriving the volume of ocean basins based on a global plate kinematic model we investigate the influence of back arc basins spreading asymmetry large igneous provinces lips sediment thickness and passive margins on ocean basin volume since 200 ma we find that less constrained plate tectonic elements such as the presence of back arc basins or spreading asymmetry may contribute up to 120 m or 150 m to sea level respectively changes in the sea level related to sedimentation and lips are respectively 75 165 m and 45 m changes in sea level associated with passive margin formation are almost negligible at present day though were much larger in the cretaceous and the assumed sedimentation style strongly influences the rate and magnitude of sea level change we incorporate predictions for these components during times where ocean basins are predominantly synthetic reconstructions and find that sea level driven by fluctuating ocean basin volume has changed by 200 m since the jurassic which is comparable to previous estimates our revised estimates will need to be combined with other processes driving long term sea level change including mantle convection driven dynamic topography and glacio eustasy for constructing a complete eustatic sea level curve understanding and quantifying the uncertainties in the volume of ocean basins has implications for modelling subduction flux the oceanic carbon cycle and heatflow and is important for exploring earth s evolutionary cycles especially during times in the geologic past where much of the ocean basin history has been lost

long term sea level fluctuations driven by ocean basin dynamics earth9s long term sea level history is characterized by widespread continental flooding in the cretaceous period 145 to 65 million years ago followed by gradual regression of inland seas however published estimates of the late cretaceous sea level high differ by half an order of magnitude from 40 to 250 meters above the present level the low estimate is based on the stratigraphy of the new jersey margin by assimilating marine geophysical data into reconstructions of ancient ocean basins we model a late cretaceous sea level that is 170 85 to 270 meters higher than it is today we use a mantle convection model to suggest that new jersey subsided by 105 to 180 meters in the past 70 million years because of north america9s westward passage over the subducted farallon plate this mechanism reconciles new jersey margin based sea level estimates with ocean basin reconstructions

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

gplates building a virtual earth through deep time gplates is an open source cross platform plate tectonic geographic information system enabling the interactive manipulation of plate tectonic reconstructions and the visualization of geodata through geological time gplates allows the building of topological plate models representing the mosaic of evolving plate boundary networks through time useful for computing plate velocity fields as surface boundary conditions for mantle convection models and for investigating physical and chemical exchanges of material between the surface and the deep earth along tectonic plate boundaries the ability of gplates to visualize subsurface 3 d scalar fields together with traditional geological surface data enables researchers to analyze their relationships through geological time in a common plate tectonic reference frame to achieve this a hierarchical cube map framework is used for rendering reconstructed surface raster data to support the rendering of subsurface 3 d scalar fields using graphics hardware accelerated ray tracing techniques gplates enables the construction of plate deformation zones regions combining extension compression and shearing that accommodate the relative motion between rigid blocks users can explore how strain rates stretching shortening factors and crustal thickness evolve through space and time and interactively update the kinematics associated with deformation where data sets described by geometries points lines or polygons fall within deformation regions the deformation can be applied to these geometries together these tools allow users to build virtual earth models that quantitatively describe continental assembly fragmentation and dispersal and are interoperable with many other mapping and modeling tools enabling applications in tectonics geodynamics basin evolution orogenesis deep earth resource exploration paleobiology paleoceanography and paleoclimate

cool la nina during the warmth of the pliocene the role of el nino southern oscillation enso in greenhouse warming and climate change remains controversial during the warmth of the early mid pliocene we find evidence for enhanced thermocline tilt and cold upwelling in the equatorial pacific consistent with the prevalence of a la nina like state rather than the proposed persistent warm el nino like conditions our pliocene paleothermometer supports the idea of a dynamic ocean thermostat in which heating of the tropical pacific leads to a cooling of the east equatorial pacific and a la nina like state analogous to observations of a transient increasing east west sea surface temperature gradient in the 20th century tropical pacific

the bengal depositional system from rift to orogeny abstract the bengal depositional system is defined as the surface depositional environments and the underlying sediment accumulation extending from the alluvial lacustrine and paludal sediments of the lower ganges and brahmaputra rivers across the bengal delta the bangladesh continental shelf and slope to and including the bengal fan together it is one of the greatest sediment accumulations in the modern world and is comparable in volume to the great sediment accumulations of the geological past the history of formation started with the mesozoic breakup of eastern gondwanaland the northward drift of india its collision with the southern margin of asia rotation and bending of the western sunda arc and the penetration of the indian continental mass into southern asia during this history the regional tectonics evolved and sources and provenance of the sediments changed with the ultimate uplift of the tibetan plateau and the himalayas

the cristal zn prospect amazonas region northern peru part ii an example of supergene enrichments in tropical areas abstract the cristal zn prospect is located in the northernmost part of a wide mining district corresponding to the charlotte bongara zinc project which covers an area of approximately 110 km2 in the amazonas region in northern peru the mineralized area consists of many zn occurrences that contain mixed sulfide and nonsulfide mineralizations the nonsulfide ores are interpreted to be the product of weathering of primary mvt sulfide bodies the zn concentrations of the cristal prospect are hosted by platform carbonates of the condorsinga formation early jurassic which belongs to the pucara group the prospect extends over an area of approximately 2 1 km with nearly continuous zones of zn enrichment that has been detected in soil and rock samples the nonsulfide mineralization consists mainly of semi amorphous orange to brown zinc oxides that include hemimorphite smithsonite and fe hydr oxides the most important mineralized areas are the esperanza and yolanda occurrences which were also most intensively explored in both occurrences the supergene zn carbonates and silicates infill solution cavities or replace the carbonate host rocks and or the primary sulfides forming smithsonite and hemimorphite rich mineralizations the analyzed drill core samples have on average 20 wt zn and maximum ge concentrations of 200 ppm the bongara area experienced a prolonged phase of weathering from miocene to recent under tropical climatic conditions in these conditions the weathering processes affected many pre existing sulfide deposits e g cristal florida canyon mina grande where supergene profiles were developed under locally different settings that are defined primarily on the basis of mineralogical and geochemical data contrary to the mina grande deposit at cristal the development of a karst network was minor due to limited uplift and supergene alteration did not completely obliterate the roots of the original sulfide orebody the mineralogy and geochemistry of bongara nonsulfides is dependent on two main factors at the local scale 1 uplift rates and 2 host rock composition the latter may have favored the development of more e g mina grande or less e g cristal alkaline supergene environments uplift was controlled by the activity of local faults which allowed the exposure of sulfide protores at variable elevations in different periods of time and hydrological settings such different settings resulted in the precipitation of isotopically different supergene carbonates e g smithsonites and calcites at mina grande and cristal

evolution of atlantic pacific δ13c gradients over the last 2 5 m y the evolution of interocean carbon isotopic gradients over the last 2 5 m y is examined using high resolution 13c records from deep sea cores in the atlantic and pacific oceans over much of the northern hemisphere ice ages relative reductions in north atlantic deep water production occur during ice maxima from 2 5 to 1 5 ma glacial reductions in nadw are less than those observed in the late pleistocene glacial suppression of nadw intensified after 1 5 ma earlier than the transition to larger ice sheets around 0 7 ma at a number of times during the pleistocene 13c values at dsdp site 607 in the north atlantic were indistinguishable from eastern equatorial pacific 13c values from approximately the same depth odp site 677 indicating significant incursions of low 13c water into the deep north atlantic atlantic pacific 13c values converge during glaciations between 1 13 1 05 m y 0 83 0 70 m y and 0 46 0 43 m y this represents a pseudo periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing this partial decoupling at low frequencies of the 18o and 13c signals at site 607 indicates that variations in north atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing

late pliocene onset of glaciation ice rafting and diatom stratigraphy of north pacific dsdp cores abstract the revised diatom biostratigraphy for the north pacific allows the timing of ice rafting as recorded in deep sea drilling project cores to be determined significant ice rafting began at the time of the matuyama gauss reversal boundary about 2 48 ma other bio and lithostratigraphic data from the pacific atlantic and arctic oceans and the black sea all indicate that northern hemispherical cooling and the accumulation of continental ice began at 2 4 2 5 ma we interpret all these data to indicate northern hemisphere ice cap formation at that time if so the closing of the isthmus of panama approximately 3 2 m y ago was not the immediate cause of the plio pleistocene glaciations

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

the drainage of africa since the cretaceous much of the drainage of africa is relatively youthful many of its major rivers have shown substantial changes in their courses since the break up of gondwanaland in the cretaceous in addition many of the rivers have distinctive morphological characteristics such as inland deltas cataracts and elbows of capture tectonic and climatic changes including the development of the east african rift system and the aridification of the quaternary help to explain the nature of these rivers the history of the saharan rivers the niger the nile the congo the cunene the zambezi the limpopo and the orange is reviewed

from mountain source to ocean sink the passage of sediment across an active margin waipaoa sedimentary system new zealand abstract the joint us nz source to sink initiative aims to unravel the tectonic climatic and other processes that shape the landscape from the mountains to deep ocean of two focus areas chosen world wide the waipaoa sedimentary system wss of north eastern new zealand was identified as an example of a mid latitude high sediment input system it resides within the westerly wind belt and extends across the convergence zone of the australian and pacific plates accordingly the tectonic and climatic drivers are prominent and their influences on the wss are decipherable as is documented in the suite of source to sink studies presented in this special issue of marine geology the wss is forced at several temporal and spatial scales which collectively appear as short term events storms earthquakes and volcanic eruptions superimposed on long term behavioural shifts tectonic uplift and eustatic sea level change overall the wss is undergoing uplift which has been contributing to valley incision since the last glacial maximum uplift is both gradual and intermittent the latter relating to fault and subduction related earthquakes such seismic activity destabilises the landscape and together with frequent storms generates large amounts of sediment as this sediment passes through the system part is captured in traps formed by local subsidence of the coastal plain and middle continental shelf where large thicknesses of holocene and probably older sediment are sequestered e g 200 m under the coastal plain nevertheless substantial sediment still reaches the continental slope to accumulate in canyon heads and slope basins with other deposits redistributed down slope in mass flows major volcanic eruptions also affect the sediment flux via direct input from ash fall and by enhanced erosion following volcanic destruction of terrestrial vegetation frequent storms of varying intensity play a key role in the generation and transfer of sediment major events such as cyclone bola of 1988 inundated the shelf with sediment but identifiable flood deposits were preserved only locally attesting to the effectiveness of shelf physical and biological mixing regimes despite the storms earthquakes and volcanic eruptions the largest perturbation of the wss at least in the last 2400 years has been the human deforestation of the landscape the resultant influx of sediment overwhelmed the shelf s storage capacity instead of capturing 90 the fluvial input as in pre human times the modern shelf retains only 25 the remainder escaping to the slope and elsewhere

neogene carbonate burial in the pacific ocean 1 i have compiled caco3 mass accumulation rates mars for the period 0 25 ma for 144 deep sea drilling project and ocean drilling program drill sites in the pacific in order to investigate the history of caco3 burial in the world s largest ocean basin this is the first synthesis of data since the beginning of the ocean drilling program sedimentation rates caco3 contents and bulk density were estimated for 0 5 myr time intervals from 0 to 14 ma and for 1 myr time intervals from 14 to 25 ma using mostly data from initial reports volumes there is surprisingly little coherence between caco3 mar time series from different pacific regions although regional patterns exist a transition from high to low caco3 mar from 23 20 ma is the only event common to the entire pacific ocean this event is found worldwide the most likely cause of lowered pelagic carbonate burial is a rising sea level trend in the early miocene the central and eastern equatorial pacific is the only region with adequate drill site coverage to study carbonate compensation depth ccd changes in detail for the entire neogene the latitude dependent decrease in caco3 production away from the equator is an important defining factor of the regional ccd which shallows away from the equatorial region examination of latitudinal transects across the equatorial region is a useful way to separate the effects of changes in carbonate production productivity from changes in bottom water chemistry dissolution upon carbonate burial

a tectonic model reconciling evidence for the collisions between india eurasia and intra oceanic arcs of the central eastern tethys abstract despite several decades of investigations inferences on the timing and nature of collisions along the mesozoic cenozoic eurasian margin remain controversial we assimilate geological and geophysical evidence into a plate tectonic model for the india eurasia collision that includes continuously closing topological plate polygons constructed from a time dependent network of evolving plate boundaries with synthetic plates constructed for now subducted ocean floor including back arc basins that formed on the southern eurasian margin our model is regionally constrained and self consistent incorporating geophysical data from abyssal plains offshore west australia and east antarctica including jurassic age data from offshore northwest australia limiting much of northern greater india to a 1000 km long indenter originally reaching to the wallaby zenith fracture zone southern eurasia and southeast asia are riddled with dismembered oceanic arcs indicating long lived tethyan intra oceanic subduction this intra oceanic subduction system was well established from cretaceous time in the india eurasia convergence zone in the neotethys which was consumed during greater india s northward trajectory towards eurasia from the early cretaceous fragments of obducted oceanic crust within the yarlung tsangpo suture zone between india and eurasia predominantly date to the late jurassic or mid cretaceous barremian aptian the various ophiolites along strike and a hiatus in subduction related magmatism during the tithonian aptian suggest that there was at least one generation of intra oceanic arc formation whose plate boundary configuration remains uncertain paleomagnetic and magmatic studies suggest that the intra oceanic arc was at equatorial latitudes during the early cretaceous before subduction resumed further north beneath the eurasian margin lhasa terrane with another hiatus in subduction related magmatism along southern lhasa during 80 65 ma possibly as the back arc spreading centre approached the active andean style margin in our model greater india collided with the tethyan intra oceanic arc in paleocene eocene time finally closing the tethyan seaway from mid late eocene time which is consistent with the age of the youngest marine deposits found between india and eurasia geological evidence from the collision zone indicates an age of initial arc continent collision by 52 ma followed by the soft initial continent continent collision between india and eurasia by 44 2 ma this timing is supported by marine geophysical data where the spreading centres in the indian ocean record a drastic decline in seafloor spreading rates and changes in spreading directions first at 52 ma followed by another reorganisation at 43 ma the abandonment of spreading in the wharton basin and the onset of extrusion tectonics in asia by 36 ma are likely indicators of hard complete continent collision and highlight the multi stage collisional history of this margin our continuously evolving network of mid ocean ridge and subduction zone geometries and divergence convergence vectors through time provide a basis for future refinements to assimilate new data and or test alternative tectonic scenarios

extraction of high resolution carbonate data for palaeoclimate reconstruction temporal variations in the calcium carbonate content of deepsea sediments provide direct stratigraphic as well as important palaeoenvironmental information relating to the global carbon cycle here i present an algorithm that allows carbonate content and porosity to be accurately predicted from saturated bulk density in equatorial pelagic carbonates applying the algorithm to continuous laboratory measurements of density made on dsdp and oop cores yields a nearly continuous carbonate record for the upper 200 m of the sediment section long ultra high resolution carbonate curves of this type should yield new insight into the evolution of the carbon chemistry of the oceans as well as the role of external milankovitch forcing in the development of the carbonate system the algorithm can also be applied to quantitative high resolution seismic data thereby enabling detailed carbonate records to be extracted from remotely derived geophysical data

radiolarian palaeoecology and radiolarites is the present the key to the past abstract radiolarian productivity pulses and related radiolarite deposition are phenomena difficult to understand from an exclusively actualistic viewpoint evolutionary selection pressure among silica secreting marine plankton both radiolarians and diatoms has led toward more economic usage of rapidly shrinking nutrient resources including dissolved silica of the photic zone in the late cenozoic oceans and in particular a substantial modification of oceanic cycle by the diatom explosive radiation even if there is a proved link between biomineralization and dissolved silica loading among the phytoplankton only the relative independence of modern siliceous planktic biotas from the available silica pool reflects mainly their progressive physiological specialisation during evolutionary history oceanic chemistry and productivity as well as patterns of circulation upwelling have changed radically during the phanerozoic radiolarites apparently represent an anachronistic facies as exemplified by their long lived and ocean wide distribution in palaeo pacific and hitherto highlighted actualistic models of localized intra oceanic wind driven upwelling loci are of largely questionable applicability in addition to plate drift hypersiliceous domains and intervals are explainable mostly by a large scale volcano hydrothermal activity during major plate boundary reconfigurations which in many ways favoured siliceous biotas acme and their skeletal remains accumulation and preservation factors tied to rapid voluminous submarine eruptions such as thermal buoyant megaplumes and basin overturns offer a viable alternative for traditional climatic circulation scenarios in case of hypersiliceous high productivity events irrelevant to greenhouse to icehouse climatic change the evolving carbon and silica cycles were coupled through the greenhouse effect and enhanced chemical weathering volcano hydrothermal and tectonic uplift events related mostly to extensive rifting and or accelerated oceanic spreading were the endogenous driving force that created this perturbation of the exogenous system the present biogeochemical cycle is representative only for the overall silica depleted post eocene oceanic ecosystems which broadly correlates with a major expansion of diatoms groups extremely efficient in silica removal and closely linking the silica budget with phosphorus and nitrogen cycles thus an orthodox uniformitarian approach to biosiliceous sedimentation based on a silica starved vigorous ocean is of limited significance when applied to the pre neogene settings especially in the peculiar planktic habitats of epeiric seas as well as during biotic crises marked by strong geotectonic overprint the major turnovers in marine siliceous biota composition in particular after the end permian radiolarite gap may have been coupled with discernible changes in an increasing biological control on the long term oceanic silica cycling punctuated equilibrium the evolutionary turnovers have induced a stepdown decrease of dissolved silica levels through the phanerozoic contemporaneously with the general secular trend of upward scaling of nutrient related ecological processes and increased effectiveness of resource utilization

variation of ocean sediment thickness with crustal age global ocean sediment thickness and present day ocean sediment accumulation rates are analyzed with respect to the age of the underlying ocean crust trends in average sediment thickness and present day accumulation rate are well fit by cubic polynomials in crustal age for the global ocean and for individual ocean basins sediment thickness and accumulation rates are larger in the north and south atlantic and indian oceans compared to the pacific ocean primarily because the anomalous sediment accumulations that followed continental rifting and collision in the atlantic and indian ocean basins are missing in the pacific ocean modern ocean sediment accumulation rates extrapolated into the past assuming steady state conditions account within uncertainties for the global average sediment thickness on 0 65 ma cenozoic age ocean crust while the profile of anomalously thick sediments on older mesozoic age ocean crust is well fit by adding localized diffusive sediment transport from a steady state source referenced to the adjacent continental margin apart from a distinct 0 5 ma quaternary age sediment pulse deviations in average sediment thickness from this simple model are generally small and are uncorrelated across ocean basins

nonlinear response of pliocene climate to orbital forcing evidence from the eastern equatorial pacific a high resolution radiolarian record from the eastern equatorial pacific is used to examine paleoceanographic events during the pliocene from 1 8 to 4 9 ma these data provide a means to evaluate the response of the equatorial pacific to the onset of northern hemisphere glaciation near 2 47 ma and to the closure of the isthmus of panama near 3 2 ma responses are recorded both as long term trends and as variations within the milankovitch band 104 to 105 years radiolarian based sea surface temperature sst estimates indicate a mean cooling from lower to upper pliocene but no significant changes occur near the onset of northern hemisphere glaciation and no abrupt changes are observed before or after the closure of the isthmus spectral and cross spectral analyses of this sst time series indicate concentrations of variance within the precession 23 kyr and obliquity 41 kyr bands in several but not all time intervals variance is commonly concentrated at lower frequencies cross spectral analysis of sst time series and calculated orbital variations indicates that the sst record is not coherent with and therefore not linearly related to orbital variations detailed time series analysis of the sst and 18o time series indicates the absence of a direct linear relationship but rather the presence of a strongly nonlinear relationship between pliocene climatic variables and earth s orbit high coherence is seen between the amplitude of the 23 kyr component of sst and the amplitude modulation of precession the amplitude modulation of the 41 kyr component of the sst record is dissimilar to the amplitude modulation of obliquity but is extremely similar to and coherent with the amplitude of the 23 kyr component of sst the amplitude modulations of sst and 18o at a range of frequency bands have the same features features that roughly follow the modulation of precession this suggests a strongly nonlinear response of equatorial pacific sst and planktonic 18o to orbital forcing in the pliocene such a response extending over a number of frequency bands has not previously been seen in a paleoclimatic data set but may be consistent with proposed models describing paleoclimatic variability although the reasons for this response are still unclear it is evident that strong nonlinearities in climate are present during this time

drainage evolution of the lower narmada valley western india abstract various tectonic disturbances from the cretaceous to the present day have modified the geomorphic features of western india compression and extensional stresses generated by the northerly moving indian plate and its collision with the eurasian plate have brought about frequent changes in the drainage system and other features different segments that lie between several regional faults have encountered many upheavals and subsidences during the major part of the tertiary the tributaries of the narmada mahi and other westerly flowing rivers had much larger catchment areas that extended to the north the compressional stresses exerted during the pliocene and pleistocene epochs have shortened the basin of these rivers the release of stresses during the early pleistocene is mainly responsible for the development of the present highlands and lower surfaces based on structural studies subsurface data sedimentation in different basins and the area of provenance and movement of the indian plate the authors have suggested successive stages of the landform development in the lower reaches of the narmada valley

age and implications of the forest bed falkland islands southwest atlantic ocean evidence from fossil pollen and spores diverse pollen and spore assemblages microfloras are preserved in organic clays and lignites associated with fossil tree remains in the forest bed at present these microfloras provide the only reliable basis for determining the age composition structure and affinity of the forest bed community the bed is suggested to be middle miocene to early pliocene age range oligocene early pliocene based on the time distribution of a number of rare pollen types and the present day ecology of their nearest living relatives in central southern america and the southwest pacific the wet forest community whose remains form the forest bed was a form of broadleaf gymnosperm temperate rainforest in which dacrydium lagarostrobos and podocarpus are likely to have formed an overstorey above a closed canopy dominated by nothofagus nothofagus spp the latter subgenus is now endemic to uniformly wet regions in southern south america whilst two of the tall gymnosperms dacrydium lagarostrobos are now endemic to the southwest pacific region an extinct probable shrub sized conifer podosporites microsaccatus appears to have formed the ground cover ferns and fern allies were very rare in contrast to most living nothofagus gymnosperm communities fossil pollen and spore types produced by uncommon subcanopy tree shrub and fern species potentially provide a means for more accurately dating the deposit once their time of first occurrence and extinction at subantarctic latitudes in the southwest atlantic region is established nearest living equivalents given in parentheses clavatipollenites cf glarius hedyosmum thymelaepollis sp ovidia type and cyatheacidites annulatus lophosoria this will require palynostratigraphic analysis of late palaeogene neogene sediments recovered from basins surrounding the falkland islands for example from dsdp site 329 drilled on the maurice ewing bank at the eastern margin of the falkland plateau

ocean basin evolution and global scale plate reorganization events since pangea breakup we present a revised global plate motion model with continuously closing plate boundaries ranging from the triassic at 230 ma to the present day assess differences among alternative absolute plate motion models and review global tectonic events relatively high mean absolute plate motion rates of approximately 9 10 cm yr 1 between 140 and 120 ma may be related to transient plate motion accelerations driven by the successive emplacement of a sequence of large igneous provinces during that time an event at 100 ma is most clearly expressed in the indian ocean and may reflect the initiation of andean style subduction along southern continental eurasia whereas an acceleration at 80 ma of mean rates from 6 to 8 cm yr 1 reflects the initial northward acceleration of india and simultaneous speedups of plates in the pacific an event at 50 ma expressed in relative and some absolute plate motion changes around the globe and in a reduction of global mean plate speeds from about 6 to 4 5 cm yr 1 indicates that an increase in collisional forces such as the india eurasia collision and ridge subduction events in the pacific such as the izanagi pacific ridge play a significant role in modulating plate velocities

a late miocene subtropical dry flora from the northern altiplano bolivia abstract a variety of evidence suggests that the altiplano of the central andes the second highest and largest plateau on earth underwent significant uplift in the late miocene pliocene the most important datum supporting recent uplift is a collection of the 10 66 0 06 ma jakokkota flora from west central bolivia which implies a paleoelevation no more than 1600 1200 m today the site has an elevation of almost 4000 m in order to test the reliability of this estimate the present study analyzes a new collection of the jakokkota flora from a lacustrine unit that is 0 2 0 5 myr younger than the previously analyzed collection from a fluvial unit climate estimates based on leaf morphology for the two collections are statistically indistinguishable the combined flora has a mean annual temperature of 21 5 2 0 c and a mean annual precipitation of 550 180 mm the similarity of the climate estimates for the two floras suggests that there was not a significant climate change between them nor a significant bias in the leaf morphology due to differing taphonomic processes the climate estimate for the combined flora thus presents a representative picture of the late miocene climate of the northern altiplano if one assumes that the climate of the tropics has not changed significantly since the late miocene as is suggested by marine isotopic data then the paleoclimate of the jakokkota flora implies a paleoelevation of 1160 600 m thus the jakokkota flora supports the hypothesis of a young age for the altiplano

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

numerical climate modeling a frontier in petroleum source rock prediction results based on cretaceous simulations organic productivity and preservation are primary controls of the distribution of petroleum source beds both organic productivity and preservation are in part a function of geographic setting and climate therefore the prediction of paleoclimates is a major frontier in petroleum source rock prediction a climate model based on the fundamental laws thought to govern atmospheric circulation is applied here to the prediction of upwelling regions associated with very high productivity and bottom conditions that may become anoxic despite a high oxygen supply the potential and limitations of climate modeling in the prediction of upwelling regions are examined by 1 demonstrating the ability of the model to predict present day winds and upwelling regions 2 demonstrating t at the model and the location of upwelling regions is sensitive to geography continental positions sea level and topography and 3 investigating whether the model sensitivity to past geographies is realistic i e if predicted upwelling regions for the cretaceous period correspond to source rock localities the model predictions of ocean and coastal upwelling compare very favorably with present day observations and with estimates of primary productivity the location of middle latitude and high latitude upwelling locations are sensitive to model specified geography the location of low latitude upwelling is less sensitive to changes in global geography if coastlines are oriented appropriately despite some limitations a comparison of source rock localities with model predictions is promising the results of these studies suggest that numerical climate modeling is a potential tool in petroleum source rock prediction

thickness and spatial distributions of clastic dykes northwest sacramento valley california abstract the geometry and distribution of the clastic dykes of the ono district north sacramento valley are examined within stream sections five traverses along dry stream beds provide good exposure allowing the spacing thickness and geometry of the dykes to be recorded the spatial and thickness distribution of the dykes are considered using cumulative frequency plots allowing a visual estimation of a best fit distribution dyke thickness conforms best to a log normal distribution there is also a characteristic minimum dyke thickness in a traverse and this is attributed to the minimum aperture that a fluid with sand clasts is able to exploit dyke spacing however shows a good correlation with a power law distribution for four traverses suggesting that there is a mechanistic control on the spatial distribution plotting dyke thickness against minimum dyke spacing reveals that thin dykes do not generally intrude in isolation unlike veins and igneous dykes clastic dykes continue to provide preferential pathways for fluid flow subsequent to their intrusion thus inhibiting intrusion in the area surrounding a pre existing dyke a combination of this process and dyke branching provides the best model for the observed spatial and thickness distribution of clastic dykes seen in the ono district california

compound specific radiocarbon dating of the varved holocene sedimentary record of saanich inlet canada 1 the radiocarbon contents of various biomarkers extracted from the varve counted sediments of saanich inlet canada were determined to assess their applicability for dating purposes calibrated ages obtained from the marine planktonic archaeal biomarker crenarchaeol compared favorably with varve count ages the same conclusion could be drawn for a more general archaeal biomarker gdgt 0 although this biomarker proved to be less reliable due to its less specific origin the results also lend support to earlier indications that marine crenarchaeota use dissolved inorganic carbon dic as their carbon source the average reservoir age offset r of 430 years determined using the crenarchaeol radiocarbon ages varied by 110 years this may be caused by natural variations in ocean atmosphere mixing or upwelling at the ne pacific coast but variability may also be due to an inconsistency in the marine calibration curve when used at sites with high reservoir ages

evidence for a change in the periodicity of tropical climate cycles at 2 4 myr from whole core magnetic susceptibility measurements the earth s orbit about the sun is influenced by gravitational interactions with the moon and other planets the resulting orbital perturbations give rise to cyclical variations in orbital eccentricity obliquity and precession with periods of 100 41 19 and 23 kyr respectively1 these variations are climatically important because they affect the seasonal and latitudinal distribution of solar radiation magnetic susceptibility measurements in deep sea sediment cores can be used as a sensitive indicator of temporal variations in the concentration of terrigenous material supplied to the sea bed here we use this approach to study the evolution of cycles of terrigenous sedimentation at ocean drilling program sites in the arabian sea and the eastern tropical atlantic we show from spectral analyses of the two susceptibility time series spanning the past 3 2 3 5 myr that the records are driven strongly by orbital forcing before 2 4 myr before present bp both records are strongly influenced by the 23 and 19 kyr periodicities but after 2 4 myr they are both significantly influenced by the 41 kyr periodicity this shift coincides with the beginning of major northern hemisphere glaciation which indicates for the indian ocean site that the supply of terrigenous sediment carried by monsoonal winds has responded to the rapid increase in ice cover at this time we cannot however exclude possible effects of changes in bottom water circulation on the susceptibility record of the atlantic site

fluctuations in biosiliceous production and the generation of early cretaceous oceanic anoxic events in the pacific ocean shatsky rise ocean drilling program leg 198 integration of geophysical logs with sedimentological biostratigraphic and physical properties data from poorly recovered chert rich sequences at ocean drilling program leg 198 sites 1207 and 1213 allows us to propose an aptian albian early cretaceous depositional history for shatsky rise north pacific ocean the logs indicate that the lower aptian and lower albian deposits are relatively lithified and unporous compared to contiguous sediments these characteristics are best explained by increased siliceous cementation that resulted from an elevated flux of radiolarians to the seafloor the intervals of increased biosiliceous production may record a biotic response to enhanced nutrient delivery coeval with but longer in duration than oceanic anoxic events oaes 1a early aptian and 1b early albian on shatsky rise oae 1a is represented by organic carbon rich sediments but oae 1b is not thus black shale deposition in the pacific ocean was only possible when a carbon burial threshold was crossed we speculate that this threshold was related to the balance between productivity and carbon oxidation and that ultimately the supply of biolimiting nutrients through hydrothermal alteration of basalt may have been the key to the development of black shale in the pacific basin

late cenozoic changes in atmospheric circulation deduced from north pacific eolian sediments abstract isolation and analysis of the eolian component of late cenozoic pelagic sediments from the north pacific provides direct information concerning changes in atmospheric circulation a 50 increase in intensity of both the prevailing westerlies and the tradewinds coincides with increasing pole to equator temperature gradients resulting from the onset of northern hemisphere glaciation at the same time the mass flux of dust from continents to the north pacific increased by a factor of 4 5 apparently reflecting significantly increased continental aridity associated with the late cenozoic glacial ages

measurement and characterisation of spatial distributions of fractures abstract a variety of line sample 1 d and map 2 d datasets of faults and joints has been used to investigate the spatial distributions of fractures and to test techniques of fractal analysis the natural fracture datasets have been supplemented by synthetic datasets with known characteristics the fault datasets investigated range in scale from regional to outcrop and the joint datasets are derived from outcrop 1 d datasets were analysed by the spacing population interval counting and fracture number interval counting techniques 2 d datasets were analysed by box counting and fracture number box counting techniques results indicate that fracture spacing can be characterised in line samples using either the 1 d interval counting technique or more simply by measuring the spacing population as the cumulative frequency distribution of spaces between adjacent fractures tectonic faults frequently show a power law spacing population indicating fractal dimensions of between 0 4 and 1 0 but except for outcrop data truncation effects degrade the analysis unrefined joint datasets commonly show negative exponential or lognormal spacing cumulative frequency distributions however single orientation joint sets are characterised by a regular spacing and are therefore non fractal for both fault and joint map data box counting techniques do not yield the power law relationship between box size and the number of boxes that is expected of fractal geometries it is concluded that 2 d box counting techniques are too insensitive to characterise the many different parameters of a fracture array the fracture density technique appears not to discriminate between very different fracture patterns and therefore does not provide useful results a fracture pattern incorporates several attributes e g size distribution orientation linkage density roughness each of which may scale independently and each of which may be fractal with its own fractal dimension full characterisation of fracture patterns will therefore require independent analysis of each of these attributes

fractured basement play development on the uk and norwegian rifted margins fractured crystalline basement reservoirs basement on the uk continental shelf ukcs and the norwegian continental shelf ncs have been underexplored over the last 12 years hurricane energy has deliberately set out to explore basement potential by exploring and appraising the rona ridge west of shetland and the rona ridge lancaster field is now being progressed towards being the first uk basement field development the norwegian basement play is also recognized as a potentially material resource through serendipitous oil discoveries with the 16 1 15 well drilled in 2011 being the first successful full scale basement test on the ncs building on this success the 2018 rolvsnes appraisal well 16 1 28 s has demonstrated the significant basement potential of the extensive utsira high and confirmed the materiality of a norwegian basement play the rona ridge and utsira basement discoveries are used as a comparison with two other yet to be evaluated prospective basement plays on the ncs with the objective of establishing technical subject areas where future ukcs and ncs collaboration would aid in accelerating understanding of the ukcs ncs basement play

global sediment thickness data set updated for the australian antarctic southern ocean we present a new 5 min sediment thickness grid for the australian antarctic region 60 e 155 e 30 s 70 s new seismic reflection and refraction data have been used to add detail to the conjugate australian and antarctic margins and intervening ocean floor where regional sediment thickness patterns were poorly known previously on the margins sediment thickness estimates were computed from velocity depth functions from sonobuoy refraction velocity solutions ground truthed against seismic reflection data for the southeast indian ridge abyssal plains sediment thickness contours from geli et al 2007 were used the new regional minimum sediment thickness grid was combined with the global national geophysical data center ngdc sediment grid to create an updated global grid even using the minimum estimates sediment accumulations on the extended australian and antarctic continental margins are 2 km thicker across large regions and up to 9 km thicker in the ceduna basin compared to the global ngdc compilation of sediment thickness data

the himalayas organic carbon burial and climate in the miocene cooling ages of rock in the himalayas imply that rapid exhumation between the main central thrust system and the south tibetan detachment system occurred between 21 and 17 ma the generation of relief and enhanced weathering which followed this event may have resulted in a pronounced increase in the delivery of dissolved strontium carbon phosphorus and other chemical weathering products to the ocean richter et al 1992 the increased supply of nutrients stimulated productivity in oceanic upwelling zones and expansion of the oxygen minimum zone leading to enhanced burial and preservation of organic matter in the monterey formation and other deposits from this interval a downdraw of atmospheric co2 associated with enhanced chemical weathering rates and organic matter burial may have led to global cooling and the expansion of the antarctic ice sheet by 15 ma the above scenario differs from the monterey hypothesis of vincent and berger in that co2 downdraw is primarily via silicate weathering rather than organic carbon burial and that organic carbon burial is driven by increased delivery of nutrients to the ocean rather than by stronger upwelling a carbon mass balance calculation which assumes that river fluxes have been increasing over the last 40 ma predicts that absolute organic carbon burial increased over this interval while at the same time the fraction of carbon buried as organic matter versus carbonate decreased this implies that the organic carbon cycle has acted as a net source of co2 to the atmosphere over the late cenozoic

global cenozoic paleobathymetry with a focus on the northern hemisphere oceanic gateways abstract the evolution of the northern hemisphere oceanic gateways has facilitated ocean circulation changes and may have influenced climatic variations in the cenozoic time 66 ma 0 ma however the timing of these oceanic gateway events is poorly constrained and is often neglected in global paleobathymetric reconstructions we have therefore re evaluated the evolution of the northern hemisphere oceanic gateways i e the fram strait greenland scotland ridge the central american seaway and the tethys seaway and embedded their tectonic histories in a new global paleobathymetry and topography model for the cenozoic time our new paleobathymetry model incorporates northeast atlantic paleobathymetric variations due to iceland mantle plume activity updated regional plate kinematics and models for the oceanic lithospheric age sediment thickness and reconstructed oceanic plateaus and microcontinents we also provide a global paleotopography model based on new and previously published regional models in particular the new model documents important bathymetric changes in the northeast atlantic and in the tethys seaway at eocene oligocene transition 34 ma the time of the first glaciations of antarctica believed to be triggered by the opening of the southern ocean gateways i e the drake passage and the tasman gateway and subsequent antarctic circumpolar current initiation our new model can be used to test whether the northern hemisphere gateways could have also played an important role modulating ocean circulation and climate at that time in addition we provide a set of realistic global bathymetric and topographic reconstructions for the cenozoic time at one million year interval for further use in paleo ocean circulation and climate models

influence of oceanic anoxic events on the evolution of mid cretaceous radiolaria in the north atlantic and western tethys abstract mid cretaceous aptian turonian extinction radiation events of radiolaria from the north atlantic and western tethys are summarized in relation to oceanic anoxic events oae from investigations of radiolarian faunas black shales and stable carbon isotopes extinction and radiation events of radiolaria can be observed from the late early aptian the earliest albian the latest albian and the cenomanian turonian boundary these events correlate well with organic carbon rich sediments that contain type ii kerogen and show positive 13c excursions they correspond to the oceanic anoxic events oae in the early aptian oae 1a selli level early albian oae 1b late albian oae 1d and latest cenomanian oae 2 bonarelli level detailed investigations of the two most significant events the selli and the bonarelli level in the umbria marche basin of central italy show that extinctions coincide with the first occurrence of marine black shales type ii kerogen and the most prominent rise of 13corg values stepwise extinctions and continuous radiations precede and follow the events similar patterns are evident for the oae 1b and 1d black shales dominated by terrestrial organic matter type iii kerogen e g oae 1c are not characterized by isotopic excursions or by radiolarian extinction radiation events contemporaneous drowning events documented from carbonate platforms around the investigated basins provide a link to a model where flooding of lowlands and leaching of nutrients during a relative rise of sea level lead to an increased productivity and an expansion of the oxygen minimum zone omz because of the loss of deep habitats deeper dwelling forms become extinct shallower dwelling radiolarians survive a narrowing of the omz during highstands and relative sea level falls together with a coupled decrease of the nutrient supply leads to the development of new niches and therefore to radiation

radiolarian assemblage distributions and paleoceanography of the eastern equatorial pacific ocean during the last 127 000 years abstract mathematical treatment q mode factor analysis of radiolarian species abundance data in equatorial pacific core tops yields four oceanographically meaningful assemblages the distribution of these assemblages in surface sediments can be related to the major surface and subsurface characteristics of the equatorial circulation system western tropical mixed layer flow coastal upwelling and the oxygen minimum layer eastern equatorial divergence upwelling and the equatorial undercurrent and the subtropical water masses of both hemispheres changes in the distribution of radiolarian assemblages during the glacial interglacial cycle spanning the last 127 000 yr are observed in two equatorial pacific piston cores these changes reflect fluctuations in the boundaries of equatorial water masses in response to variations in the position and strength of the tradewind system and tend to precede major glacial interglacial transitions by several thousand years a history of atmospheric circulation in the equatorial pacific has been developed for the last 127 000 yr fluctuations in tradewind intensity north south shifts in the latitudinal position of the tradewind maxima and perhaps a change in the zonality of the tradewinds during the last 127 000 yr have been inferred from downcore quartz abundance and radiolarian assemblage distribution patterns oxygen isotopic fluctuations during the last 127 000 yr indicate that continental ice volume was much greater during glacial stage 2 29 000 b p to 11 000 b p than during glacial stage 4 73 000 b p to 61 000 b p large changes in atmospheric and oceanic circulation patterns also are indicated by the distribution of radiolarian assemblages during the two glacial periods during stage 2 oceanic circulation was more intense the southeast tradewind maximum was closer to the equator and wind stress was more meridional than during stage 4

broad region of no sediment in the southwest pacific basin a broad region nearly the size of the mediterranean sea exists in the central south pacific ocean that is devoid of sediment and has been so since the late cretaceous the requirements for remaining sediment free are very low biological productivity a shallow calcite compensation depth essentially no dust input and no deposition of hydrothermal oxides and hydroxides one or two of these conditions are common but nowhere else do all four occur the combined effect of these sediment inhibiting factors is a consequence of crustal age seawater chemistry and atmospheric oceanographic and physiographic isolation furthermore this unique combination of conditions has prevailed for more than 80 million years

the paradox of drowned carbonate platforms and the origin of cretaceous pacific guyots geochemical stratigraphic and palaeolatitudinal data from deep boreholes drilled through pacific guyots flat topped seamounts help to explain the drowning of these cretaceous shallow water carbonate platforms that once thrived through the accumulation of biogenic and inorganic calcium carbonate sediment in mid oceanic regions the platforms drowned sequentially over a 60 million year interval while they were being transported northward by pacific plate motion through a narrow equatorial zone 0 10 s such platforms were apparently resistant to the effects of cretaceous oceanic anoxic events although the mechanism responsible for drowning remains unknown the tropics have not always been the refuge for atolls that they are today

influences of high and low latitude processes on african terrestrial climate pleistocene eolian records from equatorial atlantic ocean drilling program site 663 high and low latitude forcing of terrestrial african paleoclimate variability is demonstrated using 900 ka eolian and biogenic component records from ocean drilling program site 663 in the eastern equatorial atlantic terrigenous eolian dust and phytolith savannah grass cuticle accumulation rate records vary predominantly at 100 and 41 kyr periodicities and spectral phase estimates implicate high latitude forcing the abundance of freshwater diatoms melosira transported from dry african lake beds varies coherently at 23 19 kyr orbital periodicities and at a phasing which implicates low latitude precessional monsoon forcing modeling studies demonstrate that african climate is sensitive to both high and low latitude boundary conditions african monsoon intensity is modulated by direct insolation variations due to orbital precession whereas remote high latitude forcing can be related to cool north atlantic sea surface temperatures ssts which promote african aridity and enhance dust transporting wind speeds the site 663 terrigenous and phytolith records covary with north atlantic sst variability at 41 n site 607 we suggest that pleistocene african climate has responded to both high latitude north atlantic sst variability as well as low latitude precessional monsoon forcing the high latitude influence dominates the sedimentary record prior to circa 2 4 ma terrigenous variations occurred primarily at precessional periodicities 23 19 kyr indicating that african climate was largely controlled by low latitude insolation variations prior to the onset of high amplitude glacial interglacial climate change

a correction for sediment load upon the ocean floor uniform versus varying sediment density estimations implications for isostatic correction abstract the isostatic correction for the sediment load on oceanic basement has often been calculated using a uniform sediment density irrespective of either water depth or total sediment thickness an alternative method is proposed here in which the sediment density is calculated using the density depth equations of hamilton 1976 for calcareous clay and terrigenous sediment sequences this alternative method takes into account the water depth and total sediment thickness when estimating the sediment density for example deep water 4000 m sediment sequences are likely to be clay rich thick sediment sequences 2000 m usually have a high terrigenous component and shallow sequences are likely to be calcareous rich sediment thicknesses in excess of 1500 m are generally close to a continental margin these density estimations are compared with measurements from 9 ocean drilling program drill sites 1 deep sea drilling project drill site and from densities derived from seismic interval velocities the most commonly used estimates of uniform sediment density were used to calculate isostatic corrections for a 12 km thick sediment sequence these results were then compared with the results determined using the proposed alternative method of estimating sediment densities the proposed method produces isostatic corrections similar to those derived by published methods for sediment sequences

critical stress localization of flow associated with deformation of well fractured rock masses with implications for mineral deposits fluid flow and deformation of fractured rock masses is investigated using numerical models based on distinct element methods udec which couple mechanical and hydraulic behaviour a series of numerical experiments is presented in which diffuse flow through fracture networks changes to highly localized flow at a critical stress state slip on parts of the fracture network causes the opening up of some fractures often at fracture intersections thus a change in the stress state results in a sudden localization of deformation and fluid flow a series of plots of hydraulic conductivity v differential stress are presented for some natural fracture networks to demonstrate the influence of fracture network geometry and in situ stress on the critical phase boundary between diffuse and localized flow the onset of localized deformation and fluid flow is a critical point phenomenon resulting in fractal properties fractal and multifractal techniques are used to characterize heterogeneity of the flow in order to generalize the results of the modelling of discrete systems to a continuum based description of the flow the significance of the models and their implications for crustal behaviour are discussed in relation to hydrothermal mineralization and natural vein systems

pliocene pleistocene evolution of eastern tropical pacific surface water circulation and thermocline depth we evaluated the response of eastern equatorial pacific upper water column hydrography to the panama seaway closure and the initiation of large scale northern hemisphere glaciation the 18o gradient between globorotalia tumida and globigerinoides sacculifer indicates a general shoaling of the thermocline between 4 2 and 3 0 ma which may be related to a recorded decrease in southeast trade wind strength the 13c gradients suggest that surface water nutrient concentrations have increased during the last 5 myr and that upwelling intermediate waters began to change sources at 3 2 ma changes in the trans pacific east west temperature and nutrient gradients at 4 0 and 1 5 ma are coincident with the seaway closure and a major phase of northern hemisphere glaciation changes in the sensitivity of surface circulation to milankovitch forcing 18o records linearly related to orbital variations only after 3 2 ma are associated with the seaway closure pleistocene initiation of 100 and 41 kyr cycles in the thermocline depth proxy may suggest that the hydrographic response to milankovitch forcing is enhanced by air sea interactions which maintain the relatively steep pleistocene trans pacific gradients the 13c records are dominated by the 41 kyr period and are usually coherent with high latitude climate suggesting that associated changes in the global carbon reservoir dominate the tropical 13c signals

seasonal trends and preservation biases of polycystine radiolaria in the northern california current system we analyzed a 2 year sediment trap record of 76 species of radiolaria from three locations across the northern california current system q mode factor analysis identifies the fundamental trends in the radiolarian data with a five factor model that explains 86 of the trap data the factor assemblages that emerge from this analysis have temporal and spatial aspects that reflect fundamental oceanographic features of the eastern north pacific the most dominant process revealed by this analysis is related to the seasonality of the california current two factors illustrate this the california current factor which has highest loadings during summer and fall and the winter factor which is most important in the winter and spring together they account for 75 of the information in the trap samples from the two moorings located in the coastal region extending to 300 km offshore the oceanic environment sampled by the mooring 650 km offshore is strongly influenced by transitional waters and those from the central and subarctic gyres loadings of the three factors related to these oceanographic regions show marked differences between years which illustrates the latitudinal variability in the divergence of the north pacific current spatial distributions of the trap factors in surface sediments beneath the california current system generally agree with the temporal and spatial patterns they exhibit in the traps nonetheless the trap factor model can only describe up to 50 of the radiolarian sediment data which means the species ratios in the sediment traps are significantly different than those in the sediments a factor model using only robust species reveals the same basic trends as the first analysis but the culled model is able to describe a larger fraction of the sediment data 63 91 in sediments directly beneath the mooring sites however the increase in the amount of sediment data explained by the culled model is not distributed equally across all factors but is due to very high estimates of one factor in the coastal sediments the california current factor at the nearshore mooring site 130 km offshore this factor explains 69 of the sediment data versus only 32 of the data in the traps where it was derived this discrepancy suggests that either these two years of trap data are anomalous and have underestimated the predominance of the california current assemblage over long time periods or the culled factor model rather than eliminating the dissolution bias actually overemphasizes the importance of well preserved species in the coastal environment

variation in the form and distribution of dykes in the mull swarm scotland the dykes of the mull swarm part of the british tertiary igneous province have been examined in a series of well exposed coastal sections traverses through the dyke swarm show systematic changes in the thickness and spacing of dykes both of which are typically log normally distributed both the geometric mean thickness and spacing of dykes increase with distance from the mull centre concordant with a decrease in crustal extension variations in the thickness and spacing result from changes in character of the magma flow it is inferred that the magma flux was fairly evenly distributed near the mull centre but farther away from the source it becomes focused into larger dykes the form orientation and opening direction are also observed to vary with distance away from the volcanic centre on mull the dykes intrude a range of pre existing fractures the range of fractures used decreases with distance from the centre this together with other features of the form of the dykes have been interpreted in terms of the varying magma pressure and regional stress which is expressed as the r ratio analysis of the variable strikes of fracture filled dykes is consistent with decreasing magma pressure with distance from the mull centre assuming that regional stresses were relatively invariant across the same distance

tectonic evolution of the northern pacific plate and pacific farallon izanagi triple junction in the late jurassic and early cretaceous m21 m10 abstract magnetic lineations in the northwestern pacific near the shatsky plateau were interpreted to trace the tectonic history of the northern pacific plate from the time of anomalies m21 to m10 at m22 time the pacific farallon izanagi p f i triple junction was located southwest of the plateau and migrating north northwest with respect to the pacific plate shortly thereafter the stress field acting on the three plates changed significantly and the pacific lzanagi ridge reacted by pivoting 24 clockwise from m21 to m19 time several ridge propagation events occurred while the ridge adjusted to the new spreading regime to the east of the m22 location of the junction it appears that this reorganization triggered a series of at least three ridge jumps along the pacific farallon ridge the geometry of magnetic isochron m21 suggests that several triple junctions existed simultaneously during the reorganization bordering one or more microplates differences in the spreading rate of the japanese magnetic lineations north of the plateau imply that one microplate which we call the shatsky microplate existed until about m15 m13 time it was probably captured by either the farallon or the izanagi plate and subsequently destroyed by subduction after m15 the p f i triple junction was reformed on seafloor that is now beneath the shatsky plateau the junction drifted generally northeast either in a ridge ridge ridge or in a ridge fault fault configuration perhaps alternating between the two from m11 m10 time the stress field on the three plates changed again and the pacific farallon ridge southeast of the plateau reoriented 15 clockwise at this time the p f i junction assumed a ridge ridge ridge geometry at the northeast end of the plateau

the impact of calcareous nannofossils on the pelagic carbonate accumulation across the jurassic cretaceous boundary abstract calcareous nannofossils were important producers of pelagic carbonates in mesozoic oceans in order to better understand the origin of mesozoic pelagic carbonates we studied upper jurassic to lower cretaceous sediments in the central atlantic ocean dsdp sites 105 367 534a with respect to their content of calcareous nannofossils the interval under investigation is characterized by a significant increase in the deposition of carbonate rich sediments a trend that goes along with the rapid radiation of calcareous nannofossils the assemblage composition and the size variation of common taxa were analyzed and subsequently the contribution of this phytoplankton group to the pelagic carbonate accumulation was calculated results reveal two long term changes of the nannofossil assemblage composition 1 the early tithonian coccolith assemblages are of low diversity watznaueria spp cyclagelosphaera spp zeugrhabdotus spp whilst the mid to late tithonian assemblage is dominated by nannoliths conusphaera mexicana polycostella beckmannii nannoconus spp and large sized watznaueria 2 the early berriasian is characterized by a shift from the late tithonian nannolith rich assemblage to a highly diverse coccolith assemblage morphometric studies of the placolith genus watznaueria show for all three dsdp sites large sized forms of this genus in the mid and late tithonian followed by a decrease of up to 2 m for the mean size in the earliest berriasian at dsdp site 105 the studied nannolith taxa show an increase in size during the mid tithonian to berriasian interval the records of both nannofossil carbonate estimates and the measured bulk rock carbonate reveal two periods of increase in the nannofossil carbonate record of dsdp site 105 a first significant increase of the carbonate accumulation is observed in the mid and late tithonian probably caused by mass occurrences of strongly calcified taxa c mexicana p beckmannii nannoconus spp watznaueria cf manivitae this interval is here named nannofossil calcification event nce the second carbonate maximum in the late berriasian is related to a rise in absolute abundances of nannofossils this peak is amplified by an overall increase of the sedimentation rate the calculated accumulation rates of nannofossils nannofossil carbonate and bulk rock carbonate for the late berriasian are on the same scale as values from recent ocean surface sediments a comparison of nannofossil carbonate values with the bulk rock carbonate content shows that on average only 27 of the total carbonate can be explained by our nannofossil carbonate estimates this discrepancy is most likely caused by the high amount of unidentifiable micrite and fragments of calcareous nannofossils other factors contributing to the error are possible inaccuracies in the determination of absolute abundances and nannofossil volume calculations the nce occurs during a long term sea level fall dry climate and presumed low pco 2 levels a decline in abundance of strongly calcified nannofossils coincides with the opening of the pacific atlantic seaway via central america which may have had a substantial impact on the palaeoceanographic situation in the central atlantic ocean these changes are here considered to have at least partly caused the shifts in abundance size and assemblage composition of calcareous nannofossils observed across the jurassic cretaceous boundary interval

equatorial pacific sea surface temperatures faunal patterns and carbonate burial during the pliocene abstract a high resolution record of radiolarian faunal abundances from the eastern equatorial pacific is compared to records of carbonate and noncarbonate burial to examine the evolution of eastern tropical pacific climate processes during the pliocene these data provide a means to evaluate the sensitivity of the equatorial pacific to the onset of northern hemisphere glaciation around 2 8 2 5 ma to the closure of the isthmus of panama around 4 4 3 2 ma and to orogeny related weathering changes before 4 0 ma radiolarian faunal assemblages and sea surface temperature sst estimates indicate a gradual cooling from early to late pliocene but no significant changes occur near the onset of northern hemisphere glaciation records of carbonate and noncarbonate mass accumulation show a long term decrease from the miocene pliocene boundary to the upper pliocene greater carbonate burial in the early pliocene relative to the late pliocene parallels a gradual cooling from early to late pliocene and may reflect changes related to isthmus closure or widespread orogeny no significant time domain changes are seen in the eastern equatorial pacific that could be related to the onset of northern hemisphere glaciation evolutive spectral analyses of these equatorial pacific climate parameters indicate that variance in sst and seasonality commonly concentrate at frequencies not linearly related to orbital variations furthermore cross spectral comparisons with a high resolution benthic 18 o record indicate that the surface ocean and carbonate flux share little coherent variance with high latitude climate processes during the pliocene given the high degree of chronostratigraphic control in these records these results suggest that milankovitch band surface ocean processes as well as carbonate burial in the equatorial pacific are decoupled from high latitude climate processes during the pliocene

covariance patterns of foraminiferal dgr18o an evaluation of pliocene ice volume changes near 3 2 million years ago oxygen isotope data for a pliocene interval from 3 6 to 2 8 million years ago show a mean increase 0 5 per mil of benthic delta 18 o at about 3 2 million years ago whereas planktic delta 18 o does not increase this lack of covariance indicates that the event at 3 2 million years did not result in a permanent increase in the ice budget of either the northern or the southern hemisphere

equatorial pacific calcite preservation cycles production or dissolution in the equatorial pacific ocean the depth and shape of the calcite lysocline appears to have changed significantly in response to climate forcing farrell and prell 1989 taking the farrell and prell record at face value the lysocline apparently became steeper during each of the last eight glacial stages also the accumulation rate of calcite during the last glacial maximum was 2 4 times higher than it was during the previous interglacial arrhenius 1952 1988 broecker 1971 farrell 1991 a numerical model for calcite dissolution in sediment is used to interpret these observations the model was validated by comparison with observations from the present day ocean these results are presented elsewhere if the lysocline fluctuations in the equatorial pacific are primarily a dissolution record then changes in the glacial pacific co3 of 20 40 m can be inferred here i offer the alternative explanation that cycles in equatorial production are responsible for the observations higher rates of calcite and organic carbon rain to the sediment in the equatorial region would have depressed the calcite lysocline and increased the calcite accumulation rate as observed a twofold increase in glacial production appears to be adequate to explain the observations but a precise determination is prevented by uncertainties in some of the model parameters

predicting sediment thickness on vanished ocean crust since 200 ma tracing sedimentation through time on existing and vanished seafloor is imperative for constraining long term eustasy and for calculating volumes of subducted deep sea sediments that contribute to global geochemical cycles we present regression algorithms that incorporate the age of the ocean crust and the mean distance to the nearest passive margin to predict sediment thicknesses and long term decompacted sedimentation rates since 200 ma the mean sediment thickness decreases from 220 m at 200 ma to a minimum of 140 m at 130 ma reflecting the replacement of old panthalassic ocean floor with young sediment poor mid ocean ridges followed by an increase to 365 m at present day this increase reflects the accumulation of sediments on ageing abyssal plains proximal to passive margins coupled with a decrease in the mean distance of any parcel of ocean crust to the nearest passive margin by over 700 km and a doubling of the total passive margin length at present day mean long term sedimentation rates increase from 0 5 cm ky at 160 ma to over 0 8 cm ky today caused by enhanced terrigenous sediment influx along lengthened passive margins superimposed by the onset of ocean wide carbonate sedimentation our predictive algorithms coupled to a plate tectonic model provide a framework for constraining the seafloor sediment driven eustatic sea level component which has grown from 80 to 210 m since 120 ma this implies a long term sea level rise component of 130 m partly counteracting the contemporaneous increase in ocean basin depth due to progressive crustal ageing

isotopic paleoceanography of the caribbean and east pacific role of panama uplift in late neogene time comparisons of carbon isotopic data on benthic foraminifera from deep sea drilling project sites 502 western caribbean and 503 eastern pacific indicate that the difference between the atlantic and the pacific in the per mil enrichment in carbon 13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago when the difference reached the modern level 1 per mil comparisons of planktonic foraminiferal oxygen isotopic data for the caribbean and the pacific suggest that the salinity of caribbean surface waters began increasing 4 million years ago possibly in response to shoaling of the panama isthmus these results suggest that modern circulation patterns in the caribbean and eastern pacific developed by 3 million years ago in concert with changing tectonic climatic and biogeographic patterns

structural controls of fracture orientations intensity and connectivity teton anticline sawtooth range montana the teton anticline is a multiple hinge anticline containing fractured mississippian devonian carbonates in the frontal part of the sawtooth range in montana the structure serves as a good surface analog for fracture patterns and connectivities within subsurface folded carbonate reservoirs the primary fracture sets are longitudinal and transverse relative to the axis of the fold although two additional oblique sets are also present the length and density of the longitudinal fracture sets are strongly controlled by position relative to multiple hinges the transverse fractures are related to changes in fold plunge and exhibit less variation in fracture density fracture connectivity is dependent on the number of fracture sets their orientations and dispersions and the densities of the fracture sets the connectivity is measured using two parameters the fractional connected area fca which represents the fraction of the total sample area that is connected by fractures and the distribution of clusters of different sizes in any given area because the longitudinal fractures represent the dominant fracture set and also show the most variation with structural position the fracture connectivity as measured by both the fcas and the distribution of cluster sizes is greater in the vicinity of the fold hinges the results and approaches used in the study have some important implications for subsurface folded fractured carbonate reservoirs the analysis of sparsely distributed fracture data from wells must be integrated with an understanding of the controls of the macroscopic structure on fracture parameters to effectively simulate fracture patterns and connectivities around subsurface structures

radiolarian and silicoflagellate response to oceanographic changes associated with the 1983 el nino strong seasonal signals in fluxes and composition of siliceous microfossils have been recorded in sediment traps from two sites in the equatorial pacific deployed from december 1982 to march 1984 during the early part of the sampling period the 1982 83 el nino event had a profound effect on the radiolaria and silico flagellates within these two areas during the el nino the radio larian trap assemblages at site c 1 n 139 w most resembled faunal assemblages in western equatorial pacific sediments whereas the trap assemblages resembled equatorial divergence sediments in the latter half of the period at site s 11 n 140 w the radiolaria and silicoflagellate species can be correlated with organic carbon fluxes in general silicoflagellate shell fluxes are correlated to total opal fluxes where radiolarian fluxes do not exhibit this relationship approximately 20 25 of the total count of radiolaria in traps are not present in underlying sediments with a significant loss of the weakly silicified forms however the comparison of trap sample assemblages with underlying sediments reported here shows that dissolution does not alter relative abundances of the fossil species used in palaeoclimatic reconstructions a significant difference is observed between the silicoflagellate trap assemblage and the underlying sediment assemblage

late miocene onset of the amazon river and the amazon deep sea fan evidence from the foz do amazonas basin new biostratigraphic isotopic and well log data from exploration wells on the outer continental shelf and uppermost amazon deep sea fan brazil reveal that the amazon river was initiated as a transcontinental river between 11 8 and 11 3 ma ago middle to late miocene and reached its present shape and size during the late pliocene prior to the late miocene the continental shelf was a carbonate platform that received moderate siliciclastic sediment supply from the proterozoic basement in eastern amazonia average sedimentation rates on the amazon fan show three stages of development 1 11 8 6 8 ma ago low sedimentation rates 0 05 m ka prevailed on the fan because the amazon river was not yet entrenched and some sediments were partially trapped in continental basins 2 6 8 2 4 ma ago sedimentation rates 0 3 m ka increased the river entrenched and deposition fully migrated onto the amazon fan 3 2 4 ma ago to the present very high sedimentation rates 1 22 m ka with peaks of 11 m ka prevailed on the fan and the modern amazon river developed all these paleogeographic and depositional events are closely related to andean tectonism late miocene pliocene and were exacerbated by global cooling and sea level fall during the late miocene

radiolarian assemblages in surface sediments along longitude 175 e in the pacific ocean abstract this study of 24 surface sediment samples along longitude 175 e between latitudes 48 n and 14 s in the western pacific ocean documents the relationship between the modern distribution of radiolarian assemblages and present oceanographic conditions ninety two species were classified into eight clusters by using r mode cluster analysis q mode cluster analysis was used to distinguish five geographical zones which were interpreted to represent the tropical southern subtropical northern subtropical transitional and subarctic climatic zones species richness diversity and equitability are highest in the tropical and transitional zones we attempted to formulate new regression equations considering ecological information on the vertical distribution of radiolarian species transfer functions were derived from regression analysis of radiolarian assemblages to observed sea surface temperature sst values the transfer functions have a standard error of 1 16 c in the estimate of winter sst 0 81 c in that of summer sst

planktogenic eustatic control on cratonic oceanic carbonate accumulation data on mass age distributions and latitudinal limits of mesozoic cenozoic shelf carbonate on cenozoic deepening of the ccd in all major ocean basins and on the abundance of pelagic chalk in epicontinental carbonate sequences indicate that the primary locus of global limestone deposition has gradually shifted from shallow cratonic to deep oceanic settings since jurassic time this change is generally coincident with progressive emergence of continents during global regression as well as with taxonomic diversification of calcareous plankton and implicates one or both processes as the primary control on carbonate sediment partitioning between shallow and deep marine reservoirs widespread pelagic carbonate does not occur with phanerozoic ophiolite sequences until the late mesozoic and generally corresponds to origins of planktonic foraminifera and diversification of coccolithophorids similarly cratonic chalk is largely re stricted to cretaceous sections correlation of mesozoic cenozoic positions of t

controls on biogenic silica burial in the southern ocean understanding the controls on opal export in the southern ocean can inform both the prediction of how the leakage of silicic acid from the southern ocean responds to climate and the interpretation of paleo proxies we have compiled a database of 185 230thorium normalized opal burial rates and 493 opal concentration measurements in southern ocean sediments and matched these with environmental climatologies by subdividing the southern ocean on the basis of oceanographic regions and interpolating the opal burial rates we estimate a total biogenic si burial south of 40 s of 2 3 1 0 tmol si yr 1 in both the seasonally ice covered and permanently ice free regions we can explain 73 of opal burial variability from surface ocean properties where sea ice is present for at least part of the year the length of the ice free season determines the upper limit of opal burial in the underlying sediments in the ice free regions of the southern ocean the supply of silicic acid through winter mixing is the most important factor our results do not support a strong role of iron in controlling opal burial we do however find that satellite derived net primary production increases with increasing modeled dust delivery these findings support the decoupling between carbon and opal fluxes in the southern ocean when corrected for opal dissolution the observed opal fluxes are in reasonable agreement with fluxes simulated using an ocean biogeochemical model however the results suggest current preservation algorithms for opal could be improved by incorporating the composition of particle flux not only its magnitude

basement exploration west of shetlands progress in opening a new play on the ukcs abstract commercial production of hydrocarbon from fractured crystalline basement is well documented with petroleum basins across the globe hosting fractured basement fields the uk is an anomaly within this global phenomenon as despite numerous serendipitous discoveries of basement oil in the north sea and the west of shetlands there is currently no commercial field on the united kingdom continental shelf ukcs that is reliant on oil production from fractured basement recognizing that this situation presented an exploration niche hurricane energy plc hurricane was formed to focus on ukcs basement exploration and concentrated its efforts in acquiring exploration acreage in the west of shetlands in 2009 hurricane drilled the first well designed to explore the basement play on the ukcs leading to the lancaster discovery with a contingent resource range 1c 3c of 62 456 million barrels of oil equivalent mmboe the lancaster discovery is presented to summarize the challenges and processes that have been applied in the exploration and evaluation of the west of shetlands basement play conclusions from this work indicate that basement hydrocarbon resource potential is of such significance that it may represent a strategic resource for the uk with over 1154 mmboe of 2c and mean unrisked prospective resources so far identified

long climatic time series from sediment physical property measurements abstract with an accurate understanding of the lithologic dependence of pre compaction porosity in pelagic sediments it should be possible to calculate mass accumulation rate histories of sedimentary phases to generate proxy carbonate logs from core density scans and from seismic profiles and to reconstruct the mechanical and chemical processes that occur during burial and lithification we demonstrate that routinely made continuous gamma ray attenuation porosity evaluator grape wet bulk density measurements of sediments show a positive relationship to carbonate content in a variety of pelagic environments mineralogically related differences in packing rather than differences in grain density appear to control wet bulk density variations a hyperbolic model calibrated at dsdp odp drill ites quantifies the relationship of density to carbonate content in different pelagic environments the curvilinear relationships appear to converge to a similar wet bulk density 1 71 0 07 g cm3 porosity 58 at 100 carbonate content but they exhibit differing porosity at zero carbonate content wet bulk densities for a given carbonate content depend on the non carbonate mineralogy and grain size and increase systematically from opal to clay to quartz lithic fragment dominated settings because contrasts in sediment wet bulk density control the seismic response of unlithified sediments it should be possible to generate carbonate profiles remotely in carbonate rich settings after core calibration of the seismic system our model can generate long proxy carbonate curves with a typical sample spacing of 0 6 1 cm from existing grape data bases in equatorial pacific equatorial atlantic and northern atlantic locations over the past 6 m y these time series are used to investigate the long term evolution of climate in the milankovitch frequency band as well as to reconstruct patterns of carbonate sedimentation over time sedimentation bears the imprint of milankovitch cyclicity superimposed on long term trends the switch in carbonate sedimentation from 41 kyr periodicity during the matuyama chron to dominant 100 kyr periodicity in brunhes chron previously described in the north atlantic occurs in equatorial atlantic and pacific locations as well the lithological dependency of porosity in uncompacted pelagic sediments also has important implications for understanding later compaction and diagenetic modification of pelagic sediments in particular the grape observations suggest that differential burrow flattening observed in lithified limestone marl alternations results from mechanical and pressure solution compaction of strata that had strong primary porosity differences rather than from diagenetic unmixing of carbonate

paleoceanography and the diachrony of radiolarian events in the eastern equatorial pacific the development of an orbitally tuned time scale for the odp leg 138 sites provides biostratigraphers a very high resolution chronostratigraphic framework with this framework we are better able to define which of the first and last appearances of species appear to be synchronous in addition the geographic distribution of sites provides the means with which the detailed spatial patterns of invasion of new species and the extinction of older species can be mapped these maps not only provide information on the process of evolution migration and extinction they can also be related to water mass distributions and near surface circulation of the ocean of 39 radiolarian events studied at 11 sites in the eastern equatorial pacific 28 were found to have a minimum range in their estimated age that exceeded 0 15 m y the temporal pattern of first and last appearances of these diachronous events have coherent spatial patterns that indicate shifts in the areas of high oceanographic gradients over the past 10 ma these changes in the locations of high gradient regions suggest that the south equatorial current sec was north of its present position prior to approximately 7 ma there was a southward shift in the northern boundary of this current between approximately 6 and 7 ma and the development of a relatively strong gradient between the northeastern and northwestern sites between approximately 3 7 and 3 4 ma there was a very slight northward shift in the northern boundary of the sec and the steep gradients between the northeastern and northwestern sites may have disappeared this change is thought to be associated with the closing of the isthmus of panama the temporal spatial patterns of diachronous events younger than 3 4 ma are consistent with patterns of circulation in the modern ocean

the influence of caco3 dissolution on core top radiocarbon ages for deep sea sediments radiocarbon ages on caco3 from deep sea cores offer constraints on the nature of the caco3 dissolution process the idea is that the toll taken by dissolution on grains within the core top bioturbation zone should be in proportion to their time of residence in this zone if so dissolution would shift the mass distribution in favor of younger grains thereby reducing the mean radiocarbon age for the grain ensemble we have searched in vain for evidence supporting the existence of such an age reduction instead we find that for water depths of more than 4 km in the tropical pacific the radiocarbon age increases with the extent of dissolution we can find no satisfactory steady state explanation and are forced to conclude that this increase must be the result of chemical erosion the idea is that during the holocene the rate of dissolution of caco3 has exceeded the rain rate of caco3 in this circumstance bioturbation exhumes caco3 from the underlying glacial sediment and mixes it with caco3 raining from the sea surface

appraisal of fracture sampling methods and a new workflow to characterise heterogeneous fracture networks at outcrop abstract characterising fractures at outcrop for use as analogues to fractured reservoirs can use several methods four important fracture data collection methods are linear scanline sampling areal sampling window sampling and circular scanline sampling in regions of homogeneous fracture networks these methods are adequate to characterise fracture patterns for use as outcrop analogues however where fractures are heterogeneous it is more difficult to characterise fracture networks and a different approach is needed we develop a workflow for fracture data collection in a region of heterogeneous fractures in a fold and thrust belt which we believe has applicability to a wide variety of fracture networks in different tectonic settings we use an augmented circular scanline method along with areal sampling to collect a range of fracture attribute data including orientation length aperture spatial distribution and intensity this augmented circular scanline method more than halves the time taken for data collection provides accurate unbiased data that is representative of local fracture network attributes and involves data collection of a wider range of fracture attributes than other sampling techniques alone

sedimentation controls on methane hydrate dynamics across glacial interglacial stages an example from international ocean discovery program site u1517 hikurangi margin