earth s magnetic field in the early 19th century from french sources 1 we present both a description of a new magnetic data set covering predominantly the 18th and 19th centuries and the results derived from it for the small window 1820 1850 from which the bulk of the data originate the data set comprises measurements of declination taken overwhelmingly on french naval and hydrographic vessels a list of the vessels is given for one of the data sets when augmented by extant inclination measurements the data are capable of resolving the magnetic field at the core mantle boundary to a high degree of fidelity and thus are a valuable addition to the data set of historical geomagnetic measurements

climate fluctuations of the weddell sea and its surroundings in a transient climate change scenario the response of the weddell sea and antarctic peninsula to anthropogenic forcing simulated by a global climate model is analyzed the model despite its low resolution is able to capture several aspects of the observed regional pattern of climate change a strong warming and depletion of the sea ice cover in the western weddell sea contrasts with a slight cooling and a sea ice extension in the eastern weddell sea this simulated long term climate change is modulated by interdecadal variability but also affected by some abrupt regional changes in the oceanic mixed layer depth between 1960 and 2030 a reorganization of the deep convection activity in the weddell sea sustains the opposition between the eastern and western weddell sea the deep convection collapses in the western weddell sea in the 2030s the sea ice retreat trend is then followed by an increase of the sea ice cover in the western weddell sea in the eastern weddell sea another abrupt collapse of the deep convection activity occurs around 2080 this event is followed by a rapid cooling and sea ice extension during the next 20 years most of the surface changes are associated with large scale atmospheric circulation changes that project on the dominant mode of natural variability but also with oceanic convection and circulation changes

field scale reservoir zonation of the albian turonian sarvak formation within the regional scale geologic framework a case from the dezful embayment sw iran abstract the albian turonian sarvak formation is the second most important reservoir of iran in this study an integrated field scale reservoir zonation is applied to the sarvak reservoir in one oil field of the dezful embayment sw iran to understand the distribution of speed barrier and baffle zones the geologic controls of depositional and post depositional factors on the suggested reservoir zonation are also discussed here based on the results the studied reservoir is composed of seven zones with different reservoir qualities the best reservoir zones show considerable amount of dissolution pores and are developed beneath regional scale paleo exposure surfaces that are also recognizable in coeval strata on the arabian plate these surfaces represent recurring subaerial exposure episodes during the development of the sarvak formation through which meteoric diagenesis highly affected the rock record leading to the development of paleo karst profiles with noticeable dissolution pores in the strata beneath the paleo exposure surfaces however the long lasting emergence time of the mid turonian exposure mt es the interface between the sarvak formation and overlying ilam formation caused the over maturation of the related paleo karst profile and the deterioration of the created reservoir quality the results of this study reveal the effects of regional scale geologic controls on the reservoir characteristics of the sarvak formation and may be also applicable to the reservoir characterization of other time equivalent strata in the arabian plate

depositional environment reservoir units evolution and hydrocarbon habitat of shuaiba formation lower cretaceous abu dhabi united arab emirates the shuaiba formation aptian is a thick porous shelf carbonate present in the subsurface over much of the arabian gulf it is the uppermost formation of the thamama group lower cretaceous and is overlain by the nahr umr formation albian and overlies the kharaib formation barremian the formation is divided into nine reservoir units a to i from the base upward reservoir units a b and c represent calcareous algal platform sediments showing some open marine influence they are dominated by chalky lime mudstones to wackestones with abundant codiacian green algae bacinella irregularis and lithocodium aggregatum and stylolite seams reservoir units d and f are deeper open marine shelf facies dominated by dense argillaceous lime mudstones to wackestones whic are burrowed and bioturbated reservoir units g and i represent lagoonal facies dominated by dense argillaceous wackestones to packstones which are sparsely fossiliferous and commonly stylolitic reservoir unit h represents a shallow water coarser grained shelf limestone containing abundant rudists algae orbitolinids and other foraminifers reservoir unit ho represents a shoal facies characterized by wackestone to packstone sediment with abundant orbitolina and scattered rudist debris and other foraminifers in northeast and southeast dhabi the basinal shuaiba equivalent bab member was deposited under slightly deeper quieter marine conditions and is dominated in parts of the section by dense argillaceous lime mudstones and shaly wackestone and calcareous shale i tervals the major reefal shuaiba buildup in abu dhabi trends northwest southeast it is in this trend that the major oil fields shah bu hasa and zurarah shaybah were discovered and from which some wells produce in western abu dhabi e g ruwais 2 hydrocarbons also occur outside of the rudist trend in the shuaiba formation in the asab jarn yaphour and sahil onshore oil fields and the zakum and mandous offshore oil fields local reefal anomalies are also encountered in parts of the deep marine basin of eastern abu dhabi these are formed by an unusual pre reefal growth of orbitolinids rudists and algae an isolated buildup patch reef consisting of coralgal boundstones encountered in jarn yaphour and zabbara fields may represent organic growth over either a rising salt structure or an uplifted zone formed by deep seated faults geochemical studies reveal that the main source for the thamama oils are the upper jurassic dukhan formation onshore abu dhabi or diyab formation offshore abu dhabi however some shuaiba source rocks may have existed in intrashelf basinal areas in the upper thamama zone the nahr umr shale acts as a seal for the shuaiba reservoir in this area

secular variation in north america during historical times summary the secular variation of the declination inclination and total force of the geomagnetic field has been plotted for 74 locations in north america a comparison of the occurrences of maxima and minima in the sv clirves from different stations shows little evidence of drift in north america although a declination maximum exhibits westward drift up to 1915 all other extrema in declination inclination and total intensity occur almost simultaneously over a wide area the major feature of sv in north america appears to be a 4000 nt decrease in the total field since 1850 which may be due to a decrease in the dipole moment coupled with the decay of a large non dipole anomaly situated under the continent short period changes in the rate of decrease are possibly jerks of the magnetic field maximum entropy spectral analysis of all three components of the field indicates periods of 102 and 53 yr

early cretaceous platform margin configuration and evolution in the central oman mountains arabian peninsula the hajar supergroup middle permian lower cretaceous of northeastern oman records rifting and development of a passive margin along the edge of the arabian platform facing neo tethys the jurassic and lower cretaceous part comprising the sahtan kahmah and wasia groups was deposited during the maximum extent of the broad epicontinental sea landward of this margin these limestone units reach a total of 1500 m in thickness and they correlate with the principal hydrocarbon reservoirs of the arabian peninsula the trace of the jurassic and cretaceous margin in northeastern oman followed a zigzag series of rift segments resulting in promontories and reentrants that changed in position through time in response to the configuration and differential motion of underlying rift blocks in an overall extensional regime synsedimentary normal faulting with 600 m of throw occurred locally during the middle jurassic whereas during the late jurassic the margin was subjected to erosion from variable uplift of up to 300 m before subsiding to below storm wave base this uplift may have been caused by compression from oceanic crust that obducted along the southeastern side of the platform subsequently lower cretaceous strata document varying rates of block subsidence the lower cretaceous succession in the central oman mountains and adjacent subsurface began with regional drowning around the jurassic cretaceous boundary the succession in the east saih hatat records a single regressive sequence culminating in the progradation of the shallow water carbonate platform by the cenomanian however the succession in the west jebel akhdar and interior is dominated by shallow water carbonate facies but punctuated by a second regional drowning in the late aptian a third late cretaceous drowning terminated deposition of the wasia group in the turonian and was caused by convergence of oceanic crust and foreland basin formation although previously ascribed to eustatic sea level rises the two early cretaceous drowning events can be explained as consequences of the tectonic behavior of the platform the earlier event rayda formation occurred when first uplift tilted the eastern side of the platform and induced a relative sea level stillstand and widespread evaporative conditions in the interior hith anhydrite and then the eastern side subsided rapidly to below storm wave base forming a broad embayment starved of periplatform sediment by contrast the second drowning nahr umr formation was due to detrital influx generated by uplift on the west side of the platform both tectonic episodes led to a reduction in the calcium carbonate generating capacity of the epicontinental sea causing shallow water fa ies to be abruptly overlain by deeper water facies the effects from these two drownings eventually diminished and shallow water environments reestablished themselves the overall succession appears independent of eustatic sea level change

paleoenvironmental changes during the late albian oceanic anoxic event 1d an example from the capacho formation southwestern venezuela abstract the late albian early cenomanian oceanic anoxic event 1d oae 1d 103 to 99 5 ma represents a global interval of enhanced organic carbon burial due to widespread oxygen deficiency in the water column and or increased primary productivity the biostratigraphy and geochemistry of organic rich sediments in the la grita member capacho formation in southwestern venezuela were studied to document the paleoenvironmental conditions that governed the deposition of this succession during oae 1d carbon isotope 13ccarb and 13ccorg chemostratigraphy and biostratigraphic constraints show that the la grita member spans the late aptian period rotalipora appenninica zone and that oae 1d is well recorded in this succession a prominent increase in total organic carbon toc values up to 10 is clearly recorded through the onset of oae 1d coinciding with a prominent change in overall redox sensitive proxies suggesting that the la grita member sediments accumulated under anoxic and possibly euxinic bottom water conditions in a partially restricted basin the detrital proxies suggest that the greenhouse climate prevailing during oae 1d induced significant acceleration of the hydrologic cycle and an increase in continental chemical weathering rates overall the carbon and oxygen isotope records toc contents as well as the detrital proxies show cyclic variation during the late albian stage these variations support the hypothesis that orbital forcing likely also modulated the equatorial monsoonal activity during the oae 1d

spatial geochemistry of a carboniferous platform margin to basin transect balancing environmental and diagenetic factors abstract conventional one dimensional chemostratigraphy of marine carbonates assesses the chemical archive of individual stratigraphic sections and their correlation in space and time whereas this approach has shown to be of value when linking isobathymetric domains usually characterised by similar facies more caution is needed when correlations are extended across different physiographic settings and hence different facies belts here the spatial geochemical record of pennsylvanian platform margin to basin transects across a bathymetric range of about 800 m is documented and discussed in a process oriented context particularly the presence of layered palaeo water masses and their potential control on slope facies distribution and geochemical properties requires attention whereas carboniferous thermo and or chemo clines most likely affected depth related slope facies zonation it was facies change and hence variances in porosity permeability properties that controlled differential early burial diagenetic alteration specifically the lower slope related breccia facies is characterised by higher volumes of early burial carbonate cements this implies that these sediments entered the shallow burial domain with a considerable open pore space and gave way to an increased rock fluid ratio whereas the 13 c record is invariant with bathymetry the more diagenesis sensitive 18 o proxy records pronounced shifts observed across major facies boundaries from this it is concluded that although the primary controlling factor of slope facies distribution with depth is probably palaeoceanographic in nature it is differential rock fluid ratios that control the first order spatial shifts in 18 o composition these findings show that one dimensional chemostratigraphy will severely underestimate the complexity of three dimensional bathymetric data sets across platform margins this is of relevance for the interpretation of the geochemical archive of fossil carbonate platforms in general

late aptian to late albian sea level fluctuations constrained by geochemical and biological evidence nahr umr formation oman abstract the aptian to albian interval of the vast arabian platform was studied in northern oman nahr umr formation for its paleoceanographic and sea level record the sections indicate seven transgressive regressive cycles overprinted by small scale sea level fluctuations the peak of regression lead to emergence and exposure of the sea floor and overprinted marine hardground surfaces the subaerial overprint of marine hardgrounds is difficult to recognize in the field however four independent lines of evidence document emergence these are 1 pronounced negative excursions in carbon and partly in oxygen isotope composition beneath hardbottoms they are attributed to the influx of light soil derived carbon and light oxygen from meteoric water 2 sparite filled rudists beneath hardbottoms contain primary brackish water fluid inclusions of very low salinity interpreted as cement precipitation in the phreatic marine meteoric mixing zone or pollution of meteoric freshwater by residual salt 3 symbiont bearing and thus light dependent orbitolinids display small conical morphotypes in the shallow well illuminated water prior to exposure and hardbottom formation large flat morphotypes are characteristic of the transgressive shales above those surfaces and document deeper less illuminated waters 4 the presence of mycorrhiza microcodium the exposure surfaces overlie facies incomplete shallowing upward successions or subtidal sediments but unequivocal evidence for erosion before or during emergence is lacking correlation of transgressive regressive events in oman with other sea level curves suggests the record of spasmodic regional tectonism combined with a strong eustatic component

pseudospherulitic fibrous calcite in paleo groundwater unconformity related diagenetic carbonates paleocene of the ager basin and miocene of the madrid basin spain abstract massive decimeter thick intervals formed by mosaics of subspherical calcite crystals displaying an intracrystalline fibrous microfabric have been found in paleocene and miocene strata in spain the fibrous microfabric is marked by inclusion defined fibers that radiate from the central parts of the crystals which can be termed pseudospherulites and not spherulites because they are single crystals and not polycrystalline aggregates the horizons of pseudospherulitic calcite appear in meter scale laterally persistent levels of crystalline limestones that exhibit complex pseudospar fabrics they are interbedded with peritidal and or lacustrine deposits they grade downward into bedded dolomicrites and they can be linked to unconformities several meters higher in the section above intervening unaltered limestones the pseudospar zones are interpreted as early diagenetic paleo groundwater alteration products after dolomicrites the pseudospherulites are composed of low mg calcite with low contents of fe and mn and they have a stable isotope composition indicative of precipitation from meteoric water they form xenotopic mosaics in which goethite palygorskite and sepiolite may be present as inclusions and in the intercrystalline matrix cathodoluminescence microscopy reveals peripheral growth of the pseudospherulites which results from several phases of precipitation and even of dissolution the first phase of crystal growth may show rhombic habits and may contain corroded dolomite inclusions interpreted as an indication of growth at the expense of dolomicrite by a dissolution precipitation process the second phase of crystal growth is fibrous sensu stricto exhibits lobate growth laminae and shows indications of displacive growth the pseudospherulitic fabric is not relict and the pseudospherulites do not represent speleothems recrystallized microcodium or neomorphosed spherulitic carbonate instead they are interpreted as split crystals that grew within dolomicritic host sediments in part by dissolution precipitation and in part by displacement the hypothesis of a dolomicritic host is supported by the geological and diagenetic setting by the presence of corroded dolomite inclusions within the pseudospherulites and by the relationship between their growth and the authigenesis of sepiolite palygorskite and goethite the pseudospherulites grew in the shallow subsurface at or near the water table from predominantly oxidizing meteoric water and under periodically fluctuating geochemical conditions saturation redox caused by fluctuations of the water table during periods of subaerial exposure the presence of fossil bacteria within the pseudospherulites the anastomosing pattern of the inclusion defined fibers and the lobate growth forms of the fibrous calcite suggest some bacterial influence in the genesis of the pseudospherulitic fabric

geology and reservoir characteristics of carbonate buildup in giant bu hasa oil field abu dhabi united arab emirates bu hasa field in abu dhabi was the first giant oil field in the arabian gulf to produce from the lower cretaceous shuaiba formation aptian the field has a productive area of about 155 673 ac 63 047 ha and 12 6 billion bbl of oil reserves the formation is composed mainly of rudistid and algal sediments rudistid mounds having overlain and built up the topography of an algal platform the position and elevation of the platform edge combined with rising eustatic sea level created a tendency toward both vertical and lateral growth and regulated the form and distribution of the rudist accumulation the shuaiba formation has good reservoir quality ranging in porosity from 18 25 and with average permeability exceeding 100 md nine reservoir units a i classified by their porosity permeability and lithology can be clearly defined from the logs eleven main lithofacies have been defined in the shuaiba from detailed core descriptions these lithofacies were deposited in three main phases the earliest phase consisted of chalky mud supported sediment with some algal colonies followed by a middle phase characterized by a thick algal platform during this stage of deposition a shallow water carbonate platform developed over the south and central part of the field grading into deeper open marine sedimentation toward the north the late phase was characterized by rudistid buildups mainly caprinids and caprotinids the growth of the thick algal platform in the south and central areas controlled the initial distribution of the main rudistid buildup toward the north small rudistid reefs are sparsely developed and present only n the latest stage on high energy shoals

rudists as gregarious sediment dwellers not reef builders on cretaceous carbonate platforms abstract it has sometimes been claimed that rudist bivalves competitively displaced corals from reef frameworks during the cretaceous this hypothesis combines two assertions 1 that the autecology of rudists was convergent with that of reef building corals and 2 that rudist formations commonly developed as reefs we dispute both assertions and thus reject the hypothesis of competitive displacement we argue instead that mobile sediments rather than frameworks dominated the margins and tops of most of the extensive carbonate platforms of the period and that it was on these non reefal biotopes that the rudists flourished definitions of reefs tend to combine two major elements 1 a robust biogenic framework with accompanying sedimentary and diagenetic components and 2 topographical relief such definitions are clearly rooted in recent coral reefs in which endosymbiotic zooxanthellae permit the extensive growth of colonial coral frameworks in shallow but relatively nutrient poor waters coralline algae and cementation may contribute significantly to the growth of rigid structures and topography is largely the legacy of pleistocene changes in sea level in rudist formations in contrast individual rudist congregations are volumetrically limited relative to sediment they are often loosely constructed and they evidently showed little if any original relief tabular and small lenticular units predominate these differences in structure and palaeoenvironmental situation between rudist and modern coralgal associations reflect the different autecologies of the constituent organisms the clonal growth of corals predisposes them to the development of frameworks projecting above the sediment surface herein termed superstratal growth by contrast the aclonal development of rudists was better suited to the opportunistic occupation of a variety of temporarily available substrata by large numbers of individuals in particular elevator rudists in which the entire commissure exhibited upward growth evidently grew with their shells largely embedded in and supported by the ambient sediment herein termed constratal growth moreover the tolerances and growth responses of rudists to such factors as water turbidity nutrients and current regime were quite different from those of the majority of reef building corals despite repeated assertions in the literature that rudists possessed zooxanthellae only a few species show any evidence for such a symbiosis and other evidence suggests that most lacked them in view of these differences in their preferred biotopes competition between rudists and corals is doubtful even though members of both groups co occur in many areas the relative decline of coral frameworks in the cretaceous was thus probably independently caused

historic and paleomagnetic secular variation and the earth s core dynamo process this paper attempts to summarize briefly the recent and ongoing efforts of the geomagnetism and paleomagnetism community to understand both the earth s magnetic field secular variation and its implications for the core dynamo process secular variation is defined in this paper as the general spatio temporal variation of the field secular change will refer to the first time derivative of the spatial field strict geomagnetic definition of secular variation we will emphasize here the long term 10 year or longer behavior of the historic secular variation hsv for this is the variation that is comparable with the paleomagnetic secular variation psv two important related topics the 1969 1970 geomagnetic jerk in secular acceleration and the spatial geomagnetic field components due to crustal or mantle sources are treated more fully in other reviews

modeling the enso modulation of antarctic climate in the late 1990s with the polar mm5 abstract the polar fifth generation pennsylvania state university ncar mesoscale model mm5 is employed to examine the el nino southern oscillation enso modulation of antarctic climate for july 1996 june 1999 which is shown to be stronger than for the mean modulation from 1979 to 1999 and appears to be largely due to an eastward shift and enhancement of convection in the tropical pacific ocean this study provides a more comprehensive assessment than can be achieved with observational datasets by using a regional atmospheric model adapted for high latitude applications polar mm5 the most pronounced enso response is observed over the ross ice shelf marie byrd land and over the weddell sea ronne filchner ice shelf in addition to having the largest climate variability associated with enso these two regions exhibit anomalies of opposite sign throughout the study period which supports and extends similar findings by other investigators the dipole structure is observed in surface temperature meridio

sedimentology rhythmicity and basin fill architecture of a carbonate ramp depositional system with intermittent terrigenous influx the albian kharfot formation of the jeza qamar basin dhofar southern oman abstract the albian kharfot formation is preserved in the eastern margin of the jeza qamar basin which straddles across the oman yemen border this study addresses the sedimentological attributes of the formation and deduces its depositional setting cyclicity and relative sea level changes in local within the basin and regional arabian contexts the interaction among siliciclastic influxes in situ carbonate production and tectono climatic controls on the stacking nature of the various lithofacies that build up the formation is discussed in the study area the formation lies unconformably over barremian aptian qishn formation and conformably under late albian turonian dhalqut formation the kharfot formation thickens from 140 m in the eastern side of the study area to 300 m at the oman yemen border it consists of eight lithofacies orbitolina rich marls peloidal bioclastic packstone bioclastic mudstone to wackestone argillaceous bioclastic floatstone to rudstone bioclastic rudstone sandy peloidal bioclastic mudstone to packstone peloidal bioclastic grainstone and dolostone the vertical arrangement of these lithofacies defines recurring meter to decameter scale shallowing upward units deposited on a westward deepening inner to outer ramp setting tectonic rejuvenation of the siliciclastic source area was accompanied by warm humid climatic conditions as suggested by high kaolinitic marls of the kharfot fm and coeval quartz rich sandstone units harshiyat fm the shallowing upward rhythmic sedimentation of the formation has close resemblance with cycles of the nahr umr formation in northern oman and partially comparable with the global sea level changes the kharfot basin was an intrashelf depression that was part of the much larger arabian epeiric platform the latter is defined by a rimmed margin in northern oman where al hassanat formation represents platform margin deposits and nahr umr formation representing back rim intrashelf depression which received fine grained siliciclastic influx from the land westward in southern oman where kharfot formation accumulated the platform was unrimmed ramp type basin with high fine clastic influx along with elevated carbonate production

radiaxial fibrous calcites a new look at an old problem abstract marine radiaxial fibrous and fascicular optic calcites are very common but poorly understood pore filling cements in paleozoic and mesozoic marine neritic and upper bathyal limestones the main diagnostic feature of these cements is their converging or diverging crystal c axis respectively the reasons for this anomalous texture are at present unknown another controversy is due to the relative lack of occurrences in cenozoic strata and their apparent absence in quaternary marine limestones despite these uncertainties marine fibrous cements are thought by some to be amongst the best proxies for the geochemistry of ancient oceans because of the absence of metabolic effects during their precipitation applying electron backscatter diffraction analysis we here for the first time document radiaxial fibrous and subordinate fascicular optic fibrous biominerals from well preserved jurassic and cretaceous low mg calcite belemnite rostra the finding of fibrous biogenic calcites in combination with the recent description of holocene and modern fibrous calcites in stalagmites represents in the view of the authors a significant advance in carbonate research here these findings are placed in their wider processes oriented context and the significance of biogenic and speloan fibrous calcite for their marine counterparts is assessed comparing the physico chemical and organomineralic properties of different precipitation sites indicates that the diagnostic variations in the crystal c axis orientation are not related to a specific nucleation environment or substratum in contrast preliminary crystallographic analyses suggest that kinetic factors during nucleation or subtle gradients in the statistical replacements of ca 2 by mg 2 in the crystal structure may lead to local strain resulting in converging or diverging crystal c axes

simulations of southern hemisphere warming and antarctic sea ice changes using global climate models a combination of modelling techniques is used in conjunction with the limited available observational data to examine antarctic sea ice changes with global warming over the past century firstly a coupled global climate model is forced by prescribing the effect of increasing greenhouse gases from last century to the present secondly the gisst u k meteorological office global sea ice and sea surface temperature observational dataset is used to force an atmosphere sea ice model to compute changes in the antarctic sea ice from last century to the present thirdly the global sea surface temperature sst anomalies derived from the coupled model are used to force the atmosphere sea ice model over the same period the change in the southern hemisphere annual mean surface temperature simulated by the coupled model with greenhouse gas forcing is about 0 6 c which is similar to the observed change over the antarctic poleward of 60 s the corresponding simulated change is about 0 7 c which also appears compatible with observations the reduction in summer sea ice extent simulated by the csiro commonwealth scientific and industrial research organisation coupled model is 0 44 lat which is in general less than the observed change for the two sst forcing cases the changes are in general larger than indicated by the observations it is concluded that future changes of reduced sea ice extent from increasing greenhouse gases as simulated by the csiro coupled model are not expected to be overestimates

the descriptive nomenclature and classification of growth fabrics in fossil scleractinian reefs abstract framework sensu stricto is a concept originally relating to modern reefs and is defined by structural ecological and sedimentological criteria however in the geological literature the term framework has come to be applied to almost any organically influenced in situ accumulation including non calcareous non rigid facies associated with sea grasses this drastic departure from the original meaning is misleading and scientifically unhelpful the concept of wave resistance is integral to that of framework but in the geological record it is not easy to evaluate and the term may be of little comparative use between reef environments it is suggested that the term growth fabric be generally applied as a descriptive term for the presence of aggregated in situ corals or other organisms in growth position within a facies the term growth fabric should be used as an alternative to framework as a purely descriptive term the term framework should be restricted to its original definition and used only where the criteria for framework can be clearly demonstrated two end member types of scleractinian growth fabric genesis are recognised termed superstratal and constratal terms adapted from gili e masse j p skelton p w 1995 rudists as gregarious sediment dwellers not reef builders on cretaceous carbonate platforms palaeogeogr palaeoclimatol palaeoecol 118 245 267 in a superstratal growth fabric the constituent organisms collectively projected decimetres to metres above the substratum creating positive topographic relief in contrast constratal growth is where vertical organic accretion occurred at a similar rate to sediment accumulation hence the majority of the skeletal material remained continuously embedded in the sediments and only a small proportion of the skeleton projected centimetres above the sediment surface the architectural palaeoecological sedimentological and diagenetic implications of different types of growth fabric genesis is discussed a review of the classification of reef fabrics suggests that there is currently no adequate system to describe fossil scleractinian growth fabrics the most commonly used classification of reefal fabrics is that of embry and klovan 1971 embry a f klovan j e 1971 a late devonian reef tract on northeastern banks island northwest territories bull can pet geol 33 730 781 there are a number of shortcomings in this scheme which may be grouped into three categories 1 the interpretative nature of the classification 2 problems in interpreting biological effect from form and 3 insufficient categories to adequately describe mesozoic and cenozoic growth fabrics moreover there appears to be a lack of a standardised nomenclature for growth fabrics which has hindered meaningful comparisons of scleractinian growth fabrics through time and space a descriptive system based on a modification and expansion of the embry and klovan system 1971 is proposed and a revised nomenclature for growth fabrics presented the system is designed to be flexible in its application it can be used simply to describe a growth fabric or through the use of genetic and non genetic modifiers to imply types of reef building processes and growth fabric heterogeneity although the concepts and terminology discussed in this paper relate to scleractinian growth fabric they are equally applicable to fabrics comprising other organisms

morphological patterns of aptian lithocodium bacinella geobodies relation to environment and scale lithocodium aggregatum and bacinella irregularis are now extinct shallow marine life forms of unknown taxonomic origin forming part of the tropical platform biota during much of the mesozoic these organisms experienced bloom periods and temporarily replaced rudist coral assemblages during parts of the early aptian within the limitations of time resolution this out of balance facies is coeval with the oceanic anoxic event 1a related black shale deposition in oceanic basins but the triggering factors remain poorly understood here a platform wide comparison of lithocodium bacinella geobodies and morphotypes from the sultanate of oman is presented and placed in its environmental bathymetric and physiographic context lithocodium bacinella geobodies reach from kilometre scale superstructures to delicate centimetre sized growth forms clearly scale matters and care must be taken when drawing conclusions based on spatially limited observational data whilst the factors that cause lithocodium bacinella expansion should probably be considered in a global context regional to local factors affected growth patterns in a more predictable manner here the unresolved taxonomic relationship remains the main obstacle in any attempt to unravel the response of lithocodium bacinella to specific or interlinked environmental parameters as different organisms respond differently to changing environment acknowledging these limitations the following tentative patterns are observed i lithocodium bacinella tolerated a wide range of hydrodynamic levels and responded to differences in energy level or physiographic settings margin intrashelf basin inner platform by obtaining characteristic growth forms ii lithocodium bacinella favoured low sediment input but had the ability to react to higher sedimentation rates by enhanced upward growth a feature perhaps pointing to a phototrophic metabolism circumstantial evidence for continuous growth within the upper sediment column is debated iii the availability of accommodation space had a direct influence on the maximum size of geobodies formed iv fluctuating nutrient levels and sea water alkalinity may have affected the growth potential of lithocodium bacinella understanding the relationship between lithocodium bacinella morphogenesis on a wide range of scales and local environmental parameters allows for better prediction of the spatial distribution of reservoir properties and also results in an improved interpretation of palaeoenvironments this study might represent a useful first step in this direction

fluid flow reconstruction in hanging and footwall carbonates compartmentalization by cenozoic reverse faulting in the northern oman mountains uae abstract in this paper the diagenesis from either side of a major cenozoic reverse fault in the northern oman mountains is documented detailed petrographical and geochemical analysis of calcite filled fractures in carbonate strata of late triassic and early cretaceous age in the hanging wall and footwall in wadi ghalilah reflect a different diagenetic history in both hanging wall and footwall most of the fractures are pre burial extensional in origin formed by a crack seal mechanism and the calcite vein infill has a host rock buffered signature in the hanging wall the fluid responsible for calcite precipitation of these extensional fractures was a marine fluid at 60 c these veins predate deep burial and contractional tectonic deformation and consequently do not provide any information about syntectonic fluid flow neither do the pre burial extension fractures in the footwall which are also host rock buffered the fractures post dating the tectonic stylolitization in the footwall by contrast show evidence of syntectonic migration of saline formation waters at temperatures between 80 and 160 c during contractional deformation these fluids probably were sourced from the subsurface via the reverse fault which acted as a fluid conduit at the same time however this fault functioned as a permeability barrier towards the hanging wall since no evidence of syntectonic fluid flow is present here in this way compartmentalization of the hanging wall and footwall block was realized

fractal nature of stratigraphic sequences orders of stratigraphic sequences are being used loosely and with widely varying definitions the orders seem to be subdivisions of convenience rather than an indication of natural structure it is proposed that at least at time scales of 103 106 yr sequences and systems tracts are scale invariant fractal features in which units bounded by exposure surfaces and units bounded by flooding surfaces are about equally likely support for this conceptual model derives from the well known facts that 1 sediment architecture is largely scale invariant over a wide range of scales in time and space 2 first order trends of sea level movements and sedimentation rates are fractal on all geologically relevant time scales and 3 detailed studies in carbonates indicate approximately equal abundance of flooding surfaces and demonstrable exposure surfaces among unit boundaries finally traces of prograding shelf edges that step up and step down in response to sea level changes are demonstrated in this study to have a fractal nature

recent sedimentary facies of isolated carbonate platforms belize yucatan system central america abstract distribution of recent sedimentary facies is significantly different in four closely spaced isolated carbonate platforms off the coasts of belize and yucatan se mexico these differences are largely controlled by variations in submarine topography which are likely the result of differential subsidence and karstification from platform to platform a variety of depositional styles and patterns is found in platform interiors that developed during the same holocene sea level rise composition and texture of surface sediment samples were used to define four major sediment types and to distinguish nine depositional environments within the platforms facies maps are based on analysis of 454 sediment samples and high resolution satellite imagery glovers reef is characterized by a circular facies distribution the nearly continuous reef margin is composed of a coral red coralline algae halimeda grainstone mixed nonskeletal peloidal skeletal wackestones and packstones are present in shallow lagoon parts 5 m water depth behind the margin the deep interior from 5 to 18 m water depth is characterized by mollusk foram halimeda wackestones with over 860 patch reefs of coral red algae halimeda mollusk packstones lighthouse reef also has a coral grainstone and coral red algae halimeda grainstone rim but the facies distribution in the interior is strongly asymmetrical the 8 m deep eastern lagoon is floored by mollusk foram halimeda wackestones and packstones the 3 m deep western lagoon has the mixed peloidal skeletal wackestone to grainstone facies a linear trend of coalescing patch reefs and skeletal grainstone facies separates the two lagoons banco chinchorro is similar to lighthouse reef inasmuch as facies distribution patterns of the interior are strongly asymmetrical mollusk foram halimeda wackestones grainstones are present in eastern lagoon areas whereas shallow 5 m western parts of the lagoon are composed of mixed peloidal skeletal grainstones packstones and wackestones most of turneffe islands is protected on the east by lighthouse reef accordingly turneffe has a narrower reef and skeletal grainstone rim than the other two platforms restricted interior lagoons are up to 8 m deep and are enclosed by wide mangrove rims and surface sediments dominated by halimeda rich wackestone rich in organic matter coral patch reefs are absent in contrast the unprotected northernmost part of turneffe has a wide reef and grainstone rim and the open lagoon area consists of mollusk foram halimeda wackestones packstones with abundant patch reefs

controls on carbonate platform evolution on active fault blocks the lower cretaceous castro urdiales platform aptian albian northern spain abstract four contrasting carbonate sequences developed in a tectonically active extensional setting in the lower cretaceous aptian albian castro urdiales platform of north spain the four carbonate phases p1 p4 early aptian late aptian earliest albian and early late albian respectively are identified across the platform to basin transition on the basis of sedimentary geometries and internal facies patterns they are vertically separated by four incipient drowning events d1 d4 middle aptian aptian albian boundary early albian and late albian the first carbonate stage p1 corresponds to a low relief carbonate platform characterized by widespread shallow marine depositional environments with a nearly flat organization the second platform stage p2 developed as a rimmed carbonate platform the third carbonate stage p3 evolved from a low relief aggradational platform substage a to a progradational offlapping platform substage b and back to a backstepped aggradational rimmed platform substage c responding to changes in differential subsidence and carbonate production at the beginning of the albian the castro urdiales carbonate platform was broken up by extensional tectonic movements with formation of fault blocks bounded by ne sw and nw se trending faults on the crests of uplifted blocks meteoric processes were active whereas grabens and half grabens acted as channel conduits for terrigenous rich deposits subsidence rates increased during the late early albian late albian the crests of rotated blocks formed paleohighs that nucleated small residual carbonate platforms carbonate stage p4 that were surrounded by deeper water basins this study suggests that the evolution of carbonate platform sequences in the lower cretaceous of castro urdiales was primarily controlled by changes in accommodation space which were most likely driven by intraplate stresses related to extension in the north spanish continental margin during the opening of the north atlantic drowning events in the castro urdiales platform coincide with major crises of cretaceous carbonate production worldwide suggesting that regional tectonism and global oceanic changes interacted to cause phases of platform demise

facies analysis of an upper cretaceous high energy rudist dominated carbonate ramp matese mountains central southern italy subtidal and peritidal cycles abstract upper cretaceous shallow water limestones rich in rudists have been studied in the matese mountains they show a preponderance of skeletal components molluscs and benthic foraminifers and a lack of non skeletal grains the most prominent sediments of the studied stratigraphic interval are rudist dominated fine to coarse grained lithologies most of the senonian successions are characterized by massive neritic limestones rich in molluscs mostly rudists and subordinate gastropods and a few corals the sediments were generated in situ on shelves where rudist bivalves were the primary sediment producers these sediments were actively moved by storms waves and swells the finer fractions were probably winnowed out and deposited in deeper water well bedded dolomitized mudstones wackestones microbial laminites and benthic foraminifer wackestones characterize some successions where they rhythmically alternate and testify to deposition in tidal flat environments the lithofacies faunal and taphonomic characters and the sedimentary structures are typical of a ramp like open shelf with local peritidal deposition the vertical lithofacies organization consists of numerous decimetre to metre scale shallowing upward subtidal and peritidal cycles a complete transition from peritidal to subtidal cycles has been recognized and documented the peritidal cycles are usually bounded by desiccation surfaces and or dolomitized crusts followed by shallow subtidal to peritidal facies of the next cycle the subtidal cycles are typified by rudist floatstones passing to large scale cross bedded bioclastic packstones grainstones current and storm structures are distinctive features in shallower water environments the effects of submarine erosion prevail hardgrounds commonly developed and the resulting cycles are usually truncated the formation of the peritidal cycles appears to have been controlled by accommodation space in response to fluctuations in relative sea level the formation of the subtidal cycles was determined by sedimentation rates in response to fluctuations in the zones of fair weather and storm wave reworking in turn controlled by relative sea level this indicates that sediment production and supply were important controlling factors in the cycle formation during the early senonian stratigraphic interval the recognition of similar depositional styles in other early senonian successions cropping out in the southern apennines suggests that this type of sedimentation is a recurring attribute of the upper cretaceous open shelves

reply to the comment on orbitally forced climate and sea level changes in the paleoceanic tethyan domain marl limestone alternations lower kimmeridgian se france by s boulila m de rafelis l a hinnov s gardin b galbrun p y collin palaeogeography palaeoclimatology palaeoecology 292 2010 57 70 abstract a recent paper by boulila et al 2010 reports on orbitally forced cycles recorded as marl limestone alternations in one lower kimmeridgian section chateauneuf d oze se france tethyan domain in an attempt to illustrate the in situ i e pelagic origin of carbonates in marls and limestones the authors challenged the results of previous work concerning sections from other tethyan areas of similar age which demonstrate that nannofossil abundance is originally higher in marls than in limestones boulila et al 2010 present data acquired with optical and scanning electron microscopes estimating nannofossil contribution to the rocks however their selected illustrations do not support a high contribution of the nannofossils to the carbonate fraction of their samples or their interpretation of the finest fraction of the rocks micarbs furthermore according to their data on carbonate content of the rocks they did not analyse true marl limestone alternations but slightly argillaceous limestones and limestones boulila et al 2010 also criticize earlier work providing a sequence stratigraphy interpretation of the chateauneuf d oze section however contrarily to these earlier works they did not consider platform to basin correlations that are essential in order to understand the sedimentary dynamics at the basin wide scale this comment challenges the work by boulila et al 2010 that largely underestimates the role of carbonate production on shallow platforms and its subsequent export basinwards as a major mechanism controlling the sedimentation in epicontinental basins

geomagnetic secular variations in greece through the last 6000 years obtained from lake sediment studies summary geomagnetic declination and inclination secular variation curves have been constructed back to 6000 yr bp from palaeomagnetic measurements of sediments cored in lakes volvi trikhonis and begoritis greece they have been dated by palynological studies and by comparison with observatory and archaeomagnetic records radiocarbon ages are all affected by the old carbon factor cores from all three lakes contain a thin ash layer which we associate with the pompeii eruption of vesuvius in ad 79 averaged curves of secular variations of declination and inclination have been computed for the whole study the broader scale pattern of secular variations is basically similar to lake sediment records from the uk poland and switzerland though finer detail in the structure of some of the principal features is resolved

records of geomagnetic secular variation since 1200 ad and the potential for chronological control of lake sediments in northern alberta we assess whether absolutely aged declination changes can be used to date recent massive lake sediments at the sub century scale three issues limiting such studies are addressed recovery of undisturbed recent lake sediments assessment of the reliability of the geomagnetic record and the comparison of lake sediment records with historic re cords a 793 year long geomagnetic chronology was obtained from the annually laminated sediment of rainbow lake a sediment disturbance was minimized by freezing the sediment in situ and maintaining this state for geomagnetic analyses geomagnetic chronologies ca 600 years long from the massive sediments of fariya lake and ninisith lake were collected in removable plastic tubes using a piston corer sediment disturbance was minimized by ex situ draining of water from the plastic tubes the reliability of the geomagnetic record was assessed using a measure of internal co herence with an absolute cutoff of 15 by further separating the samples at coherence values of 5 and 7 5 it was possible to identify zones of disturbance and reduced compaction the most reliable samples had a high magnetic in tensity due to high inputs of magnetic minerals sediment compression and inputs of stable magnetic minerals neither freezing nor dewatering of the sediments appeared to decrease reliability of the geomagnetic record the declination chronology from the annually laminated sediments was significantly correlated with a 230 year long historical record from churchill manitoba and with the massive lake sediment chronology from fariya lake geomagnetic dating was not possible however because of the large amplitude in the annually laminated sediment declination record the large number of years of sediment in many specimens and the lack of reliability for samples that contain few years of sedi ment per specimen

hybrid carbonates in situ abiotic microbial and skeletal co precipitates abstract abiotic bioinduced and biocontrolled carbonates are process based sediment categories they successively reflect increasing levels of biotic control over carbonate precipitation from aqueous solutions are often closely linked to depositional environment and change with time hybrid carbonates are intimate in situ combinations of two or more of these categories hybrid carbonates are widespread and diverse in the marine geological record and reflect large scale changes in carbonate precipitation through time they also occur in fluvial and lacustrine carbonates marine and non marine reef systems and methane seep deposits plots of hybrid carbonate composition in time and space reveal complex backtracking and looping patterns that reflect changes in environmental conditions and biological processes of carbonate production recognition of hybridity emphasizes the importance of distinguishing abiotic and bioinduced precipitates until they were diversified by skeletal carbonates in the late proterozoic precambrian hybrid carbonates were abiotic bioinduced combinations during the phanerozoic hybrid carbonates were conspicuous during periods of overlap or transition between intervals of microbial and skeletal carbonate abundance microbial skeletal dual hybrids are common during the cambrian mid ordovician late devonian mississippian and late jurassic early cretaceous abiotic microbial skeletal triple hybrids were common from late pennsylvanian to mid triassic shallow marine hybrid carbonates declined in abundance after the mid cretaceous although late cenozoic reefs contain some striking examples of microbial skeletal hybrids recognition of hybrid carbonates draws attention to fundamental processes underlying carbonate sedimentation and their patterns and drivers of change in time and space

microbial foraminiferal episodes in the early aptian of the southern tethyan margin ecological significance and possible relation to oceanic anoxic event 1a two regionally significant microbial foraminiferal episodes 150 kyr each occur within the early aptian shallow marine platform in oman and throughout eastern arabia the stratigraphically lower of these two intervals is characterized by isolated or coalescent domes that share similarities with modern open marine stromatolites from the exuma cays bahamas the upper interval is predominantly built by a problematic lithocodium bacinella consortium in buildup and massive boundstone facies based on highresolution chemostratigraphy these shoalwater intervals are coeval with oceanic anoxic event 1a oae1a livello selli field evidence demonstrates that the buildup episodes alternate with stratigraphic intervals dominated by rudist bivalves this biotic pattern is also recognized in other coeval tethyan sections and is perhaps a characteristic shoalwater expression of the oae1a the short lived regional expansions of this microbial foraminiferal out ofbalance facies cannot be explained by local environmental factors salinity and oxygen level alone and the buildup consortia do not occupy stressed refugia in the absence of grazing metazoans judging from recent analogues the main fossil groups i e microbial assemblages macroalgae larger sessile foraminifera and rudist bivalves all favoured elevated trophic levels but with different tolerance limits the implication of this is that the influence of palaeofertility events possibly related to oae1a on carbonate platform community structures must be investigated the observations made in these coastal sections are a significant first step for the improved understanding of the early aptian period of biotic oceanic and climatic change

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

long period geomagnetic secular variations since 12 000 yr bp a comparison of secular variation records of the geomagnetic field inclination obtained from palaeomagnetic studies of european and north american post glacial and late glacial sediments suggests that geomagnetic westward drift has persisted through the past 12 000 yr between 12 000 and 2 500 yr bp the overall average drift rate was between 0 14 and 0 16 deg yr 1 at 2 500 yr bp it is tentatively suggested that the drift rate increased and rose to a maximum of nearly 0 5 deg yr 1 before decreasing to historically observed values of 0 25 deg yr 1

global environmental controls on cretaceous reefal ecosystems abstract the hypothesis of global environmental control of reefal ecosystems is developed in order to explain the dramatic biotic changes in cretaceous benthic communities during a 30 m y period in the early cretaceous the dominant biota in the reefal ecosystem changed from corals algae and rudists to rudists with minor coral species this change included the reduction of the binder niche which in the early cretaceous was occupied by stromatoporoids and algal cyanobacterial associations the role of bafflers increased during the mid cretaceous as first the radiolitids then the hippuritids diversified and increased in abundance the characteristic encrusters changed from green algae and bryozoans to red algae the orbitolinid foraminifers were replaced by the alveolinids the biotic changes are reflected in the feeding habit substrate niche relationships within the communities and the biotic processes of competition for space and nutrients these changes were closely linked with major though subtle global shifts in oceanographic current systems in water mass chemistry in nutrient levels and in plate positions and oceanic volcanism associated with super plume activity the development of widespread anoxic water masses influenced the composition of the oceans and the atmosphere itself the feedback interactions among these processes may have had an indirect but unalterable affect on the composition and structure of cretaceous reefs particularly the frequency of sea level rise and flooding of the shelf with low oxygen waters increased by two times during the mid cretaceous this increased frequency of stress upon the benthic communities may have crossed the threshold resulting in the biotic changes such as the replacement of corals by rudists as the most abundant reefal group

late quaternary paleomagnetic record of the goderich basin lake huron paleomagnetic analysis of two cores taken of the late quaternary sequence of the goderich basin lake huron resulted in high resolution declination inclination intensity of magnetization j magnetic susceptibility k and q ratio j k curves there was a consistent relative relationship of the features along the curves of all five parameters for both cores studied which confirms the reproducibility of the method and suggests that paleomagnetic curves can be used for time parallel correlation of the late quaternary sequence of the goderich basin

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

high rate sea level change during the mesozoic new approaches to an old problem abstract it is generally assumed that the effects of tectonism sediment accumulation and compaction and eustasy on accommodation change cannot be untangled on a regional scale hence most reconstructions of past eustatic change have focused on global correlations here this approach is questioned in the time domain of few my and less global cycle correlation is often unreliable and the effects of isostasy on sea level show strong provincial variations in contrast on a regional scale cycle correlation is more precise and regional tectonism has predictable limitations these considerations form the base for an assessment of the poorly understood causes of high rate sea level change in the mesozoic three well documented regional semi quantitative sea level curves are chosen here for reference jurassic of britain cretaceous of russia albian of oman the absolute numbers of amplitudes are open to question but the order of magnitude rates of several meters to tens of meters per my is a robust property of all three curves even when considering large error bars variable mechanisms that cause these regressive transgressive cycles are considered but rejected with exception of the controversial issue of glacio eustasy or unknown mechanisms therefore orbital forcing of glacio eustasy is assessed freezing melting cycles of higher altitude ice shields can explain high rate sea level change with moderate amplitudes but conclusive evidence is buried beneath 3 km of east antarctic ice thus although several ambiguities of global sea level correlation are avoided by the regional approach the causes of high rate mesozoic sea level change remain poorly understood

lake sediment record of the geomagnetic secular variation in britain during holocene times summary a palaeomagnetic record of the geomagnetic secular variation during the last 10000 years has been obtained from 10 cores of sediment from loch lomond scotland lake windermere north england and llyn geirionydd north wales a time scale is provided by 30 radiocarbon age determinations and pollen analyses on several of the cores the main swings and much fine detail of both declination and inclination records repeat well between cores and between lakes and the overall record is much more detailed than previous european records the new record shows that neither declination nor inclination swings have been periodic over the past 10000 years but that the main swings have become progressively shorter in duration during that time each swing is characterized by fine detail which enables use of the record as a secondary method of dating other european sediments the motion of the geomagnetic vector has been predominantly clockwise throughout the time period spanned but confirms a period of anticlockwise motion from 1100 to 600 bp first discovered by british archaeomagnetic investigations the record agrees with british and czechoslovakian archaeomagnetic records but not with japanese archaeomagnetic or north american lake sediment records this suggests that the secular changes are controlled by local growing and decaying drifting sources rather than by wobbling of the main geomagnetic dipole

time series analysis of the 10 000 yr geomagnetic secular variation record from se australia summary a 10 000 yr continuous secular variation record from intensively dated lake sediments in se australia has been subjected to periodogram and maximum entropy method analysis tests on synthetic data reveal some of the limitations of the latter method particularly when applied to complex number series anticlockwise precession of the magnetic vector at a period of 5000 1000 yr is tentatively ascribed to dipole precession and clockwise precession at a period of about 2800 yr is probably due to westward drift of features of the non dipole field the effect of calibrating the radiocarbon time scale is important and results in periodicity shifts of up to 25 per cent even for well dated lacustrine sequences power spectra are poorly constrained it is thus possible that the geomagnetic secular variation on a time scale of thousands of years is more uniform than often supposed mismatches between declination and inclination spectra can arise as a natural consequence of certain types of source mechanism and should not be simply attributed to figments of the analysis employed

stratigraphy and tectonosedimentary evolution of a late aptian albian carbonate margin the northeastern jebel akhdar sultanate of oman abstract upper aptian albian shallow water carbonates with rudists large foraminifera and calcareous algae are described from northern oman in the northeastern part of the parautochton of jebel akhdar the corresponding lithostratigraphic unit the al hassanat formation is partly a time equivalent of the nahr umr shales of albian p p age which have a wide extent on the arabian craton the al hassanat platform developed in two main phases first during the late aptian early albian the platform was fringing an emerged area central jebel akhdar with a limited extent basinward then during the middle albian the flooding of the central jebel akhdar resulted in an extensive development of the platform and a connection with the nahr umr shelf this sedimentary evolution and its palaeogeographic expressions were mainly controlled by structural patterns extensive uplift and block faulting to the edge of the antecedent early aptian platform with a significant differential subsidence then a sag of the arabian promontory this tectonosedimentary dynamics was related to the migration of the oceanic adjacent tethyan plate and took place during the global geodynamic albian revolution

textural elemental and isotopic characteristics of pleistocene phreatic cave deposits jabal madar oman abstract two main types of karst formation are commonly known the surficial meteoric one and the subsurface hypogenic karst which can be related to both carbonic h2co3 and sulfuric h2s acids this paper documents evidence for a third co2 regime related type of karst that is less commonly described petrographic and geochemical properties of exhumed pleistocene phreatic cave deposits from the diapiric jabal madar dome in northern oman are documented and discussed in a process oriented context these calcites form at the interface between two fundamentally different diagenetic and hydrogeological domains the deep seated hydrothermal and the near surficial meteoric vadose one four calcite phases are recognized i acicular ii blocky to stubby elongated iii proto palisade and iv macro columnar calcites the macro columnar calcites forming the last stage of precipitation are conspicuous due to their cyclical red zonation and they form the main geochemical focus of this study fluid inclusion data point to fluid temperatures of between 30 to 50 c monophase liquid inclusions and elevated salinities 1 6 to 7 3 wt nacl equivalent low carbon isotope data 8 to 9 are in agreement with the influx of soil zone co2 whereas decreasing 18o 15 values might point to mixing of saline hydrothermal and 18o depleted meteoric freshwater i e two fluid sources trace element and stable isotope data shift between the different cement phases and vary cyclically across the red zoning in macro columnar calcites with respect to the intra crystal variability these patterns are perhaps best explained in the context of redox potential two interpretations are presented the one favored here suggests that the cyclical red zoning in macro columnar calcites is controlled by pleistocene monsoonal climate patterns

increased terrigenous influx but no drowning palaeoenvironmental evolution of the tunisian carbonate platform margin during the late aptian during the aptian some carbonate platforms of the sub tropical realm for example on the northern tethys margin or in the gulf of mexico were affected repeatedly by severe perturbations in the carbonate production factory and drowning preferentially during global warming events such as the early aptian oceanic anoxic event 1a and a prominent mid late aptian warming interval these platform growth crises have been explained mainly by strongly increased coastal runoff for example siliciclastics and nutrients in combination with pronounced eustatic sea level rises in the last few years increasing evidence suggests that carbonate platforms of lower latitudes were generally less or even not affected by environmental perturbations during these events this raises the question as to the responsible factors that promoted platform growth or decline in different latitudinal areas in this study upper aptian middle gargasian to uppermost clansayesian inner tropical carbonate ramp deposits of the serdj formation at djebel serdj north central tunisia are studied in detail with regard to microfacies lithology biostratigraphy and chemostratigraphy these data allow reconstruction of the palaeoenvironmental evolution of the tunisian carbonate platform margin and investigation of its response to the prominent mid late aptian warming interval the unusually expanded 600 m thick serdj formation consists of limestones marlstones and siltstones suggesting deposition within mid ramp to inner ramp palaeoenvironments deposits of the mid late aptian are represented by quartz rich platform carbonates and siltstones probably resulting from increased coastal runoff on the tunisian shelf as a response to global warming and accelerated water cycling the siliciclastic input was accompanied by elevated nutrient levels as indicated by a partial decline in the abundance of oligotrophic biota and mass occurrences of orbitolines and green algae carbonate platform drowning during the mid late aptian as reported from the sub tropical realm has not been identified a comparison with other tropical river influenced platforms suggests that none of them drowned during the mid late aptian one important reason might be widespread arid to semi arid climatic conditions within lower latitudes during that time promoting platform growth due to comparably low nutrient runoff

calciclastic submarine fans an integrated overview abstract calciclastic submarine fans are rare in the stratigraphic record and no bona fide present day analogue has been described to date possibly because of that and although calciclastic submarine fans have long intrigued deep water carbonate sedimentologists they have largely been overlooked by the academic and industrial communities to fill this gap we have compiled and critically reviewed the existing sedimentological literature on calciclastic submarine fans thus offering an updated view of this type of carbonate slope sedimentary system calciclastic submarine fans range in length from just a few to more than 100 km three different types can be distinguished 1 coarse grained small sized most calciclastic submarine fans were formed on low angle slopes and were sourced from distally steepened carbonate ramps subjected to high energy currents under these conditions shallow water loose grainy sediments were transferred to the ramp slope and eventually funnelled into the submarine fan by sediment gravity flows these conditions seem to have been more easily met on leeward margins in which the formation of reefs was hampered by cool waters nutrient enrichment or oligophoty another circumstance that contributes to the transfer of shallow water sediments to the distal ramp slope is a low sea level forcing the carbonate factory closer to the slope break and destabilizing sediments by increased pore water pressure however the most important factor controlling the development of calciclastic submarine fans was the existence of an efficient funnelling mechanism forcing sediment gravity flows to merge downslope and build up a point sourced sedimentary accumulation in most cases this occurred through a major slope depression associated with tectonic structures an inherited topography or large scale mass failures

the growth fabric of gregarious rudist elevators hippuritids in a santonian carbonate platform in the southern central pyrenees abstract the growth fabrics of living congregations of erect sessile epifauna range between two extremes with superstratal growth the growing skeletons project well metres above the ambient sedimentary surface creating an upstanding framework which may be secondarily filled by sediment as in modern tropical coral reefs with constratal growth by contrast the growing tips of the skeletons project little centimetres from the seafloor such that the bulk of the skeletal fabric is embedded in and supported by the accumulating interstitial sediment as in pinna and oyster beds here we investigate the original growth fabrics and palaeorelief of hippuritid congregations in the santonian rudist formations around the sant corneli anticline near tremp in the southern central pyrenees the study particularly concentrates on a hippuritid lithosome exposed over some 0 25 km2 on the northern flank of the anticline four aspects are analysed 1 the lithosome is shown to have a tabular biostromal geometry and like others in the area is covered by a laterally accreted bioclastic blanket 2 specimens in upright life position show that the pioneers of the paucispecific congregations grew in bouquets but later recruits settled on the flanks of established and fallen shells adults were only loosely clustered and supported by the accumulating interstitial sediment 3 most shells however are now horizontal with respect to the bedding and densely stacked dense horizontal fabric or d h f this fabric is shown to be a result of current induced removal of sediment and toppling of shells 4 in contrast to the open marine aspect of the overlying bioclastic sediments the fine matrix sediment of the hippuritid lithosomes is faunally restricted and appears largely derived from the in situ biodegradation of shells we conclude that the hippuritid congregations grew constratally i e without any supporting biogenic framework and that they formed biostromal accumulations lacking relief so there is no justification for calling them reefs as some authors have done rather these rudists grew as gregarious sediment dwellers in the restricted waters of the platform top where they were sporadically disturbed by storms and eventually blanketed by bioclastic material swept in from the platform margin

an estimate of albian sea level amplitudes and its implication for the duration of stratigraphic hiatuses abstract carbonate platform tops are reliable but incomplete recorders of past sea level fluctuations as they are riddled with hiatuses of various durations basinal sections represent a more complete record but fail to register regressive transgressive events with small to moderate amplitudes we seek to avoid these problems by combining information on past sea level fluctuations from coeval platform top slope and basinal sections the outcome of this study is a semiquantitative albian sea level curve from the southern tethyan margin in oman in subaerial exposure surfaces the northern oman margin recorded 4 high amplitude 50 m 6 intermediate amplitude 30 m and 26 low amplitude 10 m regressive transgressive cycles hiatuses that cap the platform top depositional sequences might account for between 30 to 70 of the cycle duration the resulting platform top depositional sequences have frequencies in the order of 230 20 kyr i e they are in the time range of orbital eccentricity cycles it appears that at least some of these albian regressive transgressive cycles were rapid and punctuated as opposed to sinus shaped milankovitchian sea level oscillations

the worldwide character of the 1969 1970 impulse of the secular acceleration rate abstract this paper continues earlier studies to ascertain whether the distribution of the 1969 1970 jump of the secular variation rate has a worldwide character the geometry of the jump presents some similarities with the geometry of the secular variation itself we give a new estimation of the westward drift rate and information about spatial and temporal variations of the secular variation field

an ocean facing aptian albian carbonte margin oman a high energy aptian albian platform margin in northern oman fronted onto an open oceanic basin making the area a valuable analogue for coeval guyot margins most similar aged carbonate margins described in the literature faced either intracratonic or minor oceanic basins the studied margin is characterized by a stabilized outer rim which although it did not rise discernibly above the adjacent lagoonal deposits flanked a steep upper slope 32 40 basinwards with a relief of at least 30 m two main facies provided the rigidity of the outer margin lithocodium boundstones that constituted up to 50 of the rock volume and marine fibrous cements that occluded up to 35 of primary pore space in contrast coral rudist patches and other shelly sessile benthos were distributed irregularly and the rudist bioherms of the outer margin were often disrupted with shells being transported and redeposited the inner margin is characterized by wedge shaped storm layers that radiate from the platform top lagoonwards where they interdigitate with carbonate sands and small rudist bioherms polygenetic discontinuity surfaces that bear evidence of both marine hardground and subaerial exposure stages are prominent features of the margin throughout the latest aptian to middle albian the platform succession recorded some 30 relative sea level falls of which seven reached amplitudes of many tens of metres these seven high amplitude falls in sea level are recorded across the entire south eastern portion of the arabian craton and are probably of eustatic origin