carbonate factories a conundrum in sedimentary geology abstract describing characterizing and interpreting the nearly infinite variety of carbonate rocks are conundrums intricate and difficult problems having only conjectural answers that have occupied geologists for more than two centuries depositional features including components rock textures lithofacies platform types and architecture all vary in space and time as do the results of diagenetic processes on those primary features approaches to the study of carbonate rocks have become progressively more analytical one focus has evolved from efforts to build reference models for specific phanerozoic windows to scrutinize the effect of climate and long term oscillations of the ocean atmosphere system in influencing the mineralogy of carbonate components this paper adds to the ongoing lively debates by attempting to understand changes in the predominant types of carbonate producing organisms during the mesozoic cenozoic while striving to minimize the uniformitarian bias our approach integrates estimates of changes in ca2 concentration in seawater and atmospheric co2 with biological evolution and ecological requirements of characteristic carbonate producing marine communities the underlying rationale for our approach is the fact that co2 is basic to both carbonates and organic matter and that photosynthesis is a fundamental biological process responsible for both primary production of organic matter and providing chemical environments that promote calcification gross photosynthesis and hypercalcification are dependent largely upon sunlight while net primary production and e g subsequent burial of organic matter typically requires sources of new nutrients n p and trace elements our approach plausibly explains the changing character of carbonate production as an evolving response to changing environmental conditions driven by the geotectonic cycle while identifying uncertainties that deserve further research with metazoan consumer diversity reduced by the end permian extinctions excess photosynthesis by phytoplankton and microbial assemblages in surface waters induced by moderately high co2 and temperature during the early mesozoic supported proliferation of non tissular metazoans e g sponges and heterotrophic bacteria at the sea floor metabolic activity by those microbes especially sulfate reduction resulted in abundant biologically induced geochemical carbonate precipitation on and within the sea floor for example with the opening of tethyan seaways during the triassic massive sponge microbe boundstones the benthic automicrite factory formed steep massive and thick progradational slopes and locally mud mounds as tectonic processes created shallow epicontinental seas photosynthesis drove lime mud precipitation in the illuminated zone of the water column the resulting neritic lime mud component of the shallow water carbonate factory became predominant during the jurassic paralleling the increase in atmospheric pco2 while the decreasing importance of the benthic automicrite factory parallels the diversification of calcifying metazoans phytoplankton and zooplankton with atmospheric pco2 declining through the cretaceous the potential habitats for neritic lime mud precipitation declined at the same time peak oceanic ca2 concentrations promoted biotically controlled calcification by the skeletal factory with changes produced by extinctions and turnovers at the cretaceous tertiary boundary adaptations to decreasing ca2 and pco2 coupled with increasing global temperature gradients i e high latitude and deep water cooling and strategies that efficiently linked photosynthesis and calcification promoted successive changes of the dominant skeletal factory through the cenozoic larger benthic foraminifers protist protist symbiosis during the paleogene red algae during the miocene and modern coral reefs metazoan protist symbiosis since late miocene

kimmeridgian palaeogeography and basin evolution of northeastern iberia abstract two sedimentary basins were developed during the kimmeridgian in the northeastern part of iberia the basque cantabrian basin to the northwest and the iberian basin to the east these basins were mainly filled by carbonates deposited in a shallow epicontinental sea that was connected to the open marine realms of both the north atlantic and the western tethys respectively during the late jurassic they were temporarily linked by means of the soria seaway the uppermost oxfordian to lowermost tithonian of northeastern iberia consists of two depositional sequences sequence j3 5 spans latest oxfordian to early late kimmeridgian times sequence j3 6 spans the late kimmeridgian and early tithonian during sequence j3 5 coralgal reefs were developed in the sedimentary domains of the basque cantabrian basin and the soria seaway whereas the marginal areas of the iberian basin were dominated by oolitic shoals with variable siliciclastic influence outer ramp areas located in the central and eastern part of the iberian basin were dominated by carbonate muds and marls during the late kimmeridgian earliest tithonian shallow reefal and oolitic facies prograded over the micritic outer ramp facies the sedimentation areas were reduced and sequence j3 6 was only deposited in the iberian basin most of the western margin of the iberian basin and the southern areas of the soria seaway were covered by reefal facies during this sequence major transgressive events in the iberian basin took place in the latest oxfordian early kimmeridgian and in the middle late kimmeridgian whereas eustatic falls in sea level are recognised at the onset of the late kimmeridgian and at the kimmeridgian tithonian transition these events have also been described in other west european basins synsedimentary extensional tectonics is also evident and has been related to the onset of the late jurassic early cretaceous rifting stage synsedimentary normal faulting resulted in the presence of several troughs and highs within the basin the tectonic uplift of the western basin margin explains the progressive basinwards shift of the shorelines as observed in the iberian basin towards the end of the jurassic

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

controls and predictability of carbonate facies architecture in a lower jurassic three dimensional barrier shoal complex djebel bou dahar high atlas morocco spatial information on lithofacies from outcrops is paramount for understanding the internal dynamics external controls and degree of predictability of the facies architecture of shallow water carbonate platform tops to quantify the spatial distribution and vertical stacking of lithofacies within an outer platform shoal barrier complex integrated facies analysis and digital field technologies have been applied to a high relief carbonate platform exposed in the djebel bou dahar lower jurassic high atlas morocco the outer platform is characterized by subtidal cross bedded coarse grainstone to rudstone grading into supratidal pisoidal packstone rudstone with tepees that together formed a 350 to 420 m wide shoal barrier belt parallel to the margin this belt acted as a topographic high separating a restricted lagoon from the subtidal open marine region low energy tidal flats developed on the protected flank of the barrier facing the lagoon lithofacies patterns were captured quantitatively from outcrop and integrated into a digital outcrop model the outcrop model enabled rapid visualization of field data and efficient extraction of quantitative data such as widths of facies belts in addition the spatial heterogeneity was captured in multiple time slices i e during different phases of cyclic base level fluctuations in general the lateral continuity of lithofacies is highest when relative water depth increased during flooding of the platform top establishing low energy subtidal conditions across the whole platform and when the accommodation space was filled with tidal flat facies heterogeneity increased during deposition of the relief building bar facies that promoted spatial diversification of depositional environments during the initial phases of accommodation space creation cycles commonly are composed of a thin transgressive tidal flat unit followed by coated grain rudstone bar facies lateral to the bar facies pisoidal grainstone beach deposits accumulated these bar and beach deposits were overlain by subtidal lagoonal facies or would grow through the maximum flooding and highstand there the bars either graded into supratidal pisoidal facies with tepees when accommodation space was filled or were capped by subaerial exposure due to a sea level fall modified embedded markov analysis was used to test the presence of common ordering in vertical lithofacies stacking in a stationary interval constant depositional mode analysis of individual sections did not reveal any ordering which may be related to the limited thickness of these sections composite sections however rejected the null hypothesis of randomness the addition of stratigraphically significant information to the markov analysis such as exposure surfaces and lateral dimensions of facies bodies strengthens the verdict of unambiguous preferential ordering through careful quantitative reconstruction of stratal geometry and facies relationships in fully integrated digital outcrop models accurate depositional models could be established that enhanced the predictability of carbonate sediment accumulation 2009 the authors journal compilation 2009 international association of sedimentologists

ice age at the middle late jurassic transition a detailed record of sea surface temperatures in the northern hemisphere based on migration of marine invertebrate fauna ammonites and isotopic thermometry 18o values of shark tooth enamel indicates a severe cooling at the middle late jurassic transition mljt about 160 ma ago the magnitude of refrigeration 1 3 c for lower middle latitudes and its coincidence in time with an abrupt global scale fall of sea level documented through sequence stratigraphy are both suggestive of continental ice formation at this time ice sheets may have developed over the high latitude mountainous regions of far east russia the drastic cooling just post dated the middle late callovian widespread deposition of organic rich marine sediments e g northwestern europe central atlantic and arabian peninsula this thermal deterioration can thus be ascribed to a downdraw in atmospheric co2 via enhanced organic carbon burial which acted as a negative feedback effect i e the inverse greenhouse effect the glacial episode of the mljt climaxed in the late callovian lasted about 2 6 myr and had a pronounced asymmetrical pattern composed of an abrupt 0 8 myr temperature fall opposed to a long term 1 8 myr stepwise recovery the glacial conditions at the mljt reveal that atmospheric co2 levels could have dropped temporarily to values lower than 500 ppmv during mesozoic times

geodynamic control on carbonate diagenesis petrographic and isotopic investigation of the upper jurassic formations of the paris basin france abstract the oxfordian and kimmeridgian carbonates of the eastern edge of the paris basin display poor reservoir properties stable isotope investigation of these non recrystallized cements through both microdrilling sampling and in situ sims secondary ion mass spectrometry analysis shows that they originated from slightly buffered meteoric fluids 3 smow to 8 smow flowing through the malm carbonate aquifers of the eastern edge of the paris basin after a review of the post upper jurassic history of the paris basin it appears that meteoric water supplies leading to such cementations were associated with the evolution of the basin s geodynamic setting and notably with the lcu late cimmerian unconformity major event which corresponds to the uplift of the london brabant massif denudation of the oxfordian and kimmeridgian carbonates on the southern flank of the london brabant massif to the north of the study area then lead to lateral recharging of the associated aquifers with meteoric fluids this scenario is similar to the one proposed to explain cementations of the jurassic carbonates in the wessex weald basins which emphasizes the main role played by the cretaceous unconformities over carbonate diagenesis at the scale of the northwestern tethys margin

sea water circulation on an oolite dominated carbonate system in an epeiric sea middle jurassic switzerland the middle jurassic burgundy carbonate platform occupied a central part of the central european epeiric sea during the middle jurassic the facies architecture of the oolitic calcarenite bodies was affected by tidal currents on the platform and relative sea level changes the 13c values of inorganic carbonates sampled in biostratigraphic defined intervals do not match very well between closely spaced sections and hence are of restricted use for stratigraphic purposes it appears that the platform interior might have been decoupled from the global carbon pool although deposited in a rapidly accumulating setting the recorded isotope signatures might be affected by some local stratigraphic gaps nonetheless the carbon isotope data imply lateral changes of the platform waters these appear to be related to the position on the platform and to the sediment dispersal pattern as evidenced by clay minerals adjacent to the eastern margin of the platform detrital chlorite and illite occur in considerable proportions both ascribed to a boreal source to the east and the north east in contrast smectite rich mixed layer clay mineral content increases significantly towards the platform interior pointing to a delivery from the north west all these data are suggestive of an overall clockwise current pattern in the central european epeiric sea during the middle jurassic

the ponto caspian basin as a final trap for southeastern scandinavian ice sheet meltwater this paper provides new data on the evolution of the caspian sea and black sea from the last glacial maximum until ca 12 cal kyr bp we present new analyses clay mineralogy grain size nd isotopes and pollen applied to sediments from the river terraces in the lower volga from the middle caspian sea and from the western part of the black sea the results show that during the last deglaciation the ponto caspian basin collected meltwater and fine grained sediment from the southern margin of the scandinavian ice sheet sis via the dniepr and volga rivers it induced the deposition of characteristic red brownish chocolate coloured illite rich sediments red layers in the black sea and chocolate clays in the caspian sea that originated from the baltic shield area according to nd data this general evolution common to both seas was nevertheless differentiated over time due to the specificities of their catchment areas and due to the movement of the southern margin of the sis our results indicate that in the eastern part of the east european plain the meltwater from the sis margin supplied the caspian sea during the deglaciation until 13 8 cal kyr bp and possibly from the lgm that led to the early khvalynian transgressive stage s and chocolate clays deposition in the now emerged northern flat part of the caspian sea river terraces in the modern lower volga and in its middle basin in the western part of the east european plain our results confirm the release of meltwater from the sis margin into the black sea that occurred between 17 2 and 15 7 cal kyr bp as previously proposed indeed recent findings concerning the evolution of the southern margin of the sis and the black sea show that during the last deglaciation occurred a westward release of meltwater into the north atlantic between ca 20 and 16 7 cal kyr bp and a southward one into the black sea between 17 2 and 15 7 cal kyr bp after the red layers chocolate clays deposition in both seas and until 12 cal kyr bp smectite became the dominant clay mineral the east european plain is clearly identified as the source for smectite in the caspian sea sediments in the black sea smectite originated either from the east european plain or from the danube river catchment previous studies consider smectite as being only of anatolian origin however our results highlight both the european source for smectite and the impact of this source on the depositional environment of the black sea during considered period

carbonate systems along nutrient and temperature gradients some sedimentological and geochemical constraints research over the past several decades has clearly demonstrated that changes in the ocean environment have had major impacts on carbonate systems changes in climate ocean circulation and seafloor spreading rates have influenced temperature and seawater chemistry including carbonate saturation state and nutrient availability and thereby have determined boundary conditions for the biota that form carbonate platforms in turn the biota determine accumulation rates and facies zonations thus controlling platform geometry and facies dynamics in the first section of this paper we examine how nutrient availability influences carbonate facies associations we first discuss the role of temperature and nutrient gradients in the modern ocean and their influence on biotic associations then we discuss how carbonate sedimentation can be characterized along nutrient gradients in the second section we review proxies currently used to reconstruct paleoproductivity in open ocean environments and discuss their applicability to neritic carbonate systems we highlight the variety of existing proxies and their limitations and suggest that multiple lines of evidence are needed for valid interpretations our short review discusses sedimentological biogenic and geochemical proxies that can be used to reconstruct past nutrient fluxes and to constrain paleoceanographic controls over the distribution of carbonate associations however it also reveals that more data and case studies are needed that integrate shallow and deep water carbonate sequences and elucidate the links between temperature vs nutrient supplies changes and facies in ancient carbonate sequences

sequence stratigraphy and tectonosedimentary history of the upper jurassic of the eastern paris basin lower and middle oxfordian northeastern france in the present study the difficulty which lies in the identification of sea level fall discontinuities in deep depositional environments led the authors to use the transgressive surfaces i e the most noticeable surfaces in the present case to determine depositional cycles four 3rd order lower and middle oxfordian cycles were identified s1 s2 s3 and s4 in the eastern paris basin these four cycles can be organised into two lower frequency cycles so i and so ii which comprise the s1 s2 and the s3 s4 cycles respectively during the time intervals of the s1 s2 and s3 cycles sedimentation occurred along a southward dipping carbonate siliciclastic ramp prograding from the northern ardennes area the s4 cycle shows the development of a reefal distally steepened ramp which subsequently evolved into a flat topped platform as a result of the compensation infill of the available accommodation space by the carbonate production during a climatic warming in this case reef growth isopach and facies maps suggest synsedimentary activities of hercynian faults coevals with the floodings of the so i and so ii cycles one of these events generated a diachronism of the maximum flooding plicatilis zone during the so ii cycle between the northwestern and southeastern parts of the studied area the depositional patterns found in the eastern paris basin and the swiss jura show great similarities for the early middle oxfordian both regions were probably connected and recorded the same tectonosedimentary evolution in contrast a tectonic control certainly generated differences between the sequence stratigraphic framework of the eastern paris basin and the eustatic chart

sequence development in an isolated carbonate platform lower jurassic djebel bou dahar high atlas morocco influence of tectonics eustacy and carbonate production six sequences each with a distinct shape stratal anatomy bounding surfaces lithofacies composition and stacking patterns were identified in the djebel bou dahar isolated carbonate platform which developed in a half graben in the high atlas marine rift basin during the early jurassic sequences are believed to have a complex multi process origin as the result of tectonic processes regional subsidence and fault block rotation overprinting the eustatic signal in addition changing carbonate producers with shifting centres of deposition and relative accumulation potential influenced the filling and anatomy of the accommodation space that had been created by the hybrid tectonic and eustatic processes sequences i and ii are tabular in shape and interpreted to primarily reflect the combined processes of uniform tectonic subsidence and eustacy which resulted in a ramp to shelf carbonate system with lagoon and tidal flat lithofacies onset of a rifting episode around the base of the lotharingian and fault block rotation were responsible for the development of the angular unconformity with the underlying sequence ii and the progressive development of a shallow water isolated platform and the wedge shaped depositional sequences iii to vi during the lotharingian and pliensbachian concurrent variations in palaeoceanographic conditions and in the carbonate factory caused a shift towards a flat topped platform geometry with high energy coated grains and sub photic sponge microbial deposition around the margin the aggradational to retrogradational character of sequences iii iv and vi is inferred to be a result of the combined effect of in situ carbonate production coupled with high rates of creation of accommodation space in the hanging wall environmental effects on carbonate production were the most probable cause for drowning of the djebel bou dahar platform during the toarcian but also influenced the filling and geometry of sequences iv to vi this study suggests that the commonly accepted model of pulse driven sequence development in half grabens may not be fully applicable for the djebel bou dahar where a more continuous rotation at sequence scale associated with subsidence pulses of the djebel bou dahar block seems to have interacted with eustacy and carbonate production to generate sequences continuous rotation is suggested by the presence of regular patterns of diverging strata and numerous minor exposure surfaces in lagoonal deposits of sequences v and vi in addition this study demonstrates that eustacy and variations in the carbonate factory might be as significant as tectonics in sequence development and platform drowning in carbonate platforms within rift basins this observation could imply that the effects of eustacy and the carbonate factory might not have been correctly recognized in other similar carbonate platforms due to a tectonic biased interpretation

proximal distal facies relationships and sedimentary processes in a storm dominated carbonate ramp kimmeridgian northwest of the iberian ranges spain abstract facies analysis of the upper kimmeridgian rocks in the outcrops located near ricla zaragoza province northeast spain and the integration of the resultant data in a broader context the northern part of the iberian basin has produced two general models showing the facies distribution and the processes that controlled the sedimentation in the kimmeridgian carbonate ramp using these two models the transition from shallow to relatively deep environments of the carbonate ramp is examined in detail model 1 corresponds to the development of a mixed carbonate siliciclastic ramp during a slow rise and stillstand of sea level sequence 1 hst whereas model 2 represents the growth of a pure carbonate ramp during a rapid rise of sea level sequence 2 tst carbonate production was higher in the shallow ramp domains coral reefs and oolitic shoals in model 1 and reefs in model 2 than in deeper domains where there is no indication of significant pelagic or benthic production the activity of unidirectional return flows induced by winter storms and hurricanes played an important role in the redistribution of the sediment across the ramp generating different coarse grained deposits in the inner and mid ramp settings dunes lower scale bedforms and tempestites occur in model 1 and storm lobes bars and tempestites in model 2 moreover a significant bulk of the carbonate mud produced in shallow areas would eventually be resedimented in the outer ramp as suspended load in the density currents stillstand of sea level in model 1 involved a rapid progradation of the inner and proximal mid ramp carbonate and siliciclastic facies the rapid relative sea level rise of model 2 is determined by the dominance of the carbonate facies and by the presence of aggradational geometries in the transitional area between shallow and deep ramp domains the presence of relatively thick sections in the outer ramp settings instead of condensed sections as observed in model 1 during times of sea level rise model 2 can mainly be explained by the increase of the shallow production in the reef dominated areas

sequential and climatic framework of the growth and demise of a carbonate platform implications for the peritidal cycles late jurassic north eastern france the middle oxfordian of the eastern paris basin constitutes a remarkable example of the growth and demise of a carbonate platform fischer plots sedimentary and diagenetic features allow the identification of four depositional cycles s5 to s8 in the transversarium zone they are inserted in a lower frequency cycle of increased decreased accommodation space soiii the long term period of accommodation creation occurred during the older s5 and s6 cycles the maximum accommodation zone being located in the lower part of the s6 cycle this high accommodation period was tectonically controlled and was coeval with local distensive activity of a hercynian fault a major minimum accommodation zone exists during the s8 cycle at that time the platform was isolated and presented both a windward and a leeward margin the growth of the platform was favoured by a warm and arid climate oligotrophic conditions and reduced siliciclastic input during a highstand in relative sea level these palaeoenvironmental features favoured the proliferation of phototrophic organisms producing carbonate material the death of the platform was generated by a reduction in the carbonate production surface during a lowstand in relative sea level and by the appearance of mesotrophic conditions induced by the increase in siliciclastic inputs at the beginning of a period with a cooler and more humid climate in the eastern paris basin during the middle oxfordian the parasequences are ordered and present greenhouse characteristics in contrast at the beginning of the s8 cycle the randomness in the thickness of contiguous parasequences increased decreased carbonate production during the lowstand caused by a transition from photozoan to heterozoan benthic communities certainly favoured this randomness and the appearance of catch down parasequences

deglaciation of fennoscandia abstract to provide a new reconstruction of the deglaciation of the fennoscandian ice sheet in the form of calendar year time slices which are particularly useful for ice sheet modelling we have compiled and synthesized published geomorphological data for eskers ice marginal formations lineations marginal meltwater channels striae ice dammed lakes and geochronological data from radiocarbon varve optically stimulated luminescence and cosmogenic nuclide dating this is summarized as a deglaciation map of the fennoscandian ice sheet with isochrons marking every 1000 years between 22 and 13 cal kyr bp and every hundred years between 11 6 and final ice decay after 9 7 cal kyr bp deglaciation patterns vary across the fennoscandian ice sheet domain reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins for example the ice sheet margin in the high precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice marginal deposits in many fjords and coastal valleys retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern sweden and rapid retreat of the calving ice margin in the baltic basin our reconstruction is consistent with much of the published research however the synthesis of a large amount of existing and new data support refined reconstructions in some areas for example the lgm extent of the ice sheet in northwestern russia was located far east and it occurred at a later time than the rest of the ice sheet at around 17 15 cal kyr bp we also propose a slightly different chronology of moraine formation over southern sweden based on improved correlations of moraine segments using new lidar data and tying the timing of moraine formation to greenland ice core cold stages retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet with the lowest rates on the high elevation and maritime norwegian margin retreat rates compared to the climatic information provided by the greenland ice core record show a general correspondence between retreat rate and climatic forcing although a close match between retreat rate and climate is unlikely because of other controls such as topography and marine versus terrestrial margins overall the time slice reconstructions of fennoscandian ice sheet deglaciation from 22 to 9 7 cal kyr bp provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the fennoscandian ice sheet and are an important resource for testing and refining ice sheet models

paleoclimatic control of biogeographic and sedimentary events in tethyan and peri tethyan areas during the oxfordian late jurassic abstract the paleobiogeographical distribution of oxfordian ammonites and coral reefs in northern and central europe the mediterranean area north and east africa and the middle east and central asia is compared with the distribution in time and space of the most important lithofacies interest in the oxfordian is focused on changes in facies and in biogeographical patterns that can be interpreted as the results of climatic events paleotemperature trends inferred from oxygen isotopes and paleoclimatic simulations are tested against fossil and facies data a late callovian early oxfordian crisis in carbonate production is indicated by the widespread absence of lower oxfordian reefal formations there is a gap hiatus in deposition on epicontinental platforms with middle oxfordian deposits resting paraconformably on upper callovian while shales accumulated in adjacent intracratonic basins simultaneously in mediterranean tethys radiolarites accumulated in deep troughs while rosso ammonitico facies formed on pelagic swells however deposition on swells was also discontinuous with numerous gaps hiatuses and sequences that are much reduced in thickness middle callovian deposits are generally overlain by middle oxfordian limestones the dearth of carbonates is consistent with a cooling event lasting about 1 my by the middle oxfordian a warming leading to greenhouse type conditions is suggested on the basis of both biogeographical mostly coral reef distribution and geochemical data carbonates spread onto an extensive european platform while radiolarites reached a maximum development in the mediterranean tethys two distinct latitudinal belts with seemingly different accumulation regimes are therefore inferred similar latitudinal belts were also present in the late oxfordian when carbonates were widespread the distribution of reefal facies in the late oxfordian early kimmeridgian fits relatively well with gcms simulations that imply low rainfall in the tethyan mediterranean area and slightly higher precipitation in central and northern europe local salinity variations reflecting more arid or humid conditions may bias the paleotemperature signal inferred from 18o values biogeographical and facies distributions combined with 18o values unravel the ambiguity and support a late callovian early oxfordian cooling followed by warming in the later oxfordian

gold mineralisation in the essakane goldfield in burkina faso west african craton abstract the west african craton is known for its structurally hosted au deposits in ghana burkina faso cote d ivoire mali and niger the essakane goldfield in northeast burkina faso has produced 1 606 000 oz of gold since 2010 from the essakane main zone the essakane goldfield is made up of several exploration and artisanal sites that include essakane main zone gossey falagountou sokadie tin zoubratan essakane north and south korizena bom kodjele tin taradat tassiri gaigou and takabangou gold mineralisation in sheeted and stockworks quartz carbonate and tourmaline veins occurs with pyrite arsenopyrite and traces of pyrrhotite galena and hematite it is hosted in sheared folded and contact metamorphosed volcanic volcanoclastic and sedimentary birimian supergroup sequences the maximum age of gold mineralisation in the essakane goldfield is syn deformational and formed during the eburnean orogeny d2 at 2130 1980 ma

palaeoglaciology of an ice sheet through a glacial cycle the european ice sheet through the weichselian abstract satellite images provide unique means of identifying large scale flow generated lineations produced by former ice sheets they can be interpreted to reconstruct the major elements which make up the integrated large scale structure of ice sheets ice divides ice streams interstream ridges ice shelves calving bays the evolving palaeoglaciological structure of the european ice sheet during its decay from the last glacial maximum lgm is reconstructed by reference to these components and in the context of a new map showing isochrons of retreat during the retreat phase in particular the time dependent dynamic evolution of the ice sheet and the pattern of ice stream development are reconstructed crossing lineations are widespread the older ones are suggested to have formed during molten bed phases of ice sheet growth and preserved by frozen bed conditions during the glacial maximum particularly in areas which lay during deglaciation beneath ice divides and inter ice stream ridges both areas of slow flow and possibly frozen bed conditions four phases of growth a1 to a4 and five phases of decay r1 to r5 are used to describe the major climatically and dynamically determined stages in the evolution of the ice sheet through the last glacial cycle the growth and decay patterns are quite different and associated with major shifts in the ice divide reflecting growth from the fennoscandian mountains and decay away from marine influenced margins these patterns were determined by the locations of nucleation areas spatial patterns of climate and calving at marine margins the prevalence of streaming within the retreating ice sheet suggests that the mean elevation of the ice sheet was lower than predicted from glaciological models which do not include streaming and that this might reconcile glaciological models and earth rheology models which infer paleao ice sheet thickness by inverting sea level data

glaciers in the polar urals russia were not much larger during the last global glacial maximum than today abstract 10 be exposure dates from boulders indicate that the chernov moraines located only 1 km beyond the chernov glacier in the polar urals russia were formed during the time of the last global glacial maximum lgm six samples from large boulders on the moraine yielded a mean age of 21 5 2 3 std error kyr the distinct semicircular usa moraine is located beyond the western flank of the urals boulders in the valley between the chernov and usa moraines yielded some spread in 10 be ages but four out of seven yielded ages 50 60 kyr we conclude that the usa and chernov moraines represent the maximum glacier extent during marine isotope stages mis 4 and 2 respectively the exceptionally small extent of the lgm glacier is explained with a dry lgm climate but also with the fact that present day cirque glaciers in the polar urals are extremely favoured by topographical factors such as leeward accumulation and shadowing mountain walls advantages which decrease when the glaciers grow

160 m y record of marine sedimentary phosphorus burial coupling of climate and continental weathering under greenhouse and icehouse conditions a compilation of all meaningful phosphate data published in the proceedings of the deep sea drilling project and the ocean drilling program is used here for the extraction of a 160 m y marine burial record of bulk phosphorus all sediment types 5648 measurements and a 100 m y marine burial record of biogenic phosphorus pelagic biogenic sediment types 1754 data these records serve as estimates for total and dissolved bioavailable phosphorus flux rates which in turn are highly dependent on total and chemical continental weathering rates respectively the similarity of both records indicates that in the past 100 m y changes in total weathering rates may have been tracked by changes in chemical weathering rates prior to 32 ma phosphorus burial and long term sea level change are positively correlated from 32 ma to the present this correlation is inverse this points to a fundamental change in feedback mechanisms between continental weathering phosphorus and climate which was probably linked to the onset of major glaciation

δ18o values of coexisting brachiopods and fish temperature differences and estimates of paleo water depths to estimate vertical thermal gradients and paleo water depths to marine platforms we present a new method based on the difference between 18 o values of contemporaneous brachiopod carbonate and fish phosphate present day marine fauna of well known ecology from the surface to the sea floor record isotopic temperatures that agree with measured temperatures we predict distributions of isotopic data that result from sampling strategy basin morphology and fauna ecology and discuss limitations application of the method to the jurassic paris london basin gives vertical thermal variations of up to 14 c associated with depths varying from a few meters to 170 30 m the estimated depths are minimum values and are greater than those estimated from sedimentological criteria for this ancient epicontinental sea

extinction survival and recovery of corals from the triassic to middle jurassic time recognizing extinction events and determining their cause at the triassic jurassic t j transition and near the pliensbachian toarcian lower jurassic boundary is a field of growing interest we provide arguments for these events through a literature based new evaluation of coral diversity from triassic to dogger and a new palaeobiogeographical map the t j extinction of corals is clearly related to the breakdown of reef environments origination curves show that hettangian the lowest jurassic stage was not only a survival phase but already rather a recovery phase post extinction evolution of reefs and their survival only in the northernmost margin of the tethys support the hothouse hypothesis for the t j extinction event during pliensbachian many new taxa appear but mostly solitary corals not really framebuilders many of these taxa do not occur anymore during the following stages the new increase in diversity is related to the development of bajocian middle jurassic reefs

a facies model for internalites internal wave deposits on a gently sloping carbonate ramp upper jurassic ricla ne spain abstract internal waves are waves that propagate along the pycnocline the interface between two density stratified fluids even though internal waves are ubiquitous in oceans and lakes their impact in the sedimentary record has remained largely unrecognized internal waves can remobilize the sediment from the depth at which the internal waves break onto the sea floor in shelf or ramp settings internal wave deposits internalites have to be distinguished from tempestites while in slope and deeper settings internalites require distinction from turbidites the upper kimmeridgian carbonate ramp succession cropping out near ricla ne spain provides some key evidence to differentiate the depositional processes induced by breaking internal waves from those related to surface storm waves sandy oolitic grainstone eventites previously interpreted as tempestites contain evidence of reworking by turbulent events related to breaking internal waves underlying rationale are 1 they occur in distal mid ramp position detached from the coeval shallow water successions 2 they do not have the characteristic coarsening and thickening upward trend of storm deposits 3 they gradually thin out to disappear both up dip and down dip interbedded with mid ramp lime mudstones and 4 they show little or no erosion towards the shallower areas a facies model for internalites produced by two sediment populations sand and mud on a gently sloping carbonate ramp is proposed the individual internalites occurring at ricla include several architectural elements sequentially organized in dip direction which can be related to the flows associated with breaking internal waves erosion in the breaker zone swash run up and tractive backwash flow individual internalites stack with down and up slope shingling configuration in dm thick packages thought to reflect the up slope and down slope migration of the breaker zone in turn related to depth variations of the palaeo pycnocline packages occur in dm to m thick clusters suggested to reflect changes in sediment supply and or variations in water stratification affecting the energy of internal waves

perturbation of the carbon cycle at the middle late jurassic transition geological and geochemical evidence a compilation of new and published stratigraphic paleontological and geochemical data is used to detect the reciprocal influences of carbon cycling and global environmental changes in the jurassic a major perturbation of the surface carbon cycling accompanied by pronounced climate and sea level fluctuations waxing and waning of continental ice affected earth history around the middle late jurassic transition mljt we establish the respective timing of changes of carbonate and organic matter sedimentation and global fluctuations of sea surface temperatures paleobiogeography and o isotope paleothermometry and sea level sequence stratigraphy so that causative mechanisms and feedback effects can be considered it is apparent that the global sea level rise and warming initiated in the late bathonian led to a constriction of carbonate platforms to low latitudes and enhanced marine organic deposition sea level and temperature optima were achieved several million years later during the middle callovian a detailed record of sea surface temperatures in the northern hemisphere based on migration of marine fauna and isotopic thermometry indicates that a drastic climatic decline set in during the early late callovian just post dating the increased capture of organic matter by marine sediments this decline in temperature is interpreted in terms of an inverse greenhouse effect triggered by drawdown of co 2 consequent upon excess carbon burial the magnitude of refrigeration and its coincidence in time with an abrupt global scale fall of sea level are both suggestive of continental ice formation at this time carbonate sedimentation was jeopardized at the mljt as a result of both global cooling and presumed p c o 2 lowering and resumed abruptly during the middle oxfordian by spreading again over mid latitude zones salient conclusions are that 1 the pattern of excess carbon burial coincident with elevated temperature but followed by climatic deterioration supports the general hypothesis that a major control on mesozoic climate was the abundance of atmospheric co 2 2 significant masses of continental ice may have formed during this part of the jurassic and correlatively high co 2 levels were certainly not sustained throughout this period 3 the global carbonate sedimentation budget correlated with the surface temperature and sea level but the latitudinal spreading of type tropical carbonates was not simply related to the thermal status of seawaters 4 on a global scale the c o r g and c i n o r g burial rates were coupled apparently through the correlation existing between the co 2 level and surface temperature

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

transgressive regressive cycles and jurassic palaeogeography of northeast iberia abstract a correlation and sequence stratigraphy study of jurassic successions has been carried out in the main sedimentary basins of northeast iberia i e asturias basque cantabrian and iberian basins based on the identification of transgressive regressive cycles the development and palaeogeographic evolution of the epicontinental carbonate platforms of northeast iberia were largely controlled by major tectonic activity at three main intervals at the beginning of the jurassic in the lower middle jurassic transition and during the uppermost jurassic respectively during early jurassic times northeast iberia was the site of a single and large carbonate ramp opened to the north this carbonate ramp suffered a progressive drowning evolving from an inner to hemipelagic ramp systems with the local development of suboxic environments in the deepest areas located to the north during the middle jurassic different open carbonate platforms were formed including the development of swells in intermediate areas during the upper jurassic the outer ramp areas were progressively moving to the east iberian basin and the ammonite faunas showing a markedly tethyan affinity thereafter three first order t r cycles bounded by major discontinuities associated with significant time gaps are identified they extend respectively from the latest rhaetian to the early aalenian from the middle aalenian to the early oxfordian and from the early oxfordian to the late berriasian major transgressive peaks occurred at the middle toarcian bifrons zone at the late bajocian upper niortense and garantiana zones and at the mid kimmeridgian divisum zone each of the first order cycles includes four second order t r cycles cycles 1 1 1 4 are identified in the northern basins cycles 2 1 2 4 display some differences in age of transgressive peaks from one basin to another cycles 3 1 3 4 are mainly identified in the iberian basin the correlation with other separated boreal and thethysian basins demonstrates that the number and age of t r cycles varies from one basin to another and are mainly controlled by the local or regional tectonic development the transgressive peaks may reflect episodes of eustatic rise during the jurassic however their different age from one basin to another is explained by different subsidence evolution

modeling evidences for global warming arctic seawater freshening and sluggish oceanic circulation during the early toarcian anoxic event 1 the paleoecological disturbances recorded during the early toarcian warming event 183 myr ago including marine anoxia sea level rise seawater acidification carbonate production crisis and species extinctions are often regarded as past examples of earth s possible responses to the rapid emergence of super greenhouse conditions however physical mechanisms explaining both the global and local expressions of paleoenvironmental events are still highly debated here we analyze the paleoclimatic and paleoceanographic consequences of increases in atmospheric pco2 levels at a multiscale resolution using a fully coupled ocean atmosphere model foam we show that in association with stronger high latitude precipitation rates and enhanced continental runoff the demise of polar sea ice due to the global warming event involved a regional freshening of arctic surface seawaters these disturbances lead to progressive slowdowns of the global oceanic circulation accountable for widespread ocean stratification and bottom anoxia processes in deep oceanic settings and epicontinental basins in agreement with very negative oxygen isotope values measured on fossil shells from the nw tethys our simulations also show that recurrent discharges of brackish and nutrient rich arctic surface waters through the viking corridor could have led to both vertical and geographical gradients in salinity and seawater 18o in the nw tethyan seas locally contrasted conditions in water mass density and rises in productivity rates due to strong nutrient supplies could partly explain the regional severity of the anoxic event in the restricted euro boreal domains as it has been previously suggested and modeled regionally

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

discriminating between tectonic and eustatic controls on the stratigraphic record in the paris basin the quantification of tectonic and eustatic factors in the control of the sedimentary record is one of the main questions in sedimentary basin dynamics we propose two methods allowing i 3d measurement of accommodation at basin scale and ii to decipher between local 10 100 km wavelength and basin scale accommodation the local signal is necessarily of tectonic origin the basin scale signal is of both eustatic and large tectonic origin the measurement of accommodation requires a high resolution time lines calibrated in ages sequence stratigraphy on well logs and biostratigraphy on cores b decompacted lithologies well logs and c palaeodepth palaeoaltitude sedimentology and well logs application of these methods to the intracratonic paris basin during the lias early jurassic suggests a tectonic origin for the 1 5 myr stratigraphic cycles with basin scale flexure during transgressive half cycles and 10 100 km uplift of basement units during regressive half cycles

the last glacial maximum extent of the scandinavian ice sheet in the valday heights western russia evidence from cosmogenic surface exposure dating using 10be abstract recent synoptic studies have summarized the former spatial extent and chronology of the last scandinavian ice sheet sis and provide exceptional compilations of empirical datasets the latter represent the primary source of information for the modelling community to test and develop thermomechanical ice sheet model which are then further embedded into climatic and general circulation models the last glacial maximum lgm extent and chronology of the sis across continental europe were highlighted as being the least well known thus generating the biggest uncertainties in the reconstruction of the ice sheet while early geomorphological studies of the ice sheet marginal belts are numerous and detailed in western russia geochronological data are virtually inexistent in an attempt to fill in this gap we conducted a series of sampling campaigns for surface exposure dating using 10be in the western and northwestern regions of russia we present here the first results from the valday heights where glacial deposits constitute well preserved margins of the sis a total of 16 samples firmly establish the timing of the lgm in the valday heights at 20 1 0 4 ka the valday heights acted as a natural wall for the last maximum advance of the sis during mis2 constraining the eastern flank of the ladoga ilmen lovat ice stream to the west of the hills the valday heights were only overran by previously more extensive glacial advances as suggested by older exposure ages obtain on erratic boulders 31 2 1 4 to 47 1 1 5 ka located east of the lgm limit

three dimensional facies modeling of carbonate sand bodies outcrop analog study in an epicontinental basin triassic southwest germany this article is the first part of an integrated study to characterize the anatomy and geometries of carbonate shoal reservoir bodies in epicontinental settings it is based on outcrop analog data from triassic layer cake carbonates in the south german basin which were deposited along an epicontinental very gently inclined carbonate ramp the database of this study consists of 56 measured sections supplemented by six shallow cores and wireline logs covering an area of 25 by 36 km 15 by 22 mi the potential reservoir bodies consist generally of midramp shoal and shoal fringe facies types which are composed of skeletal and oolitic carbonate packstones and grainstones with significant amounts of porosity the upper muschelkalk is composed of a lower transgressive and an upper regressive interval within these shoal bodies show not only similarities but also major differences in character geometry and distribution these reflect the conditions of an epeiric system which reacts strongly to small changes in accommodation the accommodation seems to be mainly triggered by the interaction of hierarchically organized large medium and small scale relative sea level changes and a subtle paleorelief at the level of medium scale cycles distinct two dimensional cyclicity styles can be differentiated which record the lateral facies distribution along the depositional gradient different styles of medium scale cycles include different types of shoal bodies 1 transgressive crinoidal shoal style shoal bodies mean width 21 km 13 mi mean length 37 km 23 mi mean thickness 4 2 m 13 7 ft with low facies differentiation deposited on top of subtle paleohighs 2 skeletal sheets style thin reservoir sheets mean width 5 1 km 3 1 mi mean length 11 1 km 6 8 mi mean thickness 0 3 m 0 9 ft of reservoir facies on top of the paleohighs 3 regressive oolitic shoal style shoal bodies mean width 14 6 km 9 0 mi mean length 20 8 km 12 9 mi mean thickness 0 69 m 2 2 ft with high facies differentiation on the flanks of paleohighs and 4 low accommodation style patchy and mosaic distribution of shoal bodies mean width 11 2 km 6 9 mi mean length 26 km 16 mi mean thickness 0 69 m 2 2 ft all data were loaded into three dimensional 3 d modeling software to distribute 14 facies types and model the 3 d stratigraphic architecture the resulting facies distribution implies that volume and dimensions of the shoal bodies are mainly controlled by the combination of stratigraphic cycles and a subtle paleorelief which is indicated by overall thickness changes of succession high energy shoal facies types occur only in and around areas with a reduced overall thickness whereas areas with a thicker development are dominated by low energy muddy facies types all observations combined point to the presence of a subtle paleorelief which could be induced by slight differential subsidence of inherited paleotectonic basement blocks on the kilometer to regional scale previous studies suggest simple layer cake stratal patterns however in the full 3 d view the apparent layer cake stratigraphy turned out to be a pseudolayer cake with very gentle 0 01 0 001 dip clinoform geometries these very subtle offlapping pinch out geometries may have been overlooked in epeiric reservoir systems elsewhere

effect of changes in d18o content of the surface ocean on estimated sea surface in past warm climate 1 using a coupled climate model of intermediate complexity including oxygen 18 climber 2 we investigate the evolution of the distribution of surface water 18o composition under warm climate conditions we then determine the impact of changes of the surface water 18o distribution on ocean surface temperatures inferred from calcite oxygen 18 our results show that published temperature reconstructions based on oxygen 18 from calcite are systematically biased by 2 to 4 c in the absence of major oceanic circulation changes and up to 7 c in the presence of major oceanic circulation changes as the bias introduced is shown to vary with latitude our work has major implications on past latitudinal temperature gradient reconstructions based on oxygen 18 measurements

thermal evolution of tethyan surface waters during the middle late jurassic evidence from δ18o values of marine fish teeth 1 oxygen isotope compositions of phosphate from vertebrate tooth enamel were measured to determine the evolution of tropical sea surface 0 owing to limited growth of continental ice during the early middle oxfordian the resulting sea level fall is estimated to be at least 50 m and is compatible with a global regression stage the middle oxfordian thermal minimum is followed by a new warming stage of 3 4 c from the middle to the late oxfordian

carbon cycle perturbation in the middle jurassic and accompanying changes in the terrestrial paleoenvironment abstract carbon isotope analyses of fossil wood from the middle jurassic ravenscar group yorkshire ne england reveal a significant excursion toward light isotopic values 13c change of 3 to 4 at about the aalenian bajocian boundary 174 ma a positive carbon isotopic excursion is also shown for the middle bajocian 170 ma but is less clearly defined these isotopic patterns are very similar to the few published marine carbonate records available for this time in particular one based on belemnites from the hebrides basin nw scotland and others from pelagic limestones in italy the similarity of the terrestrial and marine isotope curves is an indication that the observed isotopic signal is a global phenomenon through parts of the ravenscar group the scarborough formation supplementary data from bulk organic carbon and palynofacies analysis confirm that isotopic curves based on bulk analyses may be strongly influenced by the balance of terrestrial versus marine organic matter present in th

the jurassic succession in west central argentina stratal patterns sequences and paleogeographic evolution abstract jurassic rocks in west central argentina are predominantly marine and marginal marine siliciclastics associated with prominent but volumetrically subordinate carbonates and evaporites facies developments were ruled by paleogeographic persistence within the southern infratropical latitude belt within 40 50 s and by siliciclastic derivation from the patagonian hinterland to the southwest minor volcanic and volcaniclastic supply arrived from the west out of a magmatic belt related to circum pacific convergence timing of the main marine flooding events and general correspondence with the high rank stratal packaging recorded in western north america suggest that global eustasy was also a factor in controlling the local stratigraphic record early jurassic sedimentation occurred within a series of semi isolated depocentres linked to fault bounded triassic troughs the sinemurian toarcian deposits record depocentre expansion and coalescence these trends were coeval with progressively more widespread marine invasions from the northwest and west leading to an elongate marine seaway which connected central patagonia with the pacific domain during the aalenian bajocian the region was subject to a more subdued tectonism and the foreland side of the basin became fringed by an extensive clastic embankment bathonian and early callovian were times when coarse clastics prograded into the basin while the marine embayment shrank as a result of stepwise forced regressions during late callovian to oxfordian globally rising sea level the depocentre witnessed the appearance of cosmopolitan invertebrates and a stratal pattern of basin widening and depositional underbalance that promoted cratonward onlap and inception of widespread carbonate deposition ooidal coralline carbonate development was terminated after a relatively sudden messinian style event that desiccated a large tract of the andean basin and favored massive precipitation of anhydrite in the course of the kimmeridgian the evaporite basin was largely flooded by siliciclastics and turned into a broad and featureless mudflat salina complex linked to a widespread erg and to an ephemeral drainage system by the tithonian at a period of peak oceanic stand marine connection was reinstated and recorded as the most widespread jurassic transgression across the neuquen aconcagua embayment shelfal deposition consisted of molluscs and ooid dominated carbonate terraces that grew in pulses tuned to eustatic fluctuations like in other prolific petroleum provinces around the world the tithonian basinal strata involve widespread euxinic deposits featuring unusually high organic content

calculating the long term displacement rates of a normal fault from the high resolution stratigraphic record early tethyan rifting french alps displacement rates of normal faults deduced from stratigraphic data are often unreliable here we calculate the velocity of motion on a normal fault from the variations in accommodation potential on both sides of the fault within a highresolution time frame established by biostratigraphy and physical stratigraphy our example is the ornon normal fault bounding the early jurassic bourg d oisans basin formed during tethyan rifting we show that motion on the fault was discontinuous when examined at high resolution and over a long time interval during a first interval hettangian to sinemurian arietites bucklandi zone a low rate of displacement 202 423 m myr 1 coeval with diffused extensional deformation throughout the sedimentary basin is observed a second interval of localized deformation early sinemurian caenisites turneri zone is characterized by higher rates of displacement on the fault 1846 m myr 1 our results concur with recent numerical models identifying the main stages of extensional deformation

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

record of the vistula ice lobe advances in the late weichselian glacial sequence in north central poland during the last glacial maximum lgm the vistula ice lobe was one of the key morphological elements at the southern margin of the scandinavian ice sheet in north central poland the area of the vistula ice lobe experienced two ice sheet advances of varied extent the older one is correlated with the leszno brandenburg phase and the younger one is correlated with the poznan frankfurt phase sedimentological research and luminescence dating of the late weichselian glacial sequence in the vistula ice lobe area was conducted a new scenario of the late weichselian ice events in the area is presented the limit of the leszno phase within the vistula ice lobe was much smaller than had been accepted previously and its age is estimated to be about 20 300 bp significant ice sheet retreat was

sequence stratigraphy and bedding rhythms of an outer ramp limestone succession late kimmeridgian northeast spain facies stratal and spectral analyses of an outer ramp lime mudstone succession aguilon north iberian ranges spain are presented in this work the studied succession is late kimmeridgian eudoxus and beckeri zones in age and comprises the transgressive and highstand deposits of a third order depositional sequence a number of higher order sequences bundles and sets of bundles have been identified based on the comparative analysis of the bedding planes the bundles and sets of bundles show a well defined stratal pattern spectral analysis has provided further independent confirmation of the cyclical nature of the bundles and sets of bundles defined from field analysis the bundles have variable thickness from 1 to 2 m and are formed by up to 10 micritic beds they have been related to sea level changes controlled by the orbital precession cycle affecting the shallow productivity area a significant amount of the lime mudstones accumulated in outer ramp settings were derived from resedimentation of the shallow carbonate production areas many of the bundles show a lower interval with a thinning and fining up trend indicating a progressive decrease of the carbonate production and carbonate export during periods of high frequency sea level rise the late transgressive and highstand deposits show sets of bundles groups of five bundles from 5 to 8 m probably related to sea level changes controlled by the short eccentricity cycle the overall thickness and the stacking pattern observed in the sets of bundles are controlled by the long term sea level variation the sets of bundles located in the late transgressive deposits show thinner micritic beds in their lower or middle part the sets of bundles found in the highstand deposits are thinner and show a thickening up and thinning up trend on the studied carbonate ramp during periods of long term sea level rise the overall carbonate production and carbonate export is high although the superposition of the high frequency sea level rises may result in episodic flooding and drowning of the shallow ramp areas during periods of long term early highstand of sea level the overall carbonate production and carbonate export is more reduced but it has maximum peaks during the transgressive and early highstand intervals of the high frequency sea level cycles sedimentation during the long term sea level fall late highstand was scarce and discontinuous in the outer ramp area and resulted in the overall thickness reduction of the sets of bundles d 2003 elsevier science b v all rights reserved

distribution of clay minerals in early jurassic peritethyan seas palaeoclimatic significance inferred from multiproxy comparisons article i nfo a set of published unpublished and new clay mineral data from 60 european and mediterranean localities allows us to test the reliability of clay minerals as palaeoclimatic proxies for the pliensbachian toarcian period early jurassic by reconstructing spatial and temporal variations of detrital fluxes at the ammonite biochronozone resolution in order to discuss their palaeoclimatic meaning a compilation of low latitude belemnite 18 o 13 c mg ca and 87 sr 86 sr values is presented for the first time for the whole pliensbachian toarcian period once diagenetic and authigenic biases have been identified and ruled out kaolinite content variation is considered as a reliable palaeoclimatic proxy for the early jurassic major kaolinite enrichments occur during times of low 18 o high mg ca and increasing 87 sr 86 sr implying warm climates and efficient runoffs during the davoei falciferum and bifrons zones conversely cooler and drier times such as the late pliensbachian or the late toarcian are characterized by low hydrolysis of landmasses and correspond to kaolinite depleted intervals secondary factors as modifications of sources or hydrothermalism may sporadically disturb the palaeoclimatic signal e g in the bakony area during the late pliensbachian in addition a spatial comparison of clay assemblages displays significant kaolinite enrichments towards northern parts of the peritethyan realm probably related to the latitudinal zonation of hydrolyzing conditions this implies enhanced runoffs on northern continental landmasses that reworked kaolinite rich

carbonate production and offshore transport on a late jurassic carbonate ramp kimmeridgian iberian basin ne spain evidence from outcrops and computer modelling

impact of bedrock surface topography on spatial distribution of quaternary sediments and on the flow pattern of late weichselian glaciers on the east european craton russian plain this paper presents the first high quality maps of the bedrock surface topography and the quaternary sediment distribution for the late weichselian glaciation area on the east european craton eec and the reasoning behind the estimated sediment distribution geographic information system gis based three dimensional model of the bedrock surface topography the current digital terrain model dtm and the ice flow pattern of the last glaciation provided the main source data for the analyses and interpretations in the current continental area of the western eec which was covered by the last scandinavian ice sheet sis the bedrock lies overwhelmingly 85 above the contemporary sea level with an average altitude of 54 m above sea level the topography of the bedrock surface is very well reflected in the current topography and an 80 m difference in the ice bed surface altitudes results in the topographic focusing of the ice flow and thus all late weichselian ice streams were accommodated to the depressions in the subglacial surface such depressions are characterised by a thin 10 m layer of sediment with one till bed just 50 m upslope from the bottom of the depressions the thickness of the sediment increases two to threefold and comprises five or more till layers indicating relief enhancement through subsequent glaciations the average calculated thickness of the quaternary deposits in the study area was 49 m and the total volume of sediments was 20 280 km3

millennial scale fluctuations of the european ice sheet at the end of the last glacial and their potential impact on global climate abstract reconstructing northern hemisphere ice sheet oscillations and meltwater routing to the ocean is important to better understand the mechanisms behind abrupt climate changes to date research efforts have mainly focused on the north american laurentide ice sheets lis leaving the potential role of the european ice sheet eis and of the scandinavian ice sheet sis in particular largely unexplored using neodymium isotopes in detrital sediments deposited off the channel river we provide a continuous and well dated record for the evolution of the eis southern margin through the end of the last glacial period and during the deglaciation our results reveal that the evolution of eis margins was accompanied with substantial ice recession especially of the sis and simultaneous release of meltwater to the north atlantic these events occurred both in the course of the eis to its lgm position i e during heinrich stadial hs 3 and hs2 31 29 ka and 26 23 ka respectively and during the deglaciation i e at 22 ka 20 19 ka and from 18 2 0 2 to 16 7 0 2 ka that corresponds to the first part of hs1 the deglaciation was discontinuous in character and similar in timing to that of the southern lis margin with moderate ice sheet retreat from 22 5 0 2 ka in the baltic lowlands as soon as the northern summer insolation increase from 23 ka and an acceleration of the margin retreat thereafter from 20 ka importantly our results show that eis retreat events and release of meltwater to the north atlantic during the deglaciation coincide with amoc destabilisation and interhemispheric climate changes they thus suggest that the eis together with the lis could have played a critical role in the climatic reorganization that accompanied the last deglaciation finally our data suggest that meltwater discharges to the north atlantic produced by large scale recession of continental parts of northern hemisphere ice sheets during hs could have been a possible source for the oceanic perturbations i e amoc shutdown responsible for the marine based ice stream purge cycle or so called he s that punctuate the last glacial period

continuity and facies heterogeneities of shallow carbonate ramp cycles sinemurian lower jurassic north east spain the lateral continuity and facies heterogeneities of metre scale cycles in a greenhouse lower jurassic sinemurian carbonate ramp from the northern iberian basin spain was evaluated from extensive field analysis carried out on a well exposed 12 km long outcrop eleven high frequency continuous cycles and their bounding surfaces are traceable laterally through the entire outcrop however three of these cycles are found to split laterally into discontinuous cycles of more limited distribution up to 3 to 5 km of lateral extent the continuous and discontinuous cycles have a similar field expression in one dimensional logs as a consequence the number of cycles that can be differentiated is variable along the logged sections i e from 11 to 16 cycles have variable facies heterogeneities and sedimentary trends depending on the environment of formation shallowing upward and symmetrical cycles occur in protected lagoon tidal flat areas and in the open marine high energy domain these cycles show significant facies heterogeneities which were controlled mainly by lateral migration of a mosaic of facies over an irregular topography deepening upward and aggradational cycles are generated in low energy sub wave base open marine areas facies are laterally homogeneous reflecting low potential for carbonate accumulation and inability to fill the created accommodation space in this low relief and relatively deep area cycle boundaries are generated by stages of rapid accommodation gain involving the flooding of the carbonate ramp they are more likely to originate from regional tectonic pulses related to the extensional tectonics operating in the northern iberian basin rather than greenhouse low amplitude eustacy discontinuous cycles tend to occur in thickened areas and are interpreted as originating from the infill of wedge shaped accommodation space resulting from differential subsidence i e local tectonic pulses in conclusion where thickness variations occur in extensional settings lateral continuity of cycles should not be expected in less well exposed or in one dimensional sections and in wells it would not be possible to distinguish continuous from discontinuous cycles or to understand such two dimensional heterogeneities identification of unique cycle forming mechanisms or attempting cyclostratigraphic long distance correlation of cycles is unrealistic without a detailed analysis of the architecture of cycles in laterally continuous outcrops

environmental control on granular clinoforms of ancient carbonate shelves the purpose of this paper is to document the influence of depositional environments on shallow water low relief clinoforms from the description of five ancient carbonate platforms the neoproterozoic namibia middle jurassic france lower cretaceous france upper cretaceous oman and miocene turkey these examples have been investigated on the basis of field observations the clinoforms are described with reference to geometric and compositional attributes declivity shape height sedimentary structures sediment fabric and components the results show great variability in stratal geometry declivity and facies distribution 1 depositional profiles vary from exponential to sigmoidal to oblique 2 maximal slope angles range from 3 to 25 most of them being grouped between 10 and 18 3 facies differentiation identified from lateral facies successions along beds and vertical facies successions through beds is pronounced to subtle this study documents linkages between depositional environments and clinoform attributes proximal shallow clinoforms display round edged exponential profiles sediment deposition has resulted from unidirectional currents in the upper convex section and storm generated oscillatory currents in the lower concave part the sediment fabric changes gradually along this type of clinoform there is little vertical facies differentiation through these clinobeds which have formed from a continuous amalgamation of deposits by contrast distal clinoforms shelf break distally steepened ramp settings yield a much broader spectrum of profiles and are generally shorter and steeper sedimentary structures in gravel sized deposits of the upper slope indicate pure traction by unidirectional currents conversely marks of oscillatory flows undular wavy top bounding surfaces of clinobeds are common in the lower slope intercalation of massive fine grained deposits suggests offshore transport of carbonate mud by suspension each distal clinobed represents a single flow event accordingly facies differentiation is weak laterally but may be pronounced through the clinobeds our study suggests that low relief forms of proximal shallow environments which contain coarse grained and photo independently produced debris record hydrodynamic equilibrium profiles whereas the higher relief forms of this setting rather reflect a high differential production rate of carbonate sediment with water depth the carbonate sediment of the distal clinobeds mainly derives from skeletal production by oligophotic and photo independent biota of the middle shelf ramp and upper portion of the clinoforms the contribution by in situ skeletal biota only becomes significant on the lower slope indicating that the distal submerged slopes of carbonate platforms are not organically but hydrodynamically generated our compilation shows that the slope angles of shallow marine low relief clinoforms do not simply correlate to the sediment grain size and fabric in contrast to what has been documented for the high linear slope profiles this difference stems from the depositional settings namely the involved transport mechanisms low relief clinoform accretion seems to be dominantly influenced by wave induced sediment transport in contrast to linear flanks of high relief clinoforms that build to the angle of repose and for which gravity is the primary transport process

late triassic and early jurassic palaeogeography of the world abstract a new version of global and regional palaeogeographic maps is presented for two time intervals these maps depict the plate tectonic configuration palaeoenvironment and lithofacies during the late triassic carnian norian and early jurassic hettangian toarcian time the individual maps illustrate the general conditions present during the maximum marine transgressions of higher frequency cyclicity within the absaroka sequence of sloss during triassic time pangaea began to stretch initiating the rifting and future break up of the supercontinent the continued northward drift of the cimmerian continent corresponded with the progressive closure and consumption of palaeotethys oceanic crust and the opening of the neotethys ocean the most significant late triassic convergent event was the indosinian orogeny occurring as a result of the consolidation of south china and north china blocks also indochina and indonesia were sutured to south china at the same time the qiangtang block approached the eurasian margin the consolidation of the north chinese and amurian blocks left open a large embayment of panthalassa between amuria and laurasia the so called mongol okhotsk ocean active subduction existed along the margin of this ocean dipping cratonwards towards east siberia the last collisional events of the uralian orogeny took place during the triassic and early jurassic time the conclusion of the uralian orogeny was accompanied by uplift of the adjacent areas of eastern europe and western siberia during the early jurassic the palaeotethys ocean was finally closed and the cimmerian continent collided with asia causing the cimmerian orogeny the time around the triassic jurassic boundary marked an important biotic extinction event plate tectonic activity caused palaeogeographic and palaeoclimatic change which may have contributed to the mass extinction from the plate tectonic and palaeogeographic point of view the following events could have influenced the extinction 1 the closure of palaeotethys and assembly of the asian part of pangaea 2 the break up of pangaea in the future central atlantic area and transition from rifting to drifting and 3 the very extensive basaltic volcanism of the central atlantic magmatic province

quaternary glaciations of northern europe this paper presents the outcome of a workshop held in berlin in february 2009 concerned with current research on the glacial history of northern europe including the british isles the methodologies presently used to resolve this topic are outlined particular attention is given to new analytical methods deriving from high resolution remote imaging of glacial terrain both on land and on the sea bed key new stratigraphic sections higher resolution results from conventional geochronological methods like radiocarbon and more recently developed technologies such as luminescence and cosmogenic radionuclide dating the relationships between the results derived from these two methods are discussed in further detail along with possible explanations for these differences an outline of a most likely glacial history of the scandinavian and british and irish ice sheets is presented along with possible links to global climate change as represented by the marine isotope mis record tentative evidence for glaciation is identified in mis 22 16 12 10 8 6 4 and 2 and correlations of phases within the last glaciation are also explored for both the scandinavian and british and irish ice sheets the results show that the character and extent of glaciation in different parts of the region are not synchronous and much more geochronological work is required before regional correlations can be established with confidence

the first estimation of fleuve manche palaeoriver discharge during the last deglaciation evidence for fennoscandian ice sheet meltwater flow in the english channel ca 20 18 ka ago the fleuve manche english channel palaeoriver represents the largest river system that drained the european continent during pleistocene lowstands particularly during the elsterian marine isotope stage 12 and saalian drenthe mis 6 glaciations when extensive ice advances into the north sea area forced the central european rivers to flow southwards to the bay of biscay ne atlantic numerous long piston cores and high resolution acoustic data from the northern bay of biscay have been correlated using a well constrained chronostratigraphical framework and for the first time allow the estimation of the discharge of the fleuve manche palaeoriver at the end of the last glacial period i e weichselian our results discussed in the light of relationships between river loads and drainage area characteristics strongly suggest that the bay of biscay collected sediment laden meltwater from the northern european lowlands and the southern part of the fennoscandian ice sheet at the end of the last glacial period and particularly during the paroxysmal phase of the european deglaciation ca 20 18 ka ago this demonstrates that the fleuve manche drainage area at that time was equivalent to those dating from the major elsterian and saalian drenthe glaciations based on our data we propose a revision of the palaeogeographical and palaeoglaciological evolution of the north sea area while showing that the british and fennoscandian ice sheets entered the north sea basin until ca 18 ka initiating isostatic adjustment of the basin this allowed the north sea fluvial system to flow southwards through the dover strait finally we discuss the fleuve manche freshwater discharge during the maximum european ice sheet retreat ca 18 ka the estimated discharge at this time appears important and sufficiently sustained to possibly contribute to the profound destabilisation of the thermohaline circulation recognised in the north atlantic from ca 18 to 16 ka

depositional environments and iron ooid formation in condensed sections callovian oxfordian south eastern paris basin france carbonate platforms across western europe were superseded at the middle upper jurassic callovian oxfordian boundary either by alternating marl limestone and widespread marl deposits or by condensed sections containing iron ooids the characteristics of marine condensed sections in the south eastern part of the paris basin france and their distribution pattern are examined here and a model of iron ooid formation is developed iron ooids are found from the shoreface to the offshore zone they are most abundant in the median to distal offshore transition zone where they originally formed they also occur commonly albeit often as reworked grains in the proximal offshore zone to which they were transported the contemporaneous thick predominantly marl sections that occur laterally are devoid of iron ooids and were deposited in deeper settings distal offshore zone the iron ooids are composed of goethite typically they have a nucleus made up of a clump of goethite crystals and a laminated cortex three distinctive nanostructures are identified in the cortex laminae i a nanograined crystalline structure typical of primary goethite ii a secondary nanoflaked structure thought to have formed mechanically by reorientation of the goethite crystals and iii a coalesced structure acquired by subsequent diagenetic recrystallization the iron ooids formed successively i by lamina growth when goethite precipitated in the surface layer of the sediment nanograined structure and ii by interruption of growth when the ooids were remobilized by hydrodynamic agents as reflected by the flaked nanostructure iii these two nanostructures were sometimes transformed into a coalesced structure by recrystallization when ooids were buried

middle and late weichselian devensian glaciation history of south western norway north sea and eastern uk data from eastern england scotland the northern north sea and western norway have been compiled in order to outline our current knowledge of the middle and late weichselian glacial history of this region radiometric dates and their geological context from key sites in the region are presented and discussed based on the available information the following conclusions can be made i prior to 39 cal ka and most likely after ca 50 cal ka scotland and southern norway were extensively glaciated most likely the central north sea was not glaciated at this time and grounded ice did not reach the shelf edge ii during the time interval between 29 and 39 ka periods with ameliorated climate including the alesund sandnes and tolsta interstadials alternated with periods of restricted glaciation in scotland and western norway iii between 29 and 25 ka maximum weichselian glaciation of the region occurred with the fennoscandian and british ice sheets coalescing in the central north sea iv decoupling of the ice sheets had occurred at 25 ka with development of a marine embayment in the northern north sea v between 22 and 19 ka glacial ice expanded westwards from scandinavia onto the north sea plateau in the tampen readvance vi the last major expansion of glacial ice in the offshore areas was between 17 5 and 15 5 ka at this time ice expanded in the north western part of the region onto the maloy plateau from norway and across caithness and orkney and to east of shetland from the moray firth the norwegian channel ice stream ncis which drained major parts of the south western fennoscandian ice sheet was active at several occasions between 29 and 18 ka

high resolution sequence stratigraphy of an alluvial fan fan delta environment stratigraphic and geodynamic implications an example from the keuper chaunoy sandstones paris basin abstract facies analysis of the chaunoy formation conducted as the first stage of this study reveals that the corresponding fluvial system essentially involved bedload deposition 2 d and 3 d megaripple migration and debris flow deposition such processes are characteristic of alluvial fan depositional environments these alluvial fan deposits pass laterally eastward into a shallow lacustrine environment in stage 2 of the study electrofacies are defined by well log analysis and then matched with sedimentary facies defined by core analysis electrofacies associations and depositional environments are then inferred directly from well logs on this basis six electrofacies characterizing the main sedimentary facies associations and depositional environments within the chaunoy formation are defined channel lag deposits channel infilling lake or flood plain overflow deposits and paleosols stage 3 involves establishing correlations based on high resolution sequence stratigraphy within these continental deposits the procedure consists in analysing high frequency fluctuations in baselevel defined from sedimentological studies and calibrated on well log signatures the correlations show that the top of the chaunoy formation is diachronous the formation is subdivided here into three stratigraphic units from base to top chaunoy i ii and iii this study shows that the degree of preservation of continental deposits varies with stratigraphic cycle genetic sequences and genetic sequence sets are asymmetrical with the baselevel rise being better preserved than the baselevel fall while for minor cycle deposits may be similarly preserved during baselevel rise and fall the sequence stratigraphy pattern of the genetic sequences and the genetic sequence sets can result from climatic and or tectonic factors but their effects are difficult to distinguish at the scale of the minor chaunoy i cycle or the chaunoy ii cycle preservation is similar during the baselevel rise and fall that implies that the chaunoy minor cycles were influenced by load discharge resulting in greater accommodation space which could result from climatic or tectonic fluctuations the chaunoy formation was deposited as part of a major baselevel rise during the carnian liassic cycle during this cycle the paris basin was generally tilted to the northwest producing the intra marnes irisees superieures truncation which seems to have been induced by large scale wavelength tectonic deformation detailed isopach maps of minor baselevel cycles in chaunoy i with inferred depositional environments are used to define the extent of depositional environments and fault activity during baselevel rise and fall during emplacement of the braided alluvial fan and lacustrine deposits of the chaunoy formation fault activity which was confined to the western part of the basin controlled the preservation potential i e the thickness of the deposits and depositional environment profiles within the chaunoy i and ii cycles the increased thickness of the sandstone deposits to the northeast and the onlap at the top of chaunoy i can be explained by local fault activity and by the general tilting of the basin the chaunoy iii sandstones are confined to the western part of the basin and seem to have been controlled by local factors only

growth and demise of the jurassic carbonate platform in the intracratonic paris basin france interplay of climate change eustasy and tectonics it is usually very difficult to identify and quantify the relative influence of tectonics eustasy and climateon carbonate system evolution from sedimentary records in order to improve our understanding of these mechanisms we have traced for the first time the evolution of the eastern paris basin platform throughout the entire jurassic period this carbonate platform underwent eight successive growth and demise phases with different depositional profiles ranging from ramps to flat topped geometries the eight carbonate growth periods are compared with the standard sea level curves local tectonic regimes and recently published oxygen isotope and or clay mineralogy databases prograding heterozoan facies along ramp profiles mark periods dominated by second order eustatic sea level rise relatively cool sea surface temperatures and mesotrophic and humid conditions hettangian pliensbachian late oxfordian tithonian during these periods variable detrital contents in the sedimentary succession hampered the efficiency of shallow marine carbonate factories higher sea surface temperatures oligotrophic and humid conditions associated with either eustatic sea level rise or very high local subsidence occurred during the early bajocian and the mid oxfordian these seawater properties seem to have favoured the aggradation of scleractinian corals forming dome shaped bioherm buildups an oolitic and lime mud carbonate system deposited during the bathonian second order eustatic sea level fall is characterised by miliolid rich micritic facies on a rimmed ramp under stable cooler and drier conditions the secondorder maximum flooding associated with a sea surface temperature decline and or a seawater eutrophication caused at least five carbonate demise periods i e toarcian earliest late bajocian callovian oxfordian transition earliest late oxfordian and kimmeridgian

correlation of reefal oxfordian episodes and climatic implications in the eastern paris basin france oxfordian reefal episodes of lorraine and burgundy have a long time been considered as contemporaneous biostratigraphic data and sequential evolutions peculiar to each region indicate their structural autonomy during oxfordian times a north south oriented well logging transect shows that during the middle oxfordian a shallow reefal platform developed in lorraine while thin deeper deposits occurred in burgundy in spite of their different ages reefal episodes of middle oxfordian in lorraine and upper oxfordian in burgundy exhibit a broadly similar vertical evolution of coral communities during the late oxfordian the contemporaneous occurrence of a diversified assemblage in the burgundy region a colder coral assemblage characterized by eurytopic genera and the decrease in seawater isotopic temperatures in lorraine can be explained by a shift in trophic conditions a climatic change related to structural rearrangements in this strategic place and a modification of oceanic circulations between the arctic and the tethyan regions

a dominant tectonic signal in high frequency peritidal carbonate cycles a regional analysis of liassic platforms from western tethys abstract meter scale peritidal carbonate cycles are a common feature of the geological record but debate continues about what processes lead to their formation three conceptual models or a combination thereof are commonly invoked to explain cycle formation eustasy tectonics or autocyclicity these three models are tested with a large new dataset from different early jurassic plate margins from western tethys study of seven logged sections from spain italy greece tunisia morocco and gibraltar enables an analysis of the possible roles of local versus regional patterns and controls on cyclicity within a sinemurian time slice cycle types are diverse and include shallowing upward cycles parasequences but also deepening upward and diagenetic cycles high frequency sequences and subtidal cycles numbers of cycles per section and cycle stacking patterns within this time slice vary from section to section statistical tests runs tests time series and bundling all indicate random stacking of cycles within sections and an absence of any bundling of thicknesses or of facies trends assessment of cycle types by their occurrence and stacking patterns indicates little support for either eustasy or autocyclicity being the dominant cycle forming mechanism however the variability in numbers of cycles per section thickness variations of the sections cycle type variability and randomness of stacking patterns all favor a pulsed tectonic control for the creation and filling of accommodation space this conclusion is further supported by evidence that has largely arisen during the course of this study of syndepositional extensional tectonics in the sinemurian on these rifted tethyan margins although tectonics appears to be the dominant control superimposed eustasy and or autocyclic processes cannot be discounted

deglaciation of the eurasian ice sheet complex the eurasian ice sheet complex eisc was the third largest ice mass during the last glacial maximum with a span of over 4500 km and responsible for around 20 m of eustatic sea level lowering whilst recent terrestrial and marine empirical insights have improved understanding of the chronology pattern and rates of retreat of this vast ice sheet a concerted attempt to model the deglaciation of the eisc honouring these new constraints is conspicuously lacking here we apply a first order thermomechanical ice sheet model validated against a diverse suite of empirical data to investigate the retreat of the eisc after 23 ka bp directly extending the work of patton et al 2016 who modelled the build up to its maximum extent retreat of the ice sheet complex was highly asynchronous reflecting contrasting regional sensitivities to climate forcing oceanic influence and internal dynamics most rapid retreat was experienced across the barents sea sector after 17 8 ka bp when this marine based ice sheet disintegrated at a rate of 670 gigatonnes per year gt a 1 through enhanced calving and interior dynamic thinning driven by oceanic atmospheric warming and exacerbated by eustatic sea level rise from 14 9 to 12 9 ka bp the eisc lost on average 750 gt a 1 peaking at rates 3000 gt a 1 roughly equally partitioned between surface melt and dynamic losses and potentially contributing up to 2 5 m to global sea level rise during meltwater pulse 1a independent glacio isostatic modelling constrained by an extensive inventory of relative sea level change corroborates our ice sheet loading history of the barents sea sector subglacial conditions were predominately temperate during deglaciation with over 6000 subglacial lakes predicted along with an extensive subglacial drainage network moreover the maximum eisc and its isostatic footprint had a profound impact on the proglacial hydrological network forming the fleuve manche mega catchment which had an area of 2 5 106 km2 and drained the present day vistula elbe rhine and thames rivers through the seine estuary during the bolling allerod oscillation after c 14 6 ka bp two major proglacial lakes formed in the baltic and white seas buffering meltwater pulses from eastern fennoscandia through to the younger dryas when these massive proglacial freshwater lakes flooded into the north atlantic ocean deglaciation temporarily abated during the younger dryas stadial at 12 9 ka bp when remnant ice across svalbard franz josef land novaya zemlya fennoscandia and scotland experienced a short lived but dynamic re advance the final stage of deglaciation converged on present day ice cover around the scandes mountains and the barents sea by 8 7 ka bp although the phase lagged isostatic recovery still continues today

the last deglaciation of the southeastern sector of the scandinavian ice sheet the scandinavian ice sheet sis was an important component of the global ice sheet system during the last glaciation but the timing of its growth to or retreat from its maximum extent remains poorly known we used 115 cosmogenic beryllium 10 ages and 70 radiocarbon ages to constrain the timing of three substantial ice margin fluctuations of the sis between 25 000 and 12 000 years before the present the age of initial deglaciation indicates that the sis may have contributed to an abrupt rise in global sea level subsequent ice margin fluctuations identify opposite mass balance responses to north atlantic climate change indicating differing ice sheet sensitivities to mean climate state

timing of the late vistulian weichselian glacial phases in poland abstract the lower vistula region in northern poland is a stratotype area for the vistulian weichselian glaciation and during last glacial maximum lgm the southernmost extension of the scandinavian ice sheet occurred in western poland and in eastern germany reinterpretation of the available geochronological data radiocarbon 36 cl and 10 be ages supplied with new field geological evidence mostly for the late vistulian ice sheet limits and movement directions was focused in three key regions in poland during the late middle vistulian there was one or two ice sheet advances in the lower vistula region the late vistulian maximum ice sheet limit in poland was time transgressive and occurred at 24 19 kyrs bp generally the younger to the east ice sheet limits during the leszno phase occurred at 24 cal 10 be 36 cl kyrs the poznan phase ice sheet limit was dated to 19 10 be 36 cl kyrs and the pomeranian phase ice sheet limit about 16 17 10 be 36 cl kyrs every late vistulian glacial phase in poland was preceded by an ice sheet retreat

subglacial sediment proglacial lake level and topographic controls on ice extent and lobe geometries during the last glacial maximum in nw russia abstract investigations in sections along the rivers severnaya dvina and vaga and morphological mapping based on a new digital elevation model and landsat imagery allow for a reinterpretation of the extent of the scandinavian ice sheet during the last glacial maximum lgm the reconstruction provides a much better link between stratigraphical and morphological expression of glaciation than previous proposals most striking is the configuration of long low gradient ice lobes ice streams extending for some 300 400 km up the wide and smooth river valleys their extremely low surface gradients are evidenced by glacial trimlines that formed along the sides of the ice lobes in contact with the gentle valley slopes in the main valleys end moraines marking terminal positions are present whereas drumlins are rare in the peripheral areas of the ice sheet but found in some tributary valleys at somewhat higher elevations large drumlin fields however are found farther up ice the glacial sediment succession is composed of waterlain sediments and tills the sediments provide evidence of distal ice damming glacier overriding and retreat and finally distally glaciolacustrine sedimentation and lake drainage the diamicton unit associated with the lgm shows evidence of basal coupling although more striking is the abundant evidence for ice bed decoupling these include in situ waterlain sediments within tills and clastic sills running along the till substrate contact showing lift off these features indicate that the weight of the glacier lobes was to a large extent carried by pore water pressure in subglacial sediments and that subglacial shear and erosion were moderate thus fast ice flow in the lobes is envisaged the balance between glacier weight and pore water pressure was probably maintained over time by the buoyancy effect of glaciers advancing into proglacial lakes subglacial lakes may have formed by capture of proglacial lakes during glacial advance the combination of low gradient ice and decoupled beds indicate that glacier advance and extent was largely controlled by lake levels and topographic thresholds this is taken to indicate that steeper gradient ice much farther upstream was providing the gravitational push a presumably abrupt change in ice surface profile is supported by the mapped distribution of glacial bedforms the model presented herein potentially has wide applicability for large parts of northern russia as the topographic setting and glacier advance in lakes across fine grained low permeable sediments provide very similar conditions

abrupt drainage cycles of the fennoscandian ice sheet continental ice sheets are a key component of the earth s climate system but their internal dynamics need to be further studied since the last deglaciation the northern eurasian fennoscandian ice sheet fis has been connected to the black sea bs watershed making this basin a suitable location to investigate former ice sheet dynamics here from a core retrieved in the bs we combine the use of neodymium isotopes high resolution elemental analysis and biomarkers to trace changes in sediment provenance and river runoff we reveal cyclic releases of meltwater originating from lake disna a proglacial lake linked to the fis during heinrich stadial 1 regional interactions within the climate lake fis system linked to changes in the availability of subglacial water led to abrupt drainage cycles of the fis into the bs watershed this phenomenon raised the bs water level by 100 m until the sill of the bosphorus strait was reached flooding the vast northwestern bs shelf and deeply affecting the hydrology and circulation of the bs and probably of the marmara and aegean seas

tectonic and eustatic control on a mixed siliciclastic carbonate platform during the late oxfordian kimmeridgian la rochelle platform western france boreal and tethyan realms of western europe present significant sedimentological paleontological and stratigraphic differences the purpose of this study is to constrain regional versus global controls on the dynamics of a sedimentary system located at the interface of these two realms in order to better understand the origin of their differences detailed sedimentological palynofacies and calcareous nannofossil analyses were performed on two sections from the la rochelle platform western france the pas section includes part of the late oxfordian and early kimmeridgian and the rocher d yves section is assigned to the late kimmeridgian they correspond to monotonous marl argillaceous limestone alternations limestones are essentially mudstones with echinoderms bivalves and foraminifera that suggest low energy open marine conditions highly bioclastic and or peloidal deposits occur commonly and show wackestones to wacke pack grainstones textures these deposits indicate frequent high energy events and are interpreted as storm deposits marls dominate in the most proximal depositional environments while calcareous deposits are more important in more distal environments the rocher d yves section is globally more marly than the pas section suggesting a more proximal setting palynofacies are dominated by woody particles suggesting shallow water proximal depositional environments calcareous nannofossils are ascidian spicules coccoliths and schizospheres watznaueria britannica dominate calcareous nannofossil assemblages in the pas section the rocher d yves assemblages are quasi exclusively composed of cyclagelosphaera margerelii and indicate more proximal paleoenvironments than those of the pas section different orders of depositional sequences are defined with sequence boundaries corresponding to the most rapid relative sea level falls they are hierarchically stacked and correlate on the basis of ammonite zones with the sequences of contemporaneous sections from tethyan and boreal realms the stacking pattern of these sequences suggests an orbital control on sedimentation small medium and large scale sequences correspond to precession 20 ky cycles and to 100 ky and 400 ky eccentricity cycles respectively the elementary sequences have durations shorter than 20 ky the kimmeridgian was a period of global sea level rise that ended in the late kimmeridgian more proximal depositional environments in the rocher d yves section late kimmeridgian than in the pas section early kimmeridgian imply a progradation of the la rochelle platform during the kimmeridgian this progradation resulted from a slowdown of the subsidence in the aquitaine basin during the kimmeridgian corresponding to the first steps of atlantic ocean opening high frequency cycles on the la rochelle platform formed in sync with milankovitch orbital cycles while tectonics controlled the formation of the low frequency cycles

the local last glacial maximum of the southern scandinavian ice sheet front cosmogenic nuclide dating of erratics in northern poland abstract this paper presents new results of terrestrial cosmogenic nuclide dating of erratics in northern poland we report the first exposure ages of erratics located on the pre local last glacial maximum and the local last glacial maximum moraines in poland published radiocarbon ages are calibrated and used as a background indicator of the possible time window for the local last glacial maximum the terrestrial cosmogenic nuclide exposure ages presented in this study indicate that 1 exposure ages of erratics located on the pre local last glacial maximum moraines 15 9 1 4 to 101 7 8 5 ka are not clustered around any specific time interval 2 the age of the ice sheet retreat from the local last glacial maximum ice limit in western poland is 20 7 0 8 ka and the probable duration of the local last glacial maximum in western and central poland is between 25 ka and 21 ka 3 the age of the ice sheet retreat from the local last glacial maximum ice limit in eastern poland is 17 3 0 5 ka and the probable duration of the local last glacial maximum in eastern poland is between 22 ka and 18 ka our results show that the local last glacial maximum ice limit in western and central poland is probably 3 ka older than in eastern poland

the origin and timing of multiphase cementation in carbonates impact of regional scale geodynamic events on the middle jurassic limestones diagenesis paris basin france the middle jurassic carbonates of the eastern part of the paris basin display surprisingly low values of porosity and permeability 15 and k 0 5 md the main objective of this study is to determine the causes and timing of the cementation that altered the petrophysical properties of these carbonates thereby destroying their potential as oil reservoirs a fate that did not befall their equivalents in deeper central parts of the paris basin using petrographic and geochemical analyses stable o and c isotopes sr isotopes major elements we identify six calcitic spar stages two dolomite stages and several episodes of fracturing and stylolitization ordered in paragenetic sequence cement quantification shows the predominance of two blocky calcite cement stages 75 of total cementation o and sr isotopes from these calcite cements suggest that the parent fluids resulted either from a mixing of trapped jurassic seawater and meteoric water or from buffered meteoric waters in the geological history of the paris basin major meteoric water inputs were possible during the early cretaceous when the middle jurassic carbonates cropped out at its northern and eastern borders lateral meteoric recharge may have occurred as a result of two separate uplift events late cimmerian unconformity and late aptian unconformity and the related exposures of carbonates to the north of the study area this palaeohydrological circulation brought about a significant reduction of porosity from 40 to 10 through calcite cement precipitation the early cretaceous events are of great importance in the diagenetic evolution of the sedimentary basins bordering the london brabant massif across all of northwestern europe a subsequent dolomite and calcite cementation stage accounts for about 5 of the total cement volumes this late cementation may have been caused by hydrothermal fluids ascending along permeable fractures during the late oligocene extension episode

duration of the early bajocian and the associated δ13c positive excursion based on cyclostratigraphy the early bajocian about 172 ma ago was a period of tectonic changes a global carbon isotope positive excursion and biological diversification of marine invertebrates e g ammonites radiolarians and coccolithophores unfortunately both the duration of the early bajocian and the associated palaeoenvironmental changes are still poorly constrained we propose here an estimate of the duration of this sub stage based on a cyclostratigraphic analysis of the carbonate content from the chaudon norante section french subalpine basin france the chaudon norante succession has been correlated with les dourbes section using greyscale variations to detect possible local hiatuses the duration estimated here for the entire early bajocian is 4 082 ma two intervals were identified in the positive 13 c excursion an increase of carbon isotope values lasting 1 36 ma and climax isotope values lasting for 2 72 ma a cooling at high latitudes and warming at low latitudes may have enhanced the earth s temperature gradient leading to an increase in humidity which in turn triggered ocean eutrophication at the origin of the 13 c positive excursion supplementary material the complete dataset presented in the paper a colour version of the figure 8 and correlation of 13 c excursions between our studied site and contemporaneous sites are available at www geolsoc org uk sup18555

depositional sequences in deep shelf environments a response to sea level changes and shallow platform carbonate productivity oxfordian germany and spain abstract oxfordian deep shelf deposits of southern germany and southern spain are characterized by marl limestone alternations that are stacked into small scale medium scale and large scale depositional sequences the german sections contain autochthonous sponge reefs and associated fragments of microbialites whereas the sections studied in spain display tempestites composed of autochthonous deeper water and allochthonous shallow water particles the facies of the german limestones and marl layers has been analyzed in detail condensed intervals implied by glauconitization of particles abundant cephalopods intense bioturbation and generally more marls are also enriched in sponge reefs and associated particles and in nannofossils limestone rich intervals however contain fewer sponges and fewer nannofossils neither bioerosion of sponge reefs nor nannofossil blooms can thus explain the abundance of carbonate mud that forms the limestones consequently it is suggested that most of the carbonate mud is exported from shallow platform areas where carbonate productivity is high the clay fraction was derived from weathering of massifs in the hinterland the observed depositional sequences can be correlated between the studied sections in germany and spain situated in different paleotectonic and paleoclimatic domains and also between deeper water sections and platform sections this suggests that they formed through allocyclical processes comparision with published time scales implies that the small scale and medium scale sequences formed in tune with the 100 kyr and 400 kyr orbital eccentricity cycles respectively however the number of marl limestone alternations is not always consistent with the expected number of 20 kyr precessional cycles 5 per 100 kyr cycle the large scale sequences reflect long term third order sea level changes the observed marl limestone alternations are interpreted to have formed through cyclically varying export of carbonate mud from the platform towards the deep shelf the variations being controlled by climatically induced high frequency sea level fluctuations enhanced marl deposition on the deep shelf can be related to sea level fall causing exposure of the shallow platform and reducing the area of carbonate production or by rapid sea level rise maximum flooding leading to partial or total drowning of the platform and or to retrogradation of facies belts enhanced carbonate deposition occurs during transgression when large production areas are created on the platform or during late highstands when progradation is forced and carbonate mud export enhanced depending on the long term trend of sea level change on which the high frequency fluctuations are superimposed one high frequency 20 kyr sea level cycle can thus create one or two marl limestone alternations or only marly deposits consequently one 100 kyr eccentricity cycle may be formed of a variable number of marl limestone alternations commonly 2 to 8 the studied deeper water depositional sequences thus are strongly linked to the history of the adjacent shallow carbonate platforms

keuper stratigraphic cycles in the paris basin and comparison with cycles in other peritethyan basins german basin and bresse jura basin abstract high resolution sequence stratigraphy of the keuper paris basin is used to establish correlations between the basin centre evaporite series and the basin margin clastics series the high resolution correlations show stratigraphic cycle geometries the keuper consists of five minor base level cycles whth occur in the upper portion of the scythian carnian major base level cycle and the lower part of the carnian liassic major base level cycle the maximum relative rate of subsidence for the base level fall phase of the scythian carnian major cycle occurs in the eastern part of the paris basin during the base level rise phase of the carnian liassic major cycle the area of highest rate of subsidence shifted westwards and northwards this shift records the first occurrence of an independent paris basin which was no longer merely the western margin of the german basin two phases of tectonic movement influenced evaporite sedimentation and sequence geometries by creating areas of subsidence where halite could accumulate the second within the marnes irisees superieures induced a general westward and northward tilt of the basin concurrent migration of depocentres to the west and north produced an intra marnes irisees superieures truncation comparison of the stratigraphic records of the paris basin and of other triassic peritethyan basins german basin bresse jura basin and south east basin reveals numerous similarities the coastal onlap curve of the german keuper aigner and bachmann 1992 exhibits many similarities with the sequence evolution of the paris basin but the triassic succession is more complete in the german basin and more cycles are observed the major difference between these two basins during the keuper is that the marnes irisees inferieures minor base level cycle does not occur in the german basin in the bresse jura basin the major difference concerns the lettenkohle one minor base level cycle is recorded in the paris basin while no cycle is observed in the bresse jura basin

integrated sequence stratigraphy facies stable isotope and palynofacies analysis in a deeper epicontinental carbonate ramp late jurassic sw germany abstract sequence stratigraphy in deeper water epicontinental carbonates such as in the upper jurassic of southern germany is difficult because the recognition of parasequences sequences and sequence boundaries is impeded by the paucity in diagnostic sedimentological criteria or stratal surfaces using the genetic stratigraphic approach and integrating facies stable isotope c o and palynofacies analysis two types of genetic depositional sequences can be discriminated small scale sequences are stacked into medium scale sequences which may record a 400 kyr milankovitch signal the medium scale sequences were correlated regionally using both gamma ray logs and stable isotope records regional correlations show that the depocentres are controlled by underlying palaeotectonic elements late palaeozoic troughs the rise fall turnarounds of medium scale sequences are marked by negative 18o peaks temperature maxima and reduced absolute palynoclast contents the fall rise turnarounds are marked by positive 18o peaks temperature minima and high absolute palynoclast contents the initiation and termination of sponge microbial mounds show characteristic patterns thrombolitic microbialites form during intervals of 1 reduced input of terrestrial palynomorphs interpreted as an increase in distality 2 decreasing 13c trends interpreted to be related to decreasing nutrient supply and 3 decreasing 18o values interpreted as phases of warming and rising relative sea level in contrast thrombolitic stromatolitic microbialites were found to occur during phases of 1 increasing input of terrestrial palynomorphs interpreted as an increase in proximality 2 increasing 13c values interpreted to reflect increasing terrestrial input and nutrient supply as well as increasing 18o values interpreted as phases of cooling and relative sea level falls isotopic and palynofacies evidence suggests that bioherms were terminated by sudden input of nutrients during relative sea level falls sedimentological criteria were clearly not sufficient to delineate a robust sequence stratigraphic framework

facies and climate environmental changes recorded on a carbonate ramp a sedimentological and geochemical approach on middle jurassic carbonates paris basin france a detailed sedimentological geochemical and mineralogical study is carried out on the early bajocian to early callovian middle jurassic limestones of the paris basin objectives are to document and explain the facies changes in the context of the climate environmental evolution at the nw european scale deposits include 18 lithofacies which are stacked into 10 third order depositional sequences at a greater time scale 4 biosedimentary packages are distinguished by their allochems associations 1 an intracratonic carbonate environment with coral reefs and crinoid rich facies is typical of the early bajocian 2 a major facies change occurred at the early late bajocian transition with a shift from crinoid and coral rich facies to ooid rich facies during the late bajocian a southward dipping ooid ramp with successive progradational trends was emplaced 3 a large lagoon protected by ooid shoals developed during the bathonian in a muddy ramp setting 4 at the bathonian callovian boundary a second major change occurred with the lagoonal facies being superseded by an ooid bioclastic crinoids corals ramp associated with a waning of carbonate productivity retrogradational trend our geochemical study including a compilation of bibliographic data allows us to refine the existing sea surface palaeotemperature pattern a cooling from the latest early bajocian to the late bajocian and a subsequent warming from the earliest callovian to the early middle callovian transition are described using a proxy of sea surface temperatures together with 13c and mineralogical data our new 18o values suggest a palaeo climatic palaeo environmental control of facies in this shallow carbonate ramp environment

spatial and temporal distribution of ooids along a jurassic carbonate ramp amellago outcrop transect high atlas morocco carbonate ramp systems are widespread throughout the geological record but very few areas have seismic scale continuous and structurally undeformed outcrops that allow reliable interpretation of facies distributions and stacking patterns the amellago outcrop shows the detailed depositional and stratigraphic relationships of an ooid dominated ramp system that is almost completely exposed along a dip profile 37 km long and 1000 m thick in the lower to middle jurassic of the southern high atlas morocco ammonite and brachiopod fauna provide excellent biostratigraphic control on small scale stacking patterns at amellago the evolution of depositional environments is evident at different scales of space and time during this period of tectonic quiescence dominated by thermal subsidence an important observation is that the amellago ramp system contains micrite rich ooid free intervals that alternate with ooid rich intervals the ooid rich intervals are mainly in the late transgressive and highstand system tracts whereas the ooid free intervals occur in the early transgressive phase more than 25 such alternations were recorded in high frequency cycles and at the scale of one large cycle at the aalenian bajocian transition these compositional changes and the associated different ramp geometries are interpreted to result from the combined effects of eustatic sea level and climatic changes

patterns of quaternary ice sheet erosion and deposition in fennoscandia and a theoretical framework for explanation it has long been recognised that the formerly glaciated area of fennoscandia shows large spatial differences in thicknesses of quaternary deposits mainly tills and exhibits distinct patterns of glacial scouring and deep linear erosion the reasons for this striking zonation have been elusive and in particular the relative roles of mountain ice sheets mis and full sized fennoscandian ice sheets fis in shaping the landscape surface need clarification on the basis of current advances in our understanding of the climate evolution and basal thermal organisation of ice sheets we perform spatio temporal qualitative modelling of ice sheet extent and migration of erosion and deposition zones through the entire quaternary and proceed to suggest an explanatory model for the current spatial pattern of quaternary deposits and the two different types of erosion zones we use the spatial distribution of fjords and deep non tectonic lakes for delineating zones of deep glacial erosion and relict landscapes as markers for frozen bed conditions on the basis of the amount of exposed bedrock the landscape was classified into a tripartite system of drift thickness thick drift intermediate drift thickness absence of drift scoured zones it is found that a centrally placed central and northern sweden zone of thick drift cannot be explained by deposition under fis style ice sheets but is instead likely to be the combined result of marginal deposition of fluctuating mis style ice sheets primarily during the early and middle quaternary and the inefficiency of later east centered fis style ice sheets in evacuating this drift from underneath their central low velocity and possibly frozen bed areas the western fjord zone of deep glacial erosion formed underneath both mis and fis style ice sheets during the entire quaternary while the eastern lake zone of deep glacial erosion is exclusively related to mis style ice sheets and formed largely during the early and middle quaternary the scouring zones formed under conditions of rapid ice flow towards bathymetrically defined calving margins of fis style ice sheets they likely reflect process patterns of the last two or three fis style ice sheets the three landscape zones differ in their degree of permanence with the deep erosion zones being a long lasting legacy in the landscape more likely to be enhanced than obliterated by subsequent glacial events the thick drift cover zone once established appears to have been surprisingly robust to erosion by subsequent glacial events the scouring zones appear to be the most recent and ephemeral of the three zones with possible major alterations during single glacial events

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

plate tectonic evolution of the southern margin of eurasia in the mesozoic and cenozoic abstract thirteen time interval maps were constructed which depict the triassic to neogene plate tectonic configuration paleogeography and general lithofacies of the southern margin of eurasia the aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework the hercynian orogeny was completed by the collision of gondwana and laurussia whereas the tethys ocean formed the embayment between the eurasian and gondwanian branches of pangea during late triassic early jurassic times several microplates were sutured to the eurasian margin closing the paleotethys ocean a jurassic cretaceous north dipping subduction boundary was developed along this new continental margin south of the pontides transcaucasus and iranian plates the subduction zone trench pulling effect caused rifting creating the back arc basin of the greater caucasus proto south caspian sea which achieved its maximum width during the late cretaceous in the western tethys separation of eurasia from gondwana resulted in the formation of the ligurian penninic pieniny magura ocean alpine tethys as an extension of middle atlantic system and a part of the pangean breakup tectonic system during late jurassic early cretaceous times the outer carpathian rift developed the opening of the western black sea occurred by rifting and drifting of the western central pontides away from the moesian and scythian platforms of eurasia during the early cretaceous cenomanian the latest cretaceous paleogene was the time of the closure of the ligurian pieniny ocean adria alcapa terranes continued their northward movement during eocene early miocene times their oblique collision with the north european plate led to the development of the accretionary wedge of the outer carpathians and its foreland basin the formation of the west carpathian thrusts was completed by the miocene the thrust front was still propagating eastwards in the eastern carpathians during the late cretaceous the lesser caucasus sanandaj sirjan and makran plates were sutured to the iranian afghanistan plates in the caucasus caspian sea area a north dipping subduction zone jumped during paleogene to the scythian turan platform the shatski terrane moved northward closing the greater caucasus basin and opening the eastern black sea the south caspian underwent reorganization during oligocene neogene times the southwestern part of the south caspian basin was reopened while the northwestern part was gradually reduced in size the collision of india and the lut plate with eurasia caused the deformation of central asia and created a system of nw se wrench faults the remnants of jurassic cretaceous back arc systems oceanic and attenuated crust as well as tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems

stratigraphy and sedimentology of the great oolite group in the humbly grove oilfield hampshire abstract the main reservoir of the humbly grove oilfield comprises variably dolomitic grainstones and packstones representing the bathonian great oolite group the bathonian sequence commences in lower fuller s earth claystones which coarsen upwards into oncolitic claystones and skeletal packstones probably equivalent to the fuller s earth rock above is a variable succession of wackestones and thin packstones which have a distinctive sandstone at their base this sequence is named here the hester s copse formation the succeeding great oolite limestone is predominantly oolitic and cross bedded on a variety of scales it exhibits both coarsening and fining sequences which have locally well developed capping hardgrounds and burrowed horizons the great oolite limestone is subdivided into three members the lowest the humbly grove member and the highest the herriard member begin with massive shoal oolite deposition but each then pass upward into more interbedded sequences representing a more transgressive environment the middle member the hoddington is a thin but widely correlatable wackestone the overlying forest marble commences abruptly in claystones but there is an upward increase in both the incidence and thickness of discrete oolitic limestones both the great oolite limestone and forest marble were affected by early fresh water dissolution and cementation in addition to the localized development of submarine cements the top of the great oolite group is represented by the cornbrash the lower cornbrash is a thin micritic limestone while the upper cornbrash is a calcareous claystone which passes upwards into the kellaways clay the bathonian sequence overlies the dolomitic limestones of the inferior oolite the lower fuller s earth claystones being interpreted as a basinal marine mudstone sequence marking a substantial deepening and transgressive phase at the opening of the bathonian these mudstones shoal upwards into the quiet but photic water deposits of the fuller s earth rock the hester s copse formation represents the temporary development of wave dominated terrigenous shoreface and lagoonal conditions renewed transgression established a high energy tide dominated carbonate shelf upon which the great oolite limestone was deposited as a series of shoal oolites channels tidal deltas and spill overs periodic exposure of the carbonate sand bodies led to the production of early dissolutional and cementation fabrics that post date and largely obliterate submarine cements the forest marble opened with a further phase of deepening and the temporary establishment of muddy facies subsequently discrete tide dominated ridges and linear channelized oolitic sands prograded into the area the latest bathonian is marked by subsidence of the carbonate ramp to the south of the london platform the cornbrash kellaways clay sequence accumulating under progressively deepening waters

capturing and modelling metre scale spatial facies heterogeneity in a jurassic ramp setting central high atlas morocco each simulation algorithm including truncated gaussian simulation sequential indicator simulation and indicator kriging is characterized by different operating modes which variably influence the facies proportion distribution and association of digital outcrop models as shown in clastic sediments a detailed study of carbonate heterogeneity is then crucial to understanding these differences and providing rules for carbonate modelling through a continuous exposure of bajocian carbonate strata a study window 320 m long 190 m wide and 30 m thick was investigated and metre scale lithofacies heterogeneity was captured and modelled using closely spaced sections ten lithofacies deposited in a shallow water carbonate dominated ramp were recognized and their dimensions and associations were documented field data including height sections were georeferenced and input into the model four models were built in the present study model a used all sections and truncated gaussian simulation during the stochastic simulation for the three other models model b was generated using truncated gaussian simulation as for model a model c was generated using sequential indicator simulation and model d was generated using indicator kriging these three additional models were built by removing two out of eight sections from data input the removal of sections allows direct insights on geological uncertainties at inter well spacings by comparing modelled and described sections other quantitative and qualitative comparisons were carried out between models to understand the advantages disadvantages of each algorithm model a is used as the base case indicator kriging model d simplifies the facies distribution by assigning continuous geological bodies of the most abundant lithofacies to each zone sequential indicator simulation model c is confident to conserve facies proportion when geological heterogeneity is complex the use of trend with truncated gaussian simulation is a powerful tool for modelling well defined spatial facies relationships however in shallow water carbonate facies can coexist and their association can change through time and space the present study shows that the scale of modelling depositional environment or lithofacies involves specific simulation constraints on shallow water carbonate modelling methods

drowning of a carbonate platform as a precursor stage of the early toarcian global anoxic event southern provence sub basin south east france the toarcian oceanic anoxic event is well known as coinciding with a carbonate crisis coupled with organic matter accumulation and perturbation of the carbon cycle expressed by carbon isotope excursions in this palaeoenvironmental setting the present research attempts to better constrain the palaeoenvironmental conditions leading to the drowning of a carbonate platform during late pliensbachian to early toarcian times this study is based on the integrated sedimentological diagenetic and geochemical stable isotopes and rock eval pyrolysis analysis of several stratigraphic successions located in the southern provence sub basin south east france eodiagenetic ferroan calcite cements below two hardground surfaces at the pliensbachian toarcian transition record episodic eutrophication events such events were precursor stages of a global palaeoenvironmental perturbation i e a global carbon cycle perturbation that led to the demise of the carbonate platform and occurred prior to the toarcian oceanic anoxic event subsequently the acme of the palaeoenvironmental deterioration that coincided with the toarcian oceanic anoxic event is recorded by a pronounced negative carbon isotope excursion 3 followed by a positive one 2 87 organic matter preservation and inferred high temperature of surface sea water ca 25 c as given by oxygen isotope values from chondrichthyan tooth enamel sedimentological comparisons as well as chemostratigraphic and biostratigraphical correlations between the early toarcian sedimentary series of the southern provence and eastern dauphinois sub basins indicate that tectonic tilting occurred earlier in the southern provence sub basin this resulted in the preservation of organic rich deposits in the first sub basin and depositional hiatus in the second sub basin thus local conditions such as contrasting structural setting could markedly modify the sedimentary signature of a global climatic event

a mechanism for brief glacial episodes in the mesozoic greenhouse 1 the mesozoic perhaps the longest period of warmth during the phanerozoic earth history has been repeatedly affected by short lived cold interludes lasting about one million years while the origin of these cold snaps has been classically attributed to a temporary atmospheric co2 drawdown quantified mechanisms explaining these instabilities of the carbon cycle are still lacking based on a climate carbon cycle model we show that the general demise of carbonate platforms accompanying these short lived cold interludes is a powerful mechanism capable of generating a fast atmospheric co2 decrease and a moderate sea level drop associated with ice sheet buildup the temporary nature of the carbonate production decline explains the relative short time of these cold events but makes it possible to account for ice sheet waxing and waning

elevation changes of the fennoscandian ice sheet interior during the last deglaciation the dynamics of ice sheet interiors during the last deglaciation are poorly constrained hindering evaluation of ice sheet models we provide direct evidence of fennoscandian ice sheet fis interior behaviour during deglaciation through surface exposure dating our results demonstrate early thinning of the fis prior to the younger dryas yd 12 8 11 7 ka interior thinning in central norway was concurrent with retreat along the coastline exposing ice free mountainous tracts potentially as early as 20 15 ka the fis then formed moraines in these ice free tracts during the yd this is contrary to current hypotheses advocating a landscape fully covered by cold inactive ice during this period present empirical and model reconstructions fail to capture rapid interior down wastage increasing uncertainties in ice sheet volume estimates and sea level contributions

ice flow pattern and extent of the last scandinavian ice sheet southeast of the baltic sea a review of scientific literature geological maps and available previous digital data on ice marginal positions glacial landforms and sediment distribution are utilised to reconstruct ice streams and lobes and the maximum lgm and subsequent recessional ice marginal positions of the scandinavian ice sheet sis southeast of the baltic sea this paper presents preliminary results of the ongoing research that aims to build a geographic information system gis based model on the extent and timing of the last sis in the area between its maximum extent and the baltic sea digitized subglacial bedforms ice marginal and other glacial landforms and features from published sources are compared and validated against digital elevation model dem this has allowed specifying revising and questioning the location of the lgm and to interpret and correlate the post lgm ice streams with marginal positions morphological evidence demonstrates that large ice streams of between 100 and 300 km lengths were in operation ca 2 3 ka after the lgm and formed the middle and north lithuanian end moraines ice streams from the onega and white sea basins had high lateral slopes and clearly channelled flow while the ice streams that drained the ice sheet through the ladoga ilmen depression and in the eastern baltic usually had a fan shaped flow pattern and morphologically unclear lateral slopes in elevated areas and highlands that are located between ice streams a crossing of lineated bedforms is common one set of the crossing lineations on zemaitia eastern kursa vidzeme haanja latgale and sudoma highlands that are 200 350 km inside of the lgm margin has northwest southeast orientation that in general conforms to the direction of ice flow during the lgm and baltija phases it is expected that the presented compilation will stimulate discussions and scrutiny of earlier published data and generate ideas for future investigations