high frequency cyclicity in a vertical alternation of gilbert type deltas and carbonate bioconstructions in the late tortonian tabernas basin southern spain abstract the deltaic succession in the tabernas basin represents the first deposition of marine sediments deposited during the late tortonian transgression that linked the mediterranean sea to the atlantic ocean through the basins of the betic cordillera the 100 m thick succession consists of seven 5 to 20 m thick vertically stacked wave dominated gilbert type deltas towards the top of each unit coral reef patches overlie the delta plain and are in turn overlain by calcarenites formed by accumulation of branching red algae colonies locally the calcarenite deposits fill microkarst depressions developed on the reefal carbonates during emergence unlike the corals the red branching algae colonies grew at a few metres depth under low energy conditions below wave base the calcarenites derived from branching red algae colonies formed when the delta plain was drowned creating the new accommodation space needed for the progradation of the delta forming of the overlying unit the repeated alternation of coral reef carbonates tropical carbonates and carbonates with bryomol skeletal assemblages temperate carbonates in the deltaic succession is linked to relative sea level changes reflecting the sum of glacio eustatic sea level fluctuations and tectonic subsidence each delta unit is represented by a transgressive systems tract built by the stacking of distributary mouth bars capped by reef patches a maximum flooding surface represented by branching red algal calcarenites and a highstand systems tract consisting of progradational wave dominated gilbert type delta because of the general increase in accommodation space controlled by glacio eustatic sea level rise and tectonic subsidence beach topset strata and distributary mouth bars were preserved in the cases studied subsidence rates exceeded the glacio eustatic sea level lows preventing the development of normal lowstand systems tracts in the delta stack

organic rich layers in the metochia section gavdos greece evidence for a single mechanism of sapropel formation during the past 10 my abstract three well developed 10 ma old sapropels from the island of gavdos greece were selected for a detailed geochemical micropaleontological and sedimentological study the sapropels are characterized by a high organic carbon and a low carbonate content productivity was higher during sapropel formation as indicated by increased ba contents and higher percentages of the planktonic foraminiferal species neogloboquadrina acostaensis enrichment of mo and v in the sapropels indicates less oxygenated bottom water conditions which is supported by the flourishing of low oxygen tolerant benthic foraminifera variation in grainsize and the ti al ratio point to an alternating dominance of fluvial sapropels and eolian derived homogeneous intervals terrigenous clastics evidence for a local origin of the enhanced fluvial input comes from the gradual replacement of the sapropels by cyclic turbidite sequences which were fed by bed load type rivers the increased fluvial input during sapropel formation increased the sedimentation rate and caused the observed carbonate depletion the results obtained for the gavdos sapropels are consistent with those of previous studies of younger sapropels and related caco 3 cycles in the mediterranean the consistency in most of the geochemical and micropaleontological characteristics indicates that all sapropels and related layers are the result of a single mechanism for at least the past 10 my namely precession induced dry wet oscillations in the mediterranean climate still the effect of this mechanism on the intensity of surface water productivity dilution and diagenetic signals may differ from site to site depending on location depositional environment and intensity of the astronomical forcing

the gibraltar corridor watergate of the messinian salinity crisis abstract the existence and evolution of a messinian salt giant in the mediterranean sea has caused much debate in the marine science community especially the suggestion that the mediterranean was a deep desiccated basin during the messinian salinity crisis msc 5 97 5 33 ma triggered by a temporal disconnection from the global ocean made it a well known crisis beyond the scientific boundaries approximately 50 years after this provocative statement it remained unknown which mediterranean atlantic seaway delivered the 5 6 of the global ocean s salt into the mediterranean basin here we review the changes in mediterranean atlantic connectivity throughout the late miocene in order to locate date and quantify the missing messinian gateway that provided the salt water inflow during the msc we conclude that all the known pre msc gateways through southern spain and northern morocco were closed leaving the gibraltar corridor at its messinian configuration as the sole candidate we consider the possibility of longer and narrower straits existing at depth below the present gibraltar region and using strait dynamic theory we calculate its dimensions during the messinian based on the salinity changes in the mediterranean a marine messinian gateway through the gibraltar corridor is in agreement with growing evidence that atlantic waters reached the mediterranean sea during all three stages of the msc

soft sediment deformation structures induced by cyclic stress of storm waves in tempestites miocene guadalquivir basin spain the identification of triggering agents for soft sedimentation structures is an enigmatic geological problem mainly seismic induced soft sediment structures have been recognized in ancient sediments rather than those resulting from storm waves we analyse soft sediment deformation structures in upper miocene calcarenitic tempestites of the guadalquivir basin southern spain the most common structures are load casts which vary in height and width from 10 centimetres to several metres the structures are always restricted to a small part of the stratigraphic sections in exclusive association with tempestites the analysed soft deformation structures are interpreted to be the result of liquidization processes chiefly from their inferred depositional environment and subordinately from the deformation style we have devised basic criteria to identify the trigger mechanism in these soft sediment deformation structures the liquefaction was triggered by pore pressure changes induced by cyclic and residual stress of storm waves

late highstand patterns of shifting and stepping coastal barriers and washover fans late messinian sorbas basin se spain abstract the late messinian sorbas member up to 75 m thick consists in its type area of a parasequence set of three prograding coastal barriers sequences i iii associated with lagoon and washover sediments around the town of sorbas these strata can be studied exceptionally well due to absence of burrowing by raised messinian salinities and exposure along a network of up to 30 m deep canyons fifteen vertical sections were logged and carefully correlated this permits to reconstruct and discuss patterns of relative sea level movements between decimetres up to 15 m within a parasequence excellent examples of non tidal transgressive facies are characterized by lagoon and washover sediments instead of the usual combination of washover and tidal deposits channel and flood tidal delta implications for the sandstone connectivity are given the lower two sequences are deposited in a relatively large tectonically enhanced wedge shaped accommodation space they show both fining up deepening sequences followed by prograding coarsening up shoaling sequences and can be compared to the classical parasequences of the western interior basin usa progradation of sequence ii was interrupted by a major slide event most likely triggered by an earthquake which caused more than 400 m seaward slumping of a stretch of 1 km of coastal sands the architecture of sequence iii is more complex due to limited accommodation space characteristic for the late highstand so that this setting was very sensitive to sea level fluctuations this resulted in an intricate pattern of juxtaposed and superposed lagoonal muds washover fans and swash zones so called stranded coastal barriers occur which were left behind after seaward jump of the coastline over more than 1 5 km during forced regression the pattern of reconstructed sea level positions is well comparable to the sequential pattern shown by the correlated equivalents along the northern basin margin which belong to the so called terminal carbonate complex the problem of ranking the complex sequence iii as one or more parasequences and its consequences for cyclostratigraphy are shortly discussed two models of washover formation are given respectively during more rapid and more slow sea level rise the influence of synsedimentary folding on the location of barriers is discussed and also the source area of extra and intraclasts supplied to barriers and washovers after deposition of the sorbas member the sea withdrew from the sorbas basin probably as a result of the major downdrop in the mediterranean at the maximum isolation during the salinity crisis it is suggested that the semi enclosed setting of the basin resulted only in limited localized erosion in contrast to the deeper adjacent vera basin which was more open to the mediterranean

rhodolith assemblages from the lower tortonian carbonate ramp of menorca spain environmental and paleoclimatic implications abstract lower tortonian distally steepened carbonate ramp of menorca mostly consists of foramol and rhodalgal facies deposited in inner middle ramp ramp slope and outer ramp settings red algae are abundant from the middle ramp to the lower part of the slope and their taxonomic assemblages are clearly related to the bathymetric position melobesioids percentage increases basinward passing from 55 8 in the middle ramp to 97 in the toe of slope mastophoroids are more abundant in the middle ramp 43 1 and decrease toward deeper paleoenvironments 1 2 lithophylloids and sporolithaceans appear as accessory components from the middle ramp to slope settings the percentage of melobesioids and mastophoroids observed in the middle ramp suggest that growth of the rhodoliths started in a water depth below 10 20 m the deepest occurrence of the rhodoliths is in the ramp slope environment where the dominance of melobesioids and the low percentage of shallower water subfamily suggests a water depth range of 70 to 100 m shape and structure of rhodoliths are indicative of high energy conditions in all ramp settings and they do not reflect a decrease in hydrodynamic energy related to water depth increase these conditions are related to the presence of unidirectional currents that produced cross bedded grainstones existing in the middle ramp ramp slope and at the toe of the ramp slope settings the high percentage of mastophoroids in the shallowest environments and the presence of lithoporella and sporolithon in the coralline assemblages suggests that carbonate production took place in tropical waters

neogene coralline algal growth forms and their palaeoenvironments in the almanzora river valley almeria s e spain abstract the almanzora river valley is an elongate e w depression containing mainly neogene sediments during the late tortonian several horizons of crustose coralline algae developed in three distinct sedimentary contexts a on coastal platforms and talus slopes b on fan deltas and c associated with corals in patch reefs growing at the furthermost extremes of coastal fan deltas in the former two cases the predominant growths are as rhodoliths associated with mobile substrates in the coastal systems an increase in depth results in a change in both the morphology and the composition of the rhodoliths with depth there is a significant increase in the diversity of algal species and a concomitant increase in the size of the algal covering compared to the nucleus and thus the morphology of the rhodolith depends less and less on the shape of the nucleus itself the massive crusts and columns which mark the limit of development of the shallow water rhodoliths in the deeper examples are covered by branching and thin leafy laminar growths in the fan deltas the development of the rhodoliths is similar to that of the deeper coastal zones in the patch reefs the specific composition of the algal associations changes somewhat and the growths developed on a stable substrate under low energy conditions are mainly vertical branches arising from thin crusts

extending the astronomical polarity time scale into the miocene an astronomical time scale is presented for the late miocene based on the correlation of characteristic sedimentary cycle patterns in marine sections in the mediterranean to the 65 n summer insolation curve of la90 1 2 with present day values for the dynamical ellipticity of the earth and tidd dissipation by the moon this correlation yields ages for all sedimentary cycles and hence also for the recorded polarity reversals and planktonic foraminiferal and dinoflagellate events the tortonian messinian t m boundary placed at the first regular occurrence of the globorofuliu conomiozea group in the mediterranean is dated at 7 24 ma the duration of the messinian is estimated at 1 91 myr because the miocene pliocene boundary has been dated previously at 5 33 ma 3 the new time scale is confirmed by oar 3gar ages of volcanic beds and by the number of sedimentary cycles in the younger part of the mediterranean messinian

record of climatic change in neritic carbonates turnover in biogenic associations and depositional modes late miocene southern spain in order to evaluate the geological record of climatic change in neritic carbonates we studied late miocene rock outcrops in southern spain six episodes of reef growth are documented burdigalian to messinian in neogene basins of the betic cordillera which were located close to the margin of the global reef belt the reefs are characterized by various zooxanthellate corals which decrease in diversity with time andhalimeda the youngest reefs of the latest messinian are characterized by the dominance of the genusporites late miocene coral reefs and reef rimmed platforms alternate over time with non reefal carbonate ramps characterized by skeletal calcirudites or with gypsum such as that formed during the messinian salinity crisis the calcirudites lack reef corals calcified green algae and extensive marine cement but exhibit skeletal components described from both modern and fossil nontropical carbonates these include bryozoans mollusks foraminifers echinoderms and minor balanids as well as coralline algae of a bryomol association the presence of some larger foraminifers indicates high temperatures close to the lower temperature threshold of the reef assemblage sea level lowstands and highstands are documented by wedges of bryomol carbonate and chlorozoan patch reefs or prograding platforms thus temperate climate depositional modes correspond to relatively low sea levels and warm water modes to high sea levels the neogene infill of the agua amarga and sorbas basins documents two of these cycles other climate sea level cycles including messinian gypsum in the cool water depositional mode are well established in adjacent neogene basins in southern spain this type of composite sequence seems to occur only along the margin of the global reef belt and indicates an oscillatory latitudinal movement of the margin which is associated with global climatic change the analysis of turnover in neritic depositional carbonate systems may therefore be considered a sensitive tool for reconstructing climatic change from the fossil record however warm water modes and temperate water modes of carbonate sedimentation and diagenesis differ significantly for this reason the interpretation of composite system sequences by sequence stratigraphy requires an extended concept the particular type of mixed bryomolchlorozoan depositional sequence also bears some potential for drowning because sea level rise may be faster than the net production rate of temperate carbonate systems

messinian pre evaporite sapropels and precession induced oscillations in western mediterranean climate abstract cyclical fluctuations in planktic foraminiferal assemblages have been recognized in the pre evaporitic messinian in a marginal basin of the western mediterranean the fluctuations coincide with a dominantly precession controlled sedimentary cyclicity sapropels during sapropel deposition high planktic foraminiferal diversities are indicative of relatively stable marine conditions while during homogeneous marl deposition low diversities seem to indicate the presence of unfavourable more saline surface water conditions the dominance of a precession related signal indicates that regional climate oscillations rather than obliquity related glacio eustatically controlled influxes of atlantic and or mediterranean waters are responsible for the faunal fluctuations and sedimentary cyclicity our scenario links the persistence of normal marine conditions during sapropel formation with increased rainfall and run off along the western mediterranean at times that perihelion occurred in northern hemisphere summer less favourable highly saline surface water conditions prevailed during periods of drier climate induced by opposite precessional extremes the cyclical oceanographic fluctuations could also have governed periodic reef growth along the margins

lithology mapping of a mixed siliciclastic carbonate evaporite system using 3d seismic and well data lower triassic jialingjiang formation sichuan basin southwestern china abstract high quality three dimensional 3d seismic data acquired in the central sichuan basin southwestern china offer an opportunity to map complex lithologies in a mixed siliciclastic carbonate evaporite system in the lower triassic jialingjiang t1j formation the formation consists of siliciclastics limestone dolostone anhydrite and salt the lithologies consist several source reservoir cap assemblages in the area lithologies in the t1j formation change rapidly in the vertical direction forming different interbed patterns in thin layers in the mean time the lateral extend of each lithology is complex this vertical and lateral distribution makes it difficult to predict lithology by single seismic attribute therefore principle component analysis pca was applied to tens of seismic attributes to extract useful information the first three components contain most 83 02 99 85 of the lithology information preserved in seismic attributes which were used to correlate with lithology content calculated by core calibrated wireline logs correlation coefficients of the three seismic components with lithologies are significantly higher 0 37 0 79 than those of individual seismic attributes near zero to 0 58 different assemblies of end member lithologies were selected from anhydrite siliciclastics tight dolostone limestone and salt to perform pca in different sequences lithologic content distribution of individual end members was shown by color blending method to map the lithology mixture sedimentary history in the t1j formation was reconstructed based on lithology mixture maps and regional geology background in the study area eight 4th order sequences were interpreted in the t1j formation only the second sequence was influenced by siliciclastic input forming a complete mixed siliciclastic carbonate evaporite system open platform and or restricted evaporative environment dominated the other seven sequences forming a mixed carbonate evaporite system

experimental syntectonic hydration of basalt abstract this paper outlines in general terms the role of metamorphic transformations during rock deformation long duration triaxial stress relaxation tests at 600 c 160 mpa confining pressure on wet crushed basalt sheared in sawcuts made in intact basalt cylinders are reported mechanical data are interpreted in terms of a material which shows a small strain rate sensitivity to large variations in applied stress but which work hardens dramatically as a result of marked microstructural changes which occur during straining permanent distortions of c 20 were produced in the samples tests at 100 mpa pore water pressure resulted in the formation of oriented overgrowths of amphibole preferentially developed on less stressed interfaces between original grains and in pore spaces substantial redistribution of feldspar also occurred at low pore pressures no amphibole formed and only feldspar was recrystallized much of the original porosity of the rock was eliminated in all cases the mechanical and microstructural data are interpreted in terms of flow by some combination of grain sliding and diffusional accommodation with the reprecipitated diffused material being the product of a chemical reaction involving all original solid phases plus water from a consideration of the effects of the reaction on the chemical potential gradients driving diffusion it is concluded that although the syntectonic hydration exerts a profound effect on the microstructural and mineralogical development of the rock during deformation there is no substantial enhancement of the rate of strain similar microstructural developments also occur in natural rocks deformed during retrogressive metamorphic events and examples are described for comparison

the european record of the gerbil myocricetodon rodentia mammalia and its bearing on the messinian salinity crisis abstract the gerbillid myocricetodon is mainly known from the miocene of africa and asia but some small samples of this genus have been identified in southwestern europe interpreted as immigrants driven by the messinian salinity crisis however the specific determination of these european populations and their relationships with african forms have proved controversial the population from negratin 1 guadix basin southern spain was attributed to the african species myocricetodon jaegeri but other european samples have still not been determined at the specific level here we describe the material of myocricetodon from almenara m eastern spain which represents the most abundant sample of the genus known from europe confirming its assignation to m jaegeri we also analyze material from salobrena pino mojon southern spain and castelnou 3 southern france concluding that these samples belong to the same species the presence of these coeval and conspecific populations of myocricetodon is explained by a single migratory event from northern africa the occurrence of myocricetodon interpreted as an indicator of warm and arid conditions is restricted to southern and eastern spain and the southeastermost extreme of france being mainly limited to the mediterranean coast it is absent in other iberian areas such as the granada cabriel and teruel basins despite their rich and well studied record of late miocene mammals this distribution suggests the existence of different environmental more humid conditions in those areas during the latest miocene as already proposed for the granada basin our data also indicate that the presence of myocricetodon in europe was limited to a short interval close to the miocene pliocene boundary contrarily to other gerbils namely debruijnimys which persisted during the pliocene this suggests that myocricetodon could be extremely sensitive to environmental factors and its occurrence in europe was linked to a specific moment of arid conditions

a stratigraphic framework for the pliocene pleistocene continental sediments of the guadix basin betic cordillera s spain the central sector of the guadix basin betic cordillera s spain hosts some of the most significant pleistocene large mammal sites in europe the basin infill is divided into six genetic units the three lower with marine sediments and the remainder mainly continental as the environmental characterization of the sediments is crucial to understand the ecologic and geologic processes leading to the formation of these sites a stratigraphic sedimentologic and petrologic study is presented combining a lithologic correlation with previous biostratigraphic data and new magnetostratigraphic data a detailed litho bio and magnetostratigraphic scheme has been developed for the study area it shows the stratigraphic architecture of the central sector of the guadix basin together with the age and the relative spatial position of the most important mammal sites as well it has been also helpful to identify several isochronous surfaces to establish the exact position and the age of the boundary between the two last units of the continental infill in the guadix basin and to calculate sedimentation rates

determination of the stress conditions of the ductile to brittle regime along the asuke shear zone sw japan abstract the stress conditions of the ductile to brittle regime have been assessed along the asuke shear zone asz which strikes ne sw in the cretaceous ryoke granite terrain in sw japan along the asz pseudotachylyte and mylonitized pseudotachylyte are locally developed together with cataclasite the simultaneous operation of dislocation creep and grain size sensitive creep as indicated by the coexistence of the z maximum and relatively random c axis lattice preferred orientations as well as the sizes of dynamically recrystallized quartz grains 6 40 7 79 m in the mylonitized pseudotachylyte suggest differential stresses of 110 130 mpa at 300 c the e twin morphology twinning ratio and distribution of the glide direction on the e twin plane of the twinned calcite in the amygdules of the pseudotachylyte suggest the stress conditions of the 1 and 3 axes trend 228 and 320 and plunge 55 and 1 respectively and indicate differential stresses of 40 80 mpa at 150 200 c based on kinematic indicators in the fault rocks the stress conditions estimated from calcite twins and the cooling history of the granitic protolith the asz is inferred to have been activated under a stress state that caused sinistral normal movements before and after pseudotachylyte formation at 70 50 ma

continental deposits magnetostratigraphy and vertebrate paleontology late neogene of eastern spain abstract eleven sections have been sampled for magnetostratigraphy in the fossil mammal productive late neogene basins of eastern spain the characteristic direction of magnetization was determined through progressive thermal and alternating field demagnetization it was possible to correlate the magnetozones from the various sections to the gpts as well as to the fossil mn zones within the sediment the mn zone boundaries based on this correlation are as follows mn 11 12 8 1 my mn 12 13 6 my mn 13 14 4 9 my mn 14 15 4 18 my mn 15 16 3 58 my new fossil lists are presented for the fuente del viso and loma del castillo faunas in the cabriel basin

precession punctuated growth of a late miocene submarine fan lobe on gavdos greece sedimentary cycles in an upper miocene succession of hemipelagic sediments marls and laminites sapropels were deposited in an outerarc basin and are related to the astronomical cycles of precession and eccentricity individual marl laminite couplets correspond with the cycle of precession which has a periodicity of about 22 kyr the lower part of the succession contains a turbidite interval comprising a number of distinct turbidite sequences the turbidite sequences occur within or substitute entirely the laminite beds so that turbidite deposition is similarly precession punctuated the turbidite facies is characteristic for small prograding fan lobes fed by small volume turbidites the abundant plant remains the local palaeogeographic setting and the association with laminites related to wet climate suggest a river fed submarine fan lobe where the timing of sediment transport is largely controlled by river floods during periods of high precipitation and continental run off the onset and ending of the turbidite interval is most likely linked with either autocyclic processes or by tectonic steepening of the hinterland relief sea level changes seem least important for the triggering of turbidites which is in contrast with current beliefs

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

astrochronology for the messinian sorbas basin se spain and orbital precessional forcing for evaporite cyclicity the sorbas basin of se spain contains one of the most complete sedimentary successions of the mediterranean reflecting the increasing salinity during the messinian salinity crisis a detailed cyclostratigraphic study of these successions allows a correlation of the sedimentary cycle patterns to astronomical target curves here we present an astrochronological framework for the messinian of the central part of the sorbas basin this framework will form a solid basis for high resolution correlations to the marginal carbonate facies and to the central mediterranean area the early messinian abad member contains 55 precession induced sedimentary cycles marked by homogeneous marl opalrich bed alternations in the lower abad and by homogeneous marl sapropel alternations in the upper abad astronomical tuning results in an age of 5 96 ma for the transition to the yesares evaporites and thus for the onset of the messinian salinity crisis the marl sapropel cycles of the upper abad are replaced by gypsum sapropel cycles 14 in the yesares member indicating that the evaporite cyclicity is related to precession controlled oscillations in circum mediterranean climate as well as a consequence gypsum beds correspond to precession maxima insolation minima and relatively dry climate sapropelitic marls to precession minima insolation maxima and relatively wet climate an alternative glacio eustatic obliquity control for evaporite cyclicity can be excluded because the number of sedimentary cycles with a reversed polarity is too high sedimentation during the abad yesares and the overlying coastal sequences of the sorbas member took place in a continuously marine environment indicating that marine conditions in the sorbas basin prevailed at least until 5 60 5 54 ma according to our scenario deposition of the yesares and sorbas member took place synchronously with deposition of the lower evaporites in the central mediterranean finally the continental zorreras member consists of 8 sedimentary cycles of alternating reddish silts dry climate and yellowish sands wet climate which correlates very well with the upper evaporites and lago mare facies of the mediterranean q 2001 elsevier science b v all rights reserved

progress in microboudin method for palaeo stress analysis of metamorphic tectonites application of mathematically refined expression abstract the microboudin method for palaeo stress analysis is mathematically refined by incorporating the recently proposed shear lag model which describes the relationship between stress distribution along a fibre embedded within an elastic matrix and the far field differential stress applied to the matrix the refined probability density function of fractured fibres g with respect to the aspect ratio of the fibre r and the stress parameter is given by g r 1 exp m 1 m r m e f e q m 1 1 e q e f 1 cosh ar m where eq and ef are the elastic constants of the matrix and fibre m is the weibull modulus of the fibre material and a is a constant the stress parameter is defined as 0 s where 0 is the far field differential stress applied to the matrix and s is the modal fracture strength of the fibre material at r 1 this method is applied to tourmaline and piemontite boudins in quartzose rocks from six areas and it is revealed that the probability density function adequately models the proportion of boudinaged tourmaline and piemontite grains the value of is determined for each sample allowing 0 to be determined by this method when s is known

a calibrated mammal scale for the neogene of western europe state of the art abstract a magnetobiostratigraphically calibrated mammal scale for the neogene of western europe is presented in this paper the mammal neogene mn units originally proposed by mein report on activity rcmns working groups 1975 have been re defined here on the basis of first appearances of selected small and large mammal taxa the chronology of the lower boundaries of each unit had been established mostly after the significant magnetobiostratigraphic framework developed in the last decade in a number of spanish basins ebro calatayud daroca valles penedes teruel fortuna cabriel and guadix baza in the case of the early and middle miocene particularly mn 1 mn 2 and mn 3 the authors have also taken into account the magnetobiostratigraphic framework developed in the north alpine foreland basin some alternative correlations of the magnetostratigraphic data from this last basin are proposed in order to achieve a higher degree of consistence with the data from the iberian basins a quite well established magnetostratigraphic calibration of the mn boundaries can be proposed for most of the neogene from middle miocene to late pliocene on the other hand the chronological boundaries of the early miocene mn units are still poorly constrained due to 1 scarcity of well studied continuous thick magnetostratigraphic sections 2 the difficulty in defining the boundaries of the mn zones for this time span due to the relative homogeneity and persistence of the fossil rodent faunas and the absence of significant large mammal dispersal events some of the troubles which arise with the application of the mn units strengthen the need to take into account the palaeobiogeographical meaning of these units and their real suitability to date and correlate through extensive geographic areas

types of mixing and heterogeneities in siliciclastic carbonate sediments abstract mixed siliciclastic carbonate deposits consist of a suite of different types of mixing between the two components from bed core plug to stratigraphic seismic scales producing a high vertical and lateral lithological variability mixed deposits results from the interaction of siliciclastic input and coeval carbonate production controlled by temporal and or spatial factors although mixed deposits are very diffuse in the geological record studies about these deposits are scrappy and not well encoded accordingly mixed deposits represent a labyrinth for researchers who want to investigate them for the first time in this paper different types of mixing compositional versus strata controlled by different allocyclic e g sea level climate and or autocyclic e g depositional processes factors that operate at different scale are documented mixing is recognized and described at three main scales of observation bed core plug scale lithofacies well log scale and stratigraphic seismic scale i compositional mixing reflects the contemporaneous accumulation of the two heterolithic fraction in space and time this type of mixing is observable at lamina to bed scale locally producing depositional structures diagnostic for particular depositional environments ii strata mixing results from the alternation of the two heterolithic fraction in time this type of mixing is observable at lithofacies to stratigraphic scale and can be related to depositional processes climatic variations and or relative sea level changes a correct identification of these different types of mixing and the scale of their occurrence is crucial in revealing i physical processes that control the sedimentation ii environmental factors that influence the carbonate factory related to the siliciclastic dispersal mechanisms and iii internal heterogeneity of the resulting sedimentary deposit furthermore the petroleum industry is interested to unravel new insights about internal properties of mixed siliciclastic carbonate systems e g porosity permeability and to reconstruct predictive 3d models for the related reservoirs the correct prediction of internal heterogeneity and the recognition of lateral and vertical compartmentalization have an important impact on hydrocarbon exploration and exploitation

reservoir characterization and hydrocarbon accumulation in late cenozoic lacustrine mixed carbonate siliciclastic fine grained deposits of the northwestern qaidam basin nw china abstract late cenozoic lacustrine mixed carbonate siliciclastic sequences in the northwestern qaidam basin nw china are mainly composed of high porosity and low permeability fine grained rocks but have big potentials of oil gas commercial production however how these fine grained rocks generate high quality reservoirs and accumulate hydrocarbons remains poorly known this study focuses on shallow buried shang youshashan formation middle late miocene n22 and shizigou formation late miocene pliocene n23 reservoirs and hydrocarbons in xiaoliangshan area of the northwestern qaidam basin we conduct mineralogy petrography and porosity and permeability analysis for reservoir rocks and biomarker analysis for hydrocarbons and potential source rocks the results indicate that the n22 high quality reservoirs are dominated by fractured marlstones and lime mudstones and constitute structural traps whereas the n23 hydrocarbon reservoirs are mainly composed of siliciclastic dominantly rocks and form stratigraphic lithologic traps similar biomarker ratios between crude oil samples and paleogene organic matter rich rocks reveal that hydrocarbons in the shallow system were likely derived from deep buried source rocks rather than late cenozoic lacustrine fine grained rocks themselves in this case large scale vertical fractures created by kink band structures in the northwestern qaidam basin are supposed to facilitate hydrocarbon migration and accumulation preliminary production data and exploration well oil gas test results demonstrate highest yields and thus large hydrocarbon potentials in the n22 marlstone and lime mudstone reservoirs collectively we suggest that relatively high permeability fractured and carbonate rich reservoirs on structural highs are favorable targets for future oil gas exploration in the northwestern qaidam basin this petroleum system provides a typical and significant example for hydrocarbon exploration and development in mixed carbonate siliciclastic fine grained rocks of nonmarine petroliferous basins

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

late miocene stratigraphy and palaeogeographic evolution of the intramontane guadix basin central betic cordillera spain implications for an atlantic mediterranean connection abstract the guadix basin is an intramontane basin located in the central sector of the betic cordillera its late miocene stratigraphic record is divided into three depositional sequences limited by unconformities representing tectonic and or eustatic events depositional sequence i late tortonian is composed by two systems tracts the lower marks the beginning of marine sedimentation in the basin and comprises three retrograding lithological complexes or depositional systems coastal shallow platform and pelagic basin and is interpreted as a transgressive systems tract the upper systems tract consists of a shallow shelf prograding into a pelagic basin this systems tract exhibits a typically regressive pattern and was deposited during high sea level and is therefore interpreted as a highstand systems tract depositional sequence ii late tortonian is composed of both continental alluvial cones and shallow marine gilbert type delta shallow shelf and reef depositional systems the deposits of this sequence record a significant fall in sea level and are interpreted as a lowstand systems tract depositional sequence iii late turolian ventian or late tortonian messinian was formed of solely retrograding continental depositional systems alluvial fan lacustrine fan delta mud flat and lacustrine with this sequence begins the continental sedimentation in guadix basin in an endorheic context the palaeogeographic evolution of the guadix basin during the late miocene can thus be divided into three stages the first corresponds to depositional sequence i and is characterised by the development of shallow marine environments on the basin margins and deep water deposits in its centre during this stage the basin was connected to the west with the atlantic ocean via the granada and guadalquivir basins and toward the east with the mediterranean sea through the almanzora and campo coy basins in the second stage represented by depositional sequence ii most of the basin was occupied by shallow marine environments during this stage the connection with the atlantic and mediterranean was only open through the guadalquivir and campo coy basins respectively finally the third and last stage corresponding to depositional sequence iii is characterised by the development of continental environments throughout the basin this stage records the definitive closing of the connections with the atlantic ocean and the mediterranean sea

cyclically arranged storm controlled prograding lithosomes in messinian terrigenous shelves bajo segura basin western mediterranean abstract this work focuses on a messinian shallow marine terrigenous unit termed the la virgen formation which forms part of the sedimentary infill of the bajo segura basin betic margin of the western mediterranean this formation was deposited during a high sea level phase prior to the onset of the messinian salinity crisis stratigraphically it comprises a prograding stack of sandstone lithosomes alternating with marly intervals 1st order cyclicity these lithosomes are characterized by a homoclinal geometry that tapers distally and interfinger with pelagic sediments rich in planktonic and benthic microfauna torremendo formation an analysis of sedimentary facies of each lithosome reveals a repetitive succession of sandy storm beds tempestites which are separated by thin marly layers 2nd order cyclicity each storm bed contains internal erosional surfaces 3rd order cyclicity that delimit sets of laminae two categories of storm beds have been differentiated the first one includes layers formed below storm wave base swb characterized by traction structures associated to unidirectional flows the second category consists of layers deposited above the swb which display typical high regime oscillatory flow structures the 1st order cyclicity recorded in the la virgen formation corresponds to sapropel homogeneous marl precessional cycles formed in a pelagic basin context torremendo formation

sediment deformation structures and the palaeotectonic analysis of sedimentary basins with a case study from the carboniferous of northern england

climatic control on palaeohydrology and cyclical sediment distribution in the plio quaternary deposits of the guadix basin betic cordillera spain abstract a cyclical pattern can be observed in the central sector of the guadix basin southern spain in the late pliocene quaternary alluvial fan deposits prograding into its axial valley a climatic significance has been attributed to this cyclicity on the basis of sedimentological and preliminary isotopic studies the progradation phases of the alluvial fans are here attributed to more arid time intervals in which the vegetation cover would be less developed erosion and sediment supply would be higher and base level would be lower in contrast the time intervals during which the fluvial system sediments dominated the area are inferred to be wetter and base level higher with vegetation cover retaining the soils and preventing erosion permanent water supply to the river would therefore facilitate the aggradation of the floodplain and prevent progradation of the fans starting from a litho bio and magnetostratigraphical frame provided for the area an age is assigned to the alternation of the reddish sediments of the transverse alluvial fans and the greyish to white fluvio lacustrine sediments of the axial drainage system a cyclicity of ca 100 ky has been identified in most of the alluvial fan progradation phases falling within milankovitch high frequency eccentricity periodicities correlation of the phases with insolation curves is accordingly discussed as a possible origin for the cyclicity finally the results offer new insights into early hominin occupation patterns in the region through the identification of predictable resources of permanent fresh water that would have remained available throughout the recorded time span that includes the early middle pleistocene transition even during times of aridification

high frequency rhythmicity in a mixed siliciclastic carbonate shelf late miocene guadix basin spain a model of interplay between climatic oscillations subsidence and sediment dispersal abstract rhythmites in pelagic sediments can include information on paleoclimate and with orbital cycles this paper documents and interprets an unusual rhythmic succession from a cool water shallow marine shelf that includes features of mediterranean type ramps and open ocean type ramps in the subsiding southwestern margin of the guadix basin southern spain betic cordillera during the late tortonian a 640 m thick succession was deposited over a short period 7 8 7 2 ma this succession contains 30 sedimentary packages or rhythmites each defined by two facies associations a mixed cross stratified siliciclastic skeletal sandstone and a homogeneous marl rich in planktonic foraminifera sandstones ranging in thickness from 3 m to 20 m contain coralline algae bivalves bryozoans benthic foraminifera echinoids and brachiopods typical temperate water shelf biofacies these units exhibit cross strata sets up to four meters high interpreted to have been produced by strong unidirectional currents the marly deposits range in thickness from 2 to 17 m and contain an association of cold water planktonic foraminifera as well as thin sandstone layers that exhibit normal grading corresponding to typical incomplete bouma sequences or a lower division with planar lamination and an upper division of very fine to fine grained sandstone with hummocky and swaly cross stratification on the basis of the sedimentary structures the sandstone layers are interpreted as sporadic turbidity flows and storm ebb surge deposits on the basis of the sedimentary structures the hydrodynamic conditions during deposition of the mixed siliciclastic carbonate interval were high energy based on sedimentary and biogenic features of the rhythmites and their temporal durations ca 20 ka rhythmicity is interpreted to reflect alternating cool wet and cold dry climate episodes driven by precession orbital cycles this occurrence of alternating mixed carbonate siliciclastic sedimentation and pelagic sediments represents a unique occurrence in the geologic record

palaeostress estimation using calcite twinning experimental calibration and application to nature abstract by means of high temperature deformation experiments on calcite rocks of different grain sizes we have established the relationships between differential stress and twinning incidence twin density and volume fraction and the way that these relationships depend on grain size both twinning incidence and volume fraction increase with grain size at a constant level of differential stress log twin density is proportional to stress but is independent of grain size at a given grain size volume fraction of twinning increases non linearly with differential stress twinning activity measured by twinning incidence increases linearly with stress the behaviour of each of these parameters is independent of temperature strain and strain rate these relationships can be used as a basis for the estimation of palaeostress values in naturally deformed calcite rocks this is illustrated by a study of twinning activity in limestones close to thrust faults in the cantabrian zone of the variscan orogenic belt in northwestern spain high peak differential stresses were measured ranging from 150 to 250 mpa using the turner dynamic analysis technique however it is clear that shear stresses resolved parallel to the fault planes were very low the attainment of high stress differences when the resistance to faulting was low is attributed either to bending forces induced during the motion of the non planar surfaces relative to each other or to the stress peak being attained prior to the localization of deformation onto the fault surfaces

hummocky cross stratification like structures in deep sea turbidites upper cretaceous basque basins western pyrenees france by mulder et al 2009 sedimentology 56 997 1015 discussion

effect of temperature and pore fluid on the strength of porous limestone the presence of pore fluid in rocks generally reduces brittle strength the role of water weakening in porous carbonate rocks and the effect of enhanced deformation on concomitant transport property evolution are poorly understood the interaction between pore fluid and deformation mechanisms in carbonate rocks is complicated by crystal plasticity and solubility in calcite at low temperatures and pressures to explore this system we perform conventional triaxial deformation experiments on indiana limestone 16 porosity over a range of temperatures 23 75 c and effective confining pressures 10 50 mpa samples are deformed with pore fluids of different saturation states with respect to calcite host rock samples tend to fail by distributed deformation sample permeability is reduced by up to an order of magnitude during deformation even in samples exhibiting dilatancy compactive yield strength associated with shear enhanced compaction is greatly reduced in saturated samples compared to dry samples dilatancy is suppressed and compaction enhanced at elevated pressures greater weakening effects are observed when pore fluid is far from equilibrium with carbonate rock observed weakening results from the interaction between microcracking mechanical twinning and pressure solution

biocalcarenite and mixed cool water prograding bodies of the mediterranean pliocene and pleistocene architecture depositional setting and forcing factors

non tropical carbonate deposits on the modern new zealand shelf abstract extensive ca 50 000 km 2 shallow marine platforms 70 caco 3 despite proximity to a tectonically active plate margin in these regions the terrigenous sediment supply is presently low and growth of epibenthos is fostered by firm substrates rock gravels shells seaweeds and the generally energetic nature and high nutrient levels of open shelf waters rapid transition into adjacent terrigenous dominated facies is characteristic irrespective of water depth the carbonates are coarse grained and fragmental carbonate mud is rare calcite dominates over aragonite high mg calcite widespread off northern new zealand is rare in the south skeletal material is dominated by bryozoans and bivalve molluscs with significant local contributions from foraminifers barnacles calcareous red algae and echinoderms the name bryomol is suggested for this distinctive temperate region skeletal carbonate facies which can be usefully subdivided based on dominant zoarial growth forms of the bryozoan component known to be habitat related bioerosion is an important mechanism of skeletal fragmentation and degradation many grains especially aragontic bivalves are infested by endolithic borers and have low preservation potential ages of skeletal material in the surficial deposits range from more than 20 000 years b p to modern which is consistent with both low rates of carbonate production and sediment accumulation and the wide range in preservation state of grains some data suggest that the skeletal carbonates are dispersed and mixed mainly during infrequent movement of sand ribbons sand waves and sand sheets driven by storm assisted tidal flows tracts of modern palimpsest and relict carbonates can occur in juxtaposition the facies characteristics of the new zealand shelf carbonate deposits contrast significantly with those of the classical bahaman type carbonate model however they are similar to those reported from many other mid to high latitude carbonate shelves and afford good analogues for most onland occurrences of new zealand cenozoic limestones

lithofacies diagenetic spectra and sedimentary cycles of messinian late miocene evaporites in se spain abstract messinian evaporites have been deposited within a number of connected basins that formed the so called betic strait in se spain during the late miocene pre syn and postevaporitic sedimentary successions may well be compared with other strata of the same age surrounding the mediterranean sea there is no evidence for a cataract like connection of these basins with a strong unidirectional flow regime before and during the formation of messinian evaporites as previously suggested the most frequently occurring gypsum lithofacies presumably related to shallow water depositional environments are crystalline selenitic gypsum grass like gypsum laminated gypsum and cross bedded gypsarenite only few real sabkha type chicken wire alabastrine gypsum have been identified evenly laminated gypsum together with graded gypsarenites turbidites gypsrudites debrites and slumps is restricted to basins or parts of basins with considerable paleoslopes evidence for diagenetic overprinting is abundant in all outcrop areas studied this includes the formation of giant gypsum twin crystals super cones and alabastrine nodular gypsum the formation of messinian evaporites in se spain is thought to be controlled by a superimposed third order sea level lowstand smaller sedimentary units fall well into the range of fourth to sixth order cyclic and rhythmic successions they are clearly related to basin dynamics or to autogenetic processes of the local facies zone facies dynamics none of the smaller scale cycles fourth and higher order as observed in outcrops are related to high frequency eustasy

new aspects of deformed cross strata in fluvial sandstones examples from neoproterozoic formations in northern norway abstract extensive 20 200 m long exposures of tabular cross sets in neoproterozoic fluvial sandstone in northern norway demonstrate that deformed cross strata in the form of recumbently folded cross strata with associated massive sand are localized features passing in both up and down current direction into undeformed concave upward or sigmoidal cross strata the deformation occurs in down current inclined tangential wedge shaped zones beneath reactivation surfaces and less commonly as flat topped lenticular zones the localized nature of the sediment deformation is attributed to local liquefaction below the top of the bed in the case of the flat topped lenses and at the dune front in the case of the more common tangential wedges the position of the flat topped lenses suggests deformation by the shear stress of high velocity suspension laden currents although liquefaction of the dune front implies the action of gravity forces it is argued that the fluvial currents were the main driving force at the instant of bed liquefaction post folding gravitational shearing probably enhanced the deformation within the upper part of the wedges with their long flat lying toeset resulting from redeposition of downslope moving liquefied sand the down current alternation of deformed tangential wedges and undeformed cross strata suggests that the mechanism that triggered the liquefaction of the dune lee side was related to the fluvial system itself and hence was of autokinetic origin the tabular cross sets have previously been interpreted as a product of the dune upper stage plane bed flow regime in this flow context it can be speculated that the liquefaction and deformation occurred when the flow conditions approached the plane bed phase probably inducing a highly differential turbulent pattern and pressure fluctuations sufficient to liquefy the fine medium sand the small flat topped deformation lenses also suggest liquefaction by cyclic loading whereas the solitary nature of the large lenses may alternatively be the result of impulsive loading from bank collapse in less well exposed fluvial successions the auto or allokinetic origin of recumbently folded cross strata may be difficult to determine however the common occurrence of recumbent folds in cross stratified fluvial sandstones and their virtual absence in marine cross stratified deposits suggests strongly that in the majority of cases the deformation was autokinetic resulting from flow phenomena typical of river channels this kind of deformation structure should thus not be attributed to an allokinetic seismic triggering mechanism unless independent evidence of fault activity can be documented

using neutron diffraction to examine the onset of mechanical twinning in calcite rocks experimental calibration of the calcite twin piezometer is complicated by the difficulty of establishing the stresses at which the twins observed in the final deformation microstructures actually formed in principle this difficulty may be circumvented if the deformation experiments are performed in a polychromatic neutron beam line because this allows the elastic strain and hence stress in differently oriented grains to be simultaneously monitored from diffraction patterns collected as the experiment is proceeding to test this idea small strain 0 3 uniaxial compression experiments have been performed on carrara marble grain size 150 m and solnhofen limestone 5 m at temperatures of 20 600 c using the engin x instrument at the isis neutron facility uk at the lowest temperatures 25 c carrara 200 c solnhofen the deformation response was purely elastic up to the greatest stresses applied 60 mpa carrara 175 mpa solnhofen the sign of the calcite elastic stiffness component c14 is confirmed to be positive when the obverse setting of the calcite rhombohedral lattice in hexagonal axes is used in the carrara marble samples deformed at higher temperatures elastic twinning was initiated at small stresses 15 mpa in grains oriented such that the schmid factor for twinning was positive on more than one e twin system at greater stresses 65 mpa at 200 c decreasing to 41 mpa at 500 c there was an abrupt onset of permanent twinning in grains with large schmid factors for twinning on any one e twin system no twinning was observed in the solnhofen limestone samples deformed at 200 or 400 c at applied stresses of 180 mpa these results highlight the potential of this approach for detecting the onset of twinning and provide through experiments on samples with different microstructures a strategy for systematically investigating the effects of microstructural variables on crystallographically controlled inelastic processes

grain fabric in hummocky cross stratified storm beds genetic implications abstract a detailed analysis of grain fabric in samples from hummocky cross stratified hcs storm beds suggests that these shallow marine sandstones were deposited from waning combined oscillatory unidirectional flows particle a axis orientations in the deposits in plan view parallel to visible lamination vary widely but have a mean orientation approximately normal to unidirectional paleoflow indicators sole marks and subparallel to regional shoreline this alignment of a axes is attributed to deposition under combined flows with a multidirectional oscillatory component produced by wind induced surface gravity waves with a modal crest orientation approximately parallel to the shoreline imbrication of particles varies in both the horizontally laminated and hcs intervals of the hcs stor beds due to waxing and waning of boundary shear stress caused by the oscillatory component of the flow in the basal horizontally laminated interval of an hcs storm bed grain imbrication angles vary about a mean of approximately 13 from the horizontal dipping into the paleoflow inferred from sole marks this preferred imbrication direction is attributed to boundary shear stress influenced by the unidirectional component of the combined flow however quasi cyclic variation in imbrication angle over a broad range and periodic reversal of imbrication direction suggest that the oscillatory component was also significant during deposition of the horizontally laminated interval in hcs intervals imbrication angles vary about a mean that is parallel to visible laminae suggesting th t oscillatory flow had become predominant the sequence of structures and changing patterns of fabric through these hcs storm beds is consistent with deposition under waning combined flows erosional scour forming the sharp base and unidirectional sole marks occurred in response to combined flows with an effective unidirectional component the unidirectional component continued to influence the direction of boundary shear stress during deposition of the horizontally laminated sands but waned and became negligible relative to a strong oscillatory component during formation of hcs

calcite twinning and determination of paleostress orientations three methods compared the classic turner 1953 method of determining 1 and 3 from an analysis of calcite twins is compared with a graphical method modified after dietrich and song 1984 and a newly devised method which treats calcite twin glide directions and twin planes in an analogous way to slickensides on fault planes all three methods provide similar positions for 1 but none gives a reliable position for 3 if a c axes preferred orientation exists 3 can most successfully be identified as the axis of a girdle of turner compression axes computer assisted adaptations of the turner method are recommended as the most rapid and internally consistent means of determining 1 and 3 the manual graphical method provides a useful check on turner determinations of 1 and a means of cleaning data

sequences of thrusts and displacement transfer in the superposed duplexes of the esla nappe region cantabrian zone nw spain abstract in a cross section through the southern arm of the cantabrian zone several duplexes have been identified below the esla nappe which is the uppermost and main thrust sheet of the area the folds deforming the esla nappe are culmination walls linked to frontal and lateral ramps belonging to the lower thrust sheets the thrust sequence can be established on the basis of quantitative analysis of displacement transfer and out of sequence thrusting the primitive footwall ramps of the esla nappe region were often subsequently broken by decollements developed in successively lower stratigraphic levels of these footwalls the kinematics of the lowest duplex are more complicated than those of typical duplexes described elsewhere some thrusts transfer only part of their displacement to the roof thrust while the remaining part is accommodated along the higher thrusts of previously emplaced duplexes cutting out of sequence one or more floor or roof thrusts cumulative displacement of the thrusts in this region is about 90 km giving a present thickness 3 times that of the original pre orogenic sequence together with a translation of at least 60 km for the synorogenic basin

hydrography and nutrient dynamics in the northern south china sea shelf sea nosocs abstract the hydrographic characteristics and the distributions of nitrate nitrite or n n and soluble reactive phosphate or srp in the northern south china sea shelf sea nosocs were determined in four transects across the shelf in the summer of 2010 and in two transects in the winter of 2011 the nosocs may be sub divided into the inner shelf the middle shelf and the outer shelf at water depths of 0 was found when salinity dropped below about 33 in these fresher waters which were found exclusively in the inner shelf during this study srp potentially could become the limiting nutrient

stratigraphic organization of late pleistocene deposits of the western part of the golfe du lion shelf languedoc shelf western mediterranean sea using high resolution seismic and core data detailed analysis of shallow penetration single channel seismic data integrated with piston core data reveals that the stratigraphic architecture on the rhone shelf of the western mediterranean sea is characterized by a complex stratigraphy comprising both the regressive and transgressive parts of late pleistocene depositional sequences several cycles of deposition are observed and are interpreted to be associated with fourth or possibly fifth order cycles of relative change of sea level the regressive parts of the sequence are inferred to have been deposited either during late highstand or during periods of relative fall of sea level these deposits are characterized in some instances by discrete downstepping wedges and internal downward shift surfaces however in other instances this evidence is not present the transgressive parts of the depositional sequences are characterized by backstepping wedges and isolated sand bars in general these types of deposits are more common on the western part of the rhone shelf and are largely absent on the extreme eastern part of the shelf the transgressive deposits seem to be preferentially preserved at both inner and outer shelf locations and less so in the middle shelf the exception to this is the area near the rhone delta depocenter where transgressive deposits are observed across the entire shelf key surfaces separating stratigraphic units include ravinement surfaces downlap surfaces and subaerially formed erosional surfaces these stratal discontinuity surfaces constitute the basis for analysis of the stratigraphic architecture this area is dominated by seismic reflection geometries suggesting a high energy depositional environment relatively steeply dipping seismic reflections bounded by horizontal to irregular erosional surfaces characterize most of the upper pleistocene section in this area the high energy seismic facies correspond to three types of deposits 1 thick regressive sands of lobate delta front origin 2 retrogradational beach barriers overlying the regressive wedge on the outer to middle shelf and 3 late transgressive beach sands and ridges observed at the inner shelf the stratigraphic complexity illustrated here is likely analogous to similar although commonly undetected complexity that characterizes petroleum fields in shallow shelf settings a variety of geomorphic elements have been interpreted here these include transgressive sand bars wave dominated distributary mouth bars recurved spits isolated shelf edge shoreface beaches and distributary channels these elements are consistent with an interpretation of a depositional environment characterized by wave dominated delta deposition the morphology of the delta in the eastern part of the shelf i e near the depocenter seems to be consistent from the outer to inner shelf location suggesting that the position of the shoreline relative to the shelf edge and the presence of submerged shelf outboard of the shoreline had only minor impact on deltaic deposition moreover climatic change and changes of fluvial discharge that likely characterized this area during the end page 119 late pleistocene similarly had only minor effect on delta morphology

towards an improved understanding of the mechanical properties and rheology of the lithosphere an introductory article to rock deformation from field experiments and theory a volume in honour of ernie rutter ernie rutter s influential contribution to our understanding of rock deformation spans the whole continental crust from deformation just under the grass e g rutter green 2011 to melt migration in the lower crust e g rutter neumann 1995 ernie has also worked on many aspects of the deformation of oceanic crust rutter brodie 1988 however here we reflect on the wide range of deformation conditions ernie has studied by presenting key aspects of the strength and rheology of the continental lithosphere as we understand it today with the aim of providing the context for the contributions included within this volume the continental crust forms just over a third of the earth s surface and it is different from the crust of any other planet in our solar system it is rich in those elements that partition in a silicate melt and its formation and evolution determined the composition of the mantle and that of the atmosphere hawkesworth 2006 thanks to its physical and chemical fingerprint the earth s crust has sustained life uninterrupted for 3 8 ga and it is the source of major natural resources such as hydrocarbons and mineral deposits and others such as geothermal energy the continental crust is less dense than its oceanic counterpart and is therefore more buoyant it forms a substantial part of the cold thermal layer of the earth and its rheology from greek r1v rhe flow and logia logia study the study of the flow of matter is a key factor controlling plate tectonic processes at the earth s surface and in its interior davies 2011 beneath the continental crust lies the lithospheric mantle and together they form the continental lithosphere considerable variations in structure thickness and composition of the continental lithosphere mean that despite its importance we currently have limited understanding of the rheology of this complex system thatcher pollitz 2008 significant advances in our knowledge of continental rheology have been possible through

precession related sapropelites of the messinian sorbas basin south spain paleoenvironmental significance abstract the sorbas basin southern spain is a narrow and elongated basin located in the betic corridor that formed the northern connection between the atlantic and the paleomediterranean during the late miocene in the centre of the basin about 120 m of well preserved cyclic marine sediments crop out ranging in age from 7 2 to 6 myr these cycles make up the abad member and are an excellent example of precession control over sedimentation in the upper part of the sequence upper abad member the cycles include organic rich laminated brown marls sapropelites alternating with homogeneous marls displaying diatomite layers the om rich laminated marls are the westernmost sapropelites of the mediterranean this paper is a geochemical mineralogical sedimentological and micropaleontological analysis of three cycles with sapropelites the data enable us to distinguish two main climatic scenarios the climate which dominated each of these scenarios regulated the sedimentology and the physico chemistry of the water column resulting in the sapropelite homogeneous marl cyclic alternations the sapropelites developed during a climate characterised by a long period of temperate and humid conditions that occur at times of precession minima these climatic conditions changed progressively to a subarid and drier weather during which homogeneous sediments were deposited the changes between these scenarios were gradual as expected from precession dynamics our data suggest that the change from the subarid to the humid climate transition from homogeneous marls to laminated sapropelites took place at a faster rate or at least was recorded more rapidly by the sediments than the transition from the humid interval to the sub arid period

development of a prograding carbonate wedge during sea level fall lower pleistocene of rhodes greece a lower pleistocene carbonate platform is described from north east rhodes greece it comprises a succession of warm temperate calcarenites the cape arkhangelos calcarenite facies group developed in a steep sided coastal basin the depositional setting for the sediments is a carbonate wedge developed within a larger scale forced regression deposition began with aggradation of storm dominated lower and upper shoreface deposits later the development of a prograding platform produced giant clinoform foresets a marked alternation of cross bedded and bioturbated clinoforms indicates seasonal transport of carbonate material off the platform periodically the platform edge has been deeply scoured by exceptional storms after which further deposition repaired the platform margin and progradation resumed more than 20 such major storm cycles are preserved applying sequence stratigraphy to this succession leads to two different possible interpretations one with a lowstand systems tract and one with a forced regressive systems tract depending on the scale of view the implications of this are discussed the present example shows clearly that the application of sequence stratigraphic models to real carbonate sequences requires careful consideration of scale and context before interpretations are made

the role of wave reworking on the architecture of storm sandstone facies bell island group lower ordovician eastern newfoundland stacked shallow marine cycles in the lower ordovician bell island group of bell island newfoundland show upward thickening and upward coarsening sequences which were deposited on a storm affected shelf in the beach formation each cycle has a facies sequence comprised from base to top of dark grey mudstones light grey mudstones tabular sandstones and mudstones lenticular sandstones and mudstones and thick bedded lenticular sandstones reflecting a progressive increase of wave orbital velocities at the sediment surface the mudstones and tabular sandstones reflect an environment in which the sea floor lay in the lower part of the wave orbital velocity field and in which tempestites were deposited as widespread sheets from weak combined flow currents the lenticular sandstones in the succeeding facies are wave reworked sands commonly lying in erosional hollows and having erosional tops and internal hummocky cross stratification planar lamination is relatively uncommon and sole marks are mainly absent in this facies oscillatory currents were dominant and accumulated sand in patches generally 10 30 m in diameter the facies formed on the inner shelf where the oscillatory currents generated by storm waves had powerful erosional effects and also determined the depositional bedforms mud partings and second order set boundaries within sandstone beds are believed to separate the products of individual storms so that many lenticular sandstone beds represent the amalgamation of several event beds this interpretation has important implications for attempts to estimate event frequency by counting sandstone beds within a sequence and for estimates of sand budgets during storm events the thick bedded lenticular facies appears to have been formed by erosion of the mud beds between the lenticular sands leading to nearly complete amalgamation of several lenticular sand bodies except for residual mud partings in the overlying redmans formation the process of amalgamation progressed even further so that nearly all the mud partings were removed resulting in the formation of thick bedded tabular sandstones sequence stratigraphic analysis of the cyclical sequence suggests that the cycles were eustatically controlled the rising limb of the sea level curve produced only the dark grey mudstone part of the cycle while the remainder of the cycle was deposited on the falling limb there is a gradational but rapid facies transition from the tabular to the lenticular sandstone facies which is interpreted as occurring at the inflexion point on the falling limb the thick bedded facies of the beach formation and the thick bedded tabular facies of the redmans formation represent periods of maximum sea level fall the stacked cycles in the beach formation are interpreted as an aggradational high frequency sequence or parasequence set bounded at the top by a sequence boundary and succeeded by the three aggradational parasequences of the redmans formation the recognition of storm facies with sandstone beds of very different bed length has important implications for the reservoir modelling of such facies

late miocene pleistocene tectono sedimentary evolution and subsidence history of the central betic cordillera spain a case study in the guadix intramontane basin the guadix basin became established as an intramontane basin in the central sector of the betic cordillera at the beginning of late miocene time its geodynamic evolution starts with a unit of tortonian marine sediments and is completed by a unit of late turolian pleistocene continental sedi ments in the two units six depositional sequences have been differentiated whose boundaries in most cases coincide with tectonic events geohistorical diagrams show the results of quantitative analyses of subsidence in the northern sector of the basin and permit correlation of the main events with signif icant changes in the history of subsidence and uplift a period of strong subsidence occurred at the beginning of tortonian time causing the formation of a marine basin 800 m deep the mid and end tortonian tectonic events involved periods of uplift leading to shallowing in the basin after continen talization at the end of the tortonian the basin was uplifted continuously from late turolian to late pleistocene times finally accumulating sediments at a height of 1000 m