aragonite relic preservation in jurassic calcite replaced bivalves shells of the aragonite bivalve neomiodon great estuarine group jurassic scotland replaced by coarse neomorphic calcite contain oriented relics of the original aragonite ultrastructure the presence of these relics in such old altered shells as well as the high sr content of the replacement calcite indicate that the process of calcite replacement of aragonite is not a cumulative slow process involving repeated alteration events but rather a rapid one step process aragonite relics once encased in neomorphic spar will survive as unequivocal evidence of original aragonite mineralogy barring total remobilization of the enclosing stable calcite a generally unlikely event the retention of this residual aragonite and high sr calcite supports recent isotopic studies which suggest that the multiple phases of alteration recrystallization invoked in earlier literature are unlikely events in the diagenesis of most undolomitized limestones retention of aragonite relics appears to be independent of whether alteration occurs in shallow meteoric or as in the case of our neomiodon material deeper burial environments pseudopleochroism of the replaced neomiodon shells appears to be due to organic largely graphitic relics not to the aragonite relics

sedimentology and isotope geochemistry of carnian deep water marl limestone deposits from the sicani mountains sicily environmental implications and evidence for a planktonic source of lime mud abstract the upper triassic halobia bearing marl limestone deposits from the sicani mountains sicily record the sedimentary evolution of the sicanian basin through the middle and late carnian time dark marls and interbedded grey calcilutites of julian age are characterized by abundant pyrite sparse bioturbation and negative carbonate carbon 13c values they accumulated in a basin with dominantly anoxic to dysaerobic bottom waters lower tuvalian dark grey pyritic marls and calcilutites which contain carbonate minerals with relatively high mn contents and widely fluctuating 13c signatures were deposited under dysaerobic conditions middle and upper tuvalian cherty limestones show intense bioturbation and nearly invariable positive 13c values around 2 for calcite they form a thick and monotonous succession accumulated in a deeper and more oxygenated basin the halobia bearing deposits preserve some calcareous nannoplanktonic forms the nannofossils varying in size from 7 to 32 m are significantly abundant in the cherty limestones pointing to a notable role of the calcareous nannoplankton as a source of carbonate mud in the deep water basins of the southern tethys during the late triassic time

contemporary tectonic motion of the eastern snake river plain a campaign global positioning system study a comparison of precision campaign gps data from 1995 and 2004 from ten benchmarks on the eastern snake river plain esrp has revealed that the province moved 2 8 0 3 mm yr to the sw 232 4 6 3 relative to a fixed north american reference frame the benchmarks had no measurable displacement relative to one another at the resolution of the gps during the nine year study evidence that the province moves as a rigid non extending block this scenario is supported by the aseismic nature of the province and the lack of measurable horizontal stress in boreholes however an additional small component of intra plain extension must also be invoked to account for the observed nw trending volcanic rift zones that transect the esrp we suggest that intra plain extension is too slow 1 mm yr to measure using our campaign gps methods but may be sufficient over millennial time scales to accommodate rift zone formation slower velocities measured on three benchmarks within the neighboring basin and range seismic parabola are consistent with this region serving as a zone of detachment between the north american craton and the faster moving esrp

cone penetration test cpt based subsurface soil classification and zonation in two dimensional vertical cross section using bayesian compressive sampling a novel method is developed in this study for soil classification and zonation in a two dimensional 2d vertical cross section using cone penetration tests cpts a cpt is usually performed verti

cyclic sedimentation in the southern alpine rhaetic the importance of climate and eustasy in controlling platform basin interactions uppermost triassic rhaetic facies as developed in the southern alpine region of northern italy were deposited in a rapidly subsiding fault dissected trough the lombardy basin bounded by carbonate platforms the main part of the rhaetic succession consists of 10 m scale asymmetric cycles each divided into three parts a lower shale portion a central rhythmic portion consisting of repeated marl limestone couplets the limestone parts of which thicken upward and an upper wholly carbonate unit a study of the diagenetic history of the series demonstrates that both the major asymmetric cyclicity and the limestone marl couplets of the central rhythmic member together constituting a compound cyclic form are fundamentally depositional in nature it is suggested that this compound cyclicity resulted from the superposition of a low frequency approximately 100 000 year periodicity asymmetric carbonate mud signal with a higher frequency terrigenous mud signal field petrographic and geochemical investigations suggest that the basinal carbonate is predominantly allochthonous in origin having been derived as relatively pure aragonitic mud from adjacent carbonate platforms it is postulated that the asymmetric carbonate signal was linked to the ecological effects of eustatic fluctuation on platform carbonate systems repeated subaerial exposure of subtidal muds in shallow areas indicates that such sea level variations occurred a model is presented in which the basinward export of carbonate was negligible in the deepening phase increased to a maximum during shallowing and was finally halted by the emergence of large platform flats in contrast the higher frequency terrigenous mud signal of the basin is thought to have been climatically modulated fluctuations of a shorter period than those predicted by the milankovitch theory affected hinterland precipitation and runoff particularly rapid subsidence and high depositional rates may have allowed the preservation of this signal

sea level highstand and lowstand shedding related to shelf margin aggradation and emersion upper eocene oligocene of maiella carbonate platform italy abstract sequence stratigraphic analysis of the upper eocene lower oligocene of the maiella carbonate platform allows the timing of shelf aggradation and erosion to be linked to shedding onto the slope and relative sea level stands the shelf was eroded during lowstands and the lowstand slope sediments are thin channelized lithic breccias with clasts eroded from an emerged reef tract highstand shedding of skeletal sands from the inner shelf resulted in thick coarsening and thickening upward successions of turbidites

glacial versus interglacial sedimentation rates and turbidite frequency in the bahamas the southern tongue of the ocean is a 1300 m deep flat floored basin in the bahamas that receives large amounts of sediment from the carbonate platforms surrounding it on three sides we have examined five 8 13 m long piston cores and determined bulk sedimentation rates turbidite frequency and turbidite accumulation rates for the past two glacial and interglacial periods the mean of bulk sedimentation rates is four to six times higher in interglacial periods average accumulation rates of recognizable turbidites are higher by a factor of 21 to 45 and interglacial turbidite frequency is higher by a factor of 6 to 14 sediment composition indicates that increased interglacial rates are due to higher accumulation of platform derived material additional data from other bahamian basins as well as published material from the caribbean strongly suggest that highstand shedding is a general trend in pure carbonate depositional systems carbonate platforms without a siliciclastic component export more material during highstands of sea level when the platform tops are flooded and produce sediment the response of carbonate platforms to quaternary sea level cycles is opposed to that of siliciclastic ocean margins where sediment is stored on the inner shelf during highstands and passed on to continental rises and abyssal plains during lowstands of sea level

speculations on the controls on cyclic peritidal carbonates ice house versus greenhouse eustatic controls abstract metre scale peritidal cyclothems which are distinctive components of lower palaeozoic and many mesozoic platform carbonates are not common in carboniferous sequences in their place the platform sequences are characterized by 5 10 m thick largely subtidal limestones with prominent exposure surfaces the former type of platform cyclothems developed during greenhouse phases when in the absence of major continental ice sheets sea level oscillations were caused by small scale obliquity and precession milankovitch rhythms under such conditions platforms rapidly aggraded with the deposition of peritidal cyclothems the carboniferous was an ice house phase when the waxing and waning of gondwanan ice sheets caused by eccentricity rhythm generated climatic changes created high amplitude rapid falls and rises in sea level the resulting carbonates reflect such changes with catch up subtidal dominated sequences and pronounced subaerial exposure surfaces capping the cyclothems

astronomical theory of the pleistocene ice ages a brief historical review abstract this paper traces the evolution of the astronomical theory of the pleistocene ice ages from its origin in the work of adhemar and croll through its quantitative transformation in the hands of milankovitch to its current renaissance emphasis is given to the interplay between climatic theory and geologic observation from 1941 when milankovitch published his final version of the theory until the early 1970s most attempts to test the theory empirically were carried out in the time domain by comparing the geologic record of climate with predicted climate curves these attempts ran into serious difficulties particularly the inaccuracy of the geologic time scale and the ambiguity of climate predictions early attempts to evaluate the theory with simple radiation balance models appeared to indicate that the climatic response to secular changes in the orbit would be too small to be observed geologically but by the mid 1970s the advent of an improved time scale for pleistocene marine deposits and the availability of long closely sampled records made it possible to arrange generalized but unambiguous tests of the theory in the frequency domain by comparing orbital and climatic spectra these results decisively confirmed the idea that orbital variations significantly influenced the earth s climate during the pleistocene but they did not tell us how this influence was exercised the emphasis of current work has therefore shifted to the identification and quantitative modeling of physical mechanisms by which the climate system responds so dramatically to the predicted rather subtle changes in radiative boundary conditions

closed system marine burial diagenesis isotopic data from the austin chalk and its components the carbon and oxygen isotopic composition of the austin chalk was examined in cores representing a range of depths from surface to 3000 m in order to document the effects of burial diagenesis on carbon and oxygen isotopic composition low magnesium calcite oysters were separated from 500 pm wide areas and analysed to estimate the starting composition of cretaceous marine sediment these gave an average value of 2 5 6 o 2 0 6i3c pdb the compositions of micrite intergranular cement and fracture cement were analysed and their deviation from this original marine composition was evaluated to document the progression of chalk diagenesis interestingly micrite exhibits only minor variation in composition from marine values despite present burial depth ranges in excess of 3000 m the average deviation from 6 o marine is less than 1 5 o furthermore intergranular cement and particularly fracture cements which occur only in the deepest cores and which clearly post date micrite lithification are generally indistinguishable from micrite in composition isotopic compositions exhibit no correlation with depth of burial despite abundant petrographic ev idence of deep burial diagenesis this uniformity in composition is interpreted as reflecting a closed rock dominated diagenetic system in which the compositionsof precipitated carbonate cements were controlled by the composition of dissolving carbonates during lithification as such the composition of burial cement is not representative of the rock water temperatures during precipitation thus in the context of isotopic analyses from other carbonate systems unless the degree of openness of the diagenetic system is known oxygen isotopic signatures of cements cannot directly be converted to the rock water temperatures at which they were precipitated unless the composition of the ambient porefluid is also known

hemipelagic shelf sedimentation and climatic cycles the basal jurassic blue lias of south britain abstract the sedimentology cyclicity and hiatuses of the blue lias formation basal jurassic were investigated at five localities in south britain most carbonate mud which is the dominant carbonate component has been neomorphosed to microspar however carbonate mud was apparently supplied by coccoliths in zooplankton faecal pellets suggesting hemipelagic sedimentation clay is assumed to have been supplied by rivers the three sediment types involved reflect cyclic changes in bottom water oxygenation levels combined with changes in the clay to carbonate mud ratio walsh power spectra have been applied for the first time to measured sections in order to investigate the control of cyclicity this application is analogous to palaeoclimatological studies of pleistocene oxygen isotope ice volume records the spectra show that 1 or 2 sedimentary cycles of constant thickness occur in four out of five sections each of which represents several million years the maximum possible duration of these cycles is too short for their generation by sea level changes their regularity stability and order of duration tens of thousands of years are consistent with the hypothesis of sedimentary cyclicity controlled by climatic change itself forced by orbital changes in insolation milankovitch theory the duration of both cycles recognised is less than 93 000 years 93 ka and may record changes in orbital precession 21 ka and obliquity 41 ka assuming that one ammonite zone represents 1 ma comparison of the longest possible with the implied durations of the cycles suggests that the sections are at best 20 40 complete loss of sediment may have occurred during winter storms or hurricanes a model relating the sedimentary cycles to changes in the volume of runoff is proposed

hydrocarbon provinces in the swiss southern alps a gas geochemistry and basin modelling study abstract in order to evaluate the petroleum potential of southern switzerland south alpine fold and thrust belt gas geochemical investigations including free and adsorbed gases were combined with a basin modelling analysis the palaeotectonic setting and alpine orogenic movements were recognized as main controls in the evolution of the petroleum generation potential three main hydrocarbon provinces are distinguished 1 the arbostora anticline which developed from an early jurassic high has excellent but immature source rocks which probably at no time generated hydrocarbons because of their swallow level in the nappe edifice 2 the stabio anticline south of the arbostora anticline in southernmost switzerland where wet gases are observed at the surface that are likely to have been generated from late cretaceous to present day from triassic source rocks occurring deeper in the nappe pile and 3 the m generoso basin with prevailing petroleum generation in the early jurassic and possible minor generation in marginal areas during cretaceous and tertiary times

deep water stratigraphic cyclicity and carbonate mud mound development in the middle cambrian marjum formation house range utah usa in mid middle cambrian time shallow water sedimentation along the cordilleran passive margin was abruptly interrupted by the development of the deep water house range embayment across nevada and utah the marjum formation 330 m in the central house range represents deposition in the deepest part of the embayment and is composed of five deep water facies limestone argillaceous limestone rhythmites shale thin carbonate mud mounds bioturbated limestone and cross bedded limestone these facies are cyclically arranged into 1 5 to 30 m thick parasequences that include rhythmite mound rhythmite shale rhythmite bioturbated limestone and rhythmite cross bedded limestone parasequences using biostratigraphically constrained sediment accumulation rates the parasequences range in duration from 14 to 270 kyr the mud mounds are thin 2 m closely spaced laterally linked symmetrical domes composed of massive fenestral peloidal to clotted microspar with sparse unoriented poorly sorted skeletal material calcitized bacterial filaments tubes and abundant fenestrae and stroma tactoid structures these petrographic and sedimentological features suggest that the microspar peloids clots and syndepositional micritic cement were precipitated in situ from the activity of benthic microbial communities concentrated growth of the microbial communities occurred during periods of decreased input of fine detrital carbonate transported offshore from the adjacent shallow water carbonate platform in the neighbouring wah wah range and throughout the southern great basin coeval mid middle cambrian shallow water carbonates are composed of abundant metre scale upward shallowing parasequences that record high frequency 104 105 years eustatic sea level changes given this regional stratigraphic relationship the marjum formation parasequences probably formed in response to high frequency sea level fluctuations that controlled the amount of detrital carbonate input into the deeper water embayment during high frequency sea level rise and early highstand detrital carbonate input into the embayment decreased as a result of carbonate factory retrogradation resulting in the deposition of shale base of rhythmite shale parasequences or thin nodular rhythmites followed by in situ precipitated mud mounds lower portion of rhythmite mound parasequences during the ensuing high frequency sea level fall lowstand detrital carbonate influx into the embayment increased on account of carbonate factory pro gradation towards the embayment resulting in deposition of rhythmites upper part of rhythmite mound parasequences reworking of rhythmites by a lowered storm wave base cross bedded limestone deposition or bioturbation of rhythmites by a weakened lowered o2 minimum zone bioturbated lime stone deposition this interpreted sea level control on offshore carbonate sedimentation patterns is unique to palaeozoic and earliest mesozoic deep water sediments after the evolution of calcareous plankton in the jurassic the presence or absence of deeper water carbonates was influenced by a variety of chemical and physical oceanographic factors rather than just physical transport of carbonate muds

bearing capacity of strip footings on sand over clay estimation of the bearing capacity of shallow foundations on layered soil profiles such as a sand layer of finite thickness over clay is mainly based on empirical models resulting from the interp

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

facies architecture of an early jurassic carbonate platform slope jbel bou dahar high atlas morocco the plateau of jbel bou dahar high atlas morocco represents an outstanding example of a well preserved early mesozoic carbonate platform field observations of the large scale sedimentary structures and the arrangement of lithofacies associations within the mid and lower slope were combined with detailed microfacies analyses and gamma ray measurements the investigations were carried out in order to 1 resolve the sequence stratigraphic architecture of the slope and 2 reconstruct the sediment export patterns and depositional processes related to high frequency sea level variations the slope strata are arranged into two different types of lithofacies associations that are bounded by characteristic discontinuities and show a specific occurrence along the investigated slope section the steep 8 18 mid slope is dominated by thick to medium bedded limestone successions that were able to maintain a high angle of repose due to their detrital composition the sediment packages are bounded by basal low angle unconformities and wedge out within the lower slope or thin into the adjacent basin as single carbonate layers the sediments are characterized by coarse grained and poorly sorted floatstones to rudstones which show low gamma ray values and contain components derived mainly from the platform edge the facies associations were interpreted as debris flow deposits that were exported during sea level lowstands when the flattened platform top and extended parts of the margin were exposed and sediment production was restricted mainly to the outer margin and upper slope section in contrast the gently dipping lower slope 4 18 is characterized by rhythmic limestone marl alternations that show increasing thicknesses with increasing distance from the platform from the lower part of the mid slope down the successions onlap the debris flow deposits forming a characteristic interfingering pattern of different lithofacies associations the medium to thin bedded carbonates of the limestone marl alternations comprise two different microfacies types 1 mudstones to wackestones with high gamma ray values and a mixed shallow marine to deep marine microfacies overlain by 2 well sorted arenitic packstones to grainstones with low gamma ray values and a shallow marine component composition the latter points to the platform interior and margin as primary source areas the shallow marine material was exported during sea level highstands when the carbonate factory included the entire platform margin and the flooded lagoons of the platform top during these periods the exported fine grained sediments could maintain only low angles of repose thus they bypassed the steep upper and mid slope sections developed into turbidites during downslope transport and were finally redeposited on the gently dipping lower slope and in the adjacent basin the architecture of the investigated slope area shows a characteristic interfingering of different facies associations that can be interpreted as genetic highstand and lowstand stratigraphic sequences the arrangement of these sequences along the slope as well as their composition were controlled by high frequency sea level fluctuations affecting the primary sediment production source area export patterns and sedimentary processes resulting in a shift of the depositional centers during different sea level stands

rigorous plasticity solutions for the bearing capacity of two layered clays this paper applies numerical limit analysis to evaluate the undrained bearing capacity of a rigid surface footing resting on a two layer clay deposit rigorous bounds on the ultimate bearing capacity are obtained by employing finite elements in conjunction with the upper and lower bound limit theorems of classical plasticity both methods assume a perfectly plastic soil model with a tresca yield criterion and generate large linear programming problems the solution to the lower bound linear programming problem is obtained by modelling a statically admissible stress field whereas the upper bound problem is solved through modelling a kinematically admissible velocity field results from the limit theorems typically bracket the true collapse load to within approximately 12 and have been presented in the form of bearing capacity factors based on various layer properties and geometries a comparison is made between existing limit analysis empirical and semi empirical solutions this indicates that the latt

millennial scale paleoclimate cycles recorded in widespread palaeozoic deeper water rhythmites of north america rhythmically interbedded limestone and shale or limestone and chert rhythmites are a common feature of many deep water phanerozoic carbonate marine deposits seventeen different palaeozoic rhythmite successions from across north america 8 studied in detail 9 studied in reconnaissance are described and summarized individual rhythmite couplets 4 20 cm thick are composed of fine grained laminated to massive detrital limestone alternating with shale or marl or laminated spiculitic chert stratigraphic and primary depositional features within rhythmites and associated facies indicates that the carbonate rich and carbonate poor interbedding is the result of repetitive changes in sediment input primary rather than due to diagenetic redistribution of calcareous material secondary the average duration of individual rhythmite couplets is calculated using spectral analysis to determine couplet thickness combined with biostratigraphically calibrated undecompacted average sediment accumulation rates the duration of rhythmite couplets from the eight well studied successions ranges between 150 and 4900 yrs with the majority lying between 1000 and 3000 yrs i e millennial scale the paucity and low diversity of skeletal and trace fossils preserved suspension laminae lack of sediment reworking and facies associations indicate rhythmite accumulation was favored by 1 deposition below storm wave base which limited reworking by currents 2 dysaerobic bottom waters which restricted bioturbation and intermixing of interbedded lithologies and 3 proximity to nearshore carbonates supplying abundant fine grained detrital carbonate these combined conditions were best met along flooded subtropical continental shelves or epeiric seas during my scale 3rd order sealevel rises the rhythmic alternation between carbonate rich and carbonate poor layers is interpreted to represent millennial scale paleoclimatic changes related to 1 wet dry climate cycles which influenced the amount of continent derived eolian and or fluvial sediment input 2 variations in offshore transport via storm generated or density currents of nearshore derived terrigenous or carbonate sediments and or 3 changes in wind driven upwelling and availability of recycled biogenic silica the various rhythmite successions accumulated under dramatically different paleoenvironment and paleogeographic conditions including active to passive tectonic settings equatorial to subtropical latitudes long term icehouse through greenhouse climatic conditions calcite versus aragonitic seas variable atmospheric co2 concentrations before and after land plant and animal evolution and across widely varying ocean basin configurations if our short term paleoclimatic interpretations for the rhythmites are correct then it is apparent that millennial scale climate changes occurred over a very wide spectrum of paleoceanographic paleogeographic paleoclimatic tectonic and biologic conditions and over time periods from the cambrian to the quaternary given this it is difficult to invoke models of internally driven thermohaline oceanic oscillations or continental ice sheet instabilities to explain their origin instead we suggest that

global sea level trend in the past century data derived from tide gauge stations throughout the world indicate that the mean sea level rose by about 12 centimeters in the past century the sea level change has a high correlation with the trend of global surface air temperature a large part of the sea level rise can be accounted for in terms of the thermal expansion of the upper layers of the ocean the results also represent weak indirect evidence for a net melting of the continental ice sheets

bearing capacity of a sand layer on clay by finite element limit analysis rigorous plasticity solutions for the ultimate bearing capacity of a strip footing resting on a sand layer over clay soil are obtained by applying advanced upper and lower bound techniques the study compares these solutions with other published results and investigates the effect of various strength and geometry parameters assuming the soil layers obey an associated flow rule the results presented typically bound the collapse load to within 10 or better key words limit analysis bearing capacity layered soils finite elements

stratigraphy and palaeoenvironmental analysis of the triassic jurassic transition in the western southern alps northern italy abstract high resolution stratigraphic studies were carried out on the rhaetian hettangian succession of the bergamasc alps western southern alps italy in order to characterise the stratigraphic and palaeoenvironmental evolution of the lombardian succession across the triassic jurassic t j boundary the t j boundary in the bergamasc alps is sandwiched between the rhaetian carbonate ramp succession of the zu limestone formation and the malanotte formation a new lithostratigraphic unit introduced in this paper deposited during relative sea level rise in the earliest hettangian the zu limestone is organised into subtidal mixed shale carbonate asymmetric cycles documenting the regional evolution from a distal to a proximal depositional environment of an articulated homoclinal carbonate ramp the malanotte formation lacks cyclicity and shows thin bedding and a dominant micritic facies documenting the subtidal evolution of a relatively homogenous outer carbonate ramp environment the microfloral associations record a gradual evolutionary change at the t j boundary whereas the biocalcifying communities appear to be severely affected by the end triassic biotic crisis

the interpretation of cyclic successions of the middle and upper triassic of the northern and southern alps abstract theories regarding the formation of sedimentary cycles in the 3rd 4th and 5th order bands are reviewed with reference to the middle and upper triassic of the northern calcareous alps nca and southern alps milankovitch autocyclic and tectonic theories are discussed together with an evaluation of concepts of chaotic sedimentation and a case example from the nca concerning eustasy 3rd 4th and 5th order sea level fluctuations were probably a low amplitude low rate phenomenon caused by fluctuations in the volume of mountain glaciers and ocean water during the triassic the mid and late triassic was a non glacial interval in which polar regions may have been ice free so glacio eustasy can not be expected eustatic sea level variations in the 3rd 4th and 5th order bands seem to have left no useful imprint on cyclic successions in the region whatever record there may be is inextricably mixed with two other signals tectonic activity and autocycles the review shows how sedimentation in the triassic of the area was strongly influenced by tectonic activity this is as true for the middle and late triassic of the nca as it is for the southern alps tectonic activity may be responsible for large scale cyclicity 4th to 3rd order scale although seismogenic structures have yet to be identified and described in carbonate successions of the alps candidates do exist slumped and microfaulted layers in laminated sediments of the seefeld basin upper triassic nca have been described as the products of fault movements the sedimentary record from the nca and southern alps also leaves little doubt that autocyclic processes were important in all environments except perhaps the deep sediment starved basins most small scale platform cycles 5th order scale in the region can be related to autocyclic processes and in shallow basinal successions to events such as storms previous workers have not been consistent in their interpretation of cyclic successions in the area applying diverse theories to similar successions so far the steinplatte hochkonig platform with attached kossen basin is the only example interpreted with reference to tectonics and autocyclicity eustasy was probably not the most important factor in cycle generation in the triassic of the nca and southern alps such an approach could prove useful in future studies

multifactorial control on deposition of epicontinental hemi pelagic carbonates during the earliest kimmeridgian prebetic zone southern spain abstract two successions of marly limestone limestone couplets occasionally with significant intercalations of marls have been investigated in the lower kimmeridgian platynota zone in the central sector of the prebetic zone southern spain the aim of this paper is to identify and evaluate possible interactions between global signals orbital fluctuations climate and eustasy and local regional tectonics forcing deposition and ecospace on an epicontinental shelf high resolution ammonite biostratigraphy together with sedimentological stratigraphical mineralogical data and ecostratigraphic interpretations were re examined to provide evidence for the combined action of tectonics eustasy and insolation fluctuations on sedimentation in two sections which clearly differ in stratal pattern both in the average thickness of limestone beds and in the frequency and character of marl intercalations the detailed analysis of stratal patterns was used to identify and calibrate the influence of the different factors investigated the identification of significant bedding planes in the sections studied enabled the recognition of eight bundles of beds major cycles the analysis and comparison of their internal structure together with the information about tectonic and eustatic influences enabled us to interpret the lower part of the sections bundles 1 and 2 as being forced by interactions between orbital signals and tectonics the upper part bundles 6 7 and 8 as being caused by interactions between orbital signals and eustasy and the middle part bundles 3 4 and 5 as being related mainly to orbital forcing

a guide to phanerozoic cold polar climates from high latitude ice rafting in the cretaceous the high latitude extent of warm climate indicators at certain times in earth history has been considered as evidence that the globe was ice free for long intervals despite theoretical considerations and results from numerical modelling experiments1 2 indicating that this was unlikely one of the warmest periods the cretaceous displays faunal and floral evidence for cool temperate to sub tropical conditions very near to the poles however our studies of lower cretaceous mudstones of central australia that contain outsized exotic blocks have led to the conclusion that the blocks were emplaced by ice rafting implying that high latitude ice was present at sea level strata of a similar origin of mid jurassic to mid cretaceous age occur on other continents that were positioned between 65 and 78 palaeolatitude indeed there is a record of high latitude ice rafting throughout the phanerozoic suggesting that ice was present on earth for much of its history and that ice free conditions could have been at most only episodic over the past 600 myr

the use of burrows to detect compaction and sliding in fine grained sediments an example from the cretaceous of s e france in the french southern alps alternating pelagic limestones and marls of hauterivian age contain a dense network of burrows differences between the original and preserved forms of the burrows provide evidence of sediment deformation a total compaction from early dewatering of sediment to deep burial compression caused flattening of burrows parallel to bedding its relation to carbonate is measured and a tentative mathematical relation is proposed b synsedimentary slumping is shown by total disordering of the bioturbation network in the displaced layers c a more characterized deformation is occasionally visible only on the upper part of some limestone beds the sliding is indicated by the dip of burrows in the same direction as the flow d similar embryonic flows occur in the middle of rare limestone beds it is thus suggested that this can account for some of the double beds that occur in pelagic alternations of calcareous and marly beds

deep crustal extensional faulting in the ivrea zone of northern italy abstract the ivrea zone in northern italy consists of amphibolite and granulite facies metasedimentary metabasic and ultrabasic rocks and is thought to represent a section through the deep continental crust detailed mapping of the high grade part of this zone has revealed a series of high temperature shear zones which after the effects of later low temperature faulting and folding have been removed appears to accommodate extension of the sequence the shear zones formed at temperatures similar to those at which thermal equilibration occurred in the host rocks and locally show evidence for development under prograde conditions these observations fit well with thermal effects calculated from a simple heat flow model for extensional faulting in this model the effects of shear heating and displacement of cool hanging wall rocks against hotter footwall rocks are calculated these observations indicate that faulting as a mode of failure may be important during extension of the lower continental crust especially when basic rocks are the dominant components of the rock pile a restored section through the extended lower crust as observed in the ivrea zone is presented and the extent to which the features observed are able to explain seismic reflectivity of the lower crust is discussed

the marl limestone rhythmites from the lower kimmeridgian platynota zone of the central prebetic and their relationship with variations in orbital parameters abstract the origin of the rhythmic marl limestone bedding recognized in lower kimmeridgian platynota zone succesions of the central prebetic southern spain is interpreted a detailed analysis was carried out on the basis of field observations and mathematical procedures of two sections characterized by the variable alternation of marly and limestone horizons the study primarily reveals signs of a possible secondary imprint in the stratification however we conclude that this imprint cannot have been sufficiently important to cause the recorded stratification or significantly alter the existing primary bedding the mathematical procedure applied to the thicknesses of the beds reveals the existence of different orders of cyclicity that are not recognizable in the field we were able to date these cycles by detailed biostratigraphy and the application of fourier spectral analysis the close relationship between the timing calculated for the marl limestone rhythms recognized in the lower kimmeridgian platynota zone successions and the periodicity assumed for milankovitch cycles has been shown for the first time in the prebetic zone and leads us to accept the influence of orbital variations on sedimentation in the sector that was studied we have also been able to recognize the influence of local factors which determined differences in the depositional organization in the sections studied

late triassic to late jurassic evolution of the adriatic carbonate platform and budva basin southern montenegro abstract southeastern montenegro is the only part of the adriatic carbonate platform adcp that bears record of its evolution from a ramp through a distally steepened ramp to a platform in this paper we present the sequence stratigraphy of the late triassic to late jurassic rocks from this part of tethys for the first time in the literature we discovered and described three new facies hardground and cerebroid oolites of the livari supersequence and black pebble conglomerate of the tejani supersequence the mid ramp and lower ramp cherty oolite wackestone and mudstone facies of the livari supersequence as well as oolite conglomerate facies of the stari bar supersequence were partially or completely reinterpreted the middle and late triassic rifting separated the adcp from the other south tethyan carbonate platforms and created the intraplatform budva basin the adcp evolved through three morphologic stages a detached ramp livari supersequence rhaetian early toarcian a distally steepened ramp tejani supersequence early toarcian middle callovian and an accretionary rimmed platform stari bar supersequence oxfordian to neogene the rhaetian regression is marked by a regional unconformity surface that represents a type s sequence boundary at the base of the livari supersequence lowstand wedge of the halobia limestone was the oldest sediment in the budva basin tst and hst of the livari supersequence include supratidal and intertidal inner ramp sediments ooid shoals and cyclic shallowing up parasequences of the mid ramp sedimentation rates were high in the inner ramp while budva basin received relatively thin accumulation of siliceous plankton a brief exposure of supratidal flats and ooid bars represents a type p sequence boundary between the livari and the tejani supersequences which was flooded by the early toarcian transgression tst and hst of the tejani supersequence consist of supratidal lagoon and shoal sediments in the inner ramp and deeper water carbonates of the mid and outer ramp highstand shedding of the sediment from the steepened ramp left thick deposits in the budva basin the bathonian regression is marked by a regional unconformity that represents a type s sequence boundary between the tejani and stari bar supersequences stari bar oolite conglomerate is a lowstand wedge of the stari bar supersequence the middle callovian transgression induced aggradation of ooid shoals deep into the platform interior oxfordian coral reefs created a rimmed platform and restricted export of the shallow carbonates into the budva basin

millennial scale climate origins for stratification in cambrian and devonian deep water rhythmites western usa abstract basinal facies of the middle cambrian marjum formation western utah and middle devonian denay limestone central nevada are characterized by thin rhythmically interbedded limestone and marl layers deep water rhythmites limestone layers average thickness range of 4 3 5 5 cm are composed of laminated to massive pelleted lime mudstone marl layers average thickness range of 0 7 1 7 cm are characterized by laminated argillaceous dolomitic mudstone the absence of current or wave reworked features paucity of bioturbation and skeletal fossils stratigraphic relationships with adjacent facies and the dark color indicate that limestone and marl layers in both rhythmite successions were deposited in quiet dysaerobic waters below storm wave base both limestone and marl layers are composed of submillimeter thick graded laminae which represent discrete depositional events from dilute density currents generated by high frequency storms or distal turbidity currents fluctuations in primary pelagic productivity cannot account for variations in carbonate influx because calcareous microfossils did not evolve until the mesozoic instead the rhythmic interbedding is interpreted to reflect climatically controlled variations in fluvial and or eolian influx or changes in marine currents storm or distal turbidity currents which transported shallow platform derived carbonate material into the deep water region spectral analysis of carbonate time series were compared to lithologic rank series and particularly for the middle cambrian rhythmites were found to be statistically indistinguishable the durations of significant spectral peaks were estimated from calculating the average sedimentation rates from the two biostratigraphically controlled stratigraphic sections these rates range between 4 3 4 1 cm k y and 21 2 29 2 cm k y for the cambrian and 3 6 1 8 cm k y to 5 1 7 4 cm k y for the middle devonian application of these sedimentation rates to the marjum couplets suggests that individual couplets represent between 190 2100 years of time the denay couplets represent 800 1900 years the good agreement between empirical holocene hemipelagic sedimentation rates and the sedimentologic evidence of relatively high depositional rates for the paleozoic rhythmites supports this millennial scale interpretation these results combined with that from previous work in paleozoic evaporite and carbonate successions suggest that millennial scale paleoclimatic variations affected marine and marginal marine sedimentation as far back in time as the cambrian millennial scale climatic change appears to be a permanent feature affecting the oceans and atmosphere and is apparently largely unaffected by major changes in phanerozoic paleogeography tectonics and atmospheric composition

high frequency depositional cycles in the muschelkalk middle triassic of southern poland origin and implications for germanic basin astrochronological scales abstract high frequency depositional cycles are often used for long distance correlations within sedimentary basins and constructing high resolution chronostratigraphic scales calibrated to the orbital clock such an approach has been used for the tropical epicontinental muschelkalk sea covering most of europe in the middle triassic this paper aims at establishing the spatial extent and internal architecture of shallow marine muschelkalk cycles within a small 120 by 50 km area of the germanic basin to identify their local vs regional distribution and cycle forming mechanisms three groups of cycles are distinguished 1 peritidal cycles representing a tidal flat lagoon system which experienced longer periods of emersion 2 shallow subtidal cycles formed around the fair weather wave base and 3 deep subtidal cycles developed around the storm wave base the three cycle types differ markedly in the composition facies homogeneity sedimentary trends hierarchical organization continuity and degree of lateral changeability and complexity which collectively translates into the ease of cycle recognition despite the differences the defined cycles do not extend laterally beyond the studied area and have laterally variable facies heterogeneities sedimentary trends and thicknesses this variability resulted from more or less mosaic infilling of accommodation space reflecting local bathymetry physicochemical conditions and carbonate production and accumulation rates on the platform accommodation space evolved by the interplay of eustatic sea level fluctuations regional subsidence and synsedimentary tectonic block movements but the contribution of these factors changed over time and was to varying degrees masked for each of the three cycle types by intrinsic sedimentary processes the study shows that middle triassic cycles of the germanic basin have a local to sub regional distribution and thereby are inappropriate for basin wide correlations and chronostratigraphic inferences it also strengthens the opinion of several workers that correlation of idealized cycles is unrealistic without checking the horizontal continuity of facies and key surfaces directly in the field

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

pre quaternary sea level changes while the paramount importance of global sea level changes has been widely accepted by quaternary geologists throughout this century it is only within the last decade that such changes in the rest of the phanerozoic have received much attention there are two principal reasons for this arousal of interest first increased exploration of the stratigraphic record across the earth both on land and under the sea and significant improvement in biostratigraphic correlation have drawn attention to what appear to have been globally synchronous events second oceanographic research has demonstrated the importance of tectonically controlled changes in the cubic capacity of the ocean basins notably variations in ridge volume which provide a ready mechanism for sea level changes even at nonglacial times the adjective eustatic was first proposed for global changes of sea level by suess 1906 in his great treatise the face of the earth the corresponding noun is eustasy not eustacy as it is commonly misspelt the unconvinced reader need only think of ecstasy eustatic sea level changes can be inferred as suess recognized by a plotting the temporal spread of marine sediments over the continents and b estimating the depositional depth variations in marine stratal sequences which can be correlated across and between continents to these methods can be added seismic stratigraphy in which biostratigraphically age determined seismic sequences on the con tinental margins are analyzed in terms of cycles of coastal onlap and offiap when the results of these methods are broadly in accord confidence in a eustatic interpretation is increased but the range of confidence can vary considerably it is widely accepted that there was an exceptionally high sea

bearing capacity of plane strain footings on layered soils a study has been carried out of the bearing capacity of sand layers overlying clay soils for the case where the thickness of the sand layer is comparable to the width of a rigid foundation placed on the soil surface a review of previous work is given and a discussion is presented of the dimensionless groups that govern the behaviour of this type of foundation a parametric study is carried out using both finite element and finite difference methods this study is based on the use of soil parameters obtained from an assessment of the range of values that might be expected to be appropriate for full scale structures the results of the parametric study are used to illustrate the mechanics of the system and also to develop charts that may be used directly in design in particular the results illustrate that the shear strength of the clay has an important influence on the mechanisms of load spread within the fill resume lion a roaliso une otude sur la capacito portante de couches de sable reposant sur des sols argileux pour le cas oo liopaisseur de la couche de sable est comparable la largeur diune fondation rigide posoe sur la surface du sol lion prosente une revue des travaux antorieurs et une discussion sur les groupes sans dimension qui rogissent le comportement de ce type de fondation une otude paramotrique est roalisoe en utilisant les mothodes tant des oloments finis que des difforences finies cette otude est fondoe sur liutilisation des paramtres de sols obtenus en partant de liovaluation de la plage des valeurs que lion pourrait siattendre trouver dans des structures pleine ochelle les rosultats de liotude paramotrique ont oto utilisos pour illustrer le mocanisme du systme et aussi pour dovelopper des abaques qui peuvent tre utilisoes directement dans la conception en particulier les rosultats illustrent que la rosistance au cisaillement de liargile a une influence importante sur les mocanismes de ropartition de la charge liintorieur du remblai mots clos capacito portante sols multicouches analyse numorique traduit par la rodaction

repeated subaerial exposure of subtidal carbonate platforms triassic northern italy evidence for high frequency sea level oscillations on a 104 year scale triassic carbonate platforms in northern italy ladinian latemar carnian durrenstein norian dolomia principale consist of hundreds of stacked meter scale cycles each made of a subtidal unit with a cap rock that carries vadose cements pisoids and tepee structures these diagenetic caps are interpreted to be due to subaerial exposure of the subtidal sediments the absence of peritidal deposits rules out progradation as the cause of the exposure i e these are not ginsburg autocycles thus the repeated exposure must be the result of relative sea level oscillations which based on the number of cycles and time intervals involved occurred with an average frequency in the 104 year range we postulate a combination of small scale high frequency eustasy and local tectonic movements e g differential subsidence in the norian and infrequent pulses of uplift in the ladinian to explain the cyclicity and its internal variations

a transition from carbonate shelf to pelagic basin environments of deposition rifting and depositional systems in the jurassic of northeastern tunisia jurassic deposition in the maghrebian tethys was governed by eustasy and rifting two periods were delineated 1 a carbonate shelf rhaetian early pliensbachian and 2 a platform basin complex early pliensbachian callovian the carbonate shelf evolved in four stages generating three sedimentary sequences j1 to j3 separated by boundary sea level falls drawdown exposure and local erosion sediment facies bear evidence of sea level rises and falls lateral changes in lithofacies indicate shoaling and deepening upward during the sinemurian a major pulse of rifting with an abrupt transition from carbonate shelf to pelagic basin environments of deposition marks the upper boundary of the lower pliensbachian carbonate shelf deposits this rifting episode with brittle fractures broke up the rhaetian early pliensbachian carbonate shelf and has created a network of grabens half grabens horsts and stacked ramps following this episode a relative sea level rise led to pelagic sedimentation in the rift basins with local anoxic environments that also received debris shed from uplifted ramp crests another major episode spanning the whole early pliensbachian bajocian is suggested by early brecciation mass flows slumps olistolites erosion pinch outs and sedimentary prisms a later increase in the rates of drifting marked a progress toward rift cessation during the late jurassic these jurassic carbonates with detrital deposits and black shales as the source rocks in northeastern tunisia may define interesting petroleum plays pinch out flanking ramps onlaps and structurally upraised blocks sealed inside grabens source rock maturation and hydrocarbon migration began early in the cretaceous and reached a maximum during the late tortonian pliocene atlassic orogeny