late mississippian glacio eustasy recorded in the eastern paleo tethys ocean south china abstract long lived and extensive glaciation during the carboniferous and early permian has been the focus of many studies over the past decade revealing systematic changes in sea level and climatic conditions the nature of the inception of carboniferous glaciation however remains poorly resolved with uncertainty regarding the timing and dynamics of buildup of continental ice sheets here we present detailed sedimentary facies and depositional cycles from upper mississippian shallow water platform and contemporaneous carbonate slope successions from the eastern paleo tethys ocean region south china to reveal systematic variations that provide insight into the sedimentary response to the onset of carboniferous glaciation based on detailed sedimentological logging and facies analysis four upper visean cycles and four serpukhovian cycles were identified from the carbonate platform yashui section bounded by either subaerial surfaces or zones or transgressive surfaces the cycle tops roughly correspond to intervals rich in normally graded bioclastic wacke to packstones and with distinct rises 1 in conodont 18opo4 in the carbonate slope naqing section in particular the four serpukhovian cycles correlate well to depositional cycles defined in the lower yangtze platform succession of south china and in the cyclothemic successions in the donets basin ukraine suggesting a glacio eustatic control most likely caused by repeated advance and retreat of gondwana glaciation during the onset but prior to widespread glaciation across the mid carboniferous boundary

late paleozoic glacial episodes in gondwanaland reflected in transgressive regressive depositional sequences in euramerica the late paleozoic glaciation of gondwanaland comprised two short episodes in the famennian i and visean ii confined to brazil and adjacent northwest africa and a long episode that started in the namurian iiia of eastern australia and bolivia argentina expanded to cover much of gondwanaland in the stephanian asselian iiib and collapsed in the early sakmarian iiic dropstones in eastern australia indicate that small ice centers lingered to the kazanian across the belt of low latitudes north of gondwanaland short ranging fossils in widespread shallow marine and paralic deposits indicate synchronous deposition of transgressive regressive sequences in different parts of euramerica these sequences correlate with glacial events in gondwanaland at three levels a four major regressions in euramerica in the famennian 1 visean 2 namurian 3 stephanian 4 and the tastubian transgression that preceded the sterlitamakian regression 5 also recorded in gondwanaland correlate with glacial episodes i ii and iiia iiib and iiic b the time interval of cyclothemic deposition in euramerica brigantian or latest visean to sterlitamakian correlates with that of glacial episode iii and c the dominant period of the euramerican cyclothems as estimated from the middle and late pennsylvanian deposits of the mid continent of north america and of the thickest known gondwanaland glacigenic sediment the earliest permian lyons group of western australia is 0 4 ma equivalent in turn to the long orbital eccentricity period of the quaternary ice age and the dominant period of fluctuation of the late miocene antarctic ice cap the three levels of correlations confirm wanless and shepard9s 1936 hypothesis that the late paleozoic cyclothems are controlled largely by sea level fluctuations related to the gondwanaland glaciation

paleolatitude distribution of phanerozoic marine ooids and cements opdyke b n and wilkinson b h 1990 paleolatitude distribution of phanerozoic marine ooids and cements palaeogeogr palaeoclimatol palaeoecol 78 135 148 data on 493 phanerozoic marine ooid and cement occurrences indicate that the dominance of calcite versus aragonite in tropical marine settings has changed in response to variation in atmospheric co2 and or oceanic temperature gradient holocene ooid and cement precipitation occurs over similar latitudes with means centered around 24 and 28 respectively aragonite and calcite also display roughly comparable distributions with average occurrences between 25 and 28 surface seawater saturation values requisite for ooid cement carbonate precipitation are at least 3 8 rs for aragonite and 3 4 a s for calcite ancient ooid cement occurrences vary in space and time with depositional zones generally closer to the equator during continental emergence greatest extent correlates with periods of maximum transgression aragonite formation is favored in more equatorial localities than calcite when cement ooid distributions are narrow and continents are emergent similarity of latitude distribution of marine ooids cement and biogenic carbonate suggests that physicochemical processes that control levels of carbonate saturation were more important in predicating sites of limestone accumulation in phanerozoic seas than biological processes related to net productivity of various carbonate platform communities continental position and tropical shelf area available for carbonate accumulation dictates the relative abundance of shallow water inorganic carbonate precipitates in space and time

the onset of the permo carboniferous glaciation reconciling global stratigraphic evidence with biogenic apatite δ18o records in the late visean the 18 o values of phosphatic microfossils recovered from nw ireland are used to determine the timing and magnitude of cooling associated with the onset of the carboniferous glaciation microfossil fish 18 o apatite demonstrates a 2 4 v smow shift which once corrected for 18 o seawater changes owing to evolving ice volumes equates to an approximate 4 5 c reduction in equatorial sea surface temperature between the earliest asbian and the mid brigantian late visean both conodont and microfossil fish 18 o apatite indicate stabilization of an icehouse climate during the brigantian and into the serpukhovian substantial late visean cooling identified herein is in good agreement with global glacioeustatic records supplementary material further information on the palaeogeography lithostratigraphy and palaeoenvironments of the sections examined as well as the sample composition and analytical methods of oxygen isotope analyses is available at http www geolsoc org uk sup18511

experiments on the terminal fall of the valves of bivalve molluscs loaded with sand trapped from a dispersion abstract paradoxically whereas turbidity currents are considered to flow swiftly the transported valves of bivalve molluscs found in their deposits typically lie concave up the attitude of least and also little resistance to overturning by a traction current but the stable attitude in free fall a valve can however enhance its overturning resistance at the bed by having previously trapped dispersed sand on its concave upper side while sinking stably through the current a maximum increase of immersed mass by a few to many times is theoretically possible the effectiveness of this mechanism is in practice controlled by the extent to which the sand load can grow without causing the sinking particle to fall unsteadily pitching or gyration of the valve leads to some sand spillage and tumbling to total loss tank experiments on the free fall of valves of 15 british mollusc species show that the regime of steady fall covers large relative loadings provided that the length and breadth of the valve are similar and the particle is not too flat large loadings are possible because the valves mainly fall concave up a valve in this attitude when fully laden resembles a cone with a spherical cap the growth in mass by sand entrapment as a valve sinks through a turbidity current is therefore an appealing way for the particle to reduce its chances of being overturned on reaching the bed and so be preserved concave up

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

estimation of effective porosity using geostatistics and multiattribute transforms a case study the middle eocene kalol formation in the north cambay basin of india is producing hydrocarbons in commercial quantity from a series of thin clastic reservoirs these reservoirs are sandwiched between coal and shale layers and are discrete in nature the kalol formation has been divided into eleven units k i to k xi from top to bottom multipay sands of the k ix unit 2 8 m thick are the main hydrocarbon producers in the study area apart from their discrete nature these sands exhibit lithological variation which affects the porosity distribution low porosity zones are found devoid of hydrocarbons in the available 3d seismic data these sands are not resolved and generate a composite detectable seismic response making reservoir characterization through seismic attributes impossible after proper well to seismic tie the major stratigraphic markers were tracked in the 3d seismic data volume for structural mapping and carrying out attribute analysis the 3d seismic volume was inverted to obtain an aco

lithology and hydrocarbon mapping from multicomponent seismic data elastic rock properties can be estimated from prestack seismic data using amplitude variation with offset analysis p wave s wave and density reflectivities or contrasts can be inverted from angle band stacks the reflectivities are then inverted to absolute acoustic impedance shear impedance and density these rock properties can be used to map reservoir parameters through all stages of field development and production when p wave contrast is small or gas clouds obscure reservoir zones multicomponent ocean bottom recording of converted waves p to s or ps data provides reliable mapping of reservoir boundaries angle band stacks of multicomponent p wave pz and ps data can also be inverted jointly in this paper aki richards equations are used without simplifications to invert angle band stacks to reflectivities this enables the use of reflection seismic data beyond 30 of incident angles compared to the conventional amplitude variation with offset analysis it in turn provides better shear impedance and density estimates an important input to amplitude variation with offset analysis is the v s v p ratio conventional methods use a constant or a time varying v s v p model here a time and space varying model is used during the computation of the reflectivities the v s v p model is generated using well log data and picked horizons for multicomponent data applications the latter model can also be generated from processing v s v p models and available well data reservoir rock properties such as poisson s ratio and bulk modulus can be computed from acoustic impedance shear impedance and density for pore fill and lithology identification and are the lame constants and p is density these estimations can also be used for a more efficient log property mapping v p v s ratio or poisson s ratio and weighted stacks such as the one computed from and are good gas oil and oil water contact indicators i e pore fill indicators while mainly indicates lithology is also affected by pressure changes results from a multicomponent data set are used to illustrate mapping of gas oil and water saturation and lithology in a tertiary sand shale setting whilst initial log crossplot analysis suggested that pore fill discrimination may be possible the inversion was not successful in revealing fluid effects however rock properties computed from acoustic impedance shear impedance and density estimates provided good lithology indicators pore fill identification was less successful neural network analysis using computed rock properties provided good indication of sand shale distribution away from the existing wells and complemented the results depicted from individual rock property inversions

quantification of the effects of eustasy subsidence and sediment supply on miocene sequences mid atlantic margin of the united states we use backstripping to quantify the roles of variations in global sea level eustasy subsidence and sediment supply on the development of the miocene stratigraphic record of the mid atlantic continental margin of the united states new jersey delaware and maryland eustasy is a primary infl uence on sequence patterns determining the global template of sequences i e times when sequences can be preserved and explaining similarities in miocene sequence architecture on margins throughout the world sequences can be correlated throughout the mid atlantic region with sr isotopic chronology 0 6 m y to 1 2 m y eight miocene sequences correlate regionally and can be correlated to global 18 o increases indicating glacioeustatic control this margin is dominated by passive subsidence with little evidence for active tectonic overprints except possibly in maryland during the early miocene however early miocene sequences in new jersey and delaware display a patchwork distribution that is attributable to minor tens of meters intervals of excess subsidence backstripping quantifi es that excess subsidence began in delaware at ca 21 ma and continued until 12 ma with maximum rates from ca 21 16 ma we attribute this enhanced subsidence to local fl exural response to the progradation of thick sequences offshore and adjacent to this area removing this excess subsidence in delaware yields a record that is remarkably similar to new jersey eustatic estimates we conclude that sea level rise and fall is a fi rstorder control on accommodation providing similar timing on all margins to the sequence record tectonic changes due to movement of the crust can overprint the record resulting in large gaps in the stratigraphic record smaller differences in sequences can be attributed to local fl exural loading effects particularly in regions experiencing largescale progradation

deltaic sedimentation in an unstable tectonic environment the lower limestone group lower carboniferous of east fife scotland the lower limestone group which outcrops extensively on the east coast of fife southeast scotland consists of interbedded sandstones siltstones and claystones with occasional coal seams and limestone beds several of the coals have been mined economically in the past the sequence was deposited in a shallow water deltaic setting three facies associations have been distinguished 1 laminated claystones and marine bioclastic limestones which were deposited in prodelta and marine shelf environments 2 crudely coarsening upward sandstone units interpreted as delta front deposits of fluvially dominated though wave influenced shallow water deltas and 3 interbedded clastic sedimentary rocks and coals deposited in delta plain environments the sequence as a whole accumulated by repeated progradation and abandonment of deltaic complexes palaeosol profiles of four types are superbly preserved within the delta plain facies association these are 1 organic soils peats now coal seams 2 gley palaeosols which formed in persistently waterlogged conditions 3 freely drained soils which formed on a quartz sand rich substrate and 4 similar profiles formed by free drainage through variable substrates and involving b horizon accumulation of concretionary iron oxides compound palaeosols are common deposition of the lower limestone group was influenced by the tectonic and volcanic instability of the fife area during visean times frequent seismic events centred on active fault lines caused local uplift of parts of the normally waterlogged delta plain environment allowing the formation of well drained soils peats coals were best developed and least affected by oxidation in an elongate fault bounded zone of enhanced subsidence

approaches to defining reservoir physical properties from 3 d seismic attributes with limited well control an example from the jurassic smackover formation alabama much industry interest is centered on how to integrate well data and attributes derived from 3 d seismic data sets in the hope of defining reservoir properties in interwell areas unfortunately the statistical underpinnings of the methods become less robust in areas where only a few wells are available as might be the case in a new or small field especially in areas of limited well availability we suggest that the physical basis of the attributes selected during the correlation procedure be validated by generating synthetic seismic sections from geologic models then deriving attributes from the sections we demonstrate this approach with a case study from appleton field of southwestern alabama in this small field dolomites of the jurassic smackover formation produce from an anticlinal feature about 3800 m deep we used available geologic information to generate synthetic seismic sections that showed the expected seismic response of the target formation then we picked the relevant horizons in a 3 d seismic data volume that spanned the study area using multiple regression we derived an empirical relationship between three seismic attributes of this 3 d volume and a log derived porosity indicator our choice of attributes was validated by deriving complex trace attributes from our seismic modeling results and confirming that the relationships between well properties and real data attributes were physically valid additionally the porosity distribution predicted by the 3 d seismic data was reasonable within the context of the depositional model used for the area results from a new well drilled after our study validated our porosity prediction although our structural prediction for the top of the porosity zone was erroneous these results remind us that seismic interpretations should be viewed as works in progress which need to be updated when new data become available

onset of late palaeozoic glacio eustasy and the evolving climates of low latitude areas a synthesis of current understanding studies of depth sensitive carbonate successions in the uk indicate that regular orbitally forced glacio eustatic sea level oscillations which characterized the late palaeozoic started abruptly around 330 ma early asbian the gondwanan ice sheet was highly sensitive to orbitally forced variations in solar insolation and the resultant sea level oscillations had an approximate 100 ka periodicity studies of fossil soils and palaeokarst from low latitude settings suggest that pre asbian climates were relatively stable with infrequent changes however climatic changes became increasingly frequent in the asbian and brigantian with regular fluctuations of a sub 100 ka periodicity occurring during glacial lowstand intervals

reservoir prediction of deep water turbidite sandstones with seismic lithofacies control a case study in the c block of lower congo basin abstract currently conventional forecasting methods of well to seismic integration are unable to identify turbidite channel sandstones due to scarcity of well data in deepwater areas small geophysical differences between sandstones and mudstones of turbidite channels and strong sandstones heterogeneity the reservoir prediction of deep water turbidite channels is still a difficult issue in deep water research on the basis of previous studies we propose a new technology named reservoir prediction of deep water turbidite sandstones with seismic lithofacies control in view of the characteristics of deep water turbidite sandstones this new technology improves the reservoir prediction of complex sedimentary systems after classifying seismic lithofacies and connecting lithofacies with rock physics furthermore it can accomplish the genetic classification statistics of rock physics improve conversion accuracy of seismic elastic parameters reservoir parameters and achieve the quantitative reservoir prediction under the double control of seismic geomorphology and seismic lithofacies the c block of lower congo basin is characterized by few well data complex lithology but high resolution seismic we use the technology to predict the reservoirs of this area and have achieved excellent results this has great significance for the later exploration

paleogeographic setting of pennsylvanian tyler formation and relation to underlying mississippian rocks in montana and north dakota pennsylvanian sedimentary rocks in the northern rocky mountains and in the northern great plains of the united states were deposited primarily on a broad marine shelf between the north american craton and the late paleozoic continental margin in idaho and adjacent states the lower pennsylvanian morrowan tyler formation comprises detrital sediments and some limestone beds in montana and north dakota that were deposited along an eastward transgressing marine shoreline after regional uplift warping and faulting had resulted in an erosional unconformity on top of mississippian strata the lower pennsylvanian shoreline finally extended onto the cratonic interior in eastern north dakota initial tyler sediments were deposited as a deltaic and fluviolacustrine complex succeeded by littoral deposits as the early pennsylvanian shoreline transgressed eastward across the shelf sediments were derived mostly from mississippian rocks exposed and eroded in south central montana and adjacent parts of wyoming and from the cratonic hinterland in eastern north dakota the tyler formation is subdivided into the stonehouse canyon member at the base the bear gulch member and the cameron creek member at the top the stonehouse canyon member consists of dominantly carbonaceous mudstone and lenticular sandstone beds that accumulated on a delta shore and plain as offshore bar beach channel levee lake and swamp and related deposits the bear gulch member which intertongues with the upper part of the stonehouse canyon member consists mainly of planar bedded calcareous mudstone that probably formed in a bay or an estuary adjacent to the delta the cameron creek member which overlies the two other members is dominantly red mudstone and represents oxidized subaerial and shoreface deposits on the upper delta platform the alluvial plain and the inte tidal mud flats of the encroaching sea the cameron creek grades upward into marine strata of the lower and middle pennsylvanian alaska bench limestone pennsylvanian deltaic deposition ceased in the region as the transgressing sea inundated the terrains that had previously supplied sediments to the tyler delta

significance of subtidal microbial deposits in shark bay australia abstract microbial deposits at shark bay australia constitute one of the largest and most diverse modern occurrences around the world the microbial carbonate system has developed in response to environmental change from near open marine into restricted embayment with hypersalinity and high evaporation bacterial sediments started depositing at about 2000 years bp after the holocene maximum flooding of sea level about 6800 years bp due to increasing salinity as the sea level fell by about 2 5 m within the holocene highstand system tract the extent and types of subtidal microbial substrate in this world heritage area have not previously been fully systematically mapped and described here we document the importance of subtidal microbial deposits occupying as much as 10 times the occurrence area of the intertidal microbial mats and stromatolites and demonstrate that deeper structures have a cerebroid external morphology with a non laminated internal fabric subtidal structures contain consistently different internal fabrics with carbonate grains and fragments interbedded with aragonitic micrite arranged in millimetric laminae or sub spherical patches which display fabrics such as well laminated smooth coarse laminated wavy colloform sub laminar to irregular with voids and biofragments of bivalves microbial pavement irregular clotted pustular and non laminated cerebroid constituting carbonate sediment with stromatolitic facies smooth and colloform thrombolitic facies pustular and cryptomicrobial non laminated cerebroid and microbial pavement each microbial structure grows in specific settings according to water depth msl with cerebroid build ups commonly occurring between 1 and 2 5 m and microbial pavement extending as deep as 6 m because of the late holocene sea level fall microbial structures often record in their internal features a shallowing up carbonate cycle these newly documented extensive subtidal microbial structures with distinctive morphologies and fabrics have importance as modern occurrences and provide potential analogues for understanding ancient microbial systems and environments

coral reefs and growth dynamics of a low angle carboniferous platform records from tianlin southern china abstract metazoan reef building receded globally during the carboniferous after the late devonian extinction events shallow water bioconstructions were generally small and scarce and corals played a minor role in their construction however in southern china one large 50 m high and three small 6 16 m high coral reefs dating from the late visean serpukhovian have recently been discovered in two localities in guangxi to understand the occurrence of these coral reefs and to constrain the factors that controlled their growth three sections around langping guangxi were measured and selected samples were analysed using petrography biostratigraphy and chemostratigraphy the depositional environment of these exceptional mississippian reefs was interpreted as a low angle platform 1 2 5 recording oligotrophic conditions and normal salinity the three small reefs have grown around the fair weather wave base whereas the large coral reef has grown in a deeper environment between the fair weather and storm wave base during carboniferous the global temporal reef distribution can be partly ascribed to paleoclimate changes however in southern china the growth of extended mississippian coral reefs is restricted to a short time window the late visean serpukhovian which coincides with high amplitude and high frequency sea level fluctuations most likely related to glacial pulses recent studies revealed that several rugose coral species survived the mid carboniferous glaciation event thanks to the persistence of warm water ocean currents maintaining tropical conditions on the platform due to the scarcity of extended coral reefs elsewhere it cannot be excluded that tianlin provided an ecological refuge for corals related to oceanic currents another potential favorable factor could be the mid ramp depositional setting the deep water platform areas could potentially provide more stable conditions less affected by global stress events however the deep reef refugia hypothesis remains debatable as only very few studies have explored its validity at the community level even if the causes of the occurrence of an extended coral reef in southern china cannot be fully constrained the existence of this large coral framework in the late visean serpukhovian provides additional evidence that coral communities did build reefs after the late devonian extinction events

estimation of the gas hydrate resource volume in a small area of the ulleung basin east sea using seismic inversion and multi attribute transform techniques we estimated the volume of gas hydrate and in place gas in a small 37 km 58 km area of the ulleung basin east sea from a dense grid of 2 d seismic and logging while drilling lwd data using seismic inversion and multi attribute transform techniques multi attribute transform finds the relationship between any measured or calculated logs and the combination of the seismic attributes and the acoustic impedance computed from inversion we assumed that the bottom simulating reflector marks the base of the gas hydrate stability zone ghsz first the pore space gas hydrate saturation at the wells was estimated from the simplified three phase biot type equation then the porosity and the pore space gas hydrate saturation along the seismic lines were predicted from multi attribute transform the ghsz was divided into ten layers of the equal time thickness the time thickness of each layer was converted into depth using the time depth relationship constructed from seismic to well tie at the wells and gridded at 500 m cell size the average porosity and pore space gas hydrate saturation were computed for each layer and multiplied to obtain the average total gas hydrate saturation which was gridded with the same cell size as the thickness grid thus each 2 d cell is represented by a rock volume and an average total gas hydrate saturation the gas hydrate volume for each cell was computed by the multiplication of the cell rock volume and the average total gas hydrate saturation finally the total gas hydrate volume was computed by summing the gas hydrate volumes of all cells the estimated gas hydrate and in place gas volumes in the study area are about 3 43 109 m3 1 21 1011 ft3 and about 4 50 1011 m3 1 59 1013 ft3 respectively the more conservative estimates excluding the top three layers that comprise about 50 m of the near seafloor sediments where the lwd data are often unreliable are 3 03 109 m3 1 07 1011 ft3 for gas hydrate and about 3 97 1011 m3 1 40 1013 ft3 for gas

seismic guided estimation of log properties part 1 a data driven interpretation methodology seismic data are routinely and effectively used to estimate the structure of reservoir bodies but often play no role in the essential task of estimating the spatial distribution of reservoir or rock properties yet for a long time we have been using attributes or other features of seismic data to gain useful clues in the interpretation process since the 1960s we have known that reflection amplitude is sensitive to the thickness of thin beds in the 1970s bright spots were discovered to be useful in forecasting the presence of gas sands then in the 1980s amplitude variation with offset avo analysis was identified as an even more refined indicator for gas sands or other situations giving rise to poisson s ratio contrasts other examples exist such as predicting porosity from calibrated acoustic impedance values computed from seismic data

a new stratigraphic framework built on u pb single zircon tims ages and implications for the timing of the penultimate icehouse parana basin brazil

kaolinite smectite mixed layer clays in the jiujiang red soils and their climate significance abstract clay mineralogy of the jiujiang soils classified as red earth on summit and slope were investigated using x ray diffraction xrd cation exchange capacity cec determination and high resolution transmission electron microscopy hrtem the xrd results show that the soils included kaolinite illite vermiculite and mixed layer i s and k s as clay minerals in xrd patterns of clay separates the low angle shoulder on the kaolinite 001 peak shifted to 8 a on glycolation indicating the presence of mixed layer k s clays in the soils kaolinite content in the interstratified kaolinite smectites was estimated to be 95 for samples of the middle to lower soil profile and 60 for that of the upper portion respectively a broad reflection for 10 14 a disappeared and an 18 7 a peak occurred in the xrd patterns after formamide treatment the 10 a peak became much more intense on heating to 400 c indicating that the 10 14 a peak was expandable and easily contractible and thus originated from mixed layer illite smectite i s clays after heating to 550 c the 7 a peak disappeared while the 10 a peak became more intense and showed a low angle tail indicating the interstratified smectite component was hydroxy interlayered the higher cec values of the jiujiang clay separates 22 2 27 3 cmol kg also pointed to the occurrence of smectite in the soils hrtem analysis showed different lattice fringes for clay particles in the samples a great majority of layer spacings were in the range 10 20 a with a minority of 7 and 25 a particles with 7 a fringes showed a lateral transition of two 7 a kaolinite layers merging into one 12 a smectite layer this can be interpreted as the partial intercalation of one smectite layer in kaolinite there was no long range order in the stacking sequence of k s layers and the interstratification was of a random nature in the uniform soil horizon of the upper profile there was more vermiculite and illite but less i s and k s while in the net like soil horizon of the middle lower profile there was more kaolinite i s and k s with only a trace of vermiculite the occurrence of k s clays confirmed that the jiujiang red earth was derived from syndepositional pedogenesis and the climates changed from warm and seasonally dry to warm and more humid conditions during the soil forming period

use of volume based 3 d seismic attribute analysis to characterize physical property distribution a case study to delineate sedimentologic heterogeneity at the appleton field southwestern alabama u s a abstract in this paper we illustrate the use of 3 d seismic attribute studies for predicting the distribution of physical properties in the subsurface using a data set consisting primarily of digital logs and seismic data we show how correlations can be made between seismic attributes and physical properties porosity and how those relationships can be exploited to predict the distribution of the property of interest in three dimensions the results of these studies 1 provide quantitative site specific 3 d models of physical properties that are of more use for applied studies than qualitative 2 d models commonly derived from facies modeling or sequence stratigraphic analysis 2 are generally more geologically reasonable than studies based on geostatistics alone 3 can provide sedimentary geologists with fundamental insights into depositional and or diagenetic controls on the distribution of properties of interest 4 need to be rigorously evaluated by integrating other types of data and analyses and 5 are best thought of as supplementing rather than replacing conventional geologic analyses the concepts and methods we illustrate may have application in various branches of sedimentary geology our study area is appleton field in southern alabama at this location we predict the 3 d distribution of porosity in carbonates of the upper jurassic smackover formation using a probabilistic neural network and a combination of four attributes our results suggest that porosity was best developed and preserved in thrombolite facies of the reef front

rapid onset of late paleozoic glaciation on gondwana evidence from upper mississippian strata of the midcontinent united states direct evidence of the late paleozoic glaciation of gondwana from glacial deposits suggests that geographically extensive continental glaciation began some time in the namurian late mississippian however the timing and characteristics of the onset of glaciation are poorly understood because of a lack of reliable paleontological control and reworking of initial glacial deposits by subsequent glacial advances indirect evidence of glaciation preserved in unconformity bounded low latitude ramp sequences in the illinois basin united states suggests that geographically extensive continental glaciation of gondwana actually began in the late visean an abrupt change from carbonate dominated sequences bounded by disconformities with little evidence of erosion to mixed carbonate siliciclastic sequences bounded by unconformities with deep incised valleys was likely produced by a three fold increase in the magnitude of eustatic sea level fluctuations the increase in the magnitude of sea level fluctuations was likely driven by an equally abrupt increase in ice volume and marks the onset of the geographically extensive late paleozoic glaciation of gondwana a possible explanation for the rapid onset of glaciation is the closing of the equatorial seaway between laurussia and gondwana closing of this seaway would have led to an abrupt change in oceanic and atmospheric circulation patterns that could have initiated major continental glaciation in the southern hemisphere

prediction of effective porosity from seismic attributes using locally linear model tree algorithm in this study a locally linear model tree algorithm was used to optimize a neuro fuzzy model for prediction of effective porosity from seismic attributes in one of iranian oil fields located southwest of iran valid identification of effective porosity distribution in fractured carbonate reservoirs is extremely essential for reservoir characterization these high accuracy predictions facilitate efficient exploration and management of oil and gas resources the multi attribute stepwise linear regression method was used to select five out of 26 seismic attributes one by one these attributes introduced into the neuro fuzzy model to predict effective porosity the neuro fuzzy model with seven locally linear models resulted in the lowest validation error moreover a blind test was carried out at the location of two wells that were used neither in training nor validation the results obtained from the validation and blind test of the model confirmed the ability of the proposed algorithm in predicting the effective porosity in the end the performance of this neuro fuzzy model was compared with two regular neural networks of a multilayer perceptron and a radial basis function and the results show that a locally linear neuro fuzzy model trained by a locally linear model tree algorithm resulted in more accurate porosity prediction than standard neural networks particularly in the case where irregularities increase in the data set the production data have been also used to verify the reliability of the porosity model the porosity sections through the two wells demonstrate that the porosity model conforms to the production rate of wells comparison of the locally linear neuro fuzzy model performance on different wells indicates that there is a distinct discrepancy in the performance of this model compared with the other techniques this discrepancy in the performance is a function of the correlation between the model inputs and output in the case where the strength of the relationship between seismic attributes and effective porosity decreases the neuro fuzzy model results in more accurate prediction than regular neural networks whereas the neuro fuzzy model has a close performance to neural networks if there is a strong relationship between seismic attributes and effective porosity the effective porosity map presented as the output of the method shows a highporosity area in the centre of zone 2 of the ilam reservoir furthermore there is an extensive high porosity area in zone 4 of sarvak that extends from the centre to the east of the reservoir

sequence stratigraphy and onlap history of the donets basin ukraine insight into carboniferous icehouse dynamics abstract the degree to which permo carboniferous cyclothemic successions archive evidence for long term variations in ice volume during the late paleozoic ice age is insufficiently resolved here we develop the sequence stratigraphy and onlap offlap history for a 33 my interval of the carboniferous using the u pb calibrated succession of the donets basin ukraine in order to assess the relationship between sea level high latitude changes in glacial extent and climate integrated subsurface and outcrop data permit meter scale correlation of 242 biostratigraphically constrained limestones and coals and in turn individual cyclothems across 250 km of the donets basin rapid uniform subsidence and basinwide continuity of marker beds indicate pennsylvanian deposition under relatively stable tectonic conditions three scales of sequences avg durations of 140 ky 480 ky and 1 6 my are recognized on the basis of stratigraphic stacking patterns and basinwide architecture of marine to terrestrial facies assemblages the hierarchy of sequences and the geographic and stratigraphic positions of shifts in base level sensitive facies across the donets ramp permit the construction of an onlap offlap history at a sub 400 ky scale major sea level lowstands occur across the mid carboniferous boundary and during the early moscovian these lowstands coincide with glacial maxima inferred from high latitude glacigenic deposits the middle to late pennsylvanian is characterized by a stepwise onlap culminating in an earliest gzhelian highstand suggesting contraction of carboniferous ice sheets prior to the initiation of early permian glaciation the stratigraphic position of climate sensitive facies within individual donets cyclothems indicates a turnover from seasonal sub humid or semi arid climate to everwet conditions during the late lowstand and maximum ice sheet accumulation comparison of the stratigraphic and aerial distribution of coals and evaporites in the donets basin with the onlap offlap history further indicates everwet conditions during lowstands and inferred glacial maxima and drier climate during onlap and inferred ice sheet contraction at the intermediate 0 8 to 1 6 my and long 106 yr time scales taken together the relationship between inferred climate and glacioeustasy suggests a likely teleconnection between high latitude ice sheet behavior and low latitude atmospheric dynamics

depositional processes on an ancient and modern muddy shelf northern california the modern eel river shelf and analogous pleistocene rio dell formation in northern california provide an ideal opportunity to combine the advantages of studying a modern environment with those of studying an ancient sequence and thereby enables further understanding of muddy shelf processes the modern shelf is the site of accumulation of a thick deposit of holocene mud both large scale sediment distribution patterns and small scale stratigraphy on the shelf indicate that river floods play an important role in sediment accumulation even on a high energy storm dominated coast the major factors in preservation of this flood signature are the cohesive behaviour of fine grained sediments and episodically rapid rates of sediment input the rio dell formation includes approximately 400 m of mostly fine grained shelf deposits that accumulated offshore from a palaeo eel river mouth the shelf sediments comprise four depositional sequences sequence 1 records progradation from outer to inner shelf depths facies trends closely resemble across shelf trends on the modern shelf suggesting that processes were similar detailed examination of these deposits provides insight into the nature and role of various processes on both the ancient and modern shelf muddy facies of the rio dell sequence are characterized by bioturbated clayey silts interbedded with event layers of several types clay rich silt layers are interpreted as flood deposits and physically stratified coarse silt layers are interpreted to record transport and deposition of coarse silt on the midshelf during storms sediment transport calculations and consideration of grain size distributions of bioturbated sediments which form the bulk of the rio dell sequence suggest that these sediments are the result of biological homogenization of the fine grained flood deposits and of the coarser grained storm deposits the results of this study in general indicate that fine grained shelf deposits do preserve a distinguishable if subtle record of depositional processes

linked sequence development and global climate change the upper mississippian record in the appalachian basin the character and relative stratigraphic position of paleoclimatic indicators within upper mississippian strata of southern west virginia suggest a link between eustasy and patterns of continental to global scale atmospheric circulation at the cyclothem scale annual rhythms in marine facies and paleovertisols and lacustrine carbonates in terrestrial units indicate that seasonal semiarid climatic conditions prevailed during highstand progradation in contrast leached paleosols and coals that underlie sequence boundaries and occur within transgressive heterolithic facies are suggestive of humid climatic conditions during late highstand through early transgression milankovitch band glacial interglacial cyclicity may explain both sequence development and the evidence for late mississippian climate fluctuations in the appalachian basin shifts from seasonal to humid climatic conditions are attributed to systematic variation in monsoonal circulation whereby seasonal moisture became restricted to the equatorial belt during the lowstands of each 400 k y glacial interglacial cycle

onset of the late paleozoic glacioeustatic signal a stratigraphic record from the paleotropical oil shale bearing big snowy trough of central montana u s a

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

bedding parallel fibrous veins beef and cone in cone worldwide occurrence and possible significance in terms of fluid overpressure hydrocarbon generation and mineralization abstract bedding parallel fibrous veins are common worldwide in sedimentary basins especially within strata of low permeability the term beef refers to bedding parallel veins of fibrous minerals where the fibres are mutually parallel and have formed quasi vertically more complex on a smaller scale are cone in cone structures yet these are also common within bedding parallel veins for both beef and cone in cone we have compiled a worldwide catalogue 157 localities typically the veins consist mainly of white gangue minerals for example calcite gypsum or quartz but may also contain accessory minerals of economic interest for example bitumen sulphides emerald pitchblende or gold fluid inclusions may contain oil or gas calcite beef 110 localities is common in organic rich shale of marine carbonate origin especially of 1 cambrian ordovician 2 devonian carboniferous 3 early jurassic or 4 cretaceous to palaeogene ages gypsum beef 30 localities is common in evaporitic or lacustrine strata of continental origin especially of triassic or neogene ages quartz beef 17 localities is common within meta turbidite sequences especially of ordovician or proterozoic ages because these modal ages seem to reflect climatic controls we infer that the fibre forming mineral species have not travelled far vertically the same conclusion holds for accessory minerals typical temperatures of formation are 1 up to 60 c for gypsum beef 2 70 c to 120 c for calcite beef and 3 200 c to 350 c for quartz beef hydrocarbon bearing calcite beef may be a good indicator of a petroleum system in which oil or gas migrate together with aqueous solutions we argue that beef and cone in cone layers result from tensile fracturing and vertical dilation coeval with fibre growth possible causes are either 1 force of crystallization or 2 seepage forces due to fluid overpressure for layers that form at depths of several km fluid overpressure is the more likely cause

prediction of 3 d fluid permeability and mudstone distributions from ground penetrating radar gpr attributes example from the cretaceous ferron sandstone member east central utah a 3 d fluid permeability distribution is estimated inside a channel sandstone reservoir analog in the cretaceous ferron sandstone fluvio deltaic complex in east central utah from ground penetrating radar gpr attributes fluid permeability measurements at 5 cm spacing along four boreholes and one pseudohole section at the adjacent cliff face are used together with instantaneous amplitude and frequency attributes of gpr data to predict fluid permeabilities away from the measured vertical transects and to delineate the distribution and geometry of mudstone layers inside the reservoir analog statistically significant relationships are determined between the well data fluid permeability and mudstone content and the gpr attributes these calibrations are applied to the entire gpr volume to estimate the 3 d fluid permeability variation and the lateral development of mudstone units measured and predicted fluid permeabilities range from 0 1 to 290 md one of the five units considered contained no mudstone lay

meteoroid mayhem in ole virginny source of the north american tektite strewn field new seismic reflection data from chesapeake bay reveal a buried 85 km wide 1 5 2 0 km deep peak ring impact crater carved through upper eocene to lower cretaceous sedimentary strata and into underlying pre mesozoic crystalline basement rocks a polymictic late eocene impact breccia composed mainly of locally derived sedimentary debris determined from four continuous cores surrounds and partly fills the crater structural and sedimentary characteristics of the chesapeake bay crater closely resemble those of the miocene ries peakring crater in southern germany we speculate that the chesapeake bay crater is the source of the north american tektite strewn field

pennsylvanian tropical rain forests responded to glacial interglacial rhythms pennsylvanian tropical rain forests flourished during an icehouse climate mode although it is well established that milankovitch band glacial interglacial rhythms caused marked synchronous changes in pennsylvanian tropical climate and sea level little is known of vegetation response to orbital forcing this knowledge gap has now been addressed through sequence stratigraphic analysis of megafloral and palynofloral assemblages within the westphalian d cantabrian sydney mines formation of eastern canada this succession was deposited in a low accommodation setting where sequences can be attributed confidently to glacio eustasy results show that long lived low diversity peat mires dominated by lycopsids were initiated during deglaciation events but were mostly drowned by rising sea level at maximum interglacial conditions only upland coniferopsid forests survived flooding without significant disturbance mid to late interglacial phases witnessed delta plain progradation and establishment of high diversity mineral substrate rain forests containing lycopsids sphenopsids pteridosperms cordaites and tree ferns renewed glaciation resulted in sea level fall paleovalley incision and the onset of climatic aridity glacial vegetation was dominated by cordaites pteridosperms and tree ferns hydrophilic lycopsids and sphenopsids survived in paleovalley refugia findings clearly demonstrate the dynamic nature of pennsylvanian tropical ecosystems and are timely given current debates about the impact of quaternary glacial interglacial rhythms on the biogeography of tropical rain forest

modern carbonate siliciclastic transitions humid and arid tropical examples climate and tectonic setting largely control characteristics of transitions between carbonate and siliciclastic sediments in depositional systems three examples selected from both humid and arid tropical settings are discussed order to illustrate details of these relationships the eastern shelf area of nicaragua is an area where siliciclastic and carbonate sediments actively interfinger under humid tropical conditions extremely high rainfall 4 5 m yr 1 in the southern part of coastal plain coupled with a correspondently high sediment flux to the nearshore shelf results in an inner shelf that is dominated by siliciclastics density gradients and persistent momentum provided by the trade winds force turbid coastal waters to the south and confine siliciclastic sediments to a coast parallel zone approximately 20 km wide the remainder of the broad shelf is characterized by carbonate sediments and reefs the mid shelf area has a coarse carbonate sediment cover composed largely of the calcareous green alga halimeda the outer shelf displays rugged topography associated with reef development skeletal carbonates containing abundant coral and coralline algal grains are characteristic of the seaward margin of the shelf significant amounts of siliciclastic sediment are confined to the nearshore part of the shelf and the transition from siliclastics to carbonates occurs over a distance of 20 km or less a second example from the humid tropics focuses on the living reefs of indonesia that are surrounded by fine grained siliciclastics a warm rainy climate results in rapid weathering of volcanic rocks from the indonesian archipelago and abundant sediment input to the shallow 40 70 m deep sunda shelf in the northern hemisphere winter monsoonally driven marine processes rrive water and sediment to the east down the axis of the java sea during summer the direction of transport is reversed this bidirectional process regime not only leaves its imprint in reef and carbonate platform morphology but also results in widespread distribution of siliciclastics from adjacent source areas isolated reefs as well as small and generally elongate reef rimmed carbonate platforms 0 5 10 km long rise 40 50 m above a sea floor composed largely of siliciclastic sediments in these cases facies transitions are very abrupt until environmental conditions curtail the carbonate producing communities of these platforms carbonate buildups and associated skeletal sediments will coexist with wider spread and more abundant siliciclastics a third example from a low latitude arid setting shows that facies transitions from carbonates to siliciclastics typically take place over short distances the lack of significant rainfall coupled with high relief along fault controlled basin margins promotes aperiodic but powerful episodes of siliciclastic that build directly into the marine environment high sloping and narrow coastal plains composed of overlapping fans result the steep seaward ends of these fans are maintained and protected from marine erosion by coral reefs and associated carbonates regionally siliciclastic to carbonate facies changes in these arid settings take place over very shor distances a few kilometers at most however on a local scale carbonates may be replaced by siliciclastics over distances as small as a few tens of meters

high precision u pb zircon ca id tims dates from western european late visean bentonites three new u pb zircon chemical abrasion isotope dilution thermal ionization mass spectrometry dates obtained from late visean belgian bentonites are reported and are used to estimate the periodicity of early warnantian shallowing upwards carbonate parasequences that are interbedded with the dated bentonites early warnantian parasequences exhibit mean cycle periodicity values that are consistent with the c 100 ka milankovitch cycle which is the dominant milankovitch frequency recognized from recent pleistocene glacial records and thus strengthen the arguments for 1 these sedimentary cycles being of glacio eustatic origin and 2 the initiation of the main phase of late palaeozoic glaciation before the start of or during earliest warnantian times the new dates also provide additional high precision age constraints for the improved calibration of the mississippian time scale using the new dates the stratigraphical age of the clyde plateau volcanic formation midland valley of scotland is revised from holkerian to early asbian supplementary material u pb zircon ca id tims data tables and the method of the mean cycle periodicity calculations are available at www geolsoc org uk sup18747

deposition of the bear gulch limestone a carboniferous plattenkalk from central montana the carboniferous bear gulch limestone of the central montana big snowy trough is a lithographic limestone analogous to the plattenkalk carbonates of the mesozoic european middle eastern tethyan belt it contains an excellently preserved chitinous and phosphatic marine fauna petrographic and field studies synthesized with palaeontological data provide insights into depositional history tectonic activity initiated development of small en echelon basins rims of these basins were sites of high primary productivity photosynthesis by subtidal cyanobacterial mats and algae caused in situ precipitation of micrite cyanobacteria and algae also provided a food source for benthic and nektonic organisms which provided food for predators respiration in turn provided carbon dioxide for continued photosynthesis thus a balanced ecosystem evolved productivity in the water column used up available oxygen resulting in dysaerobic to anaerobic conditions in the bottom waters and sediments this plus high sedimentation rates of carbonate ooze transported downslope aided in preservation of whole body fossils there are no likely modern analogues known for the bear gulch limestone however comparisons with mesozoic plattenkalke demonstrate that it is most closely analogous to those deposited in shallow water back reef areas of the tethyan carbonate platform rather than to those deposited in the deeper water shelf edge environment this is in agreement with the water depth of roughly 40 m estimated for the bear gulch limestone

eustatic and tectonic controls on deposition of hybrid siliciclastic carbonate basinal cycles discussion with examples changes in sea level represent one of the dominant controls on basinal sedimentation adjacent to mixed carbonate siliciclastic sediment source areas sedimentary responses to sea level change of the siliciclastic and carbonate components of these hybrid systems commonly result in deposition of alternating siliciclastic and shelf derived carbonate basinal deposits such deposition is particularly pronounced adjacent to carbonate platforms where alternate immersion exposure of the flat platform top results in carbonate highstand deposition and siliciclastic lowstand deposition in contrast small to moderate amplitude sea level drops in distally steepened ramp settings may expose only the inner part of the gently sloping shelf resulting in lowstand deposition of mixed sil ciclastic allodapic footnote 3 carbonate sediments along active margins tectonic uplift and subsidence of sediment source areas act as additional major controls on deposition of siliciclastic carbonate basinal cycles two of the most important tectonic effects are 1 uplift of siliciclastic sediment source areas resulting in increased erosion and swamping of carbonate shelf sources and 2 exposure or immersion of shelf carbonate sediment source areas due to vertical tectonic movements most published seismic stratigraphic studies of sea level control on deep sea sedimentation focus on lowstand deposition of siliciclastic sediment and commonly neglect the contribution of allodapic carbonate sediment deposited during sea level highstands however the examples discussed in this paper indicate that highstand carbonate deposits may make up a significant proportion of many hybrid carbonate siliciclastic basinal sequences

how big was the chesapeake bay impact insight from numerical modeling the chesapeake bay impact structure virginia is the largest impact crater in the united states the important question of how large the impactor was that formed the crater remains unanswered this is primarily due to peculiarities of the crater structure revealed by seismic exploration that complicate comparisons with other terrestrial and extraterrestrial craters one potential explanation for the unusual structure of the chesapeake bay crater is that the cratering process was affected by rheologic variations in the target at the time of impact using numerical modeling we find that for a sufficient contrast in material strength between the sedimentary and crystalline units at the chesapeake bay impact site we can produce a model of the final crater that is consistent with observational constraints and hence we can infer the energy released during the impact 1 75 3 10 6 mt in the absence of target strength variations the final crater diameter is likely to have been 40 km rather than the observed 80 90 km

co2 forced climate and vegetation instability during late paleozoic deglaciation the late paleozoic deglaciation is the vegetated earth9s only recorded icehouse to greenhouse transition yet the climate dynamics remain enigmatic by using the stable isotopic compositions of soil formed minerals fossil plant matter and shallow water brachiopods we estimated atmospheric partial pressure of carbon dioxide pco2 and tropical marine surface temperatures during this climate transition comparison to southern gondwanan glacial records documents covariance between inferred shifts in pco2 temperature and ice volume consistent with greenhouse gas forcing of climate major restructuring of paleotropical flora in western euramerica occurred in step with climate and pco2 shifts illustrating the biotic impact associated with past co2 forced turnover to a permanent ice free world

rapid sea level rise abstract several global and regional factors contribute to observed sea level change along any particular coast global processes include changes in ocean mass glacio eustasy from ice melt ocean volume steric effects viscoelastic land movements glacioisostatic adjustment gia and changes in terrestrial water storage regional processes often connected to steric and glacial changes include changes in ocean circulation meridional overturning circulation moc glacial melting local gia regional subsidence and others paleoclimate instrumental and modeling studies show that combinations of these factors can cause relatively rapid rates of sea level rise exceeding 3 mm yr 1 over various timescales along particular coasts this paper discusses patterns and causes of sea level rise with emphasis on paleoclimatological records it then addresses the hypothesis of late holocene pre 20th century sea level stability in light of paleoclimatic evidence notably from reconstructions of sea surface temperature and glacial activity for significant climate and sea level variability during this time the practical difficulties of assessing regional sea level sl patterns at submillennial timescales will be discussed using an example from the eastern united states

deep drilling into the chesapeake bay impact structure samples from a 1 76 kilometer deep corehole drilled near the center of the late eocene chesapeake bay impact structure virginia usa reveal its geologic hydrologic and biologic history we conducted stratigraphic and petrologic analyses of the cores to elucidate the timing and results of impact melt creation and distribution transient cavity collapse and ocean water resurge comparison of post impact sedimentary sequences inside and outside the structure indicates that compaction of the crater fill influenced long term sedimentation patterns in the mid atlantic region salty connate water of the target remains in the crater fill today where it poses a potential threat to the regional groundwater resource observed depth variations in microbial abundance indicate a complex history of impact related thermal sterilization and habitat modification and subsequent post impact repopulation

porosity prediction from seismic attributes of the ordovician trenton black river groups rochester field southern ontario this article integrates three dimensional 3 d seismic attributes and log data to determine porosity distribution of the ordovician trenton black river groups within the rochester field southern ontario the rocks are composed of tight limestone parts of which were dolomitized to form porous reservoir rock previous studies of the trenton black river dolomite reservoirs have indicated a close relationship between faulting and reservoir development but few published studies have attempted to examine these relationships using 3 d seismic data this study explores the stratigraphy and structure of the rochester fault related dolomite reservoir using 3 d seismic data and neural networks to predict porosity by predicting porosity using seismic attributes vertical and lateral distributions of porosity that can be used to guide development and exploration drilling for optimal hydrocarbon recovery were obtained the sites of highest porosity were found to be along and within the fault zones faults extending from the basement into overlying paleozoic rocks are composed of several short plane vertical and subvertical fault segments however some of these faults appear to have originated and died within the paleozoic rocks they cannot be traced to the basement because of little or no offset where they penetrate the basement although the five identified attributes are considered important in exploration for fault related dolomite reservoirs the single most important attribute to employ is the amplitude envelope because the other attributes are mathematically related to it furthermore the sags that are seen in the rochester field are due to the combined effects of low velocity pushdown and faulting methods and results presented in this study can be used to explore and develop fault related dolomite reservoirs elsewhere in similar geologic settings

the chesapeake bay bolide impact a convulsive event in atlantic coastal plain evolution abstract until recently cenozoic evolution of the atlantic coastal plain has been viewed as a subcyclical continuum of deposition and erosion marine transgressions alternated with regressions on a slowly subsiding passive continental margin their orderly succession modified mainly by isostatic adjustments occasional appalachian tectonism and paleoclimatic change this passive scenario was dramatically transformed in the late eocene however by a bolide impact on the inner continental shelf the resultant crater is now buried 400 500 m beneath lower chesapeake bay its surrounding peninsulas and the continental shelf east of delmarva peninsula this convulsive event and the giant tsunami it engendered fundamentally changed the regional geological framework and depositional regime of the virginia coastal plain and produced the following principal consequences 1 the impact excavated a roughly circular crater twice the size of rhode island 6400 km2 and nearly as deep as the grand canyon 1 3 km deep 2 the excavation truncated all existing ground water aquifers in the target area by gouging 4300 km3 of rock from the upper lithosphere including proterozoic and paleozoic crystalline basement rocks and middle jurassic to upper eocene sedimentary rocks 3 synimpact depositional processes including ejecta fallback massive crater wall failure water column collapse and tsunami backwash filled the crater with a porous breccia lens 600 1200 m thick at a phenomenal rate of 1200 m hr the breccia lens replaced the truncated ground water aquifers with a single 4300 km3 reservoir characterized by ground water 1 5 times saltier than normal sea water chlorinities as high as 25 700 mg l 4 a structural and topographic low created by differential subsidence of the compacting breccia persisted over the crater at least through the pleistocene in the depression are preserved postimpact marine lithofacies and biofacies upper eocene lower oligocene lower miocene not known elsewhere in the virginia coastal plain 5 long term differential compaction and subsidence of the breccia lens spawned extensive fault systems in the postimpact strata many of these faults appear to reach the bay floor and may be potential hazards for motion sensitive structures in population centers around chesapeake bay near surface fracturing and faulting generated by the impact shock may extend as far as 90 km from the crater rim 6 having never completely filled with postimpact sediments the sea floor depression over the crater appears to have predetermined the location of chesapeake bay 7 as large impact craters are principal sources for some of the world s precious metals it is reasonable to expect that metal enriched sills dikes and melt sheets are present in the inner basin of the crater in addition to these specific consequences the crater and the convulsive event that produced it have widespread implications for traditional interpretations of certain structural and depositional features of the atlantic coastal plain particularly in southeastern virginia

carbonate platform facies models various types of carbonate platforms are characterized by distinctive profiles facies and evolutionary sequences ramps may be homoclinal or distally steepened and may have fringing or barrier shoal water complexes of ooid pellet sands or skeletal banks homoclinal ramps pass seaward into deeper water without major break in slope and lack deep water breccias distally steepened ramps may be low energy and characterized by widespread shallow subwave base mud blankets or high energy with coastal beach dune complexes and widespread skeletal sand blankets slope facies may contain abundant breccias of slope derived clasts rimmed shelves have relatively flat tops and marked break in slopes at the high energy shallow shelf edge where they pass into deep water such shelves may be aggraded with peritidal facies extending over much of the shelf or incipiently drowned depending on magnitude of sea level fluctuations they may be accretionary or bypass types that include gullied slope escarpment and high relief erosional forms intrashelf basins occur on some shelves controlling distribution of reservoir and source beds isolated platforms are surrounded by deeper water and may be located on rifted continental margins or on submarine volcanoes most have high relief rimmed margins platforms that have been subjected to rapid sea level rise may be incipiently drowned and characterized by raised rims elevated patch or pinnacle reefs and widespread subwave base carbonate or fine clastic blankets completely drowned shelves develop where the shelf is submerged to subphotic depths terminating shallow water deposition and commonly resulting in blanketing of the shelf by deeper water facies some margins show extensive down to basin faulting that is contemporaneous with carbonate deposition or associated with thick prograding clastic sequences the various types of platforms change in response to variations in sedimentation subsidence or sea level rise and may form distinctive evolutionary sequences the relatively few models presented appear to accommodate most geological examples some of which contain major reservoir facies

climatic basis for sluggish macroevolution during the late paleozoic ice age rates of origination and extinction for marine invertebrates fell at the onset of the late paleozoic ice age in late mississippian time and remained low until glaciation ended in middle permian time through the use of a database of stratigraphic and geographic occurrences of brachiopod genera these macroevolutionary changes are traced to the loss of genera with narrow latitudinal ranges which had intrinsically high turnover rates at the onset of glaciation in late visean time when glaciation waned in late sakmarian time narrowly distributed genera rebounded abruptly and restored the global fauna to its pre ice age configuration because narrowly distributed brachiopod genera had dominated tropical diversity the major biotic effects of the late paleozoic ice age were felt at low latitudes the climatic regime of this ice age thus altered the marine ecosystem to one characterized by broadly adapted long lived genera

high tide of the warm pliocene implications of global sea level for antarctic deglaciation we obtained global sea level eustatic estimates with a peak of 22 m higher than present for the pliocene interval 2 7 3 2 ma from backstripping in virginia united states new zealand and enewetak atoll north pacifi c ocean benthic foraminiferal 18 o values and mg ca 18 o estimates statistical analysis indicates that it is likely 68 confi dence interval that peak sea level was 22 5 m higher than modern and extremely likely 95 that it was 22 10 m higher than modern benthic foraminiferal 18 o values appear to require that the peak was 20 21 m our estimates imply loss of the equivalent of the greenland and west antarctic ice sheets and some volume loss from the east antarctic ice sheet and address the longstanding controversy concerning the pliocene stability of the east antarctic ice sheet

strontium and carbon isotopic evidence for decoupling of pco2 from continental weathering at the apex of the late paleozoic glaciation

three dimensional seismic based definition of fault related porosity development trenton black river interval saybrook ohio oil and gas reservoirs of the ordovician trenton black river interval in the appalachian basin are commonly associated with fault related hydrothermal dolomites however relationships between porosity development and fault geometry in these fields are poorly documented in this article we integrate three dimensional 3 d seismic and wire line data from the trenton black river interval at saybrook field in northeastern ohio to study relationships between faulting and porosity development there faults were mapped using a combination of amplitude and coherency versions of the seismic data and a 3 d porosity volume was generated for the trenton black river interval by integrating attributes derived from the seismic data with log based measures of porosity the productive trend in the trenton black river interval at saybrook is controlled by a 3 4 mi 5 5 km long northwest southeast oriented basement fault that was probably reactivated during the taconic orogeny i e late ordovician strike slip movement along the fault generated en echelon synthetic shear faults that branch at least 1350 ft 411 5 m upward into the trenton black river interval the best porosity is developed in areas between overlapping synthetic shear faults antithetic shear faults probably formed at these locations and when combined with minor dip slip movement created conduits for subsequent porosity generating fluids circular collapse structures associated with localized extension between overlapping shear faults are the primary drilling targets and horizontal wells running parallel to the strike of the fault would have the best chances of intercepting good porosity development

model for transgressive black shales many black shales in thick epicontinental basinal successions formed beneath an oxygen restricted puddle of deep water other black shales formed during rapid transgression when basinal deposition expanded to cover basin margin areas normally characterized by shallow water deposition an expanding puddle model is developed from the early jurassic of england wherein rapid sea level rise leads to marine sediment starvation due to sediment entrapment in flooded river valleys subsidence sea level rise and decreased sediment supply during early transgression are suggested to lead to rapid deepening and therefore the expansion of the are of the puddle such that in previously shallow water areas black shales rest on condensed basal transgressive lags or unconformities that in turn rest on shallow water facies reestablishment of sediment influx and aggradation in excess of any continued sea level rise cause shallowing throughout the basin and the cessation of black shale formation

character of the alleghanian orogeny in the southern appalachians part ii geochronological constraints on the tectonothermal evolution of the eastern piedmont in south carolina a nearly concordant u pb zircon age of 550 4 ma is interpreted to closely date crystallization of the epizonal little mountain metatonalite in the southeastern part of the charlotte belt in south carolina this confirms field studies which indicate that the charlotte belt contains a plutonic metaigneous complex that developed as a sub volcanic arc infrastructure contemporaneous with vulcanism manifested in the carolina slate belt both paleontological and geochronological controls indicate that the south carolina slate belt is mostly younger than 570 ma cambrian whereas the slate belt in north carolina and virginia is mostly of late proterozoic age a regionally significant mid paleozoic ca 340 360 ma thermal event is suggested by discordant 40ar 39ar whole rock age spectra of slate phyllite in the northwestern carolina slate belt and from hornblende in the southeastern charlotte belt it is uncertain if this event was associated with deformation in the eastern piedmont however mid paleozoic deformation has been previously documented elsewhere in the western piedmont a slightly disconcordant u pb zircon age of 317 4 ma is interpreted to closely date initial crystallization of the deformed edge field granite and confirms a record of late paleozoic penetrative deformation in the kiokee belt of south carolina u pb isotope data for the lake murray orthogneiss and clouds creek granite are discordant and suggest that the magmas of these plutons were derived by partial melting of a sialic precam brian source and then emplaced in the eastern piedmont at ca 315 ma prior to or during the early stages of the alleghanian orogeny the thermal maximum of alleghanian regional metamorphism amphibolite facies in the kiokee belt greenschist facies in the southeastern part of the carolina slate belt occurred during ca 295 315 ma during the late carboniferous and early permian the eastern piedmont experienced differential uplift erosion and relatively rapid postmeta morphic cooling isothermal surfaces were folded into an antiform synform antiform configuration corresponding to the kiokee carolina slate and charlotte belts respectively the geochronological data provide the following calibration for the late paleozoic deformational chronology recorded in the kiokee and carolina slate belts d2 lake murray deformation ca 295 315 ma d3 clarks hill deformation ca 285 295 ma and d4 irmo deformation ca 268 290 ma

concavity orientations of bivalve shells in estuarine and nearshore shelf sediments georgia box core x ray radiographs from estuarine and closely adjacent nearshore shelf sediments of georgia were used to study interrelationships among detrital valve orientations sediment textures and physical and biogenic sedimentary structures the cores represent preserved sediment sequences and thus should be more indicative of the rock record than shell orientations observed on substrate surfaces with little bioturbation physical processes mainly govern shell configurations horizontal concave down valves predominate in large and small scale crossbedded sands laminated sands and thin shell beds inclined concave down valves also are common together with lesser numbers of horizontal concave up valves vertical and inclined concave up valves predominate in thick shell beds shell filled burrows and thin shell beds consisting of shell ornamented diopatra tube fragments horizontal concave up valves also are common in each of these and inclined concave down valves are abundant in thick shell beds with progressively more intense bioturbation as is commonplace in estuarine and nearshore shelf sediments proportions of horizontal and inclined concave down valves decrease as those of vertical and inclined concave up valves increase the latter two becoming dominant the abundance of horizontal concave up valves increases initially but decreases between 90 and 100 percent bioturbation some of these results especially the predominance of vertical and inclined concave up valves differ from those of previous workers small sizes of dominant georgia bivalves probably account for much of the difference because of pronounced local variations large numbers of measurements also are imperative

definition of subsurface stratigraphy structure and rock properties from 3 d seismic data abstract this paper summarizes how three dimensional 3 d seismic technology is being used primarily in the petroleum industry to define subsurface structure stratigraphy and rock properties a 3 d seismic data volume a provides a more accurate image of the subsurface than can be obtained with 2 d seismic methods b is continuous and so has a much greater spatial sampling than is obtained with 2 d seismic or other subsurface data e g wells and c can be viewed and interpreted interactively from a variety of perspectives thus enhancing the interpreter s ability to generate an accurate description of subsurface features of interest seismic interpretation was once the almost exclusive realm of geophysicists however most 3 d seismic interpretation today is conducted by multidisciplinary teams that integrate geophysical geological petrophysical and engineering data and concepts into the 3 d seismic interpretation these factors plus proper survey design help to increase the chances of success of a 3 d seismic interpretation project although there are cases where the technology is not appropriate or cannot be applied for economic reasons or otherwise the general success of 3 d seismic has led it to become a mainstay of the petroleum industry the approach and technology first developed in that industry have potential applications in other applied and fundamental earth science disciplines including mining environmental geology structural geology and stratigraphy

age constraints of the glaciation in the parana basin evidence from new u pb dates the absence of absolute dating in glacial deposits of the parana basin prevents better understanding of the complete history of the late palaeozoic ice age in western gondwana and the climatic change that took place in the late carboniferous in this study new u pb radiometric ages date the topmost glacial deposits of the itarare group at 307 7 3 1 ma kasimovian moscovian and the base of post glacial deposits of the rio bonito formation at 298 8 1 9 ma ghzelian asselian correlation of glacial and post glacial deposits of the parana basin with other southwestern gondwana basins shows that the end of the late palaeozoic ice age is asynchronous supplementary material laser ablation inductively coupled plasma mass spectrometry u pb zircon data and methods for the ash sample of the itarare group and the tonstein sample of the rio bonito formation are available at https doi org 10 6084 m9 figshare c 3278273

sequential colonization of muddy turbidites in the eocene beloveža formation carpathians poland abstract a 100 350 m thick succession of centimeter thick fine grained turbidites form the lower mud dominated part of a prograding deep sea fan in the eocene belove a formation in the carpathian mountains of poland these strata contain over 50 ichnotaxa only six of which are common phycosiphon nereites chondrites scolicia halopoa ophiomorpha polished slabs and examination of cross cutting relationships show that post event colonization was sequential using modern analogues it can be shown that the colonization of different depth levels in the sediment at different times reflects changing geochemical conditions especially the re adjustment and re establishment of the redox boundary modern analogues allow an assessment of the timing of each colonization phase the phycosiphon producers entered first and occupied the well oxygenated muds 5 40 mm below the sediment surface as the redox boundary reformed nereites producers entered and probably utilized microbial matter just above the redox boundary about 15 30 mm below the sediment surface subsequently chondrites producers penetrated down to the oxygen deficient layers of the event bed or even deeper levels the halopoa producers entered with phycosiphon but reworked coarser layers contemporaneously with this sequential colonization deep permanent bioturbators which were unaffected by the event cross cut the post depositional suite the variability of the resultant ichnofabrics can be attributed in part to a patchy distribution of the benthos and the relative frequency of turbidite events five ichnofabrics which reflect the successive colonization episodes are recognized each was modified by elements of the permanent infauna

experiments on the settling overturning and entrainment of bivalve shells and related models an experimental and theoretical examination has been made of the settling entrainment and overturning of 176 valves representing 16 common northwest european marine bivalve species together with a comparative study of 15 plastic models in the form of segments from cylindrical tubes settling behaviour in both stagnant and moving water depends on particle mass symmetry and concavo convexity separated empty bivalve shells spin and spiral while settling and if sufficiently elongated also pitch at the observed reynolds numbers the shells and models fall concave up the terminal fall velocity increasing as the square root of the unit immersed mass or weight the drag coefficient is independent of reynolds number but increases with surface roughness and particularly particle elongation turbulence slightly lowers the critical elongation for pitching a separation vortex lies captive on the upper side of each descending particle consequently an empty bivalve shell traversing a suspension of sand traps grains on its upper side at a rate proportional to their volume concentration and terminal fall velocity this process increasing the effective shell mass is limited only by the capacity of the shell and grain spillage due to the possible onset of pitching the ratio non dimensional of a quantity proportional to the applied fluid force and the particle unit immersed weight consistently describes the entrainment of concave up and convex up particles and also the immediate overturning of a valve on settling concave up to the bed these thresholds vary in relative magnitude with bed particle friction and particle concavo convexity in general convex up particles are the most stable the concave up entrainment and overturning thresholds are of a substantially lower but similar magnitude the high frequency of concave up bivalve attitudes in turbidites is understandable largely in terms of the ability of a settling valve to increase in effective mass by grain entrapment convex up attitudes in the lower parts of turbidites may record currents stronger than the overturning threshold

subsidence along the atlantic coast of north america insights from gps and late holocene relative sea level data the atlantic coast of north america is increasingly affected by flooding associated with tropical and extratropical storms exacerbated by the combined effects of accelerated sea level rise and land subsidence the region includes the collapsing forebulge of the laurentide ice sheet high quality records of late holocene relative sea level rsl rise are now available allowing separation of long term glacial isostatic adjustment induced displacement from modern vertical displacement measured by gps we compare geological records of late holocene rsl to present day vertical rates from gps for many coastal areas there is no significant difference between these independent data exceptions occur in areas of recent excessive groundwater extraction between virginia 38 n and south carolina 32 5 n the present day subsidence rates in these areas are approximately double the long term geologic rates which has important implications for flood mitigation tide gauge records therefore should be used with caution for studying sea level rise in this region

high precision u pb calibration of carboniferous glaciation and climate history paganzo group nw argentina the duration and geographic extent of carboniferous glacial events in southern gondwana remain poorly constrained despite recent evidence for a more dynamic glacial history than previously considered we report 10 high precision 2 0 1 u pb ages for the permian carboniferous paganzo group nw argentina that redefi ne the chronostratigraphy of the late paleozoic paganzo and rio blanco basins and signifi cantly refi ne the timing of glacial events and climate shifts in the western region of southern gondwana radiometric calibration of the paganzo group indicates three pulses of carboniferous glaciation in the mid visean the late serpukhovian to earliest bashkirian and between the latest bashkirian to early moscovian an abrupt shift in depositional style from high sinuosity single storied fl uvial deposits and clay rich paleosols to low sinuosity multi storied feldspathic fluvial deposits inter calated with eolianites and calcic paleosols is constrained to the latest moscovian and earliest kasimovian these constraints indicate a relatively abrupt climate shift from humid subhumid to nonseasonal semiarid regional climate conditions that occurred signifi cantly earlier than previously inferred early permian this period of high latitude aridity was contemporaneous with a shift to dryland depositional environments and a major vegetation regime shift documented throughout the pangean paleotropics in the pennsylvanian

stratigraphic architecture of the tonganoxie paleovalley fill lower virgilian in northeastern kansas lower pennsylvanian paleovalley confined sandstones are important petroleum reservoirs in the midwest in kansas such reservoirs have produced approximately 220 million bbl of oil and 1 7 tcf of gas valley fill successions tend to become muddy upward but there can be considerable local heterogeneity in which reservoir sandstones pass laterally into muddy sandstones or nonreservoir shales the lack of understanding of this reservoir heterogeneity can lead to low drilling success rates the tonganoxie paleovalley upper pennsylvanian northeastern kansas contains facies very similar to lower pennsylvanian morrowan valley fills and can provide an outcrop and subsurface based model of sandstone deposition the tonganoxie paleovalley was incised during lowered sea level and filled during the subsequent transgression the main paleovalley is approximately 41 m deep 11 km wide and 240 km long and was fed by 1 km wide tributary valleys oriented roughly normal to the trunk valley sandstones occur in four distinct architectural elements that were deposited during different phases of transgression type i sandstone consists of a belt of sandstone and conglomerate 3 18 m thick and confined to the trunk valley and wider portions of tributary valleys type i sandstone consists of amalgamated channel fills has little or no mud and has the highest porosity and permeability the type i sandstone is overlain by estuarine deposits of sandstone type ii sandstones rippled argillaceous sandstone to sandy mudstone and coal most of the paleovalley was filled during this stage the type ii sandstones are narrow 1 5 km wide arcuate bodies up to 8 km long and were likely deposited in tidal point bars near the fluvial to tidal transition are either isolated sandstone bodies or are incised into type i sandstone the higher mud content is expected to reduce porosity and permeability compared to fluvial facies type iii sandstone bodies occur at the upstream limits of narrow tributaries and are probably bay head deltas well logs indicate a range of mud content type iv sandstone is a thin 3 m discontinuous sheet of marine sandstone deposited after most of the paleovalley had been filled

facies sequences on a carbonate ramp the carboniferous limestone of south wales during early carboniferous times a major sea level rise led to the development of an extensive carbonate ramp over what is now south wales differential subsidence and sea level changes resulted in distinctive facies sequences in the ramp succession and a model is offered which recognizes three distinct geomorpho tectonic settings inner mid and outer ramp the inner ramp zone occurs in the more landward part of the province and was an area undergoing little or no subsidence the sequence is dominated by oolitic grainstones and peritidal limestones representing shoal and back shoal environments the peritidal units are transgressive deposits consisting of stacked asymmetrical shallowing up cycles the sequence contains many subaerial breaks and tectonic uplift resulted in base level changes and fluvial incision the mid ramp zone sequence is intermediate in thickness between the inner and outer ramp successions and consists mainly of bioclastic limestones deposited below fairweather wave base sedimentation periodically exceeded sea level rise and subsidence and regressive progradational oolitic sand bodies developed the thickest of which are stacked units with up to four individual sand bodies storm processes were of major importance in this setting the outer ramp zone is represented by a thick sequence of muddy bioclastic limestones deposited below storm wave base and major waulsortian reef mounds also developed none of the shallowing phases seen in the other ramp zones can be detected in this sequence subsidence and eustatic sea level rise seem to have been the major controls on deposition but the recognition of eustatic sea level falls is difficult the detailed facies model for ramp carbonates presented here may be applicable elsewhere in the geological record

carboniferous climate teleconnections archived in coupled bioapatite δ18opo4 and 87sr 86sr records from the epicontinental donets basin ukraine abstract reconstructions of paleo seawater chemistry are largely inferred from biogenic records of epicontinental seas recent studies provide considerable evidence for large scale spatial and temporal variability in the environmental dynamics of these semi restricted seas that leads to the decoupling of epicontinental isotopic records from those of the open ocean we present conodont apatite 18 o po 4 and 87sr 86sr records spanning 24 myr of the late mississippian through pennsylvanian derived from the u pb calibrated cyclothemic succession of the donets basin eastern ukraine on a 2 to 6 myr scale systematic fluctuations in bioapatite 18 o po 4 and 87sr 86sr broadly follow major shifts in the donets onlap offlap history and inferred regional climate but are distinct from contemporaneous more open water 18 o po 4 and global seawater sr isotope trends a 1 to 6 offset in donets 18 o po 4 values from those of more open water conodonts and greater temporal variability in 18 o po 4 and 87sr 86sr records are interpreted to primarily record climatically driven changes in local environmental processes in the donets sea systematic isotopic shifts associated with myr scale sea level fluctuations however indicate an extrabasinal driver we propose a mechanistic link to glacioeustasy through a teleconnection between high latitude ice changes and atmospheric pco2 and regional monsoonal circulation in the donets region inferred large magnitude changes in donets seawater salinity and temperature not archived in the more open water or global contemporaneous records indicate a modification of the global climate signal in the epicontinental sea through amplification or dampening of the climate signal by local and regional environmental processes this finding of global climate change filtered through local processes has implications for the use of conodont 18 o po 4 and 87sr 86sr values as proxies of paleo seawater composition mean temperature and glacioeustasy

source rock potential of evaporitic environment examination of modern saline lakes solar evaporation ponds and lagoons shows that the evaporitic environment can be very productive of organic matter few species survive in the brines but those that do commonly exist in great profusion in a marine evaporitic embayment the flow of surface currents is persistently toward regions of highest salinity so that there is a continual supply and concentration of nutrients prolific growth of phytoplankton may be similar to that in areas of upwelling in modern oceans only carbonates precipitate in the mesosaline part 4 to 12 salinity of such an evaporitic environment and no great dilution of organic matter by clastic or biogenic sediments occurs because stratification of brine may occur and reducing conditions may be a sociated with the bottom waters much of the organic matter produced can be preserved upon maturation the result may be a rich carbonate source rock frequently unrecognized in the geologic column in the middle east mesosaline conditions are known to have occurred many times from the triassic to cretaceous and may be responsible for the vast reserves of petroleum in the area evaporitic conditions may also have played a part in the petroleum productivity of many other areas including the michigan and paradox basins

stratigraphic imprint of the late palaeozoic ice age in eastern australia a record of alternating glacial and nonglacial climate regime stratigraphic and sedimentological data from new south wales and queensland eastern australia indicate that the late palaeozoic ice age comprised at least eight discrete glacial intervals each 1 8 ma in duration here termed glaciations separated by nonglacial intervals of comparable duration these events spanned an interval from mid carboniferous c 327 ma to the early late permian c 260 ma and illustrate a pattern of increasing climatic austerity and increasingly widespread glacial ice from initial onset until an acme in the late early permian followed by an opposite trend towards the final demise of glaciation in the late permian the alternating glacial nonglacial motif suggests that the late palaeozoic ice age was considerably more dynamic than previously thought these patterns are remarkably consistent with recent interpretations of palaeofloral change eustatic sea level fluctuations and co 2 climate glaciation relationships for this interval of time the detailed record of alternating glacial and nonglacial climate mode disclosed herein may facilitate more closely resolved evaluations of stratigraphic records elsewhere notably in far field ice distal northern hemisphere successions

ice volume and paleoclimate history of the late paleozoic ice age from conodont apatite oxygen isotopes from naqing guizhou china abstract a high resolution and continuous conodont apatite oxygen isotope record spanning the late visean to middle permian is reported from south china which is interpreted with respect to the ice volume and or tropical seawater temperature history of the late paleozoic ice age lpia the presented 18o record shows significant fluctuations in 18o from the late visean to middle permian with highest values observed in the bashkirian early pennsylvanian the 18o maximum coincides with a major eustatic sea level fall recorded in low latitude successions and postdates the significant increases in 87sr 86sr and 13ccarb measured on well preserved brachiopod calcite which can be interpreted as reflecting intensified weathering as consequence of the closure of rheic ocean as well as enhanced carbon burial both processes may have contributed to lower greenhouse gas levels and cooled down the earth s surface triggering the maximum glaciation the high bashkirian 18o values are interpreted to represent the glacial maximum of the lpia a coeval change in faunal composition and a decreasing diversity in climate sensitive marine invertebrates can be ascribed to icehouse cooling and or loss of habitat despite inconsistencies with earlier interpretations that the early permian represented the glacial maximum of the lpia as inferred from gondwanan glacial sediments records the suggested bashkirian glacial maximum agrees well with ice extent estimates based on the regional tectonic history in gondwana which suggests that the bashkirian glaciation occurred during gondwana interior uplift promoting maximum ice cover of the entire lpia however maximum glaciation is only poorly represented in the depositional record because large parts of the glacial deposits were possibly removed by erosion as outlined by a major regional unconformity

the magnitude of late paleozoic glacioeustatic fluctuations a synthesis a comprehensive literature review shows that the magnitude of eustatic fluctuations varied throughout the carboniferous and permian and that at least eight distinct phases can be recognized facies juxtapositions in carbonate successions and erosional relief in clastic successions indicate that glacioeustatic fluctuations of 20 25 m and occasionally as much as 60 m took place throughout the early mississippian tournaisian a widely recognized glacial period middle mississippian mid chadian through holkerian shallow marine carbonate and clastic successions indicate that eustatic fluctuations were 10 25 m a decrease that matches well with the paucity of coeval glacial deposits late visean asbian through mid brigantian glacioeustatic fluctuations of 10 50 m record the initial phases of ice accumulation in advance of the widespread mid carboniferous glacial event the latest mississippian earliest pennsylvanian mid brigantian through langsettian was a time of widespread glaciation and strata of this age commonly exhibit evidence of glacioeustatic fluctuations of as much as 40 100 m although middle pennsylvanian duckmantian through asturian glacial deposits are present in eastern australia paleovalley depths suggest that coeval glacioeustatic fluctuations were less than 40 m glacioeustatic fluctuations of as much as 100 120 m have been widely reported from late pennsylvanian earliest permian stephanian through mid sakmarian successions in north america an increase that corresponds to the growth of large ice sheets across much of gondwana and the accumulation of ice in the northern hemisphere incision and facies juxtaposition in early middle permian mid sakmarian through kungurian successions in eastern australia indicate that glacioeustatic fluctuations of 30 70 m occurred during the waning stages of major glaciation erosional relief in paleoequatorial carbonates and the presence of coeval glacial deposits in australia suggests that eustatic fluctuations of 10 60 m occurred during the final stages of glaciation in the middle to late permian roadian through capitanian but the modest size of most of these fluctuations makes it difficult to isolate the glacioeustatic signature this review demonstrates that far field cyclic successions record changing glacial conditions in gondwana that the magnitude of glacioeustatic fluctuations was directly related to the volume of glacial ice that carboniferous permian glacioeustasy was more variable than previously recognized and that generalizations from short temporal intervals are probably not representative of the late paleozoic ice age as a whole although any attempt to quantify the magnitude of ancient eustatic changes is based on caveats and assumptions this review incorporates the results of over 100 published papers on the topic in an attempt to minimize the errors inherent in any one study

clay minerals in soils as evidence of holocene climatic change central indo gangetic plains north central india clay mineral assemblages of a soil chrono association comprising five fluvial surface members qgh1 to qgh5 of the indo gangetic plains between the ramganga and rapti rivers north central india demonstrate that pedogenic interstratified smectite kaolin sm k can be considered as a potential indicator for paleoclimatic changes during the holocene from arid to humid climates on the basis of available radiocarbon dates thermoluminescence dates and historical evidence tentative ages assigned to qgh1 to qgh5 are 500 yr b p 2500 yr b p 8000 tl yr b p and 13 500 tl yr b p respectively during pedogenesis two major regional climatic cycles are recorded relatively arid climates between 10 000 6500 yr b p and 3800 yr b p were punctuated by a warm and humid climate biotite weathered to trioctahedral vermiculite and smectite in the soils during arid conditions and smectite was unstable and transformed to sm k during the warm and humid climatic phase 7400 4150 cal yr b p when the humid climate terminated vermiculite smectite and sm k were preserved to the present day the study suggests that during the development of soils in the holocene in alluvium of the indo gangetic plains climatic fluctuations appear to be more important than realized hitherto the soils older than 2500 yr b p are relict paleosols but they are polygenetic because of their subsequent alterations

wave enhanced sediment gravity flows and mud dispersal across continental shelves reappraising sediment transport processes operating in ancient mudstone successions recent studies of marine shelf sediment dispersal show that wave enhanced sediment gravity flows are widespread phenomena and can transport large volumes of fluid mud rapidly across low gradient shelves flow evolution is controlled by sediment supply seabed gradient and spatial distribution of wave energy at the seabed using existing flow models we predict that such flows in mud dominated sediments will develop a three part microstratigraphy produced by changing flow conditions beginning with wave induced turbulent resuspension then development of a wave enhanced sediment gravity flow prior to lutocline collapse and suspension settling petrographic examination of modern flow deposits collected from the eel shelf reveals that resultant beds possess a microstratigraphy consistent with our hypothesis a silt rich basal subunit with curved ripple laminae abruptly overlain by a subunit composed of continuous intercalated silt clay laminae and an upper clay rich drape analyses of beds from ancient mud rich outer shelf and basinal successions cleveland ironstone jurassic uk and mowry shale cretaceous united states show that they too contain beds with this three part organization suggesting that such flows were active in these ancient settings too recognition of these microstructures in these ancient mud dominated successions demonstrates that sediment in these settings was commonly reworked and transported advectively downslope by high energy events contrasting with previous interpretations of these units that deposition was dominated by quiescent suspension settling identification of these recognition criteria now allows the products of this newly recognized sediment dispersal mechanism to be identified in other shale dominated successions

impact effects and regional tectonic insights backstripping the chesapeake bay impact structure the chesapeake bay impact structure is a ca 35 4 ma crater located on the eastern sea board of north america deposition returned to normal shortly after impact resulting in a unique record of both impact related and subsequent passive margin sedimentation we use backstripping to show that the impact strongly affected sedimentation for 7 m y through impact derived crustal scale tectonics dominated by the effects of sediment compaction and the introduction and subsequent removal of a negative thermal anomaly instead of the expected positive thermal anomaly after this the area was dominated by passive margin thermal sub sidence overprinted by periods of regional scale vertical tectonic events on the order of tens of meters loading due to prograding sediment bodies may have generated these events