lower cretaceous lacustrine source rocks in northern gabon effect of organic facies and thermal maturity on crude oil quality abstract organic facies variation which is a key factor affecting the quality of hydrocarbon accumulations is characterized for the pre salt freshwater lacustrine source rocks in the interior basin and n komi rift areas in northern gabon by integrating geochemical and geological data the kissenda shales have 0 59 2 23 total organic carbon toc and hydrogen indices hi from 458 93 mghc goc pyrolysis of isolated kerogen and gas chromatography on rock extracts indicate that these samples are overall more waxy than those from the overlying melania shales which have 0 77 4 79 toc and hi from 896 212 in addition hopane sterane ratios and c30 4 methyl sterane indices increase systematically with depth it is proposed that the early cretaceous lacustrine system in northern gabon was initially oligotrophic and contained primarily bacteria and cyanobacteria with a small population of dinoflagellates and botryococcus as trophic level increased through time the food chain length increased eukaryotic organisms became more abundant and diversified steroids increased relative to hopanoids in the sediment and the preserved organic matter became less waxy burial history modeling shows that the onal 1 structure is charged primarily by waxy oils generated from the lower kissenda shales lower wax better quality oils are expected to the southwest where the kissenda shales are more mature and the less waxy melania shales also become effective source rocks thus variation in organic facies and thermal maturity in the cretaceous pre salt source rocks result in commercial production from the rabi field vs the subcommercial discovery in the onal 1 structure

a rise in the carbonate compensation depth of western tethys in the carnian late triassic deep water evidence for the carnian pluvial event the upper triassic of the lagonegro basin southern apennines southern italy is represented by hemipelagic cherty limestones of the calcari con selce formation deposited in an oceanic setting two stratigraphic sections petina chiana and pignola 2 representative of the evolution of the lagonegro basin during the carnian have been studied in detail with a multidisciplinary approach in the pignola 2 section within the calcari con selce formation a unique interval composed of green shales and radiolarites has been identified the absence of carbonate deposition within this interval is interpreted as evidence of a contemporaneous shallowing of the carbonate compensation depth conodont and palynomorph biostratigraphy constrain the age of this interval to the julian tuvalian lower carnian upper carnian boundary the age and characteristics of this interval suggest correlation with a putative climatic event known as the carnian pluvial event which has also been recognized in continental and shallow marine successions from different european localities this event is thus now documented also in a deep marine setting like the continental and shallow water settings it is characterized by a sudden input of siliciclastics petina chiana and pignola 2 integrate current knowledge of the carnian distribution of conodonts paragondolella praelindae kozur to date known only from the lower tuvalian has now been documented from the uppermost julian moreover a drastic turnover was recorded between julian and tuvalian conodont assemblages which is clearly associated with the carnian pluvial event thus a biotic crisis oceanographic changes associated with the rise of the carbonate compensation depth increased rainfall and an anomalous siliciclastic input occur contemporaneously at the time of the carnian pluvial event a similar pattern is associated with perturbations of the carbon cycle that occur during the jurassic and cretaceous e g in the early aptian thus it is hypothesized that the carnian pluvial event may have analogous causes

a 60 year isotopic record from a mid holocene fossil giant clam tridacna gigas in the ryukyu islands physiological and paleoclimatic implications we have constructed a 60 year stable isotope record from a 14c dated fossil giant clam tridacna gigas 6216 years bp at its northernmost latitudinal limit in the geological past on kume island central ryukyu archipelago japan stable oxygen 18o and carbon 13c isotopic analyses are combined with observations of growth lines seen on the inner shell layer sixty pairs of summer winter growth lines which preserve daily growth increments were observed in the inner shell layer two growth phases characterized by a growth curve and isotopic profiles are clearly recognized throughout the growth history of this specimen no significant shifts in average values of the two isotopic ratios were detected during its growth history although the growth rate varied widely from 1 to 15 mm year over 60 years including after the onset of sexual maturity spectral analysis of the fossil tridacna 18o time series implies that decadal variability observed in the north pacific ocean during the past hundred years also existed 6000 years ago our study implies that fossil giant clams are one of the best means of inferring isotopic records of annual to decadal climate variations giant clams have the advantages of a dense shell high growth rate long lifespan and geographically and geologically broad distributions

rifted margin source rock deposition a carbon isotope and biomarker study of a west african lower cretaceous lacustrine section lower cretaceous passive margin sections penetrated in wells peripheral to the deep basinal development of pre salt sediments of the liawenda ponta vermelha troughs in the lower congo coastal basin revealed sustained source potential kerogen type kinetic ea a and carbon isotopic data plus rock extract biomarker signatures confirmed large systematic organofacies variations within these rift phase sediments an inverse correlation between 25 28 30 trisnorhopane and gammacerane abundances suggested three major depositional regimes reflecting salinity and water depth control 13c depleted basal sediments showing strong gammacerane 4 methyl sterane signatures were segregated by a major isotopic excursion this event represented the transition between saline playa lake to deeper water stratified conditions supporting a high level of anoxia for these intermediate sediments sterane and tricyclic diterpane abundances plus sterane hopane ratios had marine connotations and could be interpreted as the result of intermittent marine incursions fore shadowing irreversible oceanic ingression a resurgence of gammacerane abundance in the uppermost sediments typified littoral shallow marine depositional conditions recognition of a possible non ubiquity in lacustrine depositional conditions during the opening of a rifted margin provides further insight into the complexity and attendant controls on hydrocarbon generation in such habitats

palaeoenvironments of the late triassic rhaetian sea implications from oxygen and strontium isotopes of hybodont shark teeth the oxygen and strontium isotopic composition of 125 teeth of the hybodont sharks lissodus and hybodus from various late triassic rhaetian bone bed localities in the central european basin are used as environmental and ecological tracers for the shallow epicontinental rhaetian sea the preservation of tooth enameloid was ascertained by cathodoluminescence microscopy mean 18op values differ regionally across the rhaetian sea with values of 18 6 0 6 near the western gate 16 1 0 8 in the east 15 4 0 6 in the southeast and 17 7 0 9 in the south the 18op values in the eastern rhaetian sea are 4 5 lower relative to tethyan seawater while teeth from the southern and western parts close to the marine gates are less fractionated the strontium isotopic composition of teeth from most localities is more radiogenic in comparison to late triassic seawater the observed spatial 18op trend in the rhaetian sea indicates a shift from marine to brackish conditions in the south and west towards extensively brackish conditions with salinities of less than 16 in the east thus confirming the existence of two marine gates brackish conditions persisted throughout early rhaetian times and were maintained by increased fluvial discharge from the vindelician bohemian and fennoscandian highs as a result of enhanced atmospheric moisture availability in the course of the rhaetian transgression the 18op values of lissodus and hybodus indicate euryhaline behaviour of rhaetian hybodonts by exceeding modern shark intraspecific variability the lack of accordance in 18op values between different isotopically conspicuous localities in the rhaetian sea contradicts a basin wide migration pattern differences between co site taxa might indicate some degree of niche partitioning

the controlling mechanism of mid to late holocene carbon isotopic variations of tridacnidae in the south china sea abstract the carbon isotopic fractionation process in biogenic carbonate is very complex and the mechanism for seasonal and long term variations in biogenic carbonate 13c remains a matter of debate in this study 5 tridacnidae samples were collected from the south china sea and analyzed in detail to study seasonal variations the high resolution 13c records exhibited cyclic variations likely related to seasonality in environmental parameters e g chl a concentration salinity sst rainfall 57 tridacnidae were collected and analyzed to study the millennium scale changes of tridacnidae 13c during the mid to late holocene and the controlling mechanism the tridacnidae 13c over the period 500 5500 bp is statistically significantly correlated with solar activity tsi and sunspot number likely attributed to the presence of symbiotic zooxanthellae within tridacnidae s mantle lobes solar activity could significantly affect the metabolic activity of zooxanthellae tridacnidae s microenvironment and thus tridacnidae s 13c composition the decoupling between the tridacnidae 13c and solar activity over the past 200 years is most likely due to increased amount of anthropogenic co2 and the oceanic 13c suess effect this study improves our understanding about the seasonal and long term variations of 13c in tridacnidae

drill hole convergence and a quantitative analysis of drill holes in mollusks and brachiopods from the triassic of italy and poland abstract the history of predation is recorded primarily from drilling in cenozoic invertebrates quantitative data are uncommon from the triassic a period before the appearance and radiation of many known drill hole producers such as various gastropod families and octopods we present quantitative evidence of drilling from the late triassic carnian cassian formation of italy and the middle triassic anisian lower muschelkalk of poland documenting the first drill holes in triassic brachiopods a single brachiopod with a cylindrical complete drill hole was found in a brachiopod sample from of poland drilling percentage 0 3 n 365 the cassian formation yielded drill holes in gastropods bivalves and brachiopods indicating that more species are drilled than was known previously the minimum drilling percentage exclusive of incomplete drill holes of a sample from the stuores wiesen cassian formation is 1 7 n 116 5 prey selectivity is evident complete drill holes are primarily present in one gastropod species polygyrina lommeli 11 8 of specimens with a complete drill hole whereas other common species were not drilled single drill holes in brachiopods are cylindrical and complete and may be predatory in origin multiple drill holes in mollusks are common and drill holes are parabolic and often incomplete with a central boss resembling the shape of drill holes produced by extant naticid gastropods a survey of the paleozoic literature showed that such drill holes are also present in devonian and carboniferous brachiopods however naticids did not evolve until the cretaceous so we propose the term drill hole convergence for similar shaped drill holes produced by different organisms the triassic parabolic drill holes are not caused by domicile seeking or boring organisms instead we favor a predatory origin of these drill holes but we cannot entirely rule out parasitism surveying other triassic invertebrate assemblages should yield more evidence of drilling

application of organic geochemistry to sequence stratigraphic analysis four corners platform area new mexico u s a abstract the sequence stratigraphic model of sedimentation postulates the existence of a time condensed section deposited at very low sedimentation rates occurring in the uppermost transgressive systems tract and the lowermost highstand systems tract this condensed interval has of often been equated with zones of increased hydrocarbon source potential and invoked as a petroleum source rock often in the absence of supporting geochemical data in this study isotopic molecular lithostratographic and paleontological data are presented for 51 outcrop samples from a cenomanian turonian section at red wash new mexico u s a interpretations are made within a sequence stratigraphic framework ramp model sedimentation rates are estimated in order to define the location of the codensed intervalm for comparison with the zone of best source potential approximately 80 m of section were sampled the interval of maximum flooding and westernmost progression of the cretaceous seaway shoreline as defined by paleontological data is stratigraphically immediately below the occurrence of discontinuities in total organic carbon content hydrogen index and fluoramorphinite concentration in the kerogen the overall transgressive event is accompanied by increases in relative concentrations of 24 n propylcholestane total steranes and rearranged steranes these changes are consistent with a simultaneous decrease in the ratio of terrigenous organic matter to marine algal input as westward flooding proceeded the simultaneous occurrence of discontinuities in kerogen related parameters and continuous trends in bitumen related parameters probably implies mobilization of soluble organic matter across the flooding event boundary sedimentation rate estimates for six intervals in the red wash section show that the best oil source rock potential occurs immediately above the condensed interval and maximum flooding surface within the highstand systems tract previous studies of cretaceous sections in other portions of the western interior basin have located the best source rock potential below the condensed zone we conclude that the equivalence between source rock occurence and condensed sections as applied through the sequence stratigraphic model requires modification before the model may be used to predict the location of oil source rocks in a ramp setting in this respect it is critical that the data in sequence stratigraphic studies be used to define the model and not allow the model to dictate the interpretation of the data

stratigraphic and lateral variations of source rock attributes of the pematang formation central sumatra abstract the pematang formation of the central sumatra basin has been shown to be the primary if not the sole source for the basin s 10 billion barrels of recoverable oil this lacustrine unit which is restricted to a series of paleogene half grabens typifies the variability present in many rift source rock systems differences in organic facies i e level of organic enrichment kerogen composition bitumen and product character occur both stratigraphically and laterally as a result of a series of complex interactions the stratigraphic controls on organic facies within the pematang appear to be 1 the changing relationship between subsidence and sedimentation 2 long term climate trends influencing both lake level and regional vegetation patterns and 3 the evolution of the lake basin s nutrient pool these controls result in an increase in the level of organic enrichment and oil proneness toward the top of the unit superimposed on this pattern are changes in organic matter content carbon content and character palynofacies biomarker and isotopic compositions caused by short term climatic oscillations lateral controls on organic facies can be examined at two different scales basinal and sub basinal basinal variations can be related to 1 different relative subsidence rates among the various sub basins and 2 variations in lake water chemistry as a result of the nature of the paleodrainage basin on a sub basinal scale organic facies appear to be controlled by 1 hydrodynamic processes and basin circulation and 2 variations in water depth these lateral variations are manifested in the level of organic enrichment the relative proportions of oil and gas prone kerogen and variations in oil composition

climate of the supercontinent pangea numerous climate models predict that the geography of the supercontinent pangea was conducive to the establishment of a megamonsoonal circulation in general geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the triassic pangea in the late carboniferous had widespread peat formation in what is now central and eastern north america and europe and relatively dry conditions on the colorado plateau the equatorial region of the continent became drier through the end of the carboniferous by the permian the equatorial region of pangea was dry and indicators of aridity and rainfall seasonality became more widespread wind directions from colorado plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time in the triassic climate in the colorado plateau region became relatively wet though still seasonal and the few eolian sandstones indicate a major shift in wind direction at that time in addition sedimentation

δ13c and δ18o values of triassic brachiopods and carbonate rocks as proxies for coeval seawater and palaeotemperature abstract a dataset of 160 isotope 13c and 18o values from anisian ladinian carnian and rhaetian articulate brachiopod shells complemented by 158 carbon and oxygen isotope values from whole rock carbonates define the first continuous stable isotope baseline trends for the triassic seawater the carbon isotope data suggest the existence of several short term high amplitude excursions in the early triassic followed by a predominance of values around 0 5 1 during the middle triassic a rise to 3 5 during the carnian plateau at this level during the late carnian to early norian and a 1 5 decline in the middle norian to values around 2 during the late norian rhaetian interval the causation scenarios for these rapid oscillations are at present equivocal but may in part reflect a biological instability of the carbon cycle following the recovery from the end permian extinction event and or an input of mantle derived co2 from enhanced volcanic activity the 18o values from well preserved brachiopods from the tethyan realm range from 3 9 to 0 6 v pdb these values require open marine triassic seawater 18o values close to 0 v smow for the calculated temperatures to be within the range of tolerance of the coexisting reef building corals a 2 18o increase within the uppermost cordevolian and early julian suggests either a distinct temperature decline in the southern alps during that time interval an increase in seawater salinity or their combination oxygen isotope values for the muschelkalk brachiopods range between 6 2 and 2 0 and likely reflect a strong influx of meteoric waters into the germanic basin that shifted the oxygen isotopes to more negative values

arsenic enrichment in groundwater of the alluvial aquifers in bangladesh an overview arsenic in the groundwater of bangladesh is a serious natural calamity and a public health hazard most groundwater from the shallow alluvial aquifers 150 m particularly in the holocene plai

oxygen isotopes sea level changes and the temperature history of a coral reef environment in new guinea over the last 105 years abstract coral reef terraces consisting of an upward succession of fringing and barrier reef types are preserved on land along the raising coast of huon peninsula new guinea seven coral reef units i vii from the coast landwards spaced at about 20 kyr interval provide a rather complete record of sea levels oxygen isotopes and temperature of teh surface tropical ocean over the duration of the high sea level events of the last glacial cycle the systematic sampling of the coral reefs was restricted to the massive tridacna gigas species the giant clam which are about 0 7 0 enriched in 18o relative to calcite equilibrium value and the presence of symbionts seems to have no effect on the 18o of their aragonitic skeleton sea levels rose rapidly to 5 6 5 m above present during the last interglacial which on stratigraphic grounds and 18o compositions can be separated into an early phase whose 18o is similar to modern reef viia dated at 138 kyr and a late phase that is 0 6 0 heavier reef viib dated at 118 kyr fringing reefs vi v iv iii and ii record short lived high sea levels stands at 107 85 60 45 to 40 and 31 kyr respectively that stopped short of the present sea level 12 19 28 32 to 42 m the general decline of the high sea level stands corresponds to an average 18o enrichment of 1 7 0 measured between the early interstadials of isotope stage 5 vi and v and the late interstadials of isotope stage 3 iv iiia iiib and ii the maximum 18o enrichment of 1 7 0 relative to present was registered during a regressive phase of reef iiia stratigraphic evidence indicates that sea level lows in the range of 37 to 55 m below present have occurred in between the high sea level stands but those are unlikely to represent the lowest sea levels of the last glacial cycle sea levels and 18o ddta pair offer important clues regarding the partitioning of ice volume and temperature in 18o records the results suggest that the ice volume effect accounts for the observed 18o changes during the early interstadial culminations but only for 29 46 during the late interstadial culminations sea water cooling beyond the threshold limit of coral reef growth 18 c did not occur during the last glacial cycle the temperature of the surface tropical ocean was similar to present during the early interstadials of isotope stage 5 and cooler by 3 c below present during the later interstadials of isotope stage 3

synchroneity of climatic change and extinctions in the late triassic although the late triassic was a time of widespread aridity evidence exists for a significant increase in rainfall during the middle to late carnian upper triassic playa lake sediments were interrupted by late carnian fluviatile sandstones with erosive bases and high kao linite illite ratios there was also an increase in the clastic component of marine sequences during this interval middle and upper carnian marine carbonates show an extreme depletion in 13 c values consistent with increased fresh water influx large scale karstic phenomena in limestone areas subaerially exposed during the late triassic are a further indication of increased rainfall important faunal and floral changes occurred during the carnian norian interval marine invertebrate turnover was greatest at the lower middle carnian boundary and terrestrial extinctions were concentrated at the carnian norian boundary the cause of this carnian pluvial episode may have been related to the rifting of pangea through disruption of atmospheric and oceanic circulation patterns eustatic changes or the effects of volcanism associated with rifting a change in surface ocean temperature salinity or ph or habitat loss may have caused the decline of many shallow marine invertebrates at the start of the middle carnian a return to arid conditions at the carnian norian boundary would account for the turnover among terrestrial vertebrates and plants

seasonal variability of the effect of coral reefs on seawater co2 and air sea co2 exchange there are complex physical and biological processes controlling the exchange of carbon dioxide co2 between the ocean and atmosphere in coral reef ecosystems the balance of biological processes such as calcium carbonate caco3 formation and organic carbon production can either lead to co2 being retained in the oceanic environment i e oceanic sink of co2 or returned to the atmosphere through gas exchange oceanic source of co2 what remains uncertain is the fate of co2 in reefs subject to seasonal change and the annual balance of air sea co2 flux in such systems here it is shown that the bermuda coral reef acts as a source of co2 to seawater overlying the reef the magnitude of this source of co2 varies seasonally in response to changes in the reef community between coral and macroalga dominated states reflecting changes in the net balance between calcification and organic carbon production with knowledge of the calcification rate 5 6 to 10 6 g caco3 m 22 d 21 and observed modification in seawater f co2 by reef metabolism rates 20 6 to 3 3 g c m 22 d 21 and seasonal patterns of macroalgal productivity were estimated whether the bermuda coral reef system acts as an oceanic sink or source of co2 to the atmosphere not only depends on this seasonal variation but more importantly depends on the pre existing air sea co2 disequilibrium of open ocean waters surrounding the reef system the bermuda coral reef system serves as a useful model for understanding the fate of co2 in other reefs particularly those reefs changing because of environmental stress

lacustrine basin unconventional resource plays key differences abstract there has been a revival in hydrocarbon source rock characterization and development associated with growing interest in unconventional resources where these fine grained organic rich rocks act as both source and reservoir to date the exploration focus on shale reservoirs has been largely on marine systems lacustrine source rocks for conventional resources are geographically important dominating regions such as china indonesia and brazil s resource base however they have been generally untested for unconventional resources there are a number of key differences in the nature of these hydrocarbon systems that should be considered when assessing whether lacustrine systems may represent future unconventional opportunities in areas where the conventional resource base is dominated by lacustrine sourced oil among the key differences between these depositional systems is the greater sensitivity to high frequency climatic variability within lacustrine systems lacustrine systems are highly sensitive to changes in the balance between precipitation and evaporation which may lead to rapid changes in lake level potentially exceeding 600 m these changes in depositional conditions are geologically rapid and may occur over periods of thousands of years such changes can reduce the areal extent of potentially thick source rock intervals to only those portions of a basin where a permanent deep lake was present thus the core unconventional target area may be geographically limited compared with their marine counterpart although potentially areally limited a review of many lacustrine source rocks suggests that their thicknesses are often significantly greater than marine source rocks an examination of the more distal portions of lacustrine systems where better source rock potential is present reveals that there is generally limited connectivity between source and conventional reservoir in these settings such as the wind river basin waltman shale the hydrocarbons remain trapped within the shales potentially leading to over pressured hydrocarbon charged systems such conditions suggest that although areally limited viable unconventional targets may exist if suitable reservoir conditions are present finally the character of the oils produced is different in these settings with lacustrine oils being waxy and displaying different hydrocarbon generation and cracking kinetics high wax oils display distinct flow characteristics being more viscous and may offer different production challenges than their non waxy marine equivalents additionally differences in their cracking kinetics may indicate that the timing of gas generation for shale gas plays may differ significantly from marine systems

kerogen origin evolution and structure kerogen commonly defined as the insoluble macromolecular organic matter om dispersed in sedimentary rocks is by far the most abundant form of om on earth this fossil material is of prime importance as the source of oil and natural gas moreover kerogen can provide essential information on major topics such as past environments climates and biota this review reports the main advances in kerogen studies since the comprehensive synthesis edited by durand durand b ed kerogen insoluble organic matter from sedimentary rocks editions technip paris 1980 it is organized into eight sections the first two are concerned with the successive definitions of kerogen and the definition used here the different techniques used for kerogen isolation without loss or degradation and basic kerogen analysis the third and fourth focus on sedimentary om sources and preservation processes in relation to depositional environment including sedimentation conditions favourable for kerogen accumulation and extrapolation to past geological time great strides have been made in the latter topics over the last 25 years owing to a combination of classical studies in organic geochemistry and studies in other domains such as biogeochemistry oceanography hydrology and soil science along with the development of powerful analytical tools the next two sections deal with the different kerogen classifications by type and kerogen evolution and maturation upon burial in sediments structural modelling of coal and kerogen based on physical and or chemical structural analysis is described in the following section although only statistical the models thus derived provide a synthetic view of the main structural resemblances and differences among various samples in relation to source maturity or physicochemical properties finally the last section explores some of the advances in kerogen understanding expected for the near future the review includes a list containing about 500 references

triassic environments climates and reptile evolution abstract a consideration of all the available data on triassic vertebrate faunas and their stratigraphic location reveals a relatively sudden extinction event among the last of the mammal like reptiles and the herbivorous rhynchosaurs in the norian of the upper triassic this event was apparently quickly followed by the radiation of the dinosaurs also in the norian this conclusion suggests that competition was not the main factor in the initial success of the dinosaurs but opportunistic radiation following the extinction of major reptile groups a global review of triassic sedimentary facies shows that there were climatic and floral changes towards the end of the triassic it is envisaged that increasing aridity in the later triassic resulting from plate motions and particularly affecting gondwanaland and southwestern laurasia brought about floral changes and then the reptile extinctions with the rapid evolution of new floras of conifers and bennettitaleans the dinosaurs came to dominate all terrestrial faunas within the space of only a few million years

geology is useful as complexity of exploration problems increases petroleum geologists tend to consider more carefully oil formation and migration in terms of quantity quality and timing in order to assess more accurately the history of hydrocarbons in a given basin the present knowledge concerning the behavior of source rocks quantity of hydrocarbons generated composition of hydrocarbons kinetics expulsion efficiency is that differences can be attributed to a large extent to organic properties of sediments such as organic matter content organic matter quality and the pattern of the microdistribution of organic matter in the mineral fabric layered lenslike intergranular moreover field observations show that organic facies change at various scales in space and time in re ponse to variation in depositional environments and sedimentary processes the effects of these factors on the source rocks emphasize beyond the efforts to achieve comprehensive descriptions of source beds rock eval pyrolysis microscopy typing of organic matter measurement of kinetic parameters of carefully selected kerogens use of wireline logs seismic information the needs to increase our conceptual understanding of deposition of organic facies in order to improve our ability to predict the petroleum potential of sedimentary basins

seasonal climatic fluctuations in the late triassic tropics high resolution oxygen isotope records from aragonitic bivalve shells cassian formation northern italy abstract three megalodontoid bivalves from the upper triassic cassian formation n italy dolomites were sampled for 13 c and 18 o sclerochronology n 270 with more than 1000 described invertebrate species the cassian formation has one of the best records of an early mesozoic tropical fauna in addition the cassian formation is one of the very few triassic occurrences with original aragonite preservation with all studied shells consisting of pristine aragonite the presence of aragonite and crossed lamellar as well as fibrous prismatic shell microstructures shown for the first time for triassic megalodontoids suggests absence or minimal impact of diagenetic alteration the 13 c values range from 3 6 to 5 8 and show a distinct cyclicity in two studied shells whereas a third shell shows no obvious cyclicity in one bivalve specimen the cycles are somewhat offset from 18 o cycles and in the other specimen 18 o and 13 c curves are inversely correlated seasonal variation in freshwater runoff including nutrient input and subsequent changes in plankton productivity during dry and wet seasons may explain 13 c cyclicity 18 o values show a pronounced cyclicity within each of the studied shells varying from 3 6 to 1 4 the variations in 18 o suggest a pronounced seasonality in late triassic tropical shallow waters of the western tethys with inferred seasonal temperature changes ranging from 24 to 32 c influx of fresh water during the rainy seasons mega monsoon or upwelling might also explain part of the variation in 18 o the presented data suggest that the diverse cassian fauna lived under conditions characterized by warm sea surface waters with a pronounced seasonality similar conditions are reported for some modern tropical settings

stable isotopes and sclerochronology of the bivalve mesodesma donacium potential application to peruvian paleoceanographic reconstructions reconstructing the past enso el nino southern oscillation interannual variability requires very high resolution sea surface temperature sst proxies in order to compensate for the lack of coral archive in the eastern pacific cold tongue we studied the potentiality of the bivalve species mesodesma donacium as a sst tracer for the peruvian coast biomineralisation cycles and growth line formation in the shells are shown to be controlled by tides the sclerochronology based on fortnightly cycles allowed us to compare local sst data with high resolution shell records as a result of the high correlation between sst and aragonite delta 18 o we calculated a linear sst fractionation relationship for the 14 20 degrees c range t degrees c 17 41 1 15 3 66 0 16 delta 18 o arag pdb delta 18 o wat smow the difference from the commonly used grossman and ku 1986 grossman e l ku t l 1986 oxygen and carbon fractionation in biogenic aragonite temperature effect chemical geology 59 59 74 equation suggests the potential existence of a species dependence of vital effect within bivalves this preliminary equation allows monthly scale sst reconstructions with a 1 5 degrees c precision using m donacium archaeological shells from southern peru giving potential insights into the problem of past enso behaviour c 2005 elsevier b v all rights reserved

geochemical correlation of oil from the ayoluengo field to liassic black shale units in the southwestern basque cantabrian basin northern spain abstract a study of the liassic sequence in the basque cantabrian basin has shown the presence of organic rich toc hi and s 2 up to 8 7 760 and 56 5 mg g respectively pliensbachian early toarcian black shales that constitute the only feasible source rock for ayoluengo oil the stratigraphical and sedimentological data show that these black shales developed into a major transgressive sequence of hemipelagic lotharingian toarcian facies which suggests the presence of anoxic or near anoxic bottom water conditions in troughs during their deposition the 13 c composition and a detailed study of the linear branched isoprenoid steroid and hopanoid aliphatic hydrocarbons in these shales marls and the ayoluengo oil confirms this hypothesis specifically the 13 c values of the total solvent extract of the thicker shale no 2 and the oil are 29 93 and 29 88 respectively also a close similarity in the relative compositions of steranes and hopanes is observed between these samples the distributions of these compounds exhibit several distinct features the steranes in this shale and crude oil are characterized by a depletion of c 28 vs c 27 and c 29 homologues 24 vs 32 and 44 respectively which is consistent with the carbon number sterane distributions generally observed among upper paleozoic to liassic rock sourced oils furthermore hopanes and steranes are characterized by their high relative content of rearranged molecules diasteranes 13 h 17 h and 13 h 17 h series are the dominant compounds among the steranes and significant amounts of 18 h 17 methyl 28 norhopanes c 27 c 29 and c 30 homologues and 17 h 15 methyl 27 norhopanes c 30 homologue are found in the hopanoid hydrocarbons conversely the proportion of these rearranged molecules in other sediment samples from the same formation decrease with increasing carbonate content rearrangement is generally related to catalytic effects due to clay minerals which is in agreement with the lithology of the source rock attributed to the ayoluengo oil

intra annual isotopic variation in venericardia bivalves implications for early eocene temperature seasonality and salinity on the u s gulf coast abstract stable isotope compositions were determined for 166 microsamples of aragonite from the bivalve venericardia hatcheplata collected from the early eocene hatchetigbee formation in southwestern alabama these were milled from two transects one across the left valve hinge plate and one along the growth axis amplitude and spacing of about nine years of seasonal variation is very regular with peaks and troughs occurring at equal intervals and reaching consistent compositions except for some attenuation in both parameters during the last three years of life assuming an ice free world with an ocean 18o value of about 1 0 and using the aragonite water fractionation equation of grossman and ku 1986 isotope derived paleotemperatures are somewhat warmer 31 c than temperatures presently recorded anywhere on the earth s surface and exhibit significantly greater seasonality 12 c than regions with the warmest mean temperatures it is therefore likely that these very negative and extremely seasonal 18o values reflect the influence of seasonal discharge of 18o depleted river water into the eocene gulf of mexico comparison of these data with 1 mean annual temperature versus seasonal temperature variation from modern climates 2 isotopic compositions reported from coeval molluscs and 3 isotopic compositions of global meteoric precipitation and united states rivers suggest that mean annual temperature along this portion of the eocene gulf coast was in fact about 26 c and varied seasonally from a winter low of about 25 c to a summer high of 27 c differences between these temperatures and those derived from direct conversion of oxygen isotope values reflect the influence of seasonal influx of fresh 18o value of 4 7 water during deposition of this portion of the hatchetigbee formation ambient water 18o values varied between winter values of about 1 0 to less than 3 5 during the summer freshwater discharge served to seasonally depress salinity to 10 to 16 ppt along this part of the gulf coast the early eocene was perhaps the warmest time interval of the past 65 million years primarily manifest as lower equator to pole temperature gradients in this context an eocene mean annual temperature of 26 c is not much higher than modern surface water temperatures of about 24 c at 29 30 n immediately off the modern alabama coast seasonal temperature variation of 2 to 3 c about a mean of 26 c however is significantly lower than that off coastal alabama 19 to 30 c and occurs only along modern equatorial coasts at latitudes less than 19 this implies that early eocene tropical conditions extended well beyond modern latitudinal limits

speciation and enrichment of arsenic in strongly reducing shallow aquifers at western hetao plain northern china high arsenic as groundwater is widely distributed in northwestern hetao plain an arid region with sluggish groundwater flow observed as concentration in groundwater from wells ranges from 76 to 1 093 g l most water samples have high total dissolved solids with cl and hco3 as the dominant anions and na as the dominant cation the major hydrochemical types of most saline groundwaters are na mg cl hco3 and na mg cl by contrast fresh groundwaters generally belong to the na mg hco3 type high concentrations of arsenic in shallow aquifers are associated with strongly reducing conditions as evidenced by high concentrations of dissolved organic carbon ammonium as well as dissolved sulfide and fe dominance of arsenite relatively low concentrations of nitrate and sulfate and occasionally high content of dissolved methane ch4 high as groundwaters from different places at hetao plain experienced different redox processes fluoride is also present in high as groundwater ranging between 0 40 and 3 36 mg l although fluorosis poses an additional health problem in the region it does not correlate well with as in spatial distribution geochemical analysis indicates that evapotranspiration is an important process controlling the enrichment of na and cl as well as trace elements such as as b and br in groundwater

the aftermath of the carnian carbonate platform demise a basinal perspective dolomites southern alps in the dolomites of northernmost italy the carbonate platform growth came to a standstill late in the early carnian late triassic the response to this shutdown of shallow water carbonate production in the interplatform basins is largely unknown because erosion has removed most of the soft basinal sediments giving rise to today s scenic landscape of the dolomites mapping in the central part of the dolomites and newly available core material has recently revealed a wellpreserved succession of basinal rocks within the heiligkreuz hospiz basin ital ospizio di santa croce basin in this paper the regional depositional nature of arrested carbonate platform production is reconstructed by tracing its sedimentological record across the slope and into the basin the uppermost st cassian formation the time equivalent basinal rocks to the prograding carbonate platforms is overlain by the heiligkreuz formation whose basal succession was deposited in a restricted and oxygen depleted environment immediately post dating the platform demise the succession consists mainly of mudrocks marlstones and peloidal packstones with abundant low diversity ostracod and pelecypod fauna and early diagenetic dolomite c and o isotope values of the basal heiligkreuz formation post dating platform demise average 2 ae4 and 2ae4 respectively and largely overlap the isotopic composition of st cassian carbonates a shift toward slightly lower d 13 c values in the heiligkreuz formation may reflect incorporation of isotopically depleted c released during bacterial sulphate reduction in the heiligkreuz sediments sedimentological palaeobiological and geochemical indices suggest that nearnormal marine conditions persisted long after the shutdown of shallow water carbonate platform growth although there are clear indications of severely reduced oxygen levels in the restricted heiligkreuz hospiz interplatform basin the early carnian platform demise induced a distinct switch in the locus of carbonate production from the shallow water platform and slope to the basin floor and a decrease in the availability of dissolved oxygen in the basinal waters it is inferred that anoxia extended at least temporarily to the top of the carbonate slope as indicated by the onlap of normal marine mounds by dark marlstones of the basal heiligkreuz formation

mesozoic climates general circulation models and the rock record abstract general circulation models gcms use the laws of physics and an understanding of past geography to simulate climatic responses they are objective in character however they tend to require powerful computers to handle vast numbers of calculations nevertheless it is now possible to compare results from different gcms for a range of times and over a wide range of parameterisations for the past present and future e g in terms of predictions of surface air temperature surface moisture precipitation etc gcms are currently producing simulated climate predictions for the mesozoic which compare favourably with the distributions of climatically sensitive facies e g coals evaporites and palaeosols they can be used effectively in the prediction of oceanic upwelling sites and the distribution of petroleum source rocks and phosphorites models also produce evaluations of other parameters that do not leave a geological record e g cloud cover snow cover and equivocal phenomena such as storminess parameterisation of sub grid scale processes is the main weakness in gcms e g land surfaces convection cloud behaviour and model output for continental interiors is still too cold in winter by comparison with palaeontological data the sedimentary and palaeontological record provides an important way that gcms may themselves be evaluated and this is important because the same gcms are being used currently to predict possible changes in future climate the mesozoic earth was by comparison with the present an alien world as we illustrate here by reference to late triassic late jurassic and late cretaceous simulations dense forests grew close to both poles but experienced months long daylight in warm summers and months long darkness in cold snowy winters ocean depths were warm 8 c or more to the ocean floor and reefs with corals grew 10 of latitude further north and south than at the present time the whole earth was warmer than now by 6 c or more giving more atmospheric humidity and a greatly enhanced hydrological cycle much of the rainfall was predominantly convective in character often focused over the oceans and leaving major desert expanses on the continental areas polar ice sheets are unlikely to have been present because of the high summer temperatures achieved the model indicates extensive sea ice in the nearly enclosed arctic seaway through a large portion of the year during the late cretaceous and the possibility of sea ice in adjacent parts of the midwest seaway over north america the triassic world was a predominantly warm world the model output for evaporation and precipitation conforming well with the known distributions of evaporites calcretes and other climatically sensitive facies for that time the message from the geological record is clear through the phanerozoic earth s climate has changed significantly both on a variety of time scales and over a range of climatic states usually baldly referred to as greenhouse and icehouse although these terms disguise more subtle states between these extremes any notion that the climate can remain constant for the convenience of one species of anthropoid is a delusion although the recent rate of climatic change is exceptional

a review of mesozoic climates there is overwhelming evidence based on the distribution of distinctive sediments and fossils and oxygen isotope data that the climate of the mesozoic world was appreciably more equable than that of today with no polar ice caps but precise quantitative data are not available except for an episode of late cretaceous cooling there is no good documentation of any significant change in global temperature distributions through the era the distribution of coals and evaporites together with other criteria indicates a pattern of humid arid and zones appreciably different in important respects from that of today during the triassic and jurassic western pangaea in low to middle latitudes was largely arid but in the early cretaceous the lands on the margin of the newly opening central atlantic and western tethys experienced a humid climate by late cretaceous times arid zones had become very restricted in extent because of insufficient suitable data attempts at climatic modelling have had only modest success and only to a limited extent can the major long term changes in climate between the permian and the present be explained in terms of changing geography the most probable explanation of mesozoic equability is an increased atmospheric co 2 content a number of enigmas remain such as the existence of flourishing forests in polar palaeolatitudes whereas for the late cenozoic short term climatic changes can be related successfully to variations in the geometry and mechanics of the earth sun system there is a long way to go before comparable success can be claimed for the mesozoic