application of organic facies studies to sedimentary basin analysis a case study from the yitong graben china abstract an organic facies is defined in this paper as a mappable stratigraphic unit containing organic matter om of a particular genetic type in certain abundance several concepts concerning organic facies are proposed and their significance in basin analysis is discussed in detail a combined sedimentological and organic geochemical investigation has been carried out in the yitong graben and four organic facies and one organic parafacies have been recognized distinct organic basin fill sequences obfs and organic facies association ofa were developed in different sub units of this graben which indicates that the yitong graben had undergone two tectonic subsidence cycles such tectonic subsidence patterns could not have been found out without detailed organic facies analysis confirming that organic facies especially obfs and ofa study is a very useful tool not only for prediction and three dimensional mapping of petroleum source rocks but also for sedimentary basin analysis

diagenetic and catagenetic products of isorenieratene molecular indicators for photic zone anoxia a wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene a pigment of the photosynthetic green sulphur bacteria chlorobiaceae has been identified in a number of sedimentary rocks ranging from ordovician to miocene compound identification is based on nmr mass spectrometry the presence of atropisomers and stable carbon isotopes atropisomers contain an axially chiral centre which in combination with other chiral centres results in two or more diastereomers that can be separated on a normal gc column chlorobiaceae use the reverse tca cycle to fix carbon so that their biomass is enriched in 13c high 13c contents of isorenieratene derivatives therefore support their inferred origins isorenieratene derivatives include c 40 c 33 and c 32 diaryl isoprenoids and short chain aryl isoprenoids with additional aromatic and or s containing rings c 33 and c 32 compounds are diagenetic products of c 33 and c 32 carotenoids formed from isorenieratene during early diagenesis through expulsion of toluene and m xylene respectively cyclisation of the polyene acyclic isoprenoid chain can proceed via an intramolecular diels alder reaction followed by aromatisation of the newly formed ring sulphurisation is also an important process during early diagenesis competing with expulsion and cyclisation sulphur bound isorenieratane is released during progressive diagenesis due to cleavage of relatively weak ss and cs bonds cleavage of c c bonds during aromatisation of newly formed rings and during catagenesis yields short chain compounds the inherent presence of a conjugated double bond system in carotenoids implies that similar diagenetic and catagenetic reactions can occur with all carotenoids chlorobiaceae live at or below the oxic anoxic boundary layer and require both light and h 2s the presence of isorenieratene or its diagenetic and catagenetic products in ancient sedimentary rocks and crude oils is therefore an excellent indication for photic zone anoxia in the depositional environment diagenetic and catagenetic products of isorenieratene are expected to find applications in reconstruction of palaeoenvironments and in oil oil and oil source rock correlation studies their presence in several petroleum source rocks suggests that anoxia is an important environmental parameter for the preservation of organic matter

chemostratigraphy of the posidonia black shale sw germany ii assessment of extent and persistence of photic zone anoxia using aryl isoprenoid distributions aquatic depositional environments where anoxic conditions extend from bottom waters into the photic zone occurred frequently during the geologic past periods of photic zone anoxia pza can be recognized by the presence of specific lipids produced exclusively by the green sulphur bacteria chlorobiaceae that are preserved in the sedimentary record chlorobiaceae perform anoxygenic photosynthesis that requires light penetration into h2s saturated waters sediment samples integrate paleoenvironmental conditions over time intervals ranging from at best a few decades to more commonly several millennia photic zone anoxia recognized in paleoenvironmental analyses is thus defined as episodic with no further interpretation on the duration and persistence of the anoxic events we provide here a high resolution multiproxy chemostratigraphy study for the toarcian posidonia black shale from the dotternhausen section in sw germany in order to assess duration and seasonal fluctuation of photic zone anoxia based on the relative abundance of derivatives of chlorobiaceae lipids we assess the variability in the degree and persistence of photic zone anoxia using an aryl isoprenoid ratio air obtained by calculating the proportion of the short chain c13 17 versus the intermediate chain c18 22 aryl isoprenoids higher relative abundance of the short chain analogues is interpreted as indicating more intensive aerobic degradation of aryl isoprenoids air varies between values of 0 5 indicative of persistent pza phases and 3 0 for short termed episodic pza events absolute concentration of aryl isoprenoids is negatively correlated with the air which is in agreement with a progressive diagenetic breakdown of aryl isoprenoids the air decreases are validated using independent palecological and geochemical redox indicators for the posidonia shale in sw germany d 2004 elsevier b v all rights reserved

fish taphonomy and environmental inference in paleolimnology abstract the contribution of fish studies to palaeoecology generally takes the form of 1 inference from analogies in modern fish faunas and 2 fish taphonomy the pattern of death and dispersal of bones 1 modern fish faunas and associated organisms provide taxonomic ecological or functional analogues for interpretation of ancient limiting factors and behaviors these inferences presume taxonomic conservatism they also presume functional relationships between morphological form and feeding mode or habitat they become weak with increased geologic age or phyletic distance between ancient subject and modern anaogue 2 fish taphonomy may contribute information about limnology community composition life history mortality depositional environment and preservation taphonomic reconstruction of ecology and preservation depends on the applicability of analogous processes in modern ecology and l limnology in aquatic taphonomy temperature is the most important factor in determining the fate of a carcass above about 16 c depending on depth and pressure most carcasses are made buoyant by bacterial decay gases and are transported to the surface where they may decay further and fall piecemeal into deepwater environments or drift to beach environments where wave energy disarticulates abrades and scatters the bones below about 16 c most carcasses remain on the bottom until buried they may be disturbed by scavengers depending on oxygen concentration in the hypolimnion

carbonate concretions from the london clay ypresian eocene of southern england and the exceptional preservation of wood boring communities marine driftwood bored by teredinid bivalves shipworms is common in the london clay formation ypresian eocene of southern england the london clay of sheppey kent has yielded six genera of teredinids and is the most diverse fossil assemblage of the family known the presence of several genera that are known exclusively from mangroves at the present day demonstrates the potential value of teredinids in the recognition of ancient mangroves the rapid sea floor burial of logs containing numerous individuals resulted in the borings becoming completely or partially sealed by the plug like pallets in this exceptional mode of preservation valves pseudofaeces and pallets are found in life position and early cementation prevented compaction of the wood and borings the bored wood acted as centres of carbonate concretion formation cement compositions mineral associations and 13 c and 18 o stable isotope data indicate that most precipitation occurred in the iron reduction zone with sulphate reduction also being an important source of carbonate for the sheppey concretions fractures and their infilling cements are demonstrably contemporaneous with the cement zones in which they terminate it is likely that rapid changes in cement chemistry are a consequence of sudden release of fluid by dewatering events whilst more gradual shifts in chemistry were controlled be evolution through the oxic fe mn and s reduction zones teredinid boring linings and the cements which infill them may have recrystallized by a dissolution reprecipitation process which has preserved the chemistry of successive cements and has probably not significantly changed 18 o values

undrained cylindrical and spherical cavity expansion in elastic viscoplastic soils various undrained cavity expansion solutions for elastic plastic soil have been proposed previously however no solution has been presented for elastic viscoplastic evp soil until now this pape

intermittent euxinia reconciliation of a jurassic black shale with its biofacies isorenieratane is ubiquitous in the organic carbon rich peterborough member callovian uk of the oxford clay formation indicating a temporal overlap of the euphotic and sulphidic zone in the water column

marine vertebrate fauna from the late eocene samlat formation of ad dakhla southwestern moroccos zouhri and otherseocene vertebrate fauna from ad dakhla morocco

the early toarcian early jurassic and the cenomanian turonian late cretaceous mass extinctions similarities and contrasts abstract the early toarcian eto and cenomanian turonian c t mass extinctions are comparable from a wide range of scales and perspectives from a broad standpoint their similarities include virtually identical extinction intensity at the familial and generic levels widespread basinal facies deposited during sea level highstands an overall greenhouse climate and anoxia as an important causal mechanism the high resolution macroinvertebrate data analyzed here consisting of stratigraphic ranges diversity and abundance point to smaller scale similarities the two events resulted in significant ecological disruption and in both cases the biotic responses were very similar taxa inhabiting the upper water column were unaffected by anoxia and included ammonites and in the eto belemnites in addition epifaunal taxa adapted to low oxygen conditions such as the buchiids posidoniids and inoceramids flourished in the post extinction environment during the survival interval as conditions ameliorated the biota became more diverse and gradually began to resemble pre extinction biotas furthermore the 13c curves predict the end of the survival interval and suggest that the period characterized by carbon isotope excursions represent disrupted environmental conditions this points to the potential application of 13c as a tool for determining the repopulation modes and timing for other mass extinctions

mass transport in eocene pelagic chalk on the northwestern edge of the arabian platform shefela area israel glides rotational slumps debris and mud flows occur in the eocene pelagic chalk of the shefela region israel the pelagic lithofacies are present from the beginning of the eocene but mass transport is initiated only in the latest early eocene and the early middle eocene slight steepening of the palaeoslope coupled with increased sedimentation rate and early diagenetic changes lowering inherent strength led to gravity induced mass transport in the poorly consolidated pelagic sediments instability of the sediment pile was enhanced by underconsolidation and development of spacious packing associated with a relatively high rate of deposition and low initial strength due to high content of siliceous micro biota the palaeogeographic position indicated by the mass transport features is the steepened distal part of the ramp like continental margin of the arabian platform distal steepening of the ramp as part of regional downwarping is coincident with reactivation of syrian arc folding reflecting northward convergence of the arabian plate during the eocene

a survey of palaeontological sampling biases in fishes based on the phanerozoic record of great britain fishes represent more than half of all living vertebrate species but patterns of fish diversity remain little explored in the fossil record a compendium of fossil occurrences from great britain was assembled in order to address a series of questions concerning the palaeontological record of fishes there are broad similarities between british richness trajectories and those compiled from global data including an initial peak in the mid palaeozoic devonian or carboniferous depending on the compilation with a late palaeozoic trough followed by a sharp rise in diversity in the late cretaceous and paleogene the british dataset is too small to reveal any significant differences in richness between time bins using subsampling but a modelling approach based on sampling and geological proxies consistently shows lower than predicted richness in the silurian devonian and higher than predicted richness in the late cretaceous and eocene this positive excursion is robust to the exclusion of data from the early eocene london clay lagerstatte chondrichthyans sharks rays and ratfishes and osteichthyans ray finned and lobe finned fishes show contrasting relationships with geological and sampling proxies possibly reflecting different taphonomic profiles or idiosyncratic variation in the relative proportion of freshwater and marine deposits over the british phanerozoic

marine biodiversity through the late cenomanian early turonian palaeoceanographic controls and sequence stratigraphic biases changes in the marine macro and microfauna sedimentary geochemistry and surface water palaeoproductivity through the last 500 000 years of the cenomanian and first 300 000 years of the turonian are documented these are based on the succession at eastbourne the thickest and most complete section through the late cenomanian and early turonian in the anglo paris basin two levels of rapid faunal and geochemical change are identified one coincident with a significant increase in siliciclastic input at the base of the plenus marls member and the other with a marked drop in surface water productivity near the top of the same unit faunal change is demonstrated to be largely a pattern of immigration emigration rather than true extinction and our sequence stratigraphical analysis shows that it was coincident with major sea level changes no evidence is found to support the hypothesis that reduced bottom water oxygenation developed and was responsible for extinctions amongst the benthos in mid shelf environments the onset of pure chalk facies is interpreted to mark the breakdown of shelf break fronts and the spread of oligotrophic oceanic waters over much of the continental shelf initiated by rising sea level the cenomanian turonian event far from recording a mass extinction of shelf fauna is most probably an artifact caused by a significant switch in the nature of the surviving sedimentary record as a result of a major but perfectly ordinary oceanographic change

a high resolution historical record of holocene anoxygenic primary production in the black sea i reconstruct the historical record of anoxygenic primary production in the black sea over the last 8200 years by an analysis of chlorobium carotenoids in sediments anoxygenic photosynthesis in the black sea occurs only when hydrogen sulfide containing deep water penetrates the euphotic zone the data show that the black sea has experienced large fluctuations in the extent of anoxygenic primary production and therefore the depth of the h2s chemocline throughout much of the holocene changes in the depth of the h2s chemocline also shift the dominant phytoplankton populations in the water column to noncarbonate bearing species and result in the formation of intense dark bands in sediments

a multiple proxy and model study of cretaceous upper ocean temperatures and atmospheric co2 concentrations foraminiferal d 18 o and mg ca suggests that the ratio of magnesium to calcium in the turonian coniacian ocean may have been lower than in the albian cenomanian ocean perhaps coincident with an ocean 87 sr 86 sr minimum the carbon isotopic compositions of distinct marine algal biomarkers were measured in the same sediment samples the d 13 c values of phytane combined with foraminiferal d 13 c and inferred temperatures were used to estimate atmospheric carbon dioxide concentrations through this interval estimates of atmospheric co2 concentrations range between 600 and 2400 ppmv within the uncertainty in the various proxies there is only a weak overall correspondence between higher lower tropical temperatures and more less atmospheric co2 the genesis climate model underpredicts tropical atlantic temperatures inferred from odp leg 207 foraminiferal d 18 o and mg ca when we specify approximate co2 concentrations estimated from the biomarker isotopes in the same samples possible errors in the temperature and co2 estimates and possible deficiencies in the model are discussed the potential for and effects of substantially higher atmospheric methane during cretaceous anoxic events perhaps derived from high fluxes from the oxygen minimum zone are considered in light of recent work that shows a quadratic relation between increased methane flux and atmospheric ch4 concentrations with 50 ppm ch4 genesis sea surface temperatures approximate the minimum upper ocean temperatures inferred from proxy data when co2 concentrations specified to the model are near those inferred using the phytane d 13 c proxy however atmospheric co2 concentrations of 3500 ppm or more are still required in the model in order to reproduce inferred maximum temperatures

bakken madison petroleum systems in the canadian williston basin part 2 molecular markers diagnostic of bakken and lodgepole source rocks abstract the uppermost devonian mississippian bakken formation black shale and the mississippian lodgepole formation carbonate represent two of the most important source rocks in the canadian williston basin quantitative analyses of both saturated and aromatic hydrocarbon fractions reveal significant differences in the relative distributions and absolute concentrations for a wide range of molecular markers between the extracts of the two source units among others the bakken shales are characterized by their high relative abundance of trimethyl aryl and diaryl isoprenoids likely derived from green sulfur bacteria chlorobiaceae in contrast the lodgepole carbonates at similar maturity levels display a c35 homohopane prominence and abundant benzohopanes ring d monoaromatic 8 14 secohopanes and a tetracyclic monoaromatic hydrocarbon the distinctive nature of molecular marker fingerprints diagnostic of the two source rocks is clearly related to their different organic inputs and depositional environments additionally the large difference in the absolute concentrations of these compounds observed in both source units may potentially lead to biased geochemical interpretations if strictly conventional saturate based biomarker approaches were used for oil oil and oil source correlation

cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode oceanic anoxic events oaes were episodes of widespread marine anoxia during which large amounts of organic carbon were buried on the ocean floor under oxygen deficient bottom waters oae2 occurring at the cenomanian turonian boundary about 93 5 myr ago is the most widespread and best defined oae of the mid cretaceous although the enhanced burial of organic matter can be explained either through increased primary productivity or enhanced preservation scenarios the actual trigger mechanism corresponding closely to the onset of these episodes of increased carbon sequestration has not been clearly identified it has been postulated that large scale magmatic activity initially triggered oae2 refs 4 5 but a direct proxy of magmatism preserved in the sedimentary record coinciding closely with the onset of oae2 has not yet been found here we report seawater osmium isotope ratios in organic rich sediments from two distant sites we find that at both study sites the marine osmium isotope record changes abruptly just at or before the onset of oae2 using a simple two component mixing equation we calculate that over 97 per cent of the total osmium content in contemporaneous seawater at both sites is magmatic in origin a approximately 30 50 fold increase relative to pre oae conditions furthermore the magmatic osmium isotope signal appears slightly before the oae2 as indicated by carbon isotope ratios suggesting a time lag of up to approximately 23 kyr between magmatism and the onset of significant organic carbon burial which may reflect the reaction time of the global ocean system our marine osmium isotope data are indicative of a widespread magmatic pulse at the onset of oae2 which may have triggered the subsequent deposition of large amounts of organic matter

molecular indicators for palaeoenvironmental change in a messinian evaporitic sequence vena del gesso italy i variations in extractable organic matter of ten cyclically deposited marl beds abstract a screening by direct desulphurization of extracts was employed for 21 immature organic sulphur rich marl samples from 10 of the 14 evaporite cycles in an italian messinian evaporitic basin vena del gesso gessoso solfifera fm the combined information retrieved from free and sulphur bound carbon skeletons enabled a detailed palaeoenvironmental reconstruction the biomarker compositions of the marls point to large variations in the composition of species in the water column e g dinoflagellates diatoms and other algae cyanobacteria methanogens green sulphur bacteria and bacterivorous ciliates and in contributions from the continent i e land plants within each marl bed and between marl beds the marl beds were deposited within a stratified lagoon where anoxic conditions extended into the photic zone for much of the time

interaction between bottom currents and slope failure in the late cretaceous of the southern danish central graben north sea the nw european chalk group was deposited in a deep epicontinental sea traditionally conceived as a quiet depositional setting that was only affected by redeposition along structural highs the chalk sea was however locally affected by powerful bottom currents during some periods three dimensional seismic reflection data from the southern central graben show abundant intra chalk morphological elements concentrated at two stratigraphic levels within the turonian campanian sequence both levels are topped by extensive unconformities the geometry of the elements produced by alongslope processes is interpreted as caused by se directed bottom currents flowing between the bo jens and adda ridges the highest current intensities led to the formation of the two unconformities judged by the occurrence of the largest current formed channels and drifts at these two stratigraphic levels this sea floor topography was locally modified by large scale downslope mass transport stratigraphical coincidence of the largest slumps and bottom current erosion suggests a coupling between downslope and alongslope processes current erosion impinged upon the slopes during periods of highest current speeds destabilizing the slope sediments and triggering slumping the smoothing of the bathymetry following local relaxation of the tectonic inversion accounted for the coeval deactivation of alongslope and downslope processes during the succeeding maastrichtian deposition

nautiloid shell taphonomy interpretations based on water pressure abstract nautiloid taphonomy is a difficult and widely neglected topic acting as a test of many of the assumptions made in nautiloid paleobiology phylogenetic interpretations and geological facies analysis the eocene nautiloids from the offshore london clay formation of england are considered from the perspective of flooding and implosion experiments on recent nautilus the deeper water facies are often characterized by body chambers in approximate life position one or two complete septa and various types of shell debris intermediate depth facies show intact and often vertically embedded phragmocone walls with zones of internally broken and spar cemented septa taphnomic characteristics of the former facies probably result from the implosion of shells at depths of 200 or 300 m on the seafloor while those of intermediate depth facies result from the sinking of gas filled shells to the seafloor and subsequent bending stress failure of septa left unsupported by sediment in the last whorl evidence for the removal of the body from the largely unbroken shell by octopus illustrates the potential for a biological influence on the taphonomic history of nautiloids through the phanerozoic tertiary nautiloids were probably unusually prone to extensive post mortem transport a process which tends to remove shells from the fossil record under most geological circumstances

a biomarker study of depositional paleoenvironments and source inputs for the massive formation of upper cretaceous lacustrine source rocks in the songliao basin china abstract the abundance and composition of total organic carbon aliphatic and aromatic hydrocarbons including biomarkers and the 13c composition of total organic matter and individual compounds in core samples of the nenjiang formation from the sk 1 borehole of the songliao basin provide information on the paleoenvironmental conditions of lacustrine sediments formed during the upper cretaceous the distribution of n alkanes and their 13c composition and 4 methylsteranes and dinosteranes in the first member of the nenjiang formation k2n1 indicate that the organic matter largely originated from algal organisms and is dominated by types i and ii kerogen the occurrence of gammacerane aryl isoprenoids isorenieratane and low pristane phytane and diasterane sterane ratios further suggest a salinity stratified water column associated with anoxic bottom waters as well as possible photic zone oxygen depletion conditions during major source rock deposition of the k2n1 the organic geochemical data also indicate significantly different depositional environments for the second member of the nenjiang formation k2n2 sediments which are interpreted to have been deposited under a uniform salinity non stratified oxic water column consequently although the organic matter in the k2n2 sediments was largely derived from algal and bacterial sources the kerogen types are dominantly iib and iii due to the oxidative degradation of organic matter combined with a gradual increase in land plant input furthermore the occurrence and shift of two saw toothed distribution patterns of the 13c composition of c29 to c33 n alkanes with w and m patterns being isotopically heavy odd and even numbered alkanes respectively is suggestive of organic input shift or an unknown mechanism of carbon uptake or isotopic fractionation in particular the heavy even carbon numbered high molecular weight n alkanes is rare and needs further investigation

mid cretaceous albian santonian sea surface temperature record of the tropical atlantic ocean paleoclimate records of geologic time periods characterized by extreme global warmth such as the mid cretaceous are important for a better understanding of the earth9s climate system operating in an exceptionally warm mode here we applied an organic geochemical proxy tex 86 on organic matter rich albian santonian sediments recovered from ocean drilling program leg 207 sites 1258 and 1259 on demerara rise to reconstruct sea surface temperatures ssts in the western equatorial atlantic preceded by a stepwise cenomanian warming trend 31 35 c the onset of the cretaceous thermal maximum coincided here with the cenomanian turonian boundary event once established this extreme warm climate regime characterized by averaged tropical ssts close to 35 c lasted up to the turonian coniacian transition two pronounced cooler intervals 2 3 c interrupt this otherwise remarkably stable record providing the first 18 o independent evidence for middle turonian cooling that previously has been attributed to glacioeustatic sea level lowering coniacian ssts decline stepwise reaching a minimum in the santonian 32 33 c where cooling is most pronounced presumably concomitant with the first progressive opening of a deep water passage through the equatorial atlantic gateway

biomarkers reveal the role of photic zone euxinia in exceptional fossil preservation an organic geochemical perspective photic zone euxinia pze has proven important for elucidating biogeochemical changes that occur during oceanic anoxic events including mass extinction and conditions associated with unique fossil preservation organic geochemical analyses of a 380 ma invertebrate fossil which included well preserved soft tissues from the gogo formation canning basin western australia showed biomarkers and stable isotopic values characteristic of pze and a consortium of sulfate reducing bacteria which lead to exceptional fossil and biomarker preservation the carbonate concretion contained phytoplankton green sulfur bacteria chlorobi and sulfate reducing bacteria biomarkers with an increasing concentration toward the nucleus where the fossil is preserved the spatial distribution of cholestane unequivocally associated with the fossilized tissue and its high relative abundance to the total steranes suggest that the fossil is a crustacean the presence of an active sulfur cycle in this devonian system including sulfate reduction and the resulting pze played a pivotal role in the preservation of soft tissue from the fossil and its associated low maturity biomarker ratios

paleolimnology and taphonomy of some fish deposits in fossil and uinta lakes of the eocene green river formation utah and wyoming abstract in four sections in the lacustrine eocene green river formation in utah lake uinta fish are preserved on carbonate mudflats along high energy carbonate shorelines in the littoral zone and in deeper profundal areas scattered bones and scales are found throughout dropped from disintegrating floating carcasses gar scales typify shallow water deposits partly due to habitat preference beach concentrations of greatly abraded bones and scales grade offshore into storm lag layers and lenses which grade to loosely packed horizons or patches of unworn remains littoral fish fossils range from dropped bones to good skeletons with much floating lifting and scavenging preservation improves away from the waterline not only into deep and cold profundal waters where the carcasses are protected from scavenging by anoxia and prevented from floating by temperature and pressure but also onto mudflats where stranding and burial of carcasses can also protect them a section through an isolated part of the green river formation in wyoming fossil lake also ranged from profundal to littoral with minor emergence dropped body parts were found throughout but preservation quality of the best specimens improved with presumed depth the beds with the best specimens seem to have accumulated at the bottom of a deep stratified warm monomictic lake our lake uinta sections were generally shallower and suggest more fluctuations in water level but this is not relevant to broad paleolimnological interpretations because they represent marginal zones which are necessarily more sensitive to changes in depth overall fish fossils are especially informative in deeper waters where sedimentary distinctions fail

reconstructing the palaeoecosystem and palaeodepositional environment within the upper devonian lower mississippian bakken formation a biomarker approach abstract biomarkers have been used extensively to correlate oil families oil source rock relationships and source inputs and to help identify the palaeodepositional environment for a given geological sedimentary unit despite their application in characterising the bakken formation shales a number of biomarkers still appear unable to provide us a consistent understanding regarding heterogeneity in source organic matter and palaeoenvironment here we infer the palaeodepositional environment within the bakken formation shales using a biomarker suite and biomarker depth profiles we also use the occurrence and abundance of biomarkers to define organic facies and to make inferences regarding biotic interactions drawn from modern analogues the variations and co occurrence of biomarkers is explained by the existence of a proposed complex algal bacterium bacteriovore palaeoecosystem this approach not only helps explain the depth variation in occurrence and concentration of biomarkers and the molecular composition of associated organic matter but also advances the use of biomarker analysis and biomarker associations to determine a complex environment sensitive palaeoecosystem

new late cretaceous macrobaenid turtle with asian affinities from the high canadian arctic dispersal via ice free polar routes a new turtle aurorachelys gaffneyi gen et sp nov is described on the basis of a carapace and plastron of late turonian coniacian age from axel heiberg island in the high canadian arctic this turtle is a member of the macrobaenidae a group that is thought to have originated in asia it differs from all other late cretaceous macrobaenids in its nearly circular shell the earliest record of macrobaenids in north america documented by this specimen together with the earliest records of other turtle clades that presumably originated in asia indicates that turtle dispersal was episodic with most first occurrences of asian taxa in north america clustering around the turonian the high global temperatures of the turonian are interpreted as facilitating this episode of dispersal of asian turtle groups into north america islands and seamounts in the young volcanically active arctic ocean during the late cretaceous may have acted as an alternative to an alaskan intercontinental route and may have allowed macrobaenids to enter the part of north america east of the interior continental seaway

identification of aryl isoprenoids in source rocks and crude oils biological markers for the green sulphur bacteria abstract a series of c13 to c31 aryl isoprenoids 1 alkyl 2 3 6 trimethylbenzenes have been identified in reef hosted oils and their source rocks from the middle and upper silurian of the michigan basin and middle devonian of the alberta basin canada their structure has been confirmed by unambiguous synthesis of the c14 member of the series their structure and isotopic composition indicate that they are derived from isorenieratene from the chlorobiaceae family of sulphur bacteria these results are consistent with geological and geochemical studies that show that the source rocks were deposited under metahaline to hypersaline sulphate and sulphide rich water columns the distribution of other biomarkers in these oils and source rocks indicates that a diverse biota contributed organic matter to the source environment in conjunction with the aryl isoprenoids they show that there is a remarkable similarity in composition between the two sets of oils and source rocks despite their great temporal and geographic separation this reflects the similarity of their environments and emphasizes the importance of sedimentary facies in controlling the composition of organic matter in source rocks and their derived oils

high temperatures in the late cretaceous arctic ocean to understand the climate dynamics of the warm equable greenhouse world of the late cretaceous period it is important to determine polar palaeotemperatures the early palaeoceanographic history of the arctic ocean has however remained largely unknown because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice a shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated upper cretaceous organic rich sediment from alpha ridge a submarine elevated feature of probable oceanic origin a lack of carbonate in the sediments from this core has prevented the use of traditional oxygen isotope palaeothermometry here we determine arctic palaeotemperatures from these upper cretaceous deposits using tex86 a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton crenarchaeota from these analyses we infer an average sea surface temperature of approximately 15 degrees c for the arctic ocean about 70 million years ago this calibration point implies an equator to pole gradient in sea surface temperatures of approximately 15 degrees c during this interval and by extrapolation we suggest that polar waters were generally warmer than 20 degrees c during the middle cretaceous approximately 90 million years ago

mass transport in european cretaceous chalk fabric criteria for its recognition although it is a pelagic sediment fine grained calcareous ooze may be mobilized prior to general lithification and redeposited as allochthonous units numerous occurrences of allochthonous chalk have been reported in recent years having been recognized by large scale bedding features seen in outcrop smaller scale internal features such as contorted laminae and larger features such as smeared burrows and imbricated flint nodules attest to a significant amount of soft sediment deformation and synsedimentary slumping in european chalk sections of late cretaceous age truly autochthonous chalks contain complex tiered ichnofabrics and in some cases exhibit a diagenetic nodular fabric that is undisturbed by transport in some situations such as stagnant water conditions autochthonous chalks may exhibit primary lamination although this is very uncommon in european chalk sequences different types of redepositional processes produce an array of varied allochthonous fabrics glide and slump units for example contain internal deformational features produced during sliding ooze flow causes plastic deformation of chalk units internally as well as externally resuspension and fluid flow of chalk sediment produces a deposit having a totally new fabric such as a conglomerate composed of detrital chalk clasts in this paper typical macroscopic sedimentary fabric types are illustrated and the means of identifying them are discussed in terms of bioturbation features in situ diagenetic nodules versus detrital clasts physical deformation structures and development of flints

the bolca lagerstatten shallow marine life in the eocene the eocene limestones around the italian village of bolca occur in a series of distinct localities providing a unique snapshot of marine life in the early cenozoic famous for its fishes the localities of bolca also yield diverse invertebrate faunas and a rich but relatively understudied flora most fossils from bolca derive from the pesciara and monte postale sites which bear similar fossils but are characterized by slightly different taphonomic and environmental profiles although not precisely contemporaneous the age of these principal localities is well constrained to a narrow interval within the ypresian stage c 50 49 ma this places bolca at a critical time in the evolutionary assembly of modern marine fish diversity and of reef communities more generally

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

chlorobiaceae in palaeozoic seas revealed by biological markers isotopes and geology biomarker hydrocarbons in oils and sediments have considerable potential for assessing the nature of biological processes in the past but only a few can be uniquely related to particular organisms reef hosted oils in the silurian of the michigan basin canada and the devonian of western canada have high abundances of 1 alkyl 2 3 6 trimethylbenzenes their precise structures suggest that they are diagenetic products of aromatic carotenoids of the green sulphur bacteria individual components are enriched in 13c by 7 8 relative to the saturated hydrocarbons of the same oil an isotopic anomaly of this magnitude and direction correlates with a component of photosynthetic carbon assimilation by the reductive tricarboxylic acid cycle these results together with data on palaeoenvironments provide compelling evidence for the existence in ancient restricted seas of microbial communities containing chlorobiaceae organisms with distinctive biochemistry which leave morphologically identifiable remains

ichnology of a late devonian early carboniferous low energy seaway the bakken formation of subsurface saskatchewan canada assessing paleoenvironmental controls and biotic responses abstract in spite of the high interest on the late devonian early carboniferous bakken formation as one of the most important oil plays in north america and the numerous studies carried out in this unit no ichnologic analysis has been presented yet based on conventional sedimentologic data previous studies of the bakken interpreted the unit as formed entirely under open marine conditions however integration of ichnology has been key to the identification of not only open marine but also brackish water marginal marine conditions based on the geometry of the sedimentary bodies and the sequence stratigraphic framework the brackish water interval is interpreted as an embayment with limited or intermittent connection to the open sea salinity oxygen content and storms are regarded as the most important environmental parameters that controlled the distribution and nature of the trace fossils in the bakken formation sparse bioturbation relatively low ichnodiversity and the impoverished cruziana ichnofacies characterize the marginal marine deposits suggesting stressful brackish water conditions marine deposits from the middle member in contrast are highly bioturbated with a moderate ichnodiversity and the distal cruziana ichnofacies that flourished during fully marine well oxygenated conditions there is only a slight difference between the total ichnodiversity of the open marine interval ten ichnogenera and that of the brackish water interval seven ichnogenera ichnodiversity should not be considered at face value and isolated from other aspects when evaluating stress levels in order to detect a brackish water signal lack of bioturbation in the black shale of the lower and upper members resulted from anoxic conditions the passage from anoxic lower member to well oxygenated conditions middle member was gradational as is revealed by the occurrence of oxygen deficient trace fossils at the top of the lower member finally the contrasting styles in tempestite preservation in upper offshore deposits from the lower and upper open marine intervals is attributed to variations in the intensity and frequency of storm during deposition of the highstand and transgressive deposits

production and preservation of organic matter during deposition of the bakken formation late devonian and early mississippian williston basin abstract the organic rich up to 35 toc lower and upper black mudstone members of the bakken formation late devonian and early mississippian accumulated in response to both increased productivity and enhanced preservation that resulted from unique palaeogeographic palaeoceanographic and palaeoclimatic conditions during bakken deposition the semi isolated williston basin was located close to the equator 5 to 10 n in a zone of prevailing east to west winds a pattern of estuarine like marine circulation between the williston basin and open ocean conditions at the western craton edge of north america is proposed surface water discharged from the basin was replaced by nutrient rich deeper water sourced from the equatorial undercurrent in the pacific basin undercurrent flow into the williston basin upwelled providing a potentially sustainable source of nutrients to enhance productivity in the surface photic zone during black mudstone deposition in response to increased productivity that led to a high rate of organic sedimentation and quiescent deep water conditions due primarily to the geographic isolation of the basin and the restriction of estuarine like circulation to the upper water column anoxic bottom water developed on the basin floor as sea level rose during lower and upper black mudstone deposition anoxic bottom water expanded across the basin enhancing organic matter preservation conditions in the williston basin demonstrate that both increased productivity and improved preservation can be essential and complementary factors affecting organic rich mud deposition these results have potentially important implications for the accumulation of similarly organic rich deposits across the north american interior during late devonian and early mississippian time

the werra cyclotheme upper permian fore sudetic monocline poland insights into fluctuations of the sedimentary environment from organic geochemical studies abstract a study of the extracts of samples recording a transgressive regressive succession of the werra cyclothem zechstein upper permian from the southern margin of the european permian basin the fore sudetic monocline poland provides an insight into major sources of organic matter and diagenetic processes the studied cross section comprises all lithologies representative for the european basin including transgressive sandstones weissliegend and organic rich shales kupferschiefer followed by carbonates as well as regressive anhydrites with intercalations of rock salt due to the variable influence of overlapping diagenetic processes that affected the organic matter i e maturation and late diagenetic oxidation related to base metal mineralisation a reliable comparison of the biomarker results is only possible for the major upper part of the section ca 38 m including carbonates and evaporites but not for the oxidised first 2 3 m from the base of the kupferschiefer the transition from carbonate to evaporate sedimentation is associated with a shift to predominant even c numbered n alkanes increased abundance of carotanes and high homohopane index reflecting enhanced reducing conditions the presence of the c25 regular isoprenoid squalane biphytane and the rapid decrease in the pristane phytane ratio in the evaporites are mainly controlled by the important contribution from both halophilic and methanogenic archaea the occurrence of gammacerane in the anhydrites suggests development of water column stratification at some stages of the sea regression this is associated with appearance of specific aryl isoprenoids with a lycopane carbon skeleton most likely related to botrycoccus braunii race l algae lycopane derivative occurrence suggests that such an algal race could have occurred since permian currently known recent eocene the presence of the abundant freshwater brackish algal biomarkers in evaporititic deposits can be envisaged in the costal part of the zechstein basin with temporary salt wedge estuary water stratification the algae bloomed in the top fertile fresh brackish water layer fed by rivers and the algal biomass was deposited on the sea floor covered with evaporitic brine the stratification periodically broke down during precipitation of the rock salt presumably due to a decrease in riverine water input as revealed by characteristic disappearance of gammacerane and hopane distributions similar to those observed for the carbonate rocks the methylphenanthrenes phenanthrene ratio was used together with methyldibenzothiophenes dibenzothiophene ratio to assess maturity these maturity estimations indicate that the peak of oil window has been reached which is confirmed by other biomarker maturity parameters based on sterane and hopane distributions the maturity stage of oil generation and expulsion was further confirmed by the presence of solid bitumen as cements in the sandstone underlying kupferschiefer and bitumen veins and lenses in the carbonates

magnetic and calcareous nannofossil stratigraphy of the lower palaeogene formations of the hampshire and london basins a magnetostratigraphic study of the lower palaeogene formations exposed in the hampshire and london basins southern uk has led to the identification of eight stratigraphically distinct normal polarity magnetozones within an otherwise reverse polarity sedimentary sequence which spans the late palaeocene to middle eocene a complementary study of the calcareous nannofossil biostratigraphy of these sections and related sections elsewhere in nw europe allows a correlation of this succession of normal polarity magnetozones with the biostratigraphically calibrated geomagnetic polarity timescale based on marine magnetic anomalies it is concluded that the normal polarity chrons corresponding to anomalies 20 21 and 23 are recorded within the huntingbridge earnley and wittering divisions of the bracklesham group respectively that anomalies 24a and 24b are represented within divisions d to b2 of the london clay and anomaly 26 is represented in the lower part of the thanet beds an additional normal polarity magnetozone within the oldhaven beds is believed to represent a short normal polarity event between anomalies 24b and 25 anomalies 22 and 25 appear not to be represented in the uk lower palaeogene succession because of major unconformities at the early middle eocene boundary within the wittering division of the bracklesham group and within the late palaeocene respectively the former appears to correlate with a widespread erosional event in the oceans identified from seismic records vail et al 1979 and interpreted as reflecting a major eustatic sea level fall

aryl isoprenoids and diaromatic carotenoids in paleozoic source rocks and oils from the western canada and williston basins abstract aryl isoprenoids in the range c13 c31 have been identified in source rock bitumens and oils from several paleozoic age petroleum systems in the western canada and williston basins the principal compounds possess the 2 alkyl 1 3 4 trimethyl substitution pattern characteristic of diaromatic carotenoids found in the chlorobiaceae family of photosynthetic sulfur bacteria two c40 perhydrodiaromatic carotenoids which are structurally related to the presumed precursors of the aryl isoprenoids have also been identified in oils and source rock bitumens of the duvernay late devonian petroleum system pyrolysis gas chromatograms of kerogens isolated from several paleozoic source rocks show an unusual abundance of 1 2 3 4 tetramethylbenzene it is proposed that this compound arises from cleavage of diaromatic carotenoid moieties which have been incorporated into the kerogen structure with increasing maturation concentrations of the aryl isoprenoids in duvernay source rock bitumens increase to a point whereas the c40 perhydrodiaromatic carotenoids decrease steadily previous studies have suggested that aryl isoprenoids may be indicators of enhanced salinity environments this is not supported by the present work which shows high concentrations in source rocks associated with presumed normal marine salinities there is however a general association with intervals of condensed clastic or mixed clastic carbonate sedimentation within carbonate depositional systems from the association found and from parallels to modern habitats of photosynthetic bacteria it can be inferred that these biomarkers indicate prolific bacterial growth in a stratified water column at and below the oxic anoxic boundary layer in sub tropical to tropical marine environments

extremely high sea surface temperatures at low latitudes during the middle cretaceous as revealed by archaeal membrane lipids the middle cretaceous 125 88 ma greenhouse world was characterized by high atmospheric co 2 levels the general absence of polar ice caps and much higher global temperatures than at present both 1 8 o based and model based temperature reconstructions indicate extremely high sea surface temperatures ssts at high latitudes however there are a number of uncertainties with sst reconstructions based on 1 8 o isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the 1 8 o value of cretaceous seawater the paleoecology of middle cretaceous marine organisms and seawater ph here we applied a novel sst proxy i e text tetraether index of 86 carbon atoms based on the membrane lipids of marine crenarchaeota derived from middle cretaceous sedimentary rocks deposited at low latitudes the text proxy indicates that tropical ssts in the proto north atlantic were at 32 36 c during the early albian and late cenomanian early turonian this finding agrees with sst estimates based on 1 8 o paleothermometry of well preserved foraminifera as well as global circulation model calculations the text proxy indicates cooler ssts 27 32 c for the equatorial pacific during the early aptian which is in agreement with sst estimates based on 1 8 o paleothermometry

northwestern european paleogene magnetostratigraphy biostratigraphy and paleogeography calcareous nannofossil evidence global calcareous nannofossil biostratigraphy is used to correlate the paleogene chronostratigraphic units of northwestern europe and standard nannofossil biozones such biostratigraphic correlations show that the lithostratigraphic sequence is discontinuous and allows interpretation of the paleogeography of northwestern europe during the paleogene and evaluation of the influence of global sea level eustatic changes on northwestern european stratigraphy a well documented unconformity occurs near the lower middle eocene boundary in the paris basin this unconformity which also can be traced in the london hampshire basin and in belgium correlates with a coastal offlap event presumed sea level of vail et al on the basis of magnetostratigraphic biostratigraphic correlations the duration of the hiatus associated with this unconformity can be estimated to be 0 6 to 1 5 m y in the hampshire basin and 2 to 4 m y in the paris basin

kinematic pile response to vertical p wave seismic excitation an analytical solution based on a rod on dynamic winkler foundation model is developed for the response of piles in a soil layer subjected to vertical seismic excitation consisting of harmonic compressional waves closed form solutions are derived for 1 the motion of the pile head 2 the peak normal strain in the pile and 3 the group effect between neighboring piles the solutions are expressed in terms of a dimensionless kinematic response factor iv relating pile head motion and free field soil surface motion a dimensionless strain transmissibility factor ie relating pile and soil peak normal strains and a pile to pile interaction factor measuring group effects it is shown that a pile foundation may significantly reduce the vertical seismic excitation transmitted to the base of a structure

a review of selected engineering geological characteristics of english chalk abstract chalk is a variable material the properties of which are dependent upon its composition textural features and diagenetic history with the exception of certain horizons in the lower chalk that contain appreciable amounts of clayey material the english chalk is a remarkably pure micritic carbonate rock that generally can be divided into coarse and fine fractions the latter comprises 70 80 of chalk cementation took place more or less contemporaneously with deposition so that the sediment was able to support relatively high overburden pressures hence high values of porosity were retained chalk varies appreciably in density and hardness the harder chalks are the result of diagenetic processes and bioturbation that brought about densification in soft chalks the grains are only bound together at the points of contact by thin films of calcite the latest classification of chalk is based on an assessment of intact dry density discontinuity aperture and discontinuity spacing chalk tends to vary from moderately weak to moderately strong and its strength is significantly reduced on saturation under triaxial loading conditions diagonal shear failure tends to occur at lower confining pressures but at higher confining pressures barrel shaped failure occurs indicating plastic deformation and textural disaggregation similarly at low loading chalk exhibits low volume compressibility but much more significant consolidation occurs if the yield stress is exceeded chalk undergoes dissolution and so solution features are found throughout its outcrop mineworkings in the chalk extend back into the distant past the most ancient being those excavated in the neolithic age for flint several types of workings exist collapse of old mineworkings most of which are unrecorded is difficult to predict the potential for subsidence caused by the collapse of both mineworkings and dissolution features affects development and its occurrence can lead to the abandonment of property or worse the loss of lives

composite ichnofabrics and tiering of burrows infaunal communities in marine environments typically are tiered that is different taxa live at different depths within the sediment tiered suites of biogenic structures yield complex biogenic sedimentary fabrics ichnofabrics with the traces of deep burrowing organisms overprinted on those of shallow burrowing organisms careful analysis of crosscutting relationships of burrows in such composite ichnofabrics allows reconstruction of the tiered nature of fossil endobenthic communities it is important to recognize that the best preserved and most prominently displayed trace fossils in most assemblages usually represent the deepest tier thus they were farther removed from the sea floor and therefore less indicative of actual sea floor conditions than the more poorly preserved traces of the shallower tiers on which the deeper traces are juxtaposed

dynamic response of pile groups subjected to horizontal loads this paper presents an analytical method for calculating the dynamic impedance of pile groups comprising an arbitrary number of cylindrical piles connected with a rigid cap the solution allows con

petroleum potential of the middle member bakken formation williston basin abstract the bakken formation is a widespread clastic unit between the mississippian madison group and the upper devonian big valley torquay or three forks formations the formation typically consists of three members a lower and upper organic rich shale and a middle calcareous sandstone and siltstone the three members of the bakken formation exhibit an onlapping relationship and converge and thin toward the margins or marginal shelf areas of the williston basin in manitoba the lower member is absent except for waskada field several correlative lithofacies have been recognized in the middle member the lowermost unit of the middle member is a regressive deposit the upper portions of the middle member show transgressive and regressive cycles and intertidal deposits interfinger with their distal equivalents conventional bakken production is restricted to areas where it is a thermally mature source rock the greater part of bakken production in recent years has been taken from the shale of the upper and lower members although there are outlying fields which produce from a sandstone within the middle member this suggests that there has been a migration of bakken oil from the central portion of the basin the sandstone unit may provide a conduit for migration

pile groups under axial loading an appraisal of simplified non linear prediction models the settlement behaviour of vertically loaded pile groups has been the subject of an extensive body of research over the past two decades in particular this work has identified the over conservat