carbonate factories a conundrum in sedimentary geology abstract describing characterizing and interpreting the nearly infinite variety of carbonate rocks are conundrums intricate and difficult problems having only conjectural answers that have occupied geologists for more than two centuries depositional features including components rock textures lithofacies platform types and architecture all vary in space and time as do the results of diagenetic processes on those primary features approaches to the study of carbonate rocks have become progressively more analytical one focus has evolved from efforts to build reference models for specific phanerozoic windows to scrutinize the effect of climate and long term oscillations of the ocean atmosphere system in influencing the mineralogy of carbonate components this paper adds to the ongoing lively debates by attempting to understand changes in the predominant types of carbonate producing organisms during the mesozoic cenozoic while striving to minimize the uniformitarian bias our approach integrates estimates of changes in ca2 concentration in seawater and atmospheric co2 with biological evolution and ecological requirements of characteristic carbonate producing marine communities the underlying rationale for our approach is the fact that co2 is basic to both carbonates and organic matter and that photosynthesis is a fundamental biological process responsible for both primary production of organic matter and providing chemical environments that promote calcification gross photosynthesis and hypercalcification are dependent largely upon sunlight while net primary production and e g subsequent burial of organic matter typically requires sources of new nutrients n p and trace elements our approach plausibly explains the changing character of carbonate production as an evolving response to changing environmental conditions driven by the geotectonic cycle while identifying uncertainties that deserve further research with metazoan consumer diversity reduced by the end permian extinctions excess photosynthesis by phytoplankton and microbial assemblages in surface waters induced by moderately high co2 and temperature during the early mesozoic supported proliferation of non tissular metazoans e g sponges and heterotrophic bacteria at the sea floor metabolic activity by those microbes especially sulfate reduction resulted in abundant biologically induced geochemical carbonate precipitation on and within the sea floor for example with the opening of tethyan seaways during the triassic massive sponge microbe boundstones the benthic automicrite factory formed steep massive and thick progradational slopes and locally mud mounds as tectonic processes created shallow epicontinental seas photosynthesis drove lime mud precipitation in the illuminated zone of the water column the resulting neritic lime mud component of the shallow water carbonate factory became predominant during the jurassic paralleling the increase in atmospheric pco2 while the decreasing importance of the benthic automicrite factory parallels the diversification of calcifying metazoans phytoplankton and zooplankton with atmospheric pco2 declining through the cretaceous the potential habitats for neritic lime mud precipitation declined at the same time peak oceanic ca2 concentrations promoted biotically controlled calcification by the skeletal factory with changes produced by extinctions and turnovers at the cretaceous tertiary boundary adaptations to decreasing ca2 and pco2 coupled with increasing global temperature gradients i e high latitude and deep water cooling and strategies that efficiently linked photosynthesis and calcification promoted successive changes of the dominant skeletal factory through the cenozoic larger benthic foraminifers protist protist symbiosis during the paleogene red algae during the miocene and modern coral reefs metazoan protist symbiosis since late miocene

sediment transport processes in an ancient mud dominated succession a comparison of processes operating in marine offshore settings and anoxic basinal environments abstract few studies describe and compare the transport mechanisms operating to disperse mud in different parts of basins instead the physical processes operating to disperse mud in offshore environments where storm and tidal processes are interpreted to dominate are generally considered in isolation from those occurring in basinal settings where changes in bottom water anoxia and suspension settling from buoyant plumes are mostly interpreted to dominate using microtextural mineralogical and geochemical data derived from the analyses of 151 thin sections obtained from the lower jurassic mudstone dominated succession exposed on the coast of ne england we investigate how varying sediment dispersal mechanisms bioturbation and early diagenesis operated to produce the lithofacies variability observed in particular we consider the processes of sediment delivery while bottom waters were interpreted to be euxinic analyses of these samples reveal that the succession is highly variable at millimetre to centimetre scales six main lithofacies were observed 1 sand and clay bearing silt rich mudstones 2 silt bearing clay rich mudstones 3 clay rich mudstones 4 clay calcareous nannoplankton and organic carbon bearing mudstones 5 fine grained muddy sandstones 6 cement rich mudstones these units are organized typically into stacked successions of sharp based normally graded thin

heterogeneity of the lower silurian longmaxi marine shale in the southeast sichuan basin of china this study characterizes the vertical heterogeneity of the lower silurian longmaxi marine shale in the southeast sichuan basin based on core description thin sections observation geological chemistry data interrogation and qemscan image analysis lithofacies associations mineralogy graptolite species occurrence rock fabrics as well as toc total organic carbon and gas content change noticeably and regularly in the lower silurian longmaxi marine shale within sequence stratigraphic framework lithofacies associations mainly include in situ graptolite rich and siliceous shale in the transgressive systems tract tst micro offsite graptolite rich shale and shale interbedded with siltstone laminaes in the early highstand systems tract ehst and micro offsite graptolite rich and carbonate rich shale in the late highstand systems tract lhst the tst has a greater abundance of diplogratus than ehst and lhst and has a lesser level of monograptus which is conversely higher in the ehst and lhst the tst shale is silica rich while the lhst shale is generally clay rich the ehst shale is more balanced in its silica and clay content than the tst and lhst are the sedimentary structure and fabric of shale shows that shale is homogenous in the tst with laminaes well developed in the ehst but decreasing in the lhst toc and gas content are highest in the tst and decrease upward the tst with high toc high gas content high brittle minerals silica rich and anoxic suboxic to dysoxic sedimentary environment is the most potential shale gas target interval in the study area our research also shows that the toc mainly controls shale gas accumulation and that the redox conditions mainly control the preservation of organic matter the silica also plays a significant role in shale gas content due to its contribution to hydraulic fracturing finally the study proposes a depositional and heterogeneity model for the lower silurian longmaxi marine shale in the study area

high resolution facies analyses of mudstones implications for paleoenvironmental and sequence stratigraphic interpretations of offshore ancient mud dominated successions abstract the extent of lithofacies variability in fine grained sedimentary rocks is very poorly known in comparison to that present in coarser grained clastic and carbonate successions the absence of this information means that sediments present on continental shelves are rarely considered as integrated systems because fine grained facies such as shales are mostly excluded from sophisticated regional facies models to shed light upon lithofacies and grain size in shale dominated successions so that they can be incorporated into shelf wide depositional models the blackhawk formation of the mancos shale campanian age exposed in the book cliffs utah was investigated using combined field whole rock geochemical optical and electron optical methods these sediments show systematic grain size variations are intensely bioturbated and composed predominantly of detrital clays mainly dioctahedral micas quartz and feldspar with minor pyrite and organic matter they are organized into very thin 10 mm upward fining genetic beds they exhibit both systematic lateral 103 m scale and vertical 10 2 to 100 m scales lithofacies variability preferentially cemented units occur close to sequence boundaries unconformities these cemented units typically contain a very different detrital assemblage including significant quantities of chlorite from the rest of the succession and are located close to levels where there are marked stacking pattern discontinuities overall lithofacies variability is interpreted in terms of deposition occurring on an oxic continental shelf with the coarser grained facies being deposited in proximal settings offshore transition zone in contrast to the finer grained units that were deposited in more distal environments offshore zone storms are interpreted to have been the dominant mechanism dispersing the sediment once deposited the surface layers of the sediment were intensely reworked by burrowing organisms preferential preservation of ichnogenera from mid and lower tiers suggest that the depositional environment was energetic and erosion commonly removed the surface sediment layers prior to deposition of thin 10 2 m storm beds the larger scale 100 m upward coarsening units that are composed of stacked beds are interpreted to be parasequences preferential cementation at levels where large scale stacking patterns change is interpreted to occur at horizons where there were breaks in sediment accumulation and bacterial metabolic processes were able to supply sufficient solutes to fill uncompacted pore space with cement the presence of a very different detrital assemblage in these units suggests that winnowing occurred despite their relatively innocuous appearance in the field these surfaces are likely to be significant bypass surfaces over which sediment was delivered to the deeper parts of the basin during times of relative lowstand of sea level

late jurassic palaeoclimatic change from clay mineralogy and gamma ray spectrometry of the kimmeridge clay dorset uk abstract the late jurassic was a time of increasing aridity in nw europe here a new clay mineral dataset is presented from a 600 m thick composite core through the kimmeridge clay formation southern england clay mineral assemblages comprise mainly illite and kaolinite with minor randomly interstratified illite smectite mixed layer clays sem observations indicate that clay minerals are mainly detrital except in silty strata of late tithonian age which contain abundant pore filling kaolinite aggregates th k ratios determined from gamma ray spectrometry mirror palaeoclimatically significant variations in kaolinite illite ratios with notable exception where diagenetic kaolinite occurs comparison with age equivalent strata identifies regional cyclic variations in clay minerals at the 100 300 m scale small scale 10 20 m variations in clay minerals and th k also occur it is proposed that the region experienced progressively intense humidity through the kimmeridgian followed by a return to more arid conditions during the early tithonian following a mid tithonian peak in aridity the hudlestoni event9 more humid climatic conditions returned prior to the development of latest tithonian intense aridity late jurassic climate was apparently subject to synchronously cyclic changes across a broad area of the laurasian continent such changes could not have resulted from mountain building or continental rotations supplementary material clay data are available at http www geolsoc org uk sup18376

mudstone sedimentation at high latitudes ice as a transport medium for mud and supplier of nutrients abstract controls on mudstone deposition at high latitudes are poorly known relative to low latitudes in recent sediments deposited in these environments ice significantly influences sediment transport and primary productivity the products of ice transport are relatively well known in glacimarine settings but are less well known from below melting sea ice this latter setting is significant as today it is associated with high primary organic productivity the aim of this study is to assess how sea ice might have controlled lithofacies variability and organic matter distribution and preservation in an ancient marine siliciclastic mudstone dominated succession deposited at high latitudes combined sedimentary logging optical and electron optical backscattered electron imagery geochemical and isotopic methods were used to determine sample variability in forty five samples collected from the lower cretaceous succession in the mikkelsen bay state 1 borehole north slope alaska the succession overall fines upward and contains muddy sandstones and sand and silt bearing clay rich mudstones towards its base in contrast to clay rich and clay dominated mudstones towards its top some of the mudstone units exhibit thin 5 mm relic beds that fine upward weakly in some units small 0 5 mm bed parallel silt filled microburrows disrupt depositional laminae whereas in others pervasive burrowing completely obliterates original depositional textures many of the units are pelleted these mudstones are unusual in that they contain minor but very striking outsize grains composed of subrounded to rounded sand and granule size material in addition they are good petroleum source rocks with between 2 8 and 5 9 wt total organic carbon of predominantly type ii kerogen the organic matter has an isotopic signature ranging from 25 4 13c to 28 1 13c thin tuffs 20 mm and carbonate cemented units are also present given the absence of significant polar ice in the early cretaceous the outsized grains are interpreted to have been deposited from a combination of melting dirty anchor and fast ice the mud fraction which forms the bulk of the sediment is interpreted to have been deposited from melting sediment laden frazil ice and fast ice after deposition sediments were partially reworked by bottom currents generated by brine rejection during sea ice formation sympagic organisms grazing on algae and bacteria both within and below the ice pelleted the sediment bioturbation which varies through the succession indicates that sedimentation probably occurred beneath a predominantly oxic or dys oxic water column in this setting productivity was fueled by nutrients released from melting sea ice in the marginal ice zone the good petroleum source potential of these mudstones is attributed to high organic productivity coupled to episodic and rapid sedimentation rather than existence of bottom water anoxia linked to upwelling because sea ice rafting was probably the dominant sediment transport mechanism it is not appropriate to use sequence stratigraphic methodology to predict lithofacies variability in this environment

a sequence stratigraphic interpretation of a mudstone dominated succession the lower jurassic cleveland ironstone formation uk microfacies analysis using optical and backscattered electron imagery has been undertaken on 37 samples from the cleveland ironstone formation staithes yorkshire uk four lithofacies were encountered clay rich mudstones silt rich mudstones sand rich mudstones and concretionary carbonates two types berthierine siderite rich ironstones and apatite rich concretionary horizons successive units were found to stack systematically into upward coarsening units on a small 0 1 1 0 m scale upward coarsening and upward fining packages were also found on a larger 1 0 3 0 m scale the small scale upward coarsening units are interpreted to be parasequences while the large scale upward fining and upward coarsening packages are interpreted to be retrogradational and progradational parasequence sets respectively the ironstones occur at the level where the stacking patterns change from being overall progradational to retrogradational while the apatite rich concretionary units occur at the level where the stacking patterns change from being retrogradational to progradational the concretionary carbonates are interpreted to have formed close to at major stratal surfaces the ironstones are interpreted to be either the correlative equivalent of sequence boundaries or part all of the forced regressive system tract while the apatite rich units are interpreted to have precipitated close to at maximum flooding surfaces condensed sections and or major transgressive surfaces

a lithofacies study of the peterborough member oxford clay formation jurassic uk an example of sediment bypass in a mudstone succession thirteen samples from the peterborough member oxford clay formation middle jurassic from quest pit stewartby central england were examined in detail using a combination of optical microscopy and backscattered electron imagery the majority of the samples were clay rich mudstones two were silt rich mudstones and one was a muddy sandstone the dominant components of these samples are fine grained clays illite mixed layer illite smectite kaolinite and amorphous organic matter minor components include authigenic pyrite framboidal and euhedral silt sized quartz grains calcareous nannoplankton mainly disarticulated coccolith plates and a variety of early carbonate cements some of the mudstones were found also to contain abundant foraminifera temporal trends between samples in grain size foraminiferal abundance and total organic carbon contents were observed these mudstones were deposited in a shallow epeiric sea where productivity was high and the bottom waters were oxic relative sea level change coupled to a lack of available accommodation space within the basin at low sea level stands is invoked to explain the observed mudstone stacking patterns

local to global controls on the deposition of organic rich muds across the late jurassic laurasian seaway muds deposited in large scale epicontinental seaways provide deep insights into palaeoclimates biogeochemical cycles sedimentation processes and organic carbon burial during exceptionally warm periods throughout the phanerozoic temporal changes can be monitored at single locations but the key larger scale oceanographical and related biogeochemical processes are likely to be more clearly revealed by comparisons between individual sub basins within seaways here we compare inorganic geochemical records from the jurassic upper pectinatites wheatleyensis to lower pectinatites pectinatus ammonite zones of the swanworth quarry 1 core from the wessex basin dorset uk to time equivalent records from the ebberston 87 core in the cleveland basin yorkshire uk 400 km apart our synthesis shows that while the dorset sediments were deposited in an energetically more dynamic setting than the yorkshire sediments the overarching climatic and oceanographical processes responsible for variations in organic carbon enrichment and sedimentation were similar intervals of coeval organic carbon rich sedimentation occurred in both basins and a particulate shuttle was intermittently active in both basins consistent with recent climate simulations we conclude that tropical climate conditions associated with enhanced nutrient supply were key drivers of sedimentation between the jurassic wessex and cleveland basins

compositional controls on early diagenetic pathways in fine grained sedimentary rocks implications for predicting unconventional reservoir attributes of mudstones diagenesis significantly impacts mudstone lithofacies processes operating to control diagenetic pathways in mudstones are poorly known compared to analogous processes occurring in other sedimentary rocks selected organic carbon rich mudstones from the kimmeridge clay and monterey formations have been investigated to determine how varying starting compositions influence diagenesis the sampled kimmeridge clay formation mudstones are organized into thin homogenous beds composed mainly of siliciclastic detritus with some constituents derived from water column production e g coccoliths s depleted type ii kerogen as much as 52 6 total organic carbon toc and others from diagenesis e g pyrite carbonate and kaolinite the sampled monterey formation mudstones are organized into thin beds that exhibit pelleted wavy lamination and are predominantly composed of production derived components including diatoms coccoliths and foraminifera in addition to type iis kerogen as much as 16 5 toc and apatite and silica cements during early burial of the studied kimmeridge clay formation mudstones the availability of detrital fe iii and reactive clay minerals caused carbonate and silicate buffering reactions to operate effectively and the pore waters to be fe ii rich these conditions led to pyrite iron poor carbonates and kaolinite cements precipitating preserved organic carbon being s depleted and sweet hydrocarbons being generated in contrast during the diagenesis of the sampled monterey formation mudstones sulfide oxidation coupled with opal dissolution and the reduced availability of both fe iii and reactive siliciclastic detritus meant that the pore waters were poorly buffered and locally acidic these conditions resulted in local carbonate dissolution apatite and silica cements precipitation natural kerogen sulfurization and sour hydrocarbons generation differences in mud composition at deposition significantly influence subsequent diagenesis these differences impact their source rock attributes and mechanical properties

annual layering in the upper jurassic kimmeridge clay formation uk quantified using an ultra high resolution sem edx investigation abstract this paper reports the results of an ultra high resolution investigation of the geochemistry of the late jurassic kimmeridge clay formation kcf using scanning electron microscope energy dispersive x ray analysis sem edx sub millimetre banding is revealed in which each band approximately 112 m thick comprises a couplet of coccolith rich and coccolith poor sediment major element analysis reveals that regularly spaced peaks in the relative amount of calcium are associated with coccolith rich bands it is argued that each couplet represents an annual layer the calcium peaks corresponding to an annual bloom of coccolithophorids there is also a broad correlation between the calcium aluminium ratio and the ratios of sodium aluminium phosphorus aluminium and potassium aluminium to calcium aluminium ratios we tentatively suggest that there may be a link here sodium phosphorous and potassium today being key nutrients for coccolith productivity aluminium is taken as representing the background terrigenous clay fraction if each banded couplet is indeed annual and if the thickness of such bands were to be representative of the kcf as a whole then the post compactional thickness is broadly in agreement with sedimentation rates of 100 m per year calculated by oschmann 1990 this study confirms the view that the kcf in southern england accumulated in a predominantly anoxic environment that favoured the preservation of organic material within the bottom sediment bundles of bands clustering in groups of about 8 10 are tentatively related to short term changes in insolation possibly sun spot cycles

early diagenetic pyrite morphology in a mudstone dominated succession the lower jurassic cleveland ironstone formation eastern england abstract diagenetic pyrite in the mudstones and ironstones of the lower jurassic cleveland ironstone formation of eastern england exhibits two distinct morphologies framboidal pyrite commonly associated with organic matter and euhedral pyrite associated with detrital clay pellets these two morphologies are mutually exclusive in occurrence framboidal pyrite is present in clay rich mudstones ooidal ironstones apatite rich units and some silt rich mudstones euhedral pyrite is present in silt rich and sand rich mudstones 34s isotopic analysis of six samples of pyrite suggests that both types of pyrite morphology precipitated during early diagenesis from porewaters with open access to overlying sea water although both probably acted as sites for continued pyrite precipitation during burial it is proposed that framboidal pyrite precipitated from iron dominated porewaters at sites of sulfide supply i e in the region of organic matter as a result of bacterial sulfate reduction where locally sulfide production rates were high enough for porewaters to reach supersaturation with respect to fes euhedral pyrite also precipitated from iron dominated porewaters but sulfide production rates from organic matter was such that fes saturation was not reached at the sites of sulfide production instead euhedral pyrite was precipitated directly from porewater when fes2 saturation was reached the control over pyrite morphology was probably the amount and reactivity of the organic matter within the deposited sediments the sand rich mudstones contained less reactive organic matter due to clastic dilution and deposition in shallower environments with o2 rich bottom waters the ironstones and apatite rich units were deposited under very low sedimentation rates and as a result organic matter contents were very low and iron reduction dominated early diagenesis which inhibited sulfate reduction the presence of minor framboidal pyrite within these units however suggests that sulfide reduction took place in micro environments during early diagenesis

organism sediment interactions in shale hydrocarbon reservoir facies three dimensional reconstruction of complex ichnofabric geometries and pore networks abstract the lithological and mineralogical characteristics of mudstones and siltstones and their stress strain behavior at the meter to nanometer scale can play a critical role in the exploitation of unconventional shale reservoirs shale fabrics that result from bioturbation can produce extensive interconnected networks of biologically redistributed sediment grains within reservoir mudstone facies the presence of biologically generated heterogeneities may substantially affect reservoir stimulation and thus production from shale facies this study presents volumetric evaluation of ichnofabrics dominated by phycosiphon like and aff chondrites and provides insights into the impact of trace fossils on the rheological and petrophysical characteristics of mudstones it is calculated that in addition to creating significant volumes of silty clay poor zones of enhanced porosity and permeability trace fossils create interpenetrating frameworks of brittle material that reduce communication distances from the low permeability matrix to the higher permeability silt rich burrows reducing communication distances to less than 1 cm increases the potential for diffusive transport of hydrocarbon molecules from the tight matrix to the wellbore connected volumes this is because shale ichnofabrics create abundant fracture prone planes of weakness and increase the surface area of the interface between the hydrocarbon rich matrix and porous burrow fills thereby promoting fluid exchange understanding of the three dimensional characteristics of ichnofabrics may form the basis of future modeling of fracture spacing and complexity that is critical to shale gas reservoir characterization

a role for organic petrology in integrated studies of mudrocks examples from devonian black shales of the eastern us abstract over the years the study of mudrocks has lagged far behind that of other lithologies a circumstance that is in part due to their fine grained nature and in part due to economic realities yet within petroleum systems mudstones are usually the main source of hydrocarbons and typically are also important as hydrocarbon seals recent work on late devonian mudstones from the eastern us shows that much progress can be made through an integration of outcrop study macro and micropaleontology ichnofossils gamma ray spectroscopy microscopic examination of thin sections in transmitted and reflected light electron microscopy sem bse electron microprobe carbon and sulfur isotopes and organic geochemistry erosion surfaces within this black shale succession have been traced over large distances and provide the foundation for a sequence stratigraphic re interpretation of these rocks evidence of storm wave reworking of the seabed as well as the realization that benthic colonization was much more widespread than previously believed suggest that anoxic conditions in the water column were not a controlling factor in the accumulation of the large quantities of organic matter found in these shales these distal devonian shales accumulated slowly and allowed accumulation of large proportions of organic matter in modern settings of abundant organic matter accumulation the original material is broken down by bacteria within a matter of months into a mass of largely unidentifiable organic particles and extracellular bacterial slime although one can still find identifiable material within this mass slime and amorphous material strongly dominate after burial and maturation this material turns into the various organic macerals that organic petrologists are accustomed to describe one might wonder in this context how much information about the origin of a given mudstone unit can we hope to extract through organic petrology in order to illustrate how organic petrology of mudrocks can contribute to their better understanding late devonian black shales of the eastern us will be examined from a sedimentological perspective combining sedimentologic and geochemical data with basic observations on organic petrology illustrates how the latter can contribute to more realistic scenarios of black shale genesis

maximizing information from fine grained sedimentary rocks an inclusive nomenclature for mudstones abstract a simple nomenclature for fine grained sedimentary rocks is proposed based on sedimentary structures present and abundance of all materials forming more than 10 of rock volume irrespective of their origin allochthonous autochthonous and diagenetic a mudstone sedimentary rock that comprises 50 grains 90 clay silt and sand bearing clay rich mudstone 50 to 90 clay 10 to 50 sand 10 to 50 silt and calcite ce ment calcareous nannoplankton and clay bearing mudstone all components 10 to 50 textural information can and should be incorporated into this scheme by prefixing the rock name with descriptions such as bioturbated and thin bedded such a nomenclature is necessary to fully describe variability within fine grained sedimentary rocks that hitherto have typically been described using selected constituents of varying significance such as total organic carbon fissility parting spacing ray signature and lamination using the inclusive nomenclature proposed here will improve opportunities to compare all fine grained sediments aid interpretation of depositional and diagenetic controls of variability and enable these rocks to be more easily integrated into basin scale facies models

depositional controls on mudstone lithofacies in a basinal setting implications for the delivery of sedimentary organic matter deep water mudstones from ancient epicontinental settings are significant repositories for organic matter but the detailed temporal variations of and controls on the abundance and type of organic matter om is little studied using micro petrographic and geochemical data from late mississippian mudstones of the widmerpool gulf uk the processes that delivered fine grained sediment to this basin during a glacioeustatic sea level cycle are interpreted from detailed lithofacies analysis seven primary lithofacies are identified from core which show specific and systematic variations in total organic carbon toc content and bulk carbon isotope composition of organic material 13corg during sea level highstands thin bedded carbonate bearing mudstones are the dominant facies deposited contain up to 6 6 toc average 4 6 1 3 and have mean 13corg of 28 5 0 9 during phases of lower sea level thin bedded silt bearing clay rich mudstones with up to 4 1 toc average 2 3 0 8 mean 13corg 28 2 1 0 were interbedded with more organic lean graded silt bearing mudstones and sand bearing silt rich mudstones average toc 1 7 0 6 derived from turbidity currents the latter mean 13corg 26 2 0 7 are closely linked to significant proportions of terrestrial plant material while some rare plant debris and sand bearing mudstones produced from debris flows have more than 7 0 toc and 13corg 26 0 the 13c values of wood fragments ranged from 27 1 to 24 0 and therefore the 13corg is interpreted as a function of the ratio of marine and terrestrial organic matter more negative values in the carbonate bearing and the clay rich mudstones indicate marine planktonic algae whereas the least negative values reflect greater contribution of terrestrial plant material the data suggest that the marine conditions prevailed and supported marine planktonic algae throughout different sea level stages marine om was delivered to the sea floor by continuous hemipelagic settling whereas terrestrial om was delivered by sediment density flows variations in bioproductivity and dilution by siliciclastics influenced the burial rate of marine om organic rich mudstones preserved in these marine basins are potential hydrocarbon source rocks especially as unconventional shale gas reservoirs detailed microtextural and compositional analysis coupled with rigorous geochemical parameters as used in this study are important for the understanding of the source rock potential of basinal mudstones and of fine grained organic rich sediments in general

sedimentary process control on carbon isotope composition of sedimentary organic matter in an ancient shallow water shelf succession 1 source and delivery mechanisms of organic matter are rarely considered when interpreting changing 13c through sedimentary successions even though isotope excursions are widely used to identify and correlate global perturbations in the carbon cycle combining detailed sedimentology and geochemistry we demonstrate how organic carbon abundance and 13c values from sedimentary organic matter from carboniferous aged mudstones are influenced by the proportion of terrestrial versus water column derived organic matter silt bearing clay rich shelf mudstones that were deposited by erosive density flows are characterized by 1 8 2 4 organic carbon and high 13c values averaging 22 9 0 3 n 12 typically these mudstones contain significant volumes of terrestrial plant derived material in contrast clay rich lenticular mudstones with a marine macrofauna are the products of the transport of mud fragments eroded from pre existing water rich shelfal muds when shorelines were distant and biological productivity in the water column was high higher organic carbon 2 1 5 2 and lower 13c values averaging 24 3 0 5 n 11 characterize these mudstones and are interpreted to reflect a greater contribution by isotopically more negative amorphous organic matter derived from marine algae differences in 13c between terrestrial and marine organic matter allow the changing proportions from different sources to be tracked through this succession combining 13c values with zirconium measured from whole rock here used as a proxy for detrital silt input provides a novel approach to distinguishing mudstone provenance and ultimately using 13c to identify oil prone organic matter in potential source rocks these results have important implications for using bulk organic matter to identify and characterize global c isotope excursions

late jurassic early cretaceous climate change record in clay minerals of the norwegian greenland seaway abstract the humid climate of northwestern europe during the late jurassic early cretaceous was punctuated by a widespread arid phase there are few well constrained and complete sections that document this climate shift from semi humid to arid and back to more humid conditions detrital clay minerals formed in soils and derived through weathering may be used as palaeoclimatic proxies and here clay mineral assemblages from several well constrained sections from the norwegian continental shelf are presented as a n s transect of the norwegian greenland seaway palaeoclimate signals in most of the clay mineral sections are complicated by diagenetic overprinting yet towards the boreal realm of the norwegian greenland seaway there is a discernible palaeoclimatic signal in the clay mineralogy of well 16 3 4 at 30 n kaolinite is known to have reappeared in the clay mineralogical record in the upper part of calpionellid zone b early mid berriasian however we find an absence of kaolinite at 40 n in well 16 3 4 from the north sea until the late berriasian suggesting that initiation of the first humid phase in the early cretaceous norwegian greenland seaway was diachronous

small scale 5 0 m vertical heterogeneity in mudstones implications for high resolution stratigraphy in siliciclastic mudstone successions 48 mudstone samples from the peterborough member oxford clay formation have been analysed to determine the small scale vertical and lateral lithofacies variability in this succession the samples were collected every 0 15 m from saxon and king9s dyke brickpits whittlesey peterborough uk over a short vertical interval 15 m the sampled interval spans the obductum to the grossouvrei subzones of the callovian upper jurassic lithofacies present were described using combined field logging optical and backscattered electron optical techniques the succession predominantly comprises silt rich mudstones with subordinate clay rich mudstones shell beds and shell pavements the individual units are variously composed of detrital clay quartz pyrite calcite with minor apatite kaolinite and glauconite in some units millimetre scale upward fining couplets are present elsewhere the original bedding structures have been destroyed by bioturbation comparison of successive thin sections reveals that upward coarsening is present on a metre scale and that shell enriched units are located close to the tops of these upward shoaling units comparison of samples collected laterally on a 0 01 1 0 m scale from the same level 3 0 m below the top of bed 14 indicates that there is lateral lithofacies variability the small scale 0 001 m couplets are interpreted to be beds deposited by waning flow currents significant breaks between these depositional events allowed a dysaerobic infauna to colonize the sediment the metre scale upward coarsening intervals which are capped by shell enriched units are interpreted to be parasequences the observed small scale lateral lithofacies variability is interpreted to be a product of small but significant vertical miscorrelation errors rather that systematic lateral facies changes these data suggest that producing reliable bed scale lateral correlations over distances of more than 1 km in this and successions like it will be very difficult

large thin slicing a new method for the study of fabrics in lithified sediments this paper outlines a new method for the study of sedimentary fabrics in well lithified facies the technique involves the cutting of large thin slices of rock that can then be viewed in transmitted light the utility of this methodology is demonstrated in sandstone soft siltstone and even schist the technique is particularly pertinent to sedimentary geologists studying lithologically homogeneous sediments in which physical and biogenic sedimentary fabrics are difficult to discern due to a lack of contrast

the nature of porosity in organic rich mudstones of the upper jurassic kimmeridge clay formation north sea offshore united kingdom abstract analyses of organic rich mudstones from wells that penetrated the upper jurassic kimmeridge clay formation offshore united kingdom were performed to evaluate the nature of both organic and inorganic rock constituents and their relation to porosity in this world class source rock the formation is at varying levels of thermal maturity ranging from immature in the shallowest core samples to mature in the deepest core samples the intent of this study was to evaluate porosity as a function of both organic macerals and thermal maturity at least four distinct types of organic macerals were observed in petrographic and sem analyses and they all were present across the study area the macerals include in decreasing abundance 1 bituminite admixed with clays 2 elongate lamellar masses alginite or bituminite with small quartz feldspar and clay entrained within it 3 terrestrial vitrinite fusinite semifusinite grains and 4 tasmanites microfossils although pores in all maceral types were observed on ion milled surfaces of all samples the pores largely nanopores with some micropores vary as a function of maceral type importantly pores in the macerals do not vary systematically as a function of thermal maturity insofar as organic pores are of similar size and shape in both the immature and mature kimmeridge rocks if any organic pores developed during the generation of hydrocarbons they were apparently not preserved possibly because of the highly ductile nature of much of the rock constituents of kimmeridge mudstones clays and organic material inorganic pores largely micropores with some nanopores have been observed in all kimmeridge mudstones these pores particularly interparticle i e between clay platelets and intraparticle i e in framboidal pyrite in partially dissolved detrital k feldspar and in both detrital and authigenic dolomite are noteworthy because they compose much of the observable porosity in the shales in both immature and mature samples the absence of a systematic increase in organic porosity as a function of either maceral type or thermal maturity indicates that such porosity was probably unrelated to hydrocarbon generation instead much of the porosity within mudstones of the kimmeridge appears to be largely intraparticle and interparticle adjacent to inorganic constituents so the petroleum storage potential in these organic rich mudstones largely resides in inorganic pores

preparation and analysis techniques for studies of laminated sediments laminated sediments commonly represent the highest resolution continuous records available of marine and lacustrine variability to exploit this information effectively careful sampling and preparation procedures must be followed thus the method of analysis chosen must have sufficient resolution to recover the data the scanning electron microscope because of its good spatial resolution is an ideal tool for analyzing laminated sediment fabric backscattered electron imagery produces preserved flux data on intra annual time scales which enables high resolution fabric studies palaeoenvironmental reconstructions and compilation of data for time series analysis this contribution summarizes the techniques used for laminated sediment fabric investigation and discusses the use of the scanning electron microscope including the best preparation method for thin sections and the procedure for backscattered electron imagery analysis

mudstone lithofacies in the kimmeridge clay formation wessex basin southern england implications for the origin and controls of the distribution of mudstones abstract lithofacies analysis has been undertaken on a suite of apparently monotonous organic rich mudstones from the upper jurassic kimmeridge clay formation kcf in the wessex basin southern england using a combination of hand specimen description whole rock geochemistry optical petrography and electron optical petrography five lithofacies have been identified these are clay rich mudstones silt rich mudstones nannoplankton rich mudstones laminated mudstones and concretionary carbonates these facies can be distinguished from one another on the basis of physical sedimentary structures and the relative proportions of allochthonous autochthonous and diagenetic components in each all five of the kcf lithofacies studied were deposited in a marine shelf environment below fair weather wave base but in relatively shallow water close to storm wave base deposition occurred in regions where sand and other coarse clastic allochthonous debris were not being supplied and the bottom waters varied from oxic to anoxic the main factors influencing the development of the five facies were distance from source area primary productivity bottom water anoxia absolute bathymetry clastic dilution and local sediment accumulation rates specifically the clay rich mudstones were deposited in regions farthest down the sediment transport paths commonly in areas by passed by the main sediment supply and beneath surface waters of relatively low primary productivity in contrast the silt rich mudstones were deposited in more proximal areas closer to the source of the sediment in regions where surface productivity and sediment accumulation rates were much higher the nannoplankton rich mudstones accumulated beneath regions where productivity in the surface water layers was fairly high dominated by coccolithophoroid production and the supply of clastic sediment was insufficient to significantly dilute the autochthonous fraction of the sediment unlike the other facies laminated mudstones were deposited in areas where the bottom waters were anoxic surface productivity was enhanced and local sediment accumulation rates were high the concretionary carbonates were precipitated by diagenetic processes in areas where sediment accumulation rates were very low these facies descriptions have enabled a detailed sedimentological study of the kimmeridge clay formation to relate depositional and diagenetic processes directly to the facies present thereby allowing classical facies analyses to be undertaken on apparently homogeneous mudstone successions

sedimentologic character of ancient muddy subaqueous deltaic clinoforms down cliff clay member bridport sand formation wessex basin u k abstract muddy subaqueous clinoforms are a common feature of many modern deltas particularly those developed in basins with strong waves tides or oceanographic currents ancient examples have only rarely been reported implying that they are under recognized herein the sedimentological characteristics of muddy subaqueous deltaic clinoforms from the lower jurassic down cliff clay member of the bridport sand formation wessex basin uk are described and interpreted as a reference to re evaluate other ancient shallow marine mudstone successions deposits below the down cliff clay clinoforms consist of erosionally based bioclastic sandy limestone beds intercalated with upward thickening fossiliferous claystones and siltstones facies association a which record upward increasing water depth under conditions of minor input of clastic sediment and reworking by storm waves these deposits are downlapped by foreset to toeset deposits of the subaqueous deltaic clinoforms which comprise claystones and siltstones that contain calcareous nodules and are variably bioturbated by a low diversity trace fossil assemblages dominated by chondrites facies association b these foreset to toeset deposits record slow deposition undecompacted sediment accumulation rate of c 4 4 m myr from suspension fall out and distal sediment gravity flows under conditions of intermittent and or poor oxygenation of bottom waters clinoform foreset deposits dip paleoseaward at 2 and consist of siltstones and sandy siltstones that are moderately to completely bioturbated by a high diversity trace fossil assemblage facies association c thin

bedload transport of mud across a wide storm influenced ramp cenomanian turonian kaskapau formation western canada foreland basin abstract mudstone dominated shallow marine rocks of the kaskapau formation were deposited on a low gradient ramp that spanned the foredeep of the western canada foreland basin during the late cenomanian to middle turonian organic clay rich and silt rich mudstone accumulated on the flank of the forebulge 200 km from the western shoreline within this mudstone a large proportion of the clay minerals are organized into silt and very fine sand size aggregate grains these aggregates were produced both in the water column as marine snow and phytodetritus and also through reworking of previously deposited cohesive mud to form intraclasts the latter along with siliceous silt grains form wave and combined flow ripples graded beds scour fills and ripple tail lamination where sand size sediment comprising detrital siliceous calcareous bioclastic or phosphatic grains is present it is molded into combined flow ripples hcs gutter casts and lags thus all sediment grades indicate storm wave and current reworking of the sea floor at a distance of 200 km offshore the common occurrence of clay minerals in the form of aggregate grains organized into combined flow ripples and parallel lamination implies advective transport of clay minerals as bedload driven by combined flows across a very low gradient ramp on the distal part of this ramp latest cenomanian rocks include thin tongues of sw prograding quartz rich sandstone that was derived from an emergent forebulge this source was drowned during the early turonian eustatic rise when the sediment abruptly changed to organic rich mudstone dominated by clay mineral aggregates this compositional change was mainly a response to a sudden increase in distance to detrital sources in the west rather than a dramatic increase in water depth throughout much of early to middle turonian time the sea floor in the forebulge region lay above effective storm wave base for silt estimated at 70 m at sea level lowstands wave winnowing and erosion of the sea floor concentrated bioclastic lags at the top of siltier upward sequences lags are interpreted to correspond to falling stage lowstand and early transgressive systems tract deposits on the western margin of the basin previous studies may have substantially overestimated water depth for organic and clay rich calcareous mudstones in the western interior seaway

origin and characterization of eagle ford pore networks in the south texas upper cretaceous shelf abstract recent studies have shown that the loss of primary pores and the development of secondary pores in mudrocks are primarily controlled by burial diagenesis of the mineral matrix and thermal maturation of organic matter om however the lack of quantitative data on nanometer to micrometer scale rock properties has limited the ability to define and predict petrophysical properties and fluid flow in these fine grained rocks to upscale these rock properties quantitative data are needed at multiple scales representative eagle ford group samples were collected from continuous cores taken from two adjacent oil producing wells in karnes county texas to investigate small scale variations in mineralogy diagenesis and pore type point count and pore tracing methods were used to systematically quantify pore types and determine the size and shape of the identified pores the two cores from the eagle ford are dominated by modified mineral pores although secondary om pores in migrated petroleum bitumen are also important the mineral pore network includes 1 primary mineral pores originally saturated with formation water and 2 modified mineral pores containing migrated petroleum bitumen and or residual oil the om pore network includes 1 primary om pores and 2 secondary om pores including relatively large less abundant om bubble pores and relatively small more abundant om spongy pores the abundance of om spongy pores correlates positively with total organic carbon toc content and that of mineral pores weakly correlates with the volume of quartz plus feldspar studied samples have similar thermal maturities although samples from one deeper core are slightly more mature than the other except for thermal maturation the strong micrometer scale heterogeneity of rock components and properties texture fabric mineralogy and toc impacts the abundance distribution and type of pores this micrometer scale heterogeneity in porosity and pore networks would in turn significantly impact matrix permeability

sedimentological and ichnological characterization of the middle to upper devonian horn river group british columbia canada insights into mudstone depositional conditions and processes below storm wave base abstract the middle and upper devonian horn river group in northeastern british columbia canada consists predominantly of organic rich mudstones that are typically described as black shales this stratigraphic unit has seen substantial exploration and development for natural gas during the last decade although black shales such as the horn river group have historically been interpreted as deposited in anoxic deep water basins detailed sedimentological and ichnological analyses of eleven horn river group cores indicate that the depositional conditions varied significantly with respect to paleoenvironments redox conditions and physical processes resulting in distinctive sedimentary facies this study integrates data on lithology and physical and biogenic sedimentary structures from detailed core descriptions combined with total organic carbon content to better understand depositional processes and conditions ten mudstone lithofacies and three lithofacies associations are identified massive mudstones and pyrite rich mudstones display very rare planar lamination and graded beds and scarce bioturbation bi 0 1 and are interpreted to represent anoxic waters below storm wave base swb with conditions of relatively low to moderate energy heterolithic laminated and more bioturbated lithofacies are interpreted to represent oxygenated waters below swb with relatively high energy conditions overall bioturbation intensity varies between moderate to intense bi 3 6 where these lithofacies are not intensely bioturbated oxygenated lithofacies show combinations of well preserved physical sedimentary structures including horizontal parallel lamination soft sediment deformation double mud drapes graded beds and current ripples a third lithofacies association represents conditions intermediate between anoxic and oxygenated lithofacies associations mainly based on local changes in the ichnological characteristics these lithofacies show either intense or sparse bioturbation bi 4 6 or bi 0 1 respectively depending on the core location possibly indicating local changes in the depositional conditions and processes e g variations in the oxygen content and or sedimentation rate they can also be found in thick anoxic and oxygenated deposits these lithofacies display intervals of faint lamination amalgamated current ripples and normally graded bedding the cores collectively display significant spatial and stratigraphic heterogeneity in lithology sedimentary structures and bioturbation that are related to relative water depth oxygen content sediment input and deep water currents we interpreted bioturbation intensity to vary mainly as a function of oxygen content related to proximity to the basin margin and sea level fluctuations although secondary stress conditions e g nutrient content and sedimentation rate may also be important unbioturbated and massive fabrics represent anoxic to dysoxic conditions current generated structures are present mainly in the central and distal parts of the basin and are interpreted to represent the presence of contour currents in the proximal parts of the basin laminated and heterolithic units are more common and more bioturbated than in the central and distal basin this study thus can provide significant insights into other shale basins that show similar lateral and vertical variations integration of multidisciplinary studies particularly sedimentology ichnology and total organic carbon aids in understanding and modeling the complexity of these systems

amplitude distribution of seismic waves for laterally heterogeneous structures including a subducting slab summary we demonstrate the effects that the subducting plate 3 d velocity and q structures of the upper mantle beneath japan can have on the amplitudes of seismic waves observed above the inhomogeneous structure and we explore the possibility of finding the fine velocity and q structures by means of the amplitude distribution the methods used for the computation of the seismograms are the ray tracing and also gaussian beams which give more accurate amplitudes at caustics and shadow zones first we construct a slab velocity model by calculating the temperature distribution within and around the subducting slab and investigate the effects of relative source location within the slab possible detachment of shallow and deep parts of the slab and elevation and depression of the 400 km discontinuity within the slab the possibility of detecting the location of the leading edge of the subducted slab is also examined by calculating the amplitude distribution of incident plane waves the distribution of the ray amplitudes is also calculated for a velocity model including the pacific plate subducting beneath japan we finally adopt a 3 d velocity and q structure model including the subducting pacific plate and philippine sea plate in the uppermost mantle beneath japan obtained from previous studies the calculations for incident plane waves reveal that there may be large variations of the amplitudes on the surface it is found that the maximum amplitude distribution of waveforms calculated by the gaussian beam method for most of the above cases gives a smoothed pattern of the corresponding ray amplitudes and that the amplitudes for low frequency waves are smoother than those of high frequencies from all these calculations we find that the amplitude distributions are very sensitive to the velocity heterogeneities suggesting that the amplitude distribution may be used to obtain the source location within the slab and fine velocity and q structures of the upper mantle near the subduction zone

grain assemblages and diagenesis in organic rich mudrocks upper pennsylvanian cline shale wolfcamp d midland basin texas grain assemblages in the organic rich cline shale in the midland basin are dominated by components of extrabasinal derivation 11 4 to 98 5 vol average volume 82 6 major extrabasinal components include k rich clay minerals detrital quartz albite k feldspar micas and lithic fragments intrabasinal components include mainly biosiliceous allochems sponge spicules and radiolarians agglutinated foraminifera ca phosphate peloids clay rich peloids organomineralic aggregates intraclasts and other biocalcareous allochems authigenic minerals are most evident as grain replacements euhedral ankerite ca phosphate cement and precipitates in large pores a strongly localized spatial distribution of diagenetic products at micron to centimeter scales is observed in most siliciclastic samples except in biosiliceous allochem rich ones in which abundant intergranular pore filling clay size microquartz cement is observed compaction is evident in the cline shale because of low porosity and generally low cement volumes neither textural variation nor bulk mineral composition alone is sufficient to confidently decipher the rock bulk property e g total organic carbon and reservoir quality variation e g porosity and permeability however a good negative relationship between the ratio of extrabasinal to intrabasinal grains and favorable reservoir properties is observed in the cline shale specifically higher porosity permeability and total organic carbon are observed in samples representing the extreme end members of intrabasinal derived biosilica rich layers nickel a recognized proxy for paleoproductivity exhibits a positive relationship with intrabasinal grain content and reservoir properties x ray fluorescence based analysis of nickel can be a rapid and cost effective way to delineate favorable unconventional reservoir quality in the cline shale

hadley circulation and precipitation changes controling black shale deposition in the late jurassic boreal seaway new climate simulations using the hadcm3l model with a paleogeography of the late jurassic 155 5 ma and proxy data corroborate that warm and wet tropical like conditions reached as far north as the uk sector of the jurassic boreal seaway 35 n this is associated with a northern hemisphere jurassic hadley cell and an intensified subtropical jet which both extend significantly poleward than in the modern july september deposition of the kimmeridge clay formation kcf occurred in the shallow storm dominated epeiric boreal seaway high resolution paleo environmental proxy data from the kimmeridge clay formation kcf 155 150 ma uk are used to test for the role of tropical atmospheric circulation on meter scale heterogeneities in black shale deposition proxy and model data show that the most organic rich section eudoxus to mid hudlestoni zones is characterized by a positive 13corg excursion and up to 37 wt total organic carbon toc orbital modulation of organic carbon burial primarily in the long eccentricity power band combined with a clear positive correlation between toc carbonate free and the kaolinite illite ratio supports peak organic carbon burial under the influence of very humid climate conditions similar to the modern tropics this reinterpretation of large scale climate relationships supported by independent modeling and geological data has profound implications for atmospheric circulation patterns and processes affecting marine productivity and organic carbon burial further north along the boreal seaway including the arctic

varves in marine sediments a review the global compilation of reported marine varved sedimentary records throughout the quaternary contains 52 sites marine varve deposition and preservation typically depend on environmental and sedimentological conditions such as a sufficiently high sedimentation rate severe depletion of dissolved oxygen in bottom water to exclude bioturbation by macrobenthos and a seasonally varying sedimentary input to yield a recognizable rhythmic varve pattern additional oceanographic factors include the strength and depth range of the oxygen minimum zone omz and regional anthropogenic eutrophication from point sources such as large polluted rivers quaternary marine varves are not only found in those parts of the open ocean that comply with these conditions but also in fjords embayments and estuaries with thermohaline density stratification and nearshore marine lakes with strong hydrologic connections to ocean water this review critically describes settings and sedimentological characteristics of marine sites where varves have been reported broader applications of marine varve records are discussed for example in terms of radiocarbon calibration on high resolution time scales constraining paleoceanographic variability and global change teleconnections diagnosing factors affecting modern fish population dynamics based on past performance detailing biogeochemical cycles and deciphering complex factors influencing marine productivity varves in saline water bodies without hydrologic connection to the global ocean are not included in this review and instead pertain to the companion review on lacustrine varves where also general and fundamental principles of varve deposition classification and dating are covered zolitschka et al 2015 the postulated occurrence of varves in pre quaternary rocks is critically discussed in this review with representative examples in the case of non evaporitic laminations in fine grained ancient marine rocks such as banded iron formations and black shales laminations may not be varves but instead may have multiple alternative origins such as event beds or formation via bottom currents that transport and sort silt sized particles clay floccules and organic mineral aggregates in the form of migrating bedload ripples

astrochronology of the late jurassic kimmeridge clay dorset england and implications for earth system processes the late jurassic kimmeridge clay formation kcf is an economically important organic rich source rock of kimmeridgian early tithonian age the main rock types of the kcf in dorset uk include grey to black laminated shale marl coccolithic limestone and dolostone which occur with an obvious cyclicity at astronomical timescales in this study we examine two high resolution borehole records swanworth quarry i and metherhills 1 obtained as part of a rapid global geological events rgge sediment drilling project datasets examined were total organic carbon toc and borehole wall microconductivity by formation microscanner fms our intent is to assess the rhythmicity of the kcf with respect to the astronomical timescale and to discuss the results with respect to other key late jurassic geological processes power spectra of the untuned data reveal a hierarchy of cycles throughout the kcf with similar to 167 m similar to 40 m 9 1 m 3 8 m and 1 6 m wavelengths tuning the similar to 40 m cycles to the 405 kyr eccentricity cycle shows the presence of all the astronomical parameters eccentricity obliquity and precession index in particular similar to 100 kyr and 405 kyr eccentricity cycles are strongly expressed in both records the 405 kyr eccentricity cycle corresponds to relative sea level changes inferred from sequence stratigraphy intervals with elevated toc are associated with strong obliquity forcing the 405 kyr tuned duration of the lower kcf kimmeridgian stage is 3 47 myr and the upper kcf early part of the tithonian stage elegans to fittoni ammonite zones is 3 32 myr two other chronologies test the consistency of this age model by tuning similar to 8 10 m cycles to 100 kyr short eccentricity and similar to 3 5 m cycles to 36 kyr jurassic obliquity the obliquity tuned chronology resolves an accumulation history for the kcf with a variation that strongly resembles that of earth s orbital eccentricity predicted for 147 2 ma to 153 8 ma there is evidence for significant non deposition up to i million years in the lowermost kcf baylei mutabilis zones which would indicate a kimmeridgian oxfordian boundary age of 154 8 ma this absolute calibration allows assignment of precise numerical ages to zonal boundaries sequence surfaces and polarity chrons of the lower m sequence c 2009 elsevier b v all rights reserved

original sediment composition of the lower cretaceous lacustrine tight oil mudstone and influences on diagenesis and organic matter content the erennaoer sag in erlian basin ne china abstract the original sediment composition is of great value to providing an understanding of depositional environment and hydrocarbon generation potential but it is easily altered by diagenesis and difficult to recognize in this study we examine carbonate rich tight oil mudstones of the lower cretaceous arshan formation in the erennaoer sag of the erlian basin as an example based on analyses of mineralogy stable carbon and oxygen isotopes and trace rare earth elements the original composition of the arshan mudstones has been reconstructed results show that the original arshan mudstone composition was mainly siliciclastic detritus tuffaceous and clay matrix which has a major impact on diagenesis and organic matter content the erupted volcanic ashes were beneficial to the introduction of nutrients an increase in biomass and an associated increase in to the preservation of organic matter which has been suggested by an improvement of toc of arshan tuffaceous mudstones with average contents of 2 82 the volcanic ashes in the studied mudstones had also enhanced methanogensis during the shallow burial additionally the early alteration products of authigenic minerals include analcime or zeolite most of which is entirely altered to analcime and chlorite the formation of major eogenetic carbonate cements include early dolomite and calcite which were related to volcanic materials and methanogenesis at shallow depths

toarcian black shales in the dutch central graben record of energetic variable depositional conditions during an oceanic anoxic event the wrong figure was printed in place of figure 4 in the february 2012 issue of jsr p 114 please

in a changing climate weakening tropical easterly jet induces more violent tropical storms over the north indian ocean 1 tropical easterly jet tej of summer monsoon over the north indian ocean is weakening in recent years the absolute easterly shear shows a strong negative correlation significant at 99 9 level by students two sided t test with the number of severe storms suggesting that a decrease in easterly shear is favorable for the formation of more severe tropical storms for the first time in recorded history a category 5 hurricane formed in june 2007 together with two more severe tropical storms over the north indian ocean thus if the present decreasing trend of tej intensity continues there is a strong likelihood of the formation of tropical cyclones of hurricane intensity even during the summer monsoon presently these intense systems are known to form only in the pre and post monsoon seasons when the vertical wind shear is small

formation of holocene sedimentary laminae in the black sea and the role of the benthic flocculent layer holocene black sea sediments recovered in 1988 and 1993 from box cores and gravity cores were analyzed geochemically microscopically and with backscattered electron imagery bsei in order to determine the temporal geochemical and sedimentological relationships between the benthic flocculent layer often referred to as the fluff layer and the formation of underlying laminated unit i sediments existence of a permanent benthic fluff layer in the black sea basin is suggested acting as a geochemical transition layer within which all sedimentary particles are hydraulically sorted and particles subject to dissolution or organic remineralization are altered prior to accumulation we propose that particle residence time within the benthic fluff layer is a key factor in determining sedimentary microfabric and geochemical composition of laminated unit i sediments we present a schematic model depicting the above relationships and use it to propose a paleoflux scenario for laminae formation in the unit ii sapropel

insights into marls from optical and back scattered electron petrography an example from the outer carpathians poland abstract this paper is a study of grain provenance depositional processes and the relationship of those processes to composition and diagenesis of fine grained rocks based on high resolution petrography the marly successions deposited in siliciclastic flysch and related to the paleotectonics of the northern domain of the tethys ocean outer carpathian basin were examined the following marls were studied upper jurassic marls from the vendryn formation goleszow marls upper cretaceous siliceous fucoid wegierka weglowka frydek jasienica and egocina marls eocene cko budzow zembrzyce and leluchow marls and oligocene sub cergowa and grybow marls these marls are products of the redeposition of shelf sediments into deeper parts of the basin knowledge of their diagenetic history can contribute to the evaluation of the petroleum potential of the polish outer carpathians thin section analysis by optical and electron back scattered microscopy fesem bse highlights the similarity of all these marls with respect to composition grain size sedimentary features and diagenetic changes they differ only in the quantitative proportion of constituents the relative extent of key microfacies and diagenetic effects the diagenetic modifications recognized in the rocks studied are characteristic of the processes operating in the sedimentary environment and during burial diagenesis thin section petrography of the marls reveals fine mostly silt size siliciclastic material and bioclasts supported by matrix siliciclastic particles comprise mostly quartz micas feldspars glauconitic nodules and lithoclasts calcareous and siliceous bioclasts mostly microfossils foram and sponge spicules and a few radiolarians and diatoms and coccospheres are variably preserved they may occur as calcite silica and clay pseudomorphs additional components include peloids and stringers of brown organic matter millimeter scale fabric analysis provides detailed insight into the processes of transport and deposition five microfacies are identified parallel laminated wavy and lenticular laminated homogeneous exhibiting preferred orientation of elongated components bioturbated and bioclast bearing the range of microfacies suggests that the marl sediment was deposited while currents were active the depositional settings identified range from traction reworking by bottom currents supply by nepheloid flow indistinctly bounded laminae possible eolian input laminae a few grains thick and biogenic reworking of sediments back scattered electron images reveal that the matrix consists of coccolithophorid remains with varying abundances of clay silica and carbonate cements five varieties of matrix are distinguished 1 carbonate clay silica bearing 2 carbonate clay supported 3 carbonate silica supported 4 clay silica supported and 5 clay dominated clay appears as rosette and lamellar aggregates silica as nanoquartz microspheres clusters coatings quartz overgrowths and occasionally opal ct as lepispheres and aggregates moss like in appearance and calcite as overgrown coccoliths pseudomicrite micrite and microspar pyrite framboids are present in some samples intrabiotic and intergranular cements are developed also present are partially dissolved coccolith placoliths silica and clay replaced micarb and grains similar in appearance to volcanic glass shards that now consist of calcite and quartz bioclasts may have been a source for calcite and silica cements volcanic glass may have been a source for authigenic silica and clay minerals this is suggested by the close spatial juxtaposition of silica microspheres and authigenic clay cauliflower like aggregates the authigenic origin of the clay in these marls is also suggested by the presence of overgrown coccoliths because recrystallization of shields is reduced when clay is present so that the overgrowths must have been formed in an environment where clay minerals were scarce initially despite diagenetic changes the presence of pyroclasts is still recognizable there are quartz crystal chips shard shaped grains volcanic rock fragments and minerals biotite apatite zircon the marls studied could be described as impure fine grained detrital limestones chalky in type with evidence of redeposition and possible volcanic ash input the marl depositional system within the outer carpathian basin was associated with tectonic movements which initiated chalk type facies and this was particularly widespread in the upper cretaceous and paleocene