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Porter S.J.,University of British Columbia | Porter S.J.,Durham University | Porter S.J.,Chemostrat Ltd | Smith P.L.,University of British Columbia | And 4 more authors.
Earth and Planetary Science Letters | Year: 2014

Recognising variations in the carbon isotope compositions of marine organic-rich sedimentary rocks can provide insight into changes in ocean chemistry throughout geological time. Further, identification of global excursions in the carbon isotope record has proved to be valuable as a chronostratigraphic correlation tool. This investigation presents new high-resolution organic carbon isotope data (δCorg13) for marine sediments from 2 regions in North America (Last Creek, British Columbia, Canada and Five Card Draw, Nevada, USA). The carbon isotope profiles demonstrate that there were significant differences between the carbon reservoirs at Five Card Draw and Last Creek, notably in the upper part of the Leslei Zone. The δCorg13 values show a gradual positive CIE (~2‰) at Last Creek in the upper part of the Leslei Zone. This corresponds to a coeval positive CIE of similar duration in Dorset, UK (upper Turneri Zo≠ Jenkyns and Weedon, 2013), suggesting that this may be a global marine carbon isotope signature, and likely reflects a widespread increase in primary productivity during the Early Sinemurian. In addition, a brief negative CIE is observed in the uppermost Lower Sinemurian at Last Creek. This negative excursion is not recorded in the Dorset section, suggesting localised upwelling of 12C-rich bottom-waters at Last Creek. Further, the signals identified at Last Creek are not present in coeval sections at Five Card Draw, thus highlighting a significant difference between these localities. Osmium (Os) isotope data (initial 187Os/188Os values) provide a quantitative determination of the contrasting depositional environments of Five Card Draw and Last Creek (at least partially restricted with high levels of continental inundation and open-ocean, respectively). This demonstrates that basinal restriction may act as a major factor that controls isotopic stratigraphic signatures, thus preventing the identification of global or widespread regional excursions. © 2014.


Marynowski L.,University of Silesia | Zaton M.,University of Silesia | Rakocinski M.,University of Silesia | Filipiak P.,University of Silesia | And 2 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2012

Presented for the first time in this paper are the results of a detailed multi-proxy investigation conducted on the Hangenberg Black Shale (HBS) from the Polish part of the Laurussian Shelf, which provide details about the environmental conditions in existence during deposition of the shale and the role played by anoxic conditions in the mass extinction events that occurred at the end of the Devonian times. Inorganic and organic redox indicators indicate that bottom water redox conditions changed periodically from being mainly anoxic/euxinic to oxic or being partially depleted in oxygen. U/Th values above 1.25, Ni/Co values above 7 and V/(V. +. Ni) values above 0.8 recorded from the lower part of the HBS all point to anoxic/euxinic conditions being present, as do high total organic carbon contents (TOC) above 10% and degree of pyritisation (DOP) values around 0.75%. However, the presence of benthic fauna over the lower part of the HBS attests to opportunistic colonisation of the seafloor during oxic episodes. Evidence for similar episodes has also been recognised over the middle part of the HBS, e.g., U/Th values below 1.25, Ni/Co values below 4, V/(V. +. Ni) values below 0.8, TOC values of 3% to 5.5% and DOP values of 0.4% to 0.75%, plus the common occurrence of benthic fauna. Anoxic conditions returned during the deposition of the upper part of the HSB, though they were not as well developed as when the lower part of the shale was laid down.Of interest is the presence of small pyrite framboids and isorenieratene biomarkers in all the analysed samples, which suggest that euxinic conditions persisted in the photic zone of the water column. A twenty centimetre thick layer of volcanogenic deposits (tuffites) is present in the middle part of the HBS, the geochemical characteristics of which are typical of ocean floor basalts. The occurrence of volcanogenic material below and within the HBS, together with an absence of calcium carbonate over its upper part, the presence of abundant tetrads just above the black shale and a drastic decrease in faunal frequency in the upper part of the HBS imply that volcanism may have caused oceanic acidification (or hypercapnia) that in turn potentially may have influenced the Hangenberg mass extinction event. © 2012 Elsevier B.V.


Porter S.J.,Durham University | Porter S.J.,Chemostrat Ltd. | Selby D.,Durham University | Cameron V.,University of Bristol
Chemical Geology | Year: 2014

New Ni stable isotope data (δ60Ni) determined by double-spike MC-ICP-MS for two geologically distinct suites of organic-rich marine sediments from the Sinemurian-Pliensbachian (S-P) Global Stratotype Section and Point (GSSP; Robin Hood's Bay, UK) and the Devonian-Mississippian Exshaw Formation (West Canada Sedimentary Basin) is presented herein. These sediments yield δ60Ni values of between 0.2‰ and 2.5‰, and predominantly have Ni isotopic compositions that are heavier than those of abiotic terrestrial and extraterrestrial samples (0.15‰ and 0.27‰), and in some cases present-day seawater (1.44‰) and dissolved Ni from riverine input (0.80‰). In addition, the observed degree of isotopic fractionation in the marine sediments is far greater than that of these other sample matrices. However, a strong similarity is exhibited between the δ60Ni values of the organic-rich sediments studied here and those of ferromanganese crusts (0.9-2.5‰), suggesting that factors ubiquitous to the marine environment are likely to play a key role in the heightened level of isotopic fractionation in these sample matrices.A lack of correlation between the Ni stable isotope compositions of the organic-rich sediments and Ni abundance suggests that isotopic fractionation in these sediments is not controlled by incorporation or enrichment of Ni during sediment accumulation. Further, no relationship is observed between δ60Ni and TOC concentrations or bottom-water redox conditions, indicating that the organic carbon reservoir and levels of oxygenation at the sediment-water interface do not exert a primary control on Ni isotope fractionation in marine sediments. Following examination of these relationships, it is therefore more likely that the heavy Ni isotope compositions of marine sediments are controlled by the weathering environment and the dominant sources of dissolved Ni into the global ocean reservoir. © 2014.


Hildred G.,Chemostrat Inc. | Scmidt K.,Pioneer Natural Resources Inc. | Pearce T.,Chemostrat Ltd.
3rd EAGE Shale Workshop: Shale Physics and Shale Chemistry | Year: 2012

Over the few past years shale resource plays have become increasingly important hydrocarbon plays. In the USA, formations such as the Barnett Formation, the Haynesville Formation and the Eagle Ford Shale Formation have become major hydrocarbon exploration targets. However, understanding the controls on reservoir quality in these shale formations is still in its infancy, despite thousands of well penetrations. In this paper, the Eagle Ford Shale Formation is used to demonstrate how inorganic whole rock geochemical data that are primarily obtained to provide stratigraphic correlations can be used to help understand mineralogy, organic content and rock brittleness. The primary application of whole rock geochemical data is to provide a chemostratigraphic correlation, which is of primary importance for temporally and geographically constraining other reservoir characteristics. The Eagle Ford Shale Formation is divisible into 4 geochemical units, based on changing values of P, Th/U and Cr/Th. The top of formation is readily geochemically defined by a decrease in the values of U, Cr/Th and V. Placing the top of the Eagle Ford Formation with confidence in itself is an important aspect for the drilling of horizontal wells. Reservoir quality in shale resource plays is dependent on numerous factors, including mineralogy, terrigenous input, bottom water conditions on deposition and TOC values. Mineralogically, the Eagle Ford Shale Formation is relatively simple, comprising quartz (av. 13%), calcite (av. 50%) and clay minerals (illite, illite/smectite, kaolinite and chlorite ) (av. 27%), with lesser amounts of pyrite, apatite and plagioclase feldspar. TOC values are typically between 1% and 7%. Each of these mineral phases and the TOC contents are readily modeled from the same elemental dataset used to define chemostratigraphic correlation framework. Furthermore, consideration of redox-sensitive elements, such as V, Ni, Th, U and Co provides a means to determine the degree of anoxia during deposition. The mineralogy plays an important role in how readily the formation can be fractured and because the inorganic geochemistry is directly linked to mineralogy, it is possible to calculate the relative brittleness of the mudstones. The methodologies demonstrated here in the Eagle Ford Shale Formation to define chemostratigraphic correlations, determine mineralogy and better understand bottom water conditions are readily applicable to any shale gas resource play around the world.


Wright M.,Chemostrat Inc. | Ratcliffe K.,Chemostrat Ltd. | Mathia E.,Chemostrat Ltd.
Society of Petroleum Engineers - Unconventional Resources Technology Conference, URTeC 2015 | Year: 2015

Samples from two shale successions from two boreholes drilled in the Lower Permian strata of the Delaware Basin were investigated and assessed in terms of palaeoredox conditions during the sediment deposition, basin hydrography, and the application of the elemental data for the organic carbon content prediction. The strata, composed of the alternating calcareous shale/limestone and siliciclastic shale intervals showed to have only minor biogenic silica input, with the major biogenic component being of the carbonate source, and the siliciclastic fraction dominated by the terrigenous material. The authigenic enrichment in elements typical for anoxia and elevated palaeoproductivity (Ni, Cr, V, Cu, Mo, U) was revealed to be inconsistent throughout the shale sequence, with the major change in the trace element - Total Organic Carbon (TOC) correlation trends at TOC ca. 2%. For organic- lean rocks, low concentrations in all the redox elements, and their high normalized values as compared to reference shales, suggest deposition in anoxic/euxinic waters, but with the redox signature masked by the strong carbonate dilution. In the organic-rich rocks, multi-element covariations show patterns typical for anoxia, with elemental concentrations not affected by the slow background terrigenous sedimentation. The limited enrichment in Mo and U in the most organic-rich shales (up to 7% TOC) suggest that the hydrographic conditions had a critical effect on the limited deposition of the most conservative trace elements during the terrigenous sedimentation intervals. In such scenario, Nickel (Ni) proved to be a valuable proxy for the organic carbon deposition, with a sufficient predictive power to predict TOC in unknown shale successions. The evaluation of the Lower Permian Shale successions showed how critical the geochemical approach is when assessing shale sequences in relatively unknown basins, and their potential to store hydrocarbons. Copyright 2015, Unconventional Resources Technology Conference.


Perri F.,University of Calabria | Caracciolo L.,Chemostrat Ltd. | Cavalcante F.,CNR Institute of Methodologies for Environmental analysis | Corrado S.,Third University of Rome | And 3 more authors.
Basin Research | Year: 2016

Paleothermal indicators based on clay mineral and organic matter analyses, were integrated with mudrock geochemistry and stratigraphic data to define the sedimentary evolution of the southwestern Thrace Basin during the Eocene to Oligocene. This multi-method approach allowed us to reconstruct the burial evolution of the basin in Eocene and Oligocene times and to study the mudrock composition and relate this to their provenance and source area weathering. The studied mudrocks show similar chemical variations. The distribution of some major and trace elements for the studied samples reflect heterogeneous source areas containing both felsic to mafic rocks. In particular, the Light Rare Earth Elements/Transition elements (LREEs/TEs) ratios are very high for the Avdira and Organi samples (on the average between 1.5 and 2.2 for (La + Ce)/Cr and 3.5-8 for (La + Ce)/Ni), suggesting a felsic source(s), and very low for the Samothraki, Limnos, Paterma and Iasmos samples (on the average between 0.4 and 0.6 for (La + Ce)/Cr and 0.6-1 for (La + Ce)/Ni), suggesting a mainly basic source(s). The mineralogical composition coupled with the A-CN-K and A-N-K plots suggest a complex evolution. The clay mineral data (illite percentage in I/S and the stacking order R and the Kübler Index) coupled to vitrinite reflectance analysis indicate a high to intermediate diagenetic grade for the Middle to Upper Eocene samples (from Iasmos, Gratini, Organi, Paterma, Esimi and Samotraki sections) and a low diagenetic grade for the Upper Eocene to Oligocene samples (from Limnos and Avdira sections). These data helped in interpreting the geodynamic evolution of the studied basins where the magmatic activity plays an important role. In particular, Middle to Upper Eocene sediments show high to intermediate diagenetic grade since they are located in a portion of the basin dominated by Eocene to Oligocene magmatic activity and intrusion of granitoids, whereas, the Upper Eocene to Oligocene sediments are not involved in important magmatic activity and intrusion of granitoids and, thus, show low diagenetic grade. Furthermore, Middle to Upper Eocene sediments experienced deeper burial processes caused by lithostatic load, rather than the uppermost Eocene and Oligocene sediments, in relation of their position along the stratigraphic succession. These data suggest a burial depth of at least 3-4 km with a tectonic exhumation mainly related to the extensional phases of the Miocene age. © 2016 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.


Nyhuis C.J.,University of Cologne | Riley D.,Chemostrat Ltd. | Kalasinska A.,Origin Analytical Ltd.
Geologie en Mijnbouw/Netherlands Journal of Geosciences | Year: 2016

Sedimentological data acquired by thin section petrography is a rich source of information to better understand and interpret depositional environments that are dominated by fine-grained deposits. This study provides an evaluation of the sedimentological and geochemical changes recorded over Upper Viséan to Lower Namurian successions preserved in a core section from a well drilled in the southern part of the Netherlands. Facies analysis and the recognition of microfacies associations allow detailed interpretations of depositional environments. Interpretation of additional geochemical data acquired by portable X-ray fluorescence analyses has resulted in a chemostratigraphic zonation for the core section. The zonation reflects stratigraphic changes in the mineralogy of the sedimentary successions. Integration of the microfacies associations and the chemostratigraphic zonation has led to the identification of three so-called depositional zones, which show the development of depositional settings from Late Viséan to Early Namurian times. Depositional Zone 1 consists of fine-grained turbiditic limestones and mudstones deposited in a distal carbonate ramp setting during Latest Viséan times. The overlying Depositional Zone 2 corresponds to the Geverik Member (Lower Namurian) and is particularly heterogeneous in geochemical and lithological terms: the zone reflects a complex interplay between different parameters such as sediment source, transport mechanisms and oxygen content that are assumed to be governed by fluctuating sea levels and changing depositional environments (from basinal to shallow marine settings). Sandy lenticular mudstones are predominant in the lower part of Depositional Zone 2 and show that sedimentation was via erosive bedload, whilst the common fossiliferous mudstones present within the upper part of the same zone yield evidence for increased endobenthic activity in dysoxic conditions. The successions assigned to Depositional Zone 3 ( = Epen Formation - Namurian) are the products of cyclic sedimentation of a terrestrial sourced delta. Copyright © Netherlands Journal of Geosciences Foundation 2015.


Nyhuis C.J.,University of Cologne | Riley D.,Chemostrat Ltd | Kalasinska A.,Origin Analytical Ltd
Geologie en Mijnbouw/Netherlands Journal of Geosciences | Year: 2015

Sedimentological data acquired by thin section petrography is a rich source of information to better understand and interpret depositional environments that are dominated by fine-grained deposits. This study provides an evaluation of the sedimentological and geochemical changes recorded over Upper Viséan to Lower Namurian successions preserved in a core section from a well drilled in the southern part of the Netherlands. Facies analysis and the recognition of microfacies associations allow detailed interpretations of depositional environments. Interpretation of additional geochemical data acquired by portable X-ray fluorescence analyses has resulted in a chemostratigraphic zonation for the core section. The zonation reflects stratigraphic changes in the mineralogy of the sedimentary successions. Integration of the microfacies associations and the chemostratigraphic zonation has led to the identification of three so-called depositional zones, which show the development of depositional settings from Late Viséan to Early Namurian times. Depositional Zone 1 consists of fine-grained turbiditic limestones and mudstones deposited in a distal carbonate ramp setting during Latest Viséan times. The overlying Depositional Zone 2 corresponds to the Geverik Member (Lower Namurian) and is particularly heterogeneous in geochemical and lithological terms: the zone reflects a complex interplay between different parameters such as sediment source, transport mechanisms and oxygen content that are assumed to be governed by fluctuating sea levels and changing depositional environments (from basinal to shallow marine settings). Sandy lenticular mudstones are predominant in the lower part of Depositional Zone 2 and show that sedimentation was via erosive bedload, whilst the common fossiliferous mudstones present within the upper part of the same zone yield evidence for increased endobenthic activity in dysoxic conditions. The successions assigned to Depositional Zone 3 ( = Epen Formation – Namurian) are the products of cyclic sedimentation of a terrestrial sourced delta. Copyright © Netherlands Journal of Geosciences Foundation 2015


Martin M.A.,BG Group | Wakefield M.,BG Group | MacPhail M.K.,Australian National University | Pearce T.,Chemostrat Ltd. | Edwards H.E.,Chemostrat Ltd.
Petroleum Geoscience | Year: 2013

Large gas reserves are trapped in the coals of the Middle Jurassic (Callovian) Walloon Subgroup (lower part of the Injure Creek Group) in the Surat Basin, eastern Australia. The series is divided into the Juandah Coal Measures (upper), Tangalooma Sandstone and Taroom Coal Measures (lower). The upper and lower units are locally further subdivided. These economically important coals were deposited in an alluvial plain setting within an interior basin, which has no recorded contemporaneous marine influence. The coals are typically bituminous, perhydrous and low rank with a high volatile content. Despite individual ply (bench) thicknesses typically less than a metre, series of plies or seams of coals up to 10 m thick have historically been tentatively correlated across the entire play area (over 150 km). © 2013 EAGE/Geological Society of London.


Cram F.M.,Hansa Hydrocarbons Ltd | Morgan T.,Chemostrat Ltd | Pearce T.J.,Chemostrat Ltd | Martin J.H.,Chemostrat Ltd
76th European Association of Geoscientists and Engineers Conference and Exhibition 2014: Experience the Energy - Incorporating SPE EUROPEC 2014 | Year: 2014

The Permian Rotliegend Group is a prolific reservoir interval holding a significant proportion of north west Europe's gas reserves, and as such is one of the most studied stratigraphic intervals. The study area is on the margin of the Rotliegend sandstone fairway and straddles the Netherlands/German median line An integrated approach to stratigraphy has been undertaken, incorporating different techniques on different lithology types including inorganic geochemistry, petrography, heavy mineral analysis, zircon geochronology and palynology, and has resulted in a high resolution stratigraphic framework independent of lithology or facies. This study introduces a new chemostratigraphic breakdown for the basal Rotliegend section which, when integrated with the other techniques can help understand the early basin fill geometry and architecture. This study also extends the chemostratigraphic breakdown of the upper Carboniferous into the German North Sea allowing new calibration when mapping the Base Permian Unconformity subcrop. The improved stratigraphic understanding has had a significant impact on hydrocarbon prospectivity in the study area.

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