Organic-rich Layers Research Articles

Surface and deep water variability in the Western Mediterranean (ODP Site 975) during insolation cycle 74: High-resolution calcareous plankton and molecular biomarker signals

We reconstructed changes in productivity and surface/subsurface and deep-water dynamics in the Western Mediterranean through a multi-proxy study of Ocean Drilling Program Site 975 between late Marine Isotope Stage (MIS) 20 and early interglacial MIS 19. Our high-resolution study (down to ~200-year resolution) combines calcareous plankton assemblages (coccolithophores and foraminifera), biomarkers (C37-alkenones, n-alkanes, n-alcohols) and elemental proxies (total organic carbon, total nitrogen, calcium carbonate). Surface water conditions are derived (i) from high-resolution δ18O and δ13C records obtained from the planktonic foraminifer Globigerina bulloides, and (ii) from summer and winter, foraminifera-based sea surface temperature reconstructions (SSTJAS-foram, SSTJFM-foram) achieved through transfer function. The integration of the whole dataset makes it possible to identify in the Balearic Sea, and to accurately characterize for the first time, an Organic Rich Layer (ORL) during latest MIS 20-early MIS 19, close to i-cycle 74. Its presence is marked firstly by higher values of total nitrogen (TN) and an increase of total C37-alkenone and total organic carbon (TOC) preserved in the sediments. The multi-proxy approach reveals that the deglacial phase played a prominent role for ORL formation that was characterized by centennial scale phases. The alcohol preservation index (API) suggests that the shoaling of the circulation, which boosted marine productivity, started in the deglaciation and, in combination with freshening by Atlantic water inflow/riverine input and surface water buoyancy during sea level rising, culminated during the ORL event. At this time calcareous plankton proliferated on subsurface-surface waters, benefiting from ameliorating conditions, which promoted maximum marine productivity and higher organic matter preservation on the seafloor.

Changes in western Mediterranean thermohaline circulation in association with a deglacial Organic Rich Layer formation in the Alboran Sea

The accumulation of an Organic Rich Layer (ORL) during the last deglaciation in the Alboran Sea (western Mediterranean Sea) and its link to changes in deep and intermediate water circulation are here investigated. Benthic foraminiferal assemblages and the shallow infaunal foraminifer Uvigerina peregrina δ13C record support the establishment of sustained high organic matter fluxes, and thus eutrophic conditions at the sea floor, during the late phase of the ORL (Younger Dryas to early Holocene periods). Since organic matter fluxes were lower (mesotrophic conditions) during the Bølling-Allerød period, they cannot be solely responsible for the ORL initiation. Geochemical, sedimentological and micropalaeontological proxies support a major weakening of the deep-water convection in the Gulf of Lion as the main driver for the development of poorly-ventilated conditions from intermediate depths (946 m) to the deep western Mediterranean basin that promoted the beginning of the ORL deposition. Nevertheless, a better ventilation at intermediate depths was established during the late ORL, while the deep basin remained poorly ventilated. We propose that our data reflect the arrival of a new better-ventilated intermediate water mass analogue to the current Levantine Intermediate Water (LIW) and/or a new intermediate water mass from the Gulf of Lion. The ultimate source of this water mass needs to be further explored but chronologies of the changes recorded here indicate that intermediate and deep ventilation phases were decoupled between the western and eastern Mediterranean basins during the deglaciation and early-middle Holocene.

Organické uloženiny fluviální výplně údolního dna řeky Bečvy u Oseku nad Bečvou a jejich vztah k vývoji sedimentace

Organic matter, like pollen, plant detritus or subfossil woods can be found in sequences of fluvial sediments. Detail study of these remains help to assess age of accumulation processes, especially during the Holocene erosion/accumulation cycle. Two localities with exposed infill of the Bečva River valley were found near Osek nad Bečvou. The first outcrop is a gravel pit 1 km south of Osek nad Bečvou village. The second one is a river-cliff on the left bank of the Bečva River, 1 km westward of Oldřichov village, formed mostly during the extreme flood in 1997. Fluvial sediments, 4–5 m thick, of the the so called “lower flood-plain level” were exposed on both localities. At the base of the Oldřichov river-cliff was encountered a horizon of boggy soil with subfossil trunk at the base. In the gravel pit near Osek nad Bečvou was exposed layer of clay/silt with plant detritus. Up to 2 m thick middle/coarse grained gravel, situated beneath underground water level, underlie the organic-rich sediments in both localities. Badenian clay represents the bedrock of the river valley. Organic-rich layers are overlaid by middle/coarse grained gravel sediments passing gradually to sandy silt of the flood plain. Pollen analyses were made from the organic-rich layers and dendrological analysis, dendrochronology and radiometric dating from subfossil trunk.Organic-rich layer from Osek (sample LS001) was assigned to the early Holocene based on pollen analysis and represents the oldest age found. The Oldřichov samples come from oxbow sediment. The sample LV030V was poor in pollen grains and inconclusive. The sample LV030Z indicates Holocene climate optimum (Atlantic). This supposed age is compatible with radiometric dating of the subfossil trunk from the base of the layer. Radiocarbon dating using wiggle matching method gave age of 7 070–6 775 BC.Based on these data, repeated erosion/accumulation events during Late Pleistocene and Holocene are evident in Bečva River valley fill. Late Pleistocene accumulation was replaced with erosion during Late Pleistocene-Holocene transition. Erosion on the break of the Pleistocene and Holocene partly removed upper Pleistocene gravels so in places left reached level 2 m above the bedrock. The first third of Holocene (time of all interpreted data) seems to be very stable from erosion/accumulation evolution point of view. More dynamic evolution started with accumulation of “higher flood-plain level” (from cca 214 m a. s. l. up to 221 m a. s. l.). Subsequent erosion formed relatively deep cut in the northwest part of the flood plain which was filled relatively quickly by sediments as consequence of deforestation connected with a colonization of upper parts of Bečva River drainage area. This is supported by finds of much younger subfossil trunks dated from 1 century BC up to top of Middle-Age period in this accumulation (Vít et al. 2009). The surface of this accumulation is the so called “lower flood plain level” where periodicity of the inundation during floods is more regular then on the upper one.

Precessional Cyclicity of Seawater Pb Isotopes in the Late Miocene Mediterranean

AbstractAstronomical tuning in the Mediterranean region is primarily based on organically‐mediated proxies, such as cyclicity of organic rich layers or changes in foraminiferal assemblages. Both during and post deposition, organic proxies can be affected by complex processes not immediately related to the changes in precession (insolation) they are assumed to reflect. Here we present an isotopic proxy which exhibits precessional cyclicity yet is inorganic. Seawater lead (Pb) isotope records over four precessional cycles between 6.6 and 6.5 Ma, from bulk sediment leachates of three Messinian, circum‐Mediterranean marginal locations, show variations consistent with precessional cyclicity. During insolation minima, the Pb isotope signatures from all three sites converge to similar values, suggesting a regional process is affecting all three locations at that time. Data from the marginal sites are compared with new data from ODP Site 978 and published data from a variety of geological archives from the Mediterranean region to determine the mechanism(s) causing the observed variability. While the comparisons are not fully conclusive, the timing of events suggest that increased dust production from North Africa during insolation minima is the most likely control. This hypothesis implies that authigenic marine Pb isotope records have the potential to provide a reliable inorganic tie point for Mediterranean cyclostratigraphy where sub‐precessional resolution is required. An inorganic tie point could also provide the means to resolve long‐standing problems in Mediterranean stratigraphy on precessional and sub‐precessional timescales which have been obscured due to post‐depositional changes (e.g., sapropel burn‐down) or suboptimal ecological conditions (e.g., the Messinian Salinity Crisis).

The Stability of Fe-Isotope Signatures During Low Salinity Mixing in Subarctic Estuaries

We have studied iron (Fe)-isotope signals in particles (> 0.22 µm) and the dissolved phase (< 0.22 µm) in two subarctic, boreal rivers, their estuaries and the adjacent sea in northern Sweden. Both rivers, the Råne and the Kalix, are enriched in Fe and organic carbon (up to 29 µmol/L and up to 730 µmol/L, respectively). Observed changes in the particulate and dissolved phase during spring flood in May suggest different sources of Fe to the rivers during different seasons. While particles show a positive Fe-isotope signal during winter, during spring flood, the values are negative. Increased discharge due to snowmelt in the boreal region is most times accompanied by flushing of the organic-rich sub-surface layers. These upper podzol soil layers have been shown to be a source for Fe-organic carbon aggregates with a negative Fe-isotope signal. During winter, the rivers are mostly fed by deep groundwater, where Fe occurs as Fe(oxy)hydroxides, with a positive Fe-isotope signal. Flocculation during initial estuarine mixing does not change the Fe-isotope compositions of the two phases. Data indicate that the two groups of Fe aggregates flocculate diversely in the estuaries due to differences in their surface structure. Within the open sea, the particulate phase showed heavier δ56Fe values than in the estuaries. Our data indicate the flocculation of the negative Fe-isotope signal in a low salinity environment, due to changes in the ionic strength and further the increase of pH.

A unique methionine-rich protein–aragonite crystal complex: Structure and mechanical functions of the Pinctada fucata bivalve hinge ligament

The bivalve hinge ligament holds the two shells together. The ligament functions as a spring to open the shells after they were closed by the adductor muscle. The ligament is a mineralized tissue that bears no resemblance to any other known tissue. About half the ligament is composed of a protein-rich matrix, and half of long and extremely thin segmented aragonite crystals. Here we study the hinge ligament of the pearl oyster Pinctada fucata. FIB SEM shows that the 3D organization is remarkably ordered. The full sequence of the major protein component contains a continuous segment of 30 repeats of MMMLPD. There is no known homologous protein. Knockdown of this protein prevents crystal formation, demonstrating that the integrity of the matrix is necessary for crystals to form. X-ray diffraction shows that the aragonite crystals are more aligned in the compressed ligament, indicating that the crystals may be actively contributing to the elastic properties. The fusion interphase that joins the ligament to the shell nacre is composed of a prismatic mineralized tissue with a thin organic-rich layer at its center. Nanoindentation of the dry interphase shows that the elastic modulus of the nacre adjacent to the interphase gradually decreases until it approximates that of the interphase. The interphase modulus slightly increases until it matches the ligament. All these observations demonstrate that the ligament shell complex is a remarkable biological tissue that has evolved unique properties that enable bivalves to open their shell effectively innumerable times during the lifetime of the animal. Statement of significanceThe hinge ligament shell complex is a unique functioning structural tissue whose elastic properties enable the shell to open without expending energy. Methionine-rich proteins are not known elsewhere raising fundamental questions about secondary and tertiary structures contributing to its elastic properties. The segmented and extremely thin aragonite crystals embedded in this matrix may also have unexpected elastic materials properties as they flex during compression. The structure of the interphase comprises a fascinating biological joint that connects two very different materials. The interphase materials, including the nacre, are graded with respect to elastic modulus so as to approximately match the connecting components. The interphase incorporates a thin organic rich layer that presumably functions as a gasket. This study raises many fundamental questions relevant to the diverse fields of protein chemistry, biomineralization and biological materials.

A Unique Methionine-Rich Protein - Aragonite Crystal Complex: Structure and Mechanical Functions of the Pinctada Fucata Bivalve Hinge Ligament

The bivalve hinge ligament holds the two shells together. The ligament functions as a spring to open the shells after they were closed by the adductor muscle. The ligament is a mineralized tissue that bears no resemblance to any other known tissue. About half the ligament is composed of a protein-rich matrix, and half of long and extremely thin segmented aragonite crystals. Here we study the hinge ligament of the pearl oyster Pinctada fucata. FIB SEM shows that the 3D organization is remarkably ordered. The full sequence of the major protein component contains a continuous segment of 30 repeats of MMMLPD. There is no known homologous protein. Knockdown of this protein prevents crystal formation, demonstrating that the integrity of the matrix is necessary for crystals to form. X-ray diffraction shows that the aragonite crystals are more aligned in the compressed ligament, indicating that the crystals may be actively contributing to the elastic properties. The fusion interphase that joins the ligament to the shell nacre is composed of a prismatic mineralized tissue with a thin organic-rich layer at its center. Nanoindentation of the dry interphase shows that the elastic modulus of the nacre adjacent to the interphase gradually decreases until it approximates that of the interphase. The interphase modulus slightly increases until it matches the ligament. All these observations demonstrate that the ligament shell complex is a remarkable biological tissue that has evolved unique properties that enable bivalves to open their shell effectively innumerable times during the lifetime of the animal.

Characteristics of microorganisms and origin of organic matter in Wufeng Formation and Longmaxi Formation in Sichuan Basin, South China

Abstract To evaluate the characteristics of microorganisms and the origin of organic matter of the Wufeng Formation and Longmaxi Formation (WF-LMX) in Sichuan Basin (South China), the type and number of microorganisms were determined in this study using scanning electron microscope (SEM) microphotographs and microbial extraction. The contribution of various microorganisms to organic matter was analyzed in combination with the data of biomarkers and total organic carbon (TOC). It can be deduced from the paleogeography and pristine/phytane (Pr/Ph) ratio that the microorganisms of WF-LMX resided in 60 m–200 m deep shelf with anoxic bottom water. From SEM microphotographs and microbial microscopy analysis, it was demonstrated that the microorganisms in the WF-LMX can be divided into 3 types: planktonic algae (mainly including acritarchs and green algae), fungi, and benthic algae. Acritarchs were the most common microorganisms in the WF-LMX with the average relative content of 60.5%. The average relative contents of benthic algae, fungi, and green algae were 17.6%, 18.0% and 3.9%, respectively. Since the acritarchs and green algae in the Wufeng Formation and the Longmaxi Formation basically belong to planktonic algae, the relative content of planktonic algae in them is about 64.4%. The strata of WF-LMX can be divided into 3 sections based on the distribution characteristics of various microorganisms. The relative content of acritarchs gradually decreased upwards, while that of benthic algae gradually increased. The multiple proxies of biomarkers proved that the planktonic algae was the main source of organic matter in the WF-LMX. Combining the statistical data of microorganisms, it was considered that the organic matter in WF-LMX was mainly derived from acritarchs, which might be the components of planktonic algae. The fungi had a significant contribution to the organic matter in organic-rich layers (TOC > 2.0%) rather than in organic-poor layers, while green algae and benthic algae made little contribution to the organic matters in WF-LMX.

Depositional environment and hydrocarbon potential of the Oligocene Menilite Formation in the Western Carpathians: A case study from the Loučka section (Czech Republic)

Abstract The Eocene-Oligocene boundary in the Paratethys area represents a period associated with a major extinction event followed by anoxic events. A good understanding of the factors controlling the formation of organic-rich layers is a key for prediction of source rock distributions. An excellent opportunity to study these factors is provided by the Loucka section situated in the Silesian Unit of the Czech Republic. The Menilite Formation is subdivided into the Subchert Member, Chert Member, Dynow Marlstone and Sitbořice Member and comprises non-calcareous shales, marlstones and cherts. The lithological variations reflect strongly depositional environment, which caused strong changes in geochemical parameters and source rock potential. The ratio of total organic carbon to total sulphur (TOC/TS) and methylated 2-methyl-2 (trimethyltridecyl) chroman (MTTC) ratios supported by paleontological evidence show normal marine to brackish water conditions. Pr/Ph ratios indicate strictly anoxic conditions during deposition of the upper part of the Subchert Member and the lower part of the Chert Member. Very low steranes/hopanes ratios reflect strong bacterial activity during deposition of the Chert Member. Very high HI values (>600 mg HC/g TOC) and the apparent absence of terrestrial macerals suggest that high amounts of C29 steranes and long-chain n-alkanes in this member result from the input of algal material. The Menilite Formation contains mainly type II kerogen and typically holds a “good” source rock potential. HI values > 600 mg HC/g TOC are observed in the Chert Member, while values The source potential index (SPI) of the entire succession of the Menilite Formation is about 1.25 t HC/m2, which is significantly lower than SPI determined for the Polish and Ukrainian Carpathians, but mainly due to the lower thickness.

Magnetic mineral assemblage as a potential indicator of depositional environment in gas-bearing Silurian shales from Northern Poland

SUMMARYOrganic matter preservation and associated conditions during deposition, important in the context of fossil fuel exploration, are commonly determined by advanced geochemical analyses. However, the relation between organic matter preservation and magnetic mineral composition remains poorly constrained. The aim of the studies was to check the potential of magnetic mineral differentiation between facies containing various amounts of organic matter as a factor to better understand the processes which influence water chemistry at the bottom of sedimentary basins, and thus to better understand factors controlling the preservation of organic matter. To determine the composition and the properties of magnetic minerals, detailed low-temperature measurements of Saturation Isothermal Remanent Magnetization and hysteresis loops were performed on two types of rocks, Silurian shales from the Baltic Basin (northern Poland). The analysed shale facies are characterized by similar thermal evolution, but different amounts of organic matter: the Pelplin Formation, containing a modest content of organic matter, in which we also examined early diagenetic carbon concretions; and the Jantar Formation, which represents an organic-rich ‘sweet spot’ layer. In both facies, the results indicate the presence of multi- or pseudo-single domain magnetite, which is interpreted as detrital in origin. However, the main observation gained from this study is the relation between magnetic mineral assemblage in the studied shales and the amount of organic matter: in the rocks with modest amounts of organic matter we observed hematite, while in organic-rich layers hematite was absent. Hematite (mostly single-domain grains) preserved in the Pelplin Formation suggests that stable oxygen-rich conditions were present at the bottom of the sedimentary basin continuously during deposition, concretion cementation and compaction. In turn, its absence in the Jantar Formation suggests that during sedimentation and early diagenesis more anoxic conditions appeared. Generally, findings show that the presence of hematite is related to the significantly lower amount of organic matter in sedimentary rocks. Thus, presence of this mineral may be a useful indicator of organic matter preservation.

Effect of lithofacies on shale reservoir and hydrocarbon bearing capacity in the Shahejie Formation, Zhanhua Sag, eastern China

By using microscope, nuclear magnetic resonance (NMR), hydrocarbon generation and expulsion and nitrogen adsorption, reservoir properties and oil-gas bearing capacity of different shale lithofacies were examined with the continental shale of Zhanhua Sag in the Jiyang Depression of the Bohai Bay Basin as the examples. The results showed that the organic-rich laminar lithofacies have the best oil and gas bearing properties, while the organic-rich layer lithofacies take second place. The laminar lithofacies mainly developed mesopores and macropores, even microcracks, and the porosity connectivity is better than that of the layer lithofacies. The micropores and mesopores are mainly developed in the layer lithofacies, so the reservoir space is small. Therefore, the lithofacies with laminar not only increases the storage space of reservoir but also can improve the mobility of oil and gas. By the actual oil production comparison of different lithofacies, the hydrocarbon generation quantity of the organic-rich lithofacies is 336.68t, otherwise, the organic-contain lithofacies only 40.49t. Therefore, the organic-rich laminar lithofacies have the best oil production effect and can be used as a favorable target for oil and gas exploration in shale.

Aptian\u2013Albian shale oil unconventional system as registration of Cretaceous oceanic anoxic sub-events in the southern Tethys (Bir M\u2019Cherga basin, Tunisia)

The Bir M’Cherga basin (North-east Tunisia), with about 600 km2 area, had recorded four Middle Cretaceous source rocks well stratigraphically correlated with the four known oceanic anoxic sub-events: OAE1a, OAE1b, OAE1c, and OAE1d. Variety of lithology, thickness and organic richness had characterized these source rocks. The sedimentary tectonic analysis, the petrology and geochemistry study established the petroleum system of these source rocks. Basin formation began early in the Barremian–Aptian interval by synsedimentary tectonics reactivating old basement faults. During the Aptian–Albian, the formed basin had a depocenter that recorded thicker black shales while its NW and SE edges remained raised under the Triassic halokinetic activities. The evolution of the sedimentary filling during this period generated two sedimentary cycles corresponding to two filling second-order fining and thickening upwards sequences. The black shales that constitute these source rocks are formed between subtidal and external platform environment and are interbedded with juxtaposed high organic rich layers and poor ones. The rich organic facies consists of dark shale that constitutes the source rock. The poor organic beds formed by light grey and nodular limestones constitute an intra host reservoir. Thereby, petroleum system consists in an “unconventional oil shale hybrid systems with a combination of juxtaposed organic-rich and organic-lean intervals associated to open fractures”. The kerogen is essentially amorphous, with marine planktonic origin and low ligneous organic matter contribution. This organic material of dark facies had been well preserved in an anoxic environment with little or no energy. Light grey limestones were of oxic-to-sub-oxic environment. The stage of the thermal evolution for these source rocks provided by IH/Tmax diagram is of the “oil window”. The average transformation ratio (TR) is estimated as 45% suggesting thus black shales are oil shale resources which still close about untransformed 55% of its hydrocarbon generating potential. The expulsion and release of oil into these source rocks are proven by the observation of hydrocarbons filling micro-cracks and by the variable values of the oil saturation index OSI ranging from 0 to 138%. The latter exceeds 100% near the paleo-high reliefs indicating two “oil crossover” areas attributed to the high degree of oil source rock saturation and accumulation of hydrocarbons considered ideal for hydraulic fracturing. This oil crossover is a consequence of secondary migration into black shale source rock, achieved by various faults created during the distensive phase that were reactivated again several times.

High-resolution image analysis of laminae (organic-rich with calcareous nannofossils) in a black shale sequence: probability of orbital and suborbital climate cycles in the latest Cenomanian

We conducted a high-resolution image analysis of the lamination present in a core interval of black shale from Hole 1260B (ODP Leg 207) on the Demerara Rise in the western tropical Atlantic. Gray scale digital image analysis results revealed environmental cyclic patterns that could be related to orbital and suborbital changes during the latest Cenomanian (94 Ma). High-resolution nannofossil biostratigraphy provided the detailed chronological information needed to constrain the time intervals of each cyclic event. A study of thin sections showed that the basic pattern of the millimeter-scale laminae was couplets of alternating dark organic-rich layers and white biogenic test layers. The composition of the dark organic-rich layer appeared to include the remains from microbial organisms with a chain-like structure. From the combination of the gray scale and thin section analyses, three well-expressed cyclic patterns could be recognized in the black shale interval, namely (1) meter-scale cyclic events (average interval of approximately 413 mm), (2) centimeter-scale cyclic events (approximately 10–30 mm intervals), and (3) millimeter-scale cycles (average interval of approximately 5 mm). These cyclic events could imply approximately 40 ky, 1–3 ky, and 300–700 yr time spans, respectively, on the basis of biostratigraphy. In addition, two other cyclic patterns indicating approximately 20 ky and 60–150 yr time intervals were weakly expressed.

The palaeoceanographic crisis of the Early Aptian (OAE 1a) in the Vocontian Basin (SE France)

The Vocontian Basin (SE France) which presents lower Aptian expanded successions characterized by major lithological changes, is particularly suitable to determine palaeoenvironmental changes occurring across the OAE 1a. A multidisciplinary study (sedimentology, CaCO3, TOC, carbon and oxygen stable isotopes, micropalaeontology, cyclostratigraphy) was carried out in the Notre-Dame-de-Rosans section in order to establish a detailed chronological framework of these changes. The OAE 1a corresponds to carbon isotope segments C3–C6, and it lasted for 1.2 Myr. A first drop in the carbonate production occurs 500 kyr before the OAE 1a (upper part of the carbon isotope segment C2), and could result from both onset of “Urgonian” carbonate platform demise and associated reducing export of platform-derived sediments into the basin, and nannoconid crisis. A second drastic drop (crash) in the carbonate production is recorded within the lower part of the OAE 1a (latter part of segment C3 to C5) and is explained by a strong dissolution. This study then shows that the onset of the major carbonate crisis, that occurs before the OAE 1a, could be due to both rise in sea-level and in marine surface water fertility, whereas its “acme” that occurs within the OAE 1a, could be related to CO2-induced ocean acidification. Black shales of the “Niveau Goguel” occur in the upper part of the OAE 1a and represent the lower part of segment C6. Surface-waters primary producers are principally represented by cyanobacteria, whereas nannofossil primary productivity is reduced, and deep-water anoxia prevailed during the deposition of “the Niveau Goguel”. The last 300 kyr of the OAE 1a are characterized by a partial recovery of both nannofossil primary productivity and pelagic carbonate production, which sharply increase just after the end of the event. This study also shows that organic-rich layers associated to the OAE 1a are diachronous in the Tethyan realm.

Generation of Pseudo-synthetic Seismograms from Gamma-Ray Well Logs of Highly Radioactive Formations

The conventional synthetic seismogram is created with a sonic and a density log; however, the sonic log can be replaced with the resistivity, neutron, gamma-ray or spontaneous potential log to produce a pseudo-sonic (PS) log. More recent techniques involve combining an SP log and a GR log to produce a PS log. In the past, a drawback in using GR logs for the PS is the presence of highly radioactive and often organic-rich layers possessing abnormally high GR readings. To improve the pseudo-sonic log produced from the gamma-ray log, a technique was developed to statistically treat the outliers from the wells in the Hugoton Embayment that encountered predominantly shale, sandstone, limestone, and dolomite and whose logged sections included both normal and abnormally high GR readings. To demonstrate a wider-range application of our method, the procedure was applied to wells from the Hugoton Embayment, Central Kansas Uplift, Sedgwick Basin, Salina Basin, Forest City Basin and Nemaha Uplift. The correlation coefficients between the PS and the conventional sonic for the six basins were 0.75, 0.92, 0.86, 0.91, 0.77, and 0.70, respectively. Also, the match between the resulting conventional synthetic seismogram and the pseudo-synthetic seismogram from a blind test well for each area was quite good. Provided the outliers have been properly treated, the GR log is a viable tool for creating pseudo-sonic logs and pseudo-synthetic seismograms for exploration in oil and gas basins where there are few wells with sonic logs or where sonic log quality is poor.

Phosphatized tungsten-metabolizing coccoid microbes interpreted from oil shale of an Eocene lake, Green River Formation, Utah, USA.

Microscopic globular structures have been observed in some beds of oil shale from eastern Utah. These beds comprise carbonate-dominated mud that is interlaminated with variably thick and continuous organic-rich layers. Collectively they are enriched in phosphorus, REEs, and actinides. The beds are considered of lacustrine origin and assigned to the Eocene Green River Formation. The globules themselves are of microcrystalline carbonate fluorapatite (μCFA), often contain concentric internal structures, and usually group together in clusters of up to 80, possibly more. Detailed SEM and microprobe analyses have revealed tungsten (W) to be almost exclusively associated with the globular clusters found within the more organic-rich laminae, often at concentrations of over 200ppm, two orders of magnitude above shale standards. The globular structures are present in freshly cut sections where they occasionally grade into a μCFA matrix cement. This, together with the draping of the clusters by stringers of organic matter that would have accumulated in the Eocene lake, confirms that the structures are not a contaminant. The limited range of sizes and globular shapes is consistent with the morphology of coccoidal bacteria: Concentric internal structures may represent remnants of the nucleoid and cell wall. Paired concentric structures may indicate cell division (reproduction) processes were occurring until mineralization. The phosphate mineralization itself may have been promoted by release of phosphate from the stressed cells, bringing porewaters to supersaturation, or by the cells acting as nucleation sites. The recording of trace amounts of W almost exclusively in globular clusters preserved in the most organic-rich stringers (anoxia prone) further suggests facultative use of W-enzymes in a microbial metabolism. Combined, their context, morphology, and indication of biogenic process are strong evidence that the structures are fossilized (phosphatized) microbes, possibly sulfate-reducing bacteria, or methanogenic archaea.

The reservoir characterization and shale gas potential of the Niutitang formation: Case study of the SY well in northwest Hunan Province, South China

Marine shale is extensive throughout the subsurface, and commercially well-developed as natural gas producers throughout south China, attracting attention in recent years by both politicians and scientists on a variety of issues. Previous research on shale has predominantly focused on the Longmaxi and Niutitang Formations in the Sichuan Basin, but rarely on the periphery in northwestern Hunan Province where the Niutitang Formation has long been known as a potential shale gas reservoir. In this study, hydrocarbon generation potential, reserving performance, and shale gas potential of the Niutitang Formation from northwestern Hunan Province was studied to determine its gas producing potential. Total organic carbon (TOC) analysis, rock-eval pyrolysis, vitrinite reflectance and organic maceral analysis, mercury intrusion, nitrogen adsorption, and methane adsorption were run on a total of 52 samples from the SY well consisting of the Upper and Lower Members of the Niutitang Formation. Analysis of the results showed that the Niutitang shale has high TOC content (2.37% on average), high thermal maturity (3.15% on average), and oil-prone kerogen types, indicating good shale gas potential in the study area. The shale consists of relatively high concentrations of brittle minerals (quartz and feldspar, 69% on average) and low clay content (22% on average), indicating a brittle shale. The shale is a tight formation, with measured porosity averaging 2.66% (free gas potential) and methane adsorption capacity averaged 1.55 cm3/g (adsorbed gas potential). TOC and burial depth control reservoir space of the shale. The Lower Member samples had lower porosity but higher methane adsorption capacity than those from the Upper Member, indicating that a relatively larger amount of gas may occur as adsorbed gas in the Lower Member. It is suggested that the Lower Member of the Niutitang Formation is the ideal location for exploration and development of shale gas due to consistently thick organic-rich layers, high TOC content, high brittleness index, and stronger adsorption capacity.

Sub-marine Continuation of Peat Deposits From a Coastal Peatland in the Southern Baltic Sea and its Holocene Development

Coastal low-lying areas along the southern Baltic Sea provide good conditions for coastal peatland formation. During the Holocene, the transgression of the Littorina Sea has caused coastal flooding, submergence and erosion of ancient coastlines and former terrestrial material. The present Heiligensee & Hutelmoor peatland (located near Rostock in Northern Germany) was found to continue more than 90 m in front of the coastline based on on- and offshore sediment cores and geo-acoustic surveys. The seaward areal extent of the peatland is estimated with 0.16-0.2km2. The offshore limit of the former peatland roughly coincides with the offshore limit of a dynamic coast-parallel longshore bar, with peat deposits eroded seawards. While additional organic-rich layers were found further offshore below a small sand ridge system, no connection to the former peatlands can be established based on 14C age and C/N ratios. The preserved submerged peat deposits with organic carbon contents of 37 % in front of the coastal peatland Heiligensee & Hutelmoor was radiocarbon-dated to 6725 +/- 87 and 7024 +/-73 cal yr BP, respectively, indicating an earlier onset of the peatland as presently published. The formation time of the peat layers gives information about the local sea level rise. The local sea level curve derived from our 14C-dated organic-rich layers is in general agreement to nearby sea level reconstructions (North Rugen and Fischland, Northern Germany), with differences explained by local isostatic movements.

Model-based interbed multiple attenuation: a case study of Najmah reservoir, North Kuwait Jurassic

The Late Jurassic Najmah Formation of Northeast Kuwait consists of a fractured tight carbonate reservoir and organic-rich kerogen layer (Figure 1). Development of the Najmah reservoir is contingent on recognizing naturally fractured areas. Prior to seismic reservoir characterization, it is essential to ensure that the data quality is reliable before extracting any information from the seismic data. Noise contamination can obscure the reflections of interest, leading to inaccurate interpretation and the need for further data analysis for reservoir delineation. Data acquired in the study area indicates that P-wave seismic data within the reservoir interval suffers from the interference of coherent noise related to the interbed multiple. The interbed multiple is a serious problem that is common in the land seismic datasets in the Middle East (Al-Khaled et al., 2008; Al-Nahhas et al., 2008; El-Emam et al., 2011, 2005; Lesnikov and Owusu, 2011; Ras et al., 2012; Sonika et al., 2012; Wu et al. 2011). This study utilized a 9 mile2 (23.3 km2) 3D full azimuth P-wave seismic data set provided by Kuwait Oil Company (KOC) to the Reservoir Characterization Project (RCP) at the Colorado School of Mines. The seismic data was a preliminary result of pre-stack time migration from continuing seismic data processing. Short and long period demultiple and interbed demultiples were applied during the original data processing. A synthetic seismogram of well B portrays the reservoir interval with greater amplitude than the seismic data (Figure 2). This anomaly is consistently observed for all seismic well ties of ten available wells within the 3D seismic data. Furthermore, inside-outside corridor stack analysis of zero-offset VSP (Vertical Seismic Profile) depicts similar amplitude difference that indicates the presence of noise interference from multipathing of seismic energy above the reservoir interval. Evidence of the presence of multiples can be observed from the raw stack of down-going wavefields of the zero-offset VSP. Interbed multiple effects on the seismic data can be seen as a periodic repetition of reflection events, either individual events or interference with primaries. In this case, the multiples seem to interfere with the primary reflection. This study reveals interbed multiples related to the first anhydrite layer within the Gotnia Formation above the reservoir layers are the primary cause of the interference. Applying model-based interbed multiple attenuation reduces the noise interference and improves the imaging of the reservoir section. The multiple-attenuated seismic data have a better correlation with synthetics derived from ten control wells used in this study, leading to better seismic inversion accuracy and reservoir characterization.

Advanced surface logging technology for unconventional plays: well-site applications in tight reservoirs

Advanced surface logging technology for unconventional plays: well-site applications in tight reservoirs