Geochemical characteristics of the lower part of Shayi Member in Lixian Slope,Raoyang Sag,Bohai Bay Basin,Northern China: Implications for organic matters origin,thermal maturity and depositional environment

The lower part of Shayi Member (Es1x Sub-Member) composed mainly of dark mudstones and shales is the dominant source rocks for the Lixian Slope. Based on organic petrology, organic and inorganic geochemistry analyses of several mudstone and shale samples selected from Es1x Sub-Member, this research provides an overview on type, origin and thermal maturity of organic matters, as well as depositional environment of Es1x Sub-Member. Kerogen microscopy observation shows that the macerals are dominated by sapropelinite with a significant mixture of vitrinite and inertinite, indicating that aquatic algal-bacterial organic matter inputs are dominate with a significant contribution of terrigenous organic matter inputs. This statement is supported by n-alkane patterns distribution characteristics, high (n-C₂₁ + n-C₂₂)/(n-C₂₈ + n-C₂₉) values (average = 1.77), the plot of high Ph/n-C₁₈ values (average = 4.15) versus low Pr/n-C₁₇ values (average = 1.13), and high proportion of C₂₇ sterane and C₂₉ sterane (average = 37.7 and 42.0%, respectively). In addition, the rather low Pr/Ph values (average = 0.38), high gammacerane index values (average = 0.30), high V/Ni and V/(V + Ni) values (average = 11.84 and 0.89, respectively), high Sr/Ba and Sr/Cu values (average = 8.54 and 108, respectively), indicative of a saline water condition and a anoxic depositional environment. The low C29 sterane ααα 20S/(20S + 20R), C₂₉ sterane αββ/(αββ + ααα), C₃₁ homohopane 22S/(22S + 22R), C₃₂ homohopane 22S/(22S + 22R), Ts/(Ts + Tm) values and relatively high moretane/hopane values show that the level of thermal maturity of organic matters in Es1x Sub-Member are low.     

Geochemical Characterization Given by Rock-Eval Parameters and N-alkanes Distribution on Ypresian Organic Matter at Jebel Chaker, Tunisia

Sedimentary rock samples from Jebel Chaker in the eastern part of the Ypresian basin in central‐northern Tunisia were analyzed using various geochemical methods in order to decipher their organic signature. Examination of the distribution of total organic carbon (1.04–1.82%) suggests that the petroleum potential of Ypresian facies is not ignored in such area. The Ypresian episode permitted the accumulation of organic matter, which is typically marine plankton as indicated by the unimodal distribution of N‐alkane at nC₁₈ and by the predominance of the aliphatic hydrocarbons compared to the aromatics. It is concluded that the Ypresian organic matter is relatively immature, as indicated by the high content of polar compounds (3–67%) in bitumen. This conclusion is supported by the relative low T_max values (433–438°C), suggesting that the organic matter is located towards the end of diagenesis and beginning of catagenesis. These new results testify to the establishment of suboxic conditions that led to the accumulation and preservation of good quantities of organic matter in central‐northern Tunisia during the Ypresian. Due to their geochemical characteristics, the Chaker facies represent new potential source rocks in central‐northern Tunisia.     

The advantages of using n-alkanes, triterpane, and steranes to determine the characterization of sedimentary organic matter

The current geochemical study of n-alkanes, steranes, and triterpanes in bitumen from the Late Maastrichtian–Paleocene El Haria organic-rich facies in West of Gafsa, southern Tunisia, was performed in order to characterize with accuracy their geochemical pattern. The type of organic matter as deduced from n-alkanes, steranes, and triterpanes distributions is type II/III mixed oil/gas prone organic matter. Isoprenoids and biomarkers maturity parameters (i.e., T _s/T _m, 22S/(22S?+?22R) of the C₃₁ αβ-hopanes ratios, 20S/(20R?+?20S) and ββ/(ββ?+?αα) of C₂₉ steranes), revel that the organic-rich facies were deposited during enhanced anoxic conditions in southern Tunisa. The organic matter is placed prior to the peak stage of the conventional oil window (end of diagenesis–beginning of catagenesis). All these result are suggested by total organic carbon analysis, bitumen extraction and liquid chromatography data. Thus, the n-alkanes, triterpane, and steranes study remains valuable and practical for geochemical characterization of sedimentary organic matter.     

Evaluation of Organic Matter,Hydrocarbon Source,and Depositional Environment of Onshore Warkalli Sedimentary Sequence from Kerala-Konkan Basin,South India

Multidisciplinary analysis of the carbonaceous sediments of Warkalli Formation (Mio-Pliocene) from the Warkalli cliff section has been done to assess the source of organic matter, palaeodepositional settings and the hydrocarbon potential. The n-alkane distribution from n-C₁₂ to n-C₃₃ along with bimodal distribution indicates significant organic matter contribution from microbial activity and higher plants. The contribution from angiosperm source vegetation is indicated by the oleanane type of triterpenoids. The hopanes distribution indicates the immature stage of the organic matter, which is in agreement with the T_max (av. 401 °C) and huminite reflectance (av. 0.28% R_r) values. The total organic carbon (TOC) contents vary between 0.8 and 6.72 wt. % in the studied sediments. Hydrogen index and oxygen index values range from 16 to106 mg HC/g TOC, and 113 to 344 mg CO₂/g TOC, respectively. The maceral content is low, being dominated by the detrohuminite submaceral and the mineral matter accounts for 68 to 77% of the total composition. The phytoclast group (63–87%) is dominant with subordinate amorphous organic matter (4–35%). The study shows that the sediments were deposited in a marginal suboxic basin with intermittent variations. All the parameters unequivocally suggest that the studied sequence holds the potential to generate gaseous hydrocarbons.     

Sedimentary and organic facies investigation of the Gurpi Formation (Campanian–Paleocene) in southwest of Zagros,Iran

The Gurpi Formation in the southwest of Iran has been studied for microfacies and bulk organic geochemistry in order to elucidate its depositional environment and petroleum source rock characteristics. The obtained results ended up with four types of organic facies and three types of microfacies through the formation. Three microfacies types differentiated including Pelagic mudstone Wackstone, microbioclast Packstone and bioclastic Packstone reflect a distal outer ramp or basinal environment. Combination of palynofacies and organic geochemistry resulted in differentiation of four organic facies corresponding to organic facies B, BC, C and CD of Jones 1987. Detailed organic facies shows that the formation is characterized by low values of TOC, high percentages of amorphous organic matter and black phytoclasts, rare marine algae thereby representing a mixture of terrestrial and marine kerogen that confirm the formation was deposited in a distal anoxic to oxic condition. The formation shallows upward to the Microbioclast Packstone facies below the Lopha Member reaching its minimum depth in boundstones of this member in uppermost Campanian and then is followed by stagnant condition and high contents of organic matter in suboxic to anoxic condition that favoured accumulation of organic matter in early Maastrichtian. Organic geochemical and petrographical data indicate that the formation is not potentially suitable for petroleum production except for the minor interval (organic facies 2) in early Maastrichtian. Tmax values vary between 340 and 440 °C confirming immaturity trends indicated by Rock-Eval data.     

Relation entre évolution de la matière organique et caractéristiques géostructurales : exemple du bassin yprésien en Tunisie centro-septentrionale

The geochemical analysis of the organic-rich facies from the Ypresian basin in central–northern Tunisia shows that the organic matter is marine originated (type II) and displays a low thermal maturity level in outcropping samples. This study proves that the distribution, conservation and, therefore, the composition of the organic matter have been controlled by the dynamic of the Ypresian basin. The Ypresian period corresponds to an anoxic event, which led to the accumulation and preservation of good quantities of organic matter derived from a high primary production. To cite this article: A. Arfaoui, M. Montacer, C. R. Geoscience 338 (2006).     

Synthesis of the organic mineral evenkite

The synthesis of an analogue of the organic mineral evenkite included preparation of a mixture of ten individual molecular homologues of normal paraffin C _n H_{2n + 2} (n = 19–28), melting of this mixture, and subsequent slow cooling under controlled conditions. The symmetrical distribution of these homologues by the number of carbon atoms in the molecule (dominant homologue n = 23) and the X-ray pattern of synthesized evenkite—a ten-component solid solution of n-paraffins—correspond to the characteristics of natural evenkite.     

Source rock potential of the Middle Jurassic to Middle Pliocene,onshore Nile Delta Basin,Egypt

Organic geochemical characterization of cutting samples from the Abu Hammad-1 and Matariya-1 wells elucidates the depositional environment and source rock potential of the Jurassic and Lower Cretaceous successions and the Middle Miocene to Pleistocene section in the southern and eastern Nile Delta Basin. The burial and thermal histories of the Mesozoic and Miocene sections were modeled using 1D basin modeling based on input data from the two wells. This study reveals fair to good gas-prone source rocks within the Upper Jurassic and Lower Cretaceous sections with total organic carbon (TOC) averaging 2.7% and hydrogen index (HI) up to 130 mg HC/g TOC. The pristane/n-C₁₇ versus phytane/n-C₁₈ correlation suggests mixed marine and terrestrial organic matter with predominant marine input. Burial and thermal history modeling reveals low thermal maturity due to low heat flow and thin overburden. These source rocks can generate gas in the western and northern parts of the basin where they are situated at deeper settings. In contrast, the thick Middle Miocene shows fair source rock quality (TOC averaging at 1.4%; HI maximizing at 183 mg HC/g TOC). The quality decreases towards the younger section where terrestrial organic matter is abundant. This section is similar to previously studied intervals in the eastern Nile Delta Basin but differs from equivalents in the central parts where the quality is better. Based on 1D modeling, the thick Middle Miocene source rocks just reached the oil generation stage, but microbial gas, however, is possible.     

Biostratigraphy and depositional environment of the Miocene limestone bed of Baripada,Mayurbhanj district,Odisha: Foraminiferal,sedimentological and bulk organic geochemical evidences

Baripada Marine Beds (BMB) have been studied extensively in terms of its mega fossil content. However, not much has been discussed about the foraminiferal content and the organic matter assemblage in these beds. The fossiliferous sequence of BMB consists of sandstone, shale and limestone units. The present study is persued on the limestone unit of BMB. Foraminiferal, thin section and rock-eval pyrolysis studies were performed on the 33 surface samples collected from five sections of Jamdapal and Mukurmatia region along the Budhabalang river bank. Foraminifera are less abundant in the samples of Jamdapal, whereas Mukurmatia is comparatively rich. First appearance datum of Globorotalia menardii[ranges since middle Miocene (12.6 Ma); FAD at planktic foraminiferal zone N12] and last appearance datum of Neogloboquadrina continuosa [ranges between early Miocene (23.2 Ma) to late Miocene (8.3 Ma); FAD at planktic foraminiferal zone N4B and LAD at N16] together suggest that the limestone unit was deposited in between 12.6 to 8.3 Ma within the upper Miocene. Also, the association of shallow water benthic foraminifera (Species of Ammonia, Asterorotalia, Bolivina, Buliminella, Cibicides, Challengerella, Criboelphidium, Cribononion, Elphidium, Hanzawaia, Nonionella) and planktic foraminifera (Globigerina falcoensis, Globigerina woodi, Globorotalia menardii, Neogloboquadrina continuosa) together with oyster bank and shark teeth suggest deposition of limestone within well oxygenated, tropical, shallow water, open marine condition (within 40m water depth). Lithological and thin section studies together with global sea level fluctuation history advocate that upper Miocene marine transgression promoted the formation of this unit. Bulk organic geochemical data obtained by the rock-eval pyrolysis studies on selected samples indicate a low total organic carbon (TOC), with low hydrogen index (HI), high oxygen index (OI). The organic facies is characterised by type-IV kerogen with major contribution from near shore terrestrial plants. This also suggests deposition in shallow, oxygenated environments that did not promote significant accumulation and preservation of organic content in sediments.     

Morphological features of Cretaceous dinocysts of genus <Emphasis Type="Italic">Vesperopsis</Emphasis>, Bint, 1986, their facies confinement,and stratigraphic significance

A comparative morphological analysis is performed for 13 valid dinocyst species of genus Vesperopsis. Their distribution over Eurasia and North America in the Hauterivian–Cenomanian is traced and the characteristics of these deposits are given. Three species of the most stratigraphically significant dinocysts are distinguished: V. fragilis for the Upper Hauterivian of Western Siberia and V. mayi and V. longicornis for the Aptian of East Greenland. Analysis of facies confinement of the dinocysts Vesperopsis made it possible to group species of the considered genus over conditionally preferable paleosettings. Continental facies (freshwater, brackish-water) are characterized by species V. yanjiensis, V. glabra, V. sanjiensis, and V. jixianensis, while V. zhaodongensiis, V. didaoensis, and V. dolabella are typical of the coastal–marine facies, and V. digitatа, V. nebulosa, and V. mayi are typical of marine facies.     

Specifics of the Neoarchean Plume–Lithospheric Processes in the Kola–Norwegian Province of the Fennoscandian Shield: II. Petrology and Geodynamic Nature of Komatiite–Tholeiite Association

Numerical modeling of the generation and evolution of parental melts of the komatiite–tholeiite association of the Uraguba structure was carried out using previously obtained geochemical and isotope data. It was established that komatiite, komatiite and tholeiite basalts depleted in LREE and having ε_Nd(Т = 2.79) = +2.9…+3.2 were generated by equilibrium partial melting (F > 15%) of a depleted source (garnet-bearing Ol_0.63 + Opx_0.22 + Cpx_0.06 + Grt_0.09 mantle peridotite) at 4–8 GPa, while the genesis of primary melts of LREE-enriched komatiites (La_N/Sm_N ~ 1.2–1.6) with ε_Nd(Т = 2.79) = +2.5…+2.2 was related to the equilibrium partial melting (F > 20%) of an “enriched mantle peridotite” (EM–Ol_0.60 + Opx_0.20 + Cpx_0.08 + Grt_0.12) at pressure of 2.5–4 GPa. Coexistence in space and time of two types of melting products of mantle peridotites formed at different depths is explained by melting of different parts of adiabatically ascending mantle plume.     

The gas density and “volume” Schmidt law for spiral galaxies

The equilibrium thickness of the isothermal layers of interstellar gas and volume gas densities ρ _gas in the plane of the disk as a function of galactocentric distance R are computed for seven spiral galaxies (including the Milky Way) using an axisymmetrical model. In this model, the thickness of the stellar disk varies with R and remains approximately equal to the minimum thickness of a stable equilibrium disk. We found the disk thickness to increase toward the periphery in at least five of the seven galaxies. The density of the stellar disk decreases with R faster than ρ _gas , so that gas dominates at the disk peripheries in terms of density. A comparison of the azimuthally averaged star formation rate SFR and the gas density shows the absence of a universal Schmidt law SFR ～ρ _gas ⁿ for galaxies. However, the SFRs in various galaxies are better correlated with the volume than the gas surface density. The parameter n in the Schmidt law formally calculated using the least-squares method lies in the interval 0.8–2.4, being, on average, close to 1.5. The values of n calculated separately for the molecular gas display substantial scatter, but are, on average, close to unity. The value of n appears to increase with decreasing ρ _gas , so that the fraction of gas that actively participates in star formation decreases with n.     

Impact of pore water conductivity and porosity on the electrical conductivity of kaolinite

The purpose of this study is to quantify the magnitudes of surface conduction and pore water conduction from the measured electrical conductivity of kaolinite, with the ultimate goal of estimating the electrical conductivity of kaolinite with a wide range of pore water conductivities (σ _w = 0.013–3.356 S/m) and porosities (n = 0.368–1.0). Therefore, the theoretical background of the electrical conductivity in soils was reviewed, and electrical conductivity measurements on kaolinite were performed using both slurry and consolidation tests in this study. The results of this study demonstrate that the variations of measured electrical conductivity (σ _mix) with n are debatable according to the values of σ _w, because a decrease in n results in both an increase in surface conduction (K _s) and a decrease in pore water conduction (K _w); this causes the relative magnitude of K _s compared to that of K _w to vary with σ _w and n. Consequently, this study develops the relation between the porosity-normalized K _s/K _w and 1/σ _w. Additionally, the surface conductivity of the tested kaolinite is back-calculated and compared with the previous relationship between K _s and zeta potential of kaolinite. The measured and estimated σ _mix values are compared with the varying pore water conductivity and porosity values.     

Physical properties of molecular clouds as functions of their Galactocentric distance from CS and C<Superscript>34</Superscript>S observations

Twenty-eight CS molecular clouds toward HII regions with Galactocentric distances from ～ 4 to 20 kpc have been studied based on observations obtained in the J=2→1 lines of CS and C³⁴S on the 20-meter radio telescope of the Onsala Space Observatory (Sweden) in March 2001. All 28 clouds have been mapped with an angular resolution of ～40″. The peak intensity in the C³⁴S line has been measured for 20 objects. An LTE analysis has been performed and the parameters of the molecular cloud cores derived. The core sizes are d_A=0.3–4.8 pc, with a median value of ～1.6 pc. The mean hydrogen densities in the cloud cores are n_H2=3.5×10²–3.7 × 10⁴ cm^?3, with a median value of ～7.2×10³ cm^?3. The value of n_H2 ends to decrease with increasing Galactocentric distance of the cloud. The masses of most clouds are 10²?6×10³M_⊙, with the most probable value being M_CS～10³M_⊙. The data follow the dependence M_CS ∝d _A ^(2.4–3.2) . As a rule, the cloud masses are lower than the virial masses for M_CS<10³M_⊙.     

DasT-P-Feld der Diagenese und niedrigtemperierten Metamorphose aufgrund von Mineralreaktionen

It is attempted to determineT, P values for the lowgrade metamorphic facies. From geologic-petrographic observations and from experiments mineralreactions are outlined which characterize the zeolitic-, the glaucophane- and the greenschistfacies, respectively. Only such reactions are considered which are univariant if P_f=P_s; thus aP-T grid can be arrived at. Experimental data on the equilibria of the relevant reactions is taken from the literature and from own experiments. Experimental results are always checked against known field-observations. Contrary to current opinium, we arrive at rather higher temperatures for the beginning of the lowgrade metamorphic facies: Diagenesis. From sedimentation up to slightly below 300° C. Zeolitic facies. From slightly below 300° C up to about 400° C. Greenschistfacies. From about 400° C up to about 550° C. Glaucophaneschistfacies. Under pressures of at least 6–7 kb this facies begins somewhat above 300° C, probably at about 330° C, grading into high-pressure greenschistfacies.     

Comparison of Organic Matter from Upper Jurassic Oil Shale of the East European Platform and the Bazhenov Formation by Molecular and Isotopic Data

The molecular and isotopic composition of an extract from the rocks of the Bazhenov Formation in the southeast part of Western Siberia, oils that are genetically related to this formation, and products of hydrous pyrolysis of the organic matter of oil shale (Middle Volgian) of the East European Platform were studied. Common features and differences in their molecular composition were shown. The carbon isotope composition for C₁₄–C₃₀n-alkanes was determined for the first time; a negative isotope anomaly was revealed for C₂₆n-alkane in all samples studied. It was concluded that in spite of the geographical distance, specific biota was revealed in the Volga Basin. This biota conditioned an isotopic indicator, which is genetically significant.     

Distribution of <Emphasis Type="Italic">n</Emphasis>-alkanes in the ferromanganese nodule–sediment–pore water system (Clarion–Clipperton Fracture Zone)

The paper presents the first results of a comparative study of the composition and distribution of organic matter (OM) (C_org, n-alkanes, Pr, Phy) in samples of the ferromanganese nodule–sediment–pore water system taken at a single site in the Clarion–Clipperton Fracture Zone, Pacific Ocean. Samples were taken during Cruise 120 of R/V James Cook in 2015. The results of the comparison of organogeochemical parameters in the lipid fraction of OM in ferromanganese nodules of different size and morphology with the underlying sediment (0–1 cm) and pore water revealed both principle genetic affinity of OM therein and significant discrepancies between the processes of diagenesis during the formation and growth of each individual ore sample.     

Experimental study of amphibole interaction with H<Subscript>2</Subscript>O–NaCl Fluid at 900°C, 500 MPa: toward granulite facies melting and mass transfer

Interaction between natural pargasite [Prg, SiO₂ = 43.89 wt %, FeO/(FeO + MgO) = 0.35, (Na + K)_A = 0.51] and H₂O–NaCl fluid, whose composition (NaCl mole fraction) varied within the range X _NaCl = NaCl/(NaCl + H₂O) = 0–0.45, was experimentally studied in an internally heated apparatus at 900°C and 500 MPa. Natural pargasite begins to melt at a temperature 120–150°C lower than its synthetic analogue. In the presence of pure H₂O, the subliquidus mineral assemblage involves amphibole Hbl ₁, whose composition is closely similar to the starting Prg, clinopyroxene Cpx, calcic plagioclase Pl, and minor amounts of hercynite-magnetite spinel. With increasing X _NaCl, the subliquidus assemblage systematically changed: calcic plagioclase disappeared and more Fe- rich amphibole Hbl ₂ appeared at X _NaCl = 0.07; Cpx disappeared at X _NaCl = 0.14; and appearance of Na-Phl compositionally close to wonesite and almost complete disappearance of Hbl ₁ was observed at X _NaCl = 0.31. The composition of the melt also changed: its Na₂O gradually increased (from 1.5 to 9–10 wt %), and CaO and SiO₂ decreased(from 8.6 to 2 wt % and from 64 to 60 wt %, respectively, in recalculation to the anhydrous basis); at X _NaCl ≥ 0.35, the melt was transformed from quartz- to nepheline-normative. The maximum Cl concentration of 1.2 wt % was measured in the melt poorest in SiO₂. The experimental products contained spherical objects less than 10 μm in diameter that consisted of material that precipitated from the quenched fluid. These particles are richer than the melt in SiO₂ (62–80 wt %) and poorer in Al₂O₃ (11–19 wt %) in experiments with X _NaCl ≤ 0.24, but the differences between the compositions of the melt and particles decreased with increasing XNaCl. The relatively high concentrations of aluminosilicate material in the fluid is most likely explained by the high solubility of the melt in the fluid phase, with the formation in the fluid aqueous Si, Al–Si, Na–Al–Si, and other polymeric species. It is suggested that interaction of host rocks with such fluids, rich in granitic components, might be responsible for granitization (charnockitization) of mafic, and, particularly, ultramafic rocks described in the literature.     

Ivsite,Na<Subscript>3</Subscript>H(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>, a new mineral from volcanic exhalations of fumaroles of the Fissure Tolbachik Eruption of the 50th Anniversary of the Institute of Volcanology and Seismology,Far East Branch,Russian Academy of Sciences

Fine-granular (<0.1 mm) flattened colorless transparent crystals of ivsite form white aggregates. The empirical formula (Na_2.793Cu_0.056)_2.849HS_2.016O₈ is close to the ideal Na₃H(SO₄)₂. The structure was refined up to R = 0.040. Ivsite has a monoclinic symmetry, P2₁/c, a = 8.655(1) Å, b = 9.652(1) Å, c = 9.147(1) Å, β = 108.76(1)°, V = 723.61(1) ų, Z = 4. Na atoms occur at six- and seven-fold sites (NaO₆ and NaO₇); S atoms, in isolated SO₄ tetrahedrons; these polyhedrons form a three-dimensional framework. The diagnostic lines of powder diffraction patterns (d[Å]–I–hkl) are 4.010–53–12-1, 3.949–87–012, 3.768–100–210, 3.610–21–20-2, 3.022–22–031, 2.891–42–22-2, 2.764–49–31-1, and 2.732–70–13-1.