Novel C26 tetracyclic degraded bicadinanes in oil sands from the Haitoubei–Maichen Sag of the Beibuwan Basin,South China Sea

Three C₂₆ tetracyclic terpanes were detected in the saturated hydrocarbon fractions of oil sand samples especially rich in bicadinanes W, T and R from the Oligocene Huizhou Formation in the XW-1 well in the Haitoubei–Maichen Sag of the Beibuwan Basin. Their mass spectra show molecular ions of the three tetracyclic terpanes at m/z 358, and their key fragment ions at m/z 343 (M⁺-15) and m/z 315 due to loss of an isopropyl group. These characteristics are very similar to that of C₃₀ cis–cis–trans (W) and trans–trans–trans (T) bicadinanes. In addition, the relative abundances of the C₂₆ tetracyclic terpanes show an excellent positive correlation with the C₃₀ bicadinanes W and T in 27 oil sand samples. Therefore, the three C₂₆ tetracyclic terpanes are tentatively identified as degraded bicadinanes, which like bicadinanes, may indicate input from dammar resins and can be used to discriminate the origin of crude oils.     

Calcification rate and the stable carbon, oxygen, and nitrogen isotopes in the skeleton, host tissue, and zooxanthellae of bleached and recovering Hawaiian corals

We tested the effectiveness of stable isotopes as recorders of physiological changes that occur during coral bleaching and recovery. Montipora capitata and Porites compressa fragments were bleached in outdoor tanks with seawater temperature raised to 30 °C (treatment corals) for one month. Additional fragments were maintained at 27 °C in separate tanks (control corals). After one month, (0 months recovery), buoyant weight was measured and a subset of fragments was frozen. Remaining fragments were returned to the reef for recovery. After 1.5, 4, and 8 months, fragments were collected, measured for buoyant weight, and frozen. Fragments were analyzed for stable carbon and oxygen isotopic compositions of the skeleton (δ¹³C_s; δ¹⁸O_s) and nitrogen and carbon isotopic compositions of the host tissue (δ¹⁵N_h; δ¹³C_h) and zooxanthellae (δ¹⁵N_z; δ¹³C_z). δ¹³C_s decreased immediately after bleaching in M. capitata, but not in P. compressa. δ¹⁸O_s of both species failed to record the warming event. During the remaining months of recovery, δ¹³C_s and δ¹⁸O_s were more enriched in treatment than control corals due to decreases in calcification and metabolic fractionation during that time. Increased δ¹⁵N_h of treatment P. compressa may be due to expelled zooxanthellae during bleaching and recovery. Increased δ¹⁵N_z at 1.5 months in treatment fragments of both species reflects the increased incorporation of dissolved inorganic nitrogen to facilitate mitotic cell division and/or chl a/cell recovery. Changes in δ¹³C_h and δ¹³C_z at 1.5 months in treatment M. capitata indicated a large increase in heterotrophically acquired carbon relative to photosynthetically fixed carbon. We experimentally show that isotopes in coral skeleton, host tissue and zooxanthellae can be used to verify physiological changes during bleaching and recovery, but their use as a proxy for past bleaching events in the skeletal record is limited.     

Fatty acid geochemistry of a 200 m sediment core from Lake Biwa,Japan. Early diagenesis and paleoenvironmental information

Fatty acids (FAs), β- and ω-hydroxy acids, α,ω-dicarboxylic acids and n-alkanes were studied in a 200 m sediment core taken from Lake Biwa, Japan. FAs showed bimodal distribution with peaks at C₁₆ and C₂₂-C₂₈. Their distribution patterns clearly changed with depth from lower molecular weight (C₁₂-C₁₉) predominance to higher molecular weight (C₂₀-C₃₂) predominance in the upper 20 m interval. Analyses of related compounds (β- and ω-hydroxy acids and α, ω-dicarboxylic acids) suggest that β- and ω-oxidative degradation of C₁₂-C₁₉ FAs has occurred in the sediments.The ratio of bound C₁₂-C₁₉ to unbound FAs increases with depth in the upper 0–1 m sediments, suggesting that unbound FAs are more labile. However, the ratio varies significantly in deeper sections and may be associated with water temperature.In the sediments deeper than 20 m in depth, C₁₂-C₁₉ FAs gradually decrease. On the other hand, higher molecular weight FAs (HFAs: C₂₀-C₃₂), which were probably derived from terrestrial plants, increase in concentration from 20 m to 100 m, suddenly decrease at 100 m and show progressively lower concentration in deeper sediments. These fluctuations are interpreted in relation to paleolimnological changes of the lake and the drainage basin. ω-Hydroxy C₂₀-C₃₀ acids and C₂₀-C₃₀α, ω-dicarboxylic acids show a distribution pattern similar to HFAs. Branched chain FAs, ω-hydroxy acids and C₉-C₁₉α,ω-dicarboxylic acids show a major peak around 3–15 m in depth. This peak is probably caused by increased bacterial activity in the water column and surface sediments in the past, which may be associated with an increase in primary production of the lake.     

Solar insolation driven periodicities in southwest monsoon and its impact on NE Arabian Sea paleoceanography

In the northeastern(NE) Arabian Sea,the fluctuation in terrestrial and freshwater runoff directly depends on southwest monsoon(SWM) precipitation as well as the meltwater flux provided by Indus River.Therefore,analysis of multi-proxy spectral signatures was carried out to trace the high-resolution SWM periodicities and their influence on the productivity,regional sea level fluctuations and depositional processes in the NE Arabian Sea.The time series data of stable isotopes of oxygen(δ~(18)O_(G.ruber)).carbon(δ~(13)C_(G.ruber) and δ~(13)C_(org)) and nitrogen(δ~(15)N).Total Organic Carbon(TOC),planktic-benthic foraminiferal ratio(P/B ratio) and63 μm coarse fraction(CF) were used from two coastal sedimentary cores located offshore Saurashtra,NE Arabian Sea(Core SK-240/485 having 88 m water depth;Core GC/SK-240/496 having 174 m water depth).The REDFIT based spectral analysis recorded significant periodicities(90% significance) in δ~(18)0 time series centered at~1609,~667,~525,~296,~290 and~256 years.Further,the significant periodicities recorded in carbon isotopes time series(δ~(13)C_(G.ruber) and δ~(13)C_(org))centered at~681,~512,~471,~452,~438,~360,~292,~275,~269,~245 and~209 years.The significant periodicities in TOC include~471 and-322 years whereas δ~(15)N time series recorded significant periodicity centered at-360 years.The significant periodicities in P/B ratio time series centered at~512,~388,~304,~250,~235,~217,~152,~139 and~135 years while CF recorded~268,~216,~209,~198,~188,~173 and~140 years significant periodicities.The observed periodicities in the multi-proxy record consist of similar cycles(within the radiocarbon dating error) which also natch with previously reported solar insolation influenced SWM and other global and regional cycles.Further,the stationarity of the data has been verified using wavelet analysis and shows similar periodicities as observed in REDFIT analysis.Thereafter,the depositional behaviour was studied using correlation analysis of the common periods of δ~(18)0 time series of both the cores.The result suggests that the depositional behaviour was different for both the core sites during the early Holocene and became similar during the middle Holocene.The correlation analysis of Total Solar Index(TSI) with δ~(18)O time series reveals a significant correlation with the core SK-240/485 whereas an insignificant correlation with the core GC/SK-240/496.These observations suggest that the solar insolation has been a leading factor responsible for the SWM trends during the Holocene which may have further influenced the productivity.regional sea level fluctuations and depositional conditions in the NE Arabian Sea.However,these trends are better preserved in shallow marine sediments as compared to the deeper marine sediments.     

Identification of an extended series of tricyclic terpanes in petroleum

A series of tricyclic terpanes from C₁₉ to C₄₅ has been identified in petroleum by gas chromatographic mass spectroscopic (GCMS) analysis. This discovery extends the previously known homologous series reported from C₁₉ to C₃₀. A method of preparation of a tricyclic terpane concentrate is described which facilitates tricyclic terpane analysis by the GCMS m/z 191 fragment. Metastable scanning GCMS is described as an additional method for characterization of the tricyclic terpanes.     

Structural identification and mass spectral interpretation of C3n highly branched alkanes in sediment and aquatic extracts and evidence for their anthropogenic origin

The structures of two distinctive series of C_3n highly branched alkanes (HBAs), previously detected in sedimentary and aquatic extracts, were identified as polypropylene (PP) oligomers with different end groups, using gas chromatography (GC) and mass spectrometry (MS) correlation with diastereoisomeric mixtures of authentic C₁₅ and C₁₈ standards. A C₁₅ member of the earlier eluting series was assigned as 2,4,6,8-tetramethylundecane and a C₁₅ member of the later eluting series as 4,6,8-trimethyldodecane. The C_3n HBA GC–MS profiles of extracts from a typical PP GC sample vial lid were also shown to closely match those previously detected in sediment and water extracts, providing convincing evidence that the purported environmental occurrences are a result of PP contamination. Both C_3n series correspond to the first eluting diastereoisomer of the respective standards, also consistent with an industrial isotactic PP source. Mass spectra of all five standards are presented to help assignment of new polymethyl alkanes.     

Organic geochemistry and depositional environment of the Aptian bituminous limestone in the Kale Gümüşhane area (NE-Turkey): An example of lacustrine deposits on the platform carbonate sequence

The Jurassic–Lower Cretaceous aged carbonate sequence is widely exposed in the southern zone of Eastern Pontides. Aptian black bituminous limestone is found in the upper part of this sequence in the Kale area (Gümüşhane). This limestone contains faunal remains (e.g., gastropod, ostracod, characean stems and miliolid type benthic foraminifera) that indicate a freshwater, lacustrine depositional environment.The total organic carbon (TOC) values of the bituminous limestone samples range from 0.11–1.30% with an average TOC value of 0.54%. The hydrogen index (HI) varies from 119–448 mg HC/g TOC (average HI 298 mg HC/g TOC) indicating that the limestone contains gas prone as well as oil prone organic matter. Pyrolysis data prove that the organic matter content in the bituminous limestone consists of Type II kerogen. The average T_max value for bituminous limestone samples is 438 °C (434–448 °C). Bitumen/TOC ratios for bituminous limestone are 0.05 and 0.04. The T_max values and the ratios indicate that the bituminous limestone samples contain early mature to mature organic matter.Analysis of solvent extracts from the two richest bituminous limestones show a predominance of high carbon number (C₂₆–C₃₀) n-alkanes. The Pr/Ph ratio and CPI value are 1.34 and 0.96, respectively. C₂₉ is the dominant sterane, with C₂₉ > C₂₇ > C₂₈. The bituminous limestone samples have low C₂₂/C₂₁ ratios, high C₂₄/C₂₃ tricyclic terpane ratios and very low C₃₁R/C₃₀ hopane ratios (<0.25). These data are consistent with the bituminous limestones being deposited in a lacustrine environment.     

3D Elastic Solutions for Laterally Loaded Discs: Generalised Brazilian and Point Load Tests

This paper investigates the application of a double Fourier series technique to the construction of an elastic stress field in a cylindrical bar subject to lateral boundary loads. The lateral loads, including the constant load boundary conditions, are represented by two Fourier series: one on the perimeter of the circular section (r ₀, θ) and the other on the longitudinal curved surface parallel to the bar axis (z). The technique invokes acceptable potential functions of the Papkovich–Neuber displacement field, satisfying the governing partial differential equations, to assign appropriate odd and even trigonometric Fourier terms in cylindrical coordinates (r, θ, z). The generic solution decomposes the problem of interest to a state of stress caused by two independent boundary conditions along the z axis and θ-polar angle, both superimposed on a solution for which these potentials are the product of the trigonometric terms of the independent variables (θ, z). Constants appearing in the resultant second-order partial differential equations are determined from the generally mixed (tractions and/or displacements) boundary conditions. While the solutions are satisfied exactly at the ends of an infinite bar, they are satisfied weakly on average, in the light of Saint Venant’s approximation at the two ends of a finite bar. The application of the proposed analysis is verified against available elastic solutions for axisymmetric and non-axisymmetric engineering problems such as the indirect Brazilian Tensile Strength and Point Load Strength tests.     

Novel family of hexacyclic hopanoid alkanes (C32C35) occurring in sediments and oils from anoxic paleoenvironments

Four novel hexacyclic alkanes, fairly common in crude oils and rock extracts from evaporitic series, have been tentatively identified on the basis of GC/MS data as C₃₂, C₃₃, C₃₄ and C₃₅ hexahydrobenzohopanes. These structures, only recorded in carbonate-anhydrite sequences, i.e. very anoxic paleoenvironments, tend to concentrate when pristane to phytane ratios increase. Changes in their relative concentration to αβ hopanes appear to be more related to variations in source and/or environmental conditions than to maturity. The ratio of the novel hexacylic C₃₅ hopane to C₃₅ αβ hopane, compared with other biomarker ratios, suggests that hexacyclic alkanes and hopanes are byproducts of the same hopanoid precursors via different chemical reactions. In addition the novel hexacyclic alkanes are bacterially resistant and may serve as a useful family to define the paleoenvironment (viz. very anoxic) of the parent source rock of a drastically biodegraded oil.     

Estimation of contaminant transport parameters for a tropical sand in a sand tank model

This research describes the goals, design and implementation of a quasi natural gradient, laboratory scale, sand tank (aquifer) model experiment. The model was used to study the transport of an inorganic tracer (Chloride) in groundwater, within a tropical aquifer (porous medium) material. Three-dimensional sand tank (1.8 m × 0.3 m × 0.8 m) experiments were conducted to investigate contaminant transport and natural attenuation within the sand tank. In all, 360 samples were collected during 24 sampling sessions, for the three days of the tracer experiments in the Sand Tank. The Owena sand is a poorly graded sand with 88.1 % sand and 11.9 % gravel. Geotechnical properties including; coefficient of uniformity C_u = 2.53, coefficient of gradation C_z = 0.181, hydraulic conductivity K = 5.76 × 10^?4 m/s, bulk density p = 1.9 Mg/m³, effective porosity n_e = 0.215 and median grain diameter D₅₀ = 0.55 mm, were determined. Other relevant hydraulic and solute transport parameters, such as dispersion coefficients and dispersivities were also established for the tropical soil.     

Biogeochemical controls on reaction of sedimentary organic matter and aqueous sulfides in holocene sediments of Mud Lake, Florida

The distribution and quantity of organic sulfur and iron sulfur species were determined in the Holocene sediments from Mud Lake, Florida. The sediments of this shallow, sinkhole lake are characterized by high sulfur and organic carbon contents as well as active sulfate reduction. They record a shift from a basal peat (below 2 m) comprised of water lily-dominated organic matter to the present cyanobacterial/algal-dominated lake deposit (upper 1 m). This shift in depositional environment and subsequent organic matter source was accompanied by variation in the amount of reactive iron delivered to the sediments, which in turn influenced the type and extent of organic matter sulfurization. Extractable intramolecular organic sulfur is principally found as C₂₅ highly branched isoprenoid (HBI) thiolanes. Extractable polysulfide-linked lipids, determined by selective chemical cleavage with MeLi/MeI and analyzed as methylthioethers (MTE), are dominated by n-alkanes with sulfur attachments at position 1 and 2, as well as lower amounts of C₂₅ HBI-MTE. The δ¹³C values and carbon-chain length distribution of both series of n-alkylMTE indicate that they are derived from distinct biological precursors. Among the n-alkylMTE with sulfur attachment at position 1 there are three homologous series: one saturated and two with both cis and trans enethiol isomers. The identification of the enethiol in the sulfur-linked macromolecules indicates that n-alkylaldehydes are precursors lipids. The intervals of high concentration of bulk organic sulfur and sulfurized lipids coincide with the intervals of high mineral sulfur content (acid volatile sulfide and chromium reducible sulfur). We suggest that the main control on the enhanced addition of sulfur to the organic matter in Mud Lake was the increased formation of polysulfides during the reduction of iron hydroxides and the subsequent reaction of those polysulfides with mildly oxidized sedimentary organic matter.     

57Fe Mössbauer spectroscopy and magnetization of cation deficient Fe2TiO4 and FeCr2O4. Part II: Magnetization data

Magnetic properties are reported for synthetic cation deficient Fe₂TiO₄ and FeCr₂O₄ particles (<1 μm). Cation deficiency, achieved by oxidation, is characterized by the oxidation parameter z which represents the fraction of Fe²⁺ ions converted to Fe³⁺ in the spinel lattice (0≤z≤1). Fe₂TiO₄ (z=0.85) has a Curie temperature T _c that can only approximately be given with a value in the range 400–700 K and it has a magnetic moment per formula unit M≈0.50 μ_B (μ_B=Bohr's magneton) at 4.2 K, for FeCr₂O₄ it is T _c≥520 K and M (4.2 K) ≈0.16 μ_B. Magnetic hysteresis parameters at various temperatures show in part characteristic features due to relaxation phenomena. In the Ti-spinel, the latter are caused by a superposition of superparamagnetism and spin relaxation and in the Cr-spinel by superparamagnetism, in agreement with Mössbauer data (part I of this paper). The cation and vacancy distribution and magnetic coupling are discussed in both compositions with respect to magnetic moment data considering magnetic dilution by incorporated vacancies, and in the Ti-spinel also by non magnetic Ti⁴⁺.     

Distribution,abundance and carbon isotopic composition of gaseous hydrocarbons in Big Soda Lake,Nevada: An alkaline,meromictic lake

Distribution and isotopic composition (δ¹³C) of low molecular weight hydrocarbon gases were studied in Big Soda Lake (depth = 64 m), an alkaline, meromictic lake with permanently anoxic bottom waters. Methane increased with depth in the anoxic mixolimnion (depth = 20–35 m), reached uniform concentrations (55 μM/l) in the monimolimnion (35–64 m) and again increased with depth in monimolimnion bottom sediments (>400 μM/kg below 1 m sub-bottom depth). The μ¹³C[CH₄] values in bottom sediment below 1 m sub-bottom depth (<?70 per mil) increased with vertical distance up the core (δ¹³C[CH₄] = ?55 per mil at sediment surface). Monimolimnion δ¹³C[CH₄] values (?55 to ?61 per mil) were greater than most δ¹³C[CH₄] values found in the anoxic mixolimnion (92% of samples had δ¹³C[CH₄] values between ?20 and ?48 per mil). No significant concentrations of ethylene or propylene were found in the lake. However ethane, propane, isobutane and n-butane concentrations all increased with water column depth, with respective maximum concentrations of 260, 80, 23 and 22 nM/l encountered between 50–60 m depth. Concentrations of ethane, propane and butanes decreased with depth in the bottom sediments. Ratios of $\text{CH}{}_4\text{[C}{}_2\text{H}{}_6\text{+ C}{}_3\text{H}{}_8\text{]}$ were high (250–620) in the anoxic mixolimnion, decreased to ~161 in the monimolimnion and increased with depth in the sediment to values as high as 1736. We concluded that methane has a biogenic origin in both the sediments and the anoxic water column and that C₂-C₄ alkanes have biogenic origins in the monimolimnion water and shallow sediments. The changes observed in δ¹³C[CH₄] and $\text{CH}{}_4\text{(C}{}_2\text{H}{}_6\text{+ C}{}_3\text{H}{}_8\text{)}$ with depth in the water column and sediments are probably caused by bacteria] processes. These might include anaerobic methane oxidation and different rates of methanogenesis and C₂ to C₄ alkane production by microorganisms.     

Molecular characterization of Type I kerogen from the Green River Formation using advanced NMR techniques in combination with electrospray ionization/ultrahigh resolution mass spectrometry

This study describes a new approach for characterizing high molecular weight compounds in Type I kerogen, involving both nuclear magnetic resonance (NMR) spectroscopy and Fourier transform ion cyclotron mass spectrometry (FTICR-MS). Kerogen isolated from the Mahogany zone of the Green River Formation was examined directly using high resolution magic angle spinning (HRMAS) NMR to obtain liquid-like multidimensional spectra. It was then successively extracted with n-pentane, dichloromethane and pyridine. Pyridine extraction was also performed for comparison with the successive extractions. Using solid-state NMR, we show that the sum of the successive extracts and the single pyridine extract are quantitatively representative of the unextracted kerogen. This suggests that a non-invasive characterization of Green River kerogen can be obtained by examining the soluble extracts, all of which were subjected to ESI-FTICR-MS to identify a wide series of compounds. Series of polar CHO, CHOS and CHON compounds between C₁₂ and C₅₀₊ were found. In all the extracts the two homologous series of acids (C_nH_2nO₂ and C_nH_2n−2O₄) dominated. Collision-induced dissociation was also employed to identify the different functional groups comprising the different series. The CHO series contained carboxylic acid and alkoxyl groups, whereas the CHOS and CHON series contained sulfoxide groups and nitrile-type compounds. The results also show that pyridine extraction can be used either for screening a large series of samples or for the specific study of CHO compounds. However for a detailed and complete study of the different homologous series we recommend using the successive extraction protocol.     

Novel C15 sesquiterpanes in Niger Delta oils: Structural identification and potential application as new markers of angiosperm input in light oils

Two new C₁₅ sesquiterpanes have been isolated from a Niger Delta oil. Based on nuclear magnetic resonance (NMR) data, their structures are similar to the ring D and E part of oleanane. The mass spectra show an m/z 193 base peak typical of rearranged drimanes. They have been found only in oleanane-containing oils with a Cretaceous or Tertiary source. Data are presented for 34 such oils from Angola, Canada, Greece, India, Indonesia, Iran, New Zealand, Nigeria, Thailand and Vietnam. The ratio between the new sesquiterpanes and rearranged drimanes roughly follows the oleanane index. They are absent from marine oils whose source rock age (Jurassic or older) predates the evolution and proliferation of angiosperms. They are probably formed via degradation of functionalized oleanoids or by cleavage of seco-oleananes. These sesquiterpanes may be useful as markers of angiosperm input in light oils (jet fuel, diesel or condensates) usually devoid of higher molecular weight markers for higher plant input.     

Biomarker distributions as indicators for the depositional environment of lacustrine sediments in the Valjevo-Mionica basin (Serbia)

In this study, the molecular composition and biomarker distribution of lacustrine sediments from Val-1 drillhole in the central zone of the western part of the Valjevo-Mionica basin were investigated at depth interval of 0–400 m. Former investigations have shown that the core material can be separated into six depth intervals based on bulk geochemical, mineralogical and sedimentological characteristics. Concerning the quality of organic matter, presence of specific minerals, and high salinity and anoxicity, or alkalinity, three zones are of highest interest, defined at depth intervals of 15–75 m (A), 75–200 m (B) and 360–400 m (F). The first aim of the study was to identify which biomarkers characterize these specific intervals. The second aim, addressing the transitions zones of these intervals, was to extend the changes in the characteristics of the organic substance, to reflect the changes of conditions in the depositional environment as well as to define biomarker parameters which are the most sensitive sedimentological indicators.The sediments from the hypersaline anoxic and alkaline environment show high contribution of algal precursor biomass, what is in accordance with the good quality of organic substances in the sediments from these zones. High squalane content and low content of regular isoprenoid C₂₅ are typical for hypersaline anoxic environment, whereas sediments from alkaline environment have high regular isoprenoid C₂₅ content.Transition to specific sedimentation zones is characterized by change in total organic matter content, and of both free and pyrolysis-derived, and change in hydrogen index value. In the biomarker distributions, more significant changes were detected in distributions of n-alkanes and isoprenoids, compared to polycyclic alkanes. The most intensive changes in alkane distribution are reflected in changes in n-C₁₇ content compared to n-C₂₇, and phytane compared to n-C₁₈. In addition, significant sensitivity was seen in ratios between squalane and n-alkane C₂₆ (hypersaline depositional environment), or isoprenoid C₂₅ and n-alkane C₂₂ for high alkalinity environment.This study showed that Sq/n-C₂₆ ratio can be used to assess the quality of organic substance in immature lacustrine sediments.     

Biomarker lipids of the freshwater fern Azolla and its fossil counterpart from the Eocene Arctic Ocean

Eocene sediments recovered from the Lomonosov Ridge in the central Arctic Ocean during Integrated Ocean Drilling Program Expedition 302 contain high amounts of fossil remains of the free floating freshwater fern Azolla. Both extant Azolla and the sediments from the Arctic Azolla interval were found to contain relatively high quantities of compounds identified as 1,ω20 C₃₀–C₃₆ diols. Furthermore, structurally related mid-chain hydroxy fatty acids, long chain n-alkanols and keto-ols were discovered. The different series have a common feature: there is always a hydroxy group at the ω20 position. In addition, structurally related C₂₉ ω20,ω21 diols, C₂₉ 1,20,21 triols, C₂₉ dihydroxy fatty acids as well as a series of wax esters containing these mono- and dihydroxy lipids are reported. Selective extraction of Azolla surface lipids revealed that these compounds are most likely present in the leaf waxes of the fern. The suite of long-chain, mid-chain ω20 hydroxy wax constituents is described for the first time. As they are well preserved in the Eocene sediments, these lipids may serve as palaeo-environmental indicators of the Arctic Azolla interval and as markers for the past occurrence of Azolla in general.     

An artificial neural network for groutability prediction of permeation grouting with microfine cement grouts

The use of microfine cements in permeation grouting has been growing as a strategy in geotechnical engineering because it usually provides improved groutability (N). One of the major challenges of using microfine cement grouts is the ability to estimate the N within a reasonable level of error. The suitability of traditional groutability prediction formulas, which are mostly based on the grain-size of the soil and the grout, is questionable for semi-nanometer scale grout. This study first investigated the accuracy of the current formulas; we found that the accuracy ranges from 45% to 68%, a level that is not adequate for practical engineering. An alternative approach, based on a Radial Basis Function Neural Network (RBFNN), was developed. RBFNN provides a prediction with a 95.8% accuracy within a short time frame. Several parameters were considered in our proposed network; besides the grain-size of the soil (D₁₀/D₁₅), other important parameters included the void ratio (e), the fines content (FC), the uniformity coefficient (C_u), the coefficient of gradation (C_z) and the water-to-cement ratio (w/c). A total of 240 in situ data samples were collected to support the training and testing of the network. After finding a good correlation between the field observation and the RBFNN output, it was concluded that RBFNN is a suitable and reliable tool to predict the outcome of permeation grouting when microfine cement grout is used.     

Hydrocarbons in 60 northeast Gulf of Mexico shelf sediments: a preliminary survey

Hydrocarbon results from gas chromatography of 60 recent sediment and 10 benthic algae samples delineate two distinct shelf environments in the northeastern Gulf of Mexico.Sediments off Florida (shell hashes and sands) have moderate amounts of lipids/total sediment (average 113ppm ± 80%) but low hydrocarbon levels (average 3.06 ppm ± 41%). Aliphatic hydrocarbons are dominated by a series of branched or cyclic, unsaturated C₂₅ isomers. The major n-alkane is n-C₁₇. The n-alkane and isoprenoid patterns are consistent with a marine hydrocarbon source.Sediments closer to the Mississippi River (silts and clays) contain large amounts of lipids (average 232 ppm ± 53%) and hydrocarbons (average 11.7 ppm ± 55%) to total sediment. Aliphatic hydrocarbons are mainly odd carbon number high molecular weight n-alkanes, indicating a terrigenous hydrocarbon source. Isoprenoids are present in greater abundance than in sediments off Florida (n-C₁₇/ pristane and n-C₁₈/phytane ratios ~2to 3). Relatively large amounts of n-C₁₆, together with an even distribution of n-alkanes in the range C₁₄–C₂₀ and a substantial unresolved envelope all point to a fossil fuel input to the Mississippi samples.Samples off the Alabama coast show intermediate characteristics.