Monocyclic alkanes in Ordovician organic matter

The major compounds in the C₁₅₊ branched/cyclic alkane fractions of two Ordovician oils (Pine Unit and Midland Farms oils) and an immature Ordovician rock (Guttenberg Oil Rock) are monocyclics. One series of these compounds was identified as n-alkylcyclohexanes and another tentatively identified as methyl-n-alkylcyclohexanes. The carbon number distribution of these compounds resembled those of the n-alkanes found in these samples with an odd carbon number predominance. It is suggested that the monocyclic alkanes, in these Ordovician samples, may be principally derived from the cyclisation of straight-chain algal fatty acids, by mechanisms that involve decarboxylation. However, there is evidence from the m/z 97 fragmentograms of these samples, to indicate that methyl-n-alkylcyclohexanes can also be derived from fatty acids by a less preferred mechanism that does not involve decarboxylation or from other precursors.In addition, a sample of kerogen from the Guttenberg Oil Rock was hydrously pyrolysed. The saturated hydrocarbon products of this experiment showed very similar distributions (including monocyclics) to those observed in the Ordovician oils. This suggests that although the oils and the Guttenberg Oil Rock come from widely differing geographical locations, their precursor (algal derived) organic matter was very similar.     

Aliphatic components of Victorian brown coal lithotypes

Victorian brown coal occurs in five major lithotypes distinguishable by colour index, petrography and bulk chemical analyses. The distributions of solvent extractable (free) and base hydrolysable (bound) n-alkanes, n-monocar?ylic acids, n-?,ω-dicar?ylic acids, n-ω-hydroxycar?ylic acids and n-alcohols were determined for samples of each of the five lithotypes (lithotype profile) and for seven samples of identical lithotype classification spanning a 100 m interval (depth profile) taken from a continuous bore core. The distributions of free molecular components in all classes are indicative of the predominant higher plant origin of this immature coal and provide strong support for the view that different lithotypes have derived from different, yet fairly specific paleobotanical communities. Despite an overall similarity in the distributions of aliphatic components from samples of identical lithotype classification, changes in the absolute concentrations and carbon preference indices (CPIs) of specific functional classes are observed in response to catagenetic influences even across the very small rank interval of the depth profile samples. Molecular distributions of bound components are similar to those of their free counterparts except that CPIs are generally lower and the relative contributions of lower molecular weight homologues (i.e. <C₂₂) are higher. Thedistributions of bound dicar?ylic acids and hydroxycar?ylic acids appear to reflect variations in the oxic/anoxic nature of the depositional paleoenvironments.     

Free fatty acid analysis of the early proterozoic animikie group,Minnesota and Ontario

The Early Proterozoic iron formation-slate sequences of the Animikie Group have been analyzed for fatty acids and the results discussed in light of the regional metamorphic history and kerogen H/C and N/C atomic ratios. No fatty acids, free or inorganically bound, were detected. The highest H/C ratios are found in the Gunflint (mean = 0.57) and lowest in the Virginia State (0.19). The lower H/C ratio in the Biwabik (mean = 0.45) is interpreted as a function of higher metamorphic grade in that iron formation. The absence of fatty acids is attributed to dehydrogenation and cyclization of the original material to the present H/C ratio of about 0.5. The Gunflint Iron-Formation, which represents those conditions most likely to preserve chemical fossils in the Animikie Group has already exceeded minimum conditions for fatty acid preservation. Hydrogen to carbon ratios in pelitic rocks are consistently lower than their underlying iron-formation. It is suggested that sulfur and/or clay alter the kinetics of the dehydrogenation reaction, creating lower H/C ratios in the pelites.     

Comparison of lipid character of sediments from the Great Lakes and the Northwestern Atlantic

Geolipid compositions of surficial sediments from Lake Michigan, Lake Huron, and from three locations in the Northwestern Atlantic were determined to compare source inputs and alteration processes in different sedimentary environments. Fatty acids, sterols, fatty alcohols, and alkanes were examined in both unbound and bound extracts of these samples. Significant amounts of long chain fatty acids, alcohols, and hydrocarbons are present in the deep ocean station, yet this location contains a proportionally larger amount of short chain geolipids than do marine stations closer to shore. Larger proportions of long chain lipids present in the Lake Michigan, Lake Huron, and Gulf of Maine samples relative to the open ocean samples reflect larger inputs of land-derived lipids to sediments closer to terrigenous sources. Marine samples contain a more complex mixture of sterols than is found in lake sediments, suggesting that sterol inputs and alteration processes in the marine environment are more complex than in lacustrine settings. Ratios of 16:1/16:0 and 18:1/18:0 fatty acids decrease with increasing distance from land, which suggests that fatty acid degradation before and during deposition becomes more extensive in the open deeper ocean stations.     

The removal of dissolved humic acid during estuarine mixing

A simple method for the determination of dissolved humic acid based on carbon analysis is presented. This method was used to measure the distribution of dissolved humic acids in seven coastal plain estuaries located in the middle-Atlantic United States. Results indicate that 100% of the dissolved humic acid was removed during estuarine mixing, although concurrent measurements of dissolved organic carbon showed either production or conservative behavior in regions of the estuary where humic acid removal was observed. It is apparent from these observations that removal of dissolved humic acid is a minor part of the estuarine transport of dissolved organic carbon.Laboratory experiments carried out by mixing river water with sea water demonstrated that salt-induced removal of dissolved humic acid was insignificant in two of three estuaries studied. These results suggest in situ removal of dissolved humic acid may not be universally caused by increasing estuarine salinity.     

Physils and organic matter-base palaeoenvironmental records of the K/Pg boundary transition from the late Cretaceous-early Palaeogene succession of the Um-Sohryngkew River section of Meghalaya,India

A continuous, shallow marine succession of the Um-Sohryngkew River section is distinct as it contains late Maastrichtian-early Danian planktonic foraminiferal zones and the K/Pg boundary, although K/Pg transition events remain inconclusive. Physils divide entire succession in to lower, middle and upper sub-divisions and represent anomalous values of redox-sensitive elements (δCe, La/Yb and Gd/Yb) in biozone CF3. Organic matter when analyzed show TOC and C spikes in biozone CF3. Illite thermometry also revealed sudden increase in the palaeo-temperature (>140 °C) for yellowish brown 1–2 mm thick organic rich clay layer in biozone CF3. Interestingly, conspicuous increase in the short chain n-alkanes and fatty acids is observed in the biozone CF3, although, long chain n-alkanes (C₂₇–C₃₃) derived from terrestrial plants show low abundance throughout the succession.High amount of combustion derived fluoranthene, pyrene, chrysene, benzo(a) anthracene PAH compounds found in the biozone CF3 are analogous to those reported from the K/T boundary sections of Stevns Klint, Gubbio, Woodside Creek and Arroyo el Mimbral. The pyrolitic signatures of these organic macro-molecules reflect global fire, caused distress to biota (during the deposition of biozone CF3 layer) which is coincidental with the well documented Ce anomaly layer, but, preceded by planktonic foraminiferal change in biozone P0 and PGE anomaly bearing layer in the biozone CF2. These organic macro-molecules reflect global fire, induced by the heat supplied by the late Cretaceous Abor and/or Deccan extrusions perhaps linked with the K/T transition events as later initiated prior to the K/Pg boundary, however, the main episode of Deccan volcanic activity occurred ∼300 ky earlier or at the K/Pg boundary itself. The deposition of 1–2 mm thick, yellowish brown, smooth (with conchoidal fracture) pyrite nodules and micro-spherules bearing organic rich clay layer marked with the decrease in the carbonate content (2.43%) that lies at the contact between the silty mudstone and grey calcareous shale located in the biozone CF3 of this succession coincides with the first appearance of Pseudoguembelina hariaensis representing age of 66.83–65.45 Ma is also related to the India’s collision with the Eurasia and Burma andextrusion of Abor volcanic.These events also endorse succeeding events such as anomalous concentration of platinum group of elements and concentration of spherules during biozone CF2, which are other end Cretaceous events before the advent of the K/Pg boundary.     

A quantitative study of the degradation of whale bone lipids: Implications for the preservation of fatty acids in marine sediments

The degradation and preservation affecting the biomarker record of ancient metazoa are not fully understood. We report on a five month experiment on the fate of fatty acids (FAs) during the degradation of recent whale vertebrae (Phocoena phocoena). Whale bones were analysed for extractable FAs and macromolecularly bound n-acyl compounds. Fresh bone showed extractable FAs dominated by 16:1ω7c, 16:0, 18:1ω9c and 18:0. Calculated degradation rate constant (k) values showed a rapid decrease in FA concentration, with k values higher for unsaturated than for saturated compounds (0.08/day for 18:1ω9c, 0.05/day for 16:0). The appearance or increased abundance of distinctive methyl branched (e.g. i/ai-15:0 and -17:0, 10Me-16:0) and hydroxy FAs (e.g. 10OH-16:0 and 10OH-18:0) were observed, providing clear evidence for the microbial degradation of bone organic matter and an input of lipids from specialised bacteria. Catalytic hydropyrolysis (HyPy) of demineralised extraction residues released up to 0.13% of the total n-C₁₆ and n-C₁₈ moieties in the degraded bones. This revealed that only a small, yet sizeable, portion of bone-derived fatty acyl units was sequestered into (proto)kerogen during the earliest stages of degradation.     

钾铵基聚合物钻井液抑制性研究

大牛地气田石盒子组泥岩发育,钻井液抑制性不足,易发生井壁失稳事故,严重影响施工安全和施工进度。在分析石盒子组泥岩段失稳机理的基础上,开展了钾铵基聚合物钻井液抑制性研究。放大蒙脱石和伊蒙混层矿物含量,评价和优选出具有高效抑制性的钾铵基聚合物钻井液体系。该体系具有较低的线性膨胀率和较高的滚动回收率,对大牛地气田预防泥岩段井壁失稳具有重要的实际意义。     

温度、光照、pH值对后棘藻生长及脂肪酸含量的影响

报道了环境因子对富含 EPA (2 0∶ 5ω3)的海洋微藻后棘藻 (Ellipsoidion sp.) 70 - 0 1的生长速度、总脂及脂肪酸含量的影响。结果表明 ,后棘藻具有较快的生长速度和较高的脂肪酸含量 ,总脂含量为 31～ 36 % ,主要脂肪酸为 14∶ 0、16∶ 0、16∶ 1、18∶ 1ω9、18∶ 1ω7、18∶ 2 ω6、2 0∶ 4 ω6、2 0∶ 5ω3。生长的温度范围为 15～ 30℃ ,2 5℃时生长速度最快。温度对总脂含量影响很小 ,但对EPA和 PUFA含量影响较大。在 2 5℃时有最大的 EPA和 PUFA含量。适宜光强为 10 8.75μmolm-2 s-1～ 2 4 4 .15μmolm-2 s-1,在 145.54μmolm-2 s-1时 EPA产率较大。在起始 p H6 .5～ 9范围内 ,p H8.5时有最大的生长速率和总脂含量 ,而 EPA和 PUFA在起始 p H7.5时最大 ,分别占脂肪酸的 18.77%和 2 3.38%。实验条件下后棘藻 EPA产率最大的条件为温度 2 5℃ ,光强 145.54μmolm-2 s-1,p H为 7.5～ 8.5。     

Distributions of carbohydrate species in the Gulf of Mexico

In order to study the role of polysaccharides in the cycling of marine organic matter and transparent exopolymeric particles (TEP), the concentrations of total carbohydrates (p-TCHO), total uronic acids (URA) and total acid polysaccharides (APS) in suspended and sinking particles, as well as carbohydrates in the filter-passing “dissolved” phase (d-TCHO), were measured in vertical profiles along a N–S transect in the Gulf of Mexico, across a cold core (CCR) and a warm core (WCR) ring (eddy) during both July 2000 and May 2001. The concentrations of d-TCHO in 2000 ranged from 4 to 22 μM C, with a subsurface maximum, which was located slightly above the depth of chl a maximum, amounting to, on average, 34% of DOC in the CCR, and 13% in the WCR. The concentration of particulate carbohydrates (p-TCHO) in different size fractions (0.7–10, 10–53, and >53 μm) ranged from 0.04 to 1.1, 0.005 to 0.40, and 0.006 to 0.26 μM C, respectively, indicating that carbohydrates are mostly concentrated in small particles (0.7–10 μm). URA and APS were similarly concentrated in small particles, in which, on average, URA accounted for 87% and 57% of total URA, and APS for 92% and 88% of total APS in 2000 and 2001, respectively. URA accounted for 3–9% of carbohydrates in suspended particles, suggesting that URA are a minor component of the p-TCHO pool. Due to its surface-reactive nature, URA could play a major role in the coagulation of particles and macromolecules despite its relatively low abundance. While, on average, p-TCHO and total APS were more enriched in suspended particles than in sinking particles in both 2000 and 2001, the opposite was true for URA in both years. The greater contents of URA that are present in settling particles compared to suspended particles could indicate a mass flow in the direction of sinking particles, either caused by coagulation, by bacterial reworking of particulate and colloidal organic matter, or by their more refractory nature.