Pyrolysis-GC-MS and NMR studies of dissolved seawater humic substances and isolates of a marine diatom

¹³C- and ¹H-NMR spectra were obtained for humic substances isolated from a coastal marine environment and also for the intracellular and extracellular extracts of a marine diatom. Phaeodactylum tricornutum Bohlin. Highly branched alkyl chains constitute a large proportion of the structure of the marine humic material, whereas aromatic components are less important. Carbohydrate-type materials, possibly uronic acids, are also present in appreciable amounts. Furans (derived from carbohydrates). pyrroles and nitriles (derived from proteins, nucleic acids and/or tetrapyrroles) and phenols and methylphenols (non-lignin derived) are pyrolysis products derived from pyrolysis-gas chromatography-mass spectrometry of the extracts. The results indicate the similarities in chemical structure of P. tricornutum exudate and dissolved marine humic material.     

The kerogen type, depositional environment and maturity, of the Irati Shale, Upper Permian of Paraná Basin, Southern Brazil

Two samples from the upper and lower horizons of the Irati oil shale of the Paraná Basin, Brazil were sampled in a single borehole, and analysed using organic petrography and geochemistry. The results are interpreted in terms of the kerogen type, maturity and depositional environment of the two horizons.Organic petrography shows the oil-shales to be composed of a mineral groundmass, mainly clay minerals, carbonate and pyrite, associated, and sometimes impregnated, with fluorescing organic material and disseminated phytoclasts. Humic material is fairly rare and mostly present as very small particles. The liptinitic particles are mostly alginite (A and B), sporinite and more rarely resinite. Reflectance measurements (upper seam = 0.34% R₀; lower seam = 0.40% R₀) indicate an equivalent rank of lignite/sub-bituminous coal (ASTM), i.e. immature with respect to oil and gas generation. Different organic geochemical methods (Rock-Eval pyrolysis, solvent extraction, GC and GC-MS) demonstrate both samples to be immature, rich oil-shales (100–114 kg/ton) containing Type I kerogen, of a dominantly bacterially-degraded algal origin deposited in a lacustrine environment. The presence of Botryococcus suggests deposition under fresh/brackish water conditions.A tentative interpretation of the extract and vitrinite reflectance data suggests a maximum paleo-burial of between 1.3 and 2.8 km for the analysed section of the Irati Formation.     

Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 2. Trace element compositions of melts and minerals

The trace element compositions of melts and minerals from high-pressure experiments on hydrous pyroxenites containing K-richterite are presented. The experiments used mixtures of a third each of the natural minerals clinopyroxene, phlogopite and K-richterite, some with the addition of 5% of an accessory phase ilmenite, rutile or apatite. Although the major element compositions of melts resemble natural lamproites, the trace element contents of most trace elements from the three-mineral mixture are much lower than in lamproites. Apatite is required in the source to provide high abundances of the rare earth elements, and either rutile and/or ilmenite is required to provide the high field strength elements Ti, Nb, Ta, Zr and Hf. Phlogopite controls the high levels of Rb, Cs and Ba.Since abundances of trace elements in the various starting mixtures vary strongly because of the use of natural minerals, we calculated mineral/melt partition coefficients (D_Min/melt) using mineral modes and melting reactions and present trace element patterns for different degrees of partial melting of hydrous pyroxenites. Rb, Cs and Ba are compatible in phlogopite and the partition coefficient ratio phlogopite/K-richterite is high for Ba (1 3 6) and Rb (12). All melts have low contents of most of the first row transition elements, particularly Ni and Cu ((0.1–0.01) × primitive mantle). Nickel has high D_Min/melt for all the major minerals (12 for K-richterite, 9.2 for phlogopite and 5.6 for Cpx) and so behaves at least as compatibly as in melting of peridotites. Fluorine/chlorine ratios in melts are high and D_Min/melt for fluorine decreases in the order apatite (2.2) > phlogopite (1.5) > K-richterite (0.87). The requirement for apatite and at least one Ti-oxide in the source of natural lamproites holds for mica pyroxenites that lack K-richterite. The results are used to model isotopic ageing in hydrous pyroxenite source rocks: phlogopite controls Sr isotopes, so that lamproites with relatively low ⁸⁷Sr/⁸⁶Sr must come from phlogopite-poor source rocks, probably dominated by Cpx and K-richterite. At high pressures (>4 GPa), peritectic Cpx holds back Na, explaining the high K₂O/Na₂O of lamproites.     

生油煤形成的环境制约

通过对不同沉积环境下形成煤系源岩生烃潜力的对比研究，揭示出成煤古环境对煤成烃生成具有控制作用，并根据煤系源岩中赋存大分子有机质裂解产物分子的组成特征，提出了识别有利成烃煤相的分子有机地球化学方法——氢指数-苯酚/辛烷图解判识法。结果表明，沼泽环境覆水越深，煤中有机质富氢程度越高，生油气性能越好，裂解产物表现为正构烷烃和正构烯烃相对含量增加，以低本酚/辛烷值和高氢指数为特征；反之，沼泽环境覆水越浅，煤中有机质氢含量越低，裂解产物以高含量酚类化合物和芳香烃为特征，生油气性能关。由此表明，覆水型沼泽应是煤在烃，特别是煤成油生成的有利相带。     

利用干酪根热解动力学模拟实验研究塔里木盆地下古生界古地温

通过热解动力学模拟实验，对塔里木盆地塔参1井奥陶系干酪根的热演化过程进行了模拟，以此基础上利用KINETICS软件求取干酪根镜质体反射率（R0）的生成动力学参数，并结合塔参1井的沉积埋藏史，计算塔参1井寒武－奥陶系的古地温，这对于研究塔里木盆地下古生界高过成熟烃源岩的古地温是一种新方法。     

Geochemical characterization of soil organic matter and variability of a postglacial detrital organic supply (chaillexon lake,france)

Geochemical analysis of sedimentary organic matter in recent lacustrine sediments appears to be a useful tool in providing information concerning past environmental conditions. However, such analysis is often made without knowing the geochemical characteristics of the organic matter derived from the watershed and, more explicitly, its soils. The present work deals with (i) a geochemical investigation (Rock-Eval pyrolysis) of soil organic matter sampled in a lake watershed, and (ii) the study of the sedimentary organic matter trapped in the lake deposits. The research was conducted on Chaillexon Lake which was created by a rock collapse that dammed the palaeovalley of the Doubs River about 12 000 years ago. Since this event, the sediment trap provides a continuous palaeoclimatic record for the Postglacial period. Results obtained lead to two main conclusions. First, the variability of Rock-Eval pyrolysis values observed in soils modifies the common interpretation given to these parameters in the characterization of sedimentary organic matter. Indeed, variations in these parameters point not only to varying proportions of terrestrial and lacustrine organic matter in a lacustrine infilling but also to variations of the terrestrial supply linked with the evolution of vegetal cover in the catchment. The second conclusion is that the story of the Chaillexon lacustrine system is marked by a rather sudden soil and forest development at the Preboreal–Boreal transition (9000 BP ). Copyright © 1998 John Wiley & Sons, Ltd.     

Origins and maturity of organic matter in mid-Cretaceous black shales from ODP Site 1138 on the Kerguelen Plateau

We have conducted elemental, isotopic, and Rock-Eval analyses of Cenomanian–Santonian sediment samples from ODP Site 1138 in the southern Indian Ocean to assess the origin and thermal maturity of organic matter in mid-Cretaceous black shales found at this high-latitude location. Total organic carbon (TOC) concentrations range between 1 and 20 wt% in black to medium-gray sediments deposited around the Cenomanian–Turonian boundary. Results of Rock-Eval pyrolysis indicate that the organic matter is algal Type II material that has experienced modest alteration. Important contributions of nitrogen-fixing bacteria to the amplified production of organic matter implied by the high TOC concentrations is recorded in δ¹⁵N values between −5 and 1‰, and the existence of a near-surface intensified oxygen minimum zone that favored organic carbon preservation is implied by TOC/TN ratios between 20 and 40. In contrast to the marine nature of the organic matter in the Cenomanian–Turonian boundary section, deeper sediments at Site 1138 contain evidence of contributions land-derived organic matter that implies the former presence of forests on the Kerguelen Plateau until the earliest Cenomanian.     

热模拟实验中煤岩显微组分烷烃系列化合物地球化学特征

塔里木盆地侏罗系煤岩显微组分在封闭体系热模拟产物的色质分析表明,各显微组分的正构烷烃系列化合物的碳数均呈双峰型分布。随着温度的升高,后峰相对强度逐渐降低,表明正构烷烃系列化合物在热作用下易发生降解。由于各显微组分化学组成和结构的不同,它们的生烃过程也各不相同。镜质组热降解排烃需要较高热能,以产气为主;壳质组热效应作用下可以有效排烃,为好生烃组分;惰质组虽然生烃潜力有限,但产出烃类的稳定性较好,不易受热降解效应的影响,可以作为气源岩。在整个热模拟实验中,煤岩各显微组分表现为姥鲛烷优势,随着热模拟温度生高,Pr/Ph值表现为先增加后逐渐降低的变化趋势。     

Iron oxide precipitate in seepage of groundwater from a landslide slip zone

Orange precipitate was collected at the mouth of groundwater drainage tubes from the Kumanashi Landslide slip zone in Toyama prefecture, Northwest Japan. Data from XRF, X-ray diffraction, and Mössbauer spectroscopy determined the precipitate as hydrous ferric oxide (HFO) bearing multi-elements such as phosphorous, silica, calcium, etc. The occurrence of HFO may indicate an oxidation of ferrous iron in the percolated groundwater from the slip zone. Moreover, the precipitate iron should be mobilized with groundwater circulation from the slip zone, whose reducing condition was determined by the iron speciation on the same type of landslide profiles within the study area in previous studies. The HFO precipitate may be considered as a secondary reliable indicator to locate the seepage of a slip zone on surface, especially for a landslide newly investigated under wet-warm climate.