Tsutomu Machihara

Diagenesis of biomarkers in Biwa Lake sediments over 1 million years

Abstract Lipid biomarker compounds ( n -alkanoic acids, n -alkanols, sterols, n -alkanes, chlorophyll derivatives) and total lipid carbon in a chloroform extractable fraction, isolated from sedimentary deposits up to ∼2 Ma old of a 1400 m core sample of Lake Biwa, were analyzed by gas chromatography, gas chromatography-mass spectrometry and a thin-layer chromatography-flame ionization detection analyzer (TLC-FID) to investigate their diagenesis and their utilities as biomarkers. The samples are divided into two parts at a depth of 911.4 m. The samples below 911.4 m are basement rock. The upper core is composed of clay from the surface to 249.5 m in depth, and alternated with slit, clay and gravels from 249.5 to 911.4 m. The organic compound carbon, obtained by hydrolysis of the lipid fraction by alkali solution, comprised from 11 to 35% of the total lipid carbon. TLC-FID analysis indicated that significant amounts (about 70–80%) of the total lipid carbon were present in the polar fraction and small proportions were simple lipids. The amounts of n -alkanols were comparable to those of n -alkanoic acids and sterols, while contemporary lacustrine sediments usually contain a larger amount of n -alkanoic acids than of n -alkanols. Normal alkanes, maximizing in abundance at C 27 or C 29 , were most abundant among the lipid compounds. Variation in the distributions of sterols and stanols seemed to preserve the information of input sources and the C 27 /C 29 ratios were correlated to the C/N of the sediments. The composition of n -alkanols, maximizing at C 24 or C 18 , appeared to indicate an aquatic paleoenvironment—a paleowater depth at least in the upper 250 m. Ratios of shorter to longer chain n -alkanoic acids, which had been believed to be an indicator of autochthonous to allochthonous origins, clearly increased with time. A marked correlation between chlorophyll derivatives (ratio of chlorophyll derivatives to total lipid carbon) and paleotemperature was found.

Algal lipids as a possible contributor to the polymethylene chains in kerogen

Lipid fraction and cell-wall materials have been separated from three types of algae (blue green, Microcystis sp.; green, Scenedesmus sp. and diatomaceous Diatoma sp.) and their KMnO4 oxidation products (aliphatic α,ω-C2-C12 dicarboxylic acids; aliphatic normal C14–C24 monocarboxylic acids; benzoic acid and C18 isoprenoidal ketone) examined by gas chromatography and gas chromatographymass spectrometry. The results suggest that the lipid material could make a greater contribution to polymethylene chains in kerogen than the cell-wall material, when the kerogens are mainly derived from algal components.

Study of petroleum generation by compaction pyrolysis—I. Construction of a novel pyrolysis system with compaction and expulsion of pyrolyzate from source rock

Abstract A compaction pyrolysis system was developed to simulate changes of source rocks during the course of burial and subsidence in a sedimentary basin. This system can reproduce a number of phenomena that previous methods could not achieve. With programmed temperature and pressure controllers, the system can simulate the following facets of sediment diagenesis in the natural system: 1. (a) Increase in temperature, overburden pressure, and fluid pressure during burial and subsidence of a formation. 2. (b) Petroleum generation from thermal degradation of kerogen. 3. (c) Expulsion of interstitial and bound water during compaction of sedimentary rocks. 4. (d) Expulsion of oil and gas generated. 5. (e) Phase changes of clay minerals, zeolites, and silica minerals due to increases in temperature and pressure. In addition, comparison of compaction pyrolysis with non-compacting hydrous pyrolysis shows the following: 1. (1) The composition of gas from compaction pyrolysis was similar to that of natural gases, containing only small proportions of unsaturated hydro-carbons. In contrast, gas from hydrous pyrolysis contain 5–10% unsaturated hydrocarbons. 2. (2) Both compaction and hydrous pyrolysis produced oils resembling crude oil in the natural system. 3. (3) While macerals after hydrous pyrolysis showed abundant holes by evaporation of volatile products by pyrolysis, macerals after compaction pyrolysis showed fewer holes. However, in samples from compaction pyrolysis, deformation from compaction was observed. 4. (4) During the compaction pyrolysis experiment, expulsion of oil and gas from source rock (compaction cell) was observed with the increase in fluid pressure and fluid volume. In summary, compaction pyrolysis permits a more realistic reproduction of natural phenomena, as a result of which a more detailed study of petroleum generation and migration is possible.

Early stage incorporation of biolipids into kerogen in a lacustrine sediment: Evidence from alkaline potassium permanganate oxidation of sedimentary lipids and humic matter

Abstract Lipids, fulvic acid, humic acid and kerogen were isolated from a lacustrine sediment in which the organic matter is probably derived predominantly from phytoplankton (Lake Haruna, Japan). An alkaline KMnO 4 oxidation study of the organic matter showed that distributions of polymethylene chain lengths in the lipids, humic acid and kerogen fractions are almost the same. The polymethylene chains in the sediment are dominant in the kerogen, lipids and humic acid, their relative abundance estimated by the oxidation being: kerogen (42% of the total amounts of polymethylene chains estimated) > lipids (38%) > humic acid (19%) > fulvic acid (1%). It was concluded that algal lipids may have been incorporated into the kerogen and humic acid fractions after the death of the algae and during, after, their deposition.

Steranes and triterpanes in the Beacon Supergroup samples from southern Victoria Land in Antarctica

Steranes and triterpanes in Beacon Supergroup samples (sedimentary rock and silicified wood) from Allan Hills and Carapace Nunatak of southern Victoria Land in Antarctica were studied to elucidate sources of organic materials, sedimentary paleoenvironment and thermal history after deposition. Relative abundances of C27, C28 and C29 steranes and visual kerogen results of Beacon Supergroup samples from Allan Hills imply that organic materials in the sedimentary paleoenvironments are contributed mainly by vascular plants with some influence of microorganisms, while those of the Carapace Nunatak sample may be largely due to fern spores. The pristanephytane and pristaneheptadecane ratios of the samples were generally close to unity and between 0.50 and 0.99, respectively, suggesting that the sedimentary paleoenvironment was shallow lacustrine with alternating oxic and anoxic conditions. The (22S22R)-17α(H),21β(H)-C31-C33 triterpane ratios are approximately at thermal equilibrium values (ca. 1.5) in most samples, while the (20S20R)-5α(H), 14α(H), 17α(H)-C29 sterane ratios and the (20R + 20S)-5α(H), 14β(H), 17β(H)5α(H), 14α(H), 17α(H)-C29 sterane ratios vary from 0.0 to 1.1 and from 0.0 to 1.4, respectively. Most of the (20S20R)-5α(H), 14α(H), 17α(H)-C29 sterane ratios did not reach thermal equilibrium values. The correlation coefficient between the (20S20R)-5α(H), 14α(H), 17α(H)-C29 sterane ratios and (20R + 20S)-5α(H), 14β(H), 17β(H)5α(H), 14α(H), 17α(H)-C29, sterane ratios is very high (0.96). These variable maturities probably reflect thermal effects of basaltic dikes on the Beacon Supergroup at Allan Hills and Carapace Nunatak during Jurassic time. Thermal stresses on the Beacon Supergroup prior to basaltic intrusion have been estimated to be quite low, so the paleotemperatures of this formation have been quite low.

Structural changes of young kerogen during laboratory heating as revealed by alkaline potassium permanganate oxidation

Abstract Kerogen was isolated from a marine sediment from Tanner Basin, offshore California. Samples of the kerogen were heated under an inert atmosphere at various temperatures and times. The heated and unheated kerogens were subjected to alkaline potassium permanganate oxidation followed by GC/ MS analysis of the products. The kerogens yielded primarily aliphatic C 2 –C 14 α,ω-dicarboxylic acids and benzene mono-to-pentacarboxylic acids. Yields of aliphatic dicarboxylic acids from kerogen decreased with increasing thermal alteration. Yields of benzenecarboxylic acids increased steadily with increasing thermal alteration. The data support the concept that thermal maturation during natural burial of this type of kerogen results in the generation of aliphatic hydrocarbons from an increasingly aromatic residue.

CHARACTERISTICS OF KEROGENS FROM RECENT MARINE AND LACUSTRINE SEDIMENTS : GC/MS ANALYSIS OF ALKALINE PERMANGANATE OXIDATION PRODUCTS

Abstract Extensive studies have been carried out by many workers on sedimentary kerogens. However little is known of the details of the chemical structure of kerogens and of the relation between immature and mature kerogens on a molecular basis. The present authors have been studying young kerogens (kerogens in young sediments). This study aimed to determine the structural pecularities of young kerogens from marine and lacustrine sediments. Kerogen samples were isolated from marine (Tanner Basin, offshore California) and freshwater lake (Lake Haruna, Japan) sediments. The kerogens belong to Type II or III. These kerogens were oxidized by alkaline permanganate and analyzed for their degradation products by GC/MS. The major degradation products are aliphatic normal α,ω-dicarboxylic acids with carbon numbers of 4–14; aliphatic normal monocarboxylic acids with carbon numbers of 8–26, and benzene mono-, di- and tetracarboxylic acids. A marked difference between kerogens from two environments was observed in the distribution of aliphatic dicarboxylic acids: C 4 -C 10 acids are higher for marine kerogens than for lacustrine kerogens. This difference is probably due to the difference in the fatty acid composition of precursory materials (e.g. phytoplankton). These results indicate that the molecular structure of kerogens reflects generally the molecular composition of precursory materials, and consequently the present alkaline KMnO 4 oxidation method is useful for subtyping of kerogens.

Possible carotenoid-derived structures in fossil kerogens

The unique KMnO/sub 4/ degradation products of ..beta..-carotene, previously identified as 2,2-dimethyl succinic acid (C/sub 6/) and 2,2-dimethyl glutaric acid (C/sub 7/) have been found in the oxidation products of Green River shale (Eocene, 52 x 10/sup 6/ yr) and Tasmanian Tasmanite (Permian, 220-274 x 10/sup 6/ yr) kerogens. These two compounds were also detected in KMnO/sub 4/ degradation products of young kerogens from lacustrine and marine sediments. The results indicate that kerogens incorporated carotenoids (possibly ..beta..-carotene) at the time of kerogen formation in surface sediments. Both acids are useful markers to obtain information on biological precursors contributing to the formation of fossil kerogens.