Senescence- and death-related alteration of chlorophylls and carotenoids in marine phytoplankton

This report extends previous work ([Louda et al., 1998a] and [Louda et al., 1998b]. Chlorophyll degradation during senescence and death. Organic Geochemistry 29, 1233–1251.) in which we detailed type-I (alteration) and -II (destruction) degradation of chlorophyll with representative fresh water phytoplankton. The present study covers similar experiments with marine phytoplankton, namely, a cyanobacterium (“ANA” Anacystis sp), a coccolithophore (“COC” Coccolithophora sp.), a dinoflagellate (“GYM” Gymnodinium sp.) and two diatoms (“CYC” Cyclotella meneghiniana and “THAL” Thalassiosira sp.). Mg loss (‘pheophytinization') was rapid and continuous in all species under room-oxic conditions and slow or sporadic under anoxic conditions. The proportion of dephytylated pigments (pheophorbides-a, chlorophyllides-a), relative to the phytylated forms (chlorophyll-a, pheophytins-a), increased over the first year under room-oxic conditions and in room-anoxic conditions only in “CYC”. Pheophorbide-a was converted to pyropheophorbide-a within 15 months only in “THAL” and “ANA”, and slightly in “COC”. After 9–15 months of oxic incubation, “COC” was found to contain traces of purpurin-18 phytyl ester. Consideration of carotenoid pigments is also included herein. All fucoxanthin containing species, except “THAL”, exhibited conversion of fucoxanthin to fucoxanthinol in room-oxic conditions. Diadinoxanthin was rapidly de-epoxidized to give diatoxanthin within the first 2–4 weeks. Diatoxanthin then disappeared from all species by 15 months with a concurrent increase in a pigment which we tentatively identify as a cis-zeaxanthin. Incubations of pure cultures are found to be an effective way by which to model the early type-I reactions for both chlorophylls and carotenoids. The influence of oxygen during senescence-death and the onset of early diagenesis is of paramount importance. The absence of oxygen and, by inference, aerobic microbiota, retards the breakdown of these pigments dramatically.     

The optical features and hydrocarbon-generating model of “barkinite” from Late Permian coals in South China

Leping coal is known for its high content of “barkinite”, which is a unique liptinite maceral apparently found only in the Late Permian coals of South China. “Barkinite” has previously identified as suberinite, but on the basis of further investigations, most coal petrologists conclude that “barkinite” is not suberinite, but a distinct maceral. The term “barkinite” was introduced by (State Bureau of Technical Supervision of the People's Republic of China, 1991, GB 12937-91 (in Chinese)), but it has not been recognized by ICCP and has not been accepted internationally.In this paper, elemental analyses (EA), pyrolysis-gas chromatography, Rock-Eval pyrolysis and optical techniques were used to study the optical features and the hydrocarbon-generating model of “barkinite”. The results show that “barkinite” with imbricate structure usually occurs in single or multiple layers or in a circular form, and no definite border exists between the cell walls and fillings, but there exist clear aperture among the cells.“Barkinite” is characterized by fluorescing in relatively high rank coals. At low maturity of 0.60–0.80%R_o, “barkinite” shows strong bright orange–yellow fluorescence, and the fluorescent colors of different cells are inhomogeneous in one sample. As vitrinite reflectance increases up to 0.90%R_o, “barkinite” also displays strong yellow or yellow–brown fluorescence; and most of “barkinite” lose fluorescence at the maturity of 1.20–1.30%R_o. However, most of suberinite types lose fluorescence at a vitrinite reflectance of 0.50% Ro, or at the stage of high volatile C bituminous coal. In particular, the cell walls of “barkinite” usually show red color, whereas the cell fillings show yellow color under transmitted light. This character is contrary to suberinite.“Barkinite” is also characterized by late generation of large amounts of liquid oil, which is different from the early generation of large amounts of liquid hydrocarbon. In addition, “barkinite” with high hydrocarbon generation potential, high elemental hydrogen, and low carbon content. The pyrolysis products of “barkinite” are dominated by aliphatic compounds, followed by low molecular-weight aromatic compounds (benzene, toluene, xylene and naphthalene), and a few isoprenoids. The pyrolysis hydrocarbons of “barkinite” are mostly composed of light oil (C₆–C₁₄) and wet gas (C₂–C₅), and that heavy oil (C₁₅⁺) and methane (C₁) are the minor hydrocarbon.In addition, suberinite is defined only as suberinized cell walls—it does not include the cell fillings, and the cell lumens were empty or filled by corpocollinites, which do not show any fluorescence. Whereas, “barkinite” not only includes the cell walls, but also includes the cell fillings, and the cell fillings show bright yellow fluorescence.Since the optical features and the hydrocarbon-generating model of “barkinite” are quite different from suberinite. We suggest that “barkinite” is a new type of maceral.     

Solid bitumen reflectance and Rock-Eval Tmax as maturation indices: an example from the “Nordegg Member”, Western Canada Sedimentary Basin

Marine, organic-rich rock units commonly contain little for vitrinite reflectance (VR₀) measurement, the most commoly used method of assessing thermal maturity. This is true of the Lower Jurassic “Nordegg Member”, a type I/II, sulphur-rich source rock from the Western Canada Sedimentary Basin. This study examines the advantages and pitfalls associated with the use of Rock-Eval T_max and solid bitumen reflectance (BR₀) to determined maturity in the “Nordegg”. Vitrinite reflectance data from Cretaceous coals and known coalification gradients in the study area are used to extrapolate VR₀ values for the “Nordegg”.T_max increases non-linearly with respect to both BR₀ and extrapolated VR₀ values. A sharp increase in the reflectaance of both solid bitumen and vitrinite occurs between T_max 440–450°C, and is coincident with a pronounced decrease in Hydrogen Index values and the loss of solid bitumen and telalginite fluorescence over the same narrow T_max interval. This T_max range is interpreted as the main zone of hydrocarbon generation in the “Nordegg”, and corresponds to extrapolated VR₀ values of 0.55–0.85%. The moderate to high sulphur contents in the kerogen played a significant role in determining the boundaries of the “Nordegg” oil window.A linear relationship between BR₀ and extrapolated VR₀, as proposed elsewhere, is not true for the “Nordegg”. BR₀ increases with respect to extrapolated VR₀ according to Jacob's (1985) formula (VR₀=0.618×(BR₀)+0.40) up to VR₀≈0.72% (BR₀≈0.52%). Beyond this point, BR₀ increases sharply relative to extrapolated VR₀, according to the relatioship VR₀ = 0.277 × (BR₀) + 0.57 (R² = 0.91). The break in the BR₀−VR₀ curve at 0.72%VR₀ is thought to signifiy the peak of hydrocarbon generation and represents a previously unrecognized coalification jump in the solid bitumen analogous to the first coalification jump of liptinites.     

Geochemistry of hydroxy acids in sediments—I. Some freshwater and brackish water lakes in Japan

Series of α, β, ω and (ω-1) hydroxy fatty acids (FAOHs) were determined in several freshwater and brackish water lacustrine sediments in Japan. Analytical procedure used was digestion of the solvent-extracted sediment with HF/HCl followed by solvent and saponification extraction of the residue. Abundances of α/β and ω-FAOH determined by this procedure were 2–3 times higher than those obtained by single alkaline saponification and of the same order with those provided by HCl hydrolysis. Major portion of α/β-FAOH was obtained by solvent extraction of the acid-treated sediments, while subsequent alkaline saponification was needed for the majority of ω-FAOH to be recovered. Thus determined FAOHs comprised 33–61% (Av. = 42%) of the “bound” acid constituents in the lacustrine surface sediments. The α/β and ω-FAOH composition was principally the same among the samples examined, except for relative proportions of the iso to anteiso C₁₅ and C₁₇ ß(α)-FAOH, which showed significant variations in the ranges of 0.30–1.1 and 0.46–1.5, respectively. In the holomictic lakes, the ratios together with the same ratios of the “bound” branched monocarboxylic acids tended to decrease with increasing water depth of the lakes, suggesting that the ratios may indicate an extent of the early diagenetic alteration of the bacteria-derived lipids either in water column or in surface sediment.     

Calcareous nannoplankton, planktonic foraminiferal, and carbonate carbon isotope stratigraphy of the Cenomanian–Turonian boundary section in the Ultrahelvetic Zone (Eastern Alps, Upper Austria)

Ultrahelvetic units of the Eastern Alps were deposited on the distal European continental margin of the (Alpine) Tethys. The Rehkogelgraben section (“Buntmergelserie”, Ultrahelvetic unit, Upper Austria) comprises a 5 m thick succession of upper Cenomanian marl-limestone cycles overlain by a black shale interval composed of three black shale layers and carbonate-free claystones, followed by lower Turonian white to light grey marly limestones with thin marl layers. The main biostratigraphic events in the section are the last occurrence of Rotalipora and the first occurrences of Helvetoglobotruncana helvetica and Quadrum gartneri. The thickest black shale horizon has a TOC content of about 5%, with predominantly marine organic matter of kerogen type II. Vitrinite reflectance and Rock-Eval parameter T_max (<424 °C) indicate low maturity. HI values range from 261 to 362 mg HC/g TOC. δ¹³C values of bulk rock carbonates display the well documented positive shift around the black shale interval, allowing correlation of the Rehkogelgraben section with other sections such as the Global Boundary Stratotype Section and Point (GSSP) succession at Pueblo, USA, and reference sections at Eastbourne, UK, and Gubbio, Italy. Sediment accumulation rates at Rehkogelgraben (average 2.5 mm/ka) are significantly lower than those at Pueblo and Eastbourne.     

Environmental control of carbon isotope variations in Pennsylvania black-shale sequences, Midcontinent, U.S.A.

A reversal of the conventional carbon isotope relationship, “terrestrial-lighter-than-marine” organic matter, has been documented for two Pennsylvanian (Desmoinesian) cyclothemic sequence cores from the Midcontinent craton of the central United States. “Deep” water organic-rich phosphatic black shales contain a significant proportion of algal-derived marine organic matter (as indicated by organic petrography, Rock-Eval hydrogen index and ratios) and display the lightest δ¹³C-values (max −27.80‰ for kerogen) while shallower water, more oxic facies (e.g. fossiliferous shales and limestones) contain dominantly terrestrial organic matter and have heavier δ¹³C_kerogen-values (to −22.87‰ for a stratigraphically adjacent coal). δ¹³C-values for extract fractions were relatively homogeneous for the organic-rich black shales with the lightest fraction (often the aromatics) being only 1‰, or less, more negative than the kerogen. Differences between extract fractions and kerogens were much greater for oxic facies and coals (e.g. saturates nearly 5‰ lighter than the kerogen).A proposed depositional model for the black shales calls upon a large influx of nutrients and humic detritus to the marine environment from the laterally adjacent, extremely widespread Pennsylvanian (peat) swamps which were rapidly submerged by transgression of the epicontinental seas. In this setting marine organisms drew upon a CO₂-reservoir which was in a state of disequilibrium with the atmosphere, being affected by isotopically light “recycled-CO₂” derived from the decomposition of peaty material in the water column and possibly from the anoxic diagenesis of organic matter in the sediments.     

Middle Pleistocene climate and habitat change at Zhoukoudian, China, from the carbon and oxygen isotopic record from herbivore tooth enamel

The Pleistocene deposits at Zhoukoudian, often referred to as the “Peking Man” site, contain dental remains from a diverse group of herbivores, including Equus sanmeniensis, Cervus elaphus, Cervus nippon, Megaloceros pachyosteus, Sus lydekkeri, and Dicerorhinus choukoutienensis. The carbon and oxygen isotopic compositions of structural carbonate within the enamel of these teeth are used to reconstruct the paleodiet and paleoenvironment of the mammals. The δ¹³C values of enamel from Zhoukoudian range from −2.3‰ to −13.0‰, indicating that these mammals consumed between 25% and 100% C₃ plants. The presence of significant amounts of C₄ plants in the diets of some herbivore species indicates that at the onset of the Middle Pleistocene local habitats included mixed C₃/C₄ vegetation. By approximately 470,000 yr ago, C₃ plants dominated the diets of herbivores studied, suggesting that the abundance of C₄ flora had decreased in the area. For all deer analyzed in this study, the values of δ¹³C and δ¹⁸O decrease substantially from about 720,000 to 470,000 yr ago. This trend may be due to a strengthening of the winter monsoon during the Middle Pleistocene.     

The Cenomanian/Turonian Boundary Event (CTBE) at Wunstorf, north-west Germany, as reflected by marine palynology

The Cenomanian/Turonian Boundary Event (CTBE) at Wunstorf, north-west Germany, has been analysed palynologically by high resolution sampling to reconstruct changes in relative sea-level and water mass character within photic zone waters. Based on changes in the ratio of terrigenous sporomorphs to marine palynomorphs (t/m index), the distribution of the organic-walled algal taxa as well as of selected dinocyst taxa and groups the section can largely be subdivided into pre-“plenus-bed” and post-“plenus-bed” intervals, reflecting different stages of third-order relative sea-level cycles and/or changes in water mass influence in the photic zone. Accordingly, the pre-“plenus-bed” interval is placed in a transgressive systems tract starting at the “facies change” event (C. guerangeri/M. geslinianum ammonite Zone boundary) with the maximum flooding surface at the top of the “Chondrites II” bed (top of R. cushmani Biozone). A highstand systems tract is suggested from the base of the “plenus-bed” up the base of the “fish-shale” event. Within the “fish-shale” event interval, a transgressive systems tract is suggested to start at the base of the thin, grey-green marly interbed. The Cenomanian/Turonian boundary proper, as defined by the first occurrence of Mytiloides spp., as well as the lowermost Turonian are located within the initial phase of a transgressive systems tract. With respect to water mass characteristics within photic-zone waters, the pre-“plenus-bed” interval is predominantly characterized by warm water masses that changed gradually towards the deposition of the “Chondrites II” bed, where a strong influence of cool and/or salinity-reduced waters is indicated by various palynological proxies. Within the post-“plenus-bed” interval a mixture and/or alternation of warmer and cooler waters is indicated, with the warmer water influence increasing gradually towards and within the Lower Turonian stage. The increased proportions of prasinophytes within the “Chondrites II” bed and parts of the “fish-shale” interval may indicate availability of reduced nitrogen chemospecies, especially ammonium, within photic-zone waters as a function of a vertical expansion of the oceanic O₂-minimum zone.     

Effect of maturity on carbon isotope ratios of oils and condensates

For modelling isotopic variations in oils it is convenient to differentiate the effects of oil generation ( 100–150°C) from the effects of oil to gas cracking ( 150–180°C). During generation, δ¹³C of kerogen may increase by up to 1% due to release of isotopically light oil and gas, although most kerogens show little or no chan δ¹³C of the generated oil increases by between 0 and 1% (av. 0.5%) due to mixing of isotopically heavy oil with an initial isotopically light unbound fraction, possibly of bacterial origin. The change occurs mostly over the first 20% of generation. During oil to gas cracking, kinetic isotope effects become important and the effect on δ¹³C of the remaining oil can be modelled as a Rayleigh process. δ¹³C increases by 1.5% by 50% cracking. Insufficient data are available to calibrate the effects at higher levels of cracking, and modelling these variations is hindered by a lack of understanding of the mechanism of pyrobitumen formation. However, increases greater than about 4% are unlikely to be observed. With increasing maturity, the low molecular weight fractions become isotopically heavy faster than the high molecular weight fractions. As a result, any separation of the low molecular weight fraction into a gas phase (“condensate formation”) will produce an isotopic difference between oil and condensate that depends on maturity. In the early stages of generation the condensate may be up to 1% lighter than the remaining oil. With increasing maturity, this difference at first decreases and then increases in the opposite sense. By half way through oil to gas cracking the condensate may be 1.5% heavier than the residual liquid. More subtle rearrangement reactions may result in small, but significant, changes to the shape of the isotope “type-curves” when different oil fractions are compared.     

Experimental deformation of diopside and websterite

Diopside single-crystals, oriented favorably for twin gliding on both systems: (001) [100] and (100)[001] have been deformed in a Griggs apparatus using talc as pressure medium. The latter mechanism is dominant at temperatures (T) below 1050° C at strain rates () of 10⁻³ sec⁻¹, and below 800° C at ; at higher temperatures translation gliding on (100)[001] accompanied by syntectonic recrystallization is dominant but other glide systems also operate. Tests at a single set of conditions, T- and -incremental tests and stress-relaxation experiments have been carried out on websterite (68% CPX, 32% OPX), both in talc (“wet”) and talc-AlSiMag (“dry”) assemblies. Most tests were performed in the high-T regime, where syntectonic recrystallization and “relatively nonselective” glide are dominant. The mean size of recrystallized clinopyroxenes (D, μm) appears to be related to stress (σ, kb) as D = 60σ^−0.9. The mechanical data fit the power law exp(-Q/RT)σⁿ, where for the “wet” experiments A = 10^5.9kb⁻ⁿsec⁻¹, Q = 91.2 kcal/mole, n = 5.3; for σ < 3.5 kb n appears to decrease to 3.3. For the “dry” experiments A = 10^2.2, Q = 77.9, and n = 4.3 for σ < 7.0 kb. Clinopyroxene in the upper mantle occurs as ca. 0–15% mixed phase in peridotites and websterites occur as thin layers. Stresses in these materials will then be near those in the olivine-rich matrix. At , the equivalent viscosity of dry websterite is less than that of dry dunite at depths to 60 km but it increases rapidly at higher pressures; at 240 km it is 10⁶ greater than that of dunite. This may account for the low strains and passive behavior observed for clinopyroxene crystals in most peridotites and websterites, that presumably have formed at great depth. Attenuated folds of websterite in peridotite—evidence of more ductile behavior—may then have formed at shallower levels; alternatively they may have formed under “wet” conditions.     

Geochemical characterisation of organic matter in Keg River Formation (Elk point group, Middle Devonian), La Crete Basin, Western Canada

Carbonates from the Keg River Formation, La Crete Basin, Alberta, western Canada were examined in order to define: (a) oil source rock potential; (b) bulk maceral composition; (c) extract yield; and finally (d) facies variations using PY-GC-MS. Thirty samples from 6 different wells were examined from the lower Keg River member and 4 from the upper Keg River member using conventional geochemical methods. As maturity differences are absent within the sample set, variations in TOC, T_max, hydrogen index, organic petrography and extract yields are caused by variability in organic matter input, which is revealed by molecular characterisation using PY-GC-MS. Lower Keg River member bituminous wackestones are excellent potential source rocks containing Types I–II and Type II organic matter. Types I–II organic matter contains large well preserved (up to 200μm in diameter) thick-walled Tasmanites (10–15% of sample) and akinete algal cells indicative of algal blooms within an amorphous bituminite. Type II organic matter contains a higher proportion of degraded alginites/bituminite relative to well-preserved alginites. Extract yields (mg/g TOC) were seen to increase from Types I–II to Type II organic matter. PY-GC-MS revealed that 1,2,3,4-tetramethylbenzene was a major peak in most samples. This is a pyrolysis product arising from β-cleavage of C₄₀ diaromatic carotenoids incorporated within the kerogen during diagenesis. The source of this compound is thought to be from an unknown diaromatic compound with a 2,3,6-/3,4,5-trimethyl substitution pattern and isorenieratene, which is specific to photosynthetic green sulphur bacteria (Chlorobiaceae) suggesting that the photic zone was at least partially anoxic during deposition of these samples. The relative abundance of this compound/n-C11-alkene and organic sulphur (calculated from the thiophene ratio) both increase from Types I–II to Type II organic matter. This trend was grossly similar to the trend seen in the variability of extract yield with hydrogen index. A similar trend for HI and T_max indicates samples containing a higher proportion of degraded alginites/bituminite relative to well-preserved alginite are more labile than Type I–II organic matter. Upper Keg River member marls contain Type II organic matter, which is characterised by heavily degraded algal material within a bituminous groundmass. Pyrolysates of two of the marl samples contain only low amounts of 1,2,3,4-tetramethylbenzene, in contrast to the bituminous wackestones, indicating that the depositional environment/source input was different during deposition of the marl samples. Although both marls contain similar organic matter, their pyrolysates were significantly different. One marl (1141.9 m) was highly paraffinic containing dominantly short-chain alkene/alkane doublets, while the other marl (1137.6 m) contained a bimodal n-alkane/alkene distribution and high amounts of alkylphenols, which may be derived from preservation of resistant algal polyphenolic molecules or suggest a terrestrial input.     

Characterisation of brown coal humic acids and modified humic acids using pyrolysis gcms and other techniques

It has been proposed that Victorian brown coal can be considered as a two-component structure — a lignocellulosic “host”, containing various amounts of weakly bound or entrapped “guest” material together with very small amounts of inorganic and/or mineral matter. The latter predominantly consists of wax esters and/or terpenoid material. In this paper we describe attempts to gain structural information regarding the more complex, “host” component of the coal. Our initial model compound has been humic acid that can be readily obtained from the coal by alkaline extraction. It has been found that “pure” humic acid, free from material associated with the “guest” components of the coal, can be obtained by a highly selective, low-yielding alkaline extraction. This humic acid has been studied by nmr spectroscopy and pyrolysis gas chromatography-mass spectroscopy (py-gc/ms). The products arising from py-gc/ms have been compared with those obtained from similar pyrolysis of whole coals. Alkylation of humic acids using alkyl halides in the presence of base has been successfully carried out and reactivity of the resulting materials compared with those of the parent coal and humic acid.     

Surface carbonate and land-derived clastic marine sediments from southern Chile: mineralogical and geochemical investigation

Surface carbonate and land-derived deposits in the sea off southern Chile were investigated for their mineralogical and geochemical composition. The data were related to environmental features and compared with those of similar temperate and polar carbonate deposits from Tasmania, New Zealand, Arctica, and Antarctica. The mineralogy of the siliciclastic fraction is typical of cold areas and is mainly composed of chlorite, mica, quartz, feldspars and amphibole. The CaCO₃ content varies from 30 to 90%; carbonate mineralogy is made up of low-Mg calcite, high-Mg calcite and minor amounts of aragonite. The Ca, Mg, Sr, Fe, and Mn contents of bulk carbonates and some selected skeletal hard parts are comparable to those of carbonates from Tasmania. The elemental composition is mainly related to carbonate mineralogy, skeletal components, and seawater conditions. The δ¹³C and δ¹⁸O values of carbonates are positive, and their field falls between the “seafloor diagenesis” and “upwelling water” trend lines, because the sediments are likely to be in equilibrium with waters of Antarctic origin. The mineralogical, elemental, and isotopic compositions of carbonates from southern Chile show better similarities with the “temperate” carbonates from Tasmania and New Zealand than with the “polar” carbonates from Arctica and Antarctica. Carbonate deposition is allowed by the low terrigenous input, the low SPM concentration and, probably, the upwelling of seawater from Antarctica.     

Late Barremian to early Aptian calcareous nannofossil paleoceanography and paleoecology from the Ocean Drilling Program Hole 641C (Galicia Margin)

Calcareous nannofossil assemblages at Site 641C (Galicia Margin, North Atlantic) were investigated in order to determine changes in fertility and temperature of surface waters. Taxa such as Zeughrabdotus spp. <3.5 μm, Biscutum constans, Discorhabdus rotatorius and Diazomatolithus lehmanii, which thrived in higher fertility conditions, are particularly abundant across the CM0 interval as opposed to those with oligotrophic affinities such as Watznaueria spp. and Nannoconus spp., which are generally reduced in abundance. The abundances of nannoconids are much lower than those observed in Tethyan sections, indicating higher fertility conditions. Slumpings and low recovery prevent the identification of the onset of the “nannoconid crisis”, but a sharp drop in nannoconid abundances, observed prior to the CM0 interval, correlates with the “nannoconid decline” observed in several Tethys sections.The normalized ratio between low and high fertility taxa (Fertility Index) was used to characterize the nannofossil assemblages in terms of productivity changes. The highest values of the Fertility Index were observed across magnetic chron CM0. The paucity of cold water taxa such as Seribiscutum spp. and Repagulum parvidentatum suggests warm water conditions throughout the deposition of upper Barremian–lower Aptian sediments on the Galicia Margin.     

Evidence for cyclic reactions between andalusite, “sericite” and sillimanite, mount franks area, willyama complex N.S.W

In the Mt. Franks area of the Willyama Complex, microfabric evidence suggests that the alteration of andalusite to sillimanite has taken place by a process similar to that suggested by Carmichael (1969). Andalusite is pre- to syn-S₂ in age. Alteration to “sericite” has resulted in the formation of “sericite” laths, some of which are crenulated about S₂, and some which are syn- and post-S₂. “Fibrolite” occurs in these andalusite—“sericite” aggregates within the sillimanite zone and is wholly embedded in “sericite”. “Fibrolite” is pre- to syn-S₂ in age. This evidence is interpreted as suggesting that the formation of sillimanite from andalusite took place via a “sericite” phase.Further microfabric observations are interpreted to imply constant volume for the reaction aluminosilicate → “sericite”. This suggests a situation in which Al³⁺ is relatively mobile but Al⁴⁺ is relatively immobile. This suggestion differs from Carmichael's (1969) idea of Al³⁺ immobility.     

Methane-induced dolomite “chimneys” on the Kuroshima Knoll, Ryukyu islands, Japan

The Kuroshima Knoll is about 26 km south of Ishigaki Island in the southern part of the Ryukyu Arc. The area is considered to be the source area of “The 1771 Yaeyama Earthquake Tsunami”, which was due to the submarine landslide caused by an earthquake. It has been cleared from some investigations using “Dolphin 3K” and “Shinkai 2000” that there are large-scale dead Calyptogena colonies, many gravels of fallen dolomite chimneys and carbonates on the top of the Knoll [Matsumoto, T., Uechi, C., Kimura, M., 1997; Machiyama, H., Matsumoto, T., Matsumoto, R., Hattori, M., Okano, M., Iwase, R., Tomaru, H., 2001b.]. Carbonates of Kuroshima Knoll have various shapes and macroscopic textures. These have been classified into 4 types; shell crust (pavement), chimney, burrow, and nodule. It is clear that all chimney and burrow carbonates are composed of dolomite, while shell curst and nodule are composed of calcite, sometimes both calcite and dolomite. These carbonates are considered to have been formed by cold seep, because they are characterized by the light carbon isotopic ratio (semi-biogenic) and the heavy oxygen isotopic ratio. This suggests that methane hydrate layers develop under this survey area and the water that has the heavy oxygen and the light carbon isotopic ratio is derived from the dissociation of methane hydrate.     

Biomarkers in upper Holocene Eastern North Sea and Wadden Sea sediments

Total extracts of sediment cores from five different stations in the North Sea and Wadden Sea were analysed for their biomarker composition. Only sediments of the Skagerrak contained significant amounts of marine biomarkers (mainly alkenones), other sites contained predominantly terrestrial biomarkers. Bioturbation in the Skagerrak is, however, far too high to determine sea surface temperature (SST) changes within short time intervals. These results indicate that biomarkers contained in these sediments are not useful to reconstruct climate fluctuations during the upper Holocene. High amounts of α-, β- and ω-hydroxy fatty acids as well as small amounts of α, β-dihydroxy fatty acids were released from the insoluble organic material of the sediments from the Wadden Sea station, indicating a significant input of the eelgrass Zostera marina. This was confirmed by microscopic observations. This is the first time the α,β-dihydroxy fatty acids have been found in a sediment core and they have proven to be potential biomarkers for these seagrass species.     

Porphyry copper deposits of the CIS and the models of their formation

Deposits of the “porphyry” family (essentially porphyry copper and gold-porphyry copper, gold-bearing porphyry molybdenum-copper, gold-containing porphyry copper-molybdenum and porphyry molybdenum deposits) are associated in time and space with granitoid magmatism mainly in Phaerozoic volcano-plutonic belts. Whatever their age, the deposits belong to two types of belts: basaltic belts, representing axial zones of island arcs, or andesitic belts formed within active continental (Andean-type) margins.The petrochemistry of ore-bearing magmatism related to the nature of the substratum of volcano-plutonic belts, reveals a number of essential characteristics, both in composition and zonation of wallrock alteration and ore mineralization. These characterisics enabled previous researchers to establish four models of porphyry copper deposits based on their lithologic associations, e.g., “diorite”, “granodiorite”, “monzonite” and “granite”.Pophyry copper deposits are thought to be the product of self-generating “two-fluid mixing” ore-magmatic systems. Porphyry intrusions are pathways for energy and metals from deep-seated magma chambers, of which the upper mineralized parts are accessible for observation. The relationship between magmatic fluids and meteoric water participating in the ore-forming processes (dependent on the structural-petrophysical conditions of formation), provide a subdivision for the porphyry copper ore-magmatic systems into three types: “open”, “closed” and “transitional”.Concurrently, a common trend in the evolution of the systems has been established, from a nearly autoclave regime of structural-and ore-forming processes to a gradual increase in the importance of hydrothermal recycling. The completeness of the OMS (ore-magmatic system) development according to this scheme, which determines the existence of various OMS types, depends on many factors, the most important being the depth of formation of porphyry intrusive bodies, the petrophysical peculiarities of the host rocks and the palaeohydrogeological conditions of ore deposition.Although rock fracturing (especially defluidization: second boiling) and contraction are caused by the same mechanisms, the stockwork growth in “open” and “closed” systems, relative to the wall rock, takes place in opposite directions, primarily due to different petrophysical parameters of the near-stock environment.In “open” systems structural and ore metasomatic processes are finalized. Fractures extend progressively from porhyry stocks into the marginal parts of the intrusive framework and extension of large-scale recycling of magmatic and activated meteoric water, in the same direction, result in the formation of ore-bearing stockworks. These are large in all dimensions, cover mainly hanging-wall zones and are characterized by clearly defined concentric mineral zoning and extensive geochemical haloes.In a “closed” OMS with centripetal growing fractures, hydrothermal convection is stunted. The vertical extension of recycling cells is restricted and the volume of meteoric water involved in circulation during the period of ore deposition is relatively small. As a result, relatively small intra-intrusive lenticular stockworks are developed which are characterized by close co-existence of several generations of mineralization with fragmentary preservation of the earliest ones. These are characterized by the elements of “reverse” zoning, increased density of the veinlets and metal content, as well as poorly developed hanging-wall dispersion haloes.     

Magnetic overprints in granitoids and metamorphic rocks from Limousin (France): evidence for Late Variscan rotations, crustal folding and tilting

Generally, the lack of bedding criteria in basement units hampers the interpretation of paleomagnetic results in terms of geotectonics. Nevertheless, this work demonstrates that successive remagnetizations recorded in Early Carboniferous metamorphic and plutonic units, without clear bedding criteria, can be used to constrain a polyphased tectonic evolution consisting of a regional clockwise rotation, followed by a folding phase, a tilting phase and a second regional clockwise rotation.Metamorphic, ultrabasic, tonalitic and granitic rocks from different parts of Limousin (western French Massif central; 45.5°N/1.25°E), which underwent metamorphism during Devonian–Early Carboniferous or were intruded in the Early–Middle Carboniferous, were sampled in order (a) to identify the magnetic overprinting phases and the related tectono-magmatic events and (b) to constrain the regional and plate tectonic evolution of Limousin. Paleomagnetic results from 32 new and 26 sites investigated previously show that at least 90% of the magnetization isolated in rocks older than 330 Ma are overprints. In agreement with results from adjacent areas of the Variscan belt, the major overprinting phases occurred: (a) in the last stages of the major exhumation phase [332–328 Ma; mean Virtual Geomagnetic Pole (VGP) “Cp”: 37°N/70.5°E], (b) during the post-collisional syn-orogenic extension (325–315 Ma; VGP “B”: 11°N/114°E), (c) in the Latest Carboniferous and Early Permian (VGP “A1”: 27°N/149°E) and (d) in the Late Permian (VGP “A”: 48°N/146°E). The Middle–Late Carboniferous overprints “Cp” and “B” are contemporaneous with emplacement of leucogranitic, crustal derived plutons, and probably result from the hydro-thermal activity related to the magmatism. The drift from “Cp” directions to “B” directions implies that after 330 Ma, Limousin underwent a clockwise rotation by 65°, together with the Central Europe Variscides. The “Bt” components, the VGPs of which deviate from the mean apparent polar wander path (APWP) of the belt, are interpreted as “B” overprints tilted during Late Variscan tectonics, that is, in the time range 325–315 Ma. The first and most important generation of “Bt” overprints was tilted during NW–SE folding associated with NE–SW shortening, updoming and emplacement of leucogranitic plutons. The second generation reveals southeastward tilting due to NE-striking normal faulting. The drift from “B” to “A1” directions implies that Limousin has participated to the second clockwise rotation by 40° of the whole belt in Westphalian times.     

Palaeomagnetic data from the precambrian Gwalior traps, Central India

From alternating-field and thermal demagnetization studies on two dolerite “Traps” in the Gwalior Series (Central India), dated at 1830 ±200 m.y., three different palaeomagnetic directions could be distinguished. The characteristic magnetization component, which is considered as the primary magnetization, has a mean direction: D=78°, I=+34.5°, α₉₅=5°, k=369, N=4 (Pole): 155.5°E19°N, dp=3°, dm=5.5°.A comparison of the presented data with other Precambrian and Phanerozoic data from the Indian subcontinent might suggest that the Indian subcontinent underwent a continuous anticlockwise rotational movement during the last 1800 m.y.