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PubMed1993

Aqueous high-temperature and high-pressure organic geochemistry of hydrothermal vent systems.

Hydrothermal systems associated with oceanic spreading centers are now recognized as relatively common phenomena, and the organic chemical alterations occurring there are rapid and efficient. In the marine hydrothermal systems at water depths > 1.5 km, the conditions driving chemical reactions are high temperatures (up to >400 degrees C), confining pressures (>150 bar), and other parameters such as pH, Eh, and mineralogy in an aqueous open flow medium. Continental hydrothermal systems may also be of interest, as, for example, in failed or dormant rifts and regions around piercement volcanoes. Organic matter alteration by reductive reactions to petroleum hydrocarbons occurs in hydrothermal systems over a wide temperature window (approximately 60 to >400 degrees C), under elevated pressure, and in a brief geological time (years to hundreds of years). The products are rapidly moved as bulk phase or in fluids from the regions at higher temperatures to areas at lower temperatures, where the high molecular weight material separates from the bulk. These conditions are conducive to organic chemistry which yields concurrent products by primarily reduction (due to mineral buffering), oxidation (high thermal stress), and synthesis reactions. This chemistry is just beginning to be elucidated by the geochemical community, but there are various industrial applications which provide useful preliminary insight. Therefore, the behavior of organic matter (inclusive of methane to high molecular weight compounds > C40) in warm to supercritical water needs to be characterized to understand the implications of this novel phenomenon in geological and geochemical processes, and the chemistry occurring over the full temperature spectrum of hydrothermal systems is of relevance to origins of life research.

Carbon Radioisotopes↗
PubMed1995

Determination of alpha-dialkylamino acids and their enantiomers in geological samples by high-performance liquid chromatography after derivatization with a chiral adduct of o-phthaldialdehyde.

Derivatization with o-phthaldialdehyde (OPA) and the chiral thiol N-acetyl-L-cysteine (NAC) is a convenient and sensitive technique for the HPLC detection and resolution of protein amino acid enantiomers. The kinetics of the reaction of OPA-NAC with alpha-dialkylamino acids was investigated. The fluorescence yield of alpha-dialkylamino acids was only about 10% of that of protein amino acids when the derivatization was carried out at room temperature for 1-2 min, which is the procedure generally used for protein amino acid analyses. The fluorescence yield of alpha-dialkylamino acids can be enhanced by up to ten-fold when the derivatization reaction time is increased to 15 min at room temperature. The OPA-NAC technique was optimized for the detection and enantiomeric resolution of alpha-dialkylamino acids in geological samples which contain a large excess of protein amino acids. The estimated detection limit for alpha-dialkylamino acids is 1-2 pmol, comparable to that for protein amino acids.

Acetylcysteine↗
PubMed1986

Global geochemical cycles of carbon, sulfur and oxygen.

Time resolved data on the carbon isotopic composition of carbonate minerals and the sulfur isotopic composition or sulfate minerals show a strong negative correlation during the Cretaceous. Carbonate minerals are isotopically heavy during this period while sulfate minerals are isotopically light. The implication is that carbon is being transferred from the oxidized, carbonate reservoir to the reservoir of isotopically light reduced organic carbon in sedimentary rocks while sulfur is being transferred from the reservoir of isotopically light sedimentary sulfide to the oxidized, sulfate reservoir. These apparently oppositely directed changes in the oxidation state of average sedimentary carbon and sulfur are surprising because of a well-established and easy to understand correlation between the concentrations of reduced organic carbon and sulfide minerals in sedimentary rocks. Rocks rich in reduced carbon are also rich in reduced sulfur. The isotopic and concentration data can be reconciled by a model which invokes a significant flux of hydrothermal sulfide to the deep sea, at least during the Cretaceous.

Atlantic Ocean↗
PubMed1987

The role of minerals in the thermal alteration of organic matter--III. Generation of bitumen in laboratory experiments.

A series of pyrolysis experiments, utilizing two different immature kerogens (from the Monterey and Green River Formations) mixed with common sedimentary minerals (calcite, illite, or Na-montmorillonite), was conducted to study the impact of the mineral matrix on the bitumen that was generated. Calcite has no significant influence on the thermal evolution of bitumen and also shows virtually no adsorption capacity for any of the pyrolysate. In contrast, montmorillonite and illite, to a lesser extent, alter bitumen during dry pyrolysis. Montmorillonite and illite also display strong adsorption capacities for the polar constituents of bitumen. By this process, hydrocarbons are substantially concentrated within the pyrolysate that is not strongly adsorbed on the clay matrices. The effects of the clay minerals are significantly reduced during hydrous pyrolysis. The strong adsorption capacities of montmorillonite and illite, as well as their thermocatalytic properties, may in part explain why light oils and gases are generated from certain argillaceous source-rock assemblages, whereas heavy immature oils are often derived from carbonate source rocks.

Bentonite↗
PubMed1986

Exobiology and future Mars missions: the search for Mars' earliest biosphere.

The primordial Mars may have possessed a thick carbon dioxide atmosphere, with liquid water common on the surface, similar in many ways to the primordial Earth. During this epoch, billions of years ago, the surface of Mars could have been conducive to the origin of life. It is possible that life evolved on Mars to be later eliminated as the atmospheric pressure dropped. Analysis of the surface of Mars for the traces of this early martian biota could provide many insights into the phenomenon of life and its coupling to planetary evolution.

Aluminum Silicates↗
PubMed1992

Microfossils and possible microfossils from the Early Archean Onverwacht Group, Barberton Mountain Land, South Africa.

There is widespread textural evidence for microbial activity in the cherts of the Early Archean Onverwacht Group. Layers with fine carbonaceous laminations resembling fossil microbial mats are abundant in the cherty metasediments of the predominantly basaltic Hooggenoeg and Kromberg Formations. In rare cases, filamentous microfossils are associated with the laminae. The morphologies of the fossils, as well as the texture of the encompassing laminae suggest an affinity to modern mat-dwelling cyanobacteria or bacteria. A variety of spheroidal and ellipsoidal structures present in cherts of the Hooggenoeg and Kromberg Formations resemble modern coccoidal bacteria and bacterial structures, including spores. The development of spores may have enabled early microorganisms to survive the relatively harsh surficial conditions, including the effects of very large meteorite impacts on the young Earth.

Carbon↗
PubMed1995

Integrated approaches to terminal Proterozoic stratigraphy: an example from the Olenek Uplift, northeastern Siberia.

In the Olenek Uplift of northeastern Siberia, the Khorbusuonka Group and overlying Kessyusa and Erkeket formations preserve a significant record of terminal Proterozoic and basal Cambrian Earth history. A composite section more than 350 m thick is reconstructed from numerous exposures along the Khorbusuonka River. The Khorbusuonka Group comprises three principal sedimentary sequences: peritidal dolomites of the Mastakh Formation, which are bounded above and below by red beds; the Khatyspyt and most of the overlying Turkut formations, which shallow upward from relatively deep-water carbonaceous micrites to cross-bedded dolomitic grainstones and stromatolites; and a thin upper Turkut sequence bounded by karst surfaces. The overlying Kessyusa Formation is bounded above and below by erosional surfaces and contains additional parasequence boundaries internally. Ediacaran metazoans, simple trace fossils, and vendotaenids occur in the Khatyspyt Formation; small shelly fossils, more complex trace fossils, and acritarchs all appear near the base of the Kessyusa Formation and diversify upward. The carbon-isotopic composition of carbonates varies stratigraphically in a pattern comparable to that determined for other terminal Proterozoic and basal Cambrian successions. In concert, litho-, bio-, and chemostratigraphic data indicate the importance of the Khorbusuonka Group in the global correlation of terminal Proterozoic sedimentary rocks. Stratigraphic data and a recently determined radiometric date on basal Kessyusa volcanic breccias further underscore the significance of the Olenek region in investigations of the Proterozoic-cambrian boundary.

Animals↗
PubMed1994

Depositional and tectonic setting of the Archean Moodies Group, Barberton Greenstone Belt, South Africa.

The 3.22-3.10 Ga old Moodies Group, uppermost unit of the Swaziland Supergroup in the Barberton Greenstone Belt (BGB), is the oldest exposed, well-preserved quartz-rich sedimentary sequence on earth. It is preserved in structurally separate blocks in a heavily deformed fold-and-thrust belt. North of the Inyoka Fault, Moodies strata reach up to 3700 m in thickness. Detailed mapping, correlation of measured sections, and systematic analysis of paleocurrents show that the lower Moodies Group north of the Inyoka Fault forms a deepening- and fining-upward sequence from a basal alluvial conglomerate through braided fluvial, tidal, and deltaic sandstones to offshore sandy shelf deposits. The basal conglomerate and overlying fluvial facies were derived from the north and include abundant detritus eroded from underlying Fig Tree Group dacitic volcanic rocks. Shoreline-parallel transport and extensive reworking dominate overlying deltaic, tidal, and marine facies. The lithologies and arrangement of Moodies Group facies, sandstone petrology, the unconformable relationship between Moodies strata and older deformed rocks, presence of at least one syndepositional normal fault, and presence of basaltic flow rocks and airfall fall tuffs interbedded with the terrestrial strata collectively suggest that the lower Moodies Group was deposited in one or more intramontane basins in an extensional setting. Thinner Moodies sections south of the Inyoka Fault, generally less than 1000 m thick, may be correlative with the basal Moodies Group north of the Inyoka Fault and were probably deposited in separate basins. A northerly derived, southward-thinning fan-delta conglomerate in the upper part of the Moodies Group in the central BGB overlies lower strata with an angular unconformity. This and associated upper Moodies conglomerates mark the beginning of basin shortening by south- to southeast-directed thrust faulting along the northern margin of the BGB and suggest that the upper Moodies Group was deposited in a foreland basin. Timing, orientation, and style of shortening suggest that this deformation eventually incorporated most of the BGB into a major fold-and-thrust belt.

Aluminum Silicates↗
PubMedDate not supplied

Inquiring into indicators and origin of catastrophic events at stratigraphic boundaries.

Since 1982, numerous indicators of catastrophic events have been observed at the main stratigraphic boundaries in China during the Phanerozoic, i.e. Precambrian-Cambrian, Permian-Triassic, Cretaceous-Tertiary as well as Ordovician-Silurian and Devonian-Carboniferous boundaries. These markers are boundary clay layer, microspherules, high Ir anomaly, mass extinction of organisms and impact of meteorite. We support the hypothesis of the extraterrestrial origin of catastrophic events and suggest that the events at different stratigraphic boundaries might be different in features and processes.

Aluminum Silicates↗
PubMed2004

Determination of thorium concentrations and activity ratios in silicate rocks by alpha spectrometry.

A detailed radiochemical procedure for alpha spectrometry measurements of thorium concentrations and of 230Th/232Th activity ratios in silicates is presented. The Th behaviour, during each step of the chemical process, was investigated by using a 234Th tracer, which is a gamma-ray emitter. The described chemical processing provides relatively high thorium yields, which varied between 56% and 88%, in the analysis of GB-1 (granite) and BB-1 (basalt) Brazilian geological standards. Also, the application of the established radiochemical method allowed a determination of both Th concentrations and activity ratios with high reproducibility, on the order of 2%. The estimation of the concentration result accuracy is also about 2%, which was calculated by using published data obtained from neutron activation analysis as reference values.

Alpha Particles↗
PubMed2006

Provincial geology and the Industrial Revolution.

In the early nineteenth century, geology was a new but rapidly growing science, in the provinces and among the gentlemen scientists of London, Oxford and Cambridge. Industry, particularly mining, often motivated local practical geologists, and the construction of canals and railways exposed the strata for all to see. The most notable of the early practical men of geology was the mineral surveyor William Smith; his geological map of England and Wales, published in 1815, was the first of its kind. He was not alone. The contributions of professional men, and the provincial societies with which they were connected, are sometimes underestimated in the history of geology.

England↗
PubMed2004

Natural radioactivity and radiation exposure in the high background area at Chhatrapur beach placer deposit of Orissa, India.

A high natural background radiation area is reported for the Chhatrapur beach placer deposit of Orissa state, on the southeastern coast of India, due to the presence of radiogenic heavy minerals. The average activity concentrations of radioactive elements 232Th, 238U and 40K were measured by gamma-ray spectrometry using a HPGe detector, and found to be 2500 +/-1850, 230 +/- 140 and 120 +/- 35 Bq kg-1, respectively, for the bulk sand samples. The absorbed gamma dose rates in air due to the naturally occurring radionuclides varied from 375 to 5000 nGy h-1, with an average value of 1625 +/- 1200 nGy h-1. The external annual effective dose rate of the region ranged from 0.46 to 6.12 mSv y-1, with an average value of 1625 +/- 1200 mSv y-1. The absorbed gamma dose rate levels of Chhatrapur beach area were similar to the monazite sand-bearing high background radiation areas of southern and southwestern coastal tracts of India and other similar areas of the world. The major contributors to the enhanced level of radiation are monazite and zircon sands.

Environmental Exposure↗
PubMed2005

Sulfur and strontium isotope geochemistry of tributary rivers of Lake Biwa: implications for human impact on the decadal change of lake water quality.

To study the deterioration of the water quality in Lake Biwa, Japan, over the last 40 years, we measured the concentrations and isotopic ratios of sulfur and strontium of water in 41 inflowing rivers and one discharging river. The concentrations of SO4 and Sr of inflowing rivers at downstream sites were generally high in the southern urban area and in the eastern area, where a large agricultural plain is situated, but low in the northern and western areas, whose watersheds are mountainous and with low population density. SO4 and Sr concentrations are also lower at upstream sites, which are closer to mountainous areas. Thus, the inflowing river receives large amounts of SO4 and Sr as it flows across the plain, where human activity levels are high. The delta34S or 87Sr/86Sr values of most eastern rivers at downstream sites are lower than those of water in Lake Biwa, and values become more uniform as the proportion of the plain area in the watershed increases. River water in other areas has higher values of delta34S or 87Sr/86Sr than the lake water. This result indicates that the decadal decrease of delta34S and 87Sr/86Sr in the lake water has been caused mainly by the increased flux of SO4 and Sr from rivers in the eastern plain. We assume that in the plain, sulfur, nitrogen, and organic compounds induced by human activities generate sulfuric, nitric, and organic acids in the water, which accelerate the extraction of Sr from bedrocks, leading to the generation of Sr in the river water in the area.

Environmental Monitoring↗
PubMed2005

Geomicrobiology in oceanography: microbe-mineral interactions at and below the seafloor.

Oceanography is inherently interdisciplinary and, since its inception, has included the study of microbe-mineral interactions. From early studies of manganese nodules, to the discovery of hydrothermal vents, it has been recognized that microorganisms are involved at various levels in the transformation of rocks and minerals at and below the seafloor. Recent studies include mineral weathering at low temperatures and microbe-mineral interactions in the subseafloor "deep biosphere". A common characteristic of seafloor and subseafloor geomicrobiological processes that distinguishes them from terrestrial or near-surface processes is that they occur in the dark, one or more steps removed from the sunlight that fuels the near-surface biosphere on Earth. This review focuses on geomicrobiological studies and energy flow in dark, deep-ocean and subseafloor rock habitats.

Bacteria↗
PubMed2006

A molecular dawn for biogeochemistry.

Biogeochemistry is at the dawn of an era in which molecular advances enable the discovery of novel microorganisms having unforeseen metabolic capabilities, revealing new insight into the underlying processes regulating elemental cycles at local to global scales. Traditionally, biogeochemical inquiry began by studying a process of interest, and then focusing downward to uncover the microorganisms and metabolic pathways mediating that process. With the ability to sequence functional genes from the environment, molecular approaches now enable the flow of inquiry in the opposite direction. Here, we argue that a focus on functional genes, the microorganisms in which they reside, and the interaction of those organisms with the broader microbial community could transform our understanding of many globally important biogeochemical processes.

Biochemistry↗
PubMed1984

Computerised gas chromatographic-mass spectrometric analysis of complex mixtures of alkyl porphyrins.

Computerised capillary gas chromatography-mass spectrometry (GC-MS) analysis of complex mixtures of alkyl porphyrins, as their bis-(trimethylsiloxy)silicon(IV) and bis(tert.-butyldimethylsiloxy)silicon(IV) derivatives, is described. The latter derivative is more suitable for routine GC-MS analysis. This computerised GC-MS approach, when applied to the alkyl porphyrins of two geological samples, a bitumen (Gilsonite, Eocene age, UT, U.S.A.) and a crude oil (Boscan, Cretaceous age, West Venezuela), has revealed the highly complex compositions of these fractions. Computer-aided data processing, using relative retention index (RRI) calculations, facilitated the classification of the chromatographic peaks according to structural type and membership of pseudo-homologous series. Computerised GC-MS is compared with, and contrasted to high-performance liquid chromatography as a means of petroporphyrin analysis.

Chemistry Techniques, Analytical↗
PubMed2002

Relationship between ore deposits in river catchments and geochemistry of suspended particulate matter from six rivers in southwest France.

Here we present original data on the geochemical composition of fluvial particulate matter transported by the rivers of the Adour/Garonne basin, which drains one-fifth of the French land surface. Suspended particulate matter from the six main rivers in the basin, sampled at 'normal' flow and during a flood, is compared in terms of: grain size; particulate organic carbon; Fe; Mn; and trace element concentrations (e.g. Zn, Cd, Pb, Cu, Mo, Sn, Ni, Co, Cr, V, As, Hg, U, Th, W, Au, Ag, Ta). Three of the six studied rivers (Garonne, Dordogne and Isle Rivers) are the main tributaries of the Gironde estuary (southwest France), known for Cd pollution. The Adour and Gaves Rivers enter the Adour Estuary and the Charente River reaches the ocean by the Charente Estuary. Our data show, that Cd (and Zn) are not the only trace elements of eco-toxicological relevance transported into the Gulf of Biscay by these six rivers. Potentially toxic elements (e.g. As, Sn, U, Cu, Ag) show elevated concentrations in river particulates entering the estuaries, compared to world average concentrations [Martin and Whitfield, 1983, The significance of the river input of chemical elements to the oceans. In: C.S. Wong, E. Boyle, K.W. Bruland, J.D. Burton, E.D. Goldberg (editors), Trace Metals in Sea Water, Plenum, New York: pp. 265-296]. Comparing SPM sampled during 'normal' discharge and flood, the basin shows a distinct trace element composition of SPM mostly related to ore deposits in the upper basins (Massif Central and Pyreneans). This geochemical signal is partly masked during floods due to changes in grain size, but also due to increased erosion of the lower parts of the basins. This study proves pumping/centrifugation to be the most appropriate sampling/separation technique (recovery, representativity, contamination) by comparing different methods of SPM recovery.

Disasters↗