Geology topics

Bernd R. T. Simoneit

Publications and source records attributed to Bernd R. T. Simoneit.

9 recordsLinked to original sources

USGS2004

Thermal alteration of Cretaceous black shale from the Eastern Atlantic. III: Laboratory simulations

Laboratory thermal alteration (pyrolysis) experiments were carried out on composited Cretaceous black shale samples from DSDP Hole 368. Dried rock samples (low water-rock ratio) were heated in an inert atmosphere in the range of 250–500°C and the resultant bitumen and kerogen concentrates were characterized. Pyrobitumen forms initially (250°C), then major hydrocarbon generation occurs from 300–360°C and oxygenated products ( e.g. alkanoic acids) have a maximum yield at 330–360°C with minor generation to 500°C. Dealkylation of the aromatic hydrocarbons to the parent polynuclear aromatic hydrocarbons occurs above 400°C. The kerogens become more aromatic with increasing pyrolysis temperature (atomic H/C decreases from 1.2 to 0.5 and vitrinite reflectance increases to 3%). The temperature ranges of pyrobitumen, bitumen, and PAH formation in dry pyrolysis experiments are of utility in correlating with field data on ore genesis.

Atlantic Ocean, Cape Verde Rise↗

USGS2002

Geochemistry of fluid phases and sediments: Relevance to hydrothermal circulation in Middle Valley, ODP Legs 139 and 169

Geochemical and isotopic studies of pore fluids and solid phases recovered from the Dead Dog and Bent Hill hydrothermal sites in Middle Valley (Ocean Drilling Program Leg 169) have been compared with similar data obtained previously from these sites during Ocean Drilling Program Leg 139. Although generally the hydrothermal systems reflect non-steady state conditions, the data allow an assessment of the history of the hydrothermal processes. Sediment K/A1 ratios as well as the distribution of anhydrite in the sediments suggest that the Dead Dog hydrothermal field has been, and still is, active. In contrast, similar data in the Bent Hill hydrothermal field indicate a waning of hydrothermal activity. Pore fluid and hydrothermal vent data in the Dead Dog hydrothermal field are similar in nature to the data collected during ODP Leg 139. In the area of the Bent Hill sulfide deposit, however, the pore water data indicate that recent wholesale flushing of the sediment column with relatively unaltered seawater has obliterated a previous record of hydrothermal activity in the pore fluids. Data from the deepest part of Hole 1035A in the Bent Hill locality show the presence of hydrothermal fluids at greater depths in this area. This suggests the origin of the hydrothermal fluids found to be emanating from Hole 1035F, which constitutes one of the first man made hydrothermal vents in the Middle Valley hydrothermal system. Similarly, CORKed Hole 858G, because of seal failures, has acted as a hydrothermal vent, with sulfide deposits forming inside the CORK. ?? 2002 Elsevier Science Ltd. All rights reserved.

Applied Geochemistry↗

USGS1998

The deep structure of a sea-floor hydrothermal deposit

Hydrothermal circulation at the crests of mid-ocean ridges plays an important role in transferring heat from the interior of the Earth. A consequence of this hydrothermal circulation is the formation of metallic ore bodies known as volcanic-associated massive sulphide deposits. Such deposits, preserved on land, were important sources of copper for ancient civilizations and continue to provide a significant source of base metals (for example, copper and zinc). Here we present results from Ocean Drilling Program Leg 169, which drilled through a massive sulphide deposit on the northern Juan de Fuca spreading centre and penetrated the hydrothermal feeder zone through which the metal-rich fluids reached the sea floor. We found that the style of feeder-zone mineralization changes with depth in response to changes in the pore pressure of the hydrothermal fluids and discovered a stratified zone of high-grade copper-rich replacement mineralization below the massive sulphide deposit. This copper-rich zone represents a type of mineralization not previously observed below sea-floor deposits, and may provide new targets for land-based mineral exploration.

Nature↗

USGS1994

Comparison of 14C ages of hydrothermal petroleums

In order to set limits on the time frame of formation of hydrothermal petroleum, we have obtained 14 C ages on samples from three diverse regions; Gulf of California (Guaymas Basin), Northeast Pacific Ocean (Escanaba Trough and Middle Valley), and the East African Rift (Tanganyika Trough). The results date the source of carbon and therefore provide maximum ages for the formation and emplacement of the hydrothermal petroleums. The youngest petroleum occurs iin the Souther Trough of Guaymas Basin (3200–6600 yr, mean 4692 yr); in the Northern Trough the petroleum is slightly older (7400 yr). Significantly older hydrothermal petroleum occurs in Escanaba Trough (17,000 yr) and Middle Valley (29,000 yr). A continental example from the East African Rift has an age of 25,000 yr, comparable to the ages observed in the oceanic samples from the Northeast Pacific Ocean. These ages affirm that hydrothermal petroleum formation is a very rapid process and took place some time between the latest Pleistocene and the present in these active hydrothermal systems.

Organic Geochemistry↗

USGS1990

Deep-water hydrocarbon seeps in Guaymas Basin, Gulf of California

Acoustically discovered hydrocarbon seeps along a transform fault zone on the Sonoran margin of Guaymas Basin and in the Southern Trough of Guaymas Basin were examined and sampled during dives of DSV Alvin . Seepage of methane and heavier hydrocarbons occurs through shallow pockmarks along the eroding crest of a steep anticline, 1600 m below sea level. Extensive ledges of aragonite crop out around the rims of the pockmarks; isotopic analysis indicates that carbonate precipitation is a result of methane oxidation. Seepage zones within the pockmarks support dense communities of Calyptogena , half buried in the mud; tubeworms ( Lamellibracheae sp.) have colonized many of the aragonite outcrops. Though the margin site is only a few kilometers from a high-temperature sulfide-precipitating and petroleum-discharging vent system at a nearby center, its structural setting is more akin to pockmarks described from continental shelves, and its chemosynthetic fauna is more like that around low temperature seeps on other continental slopes and margins (e.g. Oregon, U.S.A., and Japan). The seep in the Southern Trough is a condensate-type petroleum (C 1 -C 40 ) and rises as a plume from a young vent-mound system about 2000 m below sea level.

Gulf of California↗

USGS1989

Chemical affinities between the solvent extractable and the bulk organic matter of fossil resin associated with an extinct podocarpaceae

Analyses by GC-MS and GC-IR of resin associated to Dacridiumites mawsonii deposits, an extinct species of Podocarpaceae occurring on the South Island of New Zealand during the Bortonian (Middle Eocene), have revealed that dehydroabietic acid is the predominant component of the solvent soluble fraction. Accordingly, this diterpenoid has been selected as the principal component material for spectroscopic comparison with the bulk resin using IR and CP/MAS 13 C NMR.

South Island↗

USGS1988

The molecular composition of ambers

Bulk (elemental composition, IR, CP/MAS 13 C NMR) and molecular (GC-MS) analyses have been performed on a series of ambers and resins derived from different locations (Dominican Republic, Philippines, Canada, Israel, New Zealand, Chile) having diverse botanical affinities ( Araucariaceae, Hymenaea ) and variable age (from Holocene to Early Cretaceous). No major differences have been observed from the elemental composition and the spectroscopic data; however, the molecular analyses of the solvent extractable fraction show that a specific mixture of components is present in each sample. These are mainly diterpenoid products that in general are also found abundantly in the higher plants from which the ambers and resins originate. Nevertheless, a direct relationship between major terpenoid constituents in fossil resins and precursor plant materials can only be established for the younger samples. Irrespective of the geographical or botanical origin of the ambers and resins, several common age-dependent molecular transformation trends can be recognized: (1) progressive loss of olefinic bonds (especially those located in exocyclic positions), (2) decrease of functionalized products, and (3) increasing proportion of aromatized components. However, even in the samples of older age (Cretaceous) the degree of aromatization is very low when compared with that of other higher-plant related materials such as fossilized woods or low rank coals. This indicates that maturation must involve essentially olefin polymerization processes instead of extensive aromatization.

Organic Geochemistry↗

USGS1986

Cyclic terpenoids of contemporary resinous plant detritus and of fossil woods, ambers and coals

Cyclic terpenoids present in the solvent extractable material of fossil woods, ambers and brown coals have been analyzed. The sample series chosen consisted of wood remains preserved in Holocene to Jurassic sediments and a set of of ambers from the Philippines (copalite), Israel, Canada and Dominican Republic. The brown coals selected were from the Fortuna Garsdorf Mine and Miocene formations on Fiji. The fossil wood extracts contained dominant diterpenoid or sesquiterpenoid skeletons, and aromatized species were present at high concentrations, with a major amount of two-ring aromatic compounds. Tricyclic diterpenoids were the predominant compounds in the ambers. Aromatized derivatives were the major components, consisting of one or two aromatic ring species with the abietane and occasionally pimarane skeletons. The saturated structures were comprised primarily of the abietane and pimarane skeletons having from three to five carbon (C 1 , C 2 , etc.) substituents. Kaurane and phyllocladane isomers were present in only minor amounts. Bicyclic sesquiterpenoids as saturated and partial or fully aromatized forms were also common in these samples, but only traces of sesterterpenoids and triterpenoid derivatives were found. The brown coal extracts were composed of major amounts of one- and two-ring aromatized terpenoids, with a greater proportion of triterpenoid derivatives than in the case of the woods and ambers. This was especially noticeable for the German coal, where the triterpenoids were predominant. Open C-ring aromatized structures were also present in this coal. Steroid compounds were not detectable, but some hopanes were found as minor components in the German brown coal. An overview of the skeletal structure classes identified in each sample, as well as the general mass spectrometric characteristics of the unknown compounds are included in the present paper. It can be concluded from these structural distributions that aromatization is the main process for the transformation of terrestrial cyclic terpenoids during diagenesis, constituting a general pathway for all terpenoids.

Organic Geochemistry↗

USGS1982

Organic geochemistry and pore water chemistry of sediments from Mangrove Lake, Bermuda

Mangrove Lake, Bermuda, is a small coastal, brackish-water lake that has accumulated 14 m of banded, gelatinous, sapropelic sediments in less than 10 4 yr. Stratigraphic evidence indicates that Mangrove Lake's sedimentary environment has undergone three major depositional changes (peat, freshwater gel, brackish-water gel) as a result of sea level changes. The deposits were examined geochemically in an effort to delineate sedimentological and diagenetic changes. Gas and pore water studies include measurements of sulfides, ammonia, methane, nitrogen gas, calcium, magnesium, chloride, alkalinity, and pH. Results indicate that sulfate reduction is complete, and some evidence is presented for bacterial denitrification and metal sulfide precipitation. The organic-rich sapropel is predominantly algal in origin, composed mostly of carbohydrates and insoluble macromolecular organic matter called humin with minor amounts of proteins, lipids, and humic acids. Carbohydrates and proteins undergo hydrolysis with depth in the marine sapropel but tend to be preserved in the freshwater sapropel. The humin, which has a predominantly aliphatic structure, increases linearly with depth and composes the greatest fraction of the organic matter. Humic acids are minor components and are more like polysaccharides than typical marine humic acids. Fatty acid distributions reveal that the lipids are of an algal and/or terrestrial plant source. Normal alkanes with a total concentration of 75 ppm exhibit two distribution maxima. One is centered about n -C 22 with no odd/even predominance, suggestive of a degraded algal source. The other is centered at n -C 31 with a distinct odd/even predominance indicative of a vascular plant origin. Stratigraphic changes in the sediment correlate to observed changes in the gas and pore water chemistry and the organic geochemistry.

Mangrove Lake↗