Identification and occurrence of 25-norbenzohopanes in biodegraded bitumen from Palaeozoic carbonates in northern Alberta     

Barry Bennett  Chunqing Jiang  Stephen R. Larter 《Organic Geochemistry》2009,40(6):667-670

In addition to the previously reported 25-norhopanes and 25-norhopanoic acids, for the first time we report the identification of 25-norbenzohopanes. The hydrocarbon composition of the bitumen from Palaeozoic carbonates in northern Alberta displays molecular evidence for severe levels of biodegradation characterised by the removal of C₃₀–C₃₅ hopanes. Biodegradation is also indicated by the removal of C₃₂ and C₃₃ benzohopanes. The appearance of C₃₁ and C₃₂ 25-norbenzohopanes corresponds to the decrease in C₃₂ and C₃₃ benzohopanes, suggesting that 25-norbenzohopanes originate by demethylation of benzohopane counterparts. Demethylation at C-10 in the hopanoids affects a broader class of compounds that so far includes the hopanes and hopanoic acids, as well as the benzylated hopanoid species.  相似文献   

Comparison of pelagic and nepheloid layer marine snow: implications for carbon cycling   总被引：5，自引：0，他引：5  

Barbara Ransom  Kevin F. Shea  Patti Jo Burkett  Richard H. Bennett  Roy Baerwald 《Marine Geology》1998,150(1-4):39-50

Marine snow from upper and mid-water (i.e., pelagic) depths on the California margin is texturally and compositionally different from that traveling in the nepheloid layer. Transmission electron microscopy shows that pelagic marine snow consists primarily of bioclasts (e.g., diatom frustules, foram tests), organic matter, and microbes. These components are entrained as discrete particles or small aggregates μm in diameter) in a loose network of exocellular, muco-polysaccharide material. Clays are infrequent but, when present, are constituents of comparatively compact organic-rich microaggregates. Microbes are abundant and appear to decrease in number with increasing water depth. In contrast, marine snow aggregates collected from just above the sea floor in the nepheloid layer are assemblages of clay particles, clay flocs, and relatively dense clay–organic-rich microaggregates in an exocellular organic matrix. Bioclasts and microorganisms occur only rarely. The prevalence of clay–organic-rich aggregates in the nepheloid layer suggests that, prior to final deposition and burial, marine snow from the pelagic zone is subject to disaggregation and recombination with terrigenous detrital material near or at the sea floor. Results have significant implications for the accumulation and burial rates of organic carbon on continental margins and the aging and bioavailability of sedimentary organic matter. Samples examined were collected offshore of northern and central California.  相似文献   

Sensitivity of Simulated Hyporheic Exchange to River Bathymetry: The Steinlach River Test Site     

Reynold Chow  Hao Wu  Jeremy P. Bennett  Jürnjakob Dugge  Thomas Wöhling  Wolfgang Nowak 《Ground water》2019,57(3):378-391

This study determines the aspects of river bathymetry that have the greatest influence on the predictive biases when simulating hyporheic exchange. To investigate this, we build a highly parameterized HydroGeoSphere model of the Steinlach River Test Site in southwest Germany as a reference. This model is then modified with simpler bathymetries, evaluating the changes to hyporheic exchange fluxes and transit time distributions. Results indicate that simulating hyporheic exchange with a high-resolution detailed bathymetry using a three-dimensional fully coupled model leads to nested multiscale hyporheic exchange systems. A poorly resolved bathymetry will underestimate the small-scale hyporheic exchange, biasing the simulated hyporheic exchange towards larger scales, thus leading to overestimates of hyporheic exchange residence times. This can lead to gross biases in the estimation of a catchment's capacity to attenuate pollutants when extrapolated to account for all meanders along an entire river within a watershed. The detailed river slope alone is not enough to accurately simulate the locations and magnitudes of losing and gaining river reaches. Thus, local bedforms in terms of bathymetric highs and lows within the river are required. Bathymetry surveying campaigns can be more effective by prioritizing bathymetry measurements along the thalweg and gegenweg of a meandering channel. We define the gegenweg as the line that connects the shallowest points in successive cross-sections along a river opposite to the thalweg under average flow conditions. Incorporating local bedforms will likely capture the nested nature of hyporheic exchange, leading to more physically meaningful simulations of hyporheic exchange fluxes and transit times.  相似文献   

Integrated geophysical exploration in onshore frontier basins     

F. Martini  E. Rogers  S. Bennett  R. Davi  J.T. Doherty  J. Mongan 《Geophysical Prospecting》2019,67(6):1664-1675

Faced with the challenge of rapidly screening a huge expanse of frontier exploration acreage, often characterized by sparse vintage data, it is our experience that a combination of appropriate air- and ground-based geophysical techniques contributes positively to the exploration value chain. Airborne gravity gradiometry in conjunction with conventional gravity and magnetic data, as well as geological knowledge, add significant value to the screening process. This combination can subsequently assist in optimizing the location of the more time-consuming and expensive seismic programme. In addition, analysis and inversion of passive seismic data have also proven useful in providing depth to basement estimates, and results derived from all the techniques investigated have been consistent within several study areas. Following initial tests, where the data were independently analysed and cross-checked for consistency (including comparisons with active source seismic data and well data, when available), the company now routinely adopts the integration of these techniques in our frontier exploration acreage to support sedimentary basin delineation and mapping. This allows the optimal positioning and focussing of the higher spend and higher footprint programmes, such as active reflection seismic.  相似文献   

Distribution of glaciofluvial sediment within and on the surface of a high arctic valley glacier: Marthabreen,Svalbard     

Neil F. Glasser  Matthew R. Bennett  David Huddart 《地球表面变化过程与地形》1999,24(4):303-318

Marthabreen is a 7·8 km long valley glacier in SW Spitsbergen. The glacier is partially covered by a layer of angular debris derived from rockfall in its accumulation area, pierced in places by pinnacles and ridges of glaciofluvial sediment. These concentrations of glaciofluvial sediment fall into three categories: (1) debris pinnacles; (2) longitudinal sediment dykes; (3) longitudinal ridge accumulations. Debris pinnacles are slabs of sediment (predominantly sands, gravels and cobbles) elevated to the glacier surface along thrusts. Longitudinal sediment dykes are low (<0·5 m high) ridges of debris melting out of vertical sediment dykes within the body of the glacier. They are composed of a range of facies including sands, granule gravels, pebble gravels and diamiction. These dykes are sub-parallel to the longitudinal foliation on the glacier and form during folding of the stratification. Longitudinal ridge accumulations are higher (>1 m high) ridges of sorted sand and gravels which are not associated with penetrative ice structures. Their occurrence downglacier of sediment dykes and debris pinnacles suggests that they originate as supraglacial or englacial channels or tunnels filled by sediment derived from the dykes or thrusts. The presence of large quantities of glaciofluvial sediment on the surface of Marthabreen does not imply englacial water flow at high levels within the glacier, but is related to ice deformational processes such as thrusting and folding of debris-rich stratification. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Long-Period Magnetotelluric Measurements Near the Central California Coast: A Land-Locked View of the Conductivity Structure Under the Pacific Ocean   总被引：2，自引：0，他引：2  

R. L. Mackie  B. R. Bennett  T. R. Madden 《Geophysical Journal International》1988,95(1):181-194

  相似文献   

Match probability statistics and gamma-ray burst recurrences in the BATSE catalog     

Sun Hong Rhie  David Bennett 《Astrophysics and Space Science》1995,231(1-2):27-30

We developmatch probability statistics to test the recurrences of gamma-ray bursts in the BATSE catalog 1B and 2B. We do not find a signal of repetitions at the match level of 10^–3.  相似文献   

An Array Experiment with Magnetic Variometers Near the Coasts of South-east Australia     

F. E. M. Lilley  D. J. Bennett 《Geophysical Journal International》1972,29(1):49-64

  相似文献   

Long-term forest dynamics of the temperate zone: A case study of Late-Quaternary forests in eastern North America Ecological Studies Vol 63. P. A. DELCOURT and H. R. DELCOURT Publisher Springer-Verlag,New York/Berlin 1987 Dm 158.00 (hard cover) (439 pp) ISBN 0 387 964959 and 3540 964959     

Keith D. Bennett 《第四纪科学杂志》1989,4(1):92-94

  相似文献   

Estimation of Biodegradation Rates Using Respiration Tests During In Situ Bioremediation of Weathered Diesel NAPL   总被引：3，自引：1，他引：2  

G.B. Davis  C.D. Johnston  B.M. Patterson  C. Barber  M. Bennett 《Ground Water Monitoring & Remediation》1998,18(2):123-132

Respiration tests were carried out during a seven month bioremediation field trial to monitor biodegradation rates of weathered diesel non-aqueous phase liquid (NAPL) contaminating a shallow sand aquifer. Multiple depth monitoring of oxygen concentrations and air-filled porosity were carried out in nutrient amended and nonamended locations to assess the variability of degradation rate estimates calculated from respiration tests.
The field trial consisted of periodic addition of nutrients (nitrogen and phosphorus) and aeration of a 100 m² trial plot. During the bioremediation trial, aeration was stopped periodically, and decreases in gaseous oxygen concentrations were logged semi-continuously using data loggers attached to recently developed in situ oxygen probes placed at multiple depths above and within a thin NAPL-contaminated zone. Oxygen usage rate coefficients were determined by fitting zero-and first-order rate equations to the oxygen concentration reduction curves, although only zero-order rates were used to calculate biodegradation rates. Air-filled porosity estimates were found to vary by up to a factor of two between sites and at different times.
NAPL degradation rates calculated from measured air-filled porosity and oxygen usage rate coefficients ranged up to 69 mg kg^-1 day^-1. These rates are comparable to and higher than rates quoted in other studies, despite the high concentrations and weathered state of the NAPL at this test site. For nutrient-amended sites within the trial plot, estimates of NAPL degradation rates were two to three times higher than estimates from nonamended sites. Rates also increased with depth.  相似文献