Creep deformation of slope sediments in the Canadian Beaufort Sea

High resolution seismic profiles from the Canadian Beaufort Sea continental slope characteristically show a surficial 50 m thick conformably stratified unit overlying an irregular erosion surface. This stratified unit appears to be compressionally folded and associated with minor faults. At the shelf break, there are numerous indicators of a tensional regime, such as a large, slope-parallel graben and numerous mud diapirs. Although a large-scale slide-scar was mapped in one area, most of the slope is interpreted to be deforming by a creep mechanism. Preliminary calculations can provide reasonable values for the fold wave length and rate of deformation, supporting the suggestion that time dependent creep deformation has occurred in this area.     

Effects of salinity and clay type on oil-mineral aggregation

Effects of salinity and clay type on the aggregation process of crude oil and clay particles (oil-mineral aggregates--OMA) were studied in the laboratory. OMA were generated by shaking various oil/clay mixtures in water at 20 degrees C and at a pre-determined energy level. Shape, median and maximum sizes, size distribution and concentration of oil droplets forming OMA were measured using epi-fluorescence microscopy. Results showed that the median and maximum sizes and the concentration of mineral-stabilized droplets increase rapidly when salinity increases from zero to a critical aggregation salinity in the range of 1.2-3.5 ppt. The magnitude of the increase of droplet size is controlled by clay type, while the increase of droplet concentration is influenced by oil type. Size distributions of oil droplets are self-similar, but their magnitudes depend on salinity and oil type. The effect of salinity on droplet size distribution is strongly influenced by clay type. Empirical relationships are derived to calculate concentration and size distribution of mineral-stabilized droplets.     

Geology,sediment patterns,and widespread deformation on the sea floor off Western Samoa revealed by wide-swath imagery

GLORIA and SeaMARC II sea-floor images of offshore Western Samoa reveal large-scale mass movements, volcanism, and structural modification. These processes are driven by hot-spot mantle diapirism and nearby plate subduction. Debris avalanche deposits extend from the island slope onto the adjacent abyssal plains, covering at least 20,000 km². Sediment flows occur in sheets up to 30 km wide; slump structures are common on steep slopes. Volcanic cones and lava sheets are evident on lower slopes and abyssal plains. Major volcanic rift zones on the island of Savaii continue offshore. Subduction-induced flexure has produced intense tensional fracturing on the outer wall of the Tonga Trench.     

Habitats and Characteristics of the Sea Urchins Lytechinus variegatus and Arbacia punctulata (Echinodermata) on the Florida Gulf-Coast Shelf

Abstract Lytechinus variegatus and Arbacia punctulata have been studied primarily in inshore, shallow‐water areas. However, they are abundant in deeper waters on the Florida gulf‐coast shelf and seem important components of the benthic communities there. Lytechinus variegatus occurs alone on sand bottoms and A. punctulata occurs alone on rubble bottoms in these deeper waters. The species also co‐occur there on ­heterogeneous bottoms, each in a distinct microhabitat with A. punctulata on rubble and L. variegatus on surrounding sand. Characteristics of the sea urchins in these different deeper‐water habitat types and at one nearshore site with a heterogeneous rubble‐sand bottom were compared. Over the 2‐year study, offshore individuals of both species had low gut and gonad indices and the maximum size of individuals did not change. This suggests food limitation and low production. Offshore, A. punctulata had a higher Aristotle's lantern index and lower gut and gonad indices in populations where it ­co‐occurred with L. variegatus compared to populations where it occurred alone. The ­Aristotle's lantern index of L. variegatus did not differ among the offshore sites. Neither species seemed food limited at the nearshore site. Although productivity is lower at the offshore sites, both species extend their distribution and reproduction potential by existing there.     

HyLogging unconventional petroleum core from the Cooper Basin,South Australia

The Cooper Basin is currently Australia's premier onshore hydrocarbon-producing province and hosts a range of unconventional gas play types, including the very extensive basin-centred and tight gas accumulations in the Gidgealpa Group, both shallow and deep dry coal seam gas associated with the Patchawarra and Toolachee formations, as well as the shale gas plays in the Murteree and Roseneath shales. Characterisation of mineralogical properties of shales is critical to hydraulic fracture design and development of unconventional hydrocarbon resources. Properties are sensitive to variations in mineralogy, especially clays, and historically, acquisition of a suite of rock mechanics analyses has been on a point-source basis rather than on a continuous sampling approach, which is uncommon. In this paper, a near-continuous 382 m cored section, comprising the lower Permian Daralingie Formation, Roseneath and Murteree shales, the Epsilon Formation and the top portion of the Patchawarra Formation from Holdfast-1 well (DH261958) in the southern Cooper Basin, was measured using robotic core scanning spectroscopy with automated mineral identification. HyLogger 3 incorporates visible, near infrared, shortwave infrared and thermal infrared hyperspectral measurements recorded every 0.8 cm along the core at the rate of approximately 1 m per minute. These data are co-registered with a high-resolution image and a laser profile of the core. X-ray diffraction and thin-section petrology from the Holdfast-1 well-completion report (Beach Energy, 2011 Beach Energy (2011). Holdfast 1 well completion report. South Australian Department of State Development. Open file WCR 2010/000390. Retrieved from: https://sarigbasis.pir.sa.gov.au/WebtopEw/ws/samref/sarig1/image/DDD/HOLDFAST_001.zip [Google Scholar]) provided relative proportions of minerals including quartz, kaolinite, dickite, muscovite, illite, chlorite and siderite that enabled the modelled vs actual mineralogies to be constrained in the thermal infrared with a correlation coefficient of 0.85 for quartz, 0.79 for muscovite and 0.68 for kaolin; illite and siderite were more poorly correlated. HyLogger logging, when integrated with other petrophysical and analytical core data, provides a useful tool to better understand unconventional reservoirs and may assist in identification of zones that are conducive to fracture stimulation.     

Parameterization,sensitivity analysis,and inversion: an investigation using groundwater modeling of the surface-mined Tivoli-Guidonia basin (Metropolitan City of Rome,Italy)

With respect to model parameterization and sensitivity analysis, this work uses a practical example to suggest that methods that start with simple models and use computationally frugal model analysis methods remain valuable in any toolbox of model development methods. In this work, groundwater model calibration starts with a simple parameterization that evolves into a moderately complex model. The model is developed for a water management study of the Tivoli-Guidonia basin (Rome, Italy) where surface mining has been conducted in conjunction with substantial dewatering. The approach to model development used in this work employs repeated analysis using sensitivity and inverse methods, including use of a new observation-stacked parameter importance graph. The methods are highly parallelizable and require few model runs, which make the repeated analyses and attendant insights possible. The success of a model development design can be measured by insights attained and demonstrated model accuracy relevant to predictions. Example insights were obtained: (1) A long-held belief that, except for a few distinct fractures, the travertine is homogeneous was found to be inadequate, and (2) The dewatering pumping rate is more critical to model accuracy than expected. The latter insight motivated additional data collection and improved pumpage estimates. Validation tests using three other recharge and pumpage conditions suggest good accuracy for the predictions considered. The model was used to evaluate management scenarios and showed that similar dewatering results could be achieved using 20 % less pumped water, but would require installing newly positioned wells and cooperation between mine owners.     

Estimates of primary production by remote sensing in the Arctic Ocean: Assessment of accuracy with passive and active sensors

The Arctic Ocean, including its regional shelf seas, is assumed to play an important role in the global carbon cycle. However, the true magnitude of annual production is unknown, as in situ data are sparse in time and space. Remote sensing technology has the potential to provide large scale estimates of phytoplankton biomass at much higher frequency and spatial coverage than shipboard observations in this remote region. Subsurface peaks in both biomass and primary production (PP), which are the characteristics of the Arctic, are shown to limit the reliability of ocean color based integrated PP (IPP) models in the Chukchi Sea. Here we report that the retrievals of IPP from remotely sensed ocean color data were accurate only when limited to 1.2 optical depths, which severely constrains the utility of ocean color remote sensing for the assessment of Arctic Ocean dynamics.Active sensors such as LIDAR, can, in combination with passive ocean color, dramatically improve our ability to estimate IPP for the Arctic. IPP retrievals were improved to within a factor of 2–3 of the measured values, when the vertical distribution of Chl a was determined to a resolution of 1 m using modeled LIDAR retrievals of the beam attenuation coefficient. This was far better than models using only passive ocean color. The instrument specifications of the current NASA spaceborne LIDAR (CALIOP) allow for the retrieval of K_d at a depth resolution of 23 m. Even with this constraint, however, the accuracy of the modeled IPP was improved over passive ocean color retrievals to approximately a factor of 3. The Arctic is a perfect location to merge ocean color and LIDAR measurements as the polar orbit of CALIOP provides complete grid coverage of the area every 8 days, crossing the horizontal gradients in Chl a already known to exist from passive ocean color observations.     

Is correlation dimension a reliable proxy for the number of dominant influencing variables for modeling risk of arsenic contamination in groundwater?

The correlation dimension (CD) of a time series provides information on the number of dominant variables present in the evolution of the underlying system dynamics. In this study, we explore, using logistic regression (LR), possible physical connections between the CD and the mathematical modeling of risk of arsenic contamination in groundwater. Our database comprises a large-scale arsenic survey conducted in Bangladesh. Following the recommendation by Hossain and Sivakumar (Stoch Environ Res Risk Assess 20(1–2):66–76, 2006), who reported CD values ranging from 8 to 11 for this database, 11 variables are considered herein as indicators of the aquifer’s geochemical regime with potential influence on the arsenic concentration in groundwater. A total of 2,048 possible combinations of influencing variables are considered as candidate LR risk models to delineate the impact of the number of variables on the prediction accuracy of the model. We find that the uncertainty associated with prediction of wells as safe and unsafe by LR risk model declines systematically as the total number of influencing variables increases from 7 to 11. The sensitivity of the mean predictive performance also increases noticeably for this range. The consistent reduction in predictive uncertainty coupled with the increased sensitivity of the mean predictive behavior within the universal sample space exemplify the ability of CD to function as a proxy for the number of dominant influencing variables. Such a rapid proxy, based on non-linear dynamic concepts, appears to have considerable merit for application in current management strategies on arsenic contamination in developing countries, where both time and resources are very limited.