Evaluating the geothermal heat pump potential from a thermostratigraphic assessment of rock samples in the St. Lawrence Lowlands,Canada

The installation cost and the performance of geothermal heat pump systems are influenced by the thermal state and properties of the subsurface. The ground ability to transfer heat described by thermal conductivity is a dominant factor affecting the favorability of closed-loop ground heat exchangers installed in vertical boreholes. A study that aimed at evaluating the geothermal heat pump potential by mapping the thermal conductivity of rock sequences was, therefore, performed for the St. Lawrence Lowlands sedimentary basin in Canada. Thermal conductivity was measured in the laboratory on rock samples collected in outcrops and used to complete design calculations of a geothermal system with a single borehole. Results allowed the definition of thermostratigraphic units that can be linked to depositional environments. Basal quartz-rich sandstones formed in a rift environment show a high geothermal potential. Overlying dolomites, argillaceous limestones and shales deposited in a passive margin evolving to a foreland basin exhibit a transition toward the top from high to low geothermal potential. Upper turbidites and molasses have a moderate geothermal potential. The thermal conductivity of the thermostratigraphic units is dominantly influenced by the mineralogy of the sedimentary rocks. Understanding their origin is a key to improve geothermal resource assessment and system design to anticipate new installations in the area.     

Parametric study using FEM for the stability of the RCC Tannur dam

Parametric study was carried out in this paper using the Finite Element Method (FEM) to study the effects of variations of the two parameters, i.e., variations in batter slope and foundation properties under static and dynamic loading conditions on the distribution of the peak stresses within the dam and foundation soils. The response spectra for the operating basis earthquake (OBE) and the maximum credible earthquake (MCE) were used in the dynamic analysis. It is shown that the distribution of peak stresses across base of dam and the extent of tensile zone on the foundation soils at the foundation level vary with the variations in the batter slope. Generally, as the batter slope increases the extent of the tensile zone at the foundation level decreases but not necessarily the maximum tensile stresses. However, an optimum batter slope could be achieved based on the results of this parametric study. It should be noted that the greatest tension is developed in the rock adjacent to the toe of the batter. For the foundation mechanical properties, it has been shown that the assessment of accurate soil mechanical properties has a great effect on the computed design stresses from finite element analysis. However, the greatest effect of the foundation properties was on the stresses at the base of dam while it has a negligible effect within the dam body.     

Age assignment of a diatomaceous ooze deposited in the western Amundsen Sea Embayment after the Last Glacial Maximum

Reliable dating of glaciomarine sediments deposited on the Antarctic shelf since the Last Glacial Maximum (LGM) is challenging because of the rarity of calcareous (micro‐) fossils and the recycling of fossil organic matter. Consequently, radiocarbon (¹⁴C) ages of the acid‐insoluble organic fraction (AIO) of the sediments bear uncertainties that are difficult to quantify. Here we present the results of three different methods to date a sedimentary unit consisting of diatomaceous ooze and diatomaceous mud that was deposited following the last deglaciation at five core sites on the inner shelf in the western Amundsen Sea (West Antarctica). In three cores conventional ¹⁴C dating of the AIO in bulk samples yielded age reversals down‐core, but at all sites the AIO ¹⁴C ages obtained from diatomaceous ooze within the diatom‐rich unit yielded similar uncorrected ¹⁴C ages between 13 517 ± 56 and 11 543 ± 47 years before present (a BP). Correction of these ages by subtracting the core‐top ages, which probably reflect present‐day deposition (as indicated by ²¹⁰Pb dating of the sediment surface at one core site), yielded ages between ca. 10 500 and 8400 cal. a BP. Correction of the AIO ages of the diatomaceous ooze by only subtracting the marine reservoir effect (MRE) of 1300 a indicated deposition of the diatom‐rich sediments between 14 100 and 11 900 cal. a BP. Most of these ages are consistent with age constraints between 13.0 and 8.0 ka for the diatom‐rich unit, which we obtained by correlating the relative palaeomagnetic intensity (RPI) records of three of the sediment cores with global and regional reference curves. As a third dating technique we applied conventional radiocarbon dating of the AIO included in acid‐cleaned diatom hard parts extracted from the diatomaceous ooze. This method yielded uncorrected ¹⁴C ages of only 5111 ± 38 and 5106 ± 38 a BP, respectively. We reject these young ages, because they are likely to be overprinted by the adsorption of modern atmospheric carbon dioxide onto the surfaces of the diatom hard parts prior to sample graphitisation and combustion for ¹⁴C dating. The deposition of the diatom‐rich unit in the western Amundsen Sea suggests deglaciation of the inner shelf before ca. 13 ka BP. The deposition of diatomaceous oozes elsewhere on the Antarctic shelf around the same time, however, seems to be coincidental rather than directly related. Copyright © 2009 John Wiley & Sons, Ltd.     

Palaeomagnetic correlation and dating of Plio/Pleistocene sediments at the southern margins of the North Sea Basin

A series of discontinuous sediment sequences, of Plio/Pleistocene age, occur onshore around the southern North Sea margins, notably in the East Anglian region of Britain. Intensive lithological and palaeontological analyses of these sediments have shown that they record both major and minor oscillations in climate, sea level and environmental conditions. However, significant uncertainties exist regarding the absolute and relative chronostratigraphies of many of these sequences, hindering understanding of the relative impacts of climatic, eustatic and tectonic changes on the palaeogeographic development of the southern North Sea basin. Here, a number of key East Anglian Plio/Pleistocene sites are subjected to robust palaeomagnetic and mineralogical examination, in order to determine those sediments which display reliable, syn‐depositional magnetic polarities, which are thus of use in ascribing a palaeomagnetically determined age from comparison with the Geomagnetic Polarity Timescale (GPTS). Based on a range of palaeomagnetic and complementary mineralogical methods, reliable palaeomagnetic directions were obtained from eight sites, with reversed polarities displayed by sediments from three sites. These polarity determinations can be used to infer absolute ages and test published, between‐site correlations. Copyright © 2005 John Wiley & Sons, Ltd.     

Support vector regression to predict asphalt mix performance

Material properties are essential in the design and evaluation of pavements. In this paper, the potential of support vector regression (SVR) algorithm is explored to predict the resilient modulus (M_R), which is an essential property in designing and evaluating pavement materials, particularly hot mix asphalt typically used in Oklahoma. SVR is a statistical learning algorithm that is applied to regression problems; in our study, SVR was shown to be superior to the least squares (LS). Compared with the widely used LS method, the results of this study show that SVR significantly reduces the mean‐squared error and improves the correlation coefficient. Copyright © 2008 John Wiley & Sons, Ltd.     

Sponges as sentinels: patterns of spatial and intra-individual variation in trace metal concentration

If sponges are to be effective biomonitors we require a better understanding of the spatial scales over which metals vary in these organisms. We determined how concentration of Cd, Zn, Cu, Pb, Hg and Se varied over four spatial scales for two common estuarine sponge species in the Sydney region. We examined variability with a fully nested sampling design; between coastal lakes, within coastal lakes, between sponges and within sponges. Calculation of variance components confirmed that 'within-sponge' variation in Cd, Zn, Cu, Pb and Se concentrations were low (1-14%) relative to the two largest spatial scales (49-98%) examined. In contrast, Hg concentrations exhibited marked variability 'between-sponges' and were below detection at one location. There was little evidence that sponge size was a good predictor of metal concentration. Taken together, these outcomes confirm that fragments of these sponges could be successfully transplanted and therefore show promise as biomonitors of metal contamination.     

Geochemical response of acid groundwater to neutralization by alkaline recharge

Solute transport and chemical neutralization (pH 3 to 7) within a shallow heterogeneous aquifer producing acid mine drainage (AMD) are examined at an abandoned surface coal mine in West Virginia. The aquifer is undergoing partial neutralization by mixing with alkalinity from a leaking sludge disposal pond, extending in preferential zones controlled by aquifer heterogeneity. Hydraulic heads interpolated from wells indicate leakage from a central alkaline (pH 7.1, 0.72 meq/L alkalinity) sludge pond is a principal source of recharge. Chemically-conservative sodium, added to AMD during treatment and leaked into the aquifer with the sludge, develops a dispersion plume over a restricted portion of the aquifer that correlates with pH, hydraulic head, and dissolved metals distributions. Concentrations of aluminum, iron, sulfate and acidity display higher concentrations downgradient from the pond as sludge alkalinity is consumed along flow paths. Before reaching springs, most dissolved iron is oxidized and hydrolyzed, likely precipitating in the aquifer as a ferric hydroxide or hydroxysulfate phase. The spatial pattern of iron and aluminum concentrations suggests accelerated oxidation caused by gas transport along the outer slopes of the spoil. Dissolved aluminum concentrations increase with total acidity, suggesting that dissolution of silicate minerals results from acidity released by iron hydrolysis. Neutralization reactions and higher pH are favored in more highly permeable portions of the spoil, where ferrihydrite and aluminum hydroxysulfate minerals (such as basaluminite) are supersaturated. In acid-producing zones at pH < 4.5, jurbanite is near equilibrium and an aluminum-sulfate phase with similar properties may limit aluminum concentrations, but become undersaturated in zones of advancing neutralization. At this particular site, ferrous iron produced by pyrite oxidation is almost completely oxidized over short transport distances, allowing hydrolysis of iron and aluminum should sufficient alkalinity be added to these acid waters.     

Petrography of Lower Cretaceous sandstones on Spitsbergen

The sandstone petrography of sample suites from four sites spanning the Rurikfjellet (Hauterivian) to Carolinefjellet (Aptian-Albian) formations in central Spitsbergen was investigated. The sandstones show a distinct stepwise shift in composition from quartz arenites to sublitharenites and lithic arenites, typically within the upper part of the Helvetiafjellet Formation. This shift is related to the introduction of 10 - 25% (grain%) plagioclase grains and volcanic lithics, and a notable increase in basement and sedimentary lithics. Quartz grain character also changes, and grain shapes become more varied. The shift is also associated with the transgressive arrival of marine sediments in the area, and the introduction of sands from the east-northeast by shore-parallel transport. Regional regression and subsequent transgression, and the change in sandstone composition is attributed to the development of the High Arctic Large Igneous Province in the region. The relative constancy of sand composition and volume of volcanic detritus within the Carolinefjellet Formation suggests long term (∼20 M) stability of the sediment system and a large volcanic source area, consistent with LIP (Large Igneous Province) derivation, along with significant exposure of basement rocks. Sample spacing and sediment recycling and mixing do not allow detection of events that would have changed sandstone composition that were less than ∼1 M duration. Preservation of significant amounts of plagioclase in a sediment-starved shelf can be explained by relatively cold climatic conditions.