Trace metals in the surface sediments were measured to investigate the spatial distribution and annual variations of metals (Cr, Co, Ni, Cu, Zn, As, Cd, Pb, Hg) and to evaluate the pollution status for metals from the artificial Saemangeum Lake that was created by the dike construction. The highest concentrations of metals were found in the river mouth and metal concentrations gradually decreased toward the dike. Anthropogenic pollution sources from two rivers exist, while the clay fraction of sediment and TOC were found to be major controlling factor on metal concentrations such as Cu, Zn, As, Pb and Hg. Results of annual variations during 2002-2010 showed that metal concentrations increased after the completion of the dike in 2006. This indicates that the dike construction lead to increased metal concentrations in sediments due to the limited water exchange, the reduction of water current velocity and the changes of redox condition, especially developing suboxic condition in bottom water after the dike construction. Assessment of pollution status for metals indicates that Saemangeum Lake was characterized as unpolluted to moderately contaminated. Even though the lake is presently unpolluted, on-going reclamation of land for residential and industrial purposes might lead to serious contamination by various pollutants. Proper management for sustainable development should be necessary to prevent metal pollution in study area.
It is hypothesized that carbon and nitrogen isotopic compositions (δ13C and δ15N) of fossil wood fragments will provide useful information regarding conditions prior, during, and after deposition. Eleven fossil wood samples were collected from the Sinemurian-lowermost Pliensbachian marly hemipelagic deposits of the Água de Madeiros Formation at S. Pedro de Moel (Lusitanian Basin, Portugal), and analyzed using optical and geochemical methods to confidently determine their use in palaeoenvironmental studies. Organic petrography observations show that the fossil wood samples contain a wide variety of particles mostly related to the phytoclast group, but also include resin impregnations, palynomorphs, and/or marine amorphous organic matter. A significant positive correlation between total carbon content and δ13C is observed (defined by 8 out of 11 samples), and most samples have high δ15N. These data suggest that isotopic compositions of the studied samples were severely affected by sedimentary and diagenetic processes (biological or related to early diagenesis and coalification). It is evident that various processes of alteration either acted on different samples of the studied stratigraphic interval, or occurred with different magnitudes. It is considered that future stable isotopic studies on fossil wood should involve detailed screening as presented in this study, to ensure a proper understanding of the biological (mostly biodegradation) or diagenetic processes affecting samples and their impact on the determined chemical proprieties.
Caprock integrity is an important subject, as it is closely related to the leakage of injected CO2 into geological formations. Thus, it is necessary to evaluate how injected CO2 affects caprocks during CO2 storage projects. This study assessed CO2 migration into a caprock from the injection reservoir and its interaction with the rock minerals of the caprock and brine. The caprock is the Sayindere Formation, which is a regionally extensive caprock in oil fields located in the southeastern part of Turkey including the Caylarbasi oil field, which has been previously identified and modeled as a potential CO2 storage site. The upper part of the Sayindere Formation consists of clay, and the lower part consists of clayey limestone. In this work, we performed 2-D radial modeling of CO2 injection at an annual rate of 1 million tons into the reservoir for 50 years and investigated its impact on the overlying caprock. The simulation was continued for further 1000 years without CO2 injection to evaluate the caprock evolution over longer time periods. Calcite dissolution was observed in the reservoir as well as the caprock. However, no significant increase in the porosity and permeability associated with calcite dissolution was observed in either formation. Minor diffusion of the injected CO2 into the lowermost layer of the caprock was observed over the simulation years. After 1000 years of post-injection, 70% of the injected CO2 was trapped in the reservoir under the caprock as a plume in a free phase, and the rest was dissolved in the reservoir brine. Sensitivity analyses were performed to determine how permeability anisotropy and reactant surface area of minerals affect the numerical results. Minor variations in the spatial distributions of CO2 saturation were observed when the permeability anisotropy was changed. No significant variation in the numerical results was observed with changes in the surface area of minerals. The simulation results suggest that the Sayindere formation is a very good caprock for potential CO2 storage. This work provides information for future decision-making and for development of CO2 storage demonstration projects in Turkey.
The origin of boron in boron-rich salt lakes in the Tibetan Plateau has long been the subject of debate. The Damzung Co Salt Lake in central Tibet has high boron concentrations (B = 276-313 mg/L) and is an ideal site for investigation. The aim of this study is to analyze the boron geochemistry and isotope composition of surface brine, source water, country rock, and Quaternary deposits (carbonate clay, stromatolite, and travertine) in the lake, to understand the unusual boron enrichment of the salt lakes in Tibet. Concentrations of boron in stream water samples from the basin are low (B = 0.172-2.08 mg/L), with the exception of one sample that has an input of geothermal water (B = up to 13.6 mg/L). Their variable boron isotope compositions represent the characteristics of country rock weathering input (δ11B = -8.6 to -0.5‰). Hot springs have much higher boron concentrations (B = 3.31-49.4 mg/L) than streams and cold springs (B = 0.434-4.82 mg/L). Boron isotope data show that the δ11B values of streams, hot springs (-9.8 to -8.5‰), and cold springs (-14.5 to -1.2‰) are much higher than those of the salt lake (-18.5 to -17.4‰), except in samples containing Quaternary deposits. This finding, therefore, rules out the possibility that the present boron deposits originate from country rock weathering or hot springs, as historically proposed by Chinese scientists. The slight variability in boron isotopic composition in the present lake indicates only one major boron source. Three samples containing Quaternary deposits have different boron isotopic compositions with -37.2 to -35.3‰ (carbonate clay), -29.5 to -24.9‰ (travertine), and -28.2 to -26.7‰ (stromatolite). The fractionation factor between carbonate clay and the lake are very similar to that between seawater, sediment and carbonate in a similar pH range, compared with stromatolite and travertine. Hence, we conclude that early carbonate clay deposits within the lake basin are the present main source of boron in the Damxung Co Salt Lake.
High natural fluoride (up to 6.1 mg/l) and boron (up to 2.1 mg/l) concentrations in groundwater are recorded in western Estonia, where a carbonaceous Silurian-Ordovician aquifer system is the main source of drinking water. The aim of this study is to examine the dissolution of boron and fluoride from different carbonate rocks using batch dissolution tests. The total boron and fluorine concentration within carbonate rocks varies between 100-1000 and 5-150 mg/kg, respectively. Generally, boron and fluoride concentrations increase as the amount of terrigenous material in the rock increases. Laboratory leaching experiments showed that the amount of leached boron and fluoride was proportional to the content of these elements in the rock samples. Further, boron and fluoride concentrations in leachates were positively correlated with the amount of terrigenous material in rocks. Both boron and fluoride concentrations in leachates continually rose over 49 days of leaching. Long-term water-rock interaction is responsible for the high boron and fluoride contents in groundwater of western Estonia.
A geochemical and chemostratigraphical study was undertaken on Campanian-Maastrichtian sedimentary rocks (the Colón-Mito Juan sequence and the upper La Luna Formation) in the southwestern Maracaibo Basin, Venezuela. The objectives of this work were to determine the paleoenvironmental and physico-chemical characteristics of the Colón-Mito Juan sequence and its possible subdivision into chemofacies and to study the main chemical differences between the Colón, Mito Juan, and La Luna Formations within the study region. One hundred and ninety-one rock samples were collected, and bulk inorganic geochemistry (TiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, P2O5, C, S, Rb, Cs, Ba, Sr, Th, U, Y, Hf, Mo, V, Cr, Co, Cu, Ni, Sc, La, Ce, Nd, Sm, Eu, Yb, Lu, As, Sb, Zn, and Be) was analyzed by instrumental neutron activation analysis or inductively coupled plasma-atomic emission spectroscopy; total sulfur and carbon analyses were performed by a LECO SC-432 apparatus and coulometry, respectively. Multivariate statistical techniques were applied to evaluate correlations within this group of variables. Using cluster-constrained analysis, eight subdivisions, or chemical facies, were defined: two chemofacies differentiating the intervals controlled by biogenic deposition and by the predominant clastic contribution; three chemofacies correlating with the lithologic units (La Luna, Colón, and Mito Juan); and another three chemofacies related to changes in the paleoredox conditions along the stratigraphic column. All of the units studied were deposited under a relatively constant climate regime, and the composition of the sediment source showed no significant changes. The prevailing physico-chemical regime was disoxic-oxic, with a trend of increasing oxygen concentrations towards the top of the column.
Recently, how to quantitatively estimate the growth rate of continental crust is an enigmatic issue. With the development of ICP-MS technology, the U-Pb dating and Lu-Hf isotopic compositions of detrital zircons from the fluvial sediments can provide an effective and simple approach to constrain the growth rate and evolutionary history of continental crust. In this paper, 189 concordant detrital zircons from the Laoha River have been analyzed for U-Pb ages and Lu-Hf isotopic compositions by excimer LA-MC-ICP-MS. Detrital zircons from samples LH and LH2 show three major age groups, i.e., 2370 Ma~2572 Ma, 1728~2087 Ma, 127~376 Ma and 2374~2598 Ma, 1765~2087 Ma, 119~405 Ma, respectively. They have the common prominent two stage Hf model ages with a peak at ca. 2.7 Ga, which is consistent with the global continental crust. These indicate that the timing of the strongest magmatic events is at ca. 2.5 Ga and 1.8 Ga, and the best estimation age of mantle extraction of the northeast margin of North China Craton is ca. 2.7 Ga. The detrital zircons with U-Pb ages of ~1.8 Ga and ~2.5 Ga have the two stage Hf model ages of ca. 2.7 Ga, whereas εHf(t) values are different from those of depleted mantle. These indicate that the majority of continental crust of the northeast margin of North China Craton at time of ~1.8 Ga originated from the reworking of ~2.7 Ga crust. About 5% of the present crustal volume in the northeast margin of North China Craton was formed at 2.9 Ga; whilst ~64% of the present crustal volume in the northeast margin of North China Craton has been formed at 2.5 Ga, which is higher than that of previous studies. It suggests that the continental crust growth in the North China Craton is not uniform, but it is consistent with the episodic growth of global continental crust (60%). Moreover, the majority continental crust of the northeast margin of North China Craton has been formed at 1.8 Ga (84%) as previously interpreted. Finally, we have used formulas to quantitatively calculate the reworking rate and give a suggestion that the time of 2.5 Ga is also the main growth period of continental crust of the North China Craton, and the time of 1.8 Ga is the strongest reworking period of the continental crust in the craton. In addition, the reworking rate began to drop after reactivating in the North China Craton, and the addition of depleted mantle was gradually increased.
Microbial activity in marine sediment plays an important biogeochemical role in cycling of carbon and other elements. Acetate is a key intermediate of various microbial metabolic pathways. In this study, we measured concentrations and stable carbon isotopic compositions (δ13C) of acetate in pore water of two core samples stored at near in-situ temperatures (4°C) within 3 hours and at room temperatures (25°C) for 19 hours after sample recovery. Acetate concentrations at 4°C were less than 3 μM throughout the sediment column, whereas they increased up to 13 μM in the samples stored at 25°C and corresponding δ13C values of acetate were enriched up to 8.7‰ relative to those of total organic carbon. Our results indicate that acetate-mediated microbial activity is rapidly changed with temperature increase and possible air contamination, and also suggest that sample processing at near in-situ temperatures in the short-term is required for accurate pore-water geochemical analysis.