Future seagrass beds: Can increased productivity lead to increased carbon storage?

While carbon capture and storage (CCS) is increasingly recognised as technologically possible, recent evidence from deep-sea CCS activities suggests that leakage from reservoirs may result in highly CO₂ impacted biological communities. In contrast, shallow marine waters have higher primary productivity which may partially mitigate this leakage. We used natural CO₂ seeps in shallow marine waters to assess if increased benthic primary productivity could capture and store CO₂ leakage in areas targeted for CCS. We found that the productivity of seagrass communities (in situ, using natural CO₂ seeps) and two individual species (ex situ, Cymodocea serrulata and Halophila ovalis) increased with CO₂ concentration, but only species with dense belowground biomass increased in abundance (e.g. C. serrulata). Importantly, the ratio of below:above ground biomass of seagrass communities increased fivefold, making seagrass good candidates to partially mitigate CO₂ leakage from sub-seabed reservoirs, since they form carbon sinks that can be buried for millennia.     

Physical conditions driving the spatial and temporal variability in aquatic metabolism of a subtropical coastal lake

We investigated the importance of meteorological and lake physical conditions for temporal, horizontal and vertical differences in the concentration of dissolved oxygen (DO) and water temperature, and the derived daily estimates of gross primary production (GPP), ecosystem respiration (R) and net ecosystem production (NEP). Our study was conducted in a subtropical and polymictic lake in Southern Brazil, during a spring–summer transition. Metabolic rates were determined from two sites using the open water oxygen technique. At the central deep site, oxygen sondes were deployed at three depths to assess patterns in vertical variability. During 10 days, an additional DO and temperature sonde was placed near the shoreline allowing us to compare metabolic differences in the surface layers between the central pelagic and littoral site. While GPP was similar, R was significantly higher at the shallower littoral site, causing NEP to be lower, although NEP was still positive. The littoral site had less diel changes in DO and higher daily variability in all metabolic rates. Variability in GPP and R at the littoral site was related to temperature, wind speed and rainfall suggesting that short-term variability in metabolic rates in shallow areas are sensitive to resuspension of sediments caused by a less stable water column. A clear vertical gradient was furthermore found for the metabolic rates at the central deep part of the lake, related to the light extinction, with highest GPP around 0.3 m and decreasing with depth, while respiration showed the inverse pattern. Below subsurface, respiration prevailed at 5.0 m depth and was uncoupled to primary production. Under conditions with high light and temperature, and low wind speeds, the mixing depth became shallower, in turn increasing the water column stability at the deep pelagic site, which resulted in higher mean light available and higher GPP in the water column. Our results confirm that deployment of sensors in different sites and depths allows for spatially, as well as temporally more representative estimates of lake metabolism.     

Basin scale distribution of organic matter in marine fine-grained sedimentary rocks: Insight from sequence stratigraphy and multi-proxies analysis in the Montney and Doig Formations

The occurrence of hydrocarbons in self-sourced reservoirs strongly depends on the concentration and maturity of organic matter in sediments. Therefore, understanding the distribution of organic heterogeneity at the time of deposition is key to reduce the risk in exploration and development of unconventional resources. This study focuses on the Lower and Middle Triassic Montney and Doig Formations (Alberta and British Columbia). Samples from outcrops, cores and cuttings were analyzed for organic content with a Rock-Eval VI and for major and trace element concentration using ICP-MS and ICP-AES techniques. The interpretation of the analysis results in relation with the stratigraphic architecture provides a mean to better understand the distribution of the organic heterogeneities and the variations of primary productivity, sedimentation rates and anoxia that control the development of source rocks.The key findings of this analysis are:- The basin-scale distribution of the organic matter suggests that the two major source-rock intervals of the Lower and Middle Triassic correspond to the sequence 3 (Spathian Montney unit) and to the transgressive systems tract of sequence 4 (Doig phosphate zone).- The dominant controls on organic matter accumulations vary through time. The Montney source-rock interval is interpreted to be associated with a major basin restriction triggering anoxia during a second-order falling stage of relative sea level. The organic accumulation of the Doig phosphate zone is interpreted as being controlled by a sharp decrease of the sedimentation rate, combined with an increase of the primary productivity.- The spatial and temporal variations of anoxia, primary productivity and dilution reflect the geodynamic evolution of the basin that ultimately controls the basin physiography as well as the sources of nutrient and sediments.     

Control of facies,maturation and primary migration on biomarkers in the Barnett Shale sequence in the Marathon 1 Mesquite well,Texas

A great deal is known about the genetic relationships between biomarkers and their biogenic precursors in organic rich rocks. The same is true of the way in which biomarker compound ratios change during maturation. On the other hand, very little is known about whether a crude oil can fully retain its inherent compositional ancestry during expulsion from a source rock. Thanks to shales being characterized in great detail for their unconventional resource potential, new information is gradually coming to light. Here we report on observations in biomarker geochemistry of a thermally mature core of the Barnett Shale, in which organofacies and maturity are essentially the same, but where intraformational sources and reservoirs have already been reported.Our results indicate that most biomarkers are not fractionated as the primary migration of petroleum within source rocks takes place. The 20S/(20S + 20R) ratio of C₂₇ steranes is uniform in the whole source-rock sequence, while the 20S/(20S + 20R) ratio of C₂₉ steranes shows indistinctly high values in the reservoir unit. The 20S/(20S + 20R) ratio of diasteranes and the 22S/(22S + 22R) ratio of C₃₁ 17α-hopanes do not appear to have been fractionated, which may be a result of the thermal isomerization reactions predominating over and masking out the possible fractionation effects. Diasteranes/steranes ratios do not exhibit features that suggest an association with fractionation, but rather are broadly correlated with lithology. However, compared to the diasteranes/steranes ratios, the Ts/(Ts + Tm) ratio is much more sensitive to changes in mineral compositions. Variations in the Ts/(Ts + Tm) ratio show a positive correlation (R² = 0.73) with mixed-layer illite-smectite content. Fractionation in the Ts/(Ts + Tm) ratio, if it has so occurred, may be subsequently overprinted by in-situ clay-catalyzed reactions.     

Petrographic and geochemical characteristics of the lacustrine black shales from the Upper Triassic Yanchang Formation of the Ordos Basin,China: Implications for the organic matter accumulation

The lacustrine black shales in the Chang7 Member from the Upper Triassic Yanchang Formation of the Ordos Basin in Central China are considered one of the most important hydrocarbon source rocks. However, the mechanism of organic accumulation in the black shales remains controversial. To resolve the controversy, with the former paleontological data of Yanchang Formation and sedimentation rate data of the Chang7 black shales, we investigated the typical intervals of the Chang7 black shales (TICBS) which were obtained by drilling in Yaowan at the southern margin of the Ordos Basin and performed various sedimentary, isotopic and geochemical analysis, including the sedimentary petrography, pyrite morphology, total organic carbon (TOC) and total sulfur (TS), the ratio of pyritic Fe to total Fe (DOP_T), major and trace elements, together with pyritic sulfur isotopes (δ³⁴S_py). The high sulfur content, enrichment of redox-sensitive trace metals, and the lower sedimentation rate of the TICBS in addition to the presence of marine spined acritarchs and coelacanth fossils indicate that the TICBS were deposited in a lacustrine environment possibly influenced by seawater. The petrographic observations show a thick layer of black shale with interlayers of thin layered siltstone (silty mudstone) and laminated tuff, which were related to the turbidity currents and volcanism, respectively. The U/Th, C-S, and Mo-U covariations, pyrite morphology, DOP_T, combined with the δ³⁴S_py, suggest that the deposition occurred beneath the anoxic-sulfidic bottom waters, which was intermittently influenced by the oxygen-containing turbidity. The Ni/Al and Cu/Al possibly show extremely high to high primary productivity in the water column, which might be connected with the substantial nutrients input from seawater or frequently erupted volcanic ash entering the lake. In addition, the coincidence of an increased abundance of TOC with increased P/Al, Ni/Al, Cu/Al and U/Th, as well as relatively consistent Ti/Al suggest that the accumulation of the organic matter might be irrelevant to the clastic influx, and was mainly controlled by the high primary productivity and anoxic-sulfidic conditions. Further, the covariations of TOC vs. P/Al and TOC vs. Ba/Al indicate that the high primary productivity led to the elevated accumulation and burial of organic matter, while the anoxic to sulfidic conditions were likely resulted from an intense degradation of the organic matter during the early diagenesis. In summary, the organic matter accumulation is ultimately attributed to the high primary productivity possibly resulted from seawater or volcanic ash entering the lake.     

Towards a framework for delineating sub-districts for primary health care administration in rural Ghana: A case study using GIS

This paper examines the need to carry out primary health care administration, programming and planning beyond the established 110 districts in Ghana. The framework for delimiting the sub-districts is offered by the availability of digital data such as the district boundary, site location, road network and population. Using the specified travel distance from predetermined sites, network analysis generates approximate polygons around the health centres to create functional areas ? the health sub-districts. Additional sites are proposed based on a set of criteria which includes proximity, centrality, population and existing level of infrastructural development in an attempt to improve coverage and bring the total utilization of health facilities closer to 100% in the study area.     

声雷达研制及声雷达试观测工作

报告了声雷达的研制及试观测的情况。     

格里戈良分带指数法在小龙钨矿区深部地球化学找矿预测中的应用

运用格里戈良分带指数法研究确定了小龙钨矿原生是晕轴向分带序列，该分带序列准确地反了矿床元素垂向变化规律，对指导本区深部铜、银、钨地球化学找矿预测评价和坑道工程署有重要意义。     

桑掌沟煤矿采空区工程地质综合勘察及对公路路基影响的初步评价

通过对桑掌沟村办煤矿采空区进行的地质采矿调查、地球物理探测和钻探等勘察工作，查明了该矿采空区的地质与工程地质特征、采空区的分布范围及塌陷冒落特征等，依据这些综合勘察结果，认为路基下伏的采空区将会使地表继续变形，影响高速公路路基路面的正常使用和维修。建议在路面基底层下部加铺一层土工织物或用稀少注浆孔内注浆来加固地基，如能充填采空区则可彻底解决地表变形问题。     

老鸦巢金矿床勘探方法与网度探讨

老鸦巢金矿床原是一个铅锌老矿山,经研究发现在贫铅锌贡铁矿矿体中伴生自然金构成独立金矿床。勘探金矿时利用已有坑道,配合坑内水平钻探。为选取合理钻探口径,在已有穿脉进行采样模拟试验,结果表明7×3cm刻槽样与φ75钻进的岩矿心样相当,从而采用φ75坑内水平钻代替坑探圈定矿体,加快勘查周期,节约了费用。通过网度试验表明,40×25m网度求取C级储量是合理的。