新疆且末县米特河地区1:5万水系沉积物地球化学特征及找矿意义

根据1:5万水系沉积物地球化学测量工作成果,对采集的3138件样品中Cu,Pb,Zn,Au,Ag,W,Sn,Mo,Bi,As,Sb,Cr,Co,Ni共14种元素进行分析测试。研究结果表明,Au,Ag,Cu,Ni是区内最有找矿潜力的成矿指标元素;聚类分析所划分的4类元素簇群,主要与中低温成矿元素、阿尔金南缘断裂、蛇绿混杂岩相关,通过因子分析得到Ni-Cr-As-Sb-Cu-Bi,W-Bi-As-Cu,Bi-W,As,Ag-Zn-Pb,Cu-Bi-As共6类元素组合。其中Cr,Ni,Sb,Cu,As,Bi组合反映出与低温热液活动和断裂构造活动有关;Cr,Ni元素的富集主要与研究区内叶桑岗蛇绿混杂岩带关系密切;Ag,Pb,Zn组合则与地层低温热液元素局部富集和断裂构造活动密切相关。在综合异常分析和查证的基础上,结合区域成矿地质条件、区内矿产地质特征,圈定、划分出2个找矿远景区,并指出了研究区内以金、铜、银、镍为主要优势矿种,铅、锌为潜力矿种。     

滨州海岸带土壤和海底沉积物重金属空间分布特征

通过对滨州近海海域海底沉积物测试数据及海岸带陆域土壤地球化学分析,对滨州海岸带陆域土壤和海底沉积物中7种重金属(Hg,Cd,Pb,Cu,Zn,Cr,Ni)的空间分布特征进行了研究,并绘制了各指标含量陆海联合分区图。分析结果表明,滨州市海岸带重金属元素含量基本上均低于国标规定的海洋一类沉积物的最高标准,仅有个别元素含量超过一级标准值,表明局部存在一定的重金属污染。从滨州海岸带重金属含量空间分布上来看,除Hg元素外,其余重金属元素含量呈现一定的规律,基本上陆域含量高于海域含量,且大部分元素都呈现出陆域城镇值高,郊区值低的态势。区内化工企业较发达,Ni,Cr属于中度变异区,Cd,Hg,Pb属于高度变异,受人为影响因素较大,考虑区内土壤及海底沉积物重金属富集主要来源于工业"三废"。     

The ability of detainment bunds to decrease sediments transported from pastoral catchments in surface runoff

Erosion leading to sedimentation in surface water may disrupt aquatic habitats and deliver sediment-bound nutrients that contribute to eutrophication. Land use changes causing loss of native vegetation have accelerated already naturally high erosion rates in New Zealand and increased sedimentation in streams and lakes. Sediment-bound phosphorus (P) makes up 71–79% of the 17–19 t P y⁻¹ delivered from anthropogenic sources to Lake Rotorua in New Zealand. Detainment bunds (DBs) were first implemented in the Lake Rotorua catchment in 2010 as a strategy to address P losses from pastoral agriculture. The bunds are 1.5–2 m high earthen stormwater retention structures constructed across the flow path of targeted low-order ephemeral streams with the purpose of temporarily ponding runoff on productive pastures. The current DB design protocol recommends a minimum pond volume of 120 m³ ha⁻¹ of contributing catchment with a maximum pond storage capacity of 10 000 m³. No previous study has investigated the ability of DBs to decrease annual suspended sediment (SS) loads leaving pastoral catchments. Annual SS yields delivered to two DBs with 20 ha and 55 ha catchments were 109 and 28 kg SS ha⁻¹, respectively, during this 12-month study. The DBs retained 1280 kg (59%) and 789 kg (51%) of annual SS loads delivered from the catchments as a result of the bunds' ability to impede stormflow and facilitate soil infiltration and sediment deposition. The results of this study highlight the ability of DBs to decrease SS loads transported from pastures in surface runoff, even during large storm events, and suggests DBs are able to reduce P loading in Lake Rotorua.     

Cl/Br of scapolite as a fluid tracer in the earth's crust: insights into fluid sources in the Mary Kathleen Fold Belt,Mt. Isa Inlier,Australia

A combination of analytical methods, including trace element analysis of Br in scapolite by LA‐ICP‐MS, was employed to unravel the fluid–rock interaction history of the Mary Kathleen Fold Belt of northern Australia. Halogen ratios in the metamorphic and hydrothermally derived scapolite from a range of rock‐types record interaction between the host rocks and magmatic‐hydrothermal fluids derived from granite plutons and regional metamorphism. The results show that halite‐dissolution supplied at best only minor chlorine to fluids in the Fold Belt. Chlorine/bromine ratios in metamorphic scapolite indicate that fluids were dominantly derived from basinal brines formed from sub‐aerial evaporation of seawater beyond the point of halite saturation. This bittern fluid infiltrated the underlying sedimentary sequences prior to regional metamorphism. Zoned scapolite in a major late metamorphic mineralized shear‐zone records three discrete pulses of magmatic and metamorphic fluid, and it is suggested that fluid mixing may have assisted mineralization along and around this shear‐zone. As a crucial prerequisite for halogen fluid tracer studies using scapolite, we find in our samples that Cl and Br do not fractionate when incorporated in scapolite. Furthermore, unaltered rims of heavily retrogressed scapolite show indistinguishable Cl/Br signatures compared with fresh grains from the same sample indicating retrograde metamorphism did not significantly affect Cl and Br signatures in scapolite group minerals.     

Influence of late holocene pyroclastic eruptions on the sedimentary geochemistry of Lake Rotoiti,North Island,New Zealand

Lake Rotoiti in Taupo Volcanic Zone was formed by damming of the drainage system through the floor of Okataina Caldera. Basin sediments are predominantly silt or sand, with mineralogy consistent with derivation from local silicic rocks and airfall tephras. Sandy lithofacies around the shoreline are wave worked deposits. Sand and gravel lithofacies in deeper water and on steep slopes are largely relict or airfall tephras, or both. Profundal sediments are diatomaceous silts. Organic-rich diatomaceous silts also accumulate in near-shore wave-damped zones under weed beds.Short cores penetrated the Tarawera (1886 AD) and Kaharoa (1180 AD) Tephras, identified by their stratigraphic position, geochemistry and mineralogy. Localised slumping is evidenced from secondary tephras interbedded and redeposited within the basin silts. Sedimentation rates in the basins, estimated from the age of bounding tephras, are 0.9 to 4.0 mm y^-1, and are highest under the influence of inflowing water from adjacent Lake Rotorua. For several hundred years prior to the Tarawera eruption sediment accumulation rates and the sediment geochemistry remained unchanged; deposition was predominantly biogenic opaline silica with a small terrestrial component. The Tarawera eruption deposited a terrestrial-silica, aluminum-rich primary tephra across the lake, which was followed by reworked tephra from within the catchment, the effects of which were progressively diluted by biogenic opaline silica as conditions stabilised. While the major effects of the eruption have been rapidly absorbed the lake has not returned to pre-eruption background conditions. A new equilibrium has been attained in which Tarawera Tephra continues to be eroded into the lake and is the principal source for a doubling of sedimentation rates following the eruption. High arsenic levels in some diatomaceous silts are attributed to episodic venting of hydrothermal fluids or gases into the water column.     

The occurrence of Greigite in sediments from Loch Lomond

Greigite has been identified in the sediments of Loch Lomond using X-ray diffraction. Greigite is the dominant magnetic mineral in the oldest sediments recovered, while magnetite predominates in the younger sediments which had previously been used for palaeomagnetic secular variation studies. A layer of sediment in between these two magnetic mineral regimes has very low magnetic concentrations, probably as a consequence of magnetite dissolution associated with sulphide rich pore-waters produced at the time of a marine incursion. The greigite largely oxidises once the sediment is exposed to air, but if freeze dried the greigite becomes surprisingly stable. Following freeze drying the greigite can be heated to 280°C in air before it alters and loses its strong ferrimagnetic properties.     

Microbial nitrogen transformations in sediments and inorganic nitrogen fluxes across the sediment/water interface on the South Island West Coast,New Zealand

In January 1982, sediment microbial N transformations and inorganic N fluxes across the sediment/water interface were studied at nine sites off the South Island West Coast, New Zealand. The sediments showed a great variety in physical, chemical and biological properties. The sediment organic matter had a molar $\text{C}\text{N}$ ratio of 5.9–10.9, and the total $\text{N}\text{P}$ ratio was 1.2–4.0. The denitrification capacity in the top 7.5 cm of sediment was 0.1–77.2 mmol N m^?2 day^?1 and generally declined with increasing sediment depth. The in situ denitrification rate was 0.02–1.84 mmol N m^?2 day^?1 and highest activities were generally found in surface sediments and at 6–7.5 cm depth. Denitrification accounted for 82–100% of total nitrate reduction. Net N mineralization was indirectly estimated at 0.6–2.4 mmol N m^?2 day^?1, and the experimental determination of this N transformation gave 0.6–3.2 mmol N m^?2 day^?1. Denitrification accounted for 3–75% of net N mineralization. The diffusive flux of ammonium and nitrate across the sediment/water interface was 0.1–0.7 and 0.1–0.6 mmol N m^?2 day^?1, respectively.     

Evidence for phosphorus limitation in carbonate sediments of the seagrass Syringodium filiforme

The seagrass Syringodium filiforme was examined in an ecological analysis of plant nutrient requirements and nutrient resource availability. Assessment of the sediment geochemistry in a San Salvador Island seagrass bed indicated that phosphorus was not readily accessible to the plants. Ammonium regeneration in the fine-grained carbonate sediments was high, and interstitial concentrations averaged ca. 100 μM while phosphate replenishment to interstitial water was low, and concentrations were generally less than 2 μM. Analysis of the seagrass leaf tissue content (C : N : P = 1390 : 47 : 1, atomic wt) suggested that nitrogen and phosphorus were both depleted relative to carbon. However, this high N : P for S. filiforme and the low concentration of phosphate available in the interstitial water established the likelihood that plant acquisition of phosphorus was limited. The finding of high root biomass relative to leaf biomass in these seagrass beds corroborates this evidence by depicting a method of plant adaptation that increases nutrient absorptive root surface area.     

Holocene floodplain diachronism and inherited downstream variations in fluvial processes: A study of the river Perry,Shropshire, England

This paper attempts to explain downstream variations in the rates and processes of Holocene floodplain formation in a small to medium-sized, lowland catchment in Central England. Four macro-reaches were identified and horizons from at least one stratigraphic cross-section from each were radiocarbon dated. Considerable diachronism was revealed with the basal age and hence minimum residence time of the top two metres varying from 1000-9000yrs. The trend, a decrease in minimum residence time downstream, is explained by the basin-and-gorge bedrock long-profile inherited from the Devensian glaciation of the area. This is illustrated by a positive relationship between the mean floodplain accumulation rate and the SL index (slope-stream length product). Pollen analysis of the organic sediments shows that floodplain clearance took place around 1 300 BP, but probably locally, pre-dated and post-dated accelerated alluviation associated with agricultural expansion in the catchment. This study concludes that (a) different macro-reaches in this small to medium-sized catchment have adjusted in different ways to long-term catchment changes as part of autogenic floodplain evolution, (b) this has involved a change in the catchment's sediment conveyance characteristics during the Holocene, and (c) an important control on channel behaviour and floodplain sedimentation throughout the Holocene (as well as at present) has been the valley slopes inherited from the Quaternary glaciation of the area.     

A comparative study of mercury contamination in the Tagus estuary (Portugal) and major French estuaries (Gironde,Loire, Rhône)

Concentrations of mercury were determined for the waters, suspended matter and sediments of the Tagus and of major French estuaries.The Tagus estuary is one of the most contaminated by mercury derived from the outfalls of a chloralkali plant and from other industrial sources. In deposited sediments the median level, 1·0 μg Hg g^?1, is twenty times higher than the natural background and Hg contents depend on the sediment grain-size, age and the distance from waste-outfalls. Suspended matter is more regularly and highly contaminated (median value: 4·5 μg Hg g^?1). In the French estuaries Hg levels in the suspended material decrease with salinity due to dilution and/or remobilization processes. In June 1982, in the Loire estuary, high values of Hg are observed in the middle estuary and attributed to urban and industrial sources.In the Tagus estuary, the general distribution of total dissolved Hg confirms the contamination: it increases seaward from 10 ng 1^?1 in the river to 80 ng 1^?1 in the estuary outlet. The dissolved Hg is almost totally organic in the river, inorganic in the middle estuary due to inorganic Hg effluents and again organic in the lower estuary. This variation is related to the dissolved organic carbon values. The dissolved Hg levels in the Loire Estuary (5–300 ng 1^?1) are much higher than in the Gironde estuary (3–6 ng 1^?1) and of the same order as those observed in the Tagus estuary.