东太平洋中国开辟区沉积物中热水活动的矿物学及地球化学证据

通过对东太平洋多金属结核中国开辟区表层沉积物和短柱状沉积物的系统观察和分析，首次根据矿物学和地球化学两方面的证据，发现中国开辟区沉积物中热水活动及其产物的存在。X射线衍射分析表明，沉积物样品中普遍含有重晶石，部分样品中含量高达10％以上，扫描电镜观察发现，重晶石均为完整自形晶，并与同为自形的石英及钠长石共生。根据本区重晶石的地质背景及结晶形态，可以认为它的形成环境与加利福尼亚湾瓜伊马斯盆地（Guaymas)相似，属热水成因，伴生的石英和钠长石亦为常见的热水矿物，。这一共生组合的形成温度不低于70℃。地球化学研究发现，在柱状沉积物剖面上，Ba的垂向分布有两种类型，一种为平稳型，在一定深度范围内无明显变化。另一种为跃升型，并伴有其他活泼组分的同步变化，跃升型可视为热水活动在沉积历史上的记录，迄今为止，热水矿物组合主要见于东区的表层沉积物，而在西区，Ba在沉积物中的富集主要见于10cm以下层位，根据沉积速率推算，在中国开辟区西区的热水化活动记录比东区至少早0．1Ma。     

中国白垩纪沙漠中的戈壁沉积

戈壁是广义沙漠体系的一个组成部分，然而在沙漠研究尤其在古沙漠研究中未得到充分的重视。笔者根据近年来的古今沙漠的研究，讨论了戈壁的形成作用、中国白垩纪沙漠戈壁沉积和风磨石的形成和分布特征，以便引起广大同行的重视。     

Freshwater snail communities and lake classification. An example from the Åland Islands, southwestern Finland

The freshwater snail fauna in 51 lakes on the Åland Islands was investigated. By means of cluster analysis it appears that lakes may be divided into four groups on the basis of snail species composition. The lakes of the four groups show a spatial distribution which is related to topographical differences, terrestrial vegetation and land use. Snails may be divided on the basis of water hardness into hard water species and calcium indifferent species or into demanding and modest/indifferent species when clustering is based on presence/absence.     

ON THE NUMBER OF FRACTIONS TO COMPUTE TRANSPORT OF SEDIMENT MIXTURES

1 INTRODUCTIONMany hydro-momhological mathematical models neglect the innuence of river bed maerialheterogeneity and its time and space changes during transport and related erosion/dePosition processes. Inthese models a rePresentative diameter of the river bed grain-size distribution (for examPle d5o) isspecified as initial data in each comPutational point of the modeled domain. Different d5o can be assignedto each ghd point but temPoral changes in bed material gradation cannot be simula…     

The Upper Permian Sedimentary Facies and Its Role in the Dajing Cu-Sn Deposit, Linxi County, Inner Mongolia, China

Abstract: Exhaustive investigations were launched for confirming the upper Permian host rocks of the Dajing Cu-Sn Deposit, probing into the possibility that Dajing is a Sedex type deposit during cosedimentation, complementing the deficiency of previous researches and going further into substantiating the role of the upper Permian strata in the control of ore distribution. After more than two years work, we reclassified the sedimentary facies in the Dajing area and its periphery as shallow fresh water lake and delta. Indicative sedimentary structures, such as ripple marks, rain marks, and mud cracks combined with contemporary fossils, were revealed. Having measured the flow directions, performed chemical comparison, and analyzed various sediments from sourceland in the Dajing area by XRF, we consequently redivided the strata into four sedimentary members, among which P₂l₁ and P₂l₂ were concluded as significant ore-hosted strata. The upper Permian basin was a lateral rift basin. The water and sediments in the basin are much deeper and thicker in the north than those in the south.
The indicators of special sedimentary facies, such as gravity flow, brine pool and synchronogenic stratiform structure of the ore cannot be found in the Dajing area. There was no growth fault, assemblage of sulfide and sulfate, and no zonation as well.
On the basis of study in this area, taking into account the paleosedimentary environment as capriciously flowing shallow lake, which approximated the state of oxidation, we figured that the paleogeography made it prohibitively difficult to form stratiform sulfide deposits which are prone to form in deoxidized environment. It can be ruled out the possibility that the Dajing deposit is a syngenetic deposit during sedimentation.     

Pollution vulnerability of the Quaternary aquifer near Cairo, Egypt, as indicated by isotopes and hydrochemistry

The present study was conducted to delineate the pollution vulnerability of the Quaternary aquifer in two areas, Imbaba and Shobra El-Khima, near Cairo, Egypt. Environmental isotopes combined with hydrochemistry were used for this purpose. The groundwater in the Imbaba area (average total dissolved solids about 900 mg/L; sodium/chloride, sulfate, and bicarbonate water types) is more mineralized than groundwater in the Shobra El-Khima area (average total dissolved solids 500 mg/L; calcium and sodium/bicarbonate water type). A high nitrate content and significant mineralization in the groundwater are probably due to contamination of recharge to the aquifer by irrigation drainage, deteriorated sewage networks, and septic tanks. The deuterium and oxygen-18 compositions of the groundwater are depleted compared to Nile River water, which is the main source of aquifer recharge. This less isotopically enriched water probably represents older Nile water recharge that flooded the region before construction of the Aswan High Dam in 1963, or it is a mixture of a young water and originally deposited paleowater that was in deeper horizons at a time of cooler and more humid climate. Intensive pumping has moved the paleowater higher in the aquifer. Groundwater in the Shobra El-Khima area has higher residence time, based on the tritium concentration, than groundwater in the Imbaba area. The percentage of the isotopically depleted water equals 75% in the Shobra El-Khima and 35% in Imbaba, and the thickness of the clay cap above the aquifer is 38 m in Shobra El-Khima and 20 m in Imbaba. These factors are indicative of the rate of recharge to the aquifer and were used to evaluate the pollution vulnerability in the two areas. Electronic Publication     

Caspian Sea amphipods: biodiversity,systematic position and ecological peculiarities of some species

In the Caspian Sea, one group of crustaceans, the Amphipoda, is represented by 72(70?) species, 60(58?) of which are gammarids, arranged in 20 genera. Almost all are endemic to the Ponto-Caspian zoogeographical region. To simplify the taxonomy of the genusGammarus Fabricius s.l., the Caspian gammarids ought to be grouped in 4 genera:Dikerogammarus Stebbing,Pontogammarus Sowinsky,Stenogammarus Martynov, andChaetogammarus Martynov. Taking into account the influence of different ecological factors on the external morphology of gammarids, we consider that all described forms ofDikerogammarus haemobaphes (Eichwald),D. villosus (Sowinsky),D. palmatus Martynov,D. fluviatilus Martynov, and perhapsD. aralensis (Uljanin) are one species —D. haemobaphes. Study of the ecological area and distribution ofIphigenella andrusovi Sars,Pandorites podoceroides (Grimm) andChaetogammarus placidus Sars indicates that these species are endemic to the Caspian Sea.     

The late Quaternary development of three ancient tarns on southwestern Cumberland Peninsula, Baffin Island, Arctic Canada: paleolimnological evidence from diatoms and sediment chemistry

Sediment diatom and chemical analyses of cores from three poorly buffered extra-glacial lakes on the northeastern margin of the Canadian Shield (Cumberland Peninsula, Baffin Island) record interactions between aquatic and terrestrial spheres that were influenced by late Quaternary climatic conditions. Although differences exist between each of the lakes, notably with regards to the intensity of pre-Holocene catchment erosion and the timing of the onset of organic sedimentation, an underlying pattern of lake ontogeny, common to all three lakes, is identified. Although intensified watershed erosion characterized the Late Wisconsinan and Neoglacial cold periods, the lakes nonetheless remained viable ecosystems at these times. Sudden catchment stabilization during the late-glacial to earliest Holocene is associated with incipient organic sedimentation. Lake-water pH increased at this time, likely in response both longer base cation residence times as lake flushing rates decreased, and enhanced alkalinity production from sediment biogeochemical reactions. Subsequently, as the catchments remained stable during the productive early Holocene (c.9–7 ka BP), then gradually received a renewed increase of minerogenic sedimentation, the breakdown of sources of lake alkalinity resulted in natural acidification. Burial of cation-rich mineral sediments and the loss of permanent sedimentary sinks for the products of microbial reduction likely impeded within-lake alkalinity production, and catchment-derived base cations appeared ineffective in curtailing pH declines. The general nature of the Holocene development of these lakes is similar to that observed elsewhere on crystalline terrains, following deglaciation. Our data therefore suggest that catchment glaciation is not a necessary precursor for models of lake development characterized by initial base cation enrichment and subsequent gradual acidification.     

Suspended sediment transport and deposition in a high arctic meromictic lake

A study of sedimentary processes and sediment yields in a high arctic meromictic lake (Lake C2, Taconite Inlet, Northern Ellesemere Island, Canada) was undertaken from May 1990 through August 1992 to understand the links between climatic controls, hydrology, and the laminated sediment record preserved in the lake. Understanding the relationships between processes and the sediment record is critical for interpreting the climatic significance of the laminated sediments in a region where high resolution climate proxy records are quite limited.Sediment transport to Lake C2 is dominated by fluvial processes. During the early part of the melt season slushflows transport sediment to the lake surface. Subsequently, suspended sediment is delivered to the lake by the main inlet stream and distributed lakeward by a plume emanating the main inlet channel. Due to the strong density stratification of the water column the plume distributes sediment downlake by overflows and interflows in the epilimnion. In general, overflows are generated by lower discharge events whereas interflows penetrate to the halocline during high discharge with increased suspended sediment concentration.Sediment trap analysis demonstrates that suspended sediment transport and deposition responds to diurnal through annual changes in stream discharge. Seasonal and annual sediment trap yields agree with average accumulation rates determined from varve thickness measurements and cumulative suspended sediment discharge from the main inlet stream indicating a close link between climatological, hydrological, and sedimentological controls and varve deposition.This is the fourth in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.