A Mid-Miocene erosional unconformity from the Durban Basin,SE African margin: A combination of global eustatic sea level change,epeirogenic uplift,and ocean current initiation

Erosional unconformity surfaces are key indicators for the variations in eustatic sea level, ocean dynamics and climatic conditions which significantly affect depositional environments of sedimentary successions. Using a dense grid of 2D seismic data, we present new evidence from a frontier basin, the offshore Durban Basin, of a mid-Miocene age erosional unconformity that can be correlated with analogous horizons around the entire southern African continental margin.In the Durban Basin, this unconformity is typified by the incision of a mixed carbonate-siliciclastic wedge and ramp margin by a series of submarine canyons. Epeirogenic uplift of southern Africa characterised this period, with erosion and sediment bypass offshore concomitant with increases in offshore sedimentation rates. Although epeirogenic uplift appears to be the dominant mechanism affecting formation of the identified sequence boundary, it is postulated that an interplay between global eustatic sea-level fall, expansion of the east Antarctic ice sheets, and changes in deep oceanic current circulation patterns may have substantially contributed to erosion during this period.     

中西非裂谷系形成的动力学机制

中西非裂谷系是沿中非剪切带及邻区发育的一系列中新生代裂谷盆地,其成因机理一直存在争议。中西非裂谷系的构造演化主要经历了三个演化阶段,其中在早白垩世进入强烈断陷期,是盆地形成的重要阶段。以早白垩世中西非裂谷系的地质背景为基础,运用弹性力学有限元数值模拟方法,通过应力场和应变场的分析,为中西非裂谷系形成的力学机制提供依据。模拟结果表明,早白垩世非洲大陆内部走滑和伸展作用并存,中非剪切带不是所谓的"转换断层",而是与中西非裂谷系同时形成和发育的构造。中西非裂谷系是在中新生代泛大陆裂解时期,非洲板块绕西北非地块逆时针旋转,非洲内部不同地块在统一构造应力场作用下,由于伸展和走滑的差异作用形成和发育的。      

Recent lake level variations in Lake Haubi, central Tanzania, interpreted from pollen and sediment studies

Variations in pollen assemblages and in physical and chemical composition of a dated sediment record from the small Lake Haubi in north central Tanzania, reveal lake level fluctuations since the late 19th century. Lake Haubi changed from a seasonally inundated swamp to a lake in the beginning of the 20th century. With the exception of 1942-44, when it dried out completely, it remained water filled until 1994 when it again turned into a swamp. The lake level fluctuations in Lake Haubi are largely in phase with fluctuations of the larger East African lakes levels during the 20th century, and are therefore interpreted as being mainly controlled by regional climatic fluctuations. However, the initial formation of Lake Haubi at the turn of the century was likely due to local catchment specific causes, e.g. changes in land use, as the rapid increase in the water level at this time does not correspond to other lake level records from the region.     

DIFFERENCES BETWEEN DRY AND WET SUMMER IN THE VERTICAL MOTION ON NORTH SIDE OF QINGHAI-XIZANG PLATEAU AND THE THERMAL IMPACT OF PLATEAU

To better analyse and understand the causes of Northwest China(NW China)arid climateformation,firstly the dry and wet standards were chosen and the yearly dry and wet grades on thenorth side of Qinghai-Xizang Plateau(hereafter NSQXP)in summers were classified utilizing therainfall data of five stations over the area in June-August of 1952—1990.Then the differencesbetween the vertical motion over the Qinghai-Xizang Plateau(QXP)and NSQXP in dry and wetsummers were comparatively analyzed using the ECMWF's gridded data of June—August of 1979—1986.Finally the connection between the QXP surface thermal condition and the dry and wetsummers on the NSQXP was discussed as well.The main results are the following:(1)the dry and wet standards taking the rainfall standarddeviation as criterion are suitable for the arid climate area;(2)the QXP may be,to some extent.responsible for the environment background of Middle Asia,NW China and North China aridclimate areas;(3)there are the striking differences between the dominant vertical motion over theQXP and NSQXP in the dry and wet summers of NSQXP:(4)the QXP surface thermal conditionis.to a great extent,responsible for the year—to—year variation of NW China arid climate aswell.     

全新世期间亚洲和非洲干旱区环境的短尺度变化

过去对北非和中国干旱区140 ka BP来环境演化的初步对比表明,两地的干旱度在万年时间尺度上基本同步。这种关系是否也适用于全新世百年尺度的干旱事件,仍是有待研究的问题。本文对撒哈拉地区569个地表淡水指示物和我国北方干旱区158个古土壤和湖泊沉积的14C年代数据进行了时空频数统计分析,揭示出两地沙漠在全新世期间至少经历了三次同时性的、百年-千年尺度的干旱事件, 叠置于季风气候对地球轨道变化响应的总体趋势上;沙漠在纬向上的进退主要受控于季风前沿的伸缩幅度, 说明两个季风系统的短尺度变化可能受统一因素控制。最为显著的干旱事件发生于约4 ka BP。两地干旱区在过去认为的6 ka BP 前后的全新世气候适宜期并没有表现为稳定的湿润环境。我国过去发现的该时期不少的干旱证据被解释为高温所导致的强烈蒸发作用所致。但全新世中期的干旱期在热带的存在及其与冰心记录中低甲烷事件的吻合难以用蒸发来解释,而应与夏季风环流的减弱有关。     

中国开拓非洲市场的营销策略研究

本文从国际贸易地理出发,运用市场营销学原理,将非洲市场细分为三大市场体系和若干拟重点开发的子市场,并着重论述中国开拓非洲各大市场的营销策略和对策措施。     

Dissolved Iodate and Total Iodine During an Extreme Hypoxic Event in the Southern Benguela System

Dissolved iodate and total iodine were studied in St Helena Bay, South Africa, during a period of acute hypoxia, following upwelling off Cape Columbine. Despite the generally high concentrations of chlorophyll α (10–30 mg m⁻³) total iodine concentration was essentially constant in the main part of the Bay, and similar to that found elsewhere in the oceans. Occasional, lower concentrations of total iodine (0·28 to 0·42 μM) were found with exceptionally high chlorophyll α concentrations (500 mg m⁻³) in shallow waters. In contrast, iodate was found to be reduced to iodide at both the surface and the bottom of the Bay. The implications of these changes are discussed, given that the surface waters reflect sustained eutrophication while the bottom waters are hypoxic as a result of the organic-rich sediment from the waters above.     

GLOBAL AND LOCAL CHANGE ON THE PORT‐CITY WATERFRONT*

ABSTRACT. Successful waterfront redevelopment requires an understanding of global processes and an appreciation of the distinctiveness of port‐city locations. Waterfront revitalization occurs at the problematic and controversial interface between port function and the broader urban environment. It reflects varied forces and trends, involves community attitudes and environmental sensitivities, and influences transport evolution and urban change. The revitalization phenomenon is examined using community attitudes in Canada and urban regeneration in East Africa to illustrate retrospective and prospective dimensions.     

The Geography of Edible Insects in Sub-Saharan Africa: a study of the Mopane Caterpillar

Entomophagy, the human consumption of insects, has not received significant attention in Western literature, despite the critical role which it plays as a protein supplement in many parts of the world. This paper explores the importance of entomophagy in Africa within the context of food security and indigenous technical knowledge. These issues are further investigated through a case study of the mopane caterpillar in Southern Africa. The findings clearly indicate the contribution which insects make to the diet of rural Africans.