Sedimentation patterns in the Selenga River delta under changing hydroclimatic conditions

The Selenga River delta (Russia) is a large (>600 km²) fluvially dominated fresh water system that transfers water and sediment from an undammed drainage basin into Lake Baikal, a United Nations Educational, Scientific, and Cultural Organization World Heritage Site. Through sedimentation processes, the delta and its wetlands provide important environmental services, such as storage of sediment‐bound pollutants (e.g., metals), thereby reducing their input to Lake Baikal. However, in the Selenga River delta and many other deltas of the world, there is a lack of knowledge regarding impacts of potential shifts in the flow regime (e.g., due to climate change and other anthropogenic impacts) on sedimentation processes, including sediment exchanges between deltaic channels and adjacent wetlands. This study uses field measurements of water velocities and sediment characteristics in the Selenga River delta, investigating conditions of moderate discharge, which have become more frequent over the past decades (at the expense of peak flows, Q > 1,350 m³ s^?1). The aims are to determine if the river system under moderate flow conditions is capable of supporting sediment export from the main distributary channels of the delta to the adjacent wetlands. The results show that most of the deposited sediment outside of the deltaic channels is characterized by a large proportion of silt and clay material (i.e., <63 μm). For example, floodplain lakes function as sinks of very fine sediment (e.g., 97% of sediment by weight < 63 μm). Additionally, bed material sediment is found to be transported outside of the channel margins during conditions of moderate and high water discharge conditions (Q ≥ 1,000 m³ s^?1). Submerged banks and marshlands located in the backwater zone of the delta accumulate sediment during such discharges, supporting wetland development. Thus, these regions likely sequester various metals bound to Selenga River sediment.     

Genetic connectivity among populations of two congeneric direct-developing whelks varies across spatial scales

We examined the phylogeographic structure of two congeneric, direct-developing, intertidal whelks endemic to New Zealand, Cominella virgata and C. maculosa. A total of 855 specimens were collected from 23 rocky shore locations and we used them to determine the level of DNA sequence variation at the mitochondrial DNA (mtDNA) cytochrome c oxidase subunit I gene. Cominella virgata and C. maculosa have relatively high levels of haplotype diversity but low levels of nucleotide diversity. Sample sites formed regional groups that were composed of genetically differentiated populations, a finding consistent with their limited dispersal abilities. Cominella virgata showed higher levels of regional differentiation than C. maculosa, and there were also species-specific differences in genetic patterns within some regions. Both species exhibited genetic homogenisation among proximate sites within groups, suggesting some dispersal does occur between areas that are not connected by contiguous rocky shore habitat.     

黄河调水调沙期间黄河入海水沙的扩散与通量

以2007年夏季黄河调水调沙期间黄河三角洲海域3断面连续站及渤海南部24个大面站观测的流场、温度、盐度及含沙量资料为依据,分析了调查区水沙扩散特征,计算了各连续站的拉格朗日余流及泥沙输送单宽通量。结果表明,黄河入海泥沙扩散范围非常有限,主要分布在南至莱州湾西南部、北至北纬38°附近离岸约20km以内的带状沿岸区域;但黄河冲淡水出现大面积扩散,覆盖了整个莱州湾的北部和中部,最远可至龙口附近,黄河入海水沙扩散不同步。在现行河口和钓口流路废弃河口存在两个高浓度泥沙中心,分别对应于黄河入海泥沙和废弃钓口流路海域底质再悬浮产生的两个泥沙来源。河口及三角洲近岸切变锋的阻隔及辐聚作用,是大部分黄河入海泥沙沉积在河口及沿岸13m水深以内的主要动力因素。受余流方向及水体垂向湍动较弱的影响,两个高浓度泥沙中心很少有泥沙交换。冲淡水的大面积扩散主要受表层余环流的影响。余流及悬浮泥沙通量计算显示,夏季黄河入海水沙在近岸主要向东北方向扩散。     

塔南凹陷下白垩统南屯组砂体展布特征及分散机制

通过对研究区下白垩统南屯组沉积时期重矿物组合、砂岩组合和地震反射特征资料的综合研究,确定了沉积物的物源方向和砂体展布特征。研究发现同生断裂组合对砂体起到了分散及阻挡的作用,根据同生断裂的组合以及与砂体的制约关系,划分出掀斜型阶梯状、未掀斜型阶梯状和极性3种类型的控砂断裂组合。并根据物源特征和砂体展布特征,将控砂断裂组合分为"横向砂体"和"纵向砂体"2种砂体展布类型;综合各类断裂组合对砂体的控制作用,总结出"诱导型"和"遏制型"两种控砂机制模式。本次研究对在断陷湖盆开展构造对沉积控制作用及分散机制研究提供一个实例。     

改革开放以来珠三角城市规模结构及其分形特征

利用珠三角改革开放以来的人口规模数据,运用位序-规模法则分析城市人口规模变化规律,同时运用分形理论阐释了珠三角的位序规模曲线及其特征。结果表明,80年代以来,城市人口规模已从首位分布向位序-规模分布转变,次级城市发育快于首位城市,人口空间分布由集中趋于分散;2000年后广州中心城市功能得到强化,区域人口分布分维值降低,人口重趋集中;随着行政区划的调整和户籍制度的改革,城市规模结构已从传统“金字塔形”向“纺锤形”转变;未来城市规模结构的“集中”和“分散”趋势将长期并存,呈现“大分散,小集中”的局面。     

一次人工消雨试验数值模拟及物理过程分析

利用中尺度非静力WRF模式对一次人工消雨过程进行了数值模拟试验。试验结果及实况资料分析表明,在大片的降水云系中对局部的降水云进行过量AgI播撒,由于潜热释放增温使得降水云内的对流加强,促使大量小冰晶在高空向四周流散,云体消散,地面降水量减弱。由此可见,选择合适的作业高度、作业部位是人工消雨取得最佳效果的必要条件。     

超大陆旋回与成矿作用

世界上绝大多数大矿床都是超级地质作用导致矿石异常集中的结果,一般多发生于一个地质作用结束的时期.地壳形成作用和板块构造、地幔柱模型已经成为如何认识矿床形成的关键所在,现代矿床成功的探索实践历史就是对大陆和海洋的深人认识进程.因此,矿床形成与全球构造和大陆的演化关系是研究成矿动力学的基础.本文以全球活动构造的视角,从超大陆聚散的历史纪录角度,对活动的地球演化环境下的成矿作用进行总结探索,以图激发对该领域更为深入的研究和思考.     

Provenance of Permian Delaware Mountain Group,central and southern Delaware Basin,and implications of sediment dispersal pathway near the southwestern terminus of Pangea

ABSTRACT

The Delaware Basin is located near the southwestern end of the Alleghanian–Ouachita–Marathon orogenic belt. The basin is mostly filled by Permian clastic rocks of the Delaware Mountain Group with ramp- to shelf-carbonate rimming basin edges. The Delaware Mountain Group has been well-documented as a deep-water clastic reservoir unit in the prolific Permian Basin, but its sources and related sediment dispersal pathways remain inconclusive. In this study, a total of 55 samples of the Delaware Mountain Group were collected from whole core and sidewall core from the central and southern Delaware Basin, and sandstone modal analyses and U-Pb detrital zircon geochronology were applied to constrain their potential sources. Sandstone modal analyses show that the majority of samples fall within the transitional continental source field. Age spectra of detrital zircon from five selected samples include a prominent middle Palaeozoic age cluster (~490–275 Ma), a major Neoproterozoic to early Palaeozoic age cluster (~790–510 Ma), and a series of minor age clusters of the middle to late Mesoproterozoic (~1300–920 Ma), early Mesoproterozoic (~1600–1300 Ma), late Palaeoproterozoic (~1825–1600 Ma), and Archaean and Palaeoproterozoic (> ~1825 Ma). Integrating detrital zircon data from all potential sources and coeval sandstones from the northern Delaware Basin suggests that the majority of sediment was derived from the Appalachian foreland, the Ouachita orogenic system, and the peri-Gondwanan terranes. Variation in the abundance of the different age groups reveals a provenance shift between deposition of the Brushy Canyon Formation and the Cherry and Bell Canyon Formations. To accommodate the composition, and the stratigraphic and spatial age spectral variations, we proposed that the sediment dispersal pathway includes a transcontinental fluvial system from the Appalachian orogenic belt to the east, a regional scale fluvial system from the Ouachita orogenic belt to the north and northeast, and a local, proximal fluvial system from the peri-Gondwanan terranes to the south and southeast.     

Phylogeography of the bluespotted cornetfish,Fistularia commersonii: a predictor of bioinvasion success?

Biological invasions result in huge ecological and economic impacts; therefore, a great amount of effort is dedicated to predicting the potential success of newly established or candidate bioinvaders. Thus far, over 90 species of fish have entered the Mediterranean Sea via the Suez canal, the so‐called Lessepsian bioinvaders. The bluespotted cornetfish, Fistularia commersonii, is remarkable in its ability to disperse within the Mediterranean and has been dubbed ‘the Lessepsian sprinter’. In just a few years, starting in 2000, it expanded over the entire area, from the Suez Canal to Gibraltar. Theoretical predictions correlate the dispersal capabilities of an invader in its native range (using the population genetic metrics, F_st, as a proxy) with its dispersal capability in its invading area (continuous extent of spread, CES). Here, we estimated the population genetic characteristics of Indo‐Pacific native populations of F. commersonii in order to determine if this Lessepsian ‘sprinter’ fits the predictive model of dispersal. Indeed, we found that even in the case of such a very rapid range expansion, the predicted relationship between F_st and CES is fulfilled in F. commersonii.     

Reef fish display station-keeping and ranging behaviour in the Pondoland Marine Protected Area on the east coast of South Africa

This study assessed the role of the Pondoland Marine Protected Area (MPA) in the Eastern Cape province of South Africa by evaluating retention versus ‘spillover’ of exploited fishery species that were tagged in a 400 km² no-take zone of the MPA. From April 2006 to July 2010, 2 124 fish comprising 36 species were tagged in the MPA, with an overall recapture rate of 23%. Findings for four important species (Polysteganus praeorbitalis, Chrysoblephus puniceus, Epinephelus andersoni and Epinephelus marginatus) are presented. Recapture rates ranged from 8% to 60% and time-at-liberty from 0 to 1 390 d. Individuals of all four species displayed highly localised station-keeping behaviour. For all four species, the 95th percentile of intra-study site movements was <750 m (linear distance) and many recaptures were within 250 m of the release site, showing that some fish spend most of their time in the MPA's no-take zone. However, some fish moved beyond the boundary of this zone in a north-easterly direction (range 3–1 059 km), where they would be available to the boat-based fishery in KwaZulu-Natal. The combination of resident individuals with some with ranging behaviour suggests that the MPA can provide a conservation role for these species, while exporting some individuals into nearby fisheries.