古尔班通古特沙漠大气边界层参数化方案的模拟评估[1]

为准确描述我国最大的固定/半固定沙漠-古尔班通古特沙漠区域的大气边界层结构,本文利用该沙漠腹地2017年的梯度铁塔和通量观测数据,基于中尺度气象模式WRF (Weather Research and Forecast v3.7.1),分析了5种边界层参数化方案在古尔班通古特沙漠的适用性。结果表明：1）采用WRF模拟沙漠腹地近地层内的边界层特征时,2m气温的模拟存在冷偏差,5种边界层参数化方案均能较好地模拟出四个季节2m气温的日变化特征,其中非局地方案ACM2(Asymmetric Convective Model version 2)对2m气温效果最好,局地方案BL方案的模拟偏差最大;2）5种边界层参数化方案均能够模拟出10m风速的日变化特征,其中局地方案BL(Bougeault-Lacarrere)对10m风速效果最佳;3）采用WRF模拟沙漠近地层内的地表通量特征时,感热通量存在高估现象,潜热通量存在低估现象,5种边界层参数化方案均能较好地模拟出四个季节模拟时间段内地表净辐射通量的日变化特征,其中局地方案MYJ(Mellor-Yamada-Janjie)的模拟精度最高。     

Effects of convective available potential energy,temperature and humidity on the variability of thunderstorm frequency over Bangladesh

Theoretical and Applied Climatology - The present study examines the effects of convective available potential energy (CAPE), temperature and humidity on the spatiotemporal variation of...     

The Pushtashan juvenile suprasubduction zone assemblage of Kurdistan (northeastern Iraq): A Cretaceous (Cenomanian) Neo-Tethys missing link

The Pushtashan suprasubduction zone assemblage of volcanic rocks, gabbros, norites and peridotites occurs in the Zagros suture zone, Kurdistan region, northeastern Iraq. Volcanic rocks are dominant in the assemblage and consist mainly of basalt and basaltic andesite flows with interlayered red shale and limestone horizons. Earlier lavas tend to be MORB-like, whereas later lavas display island arc tholeiite to boninitic geochemical characteristics. Tholeiitic gabbros intrude the norites and display fractionation trends typical of crystallisation under low-pressure conditions, whereas the norites display calc-alkaline traits, suggesting their source included mantle metasomatised by fluids released from subducted oceanic crust. Enrichment of Rb, Ba, Sr, Th and the presence of negative Nb anomalies indicate generation in a suprasubduction zone setting. Trondhjemite and granodiorite intrusions are present in the volcanic rocks, gabbros and norites. SHRIMP U-Pb dating of magmatic zircons from a granodiorite yields a mean~(206)Pb/~(238)U age of 96.0 ±2.0 Ma(Cenomanian). The initial ε_(Hf) value for the zircons show a narrow range from +12.8 to+15.6, with a weighted mean of + 13.90±0.96. This initial value is within error of model depleted mantle at 96 Ma or slightly below that, in the field of arc rocks with minimal contamination by older continental crust. The compositional bimodality of the Pushtashan suprasubduction sequence suggests seafloor spreading during the initiation of subduction, with a lava stratigraphy from earlyerupted MORB transitioning into calc-alkaline lavas and finally by 96 Ma intrusion of granodioritic and trondhjemitic bodies with juvenile crustal isotopic signatures. The results confirm another Cretaceous arc remnant preserved as an allochthon within the Iraqi segment of the Cenozoic Zagros suture zone. Implications for the closure of Neo-Tethys are discussed.     

Arsenic contamination in groundwater and its proposed remedial measures

Arsenic contamination occurs in groundwater of Bangladesh mainly from the alluvial and deltaic sediments. Arsenic contamination of groundwater in Bangladesh was first detected more than a decade ago and the ’shallow tubewells’ were reported as the main source of arsenic contaminated water. From the nutritional and metabolic points of view, arsenic is likely to adversely affect human health and nutrition. Up to now, several studies have been carried out on this context; however, inadequate knowledge on arsenic sources, mobilization and transport still remains as a constraint due to lack of data, information and technological advances. Thus, a review study has been undertaken on the sources of arsenic, its causes, mobilization, transport, effects on human health, arsenic test procedures and removal methods, in the context of groundwater contamination in Bangladesh, and finally sustainable remedial measures of arsenic have been proposed. This study suggests that laboratory facilities for testing of arsenic and effects of enhanced groundwater pumping, phosphate fertilizer etc., need to be updated, expanded and studied. This review work is significant to further knowledge improvement, as the topic is general and worldwide. It can be concluded that the integration of the proposed remedial measures with the national geographic information system interface database relating to arsenic for analysis, production of hazard maps, and dissemination on television show for the planners, engineers, managers, field supervisors and affected people, can reach at the sustainable solution for mitigating arsenic and associated problems successfully in Bangladesh.     

The Okavango giant mafic dyke swarm (NE Botswana): its structural significance within the Karoo Large Igneous Province

The structural organization of a giant mafic dyke swarm, the Okavango complex, in the northern Karoo Large Igneous Province (LIP) of NE Botswana is detailed. This N110°E-oriented dyke swarm extends for 1500 km with a maximum width of 100 km through Archaean basement terranes and Permo-Jurassic sedimentary sequences. The cornerstone of the study is the quantitative analysis of N>170 (exposed) and N>420 (detected by ground magnetics) dykes evidenced on a ca. 80-km-long section lying in crystalline host-rocks, at high-angle to the densest zone of the swarm (Shashe area). Individual dykes are generally sub-vertical and parallel to the entire swarm. Statistical analysis of width data indicates anomalous dyke frequency (few data <5.0 m) and mean dyke thickness (high value of 17 m) with respect to values classically obtained from other giant swarms. Variations of mean dyke thicknesses from 17 (N110°E swarm) to 27 m (adjoining and coeval N70°E giant swarm) are assigned to the conditions hosting fracture networks dilated as either shear or pure extensional structures, respectively, in response to an inferred NNW–SSE extension. Both fracture patterns are regarded as inherited brittle basement fabrics associated with a previous (Proterozoic) dyking event. The Okavango N110°E dyke swarm is thus a polyphase intrusive system in which total dilation caused by Karoo dykes (estimated frequency of 87%) is 12.2% (6315 m of cumulative dyke width) throughout the 52-km-long projected Shashe section. Assuming that Karoo mafic dyke swarms in NE Botswana follow inherited Proterozoic fractures, as similarly applied for most of the nearly synchronous giant dyke complexes converging towards the Nuanetsi area, leads us to consider that the resulting triple junction-like dyke/fracture pattern is not a definitive proof for a deep mantle plume in the Karoo LIP.     

Impacts of Depositional Facies and Diagenesis on Reservoir Quality: A Case Study from the Rudist-bearing Sarvak Formation, Abadan Plain, SW Iran

An integrated geological-petrophysical analysis of the rudist-bearing sequence of the Cretaceous Sarvak Formation is given one giant oilfield, and provides an improved understanding of this main reservoir in the Abadan Plain, in the Zagros Basin, SW Iran. The main objective of this study is to evaluate reservoir potential of the Sarvak Formation, and then to utilize the calibrated well log signature to correlate reservoir potential in un-cored wells. Eight main facies are recognized and categori...     

Sur les anomalies structurales de l'anticlinal de l'oued Bahloul de Tunisie : héritage tectonique et plissement cisaillant de couverture

The Oued Bahloul structure exists in the central Atlas of Tunisia. This structure is oriented N70 and it shows a very particular geometry characterized by: (i) an important disharmony between the northern and the southern flanks; (ii) a dissymmetry between the east and the west parts of the structure; (iii) several gaps and progressive unconformities present in the Cretaceous and Eocene series.Three major tectonic directions characterize this structure: (i) the N120 appears in the western part of the anticline; (ii) some north–south faults distinguish the oriental part; (iii) the strike fault, which is confirmed by seismic data, affects the central part of this anticline. To cite this article: A. Saadi et al., C. R. Geoscience 338 (2006).