Subsurface sediment accumulation patterns and their relationships with tectonic lineaments in the semi-arid Luni river basin, Rajasthan, Western India

Sediment accumulation patterns in the Luni basin have been studied on the basis of tubewell lithologs and Bouguer gravity anomaly profiles. East–West geologic transects using these data reveal several sediment-filled graben depressions, for example, the Digrana-Bhawal graben in the northern part, the Mangta-Sindari, Sindari-Bhimgoda, and Bhimgoda-Juna Motisara grabens in the central part; and the Dungari-Ratanpura and Ratanpura-Khanpur grabens in the southern part. Maximum sediment accumulation of more than 300 m is located in the southwestern part of the Luni basin, more specifically in the Ratanpura-Khanpur graben. Minor depressions also occur towards west of Jodhpur and east of Bhadrajun.Sediment filling in these graben depressions commenced with thick clay deposits followed by multistoried fining up sand and gravel sequences. Sediment accumulation centres are coincident with major tectonic lineaments and thus indicate that important loci of sediment accumulation are, possibly, a response to synsedimentary tectonics.     

Gravity anomalies and flexure of the lithosphere at Ascension Island

Ascension Island, in the northern South Atlantic, forms the summit of a volcanic edifice 60 km in diameter which places a substantial load on the underlying young oceanic lithosphere. An analysis of a combined data set of recent and historical surface-gravity and bathymetry measurements on and around the island suggests that the lithosphere responds to this load by flexure equivalent to that of an elastic plate only ≈ 3 km thick, and that the mean density of the volcanic edifice is ≈ 2500 kg m^-3. A steep gravity gradient across the island cannot be explained by a simple flexural model and must be attributed to lateral density variations within the volcano itself. The effective elastic thickness is considerably less than the expected ≈ 12 km mechanical thickness of the ≈ 6 Ma lithosphere loaded by the volcano, and less even than zero-age elastic thicknesses commonly observed at slow-spreading ridges with axial rift valleys. The unusually small elastic thickness may be attributed to the combined effects of the high curvature beneath the island, which produces bending stresses that are limited by the yield stress envelope, localized heating of the lithosphere during emplacement of the island, and crustal thickening. When these factors are taken into account, the observed flexure is consistent with rheological models based on experimental rock mechanics.     

两千年来中国经济重心变迁的量化分析——基于人口和城市数据的代用分析

基于历史文献及统计年鉴中的人口和城市数据,采用历史时间断面方法和现代GIS空间分析方法,对过去2 000 a来（公元2—2015年）中国经济重心的变迁轨迹进行量化研究,结果表明：1）中国经济重心总体上是趋向东南迁移,唐代以前主要向西南移动,北宋以后主要向东南移动,中国经济的空间分异先以由南北差异为主,后以东西差异为主;“沈（阳）-兰（州）-西（双版纳）弧线”东南侧的经济发展过程与格局很大程度上可代表整个中国的经济发展过程与格局。2）中国经济重心变迁与其人口重心、城市重心的变迁关系十分密切,3类重心分布区域正是古称“中原”的地区,且3类重心始终位于几何中心的东部,中国东、西部的经济差异由来久远,且相对稳定。3）中国经济重心变迁受人口格局和城市格局变化的双重制约,随着时间推移,单位人口的经济当量趋于降低,单位城市的经济当量趋于上升,城市经济格局对总体经济格局的影响日益显著。