Shore‐Zone Sedimentation and Facies in a Closed Rift Lake: The Holocene Beach Deposits of Lake Bogoria, Kenya
Shore‐Zone Sedimentation and Facies in a Closed Rift Lake: The Holocene Beach Deposits of Lake Bogoria, Kenya
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封闭裂谷湖岸区沉积和相：肯尼亚博戈里亚湖全新世海滩沉积物
DOI：
10.1002/9781444303919.ch9
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发表时间：
2009
影响因子：
2
通讯作者：
R. Owen
中科院分区：
文献类型：
--
作者：
R. Renaut;R. Owen
小型海滩酒吧、唾沫和障碍物主要由粗沙、颗粒和鹅卵石组成，沿着博戈里亚湖的大部分现代海岸线存在，博戈里亚湖是肯尼亚裂谷中的一个常年盐碱湖。它们的分布和组成研究表明，大部分沉积物来自外围扇三角洲，包括洪水带来的物质，以及来自较老的暴露的扇三角洲沉积物的侵蚀。许多沉积物被沿湖轴吹来的风引起的沿岸流重新分配。在湖周围，由角砾石组成的一系列后退的滨海阶地记录了与全新世较高的湖泊水位有关的海岸线沉积。在阶地形成过程中，许多扇三角洲台地被淹没，浅滩效应减弱，从而增加了大部分海岸线周围的波浪能量。阶地记录了全新世湖面波动的复杂历史。尽管小型盐湖是海滩发育的不利位置，但综合因素，包括细长的形式、大量的河流流入和陡峭的边缘为海岸地带提供粗碎屑，允许狭窄的滨海碎屑堆积。就资源而言，裂谷中的海岸线碎屑沉积可容纳含金属砂矿，并可作为石灰和集合体的来源。随着湖泊规模和集水岩中石英含量的增加，它们作为油气藏的潜力也在增加。富含火山的集水区的滨海砂岩由于其在成岩作用中的高反应性而不利。
Small beach bars, spits, and barriers, composed predominantly of coarse sand, granules, and pebbles, are present along much of the modern shoreline of Lake Bogoria, a perennial saline, alkaline lake in the Kenya Rift Valley. Study of their distribution and composition indicates that most of the sediments are derived from peripheral fan‐deltas, including material brought down in flood, and that derived by erosion of older exposed fan‐delta sediments. Much of the sediment is redistributed by longshore currents, induced by winds funnelled along the axis of the lake.Surrounding the lake, a series of regressive littoral terraces, composed of angular gravels, record shoreline sedimentation associated with former higher lake levels during the Holocene. During terrace formation, many fan‐delta platforms were drowned and shoaling effects reduced, thereby increasing wave energy around much of the shoreline. The terraces record a complex history of Holocene lake‐level fluctuations.Although small saline lakes are unfavourable locations for beach development, a combination of factors, including the elongate form, significant fluvial inflow, and steep margins to supply coarse debris to the shore zone, permit a narrow zone of littoral clastic accumulation.In terms of resources, shoreline clastic sediments in rifts can host metalliferous placer deposits, and can be sources of lime and aggregate. Their potential as hydrocarbon reservoirs increases with lake size and the quartz content of the catchment rocks. Littoral sands in volcanic‐rich catchments are unfavourable owing to their high reactivity during diagenesis.