THE RELATION BETWEEN TECTONIC ACTIVITY AND SEDIMENTARY FRAMEWORK:EVIDENCE FROM THE LAKE ALBERT, EAST AFRICAN RIFT SYSTEM
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摘要:
Albert湖盆作为东非裂谷系重要的裂谷盆地，具有巨大的油气资源潜力。但前期资料匮乏，制约着Albert盆地的研究进展，目前仍存在着构造活动背景下沉积物响应特征不明确等亟待解决的问题。通过录井、测井及地震地质资料，结合Google Earth对该区盆地结构、湖盆断裂体系和沉积体系开展研究，并深入探讨构造对沉积物分配的控制作用。研究表明，Albert湖盆发育非对称式地堑结构，盆地两侧以正断层发育为主，西侧陡，东侧缓；主要为三角洲-湖泊沉积体系，其中三角洲包括三角洲平原及前缘亚相，湖泊包括滨浅湖及深湖亚相。不同裂谷演化时期，构造对沉积物分配控制作用明显。低扩张阶段南侧断层活动强烈，沉积物主要从北侧入湖，主要发育河流及正常三角洲；初始断裂阶段西北侧断层活动强烈，沉积物从东南侧入湖，主要发育扇三角洲及辫状河三角洲；第2断裂阶段断裂活动基本终止，沉积物从东南、东北两方向入湖，主要发育扇三角洲、辫状河三角洲及河流相。湖盆内主要发育同向叠置型和相向平行型2类构造调节带，断层组合样式形成的构造低部位，作为沉积物搬运的有利通道，对沉积物的分配起到控制作用。
Abstract:The Lake Albert is a rift basin with large hydrocarbon potential as a part of the East African Rift System. The study of lake geology is limited for lacking of data. The sedimentation under the tectonic background remains unclear up to date.This paper is devoted to the basin tectonics and lake sedimentation based on logging, drilling, seismic data and the data from Google Earth. The Lake Albert is an unsymmetrical graben formed under active tectonics. A steep normal fault occurs in the west and a gentle slope in the east.Three major facies occur as infillings in the lake, i.e. the deep lacustrine, the shallow lacustrine and delta deposits consisting of deltaic plain and deltaic front. Structures have obvious control over the sedimentation pattern. Sediments came from the north side where fluvial and deltaic deposits prevailed.The first phase of rifting was characterized by strong tectonic activity on the northwest side of the lake, and in the second phase fan-delta and braid river delta facies developed astectonic activities weakened. Sediments were supplied from the southeast and northeast sides of the lake and dominated by fluvial fan delta and braid river delta deposits.There are two major transverse fault zones in the Lake Albert, a synthetic overlapping zone and a convergent collateral zone.The structural pattern of the fault assemblage formed in a relatively low position, which is the dominant path of transportation.Above all, the transverse fault zones have obvious control over the distribution pattern of depositional system.
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Key words:
- East African Rift System /
- Lake Albert /
- fault system /
- sedimentary facies /
- transverse fault zones
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表 1 沉积相类型及特征(据文献[21]修改)
Table 1. Sedimentary facies and their characteristics (modified from reference [21])
沉积相类型 岩性 沉积构造 生物特征 
岩性剖面图 湖泊沉积体系 深湖亚相 层状暗色泥岩 铁质结核，石膏 有葡萄球藻，淡水双壳类少，富含有机质 
滨浅湖亚相 以泥岩为主，暗色泥岩和粉砂到中砂交替出现，分选差 泥岩：块状、水平层理砂岩：交错层理和平行层理 构造多来源于母岩，偶见水平、竖直生物潜穴，可见盘兴藻，局部富含有机质 
三角洲沉积体系 三角洲前缘亚相 主要以细粒砂岩为主 交错层理，冲刷面 有禾木科 
三角洲平原亚相 主要是中粒砂岩，可见细粒到粗粒砂岩；分选好，向上变粗 水流波痕，爬升波痕和沙坝叠加而成的巨型交错层理 偶见垂直生物潜穴，泥岩之间可见盘兴藻 
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