Characterisation and gradient constraint of mixed debris flow/braided river dominated fans by analysis of Skeleton Coast fan systems in NW Namibia

关于地面扇的分类及其与河流的区别一直存在争议。一方面，由(a)泥石流、(B)辫状河和(C)低弯度/曲流河主导的末端成员组成的地面扇谱的观点在科学界得到了相当大的认可。另一方面，认为该谱发育不完全，在大的低坡度河漫滩和小的高坡度冲积扇之间存在着明显的水力特征和沉积坡度的天然间隙。后一种分类将冲积扇限制为泥石流主导类型，排除河流主导的冲积扇。冲积扇系统，南扇、盐扇、梅苏姆扇和霍林巴伊扇，位于纳米比亚西北部骷髅海岸，可能在辫状河主导和泥石流主导的扇系统之间架起一座桥梁。这些风扇将通过整合地形测绘、激光测量、卫星和航空照片图像以及SRTM数据来分析其几何形状、排水网络和通道限制控制，以开发风扇表面的3D数字模型。通过对现代和古代扇系岩相组合的测井和定年、古流指标的定向测量以及沉积物的结构和成分性质分析，旨在了解沉积过程的性质和成因、沉积活动的年龄和持续时间、近期过程史和古相序列。因此，该项目将极大地支持对与扇系统相关的沉积过程控制的理解，并有助于综合分类。此外，还需要将扇形岩与古代的同类岩进行比较，以确定它们在岩石记录中的重要性。这一观点将有助于重新评价油气勘探中的扇相，特别是靶生扇相。

There is a controversy concerning the classification of subaerial fans and their distinction from rivers. On one hand the view of a spectrum of subaerial fans comprising (A) debris flow, (B) braided river and (C) and low sinuosity/meandering river dominated end members has gained considerable acceptance in the scientific community. On the other hand it has been proposed that this spectrum is only incompletely developed and that an obvious natural gap in hydraulic character and depositional slope is existing between large low gradient river floodplains and small high gradient alluvial fans. The latter classification would restrict alluvial fans to debris flow dominated types and exclude fans dominated by rivers.Alluvial fan systems, the Sout, Salt, Messum and Horingbaai Fans, of the Skeleton Coast, northwestern Namibia, potentially bridge a gap between braided river dominated and debris flow dominated fan systems. These fans will be analysed in view of their geometries, drainage networks and controls of channel confinement by means of integrating terrain mapping, laser surveying, satellite and aerial photo imagery as well as SRTM data to develop 3D digital models of the fan surfaces. Logging and dating of lithofacies assemblages in modern and ancient fan successions, directional measurements of palaepurrent indicators and analysis of textural and compositional properties of sediments aim to understand nature and causes of depositional processes, age and duration of activity, recent process history and ancient facies sequences. The project will thus considerable support the understanding of controls on depositional processes associated with fan systems and contribute to an integrated classification. Furthermore, the fans need to be compared with ancient equivalents in order to establish their importance in the rock record. This point of view will contribute to the re-evaluation of fan facies in hydrocarbon exploration, specifically with respect to target generation.