Geo-Marine Letters ( IF 2.1 ) Pub Date : 2021-07-06 , DOI: 10.1007/s00367-021-00702-x Burg Flemming 1 , Keith Martin 2
The study deals with a large sand body (spit-bar) attached to the eastern tip of the Robberg Peninsula, Plettenberg Bay, South Africa. To date, the bar has prograded about 8 km beyond the tip of the peninsula. The bar top is predominantly composed of medium sand, the upper slope of fine sand, and the lower slope of fine muddy sand. Stratigraphically, the sedimentology thus documents an upward coarsening, calcareous quartz-arenitic depositional sequence. The spit-bar as a whole forms the eastern end of a sediment compartment that is clearly distinguishable from neighbouring compartments on the basis of its geomorphology, the textural characteristics of the sediment, and the distribution of sediment thicknesses. Aeolian overpass across the peninsula appears to have formed a fan-like sand deposit in its rear, which is perched upon the upper shoreface of the bay as suggested by the bathymetry to the north of the peninsula. It forms an integral part of the sediment body defining the spit-bar. The estimated volume of sand stored in the spit-bar amounts to 5.815 km3, of which 0.22 km3 is contributed by the aeolian overpass sand. The sediment sources of the spit-bar are located up to 100 km to the west, where a number of small rivers supply limited amounts of sediment to the sea and numerous coastal aeolianite ridges in the Wilderness embayment have been subject to erosion after becoming drowned in the course of the postglacial sea-level rise since about 12 ky BP. By contrast, the sediment volume in the adjacent compartment B to the north (Plettenberg Bay), which has been supplied by local rivers, amounts to only 0.127 km3. In a geological context, large sand bodies such as the Robberg spit-bar are excellent exploration models for hydrocarbons (oil and gas).
中文翻译:
以多床荷载边界为特征的沿海陆架区的沉积学:Plettenberg 湾,内 Agulhas 银行,南非
该研究涉及连接到南非普莱滕贝格湾罗伯格半岛东端的一个大型砂体(吐沙坝)。迄今为止,该酒吧已扩展到半岛尖端以外约 8 公里处。坝顶以中砂为主,上坡为细砂,下坡为细泥砂。因此,在地层学上,沉积学记录了向上粗化的钙质石英-砂质沉积序列。吐沙坝作为一个整体形成了一个沉积隔间的东端,根据其地貌、沉积物的质地特征和沉积物厚度的分布,可以明显地将其与相邻隔间区分开来。横跨半岛的风成立交桥似乎在其后方形成了扇状的沙子沉积物,根据半岛北部的水深测量显示,它位于海湾的上岸。它形成了界定吐沙坝的沉积体的一个组成部分。估计储存在吐沙口的沙子量达 5.815 公里3,其中0.22 km 3是由风积立交沙贡献的。吐沙坝的沉积物来源位于西面 100 公里处,那里有一些小河流向大海供应有限量的沉积物,荒野海湾的许多沿海风尘脊在被淹没后受到侵蚀。自大约 12 ky BP 以来的冰后海平面上升过程。相比之下,由当地河流供应的北部相邻隔室 B(普利登堡湾)的沉积物体积仅为 0.127 km 3。在地质背景下,大型砂体(如 Robberg spit-bar)是碳氢化合物(石油和天然气)的极好勘探模型。