当前位置: X-MOL 学术Geo-Mar. Lett. › 论文详情
Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)
Shelf architecture and recent sediment stratigraphy of the Chameis Bay area, southern Namibia
Geo-Marine Letters ( IF 2.1 ) Pub Date : 2021-06-29 , DOI: 10.1007/s00367-021-00700-z
Heike Fourie , Bjorn P. von der Heyden , Kegan Strydom

Abstract

Chameis Bay is located about 115 km north of the Orange River mouth and falls within the Sperrgebiet, an area which hosts the world’s largest gem diamond deposit. Although significant quantities of diamonds have been recovered both on land and from offshore deposits in the Chameis Bay area, the marine geology of this important tract of coastline has not previously been described in the scientific literature. Here, we report the nearshore geomorphology and seismic stratigraphy offshore of Chameis Bay through analyses of bathymetrical and seismic datasets. These data have been complemented with lithogical data obtained from 70 reverse-circulation boreholes which helped to confirm and constrain the sedimentary stratigraphy of the study area. These datasets identified four major lithological units; viz. a Precambrian basement which predominates as the footwall in the nearshore regions of the study area, a Cretaceous clay unit that represents the offshore footwall lithology and two unconsolidated Cenozoic sedimentary units. The distribution of these unconsolidated sediments is strongly controlled by the ambient accommodation space which can be quantified by considering the architecture of the respective footwall units. Architectural features within the study site include two prominent wave-cut platforms, two coast-parallel sea cliffs, and a shelf-break formed at the contact between the Precambrian basement and the Cretaceous clay footwall. Accommodation space exists on the seaward of the two wave-cut platforms, which is cut into the Precambrian basement footwall and which lies below the fair-weather wave base, and at the break in slope at the contact between the two footwall units. The former accommodation space is most notable for gravel entrapment and preservation since gulley-controlled jointing and erosional depressions at lithological contacts represent ‘fixed’ trapsites from which coarse material is less likely to be remobilised. In contrast, the trapsites formed on the soft Cretaceous clay footwall are regarded as ‘mobile’ trapsites since they can be easily reconfigured by continuing erosional processes. As a result, the gravel bodies found above the Cretaceous clay are generally thin and poorly developed. The implications of these two different trapsites are briefly discussed in terms of diamond preservation potential, where anticipated diamond sources to the Chameis Bay near-shelf include the Orange River mouth as well as material that has been reworked from proximal sources. These results represent the first detailed description of the marine geology of the Chameis Subterrane thrust sheet and complement existing understanding of the Sperrgebiet’s marine geology which largely derives from study sites on the Oranjemund Subterrane where linear beaches predominate.

Graphical abstract



中文翻译:

纳米比亚南部查梅斯湾地区的陆架结构和近期沉积地层

摘要

Chameis Bay 位于奥兰治河口以北约 115 公里处,位于 Sperrgebiet 内,该地区拥有世界上最大的宝石钻石矿床。尽管在 Chameis 湾地区的陆地和近海矿床中已经发现了大量钻石,但之前科学文献中并未描述过这条重要海岸线的海洋地质。在这里,我们通过对测深和地震数据集的分析报告了 Chameis 湾近海的近岸地貌和地震地层学。这些数据与从 70 个逆循环钻孔中获得的岩性数据相辅相成,有助于确认和约束研究区的沉积地层。这些数据集确定了四个主要的岩性单元;即。a 前寒武纪基底,主要作为研究区近岸地区的下盘,白垩纪粘土单元代表近海下盘岩性和两个松散的新生代沉积单元。这些松散沉积物的分布受到周围居住空间的强烈控制,可以通过考虑各个下盘单元的结构来量化。研究地点内的建筑特征包括两个突出的波浪切割平台、两个与海岸平行的海崖,以及在前寒武纪基底和白垩纪粘土下盘接触处形成的陆架断裂。两个波浪切割平台的向海存在容纳空间,该平台切入前寒武纪基底下盘,位于晴天波浪基地下方,以及在两个下盘单元之间的接触处的坡度中断处。以前的容纳空间最值得注意的是砾石截留和保存,因为岩性接触处的沟壑控制节理和侵蚀洼地代表“固定”陷阱,粗物质不太可能从中重新移动。相比之下,在白垩纪软粘土下盘形成的圈闭点被视为“移动”圈闭点,因为它们可以通过持续的侵蚀过程轻松重新配置。因此,在白垩纪粘土上方发现的砾石体通常较薄且发育不良。从钻石保存潜力的角度简要讨论了这两个不同陷阱位点的影响,Chameis Bay 近陆架的预期钻石来源包括奥兰治河口以及从近端来源重新加工的材料。这些结果代表了 Chameis Subterrane 冲断层海洋地质的首次详细描述,并补充了对 Sperrgebiet 海洋地质的现有理解,后者主要来自 Oranjemund Subterrane 的研究地点,其中线性海滩占主导地位。

图形概要

更新日期:2021-06-29
down
wechat
bug