Stratigraphy and sedimentology of the Upper Cretaceous to Paleogene Kilwa Group, southern coastal Tanzania
Stratigraphy and sedimentology of the Upper Cretaceous to Paleogene Kilwa Group, southern coastal Tanzania
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DOI：
10.1016/j.jafrearsci.2006.04.003
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发表时间：
2006-08-01
影响因子：
2.3
通讯作者：
Wade, Bridget S.
中科院分区：
文献类型：
--
作者：
Nicholas, Christopher J.;Pearson, Paul N.;Wade, Bridget S.
自100多年前首次对其地层学发表评论以来，坦桑尼亚南部沿海的地质学仍然知之甚少。然而，新的实地调查结合浅钻探沿着Kilwa和Lindi之间的海岸开始解决的沉积历史和构造演化的这一地区在过去的85马。在这里，我们提出了第一次尝试综合这些研究的结果，提供一个连贯的沉积学，岩性和层序地层框架，包括新的地质图，为上白垩统和古近纪的海岸带。Santonian渐新世沉积物出沿着广泛的沿海带南部的Rufiji河从Kilwa半岛在坦桑尼亚南部的林迪河。在类似的55马，超过1公里的一个广泛均匀的，中到外陆架粘土为主的继承沉积在被动边缘，我们在这里定义为基卢瓦组。这是不整合横跨大陆架上的Albian泥灰岩，本身是不整合覆盖浅水中新世粘土和更近的石灰岩，砂和砾石。根据特徴次生岩性和岩相，可在基卢瓦群内识别出四个地层，在此首次描述：Nangurukuru、Kivinje、Masoko和Pande地层。这些地层包括通过古新世-始新世和始新世-渐新世边界的整合地层间隔。在基卢瓦群内，目前可识别出12个层序地层旋回，表明从Santonian到早渐新世时期，整个边缘相对均匀和持续的沉降。在上白垩统和古近系之间还有一个更大的边界面，但在林迪地区可能部分整合。虽然所有地层的主要岩性为粘土或粘土岩，但渗透性更强的层段含有普遍存在的较粗的硅质岩沉积物，这些层段已发现原油痕迹，这些原油可能是从层序的较低层运移而来的。因此，基卢瓦群也为南部海岸带油气成藏提供了重要的新证据。(c)2006爱思唯尔有限公司保留所有权利。
The geology of southern coastal Tanzania has remained poorly understood since the first comments on its stratigraphy were made over 100 years ago. However, new field surveys combined with shallow drilling along the coast between Kilwa and Lindi are beginning to resolve the depositional history and structural evolution of this region over the past 85 Ma. Here we present the first attempt to synthesize the results of these studies to provide a coherent sedimentological, litho- and sequence stratigraphic framework, including new geological maps, for the Upper Cretaceous and Paleogene of the coastal zone.Santonian to Oligocene sediments crop out along a broad coastal belt south of the Rufiji River from the Kilwa peninsula to Lindi Creek in southern Tanzania. During similar to 55 Ma, over 1 km of a broadly homogeneous, mid to outer shelf clay-dominated succession was deposited across the passive margin, which we define here as the Kilwa Group. This lies disconformably across the shelf on Albian marls and is itself unconformably overlain by shallow water Miocene clays and more recent limestones, sands and gravels. Four formations can be identified within the Kilwa Group on the basis of characteristic secondary lithologies and facies, described here for the first time; the Nangurukuru, Kivinje, Masoko and Pande Formations. These formations include conformable stratigraphic intervals through both the Paleocene-Eocene and Eocene-Oligocene boundaries. Within the Kilwa Group, 12 sequence stratigraphic cycles can be identified at present, demonstrating relatively uniform and continual subsidence across the margin from Santonian to Early Oligocene time. A further major bounding surface is present between the Upper Cretaceous and Paleogene, but this may become partly conformable in the Lindi area. Although the principal lithology in all formations is clay or claystone, there are more permeable intervals containing pervasive coarser siliciclastic sediments and these have yielded traces of crude oil which is likely to have migrated from lower in the succession. The Kilwa Group thus also provides important new evidence for petroleum play development in the southern coastal zone. (c) 2006 Elsevier Ltd. All rights reserved.