New Olduvai Basin stratigraphy and stratigraphic concepts revealed by OGCP cores into the Palaeolake Olduvai depocentre, Tanzania
New Olduvai Basin stratigraphy and stratigraphic concepts revealed by OGCP cores into the Palaeolake Olduvai depocentre, Tanzania
复制标题
坦桑尼亚 Palaeolake Olduvai 沉积中心 OGCP 岩心揭示的新 Olduvai 盆地地层学和地层学概念
DOI：
10.1016/j.palaeo.2020.109751
复制
发表时间：
2020
影响因子：
3
通讯作者：
Njau, J
中科院分区：
文献类型：
--
作者：
Stanistreet, I G;Stollhofen, H;Deino, A;McHenry, L;Toth, N;Schick, K;Njau, J
奥杜威峡谷取心项目（OGCP）在奥杜威盆地沉积中心的中央古湖的三个地点钻了四个钻孔1A、2A、3A、3B。在岩心上部可识别出先前已知的I、II、III、IV层、Masek层和Ndutu层，并从这些地层中识别出主要的湖相组合。这些描述，然后解释其古环境意义。然而，从自然露头暴露中已知的地层是下面地层的两倍多。例如，岩心2A中额外135 m的前地层I地层记录了源自恩戈罗恩戈罗火山的扇三角洲的整个火山历史。在该扇层序之下是一段河湖相非火山碎屑沉积。对于后者，引入了新的地层术语Naibor Soit Formation，因为这些地层首次在Naibor Soit Inselberg两侧的钻孔2A和3A中发现，因此它们重叠在其基底地形上。上面的火山源单元被命名为恩戈罗恩戈罗组，包括标记凝灰岩CFCT（粗长石晶体凝灰岩）和Naabi凝灰岩在其最顶部。只有恩戈罗恩戈罗主要来源的扇体上方的主要湖相沉积物现在归属于下层I。此处定义的恩戈罗恩戈罗组包含主要凝灰岩标志物NgA至NgQ，以及与河湖相Naibor Soit组的粘土岩和互层砂岩交指和上覆的火山岩扇三角洲沉积。钻孔1A和2A与第I层玄武岩相交，但不与钻孔3A相交，其中熔岩的位置由三个分离的火山岩砂岩层标记，包含卵石大小的玄武岩火山渣，可能与地点9A和Orkeri的三个复杂玄武岩流相关，并允许评估同玄武岩沉积。不整合界面层I、II、III、IV、Masek层和Ndutu层为层序地层学概念的新应用提供了重要的地层标志，因为它们标志着Palaeolake Olduvai的低位，指导露头与岩心的对比。主要的不整合面被识别为：（1）岩芯1A，其中下层II Crocket山谷切口面切出凝灰岩IF;（2）岩芯1A，其中层II、III、IV和Masek层内的不整合面和相被识别;（3）岩芯2A和3A，其中凝灰岩IF被识别为低于下层至中层II不整合面;（4）岩芯3A中的下层I粘土岩和凝灰岩IA，与西部峡谷66 e地点的类似沉积单元相关，但由于新发现的主要不整合，导致I层熔岩直接位于CFCT标志物顶部，因此在岩芯2A中没有。
The Olduvai Gorge Coring Project (OGCP) drilled four boreholes 1A, 2A, 3A, 3B at three sites into the central palaeolake of the Olduvai Basin depocentre. Previously known Beds I, II, III, IV, Masek Beds and Ndutu are identifiable in the upper part of the cores, and from these formations predominantly lacustrine facies associations are recognised. These are described and then interpreted in terms of their palaeoenvironmental significance. However, stratigraphy known from natural outcrop exposures is more than doubled by strata intersected below. For example, an extra 135 m of pre-Bed I stratigraphy in Core 2A records the entire volcanic history of a fan-delta sourced from Ngorongoro Volcano. Beneath that fan sequence is an interval of fluvio-lacustrine non-volcaniclastic sediments. For the latter the new stratigraphic term Naibor Soit Formation is introduced, because these strata were discovered for the first time in Boreholes 2A and 3A, to either side of Naibor Soit Inselberg, where they thus lap onto its basement topography. The volcanically sourced unit above is named Ngorongoro Formation, including Marker Tuffs CFCT (Coarse Feldspar Crystal Tuff) and the Naabi Ignimbrite within its topmost portion. Only the dominantly lacustrine sediments above the main Ngorongoro sourced fan body are now attributed to Lower Bed I. The Ngorongoro Formation defined here contains primary Tuff Markers NgA to NgQ, and volcaniclastic fan-delta deposits that interfinger with and overlie claystones and interbedded sandstones of the fluvio-lacustrine Naibor Soit Formation. Boreholes 1A and 2A intersect the Bed I Basalt, but not Borehole 3A, where the position of the lava is marked by three separated volcaniclastic sandstone layers, containing pebble-sized basalt scoriae, likely correlating to three complex basalt flows at Locality 9A and Orkeri and allowing assessment of syn-basalt sedimentation. Disconformities bounding Beds I, II, III, IV, Masek Beds and Ndutu Beds provide important stratigraphic markers for the novel application of sequence stratigraphic concepts, as they mark lowstands of Palaeolake Olduvai, guiding outcrop to core correlations. Major disconformities are identified in: (1) Core 1A, where the Lower Bed II Crocodile Valley Incision Surface cuts out Tuff IF; (2) Core 1A, where disconformities and facies within Beds II, III, IV, and Masek Beds are identified; (3) Cores 2A and 3A, where Tuff IF is identified below the Lower to Middle Bed II disconformity; and (4) Lower Bed I claystones and Tuff IA in Core 3A that correlate to similar sedimentary units from Locality 66e in the Western Gorge, but which are absent from Core 2A because of a newly identified major disconformity, which causes the Bed I lava to sit directly on top of the CFCT marker.
登录
查看更多内容
坦桑尼亚恩戈罗恩戈罗火山口火山岩的古地磁和钾-氩时代
DOI：
--
发表时间：
1971
期刊：
影响因子：
--
作者：
C. S. Grommé;T. Reilly;A. Mussett;R. L. Hay
通讯作者：
R. L. Hay
利用隐秘凝灰岩和火山碎屑砂岩的单粒地球化学改善了坦桑尼亚奥杜瓦伊峡谷的地层框架
影响因子：
2.3
作者：
McHenry L.J;Stollhofen H. Stanistreet I.G.
通讯作者：
Stollhofen H. Stanistreet I.G.
坦桑尼亚奥杜瓦伊峡谷 DK 地区的植被景观
DOI：
10.1016/j.palaeo.2015.02.022
发表时间：
2015
期刊：
Palaeogeography, Palaeoclimatology, Palaeoecology
影响因子：
--
作者：
Albert;Bamford;Stanistreet;Stollhofen;Rivera-Rondón;Rodríguez-Cintas
通讯作者：
Rodríguez-Cintas
恩戈罗恩戈罗火山高地及其与奥杜瓦伊峡谷火山沉积物和东非裂谷火山活动的关系。
影响因子：
3.2
作者：
G. Mollel;C. Swisher
通讯作者：
C. Swisher
早期人类时代的精细分辨率，坦桑尼亚奥杜瓦伊峡谷的床 I 和 II。
影响因子：
3.2
作者：
I. Stanistreet
通讯作者：
I. Stanistreet