Beyond the Nadir: Early Cretaceous-Cenozoic archives of the northern Equatorial Atlantic Gateway

超越最低点：赤道大西洋北部门户的早白垩世-新生代档案

• 批准号: NE/W009927/1
• 负责人: Uisdean Nicholson
• 金额: $ 15.48万
• 依托单位: Heriot-Watt University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FW009927%2F1
• 关键词: Beyond; Nadir; Early; Cretaceous; Cenozoic

This proposal seeks to build a stratigraphic framework from seismic reflection data to prepare for a future ocean drilling proposal in West Africa. This drilling proposal will aim to understand (1) the timing of separation of South America and Africa, forming the 'Equatorial Atlantic Gateway' when the ocean basins of the North Atlantic and South Atlantic were connected for the first time; (2) ocean conditions (temperature, chemistry, oxygen content) during extreme warm periods in Earth history; and (3) to understand the environmental consequences of a potential meteorite impact ~65 million years ago.The first objective, to understand the opening of the Equatorial Atlantic Gateway (EAG), is important as this event had a major influence on Earth's climate and weather patterns, because of changing ocean circulation conditions. However, there are major uncertainties in our understanding of this event, particularly when it formed, as it occurred some time during the 'Cretaceous Normal Superchron' (CNR) - a period of unusual stability in Earth's magnetic field. Magnetic field reversals are important for dating the age of ocean crust, but this is not possible during the CNR. Our seismic reflection data, coupled with biostratigraphic data from exploration boreholes, will provide new constraints on the tectonic events that led to the EAG opening. It will also highlight areas where we can drill and directly sample and date the sediments that record these events, as well as the oldest ocean crust that records the separation of the continents. It will also provide new insights into the sequence of tectonic events that occurred during the opening of the EAG and the long term deepening of the gateway through time.The second objective is to understand the state of the Earth's oceans during the Cretaceous period and Cenozoic. During the Cretaceous period in particular, the global climate and the ocean of the Atlantic was much warmer than in the present day, and it was characterised by periods of intense anoxia (low oxygen levels) and burial of organic carbon. These events, called Oceanic Anoxic Events (OAEs), appear to have been triggered by episodes of intense greenhouse gas emissions from massive volcanic eruptions and lasted hundreds of thousands to perhaps a million years. Although they've been drilled many times, we don't have good information on how extensive they were - how much of the water column was affected for example - or on feedback processes recorded in these sediments. We plan to identify sites for drilling along a depth transect, and where seismic data indicates that they are exceptionally thick, to obtain important new information on these events.Finally, we aim to build on an existing IODP proposal (1004-APL) to understand the consequences of a meteorite impact at the end of the Cretaceous period. The Nadir Crater formed at approximately the same time as the dinosaur-killing Chicxulub Crater in Mexico and may be related to that event. The crater has been identified on 2D seismic data but newly acquired 3D data will illuminate the crater morphology and character much more clearly, allowing us to build more robust models of the environmental consequences of this event (landslides, ejecta, tsunamis). This will also highlight alternative (for proposal 1004-APL) or additional (for the new proposal) drill sites to test the impact crater hypothesis and understand its consequences. Drilling the crater will be necessary to test whether this feature was indeed formed by an impact crater and, if so, the precise age of the crater. This will allow us to date it precisely and to test whether the Chicxulub event was actually a binary system (two asteroids) or part of a longer lived 'impact cluster' over a course of hundreds of thousands or several million years.

该提案旨在根据地震反射数据建立一个地层框架，为西非未来的海洋钻探提案做好准备。该钻探计划旨在了解（1）南美洲和非洲分离、形成“赤道大西洋门户”的时间，北大西洋和南大西洋海盆首次连接的时间； (2) 地球历史上极端温暖时期的海洋条件（温度、化学成分、氧含量）； (3) 了解大约 6500 万年前潜在陨石撞击的环境后果。第一个目标是了解赤道大西洋门户 (EAG) 的开放，这一点很重要，因为这一事件对地球气候和地球气候产生了重大影响。由于海洋环流条件的变化而导致的天气模式。然而，我们对这一事件的理解存在重大不确定性，特别是它形成的时间，因为它发生在“白垩纪正常超纪元”（CNR）期间——地球磁场异常稳定的时期。磁场反转对于确定洋壳年龄很重要，但在 CNR 期间这是不可能的。我们的地震反射数据与勘探钻孔的生物地层数据相结合，将为导致 EAG 开口的构造事件提供新的约束。它还将突出显示我们可以钻探、直接采样和测定记录这些事件的沉积物的区域，以及记录大陆分离的最古老的洋壳。它还将为 EAG 打开期间发生的构造事件序列以及门户随时间的长期加深提供新的见解。第二个目标是了解白垩纪和新生代期间地球海洋的状态。特别是在白垩纪时期，全球气候和大西洋海洋比现在温暖得多，其特点是严重缺氧（低氧水平）和有机碳埋藏时期。这些事件被称为海洋缺氧事件（OAE），似乎是由大规模火山喷发产生的大量温室气体排放引发的，并持续了数十万至一百万年。尽管它们已经被钻探了很多次，但我们没有关于它们的范围有多大（例如有多少水柱受到影响）或这些沉积物中记录的反馈过程的详细信息。我们计划确定沿深度横断面进行钻探的地点，以及地震数据表明它们异常厚的地点，以获得有关这些事件的重要新信息。最后，我们的目标是在现有的 IODP 提案 (1004-APL) 的基础上了解白垩纪末期陨石撞击的后果。纳迪尔陨石坑大约与墨西哥恐龙灭绝的希克苏鲁伯陨石坑同时形成，可能与该事件有关。该陨石坑已通过 2D 地震数据识别出来，但新获取的 3D 数据将更清楚地阐明陨石坑的形态和特征，使我们能够针对该事件（山体滑坡、喷射物、海啸）的环境后果建立更稳健的模型。这还将突出显示替代（对于提案 1004-APL）或额外（对于新提案）钻探地点，以测试撞击坑假设并了解其后果。需要对陨石坑进行钻探，以测试该特征是否确实是由撞击坑形成的，如果是，则需要测试该陨石坑的准确年龄。这将使我们能够准确地确定它的年代，并测试希克苏鲁伯事件是否实际上是一个双星系统（两颗小行星），还是一个生命周期较长的“撞击星团”的一部分，历经数十万年或数百万年。

项目成果

Seismic stratigraphy of the Guinea Plateau before, during and after the opening of the Equatorial Atlantic Gateway

赤道大西洋门户开通前、开通期间和开通后几内亚高原的地震地层

• DOI: 10.31223/x5ph49
• 发表时间: 2024
• 作者: Aduomahor B

The Nadir Crater offshore West Africa: A candidate Cretaceous-Paleogene impact structure.

• DOI: 10.1126/sciadv.abn3096
• 发表时间: 2022-08-19
• 期刊: Science advances
• 影响因子: 13.6