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.

该提案旨在从地震反射数据中建立一个地层框架，以准备西非未来的海洋钻井建议。这项钻井建议将旨在了解（1）南美和非洲分离的时机，形成“赤道大西洋门户”，当时北大西洋和南大西洋第一次连接时； （2）在地球历史极端温暖时期，海洋条件（温度，化学，氧含量）； （3）了解6500万年前潜在的陨石影响的环境后果。要了解赤道大西洋门户（EAG）的开放的第一个目标非常重要，因为此事件对地球的气候和天气模式产生了重大影响，因为改变了海洋循环条件。但是，我们对这一事件的理解有主要的不确定性，尤其是当它形成时，因为它在“白垩纪正常超级围座”（CNR）（CNR）中发生了一段时间 - 地球磁场中异常稳定的时期。磁场逆转对于约会海皮时代很重要，但这在CNR期间不可能。我们的地震反射数据，再加上来自Exploration钻孔的生物地层数据，将对导致EAG开放的构造事件提供新的约束。它还将重点介绍我们可以直接钻孔，直接采样并与记录这些事件的沉积物以及记录大陆分离的最古老的海壳。它还将提供有关EAG开放期间发生的构造事件顺序的新见解，并在时间上长期加深了门户。第二个目标是了解白垩纪时期和新生代期间地球海洋状态。尤其是在白垩纪期间，大西洋的全球气候和海洋比今天温暖得多，其特征是强烈的缺氧时期（低氧气水平）和有机碳的埋葬。这些称为海洋缺氧事件（OAE）的事件似乎是由大规模火山喷发的强烈温室气体发射引发的，并且持续了数十万至一百万年。尽管它们已经钻了很多次，但我们没有关于它们的广泛信息的良好信息（例如，水柱受到了多少影响）或在这些沉积物中记录的反馈过程中。我们计划识别沿深度样带钻孔的地点，地震数据表明它们非常厚，以获取有关这些事件的重要新信息。从本文中，我们的目的是建立在现有的IODP提案（1004-APL）的基础上，以了解在际星际时期结束时陨石影响的后果。 Nadir火山口与墨西哥的杀恐龙的Chicxulub火山口大约同时形成，可能与该事件有关。在2D地震数据上已经确定了火山口，但是新获得的3D数据将更加清楚地阐明火山口形态和特征，从而使我们能够建立更强大的该事件环境后果的模型（Landslides，Exjecta，ejecta，Tsunamis）。这还将突出显示替代方案（对于提案1004-APL）或其他（对于新提案）钻机，以测试火山口假设并理解其后果。必须钻火山口，以测试该功能是否确实是由撞击火山口形成的，如果是的，则是火山口的确切年龄。这将使我们能够准确地与之约定，并测试Chicxulub事件实际上是二进制系统（两个小行星）还是在数十万或数百万年内更长的寿命“撞击集群”的一部分。

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