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地层框架，为西非今后的海洋钻探提案做准备。这项钻探计划旨在了解（1）南美洲和非洲分离的时间，当北大西洋和南大西洋的海洋盆地首次连接时，形成了“赤道大西洋门户”;（2）海洋条件（温度，化学，氧含量）在地球历史上的极端温暖时期;（3）了解6500万年前可能的陨石撞击的环境后果。第一个目标，了解赤道大西洋门户（EAG）的打开，由于海洋环流条件的变化，这一事件对地球的气候和天气模式产生了重大影响。然而，我们对这一事件的理解存在重大的不确定性，特别是当它形成时，因为它发生在“白垩纪正常超时”（CNR）期间的某个时间-地球磁场异常稳定的时期。磁场反转对于确定洋壳的年龄很重要，但在CNR期间这是不可能的。我们的地震反射数据，再加上生物地层数据从勘探钻孔，将提供新的约束的构造事件，导致EAG开放。它还将突出我们可以钻探和直接采样并确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海洋地壳。此外，研究亦会提供新的资料，以了解在东亚走廊开启期间所发生的构造事件的先后次序，以及该通道随时间而不断加深的过程。第二个目的是了解白垩纪及新生代期间地球海洋的状况。特别是在白垩纪时期，全球气候和大西洋的海洋比现在温暖得多，其特征是强烈缺氧（低氧水平）和有机碳埋藏的时期。这些事件被称为海洋缺氧事件（OAEs），似乎是由大规模火山爆发产生的强烈温室气体排放事件引发的，持续了数十万年到一百万年。虽然它们已经被钻了很多次，但我们没有关于它们有多广泛的信息-例如有多少水柱受到影响-或者这些沉积物中记录的反馈过程。我们计划确定钻探地点沿着一个深度样带，地震数据表明，他们是非常厚的，以获得重要的新信息，这些事件。最后，我们的目标是建立在现有的IODP建议（1004-APL），以了解白垩纪末期的陨石撞击的后果。纳迪尔陨石坑与墨西哥境内的希克苏鲁布陨石坑几乎同时形成，可能与该事件有关。该陨石坑已在2D地震数据上被识别，但新获得的3D数据将更清楚地阐明陨石坑的形态和特征，使我们能够建立更强大的模型来研究这一事件（山体滑坡，喷出物，海啸）的环境后果。这还将突出说明备选（针对1004-APL提案）或额外（针对新提案）钻探地点，以检验撞击坑假设并了解其后果。有必要对陨石坑进行钻探，以测试这一特征是否确实是由撞击陨石坑形成的，如果是的话，陨石坑的确切年龄。这将使我们能够精确地确定它的日期，并测试希克苏鲁布事件实际上是一个双星系统（两颗小行星）还是一个寿命更长的“撞击星团”的一部分，时间长达数十万或数百万年。

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