Evidence of marine target impacts, binary impact craters, or impact clusters are rare on Earth. Seismic reflection data from the Guinea Plateau, West Africa, reveal a ≥8.5-km-wide structure buried below ~300 to 400 m of Paleogene sediment with characteristics consistent with a complex impact crater. These include an elevated rim above a terraced crater floor, a pronounced central uplift, and extensive subsurface deformation. Numerical simulations of crater formation indicate a marine target (~800-m water depth) impact of a ≥400-m asteroid, resulting in a train of large tsunami waves and the potential release of substantial quantities of greenhouse gases from shallow buried black shale deposits. Our stratigraphic framework suggests that the crater formed at or near the Cretaceous-Paleogene boundary (~66 million years ago), approximately the same age as the Chicxulub impact crater. We hypothesize that this formed as part of a closely timed impact cluster or by breakup of a common parent asteroid.

中文翻译：

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西非近海的纳迪尔火山口：一个候选的白垩纪-古近纪撞击结构

海洋目标撞击、二元撞击坑或撞击团的证据在地球上很少见。来自西非几内亚高原的地震反射数据显示，在约 300 至 400 米的古近纪沉积物之下，有一个 ≥8.5 公里宽的结构，其特征与一个复杂的撞击坑一致。其中包括阶梯状火山口底部上方的升高边缘、明显的中央隆起和广泛的地下变形。火山口形成的数值模拟表明，一颗 400 米以上的小行星撞击海洋目标（水深约 800 米），导致一连串巨大的海啸波，并可能从浅埋黑色页岩沉积物中释放大量温室气体. 我们的地层框架表明火山口形成于白垩纪-古近纪边界处或附近（约 6600 万年前），与希克苏鲁伯撞击坑的年龄大致相同。我们假设这形成为一个紧密定时的撞击星团的一部分，或者是由一个共同的母小行星的分裂形成的。