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Landscape evolution across the Cretaceous/Paleogene boundary in southwestern North Dakota, USA

机译：美国北达科他州西南部白垩纪/古代界面的景观演变

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The Hell Creek Formation and overlying Fort Union Formation record a geologically rapid base-level rise that was approximately contemporaneous with the K/Pg extinction and deposition of Chicxulub-impact indicators. An outstanding question that remains is whether this base-level rise is attributable to: 1) a multi-thousand-year transgression adjacent to a relatively low-relief coastal plain, causing a rise in the water table; or 2) catastrophic flooding due to upland denudation, rapid channel accretion, and hydrologic reorganization resulting from wildfires/deforestation consequential of the impact. Herein we aim to address which of these hypotheses is most consistent with a paleolandscape reconstruction at Mud Buttes, a locality where the boundary clay (BC) is coincident with the Hell Creek-Fort Union contact. One hundred twenty-seven trenches were examined laterally across similar to 2 km transect of K/Pg boundary. The uppermost Hell Creek is comprised of three pedotypes: Pale-Silt Inceptisol (PSI), Olive-Clay Vertisol (OCV), and Chocolate-Clay Vertisol (CCV), which range from moderately well-drained, to variable to poorly drained, to very poorly drained, respectively. All of the BC occurs superjacent to the CCV, despite this pedotype accounting for only similar to 50% of the pre-event landscape. The edaphic features preserved in the CCV pedotype are not attributable to Paleogene overprinting, which indicates that hydromorphic conditions began prior to the impact. Furthermore, 46% of BC is overlain by lignite, despite lignite occurrence on 17% of the earliest Paleogene landscape. This reveals that the poorest-drained landscape positions of the latest Cretaceous persisted across the boundary. These relationships are most consistent with a non-catastrophic base-level rise. (C) 2020 Elsevier Ltd. All rights reserved.
机译：地狱溪组建和覆盖堡联盟形成记录了地质快速的基础级升高，近似同期，k / pg消灭并沉积肾小管冲击指标。一个突出的问题仍然是这种基础级别的上升是归属于：1）与相对低浮雕沿海平原相邻的多万年过渡，导致水位升起;或2）由于普通的剥削，快速的通道增生，以及由野火/砍伐造成影响的野外火灾造成的水文重组引起的灾难性洪水。在此，我们的目标是解决哪些假设与泥浆拍摄的古兰景观重建是最符合的，其中边界粘土（BC）与地狱溪堡联盟联系人一致的地方。横向检查一百二十七个沟槽，与K / PG边界的2km横断面相似。最上面的地狱溪由三个小型网站组成：苍白淤泥刚性（PSI），橄榄粘土Vertisol（OCV）和巧克力粘土vertisol（CCV），其范围从中度良好排出，变化到耗尽不良，到耗尽很差。所有BC都会发生在CCV中，尽管该网托类型仅占用的50％的前景观。在CCV网型中保存的仿效特征不归因于古雄叠印，这表明潮湿条件开始在撞击之前。此外，尽管最早的古雄景观的17％的距离发生了褐煤，但46％的BC被褐煤浸没。这揭示了最贫穷的横向破坏的景观位置，最新的白垩纪持续存在。这些关系与非灾难性的基础级别上升最符合。 （c）2020 elestvier有限公司保留所有权利。

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