Abstract

Palynological analysis of Site M0077A in the Chicxulub impact crater has yielded a record of the immediate Cretaceous/Paleogene (K/Pg) recovery from ground zero of the end-Cretaceous mass extinction, followed by a record of the Paleocene–Eocene Thermal Maximum (PETM) and later Ypresian (Eocene), including the Early Eocene Climatic Optimum (EECO). Eight specimens of the dinoflagellate cyst Trithyrodinium evittii have been observed near the base of the K/Pg transitional unit; these likely represent a post-impact dinoflagellate disaster recovery assemblage deposited within several days following the impact, although the possibility that some or all of the T. evittii specimens are reworked Maastrichtian cysts cannot be fully excluded. Despite high-resolution sampling of the lowermost Paleocene successions, the oldest identifiable terrestrial palynomorphs observed in the Site M0077A core, two specimens of Deltoidospora fern spores, occur at least ∼200,000 years after the impact. Other than these occurrences, the Paleocene section is nearly barren in terms of palynomorphs, likely a result of poor preservation of organic material combined with a long recovery time for vegetation in the vicinity of the crater. Pollen and fungal spore concentrations spike in an anoxic dark shale deposited during the PETM around 56 Ma, with a diverse pollen assemblage indicating the presence of a coastal shrubby tropical forest in the geographic vicinity, likely in the Yucatán Peninsula to the south. In the marine realm, this interval is characterized by thermophilic assemblages of dinoflagellate cysts. Stratigraphically constrained cluster analysis identified four statistically robust sample clusters in the lower Eocene successions, with Malvacipollis spp. and Milfordia spp. abundances driving the highest average dissimilarity between clusters. A second notable spike in palynological concentrations above the PETM section may represent another early Eocene hyperthermal event. Pollen and plant spore concentrations generally increased during the EECO, associated with increases in terrestrial input during basin infilling.

摘要

在Chicxulub撞击坑中对M0077A站点进行的孢粉学分析已产生记录，表明白垩纪末次灭绝的地面零点使白垩纪/古近纪（K / Pg）立即恢复，随后记录了新世-始新世热最大值（PETM） ）和后来的伊普尔人（始新世），包括早期始新世气候最佳（EECO）。在K / Pg过渡单元的底部附近观察到了8个甲鞭毛囊藻Trithyrodinium evittii标本。这些可能代表了撞击后数天内沉积的鞭毛后灾难恢复组合，尽管某些或全部的T. evittii标本被重做无法完全排除马斯特里赫特囊肿。尽管对最下层的古新世演替进行了高分辨率采样，但在Site M0077A岩心中观察到了最古老的可识别陆地古貌，这是两个Deltoidospora标本蕨类孢子发生在撞击后至少约20万年。除这些事件外，古新世断层的古土壤形态几乎是贫瘠的，这可能是由于有机物质保存不良以及火山口附近植被恢复时间长的结果。花粉和真菌孢子浓度在PET Ma期间约56 Ma的缺氧暗页岩中浓度升高，花粉组合多样，表明该地理区域可能存在沿海的灌木状热带森林，可能在南部的尤卡坦半岛。在海洋领域，此间隔的特征是嗜鞭毛囊肿的嗜热性组合。地层约束聚类分析确定了始新世较低演替中的四个统计学上稳健的样本聚类，其中有马尔瓦西泊利斯spp。和米尔福德菌属。丰度导致群集之间的平均差异最高。在PETM断面之上，第二个明显的孢粉浓度峰值可能代表了另一个始新世早期高温事件。在EECO期间，花粉和植物孢子的浓度通常会增加，这与盆地充填期间的地面投入量增加有关。