Data from: Blooms of aberrant planktic foraminifera across the K/Pg boundary in the Western Tethys: causes and evolutionary implications

Here we report a detailed study of the different categories and types of abnormal morphologies in planktic foraminifera recognizable in the lowermost Danian mainly from the El Kef and Aïn Settara sections, Tunisia. Various types of abnormalities in the test morphology were identified, including protuberances near the proloculus, abnormal chambers, double or twinned ultimate chambers, multiple ultimate chambers, abnormal apertures, distortion in test coiling, morphologically abnormal tests, attached twins or double tests, and general monstrosities. Detailed biostratigraphic and quantitative studies of the Tunisian sections documented a major proliferation of aberrant planktic foraminifera (between approximately 5 and 18% in relative abundance) during the first 200Kyr of the Danian, starting immediately after the Cretaceous/Paleogene (K/Pg) boundary mass extinction (spanning from the Guembelitria cretacea Zone to the lower part of the P. pseudobulloides Zone). This contrasts with the proportionately low frequency of aberrant tests (generally < 2%) identified within the uppermost Maastrichtian, suggesting more stable environmental conditions during the last ~50-100Kyr of the Cretaceous. Two main pulses with abundant aberrant tests were recognized in the earliest Danian, the one recorded in the well-known K/Pg boundary clay being the more intense of those (maxima of >18%). These main pulses of aberrants coincide approximately with relevant quantitative and evolutionary turnovers in the planktic foraminiferal assemblages. In this paper we explore the relation of these high values of the foraminiferal abnormality index with the environmental changes induced by the meteorite impact of Chicxulub in Yucatan, Mexico, and the massive eruptions of the Deccan Traps, India.

本研究针对突尼斯El Kef与Aïn Settara地层剖面中丹尼阶最底部可识别的浮游有孔虫（planktic foraminifera）异常形态的不同类别与类型展开详细探究。研究共识别出多种壳体（test）形态异常类型，包括初房（proloculus）附近的突起、异常壳室、双生/孪生终壳室、多终壳室、异常壳口、壳体旋向畸变、形态异常壳体、附着式孪生壳体/双壳体以及一般性畸形。对突尼斯地层剖面开展的详细生物地层学与定量研究表明，在白垩系-古近系（K/Pg）界线大灭绝事件发生后即刻开始的丹尼阶最初20万年期间，异常浮游有孔虫的相对丰度出现显著增长，其占比约为5%至18%，地层跨度覆盖白垩球室虫（Guembelitria cretacea）带至假泡虫（P. pseudobulloides）带的下半部。这一现象与马斯特里赫特阶顶部地层中观测到的异常壳体极低出现频率（通常<2%）形成鲜明对比，暗示白垩纪最后约5至10万年期间环境条件更为稳定。在丹尼阶最早期地层中，共识别出两期异常壳体大量出现的主要峰值事件，其中赋存于著名K/Pg界线黏土中的那一期强度更高，峰值占比超过18%。这些异常壳体的主要峰值事件，大致与浮游有孔虫组合的相关定量与演化更替事件相吻合。本文探讨了有孔虫异常指数与墨西哥尤卡坦半岛希克苏鲁伯陨石撞击以及印度德干暗色岩（Deccan Traps）大规模火山活动所引发的环境变化之间的关联。