Abstract

Stratigraphic horizons of the Cretaceous oceanic anoxic events (OAEs) are constrained for the first time at the northwestern margin of the Indian Plate, Pakistan, using high-resolution planktonic foraminiferal biostratigraphy. In this study, 15 planktonic foraminiferal biozones have been erected, suggesting an early Aptian to early Maastrichtian age for the studied section. Based on the established biozones, the stratigraphic positions of the Cretaceous OAEs are defined. The lowermost organic-rich interval occurs in the Hedbergella delrioensis and Globigerinelloides algerianus zones of the early to late Aptian, which correlate with the Selli (OAE 1a) and Fallot events. The next interval with the abundant presence of organic matter occurs in the Ticinella bejaouaensis zone (latest Aptian) and correlates with OAE1b. The third organic-rich interval falls in the Biticinella breggiensis zone of the middle to late Albian and correlates with the OAE1c. The fourth organic-rich horizon straddles the Cenomanian − Turonian boundary and corresponds to OAE2. The fifth organic-rich interval falls in the Globotruncana ventricosa zone of middle to late Campanian age and correlates with the Campanian isotopic event. The evolution of planktonic foraminifera in this part of the Tethys Ocean, is driven by OAEs, e.g. at the base of OAE2, a mass extinction of foraminiferal species, mainly rotaliporids, occurred, and at the end of OAE2, simultaneous appearances of the whiteinellids, marginotruncanids and dicarinellids indicate the fastest rate of speciation.

1. KEY POINTS

2. The planktonic foraminiferal biostratigraphic investigations revealed an early Aptian to early Maastrichtian age for the Parh Formation exposed in the Mughal Kot Section, Pakistan.

3. Based on biostratigraphic data, stratigraphic positions of the OAE1a, OAE1b, OAE1c, OAE2 and Campanian events are constrained.

4. An evolutionary link of major planktonic foraminiferal genera with Cretaceous OAEs has been observed.

摘要

使用高分辨率浮游有孔虫生物地层学首次将白垩纪海洋缺氧事件 (OAE) 的地层限制在印度板块的西北边缘。在这项研究中，已经建立了 15 个浮游有孔虫生物区，表明所研究部分的早期 Aptian 至早期 Maastrichtian 时代。根据已建立的生物带，确定了白垩纪 OAE 的地层位置。最低的富含有机物区间发生在早到晚 Aptian的Hedbergella delrioensis和Globigerinelloides algerianus区域，这与 Selli (OAE 1a) 和 Fallot 事件相关。下一个有机质丰富的区间出现在Ticinella bejaouaensiszone（最新的 Aptian）并与 OAE1b 相关。第三个富含有机质层段位于阿尔比斯中晚期的Biticinella breggiensis带，并与 OAE1c 相关。第四个富含有机物层位横跨 Cenomanian - Turonian 边界，对应于 OAE2。第五个富含有机质层段位于坎帕阶中晚期的Globotruncana ventricosa带，并与坎帕阶同位素事件相关。特提斯洋这一部分浮游有孔虫的进化是由 OAE 驱动的，例如 在OAE2的基部，有孔虫类，主要是轮虫类，发生了大规模的灭绝，而在OAE2的末期，whiteinellids、marginotruncanids和dicarinellids同时出现表明物种形成速度最快。

1. 关键点

2. 浮游有孔虫生物地层学调查揭示了巴基斯坦莫卧儿科特地区出露的 Parh 地层的早期 Aptian 至早期 Maastrichtian 时代。

3. 根据生物地​​层数据，OAE1a、OAE1b、OAE1c、OAE2 和坎帕阶事件的地层位置受到限制。

4. 已经观察到主要浮游有孔虫属与白垩纪 OAE 的进化联系。