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Planktonic foraminiferal biostratigraphy of the Cretaceous strata, Indus Basin, Pakistan, Eastern Tethys: implications for oceanic anoxic events

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. KEY POINTS The planktonic foraminiferal biostratigraphic investigations revealed an early Aptian to early Maastrichtian age for the Parh Formation exposed in the Mughal Kot Section, Pakistan. Based on biostratigraphic data, stratigraphic positions of the OAE1a, OAE1b, OAE1c, OAE2 and Campanian events are constrained. An evolutionary link of major planktonic foraminiferal genera with Cretaceous OAEs has been observed.