Upper Campanian-lower Maastrichtian integrated carbon isotope stratigraphy and calcareous microplankton biostratigraphy of North-central Tunisia

Highlights

• Integrated carbon isotope, calcareous nannofossil and planktonic foraminiferal analyses of the Campanian–Maastrichtian in Tunisia.

• Evaluating the isochroneity and diachroneity of the recognized microplankton bioevents.

• Carbon isotope stratigraphy allows for high-resolution global correlations.

Abstract

A comprehensive stratigraphic framework is presented for the upper Campanian-lower Maastrichtian succession of the Elles section in North-central Tunisia. This has been done by applying an integrated approach including calcareous nannofossil and planktonic foraminiferal biostratigraphy in conjunction with carbon isotope stratigraphy. The studied interval spans from the Uniplanarius sissinghii (CC21) to Reinhardtites levis (CC24) calcareous nannofossil zones and their coeval planktonic foraminiferal zones from the Contusotruncana plummerae Zone to Planoglobulina acervulinoides Zone. Seven positive and negative δ¹³C events have been recognized and considered for high-resolution global correlation. Isochroneity and diachroneity of the microplankton bioevents regarding the carbon isotope stratigraphy were assessed. Some discrepancies were reported, and some of them denote actual diachronism. However, the impact of the different taxonomic concepts and/or environmental issues cannot be totally excluded. The Campanian/Maastrichtian boundary has been precisely positioned within the lowermost part of the El Haria Formation at the base of the δ¹³C event CMBc (72.15 ± 0.05 Ma). This level projects directly below the first occurrence of the planktonic foraminifer Gublerina cuvillieri and about 9.4 m below the last occurrence of the nannofossil Uniplanarius trifidus.

Introduction

Several major paleobiologic, paleoclimatic, and paleo-oceanographic fluctuations have been documented throughout the Campanian-Maastrichtian interval. Although these fluctuations have been documented through time, several paleo-latitudinal-driven discrepancies were also recognized. Consequently, distinct paleobiogeographic realms (e.g., Tethyan, Intermediate, Boreal, and Austral) are known with significant inconsistencies within the stratigraphic ranges of micro-planktonic bioevents at different paleolatitudes (Coccioni and Premoli-Silva, 2015; Gardin et al., 2012; Hewaidy et al., 2019; Huber et al., 2008; Li and Keller, 1998a; Pérez-Rodríguez et al., 2012; Robaszynski and Caron, 1995; Voigt et al., 2012; Wendler, 2013). Microplankton biostratigraphy is a helpful tool for regional correlations. However, its applicability for detailed global correlation is commonly restricted by several factors, including endemism of marker taxa, diachronism of origination and extinction levels, absence of index species due to preservation quality, and the application of various biostratigraphic approaches. However, the carbon isotope change over the geologic history offers consistent trends across different latitudes. Therefore, the incorporation of different microplankton biostratigraphy and carbon isotope stratigraphy constitute an enhanced stratigraphic tool applicable for global comparisons (Boussaha et al., 2016; Farouk et al., 2019, Farouk et al., 2018; Jarvis et al., 2002; Linnert et al., 2018; Razmjooei et al., 2018; Sabatino et al., 2018; Thibault et al., 2012a; Voigt et al., 2012, Voigt et al., 2010; Wendler, 2013). This would also help to test the diachroneity of the microplankton bioevents.

In Tunisia, the Campanian/Maastrichtian boundary (CMB) and planktonic foraminiferal bioevents regarding the lithostratigraphic context are problematic. Li and Keller (1998b) and Li et al. (1999), in their studies of the Campanian-Maastrichtian planktonic foraminifera in some Tunisian outcrops, recorded most of the bioevents at a higher stratigraphic position. For instance, they reported the Radotruncana calcarata Zone (CF10) within the interbedded limestone/marl beds, which are now considered as belonging to the uppermost part of the Abiod Formation. This level is surprisingly higher compared to other studies that restrict this zone to the middle members of the Abiod Formation and assign the uppermost part of the Abiod Formation to the lower part of the Gansserina gansseri Zone (Bey et al., 2012; Jarvis et al., 2002; Mabrouk, 2015; Robaszynski et al., 2000; Robaszynski and Mzoughi, 2010). The position of the CMB relative to the rock units was also a matter of controversy. It has been placed within the upper part of the Abiod Formation according to some studies (e.g., Jarvis et al., 2002; Mabrouk, 2015; Robaszynski et al., 2000; Robaszynski and Mzoughi, 2010). While in other studies, the upper part of the Abiod Formation is considered to be late Campanian in age, and the CMB falls within the lower part of the El Haria Formation (Li et al., 2000, Li et al., 1999; Saïdi and Zaghbib-Turki, 2020, Saïdi and Zaghbib-Turki, 2016).

The Elles section has received much scientific interest, and has been the subject of several studies due to its reliability as a stratotype section for the Cretaceous/Paleogene Boundary (KPgB) based on planktonic and benthic foraminifera, nannofossil, and stratigraphy records (Gardin, 2002; Hennebert et al., 2009; Karoui-Yaakoub et al., 2002; Keller et al., 2002; Li et al., 2000, Li et al., 1999; Li and Keller, 1998b; Robaszynski and Mzoughi, 2010; Zaghbib-Turki et al., 2001, Zaghbib-Turki et al., 2000). However, most of these studies paid much attention to the late Maastrichtian-early Danian interval. Consequently, only few studies treated the upper Campanian-lower Maastrichtian part of the section. Here, we present a comprehensive consideration for that interval based on the integration between different stratigraphic approaches, including planktonic foraminifera and calcareous nannofossil biostratigraphy as well as carbon isotope stratigraphy. This would be helpful in determining the accurate level of the CMB and offers comprehensive criteria relevant for global correlations. Furthermore, a comparison of our integrated data with those reported from other localities provides an appropriate opportunity to assess the consistency of the different plankton bioevents.