Carbon Isotope Stratigraphy of the Uppermost Aptian–Lower Cenomanian Strata from the Lut Block, East Iran

Abstract

The Mid-Cretaceous interval has been recognized as a crucial period in Earth’s history, such that a number of studies on Neo-Tethyan successions illustrated intense evolutions in the nature of Mid-Cretaceous ocean chemistry, sea level, and marine faunal communities. However, much less investigations have been conducted in the Sistan Ocean, in the eastern Neo-Tethys. Here, the Nimbolook section (Lut Block, central Iran) has provided an opportunity to address these shortcomings and provide a better understanding of the paleoenvironmental changes in this region. The biostratigraphic analysis and age interpretation of the Nimbolook section have been performed in earlier investigations by means of planktonic foraminifera, ammonites and calcareous nannofossils. This provided a reliable age framework for the chemostratigraphic interpretations. In the Nimbolook section, the δ13C stratigraphy was carried out on a total of 41 samples, which ranged between -3.26‰ and 2.86‰ with an average of 1.09‰ (standard deviation = 1.15‰), and expanded within the upper Aptian to lower Cenomanian stages. However, there is a prominent negative shift at the base of the section, accompanied by episodes of sea-level fluctuations. Notably, according to the age-diagnostic calcareous nannofossils records, this carbon isotope negative shift (0.88‰ to -3.26‰) is straddling between late Aptian and Early Albian ages. Furthermore, these new chemostratigraphic observations could be interpreted as being the coeval data from the reference well-studied successions in other parts of the world, tentatively reflecting the oceanic anoxic event (OAE) 1b.