Palaeoenvironmental interpretation and isotope stratigraphy of the Campanian–Danian successions in the Zagros Foreland Basin (Kabir Kuh, Lurestan, Iran)

Abstract

The successions of the Gurpi Formation and the lower Pabdeh Formation were examined through analyses of lithology, sequence stratigraphy, stable isotope stratigraphy, and ichnofossils in the Jahangir Abad and Abhar sections of the Kabir Kuh anticline within the Lurestan Zone. Stratigraphic correlation with the well-dated Gandab section, located within the same anticline, indicates a late Campanian to early Danian age for these successions. This correlation further confirms the presence of notable carbon isotope excursions associated with the Campanian-Maastrichtian Boundary Event (CMBE) and Mid-Maastrichtian Event (MME). Field observations, along with sedimentological and paleontological analyses, suggest that the Kabir Kuh area was situated within the fore-bulge of the Zagros foreland basin during the Late Cretaceous. Changes in lithology, fossil content, and ichnofacies indicate a significant decrease in water depth at the end of the Campanian and the beginning of the Maastrichtian. This interval contains shallow marine macrofossils, including oysters (mainly Lopha), benthic foraminifers, and fossil debris traces, indicative of a high-energy environment. In contrast, shallow-water facies are not recorded within the middle and late Maastrichtian sequences. These sequences are composed of pelagic mud-dominated facies containing deep-sea ichnofossils, indicating a rapid increase in water-depth during the middle–late Maastrichtian. The observed late Campanian to early Maastrichtian shallowing is associated with the development of the Zagros fore-bulge, while the subsequent deepening and significant sediment deposition during the mid to late Maastrichtian are attributed to the subsidence of the basin. This research re-evaluates and refines the existing sequence stratigraphic and sedimentary models of the Zagros foreland basin, offering new perspectives on its geological evolution.