Sequence stratigraphy of the Gurpi Formation (Campanian–Paleocene) in southwest of Zagros, Iran, based on palynomorphs and foraminifera

Abstract

The Gurpi Formation is a well-known source rock in the Zagros basin, which stretches from northeast to southwest Iran. Sequence stratigraphy was done based on the integration of evidence derived from palynological proxies and foraminiferal data. According to sequence stratigraphy, seven time lines including four sequence boundaries of type II and three maximum flooding surfaces with a resolution varying from 1 to 5 MY and three complete third-order sequences and one transgressive systems tract (TST) were differentiated. Maximum flooding surface of the first sequence in middle Campanian probably equates the 70-Ma maximum flooding surface (MFS) K175 of Sharland et al. (GeoArabia P: 371, 2001), and MFS of the second sequence in early Maastrichtian is correlated with the marked 68-Ma MFS (MFS K180) of Sharland et al. (GeoArabia P: 371, 2001) that is recorded in many parts of the Arabian Plate. Correlation with the Haq global eustatic curve, though uncertain because of the effect of local tectonics over the relative sea level changes, however, could be possible with the 69.5 Ma. Also, purple shales of the base of the Pabdeh Formation with a Thanetian age are defined as a MFS, correlation of which with the marked 58-Ma MFS (MFS Pg10) of Sharland et al. (GeoArabia P: 371, 2001) and with 56.5-Ma MFS of Haq seems likely. The relative sea level curve resulted in this study is not well in accord with the existing eustasy curves for the middle Campanian-late Paleocene indicating effect of tectonic on relative sea level changes during this period.