Diachroneity in the closure of the eastern Tethys Seaway: evidence from the cessation of marine sedimentation in northern Pakistan

Abstract

The biostratigraphic information from the last remnants of the Tethys Seaway in northern Pakistan was used to date the cessation of marine sedimentation as a result of the closure of the eastern Tethys Seaway and to give a minimum time for the India–Asia collision. The current detailed biostratigraphic investigations of the Eocene Kohat Formation in the Kohat Basin divulged that the rock unit in the study area contains age-diagnostic larger benthic foraminiferal (LBF) species of middle Eocene age. Based on the association of identified LBF species, two local biozones, i.e. PKBZ 1 and PKBZ 2, are documented and are comparable with published SBZ 13 and SBZ 14 zones, suggesting an early to middle Lutetian age of the rock unit. The integration of current biostratigraphic information of the Kohat Basin with detailed literature on other basins suggests that the closure of the eastern Tethys Seaway in Pakistan occurred in four stages: (i) closure of the northwestern Kohat region during the early Ypresian (55.9–55 Ma), (ii) followed by the closure in the Potwar region, apart from its northwestern domain, during the middle to late Ypresian (54–49.9 Ma), (iii) closure of the Tethys Seaway in the Hazara–Kashmir and northwestern Potwar regions during the early Lutetian (49–45.8 Ma) and (iv) the final stage of Tethys closure has occurred in the Kohat region during the middle Lutetian 1 (45.8–43.6 Ma). The biostratigraphic information in the current study suggests that the final stage of eastern Tethys closure in northern Pakistan occurred at 45.8–43.6 Ma, and thus it gives a minimum age for the India–Asia collision. Such diachroneity can be observed elsewhere in the eastern Tethys, including Iran, Nepal, Bangladesh, Turkey and Tibet. The closure started first in eastern Tethys, continued in both eastern and western Tethys, and was finally completed in eastern Tethys.

KEY POINTS

1. Biostratigraphic investigations of the youngest marine remnants of the Kohat Basin, northern Pakistan, show an early Lutetian to middle Lutetian 1 age.

2. The current results, augmented by published data, suggest diachroneity in the closure of Tethys Seaway in northern Pakistan.

3. The diachroneity in the closure of Tethys Seaway also exists in southern Pakistan, Iran, Nepal, Bangladesh, Turkey and Tibet. The closure initiated first in eastern Tethys, continued in eastern and western Tethys, and was finally completed in eastern Tethys.

Keywords:

• Eocene
• larger benthic foraminifera
• eastern Tethys
• carbonates
• closure
• collision

Acknowledgements

The authors are thankful to the Department of Geology, University of Swabi, Pakistan for providing laboratory facilities to carry out microscopic studies. The authors are also thankful to Mr. Nowrad Ali for helpful discussions and suggestions for the improvement of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).