Integrated stratigraphy and palaeoenvironment of the P/E boundary interval, Rakhi Nala section, Indus Basin (Pakistan)
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ORIGINAL PAPER
Integrated stratigraphy and palaeoenvironment of the P/E boundary interval, Rakhi Nala section, Indus Basin (Pakistan) Muhammad Hanif & Malcolm B. Hart & Stephen T. Grimes & Melanie J. Leng
Received: 11 October 2012 / Accepted: 11 December 2012 # Saudi Society for Geosciences 2012
Abstract Marine sedimentary section across the Paleocene/ Eocene (P/E) boundary interval is preserved in the Dungan Formation (Lower Indus Basin), Pakistan. Four dinoflagellate zones in the P/E interval of the Rakhi Nala section (Lower Indus Basin) are identified and correlated. The quantitative analysis of the dinoflagellate cyst assemblages together with geochemical data are used to reconstruct the palaeoenvironment across the P/E interval. The dinocyst assemblages allow the local correlation of the Dungan Formation (part) of the Sulaiman Range with the Patala Formation (part) of the Upper Indus Basin and global correlation of the Zone Pak-DV with the Apectodinium acme Zone of the Northern and Southern hemispheres. The onset of the carbon isotopic excursion (CIE) associated with Paleocene Eocene Thermal Maximum (PETM) is used globally to identify the P/E boundary. The CIE for the total organic carbon (fine fraction) δ13CFF is of a magnitude of −1.7‰ is recorded for the first time in the Indus Basin. The Apectodinium acme precedes and straddles the onset of the CIE in the Indus Basin. This Apectodinium acme is also accompanied by a planktonic and benthonic foraminifera “barren zone.” The CIE in the Indus Basin, coupled with the changes in the dinocyst distribution and the benthonic and planktonic foraminifera assemblages, provides evidence of M. Hanif : M. B. Hart : S. T. Grimes School of Geography, Earth and Environmental Sciences, Plymouth University, Plymouth, UK M. Hanif (*) National Centre of Excellence in Geology, University of Peshawar, Peshawar, Pakistan 25120 e-mail: [email protected] M. Hanif e-mail: [email protected] M. J. Leng NERC Isotope Geosciences Laboratory, BGS, Nottingham NG12 5GG, UK
the changes associated with the PETM in this little-known part of the world. The benthonic foraminiferal assemblage indicates bathyal environment of deposition at the time of P/ E boundary interval; the presence of dominantly open marine dinoflagellates and high planktonic foraminiferal ratio suggest that the water column at this site was well connected with the rest of the Tethys. Keywords Paleocene . Eocene . Indus Basin . Foraminifera . Dinoflagellates . Isotopes
Introduction The Earth experienced climatic variations from a warm “greenhouse” to a cooler “icehouse” world during the Paleogene (Zachos et al. 2001). The Paleocene (65 to ~55 Ma) was a time of great environmental change, within both the marine and terrestrial realms and represents a period of significant perturbation and punctuated biotic changes, bounded by two important events in Earth history, the Cretaceous/Paleogene extinction event at the base and the Paleocene–Eocene Thermal Maximum (PETM) at its end. The PETM is a relatively brief (100 t
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