Lithofacies, depositional environments, regional biostratigraphy and age of the Chitarwata Formation in the Bugti Hills, Balochistan, Pakistan Grégoire Métais a,e, * , Pierre-Olivier Antoine b , S.R. Hassan Baqri c , Jean-Yves Crochet d , Dario De Franceschi e , Laurent Marivaux d , Jean-Loup Welcomme f a Section of Vertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, PA 15213, USA b Laboratoire des Mécanismes et Transferts en Géologie, Institut des Sciences de la Terre, 14 Avenue Édouard Belin, F-31400 Toulouse, France c Earth Sciences Division, Pakistan Museum of Natural History, Garden Avenue, Shakarparian, 44000 Islamabad, Pakistan d Laboratoire de Paléontologie, Institut des Sciences de l’Évolution, CNRS-UMR 5554, Université Montpellier II, c.c. 064, Place Eugène Bataillon, F-34095 Montpellier Cedex 5, France e Paléobiodiversité et Paléoenvironnements, UMR 5143 (CNRS, MNHN, UPMC), Département Histoire de la Terre, Muséum National d’Histoire Naturelle, 8 rue Buffon, CP 38, F-75231 Paris Cedex 05, France f 123 rue du Château d’eau, 34270 Le Triadou, France article info Article history: Received 17 January 2007 Received in revised form 15 February 2008 Accepted 10 April 2008 Keywords: Lithofacies Paleoenvironment Biochronology Chitarwata Formation Oligocene Bugti Hills Pakistan abstract The Oligocene-early Miocene Chitarwata Formation records a critical interval of terrestrial sedimentation that predates the Siwalik deposits on the Potwar Plateau of north-central Pakistan. This Oligocene-early Miocene time interval has long been considered as lacking in the entire Indo-Pakistan region. The Chitarwata Formation is widely exposed in the Sulaiman Range, but has never been described in detail in the Sulaiman Lobe, where the famous fossiliferous strata called ‘Bugti Bone Beds’ have been known for over a century and half. The Chitarwata Formation represents coastal-delta at the base, and plain and fluvial environments at the top. Lithofacies and sedimentary structures of the Chitarwata Formation in the Bugti area are described in detail, and show a clearly distinct lithologic pattern, different from that reported from the Zinda Pir area. The Chitarwata Formation also records an important transition in the evolution of the drainage systems in the area during the late Paleogene and early Neogene. This transition from the west-flowing paleo-Indus fluvial system to the development of the ancestral Indus drainage sys- tem may explain the numerous hiatuses that characterize the Chitarwata Formation. The abundance of fossil mammals from the Chitarwata and overlying Vihowa formation in the Bugti Hills provides critical biochronologic information that sheds new light on biostratigraphic correlation with the Zinda Pir area and for the entire Sulaiman Range. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Paleogene sedimentary strata exposed in the Sulaiman Range of Pakistan record the transition from marine shelf to terrestrial depo- sition episodes related to the uplift and erosion of the orogenic Himalayan highlands. Deposition of these thick detrital units re- sulted from the collision between the Indian and Asian plates, which began near the Paleocene/Eocene transition, 55 Ma (Beck et al., 1995; Clift et al., 2001). The Oligocene–Miocene Chitarwata Forma- tion spans an important interval of tectonic and sedimentary history that records the regional transition from marginal marine to fluvial environments, as well as the establishment of the present drainage of the Indus River and its tributaries. The Chitarwata Formation is widely exposed throughout the eastern part of the Sulaiman Range, and consists of coastal, deltaic, and fluvial sediments that have yielded numerous fossil vertebrates. The Chitarwata Formation is now considered as partly Oligocene in age (Welcomme and Gins- burg, 1997; Welcomme et al., 2001), although it was originally re- garded as an early Miocene unit that underlay Siwalik-like deposits of the region based both on fossil assemblages (Downing et al., 1993) and magnetostratigraphic data (Friedman et al., 1992). The age of the lowermost part of the formation remains contentious (Lindsay et al., 2005). The Chitarwata Formation has been intensively studied in two main areas approximately 200 km apart: the Bugti Hills of Balochistan and the Zinda Pir Dome of Punjab (Fig. 1). The type section of the Chitarwata Formation is approximately 400 m thick at Chitarwata Post in the Northern part of the Sulaiman Range, approximately 120 km north of the Zinda Pir area (Hemphill and Kidwai, 1973). Downing et al. (1993) recognized three distinct units (lower, middle, upper) in the Chitarwata Formation at Dalana, in the Zinda Pir Dome. Lindsay et al. (2005) reinterpreted the magnetic se- 1367-9120/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2008.04.006 * Corresponding author. Address: Section of Vertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, PA 15213, USA. Tel.: +33 140793004; fax: +33 140793580. E-mail addresses: metaisg@carnegiemnh.org, metais@mnhn.fr (G. Métais). Journal of Asian Earth Sciences 34 (2009) 154–167 Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jaes