INTRODUCTION

Raza and Meyer (1984) reported on brief reconnaissance in the Bugti area and tried to resolve several systematic problems. They evaluated the then known chronological data and concluded that an early Miocene age was reasonable for the assemblage. Although they suspected that fossils occurred throughout some stratigraphic thickness, the parsimonious view at the time was to consider the whole assemblage to be early Miocene in age. In 1978, I.U. Cheema (then with the Geological Survey of Pakistan [GSP]) collected sediment from Pazbogi Nala that produced a new group of rodents, the Baluchimyinae (Flynn et al. 1986), from the Bugti Beds of Baluchistan. Following Raza and Meyer, the Pazbogi Nala assemblage was considered early Miocene in age.

Later, extensive and well-organized fieldwork by French paleontologists and geologists (Welcomme et al. 1999, 2001) showed that fossils in the Bugti area span a long interval of time. The classic Bugti Bone Beds are concentrated low in the sequence, but many of the fossils, including proboscideans, occur stratigraphically higher. French colleagues suspected an Oligocene age for the Bugti rodents. Now faunal and stratigraphic data demonstrate conclusively that the Bugti Bone Beds significantly antedate earlier estimates, possibly dating to the early Oligocene in their interpretation. They found new site (Paali C2) with rich microfauna (Marivaux et al. 1999, Marivaux and Welcomme 2003) low in the sequence that was taxonomically similar to the material reported earlier from Pazbogi Nala.

While the French teams worked in the Bugti area, our group investigated sequences in the Zinda Pir Dome of the Sulaiman Range near Dera Ghazi Khan (Figure 1), where the Siwalik-like Vihowa, Litra, and Chaudhwan Formations overlie Bugti-like sediments of the Chitarwata Formation. The geology of the Zinda Pir Dome area was described by Hemphill and Kidwai (1973) in the context of a joint GSP-USGS mapping project. Our studies added paleomagnetic and biostratigraphic data for the Chitarwata and lower Vihowa Formations in the vicinity of Dalana, near the southern nose of the Zinda Pir Dome. We duplicated the Bugti microfauna low in the Chitarwata Formation in the Dalana region (Flynn and Cheema 1994), as well as adding microfauna and macrofauna of more modern aspect in higher levels of the Chitarwata Formation. We also collected fauna from the Vihowa Formation, resembling the basal Siwalik mammals recovered on the Potwar Plateau.

Together with Bugti, the Zinda Pir Dome sequence provides a more complete record of mid-Cenozoic evolution in southern Asia than was previously available. Our purpose is to report on the stratigraphy, sand-body analysis, fossils, and magnetic reversal stratigraphy of the Chitarwata-Vihowa sequence in the Dalana area. Interpretation of the paleomagnetic signal in the Dalana area has proven difficult. Problems involve stratigraphic hiatuses and weak, unreliable magnetic properties of some rock samples, low overall rate of sedimentation but locally highly variable sedimentation, and absence of datable volcanic deposits. However, although not conclusive in itself, the paleomagnetic information limits age estimates and supports greater antiquity for the base of the terrestrial sequence. We now conclude that deposition of the Chitarwata Formation in the Zinda Pir Dome area began during the Oligocene Epoch; however, resolution of the Oligocene chronology remains a problem.

Origin of the Zinda Pir Dome Initiative

Will Downs joined the Pakistan paleontological field crew during the 1980 field season and became the prime instigator of the small mammal project from 1989 until his untimely death in December 2002. The combined Yale University-GSP and Dartmouth-Peshawar University field parties had been working in Pakistan since 1973 to refine the biostratigraphic framework for the Potwar Plateau. Louis Jacobs initiated the small mammal fossil program in the 1970s, but rodent collecting thrived from 1980 until the last full-fledged field season in 2000 due to the energy and enthusiasm of Will Downs. Field programs in Pakistan declined thereafter, but Will continued doing field work with Steve Ward, Raza, Cheema, and Rajpar in the Zinda Pir area (Raza et al. 2002). Will Downs was the driving force for fieldwork in the Zinda Pir area since its beginning.

During the latter part of the 1980s, working primarily on the Potwar Plateau, our combined efforts yielded an impressive record (more than 18 my) of Siwalik paleontology and chronology (much of which is summarized in Badgley and Behrensmeyer 1995). Thereafter, our attention turned to the major hiatus that underlies the Siwalik sequence on the Indo-Pakistan subcontinent. For years our travel to Pakistan included flights between Karachi in the south and Rawalpindi on the Potwar Plateau, where our Siwalik fieldwork took place. The route between Karachi and Rawalpindi traversed thick exposures of Siwalik-like strata along the forelands of the Sulaiman Range, west of Multan. Farther southwest of Multan, we knew that the Bugti Beds produced another impressive record of fossil mammals, and as our work on the Potwar Plateau reached maturity, our ambitions for doing fieldwork in the foothills of the Sulaiman Range grew.

The joint GSP-USGS project of Hemphill and Kidwai (1973) focused on the northern part of the Zinda Pir Dome. They recognized and named Siwalik-like sediments (Vihowa, Litra, and Chaudhwan Formations) in the Sulaiman Range and an older suite of terrestrial sediments they named the Chitarwata Formation. They believed the Chitarwata Formation was continuous with the Bugti Beds about 160 km south of the Zinda Pir Dome. Vertebrate fossils were virtually unknown from either the Siwalik-like beds or the underlying Chitarwata Formation in the Zinda Pir Dome until Raza and colleagues found evidence of fossils during an initial reconnaissance in 1988.

Study of the sedimentary sequence in the Dalana area began as a collaboration with the Pakistan Museum of Natural History (PMNH) in January 1989 when Downs, Lindsay, and Cheema flew from Islamabad to Multan and continued by bus to Dera Ghazi Khan (D.G. Khan), west of the Indus River. Four days were spent at D.G. Khan, making daily excursions by rental car (arranged by Cheema’s cousin Nuveed Chaudhry) into the foothills of the Sulaiman Range to the west. About a ton of sediment from the Chitarwata and Vihowa Formations, collected near the village of Dalana, was hauled back to our base camp near Chinji on the Potwar Plateau, to process for small mammal fossils. Will, as principal collector, supervised screening of that preliminary sample of Zinda Pir sediment and transported the concentrate to the USA.

Will processed the screen-washed residue by heavy liquids at the Bilby Research Center, Northern Arizona University, during the following spring and summer. We were delighted to find that most of the rodents collected from the Chitarwata Formation were baluchimyines similar to those found by Cheema at Bugti. Preliminary analysis (Flynn and Cheema 1994) highlighted two new genera and four new species from the Dalana area.

A major effort was made in 1990 to collect more fossils from the Dalana area, place the fossils in a stratigraphic framework, sample the sediments for magnetic stratigraphy, and search for chronologic markers in those beds. Our results were published by Friedman et al. (1992) and Downing et al. (1993). Unfortunately, fieldwork was cut short in 1991 by the Gulf War and did not resume in the Dalana area until 2000, this time supported by the National Geographic Society. The results of that fieldwork and a summary of subsequent studies follow below. The most recent report of Zinda Pir paleontologic-geologic work (Raza et al. 2002) summarizes on-going investigations, especially those in younger sediments equivalent to the Siwaliks of the Potwar Plateau.