IMPLICATIONS AND CONCLUSIONS

Our paleocurrent data suggest that there was an appreciable interval during the late Oligocene and early Miocene during which the Zinda Pir area was a stable coastline with paleodrainage chiefly from the northwest toward the southeast. This Chitarwata coast formed the northern and western edge of the Tethys-sea-marine foredeep, a structure recognized in sedimentary deposits in the Kohat Basin to the north by Pivnik and Wells (1996). The presence of marine invertebrates and oncolites in the early ?Miocene Murree Formation (Pivnik and Wells 1996) suggests that this marginal marine facies may have extended as far as the Kohat Plateau to the northwest. Moreover, this coastline was likely structurally isolated by a northern forebulge and regional highlands to the west from the main recycled orogenic detritus observed in the concurrent fluvio-deltaic deposits of the Katawaz Basin and the subsequent fluvial deposits of the Vihowa Formation. It is notable that Vihowa sedimentation predates deposition of the Kamlial Formation on the Potwar Plateau by at least a million years. This timing implies that initial Indus River deposition in the Himalayan foreland was asynchronous across the Himalayan front near the syntaxis.

In contrast to the Chitarwata Formation coastline, the Bugti Hills area of deposition is interpreted as a major fluvio-deltaic environment occupying a vast floodplain (Welcomme et al. 2001). It is difficult to reconcile the lithostratigraphic, paleoenvironmental, and taphonomic differences in the Chitarwata Formation between the Bugti Hills and Zinda Pir Dome areas as just a product of coeval or diachronous lateral variation in the same depositional system. Based upon the prevailing knowledge of regional deposition of the Indus River in the Oligocene and early Miocene summarized above, it is plausible that the more southerly Bugti Member of the Chitarwata Formation at Bugti Hills, with its exceptional Oligocene vertebrate faunas (Welcomme and Ginsburg 1997, Marivaux et al. 1999, Antoine et al. 2003, Metais et al. 2003), was a phase of fluvio-deltaic sedimentation related to distal deposition in the Katawaz drainage system as part of the Shaigalu Delta. In this scenario, the extensive Bugti Hills fluvio-deltaic environment would represent primary Indus River drainage from northern highlands rather than from western orogenic highlands as suggested by Welcomme et al. (2001). If correct, significant differences in fossil preservation and biostratigraphic relationships would be expected between the Zinda Pir and Bugti sediments. Moreover, vertebrates recovered in the Shaigalu member of the Khojak Formation might compare favorably in age to those at the Bugti Hills. Future comparison of provenance signals with respect to sandstones in the Chitarwata Formation from the Zinda Pir and the Bugti Hills areas should clarify whether they are indeed distinct in composition as well as clarify the timing and character of their signals and relationship to the concurrent Indus River drainage.