The Siwaliks of Pakistan: Time and Faunas in a Miocene Terrestrial Setting

Abstract

Mageetostratigraphy provides unparalleled chronologic precision for long terrestrial sedimentary records. The Siwaliks of the Potwar Plateau, northern Pakistan, present perhaps the best example of a sequence of well dated faunal horizons spanning most of the Neogene in a single terrestrial biogeographic province. Temporal control on fossil localities tied to multiple paleomagnetic sections is ca . 0.1 m.y., less given special conditions of short magnetozone duration or superpositional relationships. New correlations are presented for two long sections in the lower Siwaliks showing the power and the limitations of magnetostratigraphic correlation within the Siwalik depositional setting. Correlation of Potwar fossil localities to those of an East African section, also dated paleomagnetically, are established with fossil localities from those two biogeographic provinces shown to be coeval on a scale of 105 yr. the composite biostratigraphy rendered by the thick, well exposed, well dated Potwar Siwaliks enables definition of sequential biochronologic units without gaps. Utility of the biochronology lies in correlating isolated deposits to the Potwar composite; for studies within the Potwar, locality relationships and the biostratigraphy itself are the operational units. The history of the Siwalik fauna shows turnover episodes, but they differ in intensity, diversity of groups affected, and coincidence of first and last occurrences, probably reflecting different causes. Studies on the evolution of lineages are rendered more powerful by magnetostratigraphy: temporal control tests patterns of speciation, yields confident estimates on true temporal ranges of fossil taxa, and shows that rodent species longevities exceeded 2 m.y. on average.