A contribution to the study of the Eocene in western Pakistan and western India: D. Discussion of the faunas of the certain standard sections, and their bearing on the classification and correlation of the Eocene in western Pakistan and western India

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Summary: Local palaeontologieal subdivisions are established for the Eocene of the Rakhi Nala, Zinda Pir and Kohat areas as a result of the examination of extensive collections of fossils recently made in these areas. The distribution of the different phyla in various facies developments is discussed. Comparison is made with the pre-existing major subdivisions of the Eocene in western Pakistan and western India. In the Rakhi Nala and Zinda Pir area, it is concluded that the Khirthar-Laki boundary has previously been taken at too low a horizon, and that beds previously referred to as lower Middle Khirthar include representatives of the upper Middle Khirthar, the Upper Khirthar, and still younger horizons of Upper Eocene age. The lithological and mapping evidence and the palaeontologieal evidence from the Rakhi Nala and Zinda Pir areas are each considered separately and finally synthesized in order to arrive at as precise a correlation as is possible. The evidence from the Kohat Eocene beds has been synthesized with that from the Rakhi Nala-Zinda Pir area in like manner, and it is evident that only the major palaeontological subdivisions can be correlated. The present investigations have confirmed the usefulness of the terms “Ranikot Series”, “Laki Series” and “Khirthar Series” for subdivisions of the Eocene in western Pakistan and western India. The writer considers that the basic and fundamental soundness of these terms is not affected by the fact that beds and faunas have occasionally been incorrectly allocated to one or other of them. Certain beds, which are here named the “ Tapti Series ”, and which are not of very widespread occurrence, contain a fauna which is distinct from that of the Khirthar Series below and is of Upper Eocene age. The fauna of this series, in addition to several species of Upper Eocene age and a number of new species, includes the genus Pellatispira , which is also of Upper Eocene age and has not yet been unquestionably recorded from horizons as low as those containing the genus Assilina . A consideration of all the available evidence indicates that published information concerning the ranges of some species is incomplete and that in some cases the existing conception of a species requires modification. The author is of the opinion that the “ zones ” which have been previously proposed within the Ranikot, Laki and Khirthar Series are of local rather than regional value, and that there has been too great a readiness to assign regional chronological significance to local facies faunas. It is evident that further work is necessary before regional zoning of the series can profitably be attempted.

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