Late Paleocene to Early Eocene Larger Foraminiferal Biostratigraphy of the Nammal Formation in the Central Salt Range, Pakistan

Abstract

In order to establish a shallow benthic zonation scheme, the larger foraminiferal assemblages (Late Paleocene to Early Eocene) from the upper most beds of the Patala Formation to the top of the Nammal Formation were investigated at five localities of the central Salt Range. Semi-quantitative distribution of 20 species related to the genera Alveolina, Assilina, Dictyokathina, Lockhartia, Miscellanea, Nummulites, Operculina, Ranikothalia and Sakesaria are graphed. For a segment of the Late Paleocene to Early Eocene time, three benthic foraminiferal zones I.e. Zone SB4, Zone SB5 and Zone SBG are recognized. Due to the variations in the stratigraphic ranges of certain larger foraminiferal species, minor amendments in the zonal definitions are proposed. However, the zonal boundaries seems coeval to that of the standard shallow benthic zonation. For the Alveolina based zonation, the zonal boundaries are better defined by the FOs of the subsequent younger species. Based on the larger foraminiferal extinction, the Zone SB5 is proposed to subdivide into older SB5a and younger SB5b subzones. This subdivision is used to facilitate the definition of Paleocene/Eocene boundary which stratigraphically lies in the lower part of the Nammal Formation in the study area. Both, lower and upper boundaries of the Nammal Formation in the Salt Range are -dichronous, and are getting younger towards the west. The study also helped to establish the lower lIerdian stage in Pakistan.