Reticulate Nummulites (N. fabianii Linage) and Age of the Pellatispira-Beds of the Drazinda Formation, Sulaiman Range, Pakistan

Authors: Ozcan E*, Yücel AO, Erbay S, Less G, Kaygili S, Ali N and Hanif M

Volume 2, Issue 1

Abstract

The Eocene shallow marine Pellatispira-beds in the upper part of the Drazinda Formation represent the latest phase of Cenozoic Tethyan marine deposition in the Sulaiman Range, West Pakistan. The unit consists of stratigraphically important taxa as Heterostegina, Silvestriella, Pellatispira, a new Baculogypsina (possibly ancestral to modern Baculogypsina) and reticulate Nummulites implying a latest middle to late Eocene (late Bartonian-Priabonian) age. A more precise age of the unit requires the biometric study of reticulate Nummulites, the evolutionary scheme of which is better known from the peri-Mediterranean region in the Tethys. This group, which was subdivided into a series of successive chrono-species based on the biometry of inner cross-diameter of proloculus and changes in the types of granulation/reticulation on the test surface in the late Eocene-late Oligocene interval, appears to have a significant biostratigraphic potential for a high-resolution biostratigraphy in the peri-Mediterranean region (Western Tethys). The reticulate Nummulites in two samples from Rakhi Nala and Zinda Pir, ZP22 and RNB10, were studied and compared with those from the peri-Mediterranean region. The isolated specimens have a weak surface granulation externally, a distinct small umbonal granule (pile) and typical reticulation. The samples ZP22 and RNB10 from Zinda Pir and and Rakhi Nala sections have an average inner cross diameter of proloculus of 152.0 and 153.0 μm respectively. The reticulate Nummulites in both samples are assigned to N. hormoensis, a chrono-species characteristic for the shallow benthic zone (SBZ 18), referable to latest Bartonian-early Priabonian time interval. Since Heterostegina in peri-Mediterranean region and in Pakistan belongs to different lineages, a correlation of N. hormoensis in the studied samples with the wellestablished evolutionary scheme of Heterostegina reticulata and H. armenica lineages from the Western Tethys was not possible.

Keywords: Reticulate Nummulites; Biometry; Priabonian; Pellatispira-beds; Drazinda Formation; Pakistan

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