FROM WEST PAKISTAN 85 



V. OSTRACODA AND EARLY TERTIARY CORRELATION 

 IN THE SULAIMAN RANGE 



(a) BlOSTRATIGRAPHIC UNITS 



Throughout the succession the ostracods have revealed a fairly shallow-water 

 marine environment. Although Eames (1952a) has recorded small freshwater 

 gastropods in the lower part of the Lower Chocolate Clays (in his local zones 8 & 9) of 

 the Rakhi Nala section, he believes they were carried down from a closely neigh- 

 bouring source and deposited under estuarine conditions. No freshwater ostracods 

 have been found, however, and the presence of Neocyprideis sp. in the Shales with 

 Alabaster could represent either estuarine or super saline conditions. 



Except for a few gaps, ostracods occur throughout almost the whole succession. 

 At many horizons, particularly in the Eocene, samples are completely crowded with 

 ostracods. The diversity of the fauna being suggestive of ideal conditions. They 

 usually occur in association with larger and smaller benthonic Foraminifera, but 

 are very rare or almost absent in samples with rich pelagic Foraminifera. The most 

 conspicuous gap in the Eocene succession of the Rakhi Nala and Zao River sections 

 which has not yielded any ostracods is the Platy Limestone and the lower part of the 

 Lower Chocolate Clays. In the Zao River section the top 600 ft. of the Upper 

 Chocolate Clays are devoid of any recognizable ostracods, although at a few horizons 

 some Nummulites have been found. 



Rakhi Nala Section 



The following ostracod biostratigraphic units in the Rakhi Nala section have been 

 recognized (see Table 4). Each unit is identified by a distinct ostracod fauna, a 

 change of faunal suite marking the base. 



Ostracod Biostratigraphic Unit I , Palaeocene (lower part) 



The first Tertiary ostracod assemblage is encountered in the lower part of the 

 Gorge Beds (samples from the Venericardia Shales were not available for study). 

 Seven out of the eight species recorded are restricted to the unit. The species which 

 ranges up into Unit II is Trachyleberis (Acanthocythereis) usitata sp. nov. Alocopo- 

 cythere rupina sp. nov., Neocyprideis ? sp.A and Bairdia sp.A are abundant and make 

 up over 80% of the ostracod fauna. 



Ostracod Biostratigraphic Unit II, Palaeocene (upper part) 



This Unit contains the Lower Rakhi Gaj Shales. Ostracods are very rare and 

 have only been found in the upper part which is very rich in pelagic Foraminifera. 

 The ostracods, although very rare, are easily distinguishable from the assemblages 

 below and above. Of the eight species found, all are restricted to the present Unit, 

 with the exception of Trachyleberis (Acanthocythereis) usitata sp. nov. which is also 

 present in the underlying Unit. 



Ostracod Biostratigraphic Unit III, Lower Eocene (lower part) 



This includes the Upper Rakhi Gaj Shales, Green and Nodular Shales and Rubbly 

 Limestones. Eames' local zones 3, 4, 5 and 6 he in this Unit. 



