FROM WEST PAKISTAN 89 



Ostracod Biostratigraphic Unit IV, Lower Eocene {upper part) 



Like the Zao River section, the base of the Unit is taken arbitrarily at the base of 

 the 4 ft. limestone, which is 320 ft. below the base of the Platy Limestone. The 

 Platy Limestone is only 40 ft. thick in this section. The 12,450 ft. thick sediments 

 below the 4 ft. limestone are barren except for a few horizons which contain poorly 

 preserved pelagic Foraminifera. These probably represent the following lithological 

 units in ascending order : Upper Rakhi Gaj Shales, Green and Nodular Shales, 

 Rubbly Limestones and lower part of the Shales with Alabaster. 



Only the upper part of the Unit has yielded ostracods and the fauna is similar to 

 that of the Zao River and Rakhi Nala sections. About 70% of its species are in 

 common with the Zao River section. Over 40% of the species of the Unit in the 

 Rakhi Nala have been recorded from the Shpalai Khwara section. Stigmatocythere 

 obliqua sp. nov. is very abundant, particularly in sample 24686, which is absolutely 

 crowded with this species. Some other common species are : Neocyprideis ? sp. B, 

 Pontocyprella sp.B, Cytherella sp.B, Cytherella sp. and Genus C sp.2. 



(b) Statistical Correlation of ranges of Ostracod Species Common to the 

 Rakhi Nala and Zao River Sections. 



The tops and bases of ostracod species common to the Rakhi Nala and Zao River 

 sections have been plotted on a graph (Fig. 6). These fall into two rectilinear 

 patterns, one in biostratigraphic Unit IV and the other in biostratigraphic Unit V. 



The tops and bases of ostracod species in biostratigraphic Unit IV (i.e in the 

 Shales with Alabaster) lie almost in a straight line on the graph ; this, however, is 

 because ostracods have only been found at two horizons in the Zao River section. 

 The Equations of Correlation for the array of biostratigraphic Unit V (i.e. above the 

 Platy Limestone) can be computed from the data given in Appendix 2. This 

 method has been discussed in detail by A. B. Shaw in his book 'Time in Stratigraphy', 

 published in 1964. The points marked ' + ' in Appendix 2 have been omitted because 

 they fall outside the main array. Eighty-one points have been considered. The 

 Equations of Correlation between the Rakhi Nala and Zao River sections can be 

 calculated as follows : 



RN = RN + £ ( RN ~ RN ) (ZR— ZR) (2R—ZR), where RN = Rakhi Nala and 



S(ZR— ZR)' 



6638+ ^5228 (ZR-2253) 

 ^ 48,697965 v ™ 



ZR = Zao River. 



= 0-4451 ZR + 5035 • 2 (1) 



and 



ZR = ZR + S(RN~RN) (ZR-ZR) ^ 



E(RN— RN) 2 



