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Brachiopods and Permian Correlations
Some of the largest Permian faunas are derived from localities that have no continuous stratigraphic sections; these should not be used as references for age determinations. The continuous section in the Salt Range, West Pakistan, extends from the Artinskian through the Guadalupian, and the dolomite unit at the base of the Mianwali Formation contains brachiopods that provide links to the Dzhulfian and Changhsingian. The ammonites in the dolomite are unidentifiable and hence cannot support a Triassic age determination in the face of evidence for a Permian age suggested by the brachiopods and conodonts. An analogous situation at Guryul Ravine, Kashmir, places the Permian-Triassic boundary within Middlemiss’s “black shales” rather than at the top of the Zewan Series.
The range of the ammonite Cyclolobus extends from the Kalabagh Member of the Wargal Limestone into the upper part of the Chhidru Formation, but not to the very top of that unit. The range of Cyclolobus thus begins at the same level as that of Xenodiscus, but does not extend as high (evidence from the Dzhulfia section).
Brachiopod genera from 14 Upper Permian localities are compared by two binary coefficients of similarity, the Otsuka and the Phi. Dendrograms and trellis diagrams provided by computer application of the two coefficients show three major groupings: an Asian group plus Sicily, an Arctic group, and a Texas group. Analysis of similarity within these groups tends to confirm many hitherto established correlations.
A Guadalupe age is suggested for the Chhidru Formation, with Dzhulfian and Changhsingian elements in the dolomite unit. Amarassian and Araksian stages proposed on the basis of ammonite phylogenies are rejected on the basis of the lithic and biostratigraphic succession in the Salt Range.
A hiatus occurs between the Chhidru Formation and the overlying dolomite unit, perhaps between the Zewan Series and the “black shales”, and between the Phosphoria and Dinwoody Formations in North America. Permian fossils occur above this paraconformity, suggesting that the stratigraphic break near the end of the Paleozoic is not coincident with the faunal extinction that marks the Permian-Triassic boundary.
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