Abstract

The orbitoidiform foraminifers from the Paleocene of the Pakistan Salt Range, traditionally designated by “Orbitosiphon” or “Actinosiphon”, include two different genera, both with a concave-convex test shape. The first of these is characterized by a typically orbitoidal growth with lateral chamberlet layers on both sides of the equatorial layer, and corresponds to Lepidocyclina (Polylepidina) punjabensis Davies, the type species of the genus Orbitosiphon Rao. The second genus, named here Setia nov. gen., is characterized by orbitoidal chamberlet cycles and differentiated dorsal and ventral sides, with lateral chamberlets on the dorsal side and a canal system resembling that of miogypsinids on the ventral side. It includes two species, S. tibetica (Douvillé 1916) and a stratigraphically lower, structurally more simple new species, S. primitiva sp. nov. Both genera are found in the top of the Hangu Formation, the Lockhart Limestones, and at the base of Patala Formation from the Salt Range “Laki Beds”, which comprise the middle and upper parts of the Paleocene. The test of the new genus Setia shows a new morphostructural type, resembling that of miogypsinids, but with orbitoidal growth. Both Setia and Orbitosiphon became extinct before the arrival of orthophragminids (Discocyclina and Orbitoclypeus) to the basin (together with Nummulites, Assilina and Alveolina), and therefore are never found together with the latter. The reports of orthophragminids from the Lockhart Limestones and the lower part of Patala Shales actually correspond to misidentified O. punjabensis or S. tibetica. On the other hand, the American Paleocene genus Actinosiphon cannot be related to either Orbitosiphon or Setia. Although it is similar to the former, it differs in several characters, such as the shape and arrangement of equatorial chamberlets and the stolon system.

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