Middle Triassic radiolarian fauna from southwest Yunnan, China

Abstract

A highly diverse radiolarian fauna of Anisian age has been recovered from an 11 m continuous succession of siliceous rocks with tuffs and mudstones in the Changning-Menglian belt of southwestern Yunnan, China. Seventy-three radiolarian species and subspecies, among which, six new species, one new subspecies and 36 unidentified species, are included in the investigation. The 6 new species and 1 new subspecies are Triassocampe goricani, Triassocampe dumitricai, Triassocampe coronata inflata, Triassocampe relica, Archaeospongoprunum muyinense, Neopaurinella deweveri and Neopaurinella kozuri. Based on morphological comparison and stratigraphical range, some possible evolutionary relations are suggested. Four radiolarian zones, namely, Triassocampe deweveri Zone (late Anisian), Triassocampe coronata coronata Zone (middle Anisian), Triassocampe coronata inflata Zone (middle Anisian), and Triassocampe dumitricai Zone (early Anisian) are established. The Early Triassic radiolarian fauna in this area has a very low diversity and mainly consists of survivors of the Permian radiolarians. The recovery of the Triassic radiolarian fauna takes place in early Anisian. In this period, the multicyrtid nassellarians are moderately diverse and characterized by having a slender shell with weak constriction among segments; the spumellarian species are characterized by having needle-like main spines. In the middle and late Anisian, the shells of the multicyrtid nassellarians became strong with developed constrictions between segments, and both the spumellarians with needle-like spines and the spumellarians with three-bladed spines are diverse.