Late Carboniferous marine invertebrate zones of eastern Australia

Abstract

Brachiopods of the Marginirugus barringtonensis and Levispustula levis Zones comprise the youngest of three major Carboniferous biostratigraphic units in eastern Australia. The remarkable change in the composition of marine invertebrates between the second and third of these units, a transition that only two brachiopod species are known to survive, has been attributed to the isolation of eastern Australia and to a drop in temperature. The Marginirugus barringtonensis and Levipustula levis Zones are redefined from reference sections in the Myall region, N.S.W.; the L. levis Zone now includes the Syringothyris bifida Zone of Campbell (1961). Faunal sequences show that these two zones are closely related and that there is no hiatus between them, as formerly proposed by McKellar (1965). Conodonts identified by Mr. D. Crane indicate a late Viséan to early Namurian age for the Marginirugus barringtonensis Zone, and an age of early Namurian for the base of the Levipustula levis Zone; brachiopod evidence indicates that the L. levis Zone extends into the Westphalian. The younger Auriculispina levis Zone from the Yarrol Basin may be coeval with the Trigonotreta campbelli Zone from N.S.W. Faunas from both the L. levis and A. levis Zones are present in Argentina and many species from the L. levis Zone have affinities with forms from the Baikal region, U.S.S.R. Correlations based on the zones have eliminated the need for a hiatus between the Branch Creek and Baywulla Formations in the Yarrol Basin. Taxa described from the Marginirugus barringtonensis and Levipustula levis Zones in the Myall region include Yagonia gibberensis Roberts gen. et sp. nov., Bulahdelia myallensis Roberts gen. et sp. nov., Alispirifer yagonensis Thompson sp. nov., A. alatus Thompson sp. nov., Licharewia bootiensis Thompson sp. nov., Spirifer pristinus (Maxwell), Spiriferi sp., Neospirifer campbelli Maxwell and N. senilis Maxwell.