Reassessment of agnostids and trilobites from the lower Wagonga Group (Furongian), the oldest fossils in the eastern Lachlan Orogen, N.S.W., and their significance

Abstract

Reassessment of the agnostid and trilobite assemblages originally figured by Bischoff and Prendergast (1987) from the lowest Wagonga Group (herein informally named the “lower formation”), allows for a more precise interpretation of the unit’s age which was previously assigned a very approximate range of “Middle” to “Late” Cambrian. The presence of Micragnostus (=Innitagnostus) cf. medius (Shergold, 1980), Onchonotellus cf. kuruktagensis (Zhang, 1981), Wuhuia aff. silex Shergold, 1980 and an indeterminate species of Pseudorhaptagnostus Lermontova, 1951, correlate with early Iverian assemblages in the Georgina Basin, Queensland, and early Jiangshanian taxa in South China (between the Wentsuia iota-Rhaptagnostus apsis to Peichiashania secunda-Prochuangia glabella trilobite assemblage zones of Australia). The paraconodonts Westergaardodina bohlini Müller, 1959 and Westergaardodina kleva Müller, 1959 further support a Jiangshanian age.

The consistent faunal composition across all limestone olistoliths and beds suggests a penecontemporaneous origin, contradicting previous interpretations that the limestones resulted from prolonged erosion of an older carbonate platform. Instead, we propose a dynamic depositional environment on the flanks of a volcanic seamount, with limestone blocks transported via debris flows during volcanic events, analogous to modern deep-sea sedimentation processes. Faunal similarities with the Australian craton suggest proximity of this seamount to the eastern Gondwana margin during the Cambrian.