Fossils, rocks and Cambrian clocks: A multi-proxy approach to chronologically subdividing the lower Cambrian of the Arrowie Basin, South Australia
thesisposted on 2022-03-28, 17:22 authored by Marissa J. Betts
Global correlation of early Cambrian strata has been notoriously difficult, mainly due to diachronism and endemism of key fauna. Until now, the stratigraphic distribution of early Cambrian taxa from Australia has been poorly resolved, preventing effective correlation and isolating the South Australian successions from a global chronostratigraphic synthesis. Papers1 and 2 describe a new biostratigraphic framework for the early Cambrian (Terreneuvian-Series 2, Stage 4) of South Australia utilising phosphatic shelly fauna. Three new shelly fossil zones are defined based on temporal range data compiled from 21 measured stratigraphic sections across the Arrowie Basin (and a section from the Stansbury Basin). Stratigraphic ranges of key shelly fauna are predictable and repeatable, enabling robust correlation with strata in coeval neighbouring basins. Additionally, while cosmopolitan genera facilitaterudimentary global correlation, species-level correlation is often possible. δ¹³C chemostratigraphy is an independent temporal proxy that, when combined with biostratigraphy, facilitates robust global correlation. δ¹³C curves from nine stratigraphic sections are closely comparable to the global curve for the Cambrian. Paper 3 integrates early Cambrian biostratigraphy, chemostratigraphy and radiometric dates from the early Cambrian of South Australia for the first time, and puts the successions into a global context. Papers 4 and 5 document new bradoriid arthropod assemblages and investigate functional morphologyof their “bivalved” carapace. A total of nine new bradoriid species are described (including two new genera; papers 2 and 5), contributing considerably to known bradoriid diversity in East Gondwana. The early Cambrian explosion of life was the most significant phase of animal evolution in Earth’s history. The timing and tempo of important events occurring in East Gondwana at this time can now be bracketed within a tightly resolved chronostratigraphy. This study elevates the early Cambrian of South Australia from a “blank canvas” to one of the most chronostratigraphically well-resolved regions in the world.