Shelly fauna from the Cambrian (Miaolingian, Guzhangian) Shannon Formation and the SPICE event in the Amadeus Basin, Northern Territory

Abstract

A low-diversity assemblage of linguliformean brachiopods, hyoliths, molluscs, bradoriid arthropods and echinoderms (ten taxa in total) is documented from the upper Shannon Formation (Cambrian, Miaolingian, Guzhangian; Mindyallan) in the Ross River Syncline and Todd River Anticline area, NE Amadeus Basin, central Australia. Taxa described include: the linguliformean brachiopods <I>Treptotreta jucunda</I> Henderson & MacKinnon, 1981, <I>Opisthotreta</I> sp., <I>Stittia?</I> sp., an undetermined acrotretid and an undetermined linguloid; the molluscs <I>Kobayashiella? heritagensis</I> Webers, Pojeta & Yochelson, 1992 (a paragastropod), and <I>Apoptopegma joyceae</I> sp. nov. (a rostroconch); the bradoriid <I>Mongolitubulus</I> sp.; Hyolithida gen. et sp. indet.; and isolated echinoderm plates. All fauna (including previously documented trilobites) from the upper Shannon Formation disappear at the beginning of a ∼5‰ positive shift in δ13C, identified as the Steptoean Positive Isotopic Carbon Excursion (SPICE). Despite previous links between SPICE and a global extinction, as well as the disappearance of all faunal elements in the uppermost Shannon Formation, certain taxa reported herein range through the event elsewhere in the world. The occurrence of <I>Treptotreta jucunda</I> and <I>Kobayashiella? </I> in younger (Furongian) deposits indicates these species survived the SPICE extinction event. This study advocates for more systematic and comprehensive sampling through stratigraphic intervals where the SPICE event occurs, especially for range data of complete faunas (rather than individual taxonomic groups), to facilitate a more complete picture of diversity trends through this important phase.