Chemo-biostratigraphy of the Dzabkhan Craton: Refining the Ediacaran-Cambrian Transition in Southwestern Mongolia

The Ediacaran-Cambrian (Ed-C) transition is recognised as a globally significant juncture, with sedimentary records found across numerous cratons worldwide. Here we report a sedimentary sequence from the Dzabkhan micro-continent in SW Mongolia, spanning the late Ediacaran-Cambrian Stage 3 interval, revealing several major positive and negative C isotope excursions and interpret the first excursion as the onset of the basal Cambrian carbon isotope excursion (BACE). Our study comprehensively discusses synchronous stratigraphies from Mongolia, Kazakhstan, South China, Tarim, Siberia, Morocco, and Newfoundland. Most records consistently exhibit a distinctive pattern that includes the first appearance datum (FAD) of Small Skeletal Fossils, negative carbon isotope excursions, and strontium isotope uptrends. While the Ed-C boundary is defined by the FAD of ichnospecies Treptichnus pedum , the appearance of this ichnospecies is limited to siliciclastic environments and is diachronous between regions. Meanwhile, other bio- or chemostratigraphic signatures have also been considered as auxiliary markers to define the base of the Cambrian. Therefore, the small skeletal fossils Protohertzina anabarica , P. unguliformis and Anabarites trisulcatus , strontium and carbon isotope excursions are here utilized as potential supplementary diagnostic tools. Furthermore, our palaeoenvironmental reconstructions elucidate the variations in carbon and strontium isotope trends spanning this period, which may reveal carbon cycling and tectonic processes during sedimentation on the Dzabkhan Craton. These environmental changes may further support redefining the boundary. • New Chemo-biostratigraphic record for the Ediacaran–Cambrian Orolgain Gol section. • New comprehensive pattern for identifying Ediacaran-Cambrian boundary. • Carbon cycle and strontium isotope validate the Ed-C boundary defined biologically.