Locating the BACE of the Cambrian: Bayan Gol in southwestern Mongolia and global correlation of the Ediacaran--Cambrian boundary.

Citation metadata

From: Earth-Science Reviews(Vol. 229)
Publisher: Elsevier Science Publishers
Document Type: Report
Length: 617 words

Document controls

Main content

Abstract :

Keywords Cambrian; Ediacaran; GSSP; ASSP; Protohertzina; Treptichnus; Chemostratigraphy; Chronostratigraphy; BACE Abstract The diversification of animals during the Cambrian Period is one of the most significant evolutionary events in Earth's history. However, the sequence of events leading to the origin of 'modern' ecosystems and the exact temporal relationship between Ediacaran and Cambrian faunas are uncertain, as identification of the Ediacaran--Cambrian boundary and global correlation through this interval remains problematic. Here we review the controversies surrounding global correlation of the base of the Cambrian and present new high-resolution biostratigraphic, lithostratigraphic and [delta].sup.13C chemostratigraphic data for terminal Ediacaran to basal Cambrian strata in the Zavkhan Basin of Mongolia. This predominantly carbonate sequence, through the Zuun-Arts and Bayangol formations in southwestern Mongolia, captures a distinct, negative [delta].sup.13C excursion close to the top of the Zuun-Arts Formation recognized as the BAsal Cambrian carbon isotope Excursion (BACE). In this location, the nadir of the BACE closely coincides with first occurrence of the characteristic early Cambrian protoconodont Protohertzina anabarica. Despite recent suggestions that there is an evolutionary continuum of biomineralizing animals across the Ediacaran--Cambrian transition, we suggest that this continuum is restricted to tubular forms, and that skeletal taxa such as Protohertzina depict 'true' Cambrian representatives that are restricted entirely to the Cambrian. Employing the first appearance of the trace fossil Treptichnus pedum to define the base of the Cambrian suffers significant drawbacks, particularly in carbonate settings where it is not commonly preserved. As T. pedum is the only proxy available to correlate the Cambrian Global boundary Stratotype Section and Point (GSSP) defined at Fortune Head, Newfoundland, we suggest that the GSSP be redefined elsewhere, in a new stratigraphic section that contains secondary markers that permit global correlation. We propose the nadir of the BACE as the favored candidate to define the base of the Cambrian. However, it is essential that the BACE be complemented with secondary markers. In many global sections the nadir of the BACE and the first occurrence of the genus Protohertzina are closely juxtaposed, as are the BACE and T. pedum. Hence these taxa provide essential biostratigraphic control on the BACE and increase potential for effective global correlation. We also recommend that an Auxiliary boundary Stratotype Section and Point (ASSP) be simultaneously established in order to incorporate additional markers that will aid global correlation of the Ediacaran--Cambrian boundary. The BAY4/5 section through the upper Zuun-Arts and Bayangol formations yields key shelly fossils and [delta].sup.13C values and is therefore an ideal candidate for consideration as the GSSP for the Ediacaran--Cambrian boundary. Author Affiliation: (a) State Key Laboratory of Continental Dynamics, Shaanxi Key Laboratory of Early Life and Environments, Department of Geology, Northwest University, Xi'an 710069, China (b) Department of Palaeobiology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden (c) Palaeoscience Research Centre, School of Environmental and Rural Science, University of New England, Armidale, New South Wales 2351, Australia (d) Institute of Paleontology, Mongolian Academy of Sciences, 15160, Ulaanbaatar, Mongolia (e) State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China (f) Key Lab of Submarine Geosciences and Prospecting Techniques, Ministry of Education, and College of Marine Geosciences, Ocean University of China, Qingdao 266100, PR China (g) School of Arts and Sciences, National University of Mongolia, Ulaanbaatar, 14200, Mongolia * Corresponding authors at: State Key Laboratory of Continental Dynamics, Shaanxi Key Laboratory of Early Life and Environments, Department of Geology, Northwest University, Xi'an 710069, China. Article History: Received 7 September 2021; Revised 22 January 2022; Accepted 25 March 2022 Byline: Timothy Topper [timothy.topper@nwu.edu.cn] (a,b,*), Marissa J. Betts [marissa.betts@une.edu.au] (a,c,*), Dorj Dorjnamjaa (d), Guoxiang Li (e), Luoyang Li (b,f), Gundsambuu Altanshagai (d,g), Batkhuyag Enkhbaatar (d,g), Christian B. Skovsted [christian.skovsted@nrm.se] (a,b,*)

Source Citation

Source Citation   

Gale Document Number: GALE|A703357066