ORIGINAL ARTICLE Scanning electron microscopic imaging and nano-secondary ion microprobe analyses of bacteria-like nanoball structures in oncoids from the Ediacaran Boonall Dolomite of Kimberley, northwestern Australia: testing their biogenicity Zhong-Wu Lan • Zhong-Qiang Chen Accepted: 27 November 2011 / Published online: 7 February 2012 Ó Springer-Verlag 2012 Abstract Nanoball structures have been frequently detected in modern and ancient sedimentary rocks world- wide. They are widely believed to be biological in origin due to their similar morphology to modern bacteria. Abundant, well-preserved nanoball structures from the oncoids of the Boonall Dolomite of Ediacaran age in the Kimberley region, northwestern Australia are being described. Scanning electron microscopic imaging indicates that these minute objects are identical with nanobacteria previously documented elsewhere. However, nano-sec- ondary ion microprobe (NanoSIMS) imaging analysis could not reveal the presence of organic elements such as C, N and S in the nanoball-like structures. Therefore, a biological origin for the Ediacaran nanoball structures seems unlikely. NanoSIMS imaging analysis may well be needed for other occurrences of nanoball structures in order to determine if all of these similar objects are really of biological origin. Keywords Nanoball structures Á SEM Á NanoSIMS Á Oncoids Á Ediacaran age Á Northwestern Australia Introduction Nanoball structures were first documented by Folk (1993) about two decades ago. Such nanoball structures were found in hot springs travertine. There, hot spring nanoball structures were found in association with carbonate grains. As such, Folk (1993) assumed that these tiny objects could have precipitated the carbonate minerals, and thus could be nanobacteria. Following Folk’s assumption, McKay et al. (1996) suggested the existence of nanobacteria in extra- terrestrial rock samples. Since then, nanobacteria have been widely accepted as a term representing nano-scale bacteria-like objects. Nanobacteria have been thought to play a crucial role in precipitating minerals and oxidizing metals on Earth (Folk 1999, 2005; Folk and Chafetz 2000; Folk and Lynch 2001; Folk and Rasbury 2002; Folk and Taylor 2002). The high-resolution scanning electronic microscope (SEM) enables better understanding of the morphology of nanoball structures preserved in ancient rocks. Such nanoball structures are usually ovoid-like, ellipsoidal or spheroidal in outline and measure from 50 to 200 nano- meter (nm) in diameter. The nanoball structures have been widely documented from silicate, carbonate, sulfide and minerals of Early Proterozoic to Holocene age (Folk and Lynch 1997; Folk 1999, 2005; Folk and Chafetz 2000; Folk and Rasbury 2002) and from meteorites (Mckay et al. 1996). These tiny objects have even been detected in human blood (Akerman et al. 1993) and experimentally cultured (Folk and Taylor 2002; Sommer et al. 2004). Z.-W. Lan (&) State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China e-mail: lzw1981@126.com Z.-W. Lan Key Lab of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China Z.-W. Lan Á Z.-Q. Chen School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia Z.-Q. Chen State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (Wuhan), Wuhan 430074, China 123 Carbonates Evaporites (2012) 27:33–41 DOI 10.1007/s13146-011-0081-2