Enigmatic Ediacaran megascopic bedding plane structures on the Sonia Sandstone, Jodhpur Group, Marwar Supergroup, India: seaweed or problematica?

Abstract

The present study discusses the origin and affinity of enigmatic Ediacaran bedding plane structures reported earlier from the Sonia Sandstone of the Marwar Supergroup (Ediacaran to Lower Cambrian). These forms are conspicuously large, non‐carbonaceous and three‐dimensionally preserved. Morphologically, these structures are not comparable with any known plant/animal fossil, trace fossil, microbially induced sedimentary structures (MISS) found in the Ediacaran assemblages or any other extant forms and are invariably associated with MISS. Past researches on these fossils did not resolve their affinity, form and function. The present forms have certain features akin to seaweed organization such as thallus, loop pattern within the thallus, variously positioned nodes/swellings, tapering at the end of thallus, branching pattern and rarely occurring holdfast‐like features. Systematic description, incorporating detailed morphological features, population size, their relationship with associated sediments and stratigraphic distribution, is based on the study of 54 specimens. Subtidal to intertidal models of depositional sedimentary environment, palaeoecology, biogenicity, affinity, taphonomic changes, association of these forms with MISS and other parameters are also discussed. A succession of plausible interpretations is offered; seaweed is the most likely interpretation. The Marwar Supergroup, thus, unravels some of the hitherto enigmatic forms of the Ediacaran Period (635–541 Ma). Copyright © 2016 John Wiley & Sons, Ltd.

Ediacaran pithy macroalgaLanceaphytonn. gen. from South China

“…Macroscopic algae have been reported in the Paleoproterozoic (e.g., Hofmann and Chen, 1981; Han and Runnegar, 1992; Yan, 1995; Zhu and Chen, 1995; Yan and Liu, 1997; Zhu et al, 2000; Sun et al, 2004), Mesoproterozoic (e.g., Walter et al, 1976; Du et al, 1986; Kumar, 1995, 2001; Dutta et al, 2006; Sun et al, 2006; Sharma and Shukla, 2009a, b; Babu and Singh, 2011; Zhu et al, 2016), and early–middle Neoproterozoic (e.g., Hofmann and Aitken, 1979; Du, 1982; Du and Tian, 1982, 1985a, b; Duan, 1982; Duan et al, 1985; Hofmann, 1985, 1992; Walter et al, 1990; Ye et al, 2015). However, abundant and diverse macroalgae are found from the late Neoproterozoic Ediacaran strata (e.g., Gnilovskaya, 1971, 1990; Zhu and Chen, 1984; Chen and Xiao, 1991, 1992; Ding et al, 1992, 1996; Steiner et al, 1992; Chen et al, 1994; Steiner, 1994; Yuan et al, 1995, 1999, 2011, 2016; Xiao et al, 2002, 2013; Grazhdankin et al, 2007; Wang et al, 2007, 2014, 2015a, 2016a, b, 2017; Tang et al, 2008a, 2009; Singh et al, 2009; Marusin et al, 2011; Pandey and Sharma, 2017; Ye et al, 2019). Macroalgae emerged in the Paleoproterozoic and prosperously developed in the Ediacaran, which is important for understanding the biotic and environmental evolution at the dawn of animal life.…”

“…1700 Ma) in North China (see Hofmann and Chen, 1981; Yan, 1995; Zhu and Chen, 1995; Yan and Liu, 1997; Wang et al, 2020a). With a holdfast composed of a tapering or globular rhizome and filamentous or disk-like rhizoid, abundant and diverse eukaryotic macroalgae were found in the Ediacaran from Australia (Xiao et al, 2013), India (Singh et al, 2009; Sharma et al, 2016; Pandey and Sharma, 2017), Namibia (Leonov et al, 2009), Russia (Gnilovshaya, 1971, 1990; Gnilovshaya et al, 1988; Grazhdankin et al, 2007; Marusin et al, 2011), and South China (Zhu and Chen, 1984; Chen and Xiao, 1991, 1992; Ding et al, 1992, 1996; Steiner et al, 1992; Chen et al, 1994, 2000; Steiner, 1994; Yuan et al, 1995, 1999, 2011, 2016; Xiao et al, 1998, 2002; Wang et al, 2007, 2011, 2014, 2015a, 2016a, 2017; Tang et al, 2008a, 2009; Ye et al, 2019). However, the emergence of pithy macroalgae has been debated over whether a tubular or cylindrical structure within macroalgal stipes in the middle–late Ediacaran are natural biotic structures or diagenetic abiotic structures (e.g., Ding et al, 1996; Xiao et al, 2002; Wang et al, 2007, 2015b, 2020a; Ye et al, 2019).…”

The late‐stage “ferruginization” of the Ediacara Member (Rawnsley Quartzite, South Australia): Insights from uranium isotopes

“…In contrast, recent studies (Retallack, ) have alternatively proposed a terrestrial (paleosol) depositional environment for the fossiliferous Ediacara Member. Despite major issues raised and strong debate surrounding the paleosol model (e.g., Tarhan, Droser, & Gehling, ; Xiao & Knauth, ; Xiao et al., ), it has continued to play an active role in the dialogue of the geological and biological research communities (e.g., Algeo, Marenco, & Saltzman, ; Beraldi‐Campesi, ; Beraldi‐Campesi & Retallack, ; Kump, ; Pandey & Sharma, ; Retallack, , , ,b, , ,b). One of the fundamental tenets on which the paleosol model for the Ediacara Member has rested is the argument that the iron oxide coatings present on many fossiliferous horizons represent “synsedimentary ferruginization” associated with soil horizon development, and thus, a terrestrial depositional environment for the Ediacara Member (Retallack, ).…”