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Fossil Friday: The Vindhyan Controversy and Debunking Alleged Ediacaran and Cambrian Fossils

February 16, 2024, 6:44 AM
Photo: Alleged Vindhyan worm burrows, from Seilacher et al. 1998 fig. 2, fair use.

Last year, I reported for Fossil Friday about alleged Ediacaran fossils of the genus Dickinsonia from the Vindhyan strata in India (Nature 2021), which embarrassingly turned out to be nothing but rotten bee hives (Bechly 2023b).

“The Vindhyan Supergroup, located in central peninsular India, is one of the largest and thickest Precambrian sedimentary successions of the world, outcropping over an area of over 104,000 km2” (Turner et al., 2014). The dating of the Vindhyan Supergroup and the identification of its fossils has been a matter of immense controversy for decades, because it was initially geologically dated to an early Proterozoic age, but allegedly contains carbonaceous and phosphatized fossils (annulated tubes, embryo-like globules with polygonal surface pattern, filamentous and coccoidal microbial fabrics) as well as skeletal fossils that have been interpreted as related to Ediacaran or even Cambrian phyla. During this controversy, which includes numerous technical publications, many claims about the original fossil descriptions have been shown to be erroneous and most of the alleged fossils were later shown to be diagenetic artifacts. In particular, the alleged skeletal fossils simply did not exist, which is quite remarkable to say the least. However, new fossils were described and posed new problems. Here is the revealing story of this controversy.

Alleged Worm Burrows

This Fossil Friday features alleged worm burrows described from supposedly 1.1-billion-year old Precambrian rocks of the Vindhyan Supergroup by Seilacher et. (1998). This determination was quickly disputed and even the biogenic origin of these traces was challenged (Morris et al. 1998, Brasier 1999, Rai & Gautam 1999, Ahluwalia et al. 2000, Budd & Jensen 2000). One of the original describers, Friedrich Pflüger from Yale University, commented that he is 85 percent confident about the identification and that there would be no opposition if the fossils were younger (Pflüger quoted in Kerr 1998a). In a response to the critique Seilacher et al. (1999) concluded that “the most critical issue now is not the nature, but rather the age, of the Chorhat burrows.” Indeed, around the same time Azmi (1998) described alleged fossils of small shelly fauna and brachiopods as well as alleged phosphatized metazoan embryos (similar to those of the famous Ediacaran Doushantou Formation in China), which arguably would establish a Lower Cambrian age even for the Lower Vindhyan strata. Nevertheless, Seilacher and his colleagues stood by their discovery and strongly doubted that a single paper could refute the numerous other studies that found a Precambrian age for the Vindhyan strata (Seilacher quoted in Kerr 1998b).

Indeed, a few months later, Azmi’s results were not just questioned, but the alleged fossils found to be not fossil organisms at all (Kerr 1998c, 1999, Brasier 1999), which was later confirmed by Bengtson et al. (2009) and Kumar (2016). At a workshop “none of the specialists at hand could be convinced that Azmi’s fossil were actually formed by living creatures” (Kerr 1999, also see Kher 2017). But the saga continued. In the next year a new study by Banerjee & Frank (1999) dated the Vindhyan layers to be only 620 million years old and boldly claimed to be “absolutely confident we can reject the very old age of 1.1 billion years” (Frank quoted in Kerr 1999). Again a year later Kathal et al. (2000) described a putative specimen of the Ediacaran organism Spriggina from the Vindhyan Supergroup, which would arguably confirm the younger date. However, they could not exclude an alternative identification as segmented macro-alga. The very next year it was shown to be just another pseudofossil (Kumar 2001, 2016). As we see, the alleged Dickinsonia fossils that turned out to be rotten bee hives (Kwafo et al. 2023; see Bechly 2023b), are in pretty good company. But also the dating circus continued, because Rasmussen et al. (2002) redated the sediments of the Chorat sandstone, where the assumed worm burrows were found, with U-Pb zircon dating to a much older age of 1.6 billion years and speculated about the implications for the early evolution of animals. Likewise, Ray et al. (2002) redated the layers, where the alleged Ediacaran Spriggina fossil was found, to a similarly ancient age of 1.631 billion years, using U-Pb zircon dating and Sr isotope data. More recent radiometric studies arrived at similar ages of 1.6 billion years for the Lower Vindhyan Supergroup (e.g., Mishra et al. 2018, Lan et al. 2021). More and more, radiometric datings produced results that were highly incompatible with the paleontological results from biostratigraphy.

Sounds like Strong Evidence?

The carbonaceous Chuaria–Tawuia assemblage described by Srivastava (2002) are one of the few exceptions to the rule, and were accepted as genuine fossils of multicellular algae by Kumar (2001, 2016). Srivastava (2002) suggested an Neoproterozoic upper age limit of 950-700 million years for the uppermost Vindhyan Supergroup, which would clearly predate the Ediacaran Avalon Explosion. Later, Srivastava (2004, 2009, 2012a, 2012b) described different carbonaceous microfossils, and discussed their bearing on macroevolution from prokaryotes to eukaryotes and unicellularity to multicellularity. Based on the fossil evidence she suggested a Ediacaran upper age limit for the Vindhyan Supergroup. This was also based on the work by De (2003, 2006), who described a diverse Ediacaran fossil assemblage with iconic genera such as Cyclomedusa, Ediacaria, Tribrachidium, and Spriggina from Upper Vindhyan layers. He attributed these to soft-bodied metazoan animals such as coelenterates and possible stem annelids and arthropods. He drew elaborate conclusions on the phyletic diversity and dating of this fossil locality. Sounds like strong evidence, but it all collapsed when it was later shown (Kumar 2016) that these fossils were neither Ediacaran nor even fossil organisms, which also applies to some but not all of the fossils described by Srivastava.

Less controversial was the discovery of microbial mat structures called Arumberia and Beltanelliformis (Kumar & Pandey 2008), which had a wide distribution during the Late Precambrian-Cambrian transition, and thus suggested a 600-550 million year old Ediacaran age for the Maihar Sandstone of the Upper Vindhyan Supergroup, for which sedimentation must have ended near the Ediacaran period about 630 million years ago (Turner et al. 2014, Kumar 2016). Arguably, this was also supported by the absence of typical Cambrian fossils, as well as radiometric U-Pb dating of zircon crystals (Lan et al. 2020). However the latter radiometric dates were ambiguous and partly also supported an older 900 million year age. Concerning these zircon datings geologist Joseph Meert (University Florida), who is an expert on the Vindhyan strata, kindly wrote me that “these are ages of detrital zircons which do not give the age of the rocks in which they are found. Detrital zircons are derived from older rocks that were eroded and the resistant zircon crystals were then transported to the depocenter and incorporated into the younger rocks. A single detrital zircon age is considered almost meaningless because contamination is possible when processing large samples.  We look for populations of zircons when conducting detrital zircon studies. The youngest population of zircons found in the Upper Vindhyan rocks is about 1000 million years (Turner et al., 2014). Thus, the only radiometric constraint we have on the Upper Vindhyan at present is that it must be younger than 1000 million years” (Meert pers. comm. 2023). This problem was already indicated by Lan et al. (2020), who remarked that “uncertainties in obtaining the youngest age of detrital zircons mean care must be taken when using detrital zircon age for tectonic regime classification.” Reworking of much older detrital zircons was documented by Lan et al. (2021), who found very disparate age groupings of 3.5-2.9 vs 2.7-2.4 vs 1.9-1.5 Ga vs 1.3-1.0 billion years.

Azmi et al. (2008) reviewed the “discordant geo- and biochronological ages of the Vindhyan Supergroup.” They found that “Against exceptionally long duration of ~1200 million years (~1800-600 Ma) from late Paleoproterozoic to late Neoproterozoic age based on geochronology, diverse paleontological evidences (metazoan traces, small shelly fossils, fossil embryos, calcareous skeletal algae, sponge spicules, acanthomorphic acritarchs, scolecodont-like structures and metaphytes) suggest a much shorter duration of Vendian-Early Cambrian (~650-520 Ma) for deposition of the VSG.” The authors suggested that the younger dating agrees better with the regional geology. However, this of course would presuppose the identifications of the fossils to be correct, which was later refuted (Bengtson et al. 2009, Kumar 2016).

A Fringe Argument

Basu (2009) also tried to resolve the conflict between the biostratigraphic dating of many fossils to an Ediacaran age of 635-543 Ma and the radiometric U-Pb dating of the rocks to an Proterozoic age of 1630-1000 Ma. He made the very unusual and controversial suggestion that in a way both are right and the Ediacaran organisms extend far deeper into the past as generally recognized and their absence from other Meso- and Paleoproterozoic localities is just an artifact of preservation. Virtually no other expert supports this fringe argument.

More carbonaceous fossils were described by Singh et al. (2009) and interpreted as various eukaryotic multicellular algae similar to the Miahoe biota in China. However, this work suffered like so many others from severe shortcomings. Kumar (2016) commented that “the problem with this report is that the fossil material is very poorly preserved and the photographs are of very bad quality, most of them being out of focus. This makes the report less meaningful and individual identifications useless.” Peer review did not prevent the publication of such junk science in the Journal of Evolutionary Biology Research.

Ominous Fossils

Concerning the ominous filamentous and globular fossils described by Azmi (1998) and Azmi et al. (2007) as Ediacaran and Cambrian fossils, a new study by Bengtson et al. (2009) attempted to resolve the controversy about their interpretation and dating. Based on their Pb-isotope analysis the authors suggested that these rocks are even older (about 1.65 billion years), but that the few genuine fossils have no relationship to later organisms. The annulated and septate tubes were recognized as filamentous algae similar to the modern Spirogyra, while the alleged embryo-like structures were identified as pseudofossils produced by gas bubbles. The authors clearly state that “none of the fossils, however, can be ascribed to uniquely Cambrian or Ediacaran taxa”, which makes the whole biostratigraphic argument for a younger age (e.g., by Azmi et al. 2008) a moot point.

Bengtson et al. (2017) described three-dimensionally preserved filamentous red algae from the 1.6 billion year old Lower Vindhyan Supergroup, with even cellular and subcellular structures preserved in the phosphatized fossils. These could represent the oldest known Rhodophyta and one of the earliest fossil records of multicellular eukaryotes, “suggesting that eukaryotes may have a longer history than commonly assumed.” Kher (2017) commented that this work would at least partly rehabilitate the work of Indian geologist Rafat Azmi, which was considered as highly suspicious (especial in the wake of the notorious Gupta scandal, see Bechly 2023a) after some of his finds were shown to be pseudofossils and an investigation by the Geological Society of India was unable to find the fossil he claimed to have found.

The seminal work of Turner et al. (2014) showed that “the age of the Lower Vindhyan is reliably constrained to the Paleo-Mesoproterozoic interval whereas the age of the Upper Vindhyan sedimentary sequence is the subject of considerable controversy.” The authors “argue that deposition of the Upper Vindhyan sequence closed near the end of the Mesoproterozoic (~1000 Ma) whereas deposition in the Marwar basin was confined to the Ediacaran– Cambrian interval (~ 570–521 Ma).” For the Lower Vindhyan sequence the authors found that “sedimentation in the Lower Vindhyan basin began < 1850 Ma and ended around ~ 1550–1600 Ma”. For the Upper Vindhyan sequence they “put the onset of Upper Vindhyan sedimentation in the Mesoproterozoic (>1100 Ma) and the cessation of sedimentation as young as Cambrian”. For the Marwar Basin they found a Neoproterozoic-Cambrian (Ediacaran) age of 635-521 million years, which is also confirmed by more recent U-Pb zircon datings (Lan et al. 2020). A similar constraint around 900-1100 million years for the Upper Vindhyan was previously suggested by the paleomagnetic and radiometric datings of Gregory et al. (2006), Malone et al. (2008), and Gopalan et al. (2013).

In his critical overview of the megafossils from the Vindhyan Basin, Kumar (2016) wrote:

The age of the Vindhyan Supergroup has been debated since the beginning of the last century but it acquired an international dimension by the so called discoveries announced by Azmi (1998), Seilacher et al. (1998) and Kathal et al. (2000) as their inferences challenged the established concept of evolution of early life. All the three discoveries were subsequently challenged on the basis of critical scrutiny of their identification as fossils and also evaluated on the basis of recently acquired robust radiometric age and palaeomagnetic data. …. The Ediacaran fossils described by De (2003, 2006) have not been accepted as fossils, as such, the age of the Bhander Limestone and the Sirbu Shale from where these fossils have been reported could not be assigned the Ediacaran age.

Kumar (2016) concluded that:

The Vindhyan Supergroup constitutes one of the largest Proterozoic basins of the world which attains a huge thickness of more than 5000m in central India. The rocks of the Vindhyan Supergroup are unmetamorphosed and more or less undeformed and the age of the Supergroup can be bracketed between ca. 1800 Ma to ca. 650 (?) Ma. These rocks have been consistently searched for evidences of early life for more than a hundered years. Because of this, a large number of reports about the presence of megascopic life have been published from these rocks. These reports need scrutiny as many reports have described abiotic structures also as fossils. … All noncarbonaceous fossils described as burrows, drag marks and trace fossils reported from both the lower and upper Vindhyans are rejected as fossils and considered as pseudofossils or nonfossils as these can be produced by many inorganic processes also, and the animals which could have produced these marks had not evolved during the deposition of the Vindhyan sediments. The reported Ediacaran fossils from the Upper Vindhyans are considered to be the weathering products of structures produced by inorganic processes and/or related to microbial mat structures. Thus, the presence of typical Ediacaran animal and plant fossils are not accepted in the Vindhyan rocks. … On the basis of mega-fossil records, the upper age of the Vindhyan Supergroup can be suggested as Pre-Ediacaran.

Smoke and Mirrors

We can conclude that after more than two decades of paleontological research and thousands of published pages, the alleged fossil evidence from the Vindhyan strata about Ediacaran biota and Cambrian phyla, and their bearing on the related Avalon and Cambrian Explosions, largely evaporated. The fancy speculations about the evolution of multicellular life and early animals turned out to be just smoke and mirrors. Most of the fossils that were described by distinguished scientists, including my own teacher Adolf Seilacher, were later revealed to be inorganic pseudofossils or microbial artifacts. All that is left are a few genuine Precambrian algal fossils of uncertain age prior to the Ediacaran, which is neither surprising nor particularly interesting, even from a mainstream evolutionist point of view. And what about the controversy about the age of the Vindhyan Supergroup? It remains a hotly debated issue even after 25 years of research with ever more sophisticated methods. Kwafo et al. (2023) concluded that “The age … remains contentious. We, along with many others, have discussed the Upper Vindhyan age controversy at length and look forward to resolving this long-lived debate.” Paleontology can be an extremely frustrating discipline, but at least it provides rock solid proofs for the truth of Darwinian evolution beyond any reasonable doubt, no?

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