A Review of Biotic Signatures Within the Precambrian Vindhyan Supergroup: Implications on Evolution of Microbial and Metazoan Life on Earth

Journal of Mineralogical and Petrological Sciences, Volume 115, page 162–174, 2020

REVIEW

A review of biotic signatures within the Precambrian Vindhyan Supergroup: Implications on evolution of microbial and metazoan life on Earth

Adrita CHOUDHURI*, Santanu BANERJEE** and Subir SARKAR***

*Department of Earth Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur Campus, Nadia 741 246, West Bengal, India **Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India ***Department of Geological Sciences, Jadavpur University, Kolkata 700032, India

This study presents a review of the wide spectrum of biotic signatures within the Precambrian Vindhyan Super- group deposited during the ‘boring billion’ and assesses their biological affinity and age implications. The sedimentation took place in wide–ranging palaeo–environments from fluvial to offshore through shallow marine. While the lower part of the ~ 4500 m thick Vindhyan succession is older than 1650 Ma, the age at its top part is poorly constrained, ranging from 1000 to 650 Ma. Microbial records are abundant in the form of stromatolites in limestone and microbially induced sedimentary structures (MISS) on both siliciclastics and carbonates across the Vindhyan succession. The wide morphological variation of these two features corresponds to depositional processes, early cementation, as well as lithological variations. The stromatolite record, as well as calcified and chertified microbial fossils, attest to the Mesoproterozoic to Neoproterozoic age of the sediments. Although the carbonaceous body fossils do not have age implications, they indicate the proliferation of algal life during the Meso– to Neoproterozoic time. The Ediacaran–like fossils mostly relate either to ‘discoidal microbial colony’ or detached pieces of microbial mat. Wide–ranging putative metazoan fossil reports remain the focal point of attention for many years. Although most of these reports are found to be microbially originated, some of these features have the potential to highlight the evolution of multicellular life during the Precambrian.

Keywords: Stromatolite, Microbial mat, Discoidal microbial colony, Proterozoic, Vindhyan, Carbonaceous fossils

INTRODUCTION El Albani et al., 2019). Microbes dominated the Precam- brian atmosphere and microbial mat cover developed A large part of the Precambrian biosphere was dominated profusely on the seafloor. The weakly metamorphosed entirely by the microbiota and devoid of any major bio- Precambrian Vindhyan Supergroup of Indian peninsula logical evolution, hence it is considered to be ‘boring often yields a wide spectrum of biotic records for under- billion’ (1.8–0.8 Ga) (Brasier and Lindsay, 1998; Mu- standing the evolution of life on earth (Sarkar et al., 1996; kherjee et al., 2018). The sedimentary records of the early Seilacher et al., 1998; Sarkar et al., 2004; Bengtson et al., biotic signatures are poorly preserved, and therefore sci- 2009; Banerjee et al., 2014; Bengtson et al., 2017). The entists search for indirect evidence of early life. The mi- Vindhyan succession has yielded wide–ranging microfos- crobial record of Earth dates back to 3700 Ma (Nutman et sils, organo–sedimentary structures, carbonaceous fossils, al., 2016). However, the macroscopic fossil records of the Ediacaran fossils, and trace and body fossils of metazo- Precambrian remain controversial (Han and Runnegar, ans within the Vindhyan succession (Sarkar and Bane- 1992; Knoll et al., 2006; Seilacher, 2007; Bengtson et rjee, 2019). The proliferation of moneran carpet on both al., 2009; El Albani et al., 2010; Bengtson et al., 2017; siliciclastic and carbonate sediments depositing environment led to the formation of a diverse kind of biotic sig- doi:10.2465/jmps.190827a natures (Sarkar and Banerjee, 2019), which needs a crit- S. Banerjee, [email protected] Corresponding author ical assessment. However, the role of environmental Biotic signatures in Precambrian Vindhyan basin 163 processes on the morphology of microbial features is yet an intracratonic rift setting during the Lower Vindhyan, to be established. While some of these fossils provide which evolved into a sag basin during the deposition of meaningful age for Vindhyan sediments, many of them the Upper Vindhyan sediments (Bose et al., 1997, 2001, also produce contradictory results. Therefore, the biostrat- 2015). The sedimentation took place in varying environ- igraphic relevance for fossil records needs a thorough ments including continental, shallow marine and offshore evaluation based on recent radiometric investigations. environments (Fig. 2; Bose et al., 2001). The reported fossils of the Vindhyan Supergroup are yet The age of the Vindhyan Supergroup has been a to be critically assessed for understanding the evolution of matter of debate over the last hundred years. Stromato- microbial and metazoan life in Earth’s history. lites within the Lower and Upper Vindhyans yield the age We have presented a brief review of varieties of bi- range from 1400–600 Ma (Prasad, 1980, 1984). Radio- otic signatures of the Precambrian Vindhyan Supergroup. metric dating and palaeobiological evidence until the last The objectives of the paper are: a) to present the wide century provided Meso– to Neoproterozoic age for the spectrum of biotic signatures with the Vindhyan Super- Vindhyan sediments (Rasmussen et al., 2002). The age group, b) assess the environmental processes on micro- of the Lower Vindhyan/Semri Group is well established bial features, and c) to indicate the complexity in estab- (~ 1.8–~ 1.5 Ga) by U–Pb, Pb–Pb geochronology by dif- lishing metazoan affinity of the potential features. We ferent groups of researchers (see Sarkar and Banerjee, have provided detailed elaborations of all varieties of mi- 2019). On the contrary, the age of the Upper Vindhyan crobial mat related structures and described all varieties remains controversial. On the basis of palaeomagnetic of biogenic features within the Vindhyan Supergroup. and detrital zircon data, many investigators suggested

GEOLOGICAL BACKGROUND

The Vindhyan Basin (~ 104000 sq. km area and ~ 4.5 km thick) is the largest Proterozoic basin in India, the rocks of which are exposed in central and western India (Fig. 1). The gently metamorphosed and less deformed Vindhyan Supergroup overlying the Archean basement has two major subdivisions, the Lower Vindhyan/Semri Group and the Upper Vindhyan Group, separated by an unconformity (Fig. 2; Chanda and Bhattacharyya, 1982; Bose et al., 1997, 2001; Mondal et al., 2019). The sedimentation took Figure 1. Geological map showing outcrops of the Vindhyan Su- place within a westward opening epicontinental basin in pergroup in the Son valley and inset showing map of India.

Figure 2. Stratigraphy, age, and palaeogeography of the Vindhyan Supergroup. 164 A. Choudhuri, S. Banerjee and S. Sarkar that the closure of the basin before ~ 1.0 Ga (Fig. 2; Sar- are round–headed, inclined and branched. Microbial lam- kar and Banerjee, 2019 and references cited therein). inite of very low height with wavy and crinkly laminae overlies small stromatolites. All these three varieties of BIOTIC RECORDS WITHIN THE VINDHYAN stromatolites occur in repeated cycles within the Kajrahat SUPERGROUP Limestone, with large stromatolite at the base, followed by the small variety and are capped by microbial laminite. Palaeobiological remains of the Vindhyan Supergroup The transition between different varieties of stromatolites may be categorized as stromatolites, macroscopic carbo- is always gradational within the cycles. The thickness of naceous remains, microfossils, small shelly fossils, pseu- cycles varies from 40 to ~ 110 cm. Cycles comprising all do–Ediacaran fossils, and microbially induced sedimen- three varieties of stromatolites indicate periodic changes tary structures (MISS). Microbial mats probably colo- in water depth within the depositional site (Banerjee et al., nized on the sedimentary surfaces during the Precambrian 2007). While large stromatolite indicates the deposition in both in carbonates and in siliciclastics (e.g., Schieber, the deep shelf environment, the small variety and micro- 1999; Parizot et al., 2005; Sarkar et al., 2006; Schieber bial laminite point to intertidal and supratidal environ- et al., 2007; Banerjee et al., 2010, 2014; Sarkar et al., ments respectively (Banerjee et al., 2007). 2014a). Stromatolite bears the interaction between benth- The Bhander Limestone Member exhibits different ic microbial communities and detrital/chemical sediments varieties of stromatolites. Both laterally attached and de- with records of three–dimensional convex upward geom- tached forms of stromatolites are abundantly present etry. In contrast to carbonate settings, the recognition of (Figs. 4b–4e). The latter variety branches upward, with the microbiota within terrigenous sedimentary rocks has prominent inter–columnar areas (Fig. 4f). Stromatolites often some limitations. Therefore, their identification de- may be micro–digitate, domal, arch–shaped, inclined and pends on indirect signatures/proxy structures resulted branched (Figs. 4b–4j). One form may change into other from trapping, binding, baffling, and biostabilisation of morphotypes vertically (Figs. 4d, 4k, and 4l). Digitate the non–cohesive clastic sediments. These proxy features stromatolites are of laterally attached micro–scale variety, are referred to as microbial mat induced sedimentary surrounded by comparatively larger laminae (Fig. 4b). structures (Noffke, 2010). The range of biotic signatures Large arch–shaped stromatolites are laterally attached in the Vindhyan Supergroup also covers carbonaceous and are occasionally draped by wave ripples (Fig. 4h). body fossils including Chuaria and Tawuia, calcified Inclined, branched and small–headed varieties overlie and chertified microbial fossils, as well as traces of mac- the large arch–shaped stromatolites (Figs. 4e and 4f). In- roscopic fossils. A brief description of all kinds of biotic clined columnar varieties show branching of the columns signatures is given below. with wide inter–columnar space. Small–headed stromatolites generally overlie the inclined columnar variety (Fig. Stromatolites 4j). They appear circular on the bedding plane. Occasion- ally desiccation cracks occur on the bedding surface of Several workers reported stromatolites within different small stromatolites. stratigraphic intervals of the Vindhyan Supergroup and The different morphology of the stromatolites within inferred Lower to Upper Riphean age (1600–650 Ma) the Bhander Limestone indicates the variation in water (Fig. 3). The upper part of the ~ 1.7 Ga–old Kajrahat depth within the depositional environment (Sarkar and Limestone preserves significant stromatolite varieties Bose, 1992; Sarkar et al., 1996). Large stromatolites in- (Fig. 4a). The size of the stromatolite varies from large dicate a relatively deeper water environment compared to (average column height of 20 cm and diameter of 6 cm) the small variety. The inclined stromatolites represent to small (column height and diameter of 3.5 cm and 1.8 shallow water conditions within fair/storm weather wave cm) (Banerjee et al., 2007). While columns of large stro- base (Sarkar et al., 1996). The presence of occasional matolites are mostly conical, those in small stromatolites desiccation cracks on the bedding surface of the small–

Figure 3. Salient reports of stromatolites within the Vindhyan Supergroup. Biotic signatures in Precambrian Vindhyan basin 165

Figure 4. Field photographs showing: (a) Stromatolites in Kajrahat Limestone. (b) Digitate form of stromatolites from Bhander Lime- stone. Note the individual stromatolites are laterally attached. (c) Laterally attached and domal stromatolites of Bhander Limestone. (d) Laterally detached columns of stromatolites of the Bhander Lime- stone. Note the intercolumnar area is filled up by micritic sediments. Also note that laterally detached stromatolites change vertically to small stromatolite variety. (e) In- clined stromatolites columns of the Bhander Limestone. (f) In- clined and branched variety of stromatolites columns from Bhander Limestone. (g) Large arch–shaped stromatolites from Bhander Lime- stone. (h) Wave ripples on top of large arch– shaped stromatolites from Bhander Limestone. (i) Asym- metric growth of large arch–shaped stromatolites from Bhander Lime- stone. (j) Small–scale stromatolites with desiccation cracks of Bhander Limestone. (k) Inclined stromatolite columns vertically changes upward to small stromatolites which again becomes inclined variety upward. (l) Large arch–shaped stromatolite changes upward into inclined and branched stromatolite variety. Ham- mer length, 38 cm; Scale length, 15 cm; Pen length, 14.5 cm; Knife length, 8.5 cm. headed stromatolites supports a very shallow water envi- plane structures representing a proxy of the microbiota. ronment, with occasional exposure. The rare presence of The microbial mat usually forms three–dimensional stro- wave ripples on the bedding surface of the large arch– matolites in carbonate depositional settings, while two–di- shaped stromatolites indicates occasional wave influence. mension MISS occurs exclusively in siliciclastic settings. Branching of inclined columnar stromatolites supports Although wide varieties of MISS are well–known from wave/current actions (Sarkar et al., 1996). The preferred modern carbonate environments (Bose and Chafetz, inclination in stromatolites indicates either action of 2011), wrinkle structures were only reported from the strong current within the depositional environment or ancient rocks (Xiaoying et al., 2008; Luo et al., 2013). the phototactic movement of the microbial colony (Sarkar Recently Sarkar et al. (2016, 2018) expanded the list of et al., 1996). two–dimensional carbonate MISS from the lower parts of the Rohtas Limestone and Bhander Limestone of the Microbially induced sedimentary structures (MISS) in Vindhyan Supergroup (Figs. 5 and 6). These workers con- carbonates sidered carbonate MISS comparable to those found in siliciclastic rocks (Figs. 7–9). Although the MISS has been studied in detail from the The three–dimensional stromatolites reflect the early siliciclastic rocks, carbonates of the Vindhyan Supergroup cementation and repetitive process of baffling, trapping also display a similar group of two–dimensional bedding and mineralization in limestone. However, the absence 166 A. Choudhuri, S. Banerjee and S. Sarkar

Figure 5. Field photographs showing: (a) Wrinkle structures and synaeresis cracks on the bedding plane of the Bhander Limestone. (b) Pustules (arrowed) on the bedding plane of the Rohtas Limestone. (c) Domes (arrowed) and their casts preserved on the bedding plane of the Rohtas Limestone. (d) Astropolithons with central craters (arrowed) preserved in the Rohtas Limestone, (e) Loads at the sole of the bed (right side) and their casts on top of the underlying bed (left side) preserved in the Bhander Limestone. (f) Palimpsest ripples preserved in the Bhander Limestone, with thin calc–arenite layer mimicking the underlying ripple morphology. (g) Swarms of setulfs (arrowed) on the bedding plane of the Bhander Limestone. (h) Irritatingly sharp–crested ripples in the Bhander Limestone. (g) Cracks preserved on the bedding plane of the Rohtas Limestone. Knife length, 8.5 cm; Hammer length, 38 cm; Pen length, 14.5 cm. of early cementation results in two–dimensional geome- Microbially induced sedimentary structures (MISS) try in MISS. Most MISS in carbonates involves micro– within siliciclastics scale deformation indicating delayed cementation of the carbonate sediments. The activity of sulfate reducing bac- The Vindhyan Supergroup is globally well known for ex- teria (SRB) facilitates the CaCO3 precipitation within a cellent preservation of MISS from siliciclastics within thin microbial mat (Sarkar et al., 2016). The delayed ce- Kheinjua and Bhander Formations (Sarkar et al., 2004, mentation of the sediments corresponds to the acidic 2005; Banerjee and Jeevankumar, 2005; Sarkar et al., composition of EPS secreted by the microbes (Sarkar et 2006; Banerjee et al., 2006; Sarkar and Banerjee, 2007; al., 2018 and references cited therein). The near–equato- Schieber et al., 2007; Banerjee et al., 2010, 2014; Sarkar rial palaeolatitudinal position of India (Scotese, 2001; Pe- et al., 2014b, 2016). The sandstone beds at top of HSTs sonen et al., 2003; Evans and Mitchell, 2011; Zhang et (Highstand Systems Tracts) bear excellent MISS varieties al., 2012) during the Mesoproterozoic time might have on the bed–surfaces in different stratigraphic intervals. restricted the growth of SRB, and the rate of sulfur re- However, the prolific mat growth in shales corresponds duction, resulting the delayed cementation and preserva- to maximum flooding zones (Figs. 7–9). The morpholog- tion of MISS in carbonates (Sarkar et al., 2016, 2018; ical variations of these features (Figs. 7 and 8) correspond Choudhuri, 2019). to growth, destruction and diagenesis of microbial mats. Carbonaceous shale (total organic carbon content Biotic signatures in Precambrian Vindhyan basin 167

Figure 6. MISS recorded within carbonates of the Vindhyan Supergroup. exceeding 1.5%) associated with the stratigraphically Carbonaceous macrofossils and microfossils condensed zones exhibits wavy, crinkly, carbonaceous laminae, pyritic laminae, pseudo cross–strata, rolled–up, Figure 10 provides a summary of various kinds of carbo- and folded carbonaceous laminae within Rampur Shale, naceous fossils and calcified/certified microfossils within Sirbu Shale, and in Kajrahat Formation, suggesting mi- the Vindhyan Supergroup. While these reported fossils crobial mat growth in mid– to outer–shelf depositional provide a broad Mesoproterozoic age for the Semri/Low- conditions (Figs. 7d and 7e; Banerjee et al., 2006; Sur er Vindhyan Group, the same indicates a Neoproterozoic et al., 2006). Banerjee and Jeevankumar (2005) and Sar- age for the Upper Vindhyan (Venkatachala et al., 1996; kar et al. (2004, 2005, 2006) recorded several microbial Sarkar and Banerjee, 2019). However, the age implica- structures within Vindhyan shales. Recent ultramicro- tion of these fossils remains controversial (cf. Brasier et scopic studies within Rampur Shale have revealed differ- al., 2002). ent morphotypes of the microbial population (Mondal et al., 2019). 168 A. Choudhuri, S. Banerjee and S. Sarkar

Figure 7. Field photographs showing: (a) Setulfs (arrowed) on the bedding plane of the Upper Bhander Sandstone. (b) Disc–shaped microbial colonies (arrowed) and (c) Sand bulges (arrowed) preserved within the Sirbu Shale. (d) Photomicrograph under plane polarized light showing wavy carbonaceous laminae of black shale in the Kajrahat Formation. (e) Photomicrograph under reﬂected light framboidal pyrites along the crinkly laminae in the Rampur Shale.

Ediacaran–like fossils lated cracks (Kumar, 2001). Azmi (1998) reported controversial small shelly fossils of Cambrian age affinity Several reports indicate the presence of probable Ediacar- from the phosphoritic stromatolitic dolomite in the basal an–like fossils within the Vindhyan Basin including Ed- part of the Vindhyan Supergroup from Chitrakut area. iacaria flindersi, Cyclomedusa davidi, Medusinites, Me- Bengtson et al. (2009, 2017) reinterpreted the fossils as dusinites asteroides, Dickensonia, and Beltanelliformis filamentous and coccoid cyanobacteria and filamentous brunsae (for details see Sarkar and Banerjee, 2019). De eukaryotic algae and confirmed their Mesoproterozoic (2003) reported possible Ediacaran fossils within the age. Bengtson et al. (2017) considered these multicellular Bhander Formation to consider the Proterozoic age for fossil organisms as the earliest known crown group of the Vindhyan. However, researchers questioned the Edia- eukaryotes. Recently Sallstedt et al. (2018) provided the caran affinity of the features because of their resemblance evidence of oxygenic phototrophy developed by the with MISS (Banerjee et al., 2010, 2014; Sarkar and Bane- filamentous microorganisms from the same stratigraphic rjee, 2019). interval.

Macroscopic/metazoan fossils Trace fossils

A few authors reported traces of advanced organisms Discovery of traces of motile organisms/worm burrows within the Vindhyan succession (see Venkatachala et living under thin microbial mat cover from the Chorhat al., 1996 for details). Later workers considered these re- Sandstone (Sarkar et al., 1996; Seilacher et al., 1998) ports as considered them as dubiofossils (Chakrabarti, raised many debates within the scientiﬁc community. 2001; Sarkar and Banerjee, 2019). The metazoan fossil The reports of Chorhat worm burrows were criticized reports of Misra and Awasthi (1962), Mathur (1983), and by several workers (Conway Morris, 2000; Fedonkin, Singh and Sinha (2001) possibly represents shrinkage–re- 2003; Peterson and Butterﬁeld, 2005; Jensen et al., Biotic signatures in Precambrian Vindhyan basin 169

Figure 8. Field photographs showing MISS within the Chorhat Sandstone, Vindhyan Supergroup: (a) Spindle–shaped cracks preserved within the ripple troughs. (b) Wrinkle structures preserved on the bedding plane. (c) Sand bulges in multiple numbers on the bedding plane. (d) Patchy ripples. (e) Bulbous loads at the bottom of the sandstone (right) and their casts preserved on top of the underlying ripple (left) laminated sandstone. (f) Elliptical sand clasts (arrowed). (g) Elongated silt curls (arrowed). (h) Thin layer of microbial mat mimics the underlying ripple laminated sandstone generating palimpsest ripple. Knife length, 8.5 cm. 170 A. Choudhuri, S. Banerjee and S. Sarkar

Figure 9. Brief descriptions and interpretations of MISS within siliciclastics of the Vindhyan Supergroup.

2005; Knoll et al., 2006). Seilacher (2007), however, DISCUSSION AND CONCLUSIONS withdrew the original interpretation of Chorhat triploblastic worm burrows mainly because of the radiometric The Precambrian Vindhyan Supergroup hosts diverse dates which constrain the age of deposition older than types of biotic signatures including microbial mat in- 1.6 Ga. duced sedimentary structures (MISS), micro and macro- Biotic signatures in Precambrian Vindhyan basin 171

Figure 10. Salient reports of carbonaceous macrofossils and microfossils in the Vindhyan Supergroup (see Sarkar and Banerjee, 2019 for original citations of fossils reports). fossils, carbonaceous fossils, Ediacaran–like fossils, and the Vindhyan Supergroup develop within shallow marine traces of megascopic fossils (see Sarkar and Banerjee, littoral–supratidal environments whereas carbonate MISS 2019 and references cited therein for details). Stromato- represents restricted to quiet lagoonal environments. On lites or microbialites are three–dimensional organo–sedi- the other hand, variations in stromatolite morphology mentary structures formed as a result of interaction be- both from the Kajrahat Limestone and Bhander Lime- tween the benthic microbial mat and the sediments stone correlates with the change in the water depth of through trapping, binding, baffling of the sediments, the depositional basin. Therefore, both stromatolites and and biostabilisation. Stromatolites acquire three–dimen- MISS are useful tools for high–resolution palaeo–envi- sional structures through repetitive mineralization and ronmental interpretations in Proterozoic shallow marine fossilization (Noffke, 2000; Noffke et al., 2003; Noffke, successions (Banerjee et al., 2014). 2010; Noffke and Awramik, 2013). Apart from the stro- Many of the MISS structures, e.g., Manchuriophy- matolites, Vindhyan siliciclastic rocks preserve an array cus, have previously been thought of as metazoan burrows of bedding plane microbial mat related structures with (Kulkarni and Borkar, 1996 and many others). The re–ex- two–dimensional geometry, known as MISS (see Fig. amination of these features, however, confirmed the mi- 9). The prolific growth of microbial mat on sediment sur- crobial mat origin of the sinuous cracks on the sandstone faces stabilized the sediments, resulting in a reduced rate surfaces (Sarkar et al., 2006, 2008; Banerjee et al., 2010, of erosion compared to that in Phanerozoic time. The re- 2014). Many of the wrinkle structures, petee–ridges, and duced rate of sedimentation results in the preservation of gas domes with central depressions were mistakenly in- regressive system tracts more in numbers than that of terpreted as organism remnants, horizontal burrows, and transgressive system tracts (TST) during the Proterozoic jellyfish impressions, respectively by different workers time (Sarkar et al., 2005; Catuneanu, 2006; Sarkar et al., (see Banerjee et al., 2010 and Sarkar and Banerjee, 2014a). Therefore, MISS in Proterozoic rock records has 2019 for a detailed discussion). Upon comparison with an immense influence on the preservation of the system their modern equivalents, many of these features were ex- tracts (Sarkar et al., 2005; Banerjee and Jeevankumar, plained as MISS (Banerjee et al., 2010, 2014). Apart from 2005; Eriksson et al., 2010; Banerjee et al., 2014). De- organo–sedimentary structures, the Vindhyan Supergroup pending on their preferential relationship to the palaeo– yielded several carbonaceous macro and microfossils, and environments, MISS were classified into three broad cat- Ediacaran–like fossils (Fig. 10; Sarkar and Banerjee, 2019 egories – (a) occurring in shallow marine littoral–supra- and references cited therein). However, many of the Edi- tidal settings, (b) shallow subtidal to deep marine set- acaran–like fossils were later re–interpreted as discoidal tings, and (c) those not having any preferential occur- microbial mat growth/colony (Banerjee et al., 2010). rence to an environmental setting (Eriksson et al., Seilacher et al. (1998) documented traces of triplo- 2010). Although siliciclastic formations yielded MISS blastic worm burrows under mat cover on the sandy bed in the past, recent studies indicated the formation of sim- surfaces of the Chorhat Sandstone. This sensational re- ilar features within ancient carbonate sediments in case port inspired many scientists for the search of an ad- of late cementation (Fig. 6; Sarkar et al., 2016, 2018; vanced mode of life from ancient rocks before the Cam- Choudhuri, 2019). Most of the siliciclastic MISS within brian explosion. Subsequently, the age of the Chorhat 172 A. Choudhuri, S. Banerjee and S. Sarkar

Sandstone was constrained to ca 1.6 Ga (Rasmussen et Central India. Journal of Geological Society of India, 52, 381– al., 2002). This prompted Seilacher (2007) to discard his 389. ffi Banerjee, S. and Jeevankumar, S. (2005) Microbially originated idea of triploblastic worm burrows. However, it is di - wrinkle structures on sandstone and their stratigraphic con- cult to explain the origin of these structures having context: Palaeoproterozoic Koldaha Shale, central India. Sedi- stant width, pervasive shapes (both branching and mean- mentary Geology, 176, 211–224. dering pattern) with a diverse orientation by physical/ Banerjee, S., Bhattacharya, S.K. and Sarkar, S. (2006) Carbon and chemical processes. Moreover, recent reports of multi– oxygen isotope compositions of the carbonate facies in the fi Vindhyan Supergroup, central India. Journal of Earth System chambered organisms and bundles of tubular laments Science, 115, 113–134. within the Semri Group (cf. Bengtson et al., 2009, Banerjee, S., Bhattacharya, S.K. and Sarkar, S. (2007) Carbon and 2017) have again created an option for the scientific com- oxygen isotopic variations in peritidal stromatolite cycles, Pa- munity to rethink about the metazoan divergence before leoproterozoic Kajrahat Limestone, Vindhyan basin of central India. Journal of Asian Earth Science, 29, 823–831. the Cambrian explosion. Recent findings of multicellular Banerjee, S., Sarkar, S., Eriksson, P.G. and Samanta, P. (2010) Mi- organisms, cf. Franceville biota of 2.1 Ga (El Albani et crobially related structures in siliciclastic sediment resembling al., 2010, 2014), Stirling biota of ~ 1.8 Ga (Bengtson et Ediacaran fossils: examples from India, ancient and modern. al., 2017), Montana biota of 1.5–1.3 Ga (Zhu et al., In Microbial Mats: Modern and Ancient Microorganisms in fi 2016), and motile organisms from 2.1 Ga old rocks (El Strati ed System (Seckbach, J. and Oren A. Eds.). Springer, Berlin, 111–129. Albani et al., 2019), inspire a re–assessment of the Banerjee, S., Sarkar, S. and Eriksson, P.G. (2014) Palaeoenviron- Vindhyan metazoan records for the evolution of ad- mental and biostratigraphic implications of microbial mat–re- vanced life forms during Precambrian. Therefore, a de- lated structures: examples from modern Gulf of Cambay and tailed investigation with most advanced techniques is Precambrian Vindhyan basin. Journal of Paleogeography, 3, – necessary to correctly assess the affinity of some of the 127 144. Bengtson, S., Belivanova, V., Rasmussen, B. and Whitehouse, M. problematic features within the Vindhyan succession. We (2009) The controversial “Cambrian” fossils of the Vindhyan conclude the following points based on our investigation are real but more than a billion years older. Proceedings of the of biogenic structures within the Vindhyan Supergroup. National Academy of Sciences of USA, 106, 7729–7734. a) The radiometric dating brackets the Vindhyan Super- Bengtson, S., Sallstedt, T., Belivanova, V. and Whitehouse, M. – group within 1.7 to 1.0 Ga while stromatolites, car- (2017) Three dimensional preservation of cellular and subcel- lular structures suggests 1.6 billion–year–old crown–group red bonaceous fossils, and microfossils provide Meso- algae, PLOS Biology, 35, 1–38. proterozoic to Neoproterozoic ages for the same. Bickford, M.E., Mishra, M., Muelle, P.A., Kamenov, G.D., et al. b) Microbial mat proliferates on the Vindhyan Sea, (2017) U–Pb age and Hf isotope compositions of magmatic leaving a wide range of proxy features in both sili- zircons from a rhyolite flow in the Porcellanite Formation in ciclastics and carbonates. the Vindhyan Supergroup, Son Valley (India): implications for its tectonic significance. Journal of Geology, 125, 367–379. c) Many of the fossil reports of metazoan life have Bose, P.K., Banerjee, S. and Sarkar, S. (1997) Slope–controlled been re–interpreted as microbial mat originated sedi- seismic deformation and tectonic framework of deposition mentary structures. of Koldaha Shale, India. Tectonophysics, 269, 151–169. d) In view of recent reports of the existence of meta- Bose, P.K., Sarkar, S., Chakraborty, S. and Banerjee, S. (2001) Overview of the Meso to Neoproterozoic evolution of the zoan life in rocks of Palaeoproterozoic age from oth- Vindhyan basin, central India. Sedimentary Geology, 141, er parts of the world, the Vindhyan fossils need a 395–419. thorough re–examination in the future for their exact Bose, P.K., Sarkar, S., Das, N.G., Banerjee, S., et al. (2015) Pro- affinity without having any bias. terozoic Vindhyan basin: configuration and evolution. Geo- logical Society of London Memoirs, 43, 85–102. Bose, S. and Chafetz, H.S. (2011) Morphology and distribution of ACKNOWLEDGMENTS MISS: a comparison between modern siliciclastic and carbonate settings. In Microbial Mats in Siliciclastic Depositional AC acknowledges DST INSPIRE Faculty program (DST/ Systems Through Time (Noffke, N. and Chafetz, H. Eds.). INSPIRE/04/2017/002038). SS acknowledges RUSA 2.0 SEPM Special Publication, 101, 3–14. grant of Jadavpur University. Authors acknowledge their Brasier, M.D. and Lindsay, J.F. (1998) A billion years of environmental stability and the emergence of eukaryotes: new data respective institutes and universities for the infrastructur- from northern Australia. Geology, 26, 555–558. al facilities. Brasier, M.D., Green, O.R., Jephcoat, A.P., Kleppe, A.K., et al. (2002) Questioning the evidence of earth’s oldest fossils. Na- REFERENCES ture, 416, 76–81. Catuneanu, O. (2006) Principles of Sequence stratigraphy. Elsevier, Azmi, R.J. 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