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Proterozoic ministromatolites with radial‐fibrous fabric
Abstract
Small digitate stromatolites with diameters in the range of 0·2–20 mm (ministromatolites) are common in Early and Middle Proterozoic carbonate sequences, and extend stratigraphically from the Archaean to the Holocene. An occurrence of columnar and stratiform types exhibiting a primary or early diagenetic radial-fibrous fabric and microscopically crinkled (microcrenate) lamination is described from the ˜ 1·9 Gyr old Belcher Supergroup (McLeary Formation) in southeastern Hudson Bay, Canada. The structures, which can be considered to be a variety of tufa, are unusually well preserved because of early diagenetic silicification. Columnar types are referable to Pseudogymnosolen (Asperia), and are morphologically similar to other occurrences of these taxa in coeval dolostones in northwestern and eastern Canada, where the fabric is normally preserved by a secondary mosaic of dolomite. The textural evidence of angulate cross-sections and rectilinear divergent patterns indicates that the radial-fibrous fabric represents primary or very early diagenetic precipitation, and that pseudogymnosolenids with mosaic dolomite originally also had radial-fibrous structure. The precipitation may have been within, or on, microbial mats.
... Besides, the cooccurrence of ACF and the stromatolites in the Huaiyincun Formation (Figs. 6A and 6B) is not unique and a rather common phenomenon. Similar features can be found in many other ACFbearing strata from Archean to Phanerozoic (e.g., Hofmann and Jackson, 1987;Pruss et al., 2008;Allwood et al., 2009;Kiyokawa et al., 2006;Friesenbichler et al., 2018), which implies a close relationship between microbial activity and the growth of ACF. Meanwhile, the extremely low seawater sulfate concentration during the Huaiyincun deposition (discussed in Ouyang et al., 2020) would have inhibited bacterial sulfate reduction, preventing the scavenging of dissolved Fe 2+ . ...
... Most of them are restricted to carbonate formed in peritidal environments (Bergmann et al., 2013), including the Jixian, Billyakh, and Dismal Lake groups in China, Siberia, and Canada, respectively (Xiao et al., 1997;Bartley et al., 2000;Seong-Joo and Golubic, 2000;Kah et al., 2006;Tang et al., 2017). Occurrences of ACF have also been reported in Archean and Paleoproterozoic successions (Fig. 13A) (e.g., Allwood et al., 2009; Grotzinger, 1989;Grotzinger and James, 2000;Grotzinger and Reed, 1983;Hofmann et al., 2004;Hofmann and Jackson, 1987;Kah and Knoll, 1996;Kusky and Hudleston, 1999;Sami and James, 1996;Grotzinger, 2004, 1996;Winefield, 2000), with the oldest record traced back to the 3.35 Ga Strelley Pool Formation in Western Australia (Grotzinger, 1989;Allwood et al., 2009). It is also noteworthy that there is an absence of credible records of ACF from the initiation of the GOE until the end of the LJE, followed by the return of ACF in post-LJE strata (Fig. 13A). ...
... It is interesting to note that the occurrence of the ACF within the Huaiyincun Formation postdates the decline of δ 13 C carb at the termination of the Paleoproterozoic LJE (from > + 5‰ to ∼0‰) (Fig. 2) (She et al., 2016;Ouyang et al., 2020). In addition, post-LJE ACF have also been reported from the coeval Belcher Group and Bear Creek Group in northern Canada, Libby Creek Group in western USA (Hofmann and Jackson, 1987;Bekker and Eriksson, 2003;Bergmann et al., 2013), and late Paleoproterozoic successions in central India and northern Australia (Winefield and Creek, 2000;Sharma and Shukla, 2019). These likely indicate the onset of organic matter oxidation because the latter would not only produce a negative δ 13 C carb anomaly, but also consume O 2 in seawater, therefore creating a suitable environment for the formation of ACF. ...
The initial accumulation of atmospheric oxygen is marked by the unprecedented positive δ13Ccarb excursions of the Lomagundi-Jatuli Event (LJE) and records an interval of abnormal O2 production through elevated rates of organic carbon burial. Emerging evidence suggests that the post-LJE atmosphere-ocean system might have suffered a significant deoxygenation. These dynamic perturbations in the oceanic redox state and biogeochemical cycles would have led to fundamental changes in carbonate precipitation dynamics. Here, we report the discovery of centimeter-sized crystal fans in the post-LJE Huaiyincun Formation, Hutuo Supergroup in the North China Craton. The hexagonal cross-sections and square terminations suggest that these fan-like dolomitic structures were originally aragonite crystal fans (ACF). Variations of stromatolite morphology and frequent occurrences of storm-related deposits in the Huaiyincun Formation point to repeated cycles of sea level changes. The bedding-parallel distribution of the ACF and the homogeneous δ13C values of the ACF-bearing dolostones are consistent with a primary depositional origin for the ACF. An updated compilation of published records of ACF throughout geological history highlights a clear absence of ACF from the initiation of the Paleoproterozoic Great Oxidation Event until the end of the LJE, and a global reappearance of ACF in the post-LJE late Paleoproterozoic. We propose that the reappearance of ACF is in agreement with the expansion of the oceanic dissolved inorganic carbon reservoir. At the same time, consumption of dissolved oxygen during the oxidation of organic matter might have been stimulated by ferruginous deep seawater, facilitating the formation of Huiayincun ACF.
... However, genesis of MDS has long been disputed due to the abundance of radial-fibrous texture and a lack of convincing microfossils (Grotzinger and Reed, 1983;Hofmann and Jackson, 1987;Knoll et al., 1993;Sergeev et al., 1995;Grotzinger and Knoll, 1999;Riding, 2008;Riding and Virgone, 2020). Radial-fibrous textures are usually interpreted as abiotic acicular aragonite precursors that indicate calcium carbonate saturation of surface seawater (Grotzinger and Knoll, 1999;Riding and Virgone, 2020). ...
... aragonite crystal fans) that characterize the Neoarchean to Paleoproterozoic (>1.6 Ga) carbonate successions worldwide (Grotzinger and Knoll, 1999). As abiotic processes can contribute to form these circularly concentric and radial patterns, an abiotic carbonate precipitation scenario is plausible for the accretion of MDSs (Grotzinger and Reed, 1983;Hofmann and Jackson, 1987;Knoll et al., 1993;Sergeev et al., 1995;Grotzinger and Knoll, 1999;Riding, 2008), although heterotrophic bacterial metabolism may have facilitated carbonate precipitation and nucleation during MDS formation (Knoll and Semikhatov, 1998). However, the ultrastructures of such radial-fibrous textures in carbonate precipitates have been rarely uncovered, although their microstructures are often observed under optical microscopes. ...
... Both macroscopic and microscopic features of the Wumishan stromatolites are identical to that of typical microdigitate stromatolites, which have been described from the Neoarchean to Paleoproterozoic (>1.6 Ga) worldwide (Grotzinger and Reed, 1983;Hofmann and Jackson, 1987;Knoll et al., 1993;Sergeev et al., 1995;Grotzinger and Knoll, 1999;Tang et al., 2013b). In North China, the morphologically identical tiny stromatolites were first reported by Liang et al (1984) from the Wumishan Formation of the Jixian section, Tianjin City, North China. ...
Stromatolites have been widely reported from the Archean and Paleoproterozoic successions worldwide, and they could represent one of oldest life forms on Earth. Of these, a group of small stromatolites occur as microdigitate low-relief columns, and are also conspicuous in the field. However, biogenicity of these microdigitate stromatolites (MDSs) has long been disputed due to to the abundance of radial-fibrous texture and a lack of convincing microfossils. New examples of MDS are documented from the Mesoproterozoic Wumishan Formation of the Jixian area, North China. Vertically oriented fibrous fabrics are conspicuous and penetrate laminae as well as microscopic spheroids, which point to an abiotic genesis for this specific fabric. Stromatolite laminae contain abundant spheroids, typically 15–30 μm in diameter, with single or double outlines and they occur as solitary coccoid-like microfossils or in small aggregated colonies. Spheroids show strong fluorescence under both green and purple exciting lights, consistent with their composition of organic matter. Spheroids are abundant in the Wumishan stromatolites and they are categorized into two types. The first kind comprises micrite nuclei surrounded by sparitic sheaths, without nano-particle coatings. A smooth to grainy spheroidal surface defines the first kind of spheroids that also has a distinct rounded opening, which is often broken probably due to diagenesis and silicification. The second kind of spheroids is usually covered with nano-particles and lacks circular opening on surface. These spheroids possess large nuclei of single sparitic calcite coated with thin sparry sheaths. Overall, the Wumishan spheroids resemble coccoidal microorganisms reported from other Archean-Paleoproterozoic strata worldwide, but they are also better preserved. The rounded opening on spheroid surface is interpreted as division point of unicells during reproduction of the life cycle of bacteria akin to Myxococcoides grandis. Clump-like micro-particle aggregates in nuclei could represent daughter cells released from the parental envelope, similar to the reproduction process and life cycle suggested for similar spheroidal microfossils from other similar Precambrian occurrences. The Wumishan spheroids therefore may represent fossilized prokaryotes that could have contributed to construct the MDS. Moreover, filamentous microfossils are occasionally present in the coloumns of stromatolites, and they resemble filamentous cyanobacteria, but may not be major constructors of MDS due to their rarity in the buildups. Three types of nano-particles are also conspicuous: (1) putative organic relics, such as fragmented filaments and mucuslike biofilms (purported EPS), (2) organominerals, including nanoglobules, polyhedrons, and their aggregates, and (3) dumbbell-shaped nano-particle aggregates. All of these nano-particles are interpreted to be likely biogenic in origin, and many of them were found from the radial-fibrous fabrics of carbonate precipitates in the MDS, implying that some heterotrophic bacteria may have afficliated the precipitation of radial fibers in deep-time radial-fibrous carbonate precipitates. Therefore, abundant and diverse biosignatures (spheroids, tubular filaments, and nano-particles) are identified in the Wumishan MDSs, and we conclude that diverse filamentous and coccoidal micro-organismscontributed to the formation of the Wumishan stromatolites.
... Papineau et al., 2005). Yet, studies of the carbonate fraction, and the possibility for some of the silica cements to be a replacement product after carbonates (e.g., Ricketts, 1983;Grotzinger and Read, 1983;Grotzinger, 1986;Hofmann and Jackson, 1987;Buick and Dunlop, 1990), have received less attention (but see Markun and Randazzo, 1980;Sommers et al., 2000). ...
... This is very different from primary authigenic chalcedony, which is known by exhibiting optical properties that result in a lower refractive index in the direction of the fibers; termed length-fast (Flörke et al., 1991;Graetsch, 1994;Wahl et al., 2002). In microfossiliferous stromatolites from the correlative Paleoproterozoic rocks of the Belcher Islands (central Hudson Bay, Canada) ( Baragar and Scoates, 1981), this kind of cement was defined as replacive chalcedony after aragonite (Hofmann and Jackson, 1987). Similar fabrics, now composed of calcite or dolomite, are also known from numerous Phanerozoic carbonate rocks and have been interpreted as replacement products of former submarine aragonite (i.e., Davies, 1977;Mazzullo, 1980;Given and Lohmann, 1985). ...
... Another first generation isopachous cement appears to have been a Mg-rich carbonate, such as dolomite. As discussed above, an analogous observation was made in Paleoproterozoic stromatolites from the Belcher Islands (Hofmann and Jackson, 1987), and early formed dolomite has been also recently described in the correlative Michigamme Formation in Michigan, USA (Hiatt et al., 2015). The evidence shows that the primary carbonates precipitated subaqueously in close association with decaying organic matter, some of which was preserved as kerogen within the boundaries of rhombohedral crystals (e.g., Fig. 6C). ...
Shale-normalized Rare Earth Element (REE) patterns and transition metal abundances in banded iron formations (BIF) and shales have long been used as paleoenvironmental proxies to investigate the evolving geochemistry of Precambrian oceans. Apparent similarities between the REE of modern stromatolites and contemporary seawater values also mean that some ancient stromatolites could record paleo-ocean chemistry. To test this hypothesis, we present comparative mineralogical, textural, and spectral analyses of multifurcate, silicified and iron oxide/carbonate-rich, stromatolites from the ca.1.88 Ga Gunflint Formation (Ontario, Canada). Previous studies show that these organo-sedimentary structures represent the initiation of shallow marine sedimentation in the Animikie Basin on the southern tip of the Superior Province. We present evidence that these structures were originally stabilized by aragonite and Mg-bearing carbonates. Fabrics indicative of stromatolite accretion under local hypersaline conditions are also present, with La anomalies suggestive of laterally variable freshwater runoff. The admixture of partially evaporated seawater and silica-oversaturated deep seawater led to pervasive silicification of metastable carbonates and preservation of less soluble early diagenetic carbonate cements. Bulk rock transition metal contents point to lateral variability and dissimilar partitioning and fractionation during mineral formation, yet Ce anomalies amongst samples are similar. Considering the pronounced differences between the REE partitioning between Fe oxyhydroxide precipitates and carbonates, our results point to hematite and siderite as secondary minerals that postdate the stabilization of these structures by carbonates and silica. Stratabound relations of the Fe-rich stromatolites with diabase sills and dikes indicate that the pore water fluids evolved towards a localized state of hematite and siderite oversaturation towards the Mesoproterozoic. If hematite and siderite are both early diagenetic phases, then the Ce anomalies of these stromatolites may be a poor measure of the redox conditions of the shallow areas of the Animikie Basin at the time of accretion.
... In certain cases, fabrics are so well preserved that they imply neomorphic inversion of aragonite and high-Mg calcite directly to dolomite without a low-Mg calcite intermediary (Grotzinger & Read 1983). In rare instances, primary fabrics have been replaced by chert before neomorphic recrystallization, allowing clear distinctions to be made between laminae formed by sediment deposition, precipitation of sea-floor mineral crusts, and growth of microbial mats (Figure 4; see also Bartley et al 1999, Hofmann & Jackson 1987, Kah & Knoll 1996). Much evidence has been supplied for the involvement of loose sediment in the formation of laminae (summarized in Semikhatov et al 1979); in contrast, the role of in situ precipitation has sometimes been viewed skeptically (e.g. ...
... Horodyski 1975, Walter et al 1988). Over the past decade it has become increasingly clear that in situ mineral precipitation is an important accretion mechanism in ancient stromatolites (Figures 2?6; see also Bartley et al 1999, Grotzinger 1986a, Grotzinger & Read 1983, Hofmann & Jackson 1987, Kah & Knoll 1996, Knoll & Semikhatov 1998 ). In some remarkably wellpreserved stromatolites of late Archean age, it can be observed that the only components in the stromatolite structures were microbial mats, early marine cement, and later porosity-occluding burial cement?sedimentary particles are completely absent (Sumner 1997). ...
... In ancient stromatolites, however, diagenesis characteristically has erased most evidence for early, pore-filling cements, and arguments for early lithification were, thus, traditionally based on indirect criteria such as the growth of steep or even overhanging margins (Donaldson 1976), the ability to withstand strong currents (Hoffman 1974), the chemical purity of lamination (Serebryakov & Semikhatov 1974 ), and the ability to form reefal escarpments with up to hundreds of meters of relief (Grotzinger 1986b). As mentioned previously, more recent studies supply direct petrographic evidence not only for early lithification , but also for growth of encrusting marine cement directly on the growing P1: APR/SAT/spd P2: NBL/plb QC: NBL/anil T1: NBL Bartley et al 1999, Grotzinger & Read 1983, Hofmann & Jackson 1987, Kah & Knoll 1996, Knoll & Semikhatov 1998, Sami & James 1996, Sumner 1997, Sumner & Grotzinger 1996a). The processes of early lithification and growth of sea-floor crusts are poorly understood. ...
Stromatolites are attached, lithified sedimentary growth structures, accretionary
away from a point or limited surface of initiation. Though the accretion process is
commonly regarded to result from the sediment trapping or precipitation-inducing
activities of microbial mats, little evidence of this process is preserved in most Precambrian
stromatolites. The successful study and interpretation of stromatolites
requires a process-based approach, oriented toward deconvolving the replacement
textures of ancient stromatolites. The effects of diagenetic recrystallization
first must be accounted for, followed by analysis of lamination textures and deduction
of possible accretion mechanisms. Accretion hypotheses can be tested
using numerical simulations based on modern stromatolite growth processes. Application
of this approach has shown that stromatolites were originally formed
largely through in situ precipitation of laminae during Archean and older Proterozoic
times, but that younger Proterozoic stromatolites grew largely through the
accretion of carbonate sediments, most likely through the physical process of microbial
trapping and binding. This trend most likely reflects long-term evolution
of the earth’s environment rather than microbial communities.
... Extensive carbonate platforms likely reflect a combination of globally high sea level, elevated marine carbonate saturation (Grotzinger, 1989;Bartley and Kah, 2004) and generally temperate climates in the aftermath of the $2.3 Ga Huronian Glaciation (Eriksson et al., 1998;Bekker et al., 2005). Unlike modern carbonate platforms, Paleoproterozoic carbonate platforms were marked by a wide variety of microbialite morphologies, an abundance of seafloor precipitates (Hofmann and Jackson, 1987;Grotzinger, 1989;Sami and James, 1996), and only rare deposition of authigenic gypsum evaporites (Pope and Grotzinger, 2003;Zentmyer et al., 2011). ...
... Silicification is common within crinkly laminite facies, but is typically restricted to thin horizons. Thicker dololutite horizons contain discrete horizons containing sub-mm-scale, uniform-thickness laminae that often form cmscale, cylindrical columnar structures, commonly termed microdigitate stromatolites, asperiform stromatolites, ministromatolites or microbial tufa (Grey and Thorne, 1985;Hofmann and Jackson, 1987;Grotzinger, 1990). Previous workers (Sharma and Shukla, 1998) have shown that ministromatolites within the crinkly laminaite facies are composed of alternating laminae of dark-pigmented micrite and radial fibrous calcite within a matrix of dololutite. ...
... Stromatolitic fabrics within sampled Vempalle carbonate rocks are, similarly, uniform in their petrographic expression, consisting of crinkly to smooth lamination defined by alternating micrite and microspar ( Fig. 6C and D). Stromatolitic fabrics in this study are considerably less complex than those recorded in Vempalle Formation stromatolites described by Riding and Sharma (1998), who document a wide range of clotted (e.g., grumeleuse; Carozzi, 1970) to radial-fibrous (e.g., asperiform; Hofmann and Jackson, 1987) microfabrics. Clotted textures are interpreted to represent mineral precipitation within cyanobacterial EPS (Hofmann, 1969;Bertrand-Sarfati, 1976;Monty, 1976Monty, , 1981Turner et al., 1993), or potentially within a non-cyanobaterial biofilm (Reitner, 1993;Riding and Sharma, 1998). ...
... Desiccation features and microbial components such as filament molds or casts are not present. As discussed recently in the literature, many stromatolites are likely to have formed in response to in situ precipitation of calcite and or aragonite as crusts on the sea floor (Grotzinger and Read 1983; Hofmann and Jackson 1987; Sami and James 1996; Kah and Knoll 1996; Sumner 1997; Bartley et al. in press). However, most of the examples that are cited in these studies are Mesoproterozoic and older, formed during a time in earth history when sea-floor precipitation may have been widespread in unrestricted marine environments (Grotzinger and Kasting 1993; Sumner and Grotzinger 1996 ). ...
... Studies of the lamination textures in ancient stromatolites provide evidence for growth of stromatolites through accretion of loose sediment (micrite , grains) and in situ mineral precipitation. Although much evidence has been supplied for the involvement of loose sediment in forming lamination (summarized in Semikhatov et al 1979), it has become increasingly clear over the last decade that in situ mineral precipitation is indeed an important accretion mechanism in ancient stromatolites (Grotzinger and Read 1983; Grotzinger 1986; Hofmann and Jackson 1987; Kah and Knoll 1996; Knoll and Semikhatov in press; Bartley et al. in press; Pope and Grotzinger in press). Stromatolite laminae that form by in situ precipitation require both an increase in the calcium carbonate saturation of seawater and a decrease in the flux of loose, clastic carbonate sediment to the site of deposition (Grotzinger 1990; Grotzinger and Knoll 1999). ...
... In some remarkably well preserved stromatolites of late Archean age it can be observed that the only components that constitute the stromatolite were microbial mats, early marine cement, and later porosity-occluding burial cement; sedimentary particles are completely absent (Sumner 1997). Stromatolites with very thin and/or isopachous lamination are regarded to have formed hard, synsedimentary crusts directly on the sea floor (Grotzinger and Read 1983; Hofmann and Jackson 1987; Grotzinger and Knoll 1995; Sami and James 1996; Kah and Knoll 1996; Grotzinger and Rothman 1996; Sumner 1997; Bartley et al. in press; Pope and Grotzinger in press). Although bacteria may play a role in catalyzing mineral precipitation (Buczynski and Chafetz 1991; Vasconcelos et al. 1995 ), it is clear in several cases that mineral precipitation did not template microbial mats and so the texture and morphology of these thinly laminated stromatolites is considered to be the result of chemical processes dominating over biological processes (Hofmann and Jackson 1987; Bartley et al. in press; Grotzinger in press; Grotzinger and Knoll 1999). ...
The transition between carbonate platforms or isolated carbonate buildups and overlying evaporites commonly is marked by assemblages of stromatolites and interlaminated carbonates and evaporites. Stromatolites display lamination textures that vary from peloidal and discontinuous on a scale of a millimeter to a few centimeters, to isopachous and continuously laminated on a scale of a centimeter to a few meters. The isopachous lamination texture may be composed of either: (1) micritic or radial-fibrous calcite, or (2) dolomite, Isopachous stromatolitic laminae are remarkably uniform, varying little in thickness over a given lateral distance, in contrast to stromatolites formed of peloidal laminae, which show marked variation in thickness over an equivalent lateral distance. These isopachous textures are uncommon on most open-marine carbonate platforms and apparently developed in transitional carbonate to-evaporite settings because of increasing temperature, salinity, and anoxia related to water stratification, which would have created ecologic restriction and an opportunity for stromatolite growth. Stromatolites with isopachous lamination are here interpreted to have formed as a result of in situ precipitation of sea-floor-encrusting calcite and possibly dolomite, whereas the stromatolites composed of peloidal, discontinuous lamination are inferred to have formed by trapping and binding of loose carbonate sediment in microbial mats, While the presence of microbes in almost all nearsurface environments nullifies use of the term "abiotic" to describe most precipitated minerals, we interpret growth of the isopachous stromatolites to have been dominated by chemogenic precipitation in the absence of microbial mats, and the growth of peloidal stromatolites to have been controlled by sedimentation in the presence of microbial mats, These transitional stromatolite facies are best developed atop Proterozoic and Paleozoic carbonate platforms that underlie major evaporite successions. However, inspection of Jurassic and younger evaporite basins, such as the Messinian of the Mediterranean region, shows that stromatolites with thin, isopachous lamination and radial-fibrous textures, though present, are rare. Instead, these facies may have been replaced by stromatolites with peloidal, elastic textures and by low-diversity diatomaceous and coccolith mudstones, Accumulation of the mudstones would have imposed two important effects: (1) Production of coccoliths would have helped extract calcium carbonate from seawater, thus lowering the growth potential for precipitation of sea-floor-encrusting stromatolites. (2) Settling of both coccoliths and diatoms would have created a sediment flux to the sea floor, which would have served to impede growth of precipitated stromatolites because of smothering of growing crystals.
... Ga) carbonate successions, but they declined significantly in Meso-and Neoproterozoic (,1.6 Ga) carbonates (Grotzinger and Knoll, 1999). The abundance of radial-fibrous texture indicative of an acicular aragonite precursor and the general lack of microbial fossils in MDS have led most researchers to interpret MDS as a special type of stromatolites formed mainly through abiotic carbonate precipitation (e.g., Grotzinger and Reed, 1983;Hofmann and Jackson, 1987;Knoll et al., 1993;Sergeev et al., 1995;Grotzinger and Knoll, 1999). While heterotrophic bacterial metabolism may have facilitated carbonate precipitation and nucleation during MDS formation (Knoll and Semikhatov, 1998), the ocean seawater chemistry, particularly the calcium carbonate saturation of surface seawater, may have been the major controlling factor behind the rise and decline of MDS in Proterozoic carbonate successions (e.g., Grotzinger and Kasting, 1993;Grotzinger, 1994;Sumner and Grotzinger, 1996). ...
... Morphologically distinct bacterial fossil preservation in Archean-Paleoproterozoic successions could be difficult owing to the lack of in vivo cyanobacterial calcification at potentially high pCO 2 (Riding, 2006;Kah and Riding, 2007) and destruction of primary textures during diagenesis and metamorphism (Grotzinger and Reed, 1983;Hofmann and Jackson, 1987;Grotzinger and Knoll, 1999). Recent studies indicate that micron-to nanometer-scale microstructures, such as nanoglobules (or nanospheres), micropeloids, fibrous fabrics, and micritized extracellular polymeric substances (EPS), record organomineralization processes within a syndepositional microbial community, and they may be used as signatures for microbial activities in stromatolite-forming microbial mats (e.g., Dupraz et al., 2004Dupraz et al., , 2009Benzerara et al., 2006Benzerara et al., , 2010Pacton et al., 2010;Perri et al., 2012). ...
... The morphology and structures of the MDS from the Wumishan Formation are similar to those documented from Neoarchean-Paleoproterozoic successions (Hofmann and Jackson, 1987;Grotzinger and Knoll, 1999). In morphologic classification, these MDS belong to the group of ministromatolites (Liang et al., 1984;Hofmann and Jackson, 1987;Qiu and Liang, 1993). ...
Microdigitate stromatolites (MDS) are common in Neoarchean–Paleoproterozoic successions but declined and gradually disappeared in Mesoand Neoproterozoic carbonates. The abundance of well-preserved fibrous fabrics and the absence of identifiable microbial fossils in MDS have been taken as evidence of their abiotic origin in carbonate-supersaturated and anoxic Precambrian oceans. Micron- and nanometer-scale features of MDS from the Mesoproterozoic Wumishan Formation (ca. 1.45–1.5 Ga) of the North China platform composed of alternating submillimetric dark and light laminasets are morphologically similar to those reported from elsewhere in the geological record. The dark laminasets are micritic and contain abundant fuzzy-edged micropeloids and filaments. The micropeloids are commonly 10–70 mm in diameter and commonly surrounded by thin (,10 mm) rims composed of amorphous micrite or microsparite (some rims now replaced by silica). The filaments are morphologically similar to the bacterial filaments in modern microbialites and contain kerogenous components as indicated by Raman spectrometry analysis. All the laminasets are characterized by fibrous fabrics that are expressed by alternating brown fibers (,10–25 mm) and light microsparitic strips of approximately equal width in transverse direction. Filaments, relics of putative extracellular polymeric substances (EPS), micropeloids, and nanoglobules are closely associated with the brown fibers. These organomineralization-related features suggest a biogenic origin for the MDS of the Wumishan Formation and may have an implication to other MDS from the Neoarchean–Paleoproterozoic successions. Microbially induced micro- and ultrastructures including fibrous fabrics, filaments, micropeloids, and nanoglobules are best preserved in silicified MDS samples, implying that early silicification is critical for the preservation and recognition of organominerals.
... Laminated or radial-fibrous microbialites with fine, extremely even and uniformly thick lamination, regardless of depositional orientation are considered as "precipitates" (Grotzinger and Read, 1983;Hofmann and Jackson, 1987). These precipitates formed almost exclusively by inorganic deposition of calcium carbonate, with little evidence of involvement of cyanobacteria. ...
... When the nucleation occurred slightly below the sediment-water interface, the radial fan-like structures were formed (Bartley et al., 2000). The size and shape of fibrous crystals resembles the fibers that constitute botryoidal aragonite (Ginsburg and James, 1976;Folk and Assereto, 1976;Grotzinger and Read, 1983;Hofmann and Jackson, 1987;Perrin et al., 2014;Lee and Lindgren, 2015), although this growth habit may also occur in calcite (Bartley et al., 2000). Occurrence of laminites, stromatolites, microbial features in the Kajrahat Limestone suggest that suitable physical and chemical environment was available for the formation of fan fabric found in limestone. ...
Present study records the Fan-Fabric Structures from the late Palaeoproterozoic Kajrahat Limestone of the Vindhyan Supergroup, India exposed in Katni district, M. P. Centimeter (cm) size carbonate fans (1 to 10 cm in length) radiating in upward direction are part of a stromatolite dominated Kajrahat Limestone in the area. The Kajrahat FFS represent their widespread occurrence in the Proterozoic successions of India. Our study establishes that these fans were originally precipitated and not the result of a late diagenesis or any other post sedimentation process. These fan-fabric structures were deposited in intertidal to sub-tidal environments. Globally, fan-fabrics structures are considered a common feature of the Archaean to early Mesoproterozoic carbonate platforms.
... Therefore, some of the Precambrian stromatolites are believed to be chemical precipitates in supersaturated water conditions (Lowe, 1994;Grotzinger and Knoll, 1999;Riding, 2008). In addition to extremely large stromatolites, mm-scale ministromatolites are a peculiar type in Precambrian (Grotzinger and Reed, 1983;Grey and Thorne, 1985;Liang et al., 1985;Hofmann and Jackson, 1987;Cao, 1991;Knoll et al., 1993;Sergeev et al., 1995). One of the ministromatolites named microdigitate stromatolites (MDS) occurs from Neoarchean to Paleoproterozoic (<1.6 Ga) but declined significantly in the Meso-and Neoproterozoic carbonates (Grotzinger and Knoll, 1999). ...
... The richness of fibrous chemical cement but the absence of identifiable microbial fossils in MDS have been taken as evidence for an abiotic origin in carbonate-supersaturated Precambrian oceans (Grotzinger and Reed, 1983;Grey and Thorne, 1985;Grotzinger, 1989a;Grotzinger and Knoll, 1999;Pope et al., 2000). Although some previous research found evidence of biogenicity for ministromatolite, such as banded or microcrenate lamination microstructure (Hofmann and Jackson, 1987) and employed binomial nomenclature for it (Liang et al., 1985;Grey and Thorne, 1985), these structures are similar to modern tufa, carbonate cement and speleothem. This led to more than a few perspectives supporting a chemical origin for them (Hofmann, 1976;Grotzinger and Reed, 1983). ...
Although the biogenicity of the very common millimeter-sized ministromatolites in the Proterozoic has been noted, direct biotic evidence is missing, leading to the discussion of a chemical origin that differs from that of the cyanobacteria-related stromatolites in the Phanerozoic. Distinctive ministromatolites were recently discovered in a microbial dolostone interval of the Mesoproterozoic Wumishan Formation, at Lingyuan, North China. Thin section examination of the ministromatolites reveals the presence of abundant coccoidal microfossils ranging 10–30 μm in diameter. Petrofabric analysis shows that the ministromatolites experienced three periods of diagenetic silicification, and that the microfossils are exclusively preserved within early diagenetic chert. This supports the view that silicification penecontemporaneous with mat growth is the key to unique preservation of microfossils. In contrast, the absence of microfossils in most Precambrian carbonate stromatolites may well be interpreted as the lack of hydrochemical conditions favorable for early silicification. Although chemically-formed fibrous carbonate minerals are the dominant components of these ministromatolites, the presence of abundant microfossils indicates that the role of microorganisms in the formation of ministromatolites has previously been underestimated. Therefore, this research suggests that Mesoproterozoic ministromatolites were not solely chemical products but consist of complex associations of both biotic and chemical fabrics.
... In China, Pseudogymnosolenaceae mainly occur in Mesoproterozoic strata that are dated to 1500-1200 Ma (Liang et al. 1984;Qiu and Liang 1993;Cao and Yuan 2009), such as the Wumishan Formation, Gaoyuzhuang Formation and Yangzhuang Formation on the North China Block, and the Kunyang Group on the Yangtze Craton (Liang et al. 1984;Qiu and Liang 1993;Cao and Yuan 2006). Pseudogymnosolenaceae have three significant characteristics (Liang et al. 1984;Hofmann and Jackson 1987;Qiu and Liang 1993): (1) column diameters are generally 0.02-2.00 cm, (2) grow synchronously, and (3) mostly have radial-fibrous fabrics and microcrenate lamellae. ...
... cm, (2) grow synchronously, and (3) mostly have radial-fibrous fabrics and microcrenate lamellae. Pseudogymnosolenaceae have most commonly been interpreted as inorganic structures (Grotzinger and Read 1983;Hofmann and Jackson 1987;Grotzinger and Rothman 1996;Sumner and Grotzinger 1996;Grotzinger and Knoll 1999;Grotzinger and James 2000;Bartley and Kah 2004;Mei et al. 2008;Riding 2008), but other scholars believe that they are related to microorganisms (Liang et al. 1984;Tang et al. 2012Tang et al. , 2013 due to the filamentous algal fossils preserved in their laminae (Liang et al. 1984), abundant bacterial residues and microspherules that constituted their ultramicrostructures (Tang et al. 2012(Tang et al. , 2013, and their radial-fibrous fabrics, which have been interpreted to be resulted from bioinduced mineralization (Tang et al. 2012(Tang et al. , 2013. Pseudogymnosolenaceae are characterized by alternations of dense light and dark laminae (approximately 1 mm thick) and synchronous growth of stromatolite laminae with neighboring sedimentary laminae, which indicate that the hydrodynamic conditions of their sedimentary environment were weak and stable (Liang et al. 1984). ...
The origin process of manganese ores remains unsolved worldwide. Exploring the origins of stromatolites that contain manganese may be a key to deciphering the sedimentary environments and metallogenic processes of these deposits. However, only a few manganese stromatolites have been discovered and described until now. Microbialites are well developed in the manganese deposits, located near the top of the Ediacaran Doushantuo Formation in Chengkou area of Chongqing, northern Yangtze Craton, but has not been explicitly studied; and whether they are true stromatolites or Epiphyton microbialites remains controversial. Based on field and core observations and thin section microscopy, the characteristics of five types of manganese stromatolites and their growth modes are described in detail in this study. The results show that these stromatolites grew in a biostrome in shoal and lagoon environments and were syngenetic with oncolites and oolites on a carbonate ramp behind the shoal. Manganese stromatolites can be categorized into three forms: (1) stratiform; (2) columnar, which includes branched and columnar types; and (3) stratiform-columnar, which is a transitional type. Based on a criterion that the diameter is less than or greater than 1 mm, columnar stromatolites are further divided into micro-columnar (< 1 mm) and columnar (> 1 mm) columns, which display synchronous growth and are similar to Pseudogymnosolenaceae. Their shapes are mainly controlled by water depths and hydrodynamic strengths. The greater the water depth, the more columnar the columns tend to be. Excessively strong hydrodynamic conditions decrease the growth rate of stromatolites, and they even stopped growth due to wave damage. Furthermore, pillared laminar textures (not Epiphyton ), which consist of dendritic, micro-branched and micro-columnar stromatolites, are a common feature of the larger stratiform, stratiform-columnar and columnar stromatolites. The alternations of laminae with different internal textures record subtle fluctuations in water depths and hydrodynamic strengths, which indicate that stromatolite growth is controlled by tidal cycles at the lamina level. Therefore, it is possible that the vertical evolution of the stromatolites could reveal the changing characteristics of both local and regional sedimentary environments, i.e., stromatolite shape changes from columnar to stratiform can represent the onset of shallower environments with weak hydrodynamic conditions. In addition, as important reef builders in shallow carbonate ramps, microstromatolites accelerate the development from ramp to platform. Indicators of microbial control on stromatolite shapes and manganese sedimentation processes include the fabric of stromatolite laminae, organic rhodochrosite with a micritic texture that is usually clotted, spherical, tubular, fibrous or dendritic, which suggests that the laminae resulted from microbially induced in situ precipitation.
... Earth, both amorphous silica and high-Mg carbonate minerals such as primary or early diagenetic dolomite can nucleate on cell surfaces and within organic matrices to preserve microbial textures 31,133 or even body fossils 30, 102,134 . In some instances where silica and dolomite occur together, silica demonstrably replaced the original carbonate [135][136][137] ; in others, the precipitation of amorphous silica in surface mats and cells preceded 120,126 or accompanied the precipitation of carbonate minerals 138,139 . Carbonaceous material is typically reported in both silica-rich and carbonate-rich phases, but the nm-scale spherules of amorphous silica that precipitate during very early diagenesis enable the preservation of much finer microbial textures and body fossils [140][141][142][143][144][145] . ...
... For example, the rapidly growing crystalline crusts in modern carbonate-precipitating hot springs are comprised of radial-fibrous and ray-like densely packed calcite or aragonite crystals with axes perpendicular to the growth surface 164,173,194,195 (Fig. 6). These textures, sometimes also called 'palisade' crystals 173 or 'radial-fibrous' crystals 136,137,182,[196][197][198] , have been attributed to the abiotic mineral precipitation in carbonate deposits that reflect growth controlled by local growth processes 71 , rather than microbial presence or activity (Fig. 6). However, the rapidly precipitating minerals are known to entomb microbial aggregates or sheaths of large filamentous cyanobacteria 164,183,189,199,200 . ...
The recognition of past habitable environments on Mars has increased the urgency to understand biosignature preservation in and characterize analogues of these environments on Earth. In this Review, we examine the detection and interpretation of potential biosignatures preserved in deposits rich in carbonates, silica and clay. Many of the earliest chemical, textural and morphological evidence of life on Earth are found in carbonates and carbonate-hosted phases. Early diagenetic chert within carbonate deposits can exceptionally preserve microbial body fossils, and clay minerals that form in ultramafic terrains can protect organic matter. On Mars, similar deposits older than 3.5 billion years could contain biosignatures or remnants of prebiotic processes that have long been erased from Earth. Terrestrial analogues for the deposition of magnesium carbonate minerals in Jezero crater, Mars, present patterns that can guide the collection of samples with the highest astrobiological potential by the Perseverance rover. Continued characterization of terrestrial analogue sites and rigorous examination of the processes that impact the preservation of isotopic signals, organic compounds, and microbial textures and fossils will advance the interpretation of Martian deposits.
... Crystal fans are often associated with post-Marinoan cap carbonates where they can be spectacularly preserved (Grotzinger and James, 2000;Sumner and Grotzinger, 2000;James et al., 2001;Hoffman and Schrag, 2002;Corsetti et al., 2004;Babinski et al., 2007;Pruss et al., 2008). However, Ediacaran occurrences represent a rare and transient re-establishment of this fabric, which is more frequently observed in Archean and Paleoproterozoic successions (Grotzinger and Read, 1983;Hofmann and Jackson, 1987;Kah and Grotzinger, 1992;Kah and Knoll, 1996;Sumner and Grotzinger, 1996;Grotzinger and James, 2000;Higgins et al., 2009;Bergmann et al., 2013). Seafloor precipitate textures continue into the Meso-and Neoproterozoic, but decrease markedly in size, abundance, and environmental distribution, until expanding again briefly but globally following the Marinoan glaciation, and with rare occurrences thereafter. ...
... We hypothesize that the replacement of Ω-increasing (anaerobic) with Ω-decreasing (aerobic or otherwise oxygen-dependent) metabolisms leaves a signature in the carbonate textural record. Consistent with earlier reports (Grotzinger and Read, 1983;Hofmann and Jackson, 1987;Kah and Grotzinger, 1992;Sumner and Grotzinger, 1996;Kah and Knoll, 1996;Semikhatov and Raaben, 1996;Knoll and Semikhatov, 1998;Grotzinger and Knoll, 1999;Grotzinger and James, 2000;Higgins et al., 2009;Bergmann et al., 2013), Microstrat shows that seafloor macro-and micro-precipitates are abundant in Archean and Paleoproterozoic carbonate deposits across the observed depth gradient, but are uncommon thereafter. We suggest that the abundance of seafloor precipitate textures is consistent with the presence of precipitation-promoting anaerobic metabolisms dominating an anoxic sediment-water interface during the Archean and Paleoproterozoic intervals. ...
Carbonate minerals have precipitated from seawater for at least the last 3.8 billion years, but changes in the physical and chemical properties of carbonate rocks demonstrate that the nature, loci, and causes of this precipitation have varied markedly through time. Biomineralization is perhaps the most obvious time-bounded driver. However, other changes in the sedimentological character of Archean and Proterozoic carbonates offer an under-considered record of fluctuations in Earth’s chemical, biological, and physical systems before and during the rise of animal life. Geobiologists and geochemists have successfully used large geochemical datasets to track changes in Earth’s surface chemistry through time, but inconsistencies between proxies make the recognition of clear spatial-temporal patterns challenging. In order to place new constraints on the environmental history of Archean and Proterozoic oceans, especially with regard to redox state, we present for the first time a high-resolution database of global Precambrian and Cambrian carbonate sedimentation.
Our initial datasbase, named Microstrat, comprises carbonate-bearing successions dating from c. 3.4 billion to ~500 million years old; these include more than 130 carbonate-bearing formations, digitized at the highest stratigraphic resolution possible and classified by environment of deposition. Lithofacies details are recorded at the finest scale available, including a range of microbial and other depositional fabrics, mineralogy, environment of deposition, age and location. We interrogate the Archean, Proterozoic, and Cambrian carbonate records, testing both long-standing and novel hypotheses about changes in Earth’s carbonate system through time. Changes in carbonate sedimentology illuminate global changes in bioturbation and microbial community structure; the depth-dependent timing of marine oxygenation and the transition from anaerobic to aerobic respiration at and within the seafloor; and temporal changes in patterns of dolomitization. Shifts in both the loci of carbonate precipitation and in markers of animal activity are consistent with time- and depth-dependent trends in ocean oxygenation. We also note changes through time in the morphologies of stromatolites and thrombolites, which we suggest reflect secular shifts in carbonate precipitation, clastic sediment transport, and eukaryotic evolution. Observations from the database and petrographic studies confirm that the nature and extent of Proterozoic dolomite contrasts with that of dolomite in the Phanerozoic, consistent with dolomite being an early or even, in some cases, primary precipitate prior to the Cambrian Period. Because this database preserves environmental context and the stratigraphic relationships of carbonate features rather than tracking the occurrence of single features through time, it permits new and detailed analyses of the physical sedimentology of Precambrian carbonates and correlations in time and space among different features.
We also consider how to build upon this initial dataset. Capturing and analyzing sedimentological data is difficult. Analysis becomes more challenging when data have been collected by multiple researchers working across Earth’s entire history and surface. Field observations have a great deal of power to describe and explain changes in Earth’s surface environments, yet they are often reported in idiosyncratic ways that make it difficult to compare them, obscuring their true explanatory power. Microstrat is an effort to pool idiosyncratic sedimentological data in hopes of illuminating Archaean, Proterozoic, and Cambrian carbonate depositional environments, yet it is unavoidably limited. We describe how other researchers can help to build Microstrat into a community-curated database by reporting and sharing data.
... For a long time, all laminated sedimentary structures found in the Precambrian rocks were supposed to be of organo-sedimentary origin, i.e. stromatolites, that formed as a result of trapping, binding and precipitation of carbonate sed-iments by colonies of microorganisms, presumably the blue-green algae (Walter, 1976). In recent years, it has been found that many microlaminated structures found in the Archean and Paleoproterozoic rocks and previously termed as "microdigitate stromatolites" formed as a result of calcium carbonate precipitation from oversaturated seawater (Grotzinger and Read, 1983;Hofmann and Jackson, 1987;Grotzinger, 1986Grotzinger, , 1989Grotzinger, , 1994Kah and Knoll, 1996;Golubic, 1999, 2000;Bartley et al., 2000). These predominantly inorganic structures were named "precipitates" in contrast to "stromatolites" which are presumed to have deposited mainly as a result of metabolic activity of cyanobacteria. ...
... When the nucleation occurred slightly below the sediment-water interface, the radial fan-like structures were formed (Bartley et al., 2000). The size and shape of fibrous crystals resembles the fibers that constitute botryoidal aragonite (Ginsburg and James, 1976;Folk and Assereto, 1976;Grotzinger and Read, 1983;Hofmann and Jackson, 1987), although this growth habit may also occur in calcite (Bartley et al., 2000). ...
The Jaradag Fawn Limestone Formation (∼1.6 Ga, Semri Group, Vindhyan Supergroup, India) contains abundant microfossils and precipitates in early diagenetic (bedded and stromatolitic) cherts. The silicified carbonate precipitates and associated micritic event laminae were formed at or near the sediment–water interface and presumably lithified very rapidly. The precipitates, deposited inorganically without active participation of cyanobacterial mats, can be grouped into three morphological categories: radial-fibrous fans, microlaminated stratiform laminae and poorly differentiated laminated stratiform laminae. A diverse assemblage of cyanobacteria is preserved both within precipitates where preservation is excellent, and in other synsedimentary textures. Precipitates and microfossil assemblages from four Mesoproterozoic formations of Siberia are described and compared with those from Jaradag Fawn Limestone. Comparison of the Indian and the Siberian precipitates and associated microfossil assemblages reveals an almost identical pattern for contemporaneous Mesoproterozoic carbonate precipitates and microbiotas in cherts. The microbial assemblages, almost exclusively composed of the remnants of cyanobacteria, are dominated by entophysalidacean members and short trichomes, and can be termed as “typical Mesoproterozoic microbiotas”. Co-occurrence of these microbiotas and precipitates is probably related to the depositional environment of the Mesoproterozoic tidal flats, with high carbonate saturation. Neoproterozoic depositional conditions changed drastically, as did the composition of microbial communities.
... For a long time, all laminated sedimentary structures found in the Precambrian rocks were supposed to be of organo-sedimentary origin, i.e. stromatolites, that formed as a result of trapping, binding and precipitation of carbonate sed-iments by colonies of microorganisms, presumably the blue-green algae (Walter, 1976). In recent years, it has been found that many microlaminated structures found in the Archean and Paleoproterozoic rocks and previously termed as "microdigitate stromatolites" formed as a result of calcium carbonate precipitation from oversaturated seawater (Grotzinger and Read, 1983;Hofmann and Jackson, 1987;Grotzinger, 1986Grotzinger, , 1989Grotzinger, , 1994Kah and Knoll, 1996;Golubic, 1999, 2000;Bartley et al., 2000). These predominantly inorganic structures were named "precipitates" in contrast to "stromatolites" which are presumed to have deposited mainly as a result of metabolic activity of cyanobacteria. ...
... When the nucleation occurred slightly below the sediment-water interface, the radial fan-like structures were formed (Bartley et al., 2000). The size and shape of fibrous crystals resembles the fibers that constitute botryoidal aragonite (Ginsburg and James, 1976;Folk and Assereto, 1976;Grotzinger and Read, 1983;Hofmann and Jackson, 1987), although this growth habit may also occur in calcite (Bartley et al., 2000). ...
... Hofmann and Jackson (1987) Turner et al. (1993) Défarge et al. (1996) Knoll and Semikhatov (1998) Riding and Sharma (1998) Duane and Al-Zamel (1999) Seong-Joo and Golubic (1999) Bartley et al. (2000) Seong-Joo et al. (2000) Turner et al. (2000) Riding (2000) Raaben (2006) Riding (2008) *Note the overlapping of meanings and how it constantly repeats. When interpreted as isolated terms, they are comprehensive (although with some exceptions); however, the overview of the literature is a mixed, confusing glossary. ...
Abstract Stromatolites are laminated biosedimentary structures of great importance for paleobiological, paleoecological, and paleoenvironmental analyses, mainly in Precambrian rocks. Their value is related to the glimpse of past life recorded in their lamination, fabric, and, eventually, due to the preservation of organic matter, including microfossils, and because their deposition is directly influenced by environmental conditions. Although stromatolites are widely described in microscopic scale, there is a lack of standardization of their nomenclature, precluding better paleoenvironmental and paleobiological interpretations. In this study, we propose a guide for the microscopic analysis of fossil stromatolites and, possibly, thrombolites, and provide a review of specialized literature and the bibliometric context of main terms. The goal is to contribute to the improvement of their application through systematization of microscopic data, in the face of novel paleoecological and paleobiological approaches and for astrobiological prospection for microbialites in therock record of Mars.
... Very small, often millimetric, stromatolite columns, that are widespread and locally abundant in Proterozoic carbonates (Riding, 2008), have variously been termed digitate stromatolite (Donaldson, 1963), microstromatolite (Hofmann, 1969a, p. 15;Raaben, 1980;Lanier, 1986), 'tiny arborescent stromatolite' (Hofmann, 1975), microdigitate stromatolite (Hoffman, 1972;Grotzinger & Read, 1983) and ministromatolite (Hofmann & Jackson, 1987). Their fabrics range from irregularly laminated and peloidal to evenly layered and radially fibrous, and have variously been interpreted as biogenic (Grey & Thorne, 1985) or abiotic (Grotzinger, 1986), and they have often been described from restricted nearshore environments (Hofmann, 1975). ...
Microbial carbonates formed stromatolitic, thrombolitic, dendrolitic and maceriate (mazelike) fabrics in shallow marine Cambrian–Early Ordovician carbonates encircling Laurentia. However, poor preservation often hinders recognition of their specific components. Well‐preserved examples of normal shallow marine limestones in the ca 490 Ma upper Cambrian Point Peak Member, Wilberns Formation, central Texas, include stromatolitic cones, steep‐sided laminated rimmed columns with grainy interiors, and laminated and maceriate domes. Together these decimetre to metre‐thick biostromes. In these examples, a single component, microstromatolite, on its own or with minor calcimicrobes, creates macroscopic stromatolitic, dendrolitic, thrombolitic and maceriate fabrics. Microstromatolites constructed upward widening stromatolitic cones that developed into columns with laminated rims surrounding slightly depressed interiors. These columns accumulated allochthonous sediment by a ‘bucket effect’. Their interiors contain either clusters of dendrolitic microstromatolite or ragged columns of laminated stromatolite–sponge biolithite, and are often characterized by a ‘mottled’ fabric that superficially resembles thrombolite. This mottling was formed by localized dolomitization around millimetric burrows that otherwise do not appear to have significantly influenced the biolithite fabric. Calcimicrobes, including cyanobacteria (Razumovskia) and microproblematica (Renalcis and Tarthinia), impart a mesoscopic clotted appearance to maceriate fabric, and locally to column rims, both of which are dominated by microstromatolite. Similar component‐fabric relationships should be recognizable in rimmed columns and domes that were locally abundant elsewhere in Cambrian–Early Ordovician shallow carbonate seas.
... Carbonates formed in shallow water at elevated sea level and higher carbonate saturation are dominated by inorganic precipitates and microbialites, a non-skeletal organo-sedimentary deposit formed by the benthic microbial community. Unlike Archean and Neoproterozoic carbonates, Palaeoproterozoic carbonates are restricted in occurrence and described principally under peritidal setting [6][7][8][9][10][11][12] . ...
Facies and facies succession analysis from four sections in a ~12 m thick carbonate succession, hitherto undescribed, exposed over an east-west transect over 600 km from the topmost part of the Palaeoproterozoic Sleemanabad Formation, Mahakoshal Group, Central India reveals facies development in a proximal-distal relation. The facies types include microbialite and stromatolite, interbedded limestone-mudstone, intraclastic conglomerate, pyrite bearing dark-coloured limestone and massive/normal-graded conglomerate and fine-grained sandstone. While microbialites and isolated stromatolites (rarely conjoined) with seafloor precipitate are interpreted as a product of proximal peritidal deposition, the dark-coloured pyrite bearing limestone represents the distal platform deposition below storm wave base.
... Precambrian deposits contain extremely large stromatolites, measured in tens of meters in height and diameter, including size ranges that are not known from the Phanerozoic (Beukes, 1987;fralick & riDing, 2015). In contrast, ministromatolites one to several millimeters across are most common in the Neoarchean and Paleoproterozoic (hofmann & jackson, 1987;meDveDev & others, 2005). Upper Paleoproterozoic and Mesoproterozoic marine stromatolites display many diverse macrostructures rarely observed in Phanerozoic deposits, including simple and complexly branching forms (clouD & semikhatov, 1969;aWramik & sprinkle, 1999). ...
Microbially induced, lithified structures known as microbialites are both geologically and biologically significant, forming extensive sedimentary, geochemical, and microbiological records in modern and ancient environments. Depositional settings range from deep ocean hydrocarbon seeps, hydrothermal vents, and whale falls, to cool water carbonate banks—abundant occurrences within peritidal zones and,
finally, to non-marine environments such as lakes, rivers, and springs. More than three billion years of Earth’s biosphere is primarily
recorded within microbialites, including the oldest macrofossils on the planet. Even with diminished diversity and abundance during the Phanerozoic, periodic microbialite resurgences after mass extinctions are used as indicators for relative environmental recovery. Microbialites are also targeted by astrobiology studies for their ability to form in harsh environments and their capacity to preserve specific biosignatures. Yet, despite the broad scientific significance of microbialites, many authors note a lack of consistent terminology, while others address the challenges of differentiating microbialites from numerous abiogenic sedimentary deposits.
This chapter aims to provide the reader with a basic working guide for field and laboratory descriptions of microbialites, and to synthesize the various terminologies present in the literature. As a guide, this contribution is meant to complement the various review articles that focus more specifically on the fossil record of microbialites.
... Впервые термин «министроматолиты» был предложен Эдхорном и Андерсеном в 1977 году для столбчато-пластовых строматолитов, высота которых -от нескольких миллиметров до более сантиметра [Edhorn, Anderson, 1977]. Хофманн и Джексон через 10 лет используют данный термин для обозначения неветвящихся пальцевидных столбчатых строматолитов с поперечным диаметром от 0,2 до 20 мм [Hofmann, Jackson, 1987]. В текущем исследовании принимается, что один из этих критериев -диаметр или высота построек -обычно не превышает 1 см. ...
The main subdivisions among the most widespread column types in the Paleoproterozoic complex of Karelian ministromatolites were identified based on their characteristic morphological features. That helps to refine the classification of the class Ministromatophyceae (ministromatolites) and systematize the available material. Individual petrographic thin sections with ministromatolites were analyzed by the Raman scattering method. The results show the rock composition and the morphology details of clotted material. Morphologically, structures found in the clotted material can be compared to modern cyanobacteria, suggesting the structures are biogenic. The spectra of carbonaceous material in their composition support this point of view.
... This type of deposition has occurred since the Proterozoic and forms reefs and carbonate sediments, including stromatolites, thrombolites, dendrites and oncolites. Many case studies are available in the literature (Golubic 1973(Golubic , 1976Zhang and Hofmann 1982;Hofmann 1987;Zhuravlev and Wood 1996;Feldmann Edited Knoll and Semikhatov 1998;Myrow 2002;Riding 1991Riding , 2000Riding and Liang 2005;Rowland and Shapiro 2002;Kruse and Zhuravlev 2008;Hicks and Rowland 2009;Adachi et al. 2011). The Lower Ordovician marine carbonate deposits in the Yangtze Plate developed continuously, and the associated microbialites and reefs are widely distributed (Zhu et al. 1990(Zhu et al. , 1995(Zhu et al. , 2006Mei and Lu 1991;Li and Wu 2001;Yang 2018;Xiao et al. 1993Xiao et al. , 1995Xiao et al. , 2004Xiao et al. , 2011Adachi et al. 2011;Wang et al. 2012). ...
This study is the first systematic assessment of the Lower Ordovician microbial carbonates in Songzi, Hubei Province, China. This paper divides the microbial carbonates into two types according to growth patterns, namely nongranular and granular. The nongranular types include stromatolites, thrombolites, dendrolites, leiolites and laminites; the granular types are mainly oncolites and may include a small amount of microbiogenic oolite. According to their geometric features, the stromatolites can be divided into four types: stratiform, wavy, columnar and domal. Additionally, dipyramidal columnar stromatolites are identified for the first time and represent a new type of columnar stromatolite. The thrombolites are divided into three types: speckled, reticulated and banded. The grazing gastropod Ecculiomphalus and traces of bioturbation are observed in the speckled and reticulated thrombolites. This paper considers these two kinds of thrombolites to represent bioturbated thrombolites. These findings not only fill gaps in the field of domestic Ordovician bioturbated thrombolites but also provide new information for the study of thrombolites. Based on the analysis of the sedimentary characteristics of microbialites, the depositional environments of the various types of microbialites are described, and the distribution patterns of their depositional environments are summarized. The relationship between the development of microbialites and the evolution and radiation of metazoans during the Early to Middle Ordovician is discussed. Consistent with the correspondence between the stepwise and rapid radiation of metazoans and the abrupt reduction in the number of microbialites between the late Early Ordovician and the early Middle Ordovician, fossils of benthonic grazing gastropods (Ecculiomphalus) were found in the stromatolites and thrombolite of the study area. It is believed that the gradual reduction in microbialites was related to the rapid increase in the abundance of metazoans. Grazers not only grazed on the microorganisms that formed stromatolites, resulting in a continuous reduction in the number of stromatolites, but also disrupted the growth state of the stromatolites, resulting in the formation of unique bioturbated thrombolites in the study area. Hydrocarbon potential analysis shows that the microbialites in the Nanjinguan Formation represent better source rocks than those in the other formations.
... The formation of silico-carbonate "abiotic" nodules by interactions between sediments and microorganisms lead to the formation of the accretion laminae observed in these nodules and in the stromatolites, from the Proterozoic [22][23][24] to modern analogues [25]; and microbially mediated calcification can be traced back for at least the Proterozoic [26][27][28][29][30]. Additionally, these "abiotic" concretions typically develop from a central point and present often a zonal concentric structure; they may contain concentric and lateral accretion laminae [31], characterized by variations in the isotopic and geochemical compositions of the different growth zones [32]. Other carbonate concretions are growing from inert clumps of organic matter, typically in fine sediments, probably as a result of the diffusion of carbon dioxide during the decomposition of organic matter through microbial processes [33][34][35]. ...
A colony of silico-carbonate Akouemma nodules found in Akou River sedimentary formations of the Palaeoproterozoic Okondja Basin consists of two groups, spheroidal (ovoid) nodules and elongated nodules. These nodules, which consist of two hemispheres separated by a median disc, are composed essentially of micro-quartz associated with calcite of extra-polymeric substance (EPS) type, clay minerals, organic carbon and oxides and sulphides of iron. They contain tubular microfossils, pluricellular clusters, microorganisms and vesicles, and have undergone considerable deformation by mutual lateral compression in tabular beds. They were interpreted as biogenic nodules hosting microorganisms. We provide the following additional supporting evidence: Akouemma nodules exhibit internal fibro-radial fabrics initially composed of fibres and carbon particles; the initially well-organized structures are decaying and are in particles and fragments that are dispersed in the undeformed siliceous mass. These internal fabrics are strongly highlighted by Al- K- (Ti)-rich clay minerals that are often in close association with fibres and carbon particles. They had likely a vegetative reproduction by duplication. We infer that the Akouemma nodules are macrofossils of sessile soft-plastic body organisms. These macrofossils, recently dated at 2.2 Ga, are designated “Akouemma hemisphaeria” and bring a new vision to the “large colonial organisms” found in the Franceville Basin.
... Laminae are made of radiating cements which may contain detrital sediments as well. This is the model detailed in Hofmann and Jackson (1987) and Grotzinger and Knoll (1999) and references therein. ...
... Remarks-Biogenecity of the Asperia and synonymous forms are critically debated. Hofmann and Jackson (1987) considered these forms as abiogenic whereas Grey, (1984) held these structures as biogenic with substantiating evidences. , , Riding and Sharma (1998) 1978 Asperia aspera Semikhatov, p. 120 1984Yelma digitata Grey 1984, p. 50-52 1985 Asperia ashburtonia Grey, p.101-102 1994a Asperia digitata Grey, p. 196, comb. ...
... The genesis of stromatolites has also been debated at several levels and most of the stromatolite researchers agree with Hoffman (1973) that "something that haunts geologists working on ancient stromatolites is the thought that they might not be biogenic at all." In many cases, biogenic origin has been established (Grey, 1984;Sharma & Shukla, 1998;Riding & Sharma, 1998;Batchelor et al., 2004Batchelor et al., , 2005, while, in some other cases no proof could be found (Hofmann & Jackson, 1987;Grotzinger & Rothman, 1996;Sharma & Sergeev, 2004). In order to classify stromatolitic structures, researchers have proposed a number of schemes. ...
Indian subcontinent with extensive Archaean and Proterozoic sedimentary successions has number of stromatolites occurrences which offers avenues of stromatolites studies. The present paper traces the efforts, strengths and gaps in stromatolites studies in India and summarizes significant Indian contributions made in the past in the country and briefly mentions the global advancements made in this field. The overview covers the period of active research from 1908-2005.
... This fibrous layer of the tussocky microfabric could have precipitated like the aragonite cement of the salinas on the mat surfaces or biologically mediated mineralization of the surface. The columnar ministromatolites are mostly confined to the supratidal or peritidal depositional environment where growth of such fabric is very common (Hofmann & Jackson, 1987; Grotzinger, 1989 Grotzinger, , 1993). But in such environments excessive growth of dense/dark pigment of microbes has also been noted (Knoll, 1989; Kah & Knoll, 1996) and is attributed to long exposures to air, shallow water or prolonged UV radiation or insolation to offset the increased environmental stress (Golubic & Hofmann, 1976 ). ...
... Remarks-Biogenecity of the Asperia and synonymous forms are critically debated. Hofmann and Jackson (1987) considered these forms as abiogenic whereas Grey, (1984) held these structures as biogenic with substantiating evidences. , , Riding and Sharma (1998) 1978 Asperia aspera Semikhatov, p. 120 1984Yelma digitata Grey 1984, p. 50-52 1985 Asperia ashburtonia Grey, p.101-102 1994a Asperia digitata Grey, p. 196, comb. ...
... Microdigitate stromatolites (Hofmann & Jackson, 1987) are observed over an 8-cm-thick unit, situated between the oncolites and the horizontally branching stromatolites in Transect 12. The microdigitate stromatolites are very tightly packed, are approximately 5 cm high and have columns typically only 3-4 mm wide that branch only at the top (Fig. 9D). ...
... Stromatolites are conspicuous features in many Archean and Proterozoic carbonate strata, but the relationships between microscopic processes that build individual laminae and the preservable macroscopic shapes of stromatolites are not well understood. Evidence that microbial growth, movement and orientation influenced the formation of stromatolite laminae is particularly elusive in progressively older stromatolites owing to the abundance of precipitated cements and recrystallization (e.g., Hofmann & Jackson, 1987; Kah & Knoll, 1996; Bartley et al., 2000; Pope & Grotzinger, 2000). Small conical stromatolites and tufts as old as 3.0 billion years stand out as a biologically influenced end-member of precipitated stromatolites with modern , distinctly biogenic analogs that grow only in the presence of cyanobacteria (Fig. 1, Walter et al., 1972 Walter et al., , 1976 Grey, 1980; Beukes & Lowe, 1989; Buick, 1992; Jones et al., 2002; Bosak et al., 2009; Petroff et al., 2010). ...
... Laminae are made of radiating cements which may contain detrital sediments as well. This is the model detailed in Hofmann and Jackson (1987) and Grotzinger and Knoll (1999) and references therein. ...
... Recent work has demonstrated the importance of the 'precipitating model' in forming stromatolite laminae. Although cited as having largely occurred in the Neoarchean and Paleoproterozoic, precipitate stromatolites are found throughout the rock record (Hofmann and Jackson, 1987;Knoll and Semikhatov, 1998). Arguments exist as to whether the precipitation is driven by abiotic or biotic processes (Grotzinger and Knoll, 1999). ...
Stromatolites are trace fossils that record the interaction between microbial communities and sediments. Macroscopically, the shape of the stromatolite may represent stronger environmental controls. Study of the scalar attributes can yield insight into microbialethology, and foster biostratigraphic and facies analysis over the past 3500 million years. Stromatolites have largely been treated as structures analogous to colonial organisms or eukaryotic algae, even though only a fraction of fossil occurrences contains an organic component and none are made by a singular colonial animal orindividual plant. Stromatolites and other microbialites are primarily composed of mechanical sediments and cements produced through the activities of a microscopic consortium. The internal fabric and macroscale attributes of stromatolites have been used for biostratigraphic correlation and facies analysis, even though the taxonomic affinities of the microbial community are usually unknown. Indeed, it is quite probable that a particular microbial ecosystem may be responsible for more than one type of microbialite, and several different microbial consortia may construct a unique microbialite.
... Baker et al. (1993), which are related to the cumulative growth of calcite as a consequence of alternate warm (enhanced growth) and cold weather (limited growth) in the secondary carbonate growth phases. According to Hoffmann and Jackson (1987), the dark layers reflect a higher production of pigment by microorganisms during periods of environmental stress. Casanova et al. (1988) have suggested that the stromatolitic Quaternary formations are made by bacteria, which have formed the building structure . ...
Weathering and mineralogical processes observed in a marble quarry in Turkey are compared with similar processes occurring on monument surfaces. Patina formations (microstromatolitic, microlaminated, monolayered) as well as destructive processes (mainly biopitting and bioerosion) are associated with microbial colonisation of the rock surfaces and one influenced by microclimatic conditions. Patina stratification is independent of substrate rock, but is affected by the position and orientation of rock surfaces. The different layers formed by mineralisation processes may reflect the seasonality of climatic events and the consequent colonisation. Bio-deteriorative processes take place mainly when the climatic conditions cause the organisms to live below the surface.
... In sediment sealing, a layer of loose grains are, first, deposited on the seafloor in depressions and, second, microbes spread laterally over the sediments to form a sealing cap or mat [Bartley et al., 2000;Shapiro, 2005]. In surficial crystal precipitation, the microbes decompose organic matter which changes the local chemistry and promotes the precipitation of carbonate crystals on top of, or adjacent to, the microbial mats [Hofmann and Jackson, 1987]. After a covering layer of sediments accumulates, the microbes again spread over the loose grains. ...
Paleoproterozioc (ca. 1.9 Ga) stromatolites from the Biwabik Iron-Formation (Minnesota, United States) contain fossil forms which in the literature have been attributed to ancient microbes including iron-oxidising bacteria and cyanobacteria. To search for valence state fossils, we measured Fe3+/SigmaFe (SigmaFe = Fe2+ + Fe3+) transverse to the laminae of a Biwabik, probably biogenic stromatolite and compared the results with a scan across the enclosing, likely abiotic sedimentary rock (or interstromatolite fill). To obtain Fe3+/SigmaFe and information about the site symmetry and crystal field strength, we used L3 (2p3/2 -> 3d) soft X-ray absorption spectroscopy and interpreted the measurements using our calculated spectra. We found that Fe3+/SigmaFe is approximately constant at 0.3 within the stromatolite, increases steeply to around 0.6 in the region of the stromatolite-fill boundary, and then reduces significantly in the interstromatolite fill. The crystal field strength for octahedral Fe3+ increased and became more irregular as the scan moved from the stromatolite into the fill. Our results tentatively suggest that a combination of ancient biological and later diagenetic processes can produce steep gradients in Fe3+/SigmaFe and alterations in the crystal field strength across a probable abiotic-biotic boundary. To describe the L3 absorption spectra in the stromatolite-fill region, it was necessary to include a significant Fe3+ tetrahedral component, which suggests the presence of magnetite. At other positions, fits using only octahedral Fe2+ and Fe3+ theoretical curves satisfactorily reproduce the spectra. The search for a possible new type of spatial biosignature in the valence state record for ancient stromatolites might help differentiate between the biogenic stromatolites and abiogenic stromatolite-like structures and could even be relevant to the search for fossil evidence of life in extraterrestrial rocks.
... Remarks-Biogenecity of the Asperia and synonymous forms are critically debated. Hofmann and Jackson (1987) considered these forms as abiogenic whereas Grey, (1984) held these structures as biogenic with substantiating evidences. , , Riding and Sharma (1998) 1978 Asperia aspera Semikhatov, p. 120 1984Yelma digitata Grey 1984, p. 50-52 1985 Asperia ashburtonia Grey, p.101-102 1994a Asperia digitata Grey, p. 196, comb. ...
Systematics of the stromatolites of the Proterozoic Kaladgi Basin is attempted. The main purpose is to document the diversity and distribution of the various stromatolite forms occurring in the Bagalkot Group of the Kaladgi Supergroup. An assemblage of six taxa is recognized from the Bagalkot Group. The forms Asperia digitata (=Yelma digitata), Ephyaltes edingunnensis, Eucapsiphora leakensis, Kussoidella karalundiensis , Pilbaria deverella and Yandilla meekatharrensis are described. These forms are not recorded from any other Proterozoic Sequence of India of the Palaeoproterozoic age. Similar forms are recorded from Africa, Australia, Canada and China. Asperia digitata, a digitate stromatolite, is known from the Proterozoic Sequence of the Palaeoproterozoic age in other parts of the world. Poorly
constrained age of the Bagalkot Group of the Kaladgi Supergroup can be ascertained on the basis of t he reported assemblage as Late Palaeoproterozoic to Early Mesoproterozoic (Orosirian-Statherian to Calymmian Period).
... It seems that this dark layer is syperficially comparable to the modern calcified mats of the cyanobacteria Rivularia, in which elongate calcite crystals are parallel to the vertically or radially arranged filaments. Another interpretation is that the fibrous fabric is entirely chemogenic, resuiting from radial growth of a fibrous mineral , most likely aragonite or calcite, which was subsequently replaced by silica (Hofmann and Jackson, 1987). Therefore, the author hesitates to suggest that this fabric may be attributed to tidal cycles in sediment supply or algal growth. ...
The mat-ministromatolite bioherms from the Proterozoic Wumishan Formation exhibit three orders of cyclic growth patterns. The growth cycle can be interpreted in terms of daily, monthly and seasonal periodicities. Mat-ministromatolite bioherms used as palaeontological clocks are limited to a short (daily and monthly) growth cycle. Based on the study of these stromatolites, it is estimated that there may have been about 40 to 49 palaeo-days per palaeo-month of 1200 Ma age.
The Paleoproterozoic Belcher Group (ca. 2.0 to 1.83 Ga) occurs on the remote Belcher Islands of Hudson Bay in Nunavut, Canada. It includes nearly nine kilometres of well-preserved siliciclastic and carbonate sedimentary rocks, deposited initially in a marginal to shallow marine setting representing one of the first true continental shelf environments on the proto-Canadian Shield. A wide variety of depositional facies exists within the Belcher Group, and it is particularly well known for its spectacular stromatolites in dolostone. In addition to these macroscopic features, two of its formations (Kasegalik and McLeary) contain intact microfossils of Eoentophysalis belcherensis, the oldest known occurrence of cyanobacteria in the geological record. The uppermost part of the Belcher Group contains sedimentary rocks of very different character that represent a younger foreland basin that developed in response to accretionary and collisional processes of the Trans-Hudson orogen. These younger formations (Omarolluk and Loaf) consist of a thick sequence of turbidites, overlain by arkose and other immature clastic sedimentary rocks. A defining characteristic of the Omarolluk Formation is the presence of calcareous concretions. The Omarolluk Formation shares attributes with “omars”, which are glacially transported clasts that occur both locally and further afield throughout parts of Canada and the northern United States and have helped characterize Pleistocene ice-flow trends across the continent. The Belcher Group also includes two formations dominated by spectacular mafic volcanic rocks. The earlier episode, represented by the Eskimo Formation, reflects eruption of largely subaerial volcanic flows interpreted to represent flood basalt associated with the rifting of Archean basement during the establishment of the continental shelf. A later volcanic episode (the Flaherty Formation) is dominated by submarine pillowed basalt flows and has been assigned to varied tectonic settings, including volcanic arcs related to subduction and oceanic plateaus related to mantle plume activity and renewed rifting along the continental margin. This later volcanism marks the transition from shelf to foreland basin. Mafic sills and related intrusions (Haig intrusions) occur in the middle and lower part of the Belcher Group. Thermal and chemical interactions between mafic magma and calcareous shale generated unusual rocks that are well known in Nunavut as high-quality artisanal carving stone. The Belcher Group also contains Superior-type iron formations that have attracted past exploration interest. The Belcher Group is a unique geological entity defined by its wide variety of rock types, its superb exposures, and its potential to illustrate many important geological processes in a formative time in Earth’s history. It is also a unique microfossil paleontological resource, and its deposition brackets a crucial and much-debated interval of Precambrian atmospheric and oceanic evolution. It represents an important scientific resource in the context of understanding such changes. This general review paper highlights its most important features, discusses its potential for future research and contributes to wider discussions about its possible future role as a protected area within Nunavut.
After the Elatina glaciation of Snowball Earth, at least four distinct glacial advances and sea-level retreats punctuated Ediacaran time: Gaskiers glaciation (580 Ma), Fauquier glaciation (571 Ma), Bou-Azzer glaciation (566 Ma) and Hankalchough glaciation (551 Ma). Tillites or diamictites are commonly controversial, but periglacial paleosols with distinctive physical structure and degree of chemical weathering offer supporting evidence of glaciation and sea-level change useful for stratigraphic correlation. This paper reviews glacial advances of the Ediacaran stratotype and other sequences, and also reveals the value of paleosols and chemical index of alteration to understand the upper Squantum and Brookline members of the Roxbury Conglomerate near Boston, Massachusetts. The Boston Bay ice wedges are periglacial paleosols, and evidence of maritime glacial climate like that of modern coastal Greenland and Arctic Canada. Simple discoidal vendobiont fossils (Aspidella terranovica) in the Dorchester Member of the Roxbury Conglomerate and in the Cambridge Argillite are in heterolithic shale–siltstone facies that are interpreted as intertidal to shallow marine environments. Local marine transgressions and other paleosols showing significant chemical weathering represent temperate interglacial paleoclimates. Short glacial advances affecting climate and sea-level enable subdivision of the Ediacaran Period.
• KEY POINTS
• Four distinct glacial advances and sea-level retreats punctuated Ediacaran time: Gaskiers (580 Ma), Fauquier (571 Ma), Bou-Azzer (566 Ma), Hankalchough (551 Ma).
• Paleosols with distinctive structures such as ice wedges were periglacial.
• Squantum Member diamictites near Boston, Massachusetts are Gaskiers age.
Abiotic, Bioinduced and Biocontrolled carbonates are process-based sediment categories. They successively reflect increasing levels of biotic control over carbonate precipitation from aqueous solutions, are often closely linked to depositional environment, and change with time. Hybrid Carbonates are intimate in situ combinations of two or more of these categories. Hybrid Carbonates are widespread and diverse in the marine geological record and reflect large-scale changes in carbonate precipitation through time. They also occur in fluvial and lacustrine carbonates, marine and non-marine reef systems, and methane seep deposits. Plots of Hybrid Carbonate composition in time and space reveal complex ‘backtracking’ and ‘looping’ patterns that reflect changes in environmental conditions and biological processes of carbonate production. Recognition of hybridity emphasizes the importance of distinguishing abiotic and bioinduced precipitates. Until they were diversified by Skeletal Carbonates in the late Proterozoic, Precambrian Hybrid Carbonates were Abiotic-Bioinduced combinations. During the Phanerozoic Hybrid Carbonates were conspicuous during periods of overlap or transition between intervals of Microbial and Skeletal carbonate abundance. Microbial-Skeletal Dual Hybrids are common during the Cambrian-mid Ordovician, Late Devonian-Mississippian, and Late Jurassic-Early Cretaceous. Abiotic-Microbial-Skeletal Triple Hybrids were common from Late Pennsylvanian to mid-Triassic. Shallow marine Hybrid Carbonates declined in abundance after the mid-Cretaceous, although Late Cenozoic reefs contain some striking examples of Microbial-Skeletal Hybrids. Recognition of Hybrid Carbonates draws attention to fundamental processes underlying carbonate sedimentation, and their patterns and drivers of change in time and space.
The Labrador Trough in northern Québec and Labrador is a 900 km-long Rhyacian–Orosirian orogenic belt containing mixed sedimentary-volcanic successions. Despite having been studied intensively since the 1940s, relatively few chemostratigraphic studies have been conducted. To improve our understanding of the Labrador Trough in the context of Earth history, and better constrain the local record of the Lomagundi-Jatuli carbon isotope excursion, high-resolution sampling and carbon isotope analyses of the Le Fer and Denault formations were conducted. Carbonate carbon isotopes (δ<sup>13</sup>C) in the Le Fer Formation record a large range in values from -4.4 to +6.9‰. This large range is likely attributable to a combination of post-depositional alteration and variable abundance of authigenic carbonate minerals; elemental ratios suggest that the most <sup>13</sup>C-enriched samples reflect the composition of the water column at the time of deposition. Cumulatively, these data suggest that the Lomagundi-Jatuli Excursion was ongoing during deposition of the Le Fer Formation, approximately 2 km higher in the stratigraphy than previously recognised. However, the possibility of a post-Lomagundi-Jatuli Excursion carbon isotope event cannot conclusively be ruled out. The directly overlying Denault Formation records a range in δ<sup>13</sup>C values, from -0.5 to +4.3‰, suggesting that it was deposited after the conclusion of the Lomagundi-Jatuli Excursion and that the contact between the Le Fer and Denault formations occurred sometime during the transition out of the Lomagundi-Jatuli Excursion, ca. 2106 to 2057 Ma.
A laminated deposit is a record of cyclic changes of physical, geochemical, and microbiological conditions. The laminated pattern is often quite regular. In lacustrine verves, regular seasonal changes in weather conditions accumulate a characteristic alternation of siliciclastic muddy particles and authigenic minerals. Based on patient search of the lamina counting and ¹⁴C dating, time series of geochemical and paleontological proxies in the lacustrine verves have decoded an excellent record of ancient climates (e.g., Nakagawa et al. 2003). Some stalagmites are also laminated annually, associated with seasonal change in physical and geochemical properties of dripwater. Distinct patterns in the drip rate, the saturation states, and fulvic acid content between summer and winter or between wet and dry seasons leave annual change in carbonate crystal fabrics and fluorescence (Shopov et al. 1994; Baker et al. 1999). Because U-Th isotopes support accurate dating, stalagmites have been used for paleoclimatic studies (e.g., Fairchild and Baker 2012). Another example of annual lamination is observed in tufas, non-hydrothermal carbonate precipitates developed in streams and rivers in limestone area. Origin of the lamination in tufas is somehow similar with that of the stalagmite lamination. However, tufas have one- or two-order wider lamination (or growth rate) than stalagmite. Because of the thicker lamination, tufas are available for higher-resolution analysis of the past climates (e.g., Kano et al. 2004).
Pleistocene fibrous aragonite fabrics, including crusts and spherules, occur in the Danakil Depression (Afar, Ethiopia) following the deposition of two distinctive Middle and Late Pleistocene coralgal reef units and pre‐dating the precipitation of evaporites. Crusts on top of the oldest reef units (Marine Isotope Stage 7) cover and fill cavities within a red algal framework. The younger aragonite crusts directly cover coralgal bioherms (Marine Isotope Stage 5) and associated deposits. Their stratigraphic position between marine and evaporitic deposits, and their association to euryhaline molluscs, suggest that the crusts and spherules formed in restricted semi‐enclosed conditions. The availability of hard substrate controls crust formation with crusts more often found on steep palaeo‐slopes, from sea‐level up to at least 80 m depth, while spherules mainly occur associated to mobile substrate. Crusts reach up to 30 cm in thickness and can be microdigitate, columnar (branching and non‐branching) or non‐columnar, with laminated and non‐laminated fabrics. Two different lamination types are found within the crystalline fabrics: (i) isopachous lamination; and (ii) irregular lamination. These two types of lamination can be distinguished by the organization of the aragonite fibres, as well as the lateral continuity of the laminae. Scanning electron microscopy with energy dispersive X‐ray spectroscopy analyses on well‐preserved samples revealed the presence of Mg‐silicate laminae intercalated with fibrous aragonite, as well as Mg‐silicate aggregates closely associated to the fibrous aragonite crusts and spherules. The variety of observed fabrics results from a continuum of abiotic and microbial processes and, thus, reflects the tight interaction between microbially mediated and abiotic mineralization mechanisms. These are the youngest known isopachous laminated, digitate and columnar branching fibrous crusts associated with a transition from marine to evaporitic conditions. Understanding the context of formation of these deposits in Afar can help to better interpret the depositional environment of the widespread Precambrian sea‐floor precipitates. This article is protected by copyright. All rights reserved.
Ministromatolites, the small-sized columnar organogenic structures with columns ≤20 mm across, appeared in geological records at about 2.9 Ga to be rather abundant 2.8-2.5 Ga ago. Taxonomic composition of their Archean assemblages is studied fragmentarily: only four form genera and six form species have been described, including two genera and one species, which transit into the Lower Proterozoic. The representative Early Proterozoic ministromatolites ranging in age from 2.3 to 1.65 Ga include 41 form species of 16 form genera, which are attributed to five supergeneric groupings based on principal morphological features. The succeeding ministromatolite assemblage of the Early Riphean-initial Middle Riphean (1.65-1.2 Ga) consists of 62 form species representing 15 form genera, of which only three genera and one species are in relation with the Early Proterozoic ministromatolites. In general, the Riphean ministromatolites are less diverse than the Early Proterozoic taxa, because one pre-Riphean supergeneric taxon of a complex structure became extinct, forms with cylindrical vertical columns turned out to be dominant, and extended laminae of short-column buildups appeared. Simultaneously, the Riphean ministromatolites show tendency toward diminishing in diameter and height of columns interconnected via frequent bridges. In the second half of the Middle Riphean ministromatolites disappeared to be found again in the Lower Paleozoic. Morphological trends typical of Proterozoic ministromatolites have no continuation in their Early Paleozoic assemblages and differ from morphological changes in concurrent common-sized columnar stromatolites. It seems reasonable therefore to think that stromatolites of different size and age are products of life activity of different associations of microorganisms.
The Vempalle and the Tadpatri formations of the Cuddapah Supergroup of India are well known for their stromatolites. Absolute dates of the rock containing these stromatolites range between < 1800 Ma to > 1550 Ma. The stromatolites have been grouped into three assemblage zones. The characteristic forms of these three assemblages are (1) Pilbaria-Asperia, (2) Gymnosolen-Tibia and (3) Conophyton-Collumnocollenia in a younging sequence at different stratigraphic levels of the Cuddapah Supergroup. The assemblages consist of some typical Palaeoproterozoic stromatolites, viz., Asperia, Microstylus, Alcheringa, Paraboxonia and Tibia. The morphological features, microstructure and microfabric of these assemblages are comparable with Chinese forms and are characteristic of the Palaeoproterozoic age. Banded and streaky types dominate the microstructures and microfabrics are characterized by the granular, vermiform, pelloidal and tussocky types, and are similar to those recorded in Chinese forms. These microstructure and microfabrics are described and their genesis have been discussed. Comparison of the microstructure and microfabric with microstructure and microfabric of Chinese Palaeoproterozoic and younger stromatolite forms suggest that they may be identical to Chinese forms but these could not exclusively be considered as characteristic of Palaeoproterozic stromatolite assemblage. On the contrary morphological forms of the stromatolites are more reliable from the biostratigraphic point of view and are not frequently repeated in the earth history.
The sedimentary record reveals first-order changes in the locus of carbonate precipitation through time, documented in the decreasing abundance of carbonate precipitation on the seafloor. This pattern is most clearly recorded by the occurrence of seafloor carbonate crystal fans (bladed aragonite pseudomorphs neomorphosed to calcite or dolomite), which have a distinct temporal distribution, ubiquitous in Archean carbonate platforms, but declining through Proterozoic time and extremely rare in Phanerozoic basins. To understand better the potential influences on this pattern, we built a mathematical framework detailing the effects of organic matter delivery and microbial respiratory metabolisms on the carbonate chemistry of shallow sediments. Two nonunique end-member solutions emerge in which seafloor precipitation is favorable: enhanced anaerobic respiration of organic matter, and low organic matter delivery to the sediment-water interface. This analysis suggests that not all crystal fans reflect a unique set of circumstances; rather there may have been several different geobiological and sedimentary mechanisms that led to their deposition. We then applied this logical framework to better understand the petrogenesis of two distinct crystal fan occurrences the Paleoproterozoic Beechey Formation, Northwest Territories, Canada, and the middle Ediacaran Rainstorm Member of the Johnnie Formation, Basin and Range, United States using a combination of high-resolution petrography, micro X-ray fluorescence and wavelength dispersive spectroscopy, C isotopes, and sedimentary context to provide information on geobiological processes occurring at the sediment-water interface. Interestingly, both of these Proterozoic examples are associated with iron-rich secondary mineral assemblages, have elevated trace metal signatures, and sit within maximum flooding intervals, highlighting key commonalities in synsedimentary geobiological processes that led to seafloor carbonate precipitation.
: The Mesoproterozoic Wumishan Formation at the Jixian section in Tianjin is a set of more than 3000-m-thick stromatolitic carbonate succession. In this succession, several lithofacies units, that is, the subtidal stromatolitic biostrome, the thrombolitic bioherm, tidal-flat micritic dolomite and lagoon dolomitic shale, make up many meter-scale cycles of the peritidal carbonate type that have been nominated as the Wumishan cycles. Importantly, many microdigital stromatolites make up the stromatolitic biostrome unit of the Wumishan cycles in the lower part of the Wumishan Formation. These microdigital stromatolites have been grouped as a stromatolitic assemblage by paleontologists, that is, “Pseudogymnosolen mopanyuensis-Scuphus-Yangzhuang columnaris” assemblage. These microdigital stromatolites had also been interpreted as the aragonite (tufa) sea-floor precipitates by sedimentologists, and has further been thought as the special products of the transitional period from the sea-floor aragonite precipitates of the Archean to the clastic and muddy carbonates of the Neoproterozoic. Although there are some restrictions for the stratigraphic meaning of the concept of the stromatolitic assemblage, detailed studies on classification by paleontologists provide an important clue to understand the sedimentological meaning of the microdigital stromatolites. Furthermore, an important and obvious horizon for the end of the microdigital stromatolites was recorded in the Mesoproterozoic Wumishan Formation at the Jixian section, which provides useful information to understand the stromatolite decline occurred at c.1250 Ma and the evolving carbonate world of the Precambrian.
When and how life on Earth started is still an open question. Biochemical fingerprints stored in the ancient rock record indicate the presence of traces of life back to some of the oldest sedimentary rocks on the planet. The Earth has thus harboured life throughout most of its geologic history, and biological processes have contributed significantly to shaping the environmental conditions on the surface of the planet. Tracking the nature of ancient life using morphological, mineralogical, chemical and isotopic proxies in the rock record on Earth needs, however, to surmount a number of obstacles. Most important are the effects of post-depositional alteration of the sedimentary host rocks due to exposure to metamorphic temperatures and pressures and metasomatism during the protracted time before their present exposure. Diagenetic and metamorphic overprints may have resulted in recrystallisation of the original mineral assemblages and deformation of the original textural features in the sedimentary rocks, in many cases blurring the biologic signatures and jeopardizing the reliable interpretation of the nature of the lifeform.
A large travertine mound at Pancuran Pitu, Central Java, Indonesia, displays various types of lamination reflecting different hydrological conditions. To understand the geomicrobiological processes of the laminated travertines, we investigated the mound's hydrology, water chemistry, texture, microbial composition, and volume percentage of carbonate mineral (VPC). We identified four types of travertines: dense travertine (80% VPC, flow rate ~ 200 cm/s), lithified microbial travertine (60% VPC, flow rate ~ 70 cm/s), fragile microbial travertine (30% VPC, flow rate ~ 10 cm/s), and poorly lithified microbial mat (< 10% VPC, flow rate < 5 cm/s). The first two types exhibited regular lamination at sub-mm intervals that was associated with the distribution of cyanobacteria and organic substances. The dense travertine consisted of alternation of crystalline and banded layers at ~ 160-μm intervals, which resembles the daily lamination of an aragonite travertine from southwest Japan. The banded layer formed during the day, exhibited porosity, and contained organic substances. Lamination in the lithified microbial travertine was likely formed by the daily growth cycles of filamentous cyanobacteria. The daytime surface of this travertine appeared to be sub-mm-thick cyanobacterial biofilm with spheroidal aggregates of aragonite, which covered a crystalline layer consisting of radially expanded needle crystals. The crystalline layer was likely formed during the night when the cyanobacterial growth was interrupted. These regularly laminated travertines fabrics appeared to be similar to certain Precambrian stromatolites. Regularity of the lamination was less in the other two microbe-rich types at low-flow sites. The majority of the aragonite occurred as spherical aggregates within the microbial mat, although thin (10–50 μm) crystal layers in the fragile microbial travertine may indicate daily intervals. As represented in the relationship among the VPC, flow rate, and precipitation rate of aragonite, the travertines were more consolidated with increasing hydrodynamic energy because of the activation of carbonate precipitation and the inhibition of thick cyanobacterial biofilm development.
Through early lithification, cyanobacterial mats produced vast amounts of CaCO3 on Precambrian carbonate platforms (before 540 Myr ago). The superposition of lithified cyanobacterial mats forms internally laminated, macroscopic structures known as stromatolites. Similar structures can be important constituents of Phanerozoic carbonate platforms (540 Myr to present). Early lithification in modern marine cyanobacterial mats is thought to be driven by a metabolically-induced increase of the CaCO3 saturation state (ΩCaCO3ΩCaCO3) in the mat. However, it is uncertain which microbial processes produce the ΩCaCO3ΩCaCO3 increase and to which extent similar ΩCaCO3ΩCaCO3 shifts were possible in Precambrian oceans whose chemistry differed from that of the modern ocean. I developed a numerical model that calculates ΩCaCO3ΩCaCO3 in cyanobacterial mats and used it to tackle these questions. The model is first applied to simulate ΩCaCO3ΩCaCO3 in modern calcifying cyanobacterial mats forming at Highborne Cay (Bahamas); it shows that while cyanobacterial photosynthesis increases ΩCaCO3ΩCaCO3 considerably, sulphate reduction has a small and opposite effect on mat ΩCaCO3ΩCaCO3 because it is coupled to H2S oxidation with O2 which produces acidity. Numerical experiments show that the magnitude of the ΩCaCO3ΩCaCO3 increase is proportional to DIC in DIC-limited waters (DIC < 3–10 mM), is proportional to pH when ambient water DIC is not limiting and always proportional to the concentration of Ca2+ in ambient waters. With oceanic Ca2+ concentrations greater than a few millimolar, an appreciable increase in ΩCaCO3ΩCaCO3 occurs in mats under a wide range of environmental conditions, including those supposed to exist in the oceans of the past 2.8 Gyr. The likely lithological expression is the formation of the microsparitic stromatolite microtexture—indicative of CaCO3 precipitation within the mats under the control of microbial activity—which is found in carbonate rocks spanning from the Precambrian to recent. The model highlights the potential for an increase in the magnitude of the ΩCaCO3ΩCaCO3 shift in cyanobacterial mats throughout Earth’s history produced by a decrease in salinity and temperature of the ocean, a decrease in atmospheric pCO2 and an increase in solar irradiance. Such a trend would explain how the formation of the microsparitic stromatolite microtexture was possible as the ΩCaCO3ΩCaCO3 of the ocean decreased from the Paleoproterozoic to the Phanerozoic.
Early diagenetic chert nodules and beds in the upper Mesoproterozoic Angmaat (formerly Society Cliffs) Formation, Baffin and Bylot islands, preserve microfossils and primary petrofabrics that record microbial mat deposition and lithification across a range of peritidal carbonate environments. Five distinct microfossil assemblages document the distribution of mat-building and mat-dwelling populations across a gradient from restricted, frequently exposed flats to more persistently subaqueous environments. Mats built primarily by thin filamentous or coccoidal cyanobacteria give way to a series of more robust forms that show increasing assemblage diversity with decreasing evidence of subaerial exposure. Distinct fabric elements are associated with each microbial assemblage, and aspects of these petrofabrics are recognizably preserved within unsilicified carbonate in the same beds. These include some features that are distinctly geologic in nature (e.g., seafloor cements) and others that reflect microbial growth and decomposition (e.g., tufted microbialites). A particularly distinctive, micronodular fabric is here interpreted as carbonate infilling of primary voids within microbial mat structures. Such structures mark the co-occurrence of cyanobacterial photosynthesis that produced oxygen gas, filamentous mat builders that imparted the coherence necessary to trap gas bubbles, elevated carbonate saturation required to preserve void fabrics via penecontemporaneous cementation, and a relative paucity of detrital sediment that would have inhibited mat growth. Petrofabrics preserved in Angmaat samples are widespread in upper Paleoproterozoic and Mesoproterozoic carbonate successions but are rare thereafter, perhaps recording, at least in part, the declining carbonate saturation state of seawater. Covariation of microfossil assemblages with petrofabrics in both silicified and unsilicified portions of carbonate beds supports hypotheses that link stromatolite microstructure to the composition and diversity of mat communities.
Silicified stratiform stromatolites of the Mesoproterozoic Gaoyuzhuang Formation (1.4–1.5Ga), China, contain well-preserved microfossils. The cherts also harbor varied synsedimentary precipitates and void-filling cements, replaced by early diagenetic silica minerals. These precipitates disclose microenvironments characterized by supersaturated solutions in protected, shallow depressions within an intertidal setting. The precipitates provided surfaces for selective microbial settlement, and rigid sediment matrix for microbial growth. Together with early silicification, the frequent precipitation events contributed to preservation of microfossils by reducing sediment compaction and shearing. Fossiliferous cherts display fine, flat and wavy lamination, characterized by an alternation of highly silicified, thin organic-rich layers with thick sediment-rich layers. Organic-rich layers are dominated either by coccoid or by filamentous microfossils, whereas sediment-rich layers contain abundant synsedimentary precipitates, within which the microfossils are preserved in their growth position. Four dominant microfossils Coccostratus dispergens n. gen. et sp., Eoentophysalis belcherensis, Eoschizothrix composita and Siphonophycus inornatum occur contiguously through several tens of laminae, and are identified as main frame-building biological components of Gaoyuzhuang stromatolites. Community composition, microbial density, distribution, orientation and developmental patterns of the frame-building microfossils are closely correlated with the changing depositional events of Gaoyuzhuang cherts, contrasting conditions of sedimentary kinetics with those of sedimentary stasis. Each assemblage of frame-building microfossils responded to sedimentation with different mechanisms to escape burial. High sedimentation rates correlate with scattered colonies of coccoids and with loose webs of predominantly upright filaments. Low sedimentation rates correlate with dense, laterally connected colonies of coccoids and with a change in filament orientation from vertical to horizontal. In multi-trichomous microfossil Eoschizothrix composita, low sedimentation rates are also accompanied with an increase in number of trichomes per filament. The observed morphological variability of the frame-building microfossils is explained by microbial development, reproduction and behavior by interactions between sedimentological and biological controls.
The study area is located in the Levantino sector of the Iberic Chain, along the western margin of the Province of Valencia, Eastern Spain (Fig. 1). This region shows a series of NW-SE trending belts made of Mesozoic rocks (Jurassic and Cretaceous) separated by Neogene basins and diaspiric outcrops of Triassic material. Figure 2 gives a schematic stratigraphical section of the Jurassic and lowermost Cretaceous deposits.
Tepee structures, banded aragonite cements, and pisoliths are currently forming in Lake MacLeod, a carbonate-evaporite salina in Western Australia. Although Lake MacLeod is separated from the Indian Ocean by a barrier, it lies 3 4 m below sea level, which promotes the seepage of seawater through the barrier and its discharge from vents and seepage mounds around the margin of the salina. Discharging waters have precipitated and diagenetically altered carbonate sediments within these seepage mounds to form tepee structures of lithified protodolomite overlying cavities that are lined with banded aragonite cement and floored by both cement and pisoliths. Significant variations in delta18O (5.10/00 PDB) and delta13C (5.50/00 PDB) of the aragonite cements were documented and are thought to record shifts in the isotopic composition of the water brought about by the effects of evaporation, influx of meteoric water, and oxidation of organic water. Carbon-14 dating of cements indicates that cementation began about 3400 B.P. and has proceeded at a rate of about 0.2 to 0.4 mm/100 yr, the highest rate occurring during evaporative episodes. By analogy with Lake MacLeod and other Australian salinas, peritidal tepee structures and associated diagenetic carbonates in the Permian Capitan Reef complex may owe their origin to speleanlike diagenesis operative in a marine groundwater discharge zone.
Most Precambrian dolostones are considered here to represent replacement of original limestone or calcareous sediment, and hence such dolostone sequences can be interpreted in much the same way as Phanerozoic dolostone sequences. The sequential development of dolomite is recorded in a middle Precambrian carbonate-clastic platform succession in the Belcher Islands. The timing of dolomite formation ranges from penecontemporaneous (eogenetic) to late burial (mesogenetic). The platform sequence is divided into three distinctive megacycles. Pervasive dolomitization of the platform sequence did not occur until a later stage of burial diagenesis, and postdated the main stage of silica diagenesis. Recrystallization was a late mesogenetic event that resulted in only minor crystal enlargement; stylolitization also produced local crystal growth but was not responsible for pervasive dolomitization. Fracture-filling dolomite accumulated as a result of deformation and uplift during the Hudsonian orogeny (telogenesis). -from Author
Most calcite in speleothems is composed of columnar crystals (palisade calcite) and exhibits fabrics similar to those in some porefilling calcites interpreted to be replacive after acicular carbonate cements. The columnar crystals do not interfere with each other's growth (suggesting that they are secondary features) and this, together with the occurrence of layers of acicular calcite in some speleothems, leads to a conclusion that columnar crystals have replaced acicular carbonate. The evidence, however, is misleading. The same crystal fabrics can be explained by normal, but somewhat complex, growth processes. Inclusions (and patterns made by them) constitute the most important clues to the origin of the columnar crystals. Most inclusions are fluid-filled cavities and six types of growth layering are distinguished on the basis of variations in inclusion abundance, size and pattern. Growth layers defined by parallel, linear inclusions are interpreted to have formed during the incomplete lateral coalescence of numerous syntaxial overgrowth crystallites which grow upon the speleothem surface. The linear inclusions represent remnants of the former inter-crystallite spaces. Complete crystallite coalescence generates inclusion-free calcite, whereas inhibition of the lateral coalescence of the overgrowth crystallites generates layers of acicular calcite. During episodes of cave-flooding, however, he crystallites merge and overgrow each other and precipitation eventually occurs upon large, planar crystal faces. It is believed that the distinctive fabrics of palisade calcite are formed because precipitation usually occurs from thin water films that flow over the growing speleothem surfaces. Large crystal terminations do not form on the speleothem surface because they form projections that disturb the water flow away from the projections which, as a consequence, are gradually eliminated. Small crystal terminations (crystallites), on the other hand, do not disturb the water-flow and thus come to dominate the growth surfaces. Petrographic distinction columnar calcite crystals in speleothems (and other vadose calcites with similar fabrics) and mosaics of columnar crystals that have replaced earlier, acicular-carbonate cements is commonly difficult. Such distinctions are attempts to distinguish between calcite crystals that have grown penecontemporaneously from numerous syntaxial overgrowths (calcites in speleothems) and other calcites in which replacement occurs at a much later date, possibly accompanied by replacement of a metastable phase (replacement of acicular cements).
The Rocknest Formation (Fraser and Tremblay, 1969) is exposed in an area 200 km long and 100 km wide in the northwest corner of the Canadian Shield. It is part of the Ep-worth Group, which comprises the supracrustal rocks in the foreland fold and thrust belt of the Coronation geosyncline (Hoffman, 1973a). These rocks were deposited between 2,200 and 1,800 million years ago.
The Permian Capitan Reef pisolite of New Mexico locally contains pore-fillings of square-ended rays 2-3 mm long, which we interpret as having originally formed as aragonite crystals. This indicates that the vadose soil waters that formed the rays had a Mg/Ca ratio greater than 2.
Strontium-rich aragonite crusts exhibiting various morphologies coat both discreet particles and beach rock within the supratidal zone of the Trucial Coast. They are best developed in protected lagoonal settings, although polished “pelagosite” crusts are common within the “splash zone” exposed to wave action. The morphology, both of coated grains and associated aragonite sheets, changes from smooth to highly irregular as one crosses into the upper parts of the supratidal zone. The latter frequently have dripstone morphologies. Micro-dripstones are developed on the under surfaces of many beach rock layers and are composed partly of detrital sediment which is deposited on the roof of small caverns by a rising water table to produce “sedimentary dripstone”. Although many of these aragonitic encrustations resemble lithified algal stromatolites, their dripstone morphologies, nanostructures and invariably lithified character strongly suggests that they are formed by physico-chemical precipitation from sea water. Criteria are given which may permit the distinction between supratidal tufas (here termed “coniatolites”), lithified stromatolites, and cave tufas.
A specimen of flowstone, three cm thick, contains an important variety of carbonates. Ordinary length-fast calcite forms large, clear columnar crystals. Length-slow calcite forms bundles of fibers, some in bands resembling coconut meat, and also zoned crystals; these crystals appear to be the first type of calcite formed after halts in crystallization. Areas thought to have formerly been fibrous aragonite are now converted to calcite; they are recognized by ghost square-ended rays 0.2-0.7 mm wide and 2-4 mm long, now replaced by a mosaic of equant calcite spar crystals 0.05-0.2 mm across. Some fibrous crystals remaining within this spar probably represent surviving original aragonite. Some solution also took place in this zone, as well as inversion of aragonite to calcite. Inversion probably took place when the bathing solutions had the proper intermediate pH to just dissolve aragonite and precipitate calcite, the ions "hopping across" the liquid film from one lattice to the other. Solution took place at lower pH, where ions left the system. Examples of similar square-ended rays once aragonite but now converted to sparry calcite, are shown from the Triassic of the Italian Alps, thus these fabrics can be fossilized. Presumably all aragonite rays were precipitated by waters with a Mg/Ca ratio greater than 2.
Botryoidal aragonite commonly rims and fills voids in Holocene reef-wall limestone of the seaward-facing margins of Belize (British Honduras) barrier and atoll reefs. The cavernous, well-cemented reef-wall limestone that occurs between 65 and 120 m on the barrier reef consists of reef corals encased in algal-plate (Halimeda) packstone-wackestone; the botryoidal aragonite occurs in cylindrical bivalve borings, in polygonal shelter cavities, and in laminar to amoeboid voids of unknown origin. Mamelons of the fibrous aragonite as much as 5 cm thick often rim void ceilings, occasionally grow from void floors, and frequently fill voids completely. In other cavities the mamelons overlie floors of cemented internal sediment, and in still others they have laminations of internal sediment. The aragonite is clearly marine: (1) it occurs within an unaltered reef limestone less than 13,000 yr old; (2) benthic fora-minifera occur locally within mamelons, and in others there are laminations of marine sediment; and (3) the aragonite has an average Sr2+ content of 8,300 ppm, an 018 average of +1.0 0/00, and a C13 average of +4.2 00/0, all characteristic of marine precipitation. The mamelons of botryoidal aragonite are similar in shape, texture, and fabric to some of the common cavity-filling cements in Paleozoic reef limestones.
Describes 140 to 160 shallowing-upward cycles (1 to 15 m thick) that contain distinctive marker beds and can be correlated for > 200 km parallel to strike and > 120 km perpendicular to strike. Cycles are grouped according to cycle base lithology, which reflects paleogeographic position on the platform.-from Author
Abundant precipitation of aragonite is suggested by well-preserved
fabrics in dolostones of the lower Proterozoic (1.9 Ga) Rocknest
Formation. Fabrics include dolomite and silica after botryoidal
aragonite in tepee structures and seafloor cement fans, and cement
crusts in cryptalgal tufas. Aragonite was common on the 1.9-Ga Rocknest
shelf, as it is on modern tropical shelves. A search for similar marine
cement fabrics in other Precambrian carbonates should help resolve
whether aragonite was an important precipitate from Precambrian tropical
seas (implying an ocean carbonate chemistry similar to today), or if
aragonite precipitation was restricted to rare times in the past,
calcite (and even dolomite) being the main carbonates precipitated (as
recently suggested by some authors).
New occurrences of typical Riphean stromatolite and microphytolite groups are reported and illustrated from typical Aphebian sequences in Canada. These include Minjaria, Colonnella, and Kussiella from the Mistassini Group of central Quebec, Gymnosolen, Jacutophyton garganicum, Minjaria, Colleniella, Kussiella, Tungussia, Lenia, Osagia, and Vesicularites from the Belcher Supergroup in Hudson Bay, and Asterosphaeroides (Nelcanella) and Radiosus from the Manitounuk Supergroup of the southeastern coast of Hudson Bay. These occurrences are at variance with prevailing views of Riphean “biostratigraphy”. They call into question the validity of age assignments based only on stromatolite groups, as well as the premise that prokaryotic evolution is mainly responsible for observed trends in gross morphology.The systematics of stromatolites is re-examined in the second part of the paper, and a more objective, morphometric (stereometric) approach is discussed. Example illustrate how differences and similarites whitin and between stromatolite groups can be expressed quantitatively. The morphologic attributes chosen comprise the shapes of lamina profiles, cross sections (plan views), and longitudinal sections (silhouettes). Microstructures are illustrated photographically; they were not analysed morphometrically and await further study.
This chapter discusses the origin and development of cryptalgal fabrics. The term cryptalgal can be used to designate all biosedimentary structures that originated through the sediment binding and the mineral-precipitating activities of non-skeletal algae, mainly blue-green algae, and of bacteria. Such cryptalgal structures are quite diversified in the geological column. The study of cryptalgal fabrics is but one of the multiple approaches to stromatolitic carbonates, an approach that ranks third in the hierarchy of characteristics of the sediments is discussed in this chapter. Finally, cryptalgal fabrics may be divided in two main groups: (1) the layered fabrics, and (2) the non-layered fabrics according to the presence or the absence of a conspicuous biosedimentary layering.
In this book an attempt is made to provide a theoretical background for
the study of the structure of very dense matter. The densities under
investigation are those between 104 to
1016g/cm3 found in inert stellar
objects like the white dwarfs and neutron stars. Even though dense
matter physics is also related closely to contemporary investigations in
heavy ion collisions and the early universe, the author makes little
reference to these issues. Instead emphasis is placed on the stellar
objects with the final aim in deriving the appropriate equation of state
for matter forming them.
The branching columnar stromatolite Pilbaria perplexa Walter 1972 and the microdigitate Asperia ashburtonia Grey 1985 occur together in upward shallowing sedimentary sequences in the 2 Ga Duck Creek Dolomite. The distribution of stromatolite taxa is controlled principally by sedimentary environment. P. perplexa grew in shallow lagoons with the larger P. cf. perplexa extending into the low intertidal zone. A. ashburtonia occupied a high intertidal or supratidal setting, probably in laterally restricted pools.Throughout the world pilbariform and asperiform stromatolites occur in stratigraphic units of different ages. Within each group, the taxa are not identical, although morphologies are broadly similar. The taxonomic variations may be due to evolutionary development, rather than environmental factors.
Precambrian 50,1040-1073. 175-205. (Aphebian) microfossils from Belcher Islands Belcher Islands, Northwest Territo-ries Algae and algal limestone from the Oligocene of South ParkOrigin of fabrics in speleothems composed of columnar calcite crystals
- H J Hofmann
- G D Jackson
- G D Jackson
- Pp
- J H Johnson
HOFMANN, H.J., & JACKSON, G.D. (1969) Precambrian 50,1040-1073. 175-205. (Aphebian) microfossils from Belcher Islands, Hudson Bay. Can. J. Earth Sci., 6,1137-1 144. JACKSON, G.D. (1960) Belcher Islands, Northwest Territo-ries. Pap. geol. Surv. Canada, 60-20,13 pp. JOHNSON, J.H. (1937) Algae and algal limestone from the Oligocene of South Park, Colorado. Bull. geol. SOC. Am., KENDALL, A.C., & BROUGHTON, P.L. (1978)Origin of fabrics in speleothems composed of columnar calcite crystals. J. sedim. Petrol., 48,519-538.
The relation-ship between morphology, microstructure, and microbiota in three vertically intergrading stromatolites from the Gunflint Iron Formation. Can Carbonate sediments and their diagenesis Algal reefs and oolites of the Green River Formation
- S M Awramik
- M A Semikhatov
- R G C Bathurst
- W H Bradley
AWRAMIK, S.M., & SEMIKHATOV, M.A. (1979) The relation-ship between morphology, microstructure, and microbiota in three vertically intergrading stromatolites from the Gunflint Iron Formation. Can. J. Earth Sci., 16,494495. BATHURST, R.G.C. (1971) Carbonate sediments and their diagenesis. Developments in Sedimentology, 12. Elsevier, Amsterdam, 620 pp. BRADLEY, W.H. (1929) Algal reefs and oolites of the Green River Formation. Proj: Pap. U S. geol. Surv., 154G, 203-223.
The algal flora of the Tongying Formation (Upper Sinian System) in southwes-tern China The filling of the Circum-Ungava Geosyn-cline. In: Symp. Basins & Geosynclines of the Canadian Shield
- R-J Cao
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- W-J Zhao
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- W R A Baragar
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CAO, R-J. (1983) Microflora of Precambrian-influence on stromatolitic morphology. Bull. Nanjing Inst. Geol. Pa-leont., Academia Sinica, 6, 1-7. (In Chinese with English abstract.) CAO, R-J. & ZHAO, W-J. (1978) The algal flora of the Tongying Formation (Upper Sinian System) in southwes-tern China. Mem. Nanjing Inst. Geol. Paleont. Academia Sinica, 10, 1-40, (In Chinese with English abstract.) DIMROTH, E., BARAGAR, W.R.A., BERGERON, R., &JACKSON, G.D. (1970). The filling of the Circum-Ungava Geosyn-cline. In: Symp. Basins & Geosynclines of the Canadian Shield (Ed. by A. J. Baer), pp. 45-142. Pap. geol. Surv. Canada, 70-74,265 pp. DONALDSON, J.A. (1963) Stromatolites in the Denault Formation, Marion Lake, Coast of Labrador, Newfound-land. Bull. geol. Surv. Canada, 102,33 pp.
Precambrian microflora, Belcher Islands, Canada: significance and systematics On Aphebian stromatolites and Riphean stromatolite stratigraphy Precambrian fossils in Canada-the 1970s in retrospect
- H J J Hofmann
- Paleonr
- H J Hofmann
- H J Hofmann
HOFMANN, H.J. (1976) Precambrian microflora, Belcher Islands, Canada: significance and systematics. J. Paleonr., HOFMANN, H.J. (1977) On Aphebian stromatolites and Riphean stromatolite stratigraphy. Precambrian Res., 5, HOFMANN, H.J. (1981) Precambrian fossils in Canada-the 1970s in retrospect. In: Proterozoic Basins ofCanada (Ed. by F. H. A. Campbell), pp. 419-443. Pap. geol. Surv. Canada, 81-10.
Evidence for primary aragonite precipitation
- J P Grotzinger
- Reed =read ]
GROTZINGER, J.P., & REED [=READ], J.F. (1983) Evidence for primary aragonite precipitation, lower Proterozoic (
On Pseudogymnosolenidae of Late Precambrian in China On Pseudogymnosolenaceae of Late Precambrian of China
- L M Lebedev
- Pp
- Y Liang
- R-J Cao
- L Zhang
- S Qiu
- Z Xiao
- R Du
- R-G Cao
- D Bu
- Zhu
- Z Gao
- Y Liang
- R-J Cao
- L Zhang
- S Qiu
- Z Xiao
- R-G Cao
- J Duan
LEBEDEV, L. M. (1 967) Meiacolloids in endogenic deposits. Plenum Press, New York, 298 pp. LIANG, Y., CAO, R-J., ZHANG, L., QIU, S., XIAO, Z., Du, R., CAO, R-G., Bu, D., ZHU, s., & GAO, Z. (1983) On Pseudogymnosolenidae of Late Precambrian in China. Bull. Chinese Acad. geol. Sci. 6,125-130. (In Chinese, with English abstract.) LIANG, Y., CAO, R-J., ZHANG, L., QIU, S., XIAO, Z., CAO, R-G., DUAN, J., Du., R., Bu., J., & GAO, 2. (1984) On Pseudogymnosolenaceae of Late Precambrian of China. Scientia Sin., B27 (5), 534-546.
Ed.) (1976) Stromnfolites; Developmenis in Sedimentology
- M R Walter
WALTER, M.R. (Ed.) (1976) Stromnfolites; Developmenis in Sedimentology, 20. Elsevier, Amsterdam, 790 pp. (Manuscripi received 11 November 1986: revised manuscripi received 29 April 1987)
- Johnson J.H.
Biostratigraphic studies of stromatolites from the Proterozoic Earaheedy Group, Nabberu Basin, Western Australia
- Grey K.
Belcher Islands, Northwest Territories
- Jackson G.D.
On Pseudogymnosolenaceae of Late Precambrian of China
- Liang Y.
Mikrostromatity‐kharakteryi element nizhneproterozoyskogo stromatolitovogo kompleksa
- Raaben M.E.
Stromatolites in the Denault Formation, Marion Lake, Coast of Labrador, Newfoundland
- Donaldson J.A.
Precambrian microflora, Belcher Islands, Canada: significance and systematics
- Hofmann H.J.
Precambrian fossils in Canada—the 1970s in retrospect
- Hofmann H.J.