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Hardened Subtidal Stromatolites, Bahamas
Abstract
Hardened, high-relief stromatolites have been discovered along the margins of some Bahamian platforms. They occur in high-energy
(tidal) oolitic sand environments in waters ranging in depth from about 1 to 5 meters. Physical stress produced by actively
migrating bed forms of oolitic sand appears to exclude grazing gastropods and subsequent community successions, permitting
stromatolite growth.
... Consequently, numerical models of microbialite accumulations require explicit and implicit calculation of several interacting physical, chemical and biological processes. The modelled process and product represent modern agglutinated microbialites in marine environments, such as Shark Bay and the Bahamas, where both in-situ precipitation and sediment trapping and binding are important accumulation processes (Logan, 1961;Dravis, 1983;Reid et al., 2000;Riding, 2011a;Suarez-Gonzalez et al., 2019). ...
... Modern microbialites commonly have multiple phases of accumulation (Paull et al., 1992;Jahnert and Collins, 2012;Carvalho et al., 2018), and the averaged growth rate decreases with increasing time span of observation (Table 2) (Sadler, 1981;Schlager, 1999), so the input maximum growth rate is set to 5 mm per year, and a total of 250 years EMT can produce microbialites with height of approximately 1 m or less, consistent with observations from modern systems, such as Shark Bay (Playford et al., 2013), Bahamas (Dravis, 1983), and Bermuda (Gebelein, 1969). Maximum accumulation rate of suspended sediment is 4 mm per year, which is a reasonable rate for non-compacted sediment to be deposited and form packstones in marine settings. ...
... Playford et al. (2013) also noted that some stromatolites in the south of Carbla Point are apparently inclined towards prevailing wind direction, resulting from rapid accretion of a mixture of carbonate and siliciclastic sand particles on the side exposed to upcurrent flow. These elongated forms with asymmetric features are also observed in Bahamas (Dravis, 1983;Dill et al., 1986), Bermuda (Gebelein, 1969), and are consistent with our modelling results (Fig. 7). ...
Microbialites span a substantial fraction of Earth history, and have important meanings for understanding long-term history of life and environment. Key controls on microbialite morphology and distribution include substrate topography, hydrodynamic conditions, water depth, salinity, light intensity, and sedimentation rates. This leads to potentially complex combinations of control by internal spatial feedbacks and also external factors. This complexity is explored here using Stromatobyte3D, a new numerical stratigraphic forward model that calculates microbialite accumulation due to in-situ precipitation, sediment trapping and binding, and sedimentation from suspension, controlled by evolving topography and water flow due to waves, tides or other currents. Results show that with increasingly strong spatial interactions of microbialite growth with water and suspended sediment, particularly the influence of hydrodynamics on in-situ microbialite growth and suspended sediment deposition patterns, three distinct microbialite morphologies are produced, from isolated columns, through elongated mounds, to ridges elongated in the dominant flow direction. Quantitative analysis demonstrates a dominant antecedent substrate topographic control on microbialite nucleation and growth in the absence of water flow, declining as hydrodynamic processes and strong spatial interactions are introduced causing mounds to accrete and coalesce laterally in the flow direction. Formation of coherent morphological patterns, produced by spatial interactions between topography, hydrodynamics, microbialite growth, and sedimentation from suspension, and independent of initial condition, is evidence of spatial self-organization. Modelled morphologies are strikingly similar to observations from modern marine agglutinated microbialite strata, suggesting modelled processes and their behaviours are realistic, and can therefore be useful to assist field interpretations of observed microbialite morphologies where similar processes were operating together.
... For example, high salinity can shift microbial communities to species that can tolerate osmotic stress , Dillon et al. 2013, Gerdes et al. 1985, Oren 2011, Reid et al. 2021 or change production of extracellular polymeric substances (EPS) to isolate the microbes from the environment (Kim & Chong 2017, Mayer et al. 1999, Suosaari et al. 2022b, Zhao et al. 2016. Notably, microbialites have been found in a wide range of environmental conditions, including low-pH (Burne et al. 2014), alkaline (Arp et al. 1999(Arp et al. , 2003Kempe et al. 1991;Reitner et al. 1996), open marine (Dill et al. 1986, Dravis 1983, Reid et al. 1995, and hypersaline (Logan et al. 1974, Playford et al. 2013, Suosaari et al. 2016a) environments, demonstrating that chemical windows vary greatly. Nutrient and trace element concentrations can also fuel microbialite formation in harsh environments (e.g., Rasuk et al. 2020;Sancho-Tomás et al. 2018Saona et al. 2020;Visscher et al. 2020). ...
Microbialites provide geological evidence of one of Earth's oldest ecosystems, potentially recording long-standing interactions between coevolving life and the environment. Here, we focus on microbialite accretion and growth and consider how environmental and microbial forces that characterize living ecosystems in Shark Bay and the Bahamas interact to form an initial microbialite architecture, which in turn establishes distinct evolutionary pathways. A conceptual three-dimensional model is developed for microbialite accretion that emphasizes the importance of a dynamic balance between extrinsic and intrinsic factors in determining the initial architecture. We then explore how early taphonomic and diagenetic processes modify the initial architecture, culminating in various styles of preservation in the rock record. The timing of lithification of microbial products is critical in determining growth patterns and preservation potential. Study results have shown that all microbialites are not created equal; the unique evolutionary history of an individual microbialite matters.
... (2) Siliceous stromatolites from Yellowstone National Park in the USA and the Frying Pan Lake in North Island of New Zealand [21][22][23]. (3) Carbonate stromatolites from the Hamelin Pool in Shark Bay of Australia, the Li le Darby Islands in the Bahamas, and the Lagoa Vermelha of southeastern Brazil [5,12,[24][25][26][27][28][29][30][31]. Although differences occur among these modern stromatolites in morphology, size, components, and growth pa ern, they can provide analogs for understanding the formation of ancient stromatolites as well as depositional environments, and they provide key insight into microbial biomineralization during stromatolite accretion [16,32,33]. ...
Stromatolites, among the earliest fossils in Earth's history, are widely distributed on the margins of the North China Precambrian carbonate platform. The formation processes of stromatolites reveal the biomineralization and evolution of early life in the Precambrian. The well-preserved stromatolitic dolostones recorded in the Ganjingzi Formation are developed around Yuanjiagou village, in southern Liaoning Province. The morphology of the Ganjingzi stromatolites manifests in stratiform, columnar, and domal forms. A tripartite lamina structure including light laminae and two types of dark laminae is observed in thin sections. The origins of dark laminae were related to microbial metabolism, while the light laminae were the result of the recrystallization of synsedimentary marine cement. Hardground substrate and carbonate fragments were suitable for microbes to colonize, suggesting that microbes can adapt to various current energy settings. A comparison of the growth environment, morphology, and laminae features between the Ganjingzi stromatolites and modern carbonate stromatolites from Hamelin Pool and Lagoa Vermelha suggest that the Ganjingzi stromatolites may have been formed in a restricted tidal-flat setting with high salinity and evaporation. The role of microbes that form modern stromatolites in inducing precipitation of carbonate or binding sediments, might contribute to the formation of the Ganjingzi stromatolites. The formation process of the Ganjingzi stromatolites indicates that the microbial communities, favorable substrate, and synsedimentary marine cement were the key factors in promoting the development of the Neoproterozoic stromatolites on the northeastern margin of the North China Craton.
... Modern stromatolites are restricted to relatively rare occurrences (e.g. Logan, 1961;Dravis, 1983;Dill et al., 1986;Reid et al., 1995), but flat laminated microbial mats and the sedimentary structures they form are more widely distributed and carry equal significance in the documentation and interpretation of Earth history (Schopf, 2006;Grotzinger & Al-Rawahi, 2014). This makes them a promising target for modern analogue studies. ...
To interpret microbially influenced paleoenvironments in the sedimentary record, it is crucial to understand what processes control the development of microbial mats in modern environments. This article reports results from a multiyear study of Little Ambergris Cay, Turks and Caicos Islands, an uninhabited island floored by broad tracts of well‐developed microbial mats on the wind‐dominated and wave‐dominated Caicos Platform. Uncrewed aerial vehicle‐based imaging, differential global positioning system topographic surveys, radiocarbon data, and in situ sedimentological and microbial ecological observations were integrated to identify and quantify the environmental factors that influence the distribution and morphologies of Little Ambergris Cay microbial mats, including their response to large storm events. Based on these data, this study proposes that Little Ambergris Cay initially developed from the accretion and rapid lithification of carbonate sediment delivered by converging wave fronts in the lee of adjacent Big Ambergris Cay. Broad tracts of microbial mats developed during late Holocene time as the interior became restricted due to beach ridge development. Minor elevation differences regulate subaerial exposure time and lead to three categories of microbial mats, differentiated by surface texture and morphology: smooth mats, polygonal mats and blister mats. The surface texture and morphology of the mats is controlled by subaerial exposure time. In addition to elevation, the spatial distribution of mats is largely controlled by hydrodynamics and sediment transport during large storm events. This detailed assessment of the controls on mat formation and preservation at Little Ambergris Cay provides a framework within which to identify and understand the interactions between microbial communities and sediment transport processes in ancient high‐energy carbonate depositional systems.
... It is commonly thought that modern stromatolites only occur in extreme, low nutrient environments where most other life forms cannot survive, e.g., Shark Bay, Western Australia (hypersaline marine embayment), Yellowstone National Park, U.S. (hot springs), etc. However, modern stromatolites also occur in habitable environments such as in openmarine (normal salinity) conditions in the Bahamas (Dravis, 1982) and the freshwater Pavilion Lake, Canada (Brady et al., 2010). In fact, the common feature shared by these localities is unusually high alkalinity and elevated concentrations of carbonate-forming cations (Ca and Mg). ...
... On modern coastlines, mapped occurrences of microbialite-forming environments are limited and represent a small proportion of modern shallow-water coastal habitats. The most widely cited (and until recently, only known) open-marine analogue for ancient stromatolites is that of the Bahamas carbonate system (Dravis 1983;Dill et al. 1986;Reid et al. 1995). Given that for most of the Precambrian shallow-water coastlines were dominated by microbialites in siliciclastic environments (Riding 2000), and carbonate sedimentary systems did not exist, these modern analogues provide only limited comparability with ancient microbialites. ...
Contemporary microbialite formation has been documented on rock coasts in a variety of geomorphic, oceanographic, and climatic settings. Based on a synthesis of these diverse occurrences plus new observations, a generalized model is presented. At each locality microbialite development is associated with discharge of mineralized freshwater in the coastal zone. Microbialite formation in the high intertidal and supratidal zones of rock coasts occurs in a variety of sub-environments (cliff face, shore platform surface, platform surface pools, boulder beach, and sand beach) and forms a variety of laminated rock encrustations and oncoids. Allochthonous microbialites occur on the backshore as breccias of reworked microbialite clasts, oncoids transported from rock pools, and partly encrusted boulders. The microbialite-influenced rock coast is a distinct type of siliciclastic environment that offers potential comparison for ancient microbialite occurrences. It has preservation potential in both transgressive and regressive settings. Potential ancient examples are suggested.
... Ancient stromatolites from peritidal to shallow subtidal settings are commonly supposed to represent cyanobacterially dominated biofilms and microbial mats (see Monty 1977;Arp et al. 2001), analogous to modern stromatolites (Walter 1972;Dravis 1983;Arp et al. 1999;Dupraz et al. 2013). However, stromatolites can also be formed by lightindependent chemolithotrophic or heterotrophic microbial communities, as for instance observed in caves and/or deep-water environments (Playford et al. 1976;Cox et al. 1989;Böhm & Brachert 1993;Heim et al. 2015Heim et al. , 2017. ...
The so‐called Permian–Triassic mass extinction was followed by a prolonged period of ecological recovery that lasted until the Middle Triassic. Triassic stromatolites from the Germanic Basin seem to be an important part of the puzzle but have barely been investigated so far. Here, we analysed late Anisian (upper Middle Muschelkalk) stromatolites from across the Germanic Basin by combining petrographic approaches (optical microscopy, micro X‐ray fluorescence, Raman imaging) and geochemical analyses (sedimentary hydrocarbons, stable carbon and oxygen isotopes). Palaeontological and sedimentological evidence, such as Placunopsis bivalves, intraclasts and disrupted laminated fabrics, indicate that the stromatolites formed in subtidal, shallow marine settings. This interpretation is consistent with δ13Ccarb of about −2.1‰ to −0.4‰. Occurrences of calcite pseudomorphs after gypsum possibly suggest occasionally elevated salinities, which is well in line with the relative rarity of fossils in the host strata. Remarkably, the stromatolites are composed of microbes (perhaps cyanobacteria and sulphate‐reducing bacteria) and metazoans such as non‐spicular demosponges, Placunopsis bivalves and/or microconchids. Therefore, these ‘stromatolites’ should more correctly be referred to as microbe‐metazoan build‐ups. They are characterized by diverse lamination types, including planar, wavy, domal and conical ones. Microbial mats likely played an important role in forming the planar and wavy laminations. Domal and conical laminations commonly show clotted to peloidal features and mesh‐like fabrics, attributed to fossilized non‐spicular demosponges. Our observations not only point up that non‐spicular demosponges are easily overlooked and might be mistakenly interpreted as stromatolites, but also demonstrate that microbe‐metazoan build‐ups were widespread in the Germanic Basin during Early to Middle Triassic times. In the light of our findings, it appears plausible that the involved organisms benefited from elevated salinities. Another (not necessarily contradictory) possibility is that the mutualistic relationship between microbes and non‐spicular demosponges enabled these organisms to fill ecological niches cleared by the Permian–Triassic crisis. If that is to be the case, it means that such microbe‐metazoan associations maintained their advantage until the Middle Triassic.
Following the end-Permian crisis, microbialites were ubiquitous worldwide. For instance, Triassic deposits in the Germanic Basin provide a rich record of stromatolites as well as of microbe-metazoan build-ups with nonspicular demosponges. Despite their palaeoecological significance, however, all of these microbialites have only rarely been studied. This study aims to fill this gap by examining and comparing microbialites from the Upper Buntsandstein (Olenekian, Lower Triassic) and the lower Middle Muschelkalk (Anisian, Middle Triassic) in Germany. By combining analytical petrography (optical microscopy, micro X-ray fluorescence, and Raman spectroscopy) and geochemistry (δ13Ccarb, δ18Ocarb), we show that all the studied microbialites formed in slightly evaporitic environments. Olenekian deposits in the Jena area and Anisian strata at Werbach contain stromatolites. Anisian successions at Hardheim, in contrast, host microbe-metazoan build-ups. Thus, the key difference is the absence or presence of nonspicular demosponges in microbialites. It is plausible that microbes and nonspicular demosponges had a mutualistic relationship, and it is tempting to speculate that the investigated microbial-metazoan build-ups reflect an ancient evolutionary and ecological association. The widespread occurrence of microbialites (e.g., stromatolites/microbe-metazoan build-ups) after the catastrophe may have resulted from suppressed ecological competition and the presence of vacant ecological niches. The distribution of stromatolites and/or microbe-metazoan build-ups might have been controlled by subtle differences in salinity and water depth, the latter influencing hydrodynamic processes and nutrient supply down to the microscale. To obtain a more complete picture of the distribution of such build-ups in the earth’s history, more fossil records need to be (re)investigated. For the time being, environmental and taphonomic studies of modern nonspicular demosponges are urgently required.
This chapter discusses the effects of the physical, chemical and biological evolution of the earth. This chapter emphasizes on the application of recent data, the most important of these qualifying conditions being: (1) the importance of bacteria in the Early Precambrian stromatolites; (2) the importance of both environmental and evolutionary factors in explaining the change in stromatolite structures; (3) the effects of the absence of metaphytes and metazoans on the distribution and diversity of stromatolites in the early and middle Precambrian; (4) the effects of the development of metaphytes and metazoans on the Phanerozoic distribution and diversity of stromatolites; and (5) the importance of the development of calcareous red algae in modifying the role of blue–green algae in Mesozoic and Cenozoic reefs. It is possible to apply the data on recent stromatolites to the solution of many of the remaining problems in the study of stromatolites.
The abundance of stromatolites (algal laminated sedimentary structures) in the Precambrian followed by a decline in the Phanerozoic
is explained by the evolution and diversification during the Phanerozoic of grazing animals which feed on surface algal mats
and of burrowing animals which destroy sedimentary laminations.