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Schematic microbial head with idealized sequence of internal fabrics and their relative water depths. The structures often display a vertical sequence of internal fabrics in shallowing-upward arrangement or show truncated fabric sequences depending on environmental setting and timing of growth history.
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The distribution, nature and extent of microbial deposits in Hamelin Pool, Shark Bay have been investigated and mapped with emphasis on the occurrence, external morphologies, internal fabrics, constructional mechanisms, microbial communities, growth rates and sediment associations in the intertidal and previously little researched subtidal zone.
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... Similar sedimentation conditions have been described for the accumulative sub-basin of Shark Bay on the west coast of Australia. As in members V and VI, sediments in this basin are characterized by the abundance of microbial formations together with the peloid and bioclastic components that are accumulated on tidal flats and in shallow (<10 m) subtidal zones (Collins and Jahnert, 2014;Jahnert and Collins, 2012). ...
Results of the study of Lower Devonian rocks in the Chernyshev Ridge to determine their hydrocarbon (HC) generation potential are presented. Assessment of the organic matter (OM) content in Lower Devonian rocks showed that most of the studied section is characterized by low Corg concentrations (<0.3%). Elevated OM contents were determined only in Unit III rocks of the Ovinparma regional stage, which are considered as potential petroleum source rocks: Corg 0.13–0.35 and 0.54–1.44%, respectively, in the carbonate and clayey–carbonate rocks. Based on the Rock-Eval pyrolysis data, S1 + S2 (0.04–6.20 mg HC/g rock) and hydrogen index (HI) value (19–430 mg HC/g Corg), they are characterized as poor and moderate petroleum source rocks. These source rocks were deposited under open-marine outer ramp conditions during the marine transgression. The OM maturity of the petroleum source rocks, determined based on the bituminite
reflectance value, RVeq (0.75–0.81%), maximum HC yield temperature, Tmax (437–449°C), and conodont color alteration index, CAI (1.5), corresponds to the middle of the main oil generation zone (catagenesis grade MC2). Thus, the presence of rocks with the HC generation capacity and sufficient OM maturity for oil generation indicates that unit III source rocks of the Ovinparma regional stage represent an effective element of the Lower Devonian petroleum system.
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... However, these experiments were conducted in the absence of any flow and sediment motion, so it remains unclear what flow (velocity, bed shear stress), sediment, and substrate characteristics (height and surface area of the topographic highs as well as their surface roughness) allow the initial colonization of sediment beds in environments that experience continuous or very frequent movement and deposition of sand grains. Of note, stromatolites and thrombolites are common in modern environments with strong waves, tidal currents, and frequently mobilized sediments such as Shark Bay in Western Australia (Jahnert and Collins 2012) and Exuma Bay, The Bahamas (Reid et al. 1995). ...
The growth of most stromatolites is a result of interactions among the growth of microbial mats, mineral precipitation, water flow, and sediment movement. Here, we ask how oxygenic photosynthetic microbes colonize surfaces and interact with sediments in high‐energy environments that contain constantly moving sand. For this, we investigate cyanobacterial growth on centimeter‐scale concrete spheres in a continuously agitated wave tank. Cyanobacteria are unable to colonize moving sand, but establish biofilms on spheres within 5–6 weeks. These biofilms trap up to 0.5 g/cm ² of sand on the top and 0.3 g/cm ² on the sides within 25 weeks. The colonization does not depend on the size of the spheres, but instead depends on their surface roughness. Cyanobacteria easily colonize spheres with a surface roughness that matches the bed grain size (0.3 mm), but cannot colonize the initial topographic highs with a roughness of ~0.001 mm. In both cases, recesses on the surfaces of the spheres protect cyanobacteria from sandblasting. Thus, microbial biofilms can become established even in high‐energy environments, if topographic highs are large enough not to be rolled around by the flow and rough enough to provide attachment loci. If cementation occurs within biofilms, the interplay among biofilm growth, sediment trapping, and cementation can lead to the upward as well as lateral growth of stromatolites. These experimental observations can explain the preferential upward growth of stromatolites on topographic highs in areas with frequently mobilized sediment grains, including modern stromatolites in the intertidal zone in Shark Bay and the subtidal zone in The Bahamas.
... Beachrock sensu stricto has been advocated as a reliable sea-level indicator (Mauz et al., 2015) and other carbonate deposits such as aeolianites, tufa and speleothems in coastal environments (Faulkner and Crae, 2022;Faulkner and Crae, 2018;Howie and Ealey, 2010), all act as potential shoreline indicators. Microbialites occur in a range of coastal environments including hypersaline lagoons (Jahnert and Collins, 2012;Logan, 1961;Suosaari et al., 2022), open marine (Dill et al., 1986;Reid et al., 1995) and mixed environments within coastal ponds (Saint Martin and Saint Martin, 2015). Contemporary tufa microbialites at the intersection between groundwater springs and the upper-intertidal to supratidal zones, have been observed globally (Cooper et al., 2013;Forbes et al., 2010;Perissinotto et al., 2014;Rishworth et al., 2020b;Smith et al., 2018). ...
Modern and Holocene tufa microbialites have been documented globally on groundwater spring-fed supratidal
rock coasts. Here, we document the first emergent facies assemblage and demonstrate its utility as a palaeo-
shoreline (and sea-level) indicator. At Cape Freycinet, Western Australia, discrete palaeo-spring-associated de
posits comprise five distinct facies that collectively define a Quaternary shoreline on a granitic rock coast similar
to the contemporary coast. A palaeosol facies, passes laterally seaward into tufa microbialite on sub-horizontal
bedrock, associated with oncoids. The most seaward facies is a microbially-cemented sand representing depo
sition in the upper-intertidal to supratidal zone of a sandy embayed beach, flanked by prominent headlands. A
tufa-lithoclast breccia indicates occasional high-energy events. Facies distributions are controlled by bedrock
topography in relation to palaeo-sea-level and the distinct suite of marginal marine, springline-associated facies
define a Quaternary palaeo-shoreline at ca. +13 m above sea-level. The approach demonstrates the utility of
marginal marine microbialite and related carbonate deposits as indicators of Quaternary sea-level on rock coasts.
... Pustular, smooth, colloform, and cerebroid morphologies have been identified Collins, 2011, 2012;Logan et al., 1974;Suosaari et al., 2019b). However, as noted by Jahnert and Collins (2012), classification based on surface morphology may not be useful regarding the fabric and internal morphologies due to complex or compound microbialites with possible growth hiatuses. The same terms, pustular, smooth, and colloform, have also been applied to Exuma Cays and Highborne Cay, The Bahamas (Reid et al., 1995;Stolz et al., 2009), and to the external biofilm surface of tufa deposits (e.g. ...
... A comparable pustular mesostructure from Shark Bay, Western Australia, was first describe by Logan et al. (1974) as "brown surfaces of gelatinous pustules composed of mucilage (1-2 cm thick)" (Jahnert and Collins, 2011) from the shallow intertidal environment. The pustular morphology is described as having a clotted fabric and is therefore thrombolitic (Jahnert and Collins, 2012). It has also been described from occurrences in normal-salinity marine environments in Exuma Cays, associated with Schizothrix mats (Reid et al., 1995), and Highborne Cay, The Bahamas, associated with Schizothrix and Solentia mats and biofilms (Stolz et al., 2009); from hypersaline Rivularia-rich microbial mats in Laguna Negra, Argentina Mlewski et al., 2018); and from occurrences in peritidal environments (Gerdes and Krumbein, 1994). ...
Microbialites are known from a range of terrestrial, freshwater, marine, and marginal settings. The descriptive terminology used in each instance depends largely on the historical legacy derived from previous studies in similar environments. This has led to a diversity of nomenclature and a lack of conformity in the terms used to describe and categorise microbialites. As the role of microbial mats and biofilms is increasingly recognised in the formation of tufa and terrestrial carbonates, deposits such as tufa microbialites bridge the spectrum of microbialites and terrestrial carbonate deposits. Groundwater spring-fed tufa microbialites in supratidal rock coast environments that occur at the interface of terrestrial and marine domains demonstrate the need for an integrative and systematic nomenclature approach. To date, their global distribution and complex relationships with pre-defined deposits have resulted in the application of a variety of descriptive terminologies, most frequently at the macro- and mesoscale. Here we review and consolidate the multi-scale library of terminologies for microbialites and present a new geomorphological scheme for their description and classification. This scheme has greater alignment with terrestrial carbonate nomenclature at the macroscale and with marine and lacustrine microbialites at the mesoscale. The proposed terminology can primarily be applied to tufa microbialites in spring-fed supratidal environments but may also be applicable in other relevant depositional environments including terrestrial carbonates, microbial mats, and other microbialites.
... Previous studies in Highborne Cay and Shark Bay did note a high relative abundance of diatoms present in the microbialite communities, however, the varied abundance of each diatom clade was not clear 27 . Although a key role for diatoms in accretion of microbialites and microbialite-forming mats has long been accepted 2,53-55 , their contribution to microbialite accretion is controversial both in Shark Bay 56,57 and Highborne Cay locations 35,57,58 . Nevertheless, diatoms are major EPS producers and inevitably play a role in microbialite ecology. ...
Protists are less studied for their role and diversity in ecosystems. Notably, protists have played and still play an important role in microbialites. Microbialites, or lithified microbial mats, represent the oldest evidence of fossil biofilms (~3.5 Gyr). Modern microbialites may offer a unique proxy to study the potential role of protists within a geological context. We examined protist diversity in freshwater (Kelly and Pavilion Lake in British Columbia, Canada) and marine (Highborne Cay, Bahamas) to hypersaline (Shark Bay, Australia) microbialites to decipher their geomicrobiological role. The freshwater microbialite communities were clearly distinct from their marine and hypersaline counterparts. Chlorophytes had higher numerical abundance in freshwater microbialites; whereas pennate diatoms dominated numerically in marine microbialites. Despite the differences, protists across ecosystems may have adopted similar roles and functions. We suggest a consistent biogeochemical role of protists across microbialites globally; but that salinity may shape protist composition and evolution in these ecosystems.
... The association of columnar/conical stromatolites with coarse clastic carbonate and siliciclastic detritus suggests deposition in a submerged subtidal environment (Dravis, 1983;Grotzinger, 1989;Kah et al., 2006;Jahnert and Collins, 2012;Siahi et al., 2016). The domal stromatolites likely developed in middle-lower intertidal to shallow subtidal environments similar to their modern counterparts, which are reported from marine intertidal mudflats, protected lagoons, and shallow subtidal environments (Monty, 1967;Jahnert and Collins, 2012). ...
... The association of columnar/conical stromatolites with coarse clastic carbonate and siliciclastic detritus suggests deposition in a submerged subtidal environment (Dravis, 1983;Grotzinger, 1989;Kah et al., 2006;Jahnert and Collins, 2012;Siahi et al., 2016). The domal stromatolites likely developed in middle-lower intertidal to shallow subtidal environments similar to their modern counterparts, which are reported from marine intertidal mudflats, protected lagoons, and shallow subtidal environments (Monty, 1967;Jahnert and Collins, 2012). The absence of sedimentary structures indicating subaerial exposure and the cooccurrence of different oncoid types (large irregular and small spherical oncoids) with clastic detritus and rip-up clasts indicate that the oncoids formed in a subtidal zone episodically influenced by storms (Logan et al., 1964;Leeder, 1975;Smith, 1986;Siahi et al., 2016). ...
... Since the 1980s, taphonomic models for the genesis of bioclastic concentrations have been proposed based on present-day (Aigner, 1985;Seilacher, 1985;Kidwell, 1991Kidwell, , 2002Kowalewski et al., 1994;Kowalewski & Labarbera, 2004;Jahnert & Collins, 2012) and ancient (Kreisa, 1981;F€ ursich & Oschmann, 1993;Dattilo et al., 2008;Puga-Bernab eu & Aguirre, 2017; Garc ıa-Ramos & Zuschin, 2019) marine deposits. Despite numerous taphonomic studies about shell concentrations generated in restricted to closed basins, especially for the Palaeozoic sedimentary inland successions (e.g. ...
Event deposition accounts for a large part of the preserved sedimentary record. Tempestites, tsunamites and turbidites are among the most common event deposits in marine and lacustrine systems. While facies models exist for these deposits, the challenge lies in the fact that diverse triggers can give rise to analogous depositional processes and comparable taphonomic features, making it difficult to pinpoint the precise trigger for an event bed. Hence, five distinct modern-type shell concentrations are studied in Permian strata from the Paraná Basin, West Gondwana, to access the parameters to discriminate event phenomena, and their associated depositional and taphonomic processes. During this time interval, the basin underwent continuous continentalization due to orogenic events, leading to the entrapment of epeiric marine waters and the transformation of the system into a megalake, supporting a diverse and endemic freshwater bivalve fauna. While sedimentation was primarily influenced by meteorological events, certain stratigraphic intervals were also affected by tectonically active periods and meteor impact events. The different products are categorized into bioclastic sandstone, shell bed, shell-rich phosclast rudstone and shell-rich conglomerate that are interpreted as proximal and distal tempestites and tsunamites, respectively. Finally, the products and the processes that lead to the deposition of tempestites and tsunamites are compared to establish diagnostic signatures that may be applied to differentiate these event concentrations in analogous settings from the geological record.
... nearshore, with coverage extending over 100 km along the coast. They persist as there is little competition with eukaryotic algae and little fish and invertebrates grazing in hypersaline waters [7][8][9]. ...
Hypersaline Hamelin Pool, with mean salinity >65, is located in Shark Bay, Western Australia. The high salinity has reduced its biodiversity, but it is home to a diverse assemblage of modern marine stromatolites. The limited exchange of water between Hamelin Pool and the rest of Shark Bay, due to the presence of the shallow Faure Sill together with high evaporation and low rainfall-runoff have resulted in a hypersaline environment. With climate-change-induced mean sea level rise (MSLR), hydrodynamic processes that maintain the hypersaline environment may be affected and are the focus of this paper. Oceanographic observations, together with hydrodynamic model results, were used to examine the hydrodynamic processes under present and future MSLR scenarios. A large attenuation in the tidal range, changes in the tidal characteristics, and current speeds together with a strong salinity gradient were observed across the Faure Sill under present-day conditions. Under an MSLR scenario of 1 m, the tidal amplitude decreased by up to 10% to the north, whilst to the south, the tidal range increased by up to 15%. Regions of strong vertical stratification were present on both sides of the Faure Sill. The simulations indicated that, under MSLR scenarios, these regions expanded in area and exhibited higher levels of vertical stratification. The salt flux across the Faure Sill was maintained as a diffusive process under MSLR scenarios.
... in the studied material. Similar micrite cement is also reported from Hamelin Pool, Shark Bay byJahnert and Collins (2012) and Suosaari et al. (2016, Figure 7d).5.3 | BioconstructionsBioconstructions are composed of various main elements arranged in complex internal successions and can be classified into four major types. These can be intergrown with each other or may occur in temporal successions: F I G U R E 1 3 Serpulid-Nubecularia-microbial boundstones from Vienna-Ruzickagasse. (a) A basal Nubecularia-coralline algal boundstone (Nc) is overlain by serpulid-Nubecularia-microbial boundstone (s-serpulids, N-Nubecularia, mb-microbial carbonate) with large primary cavities. ...
Nubecularia bioherms represent unique bioconstructions that are restricted to the upper Serravallian of the Paratethys and have been reported since the 19th century. They occur in the Central Paratethys in the late Sarmatian and the Eastern Paratethys in the Bessarabian both regional stages of the respective Paratethyan areas. In this study, several locations in the Vienna and Styrian basins of the Central Paratethys were studied out of which four localities were documented in detail (Wolfsthal, Maustrenk, St. Margarethen-Zollhaus, Vienna-Ruzickagasse) to reconstruct their sedimentary setting, their internal composition, and their indications of environmental parameters. The detailed studies included logging of outcrop sections, petrographic, facies and biotic analyses of polished slabs and thin sections and also cathodoluminescence analyses. These concluded that these bioconstructions are not only composed of the foraminifer Nubecularia but represent a complex mixture and interrelationships of Nubecularia, serpulids and microbial carbonate. Four boundstone types can be differentiated: Nubecularia boundstone, Nubecularia-coralline algal boundstone, stro-matolitic/thrombolitic boundstone and serpulid-nubeculariid-microbial boundstone. The first 3 types are characteristic of specific localities; the fourth type occurs in all studied locations and represents the terminal association on top of the three other types. The three basal boundstones are predominantly of columnar growth form irrespective of dominance of Nubecularia, coralline algae or microbial carbonate, and the terminal boundstone is widely irregularly organized. The general depositional environment is characterized by cross-bedded oolitic grainstones with abundant quartz grains, miliolid foraminifers and mollusks. Intercalated are microbial carbon-ates mostly stromatolites but also thrombolites. This indicates a general high water energy environment interrupted by more calm periods when the microbial carbonate was built. The 3 basal types of bioconstructions are interpreted to reflect decreasing food supply and/or oxygenation from Nubecularia over Nubecularia-coralline algal to stromatolitic/thrombolitic boundstone. The serpulid-nubeculariid-microbial bound-stone reflects an internal succession with a decrease of the same parameters. Water
... The earliest development of the microbialites represents the compelling evidence for life survival on Earth (Allwood et al. 2006) and their occurrences can be widely recorded from the Archean to the Holocene (Riding 2000;Li et al. 2022). As major producers of microbialites, the photoautotrophic (e.g., cyanobacteria) and heterotrophic (e.g., sulfate reducing bacteria) microorganisms play an essential role in the construction of the microbial biofilms, mats, the laminated/clotted structures, and the framework in Earth-surface environments, which can live on all sedimentary surfaces from lands to Oceans (Logan 1961;Dill et al. 1986;Burne 1991;Montaggioni and Camoin 1993;Nealson 1997;Riding 2000;Oliveri et al. 2010;Jahnert and Collins 2012), including particularly lakes (Wright 1999;Dupraz (2024) 39:5 5 Page 2 of 17 Freytet and Plet 1996), caves, and hot springs (Fouke et al. 2000). Lacustrine microbialites have been widely used to interpret palaeo-climate and palaeo-hydrology of continental areas as they preserve traces of lake level, relative humidity, and aquatic chemistry (Smith and Mason 1991;Casanova and Hillaire-Marcel 1992;Bouton et al. 2016). ...
Studying the lacustrine microbialites in the Western Qaidam Basin in the northeastern margin of the Qinghai–Tibetan Plateau may provide clues to the sedimentary record, the depositional model, and the hydrocarbon potential. Based on geological, geochemical, and seismic data, the sedimentary characteristics and hydrocarbon potential of Eocene lacustrine microbialites in Western Qaidam Basin are estimated. Three microbialites are identified In the Eocene lacustrine system of the Qaidam Basin, including the thick thrombolites in relatively high-energy near-shore settings, the small-scale stromatolites and thrombolites in extremely shallow water environment, and the laminates in relatively deep water of intrabasinal environments. Three sedimentary models have been established, including the marginal steep slope zone, the marginal gentle slope zone, and the intrabasinal deep-water zone, respectively. The framework pores, intergranular pores, dolomite intercrystalline pores, dissolved pores and interlayered fractures commonly composed the pore spaces of microbialites. The Fossil Group of Botryococcus (a lipid-rich algae) contributed the main source of hydrocarbons particularly in saline water in Western Qaidam Basin. The development of Eocene lacustrine microbialites on the northeastern Qinghai–Tibetan Plateau provides a new perspective to explore the complex mineralization processes and hydrocarbon potential of microbialites.
