Explore the vast range of titles available.

Precambrian stromatolites have received in depth, consideration from geologists and paleontologists; they were indeed searching for biosedimentary structures that were sufficiently characteristic and widely distributed to be considered as useful tools for stratigraphic correlation. Silicified stromatolites are also of interest as they contain preserved traces of ancient life. Calcareous Phanerozoic stromatolites have not received very much attention from geologists. Logan's too schematic morphological classification of 1964, was not so helpful to the knowledge of Phanerozoic stromatolites because neither their morphology nor their microstructure were studied in the same detail in which Proterozoic stromatolites have now been described. We therefore know little about the Phanerozoic stromatolites which, do, however, show an interesting range of diversification. A major questions stiII remaining to be answered include the history of stromatolite development and wether their morphology has \"evolved\" in addition to detailed information concerning Cenozoic nonmarine stromatolites which precipitate carbonate and the Recent giant stromatolites which trap particles. For these reasons Claude Monty, in 1981, launched the first volume of what was going to be a series on \"Phanerozoic stromatolites\" in order to describe their morphology, microstructure and paleoecology and to present them in their stratigraphic context.

Stromatolites can be traced back to ∼3.5 billion years. They were widespread in the shorelines of ancient oceans and seas. However, they are uncommon nowadays, and basic information is lacking about how these unique carbonate structures developed. Here we study the unusually thick (3–5 cm) biofilms of the 79.2 °C outflow from Köröm thermal well (Hungary) and demonstrate that its microbial mat – carbonate architecture is similar to fossilized microdigitate stromatolites. Our observations reveal vertically oriented fibrous mineral fabrics, typical of stromatolites, in the red biofilm and clotted mesostructures, typical of thrombolites, in the green biofilm. These layers contain carbonate peloids and show network structures, formed by filamentous microbes. The 16S rRNA gene-based amplicon sequencing implies that numerous undescribed taxa may contribute to the carbonate mineralisation. The biofilms abundantly contain the phyla Bacteroidota, Pseudomonadota and Cyanobacteria. Geitlerinema PCC-8501 and Raineya are characteristic for the green biofilm, whereas uncultured Oxyphotobacteria, unc. Saprospiraceae and unc. Cytophagales are abundant in the red biofilm. A hydrogen-oxidizing Hydrogenobacter within the phylum Aquificota and unclassified Bacteria together with the phylum Deinococcota dominate the water and carbonate samples. The morphological structure and taxonomic composition of Köröm biofilm is a unique representation of the development processes of microbialite formations.

Jara‐Muñoz et al. report a new set of U‐Th and 14C dates obtained from stromatolites scattered along the western slopes of the Dead Sea escarpment and use them to establish a new lake‐level curve for part of the last glacial cycle. This curve is fundamentally different from previous reconstructions (Bartov et al., 2002, 2003; Hazan et al., 2005; Lisker et al., 2009; Machlus et al., 2000; Torfstein, Goldstein, Stein, & Enzel, 2013) and is characterized by very significant vertical uncertainties, which in practice, ignore the millennial‐timescale resolution of Lake Lisan dynamics that has been widely discussed before (Bartov et al., 2003; Haase‐Schramm et al., 2004; Torfstein, Goldstein, Stein, & Enzel, 2013), with important implications for understanding regional hydroclimate regimes and linkage to global climate engines. The differences between the new and previous lake‐level reconstructions warrant a critical evaluation of the new findings. We argue that rather than strengthening and refining the existing body of observations, the new data have been used separately, resulting in a misleading record. Key Points A new stromatolite‐based lake level reconstruction of the last glacial Lake Lisan contrasts previous reconstructions

Plate tectonics is a fundamental factor in the sustained habitability of Earth, but its time of onset is unknown, with ages ranging from the Hadaean to Proterozoic eons 1 – 3 . Plate motion is a key diagnostic to distinguish between plate and stagnant-lid tectonics, but palaeomagnetic tests have been thwarted because the planet’s oldest extant rocks have been metamorphosed and/or deformed 4 . Herein, we report palaeointensity data from Hadaean-age to Mesoarchaean-age single detrital zircons bearing primary magnetite inclusions from the Barberton Greenstone Belt of South Africa 5 . These reveal a pattern of palaeointensities from the Eoarchaean (about 3.9 billion years ago (Ga)) to Mesoarchaean (about 3.3 Ga) eras that is nearly identical to that defined by primary magnetizations from the Jack Hills (JH; Western Australia) 6 , 7 , further demonstrating the recording fidelity of select detrital zircons. Moreover, palaeofield values are nearly constant between about 3.9 Ga and about 3.4 Ga. This indicates unvarying latitudes, an observation distinct from plate tectonics of the past 600 million years (Myr) but predicted by stagnant-lid convection. If life originated by the Eoarchaean 8 , and persisted to the occurrence of stromatolites half a billion years later 9 , it did so when Earth was in a stagnant-lid regime, without plate-tectonics-driven geochemical cycling. Magnetic palaeointensity data from the Barberton Greenstone Belt (South Africa) as well as the Jack Hills (Western Australia) show nearly constant palaeofield values between 3.9 Ga and 3.4 Ga, providing evidence for stagnant-lid mantle convection.

Stromatolites archive critical information on Precambrian marine environments, but their geochemical signals are often obscured using complex diagenetic processes. Tonian stromatolites from the Weiji Formation, North China, show selective dolomitization in dark stromatolitic laminae, forming zoned dolomites. The zoned dolomite crystals with well‐preserved growth zoning record the evolution of diagenetic fluid, yet their genesis remains controversial. To constrain selective dolomitization processes and zoned dolomite formation in stromatolites, and further assess their reliability as paleoceanographic proxies, we use LA‐ICP‐TOF‐MS elemental mapping to reveal crystallization mechanisms and early diagenetic controls in stromatolitic carbonates. Results show distinct geochemical distribution patterns between dark and light stromatolitic laminae, reflecting complex microbial‐induced diagenetic reactions during early diagenesis. Fe is preferentially concentrated in dark stromatolitic layers, while Mn anomalously accumulates in light layers (with Mn/Fe ratio up to ∼2). Meanwhile, high terrigenous‐indicative elemental contents (Al‐Si‐K) are observed in dark laminae and the adjacent clay‐rich matrix. The anomalous Fe‐Mn distribution is attributed to the redox oscillations and terrigenous pulses (ROTP) model. Selective dolomitization proceeds through an Ion‐Exchange Motor mechanism during penecontemporaneous to early diagenesis, where Mg2+ derived from seawater undergoes dehydration via clay mineral adsorption and/or microbial mediation. Within ferroan zoned dolomite, elemental zoning exhibits alternating Mn‐enriched bands and Fe‐rich zones, indicating redox‐controlled diagenesis with preferential Mn(IV) reduction prior to Fe(II) mobilization. While Precambrian stromatolites remain valuable proxies for paleo‐ocean chemistry, our results emphasize the critical need for in situ analytical approaches to distinguish primary signals from diagenetic overprints in Precambrian carbonate systems.

Changes in microbialite abundance during the Archean and Paleoproterozoic have been attributed to a variety of environmental and biological factors, yet past work looking at large‐scale patterns of microbialite abundance generally assumes shallow marine deposition rather than incorporating specific settings. We compiled Archean and Paleoproterozoic microbialite occurrences and depositional environment information to assess how microbialite development and preservation changed across settings. Microbially induced sedimentary structures formed a significant part of the record, but may be undercounted as they were identified mostly in units that also contained stromatolites. While broad trends in abundance resembled previous compilations, critically, we found that more microbialites formed in tidal environments than subtidal marine. The proportion of terrestrially influenced (including tidal) microbialites peaked during periods of craton development and following the Great Oxidation Event and Huronian Glaciations. These findings highlight the importance of continental landmasses and tectonic processes in defining the distribution and preservation of early life.

Microbialites and peloids are commonly associated throughout the geologic record. Proterozoic carbonate megafacies are composed predominantly of micritic and peloidal limestones often interbedded with stromatolitic textures. The association is also common throughout carbonate ramps and platforms during the Phanerozoic. Recent investigations reveal that Hamelin Pool, located in Shark Bay, Western Australia, is a microbial carbonate factory that provides a modern analog for the microbialite-micritic sediment facies associations that are so prevalent in the geologic record. Hamelin Pool contains the largest known living marine stromatolite system in the world. Although best known for the constructive microbial processes that lead to formation of these stromatolites, our comprehensive mapping has revealed that erosion and degradation of weakly lithified microbial mats in Hamelin Pool leads to the extensive production and accumulation of sand-sized micritic grains. Over 40 km 2 of upper intertidal shoreline in the pool contain unlithified to weakly lithified microbial pustular sheet mats, which erode to release irregular peloidal grains. In addition, over 20 km 2 of gelatinous microbial mats, with thin brittle layers of micrite, colonize subtidal pavements. When these gelatinous mats erode, the micritic layers break down to form platey, micritic intraclasts with irregular boundaries. Together, the irregular micritic grains from pustular sheet mats and gelatinous pavement mats make up nearly 26% of the total sediment in the pool, plausibly producing ~ 24,000 metric tons of microbial sediment per year. As such, Hamelin Pool can be seen as a microbial carbonate factory, with construction by lithifying microbial mats forming microbialites, and erosion and degradation of weakly lithified microbial mats resulting in extensive production of sand-sized micritic sediments. Insight from these modern examples may have direct applicability for recognition of sedimentary deposits of microbial origin in the geologic record.

Some cyanobacteria use light outside the visible spectrum for oxygenic photosynthesis. The far-red light (FRL) region is made accessible through a complex acclimation process that involves the formation of new phycobilisomes and photosystems containing chlorophyll f . Diverse cyanobacteria ranging from unicellular to branched-filamentous forms show this response. These organisms have been isolated from shaded environments such as microbial mats, soil, rock, and stromatolites. However, the full spread of chlorophyll f -containing species in nature is still unknown. Currently, discovering new chlorophyll f cyanobacteria involves lengthy incubation times under selective far-red light. We have used a marker gene to detect chlorophyll f organisms in environmental samples and metagenomic data. This marker, apcE2 , encodes a phycobilisome linker associated with FRL-photosynthesis. By focusing on a far-red motif within the sequence, degenerate PCR and BLAST searches can effectively discriminate against the normal chlorophyll a -associated apcE . Even short recovered sequences carry enough information for phylogenetic placement. Markers of chlorophyll f photosynthesis were found in metagenomic datasets from diverse environments around the globe, including cyanobacterial symbionts, hypersaline lakes, corals, and the Arctic/Antarctic regions. This additional information enabled higher phylogenetic resolution supporting the hypothesis that vertical descent, as opposed to horizontal gene transfer, is largely responsible for this phenotype’s distribution.

This study analyzes Brazilian stromatolites in Lagoa Salgada, serving as analogs for pre-salt rocks in the Santos and Campos basins. Despite their excellent petrophysical properties, such as high porosity and permeability, these reservoirs present challenges in fluid flow modeling and simulation. The research investigates various factors influencing the development of carbonate reservoirs, including diagenetic processes employing several techniques, such as microcomputed tomography (micro-CT) and digital rock physics (DRP), to study petrophysical and geological characteristics. Additionally, through numerical simulations, the properties of fluid flow in different microfacies of stromatolites are estimated, with particular emphasis on understanding and highlighting changes in the direction of fluid flow in the three characterized microfacies. These findings offer crucial insights into optimizing oil and gas exploration and production techniques in carbonate reservoirs, providing a comprehensive understanding of the dynamics of fluid transport in porous media, especially in terms of directional changes within stromatolites.

A recent field-intensive program in Shark Bay, Western Australia provides new multi-scale perspectives on the world’s most extensive modern stromatolite system. Mapping revealed a unique geographic distribution of morphologically distinct stromatolite structures, many of them previously undocumented. These distinctive structures combined with characteristic shelf physiography define eight ‘Stromatolite Provinces’. Morphological and molecular studies of microbial mat composition resulted in a revised growth model where coccoid cyanobacteria predominate in mat communities forming lithified discrete stromatolite buildups. This contradicts traditional views that stromatolites with the best lamination in Hamelin Pool are formed by filamentous cyanobacterial mats. Finally, analysis of internal fabrics of stromatolites revealed pervasive precipitation of microcrystalline carbonate (i.e. micrite) in microbial mats forming framework and cement that may be analogous to the micritic microstructures typical of Precambrian stromatolites. These discoveries represent fundamental advances in our knowledge of the Shark Bay microbial system, laying a foundation for detailed studies of stromatolite morphogenesis that will advance our understanding of benthic ecosystems on the early Earth.