Peritidal Stromatolites Research Articles

Conserved bacterial genomes from two geographically isolated peritidal stromatolite formations shed light on potential functional guilds.

Stromatolites are complex microbial mats that form lithified layers. Fossilized stromatolites are the oldest evidence of cellular life on Earth, dating back over 3.4 billion years. Modern stromatolites are relatively rare but may provide clues about the function and evolution of their ancient counterparts. In this study, we focus on peritidal stromatolites occurring at Cape Recife and Schoenmakerskop on the southeastern South African coastline, the former being morphologically and structurally similar to fossilized phosphatic stromatolites formations. Using assembled shotgun metagenomic analysis, we obtained 183 genomic bins, of which the most dominant taxa were from the Cyanobacteria phylum. We identified functional gene sets in genomic bins conserved across two geographically isolated stromatolite formations, which included relatively high copy numbers of genes involved in the reduction of nitrates and phosphatic compounds. Additionally, we found little evidence of Archaeal species in these stromatolites, suggesting that they may not play an important role in peritidal stromatolite formations, as proposed for hypersaline formations.

Peritidal stromatolites as indicators of stepping-stone freshwater resources on the Palaeo-Agulhas Plain landscape

Natural sources of freshwater are a limiting feature to the distribution of terrestrial species that rely on regular hydration, especially in coastal environments. Early modern humans would similarly be restricted by water supply and likely would have congregated or settled in close proximity to permanent water bodies such as beyond the estuarine extent of large rivers. However, along the modern south coast of southern Africa, for example, distances between freshwater from rivers can exceed what would be convenient daily walking limits. In the absence of alternative water supply, or a means of water storage, these distances would preclude human settlement beyond river borders. Recent discovery of living peritidal stromatolites forming along the southern South African coastline suggests a potential alternative water source. These unique ecosystems form only at locations where groundwater rich in calcium carbonate meets periodic marine intrusion along the coastal margin. Calcium carbonate is precipitated by cyanobacteria and sediment is trapped by diatoms, primarily, to form layered deposits that preserve into the fossil record. Critical to the formation and growth of these stromatolites is a fresh, uninterrupted supply of groundwater. During their growth, the peritidal stromatolites accumulate and retain this freshwater through the formation of rimstone dams and barrage pools at the seaward margin of neocoastal geological outcrops. Recognising the presence of permanent water sources other than rivers for early humans is challenging; however, these stromatolites provide a clear signature of an alternative water resource. Here we review the modern prevalence of peritidal stromatolites in this region, of which approximately 540 are known along a 200 km stretch of South Africa's southern coastline featuring only 11 estuaries. This is linked to features (cf. rimstone dams and barrage pools) resembling peritidal stromatolites in the adjacent Palaeo-Agulhas Plain landscape using multibeam echosounder and side-scan sonar data and contextualised as a possible water resource for early modern humans.

Macroinvertebrate variability between microhabitats of peritidal stromatolites along the South African coast

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 605:37-47 (2018) - DOI: https://doi.org/10.3354/meps12741 Macroinvertebrate variability between microhabitats of peritidal stromatolites along the South African coast Ross-Lynne A. Weston1,*, Renzo Perissinotto1, Gavin M. Rishworth1, Paul-Pierre Steyn2 1DST/NRF Research Chair in Shallow Water Ecosystems, and 2Department of Botany, Nelson Mandela University, Port Elizabeth 6031, South Africa *Corresponding author: rosslynne.weston747@gmail.com ABSTRACT: Along the coastline near Port Elizabeth, South Africa, actively accreting peritidal stromatolite systems host a persistent metazoan community, which seemingly does not disrupt or consistently graze upon these structures. Macroinvertebrate communities occurring in different microhabitats (or mesofabric types) within this system were compared. This was achieved by identifying and counting the invertebrates found across different mesofabric types at different depth profiles. Mesofabric type was an important predictor of the invertebrate assemblage but was not the primary driver of their distribution. One of the well-laminated mesofabrics had more invertebrates than expected. The seasonal changes observed (such as the greater metazoan abundance observed in colloform mat types in winter compared to the greater metazoan abundance found in rimstone mat types in summer) were attributed to resource availability, specifically macroalgae. These findings are discussed in light of top-down forcing by metazoans on stromatolite microhabitats, and the consequent refugia benefit offered by these structures. KEY WORDS: Peritidal communities · Microbialites · Mesofabric type · Niches · Invertebrates Full text in pdf format Supplementary material PreviousNextCite this article as: Weston RA, Perissinotto R, Rishworth GM, Steyn PP (2018) Macroinvertebrate variability between microhabitats of peritidal stromatolites along the South African coast. Mar Ecol Prog Ser 605:37-47. https://doi.org/10.3354/meps12741 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 605. Online publication date: October 26, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Macro- and meso-fabric structures of peritidal tufa stromatolites along the Eastern Cape coast of South Africa

Stromatolites are rare in modern ecosystems due to factors associated with seawater chemistry or biological competition that restrict their formation. Actively calcifying stromatolites, near the Kei Mouth in the Eastern Cape, South Africa, were discovered in the early 2000s. Similar deposits were later described along a 200km stretch on the south coast of Port Elizabeth. This study aims to describe the environmental setting, the macro- and meso-structures, as well as the evolution of the deposits near Port Elizabeth compared to other similar formations. Results show that the general environmental setting is consistent amongst peritidal stromatolites, including those described in this study. In all instances stromatolite growth occurs on a wave-cut rocky platform in and around rock pools. Growth is maximal within the intertidal to supratidal zone, as a result of freshwater inflow via emerging mineral springs at the base of landward slopes, and the periodic intrusion of seawater via storm surges or wave splash. In comparison with other systems, the South African stromatolite formations exhibit an additional macro-structure (beachrock/conglomerate) and four previously undescribed meso-structures: wrinkled laminar, laminar flat, rhizoliths, and blistered types. The South African stromatolites are also larger and more concentrated than other peritidal stromatolites, which could be due to this area having more suitable growth conditions.

Patterns and drivers of benthic macrofaunal communities dwelling within extant peritidal stromatolites

AbstractMetazoans contributed historically to the decline of the microbialites and continue to restrict their formation in most modern environments through grazing and burrowing pressures. Recent evidence suggests that metazoans can coexist with layered microbialites (stromatolites). However, the possible drivers of the invertebrate assemblage directly associated with these unique habitats are not well‐understood. This study measured environmental and resource variables within peritidal stromatolites along the South African coastline and related these to the infaunal metazoan community. Clitellates (Naididae and Enchtraeidae), malacostracans (Amphipoda, Isopoda and Tanaidacea), insect larvae (Chironomidae), and polychaetes (Nereididae) were the most abundant groups. The benthic macrofaunal community was most strongly related to salinity, nutrients (dissolved inorganic nitrogen and phosphorus) and macroalgal cover. This suggests that the distribution of some species was restricted by physiological tolerances associated with salinity, while others responded to resource variability within the primary producer community. The absence of an apparent relationship between stromatolite microalgal biomass or composition and the metazoan community occupying the matrix indicates that the invertebrates might be relying on other primary producers as a food resource, such as macroalgae. This suggests that the benthic macrofaunal community may have a limited direct grazing effect on the stromatolite matrix, thereby not hindering the formation of its typical layered fabric.

Peritidal stromatolites at the convergence of groundwater seepage and marine incursion: Patterns of salinity, temperature and nutrient variability

Living peritidal stromatolites forming at the interface of coastal groundwater seepage and regular marine input are known from only a few locations globally, including South Africa, Western Australia and Northern Ireland. In contrast to modern stromatolites from exclusively fresh or marine waters, which persist due to high calcium carbonate saturation states or hypersaline and erosive conditions (which exclude organisms that might disrupt or out-compete the stromatolite-forming benthic microalgae), the factors supporting stromatolite formation at peritidal locations have not been well-documented. Therefore, the aim of this study was to investigate the fine-scale physico-chemical parameters in terms of pool temperature, salinity and nutrient dynamics at three representative sites along the coastline near Port Elizabeth, South Africa. These parameters were assessed with reference to potential physical, meteorological and ocean drivers using a linear or linear mixed-effects modelling approach. Results demonstrate that nutrient inputs into the pools supporting the majority of stromatolite accretion (barrage pools) are driven by groundwater seepage site-specific properties related to anthropogenic occupation (dissolved inorganic nitrogen; DIN) as well as marine water incursion (dissolved inorganic phosphorus; DIP). Pool temperature is a function of seasonal ambient variability while salinity reflects regular state shifts from fresh to marine conditions, which are related to tidal amplitude and swell height. The regular marine incursions likely promote benthic primary biomass in the phosphorus-limited stromatolite pools, as well as preclude organisms which might otherwise outcompete or disrupt the stromatolite microalgae due to intolerances to extreme (~1.5 to ≥30) salinity variability.

Dynamic sedimentation of Paleoproterozoic continental margin iron formation, Labrador Trough, Canada: Paleoenvironments and sequence stratigraphy

The Paleoproterozoic Sokoman Formation (ca. 1.88Ga) of the Labrador Trough, eastern Canada, is a ca. 100-m-thick succession of interbedded iron formation and fine-grained, terrigenous clastic sedimentary rocks. Detailed examination of drill cores and outcrops indicates a dynamic paleoshelf where an oxygen-stratified water column, coastal upwelling of hydrothermally derived Fe and Si, as well as tide- and storm-generated currents controlled lithofacies character. Vertical and lateral facies stacking patterns record deposition through two relative sea-level cycles that produced seven distinct lithofacies comprising two unconformity-bounded sequences. Sequence 1 reflects deposition of hematitic peritidal iron formation as deep as the upper shoreface. Sequence 2 is truncated by later erosion and encompasses the change to deeper-water accumulation of magnetite and Fe silicate-rich iron formation. The character and lateral distribution of redox-sensitive facies indicate that iron formation accumulation was controlled as much by shelf hydraulics as oxygen levels. The development of a suboxic surface ocean is interpreted to reflect photosynthetic oxygen production from a combination of peritidal stromatolites and cyanobacterial phytoplankton that flourished in nutrient-rich, upwelled waters offshore.Deposition of other continental margin iron formations also occurred on Paleoproterozoic shelves that were favorably positioned for coastal upwelling. Variability between iron formations reflects intrinsic factors such as shelf profile, fluvial contribution, eolian input, evaporation rates, and coastal current systems, which influenced upwelling dynamics and the delivery of Fe, Si, and nutrients. Aridity onshore was a primary depositional control since it governed the transport and type of diluting terrigenous clastics as well as evaporative precipitation along the coastline.As in the Phanerozoic, unconformities, and transgressive and maximum flooding surfaces frame iron formation sequences, but with important differences. The absence of trace and body fossils as well as lack of terrestrial vegetation can make the recognition of these surfaces difficult. Transgressive surfaces can also be easily mistaken for Phanerozoic-style maximum flooding surfaces since stratigraphic condensation was restricted to inboard environments during ravinement. Outboard the accumulation of fresh precipitates increased sedimentation to produce a maximum flooding surface not usually marked by a prominent depositional hiatus. Understanding these differences is essential for establishing an accurate sequence stratigraphic framework. Such context is the backdrop for properly interpreting the sedimentology, oceanography, microbial ecology, and geochemistry of continental margin iron formations.

Rock pool tufa stromatolites on a modern South African wave‐cut platform: partial analogues for Archaean stromatolites?

Terra Nova, 23, 375–381, 2011AbstractCalcifying tufa stromatolites are forming on a high energy coast of the South African Indian Ocean. The tufa stromatolites form in upper intertidal to supra tidal rock pools, encrust bedrock and are linked both laterally and vertically to physico‐chemical properties of their pool water. Calcification only occurs in pools where dissolved carbonate‐rich, spring‐fed groundwater is routed, and δ18O values are consistent with calcification in a mixture of freshwater and seawater. Increasing pH and less negative isotope values away from the spring are consistent with CO2 degassing and in‐stream calcification, albeit with some in‐mixing of seawater. The rocky shore setting of these active tufa stromatolites is new and invites serious comparison with some Archaean rocky substrate peritidal stromatolites (e.g. the c. 3.45 Ga Strelley Pool sequences, Pilbara Craton). This new association shows that initial encrustation of rocky intertidal substrates can begin with freshwater influence in the intertidal zone, a facies detail that should be sought in ancient peritidal stromatolites.

Abiogenic, microbial and hybrid authigenic crusts: components of Precambrian stromatolites

Authigenic seafloor carbonate crusts include fenestrate microbialite, thrombolite, and four types here designated Fine-grained Crust, Sparry Crust, Hybrid Sparry Fine-grained Crust, and Sparry Crust plus Coarse Grains. Each of the latter four types includes at least some layered examples that have generally been regarded as stromatolites. Recognition and interpretation of these various deposits assists understanding of stromatolite development. Sparry Crust is common in the Late Archaean-Mesoproterozoic. It includes botryoidal fans and other crystal pseudomorphs, microdigitate stromatolite, dendrite, isopachous laminite, and herringbone calcite. Although differing in primary mineralogy and bedform, these are all characterized by coarse sparry, commonly radial fibrous, fabric and appear light coloured in thin-section. They have commonly been referred to as seafloor cement, although they formed at the open sediment-water interface rather than as void-fills. Two of them in particular, isopachous laminite and microdigitate ‘tufa’, typically form isopachous layers with good vertical inheritance and have been regarded as stromatolites. In contrast to Sparry Crust, Fine-grained Crust has fine-grained (micritic, clotted, peloidal, filamentous) microfabric that appears dark in thin-section, and irregular uneven layering with relatively poor inheritance. Mixed crusts, composed of millimetric alternations of Sparry and Fine-grained crust, are here termed Hybrid Sparry Fine-grained Crust. Sparry Crust with coarse allochthonous grains - here termed Sparry Crust plus Coarse Grains – includes some examples that have been given formal stromatolite names, e.g., Gongylina and Omachtenia. Sparry, Hybrid, and Fine-grained crusts are common components of Precambrian stromatolites. Their relative abundances change through time. Archaean stromatolite fabrics are commonly obscured by recrystallization, but their preserved lamina arrangements suggest that many of them could be composed mainly of Sparry or Hybrid crust. During the Palaeoproterozoic-Mesoproterozoic, Sparry Crust fabrics were common in peritidal stromatolites, whereas Hybrid Crust appears to have dominated large subtidal domes and columns. Fine-grained Crust may not have become generally abundant until the Neoproterozoic, when it commonly formed both stromatolites and thrombolites. Phanerozoic normal marine stromatolites are also typically composed of Fine-grained Crust. Present-day analogues of Sparry Crust fabrics occur in some speleothem, hot spring, and splash-zone marine crusts, and of Fine-grained Crust in lithified microbial mats. Light-dark millimetric alternations of sparry and fine-grained crust that characterize Hybrid Crust have analogues in freshwater stromatolites. Taken together, these comparisons suggest that some Precambrian stromatolites are abiogenic, some microbial, and others are intimate hybrid mixtures of the two, and that - preservation permitting - these varieties can be distinguished using microfabric and lamina criteria.

Significance of stromatolites for the environmental interpretation of the Buntsandstein (Lower Triassic) rocks

When interpreting the depositional environment of the Buntsandstein sequence, thin stromatolite layers, if present, were often overlooked or given short shrift. The present paper provides evidence of value of stromatolites for the environmental interpretation of the Buntsandstein rocks. Algal stromatolites found in western Poland occur in form of thrombolites, LLH-type structures, SH-type structures, and rarely as oncolites. Stromatolites are usually associated with oolites. Very often stromatolites show important traces of scouring and channelling action of water. Since stromatolites occurred in the zone of clastic-carbonate deposition they were covered up by continuous sheet of detrital grains. Periodic catastrophic erosion and deposition was produced by hurricanes and severe storms in the peritidal and shallow subtidal zone. It is possible to distinguish the peritidal and subtidal stromatolites. In the vicinity of stromatolites are of frequent occurrence spirorbids, conchostracs, gastropods, and rare foraminifers. Besides, spirorbids are associated with stromatolites — they constituted the initial hard substratum for the stromatolitic structures and sometimes they also occur inside stromatolites. The not-hypersaline sedimentary environment of the Buntsandstein rocks can be compared with modern environments of the Persian Gulf and the Gulf of Aqaba.