Distribution Of Stromatolites Research Articles

Palaeoecological Implications of Lower-Middle Triassic Stromatolites and Microbe-Metazoan Build-Ups in the Germanic Basin: Insights into the Aftermath of the Permian–Triassic Crisis

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.

Carbonate fabric diversity and environmental heterogeneity in the late Mesoproterozoic Era

AbstractTime-distinctive features within carbonate rocks, specifically the presence, abundance and distribution of stromatolites, molar-tooth fabric and specific morphologies of marine cement, have been identified as potential indicators of global-scale changes in the chemistry of marine environments. Recently, Cantineet al.(2019) introduced a database approach seeking to quantify spatial and temporal patterns in these carbonate features through the Precambrian. Despite the coarse temporal scale, results support earlier inferences of temporal change in carbonate sedimentation. Here, we use original field notes to dissect late Mesoproterozoic (˜1.3 to 1.0 Ga) carbonate strata at a high resolution, analyse time-distinctive carbonate fabrics within a database context and compare sedimentological patterns within this narrow time range to observations of the Proterozoic as a whole. Late Mesoproterozoic strata contain a variety of features (e.g. stromatolites, seafloor precipitates, herringbone carbonate, molar-tooth carbonate), often in close spatial and temporal proximity, that are commonly considered to be temporally restricted during the Precambrian. The spatial distribution of such features within Mesoproterozoic basins demonstrates the importance of recognizing even rare occurrences of time-distinctive facies and permits inference of environmental drivers that may have interacted to affect carbonate precipitation. Such spatial variability reflects a subtle division of Mesoproterozoic carbonate platform environments driven by globally high sea level, elevated carbonate saturation and a low-oxygen water column. The heterogeneous, mosaic nature of environments appears to be a hallmark of Mesoproterozoic carbonate sedimentation and emphasizes the importance of these basins in understanding longer-term trends in carbonate deposition.

西オーストラリア州ハメリンプールの完新世二枚貝<i>Fragum erugatum</i>の形態から復元した塩分濃度変化とストロマトライトの形成条件についての意義

Hamelin Pool is well known as one of the best and most extensive localities of modern stromatolites. The distribution of stromatolites at this locality can be explained by the existence of a high-salinity environment. Salinity variations reflect sea-level fluctuations combined with changes in landform during the post-glacial period. Stromatolite formation apparently began at 1250 BP in Hamelin Pool. It has been assumed that this event was also related to salinity changes. Focusing on Fragum erugatum (Bivalvia: Cardiidae), which is known to change the height/length ratio of shells with salinity, the author attempted to reconstruct paleosalinity over a period of 4000 years at Hamelin Pool. Shells were sampled at 13 points along a 500-m transect perpendicular to the coastline on a ridge northeast of Flagpole Landing. The height/length ratio was measured and the 14C age was determined. Furthermore, the height/length ratio was converted into a salinity scale based on several previous studies showing the relationship between ratio and salinity. Results showed that salinity rose rapidly to 58‰ when stromatolites first developed at Hamelin Pool.

Platforms: Shorikha formation of the Turukhansk uplift, Siberia

the shorikha basin characterized by a thick (>800 m) sequence of carbonate sediments in the upper part of the riphean section in the turukhansk uplift of siberia illustrates the dynamics of taxonomic diversity and abundance of stromatolite buildups related to changes in the structure of a carbonate platform (replacement of the relatively deep ramp by a spacious shallow shelf) and fluctuations of the relative sea level. it is shown that abundance and taxonomic diversity of stromatolite buildups were maximal in deep zones of the outer ramp being reduced to almost zero values in shallow settings of the carbonate shelf. the appearance of columnar stromatolites coincided in this basin only with brief sea-level rises (second-order transgressions). stromatolite-forming microbial communities represented an active producer of carbonate sediments for the entire basin, while the distribution of stromatolites through ramps was determined by geochemical barriers. disappearance of stromatolites from shallow carbonate shelves was controlled by rapid reduction in carbonate-production rates.

Growth morphologies of modern marine stromatolites: A case study from Highborne Cay, Bahamas

Stromatolites are a uniquely coupled geo-biosphere system, which potentially records important paleoenvironmental and biological information. Characterizing and distinguishing between the biological and physical factors that control stromatolite morphogenesis, therefore, has important implications for the understanding of modern stromatolites and the interpretation of ancient systems. This paper documents the occurrence and distribution of stromatolites with distinct growth morphologies in the Highborne Cay reef system and other locations in Exuma Cays, Bahamas, and explores the relative contributions of physical and biological environmental factors controlling stromatolite shape. Our observations suggest that macro-scale growth morphologies of Exuma stromatolites are primarily controlled by accommodation space, hydrodynamics, and sedimentation patterns. The latter are critical for the stromatolite ecosystem in that the suspended sediment provides grains for trapping and binding and thus stromatolite accretion. Furthermore, sediment burial removes macroalgae, allowing the prokaryotic community to dominate. Changes in sedimentation patterns and frequency allow for the colonization of stromatolites by macroalgae and boring macrofauna, which, in time, destroy and degrade the stromatolite structure.