Calcium carbonate crystal fans: Geologic occurrences and controls on growth

2021 ◽  
Author(s):  
Adam Woods
Keyword(s):  
Calcium Carbonate ◽  
Middle Triassic ◽  
Carbonate Platform ◽  
Lower Triassic ◽  
High Energy ◽  
Seawater Chemistry ◽  
Sedimentary Environments ◽  
Cap Carbonates ◽  
Depositional Systems ◽  
Intertidal Environments

<p>Fans and hemispheres comprised of crystals of calcium carbonate that directly grew on the seafloor are an intriguing feature of ancient carbonate environments. Calcium carbonate fans from across Earth history are typically made up of crystals of neomorphosed calcium carbonate that maintain an acicular morphology that is pseudohexagonal in cross – section with blunt terminations, pointing to an aragonite precursor. Crystal fans may occur as isolated bodies, or may form larger aggregates that are sometimes associated with microbialites, and form larger, reef – like structures. Some of the first occurrences of these features are within Neoarchean carbonates, when the crystals fans grew to impressive sizes, with lengths of over 1 m, formed layers of marine cement that reached thicknesses of up to several meters, are laterally continuous over 10s of km or more, and formed across carbonate platform settings from high energy subtidal settings to lower intertidal environments. Crystalline carbonate fans become less common and smaller (cm – scale) in the Paleoproterozoic, and nearly disappear prior to the Neoproterozoic, when they are associated with cap carbonates, and are primarily found in deeper water or outer shelf settings with low sedimentation rates. Seafloor cements are rare during the Phanerozoic, and are typically limited to small geographic areas with unusual sedimentary conditions, or are found in void spaces, where seawater chemistry was able to undergo modifications that would allow precipitation of cement fans. The exception is during the interval of time that followed the Permian – Triassic mass extinction, when small, cm – scale fans and hemispheres are found in Lower Triassic and lowermost Middle Triassic rocks. These cement fans occur in a variety of settings, although they are typically found in deeper water environments. Calcium carbonate fans that formed following the Permian – Triassic extinction may have microbial remains preserved within the cements, and are frequently found in close lateral or stratigraphic association with microbialites. However, some examples of post – extinction carbonate fans appear to have formed abiotically, without any microbial influence. Overall, crystalline calcium carbonate fans signal high levels of calcium carbonate supersaturation in ancient oceans. The initial decline in seafloor cement growth from the Neoarchean into the Proterozoic may have been the result of accelerated micrite production, while Neoproterozoic calcium carbonate fan growth is associated with glacial decay and retreat. Lower Triassic seafloor cements are likely the result of stratification and stagnation of the deep oceans that led to enhanced alkalinity. Calcium carbonate crystal fans are an intriguing feature of ancient carbonates that signal depositional systems and ocean chemistry that is much different from modern ocean, and provide a fascinating glimpse into non – uniformitarian sedimentary environments.</p>

Regressive-transgressive cyclothem with facies record of the re-flooding window in the Late Silurian carbonate succession (Podolia, Ukraine)

2015 ◽  
Vol 65 (3) ◽  
pp. 297-318
Author(s):  
Piotr Łuczyński ◽  
Wojciech Kozłowski ◽  
Stanisław Skompski
Keyword(s):  
Shallow Water ◽  
Gamma Ray ◽  
Carbonate Platform ◽  
High Energy ◽  
Scale Model ◽  
Small Scale ◽  
Time Interval ◽  
Sea Level Changes ◽  
Depositional Systems ◽  
Small Scale Model

AbstractThe term “re-flooding window” was recently proposed as a time-interval connected with the transgressive stage of present day peri-reefal development. In the analysis presented here, a fossil record of a re-flooding window has been recognized. Nine Late Silurian carbonate sections exposed on the banks of the Dnister River in Podolia (Ukraine) have been correlated base on bed-by-bed microfacies analysis and spectral gamma ray (SGR) measurements. Correlated were sections representing settings ranging from the inner part of a shallow-water carbonate platform to its slope, through an organic buildup. The reconstructed depositional scenario has been divided into six development stages, with the first three representing a regressive interval and the latter three a transgressive interval of the basin’s history. The re-flooding window has been identified at the beginning of a transgressive part of the succession. Surprisingly, it is characterized by an extremely fast growth of a shallow, tide-dominated platform and by deposition of calciturbiditic layers in a more basinal area. The interpreted succession is a small-scale model illustrating the reaction of carbonate depositional sub-environments to sea level changes and determining the facies position of the stromatoporoid buildups within the facies pattern on a Silurian shelf. The use of SGR analyses in shallow water, partly high-energy, carbonate facies, both for correlation purposes and for identifying depositional systems, is a relatively new method, and thus can serve as a reference for other studies of similar facies assortment.

scholarly journals New biostratigraphic evidence of Late Permian to Late Triassic deposits from Central Tibet and their paleogeographic implications

Lithosphere ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 683-696 ◽  
Author(s):  
Gui-chun Wu ◽  
Zhan-sheng Ji ◽  
Wei-hua Liao ◽  
Jian-xin Yao
Keyword(s):  
Middle Triassic ◽  
Carbonate Platform ◽  
Lower Triassic ◽  
Upper Triassic ◽  
Suture Zone ◽  
Late Triassic ◽  
Upper Permian ◽  
Early Triassic ◽  
Late Permian ◽  
The North

Abstract Triassic deposits in the Bangong-Nujiang Suture Zone are important for understanding its tectonic nature and evolutionary history, but have not been systematically studied due to a lack of biostratigraphic data. For a long time, the Upper Triassic Quehala Group featuring clasolite has been regarded as the only rocky unit. In recent years, the silicite-dominated Gajia Formation that bears radiolarian fossils was suggested to represent Ladinian to Carnian deposits. The Upper Permian and Lower Triassic rocks have never been excavated and thus are considered to be absent. This research, however, reveals that fossils aged from the Late Permian to Anisian of the Middle Triassic and Norian of the Late Triassic have been preserved in the central Bangong-Nujiang Suture Zone, which provides evidence of Upper Permian to early Middle Triassic deposits and provides new insights on the Upper Triassic strata as well. A new Triassic strata succession is thus proposed for the Bangong-Nujiang Suture Zone, and it demonstrates great similarities with those from Lhasa to the south and Qiangtang to the north. Therefore, we deduce that the Bangong-Nujiang Suture Zone was under a similar depositional setting as its two adjacent terranes, and it was likely a carbonate platform background because limestones were predominant across the Triassic. The newly acquired biostratigraphic data indicate that Lhasa and Qiangtang could not have been located on two separate continents with disparate sedimentary settings; therefore, the Bangong-Nujiang Suture Zone likely did not represent a large ocean between them. This conclusion is supported by lithostratigraphic and paleomagnetic research, which revealed that Lhasa and Qiangtang were positioned at low to middle latitudes during the Early Triassic. Combining this conclusion with fossil evidence, we suggest that the three main Tibetan terranes were in the same palaeobiogeographic division with South China, at least during the Latest Permian to Early Triassic. The Early Triassic conodont species Pachycladina obliqua is probably a fossil sign of middle to low latitudes in palaeogeography.

Patterns of Evolution of the Ediacaran Soft-Bodied Biota

2014 ◽  
Vol 88 (2) ◽  
pp. 269-283 ◽  
Author(s):  
Dmitriy Grazhdankin
Keyword(s):  
High Energy ◽  
Ecosystem Engineering ◽  
Low Energy ◽  
Geological Time ◽  
Time Intervals ◽  
Inner Shelf ◽  
Sedimentary Environments ◽  
Burrowing Activity ◽  
Ecological Associations ◽  
Channel Systems

When each of the Avalon-, Ediacara-, and Nama-type fossil assemblages are tracked through geological time, there appear to be changes in species composition and diversity, almost synchronized between different sedimentary environments, allowing a subdivision of the late Ediacaran into the Redkinian, Belomorian and Kotlinian geological time intervals. The Redkinian (580–559 Ma) is characterized by first appearance of both eumetazoan traces and macroscopic organisms (frondomorphs and vendobionts) in a form of Avalon-type communities in the inner shelf environment, whereas coeval Ediacara-type communities remained depauperate. The Belomorian (559–550 Ma) is marked by the advent of eumetazoan burrowing activity in the inner shelf, diversification of frondomorphs, migration of vendobionts from the inner shelf into higher energy environments, and appearance of tribrachiomorphs and bilateralomorphs. Ediacaran organisms formed distinctive ecological associations that coexisted in the low-energy inner shelf (Avalon-type communities), in the wave- and current-agitated shoreface (Ediacara-type communities), and in the high-energy distributary systems (Nama-type communities). The Kotlinian (550–540 Ma) witnessed an expansion of the burrowing activity into wave- and current-agitated shoreface, disappearance of vendobionts, tribrachiomorphs and bilateralomorphs in wave- and current-agitated shoreface, together with a drop in frondomorph diversity. High-energy distributary channel systems of prodeltas served as refugia for Nama-type communities that survived until the end of the Ediacaran and disappeared when the burrowing activity reached high-energy environments. This pattern is interpreted as an expression of ecosystem engineering by eumetazoans, with the Ediacaran organisms being progressively outcompeted by bilaterians.

Early and Middle Triassic trends in diversity, evenness, and size of foraminifers on a carbonate platform in south China: implications for tempo and mode of biotic recovery from the end-Permian mass extinction

Paleobiology ◽  
2011 ◽  
Vol 37 (3) ◽  
pp. 409-425 ◽  
Author(s):  
Jonathan L. Payne ◽  
Mindi Summers ◽  
Brianna L. Rego ◽  
Demir Altiner ◽  
Jiayong Wei ◽  
...  
Keyword(s):  
South China ◽  
Mass Extinction ◽  
Evolutionary Dynamics ◽  
Middle Triassic ◽  
Carbonate Platform ◽  
Early Triassic ◽  
Data Set ◽  
Recovery Pattern ◽  
Biotic Recovery ◽  
Permian Mass Extinction

Delayed biotic recovery from the end-Permian mass extinction has long been interpreted to result from environmental inhibition. Recently, evidence of more rapid recovery has begun to emerge, suggesting the role of environmental inhibition was previously overestimated. However, there have been few high-resolution taxonomic and ecological studies spanning the full Early and Middle Triassic recovery interval, leaving the precise pattern of recovery and underlying mechanisms poorly constrained. In this study, we document Early and Middle Triassic trends in taxonomic diversity, assemblage evenness, and size distribution of benthic foraminifers on an exceptionally exposed carbonate platform in south China. We observe gradual increases in all metrics through Early Triassic and earliest Middle Triassic time, with stable values reached early in the Anisian. There is little support in our data set for a substantial Early Triassic lag interval during the recovery of foraminifers or for a stepwise recovery pattern. The recovery pattern of foraminifers on the GBG corresponds well with available global data for this taxon and appears to parallel that of many benthic invertebrate clades. Early Triassic diversity increase in foraminifers was more gradual than in ammonoids and conodonts. However, foraminifers continued to increase in diversity, size, and evenness into Middle Triassic time, whereas diversity of ammonoids and conodonts declined. These contrasts suggest decoupling of recovery between benthic and pelagic environments; it is unclear whether these discrepancies reflect inherent contrasts in their evolutionary dynamics or the differential impact of Early Triassic ocean anoxia or associated environmental parameters on benthic ecosystems.

scholarly journals A Middle Triassic pachypleurosaur (Diapsida: Eosauropterygia) from a restricted carbonate ramp in the Western Carpathians (Gutenstein Formation, Fatric Unit): paleogeographic implications

2018 ◽  
Vol 69 (1) ◽  
pp. 3-16 ◽  
Author(s):  
Andrej Čerňanský ◽  
Nicole Klein ◽  
Ján Soták ◽  
Mário Olšavský ◽  
Juraj Šurka ◽  
...  
Keyword(s):  
Middle Triassic ◽  
Carbonate Platform ◽  
Small Body ◽  
Western Carpathians ◽  
Subtidal Zone ◽  
Postcranial Skeleton ◽  
Tatra Mountains ◽  
Carbonate Ramps ◽  
Shallow Subtidal ◽  
Central Western Carpathians

AbstractAn eosauropterygian skeleton found in the Middle Triassic (upper Anisian) Gutenstein Formation of the Fatric Unit (Demänovská dolina Valley, Low Tatra Mountains, Slovakia) represents the earliest known occurrence of marine tetrapods in the Western Carpathians. The specimen represents a partly articulated portion of the postcranial skeleton (nine dorsal vertebrae, coracoid, ribs, gastral ribs, pelvic girdle, femur and one zeugopodial element). It is assigned to the Pachypleurosauria, more precisely to theSerpianosaurus–Neusticosaurusclade based on the following combination of features: (1) small body size; (2) morphology of vertebrae, ribs and femur; (3) tripartite gastral ribs; and (4) microanatomy of the femur as revealed by μCT. Members of this clade were described from the epicontinental Germanic Basin and the Alpine Triassic (now southern Germany, Switzerland, Italy), and possibly from Spain. This finding shows that pachypleurosaur reptiles attained a broader geographical distribution during the Middle Triassic, with their geographical range reaching to the Central Western Carpathians. Pachypleurosaurs are often found in sediments formed in shallow, hypersaline carbonate-platform environments. The specimen found here occurs in a succession with vermicular limestones in a shallow subtidal zone and stromatolitic limestones in a peritidal zone, indicating that pachypleurosaurs inhabited hypersaline, restricted carbonate ramps in the Western Carpathians.

The onset of the early Toarcian flooding of the Pliensbachian carbonate platform of Central Tunisia (North-South Axis) as inferred from trace fossils and geochemistry

2021 ◽  
pp. SP514-2021-10
Author(s):  
Matías Reolid ◽  
Mohamed Soussi ◽  
Jesús Reolid ◽  
Wolfgang Ruebsam ◽  
Ilef Belhaj Taher ◽  
...  
Keyword(s):  
Carbonate Platform ◽  
High Energy ◽  
Trace Fossils ◽  
Energy Conditions ◽  
Local Conditions ◽  
Content Type ◽  
The North ◽  
Sea Bottom ◽  
Supplementary Material ◽  
South Axis

AbstractThe flooding of the Lower Jurassic shelf in the North Gondwana Palaeomargin during the early Toarcian occurred on a fragmented and irregular topography affected by differential subsidence—due to the activity of listric faults along the North-South Axis of Tunisia—that favoured lateral changes in facies and thickness at a kilometric scale. The onset of Toarcian sedimentation (Polymorphum ammonite Zone, NJT5c nannofossil Subzone) in two adjacent sections was characterised by the deposition of limestones under high-energy conditions. The Châabet El Attaris section was located in a depressed sub-basin, and recorded restricted environmental conditions owing to water stagnation and an oxygen-depleted sea-bottom. Therefore, dark mudstones developed, with increased TOC contents and enhanced accumulation of redox-sensitive elements. The sedimentation of limestones bearing gutter cast structures is related to gravity flows probably linked to storm activities. These processes favoured the remobilization of sediments at the sea floor, as well as oxygen input to bottom waters, as shown by the record of trace fossils including Zoophycos, Ophiomorpha, and secondarily, Chondrites and Diplocraterion. The thinly interbedded dark mudstones are locally rich in thin-shelled bivalves that re-colonised the sea bottom after the sedimentation of these high-energy deposits, and subsequently underwent mass mortality related to the return of oxygen-depleted conditions. The Kef El Hassine section is located in the upper part of a tilted, less subsident block, as indicated by its reduced thickness compared with the Châabet El Attaris section; the absence of dark mudstones implies oxic conditions. The Polymorphum Zone consists of limestones showing evidence of sedimentation under high-energy conditions, along with hardgrounds. The occurrence of Zoophycos (deep-tiers) in the upper part of some limestone beds of the Polymorphum Zone is linked to minor erosive processes. The top of the high-energy sequence—below the deposits of a marly interval corresponding to the Levisoni Zone—is interpreted as a hardground given the high content of belemnites and Arenicolites, some of them boring on the eroded Zoophycos and Thalassinoides. This study shows that the sedimentary expression of the Jenkyns Event is not uniform across Tunisia, supporting the importance of local conditions in determining the development of anoxic conditions.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5510162

Helmolepis cyphognathus, sp. nov., a new platysiagid actinopterygian from the Lower Triassic Sulphur Mountain Formation (British Columbia, Canada)

2005 ◽  
Vol 42 (1) ◽  
pp. 25-36 ◽  
Author(s):  
Andrew G Neuman ◽  
Raoul J Mutter
Keyword(s):  
British Columbia ◽  
New Species ◽  
Central Europe ◽  
Middle Triassic ◽  
Lower Triassic ◽  
Western Canada ◽  
Early Triassic ◽  
East Greenland ◽  
The Family ◽  
A New Species

A new species of stem actinopterygian, Helmolepis cyphognatus sp. nov., is reported from the Lower Triassic Sulphur Mountain Formation of western Canada (probably Smithian). This taxon differs from the only other known Early Triassic platysiagid, H. gracilis from the Lower Triassic Wordie Creek Formation of East Greenland (Griesbachian), in counts of branchiostegal rays, shape of the maxilla, shape (and possibly counts) of extrascapulars, and the size ratio of major opercular bones. In spite of their overall unfavorable preservation, the numerous available specimens amend our knowledge of the little known genus Helmolepis considerably: it has become evident that the morphology of Helmolepis cyphognatus sp. nov. comes closest to Platysiagum minus (Middle Triassic Besano Formation of central Europe). This study suggests placement of the two genera in the family Platysiagidae. Investigation of this new species also shows certain features of the cheek and the caudal fin are more primitive than previously believed, whereas the snout region is probably derived but of yet uncertain affinities in Helmolepis.

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