What Is The Makeup Of Dolostone

Dolostone

Marinoan cap dolostones are commonly overlain by limestones rich in aragonite crystal fans and/or by deep-water fine-grained siliciclastics.

From: The Geologic Time Scale , 2012

Sedimentary Petrology

Frederick L. Schwab , in Encyclopedia of Physical Scientific discipline and Technology (Third Edition), 2003

Iv.A Full general Origin and Mode of Occurrence of Mod and Ancient Carbonate Deposits

Limestone and dolostone are collectively referred to as carbonates because these two sedimentary rock types consist mainly of the minerals calcite (CaCO ₃), aragonite (CaCO_three), and dolomite [CaMg(CO₃)_two]. The term dolostone, proposed to specifically refer to the stone blazon composed of the mineral dolomite, has not gained wide usage, and sedimentary petrologists continue to habitually use the term dolomite for both the rock and the mineral. Almost all dolomite is produced by converting CaCO_iii minerals into the mineral dolomite later on the initial precipitation of either calcium carbonate mineral. This conversion process is referred to as dolomitization. Dolomitization can take identify almost immediately after limestone forms (penecontemporaneously), within a few days, weeks, or months of limestone formation (syngenetic dolomitization), or long after (years or even millions of years) (epigenetic dolomitization). Because most all dolomites were originally limestone it is appropriate to first hash out completely the process past which limestone is formed. This is because, except for the later dolomitization procedure, most dolomites form in the aforementioned initial way equally limestones. Similarly the aforementioned classification schemes can be used generally for dolomites every bit for limestones. Besides, identical depositional environments class the setting for both rock types. Afterwards this discussion of limestones, it will exist necessary to deal specifically with the item conditions that cause various limestone unit to become dolomite.

Limestone is formed almost exclusively by organisms in seawater (although there are some freshwater limestones too), either, by direct crystallization of dissolved calcium and carbonate to form shells, or every bit a by-product of the presence of organisms in seawater (which tin can alter the overall geochemical setting). In just a few noteworthy locales does direct, inorganic precipitation of carbonate occur. Carbonate deposition is nigh directly affected past the salinity of seawater (exclusively highly saline h2o volition poison carbonate-secreting organisms), its temperature (warm water promotes high organic activity), and its depth (shallow h2o is amend than deep h2o for carbonate formation and accumulation). In addition, limestone per se cannot form in areas where there is a loftier influx of terrigenous clastics. Rapid rates of influx of pebble-, cobble-, sand-, silt-, and clay-sized material both adversely affect carbonate-secreting organisms and "mask" any resulting carbonate sediments, producing instead carbonate-rich conglomerate, sandstone, and mudrock.

As a consequence of these factors, much limestone today is typically deposited in shallow water (less than 200   chiliad depth) continental shelf areas in and nearly the equator, rather than in high latitudes. Modern limestones are peculiarly common in reefs, tidal flats, lagoons, and windblown dunes developed upon shallow carbonate platforms or "banks" isolated in some manner (by altitude, by ocean currents) from terrigenous source areas. A classical site for modern shallow water carbonate deposition (which logically serves as a model for almost ancient limestone deposits) is the Bahama Banks off Florida. With i principal, and several other minor exceptions, nearly ancient limestone (and dolomite) deposits are coordinating in character and origin to these modern carbonates of the Bahama Banks.

The other chief volumetrically significant modern limestone deposits are the calcareous oozes that accumulate on the deep (3000   chiliad+) body of water floors. These oozes are equanimous of the shells of carbonate-secreting organisms that actually live about the surface of the sea waters within the photic (lighted) zone. Upon death, the shells or tests of these floating (pelagic) organisms slowly settle to the body of water bottom where they accumulate as unconsolidated calcareous ooze that eventually can be solidified past compaction, cementation, and recrystallization into deep water limestone. Such deep h2o pelagic limestones typically are bars to regions in which the maximum water depth is less than nearly 4500   m, equivalent to the calcium carbonate compensation depth or CCD. The CCD is a level below the surface of the sea at which the charge per unit of calcium carbonate solution exceeds the rate of its deposition by settling out of pelagic shells from to a higher place. Apparently the exact value of the CCD depends on the overall charge per unit of organic productivity in the surface waters every bit well as the chemic composition and temperature of the detail ocean, but, at the present time, it lies universally betwixt 4000 and 5000   one thousand. (The level of the CCD has, nonetheless, fluctuated rather dramatically in the past.) As a result, at the present time, the modern deep-sea floor deeper than 4500   m is the site of either siliceous ooze deposition (formed past the aggregating of silica-secreting pelagic organisms) or terrigenous (typically ruby) dirt-sized textile derived from the continents. As previously mentioned, aboriginal, fine-grained pelagic limestones occur only inside comparatively young sedimentary sequences (Jurassic and younger), considering the pelagic organisms capable of secreting calcium carbonate shells did not evolve until rather belatedly in earth history.

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SEDIMENTARY ROCKS | Dolomites

H.One thousand. Machel , in Encyclopedia of Geology, 2005

Seawater Dolomitization

Well-nigh postdepositional formation of massive dolostones probably results from 'seawater dolomitization'. There are a group of models of seawater dolomitization, whose common denominator is seawater as the chief dolomitizing fluid, and which differ in hydrology and/or depth and timing of dolomitization. All dolomites belonging to this grouping are postdepositional.

The Cenozoic dolostones of the Bahama platform, often used as an analogue for older dolomitized carbonate platforms elsewhere, tin be considered the type location for seawater dolomitization. Extensive petrographical and geochemical data bespeak that seawater and/or chemically slightly modified seawater was the main agent of dolomitization in the Bahama platform at shallow to intermediate depths and commensurate temperatures of less than almost 60°C.

The hydrology of and during seawater dolomitization is however very much contested. Various hydrological systems take been invoked to drive the large amounts of seawater needed for pervasive dolomitization through the Bahama platform, i.due east., thermal convection, a combination of thermal seawater convection and reflux of slightly evaporated seawater derived from above, or seawater driven by an overlying freshwater/seawater mixing zone during partial platform exposure, perchance layer past layer in several episodes.

The Bahama islands' dolostones really represent a hybrid with regard to the traditional, conventional classifications of models. Petrographical and geochemical data signal that seawater was the principal dolomitizing amanuensis, yet thermal convection, as a hydrological system and drive for dolomitization, is amend classified nether the burial (subsurface) models discussed below. Analogously, the regionally extensive Devonian dolostones in Alberta, western Canada, are besides a hybrid with regard to the conventional dolomitization models. These Devonian dolostones probably formed at depths of 300–1500   m at temperatures of about 50–80°C from chemically slightly modified seawater, and have been classified as burial dolostones. Another example is represented by the regionally extensive dolostones of the Carboniferous of Ireland, which are petrographically and geochemically very similar to the Devonian dolostones of Alberta, and whose genesis has been interpreted in an analogous way. In all cases, the hydrology that facilitated dolomitization is unclear, with thermal convection, reflux, compaction, tectonic expulsion, or a combination thereof, equally alternatives. The regionally extensive dolostones of the Cretaceous Soreq Germination in Israel stand for a Mesozoic example of this type of dolomitization. These Palaeozoic and Mesozoic dolostones can be (re-)classified along with the Cenozoic Bahama dolostones as 'seawater dolomites'. This classification dilemma arises from the historical evolution of our understanding of these dolostones, rather than invalidating the earlier 'burial' interpretations.

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The Ediacaran Period

G.M. Narbonne , ... J.One thousand. Gehling , in The Geologic Fourth dimension Scale, 2012

18.3.iv.i Carbon Isotopes (Effigy 18.5)

Basal Ediacaran "cap dolostones" are characterized by negative δ ¹³C_carb values (Knoll et al., 2006), which tend to get more negative during cap carbonate deposition reaching minima of about −v‰, after which they return to near 0‰ inside about 3 million years (Condon et al., 2005). The seawater δ¹³C tendency through the subsequent early on Ediacaran is poorly constrained due to age uncertainties. However, a render to very high positive δ¹³C_carb values (+six to 10‰) has been noted from many sections, e.g., NW Namibia and NE Svalbard (Halverson et al., 2005) and Brazil (Misi and Veizer, 1998), while the number of negative excursions recorded tin can be as many equally 5 (Sawaki et al., 2010).

FIGURE 18.5. Summary effigy of current agreement of ocean limerick evolution during the Ediacaran Period showing 1) a generalized seawater ⁸⁷Sr/⁸⁶Sr bend (two possibilities are shown for the Ediacaran Period with the curve of Sawaki et al. (2008) for South China uppermost); 2) a simplified δ¹³C bend based on various records (see text); and 3) ocean redox evolution based on Atomic number 26 speciation studies (Canfield et al., 2007, 2008; Li et al., 2010) whereby dashed lines represent more intermittent and full lines relatively continuous redox atmospheric condition.

A dominant characteristic in the Ediacaran δ¹³C record is an unusually negative δ¹³C_carb excursion with values below −x‰, commonly referred to as the Shuram (or Shuram–Wonoka) anomaly (Burns and Matter, 1993). Its magnitude is large, just its precise elapsing, historic period, and origin are uncertain (Grotzinger et al., 2011). Despite challenges to a primary estimation for this anomaly (Knauth and Kennedy, 2009; Derry, 2010), its global duplication at the same approximate level inside successions exhibiting a diverse range of facies, including Sr-rich limestones in Siberia (Pokrovskii et al., 2006; Melezhik et al., 2009; Le Guerroué, 2010), argues for a master oceanographic origin. Although no unambiguous bear witness for both glaciation and the full bibelot occurs in any single stratigraphic succession, the isotopic signature of dolomite beds within Member E in the uppermost Nyborg Germination (Norway) implies that the Mortensnes glaciation post-dated the nadir of the negative anomaly (Halverson et al., 2005). However, others disagree on the basis of pre-bibelot diamictites and evidence for cooling, respectively (Prave et al., 2009; Sawaki et al., 2010). In South Prc, at to the lowest degree three negative anomalies are nowadays inside the Doushantuo Germination with the upper bibelot EN3, perhaps coeval to the Shuram bibelot, catastrophe past 551 Ma (Condon et al., 2005). Low δ¹³C_carb values of the Shuram anomaly (EN3) appear to be decoupled from the coeval organic carbon (δ¹³C_org) record (Calver, 2000; Fike et al., 2006; McFadden et al., 2008; Bjerrum and Canfield, 2011; Grotzinger et al., 2011). Notwithstanding, the significance of the centre Ediacaran δ¹³C_org record is debatable as the human relationship betwixt δ^thirteenC_carb and δ¹³C_org is not the aforementioned in every succession.

A meaning and short-lived negative δ¹³C anomaly coincides with the Ediacaran–Cambrian boundary worldwide (due east.one thousand., Magaritz et al., 1986; Narbonne et al., 1994; Knoll et al., 1995; Saylor et al., 1998; Amthor et al., 2003) and serves as a global geochemical marker of this purlieus.

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The Atmosphere - History

Y. Donnadieu , ... Chiliad. Le Hir , in Treatise on Geochemistry (Second Edition), 2014

half-dozen.ix.6.four In the Backwash of the Snowball Glaciations

The alkalinity required to accrue the cap dolostone results from the weathering of continental carbonate during the supergreenhouse following the snowball event. This postsnowball environment needs to exist explored in more detail. It seems that the most prominent and rapid environmental perturbations occurred during the onset and subsequent relaxation of the supergreenhouse in the direct aftermath of the snowball. Modeling studies contradict earlier assertions of a highly vigorous hydrologic cycle during the supergreenhouse event, with runoff but as much as 20% higher compared to its present-day value. Consequently, weathering rates were also lower, and rather than a few hundred thousand years ( Higgins and Schrag, 2003; Hoffman et al., 1998), it most likely took >1   ×   x^half-dozen years for atmospheric CO₂ to render to preglacial values. These results too suggest that cap dolostone accumulation endured on the gild of 100   ky.

If the atmospheric condition for initiation of the snowball Earth seem to be reasonably well understood, much work remains to resolve the melting and climate throughout the deglaciation. Correctly simulating the deglaciation and ocean-level rise duration, with fully coupled climate and ice-sail models, would provide important constraints on global cap dolostone atmospheric precipitation. Only nature is more than complex than models, and it is unrealistic to wait that models will ever capture the full complexity of the Neoproterozoic ice ages. Nevertheless, models provide important clues and some quantitative constraints on the controversial question of whether these catastrophic events really did occur.

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Mineral deposits: host rocks and genetic model

Southward.K. Haldar , in Introduction to Mineralogy and Petrology (2d Edition), 2020

9.iii.7.9 Irish gaelic

Irish gaelic type of carbonate (limestone and dolostone)-hosted sulfide deposits is stratiform and stratabound, often dislocated by normal faults and occur as riftogenic basin margin with the existence of basic volcanic and plutons. Dolomitization and silicification along with silica-rich Fr-oxide zoning are mutual. The major metallic minerals in society of abundances are sphalerite, galena, and chalcopyrite with a pocket-sized amount of barium, silverish, and cadmium. The usual age of the germination is Carboniferous. Navan is the largest (preproduction ore reserves of 58  Mt @ 8.33% Zn, two.05% Lead and 244 t Ag) of the Irish Zn–Pb deposits and contains some of the well-nigh important evidence for epigenetic mineralization and is hosted in lower carboniferous platform carbonates of the early on Courceyan Navan Group (~351±4   Ma).

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Fuel Chemistry

Sarma V. Pisupadti , in Encyclopedia of Concrete Science and Technology (Third Edition), 2003

VII.A.2 During the Combustion Control Method

In an FBC organisation, limestones or dolostones are introduced into the combustion chamber forth with the fuel. In the combustion sleeping accommodation, limestones and dolostones undergo thermal decomposition, a process unremarkably known equally calcination. The decomposition of calcium carbonate, the principal constituent of limestone, proceeds according to the following equation:

(ane) $\begin{array}{l}{\text{CaCO}}_3\text{CaO}+{\text{CO}}_2\hfill \\ \text{MgCa}{\left({\text{CO}}_{\text{3}}\right)}_2\text{MgO}+\text{CaO}+2{\text{CO}}_2.\hfill \end{array}$

Calcination, an endothermic reaction, occurs at temperatures above 760   °C. Some caste of calcination is thought to be necessary before the limestone tin can react with gaseous sulfur dioxide. Calcined limestone is porous in nature due to the voidage (pores) created by the expulsion of carbon dioxide.

Capture of the gaseous sulfur dioxide is accomplished via the following reaction, which produces a solid product, calcium sulfate:

(2) $\text{CaO}+{\text{Then}}_2+\mathrm{one}/2{\text{O}}_2{\text{CaSO}}_4.$

The reaction of porous calcium oxide with sulfur dioxide produces a continuous variation in the physical structure of the reacting solid as the conversion gain. Considering of the relatively high molar volume of CaSO_four of CaO, the pore network within the reactant can be progressively blocked every bit conversion increases. For pure CaO prepared past the calcination of reagent course CaCO₃, the theoretical maximum conversion of CaCO_iii to CaSO₄ has been calculated to be 57%. In exercise, the actual conversion obtained using natural limestones is much lower due to the nature of the porosity formed upon calcination. Calcium utilizations as low every bit fifteen–20   mol% have been reported in some cases, although utilizations of about 30–40   mol% are typical. MgO will not react with sulfur dioxide at temperatures above 760   °C; therefore, the sulfation reaction of dolomite is basically the reaction of sulfur dioxide with calcium oxide.

In pressurized fluidized bed combustion, however, the partial pressure of CO₂ is so loftier that calcination does non proceed because of thermodynamic restrictions. For example, at 850   °C, calcium carbonate does not calcine if the CO₂ partial force per unit area exceeds 0.5 atmosphere. Under these atmospheric condition, the sulfation reaction is

${\text{CaCO}}_{\text{3}}\left(\text{s}\right)+{\text{And so}}_2+1/2{\text{O}}_2{\text{CaSO}}_4+{\text{CO}}_{\mathrm{two}}.$

Increasing the pressure from one to five atmospheres significantly increases the sulfation charge per unit and calcium utilization.

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Mineral Deposits

Due south.Chiliad. Haldar , Josip Tišljar , in Introduction to Mineralogy and Petrology, 2014

viii.4.9 Irish

"Irish" type of carbonate (limestone and dolostone) hosted sulfide deposits are stratiform and stratabound, oft dislocated past normal faults, and occur equally riftogenic basin margin with the presence of basic volcanic and pluton rocks. Dolomitization and silicification along with silica-rich Fr oxide zoning are mutual. The major metallic minerals in order of abundances are sphalerite, galena, and chalcopyrite with minor amount of barium, silver, and cadmium. The usual age of formation is Carboniferous. Navan is the largest (preproduction ore reserves of 58  Mt @ viii.33% Zn, two.05% Pb, and 244   t Ag) of the Irish Zn–Pb deposits and contains some of the most important evidence for epigenetic mineralization and is hosted in Lower Carboniferous platform carbonates of the early Courceyan Navan Group (∼351   ±   4   Ma).

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Geology and Hydrogeology of Carbonate Islands

Brian Jones , ... I.G. Hunter , in Developments in Sedimentology, 2004

Lithofacies.

The formation is formed entirely of fabric-retentive microcrystalline dolostone ( Jones et al., 1994b). Although mudstones and wackestones dominate, there are some grainstones and packstones (Jones and Hunter, 1994) with grains of foraminifera, red algae fragments and Halimeda beingness common. Although massive colonial (e.yard., Diploria, Montastrea, Siderastrea, Leptoseris, Porites) and branching (Stylophora, Porites) corals are mutual, there is no testify of reef evolution. Coral molds unremarkably contain casts of borings like those described by Pleydell and Jones (1988). Rhodolites, with broken branches of Stylophora or Porites every bit their nuclei, are commonly concentrated in beds or lenses up to 1 m thick.

Pores are lined with limpid dolomite cement and/or filled with coarsely crystalline calcite cement (Jones et al., 1984). Larger cavities incorporate caymanite (laminated white, red and black, microcrystalline dolostone with various sedimentary structures; Jones, 1992a), terra rossa, freshwater limestone and/or flowstone (Jones, 1992b).

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Fault sealing

Michael Kettermann , ... David C. Tanner , in Understanding Faults, 2020

8.v.ii.1 Outcrop observations

Low-porosity carbonates more often than not consist of massive platform limestones/dolostones, other massive carbonates, and well-bedded pelagic limestones that evidence different clay content. Surface exposures of faults cutting through such carbonates and exhumed from depths <iv  km are mainly characterised by dilatant and brittle processes (i.east., fracturing and cataclasis), whereas ductile processes (i.e., pressure-solution) become of import with the increase in dirt content (i.e., within pelagic limestones), pressure, and temperature (i.e., with increasing depth). Mostly, the fault zone structure shows a gradual transition from a fractured harm zone to a strongly-plain-featured fault core forth the main fault surface (Fig. 8.19A and B; due east.g., Agosta and Aydin, 2006; Agosta and Kirschner, 2003; Billi et al., 2003). Low-displacement faults may also occur within the damage zone, indicating complex processes of deformation partitioning (Fig. 8.19A).

Fig. 8.19. Outcrop images and microstructures of fault cut through massive and low-porosity limestones. (A) Panoramic view of a normal fault cutting through massive limestones. From left to correct, the mistake zone is characterized by a fractured damage zone, a cohesive mistake core, a master slip plane, a brecciated and incohesive fault core, and by low deportation faults within the damage zone. (B) Primary skid plane in massive limestones cutting through a cohesive and cataclastic fault core. (C) Detail of a cohesive cataclastic error cadre. (D) Crackle breccia texture characterized past radial extensional fractures and "exploded clasts", which show no shear strain. (Eastward) Chaotic breccia texture that show voids between clasts filled past calcite cement. (F) Cataclastic texture at microscale showing large clasts scattered within a fine matrix. (1000) Particular of the fine matrix characterized by stylolitic clast boundaries. (H) Network of calcite veins cutting through a cataclasite.

Within massive limestones/dolostones, intergranular extensional fracturing is more mutual in the early stages of deformation, producing host-rock parallelepipeds bounded by a highly connected network of fractures (Fig. eight.19A). With increasing deformation, and approaching the principal fault airplane, coarse breccias showing athwart clasts occur (Fig. 8.19F). Pre-existing weaknesses and flaws, such as primary bedding, may control the fracture pattern associated with fracturing. In the advanced stages of the cataclastic process, grain rolling, chipping, and further fracturing reduce the grain-size of breccia clasts, producing fault gouges characterized by a few angular/rounded clasts scattered within a fine-grained matrix (Fig. 8.19C; e.thousand., Billi, 2010). Mature fault zones evidence an intensely deformed fault core, up to several metres thick, filled by gouges, which are cut by a principal slip zone (Fig. 8.19B). Primary skid zones of loftier-displacement faults are typically cohesive due to the lithification past compaction and cementation, which generates cataclasites, and are characterized by smooth slip surfaces showing slickenlines, slickenfibres, and grooves (Fig. 8.19B; e.g., Fondriest et al., 2013). Recent studies have shown peculiar features of fault zones in dolostones, which are characterized by the lack of well-defined fault cores and evident shear strain, the preservation of primary sedimentary features (i.e., bedding), and the presence of highly-segmented networks of low-deportation faults (i.e., displacement up to a few tens of metres) faults surrounded by domains of cataclastic rocks. These fault zones are more often than not interpreted as the result of in-situ shattering-pulverization (due east.one thousand., Fondriest et al., 2015).

Fault zones in carbonates with variable clay contents, are characterized by multiple cores, diffuse core/harm zone boundaries, pervasive pressure level solution, veining and the occurrence of foliated tectonites (Fig. 8.20A–C). The increased clay content in the host-rock activates ductile deformation processes during faulting, such as force per unit area-solution. Pressure level-solution generates a network of stylolites by limestones and marls dissolution and insoluble materials (i.due east., phyllosilicates) concentration within dissolution seams. During deformation and with increasing strain, the fault rocks often go foliated due to the alignment of phyllosilicates, which generate a pervasive scaly textile (Fig. 8.20A–C). Foliated error rocks characteristically develop Due south-C structures by the combination of pressure level-solution and frictional sliding forth S and C planes (Fig. 8.20A–C). Faults cut through a heterogeneous sedimentary succession, characterized by carbonates and marly units, prove complex error zones, characterized by the interaction of brittle and ductile processes. By comparison dirt-rich and clay-poor fault rocks, it can be inferred that pressure-solution and frictional sliding are the dominant deformation mechanisms in clay-rich zones, characterized past distributed shear planes bounding a continuous and pervasive foliation, whereas cataclasis and sideslip localization along master slip zone are favoured in pure massive limestones (e.1000., Bullock et al., 2014; Tesei et al., 2013).

Fig. 8.20. Outcrop images and microstructures of fault cutting through clay-rich limestones and beyond heterogeneous stratigraphy. (A) Fault with a big (20   m) deportation bringing into contact marly interbeds (unit of measurement A) with limestones interbeds (unit of measurement B) and showing a staircase trace. The fault surface shows an overall straight trajectory, but its boundaries nevertheless maintain the original staircase shape, resulting in a variable thickness of the fault core. (B and C) Item of the fault core, by and large consisting of cerise marl from the marly unit A, characterized past SCC′ fabric. Note that the fault core preserves the initial staircase geometry (C). (D) Dirt-rich injection localized betwixt the primary slip airplane and the damage zone, both in carbonate rocks. (Eastward) Microstructure of South-C tectonites in marly limestones, showing a well-developed network of stylolites.

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The Cryogenian Menses

G.A. Shields-Zhou , ... B.A. Macgabhann , in The Geologic Fourth dimension Scale, 2012

17.2.four Age Constraints on Late Cryogenian Glaciation

The hypothesis that all basal Ediacaran, postal service-glacial cap-dolostone units are globally correlative (due east.grand., Dunn et al., 1971; Knoll et al., 2006) stands house in the light of increasingly robust age constraints from around the world. The top of the cap dolostone in S China, which ought to marking past correlation with the Nuccaleena Formation in Australia the finish of the Cryogenian Menstruum, is constrained in age to 635.2   ±   0.iv Ma (Condon et al., 2005). Glaciogenic strata from Namibia provide an identical age of 635.half dozen   ±   0.5 Ma (Hoffmann et al., 2004), suggesting a globally synchronous deglaciation. A SHRIMP II U/Pb historic period of 636.3   ±   4.nine Ma from lowermost strata of the glaciogenic Nantuo Formation in S China (Zhang et al., 2008b) additionally implies that some glaciogenic strata cover only a relatively short period of time biased towards the cease of the glacial episode. The top of the underlying not-glaciogenic Datangpo Germination is constrained in the same study to <654.five   ±   3.viii Ma.

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