Figure - available via license: Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported
Content may be subject to copyright.
Images showing various giant oolite morphologies within the oolitic grainstones in the top part of the Triassic Daye Formation at the Lichuan section, Hubei Province. Images (A) to (B) are circular concentric ooids, (C) is a composite ooid, (D) is an irregular eccentric ooid, and (E) is an elliptical concentric ooid. All images were taken under plane-polarized light.
Source publication
Most Phanerozoic oolites are marked by ooids with a diameter less than 2 mm. Observations on a Neoproterozoic oolite have resulted in a change of concept. The term “pisolite” that traditionally referred to oolites with a grain size of more than 2 mm, is now restricted to those coated carbonate grains formed by meteoritic freshwater diagenesis; ooli...
Contexts in source publication
Context 1
... the light microscope, there is a diversity of ooid morphologies for the oolite from the upper Daye Formation at the Lichuan section. The oolites are mainly composed of carbonate micrite ( Fig. 4; see detailed description by Mei, 2008). Their microscopic features can be summarized as ...Context 2
... Most of the ooids are circular (Fig. 4A and B), elliptical concentric ( Fig. 4E), irregular eccentric ( Fig. 4D), and some are composite (Fig. 4C). The ooid grain sizes are commonly more than 2 mm, with a few 4e5 mm; and the largest can be up to 7 mm ( Fig. 4B and E); (2) Many types of small carbonate grains, such as pellets ( Fig. 4A and B), calcisiltite (Fig. 4C), echinoderm ...Context 3
... Most of the ooids are circular (Fig. 4A and B), elliptical concentric ( Fig. 4E), irregular eccentric ( Fig. 4D), and some are composite (Fig. 4C). The ooid grain sizes are commonly more than 2 mm, with a few 4e5 mm; and the largest can be up to 7 mm ( Fig. 4B and E); (2) Many types of small carbonate grains, such as pellets ( Fig. 4A and B), calcisiltite (Fig. 4C), echinoderm bioclast (Fig. 4E), silt-sized ...Context 4
... Most of the ooids are circular (Fig. 4A and B), elliptical concentric ( Fig. 4E), irregular eccentric ( Fig. 4D), and some are composite (Fig. 4C). The ooid grain sizes are commonly more than 2 mm, with a few 4e5 mm; and the largest can be up to 7 mm ( Fig. 4B and E); (2) Many types of small carbonate grains, such as pellets ( Fig. 4A and B), calcisiltite (Fig. 4C), echinoderm bioclast (Fig. 4E), silt-sized thrombolite with worm microscopic ...Context 5
... Most of the ooids are circular (Fig. 4A and B), elliptical concentric ( Fig. 4E), irregular eccentric ( Fig. 4D), and some are composite (Fig. 4C). The ooid grain sizes are commonly more than 2 mm, with a few 4e5 mm; and the largest can be up to 7 mm ( Fig. 4B and E); (2) Many types of small carbonate grains, such as pellets ( Fig. 4A and B), calcisiltite (Fig. 4C), echinoderm bioclast (Fig. 4E), silt-sized thrombolite with worm microscopic fabric (Fig. 4D) and particular ooid ...Context 6
... Most of the ooids are circular (Fig. 4A and B), elliptical concentric ( Fig. 4E), irregular eccentric ( Fig. 4D), and some are composite (Fig. 4C). The ooid grain sizes are commonly more than 2 mm, with a few 4e5 mm; and the largest can be up to 7 mm ( Fig. 4B and E); (2) Many types of small carbonate grains, such as pellets ( Fig. 4A and B), calcisiltite (Fig. 4C), echinoderm bioclast (Fig. 4E), silt-sized thrombolite with worm microscopic fabric (Fig. 4D) and particular ooid intraclast (Fig. 4C), make up the nucleus of the ooids. Furthermore, as seen in Fig. 4E, the echinoderm bioclasts ...Context 7
... Most of the ooids are circular (Fig. 4A and B), elliptical concentric ( Fig. 4E), irregular eccentric ( Fig. 4D), and some are composite (Fig. 4C). The ooid grain sizes are commonly more than 2 mm, with a few 4e5 mm; and the largest can be up to 7 mm ( Fig. 4B and E); (2) Many types of small carbonate grains, such as pellets ( Fig. 4A and B), calcisiltite (Fig. 4C), echinoderm bioclast (Fig. 4E), silt-sized thrombolite with worm microscopic fabric (Fig. 4D) and particular ooid intraclast (Fig. 4C), make up the nucleus of the ooids. Furthermore, as seen in Fig. 4E, the echinoderm bioclasts that form the ooid nucleus have an obvious micriti- zation feature in their ...Context 8
... ooids are circular (Fig. 4A and B), elliptical concentric ( Fig. 4E), irregular eccentric ( Fig. 4D), and some are composite (Fig. 4C). The ooid grain sizes are commonly more than 2 mm, with a few 4e5 mm; and the largest can be up to 7 mm ( Fig. 4B and E); (2) Many types of small carbonate grains, such as pellets ( Fig. 4A and B), calcisiltite (Fig. 4C), echinoderm bioclast (Fig. 4E), silt-sized thrombolite with worm microscopic fabric (Fig. 4D) and particular ooid intraclast (Fig. 4C), make up the nucleus of the ooids. Furthermore, as seen in Fig. 4E, the echinoderm bioclasts that form the ooid nucleus have an obvious micriti- zation feature in their exteriors margin that may be ...Context 9
... and B), elliptical concentric ( Fig. 4E), irregular eccentric ( Fig. 4D), and some are composite (Fig. 4C). The ooid grain sizes are commonly more than 2 mm, with a few 4e5 mm; and the largest can be up to 7 mm ( Fig. 4B and E); (2) Many types of small carbonate grains, such as pellets ( Fig. 4A and B), calcisiltite (Fig. 4C), echinoderm bioclast (Fig. 4E), silt-sized thrombolite with worm microscopic fabric (Fig. 4D) and particular ooid intraclast (Fig. 4C), make up the nucleus of the ooids. Furthermore, as seen in Fig. 4E, the echinoderm bioclasts that form the ooid nucleus have an obvious micriti- zation feature in their exteriors margin that may be genetically related to microboring ...Context 10
... Fig. 4D), and some are composite (Fig. 4C). The ooid grain sizes are commonly more than 2 mm, with a few 4e5 mm; and the largest can be up to 7 mm ( Fig. 4B and E); (2) Many types of small carbonate grains, such as pellets ( Fig. 4A and B), calcisiltite (Fig. 4C), echinoderm bioclast (Fig. 4E), silt-sized thrombolite with worm microscopic fabric (Fig. 4D) and particular ooid intraclast (Fig. 4C), make up the nucleus of the ooids. Furthermore, as seen in Fig. 4E, the echinoderm bioclasts that form the ooid nucleus have an obvious micriti- zation feature in their exteriors margin that may be genetically related to microboring caused by euendolithic cyanobacteria (Chac on et al., 2006; ...Context 11
... The ooid grain sizes are commonly more than 2 mm, with a few 4e5 mm; and the largest can be up to 7 mm ( Fig. 4B and E); (2) Many types of small carbonate grains, such as pellets ( Fig. 4A and B), calcisiltite (Fig. 4C), echinoderm bioclast (Fig. 4E), silt-sized thrombolite with worm microscopic fabric (Fig. 4D) and particular ooid intraclast (Fig. 4C), make up the nucleus of the ooids. Furthermore, as seen in Fig. 4E, the echinoderm bioclasts that form the ooid nucleus have an obvious micriti- zation feature in their exteriors margin that may be genetically related to microboring caused by euendolithic cyanobacteria (Chac on et al., 2006; Garcia-Pichel, 2006;Duguid et al., 2010), ...Context 12
... mm; and the largest can be up to 7 mm ( Fig. 4B and E); (2) Many types of small carbonate grains, such as pellets ( Fig. 4A and B), calcisiltite (Fig. 4C), echinoderm bioclast (Fig. 4E), silt-sized thrombolite with worm microscopic fabric (Fig. 4D) and particular ooid intraclast (Fig. 4C), make up the nucleus of the ooids. Furthermore, as seen in Fig. 4E, the echinoderm bioclasts that form the ooid nucleus have an obvious micriti- zation feature in their exteriors margin that may be genetically related to microboring caused by euendolithic cyanobacteria (Chac on et al., 2006; Garcia-Pichel, 2006;Duguid et al., 2010), and these echinoderm bioclasts are coated by a micritic enve- lope in ...Context 13
... is possibly formed by microbes; (3) The ooid cortex is made up of even rings of dark micrite, which exhibit dark and light laminations; (4) The thickness of the ooid cortex is always larger than the size of the nucleus, and the number of ooid rings is more than several tens, which reflects the basic feature of high-energy oolites; (5) As seen in Fig. 4C, the nucleus of one large irregular-shaped composite ooid is made up of two small ooids, and this in turn is finally wrapped by even ooid rings, which result in a composite that is distinct from other aggregate grains such as grapestones and thrombolites; furthermore, this large composite reflects the basic feature of a rebirth ooid ...Context 14
... is finally wrapped by even ooid rings, which result in a composite that is distinct from other aggregate grains such as grapestones and thrombolites; furthermore, this large composite reflects the basic feature of a rebirth ooid (Simone, 1981;Fl€ ugel, 1982Fl€ ugel, , 2004Tucker and Wright, 1990;Mei et al., 1997; Siewers, 2003); (6) As seen in Fig. 4D, an eccentric ooid with a diameter of more than 3 mm indicates the basic feature of a rebirth ooid is similar to the feature reflected by a large irregular-shaped composite ooid seen in Fig. 4C, which may be the product of syndeposi- tional deformation and a discontinuity during the growing process of the ooids (Simone, 1981;Fl€ ugel, ...Context 15
... the basic feature of a rebirth ooid (Simone, 1981;Fl€ ugel, 1982Fl€ ugel, , 2004Tucker and Wright, 1990;Mei et al., 1997; Siewers, 2003); (6) As seen in Fig. 4D, an eccentric ooid with a diameter of more than 3 mm indicates the basic feature of a rebirth ooid is similar to the feature reflected by a large irregular-shaped composite ooid seen in Fig. 4C, which may be the product of syndeposi- tional deformation and a discontinuity during the growing process of the ooids (Simone, 1981;Fl€ ugel, 1982Fl€ ugel, , 2004Tucker and Wright, 1990;Mei et al., 1997;Siewers, ...Context 16
... seen in Fig. 5, the infillings of the ooids include cements of calcite spar and intraclasts. The various types of ooids shown in Fig. 4 probably belong to high-energy oolites (Simone, 1981;Fl€ ugel, 1982Fl€ ugel, , 2004Tucker and Wright, 1990;Mei et al., 1997;Siewers, 2003). The particular filling substances are those ooid intraclasts with clear ooid-ring microfabrics (Fig. 5A), which resulted from fragmentation and abrasion of oolites caused by strong currents during ...Context 17
... seen in Fig. 4, the giant oolites of the Induan in the study area demonstrate a complex formation process that is related to the precipitation of amorphous calcium carbonate (ACC) caused by microbial activity. Firstly, as seen in Fig. 4AeD, the cortex of the ooids with various morphologies demonstrates dark and light laminations are similar to the ...Context 18
... seen in Fig. 4, the giant oolites of the Induan in the study area demonstrate a complex formation process that is related to the precipitation of amorphous calcium carbonate (ACC) caused by microbial activity. Firstly, as seen in Fig. 4AeD, the cortex of the ooids with various morphologies demonstrates dark and light laminations are similar to the basic feature of stromatolites, which may indicate that these oolites are the product resulting from a spherical microbial assemblage as proposed by Brehm et al. (2003Brehm et al. ( , 2006). Secondly, some ooid rings are ...Context 19
... dark and light laminations are similar to the basic feature of stromatolites, which may indicate that these oolites are the product resulting from a spherical microbial assemblage as proposed by Brehm et al. (2003Brehm et al. ( , 2006). Secondly, some ooid rings are composed of dark amorphous micrites enriched with organic substances, as seen in Fig. 4, and this type of ooid ring has a thickness of several tens of microns that are similar to a micritic envelope, which demon- strates that the formation mechanism for this type of ooid ring is similar to the dark laminations of stromatolites and is genetically related to microbial activity. Thirdly, the basic feature of rebirth oolites ...Context 20
... and this type of ooid ring has a thickness of several tens of microns that are similar to a micritic envelope, which demon- strates that the formation mechanism for this type of ooid ring is similar to the dark laminations of stromatolites and is genetically related to microbial activity. Thirdly, the basic feature of rebirth oolites as seen in Fig. 4C and D shows that the growth of the ooid rings might be controlled by a complex precipitation process of carbonate micrites that are genetically related to the activity of microbes, and this feature cannot simply be interpreted with the chemical formation process of carbonate micrites proposed by Duguid et al. (2010). Fourthly, as seen in ...Context 21
... Fig. 4C and D shows that the growth of the ooid rings might be controlled by a complex precipitation process of carbonate micrites that are genetically related to the activity of microbes, and this feature cannot simply be interpreted with the chemical formation process of carbonate micrites proposed by Duguid et al. (2010). Fourthly, as seen in Fig. 4E, the clear micritization feature in the exterior margin of an echinoderm bioclast that constitutes an ooid nucleus might be genetically related to a microboring caused by euendolithic cyanobacteria (Chac on et al., 2006; Garcia-Pichel, 2006;Duguid et al., 2010). Therefore, the formation mechanism for these oolites (e.g. Figs. 3 and 4) ...Context 22
... the Triassic oolitic limestones at the Lichuan section, i.e., the formation in the early high-stand period of third-order sea level change (DS 2 in Fig. 2; Tong et al., 1999), and during the progradational process of an oolitic bank toward the east depositing on a carbonate ramp ( Fig. 1; Wu et al., 1994), the morphological diversity of ooids (Figs. 3 and 4), the special ooid intraclasts indicating abrasion and fragmentation during formation (Fig. 5A), and the multigenerational calcite spar cement (Fig. 5B), indicate that these oolites were generated in a high-energy subtidal environment (e.g., Reeder and Rankey, 2008). The Lower Triassic Daye Formation strata of the carbonate ramp at the ...Context 23
... more about the evolution of the carbonate world represented by giant oolites (Wu, 1992;Grotzinger and James, 2000;Fl€ ugel, 2004;Yan and Wu, 2006;Pomer and Hallock, 2008). Furthermore, this important example also provides an important clue to further research. Importantly, some of the microbial features for the Triassic giant oolite, as seen in Fig. 4, such as the relatively thick ooid rings composed of dark amor- phous micrites enriched with organic substances and nucleuses made up of echinoderm bioclasts with reworking of microbial borings, may also represent a type of post-mass-extinction disaster form in addition to microbialites, edgewise intraclasts, wrinkle structures and so ...Similar publications
The timing of recovery after the end‐Permian mass extinction has been a matter of
debate, with some authors favouring a more rapid faunal recovery during the Early Triassic and others considering a more protracted biotic reestablishment spanning until
the Middle Triassic. In this work, we investigated the lowermost Middle Triassic (Ladinian)
carbon...
Citations
... The Talung Formation represents the main chert strata, consisting predominantly of thinly-bedded spicule and radiolarian cherts, siliceous mudstones, cherty carbonate, and shales (Li et al., 1989;Yan et al., 2013). The Daye Formation is characterised by dark-grey shales, mudstones, and thinly-bedded marls in deeper basins and finely laminated micritic mudstones and oolitic grainstones at platform margins during the Griesbachian (Mei and Gao, 2012;Lyu et al., 2019). ...
Permian chert successions were geographically extensive, spanning from the palaeoequator to the northern high latitudes. Large-scale chert production was abruptly terminated in the latest Permian, resulting in a multi-million-year “chert gap” in the Early Triassic. In order to constrain the tempo of chert production changes and understand their nature, we combine proxy data with Si box model analyses and focus on the Talung Formation of South China—the most representative Upper Permian siliceous unit in the equatorial Tethys. Two deepwater sections from the northern margin of the Yangtze Platform were investigated, showing that bedded cherts had already become less common in the Clarkina changxingensisconodont zone. The waning of chert production coincided with water column deoxygenation and an increase in carbonate and siliciclastic components in the late Changhsingian. The final collapse of the chert factory in South China predated the negative δ13C excursion and climate warming but coincided with a sharp decrease in primary productivity. Together with Si box model output, we suggest that warming-induced expansion of the oceanic dissolved silica inventory (and decrease in burial efficiency) alone cannot maintain a multi-million-year chert gap. Instead, a loss of siliceous biomass during the end-Permian crisis is the primary cause of the Early Triassic chert demise.
... Lower Jurassic carbonate platforms of western Tethys (Mei & Gao, 2012;Ettinger et al. 2021). Accordingly, the Pliensbachian-Toarcian extinction is associated with a sequence boundary related to transgression (Hallam, 1997;Haq, 2018), which drowned the carbonate platform and therefore affected the carbonate factory. ...
The Viggiano Mt. platform carbonates form a layered succession cross-cut by a dense array of pressure solution seams, and five sets of fractures and veins, which together form a sub-seismic structural network associated with polyphasic tectonic evolution. To assess the influence exerted by depositional and diagenetic heterogeneities on fracture geometry, distribution and multiscale properties, we present the results of stratigraphic, petrographic, mineralogical and mesoscale structural analyses conducted at the Viggiano Mountain, southern Italy. Based on rock textures and fossil associations, we documented that the Sinemurian–Pleinsbachian carbonates were deposited in a low-energy open lagoon, the Toarcian carbonates in a ramp setting rimmed by sand shoals, and the Cenomanian carbonates in a medium- to high-energy, lagoonal–tidal setting. Fracture-density (P20) and intensity (P21) values computed after circular scanline measurements show similar trends in both Sinemurian–Pleinsbachian and Toarcian carbonates, consistent with the bed and bed-package heterogeneities acting as efficient mechanical interfaces during incipient faulting. On the other hand, P20 and P21 do not show very similar variations throughout the Cenomanian carbonates due to pronounced bed amalgamation. Throughout the study area, the aforementioned parameters do not vary in proportion to the bed thickness, and show higher values within the coarse-grained carbonate beds. This conclusion is confirmed by results of linear scanline measurements, which focus on the P10 properties of the most common diffuse fracture set. The original results reported in this work are consistent with burial-related, physical–chemical compaction and cementation processes affecting the fracture stratigraphy of the Mesozoic platform carbonates.
... In addition, the Lower Triassic margins of the Yangtze Platform and GBG commonly contain oolitic grainstone with giant ooids (up to 1 cm diameter) and composite coated grains ranging up to 6 cm across ( Figure 17C). Giant ooids are especially prevalent in the southern margins of the Yangtze Platform and GBG but also have been found on the north margin of the GBG and in numerous localities along the Yangtze Platform margin Mei & Gao, 2012). The Lower Triassic oolitic margin facies also contains abundant sheet cracks and peculiar irregular lumps or clasts of oolite with large volumes of bladed isopachous marine cements and cement fans filling the voids of sheet cracks and between the oolite clasts ( Figure 17D through F). ...
The end‐Permian extinction and its aftermath altered carbonate factories globally for millions of years, but its impact on platform geometries remains poorly understood. Here, the evolution in architecture and composition of two exceptionally exposed platforms in the Nanpanjiang Basin are constrained and compared with geochemical proxies to evaluate controls on platform geometries. Geochemical proxies indicate elevated siliciclastic and nutrient fluxes in the basal Triassic, at the Induan‐Olenekian boundary, and in the uppermost Olenekian. Cerium/Ce* shifts from high Ce/Ce* values and a lack of Ce anomaly indicating anoxia during the Lower Triassic to a negative Ce anomaly indicating oxygenation in the latest Olenekian and Anisian. Uranium and Mo depletion represents widespread anoxia in the world’s oceans in the Early Triassic with progressive oxygenation in the Anisian. Carbonate factories shifted from skeletal in the Late Permian to abiotic and microbial in the Early Triassic before returning to skeletal systems in the Middle Triassic, Anisian coincident with declining anoxia. Margin facies shifted to oolitic grainstone in the Early Triassic with development of giant ooids and extensive marine cements. Anisian margins, in contrast, are boundstone with a diverse skeletal component. The shift in platform architecture from ramp to steep, high‐relief, flat‐topped profiles is decoupled from carbonate compositions having occurred in the Olenekian prior to the onset of basin oxygenation and biotic stabilisation of the margins. A basin‐wide synchronous shift from ramp to high‐relief platforms points to a combination of high subsidence rate and basin starvation coupled with high rates of abiotic and microbial carbonate accumulation and marine cement stabilisation of oolitic margins as the primary causes for margin up‐building. High seawater carbonate saturation resulting from a lack of skeletal sinks for precipitation, and basin anoxia promoting an expanded depth of carbonate supersaturation, probably contributed to marine‐cement stabilisation of margins that stimulated the shift from ramp to high‐relief platform architecture.
... Ooids, mainly calcareous, spherical to subspherical coated grains consisting of one to several nearly concentric cortices encrusting a nucleus, are ubiquitous features of (sub) tropical oceans throughout Earth's history (Flügel, 2004;Tucker, 2011). Although there is no commonly accepted elucidation for ooid genesis, processes such as accretion of fine particles around a nucleus while agitating on a soft substrate (Mei and Gao, 2012), abiotic precipitation from an ambient supersaturated water around a nucleus (Duguid et al., 2010) and organomineralization of a surface biofilm (Diaz et al., 2014;Li et al., 2017;Batchelor et al., 2018) have been diversely put forward. Ancient ooids are 2 | VARKOUHI And JAQUES RIBEIRO valuable palaeoenvironmental proxies for water energy, temperature, salinity, seawater geochemistry and bathymetry (after Sandberg, 1975;Plee et al., 2008). ...
... 6 | DISCUSSION 6.1 | Diagenetic history of coated-grain facies According to Richter (1999), the calcitized coated grains of the Middle Triassic grain flow at Hydra formed F I G U R E 1 1 Presumed primary cortical fabric and mineralogy of studied ancient half-moon ooids and micritic/microsparitic ooids 18 | VARKOUHI And JAQUES RIBEIRO syndepositionally in an unknown shallow-water depositional environment and were shed basinwards towards Hydra. The cortical thickness is larger than the size of the nucleus for the majority of the studied ooids (see d/t ratio in Table 2) reflecting the primary depositional environment for this Middle Triassic oolite in a high-energy, agitated setting (Mei and Gao, 2012). Although a non-selective microfabric partially made up of non-oolitic, micritic/microsparitic clasts and oolitic fragments ( Figure 4A through C,H through O) in some of the analysed microfacies represents a before-relocation alteration outside this island, the Middle Triassic grain flow was diagenetically evolved after relocation (Richter, 1999). ...
This study reports on the occurrence of formerly bimineralic, ancient, calcitic coated grains, including half-moon ooids and micritic to microsparitic ooids in the Middle Anisian (Middle Triassic) grain flow from Hydra Island (Greece), and discusses their importance for palaeoseawater geochemical interpretations. The bi-partite fabric in
half-moon ooids resulted from early pre-compaction rapid dissolution of both aragonitic cortices and the more-soluble components of the high-Mg calcite core in the primary ooid, as well as the collapse of less-dissolved remnants to the bottom of the oomouldic cavity which was later filled with calcite cement. Zonal, micritic to microsparitic ooids formed through intracortical dissolution of primary aragonite lamellae
which were later replaced by (micro)sparry calcite. At the same time, recrystallization of original high-Mg calcite layers to micrite occurred. The stratigraphic occurrence of the investigated bimineralic ooids conforms to the global distribution of carbonate ooids through the Middle Triassic period. The cementation history of the grain flow hosting coated grains is well documented by the paragenetic sequence established in half-moon ooids which predicts that calcite precipitated under burial (shallow to deep) conditions. The main control on precipitation of bimineralic ooids was the Mg/Ca ratio of seawater, with lesser influences from seawater temperature, salinity and ρCO2 which promoted the degree of carbonate saturation, leading to higher precipitation rates for both aragonite and high-Mg calcite. The studied bimineralic ooids represent a change in the global carbonate factory during the Middle Triassic in response to secular variations in the chemistry of palaeoseawater.
... 4e and 4f) and echinoderm/bivalve debris along with thick cortices-several tens of lamellas-which reflect the basic feature of high-energy ooids (Figs. 4c to 4g; Mei & Gao, 2012). 3. Compound ooids: This type of ooids is rare and appears as two or three (superficial) ooids enveloped by a thin cortex of several lamellas (Figs. ...
The Upper Cretaceous Ilam carbonate Formation has been analyzed for its coated grains (fine ooids and rhodoids) in oilfields of SW Iran. The recognized coated grains are morphologically classified into several types. Petrographic and geochemical characteristics indicate that the ooids were originally composed of low-magnesium calcite (LMC; consistent with global observations), but rhodoids consisted originally of high-magnesium calcite (HMC). The overall primary mineralogy of the intervals containing coated grains has been a mixture of HMC and LMC. Co-occurrence of these mineralogies and allochemical (both ooids and rhodoids and other bioclasts) components indicates a rhodalgal-like grain association and a relatively temperate paleoclimatic conditions.
... In South China, in addition to the PTB oolite units, giant ooid banks developed four times throughout the Early Triassic: earliest Griesbachian, late Griesbachian, early Dienerian, and early Smithian (Mei and Gao, 2012). These four regional expansions of giant ooids appear to be coupled with microbial blooms. ...
... These four regional expansions of giant ooids appear to be coupled with microbial blooms. Those four occurrence peaks of Early Triassic ooids have been interpreted to be related with coeval large transgressions (Mei and Gao, 2012). Such massive ooid banks are particularly well developed in the Upper Yangtze region of the South China block. ...
Biotic activities are involved in almost all sedimentation processes throughout the evolutionary history of life on our planet. However, deep-time organism-induced sedimentation and biosedimentary records remain unclear in terms of lithologic types, strata stacking patterns and possible controlling factors. We document biosedimentary features of major transitions from microbe-dominated switching to metazoan-dominated biosedimentary systems based on the global distributions of both microbial and metazoan carbonates through Precambrian to Phanerozoic times, with emphasis on sedimentary records from China. The compilation of 150 and 180 well-documented metazoan and microbial reefs, respectively, from China, reveals that metazoan reefs proliferated during the Middle Ordovician, Middle Devonian and Middle Permian, whereas microbial reefs were well developed during the Cambrian, Late Devonian and Early–Middle Triassic, plus a moderate development during the early Silurian. These stratigraphic abundances of metazoan and microbial carbonates of China generally match the global patterns. The updated variation trends of microbial and metazoan carbonates throughout the late Precambrian and Phanerozoic reveal that there were five major microbe-metazoan transitions (MMTs): the late Ediacaran, the Cambrian, and the aftermaths of the mass extinctions of the end-Ordovician, Late Devonian, and end-Permian. The late Ediacaran MMT began with microbe-dominated oceans with occasional occurrences of metazoans. The presence of Cloudina-dominated reefs in the latest Ediacaran marks the completion of the switching of this microbe-dominated depositional system into a metazoan-dominated system. The Cambrian saw the expansion of skeletal microbes (i.e., Epiphyton, Renalcis) in the oceans; and the stratigraphic successions yield the most diverse biosedimentary deposits and/or structures of the entire Phanerozoic. The Cambrian MMT was the longest microbial-metazoan alternation period and is marked by two metazoan occurrence peaks marked by dominance of abundant archaeocyath buildups during its Epoch 2 and by maceriate and lithistid sponge reefs during the late Furongian Epoch. The early Silurian in China saw the deposition of a thick suite of organic-rich black shales followed by alternations of microbe-rich sediments (oil shales) and metazoan-bearing deposits, which are replaced by microbial and metazoan reefs during the late early Silurian. The Late Devonian MMT started during the late Frasnian and persisted into the early Mississippian, and thus extended slightly longer than the aftermath of the Frasnian–Famennian extinction interval. Alternating occurrences of microbial and metazoan reefs characterize this Late Devonian MMT. Almost all microbe-mediated sediments/structures observed in the Cambrian MMT reoccurred in the aftermath of the end-Permian mass extinction during the Early–Middle Triassic MMT, suggesting high similarities between those two MMTs. Cambrian and Early–Middle Triassic MMTs also share comparable carbon and sulfur isotopic perturbations, warming regimes, and generally oxygen-deficient seawaters. Some of these environmental and climatic extremes may also occur during other MMTs, but they usually did not occur synchronously. Most MMTs seem to have undergone four developmental stages. They initiated as microbe-dominated successions (Stage A), and then were characterized by alternations of microbe-dominated and of metazoan-bearing or bioturbated successions (Stage B). Both microbial and metazoan reefs co-occurred during Stage C; and a dominance of metazoan reefs marks the development of Stage D. Ediacaran and Cambrian MMTs seem to have undergone the first three development stages, whereas the three post-extinction MMTs experienced the full set of Stages A−D, corresponding to metazoan survival, initial recovery and full recovery. The majority of volatile-rich Large Igneous Provinces (LIPs), coupled with intensive acidification events, anoxia and global warming regimes, took place during the Mesozoic–Cenozoic. However, microbe-dominated sediments were only widely deposited during the Early Triassic, and greatly declined after that time. Therefore, it seems that microbial abundance in MMTs may not be directly related to these extreme LIP events. This is probably because a primary source of food for the metazoans might have shifted to phytoplankton (e.g., coccoliths, dinoflagellates, and radiolarians) in the marine waters since the Triassic. Certainly, the pre-Mesozoic oceans were not dominated by phytoplankton. Perturbations in the carbon isotope record characterize all MMTs, and thus may be reliable proxies indicating MMT biosedimentary systems.
... Ooids have been reported from diverse marine carbonate strata ranging across the Archean to the Phanerozoic (Tucker, 1985;Wilkinson et al., 1985;Swett and Knoll, 1989;Wright and Altermann, 2000;Armella et al., 2007;Mei and Gao, 2012;Ramkumar et al., 2013;Antoshkina, 2015;Tang et al., 2015). However, existence of ooids through the earth's geological history has emphasized maximum concentration of giant ooids in Proterozoic carbonates of marine origin. ...
This study is the first comprehensive documentation of giant ooids and related facies associations in the Kunihar Formation, Proterozoic Simla Group Lesser Himalaya, Himachal Pradesh, analysing the understanding of processes and controls on development of giant ooids. Based on field observations, supplemented by outcrop based facies analysis, petrography and delineation of environmental variations, four facies associations have been delineated: (i) Peritidal siliciclastic-carbonate (FA1) (ii) Shelf lagoon (FA2) (iii) Reef complex (FA3) (iv) Fore reef slope (FA4). Deposition of giant ooids and associated facies associations of Kunihar Formation occurred in a carbonate rimmed shelf with high tidal influence. Size of giant ooids from Kunihar Formation is the largest as compared to giant ooids from other geological formations. Kunihar giant ooids developed when normal ooids were washed from ooid shoals (intertidal) into slightly deeper regions (shallow subtidal) resulting in the increased dimension of ooids in suspension due to higher hydrodynamics. Scanning electron microscopy (SEM) studies support microbial origin of ooids, giant ooids and stromatolites of Kunihar Formation. Increased microbial activity in Kunihar Formation is attributed to increase in nutrients by virtue of weathering of underlying Darla volcanics. Abundant carbonate and Microbially induced sedimentary structures (MISS) deposition in lower part of Simla Group points to increased microbial activity which likely increased the volume of oxygen in Neoproterozoic atmosphere ushering in Ice House conditions during the subsequent deposition of Blaini Group.
Giant ooids associated with Neoproterozoic glacial deposits throughout the world, occupy stratigraphic positions below, above or between glaciations. Simla Group is another example where giant ooids lie stratigraphically below Marinoan Blaini Tillites. Increased magmatic activity and weathering before and during the Neoproterozoic glaciations increased nutrients in marine waters which increased algal growth. Thus, giant ooids were deposited due to such phases of increased microbial activity before/after glaciation, and during interglacial periods.
... However, field investigations and thin section observations show fewer fossils but abundant ooids and oncoids that are clearly different from previously documented, highly fossiliferous Permian reef-associated limestones. In South China, oolitic and oncolitic limestones were widely developed on the Yangtze Platform during the Early Triassic following the end-Permian mass extinction (Rong et al., 2010;Mei and Gao, 2012;Li et al., 2013). Therefore, the limestone block from Bayan Har should be Lower Triassic in age according to regional stratigraphic correlations and petrographic analysis. ...
The Bayan Har area, situated in the northeast of the Qinghai-Tibetan Plateau, has long been regarded as a deep-water turbidite basin during Early Triassic. However, a sequence of Lower Triassic shallow-water carbonate rocks has been documented from the region, indicating the existence of isolated seamount carbonate platforms in the basin. The seamount carbonate platform sediments differ from synchronous deep basin flysch sediments, and consist of shallow-water oncoids, ooids and cortoids. Microfacies studies reveal that the oncoids have a thick cortex comprised of irregular, non-concentric and partially overlapping micritic laminae and contain abundant well-preserved foraminifera, indicating a relatively low-energy environment in subtidal settings. Ooids exhibit thinner and more regular concentric laminations, which are interpreted to have formed by frequent overgrowth while rolling in a relatively high-energy setting. Cortoids are predominantly composed of tiny fossil fragments and intraclasts with a micritic envelope, indicating a shallow-marine warm water environment located in the intertidal or supertidal zone. Ooids in the Bayan Har area differ from those found on stable platforms, in that they sometimes nucleated onto volcanic quartz grains, reflecting an unstable tectonic setting that was frequently affected by volcanic activity. Widespread ooids and other microbial carbonates formed in the Early Triassic have been regarded anachronistic facies that are indicative of harsh marine conditions. Most Lower Triassic anachronistic facies are distributed along the shallow margin of the Tethys Ocean and the western margin of Pangea; however, Bayan Har was located in the center of the Palaeo-Tethys. The discovery of oncoids and oolites capping a seamount in this area provides strong evidence that extraordinary marine conditions spread far into the interior of the Palaeo-Tethys Ocean.
... The ooids have smooth surfaces, and are typically composed of a small micritic nucleus (0.4-2.7 mm) and a thick cortex (1.7-5.0 mm) characterized by radial fibrous aragonite (pseudomorph) with faint concentric laminae (Fig. 3F). Compared with the Middle Cambrian giant ooids from Ningxia, northwestern China and those from the Lower Triassic of South China (Mei and Gao, 2012;, the Wumishan giant ooids are obviously larger in average size, with a much higher ratio of cortical thickness to nucleus diameter ($4.0). In addition, cortices in the Wumishan giant ooids show more distinctive radial fibrous features (Fig. 3F). ...
... Study of modern oolitic sands indicates that they are extremely rare in many shallow-water carbonate-producing systems, but are notably concentrated in environments with the highest levels of pH, alkalinity, and carbonate supersaturation (Rankey and Reeder, 2009). In comparison with the modern oolitic sands (Rankey and Reeder, 2009) and the giant ooids from lower Triassic strata in south China (Lehrmann et al., 2012;Mei and Gao, 2012;Li et al., , 2015, the Wumishan giant ooids commonly have much smaller nuclei, thicker cortices, and therefore a markedly higher cortex-nucleus thickness ratio ( Fig. 6A and B). Thus, a high accretion rate in cortical growth is inferred for the Wumishan giant ooids, which invokes a highly carbonate-supersaturated environment for ooid formation (cf., Lehrmann et al., 2012;Woods, 2013;Li et al., 2015). ...
Ooids are common carbonate particles that are traditionally considered as abiogenically formed by physical and chemical processes in highly agitated environments. Recent studies point to the importance of microbial activities in ooid formation, but more case studies are required to confirm and clarify the roles of microbes and their organomineralization processes. Here we report an integrated petrographic, element geochemical, and isotopic study of Mesoproterozoic giant ooids from the Wumishan Formation (ca 1.501.45 Ga) of North China. The Wumishan giant ooids (2.014.4 mm) are composed of small micritic nuclei and thick radial fibrous cortices. Abundant organic relics, including putative bacterial filaments and mucus-like extracellular polymeric substances (EPS), are present in ooid cortices. Organominerals (e.g., nanoparticles and polyhedrons) are concentrated and lined with the axes of radial fibers, suggesting in situ mineralization of bacterial filaments. The abundance of organic relics and fiber-aligned organominerals confirms the constructive roles of microbes in the formation of the Wumishan giant ooids. The preservation of bacterial filaments/filament bundles in their growth orientation requires fast mineralization in CaCO3-supersaturated environments, which may have been controlled by the shallow chemocline in redox-stratified Mesoproterozoic basins.
... Ooids (\2 mm in diameter) and ''giant ooids'' ([2 mm in diameter; may be also termed pisoids, but pisoids commonly refer to a freshwater or terrestrial origin) are spherical, concentric, coated grains (Li et al. 2010;Mei and Gao 2012) (Fig. 10). There are a variety of ooids in the Fig. 10 Microbial ooids. ...
This study illustrates features of the Cambrian oncoids and provides a comparison with other microbial-related carbonate grains found in the Cambrian succession of the North China epeiric platform. Based on cortex structures, four types of oncoids were distinguished: thin-cortex (superficial) oncoids, laminated-cortex oncoids, clotted-cortex oncoids, and full-cortex (without nucleus) oncoids. Thin- and clotted-cortex oncoids are often associated with oolites, laminated-cortex oncoids are present within oolitic-bioclastic grainstones, and full-cortex oncoids occur in bioturbated wackestones. The oncoids with nucleus–cortex structures are easily distinguished from other carbonate grains due to the lack of nucleus–cortex structures, and from microbial-related ooids which have more circular shape and more continuous cortex than oncoids. Oncoids without nucleus and with only crudely laminated cortex (i.e., full-cortex oncoids) can be differentiated from microbialite intraclasts and microbial lumps by the following evidences: (1) microbialite intraclasts, either rounded or angular, are characterized by margins that sharply truncate the included calcified microbes or carbonate grains and, in addition, intraclast-bearing conglomerates commonly show clear sedimentary structures such as cross-stratification and normal grading; (2) microbial aggregates have irregular but smooth margins, and rather chaotic inner structures.
