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Calcareous Ooids: A Synopsis
Abstract
In 1855, Lyell gave an appropriate definition of “oolitic grains” (p. 12): “The variety of limestone called ‘oolite’ is composed of numerous small egg-like grains, resembling the roe of a fish, each of which has usually a small fragment of sand as a nucleus, around which concentric layers of calcareous matter have accumulated.” Also Sorby’s detailed description of calcareous “oolitic grains” from 1879 is still modern. He distinguished between the following three types: (1) “Concentric structure” characterizes the aragonitic oolitic grains of the hot springs at Karlsbad (CSSR) and of the modern sediments in the Bahamas. “Concentric” means, according to Sorby, layers of tangentially oriented aragonite crystals. (2) “Radiate structure” refers to the radial-fibrous structure of many calcitic fossil oolitic grains. Sorby recognized this structure as primary. This was neglected, at least for marine ooids, from Cayeux (1935) to Shearman et al. (1970) and has been reestablished by Simone (1974), Sandberg (1975) and Wilkinson and Landing (1978) only in the last ten years. (3) “Recrystallized structure” is developed in calcitized former aragonitic oolitic grains, in which “the larger irregular crystals formed in them have either no special orientation or are arranged with the principal axis converging towards the centre”.
... Limestone composed of ooids is referred to as an oolite. Although the term "ooid" has been restricted to coated grains less than 2 mm in diameter in most literatures, the ooids of different occurrences exceeding this limit without structural and mineralogical modifications have been reported so far (Richter, 1983a). Ooids typically form in agitated, shallow waters of subtropical seas where they are frequently moved as sandwaves, dunes, and ripples by tidal and storm currents, and wave action (Tucker, 2011). ...
... Strasser, 1986;Bergmann and Schmidt, 1992). In most of these research works, the diversity of ooids resulted from combination between different modes of primary formation and diagenetic alteration, although the genetic interpretation of many ooid fabrics is still controversial (Richter, 1983a;Tucker and Wright, 1990). ...
... The descriptive subdivision of coated grains into ooids and oncoids (vadoids) is stressed by Richter (1983b) because it implies less mistakes and more convenience in the field than the genetic subdivision. Calcareous ooids are defined as spherical or ellipsoidal coated grains characterized by a concentric arrangement of carbonate laminae developed around a nucleus which is variable in composition (after Flügel, 1978 andRichter, 1983a). Ooid is considered to be one of the most prevalent (Plee et al., 2008). ...
Petrographic features and diagenetic characteristics of ooid-rich grain-flow series of
Middle Triassic age are studied in the west of Kap Rigas in Hydra Island. The investigated section with a thickness of 33 m is composed of ooid limestones with some marl interlayers, and a fracture zone that cuts it. Different types of calcareous coated grains - including ooids and oncoids (vadoids) - are recognized in the analyzed thin sections, obtained from the rock samples taken from the grain-flow section, based on grain morphology and structure of cortex. The pack- and grainstones forming the grain-flow series are commonly composed of an assemblage of ooid types together with other allochthonous and detrital grains, transported from an unknown setting outside the Hydra
Island to island.
Ooid is distinguished from oncoid (or vadoid) by the regularity of its cortical envelope. Apposite to oncoid (vadoid), the sphericity of ooid is proportional to its growth criterion in a hydrodynamically-agitated environment. Morphometric analysis indicates that ooids with the most degree of sphericity are morphologically-related grains, although the original fabric of crystals in the cortexes of these ooids is not preserved.
Cathodoluminescence imaging indicates that the dull-luminescent parts of studied thin sections representing the zones of low Mn2+ concentrations are attributed to calcite precipitation in a burial environment with progressive reduced conditions. The diagenetic transformation of investigated ooid limestones has more likely happened in a burial (shallow to deep) setting as indicated by petrographic and cathodoluminescence features of coated grains and cementing material. The studied ooid types are considered to be originally composed of aragonite or Mg calcite or both, transformed to calcite during the diagenetic evolution of respective grain-flow series. The oncoids (vadoids) are believed to be carbonate bodies primarily composed of irregular, alternating Mg-calcite and aragonite laminae that have been altered to calcite. The cathodoluminescence intensities of micritic and microsparitic/sparitic calcite differ from each other since the diagenetic pore fluids
precipitating these types of calcite have different Mn2+ and Fe+2 contents.
Since the luminescent patterns are consistent in all samples within the study section, the calcite cement filling between the grains in different samples is stratigraphically correlated. This generalized pattern, from the youngest to the oldest zone in calcite cement, represents a progression from oxidizing to reducing conditions during burial diagenesis in the study section. A stratigraphic correlation is made for the sparry calcite filling inside the individual grains since it is proved to be the replacement calcite of a true pore-filling cement. The cathodoluminescence cement zonal stratigraphic synchroneity in the study section is clearly local.
... Despite being one of the sedimentary particles with the oldest continuous geological record, since the Archean (e.g. Siahi et al. 2017;Flannery et al. 2019) and with the longest history of descriptions and interpretations, since Roman times (Burne et al. 2012), they have prompted continuous discussions about their definition, classification, formation processes, mineralogy, diagenesis and evolution throughout Earth history (see some previous reviews in Kalkowsky 1908;Bucher 1918;Bathurst 1968;Teichert 1970;Fabricius 1977;Davies et al. 1978;Simone 1981;Krumbein 1983;Richter 1983a;Wilkinson et al. 1985). Some of these discussions continue nowadays (see a recent review in Diaz and Eberli 2019), mainly about determining the exact processes behind the origin and development of ooids. ...
... A general crystallographic approach to 'spherulites' defines them as "radially polycrystalline aggregates with an outer spherical envelope" (Shtukenberg et al. 2012), whereas sedimentological points of view emphasize their "radial internal structure arranged around one or more centers" and the fact that they are "formed in a sedimentary rock in the place where [they are] now found" (Bates and Jackson 1980;Verrechia et al. 1995). Concerning 'ooids', also a purely descriptive definition is adopted, following Richter (1983a), who emphasizes that they are subspherical particles "formed by a cortex and a nucleus variable in composition and size", where "the cortex is smoothly laminated" with laminae typically concentric. Therefore, the main difference between both types of subspherical particles is that unlike spherulites, ooids grow around a nucleus and show internal lamination. ...
... Although subspherical particles of the Kiritimati microbial mats have been previously referred to as 'spherulites' (Défarge et al. 1996;Arp et al. 2012;Schneider et al. 2013;Ionescu et al. 2015) or 'spherules' (Schmitt et al. 2019;Chen et al. 2020), the detailed description presented here shows that some of the subspherical particles fit perfectly in the definition of 'ooids' (Richter 1983a), as they are composed of a laminated cortex growing around a nucleus. Those with In some images, the EPS matrix is slightly shrunk and detached from the particles, due to the alcohol dehydration process during the preparation of thin sections (see "Methods"). a Transmitted light photomicrograph of a subspherical particle from the topmost layer of the Lake 2 mat, showing two tuft-like growths of radial fibrous aragonite above and below a nucleus of micropeloidal micrite. ...
Ooids (subspherical particles with a laminated cortex growing around a nucleus) are ubiquitous in the geological record since the Archean and have been widely studied for more than two centuries. However, various questions about them remain open, particularly about the role of microbial communities and organic matter in their formation and development. Although ooids typically occur rolling around in agitated waters, here, we describe for the first time aragonite ooids forming statically within microbial mats from hypersaline ponds of Kiritimati (Kiribati, central Pacific). Subspherical particles had been previously observed in these mats and classified as spherulites, but these particles grow around autochthonous micritic nuclei, and many of them have laminated cortices, with alternating radial fibrous laminae and micritic laminae. Thus, they are compatible with the definition of the term ‘ooid’ and are in fact very similar to many modern and fossil examples. Kiritimati ooids are more abundant and developed in some ponds and in some particular layers of the microbial mats, which leads to the discussion and interpretation of their formation processes as product of mat evolution, through a combination of organic and environmental factors. Radial fibrous laminae are formed during periods of increased supersaturation, either by metabolic or environmental processes. Micritic laminae are formed in closer association with the mat exopolymer (EPS) matrix, probably during periods of lower supersaturation and/or stronger EPS degradation. Therefore, this study represents a step forward in the understanding of ooid development as influenced by microbial communities, providing a useful analogue for explaining similar fossil ooids.
... Based on an assessment of the depositional structures (especially the occurrence of breccia), bed thickness and the presence of mud, Richter (1999) concluded that the Middle Triassic oolite outcrop in Hydra represents a grain flow that formed during a laminar, highly concentrated, cohesion-less flow event. This grain flow has carbonate coated grains formed syndepositionally, indurated in an unknown source area outside the Island of Hydra together with detrital grains, and transported basinwards to Hydra (Richter, 1983;. Angiolini et al.'s (1992) field observations show that only the conspicuous micrite bands within the grain flow are autochthonous ( Figure 3). ...
... The Fe enrichment (ferroan calcite lamellae) may be indicative of a radial high-Mg calcite precursor transformed to calcite under anoxic conditions during deep burial (Richter and Füchtbauer, 1978;Veizer, 1983;Flügel, 2004). Examples of formerly bimineralic, ancient, calcitized half-moon ooids with fabrics closely resembling those described here have been reported by a number of workers (Choquette, 1955;Carozzi, 1963;Mazzullo, 1977;Richter, 1983;Chatalov, 2005). Richter (1983) and Chatalov (2005) in particular described half-moon ooids from the Middle Triassic (Anisian) limestones of Episkopi (Greece) and Western Balkanides (Bulgaria), respectively. ...
... Examples of formerly bimineralic, ancient, calcitized half-moon ooids with fabrics closely resembling those described here have been reported by a number of workers (Choquette, 1955;Carozzi, 1963;Mazzullo, 1977;Richter, 1983;Chatalov, 2005). Richter (1983) and Chatalov (2005) in particular described half-moon ooids from the Middle Triassic (Anisian) limestones of Episkopi (Greece) and Western Balkanides (Bulgaria), respectively. Their investigated ooids show a bi-partite fabric developed from primary, concentric laminae of tangential aragonite that coated a high-Mg calcitic core which probably exhibited radial fabric. ...
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.
... Orientated thin sections for foraminiferal identification were made for biostratigraphic analysis. Classification of ooid types and procedures for microfacies analysis follow Richter (1983) and Flügel (2010), which use criteria, such as overall shape, cortical structure and diagenetic overprint, to classify ooids. Percentage of carbonate grains was estimated semiquantitatively by using the comparison chart of Baccelle and Bosellini (1965). ...
... These oolitic lithoclasts and accompanied ooids (0.21-0.79 mm in diameter) comprise up to 40-50 % of the rock (Fig. 4f-g). Some single ooids show asymmetrical growth with micritic laminae thickening in one direction (Fig. 4g), which possibly suggest non-turbulent periods for micritic enveloping to grow upward (Richter 1983;Strasser 1986;Flügel 2010). According to Flügel (2010), formation of compound ooids commonly undergoes two processes: (1) single ooids bound by encrustation or cementation in environment with restricted water circulation and reduced sedimentation rates and (2) regeneration of outer thin oolitic coating in agitated condition. ...
... Some of them are distorted into flattened oval, duck-like or elephantine shape; several distorted ooids link together to form zig-zag chains (Fig. 5c, f, j, k). Such distortion has been regarded to result from weakening of ooids after dissolution of originally aragonitic portion (Richter 1983;Zeng et al. 1983;Wilkinson et al. 1984;Tewari and Tucker 2011;Li et al. 2015a). Some ooids have segmented outermost cortical layers around inner micritic cores (Fig. 5j). ...
Marine carbonate ooids are environment-sensitive and hence valuable for paleoclimatic and paleogeographic reconstructions. This paper describes Permian ooids from the Baoshan Block in western Yunnan, China, in order to offer a new means to refine the uncertain paleogeographic details of this Gondwana-derived block. Four major types of ooids (micritic ooids, compound ooids, leached ooids and half-moon ooids) are documented from the Hewanjie Formation in the northern and the Shazipo Formation in the southern Baoshan Block. These ooids are dated via biostratigraphic analysis to be Wordian?early Wuchiapingian and signify an ameliorated shallow-marine temperature for the Guadalupian strata of the Baoshan Block. Results of this study, coupled with literature data, reveal diachronous debut of Permian ooids among the Gondwana-derived blocks: mostly Sakmarian in Central Taurides of Turkey, Central Iran, Central Pamir and Karakorum Block versus Wordian?Capitanian in Baoshan Block, Peninsular Thailand and South Qiangtang. In contrast, Asselian?Sakmarian strata of Baoshan Block as well as Peninsular Thailand and South Qiangtang are characterized by glaciomarine diamictites. These observations suggest that the Baoshan Block was probably situated at a considerably higher paleolatitude under distinct influence of Gondwana glaciation during the Asselian?Sakmarian than those blocks yielding Sakmarian ooids. Moreover, marine ooids are virtually absent nearby the equator within the Permian Tethys, similar to the modern situation. The Baoshan Block is accordingly interpreted to drift to warm-water southern mid-latitudes during the Wordian?Capitanian and remain to the south of Central Iran, Karakorum Block and South China, which were equatorially located in the Capitanian.
... Modern marine ooids reach diameters of 0.25 − 2 mm but are usually no larger than 1 mm. Conversely, some fossil ooids reach up to > 20 mm in size (Richter 1983;Trower 2020). These larger-than-usual (> 2 mm) ooids have been termed 'giant ooids' as opposed to 'pisoids' or 'macroids' to indicate a common origin, to emphasise similar grain genesis and to provide a differentiation from oncoids (Sumner and Grotzinger 1993;Li et al. 2021). ...
... Primary high-Mg calcites, which release excess Mg 2+ during diagenesis, may promote the formation of microdolomite and recrystallisation to low-Mg calcite (Brand and Veizer 1983;Dickson 2001;Hoffmann et al. 2016). With regard to a potential transformation of primary high-Mg calcite to secondary low-Mg calcite, Richter (1983) proposed a multistage transformation pathway in a Fe-depleted diagenetic environment, in which the more soluble, Mg-rich cortices dissolve and reprecipitate to form low-Mg-calcite first, followed by the Mg-lean layers (Richter and Zinkernagel 1981). However, this assumption ). ...
The sedimentary environment and mechanisms of formation of giant ooids (> 2 mm) are not well understood. Here, we use petrographical, mineralogical and eochemical data of giant ooids from the Lower Triassic Buntsandstein Formation of central Germany to develop a coherent formation model. Structural preservation of calcite crystallites in ooid cortices in combination with comparatively low strontium concentrations (< 545 μg/g) and the absence of dolomite in the cortex suggest a primary low-Mg calcite composition. Shale-normalised rare earth elements plus yttrium (REE + Y) patterns lack a pronounced heavy REE over light REE enrichment and show a positive cerium anomaly (Ce/Ce*SN = 1.9–3.9). Together with a missing yttrium anomaly and low Y/Ho ratios (< 40), these data are largely consistent with ooid formation in a lacustrine environment. Positive cerium and lanthanum anomalies further point to formation and deposition in an alkaline to hypersaline playa-lake environment. Based on our findings, a five-stage formation model is proposed. We suggest nucleus formation by microbial spheres, followed by calcite crystal nucleation on biofilm templates at the sediment–water interface, and crystal/
cortex growth inside the sediment pile. The spherical ooid form is achieved by wave-induced physical rolling motion after exhumation. Ooid growth ceases when the ooid reaches a critical size (here 4 mm), depending on local hydrodynamic
properties. Inhomogeneous crystal growth and the inclusion of exogenous particles lead to structural and geochemical anomalies in the ooid cortex. Results presented here have far-reaching implications for the application of REE and other trace elements as environmental proxies in ancient carbonates.
... The ooids present in this lithofacies are all concentric tangential (Richter, 1983). ...
... The carbonate ooids and peloids indicate a shallow and high-energy environment (Reijers and Ten, 1983). Lacustrine ooids of this type have been shown to be affected by, and sometimes dependent on, higher salinities, coupled with the shallow water and high agitation necessary for ooid formation (Davies et al., 1978;Popp and Wilkinson, 1983;Richter, 1983). The appearance of concentric tangential ooids versus radial ooids indicates an environment with bed load transport, high energies, and frequent abrasion (Heller et al., 1980). ...
This thesis examines a late Miocene to Pliocene sedimentary succession in the Lauca Basin, a topographically isolated, fluvio-lacustrine basin in the northern Chilean Altiplano. A sedimentary section within the Lauca Basin, composed of Lauca Formation sediments, was investigated using stratigraphic and petrographic analyses to define the Miocene to Pliocene paleoenvironmental history of the region. Geochronologic results indicate the section ranges in age from approximately 5.57 +/- 0.20 Ma to 5.44 +/- 0.16 Ma. The sedimentology of 36 samples was described, and twelve samples were analyzed petrographically. Five lithofacies were characterized: laminated mudstone (Fl), volcaniclastic mudstone (Fv), carbonate (C), evaporite (E), and muddy sandstone (SF). These lithofacies were used to characterize sedimentary structures and interpret depositional environments. These ranged from deposition from suspension in a moderate to deep lacustrine environment (Fl and Fv); deposition and precipitation of carbonates and evaporites in closed, possibly ephemeral environment (C and E); and deposition in a shallow high-energy lacustrine environment (SF). The dominant presence of evaporites and the dominantly laminated sedimentary units throughout the section suggest a closed lacustrine environment, and are indicative of seasonal or periodic changes in sediment supply. The evolution of the sedimentary section is inferred from the depositional environments combined with prior studies of the Miocene-Pliocene transition to produce a regional history at higher temporal resolution. The evolution of the Lauca Basin was influenced strongly by evaporation and precipitation, with significantly lesser influences of volcanism, tectonism, and sedimentary supply. The bulk of sediments deposited in the sedimentary section were from an arid, saline, occasionally ephemeral lacustrine environment. Advisor: Sherilyn Fritz
... Ooids are amongst the most common constituents of shallow-marine and non-marine carbonates, and have attracted interest for palaeoenvironmental determinations (Bathurst 1975; Richter 1983; Burchette et al. 1990), and as indicators of ancient sea-water chemistry (Sandberg 1983; Wilkinson and Given 1986; Bates and Brand 1990). Furthermore, an understanding of ooid development is not a purely academic pursuit, as studies of oolitic hydrocarbon reservoirs have illustrated the importance of microfabric and mineralogical variations as controls on reservoir quality (Harris et al. 1984; Moore et al. 1988; Heydari and Moore 1994). ...
... Despite the extensive literature on ooids, only a few studies, notably those of Strasser (1986) and Chow and James (1987), have examined the relationship between the origin, microfabric, facies distribution and diagenesis of ancient ooids. Understanding the primary composition and structure of ancient ooids is often problematical due to diagenetic changes which, to a greater or lesser extent, act to destroy or obscure such features (Sherman et al. 1970; Bathurst 1975; Simone 1981; Medwedeff and Wilkinson 1983; Richter 1983). Although the vast majority of ooids are marine in origin, non-marine ooids have been recognized in a variety of modern lake systems (Eardley 1938; Halley 1977; Copyright # 2002 John Wiley & Sons, Ltd. ...
... As shown by Gavish and Friedman (1969) and Budd and Hiatt (1993), high-Mg calcite inverts to low-Mg calcite without loss of textural integrity when exposed to meteoric-water diagenesis. This evidence supports the contention of Richter (1983) that ancient radial ooids from marine environments were composed originally of high-magnesian calcite. Figure 11. ...
... Micritization of original ooid structure by boring micro-organisms has also been important (Bathurst, 1975). The interpretation of ancient radial ooids as primary precipitates now is commonplace (Sandberg, 1975;Simone, 1981;Richter, 1983) and compilations of inferred ooid mineralogy through time suggests that calcite, possibly magnesiumrich, was the favored precipitate during the Jurassic and Cretaceous (Sandberg, 1983;Wilkinson et al., 1985;Strasser, 1986). Inferred original calcitic as opposed to aragonitic mineralogy of ooids has been primarily related to two factors. ...
On Resolution Guyot two major intercalations of oolitic limestone have developed, one of latest Hauterivian-Barremian age, which rests directly on edifice basalt, and the second of Aptian age, which is sandwiched between lagoonal-peritidal carbonate sediments. Both oolite packages may be interpreted as the sedimentary response to an increase in the generation of accommodation space; in the first instance, probably related to high rates of basement subsidence, in the second, to a probable eustatic rise in sea level. The ooids vary in structure from micritic and featureless through micritic and concentrically laminated to radial and commonly show combinations of these fabrics. Radial cortical structures predominate. -from Authors
... Ooids (Sorby, 1879;Kalkowsky, 1908), and their many subtypes, are spherical or ovoidal carbonate grains with concentric laminae coating a carbonate or non-carbonate nucleus (see . The one to several-micron-thick laminae of calcareous ooids consist of nanometre-sized aragonitic or calcitic batten-like crystals (needles and rods; Richter, 1983;Richter & Neuser, 1998;Scholle & Ulmer-Scholle, 2003;Flügel & Munnecke, 2010;Harris et al., 2019). Ooids have formed abundantly in shallow warm (sub-tropical) marine or lacustrine environments throughout much of Earth's history (Simone, 1980;Rankey & Reeder, 2012;Diaz et al., 2014Diaz et al., , 2015Diaz et al., , 2017. ...
Ooids are abundant carbonate grains throughout much of Earth's history, but their formation is not well understood. Here, an in‐depth study of microbial bioerosion features of Holocene ooids from the Schooner Cays ooid shoals (Great Bahama Bank, Eleuthera, Bahamas) and the Shalil al Ud ooid shoals in the Arabian/Persian Gulf (Abu Dhabi, United Arab Emirates) is presented. No obvious differences were found in ooid size distribution, cortex layer thickness, the composition of nuclei or euendolithic community when comparing ooids from both locations. Microendolithic borings are present in most studied ooid surfaces, but the intensity of (micro‐)bioerosion varies significantly. Applying an epoxy vacuum cast‐embedding technique allowed the identification of ichnotaxa and their inferred producers (various genera of diatoms, cyanobacteria, coccolithophores and unspecified bacteria). Euendolithic taxa have specific low‐light tolerances and light optima. This implies that information about the relative bathymetry (seafloor versus burial within an ooid shoal) and ecology for ooid cortex formation can be obtained via the presence or absence of their respective ichnotaxa. The history of a statistically significant number of ooid cortices can be translated into dune dynamics and the temporal variations thereof by allocating the inferred index producer to a defined burial or light penetration zone. In this context, ooid formation can be divided into four stages: (i) an agitation stage in the water column, characterized by the colonization of grains by photoautotrophs; (ii) a resting stage, characterized by temporary burial of the ooid, leading to immobilization and a shift towards heterotrophs; (iii) a sleeping stage, characterized by prolonged burial and colonization by organotrophs; and (iv) a reactivation stage, characterized by a resurfacing of the ooid and a subsequent shift towards photoautotrophs. The sleeping stage is presumably a stage of ooid degradation where bioerosion, mainly by heterotrophic fungi and bacteria is particularly active.
... Some of these ooids lost the concentric texture as a result of micritization (micritized ooids) (Fig.9G), despite the possibility that it was also lost throughout the conversion of an original aragonitic ooid to calcite (neomorphism) (Adams et al., 1987;Chatalov, 2005;Vulpius and Kiessling, 2018). Richter (1983) observed that micritic ooids are associated with oomolds and sparry relic/brickwork ooids, such as originally aragonite cortices, in the Lower Triassic of Hydra Island (Greece) and the Lower Muschelkalk of Germany. The presence of micritic ooids would appear to suggest slow sediment accumulation rates and/or low sediment mobility (Chatalov, 2005). ...
The composition and texture of beach sediments along continental coastlines vary considerably. Beach sands made completely of carbonate sediments are prevalent along Egypt's Western Mediterranean Coast. Forty-five sediment samples were collected from various locations (El-Dekhela, Kilo-21, Abu Talat, and Sidi Krir) along the Western Mediterranean Coast of Egypt. The sedimentological and mineralogical attributes of the collected sediments were investigated using collaborative techniques. The beach sediments in the coastal region between El-Dekhela and Sidi Krir consist mainly of carbonate sands that are mineralogically composed of dolomite, calcite, and aragonite with smaller amounts of quartz, sylvite, anhydrite, gypsum, and trace amounts of microcline. They contain ooids with bioclasts and very few heavy minerals, except for notable amounts of these minerals in the El-Dekhela region. These heavy minerals primarily consist of opaque minerals, amphiboles, and pyroxenes, with smaller amounts of epidote, zircon, tourmaline, rutile, garnet, kyanite, monazite, sphene, staurolite, and biotite. The combination of heavy minerals in these deposits indicates a wide variety of igneous, metamorphic, and sedimentary rock types as potential source rocks. Heavy mineral concentrations decrease westward from the Nile River's mouth near Rosetta to Egypt's Western Mediterranean Coast. Most of the studied ooids are white colored and usually have a pearly luster; these characteristics indicate that these sediments were formed in agitated water. The current study reveals that the ooids in the study area originated from a variety of sources, including autochthonous and allochthonous ooids that eroded and broke, implying that they may have originated from coastal plain carbonate ridges.
... These complex biostromes and bioherms range in texture from stromatolitic to thrombolitic, and are interbedded with ooid, coated-grain, and intraclast-rich carbonates (Fig. 4, 6C-E, 7E) Swierenga et al. 2015;Eljalafi and Sarg 2021). Micritized ooids, cerebroid ooids ( Fig. 7A-C), ooids that grow into ''shrubby'' oncoids (Fig. 7C), and clotted fabrics are common in littoral environments, all of which are indicators of abundant micritizing microbial communities associated with microbialites (Kahle 1974;Richter 1983;Flugel 2013). Aerobic, sulfatereducing, and methanogenic decay of microbial organic matter likely occurred and could have generated alkalinity in microbialites (Reid et al. 2000;Dupraz et al. 2009;Bolhuis et al. 2014;Chagas et al. 2016). ...
Integrated stratigraphic, petrographic, and geochemical data allow interpretation of biogeochemical and mineralization processes in paleoenvironmental context of ancient lacustrine environments. These indicate that lake chemistry, microbial processes, and organic matter (OM) strongly influenced dolomite formation in near-surface environments throughout deposition of the Green River Formation (Eocene, Uinta basin, Utah).
The lower Green River Formation consists of interbedded fluvio-deltaic siliciclastics, paleosols, carbonate mud, coated-grain carbonates, mollusk and ostracod limestones, and microbialites all landward of profundal OM-bearing illitic mudrocks. Calcite, dolomite, Fe-dolomite, and authigenic feldspars are common. Carbonate δ18O and δ13C are covariant, and positive excursions of carbonate δ13C (up to 6.9‰ VPDB) and organic-matter δ15N (up to 13.9‰ V-AIR) occur in profundal OM-bearing mudrocks.
The upper Green River Formation consists mainly of laminated OM-lean and OM-rich dolomitic muds (i.e., “oil-shales”). Zoned dolomite crystals with Mg-calcite centers and Fe-dolomite rims are widespread in addition to authigenic feldspars and Na-carbonates. Carbonate δ13C-enrichment (up to 15.8‰ VPDB), and organic-matter δ15N-enrichment (up to 18.4‰ V-AIR) occur in these OM-rich dolomite muds. Organic-matter δ13C is relatively invariable (mean = –29.3‰ VPDB) and does not covary with carbonate δ13C.
Trends in mineralogy, organic-matter abundance, and stable isotopes result from changing hydrologic systems, paleoclimate, lake chemistry and microbial processes coincident with the Early Eocene Climate Optimum. The lower Green River Formation paleo-lake was smaller in area and volume, heavily influenced by meteoric fluvial input, variably oxygenated, and ranged from neutral and fresh to alkaline and saline. Especially in littoral environments with abundant microbialites, dolomite formed through recrystallization of precursor carbonate involving both replacement of precursor carbonate and direct precipitation as cements and overgrowths. The upper Green River Formation paleo-lake was more expansive with widespread low-oxygen, nutrient-rich, and alkaline saline environments with increased planktic organic-matter productivity. Microbial decay of organic matter in low-oxygen environments produced alkaline lake waters through methanogenesis, possible denitrification, and bacterial sulfate reduction to a limited degree. This favored precipitation of widespread dolomite, as well as Na-carbonates, authigenic feldspars, and analcime from lake water and phreatic pore water. Extracellular polymeric substances (EPS) excreted by microbial communities provided favorable nucleation sites for Mg-carbonate, allowing kinetic barriers of low-temperature dolomite formation to be overcome. Cycling of pH due to turnover of organic matter and associated microbial processes potentially bolstered EPS generation and abiotic environmental conditions favorable to dolomite precipitation. It is likely that metastable precursor carbonate was recrystallized to ordered dolomite, but it is possible that direct precipitation occurred. Fe-dolomite overgrowths precipitated after dolomite where microbial Fe reduction occurred in stagnant, oxygen-depleted, alkaline pore waters.
... Ooids are significant particles of carbonate deposits from many different sedimentary environments since the Archaean (e.g., Kalkowsky, 1908;Davies et al., 1978;Simone, 1981;Krumbein, 1983;Summons et al., 2013;O'Reilly et al., 2017;Siahi et al., 2017;Mariotti et al., 2018;Diaz & Eberli, 2019;Flannery et al., 2019). They are typically characterized by tangential and/or radial cortices and have sizes of < 2 mm (Richter, 1983;Flügel, 2010). In some cases, ooids can reach sizes of > 2mm ("giant ooids": e.g., Sumner & Grotzinger, 1993;Li et al., 2015;2021). ...
Ooids are particles composed of a tangential or radial cortex growing around a nucleus. They are common in carbonate deposits of almost any geological age and provide insights into environmental conditions. However, abiotic or biotic factors influencing their formation remain unclear. This study aims to advance our understanding of ooid formation with a multi–analytical approach (e.g., FE–SEM, Raman spectroscopy, μ–XRF) to classic examples from Great Salt Lake (GSL; USA) and the Lower Triassic Germanic Basin (GB; Germany). Both deposits represent hypersaline shallow–water environments where ooids are closely associated with microbial mats. GSL ooids are dominantly 0.2—1 mm in size, ellipsoidal to subspherical in shape, composed of aragonite, and contain organic matter (OM). GB ooids are mainly ≤4 mm in size, spherical to subspherical in shape, composed of calcite, and currently contain little OM. Despite the differences, both ooids have the same cortex structures, likely reflecting similar formation processes. Some GSL ooids formed around detrital grains while others exhibit micritic particles in their nuclei. In GB ooids, detrital nuclei are rare, despite the abundance of siliciclastic particles of various sizes in the host rocks. GB deposits also include ″compound ooids″, i.e., adjacent ooids that coalesced with each other during growth, suggesting static in-situ development, which is supported by the lack of detrital grains as nuclei. GB ooids also grew into laminated microbial crusts with identical microstructures, further indicating a static formation. Such microbial crusts typically form through mineral precipitation associated with OM (e.g., extracellular polymeric substances), suggesting a similar formation pathway for ooids. The inferred key–role of OM is further supported by features in radial ooids from the GSL, which commonly exhibit, from their nuclei towards their surface, increasing OM contents and decreasing calcification.
... The poor sorting and the wide range of ooid size suggest that these ooids were not formed under high energy wave agitation. The absence of well-developed concentric structure suggests clay composition (Bathurst, 1975;Richter, 1983).Ooids with very similar texture deformation were described in the Eocene Green River Formation of Utah, USA (Tettenhorst and Moore, 1978), and in the Lower Cretaceous Lagoa Feia Group of Campos and Santos basins (Armelenti et al., 2016;Goldberg et al., 2017;Herlinger Jr. et al., 2017;Leite et al., 2020). ...
... The poor sorting and the wide range of ooid size suggest that these ooids were not formed under high energy wave agitation. The absence of well-developed concentric structure suggests clay composition (Bathurst, 1975;Richter, 1983).Ooids with very similar texture deformation were described in the Eocene Green River Formation of Utah, USA (Tettenhorst and Moore, 1978), and in the Lower Cretaceous Lagoa Feia Group of Campos and Santos basins (Armelenti et al., 2016;Goldberg et al., 2017;Herlinger Jr. et al., 2017;Leite et al., 2020). ...
The Pangaea assemblage resulted in significant tectonic and eustatic changes, but also a well-known desertification triggered by the increasing continentalization. While the northern hemisphere basins have been thoroughly studied, several recent studies on southern hemisphere basins bring new insight on how these events affected the Gondwana hinterlands. In this study, sedimentological and geochemical analyses of chert deposits from the Pennsylvanian Piauí Formation of the Parnaíba Basin are examined as new evidence for the onset of continentalization and aridification in the northwestern Gondwana mid-latitudes. The chert deposits correspond to three facies (stromatolites, ooidal arenites and breccias). The chert features suggest deposition in a shallow water environment and biomarkers analysis of stromatolites indicated predominance of organic matter produced by cyanobacteria in an environment characterized by high salinity and elevated pH. Such evidence suggests that the Piauí Formation cherts deposited in a shallow, saline-alkaline lacustrine environment during a period marked by increasing arid climate conditions.
... Older classifications presupposed a biological origin for oncoids and a non-biological control for the formation of ooids (e.g., Davies et al., 1978;Peryt, 1983). However, after recognizing that ooid formation required microbial mediation (e.g., Duguid et al., 2010;Diaz et al., 2015), genetic classifications were abandoned, and descriptive terms prevailed (e.g., Richter, 1983;Steinhoff and Strohmenger, 1996;Flügel, 2004). Nevertheless, there is still a paradigm whereby elongated ooids form due to the elongated shape of the nucleus and usually do not have perfectly symmetrical and concentric cortices. ...
The succession in the Tizra Formation shows an excellent exposure of a small open marine platform where alternating microbial boundstones (buildups) and oolitic/bioclastic grainstone (shoals) and packstone facies tempestites occur repetitively for a sort interval only 0.55 Myr, an scenario unknown in the geological record. The relatively small extent of the platform allows a detailed study of facies and ecological variations, to determine the controlling factors for the growth and evolution of the platform (tectonics, glacioeustatism, terrigenous imput), as well as the particular environmental/ecological conditions for the formation of microbial buildups and oolitic shoals (turbidity, energy, nutrients, chemical variations).
Although microbial mounds are well-known during the Palaeozoic, the close relationship with ooids, as observed in the studied succession, is unusual, particularly for the frequent ooids embedded in the microbial facies, an ecological parameter used by previous authors to identified shallower stages in the microbial growths.
Petrographic analysis of the ooids, as well as their ecological conditioning, suggest that less than 40% of samples yield ooids generated in situ, whereas there is a predominance of transported ooids. Ooids formed in situ, which include large irregular and elongated ooids, were generated in calmer water than the typical rounded and egg-shaped ooids. The occurrence of the predominant types of ooids in shallower-water grainstones with in situ generation, and in the deepest-water microbial facies, suggest their ease of transport. The higher production of ooids occurs during the shallowing phases of the cycles, whereas they were more easily transported during the deepening phases, whereas in the microbial buildups, no features of in situ ooid generation are found.
... Oolite deposits often are used to reconstruct past depositional environments, given that they are common throughout the geological record from the Precambrian to the present-day and indicate particular environmental conditions (Carozzi, 1961;Brand & Veizer, 1983;Richter, 1983;Strasser, 1986;Sumner & Grotzinger, 1993;Harris et al., 2019, among others). Given their deposition in close proximity to sea level and their metastable mineralogy, ooids are prone to early diagenetic alterations, and studies can provide valuable clues about the overall geological history of the strata Harris, 2019). ...
Selective dissolution of metastable minerals and certain pore types, such as moldic and oomoldic pores, are widely accepted to indicate diagenesis by meteoric fluids in carbonate rocks. In this study, oomoldic‐rich re‐sedimented carbonates from the Happy Field in the Midland Basin which contain no evidence of subaerial environments, indicate that such pores may form in other settings. Ooid dissolution in the reservoir was evaluated through petrography, scanning electron microscopy, stable isotopes (δ18O and δ13C), elemental geochemistry, and X‐ray diffraction of bioclasts, ooids and associated cements. Cements are equant low magnesium calcite; dogtooth low magnesium calcite and poikilotopic celestine cements as well as a late stage low magnesium calcite cements in lesser amounts. Equant low magnesium calcite cements are interpreted to reflect the initial stages of pore filling, synchronous with aragonitic ooid dissolution, thus implying that oomoldic pores and equant cements formed in similar fluids. Although the prominent equant low magnesium calcite cement textures mimic those often associated with meteoric fluids, geochemistry suggests a marine origin. The equant cements have δ18O (Vienna Pee Dee Belemnite) ratios between ‐2.0‰ and ‐3.5‰, and δ13C (Vienna Pee Dee Belemnite) ratios between 4‰ and 5‰. Magnesium/calcium ratios show values, ranging from 5 to 142 mmol/mol (n = 223, average 23.2 and SD = 20.1). Strontium/calcium ratios present values from 0.3 to 2.6 mmol/mol (n = 223, average 0.71 mmol/mol, SD 0.35). Geochemical data coincide with typical low‐latitude Permian marine carbonate values and further signify diagenesis within the marine phreatic realm. To explain this process, the results indicate that the dissolution of aragonite ooids and precipitation of early cements occurred in environments ranging between the seafloor to shallow burial dominated by undersaturated marine fluids. Undersaturation was triggered by organic matter decomposition occurring at the seafloor and in the shallow subsurface immediately below. These findings have broader implications for marine and burial carbonate diagenesis as well as diagenesis of re‐sedimented deposits.
... Oncoids are common in ancient and modern continental environments (for review see Peryt 1983aPeryt , 1983bMagny 1992;Freytet and Plaziat 1979) but continental ooids are known to form mainly in hypersaline or brackish lakes and thermal springs. Reviews concerning nonmarine ooids (see Simone 1981;Richter 1983; among others) refer primarily to papers describing the spectacular aragonitic ooids from Great Salt Lake, Utah (Eardley 1938;Kahle 1974;Halley 1977) and bimineralic ooids from Pyramid Lake, Nevada (Popp and Wilkinson 1983). ...
... They often exhibit regularly and concentrically laminated fabrics. Ooids can form in both marine and lacustrine settings and are associated with moderate to high energy environmental settings such as shoals (Richter, 1983;Flügel, 2004). Oncoids, in contrast, are biogenically formed (by algae or bacteria) coated grains, and commonly are larger than ooids (mm-to cm-sized), and can form in both quiet and high-energy environments. ...
This paper concerns the sedimentary successions deposited in the Mandawa Basin after the separation of East and West Gondwana during the subsequent southwards drift of Madagascar in the Late Jurassic to Early Cretaceous times. The aim of this study was to provide more specific details on the Late Jurassic and Early Cretaceous sedimentation and to report mineralogical and petrographical characteristics on the less well documented successions, namely the Kipatimu, Mitole and Nalwehe formations, in the central and northern parts of the Mandawa Basin.
The Late Jurassic and Early Cretaceous depositional environments are reviewed, based on the sedimentological, mineralogical and petrographical results presented here, supplemented by previously published work. The Late Jurassic to Early Cretaceous depositional setting mainly reflects a shallow, tidally influenced, mixed carbonate-silisiclastic coastal ramp. The succession displays cyclical sedimentation best described as a series of transgressive-regressive sequences with limestones overlain by siliciclastics. During transgressions microbial activity was high and sedimentation rates low, resulting in micro-oncoid deposition in the late Kimmeridgian – early Tithonian (Mitole Limestone Member), and oncoids and stromatolites in the Early Cretaceous (Nalwehe Limestone Member). During the regressive phases siliciclastic marginal marine sediments were deposited over the limestones. The regressive sandstones are mainly unfossiliferous and display evidence of being deposited in a tide-dominated, marginal marine environment.
... Before final burial the articular faces of columnals in some studied fossils were recovered and overgrown by epibionts (foraminifers, annelids); these latter are also displaying very small and rounded holes likely produced by acrothoracican cirripeds, algae, fungi, polychaetids, sipunculans or even sponges. Furthermore, a strong micritization of ooid cortex, dissolution of fragments of echinoderm elements, as well as the lack of preserved ooid cores, which were dissolved and replaced by sparite/microsparite crystals, point to the early diagenetic changes (comp., RICHTER, 1983). In marine environments, ooids are typically formed in intertidal and shallow-subtidal settings, and in carbonate platforms (between lagoons and open sea; WILSON, 1975). ...
... Here we suppose that the mineralisation is being produced by a non-replenishing source of necrotising microbes in region I. In this case k b = 0 and the model equations reduce to (1)- (3). Suppose that R is the limiting radius before the onset of mineralisation and this radius is reached at time τ. ...
Ooids are typically spherical sediment grains characterised by concentric layers encapsulating a core.
There is no universally accepted explanation for ooid genesis, though factors such as agitation, abiotic
and/or microbial mineralisation and size limitation have been variously invoked. Here we examine the
possible influence of microbial organomineralisation on the formation of some naturally occurring
ooids. We develop a mathematical model for ooid growth, inspired by work on avascular brain tumours,
that assumes mineralisation in a biofilm to form a central core which then nucleates the progressive
growth of concentric laminations. The model predicts a limiting size with the sequential width variation
of growth rings comparing favourably with those observed in experimentally grown ooids generated
from biomicrospheres. In reality, this model pattern may be complicated during growth by syngenetic
aggrading neomorphism of the unstable mineral phase, followed by diagenetic recrystallisation that
further complicates the structure. Our model provides a potential key to understanding the genetic
archive preserved in the internal structures of some ooids.
... Ooids are typically spherical sediment grains characterised by a cortex of concentric layers encapsulating a core (see Fig. 1). They may be nucleated on a detrital grain or a shell fragment, but any unevenness inherited from an irregularly shaped nucleus is smoothed out by successive cortical layers until a spherical form is attained [16][17][18] . Similar concentric spherical forms are displayed by kidney and gall stones 19 , cave pearls 20 and mineral deposits 21 . ...
Ooids are typically spherical sediment grains characterised by concentric layers encapsulating a core. There is no universally accepted explanation for ooid genesis, though factors such as agitation, abiotic and/or microbial mineralisation and size limitation have been variously invoked. We develop a mathematical model for ooid growth, inspired by work on avascular brain tumours, that assumes mineralisation in a biofilm to form a central core and concentric growth of laminations. The model predicts a limiting size with the sequential width variation of growth rings comparing favourably with those observed in experimentally grown ooids generated from biomicrospheres. In reality, this model pattern may be complicated during growth by syngenetic aggrading neomorphism of the unstable mineral phase, followed by diagenetic recrystallisation that further complicates the structure. Our model provides a potential key to understanding the genetic archive preserved in the internal structures of naturally occurring ooids. https://arxiv.org/abs/1708.04404
... Large, elongated nuclei (up to 1 mm across) show distinct microspar laminae over Hat surfaces but not over curved edges (PI, I: 2) such that grains increase in sphericity during growth. According toRichter (1983), this is the best diagnostic criterion which allows to distinguish between ooids and other types of grains. The length of radially arranged crystals in the laminae varies from 5 to 25 jxm and it controls the thickness of the layers. ...
... At Eclépens, this interval is roughly two metres thick. It is found near the top of the upper Pierre Jaune (Fig. 1), almost one metre below the discontinuity, a feature that pleads in favour of the second option; • earlier records of oolitic cortices leached in full (WHERRY, 1915;SANDBERG, 1975SANDBERG, , 1983RICHTER, 1983;ZEN et al., 1983;TUCKER, 1984;BATES & BRAND, 1990; ALGEO & WAT- SON, 1995) or in part, i.e., only some cortical layers (TUCKER, 1984;ALGEO & WATSON, 1995) came to the conclusion that they are dealing respectively with either aragonitic or "bimineralic" (aragonite-calcite) cortices. ...
A recent paper by Godet et al. on Urgonian carbonates from the Swiss Jura concluded that diagenesis may hinder chemostratigraphic correlations of deep- to shallow-water facies. Although we agree with this conclusion we question their arguments and interpretations. These authors correctly identified diagenesis as the key factor, but we question the timing of events in their paragenetic sequence. In particular, they reported the leaching of originally calcitic oolitic cortices but failed to discuss this puzzling feature properly. In addition, the backbone of their argument is the stratigraphic correlation of a specific sequence from three dominantly shallow-water sections together with a basinal reference section. However, a reliable alternative biostratigraphic framework shows that this attempt of long-distance correlation might be erroneous.
... Inner-ramp deposition is suggested by the abundance of ooids, which are best developed in very shallow agitated warm waters (Scoffin 1987). Alternation of low-and highwater agitation is indicated by the combination of radial and tangential textures of ooids (Richter 1983). ...
The lithofacies and macrofossil guilds of the Agrio Formation (Upper Valanginian–Lower Barremian) have been analysed using evidence from sedimentological, taphonomic and palaeoecological studies. The study area is Agua de la Mula and adjacent regions in central Neuque´n. Seven lithofacies have been recognized in the field, which indicate that the Agrio Formation was deposited in an open-marine, ramp depositional system under storm influence. Lithofacies indicate conditions that range from low-energy basin to high-energy inner ramp. Outer and mid-ramp deposits are the most abundant. Macrofossils have been grouped into 16 guilds based on tiering, life habit and feeding category. The guilds indicate normal benthic oxygen level, normal salinity, and soft–firm muddy and sandy bottoms. Suspension-feeders are more common than deposit-feeders suggesting thepredominance of suspended food particles over deposited food resources. A low input of siliciclastics and, possibly, other palaeoceanographic conditions allowed the development of oolitic facies in the inner ramp and coral patch reefs in the upper mid-ramp for a limited period of time.
... This indicates that areas on the grain surface protected from abrasion were favorable sites for microbial activity, which locally inhibited the precipitation of oolitic cortices. This interpretation has been proposed by Kahle (1974) and Richter (1983), and is supported by the frequent association of cerebroid ooids and stromatolites in pre-evaporitic environments (Kalkowsky 1908;Eardley 1938;Sandberg 1975). ...
... Here we suppose that the mineralisation is being produced by a non-replenishing source of necrotising microbes in region I. In this case k b = 0 and the model equations reduce to (1)- (3). Suppose that R is the limiting radius before the onset of mineralisation and this radius is reached at time τ. ...
Up to and including Brückmann’s review in 1721 it was generally accepted that oolites were composed of petrified fish roe. In 1879 Sorby showed that oolitic grains were not in fact eggs, but, like De La Beche in1851, suggested that they were the product of minute, prismatic crystals of carbonate “mechanically accumulating around a centre, something like the layers in a large rolled snowball”. The term “oolith” was so firmly entrenched in usage that Kalkowsky continued its use, even though he thought it “rather stupid” since the constituent grains were by this time clearly known to not be fossilized eggs. He proposed that the constituent grains be termed “Ooid” and suggested that they were produced by the activities of minute “phytoorganisms“. Bucher (1918) compared the origin and structure of ooids to those of urinary calculi such as gallstones that Schade (1908, 1910)
formed by the transformation from an emulsion colloid to solid state. If the emulsion was of pure composition the calculi formed with a radial crystalline structure, but if other colloidal impurities were present then co-precipitation gave rise to calculi with a concentric structure. Folk and Lynch (2001) suggested that “nannobacteria”, might play a role in ooid formation. Ryall (1908) also found that “nanobacteria” were implicated in the growth of concentric kidney stones in humans. It is now clear that these “nanobes” are not independent organisms, but are nevertheless composed of organic matter fragments. Duguid et al. (2010) concluded that micro-organisms do not play a primary role in ooid genesis. However Diaz et al. (2014) have concluded that carbonate precipitation in marine oolitic biofilms is spatially and temporally controlled by a complex consortium of microbes. We find that there is little evidence in nature for the “snowball model” of accretion forming concentric accumulations that typify ooids. We are examining the relevance of mathematical models of accretion to understanding the possible biotic influence on ooid growth. Ooid size has generally been arbitrarily limited to grains below 2 mm diameter, but many examples of larger “giant” ooids are recorded. Typically these forms do not occur in well-sorted accumulations. We anticipate that our mathematical models will also establish how environmental factors limit the maximum size of ooid growth.
... This indicates that areas on the grain surface protected from abrasion were favorable sites for microbial activity, which locally inhibited the precipitation of oolitic cortices. This interpretation has been proposed by Kahle (1974) and Richter (1983), and is supported by the frequent association of cerebroid ooids and stromatolites in pre-evaporitic environments (Kalkowsky 1908;Eardley 1938;Sandberg 1975). ...
Giant ooids have been considered as abnormal sediment and distributed globally in the aftermath of the end-Permian mass extinction, and represent a marine carbonate supersaturated state which is unfavourable to the survival of metazoans. The marine environment returned to normal in the early Middle Triassic when abnormal sediments became rare. However, the discovery of giant ooids in the early Middle Triassic at the Poduan section, Ceheng, Guizhou Province, could give us more 基金项目： 国家自然科学基金项目
Ooids are coated grains composed of a tangential or radial cortex growing around a nucleus. They are common in carbonate deposits of almost any geological age and provide insights into environmental conditions. However, abiotic or biotic factors influencing their formation remain unclear. This study aims to advance current understanding of ooid formation with a multi‐analytical approach (for example, field emission scanning electron microscopy, Raman spectroscopy and micro X‐ray fluorescence) to classic examples from Great Salt Lake, USA, and the Lower Triassic Germanic Buntsandstein Basin, Germany. Both of these deposits represent hypersaline shallow‐water environments where ooids are closely associated with microbial mats. Great Salt Lake ooids are dominantly 0.2 to 1.0 mm in size, ellipsoidal to subspherical in shape, composed of aragonite and contain organic matter. Germanic Buntsandstein Basin ooids are mainly ≤4 mm in size, spherical to subspherical in shape, composed of calcite and currently contain little organic matter. Despite the differences, both ooids have the same cortex structures, likely reflecting similar formation processes. Some Great Salt Lake ooids formed around detrital grains while others exhibit micritic particles in their nuclei. In Germanic Basin ooids, detrital nuclei are rare, despite the abundance of siliciclastic particles of various sizes in the host rocks. Germanic Basin deposits also include ‘compound ooids’, i.e. adjacent ooids that coalesced with one another during growth, suggesting static in situ development, which is supported by the lack of detrital grains as nuclei. Germanic Basin ooids also grew into laminated microbial crusts with identical microstructures, further indicating a static formation. Such microbial crusts typically form through mineral precipitation associated with organic matter (for example, extracellular polymeric substances), suggesting a similar formation pathway for ooids. The inferred key‐role of organic matter is further supported by features in radial ooids from the Great Salt Lake, which commonly exhibit, from their nuclei towards their surface, increasing organic matter contents and decreasing calcification.
Marine ooids have formed in microbially colonized environments for billions of years, but the microbial contributions to mineral formation in ooids continue to be debated. Here we provide evidence of these contributions in ooids from Carbla Beach, Shark Bay, Western Australia. Dark 100-240 μm diameter ooids from Carbla Beach contain two different carbonate minerals. These ooids have 50-100 μm-diameter dark nuclei that contain aragonite, amorphous iron sulfide, detrital aluminosilicate grains and organic matter, and 10-20 μm-thick layers of high-Mg calcite that separate nuclei from aragonitic outer cortices. Raman spectroscopy indicates organic enrichments in the nuclei and high-Mg calcite layers. Synchrotron-based microfocused X-ray fluorescence mapping reveals high-Mg calcite layers and the presence of iron sulfides and detrital grains in the peloidal nuclei. Iron sulfide grains within the nuclei indicate past sulfate reduction in the presence of iron. The preservation of organic signals in and around high-Mg calcite layers and the absence of iron sulfide suggest that organics stabilized high-Mg calcite under less sulfidic conditions. Aragonitic cortices that surround the nuclei and Mg-calcite layers do not preserve microporosity, iron sulfide minerals nor organic enrichments, indicating growth under more oxidizing conditions. These morphological, compositional, and mineralogical signals of microbial processes in dark ooids from Shark Bay, Western Australia, record the formation of ooid nuclei and the accretion of magnesium-rich cortical layers in benthic, reducing, microbially colonized areas.
The role of microorganisms in the formation of giant ooids is one of the areas of long-term controversy in ooidal research, but it has not been confirmed conclusively. Abundant giant ooids developed in the Zhangxia Formation of the Cambrian Miaolingian Series in North China. Giant ooids in the study area were examined by using Polarized Light Microscopy and Field Emission Environmental Scanning Electron Microscopy. The nuclei of the ooids consist of micritic pellets or radial ooids with diameters less than 2 mm and are formed in a weak-agitating seawater environment. Their cortices are concentric, and are characterized by the alternations of the dark laminae of micritic calcite or Girvanella filaments and light laminae of microsparry calcite. In the environments of inter-bank sea with the alternating development of medium and low energy and chiefly weak-agitating conditions, giant ooids were formed under the joint action of Girvanella filamentous growth, biologically-induced calcification and/or biologically-influenced calcification and inorganic calcium carbonate precipitation. The microfossils of Girvanella are distributed in inner and outer cortices of giant ooids, especially dense in the latter. This distinctly indicates that microbes play a significant role in the formation of giant ooids, and also provides a vital example for discussing the microbial origin of giant ooids.
The potash-bearing deposit was located in the Vientiane Basin of Laos where exists one of eastern Tethys metallogenic belt. The water-insoluble of Thongmang mining area in this basin were selected as carrier, through leaching and analysis, showed the water-insoluble minerals mainly include anhydrite, boracite, hilgardite, carbonate, quartz and muscovite, in which anhydrite, boracite and muscovite were dominant minerals. Mineralogical and morphological analyses of the water-insoluble minerals from different borehole-derived potash mineral strata have elucidated the evolution process of brine salt formation and restore the paleo-potassium deposit environment. The water-insoluble minerals revealed that the sedimentary environment in the late stage of salinity belongs to the shallow water disturbing environment. Accompanied by the fluvial influx and the influence continued, under the strong influence of terrestrial water body in the late salt-forming period, the evolution process of salt-forming brine will inevitably be affected. And the displacement of sedimentary center occurred during the metallogenic stage. Thus, this studies show that the characteristics of the water-insoluble can be used to retrieve the evolution process of brine salt formation and refect environment changes of the paleo-potassium deposits. In a word, the characteristics of water-insoluble minerals can provide effective information indicating the changes of sedimentary environments at the late stage of brine evolution.
The managed mineralisation of CO2 on mineral substrates has significant potential to mitigate CO2 emissions to atmosphere, using processes that are analogous to the formation of limestone in nature. High-temperatures and pressures or ambient conditions can be applied in processes that compare with the natural chemical, hydrothermal or biological formation of limestone. In the UK, recent policy developments recognise the potential of carbon utilisation and a reduction target of 40 Mt by 2030 has been set. In the present work, the analogies between natural and managed carbonate-production are briefly reviewed and the potential gains for mineralisation technology employing flue-gas a direct source of CO2 is presented. With reference to selected UK solid waste arisings, our high-level analysis indicates mineralisation is capable of permanently sequestrating 1.2 Mt/yr of CO2 each year in carbonated construction products. At a European level, nearly 7.8 Mt of CO2 can be managed in the same way. If indicative indirect CO2 savings are also considered, maximum total CO2 reductions of up to 3 and 30 Mt/yr are possible in the UK and Europe, respectively. In respect of the UKs CCUS-led CO2 reductions for the 8 years to 2030, our high-level assessment suggests that up to 24 Mt, representing 60% of the ‘target’, may be met by the mineralisation of selected industrial process residues.
Lake‐delta deposits in low‐accommodation conditions are only a few metres thick and in some cases non‐existent. Fluvial channels occur in many cases directly on top of fine‐grained lacustrine deposits with delta deposits apparently missing. The geomorphology and stratigraphy of modern deltas in Lake Eyre, Australia, and Lake Chad in Africa indicate that delta shorelines can develop in lakes, but in many cases build out into low‐accommodation settings due to highly dynamic lake‐water levels. This work suggests that low‐accommodation is critical in the development of lacustrine delta deposits and that high (frequency and magnitude) rates of lake‐level change result in ’telescoping’ deltas, the deposits of which are thin but extensive. The telescopic deltas have conformable beds, but with abrupt vertical facies changes; this apparent stratigraphic contradiction is the result of long horizontal distance translation of the depositional system. Details of two lacustrine units, in Uinta Basin in the USA and Junggar Basin in China, both of which show characteristics of telescoping, are used to develop a process based stratigraphic model for the deposits of such lake deltas. Lacustrine facies comprise cross‐stratified, ripple cross‐laminated, structureless or graded and sharp‐based sandstone beds, mudstone (structureless, laminated, rippled, rich in organic content), carbonate mudstone, ooid packstone and stromatolites. Three facies associations are critical for lake delta stratigraphy: channelized distributary deposits that occur in the delta topset; lake plain deposits that represent the fluvial over‐bank deposits and the subaerially exposed (at low lake level) lake deposits; and fine‐grained, lacustrine deposits. A key corollary of the proposed low‐gradient, telescoping lacustrine delta model is that broad and shallow channels dominate the system, but that decimetre to metre thick, gently dipping delta‐front beds form subtle deposits along the margins of the lakes. These delta depocentres migrate basinward and landward at high rates (tens of kilometres each year), building thin (metres) but laterally extensive (tens of kilometres) sandstone units through multiple transgression–regression cycles.
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.
Sorby's many discoveries (eg that some Jurassic ooids and Palaeozoic corals were originally calcitic) had geochemical implications that have only recently achieved research prominence (eg CO2 and the "greenhouse' Earth). In addition, Sorby's legacy was an application of meticulous descriptive petrography, innovative experimentation, thorough integration of detailed observation, imaginative thinking, and judicious use of analytical techniques. -from Author
ABSTRACT
The Nubian Sandstone sequence in the Aswan area of
Egypt includes several oolitic iron-ore horizons in its lower and
middle units. Sedimentological studies reveal that five
sedimentary environments prevailed during the ore formation
viz : lateritic weathering, marine tidal flat to shallow shelf,
lagoon, lacustrine, and alluvial overbank flood plain. In an
attempt to erect a model of microchemistry and ultrastructure
for oolites from each environment a combination of reflected
light microscopic study, SEM-microprobe investigation, XRD
and XRF analysis has been employed.
First generation of the grains was either an inherent
property of kaolin pisoids or accretionary-growth ooids
composed of a mixture of clay minerals, goethite, and minor
phosphate. A primary iron-formation was affected by an early
diagenetic phase which created chamosite in lagoonal and
lacustrine ooids, vivianite in lacustrine ooids, and greenalite
and cliachite in the shallow shelf ooids. The resulting ores were
enriched with iron due to downward migration of ground water.
During this late diagenetic process an ensuing generation of
chamosite was created.
Abraded shells indicated the accretionary nature of the
grains; whilst the present attitude of crystallites could be a
result of post-sedimentational readjustment
The carbonate unit Ca-2 found in the Løgumkloster-l well is located on the northern marginal carbonate platform of the North German Zechstein Basin. The ea. 43 m thick sequence includes former oncoidal/algal muds which were deposited in a relatively quiet lagoonal back-barrier environment, and ooidal carbonate sands, deposited in a rather agitated shoal environment. The carbonate sediments of Ca-2 have been subjected to a complex sequence of diagenetic events. However, the present porosity/ permeability, and thus the reservoir quality of the rocks, is primarily linked to four events: two leaching phases, a phase of chemical compaction, and a late anhydritization. The first phase of leaching created mouldic porosity. The last phase of leaching was important as it resulted in a widening of the preexisting pores and fractures and thereby facilitated percolation of sulphate solutions causing the late anhydritization, which considerably reduced the porosity/ permeability of the rock. The present pore geometry of the rock is complex. In the oolitic intervals the intra- and inter-ooidal porosity types are the most widespread. In the oncolitic/algal intervals intra- and inter-oncoidal porosity and vuggy porosity are often combined with intercrystalline porosity. The corresponding Ca-2 rock in the Brøns-l well, situated ca. 20 km northwest of the Løgumkloster- l well, was subjected to the same post-depositional evolution. Comparison with the diagenesis of the upper part of the Ca-la formation in the Aabenraa-1 well and the Ca-1 formation of the Varmes-1 well also shows close similarity in the diagenetic evolution.
The aim of this chapter is to provide an overview of diagenetic processes as they affect carbonate grains and carbonate sediments, thus giving a foundation for other carbonate chapters. Post-depositional changes may begin upon the depositional substrate (e.g. micro-infestation and dissolution). Subsequently, during burial, compaction, further dissolution, cementation, recrystallization and replacement may occur. Some of these processes lead to obvious changes but others are cryptic (e.g. the recrystallization of foraminiferans and nanno-grains), being difficult to recognize even through the closest of scrutiny employing sophisticated analytical techniques. In this chapter marine phreatic, marine vadose, fresh-water vadose, fresh-water phreatic, mixing zone and deeper burial processes are reviewed. The use of isotopic and fluid-inclusion methods of analysis are illustrated in the context of particular case studies. Diagenetic changes in carbonate sediments are the record, very often imperfectly preserved, of successive fluid-rock interactions that have occurred during burial (and uplift). Thus, any methods which enable us to recognise the sequence of diagenetic effects, and refine more closely the succession of diagenetic processes that have occurred, will enable us to interpret the evolution of fluid-types, and fluid migration pathways, in the context of burial evolution within basins. Closer understanding of these processes will enable predictive diagenetic models to be constructed, such models being applicable to a wide range of carbonate facies in many types of basin.
The 2.5-billion-year-old Carawine Dolomite of western Australia represents one of the oldest known carbonate platforms on earth, yet it displays a diverse and well-preserved suite of microfabrics. Among the latter are thin layers rich in ooids that display good radial-concentric textures. Although rarer, pisoids with similar textures are also present, and most occur at the tops of reverse-graded layers. Based on the evidence presented in this chapter, these are interpreted as primary radial ooids and pisoids that originally consisted of high Mg calcite. The ooids formed as free-rolling grains, whereas the pisoids generally formed via in situ enlargement based on fitted and elongated fabrics. The ooids and pisoids described here are believed to have formed as thin layers in a shallow, evaporative paleoenvironment. This does not preclude the existence of oolitic shoals elsewhere on the Carawine platform, but none have been reported.
The exquisite microfabrics of the Carawine ooids and pisoids demonstrate that oolitic and other delicate carbonate microfabrics can survive dolomitization and persist for vast periods of time under favorable conditions. In addition, the grains in the Carawine Dolomite are very similar to the only other reported occurrence of early Precambrian carbonate ooids and pisoids (Beukes, 1983), but are different from those described from later Precambrian carbonates. This suggests that secular changes took place in the composition of seawater during the Precambrian that were analogous to those of the Phanerozoic.
Sedimentologic and petrographic studies were conducted on ooids from allochthonous limestone bodies in the Lower Cretaceous Birafu Formation, Kochi Prefecture, Shikoku, Japan. The limestone bodies consist mainly of oolitic grainstone in which the total volume of ooids is as high as 70% in contrast with limited contents of terrigenous material (generally<20%). This suggests high-energy environments during the ooid formation and deposition. Ooid diameter varies typically between 0.1 and 0.8mm, with the extremes being 0.05 and 2.0mm, respectively. Nuclei of the ooids are constituted by lithoclasts of quartz and feldspar and bioclasts of mollusks and echinoids. The ooids exhibit a radial microfabric, although micritization of varying degree is common. Radial coatings consist of fibrous crystals 6-15μm long and 1.0-1.5μm in diameter. The ooids afford no evidence of the direct influence of micro-organisms on their formation. With the fibrous shape of the radial ooid crystals, they recall modern high-magnesian or aragonite cements typical of shallow normal marine diagenetic environments, and thus suggest an original composition of this kind. X-ray diffraction and microprobe analyses, however, consistently show MgCO3-concentration of the ooids below 1%, which implies that mineralogy of the precursor inverted to low-magnesian calcite without loss of crystal morphology when exposed to meteoric-water diagenesis.
The sequence of strata overlying the lacustrine-brackish Corinthian Marl at the Canal of Corinth is composed of eight megacycles. At least the late six (cycles A to F) are of Pleistocene age. West of the 'Barrier Ridge' (Scheiderücken) each megacycle is characterized by a change from marine to lacustrine-brackish layers; east of the ridge soils (partly with calcrete) are developed in place of lacustrine-brackish sections. Cyclicity is attributed to oscillations of the climate during the late Cenozoic. The non-marine sequences correspond to glacial periods, when the sea-level was significantly lower than today. This resulted in a drainage of the area east of the 'Barrier Ridge' while the Gulf of Corinth west of the 'Barrier Ridge' became a brackish lake, due to fresh-water influx.
The correlation of the Pleistocene layers east and west of the 'Barrier Ridge', so far disputed, was accomplished with the help of the limnocardium Neopseudocatillus catilloides, which occurs only in the non-marine part of cycle C. A tropical fauna, which immigrated from West-Africa into the Mediterranean, was first found in cycle D. This indicates a Paleotyrrhenian (Mindel/Riss interglacial period) age. The occurrence of the Tyrrenian index fossil Strombus bubonius within cycles D, E, and F suggests formation during the second last and last interglacial periods.
Different types of carbonate cement are interpreted as having formed in the marine-phreatic (submarine), meteoric-phreatic, and meteoric-vadose zones. Locally, a sequence of different generations of cement indicates alternation of non-marine and marine environments.
A distinct diagenetic jump occurs at the boundary between cycles C and D northwest of the 'Barrier Ridge'. There, the older sequence was affected by brackish-phreatic influences; skeletons of echinoids and red algae which consisted primarily of high-Mg calcite were altered to Mg2-5-calcite, East of the
'Barrier Ridge' the diagenetic jump occurs earlier due to a different hydrologie history. Locally, clay-rich portions in cycles N 1, N 2, and A contain biogenic skeletons which are still made up of high-Mg calcite because they were protected against diagenetic alteration.
The dolomitization of Pleistocene sediments which extends from northeast of the Isthmus to the area of the canal is here interpreted to be genetically related to a zone of mixing of sea-water and fresh-water which came from a north-eastern serpentinite region extremely rich in Mg.
The Isthmus of Corinth is located as a mega-graben between two E-W striking Mesozoic mountain ranges which exhibits an intense minor fracturing. The synsedimentary faults which are crossed by the canal are correlated to three episodes of tectonic activity. They produced an E-W striking horst which plunges westward from the Trapeza Mountain near Kalamaki over the 'Barrier Ridge' to New Corinth. The trend of the horst illustrates the complicated structure of the 'Antitilted Fault-Block-Crossing' ("Kippschollenkreuzung") of v.FREYBERG in the mega-graben at the Isthmus of Corinth.
Aragonitic coated grains < 1 mm in diameter with a layered cortex formed by crystals of tangential orientation are characteristic of ooids from the Bahamas (Illing 1954, Newell et al. 1960). This structure is normal for recent ooids from marine environments (for exceptions see Land et al. 1979). The µm-sized aragonite crystals are rod- or baton-shaped (Fabricius and Klingele 1970, Loreau 1970).
Vadoid is a coated grain which originated in a vadose environment. To vadoids belong grains which have been (and still are) variously termed, e.g., cave pearls, fluvial pisoids, caliche pisoids, and vadose pisoids. Although commonly of pisoid size, vadoids are often of microid size and these cases were earlier called "diagenetical ooids" (Siesser 1973), "calcrete ooids" (Read 1974), "vadose ooids" (Harrison 1977) or simply "ooids" (Braithwaite 1975, Elloy and Thomas 1981, Richter, this vol.).
The geological map of the Sheet 396 “San Severo”, here presented at the scale 1: 50.000, was investigated and surveyed using offi cial topographic maps at the scale 1: 25.000. The fi eld work benefi ts also of unpublished stratigraphic and tectonic data belonging to a doctoral thesis in sedimentary geology (Spalluto, 2004). The investigated area lies in the northern part of the Puglia region (southeastern Italy) and belongs to two main geographic and geologic domains: a) the Apulian Foreland (western sector of the Gargano Promontory) and the Bradanic Foredeep (northern sector of the Tavoliere delle Puglie). The two sectors represent respectively the foreland and the foredeep areas of the Southern Apennines chain.
Stratigraphic data collected during the survey of the Foglio San Severo produced a strong revision of the lithostratigraphy of the area respect the previous edition of the Geologic Map of Italy (scale 1:100.000) for both Meso-Cenozoic and Quaternary units. The resulting new lithostratigraphic framework allowed to
fournish new stratigraphic constraints for the geologic evolution of the area. Moreover, this framework reduces the proliferation of lithostratigraphic nomenclatures existing in literature proponing the adoption of a nomenclature valid at a regional scale. The western sector of the Gargano Promontory (eastern and northern part of the Sheet San Severo) is mostly made up of Mesozoic and Cenozoic carbonate
units formed in shallow-water environments. The oldest outcropping unit is the Calcare di Bari Fm. (Callovian p.p.-Aptian p.p.), which is about 900 m thick and form the bulk of the whole Mesozoic succession. It consists of a fairly monotonous and conformable succession of peritidal and shallow subtidal limestones formed in a broad inner-platform setting. The stacking of lithofacies and lithofacies association
in the succession allowed to recognize the following three informal members:
a) Monte Calvo mb. (Callovian p.p.-Valanginian p.p.), about 300-350 m thick; b) Borgo Celano mb. (Valanginian p.p.-Aptian p.p.), about 500-600 m thick; c) Ostreids and Requienids member (Aptian p.p.), about 80 m thick. The three members show almost constant lithofacies assemblages consisting mainly of mud-supported mudstone-wackestone formed in restricted lagoonal environments. Locally these
lithofacies are cyclically alternated to cryptmicrobial limestones and residual clay layers indicating deposition in tidal fl at environments with periods of pedogenesis due to subaerial exposure. The boundaries between members are usually sharp and are marked by the temporary disappereance of tidal fl at lithofacies outpaced by relatively deeper lagoonal ones. In each member, the rapid deepening is followed
by a gradual shallowing marked by the gradual restoration of tidal flat conditions becoming more and more widespread towards the top of each member. The calcare di Altamura fm. (Coniacian p.p.-Santonian p.p.) crops out in few areas in the southern and western part of the Sheet San Severo. It unconformably lies on a few metre thick bauxites (Turonian in age) indicating a phase of prolonged emersion of the Apulian Platform. The Calcari di Monte Acuto Fm. (Santonian p.p.) crops out in the western part of the Foglio San Severo and it is 50-60 m thick. It conformably lies on the calcare di Altamura fm. and it unconformably lies below the Tavoliere delle Puglie supersynthem. It is composed of: i) blocks of rudist limestones coming
from the calcare di Altamura fm.; ii) laminated packstone/grainstone with rudist fragments; iii) wackestone/packstone with radiolarians, planctonic foraminifers and calcispheres with intercalation of chert nodules and layers. Lithofacies suggest deposition in a slope environment.
The basalti Picritici di Mass. S.Giovanni in Pane Fm. (Paleogene ?) crops out in the northwestern part of the Sheet “San Severo”. This unit consists of blocks of pycritic basalts probably deriving from the erosion of basaltic dykes intruded in the lower Cretaceous limestones of the Calcare di Bari Fm.
Neogene units crop out in few areas at the margin of the Gargano Promontory. These units are composed of similar facies features and are formed in neritic carbonate environments. The informal Masseria di Belvedere fm. (middlelate Serravallian) is about 10-15 m thick and unconformably lies on Mesozoic
limestones. Terra rossa layers locally mark this boundary. This unit mainly consists of: i) grainstone/packstone with benthic foraminifers, serpulids, mollusks, echinoids, red algae and bryozoans fragments; ii) fl oatstone/bafflestone with corals, barnacles, bivalves and echinoids in a matrix of wackestone with planctonic foraminifers and sponge spicules. The informal Masseria Spagnoli fm.
(late Tortonian) is about 10 m thick and lies with a marked angular unconformity on Mesozoic limestones and on the Masseria Belvedere fm. It is locally covered by the cemented alluvial fans of the Gargano Promontory. This unit mainly consists of packstone/grainstone with benthic foraminifers, serpulids, mollusks, echinoids, bryozoans and rare planctonic foraminifers with intercalations of oyster and
pectinid-rich lags. The informal Masseria di Vituro fm. (late Messinian ?) is about 20-25 m thick and unconformably lies on Mesozoic limestones and it underlies the cemented alluvial fans of the Gargano Promontory. From bottom to top this unit is made up of grain-supported and coarse calcareous conglomerates fining up in microconglomerates in a grainstone matrix with benthic foraminifers and
serpulids. The upper part of the unit consists of laminated grainstone with benthic foraminifers, mollusks and red algae. The Calcarenite di Gravina Fm. (middle-upper Pliocene) is about 30-40 m thick
and unconformably lies on Mesozoic limestones and on Masseria Belvedere fm and underlies the Quaternary deposits of the Tavoliere delle Puglie supersynthem. This unit shows a fi ning-up/deepening-up trend marked by the gradual transition from coarse rudstones with mollusks, echinoids, and serpulids in a bioclastic packstone/grainstone to packstone/grainstone rich in planctonic and more rarely benthic foraminifers and with mollusks, echinoids and red algae fragments. The argille subappennine fm. (upper Pliocene - lower Pleistocene) crops out only in a very localised zone in the south-western sector of the sheet. It is composed of alternating beds of silty shales and fi ne- to medium-grained sandstones. More
data come from literature and wells carried out to describe the overlying units of the Tavoliere delle Puglie supersynthem. The argille subappennine fm. represents the substrate of many middle-upper Pleistocene units and reaches a maximum thickness of about 1.000 m in the south-eastern sector of the Sheet “San Severo”. The thickness is mainly conditioned by the structural framework of the underlying
meso-cenozoic units. The outcropping part of this formation is represented mainly by siliciclastic shallow water deposits sedimented below the base of the wave action. The middle to upper Pleistocene deposits have been grouped in the Tavoliere delle Puglie supersynthem. It is composed of 6 different terraced synthems which crops at different Altitudeson the sea level. From the older to the younger we
distinguished the following sinthems: Cava Petrilli synthem (TVP - middle Pleistocene);
Vigna Bocola synthem (TPB - middle Pleistocene); Masseria la Motticella synthem (MLM - middle to upper? Pleistocene); Foggia synthem (TGF - upper Pleistocene); Masseria del Lupo synthem (TLP - upper Pleistocene superiore); Masseria Finamondo synthem (TPF - upper Pleistocene).
Three the older synthems (TVP, TPB and MLM) were divided in 2 subsynthems that are separated by an unconformity of erosive origin (continental deposits on shallowing-upward marine deposits). The younger synthems (TGF, TLP and TPF) are represented mainly by continental deposits. The oldest synthem (TVP) is well exposed in the north-westwern part of the Sheet “San Severo”. The other synthems have been described carrying out some wells. In the studied area, the Tavoliere delle Puglie supersynthem is represented by a terraced marine and alluvial succession which developed in response to a moderate
and constant uplifting and sea-level changes. Alluvial and colluvial Quaternary deposits (late Pleistocene-Holocene), not recognized as belonging to a specifi c basin, crop out along the cliffs that bound
the western and the southern side of the Gargano Promontory (alluvial fans and slope detrital deposits) and in the main karstic valleys and sinkholes and consist of coarse and mostly disorganized calcareous conglomerates or breccias in a residual terra rossa matrix. Terraced deposits are typically cemented.
Quaternary deposits fi ll also the most important karstic caves. “Cave of the Paglicci site” is partly fi lled by late Pleistocene continental deposits, in which two important tombs of Homo sapiens and many rests of vertebrates were found. These important fi ndings and the discover of parietal paintings, make this cave the
most important paleolithic site in Italy. The tectonic features of the Sheet “San Severo” indicate that this area underwent many tectonic phases starting since the Cretaceous till the Quaternary. The foreland area (western Gargano Promontory) is mainly made up of Mesozoic carbonate units showing a monoclinal arrangement with bedding plunging mainly towards SW. The main structural features are represented by
faults and folds, which locally determine several variations in the regional setting of beds. Especially, main faults (Mattinata, Rignano and Candelaro Faults) break up the monoclinal in several blocks showing a different kinematic evolution. These faults generate sub-vertical shear zones, locally with cataclasis showing
mainly strike-slip cinematic indicators. The main structures represent also the most relevant morphologic elements of the foreland area controlling the formation of the hydrography and forming the main cliffs which physically separate the foreland from the foredeep.
The fi rst important element in the recostruction of the tectonic evolution of the area is the recognition of the sharp superposition of slope deposits of the Calcari di Monte Acuto Fm above the shallow-water limestones of the calcare di Altamura fm. This suggests that the western sector of the Gargano Promontory underwented during the Santonian a rapid drowning probably due to the formation of an intraplatform basin.
The most part of the structures mapped in the studied area are polyphasics and formed during the Apennines and Dinarides orogenesis. Published data indicate that the Mattinata Fault shows a left-lateral strike-slip movement and that the most part of structures are kinematically related to the fi eld stress produced by this fault. Stratigraphic constraints confi rm this interpretation, since the older part of
the Calcare di Bari Fm. crops out in the northern sector of the Mattinata Fault and in the southwestern sector of the Rignano Fault. This suggests that the fi eld stress acting on the area, congruent with the E-W left-lateral strike-slip deformation of the Mattinata Fault, contestually produced transpression along NW-SE oriented faults (e.g. Rignano Fault and Monte Granata Fault) and transtension along NESW oriented structures (e.g. S. Egidio pull-apart basin). Intramiocene angular unconformity between Masseria Spagnoli fm. and Masseria Belvedere fm. and the overthrusting of Jurassic limestones of the Monte Calvo member above middle/late Pliocene deposits of the Calcarenite di Gravina Fm. suggest that during Neogene
times several tectonic phases showing similar deformation features occurred.
According to the regional data, during the Plio-Pleistocene, this area (and the entire Apulian foreland) was subject to two different tectonic phases: the first one (Pliocene to lower Pleistocene in age) was related with the active subduction of the Apulian foreland beneath the southern Apenninic Chain; during this phase,
the Apulian foreland recorded an high subsidence rate (about 2 mm/yr); from the Sicilian to present-day, the entire Apulian foreland was subject to a moderate uplift (less than 0,5 mm/yr). We have found many evidences of Neotectonics. In the Apricena area (Masseria Zingari locality), some extensional features have been observed: they are represented by narrow grabens (few tens of meters in lenght) which cut the Masseria Belvedere fm. (early Miocene in age) and are trasferred to the overlying Calcarenite di Gravina Formation (late Pliocene in age). The synsedimentary activity of these grabens is documented by the presence of narrow folds and by the variations in thickness of the Calcarenite di Gravina Formation.
The maximum displacement is always less than 5 m and it decreases upwards. Along the cuts of the older and inactive railway in the same area, a complex distensive fault in the Calcarenite di Gravina Formation (and in its Miocene substrate) occurs: folds and growth structures involve the overlying calcarenites
along the primary and secondary fault planes. Last evidence of the subsidence phase is given by large-scale neptunian dykes (up to 5 m in height): they are restricted at the contact between the masseria Belvedere Fm. and the overlying Calcarenite di Gravina Formation and are represented by large conical fractures in the Miocene substratum which are fi lled by the overlying Pliocene calcarenites;
that is a record of synsedimentary extensional tectonic activity since the overlying unit suffers soft-sediment deformation and many decimetric beds are downward collapsed and/or irregularly folded during the extensional brittle deformation of the substratum.
The middle- to upper-Pleistocene uplift of this area is chiefly documented by the presence of marine and continental terraced deposits that crop out from 140 m a.s.l. to 20 m a. s. l. The documentation of faults associated with this uplift phase often very diffi cult because there are not extensive and continuous outcrops of the middle-upper Pleistocene units. Nevertheless, in a quarry located to the NW of Apricena we founded an extensional fault that cuts the entire thickness of the Colle degli Ulivi subsynthem The fault is subvertical, it is E-W oriented and the maximum vertical displacement is up to 20 m in height. Similar tectonic features
have been reported in the younger San Severo subsynthem.
A succession that includes the Permian-Triassic transition was penetrated in the David 1 Borehole (Israel), located on the Levant margin sector of the northwestern Gondwanan plate. This is a fully marine section with a complex depositional interplay of distal siliciclastic and ramp carbonate sediment. Foraminifera distribution, sedimentary microfacies, delta C-13 excursions and e-log (gamma-ray; resistivity) data were analyzed. The local P-T boundary is placed at the first appearance of Triassic taxa, but there is a 90 m interval of overlapping faunas where the Permian taxa are small species atypical of the underlying Permian strata, and some specimens are clearly reworked. Carbonate strata were deposited in mid-to outer-ramp environments under varying conditions of sea level, storm regime, and siliciclastic (mostly silty) influx. Sea level, tracked by facies shifts, follows a low-order cyclic pattern. Two higher orders of cyclicity are also present: a short-term oscillation in storm frequency in the local depositional basin and a high-order mode in which clastic supply alternates with clastic-free carbonates, interpreted as reflecting humid-arid climate shifts of a remote, continental source region. The last mode lies within the Milankovich band of frequencies. Negative delta C-13 excursions, glauconite, and pyrite-rich horizons indicate hypoxic or anoxic conditions and reflect perturbations of the global carbon system in the oceans during this time. Although lithification of the latest Permian carbonates in the transitional interval was suppressed, the state of preservation of the carbonate components is not indicative of deposition under conditions of oceanic acidification.
Coated grains, which may have skeletal cores, are non-skeletal carbonate and non-carbonate grains formed in marine as well as non-marine environments. These grains are classified according to their structure and environmental parameters (Peryt, this vol.). Peloids are micritic grains without recognizable structures and are represented by individual grains and aggregates. Ooids, oncoids, rhodoids, and vadoids are coated grains with distinct structural features.
Surficial, calcareous crust profiles, hard, irregular, subhorizontal, calcareous laminae, surrounded by crumbly, chalky carbonate, form at the surface of many limestone successions in semi-arid areas. Detailed study of Holocene profiles, developed in late Pleistocene reef limestones on northern Barbados, reveals that diagenesis of limestone in such profiles creates a diagnostic, repeatable set of textures and fabrics. The original limestone is altered by brecciation, recrystallization (to microspar), micritization and boring. The CaCO3 thus put into solution and augmented by CaCO3 from fallout and salt spray is reprecipitated as calcite (less than 4 mole percent MgCO3), in the form of crystals often, quite different from those in the vadose zone below. Calcite crystals are precipitated as flower spar, micrite, random needle fibres, and tangential needle fibres. Several of these crystal morphologies are similar to those precipitated from highly supersaturated solutions or solutions that contain appreciable amounts of other dissolved ions. These 4 basic crystal types are not only precipitated as void-filling cement, but, more important, combine to form characteristic structures such as oolith-like coated particles, pelletoids, and the laminar crusts themselves. The diagenetic textures and fabrics described above are also the basic units of many Florida and Middle East calcareous crust (caliche) profiles, suggesting that the above features may be characteristic of calcareous crust profiles in general. Fossil calcareous crusts and associated features, buried in the Pleistocene limestone succession on northern Barbados without alteration, indicate that these features may well be preserved as indicators of subaerial exposure in the fossil record.
Along the Trucial Coast of the Persian Gulf aragonite is believed to be precipitating actively in certain of the sandy intertidal zones in response to the direct evaporation of marine water. Depending upon sub-environment, the mineral occurs as an intergranular, pore-destroying cement in rock, or as a glossy crust of tangentially-oriented crystals around both rock, when it appears like a layer of lacquer paint, and grains (ooliths). Since, in the latter case, the precipitation of aragonite is not a pore-destroying process, intertidal trends may be found in the fossil record from porous oolite to tightly cemented, non-oolitic skeletal sand.
Where aragonite has precipitated as cement, the resulting intertidal rock may be recognized in the fossil record from a number of consequent diagenetic features, such as cemented algal mat structures, polygonal cracks, “teepee” structures and arcuate ridges resembling cave dams. A further characteristic is the presence of abundant lithoclasts in the intertidal rock which have depositional components similar to those of the enclosing medium.
The change from an environment where aragonite can be precipitated to one where calcite is stable can cause early aragonite cement to alter to calcite with a cryptocrystalline texture or one pseudomorphing the earlier aragonite. Whether early aragonite cement is leached or replaced by calcite must depend primarily on the climate at the time of deposition and soon after.
Ooids occur in many different environments in the Persian Gulf; blackened relict ooids are common at depths of 100 m in the center of the basin while others have been transported to desert environments up to 40 km from the shore. Most Holocene ooids occur in coastal areas in the S parts of the Persian Gulf in which they appear to be forming in a variety of settings. The most spectacular accumulations constitute tidal deltas associated with coastal barrier system in E Abu Dhabi. Other agitated environments include tidal bars situated in wide channels between islands (Yas and Bahrain) and the adjacent Arabian shoreline, and on open tidal flats and beaches in exposed embayments (Sabkha Matti). Although most ooids are forming in these agitated environments, significant quantities are forming within lagoons (Khor Odaid and Jebel Dhanna), and on the SE lee coast of Qatar Peninsula (Umm Said).
The structure of the cortex of ooids collected in these various environments has been studied by light microcope, SEM, micro-probe and other analyses, to evaluate the relationship between ooid structure and environment. Aragonitic nano-grains seem to be associated with organic material in the cortex and occur in most ooids irrespective of environment. Elongate rods (1–2 microns) of aragonite exhibit various orientations. In agitated environments on the crests of bars, or delta levées, these have a statistically tangential orientation with respect to the nucleus, and are often tightly packed or coalescent. In ooids collected from more protected depressions between bars, aragonite rods within the outermost layer of the cortex have haphazard or radial orientation and the fabric is loose. In protected lagoonal settings this radial orientation is well developed and the ooids are often unusually big and irregular in shape.
The relationship between the structure of the external layer of the cortex and the environment in which the ooid was collected indicates that the aragonitic components grow on the nucleus initially with a haphazard or radial orientation, creating a loose fabric. This primary orientation, developed mainly while the ooid is in a relatively protected micro-environment, is subsequently modified to a secondary tangential orientation on the crest of adjacent bars or beaches where crystals are physically compacted to create a dense fabric. Lagoonal ooids tend to retain their primary radial structure and may attain considerable size in the absense of physical abrasion in these protected environments.
Physical conditions favourable to ooid formation would seem to include a bar and protected channel morphology associated with reversible tidal or longshore currents which retain ooids within this favourable system. Evaporitic tidal flats seem to favour the formation of large pisooids whose formation is not related to mechanical movements.
Most Holocene ooids of the Persian Gulf have much in common with the classical Bahamian ooids. They differ mainly in their regional distribution, most forming along the continental shoreline remote from any platform edge, many accumulating in desert environments. Others form in quiet water tidal flats and have much in common with cave pearls. Although the areas of ooid formation at any given moment are small, these grains are readily dispersed. In time a sheet of oolitic sand may develop whose geometry and magnitude will not reflect that of the ooid-forming environment.
The late Missourian Plattsburg Limestone in Wilson County, Kansas contains a well developed marine pisolite associated with a phylloid-algal mound complex. A striking feature shown by this pisolite is plastic deformation caused by compaction which preceded cementation. This deformation formed chains of pisoliths, connected by apophyses. at all angle to the bedding. Evidence suggests that the pisoliths resulted from several interrupted periods of accretion, and that various states of induration existed among and within the discrete bodies prior to lithification.
Strontium-rich aragonite crusts exhibiting various morphologies coat both discreet particles and beach rock within the supratidal zone of the Trucial Coast. They are best developed in protected lagoonal settings, although polished “pelagosite” crusts are common within the “splash zone” exposed to wave action. The morphology, both of coated grains and associated aragonite sheets, changes from smooth to highly irregular as one crosses into the upper parts of the supratidal zone. The latter frequently have dripstone morphologies. Micro-dripstones are developed on the under surfaces of many beach rock layers and are composed partly of detrital sediment which is deposited on the roof of small caverns by a rising water table to produce “sedimentary dripstone”. Although many of these aragonitic encrustations resemble lithified algal stromatolites, their dripstone morphologies, nanostructures and invariably lithified character strongly suggests that they are formed by physico-chemical precipitation from sea water. Criteria are given which may permit the distinction between supratidal tufas (here termed “coniatolites”), lithified stromatolites, and cave tufas.
The major part of the Bahama Banks is covered with a mantle of sands composed of calcium carbonate. They rest on a basement of similar sediment which has been consolidated into limestone by the subaerial deposition of calcite cement. Along the extreme edges of the Banks, the sand consists of the debris of neritic organic skeletons; elsewhere it is predominantly non-skeletal, and composed of grains of cryptocrystalline aragonite. These non-skeletal sand grains have hitherto been regarded as a break-down product of the limestones, but the present study, based on the Ragged Island area in the southeast part of the Great Bahama Bank, disproves this, and shows that such derived grains are rare in the recent bottom sediment. The sand grains are instead considered to be primary: they have formed, and are now forming, by the physico-chemical and bio-chemical extraction of aragonite from the sea water, which is saturated or supersaturated with calcium carbonate. The grains develop by the progressive aragonitic cementation of friable aggregates of calcareous silt particles. Further cementation tends to join the grains into lumps, in which an outer dense cryptocrystalline layer commonly allows the slower growth of larger aragonite prisms in the interior parts. The habit and surface texture of the lumps undergo a sequence of changes when traced from the ocean edge toward the interior of the Banks. Corrasion prevents excessive lump growth, and the typical bottom sediment is a well sorted medium-grade sand. The traces of calcareous mud in the sands contain no evidence of "drewite" needles, which are restricted to the protected "shelf lagoons" west of Andros and Abaco Islands. The controlling factor in the formation and distribution of the sands is the tidal currents of cooler oceanic water which sweep onto the Banks with velocities diminishing toward the interior, precipitating calcium carbonate as the water warms and evaporates. Sedimentation is therefore most rapid along the borders of the Banks. Aided by sea-level changes, this has led to the building of lines of elongate cays, parallel, and close to the ocean edge, making each Bank a gigantic atoll. Superficial aragonite ooliths develop on the protected beaches of the cays, and in the track of currents through the inter-cay channels. East of the "Tongue of the Ocean" and elsewhere close to End_Page 1------------------------------ the borders of the Banks, there are extensive areas where the sand is swept into a curvilinear pattern-work of submarine dunes, which occasionally adopt barchan shape. These have not been sampled, but are considered favorable for the formation of true, as opposed to superficial, ooliths. Evidence from the well drilled to a depth of 14,587 feet on Andros Island suggests that calcareous sands, similar to the recent deposits, have played a large part in building the Bahama Banks.
Oolitic limestones and dolostones are among the most prominent reservoir rocks for oil and gas as well as for various other economic minerals occurring in sedimentary rocks. This paper is an attempt to relate the microstructure of ooids as revealed by stereoscan methods to certain petrophysical parameters: specific surface area, microporosity and pore radii distribution. Since no similar studies have been conducted so far on oolitic carbonate rocks the data presented in this report could serve as a basis for further petrophysical investigations on fossil, diagenetically altered, oolitic rocks.
The radial coatings of Holocene ooids are Mg-calcite, whereas the tangential and micritic coatings are aragonite. Centrifugally deposited ooid coatings are similar in many respects to centripetally deposited marine cements. The reason(s) for the mineralogical and textural variation in these apparently inorganic carbonate precipitates are not certainly known, but the rate of nucleation and precipitation, degree of agitation and presence of certain types of organic compounds appear to be the most likely explanations. -Authors
In the early stages of basin history, pore-water composition was controlled largely by surface conditions existing during sedimentation. The resulting diagenesis included cementation of beach sediments, development of pisoliths in sabkhas, freshwater leaching of carbonates due to subaerial exposure, and pervasive dolomitisation of sediments in response to the reflux of brines from sabkhas, saline lagoons and playas. As burial progressed, the influence of surface-derived pore-waters decreased and the effects of rising temperature and overburden pressure became more important in controlling rock-water interactions. The resulting series of diagenetic events included anhydritisation, pressure solution, leaching and calcitisation of dolomite, halitisation accompanying mobilisation of salt, and redolomitisation of secondary limestones and cementation of leached dolomites.-from Author
Sichuan Basin was an epicontinental sea in the late (Aurenig) of the Early Triassic. The sea was bounded to the north and west by land masses, and to the south by a submarine high, while to the east lay the open sea (Fig. 1). These paleogeographic features controlled sedimentation in the basin.
The Boomplaas Formation represents a newly recognized carbonate platform deposit (Beukes 1978) below the Campbellrand carbonate platform sequence in the lower part of the Transvaal Supergroup on the Kaapvaal craton in Griqualand West, South Africa (Fig. 1A). Deposition of the Transvaal Supergroup commenced more than 2300 m.y. ago (Button 1976) making the Boomplaas Formation one of the oldest known carbonate platform deposits in the world.
An unusual occurrence of oolitic calcarenite is exposed in South Central Texas just south of the Balcones Fault Zone. Topographic location and fossil content suggest a late Pleistocene age. Thin section examination reveals a wide variety of oolites including normal, superficial, compound and disrupted types. There is convincing evidence that the oolites were deposited, and for the most part, actually formed in a fluvial environment. The oolite formation occurs in an irregularly shaped area which roughly parallels three contemporary streams for several miles. Strata composed essentially of oolites are cross-bedded, lenticular and irregularly intercalated with poorly sorted, pisolitic calcareous conglomerate, nonoolitic calcarenite and calcareous claystone. Cut-and-fill structures and ripple marks are distinct. Whole and fragmented shells of Goniobasis sp. and Polygyra sp., freshwater and terrestrial gastropods are common. X-ray analyses show that the oolites are composed entirely of calcite. The calcium carbonate from which the oolites were formed was probably dissolved from the Cretaceous Edwards fm., which underlies the area at a depth of 210 m, and then brought to the surface by artesian springs. The contemporary streams along which the oolite formation outcrops are still spring-fed from the Edwards artesian system and are supersaturated with respect to calcite. Oxygen and carbon isotope analyses corroborate the hypothesis of a freshwater depositional environment. Many fragments associated with the oolites, as well as may oolite nuclei consist of the calcareous remains of charophytes and blue green algae. It appears that both physico-chemical and biological processes were responsible for the formation of the oolites, not only in the immediate vicinity of the srpings but downstream as well.