Sequential position and environmental significance of different types of oncoids

Dahanayake, Kapila

doi:10.1016/0037-0738(78)90060-x

Cited by 25 publications

(19 citation statements)

References 5 publications

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“…Late Jurassic marine oncoids have already been described and discussed by Dahanayake (1977Dahanayake ( , 1978Dahanayake ( , 1983 from the French Jura and by Gygi (1992) and Hug (2003) from the Swiss Jura. In this paper, the diVerent oncoid types occurring abundantly in the Hauptmumienbank ("main mummy bed") Member in the Swiss Jura are examined in order to better constrain the link between oncoid types and palaeoenvironmental and palaeoecological conditions.…”

Section: Introductionmentioning

confidence: 88%

Oncoid growth and distribution controlled by sea-level fluctuations and climate (Late Oxfordian, Swiss Jura Mountains)

Védrine

Strasser

Hug³

2007

Facies

100

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Abundant lagoonal oncoids occur in the Late Oxfordian Hauptmumienbank Member of the Swiss Jura Mountains. Four oncoid types are observed in the studied sections and classiWed according to the oncoid surface morphology, the structure and composition of the cortex, and the texture and fauna of the encasing sediment. Micritedominated oncoids (types 1 and 2) have a smooth surface. Type 1 has a rather homogeneous cortex and occurs in moderate-energy environments. Type 2 presents continuous or discontinuous micritic laminae. It is associated with a low-diversity fauna and occurs in high-energy facies. Bacinella and Lithocodium oncoids (types 3 and 4) display a lobate surface. They are dominated by microencrusters (Bacinella irregularis and Lithocodium aggregatum) and are found in low-energy facies. The stratigraphic and spatial distribution of these oncoid types shows a correlation with the sequence-stratigraphic evolution of the studied interval, and thus with relative sea-level Xuctuations. It can be shown that these sea-level Xuctuations were controlled by orbital cycles with 100-and 20-kyr periodicities. At the scale of 100-and 20-kyr sequences, types 1 and 2 oncoids are preferentially found around sequence boundaries and in transgressive deposits, while types 3 and 4 oncoids are preferentially found around maximum Xoodings and in highstand deposits. This implies that changes of water energy and water depth were direct controlling factors.Discrepancies in oncoid distribution point to additional controlling factors. Platform morphology deWnes the distribution and type of the lagoon where the oncoids Xourished. A low accumulation rate is required for oncoid growth. Additionally, humidity changes in the hinterland act on the terrigenous inXux, which modiWes water transparency and trophic level and thus plays a role in the biotic composition and diversity in the oncoid cortex.

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Section: Introductionmentioning

confidence: 88%

Oncoid growth and distribution controlled by sea-level fluctuations and climate (Late Oxfordian, Swiss Jura Mountains)

Védrine

Strasser

Hug³

2007

Facies

100

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“…In these facies, the hydrodynamic energy was high enough to keep moving the bioclasts and peloids (Dahanayake 1978). The core of aggregate 500 µm 500 µm 500 µm 500 µm 500 µm 500 µm 500 µm 500 µm 500 µm 500 µm 500 µm 500 µm 500 µm 500 µm 500 µm 500 µm (Figs.…”

Section: Oncolitic Shallows or Interbanks (Fa2)mentioning

confidence: 99%

Depositional, diagenetic and stratigraphic aspects of Macaé Group carbonates (Albian): example from an oilfield from Campos Basin

et al. 2015

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Carbonate rocks from the Macaé Group (Albian) represent an example of carbonate sedimentation related to the drift phase in Campos Basin. This study presents depositional features, integrating them with diagenetic and stratigraphic aspects of the Macaé Group carbonates including the upper part of the Quissamã Formation and the lower part of the Outeiro Formation. Macroscopic analyses in cores and microscopic ones in thin sections allowed the recognition of eleven sedimentary facies -nine of them corresponding to the Quissamã Formation and two of them representing the Outeiro Formation. These facies were grouped into five facies associations. Oolitic grainstones and oncolitic grainstones are interpreted to be deposited in shallow depth probably in shoals above the fair weather wave base. The interbanks between shoals were formed in less agitated waters and characterized by deposition of peloidal bioclastic packstones and wackestones representative of sedimentation in calm waters. Bioclastic packstones and oolitic packstones/wackestones represent allochthonous deposits related to the beginning of the regional drowning that occur in upper Quissamã Formation. Pithonellids wackestones and bioclastic wackestones with glauconite are related to deep water deposits, characteristics of the Outeiro Formation. Post-depositional features revealed the action of diagenetic processes as, micritization, cimentation, dissolution, compaction, dolomitization and recrystallization occurred during the eoand mesodiagenesis phases. Vertical facies analysis suggests shallowing upward cycles stacked in a sequence progressively deeper towards the top (from the Quissamã Formation to the Outeiro Formation). KEYWORDS:Carbonate Rocks; Quissamã Formation; Outeiro Formation; Facies; Diagenesis. RESUMO: As rochas carbonáticas do Grupo Macaé (Albiano) representam a sedimentação carbonática relacionada ao início da fase drifte na Bacia de Campos. Discutem-se aqui aspectos deposicionais, diagenéticos e estratigráficos das rochas carbonáticas do Grupo Macaé, englobando a porção superior da Formação Quissamã e a porção basal da Formação Outeiro. Análises macroscópi-cas em testemunhos e microscópicas utilizando-se lâminas delgadas permitiram o reconhecimento de onze fácies sedimentares -nove delas correspondentes à Formação Quissamã e duas à Formação Outeiro. Estas foram agrupadas em cinco associações de fácies, relacionadas às diferentes posições fisiográficas de uma plataforma carbonática. Os bancos carbonáticos estão relacionados à deposição de grainstones oolíticos e grainstones oncolíticos em profundidades rasas, acima do nível de base de ondas de tempo bom (NBTOB). Os baixios oncolíticos ou interbancos foram formados em águas menos agitadas

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“…Oncoids have been subdivided according to biotic composition, internal structures (lamination), shape and growth form as well as size (Maslov 1960; Dragastan 1964; Zhuravleva 1964;Logan et al 1964; Radwanski and Szulczewski 1966; Catalov 1970;Dahanayake 1977Dahanayake , 1978. Similar criteria have been used for categorizing rhodoids, but the types of internal structures, systematic composition of the red algae as well as the shapes of the oncoids are more relevant (Bosellini and Ginsburg 1971; Bosence 1983).…”

Section: In-depth Classificationsmentioning

confidence: 96%

“…The grain type is a common constituent of Proterozoic platform carbon- Colacicchi et al 1975 (tidal setting);Dahanayake 1977Dahanayake , 1978 Dahanayake , 1983 Dangeard 1935; Dragastan 1969; Elliott 1966; Fezer 1988 (platform margins and openmarine lagoonal settings, lagoonal carbonates); Gasche 1956; Gasiewicz 1983 (peritidal); Gygi 1969Gygi , 1992 Heim 1916; Hug 1999; Jenkyns 1972 (pelagic platform); Kutek and Radwanski 1965 (peritidal and basinal settings); Kuss 1990; Leinfelder et al 1993; Leinfelder and Schmid 2000; Massari 1983; Massari and Dieni 1983 (pelagic platform); Misik 1966; Pümpin 1965 (reef, back-reef sands); Purser 1975 (peritidal); Scherze 2001 (patch reef);. Schmid 1996 (lagoonal and reef settings) Triassic: Biddle 1983 (reef-derived material); Catalov 1970 Catalov , 1983 Fischer 1964 (tidal setting); Goldhammer et al 1990 (tidal setting); Hagemeister 1988; Jerz 1966 (siliciclastic-carbonate inner shelf); Kisten et al 1990; Peryt 1977 Peryt , 1980 Radwanski 1968; Schuler 1968; Tichy 1983.…”

Section: Precambrian and Phanerozoic Oncoidsmentioning

confidence: 99%

Microfacies Data: Matrix and Grains

Flügel

2009

Microfacies of Carbonate Rocks

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MicrofabricGrain size: Is measured by counting the longest diameter of 100 to 200 grains. Allows attribution to grain size-based classifications. 'Sorting' in micrites, as the result of competition between space and grain growth, can be used as measure of the textural maturity of fine-crystalline carbonates. Grain size ranges may reflect differences in the depositional environment (e.g. reef micrites and micrites in limestone/shale sequences). Differences in predominant crystal sizes provide indications of the potential aragonite-dominated or calcite-dominated precursors of calcite micrites. Grain contacts: Grain contacts seen under the SEM are straight, curvilinear or serrate. The percentage of specific grain contacts reflects the degree of diagenetic changes (e.g. recrystallization). Grain shape: Differentiation of anhedral, subhedral and euhedral micrite grains. Anhedral and subhedral grains forming a hypidiotopic fabric appear to be common in micritic rocks composed of grains > 4 μm. Irregular, interlocked grains form an 'amoeboid mosaic', in contrast to block-like grains forming a 'pavement mosaic' common in limestones affected by thermal stress. Most micrite grains are angular to subangular. Subrounded and rounded grains result from intergranular solution and crystal overgrowth. Inclusions in crystals: Liquid and gas inclusion pits are common in microspar crystals as well as in larger spar crystals.The composition of the inclusions indicates the conditions under which recrystallization took place. Microfenestrae: Some micrites contain round voids, 40 to 80 μm in size, which are filled with blocky calcite. The preservation of this microfenestral fabric is used as evidence against a strong mechanical compaction of the sediment prior to lithification. Boundary between calcite matrix and fossils: Diagenetic stages are distinguished by differences in the boundaries between matrix and fossils: (a) Sharp boundaries between matrix and Low-Mg calcite fossils (e.g. brachiopods, bryozoans, ostracods, trilobites) with well-preserved ultrastructures; (b) moderately sharp boundaries between matrix and fossils (recrystallized tabulate and rugose corals, stromatoporoids); and (c) boundaries between matrix and fossils (e.g. mollusks) which are difficult to recognize. Microporosity: SEM studies reveal numerous types of micropores (5-10 μm wide) in micritic limestones, including both primary and solution-enhanced intercrystalline pores, as well as micromolds, microvugs and microchannels (Pl. 7/6; see Chap. 5). Microporosity is developed in many subsurface micritic limestones, including significant petroleum reservoirs in Mesozoic and Tertiary deposits of the Middle East, North Africa, and the North American Gulf Coast. Skeletal grainsA main advantage of SEM studies of micrites is the possibility of recognizing the occurrence and abundance of planktonic nannofossils (Pl. 7/3-5, Pl. 77/23) in mudstones and wackestones in both deep-water and shallow-water settings. SEM differentiation of silt-sized and smaller bioclastic grains ...

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Sequential position and environmental significance of different types of oncoids

Cited by 25 publications

References 5 publications

Oncoid growth and distribution controlled by sea-level fluctuations and climate (Late Oxfordian, Swiss Jura Mountains)

Oncoid growth and distribution controlled by sea-level fluctuations and climate (Late Oxfordian, Swiss Jura Mountains)

Depositional, diagenetic and stratigraphic aspects of Macaé Group carbonates (Albian): example from an oilfield from Campos Basin

Microfacies Data: Matrix and Grains

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