Progressive ordering of cristobalitic silica in the early stage of diagenesis

Mizutani, Shinjiro

doi:10.1007/bf00374363

Cited by 100 publications

(74 citation statements)

References 6 publications

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“…The transformation of opal-A to opal-CT and then to quartz has been recognized in numerous sediment sections of the Atlantic Ocean (Riech and von Rad, 1979;Thein and von Rad, 1987;, the Indian Ocean (Hempel and Bohrmann, in press), and the Pacific Ocean (Keene, 1975;Hein et al, 1978), as well as in onshore sections (Iijima and Tada, 1981;Tada and Iijima, 1983;Murata and Randall, 1975;Pisciotto, 1981). Experimental investigations also support this transformation sequence (Mizutani, 1977;Kastner et al, 1977). Beside host rock lithology and interstitial water chemistry, time and temperature are the most important factors controlling the transformation of silica phases (Murata and Randall, 1975;Hein et al, 1978;Tada, in press).…”

Section: Opal-ctmentioning

confidence: 84%

Analysis of Sedimentary Facies Using Bulk Mineralogic Characteristics in Cretaceous to Quaternary Sediments from the Kerguelen Plateau: Sites 737, 738, and 744

Bohrmann¹,

Ehrmann²

1991

Proceedings of the Ocean Drilling Program

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Carbonate-free portions of Upper Cretaceous to Holocene sediment samples from the Kerguelen Plateau in the southern Indian Ocean were investigated by X-ray diffraction. Downhole variations in the content of opal-A, opal-CT, quartz, feldspar, barite, and clinoptilolite were studied at Site 737 on the northern Kerguelen Plateau and at Sites 744 and 738 on the southern Kerguelen Plateau. The variation of these components reflects temporal changes in the depositional history of the Kerguelen Plateau as well as major differences in the sedimentary evolution between the northern plateau and the southern plateau.Carbonate is the dominant component in the pelagic sediments on the Kerguelen Plateau. In addition, biogenic opal sedimentation plays an important role throughout most of the sequence. A major increase in opal accumulation is documented at all sites in late Miocene time, which is in accordance with the well-known increase in silica productivity probably caused by a major cooling step. Because of its position near the Polar Frontal Zone, sediments from Site 737 show a more extensive opal deposition than at Sites 744 and 738. An earlier productivity pulse is documented at Site 744 on the southern plateau within the early Oligocene, following the initial phase of intense East Antarctic glaciation. This cooling event resulted in higher amounts of ice-rafted terrigenous quartz and, to a lesser extent, feldspar. With the exception of the Site 744 sediments, opal deposition in Paleogene and older sediments can be reconstructed only from the diagenetic transformation products of opal-CT and probably clinoptilolite. In contrast to the southern sequence, on the northern Kerguelen Plateau higher amounts of clinoptilolite and no opal-CT were found. These major differences in the diagenetic environments may be due to extensive volcanism in the northern area. The volcanic influence at Site 737 is well recorded by the higher feldspar content and higher amounts of volcanic glass shards.

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Section: Opal-ctmentioning

confidence: 84%

Analysis of Sedimentary Facies Using Bulk Mineralogic Characteristics in Cretaceous to Quaternary Sediments from the Kerguelen Plateau: Sites 737, 738, and 744

Bohrmann¹,

Ehrmann²

1991

Proceedings of the Ocean Drilling Program

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“…Besides time, temperature controls the transformation of biogenic silica to its diagenetic polymorphs (Ernst and Calvert, 1969;Mizutani, 1977;Kastner et al, 1977, and references therein). Langseth (this volume) calculates a linear geothermal gradient of 76°C/km at Site 436.…”

Section: Discussionmentioning

confidence: 99%

“…Using this value, and assuming that 1.5°C is the temperature at the sea floor, the present temperature at the top of the Cretaceous cherts and porcellanites (sub-bottom depth 379 m) is 30°C. If diagenetic zones of silica keep pace with accumulating overburden mainly as a response to increased temperatures (Mizutani, 1977, fig. 6), then 30°C represents the approximate temperature of conversion of biogenic to diagenetic silica.…”

Section: Discussionmentioning

confidence: 99%

Chert and Porcellanite from Deep Sea Drilling Project Site 436, Northwest Pacific

Pisciotto¹

1980

Initial Reports of the Deep Sea Drilling Project

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Cretaceous chert and porcellanite recovered at Site 436, east of northern Honshu, Japan, are texturally and mineralogically similar to siliceous rocks of comparable age at Sites 303, 304, and 307 in the northwest Pacific. These rocks probably were formed by impregnation of the associated pelagic clay with locally derived silica from biogenic and perhaps some volcanic debris. Fine horizontal laminations are the only primary sedimentary structures, suggesting minimal reworking and transport. Collapse breccias and incipient chert nodules are diagenetic features related to silicification and compaction of the original sediment.Disordered opal-CT (^[101] = 4.09 Å) and microgranular quartz (crystallinity index < 1.0) are the two common silica minerals present. Some samples show quartz replacing this poorly ordered opal-CT, supporting the notion that opal-CT does not become completely ordered (i.e., d[101] = 4.04 Å) in some cases before being converted to quartz. The present temperature calculated for the depth of the shallowest chert and porcellanite at this site is 30 °C; this may represent the temperature of conversion of opal-CT to quartz. High reflection coefficients (0.29-0.65) calculated for the boundary between chert-porcellanite and clay-claystone support the common observation that chert is a strong seismic reflector in deep-sea sedimentary sections.

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“…Utilizando como patrón interno la reflexión 3,72 del e.o)Ba, el espaciado (10 1) del ópalo C-T es de 4,11 A. Dentro de la estructura del ópalo CT se considera que el espaciado (101) decrece cuando progresa el ordenamiento (A6rke, 1955;Jonest y Segnit, 1971, Mizutani, 1977, entre otros). De.acuerdo con este último autor, un espaciado de 4,11 A corresponde a las fases más desordenadas, y son típicas del ópalo consti-También podría pensarse que el CaO y el Na 2 0 son aportados por algún mineral distinto a la sílice y que existe en cantidades inferiores al límite de detección de DRX.…”

Section: Pelrología Y Geoquímicaunclassified

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Bustillo¹,

Alonso²

1989

Estud. geol.

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RESUMENSe realiza un estudio petrológico y geoquímico de los nódulos silíceos que se encuentran incluidos en sedimentos terrígenos cuaternarios de la Cuenca de Olaroz (La Puna, Argentina).Estos nódulos se localizan en abanicos aluviales que aparecen encajados, debido a los cambios en el nivel de base que se produce desde el Pleistoceno a la actualidad, durante la evolución de los cuerpos lacustres a salares.Un estudio mediante DRX revela que son rocas constituidas por ópalo C-T, con un espaciado (101) a 4,11 A, que implica un grado de desorden alto, típico de las rocas silíceas formadas en superficie y que no han sufrido enterramiento ni influencia térmica. Su composición química es anomala si se compara con rocas siliceas continentales formadas en ambiente endorreico y fuera de un marco volcánico (Mioceno de la Cuenca del Tajo).No poseyendo características de silcretas y no estando asociadas a la sedimentación evaporítica de los salares, se considera la influencia de aguas termales. La contaminación local y en un momento dado de las aguas freáticas de los abanicos aluviales por aguas termales ricas en silíce, propiciaría junto con la evaporización la precipitación de la silíceo Los nódulos silíceos crecerían desplazando el sedimento terrígeno que constituye la roca caja o reemplazando nódulos previa de ulexita. Palabras clave: Nódu/os ópalo C-T, aguas terma/es, abanicos aluviales, salares. ABSTRACfThis article reports the results of a petrological and geochemical study of silica nodules from Quaternary alluvial fallS of the Olaroz Salar. The nodules are mainly constituted by C-T opal, d. (101) spacing to 4,11 A, implying a high-disorder; this is commonly observed in opa! rocks formed in near surface environments, without burial and heating. The chemical composition of the nodules is anomalous when compared with other typical silica-rocks formed in arid continental closed basin, without any eruptive environments (for instance the Cuenca del Tajo in Spain).The siliceous nodules do not have the characteristics of the silcretes and are not associated to the evaporitic facies of the salar. Their genesis is probably related to contamination of groundwater of the alluvial fan with high-silica thermal water. The C-T opa! would thus precipitate by either displacing tbe terrigenous host-rock or replacing previous ulexite nodules.

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Progressive ordering of cristobalitic silica in the early stage of diagenesis

Cited by 100 publications

References 6 publications

Analysis of Sedimentary Facies Using Bulk Mineralogic Characteristics in Cretaceous to Quaternary Sediments from the Kerguelen Plateau: Sites 737, 738, and 744

Analysis of Sedimentary Facies Using Bulk Mineralogic Characteristics in Cretaceous to Quaternary Sediments from the Kerguelen Plateau: Sites 737, 738, and 744

Chert and Porcellanite from Deep Sea Drilling Project Site 436, Northwest Pacific

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