Transformational changes of clay minerals, zeolites and silica minerals during diagenesis

Abstract

Diagenetic transformation of clay minerals, zeolites and silica minerals in Cretaceous and Tertiary argillaceous rocks from deeply drilled wells in Japan were studied. Transformations of these minerals during diagenesis were as follows: in clay minerals, montmorillonite → montmorillonite‐illite mixed‐layer mineral → illite; in zeolites, volcanic glass → clinoptilolite → heulandite and/or analcite → laumontite and/or albite; in silica minerals, amorphous silica → low‐cristobalite → low‐quartz. Maximum overburden pressures and geothermal temperatures corresponding to these transformations in each well studied were calculated. For clay minerals, a pressure of approximately 900 kg cm−2 and a temperature of about 100°C are necessary for the transformation from montmorillonite to mixed‐layer mineral and 920 kg cm−2 and 140°C for mixed‐layer mineral to illite. Transformation from kaolinite to other minerals requires much higher pressures and temperatures than from montmorillonite to mixed‐layer mineral. For zeolites, 330 kg cm−2 and 60°C are required for the transformation from volcanic glass to clinoptilolite, 860 kg cm−2 and 120°C for clinoptilolite to heulandite and/or analcite, and 930 kg cm−2 and 140°C for heulandite and/or analcite to laumontite and/or albite. For silica minerals, 250 kg cm−2 and 50°C are necessary for the transformation from amorphous silica to low‐cristobalite and 660 kg cm−2 and 70°C for low‐cristobalite to low‐quartz. Based on these diagenetic mineral transformations, seven mineral zones are recognized in argillaceous sediments. On the other hand, from the porosity studies of argillaceous sediments in Japan, the process of diagenesis is classified into the following three stages. The early compaction stage is marked by shallow burial and viscous rocks with more than 30% porosity. The late compaction stage is characterized by intermediate burial and plastic rocks with 30‐10% porosities. The transformation stage is marked by deep burial and elastic rocks with less than 10% porosity.

Change in hydrogen isotope composition of n-alkanes, pristane, phytane, and aromatic hydrocarbons in Miocene siliceous mudstones with increasing maturity

“…Vitrinite reflectance (R o ) of siliceous mudstones from Shinjo region is in the range from 0.4 to 0.7% (Taguchi et al, 1986). Aoyagi and Kazama (1980), Suzuki (1984Suzuki ( , 1990, and Amo et al (2007) reported that paleo-maximum temperatures range from 40 to 140ºC in these samples. A set of the siliceous mudstone samples characterized by similar lithology and organic composition, but with different maturity levels, is essential in a study of diagenetic change of the D/H ratios of saturated and aromatic hydrocarbons.…”

Tectonic Implications of Illite/Smectite Diagenesis, Barbados Accretionary Prism

“…Hoffman and Hower (1979) showed that alteration of clays in the Montana disturbed belt was related to thermal insulation resulting from emplacement of thrust sheets, not to origCopyright 9 1986, The Clay Minerals Society inal depth of burial in a sedimentary basin. Aoyagi and Kazama (1980) used the temperature dependencies of porosity change and various mineral transformations (including the conversion of smectite to illite) to estimate the amount of uplift and overburden removal of some sedimentary sequences in Japan.…”

Determining the Diagenetic Conditions of Concretion Formation: Assessing Temperatures and Pore Waters Using Clumped Isotopes

“…However, the range in precipitation temperatures (from , 17 to 35uC) is probably too low to reflect formation in sediments experiencing the transition from Opal CT to quartz, which generally occurs at temperatures of , 65 to 80uC, although in diatomite cherts with less than 10 wt. % detritus the conversion can occur at much lower temperatures (, 30-40uC;Behl and Garrison 1994;Behl 2010 (Clayton et al 1966), the low temperatures of concretion formation indicate precipitation well before the onset of marked clay reordering (, 100uC, e.g., Aoyagi and Kazama 2006). Thus, silica diagenesis is the most probable cause of the pore-water 18 O enrichment.…”