Publication: Clay diagenesis and low-grade
metamorphism of Tithonian and Berriasian
sediments in the Cameros Basin (Spain)
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Publication Date
2011
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Blackwell Scientific publications
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Abstract
The clay mineral assemblages of the Tithonian and Berriasian sediments (Tera and
Oncala Groups) in the eastern part of the Cameros basin are investigated at seven localities. The
lowest-grade assemblage, located on the southern border of the basin, contains calcite + quartz +
hematite + kaolinite + mixed-layer illite-smectite (R = 1, 6585% illite layers) + discrete illite (IC
= 0.50.65D82y). Systematic increases in the illite and chlorite crystallinities suggest increasing
metamorphic grade from the northwest part of the basin to the southeast. This trend does not follow
the pattern previously described for the overlying late Berriasian–early Aptian sediments (Urbio´n and
Enciso Groups), which exhibit a higher metamorphic grade. This may result from local variations in
sedimentary facies, as well as the circulation of hot migratory fluids. Tertiary compression occurring
long after the main metamorphic event is considered to be responsible for the enhanced illite and
chlorite crystallinities measured in the SE extreme of the basin.