The Transformation of Clay Minerals During Diagenesis and Low‐grade Metamorphism: A Review

Abstract

Summary The results obtained by the author in the study of clay‐minerals diagenesis are compared critically with the principal publications in this field, giving a general picture of the transformation of sheet silicates. Kaolinite minerals are related to the surficial zones of the earth's crust where they are formed. They are characterized by the hexacoordination of aluminium. They furnish paleogeographic indications in ancient sediments. During diagenesis they are very sensitive to the geochemical environment, stable in acid conditions, unstable in alkaline conditions. However, the increase in temperature by burial causes their destruction sooner or later. In the transitional zone to metamorphism (anchizone), kaolinite is not present. Only dickite and nacrite can be observed, provided that the environment is acid. Montmorillonites are hydrated minerals. The rise in temperature and above all in pressure during burial expels water from the interlayers. Concentrated interstitial solutions of diagenesis provide cations which replace molecules of water between the layers. It is an irreversible reaction which produces 14‐Å minerals (chlorites) or 10‐Å minerals (illites), passing generally through mixed‐layer structures. The lack of montmorillonite is normal in formations which have undergone a marked burial. Mixed‐layers are intermediate stages which occur during degradation by weathering and during aggradation by deep diagenesis. This aggradation is the result of an incorporation of certain cations taken up from interstitial solutions, and of a rearrangement within the lattice. There are two major pathways: a potassium and sodium pathway, which produces the illites, then the micas, passing possibly by regular mixed‐layering of the allevardite‐rectorite type; and a magnesium pathway, which produces the chlorites, passing possibly by a regular mixed‐layering of the corrensite type. These mixed‐layers can remain stable until the border of meta‐morphism (anchizone). Micaceous clay minerals or illites form a very heterogenous group in the sediments which have been hardly diagenetized. Particles of diverse origin are found. They become more regular during burial. In deep diagenesis and the anchizone, crystallo‐graphic parameters of the illite are sufficiently well defined to serve as a scale of recrystallization, a zoneographic index. The morphology of the particles changes. Polymorphic types 1Md and 1M are replaced by the 2M‐type. The sharpness of the 10‐Å peak, conventionally called “crystallinity”, is an interesting quantitative criterium, together with the intensity ratio of the 5‐Å and 10‐Å peaks, which is related to the chemical composition of the octahedral layer. Micas in low‐grade metamorphism, called sericites by petrographers, replace the illites discussed above. They are different from the true micas by a weaker layer charge, less than 0.9 by half‐cell. They often contain sodium (paragonitic muscovites and paragonites). The octahedral charge (zero for the muscovite) is generally high, due to the replacement of...

Experimental mechanical compaction of reconstituted shale and mudstone aggregates: Investigation of petrophysical and acoustic properties of SW Barents Sea cap rock sequences

“…Moreover, Milliken and Day-Stirrat (2013) also showed majority of detrital plagioclase might get albitized because of the reaction with the sodium ions released from smectite to illite transformation. Other geochemical reactions and diagenetic changes in the temperature ranges between 70°C and 120°C are presented by many authors (such as, De Segonzac, 1970;Hower et al, 1976;Freed and Peacor, 1989;Bjørlykke, 1998;and Nadeau et al, 2002). Above 120°C, kaolinite and K-feldspar start to transform to illite clay minerals supplying further silica for quartz cementation (Chermak and Rimstidt, 1990;Giorgetti et al, 2000).…”

“…With the added consolidation, cementation, and fissility due to higher temperatures and pressures, the fine-grained argillaceous rocks transform to shales (Aplin and Macquaker, 2011). During burial, as a result of mechanical and chemical compactions, siliciclastic sediments undergo both physical and mineralogical changes (De Segonzac, 1970;Hower et al, 1976;Chilingarian et al, 1995;Vasseur et al, 1995;Bjørlykke, 1998;Dewhurst et al, 1998;Nadeau et al, 2002;Mondol et al, 2007;Thyberg et al, 2010;Nooraiepour et al, 2017b).…”

Mineralogy of Dickite and Nacrite From Northern Taiwan

“…Ross and Kerr (1930) considered them to be of hydrothermal origin. In recent years, many diagenetic occurrences of dickite have been reported (Segonzac, 1970;Keller, 1976;Frey, 1987;Cell6 et al, 1993;Shen et al, 1994;Ruiz Cruz and Andreo, 1996). Therefore, it seems that temperature is not the only factor controlling the formarion of dickite.…”

The recommended Cambrian–Ordovician global Boundary stratotype of the Xiaoyangqiao section (Dayangcha, Jilin Province), China

“…De Segonzac (1970) considered that the diagenetic formation of chlorite was preceded by the formation of corrensite, variant kinds of mixed-layer chloritevermiculite and 'chlorite labile to heating', i.e. a chlorite phase that contracts partly on heating.…”