The origin of the Triassic clay assemblages of Europe with special reference to the Keuper Marl and Rhaetic of parts of England

Abstract

Hypotheses are reviewed on the origin of the magnesium-rich Triassic clays which characterize the Germanic facies of western Europe and north Africa. Relations between clay minerals, megafacies and stratigraphy are described from 28 localities in the Triassic Keuper Marl, Tea Green Marl and Rhaetic sediments of England. Two clay mineral assemblages are recognized: (1) a detrital assemblage of mica with minor chlorite which occurs throughout all the sediments investigated, and (2) a neoformed assemblage of magnesium-rich clay minerals with a limited occurrence related to certain megafacies cycles which resulted from the transgression and regression of the Alpine facies into the Germanic facies; this assemblage includes sepiolite, palygorskite, chlorite, smectite, corrensite and irregular mixed-layer smectite/mica and smectite/chlorite minerals. The clay mineral neoformations resulted from reactions between the water masses in which the Germanic and Alpine facies were deposited. Controlling the distribution and types of minerals neoformed were the general and local variations in the chemistries of the Alpine and Germanic water masses, as well as competition for available magnesium from other mineral-forming reactions.

Origin, Diagenesis, and Mineralogy of Chlorite Minerals in Devonian Lacustrine Mudrocks, Orcadian Basin, Scotland

“…Invariably, they were interpreted as the products of transformations of detrital clay minerals, or as authigenic phases, formed by the action of the hypersaline sedimentary milieux. Indeed, syngenetic models have continued to be favoured by more recent studies (Jeans, 1978;Fisher, 1988;Lippmann and Pankau, 1988) and reviews (Hauff, 1981). However, as pointed out earlier, neither corrensite nor Mg-rich chlorite has ever been described from modern evaporitic environments (Bodine and Madsen, 1987).…”

“…However, the potential importance of such reactions in evaporite and carbonate basins has yet to be investigated. Interestingly, in cases where the distribution of carbonates also has been studied in various detail (Merrel et al, 1957;Jeans, 1978), the patterns are suggestive of clay carbonate reactions, but were interpreted otherwise. Such reactions might also explain why associated illites are often well crystallized.…”

“…The first includes those associated with volcaniclastic sediments (Almon et aL, 1976;Helmond and van de Kamp, 1984;Chang et aL, 1986;Inoue, 1987;Inoue and Utada, 1991) or various types of altered igneous rocks (Bettison and Schiffman, 1988;Schiffman and Fridleifsson, 1991). The second, those that are associated with ancient marine evaporites (Droste, 1963;Jeans, 1978;Bodine, 1985;Bodine and Masden, 1987;Lippmann and Pankau, 1988), or carbonates (Peterson, 1961;Fraser et al, 1973;Rao and Bhattacharya, 1973), or lacustrine facies (April, 1981).…”

“…The proposed mechanisms for corrensite and chlorite formation include neoformation from concentrated hypersaline brines or, alternatively, transformation of detrital clay minerals (Lucas, 1962;Jeans, 1978;Hauff, 1981;Fisher, 1988;Lippmann and Pankau, 1988). The evidence for such interpretations is basically two-fold: 1) Mgrich chlorite and corrensite occur in association with evaporitic facies from many different sedimentary basins worldwide, yet they are comparatively rare in other facies deposited under normal marine or fresh 240 Vol.…”

Authigenic Chlorite in Late Triassic Sandstones from the Central Graben, North Sea

“…Rossel, 1982). It can be generally said that, within the limits of present knowledge, detrital kaolinite is rare in late Triassic and Rhaetic sediments in the European area (Jeans, 1978). Detrital kaolinite first appears in any quantity in the late Rhaetic and early Jurassic.…”