Formation of Authigenic Illite in Palaeocene Mudrocks from the Central North Sea: A Study by High Resolution Electron Microscopy

Jennifer M. Huggett
Department of Geology, Imperial College, London, SW7 2BP, U.K.

Abstract: The mode of growth of authigenic, lath-shaped illitic particles has been investigated using field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). Two types of clay lath have been identified: overgrowths on platelets of illite or illite-smectite and discrete particles. Both are neoformed and show a slight increase in abundance with depth over the 70 m depth interval sampled. Interpretation of lattice fringe data is not unambiguous but indicates that the clay is either illite or illite-smectite with R1 structure. The formation of discrete particles of authigenic illite, or even R1 illite-smectite, is compatible with present burial depths and a regional geothermal gradient of approximately 40°C/km. This illite also differs from many previous reported occurrences of authigenic illite in mudrocks in that it appears to have formed, without being preceded by progressive iUitization of illite-smectite.

Key Words: Authigenic illite • High resolution electron microscopy • Illite-smectite

Clays and Clay Minerals; December 1995 v. 43; no. 6; p. 682-692; DOI: 10.1346/CCMN.1995.0430604
© 1995, The Clay Minerals Society
Clay Minerals Society (www.clays.org)