Morphological, Chemical, and Isotopic Evidence for an Early Diagenetic Evolution of Detrital Smectite in Marine Sediments

Norbert Clauer1, James R. O'Neil2, Chantal Bonnot-Courtois3 and Thierry Holtzapffel4
1 Centre de Géochimie de la Surface, 67084 Strasbourg, France
2 Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109
3 Laboratoire de Géomorphologie, 35800 Dinard, France
4 Laboratoire de Géologie, Université d'Angers, 49045 Angers, France

Abstract: Mineralogical (XRD), morphological (transmission electron microscopy), chemical (major, rare-earth elements, and scanning-transmission electron microscopy), and isotope (Sr, O, H) measurements were made of marine detrital smectite from shales to study their reactions during early diagenesis. Albian, Aptian, and Palaeogene smectite samples were selected from Deep Sea Drilling Project drill cores taken in the Atlantic Ocean and from outcrops and drill cores from Belgium and northern France. Detrital, fake-like smectite particles seem to have adapted to their depositional environment by isochemical dissolution and subsequent crystallization of authigenic, lath-like particles. The major-element and rare-earth element compositions of both types of particles are similar. The Sr isotope chemistry suggests that the dissolution-crystallization process occurred soon after deposition in an almost closed chemical system. Except for slight changes in the amount of Fe and the oxygen isotope composition, the reaction took place without noticeable chemical exchange with the interstitial or marine environment. Such closed-system recrystallization of clay minerals may be a common diagenetic process if the water/rock ratio is small, as in shales.

Key Words: Chemical composition • Diagenesis • Isotopic composition • Morphology • Smectite • Transmission electron microscopy • X-ray powder diffraction

Clays and Clay Minerals; February 1990 v. 38; no. 1; p. 33-46; DOI: 10.1346/CCMN.1990.0380105
© 1990, The Clay Minerals Society
Clay Minerals Society (www.clays.org)