Clays and Clay Minerals

, Volume 47, Issue 5, pp 582–590 | Cite as

Crystal Chemistry of Layer Silicates of the Miocene Green Grain (Congo Basin) from Transmission Electron Microscopy (TEM) and Analytical Electron microscopy (AEM) Observations

  • A. Wiewióra
  • P. Giresse
  • A. M. Jaunet
  • A. Wilamowski
  • F. Elsass


Transmission electron microscopy (TEM) and analytical electron microscopy (AEM) methods were used to study the crystal chemistry of phyllosilicates occurring in green grains of Miocene sediments from the Congo continental shelf. Using diagrams based on wt. % K and the (Fe + Mg)/Al ratio, minerals were distinguished from mixed-layer phases. The most abundant detrital mineral is Fe-kaolinite. The morphology and composition identify this mineral as a component of ferralitic soils. This Fe-rich kaolinite has undergone a complex process of partial dissolution and recrystallization and further enrichment in Fe and, to a lesser extent, in Mg in the marine environment. The detrital mica observed with TEM retains the original morphology and chemistry of muscovite. Alteration processes resulted in the crystallization of 1:1 trioctahedral Fe2+ and Mg-rich minerals and interstratified phases with 1:1 and 2:1 layers in varying proportions observed with the aid of high-resolution transmission electron microscopy (HRTEM) imaging. Included among the newly formed 7-Å phases are those apparently containing excess Si. The smectites are apparently neoform, and chemical analyses showed that these marine K-smectites belong to the beidellite-nontronite series and have tetrahedral substitutions similar to muscovite. Their compositions are closer to beidellite than to nontronite, although the latter was observed in association with goethite. The TEM observations and crystallochemical data show that mineral alteration ceased after forming mixed-layer minerals, and alteration did not reach the glauconitization stage. Apparently, the Miocene assemblages experienced rapidly changing environmental conditions and high sedimentation rates that continue today.

Key Words

Alteration Markers Congo Basin Detrital Phyllosilicates Green Grains Neoformed Phyllosilicates 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Amouric, M. and Parron, C. (1985) Structure and growth mechanism of glauconite as seen by high-resolution transmission electron microscopy. Clays and Clay Minerals, 33, 473–482.CrossRefGoogle Scholar
  2. Amouric, M., Parron, C., Casalini, L., and Giresse, P. (1995) A (1:1) 7-Å Fe phase and its transformation in Recent sediments: An HRTEM and AEM study. Clays and Clay Minerals, 43, 446–454.CrossRefGoogle Scholar
  3. Bailey, S.W. (1988) Odinite, a new dioctahedral-trioctahedral Fe3+-rich 1:1 clay mineral. Clay Minerals, 23, 237–247.CrossRefGoogle Scholar
  4. Elsass, F., Beaumont, A., Pernes, M, Jaunet, A.-M., and Tessier, D. (1998) Changes in layer organization of Na- and Ca-exchanged smectite materials during solvent exchanges for embedment in resin. The Canadian Mineralogist, 36, 1475–1483.Google Scholar
  5. Giresse, P. (1985) Le fer et les glauconies au large du fleuve Congo. Sciences Geologiques, Bulletin, Strasbourg, 38, 293–322.CrossRefGoogle Scholar
  6. Giresse, P. and Odin, G.S. (1973) Nature minéralogique et origine des glauconies du plateau continental du Gabon et du Congo. Sedimentology, 20, 457–488.CrossRefGoogle Scholar
  7. Giresse, P., Wiewióra, A., and Lacka, B. (1988) Mineral phases and processes within green peloids from two Recent deposits near the Congo River mouth. Clay Minerals, 23, 447–458.CrossRefGoogle Scholar
  8. Giresse, P., Oualembo, P., Wiewióra, A., Łącka, B., and Zawidzki, P. (1992) Compositions polyphasées des grains verts du bassin du Congo; Comparaison de dépôts Récents, Holocènes (103–104 ans) et Miocènes (107 ans). Archiwum Mineralogiczne, 47, 17–49.Google Scholar
  9. Herbillon, A.J., Mestdagh, M.M., Vielvoye, L., and Derouane, E.G. (1976) Iron in kaolinite with special reference to kaolinite from tropical soils. Clay Minerals, 11, 201–220.CrossRefGoogle Scholar
  10. Jepson, W.B. (1988) Structural iron in kaolinites and in associated ancillary minerals. In Iron in Soil and Clay Minerals, J.W. Stucki, B.A. Goodman, and U. Schwertmann, eds. NATO Advanced Study Institute Series, Series C: Mathematical and Physical Sciences, R. Reidel, Dordrecht, 217, 467–536.CrossRefGoogle Scholar
  11. Malengreau, N., Muller, J.P., and Calas, G. (1994) Fe-speciation in kaolins: A diffuse reflectance study. Clays and Clay Minerals, 42, 137–147.CrossRefGoogle Scholar
  12. Maley, J. (1996) The African rain forest—main characteristics of changes in vegetation and climate from the Upper Cretaceous to the Quaternary. Proceedings of the Royal Society of Edinburgh, 104B, 31–73.Google Scholar
  13. Mestdagh, M.M., Vielvoye, L., and Herbillon, A.J. (1980) Iron in kaolinite, II. The relationship between kaolinite crystallinity and iron content. Clay Minerals, 15, 1–13.CrossRefGoogle Scholar
  14. Muller, J.P. and Calas, G. (1993) Genetic significance of paramagnetic centers in kaolinites. In Kaolin Genesis and Utilization, H.H. Murray, W.M. Bundy, and C.C. Harvey, eds. Clay Minerals Society of America, Boulder, Colorado, 261–289.Google Scholar
  15. Nahon, D. (1981) Modes de répartition des métaux dans les solutions solides des altérations tropicales; applications aux concentrations supergènes ferrugineuses. In Valorisation des Ressources du Sous-Sol, D. Nahon, ed. Documents Bureau de Recherches Géologiques et Mineurs, Orléans, 47, 254–264.Google Scholar
  16. Odin, G.S., Bailey, S.W., Amouric, M., Fröhlich, F., and Waychunas, G.A. (1988) Mineralogy of the facies verdine. In Green Marine Clays, G.S. Odin, ed. Elsevier, Amsterdam, 159–206.Google Scholar
  17. Oualembo-Mophawe, P.A. (1992) Les successions de grains verts argileux méso-cénozoïques du bassin marin congolais; paléoenvironnement, sédimentologie, minéralogie et géochimie. Ph.D. thesis, Univ. Perpignan, 335 pp.Google Scholar
  18. Parron, C. (1989) Voies et mécanismes de cristallogénèse des minéraux argileux ferriferes en milieu marin. Le processus de glauconitisation: évolutions minérales, structurales et géodynamiques. Ph.D. thesis, Univ. Aix-Marseille, 411 pp.Google Scholar
  19. Porrenga, D.H. (1967) Glauconite and chamosite as depth indicators in the marine environment. Marine Geology, 5, 495–501.CrossRefGoogle Scholar
  20. Poumot, C. (1989) Palynological evidence for eustatic events in the tropical Neogene. Centre Recherche Exploration Elf-Aquitaine Bulletin, 13, 437–453.Google Scholar
  21. Sakharov, B.A., Besson, G., Drits, V.A., Kameneva, Y.U., Salyn, A.L., and Smoliar, B.B. (1990) X-ray study of the nature of stacking faults in the structure of glauconites. Clay Minerals, 25, 419–435.CrossRefGoogle Scholar
  22. Séranne, M., Séguret, M., and Fauchier, M. (1992) Seismic super-units and post-rift evolution of the continental passive margin of southern Gabon. Société Géologique de France Bulletin, 163, 135–146.Google Scholar
  23. Siesser, W.G. (1978) Leg 40 results in relation to continental shelf and onshore geology. Deep Sea Drilling Project, Internal Reports, 40, 965–979.Google Scholar
  24. Stucki, J.W., (1988) Structural iron in smectites. In Iron in Soils and Clay Minerals, J.W. Stucki, B.A. Goodman, and U. Schwertmann, eds. NATO Advanced Study Institute Series, Series C: Mathematical and Physical Sciences, R. Reidel, Dordrecht, 217, 625–675.CrossRefGoogle Scholar
  25. Środoń, J., Andreoli, C., Elsass, F., and Robert, M. (1990) Direct high-resolution transmission electron microscopic measurement of expandability of mixed-layer illite/smectite in bentonite rock. Clays and Clay Minerals, 38, 373–379.CrossRefGoogle Scholar
  26. Von Gaertner, H.R. and Schellmann, W. (1965) Rezente Sedimente in Küstenbereich der Halbinsel Kaloun, Guinea. Tschermaks Mineralogische und Petrographische Mitteilungen, 10, 349–367.CrossRefGoogle Scholar
  27. Warren, E.A. and Ransom, B. (1992) The influence of analytical error upon the interpretation of chemical variations in clay minerals. Clay Minerals, 27, 193–209.CrossRefGoogle Scholar
  28. Wiewióra, A. (1990a) Crystallochemical classifications of phyllosilicates based on the unified system of projection of chemical composition: I. The mica group. Clay Minerals, 25, 73–81.CrossRefGoogle Scholar
  29. Wiewióra, A. (1990b) Crystallochemical classifications of phyllosilicates based on the unified system of projection of chemical composition: III. The serpentine-kaolin group. Clay Minerals, 25, 93–98.CrossRefGoogle Scholar
  30. Wiewióra, A., Łącka, B., and Giresse, P. (1996) Characterization and origin of 1:1 phyllosilicates within peloids of the Recent, Holocene and Miocene deposits of the Congo Basin. Clays and Clay Minerals, 44, 587–598.CrossRefGoogle Scholar

Copyright information

© The Clay Minerals Society 1999

Authors and Affiliations

  • A. Wiewióra
    • 1
  • P. Giresse
    • 2
  • A. M. Jaunet
    • 2
  • A. Wilamowski
    • 1
  • F. Elsass
    • 3
  1. 1.Polish Academy of SciencesInstitute of Geological SciencesWarszawaPoland
  2. 2.Laboratoire de Sédimentologie et Géochimie marine, URA CNRS 715, LEA Sciences de la MerUniversité de PerpignanPerpignanFrance
  3. 3.Sciences du SolINRAVersaillesFrance

Personalised recommendations