Skip to main content Accessibility help

Formation of grain-coating chlorite in sandstones. Laboratory synthesized vs. natural occurrences

  • P. Aagaard (a1), J. S. Jahren (a1), A. O. Harstad (a1), O. Nilsen (a2) and M. Ramm (a3)...


Grain-coating chlorites in clastic quartz-rich sandstones have long been recognized as an important porosity-preserving constituent in medium- to deep-burial diagenesis. As little is known about the occurrence and origin of chlorite coatings, chlorite synthesis experiments were performed to study how grain-coating chlorites form in certain sandstones during burial. The starting material was naturally-occuring sandstones from the Oseberg and the Veslefrikk fields offshore Norway, where the same sandstone formation is buried to different depths due to faulting. Grain-coating chlorites exist below ~3000 m burial depth only. At shallower burial (2400 m), an X-ray amorphous iron containing thin clay coating is present.

The samples were heated to 200 and 250°C (at water vapour pressure) in a hydrothermal bomb for 2–4 weeks. Both starting material and end-products were studied (electron-) optically in both scanning and transmission microscopes. The TEM showed the Fe-rich precursor material to consist of a fine-grained berthierine-dominated mixed-layer. The neoformed grain coatings in the reacted samples were similar in appearance to naturally-occurring chlorite coatings. The TEM analyses of individual grains documented an Fe-rich chloritic phase with an average composition of Mg0.41Fe3.52Mn0.10Al1.51(Al0.58Si3.42)O10(OH)8. The reacted waters were found to be close to saturation with the newly formed chlorites.

Grain-coating chlorite thus appears to form in the natural environment from Fe-rich berthierine precursors at a burial depth corresponding to a temperature around 90°C.


Corresponding author


Hide All
Aagaard, P. & Egeberg, P.K. (1998) Formation waters and diagenetic modifications: General trends exhibited by oil fields from the Norwegian shelf–A model for formation waters in oil prone subsiding basins. Pp. 281–286 in: Water-Rock Interaction (Arehart, G.B. & Hulston, J.R., editors). Balkema, Rotterdam.
Aagaard, P. & Helgeson, H.C. (1983) Activity/Composition relations among silicates and aqueous solutions: II. Chemical and thermodynamic consequences of ideal mixing of atoms on homological sites in montmorillonites, illites, and mixed-layers clays. Clays Clay Miner. 31, 31207.
Aagaard, P. & Jahren, J.S. (1993) Diagenetic illitechlorite assemblages in arenites. II. Thermodynamic relations. Clays Clay Miner. 40, 40547.
Aagaard, P., Egeberg, P.K. & Jahren, J.S. (1992) North Sea clastic diagenesis and formation water constraints. Pp. 1147–1152 in: Water-Rock Interaction (Kharaka, Y.K. & Maest, A., editors). Balkema, Rotterdam.
Aase, N.E., Bjørkum, P.A. & Nadeau, P.H. (1996) The effect of grain-coating micro-quartz on preservation of reservoir porosity. Am. Assoc. Petrol. Geol. Bull. 80, 801654.
Barth, T. (1991) Organic acids and inorganic ions in waters from petroleum reservoirs, Norwegian continental shelf: a multivariate statistical analysis and comparison with American reservoir formation waters. Appl. Geochem. 6, 61.
Barth, T. & Riis, M. (1992) Interaction between organic acid anions in formation waters and reservoir mineral phases. Org. Geochem. 19, 19455.
Brown, B.E. & Bailey, S.W. (1962) Chlorite polytypism. Regular and semi-random one-layer structures. Am. Miner. 47, 47819.
Curtis, C.D., Hughes, C.R., Whiteman, J.A. & Whittle, C.K. (1985) Compositional variations whithin some sedimentary chlorites and some comments on their origin. Mineral. Mag. 49, 49375.
Egeberg, P.K. & Aagaard, P. (1989) Origin and evolution of formation waters from oil fields on the Norwegian Shelf. Appl. Geochem. 4, 4131.
Ehrenberg, S.N. (1993) Preservation of anomalously high porosity in deeply buried sandstones by graincoating chlorite–Examples from the Norwegian continental shelf. Am. Assoc. Petrol. Geol. Bull. 77, 771260.
Fritz, S.J. & Toth, T.A. (1997) An Fe-berthierine from a cretaceous laterite: Part II. Estimation of Eh, pH and pCO2 conditions of formation. Clays Clay Miner. 45, 45580.
Helgeson, H.C. & Aagaard, P. (1985) Activity/composition relations among silicates and aqueous solutions. I. Thermodynamics of intrasite mixing and substitutional order/disorder in minerals. Am. J. Sci. 285, 285769.
Helgeson, H.C, Delany, J.M., Nesbitt, H.W. & Bird, D.K. (1978) Summary and citique of the thermodynamic properties of rock-forming minerals. Am. J. Sci. 278A, 1-299.
Helgeson, H.C, Kirkham, D.H. & Flowers, G.C. (1981) Theoretical prediction of the thermodynamic behaviour of aqueous electrolytes at high pressures and temperatures: IV. Calculation of activity coefficients, osmotic coefficients, and apparent molal and standard and relative partial molal properties to 600°C and 5 kb. Am. J. Sci. 281, 2811249.
Helgeson, H.C, Knox, A.M., Owens CE. & Shock EX. (1993) Petroleum, oil field waters, and authigenic mineral assemblages: Are they in metastable equilibrium in hydrocarbon reservoirs. Geochim. Cosmochim. Ada, 57, 573295.
Iijima, A. & Matsumoto, R. (1982) Berthierine and chamosite in coal measures of Japan. Clays Clay Miner. 30, 30264.
Jahren, J.S. & Aagaard, P. (1989) Compositional variations in diagenetic chlorites and illites, and relationships with formation-water chemistry. Clay Miner. 24, 24157.
Johnson, J.W., Oelkers, E.H. & Helgeson, H.C. (1992) SUPCRT92: A software package for calculating the standard molal thermodynamic properties of minerals, gases, aqueous species, and rections from 1 to 5000 bars and 0° to 1000°C Computers and Geosciences.
Larese, R.E. (1997) Impact of diagenetic processes on sandstone reservoir quality; controls, effects, and predictive evaluation using data from natural and experimental systems. Am. Assoc. Petrol. Geol. Bull. 81, 1955.
Nelson, B.W. & Roy, R. (1958) Synthesis of the chlorites and their structural and chemical constitution. Am. Miner. 43, 43707.
Odin, G.S. (1985) La ‘verdine', facies granulaire vert, marine et cotier, distinct de la glauconie, distribution actuelle et composition. CR. Acad. Sci., Paris, 301, 301105.
Odin, G.S. (1988) Green Marine Clays. Dev. Sedimentol. Elsevier, Amsterdam.
Porrenga, D.H. (1966) Clay minerals in recent sediments of the Niger delta. Clays Clay Miner. 14, 14221.
Ramm, M. (1994) Porosity/depth trends in Upper Jurassic reservoirs, Norwegian Central Graben; an example of porosity preservationat deep burial by grain-coating micro-quartz. Am. Assoc. Petrol. Geol. Annual Meeting Abstracts.
Ramm, M., Forsberg, A.W. & Jahren, J.S. (1997) Porosity-depth trends in deeply buried Upper Jurassic reservoirs in the Norwegian Central Graben: An example of porosity preservation beneath the normal economic basement by graincoating quartz. Pp. 177–199 in: Reservoir Quality Prediction in Sandstone and Carbonates (Kupecz, J.A. & Bloch, S., editors). Am. Assoc. Petrol. Geol. Memoir, 69.
Smith, J.T. & Ehrenberg, S.N. (1989) Correlation of carbon dioxide abundance with temperature in clastic hydrocarbon reservoirs: relationship to inorganic chemical equilibrium. Marine Petrol. Geol. 6, 6129.
Velde, B., Raoult, J.-F. & Leikine, M. (1975) Metamorphosed berthierine pellets in mid- Cretaceous rocks from northeastern Algeria. J. Sed. Pet. 39, 391275.


Formation of grain-coating chlorite in sandstones. Laboratory synthesized vs. natural occurrences

  • P. Aagaard (a1), J. S. Jahren (a1), A. O. Harstad (a1), O. Nilsen (a2) and M. Ramm (a3)...


Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed