Abstract
The mineralogy and geochemistry of shales reflect the composition of the initially deposited precursor mud, subsequently modified by diagenetic processes. To see if significant geochemical differences exist between shales that mainly owe their present-day composition to either deposition or diagenesis, we compare the published mineralogical, bulk and clay-fraction geochemical, and clay-fraction O-isotopic compositions of 2 shales. One shale is from the Western Canada Sedimentary Basin (WCSB), and its composition mainly reflects primary (depositional) chemical and mineralogical variations (smectitic to illitic illite/smectite) within this unit. The other shale is from the United States Gulf Coast (USGC), and its composition mainly reflects mixed-layer illite/smectite (I/S) diagenesis of deposited smectitic clay material. The chemical and mineralogical trends of WCSB and USGC shales, including one of increasing illite content in I/S with depth or maturity, are essentially indistinguishable, in both bulk shale and clay fraction, despite the contrasting genetic interpretations for the origin of the contained I/S. Thus, similar mineralogical and chemical trends with depth or temperature can result either from inherited depositional compositional heterogeneity of the sediment, from burial metamorphism of shale or a combination of both. Interestingly, the O-isotopic compositions of the clay fractions from the WCSB and USGC are significantly different, a fact that reflects original clay formation from source material and water of quite different isotopic compositions. The discrimination between depositional and diagenetic contributions to shale composition continues to pose challenges, but a combination of bentonite, illite polytype, clay isotopic and trace and rare earth elemental analyses together with illite age analysis holds promise for future work.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Abercrombie HJ, Hutcheon IE, Bloch JD, Caritat P de. 1994. Silica activity and the smectite-illite reaction. Geology 22:22–542.
Ahn JH, Peacor DR. 1986. Transmission and analytical electron microscopy of the smectite-to-illite transition. Clays Clay Miner 34:34–179.
Awwiller DN. 1993. Mite/smectite formation and potassium mass transfer during burial diagenesis of mudrocks: A study from the Texas Gulf Coast Paleocene-Eocene. J Sed Petrol 63:63–512.
Awwiller DN. 1994. Geochronology and mass transfer in Gulf Coast mudrocks (south-central Texas, U.S.A.): Rb-Sr, Sm-Nd and REE systematics. Chem Geol 116:61–84.
Bloch J, Schröder-Adams C, Leckie DA, McIntyre DJ, Craig J, Staniland M. 1993. Revised stratigraphy of the lower Colorado Group (Albian to Turonian), western Canada. Bull Cana Petrol Geol 41:325–348.
Burst JF. 1959. Post-diagenetic clay mineral environmental relationships in the Gulf Coast Eocene. Clays Clay Miner 6:6–341.
Burst JF. 1969. Diagenesis of Gulf Coast clayey sediments and its possible relation to petroleum migration. Am Assoc Petrol Geol Bull 53:53–93.
Burst JF. 1976. Argillaceous sediment dewatering. Ann Rev Earth Planet Sci 4:4–318.
Caritat P de, Bloch J, Hutcheon I. 1994. LPNORM: A linear programming normative analysis code. Comput Geosci 20:20–347.
Caritat P de, Bloch J, Hutcheon I, Longstaffe FJ. 1994. Compositional trends of a Cretaceous foreland basin shale (Belle Fourche Formation, Western Canada Sedimentary Basin): Diagenetic and depositional controls. Clay Miner 29:503–526.
Craig H. 1961. Standards for reporting concentrations of deuterium and oxygen-18 in natural waters. Science 133:133–1834.
Cullers RL. 1994. The controls on the major and trace element variation of shales, siltstones, and sandstones of Penn-sylvanian-Permian age from uplifted continental blocks in Colorado to platform sediment in Kansas, USA. Geochim Cosmochim Acta 58:4955–4972.
Culotta R, Latham T, Sydow M, Oliver J, Brown L, Kaufman S. 1992. Deep structure of the Texas Gulf passive margin and its Ouachita-Precambrian basement; results of the CO-CORP San Marcos Arch survey. Am Assoc Petrol Geol Bull 76:76–283.
Eberl DD. 1993. Three zones for illite formation during burial diagenesis and metamorphism. Clays Clay Miner 41:41–37.
Fagel N, Andre L, Debrabant P. 1994. Geochemical tools useful in order to discriminate the distinct sedimentary components of deep-sea clays (Neogene Equatorial Indian Ocean). Mineral Mag 58A:259–260.
Freed RL, Peacor DR. 1992. Diagenesis and the formation of authigenic illite-rich I/S crystals in Gulf Coast shales: TEM study of clay separates. J Sed Petrol 62:62–234.
Hoffman J, Hower J. 1979. Clay mineral assemblages as low grade metamorphic geothermometers: Application to the thrust faulted disturbed belt of Montana, U.S.A. Soc Econ Paleontol Mineral Spec Publ 26:55–79.
Hower J, Eslinger EV, Hower ME, Perry EA. 1976. Mechanism of burial metamorphism of argillaceous sediments: 1. Mineralogical and chemical evidence. Geol Soc Am Bull 87:87–737.
Hower J, Mowatt TC. 1966. The mineralogy of illites and mixed-layer illite/montmorillonites. Am Mineral 51:51–854.
Lindgreen H, Jacobsen H, Jakobsen HJ. 1991. Diagenetic structural transformations in North Sea Jurassic illite/smectite. Clays Clay Miner 39:39–69.
Moore DM, Reynolds RC. 1989. X-ray diffraction and the identification and analysis of clay minerals. New York: Oxford Univ Pr. 332 p.
Mossmann JR. 1991. K-Ar dating of authigenic illite-smectite clay material: Application to complex mixtures of mixed-layer assemblages. Clay Miner 26:189–198.
Ohr M, Halliday AN, Peacor DR. 1994. Mobility and fractionation of rare earth elements in argillaceous sediments: Implications for dating diagenesis and low-grade metamorphism. Geochim Cosmochim Acta 58:58–312.
Perry EA, Hower J. 1970. Burial diagenesis in Gulf Coast pelitic sediments. Clays Clay Miner 18:18–177.
Pollastro RM. 1994. Clay diagenesis and mass balance—The forest and the trees. Clays Clay Miner 42:42–97.
Powers MC. 1967. Fluid-release mechanisms in compacting marine mudrocks and their importance in oil exploration. Am Assoc Petrol Geol Bull 51:51–1254.
Pye K, Krinsley DH, Burton JH. 1986. Diagenesis of US Gulf Coast shales. Nature 324:324–559.
Roden MK, Elliott WC, Aronson JL, Miller DS. 1993. A comparison of fission-track ages of apatite and zircon to the K/Ar ages of illite-smectite (I/S) from Ordovician K-bentonites, southern Appalachian basin. J Geol 101:633–641.
Schroeder PA. 1993. A chemical, XRD, and 27Al MAS NMR investigation of Miocene Gulf Coast shales with applications to understanding illite/smectite crystal-chemistry. Clays Clay Miner 41:668–679.
Velde B, Hower J. 1963. Petrographical significance of illite polymorphism in Paleozoic sedimentary rocks. Am Mineral 48:48–1254.
Yau YC, Peacor DR, McDowell SD. 1987. Smectite-to-illite reactions in Salton Sea shales: A transmission and analytical electron microscopy study. J Sed Petrol 57:57–342.
Yeh HW, Savin SM. 1977. Mechanism of burial metamorphism of argillaceous sediments: 3. O-isotope evidence. Geol Soc Am Bull 88:88–1330.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
de Caritat, P., Bloch, J., Hutcheon, I. et al. Comparison of the Mineralogical and Chemical Composition of 2 Shales from the Western Canada Sedimentary Basin and the United States Gulf Coast. Clays Clay Miner. 45, 327–332 (1997). https://doi.org/10.1346/CCMN.1997.0450303
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1346/CCMN.1997.0450303