Illite/Smectite Diagenesis and Its Variable Correlation with Vitrinite Reflectance in the Pannonian Basin

Abstract

Abstract--The correlation between illite/smectite (I/S) diagenesis and mean vitrinite reflectance (Ro) data is examined in mudrocks from a hydrocarbon exploration well (geothermal gradient 35"C km -1) from the Great Hungarian Plain of the Pannonian Basin System. The expandability of I/S decreases with depth and there is a change from random to ordered mixed-layering at about 2500 m depth. At this depth Ro is about 0.6%. Comparison of the correlation of expandability and Ro from this study to published data for the Vienna Basin and the Transcarpathian Basin, sub-basins of the Pannonian Basin System, shows that the correlation is systematically different for each sub-basin, according to their thermal histories. In the Vienna Basin (geothermal gradient 25"C km-~), for any given value of Ro, the expandability of US is less than in the Transcarpathian Basin (geothermal gradient 55*(2 km -1) and the sediments are older and more deeply buried. Data from the present study are intermediate. This variation is believed to be due to the effect of time on the smectite-to-illite reaction. Results of an optimization procedure to calculate the kinetics of the smectite-to-illite reaction, using as input the expandability depth profiles, and thermal histories constrained by comparison of observed and calculated Ro data, showed that I/S diagenesis in the Pannonian Basin System can be modelled by a single first order rate equation:-dS/dt = e log(A) -E/RT. S where S = fraction of smectite layers in I/S, t = time (Ma), e = exponential function, log(A) = frequency factor = 7.5 (Ma-l), E = activation energy = 31.0 kJ mo1-1, R = universal gas constant, and T is temperature in Kelvin. This result also suggests an important role for time. By combining the kinetics of the smectite-to-illite reaction with a kinetic model ofvitrinite maturation it is possible to define a domain within which all 'normal' (burial diagenesis) correlations between Ro and US diagenesis should lie. Such diagrams can be used to identify different thermal histories related to different geotectonic settings and 'anomalous' data such as that affected by igneous intrusions.

Transformation of Smectite to Illite In Bentonite and Associated Sediments from Kaka Point, New Zealand: Contrast in Rate and Mechanism

“…They and other workers (Ahn et al 1988;Ahn and Peacor 1989;Freed and Peacor 1989;Inoue et al 1990;Essene and Peacor 1995) have inferred that the extent of the smectite-to-illite transformation is kinetically controlled and therefore governed not only by temperature, pressure and composition, but also by additional factors. Important among these is water/rock ratio (Whitney 1990), activities of interlayer cations, especially K (Huang et al 1993), the presence of maturating organic matter (Small and Manning 1993;Small 1994), time (Ramseyer and Boles 1986;Pytte and Reynolds 1989;Pollastro 1990) and heating rate (Hillier et al 1995). Some investigators have implicitly recognized that the progress of reaction of such metastable phases is kinetically controlled by a variety of factors, but that, if all other relevant factors are constrained, then duration or temperature of reaction can be determined (Huang et al 1993).…”

Alpine metamorphism in the central segment of the Western Greywacke Zone (Eastern Alps)

“…The reaction progress of organic and inorganic temperature indicators are different (e.g. Hillier et al 1995;Sachsenhofer et al 1998). Therefore, clay mineralogical data are discussed together with the RSCM data.…”

Late-Stage Diagenesis of Illitic Clay Minerals as Seen by Decomposition of X-Ray Diffraction Patterns: Contrasted Behaviors of Sedimentary Basins with Different Burial Histories

“…Smectite illitization, especially, is shown to occur almost systematically in argillaceous diagenetic series (Burst 1969;Perry and Hower 1970;Hower et al 1976;Boles and Franks 1979;Srodofi 1979Srodofi , 1984Velde et al 1986;Glasmarm et al 1989;McCarty and Thompson 1991;Velde and Vasseur 1992;Pollastro 1993;Lindgreen 1994;Hillier et al 1995;Varajao and Meunier 1995). XRD has been the essential tool used to identify and characterize the reaction sequence:…”