Shales Toarcian

Moldowan et al (5) investigated a sediment core, spanning a depth range of 5m, of Lower Toarcian shales from W. Germany specifically at a transition zone from a rather oxidized, shallow-marine, marly sediment to an organic matter-rich, black shale. Variations in distributions of isoprenoid hydrocarbons, steranes and monoaromatic steroids were observed and were related to variations in oxidation/reduction conditions during and shortly after sedimentation. 

Ensminger A., Albrecht P., Ourisson G., and Tissot B. (1977) Evolution of polycyclic alkanes under the effect of burial (Early Toarcian shales, Paris Basin), la Advances in Organic Geochemistry 1975 (eds. R. Campos and J. Goni). ENADIMSA, Madrid, pp. 45-52. 

Mackenzie A. S., Hoffmann C. E., and Maxwell J. R. (1981) Molecular parameters of maturation in the Toarcian shales, Paris Basin, France III. Changes in aromatic steroid hydrocarbons. Geochim. Cosmochim. Acta 45, 1345-1355. 

The total oil yield obtained from the shale upon pyrolysis is usually measured by the standard Fisher assay. However, it is possible to obtain a fast and accurate measurement of the oil yield by using the Rock Eval source rock analyzer (5), which operates on small quantities of rock, such as 50 or 100 mg. Figure 3 shows the comparison between the value obtained from the Rock Eval pyrolysis and the yield of the Fisher assay on the Toarcian shales of the Paris Basin. 

A series of experiments has been carried out to observe the generation of the different classes of oil constituents. Aliquots of two kerogens from the Green River Shale (type I) (6) and the Lower Toarcian shales of the Paris Basin (type II) (7) where heated at a constant heating rate of 4°C min to different final temperatures ranging from 375°C to 550°C. A humic coal from Indonesia (type III) was also used for comparison (8). These various... 

Figure 2. Typical IR spectrum of the kerogen isolatedfrom lower Toarcian shales of the...

Figure 9. Evolution of hydrogen index vs. Tmax of Rock-Evalpyrolysis in natural Series I, II, and III (hatched) and in heated samples (identified by final temperature of pyrolysis). Key , Green River shales (GRS) a, Toarcian shales (To) and, humic...

Tissot, B., Durand, B., Espitalie, J., and Combaz, A. (1974). Influence of nature and diagenesis hydrocarbons in early Toarcian shales. Bull. Am. A.v.soc. Petrol. Geol. 55, 2177-2193. 

Dieckmann V., Schenck H.J., Horsfield B., Welte D.H. (1998) Kinetics of petroleum generation and cracking by programmed-temperature closed-system pyrolysis of Toarcian shales. Fuel 77, 23-31. 

Schaefer, R. G. Littke, R. 1988. Maturity-Related Changes in the Low Molecular-Weight Hydrocarbon Fraction of Toarcian Shales. Pergamon Press, Oxford, 887-892. 

Tissot B., Califet-Debyser Y., Deroo G. and Oudin J. L. (1971) Origin and evolution of hydrocarbons in early Toarcian shales, Paris Basin, France. Am. Assoc. Petrol. Geol. Bull. 55(12), 2177-2193. 

Schaefer R. G. and Littke R. (1988) Maturity-related compositional changes in the low-molecular-weight hydrocarbon fraction of Toarcian shales. Org. Geochem. 13, 887-892. 

Table 1. Mineralogy of the Tournemire Toarcian shales and marls...

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