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Abstract: Graptolite Reflectance in the Ordovician Shales from the Tarim Basin, Ordos Basin and Lower Yangtze, China


It was commonly difficult to evaluate the maturity of organic matter in Lower Paleozoic rocks due to the lack of higher plant fragments in those rocks. In this paper, the authors make a study of the reflectance and its dispersion spectrum of Ordovician graptolite fragments collected from the Tarim Basin, Ordos Basin and Lower Yangtze, China. The graptolite reflectance is compared with the reflectance of solid bitumen and, then, the estimated organic maturity of the Lower Paleozoic hydrocarbon-generating rocks in those areas or basins.

The random reflectance of non-granular graptolite fragments had a good linear correlation to the solid bitumen reflectance in the range 1.5-5.0R Grrandom: BRrandom = 0.882 Grrandom - 0.336 (r=0.9866).

Combining this formula with suitable BR/VR formulas, such as after Jacob (1985), the equivalent vitrinite reflectance of the Lower Paleozoic rocks could be estimated with reference to the graptolite reflectance.

AAPG Search and Discovery Article #90939©1997 AAPG Eastern Section and TSOP, Lexington, Kentucky