ISSN:
1440-1738
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
Notes:
Abstract A Triassic formation in the Turpan-Hami and Ordos basin of China gives two typical examples of occurrence of laumontite belonging to diagenetic facies. Sandstones of the Upper Triassic Yanchang Formation in the eastern sector of the Ordos basin are formed at the mature stage of mesodiagenesis at temperatures in the range of 71-120°C, while the temperatures of the oil-bearing beds Chang-6 and Chang-7 where laumontite is present are about 81-88°C. The laumontite-bearing beds of the Middle Triassic in the Hami depression are presently at the supermature stage of organic matter, the corresponding diagenetic temperature being about 140 °C. The term zeolite facies should be rejected, and the features of metamorphic stage should be clearly denned, such as closely packed grains, absence of pores and cements, and characteristic mineral assemblages including sericite, epidote, muscovite, illite (2M1), chlorite (IIb, β= 97°), dickite, pyrophyllite, graphite, chlorozeolite formed at temperatures of 200°C and Ro values of 2.5%; the stage is also characterized by schistosity and illite crystallinity of IC = 0.42°Δ 2θ. The anchimetamorphic zone is characterized by some characteristic minerals such as paragonite, rectorite, albite, laumontite, illite (1M), chlorite (Ib, P = 90°+ IIb, β= 97°) formed at temperatures of 130-200°C and Ro values of 1.3-2.5% as well as other quantitative parameters of organic matter.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1440-1738.1993.tb00092.x
