SEDIMENTARY FACIES AND DIAGENESIS OF THE MIDDLE AND UPPER DEVONIAN CARBONATE ROCKS IN THE TANGJIAWAN SECTION, GUILIN

The study area is provided for the cooperative project between the Ministry of Geology and Mineral Resources, the People's Republic of China and the Ministry of Science and Art of Niedersachsen, the Federal Republic of Germany. Eight microfacies types may be distinguished for the Middle and Upper Devonian carbonate rocks in the Tangjiawan region, includins mudstone, laminated peloid-grainstone/packstone, unlaminated peloid-grainstone/packstone, ostracode-grainstone/packstone, amphipora-wackestone, amphipora-echinoderm-wackestone, bioclastic wackestone and framestone. These microfacies types indicate varying energy index and water depth. In the light of Irwin sedimentary model (1985) of the shallow-water carbonate rocks, the Devonian(Givetian and Frasnian)strata are assigned to Y and Z zones and to the sedimentary environments of normal seas with bioherm/biostrome, restricted shallow-water and tidal flats. The maximum water depths vary from 10 to 20 m.
The carbonate rocks in the Tangjiawan section may have experinced three types of early diagenetic environments:marine, meteoric and mixed water, followed by pressure solution, recrystallization and replacement in the late diagenetic stages. The dolomitization is interpreted to have a mixed water origin, or a late diagenetic replacement origin.