湖南泥盆—石炭系界线层孢子组合及其地层意义

MIOSPORE ZONES IN THE DEVONIAN-CARBONIFEROUS BOUNDARY BEDS IN HUNAN AND THEIR STRATIGRAPHICAL SIGNIFICANCE

本文通过对湖南晚泥盆世和早石炭世早期地层孢子研究,自下而上建立了5个孢子带,1).Relispora lepidophyta-Knoxisporites literatus(LL)带;2).Retispora lepidophyta-Hymenozonotriletes explanatus(LF)带;3).Retispora lepidophyta-Verrucosisporites nitidus(LN)带;4).Vallatisporites verrucosus- Aneurospora incohatus(Ⅵ)带;5).Baculatisporites fusticulus-Auvoraspora macra(FM)带。前三个带属泥盆系,后两个带属石炭系。在湖南中部泥盆、石炭系界线划在邵东组与孟公坳组之间,湘西北地区划在梯子口组与长阳组之间。湖南晚泥盆世至早石炭世孢子带基本上可与华南和西藏珠穆朗玛峰地区同期孢子带对比,亦可与西欧、苏联和北美有关孢子带比较。

The Upper Devonian and Lower Carboniferous shallow marine carbonate and clastic deposits are well developed in central and northwestern Hunan, containing very rich miospores. According to their stratigraphical distribution, five assemblage zones may be established, with three zones in the Upper Devonian and two zones in the Lower Carboniferous; they are in ascending order as follows: 1. Retispora lepidophyta-Knoxis porites literatus (LL) Biozone 2. Retispora lepidophyta-Hymenozonotriletes explanatus (LE) Biozone 3. Retispora lepidophyta-Verrucosis porites nitidus (LN) Biozone 4. Vallatisporites verrucosus-Aneurospora incohatus (Ⅵ) Biozone 5. Baculatisporites fusticulus-Auroraspora macra (FM) Biozone The spore zones in the Devonian-Carboniferous boundary beds are comparable with the LE, LN and Ⅵ zones of Western Europe (Clayton et al., 1977). The Devonian—Carboniferous boundary that was defined during the Carboniferous Congress at Heerlen 1935 at the first appearance of Gattendor fia subinvoluta approximates the boundary between the Tnla and Tnlb. In 1979, the International Working Group recommeded an operational definition of this boundary:at the first appearance of the conodont Siphonodolla sulcata within the evolution lineage of Siphonodella. The position of appearance of the Vallatisporites verrucosus-Amurospora incokatus(Ⅵ)Zone is coincident with that of Siphonodella sulcata. Thus the boundary between the Retispora lepidophyta-Verrucosisporites nitidus (LN) Biozone and the Vallatisporites verrucosus-Aneurospora incohatus (Ⅵ)Biozone is precisely the Devonian-Carboniferous boundary. According to the spore zones, the boundaiy in Hunan should be placed between the Menggong'ao Formation and Shaodong Formation or between the Tizikou Formation and Changyang Formation.