DIVISION AND GEOLOGICAL IMPLICATIONS OF CALCAREOUS AIGAL MORPHOLOGICAL GROUPS AND ENVIRONMENTAL ZONES IN THE LOWER CAMBRIAN QINGXUDONG FORMATION,HUAYUAN DISTRICT,WESTERN HUNAN

The bioherms are widespread during deposition of the Lower Cambrian Qingxudong Formation in the Huayuan district, western Hunan. They comprise nineteen genera and species of calcareous algae and may be subdivided into four groups and seven subgroups according to their morphologies: (1) botryoidal group; (2) dendritic group including: (a) fine and short subgroup, (b) clustered and ball-shaped subgroup, and (c) dendritic subgroup; (3) tubular group including: (a) fan-shaped tubular subgroup, (b) isolated and scattered tubular subgroup, (c) clustered tubular subgroup, (d) coiled-massive and spiral subgroup, and (4) blanket hair-like group.
One or several algal morphological groups and/or subgroups can be assigned to either of four algal environmental zones of the bioherms, where the distribution of energy differs from that in the organic reefs. For example, the low-energy zone occurs at the bottom and periphery of the bioherms, whereas relatively high-energy in the central part of the bioherms, and very high-energy zone on the top of the bioherms. No differences in energy have been identified in the environments around the bioherms; all the algal environmentsl are confined to the deeper-water low-energy environments in the study area.