北祁连山东部早石炭世早期腕足动物群落的古地理意义

北祁连山东部早石炭世早期经历了一次完整的海水进退旋回。此期该区腕足动物的演化明显受控于相对海平面变化。生存环境的稳定性似乎是群落演替过程能否持久进行的基础。在影响生物群落演替的诸多因素中，底质性质及其稳定性最为重要，其次是食物供应、海水盐度和水动力强度等。各群落在时间上相互取代的主要控制因素是海水深度，与海平面的变化直接相关。而造成这一时期腕足动物群落横向变化的主要因素除了海水深度外，陆源碎屑供应量、海水循环性以及含盐度都具有十分重要的影响。本区早石炭世早期腕足动物群落的生态位介于BA1和BA2之间，缺乏BA3－BA5较深水群落（BA－Benthic Assemblage，底栖组合），说明此期该区早石炭世早期海水深度一般不超过10米。受沉积古地理环境的制约，本区早石炭世早期BA2生态域的主要分布范围局限于东部的景泰一带，向西水体明显变浅。

Palaeogeographical significance of brachiopod communities of the early Early Carboniferous in eastern part of North Qilian Mountains

A complete progressive and regressive cycle occurred in the early Early Carboniferous in the eastern part of the North Qilian Mountains. The relative sea level changes obviously controlled the evolution of brachiopods in the study area during this period. It seems that the stability of living environment is the foundation of whether the process of community evolution can take place for a long time.Among all those factors influencing the community evolution, the property and stability of substrate are most important, but the food supply, water salinity and hydrodynamics also play important roles. Vertically, the most important controlling factor of the community replacement was water depth, and it was closely related to the sea-level changes in this area. Horizontally, besides the water depth, the amount of terrigenous clastic materials, sea water circulation and its salinity also greatly influenced the distribution of benthic communities. The benthic assemblage eco-positions of brachiopod communities in the early Early Carboniferous were between BA1 and BA2, and there were no BA3- BA5 deep-water communities in this area, which indicated that the sea water depth in this period was commonly less than 10 m. Controlled by the sedimentary palaeogeographic environment, the distribution area of BA2 benthic assemblage eco-positions during the early Early Carboniferous were mainly localized around Jingtai County, and the water depth was obviously shallower westward.