太原西山七里沟晚古生代腕足动物群落及其古环境意义

Late Paleozoic brachiopod communities in the Qiligou section of the Western Mountains, Taiyuan, Shanxi, China, and their paleoenvironmental significance

太原西山七里沟晚古生代剖面含有丰富的腕足动物化石,共可识别出13个底栖生物群落。个体生态、行为习性、群落结构和岩性、岩相组合特征的研究表明熏这些群落的生态位介于BA1—BA3之间。控制腕足动物群落分布和相互取代的最主要因素是相对海平面变化。由于海平面升、降变化的速度、幅度和持续时间的不同,群落之间的这种相互更替既有突变的,也有渐变的,既可以发生在不同的旋回之间,也可以发生在同一个海水进、退旋回内。根据这些底栖生物群落生态位所显示的水深变化和剖面相序结构,该剖面本溪期至山西期共经历了11次海水进、退旋回,其中以庙沟期海侵规模最大,最大估水深10～20m,毛儿沟下灰岩与庙沟灰岩均为这一旋回的产物。

Abundant Late Paleozoic brachiopod fossils are contained in the Qiligou section of the Western Mountains, Taiyuan, Shanxi, and 13 benthic communities have been recognized. According to a detailed study of the autoecology, ethology and community structure, combined with an analysis of the lithology and sedimentary facies, the ecological positions of these communities are located between BA1 and BA3. The main controlling factor of the distribution and mutual replacement of the brachiopod communities is relative sea-level change. Because of differences in velocity, amplitude and duration of sea-level changes, the mutual replacement of two adjacent benthic communities may be not only sudden but also gradual and can occur between two different sedimentary cycles or in the same cycle of marine transgression and regression. The water-depth changes indicated by the ecological positions of these benthic communities and analysis of the facies sequence structure of the section suggest that 11 marine transgression and regression cycles occurred from the Benxian to Shanxian stages, of which the Miaogouan stage witnessed the maximum sea transgression with an estimated maximum sea depth of 10-20 m. The lower Maoergou limestone and Miaogou limestone are both the product of this sedimentary cycle.