新疆巴楚中奥陶统上部一间房组瓶筐石礁丘的演化意义

从建造时代和群落组成的角度,专论新疆巴楚地区一间房组瓶筐石礁丘的演化定位。瓶筐石作为群落的主体造礁始于早奥陶世早期,繁盛于早奥陶世晚期,中奥陶世开始趋于衰落。一间房组发育中小型点礁丘,除礁灰岩中常见的藻屑外,主要由瓶筐石并伴生少量石海绵共同形成礁格架岩。在群落组成上,一间房组的瓶筐礁丘与世界其它地区的瓶筐礁类似,但在建造时间上却显得极为特殊:中奥陶世晚期。这时,一个全新的群落——珊瑚—层孔海绵礁群落开始在世界其它地区起源,却全然不见于一间房组。一间房组的礁丘在时间上完全不吻合于早奥陶世的瓶筐石造礁事件,而是晚于此类礁繁盛期并滞后了约10Ma,是目前所发现这类礁群落在全球范围内的孓遗孤例,是承先而不启后的礁群落。

EVOLUTIONARY SIGNIFICANCE OF THE CALATHIUM REEF MOUND FROM THE YIJIANFANG FORMATION,BACHU,XINJIANG

The present paper focuses on the evolutionary significance of the Calathium reef mound from the Yijiangfang Formation, Bachu, Xinjiang based on its biotic structures and age. From the early Early Ordovician, Calathium started a key role in reef building, and then thrived in the middle Early Ordovician and declined from Middle Ordovician time onward. Small-middle scale patch reef mounds from the Yijianfang Formation are dominated by Calathium frameworks together with sparse lithisid spones. Microbialites are also common. Therefore, the biotic structure of this reef mound is similar to its earlier analogues elsewhere in the world. However, this reef building is special for its occurrence in the later Middle Ordovician. During this time interval, an innovation of reef fauna composed of a coral-stromatoporoid association origined in other areas, but was absent from the Yijianfang Formation. The occurrence of the reef mound did not match the Calathium reef-building event in the Early Ordovician, but was delayed for about 10 Ma. Thus, it is interpretated as the sole relic in the world.