黔南中三叠世Anisic期的生物礁复合体

ANISIAN REEF COMPLEX OF THE MIDDLE TRIASSIC IN THE SOUTH GUIZHOU,CHINA

黔中、黔西南的中三叠世是否存在生物礁是一个有争议的问题。本文论证Anisic期簸箕山组是一个典型的生物礁建造。簸箕山组有多种造礁生物,六射珊瑚、环口目苔藓虫以及龙介蠕虫类都是重要的造架生物,此外还有海绵和红藻类。格架洞穴是生物礁的主要结构之一,洞穴中粪粒和生物碎屑充填物的存在是生物礁结构的另一个特点。本文将珊瑚—藻礁划分为6个群落,并对礁周围的生物群落和沉积相作了论述。青岩组显示礁前和前沿礁的特点,而花溪组则为礁后泻湖沉积。它们与簸箕山组共同组成礁复合体。

There are different interpretations to the well known carbonate building-up of the Middle Triassic in the South Guizhou, and the principal debate point is whether the building-up possesses reef or it is composed of only bank. This paper shows that the Bojishan Fomation (Anisian) is mainly constituted by typical bioreef based on the study of several reef-builders and depositional environments. Ramose scleractinids are the most important builders. The sessile sperpulid worms are the secondary important builders which are always associated with scleractinids and encrusted by Tubiphytes. Besides these builders, cyslostomats (Bryozoa) and calcisponges also play a role in the reef frame. Frame-caves growing between reef organisms as reef building are another evidence of reef in which the fecal pellets and bioclasts are usually deposited. The Anisian reef complex in the South Guizhou is constructed by reef core and reef flat (the Bojishan Formation), reef front zone (the Qingyan Formation) and lagoon deposits behind reef (the Huaxi Formation).