Guadalupian algae-sponge reefs in siliciclastic environments - the reefs at Lengwu (South China) compared with the reef at Iwaizaki (Japan)

Guadalupian reefs occur locally in Guangxi, Guizhou, Yunnan and Western Zhe jiang, South China. Two types of Guadalupian reefs can be recognized, one i s developed in carbonate platforms, e.g. those in the juncture areas of Gua ngxi, Yunnan and Guizhou; the other occurs in a littoral clastic shelf. The Lengwu reef in Western Zhejiang is a representative of the latter type, wh ich is a major topic of this paper. Lengwu algae-sponge reef, more than one hundred meters in thickness, are composed mainly of sponges, hydrozoans, a lgae, bryozoans, microbes and lime mud. Reef limestones sit on the mudstone interbedded with fine sandstone of the proximal prodelta facies and are ov erlain by coarse clasts of the delta front sediments. Lengwu reef displays a lens-shaped relief, dipping and thinning from the reef core, which is rem arkably different from the surrounding sediments, showing a protruding reli ef. Sponges and microbe/algae form bafflestone, bindstone and framestone of the reef core facies. Fore-reef facies is characterized by lithoclastic ru dstone and bioclastic packstone. Reef limestone sequence is composed of thr ee cycles and controlled by sea level changes and sediment influx. Such ree f is unique among the Guadalupian reefs in South China, but seems similar i n some aspects to lwaizaki reef limestones of south Kitakami in Japan. Alga e and microbes growing around sponges to form rigid structure in Lengwu ree f are a typical feature, which is distinctly different to Guadalupian reefs in a stable platform facies of Guizhou, Yunnan and Guangxi, South China.