广西龙江泥盆纪苔藓虫的发现及其地质意义

Discovery of Devonian Bryozoa in Longjiang,Guangxi and Its Geological Significance

广西泥盆纪地层发育完整、分布广泛,为研究泥盆纪地层序列及古生物提供了良好的基础。本次研究在广西龙江地区泥盆纪地层中首次发现苔藓虫,经鉴定计有13属21种,分别为Cystiramus sp.,Eostenopora huishuiensis,Fenestella?sp.,Fistulipora collina,Fistuliramus parallelus,F.mishanensis,F.parallelus grandoporus,F.pusillus,F.sp.,Helopora hastifera,H.ninglangensis,Leptotrypa adhaerens,L.cf.adhaerens,L.lamellata,Meekopora wangyouensis,Orthopora sinensis,Petalotrypa tumida,P.cf.tumida,Semicoscimum cf.dushanensis,Rhombopora sp.和Streblotrypa sp.。对苔藓虫动物群生态特征及龙江地区泥盆纪的沉积环境进行分析,得出该区泥盆纪的沉积环境演变规律:(1)泥盆纪早期,初期处于一种潮坪相砂坪亚相沉积环境,随后演变为潮坪相混合坪亚相(砂坪、泥坪交替组成的滨岸潮间带)沉积环境→半局限-开阔台地相台凹亚相沉积环境→低能潮下带沉积环境→高能潮下带-潮坪相带沉积环境。(2)泥盆纪中期,早期海水加深,处于一种低能潮下带沉积环境;晚期演变为一种开阔台地相台棚亚相沉积环境。(3)泥盆纪晚期,早期海水加深,总体上为一种台盆相盆地亚相沉积环境;晚期海水略为变浅,但总体上仍属于一种台盆相台棚亚相沉积环境。

Devonian stratigraphy is well-developed and widely distributed in Guangxi,which provides a good target for studying the Devonian stratigraphic sequence and paleontology.Bryozoans were first discovered from the Devonian in Longjiang area(Longlin,Guangxi),including 21 species of 13 genera:Cystiramus sp.,Eostenoporahuishuiensis,Fenestella?sp.,Fistuliporacollina,Fistuliramusparallelus,F.mishanensis,F.parallelus grandoporus,F.pusillus,F.sp.,Heloporahastifera,H.ninglangensis,Leptotrypa adhaerens,L.cf.adhaerens,L.lamellata,Meekopora wangyouensis,Orthoporasinensis,Petalotrypa tumida,P.cf.tumida,Semicoscimum cf.dushanensis,Rhombopora sp.,and Streblotrypa sp.Based on the sedimentary environment and ecological characteristics of bryozoans from the Devonian Longjiang,the local sedimentary evolution is described as follows:(1)In Early Devonian,the sedimentary environment belonged to sand flat subfacies(tidal flat facies)during the earliest Devonian(D1l),then evolved into mixed-flat subfacies(shore intertidal zone with alternating mud flat and sand flat)(D1h)→platform-concave(alcove)subfacies of a half-limited-open-platform facies(D1d)→low-energy subtidal zone(D1-2s1)→high-energy subtidal zone-tidal-flat facies(D1-2s2).(2)In Middle Devonian,with the seawater deepened,the area transited into low-energy subtidal sedimentary environment(D1-2s2)→platform shelf subfacies of the platform basin(D1-2d).(3)In Late Devonian,basin subfacies(platform-basin facies)occurred with seawater deepening during the early stage(D3l),and the same subfacies maintained till the late stage(D3w)in spite of the slightly shallowing of seawater.