摘要
广西阳朔镇西北的中泥盆世吉维期深灰色中薄层灰岩相的下部产出5至7层 RothpletzellaWood,1948(罗氏藻)骨骼叠层石,其形态有大球茎状、细柱状、指状、球状或不规则球状(核形石)等变化。罗氏藻叠层石主要由 Rothpletzella sp.紧密包绕生长构成,并有Wetheredella minuta sp.nov.(细小威氏藻),Wetheredella giganta sp.nov.(粗大威氏藻)及隐藻类的参与。Rothpletzellasp.在不同形态的叠层石中并无形态大小的明显变化。推测该罗氏藻叠层石的生活环境为一较局限的浅潮下带甚至到潮间带下部。
The fossil alga Rothpletzella was found in different reef and marginal--slope facies of De-vonian carbonate platform in Guilin, and its skeleta1 stromatolites were especially well--devel-oped in dark grey, thin--bedded limestone in Yangshuo, 64 km south of Guilin City. There are 5--7 layers of Rothpletzella stromatolites occurring in the lower part of thesection consisting of thin-- to medium--bedded limestone which was inferred to be time--equiva-lent to a stromatoporoid--coral biostrome nearby. Syndepositional fault possibly caused thefacies differentiation. The thin-- to medium--bedded carbonate rocks containing Rothpletzellastromatolites are represented by laminated cryptalgal limestone, flat--pebble limestone, ten-taculitid wackestone, silex, lime mudstone, and wedge--shaped debris--flow sediments, indi-cating a shallow, restricted depositional environment and occasionally, a slope facies (Fig.1). At least 4 different morphological types of Rothpletzella stromatolites were observed inYangshuo, namely, the big bulbous form, the digitated form, the slim columnar form andthe oncoidal form (Fig. 2). Gastropod bioclasts and lime mudstone are usually the nuclei ofRothpletzella oncoids. Many transitional forms are found among the four types. Rothpletzella stromatolites are mainly composed of different fossil algal groups includingRothpletzella sp. (the dominant species), Wetheredella minuta sp. nov., W. giganta sp.nov., and spongiostromates. There are some slightly different components in different typesof stromatolites; e. g., mats and micromounds of W. minuta attaching to Rothpletzella fila-ments are only observed in big bulbous forms; while spongiostromates are common andsometimes form thick and dark laminae of the skeletal oncoids, which are seldom observed inother types of stromatolites. It is suggested that Rothpletzella stromatolites in Yangshuo might have lived in a veryshallow subtidal to lower intertidal setting based on the following evidences: (1) Rothpletzel-la stromatolites often overlain by laminated cryptalgal limestone (with tepee structure occa-sionally), dolomitized packstone, and even ooidal packstone within a rock bed; (2) cyclic oc-currence of the above depositional feature; (3)interstitial materials between Rothpletzellastromatolites often dolomitized; (4) diverse forms of Rothpletzella stromatolites indicating atypical intertidal or shallow subtidal setting where various stromatolites forms are probablyrelated to the different water energy. Rothpletzella stromatolites in Yangshuo mostly occur in lime mudstone matrix, with fewsediment particles found to be bound and trapped by filaments, probably suggesting a rela-tively quiet environment with rare sediment influx. Rothpletzella sp. has no apparent change in size and morphology in the different stroma-tolite forms. Physical factors in the depositional environment may be most important in con-trolling the forms of Rothpletzella stromatolites.
出处
《微体古生物学报》
CSCD
北大核心
1992年第4期397-407,470-471,共11页
Acta Micropalaeontologica Sinica
关键词
罗氏藻
威氏藻
骨骼叠层石
藻类
Rothpletzella
Wetheredella
skeletal stromatolites
limestone facies
Yangshuo
Guangxi
