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EARLY CAMBRIAN PHOSPHATE-REPLICATED ENDOLITHIC ALGAE FROM EMEl, SICHUAN, SW CHINA
四川峨嵋早寒武紀磷質鑄模鑽孔藻化石
摘要
Diverse and abundant phospate-replicated microborings produced by endolithic microorganisms in the shells and sclerites of early skeletal fauna, collected from the Maidiping Formation at Maidiping, Emci, Sichuan, have been examined after the acetic acid etching of the samples. During early diagenetic period, a phosphate-moulted filling event existed prior to the aragonitic (or calcitic) host-shell-dissolution (or alteration), therefore, through decalcification by acetic acid, the phosphate-replicated microborings are frequently preserved on the phosphatic internal moulds of or under the phosphatized outer layers of the skeletal fossils. The nature of the microborings suggests they were produced by endolithic algae. Six species of five genera have been examined: 1) Cunicularius halleri-unbranched cylindrical endolithic filaments with diameters of 2.5-3.0 μm; 2) Cunicularius isodiametrus sp. nov. - unbranched cylindrical endolithic filaments with diameters of 4.0-6.7 μm; 3) Endoconchia ? angusta - unbranched cylindrical endolithic filaments with spheroidal expansions, 3.0-6.0 μm in diameter; 4) Eohyella cr. elongata - branching endolithic pseudofilaments with diameters of 7.0-12.0 μm; 5) Graviglomus cf. incrustus - solitary ellipsoidal or spheroidal vesicles, boring vertically, cross-sections 7.0-38.0 μm in diameter; 6) parenchymodiscus cf. endolithicus - colonial endolithic thalli, boring vertically. each colony consisting of 10-30 ellipsoidal coccoid vesicles, cross-section 9.0-17.3 μm in diameter. Among them, the former four species are tentatively assigned to cyanophytes, and the affinity of the latter two species is uncertain.
並列摘要
四川峨嵋麥地坪剖面下寒武統麥地坪組富産微鑽孔藻化石。微鑽孔藻化石以早期帶殼後生動物殼體爲寄主，以磷質鑄模方式保存。早期成岩階段磷酸鹽膠結及充填作用在微鑽孔磷質鑄模的形成過程中起了關鍵性的作用。研究發現微鑽孔藻類主要有以下六種: Cunicularius halleri, C.isodiametrus sp. nov., Endoconchia ? angusta emend. nov., Eohyella cf. elongate, Graviglomus cf. incrustus及Parenchymodiscus cf. endolithicus, 其中前四種被歸爲藍藻，後兩種分類位置未定。