Discovery of Middle Jurassic Trace Fossil Tisoa Serres in N orthern Tibet and Its Palaeoenvironmental Significance
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摘要: 遗迹化石TisoaSeres国内尚无报导，70多块遗迹化石Tisoa标本见于藏北羌塘地区中侏罗统色哇组。本文对所采集的Tisoa标本作了详细的研究，Tisoa通常由紧靠的圆柱状平行潜穴管组成，单一潜穴管直径2～7mm间，两栖管间距1～4mm，外部由锥形或圆柱形钙质结核所包围，钙质结核直径10～25mm。保存完好的标本表明Tisoa为两个潜穴管底部相连的“Ｕ”形管，大多数只含两个平行潜穴管的标本实际上只是保存的一个“Ｕ”形管的上部。在大多数Tisoa管壁通常发育不规则的黄铁矿层或一微晶方解石薄层；栖管中常充填微晶和亮晶方解石以及黄铁矿、云母及泥质和石英。一般认为Tisoa是一种节肢动物潜穴。沉积环境分析，产Tisoa的沉积环境为正常浅海环境。Abstract: The trace fossil Tisoa Serres was unreported previously from China. Over 70 Tisoa specimens have been found in Middle Jurassic Sew a Formation in Qiang tang area, no rthern Tibet. The outcrop is located at 89°54′E in longitude and 32°07′N in latitude. Tisoa specimens consist typically of two closely parallel, cylindrical tubes that constitute the long axis of conical or cylindrical calcareous concretions. Individual tubes 2′～7mm in diameter and lying 1～4 mm apart, a rerarely branched. Calcareous concretions which covered the tubes are 10～25 mm. in di-ameter. One well-preserved specimen shows that Tisoa actually consists of a single U-shaped tube which linked at the basal part, and that the two parallel tubes constituting most specimens are actually the up-per part of a single U-shaped tube. An irregular layer of pyrite in a thin layer of microcrystalline calcite is commonly present along most tubes. The tubes are of ten filled with micrite and sparite, some with iron sulfide, mica and argillaceous as well as arenaceous quartz. Tisoa represents a dwelling burrow probably made by an arthropod. By analysis of sedimentology and palaeoecology, the upper part of Middle Jurassic Sewa Formation which bearing trace fossil Tisoa represents shallow water condition.
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Key words:
- Northern Tibet /
- middle jurassic /
- trace fossil /
- Tisoa /
- palaeoenvironment
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