塔里木地块寒武纪台地相区生物群落时空分布及其地层意义

THE SPATIAL-TEMPORAL DISTRIBUTION OF PALEOCOMMUNITIES ON THE CAMBRIAN PLATFORM OF THE TARIM BLOCK AND ITS STRATIGRAPHIC SIGNIFICANCES

塔里木地块寒武纪台地相区地层白云岩是油气勘探的主要目标之一,但是由于缺乏三叶虫等生物化石,地层的等时划分成为难点。虽然碳同位素曲线以及自然伽马曲线是两种较为有效的地层等时对比的手段,然而由于这两种数据的获得比较困难,限制了这些方法的广泛应用。通过肖尔布拉克露头剖面岩石及钻井方1、中深1、中深5、英买7、英买36和牙哈5等7个剖面的岩芯岩屑薄片中的所有生物化石碎片的研究,揭示了塔里木盆地寒武纪台地区生物群落的时空分布模式。揭示的不同剖面生物群落序列具有非常好的横向一致性,因此自下而上确定了9个具有区域地层意义的生物群落,它们分别为:1)海绵动物群落,分布于纽芬兰统幸运阶玉尔吐斯组底部;2)微生物-小壳生物群落,分布于纽芬兰统第二阶的玉尔吐斯组的顶部;3)三叶虫群落,主要分布于第二统第三阶的肖尔布拉克组和第四阶的吾松格尔组;4)包覆状-泡沫状微生物群落分布于第二统第三阶的肖尔布拉克组;5)席状-包覆状微生物群落,分布于第二统第四阶的肖尔布拉克组上部;6)棘皮类-三叶虫群落/三叶虫-棘皮类群落,首现层位位于第二统第四阶的吾松格尔组;7)棘皮类群落,主要分布于第三统鼓山阶的阿瓦塔格组,局部上延到第三统古丈阶的下丘里塔格组;8)微生物席群落,主要分布于第三统鼓山阶的阿瓦塔格组中上部,局部上延到第三统古丈阶的下丘里塔格组;9)云朵状微生物群落,主要分布于第三统古丈阶的下丘里塔格组,局部上延到芙蓉统排碧阶的蓬莱坝组,下延到阿瓦塔格组。这些群落为塔里木台地相区缺乏三叶虫化石的白云岩"哑地层"的再划分提供了依据。

Cambrian dolostones in the Tarim Block are a main target for petroleum exploration, but their stratigraphic correlation is difficultly due to the general lack of trilobites and other body fossils. Gammaray curves and carbon isotope curves are two important methods in stratigraphic subdivision and correlation of these dolostones. However, the applications of these methods are hindered by the limited availability of Gamma-ray and carbon isotope data. To improve the stratigraphic correlation of Cambrian dolostones in the Tarim Block, we analyzed the spatial-temporal distribution of Cambrian paleocommunities in the Tarim platform on the basis of petrographic data from the Xiaoerbulak section as well as drill cores and well cut- tings of the wells F1, ZS1, ZS5, YMT, YM36, and YHS. A succession of nine paleocommunities can be recognized and they have regional stratigraphic significance. These include, from bottom to top, 1） a sponge paleocommunity in the basal Yurtus Formation of the Fortunian Stage （Terreneuvian） ; 2） a microbe small shelly fossil paleocommunity in the upper Yurtus Formation of Stage 2 （Terreneuvian） ; 3） a trilobite paleocommunity in the Xiaoerbulak Formation of Stage 3 （Series 2） and the Wusonger Formation of Stage 4 （Series 2） ; 4） an encrusting microbial paleocommunity in the Xiaoerbulak Formation of Stage 3 （Series 2） ; 5） a mat-encrusting microbial paleocommunity in the upper Xiaoerbulak Formation of Stage 4 （Series 2） ; 6） an echinoderm-trilobite paleocommunity in the Wusonger Formation of Stage 4 （Series 2） ; 7） an echinoderm paleocommunity mainly in the Awatag Formation of the Drumian Stage （Series 3） and locally ranging upward into the Xiaqiulitag Formation of the Guzhangian Stage （Series 3） ; 8） a microbial mats paleocommunity mainly in the middle and upper Awatag Formation of the Drumian Stage （Series 3） and locally ranging upward into the Xiaqiulitag Formation; 9） a microbial paleocommunity mainly in the Xiaqiulitatg Formation of the Guzhangian Stage （Series 3） and locally ranging upward into the Penglaiba Formation of the Paibian Stage （Furongian） and ranging downward into the Awatag Formation. These paleocommunities provide an important basis for the subdivision and correlation of the barren dolostones on the Cambrian platform of the Tarim Basin.