中国科学院南京地质古生物研究所机构知识库

以云南晋宁梅树村和海口尖山剖面肖滩阶顶部的生屑富集层为研究对象,通过对其野外观察认为,在原"玉案山段"底部生屑富集层,与下伏泥质粉砂岩之间存在沉积间断。本文认同陈均远等(1996)和朱茂炎等(2001)的观点,筇竹寺组建组条件不足,应该废弃,"石岩头段"和"玉案山段"应更名为石岩头组和玉案山组。肖滩阶顶部生屑层很可能为风暴作用后,在海侵过程中形成的半局限潮坪洼地沉积。通过岩石光薄片、光面和揭片观察,认为唐努乌拉尔壳在玉案山组底部小壳化石富集层中的丰度最大,其次是软舌螺和开腔骨骨针,藻类和赫尔克特壳在玉案山组底部地层中也偶尔可见,拉普渥斯壳、牙形类、刺胞类?、腕足动物和其他难以识别的生物骨骼碎片则极少见。通过X射线光电子能谱分析认为,玉案山组底部的生屑富集层中含丰富有机质、铝硅酸盐岩、金属碳酸盐、金属磷酸盐、铁氧化物和硫化物等。所谓的"生屑磷块岩"中磷主要分布于磷质团块和生物骨骼等碎屑颗粒外表面和内部,围岩中磷的原子百分含量极低或为0。其全岩P2O5的重量百分含量很可能低于6%,宜根据其中铝硅酸盐和金属碳酸盐含量的相对多少将"生屑磷块岩"更名为含磷碳质生屑白云岩或含磷碳质白云质粉砂岩。滇东肖滩阶顶部的磷沉积可能与有机质的大量存在和频繁变化的水动力条件有重要关系。

Based on field investigation on the bioclatic layer in the former "Chiungchussi Formation" at Meishucun and Jianshan sections in Kunming area, eastern Yunnan, a sedimentary discontinuity between the Shiyantou and Yu’anshan members is confirmed. The results support the Chen et al.(1996) and Zhu et al.(2001)’s proposal that Chiungchussi Formation should be abandoned and the "Shiyantou and Yu’anshan members" should be renamed as formations respectively. The bioclastic layer at the base of the Yu’anshan Formation represents the reworked sediments possibly deposited in the depression area of semi-restricted tidal flat resulted from erosion and the subsequent transgression and storms. According to observation under thin sections, polished surfaces and peels, Tannuolinidae was the most abundant group in the latest Xiaotanian Stage,followed by hyoliths and chancelloriids. Algae and halkieriids can be detected in thin section occasionally.Larpworthellids, brachiopods?, cnidarians? and other problematic skeleton fragments are rarely encountered.Element compositions and their chemical states for typical sedimentary units of the bioclastic layer are studied by X-ray Photoelectron Spectroscopy(XPS). XPS characterization results show that the phosphate mainly occurs in the bolus-form deposition and calcium phosphate coatings on the fossil skeletons. The weight percentage of P2O5 is probably less than 6% in the whole rock. The concentration of sedimentary phosphate rock was possible related to the existence of abundant organic material and the frequent change in hydrodynamic conditions.