摘要
贵州中三叠世拉丁晚期扬子台地边缘地表暴露带 ,经历的时间长 ,约 1Ma(2 33～ 2 32Ma) ;形成的厚度大 (一般 10 0～15 0m左右 ,最厚可达 180m左右 )。暴露特征清楚 ,渗流豆石、窗格 (鸟眼 )构造、中 大型帐篷构造、喀斯特化角砾岩非常发育 ,这显然是潮湿 半潮湿气候条件下 ,在古隆起区形成的钙质风化壳。暴露带裂隙中的微型钟乳石 ,有覆水石、滴水石、流水石 3种类型。其18O同位素组成一般在 - 10‰ (PDB)左右 ,13 C的同位素组成一般在 1.5‰～ 2‰ (PDB)左右。18O同位素组成表明 ,钟乳石是淡水成因的 ,但13 C的同位素组成为略高于淡水成因的沉积物的值 ,这可能是不饱和的大气降水溶解了基岩 ,而获得13 C的缘故。上述 3种形态的微型钟乳石的岩石学特征也表明 ,是典型的淡水成因形成。由此可见 ,暴露带裂隙中的微型钟乳石为淡水成因的产物。
The superficial exposure belt experienced a long evolutionary time(about 1 Ma ),and formed a great thickness of sidiments(usually between 100～150 m,with the largest thickness being some 180 m) during Late Ladinian period of Middle Triassic. There exist very clear exposure features,such as vadose pisolite,fenestral(birdeye) structure,middle-large type teepee structure and karst breccia. The belt is therefore evidently a calcareous weathering crust under humid-semihumid climate condition in an ancient upwarped region. There are three types of micro-stalactite in fissures of the exposed belt,namely,drapestone,dripstone,and flostone. Their 18 O isotope composition is usually about -10‰(PDB),and their 13 C isotope values are generally between 1.5‰-2‰(PDB).The 18 O isotope composition indicates that micro-stalactites are of fresh-water origin,but their 13 C values are slightly higher than the values of the freshwater sedimentary. This is probably attributed to the fact that meteoric water dissolved pre-formed limestone (bedrock) and obtained 13 C.The three shapes of the micro-stalactite are petrologically typical of fresh-watter sediments .It is thus considered that the micro-stalactites are fresh water sediments.
出处
《地球学报》
EI
CAS
CSCD
北大核心
2004年第2期177-180,共4页
Acta Geoscientica Sinica
基金
国家重点基础研究发展规划项目 (编号G19990 42 3 10 )资助
