江北砾岩碳酸钙胶结特征及物质来源研究

STUDY ON CaCO_3-CEMENTATION AND SOURCE IN JIANGBEI CONGLOMERATE

江北砾岩是河流砾石层在地表胶结形成的沉积岩，其胶结物性质及来源问题长期以来倍受人们关注，但研究不深且存在明显争议．本文对岩石薄片和基岩、风化土壤、河成潮土、地下水、河岸滴水、河水、砂砾岩基质的化学成分进行了深入研究。化学分析结果表明，江北砾岩基质CaO含量高达30％，沿岸出露基岩、土壤CaO含量达10％左右，是河成砂土的3～10倍多，地下水、河岸滴水的Ca^2＋含量分别达116mg／L、160mg／L；HCO3^-分别为412mg／L、436mg／L，约为河水的3倍。与此同时，大量砂、砾岩薄片观察也表明，江北砾岩胶结物中含有大量的方解石．据此，我们认为江北砾岩胶结物可能主要来源于川江沿岸广泛分布的中生代基岩及其风化壳。

As sedimentary rock, Jiangbei conglomerate is fluvial gravel layer cemented on the ground surface by CaCO3. The composition and the origin of the cements have been paid much-attention to for a long time, hut the research work is not profound and there are obvious disagreements in the conclusion. The chemical composition of the conglomerate bedrock, regolith, fluvial soil, groundwater, drip water on riverbanks, river water, matrix of the sandstone and conglomerate is studied. It proves that the content of CaO is up to 30% in the matrix, about 10% in bedrock and soil along the riverbanks, which are three to ten times higher than that in the fluvial sand. The concentrations of Ca^2＋ and HCO3^- in groundwater and drip water on riverbanks are about 116mg/L, 160mg/L and 412mg/L,436mg/L respectively; about three times of the river water. At the same time, Jiangbei conglomerate＇s slices analysis also show that there are many calcites in the cements. Therefore we think the cements of Jiangbei conglomerate probably mainly originated from the wide spread Mesozoic bedrock and its weathered mantle along the Chuanjiang riverbanks.