沉积磷灰石形成中的生物有机质因素

本文研究了黔中磷块岩中磷灰石的化学成分、红外光谱、碳和硫同位素组成以及伴生微量元素和稀土元素地球化学特征,获得了若干生物有机质成因的证据.磷灰石红外光谱特征表明CO₃^2-和SO₄^2-以类质同象部分替代PO₄^2-而进入磷灰石晶格,而碳、硫同位素特征表明,这CO₃^2-及SO₄^2-的相当部分是由生物有机质分解演化而来;叠层石磷灰石的P₂O₅含量与亲生物微量元素关系非常密切,而非叠层石者关系不甚密切;稀土元素地球化学特征表明,磷灰石的形成具有两种既有联系又各不相同的作用机制,即直接的生物作用和间接的有机质作用.

MICROBIAL-ORGANIC EFFECTS ON FORMATION OF THE SEDIMENTARY APATITE

The apatites (carbonate fluorapatites) in central part of Guizhou Province have been made a thorough study depending mainly on chemical composition, IR spectrum, structural sulfur and carbon isotopic compositions, trace elements and rare earth elements. We find that the microbial organic effects are striking in apatite formation. It is showing by IR spectrum of apatite that the CO₃^2- and SO₄^2- replaced PO₄^2- into structure of apatite. In apatite, δ³⁴S is +34.2‰—42.4‰, δ ¹³C is 3.63‰-+0.10‰ . According to our study of structural sulfur and carbon isotopic composition, the SO₄^2- and CO₃^2- came mostly from the evolution of microbioaal organism. In stromatolitic apatite, the P₂O₅ is obviously related with biophile elements. But in general, it is quite different from the non-stromatolitic apatite where P₂O₅ is not closely correlated with biophile elements. REE and trace elements analyses reveal two different processes for the formation of apatite. One is direct absorption and uptake by bateria and alga. The other is indirect action. i.e. authigenous precipitaion of the apatites near surface of deposition or in pore water. In here, organic matter played an action that might provide energy for releasing phosphorus from-phosphor bearing organic compounds. Formation of phosphorites appears to have a mixed origin of above-mentioned two actions.