动物碎屑的光性变化及其研究意义

OPTICAL ALTERATION OF ZOOCLAST AND ITS STUDY SIGNIFICANCE

前泥盆纪地层中缺乏镜质体使得正确评价其有机质的热成熟度极为困难。但在下古生界中含有海生有机质笔石和几丁虫等 ,由于其光性特征随成熟度的变化而发生规律性变化而被用于表征有机质成熟度。在 4 50～ 70 0nm可见光谱范围 ,由于笔石和几丁虫的光学色散特性反射率随成熟度增加 ,表现出与镜质体及沥青相似的变化趋势。这表明 ,随成熟度增加 ,笔石和几丁虫的分子结构芳香度及芳碳定向性均发生相似的变化。在低成熟阶段 ,笔石和几丁虫的光学色散谱从蓝区到红区降低 ,表明芳环聚合程度低 ,芳碳含量少。在中等成熟阶段 ,笔石和几丁虫的光学色散谱从蓝区到红区呈平稳型式。在高成熟阶段 ,笔石的光学色散谱从蓝区到红区呈上升趋势 ,表明具有高芳香度 ,芳香分子定向性增强。在Ro ,max为 2 5%左右笔石发生结构转化 ,但直到Ro ,max达 12 %也未发生石墨化作用 ,表明笔石主要发生增碳作用。

Due to absence of vitrinite, the thermal maturity of organic matter in the Pre Devonian strata is very difficult to assess correctly. However, marine derived organic zooclasts such as graptolite and chitinozoan occurring in the Lower Paleozoic strata can be used for maturity determinations, since their optical properties show systematic changes with the maturity of the strata In the visible spectrum ranging from 450nm to 700nm, the dispersion of optical property reflectance of graptolite epiderms and chitinozoan in the Early Paleozoic sediments with increasing maturity follows trends similar to those of coal vitrinite and natural bitumen This indicates the similar molecular structural changes, e g an increase in aromaticity and ordering of aromatic carbons for graptolite epiderms and chitinozoan with increasing maturity The dispersion of optical property of graptolite and chitinozoan with a low maturity level falls from blue to red in the visible spectrum, indicating low aromatic carbon content The dispersions turn to flat from blue to red at the middle matured stage Those in highly matured sediments rise from blue to red, indicating high aromaticity and molecular ordering for graptolites The first structural transformation of graptolite occurs at the reflectance of 2 5% R o,max However, the graphitization does not occur at the graptolite reflectance of 12% R o,max , indicating the carbonization probably occurs in graptolite The optical parameters for graptolite and chitinozoan are good indicators for maturity in the Lower Paleozoic sediments