Measuring the degree of organic matter (OM) alteration caused by uranium (U) irradiation is important in the effective evaluation of the hydrocarbon potential and thermal maturity of U-rich source rocks. This study investigates OM alteration in the Baltoscandian U-rich, lower Paleozoic Alum shale obtained from three research wells in the thermally immature parts of eastern Sweden and western Estonia. The results show a marked increase in the proportion of refractory, non-generative organic carbon (NGOC) in the U-rich shale. Fluorescence spectrometry of unicellular alginites and lamalginites show a reduction of up to 95.6% in fluorescence relative intensity (RI) with increase in U content from 29 to 401 ppm. Fluorescence spectra of the liptinites exhibit a marked “red shift” as expressed by increase in red(R)/green(G) quotients. This change in fluorescence properties of the liptinites is associated with up to 77.6% decrease in hydrogen index (HI) and hence loss of hydrocarbon generation potential. Furthermore, organic molecules show significant loss of aromatic moieties as well as aliphatic constituents resulting in a more condensed macromolecular structure. The measured random reflectance of solid bitumen (BR_o) appears to be significantly elevated in micro scale proximity to the U-containing minerals. The heterogeneous distribution of U-containing minerals and the contact with solid bitumen attributes to the wider range of BR_o values and lead to the overall increase in mean BR_o in samples with high U contents. In contrast, R_o values of zooclast macerals (GR_o, e.g., graptolite, chitinozoans and vitrinite-like fragments) appear to be less influenced by U irradiation and hence are a more reliable maturity indicator in U- rich lower Paleozoic shales.

测量铀（U）辐照引起的有机物（OM）改变的程度对于有效评估富含U的烃源岩的烃势和热成熟度很重要。这项研究调查了从瑞典东部和爱沙尼亚西部未成熟部分的三个研究井获得的巴尔托斯堪迪亚U富集，下古生界明矾页岩中的OM变化。结果表明，富铀页岩中耐火，非生成性有机碳（NGOC）的比例显着增加。单细胞褐藻和拉金藻的荧光光谱显示，随着U含量从29 ppm增加到401 ppm，荧光相对强度（RI）最多降低了95.6％。脂肪族沸石的荧光光谱表现出明显的“红移”，如红色（R）/绿色（G）商的增加所表示。脂肪素的荧光性质的这种变化与氢指数（HI）降低多达77.6％有关，并因此降低了烃生成潜能。此外，有机分子显示出芳族部分以及脂族成分的显着损失，从而导致更缩合的大分子结构。实测沥青的随机反射率（BR_o）在含铀矿物质的微观尺度上似乎显着升高。含U矿物的不均匀分布以及与固体沥青的接触归因于BR _o值的更宽范围，并导致高U含量样品中的平均BR _o总体增加。相比之下，人为破骨细胞的类群蛋白（GR _o，例如，斜纹岩，壳多糖和类镜质碎片）的R _o值似乎受U辐射的影响较小，因此在富含U的下古生界页岩中是更可靠的成熟度指示剂。