Abstract Fluorescence spectroscopy via confocal laser scanning microscopy (CLSM) was used to analyze ancient sedimentary organic matter, including Tasmanites microfossils in Devonian shale and Gloecapsomorpha prisca (G. prisca) in Ordovician kukersite from North American basins. We examined fluorescence emission as a function of excitation laser wavelength, sample orientation, and with respect to location within individual organic entities and in transects across bedded organic matter. Results from spectral scans of the same field of view in Tasmanites with different laser lines showed progressive red-shift in emission maxima with longer excitation wavelengths. This result indicates steady-state Tasmanites fluorescence emission is an overlapping combination of emission from multiple fluorophore functions. Stokes shift decreased with increasing excitation wavelength, further suggesting the presence of multiple fluorophore functions with different S1 → S0 transition energies. This observation also indicates that at longer excitation wavelengths, less absorbed light energy is dissipated via collisional transfer than at shorter excitation wavelengths and may suggest fewer polar functions are preferentially absorbing. Confirming earlier results, emission spectra observed from high fluorescence intensity regions (fold apices) in individual Tasmanites are blue-shifted relative to emission from other locations in the same microfossil. We suggest high intensity emission is from photoselective alignment of polarized excitation with the fluorophore absorption and emission transition moment. The blue shift observed in regions of high intensity emission may be due to relative absence or realignment of polar species, e.g., bridging ether or ester functions, although variations in O abundance could not be confirmed with preliminary time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis. Tasmanites occurring in consolidated sediments are flattened from original spherical morphology and, in optical microscopy, this burial deformation results in generally parallel extinction (strain-influenced) and positive elongation. The deformation also induces fluorescence anisotropy observed as variations in emission wavelength when individual Tasmanites are measured from their long axis parallel to bedding, whereas this effect is absent in bedding-normal view. Transects from G. prisca-rich source layers into adjacent reservoir layers show decrease in fluorescence intensity and spectral red-shift (increase in full-width half-maximum with increasing red portion of the half-width). These results may suggest an increase in fluorescence quenching across the source-to-reservoir transition zone, consistent with an increase in aromaticity following petroleum expulsion and migration. These observations are supported by increasing reflectance values measured across similar micro-scale transects. Our results highlight the applicability of CLSM as a broad and under-utilized approach for the characterization of sedimentary organic matter and are discussed with perspective toward petroleum processes and thermal indices research.

中文翻译：

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通过共聚焦激光扫描显微镜 (CLSM) 对古代沉积有机质进行荧光光谱分析

摘要 利用荧光光谱共聚焦激光扫描显微镜（CLSM）分析了古代沉积有机质，包括泥盆纪页岩中的塔斯曼石微化石和北美盆地奥陶纪库克石中的格洛卡普斯卡（G. prisca）。我们检查了荧光发射作为激发激光波长、样品方向以及单个有机实体内和跨层状有机物横断面的位置的函数。使用不同激光线对塔斯马尼亚岩中相同视场的光谱扫描结果显示，随着激发波长的延长，发射最大值逐渐发生红移。该结果表明稳态塔斯曼石荧光发射是来自多个荧光团功能的发射的重叠组合。斯托克斯位移随着激发波长的增加而降低，进一步表明存在具有不同 S1 → S0 跃迁能量的多个荧光团功能。这一观察结果还表明，在较长的激发波长下，通过碰撞转移消耗的光能比在较短的激发波长下消耗的光能少，并且可能表明优先吸收的极性函数较少。确认早期的结果，从单个塔斯马尼亚石的高荧光强度区域（折叠顶点）观察到的发射光谱相对于同一微化石中其他位置的发射发生蓝移。我们建议高强度发射来自偏振激发与荧光团吸收和发射跃迁矩的光选择性对齐。在高强度发射区域观察到的蓝移可能是由于极性物质的相对不存在或重新排列，例如桥接醚或酯功能，尽管无法通过初步飞行时间二次离子质谱法确认 O 丰度的变化(TOF-SIMS) 分析。在固结沉积物中出现的塔斯曼石从原始的球形形态变平，在光学显微镜下，这种埋藏变形导致通常平行消光（受应变影响）和正伸长。当从平行于层理的长轴测量单个塔斯曼石时，变形还会引起荧光各向异性，观察到发射波长的变化，而在层理正常视图中不存在这种效应。来自 G 的横断面。富 prisca 源层进入相邻的储层显示荧光强度和光谱红移的降低（随着半宽度的红色部分的增加，全宽半最大值增加）。这些结果可能表明整个源-储过渡区的荧光猝灭增加，这与石油排出和迁移后芳香性的增加一致。这些观察结果得到了在类似微尺度横断面上测量的增加的反射率值的支持。我们的结果突出了 CLSM 作为一种广泛且未充分利用的方法来表征沉积有机质的适用性，并从石油过程和热指数研究的角度进行了讨论。