Using an inversion technique, we show that pollen translucency with depth can be used as a quantitative tool to estimate the thermal history of sedimentary sequences. The overall trend of translucency is a decrease with increasing depth.
In this study, three wells in southern Louisiana were examined, each having Carya (a pollen genus including present-day Pecans and Hickories) translucency measurements with depth, and one of the wells containing measurements of vitrinite reflectance with depth. High sedimentation rates (>250 ft/MM yrs of shale) require the use of a fluid flow/compaction burial history program linked with the Carya inversion algorithm. Thermal history is estimated by the interaction of a heat flux taken to be linear in time, and a time-temperature integral for the inversion of Carya translucency. The former involves β, a linear heat-flux coefficient to be determined, while the latter involves two previously unknown constants: TC, a critical temperature, below which the translucency is stable (no carbonization), and TD, a scaling constant, roughly analogous to a doubling temperature. TD and Tc are chemical constants, and should be consistent in the three wells, while β should be consistent when determined independently by vitrinite reflectance and Carya translucency inversions. Grid searches for an acceptable solution in TC vs. TD vs. βspace were carried out for each of the three wells to determine the best TD TC and β for each well. A goodness-of-fit criterion, contoured in TD vs. TC vs. βspace, defines a volume of solutions within fixed error limits. Estimates of TD= 75 ± 30°K and TC= 290 + 20°K, for the genus Carya, are consistent for all of the wells. Acceptable β ranges, determined by the Carya inversion, overlap for the neighbouring wells. and the ranges are also consistent with β determined by the independent inversion of vitrinite reflectance in one of the wells.
We conclude that Carya translucency can be used as a quantitative thermal indicator. Application of the inverse method to translucency measurements on other palynomorphs having longer. or different, age ranges than the Eocene-Recent lifetime for Carya is recommended.