Assessing Thermal Maturity through a Multi-Proxy Approach: A Case Study from the Permian Faraghan Formation (Zagros Basin, Southwest Iran)

This study focuses on the thermal maturity of Permian deposits from the Zagros Basin, Southwest Iran, employing both optical methods (Thermal Alteration Index, Palynomorph Darkness Index, Vitrinite Reflectance, UV Fluorescence) and geochemical analyses of organic matter (Rock Eval Pyrolysis and MicroRaman spectroscopy) applied to the Faraghan Formation along two investigated Darreh Yas and Kuh e Faraghan surface sections. Furthermore, an integrated palynofacies and lithofacies analysis was carried out in order to integrate the few studies on the depositional environment. The Faraghan Formation, which is widely distributed in the Zagros area, generally consists of shale intercalated with sandstones and pebble conglomerates in the lower part, followed by a succession of sandstone, siltstone and shaly intercalations and with carbonate levels at the top. The integrated palynofacies and lithofacies data confirm a coastal depositional setting evolving upwards to a shallow marine carbonate environment upwards. Rock Eval Pyrolysis and Vitrinite Reflectance analysis showed that the organic matter from samples of the Darreh Yas and Kuh e Faraghan sections fall in the mature to postmature range with respect to the oil to gas generation window, restricting the thermal maturity range proposed by previous authors. Similar results were obtained with MicroRaman spectroscopy and optical analysis such as Thermal Alteration Index and UV Fluorescence. Palynomorph Darkness Index values were compared with Rock Eval Pyrolysis and vitrinite reflectance values and discussed for the first time in the late stage of oil generation.

Optical (visual) Kerogen assessment of Enugu Shale, Anambra Basin, Southeastern Nigeria: Implications for source rock potential and thermal maturation

Palynological analysis was carried out on Ten (10) samples from outcrops of the Campanian Enugu Formation, a component lithostratigraphic unit of the Anambra Basin, using the acid maceration techniques for recovering acidinsoluble organic-walled microfossils. Two main lithological units were encountered, which include: carbonaceous shale and siltstone. Result from kerogen laboratory examination reveals two (2) main groups of palynofacies association namely; palynofacies (A and B), based on the change in particulate organic matter constituents of organic residue extract. Palynofacies A is characterized by abundant opaques debris with common terrestrial phytoclasts, which occupy the southwestern and northwestern parts of the studied area, whereas palynofacies B dominates in the northeastern part, characterised by abundant phytoclasts followed by frequent opaques debris. Kerogen type III with gas-prone material is suggested for both palynofacies. The examined exine of spore/ pollen grain are pale yellow – yellow, with Thermal Alteration Index TAI of 1+ to 2- and Vitrinite Reflectane (R o) (0.3 % - 0.4 %) in palynofacies A, and yellow – yellow brown, with Thermal Alteration Index TAI of 2- to 2, and Vitrinite Reflectane (R o) of 0.3% - 0.5% in palynofacies B. These revealed source rock that is thermally immature to slightly mature but has potential to generate mainly gas. The kerogen data generated using transmitted light microscopy correlated well with geochemical data obtained using rock-eval pyrolysis method, and this shows the method a reliable tool for assessing petroleum potential in any given sedimentary basins.

New criteria for selecting reliable Thellier-type paleointensity results from the 1960 Kilauea lava flows, Hawaii

Thellier-type paleointensity experiments associated with partial thermal remanent magnetization checks have been widely used to determine paleointensity values from volcanic and archaeological media. However, previous studies have revealed that a substantial portion of paleointensity results with positive checks for historical lava samples largely fails to predict known Earth magnetic field intensity values. To determine the fidelity of paleointensity values, conventional Thellier-type paleointensity experiments were performed on Kilauea lava flows that erupted in 1960. The positive partial thermal remanent magnetization checks for our results range from 30.28 ± 1.38 µT to 52.94 ± 1.89 µT. This strongly indicates that conventional paleointensity checks cannot guarantee the fidelity of paleointensity results, especially when the unblocking temperatures for the newly formed magnetic particles are higher than the treatment temperature. Therefore, in this study, to check for thermal alteration during heating, the temperature dependence of the hysteresis parameter measured at room temperature for the thermally treated samples was also measured. Our new results show that nearly all biased paleointensity values correspond to a ratio of the coercivity of remanence to the magnetic coercivity of > 3 and a chemical alteration index > ~ 10%, which indicates the strong effect of the domain state and thermal alteration on the fidelity of the paleointensity results. Our study provides feasible criteria to further improve the fidelity of paleointensity estimations.

Exogenous copper sulfide in returned asteroid Itokawa regolith grains are likely relicts of prior impacting body

Samples from asteroid 25143 Itokawa returned by the Hayabusa mission have been identified as LL4-6 ordinary chondrite materials and have shown it to be a rubble pile that aggregated after break-up of a parent body. Here we investigate particle RB-CV-0038 from the Itokawa regolith using scanning and transmission electron microscopy and energy dispersive spectroscopy. We identify a cubanite-chalcopyrite-troilite-pyrrhotite assemblage, the phases and structure of which are indicative of low-temperature, aqueous alteration. Cubanite is stable only at temperatures below around 250 °C and has thus far only been identified in CI carbonaceous chondrites and the comet 81P/Wild2 sample suite. Chalcopyrite is also very rare in the meteorite record and is found mostly in R chondrites and some CK chondrites. Because the Itokawa parent body experienced significant thermal alteration with little evidence of low-temperature equilibration or aqueous alteration, we propose that the assemblage we identify is most likely exogenous and represents a component of an impacting body.

Identifying Heated Rocks Through Feldspar Luminescence Analysis (pIRIR290) and a Critical Evaluation of Macroscopic Assessment

Throughout (pre)history, non-flint rocks have been used to structure fireplaces, to retain heat, to boil liquids, and to cook food. Thus far, the identification of heated non-flint rocks in archaeological contexts largely depends on a visual (macroscopic) assessment using criteria thought to be diagnostic for thermal alteration. However, visual identification can be subject to observer bias, and some heat-induced traces can be quite difficult to distinguish from other types of weathering or discolouration. In this paper, we present feldspar luminescence analysis as an independent, objective way to identify heated non-flint rocks and to evaluate the results against the established visual macroscopic method for the identification of such pieces. This is done by submitting manuported rocks with and without inferred macroscopic characteristics of heating, originating from the Last Interglacial, Middle Palaeolithic site Neumark-Nord 2/2 (Germany), to feldspar luminescence analysis (pIRIR290). Results of the feldspar luminescence analysis are compared with the visual assessments. This proof of concept study demonstrates the potential of luminescence analyses as an independent, quantitative method for the identification of heated rocks—and their prehistoric applications like hot-stone cooking, specifically for cases where macroscopic assessment cannot provide reliable determinations.