The taphonomic fate of isorenieratene in Lower Jurassic shales—controlled by iron?

Abstract

Fossil derivatives of isorenieratene, an accessory pigment in brown-colored green sulfur bacteria, are often used as tracers for photic zone anoxia through Earth's history, but their diagenetic behavior is still incompletely understood. Here, we assess the preservation of isorenieratene derivatives in organic-rich shales (1.5-8.4 wt.% TOC) from two Lower Jurassic anoxic systems (Bächental oil shale, Tyrol, Austria; Posidonia Shale, Baden-Württemberg, Germany). Bitumens and kerogens were investigated using catalytic hydropyrolysis (HyPy), closed-system hydrous pyrolysis (in gold capsules), gas chromatography-mass spectrometry (GC-MS) and gas chromatography combustion isotope ratio-mass spectrometry (GC-C-IRMS). Petrography and biomarkers indicate a syngenetic relationship between bitumens and kerogens. All bitumens contain abundant isorenieratane, diverse complex aromatized isorenieratene derivatives, and a pseudohomologous series of 2,3,6-trimethyl aryl isoprenoids. In contrast, HyPy and mild closed-system hydrous pyrolysis of the kerogens yielded only minor amounts of these compounds. Given the overall low maturity of the organic matter (below oil window), it appears that isorenieratene and its abundant derivatives from the bitumen had not been incorporated into the kerogens. Accordingly, sulfur cross-linking, the key mechanism for sequestration of functionalized lipids into kerogens in anoxic systems, was not effective in the Jurassic environments studied. We explain this by (i) early cyclization/aromatization and (ii) hydrogenation reactions that have prevented effective sulfurization. In addition, (iii) sulfide was locally removed via anoxygenic photosynthesis and efficiently trapped by the reaction with sedimentary iron, as further indicated by elevated iron contents (4.0-8.7 wt.%) and the presence of abundant pyrite aggregates in the rock matrix. Although the combined processes have hampered the kerogen incorporation of isorenieratene and its derivatives, they may have promoted the long-term preservation of these biomarkers in the bitumen fraction via early defunctionalization. This particular taphonomy of aromatic carotenoids has to be considered in studies of anoxic iron-rich environments (e.g., the Proterozoic ocean).

Multi-spectroscopic and elemental characterization of southern Australian asphaltites

“…S11) produced substantially greater ratios implying a higher Rc of 0.89 %. A similar differential was reported by Reinhardt et al (2018) between kerogen hydropyrolysates and maltene fractions. A slight opposite trend was observed for the ratios of DBT/MDBT (Fig.…”

“…isorenieratane and other aryl isoprenoids -were observed in GC×GC-TOFMS chromatograms of the aromatic fraction of the asphaltite maltenes but isorenieratane was not observed in the hydropyrolysates. Reinhardt et al (2018) observed that, in their study of Lower Jurassic shales, although isorenieratane was present in all the bitumens analysed, it was not present in the corresponding kerogen hydropyrolysates.…”

Molecular fossils within bitumens and kerogens from the ~ 1 Ga Lakhanda Lagerstätte (Siberia, Russia) and their significance for understanding early eukaryote evolution

“…Samples were analyzed for sedimentary hydrocarbons using an established methodology (Duda et al 2014a(Duda et al , b, 2016(Duda et al , 2020Reinhardt et al 2018). All laboratory materials used were heated to 500 °C for 3 h and/or extensively rinsed with acetone.…”

Applied techniques for residual oil recovery from source rocks: A review of current challenges and possible developments

“…9.08 1.60 1.32 5.20-25. 30 Reinhardt et al [57] Chlorobenzene 5.50 1.60 1.11 0.05 Bogacki and Zawadzki [58] Diethyl ether 4.40 1.20 0.71 6.90 Douglas et al [50] Dibutyl ether 3.10 1.20 0.77 0.30 Samec et al [59] Dimethyl ether 3.10 1.30 0.78 Miscible Dong et al [60] Ethyl acetate 6.40 1.80 0.90 7. 94 Li et al [61] Methyl isobutyl ketone [62] F I G U R E 3 Schematic diagram of nanoparticles fracturing chemicals penetration within shale nanopores and cavities However, the particles can be deformed and enter deep into the nanopores within the shale formation.…”

“…Hexane 1.98 0 0.66 0.01 DiStefano et al [49] Benzene 2.28 0 0.88 0.08 Douglas et al [50] Acetone 21.10 2.91 0.7845 Miscible Wang et al [51] Cyclohexane 2.02 0 0.78 0.005 Ngnie et al [52] Toluene 2.33 0.31 0.87 0.05 Abourriche et al [53] m-Xylene 2.40 0.40 0.86 0.01 Olaguer et al [54] Chloroform 4.81 1.04 1.49 0.81 Akondi et al [55] Carbon tetrachloride 2.20 0 1.58 0.08 Zhao et al [56] Methylene chloride (DCM) [57] Chlorobenzene 5.50 1.60 1.11 0.05 Bogacki and Zawadzki [58] Diethyl ether 4.40 1.20 0.71 6.90 Douglas et al [50] Dibutyl ether 3.10 1.20 0.77 0.30 Samec et al [59] Dimethyl ether 3.10 1.30 0.78 Miscible Dong et al [60] Ethyl acetate 6.40 1.80 0.90 7. 94 Li et al [61] Methyl isobutyl ketone 13.10 2.69 0.80 1.70 Samec et al [59] Cyclohexane 18.2 2.8 0.95 2.3 Dong et al [62] F I G U R E 3 Schematic diagram of nanoparticles fracturing chemicals penetration within shale nanopores and cavities However, the particles can be deformed and enter deep into the nanopores within the shale formation.…”