| 1. |
- Luo, Qingyong, et al.
(författare)
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Graptolites as fossil geo-thermometers and source material of hydrocarbons: An overview of four decades of progress
- 2020
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252 .- 1872-6828. ; 200
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Tidskriftsartikel (refereegranskat)abstract
- The thermal maturity of lower Paleozoic graptolite-bearing marine sediments, which host many hydrocarbon deposits worldwide, has long been difficult to determine due to the absence of wood-derived vitrinite particles for conventional vitrinite reflectance. In 1976, graptolite reflectance was introduced as a new indicator for organic maturity of these deposits and has been used since in many regional studies. The majority of these studies, however, were done on a limited sample set and a limited range of thermal maturity, which resulted in a number of controversial views concerning the usefulness of graptolite reflectance as an alternative paleothermal indicator and its correlation with vitrinite reflectance through various proxies. In this paper, we review previous studies and combine those analyses with new data to assess the physical and chemical characteristics of graptolite periderm with increasing thermal maturity. We conclude that graptolite random reflectance (GRor) is a better parameter for the thermal maturity assessment than graptolite maximum reflectance (GRomax) due to the better quality of available data. Combining published data with results of our study of both natural and heat-treated graptolites and vitrinite, we present a new correlation between GRor and equivalent vitrinite reflectance (EqVRo), as EqVRo = 0.99GRor + 0.08. Chemical composition of graptolite periderm is similar to vitrinite; graptolites are mainly kerogen Type II-III, are gas prone and have a substantial hydrocarbon potential. Lower Paleozoic graptolite-bearing organic-rich sediments are important shale gas source rocks and reservoirs globally and make a significant contribution to worldwide petroleum reserves
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| 2. |
- Luo, Q.
(författare)
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Optical characteristics of graptolite-bearing sediments and its implication for thermal maturity assessment
- 2018
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Ingår i: International Journal of Coal Geology. - Amsterdam : Elsevier. - 0166-5162 .- 1872-7840. ; 195, s. 386-401
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Tidskriftsartikel (refereegranskat)abstract
- Graptolite reflectance was thought to be one of the most useful thermal maturity indicators for graptolite bearing sediments, however, the relationship between graptolite reflectance and vitrinite reflectance is not well established. Graptolites, especially in the Wufeng–Longmaxi Formations from the Ordovician to Silurian of South China, have been mistaken for vitrinite-like particles or solid bitumen, which results in inconsistent data on the thermal maturity. In this paper, we have employed optical microscope techniques to describe the detailed optical characteristics of graptolites and solid bitumen in the Wufeng–Longmaxi Formations. Laboratory simulation of maturation was used to determine the relationship between graptolite reflectance and vitrinite reflectance. The organic constituents in the Wufeng–Longmaxi Formations are mainly composed of graptolites and solid bitumen. Granular and non-granular graptolites were observed in the Wufeng–Longmaxi Formations, with nongranular as the most common texture. Solid bitumen can be distinguished from non-granular graptolites by its coarse surface, weaker anisotropy, and lower random reflectance. The combination of non-polarized and polarized light is very helpful to distinguish solid bitumen from graptolite. For comparison, organic material from the early Ordovician Alum Shale Formation of Sweden and Estonia was also studied. The macerals of the Alum shales are mainly composed of lamalginites, mineral-bituminous groundmasses, graptolites, and solid bitumen.The major textures of the graptolites in the Sweden and Estonia sediments are non-granular and granular, respectively.Both non-granular graptolite and vitrinite reflectances display a systematic increase with the increase of heating temperature and time. The granular graptolites in the Estonian sample were gradually changed to nongranular graptolites following laboratory simulated maturation, indicating that granular graptolites can transform into non-granular graptolites with maturation. Solid bitumen in the Wufeng–Longmaxi Formations was derived from the solid residue of kerogen and/or post-oil bitumen. The graptolite random reflectance is a better thermal maturity indicator than graptolite maximum reflectance and is more precise due to the smaller standard deviation. Several equations are proposed to determine the thermal maturity of the graptolite-bearing sediments based on graptolite random reflectance, graptolite maximum reflectance and solid bitumen random reflectance.
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| 3. |
- Sha, Jingeng, et al.
(författare)
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Triassic-Jurassic climate in continental high-latitude Asia was dominated by obliquity-paced variations (Junggar Basin, Urumqi, China)
- 2015
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Ingår i: Proceedings of the National Academy of Sciences. - National Academy of Sciences of the United States of America : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 112:12, s. 3624-3629
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Tidskriftsartikel (refereegranskat)abstract
- Empirical constraints on orbital gravitational solutions for the Solar System can be derived from the Earth's geological record of past climates. Lithologically based paleoclimate data from the thick, coal-bearing, fluvial-lacustrine sequences of the Junggar Basin of Northwestern China (paleolatitude similar to 60 degrees) show that climate variability of the warm and glacier-free high latitudes of the latest Triassic-Early Jurassic (similar to 198-202 Ma) Pangea was strongly paced by obliquity-dominated (similar to 40 ky) orbital cyclicity, based on an age model using the 405-ky cycle of eccentricity. In contrast, coeval low-latitude continental climate was much more strongly paced by climatic precession, with virtually no hint of obliquity. Although this previously unknown obliquity dominance at high latitude is not necessarily unexpected in a high CO2 world, these data deviate substantially from published orbital solutions in period and amplitude for eccentricity cycles greater than 405 ky, consistent with chaotic diffusion of the Solar System. In contrast, there are indications that the Earth-Mars orbital resonance was in today's 2-to-1 ratio of eccentricity to inclination. These empirical data underscore the need for temporally comprehensive, highly reliable data, as well as new gravitational solutions fitting those data.
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| 4. |
- Xu, Yuanyuan, et al.
(författare)
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How similar are the venation and cuticular characters of Glossopteris, Sagenopteris and Anthrophyopsis?
- 2023
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Ingår i: Review of Palaeobotany and Palynology. - : Elsevier. - 0034-6667 .- 1879-0615. ; 316
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Tidskriftsartikel (refereegranskat)abstract
- Venation architectures and cuticular micromorphology of leaf fossils play important roles in higher-level taxonomic segregation, as these characters are broadly fixed within major plant clades. Three common fossil plant taxa are characterized by similar-shaped leaves or leaflets and anastomosing venation to such an extent that examples have commonly been assigned to the wrong taxon in past studies where fragmentary or ill-preserved material is available. We use standardized descriptions of vein cross-connection types and stomatal features to compare and contrast the venation patterns and stomatal architectures of these genera. Our reanalysis of the macro- and micromorphology of Glossopteris, Sagenopteris and Anthrophyopsis leaves reveals important differences that help segregate these taxa even on the basis of incomplete specimens. Anthrophyopsis has distinctive alignments of vein cross-connections in the outer lamina and paracytic stomata consistent with those of Bennettitales. Glossopteris has perigenous and monocyclic—normally stephanocytic to actinocytic—stomata commonly protected in pits or by overarching papillae. Sagenopteris has more consistently evanescent midribs and surficial anomocytic or stephanocytic stomata with weakly modified subsidiary cells. Considering the putatively close relationship of glossopterids (Glossopteris), Caytoniales (Sagenopteris) and Bennettitales (here encompassing Anthrophyopsis) resolved as members of the ‘glossophyte’ clade in some past phylogenetic studies, cuticular features suggest that these groups are not closely related. In addition, anastomosing venation, superficially similar to that of Glossopteris, Sagenopteris and Anthrophyopsis appears to have arisen independently in numerous other plant groups suggesting that this character has ecological or physiological benefits and is strongly prone to homoplasy.
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