Fossils in Thin Section: It is Not That Difficult

Flügel, Erik

doi:10.1007/978-3-662-08726-8_10

Cited by 5 publications

(2 citation statements)

References 97 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…sp. Dasycladaleans are preserved either as carbonaceous compressions or as calcified body fossils if, when alive, they have precipitated aragonite in the mucilage outside of the cell wall 9,18 . These mineral skeletons are essentially an external mould of the thalli (Fig.…”

Section: Comparisons Among New Fossils Protomelission? Sp Archaeocyat...mentioning

confidence: 99%

Not dasycladalean alga, but an Odyssey of the earliest Phanerozoic animal reef-builders

Yang,

Luo,

Han

et al. 2023

Preprint

View full text Add to dashboard Cite

The compacted macrofossilProtomelission? sp. from the early Cambrian Xiaoshiba Lagerstätte was recently ascribed to early dasycladalean green algae and used to disprove the bryozoan affinity of coeval phosphatized microfossils, which made the puzzling question whether the bryozoans originated in early Cambrian pending again. Our new analyses of multiple specimens which are conspecific withProtomelission? from the Chengjiang Lagerstätte indicate that they are not dasycladaleans but one of the three groups of archaeocyath-like sponges that atypically inhabited siliciclastic substrates. All the archaeocyath-like fossils share the same preservation mode and exhibit archaeocyath-type external skeletal features. Particularly, theProtomellision?-like fossils preserve structures indicative of archaeocyath aquiferous system and ontogeny. They represent the first recognized one-walled archaeocyath sponges in South China and evidence the niche expansion of archaeocyaths on their way of global radiation from Siberia, 518 million years ago. The origin of the bryozoans remains a mystery.

show abstract

Section: Comparisons Among New Fossils Protomelission? Sp Archaeocyat...mentioning

confidence: 99%

Not dasycladalean alga, but an Odyssey of the earliest Phanerozoic animal reef-builders

Yang,

Luo,

Han

et al. 2023

Preprint

View full text Add to dashboard Cite

show abstract

“…The microfacies were categorized using Dunham classification to identify the grain size, cement type, and matrices. Semi-quantitative data regarding carbonate constituents in the percentages were calculated using visual estimation charts developed by Baccelle and Bosellini [56,57]. The examination revealed highly biomineralized by-products indicative of a shallow marine environment, including fossils fragments, carbonate sediments, and surrounding cement The petrography and microfacies analyses of thin sections illuminated the key diagenetic features and microstructure present in the examined microfacies.…”

Section: Microfacies Analysis and Petrographic Descriptionmentioning

confidence: 99%

Unveiling the Diagenetic and Mineralogical Impact on the Carbonate Formation of the Indus Basin, Pakistan: Implications for Reservoir Characterization and Quality Assessment

Memon,

Tunio,

Memon

et al. 2023

Minerals

View full text Add to dashboard Cite

The Chiltan formation is a potential hydrocarbon-producing reservoir in the Indus Basin, Pakistan. However, its diagenetic alterations and heterogeneous behavior lead to significant challenges in accurately characterizing the reservoir and production performance. This manuscript aims to utilize six carbonate core samples of the Chiltan limestone to conduct an in-depth analysis of the diagenetic impacts on reservoir quality. The comprehensive formation evaluation was carried out through thin-section analysis, SEM-EDS, and FTIR investigation, as well as plug porosity and permeability measurements under varying stress conditions. In result, petrography revealed three microfacies of intraclastic packestone (MF1), bioclastic pelliodal packestone (MF2), and bioclastic ooidal grainstone (MF3), with distinct diagenetic features and micro-nano fossil assemblages. The MF1 microfacies consist of bioclasts, ooids, pellets, and induced calcite, while the MF2 microfacies contain micrite cemented peloids, algae, and gastropods. Although, the MF3 grainstone microfacies contains key features of bioclasts, milliods, bivalves, echinoderms, and branchiopods with intense micritization. Diagenesis has a significant impact on petrophysical properties, leading to increased reservoir heterogeneity. The specified depositional environment exposed the alteration of the Chiltan formation during distinct diagenetic phases in marine, meteoric, and burial settings. Marine diagenesis involves biogenic carbonates and micro-nano fossils, while meteoric diagenesis involves mineral dissolution, reprecipitation, secondary porosity, compaction, cementation, and stylolite formation. Pore morphology and mineralogy reveal a complex pore network within the formation, including a micro-nano pore structure, inter–intra particle, moldic, vuggy, and fenestral pores with variations in shape, connectivity, and distribution. Various carbonate mineral phases in the formation samples were analyzed, including the calcite matrix and dolomite crystals, while silica, calcite, and clay minerals were commonly observed cement types in the analysis. The core samples analyzed showed poor reservoir quality, with porosity values ranging from 2.02% to 5.31% and permeability values from 0.264 mD to 0.732 mD, with a standard deviation of 1.21. Stress sensitivity was determined using Klinkenberg-corrected permeability at increasing pore pressure conditions, which indicated around 22%–25% reduction in the measured gas permeability and 7% in Klinkenberg permeability due to increasing the net confining stress. In conclusion, the Chiltan formation possesses intricate reservoir heterogeneity and varied micropore structures caused by diagenesis and depositional settings. The formation exhibits nonuniform pore geometry and low petrophysical properties caused by the diverse depositional environment and various minerals and cement types that result in a low-quality reservoir. Stress sensitivity further decreases the permeability with varying stress levels, emphasizing the need of stress effects in reservoir management. The results of this study provide a solid foundation in reservoir characterization and quality assessment that has implications for predicting fluid flow behavior, providing insight into geological evolution and its impact on reservoir quality and leading to improving resource exploration and production strategies.

show abstract