Cherts, spiculites, and collapse breccias – Porosity generation in upper Permian reservoir rocks, Gohta discovery, Loppa High, south-western Barents Sea

Matysik, Michał; Stemmerik, Lars; Olaussen, Snorre; Rameil, Niels; Gianotten, Ingrid Piene; Brunstad, Harald

doi:10.1016/j.marpetgeo.2021.105043

Cited by 7 publications

(3 citation statements)

References 28 publications

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“…Confusingly, some foraminifera use sponge spicules to agglutinate their tests (Rützler & Richardson, 1996; Kamenskaya et al ., 2015). Furthermore, some trace fossils in siliceous spiculites are surrounded by brighter rings of densely packed spicules (Matysik et al ., 2018, 2021) that, although in some cases resemble sponges by having a central canal surrounded by a body‐like ring, are interpreted to have been produced due to parapodial sorting of spicules by the trace‐making organism (Goldring et al ., 1991). Such structures need careful examination to be distinguished from sponges.…”

Section: Background Reviewmentioning

confidence: 99%

Keratose sponges in ancient carbonates – A problem of interpretation

et al. 2022

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Reports of diverse vermiform and peloidal structures in Neoproterozoic to Mesozoic open marine to peritidal carbonates include cases interpreted to be keratose sponges. However, living keratose sponges have elaborate, highly elastic skeletons of spongin (a mesoscopic end‐member of a hierarchical assemblage of collagenous structures) lacking spicules, thus have poor preservation potential in contrast to the more easily fossilized spicule‐bearing sponges. Such interpreted fossil keratose sponges comprise diverse layered, network, amalgamated, granular and variegated microfabrics of narrow curved, branching, vesicular–cellular to irregular areas of calcite cement, thought to represent former spongin, embedded in microcrystalline to peloidal carbonate. Interpreted keratose sponges are presented in publications almost entirely in two‐dimensional (thin section) studies, usually displayed normal to bedding, lacking mesoscopic three‐dimensional views in support of a sponge body fossil. For these structures to be keratose sponges critically requires conversion of the spongin skeleton into the calcite cement component, under shallow‐burial conditions and this must have occurred prior to compaction. However, there is no robust petrographic–geochemical evidence that the fine‐grained carbonate component originated from sponge mummification (automicritic body fossils via calcification of structural tissue components) because in the majority of cases the fine‐grained component is homogenous and thus likely to be deposited sediment. Thus, despite numerous studies, verification of fossil keratose sponges is lacking. Although some may be sponges, all can be otherwise explained. Alternatives include: (i) meiofaunal activity; (ii) layered microbial (spongiostromate) accretion; (iii) sedimentary peloidal to clotted micrites; (iv) fluid escape and capture resulting in bird's eye to vuggy porosities; and (v) moulds of siliceous sponge spicules. Uncertainty of keratose sponge identification is fundamental and far‐reaching for understanding: (i) microfacies and diagenesis where they occur; (ii) fossil assemblages; and (iii) wider aspects of origins of animal clades, sponge ecology, evolution and the systemic recovery from mass extinctions. Thus, alternative explanations must be considered.

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Section: Background Reviewmentioning

confidence: 99%

Keratose sponges in ancient carbonates – A problem of interpretation

et al. 2022

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“…Clay type, crystal structure, and pore structure in shale gas reservoirs are altered by diagenesis, leading to a decrease in reservoir porosity and permeability. Hence, the extent of CH 4 adsorption is also controlled by diagenesis, and there are apparent differences in the occurrence of diagenetic processes and their influence on the pore structure of clay minerals. − Specifically, diagenesis results in changes of clay mineral density and porosity caused by mechanical compaction, clay mineral types and pore structure evolution caused by chemical compaction (illitization of smectite), the changes of porosity and pore connectivity caused by cementation, dissolution and recrystallization, etc. − The evolution of pore structure of clay minerals is a complex process. Although previous research has provided some crucial results, the dynamic evolution of clay adsorption capacity at different diagenetic stages, especially the reconstruction of the pore evolution process and evolution model of clay minerals, is not well investigated yet.…”

Section: Introductionmentioning

confidence: 99%

Review of the Effect of Diagenetic Evolution of Shale Reservoir on the Pore Structure and Adsorption Capacity of Clay Minerals

et al. 2022

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This Review summarizes the diagenetic evolution of clay mineral structure and pores in shale gas reservoirs. In the early diagenetic stage and in period A of the middle diagenetic stage, the intergranular and intragranular pores of clay minerals were altered by mechanical and chemical compaction, and V L (Langmuir volume) shows a positive linear correlation with clay content. In period B of the middle diagenetic stage and late diagenetic stage, intergranular pores almost disappeared, clay adsorption capacity significantly decreased, and there was a lack of apparent correlation between V L and clay content. Experimental and molecular simulations of clay adsorption capacity in shale are limited due to several drawbacks. (i) Shale samples in different diagenetic stages were characterized by strong heterogeneity, which affected the reliability of the evolution results of clay adsorption capacity. (ii) The method of selecting clay-rich shale samples, extracting clay minerals from shale, or applying pure clay minerals ignored the difference of diagenetic background, the damage of pores and structure of clay minerals, or the support of brittle minerals to shale pore system. (iii) Molecular simulation mostly employed a simplified plate model or single clay mineral model, which oversimplified the structure and diversity of clay minerals in real shale gas reservoirs. Therefore, innovative experimental simulations on the effect of diagenetic evolution on pore structure and adsorption capacity of clay minerals are necessary, which need to comprehensively weigh the combined effect of time and space on the reservoir diagenetic evolution. Besides, the visualization of shale structure, adsorption process, and CH 4 adsorption behavior of the shale constituents may help our understanding. Furthermore, a more accurate model of the molecular structure of clay minerals is indispensable, especially the dynamic evolution model with different water contents.

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“…The widespread Guadalupian cherts in the Yangtze Block in southern China are considered to be a response to PCE [4,5,[11][12][13][14]. However, the origin of cherts has been associated with biological processes, terrestrial inputs and hydrothermal activity [15][16][17][18][19][20][21]. Furthermore, current studies overwhelmingly believed that the major formation of the Guadalupian cherts in the Upper Yangtze area was related to biosilicification and hydrothermal activity caused by regional tectonic and volcanic activity [4,[22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Origin of the Multiple-Sourced Cherts in Maokou Carbonates in Sichuan Basin, South China

Zheng

Tang

et al. 2021

Minerals

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Cherts have been thought to originate from biosilicification, terrestrial inputs and hydrothermal activity. The study of cherts is helpful in understanding the paleo-ocean environment and tectonic–sedimentary processes. Large amounts of cherts occur widely in the Maokou Formation in the Sichuan Basin, which may be largely connected to the Permian Chert Event (PCE). However, the source of silica and the formation process of cherts remain debated. Here, we analyze the petrographic and geochemical features of the cherts from the Guadalupian Maokou Formation (~268–259 Ma) in six sections in the Sichuan Basin. Two main types of cherts, nodular and bedded, are recognized in the Maokou Formation. The formation of nodular cherts was mainly affected by hydrothermal fluids, whereas the bedded cherts are mainly of biogenetic origin. The Emeishan large igneous province (ELIP) caused the activation of deep faults, accompanied by intense hydrothermal activities. Correspondingly, the cherts of significant hydrothermal origin developed near the active deep faults. The intensified hydrothermal activities may provide extra silica supplies and flourish the silica-secreting organisms by the associated volcanogenic upwellings that facilitated the enrichment of cherts. The study of Maokou cherts can help to record the volcanic- and silicon-related biological activities in the eastern Paleo-Tethys Ocean and can provide significant implications for chert enrichment in analogous settings.

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Cherts, spiculites, and collapse breccias – Porosity generation in upper Permian reservoir rocks, Gohta discovery, Loppa High, south-western Barents Sea

Cited by 7 publications

References 28 publications

Keratose sponges in ancient carbonates – A problem of interpretation

Keratose sponges in ancient carbonates – A problem of interpretation

Review of the Effect of Diagenetic Evolution of Shale Reservoir on the Pore Structure and Adsorption Capacity of Clay Minerals

Origin of the Multiple-Sourced Cherts in Maokou Carbonates in Sichuan Basin, South China

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