scholarly journals SEM petrography of dispersed organic matter in black shales: A review

2021 ◽  
pp. 103874
Author(s):  
Bei Liu ◽  
Maria Mastalerz ◽  
Juergen Schieber
Keyword(s):  
Organic Matter ◽  
Black Shales

Molecular and petrographical evidence for lacustrine environmental and biotic change in the palaeo-Sichuan mega-lake (China) during the Toarcian Oceanic Anoxic Event

2021 ◽  
pp. SP514-2021-2
Author(s):  
Weimu Xu ◽  
Johan W. H. Weijers ◽  
Micha Ruhl ◽  
Erdem F. Idiz ◽  
Hugh C. Jenkyns ◽  
...  
Keyword(s):  
Organic Matter ◽  
Sichuan Basin ◽  
Large Scale ◽  
Algal Growth ◽  
Black Shales ◽  
Content Type ◽  
Oceanic Anoxic Event ◽  
Anoxic Event ◽  
Supplementary Material ◽  
The Sichuan Basin

AbstractThe organic-rich upper Lower Jurassic Da'anzhai Member (Ziliujing Formation) of the Sichuan Basin, China is the first stratigraphically well-constrained lacustrine succession associated with the Toarcian Oceanic Anoxic Event (T-OAE; ∼183 Ma). The formation and/or expansion of the Sichuan mega-lake, likely one of the most extensive fresh-water systems to have existed on the planet, is marked by large-scale lacustrine organic productivity and carbon burial during the T-OAE, possibly due to intensified hydrological cycling and nutrient supply. New molecular biomarker and organic petrographical analyses, combined with bulk organic and inorganic geochemical and palynological data, are presented here, providing insight into aquatic productivity, land-plant biodiversity, and terrestrial ecosystem evolution in continental interiors during the T-OAE. We show that lacustrine algal growth during the T-OAE accounted for a significant organic-matter flux to the lakebed in the palaeo-Sichuan mega-lake. Lacustrine water-column stratification during the T-OAE facilitated the formation of dysoxic-anoxic conditions at the lake bottom, favouring organic-matter preservation and carbon sequestration into organic-rich black shales in the Sichuan Basin. We attribute the palaeo-Sichuan mega-lake expansion to enhanced hydrological cycling in a more vigorous monsoonal climate in the hinterland during the T-OAE greenhouse.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5433544

scholarly journals Sandstone-Hosted Uranium Deposits as a Possible Source for Critical Elements: The Eureka Mine Case, Castell-Estaó, Catalonia

Minerals ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 34 ◽  
Author(s):  
Montgarri Castillo-Oliver ◽  
Joan Carles Melgarejo ◽  
Lisard Torró ◽  
Cristina Villanova-de-Benavent ◽  
Marc Campeny ◽  
...  
Keyword(s):  
Organic Matter ◽  
Low Temperature ◽  
Black Shales ◽  
Hydrothermal Fluids ◽  
Uranium Deposits ◽  
Critical Metals ◽  
Fine Grained ◽  
Critical Elements ◽  
By Products ◽  
Red Bed

The Eureka deposit in Castell-estaó in the Catalan Pyrenees is a Cu–U–V deposit, hosted by Triassic red-bed sandstones, and classified here as a low-temperature, sandstone-hosted stratabound metamorphite U deposit. The main mineralisation is stratabound, related to coal-bearing units and produced during the Alpine deformation by migration of hydrothermal fluids. In this stage, the original sedimentary and diagenetic components (quartz and calcite, micas, hematite and locally apatite) were replaced by a complex sequence of roscoelite, fine-grained REE phosphates, sulphides and Ni–Co arsenides and sulpharsenides, Ag–Pb selenides, bismuth phases, sulphosalts and uraninite. The black shales of the Silurian sediments underlying the deposit and the nearby Carboniferous volcanoclastic rocks are interpreted as the source of the redox-sensitive elements concentrated in Eureka. The sulphur source is related to leaching of the evaporitic Keuper facies. The REE transport would be facilitated by SO4-rich solutions. The reduction of these solutions by interaction with organic matter resulted in the widespread precipitation of REE and redox-sensitive elements, including many critical metals (V, Bi, Sb, Co), whereas barite precipitated in the oxidized domains. The occurrence of similar enrichments in critical elements can be expected in other similar large uranium deposits, which could be a source of these elements as by-products.

scholarly journals Mineral compositional controls on the porosity of black shales from the Wufeng and Longmaxi Formations (Southern Sichuan Basin and its surroundings) and insights into shale diagenesis

2018 ◽  
Vol 36 (4) ◽  
pp. 665-685
Author(s):  
Mei Han ◽  
Chao Han ◽  
Zuozhen Han ◽  
Zhigang Song ◽  
Wenjian Zhong ◽  
...  
Keyword(s):  
Organic Matter ◽  
Pore Size ◽  
Pore Volume ◽  
Total Pore Volume ◽  
Black Shales ◽  
Carbonate Content ◽  
Pore Sizes ◽  
Pore Size Distributions ◽  
Shale Composition ◽  
The Relationship

The effects of brittle minerals in shale diagenesis on shale pores remain controversial and it is difficult to quantify directly. However, the relationship between brittle minerals and shale pores could provide indirect guidance regarding diagenesis processes in post-mature marine shales. In this study, the pore size distribution was determined, and the relationship between pore volume and shale composition was examined in shale samples with different total organic carbon contents from the Wufeng and Longmaxi Formations, with the objective of distinguishing pore size ranges in organic matter and inorganic minerals, respectively, and studying shale diagenesis. The samples of the Wufeng and Longmaxi shales are composed of clay minerals, calcite, dolomite, quartz, feldspar, and some minor components. The pore size distributions, which were determined using nitrogen adsorption isotherm analysis of shale and kerogen, show similar trends for pore sizes less than approx. 6.5 nm but different trends for larger pore sizes. Mercury injection saturation shows that macropores account for 14.4–22% of the total pore volume. Based on a series of crossplots describing the relationships between shale composition and pore volume or porosity associated with different pore sizes as well as on scanning electron microscopy observations, organic matter pores were found to comprise most of the micro-mesopores (pore diameters < 6.5 nm). Organic matter pores and intraparticle pores associated with carbonate constitute the majority of mesopores (pore diameters 6.5–50 nm). Finally, interparticle pores associated with quartz comprise the majority of the macropores. The mesopores associated with carbonate were formed by dissolution during diagenesis, whereas the macropores associated with quartz are the remainders of the original interparticle pores. Mesopore volumes increase with increasing carbonate content while macropore volumes decrease due to the ‘pore size controlled solubility’ effect, which causes dissolved calcium carbonate to precipitate in larger macropores.

Pore types, pore-network analysis, and pore quantification of the lacustrine shale-hydrocarbon system in the Late Triassic Yanchang Formation in the southeastern Ordos Basin, China

2017 ◽  
Vol 5 (2) ◽  
pp. SF63-SF79 ◽  
Author(s):  
Robert G. Loucks ◽  
Stephen C. Ruppel ◽  
Xiangzeng Wang ◽  
Lucy Ko ◽  
Sheng Peng ◽  
...  
Keyword(s):  
Organic Matter ◽  
Clay Mineral ◽  
Mineral Content ◽  
Ordos Basin ◽  
Pore Network ◽  
Black Shales ◽  
Late Triassic ◽  
Ductile Material ◽  
Crushed Rock ◽  
Porosity And Permeability

Continental Upper Triassic Yanchang “black shales” in the southeastern Ordos Basin have been proven to be unconventional gas reservoirs. Organic-matter-lean and organic-matter-rich argillaceous mudstones form reservoirs that were deposited in a deeper water lacustrine setting during lake highstands. In the stratified lake, the bottom waters were dysaerobic to anoxic. This low-energy and low-oxygen lake-bottom setting allowed types II and III organic matter to accumulate. Interbedded with the argillaceous mudstones are argillaceous arkosic siltstones deposited by gravity-flow processes. Rock samples from the Yanchang Chang 7–9 members are very immature mineralogically. Mineral grains are predominantly composed of relatively equal portions of quartz and feldspar. The high clay-mineral content, generally greater than 40%, has promoted extensive compaction of the sediments, permitting the ductile material to deform and occlude interparticle pores. Furthermore, this high clay-mineral content does not favor hydraulic fracturing of the mudstone reservoir. The pore network within the mudstones is dominated by intraparticle pores and a lesser abundance of organic-matter pores. Interparticle pores are rare. The mean Gas Research Institute (GRI) crushed-rock porosity is 4.2%. Because the pore network is dominated by poorly connected intraparticle pores, permeability is very low (the GRI-calculated geometric mean permeability = 9.9 nd). The dominance of intraparticle pores creates a very poor correlation between GRI porosity and GRI permeability. Several methods of porosity analysis (GRI crushed rock, nitrogen adsorption, and point count) were conducted on each samples, and the results were compared. There is no significant correlation between the three methods, implying that each method measures different pore sizes or types. There is also no relationship between the porosity and permeability and total organic carbon. Much of the mature (peak oil window) organic matter is nonporous, suggesting that it is of type III. Most of the organic-matter pores are in migrated solid bitumen. Overall, the samples analyzed have low porosity and permeability for mudrocks.

Coexistence of pyrophyllite, I-S, R1 and NH4+-rich illite in Silurian black shales (Sierra de Albarracín, NE Spain): metamorphic vs. hydrothermal origin

Clay Minerals ◽  
2010 ◽  
Vol 45 (3) ◽  
pp. 383-392 ◽  
Author(s):  
B. Bauluz ◽  
I. Subías
Keyword(s):  
Organic Matter ◽  
Clay Mineral ◽  
Hydrothermal Alteration ◽  
Black Shales ◽  
Low Grade ◽  
Lower Silurian ◽  
Igneous Activity ◽  
Upper Silurian ◽  
Ne Spain ◽  
Regional Tectonics

AbstractA set of Silurian black shales from Sierra de Albarracín (NE Spain) corresponding to two different sections was studied to determine the relative influence of diagenesis, igneous activity, and regional tectonics on the clay-mineral genesis. The coexistence of pyrophyllite, I-S interstratifications (R1), ammonium-rich illite, potassium illite, kaolin, and chlorite is not the result of prograde evolution during diagenesis – very low-grade metamorphism. Three different stages may be inferred: (1) sedimentation of black shales (Aeronian, Lower Silurian, to basal Ludfordian, Upper Silurian) and the subsequent diagenetic process producing the coexistence of quartz, illite, kaolinite, organic matter, etc.; (2) intrusion of andesitic sills producing hydrothermal alteration and crystallization of pyrophyllite, ammonium-rich illites, smectite, I-S R1 phases and jarosite; and (3) and folding of shales and sills and development of penetrative schistosity during the late Variscan leading to illite and paragonite recrystallization reaching the anchizone grade.

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