scholarly journals Regional geochemical variations in a metamorphosed black shale: a reconnaissance study of the Silurian Smalls Falls Formation, Maine, USA

2020 ◽  
Vol 56 ◽  
pp. 231-255
Author(s):  
John F. Slack ◽  
M.R. Van Baalen ◽  
Douglas N. Reusch
Keyword(s):  
Organic Matter ◽  
Black Shale ◽  
Nutrient Loading ◽  
Regional Metamorphism ◽  
Enrichment Factors ◽  
Geochemical Data ◽  
The Black Sea ◽  
Three Samples ◽  
Geochemical Study ◽  
Geochemical Variations

A reconnaissance geochemical study of 21 samples of sulphidic black phyllite and schist from the Silurian Smalls Falls Formation in Maine was undertaken in order to evaluate compositional changes during regional metamorphism. These samples represent variably metamorphosed black shale. Analyzed samples come from the chlorite zone in northern Maine and the biotite, garnet, and staurolite-andalusite zones in west-central Maine. Strata of the Smalls Falls Formation are distinctive in containing abundant pyrite and/or pyrrhotite (total S = 1.2–9.7 wt%), but only minor organic matter or graphite (TOC = 0.43–1.85 wt%); TOC/S ratios are uniformly low (average = 0.37 ± 0.22). Median enrichment factors were calculated for each element by normalizing the concentration to Ti in each sample to the Ti-normalized median composition of global black shale. In the chlorite zone, moderate to large decreases in enrichment factors (-23.1 to -49.8%) are evident for V, Cr, Cu, Ni, Zn, Pb, Sb, and U, attributed here to various factors during sedimentation plus variable element mobility during diagenesis. With increasing metamorphic grade (biotite through staurolite-andalusite zones), systematic small to extreme decreases (-14.5 to -99.0%) were found for Ba, Sb, Au, and U, together with less-systematic moderate to large decreases (-35.4 to -61.1%) for V and As. Molybdenum shows an extreme decrease (-94.7%) from the garnet to staurolite-andalusite zones. Excluding Ba, these results are interpreted to mainly reflect mobility of trace elements during pyrite recrystallization, and during the metamorphic transformations of organic matter to graphite and of pyrite to pyrrhotite. Moderate to large increases for Rb (+28.1 to +61.5%) and Th (+39.1 to +47.3%) from the biotite to staurolite-andalusite zones likely record the introduction of alkalis and mass loss, respectively, during metamorphism. Three samples from one site in the garnet zone differ in having anomalously high Fe/Al and low La/Yb ratios, attributed here to epigenetic formation of pyrite and related leaching of light rare earth elements during syn-metamorphic, channelized fluid flow.Geologic and geochemical data indicate that strata of the Smalls Falls Formation were deposited during an interval of anoxia on the northwestern flank of the Central Maine Basin, for which detrital sources included an evolved continental arc. Onset of anoxia coincided with deposition of the Mayflower Hill Formation of the Vassalboro Group, on the basin’s southeastern flank, related to emergence of the Brunswick subduction complex. We suggest that this emergence played a role in promoting both lateral and vertical circulation changes, nutrient loading, and deoxygenation through subsequent basin closure that culminated with Acadian deformation and metamorphism. Based on the relatively high contents of total sulphur present in our Smalls Falls samples, sediments in the Black Sea represent the only known plausible candidate among those in modern suboxic to euxinic basins.

scholarly journals Elemental Geochemical Characterization of Sedimentary Conditions and Organic Matter Enrichment for Lower Cambrian Shale Formations in Northern Guizhou, South China

Minerals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 793
Author(s):  
Shuangbiao Han ◽  
Yuanlong Zhang ◽  
Jie Huang ◽  
Yurun Rui ◽  
Zhiyuan Tang
Keyword(s):  
Organic Matter ◽  
Deposition Rate ◽  
Black Shale ◽  
South China ◽  
Shale Gas ◽  
Geochemical Data ◽  
Shale Formations ◽  
Average Value ◽  
Geochemical Elements ◽  
Niutitang Formation

The black shale deposited in the Niutitang Formation and its adjacent strata is considered to be a favorable source rock in northern Guizhou of south China and has become a target horizon for shale gas exploration in recent years. Based on SQ-1 and CY-1 core samples, the organic matter properties and geochemical elements were obtained through experimental analysis. Provenance, paleoredox, paleoclimate, paleoproductivity and deposition conditions were analyzed, and the sedimentary effects on organic matter enrichment were discussed. The results show that total organic carbon (TOC) is between 0.22–10.10 wt.% in SQ-1, with an average of 2.60 wt.%, and TOC is between 0.23–7.7 wt.% in CY-1, with an average of 1.45 wt.%. The geochemical data of the samples indicate that the black shale of the Niutitang Formation and adjacent strata are deposited in the tectonic background of the passive continental margin. The provenance shows moderate weathering, with hot and humid paleoenvironmental characteristics and fast deposition rate. Using multiple ancient redox indicators, it is concluded that the formation has undergone changes in the oxidizing environment and anaerobic environment during deposition. According to the (La/Yb)N value (the average value of SQ-1 is 1.23 and the average value of CY-1 is 1.26), it shows a faster deposition rate of the two wells and shortens the residence time of organic matter in the microbial degradation zone. The Babio indicates that the bottom has a high paleoproductivity when deposited. Considering the influencing factors, the paleoproductivity mainly controls the organic matter enrichment, followed by ancient redox conditions and the deposition rate. The research results provide a reference for deepening sedimentary understanding and shale gas exploration in the study area.

scholarly journals Pyro-expanded black slate in sculptural art

Cerâmica ◽  
2013 ◽  
Vol 59 (349) ◽  
pp. 134-140
Author(s):  
J. C. e Costa ◽  
T. Almeida ◽  
C. S. F. Gomes
Keyword(s):  
Organic Matter ◽  
Firing Rate ◽  
Black Shale ◽  
Functional Relationship ◽  
Regional Metamorphism ◽  
Science Research ◽  
Low Grade ◽  
New Techniques ◽  
Fine Grained ◽  
Black Slate

Black slate transformed through a pyroplastic process named pyro-expansion or exfoliation has been explored in the present work in order to be used as sculptural material. Black slate is a highly fissile, fine grained and organic matter rich rock that is the product of the action of low-grade regional metamorphism on black shale (a sedimentary clay and organic matter rich, also fissile and fine grained rock). Black slate if fired at an adequate firing rate up to the temperature range 1000 ºC-1240 ºC shows great potential for the manufacture of sculptural pieces. The technical possibilities of the shaping or conformation of pyro-expanded black slate have also been studied, including the reactions that take place when two different black slate pieces are closely associated with each other, or when black slate pieces are closely associated to other materials, such as metals and ceramics. These interactions, while associating different materials that react with each other, emphasize the unique characteristics of new sculptural compositions increasing the plastic capacities of the pyro-expanded black slate. Some examples of the associations referred to will be shown, which highlight the close functional relationship between art and science; research involves the approach to new techniques and materials, looking at the development of unique plastic configurations.

scholarly journals Geological solutions concluded by petroleum geochemical data in Western Greece

2013 ◽  
Vol 47 (4) ◽  
pp. 2131
Author(s):  
N. Rigakis ◽  
V. Karakitsios ◽  
F. Marnelis ◽  
Sp. Sotiropoulos
Keyword(s):  
Organic Matter ◽  
Correlation Study ◽  
Petroleum Exploration ◽  
Geochemical Data ◽  
Geochemical Study ◽  
Oil Generation ◽  
Hydrocarbon Sources ◽  
Two Parameters ◽  
Paleogeothermal Gradient ◽  
Western Greece

A detailed petroleum geochemical study has been performed in the previous years in the Western Greece. Several source rock horizons have been identified, the oil window has been calculated for the most significant sub-basins and the oil correlation study has distinguished the different oil groups of the area, generated from different hydrocarbon sources. These results are very significant and useful for the oil exploration. But, further to these, some more geochemical observations can also be very important on solving some geological problems of the area.- A major problem is the deposition and preservation of the organic matter in the Western Greece.- The dolomitization in relation with the oil generation is also an issue.- Another issue is the calculation of the eroded overburden formations thickness.- The Paleogeothermal gradient determination is also very important.The last two parameters are absolutely necessary for organic matter maturity calculations.The study of all the above parameters completes the geochemical study of the Western Greece, and in relation with other geological studies can provide solutions in the petroleum exploration of the area.

scholarly journals Impact of Paleosalinity, Paleoredox, Paleoproductivity/Preservation on the Organic Matter Enrichment in Black Shales from Triassic Turbidites of Semanggol Basin, Peninsular Malaysia

Minerals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 915
Author(s):  
Zulqarnain Sajid ◽  
Mohd Ismail ◽  
Muhammad Zakariah ◽  
Haylay Tsegab ◽  
José Gámez Vintaned ◽  
...  
Keyword(s):  
Organic Matter ◽  
Black Shale ◽  
Distal Part ◽  
Peninsular Malaysia ◽  
Black Shales ◽  
Passive Margin ◽  
Geochemical Data ◽  
Northwestern Part ◽  
Submarine Fan ◽  
Rock Eval

Turbidite-associated black shale of the Semanggol Formation is extensively distributed in the northwestern part of the Western Belt, Peninsular Malaysia. The black shale occurs as a dark grey to black and thick to medium-bedded deposit. It represents the distal part of submarine fan system (outer-fan) overlying interbedded sandstone to shale facies of the mid-fan and conglomeratic pebbly sandstone facies of the inner-fan. Field observations and its widespread occurrence have resulted in the black shale being considered as a potential analog for a source rock in offshore Peninsular Malaysia. The present study includes detailed mineralogical (XRD, SEM, and EDX analysis), inorganic geochemical (major oxides, trace elements TEs, and rare earth elements REEs), and Rock-Eval pyrolysis analyses of the black shale samples, collected from the Gunung Semanggol, Bukit Merah, and Nami areas in northwestern Peninsular Malaysia. The primary focus of this study is to investigate the provenance, paleoredox conditions, paleoclimate, sedimentary rate, paleoproductivity, and upwelling system that would be helpful to understanding the role of these parameters in the enrichment of organic matter (OM) in the black shale. The Rock-Eval analysis shows that the black shale of the Semanggol Formation comprises type-III kerogens, which suggests organic input from a terrestrial source. The black shale also contains mature to postmature organic matter. Based on the mineralogical analysis, the mineral composition of the black shale comprises illite and kaolinite, with abundant traces of quartz and feldspar as well as few traces of titanium and zircon. Inorganic geochemical data designate black shale deposition in a passive margin setting that has experienced moderate to strong weathering, semi-arid to hot arid climate, and moderate sedimentation rate. Ratios of Ni/Co, U/Th, and V/(V+Ni) along with slightly negative to positive Ce* anomalies and UEF-MoEF cross-plot unanimously indicate anoxic/dysoxic water conditions that are suitable for organic matter preservation. Geochemical proxies related to modern upwelling settings (i.e., Cd/Mo, Co vs. Mn) show that the deep marine black shale was strongly influenced by persistent upwelling, a first-order controlling factor for organic matter enrichment in the distal part (outer fan of the submarine fan system) of the Semanggol Basin. However, productivity-controlled upwelling and a high sedimentary rate, as well as high-productivity in oxygen-depleted settings without strong anoxic conditions, has played an essential role in the accumulation of organic matter.

scholarly journals Les Roches Basiques Du Bas-Limousin (Massif Central Français) : Geochimie Et Implications Geodynamiques

2016 ◽  
Vol 12 (35) ◽  
pp. 382
Author(s):  
Jamil Ezzayani ◽  
Hassan El Hadi ◽  
Said Chakiri ◽  
Wafae Nouaim ◽  
Mohamed Allouza ◽  
...  
Keyword(s):  
Rare Earths ◽  
Regional Metamorphism ◽  
Igneous Rocks ◽  
Geochemical Data ◽  
Massif Central ◽  
Geochemical Study ◽  
Basic Rocks

The upper unit gneisses represent most of the Bas - Limousin. It is characterized by the intercalation of basic igneous rocks (metagabbro- and metadolerite). These are affected by regional metamorphism but primary textures are preserved. The aim of this work is to present new geochemical data, which allow characterizing the geochemical nature of these rocks and discussing their geodynamic meaning. Chemical analyzes of the major and traces elements were carried out at “Service commun des sciences de la terre de l’ Université de Nancy I”, rare earths elements were analyzed at CRPG of Nancy. The results of this geochemical study show that these basic rocks are comparable to continental tholeiitic rocks.

Dissolution and recrystallization in modern shelf carbonates: evidence from pore water and solid phase chemistry

1993 ◽  
Vol 344 (1670) ◽  
pp. 27-36 ◽  
Keyword(s):  
Organic Matter ◽  
Pore Water ◽  
Solid Phase ◽  
Chemical Exchange ◽  
Isotope Composition ◽  
Geochemical Data ◽  
Carbonate Sediments ◽  
Pore Waters ◽  
Carbonate Minerals ◽  
Carbonate Production

We present an overview of geochemical data from pore waters and solid phases that clarify earliest diagenetic processes affecting modern, shallow marine carbonate sediments. Acids produced by organic matter decomposition react rapidly with metastable carbonate minerals in pore waters to produce extensive syndepositional dissolution and recrystallization. Stoichiometric relations among pore water solutes suggest that dissolution is related to oxidation of H 2 S which can accumulate in these low-Fe sediments. Sulphide oxidation likely occurs by enhanced diffusion of O 2 mediated by sulphide-oxidizing bacteria which colonize oxic/anoxic interfaces invaginating these intensely bioturbated sediments. Buffering of pore water stable isotopic compositions towards values of bulk sediment and rapid 45 Ca exchange rates during sediment incubations demonstrate that carbonate recrystallization is a significant process. Comparison of average biogenic carbonate production rates with estimated rates of dissolution and recrystallization suggests that over half the gross production is dissolved and/or recrystallized. Thus isotopic and elemental composition of carbonate minerals can experience significant alteration during earliest burial driven by chemical exchange among carbonate minerals and decomposing organic matter. Temporal shifts in palaeo-ocean carbon isotope composition inferred from bulk-rocks may be seriously compromised by facies-dependent differences in dissolution and recrystallization rates.

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