Effect of sulfate on magnesium incorporation in low-magnesium calcite

2019 ◽  
Vol 265 ◽  
pp. 505-519 ◽  
Author(s):  
Katja E. Goetschl ◽  
Bettina Purgstaller ◽  
Martin Dietzel ◽  
Vasileios Mavromatis
Keyword(s):  
Low Magnesium ◽  
Magnesium Calcite

New constraints on the formation of hydrocarbon-derived low magnesium calcite at brine seeps in the Gulf of Mexico

2020 ◽  
Vol 398 ◽  
pp. 105572 ◽  
Author(s):  
Huiwen Huang ◽  
Xudong Wang ◽  
Shanggui Gong ◽  
Nicola Krake ◽  
Meng Jin ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Low Magnesium ◽  
Magnesium Calcite

Geochemistry and time-series analyses of orbitally forced Upper Cretaceous marl–limestone rhythmites (Lehrte West Syncline, northern Germany)

2005 ◽  
Vol 142 (1) ◽  
pp. 31-55 ◽  
Author(s):  
BIRGIT NIEBUHR
Keyword(s):  
Clay Minerals ◽  
Low Frequency ◽  
Geochemical Data ◽  
Carbonate Content ◽  
Element Geochemistry ◽  
Low Magnesium ◽  
Magnesium Calcite ◽  
High Carbonate ◽  
Time Series Analyses ◽  
End Members

A cyclic marl–limestone succession of Middle–Late Campanian age has been investigated with respect to a Milankovitch-controlled origin of geochemical data. In general, the major element geochemistry of the marl–limestone rhythmites can be explained by a simple two-component mixing model with the end-members calcium carbonate and ‘average shale’-like material. Carbonate content varies from 55 to 90%. Non-carbonate components are clay minerals (illite, smectite) and biogenic silica from sponge spicules, as well as authigenically formed zeolites (strontian heulandite) and quartz. The redox potential suggests oxidizing conditions throughout the section. Trace element and stable isotopic data as well as SEM investigations show that the carbonate mud is mostly composed of low-magnesium calcitic tests of planktic coccolithophorids and calcareous dinoflagellate cysts (calcispheres). Diagenetic overprint results in a decrease of 2% δ18O and an increase in Mn of up to 250 ppm. However, the sediment seems to preserve most of its high Sr content compared to the primary low-magnesium calcite of co-occurring belemnite rostra. The periodicity of geochemical cycles is dominated by 413 ka and weak signals between 51 and 22.5 ka, attributable to orbital forcing. Accumulation rates within these cycles vary between 40 and 50 m/Ma. The resulting cyclic sedimentary sequence is the product of (a) changes in primary production of low-magnesium calcitic biogenic material in surface waters within the long eccentricity and the precession, demonstrated by the CaCO3 content and the Mg/Al, Mn/Al and Sr/Al ratios, and (b) fluctuations in climate and continental weathering, which changed the quality of supplied clay minerals (the illite/smectite ratio), demonstrated by the K/Al ratio. High carbonate productivity correlates with smectite-favouring weathering (semi-arid conditions, conspicuously dry and moist seasonal changes in warmer climates). Ti as the proxy indicator for the detrital terrigenous influx, as well as Rb, Si, Zr and Na, shows only low frequency signals, indicating nearly constant rates of supply throughout the more or less pure pelagic carbonate deposition of the long-lasting third-order Middle–Upper Campanian sedimentary cycle.

The Ultrastructure of Brachiopod Shells - A Mechanically Optimized Material with Hierarchical Architecture

2005 ◽  
Vol 898 ◽  
Author(s):  
Erika Griesshaber ◽  
Klemens Kelm ◽  
Angelika Sehrbrock ◽  
Reinhart Job ◽  
Wolfgang W. Schmahl ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Distribution Pattern ◽  
Vickers Microhardness ◽  
Hierarchical Architecture ◽  
Low Magnesium ◽  
Primary Layer ◽  
Transmission Electron ◽  
Secondary Layer ◽  
Magnesium Calcite ◽  
Oceanographic Conditions

AbstractBrachiopod shells consist of low-magnesium calcite and belong to one of the most intriguing species for studies of marine paleoenvironments, variations in oceanographic conditions and ocean chemistry [6, 7, 11 – 13]. We have investigated the ultrastructure together with nano- and microhardness properties of modern brachiopod shells with transmission electron microscopy (TEM), scanning electron microscopy (SEM), nanoindentation and Vickers microhardness analyses. Brachiopod shells are structured into several layers, a thin, outer, hard, protective primary layer composed of randomly oriented nanocrystalline calcite, which is followed inward towards the soft tissue of the animal by a much softer shell segment (secondary layer) built of long calcite fibres, stacked parallely into blocks. The hardness distribution pattern within the shells is non-uniform and varies on scales as small as a few tens of microns. Our results show that the hardness of this biomaterial is controlled by two predominant features: (1.) The morphological orientation of the calcite fibres (not by the crystallographic orientation of the fibres), and (2.) the amount and distribution pattern of organic material between and within the calcite crystals.

scholarly journals THE HIGH-MAGNESIUM CALCITE ORIGIN OF NUMMULITID FORAMINIFERA AND IMPLICATIONS FOR THE IDENTIFICATION OF CALCITE DIAGENESIS

Palaios ◽  
2020 ◽  
Vol 35 (10) ◽  
pp. 421-431
Author(s):  
LAURA J. COTTON ◽  
DAVID EVANS ◽  
SIMON J. BEAVINGTON-PENNEY
Keyword(s):  
Magnesium Content ◽  
Carbonate Diagenesis ◽  
X Ray Diffraction ◽  
Larger Benthic Foraminifera ◽  
X Ray ◽  
Low Magnesium ◽  
Fossil Material ◽  
Magnesium Calcite ◽  
High Magnesium Calcite ◽  
Geochemical Studies

ABSTRACT Nummulites were one of the most abundant and widespread larger benthic foraminifera of the Paleogene, however, confusion remains within the literature as to whether their original test mineralogy was high or low magnesium calcite. As the number of studies using proxies based on Nummulites and related nummulitid geochemistry increase, it is essential to have a firm understanding of test composition to assess preservation within potential samples, and to interpret results. Here we employ a combination of X-ray diffraction, Fourier transform infra-red spectroscopy, and laser ablation ICPMS to determine magnesium content across exceptionally preserved and poorly preserved fossil material as well as modern examples of nummulitids—showing conclusively a primary intermediate to high magnesium calcite composition. This composition appears to be closely related to fluctuating ocean chemistry through the Paleogene. Using these results as an indicator of preservation we examine variation in trace element data across a suite of samples, and introduce the concept of the preservagram, a method of quickly visualizing different styles of carbonate diagenesis. Understanding the original mineralogy of nummulitids and, therefore, the extent to which specimens have been diagenetically altered, is essential as larger foraminifera are increasingly used in geochemical studies.

A precise and accurate method for the quantitative determination of carbonate minerals by X-Ray diffraction using a spiking technique

1971 ◽  
Vol 38 (296) ◽  
pp. 481-487 ◽  
Author(s):  
H. A. Gunatilaka ◽  
Roger Till
Keyword(s):  
Diffraction Method ◽  
Accurate Method ◽  
X Ray Diffraction ◽  
Carbonate Minerals ◽  
X Ray ◽  
Low Magnesium ◽  
Coefficients Of Variation ◽  
Magnesium Calcite ◽  
Peak Areas ◽  
High Magnesium Calcite

SummaryA precise and accurate X-ray diffraction method has been developed whereby the weight percentages of aragonite and low- and high-magnesium calcite are determined from the integrated peak areas of spiked and unspiked samples. The spike mixture was prepared from organisms extracted from the samples to be analysed. Use of a spiking method also avoided the preparation of working curves from artificial mixtures of carbonate minerals, which may not have the same diffraction behaviour as the unknowns. A test of the precision of the method indicates the following coefficients of variation: aragonite, 1·4 %; low-magnesium calcite, 1·5 %; high-magnesium calcite, 7·8 %. A test of the accuracy of the method indicates no significant bias in any of the carbonate results, except in samples where high-magnesium calcite values are below 10 %. Quartz may also be determined by this method (coefficient of variation 23·9 %; positive bias in values greater than 10 %).

Biocrystallization models and skeletal structure of Phanerozoic corals

1996 ◽  
Vol 1 ◽  
pp. 159-185 ◽  
Author(s):  
James E. Sorauf
Keyword(s):  
Crystal Growth ◽  
Organic Matrix ◽  
Structural Motif ◽  
Skeletal Structure ◽  
Low Magnesium ◽  
Stony Corals ◽  
Fossil Corals ◽  
Magnesium Calcite ◽  
Matrix Control ◽  
Diagenetic History

Modern understanding of skeletal microstructure in fossil corals builds on knowledge of structure and biomineralization in modern corals and diagenesis of carbonate skeletons. It is agreed that the skeleton of living stony corals, the Scleractinia, is made of fibrous aragonite, with growth of biocrystals generally according to rules of crystal growth as observed in inorganic aragonite, but here controlled by organic matrix. Fossil scleractinians all apparently fit the same model of biomineralization seen in living corals, although some early taxa (Triassic) lack septal trabeculae, rod-like framework structures typical of all living and most fossil septate corals.Paleozoic corals, both septate Rugosa and non-septate Tabulata, had a skeleton of calcite, most likely low-magnesium calcite, thus had diagenetic histories differing considerably from the aragonitic Scleractinia. Agreement is lacking as to whether a single structural motif can be defined for the calcitic corals, that is, whether the Rugosa and Tabulata originally had a calcitic skeleton built of fibrous biocrystals, analogous to the scleractinians, or whether some others originally had a non-fibrous, lamellar skeletal microstructure. The disagreement hinges on whether both of these basic configurations are biogenic, or whether the latter is sometimes or always diagenetic in origin. The presence of matrix control over biomineralization in Rugosa and Tabulata is yet to be proven, but will play an important role in models for biocrystallization in these older cnidarians. Details of diagenetic history and modification of structures in these calcitic corals likewise warrant investigation to improve our ability to interpret the Paleozoic corals.

Multi-proxy study of cannon-ball concretions with glendonites from Paleogene-Neogene sediments of Sakhalin Island: implication for concretion growth and ikaite-calcite trans-formation

2020 ◽  
Author(s):  
Kseniia Vasileva ◽  
Victoria Ershova ◽  
Oleg Vereshchagin ◽  
Mikhail Rogov ◽  
Marianna Tuchkova ◽  
...  
Keyword(s):  
Organic Matter ◽  
Pore Space ◽  
Sakhalin Island ◽  
Burial Diagenesis ◽  
Geochemical Environment ◽  
Low Magnesium ◽  
Carbonate Concretions ◽  
Sediment Formation ◽  
Magnesium Calcite ◽  
High Magnesium Calcite

<p>The objects of the current study are glendonite pseudomorphs forming the central part of cannon-ball carbonate concretions found within Miocene terrigeneous sediments of Sakhalin island (easternmost part of Russia). Twelve samples of glendonites and host carbonate concretions were examined using optical and cathodoluminescence microscopy, EDX analysis, powder X-ray diffraction and isotopic analysis. The aim of the study is to determine the origin of the concretions and the relationships between the concretion and glendonite occurrence.</p><p>Glendonites and host cannon-ball concretions were found within terrigeneous sediments of Bora (Lower Miocene) and Vengeri (Upper Miocene) formations. These formations are composed of laminated sandstones, siltstones, argillites and siliceous rocks. Dropstones are often found within these sediments as well as cannon-ball carbonate concretions, some of them with glendonites in central part. 60-90% of the cannon-ball concretion is occupied by sandy limestone (with high-magnesium calcite) and occasionally contains dolomite and pyrite. Central part of the cannon-ball concretion is occupied by glendonite (single crystal-like or star-like cluster of crystals). Glendonites are composed of several calcite generations. Rosette-like calcite crystals (“ikaite-derived calcite”) are composed of low-magnesium calcite, they are non-luminescent. Needle-like calcite cement is composed of high-magnesium calcite or dolomite and show bright-yellow cathodoluminescence. The rest of the glendonite is occupied with low-magnesium radiaxial fibrous or sparry calcite with dark-red cathodoluminescence.</p><p>Isotopic ratios of glendonites are close to those of host concretions. For host concretions δ<sup>13</sup>С varies from -20.3 to -14.9 ‰PDB, δ<sup>18</sup>О varies from +1.7 to +2.7 ‰PDB; for glendonites δ<sup>13</sup>С varies from -18.1 to -1.9 ‰PDB, while δ<sup>18</sup>О varies from +0.7 to +3.4 ‰PDB.</p><p>Close mineralogical and isotopic composition of the studied glendonites and host cannon-ball concretions suggest they were formed in similar geochemical environment. Association of glendonite occurrence along with dropstones is an indicator of cold conditions, which is well-corresponding with view on glendonites as a proxy for cooling events. Cementation of surrounding sediment (formation of the cannon-ball concretions) and glendonite formation was simultaneous and occurred during early diagenesis in the sulfate-reduction zone. The source of calcium and magnesium ions was seawater (δ<sup>18</sup>О values are characteristic for seawater). Ikaite was replaced with low-magnesium calcite; the replacement was favored by organic matter decay (δ<sup>13</sup>C values are characteristic for organic matter). Cementation of the cannon-ball concretion with high-magnesium calcite occurred together with needle-like high-magnesium calcite growth in the glendonite with increasing concentration of magnesium due to calcite extraction from the pore water. The remaining pore space was subsequently filled with radiaxial fibrous or blocky sparry calcite during burial diagenesis.</p><p>The study is supported by RFBR, project number 20-35-70012.</p>

Skeletal Low-Magnesium Calcite in Living Scleractinian Corals

Science ◽  
1975 ◽  
Vol 189 (4207) ◽  
pp. 997-999 ◽  
Author(s):  
J. E. Houck ◽  
R. W. Buddemeier ◽  
K. E. Chave
Keyword(s):  
Scleractinian Corals ◽  
Low Magnesium ◽  
Magnesium Calcite

scholarly journals Strontium and Barium in the Triassic Limestone of the Opole Silesia Deposits

2016 ◽  
Vol 61 (1) ◽  
pp. 29-46 ◽  
Author(s):  
Katarzyna Stanienda
Keyword(s):  
Carbonate Rock ◽  
Chemical Elements ◽  
Raw Material ◽  
Calcite Crystal ◽  
Carbonate Phase ◽  
Rock Samples ◽  
Low Magnesium ◽  
Magnesium Calcite ◽  
Carbonate Material ◽  
Lower Muschelkalk

Abstract This article presents the results of studies of strontium and barium content in Triassic (Muschelkalk) carbonate rock samples taken from the area of the Polish part of the Germanic Basin (the area of Opole Silesia). Sr and Ba were determined in the rocks of all formations of the Lower Muschelkalk - Gogolin Beds, Górażdże Beds, Dziewkowice (Terebratula) Beds and Karchowice Beds. Strontium and barium are chemical elements characteristic for aragonite carbonate phase. Aragonite is unstable calcium carbonate phase which is transformed such as high-Mg calcite into low magnesium calcite during diagenesis. So as Sr and Ba indicate the presence of aragonite in the primary carbonate material. Now these elements concentrate in low-Mg calcite crystal structure. The Triassic rocks of Lower Muschelkalk which are mined in different quarries of the Opole Silesia area are mainly built of low-Mg calcite with lower amounts of high-Mg calcite, protodolomite, ordered dolomite and huntite. There are smaller addition of non-carbonate minerals - quartz, chalcedony, muscovite, feldspars and iron minerals. The presence of Sr and Ba now bound in a structure of low-Mg calcite will indicate the occurrence of aragonite in the primary carbonate material. The Triassic rocks from the area of Opole Silesia were studied to determine the rocks enriched in Sr and Ba. Selected rock samples were examined using ICP AES spectrometry, XRF analysis and microprobe measurements. The results of studies show that strontium and barium occur in rocks of all Lower Muschelkalk formations. The lowest contents of these elements were determined in rocks of Gogolin Beds, higher - in rocks of other formations. The results of studies show that Sr and Ba concentrate in low-Mg calcite which dominates in Lower Muschelkalk rocks. Limestone built mainly of low-Mg calcite or “pure” calcite without substitution of other elements, especially Mg, Fe, Si and Al could be applied in lime industry or in other branches of industry, where pure quality raw material, without substitutions is needed.

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