Element Patterns of Primary Low-Magnesium Calcite from the Seafloor of the Gulf of Mexico

High-magnesium calcite (HMC) and aragonite are metastable minerals, which tend to convert into low-magnesium calcite (LMC) and dolomite. During this process, primary compositions are frequently altered, resulting in the loss of information regarding the formation environment and the nature of fluids from which the minerals precipitated. Petrological characteristics have been used to recognize primary LMC, however, neither the element distribution within primary LMC nor the effect of diagenetic alteration on element composition have been studied in detail. Here, two mostly authigenic carbonate lithologies from the northern Gulf of Mexico dominated by primary LMC were investigated to distinguish element compositions of primary LMC from LMC resulting from diagenetic alteration. Primary LMC reveals similar or lower Sr/Ca ratios than primary HMC. The lack of covariation between Sr/Ca ratios and Mg/Ca ratios in the studied primary LMCs are unlike compositions observed for LMC resulting from diagenetic alteration. The Sr/Mn ratios and Mn contents of the primary LMCs are negatively correlated, similar to secondary, diagenetic LMC. Element mapping for Sr and Mg in the primary LMC lithologies revealed no evidence of conversion from aragonite or HMC to LMC, and a homogenous distribution of Mn is in accordance with the absence of late diagenetic alteration. Our results confirm that Sr/Ca ratios, Mg/Ca ratios, and element systematics of primary LMC are indeed distinguishable from diagenetically altered carbonates, enabling the utilization of element geochemistry in recognizing primary signals in carbonate archives.

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

Sedimentary Geology ◽

10.1016/j.sedgeo.2019.105572 ◽

2020 ◽

Vol 398 ◽

pp. 105572 ◽

Cited By ~ 2

Author(s):

Huiwen Huang ◽

Xudong Wang ◽

Shanggui Gong ◽

Nicola Krake ◽

Meng Jin ◽

...

Keyword(s):

Gulf Of Mexico ◽

Low Magnesium ◽

Magnesium Calcite

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

Geological Magazine ◽

10.1017/s0016756804009999 ◽

2005 ◽

Vol 142 (1) ◽

pp. 31-55 ◽

Cited By ~ 28

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.

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

Palaios ◽

10.2110/palo.2020.029 ◽

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.

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

Mineralogical Magazine ◽

10.1180/minmag.1971.038.296.10 ◽

1971 ◽

Vol 38 (296) ◽

pp. 481-487 ◽

Cited By ~ 13

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 %).

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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

10.5194/egusphere-egu2020-4041 ◽

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

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.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 (&#8220;ikaite-derived calcite&#8221;) 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.Isotopic ratios of glendonites are close to those of host concretions. For host concretions &#948;13&#1057; varies from -20.3 to -14.9 &#8240;PDB, &#948;18&#1054; varies from +1.7 to +2.7 &#8240;PDB; for glendonites &#948;13&#1057; varies from -18.1 to -1.9 &#8240;PDB, while &#948;18&#1054; varies from +0.7 to +3.4 &#8240;PDB.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 (&#948;18&#1054; values are characteristic for seawater). Ikaite was replaced with low-magnesium calcite; the replacement was favored by organic matter decay (&#948;13C 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.The study is supported by RFBR, project number 20-35-70012.

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Formation of Authigenic Low-Magnesium Calcite from Sites SS296 and GC53 of the Gulf of Mexico

Minerals ◽

10.3390/min9040251 ◽

2019 ◽

Vol 9 (4) ◽

pp. 251 ◽

Cited By ~ 2

Author(s):

Huiwen Huang ◽

Shanggui Gong ◽

Niu Li ◽

Daniel Birgel ◽

Jörn Peckmann ◽

...

Keyword(s):

Gulf Of Mexico ◽

Dissolved Inorganic Carbon ◽

Carbon Sources ◽

Pore Fluids ◽

Pore Waters ◽

Δ13c Values ◽

Low Magnesium ◽

Subsurface Environments ◽

Wide Range ◽

Magnesium Calcite

Authigenic low-magnesium calcite (LMC)—a mineral phase that should precipitate in calcite seas rather than today’s aragonite sea—was recently discovered at the seafloor of the Gulf of Mexico (GoM) at water depths of 65 m (site SS296) and 189 m (site GC53). This study investigates the mineralogical, petrographic, and geochemical characteristics of LMC from both sites to reveal its formation process. The δ18O values of LMC from site SS296 cluster in two groups (−0.6‰ to 1.7‰; 6.3‰ to 7.5‰) and the presence of cone-in-cone texture in the samples with lower δ18O values suggest precipitation at higher temperatures and greater depth. Low δ18O values of LMC from site GC53 ranging from −9.4‰ to −2.5‰ indicate an influence of meteoric waters during formation. LMC at both sites reveals a wide range of δ13C values (−17.4‰ to 2.6‰), indicating various carbon sources including seawater and/or organic matter. This interpretation is further supported by the δ13C values of organic carbon extracted from the LMC lithologies (δ13Corg: from −26.8‰ to −18.9‰). Relatively low Sr concentrations of LMC samples regardless of variable 87Sr/86Sr ratios, ranging from 0.707900 to 0.708498 for site GC53 and from 0.709537 to 0.710537 for site SS396, suggest the exchange of Sr between pore fluids and ambient sediments/rocks. The observed wide range of 87Sr/86Sr ratios and the enrichment of Fe and Mn in LMC is in accordance with pore fluids deriving from the dissolution of Louann salt. Overall, this study reveals that the formation of LMC at sites SS296 and GC53 was favored by the presence of low Mg/Ca ratio pore fluids resulting from salt dissolution in subsurface environments when sufficient dissolved inorganic carbon was available. These results are essential for understanding the formation of marine LMC at times of an aragonite sea, highlighting the role of formation environments—open environments close to or at the seafloor vs. confined subseafloor environments typified by pore waters with a composition largely different from that of seawater.

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Mineral Phases in Carbonate Rocks of the Górażdże Beds from the Area of Opole Silesia

Gospodarka Surowcami Mineralnymi ◽

10.1515/gospo-2016-0023 ◽

2016 ◽

Vol 32 (3) ◽

pp. 67-92

Author(s):

Katarzyna Stanienda

Keyword(s):

Ftir Spectroscopy ◽

Microscopic Analysis ◽

X Ray Diffraction ◽

Geochemical Composition ◽

X Ray ◽

Rock Samples ◽

Low Magnesium ◽

Mineral Phases ◽

Magnesium Calcite ◽

High Magnesium Calcite

AbstractThis article presents the results of studies of carbonate rock samples that came from all members of the Górażdże Beds (Lower Muschelkalk – Middle Triassic), taken from the area of the Opole Silesia. Researches allowed the types of mineral phases which built the analyzed rocks to be determined. The limestone samples were collected in the Ligota Dolna Quarry, Strzelce Opolskie Quarry, Wysoka Quarry and the area of Saint Anne Mountain. Thirteen samples were taken from the Ligota Dolna Deposit, 4 samples – in the Strzelce Opolskie Quarry and 5 samples – in the area of St. Anne Mountain. Selected rock samples were examined using a microscope with polarized, transmitted light, FTIR spectroscopy, X-ray diffraction and microprobe measurements E PMA.The results of the study show that the limestone of the Górażdże Beds from the area of Opole Silesia do not exhibit diversified types according to the Ca and Mg content of. They are characterized by the Ca and Mg high purity of geochemical composition, as well as the domination of the low magnesium calcite. There are lower contents of carbonate phases rich in magnesium – high magnesium calcite (high-Mg calcite, which is also known as magnesio-calcite) and dolomite. The majority of the data was obtained through the results of the FTIR spectroscopy and microprobe measurements. Some information gave the results of microscopic analysis. The results of X-ray diffraction indicate the occurrence only low magnesium calcite in the studied samples. Dolomite was identified in some samples of Górażdże Beds and high magnesium calcite – in sample of the Wysoka Micrite Member. Smaller amounts of non-carbonate phases occurred in the analyzed rocks. Quartz, chalcedony, feldspars, micas and clay minerals were identified among the non-carbonate phases.The small diversification of the geochemical composition of the Górażdże limestones could be connected with their sedimentation environment conditions. These rocks represent the type of barrier sediments, which were formed during the sea transgression.

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