Meteoric Calcitization and Incipient Lithification of Recent High-Magnesium Calcite Muds, Belize

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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Early Cementation by High-Magnesium Calcite from Gulf Coast of Louisiana: ABSTRACT

AAPG Bulletin ◽

10.1306/2f918f09-16ce-11d7-8645000102c1865d ◽

1980 ◽

Vol 64 ◽

Author(s):

M. John Kocurko

Keyword(s):

Gulf Coast ◽

Magnesium Calcite ◽

High Magnesium Calcite

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Botryoidal High-Magnesium Calcite Marine Cements from the Upper Cretaceous of the Mediterranean Region

Journal of Sedimentary Research ◽

10.1306/d4267708-2b26-11d7-8648000102c1865d ◽

1991 ◽

Vol Vol. 61 ◽

Author(s):

Donald J. Ross (2)

Keyword(s):

Mediterranean Region ◽

Upper Cretaceous ◽

Magnesium Calcite ◽

High Magnesium Calcite ◽

The Mediterranean

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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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