Distinguishing celadonite from glauconite for environmental interpretations:a review

Celadonite and glauconite are comparable in terms of physical,chemical and mineralogical characteristics.Formation of both these minerals requires slightly oxygen-depleted conditions in a semiconfined micro-environment,facilitating the uptake of Fe into the structure.Although glauconite is ubiquitous in marine deposits,celadonite forms in both marine and non-marine environments,more commonly by altering intermediate to mafic rocks.A review of data across the geological column shows that both these minerals are more common in the Mesozoic and Cenozoic,which may be related to extensive volcanism.The composition of celadonite and glauconite is highly variable and is controlled by the availability of cations within the pore water micro-environment.The major element composition of celadonite overlaps with that of evolved to highly evolved glauconite to a large extent.Existing data and representative samples of celadonite and glauconite reveal subtle differences in X-ray diffraction parameters and Fourier transform infrared(FTIR)spectra.Celadonite shows sharper basal and hkl reflections than glauconite.It characteristically exhibits distinct 111-021,003-022,023 and 130-131,and 060 reflections at less than 1.51A,indicating a betterordered crystallographic structure than glauconite.The FTIR spectra of celadonite and glauconite show similar absorption bands although Si-O bending,Si-O stretching and OH-stretching bands are sharper and well resolved in celadonite than that of glauconite.For palaeoenvironmental interpretations,it is,therefore,necessary to examine the subtle differences in X-ray diffraction parameters and FTIR spectra to confirm the identification of these two minerals.The composition of celadonite relates closely to the host rock and depositional environment.The celadonite associated with mafic rock shows relatively high Fe,Mg and low Al contents.In contrast,those associated with felsic to intermediate composition rocks show slightly higher contents of Al and lower content of Fe,Mg.The mineral chemistry of celadonite varies from marine to continental settings.Marine celadonite contains higher Fe,Mg and lesser Al than their non-marine counterpart.Celadonite with relatively higher Al may show slightly lower interlayer K than Fe and Mg-rich celadonite for charge balancing.

Origin and geochemical characterization of the glauconites in the Upper Cretaceous Lameta Formation, Narmada Basin, central India

This study presents geochemical characteristics of glauconites in estuarine deposits within the Maastrichtian Lameta Formation in central India. Resting conformably over the Bagh Group, the Lameta Formation consists of ~4-5 m thick arenaceous, argillaceous and calcareous green sandstones underlying the Deccan Traps. The sandstone is friable, medium-to coarse-grained, well-sorted and thoroughly crossstratified, and contains marine fossils. Detailed petrography, spectroscopy and mineral chemistry indicates unique chemical composition of glauconite with high KO, MgO, AlOand moderate TFeO. Glauconite is formed by the replacement of K-feldspars, initially as stringers in the cleavages and fractures of feldspars. Incipient glauconite subsequently evolves fully, appearing as pellets. Fully-evolved glauconite pellets often leave tiny relics of K-feldspar. XRD exhibits characteristic peak of 10A from basal(001)reflection of glauconite, indicating the "evolved" character. The KO content of glauconites in the Lameta Formation varies from 5.51% to 8.29%, corroborating the "evolved" to "highly-evolved" maturation stage.The TFeOcontent of glauconite varies from 12.56% to 18.90%. The PASS-normalized-REE patterns of glauconite exhibit a "hat-shape" confirming the authigenic origin of glauconites. The slightly-negative to slightly-positive Ce anomaly value and the moderate TFeOcontent of glauconite agree well with a suboxic,estuarine condition. The replacement of K-feldspar by the glauconite contributes towards the high KO content. Compositional evolution of glauconites in the Lameta Formation is similar to those observed in many Precambrian sedimentary sequences.

Evolution of Authigenic Glauconite in Early Diagenesis

According to the data of the mineral assemblages, the sediment layers with authigenic glauconite were found in the X1 core collected from the northeast of the Beibu Gulf. Pliocene sediment layer containing a lot of foraminifera shows a shallow sea facies. Its thickness is larger than 30 m and is located at the depth below 59 m of the core.

Formation mechanisms and sequence response of authigenic grain-coating chlorite: evidence from the Upper Triassic Xujiahe Formation in the southern Sichuan Basin, China

Authigenic grain-coating chlorite is widely distributed in the clastic rocks of many sedimentary basins around the world. These iron minerals were mainly derived from flocculent precipitates formed when rivers flow into the ocean, especially in deltaic environments with high hydrodynamic conditions. At the same time, sandstone sequences with grain-coating chlorites also tend to have relatively high glauconite and pyrite content. EPMA composition analysis shows that glauconites with ‘‘high Al and low Fe’’ content indicate slightly to semi-saline marine environments with weak alkaline and weakly reducing conditions. By analyzing the chlorite-containing sandstone bodies of the southern Sichuan Xujiahe Formation, this study found that chlorite was mainly distributed in sedimentary microfacies, including underwater distributary channels, distributary channels, shallow lake sandstone dams, and mouth bars. Chlorite had a tendency to form in the upper parts of sandstone bodies with signs of increased base level, representing the influence of marine（lacustrine）transgression. This is believed to be influenced by megamonsoons in the Middle and Upper Yangtze Region during the Late Triassic Epoch. During periods of abundant precipitation, river discharges increased and more Fe particulates flowed into the ocean（lake）. In the meantime,increases or decreases in lake level were only affected byprecipitation for short periods of time. The sedimentary environment shifted from weakly oxidizing to weak alkaline, weakly reducing conditions as sea level increased, and Fe-rich minerals as authigenic chlorite and glauconite began to form and deposit.

Distribution and composition of authigenic minerals in surface sediments of the western Gulf of Thailand

Generation, morphology, and distribution of authigenic minerals directly reflect sedimentary environment and material sources. Surface sediments were collected from the western Gulf of Thailand during 2011–2012, and 159 samples were analyzed to determine detrital minerals. Authigenic minerals, including siderite, pyrite, and glauconite, are abundant whereas secondary minerals, such as chlorite and limonite, are distributed widely in the study area. Siderite has a maximum content of 19.98 g/kg and appears in three types from nearshore to continental shelf, showing the process of forming-maturity-oxidation. In this process, the Mn O content in siderite decreases, but FeOand Mg O content increase. Colorless or transparent siderite pellets are fresh grains generated within a short time and widely distributed throughout the region; high content appears in coastal area where river inputs are discharged. Translucent cemented double pellets appearing light yellow to red are mature grains; high content is observed in the central shelf. Red-brown opaque granular pellets are oxidized grains,which are concentrated in the eastern gulf. Pyrite is mostly distributed in the central continental shelf with an approximately north–south strip. Pyrite are mainly observed in foraminifera shell and distributed in clayey silt sediments, which is similar to that in the Yangtze River mouth and the Yellow Sea. The pyrite in the gulf is deduced from genetic types associated with sulfate reduction and organic matter decomposition. Majority of glauconite are granular with few laminar. Glauconite is concentrated in the northern and southern parts within the boundary of 9.5° to 10.5°N and is affected by river input diffusion. The distribution of glauconite is closely correlated with that of chlorite and plagioclase, indicating that glauconite is possibly derived from altered products of chlorite and plagioclase. The KO content of glauconite is low or absent, indicating its short formation time.

The formation of authigenic deposits during Paleogene warm climatic intervals:A review

Although Paleogene warm climatic intervals have received considerable attention for atmospheric and oceanographic changes,the authigenic mineralization associated with these time spans remains overlooked.An extensive review of the literature reveals a close correspondence between the high abundance of glauconite and warm climatic intervals during the Paleogene period.The abundance of phosphorite,ironstone,lignite and black shale deposits reveals similar trends.Although investigated thoroughly,the origin of these authigenic deposits is never understood in the background of Paleogene warming climatic intervals.A combination of factors like warm seawater,hypoxic shelf,low rate of sedimentation,and enhanced rate of continental weathering facilitated the glauconitization.The last factor caused the excess supply of nutrients,including Fe,Si,K,Mg and Al through the rivers,the cations needed for the formation of glauconite.The excessive inflow of nutrient-rich freshwater into the shallow seas further ensured high organic productivity and stratification in shallow shelves,causing hypoxia.The consequent rapid rise in sea-level during the warm periods created extensive low-relief shallow marine shelves starved in sediments.Oxygen-deficiency in the shallow marine environment facilitated the fixation of Fe into the glauconite structure.The inflow of nutrient-rich water during the warm climatic intervals facilitated the formation of phosphorite,ironstone,and organic-matter-rich sedimentary deposits as well.Although global factors primarily controlled the formation of these authigenic deposits,local factors played significant roles in some of the deposits.Therefore,phosphorites formed in marine conditions with open circulation within the tropical zone.While lush growth of rainforest covers in the tropical belt facilitated the formation of coastal lignite.

A review on palaeogeographic implications and temporal variation in glaucony composition

This study presents a review on palaeogeographic implications and temporal variations of giaucony coveringboth modern and ancient records. Phanerozoic giaucony preferably forms in a shelf depositional setting. Deep marine conditions and low seawater temperature discourage formation of glaucony. Around 75% of glaucony is recorded from the Cretaceous to the Holo- eene sediments, which are related to the abundance of the most common substrates, faecal pellets and bioclasts. TFe203 （total）, A1203, K20 and MgO contents of glaucony vary appreciably through geological time. IMhile TFe203 content of most Mesozoic and Cenozoic giaucony ex- ceeds 20%, it is always less than 20% in Precambrian varieties. High K20, A1203, MgO and low TFe203 distinguish the Precambrian glaucony from its Phanerozoic counterpart. Precambrian glaucony, preferably formed within a K-feldspar substrate, is always rich in potassium irre- spective of its degree of evolution, while high K-content in Phanerozoic evolved glaucony in- dicates significant stratigraphic condensation. K20 iJs. TFe203 relationship of glaucony exhibits three different evolutionary trends corresponding to three common modes of origin. Depositional conditions may influence the composition of glaucony as slightly reducing conditions favour Fe enrichment, whereas oxidising conditions cause Fe depletion in giaucony.