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Modulated microstructures

A TEM investigation of modulated microstructure in Recent and fossil articulate brachiopod shells from New Zealand... [Pg.28]

A common microstructure observed in many dolomites and some calcites when examined with transmission electron microscopy (TEM) is a fine modulation called modulated microstructure (e.g. Reeder and Wenk, 1979 Reeder, 1981 Wenk et ai, 1983 Wenk and Zenger, 1983 Wenk and Zhang, 1985 Miser et ai, 1987 Wenk et ai, 1991 Frisia and Wenk, 1993). Reeder and Wenk (1979) first identified... [Pg.28]

This study presents the first record of modulated microstructure in extant skeletal carbonate. Specifically, I have used TEM to investigate the internal structure of the fibrous fabric of the secondary layer in both Recent and Plio-Pleistocene brachiopod shells of Calloria inconspicua and Notosaria nigricans, and in a Late Triassic Kutchithyris sp. from New Zealand. The presence of modulated microstructure in... [Pg.29]

Modulated microstructure in New Zealand brachiopods 31 Synchrotron X-ray fluorescence microprobe analysis... [Pg.31]

Figure 4.1 TEM images showing modulated microstructure in New Zealand brachiopods. (A) fossil... Figure 4.1 TEM images showing modulated microstructure in New Zealand brachiopods. (A) fossil...
Most studies indicate that modulated microstructure in dolomite and calcite forms as a result of replacement associated with a diagenetic environment (e.g. Reeder,... [Pg.33]

Modulated microstructure occurs in calcite, as well as in dolomite, and was first identified in Jurassic oolitic limestone by Gunderson and Wenk (1981). However, chemical analysis of the oolitic limestone showed no compositional differences between areas with the modulation and those without. Since, the modulations could not be the result of compositional fluctuations of Ca-Mg as in dolomite, Gunderson and Wenk (1981) hypothesised that the rotational disorder of CO3 groups that occurred during phase transformation of aragonite to low-magnesium calcite might cause the modulations. [Pg.34]

TEM observations document the presence of distinct areas of modulated microstructure in fossil and Recent brachiopod shells. This is the first record of modulated texture in extant skeletal carbonate. There are unresolved differences of opinion regarding the underlying mechanism of formation of modulated microstructures. Although, most modulated microstructure has been associated with diagenesis, the presence of the modulated structure in Recent brachiopods eliminates a diagenetic environment as a requirement for the formation of the texture in brachiopods. Furthermore, electron microprobe measurements indicate that the calcite studied is composed of low-magnesium calcite. Thus, no major cation substitutions, such as excess Mg+ in the lattice, are responsible for the modulated microstructures in brachiopod calcite. The two most likely explanations for modulated microstructure in brachiopod calcite... [Pg.36]

See other pages where Modulated microstructures is mentioned: [Pg.298]    [Pg.249]    [Pg.252]    [Pg.127]    [Pg.130]    [Pg.77]    [Pg.2021]    [Pg.5]    [Pg.28]    [Pg.29]    [Pg.29]    [Pg.29]    [Pg.30]    [Pg.31]    [Pg.32]    [Pg.33]    [Pg.34]    [Pg.34]    [Pg.35]    [Pg.35]    [Pg.36]    [Pg.36]    [Pg.37]    [Pg.37]    [Pg.39]    [Pg.208]   
See also in sourсe #XX -- [ Pg.28 , Pg.29 , Pg.30 , Pg.31 , Pg.32 , Pg.33 , Pg.34 , Pg.35 ]



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