Diagenetic history of the Lower Port au Port Group carbonates in Western Newfoundland
The investigated Middle–Upper Cambrian carbonates span, from bottom to top, the uppermost Hawke Bay (40 m), the March Point (˜83 m thick), and the lowermost Petit Jardin (˜47 m) formations of the Port au Port Group (western Newfoundland, Canada). The deposits consist of dolomitized shallow-water car...
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| Format: | Thesis |
| Language: | English |
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Memorial University of Newfoundland
2021
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| Online Access: | https://research.library.mun.ca/15321/ https://research.library.mun.ca/15321/1/thesis.pdf |
| Summary: | The investigated Middle–Upper Cambrian carbonates span, from bottom to top, the uppermost Hawke Bay (40 m), the March Point (˜83 m thick), and the lowermost Petit Jardin (˜47 m) formations of the Port au Port Group (western Newfoundland, Canada). The deposits consist of dolomitized shallow-water carbonates ranging from microbial mudstones to oolitic grainstones. Petrographic examination of the March Point and Petit Jardin carbonates reveals three generations of dolomite: (i) micritic to near-micritic (D1, 4 μm −35 μm) fabric-retentive dolomite, (ii) coarse crystalline sucrosic (D2, 60 μm−150 μm) fabric-destructive dolomite (sub- to euhedral zoned rhombs with clear rim and cloudy core), and (iii) coarse anhedral (D3, >0.5 mm) fracture-filling saddle dolomite. The microthermometric measurements of primary two-phase fluid inclusions retained in D2, and D3 samples yielded homogenization temperatures (Tₕ) showing a general increase with burial. The mean values of Tₕ and salinity are 89.1 ± 6.4 ﾟC vs 21.2 ± 2.2 eq. wt% NaCl, and 110 ± 8.2 ﾟC vs 21.1 ± 4.7 eq. wt% NaCl, respectively. The dolomites show a decrease of Sr from D1 (90 ± 44 ppm) to D3 (47 ± 15 ppm), which reflects the influence of progressive burial. The estimated δ¹⁸O values of the D1 parent fluid (−5 to −10‰ VSMOW) are bracketed by those suggested for the Middle Cambrian meteoric and seawaters. The fluid-inclusion gas analyses provided CO₂/CH₄ and N₂/Ar ratios coherent with the conclusions from the petrographic examination and geochemical compositions. II A multi-technique evaluation of the preservation of carbonates was applied by using several petrographic and chemical screening tools. The δ¹³C and δ¹⁸O values of dolomicrites (−1.2 ± 1.1 ‰ VPDB and −6.7 ± 1.3 ‰ VPDB, respectively) exhibit an insignificant correlation (R² = 0.16) and similarly, the δ¹³3C values with their Mn/Sr ratio (R² = 0.02). This supports the preservation of at least near-primary δ¹³C signatures that can be utilized to construct a high-resolution δ¹³C profile for reliable global ... |
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