Diagenetic history of the Lower Port au Port Group carbonates in Western Newfoundland

• Main Author: Shembilu, Noel Clement
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2021
• Subjects: Canada; Hawke Bay; Newfoundland
• Online Access: https://research.library.mun.ca/15321/; https://research.library.mun.ca/15321/1/thesis.pdf

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 ...