Dolomite within the St. George Group (lower Ordovician), western Newfoundland
Seven varieties of dolomite and dolostone, the products of four stages of dolomitization, are recognized within the St. George Group (Lower Ordovician) of western Newfoundland. -- Dololaminites are syngenetic, formed in a tidal flat environment, characterized by prominent shallow water sedimentary s...
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| Format: | Thesis |
| Language: | English |
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Memorial University of Newfoundland
1984
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| Online Access: | https://research.library.mun.ca/6854/ https://research.library.mun.ca/6854/1/DouglasWayneHaywick.pdf https://research.library.mun.ca/6854/3/DouglasWayneHaywick.pdf |
| Summary: | Seven varieties of dolomite and dolostone, the products of four stages of dolomitization, are recognized within the St. George Group (Lower Ordovician) of western Newfoundland. -- Dololaminites are syngenetic, formed in a tidal flat environment, characterized by prominent shallow water sedimentary structures, local bioturbation, δ ¹⁸O values of -4 to -8 o/oo and composed of anhedral, very finely crystalline, uniformly luminescent dolomite rhombs. Siliciclastic minerals are subordinate. -- Early-diagenetic (eogenetic) dolomitization, possibly initiated by the presence of mucopolysaccharides and controlled spatially by permeability, has resulted in three varieties of dolomite and dolostone. δ ¹⁸O values range between -4 and -10 o/oo. Mottle dolomite selectively replaces body and trace fossils and is localized along pressure solution seams. Rhombs of matrix dolomite are evenly distributed in mudstones and wackestones and range in abundance from trace quantities to 80 percent. Both varieties are characterized by finely crystalline, well zoned, idiotopic to xenotopic dolomite. Though initially nucleated during early- diagenesis, they have undergone a prolonged period of growth continuing at least until the onset of pressure solution. -- Pervasive A dolostones are mottled rocks characterized by bimodal crystallinity; finely crystalline dolomite in mottles, medium crystalline dolomite between mottles. Both are xenotopic and uniformly luminescent to moderately zoned. These rocks are coincident with early phases of mottle/matrix dolomitization and may have developed due to the mixing of meteoric and marine waters. They have not been subjected to late-diagenetic periods of growth. -- Hydrothermal alteration, probably related to tectonics during initial phases of the Taconic Orogeny (Middle Ordovician), is a late-diagenetic (mesogenetic) event and in the northern portion of the study area (Great Northern Peninsula), has developed two extensive field varieties. Pervasive B dolostones are bimodal rocks resulting from ... |
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