Petrography and diagenesis of the Carboniferous Deer Lake Group and Howley Formation, Deer Lake subbasin, western Newfoundland

Gall, Quentin (1984) Petrography and diagenesis of the Carboniferous Deer Lake Group and Howley Formation, Deer Lake subbasin, western Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Deer Lake subbasin is one of two northeast-trending, mainly Carboniferous, subbasins in western Newfoundland. Within the subbasin the Deer Lake Group and Howley Formation consist entirely of non-marine sediments deposited in a half-graben which was extensively faulted along its eastern side. Petrographic investigation of nine drill cores has shown that coarse grained alluvial fan and fluviatile sediments from the North Brook, Humber Falls, and Howley Formations, and high-grade uranium-mineralized sandstone boulder samples found in Pleistocene tills above the northern body of the Humber Falls Formation, have essentially the same detrital and diagenetic mineral assemblage and display the same paragenetic sequence. The dominantly lacustrine siliciclastic and carbonate sediment samples from the Rocky Brook Formation have a mineral assemblage and paragenetic sequence different from the coarser grained formations. Basic mineralogic differences are the absence of diagenetic kaolinite and illite-montmorillonite, and the presence of "analcime" in the Rocky Brook Formation sediments. The paragenetic sequence for the North Brook, Humber Falls, and Howley Formations and the mineralized samples reflects an acidic to alkaline geochemical environment. The paragenetic sequence for the Rocky Brook Formation on the other hand appears to have developed within a more stable alkaline geochemical environment. Correlating paleomagnetic data with the derived paragenetic sequence for the three coarse grained formations suggests that the sequence took more than 40 Ma to completely develop. A postmineralization episode of hematite cementation may mean that economic quantities of uranium no longer exist in the sandstones. -- High-volatile bituminous B and C coaly material and diagenetic clay mineral assemblages extracted from the drill core samples suggest that the sediments remained within the diagenetic realm after deposition, and that maximum temperatures between about 125ﾟ C and 135ﾟ C were attained during coalification and authigenic clay growth.

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