Dolomites of the Boat Harbour Formation in the Northern Peninsula, western Newfoundland, Canada: Implications for dolomitization history and porosity control

摘要

The Boat Harbour Formation constitutes the upper part of the Lower Ordovician St. George Group on the Northern Peninsula, western Newfoundland. It ranges in thickness from 140 m (459 ft) at Main Brook to 96 m (315 ft) at Daniel's Harbour. Dolomitization of the carbonate sequence is more pervasive in the lower 30 to 40 m (98 to 131 ft) at Main Brook, whereas at Daniel's Harbour, the section is entirely dolomitized. Petrography suggests that the Boat Harbour Formation has been affected by three phases of dolomitization. The earliest (near surface or synsedimentary) phase is D1 dolomicrite (4-55 u.m), which exhibits dull to no luminescence. It commonly occurs as laminae-capping cycles and as breccias in the younger dolomite phases. It has low Sr (228 ± 30 ppm) and an average δ~(18)O value of-6.0%o ± 0.8%o (Vienna Peedee bel-emnite [ VPDB]) in the Main Brook section but more depleted signatures for δ~(18)O of-8.8%o ± l%o (VPDB) and lower Sr contents (45 + 8 ppm) in the Daniel's Harbour section. The geochemical composition suggests that Dl was developed from fluids of a mixture of meteoric and marine waters.