TITLE:
Isotopes (13C and 18O) Geochemistry of Lower Triassic Montney Formation, Northeastern British Columbia, Western Canada
AUTHORS:
Edwin I. Egbobawaye
KEYWORDS:
Isotopes, Stable Isotopes, 13C and 18O, Isotope Geochemistry, Montney Formation, Geochemistry, Chemical Element, Mineralogy, Tight Gas Reservoir, British Columbia, Western Canada Sedimentary Basin (WCSB), Triassic, Subsurface Geology
JOURNAL NAME:
Natural Science,
Vol.9 No.10,
October
30,
2017
ABSTRACT:
Oxygen isotope (δ18O) serves as paleothermometer, and
provides paleotemperature for carbonates. δ18O signature
was used to estimate the temperature of fractionation of dolomite and calcite
in Montney Formation, empirically calculated to have precipitated, between
approximately 13°C to ±33°C during Triassic time in northeastern British
Columbia, Western Canada Sedimentary Basin (WCSB). Measurements of stable
isotopes (δ13C and δ18O)
fractionation, supported by quantitative X-ray diffraction evidence, and
whole-rock geochemical characterization of the Triassic Montney Formation
indicates the presence of calcite, dolomite, magnesium, carbon and other
elements. Results from isotopic signature obtained from bulk calcite and bulk
dolomite from this study indicates depleted δ13CPDB (-2.18‰
to -8.46‰) and depleted δ18OPDB (-3.54‰
to -16.15‰), which is interpreted in relation to oxidation of organic matter
during diagenesis. Diagenetic modification of dolomitized very fine-grained,
silty-sandstone of the Montney Formation may have occurred in stages of
progressive oxidation and reduction reactions involving chemical elements such
as Fe, which manifest in mineral form as pyrite, particularly, during early
burial diagenesis. Such mineralogical changes evident in this study from
petrography and SEM, includes cementation, authigenic quartz overgrowth and
mineral replacement involving calcite and dolomite, which are typical of
diagenesis. High concentration of chemical elements in the Montney Formation-Ca
and Mg indicates dolomitization. It is interpreted herein, that calcite may
have been precipitated into the interstitial pore space of the intergranular
matrix of very fine-grained silty-sandstone of the Montney Formation as cement
by a complex mechanism resulting in the interlocking of grains.