PALEOENVIRONMENTAL CONDITIONS AND SOURCE INPUT CHANGES DURING THE DEPOSITION OF THE MONTNEY FORMATION INTERPRETED BASED ON ELEMENTAL GEOCHEMISTRY

The Montney Formation in Alberta and British Columbia of Western Canada hosts major oil and gas resources. Majority of the hydrocarbon deposits are held or trapped in low permeability carbonate siltstones and silty shales. Geological investigations have demonstrated that the Triassic Montney Formation has a complex depositional and diagenetic history, which presents peculiar challenges for exploration and optimized completion. Detailed understanding of its paleo-environmental conditions during deposition, and sources of sediment inputs are therefore critical to successfully harnessing its resources. Elemental geochemistry presents a tool that can yield high resolution data from which numerous interpretations ranging from paleoenvironment of deposition, grain sorting, provenance, lithology, mineralogy and fluid interactions can be determined. In this work, 1400 samples from seven wells within the Montney Formation in Central Alberta were analysed using energy-dispersive X-ray fluorescence (ED-XRF) to determine elemental distributions within sediments. A Montney-specific calibration was built to interpret elemental concentrations from the ED-XRF dataset to account for heterogeneities, matrix variations and unique elemental associations that may be present within the Montney formation. Sediment input sources are interpreted to be a mixture of detrital and biogenic origins based on cross-plots of elements. Ratios of elemental concentrations demonstrate varying depositional redox conditions ranging from oxic to dyoxic. The ratios of strontium to copper and rubidium to strontium were used as paleoclimate proxies, and both suggest a hot arid paleoclimate during the deposition of the Montney Formation sediments. Paleoproductivity during deposition was assessed using phosphorus to titanium ratio, which were found to be low (averagely < 1), suggesting low productivity, which coincides with organic petrographic interpretations due to isolation of the basin from the Proto-Pacific Ocean to the West.