SEDIMENTARY GEOCHEMISTRY OF THE LOWER TRIASSIC MONTNEY FORMATION, BRITISH COLUMBIA

The Lower Triassic Montney Formation of the Peace River Basin, British Columbia, is a complex succession dominated by siltstone and sandstone with shale and bioclastic packstone occurring in some areas. The facies in the Montney Formation represent a wide variety of depositional environments, ranging from middle to upper shoreface sandstones, middle to lower shoreface sandstones, and coarse siltstones, as well as finely laminated siltstones and turbidites. The Montney Formation records sediment accumulation on the northwestern margin of Pangea during the first 5 million years after the Permian-Triassic mass extinction.

Delayed earth system recovery after the Permian-Triassic mass extinction is often attributed to marine anoxia. However, the extent of marine anoxia and the influence of global versus local drivers remains poorly constrained. This study aims to further evaluate the role of anoxia, euxinia, and ferruginous conditions during the recovery period after the Permian-Triassic mass extinction. Geochemical analyses were completed on 395 m of core through the Montney Formation, including total organic carbon (TOC), pyrite sulfur contents, iron speciation, and major and minor elemental compositions. These proxies, used as signals of shifting redox conditions, can be used to interpret the depositional environment and correlate to other time-equivalent basins. Preliminary results suggest that the Montney was deposited under anoxic and ferruginous conditions. The data show only small, periodic excursions towards euxinic conditions.

Apart from providing a record of Early Triassic environmental conditions, the Montney Formation is a large unconventional reservoir for natural gas and associated hydrocarbons. In these reservoirs, accumulations of natural gas are generally formed as a result of deposition in restricted or deep marine settings. Understanding shifts in redox conditions and how they compare to parameters commonly used in characterization of source and reservoir rock is a step toward building more accurate depositional models for these basins.