THE HORN RIVER - DUVERNAY SHALE SYSTEM, WESTERN CANADA: HYDROTHERMAL PETROLEUM RESERVOIRS
The Horn River and Duvernay shale are black organic carbon-rich deposits within thicker successions of lighter colored shale with lower organic carbon content. We interpret the organic carbon-rich shale to be a result of preservation of organic matter in stratified water columns. Previous studies of fluid from dolomite on the platform margins surrounding these shale units show high temperature, but also high salinity fluids (> 20 weight percent NaCl). These fluids are more dense than seawater and hence tend to pool on the bottom resulting in stratification whic leads to anoxic conditions and preservation of organic matter. Similar anoxic black shale units are commonly recognized in association with SEDEX deposits.
Previous fluid inclusion studies of the dolomite on the platform margins show a strong temperature gradient, from average temperatures near 180 C in the Slave Point dolomite on the margin of the Horn River basin to the north to near 100 C in dolomite in proximity to the Duvernay shale to the south. Both the Horn River and Duvernay shale contain quartz cements, trace elements and hydrothermal minerals commonly associated with SEDEX deposits such as barite, sphalerite, celsian and hyalophane . The Horn River shale contains higher amounts of these constituents as well as authigenic monazite.