DEPOSITIONAL ENVIRONMENT AND ORGANIC GEOCHEMISTRY OF THE UPPER PERMIAN RAVNEFJELD FORMATION SOURCE-ROCK IN EAST GREENLAND

The Upper Permian Ravnefjeld Formation in East Greenland is composed o f shales that laterally pass into carbonate buildups and platforms of the Wegener Halvo Formation. The Ravnefjeld Formation is subdivided in to five units that can be traced throughout the Upper Permian depositi onal basin. Two of the units are laminated and organic rich, and were deposited under anoxic conditions. They are considered good to excelle nt source rocks for liquid hydrocarbons with initial average TOC (tota l organic carbon) values between 4 and 5% and HI (hydrogen index) betw een 300 and 400. The cumulative source rock thickness is between 15 an d 20 m. The source rocks are separated and enclosed by three units of bioturbated siltstone with a TOC of less than 0.5% and an HI of less t han 100. These siltstones were deposited under relatively oxic conditi ons. The organic geochemistry of the source rocks is typical for marin e source rocks with some features normally associated with carbonate/e vaporite environments [low Pr/Ph (pristane/phytane), low CPI (carbon p reference index), distribution of tricyclic and pentacyclic terpanes]. The establishment of anoxic conditions and subsequent source rock dep osition was controlled by eustatic sea level changes. The subenvironme nt (paleogeographic setting, influx of carbonate material, water depth , salinity) has some influence on a number of bulk parameters [TOC-HI relations, TOC-TS (total sulfur) relations] and, in particular, biomar ker parameters such as Pr/Ph and terpane ratios. All the basal shales or shales in the vicinity of carbonate buildups or platforms are chara cterized by low Pr/Ph, high C23 triCYCliC terpanes, and high C35 and C 33 hopanes.