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Abstract: Diagenesis of Upper Carboniferous Shallow Marine Carbonates, North Greenland

STEMMERIK, LARS, Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen NV, Denmark

Thick successions of Upper Carboniferous mixed carbonates and siliciclastics are exposed along the south coast of Amdrup Land and Holm Land in eastern North Greenland. Throughout the region, the succession consists of cyclic deposits that formed in response to high frequency and high amplitude glacio-eustatic sea-level fluctuations, and the investigated carbonates have been subjected to repeated events of subaerial exposure. However, the depositional history and diagenesis of these sediments vary considerably along strike due to different syn-depositional tectonic histories of the fault blocks. Stacked 40-150 m thick, wedge-shaped third order depositional sequences of shallow water carbonates and evaporites and shallow to deeper water siliciclastics formed on the syn-depositionally flexured south Amdrup Land block. The carbonates are dominated by phylloid algae-Palaeoaplysina buildups and biogenic grainstones that form 5-40 m shallowing upward cycles capped by subaerial exposure surfaces. They are completely dolomitised and form good potential reservoirs. In contrast, the time-equivalent carbonates on the Holm Land block consist of laterally extensive shelf carbonates, mainly biogenic wackestones and packstones and shallow marine to fluvial siliciclastics. These carbonates are all preserved as calcite with abundant early diagenetic freshwater cement related to subaerial exposure. The contrasting diagenetic style on these two fault blocks clearly relates to the depositional settings: dolomitisation and enhanced porosity occur in areas with abundant evaporites whereas calcite cementation and porosity destructive processes dominate in non-evaporitic environments. These observations are particularly relevant to exploration in the Norwegian part of the Barents Sea where Upper Carboniferous carbonates form an important reservoir target.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah