ABSTRACT: Isotope Geochemistry of Calcitized Evaporites and Dolomites within the Permian Wegener Halvo Formation, Karstryggen Plateau, East Greenland

ULMER, DANA S., and PETER A. SCHOLLE, Southern Methodist University, Dallas, TX, and LARS STEMMERICK, Greenland Geological Survey, Copenhagen, Denmark

The Late Permian Wegener Halvo Formation of Karstryggen Plateau, East Greenland, consists of a series of subtidal stromatolites, oolitic shoals, and carbonate turbidites that lay seaward of areas of supratidal carbonate and evaporite deposition. This diverse assemblage of facies was deposited on top of a highly karsted substrate, the Karstryggen Formation. Pre-existing topographic relief, syn-sedimentary sea level fluctuations, and localized uplift controlled Wegener Halvo deposition and also affected its diagenetic alteration. Among the most significant diagenetic changes are the extensive calcitization of evaporites and dolomites. These calcitized evaporite units are preserved as topographic "mounds" of white neomorphic calcite spar.

Evaporite and dolomite pseudomorphs are commonly found, and solution collapse breccias are locally present. The Carbon 13 (PDB) isotopic analyses of the calcitized evaporites range from 6.57 to -1.29o/oo (average = 3.48o/oo); the dedolomites range from 6.59 to 1.83o/oo (average = 4.75o/oo). The Oxygen 18 (PDB) values of the calcitized evaporites range from -7.14 to -22.66o/oo (average = -12.06o/oo) and the dedolomites range from -5.43 to -14.81o/oo (average = -9.97o/oo). The isotopic values of the calcites are depleted in both carbon and oxygen relative to Permian seawater, but show a meteoric signature analogous to recrystallized aragonite cements within the more marine facies of the Wegener Halvo Formation.

Field evidence and isotopic data both indicate that calcitization of evaporites and dolomites occurred during Permian meteoric exposure events. At least three exposure horizons have been identified within the Wegener Halvo Formation and are associated with red "soils," solution collapse breccias, and the calcitized evaporites and dolomites. Calcitization appears to have continued during shallow burial leading, in some instances, to intrastratal dissolution and further collapse brecciation. Considerable porosity was generated by these near-surface diagenetic reactions providing localized reservoir-quality units throughout the Karstryggen Region.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)