Palaeokarst‐influenced depositional and diagenetic patterns in Upper Permian carbonates and evaporites, Karstryggen area, central East Greenland
Authors: SCHOLLE PETER A. , STEMMERIK LARS , ULMER‐SCHOLLE DANA , LIEGRO GIUSEPPI DI , HENK F. H. 
Published: June 2006

The Karstryggen area of eastern Greenland represents the western edge of sedimentation in the Jameson Land Basin, an arm of the northern Zechstein seaway. Upper Permian strata of this area were deposited as two major sequences. The first marine incursion transgressed largely peneplaned Lower Permian strata and deposited thin, paralic conglomerates, sandstones and shales (the Huledal Formation) followed by a thick package of carbonates and evaporites (the Karstryggen Formation). Although the Karstryggen Formation represents the transgressive maximum of this sequence, it contains only marginal or restricted marine strata, including micritic, stromatolitic and peloidal carbonates and thick, but localized, bedded gypsum deposits. These lithofacies indicate that relatively arid climates prevailed in this basin, as in most of the Zechstein region.

A major regression, associated with a change to a more humid climate, terminated Karstryggen sedimentation. Pre‐existing evaporites and carbonates underwent diagenetic alteration, including widespread calcitization and dissolution of gypsum. More importantly, topographic relief in excess of 120 m was generated by fluvial drainage systems and karstic sinkholes.

A second marine incursion, accompanied by a return to a semi‐arid climate, drowned this high relief topography, producing a complex sequence of strata (the Wegener Halvø Formation) in which sedimentation was greatly influenced by the rugged underlying terrain. Marine cemented algal‐molluscan grainstones draped pre‐existing palaeotopography during the initial stages of flooding. Continued drowning led to differential sedimentation on ‘highs’ and in ‘lows’. Oolitic and bryozoan‐brachiopod grainstones formed as shoals on the crests of most prominences, whereas shales, conglomeratic debris flows, evaporites, or oolitic turbidites were deposited in the lows. More restricted sedimentation took place in the westernmost areas which lay closest to the mainland shoreline and were situated to the west of a palaeotopographic ridge. There, oolitic, stromatolitic and evaporitic strata were deposited under hypersaline conditions indicative of a return to more arid climatic conditions.

Three subcycles mark smaller scale relative changes of sea level that occurred during deposition of the Wegener Halvø Formation; they are delimited by regional surfaces with moderate relief (5–20 m) developed during subaerial exposure. Widespread diagenetic changes, including leaching of aragonitic grains, dissolution/collapse brecciation of evaporites and meteoric calcite cementation, occurred in association with these smaller scale sequence boundaries, again reflecting climatic oscillations.

Relative sea level fluctuations, coupled with regional climate changes, played a dominant role in determining both depositional and diagenetic relations in these strata. These features undoubtedly extend into subsurface parts of this basin as well as into yet unexplored areas of the northern Zechstein Basin and Barents Shelf, and may have economic significance for the localization of hydrocarbons.