Paleogeographic and Stratigraphic Differentiation of Silurian Carbonate Buildups and Biostromes of North Greenland

Abstract

Carbonate buildups of Silurian Llandovery age are common in a conspicuous belt across North Greenland. Four buildup types and one biostrome type have been recognized on the basis of paleogeographic setting: slope buildups, shelf-margin buildups (upper slope), shelf-edge, intrashelf buildups, and shelf to shelf-edge biostromes. Five buildup and biostrome facies associations have been recognized: (1) Stromatoporoid Tabulate-Coral Bindstone (slope and shelf margin), (2) Crinoidal Calcarenite (shelf edge and intrashelf), (3) Lime Mudstone (shelf margin), (4) Fenestral Dolomite (shelf edge and intrashelf), and (5) Stromatoporoid Floatstone and Rudstone (shelf to shelf-edge biostromes). Beds of chaotic breccia up to 15 m thick flank the slope, shelf-margin, and shelf-edge build ps. Two major periods of buildup, generally separated by biostromes, have been detected. Buildups developed in western North Greenland during deposition of the middle Llandovery. These were mainly shelf-edge and intrashelf Crinoidal Calcarenite buildups. Biostromes covered much of North Greenland during late Llandovery deposition. The latest Llandovery and earliest Wenlock of western North Greenland were characterized by a 350-km east-west belt of shelf-margin Stromatoporoid Tabulate-Coral Bindstone and Lime Mudstone buildups. Growth of buildups, with a single exception, was related to transgression perhaps induced by downfaulting of the shelf; biostromes resulted from either transgression or regression. Termination of earliest Llandovery buildup growth may have been a result of shallowing gases, for some buildups apparently have been eroded. Growth in the main late Llandovery-early Wenlock belt probably terminated owing to drowning and clastic influx. Data suggest that Llandovery histories of western and eastern North Greenland are different. The change appears to coincide with the Victoria Fjord arch. Reservoir potential appears to be mainly at the lower Llandovery and earlier shelf-basin contact and in the middle Llandovery or earlier allochthonous carbonate rocks off the northern and western coast. Also, reservoirs may be present in lime-mud buildups and overlying allochthonous carbonate rocks farther down the slope in Nyeboe through Wulff Lands. In Peary Land, Crinoidal Calcarenite intrashelf buildups and overlying alochthonous carbonate rocks may be present in the subsurface. However, exhumed buildups lack substantial porosity and hydrocarbon shows.