Early Ordovician (Skullrockian) Trilobites of the Antiklinalbugt Formation, Northeast Greenland, and their Biostratigraphic Significance

Abstract

The Antiklinalbugt Formation of northeast Greenland comprises peritidal to subtidal carbonate sediments, deposited in shallow shelf settings during an early Tremadocian transgressive-regressive megacycle. The succession of shales and microbial, muddy and grainy limestone, with minor dolostone at the base and top, terminates at the cryptic Fimbulfjeld disconformity. The formation has yielded trilobites collected on Ella Ø, Albert Heim Bjerge, and Kap Weber by C. Poulsen (1920s and 1930s), J. W. Cowie and P. J. Adams (1950s), and during recent field studies in 2000 and 2001. The fauna includes dimeropygidsTulepyge cowieiandT. tesellan. spp., hystricuridsMillardicurusandHystricurus, and several species ofSymphysurina. Micragnostus chiushuensis(Kobayashi, 1931) is rare, as areChasbellussp.,Clelandiasp., andLunacrania?. The presence of severalSymphysurinaspecies places the Antiklinalbugt Formation within theSymphysurinaZone.Chasbellusindicates the upper (lower Ordovician) part of theSymphysurinaZone for the lower upper Antiklinalbugt Formation. Conodonts place the middle lower formation in theCordylodus intermediusconodont Biozone, the lower upper part in theCordylodus angulatusconodont Biozone and the uppermost part in theRossodus manitouensisconodont Biozone. This combined fauna is characteristic of the upper Skullrockian Stage of the Ibexian Series, with the lower part of the Antiklinalbugt Formation lying within the uppermost Cambrian of North America, and the upper part within the lower Ordovician. The entire formation lies within the global Tremadocian Stage of the early Ordovician.

The Ordovician Exposed: Short Papers, Abstracts, and Field Guides for the 12th International Symposium on the Ordovician System

“…None compare favorably with S. woosteri. At least three other species of the genus without a pygidial spine are also present , two of which are very similar to (although probably not conspecific with) S. elegans and S. porifera from basal Ordovician strata in northeast Greenland (McCobb et al 2014). Although no conodont data have been recovered from the interval where S. elegans occurs, its association with such very basal Ordovician trilobite genera as Tulepyge and Chasbellus indicates close age equivalence with S. cf.…”