Lithostratigraphy and structure of the Koettlitz Group, McMurdo Sound, Antarctica

Abstract

Abstract The pre‐Ordovician (?Vendian) amphibolite facies Koettlitz Group consists of three formations: Marshall, Salmon Marble, and Hobbs Formations. Stratigraphic top is not known, and the sequence is often inverted by early isoclinal folding. Salmon Marble consists of two regionally mappable units, the Heald Member and the Dismal Member; the latter always marks the passage to Hobbs Formation.The following regionally mappable units form Hobbs Formation: Radian Schist Member,Con‐Rod Hills Member, Rucker Member, and Meserve Member.In Wright Valley, the Radian Schist,Con‐Rod Hills, and Meserve Members form what was described previously as Asgard Formation. The term Asgard Formation is now abandoned. Koettlitz Group rocks have undergone three phases of deformation. F 1 produced kilometre‐scale recumbent folds with axial plane schistosity and curved fold axes; F 2 formed kilometre‐scale upright tight folds trending north to northwest, and an axial plane crenulation cleavage; F 3 are upright folds and, whereas they may be important in the Koettlitz Glacier region, are minor warps between Hobbs Ridge and Kukri Hills.In the southern part, F 1 F 2 , and F 3 folds are deflected round the southern, sheared margin of a large intrusion of Larsen Granodiorite.