Stratigraphy and structural geometry of the Shublik and western Sadlerochit Mountains - Abstract

Abstract Four geological cross sections across the Shublik and western Sadlerochit Mountaiins illustrate local variations in stratigraphic relationships and structural style. Three distinct stratigraphic succesions are recognized. Mississippian through Upper Cretaceous Ellesmerian Sequence rocks unconformably overlie Devonian and older Franklinian Sequence basement and are conformably overlain by the Upper Cretaceous and younger Brookian Sequence. Structural stratigraphic units are independant of these sequences and are bound by detachment horizons. Progressively upsection, these are: within the pre-Mississippian sequence, Mississippian Kayak Shale of the Endicott Group, Jurassic Kingak Shale, and Upper Cretaceous pebble shale unit. Two of the structural stratigraphic units are well exposed in the Shublik Mountains. Between the Kayak Shale and the pre-Mississippian detachments a series of broad east-west trending panels of relatively uniform south dip define a continuous sheet which steps, flattens, and steps to deeper structural levels to the south. The steps reflect the basal detachment within the pre-Mississippian sequence stepping progressively upward to the range front on the north. Gross morphology of structures above the Kayak Shale mimic this basement geometry. In detail however, these folds are short wavelength, east-northeast trending detachment folds with both north and south vergence. Together roughly equivalent amounts of shortening is accomodated by the large scale folding above the basal detachment and the smaller scale parasitic detachment folds above the Kayak Shale. Faults breaking upward from the Kayak Shale detachment are rare. Ignek Valley to the north is a broad syncline which only units above the Kayak Shale are exposed. A third structural stratigraphic unit is documented on the north flank of the syncline where duplexing of the Kemik Sandstone occurs between detachments in the Jurassic Kingak Shale and Upper Cretaceous pebble shale unit. To the north, the structural style of the Sadlerochit Mountains differs considerably from that of the Shublik Mountains. The two structural stratigraphic units defined in the Shublik Mountains acts as a single unit in the Sadlerochit Mountains due to northward thinning of the Kayak shale. Structural style of this unit is characterized by an east-west trending, south dipping homoclinal block bound on the north by a thrust fault. Minor thrust faults propagate across the Endicott Group. This relationship documents the absence of detachment within the Kayak Shale.