Stratigraphy, sedimentology, petrography and structure of the Mount Lookout area, Awatere Valley

Powell, SJ

A thick sequence of Cretaceous and Tertiary rocks overlies Torlesse and Torlesse-like basement rocks in the Mount Lookout area, Upper Awatere Valley, Marlborough.
Torlesse Supergroup (?Jurassic- Lower Cretaceous) rocks occur to the northwest of the Awatere Fault with a thin sliver infaulted along the Lee Brook Fault. Elsewhere younger highly deformed Torlesse-like rocks of the Tone Formation (Lower Cretaceous- Motuan) form the local basement.
Rocks of the Clarence Series include the Totara, Gladstone, Winterton and Castle Creek Conglomerate Formations, all of Motuan age. They comprise about 1,500 m of massive sandstones, conglomerates, flysch-like units, and massive mudstones. They unconformably overlie Tone Formation basement as well as being interformationally unconformable. Deformation decreases up the sequence, the Totara Formation being heavily deformed, the Gladstone Formation moderately so while the Castle Creek Conglomerate Formation contains only slight fault created offsets.
The Lookout Formation (Ngaterian) comprises a thick sequence of mildly alkaline basalts and tuffs. These were effused sub-aerially from multiple fissures fed by the dykes of the Tapuaenuku Dyke Swarm (Ngaterian). Submarine flows, pillow lavas, limestones and fossiliferous tuffs indicate that the top of the volcanic pile is marine. A representative Ngaterian fauna from the tuff includes Inoceremus concentrious Parkinson and Inoceremus tawhanus nom. nov.
Raukumara Series rocks are absent. The Mata Series is represented by a thin, faulted sequence of unnamed, poorly indurated mudstone, siltstone, sandstone green sand and limestone. Large blocks of Amuri Limestone (Dannevirke) are found in a tectonic melange within the sheared mudstone.
The Clarence Series rocks were probably deposited in tectonically active basins. They show evidence for continual tectonic activity during the early to mid-late Cretaceous. The Rangitata Orogeny uplift phase probably occurred in the mid-Motuan.
Block faulting induced by the Kaikoura Orogeny (Later Cenozoic) has preserved the sequence as a gently folded syncline in the fault angle depression produced by uplift on the Awatere Fault.

viii. 127 p. photos, diagms, map (folded in pocket); 30 cm.

1985Powell

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