Cretaceous tectonostratigraphy of 'the Great Coverham section' and adjacent areas, northeastern Waiau Toa/Clarence valley, New Zealand

Late Early-Late Cretaceous strata preserved at the northeastern end of the Waiau Toa/Clarence valley, northeastern South Island, New Zealand, have been central to ongoing debates concerning the end of Mesozoic subduction on the Zealandian margin of Gondwana and the initiation of extension. New geological mapping within this area at Coverham, Kekerengu and Wharekiri, has resolved complex relationships between Cretaceous stratigraphic units and faults. Results indicate that, within the interval 110-100 Ma, Champagne and lower Split Rock formations record syn-tectonic deposition by marine mass-transport processes within confined sub-basins with steep seafloor gradients. Upper Split Rock Formation and overlying Nidd Formation record progressive burial of seafloor topography between c. 100-86 Ma. Although uncertainties remain, three or four faults appear to have been low-angle structures with normal displacements that were active within the interval c. 105-89 Ma; one of these faults experienced brief reversal of offset between c. 91 and 87 Ma. The new data are most consistent with a model of subduction shutdown between c. 105-100 Ma, following impact of the Hikurangi Plateau large igneous province at the subduction margin. Widespread uplift along the margin between 97 and 95 Ma may reflect subsequent rebound of the subducted plate.