Vertical tectonic movement in northeastern Marlborough: Stratigraphic, radiocarbon, and paleoecological data from Holocene estuaries

Abstract

Height and age information from Holocene estuarine deposits along the northeastern Marlborough coast provide a database to evaluate coastal vertical tectonics. These data are related to the postglacial marine transgression and coastal geomorphic features formed since the culmination of sea‐level rise. Four tectonic domains are recognised. The Wairau domain is characterised by subsidence at rates over 4 mm/yr. About 60% of this subsidence is tectonic and may be related to Marlborough Sounds subsidence, and 40% is a result of compaction. The Vernon Fault at the south side of the lower Wairau plain separates the Wairau domain from the high‐standing Vernon domain. The Awatere Fault marks the southern boundary between the Vernon domain and the Grassmere domain, which extends from the Awatere River valley to Mussel Point. Slight uplift (c. 1 m in 6500 yr) characterises the Grassmere domain, based on data obtained from Blind River, Lake Grassmere, and, to a lesser extent, from Awatere River fluvial terraces. The north‐trending London Hill Fault reaches the coast at Mussel Point and coincides with the boundary between the Grassmere and Cape Campbell domains. The latter is characterised by rapid uplift (16 m in c. 6500 yr). No late Quaternary traces are known on the London Hill Fault, but the data presented are indicative of Holocene activity.