Pliocene‐Quaternary sedimentation and Alpine Fault related tectonics in the lower Cascade valley, South Westland, New Zealand

Abstract

Abstract Study of Pliocene and Quaternary sediments west of the Alpine Fault in the Cascade valley, South Westland, New Zealand, has allowed determination of Alpine Fault displacement rate and coastal uplift rate over the last 3.5 m.y. Exposures of the Pliocene Halfway Formation (latest Opoitian‐Waipipian) are composed of marine sand and conglomerate deposited in c. 200–1000 m water depth. Beds are gently dipping and weakly deformed, with the direction of principal shortening oriented at a high angle to the Alpine Fault and plunging gently northwest (c. 107340°). Fiordland‐derived clasts indicate a minimum of 95–100 km of lateral offset on the Alpine Fault since deposition of Halfway Formation. Paleogeographic evidence suggests that first‐order features of the drainage were similar in Pliocene time to those of the present day. Quaternary moraines and fluvioglacial sediments are subdivided on the basis of composition and morphology into five groups: Cl (oldest) to C5 (youngest). The Cl deposits have a prov...