Late Neogene stratigraphy of the Carrington area, western Wairarapa, North Island, New Zealand

Abstract

Nearly two kilometres of mostly marine sediment accumulated in western Wairarapa during Late Neogene basement subsidence, Fossil content and lithological trends within the Upper Neogene marine strata record episodes of rise and fall in sea level which are related to the combined effects of basement subsidence, local faulting and tilting and global changes in sea level. The stratigraphy of western Wairarapa is similar to that described for Upper Neogene sediments adjacent to the Aorangi Range in south-east Wairarapa. The oldest Cenozoic sediments exposed in the Carrington area, west of Carterton are a fining-upward sequence of fluvial then marine conglomerate, sandstone, siltstone and deep water, tuffaceous mudstone (Mangaoranga Formation of Neef, 1974), which accumulated during rise in sea level between lOMy BP and 5.5 My BP. Fall in sea level after 5.5 My BP is indicated by a sudden change in lithology to shallow water limestone (Hururua Limestone Formation; new name). The limestone contains well rounded and polished cobbles of Torlesse greywacke which were derived from areas of uplift nearby. Massive mudstone and turbidite (Mangatarere Mudstone Formation; new name) accumulated during the Early Pliocene. The top of the formation consists of bioturbated mudstone and very fine sandstones which have been reworked by shallow and turbulent seas at the end of the Early Pliocene epoch (Opoitian Stage), coinciding with the sudden fall in global sea level after 3.2 My (Haq et al., 1987).

unconformity and forms the base of the Tea Creek Limestone (new name) member of the Carrington Formation (new name).This is conformably overlain by a massive, fossiliferous siltstone of Middle—Late Pliocene age (Waipipian to Mangapanian Stage), (Boys Siltstone, new name) which is the youngest marine sediment exposed in western Wairarapa. The Carrington area is structurally complex and is cut by several splinter faults of the Wairarapa Fault Zone. The Upper Neogene strata are poorly exposed and are covered in places by middle Pleistocene (Te Muna Formation) conglomerates and mudstone which accumulated during regional uplift and emergence after 2My BP, and a set of upper Pleistocene river aggradation gravels.

Keywords:

• New Pliocene stratigraphic units
• Hururua Limestone Formation
• Mangatarere Mudstone Formation
• Carrington Formation
• Tea Creek Limestone member
• Boys Siltstone member
• Mangaoranga Formation
• Onoke Group
• Soren Group
• basementsubsidence
• Miocene-Pliocene boundary unconformity
• middle Pliocene unconformity
• hardground breccia
• paleoecology
• Upper Miocene conglomerate sedimentology
• NZMS 260 S26
• Wairarapa Fault