Redefinition and interpretation of late Miocene‐Pleistocene terrestrial stratigraphy, Central Otago, New Zealand

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Abstract
The stratigraphic succession in eastern Central Otago consists of Eocene quartzose fluvial sediments and middle Tertiary marine strata (Onekakara Group), early‐middle Miocene quartzose fluvial sediments and lake deposits (Manuherikia Group), late Miocene‐Pliocene immature sandstones and conglomerates, and Quaternary terrace and fan gravels. Published literature contains at least 20 different approaches for subdivision of this succession. The late Miocene‐Pliocene conglomerates were formed during the rise of fault‐bounded greywacke and semischist mountain ranges. Conspicuous conglomerates in the upper part of this succession are widely referred to as Maori Bottom Formation, but that name was originally applied by miners to a locally auriferous erosion surface beneath Quaternary terrace and fan gravels in Otago. In addition, the term is culturally offensive. We propose the name Hawkdun Group for the late Miocene‐Pliocene succession of tectonically generated sediments in the Maniototo, Ida, and Manuherikia Basins, and propose the name Maniototo Conglomerate to replace Maori Bottom. The Hawkdun Group in Central Otago can be subdivided into two mappable units. The basal Wedderburn Formation consists predominantly of late Miocene quartzose fluvial strata recycled largely from cover strata of the St Bathans, Kakanui, and Hawkdun Ranges. Wedderburn Formation contains an upwardly increasing component of first‐cycle lithic detritus derived from these ranges, and grades up into late Miocene‐Pliocene Maniototo Conglomerate, consisting of thick beds of greywacke‐dominated conglomerate and interbedded loess horizons. In previous usage, Wedderburn Formation included some strata which more appropriately belong with the underlying Manuherikia Group. Quartzose fluvial strata and intervening marine and lacustrine strata have been aggregated by previous workers for regional mapping purposes. Correlation problems leading to aggregation have arisen largely from stacking of up to three lithologically similar quartzose conglomerate and quartzose sandstone units, but also from the difficulty in differentiating between these units where distinctive, intervening marine or lacustrine strata are absent, and where unconformities are not exposed. The redefined units as proposed above are individually mappable and eliminate the necessity for mapping of grouped units. Usage of Stranraer Group, Maori Bottom Group, Maori Bottom Formation, and Blue Gravel Member (of the latter) is discontinued. Contemporaneous, lithologic and stratigraphic correlatives of the Hawkdun Group were deposited in the Nevis, lower Manuherikia, Cromwell, and upper Clutha Basins in Central Otago, and in many other basins on both sides of the plate boundary throughout the South Island.