Karst geomorphology of the Puketoi Range, Northern Wairarapa, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Geography at Massey University

Abstract

The research described in this thesis is the first investigation of the karst geomorphology of Pliocene and Pleistocene limestones in the southern Hawke's Bay - northern Wairarapa area. The study area is the Puketoi Range, which is situated 30 km southeast of Dannevirke. The geology of the range is examined and a new geological map of the area has been completed. The Te Aute Group (Pliocene in age) forms much of the range. This consists of two limestone beds, the Te Onepu and Awapapa Limestone Formations interbedded between two mudstone beds. This is overlain by younger Pleistocene material, the Kumeroa Formation, the upper portion of which is limestone underlain by mudstone. Solutional processes and erosion within the range is investigated. Three distinctive types of water are identified: allogenic water derived from non-karst areas, autogenic water derived from the limestone, and mixed allogenic-autogenic water. Each of these water types has specific characteristics. The solutional erosion rate for a limestone basin within the range is approximately 58.2 m3/km2/yr. Selected karst and non-karst landforms and features developed on the Puketoi Range are examined. Two of these features, case-hardened limestone and bogaz, have not previously been described in detail in New Zealand. Many of the features are the result of, or have been modified by, past periglacial climatic conditions. Other landforms are developing under present climatic conditions. The characteristics of three drainage basins developed on limestone, mudstone and greywacke respectively, are investigated. The drainage density on mudstone is the highest of the three basins examined, and densities on limestone and greywacke are similar. Sediment is examined from two caves in the area. Within Ramsay's Neck Cave ancient sediment was probably deposited during the Otira Glaciation. This sediment consists of ancient cave stream sediment, forming basal gravels overlain by fine-grained sediment and, in places, speleothems. This sediment contains allophane, a volcanically derived material, which was possibly deposited after a heavy volcanic ash fall within the cave's drainage basin. The sediment examined within PT17 Cave is contemporary gravel fluctuating in response to present hydrological conditions within the cave. Surface features indicate that in the past, gravel has completely infilled the cave, re-establishing surface drainage until the gravel was flushed from the cave. The development of the Puketoi Range cuesta and its subsequent modification is examined. The two limestone beds on which the range has developed strongly control the shape and form of the range.