Coastal embayments on the east Coromandel Peninsula - stratigraphy and evolution.

Abstract adapted from thesis abstract. This thesis describes stratigraphy, morphology and sedimentology of late Quaternary deposits in a number of eastern Coromandel Peninsula embayments. Much of this information is presented on 1:12,500 scale geological and morphological maps. The author presents five stratigraphic units based on the basis of morphology, chronology and depositional environment. The study presents a model to explain the accumulation of sand within the coastal embayments during the late Quaternary, with sea level changes inferred to be the major control on sedimentation. Two main depositional phases are recorded by the barrier deposits (Pleistocene and Holocene barriers), and are associated with the last interglacial (c. 125 ky BP) and Holocene (6.5 ky BP to present) sea level stillstands. Purpose: Aim of the study was to contribute to knowledge of the late Quaternary geomorphological and geological history of the eastern Coromandel Peninsula embayments, particularly the nature and origin of the sandy barrier formations. This study was undertaken for the purposes of an MSc thesis.

Chapter one discusses the Coromandel regional setting. The next two chapters examine stratigraphy, morphology, age structure, soils and distribution of the coastal deposits. Chapter four reviews the sedimentology and composition of the coastal sequences. Chapter five is concerned with multivariate discriminant analysis of textural data to attempt differentiation of barrier depositional environments. Features of the eastern Coromandel coastal system are reviewed more closely in Chapter six. Chapter seven synthesises aspects of late quaternary sedimentation along the eastern Coromandel into a general model of coastal sedimentation. Field mapping at scale of 1:12,500. Stratigraphic descriptions and sampling of coastal deposits. Textural analyses – 130 samples from Pleistocene barrier dunes, Holocene barrier dunes, holocene sand flat, fluvial (alluvial) and fluvial (swamp) and estuary, as well as modern beach. Sand/silt/clay or gravel/sand/mud % recorded. Statistical measures of mean diameter, standard deviation, skewness and kurtosis determined for major stratigraphic units along coast. Heavy mineral percentages of total sediment for embayments along eastern Coromandel (Figure 4.3). Mineral abundance of selected beach sediments and potential sources (Table 4.2). Dune surveys (Waikawau, Wharekaho, Ohui, Whiritoa) in Appendix 4. Description of pumices in Appendix 2. Map showing locations of stratigraphic columns in Appendix 3 (31 of them from Waihi to Waikawau), but no detailed locations (small scale map). Also log of each core/column. Mineral abundance of Whiritoa, Whangamata, Opoutere, Otama sediments reported (Table 4.2) along with potential sources (Whitianga Group rocks and Coromandel Group volcanics). Mineral abundance Waikawau, Whangapoua, Otama, Wharekao, Whitianga, Cooks, Hahei, hotwater, Tairua, Opoutere, Whiritoa also given - quartz, feldspar, opaques, rock fragments (Figure 4.5). Heavy mineral content at each beach (Figure 4.3). Radiocarbon dates from sites at Otama, Tairua and some from previous studies at Hotwater beach and Opito (Table 2.4).

1986-1987

Samples collected by hand, but extensional hand auger used to retrieve samples at depth (to maximum depth of 4.5 m). A number of dune transects were surveyed using Wild NK2 theodolite. Particle size analyses results from University of Waikato’s Rapid Sediment Analyser (RSA). Mud percentages using pipette (Folk, 1968). Sediment compositional studies using binocular microscope. Acid digestion to determine CaCo3. Ferromagnesian mineral separation using Frantz Isodynamic Separator. Percentage organic matter by loss on ignition. Clay minerals investigated by X-ray diffraction. Tephra fingerprinting through titanomagnetite major element chemical analyses. Radiocarbon dating of organic materials for dates of several deposits. Many photographs and descriptions of Holocene and Pliestocene exposures. Frequency of collection: One-off data collection.

Results from individual samples not given, just characteristics of each stratigraphic unit given. Locations of samples not given.

Printed thesis, hard copy (colour) photographs. Digital Format: n/a

MSc Thesis, University of Waikato

None known. Sensitivity/Confidentiality: None known.

Study complete