Sediments and Geology of Hauraki Gulf

Study undertaken to map and describe sediment distribution patterns in the Colville Channel, Hauraki Gulf and Firth of Thames, and to describe the mineralogy of the sediments with view to identifying provenance. To develop an understanding of the geological history of the study area through Pleistocene to present times. Three sedimentary facies are recognised in the modern marine sediments flooring the Hauraki Gulf, Firth of Thames and Colville Channel: a. Colville channel facies: a coarse, skeletal carbonate rich, gravelly sand body, which is palimpsest in character and restricted to the Colville Channel. b. Central gulf facies: a gravelly carbonate, muddy sand extending southwards from the Hauraki Gulf, as a central belt, into the Firth of Thames. These sediments, which were deposited at a slightly lower sea level than the present, are being actively covered by modern marine muds in the Firth of Thames and inner Hauraki Gulf, and are partially covered by the Colville Channel Facies in the eastern outer Hauraki Gulf. c. Inner Gulf/Firth of Thames facies: a modern terrigenous sandy mud-mud blanket actively infilling the Firth of Thames and inner Hauraki Gulf, and prograding northwards. The terrigenous component of these sediments is dominantly feldspar, rhyolitic rock fragments and quartz, and derived from the rhyolitic lavas of the Central North Island. Material of local origin occurs in lesser quantities. Recent phosphatic casts and aggregates in sediments of the Central Gulf Facies in the northern Firth of Thames are considered to have formed authigenically. A strong, fine pumiceous glass component in the sediments, particularly those of the Hauraki Gulf, may be of air fall origin. Palynological analysis of a peat horizon collected from sub bottom sediments of the northern Firth of Thames indicates that mangrove swamps and Northland type rain forests surrounded the Firth of Thames and Hauraki Gulf during the last interglacial period. This is the first reported occurrence of mangrove pollen in Quaternary sediments of the region, and in particular the Firth of Thames and Hauraki Gulf. Pumiceous alluvial sands comparable to the Hinuera Formation underlie the northern Firth of Thames. Echograms in the vicinity of these sediments, and to the south, show sub-bottom horizons are consistantly tilted up to ten degrees towards the east between two linear depressions considered fault traces of the Kerepehi and Hauraki Faults. This suggests tectonic deformation of the area has been active in the recent past.

An investigation of the sedimentary facies of the modern sediments flooring the Hauraki Gulf, Firth of Thames and Colville Channel. Includes interpretation of magnetic and sidescan data throughout study area. Sediment sampling - 83 sediment samples over two cruises.

Firth of Thames and Hauraki Gulf out to Cape Rodney.

Data collected in a number of surveys. Echograms 1975 and 1980. Sub-bottom profiles 1975.

Sediment samples collected with grab sampler and seived for grain size analysis. Mineralogical analysis also undertaken. Irregular surveys.

Attribute accuracy: Details given in thesis.

All material is held at the Geology Department, University of Auckland. Hard copy charts in thesis.

Thesis available in University of Auckland Library.