Report of the Fairfield Estate drillhole (FE1) near Dunedin, Otago

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McMillan, S.G. 1995 Report of the Fairfield Estate drillhole (FE1) near Dunedin, Otago . Lower Hutt: Institute of Geological & Nuclear Sciences Institute of Geological & Nuclear Sciences science report 95/17 20 p.

Abstract: The Fairfield Estates drillhole I44 068(5) 735(5) was initiated by Institute of Geological & Nuclear Sciences engineering geologists to aid in slope stability assessment. The drillhole was deepened to meet two stratigraphic objectives: (1) the stratigraphic relationship between the Brighton Limestone and Fernhill Sand members of the Wangaloa Formation and (2) the identification of unconformities for correlation and sedimentary modelling. However, with regard to the first objective, only sediments of the Abbotsford Formation were encountered in the drillhole indicating a stratigraphically thickened section. This is interpreted as the result of a more complex structural geology than previously realised: an east-west trending fault(s), possibly with an associated fault angle depression, is now inferred on the southeast flanks of Saddle Hill. Other alternatives such as the position of the FE1 site over a basement depression or intraformational unconformities with associated cut and fill processes are also discussed. The second objective was met and three burrowed discontinuities at depths of 34.70, 55.72 and 65.16 metres were identified. These discontinuities have local and regional correlatives throughout Otago and their occurrence is consistent with previous sedimentary models. (auth)