The palynology of the Ohai coalfield, Southland
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The Upper Cretaceous Morley Coal Measures in the Ohai Coalfield are one of three non-marine formations constituting the Ohai Group. In the past, seam correlation has generally been carried out using lithological criteria, however due to dramatic thinning and splitting of seams, associated faulting, and abrupt facies changes uncertainties in coal seam correlation have frequently arisen. In order to minimize lithostratigraphic uncertainties Couper (1964) pioneered a palynological zonation which demonstrated the potential of palynology for coal seam correlation. However, Couper's early work has proved unreliable and is in need of further refinement. Recent drillholes incorporating almost fully cored sequences of the Morley Formation have permitted further palynological examination of the coal measures. Nine drillholes were selected and 140 samples taken, at 10 metre intervals, for palynological analyses. The Morley Coal Measures are unconformably overlain by the Beaumont Coal Measures. This important boundary, though difficult to detect lithologically, is readily defined on palynological grounds. Biostratigraphic subdivision of the Morley Coal Measures was investigated by the application of three quantitative techniques. These entailed the construction and analysis of: (1) Standard pollen diagrams based on relative abundances of selected taxa and groups of taxa; (2) Pollen diagrams zoned by the numerical method of cluster analysis; (3) Ratios of selected taxa of recurrent and variably high frequency. Technique (1), involving relative abundance patterns of key taxa and groups of taxa was successful in providing a basis for subdivision of the Morley Coal Measures into three pollen zones, two interzonal units and two unzoned units. The three pollen zones were, in stratigraphically descending order: The Nothofagus kaitangata acme zone, the SPPA assemblage zone, and the Tricolpites reticulatus acme zone. Techniques (2) and (3) were, in all practicality, unproductive, although results suggested that, with refinement, cluster analysis could aid the zonation of pollen diagrams.