Depositional controls on peat accumulation and coal characteristics, Dunollie and Brunner coal measures, Southern Rapahoe Sector, Greymouth.
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
This thesis reports an investigation of the stratigraphy and coal geology of upper Paparoa Coal Measures and Paleocene age Brunner Coal Measures in the Southern Rapahoe Sector of Greymouth Coalfield. Lack of any clear lithostratigraphic or biostratigraphic definition for the upper contact of Dunollie Coal Measures with Brunner sediments has handicapped previous investigations. Stratigraphic criteria for the respective units are therefore revised. Brunner Coal Measures are divided into a "Brunner Formation" comprising Eocene coal measures and a "Paleocene Brunner Formation" comprising two members. The Brunner Conglomerate Member incorporates all conglomerates previously assigned to both the Dunollie and Brunner-P and the Brunner-P Member comprises Paleocene coal measures overlying the conglomerates. Dunollie Formation extends from the first carbonaceous horizon above transitional lithosomes to the last carbonaceous occurrence below Brunner Conglomerate Member. Revised boundary criteria are applied to new Dunollie Formation isopachs, cross-sections and paleogeographic models. Over much of Greymouth Coalfield the Dunollie Formation and Brunner-P Member have only very minor coal occurrences, with organic matter more commonly occurring as leaf horizons or preserved rootlets. A key objective of this thesis is determination of reasons for relatively abundant coal occurrence in the Southern Rapahoe Sector, based on lithostratigraphic analysis of the coal measures and investigation of coal properties, including coal petrography, chemistry and palynology. Both Brunner P and Dunollie coals are dominated by vitrinite. However, volatile matter, sulphur content and TPI are higher in Brunner P coals. Angiosperm abundance increases from Dunollie to Brunner P. This floral change affects volatile matter but not TPI, which was mainly controlled by a combination of water table and nutrient supply. Elevated sulphur content does not influence volatile matter, indicating that sulphur access was diagenetic and relatively late. Unusually abundant coal occurrence in the Southern Rapahoe Sector is attributed to syndepositional faulting which constrained major fluvial activity to the north. Even so, overbank flooding and channel migration within anastomosing and meandering Dunollie fluvial systems disrupted most mires before thick peat could accumulate. Fluvial activity became further constrained during accumulation of the uppermost Dunollie, allowing development of relatively widespread, sustained mire conditions.