Substantial variation of vitrinite reflectance within the Greymouth Coalfield permits correlation of vitrinite reflectance trends with diagenetic modifications, documented from a suite of 34 sandstones taken from eight drillholes. Vitrinite reflectance and apatite fission track data provide a framework for estimating downhole paleoburial depth and paleotemperature trends; the paragenetic sequence of sandstone diagenesis is fitted to this framework. Results indicate a potential utilisation of paragenetic suites in detrital sandstones for estimating paleoburial conditions.Primarily granite-derived Eastern Compositional Suite (ECS) and primarily metasedimentary (Greenland Group)-derived Western Compositional Suite (WCS) in the Rewanui Member of the Paparoa Coal Measures (Upper Cretaceous) show different paragenetic suites of diagenetic minerals. In ECS, macrokaolinite began forming very early (pedogenesis?); interstitial microcrystalline siderite spherulites formed later but still early in diagenesis, followed by macrocrystalline (av. c. 0.5 mm) siderite, quartz overgrowths, illitisation of original clayey components, and authigenic muscovite growth. This study suggests that kaolinitisation and siderite development are complete before 2.5 km burial depth; illite begins to form early in diagensis, possibly above 1.0 km, but mainly forms below 3.0 km, at which depth authigenic mica begins to grow. In WCS, macrokaolinite is absent, probably because of differences in the original detritus and pedogenetic conditions, and paragenetic stages later than microcrystalline siderite spherulites are absent because of the elimination of original porosity resulting from deformation of metasedimentary rock fragments to pseudomatrix between 2 and 3 km paleodepth.
Vertical rank gradients are inferred from lateral variations of Rank(S r ) in successive coal horizons in the Paparoa Group and Brunner Coal Measures in Greymouth Coalfield. The gradients are lowest, c. 3 Rank(S r )/km, in the centre of the coalfield where the lateral rank pattern is simple. In the west, vertical gradients ranging from B4 to 8 Rank(S r )/km result from contrasting Upper Rewanui and Brunner lateral rank patterns. There, it is inferred that warm fluids migrated from more deeply buried coal measures further east and have enhanced Upper Rewanui ranks. For calculating Brunner burial depths, the high western vertical gradients are rejected and a gradient of 4.0 Rank(S r )/km is adopted, as it is also east of the Mt Davy Fault Zone where the gradient is unknown. Brunner burial depths increased from 1.8 km in the far west to 4.3 km in the Mt Davy area, and palaeotemperatures increased eastwards from 90Á958C to 150Á155 8C.
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