Stratigraphy and sedimentology of the Coalgate area, Canterbury, New Zealand

Abstract

Stratigraphic and sedimentologic studies of the Cretaceo-Tertiary sequence overlying Torlesse rocks in the Coalgate area permit a review of the lithostratigraphy of the region. Much new information has come from borehole logs and cores. Coal measures conformably overlain by shallow marine strata and associated igneous rocks, including View Hill Basalt, are assigned to the Eyre Group (modified name) of upper Cretaceous and possibly Paleocene age. Burnt Hill Group (new name) is erected to accommodate some 200 m of Oligocene-Miocene non-calcareous marine, estuarine, and associated igneous rocks of central and northern Canterbury. Formations include: Homebush Standstone (new name for a massive estuarine deltaic deposit) (oldest unit); Thongcaster Formation of Duntroonian age (new name for a fossiliferous clayey fine sandstone); Wairiri Volcaniclastite (new name for a tuff-breccia deposit); Chalk Quarry Sandstone of Waiauan age (modified name); Chalk Hill Clay; Sandpit Tuff (name now formalised) consisting of sandy and silty tuffs and tuff breccias; Bluff Basalt (name now formalised) including breccia, flow and dike rocks; Harper Hills Basalt (name altered and restricted in usage); Coalgate Bentonite (rank of unit changed) (youngest unit). Burnt Hill Group is overlain by 55 m of sandstone and sandy mudstone of Greenwood Formation, of probable Waipipian age, and up to 40 m of viviantic sands, clays, and gravels of possible Castlecliffian and perhaps younger age which are included in Aitkens Formation (new name). Much of the area is blanketed by Hawera Series outwash gravels which help to obscure the stratigraphic relationships of older formations in surface exposure.

Sedimentology and structure of the Malvern Hills Coal Mine, Canterbury, New Zealand

“…This is in agreement with observations made by Bell (2006) and also more or less regionally consistent (e.g. Carlson et al 1980).…”

“…Work completed locally by van der Lingen (1988) identified similar characteristic successions of coal measures and tidal clays, sands and gravel in the Broken River Formation of the Mt Somers area. The Broken River Formation forms the basal unit of the regional Eyre Group (Carlson et al 1980) consisting predominantly of unevenly stratified current-bedded white quartz sandstone, dark-grey carbonaceous silt and sand and lensoid beds of sub-bituminous coal (Gage 1970). These rocks are Late Cretaceous or Mata Series in age, and considered to be PiripauanÁHaumurian (e.g.…”

“…The coal deposits in the Malvern Hills Mine are part of the Late CretaceousÁPalaeocene Broken River Formation (Carlson et al 1980;Field & Browne 1986;van der Lingen 1988). Regionally, the entire sedimentary succession is up to 1500 m thickness (Speight 1928) with the main coal-bearing unit up to 200 m thick in places (Duff 1986).…”

“…Basic igneous dykes and sills of various Tertiary ages (e.g. PalaeoceneÁEocene View Hill Volcanics, Miocene Harper Hills and Bluff Basalts; Sewell and Gibson 1988) intrude the Late CretaceousÁPalaeocene succession in several places (Carlson et al 1980;Duff 1986;Duff & Barry 1989;Forsyth et al 2008). (Duff 1986).…”

Petrology and geochemistry of Tertiary volcanic rocks from inland Central and South Canterbury, South Island, New Zealand

“…1). These deposits are overlain by flows of the Harper Hills Basalt (Carlson et al 1980) which are tholeiitic in composition (Carlson & Rodgers 1975) and have given K-Ar ages of 12.8 and 11.0 Ma (Table 1). Similar basalt flows in the Oxford district (Oxford Basalt;McLennan 1981) containing abundant segregation veins have given a K-Ar age of c. 16 Ma (Table 1).…”