Geology of the eastern MacKenzie Pass area


Horan, Simon.


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An area of approximately 30 square kilometres was mapped containing Permian (?) Torlesse Terrane sediments of the Rollesby and Dalgety Ranges, along with Tertiary and Quaternary sediments in the southern Rollesby Valley, Mackenzie Pass area of South Canterbury.
Torlesse sediments of the Dalgety Formation (new name) , consisting. of conspicuous conglomerate, channelised sands and muds, and interbedded sandstone-mudstone beds are described and defined. Conglomerate beds, predominantly of rhyolite, crystal tuff and vein quartz clasts represent redeposited conglomerates deposited in an upper submarine fan environment.
Lithostratigraphic mapping based on five lithofacies has been carried out, facies include a conglomerate facies (corresponds to conglomerate beds of the Dalgety Formation), massive sandstone, interbedded sandstone and mudstone, mudstone and chaotic deposits. Lithofacies are consistent with deposition in a mid to upper submarine fan environment.
Detrital sandstone mineralogy suggests derivation from a dominantly plutonic source with concurrent input of volcanic detritus. Conglomerate clasts suggest an exclusively volcanic source terrane, however, the predominance of extremely durable clast types may indicate pre-depositional breakdown of less durable clasts, possibly more indicative of the true source terrane. A dominantly plutonic source with concurrent volcanic input is favoured.
Metamorphism has been to prehnite-pumpellyite facies in the Dalgety Range and to pumpellyite-actinolite facies in the Rollesby Range. Both facies are juxtaposed up against the post-metamorphic Mackenzie Pass Fault.
Deformation also includes two phases of folding and faulting on north-south and east-west trends. Folding includes steeply plunging folds inferred to have formed initially by folding about shallowly plunging fold axes and then tilted by fault movement in their present position.
Tertiary limestone and glauconite sandy-siltstones interbedded with calcareous concretionary layers, tentatively correlated to the Craigmore Limestone and Little Pareora Silt respectively are mapped. Quartz arenite sands are also described. A tentative stratigraphy, based on poorly constrained field relationships is suggested and compared to well documented Tertiary sequences described by Eade & Kennett (1962) and Fagan (1971) close to the area mapped.
Quaternary sediments include the deformed Single Hill Beds composed of interbedded low grade lignite, carbonaceous mud, green clay and angular greywacke gravels and undeformed loess, river alluvium, colluvium and alluvial fan deposits. Single Hill Beds record deposition of alluvial fan deposits in a swamp environment due to shedding of detritus on rising fault scarps. Subsequent tilting of these late Quaternary deposits indicates significant recent fault movement.

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93 leaves : ill. (some col.), maps ; 30 cm.


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Horan, Simon., “Geology of the eastern MacKenzie Pass area ,” Otago Geology Theses, accessed June 18, 2018,