Stratigraphy of the Balleny Group at Puysegur Point, South West Fiordland, New Zealand
Year:
Project type:
Advisers:
Abstract:
Tertiary sedimentation in the area about Puysegur Point, S.W. Fiordland, New Zealand, began in the Lower Oligocene. Puysegur Formation, the basal stratigraphic unit of the sequence, comprises lower deltaic plain and delta mouth coals, mudstone, sandstones and conglomerate, marine beach sands, and near-shore tide deposited sands and mudstone, interfingering with breccia conglomerate deposited as alluvial fans backed against Ordovician basement.
Conformably overlying Puysegur Formation, the Sealers Formation consists of terrigenous muddy flysch interbedded with thick sandstones, medium to thin bedded sandy flysch, and locally, conglomerates near the base. The conglomerates and thickly bedded sandstones were deposited from inertia flows in feeder channels incised into muddy flysch of the inner submarine fan and basin slope. The graded and massive bedded sandy flysch sediments represent proximal turbidity current and inertia flow deposition on the middle fan. Soft sediment deformation structures are abundant, reflecting an inherent instability of the depositional slope. Derived from local basement, sandstones are arkosic. Mudstones contain a kaolinite-illite clay mineral assemblage. The trace fossil Chondrites is characteristic of the fine grained sediment.
Outcropping as a fault bounded structural block, the highest stratigraphic unit, Chalky Island Formation, comprises about 390m of calcareous turbidites. Generally, each bed grades from sand into montmorillinite-nanno-marl and is terminated by a nanno-plankton chalk interbed. Several amalgamated thick sandstone units and rare breccias are present, representing a progradation of the submarine fan. The sandstones are arkosic and contain a transported, shelf derived, abraided macrofauna. Flute and groove molds indicate a southerly turbidity current flow direction, parallel with the subsequent main tectonic trend.
The chalk beds accumulated during periods of no turbidity current deposition, largely from fall-out of nannoflora from the euphotic zone. Some thickening of the chalk from low velocity bottom current redeposition may have occurred. Examined by both light and scanning electron microscopy, the nannofossil assemblage has strong open ocean affinities. The moderately well preserved Lower Oligocene assemblage is dominated by coccoliths of the Ericsonia ovalis, Chiasmolithus oamaruensis, and Reticulofenestra umbilica species groups.
A diverse suite of trace fossils in Chalky Island Formation is dominated by ichnogenera, notably Zoophycus and Chondrites, that have been identified from Recent and fossil ocean floor drill cores. This contrasts with the typically littoral assemblage in Puysegur Formation. The change in sedimentation style, from largely traction current deposited fluvio-marine sediments in Puysegur Formation to inertia flow and turbidity current emplaced sands of Sealers Formation, together with oceanic oozes in Chalky Island Formation in equated with an episode of rapid tectonic depression of northerly trending flysch troughs of west Southland and Westland.
Conformably overlying Puysegur Formation, the Sealers Formation consists of terrigenous muddy flysch interbedded with thick sandstones, medium to thin bedded sandy flysch, and locally, conglomerates near the base. The conglomerates and thickly bedded sandstones were deposited from inertia flows in feeder channels incised into muddy flysch of the inner submarine fan and basin slope. The graded and massive bedded sandy flysch sediments represent proximal turbidity current and inertia flow deposition on the middle fan. Soft sediment deformation structures are abundant, reflecting an inherent instability of the depositional slope. Derived from local basement, sandstones are arkosic. Mudstones contain a kaolinite-illite clay mineral assemblage. The trace fossil Chondrites is characteristic of the fine grained sediment.
Outcropping as a fault bounded structural block, the highest stratigraphic unit, Chalky Island Formation, comprises about 390m of calcareous turbidites. Generally, each bed grades from sand into montmorillinite-nanno-marl and is terminated by a nanno-plankton chalk interbed. Several amalgamated thick sandstone units and rare breccias are present, representing a progradation of the submarine fan. The sandstones are arkosic and contain a transported, shelf derived, abraided macrofauna. Flute and groove molds indicate a southerly turbidity current flow direction, parallel with the subsequent main tectonic trend.
The chalk beds accumulated during periods of no turbidity current deposition, largely from fall-out of nannoflora from the euphotic zone. Some thickening of the chalk from low velocity bottom current redeposition may have occurred. Examined by both light and scanning electron microscopy, the nannofossil assemblage has strong open ocean affinities. The moderately well preserved Lower Oligocene assemblage is dominated by coccoliths of the Ericsonia ovalis, Chiasmolithus oamaruensis, and Reticulofenestra umbilica species groups.
A diverse suite of trace fossils in Chalky Island Formation is dominated by ichnogenera, notably Zoophycus and Chondrites, that have been identified from Recent and fossil ocean floor drill cores. This contrasts with the typically littoral assemblage in Puysegur Formation. The change in sedimentation style, from largely traction current deposited fluvio-marine sediments in Puysegur Formation to inertia flow and turbidity current emplaced sands of Sealers Formation, together with oceanic oozes in Chalky Island Formation in equated with an episode of rapid tectonic depression of northerly trending flysch troughs of west Southland and Westland.
Thesis description:
ix, 163 p. : illus., maps ; 31 cm.
Department:
OU geology Identifier:
1975Lindqvist
OURArchive handle:
OURArchive access level:
Location (WKT, WGS84):
POLYGON ((166.599426481874445 -46.09324856998812,166.704169622877401 -46.097898824314839,166.686003467591632 -46.233851288454161,166.583700718328487 -46.228132017491291,166.599426481874445 -46.09324856998812))
Files
Collection
Citation
Lindqvist, Jon Kenneth., “Stratigraphy of the Balleny Group at Puysegur Point, South West Fiordland, New Zealand,” Otago Geology Theses, accessed April 23, 2025, https://theses.otagogeology.org.nz/items/show/86.