Miocene regressive strata, Dunedin district, New Zealand.
Year:
Project type:
Abstract:
Miocene regressive strata of the Dunedin district, South Island, New Zealand, are described. These strata are underlain by a terrestrial -marine transgressive sequence of late Cretaceous to Oligocene age. The basal contact of the regressive sequence is sharp, generally being marked by a regional break of middle to late Oligocene age (Marshall Paraconformity), They are overlain, and in part interlayered with, rocks of the Dunedin Volcanic Complex.
Four areas in eastern Dunedin district, viz. Karitane Peninsula, Dowling and Waipuna bays, Sandymount and Varleys Hill, are mapped and described geologically. Special attention is given to stratigraphy, lithology, paleontologic content, sedimentology (e.g. coarse fraction and grain size analyses, and quartz grain surface microtextures), petrography environment of deposition, provenance, and structure of the stratigraphic units. Age relations, regional correlation and relationship between the Miocene regressive sequence and the Dunedin Volcanic Complex are also discussed. Previous lithostratigraphic units are described and in some cases redefined. Several new lithostratigraphic units are established and described. Stratigraphic sections for all units are provided and type sections for new units are proposed.
The regressive sequence in Dunedin district is divisible into two major portions:
(1) the widespread Caversham Formation comprising marine strata deposited from Late Oligocene (Waitakian) to Early Miocene (Late Altonian).
(2) less widespread and more variable shallow marine to non-marine rock strata deposited from Early Miocene (Late Altonian? ) to Middle Miocene (Waiauan). Karitane Sequence
A well exposed succession of the Late Oligocene to Lower Miocene sequence is found at Karitane Peninsula, 38 km north-northeast of Dunedin city. It can be divided into four mapping units:
(1) Caversham Formation (Late Oligocene- Early Miocene) is subdivided into three informal members: Lower member, richly glauconitic/calcareous sandstone ("Concord Greensand"); Middle member, massive to thick bedded feldspathic litharenitic calcisiltite/calcarenite and calcareous siltstone sandstone; disconformably overlain by
(2) Karitane Formation (new unit, late Early Miocene) consisting of quartzofeldspathic siltstone, sandstone and quartz granule sandstone; overlain by
(3) Rona Nepheline-Bearing Trachyte Flows (new unit, late Early Miocene) overlain by
(4) Sulisker Formation (new unit, late Early Miocene), composed of carbonaceous siltstone and calcareous lapillistone facies.
In addition, the middle and upper members of the Caversharn Formation are further subdivided into nine component lithofacies. Otago Harbour - Otago Peninsula Sequence
The Lower-Middle Miocene regressive deposits are restricted to northern Otago Harbour (e.g. Dowling and Waipuna bays) and Otago Peninsula (e.g. Sandyrnount and Varleys Hill). The regressive sequence here is subdivided into three mapping units (in ascending order) :
(1) School Creek Formation (new unit, upper Lower Miocene; Upper Altonian ?) consisting of three lithofacies: bentonite with francolite granule-rich tuff horizon (Lithofacies SCF-1), planktonic forarniniferal muscovite subfeldsarenite (Lithofacies SCF-2) and clay-flake muscovite subfeldsarenite (Lithofacies SCF-3); overlain by
(2) the Waipuna Bay Formation (lower to upper Middle Miocene; Lillburnian to Waiauan) subdivided into two members: Dowling Bay Member, comprising clastic limestone and calcareous sublitharenite/subfeldsarenite and Pulling Point Member comprising noncalcareous muscovite subfeldsarenite with local interbeds of basaltic hyalotuff; conformably overlain by
(3) the Abernethys Creek Formation (upper Middle Miocene ? ), subaerial basaltic and trachytic tuffs.
The Dowling Bay Member of the Waipuna Bay Formation is further subdivided into four units: Unit A, bedded terrigenous forarniniferal (+ sponge spicules) calcarenite; Unit B, alternating graded bedded terrigenous calcirudite and calcarenite with some laminated and mud-draped rippled calcarenite; Unit c, massive terrigenous calcisiltite together with some graded bedded terrigenous calcarenite and spicular terrigenous calcarenite and;Unit D, parallel bedded terrigenous calcareous sandstone. Petrography and Provenance
Textural and mineralogical evidence suggests that the rocks of the Caversharn Formation were derived from three main sources:
(1) calcium carbonate material from in or adjacent to the basin of deposition,
(2) terrigenous (metamorphic detritus) 1 derived from outside the basin of deposition,
(3) glauconite pellets formed in the basin of deposition.
The calcium carbonate of the Caversham Formation was derived from disintegration of echinoderms, bryozoans, bivalves, brachiopods, coralline algae, corals, foraminiferids, minor gastropods and ostracods, The carbonate grains were abraded both by other carbonate grains and by more resistant terrigenous material. Other sources for the calcium carbonate are aggrading neomorphism and organic erosion by burrowing organisms, particularly for the source of micritic calcium carbonate.
Terrigenous components of the Karitane Formation, School Creek Formation and Waipuna Bay Formation are much the same as those of the Caversham Formation, comprising undulose monocrystalline and polycrystalline quartz, albite, muscovite, coarse-grained (i.e. muscovite-chloritealbite- quartz) and fine grained (e.g. phyllite) metasedimentary lithic fragments and accessory minerals (e.g. chlorite, epidote, biotite, garnet). Derivation by the weathering and erosion of lower grade metamorphic rocks (e.g. Haast Schist and adjoining Torlesse greywackes) is implied. Reworking of underlying Miocene regressive strata is also suggested. Furthermore, a granitic and high-grade metamorphic terrane probably contributed some of the quartz, orthoclase, microcline, well rounded tourmaline and garnet, rutile and zircon. Microprobe analyses of some detrital plagioclase (An2o-3o> is consistent with this suggestion. The most probable geographic location for this source is the FiordlandStewart Island region, 220 km south of the Dunedin district. Transport by longshore drifting, the Southland current or its ancestor is proposed.
The occurrence of highly altered volcanic material (e.g. glassy vesicular material) in the upper part of the Karitane Formation indicates that volcanism also contributed to these sediments. It is notable that the formation is overlain by a nepheline-bearing trachyte flow. Thus, it appears that the deposition of the upper part of the formation coincides with the onset of volcanism in the Karitane region.
Sediment comprising the School Creek Formation is derived from volcanic and low grade metamorphic rocks. A bentonite bed constitutes the lowest exposed portion of the formation and implies an early episode of volcanism, predating carbonate deposition of the overlying Waipuna Bay Formation. Late Altonian volcanic activity in Dunedin district is suggested. The timing of volcanism may coincide with the onset of volcanism at Karitane Peninsula.
Petrographic study of the Waipuna Bay Formation indicates that the grains are of three main types:
(1) carbonate and siliceous (e.g. sponge) material,
(2) terrigenous (i.e. sedimentary, volcanic and metamorphic detritus) and
(3) pyroclastic material.
The source of the calcium carbonate of the formation was much the same as that for the Caversham Formation. In addition, pressure solution during compaction released calcium carbonate which was re-precipitated as cement. Trachytic, basaltic and glassy vesicular lithic fragments occur in some lithofacies of the Waipuna Bay Formation, These are thought to have been derived from the rocks predating or contemporaneous with the deposition of the bentonite of the underlying School Creek Formation.
Tuff and lapilli tuff occur in marine strata of the upper member of the Waipuna Bay Formation. It is postulated that the pyroclastic material was derived from volcanoes located within the central part of Otago Harbour. Depositional Environment
The Caversham Formation is the basal unit of the regressive sequence in Dunedin district. Depositional environment of the lower member of the formation is interpreted as open marine, shelf, being deposited on an extensive erosional surface that developed throughout most of Oligocene time. Coarse fraction, grain size, calcium carbonate and foraminiferal variations up section in the middle and upper members of the Caversham Formation reflect gradual shallowing of the sea during deposition, that is from outer shelf to inne,r shelf.
The gross lithology, sedimentary structures and coarsening upwards nature of the Karitane Formation reflect a regressive trend from low energy intertidal to high energy estuary or beach environment. The Karitane Formation probably represents regressive linear clastic shoreline sedimentation or conceivably thin deltaic deposits, Orientation of channel axes indicate currents flowing in NW-SE directions. Carbonaceous quartz granule sand at the top of the Karitane Formation probably marks the onset of terrestrial conditions.
The Rona Nepheline-Bearing Trachyte Flows occur immediately above the Karitane Formation and are regarded as subaerial accumulations.
Lithologic and paleontologic relations of the Sulisker Formation indicate two episodes of the sedimentation. The first, the carbonaceous siltstone in the lower formation is interpreted as having been deposited near the boundary between marine and non-marine environments. The second, the fossiliferous calcareous lapillistone is interpreted to have been deposited in a shallow marine environment.
The School Creek Formation is interpreted as having been deposited in a lagoonal area undergoing slow sedimentation. Planktonic foraminifera in this formation may have been transported from the open sea to a lagoonal environment by tidal and storm currents. After deposition of the School Creek Formation was completed, the sea again covered the area and the clastic carbonat~s which formed the Waipuna Bay Formation were deposited.
The five units of the Waipuna Bay Formation are interpreted to represent two regressive cycles:
(1) Unit A (base): middle shelf to shallow-nearshore shelf environments
(2) Unit B: shallow subtidal to intertidal environments
(3) Unit C: shallow subtidal to high intertidal; shallow shelf environments represented towards the top
(4) Unit D: nearshore shelf environment.
(5) Unit E (Top): intertidal lagoon and tidal channel environments. The sudden .change in depositional environment within Unit C, that is from intertidal flat to shelf environment indicates abrupt transgression. The environmental changes between Unit D and E are probably related to the formation of barrier island in the offshore area and the contact between the two units is represented by a diastemic boundary.
At the end of sedimentation of Unit E the intertidal lagoonal basin had been filled, and by that time major subaerial volcanic eruptions had begun producing the tuff and lapi~li tuff of the Abernethys Creek Formation. Relations to Dunedin Volcanic Complex.
The deposition of terrigenous and bioclastic Miocene marine regressive strata in Dunedin district was interrupted and followed by volcanism, centred in the Port Chalmers-Portobello region and near Karitane Peninsula. The present discovery of bentonite beneath the Waipuna Bay Formation (Middle Miocene; Lillburnian) at Dowling Bay, and recognition of Rona Nepheline-Bearing Trachyte Flows (Lower Miocene; Late Altonian) at Karitane Peninsula indicates that volcanic activity commenced in Early Miocene (Late Altonian) time, that is slightly older than the previously understood. In addition, available K/Ar data dating of alkalic olivine dolerites in inland north Otago (i.e. Waipiata Volcanic Formation) indicates volcanism commenced there at 15-16 m.y. ago. Thus the Waipiata radiometric dates are reasonably consistent with age of initiation of volcanism in Dunedin district as indicated by data presented herein.
The Miocene regressive strata at Karitane Peninsula are folded into a north-south trending anticline with an axial plunge at about 10° northwards. This anticline is thought to be a reflection of tectonism associated with the Kaikoura Orogeny.
On the northern side of Otago Harbour (i.e. Dowling and Waipuna bays) and on the central Otago Peninsula (i.e. Sandymount and Varleys Hill) , the Miocene regressive strata are characteristically deformed by phonolitic intrusive domes, features which are numerous within the Dunedin district.
The apparent absence of Upper Miocene to Lower Pleistocene deposits in the Dunedin district reflects tectonic uplift and tilting which was evidently associated with volcanic activity and the Kaikoura Orogeny. Thus, Miocene regressive strata are overlain by Pleistocene raised beach deposits, a Pleistocene slide sheet of the Caversharn Formation and volcanic rocks and by loess deposits at Karitane Peninsula, volcanic solifluction overlies the regressive strata at northern Otago Harbour and central Otago Peninsula.
Four areas in eastern Dunedin district, viz. Karitane Peninsula, Dowling and Waipuna bays, Sandymount and Varleys Hill, are mapped and described geologically. Special attention is given to stratigraphy, lithology, paleontologic content, sedimentology (e.g. coarse fraction and grain size analyses, and quartz grain surface microtextures), petrography environment of deposition, provenance, and structure of the stratigraphic units. Age relations, regional correlation and relationship between the Miocene regressive sequence and the Dunedin Volcanic Complex are also discussed. Previous lithostratigraphic units are described and in some cases redefined. Several new lithostratigraphic units are established and described. Stratigraphic sections for all units are provided and type sections for new units are proposed.
The regressive sequence in Dunedin district is divisible into two major portions:
(1) the widespread Caversham Formation comprising marine strata deposited from Late Oligocene (Waitakian) to Early Miocene (Late Altonian).
(2) less widespread and more variable shallow marine to non-marine rock strata deposited from Early Miocene (Late Altonian? ) to Middle Miocene (Waiauan). Karitane Sequence
A well exposed succession of the Late Oligocene to Lower Miocene sequence is found at Karitane Peninsula, 38 km north-northeast of Dunedin city. It can be divided into four mapping units:
(1) Caversham Formation (Late Oligocene- Early Miocene) is subdivided into three informal members: Lower member, richly glauconitic/calcareous sandstone ("Concord Greensand"); Middle member, massive to thick bedded feldspathic litharenitic calcisiltite/calcarenite and calcareous siltstone sandstone; disconformably overlain by
(2) Karitane Formation (new unit, late Early Miocene) consisting of quartzofeldspathic siltstone, sandstone and quartz granule sandstone; overlain by
(3) Rona Nepheline-Bearing Trachyte Flows (new unit, late Early Miocene) overlain by
(4) Sulisker Formation (new unit, late Early Miocene), composed of carbonaceous siltstone and calcareous lapillistone facies.
In addition, the middle and upper members of the Caversharn Formation are further subdivided into nine component lithofacies. Otago Harbour - Otago Peninsula Sequence
The Lower-Middle Miocene regressive deposits are restricted to northern Otago Harbour (e.g. Dowling and Waipuna bays) and Otago Peninsula (e.g. Sandyrnount and Varleys Hill). The regressive sequence here is subdivided into three mapping units (in ascending order) :
(1) School Creek Formation (new unit, upper Lower Miocene; Upper Altonian ?) consisting of three lithofacies: bentonite with francolite granule-rich tuff horizon (Lithofacies SCF-1), planktonic forarniniferal muscovite subfeldsarenite (Lithofacies SCF-2) and clay-flake muscovite subfeldsarenite (Lithofacies SCF-3); overlain by
(2) the Waipuna Bay Formation (lower to upper Middle Miocene; Lillburnian to Waiauan) subdivided into two members: Dowling Bay Member, comprising clastic limestone and calcareous sublitharenite/subfeldsarenite and Pulling Point Member comprising noncalcareous muscovite subfeldsarenite with local interbeds of basaltic hyalotuff; conformably overlain by
(3) the Abernethys Creek Formation (upper Middle Miocene ? ), subaerial basaltic and trachytic tuffs.
The Dowling Bay Member of the Waipuna Bay Formation is further subdivided into four units: Unit A, bedded terrigenous forarniniferal (+ sponge spicules) calcarenite; Unit B, alternating graded bedded terrigenous calcirudite and calcarenite with some laminated and mud-draped rippled calcarenite; Unit c, massive terrigenous calcisiltite together with some graded bedded terrigenous calcarenite and spicular terrigenous calcarenite and;Unit D, parallel bedded terrigenous calcareous sandstone. Petrography and Provenance
Textural and mineralogical evidence suggests that the rocks of the Caversharn Formation were derived from three main sources:
(1) calcium carbonate material from in or adjacent to the basin of deposition,
(2) terrigenous (metamorphic detritus) 1 derived from outside the basin of deposition,
(3) glauconite pellets formed in the basin of deposition.
The calcium carbonate of the Caversham Formation was derived from disintegration of echinoderms, bryozoans, bivalves, brachiopods, coralline algae, corals, foraminiferids, minor gastropods and ostracods, The carbonate grains were abraded both by other carbonate grains and by more resistant terrigenous material. Other sources for the calcium carbonate are aggrading neomorphism and organic erosion by burrowing organisms, particularly for the source of micritic calcium carbonate.
Terrigenous components of the Karitane Formation, School Creek Formation and Waipuna Bay Formation are much the same as those of the Caversham Formation, comprising undulose monocrystalline and polycrystalline quartz, albite, muscovite, coarse-grained (i.e. muscovite-chloritealbite- quartz) and fine grained (e.g. phyllite) metasedimentary lithic fragments and accessory minerals (e.g. chlorite, epidote, biotite, garnet). Derivation by the weathering and erosion of lower grade metamorphic rocks (e.g. Haast Schist and adjoining Torlesse greywackes) is implied. Reworking of underlying Miocene regressive strata is also suggested. Furthermore, a granitic and high-grade metamorphic terrane probably contributed some of the quartz, orthoclase, microcline, well rounded tourmaline and garnet, rutile and zircon. Microprobe analyses of some detrital plagioclase (An2o-3o> is consistent with this suggestion. The most probable geographic location for this source is the FiordlandStewart Island region, 220 km south of the Dunedin district. Transport by longshore drifting, the Southland current or its ancestor is proposed.
The occurrence of highly altered volcanic material (e.g. glassy vesicular material) in the upper part of the Karitane Formation indicates that volcanism also contributed to these sediments. It is notable that the formation is overlain by a nepheline-bearing trachyte flow. Thus, it appears that the deposition of the upper part of the formation coincides with the onset of volcanism in the Karitane region.
Sediment comprising the School Creek Formation is derived from volcanic and low grade metamorphic rocks. A bentonite bed constitutes the lowest exposed portion of the formation and implies an early episode of volcanism, predating carbonate deposition of the overlying Waipuna Bay Formation. Late Altonian volcanic activity in Dunedin district is suggested. The timing of volcanism may coincide with the onset of volcanism at Karitane Peninsula.
Petrographic study of the Waipuna Bay Formation indicates that the grains are of three main types:
(1) carbonate and siliceous (e.g. sponge) material,
(2) terrigenous (i.e. sedimentary, volcanic and metamorphic detritus) and
(3) pyroclastic material.
The source of the calcium carbonate of the formation was much the same as that for the Caversham Formation. In addition, pressure solution during compaction released calcium carbonate which was re-precipitated as cement. Trachytic, basaltic and glassy vesicular lithic fragments occur in some lithofacies of the Waipuna Bay Formation, These are thought to have been derived from the rocks predating or contemporaneous with the deposition of the bentonite of the underlying School Creek Formation.
Tuff and lapilli tuff occur in marine strata of the upper member of the Waipuna Bay Formation. It is postulated that the pyroclastic material was derived from volcanoes located within the central part of Otago Harbour. Depositional Environment
The Caversham Formation is the basal unit of the regressive sequence in Dunedin district. Depositional environment of the lower member of the formation is interpreted as open marine, shelf, being deposited on an extensive erosional surface that developed throughout most of Oligocene time. Coarse fraction, grain size, calcium carbonate and foraminiferal variations up section in the middle and upper members of the Caversham Formation reflect gradual shallowing of the sea during deposition, that is from outer shelf to inne,r shelf.
The gross lithology, sedimentary structures and coarsening upwards nature of the Karitane Formation reflect a regressive trend from low energy intertidal to high energy estuary or beach environment. The Karitane Formation probably represents regressive linear clastic shoreline sedimentation or conceivably thin deltaic deposits, Orientation of channel axes indicate currents flowing in NW-SE directions. Carbonaceous quartz granule sand at the top of the Karitane Formation probably marks the onset of terrestrial conditions.
The Rona Nepheline-Bearing Trachyte Flows occur immediately above the Karitane Formation and are regarded as subaerial accumulations.
Lithologic and paleontologic relations of the Sulisker Formation indicate two episodes of the sedimentation. The first, the carbonaceous siltstone in the lower formation is interpreted as having been deposited near the boundary between marine and non-marine environments. The second, the fossiliferous calcareous lapillistone is interpreted to have been deposited in a shallow marine environment.
The School Creek Formation is interpreted as having been deposited in a lagoonal area undergoing slow sedimentation. Planktonic foraminifera in this formation may have been transported from the open sea to a lagoonal environment by tidal and storm currents. After deposition of the School Creek Formation was completed, the sea again covered the area and the clastic carbonat~s which formed the Waipuna Bay Formation were deposited.
The five units of the Waipuna Bay Formation are interpreted to represent two regressive cycles:
(1) Unit A (base): middle shelf to shallow-nearshore shelf environments
(2) Unit B: shallow subtidal to intertidal environments
(3) Unit C: shallow subtidal to high intertidal; shallow shelf environments represented towards the top
(4) Unit D: nearshore shelf environment.
(5) Unit E (Top): intertidal lagoon and tidal channel environments. The sudden .change in depositional environment within Unit C, that is from intertidal flat to shelf environment indicates abrupt transgression. The environmental changes between Unit D and E are probably related to the formation of barrier island in the offshore area and the contact between the two units is represented by a diastemic boundary.
At the end of sedimentation of Unit E the intertidal lagoonal basin had been filled, and by that time major subaerial volcanic eruptions had begun producing the tuff and lapi~li tuff of the Abernethys Creek Formation. Relations to Dunedin Volcanic Complex.
The deposition of terrigenous and bioclastic Miocene marine regressive strata in Dunedin district was interrupted and followed by volcanism, centred in the Port Chalmers-Portobello region and near Karitane Peninsula. The present discovery of bentonite beneath the Waipuna Bay Formation (Middle Miocene; Lillburnian) at Dowling Bay, and recognition of Rona Nepheline-Bearing Trachyte Flows (Lower Miocene; Late Altonian) at Karitane Peninsula indicates that volcanic activity commenced in Early Miocene (Late Altonian) time, that is slightly older than the previously understood. In addition, available K/Ar data dating of alkalic olivine dolerites in inland north Otago (i.e. Waipiata Volcanic Formation) indicates volcanism commenced there at 15-16 m.y. ago. Thus the Waipiata radiometric dates are reasonably consistent with age of initiation of volcanism in Dunedin district as indicated by data presented herein.
The Miocene regressive strata at Karitane Peninsula are folded into a north-south trending anticline with an axial plunge at about 10° northwards. This anticline is thought to be a reflection of tectonism associated with the Kaikoura Orogeny.
On the northern side of Otago Harbour (i.e. Dowling and Waipuna bays) and on the central Otago Peninsula (i.e. Sandymount and Varleys Hill) , the Miocene regressive strata are characteristically deformed by phonolitic intrusive domes, features which are numerous within the Dunedin district.
The apparent absence of Upper Miocene to Lower Pleistocene deposits in the Dunedin district reflects tectonic uplift and tilting which was evidently associated with volcanic activity and the Kaikoura Orogeny. Thus, Miocene regressive strata are overlain by Pleistocene raised beach deposits, a Pleistocene slide sheet of the Caversharn Formation and volcanic rocks and by loess deposits at Karitane Peninsula, volcanic solifluction overlies the regressive strata at northern Otago Harbour and central Otago Peninsula.
Named Localities:
Thesis description:
297 leaves : illus. (part col., part fold) maps (4 fold in pocket) ; 30 cm.
Department:
OU geology Identifier:
1978Sikumbang
OURArchive handle:
OURArchive access level:
Location (WKT, WGS84):
MULTIPOLYGON (((170.664811704980195 -45.867260439089961,170.665070886778722 -45.880601895885412,170.640830855061239 -45.87972271538775,170.640000296572509 -45.867131456502399,170.664811704980195 -45.867260439089961)),((170.678217918266995 -45.846576902378295,170.676620884051516 -45.85873751717039,170.664401033917244 -45.857535681387724,170.665159660291209 -45.845929646785002,170.678217918266995 -45.846576902378295)),((170.673751951607471 -45.796760832851554,170.653029770838288 -45.797289428870513,170.652004825077881 -45.782788921017314,170.67216163978938 -45.782630030635332,170.673751951607471 -45.796760832851554)),((170.68002352215052 -45.646068606630152,170.658300746119238 -45.645926956513975,170.656914426782208 -45.637901120965665,170.680163455071039 -45.637470480199198,170.68002352215052 -45.646068606630152)))
Files
Collection
Citation
Sikumbang, Nafrizal Nawawi., “Miocene regressive strata, Dunedin district, New Zealand.,” Otago Geology Theses, accessed April 16, 2026, https://theses.otagogeology.org.nz/items/show/113.