Chronology of the middle Miocene climatic deterioration
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The middle Miocene climatic deterioration was one of the most significant climatic events of the Cenozoic. It is marked by a 1 (0/00) enrichment of the deep sea benthic oxygen isotope record over three million years. This 1 (0/00) enrichment of the deep-sea benthic oxygen isotope record potentially equates to a volume of water equivalent to all of the present day ice on the Antarctic continent (27 million km³ of water) evaporated from the oceans and deposited on land as ice (Pekar et al, 2005).
The middle Miocene was the beginning of a period of global climatic cooling where the world's climate shifted from being warm and subtropical to more cool and seasonal. In the geological record, the effects on the biota were startling both on land and in the oceans. In the mid latitude regions of the world, palm dominated forests gave way to shrubs and temperate forests and the oceanic records indicate a dramatic cooling with the influx of sub-Antarctic microfauna in both offshore and onshore sediment records. Many questions still remain about the cause this dramatic climate crash.
GNS Science are undertaking a paleoclimate study of a ∼700 metre thick, middle Miocene, hemipelagic mudstone sequence cropping out in the Bryce Burn, Western Southland, New Zealand. This thesis represents a part of that study with the specific aim of developing a high resolution magnetostratigraphic age model that will provide the age control for the larger paleoclimate proxy data set.
A total of 537 oriented paleomagnetic samples were collected from the Bryce Burn section. Eleven magnetozones were recognised in the Bryce Burn section nine of which are correlated with the middle Miocene Geomagnetic Polarity Time Scale (GPTS) implying a sedimentation rate of between 19.7 cm/kyr and 25.1 cm/kyr. The magnetostratigraphic age model was verified by an astrochronological sedimentation rate of between 18cm/kyr and 26 cm/kyr, and antiquity of magnetisation was confirmed by a reversals test. Rock magnetic analyses indicate that single domain magnetite or titanomagnetite is the dominant remanence carrying minerals. However, greigite and goethite were also found in some specimens.
Magnetic susceptibility cycles were used to develop the astrochronological sedimentation rate and were also used as a proxy for glacially driven oceanic productivity. The magnetic susceptibility record suggests that the Antarctic glacial cycles were paced with eccentricity during the early middle Miocene, with obliquity during the middle middle Miocene and with eccentricity again during the late middle Miocene. The switch from eccentricity to obliquity paced glacial cycles occurred at ∼14.6 Ma. It was concomitant with the beginning of the Mi-3 isotope event which is marked by a ∼160 ka hiatus in the Bryce Burn section. The switch back from obliquity to eccentricity paced glacial cycles was concomitant with the maximum inflection point of the Mi-3 isotope event; and also concomitant with the coolest bottom waters or greatest global ice volume.
The middle Miocene was the beginning of a period of global climatic cooling where the world's climate shifted from being warm and subtropical to more cool and seasonal. In the geological record, the effects on the biota were startling both on land and in the oceans. In the mid latitude regions of the world, palm dominated forests gave way to shrubs and temperate forests and the oceanic records indicate a dramatic cooling with the influx of sub-Antarctic microfauna in both offshore and onshore sediment records. Many questions still remain about the cause this dramatic climate crash.
GNS Science are undertaking a paleoclimate study of a ∼700 metre thick, middle Miocene, hemipelagic mudstone sequence cropping out in the Bryce Burn, Western Southland, New Zealand. This thesis represents a part of that study with the specific aim of developing a high resolution magnetostratigraphic age model that will provide the age control for the larger paleoclimate proxy data set.
A total of 537 oriented paleomagnetic samples were collected from the Bryce Burn section. Eleven magnetozones were recognised in the Bryce Burn section nine of which are correlated with the middle Miocene Geomagnetic Polarity Time Scale (GPTS) implying a sedimentation rate of between 19.7 cm/kyr and 25.1 cm/kyr. The magnetostratigraphic age model was verified by an astrochronological sedimentation rate of between 18cm/kyr and 26 cm/kyr, and antiquity of magnetisation was confirmed by a reversals test. Rock magnetic analyses indicate that single domain magnetite or titanomagnetite is the dominant remanence carrying minerals. However, greigite and goethite were also found in some specimens.
Magnetic susceptibility cycles were used to develop the astrochronological sedimentation rate and were also used as a proxy for glacially driven oceanic productivity. The magnetic susceptibility record suggests that the Antarctic glacial cycles were paced with eccentricity during the early middle Miocene, with obliquity during the middle middle Miocene and with eccentricity again during the late middle Miocene. The switch from eccentricity to obliquity paced glacial cycles occurred at ∼14.6 Ma. It was concomitant with the beginning of the Mi-3 isotope event which is marked by a ∼160 ka hiatus in the Bryce Burn section. The switch back from obliquity to eccentricity paced glacial cycles was concomitant with the maximum inflection point of the Mi-3 isotope event; and also concomitant with the coolest bottom waters or greatest global ice volume.
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xiv, 142 leaves : ill., maps ; 30 cm. + 3 maps and 1 CD-ROM.
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2006Ohneiser
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POLYGON ((167.579618451597099 -45.961457466455663,167.610411450409401 -45.963067013753438,167.608720774838957 -45.982636246092625,167.578202084626952 -45.980295039560623,167.579618451597099 -45.961457466455663))
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Ohneiser, Christian., “Chronology of the middle Miocene climatic deterioration,” Otago Geology Theses, accessed August 12, 2026, https://theses.otagogeology.org.nz/items/show/469.