Paleomagnetic, micropaleontological and isotopic variation of the Bryce Burn section, Southland

Arthur, Kristina.

The Earth’s climate has undergone a continuous evolution throughout geological time, with trends in warming and cooling providing points of study for scientists worldwide. One such trend of climatic change is the Mid- Miocene Climatic Optimum, a period of global warmth leading up to 14.7 Ma, followed by a period of global cooling from 14.7 to 13.9 Ma, triggered by orbital variation (Holbourn et al., 2007). The Waiau Basin, Southland, New Zealand, is well situated for paleoclimate analysis during this time period, with influence from the Southern Ocean providing records of global change. The Waicoe mudstone has a steady sedimentation rate of approximately 25 cm/kyr. This allows for high resolution sampling of one sample per stratigraphic meter, or approximately one sample every 4,000 years.
This study examines a 150 m sequence that formed during an ~800,000 year period from 15.4 to 14.6 Ma. Environmental magnetism, micropaleontology and oxygen stable isotope analyses have been used to quantify the changing environment of the Waicoe mudstone in the Waiau Basin during this period. This thesis will address whether the environment of the Waiau Basin at this time was influenced by global cooling patterns and an expanding East Antarctic Ice Sheet, and whether climatic variations within the basin were driven by orbital variation. High resolution sampling also aimed to show small-scale changes within the climatic variation, as well as broader changes across the ~800,000 years studied.
The data obtained indicate deposition in a deep, cold water basin. Paleomagnetic and micropaleontological results show evidence of at least five downslope movement events within the Waiau Basin in the time period studied. These events are associated with an influx of terrigenous material and specimens of the shallow, warm water foraminifera Amphistegina sp.. Stable isotope analyses from foraminifera tests (δ18O) are inconclusive because of poor preservation of foraminifera, as shown by common pyritisation and μm-scale recrystallisation.
While the Waiau Basin may have been influenced by the global cooling indicated by other works (e.g. Field et al. (2009)), the lack of suitable foraminifera for stable isotope analyses means this hypothesis cannot be confirmed. The evidence of downslope movement events within the Waiau Basin, as well as the development of the basin in association with the Moonlight Fault System, suggests a strong local tectonic influence on the environmental changes of the Waicoe mudstone.

x, 78 leaves : ill. (chiefly col.), col. maps ; 30 cm. + 1 DVD-ROM (4 3/4 in.)

2010Arthur

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