Cyclostratigraphy of late oligocene - early miocene strata : an example from the Waiau Basin, western Southland, New Zealand.
A section of marine strata in the Waicoe sub-basin (Waiau Basin), Southland, New Zealand records the Oligocene - Miocene (O-M) epoch boundary and the Waitakian to Otaian New Zealand Stage boundary. The sedimentary succession is cyclic, is 470m thick and ranges in age from 24Ma at the base to 18-19Ma at the top as indicated by biostratigraphy. The section comprises alternating lithologies of siliciclastic sand and mud beds in the lower 1/3 of the section and alternating lithologies of bioclastic sand and mud beds in the upper 2/3 of the measured section. Facies analysis indicates a deep marine depositional environment that sourced sediment loads from the shelf margins. Shelf margins are interpreted to have been narrow margins which were vulnerable to destabilisation at the shelf break when sediment exceeded accommodation space on the shelf. Destabilisation of the shelf break is interpreted to have generated turbidite flows that were deposited in the deep marine depositional environment. Relative sea level change is interpreted to be a significant control on accommodation space on the shelf. A low relative sea level is interpreted to account for extended periods of shelf exposure that enhanced turbidite generation. Spectral analysis of cyclically varying visual grain size estimates indicates coincidence of turbidite generation with changes in Earth's orbit on 40-400kyr timescales. This suggests that glacio-eustasy was a significant influence on turbidite deposition across the O-M boundary in the Waiau Basin. The 400kyr cycle was identified by Zachos et al. (2001) as coinciding with the Mi-1 event (first glaciation in the Miocene) and a period of low amplitude in the variability of obliquity and also suggested that Mi-1 may account for an Antarctic ice sheet at this time. Grain size derived glacio-eustasy across the O-M boundary in the Waiau Basin confirm significant sea level lowering co-incident with the Mi-1 oxygen isotope event.
Advisor: Wilson, Gary
Degree Name: Master of Science
Degree Discipline: Geology
Publisher: University of Otago
Research Type: Thesis
ix, 142 leaves :ill., maps ; 30 cm. Includes bibliographical references. Thesis submitted for the Master of Science degree at University of Otago, Dunedin, New Zealand. Two folded sheets in pocket inside back cover comprise Appendix 4.1 and Appendix 4.2. University of Otago department: Geology.