Orbital forcing of mid-latitude Southern Hemisphere glaciation since 100 ka inferred from cosmogenic nuclide ages of moraine boulders from the Cascade Plateau,southwest New Zealand

摘要

Cosmogenic nuclide (Be-10) exposure dating of moraine boulders in the Cascade Valley,southwest New Zealand,reveals three phases of glaciation with similar maximum magnitude since 100 ka.In this area,8-10 lateral moraines were deposited during the Last Glacial Maximum (LGM) at 22-19 ka,and >15 lateral moraines and three end moraines were deposited during recession after the LGM.Also,three exposure ages of 29-33 ka from pre-LGM deposits may indicate increased weathering and erosion at the onset of the LGM in New Zealand,as has been suggested by other studies.An exposure age of 57.8 ± 2.7 ka from one of the highest moraines,combined with previous studies of cave speleothems,glacial features offset by the Alpine fault,the Vostok dust record,and sediment cores,supports the inference that a significant glacial phase culminated at 66-58 ka.A cluster of five exposure ages from older moraines reveals a glacial phase with at least three advance-retreat cycles at 79.0 ± 3.9 ka.Correlation between the ages of glacial periods and the timing of Southern Hemisphere summer insolation minima suggests that orbital forcing has played a first-order role in regulating glacial extent in New Zealand.