Long-term evolution of an Oligocene/Miocene maar lake from Otago, New Zealand

Foulden Maar is a highly resolved maar lake deposit from the South Island of New Zealand comprising laminated diatomite punctuated by numerous diatomaceous turbidites. Basaltic clasts found in debris flow deposits near the base of the cored sedimentary sequence yielded two new 40Ar/39Ar dates of 24....

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Bibliographic Details
Published in:Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2015-01, Vol.16 (1), p.59-76
Main Authors: Fox, B. R. S., Wartho, J., Wilson, G. S., Lee, D. E., Nelson, F. E., Kaulfuss, U.
Format: Article
Language:English
Subjects:
Debris flow
Deglaciation
Environmental changes
Geophysics
Glaciation
Lakes
maar lakes
magnetic mineralogy
Magnetic properties
Magnetism
Miocene
Miocene climate
New Zealand
Oligocene
paleoclimate
Sedimentary geology
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Summary:Foulden Maar is a highly resolved maar lake deposit from the South Island of New Zealand comprising laminated diatomite punctuated by numerous diatomaceous turbidites. Basaltic clasts found in debris flow deposits near the base of the cored sedimentary sequence yielded two new 40Ar/39Ar dates of 24.51 ± 0.24 and 23.38 ± 0.24 Ma (2σ). The younger date agrees within error with a previously published 40Ar/39Ar date of 23.17 ± 0.19 Ma from a basaltic dyke adjacent to the maar crater. The diatomite is inferred to have been deposited over several tens of thousands of years in the latest Oligocene/earliest Miocene, and may have been coeval with the period of rapid glaciation and subsequent deglaciation of Antarctica known as the Mi‐1 event. Sediment magnetic properties and SEM measurements indicate that the magnetic signal is dominated by pseudo‐single domain pyrrhotite. The most likely source of detrital pyrrhotite is schist country rock fragments from the inferred tephra ring created by the phreatomagmatic eruption that formed the maar. Variations in magnetic mineral concentration indicate a decrease in erosional input throughout the depositional period, suggesting long‐term (tens of thousands of years) environmental change in New Zealand in the latest Oligocene/earliest Miocene. Key Points: The Foulden Maar sediments can be dated to the Oligocene/Miocene boundary The magnetic fraction is a population of PSD‐sized detrital pyrrhotite Magnetic properties indicate a millennial‐scale environmental shift
ISSN:1525-2027
1525-2027
DOI:10.1002/2014GC005534