Open AccessLong‐term evolution of an Oligocene/Miocene maar lake from Otago, New Zealand
Author(s) -
Fox B. R. S.,
Wartho J.,
Wilson G. S.,
Lee D. E.,
Nelson F. E.,
Kaulfuss U.
Publication year - 2015
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2014gc005534
Subject(s) - maar , geology , phreatomagmatic eruption , tephra , sedimentary rock , paleontology , geochemistry , lithostratigraphy , clastic rock , pyrrhotite , sedimentary depositional environment , volcano , volcanic rock , pyrite , structural basin
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 40 Ar/ 39 Ar dates of 24.51 ± 0.24 and 23.38 ± 0.24 Ma (2 σ ). The younger date agrees within error with a previously published 40 Ar/ 39 Ar 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.