Crater stratigraphy and the post-eruptive evolution of Foulden Maar, southern New Zealand

摘要

Foulden Maar, Waipiata Volcanic Field, New Zealand is a partly eroded maar-diatreme formed by phreatomagmatic eruptions c. 23 Ma. Its post-eruptive evolution is reconstructed by combining outcrop, drillcore and physical core rock properties with pollen data. Facies associations in a 190 m thick composite section of the central crater sediments record four depositional stages: (1) immediate post-eruptive deposition of collapsed crater wall and tephra ring material by subaqueous gravity flows; (2) re-deposition of tephra by hyperconcentrated to turbulent gravity flows in a steep-sided lake; (3) seasonally mediated background sedimentation with recurring gravity flows in a meromictic lake; and (4) diminishing turbidity currents under decreasing relief and biogenic sedimentation over c. 130 ka. Clasts in the basal crater fill represent accidental lithic clasts of primary ejecta and indicate eruption into a mixed hard-soft rock substrate. Foulden Maar represents a 'classical' lacustrine maar crater sequence and confirms generally similar post-eruptive processes and sedimentation patterns in enclosed, lacustrine maar basins.