Stratigraphy and sedimentology of the Orakei maar lake sediment sequence (Auckland Volcanic Field, New Zealand)

Leonie Peti,Paul C Augustinus

doi:10.5194/sd-25-47-2019

Abstract

Abstract. Global paleo-climate reconstructions are largely based on observations from the Northern Hemisphere despite increasing recognition of the importance of the Southern Hemisphere mid-latitudes for understanding the drivers of the global climate system. Unfortunately, the required complete and high-resolution terrestrial records from the Southern Hemisphere mid-latitudes are few. However, the maar lakes in the Auckland Volcanic Field (AVF), New Zealand, are crucial in this regard as they form outstanding depositional basins due to their small surface-to-depth ratio, restricted catchment, and absence of ice cover since their formation, hence ensuring continuous sedimentation with anoxic bottom water. Significantly, the estimated age of the AVF of ca. 250 ka may allow development of a continuous sediment record spanning the last two glacial cycles. The Orakei maar lake sediment sequence examined in this study spans the Last Glacial Cycle (ca. 126 to ca. 9.5 ka cal BP) from the phreatomagmatic eruption to the crater rim breach due to post-glacial sea-level rise. Two overlapping cores of >100 m sediment were retrieved and combined to develop a complete composite stratigraphy that is presently undergoing a wide range of multi-proxy analyses.

Highlights

Lake sediments are important archives for Quaternary paleoenvironmental and paleo-climatic reconstruction, when sedimentation has been continuous and sedimentation rates high, as they offer a variety of high-resolution proxy records of environmental change
Many basaltic tephra layers have been recorded in the Auckland Volcanic Field (AVF) maar sediment cores, but age estimates rely on sedimentation rate extrapolation to and correlation with the source volcanoes, which mostly have not been dated unambiguously (Hopkins et al, 2015, 2017; Leonard et al, 2017; Lindsay et al, 2011; Molloy et al, 2009)
The history of the lake commenced with the maar-forming phreatomagmatic eruption, through various stages of changing deep lacustrine conditions, minor mass movement events associated with erosion/collapse of the crater rim, and deposition of distal rhyolitic and locally derived basaltic tephra layers

Summary

Introduction

Lake sediments are important archives for Quaternary paleoenvironmental and paleo-climatic reconstruction, when sedimentation has been continuous and sedimentation rates high, as they offer a variety of high-resolution proxy records of environmental change. AVF maar lakes preserve complete archives of eruptions of the local basaltic volcanoes as well as rhyolitic and andesitic volcanic systems situated in the Taupo Volcanic Zone (TVZ) and Egmont Volcano (Fig. 1) to the south of Auckland (Hopkins et al, 2015; Molloy et al, 2009; Shane, 2005; Shane and Hoverd, 2002) This is of importance as the City of Auckland, with > 1.5 million inhabitants, is situated on a potentially active volcanic field for which eruption frequencies cannot be derived from the historical record (Edbrooke et al, 2003; Molloy et al, 2009; Newnham et al, 1999).

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Results

Conclusion