Browsing by Author "Peti, L"
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- ItemDevelopment of a multi-method chronology spanning the last glacial interval from Orakei maar lake, Auckland, New Zealand(European Geosciences Union, 2020-12-15) Peti, L; Fitzsimmons, KE; Hopkins, JL; Nilsson, A; Fujioka, T; Fink, D; Mifsud, C; Christl, M; Muscheler, R; Augustinus, PCNorthern New Zealand is an important location for understanding Last Glacial Interval (LGI) palaeoclimate dynamics, since it is influenced by both tropical and polar climate systems which have varied in relative strength and timing. Sediments from the Auckland Volcanic Field maar lakes preserve records of such large-scale climatic influences on regional palaeo-environment changes, as well as past volcanic eruptions. The sediment sequence infilling Orakei maar lake is continuous, laminated, and rapidly deposited, and it provides a high-resolution (sedimentation rate above ∼ 1 m kyr−1) archive from which to investigate the dynamic nature of the northern New Zealand climate system over the LGI. Here we present the chronological framework for the Orakei maar sediment sequence. Our chronology was developed using Bayesian age modelling of combined radiocarbon ages, tephrochronology of known-age rhyolitic tephra marker layers, 40Ar∕39Ar-dated eruption age of a local basaltic volcano, luminescence dating (using post-infrared–infrared stimulated luminescence, or pIR-IRSL), and the timing of the Laschamp palaeomagnetic excursion. We have integrated our absolute chronology with tuning of the relative palaeo-intensity record of the Earth's magnetic field to a global reference curve (PISO-1500). The maar-forming phreatomagmatic eruption of the Orakei maar is now dated to > 132 305 years (95 % confidence range: 131 430 to 133 180 years). Our new chronology facilitates high-resolution palaeo-environmental reconstruction for northern New Zealand spanning the last ca. 130 000 years for the first time as most NZ records that span all or parts of the LGI are fragmentary, low-resolution, and poorly dated. Providing this chronological framework for LGI climate events inferred from the Orakei sequence is of paramount importance in the context of identification of leads and lags in different components of the Southern Hemisphere climate system as well as identification of Northern Hemisphere climate signals. © Author(s) 2020 This work is distributed under the Creative Commons Attribution 4.0 Licence.
- ItemIntegrated age modelling of numerical, correlative and relative dating of a long lake sediment sequence from Orakei maar palaeolake, Auckland, New Zealand(Copernicus GmbH, 2019-04-11) Peti, L; Augustinus, PC; Fujioka, T; Mifsud, C; Nilsson, A; Muscheler, R; Fitzsimmons, KE; Hopkins, JLAccurate and precise chronologies are fundamental for successful Quaternary palaeo-climate/environment reconstruction and correlation with global climatic events. Aside from varved lake sequences, chronologies for sediment archives typically depend on age models developed from a limited number of dated horizons, often with large associated errors, age reversals, or minimum/maximum age constraints. Whilst the approach to generating chronologies for sediment cores has moved on from linear interpolation to considering age uncertainties and developing more nuanced accumulation models, these age models rarely reach the resolution and precision desired for millennial-scale palaeo-climatic correlations, particularly beyond the limits of the more precise radiocarbon method. Bayesian modelling offers the opportunity to optimise age models by combining all available information on the depositional history of the basin. Here we address this issue for the Orakei maar palaeolake sequence from Auckland, New Zealand. The Orakei maar sequence offers a high-resolution and continuous record of climatic variations spanning much of the last glacial cycle and is one of the few from the southern hemisphere mid-latitudes. The Orakei sequence spans ca. 120 to 10 ky; our chronology is derived from tephrochronology, radiocarbon dating, post-IR IRSL luminescence dating, relative palaeomagnetic intensity changes and meteoric Beryllium-10 flux. Prior to 40 ka, our age model relies on comparison with the global PISO-1500 palaeointensity stack and 10Be-flux. We generate our age model for the time interval ca. 50 to 10 ky using Bacon (rBacon in R), using non-normal error distribution of un-calibrated ages when necessary, facies-dependent variable mean accumulation rates and accounting for thick horizons of instantaneous deposition (i.e. tephra and mass movement deposits). This approach allows us to generate a high-resolution age model suitable for correlation of millennial-scale oscillations in our record, based on environmental magnetism and meteoric 10Be flux, with global records of past climate such as polar ice core, tropical lake and speleothem archives. © Author(s) 2018. CC Attribution 4.0 license.
- ItemIntegrated age modelling of numerical, correlative and relative dating of a long lake sediment sequence from Orakei maar paleolake, Auckland, New Zealand(Australiaian Quaternary Association Inc., 2018-12-10) Peti, L; Augustinus, PC; Woodward, C; Nilson, AAccurate and precise chronologies are fundamental for any successful Quaternary paleo-climate/-environment reconstruction. Aside from varved lake sequences, all records depend on sediment core age models developed from a limited number of dated horizons, often with large errors. Hence, it is crucial to combine every piece of available information on the depositional history of the basin with modelling tools used for chronology development such as Bacon, a Bayesian age modelling package. Whilst sediment core chronology development has progressed from linear interpolation between dated horizons to considering uncertainties and Bayesian accumulation models, these age models rarely reach the resolution and precision desired for reliable paleo-climatic interpretations, especially in pre-Holocene sequences as errors increase and radiocarbon dating is not suitable anymore. We address this issue here in the context of Orakei maar paleolake sequence, Auckland, New Zealand. This record spans ca. 120 to 10 cal ka BP and is underpinned by tephrochronology, radiocarbon dating and relative changes in paleointensity of the earth magnetic field. Pre-40 cal ka BP, the age model relies on comparison with and correlation to the global PISO-1500 paleointensity stack through dynamic time warping (DTW in R). The chronology for the time interval ca. 50 to 10 cal ka BP has been estimated in Bacon (rBacon in R) with non-normal error distribution of un-calibrated ages, variable mean accumulation rates and accounting for many “slumps” (horizons of instantaneous deposition).The Orakei maar paleo-lake age model is a work in progress but serves as an example for extended age modelling from lake sediment sequences, particularly beyond the radiocarbon age limit. Furthermore, the Orakei maar sequence offers a high-resolution and continuous record of climatic variations that span much of the last glacial cycle and is one of the few from the mid-latitudes of the Southern Hemisphere. The rarity of records of this type makes Orakei maar a crucial record for development of an improved understanding of the global climate system because of its potential to be tied directly to the polar ice core and tropical lake and speleothem records.
- ItemItrax μ-XRF core scanning for rapid tephrostratigraphic analysis: a case study from the Auckland Volcanic Field maar lakes(John Wiley & Sons, Inc, 2019-07-23) Peti, L; Gadd, PS; Hopkins, J; Augustinus, PCItrax micro X-ray fluorescence (μ-XRF) core scanning is a non-destructive, rapid approach to measuring elemental concentrations and their variability in sediment cores. As such, it records elemental signatures of tephra layers, which serve as correlation tie points and chronological markers for these sedimentary archives of past climatic changes. The traditional tephra identification approach using electron microprobe-based geochemical fingerprinting of glass shards is a slow and invasive process, whilst μ-XRF scanning of rhyolite tephra in sediment cores from Auckland (New Zealand) could provide a faster, non-invasive approach to aid the recognition of tephra layers. This study highlights the potential and pitfalls in this novel approach: changes in most scanning parameters, and the use of two different Itrax core scanners, still led to similar chemical characterizations of the tephra layers. Changes in other scanning parameters have a biasing influence on the chemical characterization of the tephra, which would lead to misidentification of unknown layers. We demonstrate that μ-XRF core scanning provides a faster and non-invasive approach to correlation of sediment sequences using chemically distinct, visually pure tephra layers if a strict scanning protocol is followed. Nevertheless, an extensive database of μ-XRF-scanned rhyolite tephra is required for recognition of unknown tephra units using this approach. Copyright © 2019 John Wiley & Sons, Ltd.
- ItemMulti-method age model of a long lake sediment sequence from Orakei maar palaeolake, Auckland, New Zealand(International Union for Quaternary Research (INQUA), 2019-07-30) Peti, L; Fink, D; Fujioka, T; Mifsud, C; Nilsson, A; Muscheler, R; Fitzsimmons, KE; Hopkins, JL; Augustinus, PCMeaningful reconstructions of Quaternary palaeo-climate and -environmental reconstruction rely heavily on accurate and precise chronologies. Long and continuous lake sediment sequences are outstanding archives of past climatic change but, unless varved, depend on the development of detailed age models. Such models estimate the age-depth-relationship of the sequence from a limited number of dated horizons, which often carry large associated errors, age reversals, or minimum/maximum age constraints. Approaches to chronology development for sediment sequences have seen major improvements such as more nuanced Bayesian accumulation models but still rarely reach the resolution and precision desired for the study objectives in the context of high-resolution palaeo-climatic correlations of global events. This is particularly true beyond the limits of the well-established and more precise radiocarbon dating method. Sediment archives older than 50 ka have often not been used to its full potential for the lack of chronology estimates. In such cases, alternative methods including correlative and relative dating methods may need to be employed. Currently, a standardised method of integrating absolute dating with wiggle-matched curves of comparable proxies between the unknown and a dated sequence is lacking. Here we address this problem in the context of the Orakei maar palaeolake sequence from Auckland, New Zealand. This sediment record is a high-quality example of one of the rare high-resolution and continuous lacustrine archives of climatic variations in the southern hemisphere mid-latitudes over much of the last glacial cycle. Based on previous estimates, the Orakei sequence spans the interval ca. 126 cal ka BP to 9 cal ka BP. The presented Orakei chronology is based on absolute ages from tephrochronology, radiocarbon dating and post-IR IRSL luminescence dating. Prior to 40 ka, tuning of relative palaeomagnetic intensity changes and meteoric Beryllium-10 flux to the global PISO-1500 palaeointensity stack between absolute age markers allows to establish a novel accumulation model for the Orakei sequence. This approach allows us to generate a high-resolution age model suitable for correlation of millennial-scale oscillations from the SW Pacific to global records of past climate such as polar ice core, tropical lake and speleothem archives. © The Authors.
- ItemOrakei maar paleolake (Auckland, NZ):A multi-method approach to the composite stratigraphy of a long sediment core(Australiasian Quaternary Association Inc., 2018-12-10) Peti, L; Augustinus, PC; Woodward, CThe development of records of Quaternary environmental and –climatic changes relies largely on long, complete sediment sequences. However, coring techniques do not allow extraction of one continuous record of sedimentation to be recovered from a single drill hole. In order to reconstruct a complete record, it is common practice to drill two or more overlapping cores with a depth offset to overcome coring-induced loss and disturbance and then stitch these records together using stratigraphic markers to produce a master stratigraphy. However, details of the process used and critical uncertainties are rarely reported despite the fact that spurious correlations may alter subsequent paleoenvironmental interpretations. Here we detail the procedure employed to build a composite stratigraphy from three overlapping long lake sediment cores from Orakei maar paleolake (Auckland). Orakei maar was created by a phreato-magmatic eruption to forming a lake basin of a low surface-to-depth ratio and virtually no catchment. The accumulated sediment can be considered a direct recorder of climatic and environmental changes over the Last Glacial Cycle in the Southern Hemisphere mid-latitudes, a crucial but under-studied part of the global climatic system. Finely laminated sediment in the Orakei record can be aligned and correlated along visually distinct marker horizons, as well as tephra layers (Fig. 1), with sub-cm to mm resolution, supplemented by μ-XRF core scanning elemental and X-ray density variability. Complications arise from lateral inhomogeneities in sedimentation along the lake bottom and hence, larger differences between the three cores. These sections, usually of coarser grain size, likely caused by local landslides from the crater rim, are correlated based on: visual logging, common pattern in μ-XRF elemental and Xray density variation, and typical depth offset between the observed debris flows in the cores. Figure 1: Composite stratigraphy and lithology of Orakei maar paleo-lake record built from three overlapping sediment cores. © The Authors
- ItemTowards characterising rhyolitic tephra layers from New Zealand with rapid, non-destructive μ-XRF core scanning(Elsevier, 2019-04-04) Peti, L; Augustinus, PC; Gadd, PS; Davies, STephra layers are of importance for the construction of reliable age control in late Quaternary paleoenvironmental and volcanic hazard studies, especially in volcanically-active settings such as the North Island of New Zealand. However, their identification involves time-consuming and destructive processing steps, making the application of non-destructive μ-XRF core scanners potentially advantageous for tephra identification. Here, we investigate the potential of the Itrax μ-XRF core scanner to differentiate between rhyolitic tephra layers sourced from various northern New Zealand rhyolitic volcanic centres deposited in maar lakes of the Auckland Volcanic Field. In their macroscopic form these tephra layers are usually visibly distinct when surrounded by a dark, organic-rich sediment matrix, although their attribution to source volcanic centre and eruption typically requires examination of their mineral assemblages, combined with chemical fingerprinting of the rhyolite glass shards. We demonstrate that μ-XRF core scanning of rhyolitic tephra layers from the Taupo Volcanic Zone and Tuhua Volcanic Centre can also allow identification, and sometimes differentiation, of the tephra using μ-XRF-derived elemental counts, especially high Si, K, Ca and very low Br and Ti. Different rhyolite tephra layers vary in their relative abundances of major, minor and trace elements as is evident from electron microprobe and LA-ICP-MS analyses of their glass shards. Mo-tube based μ-XRF cannot detect Na nor Mg and is of lower reliability for the lighter elements (Ca, Al) which play an important role in traditional tephra fingerprinting. Nevertheless, we are able to demonstrate that μ-XRF core scanning data can distinguish between previously identified tephra layers using multivariate statistics. Furthermore, the study emphasises the need for a standard protocol for μ-XRF core scanning of tephra layers for this approach to be more widely applicable, especially to aid or be a substitute for conventional geochemical approaches used for tephra fingerprinting. © 2018 Elsevier Ltd and INQUA.
- ItemUsing high-resolution geochemical data from XRF core scanning to interpret major climatic events at the Uddelermeer site (The Netherlands)(International Union for Quaternary Research (INQUA), 2019-07-27) Gadd, PS; Heijnis, H; Peti, L; Engels, SHigh-resolution X-ray fluorescence (XRF) scanning data is used as a palaeoclimate proxy on a long sediment record retrieved from Lake Uddelermeer. Lake Uddelermeer is the only lake in The Netherlands to contain a continuous record of environmental and climate change from the late Pleistocene to present. Due to its unique character, the lake has been studied by various research groups since the 1950s. Here we focus on a newly retrieved sediment core which has been radiocarbon dated and for which a variety of palaeoecological and palaeoclimatological data is available. We scanned the 15.6 m sediment sequence at 200 µm interval and geochemical proxies were utilised to infer changes in the lake system during major climatic events, and compared our results to existing palaeoecological and palaeoclimatological data from the same sediment sequence. Commonly used proxies such as Si/Ti can imply changes in biogenic silica and Rb/Sr can suggest chemical weathering. These proxies were looked at in detail in conjunction with the dates to confirm the timing and impact of the following major events: the Bølling-Allerød, Younger Dryas, Pre-boreal oscillations, the 9.3 ka, 8.2 ka, 2.8 ka and the Little Ice Age. Additionally, the use of high-resolution XRF scanning can be very useful for finding crypto tephra, and in this presentation, we will explore the potential occurrence of the Vedde Ash (Iceland) and the Laacher See Ash (Germany) in the sediment sequence, as well as other unidentified crypto tephra during the Last Glacial termination.