Paleomagnetic Constraint of the Brunhes Age Sedimentary Record From Lake Junín, Peru

Abstract

Normalized remanence, a proxy for relative geomagnetic paleointensity, along with radiocarbon and U-Th age constraints, facilitates the generation of a well-constrained chronology for sediments recovered during International Continental Scientific Drilling Program (ICDP) coring of Lake Junín, Peru. The paleomagnetic record of the ∼88 m stratigraphic section from Lake Junín was studied, and rock magnetic variability constrained, through analysis of 109 u-channel samples and 56 discrete samples. Downcore variations in sediment lithology reflect climate and hydrological processes over glacial-interglacial time frames and these changes are strongly reflected in the bulk magnetic properties. Glacial sediments are characterized by higher detrital silt content, higher magnetic susceptibility and magnetic remanence values, and a magnetic coercivity that is characteristic of ferrimagnetic (titano)magnetite and/or maghemite. Interglacial sediments and low lake-level facies are dominated by carbonate lithologies and/or peat horizons that result in lower magnetic concentration values. Sediments with moderately high Natural Remanent Magnetization (NRM) intensity (>1 × 10 −3 A/m) have well resolved component directions and inclination values that vary around geocentric axial dipole expectations. This remanence value can be used as a threshold to filter the lowest quality paleomagnetic data from the record. Normalized NRM intensity values are also sensitive to lithologic variability, but following NRM remanence filtering, only the highest quality ferrimagnetic dominated data are retained which then show no coherence with bulk magnetic properties. Constrained by the existing radiocarbon based chronology over the last 50 kyrs and 18 U-Th age constraints that are restricted to five interglacial sediment packages, filtered normalized remanence parameters compare well with global relative paleointensity stacks, suggesting relative variations in geomagnetic intensity are preserved. By adjusting the existing age-depth model we improve the correlation between the Junín normalized intensity record and a well-dated RPI stack and RPI model. We then incorporate these paleomagnetic tie points with the existing radiometric dates using a modeling approach to assess uncertainty and refine

Relative Paleointensity Record of Integrated Ocean Drilling Program Site U1396 in the Caribbean Sea: Geomagnetic and Chronostratigraphic Observations in the Pliocene

“…These intervals often possess relatively low MAD values and relatively high r-values (Figure 6a) and are otherwise indistinguishable from NV classified sediments. As these intervals appear potentially suitable for generating RPI estimates, we do not automatically remove all VC classified intervals; instead we adopt a three-step data filtering process for the unit 1 polarity-reversal-free data set that builds on the approaches of Xuan et al (2016) and Hatfield et al (2020). First, we remove all data with r-values <0.9.…”

Development of a multi-method chronology spanning the Last Glacial Interval from Orakei maar lake, Auckland, New Zealand

“…Channell et al, 2000;Laj et al, 2004). This approach was successful in Lake Van (Turkey), where several RPI minima were aligned to provide a chronologic framework (Hatfield et al, 2020;Stockhecke et al, 2014). We use a dynamic programming algorithm to align the Orakei RPI with the virtual axial dipole moment (VADM) reference curve from the marine PISO-1500 stack (Channell et al, 2009).…”

“…We use a dynamic programming algorithm to align the Orakei RPI with the virtual axial dipole moment (VADM) reference curve from the marine PISO-1500 stack (Channell et al, 2009). Dynamic time warping (DTW) aligns time series datasets through generalised dynamic programming (Hay et al, 2019) and has been adapted for palaeomagnetic vector data by Hagen et al (2020). The DTW algorithm calculates every possible match between the reference and query time series at every stratum (data point), producing a cost matrix.…”

“…This prevents the creation of age inversions and heavily penalises alignments between points with very different indices, so that major jumps and/or hiatuses are very unlikely. The DTW approach relies on (mostly) complete time series with a substantial component that overlaps between the reference and query time series (Hay et al, 2019). Visual inspection of the Orakei RPI and the variation of the PISO-1500 VADM (Channell et al, 2009) over the period of ca.…”

An uncertainty-focused database approach to extract spatiotemporal trends from qualitative and discontinuous lake-status histories

“…Unfortunately, the GLSDB was last updated in the late 1990s and does not include the many new palaeolimnological studies published since then. An update of the chronologies of the records stored in the database is also necessary because all the chronologies were reported as uncalibrated radiocarbon dates, and because many other geochronological methods have since been applied to palaeolimnological archives (e.g., Kutterolf et al, 2016;Roberts et al, 2018;Chen et al, 2020;Hatfield et al, 2020). In parallel, awareness has grown regarding the necessity to account for uncertainties when interpreting paleoenvironmental records and their age models (e.g., Telford et al, 2004;Heegaard et al, 2005;Blaauw, 2010;Blaauw and Christen, 2011;Parnell et al, 2011;Breitenbach 2012).…”