Title: Studying glacial/interglacial cycles from downhole logging data: an application to the ICDP drilling project Lake Junín, Peru

Simona Pierdominici (1), Christian Zeeden (2), Jochem Kück (1), Donald Rodbell (3) & Marc Abbott (4)

Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ, Germany (1); Leibniz Institute for Applied Geophysics, Hannover, Germany (2); Union College, Schenectady, NY 12308, USA (3); Dep. Of Geology and Planetary Science, University of Pittsburg, USA (4)

Event: Abstract GeoUtrecht2020

Date: 2020

DOI: 10.48380/dggv-54r7-a519

Can the history of the lake records covering the glacial-interglacial cycles be reconstructed from downhole logging data without the high-resolution data derived from core analysis? To answer this question, we present a study reconstructing glacial-interglacial sediment variability and an estimate of lacustrine sedimentation rates based only on downhole logging data from the ICDP Lake Junín drilling project. We use a suite of cyclostratigraphic methods. Lake Junín is located at 4082 m in the Andes and is characterized by a thick sediment package dominated by alternating units of carbonates and glaciogenic silts with thin peat and organic-rich mud layers. The first step of our study was to investigate the consistency of cyclic sediment behavior and see that the interval from ~30-90 m shows a rather stable cyclicity with a wavelength of ca. 10 m. Natural and spectral gamma ray logging data were used for cyclostratigraphic analysis, and the astronomical spectral misfit (ASM) method was used to reconstruct the sedimentation rate. The results indicate a sedimentation rate of between 5 and 20 cm/kyr. For the second step, the TimeOpt method was applied to test for a fit of precession amplitude with eccentricity; it results in an average sedimentation rate of 15 cm/kyr. This method suggests a good fit of the precession amplitude and an eccentricity filter when applying an average sedimentation rate of 14-15 cm/kyr. Based on these information on sedimentation rate, the final step was to correlate the spectral gamma ray data with the LR04 benthic isotope stack.

: Peru

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