Sedimentation Rates at IODP Site U1424 since the Pliocene Deciphered from Spectral Analyses of RGB and GRA Bulk Density Profiles

Thursday, 18 December 2014
Thomas Joerg Gorgas, Integrated Ocean Drilling Program, Technical and Analytical Services (TAS), College Station, TX, United States, Ryuji Tada, University of Tokyo, Department of Earth and Planetary Science, Bunkyo-ku, Japan, Tomohisa Irino, Hokkaido University, Faculty of Environmental Earth Science,, Sapporo, Japan, Steven C Clemens, Brown University, Geological Sciences, Providence, RI, United States, Martin Ziegler, Cardiff University, Cardiff, United Kingdom, Ann E Holbourn, University of Kiel, Kiel, Germany, Richard W Murray, Boston Univ, Boston, MA, United States and Carlos A Alvarez Zarikian, Integrated Ocean Drilling Program, College Station, TX, United States
Sedimentation Rates (SRs) for IODP Site U1424 in the Japan Basin (40o11.40’N, 138o13.90’E) were calculated by performing spectral analysis in the depth domain on both RGB color and Gamma-Ray-Attenuation (GRA) bulk density data. Inversion and integration of SRs versus depth from spectral analysis yielded detailed SR profiles in both time and depth domains. Our results show a greater variability in calculated SR’s, which differed from those established through coarse-scaled biostratigraphic and paleomagnetic data. SR profiles from our analysis exhibit similar excursions and features in both depth and age domains, with GRA representing a smoothed version of the SR profile derived from RGB data while exhibiting slight offsets in high-to-low SRs downhole versus those observed in RBG data. Both GRA and RGB profiles show a distinct periodicity in the waveband of Milankovitch cycles. The pronounced Milankovitch cyclicity suggests that climate variability and trends in SRs at Site U1424 was responding to insolation patterns during the past 4.5 Myr. A dominance of the 100 ky cycle (eccentricity) throughout the entire normalized spectral amplitude profile might be observed; however, for the purpose of fine-tuning our high-resolution Age-Depth model to fit the low-resolution Age-Depth model from biostratigraphic and paleomagnetic data, choosing obliquity (41 ky) and precession (19-23 ky) cycles as tuning-frequency produced a closer fit between high-and-low-resolution models than using the prominent eccentricity cycles (100 and 400 ky). Relatively low SRs are found when evolutive amplitude spectra are dominated by obliquity and eccentricity periods. In contrast, significant SR peaks at Site U1424 often occur when strong precessional amplitudes coexist with obliquity and eccentricity cycles. Lower SR values at Site U1424 are interpreted to reflect a decrease in diatom flux and relative increase in detrital fraction. By contrast moderate to higher SRs were associated with lower GRA density and due to a higher diatom flux.