Pyloniid stratigraphy – a new tool to date tropical radiolarian ooze from the central tropical Indian Ocean

Abstract

Pyloniid stratigraphy, a faunal abundance-variation stratigraphic tool, similar to Cycladophora davisiana stratigraphy employed at high latitudes, is found to work well for tropical radiolarian ooze. The relationship between the spatial distribution of 25 modern radiolarian groups in surface sediments and monsoonal surface salinity from the central Indian Ocean is analyzed. Among them, Pyloniids exhibit the potential to serve in the same way as the C. davisiana stratigraphy. Down-core (temporal) variation of % Pyloniids in a sediment core is compared with (i) the sum of the Earth’s orbital eccentricity, axial tilt and precession (ETP), (ii) solar insolation at the core site (8°S) and 65°N, and (iii) the SPECMAP-δ 18O stratigraphy. The multi-taper (MTM) spectral analysis of Pyloniids for the last 485 ka in a core (AAS 2/3) reveals significant climatic cycles at the eccentricity (100 ka), tilt (41 ka) and precession (23 ka) bands. Cross-spectral analyses suggest coherent (>90%) Pyloniid cycles lag both the ETP and June insolation (65°N) by <9 ka at 100-ka eccentricity and are almost (<2 ka) in-phase with 41-ka tilt and 23-ka precession cycles. Coherent Pyloniid cycles lag SPECMAP-δ 18O by 14 ka at 41-ka tilt and 6 ka at 23-ka precession, while they lag insolation at the core site by 7 ka at 100-ka, lead 18 ka at 41-ka and show in-phase relation with 23-ka cycles. Marginal lead of <10 ka by ETP and insolation over Pyloniids at 100-ka eccentricity and in-phase relation at 41-ka tilt and 23-ka precession cycles suggest Pyloniids variation could be used as a tool to derive age models in tropical radiolarian ooze during the Late Neogene/Quaternary.