Event deposits recorded over the past 800 kyr in IODP hole U1433A (South China Sea): implications of a revised methodology for chronology and paleoclimate reconstruction

Instantaneous event deposits such as turbidites, debrites, and slumps are common and frequently occur in marginal seas. These instantaneous deposits represent seconds to days in duration, and can therefore significantly impact age-depth models and interpretation of paleoclimate history based on thick sedimentary sequences recovered in deep drill cores. However, these event deposits have rarely been considered when investigating International Ocean Discovery Program (IODP)/ODP deep cores from marginal seas. To resolve the problem, we take the South China Sea, one of the largest active marginal seas worldwide, as a typical research example. We identified 129 centimeter-to-meter-scale event layers from Hole U1433A (189–0 m, 800–0 kyr) in the southwest part of the deep South China Sea. These instantaneous event deposits account for ∼16% of the total sediment thickness in Hole U1433A, and significantly affect the reconstruction of the age-depth model and paleoclimate history. We refine the preliminary age-depth model, that is based on paleomagnetic and microfossil ages recovered from the hole, by removing instantaneous event deposits. We further test the effectiveness of our applied sedimentological approach by comparing paleoclimate profiles that include or omit those event layers. This test indicates that the event-free approach is effective and essential for a better reconstruction of the age-depth model and paleoclimate history based on the IODP deep core. Our revised sedimentological methodology may also prove suitable for other marginal seas with frequent instantaneous event deposits elsewhere in the world.