[H-QR04] Deep time perspective on the geological response to climate change

[HQR04-08] The alluvial-shelf stratigraphy in response to 630 ka-present sea level cycles: A 2D experimental study

*Miya Shairah Soriano Pamutan¹、Zhiyong Liu¹、Tetsuji Muto¹ (1.Department of Environmental Sciences, Nagasaki University)

キーワード：Quaternary, flume tank, autostratigraphy, glacial cycles, alluvial-shelf

The Quaternary follows the intriguing divergence from 41 kyr glacial cycles signaled by the onset of 100 kyr interglacials during the mid-Pleistocene. Such multiple cycles of sea level rise and fall, albeit under strictly controlled parameters, were simulated by Wang and Muto (2021) to demonstrate shelf-wide non-equilibrium responses as in the attainment of a degradation-free phase. An even earlier study by Muto and Swenson (2005) showed that alluvial grade is achievable under unsteady or allogenic sea level fall conditions. This two-dimensional flume tank experiment aims to observe such counter-intuitive autostratigraphic responses over a long-term allogenic sea level trend of the Quaternary as modeled by Bintanja and van de Wal (2008) reflecting the mid-Pleistocene Transition (MPT) and the succeeding 100 kyr glacial cycles up to present. A model simulation was conducted using constant upstream sediment supply (rate q_s) and constant water discharge (rate q_w) followed by four runs with modulations in q_s and q_w ratio and an added parameter of steady basin subsidence. The five runs captured the response of the system from 630 ka to present while the sixth and final run covered the last 1 Myr of the Quaternary. The findings of the experimental runs are as follows: 1) the depositional system overcomes a critical alluvial length (L_crt) early on resulting in a flooded alluvial surface (i.e., non-deltaic transgression) for succeeding sea level rise events; 2) meanwhile the influence of base-level fall diminishes through cycles as the alluvial-basement transition (ABT) converges towards an aggradation-sustainable trend; 3) the added factor of steady subsidence subjects the system to large-scale autoretreat and emphasizes degradational responses due to a discrepancy between constant q_s and a thicker delta-set thickness built over time. Altogether, these experimental results argue that autostratigraphic phenomena remain observable over long-term allogenic sea level changes.

References:
Wang, J., & Muto, T. (2021). Sedimentology, 68(1), 135-167.

Bintanja, R., & Van de Wal, R. S. W. (2008). Nature, 454(7206), 869-872.

Muto, T., & Swenson, J. B. (2005). Journal of Geophysical Research: Earth Surface, 110(F3).