Astronomical cycles calibrated the sea-level sequence durations of Late Miocene to Pliocene in Qiongdongnan Basin, south China sea

Abstract

Several research works have demonstrated that climate variations are consistent with quasi-periodic orbital parameters, particularly ∼1.2-Myr obliquity amplitude modulation cycle has been demonstrated as a controlling factor of glacio-eustasy sequence formation in icehouse periods. In the current research, we have studied the glacio-eustasy third-order sequences of Late Miocene to Pliocene age in Qiongdongnan Basin (QDNB), South China Sea and identified a prominent ∼1.2-Myr periodicity in a 41kyr-tuned gamma ray series of Well LS33-1-1. In the current research, we developed an astronomical time scale (ATS) for Late Miocene to Pliocene in QDNB and conducted cyclostratigraphic analyses on Huangliu and Yinggehai Formations in Well LS33-1-1 using high-resolution natural gamma-ray (GR) data. Time-series analyses on GR data revealed rich Milankovitch frequency band series and ∼5.6, 3.8 and 6.0 m cycles were respectively filtered for three segments in depth domain which presented direct correlation with 41-kyr obliquity cycles in La2004 solution. In this work, foraminiferal and calcareous nannofossil biozones in South China Sea were selected as age markers for tuning. Correlation coefficient analysis was applied to quantitatively measure the fitting of witnessed sedimentary cycles to astronomical periods and provide a possible range for sedimentation rate. Also, we developed a sedimentary noise model to detect high-resolution sea-level variations under the control of orbital forcing which were supported by previous third-order eustasy variations. In addition, six third-order sequences were identified in the range of Late Miocene to Pliocene representing astronomical forcing through both ∼1.2-Myr filtering of DYNOT model and ∼1.2-Myr modulation of obliquity amplitude based on sedimentary noise modeling. Finally, it was concluded that the ∼1.2-Myr cycle was the most important driving force for sequence development and third-order sea-level changes.