Sr-Nd isotopic composition and provenance tracing of Late Cenozoic sediments in the northern Hainan Island

The thick Late Cenozoic deposits of northern Hainan Island(Qiongbei)provide a record of paleoclimatic and paleoenvironmental changes in Hainan Island.However, there is a lack of source tracing studies on Sr-Nd isotopic methods in this sediment.In this paper, we carried provenance tracing using a borehole(ZK1-5)drilling encounter with bedrock in northern Hainan Island by Sr-Nd isotopic method.The results show that the Late Cenozoic of northern Hainan Island underwent a transition from coastal shallow marine sedimentation-marine and continental alternative deposition-terrestrial sedimentation-volcanic eruption environment from the Miocene to the Pleistocene, and that the Sr isotopic ratio of the Miocene marine sediment(mean: 0.727002)is overall higher than that of the Pliocene marine and terrestrial transition and Pleistocene terrestrial deposits(mean: 0.714917), suggesting that marine deposits were more weathered than the marine and terrestrial transitional phases.The Nd isotopic compositions of the marine, marine-terrestrial transitional and terrestrial deposits do not change significantly and are relatively consistent, suggesting that provenance did not change obviously caused by environmental changes from marine to terrestrial in the area.The distribution of ε_Nd(0)values in the Late Cenozoic sediments of Qiongbei(-14.0~-5.1)is generally consistent with the distribution of ε_Nd(0)values in the granitic rocks of Hainan Island(-14.1~-5.2), and differs considerably from the ε_Nd(0)values in the metamorphic rocks(1.2~8.5)and basaltic rocks(1.9~7.8)of Hainan Island, indicating that the source rocks are mainly from the local granitic rocks in Hainan Island, and the contribution of metamorphic rocks and basalt is small.This is probably related to the wide distribution of granitic rocks in the island.The understanding of the Sr-Nd isotopic characteristics of the Late Cenozoic sediments in the northern Hainan Island can help to deeply understand the weathering process and environmental changes on Hainan Island during the Late Cenozoic, and is of great significance for the reconstruction of the provenance and sea and land environment change in the northern South China Sea.