Influence of a rapidly uplifting orogen on the preservation of climate signals

Multi-proxy analyses of clay mineralogy, δ13Corg and C/N of organic matter, and mass-specific magnetic susceptibility of late Miocene–early Pliocene Kueichulin Fm of the Taiwan Western Foreland Basin (WFB) indicate that Taiwan became a major sediment source to the WFB near the Miocene-Pliocene transition, with the initial emergence of Taiwan, about two million years earlier than previously recognized. By the early Pliocene, Taiwan became the overwhelmingly dominant source of sediment to the WFB. This rapid sedimentation rate coupled with increasing basin accommodation space provided ideal conditions for the preservation of climate signals in its shallow-marine strata. Time-series analysis of gamma-ray records through the Kueichulin Fm confirmed the presence of orbital climate cycles imprinted in the rock record and show that the evolution of the rapidly uplifting orogen influenced the preservation of different orbital frequencies. The growth of Taiwan resulted in elevated sediment flux, increased basin accommodation, and the formation of a semi-sheltered strait, all of which served to enhance preservation of precession-driven hydroclimate variability. The evolution of Taiwan also influenced East Asian Summer Monsoon (EASM) proxy records in the South China Sea. Comparison of time-equivalent gamma-ray, δ13Corg, hematite/goethite, and magnetic susceptibility records from the WFB and EASM proxy records shows that the uplift and southwest migration of Taiwan and northwest migration of Luzon resulted in the formation of southwest-flowing currents that transported sediment from Taiwan towards the South China Sea, which is recorded as a decline in hematite/goethite values in proxy records >1000 km away. Overall, the findings of this study confirm that shallow-marine sedimentary archives can be used for resolving orbital climate oscillations, and demonstrates how different orbital signals are imprinted in the shallow-marine record at different stages of orogenesis. Additionally, this research also demonstrates that climate-independent controls, such as tectonic- and geodynamic-driven shifts in sediment transport mechanisms and sediment source, have the potential to produce "false" climate signatures, and must be considered in order to properly interpret paleoclimate records.