Influence of a Rapidly Uplifting Orogen on the Preservation of Climate Oscillations

Abstract

Climate oscillations preserved in sedimentary archives tend to decrease in resolution further back in Earth's history. High‐frequency climate cycles (e.g., ∼20‐Kyr precession cycles) are especially prone to poor preservation due to sediment reworking. Recent studies have shown, however, that given sufficient basin accommodation space and sedimentation rate, shallow‐marine paleoclimate archives record precession‐driven hydroclimate change in mid‐low latitude regions. Our study evaluates how the evolution of a rapidly uplifting orogen influences the recording of astronomical climate forcing in shallow‐marine sedimentary strata in the Taiwan Western Foreland Basin (WFB). Time‐series analysis of gamma‐ray records through the late Miocene–Pliocene Kueichulin Formation shows that during early stages of Taiwan orogenesis (before 5.4 Ma), preservation of precession‐driven East Asian Summer Monsoon variability is low despite increasing monsoon intensities between 8 and 3 Ma. The Taiwan Strait had not formed, and the southeast margin of Eurasia was open to the Pacific Ocean. Consequently, depositional environments in the WFB were susceptible to reworking by large waves, resulting in the obscuration of higher‐frequency precession cycles. From 5.4 to 4.92 Ma, during early stages of emergence of Taiwan, basin subsidence increased while sedimentation rates remained low, resulting in poor preservation of orbital oscillations. After 4.92 Ma and up to 3.15 Ma, Taiwan became a major sediment source to the WFB, and sheltered the WFB from erosive waves with the development of Taiwan Strait. The elevated sediment influx, increased basin accommodation as the WFB developed, and formation of a semi‐sheltered strait, resulted in enhanced preservation of precession‐driven East Asian Summer Monsoon variability.