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

Climate oscillations preserved in sedimentary archives tend to decrease in resolution further back in Earth's history. High-frequency climate cycles (e.g., similar to 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. Plain Language Summary Rhythmic changes in the shape of Earth's orbit (eccentricity, similar to 100-Kyr cycles), tilt (obliquity, similar to 41-Kyr cycles), and axial rotation (precession, similar to 20-Kyr cycles) drive climate change that may be preserved in sedimentary records. Orbital climate cycles are recorded in clastic shallow-marine strata where the amount of sediment transported from land to sea and space available for deposition in the basin are sufficiently high. Our study of the Kueichulin Formation in the Taiwan Western Foreland Basin (WFB) shows how a rapidly uplifting orogen influences the preservation of different climate cycles in the shallow-marine realm. During early Taiwan orogenesis (before 5.4 Ma) when the Taiwan Strait did not exist, sediment in the WFB were susceptible to reworking by erosive waves generated in the Pacific Ocean, which obscured higher-frequency precession cycles. From 5.4 to 4.92 Ma, Taiwan began to emerge from the Pacific Ocean and the WFB began to subside, but sedimentation rates were low, so climate cycles were poorly preserved. After 4.92 Ma, rapid uplift and erosion of Taiwan and WFB subsidence continued, resulting in increased sedimentation to the sea, increased sediment accumulation space, and the formation of a strait that sheltered the WFB from waves, which all served to enhance the preservation of precession.