Multi‐proxy evidence for rapidly shifting sediment sources to the Taiwan Western Foreland Basin at the Miocene–Pliocene transition

Abstract

The Taiwan Western Foreland Basin is thought traditionally to have received sediment mainly from Eurasia until the late Pliocene–early Pleistocene, after which time, the Taiwan orogen became the dominant source. However, a combination of clay mineralogy, δ13Corg and C/N of organic matter, and mass‐specific magnetic susceptibility of late Miocene to early Pliocene strata of the Kueichulin Formation indicate that onset of major sediment contributions from Taiwan occurred much earlier, and correlates closely to the uplift and initial emergence of the Taiwan orogen. Clay mineralogy shows an upsection increase in illite and illite crystallinity, and a decrease in chlorite and kaolinite after the late Miocene, and this is attributed to rapid erosion of the Taiwan orogen. Results from δ13Corg and C/N analyses show that organic material in the Kueichulin Formation changed from dominantly marine to dominantly terrestrial in the early Pliocene, and this is linked to the delivery of large quantities of terrestrial organic material from the Taiwan orogen to the adjacent Taiwan Strait. Magnetic susceptibility also decreases significantly during the early Pliocene, resulting from dilution of magnetic minerals through the influx of non‐magnetic minerals delivered from the Taiwan orogenic belt. The establishment of the growing Taiwan orogen as a major sediment source to the Western Foreland Basin occurred at the Miocene–Pliocene transition, about two million years earlier than previously recognized.

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

“…This suggests that the boundary between the Kuantaoshan Sandstone and the overlying Shihliufen Shale occurred near the Miocene‐Pliocene transition at ca. 5.3 Ma, and the boundary between the Shihliufen Shale and Yutengping Sandstone boundary occurred near 4.92 Ma (Hsieh et al., 2022). A study by Horng and Shea (2007) based on magnetic polarity records of Taiwan of the Pliocene‐Pleistocene shows that the base of the Chinshui Shale (i.e., the top of the Yutengping Sandstone) occurs near the Gilbert‐Gauss polarity boundary at 3.6 Ma.…”

“…After 4.92 Ma, continued uplift of the Taiwan orogen resulted in further subsidence of the WFB and the formation of a strait that was semi‐sheltered from the Pacific Ocean. As rapid uplift and erosion of the Taiwan orogen continued in the early Pliocene, it became the dominant sediment source to the WFB (Dashtgard et al., 2021; Hsieh et al., 2022). Sediment flux from the Taiwan orogen was likely higher after 4.92 Ma, although estimated sedimentation rates through the Yutengping Sandstone are comparable to the Kuantaoshan Sandstone in HYS‐1 (Figure 3c) even with increased basin subsidence during deposition of the Yutengping Sandstone (Nagel et al., 2018).…”

“…Magnetic polarities could not be determined for the Kuantaoshan Sandstone due to its coarse grain size, resulting in unstable remanent magnetization during thermal demagnetization; however, based on the presence of the index nannofossils Discoaster quinqueramus and Triquetrorhabdulus rugosus, it belongs to nannofossil zonations of NN11-NN12 (Raffi et al, 2020). The Shihliufen Shale shows a reversed-normal-reversed polarity sequence upwards, and the presence of Ceratolithus acutus and Ceratolithus rugosus (NN12-NN13; Raffi et al, 2020) assign the magnetic polarities to the lower Gilbert chron (C3r, C3n.4n, and C3n.3r, respectively; Ogg, 2020) across the Miocene/Pliocene boundary (Figure 1b; see Hsieh et al, 2023 for magnetobiostratigraphic data). Samples collected from the lower-middle Yutengping Sandstone interval show three normal magnetic polarities intercalated with reversed polarities, which are constrained to the mid-to upper-Gilbert chron (from C3n.3r to C2Ar; Figure 1b; see Hsieh et al, 2023) by the presence of large form (∼7 mm in diameter) of Reticulofenestra pseudoumbilicus and Sphenolithus abies (NN13-NN14; (Wilkens et al, 2017) used to tune the GR records.…”

“…This study focuses on the late Miocene to early Pliocene Kueichulin Formation (Fm; Figures 1a and 1b), which was deposited during the early stages of Luzon Arc‐Eurasian Plate collision. The Kueichulin Fm is selected for this study because it comprises (quasi) continuous shallow marine strata that were directly affected by climate‐related sea‐level fluctuations and extreme weather events (Covey, 1986; Dashtgard et al., 2020, 2021; Hsieh et al., 2022; Nagel et al., 2013, 2014). Recent studies by Vaucher et al.…”

“…This study focuses on the late Miocene to early Pliocene Kueichulin Formation (Fm; Figures 1a and 1b), which was deposited during the early stages of Luzon Arc-Eurasian Plate collision. The Kueichulin Fm is selected for this study because it comprises (quasi) continuous shallow marine strata that were directly affected by climate-related sea-level fluctuations and extreme weather events (Covey, 1986;Dashtgard et al, 2020Dashtgard et al, , 2021Hsieh et al, 2022;Nagel et al, 2013Nagel et al, , 2014. Recent studies by Vaucher et al (2021) andVaucher, Zeeden, et al (2023) showed that high-resolution climate signals were preserved in lower Pleistocene shallow-marine strata of the WFB due to high accommodation and high sedimentation rates in the basin.…”