F1: Distributary channel (86.5–70.5 m).

Facies F1 is dominated by medium- to fine-grained quartz sand (Figure 4). It exhibits the coarsest mean grain size (0.1–0.5 mm) and the highest sand content (74%–95%) of the sequence. Sorting is poor (0.85–2.22) with positive skewness (-0.58–0.66; Supplementary Table S1). Physical structures include erosional cross-stratification, notably observed near 70 m (Figure 2). A gravel-bearing horizon (ca. 10% gravel; pebble diameter ~1 cm) is present at 83.6 m. Intervening intervals are generally massive or exhibit faint horizontal lamination. A basal contact is characterized by distinct erosion, whereas the upper boundary is gradational (Figure 2). F1 contains low TOC content (mean 0.05%) and δ¹³C_org values average -22.56‰ (Figure 4). Based on the aforementioned sedimentological and geochemical characteristics, F1 is interpreted as a distributary channel (Figure 4).

Radiocarbon dating yielded an age of 36.1 cal kyr BP at a depth of 86.5 m (Figure 4). Furthermore, through stratigraphic and grain-size correlation with CJK07 core (Xu et al., 2016), the 70.5 m horizon is assigned an age of approximately 33 ka. Consequently, the sedimentary interval from 86.5 to 70.5 m is interpreted to span the period from 36.1 cal kyr BP to 33 ka (Figures 3, 4). The coarse-grained texture, combined with basal erosion and graveliferous lags, indicates deposition by high-energy, channelized traction currents capable of bedload transport (Figures 2, 3; Miall, 2014). The presence of cross-stratification supports the interpretation of active bedform migration, while massive to faintly laminated intervals are attributed to rapid deposition rates from high-concentration suspension flows (Mill, 1996). The poor sorting and positive skewness are consistent with unidirectional fluvial flows (Figure 4, Supplementary Table S1). The gradational upper boundary reflects the progressive waning of hydrodynamic energy. The depleted δ¹³C_org values indicate a terrestrial-derived organic matter source, thereby precluding significant marine influence during this interval (Figure 4; Meyers, 1994). The extremely low TOC content suggests limited organic matter preservation, most likely attributable to the oxic conditions typical of active channel settings (Figure 4).

F2: Tidal channel (70.5–54.2 m).

Facies F2 comprises dark gray to gray silt and sand, with a grain size range of 0.08–0.25 mm, exhibiting a general fining-upward sequence (Figures 2, 4; Supplementary Table S1). Specifically, a lower interval is massive and coarse-grained, structurally similar to the underlying F1 (Figure 4). A distinct scour-and-fill structure is observed at 68.1 m, and a carbonized tree trunk fragment is preserved at 67.14–67.17 m (Figure 2). By contrast, an upper interval (59.49–54.2 m) transitions into interbedded fine sand and silt (Figures 2, 4). The boundaries of the two facies are gradational (Figure 2). TOC contents and mean δ¹³C_org values are approximately 0.5% and -22.3‰, respectively (Figure 4). Intergrating these sedimentological and geochemical features, F2 is interpreted as a tidal channel (Figure 2).

Similarly, based on lithostratigraphic and grain-size correlations with the EGQD14 core (Gao et al., 2022), the 54.2 m horizon is assigned an age of approximately 15 cal kyr BP (Figure 4). Consequently, the sedimentary interval from 70.5 to 54.2 m in QDQ2 core corresponds to the period from 33 to 15 ka (Figure 4). This interpretation represents a transition from the fluvial dominance of F1 to the overlying tidal flat environment (F3; Hill et al., 2001). Fining-upward trend and Transition from massive sands to rhythmic bedding suggest a progressive decrease in channel energy and incipient tidal modulation (Hill et al., 2001). A presence of the carbonized tree trunk in the lower interval indicates persistent, high-energy terrestrial input during the early stages of channel filling (Miall, 2014). δ¹³C_org values indicate a predominantly terrestrial organic source with negligible marine contribution, consistent with a channel system still dominated by riverine output (Meyers, 1994). Low TOC content reflects poor preservation, likely due to the oxidizing conditions maintained by the dynamic interplay of high-energy fluvial and tidal flows.

F3: Tidal flat (54.2–40.2 m).

Relative to F1 and F2, Facies F3 exhibits a distinct lithological shift, characterized by dark gray, fine-grained sediments (silt and clayey silt) abundant in mica fragments, with a mean grain size of 0.01–0.2 mm (Figures 2, 4). Notably, F3 displays a more pronounced fining-upward trend compared to the underlying facies. A basal interval (53.75–50.0 m) consists of gray to grayish-blue, stiff, homogeneous silty clay (Figures 2, 4; Supplementary Table S1). Sedimentary structures are dominated by rhythmic clay-silt interlaminations, whereas the basal clay layer exhibits horizontal laminations (Figure 2). Geochemically, TOC content shows a steady increase (mean 0.29%; Figure 4). δ¹³C_org record exhibits a distinct negative excursion, with a mean value of -24.7‰ (Figure 4). An upper boundary of this facies is gradational (Figure 2). Collectively, the sedimentological, structural, and geochemical signatures of F3 point to a low-energy tidal flat, marking a distinct hydrodynamic shift in the depositional system (Figures 2, 3).

An age of 10.1 cal kyr BP at a depth of 40.2 m (Table 1). Consequently, the sedimentary interval from 54.2 to 40.2 m in QDQ2 core is constrained to the period from 15 ka to 10.1 cal kyr BP (Figure 4; Gao et al., 2022). The fine-grained texture and high mica content suggest that the sediment settled in a low-energy environment (Doyle et al., 1983). The rhythmic interlaminations are interpreted as tidal rhythmites formed under modulated tidal currents (Doyle et al., 1983). These are typical of tidal flats and are products of the last deglacial sea level rise (Zhao et al., 2017). Increased TOC content reflects enhanced preservation of organic matter, likely facilitated by rapid burial within the fine-grained matrix (Figure 4). Negative excursion in δ¹³C_org values is attributed to a shift in organic matter provenance from terrestrial-dominated to marine-influenced sources (Meyers, 1994). The gradational upper boundary suggests a progressive evolution of the depositional environment, and the basal boundary of F3 marks the beginning of the Last Deglaciation (Figures 2, 4; Lambeck et al., 2014; He and Lu, 2025).

F4: Delta front (40.2–35.7 m).

Facies F4 comprises dark gray silt and clayey silt with a mean grain size of ~0.05 mm (Figures 2, 4; Supplementary Table S1). Grain-size statistics show sorting values and skewness ranging from 0.59 to 2.45 and -0.40 to 0.18, respectively. Sedimentary structures are characterized by locally well-developed horizontal lamination. An upper interval contains abundant, well-preserved shells and bioclasts (Figure 2). Additionally, distinct layers of carbonized charcoal and plant debris occur at depths of 35.8 m and 40.0 m. Geochemically, TOC content reaches a maximum of 0.79% at 40.2 m (10.1 cal kyr BP; Figure 4). Concurrently, δ¹³C_org record exhibits a significant negative excursion (minimum -27.4‰; Figure 4). Considering the above features, F4 is interpreted as a low-energy subaqueous delta front, capping the succession (Figure 3).

An age of 9.4 cal kyr BP at a depth of 37.2 m (Table 1). Based on an estimated sedimentation rate of approximately 0.23 kyr/m, the upper boundary of this unit is extrapolated. Consequently, the sedimentary interval from 40.2 to 35.7 m in QDQ2 core is interpreted to span the period from 10.1 to 8.4 cal kyr BP (Figure 4). The fine-grained texture and grain-size data indicate a stable, low-energy hydrodynamic regime, dominated by suspension settling as evidenced by the horizontal lamination (Figures 2, 4; Supplementary Table S1; Zhu, 2020). The abundance of well-preserved marine fossils confirms a productive subaqueous marine environment (Figures 2, 4; Zhu, 2020). Peak in TOC content indicates a period of maximum preservation of organic matter (Figure 4). In this depositional context, negative excursion in δ¹³C_org is attributed to a further increase in marine organic carbon input (Figure 4; Meyers, 1994). Stratigraphically, this unit records the deepest-water environment formed during 36.1-8.4 cal kyr BP (Miller et al., 2020).

The terrestrial interval (86.5–54.2 m; 36.1 cal kyr BP–15 ka) preserves a distinct climatic signature (Figure 3). This interval corresponds to globally cold and arid climate conditions during the global glacial stage (Gao et al., 2022; Gao and Long, 2023), thus suppressing chemical weathering (Gao and Long, 2023), which is evidenced by the lowest CIA (mean 27.93) and the highest K/Al ratios (mean 1.09; Figure 5; Nesbitt and Young, 1989).

The global cooling coincided with the LGM sea-level regression, which can expose the East China Sea continental shelf and trigger the deep incised valley system (Figure 6; Li et al., 2014; Miller et al., 2020; Wang et al., 2020). Although incision likely commenced during MIS 4, the LGM lowstand facilitated the maximum development of these distributary systems (Gao and Long, 2023). Consequently, the LGM depositional setting was dominated by distributary and tidal channels, characterized by widespread sedimentary hiatuses (Figures 3, 6; Gao and Long, 2023). The widespread formation of the incised valley confirms the regional extent of this incision event (Marden et al., 2014; Barboza et al., 2021; Yu et al., 2021; Zhou et al., 2024).

The interval from 54.2 to 35.7 m (15 ka–8.4 cal kyr BP) records a transition to marine-dominated environments (Figure 3). During this time, global climate warming resulted in ice sheet melting and sea-level increasing, the incised valley thus began to accumulate tidal-current deposits (Figure 3). This progressive inundation and the formation of tide-dominated estuaries, which inevitably led to a transformation in sedimentary facies in YRE (Figure 3; Li et al., 2002; Lambeck et al., 2014; Li et al., 2014; Miller et al., 2020; Xu et al., 2020).

A pronounced positive excursion in CIA values (mean 41.62), accompanied by a marked decrease in K/Al ratios (mean 0.58), indicates intensified chemical weathering in the Yangtze River source region (Figure 5; Nesbitt and Young, 1989). This enhanced weathering is consistent with warming climate and the rapid last deglacial sea-level rise (Figure 3; Miller et al., 2020), which provides strong evidence for the facies succession (Figure 5). This facies succession is corroborated by similar successions identified in EGQD14, ZK01, ZK02, and YZ07 cores (Figure 6; Zhang et al., 2017; Gao et al., 2020, 2022). This environmental reconstruction is also confirmed by the foraminiferal and pollen assemblages from CSJA3 core, which indicate an estuarine-littoral to lagoonal environment characterized by a warm, humid climate (Yu J et al., 2016). Similar paleoenvironmental conditions were also reconstructed from the SG7 core (Li et al., 2011).

A subtle yet distinct geochemical excursion is preserved within the terrestrial F1 (75.5–70.0 m; Figure 5). The result reveals a fundamental decoupling between physical and chemical signals during this interval. Sedimentary facies, TOC, and δ¹³C_org are consistent with high-energy distributary channel deposits (F1), exhibiting no evidence of marine inundation (Figure 4). In contrast, geochemical proxies exhibit a shift, with elevated CIA values (mean 31.80) and decreased K/Al ratios (mean 0.85; Figure 5), indicating intensified chemical weathering in the source region. Chronostratigraphically, this interval corresponds to the Gehu transgression, a pre-LGM event occurring during the Late Pleistocene (Zhao et al., 2017). The Gehu transgression represents a sea-level rise event, supported by multi-level models that simulate the land-sea response to glacial cycles (Yu G et al., 2016). These models attribute the event to glacio-eustatic variations (Lin et al., 1989; Lambeck et al., 2001; Yu G et al., 2016). However, paleogeographic extent of the Gehu transgression, particularly its potential intrusion onto the northern flank of YRE, remains a topic of debate (Gao and Long, 2023).

Notably, the Gehu transgression can be ruled out due to the persistence of terrestrial facies (Figures 4, 5). Instead, the geochemical variance is best interpreted in the context of the warm, humid climate of MIS 3a, which enhanced chemical weathering rates in the Yangtze source region (Wang et al., 2001; Andersen et al., 2004; Ou et al., 2015).

To validate this climatic driver, stalagmite records from Hulu Cave document a strong East Asian Summer Monsoon pulse during this period (Wang et al., 2001), consistent with warming signals in the Tibetan Plateau—the primary headwater region of the Yangtze River (Shi and Yu, 2003). These climatic conditions account for the enhanced weathering observed in this interval (Figure 6). Furthermore, stratigraphic correlation with 090, 058, ZK01, ZK02, YD016, YD006, EGQD14, and YZ07 cores confirms that the sedimentary environment on the northern flank of the YRE remained a distributary channel throughout this period (Figure 6; Li and Wang, 1998; Zhang et al., 2017; Gao et al., 2020, 2022; Gao and Long, 2023). The warm, humid MIS 3a climate drove enhanced weathering in the Yangtze source region, whereas the magnitude of the associated Gehu transgression was insufficient to alter local sedimentary facies.