## 3 Results  
### Sedimentary Characteristics and Microfacies Types  
Previous studies have established multiple classification schemes for beach-bar systems based on compositional characteristics, spatial distribution, provenance conditions, and hydrodynamic regimes [40]. The bar facies can be sub-divided into the following three microfacies: (1) bar core (high energy), (2) bar margin (transitional), and (3) interbar (low energy). Similarly, the beach facies comprise (1) beach core, (2) beach margin, and (3) interbeach, totaling six microfacies types. The vertical succession exhibits the following characteristic stacking pattern: interbar (interbeach) \(\rightarrow\) bar margin (beach margin) \(\rightarrow\) bar core (beach core) \(\rightarrow\) bar margin (beach margin) \(\rightarrow\) interbar (interbeach). Microfacies classification schemes for beach-bar systems vary according to regional depositional environments. The vertical succession-based framework outlined above represents a comprehensive subdivision methodology [41, 42]. Integrated analyses of thin-bedded beach-bar sedimentary characteristics in the study area reveals that the E3d2 sandbodies exhibit non-stacked depositional architecture, characterized by thin sand layers (single sandbody thickness < 8 m) interbedded with thick shore-shallow lacustrine mudstones [43]. The absence of bar margin, interbar, and interbeach microfacies supports the following refined four-tier classification scheme: (1) bar core, (2) beach core, (3) beach margin, and (4) shore-shallow lake facies. This scheme aligns with the depositional framework of the study area (Table 3, Figures 3-5). A systematic investigation integrating litho-electric characteristics, seismic responses, and seismic sedimentology was conducted for the Paleogene Dongying Formation's lower submember (E3d2L). The thin-bedded beach-bar system comprises the following three microfacies: bar core, which are thick sandbodies (> 8 m thickness) with massive bedding and low-angle cross-stratification; beach core, which are laterally continuous thin sandbodies (3 to 8 m thickness) exhibiting wave-ripple cross-bedding; and beach margin, which are marginal wedge-shaped sand accumulations (<3 m thickness) with bioturbation structures. These three dominant sedimentary microfacies exhibit distinct sedimentological and geophysical signatures (Figures 3-5), characterized by: lithofacies, which are fining-upward sequences from bar core to beach margin; electrofacies, which are bell-shaped (bar core), funnel-shaped (beach margin) GR log motifs; and seismic attributes, which are high-amplitude continuous reflections for the bar core and discontinuous variable amplitudes for the beach margin. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sedimentary** & **Bar Core** & **Beach Core** & **Beach Margin** \\ \hline Lithology & Medium-to-fine sandstone & Silstone and argillaceous & Silstone, silty mudstone, \\ Thickness & \(>\)8 m & & siltstone & and mudstone \\  & Moderate (moderately & 3 to 8 m & \textless{}3 m \\ Textural Maturity & sorted; moderate to good & Moderate (moderately & Moderate–low (poorly \\  & roundness) &sorted; finer grain size) & sorted) \\  & Parallel bedding, tabular & Horizontal bedding, wavy & Lenticular bedding, \\ Sedimentary Structures & cross-bedding, and wavy & bedding, and small-scale & bioturbation structures, \\  & cross-bedding & cross-bedding & and wavy bedding \\ Paleogeographic Position & Paleogeographic highs & Relatively gentle & Margins of relatively gentle \\  & & paleogeomorphic highs & paleogeomorphic highs \\ Distribution Pattern & Localized, lobate, or & Sheet-like or elongated & Contiguous distribution \\  & irregular elliptical & banded around the bar core & around the beach core \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Identification chart for beach-bar system microfacies in the E3d2, HHK Depression. Figure 3: Core facies, lithology, and electrical properties of the bar core in the E3d2\({}^{\text{L}}\) submember, HHK Depression.