Sedimentary Facies of the Miocene In Block 103, Offshore Northern Vietnam : Grain Size Distribution Based on SEM Analysis

Grain size distribution by Scanning Electron Microscope (SEM) analysis of a core sample collected at - 2281.17 meters from the Miocene formation in Block 103, offshore North Vietnam, provide valuable information on the sedimentary characteristics and depositional environment. These methods are fundamental for reconstructing sediment transport processes and paleoenvironmental conditions. Grain size analysis, using statistical parameters and bivariate scatter plots, shows that the sediments are predominantly fine to very fine - grained sands, with mean sizes ranging from 0.06 to 0 .09 mm. The samples are generally well - sorted, suggesting a uniform depositional energy, likely associated with a stable shallow marine environment. SEM observations reveal microtextural features formed by both mechanical and chemical processes. Characteristics such as conchoidal fractures, abrasion marks, and solution pits suggest transport by subaqueous currents followed by early diagenetic alteration under marine conditions. The C - M (coarsest percentile vs. median) plot further supports bottom suspension as the main sediment transport mechanism, indicating deposition under relatively low - energy conditions typical of shallow marine settings. Overall, the integration of grain size and SEM data highlights a calm depositional regime, dominated by bottom suspension transport and marine influences. These findings contribute to understanding the sedimentary evolution and environmental history of the Miocene offshore North Vietnam.