The Distribution of High Frequency Shallow Seismic Facies on Continental Margins with Varying Boundary Conditions: A Study of the East China Sea Continental Margin

Abstract

The purpose of this study is to test the hypothesis that the distribution of near surface sedimentary deposits of continental margins with varying boundary conditions are in dynamic equilibrium with the present day hydrodynamic regime and sediment supply. Processes involved are the high influx of sediment supply, strong coastal currents, periodicity of major storm events and the waves and currents they create, tidal range and currents, and the waves and currents associated with regional storm events. Due to the extreme nature of the hydrodynamic processes and the abundant sediment supply, the East China Sea Continental Margin was chosen for this project.

Seismic records were examined and categorized into facies based on continuity, frequency, amplitude, and the geometry of the reflectors. This resulted in the classification of 28 facies. “Seismic cores” of the upper sediments were then “created” based on these facies. “Seismic cores” of the upper sediments were then “created” based on these facies. The core lengths were then “normalized” to eliminate the difference in core lengths. Q-Mode factor and Markov analyses were conducted to classify statistically significant lateral facies provinces and non-random vertical facies sequences within the provinces.

These analyses reveal 8 distinctive provinces in the study area and each contains at least one non-random vertical facies sequence. Comparison of near surface facies distribution with the distribution of sources of sediment supply and hydrodynamic forcing mechanisms indicate that large areas on the East China Sea Continental Margin are in dynamic equilibrium with the depositional conditions. This study has confirmed that combined Q-Mode factor analysis and Markov Process analysis are useful tools to quantitatively characterize the distributions of horizontal and vertical facies on continental margins with varying boundary conditions. Finally, a conclusion that can be drawn from this study is that observation of areas where there is disequilibrium between sediment distribution and hydrodynamic regime on the East China Sea (ECS) continental margin where there is adequate sediment supply and hydrodynamic activity to attain equilibrium conditions between the two; suggests that the probability of observing near surface sediments in dynamic equilibrium on continental margins with lower sediment supply and a greatly reduced hydrodynamic climate is quite low.