In the last few years, internal waves have been extensively studied by many scholars, mostly focused on the physical property and the effect on ecology and geochemistry. The geological influence, however, was rarely discussed. By EK500 and 3.5 kHz sub-bottom sonar system, it is reported that many sand waves exist in the South China Sea at 600 meter water depth. Internal waves are a very important driving mechanism in the South China Sea. Its movement over the marine bed causes unsteady flow field disturbance. In order to clarify whether the internal wave is the main factor to form sand wave, we conduct a series of numerical simulations. Most studies on the formation of sand waves are mainly in the nearshore area. Due to the difficulty in observation, only very few special discussions consider depth of 500 meters or deeper. First of all, in this thesis, we use the Korteweg de Vries (KdV) equation to derive wave and current in an internal soliton. Then, the flow field is substituted into the Regional Ocean Modeling System (ROMS) numerical model to simulate the three-dimensional movement of internal waves and the associated movement of suspended sediment in order to discuss the mechanism of sand wave formation. Finally, the variation of wavelengths of sand wave is analyzed and compared with in-situ measurement. From the simulation result, the internal wave causes the formation of sand waves. After the passage of dozens of internal waves, a flat sea floor will gradually form sand wave topography. Different depth and slope of the sea bottom will affect the sand wave wavelength also.

Observations of modern carbonate depositional environments and their accompanying depositional models have been used for decades in the reconstruction and interpretation of ancient carbonate depositional environments and stratigraphic successions. While these Holocene models are necessary for interpreting their more ancient counterparts, they inherently exclude important factors related to the erosion, diagenesis, and ultimate preservation of sediments and sedimentary structures that are ubiquitous in shallow marine carbonate environments. Andros Island, Bahamas is an ideal location to examine the validity of Holocene conceptual models, where geologically young (Late Pleistocene) limestones can be studied immediately adjacent to their well-documented modern equivalents. For this study, two 3D ground-penetrating radar (GPR) datasets (200 MHz and 400 MHz) were collected at a schoolyard in northwest Andros. These surveys reveal the geometries and internal characteristics of a peloidal-oolitic sand wave and tidal channel in unprecedented detail. These two prominent features are underlain by low-energy lagoonal wackestones and packstones, and are bordered laterally to the northwest by wackestones-packstones intermixed with thin sheets of peloidaloolitic grainstone. A deeper radar surface is observed at approximately 6 m depth dipping gently to the west, and is interpreted to be a karstified exposure surface delineating the base of a complete depositional sequence. Interpretation of the 3D radar volumes is enhanced and constrained by data from three cores drilled through the crest and toe of the sand wave, and through the tidal channel. This study is the first of its kind to capture the complex heterogeneity of a carbonate depositional package in three dimensions, where various depositional environments, sedimentary structures, and textures (mudstone to grainstone) have been preserved within a small volume.The results from this study suggest that the degree of vertical and lateral heterogeneity in preserved carbonate successions is often more complex than what can be observed in modern depositional environments, where sediments can generally only be observed in two dimensions, at an instant in time. Data from this study demonstrate the value of using two overlapping GPR datasets at differing resolutions to image the internal characteristics of a complete carbonate depositional package in three dimensions. From these datasets, a depositional model similar to other Holocene and Pleistocene carbonate depositional models is derived.