Study On Submarine Morphology Of Fujian Offshore

In this paper, submarine morphological characteristics and causes of Fujian Offshore with the macro-tidal environment were researched based on the the measured topographic data and theory of submarine morphology and dynamic geomorphology, used modern data processing techniques, quantitative analysis, combined with geological structure, hydrology, sediment, and other historical data or previous results,etc.Some conclusions were made in this research, as follow:(1) There are two second-grade geomorphological units, divided into coast geomorphology and continental shelf geomorphology from shore to sea, in the study area. Coastal geomorphology can be divided into the intertidal landscape and subaqueous slope:Intertidal landscape geomorphology are mainly composed of tidal shoal, beach, erosion platform and mangrove; Subaqueous slope can be divided into modern estuarine subaqueous delta, subaqueous accumulation slope, subaqueous erosion-accumulation slope, modern tidal sand ridges developed on the underwater slope, tidal ridge-trough system and tidal delta. Continental shelf geomorphology is mainly composed of shelf accumulation plain and shelf erosion-accumulation plain.(2) Tectonic movement since Late Trias and sealevel change as a result of climate change since Late Pleistocene shaped the topographic and morphological basic pattern of the study area, besides sedimentary environment changes as a result of sealevel change played a vital role on morphological evolution. Hydrodynamic conditions such as river, tide, current, wave and storm surge etc since Holocene administer transportation and deposition of sediments in this area, shape the erosion and accumulation morphological characteristics, and control the size and spatial distribution of submarine morphology. Since the birth of mankind, especially after the industrial revolution, human activities played an important role on the morphological evolution.(3) Study area can be divided into three regions:the North, the Middle and the South.①The North is characterized by the heavy accumulation geomorphologic types, with the complex and diverse morphology of the coast while the simple forms of offshore.②The Middle is characterized by the inclined subaqueous accumulation slope, with the accumulated effect was inferior to the North’s.③The South is characterized by the erosion-accumulation morphological types.(4) The typical geomorphologies, such as estuarine subaqueous, tidal sand ridges, tidal ridge-trough system, and submarine dunes etc, were researched. And the results as follow:①Minjiang River estuarine subaqueous is located on the delta fault subsidence basin, as a result of the whole processof the exogenetic and endogenetic, which developed in the process of sea-level fluctuations and sedimentation.②Tidal sand ridges developed on the sea area between Mazhu Islands and Baiquan Islands should not be the direct result of modern tide dynamic, also didn’t develop on regression at Late Pleistocene. It was probably that formed due to the tidal erosion during the process of the post-glacial sea-level rise, with the offshore environment at the depth of2～8m.③Tectonic movement shaped the basic pattern of tidal ridge-trough system in Xinghua Bay, and the original terrain formed as a result of filling in the the broken reefs with the dense and hard Pleistocene deposits. With a mass of river and offshore sediments since Holocene, the coarse deposits covered the original slopping topographies by the edge of waterways in the process of modern tidal effect, which was result in the formation of tidal ridges.④The large-scale submarine dunes of the South should be experienced two important evolutive periods: During the period of low sea-level in early Holocene, this region changed into the coastal shoal water, where developed the original beach, submarine sandbank, and tombolo under the ocean dynamics; Under the modern ocean currents and storm waves yet, sediments from coast and broad sea happened deposition and migration at submarine sandbank or beach, with the development of sand ripple or grain, resulted in the erosion-accumulation geomorphological features at present.⑤Numbers of underwater reefs were seen near the inshore islands and rocky coast in the study area, as a result of the collision and basement uplift on tectonic movement in the geological history.⑥Paleochannels at offshores of Quanzhou Bay, Meizhou Bay, and in the sea area between Baiquan Islands and Haitan Island are corresponding to the several main rivers along the coast of Fujian, such as Minjiang River, Jinjiang River and Jiulongjiang River, which were result of developing seaward of these rivers during the ice ages.