| The Taiwan Strait, which connects the East China Sea with the South China Sea, is the largest channel of China. Located between the mountainous Taiwan Island on the southeast and the mountainous Fujian Province, China on the northwest, the Taiwan Strait is also the channel of the East Asian Monsoon. Therefore, the west coast of the Taiwan Strait meets with the stronger wind than any other coastal area of China, especially the dominant northeast wind in autumn and winter. In addition, the west coast of the Taiwan Strait obtains huge amounts of well-sorted sediments which are originally supported by the rivers such as the Min River, the Jiulong River, and so on, and are then transported to the southwest by the northeast wind wave and Zhemin Coastal Current. As a result, the west coast of the Taiwan Strait is famous for its marvelous coastal aeolian deposits and various coastal aeolian landforms.In this research, the Changle east coast and the Zhangpu east coast, Fujian, China, which possess the most typical coastal aeolian deposits on the west coast of the Taiwan Strait, are choosed as the study area. A pulseEKKO PRO ground penetrating radar (GPR) (Sensors &. Software Inc., Canada), a kind of non-invasive ground penetrating detector, were applied to unveil the sedimentary structure of the different kinds of coastal aeolian deposits. In total, the internal structure of a coastal sand sheet, a parabolic dune, an oblique ridge, a barchan chain and coastal foredunes on the Changle east coast and the Zhangpu east coast was detected. Softwares such as EKKO_View 2, EKKO_View Deluxe and CorelDRAW X4 SP2 were employed to process two-dimensional three-dimensional radar images. On the basis of the comprehensive interpretation of different radar images, several schematic diagrams were drawn to illustrate the idealized sedimentary structure model of the coastal sand sheet, the shadow dune, the oblique ridge, the barchan dune and the parabolic dune on the west coast of the Taiwan Strait, the sedimentary environment of which was also provided. Some preliminary conclusions are achieved:(1) The physicochemical properties of the coastal aeolian deposits, such as grain size, water content and salinity, antenna frequency, and the processing steps of GPR images, such as digital filtering and gain adjustment, will all affect the result of the GPR detection. GPR performs well on the coastal aeolian deposits as the salinity is low and the stratification is clear due to the vertical grain size variation. However, marine salt water will attenuate the radar signal heavily, so it's difficult to detect the internal structure of the beach by using the GPR.(2) The coastal aeolian deposits on the west coast of the Taiwan Strait are the overlying strata on the wave-deposited beach sediments which present the hummocky cross stratification and the horizontal bedding. In contrast, the stratification of overlying coastal aeolian deposits is more complicated, which involves the horizontal bedding, the low-angle cross bedding, the high-angle cross bedding, the trough cross bedding, and so on. Every kind of coastal aeolian deposits has its own sedimentary structure model, and it may indicate the sedimentary environment. The sedimentary structure of the coastal sand sheet is single, which is mainly composed of the horizontal bedding parallel or perpendicular to the prevailing wind direction, and is the result of the stratified deposition of aeolian sands on the flat topography.(3) The sedimentary structure of the shadow dune is complex. The cross bedding dipping to the windward (northeast) is common on the windward slope while the cross bedding dipping to the leeward (southwest) is common in the leeward slope, and the high-angle cross bedding dipping inversely is common on the profile perpendicular to the prevailing wind direction. For the oblique ridge, the horizontal bedding and the low-angle cross bedding are common on the profile parallel to the prevailing wind direction, and the cross bedding dipping inversely whose top is gentle is common on the profile perpendicular to the prevailing wind direction. This kind of high-angle cross bedding dipping inversely is corresponding to abundant sand sources, dune accretion, wide beach and vegetation expansion, which are the characteristics of the progradational coast.(4) Both the top of an idealized barchan dune and the top of an idealized parabolic dune are the horizontal topsets, under which the stratificaitons parallel and perpendicular to the prevailing wind direction are of great difference. For the barchan dune, the horizontal bedding is common on the profile perpendicular to the prevailing wind direction, and the high-angle forests which are close to the threshold angle of repose (32°-34°) and dip to the leeward (southwest) are common on the profile parallel to the prevailing wind direction. For the parabolic dune, the horizontal bedding is common on the profile perpendicular to the prevailing wind direction, and the forests which are gentler than that of the barchan dune, dip to the leeward (southwest) and possess subconvex arcs are common on the profile parallel to the prevailing wind direction, which is the peculiar cross bedding of the parabolic dune. The dipping orientation of the barchan dune and the parabolic dune makes clear that the northeast wind is the dominant wind of the west coast of the Taiwan Strait, and shows the migrating process of the coastal dunes from the northeast to the southwest driven by the northeast wind.(5) There are some variations of the dune morphology and inner structure of the same kind of coastal dunes in the north and south of the west coast of the Taiwan Strait. The opening orientation of the parabolic dune in the north is NNE, and the forests dip to SSW. However, the opening orientation of the parabolic dune in the south is NE, and the forests dip to SW. In addition, the long axis orientation of the oblique ridge and the shadow dune in the north is NNE-SSW, and the forests dip to SSW, while the long axis orientation of the oblique ridge in the south is NE-SW, and the forests dip to SW. It is in accord with the direction characteristic of the prevailing wind on the west coast of the Taiwan Strait. |
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