桃園草漯沙丘沉積構造研究

沉積構造分析，有助於理解沉積作用，並藉由沉積作用的解釋推斷沉積環境。台灣對於海岸風成沙丘的沉積構造研究相對較少，本研究希望藉由觀察分析現生沙丘之沉積構造，解釋在海岸沙丘環境下所呈現的沉積構造與其沉積作用之關聯性。並使用透地雷達，觀察草漯沙丘地層結構，推測草漯沙丘的堆積方向的變化，與現生沉積構造的分析相呼應。本研究的沉積構造調查分析顯示，草漯沙丘為一在豐富河川供砂與盛行風作用下，結合小尺度風向變化、人工結構物(攔砂籬)設置、季節性風向等作用，形塑成的海岸前列沙丘。本研究根據不同的沉積方式作用、型態，將沉積構造進一步細分為水平紋理、平行紋理、顆粒流紋理、顆粒沉降流紋理等4種，並整理出沙丘不同位置沉積構造特性，沙丘前坡以板狀交錯紋理與平行紋理為主，沙丘頂為水平紋理及楔狀交錯紋理，沙丘後坡則為板狀交錯紋理、平行紋理與少量水平紋理分布。草漯沙丘的沉積物顆粒以細砂為主，具有淘選度良好、負偏態、尖頂峰等特性。沉積物因為離岸遠近而呈現不同特性，沙丘前坡處因接近海灘，而呈現海灘砂特性，沙丘頂與後坡則呈現風成砂特性，具有淘選度與偏度差異。透地雷達觀測發現，沙丘沉積方向以向內陸向南發育為主。整體而言，沙源豐富的海灘砂在向岸風作用下，經由沙丘前坡、沙丘頂、沙丘後坡向南內陸搬運堆積，並在季節性風向變化與人工結構物影響下，呈現上述的沉積構造分布與沉積物顆粒特性。根據研究結果，本研究發現除了向岸風作用外，人工結構物也是影響沉積作用的關鍵外來因素，對海岸沙丘的影響不僅呈現於沉積構造，也可透過沙丘地形進行檢視而呈現不自然的增高增陡現象。

關鍵字

海岸沙丘；沉積構造；風成作用；粒徑分析；透地雷達

並列摘要

The analysis of sedimentary structure helps to understand sedimentary processes and infer the sedimentary environment from the interpretation of sedimentary process. Taiwan has relatively few studies on the sedimentary structure of coastal aeolian dunes. This study hopes to observe and analyze the sedimentary structure of existing sand dunes to explain the correlation between the sedimentary structure and its sedimentary processes in the coastal dune environment. The ground penetrating radar (GPR) was used to observe the stratum structure of the Caota sand dunes, and infer the change of the accumulation direction of the Caota sand dunes, which responds to the analysis of existing sedimentary structures. The investigation and analysis of the sedimentary structure in this study shows that the Caota sand dunes are shaped by the effects of abundant river sand supply and prevailing winds, combined with small-scale wind direction changes, artificial structures (sand fences), and seasonal wind directions. In this study, the sedimentary structure was further subdivided into four types: horizontal lamination, parallel lamination, grainfall lamination, and grainflow lamination, according to different sedimentary processes and types, and consolidate the characteristics of sedimentary structures at different position of the dunes. Horizontal lamination and parallel lamination are the main ones of the front slope. The top of the sand dunes is horizontal and wedge shape cross lamination. The back slope of the dunes is distributed with planar cross lamination, parallel lamination and a small amount of horizontal lamination. The sediment particles of Caota sand dunes are mainly fine sand, which has the characteristics of well-sorted, negative skewness, and sharp peaks. The sediments have different characteristics due to the distance from the shore. The front slope of the dune is close to the beach and presents the characteristics of beach sand. The top and back slope of the dune presents the characteristics of aeolian sand, with differences in sorting and skewness. Ground-penetrating radar observations found that the direction of sand dune deposition is mainly inland and south. In general, beach sand with abundant sand sources is transported and accumulated to the south inland through the front slope, top of the dune, and back slope of the dune under the action of the shore wind. Because of the influence of seasonal wind direction changes and artificial structures, Caota sand dnues presents the distribution of sedimentary structures and the characteristics of sediment particles. According to the results of the study, it found that in addition to the effect of onshore wind, artificial structures are also a key factor affecting sedimentary processes. The impact on coastal dunes is not only present in the sedimentary structure, but also changed the topography of the dunes unnaturally.