Discovery of Tidal Sand Ridges and Its Significance of Pinghu Formation in Xihu Depression
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摘要: 西湖凹陷平湖组受潮汐影响作用明显，但前人研究鲜有提及潮汐砂脊这种典型的潮汐作用下的沉积体。综合运用地震、测井、岩芯及分析化验资料，在西湖凹陷平湖组发现潮汐砂脊沉积体系。潮汐砂脊在地震振幅属性图上，呈条带状特殊地貌特征；岩芯上为典型的反旋回，旋回上部发育板状交错层理、冲刷面等反映强水动力的沉积构造，旋回下部细粒沉积中则发育潮汐层理、生物扰动等沉积构造；测井曲线上，砂脊底部表现为突变界面，并且砂脊发育区重矿物相对富集。潮汐砂脊砂质纯、物性好，并多发育于泥质背景中，与周围泥岩储盖配置好，可构成良好的岩性油气藏勘探目标。另外，砂脊的发育情况可以反映不同时期西湖凹陷与南部广海的沟通情况，因此对于研究西湖凹陷的古地理具有一定的参考意义。Abstract: Pinghu Formation in Xihu Depression is obviously affected by tide, but no tidal ridges are documented which are the typical sedimentary type in the tide-dominated environment. Through comprehensive application of cores, logs and seismic data, tidal sand ridges are discovered in Pinghu Formation, Xihu Depression. In the RMS amplitude attribute map, the topographic expression of ridges is banded. In the core, the tidal sand ridge is typically coarsing upwards. In the upper part, tabular cross bedding and scour which show the strong hydrodynamic force during the sedimentation are common; while in the lower part, the sediments are fine, and tidal beddings and bioturbation structures are frequent. There is a sharp base of the ridge in well logs and the heavy minerals are rich in ridges area. Tidal ridges are excellent quality reservoir and always surrounded by mud, so the ridges are good stratigraphic trapping potentials. Whether Xihu Depression is connected with the southern open sea or not can be known by tidal ridges coverage, so the study of tidal ridges are also helpful in palaeogeographical reconstruction.
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Key words:
- tidal sand ridges /
- sedimentary facies /
- Pinghu Formation /
- Xihu Depression
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