河口湾潮坪潮汐水道发育特征及地质意义 ——以钱塘江为例

河口湾中的砂体是有利的油气储集层，但复杂的水动力变化导致古代河口湾识别困难。通过对现代钱塘江河口湾的研究表明，河口湾潮坪环境潮汐水道可以成为识别古河口湾的一种辅助标志。基于野外实地观测，结合卫星地图对潮坪环境潮汐水道的发育特征进行了详细的描述，并探讨了它的地质意义。结果表明:1）泥坪潮汐水道横截面形态主要有“V”型及宽缓的透镜状，平面上由海向陆可划分为曲折的A段、平直的B段和树状分叉的C段；2）砂坪潮汐水道横截面形态主要有“U”型和阶梯型，平面上由海向陆可划分为曲折或平直的A'段和树状分叉的B'段，A'段的平直与曲折主要受控于砂坪潮道规模的大小；3）在砂质潮坪中常见炭屑层、包卷层理、液化流痕、垮塌构造、波痕等特殊的沉积构造；不同形态和规模的潮坪潮道主要受控于潮坪坡度、沉积物粒度、河口湾形态及相对海平面高低的影响，高坡度、低海平面有利于完整序列潮道的发育；4）不同类型河口湾潮坪潮道的特征及其伴生的特殊沉积构造可以为确定地质历史时期的古河口湾及其演化提供参考。

Characteristics and Geological Significance of Tidal Channels in an Estuarine Tidal Flat:A case study from the Qiantang river estuary

Sand bodies in estuary bays favor the development of oil and gas reservoirs， but identifying them may be difficult due to complex hydrodynamic changes. This study of the modern Qiantang River Estuary Bay shows that the tidal channels in a tidal flat environment are useful as an alternative means of identifying ancient estuary bays. Field observations and satellite mapping describe in detail the development of a tidal channel in the tidal flat environment， and its geological significance is discussed. The study shows that the cross-sectional shape of the mudtidal channel is mainly V-shaped and broadly lenticular. In plan， the pattern of tidal channels is divided from sea to land into a zigzag section A， a straight section B， and a tree-branching section C. The cross-section of sand flat tidal channels is mainly a stepped U-shape. The pattern of sand-flat tidal channels， from sea to land， is divided into a zigzag or straight A’ segment and a tree-shaped bifurcated B’ segment. The A’ segment is flat， and may be straight or tortuous depending on the scale of the shape of the tidal channel. Certain sedimentary structures are common in sandy tidal flats （e.g.， charcoal layers， convoluted bedding， indications of liquefied flow， collapse structures， ripple marks）. The differences in shape and size of tidal channels are mainly due to the slope， sediment size， estuary morphology and relative sea level； steeper slopes and lower sea levels are more likely to develop a complete sequence of tidal channels. Overall， the characteristics of different types of tidal flats in estuary bays， together with their sedimentary structure， provide a reference for identifying ancient estuary bays and determining their geological evolution.