杭州湾地区全新世古河口湾砂体特征精细研究

Estuary as the seaward portion of a drowned river system which receives sediment from both fluvial and marine sources and which contains facies influenced by tidal, wave and fluvial processes is distributed widely around the world throughout geological history. Their fills are critical stratigraphic archives for unraveling earth-surface processes, depositional history, source to sink process of terrigenous materials, and the interaction between terrestrial and coastal marine.processes in the coastal settings, as well as for documenting environmental and climatic changes. The Holocene paleo-estuary in the Hangzhou Bay area is a world-famous tide-dominated estuary. Although there has been much descriptive documentation of the sedimentary characteristics, facies architecture, and depositional model for the paleo-estuarine sediments, few studies have involved the high-resolution sedimentological and environmental interpretations for the sand bodies therein. Through integrating core sedimentology, piezocone-testing (CPTU) data, micro-resistivity image logs, micro-CT images, paleontology analysis and 14C dating, this study aims to 1) investigate the sedimentary characteristics and types of the sand bodies in the Holocene Paleo-estuary in the study area in greater detail and higher resolution than what has been done previously; 2) determine the development phase and spatial distribution of the different sand bodies in the distinct time scale, and elucidate the formation mechanism for the distinct sand bodies, and 3) discuss the influence of the interaction between terrestrial and coastal marine processes, sediment supply, and sea-level change for the formation and evolution of the sand bodies in the Paleo-estuary. These results will be of great significance in in-depth knowledge of the quantitative research of the sedimentary system, the source to sink process of sediments, and the inversion of the sedimentary-dynamic processes in the Paleo-estuary. The study is also going to provide more scientific basis for the exploration and exploitation of shallow biogenic gas. Meanwhile, this study should fill the deficiency of the previous research, enrich and perfect the theory system for the estuary of same type around the world, and then provide a typical research example for the paleo-estuary in a certain extent.

本项目以沉积学、沉积动力学、第四纪地质学和测井沉积学为理论指导，以宏观和微观相结合的思路，通过采用当前成熟的沉积学研究方法，包括钻孔岩心的观察和描述、孔压静力触探曲线、地层微电阻率扫描成像、显微CT成像、古生物和14C测年分析等，在对杭州湾地区全新世古河口湾沉积特征和沉积序列高精度研究基础上，对其内部砂体特征进行精细分析，明确砂体类型；揭示各类砂体在不同时间尺度内的展布规律及其与周围沉积体的关系，进而准确判别各类砂体的成因机制；探讨海陆相互作用过程、沉积物供应以及海平面变化等因素对砂体发育演化的控制作用，进一步完善古河口湾的沉积演化模式。这对潮控型古河口湾内沉积体系的定量化研究、沉积物从源到汇过程和沉积动力作用过程反演等方面的深入认识都具有重要意义；也为杭州湾地区浅层天然气的勘探和开发提供更多科学依据；同时将会丰富国内外同类河口湾的理论体系，对古老地层中河口湾的研究也有一定的指示作用。

本项目以沉积学、沉积动力学、第四纪地质学和测井沉积学为理论指导，以宏观和微观相.结合的思路，通过采用当前成熟的沉积学研究方法，在对杭州湾地区全新世古河口湾沉积特征和沉积序列研究基础上，对其内部砂体特征进行分析，明确砂体类型，揭示砂体成因，探讨海陆相互作用过程、沉积物供应以及海平面变化等因素对砂体发育演化的控制作用，进一步完善古河口湾的沉积演化模式。这对潮控型古河口湾内沉积物从源到汇过程和沉积动力作用过程反演等方面的深入认识都具有重要意义；也为杭州湾地区浅层天然气的勘探和开发提供更多科学依据；同时将会丰富国内外同类河口湾的理论体系，对古老地层中河口湾的研究也有一定的指示作用。