Nội dung của bài viết này trình bày đặc điểm tướng đá - cổ địa lý Miocen muộn khu vực Đông Nam Miền võng Hà Nội được làm sáng tỏ trên cơ sở nghiên cứu tiến hóa trầm tích trong mối quan hệ với sự thay đổi mực nước biển và chuyển động kiến tạo. Sự thay đổi mực nước biển toàn cầu trong Miocen muộn đã tạo ra một phức tập và ba miền hệ thống trầm tích. Miền hệ thống trầm tích biển thấp (LST) đặc trưng bởi năm nhịp trầm tích aluvi. Các nhịp này được thể hiện bởi trường sóng địa chấn thô, hỗn độn, tần số phản xạ thấp. Môi trường này không thuận lợi cho quá trình tạo than. | VNU Journal of Science Earth and Environmental Sciences Vol. 37 No. 1 2021 69-80 Original Article Characteristics of late Miocene Lithofacies - Paleogeography in the Southeast Region of Hanoi Depression Nguyen Thi Phuong Thao Tran Nghi Dinh Xuan Thanh VNU University of Science Vietnam National University Hanoi 334 Nguyen Trai Thanh Xuan Ha Noi Viet Nam Received 12 May 2020 Revised 24 September 2020 Accepted 28 September 2020 Abstract The characteristics of late Miocene lithofacies in the southeast region of Hanoi depression have been revealed on the basis of sedimentary evolution in relation to sea level change and tectonic movement. During late Miocene global sea level change had created one depositional sequence and three sedimentary systems tract. The lowstand systems tract LST is characterized by 5 rhythms of alluvial lithofacies. These rhythms were represented by rough and humoc seismic wave fields. This environment was not favorable condition for coal formation. The transgressive systems tract TST was characterized by 6 transitional lithofacies rhythms. Each lithofacies rhythm consisted of 4 facies the tidal flats sand facies of the bay the mud facies of the river mouth lagoon the coastal marshy mud facies creating coal and the bay greenish-gray clay facies. The pacing process involved changes in the local sea level caused by tectonic lift. Each tectonic subsidence phase took place at a very slow velocity so it was compensated for fine-grained sediment creating marshy mud facies to develop mangroves on a large scale. It was a prerequisite to create thick coal seams distributed near the end of each rhythm. A part of highstand systems tract HST were eroded due to the improved folding process creating an angular unconformity boundary with Pliocene-Quaternary sediments. However after reconstracting of deformated section it was clear that this system tract had only one rhythm including 2 facies prodelta mud facies and alluvial fan sandstone facies. Keywords .
