Đặc điểm tướng đá - cổ địa lý Miocen muộn khu vực Đông Nam miền võng Hà Nội

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Tác giả: Xuân Thành Đinh, Thị Phương Thảo Nguyễn, Nghi Trần

Ngôn ngữ: Vie

Ký hiệu phân loại: 910 Geography and travel

Thông tin xuất bản: VNU Journal of Science: Earth and Environmental Science, 2021

Mô tả vật lý: 69-80

Bộ sưu tập: Metadata

ID: 415069

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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. Miền hệ thống trầm tích biển tiến (TST) đặc trưng bởi sáu nhịp trầm tích chuyển tiếp với bốn tướng cơ bản tướng cát bãi triều vũng vịnh, tướng bùn đầm lầy vũng vịnh, tướng bùn đầm lầy tạo than và tướng sét xám xanh vũng vịnh. Quá trình tạo nhịp liên quan đến sự thay đổi mực nước biển địa phương do chuyển động nâng - hạ kiến tạo gây ra. Mỗi pha sụt lún kiến tạo diễn ra với tốc độ rất chậm nên được đền bù trầm tích hạt mịn tạo tướng bùn đầm lầy phát triển rừng ngập mặn với quy mô lớn. Đó là điều kiện tiên quyết tạo nên những vỉa than dày phân bố ở vị trí gần cuối mỗi nhịp. Một phần trầm tích miền hệ thống biển cao (HST) bị bào mòn cắt cụt do quá trình uốn nếp nâng cao tạo nên ranh giới bất chỉnh hợp góc với trầm tích Pliocen-Đệ Tứ. Tuy nhiên, sau khi khôi phục thấy rõ miền hệ thống trầm tích này chỉ có một nhịp cơ bản gồm hai tướng tướng bùn sườn châu thổ và tướng cát nón quạt cửa sông., Tóm tắt tiếng anh, 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.

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