沅江凹陷古近纪层序地层、沉积相特征及演化

通过地震、测井和分析化验等资料，对洞庭湖盆地沅江凹陷古近系古新统桃源组及始新统沅江组、汉寿组及新河口组进行层序地层和沉积相研究，首先可将古近纪划分为2个Ⅲ级层序、5个体系域，桃源组和沅江组构成层序I，汉寿组和新河口组构成层序Ⅱ。层序Ⅰ沉积于盆地断-坳期，与下伏上白垩统分水坳组多为平行不整合接触，彼此间为典型的Ⅰ型层序界面，发育冲积扇、河流、扇三角洲、滨-浅湖和半深相沉积，湖泊沉积范围广，湖相暗色泥岩沉积是盆地主要烃源岩。层序Ⅱ形成于盆地坳陷期，发育冲积扇、扇三角洲、河流、三角洲和滨-浅湖相沉积，之后凹陷开始萎缩。烃源岩主要发育于层序Ⅰ中部的湖进体系域中上部和高水位体系域中下部位置，并且集中在层序Ⅰ高水位体系域晚期和低水位体系域底部。凹陷深洼区发育的扇三角洲及湖泊三角洲砂体储层，是油气的有利勘探地区。

CHARACTERISTICS AND EVOLUTION OF PALEOGENE SEQUENCE STRATIFICATION AND SEDIMENTARY FACIES IN YUANJIANG SAG

Using the data obtained from seismic, well log, and assaying, the research is conducted on sequence stratification and sedimentary facies of Taoyuan Formation, Yuanjiang Formation, Hanshou Formation, and Xinhekou Formation of Paleogene inYuanjiang sag in the Dongtinghu Basin. The paleogene can be divided into 2 third-order sequences, 5 systems; sequence I consists of Taoyuan Formation and Yuanjiang Formation, sequence II consists of Hanshou Formation and Xinhekou Formation. The sequence I deposited during the faulting period and depression of the basin, during the period alluvial fan facies, fluvial facies, fan delta subfacies and shore-shallow lake subfacies were developed, and it is characterized by a successive range of lake sedimentation, the duck mudstone of the lake subfacies are the main source rocks in the basin. Sequence II was deposited during the depression period and shrinkage period of basin, during the period alluvial fan facies, fan delta facies, fluvial facies, delta facies, and shore-shallow lake subfacies were developed, and later the Yuanjiang sag was depauperated. The Paleogene in the Basin experienced a progress from the deposition of alluvil fan facies or fluvial to lake facies (exclude delta facies and fan delta facies), and finally to fluvial facies. From this progress we can see that Yuanjiang sag experienced a complete cycle of evolution from the early rifting stage to expansion, and then to shrinkage. The main source rocks were developed in the upper of the TST and the bottom of the HST during the sequence I, the reservoir of sand body of lake-delta and fan delta were developed in the low-lying of the basin during the later period of the HST and the bottom of the LST of sequence I, and it is the potential areas for the exploration of oil and gas.