Parasequence-Scale Organic Facies Variations and Its Significance in Nonmarine Basin
-
摘要: 柴达木盆地北缘侏罗系由非海相冲积—三角洲及湖泊沉积体系构成。托阿尔阶的沉积序列为下部的冲积体系向上过渡为滨浅湖、中深湖沉积体系,后者发育一系列在垂向上向上变粗—变浅的旋回层并构成准层序。在准层序级别,有机相参数发生规律性变化。岩石的有机质含量向上增加,显示与粉砂质含量呈正相关。其原因可能是冲积物源的植物碎屑和粉砂颗粒具有相似的水动力均衡条件。有机母质具有高等陆生植物和低等水生生物输入的双重旋回特征。成熟度居于临界状态 (镜质体反射率平均 0.57% )。自生的黄铁矿 /菱铁矿比与沉积物堆积速率之间存在一定的联系。湖泛面位于准层序的下部且直接上覆高有机质的暗色泥岩。Abstract: The Jurassic of the northern Qaidam basin is widely recognized as the nonmar ine sediments, and interpreted as alluvial-delta and lacustrine depositional system. The depositional sequence of the Tianshuigou Fm. within the lower Jura ss ic mainly composed of the alluvial system at the base and lower and the deep lac ustrine system in the upper. Geochemical and optical analyses were undertaken on the minor cyclothems, a progradationally coarsening-and shallowing-upward paraseque nce (cycle) within the major lacustrine deposits in which Type III land-plant derived kerogen is overwhelming. The total organic carbon cont ent of the fine-grainned lithology increases upwards through the parasequence and is positively correlated with silt content, presumably due to the hydrodynam ic equivalence and common alluvial source of phytoclasts and silt particles. The section is marginally mature ( about 0.57% vitrinite reflectance). The distri bution of pyrite and siderite is apparently related to sediment accumulation rate,with frequent appearance of siderite in the lower part of the para sequence. The lacustri ne flooding surface at the base of the parasequence is overlain by black shale, and thought to have been terminated by an abrupt and major rise in relative lac ustrine level,which may be perhaps the result of tectonically driven changes in subsidence.
-
Key words:
- organic facies /
- parasequence /
- nonmarine /
- Jurassic /
- Qaidam basin
-
[1] 解习农，李思田. 陆相盆地层序地层研究特点[J] .地质科技情报，1993，12（ 1）：22～26 [2] 李思田. 沉积盆地的动力学分析[J] . 地学前缘，1995，2（3）：1～8 [3] 顾家裕. 陆相盆地层序地层学格架概念及模式[J] . 石油勘探与开发，1995，2 2（4）：6～10 [4] 杨明慧，夏文臣. 非海相前陆盆地含煤沉积层序地层分析[J] . 煤田地质与勘 探，1998，26（3）：1～5 [5] 杨明慧. 南祁连南缘弧形逆冲推覆构造[J] . 中国区域地质，1998 ，17（2） ：213～217 [6] Frank M C, Tyson R V. Parasequence-scale organic facies variations through an Early Carboniferous Yoredale cyclothem,Middle Limestone Group, Scre merston, Northumberland[J] . Journal of the Geological Society, 1995, 152 : 41～50 [7] 李佩娟，何元良，吴向午等. 青海柴达木盆地东北缘早、中侏罗世地层及植物群 [M] .南京：南京 大学出版社，1988 [8] 王明儒，胡文义，彭得华. 柴达木盆地北缘侏罗系油气前景[J] .石油勘探与开 发，1997，24（5）： 20～24 [9] Price L C, Barker C E. Suppression of vitrinite reflectance in amorp hous-rich kerogen-a major unrecognized problem[J] . Journal of Petroleum Geology, 1983, 8 : 59～84 [10] Mastalerz M, Bustin R M, Lamberson M N. Variation in chemistry of v itrinite and emifusinite as a function of associated inertinite content[J] . Internatio nal Journal of Coal Geology, 1993, 22 : 149～162 [11] Wenger L M, Baker D R. Variations in vitrinite reflectance with org anic fac ies -examples from Pennsylvania cyclothems of the Midcontinent, U.S.A[J] . Org anic Geochemistry, 1987, 11 : 411～416 [12] Hennessee E L, Blakeslee P J, Hill J M. The distributions of organ ic carbo n and sulfur in surficial sediments of the Maryland portion of Chesapeake Bay[ J] . Journal of Sedimentary Petrology, 1986, 56 : 674～683 [13] Van Wagoner J C, Mitchum R M, Campon K M, et al. Siliciclastic sequence stratigraphy in well logs,cores and outcrops[C] . AAPG Methods in Ex ploration, 1990.7 -
点击查看大图
计量
- 文章访问数: 632
- HTML全文浏览量: 9
- PDF下载量: 870
- 被引次数: 0
下载:
