重力流混合事件层特征及形成演化机制研究—以山东灵山岛地区下白垩统为例

Characteristics, formation and evolution mechanism of gravity-flow hybrid event bed is essential to perfecting deep-water gravity-flow theory and forecasting gravity-flow sandstone distribution. Outcrop and core of deep-water gravity-flow deposits in the Lower Cretaceous in Lingshan Island, Shandong Province are taken as research object in this project. Exploiting the idea of “description-interpretation-predication”, outcrop and core analysis combine with flume tank and numerical simulation experiment will be applied in this study. Based on the detail description of deep-water gravity-flow deposits in multiscale, making the composition, sedimentary structures and type of lithofacies clear. Then, the typically diagnoses criteria of hybrid event beds will be summarized. Based on the type of lithofacies, lithofacies association combine with hybrid event beds will be analyzed in both lateral and vertical to understand their distribution and evolution. The relationship between lithofacies association and sedimentary environment will be analyzed to understand the formation and evolution processes of hybrid event bed. Take advantage of similarity principle and control variable comparing, flume tank and numerical simulation experiment will carry out to analysis the formation and evolution mechanism of hybrid event bed. Finally, with the quantitative analysis of relationship between controlling factors and distribution of hybrid event beds on the constrain of outcrop, flume tank and numerical simulation experiment, the distribution patterns of hybrid event beds will be summarized with the guidance of theory of comparative sedimentology.

重力流混合事件层特征及形成演化机制研究对完善深水重力流沉积理论和准确预测重力流砂体分布意义重大。本项目以灵山岛地区下白垩统深水重力流沉积露头和对应岩心为研究对象，遵循“现象表征-本质探索-规律总结”的研究思路，采用露头、岩心分析与水槽模拟及数值模拟实验结合的研究方法，以重力流沉积特征多尺度精细表征为基础，明确其物质组成、沉积构造、岩相类型等特征，总结重力流混合事件层类型及典型识别标志；以岩相类型为依据，分析重力流混合事件层发育的垂向和侧向岩相组合类型及分布演化特征，结合岩相组合类型与沉积环境对应关系，阐明不同类型重力流混合事件层形成演化过程，以相似性原理和控制变量对比为原则，开展重力流混合事件层沉积水槽和数值模拟实验研究，探究重力流混合事件层形成演化机制；综合露头、水槽和数值模拟实验约束下的控制因素与混合事件层分布特征相关关系量化解析，以比较沉积学原理为指导，揭示重力流混合事件层分布规律。

重力流混合事件层成因与分布特征研究，对完善深水重力流沉积演化过程理论认识和准确的重力流沉积砂体分布预测意义重大。项目以灵山岛地区下白垩统深水重力流沉积露头和对应岩心为研究对象，采用露头、岩心分析、分析测试、水槽模拟及数值模拟实验结合的研究方法。根据沉积序列厚度、沉积构造、沉积单元接触关系等因素，在研究区识别出三种类型重力流混合事件层。混合事件层1总厚度分布在63~80 cm，具有明显双层结构。底部为厚10 cm左右的块状砂岩，上部被厚层泥质砂岩覆盖，内部漂浮状泥质碎屑发育，上下部沉积单元之间突变接触。该类型混合事件层主要为泥质碎屑流内部碎屑颗粒在底部聚集重排形成。混合事件层2总厚度分布在10~71 cm，具有明显三层结构。底部可见明显正粒序特征，中部为富含泥质碎屑泥质砂岩沉积，顶部为薄层粉砂沉积。下部沉积单元与中部单元之间多为渐变接触，中部与顶部单元多为突变接触。该类型混合事件层主要为高密度浊流侵蚀底部泥质基底导致流体泥质含量增加导致流体转化形成。混合事件层3总厚度分布在10 cm左右，具有明显等厚的双层结构。底部单元为块状砂岩与上部泥质砂岩突变接触，上部泥质砂岩中泥质碎屑少见，主要为分散碳质碎片和泥片。该类型的混合事件层主要为低密度浊流晚期膨胀减速导致流体转化形成。重力流混合事件层在千层崖近端朵叶和灯塔远端朵叶中均发育。三层结构由于上游侵蚀成因的重力流混合事件层比由于流体分层作用形成的双层结构的重力流混合事件层更靠近沉积近端。超临界态搬运的重力流水道流体在水道内以自组织的形式发生超临界态与亚临界态的转化；超临界流体在坡折带处易于发生强烈的水力跳跃作用，一方面导致超临界态向亚临界态的转化；另一方面由于强烈的侵蚀作用导致对下伏泥质基底的强烈侵蚀，导致流体中泥质含量的急剧增加。上部流体中泥质含量的增加导致浊流向泥质碎屑流发生转化，是研究区超临界浊流沉积与重力流混合事件层共同发育的主要原因。