The Upper Cretaceous M2 and U Sandstone members of the Napo Formation are prolific hydrocarbon producers in the Oriente Basin of eastern Ecuador. To understand the depositional origin of these reservoirs, an integrated sedimentologic, sequence-stratigraphic, and ichnologic study, using 490 ft (~149 m) of conventional core from six wells of oil fields located in the eastern part of the basin, was performed. Sedimentary facies, stratal stacking pattern, discontinuity surfaces, and trace fossils were documented. Nine lithofacies and two depositional sequences in each member were identified. Three main broad environments, fluvial, estuarine and deltaic, have been interpreted. Trace fossils are very rare in the fluvial deposits and comprise facies-crossing ichnotaxa. The trace-fossil association of estuarine deposits is of low diversity containing ichnotaxa indicative of marine influence (e.g. Asterosoma, Teichichnus). In comparison, deltaic deposits display higher ichnodiversity, and are more intensely bioturbated, locally including some ichnotaxa (e.g. Zoophycos) that suggest the system may have experienced fully marine conditions sporadically. Controlling factors are typically expressed differently in the various subenvironments as a result of the interplay of tides and river discharge. The most important stress factors were substrate type and consistency, episodic sedimentation, high energy, water turbidity, and changes in salinity. Our integrated approach may prompt similar studies in other hydrocarbon-bearing units in Ecuador.

纳波组的上白垩统M2和U砂岩成员是厄瓜多尔东部Oriente盆地的多产烃类。为了了解这些油藏的沉积成因，利用位于盆地东部的六个油田的490英尺（〜149 m）常规岩心进行了综合的沉积学，层序地层学和植物学研究。记录了沉积相，地层堆积模式，不连续面和痕迹化石。每个成员中鉴定出9个岩相和两个沉积层序。解释了河流，河口和三角洲这三个主要的广泛环境。痕迹化石在河流沉积中非常罕见，并包含横贯鱼鳞的相。星形胶质瘤（Teichichnus）。相比之下，三角洲沉积物显示出更高的鱼类多样性，并且受到了更强烈的生物扰动，局部包括一些鱼类种类（例如Zoophycos），表明该系统可能偶尔经历了完全的海洋条件。由于潮汐和河流排放之间的相互影响，在各个子环境中控制因素的表达方式通常不同。最重要的压力因素是基质类型和稠度，间歇性沉积，高能，水浊度和盐度变化。我们的综合方法可能会促使对厄瓜多尔其他含烃单元进行类似的研究。