Geometry and Facies of Stacked Shallow-Marine Sandier Upward Sequences Dissected by Erosion Surface, Cardium Formation, Willesden Green, Alberta
Geometry and Facies of Stacked Shallow-Marine Sandier Upward Sequences Dissected by Erosion Surface, Cardium Formation, Willesden Green, Alberta
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阿尔伯塔省 Willesden Green 侵蚀面、Cardium 地层解剖的堆叠式浅海桑迪尔向上层序的几何形状和相
DOI：
10.1306/703c99d3-1707-11d7-8645000102c1865d
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发表时间：
1988
期刊：
影响因子：
--
通讯作者：
C. Eyles
中科院分区：
文献类型：
--
作者：
R. Walker;C. Eyles
威尔斯登格林油田是一个狭长的砂岩体，完全被海相泥岩包裹。该油田形成于晚白垩世（土仑期），包含多达七个向上变粗的层序。这些层序厚达12米（39.3英尺），在地层上有明显区别，且没有系统的退覆现象。每个层序都从海相生物扰动泥岩开始，向上过渡为以风暴作用为主的浅海砂岩。每个层序都显示出从丘状交错层理砂岩向生物扰动泥岩的横向页岩化。等厚图显示，这些层序向盆地方向变薄的速率为15 - 67厘米/千米（9.45 - 42.21英寸/英里），并表明扩散方向从北北东到东南不等。这一套海相层序被一个盆地范围的侵蚀面切割，该侵蚀面最初是在海平面大幅相对下降之后在陆上形成的。在随后的海侵过程中，一系列阶梯状的滨面切入这一套层序，消除了陆上暴露的所有证据。在大多数地方，滨面之上覆盖着一层薄的卵石层，而卵石层又被厚厚的海侵海相泥岩所掩埋。在一些地方，卵石层增厚形成厚达20米（65.6英尺）的砾岩，这些砾岩在卡罗特溪、彭比纳、费里尔以及威尔斯登格林等地形成了储层。这些砾岩被解释为是在河口沉积的，并在局部被波浪沿滨面改造。在持续的海侵过程中，叠置的层序和滨面砾岩被海相泥岩掩埋。总体的储层特征由层序的几何形态和叠置方式决定。地层圈闭部分是由横向页岩化形成的，部分是由泥质披覆的切割滨面形成的。在局部地区，滨面砾石是良好的储层，而上覆的海侵泥岩则形成了圈闭。我们认为，该油田狭长的几何形态代表了一个以前连续的砂层的侵蚀残余；该油田不是一个离岸沙坝。
Willesden Green field is a long narrow sandstone body completely encased in marine mudstones. The field is Late Cretaceous (Turonian) in age, and contains as many as seven stacked, sandier upward sequences. The sequences are as much as 12 m (39.3 ft) thick, are stratigraphically distinct, and do not offlap systematically. Each sequence begins with marine bioturbated mudstones and passes upward into storm-dominated shallow marine sandstones. Each sequence shows a lateral shaling-out from hummocky cross-stratified sandstone into bioturbated mudstone. Isopach maps show that the sequences thin basinward at a rate of 15-67 cm/km (9.45-42.21 in./mi), and suggest dispersal directions ranging from north-northeast to southeast. The stack of marine sequences is dissected by a basin-wide erosion surface that initially formed subaerially, following a major relative lowering of sea level. During ensuing transgression, a series of stepped shorefaces was cut into the stack of sequences, removing all evidence of subaerial exposure. The shorefaces in most places are overlain by a thin pebble veneer, which in turn is buried by thick transgressive marine mudstones. In places, the pebble veneer thickens into conglomerates as much as 20 m (65.6 ft) thick that form reservoirs at Carrot Creek, Pembina, and Ferrier, as well as Willesden Green. These conglomerates are interpreted to have been deposited at river mouths, and locally reworked along the shoreface by waves. During continued transgression, the stacked sequences a d shoreface conglomerates were buried by marine mudstones. Overall reservoir characteristics are determined by the geometry and stacking of the sequences. Stratigraphic traps have been formed partly by lateral shaling-out and partly by mud-draped incised shorefaces. Locally, shoreface gravels are good reservoirs, and the overlying transgressive mudstones form the traps. We believe that the long, narrow geometry of the field represents an erosional remnant of a formerly continuous sand sheet; the field is not an offshore bar.