Point-bar deposits, although readily recognizable in most successions, are notoriously challenging to map and correlate accurately, particularly in the subsurface. Sedimentologic interpretations from microresistivity image logs, by contrast, offer an unparalleled method of accurately reconstructing point-bar architectural elements and mapping their distribution. Using an example from the Lower Cretaceous McMurray Formation, we demonstrate that the bedding dip profiles of stacked downstream migration, lateral accretion, and channel abandonment elements record the semicontinuous point-bar accretion of two erosionally juxtaposed large-scale channels. Microresistivity image-log analysis clearly demonstrates that bedding and architectural elements of these heterolithic point bars display discrete and predictable changes in dip angle and direction that are independent of autogenic variations in lithology. We advocate, therefore, that this approach be used to map the facies of point bars and predict their reservoir trends.The laterally accreted mud-sand couplets display a cyclic pattern that is consistent with a nonrandom recurring process. Based on the distribution of bioturbation in the mud beds and variations in sand-bed thicknesses, we argue that this recurring process was probably a monthly occurrence. By measuring the lateral-accretion bed thicknesses for what appears to be a 1-yr interval, a sedimentation rate of 86 cm/yr is estimated for these lateral-accretion beds. This deposition rate provides an upper limit required to deposit these point bars and improves the framing of the depositional model. We estimate that the two point bars in this study were each deposited over a period of a few hundred years.

中文翻译：

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使用高分辨率微电阻率图像测井重建古环境和地层结构：以加拿大艾伯塔省东北部 Leismer 地区 McMurray 组为例

点状沉积物虽然在大多数序列中很容易识别，但众所周知，要准确地绘制和关联它是非常困难的，尤其是在地下。相比之下，来自微电阻率图像测井的沉积学解释提供了一种无与伦比的方法来准确重建点棒结构元素并绘制其分布图。使用下白垩统 McMurray 组的一个例子，我们证明了堆叠的下游迁移、横向增生和水道废弃元素的层理倾角剖面记录了两个侵蚀并置的大型水道的半连续点坝增生。微电阻率图像测井分析清楚地表明，这些异岩点棒的层理和建筑元素显示出独立于岩性自生变化的倾角和方向的离散和可预测变化。因此，我们主张使用这种方法来绘制点状坝相并预测其储层趋势。横向增生的泥砂对显示出与非随机重复过程一致的循环模式。根据泥床中生物扰动的分布和沙床厚度的变化，我们认为这种重复发生的过程可能每月发生一次。通过测量似乎是 1 年间隔的横向增生床厚度，估计这些横向增生床的沉降速率为 86 厘米/年。这种沉积速率提供了沉积这些点棒所需的上限，并改善了沉积模型的框架。我们估计这项研究中的两个点棒都沉积了几百年。