Fluid muds are common in estuarine environments, but their ancient examples have rarely been documented due to poor comprehension of their depositional processes and characteristics. Mudstone layers in the tidally-influenced channel sequences of the middle McMurray Formation are examined in detail through microscopic observations and interpreted on the basis of recent advances in the understanding of flow dynamics of high mud-concentration flows. The mudstone layers, < 1 to 25 mm thick, are classified into three microfacies. Structureless mudstone (Microfacies 1) consists mainly of clay particles with randomly dispersed coarse grains (coarse silt to fine sand). It represents cohesive mud flows with sufficient cohesive forces to support coarse grains (quasi-laminar plug flow). Silt-streaked mudstone (Microfacies 2) is similar to Microfacies 1 in texture, but contains discontinuous streaks of coarse-silt to very-fine-sand grains. It is interpreted as being also deposited by cohesive fluid muds. The silt streaks are, however, suggestive of the presence of weak turbulence under the cohesive plug (upper transitional plug flow). Heterolithic laminated mudstone (Microfacies 3) is characterized by alternations of very thin, silt and clay laminae, which are either parallel or low-angle cross-laminated. It is interpreted as the deposits of low-amplitude bed-waves formed in lower transitional plug flows. These microfacies reflect a range of flow phases of fluid muds, which changed as flow velocities and suspended sediment concentrations fluctuated with tidal cycles. Repeated vertical changes of microfacies are suggestive of an ideal sequence of fluid muds formed during tidal acceleration and deceleration. The sequence comprising microfacies 3, 2 and 1 in ascending order represents deposition from lower transitional plug flows through upper transitional plug flows to quasi-laminar plug flows as suspended sediment concentrations increase with flow deceleration. That of the reversed order of microfacies reflects the reversed change in flow types during acceleration. These results provide the basis for recognizing fluid-mud deposits and tidal signatures in ancient estuarine sequences.

流体泥浆在河口环境中很常见，但是由于对泥浆沉积过程和特征的理解较差，因此很少记录到它们的古老实例。麦克默里中部受潮汐影响的河床序列中的泥岩层通过显微镜观察得到了详细检查，并根据对高泥浆浓度流动的流动动力学的最新进展进行了解释。厚度小于1至25毫米的泥岩层分为三个微相。无结构泥岩（微相1）主要由具有随机分布的粗粒（粗粉砂土到细砂）的粘土颗粒组成。它表示具有足够内聚力的粘性泥浆流，以支持粗粒（准层状塞流）。淤泥状的泥岩（微相2）在质地上与微相1相似，但包含不连续的从粗淤泥到极细砂粒的条纹。它也被解释为也由粘性流体泥浆沉积。但是，淤泥条纹暗示了在粘性栓塞（上部过渡栓塞流）下存在弱湍流。杂岩层状泥岩（微相3）的特征是非常薄的粉砂层和粘土层层交替出现，它们是平行的或低角度的交叉层状。它被解释为在较低的过渡活塞流中形成的低振幅基波沉积物。这些微相反映了流体泥浆的一系列流相，这些相随流速和悬浮泥沙浓度随潮汐周期的变化而变化。微相的垂直重复变化提示潮汐加速和减速过程中形成的理想流体泥浆序列。依次由微相3、2和1组成的序列表示沉积物从下部过渡栓塞流经上部过渡栓塞流到准层状栓塞流，这是因为悬浮泥沙浓度随流速的降低而增加。微相反转顺序的变化反映了加速过程中流动类型的反转变化。这些结果为识别古代河口序列中的泥浆沉积物和潮汐特征提供了基础。图2和图1以升序表示沉积物从下部过渡栓塞流经上部过渡栓塞流到准层状栓塞流，这是因为悬浮泥沙浓度随流速的降低而增加。微相反转顺序的变化反映了加速过程中流动类型的反转变化。这些结果为识别古代河口序列中的泥浆沉积物和潮汐特征提供了基础。图2和图1以升序表示沉积物从下部过渡栓塞流经上部过渡栓塞流到准层状栓塞流，这是因为悬浮泥沙浓度随流向减速而增加。微相反转顺序的变化反映了加速过程中流动类型的反转变化。这些结果为识别古代河口序列中的泥浆沉积物和潮汐特征提供了基础。