The Medicine Hat Member in Alberta, Canada, is a muddy interval with thin sandstones. However, the sedimentology and stratigraphy are poorly understood – a reflection of the limited knowledge of mud-dominated successions. Here facies analysis and stratigraphy from core and wireline logs were used to construct a depositional framework for the interval in a stratigraphical context. Sedimentological and ichnological results show that the Medicine Hat Member was deposited in shallow water within a mud-dominated subaqueous delta system under the combined influence of river flow, waves, storms and longshore currents. Four facies are recognized, which are interpreted as distal delta front, proximal prodelta, distal prodelta and interdistributary bay deposits. The distal delta front is dominated by sandy storm deposits and thin storm-flood hyperpycnites. The prodelta, on the other hand, is characterized by muddy storm deposits and wave-enhanced sediment gravity flow deposits, with only subordinate hyperpycnites. Ichnological assemblages in both the delta front and prodelta are impoverished, indicating persistent physico-chemical environmental stresses. Interdistributary bay deposits are uncommon and are differentiated based on more robust ichnological assemblages and higher bioturbation intensities. Subsurface correlations reveal shallowing-upward parasequences that have aggradational and progradational stacking patterns and a very low depositional gradient (ca 0.03° to 0.1°). The stratigraphy reflects rapid progradation with fixed accommodation in a low-gradient setting; coeval flexural subsidence in the foredeep was dampened by underlying basement structures. Furthermore, previous suggestions that the Bow Island Arch impacted sediment distributions are not substantiated by the low angle geometry of clinoforms. Data from this study supports the interpretation that Medicine Hat deltas were fed by rivers flowing north through Montana because parasequences are sandier towards the south. This study fills a crucial gap in the literature by providing a rock record example of a mud-dominated subaqueous delta system and serves as a basis for comparison in core studies of similar units globally.

中文翻译：

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上白垩统泥质为主的水下三角洲的相特征和地层：Medicine Hat 段（Niobrara 组），加拿大阿尔伯塔

加拿大艾伯塔省的梅迪辛哈特会员是一个泥泞的区间，有薄砂岩。然而，人们对沉积学和地层学知之甚少——这反映了对以泥浆为主的层序了解有限。在这里，来自岩心和电缆测井的相分析和地层学被用于在地层背景下构建该层段的沉积框架。沉积学和地质学结果表明，在河流、波浪、风暴和沿岸水流的综合影响下，梅迪辛哈特段沉积在以泥为主的水下三角洲系统内的浅水中。识别出四个相，它们被解释为远端三角洲前缘、近端前三角洲、远端前三角洲和分流间海湾沉积。远端三角洲锋以沙质风暴沉积物和薄的风暴洪水高密度岩为主。另一方面，前三角洲的特点是泥质风暴沉积物和波浪增强沉积物重力流沉积物，只有次要的高重岩。三角洲前缘和前三角洲的地质组合都很贫乏，表明存在持续的物理化学环境压力。分流间海湾沉积物并不常见，并且根据更强大的地质组合和更高的生物扰动强度进行区分。地下相关性揭示了向上变浅的准层序，这些层序具有加积和前积叠加模式和非常低的沉积梯度。表明持续的物理化学环境压力。分流间海湾沉积物并不常见，并且根据更强大的地质组合和更高的生物扰动强度进行区分。地下相关性揭示了向上变浅的准层序，这些层序具有加积和前积叠加模式和非常低的沉积梯度。表明持续的物理化学环境压力。分流间海湾沉积物并不常见，并且根据更强大的地质组合和更高的生物扰动强度进行区分。地下相关性揭示了向上变浅的准层序，这些层序具有加积和前积叠加模式和非常低的沉积梯度。约0.03° 至 0.1°）。地层反映了低梯度环境中固定住所的快速进积；前渊中同时期的弯曲下沉受到下伏地下室结构的抑制。此外，之前关于弓岛拱门影响沉积物分布的建议并没有得到倾斜形状的低角度几何形状的证实。这项研究的数据支持了梅迪辛哈特三角洲由向北流经蒙大拿州的河流补给的解释，因为平行层序向南的沙质更大。本研究提供了一个以泥为主的水下三角洲系统的岩石记录示例，填补了文献中的一个关键空白，并作为对全球类似单元的岩心研究进行比较的基础。