陆棚海泥岩的岩相特征及沉积过程

传统的沉积模式认为大部分细粒沉积岩（泥岩或页岩）的沉积发生在相对深水、低能的环境中。作为地表上分布最为广泛的沉积岩类型，泥页岩包含了对重构地质历史时期古地理、古气候的重要信息。泥页岩除了可以作为有效的烃源岩，勘探开发技术的进展更发掘出泥岩作为非常规油气储层的巨大潜力。近十年来，国内外对细粒沉积物的水槽实验、泥岩沉积微相的精细分析、以及泥岩岩相组成特征的研究取得了长足的进展。这些研究对泥岩的沉积过程和沉积模式在不同角度上提供了新的认知。大部分泥岩（甚至包括众多有机质含量高的泥岩）都可能沉积在相对浅水以及水动力条件相对较高的环境中。不同的沉积过程（底部水流）形成不同的泥岩沉积微相，并对有机质在泥岩中的埋藏富集具有重要的控制作用。以晚白垩纪北美西部内陆海道为例，总结在陆棚浅海环境中（最大水深< 200 m），位于从近岸到远岸（> 500 km）不同沉积环境（包括前三角洲/下邻滨、内陆棚、中陆棚、和外陆棚环境）中的泥岩的主要沉积过程、沉积微相特征、以及富集有机质的潜力。由于沉积过程和沉积环境是决定泥岩成分、沉积相、和岩石物理特征非均质性的首要因素，不同浅海环境中的泥岩相特征和沉积模式可有助于利用泥岩地层进行古地理、古气候的重构，并能够对预测不同陆棚浅海环境中沉积的泥岩作为有效烃源岩或有效储层的潜力提供指导。

Facies Characteristics and Depositional Processes of Shelf Mudstones:Examples from the Late Cretaceous Western Interior Seaway of North America

Conventionally,most fine-grained sedimentary rocks(mudstones or shales)were considered as deposited in relatively deep-water,low-energy environments.As the most common sedimentary rock type on the Earth’s surface,mudstones/shales contain valuable information for the interpretation of paleogeography and paleoclimate conditions through the geologic history.In addition to being effective source rocks,recent advances in drilling and completion technologies have also unlocked the enormous potential of mudstones/shales as important unconventional reservoirs.Over the past decade,significant research progress has been made in the flume experiments of fine-grained sediments,detailed facies analysis of mudstones,and close examinations of the petrographic characteristics.These studies collectively have provided novel insights into the depositional processes and depositional model of mudstones.Most mudstones(even many that are organic-rich)were indeed deposited under relatively shallow-water and energetic environments.Different depositional processes(bottom currents)dominantly control the facies variability,as well as the burial and accumulation of organic matter in mudstones.Taking the Late Cretaceous Western Interior Seaway of North America as an example,this paper summarizes the primary depositional processes,facies characteristics,and the potential for the accumulation of organic matter in mudstones deposited from different shelf environments ranging from proximal prodelta/lower shoreface to distal outer shelf environment.Because depositional processes and environments are the most important factor determining the heterogeneity in the composition,sedimentary facies,and petrophysical characteristics of mudstones,the summarized facies and depositional model for mudstones deposited in different shelf environments can aid the reconstruction of paleogeography and paleoclimate conditions from ancient mudstone successions,and provide guidance for evaluating the potential of shelf mudstones as effective source rocks or reservoir rocks.