1 The Importance of and Challenges in Studying Fine-Grained Sedimentary Rocks—Introduction and Overview

ABSTRACT Fine-grained sedimentary rocks (e.g., shale, mudrock, mudstone, claystone, chert, or chalk) are the most common rocks in the stratigraphic column. They preserve the best archives of Earth’s history for interpreting paleoclimate and paleo-oceanography; influence the flow of groundwater and hydrocarbons; serve as hydrocarbon source, reservoir, and seal; and host strata-bound resources. Advancing technology has provided access to the vast energy resources contained in these rocks—indeed, the production of “shale oil” and “shale gas” in the United States changed the energy outlook almost completely over the seven-year span of 2007–2014. Sequence stratigraphy provides an organized, integrated approach to place fine-grained rocks into a firm framework alongside sandstone and carbonate. The physical, biogenic, and chemical properties of fine-grained rocks vary in systematic ways that can be deciphered and predicted within an integrated sequence-stratigraphic framework. This chapter addresses the importance of fine-grained sedimentary rocks and the challenges in their study, followed by an introduction to the key attributes of fine-grained sedimentary rocks and to their role as source, reservoir, and seal of hydrocarbon play elements. A quantitative analysis demonstrates the importance of geological factors on hydrocarbon resource-in-place and deliverability of these so-called engineering reservoir plays. The chapter then presents the rationale for applying sequence stratigraphy to fine-grained sedimentary rocks and concludes with an overview of the organization of this Memoir. The Memoir has four main sections: (1) introductory chapters that provide overviews of the significance of fine-grained rocks, their character and classification, and techniques for studying them; (2) chapters that cover the fundamentals and examples of fine-grained rocks at successively larger scales, from the lamina to sequence-set scale; (3) case studies that illustrate all these scales of stratification with examples that span the Paleozoic to the Cenozoic and deep-marine to coastal-plain and lake settings; and (4) a summary of the controls on stratal record—mechanisms and contingencies that affect sediment supply and accommodation.