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Feb 12, 2015 - Nance and Rowe illustrate how X-ray fluorescence can be used in ... E-mail: james.h[email protected]. 4University of Texas ...
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Special section

Introduction to special section: Shale paleoenvironments Bruce Hart1, Gilles Hennenfent2, Joe Macquaker3, and Harry Rowe4

The processes that deposit mud, and the environmental conditions under which the mud is deposited, are the primary controls on the composition (i.e., mineralogy, organic content) and texture (laminations, bedding, etc.) of mudstones (“shales”). Together, these and other factors (e.g., diagenesis, subsurface stresses) control or affect geomechanical properties, anisotropy, porosity, permeability, and other factors that are fundamental controls on whether a mudstone can act as a hydrocarbon source rock, seal, or reservoir. Better understanding of depositional processes will lead to improvements in the way we analyze and predict mudstone properties. The four papers in this collection examine some of the geologic and geochemical tools and techniques that stratigraphers use to reconstruct paleoenvironments, define changes in paleoenvironments (including sequence stratigraphic analyses), and ultimately to make predictions away from existing data control. One of the papers is a review and the other three are case studies, each of which focuses on a specific formation. Turner et al. use data from the Woodford Shale to show how a sequence stratigraphic framework can be interpreted on the basis of chemostratigraphy and palynology within apparently homogeneous shale successions. This allows for future development of high-resolution interpretations within unconventional reservoirs. Albeit based on a single quarry exposure, this example illustrates how integrated data sets can

be used to make predictive, and testable, stratigraphic models. Boling and Dworkin’s measurements of total organic content, N, δ13 Corg , δ15 N, and inorganic major and trace elements are based on samples from outcrops of the Eagle Ford and underlying Pepper Formation from McLennan County, central Texas. The authors document the chemostratigraphic character of these formations using major and trace elements, organic matter abundance, and the isotopic and stoichiometric character of organic matter; these data allow the authors to identify of six distinct chemofacies that are useful for correlation purposes. Nance and Rowe illustrate how X-ray fluorescence can be used in combination with X-ray diffraction to distinguish mineral-based facies in very fine-grained rocks (mudrocks). Mineral cyclicity detected by this method can be used to target further analyses (petrography, redox-sensitive minerals, and organic isotopes) that enable development of sea-level-based models for sediment deposition and evolution of basin water-mass chemistry. Hart and Steen review the use of programmed pyrolysis (“Rock Eval”) for understanding shale paleoenvironments. The authors illustrate potential applications and limitations of the method in ways that should make the technology understandable to nongeochemists.

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Statoil, Houston, Texas, USA. E-mail: [email protected]. Chevron, Houston, Texas, USA. E-mail: [email protected]. 3 ExxonMobil, Houston, Texas, USA. E-mail: [email protected]. 4 University of Texas, Bureau of Economic Geology, Austin, Texas, USA. E-mail: [email protected]. Published online 12 February 2015. This paper appears in Interpretation, Vol. 3, No. 1 (February 2015); p. SHi–1. 2

http://dx.doi.org/10.1190/INT2014-1217-SPSEINTRO.1. © 2015 Society of Exploration Geophysicists and American Association of Petroleum Geologists. All rights reserved.

Interpretation / February 2015 SHi