Structural Diagenesis—Linked Chemical and Mechanical Processes in Sedimentary Basins

Laubach, S. E.¹, J. E. Olson¹, R. Lander², K. Milliken¹ (1) Jackson School of Geosciences, The University of Texas at Austin, Austin, TX (2) Geocosm, Austin, TX

An examination of the links between mechanical and chemical processes in sedimenta­ry basins can transform our knowledge of a part of the Earth’s interior that is of great intrin­sic and practical interest. Owing, perhaps, to decades of petroleum industry focus on shal­low parts of sedimentary basins, where original depositional fabrics may dominate petro­physical properties, artificial boundaries have arisen between the disciplines of rock mechanics, stratigraphy, sedimentary geochemistry, sedimentary and structural petrology, structural geology, and geophysics. Current efforts at drilling into deeper and less conven­tional exploration targets requires breaking these disciplinary boundaries in order to exploit new analytical techniques and instruments, laboratory tests, and mechanical and diagenet­ic models that can advance our understanding of porosity evolution in diagenetically-altered, fractured, and faulted rocks. New data and concepts that arise from such a holistic approach can be crystallized into predictive models for geological attributes where samples are sparse or nonexistent. A benefit of cross-disciplinary programs focused on fundamental processes by which rock properties evolve is a better conceptual framework for accessing future ener­gy supplies and for devising the means to extract these resources.

Despite temperatures that are elevated relative to those at the surface, reactions in deep basin settings are still dominated by kinetics, and rocks therefore preserve a complex histo­ry of their modifications. In such systems, prediction of reaction paths and mechanical behavior cannot be derived from an understanding of bulk composition and thermal condi­tions alone and a comprehensive assessment of both chemical and mechanical aspects of rock history is essential. There is an ever-growing body of evidence that, across a spectrum ranging from grain fracture in early compaction to mineral precipitation in tectonically-pro-duced veins, to mineral coatings on rock joints formed during uplift, chemical and deforma­tional histories can be deciphered in concert to reveal links that appear to be genetic.