Abstract Mudrocks are highly heterogeneous in a range of physical and chemical properties, including: porosity and permeability, fissility, colour, particle composition, size, orientation, carbon loading, degree of compaction, and diagenetic overprint. It is therefore important that the maximum information be extracted as efficiently and completely as possible. This can be accomplished through high-resolution analysis of polished thin sections by scanning electron microscopy (SEM), with the collection of large-area images and X-ray elemental map montages, and the application of targeted particle analysis. A workflow model, based on these techniques, for the digitization of mudrocks is presented herein. A range of the data that can be collected and the variety of analyses that can be achieved are also illustrated. Data collection is discussed in terms of inherent problems with acquisition, storage, transfer and manipulation, which can be time-consuming and non-trivial. Similar information and resolutions can be achieved through other techniques, such as QEMSCAN and infra-red (IR)/Raman spectroscopic mapping. These can be seen as complementary to the workflow described herein.

Automated scanning electron microscopy image collection from geological polished thin sections, in conjunction with autonomous stitching, can be used to construct high-resolution (micron- to submicron-resolution) image montages over areas up to several square centimeters. The technique is here applied to an oolitic limestone and a carbonate laminite to illustrate its application as a tool to study carbonate porosity and diagenesis. Montages constructed from backscattered images are ideally suited to the extraction of data on microporosity, with possibilities including the construction of contoured maps to illustrate the spatial variation in porosity; the construction of porosity logs to illustrate trends in porosity across thin sections; and stochastic construction of digital rock models, for subsequent permeability calculation. Montages taken with a gaseous secondary electron detector in low-vacuum mode can utilize charge contrast imaging (CCI) at a variety of scales and were used here in examining the evolution of carbonate cementation. One example is oolitic limestone, illustrating the formation of grain-lining and pore-occluding cements, as well as recrystallization of the depositional fabric. CCI montages commonly suffer from a variety of contrast and brightness artifacts due to variation in charge distribution across the individual scanned image tiles. Several remedies are discussed that can reduce these artifacts, making it easier to apply image analysis techniques across such montages.

This paper presents conceptual models of basement configurations for several structural types in the Rocky Mountains foreland—upthrusts, rotated basement blocks, and plateau uplifts. These hypotheses of structural development are supported by calculated stress states and fracture patterns derived from them. The goodness-of-fit between field observations and the final geometries of the models leads to the suggestion of possible loading conditions for the initiation of Laramide structural development of uplifts in the foreland. These suggested loading conditions for individual features lead, in turn, to a hypothesized stress state consisting of a regional component of crustal horizontal compression superposed on the controlling stress fields caused by more local load variations at depth beneath the brittle upper crust.

The inexact geometric fits of the conceptual models of Couples and Stearns (this volume) are due largely to idealizations required by the theoretical analysis. The primary reasons for the mismatch are the assumptions of continuity and isotropy. Real rocks are not adequately described by these properties. Additional considerations of the state of stress—that is, stability index and principal-stress reorientation—are interesting in themselves but do not seem significantly to affect the construction of models using the theoretical solutions. On the basis of information currently available, the mechanical models of Couples and Stearns appear reasonably sound.