Depositional and Burial Domain Influences on Microporosity Modalities in Carbonaceous Mudstones of the Upper Cretaceous Colorado Group, Western Canada Foreland Basin

Jiang, Peng; Cheadle, Burns

Fabric characteristics of intrinsic and secondary microporosity in carbonaceous mudstones provides insight into contrasting depositional and burial domain processes in the foredeep and back-bulge segments of a foreland basin. In particular, the relationship between disseminated organic matter and clay aggregates during deposition apparently influences the preservation of reactive kerogen as revealed by subsequent organic matter microporosity development during burial-related catagenesis. Laterally correlative strata spanning a foreland basin system offer the opportunity to evaluate how microfabric characteristics preserve evidence of distinct depositional and burial processes of different foreland basin segments.

The study is based on secondary electron and backscatter electron microscopy of 319 ion-milled cross-sectional surfaces from 43 samples. These samples are a representative gamut of Upper Cretaceous Colorado Group carbonaceous mudstones from thirteen cored wells spanning the Western Canada Foreland Basin (WCFB). Approximately 2600 SEM photomicrographs were acquired and evaluated in order to construct a comprehensive database of pore types. These fall into the broad categories of intercrystalline, intraparticle, organic matter and dissolution pores.

Understanding the relationship between organic matter porosity development and thermal maturity has been a principal focus of this work, with the intent to develop a generalized model for predictive purposes. The initial hypothesis posited a linear relationship between increasing thermal maturity and corresponding increase in organic matter microporosity in a transect from the back-bulge through the foredeep of the WCFB. The results, however, reveal very high degrees of spatial heterogeneity with respect to different modes of microporosity. This heterogeneity, in part, results from depositionally-imposed modes of organic matter preservation and related advective transport of clay aggregates.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013