RECONSIDERING SANDSTONE CLASSIFICATION

The classification of sandstones has a history characterized by empirical and theoretical debates. Pettijohn favored a system that explicitly included the intergranular matrix typical of “graywacke” while Krynine excluded the matrix and only considered framework grain composition. Grain-based classification became the standard as refined by Van Andel and subsequently Dott and has remained a largely static methodology for half a century. Yet field boundaries within QFR composition triangles have neither clear empirical nor theoretical origins. An alternative classification based on tectonic provenance of 228 North American sandstones was established by Dickinson. The empirically based tectonic fields are incongruous with the analytical classifications of Van Andel or Dott. The incompatibility of these approaches suggests an opportunity for further consideration of sandstone classification. The composition of a sandstone’s detrital grains is well understood to be the sum of the chemical alteration of granite with the admixture of labile lithic fragments. Herein provenance is differentiated into cratonic (<10% R), mixed (10-50% R), and epi- or pericratonic (> 50% R) domains. The cratonic domain is further divided on the basis of weathering of granite at 60% and 90%. The 60% alteration line is extended towards the R apex to define additional subfields within the mixed domain. This process-based classification system provides improved alignment with tectonic provenance QFR data and thus brings together analytic-descriptive and operational-genetic schema.