Arrested versus active silica diagenesis reaction boundaries—A review of seismic diagnostic criteria

Abstract

AbstractThis paper evaluates previously proposed diagnostic criteria that can be used to determine whether or not there is active migration of the opal‐A to opal‐CT transition zone (TZA/CT). The criteria are based on the interpretation of 2D and 3D seismic surveys and are therefore geometrical. They involve an assessment of the relationship of the TZA/CT with polygonal fault systems, differential compaction structures and tectonic folds. The most robust evidence for an inactive ‘reaction front’ between opal‐A and opal‐CT bearing sediments is the discordance of the TZA/CT relative to present‐day isotherms. Any of these may be persuasive as diagnostic criteria for the upward arrest of the diagenetic transformation at a regional scale, but actual truncation of the TZA/CT at the modern seabed is definitive for arrested diagenesis. This study argues that diagenetic assessment based solely on a single criterion independently is not reliable as an indicator for the current state of a silica transition. As a conclusion, the analysed seismic/structural criteria should be synthesised to provide a more credible interpretation for silica diagenesis. The use of modern 2D and 3D seismic data for the reconstruction of the diagenetic history of opaline silica bearing sediments offers a new approach to the study of silica diagenesis at a regional scale.