PROCESSES CONTROLLING PETROLEUM PLAY ELEMENT DISTRIBUTION IN MUD-DOMINATED DEPOSITIONAL SYSTEMS: OBSERVATIONS FROM CENOMANIAN TO CONIACIAN STRATA OF THE WESTERN INTERIOR SEAWAY, USA

Abstract:

The Late Cretaceous basin fill of the Western Interior Seaway provides an excellent natural laboratory for correlating outcrop and sub-surface stratigraphic data from updip paralic deposits, through medial argillaceous mud belts to basinal biogenic-rich deposits. Integrating outcrop and core descriptions of lithofacies with sequence stratigraphic interpretations and biostratigraphic age and environmental constraints allows depositional and diagenetic processes to be linked to play and prospect definitions of mudstone source, seal, and unconventional reservoir potential. At the sequence scale, key stratal surfaces (sequence boundaries, transgressive surfaces, and maximum flooding surfaces) can be correlated across the entire basin based on trends in lithofacies distributions and stacking patterns. At the bedset scale, independent processes operate in different parts of the basin to generate local bedset boundaries and stacking patterns, critical for subregional framework building. Various shoreline advancement and abandonment processes control nearshore classic parasequence stacking patterns. Stratal surfaces associated with middip argillaceous mud belts may relate to shifting contour-current patterns and deposits operating independent of shoreline advancements and abandonments. The biogenic processes that control stratal architecture in the distal part of the basin are in part climatically forced. The integration of stratigraphic frameworks at the basin scale requires an appreciation of these independently operating processes to differentiate basin-scale stratal surfaces from regional and subregional correlation methods that allow detailed articulation of stratigraphic frameworks for play and prospect evaluation.