Classification of Shallow Marine Depositional Complexes

Abstract

Early sequence stratigraphic models applied to shallow-marine successions revolutionized methods of reservoir prediction and characterization. In the decades following introduction of these methods, there have been fundamental improvements in our understanding of depositional process controls on reservoir architecture and internal facies variations defined within a sequence-stratigraphic context. Such improvements reflect not just a better understanding of how changes in dominant depositional processes control facies patterns, but also recognition of process changes and differential preservation as areas along the shoreline are locally abandoned by river avulsion and reworked by shoreline and shelf processes during larger-scale shifts in the position of deposition. A classification of shallow-marine stratigraphic successions is presented based on: 1) dominant depositional process (river, wave, tide), 2) shoreline trajectory, and 3) relative preservation of regressive deposits following transgression (related to accommodation/sediment-supply ratios). Although all shallow-marine deposits reflect variable interaction of river and marine processes, and there is a gradation between extremes of shoreline trajectory, we define specific reservoir complex types: 1) to highlight reservoir-element variations within a range of systems, 2) as a framework for the organization of outcrop and subsurface analog examples, 3) to provide a structure for development of a reservoir-element dimensional database, and 4) to guide stratigraphic correlation-framework definition. Thirteen shallow-marine complex types are shown relative to their position within a regressive–transgressive clastic wedge formed during deposition of either a higher or lower long-term accommodation-growth sequence. Although such classification involves simplification and generalization, our goal is to broadly define classes that span the full range of shallow-marine reservoir systems, and to highlight contrasts in stratigraphic correlation styles and facies trends that need to be considered to characterize reservoirs within diverse types of shallow-marine deposits. A catalog of examples is presented to show each complex type, key stratigraphic surfaces, and stratigraphic position within longer-term regional sequences. General correlation concepts important for prediction of facies variations within each class are highlighted by presenting outcrop and subsurface examples.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015