Wave-Influenced Deltaic Sandstone Bodies in the Viking Formation, Hamilton Lake Area, South-Central Alberta

Lynn T. Reich and S. George Pemberton
University of Alberta, Edmonton, AB

Progradational highstand parasequences of the Viking Formation are typically thought of as shelf to shoreface successions. However, in the Hamilton Lake area, isolated sandstone bodies are interpreted as deltaic in origin based on subtle sedimentological, ichnological and stratigraphic indicators of riverine discharge.

Lithologically, the delta front is similar to the shoreface except for the presence of thin organic-rich fluid mud deposits. In addition to wood and coal fragments, glaucony and siderite, indications of high sedimentation rates and fresh water input include soft-sediment deformation and syneresis cracks. As well, the trace fossil assemblage consists of a subtly stressed Skolithos-Cruziana suite with a paucity of suspension-feeding behaviors. Such indicators of deltaic influence are commonly overlooked in the Viking because of the mitigating effects of wave activity.

The deltaic nature of the Hamilton Lake sandstone bodies is also exemplified by the stratal architecture. The sandstone packages are laterally discontinuous and abruptly overlie shelf and offshore deposits, suggesting progradation in response to increased sediment supply or rapid relative sea-level fall. Furthermore, several delta lobes are identified at equivalent stratigraphic horizons signifying multiple point-sources. Interdeltaic areas accumulate thicker regional Viking shelf to offshore successions as a result of differential accumulation in the absence of deltaic deposition. Subsequently, parasequences are capped by major flooding surfaces and are associated with discontinuous trangressive deposits succeeded by distal lower offshore to shelfal mudstones. Ultimately, relative sea-level changes control the stacking pattern of deltaic and regional Viking interdeltaic deposits by influencing progradation and subsequent transgressive flooding of the deltaic succession.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005