--> Abstract: Characterizing Subtle Deltaic Influences in the Shallow Marine (Lower Cretaceous) Viking Formation at Hamilton Lake, Alberta, ; #90063 (2007)

Datapages, Inc.Print this page

Characterizing Subtle Deltaic Influences in the Shallow Marine (Lower Cretaceous) Viking Formation at Hamilton Lake, Alberta, Canada

 

Dafoe, Lynn T.1, S. George Pemberton1, James MacEachern2 (1) University of Alberta, Edmonton, AB (2) Simon Fraser University, Burnaby, BC

 

Ancient deltaic deposits are commonly misinterpreted as nondeltaic (strandplain) shoreface successions that imply deposition under normal marine (unstressed) conditions. These misinterpretations can occur where strata possess only subtle indications of deltaic sedimentation; a situation encountered in the Albian Viking Formation at Hamilton Lake. Sedimentological, ichnological, and stratigraphic features of these Viking deposits, when carefully analyzed, exhibit subtle evidence of physico-chemical stresses imparted by riverine influence on otherwise wave-dominated, fully marine deposits.

 

In the Hamilton Lake area, the Viking Formation comprises coarsening-upward successions, dominated by wave-formed structures (oscillation ripple lamination and hummocky cross-stratification) similar to shoreface deposits. Subtle sedimentological evidence of riverine input is superimposed, however, signified by local synaeresis cracks, soft-sediment deformation features, carbonaceous mudstone drapes, and coaly fragments. Ichnological suites reveal low diversities and reduced abundances of trace fossils in prodelta deposits, characterized by moderately to subtly stressed expressions of the archetypal Cruziana Ichnofacies. Delta-front deposits yield low-diversity, moderately stressed suites attributable to proximal expressions of the Cruziana Ichnofacies. With increased numbers of tempestites, suites attributable to stressed expressions of the Skolithos Ichnofacies become increasingly intercalated. In general, there is a subtle suppression of suspension-feeding structures, reduced bioturbation intensities, and reduced ichnofossil diversities, which are attributed to environmental stresses such as salinity fluctuations, water turbidity, and sediment influx. The mapped distribution of the lower sand body demonstrates a morphology consistent with both wave and riverine influence. Integrated facies characteristics reflect the dominance of wave-induced processes over associated riverine influx; hence, strata are best described as a wave-influenced deltaic complex.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California