--> Abstract: Sedimentology and Ichnology in Mixed-Energy Coasts; #90063 (2007)

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Sedimentology and Ichnology in Mixed-Energy Coasts

 

Yang, ByongCheon1, Murray Gingras1, Bob Dalrymple2, George Pemberton1 (1) University of Alberta, Edmonton, AB (2) Queen's University, Kingston, ON

 

Although coastal environments and associated deposits are extremely diverse, sedimentological models simply develop the notion that coastal deposits can be identified as wave- and tide-dominated settings that are distinctive in terms of physical processes and geomorphology. Thus, these two settings are characterized by distinctive sedimentary facies. Muddy heterolithic facies are thought to characterize tidal-flat deposits, whereas wave- and storm-generated deposits, including hummocky cross stratification (HCS), are likely to be representative of shoreface settings.

Recent coastal studies from South Korea and eastern Vancouver Island, Canada, have, however, shown that open-coast tidal flats occupy the process-sedimentological spectrum between wave- and tide-dominated depositional environments. These deposits mostly comprise wave-generated structures and hummocky cross-stratification with volumetrically minor amounts of tidally induced lamination. Our findings suggest that shoreface deposits and wave-dominated tidal flat deposits are difficult to distinguish on the basis of existing sedimentological knowledge.

However, we show that the integration of ichnological and sedimentological data has produced new criteria for the identification of open coast tidal flat deposits. These are: (1) tidally modulated rhythmic deposits that reflect the continuous change in wave energy due to water-level fluctuation; (2) a number of swash bars (> 4) are much more abundant, compared with those in foreshore (< 3); (3) the HCS wavelength decreases systematically landward due to a decrease in bottom orbital diameter; (4) overall a higher abundance of animal traces compared to the upper shoreface and foreshore of wave-dominated settings; and (5) ichnological trends might be not necessarily perpendicular to the direction of wave energy.

 

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