Facies Variability of Tidal Bar Occurrences in a Tidal-Fluvial Transition Zone, Ogeechee Estuary, Georgia, U.S.A

Gunn, Sarah C.¹, Robert Dalrymple², S. George Pemberton¹, Murray K. Gingras¹ (1) University of Alberta, Edmonton, AB (2) Queen's University, Kingston, ON

Tidal bars are a common geomorphological component of tidal environments, and knowledge of the complexities of their deposits can be applied to oil and gas exploration and reservoir development. Although the sedimentology of tidal bars has been scrutinized, there is a dearth of research aimed at addressing the lateral facies variability and proximal-distal trends between tidal-bar occurrences. Also, relatively few studies incorporated integrated ichnological data. These omissions may be partly addressed by the study of tidal bars in the tidal-fluvial transition zone of the Ogeechee Estuary, Georgia, U.S.A.

In general, tidal bars of the inner and medial parts of the Ogeechee comprise bank-attached bars residing in sinuous channels. Sinuosity, wavelength and amplitude increase towards the middle estuary. The bars are typically shallow on the inside of meanders, however, deep scours (up to 10m deep) cut across the bars. The main channels of the Ogeechee are otherwise scoured deeply (up to 15m) and there appears to be no consistent relationship between the geometry of channel meanders and the volume of sediment stored in ‘point bars'. The outer estuary is dominated by large tide-dominated channels, in which a variety of mobile, sand-dominated, longitudinal bars are dominant.

Animal traces comprise a variety of worm and arthropod tracks, burrows and trails. In general, small arthropods (e.g. Corophium volutator making Diplocraterion) are dominant in the inner and middle estuary. The middle and outer estuary hosts a variety of worms and crustaceans producing traces similar to Skolithos, Thalassinoides, Conichnus, and Planolites.