Print this pageIchnological Gradation of Subtidal Deposits, Ogeechee Estuary, Georgia, U.S.A
Sarah C. Gunn1, Murray K. Gingras1, Robert Dalrymple2, and S. George Pemberton1
1Earth & Atmospheric Science, University of Alberta, Edmonton, AB, Canada
2Geological Sciences & Engineering, Queen's University, Kingston, ON, Canada
The Ogeechee River Estuary, GA, USA, exemplifies a well - known ichnological pattern observed in estuarine deposits: the inner, freshwater reaches are characterized by low ichnological diversity, and the outer, estuarine mouths display ichnological suites comparable to diverse, fully marine environments. As subtidal deposits have the greatest preservation potential, this ichnological gradation in the subtidal of the tidal - fluvial transition zone can be useful in paleoenvironmental reconstructions, and is applicable to oil and gas exploration and reservoir development. Due to a lack of high-quality, subtidal data in current research, the Ogeechee River Estuary has been revisited to study the subtidal deposits of the tidal - fluvial transition zone in detail. Subtidal box - cores, collected and analyzed in July 2007, have been used to characterize the subtidal ichnological progression of the estuary.
The subtidal of the outer estuary comprises fine - grained sand and may include shelly material. Abundance of burrows is low, but diversity is high. Burrows of shrimp, making traces similar to Thalassinoides, and bioturbation by brittle stars are most common. Also, abundant cryptic bioturbation may mask physical sedimentary structures. The middle estuary is relatively coarser grained and also displays a diverse assortment of burrowers. Many worm burrows are present, making traces similar to Skolithos, Palaeophycus, Gyrolithes and Planolites, as well as a great deal of reworking due to cryptic bioturbation. The upper estuary displays more riverine influence, with low diversity and higher abundances locally, attributable to high population densities. Sands are coarser grained and cut by long vertical worm burrows, similar to Skolithos.
AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas