ICHNOLOGY OF ESTUARINE STORM BEDS, UPPER CRETACEOUS EUTAW FORMATION, WESTERN GEORGIA
NANSON, Lynde L. and SAVRDA, Charles E., Department of Geology and Geography, Auburn Univ, 210 Petrie Hall, Auburn University, Auburn, AL 36849-5305, nansoll@auburn.edu

The Upper Cretaceous Eutaw Formation of western Georgia is characterized by a variety of estuarine facies. Mud-dominated, distal and proximal central bay deposits exposed in the Columbus area contain numerous thin (< 30 cm), carbonaceous, hummocky cross-stratified, fine-grained sand beds that likely reflect deposition during major storm events. Storm beds are moderately bioturbated (ichnofabric index=2 to 3) and contain a moderately diverse assemblage of trace fossils. These assemblages include, in order of decreasing abundance: robust, thickly-lined Ophiomorpha; funnel- and dish-shaped structures; Teichichnus; Rosselia; Thalassinoides; Palaeophycus(?); Asterosoma; Planolites; backfilled cylindrical burrows (Taenidium?); and escape structures. Most of these ichnofossils also occur in background muds and can be attributed to the work of deposit feeders that colonized the sands upon re-establishment of fair-weather conditions. Ophiomorpha and funnel- and dish-shaped structures only are found in event-bed sands and likely are related in some way to opportunistic colonization by shrimp. Funnel- and dish-shaped structures, both of which originate from sand-bed tops and are filled with highly bioturbated muds, are intimately associated with Ophiomorpha. Funnel-shaped structures, measuring 7 to 12 cm in diameter and 5 to 8 cm in depth, locally are connected at their apices to vertical to oblique Ophiomorpha segments. Dish-shaped structures, typically 18 to 27 cm wide and 8 to 10 cm deep, commonly truncate Ophiomorpha shafts or tunnels. Some funnel-shaped structures may be related to the construction, abandonment, and/or collapse of these pellet-lined burrow networks. Dish-shaped structures closely resemble previously described ray-feeding structures. Their close link to Ophiomorpha suggests a possible predator-prey relationship.

Southeastern Section - 50th Annual Meeting (April 5-6, 2001)
Session No. 28--Booth# 12
Stratigraphy, Sediments, and Coal Geology (Posters)
Sheraton Capital Center Hotel: Oak Forest Ballroom
8:00 AM-12:00 PM, Friday, April 6, 2001
 

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