Middle / Upper Eocene Facies Architecture and Trace Fossils Interpreting the Paleoenvironment and Sedimentologic Setting of the Whale-Bearing Gehannam and Birket Qarun Formations, Wadi El-Hitan, Fayum-Egypt
Middle/Upper Eocene deposits of the whale-bearing Gehannam and Birket Qarun formations are divided into two main facies associations. Facies Association 1 (FA1) is represented by bioturbated sandstones. Facies Association 2 (FA2) is represented by gypsiferous shale, sandy siltstone, and fine-grained sandstone. Observed within the reported facies associations, are seventeen ichnospecies belonging to thirteen ichnogenera. Additionally, fossil-plant roots (rhizoliths) are identified at predictable stratigraphic levels.
Consideration of the biological and sedimentological characteristics of the facies associations suggest that FA1 accumulated in an open low-energy fully-marine bay. Facies Association 2 results from shallowing episodes, and represents landward sedimentation in low-energy bay-margin locales, possibly in poorly drained supratidal paleoenvironment. An absence of hydraulic reworking (i.e. oscillation ripples, current ripples, and hummocky cross stratification) in FA1 and FA2 suggests that clastic point-sources are dominantly hypopycnal and are deposited from suspension—nominally suggesting flashy point-source discharge—or, that aeolian sand may be an important source of sediment.
The quiescent marine bay covering the area of Wadi El-Hitan appears to represent an important biome for previously reported Eocene whales. Moreover, the preservation of the whale fossils is somewhat contradictory with the sedimentological observations, in that the sedimentation rates must be: (1) rapid enough to inter the whales and discourage scavenging; and, (2) slow enough that sediment-dwelling biota are afforded the time to eradicate essentially all of the physical sedimentary structures.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009