The Paleoenvironmental Significance of Trace Fossils from the Paleocene Imo Formation, South-eastern Nigeria

摘要

Trace fossils and lithofacies associations were studied to understand the paleodepositional environment of the Paleocene Imo Formation. The methodology involves lithologic logging to obtain sedimentological and ichnological data. Bioturbation index were used to estimate the intensity of biotubation of the various lithofacies associations. The trace fossils observed in the Imo Formation includes Ophiomorpha and Altichnus belonging to the Skolithos ichnofacies and Chondrites , Thalassinoides , Planolites , and Rosselia which belongs to the Cruziana ichnofacies. Six lithofacies association were distinguished and interpreted as follows; swaly cross-stratified sandstone represents a middle shoreface environment, laminated shale representing offshore to lower shoreface transition sediments, interbedded sandstone and shale as well as bioturbated sandstone deposited in upper shoreface environments, fossiliferous shale representing an upper offshore deposit while crossbedded sandstone is inferred to as foreshore-upper shoreface sediments. The gross depositional environment suggests sediments deposited in shallow marine environments lying between the foreshore-shoreface to offshore depositional settings.