Ameri Ameri Ameri American Journal of Science and Technology can Journal of Science and Technology can Journal of Science and Technology can Journal of Science and Technology 2014; 1(5): 277-282 Published online October 10, 2014 (http://www.aascit.org/journal/ajst) Keywords Amasiri Sandstone, Physical Sedimentary Structures, Trace Fossils Received: August 20, 2014 Revised: August 29, 2014 Accepted: August 30, 2014 Sedimentary structures and depositional environment of the Amasiri sandstone (Turonian), in Akpoha, Southeastern Nigeria Ezekiel Obinna Igwe 1 , Anthony Uwaoma Okoro 2 1 Department of Geology, Ebonyi State University, P. M. B. 053, Abakaliki, Nigeria 2 Department of Geological Sciences, Nnamdi Azikiwe University, Awka, Nigeria Email address ezekieloigwe@yahoo.com (E. O. Igwe), anthonyuokoro@yahoo.com (A. U. Okoro) Citation Ezekiel Obinna Igwe, Anthony Uwaoma Okoro. Sedimentary Structures and Depositional Environment of the Amasiri Sandstone (Turonian), in Akpoha, Southeastern Nigeria. American Journal of Science and Technology. Vol. 1, No. 5, 2014, pp. 277-282. Abstract Some physical sedimentary structures and trace fossils have been described from the Turonian Amasiri Sandstone outcropping in Akpoha area in the southern Benue Trough of Nigeria. The physical sedimentary structures are mainly parallel laminations and beddings, wavy/ripple laminations and beddings and planar cross beddings. The sediments are moderately to intensely bioturbated. The bioturbation structures consist of trace fossils represented by the Cruziana - Zoophycons ichnospecies of Crosspodia, Monocraterion, Lorenzinia and Zoophycos. The burrows are ichnofossil assemblages associated with shallow to deep-water marine settings. The cross bedding suggests deposition in moderate to high energy shallow marine shoreface environment above fairweather wave base. The wavy/ripple and parallel laminations and beddings are formed by traction and bottom current reworking in a low to moderate energy deep marine environment. The dominance and abundance of mainly deposit-feeding structures (Cruziana), sediment mining structures (Zoophycos) and absence of suspension feeding structures, the lithology, texture and physical sedimentary structures suggest a generally shallow to deep water environments. Paucity of the trace fossil assemblages in Amasiri Sandstone in some localities may be attributed to poor oxygenation of the sea bottom and salinity fluctuations in the environment. 1. Introduction The Turonian Amasiri Sandstone represents the uppermost unit of Eze-Aku Group in the study area and overlain by Santonian uncomformity in the Afikpo Syclinorium (Table 1). The Eze-Aku Group was identified as a shallow marine sequence [20]-[16]. The sandstones consist of NE-SW trending ridges believed to be of subtidal origin alternating with marine shale (Fig 1.) [2]. Evidence of storm deposition was derived by [1] after a detailed study of the Amasiri Sandstone ridges. Reference [12] reported that the Akpoha Sandstone is of marginal marine origin. Trace fossils have been described and used in the paleoenvironmental interpretation of Cretaceous sediments of the Lower Benue Trough; such as the sediments of Turonian of Eze-Aku Group [10] and Campano-Maastrichtian Nkporo Group [13]-[3]. Apart from the trace fossils documented by these few workers, the physical sedimentary structures from the Amasiri Sandstone have been largely unreported. This paper therefore intends to interprete the depositional environments of Amasiri Sandstone using sedimentary structures. It is hoped and likened to stimulate interest and encourage further research on the sedimentary structures and depositional environments of