Entitled Upper Jurassic Bivalves of Dejen - Gohatsion Section, Blue Nile Basin, Central Ethiopia

Abstract

The study area has excellent exposures of upper Jurassic sedimentary rock which is situated in north western Ethiopian plateau. This research is focused on detail field investigation, description and systematics of upper Jurassic bivalves for the reconstruction of depositional environment and ecology. Different scientific methods were followed in order to achieve and accomplish the stated research problem and the objectives of the study with three main methods. These are pre-field work, detail main fieldwork and post field work. Totally six hundred fifty-two specimens of fossil bivalves have been collected and fifty-four representative samples were prepared for systematic paleontology by identifying down to species level where possible from the Antalo limestone formations in the Blue Nile Basin from three sections with two associations. The sections from which the specimens have been collected include Filikilik section (31%), Demibeza section (48%) and Geligele section (21%). Twenty-one bivalve species have been identified and described systematically and they are belonging to two superfamily, nineteen family, three subfamily, eighteen genera, four subgenera. From the twenty one species, 16 species belong to Demibeza section (Pholadomya socialis, Bucardiomya somaliensis, Pholadomya hemicardia, Pholadomya lirata, Pholadomya aubryi, Pholadomya murchisoni, Pholadomya beamontensis, Palaeonucula lateralis, Paleonucula cuneiformis, Pterotrigonia scabra, Liostrea acuminate, Eligmus asiaticus, Actinostrean gregareum, Nanogyra nana, Nanogyra fourtaui and Ilmatogyra africana), six species were identified from Filikilik (Modiolus bipartitus, Modiolus imbricatus, Paleonucula cuneiformis, Pholadomya murchisoni, paleonucula lateralis and Nanogyra nana ) and six species from Geligele (Nanogyra fourtaui ,Ilmatogyra africana, Nanogyra nana and Liostrea acuminate, Graphaea balli and Exogyra fourtaui) are described systematically. Bivalves in the study area represent mainly Basinal environments and deep shelf. No endemic species were recorded from the studied sections