Lower Palaeogene Ostracoda, From the Sirt Basin of Libya

Paleontology

Gammudi, Amar Mohamed

University:University of Glasgow

关键词: Paleontology;   

Others  :  http://theses.gla.ac.uk/75767/1/13818502.pdf

来源: University of Glasgow

【 摘 要 】

Ostracods have been studied from 5 wells from the Sirt Basin, two from trough areas, 3 from platform areas, together with 2 outcrop sections on the western edge of the basin. The El-Fogha section, previously studied by Barsotti (1963) was resampled. 122 species and subspecies belonging to 58 genera have been recorded; 35 new species and subspecies are proposed. 39 species have been previously recorded from west Africa, North Africa and the Middle East, 10 species are certainly contaminants and come from younger sediments, the remainder are left under open nomenclature; although some of these show similarities to earlier described faunas. Most of the species recorded in this study are widely distributed in the lower Palaeogene of west, north Africa and the Middle East. The Palaeocene/Eocene boundary is marked by a large faunal turnover with the extinction of many typical Palaeocene ostracod species. The extinction of Paracosta bensoni has been used to define this boundary; studying the wells, the boundary is marked downhole by the sudden appearance of a rich ostracod fauna both in numbers of individual and in species. Four ostracod biozones have been recognised: early Eocene, late Palaeocene Paracosta bensoni zone, middle Palaeocene Paracosta Paleomokattamensis zone, and an early Palaeocene biozone. Graphic correlation techniques have been used for correlating the wells. Filtered gamma ray logs has been used to establish a L. O. C (line of correlation) between platform well YY1-6 and trough well KK1-6. This technique has given a high resolution to solve the boundary problem between the Haagfa and Khalifa formation in well KK1-6. This approach, together with the ostracod biostratigraphy, indicates that the Hagfa Shale and Khalifa Formations include younger (i.e early Eocene) strata than previously thought. The biofacies described by Bassiouni and Luger, (1990) have been recognised in the wells; these show a shallowing upwards sequence through the Palaeocene from outer shelf to near shore biofacies, with slight deepening at the start of the Eocene. Cluster analysis has helped in recognising different ostracoda associations within Bassiouni and Luger's shallow marine Afro-Tethyan type biofacies in the outcrop sections. The wide distribution of the Libyan fauna in North and West Africa, and the Middle East (Barsotti 1963, Reyment 1963, Berggren 1974 and Bassiouni and Luger 1990). The Trans-Saharan Seaway connecting Libya and North Africa with Nigeria via Mali and Niger had maximum flooding during the late Palaeocene transgression.